SaatiPrint TechTip Handbook - Catspit Screen Printing Home

HANDBOOKTech Tips

for Screen

Printers

HANDBOOKTech Tips for Screen Printers

Published by SaatiPrint U.S.A. © 2001 SaatiPrint U.S.A. Printed in U.S.A.

Visit our website at www.saati.com • email: [email protected]

Welcome to the SaatiPrint Tech Tips handbook, which we hope willbecome a valuable reference to help you achieve better results for yourcustomers.We have separated the Tech Tips from the SaatiPrint catalogin an attempt to make the information more portable and user-friendly,and to ensure that they can be independently updated and reprinted toremain as current as possible.

SaatiPrint North America was officially formed last year followingthe acquisition of the E.W. Dorn Company by the Saati AmericasMajestech Division. SaatiPrint is the only manufacturer of both highprecision woven screen-printing mesh and complementary chemicals.These leadership products are further enhanced by a full portfolio ofpre-press equipment and supplies, developed together with our supplierpartners to meet the diverse screen making needs defined within eachof the major screen-printing market segments including Graphics,Electronics, Textile, Optical Disc, Glass and Ceramic.

In addition to this Tech Tips handbook and the catalog, we havelaunched a new global web site www.saati.com, published a newFundamentals of Screen Printing book written by Andre Peyskens,and invested in a SaatiChem e-commerce web site to make it easier to purchase gallons of emulsion www.emulsionstore.com.

It is our intention to continue to reach out and find more ways to communicate with our customers, which will drive continuousimprovements in our products, process and services. Please contact us with any suggestions, which will help us to improve, and/or for personal attention to your technical problems or product needs.Thank you in advance for your help.

SaatiPrint North America

Screen printing is our passion, but our goal is customer satisfaction.

To place an order, or for more information, dial 1-800-431-2200

C O N T E N T S

FABRIC SELECTIONS

Fabric Selection Chart and Guidelines . . . . . . . . . . . . . .2-4

Saatilene® Hitech™ Mesh Specifications . . . . . . . . . . . . .5-7

Saatilene® Hitech™ Half-Calendered Polyester Specifications .8

Saatitex® Multifilament Polyester Specifications . . . . . . . . .8

Saatilon® Monofilament Nylon Specifications . . . . . . . . . .9

Saatilene® CD-Mesh Specifications . . . . . . . . . . . . . . . . .10

Saatilene® PCB-Mesh Specifications . . . . . . . . . . . . . . . .11

Saatilene® Hibond™ Mesh Specifications . . . . . . . . . .12-14

Metalester Mesh Specifications . . . . . . . . . . . . . . . .15-16

Haver Stainless Steel Wire Cloth Specifications . . . . . .17-19

Theoretical Ink Deposit . . . . . . . . . . . . . . . . . . . . . . . .20

Mesh Guidelines (4-Color Printing) . . . . . . . . . . . . . .21-22

FABRIC TENSIONING & PREPARATION

Recommendations For The Handling Of Fabrics . . . . . .24-25

Care And Use Of A Tension Meter . . . . . . . . . . . . . . . . .26

Screen Tensioning Step-By-Step Guide . . . . . . . . . . . .27-31

Using Proper Tensioning Techniques . . . . . . . . . . . . . . . .32

Avoiding Mesh Problems – Retensionable Frame . . . . .33-34

Benefits Of Stretching On An Angle . . . . . . . . . . . . . .35-36

Rapid Tensioning VS Stage Tensioning . . . . . . . . . . . . . .37

Problems Associated With Insufficient Tension . . . . . . . . .38

Choosing A Frame . . . . . . . . . . . . . . . . . . . . . . . . . . .39

How To Avoid Frame Adhesive Failure . . . . . . . . . . . . . .40

Mesh Pretreatment & Degreasing . . . . . . . . . . . . . . .41-43

STENCIL PROCESSING

How To Reduce Pinholes . . . . . . . . . . . . . . . . . . . . .46-47

What To Expect From Your Stencil . . . . . . . . . . . . . .48-55

How To Match Direct Emulsion’s Print Quality . . . . . . .56-57

Emulsion Selections & Coating Techniques . . . . . . . . . . .58

Optimizing Automatic Coating Methods . . . . . . . . . . .59-60

What Is A Stencil Rz Value? . . . . . . . . . . . . . . . . . . . .61

What Are Optimum Drying Conditions? . . . . . . . . . . .62-63

Determining Stencil Moisture Content . . . . . . . . . . . . . .64

Choosing An Exposure Unit . . . . . . . . . . . . . . . . . . . . .65

Determining Optimum Exposure . . . . . . . . . . . . . . . . . .66

Processing Steps in Producing A Pure Photopolymer Stencil 67-73

Using Radiometer To Pinpoint Correct Exposure Time . . . . .74

Benefits Of Emulsion Stencil Post-Exposure . . . . . . . . . . .75

QUALITY CONTROL & GENERAL PRESS GUIDELINES

Mesh Guidelines For Printing 4-Color Process . . . . . . .78-79

Printing 4-Color Process With UV Ink . . . . . . . . . . . . .80-85

Controlling Off-Contact For Successful Printing . . . . . . . . .86

Choosing The Best Squeegee . . . . . . . . . . . . . . . . . . . .87

Care & Maintenance To Extend Squeegee Life . . . . . .87-88

Use Of A Transmission Densitometer . . . . . . . . . . . . . . .89

Use Of A Reflection Densitometer . . . . . . . . . . . . . . . . .90

Preventive Checklist . . . . . . . . . . . . . . . . . . . . . . . .91-92

Regulatory Resources: Guidance Tools . . . . . . . . . . . .93-94

Guide To Waste Classification & Disposal . . . . . . . . . .95-96

Conversion Guides . . . . . . . . . . . . . . . . . . . . . . . .97-111

Visit our website at www.saati.com • email: [email protected]

SaatiPrint, SaatiChem, Hibond, Hitech, Saatilene, Saatilon and Saatitex are registered trademarks of The SaatiGroup. Direct Prep and Duralife are trademarks of SaatiPrint USA; Newman ST Meter and Newman Roller Frameare registered trademarks of Stretch Devices, Inc.; TQ+ and IQ150 are trademarks of Tobias Associates.

The Tech Tips, directions, recommendations and specification charts contained in this brochure are meant as guidesto the use of the products and shall not bind the company. Product specifications are subject to change withoutnotice. Complete product directions and Material Safety Data Sheets are available by dialing our toll-free number.(MSDS sheets are shipped routinely with every shipment of any products containing hazardous ingredients.)

Member of

C O N T R I B U T O R

1To place an order, or for more information, dial 1-800-431-2200

HANDBOOKFabric Selections

2 Visit our website at www.saati.com • email: [email protected]

Fabric Selection ChartAPPLICATION FABRIC MESH COUNT RANGE

inch (cm) inch (cm)

GRAPHICSPoster (UV Inks) Saatilene Hitech 380 (150) — 460 (180)

Poster (Solvent Based Inks) Saatilene Hitech 305 (120) — 420 (165)

Stickers/Self-Adhesive Saatilene Hitech 305 (120) — 420 (165)

Bottles, Containers, Misc. Objects, Saatilene Hitech 230 (90) — 460 (180)

Promotional Items Saatilene Hibond 230 (90) — 460 (180)

Saatilon 305 (120) — 460 (180)

Touch Panel Printing Saatilene Hitech 255 (100) — 380 (150)

(Polyester/Polycarbonate)

Front Panel Printing Saatilene Hitech 255 (100) — 380 (150)

Credit/Account Cards – Graphics Saatilene Hitech 305 (120) — 380 (150)

Decal – Graphic Saatilene Hibond 230 (90) — 460 (180)

Wood Decoration Saatilene Hibond 196 (77) — 330 (130)

TEXTILEWater-Based Inks Saatilene Hitech 86 (34) — 230 (90)

Flock Printing Saatilene Hitech 41 (16) — 110 (43)

Glitter Inks Saatilene Hitech 24 (9,5) — 86 (29)

Puff Inks Saatilene Hitech 30 (12) — 140 (55)

Plastisol Inks Saatilene Hitech 110 (43) — 355 (140)

Transfer Printing Sublimatic Saatilene Hitech 305 (120) — 380 (150)

Transfer Base Saatilene Hitech 110 (34) — 158 (62)

Carpet Decoration Saatilene Hitech 61 (24) — 74 (29)

ELECTRONICS“Etch” Resist Primary Image Saatilene Hitech 255 (100) — 305 (120)

“Plating” Primary Image Saatilene Hitech 305 (120) — 355 (140)

“Solder Mask” – Solvent Saatilene Hitech 125 (49) — 196 (77)

“Solder Mask” – UV Saatilene Hitech 230 (90) — 380 (150)

Legend Printing Saatilene Hitech 255 (100) — 355 (140)

CDCompact Discs Saatilene Hitech 355 (140) — 460 (180)

Saatilene CD-Mesh 355 (140) — 460 (180)

continued on next page


APPLICATION FABRIC MESH COUNT RANGEinch (cm) inch (cm)

CERAMICTiles First and Second Firing Saatilene Hibond 140 (55) — 196 (77)Tiles Third Firing Saatilene Hibond 230 (90) — 420 (165)Tiles Dry Firing Saatilene Hitech 24 (9,5) — 61 (24)Colloid Saatilene Hitech — 86 (34)

GLASSAutomotive Industry Saatilene Hibond 168 (62) — 305 (120)Domestic Appliances Saatilene Hibond 180 (71) — 380 (150)Building Sites Saatilene Hitech 168 (62) — 255 (100)

MISCELLANEOUS APPLICATIONSUV Varnishes Saatilene Hitech 380 (150) — 460 (180)Solvent-Based Varnishes Saatilene Hitech 158 (62) — 305 (120)Fluorescent Inks Saatilene Hitech 158 (62) — 305 (120)Very Low UV Ink Deposit Saatilene Hitech Half-Calendered 355 (140) — 460 (180)Uneven Surfaces Saatilon as applicationProjection Exposure Saatilene Hibond 305 (120) — 380 (150)Fine Half-Tone Saatilene Hibond 380 (150) — 460 (180)Very Long Print Runs Saatilene Hibond 380 (150) — 460 (180)High Screen Output Saatilene Hibond 86 (34) — 508 (200)

on Difficult Substrates Saatilene Hibond 196 (77) — 460 (180)

NOTE:1. Selecting a thinner thread diameter will improve ink flow and print definition.2. Selecting larger thread diameter will increase fabric durability.3. From mesh count 230 (90) and above, select dyed fabrics for optimum stencil resolution.4. PW (Plain Weave) fabric will reduce the incidence of moiré, when printing half-tones.

Fabric Selection Chartcontinued from previous page


Guidelines and Recommendations for Mesh Specifications

New mesh counts and/or thread diameters are added periodically. Please inquire.

◆ FABRIC THICKNESSFabric thickness results from the combina-tion of the number of threads, the threaddiameter and the woven structure of thefabric. Major changes in fabric thicknessresult mostly from changes in thread diameter. Because it is not obvious that athicker or thinner fabric will give a higheror lower ink deposit (a thicker mesh mayhave a lower relative open area) one less frequently considers this factor whenselecting a mesh count. However the totalfabric thickness is needed to calculate the theoretical ink volume of a mesh. Thefabric measurement is obtained in anunstretched state.

*PERCENTAGE OF OPEN AREAFigures for the percentage of open areahave been provided to use as a guide incomparing one Saati mesh to another.Please be aware that in comparing differ-ent manufacturers’ published percentageof open area data, figures will vary due to several factors. The most important difference being whether the manufacturerused nominal (before weaving) or real(after weaving) data in calculating thepublished figures. The interpretation of the conversion of the data from metric toEnglish can also contribute to differences.For practical application, we advise youdial our toll-free hot line and speak to oneof our technical representatives.

● THEORETICAL INK DEPOSITAs a reminder, the T.l.D. specification istheoretical. It is to be used as the basis for comparison to other mesh counts’ theoretical ink volumes. There are manyother factors that influence ink deposit. For example, screen tension, substrateabsorption, ink type, stencil thickness,squeegee variables, etc. One of our technical representatives can help you narrow down the mesh choices for testing,but actual print and measurement testingneeds to be done to obtain the actual inkdeposit for each individual shop. (A givenmesh count may work well with one shop’svariables and have a different result inanother shop.)

■ RECOMMENDED TENSION LEVELS The lower end of the tensioning range canbe achieved with most stretching systems,providing provisions have been made toeliminate high stress points. The higher tensions should be used by experiencedscreen makers utilizing state-of-the-artstretching systems and procedures. (Refer to “Rapid Tensioning vs. StageTensioning” Tech Tip on page 37.)

▲ Provides the comparative fabric strengthbetween mesh counts.


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xx17

50.

0034

0.00

3334

1.48

25xx

196

0.00

270.

0032

281.

22

SAA

TITE

X®:

A h

igh-

qual

ity m

ultif

ilam

ent p

olye

ster.

Avai

labl

e in

wid

ths

from

40

to 1

45 in

ches

and

mes

h co

unts

from

6xx

to 2

5xx.

Saatile

ne®

Hitec

h™

Half

-Cale

nder

ed P

oly

este

r Sp

ecif

ications

Mes

h Co

unt

Type

of

Wea

veTh

read

Diam

eter

Mes

hOp

enin

gPe

rcen

tage

of O

pen

Area

*

Over

all F

abric

Thick

ness

◆

Theo

retic

alIn

k De

posit

●

Reco

m-

men

ded

Tens

ion■

Spec

ific

Cros

s Se

ction

355

140

PW34

260.

0020

5013

6.5

0.33

20-2

90.

127

355

140

TW34

270.

0020

5014

70.

3520

-29

0.12

738

015

0PW

3421

0.00

2051

10.5

5.5

0.28

22-3

00.

136

380

150

TW34

230.

0020

5112

60.

3022

-30

0.13

642

016

5TW

3124

0.00

1742

167

0.35

20-2

80.

125

420

165

TW34

210.

0020

5212

60.

3025

-33

0.15

046

018

0TW

3117

0.00

1845

104.

50.

2323

-29

0.13

5

inch

cmTW

or P

Wm

icron

sm

icron

sin

chm

icron

s%

cm3 /

m2

cu. i

n/sq

. yd.

(N/c

m)

(SCS

mm2 /

cm)


Mes

h Co

unt

(per

inch

)Ty

pe o

fW

eave

Thre

adDi

amet

er(m

icron

s)

Mes

hOp

enin

g(in

ches

)

Over

all F

abric

Thick

ness

◆

(inch

es)

Perc

enta

ge o

fOp

en A

rea*

Theo

retic

alIn

k De

posit

●

(cu.

in./

sq. y

d.)

17PW

400

0.04

610.

0303

5521

.69

96PW

900.

0069

0.00

6742

3.64

110

PW80

0.00

630.

0057

433.

1714

0PW

610.

0047

0.00

4344

2.46

158

PW61

0.00

390.

0041

382.

0518

0PW

610.

0031

0.00

4432

1.84

196

PW50

0.00

310.

0033

371.

5823

0PW

500.

0024

0.00

3729

1.38

255

PW44

0.00

220.

0032

311.

2828

0PW

380.

0020

0.00

2832

1.17

305

TW37

0.00

190.

0028

321.

1730

5PW

370.

0017

0.00

2625

0.87

305

TW38

0.00

170.

0028

270.

9730

5PW

380.

0017

0.00

2625

0.87

330

TW38

0.00

160.

0029

260.

9735

5TW

370.

0013

0.00

2720

0.71

380

TW37

0.00

120.

0028

210.

7642

0TW

300.

0012

0.00

2325

0.76

460

TW30

0.00

100.

0024

210.

71

Saatilo

n®

Monofi

lam

ent

Nylo

n S

pec

ific

ations

SAA

TILO

N®:

A pr

ecisi

on-w

oven

mon

ofila

men

t nylo

n. D

ue to

its

inhe

rent

ela

stic

prop

ertie

s, it

is id

eal f

or p

rintin

g on

une

ven

and

curv

ed s

urfa

ces.

Exc

elle

nt a

bras

ion

resis

tanc

e an

d in

k pa

ssag

e. A

vaila

ble

in w

hite

, Ultr

a-O

rang

e, a

nd U

ltra-

Yello

w in

wid

ths

from

40

to 8

0 in

ches

. Mes

h co

unts

from

17

to 4

60 p

er in

ch.


PW:

Plai

n W

eave

(1:1

)Th

e ab

ove

are

aver

age

valu

es m

easu

red

in re

laxe

d sta

te,

man

ufac

ture

d w

ith y

arns

of a

per

fect

nom

inal

dia

met

er.

(cfr.

inte

rnat

iona

l sta

ndar

ds),

unde

r nor

mal

hyg

rom

etric

con

ditio

ns(2

0°C

=68°

F, 65

% re

lativ

e hu

mid

ity).

They

are

sub

ject

to n

orm

al v

aria

tions

up

to 7

% if

con

ditio

ns v

ary

from

thos

e sta

ted

abov

e.

Saatile

ne®

CD

Spec

ific

ations

Max

imum

Reco

mm

ende

dTe

nsio

n■

From

-To

Mes

h Co

unt

Wea

veNo

min

alTh

read

Diam

eter

Mes

hOp

enin

gFr

eeOp

enin

gFa

bric

Thick

ness

◆

Theo

retic

alIn

kDe

posit

●

Spec

ific

Cros

s-Se

ction

inch

cmµ

µ%

µcm

3/m2

mm2/

cmN/

cm30

512

0PW

3444

2754

150.

109

24-2

630

512

0PW

4035

1863

110.

151

23-2

638

015

0PW

3131

2247

100.

113

22-2

438

015

0PW

3423

1156

60.

136

25-2

746

018

0PW

2722

1641

70.

103

18-2

2

SAA

TILE

NE®

CD

-MES

H:

Com

pact

disc

spr

intin

g re

quire

s a

serie

s of

feat

ures

from

scre

en fa

bric

s su

ch a

s: te

nsile

stre

ngth

, el

evat

ed te

nsio

n, s

tabi

lity,

ste

ncil

dura

bilit

yan

d re

liabi

lity.

Thi

s is

due

to th

e pr

evai

ling

cond

ition

s w

hen

prin

ting

CD

s: lo

ng ru

ns,

fast

prin

ting

spee

d, g

ood

ink

perm

eabi

lity,

high

job

outp

ut,

quic

k pr

ess

set u

p an

d fa

stan

d ef

ficie

nt s

cree

n re

cycl

ing.

Saa

tilen

eC

D-M

ESH

is th

e fru

it of

the

late

st te

chno

logy

in fa

bric

mak

e-up

eng

inee

red

for s

uch

anap

plic

atio

n w

here

exp

ecta

tions

are

gre

at.

It of

fers

tens

ion

stabi

lity

supe

rior t

o th

at o

fhi

gh m

odul

us P

olye

ster f

abric

s w

ith a

grea

ter e

lasti

c m

emor

y an

d ex

cept

iona

lste

ncil

adhe

sion.

It e

nhan

ces

the

repr

oduc

-tio

n qu

ality

of t

he fi

nest

half-t

one

dot,

and

can

be re

cycl

ed m

aint

aini

ng th

e sa

me

prop

ertie

s.

New

mes

h co

unts

and/

or th

read

dia

met

ers

are

adde

d pe

riodi

cally

.

Plea

se in

quire

.


SAA

TILE

NE®

PCB-M

ESH

: El

ectro

nic

circ

uit

boar

ds a

re fu

ndam

enta

l to

the

perfe

ct fu

nc-

tioni

ng o

f sim

ple

or s

ophi

stica

ted

mod

ern

day

equi

pmen

t, m

achi

nery

or m

ass

com

mun

i-ca

tion

syste

ms.

The

ir pr

oduc

tion

depe

nds

onth

e hi

ghes

t kno

w-h

ow a

nd re

liabl

e m

anuf

ac-

turin

g co

mpo

nent

s. S

aatil

ene

PCB-

Mes

h is

a sc

reen

fabr

ic s

peci

ally

eng

inee

red

for t

hepr

oduc

tion

of e

lect

roni

c ci

rcui

t boa

rds

by th

esc

reen

prin

ting

proc

ess.

It is

a p

rodu

ct w

ithal

l the

nec

essa

ry in

gred

ient

s a

scre

en fa

bric

shou

ld o

ffer f

or s

uch

a de

cisiv

e en

d pr

oduc

t:hi

gh m

odul

us o

f ela

stici

ty fo

r tig

ht s

cree

n te

nsio

n; fa

st te

nsio

ning

pro

cedu

res

for t

hebu

sy s

cree

n pr

oduc

tion

depa

rtmen

t; op

timum

fabr

ic s

tabi

lity.

Saat

ilene

PC

B-M

esh

is pr

oduc

ed w

ith

a sp

ecia

l sur

face

trea

tmen

t tha

t gua

rant

ees

extre

mel

y hi

gh s

tenc

il du

rabi

lity

parti

cula

rlyfo

r ind

irect

and

cap

illary

ste

ncil

syste

ms,

and

the

mes

h m

anuf

actu

ring

tole

ranc

es a

re c

erti-

fied

to th

e IS

O 9

001

stand

ards

giv

ing

peac

e of

min

d w

hen

deal

ing

with

clo

se

tole

ranc

e ap

plic

atio

ns. S

aatile

ne P

CB-

Mes

h is

prod

uced

from

the

high

est g

rade

of m

onof

il-am

ent p

olye

ster y

arn,

and

is a

vaila

ble

in a

choi

ce o

f UV

abso

rben

t dye

s to

enh

ance

the

stenc

il ed

ge q

uality

of t

he m

ost d

eman

ding

circ

uits

imag

ed w

ith d

irect

or c

apilla

ry s

tenc

ilsy

stem

s.In

all

case

s of

prim

ary

and

seco

nd-

ary

imag

ing,

sel

ect S

aatile

ne P

CB-

Mes

h fro

m

the

rang

e of

Saa

ti sc

reen

prin

ting

fabr

ics.

PW:

Plai

n W

eave

(1:1

)Th

e ab

ove

item

s ar

e av

aila

ble

in s

tand

ard

wid

ths

of 1

15 a

nd 1

58 c

m (4

5" a

nd 6

2").

Saatile

ne®

PCB T

echnic

al Sp

ecif

ications

Max

imum

Reco

mm

ende

dTe

nsio

n■

From

-To

Mes

h Co

unt

Wea

veNo

min

alTh

read

Diam

eter

Mes

hOp

enin

gFr

eeOp

enin

gFa

bric

Thick

ness

◆

Theo

retic

alIn

kDe

posit

●

Spec

ific

Cros

s-Se

ction

inch

cmµ

µ%

µcm

3/m2

mm2/

cmN/

cm23

090

PW40

6838

6224

0.11

324

-32

255

100

PW40

5531

6019

0.12

628

-34

305

120

PW34

4529

5416

0.10

926

-33

355

140

PW34

2916

559

0.12

726

-32


ACTION TRADITIONAL FABRICTIME (MINUTES)

SAATILENE HIBONDTIME (MINUTES)

Wetting of Fabric 0.5 0.0

Roughening 5.0 0.0

Rinsing 0.5 0.0

Drying 10.0 0.0

Wetting (film) (0.5) (0.5)

Screen Coating 5.0 5.0

Drying 20.0 20.0

TOTAL TIME 41.0 25.0

TIME SAVINGS: 40%

Stencil Processing Time Chart

SAATILENE® HIBOND™: SaatileneHibond is a high tension/low elongationpolyester monofilament screen printing fab-ric, offering added bonuses to the stencilmaker and printer alike: time savings andstencil durability. While all screen fabricsimperatively require a thorough mesh treat-ment before stencil processing, SaatileneHIBOND is delivered ready to use. Its

special factory finishing renders the use ofadhesion promoters obsolete and in somecases reduces ghost imaging. Apart fromthe production time savings, it will extendthe life of stencils from single to triple andmore. This is a unique feature that is espe-cially beneficial where printing conditionsare unusually harsh either due to the natureof the substrate or that of the ink system.

New mesh counts

and/or thread diameters

are added periodically.

Please inquire.


Saatile

ne®

Hib

ond

™Te

chnic

al Sp

ecif

ications

Max

imum

Reco

mm

ende

dTe

nsio

n■Fr

om-T

o

Mes

h Co

unt

Wea

veNo

min

alTh

read

Diam

eter

Mes

hOp

enin

gFr

eeOp

enin

gFa

bric

Thick

ness

◆

Theo

retic

alIn

k De

posit

●Sp

ecifi

cCr

oss-

Secti

on

inch

cmµ

µ%

µcm

3/m2

mm2/

cmN/

cm11

043

PW80

150

4313

257

0.21

635

-37

125

49PW

7013

040

116

460.

188

30-3

412

549

PW80

120

3513

246

0.24

637

-40

129

51PW

7012

038

118

450.

196

30-3

512

951

PW80

110

3112

940

0.29

637

-40

140

55PW

6412

041

105

430.

176

26-3

114

055

PW80

9527

140

380.

276

40-4

515

862

PW64

9032

106

340.

199

30-3

417

368

PW55

8936

8932

0.16

125

-30

173

68PW

7065

2012

024

0.26

138

-42

180

71PW

5580

3391

300.

168

25-3

019

677

PW48

7836

8029

0.13

924

-26

196

77PW

5570

2890

250.

182

27-3

223

090

PW40

6838

6224

0.11

320

-24

230

90PW

4855

2781

220.

