LisaKruegerCas,llo,KIWOInc.

JimRaymont,EITInstrumentMarkets

GoldilocksandProcessControlforUVCurablePSAs

Mo$va$on

TheUVprocess

TheimportanceofproperUVcure

Se7ngandmaintainingproperUVexposureisalwaysimportant.

However,withUVPSAsitisevenmoreimportantsinceyoucannotonlyunder-curematerial,butcanover-curematerialaswell.

Mo$va$on

The“ProcessWindow”forcuringUVreac$vePSAscanberela$velynarrow;adhesiveproper$escanchangesignificantlywithbothtooliJle,and,toomuchUVenergy.

PetraBurger,FusionUV,UVCurablePressureSensi0veAdhesives

Mo$va$onInfluenceofUV-crosslinking$meontack(!),peeladhesion(")andcohesion(!).(Czech2004)

Mo$va$onInfluenceofUV-crosslinking$meontack(!),peeladhesion(")andcohesion(!).(Czech2004)

ABalancingAct

Source:Czech&Milker,(2005)Developmenttrendsinpressure-sensi0veadhesivesystems

ABalancingAct

Source:Czech&Milker,(2005)Developmenttrendsinpressure-sensi0veadhesivesystems

TheGoldilocksProblem

TypicalUVProcessWindow

ProcessWindowZonewhichallowsyoutoproducegoodqualityproduct.

Danger!Under-CureZone

NormalProcessWindow

TypicalUVProcessWindow

ProcessWindowZonewhichallowsyoutoproducegoodqualityproduct.

WarningLowerBufferZone

Danger!Under-CureZone

NormalProcessWindow

UVPSAProcessWindow

ProcessWindowZonewhichallowsyoutoproducegoodqualityproduct.

WarningLowerBufferZone

Danger!Under-CureZone

NormalProcessWindow

WarningUpperBufferZone

Danger!Over-CureZone

Manyadhesiveapplicatorsareworkingblind.

“Anything that you can measure, you have a better chance of controlling. Things that you do not measure become the cause of mysterious problems”

- Larry Goldberg. Beta Industries

UVPSAISOofUVPhotons

UVadhesiveproper$esrelynotonlyonanadhesive’sformula$on,butonhowthematerialiscured.

ThisincludestheUVlampswavelength,intensity(irradiance)and$meofUVexposure(doseorenergydensity)andchangesintheseparameters.

Whatcouldpossiblygowrong?

Variable:UVWavelength

Mercury

Gallium Iron

CourtesyHeraeusFusionUV

Variable:UVLampIrradiance

Irradiance,orhow“bright”aUVsourceisvarieswiththedesignofthelamp,anddistancefromthelamp,powersupply,bulbdiameter.

LampirradianceismeasuredinWaJs/cm2

Variable:UVEnergyDensity

•  Sinceenergydensity=irradiancex/me,anythingthataffectseitherofthesefactorschangestheenergydensity:

–  Linespeed–  Ageofthelamp

–  Lampoutputse7ngs–  DistancefromthelamptothePSA

–  Thecondi$onoflampreflectors–  Darkeningoflampelectrodes

Naturalaging

UVlampsage… andsodocoa,ngs.

Devitrifica$on/Clouding Mirroring

Blackening/Erosion ContaminatedAirflow

LampSymptoms-Aging

LampUniformity55”(140cm)bulb

UV Measurement Challenges

IrradiancemW/cm2Datacollected3/24/16

Band Le` Center Right HighestDelta

UVA 797 983 635 35.4%

UVB 713 888 573 35.5%

UVC 200 257 167 35.0%

UVV 612 757 492 35.0%

EnergyDensitymJ/cm2

UVA 243 282 234 17.0%

UVB 206 239 195 18.4%

UVC 58 68 55 19.1%

UVV 231 264 222 15.9%

UV Measurement Challenges

IrradiancemW/cm2

Band Before A`er Difference

UVA 1223 983 -19.6%

UVB 1066 888 -16.7%

UVC 277 257 -7.2%

UVV 889 757 -14.9%

EnergyDensitymJ/cm2

Band Before A`er Difference

UVA 349 282 -19.2%

UVB 284 239 -15.9%

UVC 75 68 -9.33%

UVV 309 264 -14.6%

Data collected 3/24/16

Before: Data collected with contaminated optics

After: Data collected after cleaning

InstrumentCleanliness

TheBlameGame UV Measurement Challenges

FactorsthatcanaffectUVcureperformance

•  Adhesivefilmthickness

•  SeJling/inadequatemixing

•  Shelflife

•  Substratereflec$vity

•  Inadequatesurfaceprepara$on

AdhesivefilmthicknessandUVcure

Formediumtohightack,suggestedcoa$ngweightsare0.5milsandup.Highercoa$ngweightsrequiremore“curingpower”.

Thismaybeachievedbyaddingmorelamps,increasingthewaJageofthelamps,changingtoadeeperpenetra$ngbulb,orbyslowingdownpressspeeds.Forpropercureandop$mumadhesiveresults,oneormoreofthesemethodsmayberequired.

