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User`s Manual for SUMIKASUPER LCP

1. Cylinder temp setting Mold temp setting T Mold temp actual T Injection velocity V4 V3 V2 V1 N Nozzle C2 C1 Hopper actual temp Bubble Short shot Crack Sticking Flash Warpage Other mm sec b What kind of article Please draw it at the Sketch column if possible Position Metering c What kind of grade and lot Sumikasuper LCP mm position No Sumikaexcel PES lot No Back pressure kg cm MPa Decompression d When and how often has duration from Holding pressure P1 P2 it happened Suddenly happened during mass production Regularly happened during temporary testing Percentage of fault e How about dependency cavity Cavity No vs Fault f How about molding conditions lt Information of injection machine gt Injection machine manufacturer Type or grade name of the injection machine kg cm MPa X sec X X Injection time setting Cooling time setting Monitoring Actual filling time Min cushion Cycle time sec mm sec lt Note gt lt Sketching column gt Clumping Force Max injection velocity mm sec Screw diameter Max injection pressure kg cm MPa max screw rotation Number of
2. 300 P LCP E5000 5 250 piled g PES GF Q A PEEK GF 2 PPS GF PEI CDpelcr 150 PSF j z P i D 7 PAR LY conventional E P conyentional E P 9 GF a 7 50 0 50 100 150 200 250 300 350 TDUL C Fig 1 1 Relationship between TDUL and continuous service temperature Super engineering plastics not only have higher TDULs but also superior long term heat stability TDUL only L 1 Introduction of liquid crystalline polymer indicates short term heat stability Fig 1 1 indicates the relationship between TDUL and continuous service tempera ture This parameter equals long term heat stability and is measured under the conditions described in UL 746B As shown in the figure super engineering plastics indicate both higher TDUL and over 200 C of continuous service temperature This allows these plastics to be suitable for SMT soldering or other high heat treatments in general SMT soldering temperature is over 220 C Conventional engineering plastics will exhibit similar TDULs when reinforced by glass or fibers and thus perceived higher heat resistance It should be noted however that these polymers do not have as high of continuous service temperature resistance This means that conventional engineer ing plastics are not suitable for high heat treatment such as SMT soldering It is very important to think about the hierarchy of molecular structure when considering the macro dynamics of the polymer The molecule of
3. 00 10 20 30 40 50 60 70 80 Test piece thickness mm Thickness Skin Layer Fig 2 11 Thickness dependence of flexural modulus 24 Liquid Crystalline Polymer Injection molding technology for LCP In recent years there is strong demand for materials that can be used for lighter smaller and thinner products However thin wall portions less than 0 2mm are difficult to mold even if improved LCP grades are used In these cases the thin wall fluidity depends on the characteristic of injection molding machines The purpose of this section is to investigate the relationship between thin wall fluidity of LCP and the characteristic of injection molding ma chines 3 1 Control System of Injection Process Before investigating the relationship of injection machine we will begin by summarizing the principle of the con trol system of injection machine The condition of the injection process can greatly affect the quality of molding products There are two control sys tems open loop control and closed loop control 1 Open loop control pressure screw position Computerized Numerical Controller __ Setting value velocity pressure screw position Fig 3 1 Schematic view of open loop control Open loop control is a non feedback control system Since this system has comparably lower cost and simple structure many kinds of injection machines are used for a wide variety of plastic molding Ope
4. Cheng H M and Biswas A Macromolecules 21 39 1988 Biswas A and Blackwell J Macro molecules 21 3146 1988 ibid 21 ibid 3152 1988 ibid 21 3158 1988 9 Shibaev V P Talroze R V Korobeinikova I A and Plat N A Liq Cryst 4 467 1989 10 Brostow W Polymer 31 979 1990 Demus D Mol Cryst Lig Cryst 165 45 1988 ibid Lig Cryst 5 75 1989 11 Weng T Hiltner A and Baer E J Mater Sci 21 744 1986 Ide Y and Ophir Z Polymer Eng Sci 23 261 1983 12 Nagano S Plastics 45 55 1994 13 Hsieh T T Tiu C and Simon G P J Appl Polym Sci 82 2252 2001 14 Cheng S Z D Macromolecules 21 2475 1988 Cheng S Z D Janimak J J Zhang A and Zhou Z Macro molecules 22 4240 1989 Cheng S Z D Zhang A Johnson R L and Wu Z Macromolecules 23 1196 1990 15 Field N D Baldwin R Layton R Frayer P and Scardiglia F Macromolecules 21 2155 1988 Chung T S Cheng M Pallathadka P K and Goh S H Polym Eng Sci 953 39 1999 Wiesner U Laupretre F and Monnerie L Macromolecules 27 3632 1994 Nam J Fukai T and Kyu T Macromolecules 24 6250 1991 16 Blundell D J and Buckingham K A Polymer 26 1623 1985 MacDonald W A Mol Cryst Lig Cryst 153 311 1987 17 Troughton M J Unwin A P Davies G R and Ward I M Polymer 29 1389 1988 Green D I Orchard A J Davies G R and Ward I M J Polym Sci part
5. Neat resin Company Trade Name Capacity t Y Sumitomo Chem Sumikasuper LCP 6 000 Ticona Vectra Polyplastics 7 000 DuPont Zenite 5 500 Solvay Xydar 4 500 Toray Siveras 1 000 Others Ueno LCP Rodrun etc 1 000 World Total 25 000 26 000 For your reference the portfolio line up of Sumikasuper LCPs is shown in Fig 1 22 There are 3 or 4 different base resins from lower side E6000HF lt E6000 lt E4000 lt E5000 Lower temperature grades such as E6000HF E6000 and E4000 must be moldable by using a conventional injection machine having heating ability up to 400 C however the most highest temperature grade E5000 needs the more higher ability for heating over 400 C In general such in jection machine must be special specification during ordering Table 1 7 Temperature range of each trade name LCP DTUL C In addition each base resin has several compounding grades with special formulations of fillers Each formulation is optimized for its special usage or application We would like to reveal the relationship between application and suit able compounds in the next section 1 7 Conclusion LCP has the following merits ie 1 Introduction of liquid crystalline polymer Superior thermal resistance This merit brings higher soldering resistance including Pb free soldering for electronic application Shear induce molecular alignment This effect brings very low melt viscosity for fine amp precise mold Self
6. You should refer following section a Effect of moisture A 3 Thermal decomposition of LCP The cause is longer retention time in cylinder or local over heat of cylinder In general since LCP has excellent heat stability it is hard to decompose itself except the case of causes above mentioned You should refer following sections 54 Liquid Crystalline Polymer b Retention of resin at the inside of injection machine c Temperature settings of injection machine Difference between setting value and real resin temperature d Relation between retention of LCP in cylinder and blister e Unbalance between cylinder size and molding volume B Contamination of other material B 1 Contamination of former material Insufficient purging is the cause of this problem It is important to carry out the recommendable purging procedure and to use the suitable purging material You should refer following section f Purging method of Sumikasuper LCP B 2 Contamination of purging material Sometimes the purging material also becomes the cause Only recommended purging material should be used for this purpose You should refer following section f Purging method of Sumikasuper LCP a Effect of moisture LCPs have extremely low water absorption 0 02 compared with general plastics However the moisture in the air can condense on the surfaces of resin granules This moisture can cause blistering or deco
7. o 5 40 O i T 20 po cpana aa oo Sumikaexcel PES 0 10 20 30 40 50 GF content Fig 2 3 Relationship between GF content and anisotropy Sumikasuper E6000 thin wall flow length mm U O 5 0 10 20 30 40 50 GF content Fig 2 4 Flow length dependence with GF content With this background we can turn now to the latest design of FPC Flexible Printed Circuit board connector We should think about the flow balance with main flow portion and side rib In generally conventional design has more than 0 3mm thickness at not only the main flow portion but also the rib portion The latest designed FPC con nector often has under 0 2mm thickness for both main flow portion and side ribs comparison between a and b in Fig 2 5 In this case long fiber is not able to flow from main flow portion to rib portion because the length of GF is not neg ligible This unbalanced flow will induce serious molding troubles such as short shots weld line cracks and war page In this case short GF formulation or the formulation short GF using inorganic filler together is one of the im provements Short GF has less ability to reduce the anisotropic character than long GF however as shown in this case the flow balance needs priority more than anisotropy Fig 2 5 b 19 2 Application of LCP and its technology a Conventional design having comparably thicker wall thickness b The latest design having thinn
8. 48 Liquid Crystalline Polymer hardly shrinkable Grip portion AA NA warpage a Before installing the core outs b After installing core outs Fig 4 21 Idea for improving the warpage for CPU socket 49 5 Trouble shooting during injection molding of LCP Trouble shooting during injection molding of LCP As mentioned Liquid Crystalline Polymer LCP has different properties in its molten state during molding as well as the finished part This often makes it difficult to solve several technical problems involving molding This diffi culty is due to less systematization of the polymer processing technology Many molding engineers depend upon tradi tional experiences which are often not based on chemical and rheological backgrounds In the case of conventional plastics this is not an issue as the rhological properties for each polymer depends upon similar theoretical characters even if the plastics having the different chemical structure will be used However the rheological properties of LCP are again very different thus the molding of LCP requires a somewhat different background or knowledge For example consider the crack problem of weld line In general this problem is induced by separate flow fronts from separated flow holes insert pins or un uniform thickness The text book polymer processing proposes the optimization of molding conditions including modification of mold design By increasing of pressing force betwe
9. Fig 4 4 Schematic view of model mold L n warpage flat board MMMM Ve Fig 4 5 Measuring of warpage 41 5 Trouble shooting during injection molding of LCP E6006L GF 30 E6807L GF mineral 35 warpage mm 0 200 400 600 800 1000 injection speed mm sec Fig 4 6 Relationship between injection speed and warpage After this the anisotropy at the surface of molded part was evaluated by measuring of the infra red dichloic meas urement technique Fig 4 7 shows the infra red spectra with using polarizer directed to both MD Molding Direc tion and TD Transverse Direction of the molded part by using FT IR equipment type FTS 40 with microscopy unit manufactured by DIGILAB The 1500 and 1600cm bands are ascribed to aromatic ring vibration and the 1735cm band is ascribed to the stretching of ester carbonyl group Since the surface of LCP molded part is oriented to the MD direction the transition moment of the benzene ring must be coincident with the direction of the molecular axis which indicates the flow direction of LCP at the measured portion In case the dichloic absorbance ratio D and the secondary orientation factor f forms the following relation ship f D 1 D 2 here D A A A is absorbance of MD A is absorbance of TD A 1 0 L 0 5 Polarized to TD oh D U C 0 0 G A a 0 5 Polarized to MD X 1 0 l 3500 3000 2500 2000 1500 1000 wave n
10. 11 recommendable gate position 3 Weld crack at the hole of Board to Board Connector Fig 5 19 shows a typical housing part of a board to board connector with 0 5mm pitch contact pins Core outs are already installed in the base section to improve warpage If the crack is caused by the low weld strength there is only way to improve it as shown in Fig 5 20 This is to change the direction of springs and to remove the stress from the weld portion Top DOO 000000 pka nwa iN 1 O H EA O OOOQOOO0O OD 0000000 00000000000 00000000000 00000000 0000 Bottom view The crack trouble has occurred at this portion Fig 5 19 Schematic view of the board to board connector 0 5mm pitch 70 Liquid Crystalline Polymer side wall side wall pin spring structure pin spring structure The crack occured No crack occured Pin structure A Pin structure B Fig 5 20 Relationship between the stress direction by the spring structure of pins and the crack However if the only reason of the crack is the low weld strength why does the crack occur near the gate side in this case And this is not a rare case when once the crack problem occurs If you observe the flow pattern carefully usually using the short shot molding you will be able to understand the flow pattern of this case as Fig 5 21 The formation of the weld lines is not equal for the whole portion of the holes Fig 5 22 shows the difference of the weld portion bet
11. 1b will probably become a reality In this theory it is not necessary to think about the volume shrinkage in terms of thickness This is different then conventional plastics as explained above According to our investigation and experiences almost all cases can be expressed by this flow pattern That is it is reasonable to think that the warpage of LCP molding is controllable by I 5 Trouble shooting during injection molding of LCP fitting to more suitable flow patterns a Flow pattern model b Direction of warpage flow pattern oe S gate Fig 4 2 LCP flow model Three possibilities are recommendable to fit the flow pattern First of all thickness equalization of all portions should be considered This is the first step and the most impor tant In the case of the part having both thick and thin portions the reduction of warpage is usually difficult Thicker portion should be thinner and thinner portion should be thicker This procedure is sometimes difficult to carry out due to restrictions such as product design or function However it should be noted that 0 0 1mm modi fication of the thickness sometimes could modify the flow pattern The reason of this effect is that the latest de signed part generally has under 0 5mm thickness and sometimes under 0 3mm In these cases 0 0 1mm difference is not negligible We recommend that 0 01mm modification should be tested usually this kind of modification seems as hair line bu
12. B Polym Phys 28 2225 1990 Ward I M Makromol Chem Makromol Symp 69 75 1993 18 Jin X and Chung T S J Appl Polym Sci 73 2195 1999 Sueoka K Nagata M Ohtani H Nagai N and Tsuge S J Polym Sci part A Polym Chem 29 1903 1991 1 S Nagano H Yamauchi and M Hirakawa Sumitomo Chemical 2001 20 Naitove M N Plast Technol 35 31 1985 81 5 Trouble shooting during injection molding of LCP 21 Data were adapted from following references PEEK Sumitomo Chemical Technical Note PEEK 16 32 PPS Mitsubishi Engineering Plastics general catalog G 2 11 1994 PES Sumitomo Chemical Sumikaexcel PES catalog 4 PC Mitsubishi Engineering Plastics general catalog G 2 1 1994 LCP Sumitomo Chemical Technical Note 26 5 22 S Nagano ET 52 No 4 72 2004 23 ibid S Nagano M Maeda and H Nomura SeikeiKako 97 prepn 333 1997 S Nagano M Maeda and H Nomura JP A10 323870 235 Sumitomo Chemical private technical letter 3 1994 E Nomura H Honda Y Chikaishi K and Watanabe Y SeikeiKakou 91 prepn 117 1991 for instance Nishikida K et al Material analysis by Infra Red spectra Kodansha pub 1986 Pretsch E Clerc T Seibl J and Simon W Tabellen zur Structuraufklaerung organischer Verbindungen mit spektroskopischen Meth oden Springer pub 1981 8 ed Polymer Society Solid structure of polymer Kyoritsu pub 1984 29 Y Murata and H Yokoi Se san
13. PEEK GF filled natural color black LCP GF filled natural color black white Equipment IR emission thermometer IT 240S Horiba spot diameter 1 2mmf focus 64mm emission ratio 0 86 sensor eq ee 7 rder N hopper ee s m S VWVMVVV lt lt W lt VWMV VWM CMMMea Yi Vz 2mm Fig 5 4 The measurement of actual resin temperature lt Result gt The result is shown in Table 5 5 Almost all cases show that the actual resin temperature greatly differs from the set ting temperature Table 5 5 Result of temperature measurement No Injection machine Injection rate Temperature Molding Setting temp cm sec control system material C Metering 1 Vertical type 27 ON OFF type PES 3601GL30 380 400 407 A company GF 30 20 25 2 ditto 27 PID ditto 380 375 380 GI U 3 Vertical type 89 ditto ditto 370 395 400 B company 25 30 4 Horizontal type 1 114 ditto PES 3601GL20 380 380 385 B company GF 20 0 5 5 ditto 114 ditto PBT GF30 270 275 280 5 10 92 Actual temperature C Purging 400 440 20 60 400 20 407 37 360 364 20 16 270 0 5 Trouble shooting during injection molding of LCP 6 Horizontal type 2 42 ditto LCP R 408 m 375 390 B company GF40 18 33 1 Using IT 240 infrared emission thermometer Horiba Ltd spot size 1 2mm emission rate 0 86 2 Measured at drawing strand from nozzle during purging pro
14. Schematic view of cylinder b Suitable injection condition As described above dragging air into the melt will cause both the bubble and the blister In addition to the descrip tion the following procedure is more effective to reduce bubbles To remove air in the sprue and runner smoothly the injection speed should be set lower ca 20 50 mm sec as the polymer passes through the gate After this the injection speed could be increased if necessary Fig 5 8 As de scribed at section 3 products having thinner wall thickness lt 0 2mm will need higher injection speed However it is often difficult to remove air not only in the cavities but also the sprue and runner from the air vents Usually the in jection speed is very high gt 100mm sec and the injection time is too short ca lt 0 1 sec c Suitable cavity design After improving the injection conditions the bubble may still remain at the thinner wall of the products The cause is thought to be air in the cavity that is dragged with the polymer flow as shown in Fig 5 9 A similar phenomenon was observed for calcium carbonate and long glass fiber reinforced PP by Yokoi et al According to Yokoi et al in the case of higher injection rate And Tsuji et al expanded this phenomenon to LCP theoretically by computer simulation using expanded Doi equation In this case the bubble is often observed at the thinner position beside the thicker por tion Fig 5 10 We often recommend
15. Since the polymer molecules are very long and tangled the entire polymer molecule cannot crystallize completely In addition some chemical structures hesitate to form crystallites and the molecular chain will be packed randomly These polymers are called amorphous polymers Fig 1 3 b By this reason the crystallinity of amorphous polymer is estimated as 0 The crystallites of a crystalline polymer scatter the visible rays Thus crystalline polymers are often opaque On the other hand amorphous polymers and the crystalline polymers having smaller crystallites than the wave length of visible rays are usually transparent Of course filled or reinforced polymers should be excluded in this case even if they are amorphous Both crystalline and amorphous polymers have Tg glass Transition Temperature where the molecules start mov ing by heat energy Only crystalline polymers indicate Tm Melt Temperature where the crystallites melt Both Tg and Tm are the typical measurements to determine the polymer properties Some polymers have rigid rod molecular structures that are described by the liquid crystalline transition tempera ture Tio In general these plastics are called Liquid Crystalline Polymers or designated LCP Here we would like to presume the simple molding model again using matchsticks Let us imagine that a matchbox filled with matchsticks is overturned above the funnel At first the matchsticks will remain in the upper portion
16. core out and the warpage We have also investigated the effect on warpage of the depth of core outs Fig 4 9 shows a modified model mold for this investigation The core outs were installed as shown and their depth could be modified from 0mm to 0 8mm 1 2 of bottom thickness Results are shown in Fig 4 10 The warpage was reduced with increasing the core out depth This was observed for all grades of LCP tested It is expected that this is due to the changes in the flow pattern This was confirmed by observation of short shot samples seen in Fig 4 11 The difference of the flow length between thick portion bottom and thin portion top side rib became smaller and smaller with the core out depth changed deeper and deeper This means that the main flow at the thick portion bottom was inhibited by the core outs and the flow pattern was equalized gradually So far we have outlined the relationship between flow pattern and warpage using our experimental results It seems that the observation of short shot molding is one of the most useful and important step to evaluate the flow pattern Of course recent computer simulation technology progresses very quickly and we expect that prominent software will enable more accurate evaluation in near future However we cannot yet recommend to only believe in the simulation results without further empirical test since the accuracy of simulation software is not high enough yet We should still pay attention to sho
