住友LCP完全技術手冊

SumikasuperLCPTechnicalSeminar

<contents>

1.Improvementofthewarpage

1-1.Introduction 1

1-2.Theoreticalbackgroundofthewarpageproblem 1

1-3.Experimentalanalysis 2

1-4.Casestudy

boardtoboardconnector(0.5mmpitch) 2

S/ODIMM 3

PGAsocket 4

2.High-speedinjectionmolding

2-1.Introduction 6

2-2.Thin-wallfluidityofLCPandcharacteristicof

injectionmoldingmachine

Experiment 6

Results 7

3.Reductionoftheblisteratsoldering

3-1.Introduction 9

3-2.Retentionofresinattheinsideofinjectionmachine 9

3-3.Temperaturesettingsofinjectionmachine 10

3-4.RelationbetweenretentionofLCPincylinderandblister 12

3-5.Otherpossibilities

Effectofmoisture 13

Draggingtheairintothemelt 14

Unbalancebetweencylindersizeandmoldingvolume 14

3-6.Conclusion 16

PurgingmethodofSumikasuperLCP 17

4.Reductionofthebubbleaftermolding

4-1.Introduction 18

4-2.Comparisonbetween"thebubble"and"theblister" 18

4-3.Reductionofthebubble

Suitableinjectioncondition 18

Suitablecavitydesign 19

5.Improvingtheholestrengthduringinsertingcontactpins

5-1.Introduction 21

5-2.Casestudy 21

1

Improvementofthewarpage

1-1.Introduction

Theliquidcrystallinepolymers(LCPs)arewidelyusedasmanytypesofelectricandelectronicspartsbecauseoftheirsuperioritiesinheatresistance,solderingresistance,high-temperaturestrength,chemicalresistance,thin-wallfluidity,etc.Especially,LCPsexhibitexcellentthin-wallfluidityandmoldabilityamonganyotherengineeringplastics.

However,tomoldtheproductswhichhavemanythin-wallportionsandcomplicated3-DshapeasconnectorsrequiressomehowsbasedonthespecificcharacteristicsoftheLCP.

Inthissection,wewouldliketoconsiderhowtoreducethewarpageofconnectorsmoldedbyLCPs.

1-2.Theoreticalbackgroundofthewapageproblem

Generallyspeaking,meltpolymersincludingLCPsflowtothickerportionsfirstly,thenflowtothinnerportionsbecausethepressure-lossatthinnerportionsisgreaterthanthickerportions.Inalmostcasesoftheconnectordesign,thebottomthicknessisthickerthantheribthickness.Thus,theappearanceofpolymerflowisrepresentedschematicallyasseeninFig.1-1a.ThearrowsinFig.1-1ashowthe“flowpattern”ofpolymerflow.

Fig.1-1LCPfowmodel

Especially,theLCPhasgreatdifferenceofmoldshrinkagebetweenmechanicaldirection(MD)andtransversedirection(TD).Asaresult,thethinnerportion("ribportion")willshrinkmorethanthethickerportion("bottomportion"),andthen,thewarpageexpressedinFig.1-1bwilloccur.

Inourunderstanding,thecauseofwarpageseeninLCPmoldingscanbeexpressedasstatedaboveatalltimes.Inotherwords,itisreasonabletothinkthatthewarpageofLCPmoldingsiscontrollablebychangingits“flowpattern”.

Therearethreepossibilitiestochangetheflowpattern.Thefirstandmostimportantstepistoequalizethethickness.Becauseofsomerestrictions,forexampleproductdesign,thisstepmaybedifficulttorealize.Allthesame,thisisthemostimportantpointtoreducethewarpage.

Nextwayistoinstallsomethinportionsatthickerportion(seeFig.1-2a).FlowpatternwillbeequalizedasshowninFig.1-2abyinstallingsuchthinportions("depressions")atbottomportion.

Thelastmethod(Fig.1-2b)istomovethegatepositiontothinnerportion(inthisfigure,ribportion).

Anyway,thewarpagewillreducegraduallybyusingaboveprocedures.