EffectofEnergyDensityonPSAAdhesives

Source:Burger,Skinner,Field&Draper,ExperienceswithUVCurablePSAsonaProduc0onFacility

Adhesivethickness

Conven,onalPSAs:Wetthicknessanddrythicknesscanvaryagooddeal.Thedifferencedependsprimarilyonsolidscontentandcoa$ngmethod.

UVCurablePSAs:Wetthickness,andcuredfilmthicknessaretheore$callynearlythesame,butcanbeinfluencedbyflowbeforecure,dependingonviscosity.

PrintablePSAs

AprintablePSAisahighviscosityliquid.Youneedsomeflowtowetoutthematerial.Toomuchcure,willbetoocrystallinefortheadhesivetoflowandproperlywet-out/gripthesubstrate.

PrintablePSAs

AprintablePSAisahighviscosityliquid.Flowisnecessarytowetoutthematerial.

Over-curecancausethematerialtobecometoocrystallinefortheadhesivetoflowandproperlywet-out/gripthesubstrate.

Adhesivefilmthickness

PrintableUVcurePSAformulasaregenerallyformulatedwitharela$velywideexposurela$tude.

KIWOsuggeststes$ngwith92thread/in.meshwith92micronthreaddiameter.Thisyieldsaround2milcuredthicknessprovidingabalanceofachievablestrengthversuscost.

AlwaysverifythattheUVexposurerecommenda$onwillcuretheen$rerangeofan$cipatedfilmthickness.

ProperMixing

•  Frequently,UVPSAswillnotrequires$rring,astheydonotseJle/separatetothesameextentaswaterbased/conven$onalsystems.

•  Aswithinks,UVcurePSAsshouldbes$rredbeforeuse-especiallyifsepara$onisevident-takingcarenottointroduceairbubblesintheprocess.

•  Hand/machines$r:Adispersionbladehastheadvantagethatyoucanletitrunwithaslowspeed/lowerse7ng,withoutintroducingmuchair.

•  Inthecontainer,UVPSAscommonlyappearslightlytranslucentorhazy,some$meswithaslightalmondcast.

•  Thoughnotalwaysvisible,seJling/separa$ondoesoccur.Youmayseeafilmywhiteappearanceorswirlintheadhesive-thisisdefoamersepara$on.

Properadhesivestorage

•  It'sgenerallysafetostoreUVcurablePSAsinthesamecondi$onsaswaterbased/solventbasedPSAs.

•  Donotstore/transportathighertemperaturethan40C/104F.

•  Donotstoreinsunlight/UVlight.

•  Youdonothavetoprotectfromfreezing;though,ajerexposure,theproductshouldbebroughttoroomtemperatureandproperlys$rred.

Shelflife

ShelflifeDependsontheproduct,someminimum6mo.,somemax.1year.Astheseage,thesensi$vitytoUVcuringerodes.Withsomeformula$onsgelling(spelling)occurs.

Substrate-adhesiveaffinity

Affinityoftheadhesiveformula$ontosubstrate...paper,metal,orplas$cwilldeterminethebondstrength.Thelowerthesubstrate’ssurfaceenergy,themoredifficultitisfortheadhesivetowet-outandstronglygripthesurface.

Surfacetreatmentisgoodprac$cetoachievehigherbondstrength.Polyolefins(e.g.,PPandPE)requiretreatment.Thelowtemperatureresistanceoftheseplas$csrequiresaddi$onalconsidera$on,becausethethinnergradeswilldistortunderthehigherdosagerequiredtocure1-2milfilms.

TheImportanceofacleansurface

Source:Davis(1993)

Affectofsurfaceenergyonbondstrength

Pretreatmentmayaidinthebondingperformanceofanadhesive.Substratescanbetreatedwithcorona,flameorchemicalpretreatment.

Substratecolor&reflec$vity

Darkersurfacesabsorbmorelightenergyandadarkersurfaceheatsupmorethanawhiteone.Inprac/ce,mostvaria$onisoffsetbytheexposurewindow,sothatliJleadjustmentisusuallyneeded.

Shinymetals,forexample,arelikewhitereflectthelightwhichaidsinexposure.Thereforereflec$vecolorscanbeexpectedtobeontheshorterendofexposurescale.

Summary

•  UVCurePSAsarepar$cularlysensi$vetoUVexposurelevels

•  Establishaprocesswindow.Considertheupperandlowerbounds.

•  Manyfactorscancontributetofailure,bothnaturalandself-inflicted.Bevigilant.

•  Measureyourprocesstoensureyouareopera$ngwithintheprocesswindow

ContactInforma$on

LisaKruegerCas,lloAdhesiveProductManagerKIWOInc.kiwolisa@kiwo.com(281)474-9777Web:www.kiwo.com

JimRaymontDirectorofSalesEITInstrumentMarketsuv@eit.com(703)925-1830Web:www.eit.com

Ques$ons??