Molding Technology

®

Polybutylene Terephthalate (PBT)

Technical Data Series of DURANEX® PBT

POLYPLASTICS CO., LTD.

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DURANEX® PBTPolybutylene Terephthalate

Molding TechnologyContent

1. Introduction......................................................................................................................... 2

2. Molding Conditions............................................................................................................. 2

2.1 Standard Molding Conditions ..................................................................................... 2

2.2 Pre-drying ................................................................................................................... 2

2.3 Cylinder Temperature ................................................................................................. 3

2.4 Mold Temperature, Injection Speed and Molding Cycle ............................................ 6

3. Moldability........................................................................................................................... 6

3.1 Flowability ................................................................................................................... 6

3.2 Shrinkage Characteristics........................................................................................... 8

4. Molded Product Quality ...................................................................................................... 12

4.1 Dimensional Tolerances ............................................................................................. 12

4.2 Deformation ................................................................................................................ 13

4.3 Use of Regrind............................................................................................................ 18

5. Mold Design........................................................................................................................ 20

5.1 Runner Design............................................................................................................ 20

5.2 Gate Design ................................................................................................................ 20

5.3 Gas Vents ................................................................................................................... 21

5.4 Undercut...................................................................................................................... 21

5.5 Draft ............................................................................................................................ 22

5.6 Mold Temperature Control.......................................................................................... 22

5.7 Mold Materials............................................................................................................. 22

6. Safety Precautions ............................................................................................................. 24

7. Countermeasures for Defects ............................................................................................ 25

DURANEX® is a registered trademark of Polyplastics Co., Ltd. in Japan and other countries .

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1. IntroductionDURANEX® PBT, commonly known as polybutylene telephthalate (PBT), is a highly crystalline plastic. DURANEX is available in a wide variety of grades in four categories as shown below:

(1) Unreinforced grades and grades reinforced with glass fiber and/or other inorganic fillers.(2) Slow burning and flame retardant grades.

some industrial applications, most molded parts are made of reinforced grades; therefore, considerations to prevent deformation in molding are essential. Though such considerations include design of product shapes, mold design, and selection of grades, only the first two of these will be explained in this section.DURANEX contains ester linkage in its polymer chain and care should be taken to avoid polymer degradation due to hydrolysis throughout the molding operation. Key points regarding this problem are how to control moisture level of the pellets, resin temperature and the residence time in the cylinder.Some aspects of general mold design for DURANEX are common to those for DURACON® POM, so we recommend that you also refer to "Molding Technology for DURACON® POM".

2. Molding Conditions2.1 Standard Molding Conditions

Pre-drying : 120°C, 5 hours or longer: 140°C, 3 hours or longer

Resin temperature : 250 - 270°CMold temperature : 40 - 80°CHolding pressure : 60 - 100MPaCooling time : Slightly more than plasticization time, but without sticking in moldScrew rotation : 100 - 150 rpm

2.2 Pre-dryingDURANEX® PBT, being a thermoplastic polyester, is hydrolyzed when heated while containing moisture, resulting in brittle products. Therefore, sufficient pre-drying of the pellets is necessary. The effects of pre-drying time at 120°C on certain mechanical properties are shown in Fig. 2-1 and 2-2, which indicate that at least 5 hours of pre-drying is required at 120°C. The effect of pre-drying time on moisture content is shown in Fig. 2-3, which indicates that pre-drying at 120°C for 5 hours is equivalent to 140°C for 3 hours or 160°C for 2 hours. A high temperature such as 160°C will cause discoloration, while a low temperature of 100°C or lower will not lower the moisture content down to 0.02% or less which is the target of pre-drying.

Considering these facts, the recommended pre-drying conditions are:120°C for 5 hours or longer140°C for 3 hours or longer

Rack-type ventilating dryers, and hopper dryers are useful but in any case, the drying conditions such as air temperature and flow rate must be adjusted so that the pellets will be dried uniformly under the above-recommended conditions. Especially when hopper dryers are used, make sure that no short paths are formed, and that the pellet temperature, not the preset temperature, reaches the required level.

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2.3 Cylinder TemperatureBecause the melting point of DURANEX® PBT is around 224°C,the appropriate resin temperature is from 250°C to 270°C. If the temperature exceeds 280°C, decomposition begins; therefore, a temperature around 270°C should be considered as the upper limit.

The effects of cylinder temperatures and residence time in the heated cylinder on mechanical properties of DURANEX 3300 are shown in section (a) Figs. 2-4 through 2-7, and DURANEX 3316 in section (b) Figs. 2-8 through 2-11. It is a matter of opinion what value should be regarded as the limit but in Table 2-1, the longest allowable residence times are estimated from such points as the melt index rises to 2 times of its initial value and color difference more than 2.5 of their original levels.

