psa 101- understanding psa's

7/27/2019 PSA 101- Understanding PSA's

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Adhesive Technology

the adhesive tape engin eers

UnderstandingPressure Sensitive Adhesives

PSA 101

Presented by

The Adchem Corporation


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Heres what you will learn:

Formal definition of PSA

Common PSA product formats

Rubber vs. Acrylic adhesive formats

Common factors that will:4 Influence your PSA selection

4 Determine application success


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Definition

Pressure Sensitive Adhesive:Aggressive and permanently tacky substance thatadheres with finger or hand pressure, and exerts astrong holding force

Common consumer products that use PSA: Masking tape

Packaging tape

Self-stick postage stamps

Mailing labels

Pressure Sensitive Tape Council


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Common PSA Terminology Adhesion

Ability to stick or bond to a substrate.

Cohesion Internal strength of an adhesive to itself

Substrate The surface or material to which you want your

PSA to stick. Surface Energy A measure of the molecular attraction of the facial

contact of a material. Property that will effect the ability the PSA to stick

Wet out

The ability of an adhesive to flow and/or reflowover a surface to maximize bond strength based onhigher contact area.


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Common PSA Product Formats

Adhesive Transfer Tape

or Laminating Adhesive

Double-Coated Tape (Carrier)

Single-Coated Tape--Carrier--PSA--Liner (optional)

--PSA (Exposed)--Carrier--PSA (Liner)--Liner

--PSA--Liner


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Double-Coated vs. ATT

Double-Coated Tapes

Thicker (3-10 mil)

Less conformable

Easier dispensing Level-winding or

spooling

Lower temp resistance

Removable Reinforces substrate

Transfer Tapes orLaminating Adhesive

Thinner (1-5 mil)

More conformable

More difficult dispense

No level-winding

Higher temp resistance

Permanent

Doesnt reinforcesubstrate

Biggest Difference Double-Coated Tapes have a Carrier.


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Carrier Function

Stabilize theAdhesive

Improve Handling Add Thickness

Provide Removability

Provide BarrierBetween Adhesive

Adhesive

Liner

Adhesive

Carrier

Double-Coated Tape


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Carrier Types

Polyester

Polypropylene

Polyethylene

Foam

Paper

Tissue

Double-Coated Tape

Adhesive

Liner

Adhesive

Carrier


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Release Liners

A protective covering for the adhesive toprevent unwanted adhesion and

contamination of surface during shipping andhandling.

Release liners are typically engineered to providea desired release characteristic.

Suitable liners may be:

densified Kraft

poly-coated Kraft

plastic films (PET, PE, HDPE, PP)

board


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Three Types of PSAs

Rubber PSA (Indoor)

Acrylic PSA (Outdoor)

Silicone PSA (Wide Temp)


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Rubber Adhesives

Adhesives made from natural or synthetic rubbers which are madetacky by mixing them with various compounds.

Oldest PSA High Initial Strength (Good Thumb Appeal) Economical

Performance Characteristics Include:

Adequate for short term, non-critical applications (Indoor)

Limited chemical, temperature and Ultra Violet light resistance


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Acrylic Adhesives

A combination of acrylic monomers and other compounds, formulated tocreate specific chemical structures which are tacky. Unlike rubberformulations, compounding creates a chemical change of the

components.

Permanent Bonding applications

Have a high initial bond and adhere well to most surfaces Lower initial adhesion than their rubber counterparts

They have outstanding performance features: Excellent aging characteristics (Outdoor & High Performance) Outstanding chemical and ultra violet light resistance Higher temperature stability than rubber adhesives Great for long term, durable applications!


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Polymers with an inorganic backbone and organic sidegroups that are especially formulated for premium

performance

Bond to silicone-coated and other LSE surfaces Widest temperature range High cost

Performance Characteristics Include: Suitable for long term, critical applications Higher temperature resistance, service range -30F to

500F (depending on applied load). Resistance to chemicals, moisture and ultraviolet rays Clean removability to some substrates

Silicone Adhesives


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How PSA Bonds ?

PSAs flow into the substrates.

No curing process.


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Dwell Time allows the adhesive toflowinto the Peaks & Valleys of the Substrate

Initial Adhesion

No Dwell Time

Initial AdhesionInitial Adhesion

No Dwell TimeNo Dwell TimeUltimate

Adhesion

72 hrs @ 25 C

UltimateUltimate

AdhesionAdhesion

72 hrs @ 25 C72 hrs @ 25 C


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The bond strength of Acrylic adhesives buildsover time...

Dwell TimeDwell Time

A

dhesionLevel

A

dhesionLevel

RubberRubber

AcrylicAcrylic


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Visco-Elasticity

Viscosity = Thickness

Elasticity = Stretch

Say it with Me Peanut Butter

dh i h l


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Visco-Elasticity

Viscosity allows the PSA to bond and flow.

Elasticity absorbs energy & shock.

