Improving the performance of UV cure coatings & adhesives...

Improving the performance of UV cure coatings & adhesives on plastic substratesAdhesives & Sealants Council 2017

Andy Stecher, Plasmatreat USA, LLC

• Motivation for the use of UV Cure materials

• Why UV materials have adhesion problems

• A coating innovation: UV powder coating

• What is plasma? How does it work?

• The UV powder coating solution

• UV cure adhesives examples

Outline of my remarks

• High Speed• Low Heat• Hard, durable, water-clear

finish• Environmentally friendly

technology

The advantages of UV Curing

Typical UV coated products

Overview of the UV curing process

(UV = Highly Cross-linked)

UV vs. thermal chemistry comparison

Conventional Coating

Strong cohesive and adhesive forces needed in bonding

Crosshatch tape testing

The Desired ResultThe desired outcome is easy

• Getting UV materials to stick is not easy

• Adhesion is often hard to control (Substrate, Ambient Condition, Contamination)

• Sometimes requires some kind of reformulation to the chemistry, change of substrate, or more commonly surface treatment

However there are adhesion issues

• Economy• Excellence of Finish• Energy Efficiency• Easy to Apply• Environmentally Friendly

Powder Coating Benefits: The 5 “E’s”Example: Powder Coating

Powder coated products

Tem

pera

ture

Build Hold

Time

15-60Minutes

375oF

Melt & Flow Cure

Thermoset Powder Cure ProfileThermoset Powder Thermal Profile

Chemistry Standard Cure Low Temp. Cure

Epoxy 20’ @ 350⁰F 25’ @ 235⁰F

Epoxy Polyester 20’ @ 375⁰F 25’ @ 250⁰F

Polyester 20’ @ 375⁰F 25’ @ 275⁰F

Polyurethane 20’ @ 390⁰F 25’ @ 295⁰F

Acrylic 25’ @ 350⁰F 30’ @ 250⁰F

Silicone 25’ @ 420⁰C N/A

Typical Powder Thermal Profile

Problem: Plastic Deflection Temp.

• Use a higher temperature plastic• Use a lower temperature powder• Use UV curing

Possible Thermal Solutions

Powder Application

Apply Heatto Melt Powder

Powder Flow/Leveling

Exposure to UVfor Polymerization

hν

The UV Powder Coating Process

Tem

pera

ture

Melt/Flow Stage

Exposure to UV

Time

UV Powder Temperature Profile

• Excellent Surface Properties

• Low Heat/High Speed Processing

• No Waste

• Heat Sensitive Substrates

A highly desirable technology:

UV Powder Coatings

Thermoset UV Cure

400oF

200oF

A Flashback…

In 1998 Baldor Electric Motor began UV powder coating pre-assembled electric motors.

• STATIC REMOVAL: Static attracts dust and similar contaminants which interfere with surface processes

• CLEANING: All surfaces, no matter how clean they seem, have surface contaminants that interfere with bonding and coating applications

• ACTIVATION: Advanced engineering polymers tend to be chemically inert – with few or no functional groupson which to bond

• PASSIVATION: Metals are prone to oxidation and require treatment to retard the oxidation process

The Needs for Surface Preparation?

Note: Water Surface Energy 72 mN/m (dyne)

Plastics with Low Surface Energy

Courtesy Texas A&M University

The Challenges of Solvents

• What is plasma? • How is plasma generated and applied

• Functions of plasma treatment• Cleaning of glass, plastics, metals, ceramics• Activation of Plastics (Polyolefins, etc) and Hybrids (GFRP)• Functionalization of ceran and galvanized steel

Plasma Surface Treatment

Naturally Occurring Plasmas

Low Pressure (vacuum) Atmospheric Pressure

What is Plasma?Nature’s plasma

Photo: Safe, Cost-Effective, Environmentally Friendly Man-Made Plasma

Man-made Plasma

Substrate

Inner Electrode

Ring Electrode (SS casing)

Discharge Chamber

Ionization GasHigh voltage

Current

Plasma Beam

The Plasma Treatment Process

OO

N*

* *

*N N

O

N

NN

ON

O

O

N

O

*

*

*

H H H H H H H

C C CCC C C

H H H H H H H

Attack surface contamination

Cleaning effect

Polymer Substrate-UV varnish

- OPP, PE, PET, Acetate….

Surface Contamination-Organic layers(Additives, waxes, grease…..)

Plasma Surface Treatment

C

OO

N*

* *

*N N

O

N

NN

ON

O

O

N

O

*

*

*

H H H H H H H

C C CCC C C

H H H H H H H

Polymer SubstrateOPP, PE, PET, Acetate….

UV varnish

Surface contamination

Cleaning effect

Plasma Surface Treatment

C O

N

C C C C C C C

HHHHH

H

H

H

H

H

H

H H HO

O

O

OO

O N

N

N

N

NN

N

*

* *

**

**

Polymer SubstrateOPP, PE, PET, Acetate….

