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Adhesive Application Guide.pdf

Adhesive Application Guide

lqi007
2012-07-19 0人阅读 0 0 0 暂无简介 举报

简介:本文档为《Adhesive Application Guidepdf》,可适用于工程科技领域

InnovativeEpoxyAdhesiveSolutionsforOverYears™wwwepotekcomepoxyAdhesiveApplicationGuideThisguideisaneducationaltooldesignedtoassistadhesiveusersingainingamorethoroughunderstandingofadhesivepropertiesandtestingItwascompiledthroughthecombinedeffortsofmultipledepartmentsinEpoxyTechnology,Incincluding:QualityControl,ResearchandDevelopment,TechnicalServices,SpecialFormulatingServices,ProcessControlandTechnicalSalesandMarketingAlthoughwehavebasedourinformationonthemostuptodatedataandtestingavailable,advancesintestmethodsandmaterialsareconstantlyevolvingPleaseusethisreferencepieceasaguideonlyandbesuretofollowtherecommendationslistedondatasheetsaswellasanyadditionaltechnicalinformationincludedwithyouradhesiveproductshipmentWehopethattheinformationcontainedwithinthisguideisusefulandvaluabletoyouinchoosingthebestadhesiveforyourspecificapplicationForanyadditionalassistanceneeded,pleasecontactourApplicationsExpertsatEpoxyTechnologyattechservepotekcomor()InnovativeEpoxyAdhesiveSolutionsforOverYears™TableOfContentswwwepotekcompageTableOfContentsViscosityRheologyPotLifeandWorkingLifeAdhesiveCuringKineticsofCureGlassTransitionTemperature(Tg)ThermogravimetricAnalysis(TGA)DegradationTemperatureOutgassingLapShearandDieShearLapShearDieShearDynamicMechanicalAnalysis(DMA)ThermomechanicalAnalysis(TMA)ElectricalConductivity(VolumeResistivity)ThermalConductivityViscosityRheologypageVVAAFdvdxViscosityisatermandvalueusedtodescribetheinternalfrictionofafluidThedegreeoffrictionisobservedwhenaforceisappliedtothematerialThemorefrictiondetected,themoreforcerequiredtomovethematerialorto"shear"itShearingoccurswhenthefluidisactuallymovedAlowviscosityproductlikewaterrequireslessforcetoflowthanahighviscositymaterial,likepeanutbutterTheforcerequiredtoshearamaterialcanbemeasuredandreportedusingaBrookfield®ViscometerOnetypeisaconeandplateviscometershowninfigureTheconeandplateviscometerpreciselymeasuresthetorqueestablishedbytheresistanceinafluid,sandwichedbetweenarotatingconeandstationaryplateAstorqueisdirectlyproportionaltotheshearstressinthematerial,itcaneasilybeconvertedtoabsolutecentipoise(mPas)unitsthroughknowngeometricconstantsofthecone,therateofrotation,andthestressrelatedtorque(orfromprecalculatedrangecharts)Theplateportionoftheassemblyisthesamplecup(showninfigure)whichholdsthefluidandremainsstationaryItisjacketedsothataconstanttemperatureismaintainedthroughoutthetestThecupislockedontotheviscometersothatthematerialcomesintocontactwiththeconeNewtondefinedviscositybythemodelinfigurebelowTwoparallelplanesoffluidofequalarea"A"areseparatedbyadistance"dx",movinginthesamedirection,butatdifferentvelocities(VandV)HeassumedthattheforcetomaintainthisdifferenceinspeedwasproportionaltothedifferenceinspeedthroughouttheliquidAlsocalledthevelocitygradientToexpressthis,Newtonsaidthat"η"isaconstantforagivenmaterialandiscalledits"viscosity"Thevelocitygradient,dvdx,isameasureofthechangeinspeedatwhichthelayersmovewithrespecttooneanotherThisdescribestheshearingaliquidgoesthroughandisreferredtoasthe"shearrate(S)"whichisreportedin"reciprocalsecond"(sec)ThetermFAindicatestheforceperunitarearequiredtoproducetheshearingactionItisreferredtoas"shearstress"andwillbesymbolizedby"F́"Itsunitofmeasurementis"dynespersquarecentimeter"(dynescm)figurefigureViscosityRheologyViscosityRheologywwwepotekcompageUsingthesesimplifiedterms,viscositymaybedefinedmathematicallybythisformula:ASTMTestMethodD,"StandardTestMethodforHighShearViscosityUsingaConeandPlateViscometer",isbasedontheabovedefinitionandisfollowedforviscositymeasurementsThefundamentalunitofviscosityisthe"poise"Ifamaterialrequiresashearstressofonedynepersquarecentimetertoproduceashearrateofonereciprocalsecond,itwouldproduceaviscosityofonepoise,orcentipoiseViscositycanalsobeexpressedin"milliPascalseconds"(mPas)OnemilliPascalsecondisequaltoonecentipoiseNewtonassumedthatallmaterialshave,atagiventemperature,aviscositythatisindependentoftheshearrateInotherwords,twicetheforcewouldmovethefluidtwiceasfastThisholdstrueforNewtonianfluidsonlyThefollowingisaschematic(figure)ofaconeandplateviscometerinaction:ThetypeofflowdescribedaboveistrueforNewtonianfluidsonlyThefollowinggraphsshowhowthistypeofproductbehavesFigureshowsthestraightlinerelationshipbetweenshearrate(F́)andshearstress(S)Figureshowshowtheviscosityremainsconstant(assumingtemperatureisheldconstant)withvaryingshearratesfigurefigurefigureη=Viscosity=F́S=shearstressshearrateButnotallfluidsareNewtonianintheirflowcharacteristicsInfact,thereareseveraltypesofflowbehaviorTheseproductsareclassifiedasNonNewtonianTherearethreesubgroupswithintheNonNewtonianclassification:Pseudoplastic,DilatentandPlasticViscosityRheologypagePseudoplasticmaterialswilldecreaseinviscositywithanincreaseinshearrateThisissometimesreferredtoasshearthinningFiguresdepictthis:ADilatenttypeofbehaviorasseeninfiguresandbelow,causesproductstoincreaseinviscositywithanincreasingshearrateThisisalsocalledshearthickeningandiscommonlyseenwithdeflocculatedsolidssuchasclayThethirdandfinaltypeofflowisPlasticWhenamaterialexhibitsPlasticbehaviorsimilartofiguresandbelow,itwillremainina"solid"stateuntilacertainamountofforce(yieldvalue)isappliedtoitbeforeitwillflowAgreatexampleofthisisketchupfigurefigurefigurefigurefigurefigureViscosityRheologywwwepotekcompageEpoxiescanexhibitanyoralloftheseflowbehaviorswhichisimportanttoconsiderwhenchoosinganadhesiveforaspecificapplicationThixotropyisanotherparameterthatisrelatedtoviscosityandcanbemeasuredusingaviscometerAthixotropicfluiddecreasesinviscositywithtime,whileitissubjectedtoconstantshearingasseeninfigureThistypeofbehaviorcanoccurincombinationwithanyoftheaboveflowtypesfigurefigureWhentalkingthixotropy,oftenwerefertoThixotropicIndex(TI)ThisisavaluereportedbytakingtheratiooftwoseparatereadingsatdifferentspeedsonaviscometerForexample,ifamaterialproducesareadingof,cPsatRPMand,cPsatRPM,thethixotropicindexisequalto,,orUsually,TIiscalculatedfromviscositiesmeasuredatRPMsthatareadecadeapart(iebetweenandRPMsorbetweenandRPMs)ThisnumberisalsokeyinchoosingthepropertypeofmaterialforaparticulardispensingtechniqueAlloftheprecedingterminologyanddefinitionsarealso"rheologicalparameters"RheologyisdefinedasthescienceofthedeformationandflowbehaviorofmaterialsFlowbehaviorisimportantinmanyindustrialprocessesandthesuccessorfailureofanapplicationiswidelybasedonthesepropertiesforaspecificadhesiveCoatings,moldedplastics,adhesives,personalcareitems,cosmetics,inks,cement,solderpastesandmedicinesareexamplesoftherangeofcommerciallyavailableproductswhoseviabilitydependsonhavingtheproperrheologyForalloftheabovematerials,thenecessaryrheologicalpropertiesmustbeexaminedbeforeprocessingandapplicationThefollowinggraph(figure)showshowausermaywanttobalanceviscosityandthixotropyinordertodeterminethebestapplicationmethodforagivenadhesive:PotLifeandWorkingLifepagePotlifeisametricusedtodefinethelengthoftimethatamaterialcanbehandledbeforeitsviscositychangessubstantiallyGenerally,potlifeisdefinedastheamountoftimeittakesfortheinitialviscositytodoubleFigurebelowshowstheincreaseinviscosityovertimeforatypicallowtemperaturecureepoxysystemYouwillnoticethattheviscositybuildsslowlyatfirstasthechemicalreactionbeginsHowever,thereactionitselfgivesoffheatwhich,inturn,increasestherateofreactionThisprocesscausestheviscositytoincreaseinanexponentialmannerOften,knowingthepotlifealone,isnotsufficienttodeterminehowlongagivenmaterialcanbeusedforagivenmanufacturingprocessForexample,figureshowsthenormalized(change)viscosityversustimefortwodifferentproductsBoththeblueandgreenproductsexhibitthesamepercentchangeinviscosityversustimeSincebothformulationsdoubletheirviscosityafterhours(shownasachange),theybothwouldhavehoursofpotlifeAsshowninfigure,thismaterialhasabouthoursofpotlife,ieittakesthreehoursbeforetheviscositydoubles(change)figurefigurePotLifeandWorkingLifePotLifeandWorkingLifepagewwwepotekcomHowever,asfigureshows,thetwomaterialshaveverydifferentstartingviscosityvaluesThestartingviscosityofthegreenmaterialistentimesgreaterthanthatofthebluematerialAsaresult,themagnitudeofviscositychangeoveragivenperiodoftimeforthegreenproductismuchhigherthantheblueproductInthesecases,theprocesslimitsforaspecificapplicationshouldbeusedtodefinetheworkingtimeforagivenmaterialinagivenprocessIntheexampleabove,customerAmaybeabletoworkwiththebluematerialaslongastheviscosityislowerthan,cPsThiswouldgivecustomerA,hoursofworkinglife(hourslongerthanthepotlife)Ontheotherhand,customerBmayonlybeabletoworkwiththegreenmaterialiftheviscosityislessthan,cPsInthiscase,thematerialwouldhaveaworkinglifeofonlyhoursincustomerB’sprocessThus,potlifeisadatasheetvaluedesignedtogiveafirstorderdescriptionofthespeedofviscosityincreaseovertimeHowever,theactualworkingtimeoftheproductwillbeapplicationspecificandshouldbedeterminedanddefinedbasedontheindividualprocessfigurefigureAdhesiveCuringpageThewordpolymercomesfromtheGreekwordspoly(meaningmany)andmeros(meaningparts)Assuch,polymersarelongmoleculechainscomposedofmanythousandsofsmallunits(monomers)joinedendtoendAnexampleoflinearpolyethylene,thesimplesthydrocarbonpolymer,isshowninfigure:PolymersfallintotwomaincategoriesthermoplasticsandthermosetsThermoplasticmaterialsaregenerallycomposedoflinearpolymerchainswithlittleornobranchingorsidegroupssimilartothethermoplasticpolyethylenepolymerinthediagramaboveAsaresult,thesechainsareabletoeasilyslidepasteachotherwhenheatedInthisway,thermoplasticscanbeheatedandformed,thenreheatedandreformedrepeatedlywithoutdamageOntheotherhand,thermosetsundergoachemicalreactionwheninitiallyheatedandcuredtoformathreedimensionalcrosslinkednetworkOncethesematerialsarecured,thisstructureislockedinplaceandthematerialcannotbereformedorreprocessedAnexampleofthechemicalcrosslinkstructureforacommontypeofthermosettingpolymer,anepoxy,isshowninfigurefigureAdhesiveCuringAdhesiveCuringpagewwwepotekcomfigureEpoxiesgettheirnamefromthethreemembered"epoxide"ringslocatedonthestartingepoxidemonomerInthecaseabove,thestartingmonomerisactuallyadiepoxide,whichcontainstwoepoxidegroupsoneateachendofthemonomerThehardenerintheabovesystemisadiamine,whichcontainsareactiveaminegroupateitherendofthemoleculeEachoftheepoxideringscanbeopenedbyanactivehydrogenontheendofthediaminetoproducechemicalbondsbetweentheepoxidemonomerandthehardenerThisparticulardiaminehardenerprovidesfouractivehydrogensthatarecapableofreactingwithfourdifferentepoxidemonomerstochemicallycrosslinkthemtogetherTypically,thehigherthefunctionality(numberofreactivesites)ofthehardener,themoretightlycrosslinkedtheresultingcuredthermosetwillbeIngeneral,highlycrosslinkedsystemswillhavehigherhardnessandmorethermal,chemicalandmoistureresistanceAdhesiveCuringpageKineticsofCureThecurekineticsrateforthermosettingadhesivescanbemonitoredusingDifferentialScanningCalorimetry(DSC)DSCmeasurestheenergyabsorptionofasampleasitissubjectedtoaspecifiedthermalprofileTheamountofheatcontainedinamaterialatanygiventimeisknownasitsenthalpyAsadditionalthermalenergyissuppliedtothematerial,itsenthalpywillincreaseTheleveloftheresultingtemperaturechangeinthismaterialwillbedictatedbyitsspecificheatAtagiventemperature,specificheatistheamountofthermalenergyneededtochangethetemperatureofthatmaterialbyoneunitFigurebelowshowsthecrosssectionofatypicalDSCsampleholderAsmallamountofuncuredsample(~mgofresincontent)isplacedinasmallaluminumsamplepanwithlidThesamplepanisplacedontopofanindividualchromelheatingdiscAnidenticalemptyaluminumpanisplacedonasecondchromelheatingdisctoserveasareferencefortheexperimentEnergyissuppliedseparatelytothesamplepanandthereferencepaninorderforeachofthemtoexactlymatchtheheatingrateofapredeterminedtemperatureprofileTherateofenergysuppliedtothesampletoheatitatacontrolledrateisproportionaltothespecificheatofthesampleThespecificheatofamaterialwillchangeonlyslightlywithtemperatureaslongasthatmaterialremainsinthesamephysicalstateHowever,whenthethermalprofileimposedonamaterialcausesatransitiontoanewstate,(iemelting,decomposition,curing,etc)thiswillcauseasignificantchangeinthespecificheatTherapidchangeinspecificheatatatransition,thencausesachangeintheamountofenergyneededtobedeliveredtothesampleinordertomaintainthedesiredheatingorcoolingprofileDynamicSamplerChamberReferencePanSamplerPanLidGasPurgeInletChromelDiscChromelDiscThermocoupleJunctionAlumelWireHeatingBlockChromelWireThermoelectricDisc(Constantan)StandardDSCCell*figure*CourtesyofTAInstruments®AdhesiveCuringpagewwwepotekcomChangesinstatethatabsorbenergyareknownasendothermicchangesMeltingisanexampleofanendothermicstatechangeHeatisputintothesystemtoallowmoleculesthemobilitytobegintomoveEventually,enoughheatisputintothesystemtocauseoverallflowofthemeltedmaterialAtthispoint,theheatenergybecomesconvertedtothekineticenergyoftheliquidOntheotherhand,changesinstatethatactuallyevolveenergyareexothermictransitionsHeatofreaction(curing)andcrystallizationareexamplesofexothermictransitionsFigureshowssometypicalendothermicandexothermictransitionsastheywouldappearinaDSCscanAsmentionedearlierinthissection,DSCcanbeusedtomonitorthecureofathermosettingmaterialThisisaccomplishedbysubjectingtheuncuredthermosettoacontrolledtemperaturerampandanalyzingthelocation,sizeandshapeoftheresultingexothermiccurepeakFigureshowsaDSCkineticcuringprofileforatypicalepoxysystemThepeakinthesample’sheatflowresponseislocatedabovethebaseline,representinganexothermiceventThepeakofthiscuringexothermislocatedatapproximately˚C,indicatingthatthefastestcureforthisproductwilloccuratthistemperatureTheonsetofthecurepeakforthisproductis˚CfigureAdhesiveCuringpageHowever,thisdoesnotmeanthattheproductcannotcurebelow˚CAstheenlargedportionofthekineticcurvereveals,thereisactuallyasmallamountofexothermstartingaslowas˚CThisparticularproductwillcureat˚C,butitwilltakearoundfourhoursOntheotherhand,whenthisproductiscuredat˚C,thepeakcuretemperature,itwillonlytakeaboutminutesThetotalchangeinenthalpythatthesampleundergoesduringcurecanbecalculatedbyintegratingtheareaundertheexothermpeakForthematerialinthediagramabove,thetotalheatofreactionisJgAsspecifiedinASTMD,"StandardTestMethodforTransitionTemperaturesandEnthalpiesofFusionandCrystallizationofPolymersbyDifferentialScanningCalorimetry",thistotalheatofreactioncanthenbeusedtodeterminetheextentofreactionofthematerialafteritiscuredaccordingtoadesiredcureconditionThecuredmaterialisanalyzedintheDSCusingthesamethermalprofileusedtomeasuretheuncuredmaterialFigureshowstheoriginalexothermoftheuncuredmaterialabove,alongwiththatofthesamematerialcuredat˚CforminutesfigureAdhesiveCuringpagewwwepotekcomThematerialcuredat˚CforminutesexhibitsonlyaverysmallresidualexothermpeakThisindicatesthatmostofthetheoreticalcrosslinkingreactionswerecompletedduringthecureTheenlargedviewofthecuredsampleexothermshowsthatonlyJgofreactivityremainsoftheoriginalJgheatofreactionforthismaterialThus,onlyofthematerialisleftunreactedbytheimposedcureEpoxiesdonotneedtoachieveafullreactioninordertoperformwellasadhesivesGenerally,systemsthathavebeencuredtoatleastconversionwillexhibitmechanicalandphysicalpropertiesthatdo

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