common plastic materials and resins in the injection molding process
by Lushi-Molding  | October 30th. 2019  |  Tags: Plastic Materials

10 commonly used plastic materials for injection molding and their applications


Nowadays there are numerous commercial products made of plastic and technical resins in the market. In order to achieve the perfect performance, either appearance or functionality of the plastic products, the selection of the right resin is a crucial factor, which should be considered before the product design as well as during the injection molding process.

LUSHI has lots of experience in plastics technology and injection molding for more than 10 years. Our technical know-how and deep understanding of the chemical and mechanical properties of different plastics enable us to help our customers to succeed with their projects.

In this article we will talk about the 10 common plastic materials and their properties as well as their applications in the molding industry, they are ABS, PBT, PC,PE-HD, PMMA, PP, PS, PVC, SA and POM.


ABS (Acrylonitrile-butadiene-styrene)

Chemical and mechanical properties

ABS is synthesized from three chemical monomers: 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 gloss and high strength. From a morphological point of view, ABS is an amorphous material. The polymerization of the three monomers produced a terpolymer with two phases, one was a continuous phase of styrene-acrylonitrile, and the other was a polybutadiene rubber dispersed phase. The characteristics of ABS mainly depend on the ratio of the three monomers and the molecular structure in the two phases. This can have great flexibility in product design, and thus produce hundreds of different quality ABS materials on the market. These different quality materials provide different characteristics, such as impact resistance from medium to high, finish from low to high, and high temperature distortion characteristics. ABS plastic material has super easy processability, low creep and excellent dimensional stability, and high impact strength.

Applications

Automotive industry (dashboard, wheel cover, mirror box), food processor, lawn mower, phone case, keyboard.

Injection molding process condition:

Pre-drying temperature: 80°C - 90°C
Pre-drying time: 2-4 Stunde
Melt temperature range: 210°C - 240°C
Tool temperaturer: 25°C - 70°C
Injection pressure: 500 – 1000bar
Injection speed: mittel bis hoch

Learn more about ABS resin


PBT (Polybutylene terephthalate)

Chemical and mechanical properties

PBT is one of the toughest engineering thermoplastic materials. It is a semi-crystalline material and has very good chemical stability, mechanical strength, electrical insulation properties and thermal stability. These materials have good stability under a wide range of environmental conditions. PBT has weak hygroscopic properties. The tensile strength of the unreinforced PBT is 50 MPa, and the tensile strength of the glass additive PBT is 170 MPa. Too much glass additive will cause the material to become brittle. The crystallization of PBT is very rapid, which will cause bending deformation due to uneven cooling. For materials with glass additives, the shrinkage in the flow direction can be reduced, but the shrinkage in the vertical direction of the flow is basically the same as that of ordinary materials. The general material shrinkage is between 1.5% to 2.8%. Materials containing 30% glass additives shrink between 0.3% and 1.6%. Both the melting point (225 ° C) and the high temperature deformation temperature are lower than PET materials. Vicat softening temperature is approximately 170 ° C. Due to the high crystallization temperature of PBT, its viscosity is very low, and the processing time of plastic parts is generally shorter.

Applications

Household appliances (kitchen knives, vacuum cleaner elements, electric fans, hair dryers, coffee goods), Automotive (radiator grilles, body panels, wheel covers, door and window components, etc.)

Injection molding process condition:

Pre-drying temperature: 120°C-150°C
Pre-drying time: 2-4 Stunde
Melt temperature range: 225°C - 275°C
Tool temperaturer: 40°C - 60°C
Injection pressure: mittel bis 1500bar
Injection speed: so schnell wie möglich

Learn more about PBT resin


PC (Polycarbonate)

Chemical and mechanical properties

PC is a non-crystalline engineering material, which has particularly good impact strength, thermal stability, gloss, bacterial resistance, flame retardant properties, and pollution resistance. The notched Izod impact strength of PC is very high, and the shrinkage rate is very low, generally 0.1% ~ 0.2%. PC has good mechanical properties, but poor flow characteristics, so the injection molding process of this material is difficult. When choosing the quality of PC materials, the final expectations of the product should be used as the benchmark. If the plastic part requires high impact resistance, then use a low flow rate PC material; conversely, a high flow rate PC material can be used, which can optimize the injection molding process.