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(a) Residence Time in Heated Cylinder vs. Various Properties of DURANEX® PBT 3300

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(b) Residence Time in Heated Cylinder vs. Various Properties of DURANEX® PBT 3316

Table 2-1 Cylinder Temperature vs. Allowable Residence Time of DURANEX® PBT

GradeCylinder temperature

250°C 270°CDURANEX 3300 30 min 20 minDURANEX 3316 30 min 10 min

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2.4 Mold Temperature, Injection Speed and Molding Cycle(1) Mold TemperatureBeing high in crystallization speed, DURANEX® PBT results in products with relatively glossy surfaces at the mold temperature between 40°C and 120°C. The higher the mold temperature, the better the surface gloss and dimensional stability but the larger the deformation becomes. A countermeasure for such deformation is to use lower mold temperatures, but this results in a larger deformation during annealing or use at elevated temperatures; thus precautions regarding these points are required.

(2) Injection SpeedSince DURANEX solidifies very quickly, faster injection speeds result in parts with glossier surfaces. High speed injection, however, tends to cause burn marks on the parts, so thorough consideration must be given to the gas venting.

(3) Molding CycleThe rapid solidifying speed of DURANEX makes it possible to manufacture parts with a relatively short cycle. In order to avoid sink marks or deformation and to decrease dimensional scattering, it is necessary to select an injection and dwell time slightly longer than the gate seal time.

3. Moldability3.1 FlowabilityThe melt index is frequently used as a convenient means of quality control. However, the basic flow characteristics of a material is the melt viscosity. Bar flow length and its L/t (flow length/thickness) ratio are useful parameters for practical molding operations.

(1) Melt ViscosityThe relation between shearing stress and shear rate of DURANEX® PBT 3300, when tested with a capillary rheometer, is shown in Fig. 3-1. This relationship is fundamental when designing runners and investigating material flow in cavities. The variation of melt viscosity of DURANEX 2000 and 3300 by temperature is shown in Fig. 3-2.The melt viscosities of 3300 resemble to those of DURACON® POM M90, which means that 3300 has good flow characteristic as a material reinforced with 30% glass fiber.

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(2) Bar Flow LengthThe aforementioned isothermic flow data alone are not sufficient for correct evaluation, because material flow in cavities is not isothermic. In general, it is also difficult to reproduce pressures and shear rates applied in the practical injection molding process in the above-mentioned test apparatus. Therefore, bar flow length tests are carried out on injection molding machines. As an example, the effect of molding conditions on bar flow length of 3300 is shown in Fig. 3-3.

Another way to express flow property is the L/t ratio (flow length / thickness). Fig. 3-4 shows L/t ratio of 3300 at the 260°C resin temperature and 100MPa injection pressure. For example, the fact that the flow length reaches around 30mm at a thickness of 0.5mm, indicates the possibility of molding thin sections if sufficient consideration is given to gate design.

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3.2 Shrinkage Characteristics(1) Mold ShrinkageBeing a crystalline plastic, the specific volume of DURANEX® PBT varies with temperature as shown in Fig. 3-6. Therefore, mold shrinkage of unreinforced grades is rather high as shown in Fig. 3-7.On the other hand, while reinforcement with glass fiber reduces the mold shrinkage, it also introduces anisotropy in shrinkage because the glass fibers become oriented to the flow direction in the cavity. Some examples of anisotropy in mold shrinkage are shown in Fig. 3-8. Such large anisotropies can cause deformation of molded parts. Key countermeasures to prevent deformation are product shape and gate designs.Mold shrinkage is influenced by molding conditions as shown by the examples in Fig. 3-9, 10, 11 and 12.

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(2) After-shrinkageThe dimensions of molded products change depending on the conditions under which they are used. This is caused by relaxation of molded-in stress, progress of crystallization, moisture or water absorption and thermal expansion. Therefore, it is sometimes necessary to take measures to stabilize the dimensions of molded parts in advance of use, taking these conditions into consideration.The effects of annealing temperatures on such after-shrinkage are shown in Figs. 3-15 and 16, which indicate that the higher the annealing temperature, the more the after-shrinkage is and that after-shrinkage is greater in the transverse direction than in the flow direction.Whether or not annealing is necessary to stabilize the dimensions of a part depends on the conditions under which it is to be used. Estimates based on the after-shrinkage data (Figs. 3-15 and 3-16) will be helpful.

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(3) AnnealingWhether or not annealing is necessary to stabilize the dimensions of a part depends on the conditions under which it is to be used. Estimates based on after-shrinkage data (Fig. 3-15 and 3-16) will be helpful.A high operation temperature requires a fairly high annealing temperature. For example, with very slight after-shrinkage, you may find that annealing at 175°C for 3 hours or at 190°C for one hour is necessary as seen in Figs. 3-21 and 3-22.

