Characteristics, process conditions and application range of commonly used plastic materials

1.ABS acrylonitrile-butadiene-styrene copolymer
Typical application range:
Cars (dashboards, tool hatches, wheel covers, mirror boxes, etc.), refrigerators, high-strength tools (hair dryers, blenders, food processors, lawn mowers, etc.), telephone housings, typewriter keyboards Recreational vehicles such as golf carts and jet skis.
Injection molding process conditions:
Drying treatment: ABS materials are hygroscopic and require drying treatment before processing. It is recommended to dry under conditions of 80 to 90 ° C for less than 2 hours. The material temperature should be guaranteed to be less than 0.1%.
Melting temperature: 210 to 280 ° C; recommended temperature: 245 ° C.
Mold temperature: 25 to 70 ° C. (The mold temperature will affect the finish of the plastic part, and the lower temperature will result in a lower finish).
Injection pressure: 500 to 1000 bar.
Injection speed: medium to high speed.
Chemical and physical properties:
ABS is synthesized from three chemical monomers of acrylonitrile, butadiene and styrene. Each monomer has different characteristics: acrylonitrile has high strength, thermal stability and chemical stability; butadiene has toughness and impact resistance; styrene has easy processing, high finish and high strength. From a morphological point of view, ABS is an amorphous material. The polymerization of the three monomers produces a terpolymer having two phases, one being a continuous phase of styrene-acrylonitrile and the other being a dispersed phase of polybutadiene rubber. The properties of ABS are mainly determined by the ratio of the three monomers and the molecular structure in the two phases. This allows for great flexibility in product design and results in hundreds of different quality ABS materials on the market. These different quality materials offer different properties such as medium to high impact resistance, low to high finish and high temperature distortion. ABS materials have superior processability, appearance characteristics, low creep and excellent dimensional stability and high impact strength.
 
2.PA6 polyamide 6 or nylon 6
Typical application range:
It is widely used for structural parts due to its good mechanical strength and rigidity. It is also used to make bearings because of its excellent wear resistance.
Injection molding process conditions:
Drying treatment: Since PA6 absorbs water easily, special attention should be paid to drying before processing. If the material is supplied in a waterproof material, the container should be kept closed. If the humidity is greater than 0.2%, it is recommended to dry in hot air above 80 °C for 16 hours. If the material has been exposed to air for more than 8 hours, it is recommended to perform vacuum drying at 105 ° C for more than 8 hours.
Melting temperature: 230~280°C, 250~280°C for enhanced varieties.
Mold temperature: 80~90 °C. The mold temperature significantly affects the crystallinity, which in turn affects the mechanical properties of the part. Crystallinity is important for structural components, so it is recommended that the mold temperature be 80 to 90 °C. For thin-walled, longer-flowing parts, it is also recommended to apply higher mold temperatures. Increasing the mold temperature increases the strength and stiffness of the part, but reduces the toughness. If the wall thickness is greater than 3mm, it is recommended to use a low temperature mold of 20~40 °C. For glass reinforcement the mold temperature should be greater than 80 °C.
Injection pressure: generally between 750 and 1250 bar (depending on material and product design).
Injection speed: high speed (slightly lower for reinforced materials).
Runners and gates: Because the solidification time of PA6 is very short, the location of the gate is very important. The gate aperture should not be less than 0.5*t (where t is the thickness of the plastic part). If a hot runner is used, the gate size should be smaller than with a conventional runner because the hot runner can help prevent premature solidification of the material. If a submerged gate is used, the small diameter of the gate should be 0.75 mm.
Chemical and physical properties:
The chemical and physical properties of PA6 are similar to those of PA66, however, it has a lower melting point and a wide process temperature range. It has better impact resistance and solubility resistance than PA66, but it is also more hygroscopic. Because many of the quality characteristics of plastic parts are affected by hygroscopicity, this should be taken into account when designing products using PA6. In order to improve the mechanical properties of PA6, various modifiers are often added. Glass is a common additive, and sometimes synthetic rubbers such as EPDM and SBR are added to improve impact resistance. For products without additives, PA6 shrinks between 1% and 1.5%. The addition of a glass fiber additive reduces the shrinkage to 0.3% (but slightly higher in the direction perpendicular to the flow). The shrinkage of the molded assembly is mainly affected by the crystallinity and hygroscopicity of the material. The actual shrinkage is also a function of the plastic part design, wall thickness and other process parameters.
 
