Common properties of plastic

PC/ABS polycarbonate and acrylonitrile-butadiene-styrene copolymers and mixtures

Typical applications: computer and commercial machine housings, electrical equipment, lawn gardening machines, automotive parts dashboards, interior finishes, and wheel covers.
Injection Molding Process Conditions :
Drying: Drying before processing is a must. Humidity should be less than 0.04%. Recommended drying conditions are 90~110C for 2~4 hours.
Melting temperature: 230~ 300C.
Mold temperature: 50~ 100C.
Injection pressure: depending on plastic part.
Injection speed: as high as possible.
Chemical and physical properties: PC/ABS has combined properties of plastic for both PC and ABS. For example, easy processing characteristics of ABS, excellent mechanical properties and thermal stability of PC. Ratio of these two will affect thermal stability of PC/ABS material. This mixed material of PC/ABS also shows excellent flow characteristics. Shrinkage rate is around 0.5%.

Mixture of PC/PBT polycarbonate and polybutylene terephthalate

Typical applications: Gearboxes, automotive bumpers, and products that require chemical resistance, corrosion resistance, thermal stability, impact resistance, geometric stability.
Injection molding process conditions:
Drying treatment: recommended 110 ~ 135C, about 4 hours of drying.
Melting temperature: 235~ 300C.
Mold temperature: 37~ 93C.
Chemical and Physical Properties: PC/PBT has combined properties of plastic for both PC and PBT, such as high toughness and geometric stability of PCs, as well as chemical stability, thermal stability and lubrication properties of PBT. Shrinkage rate is around 0.5%.

PE-HD high density polyethylene

Typical applications: refrigerator containers, storage containers, household kitchen utensils, sealing covers, etc.
Injection Molding Process Conditions:
Drying: No drying is required if stored properly.
Melting temperature: 220~ 260C. For larger molecules, recommended melting temperature range is between 200 and 250C.
Mold temperature: 50~ 95C. Plastic parts with a wall thickness of 6 mm or less should use a higher mold temperature, and plastic parts with a wall thickness of 6 mm or more should use a lower mold temperature. Plastic part cooling temperature should be uniform to reduce difference in shrinkage. For optimum machining cycle time, cooling tunnel diameter should be no less than 8mm and distance from mold surface should be within 1.3d (d is diameter of cooling tunnel).
Injection pressure: 700~1050bar.
Injection speed: High speed injection is recommended.
Runners and gates: Runner diameter is between 4 and 7.5 mm and runner length should be as short as possible. Various types of gates can be used, and gate length should not exceed 0.75mm. Particularly suitable for hot runner mold.
Chemical and physical properties: High crystallinity of PE-HD leads to its high density, tensile strength, high temperature distortion temperature, viscosity and chemical stability. PE-HD is more resistant to permeation than PE-LD. PE-HD has low impact strength. Characteristics of PH-HD are mainly controlled by density and molecular weight distribution. PE-HD for injection molding has a very narrow molecular weight distribution. For density of 0.91~0.925g/cm3, we call it first type PE-HD; for density of 0.926~0.94g/cm3, it is called second type PE-HD; for density of 0.94~ 0.965g/cm3 It is called third type PE-HD. It has good flow characteristics and an MFR between 0.1 and 28. The higher molecular weight, the worse flow characteristics of PH-LD, but the better impact strength. PE-LD is a semi-crystalline material with a high shrinkage after molding, between 1.5% and 4%. PE-HD is prone to environmental stress cracking. Cracking can be mitigated by using materials with very low flow characteristics to reduce internal stresses. PE-HD dissolves easily in hydrocarbon solvents at temperatures above 60C, but its solubility is better than PE-LD.

PE-LD low density polyethylene

Typical applications: bowls, bins, pipe couplings
Injection molding process conditions:
Drying: generally does not require.
Melting temperature: 180~ 280C
Mold temperature: 20~ 40C. In order to achieve uniform cooling and economical heat removal, it is recommended that cooling channel diameter be at least 8mm and distance from cooling channel to mold surface should not exceed 1.5 times diameter of cooling channel.
Injection pressure: up to 1500bar.
Holding pressure: up to 750bar.
Injection speed: It is recommended to use a fast injection speed.
Runners and Gates: Various types of runners and gates can be used. Particularly suitable for hot runner mold.
Chemical and physical properties: Commercial PE-LD materials have a density of 0.91 to 0.94 g/cm3. PE-LD is permeable to gases and water vapor. High coefficient of thermal expansion of PE-LD is not suitable for processing products for long-term use. If density of PE-LD is between 0.91 and 0.925 g/cm3, shrinkage is between 2% and 5%. If density is between 0.926 and 0.94 g/cm3, shrinkage is between 1.5%~4%. Current actual shrinkage rate also depends on injection molding process parameters. PE-LD is resistant to a wide range of solvents at room temperature, but aromatic hydrocarbons and chlorinated hydrocarbon solvents can swell it. Similar to PE-HD, PE-LD is prone to environmental stress cracking.

