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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