Cristal Liquido Zytel

7/28/2019 Cristal Liquido Zytel

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Melt

Shear

Stress

Solid

State

Outstanding Properties

Mechanical Thermal Electrical

Chemical Dimensional Processing

StartwithDuPont

Molding Guide

Zeniteliquid crystal polymer resins

6000 and 7000 SeriesHigh Temperature LCP Resins


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Zenite LCP ResinsMolding Guide

Table of Contents

Chapter 1General Information . . . . . . . . . . . . . . . . . . . . 1Resin Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Compositions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Melt Flow Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Chapter 2Molding Equipment . . . . . . . . . . . . . . . . . . . . . 2Machine Melt Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Barrel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Screw Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Nonreturn Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Nozzle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Hydraulic System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Injection Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Clamping Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Chapter 3Handling of Molding Resin . . . . . . . . . . . . . . . 5Drying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Regrind . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Chapter 4Machine Operating Conditions . . . . . . . . . . . . 7Molding Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Melt Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Nozzle Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Mold Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Injection Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Injection Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Pack Pressure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Screw Forward Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Overall Cycle Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Screw Speed and Back Pressure . . . . . . . . . . . . . . . . . . . . . 10Screw Decompression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Start-Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Cycle Interruptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Purging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11


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Table of Contents (continued)

Chapter 5Mold Design . . . . . . . . . . . . . . . . . . . . . . . . . . . 12General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Mold Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Maximizing Physical Properties . . . . . . . . . . . . . . . . . . . 12Sprues and Runners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Gate Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Gate Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Vents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Undercuts and Taper . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Mold Shrinkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Tolerances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Chapter 6Troubleshooting Guide . . . . . . . . . . . . . . . . . . 16

Chapter 7Operating Precautions . . . . . . . . . . . . . . . . . . . 18Thermal Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Off-Gases and Particulates . . . . . . . . . . . . . . . . . . . . . . . . 19Handling of Resins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19Slipping Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19


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1

Chapter 1General Information

Resin Description

Zenite is the DuPont trademark for its liquidcrystal polymer (LCP) resins. Zenite 6000 and7000 series LCP resins are wholly aromatic polyes-ter resins, and are easily melt processed. The mate-rials feature excellent toughness, dimensionalstability, and creep resistanceeven at very hightemperatures. In the molten state, the polymersrod-like molecules are somewhat aligned. With highprocessing shear stresses, the molecular alignmentis further enhanced. This, in turn, contributes toanisotropic propertiesincluding superior physicalproperties over a wide temperature range, lowthermal expansion, and low mold shrinkageespecially in the flow direction. The commercialgrades are glass- or mineral-filled. These grades ofZenite LCP resins are ideal for a wide range ofapplications in the automotive, electrical/electronic,and industrial markets.

Compositions6130 30% glass-reinforced, 256C (493F) heat

deflection temperature (HDT)

6330 30% mineral-reinforced, 235

C (455

F)HDT, more isotropic dimensionalproperties

7130 30% glass-reinforced, 295C (563F)HDT

7130HT 30% glass-reinforced, 300C (572F)HDT

Melt Flow Characteristics

Zenite LCP resins have excellent melt flowcharacteristics. Filling of long, thin channels ispossible due to the low melt viscosities at therecommended melt temperatures. Figure 1 showsthe melt viscosities are about the same as nylon 66and high density polyethylene and less than half ofmost other engineering plastics.

Figure 1. Melt Viscosity versus Melt Temperature at1000 sec1 Shear Rate

Melt Temperature, F

Melt Temperature, C

MeltViscosity,

Pas

500

300

200

100

50

30

20

300 390 480 570 660 750

150 200 250 300 350 400

HDPE

30% GR PET

Nylon 66

Zenite 7130

Zenite 6130

AcetalHomopolymer

PolyesterElastomer


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Chapter 2Molding Equipment

Zenite LCP resins can be molded in all standard

screw injection molding machines. General-purposescrews are usually adequate. Zenite LCP resins,like other glass-reinforced resins, can cause wear incertain areas of the barrel, screw, and mold. Thematerials of construction that are recommendedbelow are based on vast experience with otherDuPont glass-reinforced resins that are moldedcontinuously or for significant lengths of time. IfZenite LCP resins are to be run in such volumes,these steps should be considered.

Machine Melt CapacityThe plastifying capacity of any screw injectionmolding machine primarily depends on the screwdiameter and design.

Shot Size

Shot size is equal to the volume of molten resininjected by the screw during the cycle. The meltdensities of Zenite LCP resins are approximately45% higher than the melt density for polystyrene(the standard used for specifying molding ma-chines) at normal temperatures and pressures. For

the best molding (reasonable residence time), theshot size should utilize between 30 and 70% of themaximum stroke of the screw.

Screw Recovery Rate

Screw retraction (recovery) is influenced by cycletime, screw design, screw speed, back pressure,cylinder temperature profile, shot size, and, as withall glass-reinforced resins, screw and barrel wear.For guidelines to screw speed, see Table 4 (inScrew Speed under Chapter 4: Machine Operat-

ing Conditions).

Barrel

General

Three-zone heating control of the barrel (corre-sponding to the screws three functional zones)should be provided for precise temperature control

and high output rates. In all cases, the temperature

of the nozzle should be independently and preciselycontrolled. High wattage ceramic heater bands arerequired in order for all zones to reach and becontrolled at the high temperature settings of350380C (660715F).

A means of controlling the temperature at the barrelfeed throat must also be incorporated. Coolingwater to the feed throat should be controlled by aneedle valve. A dial thermometer can be used tomeasure the throat temperature.

Barrel length should be at least 20 times the diam-eter for uniform melt temperature at high outputs.

Wear

Bimetallic barrel liners, e.g., Xaloy1 100/101 or 800types (or equivalent), have shown outstandingresistance to wear by glass fibers.