Gives PSAs Strength

dh i h l


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Two important PSA characteristics:

AdhesionAdhesion Attraction forces joining unlike substrates

Adhesive

Substrate

Substrate

Substrate

CohesionCohesion Internal strength of material

Adhesive

Substrate

Substrate

Adh i T h l


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Viscosity and Elasticity

Maximum

Maximum

Adhesion PropertiesAdhesion Properties

Cohesion PropertiesCohesion Properties

SoftSoft FirmFirmPressure SensitivePressure Sensitive

AdhesivesAdhesives

Viscous Visco-elastic Elastic Solid

Adh i T h l


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Peel Tests measure Adhesion

Adhesion can be measured by a

test method called the Peel Test( PSTC or ASTM )

Peel Valu esthen indicate how strongly

the PSA has bonded, or adhered, to aparticular substrate

I n i t i a l adhesionindicates how well aPSA has bonded to a substrate after ashort period of time, usually seconds orminutes

Ul t im a te adh esionrefers to a PSAsbond strength after 72 hours

Both initial and ultimate adhesion aremeasured by the Peel Test

180 Peel180180 PeelPeel

90 Peel90 Peel90 Peel

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Shear Tests measure Cohesion(Internal Strength)

Cohesion can be measured by a testmethod called the Shear Test( PSTC orASTM)

Shear Valuesthen indicate the internalstrength of an adhesive

Adhesives with higher shear values (whichequates to stronger cohesion) willwithstand exposure to higher temperatures

and chemicals

Load WeightLoad WeightLoad Weight

TapeTapeTape

Test

Panel

TestTest

PanelPanel

Adh i T h l


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Forces Effecting PSA Performance

Tensile Shear

Peel

Adh i T h l


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Factors that can influence

your PSA success...

Pressure

Temperature

TimeSurface Texture

Surface Energy

Surface Contamination

Surface Contour

Environment:

Solvents/Chemicals

Temperature Exposure

Surface: Application:

UV Light Exposure

Adh i T h l


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Surface Texture

Thin Adhesive

Limited Contact

Thin AdhesiveThin Adhesive

Limited ContactLimited ContactThick Adhesive

Maximum Contact

Thick AdhesiveThick Adhesive

Maximum ContactMaximum Contact

For rough sur faces, use a thi cker adhesive!

But thicker is not always better! Use the right thickness

for your substrate; testing will help determine this.

Adhe i e Te h olo


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Surface Contour

Curved Surface combined with

thin and firm adhesive

may cause:

* Internal stresses and

* Edge lift (Flagging)

Curved Surface combined with

thickand soft adhesive

may provide:

* Maximum surface contact

* additional bond strength

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Surface Energy

Adhesion is the molecular attraction between unlikematerials, similar to magnetic force.

The surface energy of a material determines the

strength of this attraction. The higher the surfaceenergy, the greater the attraction. The lower thesurface energy, the weaker the attraction.

On an automobile, unwaxed for years, water spreads onthe sur face in large puddles. This is H igh Sur face Energy,

allowing the water to flow. On a freshl y waxed car, the water

wil l bead up. This is Low Sur face Energy keeping the water

fr om fl owing out!

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Common materials and their respective surface

energies...

Metals ABS

Kapton PolycarbonatePolyester PVC

Polyurethane Acrylic

Polyvinyl Acetate Polyethylene

Polystyrene PolypropyleneAcetal Tedlar (PVF)

EVA Teflon

Powder paints

High Surface EnergyHigh Surface EnergyHigh Surface Energy

Easy-to-adhere Hard-to-adhere

Low Surface EnergyLow Surface EnergyLow Surface Energy

good adhesive wet-out poor adhesive wet-out

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Surface ContaminationEach of these situations can result in a poor bond.

Grease, Moisture, Oil, MoldRelease Chemicals

Creates a barrier betweenadhesive and substrate

Dust, Talc, Fiber, ParticleContamination

Affects tackiness of adhesive

Reduces contact surface

area

Always clean your substrates

before applying a PSA!

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Chemical/Solvent Resistance

Solvent Effects on PSAs

Adhesive swelling

Adhesive softening

Dissolve adhesive

Many acryl ic adhesives have high cohesive strength all owing

them to wi thstand many different types of solvents for extended

per iods of time.

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Temperature Factors

Low Temperatures can have a negative affect onadhesives.

Firms & makes adhesives brittle

Reduce adhesive tack

Increase shock sensitivity So can high temperatures...

Adhesive softening

Reduce shear strength

Reduce cohesive strength

Know the temperature range of your application, then select an

adhesive that wil l meet both the high and low temperature extr emes.

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UV Light

Ultra Violet (UV) light can havenegative affects on adhesives as well:

Discoloration Brittleness

Chemical Degradation

When you know UV light wi l l be a factor, select an adhesive

that has UV resistance!

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Plasticizers

Make adhesive soft and pliable

Causes adhesives to:

Soften Turn stringy

Discolor

Some adhesives have varying resistance to plasticizer migration

allowing them to withstand the softening effect.

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Applying your PSA can be THE determining factorfor success...

Time

Allow at least 72 hours before testing theultimate adhesion strength. This gives theadhesive time to flow, effectively covering yoursubstrates.

Temperature Applying your adhesive at room temperature is

always best. Slightly higher temperatures canactually improve adhesive flow, speeding upthe the bonding process. At coldtemperatures, select an adhesive made for

application in cold temps. Pressure

Applying adequate pressure will accelerate theadhesive flow and eliminate trapped air. Thiswill ensure higher adhesive coverage of thesubstrate.

PRESSURE

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Some final tips:

Know your surfaces or substrates

Select the right adhesive

Finally, clean your substrate

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Quiz

Name Three Factors that can influence PSA Selection

Pressure

Temperature

TimeSurface Texture

Surface Energy

Surface Contamination

Surface Contour

Solvents/Chemicals

Temperature Exposure

UV Light Exposure

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Questions or Comments

psa 101- understanding psa's

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