Plastic injection molding principles, materials and applications 

Ruiyi can help you choose the right plastic material for your application, whether your project involves plastic injection molding for medical use, molded plastic parts for the automotive industry, or other projects, we can help you go from design to production faster.

6. Polystyrene (PS)

Polystyrene (PS) is a commodity plastic available in two basic types used for injection molding:

● General Purpose Polystyrene (GPPS)

● High impact polystyrene (HIPS)

GPPS is brittle and has lower dimensional stability than HIPS. HIPS is compounded with butadiene rubber to enhance its material properties. GPPS also has glass-like transparency, while HIPS is opaque. Both types of polystyrene are well suited for injection molding because they have predictable and uniform shrinkage.

PS application, class

Polystyrene is used in medical, optical, and electrical and electronic applications. Due to their higher impact strength, HIPS are often used with appliances and equipment. Injection molded GPPS is used in plastic toys, boxes, containers and pallets.

Polystyrene can be filled with glass for added strength or copolymerized with acrylic to increase clarity and improve chemical and UV stability.

7. Polyethylene (PE)

Polyethylene is one of the most versatile plastics used for injection molding. Polyethylene's high ductility, tensile strength, impact resistance, low moisture absorption and recyclability make it an ideal material for plastic containers and bags. Polyethylene (PE)

Polyethylene is the most commonly used plastic in the world. There are mainly three types:

● High density (HDPE, PEHD)

● Low density (LDPE)

● Polyethylene terephthalate (PET, PETE)

PE is the only commercial polymer that can be selected based on its density, so this measurement is important because it controls other material properties. HDPE and LDPE both have useful properties such as chemical resistance, but they differ in their respective hardness, flexibility, melting point, and optical clarity.

HDPE, LDPE and PET are all low-cost plastics that are resistant to both moisture and chemicals. LDPE is softer and more flexible than HDPE, which is an opaque material. Like LDPE, PET can be as clear as glass. Engineers and designers like these materials because they offer a variety of options in terms of optical clarity and other properties.

PE application, class

PE plastic is best known for its use in baby bottles (HDPE), plastic films (LDPE), and water bottles (PET); however, these products are not injection molded. They are made using a different type of molding called blow molding. Examples of injection molded PE include children's toys, tool boxes, wire and cable insulators, and medical device components.

PE plastics have numbered grades, with higher numbers generally indicating higher density. For example, HDPE 500 has a higher density than HDPE 300. Both grades are denser than LDPE, which also uses a grade numbering system.

8. Thermoplastic elastomer (TPE)

Thermoplastic elastomer (TPE) or thermoplastic rubber (TPR) is a mixture of rubber and plastic materials. Although TPE has the characteristics and performance of rubber, it is processed in the same way as plastic. TPR's flexibility is part of what makes it attractive to designers and engineers. TPE is also recyclable and can be recycled six times. In addition, other recycled materials can be mixed together to produce TPE.

TPE applications, clas

Injection-molded TPE is used in footwear, medical devices, automotive parts and pet products. Automotive applications include weather sealing and shockproof dust shields. Medical applications include breathing tubes, valves, catheters and ventilation masks.

9. Thermoplastic polyurethane (TPU)

Thermoplastic polyurethane (TPU) is a thermoplastic elastomer (TPE) that, like other TPEs, has rubber-like elasticity; however, injection-molded TPU has a higher hardness and can be used as a replacement for hard rubber. TPU is often chosen over TPE because TPU is better suited to extreme temperatures and chemical resistance. TPE, on the other hand, is softer and more flexible.

TPU applications, class

Injection-molded TPU is used in footwear, gaskets, casters and sporting goods. Applications also include housings or casings for electronic and medical equipment. In medical applications, TPU is sometimes used in place of polyvinyl chloride (PVC), a plastic that can cause skin irritation.

Thermoplastic polyurethanes are available in commercial, medical, and industrial grades. TPU materials are mainly divided into three categories: polyester, polyether and polycaprolactone.

10. Acrylic (PMMA)

PMMA, or acrylic, is a strong, clear thermoplastic that is a lighter weight, shatterproof alternative to glass. Because PMMA is transparent and has excellent optical clarity, it allows a high percentage of light to pass through. Acrylics have high tensile strength, can withstand loads, do not absorb odors, and can maintain tight tolerances during injection molding. The material is also resistant to sunlight and weather, making it suitable for outdoor use. Because it does not degrade when in contact with water, PMMA does not release bisphenol A (BPA), a chemical found in many plastics that can adversely affect human health.

PMMA application, class

Acrylics are used in windows, greenhouses, solar panels, bathroom enclosures and other transparent components for architectural and lighting applications.

General Purpose Acrylic is the cheapest type of PMMA and is used in commercial rather than engineering applications. Sign-grade acrylic is 10 times stronger than general-purpose acrylic, providing excellent light transmission for outdoor signs. Marine-grade acrylic resists damage from continued exposure to water and is often used by boat builders.

Alternatively, hybrid injection molding is an option. Although they are the most common types, the materials listed above are not your only options. Depending on your specific requirements, you can also choose hybrid plastics that combine the best properties of two different polymers. There are a variety of blends available, but the most common types are PC/ABS, PC/PBT, and PPE/PS.