162

27-2

924

195

PW40

6537

6524

0.11

922

-24

255

100

PW40

5531

6420

0.12

526

-28

255

100

PW48

4016

8113

0.18

130

-34

280

110

PW34

5335

5620

0.09

922

-24

280

110

PW40

4726

6918

0.13

825

-30

305

120

PW31

5340

4819

0.09

021

-24

305

120

PW34

4529

5416

0.10

824

-26

cont

inue

d on

nex

t pag

e

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22


Oth

er it

ems

avai

labl

e on

req

uest.

PW

: Pl

ain

Wea

ve (1

:1),

TW:

Twill

Wea

ve (1

:2 -

2:2)

The

abov

e ar

e av

erag

e va

lues

mea

sure

d on

pie

ce-g

ood

in re

laxe

d sta

te,

man

ufac

ture

d w

ith y

arns

of a

per

fect

nom

inal

dia

met

er (c

fr. in

tern

atio

nal s

tand

ards

), un

der n

orm

al h

ygro

met

ricco

nditi

ons

(20°

C=6

8°F,

65%

rela

tive

hum

idity

). Th

ey a

re s

ubje

ct to

nor

mal

var

iatio

ns u

p to

7%

if c

ondi

tions

var

y fro

m th

ose

state

d ab

ove.

Saatile

ne®

Hib

ond

™Te

chnic

al Sp

ecif

ications

Max

imum

Reco

mm

ende

dTe

nsio

n■Fr

om-T

o

Mes

h Co

unt

Wea

veNo

min

alTh

read

Diam

eter

Mes

hOp

enin

gFr

eeOp

enin

gFa

bric

Thick

ness

◆

Theo

retic

alIn

k De

posit

●Sp

ecifi

cCr

oss-

Secti

on

cont

inue

d fro

m p

revi

ous

page

23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

inch

cmµ

µ%

µcm

3/m2

mm2/

cmN/

cm30

512

0TW

3447

3164

200.

108

24-2

630

512

0PW

4038

2067

130.

150

27-3

230

512

0TW

4041

2370

160.

150

27-3

233

013

0PW

3439

2655

140.

118

24-2

733

013

0TW

3441

2860

170.

118

24-2

735

514

0PW

2743

3642

150.

080

16-1

835

514

0PW

3138

2848

130.

105

20-2

235

514

0PW

3429

1656

90.

127

23-2

635

514

0TW

3432

2060

120.

127

23-2

638

015

0PW

2735

2744

120.

085

17-2

038

015

0PW

3129

2049

100.

113

22-2

438

015

0TW

3134

2755

150.

113

22-2

438

015

0PW

3425

1356

70.

136

25-2

738

015

0TW

3428

1761

100.

136

25-2

742

016

5PW

2730

2546

120.

094

17-2

142

016

5PW

3125

1749

80.

125

24-2

642

016

5TW

3130

2460

140.

125

24-2

642

016

5TW

3425

1666

10.5

0.14

924

-28

460

180

PW27

2520

438

0.10

318

-22

460

180

TW31

2317

569.

50.

136

23-2

750

820

0TW

3118

1360

80.

151

23-2

7


METALESTER MESH: Metalester is a high precision screen printing fabricwhose technical characteristics are thedirect result of Saati’s latest weaving tech-nology combined with the most recentdevelopments in the physical properties of the yarn. Metalester consists of a HighModulus polyester fabric coated by elec-tro-deposition of a thin but controlled layerof nickel. This gives the product specifictechnical features that benefit a number ofindustrial screen printing applications thatcannot be satisfied with conventional poly-ester fabrics.

FIELD OF APPLICATIONS• Hollow glass

• Flat glass

• Ceramic

• Printed circuit

FEATURES• Low mesh distortion: The nickel incapsu-

lation of the mesh considerably reduces fabric elongation helping to maintainthe geometrical characteristics of the mesh

• High stability: The product’s low elongation characteristics enhance thestability of the tensioned fabric, reach-ing optimum stabilization within a veryshort period of time

• Excellent abrasion resistance: The inherent nature of the nickel bringsadded value to Metalester in terms ofmechanical abrasion compared to conventional polyester fabrics

• Antistatic: Nickel is an excellent conductor of electricity and thereforeeliminates all risk of static build up

• Heat transfer: The excellent conductivityof Metalester makes it the right choiceto print with thermoplastic inks

• Optimum stencil adhesion: Most stencil systems adhered extremely well toMetalester, particularly indirect photostencil films

New mesh counts



Please inquire.



(*) P

W =

Pla

in w

eave

1:1

. O

ther

wid

ths

avai

labl

e (c

m/

inch

): 12

0/47

- 14

0/55

and

155

/61

Met

ale

ster

Tec

hnic

al Sp

ecif

ications

Stan

dard

W

idth

Mes

h Co

unt

Wea

veTh

read

Diam

eter

Mes

hOp

enin

gFr

eeOp

enin

gFa

bric

Thick

ness

◆Th

eore

tical

Ink

Depo

sit●

Max

imum

Rec

o.Te

nsion

Leve

ls■

inch

cmµm

µm%

µmcm

3/m2

N/cm

cminc

h61

24PW

137

275

4522

510

128

105

4111

043

PW87

142

3714

253

2810

541

140

55PW

7011

036

114

4126

105

4115

862

PW75

8829

116

3426

105

4118

071

PW68

7226

9124

2610

541

196

77PW

7162

2293

2026

105

4123

090

PW45

6231

7022

2410

541

255

100

PW47

5529

7121

2410

541

280

110

PW43

4727

5916

2210

541

305

120

PW43

4124

6014

2010

541

355

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HAVER & BOECKER STAINLESS STEEL WIRE CLOTHSaatiPrint is a direct importer of Haver & Boecker Stainless Steel Wire Cloth.Precision woven in Germany under ISO9001 certification, Haver Wire Cloth ismanufactured specifically for screen print-ing. Thus it provides the ink deposit unifor-mity and close-tolerance registration youneed for your critical jobs. For maximum inkdeposit control, choose Haver’s exclusiveCT Foil calendered wire.

Haver & Boecker’s entire wire manufac-turing process has been certified to meetthe highest international quality standards(DIN EN ISO 9001). The most extensiveof the ISO standards, the 9001 certifica-tion encompasses Haver & Boecker’sproduct design, development, production,installation and service.

With input from screen printers aroundthe world, Haver’s research team hasdeveloped measuring methods and test

procedures to perfect each phase of production. Haver’s tight tolerances, fromthe selection of wire threads to the finalinspection of each roll we deliver, guaran-tee reliability. So you can count on theintegrity of the wire diameter, aperturewidth and cloth thickness.

You can achieve defined ink depositseasily with the nearly endless choices ofHaver Wire. Within any mesh count,there’s a range of wire diameters. In addi-tion, any of these can be calendered.Available diameters range from 0.0007"to 0.0055" (accurate to within 1 micron).

Offered in plain or twill weave in widthsfrom 36 to 60 inches and mesh countsfrom 60 to 500 per inch. (Ask us aboutlarger widths and cut-to-size pieces.)

You’ll receive an individual inspectionsheet with every full roll. Each productionphase is highly monitored with Haver’sclose- tolerance, electronic measuring systems.

New mesh counts



Please inquire.



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The theoretical ink deposit is an approxi-mate value used to help select the most appro-priate mesh count for the printing application.As seen in the diagram, the ink is forcedthrough the wire cloth in cubes, whose volumeis determined by the mesh aperture (w) andthe cloth thickness (D). The cubes then flowtogether to form an even wet ink film of theoretical thickness on the substrate.

Since stainless steel wire cloth can bemade with extremely thin wire diameters, itcan deposit ink cubes with very small gapsbetween them. Therefore, the ink cubes haveonly a small distance to flow and form a uniform ink deposit, and thus, print definitionwith only the most minimal serration.

In addition to the wire cloth, other factors influencing the ultimate ink deposit include:ink viscosity, surface characteristics of thesubstrate, photostencil thickness and thesqueegee speed, angle and durometer. Thetheoretical ink deposit (Vth) can be calculatedin cm3 per m2 of wire cloth using the following formula:

Vth= [ W ]2x Dw+d

WHERE:w = mesh aperture (opening/microns)

d = wire diameter (microns)

D = cloth thickness (microns)

D1 = ink thickness (microns) at initial deposit

D2 = ink deposit (microns) after flowout

Theoretical Ink Deposit


QUESTIONWe use a very high mesh count (380)and high solids content emulsion, whichwe coat to produce a ten-micron stencilthickness for a sharp image. Everythinglooks great, but we still run into problemswhen printing four-color process. Insteadof nice round dots, the image is made up of irregular shapes, and some dots are missing altogether.

We know this causes problems with controlling neutral colors and flesh tones,and suspect it contributes to moiré, sowhat can we do to make a better stencil?

SOLUTIONIt sounds like you are already making veryhigh quality stencils, and they are probablyideal for fine line or even single-colorhalftone printing.

The problem is your ink deposit is waytoo high for four-color process printing,and you are suffering from some of thesame problems that printers using UV-curedinks have had to tackle. Remember, plastisol inks are 100% “solids” too, and the stencil/mesh combination youdescribe will probably lay down an inkdeposit of around 20 microns. This won’tcause a problem with the first color down,and probably not the second either. Theproblems usually arise when trying to lay down small dots of the third or fourthcolors. The ink deposit that has already

been built up prevents the stencil from contacting the substrate evenly. In areaswhere the two don’t touch, ink will not be pulled cleanly from the screen once the squeegee passes. Instead of a flat substrate, you are trying to print on something with a topography whichresembles a microscopic version ofManhattan. The piled up dots of the firstfew colors produce a high-rise barrierbetween the screen and the substrate.

The particular 380 mesh you mention,is produced with a twill weave configura-tion where threads are inserted into every second space in the weave. This meansthat although it is very fine when measuredby the number of threads per inch, there is still a lot of space for the ink to passthrough. In comparison, plain weavemesh, where threads are inserted intoevery space in the weave, has a muchlower percentage of open area, as wellas a lower fabric thickness. This combinedeffect of the smaller openings with the thinner fabric would reduce your inkdeposit tremendously, as the below comparison shows.

A further benefit of using plain weavemesh is that you can achieve good edgedefinition and sharp dot reproduction witha much lower stencil thickness. Instead ofhaving to build up a ten-micron stencil inorder to smooth over the long knucklesformed in the twill weave fabric, you

The Advantages Of Plain Weave Mesh For 4-Color Printing

Print from a plain weave fabric. Print from a twill weave fabric.



could get away with a five-micron stencilthickness on plain weave mesh. This willshave even more precious microns offyour ink deposit, and minimize the build-up that occurs and causes problems withyour later colors. Simply lowering stencilthickness on the mesh you are using justnow is not the answer. While you willprint less ink, your halftones will sufferpoor edge definition. Star-shaped dots are a major cause of problems with tonalbalance and moiré, the very problems we are trying to control.

On a different note, another techniquethat would also help is the use of positivesthat have been separated with gray

component replacement. With these types of separations, in areas of thedesign where yellow, magenta and cyanare all present, the density of the first threepositives can be reduced. The differenceis then made up at the end by printingwith a heavier black than would be usedwith normal separations. The benefit ofthis method is that early ink build-up isminimized. This, in conjunction with theright mesh and stencil combination, willprovide you the biggest window of operation for all the other parameters youhave to control, once you get your screensto press.

continued from previous page

Mesh Type Fabric Thickness % Open Area Ink Deposit

380 TW.34 63 microns 17% 11 microns

380 PW.34 56 microns 13% 7 microns


HANDBOOKFabric Tensioning & Preparation


THE USE OF THE TENSION METERThe tension meter is above all a precisioninstrument and should be handled withcare. Before engaging in any phase oftension control, always ensure that theinstrument is zeroed. The reading indicatedon the dial or display will correspond to the tension level of the fabric in the direction of the arrows shown on the instrument. Before recording the reading,tap the fabric gently near the base of themeter. Repeat several times, making surethat the reading is always the same.When measuring metalized polyester, lift the instrument rather than sliding it at the surface of the screen.

FABRIC TENSIONING WITH PNEUMATIC CLAMPSIn addition to the loss of tension that iscreated by the inherent nature of the yarnfinding its own level of tension, additionalloss may also originate from the frameitself not being able to fully oppose thepressure of the stretched fabric.

With the pneumatic clamps, this problem is alleviated as the clamps suchas Saati Clamps create an inward bowing of the frame during the fabric tensioning phase. The movement createdby the clamps reduces the loss of tensionthat is not attributed to the fabric.

In order to avoid inconsistency in tension, it is recommended to use clampsof the same make, with identical cylindercapacity, and same sized jaws. Shortwidth jaws will lead to a more uniformstretching. Short width jaws will requiremore clamps per frame, but this will

represent a higher total cylinder capacityfor a given surface, and the workingcapacity of the pistons will be greater.However, for large size screens it is com-mon practice to use wider jaws in whichcase a compromise needs to be made.

When setting up the equipment forscreen covering there may be a small gapof 2-3 mm between each clamp. This willallow for each clamp to mold itself to thefabric movement in phase of tension. Largergaps should not be permitted as this will benoticed on the finished screen as narrowbands of fabric with a lower tension.

Although each single clamp will pull to the predetermined setting on the regulator,care should be taken that the fabric is perfectly parallel to the set of clamps foreach respective side. Failure to do this will produce uneven thread alignment in therespective direction which could lead touneven mesh opening with adverse effectson print quality.

Before engaging the fabric in theclamps, check that they are all set on thesame starting point, i.e. as close to the sideof the frame as possible. The frame itselfshould be placed perfectly level and at sucha height that the fabric is in perfect contactwith its upper surface. Height adjustingscrews are normally found on each clampto regulate the level of the frame.

Experience will dictate what the correctheight should be in order to prevent thebase of the clamps to lift during tensioning,or in extreme cases, to overturn. Lifting of one or several clamps will affect theoverall tension uniformity.

Practical Recommendations For The Correct Handling Of Fabrics



FABRIC TENSIONING – STEP 1Once the fabric has been carefully placedand locked in the clamps positioned asdescribed above, the tensioning phasecan commence.

Using the regulator control, start activating the clamps. When the regulatorgauge reads 2 bars (10-20 psi), the tension meter can be placed on thestretched fabric. At this point the tensionlevel can be entirely guided by it. It is agood practice to measure the screen atfive control points to ensure that an eventension is being applied. Both warp andweft measurements should be taken. Bearin mind that it will take a minute for the air pressure to stabilize and the clamps to settle to a given tension level.

FABRIC TENSIONING – STEP 2Once the fabric has reached the desiredlevel of tension, it will eventually stabilizeto a level of tension lower than that initiallygiven. This "natural" tension loss can beminimized by letting the fabric rest for shortperiods during stretching. It is recommendedto let the fabric stabilize itself for 10 to 30 minutes before adhering it to the frame.However, it is counterproductive to let thefabric stand for more than 30 minutes.

Once the adhesive is perfectly dry, the frame can be released from the actionof the clamps. It is not advisable for the screen to be used for productionimmediately because the tension will finally stabilize to a lower level over a24–48 hour period. If the stencils are produced within that period of time, prob-lems of registration may be encountered.



General Recommendations For The Care And Usage Of A Tension Meter

1. Always place your tension meter at a90-degree angle to the mesh threads youare measuring. (Placing the meter on a 45-degree angle will result in getting afalse “average” reading of the twothread directions.)2. Don’t rely on the tension only in thecenter of your frame/stretcher. Use a 5 or 9-point system, depending upon thesize of the stretching area. It is importantto achieve uniform tension within yourimage area to achieve maximum registra-tion on press. It is also critical to check thetension in the corners. (A common causeof mesh ripping is over-stretched corners.)3. Handle the tension meter with care. Itis not overly fragile, but dropping it willmost likely result in the need to send itback to the manufacturer for repair. Duringthe stretching process, when the meter is

not on the screen mesh, place it either onits side or in its cushioned carrying case.(Placing the meter with the probe downon a hard surface causes premature/excess wear of the unit’s spring.)4. It is beneficial to have a spare meter,which is kept in a secured area. It notonly serves as a control for checking calibration of the primary meter, but alsoserves as a backup when the primarymeter needs to be sent back to the manufacturer for recalibration.5. Check the calibration against the sparecontrol meter approximately every 2 to 4 weeks (or more) depending uponusage and abuse. The procedure is simpleand instructions are provided with the unit.If the meter is out of calibration to the extentyou cannot adjust it, then it should be sentback to the manufacturer for recalibration.

Tension check 5 points (warp and weft) on screen (I.D.).

Tension check 9 points (warp and weft) on screen (I.D.).

SaatiPrint strongly recommends the use of a quality tension gauge to assurescreen-to-screen consistency, screen tension uniformity, and accuracy. SaatiPrintsuggests implementing a 5-point systemacross the screen area to guarantee uniform tension, and also to alert you to any excessive corner tensions.

Tension Meter UseMonitor screentension easilyand accuratelywith theNewman ST-Meter®.


Screen TensioningA Step-By-Step Guide

Optimum Screen Tension • Optimized Screen Performance • Extended Screen Life

INTRODUCTIONCare in mesh handling, loading, and tensioning control how well the screen print-ing fabric will perform throughout its production life cycle. All woven material,whether synthetic or stainless steel, hasunique properties and working characteris-tics that need to be understood in order to reap the benefits from its intended use;the production screen. By following theSaatiPrint recommended tensioning proce-dures and tension levels, optimum print control and performance can be achieved.

There is no single definitive tensionlevel recommendation that covers the sev-eral different synthetic materials available,along with the many mesh counts andthread diameters. Therefore, through extensive research and development,SaatiPrint has listed the safe working tension ranges for each of their screenmesh specifications. Each thread materialtype and diameter size has a specific“yield point” in both unwoven and wovenstates. This yield point is the maximum tension/elongation point a material reachesbefore it loses its memory or recuperativeproperties. The improper handling or ten-sioning of mesh, could exceed the materi-al’s yield point and result in the meshbreaking during screenmaking, printing

or even sitting idle. Working within thesafe or recommended tension levels willaffect and control on-press variables whichinclude print registration and ink release.

It is important for the screen maker and printer to be aware of the many production variables that will influencemesh performance, e.g.:

SCREEN MAKING VARIABLES• Type of tensioning unit or retensionable

frame system• Frame format size/and profile• Fabric stabilization and method used• Working tension level

PRESS VARIABLES• Squeegee pressure• Off-contact height• Image to frame size relationship• Squeegee to frame relationship

Having an established tensioning procedure, will provide consistent screenstime after time. The following proceduresshould be used as a guide in the handlingand tensioning of mesh with your system.Incorporating some, or all, of the recom-mendations in this guide will result in consistency for screen tension and on-press performance. Plus they willextend the life of your screen.

Saati pneumatic clamps employ a unique “movable” designfor “contact-less” uniform tensioning.

This innovative, easy-to-operate system stretchesNewman Roller Frames® automatically in lessthan 2 minutes per frame.



Regardless of the tensioning system, allfabric loading procedures are basicallysimilar. Equipment manufacturers mayhave their own, or additional step-by-stepinstructions in regard to loading fabric orcorner adjustment with their system. Asidefrom these two functions, there are other

individual considerations based on thetype of stretching system. Following aredescriptions of pneumatic clamps, reten-sionable frames and mechanical systems,focusing on key areas that need to beaddressed when tensioning screen meshwith that particular system.

Pneumatic – Mechanical – RetensionableFrames

Pneumatic ClampsState-of-the-art pneumatic clamp tension-

ing systems, such as Saati clamps, offer tworegulators (either standard or optional),which allow you to control both fabric directions (warp/weft – see below), whennecessary. The format size will determinewhether or not both regulators are used.Normally format sizes approximately 40” or under, will not require the use of both regulators. For format sizes above 40”, bothregulators are recommended in order toassure optimum tension uniformity, recom-mended tension level, and fabric stability.

Whether using a single regulator ordual set-up, begin tensioning the fabric in a continuous fashion until the target tension level has been reached. With thedual regulators, be sure to alternate evenlybetween warp and weft fabric directions.The target tension level should be reachedwithin the first five minutes of tensioning.From this point, the operator must decidethe level of fabric stability required for theprint application. There is no set minimumor maximum amount of time fabric shouldremain in the tensioning system. However,in order to sufficiently stabilize fabric in apneumatic system, SaatiPrint recommendswaiting approximately 30 minutes beforeadhering.

WARP & WEFTFabric has two thread directions whichare referred to as the “warp & weft.” Thedirection running the length of the roll orbolt, is the warp direction. The oppositedirection which is the width of the rollbetween the selvedges, is known as the weft. Historically, the warp & weftdirections of synthetic mesh exhibited considerably different stretch or elonga-tion characteristics. This was mainly dueto the weaving process. With the adventof new “Hitech” low-elongation threads,along with improved weaving and finish-ing technology, the elongation has notonly decreased significantly, but hasbecome more equalized. This technologyhas made “stretch-and-glue” tensioning systems more viable, especially individualpneumatic clamp systems.

The compact manifold plug-in system offers fast andeasy setup.




Retensionable frames fall into two maincategories; draw bar and roller. Each typehas its own locking mechanism and is usually either flat locking strips or round-shaped nylon dowel rods.

Follow the frame manufacturers’ meshloading procedures, which are similar to other systems as far as working toopposite sides, and avoiding a circularset-up. Perform corner adjustments necessary, which are determined by the frame size and tension levels.

From this point forward, follow both frameand mesh manufacturers’ recommenda-tion, being sure to alternate from roller to roller and side to side, tensioning themesh uniformly. Use a tension gauge tomonitor tension both warp and weft directions, adjusting in 2-6 N/cm increments. Depending on target tensionlevel and amount of stability needed, anadditional or further corner adjustment or

softening may be necessary. This is especially true when following a “print-reclaim-retension-print” procedure.

Retensionable Frames

The H24-D is a highly precise, self-contained, continu-ously adjustable tensioning system. It is especially suitedto thick film and surface mount screens and masks, glassand containers, precision graphics and electronics.

There are a variety of mechanical systems available utilizing either rigid “one-piece” sides or individual clamps.Regardless of the type, be sure to lock meshin as squarely as possible, always workingto the opposite side. As in other systems,corner adjustment is equally important.

Depending on the model, either a 2-way or 4-way stretch is possible. Besure to alternate tensioning in 2-4 N/cm increments to maintain tension uniformity in both warp and weft directions.

Mechanical System

NOTE: mesh relaxation and tension loss will be more noticeable in both mechanical andretensionable systems versus a pneumatic system. This is due to the fact that there are nocontinuous forces being applied to the mesh, as in a pneumatic system that carries constant air pressure maintaining continual tension. Therefore closer monitoring and retensioning is necessary to achieve a stabilized working tension level with these systems.


The use of a tension meter is critical in assuring uni-form and optimum screen tension levels.



Corner Adjustment Procedure

LOADING FABRIC (ANY SYSTEM)1. Begin by aligning the mesh into thestretcher as square to the clamps as possi-ble. Use the “selvedge” or fabric roll edgeto guarantee a straight edge as you alignthe mesh. Be sure to place enough meshinto the clamping mechanism to allow forcorner adjustment (see corner adjustmentprocedure). Pneumatic clamps must bealigned against each other leaving no spaces between clamps.

2. Start on one side and lock in the mesh completely with all the clamps in that row.Make sure that there is no pinching orwrinkles between clamps, which couldlater bind or possibly fracture the meshwhile tensioning.

3. Now lock in the fabric on the oppositeside. Be sure the mesh is square, and thatthere are no wrinkles or waves in themesh as you lock it in. Start at one endand begin locking clamps one at a time,while holding the fabric some what tautand at a slight angle away from the previ-ous clamp.

4. Lock in the third row with fabric in arelaxed state. Again, from one end, lockclamps one at a time, making sure thatthere are no wrinkles or pinch points.Once completed with the third side, moveacross to the last side and repeat step #3.

NOTE: with roller frames, the procedureis similar, except locking strips are utilized as the fabric locking mechanism.


CORNER ADJUSTMENT(ANY SYSTEM)When using fine mesh counts, elevatedtension levels, or large format frames, itmay be necessary to corner adjust thefabric in the stretching set-up. This adjust-

ment compensates for any excessive cornertensions, which could result in inconsistenttension from screen center to corner, orfabric fracture. The main cause for fabricbreaking, especially while tensioning, isdue to excessive corner tension.

ALIGNMENT MARKINGDraw a line against the corner clampedge using it as a straight edge andmake approximately a 6” line. Repeat at all corner clamps.

Use clamp edge as a guide for markingadjustment line.

Use alignment grooves in roller tomake adjustment line. If roller does nothave alignment grooves, use lockingstrip channel.

Use clamp edge as a guide formarking adjustment line.


With roller frames, use pre-grooved lines in rollers as a guide to make astraight edge.


CLAMP SYSTEMRelease corner clamps, and while keepingfabric taut, move laterally in on an angle.The distance adjusted in, will be basedon format size; A 40” x 40” format sizewill require approximately 1/2” adjust-ment in.

ROLLER FRAMEUsing rigid plastic squeegee, press in onlocking strip or rods, while also pushingfabric inward, watching your lines movein laterally at an angle. Use caution as to not pinch or cut fabric in groove whileadjusting.

LATERAL ANGLE ADJUSTMENT

Release corner clamps. While holdingfabric taut laterally, bring fabric in at an angle.

While applying pressure on fabricbetween rollers at corner section,press down on locking strip or rodsusing rigid scraper. Be sure mesh/linecomes in at an angle.

Release corner clamps. While hold-ing fabric taut laterally, bring fabricin at an angle.