17. filled material the clearance between inside surface of the cylinder should become bigger This clearance difference will be also the cause of unstable metering and short shot The third step is the purging To make a habit of purging regularly is preferable to prevent the generation of black spec The details are described at section 5 4 2 f e 5 Trouble shooting during injection molding of LCP 5 4 Blister amp Bubble Blistering is a very common molding problem for LCP This problem causes serious complaints from end customers since it appears on the surface of molded parts The general perception is that this problem occurs when the thermal stability of the material is insufficient or that the procedure to remove moisture is not suitable similar to the reason of silver streaking in conventional plastics Of ten people doubt the thermal stability of LCP and are nervous about the drying temperature setting Indeed there is merit to these concerns however with careful observation you will note that there are 2 cases One is mainly observed just after molding and another is mainly observed after soldering We call that the former is bubble and the latter is blister because we think both of them are induced different reason First of all we would like to classify bubble and blister 1 Comparison between bubble and blister Table 5 3 shows the comparison between a bubble and a blister From this table b
18. fillers works better for this property Weld portion fe iy k E ve oe 1D gt Tt E amp m amp MD gt WW 7 i hy a 2a mae 7 n m Weld portion Fig 1 22 Schematic view of flow pattern at weld portion 1 6 Market situation of liquid crystalline polymer Several suppliers of LCP are known in the world Fig 1 21 shows manufacturers of LCP and their history of com mercial production At the moment there are 6 major suppliers half of them are in USA and other are in Japan For mer customers of LCP were distributed in both USA and Japan 10 years ago but now customers have expanded to Europe and Asia south east and east In recent years the Asian market share has become 80 of global demand because customers have moved their production facilities to Asian countries such as China ASEAN countries Korea etc On the other hand the suppliers of LCP have reduced during this decade Additionally several suppliers worked for marketing or trial production purposes in the past however the selection advanced Now there are 4 major trade names and subsequent 3 or 4 trade names 1971 1979 1984 1988 2000 Carborundum Dartco 1987 Amoco Solvay I NitonEkoiol Co esale Niss kd Chemical Sumitomo Chemical 1994 SN ce Du pont 1984 1998 Hoechst Celanese Ticona H Resale Polyplastics ot 1988 ray Ueno PE aaa cst srt geese sa eo E ieee jogs oa Unitika Il 1985 Mitsubishi Chem Fig 1 23 History of LC
19. however we recommend not using any other materials for this purpose 1 Purging Reagent Product Z Clean SIl Chisso Corp JAPAN Amte Clean Ex Matsushita Amtech JAPAN 2 HDPE High Density PolyEthylene 5 Trouble shooting during injection molding of LCP 3 Reground material of the same grade ex SUMIKASUPER E6807L We also recommend that the purging procedure described below see Table 5 10 should be followed In general since the purging materials have less thermal stability than LCP it is not preferable to leave the injection machine filled with purging material at the higher LCP molding temperature It is important to quickly remove the purging material when using LCP molding We also recommend that this kind of purging procedure should be carried out at least once a week even if you are not switching to other plastics The 5 to 10min investment in time is very worthwhile Carrying out this procedure fre quently reduces the generation of materials in cylinder and black spec generation Table 5 10 nen process Procedure CC emperature setting cylinder Ex 360 365 330 290 C purging material 200g temperature temp during purging notice Do not stop purging purging 4 stop the purging and change the setting temperature temp at molding temp again Ex 360 365 330 290 C ace gt soon as arriving at molding temp feed the pel same as above let purge at least 5 shots and resume the molding This p
20. is due to its typical melt viscosity behavior as shown in Fig 1 16 After liquid crys 2 1 Introduction of liquid crystalline polymer tal transition temperature the melt viscosity significantly decreases As the temperature is increased more and more there is lower dependency of the melt viscosity Itis called plateau region in general The most preferable tem perature region for injection molding is this transition temperature region and its width is around 10 C If the tem perature is lower than this transition the generation of Skin Core layer will be insufficient because of insufficient melt of LCP On the other hand if the temperature is higher than this transition the melt viscosity will be too low and un controllable for the molding This is the reason why the molding condition of LCP 1s relatively narrow The molding temperature should be set on this transition region of the melt viscosity A further important point is that the dependency of melt viscosity with temperature is relatively higher with LCP s than other plastics This tendency is similarly observed at the relationship between shear rate and melt viscosity As shown in Fig 1 17 LCP s show strong shear thinning property Accordingly LCP s exhibit excellent flowability under moderate temperature and higher shear rate condition In contrast this stronger dependence of melt viscosity with temperature and shear rate can cause other kind of prob lems 500
21. of the funnel However by adding a small vibration that puts the direction of the matchsticks in order the matchsticks will flow out from the throat of the funnel very smoothly Fig 1 4 In this case Z Liquid Crystalline Polymer the matchsticks are like the rigid rod molecules of liquid crystal polymers The action of adding vibration is like adding shear stress of molding to the polymer amorphous region crystallite a micelle model of crystalline polymer after cooling 2 Vv ON AN a LX RE a ea a ta a bmi sway eS N K polymer melt N over melt temperature Olam CL RFR z ZAD SIV MOS su Pq CL TXT YVR IN ASE SO ifs d K Ae A R q RAY AANA LORS on Wan PSR DY Ot ai One UA eS A a SRD q h Ly e4 y EA b glassy state of amorphous polymer Fig 1 3 Three dimensional model of crystalline and amorphous polymers You can also imagine that the rigid rod structure of a matchstick will be more suitable than the yarn ball due to the yarn never flowing out from the funnel throat without higher force This resembles LCPs which have extremely low melt viscosity and higher flowability and do not need the higher injection pressures required for conventional polymers Since the molecule of LCP is rigid it will form semi crystalline structures that are strongly oriented in one direction Bundles of the molecules align in both directions so that the poly
22. permeate into the every gap of un melted granules If such melt portion reaches to lower temperature region at screw side it will solidify again and paste to the granules heat om aoe a es auii higher temperature region an C V BAEAN AK ANS LE ova lower temperature region DA Q me SCrew Fig 3 17 Schematic view of cross section of cylinder Since the melt of LCP has significantly lower melt viscosity than conventional plastic melt it will easily climb over the screw edge through very small clearance between screw edge top and cylinder wall Fig 3 18 This means that back flow easily occurs for LCP If this pasted portion is generated it will rotate with the screw and lose its transportation force of materials from hopper side to nozzle side Eventually this pasted portion will prevent and plug the transportation of the material This plug is usually generated at the portion where the heat supply arrives to the critical value for melting of the granule This is especially at the compression zone of screw because heat comes not only from the outside heater but also inside by heat insulation compression Once the plug is generated the latter material is not supplied from the hopper side due to the plug although the melt material at the nozzle side from the plug will spend to the molding Then the melt material at the nozzle side 1s lost gradually and becomes hollow This situation is called as the starvation state It continu
23. polymer can often be compared to a chain or a thread of yarn In this case let us pre sume that there are about 30 pieces of yarn cut at 30cm length and then crumpled into a ball The crumpled yarn ball is then put into a funnel that has enough spout diameter in order to pull the pieces out At first the yarn will not pull out because the diameter of yarn ball is larger than that of spout If you wish to pull the pieces out you must push the ball with stick or rod from the topside of the funnel This is very similar to the molecular situation dur ing injection molding Injection molding is the molding system where molten polymer molecules with random coil shapes are pushed into the mold by high pressure They then take the form from the mold after cooling Fig 1 2 pressure yarn ball glass funnel Fig 1 2 Schematic model of general polymer during molding process Parts of the molecule chains are sometimes folded regularly during the cooling process Such folded polymer chains will assemble together through affinity Assembled portions are called semi crystalline or crystallites Since these molecules form in lines they are called crystals Fig 1 3 a Such polymers having both crystallites and not crystallized portions usually called amorphous are called crystalline polymer In general the crystal linity of crystalline polymers is up to 30 before annealing or heat treatment for increasing the crystallinity
24. problems after heat treatment such as IR reflow soldering or a post baking process Nevertheless sometimes the blister problem occurs after molding or after soldering The rea son and solution of this problem will be discussed later EA 120 C 20hr Gaschromatographchart grap Molede product sealed in glass bottle Head space Dumb bell 5g gaschromatograph Fig 1 13 The evaluation method of outgas In general the main portion of outgas is an unknown organic portion Acetic acid phenol and its derivatives are also detected in outgas The origin of such chemicals is further supported to be decomposition of LCP Table 1 4 100 l I 80 i al e I 60 i i 1 Sumikasuper LCP 40 s E500 I a E4008 20 r E6008 total amount of outgas ppm 200 300 400 molding temperature C Fig 1 14 Comparison of total amount of outgas Table 1 4 Outgas portion of LCP unknown organic materials with low boiling point 2 CH COH acetic acid O je ou Ho C oH etc phenol derivatives O jo phenol 1 3 Moldability LCP has very low melt viscosity property at molten state For this reason LCP s exhibit excellent flowability Fig 1 15 shows the temperature dependence of flow length at 1mm thickness bar flow with conventional engineer ing plastics As shown LCP s indicate much higher flow length but stronger dependence of temperature than the conventional plastics The reason
25. the resin at the inside of the nozzle the tip parts of the screw and the compression zone Especially the inside portion of the nozzle is the most important The carbonized LCP formed carbon pipe was often observed after long term production Moreover the diameter of the carbon pipe was usually 4 to 5Smm in general It is significantly narrow for the conventional plastic because of the pressure loss but it is sufficient for LCP molding On the contrary the inner diameter of the nozzle should be 4 to 5mmo for LCP molding If the inner diameter is rela tively wide the nozzle tip behaves one of the barriers of material flow due to extraordinary high dependency to the shear rate of melt viscosity of LCP In the same meaning the shut off nozzle mechanism behaves the same kind of barrier of melt flow Open nozzle should be used this was confirmed by comparison between open and shut off nozzle under the cooperation of an in jection machine manufacturer Recently many injection machine manufacturers provide special designed nozzles for LCP molding Following are the recommendations a The open type nozzle should be used for Sumikasuper LCP The shut off type nozzle is not suitable the shut off valve and its surrounding portion causes the residue which will change to the cause of black spots and the blister b The internal diameter of the nozzle should be 4 5mm the standard size ca 8mm which is not suitable for Sumikasuper LCP
26. typical pattern which is very similar with a so called flow marks It often becomes an obstruction when an LCP molded part is used for exterior parts whose ap pearance is regarded an important property The reason of this phenomenon is not clear but it may be due to the reflec tion of light upon the LCP molecular alignment at the surface This difference of alignment should be induced by the flow pattern of LCP during the flow In general the melt polymer flows in the manner of so called fountain flow Fig 5 24 However it should be ob served under the ideal condition or some special circumstances Indeed the thin walled part indicates a comparatively smooth surface It seems that the reason for this is from the melt polymer flowing in the fountain flow as mentioned above Y Mi Fig 5 24 Schematic view of fountain flow On the other hand it is known that the melt polymer meanders in the cavity for general cases As indicated by H Yokoi et al the melt polymer flows as the same manner as shown in Fig 5 25 In this case some of the melt contacts the mold wall but other parts flow with the flow eddy do not touch the mold wall UY ph light light light light dark dark dark Fig 5 25 Schematic view of eddy flow For LCP molding such unbalanced flow is the reason of the flow mark phenomenon shown in the figure This is due to the difference of orientation of the LCP molecules on the surface and different reflectivi
27. C display applications They are used to improve problems with low molecular weight LC Among these structures main chain and nematic LCP is the most important almost all LCPs produced commer cially are included this category Table 1 2 shows typical molecular structure with classification of TDUL As seen in this table all LCPs include a p hydroxibenzoic group as a mesogen but the other components are not equal The different combination of reactive groups monomers gives the different thermal resistances In general LCP is classified in three types of categories Type III is the lowest thermal resistance category and includes the early de veloped LCP X 7G manufactured by Eastman Chemical Type I is the highest heat resistance category and it indi cates more than 260 C of TDUL Main Chain Type LCP Side Chain Type LCP Combine Type LCP mesogenic unit Fig 1 8 Proposed chemical structure of LCP It needs to be emphasized that the chemical structure of each LCP is different from each other This means that each LCP manufacturer may have different properties although total properties are categorized as liquid crystalline polymer This is very similar to polyamides as well For instance PA6 and PA46 indicate much different thermal resistance however both of them have relatively higher water absorption and poor dimension stability vs polyesters Different thermal resistance is derived by their own chemical structure but
28. CP behavior Thereafter we filled more contents of useful information over 10 years and it becomes workable brochure for not only experts but also beginners of LCP molding The 1 section expresses chemical and physical properties of LCP which will become the basic to understand LCP behavior theoretically It also discloses the market situation of LCP industry The 2 section discloses examples of LCP application and concept for electric and electronic parts It will help you when you choose more suitable grade for your applications or items The 3 section shows a methodology from a little different point of view This section discloses that the performance and specification of injection molding machine are also very important for LCP molding It tends to be ignore but it sometimes influences whether you obtain molding part successfully or not The 4 section indicates several know how to solve warpage problem for connectors with actual examples This in formation will help you to develop the latest precision connectors or such electric and electronic parts successfully The last section 5 is the most important section when you suffer the molding trouble This section covers almost whole solution during using LCP December 2006 Electronic Materials division Sumitomo Chemical Co Ltd Liquid Crystalline Polymer Introduction of Liquid Crystalline Polymer Liquid crystalline polymers LCPs are widely used in many types of electric an
29. It was ascertained that the blister occurred at soldering temperatures of 250 C when the resin was retained in cylin der for 15 minutes Also the blister appeared in soldering at 210 C when the resin was retained and molded at 380 400 C Change of decompression degree had no influence on the soldering resistance in this time As a result of the above test the molding temperature and the retention time can be considered as main cause of blis ter Unfortunately the color change of the test piece is quite small even if it is molded after retaining in cylinder at 380 C in case of 400 C the color change can be recognized somewhat easily The purging procedure is inevitable when the resin is retained in the cylinder Regarding the hot runner system the situation will be more severe than above mentioned If the decompression degree is too high the air may be taken into nozzle from nozzle touch portion This air may be contained to moldings and the blister may occur in the soldering test Table 5 6 Result of retention test _ Soldering Temp test Condition Molding condition 210 Cx 6 250 Cx 6 Osec Osec 360 Cx standard conditions po fo o 360 CxX standard conditions Ss aftermoldi 360 Cx retention for 5 min 360 CX retention for 10 min 360 CX retention for 15 min 380 CX no retention 380 CX retention for 5 min 380 CX retention for 10 min 380 CX retention for 15 min 400 CX no retention 400 Cx retention for 5
30. K enkyu 43 No 11 537 1991 30 R T Maher and H T Plant Modern Plastics May 78 1974 C Maier Polym Eng Sci 36 1502 1996 31 A Galskoy and K K Wang P ast Eng 34 11 42 1978 32 H Yokoi and H Matsuda Seke kakou Symposia 98 271 1998 H Matsuda and H Yokoi Se san Kenkyu 51 267 1999 33 T Tsuji and S Chono Sekel Kakou 13 634 2001 34 A Takeuchi English for the understanding of plastic Kogyo Chosakai J apan p 226 1996 35 D V Rosato and D V Rosato Injection Molding Handbook Van Nostrand Reinhold New York 1986 I 1 Rubin Injection Molding Theory and Practice p249 Wiley New York 1972 36 K F Wissbrun Polym Eng Sci 31 1130 1991 37 M Richardson Rheol Acta 24 509 1985 38 apanese patent J P A05 125259 J P A09 143347 etc 82
31. Liguid Crystalline Polymer User s manual for Sumikasuper LCP version 3 1 amp SUMITOMO CHEMICAL Electronic Materials Div Version History ver 1 0 5 February 1996 ver 2 0 27 July 1998 ver 2 5 25 May 1999 ver 2 6 18 January 2002 ver 2 6 1 6 February 2002 ver 2 7 27 May 2004 ver 3 0 30 May 2006 ver 3 1 11 December 2006 1996 by Sumitomo Chemical Co Ltd Electronic Materials Div Tsukuba R amp D Center 6 Kitahara Tsukuba Ibaraki JAPAN 300 3294 tel 81 29 864 4177 fax 81 29 864 4745 http www sumitomo chem co jp sep english Copyright Notice All Rights Reserved at Sumitomo Chemical Co Ltd Tokyo Japan Reproduction or translation of any part of this work without the express written permission of the copyright holder is unlawful Requests for permission and translation or electronic rights should be addressed to Sumitomo Chemical Co Ltd at the address above Disclaimer This document is designed to provide information concerning engineering technology for injection molding of liquid crystalline polymer It is provided with understanding that Sumitomo Chemical Co Ltd is not engaged in no infringement of the intellectual property of the third parties during enforcing applying processing and using all information described in this document ii Liquid Crystalline Polymer lt contents gt 1 Introduction of liquid crystalline polymer 1 1 General properties of LCP 1 2 Thermal r
32. P in 2003 is estimated to be approximately 8000MT yr Before introducing the grades for this application we will begin by considering the Surface Mount Technology SMT 1 Surface Mount Technology SMT This technology comes from the integration of electronic devices This is needed due to the limited area or vol ume available when minimizing electronic equipment It is said that Japanese company SONY has developed this technology to realize the mobile gear Walkman For integration of electronic circuits all devices must be mounted and soldered on the same side of the printed cir cuit board This realizes at least 2 times integration of device mounting because both side of printed circuit board can be used instead of one side use for conventional soldering technology Fig 2 1 shows comparison between conventional technology and SMT for soldering For conventional soldering devices are mounted at the certain position where the terminal holes are set Soldering will be carried out at the oppo site side of mounted device In this case soldering heat will be added from the opposite side of circuit board For this reason the devices do not demand higher soldering stability over 240 C 240 C means the soldering temperature for conventional solder For SMT however solder is printed before mounting usually paste solder is used and devices will be mounted at the certain position The printed circuit board with mounted devices will int