3.PA12 polyamide 12 or nylon 12
Typical application range:
Water gauges and other commercial equipment, cable jackets, mechanical cams, sliding mechanisms and bearings.
Injection molding process conditions:
Drying treatment: The humidity should be below 0.1% before processing. If the material is stored in the air, it is recommended to dry it in hot air at 85 ° C for 4 to 5 hours. If the material is stored in a closed container, it can be used directly after 3 hours of temperature equilibration.
Melting temperature: 240~300°C; do not exceed 310°C for common characteristic materials, and do not exceed 270°C for materials with flame retardant properties.
Mold temperature: 30 to 40 ° C for unreinforced materials, 80 to 90 ° C for thin-walled or large-area components, and 90 to 100 ° C for reinforced materials. Increasing the temperature will increase the crystallinity of the material. ** Controlling mold temperature is important for PA12.
Injection pressure: * up to 1000 bar (low holding pressure and high melting temperature are recommended).
Injection speed: high speed (better for materials with glass additives).
Runners and gates: For materials without additives, the runner diameter should be around 30mm due to the low viscosity of the material. A large flow path diameter of 5 to 8 mm is required for the reinforced material. The shape of the flow path should be all circular. Note the entrance should be as short as possible. Various forms of gates can be used. Do not use small gates for large plastic parts. This is to avoid excessive pressure or excessive shrinkage of the plastic parts. The gate thickness* is equal to the thickness of the plastic part. If a submerged gate is used, it is recommended that the *small diameter be 0.8mm. Hot runner molds are very effective, but temperature control is required to prevent material from leaking or solidifying at the nozzle. If a hot runner is used, the gate size should be smaller than the cold runner.
Chemical and physical properties:
PA12 is a linear, semi-crystalline-crystalline thermoplastic material from butadiene. Its characteristics are similar to those of PA11, but the crystal structure is different. PA12 is a good electrical insulator and, like other polyamides, does not affect insulation properties due to moisture. It has good impact resistance and chemical stability. PA12 has many improved varieties in terms of plasticizing properties and reinforcing properties. Compared to PA6 and PA66, these materials have a lower melting point and density and have a very high moisture regain. PA12 is not resistant to strong oxidizing acids. The viscosity of PA12 is mainly determined by humidity, temperature and storage time. It is very fluid. The shrinkage is between 0.5% and 2%, depending on the material variety, wall thickness and other process conditions.
 
4.PA66 polyamide 66 or nylon 66
Typical application range:
Compared with PA6, PA66 is more widely used in the automotive industry, instrument housings and other products that require impact resistance and high strength requirements.
Injection molding process conditions:
Drying: If the material is sealed before processing, there is no need to dry. 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%, it is also necessary to carry out vacuum drying at 105 ° C for 12 hours.
Melting temperature: 260~290 °C. The product for glass additives is 275~280 °C. The melting temperature should be avoided above 300 °C.
Mold temperature: 80 ° C is recommended. The mold temperature will affect the crystallinity, which will affect the physical properties of the product. For thin-walled plastic parts, if a mold temperature lower than 40 ° C is used, the crystallinity of the plastic part will change with time, and in order to maintain the geometric stability of the plastic part, annealing treatment is required.
Injection pressure: usually between 750 and 1250 bar, depending on material and product design.
Injection speed: high speed (slightly lower for reinforced materials).
Runners and gates: Because of the short settling time of the PA66, the location of the gate is very important. The gate aperture should not be less than 0.5*t (where t is the thickness of the plastic part). If a hot runner is used, the gate size should be smaller than with a conventional runner because the hot runner can help prevent premature solidification of the material. If a submerged gate is used, the small diameter of the gate should be 0.75 mm.
Chemical and physical properties:
PA66 has a higher melting point in polyamide materials. It is a semi-crystalline-crystalline material. PA66 also maintains high strength and stiffness at higher temperatures. PA66 is still hygroscopic after molding, the extent of which depends primarily on the composition of the material, the wall thickness and the environmental conditions. When designing a product, it is important to consider the effect of hygroscopicity on geometric stability. In order to improve the mechanical properties of PA66, various modifiers are often added. Glass is a common additive, and sometimes synthetic rubbers such as EPDM and SBR are added to improve impact resistance. PA66 is less viscous and therefore has good fluidity (but not as good as PA6). This property can be used to machine very thin components. Its viscosity is sensitive to temperature changes. The shrinkage of PA66 is between 1% and 2%. The addition of glass fiber additives can reduce the shrinkage to 0.2%~1%. The shrinkage ratio is large in the flow direction and in the direction perpendicular to the flow direction. PA66 is resistant to many solvents, but is less resistant to acids and other chlorinating products.
 
