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外文翻译水溶性粘结剂高弯曲模注塑粉.doc

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外文翻译水溶性粘结剂高弯曲模注塑粉.doc

附录WatersolublebinderwithhighflexuralmodulusforpowderinjectionmoldingMINSEOKSONG,MINSOOPARK,JINKONKIM∗NationalCreativeResearchInitiativeCenterforBlockCopolymerSelfAssemblyandDepartmentofChemicalEngineering,ElectronicandComputerEngineeringDivisions,PohangUniversityofScienceandTechnology,Kyungbuk790784,KoreaILBUMCHO,KYUNGHOKIM,HWANJINSUNG,SANGHOAHNResearchInstituteofScienceandTechnology,Pohang,Kyungbuk790784,KoreaEmailjkkimpostech.ac.krAnewbindersystem,containingternarypolymerblendsofpolymethylmethacrylatePMMA,celluloseacetatebutyrateCABandpolyethyleneglycolPEG,wasintroducedforthepowderinjectionmoldingofstainlesssteelpowders.TheweightfractionofPEGinthebinderwasmaintainedtobe0.65.WhentheweightfractionofPMMAinthebinderwas0.1–0.25thustheweightfractionofCABwas0.1–0.25,thefeedstockswith56volofsteelpowdersweresuccessfullyinjectionmoldedwithoutshowinganyjetting.Furthermore,thefeedstockshavemuchhigherflexuralmoduluscomparedwiththosepreparedbyabinderconsistingonly35/65wt/wtCAB/PEGblend.Threebinaryblends,PMMA/CAB,PMMA/PEG,andCAB/PEG,werecompletelymiscibleataninjectionmoldingtemperatureof130◦C.TheextractionprocessemployedinthisstudybecomesenvironmentallyfavorableduetothemajorcomponentPEGofthebinderwhichiseasilyextractedbyasolventofwaterorethanol.Also,theshapemaintenanceduringthesolventextractionwasexcellent,andfinalsinteredpartshadexcellentdimensionalstability.Duetohighflexuralmodulusoffeedstocks,thisbindersystemcanbeemployedforpreparinglargesizedinjectionmoldarticles._C2005SpringerScienceBusinessMedia,Inc.1.IntroductionPowderinjectionmoldingPIMprocessingofmetalsorceramicshasbeenemployedtodeveloptinyandsophisticatedmetalorceramicparts,anditisaveryeconomicprocesscomparedwithacastingandamachining1,2.AmongthemanystepsinthePIM,thesuitablechoiceofabinderbecomescrucialtodeterminethemechanicalpropertiesofthefinalproduct.Waxbasedbinderscontainingabackbonematerialofpolyethyleneorapolyethyleneranvinylacetatehavebeen\\widelyusedinthepowderinjectionmoldingindustries3,4.However,organicsolventsuchashexaneandheptane,whichisnotanenvironmentallyfavorablesolvent,shouldbeusedtoextractthewax.Toavoidusinghexaneorheptaneduringtheextraction,effortshavebeenfocusedonfindingnewtypesofbindersthatwouldberemovedbyanenvironmentallyfavoredsolventsuchaswater5–11.Daviesandcoworkers7,8introducedapolymethylmethacrylate/polyethyleneglycolPMMA/PEGbindersystemforstainlesssteelpowders.Althoughaveryhighmolecularweight∼1,000,000ofPMMAwasused,thebinderwasmixedwithsteelpowderinthepresenceofwater,becausewaterisasolventoflowermolecularweight1500PEGandanemulsionmediumofPMMA.However,withoutusingemulsioncontainingwaterforPMMAparticles,abinderconsistingofPMMAandPEGmightnotbemixedeffectivelywithsteelpowders.Previously,weintroducedawatersolublebinderconsistingofcelluloseacetatebutyrateCABandvariousmolecularweightsofPEG.WefoundthatthecrystallizationofPEGdependinguponthemolecularweightaffectedprofoundlytheshapemaintenanceduringsolventextraction12,13.Namely,whenthemolecularweightofPEGwaslargerthan3400,crackswerefoundingreenpartsafterthesolventextraction.AlthoughbindersofCAB/PEGwithmolecularweightlessthan2000couldbeinjectionmolded,jettingresultingfromlowviscosityofPEGwassometimesobserved.Also,mechanicalpropertiessuchasflexuralstrengthofgreenpartsarepoor,whichrestrictsonetomakinglargesizedinjectionmoldedarticles.Inordertoovercomethesedisadvantages,weaddedPMMAtoCABasthebackbonematerial.TherationalbehindchoosingPMMAisthatiPMMAismisciblewithbothCABandPEGataprocessingtemperatureof130◦Ciiitshowsgoodadhesionwithmetalpowderduetohavingapolargroup,whichpreventsbinderseparationduringinjectionmoldingandiiiitprovidesgoodmechanicalpropertiesofgreenparts.WecouldusehighermolecularweightofPEGupto8,000whenPMMAwasemployed.AbinderconsistingofPMMA/CAB/PEGternaryblendsexhibitedhigherflexuralmodulusandsuitablerheologicalpropertiesforinjectionmoldingthusalargesizedinjectionmoldedarticlewassuccessfullyprepared.Also,weobservedthattheshapemaintenanceduringtheextractionwasexcellent,andfinalsinteredpartshadexcellentdimensionalstability.2.Experimental2.1.MaterialsPMMAwasalsokindlysuppliedbyLGMMACo,andthemolecularweightandpolydispersityofPMMAweredeterminedbyusinggelpermeationchromatographyWatersCo.withPMMAstandards.CABwith54molbutyratesidegroupwaspurchasedfromAcrosCo.