33. P indicates much more different mechanical and chemical properties from each other skin layer i highly oriented 4o _ mo core T mold i flow direction fountain flow Fig 1 9 Schematic view of fountain flow The thickness of skin layer is usually 200um under the appropriate molding conditions However molding condi tions strongly effect the generation of this Skin Core structure or thickness If strong shear force is derived by high shear rate under appropriate temperature the skin layer will be very defined until 200um However if the shear force 1s lower by the reason of lower shear rate and lower temperature not only will the skin layer thickness be less but also the Skin Core structure can disappear This will affect the fixed or stable character of LCP The core layer must disappear under 0 4mm 400um of the total thickness if the thickness of skin layer is always 200um However the skin layer comprises many stratified sub layers and micro layers Often some of the sub layers or micro layers must work like a core layer during the route of melt flow This sublayer structure is like a shell of a pie or a bamboo sheath as shown in the picture of Fig 1 10 left Each layer is very thin and strong but can peel of easily For this reason the skin material is generated when the surface of molded part is abraded or the gate is cut obliquely The reason of this abrasion is thought to be due to weak intermolecular attra
34. P production Table 1 6 shows the capacity of major suppliers of LCP with their trading names On 2004 total capacity of neat resin reached around 23 000 T y and this satisfies around 80 of demand However from 2003 to 2004 IT market including not only Personal Computer market but also OA applications expanded again with several 10 ratio than a year ago For this reason the demand and the supply of 2004 were tight It seems that all suppliers are planning to expand their production capacity within a few years Table 1 7 summarizes the temperature range of each trade name of LCP As shown this table the strategy of each 14 Liquid Crystalline Polymer supplier can be seen Major suppliers make efforts to expand their portfolio line up to cover wide temperature rages for wide variety of applications Usually the suitable temperature range is determined by molecular formulation Each supplier prepares to supply several base resin grades having different molecular structures Since each molecular structure requires the most suitable temperature region during processing keeping the temperature should be noted Especially since LCP has much excellent thermal property the suitable processing temperature is also very higher than conventional plastics Sometimes it reaches at over 400 C It is very important to confirm that your molding machine is suitable for this processing temperature before using Table 1 6 Production capacity of LCP supplier
35. Sumikasuper LCP A E7006L E6008 E4008 E amp E 400 5 q 300 E5008L lt P 5 200 re s PPS DLL pe PES3601 GL20 PEEK 450GL20 0 250 300 350 400 450 Process Temperature C Fig 1 15 Flow length 1mm thickness 10 y 10 sec D 10 mt amp PEEK PET 10 E5008 4008 Sumikasuper LCP 102 250 300 350 400 450 Temperature C Fig 1 16 Temperature dependence of melt viscosity The major problem is that it can bring quick solidification After flowing into the mold cavity heat will be removed from the melt polymer by the cooling effect of the mold This small decrease of polymer temperature will cause of huge increase of melt viscosity In extreme cases polymer will not be able to flow This effect is one of the merits of preventing flash and reason why LCP doesn t exhibit this The second problem is that this effect can cause flow hesitation Flow hesitation is mainly observed during injec tion molding of LCP It can be seen to hesitate the flow into the cavity of the mold even if the cavity is near the en trance of the flow 10 Liquid Crystalline Polymer Amorphous No Melt Viscosity log n Newtonian Shear Rate log Y Fig 1 17 Schematic view of the relationship between shear rate and melt viscosity Since the flow of LCP is prevented by something ex small size gate thin wall portion divergence etc the shear rate will be reduced Fig 1 18 corresponding to the sh
36. about the generation of Flash because excessive increase will produce unexpected decrease of the melt viscosity of the material At the same time slight increase of the injection speed and holding pressure are also effective For injection speed it must be increased more than 100mm sec if it is lower than such magnitude In the case of over 100mm sec every 10mm sec increase is recommended For holding pressure condition elongation of holding time up to 2 0 sec is recommended Since the solidification of LCP is so quick over 2 0 sec of holding time usually has no effect The gate will seal by solidification of LCP prior to 2 0 sec All procedures of this section must be done slowly because sudden changes of those parameters induce a Flash prob lem and it will link to break the mold part If no change 1s observed you should consider the following reasons and procedures 2 Flow hesitation Sometimes this problem involves Crack weld crack problem You should also refer the explanation of flow hesi tation section 3 3 and crack section 5 5 within this section It should be done carefully as flow hesitation may occur even if the thickness difference is 0 01mm for relatively thinner parts having average thickness under 0 3mm If you observe the cavity dependence or the case that the problem generated fixed portion you should reconfirm the distribution of cavity dimension during assembling of the mold the dimension change of the gate due t
37. actors when you select ma terial and the formulation of fillers for the application L5 MD Shrinkage TD Shrinkage Fig 1 21 Anisotropy of plastics Moreover LCP has very low weld strength As shown in Fig 1 22 the weld portion is the portion where the sepa rated flow gathers together again At this moment the flow pattern should be the right side in the Fig 1 22 The di rection of flow at weld portion should be transverse direction against the main flow direction MD In this case the weld portion forms the very similar structure of skin layer against the flow direction Since skin layer is derived by the integration of thin sub layers and the affinity between layers is very weak the layers are easy to peel off In addition there is a pulling force at the weld portion because the mold shrinkage at weld portion is TD vs MD for the main flow portion This kind of different structure also becomes the cause of weakness It seems like the kink of crystal and it will be the over concentration of inner stress At last the weld portion of a molded article of LCP is essentially very weak and unavoidable In general the me chanical strength of weld portion is 1 4 to 1 5 of normal portions The filling of GF usually helps to improve the weld 13 1 Introduction of liquid crystalline polymer strength however it should be noted that adding of minerals or having too much content of fillers can reduce it again In general longer GF or
38. anules to themselves However sometimes this is not enough to improve the starvation caused by this The first recommendation to eliminate this is by modifying the temperature setting of the cylinder Since excess melting at the compression zone is one of the main causes of plugging decreasing the set temperature at the hopper side is recommended In general the nozzle and front section of the cylinder should be the same temperature as the molding temperature The middle section of cylinder should be 20 to 30 degrees less from the molding temperature and the hopper side section should be at least 60 degrees from the molding temperature Ex 1 in case of the standard molding temperature as 350 C For Sumikasuper E6807LHF is as follows Nozzle 360 C Front 360 C Middle 340 C Hopper side 300 C Ex 2 in case of the standard molding temperature as 380 C For Sumikasuper E4006L is as follows Nozzle 380 C Front 380 C Middle 360 C Hopper side 320 C Ex 3 in case of the standard molding temperature as 400 C For Sumikasuper E5008L is as follows Nozzle 400 C Front 400 C Middle 360 C Hopper side 340 C The cylinder heating system having 4 heating zones including nozzle is obviously necessary for LCP molding If the current injection machine does not have fewer than 3 heating zone nozzle 2 heaters for cylinder you should consider replacing the heater system of the cylinder to a more modern one Of course the abo
39. as follows 1 jk O mn a Here k comparative modulus m specific gravity 1 Accordingly it is necessary that the comparative modulus stiffness of material must be higher and the specific gravity must be lower in order to increase the fo In addition the metal terminal less resin terminal bobbin system is proposed due to weight reduction In this sys tem shown in Fig 2 10 the conventional metal terminal part is switched to the terminal that is formed by the molded plastic This system has merit to reduce the bobbin weight and emphasizes fp see formula 1 However in this case the plastic portion will be immersed in the soldering bath with much higher temperature than the above mentioned OPU bobbin The soldering resistance reaches to from 400 to 420 C Due to the above reason higher thermal resistance material is necessary for this application such as Sumikasuper 5000 series LCP resins y fii os resin terminal metal terminal one step fabrication O Insert Molding Press Insert Metal terminal less resin terminal bobbin system Conventional structure of bobbin Fig 2 10 Schematic view of conventional and metal terminal less bobbin structure Aa 2 Application of LCP and its technology 2 Relationship between modulus and thermal resistance As with conventional plastics higher filler content of LCP will bring higher stiffness However it will also bring the increa
40. atest electronics parts having very thin walls with complicated state of the art 3 Dimensional designs However one of the most common problems is warpage which is often observed during the development of the part that requires accurate flatness The reason of this problem is due to the progress of the Surface Mount Technology SMT for soldering and assembling In general the conventional technology of soldering requires installing the terminals of the parts into the certain po sition of holes at the Printed Circuit Board PCB Soldering is then carried out at the opposite side of the PCB In SMT soldering is done at the same side on the PCB where the parts are assembled at the certain position In this case the parts designed for SMT usually known as a Surface Mount Device SMD requires superior flatness and coplanery as miss soldering can occur if there is warpage or twist Fig 4 1 In general the requirement of flatness is under 0 05mm after molding however it is not so easy to realize even if LCPs exhibit superior low shrinkage prop erty In this section we would like to show the principles of the reduction of the warpage for molded parts by LCPs mis soldering Solder not acceptable SS oresoon LY R ay O Oe m K Terminal a flat amp planery b with warpage Fig 4 1 Surface Mounting Device with without warpage during soldering 4 1 Theoretical background of the warpage problem In general warpage of a
41. both installing enough numbers of air vent see Fig 5 11 not only cavity but also runner is more effective and installing the edge at the corner of cavity see Fig 5 12 65 5 Trouble shooting during injection molding of LCP z Tia gt T Loy LL 1e P _ _ a4 i a O EEE z TS Es o oi Injection speed A mm sec ex 150 ex 30 p screw position Fig 5 8 Suitable injection condition example Tooling 7 l eal By Tooling a Loe alr VV J ooling Fig 5 9 Schematic view of dragged air in the cavity OY 6 Liquid Crystalline Polymer blister Fig 5 10 Arising spot of the bubble air vent Fig 5 11 Install the enough numbers of air vents alee Install the edge Fig 5 12 Install the edge at the corner 67 5 Trouble shooting during injection molding of LCP 5 5 Crack The main cause of cracks in LCP parts is from crack generation at the weld lines The reason why the weld strength of LCP is so weak is discussed in section 1 5 In general there are only a few choices to improve this problem For example to shift the weld line to other sections in order to prevent excess force or to increase the thickness and to equalize the surrounding portions of the weld line In addition the generation of weld is fairly complicated and we must consider the flow pattern induced by the dif ference of wall thickne
42. bove reasons some researchers have proposed several kinds of measurement For example Murata et al proposed the measurement using the Infra red IR emission thermometer and the seethe thermocouple for inside temperature of cylinder and the supersonic measurement and the integrated thermocouple for mold temperature etc Among these measurements IR emission measurement is one of the most convenient and accurate ways for evaluating the actual resin temperature although this measurement has several defects For example the emission ratio should be adjusted not only for the difference of material but also for the difference of its color Several researchers have applied to evaluate the actual temperatures of plastic molding by IR emission measure ment We have also decided to install this measurement for evaluation of the relationship between actual resin tem perature and setting temperature see Fig 5 4 Sie Liquid Crystalline Polymer apparatus Infrared emission thermometer IT 240S Horiba Ltd spot diameter 1 2mm The setting of emission ratio is very important for the infrared emission thermometer We have ascertained that reasonable value of emission ratio for many kinds of plastics is 0 86 by measuring at the production factory of resin pellets resins used for ascertainment PP non filler natural color ABS GF filled natural color black PES non filler GF filled natural color white
43. cavity Fig 5 1 Sample of Trouble shooting form Go to details 5 2 Itemized discussion Let us begin our discussion about trouble shooting for LCP molding by defining vocabulary about molding prob lems oL 5 Trouble shooting during injection molding of LCP Table 5 2 shows the definition of molding troubles using LCP in this section The surface impression of these words are very similar to those used for conventional plastics however sometimes the actual cause or meaning is quite dif ferent Accordingly the remedies are also somewhat different from conventional procedures Table 5 2 The definition of molding trouble using LCP Black spec Carbonization by burning Enforcing the purging procedure Optimizing the circumstance of injection molding Blister Decomposition of material includes contamination Specifying the target material and removing Optimizing the circumstance of injection molding Bubble Swallow of air Modifying the cavity design Weakness of weld line Modifying the cavity design Flash Excessive pressure Optimizing the molding condition in order to reduce the shock pres sure Flow mark Essential property of LCP almost impossible to improve Increasing the mold temperature Modifying the cavity design Metering Plug generation at compression zone Modifying the cylinder tempera ture setting Optimizing the screw design Short shot Flow hesitation M
44. ce the mold temperature of PEEK should be set at over 160 C because its Tg is 144 C and higher than this temperature is necessary to achieve higher crystallinity after cooling In this meaning mold temperature has little impact on LCP properties However we should notice that at a little performance change occurred at Tg which is pointed out by Ward et al Furthermore LCP s decomposition temperature is over 500 C which is much higher than most other plastics Fig 1 12 This helps LCP to have very low out gassing This is due to the origin of outgas is usually in the heat ing of the decomposed material 10 wee Liquid Crystalline Sumikasuper LCP Weight Loss 200 300 400 500 600 700 Temperature C Fig 1 12 Thermal gravimetric analysis For the same reason LCP is inertly flame retardant Hence there is no possibility of generating halogen material during molding by decomposition We should also examine the comparison of out gassing between conventional plastics Since trapping the outgas during molding is difficult and inaccurate we have carried out the evaluation under the 120 C 20hrs conditions shown in Fig 1 13 The result is shown in Fig 1 14 As shown in the figure LCP shows lower amount of outgas than conventional plastics This is important for many applications lighting medical and helps to avoid mold deposit on 8 Liquid Crystalline Polymer the tool or machine This also helps to prevent several
45. cess measuring point 1mm from nozzle tip 3 Measured at the same manner as above except for setting with injection speed 10 4 Impossible to measure because of unstable metering The reason why the actual resin temperature differs from the set temperature is thought to be the position of the probe thermocouple to control the nozzle heater is not suitable as shown in Fig 5 5 upper side In this case the thermocouple measures the temperature at the installed point but there is often heat loss due to radiation at the non covered area by the heater Accordingly the measured temperature decreases significantly when compared with the temperature at the heater position Since the heater controller works to keep the temperature at measured point the actual temperature at heater position must be higher than its set temperature see Fig 5 5 upper right From our examination the thermocouple should be installed below the nozzle heater see Fig 5 5 lower left In this case the actual temperature is almost consistent with the setting temperature We should take care when we use the word temperature As described above sometimes the temperature is not consistent with the temperature which we would like to discuss In general the word of molding temperature should be used as the meaning of the actual temperature of the resin or the temperature below heater Nozzl e heat er Ther n
46. ction force like van der Waals force or dipole dipole attraction between layers Since the generation of the skin layer and Skin Core structure are the most important feature this must be optimized in the molding conditions Liquid Crystalline Polymer CAPA iA Te ANLAT Fig 1 10 Cross section of molded part of LCP right and its schematic view left We would like to compare the property among crystalline amorphous and liquid crystalline polymers As shown in Table 1 3 amorphous polymer indicates only Tg glass transition temperature but crystalline polymer indicates both Tg and Tm melting point On the other hand LCP indicates only Tc which is the transition temperature from solid to liquid crystal state as described above This Tic however usually depends on the shear stress during measure ment It means that a higher shear stress will decrease the Tic ana lower shear stress will increase it In the attached table merits are listed in light blue zone and demerits are in light red zone Thermal resistance soldering resistance and flame retardancy are mainly derived by chemical structure Since the listed polymers commonly consist of aro matic monomers all materials indicate relatively higher thermal resistance gt 200 C Notable merits of LCP are higher soldering resistance and significantly higher flowability On the other hand de merits are lower weld strength and strong anisotropy property Table 1 3 Typical eng
47. d electronic parts due to their supe riority in high heat solder resistance high temperature strength dimensional stability overall good chemical resis tance low flammability and low water absorption LCPs especially exhibit better thin wall fluidity and moldability then any other engineering plastics thanks to their extraordinary low melt viscosity This is also the reason why LCPs are now used for the latest designed and highest precision molding parts In recent years electric and electronic parts molded with LCPs have become more important to the IT related industries as well as many consumer markets be cause of Surface Mounting Technology SMT There is much information regarding LCP resins However its properties and performance are often not understood thoroughly For this reason summarizing the basic and gen eral properties of LCP should be considered In this section we would like to survey the general properties of LCP by comparison with conventional engineering plastics 1 1 General properties of LCP Engineering plastics can be classified as plastics having over 100 C of TDUL Temperature of Deflection Under Load usually measured under 1 82MPa Plastics having over 150 C of TDUL are called Super Engineering Plastics Table 1 1 Table 1 1 Classification of plastics General Purpose Engineering Plastic E P conventional super EP ETE POM PA PBT GF PET PC modified PPE 100 150 gt TDUL C