CLAMP INTO POSITIONBring clamp down onto fabric while angleadjusting, making sure both corner clampshave been adjusted evenly. Be sure no

wrinkles are clamped in and avoid anyfabric pinching between clamps.

Once proper angle adjustment hasbeen made, clamp down, locking fabric into position.

Once proper angle adjustment hasbeen made, clamp down, lockingfabric into position.

Check for uniformity measuring angleadjustment from both rollers.



Using Proper Tensioning Techniques To Achieve The Desired Tension Level

QUESTIONI am using 305 PW 34 and I can onlytension my screens to 12-18 newtons withmy roller frames, and my mechanicalstretch-and-glue system. I know the fabricmanufacturer states that the fabric can go much higher to approximately 18-27 newtons. Is it the fabric that is failing or is it my procedure?

SOLUTIONThe greatest likelihood is that impropertensioning techniques are affecting thefabric’s performance. In order for the fab-ric to perform properly, the screen must bestretched properly. The following are afew things to check for in your system.

First, are you loading the fabric assquare to the locking channels or clampsas possible? Fabric that is loaded andstretched at an angle will not reach recommended tensions because of theuneven forces exerted on the fabric. Toavoid this, you should use the selvageedge, or a torn edge, as a guide whenlocking your fabric into your stretchingdevice. (Remember that when you tearfabric, it will tear straight.) Once the firstside is locked in as square as possible,move to the opposite side, and again lockthe fabric in as square as possible. Makesure there are no wrinkles caught in thelocking system, as this could cause fabricfailure. Now repeat the previous steps onthe remaining two sides.

Second, are you softening the corners?If you are softening, is it enough? Themajor reason fabric fails during stretchingon roller frames and mechanical systems isbecause the corner tension is higher thanthe tension in the image or print area.Excessive corner tensions can be detectedby the use of your tension meter. Place thetension meter in several areas, includingcorners of your frame, and look for hotspots, (where the tension is at least twonewtons higher than the print area). If youfind one of these hot spots, the cornersneed to be softened further. Check yourmanufacturer’s recommendation for cornersoftening techniques, or contact Saatiprintfor a free copy of our four-color stretchingbrochure that explains this procedure.

Another common problem is that youmay be over tensioning in one direction,and under tensioning in the other. You maynotice that as you tension in one direction,it affects the tension in the opposite direc-tion. With roller frames, you must pay par-ticular attention to the tension in both direc-tions. If you make an adjustment to oneside, you must make the same adjustmentto the opposite side. If you do not, youcould run the risk of skewing the threads,which would cause the fabric to fail.

One final note, you should make sure your frame is true/flat, not warped, andfree of sharp edges and burrs.


How To Avoid Mesh Problems WhenTensioning A Retensionable Frame

QUESTIONWe have a problem with our 180 meshscreens. We use Roller Frames, and like to re-tension our screens right up to themaximum level recommended for eachfabric. The problem we have run intohowever, is that some of the threads in themesh are breaking. This eventually causesthe screens to split. We originally thoughtthe problem was caused during printingby hard particles in the ink tearing up themesh. (Only the threads that go across thescreen are breaking.) However, our inksupplier assures us that the ink is not thecause. We try to keep the screens niceand even during re-tensioning by keepingthe mesh wrapped about the sameamount around each roller, and so far wehave not had any problems with our finemesh screens. Any ideas?

SOLUTIONThis is an interesting problem, and onethat highlights the intricacies of such aseemingly simple task as stretching apiece of screen mesh. Over time, printerssuch as yourselves, who test the upperlimit of the fabric’s tension-holding ability,will eventually encounter additional problems. (Above and beyond thosecaused by the normal gremlins at work in the screen room.)

Your problem with the 180 mesh in thiscase is probably caused by having agross imbalance in the amount of tensioning taking place on the warp andweft threads of the mesh. This situationcan occur after multiple re-tensionings,even though the finished tension level youmeasure on the screen may actually bewhat you require.

The root of the problem is that with anymechanical stretching system, and thisincludes self-tensioning frames, there arean infinite number of ways to arrive at anyparticular tension level. You have no doubt

noticed that when working with high-tensionscreens, that any additional tensionapplied in only one direction will actuallyincrease the tension in both directions. Asa result of this effect, it is possible to over-tension the warp (threads which run thelength of the bolt of fabric), and under-tension the weft (threads which run fromleft to right), or vice versa, and still arriveat your target tension level.

In this case, by keeping an evenamount of wrap around all four rollers ona rectangular frame and going throughmultiple re-tensionings (rather than keepingthe tension even) you have over-stretchedthe mesh in one direction.

The situation can be made even moresevere if you are using a regular polyestermesh, and you orient the fabric so that theweft threads line up with the short side ofthe frame. This is because in the normalstate of affairs, regular polyester exhibitshigher elongation of the warp threads,compared to the weft, in order to reachthe same tension level. (Unlike RollerFrames, this is compensated for automati-cally on pneumatic stretching systemsbased on individual clamps.) This differ-ence in elongation values is not alwaysthe case with all types of mesh. Hitechhigh-tension/low-elongation polyester fab-ric, in addition to holding more stable ten-sion, offers the major benefit of the warpand weft elongation being nearly equal.

With a 23” X 31” frame, for example,if you attain a fabric wrap of 1” aroundall four rollers, then this would correspondto 8.7% and 6.5% elongation of the meshin the short and long directions respective-ly. As long as the warp threads of themesh are aligned with the short side ofthe frame, the end result would be a very tight screen with even tension. This wouldhappen automatically if you stretch with40” wide mesh straight off the bolt.



If, however, you orient the mesh so thatthe weft threads are aligned with the shortside of the frame, then any imbalance inelongation values for the warp and weft,instead of working for you, is going towork against you. The net result is thatafter re-tensioning, the weft threads couldbe stretched close to breaking point, withthe warp still relatively under-tensioned.

The 180 screen you sent for evaluationhad the selvage (with mesh specificationsstamped on it) on the long side of theframe. Therefore, in this case it looks likeyou started with wider width mesh thatwas center slit, and then stretched so thatthe weft was indeed parallel to the shortside of the frame.

Now keep in mind that if you do multi-color work with tight traps, or any processprinting, you should always stretch yourmesh on the frames with the same orienta-tion in order to minimize registration prob-lems. In fact, we would recommend that

you always try to run the weft threads inthe long direction. Having the squeegeestroke run with the weft will aid in holdingtighter registration, and will improve your overall print performance.

The orientation of the fabric on theframe could probably explain why youhave not run into thread breaking andmesh splitting problems with your othermesh counts. In some situations it may notbe possible, or economical, to stretchscreens to print with the weft due to framesize versus fabric width considerations. Inthese cases, it is of utmost importance toclosely monitor your stretching procedure,and alternately advance the tension inonly 2 n/cm increments as you switchbetween the warp and weft. Although moretime consuming, this will prevent over-elon-gation and breaking of the threads, and is a better way to balance the tension than comparing the amount of fabric rolledaround each side of the frame.



Is Stretching On An Angle (On The Bias) Beneficial?

QUESTIONWe were told that stretching our screenmesh onto the frame at an angle, insteadof square, would improve our print quality.Is this true, and if so what is the bestangle?

SOLUTIONThe advice you received was partly correct,in that under some circumstances it canimprove print quality some of the time.However, it offers little if any benefit for mosttypes of printing, and requires a different,(and probably more costly approach) inyour methods of stretching screens.

The types of printing that benefit fromangling the mesh on the frame includethose where the artwork consists mostly of thin, straight parallel and perpendicularlines, such as those in circuitry, name-plates or panels. In these cases, the linesprint better because they are at an angleto the mesh threads.

Some other types of printing benefitfrom angling the mesh on the framebecause the squeegee then runs at anangle to the mesh threads. For instance,this is the case with the very fast printingspeeds involved when decorating com-pact discs. Angling the mesh in relation tothe squeegee results in improved flow andtransfer of the UV-cured inks.

These benefits, although substantial forsome types of printing, and maybe evencritical for success in the above-mentionedapplications, will not be realized withmost types of printing. In fact, most of thetime the drawbacks associated withangling the mesh on the frame will morethan offset any perceived benefits.

It’s not just a question of increasedcost, where you need to use a longer andwider piece of fabric to accommodate aframe at an angle, there are also sometechnical arguments for why it’s not agood idea.

You may suffer some unexpected distor-tion of the printed image, which will be especially exaggerated if you use an oversized squeegee, or excessive off-contact, in conjunction with too muchsqueegee pressure. This can also show up as increased difficulty in achieving registration when printing multi-colorimages, particularly in larger formats.

If you use self-tensioning frames, thenstretching at an angle, or on the bias as itis sometimes referred to, is definitely notrecommended. Although not impossible, itis very difficult, and there are severe limi-tations on how much of an angle you canachieve, and the tension level that can bereached. First of all, there is a tendency topull the mesh openings out of square, dueto the initial tensioning and pre-softeningof the corners, and this can have an effecton ink deposit, or even cause moiré.

The amount of distortion increases asthe angle is raised or as the tension levelis increased, and in addition to this, it isvery difficult during stretching to achievean even tension over the whole print area.

If you stretch and glue, even thoughyou keep the mesh openings nice andsquare, and the tension even, the screenmesh seems to be more fragile at theupper end of the recommended tensionrange because the mesh is stretchedsquare with the frame angled underneath.Things that you would normally get awaywith, such as scraping some emulsion onthe screen with an old nicked-up scoopcoater, or leaving haze-remover on for toolong, will suddenly start to split the meshfor no apparent reason.

Now, having considered the possible benefits, and also the drawbacks, if youstill want to try printing with your screenmesh stretched at an angle, then wewould recommend using 22.5 degrees.This angle has been proven to work, and




is used successfully to overcome problemsin the types of printing mentioned at thebeginning. If you don’t have a protractorto measure angles, then you can use aruler on a straight edge to measure teninches along and 4.1 inches out. Whenyou join the starting and finishing points,the angle of the line will be 22.5 degreesfrom your straight edge.

One last thing, if you print halftones or four-color process, don’t forget that youmay also have to adjust the angles of thedots on your positives in order to avoidthe formation of moiré when exposingscreens with your newly angled mesh.

Fabric printed with no angle. Fabric printed with angle.


QUESTIONIs it necessary to leave my screens in thestretcher for 2 hours before gluing?

SOLUTIONIn the past, it was thought that the meshhad to be tensioned in stages in order to achieve a properly stabilized screen.Recent studies have shown otherwise. It has been concluded that in using therapid tensioning (RT) method, tensionedscreens will normally result in a one newton or less difference in stabilized tension loss when compared with thelonger stage tensioning methods.

The RT method differs from others, inthat the tension is brought up immediatelyto the recommended tension level, withoutthe stabilizing pauses or stages in-between.This allows the mesh to begin stabilizingimmediately, and level off to the recom-mended tension level in a stabilized statemuch sooner.

The result of Saati’s extensive researchand testing has shown that there are defin-itive benefits achieved from the screenmesh when used in conjunction with theRT method. The Screen Printing TechnicalFoundation (SPTF) has also verified similarfindings in regard to the benefits of rapidtensioning Update”). For detailed informa-

Rapid Tensioning Versus Stage Tensioning

tion concerning the SPTF’s findings, contact the foundation at (703) 385-1417.

The most notable benefits the RTmethod provide are time and labor sav-ings, without sacrificing print quality, orcausing negative effects to the mesh characteristics or performance.

Although the RT method can be usedwith most stretching equipment or reten-sionable frames, our experience indicatesthat maximum performance can beachieved conveniently when using a pneumatically operated and controlled tensioning system with individual movingclamps (such as Saati Clamps). Whenincorporating the RT method into yourscreen-making process, careful monitoringand adjustments need to be made inorder to achieve the optimum performancefrom the mesh to suit your individualscreen and printing requirements. Forexample, attention must be given to assuring uniform stretching of the warpand weft, while avoiding excessive corner tensions.

For proper tensioning procedures, and more information on the RT method,please request “SaatiPrint’s TensioningManual.” This includes the most up-to-dateinstructions for mechanical and pneumatictype tensioning equipment.


QUESTIONWe are having trouble getting enough inklaydown. We have even gone down asfar as a 61 mesh for our white ink, andare still not getting good enough cover-age. We coat our screens once on theprint side, and twice on the squeegeeside, but think there might not be enoughsolids content in the emulsion. Do youthink a higher solids emulsion would helpwith our problem?

SOLUTIONIn a word…no. The impact of using athicker stencil (whether you make it byswitching to a higher solids content emulsion or simply applying more coats of the brand you are currently using) willonly be felt on the ink deposit of smalldetail, and around the perimeter of thelarger detail in your design.

Once you move a certain distanceaway from the edge of the stencil, it canno longer exert any influence on theamount of ink that is deposited. Theresponsibility for that job falls to the meshitself, with the important factors beingmesh thickness, and probably more impor-tantly its percentage of open area.

The 61 mesh that you used to printyour white with poor results normally laysdown a very thick ink deposit, actuallyway too thick for most people! Look atyour printed samples, you will see thatyou do not have a problem laying downenough ink. You do, however, have aproblem with poor coverage.

It looks like the underlying cause of yourpoor coverage problems is due to insuffi-cient mesh tension in your screens duringprinting. Instead of laying the ink on top ofthe shirt by a smooth, continuous film, you

are forcing most of it into and through theshirt. The result being that you have bothpoor coverage, and a very heavy handcaused by the thick ink film on the garment.

In these days of rigid metal frames usedwith off-contact pneumatic clamps, and self-tensioning frames, there is no goodargument for going to press with less than20 newtons of tension in your screens. Byprinting with a tighter screen, you will thenneed to reduce both the off-contact distanceand the squeegee pressure. By reducingthe squeegee pressure, you will then allowthe ink to lay on top of the shirt, instead ofbeing driven deep into the fabric. Screentension is perhaps the single most criticalelement that determines just how much control you have over the printing process,and how successful it will be.

Indeed, there are now many people who take the view that 20N is insufficienttension for their needs. That’s becauseeven higher tension levels result in betterregistration, and faster printing speedswith less smearing and ink build-up whenprinting wet on wet. Along with numerousother benefits that are outside the scope ofyour current problem. However, don’t tryto run too fast before you can walk! Investin some decent frames and/or a newstretching system, and tension your screensso they go to press with a minimum of20N. With the right print set-up, youshould then get good coverage with yourwhite ink through an 86 or 110 mesh, or maybe even a finer mesh count,depending on the surface of the garment.

Don’t be put off by the cost of somenew frames. Your rewards will be a betterlooking and feeling shirt. Remember that a gallon of ink will go much further, andthink of all the money you will save.

Problems Associated With Insufficient Tension


With any frame, care should be taken to stay within the recommended limits ofmanufacturer of the profile sizes. One ofour technical representatives can help youchoose the correct profile size for yourframe size.

WOOD FRAMESAlthough wood frames may require asmaller initial cash investment, it will soonbe realized that they are less cost-effectivein the long run. For more critical jobs,wood frames do not provide the stabilityneeded for registration, and require con-stant press adjustment. They hold moisture,which in turn can cause them to warp and bow. If screen tension and uniformityof tension are sacrificed where they arerequired, inefficiencies and quality problems occur.

RIGID METAL FRAMESThese frames provide the rigidity andstrength for higher tension levels, as wellas a longer lifetime. Printing results willimprove greatly over wood frames.

A quality made metal frame is con-structed of steel (coated), aluminum or

magnesium. Insist that these frames arewelded and not screwed together. Youcan also select the finish; either groundmechanically or sand-blasted. Both workquite well, but some people have a prefer-ence for one or the other. If you do nothave a stretcher that pre-bows the frame,insist on the thickest side-wall that is avail-able so that the frame does not lose tension due to deflection of the fabric.

SELF-TENSIONING/RETENSIONABLE FRAMESNot only do these frames serve as theirown stretcher, thereby eliminating theadditional need for a stretcher and adhesive, but they provide the ultimate in control over screen tension. You canachieve optimum screen tension and uniformity throughout the screen, in addi-tion to the longest and best possible life ofthe fabric. Achieving higher tension levelsallows closer off-contact distances, whichresults in better print edge quality andmaximized registration. Longer stencil andsqueegee life are also benefits as a resultof these closer off-contact distances.

Choosing A Frame

We offer a wide variety of frames to meet your everyday needs.


QUESTIONMy fabric is not sticking to my frame. I amusing a cyanoacrylate product on a 380PW 34 fabric. What am I doing wrong?

SOLUTIONUnfortunately, there is no one answer toyour question. Several things can causeyour adhesive to fail, whether you areusing a cyanoacrylate, urethane or othertype of adhesive. The following are somepreventive measures you can take toavoid adhesive failure.

1. You must make sure the frame-gluingsurface is not too smooth. (If you notice,new frames are sandblasted or roughenedmechanically with a grinder; this is doneto improve adhesion.) Sometimes a rough(80 grit) sandpaper is needed to give the frame some “tooth” or area that theadhesive can grab.

2. On the other hand, your frames shouldbe clean of old fabric, ink, oils, and exces-sive adhesive residue. Intimate adhesivecontact to the frame is critical, especiallyunder high tension. Adhesive-to-adhesivebonds are not as strong as adhesive-to-metal or adhesive-to-wood bonds. Framescan be cleaned (prior to applying newadhesive) with a debonder solvent, or asolvent like acetone to remove adhesive,inks, dirt, and oils.

3. It is also very important that you selectthe right adhesive viscosity for each partic-ular mesh count. In your case, on a 380PW 34, an adhesive with a low-viscosityof 100 centipoise would be recommended.A good rule of thumb is:

Trade grades of adhesive are also avail-able that are 600 centipoise for use onmesh counts from 110 to 355. Someadhesive viscosities are denoted by LV(low viscosity) and HV (high viscosity).Proper selection will ensure that the adhe-sive will flow through the fabric and provide a good bond by bridging thegap between the fabric and the frame.

How To Avoid Frame Adhesive Failure

4. When using two-part adhesives thatneed to be mixed, (versus cyanoacrylateadhesives that do not), it is important tofollow the manufacturer’s recommendationfor the proper mixing ratio. Failure to doso can cause problems with curing timesand/or solvent resistance.

5. When you activate a cyanoacrylateadhesive with either the pump or aerosoltype activator (this speeds drying time), keepin mind that it only takes a light misting tostart the curing process. If you spray toomuch activator on the adhesive, you cancause the adhesive to turn white or “bloom”.This can affect the adhesive’s strength.

6. Likewise, beware of the old adage, “If a little is good, a lot is better”, when itcomes to applying the adhesive. You onlyneed a thin coating of adhesive to adherethe fabric to the frame. If the adhesivelayer is too thick, the activator may onlycure the top portion, while the portion thatis in contact with the frame is still wet andmay not cure for a few more minutes. Ifyou feel you need a thick layer of adhe-sive for solvent resistance, add a secondlayer after the first layer is fully cured.

7. Check to make sure your frames arenot warped, and that the face of theframes are completely level. If your framedoes not lie flat, this may cause the fabricto remain raised off affected areas of theframe surface after you pass these spotswith the adhesive applicator. A quick reme-dy for this would be to add weights on theinside and/or outside of the frame duringgluing to bring the fabric into intimate con-tact with the frame. A one-inch steel barstock can be used for this purpose.

Choosing Your Adhesive Viscosity

Mesh Count RecommendedAdhesive Viscosity

255 and up 100 Centipoise

255 and under 1500 Centipoise

110 to 355 300-600 Centipoise


QUESTIONWhat is mesh pretreatment?

SOLUTIONMesh pretreatment is the process of cleaning and preparing the screen meshsurface to improve stencil adhesion andeliminate coating defects, with the ultimategoal being optimum stencil performanceand durability.

With virgin monofilament syntheticscreen mesh, we recommend using anabrasive degreaser product, followed bya degreaser/pretreatment between subse-quent stencils. For all other mesh, we rec-ommend using a degreaser/pretreatmentprior to stencil production and reuse.

Today there are carefully formulatedmesh preparations available that go astep beyond conventional degreasers. Forexample, SaatiChem’s Direct-Prep™ 2actually treats the mesh surface. Direct-Prep 2 leaves a microscopic layer of anadhesion promoter on the surface of themesh threads that improves film lamination and the coating and bonding of directphotoemulsions.

QUESTIONWhy should I degrease my screen fabric?isn’t it clean when I receive it?

SOLUTIONYes, it is. However, handling duringstretching can contaminate the mesh (skinoils, dust, etc.). These invisible contami-nants can then impair stencil adhesion.Also, as we’ve described, good meshpreparation is more than just cleaning.

A properly degreased/treated screen surface should display a thin, even film ofwater with no beading. Inadequate meshpreparation can lead to:

1) splits, spots and fisheyes in the wetemulsion coating

2) pinholes

3) blotchiness due to uneven stencil thickness

Mesh Pretreatment & Degreasing

4) dry spots or air pockets trapped underthe capillary film

5) premature stencil breakdown due to poor adhesion

QUESTIONIsn’t degreasing necessary only with capillary films?

SOLUTIONWhile it’s true that the special degreaser/mesh pretreatment products weredesigned originally for use with capillaryfilm, research has shown that the benefitsapply to an equal or greater degree todirect photoemulsions. The products weresought for capillary films because of theirability to raise the surface energy of themesh, enabling it to hold an even film ofwater on the surface.

The extra ingredient in these productsthat makes all the difference, was actuallyused in the past as a pretreatment toenable dye to adhere to polyester. As an illustrative point, consider the diazosensitizer used in emulsions to be a formof dye. The special mesh preparation provides a link to attach the emulsion poly-mers firmly to the otherwise inert polyestersurface. It is also the “wetting” action ofthe thin layer of adhesion promoter, whencombined with an effective cleaner, thatenables this type of product to improve the coating quality of your emulsion.

QUESTIONWhy not use solvents or household cleaners to degrease my screen?

SOLUTIONScreen printing solvents will dissolvegrease and oil (except silicone oils) on the fabric surface, but during evaporationthese contaminants will redeposit them-selves. Caustic degreasers should also beavoided because they increase the alkalinityof your waste water. If used in sufficientquantity, they may even raise the pH



above the limit allowed by your localwater treatment authority.

Household detergents are also unsuit-able; they contain ingredients like lanolinand perfumes that leave a film on the mesh.

QUESTIONWhy is fabric roughening or abradingnecessary?

SOLUTIONDue to the nature of virgin syntheticmonofilament mesh, it is necessary to gently abrade it before use to make itmore receptive to good stencil adhesion.If you have ever seen polyester meshunder high magnification, you can attestto the surface of the threads being assmooth and featureless as polished glass.This, combined with the fact that polyesteris a difficult substrate to stick to, meansyour emulsion coating needs all the help it can get to maximize adhesion. (Theinherent surface traits of multifilament synthetic or stainless steel mesh already

promote adequate adhesion.)This becomes more and more impor-

tant as the mesh count decreases; fewerthreads mean less surface area, and therefore less to grip. A slight rougheningof the surface increases the physical adhesion of the stencil to the fabric andenables it to better tolerate adverse conditions. For instance, it is better able to withstand the flexing and stretching thatoccurs if you ever have to print with a highoff-contact. Particularly when the humiditystarts to rise and your stencil is susceptible to losing some abrasion resistance.

Your stencil on a virgin polyester screenthat hasn’t been abraded can be com-pared to a coat of paint on an unprimedsurface. Subjected to the battering of windand rain, it begins to flake.

NOTE: household scouring powders shouldnot be used. Their grain particles are toolarge, uneven and aggressive, which cancause clogging of the mesh openings orexcessive thread damage.


Properly abraded fabric

Virgin monofilament fabric Over-abraded fabric



QUESTIONWhy is good wetting action important to stencil adhesion?

SOLUTIONAll stencil systems contain a percentage of water, so the more receptive a screen is to water, the better the stencil adhesion.Equally important is that the screen bereceptive uniformly.

QUESTIONWhat are the special mesh preparationconsiderations when using a pure photopolymer emulsion?

SOLUTIONCorrect mesh preparation is essentialwhen using a pure photopolymer emulsionin order to maximize adhesion during stencil processing, and durability on press.Prior to coating, a mesh prep/degreasercontaining a wetting agent should beused. This leaves the smooth, inert surfaceof monofilament polyester primed toadhere much better to pure photopolymerstencils. This is illustrated in the photo-graph where one half of the screen wasdegreased only with a detergent cleanerand the other side was degreased withSaatiChem’s Direct-Prep 2.

Degreased with a detergent


Degreased with SaatiChem Direct-Prep 2



HANDBOOKStencil Processing


CLEANLINESS/QUALITY CONTROLOne of the main causes of pinholes isspecks of dirt, lint fibers, adhesive residuefrom tape, or any other kind of contamina-tion that can get stuck on glass surfaces in the exposure frame, or to the artwork,or even the coated screen itself. Airbornecontamination needs to be avoided during coating, drying and storage. Thisis important particularly while the emulsionsurface is still wet.

Maintaining good housekeeping pro-cedures should prevent any build-up ofdebris on the floors, drying racks, etc.,which could be disturbed and then landon coated screens. Exposure frame glassshould be kept spotless and positivesshould be cleaned and inspected beforeuse, if necessary. Artwork which is badlyscratched will cause pinholes, and shouldtherefore be re-made. Likewise, deepscratches on the glass inside the vacuumframe will cause pinholes in your screens.If the glass is badly scratched, it shouldbe replaced, or at least reversed so thatthe scratches do not cast a sharp shadowonto the emulsion during exposure.

