Top 5 Plastic Resins Used in Injection Molding

With hundreds of commodity and engineering resins available on the market today, the material selection process for plastic injection molding can often seem daunting at first. However, it is much easier to pick a plastic when you look into the overall characteristics that these plastics have to offer.

Below are the five popular types of resins used for plastic injection molding:

ABS 

ABS (Acrylonitrile Butadiene Styrene)  is used in a wide range of industries, such as manufacturing, automotive, medical, and marine. It is an ideal material for structural applications when impact resistance, strength, and stiffness are required. It is widely used for machining pre-production prototypes since it has excellent dimensional stability and is easy to paint and glue.

Characteristics:

• Structural strength & stiffness
• Chemical-resistant
• Excellent high & low-temperature performance
• Great electrical insulation properties

Some factors to consider while using ABS is that molding it at a high temperature improves the gloss and heat resistance of the product whereas molding at a low temperature is where the highest impact resistance and strength are obtained.

Acetal

Acetal is a high-performance engineering polymer often used for parts that would otherwise be made of metal. All acetals are strong and durable making them apt for mechanical parts like gears and chain links. They are ideal for automotive, and construction applications. 

Characteristics: 

• Abrasion-resistant
• Low moisture absorption
• High strength & stiffness
• Creep resistant 

Few things to keep in mind before opting for Acetal. They are affected by strong acids or oxidizing agents but have high resistance to most chemicals.

Polypropylene

Regarded as one of the lightest and most versatile polymers, Polypropylene (PP) is made from the combination of propylene monomers. It is used in a variety of applications to include packaging for consumer products, household products, plastic parts for various industries including the automotive industry.

Characteristics: 

• High flexural strength
• Insulation
• Low coefficient of friction
• Low density
• Heat-resistant

Polypropylene’s characteristics make it ideal for tough, robust products ranging from protective car bumpers to life-saving medical tools. If you are opting for polypropylene, keep in mind that they are flammable and degraded by UV radiation.

High Impact Polystyrene

High Impact Polystyrene (HIPS) provides tough, low-cost performance and highly customizable surfaces: It can be printed, glued, bonded, and decorated easily. Due to the versatile nature of this material, they are suitable for applications in the cosmetics, display, food, medical, horticultural, industrial and custom thermoforming markets.

Characteristics: 

• High tensile strength
• Electrical insulation
• Impact-resistant
• Great dimensional stability

A major advantage is that it can be re-molded over and over again, which makes it environmentally friendly as it can always be recycled.

Low-Density Polyethylene

As the name suggests, Low-Density Polyethylene (LDPE) has a low density which means it has less mass compared to its volume. It is characterized by its short and long chain branching which gives it good clarity and processability. LPDE can be found in many consumer goods, electronics, housewares, and medical products.

Characteristics:

• Moisture-proof
• Reduced weight
• Robust
• Low crystallization capacity

Keep in mind that it is difficult to bond with other polymers, and should not be used in harsh weather or high-temperature applications.

Each type of plastic has their own properties, and it is extremely important to look at the overall defining characteristics before choosing a plastic for injection molding. If you believe a plastic is falling short of some properties, there is always fine tuning through the use of additives and fillers to get the material properties just right – that’s how you end up with over 85,000 types of plastics.