Screw Design

General

The general-purpose gradual compression screws

that are installed (OEM) in molding machines areusually suitable for molding Zenite LCP resins.Successful moldings have been accomplished withscrew compression ratios ranging from 2.0 to 3.5.For uniform melt temperature control, length/diameter ratios of 18/1 to 20/1 are recommended.

Wear

Abrasive wear by glass on injection screws occursprimarily on the lands and edges of screw flights. Intime, the root diameter will wear somewhat in thetransition and metering zones. Use heat-treated andstress-relieved alloy steel with a hard surface. Forbest results, the screw should be made of CPM-9V2

tool steel and the flight tips be hard surfaced withColmonoy No. 56.3

1Xaloy, Inc., Pulaski, VA2Crucible Co., Camillus, NY3Colmonoy Corp., Madison Heights, MI


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Nonreturn Valve

General

Hardened sliding-type ring check (nonreturn) valvesshould be used for processing Zenite LCP res-inseither the more common ring check type or aball check valve may be used. In either case, the

flow passages must be streamlined and nonre-stricted to prevent problems associated with hold-upspots. See Figure 2 for a good generalized design ofa nonreturn valve.

Figure 2. Nonreturn Valve

use of a reverse taper bore nozzle (see Figure 4) isrecommended. The nozzle temperature should beindependently and precisely controlled. The heaterband and thermocouple should be placed as farforward as practical for good temperature control.High wattage ceramic heater bands should be used

to maintain a temperature up to 380

C (715

F).Although not recommended, positive shut-offnozzles can be used when proper temperaturecontrol is provided. Again, streamlining is impor-tant and the risk of hold-up spots can be a concern.

Figure 3. Free-flow Nozzles

MELT FLOWRING SEAT

RING

Wear

Ring check valves (nonreturn valves), especiallywhen not hardened, undergo rapid and appreciablewear when used with glass-reinforced resins. Even

when properly hard-surfaced, these valves shouldbe considered expendable after 34 months of suchuse. Prior to that, worn seats and ring sleeves shouldbe reground or replaced as it is important to main-tain a pad (cushion) during melt injection. Typicalmaterials of construction are H-13 tool steel orCPM 9V for highest wear resistance. In either case,nitriding can be useful for extending the life ofcheck rings. The seat is usually hardened higherthan the sleeve; e.g., seat Rc62 and sleeve Rc55 aretypical. Experience has shown that when thenonreturn valve fails to function correctly, addi-

tional screw wear occurs and as the performance(wear) of the check valve worsens, so does thecondition of the screw.

NozzleConventional free-flow type nozzles (see Figure 3)can be used, especially with small orifice diameters.For larger diameters, or if drooling is a problem, the

Figure 4. Nozzle (with Reverse Taper) for MoldingZenite LCP Resins

DIAMETERAND ANGLE

TO SUIT

HEATER BAND

0.25 mm (0.01 in)RADIUS

50.8 mm(2 in)

25.4 mm(1 in)

3.2 mm (1/8 in) or4.8 mm (3/16 in)

DIAMETER

NOT TO SCALE

4

MELTFLOW

HEATER BANDS

THERMOCOUPLE WELL


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Hydraulic SystemWhen molding Zenite LCP resins, it is importantto be able to inject the resin into the mold at a rapidand controlled rate. Machines with shot capacitiesof 570 g (20 oz) or less should have hydraulicpumping capacities that allow the rated shot capac-

ity to be injected into the mold in 2 sec or less.Many LCP applications are small, thin-walled partsrequiring a small machine capable of injecting inthe 0.30.5 sec range. The ability to control the rateof injection is just as important as the ability to fillrapidly. For this reason, it is desirable to havepressure- and temperature-compensated flowcontrol valves installed in the hydraulic system.

Injection PressureAlthough rarely required, the injection systemshould be capable of injecting Zenite LCP resinsat melt pressures up to 1,380 bar (20,000 psi).However, lower pressures are recommended toavoid overpacking. Common injection pressures are

in the 275550 bar (4,0008,000 psi) range. Accu-rate and reproducible control of the injection pres-sure is essential for maintaining tolerance of moldeddimensions and other quality characteristics.

Clamping CapacityTypical applications feature hard-to-fill parts andprecise tolerance control. Molds should be designedand machines selected so that the clamping force is550690 bar (45 tons/in2).


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Chapter 3Handling of Molding Resin

Drying

Although Zenite LCP resins do not absorb highamounts of moisture, levels less than 0.010% arerecommended for optimum properties. The virginresin is supplied somewhat above this level in amoisture-resistant package. Therefore, any resin(virgin or regrind) must be dried before processingto avoid any chance of hydrolytic degradation. Ifdegradation should occur because of excessivemoisture, there will be no evidence (such as splay)on the surface of the parts. Figure 5 shows moisturepickup after one year immersion in water. Themoisture pick-up rate is quite slow. Even to reach

the 0.010% processing maximum requires two days.Conversely, drying of the resin is accomplished inshort time periods. Figure 6 shows such drying dataat three temperatures. Table 1 contains recommen-dations at these temperatures for resin from the bagand for resin or regrind of unknown moisturehistory.

Figure 5. Water Absorption of Zenite 6130

Total Immersion at 23

C (73

F)

ASTM D570

Table 1Recommended Drying Times, hours

Zenite LCP Resins

Drying Temperature

149C 135C 121C(300F) (275F) (250F)

Resin from Bag 1.0 1.5 2.5

Resin/Regrind ofUnknown Moisture 2.5 3.0 4.0

Figure 6. Drying Data for Zenite 6130 in aDehumidified Hopper Dryer

Dry in a dehumidified oven or hopper drier atthe recommended time and temperature foundin Table 1. Longer periods (such as overnight)

at these temperatures can be used withoutaffecting the resins moldability or properties.If the resins are to remain in ovens for longerlengths of time, it is good practice to eitherlower the heat to less than 65C (150F) or toremove and store the resin in clean, moisture-resistant containers.

The dryer air flow rate should be 3.03.7 m3/hrper kg/hr (0.81.0 CFM per lb/hr) of resinprocessed.