PEI polyetherimide

Applications: Automotive industry (engine accessories such as temperature sensors, fuels and air handlers), electrical and electronic equipment (electrical couplings, printed circuit boards, chip housings, explosion-proof boxes, etc.), product packaging, aircraft interior equipment, pharmaceutical industry (surgical instruments, tool housings, non-implanted instruments).
Injection Molding Process Conditions:
Drying: PEI has hygroscopic properties and can cause material degradation. Required humidity value should be less than 0.02%. It is recommended to dry at 150C for 4 hours.
Melting temperature: 340~400C for common type materials and 340~415C for enhanced type materials.
Mold temperature: 107~175C, recommended mold temperature is 140C.
Injection pressure: 700~1500bar.
Injection speed: Use the highest possible injection speed.
Chemical and physical properties: PEI has a very high temperature stability, even for non-reinforced PEI, it still has good toughness and strength. Therefore, superior thermal stability of PEI can be used to fabricate high temperature heat resistant devices. PEI also has good flame retardancy, chemical resistance and electrical insulation properties. Glass transition temperature is very high, reaching 215C. PEI also has very low shrinkage (typically 0.4%-0.7%) and good isotactic mechanical properties.

ABS

Typical applications: Automotive (dashboard, tool door, wheel cover, mirror box, etc.), refrigerator, high-strength tools (hair dryer, blender, food processor, lawn mower, etc.), telephone housing Body, typewriter keyboard, recreational vehicles such as golf carts and jet skis.
Injection Molding Process Conditions:
Drying treatment: ABS material is hygroscopic. It is recommended to dry before processing for at least 2 hours at 80~90C. Material temperature should be guaranteed to be less than 0.1%.
Melting temperature: 210~ 280C; recommended temperature: 245C.
Mold temperature: 25~ 70C. Mold temperature will affect smoothness of plastic part, and lower temperature will result in a lower finish.
Injection pressure: 500~1000bar.
Injection speed: medium to high speed.
ABS is synthesized from three chemical monomers of acrylonitrile, butadiene and styrene. Each monomer has different properties: acrylonitrile has high strength, thermal stability and chemical stability; butadiene has toughness and impact resistance; styrene has easy processing, high finish and high strength. Morphologically, ABS is an amorphous material. Polymerization of three monomers produces a two-phase terpolymer, one be a continuous phase of styrene-acrylonitrile and the other be a dispersed phase of polybutadiene rubber. Properties of ABS are mainly determined by ratio of three monomers and molecular structure in 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 are superior in processability, appearance characteristics, low creep, excellent dimensional stability, and high impact strength.

PA6 polyamide

Typical application range: Widely used for structural components due to good mechanical strength and stiffness. It has good wear resistance and is also used to make bearings.
Injection Molding Process Conditions:
Drying: Since PA6 absorbs moisture easily, special attention should be paid to drying before processing. If material is supplied in a waterproof material, container should be kept closed. If humidity is greater than 0.2%, it is recommended to dry in hot air above 80C for 16 hours. If material has been exposed to air for more than 8 hours, it is recommended to perform vacuum drying at 105C for more than 8 hours.
Melting temperature: 230~ 280C, 250~280C for enhanced varieties.
Mold temperature: 80~ 90C. Mold temperature significantly affects crystallinity, which in turn affects mechanical properties of part. Crystallinity is important for structural components, so it is recommended that mold temperature be 80~90C. For thin-walled, longer-flowing parts, it is also recommended to apply higher mold temperature. Increasing mold temperature can increases strength and stiffness of part, but reduces toughness. If wall thickness is greater than 3mm, it is recommended to use a low temperature mold of 20~40C. For glass reinforcements, mold temperature should be greater than 80C.
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: Due to short solidification time of PA6, location of gate is very important. Gate diameter should not be less than 0.5*t (t is thickness of plastic part). If a hot runner is used, gate size should be smaller than with a conventional runner because hot runner can help prevent premature solidification of material. If a submerged gate is used, minimum diameter of gate should be 0.75mm.

