Top 10 Plastic Injection Molding Materials
More and more industries are embracing plastic injection molding thanks to its versatility, simplicity, and high-quality finish. When manufacturers need to create precision parts with specific material qualities, there is a host of engineering thermoplastics to consider.
Plastic injection molding is a straightforward manufacturing process often used in the mass production of identical plastic parts. Plastic granules are heated until soft and directed to specially shaped injection molds. The molten material is allowed to cool down and solidify in the mold cavity where it takes the shape of the injection mold. The most common mold making materials are steel and aluminium.
If you’re thinking about plastic injection molding, you need to understand the characteristics, applications, as well as the pros and cons of different plastic materials. In this extensive exploration, I’ll discuss 10 of the most popular plastic molding materials.
Nylon Polyamide (PA)
Nylon is a semi-cyrstalline polymer that is unsurprisingly one of the most popular plastic injection molding materials. It is low cost, high performance, and very versatile with applications in virtually all industries. Nylon is a type of polyamide though the two terms are often used interchangably.
There are different types of Nylon, the most common being Nylon 6, Nylon 66, and Nylon 12. Fillers such as glass fibers are sometimes used to improve the mechanical strength and thermal properties of Nylon.
Properties
Nylon has a low coefficient of friction and is suitable for applications that are susceptible to high-friction and wear. It has excellent strength and is highly resistant to abrasion, fatigue, as well as fuel and oils. Compared to other engineering plastics, this material also has a high heat resistance.
Despite all its benefits, there are some challenges associated with molding nylon. If not properly dried, this material can take in excess moisture causing defects. It is also susceptible to shrinkage during the molding process.
Applications
Injection molded nylon is often used in;
Electrical connectors
Medical impants
Threaded inserts
Mechanical components such as gears, bushings, and bearings
Automotive applications where resistance to hydrocarbons and heat is essential.
ABS Plastic
Acrylonitrile butadiene styrene, or ABS, is a popular thermoplastic polymer that is often used for injection molding applications. It consists of three monomers: styrene, acrylonitrile, and butadiene. Its styrene content provides a shiny, visually appealing finish to injection molded parts and the butadiene delivers remarkable resilience.
Properties
ABS has a low melting point and this contributes to an easy injection molding process. It also has a low production cost, an aspect that promotes its popularity across various industries.
This engineering plastic is known for its strength and toughness, which translates to fracture and impact resistance. ABS is also a good insulator and it performs exceptionally well in both high and low temperatures.
One of the main limitations of ABS is its poor weatherability. This material can be damaged by exposure to sunlight and water.
Applications
ABS is widely used in the manufacturing sector to produce plastic injection molded parts such as;
Kitchen appliances
Sports equipment
Automotive parts
Electronics
Musical instruments
Acrylic
Acrylic is a versatile and transparent thermoplastic typically used as a high-impact-resistant alternative to glass. It also goes by its chemical name, Poly(methyl methacrylate) or PMMA in short. CNC machining is another popular method of producing acrylic items.
Properties
One of the key features of acrylic is that it has glass-like characteristics – clarity, optical transparency, and brilliance – but is way lighter and stronger. It is, therefore, an excellent alternative to glass.
Acrylic has great dimensional stability making it especially beneficial for large scale manufacturing of plastic parts. Also, this plastic material can endure weather conditions such as rainfall and sunlight and is therefore used for outdoor windows and enclosures.
Like any other material, acrylic has its downsides. This material stains easily when it comes into contact with oils or greases.
Applications
Acrylic plastic injection molding has a variety of applications including;
Medical devices
Windows
Industrial equipment such as face shields and other protective eyewear.
Mobile Phone displays
Aquarium screens
Polycarbonate (PC)
Like acrylic, polycarbonate is a transparent material known for its excellent clarity and toughness. It comes in a range of grades including film, anti-static, branched, flame retardant, and abrasion-resistant polycarbonate. This plastic injection molding material can deliver transparent and non-transparent components through material modification.
Properties
Polycarbonate has excellent optical transparency. The light transmittance of most grades ranges between 80% and 90% making this material a great option when clear parts are needed.
Another important feature of polycarbonate is its mechanical properties. This engineering plastic offers excellent strength, toughness, and both impact and heat resistance. Polycarbonate is used more frequently than acrylic, thanks to its thermal stability.
Applications
Some of the main applications of Polycarbonate molding include;
LED lighting fixtures
Medical gadgets
Playground equipment
Display screens
Automotive parts such as sunroofs, headlight assemblies, and bullet-resistant windows
Polyethylene (PE)
Polyethylene remains the world’s most commonly used plastic material. It is manufactured in varying densities and this affects the physical properties of the specific plastic resin. Here are five of the most commonly injected molded polyethylene types.
Ultra-high molecular weight polyethylene (UHMWPE)
High-density polyethylene (HDPE)
Medium-density polyethylene (MDPE)
Low-density polyethylene (LDPE)
Linear-low-density polyethylene (LLDPE)
Properties
Polyethylene is generally lightweight, a good insulator, and it has great chemical resistance. However, its stiffness, flexibility, and melting point will vary depending on the type of polyethylene. Higher-density resins offer more stiffness at the cost of increased brittleness. Conversely, lower-density plastic resins are more flexible with lower stiffness.