Applications

Electrical and commercial equipment (computer components, connectors, etc.), appliances (food processors, refrigerator drawers, etc.), transportation industry (The vehicle's front and rear lights, dashboard)

Injection molding process condition:

Pre-drying temperature: 100°C-200°C
Pre-drying time: 3-4 Stunde
Melt temperature range: 260°C - 340°C
Tool temperaturer: 70°C - 120°C
Injection pressure: so hoch wie möglich
Injection speed: niedrig bei kleiner Düse, sonst hoch

Learn more about PC resin


PE-HD (Polyethylene high density)

Chemical and mechanical properties

The high crystallinity of PE -HD results in its high density, tensile strength, high temperature distortion temperature, viscosity, and chemical stability. PE-HD is more resistant to penetration than PE-LD. PE-HD has low impact strength. The characteristics of PH-HD are mainly controlled by density and molecular weight distribution. The material has good flow characteristics with MFR between 0.1 and 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 after molding, between 1.5% and 4%. PE-HD is prone to environmental stress cracking. Cracking can be reduced by using materials with very low flow characteristics to reduce internal stresses.

Applications

Refrigerator containers, storage containers, household kitchenware, sealed lids

Injection molding process condition:

Pre-drying: No drying required
Melt temperature range: 220°C - 260°C
Tool temperaturer: 50°C - 95°C
Injection pressure: 700 - 1050bar
Injection speed: hoch

Learn more about PE-HD resin


PMMA (Polymethylmethacrylate)

Chemical and mechanical properties

PMMA has excellent optical characteristics and weather resistance characteristics. The penetration of white light is up to 92%. PMMA products have very low birefringence, which is especially suitable for making video discs, etc. PMMA has room temperature variation characteristics. With the increase of the load and the increase of time, it can lead to the phenomenon of stress cracking. PHHA has better impact resistance.

Applications

Automotive industry (signal light equipment, instrument panels), pharmaceutical industry (blood storage containers), industrial applications (video discs, light diffusers), consumer goods (drink cups, stationery)

Injection molding process condition:

Pre-drying temperature: 90°C
Pre-drying time: 2-4 Stunde
Melt temperature range: 240°C - 270°C
Tool temperaturer: 35°C - 70°C
Injection pressure: mittel
Injection speed: mittel

Learn more about PMMA resin


PP (Polypropylene)

Chemical and mechanical properties

PP is a semi-crystalline material. It is harder than PE and has a higher melting point. Because the temperature of homopolymer-type PP is higher than 0X: above, it is very brittle, so many commercial PP materials are random copolymers with T4% ethylene or clamp copolymers with higher ethylene content. Copolymer type PP material has lower heat distortion temperature (10CTC), low transparency, low gloss, and low rigidity, but it has stronger impact strength. The strength of PP increases with increasing ethylene content. The Vicat softening temperature of PP is 15CTC. Due to its high crystallinity, this material has good surface stiffness and scratch resistance. PP does not suffer from environmental stress cracking. Generally, PP is modified by adding glass fibers, metal additives or thermoplastic rubber. The flow rate MFR of PP ranges from 40 to 40. Low MFR PP materials have better impact resistance but lower ductility. For materials of the same MFR, the copolymer type is stronger than the homopolymer type. Due to the crystallization, the shrinkage of PP is quite high, generally l.S ~ 2.5%. The directional uniformity of the shrinkage is much better than that of materials such as PE-HD. 7%。 Adding 30% of glass additives can reduce the shrinkage to 0.7%. Both homopolymer and copolymer materials have excellent resistance to moisture absorption, resistance to acid and alkali corrosion, and resistance to dissolution.

Applications

Automotive industry (mainly using PP with metal additives: fenders, ventilation pipes, fans), equipment (washer door gaskets, dryer ventilation pipes, washing machine frames and covers, refrigerator door gaskets)

Injection molding process condition:

Pre-drying: No drying required
Melt temperature range: 220°C - 275°C
Tool temperaturer: 40°C - 80°C
Injection pressure: mittel bis 1800bar
Injection speed: Allgemein

Learn more about PP resin


PS (Polystyrene)

Chemical and mechanical properties

Most commercial PSs are transparent, amorphous materials. PS has very good geometric stability, thermal stability, optical transmission characteristics, electrical insulation characteristics, and a slight tendency to absorb moisture. It can resist water, diluted inorganic acids, but can be corroded by strong oxidizing acids such as concentrated sulfuric acid, and can swell and deform in some organic solvents. Typical shrinkage is between 0.4 and 0.7%.