Chemical and physical properties: Chemical and physical properties of PA6 are similar to those of PA66, however, it has a low 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 quality characteristics of plastic parts are affected by hygroscopicity, this should be taken into account when designing products with PA6. In order to improve mechanical properties of PA6, various modifiers are often added. Glass is the most 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%. Adding a fiberglass additive reduces shrinkage to 0.3% to 0.5% (but slightly higher in the direction perpendicular to process). Shrinkage of molded assembly is mainly affected by crystallinity and hygroscopicity of material. Actual shrinkage is also a function of plastic part design, wall thickness and other process parameters.

PA66 Polyamide 66 or Nylon 66

Typical Applications: Compared to PA6, PA66 is more widely used in automotive industry, instrument housings, and other products that require impact resistance and high strength.
Injection Molding Process Conditions:
Drying: If material is sealed before processing, there is no need to dry. However, if storage container is opened, it is recommended to dry it in hot air at 85C. If humidity is greater than 0.2%, vacuum drying at 105C for 12 hours is required.
Melting temperature: 260~290C. Product for glass additives is 275~280C. Melting temperature should be avoided above 300C.
Mold temperature: 80C is recommended. Mold temperature will affect crystallinity, which will affect physical properties of product. For thin-walled plastic parts, if a mold temperature lower than 40C is used, crystallinity of plastic part will change with time. In order to maintain geometric stability of plastic part, annealing 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: Due to short settling time of PA66, location of gate is very important. Gate diameter should not be less than 0.5*t (t is thickness of plastic part). If a hot runner is used, gate size should be smaller than a conventional runner because hot runner can help prevent premature solidification of material. If a submerged gate is used, minimum diameter of gate should be 0.75mm.
Chemical and physical properties: PA66 has a higher melting point in polyamide materials. It is a semi-crystalline - crystalline material. PA66 maintains high strength and stiffness at higher temperatures. PA66 is still hygroscopic after molding, extent of which depends primarily on the composition of material, wall thickness and environmental conditions. When designing a product, it is important to consider effect of hygroscopicity on geometric stability. In order to improve mechanical properties of PA66, various modifiers are often added. Glass is the most common additive, 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. Shrinkage of PA66 is between 1% and 2%. Addition of glass fiber additives can reduce shrinkage to 0.2%~1%. Shrinkage ratio is large in flow direction and in the direction perpendicular to flow direction. PA66 is resistant to many solvents but weak to acids and other chlorinating agents.

PBT polybutylene terephthalate

Typical applications: 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 ( Radiator windows, body panels, wheel covers, door and window components, etc.).
Injection Molding Process Conditions:
Drying: This material is easily hydrolyzed at high temperatures, so drying prior to processing is important. It is recommended to dry in air at 120C, 6~8 hours, or 150C for 2-4 hours. Humidity must be less than 0.03%. If drying with a hygroscopic dryer, recommended conditions are 150C, 2.5 hours.
Melting temperature: 225~275C, recommended temperature: 250C.
Mold temperature: 40~60C for unreinforced materials. Cooling channel of mold is well designed to reduce bending of plastic part. Loss of heat must be fast and even. It is recommended that mold cooling channel has a diameter of 12 mm.
Injection pressure: medium (up to 1500 bar).
Injection speed: Injection speed should be as fast as possible (because PBT solidifies very quickly).
Runners and gates: Circular 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 material. Gate diameter should be between 0.8 and 1.0*t(t is thickness of part). For submerged gates, recommended minimum diameter is 0.75mm.
Chemical and physical properties: PBT is one of the toughest engineering thermoplastics. It is a semi-crystalline material with excellent 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. Tensile strength of non-reinforced PBT is 50 MPa, tensile strength of PBT of glass additive type is 170 MPa. Excessive glass additives will cause material to become brittle. PBT crystallizes very quickly, which causes bending deformation due to uneven cooling. For materials with a glass additive, shrinkage in process direction can be reduced, but shrinkage in the direction perpendicular to process is essentially indistinguishable from that of ordinary materials. General material shrinkage rate is between 1.5% and 2.8%. Materials containing 30% glass additives shrink between 0.3% and 1.6%. Melting point (225C) and high temperature deformation temperature are both lower than PET material. Vicat softening temperature is approximately 170C. Glass trasitio temperature is between 22C and 43C. Due to high crystallization rate of PBT, its viscosity is very low, and cycle time of plastic parts processing is generally low.