EMULSION HANDLINGBubbles in the emulsion that transfer ontothe mesh during coating are a majorcause of pinholes. Diazo and dual-cureemulsions need to be stirred during sensi-tizing with a broad flat paddle until asmooth and even consistency is obtained. If you beat the emulsion with a stick, thenit will take ten times longer to enable thetrapped air bubbles to escape. The smallerthe bubble, the longer it takes to rise to thetop and pop. If the emulsion does containfine air bubbles, then they may not cause a problem when coating fine mesh, sincethe mesh openings are too small to hold abubble, but they will cause a problem withyour lower mesh counts.

Even if you start with an emulsion freeof bubbles, you can still expect to run into

pinhole problems with your coarse meshcounts if you coat too fast. The turbulencegenerated in the emulsion as the scoopcoater rides over the large woven knuck-les of lower mesh counts is a great way to make foam. Scoop coaters with asharp edge increase the likelihood of thisoccurrence due to the higher rate of shearon the emulsion.

NOTE: when coating a large number of coarse mesh screens, pour off the emulsion in the scoop coater (and let itrecover) as soon as it starts to retain a lotof bubbles. Start coating again with freshemulsion and you will have a lot less pinholes. (Refer to “What Are OptimumDrying Conditions” Tech Tip page 62-63.)

EXPOSUREOptimum exposure, or rather avoidanceof gross under exposure, is the third areathat requires attention. The first thing toavoid is batch exposing screens of verydifferent mesh counts. For example, adirect emulsion stencil on a 61 meshneeds twice the exposure compared to 110, and roughly three times when compared to 158 mesh. If you do batchexpose, then only combine screens with anarrow range of mesh counts, and don’tmix white mesh with dyed mesh screens.With a dyed fabric, even if the meshcount is the same, it still needs an approxi-mately 50% longer exposure time toenable the emulsion to harden properly.

Also, avoid coating screens whichhave lost tension. The thick patch of emul-sion that builds up in the middle of thescreen is not only difficult to dry properly,it will also not expose correctly and willcause premature breakdown on press.

Finally, do some exposure tests tocheck how near or far you are from opti-mum exposure. You may use an exposure calculator or digital radiometer. (Refer to“Determining Optimum Exposure” Tech Tip


How To Reduce Pinholes


on page 66.) Another option is using aSaati 21-step grey scale, or stepwedgewhen exposing your production screens.Position the stepwedge where you cancover it with blockout before printing.

When you wash out the stencil, you shouldhold 6 or 7 solid steps on the wedge ifyou are at the correct exposure. For everytwo steps you are short, you need to double your exposure time.

By using these tools to conduct exposure testing you canreduce your chance of pinholes which are caused byunder-exposure.


Autotype exposure calculator. TQM™ Digital Radiometer.

Stouffer Resolution Guide and Saati 21-Step Sensitivity Guide


PART 1 – INTRODUCTIONThe purpose of this guide is to give anoutline of commercially available stencilsystems and the properties they possess. In doing so, we will touch upon the various technology employed, the effect ofprocessing variables, and finally examinethe effect of some of the factors that limitwhat is achievable.

PART 2 – STENCIL TYPESCommercially available photostencils fallinto four main categories. The first isknown as Indirect Film, where the stencilimaging and developing process is car-ried out independently of the screen mesh.The finished stencil is applied to the mesh with gentle pressure, blotted withnewsprint, and dried prior to removal ofthe backing film. Although capable of thehighest quality reproduction, the thin edgeof the finished stencil is very fragile andeasily damaged, and therefore unsuitablefor long print runs or for printing on diffi-cult substrates. Indirect film is only suitablefor use on finer mesh counts that are capable of supporting the fragile stencil.See Figure 1.

The second type of stencil is known asDirect Film or Capillary Film. In this case,a much thicker layer of pre-coated photo-

graphic emulsion, that has been manufac-tured to a precise thickness, is adhered to a wet screen mesh through capillary action.After drying and removal of the backingfilm, exposure and development producesa much stronger and more firmly adheredstencil than in the previous case, but stillwith the image quality associated with afilm based product. See Figure 2.

With the third type of stencil, known asDirect/Indirect, the film is laminated to themesh with a layer of photographic emul-sion instead of water. Once this sandwichhas dried, processing is carried out thesame as for capillary film, but with theadvantage that an even more firmlyadhered and durable stencil is produced.The downside is that the stencil makingprocess is more complicated and messy,particularly in larger formats, and is alsomore costly since both film and emulsionare required. See Figure 3.

What To Expect From Your Stencil

Indirect Film• Highest resolution

(processed away from the mesh)• Excellent definition

(short print runs only)• Poor durability, 100’s of prints• Expensive• Requires skill to process

(chemical processing)• fine mesh only

Capillary Film• Very good resolution and definition• Medium durability, 1000’s of prints• Expensive• Range of thickness available to

cover most mesh counts• Automation possible

Direct/Indirect• Very good resolution and excellent

definition• Extremely durable, 1000’s of prints• Expensive, both film and emulsion

required• Messy process, requires skill• Most suitable for small format

Figure 3

Figure 1

Figure 2



That brings us to the last, and most commonly used, type of stencil which isknown as Direct Emulsion. In this case the mesh is coated with a light sensitive emulsion, which when dry is imaged andthen developed in the same fashion ascapillary film. This is by far the leastexpensive method, in terms of materialcost, and results in the most durable stencils. However it is also capable ofproducing poorer print quality than any ofthe film based systems, unless the correctchoices are made in terms of emulsiontype and methods of processing andbringing several variables under control.See Figure 4.

PART 3 – TECHNOLOGY OF STENCILSWith the exception of indirect stencil films,which generally are thin coatings of gelatincontaining an iron salt sensitizer, the othertypes of photostencil system, mainly directemulsion and capillary film, which is reallypre-coated emulsion, are based upon aresin known as polyvinylalcohol. Polyvinyl-alcohol possesses an unusual combinationof three properties that make it uniquely suit-ed to be used as the basis of most stencilmaterials. First it is a water soluble polymer,which means that stencil processing and

developing can be carried out with water,rather than organic solvents. Second, it ishighly solvent resistant, unlike most otherwater soluble polymers that tend to dissolveeven more readily in solvents, and thereforestencils are able to stand up to a wide variety of different ink types. Third, polyviny-lalcohol contains a link in it’s polymer chainthat is easily broken by the application of dilute aqueous solutions of sodium metaperiodate, (AKA emulsion remover).This means that after printing, the mesh can be recovered and reused by strippingthe stencil without harsh chemicals.

In order to make capillary films anddirect emulsions light sensitive, there is achoice of three basic types of technology,Diazo, Dual-Cure or Photopolymer. Inaddition, other ingredients such as fillersor bulking agents are added to increasethe solid content and improve wet strengthof the stencil during processing. The choiceof sensitizers, and the type or combinationof fillers used will determine the propertiesof the end product. Ancillary ingredientsinclude pigments, surfactants which improvecoating quality, and defoamers to kill bubbles during processing.

The simplest technology employs adiazo sensitizer which is actually a poly-meric yellow dye, that is unstable anddecomposes when exposed to actinic blueand UV light. When exposed, the diazoreacts with the polyvinylalcohol crosslinkingthe polymer chains and decreasing it’s solu-bility in water. This enables the stencil toform on the mesh during developing. Theother ingredients that are added duringmanufacturing of the emulsion determinewhat it’s final properties will be. Withdiazo emulsions and films, the other mainingredient is known as polyvinylacetate.Polyvinylacetate is used to add bulk,increase solids content, and due to it’swater repellent nature is also effective inincreasing the wet strength of the stencilduring processing by preventing over-

Direct/Emulsion• Good resolution• Definition poor-excellent, depends

on processing• Extremely durable, 1,000’s plus prints• Inexpensive• Easy to automate• Suitable for all size formats and

any mesh count• Widest compatibility with ink

chemistry

Figure 4




swelling of the cross-linked polyvinylalcohol,and loss of detail. If enough polyvinylac-etate is used then the final stencil canbecome water resistant enough to be usedfor printing water-based inks. The problemwith polyvinylacetate however is that it isvery sensitive to organic solvents. If a highlevel is used, then the excellent solventresistance and easy reclaiming conferredon the stencil by the use of the polyvinylal-cohol component is compromised. For thisreason, diazo emulsions tend to fall intoone of two categories, solvent resistant orwater resistant. See Figure 5.

With Dual-Cure emulsion and film, thediazo sensitizer, which is still used, is forti-fied by including an additional crosslink-ing system at the time of manufacture. Thisadditional crosslinking system is used toreinforce, or in certain cases even replace,the polyvinylacetate component of thestencil. By combining these two separatecrosslinking systems, each separately forthe two main components of the emulsion,it is possible to engineer properties intothe stencil that were mutually exclusivewith diazo sensitized products. Forinstance water and solvent resistance, orhigh solids and easy reclaiming. For thisreason, most manufacturers of stencil mate-rials now offer a universal type of dual-

cure direct emulsion that combines most of the properties of the “ideal” stencil. See Figure 6.

Photopolymer stencil products do notcontain diazo, since they are manufac-tured with a light sensitive polymer.Emulsions are supplied presensitized andready to use with no mixing required, andboth photopolymer emulsion and film havea shelf life that is measured in years, andnot weeks or months. (Diazo is affectednot only by light, but also by heat andhumidity). The other distinguishing featureof photopolymer is that exposure times area fraction of what would be used foreither diazo or dual-cure products. This isdue to the very high sensitivity of the poly-mer that is used. The resistance propertiesof photopolymer fall into the same categories as those for diazo sensitizedmaterial, either solvent or water resistant.Having said that however, the water resist-ance of commercially available photopoly-mer emulsions does not yet rival that ofdiazo. Products designed for garmentprinting are really more suited for use onlywith plastisol inks, unless a hardener isused to reinforce the screen. The very fastexposure times achievable with photopoly-mer has also enabled the development of products that are suitable for use withextremely weak light sources, such as projection exposure. See Figure 7.

Diazo EmulsionSolvent Resistant• 20-30% solids content• Easy to reclaim• Not humidity or water resistant• Inexpensive

Water Resistant• 35-45% solids content• Plastisol & water resistant• No solvent resistance

(can be difficult to reclaim)• Inexpensive

Figure 5

Dual-Cure EmulsionUniversal Type• 35-40% solids content• Solvent resistant • Water resistant (non-textile)• Easy to reclaim• Moderately expensive

Specialty Types• High solids content – up to 50%, or • Permanent (with catalyst)

Figure 6




ters that affect print quality, and these canbe measured and controlled. They are theRz value which regulates edge definition,and the stencil profile which contributes to ink deposit. See Figure 8.

Stencil profile is used, along with thescreen mesh chosen, to control inkdeposit. For certain applications a thickstencil is beneficial, for other applicationsit is advantageous to minimize the stencilbuild up. Rz of the finished stencil controlsedge definition of the print. For most typesof printing, an Rz value of 10 microns orless will result in good edge quality. Forhighly demanding printing, such as smallreversed text, or high line count halftones,a value closer to 5 microns is necessary.Below 5 microns, if the stencil becomestoo glossy, then ink splattering or cobweb-bing can occur when printing on glossysubstrates.

Capillary film is manufactured in differ-ent thickness grades, each designed foroptimum performance on a narrow rangeof mesh counts, and best results areobtained by selecting the correct gradefor the mesh count being used. Excesswater is removed from the mesh duringprocessing with a light squeegee action,pressure is not required, and would in factlead to detrimental results as the film couldbecome overdissolved. If the correct capil-lary film thickness is used, the water thatremains is sufficient to absorb half to twothirds of the original emulsion layer intothe mesh. What remains comprises thestencil profile and controls the Rz value.See Figure 9.

With direct emulsion, the factors thatare important in controlling the stencilparameters are the solids content/viscosityof the emulsion, and the coating proce-dure that is employed. High solids contentis desirable as it minimizes shrinkage ondrying. Shrinkage of the wet emulsionlayer on drying leads to high Rz values

PROCESSING VARIABLESNow, a screen printing stencil has to perform four functions. Two are importantfor any type of screen printing, since thestencil must first reproduce the image that isto be printed, and secondly be resistant toabrasion and chemical attack. The last two functions are particularly important for highquality line or halftone printing, since thestencil can help to control the amount of inkthat is printed, and is also responsible forcontrolling image accutance, more com-monly referred to as print edge definition.

Regardless of which type of stencil sys-tem is to be used, there are two parame-

Substrate

Stencil Profile and Rz

Figure 8continued on next page


Photopolymer Emulsions(presensitized with no mixing)Garment Printing• 40 -50% solids content• Very short exposure time (1/4)• Plastisol resistant• No solvent resistance

(can be difficult to reclaim)• Expensive

Graphic Printing• 30 -40% solids content• Very short exposure time (1/3)• UV ink and solvent resistant• Expensive

Projection• 20 -30% solids content• Extremely fast exposing• UV and solvent resistant• Very expensive

Figure 7


inks. The very high mesh counts, such as380 and 460, that are best at minimizingink deposit, are also good at preventingemulsion build-up during coating. The eas-iest way to minimize both stencil profile,and Rz value, for this highly demandingapplication, is to face coat the screenafter drying. This ensures that the thin stencils required to minimize ink deposit,will also provide a gasket fit onto the substrate and prevent ink from bleedingbeyond the image area under pressurefrom the squeegee to cause sawtooth linesand the star shaped halftones that causeexcessive dot gain.

Lower solids content emulsions areunable to bridge the coarsest mesh countseffectively with simple wet on wet coatingmethods, and this effectively limits themesh count range on which they can productively be used. See Figure 10.

Regardless of which type of stencil system is used, correct exposure is ofparamount importance in optimizing performance. Producing a screen printingstencil, even for use with the fine meshcounts used for printing halftones, involvesexposing a coating that is very thick incomparison with those used for other pho-tographic or imaging processes. Becauseof this, depth of cure through the stencilbecomes a real issue. Poor through cure,

Capillary FilmThickness vs. Mesh Count

Below 86 mesh or to increase thickness,piggybacking of films is recommended.

Figures: 15µ 390-50820µ 305-42030µ 230-35540µ 140-28050µ 110-23080µ 86-156

Figure 9

and poor print quality, even if you areusing a high solids content emulsion,unless particular attention is paid to themethod of coating. In order to optimizestencil profile, and minimize Rz, coatingprocedure has to be optimized for eachapplication. In general, with a high solidscontent emulsion of around 40% solids, itis possible to achieve good results withsimple wet on wet coating procedures.For very coarse screen mesh, such as 61,two coats on the print side followed byone coat on the squeegee side is all thatis required due to the open weave andhigh percentage open area of the fabric.For 110 mesh, 2+2 should suffice. Oncewe get to 230 mesh, in order to duplicatethe results that would be achieved withcapillary film, a 2+3 procedure isrequired. The additional coats on thesqueegee side of the screen in effectcause a build up of emulsion on the printside, which is where we need our stencil.The only time when an additional coatingprocedure is necessary, after the initialcoats have dried, is for instance whenprinting four color process with UV cured

Direct EmulsionSolids Content vs. Mesh Count

Figure 10




or underexposure, will cause one or moreof the following problems. Loss of detailduring processing, excessive pinholes,scum leaking into and then blockingimage areas, premature stencil break-down during printing or clean-up, and last but not least, difficult or impossiblereclaim. Remember, we are talking expen-sive screen mesh here.

Overexposure in comparison will causedetail to shrink on the screen, with eventu-al loss of parts of the image altogether,and this is usually most severe and easilynoticeable with halftones.

A minimum of 20” Hg of vacuum in theexposure frame is required to ensure goodenough contact between the artwork andthe screen during exposure. This preventsthe undercutting of the image, and subse-quent loss of detail, that occurs when lightleaks under the positive. A good lightsource fitted with a metal halide type bulbis recommended to produce optimum resultssince there is a good match between theoutput spectrum of the bulb, and the maxi-mum sensitivity of most stencil materials. It is also important that the placement of thelamp, and the reflector design, is optimizedso as to ensure even coverage of the entireimage area during exposure. Even cover-age is essential for accurate reproduction of the image, as well as stencil durability. Ifcoverage is very uneven then the exposurelatitude of the stencil material may beexceeded, and areas of the screen may beeither under, or overexposed, or sometimeseven both on the same screen. In thisrespect, dual-cure emulsions possess thewidest exposure latitude, although beingoverall very similar to diazo products inoptimum exposure time. Photopolymer emul-sions, since they expose in a fraction of thetime and have inherently much less latitude,really do require more even exposure inten-sity in order to produce consistent results.

To determine optimum exposure, anexposure calculator or 21 step grayscale

should be used. An exposure calculatorusually consists of a repeating piece ofartwork overlaid with a series of increas-ingly darker gray neutral density filters.With one test exposure, it is possible tosimulate for instance five different expo-sure times. Examination of the developedand dried stencil reveals rectangles wherethe strong yellow color from residual unex-posed diazo alters the color of the stencil.The trick is to pick the exposure factor forthe rectangle that just becomes indistin-guishable from the background, and thiscorresponds to the optimum exposuretime. With a 21 step grayscale, an expo-sure time long enough to give 7 solidsteps on a developed stencil is generallyvery close to the optimum. Since pho-topolymers do not change color on expo-sure, then the 21 step grayscale method is a more reliable method of determiningoptimum cure than an exposure calculator,although the calculator can be used todetermine the level of resolution that canbe achieved at different exposure times.

When using direct emulsion, it is notpossible to gang expose a collection ofdifferent mesh counts and ensure that thecorrect exposure time is given. Longerexposure time is required for thicker coat-ings and the coarser the mesh, the thickerthe layer of emulsion that has to be cured.

Another important variable that shouldnot be overlooked as a cause of possibleproblems is screen drying. Both capillaryfilm and direct emulsions require very thorough drying prior to exposure, sinceany residual moisture present in the coatingwill react preferentially with the photosensi-tive resins that are supposed to harden thestencil. When you expose a damp screen,you end up with a stencil that exhibits thesymptoms of having been underexposed,except that no improvement is ever seen on increasing exposure time.

The type of artwork used can alsohave a big effect on the properties of the




finished stencil. Most film positives willhave a dense black image area, a highDmax, and a clear background, a lowDmin. Vellum on the other hand rarelyachieves a Dmax much above 1.5, andat the same time, the Dmin is usuallyaround 0.3. What this means is that thevellum only allows 50% of the light toreach the stencil, and before optimumexposure is reached the insufficient Dmaxhas let light penetrate to the image areaso that washout properties and detail arecompromised. The expression, about stuckbetween the rock and the hard place, definitely applies to vellum.

Mesh preparation should not be ignoredas an area that can affect stencil perform-ance. Although screen mesh is thoroughlywashed after manufacture, dust and oilsfrom handling, along with adhesive over-spray etc. cause contamination that shouldbe removed prior to coating. Degreasedmesh, although it may be squeaky-clean is,with the exception of stainless steel wire-cloth, not very conducive to good stenciladhesion. Polyester mesh is woven fromslick, smooth PET fibers. Water based paint,or photoemulsion, does not stick well tountreated PET. For this reason it is necessaryto prepare the mesh properly in order tomaximize stencil adhesion. Physical adhe-sion can be improved by lightly rougheningthe surface of the mesh with a speciallydesigned abrasive degreaser. Chemicaladhesion can be improved by treating themesh with a meshprep containing a socalled wetting agent. After rinsing, thisleaves an adhesion promoting surfaceprimer on the mesh that enables the stencilto adhere much better. Meshpreps are evenavailable that combine degreaser, abrasiveand wetting agent all in one product. Theimprovements seen in adhesion are mostnoticeable at underexposure. Photopolymerstencil materials benefit the most of all fromgood mesh preparation since they do not

contain diazo that bonds to the fabric during exposure.

LIMITATIONSScreen mesh comprises two parts, first thethreads, and we need enough of these to support all of the detail in our image.Second the holes, the size and number of these, along with the stencil profile willcontrol how much ink is laid down. Below305 mesh, the main factor that influencesink deposit is the mesh count of the fabric,or how many threads per inch. Once weget above 305, the mesh count is lessimportant, the actual thread diameter and weaving construction, plain or twill,becomes the dominant factor in determin-ing ink deposit. Obviously the higher themesh count, the finer the detail that canbe supported on the screen.

However, the fact that there arethreads in the way at all does place limitations on what can realistically bescreenprinted. See Figure 11.

Figure 11

Minimum Size of Shadow Dot Needs2 Openings + 1.5 Threads for Stencil



Minimum Size of Highlight Dot is 1 Opening + 1.5 Threads.


As far as fine detail is concerned, thereis a minimum size of opening in the stencilthat will consistently allow ink to passregardless of where it sits on the weave of the mesh. Once the size of the detailon the screen, fine lines or halftone dots,becomes narrower than one mesh open-ing plus one and a half thread diameters,then it can be obscured by passing overthe threads and the knuckles of the weavewhere the threads cross. Choosing meshwith a thinner thread diameter can helpsqueeze out a little more detail, but at thecost of producing a more fragile screen.Mesh woven from thicker threads, as wellas producing a more robust screen ableto be used at a higher tension level forbetter registration with multicolor printing,provides better adhesion at the shadowend of a halftone range, or for holdingfine lines with reverse printing. Once thesmall specks or strings of stencil that haveto block the flow of ink, and differentiatebetween shadow tones or delineate text,become smaller than two mesh openingsplus one and a half thread diameters, theymay only adhere to one or two threads andlack sufficient adhesion to withstand the rigors of processing, never mind printing.

As an example, with halftones, the linecount or dots per inch determines the tonalrange that can consistently be printed onany particular mesh count. As the linecount increases, the smaller dots enableviewing from a closer distance without theindividual dots themselves being visible.However, increasing the line count effec-tively decreases the range of tones thatcan be held before highlights moiré, andthen cease to print, and separationbetween midtones and shadows is lost as everything collapses to a solid print.This is illustrated for 380 mesh below. See Figure 12.

If a target is set of trying to print from 10% in the highlights, up to 85% in the

shadows, for a print with good separationbetween all the tones of the halftonerange, then each mesh will have a limiton how high the line count of the halftonecan be if this is to be achieved. See Figure 13.

A perfectly prepared stencil is in factcapable of resolving finer detail than it is physically possible to print, because of the intervening influence of the mesh.However, in order to make the perfectstencil, there are many screens to beburned, obstacles to be overcome, andvariables to be controlled.

Tonal Range Printable With 380 Mesh

Figure 12

Printable Tone Range


Figure 13


How To Match A Direct Emulsion’s Print QualityPerformance With That Achieved By Capillary Film

QUESTIONWe recently switched from capillary film tohigh-solids direct emulsion, applied on an auto-matic coating machine, and are very pleasedwith the quality of our stencils on 230 and305 mesh for solvent-based printing. However,we suffer from poorer print quality on our 380mesh UV screens, most of which involvereverse printing of very fine detail.Regardless of how we coat these screens, we are unable to match the stencil thicknessachieved with capillary film. Is this the causeof our problems?

SOLUTIONAs you have discovered, reverse printing offine detail is probably the most highlydemanding and critical test for the edge defi-nition of a stencil. In order to match the qualityproduced from a film-based stencil whenusing a direct emulsion, even a high-solidsemulsion combined with a coating machine,particular attention has to be paid to optimiz-ing certain parameters.

The fact that you are unable to match thestencil build-up obtained with capillary filmwhen using direct emulsion is related to yourproblem, but is not itself the cause.

To cut a long story short, the root causeof your poor print quality when running UVcan be traced back to the small percentageof open area present in the mesh used,(which is why you chose that mesh in the firstplace, in order to minimize the ink deposit).

The use of an automatic coating machinedoes enable you to transfer an even andrepeatable amount of emulsion onto themesh every time you coat a screen, and youare correct to use a high solids content emul-sion to minimize shrinkage on drying.However, the problem with the very finemesh used for printing UV is that it not onlyminimizes ink deposit, it also impedes thetransfer of emulsion through the fabric whenusing the two-sided, wet-on-wet coating pro-cedures that normally yield satisfactory sten-cils with more open meshes. You have obvi-ously picked up this effect when monitoring

your stencil thicknesses and compared themto what was obtained with capillary film.

The poor print quality is caused not by thelack of stencil build-up, but by insufficientsmoothing over of the knuckles, which areformed during weaving of the mesh. The resultbeing that during printing, the stencil will notprovide the gasket seal required to prevent inkbleeding under non-image areas. In technicalterms, the stencil Rz value is too high. Rz (sur-face topography). (Refer to “What Is AStencil Rz Value?” Tech Tip page 61.)

Compounding the effect of the thin emul-sion coating is the fact that the finer UVmesh probably has bigger knuckles to coverin the first place. That’s because there is agood chance that with the mesh you areusing, the same diameter thread was used to produce both 305 and 380 mesh. Belowwe have illustrated what happens, by com-paring 305 and 380 mesh woven with 34 micron threads, a commonly used threaddiameter for these mesh counts.

When the threads are packed moreclosely together, not only is the percentageof open area reduced from roughly 30%with the 305 mesh, down to around 15%with the 380 mesh (which is good for mini-mizing ink deposit), but the knuckles formedby the dense weaving structure are muchmore prominent and difficult to cover.

For the 305 mesh, you might expect tocoat a high-solids content emulsion, say, twocoats on the print side, with three coats on thesqueegee side, and achieve something like a6-7 micron build-up with a nice smooth finish.With the same procedure, the 380 mesh onthe other hand, will only have a 1-2 micron


305

380


stencil thickness, and will not print with thesame quality as a film-based stencil.