Time, weeks

Moisture,%

0.08

0.06

0.04

0.02

0

0 10 20 30 40 50 60

Time, hours

Moisture,%

0.030

0.025

0.020

0.015

0.010

0.005

0

0 2 3 41

Maximum Recommended Level

145C(300F)

135C(275F)

121C(250F)


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Maintain the dew point of the inlet air at 18C(0F) or lower.

If predried in a remote dehumidified oven orhopper, the molding machine must also beequipped with a dehumidified hopper drier inorder to maintain the desired moisture level.

The temperature and dew point should be thesame as above.

It is always a good practice to sample and run amoisture analysis prior to starting up produc-tion as well as during the run at a frequencyconsistent with normal quality control proce-dures to ensure that the level is 90%) of its physi-cal properties. In addition, measurements of shrink-age on 127 12.7 1.59 mm (5 0.5 0.0625 in)bars showed only a 0.03% shrinkage increase in theflow direction and an unmeasurable change in thetransverse direction after five passes versus thevirgin resin pass. The considerations around

determining a maximum regrind percentage aremany, e.g., UL and automotive requirements,product design requirements, drying, fines, andregrind quality. We have demonstrated that goodproperty retention is possible at 100% regrindlevels. The UL yellow card listing for HX6130allows up to 50% regrind. However, customertesting around the specific end-use requirements isthe most important tool for final selection of maxi-mum regrind percentage.

Conventional plastic granulators are used for grind-ing Zenite LCP resin grades. The blades shouldbe sharp and set for close clearance and the screensize should be as large as practical for feeding theparticular machine. However, due to the fibularnature of all LCPs, a high degree of fines andragged cut can occur. To optimize the cut, spruesand runners should be fed to the grinder immedi-ately out of the mold while still hot. The fines canbe further separated by a post-screening operation.Another option is to repelletize the regrind throughan extruder. This, of course, adds an additional heathistory to the resin.

Caution: Do not mix other LCP resin regrind withZenite LCP resin regrind. Severe degradation ofother LCP resins can occur when molded atZenite LCP resin melt temperatures.

Table 2Zenite 6130 Regrind Studies

Method Regrind Retention, % Retention, %Property ASTM Level, % (6th Pass) (8th Pass)

Tensile Strength, 23C (73F) D638 100 9650 98 9625 97

Elongation at Break, 23C (73F) D638 100 10050 100 9525 90

Tensile Modulus, 23C (73F) D638 100 10050 100 10025 100

Flexural Strength, 23C (73F) D790 100 92

Flexural Modulus, 23C (73F) D790 100 94

Heat Deflection Temperature D648 100 99at 1.8 MPa (264 psi)

Izod Impact, 23C (73F) D256 50 100 10025 100


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Chapter 4Machine Operating Conditions

Molding MachineAs is good practice with all resins, the moldingmachine selected should have a shot weight thatutilizes 3070% of the maximum stroke.

Melt TemperatureAs with all resins, achieving and controlling thedesired melt (or stock) temperature is essential to asuccessful molding. The melt temperature is a resultof cylinder and screw design, heater design, screwback pressure, screw rotation rate (rpm), shot size,and overall cycle time. Table 3 provides typical

cylinder settings which can vary widely dependingon the particular equipment.

Table 3Typical Processing Conditions for Molding

Zenite LCP Resins

Rear Center Front

C (F) C (F) C (F) C (F)

6130

6150 340 (645) 343 (650) 346 (655) 349360 (660680)6330

7130 352 (665) 354 (670) 357 (675) 363371 (685700)

7130HT 354 (670) 357 (675) 360 (680) 366377 (690710)

Typical CylinderTemperatures

Zenite LCP resins exhibit excellent melt stability.

These resins have broad melting points versus otherengineering plastics. The minimum melt processingtemperature is just greater than the broad meltingpoint range as seen in Figure 7 and listed inTable 3. Although the resins can physically bemolded below the minimum in the preferred melttemperature ranges in Table 3, poor physicalpropertiesespecially brittle partscould result.Therefore, the resins should not be molded belowthe minimum values listed in Table 3.

PreferredMelt Temperature

Range

Because it is not possible to accurately predict thecombined effect of all the variables, the actual melttemperature should be measured after the machineoperation has reached equilibrium. This is best doneby taking air shots into an insulated container andmeasuring with a fast-response (needle probe)pyrometer. In order to adequately measure thetemperature, three or more air shots may be re-quired. In general, settings run lower than desiredmelt temperature due to heat provided by the screwworking with the resin.

In order for all zones to reach and be controlled atthe desired settings, high wattage ceramic heaterbands are strongly recommended and are a must forthe 7000 series.

Nozzle TemperatureThe nozzle must not affect the temperature of themelt. Ideally, the temperature of the melt enteringand leaving the nozzle should be the same. Thenozzle temperature setting will depend largely onthe design of the nozzle, the heater band placement,

the temperature of the mold in contact with the noz-zle, and the overall cycle. The nozzle temperaturesetting is usually similar to the front zone setting.

Mold TemperatureZenite LCP resins mold well over a wide range ofmold temperatures. Mold surface temperatures overa range of 40150C (100300F) have been used.The most common range is 65110C (150230F).

Figure 7. DSC Curves of Zenite LCP Resins

Temperature, C

HeatFlow,W/g

0.35

0.36

0.37

0.17

0.18

0.19

0.20 260 300280 320 340 360 380 400

350C Minimum Processing

Temperature6130

7130

HEAT-UP

363C Minimum Processing

Temperature

ZeniteResinSeries


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8

High temperatures should be used for thin, hard-to-fill parts. (Good safety practices require using high-temperature rated hoses for hot water or hot oilheaters.) Low temperatures are recommended withcomplex parts experiencing sticking problems.Since mold surface temperature is a product of

many variables (not just the cooling fluid), it mustbe measured at start-up (once on cycle) and afterany major process change.