Polyethylene is often used for indoor applications as it can be damaged by exposure to sunlight. Also, its poor high-temperature resistance means this plastic material may not be ideal for some processing applications.
Applications
Typical applications for injection-molded polyethylene include products such as;
Food containers, plastic bottles, shopping bags, and other disposable packaging.
Gas, water, and sewer pipes.
UHMWPE is used in the manufacture of body armor and medical equipment such as knee and hip implants.
Polyoxymethylene (POM)
Polyoxymethylene is a semi-crystalline, high-performance engineering polymer. It is typically utilized for projects that need low friction, high stiffness, and dimensional stability. Polyoxymethylene also goes by the name acetal or polyformaldehyde.
Properties
Polyoxymethylene is usually an opaque, white solid with a relatively high melting point. However, it can be dyed to produce different colors. Other material properties that contribute to its popularity are its high strength, excellent chemical resistance, and wear resistance.
One downside of acetal is that it degrades when exposed to UV light limiting its outdoor applications.
Applications
The primary uses of polyoxymethylene include;
High-performance engineering components like gear wheels and gun parts.
Medical devices such as insulin pens and inhalers
Musical instruments
Automotive industry for door lock systems, fuel sender units, and power windows.
Polypropylene (PP)
Polypropylene is the second-most-produced plastic polymer after polyethylene. It is a low-cost, versatile option that is also easily accessible making it a workhorse material across various industries.
Properties
Polypropylene is exceptionally lightweight making it suitable for applications that require weight reduction. It also offers a good balance of strength and flexibility. Polypropylene can endure significant stress without deformation. Further, this engineering thermoplastic has good water, chemical, and heat resistance.
Despite its numerous advantages, polypropylene has a few material limitations. The material has poor UV resistance and therefore degrades with long-term sunlight exposure. Also, compared to other plastic materials, polypropylene offers fewer color options.
Applications
Injection-molded polypropylene products include;
Plastic furniture
Kids toys
Heavy-duty packaging
Automotive parts
Fibers and fabrics
Polystyrene (PS)
Polystyrene is a transparent, lightweight synthetic polymer that delivers moderate strength in its unmodified state. It is available in two major forms;
General-purpose polystyrene (GPPS) is clear just like gas. It tends to be less stiff and more brittle compared to HIPS.
High-impact polystyrene (HIPS) is an opaque resin modified with polybutadiene elastomers to improve material characteristics such as rigidity, dimensional stability, and impact strength.
Properties
Polystyrene is an inexpensive plastic with a relatively high melting point. It is dimensionally stable and can resist moisture and impact. Importantly, polystyrene is radiation resistant meaning that it can be sterilized using radiation.
On the downside, polystyrene is flammable and has poor UV resistance.
Applications
Polystyrene is well-suited to a broad range of applications and industries like;
Medical industry to produce diagnostic gadgets and medical packaging
Automotive parts
Consumer goods
Electronics
Thermoplastic Elastomer (TPE)
Thermplastic elastomer is a polymer blend that combines a thermoplastic and a elastometric (rubber) material. The resulting material behaves like a thermoplastic while also having rubber-like properties. TPEs are, therefore, used for applications that require excellent flexibility. Also known as thermoplastic rubber (TPR), this material allows for repeated recycling.
Properties
Due to their rubber content, TPEs are flexible and will revert back to their original shape when stretched. They are also easy to work with during the injection molding process. In addition to flexibility, thermoplastic elastomers offer high impact strength, good chemical resistance, and weatherability.
However, this type of plastic is more costly compared to other plastic injection molding materials. Therefore, designers must carefully consider if a TPEs substitute would yield the same results.
Applications
Thermoplastic elastomer is used for diverse product types including;
Footwear
Medical gadgets
Electronics
Consumer goods
Sporting equipment
Thermoplastic Polyurethane (TPU)
Thermoplastic polyurethane is a popular type of thermoplastic elastomers and it is usually abbreviated as TPU. This material is between rubber and plastic, and it offers superior performance and rubber-like elasticity.
TPUs can be grouped into three main classes;
Polyester-based TPUs
Polyether-based TPUs
Polycaprolactone-based TPUs
Properties
Thermoplastic polyurethane is flexible with excellent tensile and tear strength. Relative to other TPEs, this material has superior chemical and heat resistance.
On the flipside, TPU is more expensive than other materials.
Applications
TPU is an excellent choice for manufacturing a variety of products such as;
Tubing
Automobile parts such as wheels
Footwear
Medical goods including wound coverings, infusion systems, and catheters.
Author
Gavin Leo is a technical writer at Aria with 8 years of experience in Engineering, He proficient in machining characteristics and surface finish process of various materials. and participated in the development of more than 100complex injection molding and CNC machining projects. He is passionate about sharing his knowledge and experience.