Attempting to build up a thicker andsmoother coating by applying additionalcoats to the squeegee side during wet-on-wet coating, is a futile task with meshdesigned for UV printing. The mesh is notdesigned to allow the emulsion to passthrough freely, and even if you apply anadditional three or four coats to thesqueegee side, you will be lucky to add a few microns to your stencil thickness.Meanwhile, the emulsion in the scoop coater on the print side of the screen is busy skinning over.

The surest way to guarantee the best printquality when producing this type of stencil, isto seal the fabric with a few coats on eachside, and then dry it, prior to polishing upthe print side of the screen with an addition-al coat. With this method, you will still notmatch the stencil thickness obtained withcapillary film, as the additional coat appliedafter drying will add but a micron to theoverall thickness. You should however, beable to match the print quality. Plus the factthat now that you are working with a thinnerhigh-definition stencil, there may even besome benefits in terms of controlling inkdeposit (and mileage).



QUESTIONWe use a high-solids content emulsion andare very happy with the results on our 158and 110 mesh. We have problems, howev-er, with our 61 mesh and we can’t coat our24 mesh screens at all because the emulsiondrips right through. Do we need to find anemulsion with an even higher solids content?

SOLUTIONNot necessarily. You made the right choicein deciding to use a high-solids content emul-sion, since you need high solids in order tocover your coarse mesh without too muchshrinkage. However, the first thing we needto do is make a distinction between solidscontent and viscosity, or thickness.

Emulsion manufacturers are able to con-trol solids content and viscosity independent-ly of each other. High solids does notalways mean high viscosity. In fact, manyhigh-solids content emulsions are supposedto be low in viscosity because they weredesigned primarily for producing high qualitystencils on fine mesh counts, where the flowproperties of the emulsion are more critical.Obviously in your case, where you are usingcoarse mesh with a high percentage of openarea, high viscosity along with the highsolids content is an essential feature if youare going to avoid having problems with themesh counts at the lower end of your range.

If you are using a diazo or dual-cureemulsion, you could try simply adding lesswater to the sensitizer when you mix it. If theemulsion is already too thin as supplied, or ifyou are using a pure photopolymer type thatrequires no mixing, then you may have toswitch to an emulsion with a higher viscosityspecification.

The second thing you need to address is ensuring that your coating method is opti-mized for the type of mesh you are using. As you go from 158 down to 24 mesh, thepercentage open area of the mesh increasesfrom 32% up to 55%. This, in conjunctionwith the fact that the openings are so much

bigger, means that for the coarser mesh youreally have to reduce the number of coatsyou apply. If you don’t, too much emulsionwill be transferred onto the fabric, and eventhe thickest emulsion will sag and drip if youlay it on too heavily.

For the 158 mesh screens, two coats onthe print side, followed by two or maybeeven three on the squeegee side, will pro-duce a nice smooth finish to the dried emul-sion. For the 110 mesh, two coats on eachside should be sufficient. The last two coatsshould always be on the squeegee side topush the emulsion back where it belongs onthe print side of the screen.

For the 61 mesh, cut back to only onecoat on the squeegee side. And remember,these screens should always be dried flatwith the print side underneath. By now youshould have the emulsion onto the print sideof the screen, and you want to make sure itstays there. Emulsion on the squeegee sideof the mesh is more difficult to harden prop-erly on exposure, and even when it is hard-ened, is more likely to suffer from abrasionand wear by the squeegee during printing.Thus causing pinholes and breakdown.

By the time you get to the 24 mesh, youneed to adopt a different technique. In thiscase, apply one slow coat to the print side.Then, turn the screen and apply one slowcoat to the squeegee side. Immediately afterthis, use your coater in the horizontal, untiltedposition to remove the excess emulsion fromthe print side of the screen by applying ascrape stroke. This will leave enough emulsionon the screen, but should eliminate the possi-bility for drips to form while the screen dries.

NOTE: one important point to remember is that the coarser the mesh, the slower youshould coat in order to minimize bubble formation. With the coarser mesh, forinstance 61, and particularly with 24 mesh,there is a tendency for air bubbles to gettrapped in the mesh openings. As you probably know already, every trapped bubble is a potential pinhole.

Emulsion Selection & Coating Techniques For Coarse Mesh Counts


QUESTIONWe make over one hundred screens perday on 86 mesh all the way up to 355mesh, and have recently bought an auto-matic screen coating machine fitted with a built-in dryer. Can you give us someadvice on optimum coating methods sowe get the best print quality from ourscreens without sacrificing productivity? If possible, we would like to use only one emulsion.

SOLUTIONYou can achieve what you want with onlyone emulsion. However, in order both toensure high quality, and maximize produc-tivity, you will need to change your coat-ing method to quite different techniques as you go from coarse to fine mesh.

With a 355 mesh, for example, thesmall percentage of open area with thismesh restricts emulsion transfer when sim-ple wet-on-wet coating methods are used. This means that an awful lot of coats arerequired to fill, and then smooth out themesh knuckles to optimize print qualityeven if you are using a high-solids content emulsion.

In this case, the built-in dryer should beused. The first coating/drying sequencewill seal the mesh, and then an additionaltwo coats on the print or substrate side,with drying in between, fills and polishesthe coating so that print definition is optimized. This method will provide film-quality stencils with a very thin, but repro-ducible stencil thickness. Also, becausethe mesh/coating combination is so thin,drying times will be short enough so asnot to affect your productivity adversely.

In the case of an 86 mesh, at theopposite extreme, the large mesh open-ings and high percentage of open areaenable the emulsion to flow very freely.This means that you have to be careful notto put too much emulsion on the mesh!

If you are using a high-solids contentemulsion, then the optimum settings wewould recommend would be one coat on the print side with two coats on thesqueegee side. The screen should then be removed for drying, while subsequentscreens are coated. Remember, in order toget the best quality, you should dry thesescreens print side down. If you don’t, thenthe emulsion will leak back through to thesqueegee side. Even if you do manage to harden it properly during exposure, thestencil is not only going to print badly, itwill get torn up by the squeegee as soonas you increase the pressure. This in turnwill cause all kinds of pinhole and break-down problems.

As you go higher in mesh count, youcan stay with the simple wet-on-wet proce-dure, but you will need to increase the number of coats in order to maintain theoptimum quality. For instance, with twocoats on the print side and three coats onthe squeegee side, the right emulsion on a110 mesh will produce a better stencil thanyou could ever make with capillary film.

Once you get up to 230 mesh, youneed to add an additional squeegee-sidecoat for a 2+4 procedure. However, any-one else reading this shouldn’t be fooledinto thinking that 2+4 means six individualcoating passes. With the first two coats,both substrate and squeegee sides arecoated simultaneously. After this, two more coats are then applied only to thesqueegee side, for a total of four opera-tions. In fact, since the coating trough onthe squeegee side is slightly lower thanthe one on the print side, the squeegeeside has effectively had the last threecoats. The result of this is that with theright emulsion you produce a stencil withapproximately fifteen microns thickness,with an Rz of around five microns.

Once you get to 305 mesh, you need to make a distinction between

Optimizing Automatic Coating Methods



range of mesh counts, while still allowingenough time for the productivity levels you need.

NOTE: you should use an emulsion witha high solids content. Lower solids contentproducts shrink too much on drying, withthe result that you tie up the coatingmachine by having to apply an excessivenumber of coats. Something around 35-40% solids would be ideal, but with amedium viscosity. There are plenty of dual-cure emulsions available with these prop-erties. There are some higher solids con-tent products around, but they may nothave the versatility to work with the widerange of mesh counts that you are using.Also, the viscosity of some have a tenden-cy to increase rapidly while you are tryingto work with them on the machine. Thiscan cause all types of problems, fromvarying stencil thickness to skinning over in the coating trough.

mesh woven from normal, or from heavythreads. If you are using a 305 mesh with a 34 micron thread diameter, thenthe 2+4 wet-on-wet method will work justfine. You can expect a stencil profile ofabout ten microns, and again the printquality will be similar to that achieved withcapillary film. If however, you are using305 mesh woven with 40 micron threads,then the wet-on-dry procedure developedfor the 355 mesh is more appropriate.The reason for this is that the heavierthreads reduce the percentage of openarea and restrict emulsion flow. Also, the large knuckles formed where the thicker threads cross will not smooth oversufficiently with a wet-on-wet procedure,until the stencil becomes excessively thick.In this case, resorting to wet-on-dry keepsthe thickness under control, while still providing the quality you seek.

These three or four coating proceduresshould enable you to produce the high-quality stencils you are looking for on your



Rz is a measure of the roughness orsmoothness of a surface. It is an importantscreen parameter because it measureshow efficiently the print side of the stencilcontrols edge definition when printingdemanding artwork. For example, artwork containing fine lines or halftone dots. Thestencil not only carries the detail of theimage to be printed, it also has to functionas a gasket to prevent ink from bleedingoutside the image area under pressurefrom the squeegee during the print stroke.Any undesirable spreading of the ink typi-cally causes a saw-toothed appearanceon the edge of detail and fine lines. Plus

it will obliterate fine reverse type. It alsoresults in star-shaped halftone dots thatcause dot gain and loss of contrast anddetail, and can induce localized moiré.

In order to ensure a high-quality stencil,the Rz value must be controlled within narrow limits. Too rough, and the stencilwill not gasket correctly onto the substrate.Too smooth, and the vacuum formed when printing on polished substrates willcause cobwebbing and splattering ofthe ink. Ideal values for most high-qualityprinting applications fall in the range of 4-10 microns.

What Is A Stencil Rz Value And Why Is It Important?

Stencil with high RZ Print result of stencil

Printed result of stencilStencil with low RZ


QUESTION #1We try to keep the temperature in ourscreen coating/drying room around 75 degrees Fahrenheit, and use fans and a dehumidifier to dry our screens.However, we’ve noticed that during thesummer, our busy season, screens take a long time to dry.

QUESTION #2Also, we would like to switch to using adual-cure emulsion, because we like thebetter detail and easier reclaiming, butthese screens seem to take forever to dry.We have even had some get stuck downto the glass in our vacuum frame.

SOLUTIONThe optimum drying conditions for coatedscreens are the same, regardless ofwhether you are using dual-cure emulsions,diazo emulsions, photopolymer emulsions,or even capillary film for that matter.

The reason you have had a problemwith dual-cure emulsions, is not really thatthey are any more difficult to dry thanother types. It’s simply that prior to expo-sure, they have a softer surface finish thancoatings made with other types of emul-sion, due to the plasticizing effect of the photopolymer component.

The other factor could be excessiveheat generated during exposure, whichbakes the screen onto the glass, particular-ly when you are shooting a lot of screensand things really start to heat up. Or inyour case, since you have already deter-mined that you have a drying problem,the other factor is more likely to be resid-ual moisture trapped in the screen. (Referto “Determining Stencil Moisture Content”Tech Tip on page 64.)

Regardless of what type of emulsionyou are using, residual moisture trappedin the coating prior to exposure can causea whole host of problems. Stencils madewith diazo emulsion may not be stickingto the glass in your exposure frame, butyou are probably experiencing some

other problems down the line. It may be excessive pinholes, premature stencilbreakdown, or even poor reclaimingproblems that you may not normally associate with a screen drying problem.

What are optimum drying conditionsfor any type of emulsion? Unless you arelocated in an environment like Arizona inthe summertime, we would recommendthat you split your coating and dryingoperations between two adjoining rooms.Degreased screens can still be dried inyour coating room, but you should reallyhave a separate environment to dry yourcoated screens. Ideally you should use adrying chamber, although how feasiblethis is depends on the size, and numberof screens you are coating.

When drying coated screens, thereare two important aspects. First, from a productivity point of view, you wantscreens to dry quickly. Second, from a quality point of view you want thescreens to dry thoroughly.

By thorough, we mean drying down to a very low equilibrium moisture content. De-humidified air, being drier, is obviouslymore efficient at removing moisture fromyour coated screens than normal room air.But by itself, it is not necessarily the mosteffective method. The relationship betweenrelative humidity, temperature, and dryingcapacity is fairly complicated, but fortu-nately very well understood. Heating andair-conditioning engineers routinely usepsychrometric charts, which relate thesevarying parameters, when designing climate-controlled environments.

Thus, what we would like to do is tryand explain the basis of drying in terms of these basic parameters. First, we wouldlike to introduce the concept of vaporpressure. Vapor pressure exists when youturn a liquid into a gas. When the liquidis water, then vapor pressure is the drivingforce responsible for evaporation and condensation.

What Are Optimum Drying Conditions?



When you put a wet screen in a dryingroom, the bottom line is that in order for thescreen to want to dry out, there has to be adifference in vapor pressure. A differencehas to exist between the vapor pressure ofthe moisture in the coating, and the vaporpressure of moisture already in the air. Ifthere is no difference, then the screen willnever dry. It is the size of this differencewhich controls moisture flow, and is impor-tant in determining: first, how fast yourscreens will dry, and second, how dry theyultimately become. (We should add at thispoint, to beware the salesman who tellsyou that his emulsion has a higher vaporpressure than anyone else’s!)

The vapor pressure of the moisture in a wet coating is basically dependent ontemperature, and the higher the tempera-ture the higher the pressure. The vaporpressure of the moisture already present in the air is dependent on the dew point.This is the temperature at which condensa-tion starts to form. Removing humidity fromthe air lowers the dew point, and hencelowers the vapor pressure.

The question is, what is the most effec-tive way to maximize the differencebetween these two vapor pressures? Is itto raise the temperature of the coating?Or is it to dehumidify the air?

Let’s start with, for example, a dryingroom at 75°F with a relative humidity of60%. Just say we coat some screens andleave them to dry. Now if the fans beingused to dry the screens change the air inthe room to prevent moisture building upand saturating the air, the screens will eventually dry. A look at some charts, anda quick calculation, tells us that we havebeen working with a vapor pressure difference of 0.17 psi.

Now let’s add a dehumidifier to theroom, and say we are able to lower the

relative humidity from 60%, and hold itdown to a nice dry 20% (which requiresa good de-humidifier). Consulting ourcharts, and performing the same calcula-tion, shows that the vapor pressure differ-ence is now 0.34 psi. This means wehave twice the drying capacity, in terms ofthe evaporation load that the air is able tocarry away from a wet emulsion coating.Screens should dry in about half the time,and equilibrium moisture content shouldbe lower too. If however, we allow the relative humidity to creep up, due to aheavy load of screens for example, thendrying efficiency falls off quite quickly.

Instead of using a de-humidifier, let’s saywe decide to use a heater to warm the airentering our drying room. If the air comingin was at 75°F and 60% relative humidity,and we warm it up to 100°F, although the amount of moisture in the air hasn’tchanged, the relative humidity drops toaround 25% since warmer air has a muchgreater drying capacity. We are now work-ing with a vapor pressure difference of 0.7 psi (due to the higher temperature ofthe coatings), and have four times the drying capacity of the original example.

Screens will dry faster and harder withthe application of a little heat, than with a lot of de-humidification. In this case, weare also better able to cope with adverse conditions, such as a heavy load ofscreens to be dried, or even an increasein relative humidity of the outside air.

De-humidification does start to makemore sense with very warm and dampconditions. But even dealing with tempera-tures of 90°F and relative humidity of75%, you still get greater drying efficiencyfrom a 10 degree rise in temperature,than from a de-humidifier able to remove 50 grains of moisture/lb. of air.



QUESTIONHow can I tell when my screen is dry enoughto expose?

SOLUTIONNumber one, you can’t tell by looking at it.Number two, unless it is very damp, youcan’t tell by feeling it either. You may getsome indication when you have troublepeeling the artwork back off the screen, or when the emulsion sticks to the inside of the glass in your exposure frame. But by then, it’s too late.

Your best bet is a contact moisture meter.This inexpensive electronic device will tellyou exactly how much percentage moistureis being retained in your coated and driedscreens by measuring directly on the surfaceof the emulsion.

As you know, you can definitely elimi-nate a lot of costly stencil breakdown prob-lems if you ensure that your coated screensare thoroughly dried prior to exposure. Asfar as emulsion goes, the drier the better, in order to obtain a tough stencil.

There are some guidelines you can followwhen measuring the moisture content of yourscreens to make sure that during exposuremost of the sensitizer is reacting with emulsionand not water. If the moisture content of thecoated screen is less than 4%, you shouldalways get a nice tough stencil, assumingyou are using the correct exposure time.Between 4% and 6%, you will notice a deterioration in wet stencil strength duringwashout, and you will also have more pinholes. This is most critical for emulsionsthat use a low diazo level in order to get ashorter exposure time. Above 6% moisturecontent, most emulsions will produce soft stencils regardless of exposure time, and yourun a real risk of breakdown on press. In thiscase, depending on your run length, youmay or may not have a problem when printing plastisol. However, you will have aproblem if you try to print water-based inks.

As coated screens become more damp, stencils will be progressively softer.Eventually you reach the stage where they suffer spray damage during washout,regardless of how long you expose yourscreens.

Once you are able to measure the mois-ture content of your screen, how should you proceed if it isn’t dry enough? Typically, ifthe area where you dry your screens isaffected by the weather to such a degreethat it affects the way the emulsion dries,then simply leaving the screens to drylonger is not going to make any difference.The emulsion will have reached equilibriumwith the conditions around it. At that point,all you can do is wait for the weather tochange before your screens will dry outany more (unless, you take steps to reducethe relative humidity in the area where yourscreens are drying).

Preferably you need a drying chamberin order to dry screens properly. At theleast, you really need to have a separate,dedicated drying room. There is no pointin putting a de-humidifier in the corner of a room and expecting to see a bigimprovement if doors (assuming you havethem) are open constantly, and someoneis using a pressure washer to de-hazescreens in the next room.

The temperature in the drying chamberor dedicated drying room should beapproximately 100°-110°F. Coatedscreens placed in this environment will dryfaster, and will dry down to a much lowermoisture content, as long as you use a fanto pull out the damp air and keep the relative humidity as low as possible.

Raising temperature is by far the mostefficient way of reducing relative humidityand maximizing drying capacity. After all, how many hair dryers work on theprinciple of de-humidification?

Determining Stencil Moisture Content


QUESTIONThere are mercury-vapor, metal halide, fluorescent, incandescent quartz, andhalogen lamps for exposure units eachwith its own wattage rating. What type is better? How do I compare lamp typesand wattage in order to make an intelli-gent choice?

SOLUTIONYou have to remember that stencil materialsonly respond to a narrow range of wave-lengths. Namely those corresponding toUV, violet and blue light, together knownas actinic light. This is the reason that wecan work safely under yellow lights whencoating and drying screens.

The best types of bulbs for exposingscreens should therefore have a high actinicoutput. Incandescent quartz, white fluores-cent tubes and halogen lamps spread theiroutput evenly over a wide spectrum to givethe appearance of white light. Most of theelectrical power going in is not producingthe type of light you need to shoot screens.Therefore any unit designed with thesetypes of bulbs will have a low intensity andlong exposure times.

High power mercury-vapor bulbs comein different versions, each of which emitsa great deal of actinic light. The mosteffective bulbs for exposing screens con-tain doped mercury vapor, and there aretwo main types. The diazo or metal halidelamp, which contains gallium iodide, andthe multi-spectrum or tri-metal halide, which,in addition to the gallium, also containssome iron salts.

These additional ingredients, alongwith the mercury vapor, boost the amountof useful actinic light (mainly violet/blue)which these bulbs emit.

The result is that you get about twicethe output in comparison to standard mer-cury-vapor lamps. This means a higherintensity of light delivered to the stencil

surface, and shorter exposure times.Another measure of the efficiency of an

exposure unit is the evenness of coverage.When exposing screens, depth of cure isvery important. In other words, you haveto harden the stencil evenly all the waythrough in order to avoid pinholes andpremature breakdown.

To shorten exposure times, the tempta-tion is to push the exposure unit closer tothe screen. With larger vacuum frames, thisleads to the formation of a “hot spot” in the center that gets overexposed and losesdetail. However, with a rapid fall-off inintensity towards the edges of the frame,screens here can be underexposed and full of pinholes. A good reflector designcan minimize or compensate for this effect.Once the lamp gets close enough to thescreen, however, direct illumination from the bulb will always produce a hot spot.

The moral here is to make sure yourexposure unit has enough kilowatts toenable you to pull the lamp back farenough to get even coverage, while keep-ing exposure times at a reasonable length.

On the subject of evenness of intensity,this is really the main claim to fame ofexposure systems based on fluorescenttubes. Fluorescent tubes have been devel-oped with a special phosphor coating onthe inside of the glass that produces anactinic output around ten times greaterthan that of high output white fluorescents.The best type of tube only emits a veryintense blue light of the optimum wave-length for exposing photostencils.

Typical intensity of this type of exposureunit is equivalent to a 6kW multi-spectrum at about 60" from the screen. Since 60" isthe minimum recommended distance forexposing an image of around 40" x 40",this gives these fluorescent-based exposureunits the edge in speed when it comes to exposing very large formats.

Choosing An Exposure Unit


QUESTIONWhy is optimum exposure important?

SOLUTIONScreen printing is dependent on optimumexposure time at the beginning of theprocess as a means of guaranteeing qualityand performance at the end. Since probably99% of incorrect exposure of direct photo-stencils is caused by underexposure, taking a little extra time and care during screenexposure can help you eliminate:• Loss of fine detail during washout• Excessive pinholes• Scum leaking into and blocking the

image areas• Premature breakdown during printing

or cleanup• Difficult or impossible reclaimability

QUESTIONWhat is optimum exposure?

SOLUTIONConventional and dual-cure emulsions con-tain a photosensitive ingredient, the diazo,that strongly absorbs blue and UV light.During exposure it decomposes, losing itsabsorption and causing the stencil to cross-link. This happens incrementally through thethickness of the stencil. In order for theemulsion in and behind the mesh to beproperly cross-linked, it is necessary for thehighly absorbing diazo in the emulsion infront of the mesh (i.e., closest to the lightsource) to be “bleached-out” by having along enough exposure.

Unlike diazo, emulsions pure photopoly-mer products contain light-absorbing ingredi-ents that react together to cause cross-linking.Although these products are photographicallyfaster than diazo containing systems, the sur-face layers still need to be exposed first inorder to properly cure deeper parts of thestencil. Remember, the cross-linked emulsionthat encapsulates the mesh fibers gives directstencils their superior durability, and this vital“inner” part of the stencil is most affected byunderexposure.

As most of you know, underexposingstencils on purpose as a way of guarantee-ing high resolution for fine-detail printing isa fairly common practice. While this maymake a noticeable difference in resolution

capability under adverse conditions (i.e., a low-resolution emulsion on white fabric),today’s higher quality emulsions, when usedon a correctly dyed fabric, are capable ofresolving finer details than most inks arecapable of printing. As long as you usehigh quality materials in the screen-makingprocess, resolution should not be a factorin choosing exposure time. The optimumexposure time is always the point wherethe stencil has been fully cross-linked.

QUESTIONWhat affects optimum exposure?

SOLUTIONIf you asked 100 screen makers to list thevariables that affect exposure time, chancesare they would all come up with basicallythe same answers. If, however, you askedthem to arrange the items in order of impor-tance, you would probably end up with 100different versions. Basically, you should exam-ine six different variables, listed in theapproximate order that they affect screenexposure time:• Intensity of light• Distance from lamp to screen• Mesh thickness• Mesh color• Coating thickness• Emulsion type

QUESTIONHow do I quickly and accurately predictoptimum exposure time?

SOLUTIONWhile there are several options to predictoptimum exposure, (i.e., the “color-change”method), there is a new method that elimi-nates lengthy and less accurate testing pro-cedures that are difficult to interpret. Bymeasuring the output of an exposure lamp ina narrow spectral band (i.e., violet/blue)where the photoemulsion is at its most sensi-tive, it is possible to predict what therequired exposure time will be. Throughextensive testing, manufacturers of stencilmaterials are able to compile the necessarydata that relates the exposure dose requiredby a product when used under almost anycondition. The quality control device used inthis method is a digital radiometer.

Determining Optimum Exposure


Exposure lamps of many types areused to make screens and they exist witha wide variety of spectral output, geome-try of light delivery and power. The firstthing that must be established is howmuch of the useful spectral output falls in a range that is used by the stencil materialbeing exposed. Only a fraction of therated input power of a lamp is convertedinto output with the correct wavelengthsthat can harden a stencil. This is known asactinic light, with wavelengths correspon-ding to blue, violet and ultraviolet. As canbe seen in Figure 1, metal halide, multi-spectrum and certain specialty fluorescenttubes produce light very rich in thesewavelengths. Other types of bulb are notsuitable for high quality stencil production.

If you consider the light sensitive chem-istry that is used in direct emulsions andcapillary films, then you have to deal withtwo categories. Diazo and dual-cure typescan be grouped together, as it is the diazo

sensitizer that mainly determines the lengthof exposure and the degree of latitude.Photopolymer emulsions and films employ a different sensitizer referred to as SBQ thatwill react much faster than diazo whenexposed with the correct type of lamp andwill therefore be treated separately.

Figure 2 shows the light absorptionspectrum for diazo sensitizer, with its peakin the UV at 373nm, overlaid on the out-put spectrum for a metal halide bulb. Alsoshown is the sensitivity curve for diazo. Ascan be seen, the peak in sensitivity corre-sponds to the tail of absorption wherelight is still absorbed, but less strongly andis therefore more penetrating. More onthis later when we examine optimumexposures and degree of latitude, but inshort, metal halide bulbs, sometimesreferred to as diazo or gallium lamps withtheir peak output in the 390-420 nm violet/blue range are the best choice foroptimizing exposure of diazo or dual-cureemulsions and films.