Fig.1-2Methodstochangetheflowpattern

1-3.Experimentalanalysys

Wehaveinvestigatedabovetheorybyusingmodelmoldwhichisabletochangethedepthofdepressions.Fig.1-3showsourmodelmoldusedinthisinvestigation.Thedepthofdepressionwaschangedfrom0mmto0.8mm(1/2ofbottomthickness).ResultsareshowninFig.1-4.

Fig.1-3SchematicviewofthemodelmoldFig.1-4Resultofwarpagechangeusingvarious

LCPs

ThewarpagereducedwithincreasingthedepressiondepthevenifanygradeofLCPwasused.Atthesametime,theflowpatternhadtochanged.Infact,itwasprovedbyobservationofshort-shotsamplesseeninFig.1-5.

Fig.1-5Photoofshort-shotsamples

1-4.Casestudy

1-4-1.Boardtoboardconnector(0.5mmpitch)

Fig.1-6showsschematicviewof0.5mmpitchboardtoboard(b/b)connector.Thisconnectorhadawarpageofabout10/100atoriginaldesign.Tocontroltheflowpattern,depressionswereinstalledatsidewallsasseeninFig.1-7,thenthewarpagereducedunder5/100.

Fig.1-6Schematicviewofb/bconnector

Fig.1-7Installingdepressions

1-4-2.S/ODIMM

Fig.1-9showsS/ODIMMdesignedaveragethicknessas0.03mm.Inthiscase,3typesofwarpagewereobserved.

mode1:warpageoflongitudinalderection

mode2:twisting

mode3:tumblingarmstotheinside

Fig.1-9SchematicviewofS/ODIMM

Itwasfoundthattheflowpatternwasnotequalbetweentopandbottom,topflowwasslowerthanbottomflow.Thereasonforthisisthatthethicknessoftopisthinnerthanbottom.Inthiscase,theflowpatternatthearm(oppositside)isshownasarrowsinFig.1-10,thenthearm(oppositside)warpstotopdirection,andthismoldingshowsmode2warpage.

Werecomendedequlizingthethicknessbetweentopandbottom,thewarpagesofmode1and2reducedlessthan10/100(seeFig.1-11).

Fig.1-10Flowpatternanalysis1Fig.1-11Ideaforsolution1

Themoldinghadstillwarpageof6~7/100.Thereasonofthiswarpagewastheunbalanceflowofbothtopandbottomplanes.Fig.1-12showstheflowpatternattopportion.Werecommendedinstallingprotrusionportionatfrontsideofbothtopandbottomplanes(seeFig.1-13).Thenthewarpagewascompletelyreduced.

Fig.1-14showsthechangeofflowpatternbyusingshort-shotsamples.

Fig.1-12Flowpatternanalysis2Fig.1-13Ideaforsolution2

1-4-3.PGAsocket

Fig.1-14showstheconventional2gatessystemforPGAsocket.Inthiscase,thewarpagewillbeunavoidable,especiallythegatesideinordertotheinequalityoftheflowpatternateachsideasseeninthefigure.The4gatessystemfromcenterportionshowninFig.1-15istheoneofthebestwaytosolveit.Thissystem,ofcourse,stillhasachanceofoccuringthewarpageatthegripportion(seeFig.1-16a)),however,itcanbeimprovedbyinstallingthesuitabledepressionslikethesamemannerdescribedabovesections(seeFig.1-16b)).

Fig.1-14Theconventional2gatesystemforPGAsocket

Fig.1-15The4gatessystemfromcenterportion

Fig.1-16IdeaforimprovingthewarpageforPGAsocket

2

High-speedinjectionmolding

2-1.Introduction

Recentlyyears,manycustomersarestronglyrequestingthematerialswhichareusedforlighter,smaller,andthinnnerproductsthanusualproducts.Thoseproductshavingthinportionslessthan0.2mm,however,aresometimesdifficulttomold,evenifourimprovedmaterialsareused.Inthosecases,itisunavoidablethatthethin-wallfluiditydependsonthecharacteristicofinjectionmoldingmachines.Thepurposeofthissectionistoinvestigatetherelationbetweenthin-wallfluidityofLCPandrise-upcharacteristicofinjectionmoldingmachines.

