Injection molding properties of commonly used plastics

Injection molding technology is widely used. I hope this article can give some inspiration to friends who want to understand this knowledge.——-Vito.

Injection molding properties of commonly used plastics

1. ABS (acrylonitrile-butadiene-styrene copolymer)
① Typical application scope:
Cars (dashBOARDS, TOOL bay DOORS, wheel covers, mirror boxes, etc.), REFRIGERATORS, high-strength TOOLS (HAIR dryers, blenders, food processors, lawn mowers, etc.), TELEPHONE casINGS, TYPEWRITER keyboards, recreational VEHICLES such as golf carts and jet sledges, etc.
(2) Process conditions of injection mold:
Drying treatment: ABS material has hygroscopic property, requiring drying treatment before processing. The recommended drying condition is 80 to 90 ° C for at least 2 hours. The material humidity should be less than 0.1%.
Melting temperature: 210 ~ 280℃; Recommended temperature: 245 ° C.
Mold temperature: 25 ~ 70℃. (Mold temperature will affect the finish of plastic parts, low temperature will lead to low finish).
Injection pressure: 500 ~ 1000bar.
Injection speed: medium to high speed.
③ Chemical and physical characteristics:
ABS is synthesized from acrylonitrile, butadiene and styrene. Each monomer has different characteristics: acrylonitrile has high strength, thermal and chemical stability; Butadiene has the characteristics of toughness and impact resistance; Styrene is easy to process, high finish and high strength. In terms of morphology, ABS is an amorphous material. The polymerization of the three monomers resulted in a terpolymer with two phases, one as a continuous phase of styrene-acrylonitrile and the other as a dispersed phase of polybutadiene rubber. The characteristics of ABS mainly depend on the ratio of the three monomers and the molecular structure in the two phases. This allows for great flexibility in product design, and has resulted in the market for hundreds of ABS materials of different qualities. These MATERIALS OF DIFFERENT QUALITIES OFFER DIFFERENT CHARACTERISTICS, SUCH AS MODERATE TO HIGH IMPACT RESISTANCE, LOW TO HIGH FINISH AND HIGH TEMPERATURE TWISTING PROPERTIES. ABS material has super easy workability, appearance characteristics, low creep, excellent dimensional stability and high impact strength.

2. PA6 (polyamide 6 or nylon 6)
① Typical application scope:
It is widely used in structural components because of its good mechanical strength and stiffness. Because of its good wear resistance, it is also used to manufacture bearings.
(2) Process conditions of injection mold:
Drying treatment: Since PA6 is easy to absorb water, special attention should be paid to drying before processing. If the material is supplied in a waterproof package, the container should be kept airtight. If the humidity is greater than 0.2%, it is recommended to dry in hot air above 80℃ for 16 hours. If the material has been exposed to air for more than 8 hours, vacuum drying at 105 ° C for more than 8 hours is recommended.
Melting temperature: 230~280℃, 250~280℃ for enhanced varieties.
Mold temperature: 80~90℃. Mould temperature has a significant effect on the degree of crystallinity which in turn affects the mechanical properties of plastic parts. Crystallinity is important for structural components, so it is recommended that the mold temperature be 80~90℃. High die temperatures are also recommended for thin-walled, long process plastic parts. Increasing the mold temperature can improve the strength and stiffness of plastic parts (increase the crystallinity), but reduce the toughness. If the wall thickness is larger than 3mm, a low temperature mold of 20 to 40 ° c is recommended. For glass reinforced materials, the mold temperature should be greater than 80℃.
Injection pressure: generally between 750 and 1250bar (depending on material and product design).
Injection speed: High speed (slightly lower for enhanced materials).
Runner and gate: The location of the gate is very important due to the short solidification time of PA6. Gate aperture should not be less than 0.5*t (where T is the thickness of plastic parts). If a hot runner is used, the gate size should be smaller than if a regular runner is used because the hot runner helps prevent premature solidification of the material. If a diving gate is used, the minimum diameter of the gate should be 0.75mm.