Figure 3 shows the analogous situation when photopolymer products areexposed. In this case the maximum of theabsorption peak is at a shorter UV wave-length of 342nm. This shifts the peak ofsensitivity into the 360-390 nm UV rangewhere multispectrum bulbs, also referred to as trimetal halide or sometimes as ironlamps have their strongest output. Theresult is that multispectrum bulbs are thebest choice for optimizing exposure of photopolymer emulsions and films.

This wavelength dependence of sensi-tivity of the two types of photosensitive systems results in a somewhat complicatedrelationship in their relative photographicspeeds. As an example, take a photopoly-mer emulsion that requires only 20% of theexposure time of a diazo or dual-cure ifused on an exposure system with a multispectrum bulb.

Understanding Emulsions and Stencil Exposure

Figure 1continued on next page

300nm 400nm 500nm

Mercury Vapor

Metal Halide

Multispectrum

420nmFluorescent

WhiteFluorescent


With a metal halide bulb, the pho-topolymer is less sensitive and slows downso that it now requires approximately 50%of the dual-cure exposure time. With420nm fluorescent blue tubes, the longerwavelength output is so weakly absorbedby the photopolymer, that most of the lightleaks right through and out the backsideof the coating, with the result that the fastexposing photopolymer now requiresabout 75% of the dual-cure exposure time.White fluorescent tubes, with their verylow UV output cause photopolymers toactually expose slower than most diazo or dual-cure products.

Don’t be fooled by a lack of resolution,under these or any other circumstances,into thinking that a stencil is well exposedor even overexposed. Image resolution isaffected by too many other factors to beused as a guide for determining exposuretime. For instance, a poor vacuum causedby a leaking seal or rip in the blanket cankill resolution, even at a fraction of the cor-rect exposure time. Similarly, incompatiblecombinations, such as photopolymer emul-sion, coated on white mesh, and exposedwith a fluorescent tube exposure systemshould be avoided. Combining any twoof these variables can yield acceptableresults, but all three things together is arecipe for very low-resolution stencils.

Optimum exposure time is only deter-mined by depth of cure of the stencil.Depending on the printing application, therequired thickness for a stencil, meaning

mesh plus emulsion, can range from tens tohundreds of microns. In order to minimizepinholes, premature stencil breakdown,soapy scum during developing that bleeds,dries in and can block the image, or atleast worsens reclaiming, the stencil has to be fully cured through its full thickness.

There are various techniques that canbe used to determine optimum exposureand perhaps the most well known is theuse of an exposure calculator. A typicalexample is shown in Figure 4. It utilizesa series of increasingly dark neutral densi-ty filters, overlaid on a repeating design,and allows multiple simultaneous expo-sures to be simulated, usually 100%,70%, 50%, 33% and 25%.

After processing, the finished stencilhas to be evaluated in a backlit environ-ment by the color change method, andnot for resolution. As can be seen inFigure 5, residual unused diazo showsup as a strong yellow undertone in thecolor of the stencil. The correct exposure isdetermined as the time taken for the diazosensitizer, a yellow dye, to be completelybleached out. In a test situation, no yellowundertone should be seen on one of themiddle sections of the calculator image.Once this has been achieved, the expo-sure factor for that part of the calculator is multiplied into the test exposure time, in order to find the optimum time. In anunderexposure situation, the 100% expo-sure, or Factor 1, always looks correct,and the only thing this means is that

Figure 2 Figure 3


Metal Halide Bulb Multispectrum Bulb

300 400 500300 400 500Wave length (nm) Wave length (nm)

Diazo absorbance

Diazo sensitivity

SBQ absorbance

SBQ sensitivity



another test with double the exposure time is needed in order to move the first completely bleached out section into themiddle of the calculator.

This type of exposure calculator worksperfectly only for diazo emulsions. Withdual-cures, there are often two separatecolor changes happening simultaneously,but with the extra dual-cure componentcolor change being fainter but more per-sistent. The trick then becomes determiningjust when exactly did the diazo part stopchanging color. With photopolymer stencils there is no color change, andalthough this type of exposure calculator

may be useful for determining the degreeof resolution available at several differentexposure levels, it does not indicate theextent of cure.

An alternative method is the use of agrayscale sensitivity guide, an example of which is shown in Figure 6.

In this case there are 21 continuoustone steps, with a density increase of0.15 between successive steps. It is not a halftone dot pattern. Interestingly, this0.15 density increment is the same as thatemployed for the series of filters used on the traditional exposure calculator mentioned previously. With longer expo-sure times, higher numbers of steps aresuccessfully hardened into the finishedstencil, and if used correctly, this techniquecan be can be used to determine the optimum exposure with only one test.

In almost all cases, a solid step 7 afterdevelopment indicates a correctly exposedstencil, as is shown in Figure 7.

If the initial test yields only five steps,then the exposure needs to be doubled.Six steps require an increase of 40% inexposure time. Eight steps indicates anoverexposure situation and possible loss of detail in the stencil, although no doubtfewer pinholes due to scratches, dust etc.Exposure time should be reduced to 70%of the original. Nine steps indicate a

Figure 4 Figure 5

Figure 6 and 7



8

9

10

11

12

13

14

15

16

17

18

19

20

21


double overexposure. The biggest advan-tage of this method is that it can be usedto control the degree of cure of any typeof stencil, diazo, dual-cure or photopolymer.

The last recommended method doesnot use a test film at all, instead it employsa digital radiometer to determine the pointat which all the sensitizer in the coatinghas been used up. It works like this, thephotocell with a 365nm filter is placed in the vacuum frame, behind the emulsioncoating, and the exposure is started. Atthe beginning, due to the extremely highabsorbance of the sensitizer, no light isable to reach the photocell and the

radiometer registers a reading of zero.During the exposure, as sensitizer is usedup, an increasing amount of light is meas-ured that gradually levels off. This informa-tion can be displayed in a graph, and the optimum exposure is indicated by a rollover in the gradient that shows theincrease in light intensity measured behindthe stencil. An example of this is shown inFigure 8.

Diazo emulsions finish flat, but dual-curesdisplay a lesser and longer lived gradient,due to the additional photochemistry thatalso complicates evaluations during thecolor change method. Unfortunately, thismethod does not work with photopolymerproducts. This is due to high absorptioneven at the end of the exposure processcaused by residual sensitizer. More on thislater when we discuss post exposure effects.

Now comes the tough part. In the realworld, most of the time, it is impossible tocreate a perfectly exposed screen like theexample shown in Figure 9. The mainreason is that light intensity is not evenover the whole screen. With a typicalpoint light source, that is best for reproduc-ing good detail, unless the lamp is pulledback very far from the vacuum frame, thenthe intensity of the light in the corners ofthe screen will be significantly less than inthe center. This leads to the cure profileshown in Figure 10. There are two

Figure 8

Dual-Cure

Diazo

Exposure Time

Inte

nsit

y

Figure 9 Figure 10continued on next page



scenarios shown here for the underex-posed regions of the screen. In one casea bad bulb was used and the underexpo-sure is concentrated at the foundation ofthe stencil where it adheres to the fabric.In the second case, although the stencil isequally underexposed, increased penetra-tion by the light has resulted in a moreeven cure. One result of using a goodbulb is a stencil with much wider exposurelatitude that is evidenced by fewer pin-holes and less scumming during develop-ment. It should be noted at this point, thatwhen a doped bulb such as metal halidegets old and weak, then its spectrum getscloser to that of a mercury vapor bulb.The longer wavelength intensity drops, whilethe UV output remains relatively constant.

Fluorescent exposure systems do pro-vide more uniform coverage for an evencure, but can lead to a compromise indetail, particularly with fine halftones. It isdifficult for the film positive to cast a sharpshadow on the emulsion when lit from allangles. Care also has to be taken whenexposing large screens with more thanone exposure lamp to give wider cover-age. The area of overlap between the

lamps can suffer a slight loss of detail,usually in the vertical direction when thelamps are side by side. Highly magnifiedexamples of this loss with fine detail on305 mesh are shown in Figure 11.

Now if we can assume at this pointthat you have arrived in the comfort zone.Optimum exposures have been set for allof our mesh count/color/coating combi-nations. You have adequately exposedscreens with all the detail you need, andnone of the pinholes you don’t. Now,how do you keep it that way? This iswhere our integrator comes in and compensates by increasing exposure timewhen the bulb gets old, or the powerbrowns out. It is important to match thephotocell filter to the sensitivity curve ofemulsion, since a disproportionate amountof the stencil hardening that occurs iscaused by those wavelengths that aremost penetrating but still usefullyabsorbed. For instance, a narrow pass365nm UV filter used with a metal halidebulb makes the integrator blind to fluctua-tions in the longer wavelength output thatmakes this bulb so effective in exposingdiazo and dual-cure products.

Figure 11




Now we would like to mention thebenefits of post exposure, which can be a useful technique for improving the resist-ance properties of a stencil. The benefitsoffered depend on the type of emulsionused, and can be summarized as follows.

Diazo emulsion or film - When a diazoemulsion is underexposed, the developedand dried stencil retains a yellow under-cast from the unused diazo. This partiallyexposed diazo does not wash out of thestencil during developing as it has alreadyreacted with, and become attached to,the polymers and resins that make up thestencil. So after drying it is possible to re-expose the screen, bleach out theremaining diazo and further cross-link thestencil to improve its solvent or waterresistance. However, it should be notedthat depending on the degree of initialunder-exposure, the final stencil, althoughfully chemically cross-linked, may only bea thin skin stuck to the substrate side of thescreen- mesh. It will not be as durable andresistant to pinholes as a correctlyexposed stencil, where the screen-meshhas been physically encapsulated frontand back with hardened emulsion.

There is absolutely no benefit to expos-ing a screen made with correctly exposeddiazo emulsion, since all the diazo isalready used up.

Dual-cure emulsion or film - When under-exposed, the situation is the same as for adiazo emulsion in that the unreacted diazocan further cross-link the stencil on post-exposure and improve its solvent and waterresistance. However, the difference is thateven correctly exposed dual-cures can benefit from post exposure. The reason isthat the secondary cross-linking system canbe made to polymerize further, even afterall the diazo is used up. This usuallyimproves only the solvent resistance, andcan also result in easier reclaiming, sincethe hardened polymers and resins are

affected less by ink and solvents.Photopolymer emulsion and film –

Photopolymer emulsions benefit most of allfrom post-exposure. Unlike diazo, whichcan be used with 100% efficiency if theexposure time is long enough, photopoly-mer molecules can be very stubborn. Onlya proportion of them reacts very fast, andare responsible for the short exposuretimes of photopolymer emulsions. The restof the photopolymer molecules are notaligned correctly and can cross-link onlywith difficulty. In this case, increasing theexposure time causes a loss of resolutionand detail with little payback in terms ofimproved stencil durability. However, thepotential of this unused photopolymer canbe realized with a post-exposure. The reason is that during development, whenthe stencil is wet, some of the unreactedmolecules will re-align and be availablefor crosslinking the second time around,thus resulting in improved solvent andwater resistance. In some cases, theimprovement in water resistance can be dramatic.

Finally, let’s review the influence of thefilm positive on the exposure process,since image density and resolution of thefilm output device has a major bearing onstencil quality. High quality film positiveoutput from an imagesetter will have avery low Dmin of around 0.05 (i.e. thefilm is clear and transmits more than 90%).Image areas will be a dense black, witha Dmax of 3 or more and will stop atleast 99.9% of the light. Various othertypes of output device are now in common use, and at the other end of thescale is laser toner on vellum. A Dmin of 0.3 sounds good until you realize itblocks 50% of the available light andrequires the exposure time to be doubled.Dmax is probably around 1 which stops90% of the light but, unfortunately letsthrough the other 10%. The use of a




solvent spray or heat treatment to fuse thetoner can increase density to 2, but this is barely adequate for any fine detail as1% of the light penetrates the stencil andthis can be enough to compromisewashout. Thermal imagesetter and inkjetoutput generally have very good densitiesand can be exposed without concern forburning through.

One point to remember is that anytimethat anything other than crystal clear film

is used to expose screens, then exposurecalculators or grayscale sensitivity guidesneed to be placed behind a sheet of thismaterial when making an exposure test.Otherwise the correct exposure time that is determined from the test will always be an underexposure with a real film.Photomicrographs of halftones producedon a selection of output devices areshown in Figure 12, to enable a comparison of dot quality.

Figure 12


Imagesetter ThermalImagesetter

Inkjet ThermalImagesetter


There is an option to measuring theintensity of your exposure lamp and usingthe chart of recommended exposure doseas a guideline to calculate exposuretimes. It is possible to use the radiometeras an analytical tool to pinpoint the 100% correct exposure time for any dual-cure or diazo emulsion on any mesh with yourown particular coating method and exposure lamp.

This is accomplished by placing the sen-sor from the radiometer behind the coatedscreen in an area where the emulsion is tobe fully exposed. Then, by taking a seriesof measurements during the exposure, atsay five-second intervals, it is possible to

draw a graph that shows the intensityreadings increasing rapidly as the exposureprogresses. This happens as the diazosensitizer is bleached out by actinic lightfrom the exposure lamp, thereby allowingmore light to penetrate through the backof the coating.

As optimum exposure is reached, andall the diazo has been used to harden thestencil, the intensity readings level off to a steady value and allow the absoluteoptimum exposure time to be determinedfor that particular combination of emulsion/mesh/coating method. (See table and graph below.)

Using the Radiometer to Pinpoint 100% Correct Exposure Time

Exposure IntensityMeasurements Behind Screen

Start of Exposure 0 Microwatts/cm2

5 seconds 10 microwatts/cm2















Grafic HU42 Photoemulsion Coated 2+3 on420/PW31 Amber Hitech Mesh Exposed

on 5KW Metal Halide at 40”

▲

▲

OPTIMUM

00

10

20

30

40

50

60

70

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75Exposure Time (Sec.)

OptimumExposureTime

Intensity µW/cm2


The Benefits Of Emulsion Stencil Post-Exposure

Post-exposure can be a useful tech-nique for improving the resistance proper-ties of a stencil. The benefits offereddepend however on the type of emulsionused, and can be summarized as follows.

DIAZO EMULSIONWhen a diazo emulsion is under-exposed,the developed and dried stencil retains ayellow undercast from unused diazo. Thisis the basis for the color change methodof determining optimum exposure. Thispartially exposed diazo does not washout of the stencil during developing, as ithas already reacted with and becomeattached to the polymers and resins thatmake up the stencil. After drying, it is possible to re-expose the screen, bleach-ing out the remaining diazo and furthercross-linking the stencil to improve its solvent and water resistance. However, it should be noted that depending on thedegree of initial under-exposure, the finalstencil, although fully chemically cross-linked, may only be a thin skin stuck to the substrate side of the screen mesh. Itwill not be as durable and resistant to pinholes as a correctly exposed stencilwhere the screenmesh has been physicallyencapsulated, front and back, with hardened emulsion.

There is absolutely no benefit to post-exposing a screen made with correctlyexposed diazo emulsion, since all thediazo is already used up.

DUAL-CURE EMULSIONWhen under-exposed, the situation is thesame as for a diazo emulsion in that theunreacted diazo can further cross-link thestencil on post-exposure and improve itssolvent and water resistance. However,the difference is that even correctlyexposed dual-cure stencils can benefitfrom post-exposure. The reason is that thesecond cross-linking system, the part thatmakes an emulsion dual-cure, can bemade to polymerize further, even after all the diazo is used up. This usuallyimproves only the solvent resistance, andcan also result in easier reclaiming.

PURE PHOTOPOLYMER EMULSIONPhotopolymer emulsions benefit the mostfrom post-exposure. Unlike diazo, whichcan be used with 100% efficiency if theexposure time is long enough, photopolymermolecules can be very stubborn. Only aproportion of them react very fast, andare responsible for the short exposuretimes of photopolymer emulsions. The restof the photopolymer molecules are notaligned correctly and can cross-link onlywith difficulty. In this case, increasing theexposure time causes a loss of resolutionand detail with little payback in terms ofimproved stencil durability. However, thepotential of this unused photopolymer canbe realized with a post-exposure. The reason is that during development, whilethe stencil is wet, some of the unreactedmolecules will re-align and be availablefor cross-linking the second time around.Thus resulting in improved solvent andwater resistance. In addition, the post-exposure can be made much longer thanthe original imaging exposure in order to maximize the cross-link density.



HANDBOOKQuality Control & General Press Guidelines


QUESTIONWhen printing four-color process, we knowthe importance of the angles used for thedots on the color separations. We alsoknow we have to avoid certain combina-tions of mesh count with dots per inch onthe positive in order to avoid moiré. Whatwe are looking for are some guidelines onwhich mesh specification is most suitablefor printing four-color process, and how finea dot we should be able to hold.

GUIDELINESThe first thing to realize when printing four-color process is that screen tension is ofparamount importance. Within this area,there are two factors that need to be controlled. Number one, it is importantthat all four screens are at the same tension level within one to two newtons,or you will have registration problems. Ifyou increase off-contact in order to getbetter release of one screen out of the wet ink film, then the image on that screenprints bigger, causing misregistration.

Second, a minimum tension level of20N is suggested. Less than this may not provide enough snap to cleanly releasethe stencil from the wet ink film once thesqueegee passes. Failure to achieve thismeans that the screen drags in the wet ink and causes dot gain.

To address both these points, you willhave maximum control over your screens if you use a Hitech (low-elongation) screenmesh. This type of mesh is designed to be more stable with respect to holding tension over time. This doesn’t mean, however, that you should push the fabricto its limit by trying to achieve the highestpossible tensions. It is more important toachieve consistent tension levels whileworking above the minimum requirement.

Our next recommendation is to useplain weave mesh. As a result ofadvances in weaving techniques, plain

weave mesh is available in some of thefiner mesh counts that traditionally weretoo difficult to produce, and so had to bewoven with a twill, or even a double twillconstruction. The bottom line is that plainweave mesh interferes less with the wayink flows on the print, by virtue of its mini-mal contact area, or footprint, since onlythe crown of the mesh knuckles touch thesubstrate. Twill weave mesh will causemore problems with dot gain, and caneven introduce moiré where you wouldn’texpect it.

As far as how fine a dot you should beable to hold, that depends mainly on themesh count you use, and on the threaddiameter chosen. Minimum printable dotsize, in microns, will then translate into acertain percentage of highlight dot, whichdepends on the halftone ruling (or numberof dots per inch).

This minimum detail, that you cancleanly and consistently print, correspondsto openings in the stencil that are equal toone mesh opening plus one and a halfthread diameters. Hence the relationshipwith mesh count and thread diameter.

If we choose a 305 plain weave meshwith 34 micron threads as an example,then so long as everything else is optimized(screen tension, ink, squeegee etc.), itshould be possible to print down to 100micron dots. This corresponds to 3% on a45-line halftone, but only 9% on an 85-line.Detail smaller than this, for instance if your85-line positive contains 7% dots, willalways print as a moiré pattern.

An analogous situation exists in shadowareas of the print in order to ensure stencildurability during printing. Small spots ofstencil clinging to the mesh, which yourely upon to block the flow of ink and distinguish between heavy mid to shadowtones, have to bridge between andadhere to a minimum of three meshthreads. Less than this, and shadow areas

Mesh Guidelines For Printing 4-Color Process



will quickly develop a spotty appearance,and again this may take the form of amoiré pattern. If we take the case of our305.PW 34 mesh, the darkest tone onyour positive that is safe to print corre-sponds to 94% on a 45-line halftone or80% on an 85-line.

The following table compares the tonalrange of some common halftone rulingsthat should be able to be printed throughthe mesh types shown.

If your specifications were that youhave to be able to print a tonal range of 10% – 85%, then you can see from thechart that there is a minimum mesh countthat you shouldn’t drop below. Forinstance, an 85-line halftone wouldrequire the use of a 355 mesh or higher.

Higher mesh counts than the minimumcan also be used if you want to print witha lower ink deposit, or you may be able tosimply switch thread diameter. (This, however,enters us into a whole different story!)


MESH RANGE OF DOT PERCENT

Mesh Count/Weave/ 45 Line 65 Line 85 LineThread Diameter

196.PW 55 6% – 86% 13% – 71% 21% – 51%

230.PW 48 4% – 90% 9% – 78% 15% – 63%

280.PW 40 3% – 93% 6% – 86% 11% – 75%

305.PW 34 3% – 94% 5% – 89% 9% – 80%

305.PW 31 2% – 96% 4% – 91% 7% – 85%

380.PW 31 2% – 97% 4% – 93% 6% – 88%


PART 1 – INTRODUCTIONThe complexities of screen printing fourcolor process are further complicated whenusing UV cured ink, by extra demandingrequirements in controlling ink deposit.

It’s not enough to have to deal with therelationship of dots per inch with meshcount, or carefully selecting the angle ofdots on each separation so you avoid notonly mesh/dot moiré, but even dot to dotmoiré between the overlaid colors. Nowyou also have to avoid the problems thatcan occur from printing halftones with anexcessive ink deposit. Problems will occurwhen printing third and fourth colors if inktransfer from the screen to the substrate isseverely affected by excessive ink depositfrom the first two colors down. This is dueto the high solids/low shrinkage charac-teristics of UV cured inks.

In terms of detail, highlight dots repre-sent a major challenge. For instance, a10% dot on an 85 line halftone is 0.004”across. To put this in perspective, if it were the size of a quarter, a 2” X 3/8”squeegee would be nine feet thick andforty two feet high. Therefore, in order togive ourselves the best chance of beingable to successfully reproduce over seventhousand of these 0.004” dots per squareinch of print, and to do it consistently witha carefully controlled ink deposit, weneed to be in total control of our screenmaking process.

PART 2 – THE STENCILA screen-printing stencil performs four func-tions. Two are important for any type ofscreen-printing, since the stencil must firstreproduce the image which is to be print-ed, and then be resistant to abrasion andchemical attack. The last two functions how-ever are particularly important for high qual-ity halftone printing with UV ink. The stencilwill increase the quantity of ink which isprinted, and is also responsible for control-ling image accutance, more commonlyreferred to as print edge definition.

Photostencils fall into four main cate-

gories. The first is known as Indirect Film,where the stencil imaging and developmentprocess is carried out independently of thescreen mesh. The stencil is applied to themesh with gentle pressure and dried priorto removal of the backing film. Althoughcapable of high quality reproduction, thethin edge of the finished stencil is very fragile and easily damaged and thereforeunsuitable for long print runs, or for printingsome difficult substrates.

The second type of stencil is known asDirect Film or Capillary Film. In this case,a much thicker layer of photographic emulsion is adhered to a wet screen meshthrough capillary action. After drying andremoval of the backing film, exposure anddevelopment produces a much strongerand more firmly adhered stencil than in theprevious case, but still with the image qualityassociated with a film based product.

With the third type of stencil, known asDirect/Indirect, the film is laminated to themesh with a layer of photographic emul-sion instead of water. Once this sandwichhas dried, processing is the same as forcapillary film, but with the advantage thatan even more firmly adhered and durablestencil results. The downside is that thestencil making process is more complicated,particularly in larger formats, and is alsomore costly.

That brings us to the last, and mostcommonly used type of stencil which isknown as Direct Emulsion. In this case themesh is coated with a light sensitive emul-sion, which when dry is imaged and thendeveloped in the same fashion as capil-lary film. This is by far the least expensivemethod in terms of material cost, andresults in the most durable stencils.However it is also capable of producingmuch poorer print quality than any of thefilm based systems, unless the correctchoices are made in terms of stencil mate-rials and methods of processing, andbringing several variables under control.

The two most important stencil parame-ters which affect print quality, because of

Take Control Of Your Screens For Printing 4-Color Process With UV Ink



their influence on both ink deposit andprint definition, are stencil profile and Rzvalue. See Figure 1.

Regardless of which type of stencil system is used, if fine halftones are to bereproduced, an important area wheretotal control is required is during exposure.Producing a screen-printing stencil, evenfor use with the fine mesh counts used forprinting UV cured inks, involves exposing

a coating which is very thick in compari-son with those used for other photograph-ic or imaging processes. Because of this,depth of cure through the stencil becomesa real issue. Poor through cure, or under-exposure, will cause one or more of thefollowing problems. Loss of detail in shad-ow areas during development, excessivepinholes, scum leaking into and thenblocking image areas, premature stencilbreakdown during printing or clean-up,and last but not least difficult or impossiblereclaim. Remember, we are talking expen-sive screen mesh here.

Overexposure in comparison will causeyour dots to shrink, leading to moiré in thehighlights and a lack of density in theprint, and eventually loss of parts of yourimage altogether. In order to optimize theexposure process it is important that theequipment used is capable of producinghigh resolution stencils without the need tounderexpose.A minimum of 20” Hg ofvacuum in the vacuum frame is required toensure good enough contact between theartwork and emulsion during exposure.This prevents the undercutting of the imagethat occurs when light leaks under the pos-

itive. A good point light source fitted witha metal halide, or diazo, bulb is also recommended to produce optimum results,since there is a good match between theoutput of the bulb and the maximum sensi-tivity of most stencil materials. It is alsoimportant that the placement of the lamp,and the reflector design, is optimized soas to ensure even coverage of the imagearea during exposure. Even coverage isessential for accurate reproduction as wellas stencil durability. If coverage is veryuneven then the exposure latitude of thestencil material may be exceeded, andareas of the screen may be either underor over exposed, and sometimes evenboth on the same screen!

