6 Common Plastic Resins for Injection Molding

Selecting the appropriate material is crucial for creating durable and resilient products. However, with a multitude of plastic resins available in the market, each with distinct properties, advantages, and drawbacks, it can be daunting to select the right material for your project. Fortunately, Quickparts has a team of material specialists who can provide guidance.

We possess considerable expertise in working with plastic resins, and we comprehend how various properties can influence your parts during and after production. If you require the finest plastic resins for injection molding, there are six prevalent options to consider, including Acrylonitrile Butadiene Styrene (ABS), Polycarbonate (PC), Polycarbonate-ABS (PC/ABS), Polypropylene (PP), Nylon, and Acetal, or Polyoxymethylene (POM).

In this article, we examine the characteristics, advantages, and disadvantages of these six frequently used injection molding plastic resins. Please read on to learn more about each material. Additionally, you may download this guide as a convenient offline reference.


1. ABS: Acrylonitrile Butadiene Styrene

ABS is a widely used and versatile plastic resin, known for its affordability and excellent mechanical and electrical properties. It is an engineering thermoplastic that combines the properties of three monomers: acrylonitrile, styrene, and polybutadiene. ABS provides superior hardness, toughness, strength, and rigidity, and features a colorfast, high-gloss surface finish. This plastic resin is also highly resistant to stress, impact, creep, and heat, and can be heated, cooled, and reheated without any changes to its characteristics.

ABS plastic is commonly used in various applications, such as small appliances, medical devices, enclosures for electronics, office equipment, and toys. However, parts molded with ABS are susceptible to visible knit lines on their surface. One way to prevent this is by using optimal wall thickness during the molding process, with a recommended thickness range of 0.045-0.140 inches.

When considering ABS for your product design, it is important to weigh its advantages and disadvantages. Some of the benefits of ABS plastic include its structural and dimensional stability, high impact resistance, heat and chemical resistance, abrasion and stain resistance, and surface brightness with a high-gloss finish. However, ABS plastic also has some drawbacks, such as a maximum continuous use temperature of approximately 70°C (160°F), poor solvent and fatigue resistance, poor UV resistance unless protected, poor bearing properties with high friction and wear, and high smoke evolution.

2. PC: Polycarbonate

Polycarbonate (PC) resins are amorphous engineering thermoplastics that offer excellent toughness even at -20°C. They possess natural transparency, which allows them to transmit over 90% of light, making them comparable to glass. These properties make polycarbonate resins an ideal alternative to glass, particularly when a lightweight option is needed or high-impact resistance is required. Some of the common applications of PC include bullet-proof glass, medical device components, light fixtures, and greenhouses.

In addition, PC is a natural UV filter, making it an excellent choice for eyewear applications. Moreover, PC is highly pliable and can be processed at room temperature without cracking or breaking, making it a preferred material for prototyping, especially when transparency is essential.

However, polycarbonate is susceptible to scratches. Hence, it is advisable to add a scratch-resistant coating for applications where scratching is a concern.

There are several advantages to using PC plastic, such as high impact strength, toughness, natural transparency, excellent dimensional stability, pliability at room temperature, and good heat resistance. However, it is important to note that PC is considered hazardous for food with the release of Bisphenol A (BPA).

Therefore, product designers must consider the pros and cons of PC injection molding to determine if it is the best choice for their specific application.

3. PC/ABS: Polycarbonate-ABS

PC/ABS is a widely used industrial-grade thermoplastic material that offers the combined strength and heat resistance of polycarbonate and the flexibility and high-quality surface finish of ABS. It is known for providing improved processing during the injection molding process, making it a popular choice for functional prototyping, tooling, and low-volume manufacturing.

Some common applications of PC/ABS plastic include automotive exterior and interior components, business equipment housings and enclosures, medical hardware, electrical housings, computers, and monitors.

While PC/ABS offers improved strength over ABS at a lower cost than polycarbonate, it has poor UV and fatigue endurance. However, this can be improved by adding reinforcing agents such as glass fiber, mineral fillers, and flame retardants.

Advantages of PC/ABS plastic include high impact strength even at low temperatures, good heat resistance, high stiffness, easy processing, and low overall shrinkage with high dimensional accuracy. However, some disadvantages include poor solvent resistance, low dielectric strength (not a good insulator), and low continuous service temperature (melts easily). It is essential to understand these key pros and cons to ensure that PC/ABS is the right fit for your product design.