③ Chemical and physical characteristics:
The chemical and physical characteristics of PA6 are similar to those of PA66; however, it has a lower melting point and a wide range of process temperatures. Its impact resistance and solubility resistance is better than that of PA66, but its hygroscopicity is also stronger. Because many quality characteristics of plastic parts are affected by moisture absorption, this point should be fully taken into account when using PA6 to design products. In order to improve the mechanical properties of PA6, various modifiers are often added. Glass is the most common additive, and synthetic rubber, such as EPDM and SBR, is sometimes added to improve impact resistance. For products without additives, the shrinkage of PA6 is between 1% and 1.5%. The addition of fiberglass additives reduces the shrinkage to 0.3% (but slightly higher in the direction perpendicular to the flow). The shrinkage is mainly affected by the crystallinity and hygroscopicity of the material. The actual shrinkage is also a function of plastic design, wall thickness and other process parameters.

3. PA12 (polyamide 12 or nylon 12)
① Typical application scope:
Water gauges and other commercial equipment, cable sleeves, mechanical cams, sliding mechanisms and bearings.
(2) Process conditions of injection mold:
Drying treatment: The humidity should be below 0.1% before processing. If the material is stored exposed to air, it is recommended to dry in hot air at 85 ° C for 4 to 5 hours. If the material is stored in a closed container, it can be used immediately after 3 hours of temperature equilibation.
Melting temperature: 240~300℃; Do not exceed 310℃ for materials with ordinary characteristics and 270℃ for materials with flame retardant characteristics.
Mold temperature: 30~40 ° C for unenhanced materials, 80~90 ° C for thin-walled or large-area components, and 90~100 ° C for enhanced materials. Increasing the temperature will increase the crystallinity of the material. Accurate control of mold temperature is important for PA12.
Injection pressure: up to 1000bar (low holding pressure and high melting temperature recommended).
Injection speed: High speed (better for materials with glass additives).
Runner and gate: For materials without additives, the runner diameter should be about 30mm due to the low viscosity of the material. For the enhanced material, large runner diameter of 5~8mm is required. The shape of the runner shall be all round. The injection port should be as short as possible. Many forms of sprue can be used. Do not use small sprue for large plastic parts, this is to avoid excessive pressure on plastic parts or excessive shrinkage. The thickness of the gate should be equal to the thickness of the plastic parts. If a diving gate is used, a minimum diameter of 0.8mm is recommended. Hot runner molds are effective, but require precise temperature control to prevent material from leaking or solidifying at the nozzle. If hot runner is used, the gate size should be smaller than cold runner.
③ Chemical and physical characteristics:
PA12 is a linear, semi-crystalline – crystalline thermoplastic material from butadiene. Its properties are similar to those of PA11, but its crystal structure is different. PA12 is a very good electrical insulator and will not be affected by moisture like other polyamides. It has good chemical stability against impact machines. There are many improved varieties of PA12 in terms of plasticizing and enhancing properties. Compared with PA6 and PA66, these materials have lower melting point and density, and have very high moisture return. PA12 has no resistance to strong oxidizing acids. The viscosity of PA12 mainly depends on humidity, temperature and storage time. It’s very liquid. The shrinkage is between 0.5% and 2%, depending on the type of material, wall thickness and other process conditions.

4. PA66 (polyamide 66 or nylon 66)
① Typical application scope:
Compared with PA6, PA66 is more widely used in the automotive industry, instrument shells and other products requiring impact resistance and high strength.
(2) Process conditions of injection mold:
Drying: If the material is sealed before processing, then drying is not necessary. However, if the storage container is opened, it is recommended to dry it in hot air at 85 ° C. If the humidity is greater than 0.2%, vacuum drying at 105℃ for 12 hours is required.
Melting temperature: 260~290℃. The additives on the glass products are 275~280℃. The melting temperature should not be higher than 300℃.
Mould temperature: 80℃ is recommended. Mould temperature will affect crystallinity, and crystallinity will affect the physical characteristics of the product. For thin-walled plastic parts, if the mold temperature is lower than 40℃, the crystallinity of the plastic parts will change with time. In order to maintain the geometric stability of the plastic parts, annealing is needed.
Injection pressure: usually between 750 and 1250bar, depending on material and product design.
Injection speed: high speed (slightly lower for enhanced materials).