48. developing the new industry for IT business Many componies of this business area have wished to use this eccentric polymer for such new products however sometimes they faced several molding problems It seems that the behavior of LCP is very different from conventional engineering plastic so sometimes molding engineers found it unmanageable The word of LCP is attractive and many researchers have worked about this region However almost all result of such works merely provided the discussion between theoretical back ground and obtained data or disclosed some of interesting phenomena during molding such as relationship between shear rate and apparent viscosity effect of sta tistic orientation to morphology etc Those data or information indeed are very useful for researching or developing of new material based on LCP by specialists of polymer chemistry On the other hand there are many useful and excellent literatures about plastic processing Such literatures disclose not only principle of the mechanism or theoretical background of processing but also the reason of molding trouble and its solution However such current knowledge sometimes prevents understanding the behavior of LCP and causes misunderstanding of improving immediate problem or hides the actual reason from the engineer In view of above situation the first step of this booklet gave suggestions or solutions to solve molding trouble of LCP and to help understanding of L
49. ear rate change from y to y3 This reduction of shear rate in duces great amount gain of melt viscosity Fig 1 18 corresponding to the melt viscosity change from n to n3 As shown in Fig 1 18 the viscosity gain of LCP is comparably larger than that of amorphous polymer because of higher dependency between shear rates and melts viscosity of LCP If this effect should occur the melt viscosity of LCP gradually increases until the material will not flow any more This effect doesn t often correspond to the pressure loss which is conventionally thought by general theory of material flow Unfortunately this is often observed as the mold ing problem like short shot molding or weld line crack To understand the melt viscosity property of LCP is very important to solve these kinds of problems T cn a S Amorphous w w M ma O em es seanssessasnsnsoas sssssesesesnssonsan OTE E E E neem gt a oO oh 2 2 S 3 S 2 logy logy logy Shear Rate log Y Fig 1 18 Relationship between shear rate change y to y3 and melt viscosity change n to n3 for LCP and amorphous polymer example of conventional polymer 1 4 Mechanical property LCP s have excellent mechanical properties Table 1 5 shows Sumikasuper E6000 with an unfilled base resin com pared with Polyethersulphone Flexural modulus and TDUL of LCP are much higher than those of the PES As de scribed above the orientation of rigid rod m
50. ecommended the equalization of the thickness at top and bottom portion After that the warpage of mode 1 and 2 were improved less than 0 10mm see Fig 4 16 Fig 4 16 Idea for solution 1 ii Mode 3 crooking The molding still had warpage of 6 7 100 The reason for this was due to the unbalance flow of both top and bot tom planes Fig 4 17 shows the flow pattern at top portion We recommended installing a protrusion portion at the front side of both top and bottom planes see Fig 4 18 With this the warpage was completely reduced 47 5 Trouble shooting during injection molding of LCP _ _ _ _ __ _ gt one o Horr gt A mode 3 Fig 4 17 Flow pattern analysis 2 g p protrusions y T GaTE gt Flow Panen z gde 3 Fig 4 18 Idea for solution 2 c CPU socket Fig 4 19 shows the conventional 2 gates system for CPU socket In this case the warpage will be unavoidable es pecially at the gate side due to the inequality of the flow pattern at each side as seen in the figure The 4 gate system from the center portion shown in Fig 4 20 is the one of the best ways to solve the issue This system of course still has a chance of warpage at the grip portion see Fig 4 21 a however it can be improved by installing suitable de pressions as described in above sections see Fig 4 21 b hardly shrinkable warpage Fig 4 19 The conventional 2 gate system for CPU socket
51. en face the strange problem as shown Fig 3 12 It is expected that the weld line is found at the opposite side of the gate The flow end portion however is at the near side of the gate This causes short shot problems in this area In normal situations the short shot problem should occur in the same portion with the weld lines and the flow end portion should be the same flow end portion w short shot weld crack etc OK OK Fig 3 13 Example 2 multi cavities mold with sprue amp runner Another case of flow hesitation can be observed in multi cavity molds having sprue amp runner structures drawn in Fig 3 13 In this case the short shot problem often occurs at near side of the sprue and flash occurs at far side from sprue Itis usually impossible to improve those problems by optimizing the molding conditions 2 Flow behavior of LCP Before considering the flow hesitation of LCP it will be useful to discuss the flow behavior of conventional plastic Fig 3 14 shows the relationship of pressure loss and flow length against the distance from gate using the model of example 2 of Fig 3 13 As seen in the figure inner pressure of material at the near side of the sprue is larger than far side since the pres sure loss will enlarge at far side As the result near side cavity of sprue cav 1 and 2 indicate longer flow length and it means that those cavities have the tendency to indicate flash problem since those are higher inner pr
52. en melts often this will have an effect of increasing of the weld line strength Accordingly almost all molding engineers try to improve this problem with optimization of mold ing conditions since the modification of mold design requires much time and cost In the case of LCP is this manner possible The answer is No In general the optimization of molding condition for LCP often has no meaning to increase weld line strength The reason is clearly explainable Since the difference between melt and molten state of LCP is thermodynamically very small the rheological property of melt state and solid state of material is quite similar This means that the melt of LCP is nearly equal to the solid of LCP Accordingly the once separated flow of LCP will not stick to each other any more because solid materials will not stick each other For this case the modification of mold design is necessary As mentioned above the reason of almost all problems are explainable and improvable However the thinking should be modified based on the chemical and the rheological properties of LCP In this section we would like to examine of the reasons of molding problems and try to propose the improvement with experiment or case study 5 1 Outline for trouble shooting When there is a molding problem we recommend that you should gather the correct information about the situation at first For the materials engineer or researcher the following information is the mo
53. ence warpage and also the dimensions In addition injection conditions such as cylinder temperature injection speed amp pressure or holding pressure will also not influence warpage In other words the warpage of LCP molding is not changeable by molding conditions If the warpage problem occurs we should investigate whether the flow pattern is appropriate or not If the problem suddenly occurs we should also investigate whether there is a possibility of changing the flow pattern For designing an appropriate flow pattern we have already discussed in section 4 In this section we would like to discuss the case where the warpage trouble suddenly occurs during production the initial warpage was improved before starting production Since the warpage is only influenced by flow pattern we consider the reason why the flow pattern changes The reasons are considered as follows a Viscosity change of material Each lot No material has a melt viscosity Usually such viscosity difference is controlled within a certain range which is well considered by the material company However if the specific lot No material indicates different result of viscosity we recommend asking to mate rial company for help On the other hand there is a possibility that the material viscosity changes at the customer side The main reasons are contamination of other material and insufficient drying before molding Both reasons and improvements are discussed in sect
54. er Since LCP is very sensitive to the temperature the most suitable range is within 5 C from the designated molding temperature For your reference the measurement of actual resin temperature and related problems are explained at the section 5 2 2 2 c 2 Lower clamping force If the start inspection should be carried out daily this error must be prevented This trouble sometimes happens since the clamping force setting does not change during mass production and by using the same mold and the same material and no one pays attention to this Re adjustment of the clamping force is necessary if the accuracy of the parting line or mating surface is enough for accurate molding 3 Excess injection pressure The injection pressure means not only the injection pressure setting or the holding pressure setting but also the shock pressure at the end of injection process In general LCP does not need higher injection pressure or holding pressure If these setting values are too high changing and choosing of lower value is preferable to solve In the case that these values are correct we should adjust and reduce the shock pressure In this case we should look at other ways One way is by adjusting the V P switching point and observing the molding wave monitor The details are described at section 3 1 T3 5 Trouble shooting during injection molding of LCP 5 7 Flow mark The surface of molded parts of LCP is not smooth and appears to be a
55. er wall thickness Long fiber Short fiber and or inorganic filler shortage of flowability to rib portion good flow balance to rib portion Fig 2 5 Schematic view of comparison between conventional and the latest design of connector For the above reason LCP suppliers offer several kinds of formulations Table 2 2 and Fig 2 6 show the portfolio of Sumikasuper LCP for your reference Table 2 2 Grade line up of Sumikasuper E6000HF Z series for connecter application Filler formulation Recommendable application E6007LHE Z c GEF 35 standard grade DDR RIMM DIMM E6807LHE Z c GF mineral 35 low warpage S O DDR CPU socket E6808LHE Z c GF mineral 40 super low warpage CPU socket E6808UHE Z m GF mineral 40 best for FPC connector FPC b b connector E68 1OLHF Z c GF mineral 50 best for Card connector 1 c GF chopped glass fiber standard GF for conventional engineering plastics m GF milled glass fiber short size GF for special purpose Memory card 168pins DIMM RIM m PGA ISher sow E6007LHF Z hish rmos ga D a pase nar E6808LHF Z Sumikasuper LCP highs o lower flow PCMCIA E J Z Z 2 9 E Flash Memory Socket 3 S O DDR E6810LHF Z SSE F E6807LHF Z board to board FPC E6808UHF Z Fig 2 6 Grade line up of Sumikasuper E6000HF Z series 20 Liquid Crystalline Polymer 2 2 Bobbin for backlight inverter of LCD From the middle of 2003 the FPD Flat Panel Display marke
56. es pecially the damage of delicate core pins This is due to the stronger fricative resistance between metal part of mold ex core pin and the material The spraying of mold releasing reagent or replacing to an improved grade of mold release property should be con sidered to improve this problem However we should also point out that the short shot problem could be followed by flow hesitation 1 Relation between sticking and short shot As explained in section 5 9 flow hesitation is one of the reasons for a short shot In this case most molding engi neers recognize that the cause of short shot is insufficient filling of the material They realize that they must increase the injection pressure speed holding pressure or holding time Sometimes they must try to increase the cylinder tem perature As a result the cavity is added excess pressure and it will induce over packing However this is not successful due to the actual reason being not flow ability of the material but with the flow hesi tation Accordingly we must recognize and improve the flow hesitation phenomenon for this case In general sticking problems occurs when trial molding for a new mold or material replacement In these cases we must take care whether short shot occurs at the flow end of the mold usually opposite side from the gate or not If the short shot occurs at the flow end it should be the reason of the insufficient moldability For this case t
57. es until the cancellation of the plug Fig 3 19 During this phenomenon it observes that the granule at the inlet from hopper is slipping on the screw surface The molding engineer often explains that the granule of the LCP is slipping so it is not supplied to the metering zone This phenomenon can be confirmed by using the visible cylinder equipment or by de assembling of the screw from the cylinder 30 3 Injection molding technology for LCP back WZ NEA ie e k aa by melted polymer Fig 3 18 Schematic view of the back flow of LCP melt A E FATA A AU NNN FINAALIA ANNA D vr VANE AAN ETN AENA v Plug Starvation 12 PA i WA WA W Ne N2 AAAS KN Q Ds IA z AAAA X 2 ON VON Sc a Fig 3 19 Schematic view of the Starvation and Plug phenomenon The metering time elongates during the starvation state and it is cancelled due to the cancellation of the plug Ac cordingly the metering time usually indicates cyclical deviation in this case Fig 3 20 shows typical deviation of the metering time for this phenomenon The cycle of the deviation or the period until cancellation of the plug depends on the situation or the mechanical rea son caused by the screw design screw diameter clearance change etc The schematic draw of this phenomenon for LCP should be as follows FG Liquid Crystalline Polymer 1 The granule transferred from hopper is pressed at the compre
58. esistance 1 3 Moldability 1 4 Mechanical properties 1 5 Anisotropy 1 6 Market situation of liquid crystalline polymer 1 7 Conclusion 2 Application of for liquid crystalline polymer and its technology 2 1 Connector for PC mobile digital camera etc 1 Surface Mount Technology SMT 2 Relationship between compound formulation and warpage 2 2 Bobbin for back light transformer of LCD 1 Proceeding of the back light system of LCD 2 Requirement for the inverter bobbin 2 3 OPU Optical Pick Up actuator bobbin for CD ROM DVD etc 1 Requirement for OPU actuator bobbin 2 Relationship between modulus and thermal resistance 3 Injection molding technology for liquid crystalline polymer 3 1 Control System of Injection Process 1 Open loop control 2 Closed loop control 3 2 Thin wall fluidity of LCP and characteristic of injection machine 1 Experiment 2 Result 3 3 Flow hesitation 1 What is Flow Hesitation 2 Flow behavior of LCP 3 4 Metering of LCP 1 Principle of unstable metering 2 Solution of unstable metering 4 Improvement of warpage 4 1 Theoretical background of the warpage problem 4 2 Relationship between warpage and flow pattern 4 3 Relationship between the depth of core out and the warpage 4 4 Case study a Board to board connector 0 5mm pitch b S O DIMM c PGA socket 5 Trouble shooting during injection molding 5 1 Outline for trouble shooting 5 2 Itemized discussion 5 3 Black spec burni
59. essure than far side ones At the same time far side from sprue indicates shorter flow length and short shot tendency In this case if the flash problem at near side of sprue is not so serious increasing the injection pressure or the same manner of condition optimizing is one of the best ways to improve unbalance flow length for these 5 cavities in Fig 3 15 On the other hand LCP indicates small dependence of pressure between near side and far side of sprue since LCP has very lower melt viscosity Fig 3 15 In this case until the space is filled with LCP at the runner portion the LCP will not flow into each cavity through the narrow clearance of gate At the same time however if the pressure at the gate is not high enough there will be insufficient flow into the cav ity through the narrow clearance of the gate Since LCP has a high speed solidifying property it 1s quickly cooled 32 Liquid Crystalline Polymer by the mold For these reasons plugging at the gate is generated especially at the near side of the sprue In addition LCP flow does not reach the far side of the sprue on the first stage of material flow Accordingly LCP is rather easy to flow at far side of the sprue even if the plugging generated at the near side of sprue runner pressure position flash tendency 2 short shot tendency flow length at cavity gate W O a runner Fig 3 14 Model of flow behavior for conventional plastic flow p
60. g plastics m GF milled glass fiber short size GF for special purpose 22 Liquid Crystalline Polymer 2 3 OPU Optical Pick Up actuator bobbin for CD ROM DVD etc OPU Optical Pick Up is the electronic part that enables the reading and writing of digital data which is assem bled in the CD R or DVD media drive unit Recent developments realized high speed responses through use of LCP in the actuator bobbin for laser focusing 1 Requirement for OPU actuator bobbin Fig 2 9 shows schematic view of principle of OPU actuator bobbin In order to focus the laser ray to the micron size pits on the optical disc medium that is rotating at high speeds the lens actuator must be driven to follow the high resolution This is especially true in the case where the resonance at the drive speed of the actuator induces reading amp writing errors of the digital signal Recent trends and requests ares keeping the resonance frequency higher than the driving speed frequency of actuator However it is not so easy due to the recent 40 times speed CD ROM and 10 times speed DVD ROM demanding approximately 20kHz of resonance frequency It is expected that the resonance frequency of the material should be improved to realize this specification optical disc medium Optical Pick Up bobbin resin terminal y high speed driving Fig 2 9 Schematic view of principle of OPU actuator bobbin In generally resonance frequency fo is described
61. he im provement method is very similar with normal procedure with conventional plastics If it occurs at the other sections it must be induced by the flow hesitation For this case normal procedure to 1m prove the short shot problem is not suitable 2 Improvement of sticking At the same time the response of the injection machine is also considerable If the machine is not quick in response excess shock pressure also induces over packing Fig 5 33 Accordingly we would like to recommend the following Replacing the material to a mold releasing grade this must be the basic manner to improve this problem Using of high response injection machine see section 3 1 Modifying of the flow pattern by moving of the gate position thickness balance of the cavity installing of core outs etc see section 3 3 a high response machine b lower response machine pressure Shock pressure energy of b shock pressure energy of a prenau IY Shock pressure energy a lt b Injection time Fig 5 33 Comparison of shock pressure during injection molding between high and low response machine mo 5 Trouble shooting during injection molding of LCP 5 11 Warpage As discussed in section 4 the main reason of warpage for LCP molding is the flow pattern which brings the high orientation of LCP molecule to the flow direction Since LCP does not indicate Tg glass transition temperature the mold temperature will not influ
62. hows our model mold which has a thinner wall section at the contact portion and a thicker wall section at the bottom portion with one side gate The material is introduced from the gate and flows into the base portion and the contacting portion The dependency characterization between warpage and injection speed was investigated using ultra high speed in jection machine UH 1000 manufactured by Nissei Plastic under following molding conditions Molding temperature 360 C determined by IR emission thermometer see section 3 2 V P switching pressure 39 2 MPa Holding pressure amp time 19 6 MPa for 5sec Injection speed conditions were changed within the range from 50 to 800 mm sec After molding the warpage of molded connector was measured on the flat board as described in Fig 4 5 Since the gap between molded part and the surface of flat board was not so large a multipurpose projection microscope was used The result is shown in Fig 4 6 According to the increase of injection speed the warpage was quickly decreased for the slow speed region up to 100 mm sec and gradually decreased for the faster speed region over 200 mm sec This result indicates that higher injection speed must be applicable to improve the warpage and it should be more than 100mm sec O00 OOO0000000 OO0O0000000 Oo00000000 GATE gt gt 4 247mm 1 1mm gt lt E contacting portion thinner base portion thicker A 4 LI LI 68 765mm