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(4) Dimensional Changes Caused by Water AbsorptionDURANEX® PBT, as shown in Fig. 3-23, absorbs little moisture or water, resulting in only small dimensional changes. The relation between the dimensional change and water absorption is shown in Fig. 3-24.Being easily hydrolyzed, PBT should not be used for parts which are to be used in hot water. When both the above-mentioned characteristics and this limitation are considered, the dimensional changes caused by moisture and water absorption are not significant in general.

4. Molded Product Quality4.1 Dimensional TolerancesThe dimensional tolerances for DURANEX® 2000 and 2002 are illustrated in Fig. 4-1. With precision molding, the tolerances obtainable are ±0.3% for 25mm, ±0.2% for 50mm, and ± 0.13% for 125mm. Within this dimensional range, the tolerances for DURANEX are roughly same as those for DURACON® POM.

Dimensional scattering of DURANEX 3300 measured with 120×120×3mmt flat plates indicated following results:

Single day variation (3σ) : 0.038 - 0.059%Day-to-day variation over a short period of time (3σ) : 0.12%

Similar test results with DURACON were 0.027 - 0.059% and 0.048 - 0.094% respectively. Therefore, the dimensional scattering of DURANEX 3300 is similar to or slightly larger than that of DURACON.

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4.2 DeformationUneven shrinkages of various sections of a molded part are the major cause of deformation. However, if a part shrinks uniformly, then no deformation occurs.Though all of the following three causes are major reasons for uneven shrinkage in a part, the anisotropy of the shrinkage between the flow and the transverse directions is the most important cause of deformations in reinforced grades of DURANEX® PBT.

1. Non-uniform section thickness2. Non-uniform mold temperature and pressure of melt in a cavity3. Anisotropy of shrinkage due to flow direction

(1) Shape Design vs. DeformationBecause the configuration greatly affects deformation, it is essential to design a part with shapes that minimize deformation so long as it conforms to its function. The typical deformation of some popular shapes are explained below.

(a) Disc-shaped PartsRoundness and plane flatness of DURANEX 3300 is shown as follows:Roundness : One rule-of-thumb is that the roundness of a 60 mm diameter plate is 0.15 mm or less.

When the diameter of a disc-shaped part is less than 60 mm, the roundness is nearly proportional to the diameter.

Flatness : One criterion is that the flatness of a 60 mm diameter plate is 0.3 mm or less. The relationship to diameter is same as that of roundness (proportional).

(b) Box-type PartsThe relation between concave warpage and span length is shown in Fig. 4-2. There is a rather large scattering in the data, but the figure will give a rough estimation of the amount of concave warpage.

Measures to overcome concave warpage are providing the part with ribs to shorten the span length or designing molds with an inverse warpage. Proper gate design is also effective; i.e., a pin-point gate at the center functions better than a side gate as shown in Table 4-1. Core cooling is also useful; e.g. when the core is cooled, concave warpage is reduced to as little as 20 to 30% in case of DURANEX 2000 and 2002 and to about 60% in case of glass fiber reinforced grades.

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Table 4-1 Concave Warpage vs. Gate Design (Unit: mm)Grade Side gate Pin-point gate at center2000 0.91 0.652002 0.90 0.693105 1.20 0.723200 1.15 0.943300 1.18 0.993400 1.09 0.92

6300B 0.80 0.657400W 1.05 0.80

Note 1: Measured on a box of 80(l)×40(w)×20(h)×2(t)mmNote 2: Side gate: 5(w)×3(t)mm, Pin-point gate: 1mm dia.Note 3: Mold temp.: 60°C

(c) L-shaped PartsThe deviation from right angle for various L-shaped sections is shown in Table 4-2. A triangular rib like that in shape #8 is found to be the most effective way to prevent deformation.

Table 4-2 Deviation from Right Angle (in degrees)

Moldtemp.(°C)

Grade

Shapes

30 3300 2.5 2.5 2.5 2.5 3.0 2.5 2.5 080 3300 3.0 3.0 3.0 3.0 - 3.0 3.0 0

Molding conditions: Refer to term 2.1

Forced temperature differences between the core and the cavity mold halves at the corner are effective to reduce deviation from right angle for grades like DURANEX 2000, 2002 and 6300B, as seen in Table 4-3.In case of glass fiber reinforced grade, deviation from right angle depends on the gate position as shown in Table 4-4, which indicates some instances where gates located at the corner produce less deviation than gates located at the tip, which is the conventional position.