andPEGwithdifferentmolecularweightswaskindlysuppliedbyKoreaPolyolCo.Korea.ThemolecularcharacteristicsofthesematerialsaregiveninTableI.CABandPMMAareamorphousmaterialswithaglasstransitiontemperatureof94◦Cand100◦C,respectively,measuredbyDSCPerkinElmerDSC7seriesataheatingrateof20◦C/min.Themetallicpowderwasstainlesssteel174PH,MitsubishiSteelMFGCo.havingirregularshapeandamedianparticlesizeof8.86μm.2.2.SamplepreparationandrheologicalpropertiesThefeedstock,amixtureofthebinderandmetallicpowder,wasfirstpreparedbymixingat130◦Cfor1hbyusingtheKneadingBladeTypeMixerIKAVISCCo.thenitwasshapedintoarectangularbar70.227.123.57mmLWTbyusinga180tonprecisioninjectionmoldingmachineSodickPlustechCo.Japanat130◦Candmoldtemperatureof25◦C.AnAdvancedRheometricsExpansionSystemARESusingthedynamicoscillatorymodewithparallelplatefixture25mmdiameterwasusedtomeasuretheviscosityofthebinderitself.Thestrainamplitudewas5,whichliesinlinearviscoelasticityrange.TABLEIMolecularcharacteristicsofblendcomponentsemployedinthisstudyMnPolydispersityindexTgorTm◦CPMMA63.0001.47Tg100CAB11,0002.3Tg94PEG11,5001.15Tm43PEG22,0001.10Tm50PEG33,3501.14Tm54PEG88,0001.16Tm562.3.TurbidityexperimentofPMMA/CABblendVariousblendcompositionsofPMMAandCABforturbiditytemperatureTbmeasurementwerepreparedbydissolvingapredeterminedamountofthemixtureintoluene10wtandslowlyevaporatingthesolventover8hatroomtemperature.Thesamplethicknesswas10μm.Eachspecimenwasannealedinthehomogeneousstate∼120◦Cfor4h.TheTbofeachcompositionwasmeasuredfromthesuddenincreaseinlightscatteringintensityatascatteringangleof30◦uponheatingthemixturefrom120◦Catarateof0.1◦C/min.OncetheTbofaspecimenwasestimated,theexactTbwasdeterminedbythenakedeyeuponatemperatureincrementby0.5◦Cnearthetemperatureofinterest.Thespecimenwasheldateachtemperaturefor1h.ThemaximumerrorinthevaluesofTbdeterminedwas±0.5◦C.2.4.DebindingandsinteringTwostepsofdebindingofgreenpartswereconducted.ThefirststepwastoextractPEGoutofgreenpartsbydistilledwateratroomtemperaturefor24h.Thesecondstepwasreferredtoasthethermaldebinding,wherethebackbonescomposedofPMMAandCABwerecompletelyremovedandpresinteringofmetalpowdersoccurred.Finallythesinteringofmetalpowderswascarriedout.ThermaldebindingandsinteringwerecarriedoutinatubetypefurnaceLentonThermalDesignLtd.underhydrogenatmospherebyusingthesamethermalhistoryasref.12.3.Resultsanddiscussion3.1.MiscibilitybetweenbindercomponentsThebinderemployedinPIMhasamulticomponentsystemaabackbonepolymerthatprovidesshapemaintenanceduringsolventextractionbanextractablepolymerthatisremovedduringthefirststepofthedebindingprocess,andcasurfactanttobridgebetweenthebinderandpowder1.Itisnecessarythatallcomponentsshouldbemiscibleatprocessingtemperatures.Otherwise,thebindercomponentsbecomemacrophaseseparated.Previously,weshowedthatabinaryblendofCAB/PEGhavingamolecularweightMof35000showedlowercriticalsolutiontemperatureLCSTof168◦C13.SinceMofPEGemployedinthisstudyislessthan8000,wefoundthattheCAB/PEGmixturedoesnotbecomephaseseparatedupto250◦C.ThePMMA/PEGblendbecomescompletelymiscibleattemperaturesgreaterthanthemeltingtemperatureofPEG14.Fig.1givesthephasebehaviorofthePMMA/CABblend,fromwhichtheLCSTwas142◦Cat20/80w/wPMMA/CABcomposition.Thus,weconcludethatMacrophaseseparationamongallthreebinaryblendsPMMA/PEG,CAB/PEG,andPMMA/CABblendsdoesnotoccurataprocessingtemperatureof130◦C,whichisthemixingandinjectionmoldingtemperatures.Also,whentheamountofPMMAwaschangedfrom15to25wtatafixedamountofPEG65wt,noturbiditywasdetectedupto200◦C.Figure1PhasediagramsofPMMA/CABblend.3.2.RheologicalpropertiesItisknownthatfeedstocksshouldhavealowenoughviscositytobeprocessedbyinjectionmolding.However,whentheviscositybecomestoosmall,jettingoccursduringtheinjectionmoldingprocessthustheexactshapeofmoldedarticleisimpossible.Fig.2givesthecomplexviscosityηasafunctionoffrequencyforthebinderscomposedofvariouscompositionsofPMMA/CAB/PEGswithtwodifferentmolecularweightsofPEGs.ItshowsthatasthecontentofPMMAandMofPEGincrease,theviscositybecomeslarger.WhenthebindersdonotcontainCAB,abinderconsistingof35/65wt/wtPMMA/PEGhaszeroshearviscosityηoof100Pas,regardlessofmolecularweightsofPEG.Itisknownthatwhenηoofabinderislargerthan∼20Pas,thefeedstocksincludinghighvolumeofpowderscouldnotbemoldedbyinjectionmolding1.Therefore,itisconsideredthatfeedstocksconsistingof15/20/65and25/10/65wt/wt/wtPMMA/CAB/PEG8binderand56volofsteelpowderscouldbeinjectionmolded.

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