63. idelight systems Fig 2 7 a are used for small size LCD as mobile phone PDA or PC having less than 14 size LCD etc The light for imaging 1s settled at the side por tion of LCD and the light is guided through light tube Recently white LED has begun to be used for these small size LCD applications The number of CCFLs is 1 or 2 in this case CCFLs are settled at both side of light tube Under light systems are used for large sized LCD In this case several CCFLs are necessary due to unifying the brightness for all of the area of LCD The number of CCFLs is 4 to 6 tubes for PC having 14 18 display and in the case of the flat TV having 27 AO reaches 16 to 20 tubes Accordingly since each CCFL needs an inverter for it s lighting the number of inverter bobbins is also increasing in proportion to expanding market of flat display LCD panel LCD panel diffuser diffuser OOS ee n LED CCFL M reflector CCFL inverter for lighting CCFLs the same number of CCFL are necessary a Side light system b Under light system Fig 2 7 Schematic view of the backlight system 2 Requirement for the inverter bobbin Fig 2 7 shows schematic view of assembling process of a transformer Soldering process is needed to remove the overcoat of wire to establish electric contact with contact pins The removing of the overcoat of wire is done through the thermal degradation of the overcoat material in ge
64. ine and amorphous polymers Careful examination will show a small slant of the modulus curve at around 120 C S Z D Cheng et al recog 7 1 Introduction of liquid crystalline polymer nized that LCP having several kinds of chemical structures would indicate two different crystal structures in the tem perature range of solid to nematic through annealing treatment Other researchers have since expanded the region of study for several chemical structures of LCP Some researchers have found that LCPs having Vectra like chemical structure have 2 or 3 kinds of relaxation These are named as a B and y relaxation which are very similar with conventional polymers In this case a relaxation is very similar to conventional glass transition temperature Tg This change seems very similar with the change at Tg of crystalline polymer In fact a very small and dull peak is sometimes observed in tan 6 curve of dynamic mechanical analysis at the same temperature region Liquid Crystalline 10 Sumikasuper LCP TQ 225 Tic 300 380 C according to molecular structure SSS a 10t LLL E S 9 2 10 g n O 103 Crystalline Tm 334 C RER T Amorphous PES 107 0 100 200 300 400 Temperature C Fig 1 11 Temperature dependence of modulus This means that it is not usually necessary to think about the Tg of LCP This is also why any mold temperature up to molding temperature can be chosen for LCPs For instan
65. ine just beside the injection machine In the case of blow up machine of material to stock into the certain vessel filled with dried air before blowing In addition as indicated by our experiment it is difficult to dry the granules of material completely in high humidity conditions using conventional procedures Accordingly we recommend that the resin bag should be packed or wrapped after taking it out from the bag lt Test method gt The granule of Sumikasuper E6807L has been left in the stabilized humidity oven at a certain condition described be low After treatment the material was molded to test piece by injection molding machine for evaluation of soldering resistance Test Sample E6807L 20 5 Trouble shooting during injection molding of LCP Molding Temperature 360 C Test piece 0 8 mmt mini dumbell test piece Humidification 40 C 85 RH Temperature and Humidity Camber PL 1GM Tabai Espec Co Sample was set in a humidity chamber Drying before molding 80 100 120 C for 3 hours Sample was drying for just 3 to 3 5 hours before molding at each temperature Evaluation The blister was detected after one min dipping into the soldering bath IT ilter AE a service line of pellet hopper bey i S aa blower 00 Hor P if P he anit ae Q0 Ao OND T X 7 heater a mu as injection machine Fig 5 2 Schematic view of hopper dryer and service line of pellet lt Result gt The result is sh
66. ineering plastics and properties Crystalline Liquid Crystalline SUMIKAEXCEL PES Polyphenylene Sulfid PPS SUMIKASUPER LCP FKO 80 0 Oy0 F OS 0 G OOO Hc Orgy Tg 225 C Lee sare g Tm 285 C T c 320 to 400 C Thermal resistance to 200 C Thermal resistance to 240 C Thermal resistance to 260 C Dimension accuracy Soldering resistance Excellent soldering resistance Creep Performance Excellent solvent resist Solvent stability except alkali amp steam Impact strength High flowability Superior high flowability Boiled water resistance 160 C High flame retardancy v 0 High flame retardancy v 0 0 3mmt High flame retardancy v 0 0 4mmt Higher water absorption Higher Degassing Lower weld strength Relatively lower flowability Flash Strong anisotropy 1 2 Thermal resistance LCP realizes higher TDUL Temperature of Deflection Under Load than other plastics Fig 1 11 shows tempera ture dependence of elastic modulus compared with crystalline PEEK amorphous PES and liquid crystalline Sumikasuper LCP polymers As shown in this figure it is clear that LCP keeps higher mechanical property over 200 C LCP also does not have notable decrease of modulus as shown in PEEK at 140 C meaning that LCP seems not to have glass transition behavior Thermal analysis such as differential scanning calorimetry DSC also does not indi cate the thermal transition as observed in other conventional crystall
67. ing the screw parts The second portion is the inlet of hopper side The abrasion of this portion causes excess supply of the granule to the compression zone of screw Finally such excess granule will adhere each other by generated pressure of its own compression If you find a remarkable abrasion at this area we recommend you to consider replacing of the cylinder part The third issue is the temperature setting of the cylinder The nozzle and front heater should set at the most suitable molding temperature of LCP that is used but the center heater must be set lower than 20 C than the molding tem perature Also the hopper side heater should set lower than 40 C The reason of above recommendation is due to the suppression of excess melt of LCP before the compression zone of the screw In general H2 is at the compression zone of screw If this portion set at 20 C lower than melting point of LCP the melting and generation of melt film of LCP are suppressed it is worthwhile preventing the generation of plug phenomenon In this meaning the hopper side heater also set at much lower than its melting point If the metering volume is larger than 60 of full scale of metering we must be careful as lower settings of the cen ter and hopper side heaters sometimes causes the insufficiency of melting of LCP We must be careful about the bal ance between excess and insufficiency of melting of the material oF 3 Injection molding technology for LCP at
68. injection pressure 2 176 956 2 99 1763 cm s kg cm 3118 1431 3 134 1312 4 88 1920 4 195 896 5 70 2388 5 393 445 6 58 2579 1 for machine A 6 mode is the standard position 2 for machine B 1 mode is the standard position Equipment IR emission thermometer IT 240S Horiba spot diameter 1 2mmf focus 64mm emission ratio 0 86 sensor equipment recorder 64mm 7 Ya LF wa qi AAA 2mm Fig 3 6 Schematic view of measurement of resin temperature with IR emission thermometer Actual waves of injection speed and pressure were recorded for each injection condition and the flow length of 28 Liquid Crystalline Polymer 0 2mmt cavities were measured at the same time The schematic wave is shown in Fig 3 7 velocity er Arne pressure pressure velocity Max velocity holding pressure shock pressure time injection time Fig 3 7 Schematic wave of this study 2 Results Fig 3 8 shows the relation between injection time and flow length In the case of open loop injection machines A or B flow lengths developed a tendency to increase with decreasing of injection time however injection time has not decrease under 0 10 second In contrast injection machine C had under 0 10 seconds of injection time easier than A and B then flow length has greatly improved 30 flow length mm 0 0 1 02 03 04 0 5 time sec Fig 3 8 Relation between
69. injection time and flow length The reason why these different characteristics were observed can be considered the difference of rise up character istic of injection machines That is to say compared with the rise up characteristic of pressure injection machine C is the most rapid vs B and C shown in Fig 3 9 This is due to the servo valve of the closed loop system showing quicker performance than the proportional controlled valve of open loop system It is clear when comparing the ve locity characteristics shown in Fig 3 10 29 3 Injection molding technology for LCP 1600 E X 1200 e X 800 5 uv D 400 0 0 0 1 0 2 0 3 0 4 0 5 time sec Fig 3 9 Pressure wave 200 8 Q 100 a U 2 S 0 0 0 1 0 2 0 3 0 4 0 5 time sec Fig 3 10 Velocity wave Fig 3 11 shows the relation between maximum velocity and the flow length for various injection molding ma chines including A B and C Closed loop machines show better moldability than open loop machines It is reason able to suppose that the closed loop injection machines are profitable for thin wall moldings using LCPs 30 Liquid Crystalline Polymer flow length at 0 3mm mm 0 100 200 300 400 Max injection velocity mm sec Fig 3 11 Relation between maximum velocity and flow length for various injection molding machines 31 3 Injection molding technology for LCP 3 3 Flow hesitation 1 What is Flow Hesitation We oft
70. ion 5 4 Blister amp Bubble Please refer the section b Abrasion of mold part Dimension change should also be considered We often observed that only 0 01mm difference of dimension significantly changes the flow pattern This is especially so if the dimension change occurred at the thickness of main flow portion This case should be considered when the mold is maintained or additional mold is constructed In this case such small difference of dimension often brings different results of warpage c Unsuitable molding condition As described above in general molding conditions does not influence the warpage of LCP However if original molding conditions were not suitable sometimes the deviation of the injection machine will influence to the flow pattern and cause warpage In this meaning the following cases are sometimes the cause of the problem too slow injection speed too low cylinder temperature Both reasons prevent the formation of the orientation layer of LCP so called skin layer In this case the ani sotropy must be lower than the case of suitable injection condition The most difficult case is where the initial warpage has not been improved by modifying of the mold design Sometimes modification of the original design of the mold must be necessary please refer the section 4 Suitable injection molding conditions is also one of the most important responses to reduce the problems Please refer the section 3 and use it under appr
71. is installed at the portion de scribed in the figure the weld line generates at the thin section In this case the weld crack problem cannot be avoided gate weld crack Fig 5 17 Case part and its weld crack portion The LCP introduced from the gate flows the top portions and spreads in all directions and then flows downwards Since only the front portion has a square hole the flow is divided and bumps at the bottom portion of the hole In this 69 5 Trouble shooting during injection molding of LCP case the generation of weld is not avoidable Fig 5 18 1 without change of gate location Fig 5 18 11 shows one of the most preferable solutions for this problem The LCP will flow in the same manner as the original position but after flow downwards there is less chance to generate the weld at the weak section Of course the weld will generate at the opposite side wall but there is much less probability to break because this section is much stronger Incidentally the weld line having Y character shape at the side wall indicated in the figure is one of the most pref erable to reduce the weld crack problem for case parts It means the whole flow of LCP from top and both sides are balanced If the weld line shape is far from Y character you must consider modifying the part design in order to control the flow gate gate i estimated flow pattern li after moving the gate Fig 5 18 Estimated flow pattern 1 current flow pattern
72. l The closed loop control is so called servo control system which has a feed back loop circuit of control signals and comparison systems between setting value and actual value This system not only indicates detected value of pressure or velocity but also the feed to comparison systems to keep the actual value with setting value Accordingly the velocity controllability is more reliable than open loop con trol system 26 Liquid Crystalline Polymer However this system is more expensive due to all mechanical parts requiring quicker and more accurate response This system is more suitable to realize accurate molded parts Important setting parameters are as follows Velocity setting Required pressure is determined by CNC itself V P switching position This is one of the most important settings to determine the point from velocity priority control to pressure priority control It affects to end position of injection and shock pres sure Limiting pressure setting Some machines don t have this parameter It limits the maximum pressure during velocity priority control injection process Basically this parameter has no relationship with velocity however to low of a setting will affect controllability of velocity Servo valve quick response Limitting Calculation to velocity P Compare Injection speed velocity pressure Screw position Pressure Pump pressure CNC determines limiter proper value b
73. l depression near the gate side 3 Installing the additional depression at the side wall of anti gate side to remove the back flow as seen in Fig 7 3 upper 3 additional core outs 1 additional core outs 2 side wall nn weld B Fig 5 23 Schematic view of the idea to improve the crack based of its flow pattern control 72 Liquid Crystalline Polymer 5 6 Flash Sometimes a molded part has an extra amount of material by flowing of a polymer melt into the clearance between parts ina mold This is called flash In general flash is caused by excessive injection pressure low melt viscosity excessive rapid injection or inadequate mold venting LCP usually doesn t have this flash problem even though it does have significantly lower melt viscosity and is quicker filling into the cavity with rapid injection velocity Wissbrun has tried to explain this paradox in his former work He demonstrated following evidences LCP has very close solidification temperature to injection molding temperature its latent heat is almost zero and its thermal conductivity is high This means that the large thermal diffusivity with small amount of heat induces quick solidification and its order of solidification speed is significantly larger than conventional plastics The power law exponent n is higher for LCP than that of the isotropic polymers tested by Richardson End correc tions of LCP are significantly larger and those depe
74. lugging by low pressure cooling effect etc pressure position Fig 3 15 Relationship of pressure loss between LCP and conventional plastic This situation is described as shown in Fig 3 16 In fact the inner pressure could not increase at the far side from the sprue The flow lengths to the cavities are observed per the figure The reflection of LCP flow at the end por tion of the runner induce the opposite direction flow upper part of Fig 3 16 33 3 Injection molding technology for LCP pressure position flash tendency flow hesitation appeared as short shot cav 1 cav 2 flow length at cavity 4 gate sprue runner Fig 3 16 Flow behavior of LCP at the same model This phenomenon is called Flow Hesitation and it is often observed not only in large items but also small and thin portions of accurate designed items Once this phenomenon has occurred no matter how the molding condition will be optimized there is no way to improve the molding problem induced by this phenomenon The most effective way to improve it is the modifying the flow pattern by moving the gate position thickness of the cavity or installing the core out depression etc to unify the flow pattern In general this phenomenon is observed as short shot weld crack or sticking to the mold Since these problems seem no relationship to flow hesitation they can be misdiagnosed It is desirable to consult to such experts if you
75. m Higher percentage gt 10 means that the problem is es sential but lower percentage lt 1 means that the problem may be caused by some error e How about cavity de Sometimes this is neglected but it gives us clear image about the problem pendency There should be the description of cavity No and the dependence of cavity No to the g0 Liquid Crystalline Polymer issue should be noted The cause of trouble is sometimes induced by un uniformity during mold manufactur ing for multi cavity molds The following settings should be recorded cylinder temperature mold temperature injection speed amp pressure holding pressure amp time metering position decompres sion and V P switching position Also filling time during injection process minimum cushion metering time and cycle time and drying conditions should be recorded also Information about injection machine manufacturer catalogue number and duration of use is also necessary f How about molding conditions We also recommend preparing the attached fixed form in order not to lose the important information when molding trouble has happened Fig 5 1 DATE NAME T rouble shooting form Please fill all things in this sheet as you possible lt Molding condition gt a What s happen Type of trouble Drying condition Dryer type Hopper dryer Flow mark Rack type oven Black spec other Blister Metering
76. me carbonized material by thermal decomposition reaction This is one of the reasons for black specs Another reason is the relationship between molding temperature and decomposition temperature As explained at section 1 2 LCP decompose at over 500 C and this temperature is thought as the upper limit of organic materials Higher thermal stability grades such as Sumikasuper E4000 series and E5000 series have molding temperature of 380 or 400 C Since such higher molding temperature is very close to its decomposition temperature this circumstance is very severe for the material even if it has excellent thermal stability If the material 1s exposed at these conditions for long time the decomposition can not be prevented Accordingly the best way to improve this problem is to remove the possibility of retention under molding tempera ture please also refer the section 5 4 2 b and 5 4 2 c The first step of improvement is to remove the reason In general we search and find the flow prevention structure In this meaning we recommend not to use the hot runner system and shut off valve structure of injection machine If you wish or plan to use these you must think about the risk of black spec The second step is the cleaning of inside parts of cylinder especially nozzle and the tip parts of screw Usually re placing to the new parts is strongly recommended Since the tip parts of screw must be worn out with long term using and molding with glass
77. mer matrix does not indicate the directional prop erties The bundles are called the domain structures of liquid crystal The domain structures are not detected easily due to the difference between the domains not being clear thermodynamically In other words domain like shape will be observed under the polarized microscopic investigation but the size of the domain is undetectable matchsticks glass funnel shaking shaking Fig l 4 Schematic model of Liquid Crystalline Polymer during molding process If shear stress is added to the melted LCP the rigid rod molecules are easily aligned in the same direction of the shear stress After cooling the melt will solidify and preserve this highly oriented three dimensional structure Fig 1 5 This directional property is called anisotropy The first scientist who named liquid crystals was Otto Lehmann in 1889 after discovering the birefringence phe a 1 Introduction of liquid crystalline polymer nomenon by Friedrich Reinitzer in 1888 The low molecular weight liquid crystals however demonstrated rela tively different history with polymer liquid crystals Such investigations have helped to develop the current LCD Liquid Crystal Display etc The first notable work of polymer liquid crystals started from the pioneering study by Onsager Ishihara and Flory Flory predicted lyotropic liquid crystals that indicate liquid crystallinity in dilute so lutions This s
78. min 400 Cx retention for 10 min 400 Cx retention for 15 min O Slightly colored Slightly colored O O Slightly colored Slightly colored Blistered O Blistered Blistered Blistered O O Blistered O O Blistered Blistered O Blistered Blistered Blistered 360 CxX decompression 5m 360 Cx decompression 9m 360 CX low pressure low speed Standard condition decompression degree 2mm V 50 P 30 cycle time 20 sec Low pressure low speed V 30 P 15 O shows that neither change in form nor blister was found e Unbalance between cylinder size and molding volume When using too large of an injection machine vs molding volume the measuring length becomes too short The re tention time in cylinder becomes too long In addition excessive shearing power may be added to the resin at the screw providing zone or the compressing zone due to the high power of the large injection machine In such situations the deterioration of resin can easily occur 61 5 Trouble shooting during injection molding of LCP lt Test method gt Using 2 injection machines having different screw diameters described Table 5 7 test pieces were molded and the soldering resistance measured Table 5 7 Result of the soldering test using 2 injection machines having different screw diameter Sample Amount of gas Soldering resistance ppm CC SG 150 Sumitomo Condition 1 10 8 280 285 bli