Applications

Product packaging, household goods (tableware, trays, etc.), electrical (transparent containers, light diffusers, insulation sheets, etc)

Injection molding process condition:

Pre-drying temperature: 80°C
Pre-drying time: 2-3 Stunde
Melt temperature range: 180°C - 280°C
Tool temperaturer: 40°C - 50°C
Injection pressure: 200 – 600bar

Learn more about PS resin


PVC (Polyvinylchlorid)

Chemical and mechanical properties

PVC is one of the most widely used plastic materials. PVC material is an amorphous material. PVC materials are often added with stabilizers, lubricants, auxiliary processing agents, colorants, impact agents and other additives in actual use. PVC material has non-flammability, high strength, weather resistance, and excellent geometric stability. PVC is very resistant to oxidants, reducing agents and strong acids. However, it can be corroded by concentrated oxidizing acids such as concentrated sulfuric acid and concentrated nitric acid, and it is not suitable for contact with aromatic and chlorinated hydrocarbons. The melting temperature of PVC during processing is a very important process parameter. If this parameter is improper, it will cause the problem of material decomposition. 5 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 (usually lubricants are added to improve the flow characteristics). Therefore, low-molecular-weight PVC materials are usually used. The shrinkage of PVC is quite low, generally 0.2 ~ 0.6%

Applications

Water supply pipes, house wall panels, commercial machine housings, electronics packaging, food packaging

Injection molding process condition:

Pre-drying: No drying required
Melt temperature range: 185°C - 205°C
Tool temperaturer: 20°C - 50°C
Injection pressure: bis 1500bar
Injection speed: mittel bis hoch

Learn more about PVC resin


SA (Styrene-acrylonitrile copolymers)

Chemical and mechanical properties

SA is a hard transparent material. The styrene component makes SA hard, transparent, and easy to process; the acrylic component makes SA chemically and thermally stable. SA has a strong load-bearing capacity, chemical resistance, thermal deformation resistance and geometric stability. Adding glass fiber additives to SA can increase strength and resistance to thermal deformation and reduce thermal expansion coefficient. Vicat softening temperature of SA is about 11CTC. The deflection temperature under load is about 10CTC. 7%。 SA contraction rate is about 0.3 to 0.7%.

Applications

Electrical appliances (sockets, housings), household goods (kitchen appliances, refrigerator units, TV bases, cassette boxes), automotive industry (headlight boxes, reflective environments, dashboards), household goods (tableware, food knives), cosmetics packaging, etc.

Injection molding process condition:

Pre-drying temperature: 80°C
Pre-drying time: 2-4 Stunde
Melt temperature range: 200°C - 270°C
Tool temperaturer: 40°C - 80°C
Injection pressure: 350 – 1300bar
Injection speed: hoch

Learn more about SAN resin


POM (Polyoxymethylene)

Chemical and mechanical properties

POM is a tough and elastic material that has good creep resistance, geometric stability and impact resistance even at low temperatures. POM has both homopolymer and copolymer materials. Homopolymer materials have good ductility and fatigue resistance, but they are not easy to process. Copolymer materials have good thermal and chemical stability and are easy to process. Both homopolymer and copolymer materials are crystalline materials and do not easily absorb moisture. P0M's high degree of crystallinity causes it to have a relatively high shrinkage, which can be as high as 2% to 3.5%. There are different shrinkage rates for different reinforced materials.

Applications

Gears and bearings, piping components (pipe valves, pump housings), lawn equipment.

Injection molding process condition:

Pre-drying: No drying required
Melt temperature range: 190°C - 230°C
Tool temperaturer: 80°C - 105°C
Injection pressure:700 - 1200bar
Injection speed: mittel bis hoch

Learn more about POM resin



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Email: jonas@lushimold.com
Jonas Zhan
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