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Table 4-3 Effect of Corner Cooling on Deviation in L-shaped Parts (Unit: degrees)Grade Uniformly temperature controlled mold Water-cooled inner comer2000 1.9 0.52002 2.7 0.73300 3.3 2.7

6300B 2.2 0.77400W 3.6 2.8

Table 4-4 Gate Location vs. Deviation in L-shaped Parts (Unit: degrees)Grade Gate at tip Gate at corner2000 2.1 2.82002 2.4 3.03105 3.9 1.73200 4.1 1.73300 3.2 1.63400 3.1 1.4

6300B 1.9 2.17400W 3.2 1.8

(d) Ribbed PlatesOne of the measures to improve stiffness of a part is to provide it with ribs, but some ribs tend to increase deformation of the part. Examples are listed in Table 4-5.The deformations of shape #1 that has symmetrical ribs at both ends is similar to that of shape #6 that has no ribs. Plates having ribs on only one side have some warpage making the ribbed side convex. These results can be used to minimize warpage.

Table 4-5 Warpage (mm) of Ribbed Plates

Moldtemp.(°C)

Grade

Shapes

30 3300 0.04 0.07 0.44 0.40 0.50 < 0.0480 3300 0.07 0.09 0.50 0.64 0.70 0.07

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(2) Gate Design vs. Deformation

[Example 1] Impeller (3300) (Unit: mm)Number of

gatesOne Two Three

Roundness 0.22（0.05） 0.24（0.07） 0.14（0.03）

Flatness 0.72（0.25） 0.94（0.06） 0.58（0.00）Injection pressure: 98MPa; the figures in parentheses are R for n=3.Gate: 1.5mm dia. of pin gate; disk dia.: approx. 65 mm; thickness avg.: approx. 3 mm.

[Example 2] Round parts (valve) No.2, housing (3300) (Unit: mm)Gate

positionAsymmetric 6

pointsSymmetric 4

pointsRoundness 0.15 0.15

Plane flatness

0.44 0.27

Molding conditions: refer to No.6 in Table 4-2.

[Example 3] Round parts (valve) No.1, top and bottom lids (3300) (Unit : mm)(Refer to the sketches for details.)

Number of gates One Two Three

Top lidRoundness of d1 0.17 0.18 0.05Flatness of plane A 0.18 0.16 0.08Deviation of flange from flat line (H) 0.22 0.26 0.14

Bottom lid

Roundness of d2 0.14 0.27 0.10Flatness of plane B 0.28 0.45 0.21

Injection pressure: 98MPa, the figures in parentheses are R for n=3.

Sketches of example 3

(i) Top lidGates were located at three vertexes of a regular triangle with their center at the center of the lid. The average thickness of the lid was approximately 2 mm.

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(ii) Bottom lidGates were positioned at three vertexes of an isosceles triangle with their center at the center of the lid. The average thickness was about 2 mm.

(3) Molding Conditions vs. DeformationMolding conditions which are closely related to the deformation of a part are the mold temperature, cooling time and those factors which affect pressure of melt in the cavity, such as gate size, injection speed and dwell time.

(a) Mold temperatureAs examples, the results obtained from round parts made of DURANEX 3300 are listed in Table 4-6. There is an indication that the lower the mold temperature, the better the roundness and the flatness.

Table 4-6 Effect of Mold Temperature on Roundness and Flatness of Valves (3300)

ValvesMold temp.

(°C)Diameter

(mm)Roundness

(mm)

Plane flatness

(mm)Gate

No. 245 - 48

590.14 0.26

4 pin-point60 - 65 0.15 0.27

No. 340 - 50

45.30.07 0.11

1 pin-point50 - 70 0.12 0.14

No. 440 - 50

620.10 0.11

1 pin-point50 - 60 0.10 0.16

No. 545 - 55

610.11 0.24

4 pin-point60 - 88 0.13 0.26

No.640

630.16 0.21

3 pin-point70 0.24 0.32

(b) Injection and dwell timeThe relation between injection and dwell time and flatness of a disc 120 mm in diameter and 2 mm in thickness, molded through a center pin-point gate, is shown in Fig. 4-3.This figure shows that if injection and dwell time is shorter than the gate seal time, deformation is greatly increased. This is a very important point in setting the molding cycle.

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(c) Injection speedThe effect of injection speed on deformation is not so great. However, deformation tends to reduce as injection speed increases. Examples are shown in Table 4-7.

Table 4-7 Effect of Injection Speed on Roundness and Flatness of an Impeller (3300)Injection speed

(mm/sec)Injection pressure

(MPa)Roundness

(mm)Flatness

(mm)3 98 0.20 0.658 98 0.14 0.5817 68 0.14 0.6580 68 0.11 0.63

4.3 Use of RegrindThe effect of recycling of DURANEX® PBT 3300 on their mechanical properties is shown in Table 4-8. As the recycling is repeated, severer drops of mechanical properties are found with glass fiber reinforced grades compared with unfilled grades.The relation between the solution viscosity (the intrinsic viscosity) and the recycling frequency is shown for both filled and unfilled grades in Fig. 4-4: no significant change in solution viscosity due to recycling is found. On the other hand, glass fiber length decreases as the recycling is repeated, as seen in Table 4-8 and Fig. 4-5. This indicates that the changes in mechanical properties caused by recycling stem from the breakage of glass fibers and not from deterioration of the base polymer.