79. molded part is caused by several reasons For example a volume shrinkage b retention stress and c orientation of filler However we should point out that LCP itself is a strong anisotropic material According to our experiences and experiments we found that above a to c have a relatively small affect on warpage of LCP molded parts We have found that the direction of flow in other words it is a direction of orientation of LCP rigid rod molecule has the highest affect Generally speaking melt polymers will prefer to flow into the thicker portion of the part more than the thinner por tion The reason is the pressure loss of the thicker portion is lower than thinner portion LCP is no exception to this physical rule Since LCP indicates much higher shear thinning of viscosity this tendency is much stronger than other kinds of plastics To take an example that has both thicker and thinner portions as drawn in Fig 4 2 the polymer will first flow into bottom portion followed by its flow into the upper rib portion This is due to the bottom thickness b is larger than the rib thickness a In this case the flow pattern of the material can be explained equivalently as the arrows drawn in Fig 4 2 a Since LCP has much smaller shrinkage for MD Mechanical Direction than TD Transverse Direction the bot tom the flow of LCP is MD will keep its dimension but the rib the flow of LCP is TD will shrink As a result warpage expressed in Fig 1
80. mposition of the LCP by de hydrolisis reaction The moisture should be removed by drying the material before molding recommended drying condition 120 to 140 C 4 to 24 hr It is often found that the hopper dryer is not hot enough in spite of the indicator of the dryer showing high tempera ture for example 130 C There is 2 points for the cause of this trouble a The hot air is not able to circulate because the filter of the dryer is stuffed In this case it is sometimes found that the inside temperature of dryer hopper indicates low temperature for example 40 C b The granule retain in the air service line between hopper dryer and hopper of the injection machine and those granule mix with newer granule If the granules once dried by heat are cooled then the moisture in the air condenses on the surface of gran ule again Therefore those cooled granule must be removed before molding In general people believe that the material will keep dry if the piping system is filled with dried air supplied by air dryer ex dew point 40 C However in long piping systems as shown in Fig 5 2 moisture can enter from outside through small apertures of the piping Accordingly the following is recommended if the atmosphere contains high humidity such as east and south China east southern Asian countries etc To install air condition system for drying the molding room To shorten the piping system length installing drying mach
81. n loop control however realizes lower reliability for the velocity injection speed due to it not feeding the ac tual velocity and pressure to the controlling unit Injection speed is usually affected by the flow resistance induced by the material viscosity and tool cavity design ex gate narrow portions of cavities etc Other factors such as the oil temperature and the viscosity of the molding material could also influence the real condition of the injection and thus they might be often different from the set value Important setting parameters are as follows Pressure setting this means both injection pressure and holding pressure Velocity setting hydraulic flow for hydraulic system vs velocity Usually this kind of machine uses lower response parts such as switching valves for hydraulic systems It some times causes the generation of excess shock pressure 25 3 Injection molding technology for LCP Screw position j Injection speed velocity pressure Screw position Velocity changes by Holding pressure Injection speed Pressure flow resistance setting setting setting Fig 3 2 Relationship of molding parameters change of open loop machine with screw position Pump pressure 2 Closed loop control pressure screw position compare Feed back loop Computerized Numerical Controller Setting value velocity pressure screw position Fig 3 3 Principle of closed loop contro
82. nd on both shear stress and temperature although those of iso tropic polymers depend on stress but not very much on temperature This means that the flow length of LCP at narrower sections from the wider areas is comparably shorter than that of conventional plastics and it also means that LCP has less tendency of flashing The flow length at constant pressure depends upon the power of the coefficient no of power law equation This value of LCP is also significantly larger than that of isotropic polymers This higher value affects excellent mold ability but does not affect the flash tendency Finally he concluded that quick solidification behavior and stronger dependence of melt viscosity with shear rate of LCP relates to minimizing flash and the smaller melt viscosity of LCP induces higher moldability This examination is completely consistent with the usual observation at molding and is quite correct explanation of LCP behavior However we sometimes suffer the flash trouble for the LCP molding beyond the basic behavior of LCP as described above In these cases we should notice that LCP has very low melt viscosity and it favors not only flow to the mold cavity but also to a narrower gap such as air vent if excessive injection pressure is added We would confirm following condi tions 1 Higher actual resin temperature The molding temperature should be set at moderate which is disclosed on the technical issues provided by the LCP manufactur
83. neral polyurethane polyester etc because of the reduction of tact time Since this soldering temperature is 370 to 390 C higher temperature resistance of the material is necessary If the material thermal resistance is low melting of the bobbin and slanting of contact pins will occur Fig 2 8 In addition since all electronic parts including LCD should be small and thin the material having both high heat Zl 2 Application of LCP and its technology resistance and high moldability is demanded bobbin molded byLcp Wire sl Ls mt treating Coat I Doth side T ern HON Soldering Bath contact pins 370 390 C Molding Soldering amp Pin Inserting toh end electric contact Fig 2 7 Schematic view of assembling process of transformer Melt by heat amp Slant of pin gua Terminal Soldering Bath 370 390 C Fig 2 8 Schematic view of soldering process of transformer for LCD backlight Only a few LCP suppliers provide suitable grades for this application Table 2 3 shows Sumikasuper E4000 series as one of the best grades Table 2 3 Grade line up of Sumikasuper E4000 series for bobbin application Soldering resistance m GF 40 standard grade for bobbin 370 390 C x lt 3 sec c GF 30 higher toughness 370 390 C x lt 3 sec 1 c GF chopped glass fiber standard GF for conventional engineerin
84. ng amp carbonizing 5 4 Blister amp Bubble Classification amp improvement 1 Comparison between blister and bubble 2 Reduction of the blister at soldering a Effect of moisture Aii b Retention of resin at the inside of injection machine c Temperature settings of injection machine Difference between setting value and real resin temperature d Relation between retention of LCP in cylinder and blister e Unbalance between cylinder size and molding volume f Purging method of Sumikasuper LCP 3 Reduction of the bubble after molding a Dragging of the air into the melt b Suitable injection condition c Suitable cavity design 5 5 Crack 1 Cracking problem for Coil Bobbin 2 Side wall cracking for Case part 3 Weld crack at the hole of Board to Board Connector 5 6 Flash 5 7 Flow mark 5 8 Metering 5 9 Short shot 5 10 Sticking 5 11 Warpage Reference iv Liquid Crystalline Polymer reface This booklet was originally planned to provide the presentation to molding engineers of our customers because there was little literature or references about improvement and solution of molding problems for Liquid Crystalline Polymer designated as LCP hereafter In early 1990s it was a period of actual growth of thermotropic LCP industry for electric and electronic parts such as connectors relays or coil bobbins for personal computers mobile phones or digital cameras etc It was also the same movement of
85. ns that it should be under 0 05mm after molding due to the warpage increasing by the pin tap process In recent years the customer s needs have become more precise so that tolerances after IR reflow process also should be under 0 10mm This is not easy to accomplish by the designer molder and polymer scientist The details of warpage improvement will be explained later 17 2 Application of LCP and its technology A Conventional soldering procedure printed circuit board electronic part gt me gt 240 C metal terminal printed circuit Cu soldered B Surface Mount Technological SMT soldering procedure IR reflow oven electronic part l 240 C for conventional solder metal terminal 360 C for Pb free solder T dnd gt LAP gt printed circuit Cu soldered printed Solder enabling of multi layer soldering gt Fig 2 1 Schematic view of comparison between conventional and SMT T mis soldering not acceptable Solder C eS sae A 4S SSE SS ES EL SS PCB Sz m PCB j Terminal a flat amp planery b with warpage Fig 2 2 Relationship between warpage and soldering 2 Relationship between compound formulation and warpage In general the higher filler content indicates lower anisotropic property which is the most important character for reduction of warpage However the relationship differs between filler content and anisotropy among different hy per dimensional struc
86. o abrasion or runner length difference from sprue Let us explain this kind of short shot and its solution by using an example Fig 5 27 shows a bobbin item for induction coil This item had not only a short shot problem generation of hole but also a weld crack problem The molding engineer asked us the most suitable molding condition because changing the molding temperature or increasing the injection speed did not improve these problems The reason for these problems was thought to be that the flow of LCP from the gate filled the upper rim first 76 Liquid Crystalline Polymer Fig 5 28 a then flowed to the bottom through inside ribs installed inside of cylindrical portion Fig 5 28 b After that the material filled into the bottom rim at the same time of filling the cylindrical portion without inside ribs In this case the opposite side of the gate of the cylindrical portion especially bottom side was the last part of filling due to flow hesitation Fig 5 28 c Due to the above mentioned all the energy due to increasing of temperature or injection speed was lost by filling of the material to the other portion At last the hole and weld portion existed at indicated portions upper rim gate inside rib gt D ole bottom rim Fig 5 27 Short shot problem of bobbin for inductance coil Now we should consider how to equalize the flow pattern In this case there were 3 possibilities 1 Thickening of cylindrical po
87. ocoupl e Tem Ff NOON fa ati on 420 30 C setti ng tenp actual tenp Ti ne Nozzl e heat er Ther nocoupl e Tenp a as setting tenp actual tenp Ti ne Fig 5 5 Comparison of thermocouple position in various types of injection machine d Relation between retention time of LCP in cylinder and blister As mentioned above the deterioration of resin occurs when the actual resin temperature is higher than the most suit able one This deterioration may cause blistering which may lead to retention in cylinder It was found that there is strong dependence between blister and molding actual resin temperature or the retention time of resin in cylinder lt Test methods gt Sample E6807L Molding machine PS 40E5ASE Nissei Plastic Industrial Co LTD The transformation and blister of test pieces were observed after immersing them into the soldering bath set at 210 and 250 C each for 60 sec The test pieces have been molded with various conditions of molding temperature retention time Also test pieces were molded with following conditions 60 Liquid Crystalline Polymer different decompression degree low pressure low speed lt Results gt The result is shown in Table 5 6 Neither transformation nor blister was observed when the thickness of the test pieces was thin O Smmt Meanwhile transformation and blister were observed at thick test piece 0 8mmt and its tendency depended on the molding conditions
88. odifying the cavity design Changing to high performance type injection machine Sticking Flow hesitation and excessive pressure Modifying the cavity design Changing to high performance type injection machine Warpage Unbalance of flow pattern Choosing the most suitable grade Modifying the cavity design Changing to high performance type injection machine 1 Distinction between Blister and Bubble is not so clear but the reason is different The detail about this issue will be discussed at section 5 4 2 This explanation doesn t indicate the same meaning at each item Please refer the certain explanation from next sec tion 3 Please also refer the section 3 JA Liquid Crystalline Polymer 5 3 Black spec The generation of black spec is often observed in higher thermal stability grades of LCP for example Sumikasuper E4000 series and E5000 series The cause of this is due to the viscosity properties of LCP and the thermal stability As explained at section 1 3 and 3 3 melt LCP is difficult to be processed from flow prevention structures dead zones etc Examples of this are the dead space of a manifold in hot runner systems or the valve structures of a shut off nozzle In these areas the former LCP will not be pushed out or replaced and it will remain for a long dura tion LCP has excellent thermal stability however this remaining portion of LCP will be damaged gradually In time it will beco
89. of wall thickness is recommended Diameter a and b should be the same After equalization of the thickness at cylinder portion the LCP flows more uniformly Fig 5 16 11 In addition there is the case that the short shot occurs at the weld portion and causes lower strength Higher holding pressure is sometimes available to improve this problem In general LCP requires relatively higher injection speed but lower and shorter holding pressure due to its quick solidification property However such higher injection speed some times enhances the flow hesitation For these cases allowing relatively higher holding pressure conditions is effective after packing under ordinary higher speed and lower pressure condition in order to push the LCP to the weld portion Holding pressure 80 to 90 MPa generally 40 to 50 MPa Holding time 1 5 to 2 0 sec generally up to 1 0 sec 68 Liquid Crystalline Polymer a gt b Fig 5 15 Dimensions of the bobbin i before equalization ii after equalization a lt b a b Fig 5 16 Estimated flow pattern 1 current flow pattern 11 recommendation after equalization of thickness 2 Side wall cracking for Case part The case for electronic parts has a relatively simple design but sometimes the weld crack is not negligible Espe cially if the mechanically important section has a thinner wall and also the weld lines Fig 5 17 shows a typical designed case having a thinner and thicker section If the gate
90. olecule is induced by the shear stress with the wall of mold during the material flow in the cavity as so called fountain flow see Fig 1 9 Due to the fact that this orientation of the rigid rod generates the skin layer a molded article of LCP is reinforced by itself That is the reason why LCP is sometimes called a self reinforcing material This phenomenon derives the high rigidity and thermal properties of LCP s However we should notice that the flexural strength is not high compared to the higher modulus It suggests that LCP is more brittle then other plastics In addition it should be noted that there are many differences between MD Mechanical Direction and TD Trans verse Direction of both mold shrinkage and C T E Coefficient of Thermal Expansion for LCP s Especially C T E of MD is a negative value This means that the dimension of MD will decrease with elevation of the tempera ture This is induced by the orientation of rigid rod molecule to the molding direction during processing We have to note that anisotropy is the essential property of LCP On the whole aromatic polymers have excellent flame retardant properties and LCP is no exception Both PES and LCP are classified as V O via UL 94 regulations This means that there is no chance to expand the flame through the article made by both materials LCP s exhibit such property at only 0 3mm thickness actually under 0 3mm thickness 11 1 Introduction of liquid crys
91. opriate condition 80 Liquid Crystalline Polymer lt r ef erences gt 1 for instance Tatsukami Y Asai K Inoue M Sugimoto H Hayatsu K and Kobayashi T Sumi tomo Kagaku 1987 1 20 1987 Asai K Plastics 45 76 1994 Nomura H J ETI 46 79 1998 2 for instance ed Koide N Liquid Crystalline Polymer Synthesis Molding and Application Japanese Sigma pub 1987 ed limura I Asada T and Abe A Liquid crystalline polymer Its basic and application Sigma pub 1988 Liquid crystalline polymer committee on engineering and technological system Natl Acad Press 1990 Wang X J and Zhou Q F Liquid crystalline polymers World scientific pub 2004 Suenaga J Liquid crystal polymer for molding and designing Sigma pub 1995 3 Lehmann O Z Phys Chem 4 462 1889 4 Reinitzer F Monatsh Chem 9 421 1888 gt Onsager L Ann N Y Acad Sci 51 627 1949 Ishihara A J Chem Phys 19 1142 1951 Flory P J J Proc R Soc A 234 60 1956 ibid 234 73 1956 ibid Selected Works Stanford University Press 2267 1985 6 Maier W and Saupe A Z Naturforsch A _ 14 882 1959 Maier W and Saupe A Z Naturforsch A_15 287 1960 Krigbaum W R Brelsford G and Cifferi A Macromolecules 22 2487 1989 Aharoni S M Macro molecules 21 1941 1988 7 Technical Information Tosoh corporation 107 1999 8 Blackwell J
92. oth can be easily distin guished with careful observation This difference is based on the actual reason of each case The reason of the bubble is mainly swallow of cavity air On the other hand the reason of the blister is mainly the decomposition of material in this case material does not always mean LCP Table 5 3 Comparison between the bubble and the blister the bubble after molding rare after soldering arising spot random the decomposition of material without regard to causes the dependence of molding condition a little a little the dependence of tooling design cavity design yes a little the order of frequency is yes gt a little gt rare gt no 2 Reduction of the blister at soldering The reason of the blister is the gas generated by decomposition of organic material The source of this decomposed material is thought as follows A Decomposition of LCP A 1 Production fault of LCP This means that the average molecular weight or distribution may be out of specification In general this cause is lot No dependency If you cannot find out any other fault described below you should consult to LCP manufacturer with all in formation that you collected The most important information is lot No in this case A 2 Hydrolysis of LCP Insufficient drying is the cause of this problem There is the case that the actual drying temperature differs from the setting temperature
93. ow kinds of circumstances in the solvent as solution and in high temperature circumstances over the Tio The former is called lyotropic LCP and the latter is called thermotropic LCP Some of the LCP are known as commercially produced products as shown in Fig 1 6 In this book we would like to focus to thermo tropic LCP especially aromatic polyesters because there are many kinds of commercial products in this field Lyotropic LCP Aromatic Polyamide Aramid Keviar etc Polyphenyl bis thiazole Cellulose Derivatives Thermotropic LCP Aromatic Polyester Vectra A950 etc Aromatic Polyesteramide Vectra B950 Polyazomethyne Fig 1 6 Type of Liquid Crystalline Polymer The 3 dimensional structure of the LCP molecule is also important to consider Fig 1 7 Most LCPs are nematic as the actual crystalline structure of commercially produced LCP has been studied Some of the special chemical structures are known as cholesteric liquid crystalline which comes from cholesterol with indicating light circulativ ity This sort of LCP is studied for the display application field and it is not in scope of this book Liquid Crystalline Polymer 1 1 Jo in OT Nematic Smectic A Sar Cholesteric Fig 1 7 The structure of liquid crystal The typical chemical structure of LCP is shown in Fig 1 8 Main chain type LCP is now the most common Side chain and combined type LCP are proposed for L
