FACTORS INFLUENCING THE SURFACE STRENGTH OF COATED … ppt.pdf · Continuous fine tuning of the binder level is important to cost reduction efforts – reqqypuires total systems appproach

Factors Influencing the SurfaceSt th f C t d PStrength of Coated Papers

Dan Varney – Omya Inc.

Peter Dahlvik, Guillermo Bluvol, Karl-Heinz Kagerer, and Manfred Arnold Applied Technology Service; Business Unit Paper; Omya International AGApplied Technology Service; Business Unit Paper; Omya International AGCH-4665 Oftringen

PaperCon 2011 Page 393

Objectives

To evaluate the effect of different coating color parameters on the surface strength of double coated papers insheet-fed offset (SFO) printingsheet-fed offset (SFO) printing

To correlate lab test data with observed edge picking during commercial SFO printing trials


Background

Latex binder is considered one of the most expensivecoating componentscoating components

Continuous fine tuning of the binder level is important to cost reduction efforts – requires total systems approachq y pp

One opportunity is to take advantage of the lower binder demand and higher solids potential of GCC

However, the high tack inks used in SFO printing demandadequate surface strength

Thus, a balancing act exists between optimizing coating costs and maintaining adequate coating surface strength


What is Edge Picking?

Occurs in SFO where high-tack inks are used

Coating is pulled out at the edge between printedand non-printed areas

Adversely impacts printquality and leads to morefrequent washing

printing area

Excessive edge picking can damage the rubber blankets edge picking

Thus, adequate surfacestrength is very important

g p g


Theoretical Considerations

Tack development of inks through press influenced by ink setting characteristics of coated surfaceink setting characteristics of coated surface

Ink setting impacted by pigments and latex

Fine pigments create many small pores leading to- Fine pigments create many small pores, leading to- Higher capillary pressure and faster ink setting

- Latex impact via - Chemistry of polymer- Effect on pore structure of coating layer

Choice of pigments and binders (type and amount) willgreatly affect ink/coating interaction and, thus, surfacestrength


Specially Designed Printing Method

Used redesigned printing plate and higher tack inksto exacerbate (enhance) edge picking.

This method also involved evaluating edge picking by This method also involved evaluating edge picking by

- Visual examination of prints

- Assessment of rubber blankets- Assessment of rubber blankets

- Ranking edge picking between 0 (worst) and 100 (best)


Redesigned Print Test Formh dlishort

bars in 6 colors

headlines

6th unit: blue

different screensin black

shortshort bars in 5

colors

1st unit: open areaon rubber blanket


Evaluated Parameters

Pilot coater Sheetfed offset press

Solids content of coating color

Pigment type

Man Roland R706 Press

Color sequence – KCMYCBlueg ypGCC vs. high glossing clay

Pigment fineness GCCs

q

Speed – 8000 iph

High tack – 9.5 to 10.8GCCs

Pigment psd GCC: NPSD vs. BPSD

High tack – 1st four units

Standard tack – 7.5 to 10.0

Latex level high strength SB

Calendering

Standard tack – last 2 units

Varnish unit – pressure only Calendering


Pilot Coater Trial Program

GCC 95 (80 % < 1 µm)

Cl

1

100

2

100

3

100

4

100

5

100

6

100

7

50

50

8

100

9 10 11

GCC 95 (80 % < 1 µm)

Cl

1

100

2

100

3

100

4

100

5

100

6

100

7

50

50

8

100

9 10 11

Clay (high glossing)

NPSD GCC (75 % < 1 µm)

GCC 60 (60 % < 2 µm)

50 100

100

100

Clay (high glossing)

NPSD GCC (75 % < 1 µm)

GCC 60 (60 % < 2 µm)

50 100

100

100

GCC 90 (90 % < 2 µm)

Latex SBR 7 5 7 5 7 5 5 0 5 0 5 0 7 5 7 5 7 5 7 5

100

7 5

GCC 90 (90 % < 2 µm)