Unlike many other materials, the effect of moldtemperature on shrinkage and post-molding shrink-age is quite small. The effect on transverse flow andthickness are essentially unmeasurable. On highlyaligned flow parts, there is a measurable effect inthe flow direction as the molecular alignment isfurther ordered at the higher mold temperatures orwhen annealed at very high temperatures. In eachcase, this alignment results in part growth, once outof the cavity, such that it can be larger than thecavity dimension. This is especially true for thin-wall section parts. This is shown as a negativeshrinkage in Table 5 (see Mold Shrinkage underChapter 5: Mold Design) as well as in Figure 8.This graph shows that over a 100C (180F) moldtemperature range, a small increase of 0.15%(1.5 mil/in) is seen on 3.2 mm (0.125 in) parts.Similarly, Figure 9 shows a small part growth on0.79 mm (0.032 in) parts after exposure to 260C(500F) temperature for 30 min. This growth de-

creased from 0.2% (2.0 mil/in) to 0.12% (1.2 mil/in)over the same mold temperature range.

Injection PressureDepending on the molding machine design, theinjection pressure may or may not be an indepen-dent setting. The actual injection pressure will beinfluenced by both the injection rate and the transfer(position, pressure, or time) settings. Since theseresins are quite fluid at the recommended highinjection rates, relatively low injection pressures of200400 bar (3,0006,000 psi) are usually the case.In the case of extremely hard-to-fill parts, pressuresapproaching maximum machine capability aresometimes required. Figure 10 is typical snake flowdata that is somewhat indicative of melt flowlengths possible in molding at 0.51 mm (0.020 in)thickness. In almost all cases, start-up with a low-pressure setting is recommended.

Figure 8. Mold Shrinkage versus Mold Temperature3.18 mm (0.125 in) ThicknessFlow Direction

Mold Temperature, F

Mold Temperature, C

MoldShrinkage,%

0.15105

40

7130

140 175 210 245 280

60 80 100 120 140

6130

0.1

0.05

0

0.05

0.1

0.15

Specimen: 216 mm (8.5 in) x 12.7 mm (0.5 in)

Negative mold shrinkage means part growth out ofmold to dimensions greater than the cavity dimensions.

Figure 9. Dimensional Growth in Flow DIrection withAnnealing at 260C (500F) for 30 min

Mold Temperature, F

Mold Temperature, C

PartGrowth,%

0.25 105

40

140 175 210 280

60 80 100 120 140

6130

0.2

0.15

0.1

0.05

0

245

Specimen: 0.79 mm (0.032 in) Thickness127 mm (5.0 in) x 12.7 mm (0.5 in)


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Figure 10. Flow versus Pressure12.7 mm (0.500 in) Width

Figure 11. Melt Viscosity versus Shear Rate

Injection RateInjection rate is also known as fill rate or speed.Depending on the machine design, it may be set involume per unit time over a range of distance ortime. Older machines may only utilize a highvolume (booster) pump over a time setting.

Injection rate is a key variable in the molding ofZenite LCP resins. Previously, Figure 1 showedthe significant effect melt temperature had on meltviscosity. Likewise, Figure 11 depicts the highsensitivity of these resins to shear rate. Therefore,in order to capitalize on their low viscosity and highflow capabilities, very high fill rates are utilizedover almost 100% of the stroke. Fill (or ram-in-motion) times of 0.31.0 sec are very common insmall part volumes, such as electronic connectorsand bobbins.

Fast injection rates also contribute to the anisotropicproperties, including high physical properties, lowthermal expansion, and low mold shrinkage in theflow direction.

When the fill rate is reduced, the viscosity is signifi-cantly increased such that the polymers flow canquickly stop and set up. Therefore a high injectionrate for 9598% of the stroke followed by a low

Open-end snake flow mold. Actual flow lengths will beless in conventional molds.

(5075% less) rate for the very end of the strokeallows for filling long, thin sections without incur-ring flash problems. This assumes adequate ventinghas been provided to prevent part burning at the endof flow (see Vents in Chapter 5: Mold Design).

Note: The viscosities for mold design programs

are measured by a different procedure (seeChapter 5: Mold Design).

Pack PressurePack pressure is usually about 80% that of injectionpressure. The complexity of the part and its effecton ease of ejection will also determine the optimumpack pressure. For complex parts, it is recom-mended to start with low (e.g., 138 bar [2,000 psi]),pack pressure and then increase it in small incre-ments. Because these resins set up very quickly, the

gates will quickly freeze and pack time is quiteshort versus other thermoplastic resins. For thin-wall section parts (e.g., 0.76 mm [0.030 in]), it canbe less than a second. Due to the low shrinkage ofZenite LCP resins, it is possible to overpack andstick parts, especially in the area of the sprue.Therefore, pack pressures and times should beincreased carefully.

Shear Rate, sec1

MeltViscosity,

Pas

200

500

Zenite 7130360C (680F) Melt Temp.

1,000 2,000 3,000 5,000

100

50

30

20

10

Zenite 6130355C (670F)Melt Temp.

Zenite 6130370C (698F) Melt Temp.

Injection Pressure, bar

Flow

Length,cm

30

25

20

15

10

5

200 400 600 800 1,000 1,200 1,400

4 7 10 13 16 1912

10

8

6

4

2

Injection Pressure, kpsi

Flow

Length,in

Zenite 6130355C (670F)

Zenite 7130365C (690F)


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Screw Forward TimeScrew forward time is the time interval between thestart of screw forward motion (injection) and thestart of screw retraction. The optimum screw for-ward time can be determined by molding andweighing a series of parts (not sprue and runners) at

different screw forward times. In thick section parts(e.g., 3.18 mm [0.125 in] or more), this can be doneby the traditional method of keeping the fill timeconstant by increasing the pack times (holding theoverall cycle time constant) until the part reachesmaximum weight. However, in thin section parts,pack time can be less than a second. Increasing theinjection pressure to the maximum (short of flash-ing) is the preferred method. This is particularlyeffective for achieving maximum weld line strengthtogether with using melt temperatures 10C (20F)above the maximum temperatures shown in Table 3.