94. own in table 5 4 The molded parts indicated initial performance under the certain drying condition after 1 week however the soldering resistance gradually was reduced by lower drying temperature or shorter drying times Table 5 4 1 week If the material left under above high humidity condition over 1 week the situation significantly became worse After 3 weeks all molded parts did not keep their initial performance with conventional drying machine and conditions sol dering resistance designated under 260 C which is not enough performance for recent non lead soldering with 260 C IR reflow condition This result means that the material should not leave under the high humidity atmosphere before drying even if the dry ing machine is installed with air dryer Table 5 4 Relationship between humidity and blister positive no change negative blister has generated sore ts ee lt V 20 mil i iia t l 0 20 pote te fete te terete te ts om aie EE ee ee 20 20 a ca 3hrs i el a ee 20 20 265 morc ahs 0720 J ee ee a ee 56 Liquid Crystalline Polymer 120 C 24hrs A no data 1 2 test pieces were used at each temperature condition The temperature of the soldering bath was increased by 5 C starting from 240 C 2 Indicated the number out of 20 pieces which the blister was detected after 1 min dipping into the soldering bath set up at 270 C 3 The 3rd week s ex
95. oy 5 Trouble shooting during injection molding of LCP Metering Compression Zone Zone Nozzle Cylinder Ther nocoupl e Nozzl e heat er Snme AA I Ther nocoupl e Nozzl e heat er pl H gh Wt ype gt 0 8L Recommendable design of nozzle portion Fig 5 3 Situation of retention resin at nozzle screw and cylinder The recommendable design of nozzle is also drawn in the bottom of this figure c Temperature settings of injection machine Difference between setting value and real resin temperature One of the most important causes for various molding problems is the difference between the set temperature of the injection machine and actual resin temperature Modern injection machines have digital indicators for the nozzle and cylinder temperatures so that the operator has confidence that the values recorded are equal to the actual resin tem perature Even with this the indicator value often differed from the actual resin temperature in almost machines that we meas ured lt Measurement procedure of resin temperature gt The measurement of resin temperature is usually done by sticking the pin type probe thermocouple into a round ball of purged resin In the case of the resin having the molding temperature over 300 C however the temperature re duction of the resin ball by the radiation of heat is significant and not able to ignore Thus it is difficult to measure the resin temperature precisely Because of the a
96. periment was carried on under the drying condition at 120 C only b Retention of resin at the inside of injection machine The apparent viscosity of LCP strongly depends on both temperature and shear rate in addition its dependence is stronger than general crystalline and amorphous plastics Because the apparent viscosity becomes very low under the proper injection conditions thin walled parts 0 3mmt or less are easily molded However long term running of molding generally causes the retention of resin at dead spaces of injection machine and this residue causes some deteriorations for example the contamination of black spots the increase of gas and the reduction of soldering resistance temperature including the blister Especially LCP easily remains in dead spaces of injection machine because of its low viscosity For similar reasons the purging of previous resin is somewhat more difficult than with general plastics Test method After cleaning up a screw and cylinder the black color grade of Sumikasuper LCP was molded up to 200 shots After this natural color grade was molded up to 400 shots The screw and cylinder were then taken apart for analysis of the residuary condition of the black grade Test Sample black color material Sumikasuper E6008 B natural color material Sumikasuper E6008 Molding Temperature 350 C lt Result amp Conclusions gt As shown in Fig 5 3 we should pay particular attention to the retention of
97. pyrene glass filled PC and commercially provided purging materials According to our investigation almost all materials indicated the ability of purging but did not indicate the ability 62 Liquid Crystalline Polymer of self purging by LCP In this case the purging material will remain in the cylinder of injection machine and it will decompose by the heat due to the molding temperature of LCP being higher than 300 C Such purging material doesn t have higher thermal stability as LCP What needs to be emphasized is that we should notice not only purging ability of LCP by purging material but also self purging ability of purging material by LCP For example glass filled grade of PC is widely used as purging material However the amorphous polymer such as PC has comparably higher melt viscosity it means that the purging material will not be removed by LCP because lower viscosity material has less ability to purge higher viscosity material In addition the melt viscosity of PC will enormously increase if it cooled under around 140 C This increase of viscosity also makes the purging by LCP diffi cult Accordingly glass filled PC is not suitable for purging of LCP We would like to now introduce our investigation regarding purging of LCP lt Test method gt Test method is very close to the description at 5 2 2 2 b 1 e after cleaning up of a screw and a cylinder the black color grade of Sumikasuper LCP was molded up to 200 shot
98. r products have these kinds of molding problems 34 Liquid Crystalline Polymer 3 4 Metering of LCP Stable amp short term metering is an essential function of injection molding technology for plastic molding In line screw mechanism is a very sophisticated mechanism due to having both plasticizing and injecting functions of the plastic We often suffer unstable metering during LCP molding This trouble is usually found via the unstableness of me tering time and due to clumsy forwarding of LCP granules at the hopper or the pulsation spout of melt during purging We have to say that the unstableness of metering is one of the essential problems of LCP molding In recent years LCP manufacturers have improved this phenomenon with their own technologies however it has not always been successful 1 Principle of unstable metering We must think about the melting process of LCP during the metering of the injection machine The heat in order to melt the LCP granule is only supplied from cylinder or nozzle heater Since the heaters are installed outside of cyl inder the heat always comes from outer portion of cylinder shown in Fig 3 17 Due to this reason there is tempera ture deviation at small space between screw and cylinder Accordingly the first step of melt of the granule starts from the side that is in contact with cylinder wall If the melt process starts the hardness of granule will be quickly lost and melted portion will
99. reinforcement effect This effect brings higher mechanical properties High flow ability This effect helps to mold in thin walls Barrier Resistance This effect is from the skin layer and provides probably the best gas and liquid barriers LCP has the following demerits Strong anisotropy This demerit brings the difficulty to control warpage problem Low weld strength This property brings the difficulty of designing of molded article At last LCP suppliers prepare several compound grades for fitting the many kinds of applications chopped GF GF mineral Te Ine 30 35 35 40 50 340 C Super High Temperature s E4006L K High Temperature 5 Standard Low Warpage z noe E6006L N E6807LHF Z High Flow E6007LHF Z E6808LHF Z oe E6808UHF Z Tolerant for 60 at Solder E6810LHF Z Fig 1 24 Line ups of Sumikasuper LCP 16 Liquid Crystalline Polymer Application of LCP and its technology Several applications of LCP have been established The purpose of this section is to introduce the latest technology related to each application which is necessary to understand for the best material selection The following descrip tions will disclose tips for choosing the optimized material 2 1 Connector for PC mobile digital camera etc This application field is one of the largest and the most important for LCP Over 60 of LCP materials are used for this market The total amount of this application of LC
100. roduce into the IR Infra Red reflow oven and both circuit board and devices will be heated until the soldering temperature of printed solder The soldering tem perature is usually 240 C for conventional solder and 260 C for Pb free solder Both of these temperatures are not equal to the case of conventional soldering because the circuit board will act as a heat seal for the devices In SMT the devices themselves will be heated at the same temperature as soldering Accordingly the devices for SMT are called Surface Mount Devices SMD and high heat resistance materials are needed for such devices This is one of the main reasons why LCP is now used for this application field After cooling we can obtain the assembled circuit board just like in conventional soldering however we will still be able to use the opposite side of the circuit board This technology enables to use both side of circuit boards and use of multi layer soldering At the same time we should think about the dimension precision of the device during SMT soldering The de formation of device during soldering can bring a serious misalignment problem Fig 2 2 illustrates the situation Sol dering will only be successful in the case of the molded part keeping its flatness and plane of dimension Fig 2 2 a In the case of the molded part having warpage the deformed upper side will be misaligned Fig 2 2 b In general the tolerance should be under 0 10mm for soldering This mea
101. rt shot moldings These must bring us very important information about flow pattern and the cause of warpage GATE monn ooo oo e 2 47mm gt lt _ core out core out dimension 1 5x 1 0xh Fig 4 9 Schematic view of the model mold injection speed 200mm sec E6006L j 6006 E6807L 0 2 warpage mm 0 0 0 2 0 4 0 6 0 8 1 0 depth of core out mm Fig 4 10 Relationship between core out depth and warpage for various LCPs 44 injection speed 200mm sec core out depth Omm haa a EE ET b nn O 2MM my pr atin j C aT O AA nw preas d eg a gt b gt ccrd anaes 0 6mm_ a Fig 4 11 Photo of short shot samples 45 L iquid Crystalline Polymer 5 Trouble shooting during injection molding of LCP 4 4 Case study In this section we would like to show you actual examples of warpage improvement for several connectors For proprietary reasons we have changed the design detail in these examples so that they do not reflect any actual parts a Board to board connector 0 5mm pitch Fig 4 12 shows schematic view of 0 5mm pitch board to board b b connector This connector had a warpage of about 0 10mm at original design From the observation of short shot molding the flow pattern was thought as shown in the figure In this case it is thought that the main cause of the wapage is the flow difference of top portion and bottom portion in the side
102. rtion Due to equalizing the flow difference between the inside ribs and cylindrical wall thickening of the wall of cylin drical portion was recommended The inside rib is relatively thicker than the other sections and that is the most impor tant reason of flow hesitation 2 Installing of core outs at out side of inside ribs Installing of core outs at out side of inside ribs is also effective for equalizing of the flow pattern because such core out will prevent and control the flow at this thicker portion 3 Re allocating of the gate Since the bottom rim is thicker than upper rim moving of the gate to bottom side is somewhat effective Because thicker portion should be filled firstly to prevent losing the filling energy from melt flow Above improvement ideas are shown in Fig 5 29 In this case our customer carried out all procedure according to our recommendation and the problem has improved There are still 2 reasons for the problem we recommend referring to the listed sections gate Fig 5 28 Schematic view of the LCP flow into the bobbin cavity T 5 Trouble shooting during injection molding of LCP 1 thickening of cylindrical wall 2 installing of core outs at outside of inside ribs 3 re allocating of gate Fig 5 29 Solution of the problem 78 Liquid Crystalline Polymer 5 10 Sticking Sticking to the mold is one of the most troublesome problems because it is easily linked with the mold damage
103. s Then a purging material listed below was used for purg ing of black color material and immediately the purging material was purged again by natural color material After that the screw and the cylinder were taken apart for analysis of the residuary condition of the black grade and purging ma terial itself Test sample black color material Sumikasuper E6008 B natural color material Sumikasuper E6008 Purging material listed in Table 4 8 with results Molding Temperature 350 C lt Result gt The results were shown in Table 5 8 Table 5 8 Result of aes about purging material for LCP Grade name Manufacturer Property of purging material of purging material Test results Total as Base type iim Purging Self purging Handling sessment polymer temperature ability ability HF21D HDPE Z Chisso co S29 Amteclean S Matsushita whisker amtech whisker Ex AP 10 whisker Asahi Kasei Super Hoshi n PE 4 495 o w o d o po PMMA 1 Information were adopted by eee document of each manufacturer 2 Decomposition temperature was evaluated by ourselves using TGA equipment TGA 50 of Shimadzu co Thus we recommend following listed materials as purging material for LCP see Table 5 9 We also recommend that you should not use any other materials for this purpose even if you have much experience to use LCP Table 5 9 Recommendable purging materials Any of below materials can be used for purging material
104. s or ganic chemicals or ions cannot easily permeate through crystalline portion It is the same for LCP because the skin layer of LCP is the highly crystallized portion of LCP molecule For this reason LCP s exhibit excellent gas barrier properties Fig 1 20 shows gas permeability data for many kinds of polymer films It reveals that water and oxygen permeability of LCP is superior to any other plastic film and it is close to that of Aluminum Foil 12 Liquid Crystalline Polymer P P 102 HDPE a a 10 w N Biax PP gt E sg I pe m oo 10 1 lt 10 0 So oOo Llo 10 1 10 10 10 103 104 Oxgen Permeability cc 25um m2 24hr latm Fig 1 20 Gas permeability of polymer films 1 5 Anisotropy As mentioned LCP s have strong anisotropic property and this often causes molding problems such as warpage weld crack etc Here we would like to focus attention on this issue Fig 1 21 shows the mold shrinkage for both MD and TD The dotted line indicates unity shrinkage for whole direc tions meaning that the material is isotropic 1f the plot is on this line Although crystalline polymers such as PPS or glass filled material such as PES 4101GL30 indicate weak anisotropic behavior LCPs exhibit stronger anisotropy especially non filled material E6000 This means that LCPs essentially have stronger anisotropy but GF filling re duces this property This is opposite of most conventional plastics This is one of the key f
105. se of specific gravity at the same time Accordingly the balance between filler content higher stiffness and lower specific gravity should be considered In addition since LCP has the characteristic that thinner wall thickness will bring higher modulus the thinner ac tuator will have merit of the improved design for higher resonance frequency see section 1 4 Fig 1 15 A few LCP suppliers provide some suitable grades having higher soldering resistance and higher comparative modulus with lower specific gravity Table 2 4 shows Sumikasuper E5000 series As show in Fig 2 11 in spite of Sumikasuper E5006L having only 30 GF it indicates approximately similar stiffness with E5008L which includes 40 GF It means E5006L is one of the most suitable grade for this application Table 2 4 Grade line up of Sumikasuper E5000 series for OPU actuator bobbin application Grade Filler Specific Flexural modulus 400 C dipping in Moldability Recommendable name content gravity 0 5mmt MD solder bath application ES006L c GF 30 1 60 30 GPa OK Low X40 CD ROM X16 DVD ROM DVD Video CD R RW OM etc 1 69 K i O E5008L E5008 CD DA low price CD ROM OM etc 1 c GF chopped glass fiber standard GF for conventional engineering plastics m GF milled glass fiber short size GF for special purpose 35 o E5008L p 1 69 30 E5006L p 1 60 A LCP R JGF30 p 1 60 a 2 DS 5 E 2 20 E x 15 LL 10 5
106. ss In this section we would like to show you our approach to solve this problem using actual case studies 1 Cracking problem for Coil Bobbin Coil bobbins are part of electrical inductance by winding the wire around the bobbin During the assembly process the coil bobbin was subjected to a strong winding force by the wire Fig 5 13 After wiring the problem occurred at the body of the bobbin Fig 5 14 The crack was observed at around center of the cylinder portion horizontally In ad dition the cracked line was elongated at the rib installed inner side of the cylinder gate C gt soldering molding of bobbin winding of wire Fig 5 13 Schematic flow of bobbin assembling generation of crack Fig 5 14 Crack portion of bobbin In this case the outer diameter of cylinder between brims equals d the inner diameter a is for vertical direction and is larger than horizontal direction b as seen in Fig 5 15 It means the thickness of cylinder is not equal In this case the flow pattern is as shown in Fig 5 16 The LCP flows from the gate to upper brim then downward Accordingly the LCP flow downwards through thicker side wall portions and rib portions The melt LCP arrives at bottom brim and will reflect upward where the LCP is delayed to flow Fig 5 16 1 That is it generates the flow hesita tion and the weld at the portion where both downward and upward flow bump Due to eliminating the flow hesitation the equalization
107. ssion zone 2 The melt material flows from nozzle side beyond the clearance between screw and cylinder due to its extraordi nary low melt viscosity 3 The melt material arrives to the compression zone and infiltrates to the deep portion of screw groove 4 Since the temperature at the deep portion of the screw groove is relatively lower than cylinder surface the melt material infiltrated there is re congealed and coagulates the un melted granule At last it becomes the plug The softening of the granule surface due to the temperature will promote this effect It also means that the metering time elongates Sometimes it reaches over 60 seconds 5 The plug exists until the plug starts melting and broken by the pressure of transferred granule from hopper Suddenly the metering time decreases 6 Repetition of above mentioned 30 0 20 0 10 0 metering time sec 5 10 15 20 25 shot number Fig 3 20 Typical deviation of metering time during unstable metering state 2 Solution of unstable metering First of all we should notice that the abrasion of the cylinder and screw parts causes the problem The abrasion of screw parts especially the check ring is the most important This will enhance the back flow phe nomenon during metering process due to enlargement of clearance between the screw part and the cylinder wall It reduces the plug ability of reverse direction flow of the melt If the unstable metering occurs we recommend replac
108. st important If you gather the in formation and disclose it quickly the problem will be improved more quickly The important characteristics are labeled in Table 5 1 These 6 items will be necessary when you consult about your current molding problem to the LCP manufacturer Table 5 1 Information list for quick improvement of molding problem a What has happened Type of trouble gt gt gt The classification of the trouble is described in Table 5 2 Black spec Blister amp Bubble Crack Flash Flow mark Metering Short shot Sticking Warpage etc Drawing sketch or molded part is very helpful to think about the reason of trouble If possible above mentioned should be provided to material manufacturer s engineer c What kind of grade and Of course this is the mane basic information however the molding engineer often lot No forgets to inform this The lot No is the most helpful to chase the production history at the manufacturer s factory If this information is missed it will be more difficult to understand material related issues The grade name and lot No on the material bag Should be used d When and how often It is also important to identify the cause and duration of the trouble or whether the has it happened problem has happened suddenly or regularly during production or during trial testing Also the percentage of fault is important as it will give the material engineer more clues to solve the proble
109. ster Condition 2 12 1 280 285 blister PS 40ESASE Nisse1 Normal gt 300 no blister condition SG 150 condition 1 N Cl C2 C3 C4 150T 40mm 330 330 320 310 300 C actual resin temp 350 C condition 2 N Cl C2 C3 C4 360 360 350 340 330 C actual resin temp 380 C PS 40ES ASE normal condition N Cl C2 C3 360 360 350 330 C actual resin temp 350 C lt Result gt Fig 5 6 shows the relationship between the metering for 1 shot and the max metering range If the metering for 1 shot is too short compared with maximum metering range the retention time of the polymer inside the cylinder be comes too long and it will be the cause of deterioration of polymer as mentioned above SG 150 full scale of neasuri ng 100 Po gt lt 4 for each shot PS 4OE5ASE full scale of neasuri ng 100 ee seman gt lt 28 6 f or each shot Fig 5 6 The relationship between the metering for 1 shot and the max metering range Since most of articles molded by LCP should be small the size of suitable molding machine should be small Rec ommendable specification of injection machine is as follows clamping force of the mold 50 70 Tons screw diameter 24 27 mmo For more smaller products clamping force of the mold 15 Tons screw diameter 17 mmo f Purging method of Sumikasuper LCP Several kinds of material are known for purging when using LCP resins The most popular materials are PP polypro