Runner and gate: The location of the gate is very important because the solidification time of PA66 is very short. Gate aperture should not be less than 0.5*t (where T is the thickness of plastic parts). If a hot runner is used, the gate size should be smaller than if a regular runner is used because the hot runner helps prevent premature solidification of the material. If a diving gate is used, the minimum diameter of the gate should be 0.75mm.
③ Chemical and physical characteristics:
PA66 has a high melting point in polyamide materials. It is a semi-crystalline – crystalline material. PA66 can maintain strong strength and stiffness at higher temperatures. PA66 still has hygroscopicity after forming, the degree of which mainly depends on the composition of the material, wall thickness and environmental conditions. In product design, we must consider the effect of moisture absorption on geometric stability. In order to improve the mechanical properties of PA66, various modifiers are often added. Glass is the most common additive, and synthetic rubber, such as EPDM and SBR, is sometimes added to improve impact resistance. PA66 is less sticky, so it is very liquid (but not as liquid as PA6). This property can be used to process very thin components. Its viscosity is sensitive to changes in temperature. The shrinkage of PA66 is between 1%~2%, and the shrinkage can be reduced to 0.2%~1% by adding glass fiber additive. The shrinkage rate in the flow direction and the vertical direction of the flow direction is very different. PA66 is soluble to many solvents, but is less resistant to acids and some other chlorinated agents.
5. PBT (polybutylene terephthalate)
① Typical application scope:
Household appliances (food processing blades, vacuum cleaner components, electric fans, hair dryer casings, coffee ware, etc.), electrical components (switches, electrical casings, fuse boxes, computer keyboard keys, etc.), automotive industry (radiator lattices, body panels, wheel covers, door and window components, etc.).
(2) Process conditions of injection mold:
Drying: This material hydrolyzes easily at high temperatures, so drying before processing is important. The recommended drying conditions in air are 120 ° C for 6 to 8 hours or 150 ° C for 2 to 4 hours. The humidity must be less than 0.03%. If using a hygroscopic dryer, the recommended drying condition is 150 ° C for 2.5 hours.
Melting temperature: 225~275 ° C. Recommended temperature: 250 ° C.
Mold temperature: 40~60℃ for unenhanced material. The cooling cavity of the mold should be well designed to reduce the bending of the mold. The heat must be lost quickly and evenly. It is recommended that the diameter of the cooling cavity of the mold be 12mm.
Injection pressure: medium (Max. 1500bar).
Injection rate: The fastest possible injection rate should be used (since PBT solidifies quickly).
Runner and gate: Circular runner is recommended to increase pressure transfer (empirical formula: runner diameter = plastic thickness +1.5mm). Various types of gate can be used. Hot runners can also be used, but care should be taken to prevent material leakage and degradation. The diameter of the gate should be between 0.8 and 1.0* T, where T is the thickness of the plastic parts. For submersible gate, the recommended minimum diameter is 0.75mm.
③ Chemical and physical characteristics:
PBT is one of the toughest engineering thermoplastic materials, it is a semi-crystalline material, has very good chemical stability, mechanical strength, electrical insulation properties and thermal stability. These materials have excellent stability over a wide range of environmental conditions. The hygroscopic properties of PBT are weak. The tension strength of the non-enhanced PBT is 50MPa, and the tension strength of the glass dosage form is 170MPa. Too many additives in glass will lead to brittle materials. PBT crystallizes very rapidly, which results in bending deformation due to uneven cooling. For materials with glass additives, the shrinkage rate in the flow direction can be reduced, but the shrinkage rate in the vertical direction of the process is basically no different from that of ordinary materials. The shrinkage rate of general materials is between 1.5% and 2.8%. Materials with 30% glass additive shrink between 0.3% and 1.6%. The melting point (225℃) and high temperature deformation temperature are lower than those of PET materials. The softening temperature of Vica is about 170℃. The glass trasitio temperature is between 22℃ and 43℃. Because of the high crystallization rate of PBT, its viscosity is very low, and the cycle time of plastic parts processing is generally low.