Table 4-8 Mechanical Properties vs. Recycling (Using 100% Regrind Material)Grade 3300

Recycling frequency 0 1 2 3 4 5Tensile strength retention rate (%) 100 86 81 75 70 68Flexural strength retention rate (%) 100 94 86 85 81 79Flexural modulus retention rate (%) 100 92 92 88 86 84lmpact strength retention rate (%) 100 88 80 67 57 53

Glass fiber length* (mm) 0.38 0.30 0.29 0.27 0.28 0.21* 0.52mm in virgin pellets

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On the basis of the above result, the amount of regrind should be limited to 25% and 75% should be virgin pellets. As an example, Table 4-9 shows the mechanical properties of parts molded with a mixture of 75% virgin pellets and 25% once-used regrind. Very little change occurred.When the use of regrind is limited to 25%, the probability percentage change in mechanical properties of repeatedly reused materials decreases very sharply as shown Table 4-10. Therefore, it is safe to conclude from a practical viewpoint that changes in mechanical properties caused by using regrind twice will cause no problem. It must be presupposed, however, that the molding conditions are kept under proper control to prevent adverse effects such as heat deterioration and hydrolysis in molding.

Table 4-9 Effect of Using Regrind 3300

Mechanical PropertiesComposition

All virgin pelletsVirgin pellets 75%Once-regrind 25%

Retention rate of tensile strength (%) 100 97Retention rate of lzod impact strength (notched (%)) 100 95

Retention rate of tensile impact strength (%) 100 97Retention rate of heat deflection temp. (1.82 MPa)

(%)100 100

Table 4-10 Percentage of Repeatedly Reused Material When 25% of Regrind is Continuously Mixed with 75% of Virgin Pellets

Number of

recyclingVirgin (%)

1st reuse(%)

2nd reuse(%)

3rd reuse(%)

4th reuse(%)

5th reuse(%)

1 75 252 75 18.8 6.23 75 18.8 4.7 1.54 75 18.8 4.7 1.1 0.45 75 18.8 4.7 1.1 0.3 0.1

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5. Mold Design5.1 Runner DesignIt is ideal to so design runners so that the cooling of the molten resin and the pressure loss are as little as possible, but such a design is not economical because the ratio of runner weight to product weight increases, and the cooling of runners becomes the determining factor of the molding cycle. It is recommended, therefore, that runners be designed with the smallest dimensions within the allowable range."Simplified Runner Designing Chart" illustrated in "Molding Technology for DURACON® POM" can be used for runner design of DURANEX® PBT without any significant errors.As for runner shapes, the best type is a full round runner; however, this type of runner is costly because it is necessary to cut grooves on both the stationary and the movable mold halves. Therefore, trapezoidal runners are frequently adopted. The standard dimensions for this runner are as follows:

Upper base length = (0.6 to 0.7) × Lower base lengthDepth ≈ Upper base length

DURANEX can be molded through hot runners, but the following precautions must be taken:

(1) When glass fiber reinforced grades are molded, materials for hot tips and manifolds must be carefully selected, so that serious abrasion by the glass fibers does not occur.(2) It is necessary to avoid discoloration and deterioration of the resin caused by additional residence time in hot tips and manifolds.

There should be no problems for other points, if only the general precautions on hot runner design are taken.

5.2 Gate DesignA larger gate is recommended for DURANEX than DURACON, because reduction in cavity pressure tends to cause deformation. However, gate seal times for DURANEX are shorter than those for DURACON, as shown in Table 5-1, which is favorable from the molding cycle point of view.The key points for gate are as follows:

(1) The gate type must be decided, taking product quality, productivity and automated operation into consideration.(2) The position and the number of gates affect the deformation, strength (especially the weld strength of composite grades) and appearance of a part. These are important measures for preventing deformation.(3) The gate thickness should generally be 60 to 70% of the part thickness.

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Table 5-1 Gate Seal Times for DURANEX® PBT and DURACON® POM

Mold temp.（°C）

Specimenthickness

(mm)

Gate dia.(mm)

Gate Seal Times (s)DURANEX DURACON

2000 3300 M90 GH-25

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1.00.5 2.2 1.6 3.4 2.81.0 2.2 1.6 3.4 2.8

2.01.0 6.8 4.2 8.6 6.21.5 7.0 4.6 9.0 6.4

3.01.5 10.6 6.6 13.8 10.62.0 10.8 6.8 15.8 11.2

60

1.00.5 2.6 1.8 3.8 2.81.0 2.6 1.8 3.8 2.8

2.01.0 7.0 4.2 9.8 7.01.5 7.2 4.6 10.6 7.8

3.01.5 10.8 6.8 16.6 12.82.0 11.4 7.2 18.2 12.8

80

1.00.5 2.8 2.2 4.2 3.41.0 2.8 2.2 4.2 3.4

2.01.0 7.2 4.4 11.8 7.81.5 7.4 4.8 12.6 9.0

3.01.5 11.0 7.6 19.2 15.82.0 11.4 7.8 20.6 16.8

5.3 Gas VentsImproperly designed gas vents give DURANEX parts burn marks, impairing their appearance. As mentioned previously, high speed injection is a popular way to improve surface gloss; therefore, a thorough study of gas vents is required. For a mold where gas is driven out from the parting line, the recommended method is for gas to escape from the full outer periphery of the product as seen in Fig.5-1. The depth of the vent must be 2/100mm or less.