Another important variable related toexposure is drying. Both capillary film anddirect emulsion coatings require very thor-ough drying prior to exposure, since anyresidual moisture present in the coatingwill react preferentially with the photosensi-tive resins which are supposed to hardenthe stencil. When you expose a dampscreen you end up with a stencil whichexhibits the symptoms of having beenunder-exposed, except that no improve-ment is seen on increasing exposure time.

Processing variables aside, the idealstencil for printing halftones with UV inkshould be thin and flat, and the parame-ters we need to control in order toachieve consistent, high quality results arestencil profile and Rz value. For optimumedge definition a stencil with a smooth flatunderside is required, ie a low Rz value.This is because the stencil, as well asreproducing the image, also has to actlike a gasket and prevent the ink frombleeding beyond the image area underpressure from the squeegee. The raggededge of poorly defined dots can inducemoiré, flattens contrast due to dot gain inthe highlights, and loses any separationbetween midtone and shadow areas.

Minimizing stencil profile is importantnot only because of it’s contribution ofextra ink deposit, but also because of it’s

Substrate

Stencil Profile and Rz

Figure 1




affect on durability. High profile stencilsare more prone to breakdown in shadowareas, where the image depends uponsmall isolated spots of stencil clinging tothe mesh. Mechanical abrasion, andsometimes loss of adhesion, causes heavymidtone and shadow areas to develop aspotty appearance which sometimes takesthe form of a dark moiré pattern.

Ideal values are shown in Figure 2,stencil profile should normally be in therange of 2-10 microns, ideal Rz value isnormally in the range of 4-8 microns.Smooth or polished sustrates require an Rz at the top end of the range to preventcob-webbing or splattering of the ink dueto static. For rough substrates, the lowerthe Rz the better.

With capillary film, as long as the cor-rect film thickness is selected, both stencilprofile and Rz should automatically fall inthe range of optimal values. See Figure 3.With direct emulsion the situation is not sosimple. Simple wet on wet coating meth-ods, which work so well for coarse andmedium mesh counts, usually fail to transferenough emulsion onto and through the finemesh counts which are typically used forprinting UV cured inks. The small percent-age of open area, which is what restrictsink transfer, also prevents emulsion frompassing through the mesh and building upon the print side of the screen. Even whenusing a high solids content emulsion, theshrinkage that occurs on drying may prevent us from achieving Rz values in the optimum range. See Figure 4.

This problem is most evident with meshtypes which are the best at minimizing inkdeposit, particularly if you are using asharp edge emulsion coater. In these

circumstances, an additional coat of emul-sion after drying can cut the Rz value inhalf, hopefully bringing it into the rangewe require, whilst adding barely a micronto the stencil profile. See Figure 5.Needless to say, maintaining constantstencil thickness and Rz values from screento screen is all important if consistent printresults are to be obtained, and if directemulsion is the stencil of choice, then theuse of an automatic coating machine ishighly recommended to remove variablesfrom the coating process.

Emulsion Stencil, Profile & Rz On 380 PW 34

Stencil Profile Rz40% Solids 2+3 Sharp Edge Coater 2µ 12µ

50% Solids 2+3 Sharp Edge Coater 3µ 10µ

40% Solids 2+3 Dull Edge Coater 7µ 10µ

50% Solids 2+3 Dull Edge Coater 9µ 8µ

Figure 4

Capillary Stencil, Profile & Rz On 380 PW 34

Stencil Profile Rz15µ Capillary 2µ 3µ

20µ Capillary 8µ 2µ

15µ Capillary 10µ 3µw/Emulsion

Figure 3

Stencil Properties Required for Printing UV Ink

Stencil Should Be Thin and Flat

Stencil Profile : 2–10 microns

Stencil Rz Value : 4–8 microns

Figure 2




PART 3 – THE MESHBefore deciding which type of mesh touse, important consideration must begiven to tensioning. Consistency of tensionfrom screen to screen is of paramountimportance when printing four-colorprocess, and as with any type of multi-color printing, registration problems willoccur if different tension screens are used.This is due to the higher off contactrequirement for lower tension screens caus-ing image enlargement.As a minimum,20N of tension is suggested. Printing withlow tension screens can cause poor inkrelease as the screen separates from thewet ink film, and dot gain may occur ifthe squeegee drags the stencil in the wetimage. Increased off-contact can counter-act this to a certain extent, but then theimage will print too big, and the exces-sive squeegee pressure required willcause premature stencil wear.

Now screen-printing mesh comprisestwo parts, first threads, and you needenough of these to fully support the detailin the stencil, and secondly holes, and itis the size and number of these that con-trols your ink deposit. Normally mesh-count is the dominant factor in determiningink deposit. Above 305 mesh however,when we are dealing with the types ofmesh designed for printing UV cured ink,ink deposit is no longer determined bymesh count. Thread diameter and theweaving construction itself become theover-riding considerations.

Fine mesh, which has traditionallybeen woven in a twill weave configura-

tion, with the finest counts such as 460being double twill, is now available inplain weave. In twill weave, the threadspass over one/under two, in double twillit’s over two/under two. Plain weavemesh by comparison, with it’s overone/under one configuration, has a muchlower percentage open area since athread is being inserted into every spacein the weave. This not only shrinks the sizeof the mesh openings, but also results in athinner fabric. The net result is that plainweave mesh prints less ink than twillweave mesh woven from the same thread,just what we need when printing four-colorprocess with UV cured inks. If we take380 mesh woven from 34 micron threads as an example, changing weaveconstruction from twill to plain reduces inkdeposit from 11 microns to 7 microns. See Figure 6.

Another area where plain weave meshis capable of superior results is image def-inition. With twill weave mesh, the ‘foot-print’ of the mesh on the substrate, ie thearea where the surface of the threads con-tact, is quite substantial. In some circum-stances it interferes with the flow of ink,and can cause poor print quality. Withplain weave mesh since only the crown of the mesh knuckle contacts the substrate,interference with ink flow is kept to a mini-mum, and substantial improvements in printquality can generally be seen.

Plain weave mesh suitable for printingfour-color process with UV cured ink isnow available in 355, 380, 420 and460 mesh counts. The 355 and 380mesh is even available with a choice of

Comparison of 380 Plain & Twill Weave

Fabric % Open InkThickness Area Deposit

380 PW 34 56µ 13% 7µ

380 TW 34 63µ 17% 11µ

Figure 6

Emulsion Stencil, Profile & Rz On 380 PW 34

Stencil Profile Rz40% Solids 2+3 Dry+2 Sharp Edge Coater 3µ 5µ

40% Solids 2+3 Dry+1 Dull Edge Coater 8µ 5µ

Figure 5




At the shadow end of the tonal range,the limit is reached when the small specksof stencil that have to block the flow ofink, and differentiate between the shadowtones, become smaller than two meshopenings plus one and a half threaddiameters. Smaller than this, and they mayadhere to only one or two threads andlack sufficient adhesion to withstand therigors of processing. For instance, whentrying to print a halftone which is too finefor the mesh in use, what usually happensis that the tonal range will collapse afterthe mid-tones. Once we exceed the detailcarrying capacity of the mesh, we canprint only one tonal value, and that is100%. Again the mesh count, and to a lesser extent thread diameter are theimportant factors in determining the limit of what can be satisfactorily printed. Inthis case however, unlike the highlightswhere thinner threads are better, thickerthreads extend the printable tonal rangeby offering improved adhesion. The upperlimits for 65, 85 and 100 line halftonesprinted with 380 PW34 mesh correspondto 93%, 88% and 82% dots respectively.

34 or 31 micron thread diameters. The result of this is that by selecting theappropriate mesh, ink deposit can be varied from 7 microns, up to 15 microns,depending on your application or color-matching requirements, while still realizingthe benefits of better print quality con-ferred by using plain weave fabric. See Figure 7 for mesh specifications.

PART 4 – THE LIMITATIONSWhen it comes to screen-printing halftones,the fact that we need the mesh to providesupport for the detail in our image meansthat we are not going to be able to print atonal range of 1% to 99%, See Figure 8.

At the highlight end of the tonal range,when the openings in our stencil becomesmaller than one mesh opening plus oneand a half thread diameters, then theycan be obscured by falling on or verynear a thread. Trying to print dots thissmall invariably results in a moiré pattern,despite the fact that all the rules concern-ing angles and dots per inch have beenobserved. This limit of how fine a highlightwe can satisfactorily print, depends mostlyon mesh count, and to a lesser extent onthread diameter, but using 380 PW34mesh as an example, the minimum stencilopening which will consistently print with-out moiré is 85 microns in diameter. Thiscorresponds to a 4% dot for a 65 linehalftone, 7% for 85 line, and 10% whenwe go to 100 line.

Figure 8

Minimum Size of Highlight Dot Is 1 Opening + 1.5 Threads

Minimum Size Of Shadow Dot Needs2 Openings + 1.5 Threads For Stencil



Comparison of 355, 380, 420 & 460 Plain Weave

Fabric % Open InkThickness Area Deposit

355 PW 31 48µ 28% 15µ

355 PW 34 55µ 16% 9µ

380 PW 31 48µ 20% 10µ

380 PW 34 56µ 13% 7µ

420 PW 31 49µ 17% 8µ

460 PW 27 43µ 18% 8µ

Figure 7


For more extensive information for 380mesh. See Figure 9.

When selecting the optimum mesh typeto use, both ink deposit and tonal rangeare usually taken into account. SeeFigure 10, which shows a comparisonof both ink deposit, and minimum high-light dot which can be printed throughplain weave mesh from 355 up to 460.

Two developments in methods of colorseparation, one established, and one verynew, offer improved results for certaintypes of four color process printing withUV cured inks. The first method, which iswidely used, is known as GCR or GrayComponent Replacement. It enables areduction in ink deposit in areas of theprint where yellow, magenta and cyan all

occur together. GCR will eliminate anequal amount of all three, which in someareas removes one of the colors entirely if100% GCR is used. The missing gray isthen restored with the final black printer.See Figure 11.

The second development, which is stillbeing refined, is a new method of produc-ing separations and is known as frequencymodulated halftone, or stochastic screen-ing, or random dot. The separations pro-duced by this method are based uponrandomly distributed, very small uniformsized dots, which simulate tones byincreasing in packing density. This differsfrom conventional separations, where thedots are equally spaced and simulatetones by changing size. These randomdot separations, because they have noangles, offer wider latitude in avoidingmoiré, and are also capable of reproduc-ing a wider range of tones. On the down-side, they require an extremely high reso-lution stencil, and exquisite control overscreen exposure if the image is not to belost altogether. They may also be less suit-able for reproducing certain types of artwork, as they sometimes suffer from a grainy appearance in highlight areas.However, this alternative technology offers promise in overcoming some of theproblems some of the time, and may provide the opportunity to expand the use of screen-printing into otherwise difficultapplications.

100%

90%

80%

45 65 85 100 120 133 150

70%

60%

50%

40%

30%

20%

10%

0%

Figure 9

Tonal Range Printable With 380 Mesh

5%658%85

11%10019%133

4%657%85

10%10017%133

4%657%85

10%10017%133

3%656%85

9%10015%133

3%656%85

8%10014%133

2%654%85

6%10011%133

460PW27420PW31390PW31390PW34355PW31355PW34

9µ 15µ 7µ 10µ 8µ 8µ

Plain Weave Mesh MinimumDot Size & Ink Deposit

Figure 10

Conventional Gray Component Replacement

Y M C B TOTAL Y C B TOTAL

Ink Deposit ConventionalVersus GCR

Figure 11



QUESTIONI have been told by many people thatcontrolling off-contact is the key to successin printing. But how does it really affectmy results?

SOLUTIONOff-contact is the distance between the sub-strate and the screen. This distance is need-ed to keep the screen from staying in con-tact with the substrate during printing and tocontrol proper snap-off. While off-contact isnot the only variable in the ocean of possi-ble problems, it is a decent size fish as faras press variables go. The off-contact dis-tance can affect your printing in any num-ber of ways. Before you tackle this prob-lem, however, you must make sure yourscreen has proper tension. Check yourmesh manufacturer’s tension recommenda-tions. (Refer to “Using Proper TensioningTechniques to Achieve the Desired TensionLevel” Tech Tip on page 32.)

Assuming that your screens are at theproper tension levels, we will begin bycovering the problems caused by too littleoff-contact. Poor release: if the fabricsticks to the substrate after the squeegeehas passed, and the screen is lifted, you’llnotice it takes a percentage of the ink withit and leaves mesh marks. You then havetwo options; either raise the off-contact, or slow down the print speed to accom-modate this poor release. This is a common but incorrect solutions. If you makeno adjustments, double images can appear,as well as image distortion. Not to mentionthe poor ink coverage that will result.

High off-contact, which is as common,causes a myriad of other problems.(Again, we will assume that your screen

tension is correct.) Registration problems:these occur due to the excessive fabricdeflection brought on by high off-contact.Inadequate squeegee pressure: As the off-contact distance increases, the squeegeepressure must be increased to force thefabric into contact with the substrate. Thiscauses slower press speeds, image distor-tion, squeegee wear, and screen failure.Faster snap-off: Increasing the off-contactand squeegee pressure creates a fastersnap-off. This can cause print defects suchas bubbles, smearing, incomplete images,mis-registration and print voids.

Until recently, there were only a fewways to determine the off-contact distance.The most accurate method was by using amechanical gauge. However, this processcould take valuable time away from production, so it was usually abandonedand left to the operator to “eyeball” thedistance. Now, the newly developedPositector 6000 off-contact gauge, withan easy-to-read digital display, can provide measurements automatically inminutes. Thus repeatability can be builtinto this print variable. Keep in mind, however, that this measurement providesthe actual off-contact distance, not a deter-mination of what is the proper off-contactdistance. It is up to you, through testing, to determine the proper distance requiredfor each press, screen tension, and formatsize. Having this tool to measure the distance, and maintain uniformity, makesthe process more repeatable.

NOTE: a good rule of thumb is to haveyour screen as close as possible to the sub-strate, while maintaining the proper snap-off.

Controlling Off-Contact For Successful Printing


1. DUROMETER AND PRINTINGEDGE (As Related To Ink Deposit)The lower the durometer, and the lesssharp the print edge, the more ink isdeposited. The higher the durometer, andthe sharper the print edge, the less ink isdeposited. The more irregular or rougherthe surface of the substrate is, the softerthe durometer needed. (And vice versa.)To maximize solvent resistance, alwaysuse the hardest durometer that is practicalfor the particular job. The harder thesqueegee, the more dense the urethaneand therefore the stronger the chemicalresistance.

2. COLOR CODINGUse color coding as a means of fast andeasy identification of the correct squeegeedurometer once you’ve established thehardness for your application.

3. PROFILE EDGEa) Rectangular: applies to 95+ % of flat

type printing.

b) “V” shape: applies to 90+ % of cylindrical printing. (Square is also used in some instances.)

c) Ballnose (rounded): used for more inkdeposit — generally in some textileprinting and industrial specializedheavy deposit applications. However,print edge sharpness is sacrificed. (Alsoused for direct/indirect stencil makingand emulsion reinforcement of capillaryfilm stencils.)

d) Dual-Durometer: used to optimize inktransfer efficiency and squeegee setting(pressure, angle, shear) via decreasingthe blade’s susceptibility to bending.

e) Composite: (similar to above) used formaximum rigidity.

4. LENGTH OF SQUEEGEETry to maximize the “free mesh area.” Thisis the distance between the ends of thesqueegee and the inside of the frame profile. This area is vital to provide theimportant flex and snap functions of thescreen. It affects registration, print clarity,uniformity of ink deposit, and the life ofthe stencil, fabric and squeegee.

Choosing The Best Squeegee For Your Application

Care And Maintenance To Extend Squeegee Life

Even the most solvent and abrasion resist-ant squeegees, such as our Duralife™brand, can benefit from some preventivemaintenance to maximize longevity.

1. STORAGEa) Store in a dry and generally cool area

(50–85 degrees Fahrenheit).

b) Do not store coiled; lie flat to avoid distorting the print edge.

2. MAINTENANCE/ROTATIONFor optimum squeegee life, rotate yourblades in use as much as possible. Allsqueegees tend to swell and soften tosome extent while in use. If they are given

the opportunity to dry and return to theiroriginal state, they will last longer.

a) Establish a rotation schedule, based onthe aggressiveness of your particular inksystem, to allow the squeegee to “rest”.

b) Inspect for signs of swelling -- Afterapproximately 2-4 hours of continuousprinting with aggressive inks and solvents.

After approximately 6-8 hours of continu-ous printing with moderate to weak inksand solvents.

c) Change the squeegee at the first signof swelling.



b) A blade-cut type sharpener, versus abelt or grinding wheel sharpener, willyield a print-ready squeegee after justone pass.

c) Belt or grinding wheel sharpening isacceptable for most applications. It isbest done in a two-step process usingmultiple passes (and limited pressure)that take off as little material as possi-ble. This reduces heat buildup, whichcan melt the squeegee.

STEP 1. Coarse grit (60-120) to removeworn edge.

STEP 2. Fine grit (160-300) to create asharp edge and a smooth, polished finish.


Duralife™ dual-durometer squeegees. Duralife™ composite squeegees.Duralife™ color-coded squeegees.

d) Before resting squeegee, clean thoroughlywith a solvent to remove any ink residue.

e) Never soak any squeegee in a solventfor an extended period; irreversibledamage could result.

f) Depending on the durometer, and the inkand solvent aggressiveness, the squeegeemay require a minimum of 12 to 48hours of rest before re-use or re-sharpen-ing. (Softer duros tend to absorb moreand require longer recovery.)

3. SHARPENINGa) Before sharpening, the squeegee may

require a 12 to 48-hour rest (depend-ing on ink and solvent aggressiveness)to allow any solvents to evaporate.


With the increasing use of artworkgenerated by laser printers, the need forchecking the overall density of screen positives is more crucial. Vellum can particularly be a nightmare. Use of atransmission densitometer is the ideal quality control check for maintaining thedensity criteria required for optimum performance. For example, backgrounddensity should be as low as possible.Preferably below 0.1, since a high back-ground density will cause underexposureproblems. Density of the image areashould be as high as possible. Preferablyabove 3, to prevent fogging and poorwashout.

A transmission densitometer, used in the % mode, is also ideal for checking thetonal range on halftone positives. It can be used as a QC measure on any filmssupplied, with attention paid to difficultareas, to determine if they fall within theappropriate range. screen-printing can not reproduce the 1%-99% dot range thatcan be held with offset printing. The rangethat can be reproduced successfullydepends on the mesh count chosen, andthe lines per inch count of the artwork. Ifeverything else is perfect, such as tension,ink, squeegee, etc., then the following limits apply.

Guidelines To The Use Of A TransmissionDensitometer For Screen Making

Mesh Count 65 Line 85 Line 100 Line 120 Line

305 5-89% 9-80% 13-71% --

355 4-91% 7-85% 10-79% 14-70%

380 4-93% 6-88% 9-82% 13-75%

420 3-94% 5-90% 8-86% 11-80%

460 3-95% 5-92% 7-88% 9-85%

Use the TQ+™ Densitometer to maintain consistent film positives.


A reflection densitometer can be indispensable in checking your prints toquantify ink deposit, or solve ink mixing(pigment ratio) problems that may developduring long print runs and can causeshade differences. It can also be used todistinguish hue differences with ratio ofCMYK values, and aid in color matching.

When printing four-color process, areflection densitometer can be used todetect if any of the inks are under or overstrength by quantifying problems with gray

balance in 100% print areas. If calibratedon a 100% print area of a particularcolor, it can then detect the degree of dotgain (or loss) for that color by comparisonwith the transmission density readings fromthe positive. The standard procedure is toconduct these evaluations on step wedgesthat are printed with the image. For thoseprinters who do not have the luxury of running test strips that can be trimmed off,an option is to settle on selected areas ofthe print that can be tested consistently.

Guidelines To The Use Of A ReflectionDensitometer For Screen-Printing

This advanced, menu-driven IQ 150™ ReflectionDensitometer provides the easiest means of density readings available.


Preventive Checklist(For More Predictable & Repeatable Screen Making)

1. MESH SELECTION❑ My mesh selection is based on the most suitable blend of tension/print characteristics

for the degree of detail, length of run, ink deposit thickness and substrate surface.

❑ With my mesh count, I’ve chosen the proper thread diameter for my print requirements(higher tension, longer print life, better edge definition, 4-color process).

❑ The tension level I use corresponds to the mesh count/thread diameter (thinner = lower tension).

❑ I use a plain weave with a thin thread diameter, the combination recommended foroptimum print detail.

❑ I have taken into consideration that twill weaves deposit more ink than plain weaves.

2. FRAME SELECTION & MESH TENSIONING❑ I considered the format size and tension levels used when selecting the frame type,

material and profile.

❑ When selecting my tensioning equipment, the determining factors were: my applica-tion, production capacity, tension levels, mesh type (polyester, nylon or stainless steel)and mesh count (coarse or fine).

❑ A tension meter, used correctly and optimally, is a standard part of my stretchingprocess.

❑ I avoid taking the mesh to ultimate tension levels, as this sacrifices screen life.

❑ I use the most effective frame adhesive based on such factors as solvent and waterresistance, production time requirements and odor.

❑ Production adheres to the mesh manufacturer’s recommended tension levels.

❑ Correct tensioning procedures were established by reviewing the equipment manufacturer’srecommendations, and by testing and documenting what works best in my operation.

3. MESH PREPARATION❑ The screen making area is kept as isolated and clean as possible, as airborne dust

and oils can cause pinholes and fisheyes.

❑ I degrease my screens from the first time they are used, and each time thereafter.

❑ Use of a wetting agent is standard, as it is critical for proper film application, and beneficial to uniform emulsion adhesion.

❑ A mesh prep with an abradant is used on “virgin” mesh (conventional synthetic monofilament).

❑ Household cleaners are never substituted for mesh degreasers or abradants, as they candamage the fabric, and contain oils/lanolin that can interfere with screen performance.

❑ Compressed air is not used to remove excess water from screens; it contains oils andwater impurities that can cause fisheyes and pinholes.



Preventive Checklist(For More Predictable & Repeatable Screen Making)

4. STENCIL SELECTION & APPLICATION❑ My emulsion has been chosen based on ink type, solvent and water resistance,

exposure time, artwork detail and durability.

❑ Tests have been run, and results documented, regarding what performs best in my particular operation.

❑ When coating manually, I use a screen coating trough designed for this purpose.

❑ Automatic coating has been evaluated in relation to production capacity, print requirements and the need for coating thickness consistency.

❑ The proper coating procedures are used, based on the manufacturer’s recommendationsand what works best in my process.

❑ I adjust coating sequence based on mesh specification.

❑ An emulsion thickness measuring device is used during stencil making.

❑ The proper emulsion thickness is matched to the resolution I need to hold.

❑ Stencil smoothness is matched to substrate smoothness using an Rz meter.

5. EXPOSURE❑ Dried screens are checked for residual moisture before exposure by using a stencil

moisture meter.❑ My exposure system has been matched to my particular emulsion.

❑ The correct distance between my exposure system and vacuum frame is calculated and maintained.

❑ As a process control, an exposure calculator is used regularly and properly (and readaccurately) on production screens.

❑ A radiometer is used to measure my exposure system’s lamp uniformity and intensity.

❑ A radiometer is also used to help determine appropriate exposure times.

❑ The correct exposure time is determined specifically for each mesh count and emulsion type.



Regulatory Resources: Guidance Tools

As screen printers, you are called upon to handle regulated or hazardous materials. As asafety-conscious manufacturer/supplier, we’ve included the following additional resourcesuggestions to help you learn more about the safe use, disposal and transport of suchmaterials. We’ve also included (on the next page) a step-by-step guide to waste classifica-tion and disposal. For more information or assistance, please call our Regulatory AffairsCoordinator at (847) 296-5090.

1. CODE OF FEDERAL REGULATIONS (CFR) & FEDERAL REGISTER• Regulatory bible.• Regulations as specified by the Occupational Safety & Health Administration

(OSHA/29 CFR), Environmental Protection Agency (EPA/40 CFR) & Department of Transportation (DOT/49 CFR).

• The Federal Register is the most current listing of both proposed and finalized regulations.SOURCE: Local library, safety supply companies, consulting companies, and the Government Printing Office

Phone: (202) 783-3238 • www.access.gpo.gov

2. COMPLIANCE MANUALS• Regulations are translated into layman’s terms.• Easier to understand & translate legal terminology.• Step-by-step compliance.• Some address one specific regulation.• Offer update services.SOURCE: Safety supply companies, consulting companies.

3. TRADE MAGAZINES (“OCCUPATIONAL HEALTH & SAFETY”, “ENVIRONMENTAL PROTECTION”)

• Discussions of regulations.• Regulation updates (proposed & finalized).• Informative articles written by environmental and safety professionals,

industrial engineers, chemists, etc.• Methods for waste treatment, recycling & water treatment are presented.SOURCE: Stevens Publishing Company. Phone: (972) 687-6700 • www.stevenspublishing.com

4. MONTHLY NEWSLETTERS & BULLETINS• Offer regulation updates and discussions of current “hot” topics.• The Screen Printing & Graphic Imaging Association’s (SGIA) monthly “Tabloid” includes

a government affairs section.SOURCE: Consulting companies, professional trade associations (Chemical Manufacturer’s Association and SGIA)

and trade magazines. Phone: (703) 385-1335. www.sgia.org

5. SEMINARS & COURSES• Focus on specific agencies and specific regulations.• Offer framework for understanding and complying with regulations.• Speakers/instructors are often former employees of OSHA, EPA, or DOT, consultants,

and/or industry experts.• Offer certification programs.SOURCE: Consulting companies, professional trade associations (Chemical Manufacturer’s Association and SGIA)

and trade magazines.



