02.intro to ps as hoermann
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Transcript of 02.intro to ps as hoermann
Introduction to Pressure Sensitive Adhesives:
Polymer Types
ASC Short Course
April 28, 2014
Werner A. Hoermann
What does a customer expect from a PSA?
• Adhesion on demand
• at ambient temperatures
•without the need for sophisticated equipment
• and without a steep learning curve
The Basics
• In an environment of insecure supply you need to be flexible
• Changes in user industries drive PSA development
• The adhesive is always at fault if something goes wrong
• You can’t overestimate the ability of the user to screw up
• There is no limit to the number of possible PSA formulations
and ingredients
Requests for PSA development
•Make it cheaper
•We can’t get that raw material anymore
• The customer wants more …(peel, shear, etc.)
•We need a knockoff of the competitors product X
•We have this great new product idea
Design Considerations for a PSA
• What surfaces to bond to
• What carrier (paper - label, fabric – band aid, plastic - membrane, differential release liner, etc.)
• What are the application conditions of the finished product (temperatures, time, pressure, cleanliness,
applicator sophistication)
• What are the lifetime bond stress conditions (temperatures, peel, shear, tack)
• What are the environmental stresses (uv, ozone, oxygen, plasticizers, moisture, mold, wind, etc)
• Environmental and Health considerations
• What production equipment is available
• What application (coating) equipment is available
• What raw materials are available at what price
Compounding and Coating Methods
• Compounding• Solvent based
• Water based
• 100% solids
• Coating Methods• Solvent based
• Water based
• 100% solids
• On the web x-linking
How does the PSA bonding process work?
Best Case: Excellent wet-out, plenty of contact, high surface energy
Worst Case: Bad wet-out, little contact, low surface energy
PSA Performance as a Function of Temperature
-50.0 -25.0 0 25.0 50.0 75.0 100.0 125.0 150.0
temperature (°C)
100.0
1000
10000
1.000E5
1.000E6
1.000E7
1.000E8
1.000E9
G' (P
a)
100.0
1000
10000
1.000E5
1.000E6
1.000E7
1.000E8
1.000E9
G''
(Pa)
0
0.2500
0.5000
0.7500
1.000
1.250
1.500
1.750
2.000
2.250
2.500
|tan(d
elta
)|
Temperature Sweep, 10 rad/s
Butyl Hybrid
tan delta peak
Glass Region
Transition Region
Rubber Plateau
Melt Flow
G'
G"
Softening Point
Dahlquist Criterion - 300,000 Pa
tan delta minimum
tan delta = G"/G'
What are the basic PSA material properties?
• Polymeric – above entanglement molecular weight
• Substantially amorphous (i.e. not crystalline)
• Glass transition temperature (Tg) well below room temperature
• Low modulus under bonding conditions (temperature and time
scale)
• Relatively low surface energy
PSA Polymer types
• Hydrocarbon Elastomer Based
• Acrylic Copolymers
• Silicone Based
• Polyolefins
• Polyvinyl ethers
Components of Rubber/Resin PSAs
• Polymer
High molecular weight elastomer with low Tg
• Resin
Low molecular weight oligomer with Tg typically higher than the elastomer
• Plasticizer
Low molecular weight liquid with low Tg
Elastomers for PSAs
• Natural Rubber
• Styrene-butadiene random copolymer
• Polybutadiene
• Polyisoprene
• Polyisobutylene/Butyl
• Styrene block copolymers
Elastomers for PSA
Polyisoprene (cis- 1,4)
natural rubber
synthetic PI (e.g. Natsyn®)
CH2 CH2
C C
H CH3
n
Elastomers for PSA
styrene-butadiene rubber (SBR)
butadiene-acrylonitrile (nitrile rubber)
Polybutadiene and copolymers
cis 1,4 polybutadiene
CH2 CH 2
C C
Elastomers for PSA
Polyisobutylene
butyl rubber (isobutylene and smallamount of isoprene copolymerized)
CH3
CH2 C
CH3
n
SBC Architecture
star
triblock
diblock
usually styrene-isoprene orstyrene-butadienebased
The SBC network
Physical
Crosslinks
Polystyrene Domains
(T9
95° C)
Rubber
Phase
,,/"
Rubber Phase
--- Polybutadiene (T9 -85° C)
Polyisoprene (T9 -60° C)
Polyolefin (T9 -55° C)
SBC type choice and effect
Effect of Resin on SBC
• Raises Tg of blend compared to rubber alone
• Reduces plateau modulus, acts as diluent of entanglements
once you are in the rubbery zone
• Combination of these two effects allows the system to meet
the Dahlquist criterion for tack and the requirement for high
energy loss in debonding time scale
• Tackifier must be thermodynamically miscible with polymer
Effect of Plasticizers, Oils, Liquid Resins
dilutes rubber and contributes to reduction in plateau modulus
effects a lower composite Tg than using solid
tackifier alone
General Properties of Rubber Resin Systems
• Availability of wide array of polymers, resins, plasticizers and fillers
• Can be formulated to be inexpensive
• Can be formulated to stick to a wide variety of surfaces, even non-
polar ones
• Sensitivity to light, oxygen, weathering and plasticizers, depends
upon choice of grade
• Suitable for all types of compounding and coating systems
Acrylic Copolymers
• Low Tg Monomers• 2-ethyl hexyl acrylate• butyl acrylate• iso-octyl acrylate
• High Tg monomer(s)• methyl acrylate• methyl methacrylate
• Polar monomers (typically also high Tg)• acrylic acid• Acrylamide• n-vinyl pyrrolidone
Typical Properties of Acrylic PSAs
• Moderate cost
• Adhesion varies significantly with substrate chemistry
• Very stable to oxidation, weathering
• Wide range of performance achieved through copolymerization chemistry
• High adhesion build over time to certain surfaces
• Usually no need for tackifiers
• Available for WB, SB, and 100% solid technologies
Silicone Pressure Sensitive Adhesives
• Silicone polymer/gum + Silicate resin• Partially coreacted by condensation of terminal
silanol groups on gum and resin• Evidence for two phase structure:
continuous gum-rich phasediscontinuous resin-rich phase
• Gum is low Tg, resin is high Tg
Typical properties of Silicone PSAs
• Expensive
• Sticks to virtually anything - can even bond underwater and
stay bonded on glass when wet
• Very stable to light, heat, oxygen
• Limited range of performance with formulation
• Very wide temperature range
Other Polymers for PSA’s
• high vinyl acetate EVA copolymers plus tackifiers
• atactic polypropylene
• polyvinyl ethers and copolymers with acrylics
• polyurethane
Final WordsStay flexible and open minded – There will be constantly new materials and technologies for you to work with
Think through the demands on the adhesive throughout the life cycle of the finished product
- from ingredient sourcing - to compounding - to coating - to storage - to application - to in place performance - to disposal
Formulation is only one aspect of finding a good PSA solution