5.4 UndercutAs a rule, a mold should be designed without undercut. In the case of DURANEX 3300, large undercut is not possible. The maximum is approximately 0.5%.

Glass fiber content Margin for snap-fit0 % 6 - 7 %15 % 3 - 4 %30 % 2 - 3 %

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5.5 DraftDraft should be as large as possible, within the permissible range, because of the small mold shrinkage of reinforced grades of DURANEX. Minimum taper is 1/2 to 1 degree. Sufficient consideration must also be paid to the knockout system, including the position and number of knockout pins.

5.6 Mold Temperature ControlBecause mold temperature greatly affects the molding cycle and product quality, temperature controlsystem for the mold must be studied beforehand as carefully as the runners, gates, and knockout system.

The key points are:(1) Does the control system consist of electric heaters or hot water circulation?(2) The key points for hot-water circulation system are:a) Secure sufficient heat transfer surface area.b) Locate the cooling water channels as close as possible to the cavity (to get a uniform temperature profile of cavity surface).c) Circulate sufficient amount of water. In other words, it is important to use a temperature control unit having a pump big enough to supply sufficient amount of water to overcome pressure loss in the circuit.(3) Consideration of core cooling, which can greatly improve molding cycle and product deformations.

5.7 Mold MaterialsMold material for DURANEX requires the following considerations.

(1) Wear due to glass fibers(2) Corrosion caused by gases from decomposition(3) Corrosion resulting from flame retardants

Hardening is the best way to minimize wear. A countermeasure to protect against corrosion is to select suitable mold material. To obtain reference data for corrosion resistance, test specimens of various steels were exposed to gases produced by various grades of DURANEX held at 260°C, and the discoloration and corrosion of the specimens' surfaces were observed. The samples fell in the following order.

420 > D2 > P21 > P20 > 1049

Also, the following sequence is reported in technical literature.310S, 440C > 304 > D2

These results indicate that stainless-type steels can withstand the corrosion better than others. For reference, the features of various mold materials are summarized in Table 5-2.

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Table 5-2 Characteristics of Mold Materials

Material AISI

Har

dnes

sH

RC

Wea

rre

sist

ance

Cor

rosi

onre

sist

ance

Stre

ngth

Mac

hina

bilit

y

Surfa

cefin

ish

Text

ure

proc

essa

bilit

y

Har

dena

bilit

y

Wel

dabi

lity

Carbon steel for machine structural use

1045 - 1055 15-20 C D C A++ C B C A

Stainless steel304 A B440C 55-60 A A- A B A- B B C

Carbon tool steel W1-10 63< B- CHigh speed tool steel

M2 correspondent

63 A+ B A+ B A- B- C

Alloy tool steel

O1 60< B- CD2 63-65 A B- A B A- A- A CA2 65 A B AH13 45-50 B+ C- A- B+ A A A A-

Precipitation hardened stainless steel

S17400 40 B+ A B+ C A B A A

Vacuum-melted stainless steel

420 52 A A A B A++ A

Prehardened steelP21 40 B C- B+ A+ A+ A A AP20 35 B- C- B A+ A A A A

Copper-beryllium alloy

C82800(UNS Num.)

42-48

C82500(UNS Num.)

35-42

Evaluation ranks: A (superior) > B > C > D (inferior)Within a rank: ++ (superior) > + > No sign > - (inferior)

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6. Safety PrecautionsAs long as general safety precautions in the molding industry are observed, there is no special danger in molding DURANEX® PBT. However, appropriate ventilation is recommended because there are cases where DURANEX may decompose, and the decomposed product may accumulate when heated up to extremely high temperatures, as is the case with other plastics, which may be hazardous to health.

In order to prevent thermal decomposition and to prevent gas generation and pressure generation in the cylinder, resin temperature should not be raised to 280°C or higher.

Also, if long-time stoppage is required, all the resin in the cylinder should be discharged, and the temperature should be lowered to 230°C or less.

Before pellets are supplied or the screw is rotated, sufficient time should be taken for the cylinder to heat up to at least 250°C.

Workers should wear protective glasses, especially when purging. Also, they should wear gloves when handling a hot molds, etc. While molding is stopped, the injection unit should be retracted to prevent the nozzle section from hardening due to contact with the mold.