110. t has had tremendous growth LCD Liquid Crys talline Display is one of the most promising items Lighting in the LCD requires several CCFLs Cold Cathode Fluorescent Lamp used according to the panel size LCP is now being used in the bobbin of the inverter for lighting of CCFL instead of former phenolic resins 1 Proceeding of the backlight system of LCD The principle of perceiving of the image on LCD is to view the contrast that is generated by the backlight through a polarizing panel and liquid crystalline cell We will omit the detail of technology of the liquid crystalline cell here please refer the certain literature about this technology LCD needs light from the outside because it doesn t emit light itself The former LCDs for small calculators or early mobile phones used only natural light Recent LCDs however use active backlights In general CCFL Cold Cathode Fluorescent Lamp is used for the backlights CCFL is very similar to the home use fluorescent lamp however it uses the secondary electron emission from electrode made by Ni nickel or Ta tantalum instead of a filament The merit of the electrode system is the ability of size reduction The diameter of a CCFL was 3mm several years ago however recent diameters are now 1 8mm9 The life of LCD depends on the life of CCFL Since the current CCFL has over 50 000hr life the LCD life equals over 50 000 hrs There are 2 kinds of the backlight system as shown in Fig 2 7 S
111. t it sometimes indicates noticeable improvement of warpage The second recommendation is the installation of core outs at the thicker portion see Fig 4 3a This proce dure is very similar to the conventional way of installing core outs to improve not only warpage but also subsi dence However the purpose of installation for LCP moldings is restriction and equalization of the material flow in thicker portions If installing portions of the core out is not correct the warpage can get worse Fig 4 3c For the equalization of flow pattern installing the core outs at the bottom will be suitable as shown in Fig 2 3a The third and last method is the moving of the gate position to the thinner portion Fig 4 3 b The purpose of this procedure is to make the material flow to thin portion earlier in this figure moving to rib portion This procedure can be used not only for moving the gate itself but also moving the junction of portion to portion In the next section we will examine one of these procedures using the model mold gate move installing core outs i gate gate a b C Fig 4 3 Methods for modifying the flow pattern installing core outs 40 Liquid Crystalline Polymer 4 2 Relationship between warpage and flow pattern As described above the anisotropy caused by flow pattern is the main reason of warpage in an LCP molded part Evidence of this phenomenon can be seen following experiment Fig 4 4 s
112. talline polymer but it is not proved because the thinner test piece less than 0 3mm is not obtainable without any kind of flame retardant needed This helps with ESHA and other environmental regulations and needs Table 1 5 Comparison of mechanical properties for PES and LCP Specific gravity Mold shrinkage MD 0 6 TD 0 6 Flexural strength MPa 129 Flexural modulus MPa 2 550 C T E MD aS 10 C TD 5 7 Flame retardancy Furthermore the thickness of skin layer is almost specific as 200um as described above As the total thickness be comes thinner the ratio of skin layer comparatively increases against the total thickness Since the skin layer is formed by integration of highly oriented fibrous semi crystals of rigid rod molecules it derives high mechanical prop erties As a result the strength of LCP will gradually increase with decreasing of the thickness Fig 1 19 This is typical and unusual property of LCP which does not observed at conventional plastics 350 Thickness 300 LCP Sumikasuper LCP 250 200 150 100 50 0 PES Tensile Strength MPa PBT Natural Skin Layer 0 0 5 1 0 1 5 2 0 Thickness mm Fig 1 19 Relationship between wall thickness and tensile strength The skin layer has another important feature lower permeation of gases Basically the crystal structure has a very high density and is strongly integrated by molecules Accordingly the low molecular structures like gaseou
113. tention against abrasion attention against abrasion at check ring at inlet of hopper side nozzle C r E E Q Q amp A JN WANA SSS oN temperature setting MT MT 20 C MT gt 40 C MT Molding Temp Fig 3 21 Attention about abrasion and recommendation of temperature setting of cylinder The final variable related to this problem is the screw design It is not an easy question due to the screw being in stalled inside of hard and strong steel cylinder However we can recommend several suggestions as the most suitable screw design for LCP molding based on our long term experiences see Fig 3 22 We believe that the following recommendations have often succeeded The differences are not only from basic differences of design of screw at each manufacturer of injection molding machine but also an individual difference with each product of injection machine Probably we need much more study about this region with injection machine manufacturers lt Recommendable screw design gt Compression ratio 2 0 2 2 L D 20 25 se 20 25 _____ _ 55 25 ___ 35 40 metering zone feed zone compression zone Fig 3 22 Recommendation of screw design 36 Liquid Crystalline Polymer Improvement of the warpage As mentioned LCPs have excellent performance in many areas as compared with the other engineering plastics Es pecially their excellent fluidity that is useful in the l
114. the higher water absorption property is de rived by the amide bonding group LCP is similarly in the same situation It is mostly affected to the difference of moldability Several researchers have started to reveal this difference but no one has succeeded to describe it as yet The difference of moldability is the number one cause of difficulty in molding shops Table 1 2 Typical molecular structure of commercial LCP 5 1 Introduction of liquid crystalline polymer Type Molecular Structure TDUL Example O O O Tyre toto Xydar Q Type I o pe arar 210 260 C Vectra O O O Type II tot OCH CH O O lt 210 C peoue Novaccurate PET p hydroxybenzoic group During molding process the shear stress with the wall of mold induces the specific structure In the case of injec tion molding the melt polymer flows in what is called a fountain flow Fig 1 9 The shear stress will be generated between center flow and mold wall After cooling the record of this flow is highly characteristic As shown in Fig 1 9 outer side of molded part is strongly aligned to the flow direction although the center portion is aligned transverse or random direction In general this structure is called as Skin Core structure Fig 1 10 shows the cross section of actual molded part and its schematic view to confirm this special structure This is very similar as the structure derived by crystalline polymer however each skin and core layer of LC
115. timulated many researchers interest and now there is much literature about liquid crystals It is important to point out clear fundamentals of commercially produced LCPs liquid crystalline domain direction of shear nematic liquid crystalline polymer melt over liquid crystalline transition temperature Fig 1 5 Three dimensional structure of liquid crystalline polymer The reason behind liquid crystallinity is not completely clear but we know that the rigidity of the molecule and in duced anisotropy of its shape are an important factor Such molecules are called mesogen which is derived from the former explanation of mesomorphic state Basically this is intermediate phase between solid and liquid states Many chemical structures have been examined and we know that several chemicals indicate liquid crystallinity The most important mesogen is p hydroxybenzoic acid for LCP This raw material can be polymerized by itself self po lymerization however it is obtained in an insoluble and unmelted form It is usually co polymerized by other raw materials to help reduce the process temperature Of course such copolymer still keeps its excellent heat and solvent resistance In fact few solvents attack LCPs with the most noted one being a mixed solvent of pentafluoropnenol and chloroform Another question is to determine when the liquid crystal first appears Just like low molecular weight liquid crys tal LCP appears in t
116. tures of plastics In conventional materials anisotropy increases with the filler content Anisotropy of LCP however decreases with the filler content Table 2 1 shows the relationship between GF content and anisotropy for several plastics Here anisotropic character is evaluated by TD MD ratio of mold shrinkage data And these tendencies were illustrated in Fig 2 3 Table 2 1 Relationship between GF content and anisotropy Data were calculated from TD MD ratio of mold shrinkage at 3mmt ND no data Hyper dimensional No filler GF 10 GF20 GF30 GF 40 structure Crystalline plastic PEEK Victrex PEEK PPS Novamid PA6 Amorphous plastic PES Sumikaexcel PES upilon gt Liquid crystalline LCP Sumikasuper E6000 8 45 ND ND 3 9 ND polymer 18 Liquid Crystalline Polymer It is clear that LCP has a much different relationship between GF content and anisotropic character It is thought that LCP itself has a strong anisotropic property Introducing of fillers disrobes such original property by disrupting of the alignment of rigid rod molecule of LCP In contrast the flowability of LCP will decline with increasing of the filler content Fig 2 4 Accordingly this is the reason why GF 30 40 grades of LCP are the standard formulation because this formulation is one of the best balance between anisotropy and flowability 10 0 Sumikasuper E6000 Q 8 0 PC lupilon H a 6 0 gt
117. ty of the light In this case the eddy portion as indicated dark in the figure should be the portion where the glass fiber appears to the surface Again this is due to the insufficient touching of melt polymer to mold wall by the eddy Because the sufficient touch ing to the mold wall will bring the smooth surface This means that sufficient pressure of the melt polymer covers the fillers as Glass Fiber In general higher mold temperature is useful for improving the surface condition Indeed it is known that the sur face of an LCP part molded with over 150 C of mold temperature can be improved Such parts have relatively shining and clear color surface of course the mold surface must be polished like a mirror Black color grade indicates darker black than the case molded by the condition with much lower mold temperature However the higher mold temperature induces another problem the sticking problem to the mold because of enlargement of the mold release force Since leveling of meandering during LCP flow is very difficult this phenomenon is one of the essential for LCP molding In other words the flow mark on the surface for LCP molded article is unavoidable 74 Liquid Crystalline Polymer 5 8 Metering This problem is induced by the starvation phenomenon of the melt during the metering process discussed at the sec tion 3 4 Almost all LCP manufacturers are applying additives to their compounded granule to prevent adhesion of gr
118. umber Fig 4 7 Infra red spectra of Sumikasuper LCP E6000 The result is shown in Fig 4 8 The result of f at each measured portion was described by vector with its angle and relative length 42 Liquid Crystalline Polymer When using a slower injection speed of 50mm sec LCP flows to the longitude direction at the thicker portion and flows to thinner portion from thicker portion The equivalent flow pattern light red is quite similar as Fig 4 2 Higher and higher injection speed the flow direction of thinner portion inclined to the longitude direction and became very close to the thicker portion at the bottom This means that equivalent flow patterns will change and equalize the dif ference of anisotropy between thinner and thicker portions Since increasing the injection speed reduced warpage it is clear that flow pattern changes can enable improvement in the warpage As seen in this experiment equivalent flow pattern is the most important factor in finding reasons for warpage gt 000 0000000000 OOOO000000 OOO0000000 GATE O00 0000000000 0000000000 0000000000 2 thinner portion SSPSPSEEPEPEREREIEIS AR ZG thicker portion measured portion of dichloic spectra study 50mm sec measured flow vector EE equivalent flow pattern 200mm sec 800mm sec Fig 4 8 Result of IR dichloic spectra study and equivalent flow patterns 43 5 Trouble shooting during injection molding of LCP 4 3 Relationship between the depth of
119. urging method should be execute once a week preferably Please stop the injection machine after the above step 4 is completed Starting procedure 1 Set the temp as same as 3 2 As soon as reaching the molding temp then feed the purging material in the hopper 3 Follow the same step from 3 64 Liquid Crystalline Polymer 3 Settlement of Bubble problem It is necessary to consider both the suitable molding conditions and tooling design in order to reduce the dragging of air into the cavity and possibly creation of bubbles a Dragging of the air into the melt In some cases dragged air into the melt causes bubbles the oxidation of polymer will occur and color change or black spots will be often observed in this case please refer 2 Reduction of the blister at soldering also The reasons of the air dragged into the melt are as follows 1 Too low of back pressure LCP does not need high back pressure however too low back pressure causes insufficient removal of the air dragged from hopper 11 Too high decompression degree of screw on metering process The air is dragged into the melt from nozzle touch portion 111 Too high screw rotation on metering process over 200 rpm This causes insufficient removal of the air dragged from hopper similarly with 1 sprue AW oS 3VO CBO air Ca oe oF O OTOIO OXR QO Q CO K CORO AA OY ONOON pea BREE SER SARE RERES ERC ES aa EXC CAO mold Fig 5 7
120. ve temperature setting at the hopper side is under its melting point Accordingly it should be noted that the flow of insufficient melt due to lower temperature setting might cause other problems We believe that the above example is one of the most popular and effective ways to eliminate unstable metering but we also take care about the other possibility of problems We should also take care of using a relatively high melt viscosity material and the case that the metering amount is larger than the ordinary capacity Such cases sometimes induce insufficient melting The second recommendation is the optimization of the screw design Now we have insufficient knowledge about the screw design and waiting for the many researchers studies about the relationship between the metering and the screw design We recommend referring to the section 3 4 Also the abrasion of metal parts of the screw should be noted Especially the check ring part must be kept clean and replaced often If the abrasion advances and the clearance become too large it often causes plugging This part should be replaced each 3 or 4 months The screw should also be replaced every 6 or 12 months whether or not any other problems occur T3 5 Trouble shooting during injection molding of LCP 5 9 Short shot Most people misunderstand the actual reason of short shot problem during LCP molding Usually the molding engi neer thinks that the reasons of short shot involves the flowabilit
121. wall That is the top portion indicates MD flow properties vs the bottom portion indicating TD flow proper ties To equalize the flow pattern between top and bottom portions depressions were installed at top portion of side walls as seen in Fig 4 13 the reason of this installation is limitation of top portion flow The warpage was improved with a reading under 0 05mm core outs Fig 4 13 Installing of depressions b S O DIMM Fig 4 14 shows S O DIMM that was designed having average thickness as 0 03mm In this case 3 types of war page were observed mode 1 warpage of longitudinal direction mode 2 twisting mode 3 arm tumbling to the inside GALE arm ae mode 3 L front Fig 4 14 Schematic view of S O DIMM contact pins bottom arm opposit side mode 2 46 Liquid Crystalline Polymer i Mode 1 warping and Mode 2 twisting We started from the observation and evaluation of short shot moldings As the result it was found that the flow patterns between top and bottom were not uniform the top flow was slower than bottom flow Fig 4 15 mode 1 The reason of mode 1 was thought to be that the thickness of the top was thinner than the bottom Fig 4 15 down left In this case the flow pattern at the arm opposite side of the gate was thought as shown in Fig 4 15 down right arrows Thus the arm opposite side deformed to the top direction and this molding indicated mode 2 war page We r
122. ween gate side and after center portion Since the flow pattern between both side walls and the spine is nearly equal near the gate the polymer will flow in the side wall and the spine Then the weld will form at the center of thin ribs between the holes A in Fig 5 22 At the center portion of this con nector however the polymer flow from the side wall will become faster than at the spine due to the effect of the de pressions B in Fig 5 22 weld line side wall backward flow gate ie side wall Eeo Fig 5 21 Schematic view of the flow pattern a ooo eoooooo gate Ee eee E side wall side wall 1 7 Bi Y i EGE weld weld A B Fig 5 22 Difference of the weld formation Since it is thought that the weld strength of A and B is the same the reason why the crack occurs must be related to the existence of the weld line at the rib portion between both holes As shown in Fig 5 22 A the strength of the weld section is very weak because the wall thickness is very thin However as shown in Fig 5 22 B the weld line is formed ga 5 Trouble shooting during injection molding of LCP at the spine section and the weld strength will become stronger than that in Fig 5 22A It is easily understood that the crack will not occur at the rib portion between both holes From these points some ways to improve the situation also see Fig 5 23 1 Changing the gate system from point gate to 2 point gates 2 Installing the additiona
123. y or melt viscosity of the material It is only one of the reasons the cause is really due to 4 reasons as shown in the Fig 5 26 First it is a higher melt viscosity which is the most conventional thinking way Second it is due to the flow hesitation as described at section 3 3 It is very troublesome because it is difficult to dis tinguish between shortage of fluidity or generation of flow hesitation for non expert engineers of LCP molding The appearances of both reasons are very similar however the remedy is different In the case of shortage by fluidity optimization of the molding conditions will usually work In the case of flow hesitation it will not be soluble by the same way The third reason is due to the starvation derived by the plugging described in the section 5 8 The last reason is due to dragged air Installing the air vent is one of powerful solution if the cause is insufficient exhaust of cavity air We must consider about each reason and improvement Short shot lt cause gt insufficiency of flowability higher viscosity unbalance of flow section 3 3 plugging section 3 4 bad exhaust section 4 4 3 Fig 5 26 Classification of short shot problem dragging of air 1 Insufficiency of flowability In this case molding temperature should be increased slightly We usually recommend increasing 5 to 10 C from the original setting at the nozzle and H1 Front portion heater of cylinder You must take care
124. y setting comparing actual velocity with setting Injection speed setting Holding pressure setting V P switching setting Fig 3 4 Relationship of molding parameters change of closed loop machine with screw position 3 2 Thin wall fluidity of LCP and characteristic of injection molding machine On the basis of the principle above mentioned we have carried out the investigation to clear the moldability de pendency with characteristic of the difference of injection machines 1 Experiment The 4 cavities tooling shown in Fig 3 5 cavity thickness 0 2mmt was used for this study with Sumikasuper E6008 GF 40 as LCP Injection molding machines were used shown in Table 3 1 and mold temperature was 130 C The molding temperature of each injection machine was 360 C measured by IR Infra Red emission thermome ter IT 240S Horiba Ltd Japan at 0 86 of the emission rate before each experiment Details of measuring of the molding temperature are shown in Fig 3 6 see the same manner of the description at 5 4 2 c ad 3 Injection molding technology for LCP 10 10 10 15 0 20 diameter sprue Thickness 0 2mm Runner 3 0mm Gate 0 2t x 1 5w x 2 0 Flow length average of 4 cav Fig 3 5 4 cavities model tooling Table 3 1 the list of injection molding machines of this study po A S B C closed loop clamping force cylinder diameter injection rate 1 360 467 1 79 2207 151 2790

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