We often get asked what the best plastic injection molding resin is to use for certain projects. And honestly there is no one answer for that. The best resin is the one that works for you and your unique circumstances. The good news is that there are many thousands of plastic injection molding resins to choose from with similar – but not identical – properties, so you have many potential solutions available.
When choosing a plastic, the first thing you have to consider is the part’s function and the physical environment that it’s going to be exposed to. So clearly you’ll need to consider what type of injection molding material is going to stand up to various environmental challenges such as temperature fluctuations, moisture, chemical exposure, UV light, and many more. Then the material’s strength, durability, flexibility, color, and cost come into play. Therefore, we’d like to help you refine your search by explaining the properties of the ten most common plastic injection molding resins that we use for the majority of parts that we make here at Star Rapid.
Nylon is often used to produce strong mechanical parts like bushings, gears, and bearings. It’s very common in automotive applications because not only is it tough but it helps to reduce weight and lower production costs compared to a metal analogue. You should be aware that, although it’s a strong plastic, it tends to absorb water. It’s not the ideal choice for marine applications. Nylon is also known by its chemical designation PA (Polyamide).
We use acrylic to produce transparent parts such as windows, view screens, and various lighting equipment. It’s often used as an alternative to glass due to its high tensile strength and weather and scratch resistant nature. It takes dyes and colorants very well so you can produce many aesthetic effects. On top of its optical and transparent properties, acrylic is odorless and tasteless and doesn’t contain Bisphenol A (BPA). BPA is a harmful organic compound, so plastic injection molding resins like acrylic are considered safe for food storage.
Polycarbonate is another clear injection molding resin that has excellent optical properties and is extremely durable. When molding with this amorphous thermoplastic material, precise dimensional control can be maintained as it has predictable and uniform mold shrinkage. We use polycarbonate when we need something substantially stronger than acrylic. However, be aware that if you’re making optically clear plastic parts the mold tool must be highly polished, which in turn implies the use of a higher grade of stainless steel that costs more. Now, you can see that your choice of plastic resin can very much influence the appropriate mold tool material as well.
Polyoxymethylene (POM) is a type of acetal resin used to make mechanical and automotive parts that would usually be made with metal. This engineering thermoplastic material is very strong, tough, and rigid. It’s often used to produce gears, fasteners, knife handles, and ball bearings. Although POM has high resistance towards solvents such as alcohols, gasoline, detergents and motor oils, it shouldn’t be exposed to hydrochloric acid and nitric acid.
When it comes to injection molding resins, there are two types of polystyrene that are commonly used: High Impact Polystyrene (HIPS) and General Purpose Polystyrene (GPPS). GPPS is transparent, while HIPS is opaque. Hard cases for toolboxes and bodies of power tools are also made using High Impact Polystyrene. As with so many things there is a tradeoff to be aware of. On the one hand, PS is tough and durable. It can take a lot of abuse in the field. But that also means it’s not very environmentally friendly.
Acrylonitrile Butadiene Styrene (ABS)
ABS resin is an opaque thermoplastic polymer and an engineering grade plastic. There are many advantages to using ABS. It’s tough, has good dimensional stability, it resists impacts and scratching, and is hard to break. Also, the low melting temperature makes it easy to mold. It’s commonly used to produce electronic parts such as phone adaptors, keyboard keys, and wall socket plastic guards. Why is this? Because ABS is a good insulator and won’t conduct electricity or give off fumes if it’s exposed to fire. These are important considerations for product developers working on electrical devices.
This thermoplastic injection molding material is widely used in the food storage and packaging industry because it doesn’t let chemicals mix with food products. Polypropylene (PP) can be washed in hot water without degrading, and it has high chemical and moisture resistance. PP has incredible impact strength, elasticity, and toughness. Designers should also note that PP is easy to recycle, and because of its flexibility, it can be used to make live hinges that can be bent many times without tearing.
Polyethylene (PE) is a lightweight thermoplastic molding material that has high chemical resistance, elasticity, and electrical insulating properties. It’s not especially strong or hard, but it’s inexpensive. You’ll find it everywhere in consumer plastic parts, milk bottles, medicine and detergent bottles, plastic bags, and trash cans. PE is also the most common injection molding resin for making toys because it’s non-toxic and can take a beating without complaint.
Thermoplastic Polyurethane (TPU)
Thermoplastic Polyurethane (TPU) is soft and elastic, with great tensile and tear strength. That’s why it’s often used to make parts that demand a rubber – like elasticity. You should know that TPU is more expensive than other resins but for many applications, like protective wire and cable sheaths, there really is no substitute. Another advantage is that TPU improves the grip for products that need to be held securely in the hand.
Thermoplastic Rubber (TPR)
Thermoplastic Rubber (TPR) resin is actually a mixture of plastic and rubber, and it’s easy to use in the injection molding process. It has outstanding chemical and weather resistance and high impact strength. Because of this, TPR is used in many types of fluid dispensers, flexible hoses, catheters, and other places containing different liquids, including acid.
You can find this recyclable material in medical catheters, suspension bushings and headphone cables. Thermoplastic rubber is also known as thermoplastic elastomer (TPE).
Full Injection Molding Material List
We hope this brief overview helped you to understand some of the most popular kinds of injection molding resins as well as their properties and applications. Please note that we can work with you to modify all of these materials with lubricants, glass fibers and UV stabilizers to suit your unique project needs.
You can also explore the most common injection molding defects and how to handle them. Are you ready to collaborate with us on your next manufacturing project? Request a quote today!