PC polycarbonate

Typical applications: electrical and commercial equipment (computer components, connectors, etc.), appliances (food processors, refrigerator drawers, etc.), transportation industry (vehicle front and rear lights, dashboards, etc.).
Injection Molding Process Conditions:
Drying: PC materials are hygroscopic and drying prior to processing is important. Dry conditions are recommended from 100C to 200C for 3-4 hours. Humidity before processing must be less than 0.02%.
Melting temperature: 260~340C.
Mold temperature: 70~120C.
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 exceptional impact strength, thermal stability, gloss, bacterial inhibition, flame retardant properties and stain resistance. Otched Izod impact stregth of PC is very high, and shrinkage rate is very low, generally 0.1% to 0.2%. PCs have good mechanical properties, but flow characteristics are poor, so injection moulding process of this material is more difficult. When choosing PC material, it should be based on final expectations of product. If 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 to optimize injection moulding process.

PET polyethylene terephthalate

Typical applications: Automotive (structured components such as mirror boxes, electrical components such as headlight reflectors, etc.), electrical components (motor housings, electrical couplings, relays, switches, microwave oven internals). Industrial applications (pump housings, hand tools, etc.).
Injection Molding Process Conditions:
Drying: Drying before processing is necessary because PET is more hygroscopic. It is recommended to dry at 120~165C for 4 hours. Required humidity should be less than 0.02%.
Melting temperature: for non-filling type: 265~280C; for glass filling type: 275~290C.
Mold temperature: 80~120C.
Injection pressure: 300~1300bar.
Injection speed: Higher injection speeds can be used without causing embrittlement.
Runners and gates: All conventional types of gates can be used. Gate size should be 50~100% of thickness of plastic part.
Chemical and physical properties: Glass transition temperature of PET is around 165C, and crystallization temperature range of material is 120~220C. PET is highly hygroscopic at high temperatures. For glass fiber reinforced PET materials, bending deformation is also very likely to occur at high temperatures. Degree of crystallization of material can be increased by adding a crystal strengthening agent. Transparent articles processed with PET have gloss and heat distortion temperatures. Special additives such as mica can be added to PET to minimize bending deformation. If a lower mold temperature is used, a transparent article can also be obtained using a non-filled PET material.

PMMA polymethyl methacrylate

Typical applications: automotive industry (signal light equipment, instrument panels, etc.), pharmaceutical industry (storage containers, etc.), industrial applications (video discs, light diffusers), consumer goods (beverage cups, stationery, etc.).
Injection Molding Process Conditions:
Drying treatment: PMMA is hygroscopic so drying before processing is necessary. Recommended drying conditions are 90C for 2-4 hours.
Melting temperature: 240~270C.
Mold temperature: 35~70C.
Injection speed: medium
Chemical and physical properties: PMMA has excellent optical properties and resistance to weathering. Penetration of white light is as high as 92%. PMMA products have a very low birefringence and are especially suitable for making DVDs. PMMA has room temperature creep properties. As load increases and time increases, stress cracking can occur. PMMA has good impact resistance. Shrinkage rate is around 0.5%.

POM

Typical application range: POM has a very low coefficient of friction and good geometric stability, making it ideal for gears and bearings. Because it also has high temperature resistance, it is also used in pipeline devices (valves, pump housings), lawn equipment, etc.
Injection Molding Process Conditions:
Drying: If material is stored in a dry environment, drying is usually not required.
Melting temperature: homopolymer material is 190~230C; copolymer material is 190~210C. Mold temperature: 80~105C. In order to reduce shrinkage after molding, a higher mold temperature can be used.
Injection pressure: 700~1200 bar.
Injection speed: medium or high injection speed.
Runners and gates: Any type of gate can be used. If a tunnel gate is used, it is best to use a shorter type. Hot nozzle runners are recommended for homopolymer materials. For copolymer material, either an internal hot runner or an external hot runner can be used.
Chemical and physical properties: POM is a tough, resilient material that retains excellent creep resistance, geometric stability and impact resistance even at low temperatures. POM has both homopolymer materials and copolymer materials. Homopolymer material has good ductility and fatigue strength, but is not easy to process. Copolymer material has good thermal stability, chemical stability and is easy to process. Whether a homopolymer material or a copolymer material, it is a crystalline material and does not easily absorb moisture. High degree of crystallization of POM results in a relatively high shrinkage rate of up to 2% to 3.5%. There are different shrinkage rates for a variety of different reinforced materials.

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