4. PP: Polypropylene

Polypropylene is a highly versatile and cost-effective thermoplastic that offers excellent toughness, flexibility, and heat and chemical resistance. It is commonly used in a wide range of applications, such as automotive manufacturing, furniture assembly, textiles, aerospace components, and medical devices and equipment. Additionally, PP is an excellent choice for specialized parts like living hinges.

When designing with PP, it is important to consider its limitations. For example, if impact resistance is required, it may be necessary to consider a different material such as PC/ABS.

It is crucial to weigh the advantages and disadvantages of using PP for your project. While PP is the most economical option, selecting the wrong material can lead to increased production costs in the long run.

Advantages of PP Plastic:

  • Excellent moisture resistance
  • High stiffness and impact strength
  • Good heat and chemical resistance
  • High dielectric strength
  • Food grades available
  • Easy processing

Disadvantages of PP Plastic:

  • Poor resistance to chlorinated solvents
  • Susceptible to UV-light degradation
  • Flammable (retarded grades available)

5. Nylon

Nylon is a semi-crystalline polyamide known for its high thermal stability and low density. Polyamides, or nylons, are a group of technical thermoplastics with a range of properties, from the hard and tough PA 66 to the soft and flexible PA 12.

Nylon plastic resins offer excellent wear resistance, good coefficient of friction, and impressive temperature and impact properties. Nylon also has exceptional chemical resistance and is known for being a reliable oil-resistant plastic.

This combination of properties makes nylon a suitable material for some applications where toughness and weight reduction are essential, such as automotive parts and industrial components.

Design Considerations of Nylon Plastic

Nylon is known to absorb water, which may not make it an ideal plastic for use in environments with moisture as its dimensional and structural integrity may be compromised.

When molding with nylon, shrinkage can occur, leading to reduced strength, color issues, and bent edges. This can be controlled by managing heat and molding temperatures.

Advantages and Disadvantages of Nylon Plastic Resins

Nylon is easy to process and can be a cost-effective solution for some projects. However, it is crucial to understand how its properties can impact your design intent before making a choice.

Advantages of Nylon Plastic Excellent abrasion and wear resistance High tensile and compressive strength Low coefficient of friction Lightweight option (1/7th the weight of conventional materials) Easy to machine Disadvantages of Nylon Plastic High shrinkage in molded sections Lack of stability Prone to moisture absorption, reducing strength and stiffness properties.

6. POM: Polyoxymethylene (Acetal)

Acetal, also known as POM, is a white semi-crystalline engineering thermoplastic that is widely used in injection molding. It is highly rigid down to -40°C and has excellent dimensional stability, resistance to abrasion, water absorption, creep, and heat.

POM is a popular material choice for producing high-performance engineering components, medical equipment, and electrical housings due to its low coefficient of friction. It is a good fit for products that require sliding mechanisms and gears.

However, POM has a high shrink rate of about 2%, which can lead to dimensional instability and warping in large parts with varying wall thicknesses. Adding fillets or ribs to strengthen the part can help alleviate these issues.

Here are some of the advantages and disadvantages of POM injection molding:

Advantages of POM Plastic

  • High strength
  • Rigidity down to -40°C
  • High resistance to impact, creep, abrasion, and solvents
  • Good fatigue endurance and low coefficient of friction

Disadvantages of POM Plastic

  • High shrinkage rate of about 2%
  • Poor resistance to UV radiation, acids, and alkalis
  • Flammable and not available with flame retardants

By understanding the characteristics of POM plastic, you can make an informed decision about whether it is the right material for your product design.


Get to Market at Speed with the Right Plastic

If you are having difficulty selecting the appropriate plastic resin for your part design, Quickparts can provide valuable assistance. Our material selection experts can help you make informed decisions and bring your ideas to fruition on time and within budget.

Our services include:

✔ Assistance in selecting from a wide range of plastic materials. ✔ Guidance in evaluating these material options based on your specific application requirements. ✔ Utilization of industry best practices to ensure your product is brought to market successfully.

Interested in learning more? Submit your project to us and our team of experts will be happy to provide you with professional advice. If you have any further questions, please do not hesitate to contact our friendly sales team at +1 931-766-7290 or by clicking here.