Goldilocks and Process Control for UV Curable PSAs...Goldilocks and Process Control for UV Curable...
Transcript of Goldilocks and Process Control for UV Curable PSAs...Goldilocks and Process Control for UV Curable...
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$on
LisaKruegerCas,[email protected](281)474-9777Web:www.kiwo.com
[email protected](703)925-1830Web:www.eit.com
Ques$ons??