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7. Countermeasures for DefectsDefect phenomenon

Causes Measures

BS(Black speck)

1. Material decomposition 1. Sufficient purging.2. Lower resin temperature.3. Shorten residence time in cylinder.

2. Insufficient purging3. Contamination of foreign materials

1. Sufficient purging.

Weld mark 1. Low resin temperature and/or low pressure when flow fronts meet in weld line

1. Raise the mold temperature (buried cartridge heaters in weld sections).2. Elevate resin temperature.3. Increase injection speed.4. Change the resin to a higher flow grade.5. Increase holding pressure.6. Enlarge gate size.

2. Insufficient degassing 1. Enlarge gas vent size at weld.3. Design problem 1. Provide weld escape.

2. Change flow pattern into welds by adjustment of thickness.

Silver mark 1. Volatile components like moisture, decomposed gas and air entrapped in plasticization.2. Air pocket generation by unbalanced flow in cavity.

1. Sufficient drying material.2. Don't raise resin temperature too high.3. Lower screw revolution speed. Increase screw back pressure.4. Enlarge gas vent size.5. Degas from runners.

3. Contamination of foreign materials 1. Sufficient purgingGas burn 1. Insufficient degassing 1. Slow injection speed. When

restricted product shape, adjust V-P switching position or use multi-stage injection method.2. Enlarge gas vent size.3. Lower resin temperature and/or mold temperature.

Cold slag 1. Contamination of solid resin which solidifies at cylinder head

1. Raise cylinder temperature. When nozzle-touched operation, raise mold temp.2. Enlarge slag well of runner. 3. Retreat back cylinder every cycle.

Jetting 1. When melt resin goes out from a narrow place to a wide place in mold, if its speed is too fast, resin sometimes runs out in a strand shape and does not touch cavity surface. As result, jetting, strand-like marks on molded piece occur.

1. Enlarge gate size. Alter gate position.2. Slow initial running rate at the gate.3. Lower resin viscosity; i.e., elevate resin temperature and/or mold temperature, use higher flow grades.4. Increase holding pressure.

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Glass mark, haze

1. Insufficient pressure 1. Increase holding pressure.2. Raise mold temperature and/or resin temperature.3. Enlarge gate size. 4. Increase injection speed.5. Use high-flow grade.

2. Insufficient degassing 1. Enlarge gas-vent size.3. Cold slag, jetting 1. Refer to each section in this page.

Flow mark 1. Residual jetting pattern on the surface Primary measure: Prevent jetting.1. Refer to section on jetting. Secondary measure: Make jetting mark unnoticeable if jetting occurs.

1. Elevate mold temperature.2. Increase holding pressure.

3.Alter the gate position (Make straight length short after resin passes through the gate).

-( a) After the gate position to the section where flow comes in contact with the core.-( b) Move the gate position to a thin wall section.-( c) Use a tub gate.

2. Residual flow pattern on the surface due to flow rate change, generated when resin passes corner sections or sections of non-uniform wall thickness

1. Make comers rounded.2. Make sections where wall thickness changes gently inclined and rounded.

3. Insufficient degassing 1. Enlarge gas vent size.Sink mark 1. Surface sink with shrinkage of inner part due to

insufficient cooling of thick wall and rib section and insufficient inner pressure in the cavity.

1. Lower mold temperature.2. Enlarge sprue, runners and gates.3. Increase holding pressure. Prolong holding time.4. Keep cushion amount of material until gate seals.5. Minimize rib thickness to approximately one-third of base thickness.6. Decrease thickness of thick wall sections.

Surface delamination

1. Contamination of foreign materials 1. Sufficient purging2. Shear delamination 1. Raise the mold and/or resin

temperature.2. Enlarge gates size.3. Decrease product thickness.4. Lower holding pressure.

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5. Lower injection speed.3. Large gas generation 1. Don't raise resin temperature too

high.2. Sufficient material drying.3. Don't make revolution speed too high. Don't lower screw back pressure too low.4. Lower holding pressure.5. Lower injection speed.6. If regrind material was used, lower ratio of regrind.

Blistering 1. Air catching 1. Lower screw revolution speed. Increase screw back pressure.2. Lessen suck-back amount.

2. Surface delamination 1. Raise mold temperature.2. Lower injection speed.3. Enlarge gate size.4. Increase wall thickness (of too thin parts only).5. Suppress jetting.

3. Large gas generation 1. Don't raise resin temperature too high.2. Sufficient drying.3. Shorten resident time in cylinder.

Warpage deformation

1. Anisotropy due to glass fiber orientation 1. Increase wall thickness.2. In case of ribbed product design, set gate on shorter side of product. In addition, set direction of rib for samedirection of resin flow.

