Cool-Polymer公司-导热塑料

原文：Heatsinksandotherheat-removalapplicationsareamongthelastareaswherethermoplastics—inherentthermalinsulators—haveyettoreplacemetals.Untilfairlyrecently,thatis.Modifyingplasticstoimprovetheirthermalconductivityisaburgeoningareaofopportunityforahandfulofcompounders.Theyhavetakenupthechallengeofusingplasticstosolveproblemsofheatbuild-upinelectronics,appliances,lighting,automotive,andindustrialproducts.Amongthepioneers,whoseheat-conductivecompoundshavegonecommercialinjustthelastcoupleofyears,arePolyOneCorp.,CoolPolymers,LNPEngineeringPlastics,RTPCo.,andTiconaCorp.GEPlastics,DuPont,andA.Schulmanhavedevelopmentprogramsunderway.Andlastmonth,PolyOneenteredintoajoint-developmentagreementwithCoolPolymersinordertoutilizethelatter’scapabilitiesintooldesign,thermal-managementtesting,andinjectionmoldingofprototypeapplications.Thermallyconductivecompoundsaregenerallynotconsideredtobedirectdrop-inreplacementsformetals.Instead,theyopenupabroadrangeofnewopportunitiesfor“thermalmanagement”applications.Partsmoldedoutofthisnewgenerationofmaterialscanreplacemetalsandceramicsinsomeapplications,andnon-conductiveplasticsinothers.Usesincludecustom-moldedheatsinksoncircuitboards,aswellastubingforheatexchangersinappliances,lighting,telecommunicationdevices,businessmachines,andindustrialequipmentusedincorrosiveenvironments.Heatsinksofteninvolveplasticovermoldedonametalheatpipe.Lightingapplicationsalsoincludereflectors,laser-diodeencapsulation,andfluorescentballasts.Automotiveheadlampreflectorsareindevelopment.Intemperaturesensorslikethermistors,thermallyconductiveplasticencapsulationcanhelpimprovetheresponseofthetemperaturesensoritself.Thermallyconductivecompoundsarealsousedtoencapsulatesmallmotorsandmotorbobbins.Adieselfuelpumpusesathermallyconductiveplastictohelpkeepfuelflowinginsub-freezingtemperatures.Moreexoticapplicationsmayincluderadiantfloor-heatingsystems,whereathermallyconductivefilmplacedbetweencoilscouldallowwatertoberunatlowertemperatures.Anotherpossibilityismoldingall-plasticcarradiatorsaroundcontoursofthebumperinsteadofthetraditionalsquarebox.COOLNEWMATERIALSTheheat-transferrequirementsofever-smallerandmorepower-hungryelectronicshaveopenedthedoorforthisnewgenerationofcoolingmaterials.Whereasunfilledthermoplasticshaveathermalconductivityofaround0.2W/mK(Watts/meter-°Kelvin),mostthermallyconductiveplasticcompoundstypicallyhave10to50timeshigherconductivity(1-10W/mK).Onefirm,CoolPolymers,offersproductswith100to500timestheconductivityofabasepolymer(10-100W/mK).Traditionally,aluminumhasbeentheprimematerialforcontrollinghigherheatfluxesinelectronics.Thermalconductivityofextrusion-gradealuminumalloysisnear150W/mK.Somedie-castmetalalloys(magnesiumoraluminum)areinthe50-100W/mKrange.However,itcanbearguedthatmetals’highthermalconductivitycannotbeeffectivelyutilizediftheyconductheattothesurfaceofaproductfasterthanair-flowconvectioncanremoveheatfromthesurface.AccordingtoJimMiller,productmanageratCoolPolymers,“Heattransferinmanyapplicationsisconvection-limited(thatis,design-dependent),notconduction-limited(material-dependent).”Hiscompanyhasdemonstratedtheconceptincertainapplicationswherethermallyconductiveplasticsprovideheattransferequivalenttoaluminumandcopperdesigns.AddsMarkKaptur,LNPproductmarketingmanager,“Whereconductivityisthelimitingfactor,metalisthepreferredmaterial.Buttherearemanyapplicationswhereconvectionisthelimitingfactor,andthenthermallyconductiveplasticsareabetterfit.”Also,thermallyconductiveplasticstypicallyboastlowercoefficientsofthermalexpansion(CTE)thanaluminumandcantherebyreducestressesduetodifferentialexpansion,sincetheplasticsmorecloselymatchtheCTEofsiliconorceramicsthattheycontact.Conductiveplasticsalsoweigh40%lessthanaluminum;theyofferdesignfreedomformolded-infunctionalityandpartsconsolidation;andtheycaneliminatecostlypost-machiningoperations.Manytechnologicaladvancesutilizingmicroelectronicswouldhavebeenimpossiblewithoutthermallyconductiveplastics,accordingtoMillerofCoolPolymers.“Thisabilitytocontrolheatbuild-up,yetalsoprovidelightweight,flexible,andlow-costapplicationswillmaketheseplasticsoneofthemostimportanttechnologicaldevelopmentsfordecadestocome.”InfraredphotographyfromCoolPolymersdemonstrateswhymanycomponentsmadeofplasticsoverheatandfail.Spotheatsourceswereappliedtothecenterofflatmoldedpanels—onemadewithastandardPPandonemadeofaCoolPolythermallyconductivePPcompound.Thelatterconductsheatawayfromthecenterhotspot,generatingamoreisothermicprofilethatvariesnomorethan4°Cthroughoutthepanel.ButthestandardPPpanelshowsa24°Ctemperaturedifferencebetweenitshottestandcoolestpoints.Highinitialcostiscurrentlythebiggestobstacletowideracceptanceofthermallyconductivecompounds.Akeyfactoristhehigh-pricedfillersusedtoachievegoodheatconduction,whichresultinthesecompoundscostingattheveryleasttwoandahalftimesasmuchasmetalorceramicmaterialstheymightreplace.Manythermallyconductivecompoundssellinthe$25-$45/lbrange,thoughsomewithlowerconductivitycostaslittleas$4to$6/lb.Supplierssaythetechnologyiscurrentlybestsuitedtohigh-volumeproduc