Latex SBR 7 5 7 5 7 5 5 0 5 0 5 0 7 5 7 5 7 5 7 5

100

7 5Latex SBR

Synthetic thickener

7.5

0.10

7.5

0.15

7.5

0.20

5.0

0.10

5.0

0.15

5.0

0.20

7.5

0.25

7.5

0.15

7.5

0.15

7.5

0.30

7.5

0.20

Latex SBR

Synthetic thickener

7.5

0.10

7.5

0.15

7.5

0.20

5.0

0.10

5.0

0.15

5.0

0.20

7.5

0.25

7.5

0.15

7.5

0.15

7.5

0.30

7.5

0.20

Base paper: blade precoated 78 gsm Precoat 100 GCC + starch/latex

Jet application, stiff blade12 gsm per side of topcoat

Solids content 71 68 65 71 68 65 65 65 68 68 68Solids content 71 68 65 71 68 65 65 65 68 68 68

Precoat – 100 GCC + starch/latex Topcoat viscosity – 1000 mPas

12 gsm per side of topcoat Supered to 75 gloss target


Lab Paper Testing

Ink set-off IGT – optical density – in Switzerland

Ink set-off RI Test – visual assessment – in Korea

Paper and Ink Stability Test NPA in US

D d t i k P üfb i S it l d d US Dry and wet pick Prüfbau in Switzerland and US

Print gloss Prüfbau in Switzerland and US

Hg intrusion porosimetry & paper opticals Switzerland


Ranking According to the Degree of Edge Picking

I II IVIII V

Press adjusted so that reference was about 50 on the scale

8886677

55 4411

10103311119A9A 22

99Ref.Ref.

0 20 3010 50 6040 80 9070 1000 20 3010 50 6040 80 9070 100Degree of edge picking (0 = worst / 100 = best)Degree of edge picking (0 worst / 100 best)


RI Ink Setting

66 = Fastest / 0 = Slowest

... % Solids

5

4

100HCB 60

100HCB 90

100CCB 75

3

2 7.5Styronal

7.5Styronal

7.5Styronal

2

1

71 6568 71 6568 686565 68682 3 4 5 6 7 8 9 10 11

7.5 %Latex

50/50ClayGCC

0 71 6568 71 6568 686565 68681

7.5 %Latex

7.5 %Latex

5 %Latex

5 %Latex

5 %Latex

100Clayhigh

100GCCNSPD

100GCC60

100GCC90GCC

95100 parts GCC 95 100 parts GCC 95g

glossingNSPD 60 90

7.5 % Latex7.5 % Latex


IGT Ink Setting

50Optical density (FS/WS)

... % Solids

40

30

20

10

71 6568 71 6568 686565 68682 3 4 5 6 7 8 9 10 11

7.5 %Latex

50/50ClayGCC

01

7.5 %Latex

7.5 %Latex

5 %Latex

5 %Latex

5 %Latex

100Clayhigh

100GCCNSPD

100GCC60

100GCC90

71 6568 71 6568 686565 6868

GCC95100 parts GCC 95 100 parts GCC 95

gglossing

NSPD 60 90



P&I Slopes

50The lower the better

... % Solids

40

100HCB 60

100HCB 90

100CCB 75

30

207.5

Styronal7.5

Styronal7.5

Styronal

10

71 6568 71 6568 686565 68682 3 4 5 6 7 8 9 10 11

7.5 %Latex

50/50ClayGCC

0 71 6568 71 6568 686565 68681

7.5 %Latex

7.5 %Latex

5 %Latex

5 %Latex

5 %Latex

100Clayhigh

100GCCNSPD

100GCC60

100GCC90GCC


glossingNSPD 60 90



P&I Passes to Failure

12The higher the better

... % Solids

10

8

100HCB 60

100HCB 90

100CCB 75

6

4 7.5Styronal

7.5Styronal

7.5Styronal

4

2

71 6568 71 6568 686565 68682 3 4 5 6 7 8 9 10 11

7.5 %Latex

50/50ClayGCC

0 71 6568 71 6568 686565 68681

7.5 %Latex

7.5 %Latex

5 %Latex

5 %Latex

5 %Latex

100Clayhigh

100GCCNSPD

100GCC60

100GCC90GCC


glossingNSPD 60 90



Print Glosscommercial printed papersp p p

90% (FS/WS; 75° Tappi)