2-2.Thin-wallfluidityofLCPandcharacteristicofinjecionmoldingmachine

1)Experiment

The4cavitiestoolingshowninFig.2-1(cavitythickness:0.2mmt)wasusedforthisstudywithSumikasuperE6008(GF40%)asLCP.InjectionmoldingmachineswereusedshowninTable2-1andmoldtemperaturewas130degreeC.Themoldingtemperatureofeachinjectionmachinewas360degreeC.andmeasuredbyinfraredradiationthermometer(IT-240S:HoribaLtd.,Japan)at0.86oftheradiationratebeforeeachexperiment.DetailesofmeasuringofthemoldingtemperaturearewrittenatSection3-3.

Actualwavesofinjectionspeedandpressurewererecordedforeachinjectionconditionandtheflowlengthof0.2mmtcavitiesweremeasuredatthesametime.TheschematicwaveisshowninFig.2-2.

Fig.2-14cavitiesmodeltoolingFig.2-2Schematicwaveofthisstudy

Table2-1Thelistofinjectionmoldingmachinesofthisstudy

2)Results

Fig.2-3showstherelationbetweeninjectiontimeandflowlength.Incaseofopen-loopinjectionmachinesasAorB,flowlengthsdevelopedatendencytoincreasewithdecreasingofinjectiontime,however,injectiontimehasnotdecreaseunder0.10second.Incontrast,injectionmachineChasarrivedunder0.10secondofinjectiontimeeasierthanAandB,thenflowlengthhasgreatlyimproved.

Fig.2-3Relationbetweeninjectiontimeandflowlength

Thereasonwhythesedifferentcharacteristicswereobservedcanbeconsideredthedifferenceofrise-upcharacteristicofinjectionmachines.Thatistosay,comparedwiththerise-upcharacteristicofpressure,injectionmachineCismostrapidthanBandCshowninFig.2-4,sincetheservo-valveofclosed-loopsystemshowsquickerperformancethantheproportionalcontrolledvalveofopen-loopsystem.ItisclearofcomparingthevelocitycharacteristicsshowninFig.2-5.

Fig.2-4PressurewaveFig.2-5Velocitywave

Fig.2-6showsrelationbetweenmaximumvelocityandflowlengthforvariousinjectionmoldingmachinesincludingA,B,andC.Closed-loopmachinesshowbettermoldabilitythanopen-loopmachines.Itisreasonabletosupposethattheclosed-loopinjectionmachinesareprofitableforthin-wallmoldingsusingLCPs.

Fig.2-6Relationbetweenmaximumvelocityandflowlength

forvariousinjectionmoldingmachines

3

Reductionoftheblisteratsoldering

3-1.Introduction

LiquidCrystallinePolymer(LCP),"SumikasuperLCP",isoneofthebestheat-resistantpolymers.Ithasveryhighdecompositiontemperature(over500degreeC),andgoodthermalstability.ThesepropertiesserveforelectricandelectronicspurposesrequiringtoholdatIRreflowsolderingtemperature(~260degreeC).

However,ithasbeenshowninsomecasesthattheblisterproblemoccursatthesurfaceoftheproductsaftermoldingorafterIRreflowprocess.

ItisthoughtthattheLCPblisterproblemsoccurwhenthegasbleedingfromtheLCPresinatmoldingdissolveintotheproduct,furthermore,whenitexpandwithheatofIRreflowprocess.ThesurfaceofproductgetsblistersbecausethesurfaceissoftenbytheheatofIRreflowprocess.

ThegasquantityofSumikasuperLCPsarecontrolledatlowerlevelcomparedwithotherengineeringplasticsorotherLCPs.However,ifSumikasuperLCPisusedatexceedingitsthermallimit,theincreaseofgas,blisters,andthedeteriorationofmechanicalpropertiesofLCPwillbeobserved.

Inthissection,wewouldliketoexplainhowtoreducetheblisterproblems.

3-2.Theretentionofresinattheinsideofinjectionmachine

TheapparentviscosityofLCPstronglydependsonbothtemperatureandshearrate,inaddition,itsdependenceisstrongerthangeneralcrystallineandamorphousplastics.Becausetheapparentviscositybecomesverylowundertheproperinjectionconditions,theproductshavingthethin-wallportions(0.3mmtorless)iseasilymolded.