6. PC (polycarbonate)
① Typical application scope:
Electrical and commercial equipment (computer components, connectors, etc.), appliances (food processors, refrigerator drawers, etc.), transportation industry
Front and rear lights, dashboard, etc of a vehicle
(2) Process conditions of injection mold:
Drying treatment: PC material has hygroscopic property, drying before processing is very important. The recommended drying conditions are 100 ° C to 120 ° C for 3 to 4 hours. Humidity before processing must be less than 0.02%.
Melting temperature: 260~340℃.
Mold temperature: 70~120℃.
Injection pressure: Use as high an injection pressure as possible.
Injection speed: Use low speed injection for smaller gate and high speed injection for other gate types.
③ Chemical and physical characteristics:
PC is an amorphous engineering material with excellent impact strength, thermal stability, gloss, antibacterial properties, flame retardant properties and pollution resistance. The Otched Izod impact STregth of PC is very high (the crown of impact), and the shrinkage rate is very low, generally 0.1%-0.2%. PC has very good mechanical properties, but poor flow characteristics, so the injection process of this material is difficult. When choosing the quality of PC materials, the final expectation of the product is the benchmark. If the plastic parts require high impact resistance, then use low flow rate of PC material; Instead, high turnover PC materials can be used to optimize the injection molding process.
7. PC/ABS (polycarbonate and acrylonitrile-butadiene-styrene copolymers and mixtures)
① Typical application scope:
Computer and business machine casings, electrical equipment, lawn and garden machinery, automobile parts (instrument panels, interior finishes and wheel covers).
(2) Process conditions of injection mold:
Drying treatment: Drying treatment is necessary before processing. The humidity should be less than 0.04%. The recommended drying condition is 90 to 110 ° C for 2 to 4 hours.
Melting temperature: 230~300℃.
Mold temperature: 50~100℃.
Injection pressure: depends on the molding.
Injection rate: As high as possible.
③ Chemical and physical characteristics:
PC/ABS has the comprehensive characteristics of both PC and ABS. For example, the easy machining characteristics of ABS and the excellent mechanical characteristics and thermal stability of PC. The ratio of the two will affect the thermal stability of PC/ABS material. The PC/ABS hybrid also shows excellent flow characteristics.
8. PC/PBT (a mixture of polycarbonate and polybutylene terephthalate)
① Typical application scope:
Gearboxes, car bumpers and products requiring chemical and corrosion resistance, thermal stability, impact resistance and geometric stability.
(2) Process conditions of injection mold:
Drying: It is recommended to dry at 110~135℃ for about 4 hours.
Melting temperature: 235~300℃.
Mold temperature: 37~93℃.
③ Chemical and physical characteristics:
PC/PBT has the comprehensive characteristics of both PC and PBT, such as PC’s high toughness and geometric stability and PBT’s chemical stability, thermal stability and lubrication characteristics.
9. Pe-hd (High density polyethylene)
① Typical application scope:
Refrigerator container, storage container, household kitchenware, seal cover, etc.
(2) Process conditions of injection mold:
Drying: Not necessary if stored properly.
Melting temperature: 220~260℃. For materials with large molecules, the recommended melting temperature range is between 200 and 250 ° C.
Mold temperature: 50~95℃. A higher mold temperature should be used for parts with a wall thickness of less than 6mm, and a lower mold temperature should be used for parts with a wall thickness of more than 6mm. The cooling temperature of plastic parts should be uniform to reduce the difference of shrinkage rate. For the optimal machining cycle time, the diameter of the cooling cavity should not be less than 8mm, and the distance from the die surface should be within 1.3d (where “D” is the diameter of the cooling cavity).
Injection pressure: 700~1050bar.
Injection speed: High speed injection is recommended.
Runner and gate: Runner diameter between 4 and 7.5mm, runner length should be as short as possible. All types of gate can be used and the gate length should not exceed 0.75mm. Especially suitable for the use of hot runner die.