... % SolidsLab print gloss and paper gloss

80

70

Lab print gloss and paper glossresults followed the same trend

60

5050

40

71 6568 71 6568 686565 68682 3 4 5 6 7 8 9 10 11

7.5 %Latex

50/50ClayGCC

30 17.5 %Latex

7.5 %Latex

5 %Latex

5 %Latex

5 %Latex

100 t GCC 95 100 t GCC 95

100Clayhigh

100GCCNSPD

100GCC60

100GCC90

71 6568 71 6568 686565 6868

GCC95100 parts GCC 95 100 parts GCC 95

gglossing

NSPD 60 90



RI Test Ink Setting vs. Edge Picking

6Ink setting (6 = fastest / 0 = slowest)

5

44

3

2

1R² = 0.8091

0 10 20 30 40 50 60 70 80 90 1000

Edge pick print press (100 = best / 0 = worst)


IGT Ink Setting vs. Edge Picking

50Optical density

40

R² = 0.806830

2020

10

0 10 20 30 40 50 60 70 80 90 1000



P&I Ink Tack Slope vs. Edge Picking

50The lower the better

40Passes to fail had a similarly good correlation (R2 = 0.7733)

30

20

R² = 0.7414

20

10

0 10 20 30 40 50 60 70 80 90 1000



Wet Pick vs. Edge Picking

m/s (the higher the better)

4

3Dry pick results had poor correlation as well (R2 = 0 4748)3

2

R² = 0.4574correlation as well (R2 = 0.4748)

1

0 10 20 30 40 50 60 70 80 90 1000



Pore Size Distribution - Mercury Porosimetry

0.25log differential intruded volume/cm³ g-1

0.25log differential intruded volume/cm³ g-1

Uncalendered results showed

0.20NPSD GCC (TP9)

GCC 90 (TP11)

(TP1-6) GCC 950.20

NPSD GCC (TP9)

GCC 90 (TP11)

(TP1-6) GCC 95

slightly larger pore size

0.15

0 10

GCC 90 (TP11)

GCC 60 (TP10)(TP7) GCC 95/Clay

0.15

0 10

GCC 90 (TP11)

GCC 60 (TP10)(TP7) GCC 95/Clay

0.10

0.05

(TP8) Clay0.10

0.05

(TP8) Clay

0.010.00

0.1 10.010.00

0.1 1µm diameterµm diameter


Conclusions (I)

Specially designed commercial SFO printing methodprovided differentiation regarding edge picking

Good correlation found between degree of edge picking g g p gand lab ink setting/tack measurements. Thus, quantifying ink/coating interaction as a function of time best “lab scale simulation” of surface strength

Hg intrusion porosimetry data indicated that coating pore structure mainly depends on pigment finenessy p p g

Calendering offered an improvement in surface strength


Conclusions (II)

Ink setting and ink tack results indicate that pore structure of coating layer is crucial to degree of pick strength

Slower ink setting favors higher surface strength viaPigments GCC vs clay and coarse vs fine- Pigments – GCC vs. clay and coarse vs. fine

- Higher solids - Higher latex amountg

Lower surface strength of clay coatings due to- Faster ink setting (from finer pore size)- Higher specific surface area (higher binder demand)- Hydrophobic nature of clay- Hydrophobic nature of clay


Conclusions (III)

NPSD GCC had better surface strength than expected NPSD GCC had better surface strength than expected

Choice of pigments along with maximizing coating solids p g g g g- Allowed for reduction in binder level w/o compromising

surface strengthImproved sheet and print gloss- Improved sheet and print gloss

Future work to assess further the impact of coarser claysand coating PCC


Thank You for Your Attention!


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FACTORS INFLUENCING THE SURFACE STRENGTH OF COATED … ppt.pdf · Continuous fine tuning of the binder level is important to cost reduction efforts – reqqypuires total systems appproach