Overall Cycle TimeThe total cycle time is determined by the interactionof part thickness and geometry, molding machineand part design. All Zenite LCP resins have a lowheat of fusion (~4 J/g versus 4050 J/g for manyengineering plastics) which contributes to very fastcycle times. For example, thin wall connectors areroutinely molded well under 10 sec. In general,overall cycle times are 3050% less than those ofsemicrystalline resins such as PBT, PET, and PPS.

Screw Speed and Back PressureFor large shot sizes, screw speed should be selectedso that the screw retraction time is approximately90% of the available mold closed time. This is aneffective way of minimizing hold-up time in frontof the screw. However, in most thin-wall partmolding, screw retraction time is often the limitingvariable. In order to minimize glass fiber breakage,the screw speed should be slow and with smalldiameter screws, plasticizing capabilities are

limited by clearances in the feed zone. Table 4lists practical maximum screw rpms for severalscrew diameters that meet these various criteria.

In addition, little or no back pressure should beused.

Screw DecompressionScrew decompression (or suck-back) should be aminimum and only used when necessary. Nozzledrooling can be controlled by drying the resin,proper nozzle temperature selection with goodtemperature control, and, if necessary, use of areverse taper nozzle.

Start-UpThe cylinder and screw should be cleaned prior tostart-up by using the method described underPurging. The recommended start-up procedure is:

1. Set the cylinder temperatures 30C (50F)below and the nozzle temperature 10C (20F)above the minimum processing temperature.Allow the heat to soak in for at least 20 min.Raise the cylinder temperatures to the desiredoperating temperatures. (Use Table 3 as aguide.)

2. Check to make sure that the nozzle is at settemperature and that it is open and contains nofrozen material.

3. Jog the screw. If the screw will not rotate, allowa longer heat soak in time.

4. When the screw begins to rotate, open thehopper feed slot briefly and then close. As thematerial is being pumped forward by the screw,check the load on the screw motor. If it isexcessive, increase cylinder temperatures.

5. Open the feed slide and increase back pressure

to hold the screw in the forward position.Extrude melt and adjust operating conditionsuntil the melt shows no indication of unmeltedparticles or degradation. A good melt will besmooth in appearance. If the melt is foamy,degradation is occurring. Once the melt isproper, release the back pressure.

Table 4Maximum Screw rpm versus Screw Diameter

Screw Diameter, Screw Speed,mm (in) rpm

16 (0.63) 24038 (1.5) 10076 (3.0) 80


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11

6. Take several air shots with the stroke size andcycle anticipated for the molding operation.Then check the melt temperature with a hand-held pyrometer. Since Zenite LCP resins meltquickly and set up, three to five cycle checksmay be needed to obtain an accurate melt

temperature. Make any necessary adjustmentsin the cylinder temperatures to achieve therecommended melt temperature.

7. Bring the injection cylinder forward. Startmolding on cycle at low injection pressure(except where short shots will interfere with partejection) and then adjust operating conditions toproduce quality parts.

Cycle InterruptionsDue to the excellent thermal stability of Zenite

LCP resins, minor cycle delays up to 1015 mincan usually be tolerated without purging and lossof material. If the delay is expected or reaches>15 min, empty the resin from the cylinder as somedegradation will occur. No purge compound isnecessary at this time. The cylinder temperaturesshould be lowered to 205230C (400450F).Upon resumption of the run, raise the temperaturesand reintroduce the Zenite LCP resin per thestart-up procedures. For anticipated delays greaterthan an hour, the resin must be purged sequentiallywith Rynite 545 or 555 polyester resin, followed

by a low melt index polyethylene as described inthe procedure for purging from Zenite LCP resinsto other resins.

PurgingPurging is essential before and after moldingZenite LCP resins because many plastics (includ-ing other lower melting point LCPs) degrade at theZenite LCP resins melt processing temperatures.Therefore, contamination with other resins (includ-ing other LCP resins) may cause molding difficul-

ties or resin decomposition. Refer to ThermalEffects in Chapter 7: Operating Precautions forinformation on proper handling of the purge andprovisions for local exhaust ventilation at the nozzleduring purging and processing of Zenite LCPresins.

The best purging is accomplished by using a highglass-reinforced PET such as Rynite 545 or 555,

followed by a low melt index (


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12

Chapter 5Mold Design

General

Zenite LCP resins have been molded in a varietyof molds. Many of the general construction rulesfollowed for other engineering resins are appliedwhen designing molds for Zenite LCP resins.This includes designing the tool to allow for uni-form heating and cooling. Frequently, the construc-tion of prototype molds is encouraged.

There are also significant differences from otherengineering resins. These include the low moldshrinkage, high processing temperatures and injec-tion rates, fast set-up time and, most of all, the

anisotropic nature of these resins. These offerunique opportunities in designing the mold. Most ofthese are addressed in the following comments. Forfurther information, consult with your DuPontZenite marketing/technical representative.

Note: Parameters for Mold-Flow5 and C-Flow6 areavailable on request.

Mold MaterialsZenite LCP resins are not corrosive to molds.However, glass, mineral, and other fillers may beabrasive and tool steels for cavities, cores, runnersystems, and sprue bushings should be selected andhardened as with other filled engineering polymerresins. Also, as a result of the fast injection ratesused in processing Zenite LCP resins, gates aresubject to considerable heat buildup and loss ofhardness. The use of replaceable gate block-insertsis recommended. They should be checked regularlyand replaced as needed.

Maximizing Physical Properties

The anisotropic nature of Zenite LCP resinsinclude shrinkage, thermal expansion coefficient,and basic mechanical properties. Therefore, in orderto maximize part strength, the mold design shouldtake into consideration the flow directions of one ormore melt fronts so that no weld lines are formed inareas subject to high stress in use. This will includethe selection of gate location, size and number, andvent location and size, together with the part designitself.