③ Chemical and physical characteristics:
The high crystallinity of PE-HD results in its high density, tensile strength, high twisting temperature, viscosity, and chemical stability. Pe-hd has stronger permeability resistance than PE-LD. The impact strength of PE-HD is low. The characteristics of PH-HD are mainly controlled by density and molecular weight distribution. The molecular weight distribution of PE-HD suitable for injection molding is very narrow. For the density of 0.91-0.925 g/cm3, we call it the first type PE-HD. For the density of 0.926~ 0.94g/cm3, it is called the second type PE-HD; For the density of 0.94~ 0.965g/cm3, it is called the third type PE-HD. The material has excellent flow characteristics with an MFR of 0.1 to 28. The higher the molecular weight, the worse the flow characteristics of PH-LD, but the better the impact strength. Pe-ld is a semi-crystalline material with a high shrinkage rate between 1.5% and 4% after molding. Pe-hd is prone to environmental stress cracking. Cracking can be mitigated by using materials with very low flow characteristics to reduce internal stress. Pe-hd is easy to dissolve in hydrocarbon solvents when the temperature is higher than 60℃, but its solubility resistance is better than PE-LD.
10. Pe-ld (Low density polyethylene)
① Typical application scope:
Bowls, cabinets, pipe couplings
(2) Process conditions of injection mold:
Dry: Generally not needed
Melting temperature: 180~280℃
Mold temperature: 20~40℃, in order to achieve uniform cooling and more economic deheating, it is recommended that the diameter of the cooling chamber should be at least 8mm, and the distance from the cooling chamber to the surface of the mold should not exceed 1.5 times of the diameter of the cooling chamber.
Injection pressure: up to 1500bar.
Holding pressure: up to 750bar.
Injection speed: Rapid injection speed is recommended.
Runner and gate: Various types of runner and gate can be used. Pe-ld is especially suitable for use with hot runner dies.
③ Chemical and physical characteristics:
The density of PE-LD materials for commercial use is 0.91~0.94 g/cm3. Pe-ld is permeable to gas and water vapor. The high coefficient of thermal expansion of PE-LD is not suitable for processing long – term products. If the density of PE-LD is between 0.91-0.925 g/cm3, the shrinkage rate is between 2% and 5%. If the density is between 0.926 and 0.94 g/cm3, the shrinkage is between 1.5% and 4%. The actual shrinkage rate depends on injection molding process parameters. Pe-ld is resistant to a variety of solvents at room temperature, but can be expanded by aromatic and chlorinated hydrocarbon solvents. Similar to PE-HD, PE-LD is prone to environmental stress cracking.
11. PEI (polyether)
① Typical application scope:
Automotive industry (engine accessories such as temperature sensors, fuel and air processors, etc.), electrical and electronic equipment (electrical connectors, printed circuit boards, chip cases, explosion-proof boxes, etc.), product packaging, aircraft interior equipment, pharmaceutical industry (surgical instruments, tool cases, non-implanted devices).
(2) Process conditions of injection mold:
Drying treatment: PEI has hygroscopic properties and can lead to material degradation. The humidity should be less than 0.02%. The recommended drying condition is 150℃ for 4 hours.
Melting temperature: 340~400℃ for ordinary materials; The reinforced material is 340~415℃.
Mold temperature: 107~175 ° C. It is recommended that the mold temperature be 140 ° C.
Injection pressure: 700~1500bar.
Injection rate: Use the highest possible injection rate.
③ Chemical and physical characteristics:
PEI has strong high temperature stability, even if the PEI is not enhanced, it still has good toughness and strength. Therefore, the superior thermal stability of PEI can be used to manufacture high temperature and heat resistant devices. PEI also has good flame retardant, chemical resistance and electrical insulation properties. The glass transition temperature is very high, up to 215℃. PEI also has very low shrinkage rate and good isodirectional mechanical properties.

12. PET (polyethylene terephthalate)
① Typical application scope:
Automotive industry (structural components such as reflector boxes, electrical components such as headlight reflectors, etc.), electrical components (motor housing, electrical connectors, relays, switches, microwave oven internal components, etc.). Industrial applications (pump housing, hand instruments, etc.).
(2) Process conditions of injection mold:
Drying treatment: Drying treatment before processing is necessary, because PET has strong hygroscopicity. The recommended drying conditions are 120~165℃ for 4 hours. The humidity should be less than 0.02%.
Melting temperature: for non-filled type: 265~280℃; For glass filling type: 275~290 ° C.
Mold temperature: 80~120℃.