5.PBT polybutylene terephthalate
Typical application range:
Household appliances (food processing blades, vacuum cleaner components, electric fans, hair dryer housings, coffee utensils, etc.), electrical components (switches, motor housings, fuse boxes, computer keyboard keys, etc.), automotive industry (heatsink window , body panels, wheel covers, door and window components, etc.).
Injection molding process conditions:
Drying treatment: This material is easily hydrolyzed at high temperatures, so drying treatment before processing is very important. It is recommended to dry in air at 120 ° C, 6 ~ 8 hours, or 150 ° C, 2 ~ 4 hours. The humidity must be less than 0.03%. If drying with a hygroscopic dryer, the recommended conditions are 150 ° C for 2.5 hours.
Melting temperature: 225~275°C, recommended temperature: 250°C.
Mold temperature: 40 to 60 ° C for unreinforced materials. The cooling channel of the mold is well designed to reduce the bending of the plastic part. The loss of heat must be fast and even. It is recommended that the mold cooling channel has a diameter of 12 mm.
Injection pressure: medium (*up to 1500 bar).
Injection speed: The injection speed should be as fast as possible (because PBT solidifies quickly).
Runners and gates: Round runners are recommended to increase pressure transfer (empirical formula: runner diameter = plastic thickness + 1.5mm). Various types of gates can be used. Hot runners can also be used, but care should be taken to prevent leakage and degradation of the material. The gate diameter should be between 0.8 and 1.0*t, where t is the thickness of the plastic part. If it is a submerged gate, it is recommended that the *small diameter be 0.75mm.
Chemical and physical properties:
PBT is one of * tough engineering thermoplastics. It is a semi-crystalline material with very good chemical stability, mechanical strength, electrical insulation properties and thermal stability. These materials are very stable under a wide range of environmental conditions. PBT has a weak hygroscopic property. The tensile strength of the non-reinforced PBT is 50 MPa, and the tensile strength of the PBT of the glass additive type is 170 MPa. Excessive glass additives will cause the material to become brittle. PBT; crystallization is very rapid, which will cause bending deformation due to uneven cooling. For materials with a glass additive type, the shrinkage in the process direction can be reduced, but the shrinkage in the vertical direction to the process is essentially indistinguishable from that of the conventional material. Generally, the material shrinkage rate is between 1.5% and 2.8%. Materials containing 30% glass additives shrink between 0.3% and 1.6%. The melting point (225 ° C) and high temperature deformation temperature are lower than PET materials. The Vicat softening temperature is approximately 170 °C. The glass transition temperature (glasstrasitiotemperature) is between 22 ° C and 43 ° C. Due to 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
Typical application range:
Electrical and commercial equipment (computer components, connectors, etc.), appliances (food processors, refrigerator drawers, etc.), transportation industry
(front and rear lights of vehicles, instrument panels, etc.).
Injection molding process conditions:
Drying treatment: PC materials are hygroscopic, and drying before processing is important. Dry conditions are recommended from 100 ° C to 200 ° C for 3 to 4 hours. The humidity before processing must be less than 0.02%.
Melting temperature: 260~340 °C.
Mold temperature: 70~120 °C.
Injection pressure: Use high injection pressure as much as possible.
Injection speed: low speed injection for smaller gates and high speed injection for other types of gates.
Chemical and physical properties:
PC is an amorphous engineering material with particularly good impact strength, thermal stability, gloss, ** properties, flame retardant properties and stain resistance. The PC's notched impact strength (otched Izod impactstregth) is very high, and the shrinkage rate is very low, generally 0.1% to 0.2%. PC has good mechanical properties, but its flow characteristics are poor, so the injection molding process of this material is difficult. When choosing which quality PC material to use, it should be based on the final expectations of the product. If the plastic part requires high impact resistance, then a low flow rate PC material is used; conversely, a high flow rate PC material can be used, which optimizes the injection molding process.
7.PC/ABS polycarbonate and acrylonitrile-butadiene-styrene copolymers and mixtures
Typical application range:
Housings for computer and business machines, electrical equipment, lawn and garden machines, automotive parts (dashboards, interior finishes, and wheel covers).
Injection molding process conditions:
Drying treatment: Drying before processing is necessary. The humidity should be less than 0.04%. The recommended drying conditions are 90~110 °C for 2~4 hours.
Melting temperature: 230~300 °C.
Mold temperature: 50~100 °C.
Injection pressure: depending on the plastic part.
Injection speed: as high as possible.
Chemical and physical properties:
PC/ABS has the comprehensive features of both PC and ABS. For example, the easy processing characteristics of ABS and the excellent mechanical properties and thermal stability of PC. The ratio of the two will affect the thermal stability of the PC/ABS material. The mixed material of PC/ABS also shows excellent flow characteristics.
 
8.PC/PBT mixture of polycarbonate and polybutylene terephthalate
Typical application range:
Gearboxes, automotive bumpers, and products that require chemical resistance and corrosion resistance, thermal stability, impact resistance, and geometric stability.