UV varnish

Form functional sites

Stable wetting

Plasma Surface Treatment

Topological Modification ( AFM Study of PET [1 µm] )

Untreated Plasma Treatd

Courtesy: Fraunhofer Institute for Processing Technology and Materials Research

Plasma Surface Treatment

Atmospheric Pressure Plasma Process - Activation

Plasma Surface Treatment

35

20

5

020406080

20 18 16 14 12 10 8 6 4Speed [m/min]

mN/m

Gap [mm]

Surface Energy of PolypropyleneAfter Plasma Treatment

60-80

40-60

20-40

0-20

Plasma Treatment ResultsPlasma Surface Treatment

A wide selection of standard and custom jets adapt to a wide range of part shapes and sizes..

Flexibility for many applications

Plasma flexibility

Atmospheric plasma generators are easy to

install and integrate with simple connections.

Integration of plasma onto the process line

Plasma flexibility

Powder Coating on Automotive Plastic!

• Plasma Cleaning & Activation

• Conductive Agent

• Powder Application

• Heat (IR or Convection)

• UV Cure

UV Powder / Plasma Process

Objective: To compare adhesion results of several powder coated plastics when untreated and treated with plasma.Powder Coating: PCRG 002-36-113 UV Curable powder

Substrates:• PT Natural (proprietary formulation)• Nylon• Polypropylene• ABS• PC/ABS

UV Powder Coatings

Plasma Treated No Treatment

Glass-Filled Polypropylene Substrate

UV Cured

Plasma results

Source: Powder Coating Research Group

Source: Powder Coating Research Group

Plasma results

Source: Powder Coating Research Group

Plasma results

Source: Powder Coating Research Group

Plasma results

Source: Powder Coating Research Group

Plasma results

Source: Powder Coating Research Group

Plasma results

SubstrateRating without

Openair® Plasma

Rating with Openair® Plasma

PT Natural 0B 4B

Nylon 0B 0B

Polypropylene

0B 3B

ABS 0B 4B

PC/ABS 4B 4B

Cross Hatch Test Criteria: ASTM D3359 02 “0B – 5B)

Plasma results summary

The environmental benefits of atmospheric plasma are a good fit for UV technology

• Elimination of high VOC content primers or adhesive promoters – replace these with environmentally safe plasma

• Low power consumption

• No ozone generation

• No pollutants

Plasma + UV Powder Coatings = Fit

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

Without Plasma With Plasma

Pull

Stre

ngth

Mean Std. Dev.

Not only anIncrease in

Bond performance

Increase Bond Strength

(Source: Kegel & Schmid 1999)

Plasma results on adhesives

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

Without Plasma With Plasma

Pull

Stre

ngth

Mean Std. Dev.

Not only anIncrease in

Bond performance

But a Decreasein Variance

(Source: Kegel & Schmid 1999)

Decrease Bond VariancePlasma results on adhesives

0

1

2

3

4

5

6

7

8

9

10

HDPE PP PVDF PET Nylon6

Lap

Shea

r Str

engt

h [ M

Pa]

Control Plasma treatment

SOURCE: M. Noeske et al., “Plasma jet treatment of five polymers at atmospheric pressure: surface modifications and the relevance for adhesion”, International Journal of Adhesion & Adhesives September 2003

Plasma results on adhesives

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

8.9

MP

a

8.4

MP

a

0.3

MP

a

12

.4M

Pa

12.0

MP

a

0.5

MP

a

10 .

1M

Pa

11.1

MP

a

0.2

MP

a

Tens

ile L

ap-s

hear

Str

engt

h [M

Pa] PP AP-Plasma (directly bonded)

PP AP-Plasma (bonded after 8w 60°C, 50% r.h.)

PP (without pretreatment)

PVDF AP-Plasma (directly bonded)

PVDF AP-Plasma (bonded after 8w 60°C, 50% r.h.)

PVDF (without pretreatment)

ECTFE AP-Plasma (directly bonded)

ECTFE AP-Plasma (bonded after 8w 60°C, 50% r.h.)

ECTFE (without pretreatment)

2-part epoxy system:Curing: 175°F, 2 hours

Plasma results on adhesives

UV cure: shear strength

0

5

10

15

20

25

30

Initial value 2 w 85°C/85% humidity

2 w 40°C/100% humidity

Com

pres

sion

she

ar s

treng

th (M

Pa)

PBT/PET Blend Substrate

Degreased

Atmosphericplasma

Polyamide with Cationic Bonding

0

2

4

6

8

10

12

14

16

18

20

KB554 45952

com

pres

sion

she

ar s

tren

gth

[MP

a]

CATIONIC BONDING PROCESS

Initial valuecleaned

Initial valueAPP

14 d 40 °C / 95 %cleaned

14 d 40 ° C / 95 %APP

Polyamide free-radical curing

0

5

10

15

20

25

30

4494 AD494

com

pre

ssio

n s

he

ar

stre

ng

th

[MP

a]

Initial valuecleaned

Initial valueAPP

14 d 40 °C / 95 %cleaned

14 d 40 ° C / 95 %APP

• UV offers attractive benefits to manufacturer (e.g., low heat, fast cure, tough surfaces)

• However, UV also presents greater challenges to adhesion due to the highly crosslinked chemistry

• Plasma has been shown to improve UV coating adhesion even on UV powder coatings

• Plasma improves UV adhesive bond performance.

Summary of take-aways

THANK YOU FOR YOUR ATTENTION!

Plasmatreat North AmericaElgin, IL Belmont, CA Ancaster, ON

Tel. (855) 4TH-STATEwww.plasmatreat.com