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1、CharacterizationofPressureSensitiveAdhesivesbyRheologyFredA.Mazzeo,Ph.D.TAInstruments,109LukensDrive,NewCastleDE,USAABSTRACTThreeproperties,shearresistance,tackandpeelstrength,generallycharacterizedpressuresensitiveadhesives(PSA).ThesepropertiesaredirectlyrelatedtothePSA’srespons
2、etotheapplicationofstressandmaybemeasuredusingrheology.Forexample,tackdescribestheabilitytospontaneouslyformabondtoanothermaterialunderlightpressureswithinashortapplicationtime.Asthecontacttimeincreases,highershearresistanceandpeelstrengthproperties(relatedtoamaterialslongtimeflo
3、wbehavior)arefound.AsinglerheologicaltestisdescribedtodirectlydeterminetheresponseofaPSAtovaryingdeformationtimes,relateddirectlytoitsshearresistance,tackandpeelstrengthbehavior.INTRODUCTIONAnadhesiveisusuallyapolymericmaterialappliedbetweentwosolidlayersthatformabondwithcohesive
4、strength(1).Mostadhesivesexhibitviscoelasticbehavior.Rheology,usingsmallamplitudeoscillations,maybeusedtotestadhesivesthroughoutthewholeviscoelasticprofile.Applyingsmallamplitudescausestheshearstresstobeproportionaltotheshearstrain,anecessaryconditionforlinearviscoelasticity.Inli
5、nearviscoelasticity,thedynamicmodulus(G[w])istheratioofshearstresstoshearstrainandisindependentoftheshearamplitude.Dynamicmodulusmaybeseparatedintoelastic(storage)modulus(G’)andtheviscous(loss)modulus(G”).TheratiooftheG”toG’isequaltothetangentofthephaseanglebetweenthem:tand=G”/G’
6、.TheabilitytoformabondandresistdebondingfromasubstratedetermineshowappropriateaparticularPSAisforacertainapplication.OscillatoryfrequencysweepsarewellsuitedforcharacterizingthebondinganddebondingbehaviorofaPSA.Inanoscillatoryfrequencysweep,aconstantsinusoidalamplitudeisappliedtoa
7、material,withinthelinearviscoelasticregion,whilevaryingthefrequencyoftheoscillation.Lowratesofdeformation(i.e.,lowfrequency)characterizethebondformation,whilehighfrequency(i.e.,highratesofdeformation)isusedtocharacterizedebondingbehavior.Thelatterdescribesamaterialsshearresistanc
8、eandtheformerrelatestoPSA’stackandpeelst