Regulatory Resources: Guidance Tools

6. CONSULTING COMPANIES• Offer advisory legal hotlines for compliance guidance.• Will perform safety and environmental audits of your facility.• Will assist in completing & filing complicated regulatory reports, permits,

waste documentation, etc.SOURCE: Company direct, Yellow Pages, industrial directories.

7. LOCAL & LAW LIBRARIES• To obtain copies of city/county codes, state/federal regulations (CFR, Federal Register).• Research specific areas (like wastewater treatment technology, etc.).SOURCE: Telephone directory/Yellow Pages, local business or community directory, city agencies.

8. MANUFACTURERS/SUPPLIERS• To obtain/interpret Material Safety Data Sheets (MSDS).• To obtain technical information regarding product use, handling and disposal.• Usually offer compliance assistance/guidance.• Often employ a regulatory/compliance officer and, in some cases, an entire staff.SOURCE: Product labels, product literature, MSDS, trade and/or industrial directories.

9. MATERIAL SAFETY DATA SHEETS (MSDS)• Provide an excellent quick reference source.• Provide chemical composition information; usually disclose hazardous ingredients.• Often provide OSHA, EPA and DOT information on a single document.• Sometimes offer specific methods for safe handling, pollution control and waste treatment.SOURCE: Manufacturer, supplier, distributor.

10. LOCAL AUTHORITIES• Local OSHA/EPA/DOT offices, water reclamation district

(Publicly Owned Treatment Works/POTW), county health department.• To obtain copies of regulations.• To obtain compliance assistance.• Offer 800# hotlines for regulation updates and interpretation.SOURCE: Local telephone directory, local business or community directory, government agencies,

SGIA, manufacturers/suppliers.



I. IDENTIFY THE WASTE AND/OR ITS CONSTITUENTS.A. Consult resources.

1. Review Material Safety Data Sheets (MSDS).

2. Contact the manufacturer. a) To obtain assistance interpreting the MSDS. b) To obtain component information/ingredient disclosure.

II. CLASSIFY THE WASTE (HAZARDOUS/NONHAZARDOUS).A. Consult resources.

1. Review MSDS for hazardous ingredients (usually disclosed down to 1%; carcinogens/toxins down to 0.1%).

2. Consult the Code of Federal Regulations (CFR)/compliance manuals for hazardclass definitions and lists of hazardous/regulated chemicals.a) Do the chemical constituents meet the definition of “hazardous”, as specified by

either the Occupational Safety & Health Administration (OSHA), Department of Transportation (DOT) or the Environmental Protection Agency (EPA)?

b) Are the chemical constituents specifically listed/regulated by any of the above-mentioned agencies?

c) Are the chemical constituents any of the following? – Volatile Organic Compounds (VOCs)/Federal Clean Air Act?– Ozone Depleting Chemicals (ODCs)/Federal Clean Air Act?– Hazardous Air Pollutants/Federal Clean Air Act– Toxic as per Superfund Amendments & Re-authorization Act of 1986 (SARA Title III)?– Priority Pollutants as per the National Pollutant Discharge Elimination System

(NPDES)/Clean Water Act?d) Are any of the chemical constituents either listed or characteristic hazardous

wastes, as specified by the Hazardous & Solid Waste Amendments (HSWA)/ Resource Conservation & Recovery Act of 1976 (RCRA) in Title 40 of the Code of Federal Regulations (40 CFR)?

3. Review state and local authorities’ regulations. a) Are the chemical constituents regulated under a state hazardous/solid waste

program?b) Are the chemical constituents regulated under a state/local air quality program? c) Are the chemical constituents regulated/prohibited from discharge by the local

Publicly Owned Treatment Works (POTW/sewer authority)?

4. If waste is hazardous, determine its appropriate class/characteristic (ie. ignitable, corrosive, reactive or toxic).

III. DETAIL INFORMATION ON THE PRINTING/RECLAIMING OPERATIONS AND THE QUANTITIES OF WASTE INVOLVED.A. How is the chemical (pollutant) being used in the operation?

B. If the waste is a mixture, what percentage is hazardous?

C. Is the waste (or its constituents) being emitted from your facility? If yes, then: Review state/local air permitting requirements.

Step-By-Step Guide To Waste Classification & Disposal



Step-By-Step Guide To Waste Classification & Disposal

D. Does the waste (or its constituents) enter your effluent (waste stream)? If yes, then:

1. What is the concentration of the pollutant at the point of introduction?

2. What is the water usage/consumption on a typical production day?

3. Is the effluent being substantially diluted by other waste streams?

4. What is the probable concentration of the pollutant in the exiting effluent?

5. Is the waste (or its constituents) either acidic or alkaline in nature?

6. Is the waste (or pollutant) known to be biodegradable?

7. What are the Biochemical Oxygen Demand (BOD)/Chemical Oxygen Demand(COD) values of the constituents?

IV. CONDUCT (RECOMMENDED) WASTE CHARACTERIZATION AND/OR EFFLUENT SAMPLING/TESTING.

V. MAKE GENERAL ASSESSMENT BASED ON THE ABOVE INFORMATION.A. If waste characterization and/or effluent testing can be done, then it’s advisable to

wait for the results before making a determination.

B. If the waste involved is, in fact, hazardous, consider switching to safer, non-hazardousalternatives, if possible. You may be able to significantly reduce, or eliminate, yourhazardous waste inventory and subsequent pollutants.

C. If very large quantities of waste are involved, then waste hauling may be recommend-ed (whether the waste is hazardous or not).

D. If a generally accepted method of recycling/pretreatment is plausible for the particularwaste, then it should be considered at this point.

E. Research potential recycling/pretreatment strategies. (Examples: distillation, filtration,neutralization, aeration, oil/water separation, toxics precipitation.) These recovery/pretreatment techniques can sometimes allow for recycling of solvents and/or cleaningup polluted waste streams.

F. Gather information from vendors regarding available systems, operation/maintenanceof equipment and associated costs. Weigh the pros and cons of “in-house” treatmentversus waste hauling.

G. If “in-house” treatment is not viable, and/or large quantities of “known” hazardouswaste are being generated, then it is recommended that the printer safely collect andretain the waste for haulage. Manufacturers can offer guidance in regard to handlingof waste associated with their products.



Bar

British Thermal Unit

British Thermal Unit Per Second

Centigram

Centimeter

Centipoise

Cubic Centimeter

Cubic Foot

Kilogram per square centimeter 1.01977Pascal 100000.0Pound per square foot 2088.576Pound per square inch 14.504Foot-pound 778.6Joule 1055.0Kilocalorie 0.252Kilogram-force meter 107.6Kilowatt hour 0.000293Horsepower 1.415Joule per second 1055.0Kilocalorie per second 0.252Kilowatt 1.055Dram 0.00564Gram 0.01Kilogram 0.00001Ounce 0.00035Pound 0.00002Foot 0.0328Inch 0.3937Meter 0.01Millimeter 10.0Yard 0.0109Gram-force second/square centimeter 0.0000102Kilogram per meter hour 3.6Poise 0.01Pound per foot hour 2.419Pound per foot second 0.000672Pound per inch second 0.000056Pound-force second per square foot 0.0000209Pound-force second per square inch 0.000000145Cubic foot 0.000035Cubic inch 0.06102Cubic meter 0.000001Cubic yard 0.0000013Fluid ounce 0.03382Liter 0.001Milliliter 1.0Cubic centimeter 28317.0Cubic inch 1728.0Cubic meter 0.0283Cubic yard 0.037Gallon 7.48

To Convert From To Multiply By

Conversion Guides


To Convert From To Multiply ByCubic Inch Cubic centimeter 16.387

Cubic foot 0.00058Cubic meter 0.000016Cubic yard 0.000021Fluid ounce (Imp.) 0.57677Fluid ounce (U.S.) 0.5541Gallon (Imp.) 0.00361Gallon (U.S.) 0.00433Liter 0.01639Milliliter 16.387Quart (Imp.) 0.01442Quart (U.S.) 0.01732

Cubic Meter Cubic centimeter 1000000.0Cubic foot 35.3145Cubic inch 61023.5Cubic yard 1.3079Gallon 264.2Liter 1000.0

Cubic Yard Cubic centimeter 764559.0Cubic foot 27.0Cubic inch 46656.0Cubic meter 0.7648

Fluid Ounce – Imperial Cubic inch 1.7338Fluid ounce (U.S.) 0.9607Gallon (Imp.) 0.00625Gallon (U.S.) 0.0075Liter 0.02841Milliliter 28.4132Quart (Imp.) 0.025Quart (U.S.) 0.03

Fluid Ounce – U.S. Cubic centimeter 29.57286Cubic inch 1.80469Fluid ounce (Imp.) 1.0408Gallon (Imp.) 0.0065Gallon (U.S.) 0.0078Liter 0.02957Milliliter 29.57286Quart (Imp.) 0.026Quart (U.S.) 0.03125

Conversion Guides (cont’d.)



To Convert From To Multiply ByFoot Centimeter 30.48

Inch 12.0Meter 0.305Milliliter 304.8Yard 0.333

Foot – Pound British thermal unit 0.00129Joule 1.356Kilocalorie 0.000324Kilogram – force meter 0.1383Kilowatt hour 0.000000376

Gallon – Imperial Cubic inch 277.42Fluid ounce (Imp.) 160.0Fluid ounce (U.S.) 153.723Gallon (U.S.) 1.201Liter 4.546Milliliter 4546.112Quart (Imp.) 4.0Quart (U.S.) 4.804

Gallon – U.S. Cubic foot 0.1337Cubic inch 230.947Cubic meter 0.00379Fluid ounce (Imp.) 133.2334Fluid ounce (U.S.) 128.0Gallon (Imp.) 0.8327Liter 3.7853Milliliter 3785.327Pounds of water 8.40336Quart (Imp.) 3.33Quart (U.S.) 4.0

Gram Centigram 100.0Dram 0.5644Kilogram 0.001Ounce 0.0353Pound 0.0022

Grams Per Liter Ounces per gallon 0.13353Pounds per gallon 0.008345




Gram-Force Second/ Centipoise 98070.0Square Centimeter Kilogram per meter hour 353000.0

Poise 980.7Pound per foot hour 237200.0Pound per foot second 65.9Pound per inch second 5.492Pound-force second per square foot 2.048Pound-force second per square inch 0.01422

Horsepower British thermal unit per second 0.7073Joule per second 745.7Kilocalorie per second 0.1782Kilowatt 0.7457

Inch Centimeter 2.54Foot 0.08333Meter 0.0254Millimeter 25.4Mil 1000.0Yard 0.02777

Joule British Thermal Unit 0.00095Foot-pound 0.7376Kilocalorie 0.00024Kilogram-force meter 0.102Kilowatt hour 0.000000278

Joule Per Second British thermal unit per second 0.00095Horsepower 0.00134Kilocalorie per second 0.00024Kilowatt 0.001Watt 1.0

Kilocalorie British thermal unit 3.97Foot-pound 3087.0Joule 4187.0Kilogram-force meter 426.9Kilowatt hour 0.00116

Kilocalorie Per Second British thermal unit per second 3.968Horsepower 5.614Joule per second 4187.0Kilowatt 4.187

Kilogram Centigram 100000.0Dram 564.383Gram 1000.0Ounce 35.274Pound 2.205




Kilogram Per Meter Centipoise 0.2778Hour Gram-force second/square centimeter 0.0002833

Poise 0.002778Pound per foot hour 0.672Pound per foot second 0.000187Pound per inch second 0.0000155Pound-force second per square foot 0.0000058Pound-force second per square inch 0.00000004

Kilogram Per Square Bar 0.98067Centimeter Pascal 98066.5

Pound per square foot 2048.112Pound per square inch 14.223

Kilogram-Force Meter British thermal unit 0.0093Foot-pound 7.233Joule 9.807Kilocalorie 0.00234Kilowatt 0.00000272

Kilowatt British thermal unit per second 0.9484Horsepower 1.341Joule per second 1000.0Kilocalorie per second 0.239

Kilowatt Hour British thermal unit 3413.0Foot-pound 2655000.0Joule 3597000.0Kilocalorie 860.0Kilogram-force meter 367100.0

Liter Cubic centimeter 1000.0Cubic inch 61.02Cubic meter 0.001Fluid ounce (Imp.) 35.195Fluid ounce (U.S.) 33.8148Gallon (Imp.) 0.22Gallon (U.S.) 0.264Milliliter 1000.0Quart (Imp.) 0.88Quart (U.S.) 1.0567

Meter Centimeter 100.0Foot 3.281Inch 39.37Millimeter 1000.0Yard 1.094

Micron Centimeter 0.0001Mil 0.03937




Mil Inch 0.001Micron 25.4

Milliliter Cubic inch 0.06102Fluid ounce (Imp.) 0.0352Fluid ounce (U.S.) 0.0338Gallon (Imp.) 0.00022Gallon (U.S.) 0.000264Liter 0.001Quart (Imp.) 0.00088Quart (U.S.) 0.00106

Millimeter Centimeter 0.10Foot 0.00328Inch 0.03937Meter 0.001Yard 0.00109

Ounce Centigram 2834.9Dram 16.0Gram 28.3495Kilogram 0.0284Pound 0.0625

Ounces Per Gallon Grams per liter 7.489Pascal Bar 0.00001

Kilogram per square centimeter 0.0000102Newton per square meter 1.0Pound per square foot 0.0209Pound per square inch 0.000145

Poise Centipoise 100.0Gram-force second/square centimeter 0.00102Kilogram per meter hour 360.0Pound per foot hour 241.9Pound per foot second 0.0672Pound per inch second 0.0056Pound-force second per square foot 0.00209Pound-force second per square inch 0.0000145

Pound Centigram 45359.2Dram 256.0Gram 453.5924Kilogram 0.4536Ounce 16.0

Pounds Per Gallon grams per liter 119.832




Pound Per Foot Hour Centipoise 0.4134Gram-force second/square centimeter 0.0000042Kilogram per meter hour 1.488Poise 0.004134Pound per foot second 0.000278Pound per inch second 0.0000231Pound-force second per square foot 0.00000863Pound-force second per square inch 0.00000006

Pound Per Foot Second Centipoise 1488.0Gram-force second/square centimeter 0.01518Kilogram per meter hour 5357.0Poise 14.88Pound per foot hour 3600.0Pound per inch second 0.08333Pound-force second per square foot 0.032Pound-force second per square inch 0.000216

Pound Per Inch Second Centipoise 17860.0Gram-force second/square centimeter 0.1821Kilogram per meter hour 64290.0Poise 178.6Pound per foot hour 43200.0Pound per foot second 12.0Pound-force second per square foot 0.373Pound-force second per square inch 0.0026

Pound Per Square Foot Bar 0.00048(PSF) Kilogram per square centimeter 0.00049

Pascal 47.88Pound per square inch 0.00694

Pound Per Square Inch Bar 0.06895(PSI) Kilogram per square centimeter 0.07031

Pascal 6894.8Pound per square foot 144.0




Pound-Force Second Centipoise 47880.0Per Square Foot Gram-force second/square centimeter 0.4882

Kilogram per meter hour 172400.0Poise 478.8Pound per foot hour 115800.0Pound per foot second 32.17Pound per inch second 2.681Pound-force second per square inch 0.00694

Pound-Force Second Centipoise 6895000.0Per Square Inch Gram-force second/square centimeter 70.31

Kilogram per meter hour 24820000.0Poise 68950.0Pound per foot hour 16680000.0Pound per foot second 4633.0Pound per inch second 386.1Pound-force second per square foot 144.0

Quart (Imperial) Cubic inch 69.355Fluid ounce (Imp.) 40.0Fluid ounce (U.S.) 38.43Gallon (Imp.) 0.25Gallon (U.S.) 0.3002Liter 1.1365Milliliter 1136.528Quart (U.S.) 1.201

Quart (U.S.) Cubic inch 57.75Fluid ounce (Imp.) 33.308Fluid ounce (U.S.) 32.0Gallon (Imp.) 0.2082Gallon (U.S.) 0.25Liter 0.9463Milliliter 946.3316Quart (Imp.) 0.8327

Square Centimeter Square foot 0.00108Square inch 0.15502Square meter 0.0001Square yard 0.00012

Square Foot Square centimeter 929.0304Square inch 144.0Square meter 0.0929Square yard 0.1111




Square Inch Square centimeter 6.45162Square foot 0.00694Square meter 0.00065Square yard 0.00077

Square Meter Square centimeter 10000.0Square foot 10.764Square inch 1550.388Square yard 1.196

Square Yard Square centimeter 8361.274Square foot 9.0Square inch 1296.0Square meter 0.836

Threads Per Centimeter Threads per inch 2.54Threads Per inch Threads per centimeter 0.394Yard Centimeter 91.44

Foot 3.0Inch 36.0Meter 0.915Millimeter 914.4


Fahrenheit to Celsius (OF - 32) .5555 = OC

Celsius toFahrenheit (OC x 1.8) + 32 = OF

Fahrenheit to Kelvin (OF + 459.67) .5555 = OK

Kelvin toFahrenheit (OK x 1.8) - 459.67 = OF

Celsius to Kelvin

OC + 273.15 = OK

Kelvin to Celsius

OK - 273.15 = OC

Imperialx 1.2 = U.S. GallonGallon

Poundsx 0.119 = Gallonsof Water

Cubic x 7.48 = GallonsFeet

Cubicx 0.00433 = GallonsInches

Cubicx 264.2 = GallonsMeters

Cubicx 1000 = LitersMeters

Cubic cm (cm3) = Milliliter

Cubic cm x 0.0338 = Fluid Ounces

Fluidx 29.57 = Cubic cmOunces

Liters x 1000 = Cubic cm

Grams/x 0.008345 =

Pounds/Liter Gallon

Grams/x 0.1335 =

Ounces/Liter Gallon

Pounds/x 119.8 = Grams/LiterGallon

Ounces/x 7.489 = Grams/LiterGallon

VOLUMETRIC CONVERSION FORMULAS

TEMPERATURE CONVERSION EQUATIONS



UNITS OF CAPACITY – U.S. Liquid Measure

Fluid Ounce Quart Gallon Milliliter Liter Cubic InchUnit (fl oz) (qt) (ga) (ml) (l) (in3)

Fl Ozs 1 32.0 128.0 0.0338 33.8148 0.5541Quarts 0.03125 1 4.0 0.00106 1.0567 0.01732Gallons 0.0078 0.25 1 0.000264 0.264 0.00433

Mls 29.57286 946.3316 3785.327 1 1000.0 16.387Liters 0.02957 0.9463 3.7853 0.001 1 0.01639Inches3 1.80469 57.75 231.0 0.06102 61.02 1

UNITS OF CAPACITY – Imperial Liquid Measure

Fluid Ounce Quart Gallon Milliliter Liter Cubic InchUnit (fl oz) (qt) (ga) (ml) (l) (in3)

Fl Ozs 1 40.0 160.0 0.0352 35.195 0.57677Quarts 0.025 1 4.0 0.00088 0.88 0.01442Gallons 0.00625 0.25 1 0.00022 0.22 0.00361

Mls 28.4132 1136.528 4546.112 1 1000.0 16.387Liters 0.02841 1.1365 4.546 0.001 1 0.01639Inches3 1.7338 69.355 277.42 0.06102 61.02 1

UNITS OF AREA

Square Square Square Square SquareInch Foot Yard Centimeter Meter

Unit (in2) (ft2) (yd2) (cm2) (m2)

Inches2 1 144.0 1296.0 0.15502 1550.388Feet2 0.00694 1 9.0 0.00108 10.764Yards2 0.00077 0.1111 1 0.00012 1.196Cms2 6.45162 929.0304 8361.274 1 10000.0

Meters2 0.00065 0.0929 0.836 0.0001 1



UNITS OF WORK

British Kilowatt-Foot-Pound Kgfm Joule Kilo-Calorie Thermal Unit Hour

Unit (ft-lb) (kcal) (btu) (kW-h)

Ft-Lb 1 7.233 0.7376 3087.0 778.6 26.55x105

Kgfm 0.1383 1 0.102 426.9 107.6 36.71x104

Joule 1.356 9.807 1 4187.0 1055.0 35.97x105

Kcal 0.000324 0.00234 0.00024 1 0.252 860.0Btu 0.00129 0.0093 0.00095 3.97 1 3413.0

kW-h 3.76x10–7 2.72x10–6 2.78x10–7 0.00116 2.93x10–4 1

Note: kgf=kilograms force

UNITS OF POWER

Horsepower Kilowatt Joule/Second Kcal/Second Btu/SecondUnits (hp) (kW) (Watt)

Hp 1 1.341 0.00134 5.614 1.415kW 0.7457 1 0.001 4.187 1.055

Joule/s 745.7 1000.0 1 4187.0 1055.0Kcal/s 0.1782 0.239 0.00024 1 0.252Btu/s 0.7073 0.9484 0.00095 3.968 1

Note: to convert from units/sec. to units/min., divide by 60. 1 Joule/sec. = 1 watt

UNITS OF PRESSURE

Lbf/In2 Lbf/Ft2 Pascal Bar Kg/Cm2

Units (PSI) (PSF) (Pa)

PSI 1 0.00694 0.000145 14.504 14.223PSF 144.0 1 0.0209 2088.576 2048.112Pa 6.89x103 47.88 1 1x105 9.81x104

Bars 0.06895 0.00048 0.00001 1 0.9807Kg/Cm2 0.07031 0.00049 0.0000102 1.0197 1

Note : 1 Pascal = 1 Newton/square meter (N/m2) Lbf = pounds force



THICKNESS CONVERSION CHART

Mils Microns Mils Microns Mils Microns1 25.4 9 228.6 17 431.82 50.8 10 254.0 18 457.23 76.2 11 279.4 19 482.64 101.6 12 304.8 20 508.05 127.0 13 330.2 21 533.46 152.4 14 355.6 22 558.87 177.8 15 381.0 23 584.28 203.2 16 406.4 24 609.6

*Data represents the closest possible approximation.

FRACTIONAL EQUIVALENTS

Fractional Decimal Milli- Fractional Decimal Milli-Inches Inches meter Inches Inches meter1/64 0.015625 0.397 1/2 0.50 12.71/32 0.03125 0.794 17/32 0.5312 13.4943/64 0.046875 1.191 9/16 0.5625 14.2881/16 0.0625 1.588 19/32 0.5937 15.0813/32 0.09375 2.381 5/8 0.625 15.8751/8 0.125 3.175 21/32 0.6562 16.669

5/32 0.15625 3.969 11/16 0.6875 17.4633/16 0.1875 4.763 23/32 0.7187 18.2567/32 0.21875 5.556 3/4 0.75 19.051/4 0.250 6.35 25/32 0.7812 19.844

9/32 0.2812 7.144 13/16 0.8125 20.6385/16 0.3125 7.938 27/32 0.8437 21.43111/32 0.3437 8.731 7/8 0.875 22.225

3/8 0.375 9.525 29/32 0.9062 23.01913/32 0.4062 10.319 15/16 0.9375 23.8137/16 0.4375 11.113 31/32 0.9687 24.606

15/32 0.4687 11.906 1 1.00 25.4

THICKNESS CONVERSION FORMULAS

Microns x 0.03937 = MilsMils x 25.4 = MicronsMils x 0.001 = InchesMicrons x 0.0001 = cm

MESH COUNT CONVERSION FORMULAS*

Threads/Inch x .394 = Threads/cmThreads/cm x 2.54 = Threads/Inch



MESH COUNT CONVERSION CHART*

Threads Threads Threads Threads Threads Threads Threads Threads/inch /cm /inch /cm /inch /cm /inch /cm25 10 85 34 156 61 280 11030 12 92 36 163 64 305 12037 15 96 38 173 68 330 13045 18 103 40 186 73 355 14054 21 110 43 195 77 381 15060 24 115 45 206 81 409 16163 25 123 48 215 85 420 16574 29 131 51 230 90 457 18076 30 137 54 240 95 495 19583 32 148 58 254 100 508 200

*Data represents the closest possible approximation.



SCREEN FABRIC SELECTION FORMULAS*

Mesh Count (#/cm) & Mesh Count (#/cm) & Image Thickness (cm) &To Calculate For Thread Diameter (cm) Percent Open Area (%) Fineline Resolution (cm)

Mesh OpeningMo (cm)

Percent Open Area A = (1-McD)2 —A (%)

Image Thickness lh (cm) lh = 1.82D (1-McD)2 —(Wet Film Ink Height)

Relative StrengthS (cm2/cm)

Fineline Resolution d1 = 5D —d1 (cm)

Halftone Dot Resolution —d2 (cm)

Mesh Count — —Mc (#/cm)

Thread Diameter —D (cm)

Mo = d1

.364d1

lh

.364d1

lh

51-

¹McD2

4S = ¹Mc (1- A)2

4Mc2S = or

d1

.364d1

lh51-¹d1

2

100S =

1- AMc

5d1 =

2(2Mc-Mc A)Mc2

d2 = 2 (1+McD)

Mcd2 =

Mc = d1

.364d1

lh51-

1- AMc

D = D = d1

5

AMc

Mo =

1.82A(1- A)Mc

lh =

1-McDMc

Mo =

1h.364d1

A =

Source: T. Frecska, Screen Printing Magazine*Data represents the closest possible approximation.


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