Injection pressure: 300~1300bar.
Injection rate: A higher injection rate can be used without causing embrittlement.
Runner and gate: All conventional gate types can be used. The gate size shall be 50~100% of the thickness of the plastic parts.
③ Chemical and physical characteristics:
The glass transition temperature of PET is about 165℃, and the crystallization temperature range of the material is 120~220℃. PET has strong hygroscopicity at high temperature. For glass fiber reinforced PET materials, it is also very easy to bend and deform at high temperature. The crystallization degree of the material can be improved by adding crystal enhancer. Transparent products processed with PET have gloss and thermal warping temperature. Special additives such as mica can be added to PET to minimize bending deformation. If lower mold temperatures are used, transparent products can also be obtained using non-filled PET materials.
13. PETG (ethylene glycol modified – polyethylene terephthalate)
① Typical application scope:
Medical equipment (test tube, reagent bottle, etc.), toys, display, light source cover, protective mask, refrigerator crisper, etc.
(2) Process conditions of injection mold:
Drying treatment: Drying treatment is necessary before processing. Humidity must be below 0.04%. The recommended drying condition is 65 ° C for 4 hours. The drying temperature should not exceed 66 ° C.
Melting temperature: 220~290℃.
Mold temperature: 10~30℃, 15℃ is recommended.
Injection pressure: 300~1300bar.
Injection rate: A higher injection rate can be used without causing embrittlement.
③ Chemical and physical characteristics:
PETG is a transparent, non-crystalline material. The glass transition temperature is 88℃. PETG injection molding process conditions allow a wider range than PET, and has transparent, high strength, high capricious comprehensive characteristics.
14. PMMA (polymethyl methacrylate)
① Typical application scope:
Automotive INDUSTRY (SIGNAL LIGHTS, INSTRUMENT PANELS, ETC.), PHARMACEUTICAL INDUSTRY (BLOOD storage containers, etc.), INDUSTRIAL APPLICATIONS (VIDEO DISCS, LIGHT scatterERS), daily CONSUMPTION PRODUCTS (BEVERAGE cups, stationery, etc.).
(2) Process conditions of injection mold:
Drying treatment: PMMA has hygroscopicity so drying treatment before processing is necessary. The recommended drying condition is 90℃ for 2~4 hours.
Melting temperature: 240~270℃.
Mold temperature: 35~70℃.
Injection speed: medium
③ Chemical and physical characteristics:
PMMA has excellent optical properties and weather resistance. White light has a 92% penetration. PMMA products have very low birefringence, especially suitable for the production of video discs. PMMA has room temperature creep property. With the increase of load and time, stress cracking can be caused. PMMA has good impact resistance.
15. POM (polyformaldehyde)
① Typical application scope:
POM has a very low coefficient of friction and good geometric stability, especially suitable for gear and bearings. Because of its high temperature resistance, it is also used in pipe devices (pipe valves, pump housing), lawn equipment, etc.
(2) Process conditions of injection mold:
Drying: If the material is stored in a dry environment, drying is usually not required.
Melting temperature: homopolymer material 190~230℃; The copolymer material was 190~210℃.
Mold temperature: 80~105℃. In order to reduce the shrinkage rate after molding can choose a higher mold temperature.
Injection pressure: 700~1200bar
Injection speed: Moderate or high injection speed.
Runner and gate: Any type of gate can be used. If tunneling sprue is used, it is preferable to use the shorter type. Hot nozzle runner is recommended for homopolymer materials. For copolymer materials, either internal or external heat runners can be used.
③ Chemical and physical characteristics:
POM is a tough and elastic material with excellent creep resistance, geometric stability and impact resistance even at low temperatures. POM has both homopolymer and copolymer materials. Homopolymer materials have good tensile strength and fatigue resistance, but are not easy to process. The copolymer material has good thermal stability, chemical stability and easy processing. Both homopolymer materials and copolymer materials are crystalline materials and not easy to absorb water. The high degree of crystallization of POM results in a relatively high shrinkage rate, which can reach as high as 2%~3.5%. There are different shrinkage rates for various types of enhanced materials.