Sprues and RunnersDue to the high flow characteristics of ZeniteLCP resins in high shear circumstances, sprue andrunner sizes can be smaller than many other resins.This, of course, will depend on the overall flowlength and wall thickness of the part. Single partingline runners of 38 mm (1.5 in) in length are often asthin as 1.6 mm (0.062 in) in thickness. Spruesshould always be as short as possible with diameterat the primary runner being 1.0 to 1.25 times itsthickness. Runners are progressively smaller so thatthe runner thickness at the gate is 1.25 times the

maximum part thickness. It, of course, is best tominimize the overall runner length to ensure properfill and packout of thin-wall, long flow-length parts.The best approach is to start with small runnersand sprues and increase in size as necessary. Hotsprue bushings are frequently used with ZeniteLCP resins and should be considered.

Full round runners are preferred and normally used.Trapezoidal runners are sometimes used for greaterease of machining. The slope of the sides should be5 per side, while the depth should be determined

by the diameter of an inscribed circle. The layout ofrunners should be balanced with a generous radiusat each branching for smooth and uniform meltflow.

5Moldflow Pty. Ltd., Melbourne, Australia and Moldflow, Inc.,Shelton, CT

6AC Technology, Ithaca, NY


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13

Gate LocationThe anisotropic nature of Zenite LCP resins is aproduct of both molecular and filler orientationduring the filling of the mold. This orientation isinfluenced by both the direction of flow and theflow rate. Both are important to the physical proper-

ties in any given area.Gates should be located to give a uniform anduninterrupted flow. Weld lines are relatively weakversus other plastics, which is typical for all liquidcrystal polymers. Whenever possible, multiplegating should not be used. The excellent flowcharacteristics of Zenite LCP resins usually onlyrequire a single gate. When it is impossible to avoidweld lines in a part, they should occur in areas thatwill not receive high mechanical stresses in use. Atthe same time, it is desirable to position the gate so

that venting is simple and adequate (see Vents inthis chapter). Avoid butt weld lines where two flowfronts hit head-on and stop. A melding of two flowfronts can eventually mix and become one.

To further improve strength of weld lines, vents(and in many cases overflow tabs) should be posi-tioned at weld line areas. In addition, melt tempera-tures should be raised up to 10C (20F) above themaximum temperatures shown in Table 3.

Gate Design

It is important to design gate dimensions so thatpolymer jetting into the cavity does not occur. Thebest design is to have gates located so that the meltdirectly impinges against the wall of the cavity or acore pinprovided that the core pin is registered inboth mold halves.

Parting line round gates are normally used onsmall parts and their diameter should also beabout 50% of the wall thickness. Because of theunique Zenite LCP resin shear versus flowsensitivity (see Figure 11), gate thicknesses of 30%

of wall thickness have been used (minimum dimen-sion0.5 mm [0.020 in]). Too small of a gatethickness can result in gate freeze-off or fill prob-lems. Tunnel gates are frequently used for ease of

gate separation and part ejection. They should havea minimum diameter of 0.5 mm (0.020 in) and onlybe used with a short land length. Tunnel gatesshould also be located in the ejector side of themold and designed to minimize part deflectionduring the ejection. It is best to position ejector pins

below the tunnel gates.Rectangular gates are sometimes used since thick-ness (which affects gate freeze time) and width(thus volume which controls the flow rate) can becontrolled independently. Gate thickness is usually50% or less part wall thickness and gate width is1.5 to 2 times the gate thickness. Often, a wide fangate (up to full part width) is used on flat parts forcontrol of orientation and optimum filling.

Circular or conical parts should be center gated witha sprue gate or diaphragm gate, respectively. This

will allow uniform flow fronts without weld lines.

VentsMolds must be adequately vented in order to pre-vent localized burning of the parts, damage to themold, poor weld line strength, and to allow easierfilling of the cavity. Cavities should be vented at theparting line, at ejector pins, or by inserting adummy knock-out pin into the cavity at the pointwhere air is trapped. The vent depths range from0.0080.025 mm (0.00030.0010 in) and as wide

as practical. After a land length of about 0.75 mm(0.030 in) from the cavity, the vent depth should beenlarged to about 3.2 mm (0.125 in) and extendedto the edge of the mold. In addition, runners shouldbe vented at the sprue puller and parting line.

Undercuts and TaperBecause of the high modulus and relatively lowelongation of all LCPs, undercuts should beavoided. A taper of 0.20.5 on ribs, bosses, sides,and sprues is generally satisfactory. However, an

additional 0.51.5 may be required for complexparts, parts with deep drafts, or for tools that do nothave polished surfaces.


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Mold ShrinkageThe mold shrinkage of Zenite LCP resins de-pends on the orientation of the molecules andfillers, part thickness and design, and processingconditions. Shrinkages listed in Table 5 are in-tended as a guide, using a typical mold temperature

of 93C (200F), for estimating out-of-mold dimen-sions as a function of part thickness. Negativeshrinkages (i.e., growth) can occur in the flowdirection in thin wall sections. This means in thesecases the part dimensions can be larger than thecavity dimensions.

The effects of mold temperature and high usetemperature on shrinkage have been previouslydiscussed in the Mold Temperature section ofChapter 4: Machine Operating Conditions. Alsorefer to Figures 8 and 9. The use of regrind has

little effect on mold shrinkage (see Chapter 3:

Table 5Effect of Part Thickness on Mold Shrinkage, %

Mold Temperature: 93C (200F)

Thickness Zenite 6130 Zenite 7130

mm (in) Flow Transverse Flow Transverse

0.81 (0.031) 0.07 0.5

1.62 (0.062) 0.07 0.8 0.1 0.9

3.22 (0.125) 0.1 0.7 0.0 0.8

1Disc: Edge-gated 102 mm (4 in) diameter2Plaque: End-gated 76 127 mm (3 5 in)

Handling of Molding Resin).