Unstable metering

1. Unstable or no supply of resin pellet into cylinder while metering.

1. Adjust screw revolution speed. Lower screw back pressure.2. Lower resin temperature.3. Change resin grade and/or screw pattern.4. When using regrind, use uniform pellet shape and size as much as possible. Reduce powdered resin as much as possible.

Poor mold releasability

1. Grasp of a core-pin 1. Raise holding pressure.2. Raise mold temperature.

2. Overfilling into ribs and bosses 1. Lower holding pressure.2. Lower mold temperature.

3. Mold design problem 1. Increase drafts of circumference of the cavity, bosses and ribs. And/or add ejector pins.

Void 1. Gas voidEntrapping gas in cylinder or through injection. Moisture, decomposition of resin and air.

1. Raise holding pressure. Enlarge size of gate, runner and sprue.2. Locate gate as near voids position

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as possible (usually thick wall part).3. Sufficient material drying.4. Lower resin temperature.5. Shorten molding cycle.6. Lower screw revolution speed. Raise screw back pressure.7. Decrease injection speed.8. Enlarge gas vent size.

2. Vacuum voidInner molten resin is pulled to surface due to fast solidification of surface layer, then voids occur in inner section.

1. Locate gate at the thickest section of molding.2. Enlarge gate, runner, sprue, and nozzle in accordance with thickness of molding. Increase gate thickness to more than 50%-60% of wall thickness of molding.3. Increase holding pressure. Prolong holding time.4. Keep cushion until gate seals.5. Ensure working of non-return valve does not cause back flow during holding time.6. Raise mold temperature.7. Decrease injection speed.8. Change to a high viscosity grade.

MD (Mold deposit)

1. Adhesion and build-up of degraded resin, additive agent, etc. on surface of mold.

1. Lower resin temperature.2. Sufficient material drying.3. Shorten resident time in cylinder.4. Raise mold temperature.5. Decrease injection speed.6. Enlarge gas vent size.7. If regrind material was used, lower ratio of regrind.8. Clean mold.

Surface roughness

1. MD (Mold deposit) 1. Measures against mold deposit-(a) Sufficient material drying-(b) Don't raise resin temperature too high.-(c) Enlarge gas vent size.-(d) Raise mold temperature.2. Cleaning cavities-(a) Ultrasonic cleaning of core in a solvent.

2. Insufficient resin's pressing for cavity 1. Increase holding pressure and time.2. Enlarge runners and gates.3. Raise mold temperature.4. Raise resin temperature.5. Increase injection speed.

Crack 1. Poor mold releasability 1. Refer section of "poor mold

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formation releasability" in this page.2. Embrittlement of molded product due to degradation or hydrolysis of resin.

1. Adjust resin temperature.2. Shorten resident time in cylinder.3. Sufficient material drying.4. Raise mold temperature and prolong cooling time for improving polymer crystallinity.

Drooling 1. Low viscosity of material 1. Lower cylinder temperature, especially at nozzle.2. Use a higher viscosity grade.

2. High pressure in cylinder 1. Lower screw revolution speed and back pressure. Back pressure should be set 0.2 MPa at least.2. Sufficient drying material.3. Lower cylinder temperature.4. Increase suck-back amount.

Stringiness 1. Resin in sprue top is not solidified. 1. Lower cylinder temperature. especially at nozzle.2. Lower mold temperature.3. Quicken mold opening speed and widen mold opening distance.4. Change kind, shape or type of nozzle; i.e., using shut-off type nozzle, make nozzle hole smaller.

NOTES TO USERS● All property values shown in this brochure are the typical values obtained under

conditions prescribed by applicable standards and test methods.

● This brochure has been prepared based on our own experiences and laboratory

test data, and therefore all data shown here are not always applicable to parts used

under different conditions. We do not guarantee that these data are directly

applicable to the application conditions of users and we ask each user to make his

own decision on the application.

● It is the users’ responsibility to investigate patent rights, service life and potentiality

of applications introduced in this brochure. Materials we supply are not intended for

the implant applications in the medical and dental fields, and therefore are not

recommended for such uses.

● For all works done properly, it is advised to refer to appropriate technical catalogs

for specific material processing.

● For safe handling of materials we supply, it is advised to refer to the Material Safety

Data Sheet “SDS” of the proper material.

● This brochure is edited based on reference literatures, information and data

available to us at the time of creation. The contents of this brochure are subject to

change without notice upon achievement of new data.

● Please contact our office for any questions about products we supply, descriptive

literatures or any description in this brochure.

DURANEX® is a registered trademark of Polyplastics Co., Ltd. in Japan and other countries.

POLYPLASTICS CO., LTD.JR Shinagawa East Bldg.,

18-1, Konan 2-chome, Minato-ku, Tokyo, 108-8280 Japan

Tel: +81-3-6711-8610 Fax: +81-3-6711-8618

https://www.polyplastics.com/en/

P19.04.01 R1.6 EDX-MO01