However,longtermrunningofmoldinggenerallycausestheretentionofresinatdead-spacesofinjectionmachineandthisresiduecausessomedeteriorations,forexample,thecontaminationofblackspots,theincreaseofgas,andthereductionofsolderingresistancetemperature(includingtheblister).

Especially,theLCPeasilyremainsatdead-spacesofinjectionmachinebecauseofitslowviscosity.Fromsimilarreason,thepurgingofpreviousresinissomewhatdifficultthangeneralplastics.

1)Experiment

Usingcleanscrewandcylinder,theblackcolorgradeofSumikasuperLCPwasmoldedupto200shots.Afterthat,thenaturalcolorgradewasmoldedupto400shots,thenscrewandcylinderwerebrokenuptoanalyzetheresiduaryconditionoftheblackgrade.

2)Conclusions

a)Theopen-typenozzleshouldbeusedforSumikasuperLCP.

Theshut-offtypenozzleisnotsuitable(theshut-offvalveanditssurroundingportioncausestheresiduewhichwillchangetothecauseofblack-spotsandtheblister).

b)Theinternaldiameterofthenozzleshouldbe4~5mmφ(thestandardsize,ca.8mmφisnotsuitableforSumikasuperLCP).

Fig.3-1Situationofretentionresinatnozzle,screw,andcylinder

(Therecommendabledesignofnozzleisalsodrawninthebottomofthisfigure)

3-3.Temperaturesettingsofinjectionmachine

~Differencebetweensettingvalueandrealresintemperature~

Oneofthemostimportantreasonsforvariousmoldinginferiorityisthedifferencebetweensettingtemperatureofinjectionmachineandactualresintemperature.Especially,moderninjectionmachineshavedigitalindicatorsofnozzleandcylindertemperatures,andtheoperatoreasilyhastheillusionthatthevalueappearedontheindicatorisequaltotheactualresintemperature.

However,theindicatorvalueoftendifferedfromtheactualresintemperatureinalmostmachinesthatwemeasured.

1)Measurementprocedureofresintemperature

Themeasurementofresintemperatureisusuallydonebystickingthepin-typeprobe(thermocouple)intotheroundballofpurgedresin.Incaseoftheresinhavingthemoldingtemperatureover300degreeC,however,thetemperaturereductionoftheresinballbytheradiationofheatisnotabletoignore.Thusitisdifficulttomeasuretheresintemperatureprecisely.

Itisappropriatetoemploythenon-touchmeasurementimmediatelyafterdrippingfromthenozzle.

apparatus:Infraredradiationthermometer(IT-240S:HoribaLtd.)

spotdiameter:1.2mmφ

Thesettingofradiationrateisveryimportantfortheinfraredradiationthermometer.Wehaveascertainedthatreasonablevalueofradiationrateformanykindsofplasticsis0.86bymeasuringattheproductionfactoryofresinpellets.

resinsusedforascertainment:

PP(non-filler:naturalcolor)

ABS(GFfilled:naturalcolor,black)

PES(non-filler,GFfilled:naturalcolor,white)

PEEK(GFfilled:naturalcolor,black)

LCP(GFfilled:naturalcolor,black,white)

2)Result

TheresultisshowninTable3-1.Almostcasesshowthattheactualresintemperaturegreatlydifferfromthesettingtemperature.

Table3-1Resultoftemperaturemeasurement

No

Injectionmachine

Injectionrate

Temperature

Molding

Settingtemp.