16. PP (polypropylene)
① Typical application scope:
Automotive industry (mainly using PP containing metal additives: fenders, ventilation pipes, fans, etc.), equipment (dishwasher door liners, dryer ventilation pipes, washing machine frame and cover, refrigerator door liners, etc.), daily consumer goods (lawn and garden equipment such as lawn mowers and water sprayers, etc.).
(2) Process conditions of injection mold:
Drying: If stored properly, drying is not required.
Melting temperature: 220~275℃, be careful not to exceed 275℃.
Mold temperature: 40~80℃, 50℃ is recommended. The degree of crystallization is mainly determined by the mold temperature.
Injection pressure: up to 1800bar.
Injection speed: In general, internal pressure can be minimized by using high speed injection molding. If the surface of the product is defective, then low speed injection molding at higher temperature should be used.
Runner and gate: for cold runner, typical runner diameters range from 4 to 7mm. It is recommended to use a circular injection port and runner. All types of sprue can be used. Typical gate diameters range from 1 to 1.5mm, but as small as 0.7mm can be used. For edge gate, the minimum gate depth should be half of the wall thickness; The minimum gate width should be at least twice the wall thickness. PP material can be fully used hot runner system.
③ Chemical and physical characteristics:
PP is a semi-crystalline material. It is harder than PE and has a higher melting point. Because homopolymer PP temperature above 0℃ is very brittle, so many commercial PP materials are added to 1~4% ethylene random copolymers or higher ratio ethylene content clamp copolymers. Copolymer type PP material has a lower thermal twisting temperature (100℃), low transparency, low gloss, low rigidity, but has a stronger impact strength. The strength of PP increased with the increase of ethylene content. The vicar softening temperature of PP is 150℃. Due to the high crystallinity, the surface stiffness and scratch resistance of this material are very good. PP has no environmental stress cracking problem. Usually, PP is modified by adding glass fiber, metal additives or thermoplastic rubber. The MFR of PP ranges from 1 to 40. PP material with low MFR has better impact resistance but lower tensile strength. For materials with the same MFR, the strength of copolymer type is higher than that of homopolymer type. Due to crystallization, the shrinkage of PP is quite high, generally 1.8~2.5%. And the direction uniformity of shrinkage rate is much better than PE-HD and other materials. Adding 30% glass additive can reduce the shrinkage to 0.7%. Homopolymer and copolymer PP materials have excellent moisture resistance, acid and alkali corrosion resistance, solubility resistance. However, it has no resistance to aromatic hydrocarbon (such as benzene) solvents, chlorinated hydrocarbon (carbon tetrachloride) solvents, etc. PP also does not have oxidation resistance at high temperature like PE.
17. PPE (polyacryloethylene)
① Typical application scope:
Household items (dishwashers, washing machines, etc.), electrical equipment such as controller housing, fiber optic connectors, etc.
(2) Process conditions of injection mold:
Drying treatment: It is recommended to dry at 100℃ for 2~4 hours before processing.
Melting temperature: 240~320℃.
Mold temperature: 60~105℃.
Injection pressure: 600~1500bar.
Runner and gate: All types of gate can be used. It is especially suitable for the use of shank gate and fan gate.
③ Chemical and physical characteristics:
Usually, commercially available PPE or PPO materials are mixed with other thermoplastic materials such as PS, PA, etc. These mixtures are still commonly referred to as PPE or PPO. Hybrid PPE or PPO has much better processing properties than pure materials. The characteristics vary depending on the ratio of the mixture such as PPO and PS. The mixed material with PA 66 has stronger chemical stability at high temperature. This material has little hygroscopicity and its products have excellent geometric stability. The material mixed with PS is amorphous, while the material mixed with PA is crystalline. The shrinkage can be reduced to 0.2% by adding glass fiber additives. The material also has excellent electrical insulation properties and a low coefficient of thermal expansion. The viscosity depends on the ratio of the mixture in the material, and an increase in the ratio of PPO will lead to an increase in the viscosity.
18. PS (polystyrene)
① Typical application scope:
Product packaging, household goods (tableware, tray, etc.), electrical (transparent container, light scatterer, insulating film, etc.).