TolerancesTolerances for parts molded of Zenite LCP resinsvary according to the complexity and wall thicknessof the design. Predicting dimensional uniformity

can be difficult as it will depend to a large degreeon the parts glass fiber and molecular orientation.The tolerances in Table 6 (based on the SPI format)are for 3.18 mm (0.125 in) wall section. They donot represent hard and fast rules applicable to allconditions, but rather an estimate based on experi-ence. With the small wall sections often found inZenite LCP resin moldings, the fine toleranceband often can be reduced by at least 50% in manycases.

The ability to maintain minimum tolerances is

dependent on part design, the number of cavities,mold design, the injection molding system used,


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0

COMMERCIAL

FINE

1 2 3 4 5 6 7 8 9 10 11 12 13

0.1 0.2 0.3

Table 6A Guide to Tolerances of Zenite LCP Resins

Note: The Commercial values shown below represent common production tolerances at the most economical level (see Note #2).The Fine values represent closer tolerances that can be held but at a greater cost.

Drawing Dimensions Plus or Minus in Thousandths of an InchCode mm (in)

A = Diameter(see Note #1)

B = Depth(see Note #3)

C = Height(see Note #3)

D = Bottom Wall(see Note #3)

E = Side Wall(see Note #4)

F = Hole SizeDiameter

(see Note #1)

G = Hole SizeDepth

(see Note #5)

Draft Allowanceper Side

(see Note #5)

Plus or Minus in Millimeters

150 (6.000) to 300 (12.000) for

each additional mm (inch) add(mm) [inches]

Comm. Fine

0.08 (0.003) 0.05 (0.002)

0.10 (0.004) 0.08 (0.003)

0.13 (0.005) 0.08 (0.003)

0.05 (0.002) 0.03 (0.001)

0.08 (0.003) 0.05 (0.002)

0.08 (0.003) 0.05 (0.002)

0.13 (0.005) 0.08 (0.003)

0.10 (0.004) 0.05 (0.002)

0.10 (0.004) 0.08 (0.003)

0.13 (0.005) 0.10 (0.004)

1.52.0 0.20.5

0 to 3 (0.000 to 0.125)

3 to 6 (0.125 to 0.250)

6 to 13 (0.250 to 0.500)

13 and Over (0.500 and Over)

0 to 6 (0.000 to 0.250)

6 to 13 (0.250 to 0.500)

13 to 25 (0.500 to 1.000)

Reference Notes

1. These tolerances do not include allowance for annealingcharacteristics of material.

2. Tolerances based on 3.0 mm (0.125 in) wall section.

3. Parting line must be taken into consideration.

4. Part design should maintain a wall thickness as nearly constantas possible. Complete uniformity in this dimension is impos-sible to achieve.

5. Care must be taken that the ratio of the depth of a cored holeto its diameter does not reach a point that will result inexcessive pin damage.

C

E

D

BF

FG

P/L

A

25 (1.000)

50 (2.000)

75 (3.000)

100 (4.000)

125 (5.000)

150 (6.000)

0 (0.000)


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Increase

Injec

tion

Pressure

DecreaseIn

jec

tion

Pressure

Increase

Pa

ck/Ho

ldPressure

DecreasePac

k/Ho

ldPressure

Increase

Clamp

Pressure

Increase

Injec

tion

Ra

te

DecreaseIn

jec

tion

Ra

te

Increase

Sc

rew

Forward

Time

DecreaseScrew

Forward

Time

Increase

Me

ltTempera

ture

DecreaseM

eltTempera

ture

Increase

Mo

ldTempera

ture

DecreaseM

oldTempera

ture

DecreaseN

ozz

leTempera

ture

Lower

Cen

ter

Zone

Tempera

ture

Increase

Cy

lin

der

Tempera

tures

Increase

Cy

cleTime

DecreaseCyc

leTime

Chec

kPa

dSize

(Cus

hion

)

Chec

kScrew

Re

trac

tion

Use

Me

ltDecompress

ion

Chec

kforR

es

inCon

tam

ina

tion

Ensure

Res

inIsDry

Drooling

Short Shots

Sinks

Voids in Part

Flash

Discoloration atEnd of Flow

Poor Weld Lines

Brittle Parts

Parts Stick in Mold

Sprue Sticking

Shot-to-Shot Variationin Part Size

Warpage

Screw Does Not Retractor Retracts Erratically

Problem Areas

34 1 6 2

4 2 3 1

4 3 2 1

4 3 2 1

2 1 4 5 6 3

2 4

5 4 6 1

1 4 3 5 2

2 5 3 6 7 4

1 4 2 5 8

4 3 1 6 5

4 5 2 3

2 1 4 3

Chapter 6Troubleshooting Guide

Zenite LCP Resins

5

Suggested Remedies(In order of likely cause)

Quick (Operating Conditions) Changes


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17

Repa

irMol

d

Increase

Sizeo

fGa

te

DecreaseS

izeo

fGa

te(Shear)

Change

GateLoca

tion

En

large

Ven

ts

Chec

kTool

for

Un

dercu

ts

Increase

Dr

afto

fMo

ld

Increase

Sp

rue

Taper

Use

Revers

eTaper

Nozz

le

En

large

Nozz

leOri

fice

Chec

kSpru

efor

Un

dercu

ts

Chec

kCylin

der

for

Ho

ldup

Spo

ts

Chec

kHeater

Ban

dTempera

tures

Drooling

Short Shots

Sinks

Voids in Part

Flash

Discoloration atEnd of Flow

Poor Weld Lines

Brittle Parts

Parts Stick in Mold

Sprue Sticking

Shot-to-Shot Variationin Part Size

Warpage

Screw Does Not Retractor Retracts Erratically

Problem Areas

6

5

7 8 6

5

5 6

7

36 1 5

6 3 2

1 5

7 3

1

6

2

Longer (Equipment) Changes

Suggested Remedies(In order of likely cause)


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18

Chapter 7Operating Precautions

molding conditions, and the ability of the molder.