Actualtemperature(deg.C)1)

(cm3/sec)

controlsystem

material

(deg.C)

Metering2)

Purging3)

1

Verticaltype

(Acompany)

27

ON-OFFtype

PES3601GL30

(GF30%)

380

400~407

(+20~+25)

400~440

(+20~+60)

2

ditto

27

PID

ditto

380

375~380

(-5~0)

400

(+20)

3

Verticaltype

(Bcompany)

89

ditto

ditto

370

395~400

(+25~+30)

407

(+37)

4

Horizontaltype-1

(Bcompany)

114

ditto

PES3601GL20

(GF20%)

380

380~385

(0~+5)

360~364

(-20~-16)

5

ditto

114

ditto

PBTGF30%

270

275~280

(+5~+10)

270

(0)

6

Horizontaltype-2

(Bcompany)

42

ditto

LCP-R

(GF40%)

408

4)

375~390

(-18~-33)

1)UsingIT-240infraredemissionthermometer(HoribaLtd.:spotsize1.2mmφ,emissionrate0.86)

2)Measuredatdrawingstrandfromnozzleduringpurgingprocess(measuringpoint:1mmfromnozzletip)

3)Measuredatthesamemannerasaboveexceptforsettingwithinjectionspeed10%

4)Impossibletomeasurebecauseofunstablemetering

Thereasonwhytheactualresintemperaturedifferfromthesettingtemperatureisthoughtthatthepositionoftheprobe(thermocouple)tocontrolthenozzleheaterisnotsuitableasshowninFig.3-2.

Fig.3-2Comparisonofthermocouplepositioninvarioustypesofinjectionmachine

3-4.RelationbetweenretentionofLCPincylinderandblister

Asmentionedabove,thedeteriorationofresinmayhappenwhentheactualresintemperatureishigherthanthemostsuitableone.Thisdeteriorationmaycausetheblister,whichmayleadretentionincylinder.

Itwasfoundthatthereisstrongdependencebetweenblisterandmolding(actualresin)temperatureortheretentiontimeofresinincylinder.

1)Testmethods

Sample:E6807L

Moldingmachine:PS-40E5ASE(NisseiPlasticIndustrialCo.,LTD)

Thetransfomationsandblisteroftestpieceswereobservedafterimmesingthemintothesolderingbathsetat210and250degreeCeachfor60sec.Thetestpieceshavebeenmoldedwithvariousconditionsof:

-moldingtemperature

-retentiontime

Alsotestpiecesmoldedwithconditionsof:

-differentdecompressiondegree

-lowpressure/lowspeed

2)Results

TheresultisshowninTable3-2.Neithertransformationnorblisterwereobservedwhenthethicknessofthetestpieceswasthin(0.5mmt).Meanwhile,transformationandblisterwereobservedatthicktestpiece(0.8mmt),anditstendencydependedonthemoldingconditions.

Itwasascertainedthattheblisteroccurredinsolderingtemperatureat250degreeCwhentheresinwasretainedincylinderfor15minutes.Alsotheblisterappearedinsolderingat210degreeCwhentheresinwasretainedandmoldedat380-400degreeC.

Changeofdecompressiondegreewasnoinfluenceonsolderingresistanceinthistime.

Asaresultoftheabovetest,themoldingtemperatureandtheretentiontimecanbeconsideredasmaincauseofblister.

Unfortunately,thecolorchangeoftestpieceisquitesmallevenifitismoldedafterretainincylinderat380degreeC(incaseof400degreeC,thecolorchangecanberecognizedsomewhateasily).

Thus,thepurgingprocedureisinevitablewhentheresinmayberetainedinthecylinder.Regardingthehotrunnersystem,thesituationwillbemoreseverethanabovementioned.

Ifdecompressiondegreeistoohigh,theairmaybetakenintonozzlefromnozzletouchportion.Thisairmaybecontainedtomoldingsandtheblistermayoccurinsolderingtest.

Table3-2Resultofretentiontest

Standardconditions:decompressiondegree2mm

V=50%,P=30%,cycletime=20sec

Lowpressure/lowspeed:V=30%,P=15%

"○"showsthatneitherchangeinformnorblisterwerefound.

3-5.Otherpossibilities

3-5-1.Theeffectofmoisture

SumikasuperLCPsindicateextremelylowwaterabsorption(0.02%)comparedwithgeneralplastics.However,themoistureintheaircondensesonthesurfacesofresinpellets.ThemoisturecausestheblisterorthedeteriorationoftheLCP.Themoistureneedtoberemovedbydryingbeforemolding.

recommendableconditionofdrying:

130degreeC,3hrandmore

Itisoftenfoundthatthehopperdryerisnothotenoughinspiteoftheindicatorofthedryershowinghightemperature(forexample130degreeC).Thereis2pointsforthecauseofthistrouble;

a)Thehotairisnotabletocirculatebecausethefilterofthedryerisstuffed.