(2) Process conditions of injection mold:
Drying: Drying is usually not required unless improperly stored. If drying is required, the recommended drying condition is 80 ° C for 2 to 3 hours.
Melting temperature: 180~280℃. The upper limit is 250℃ for flame retardant materials.
Mold temperature: 40~50℃.
Injection pressure: 200~600bar.
Injection rate: A fast injection rate is recommended.
Runner and gate: All conventional gate types can be used.
③ Chemical and physical characteristics:
Most commercial PS are transparent, non-crystalline materials. PS has very good geometric stability, thermal stability, optical transmission characteristics, electrical insulation characteristics and a very small tendency to moisture absorption. It is resistant to water, diluted inorganic acids, but can be corroded by strong oxidizing acids such as concentrated sulfuric acid, and can expand and deform in some organic solvents.
A typical shrinkage is between 0.4 and 0.7 percent.
19. PVC (polyvinyl chloride)
① Typical application scope:
Water supply pipe, household pipe, house wall panel, commercial machine shell, electronic product packaging, medical equipment, food packaging, etc.
(2) Process conditions of injection mold:
Drying: Drying is usually not required.
Melting temperature: 185~205℃
Mold temperature: 20~50℃
Injection pressure: up to 1500bar
Holding pressure: up to 1000bar
Injection speed: In order to avoid material degradation, generally use a fairly slow injection speed.
Runner and gate: All conventional gates can be used. If processing smaller parts, it is best to use a pin gate or a diving gate; For thicker parts, it is best to use a fan gate. Minimum diameter of needle-type gate or diving gate shall be 1mm; The thickness of the sector gate shall not be less than 1mm.
③ Chemical and physical characteristics:
Rigid PVC is one of the most widely used plastic materials. PVC material is an amorphous material. PVC material in actual use often add stabilizer, lubricant, auxiliary processing agent, color, impact resistant agent and other additives. PVC material has non-flammability, high strength, weather resistance and excellent geometric stability. PVC has strong resistance to oxidants, reducing agents and strong acids. However, it can be corroded by concentrated oxidizing acids such as concentrated sulfuric acid and nitric acid and is not suitable for contact with aromatic hydrocarbons and chlorinated hydrocarbons. PVC melting temperature is a very important process parameter in the processing, if this parameter is not appropriate will lead to material decomposition problem. The flow characteristics of PVC are quite poor, and its process range is very narrow. In particular, large molecular weight PVC materials are more difficult to process (this material usually requires the addition of lubricants to improve flow characteristics), so small molecular weight PVC materials are commonly used. PVC shrinkage rate is quite low, generally 0.2~0.6%.
20. SA (Styrene-acrylonitrile copolymer)
① Typical application scope:
Electrical (socket, shell, etc.), daily GOODS (KITCHEN EQUIPMENT, REFRIGERATOR device, TV base, cassette box, etc.), AUTOMOBILE INDUSTRY (headlight box, reflective environment, dashboard, etc.), household goods (tableware, food knives, etc.), cosmetics packaging, etc.
(2) Process conditions of injection mold:
Drying: SA has some hygroscopic properties if not stored properly. The recommended drying condition is 80℃ for 2 to 4 hours.
Melting temperature: 200~270℃. If processing thick – walled products, melting temperatures below the lower limit can be used.
Mold temperature: 40~80℃. For enhanced materials, die temperature should not exceed 60℃. The cooling system must be well DESIGNED because the mold temperature will directly affect the appearance, shrinkage and bending of the product.
Injection pressure: 350~1300bar.
Injection speed: High speed injection is recommended.
Runner and gate: All conventional gates can be used. The gate must be properly sized to avoid streaks, blotches and gaps.
③ Chemical and physical characteristics:
SA is a hard, transparent material. Styrene composition makes SA hard, transparent and easy to process; The acrylonitrile component makes SA chemically and thermally stable. SA has strong load bearing ability, chemical reaction resistance, thermal deformation resistance and geometric stability. The addition of glass fiber additive to SA can increase the strength and thermal deformation resistance, and reduce the thermal expansion coefficient. The vicar softening temperature of SA is about 110℃. The flexural deformation temperature under load is about 100℃. The shrinkage rate of SA is about 0.3~0.7%

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