Only by optimizing all of these variables can thetightest of tolerances be maintained.

As with most thermoplastic resins, the molding ofZenite LCP resins is ordinarily a safe operation.Good practice dictates that consideration should begiven to the following potential hazards:

Thermal effects

Off-gases and particulates

Slipping hazards

Thermal EffectsSkin contact with molten Zenite LCP resins caninflict severe burns. This could happen when gasesgenerate pressure in the machine cylinder andviolently eject molten polymer through the nozzleor hopper.

To minimize the chance of an accident, the instruc-tions given in this guide should be followed care-fully. Potential hazards must be anticipated andeither eliminated or guarded against by followingestablished procedures, including the use of proper

protective equipment and clothing.Be particularly alert during purging and wheneverthe resin is held in the machine at higher than usualtemperatures or for longer than usual periods oftime, as in a cycle interruption. Pay particular atten-tion to Chapter 4: Machine Operating Conditions.

When purging, be sure that the high volume(booster) pump is off and that a purge shield is in

place. Reduce the injection pressure and jog the

injection forward button a few times to minimizethe possibility of trapped gas in the cylinder whichwill cause splattering of the polymer melt.

If resin decomposition7 is suspected at any time,a purge shield should be positioned, the carriage(nozzle) retracted from the mold, and the screwrotated to empty the barrel. After the screw starts torotate, the feed throat should be closed and then asuitable purge compound (high glass content PET)introduced. The temperature can then be graduallylowered and the machine shut down. See Purging

under Chapter 4: Machine Operating Conditions forfurther details.

If jogging the injection or screw rotation buttonsdoes not produce melt flow, the nozzle may beplugged. In that case, shut off cylinder heats andfollow your established safe practices. Alwaysassume that gas at high pressure could be trappedbehind the nozzle and that it could be releasedunexpectedly. A face shield and protective longsleeve gloves should be worn at such times.

Before restarting, both the machine and material

should be evaluated to determine the cause of thedecomposition.

In the event that molten polymer does contact theskin, cool the affected area immediately with coldwater or an ice pack and get medical attention forthermal burn. Do not attempt to peel the polymerfrom the skin. Questions on this and other medicalmatters may be referred to 800-441-3637.

7Excessive gas escaping from the nozzle, severely discolored molten

polymer, screw backing up beyond the rear limit switch, etc.


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19

Because Zenite LCP resins are dried at hightemperatures, contact with hot hoppers, ovens, or airhose lines could result in severe burns. Insulation ofthese components will reduce this possibility.

Off-Gases and Particulates

During drying, purging, molding, and grindingoperations, small amounts of gases and particulatematter are released. As a general principle, localexhaust ventilation is recommended during theprocessing of Zenite LCP resins as it is for allplastic resins. A ventilation rate of 4.68 m3 (75 ft3)air/min per kg/hr (lb/hr) of resin processed will keepthe concentration of particulates (and gases) wellbelow the OSHA8 limit of 15 mg/m3 for nuisancedusts while being processed at the maximum rec-ommended times and temperatures (molding,purging, and drying).

Handling of ResinsOSHA requires Material Safety Data Sheets(MSDSs) be provided by the material manufacturersto their customers. MSDSs include such informa-tion as hazardous components, health hazards,emergency and first aid procedures, disposal proce-

dures, and storage information. DuPont suppliesMSDS information to its customers with the initialorder of a Zenite LCP resin and on the next orderafter an MSDS is revised. Zenite LCP resinMSDS will be furnished upon request from yourDuPont representative.

Slipping HazardsGranules of Zenite LCP resins are a slippinghazard if spilled on the floor. Any spills should beswept up immediately.

829CFR1910.1000


23/23

StartwithDuPont

U.S.A.

EAST

DuPont Engineering Polymers1007 Market StreetSuite D-12064Wilmington, DE 19898(302) 773-0640

MIDWEST

DuPont Engineering Polymers100 Corporate NorthSuite 200Bannockburn, IL 60015(708) 831-6420

DuPont Engineering PolymersAutomotive Products950 Stephenson HighwayTroy, MI 48007-7013(313) 583-8000

WEST

DuPont Engineering Polymers18500 Von Karman AvenueSuite 750, P.O. Box 19732Irvine, CA 92715(714) 263-6233

CanadaDuPont Canada, Inc.DuPont Engineering PolymersP.O. Box 2200Streetsville, MississaugaOntario, Canada L5M 2H3

(905) 821-5953

EuropeDuPont de Nemours Intl SA2, chemin du PavillonCH-1218 Le Grand-SaconnexGeneva, Switzerland(022) 717-51-11

Telex: 415 777

Asia PacificDuPont Asia Pacific Ltd.P.O. Box TST 98851Tsim Sha TsuiKowloon, Hong Kong852-3-734-5345

Latin AmericaDuPont S.A. de C.V.Homero 206Col. Chapultepec Morales11570 Mexico D.F.(011 525) 250-8000

JapanDuPont Kabushiki KaishaArco Tower8-1, Shimomeguro 1-chomeMeguro-ku, Tokyo 153Japan(011) 81-3-5434-6100

The data listed here fall within the normal range of properties but they should not be used to establish specification limits nor used alone as the basis of design. TheDuPont Company assumes no obligations or liability for any advice furnished or for any results obtained with respect to this information. All such advice is given and

accepted at the buyers risk. The disclosure of information herein is not a license to operate under, or a recommendation to infringe, any patent of DuPont orothers. DuPont warrants that the use or sale of any material which is described herein and is offered for sale by DuPont does not infringe any patent covering the materialitself, but does not warrant against infringement by reason of the use thereof in combination with other materials or in the operation of any process.

CAUTION: Do not use in medical applications involving permanent implantation in the human body. For other medical applications, see DuPont Medical CautionStatement, H-50102.

For more information onEngineering Polymers:

For Automotive Inquiries:

(302) 999-4592

800-533-1313

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