-Inthiscase,whenyoumeasurethepellettemperature,itindicateslowtemperature(forexample40degreeC).

b)Thepelletsretainintheairservicelinebetweenhopperdryerandhopperoftheinjectionmachine,andthosepelletsmixwithnewerpellets.

-Ifthepelletsoncedriedbyheatarecooled,thenthemoistureintheaircondensesonthesurfaceofpelletagain.Therefore,thosecooledpelletsmustberemovedbeforemolding.

Fig.3-3Schematicviewofhopperdryerandservicelineofpellet

3-5-2.Draggingtheairintothemelt

Insomecases,draggedairintothemeltcausestheblister(theoxidationofpolymerwilloccurandcolorchangeorblackspotswillbeoftenobservedinthiscase:pleaserefersection4also).Thereasonsoftheairdraggedintothemeltareasfollows;

a)Toolowbackpressure

LCPneednothighbackpressure,however,toolowbackpressurecausesinsufficientremovaloftheairdraggedfromhopper.

b)Toohighdecompressiondegreeofscrewonmeteringprocess

Theairisdraggedintothemeltfromnozzletouchportion.

c)Toohighscrewrotationonmeteringprocess(over200rpm)

Thiscausesinsufficientremovaloftheairdraggedfromhoppersimilarlywitha).

Fig.3-4Schematicviewofcylinder

3-5-3.Unbalancebetweencylindersizeandmoldingvolume

Usingtoolargeinjectionmachineagainstmoldingvolume,measuringlengthbecomestooshort.Thentheretentiontimeincylinderbecomestoolong.Inaddition,excessiveshearingpowermaybeaddedtotheresinatthescrewprovidingzoneorthecompressingzonebecauseofhighenoughpowerofsuchlargeinjectionmachine.Insuchsituations,thedeteriorationofresineasilyoccur.

1)Testmethod

Using2injectionmachineshavingdifferentscrewdiametersdescribedTable3-3,thetestpiecesweremolded,andmeasuredthesolderingresistance.

Table3-3Resultofthesolderingtestusing2injectionmachineshavingdifferentscrewdiameter

2)Result

Fig.3-5showstherelationshipbetweenthemeteringfor1shotandthemax.meteringrange.Ifthemeteringfor1shotistooshortcomparedwithmax.meteringrange,theretentiontimeofpolymerinsidethecylinderbecometoolong,anditcausesthedeteriorationofpolymer.

Fig.3-5Therelationshipbetweenthemeteringfor1shotandthemax.meteringrange

SincealmostmoldingsmoldedbyLCPissmall,thesizeofsuitablemoldingmachineisasfollows;

strengthoftighteningmold:50-70Tons

insidediameterofcylinder:24-27mmφ

Forsmallerproducts:

strengthoftighteningmold:15Tons

insidediameterofcylinder:17mmφ

3-6.Conclusion

3-6-1.Moldingconditionsrelated

a.Dryresinforover3hrsat130degreeCandmore

b.Purgetheformerresincompletely(pleasereferthefollowingpageanddisplaythisnoticebesideeachinjectionmachine.)

-Sincepreviousresinmighthavebeenretainedinthemoldingmachineandturnedintogel,whichishardtoberemovedbypurging,cleaningofcylinder,nozzle,andscrewisavailable.

c.Placetheactualresintemperatureunder380degreeC

-Itisnecessarytomeasuretheactualresintemperaturebeforesettingthemoldingtemperature.

3-6-2.Equipmentsrelated

a.Checktheactualtemperatureofpelletsinhopperdryerandovenbythermometer.

b.Checktemperaturecontrollers,thermocouples(thermo-probeforcontroller),andheaters.

-Insomecases,controllersorthermocouplesareuncontrolablebytheirdamages.

PurgingMethodofSUMIKASUPERLCP

<Recommendablepurgingmaterials>

1)

PurgingReagentProduct ZCleanS11 (ChissoCorp.:JAPAN)

AmteCleanEx (MatsushitaAmtech:JAPAN)

2)

HDPE(HighDensityPolyEthylene)

3)

Regroundmaterialofthesamegrade(ex.SUMIKASUPERE6807L)

notice:Anyofabovematerialscanbeusedforpurgingmaterial,however,pleasedonotuseanyothermaterialsforthispurpose.

<Purgingprocess>

Procedure

Temperaturesetting

1)Endofmolding

Runoutofallprecedingpelletinthehopperandcylinder

sameasmolding

(Ex.360-365-330-290deg.C)

2)Feedingof

purgingmaterial

Startthepurgingwiththepurgingmaterial(ca.200g)

sameasabove

3)Decreasingsetting

temperature

Changethesettingtemp.at-20to-30deg.Cofmoldingtemp.duringpurging

(Ex.330-335-300-270deg.C)

notice:Donotstoppurging

4)Continuingthe

purging

Runoutofallpurgingmaterial

sameasabove

5)Increasingsetting

temperature

After4),stopthepurging,andchangethesettingtemp.atmoldingtemp.again

sameasmolding

(Ex.360-365-330-290deg.C)

6)Resumingofmolding

Assoonasarrivingatmoldingtemp.,feedthepellet,purgeatleast5shots,andresumethemolding

sameasabove

notice:

-Thispurgingmethodshouldbeexecuteonceaweekpreferably,oratleastonceatwoweeks.

-Pleasestoptheinjectionmachineaftertheabovestep4)iscompleted.

Startingprocedure:1)Setthetemp.assameas3).

2)Assoonasreachingthemoldingtemp.,thenfeedthepurgingmaterialinthehopper.

3)Followthesamestepfrom3).

4

Reductionofthebubbleaftermolding

4-1.Introduction

"Theblister"onthesurfaceofthemoldingsisrarelyobserved"aftermolding"formoldeditemsusingtheLCP.Andsuchmoldingsscarecelycauseany"theblisteraftersoldering".Sinceitoftenseemslike"theblisteraftersoldering",itisconfusedthat"theblisteraftermolding"iscausedbythesamereasonas"theblisteraftersoldering".

Toclarifythedifferencebetweenbothofthem,"theblisteraftermolding"isdefinedas"thebubble"and"theblisteraftersoldering"issimplydefinedas"theblister"inthisnote.

Inthissection,wewillbeginbycomprering"thebubble"and"theblister".

4-2.Comparisonbetween"thebubble"and"theblister"

Table4-1showsthecomparisonbetween"thebubble"and"theblister".Fromthistable,itisclearthattheseareeasilyseparatedbycarefullobservationof"theblisteringtrouble".Thesecircumstantialevidencessuggestthatthecauseof"thebubble"ismainlythedraggingtheairduringmolding.

Table4-1Comparisonbetween"thebubble"and"theblister"*

Item

thebubble

theblister

aftermolding

yes

rare

aftersoldering

rare

yes

arisingspot

fixed

random

thedecompositionofmaterial(withoutregardtocauses)

rare

yes

thedependenceofmoldingcondition

temperature

no

yes

speed

yes

alittle

pressure

alittle

no

thedependenceoftoolingdesign

cavitydesign

yes

rare

airvent

yes

alittle

*:theorderoffrequencyisyes>alittle>rare>no

4-3.Reductionofthebubble

Itisnecessarytoconsiderthefittingboththesuitablemoldingconditionandthesuitabletoolingdesignforreducingthedraggingtheairinthecavity.

(1)Suitableinjectioncondition

Asdescribedat3-5-2,draggingtheairintothemeltwillcauseboththebubbleandtheblister.Inadditiontothedescriptionat3-5-2,thefollowingprocedureismoreeffectivetoreducethebubble.

Toremovetheairinthesprueandtherunnersmoothly,theinjectionspeedshouldbesetatlower(ca.20~50mm/sec)duringthepolymerpassingthroughthegate,andafterthattheinjectionspeedshouldbechangedtomorehigherifnecessary(seeFig.4-1).Asdescribedatsection2,thecurrentproductshavingthinnerwallthickness(<0.2mm)needhigherinjectionspeed.However,itisoftendifficulttoremovewholeairinnot