Injection Molding: Material Selection Guide for Commodity and Engineered Resins

Injection Molding-Material Selection Guide-for-Commodity and Engineered Resins | GreenLeaf Industries | Lenoir City, TN

When selecting the optimal plastic material for a certain injection molding application, it is prudent to use a commodity resin. This type of resin gets the job done without exception. Commodity resin is affordable and readily available. Whether the application in question is a toy, a consumer product or packaging, a commodity resin will likely suffice.

Though engineering resin is expensive compared to commodity resin, it has its own merits. This plastic material has superior thermal and mechanical properties than commodity plastics. Engineering resins holds up when subjected to high temperatures, corrosives and wear. They are commonly used in injection molding to minimize weight while boosting strength and performance. Let’s take a look at the applications and properties of resins used in injection molding.

ACRYLONITRILE BUTADIENE STYRENE  

This commodity resin is low-to-medium strength, highly resistant to impact, resistant to flash and has fair/good material flow. It has a comparably low cost. In terms of advantages, this commodity resin is easily processed, resistant to chemicals, has an excellent surface finish and is RoHS compliant. However, it has a limited resistance to weathering. This commodity resin is best used in toys, consumer goods and auto interiors.

ACRYLIC (PMMA)

PMMA has moderate strength, good material flow and is resistant to shrinkage and flash. It has a moderate cost and a low impact on mold. This resin is colorable, offers excellent insulation and weatherability. It is commonly used in aquariums, casing, lenses and for glass replacement.

HIGH DENSITY POLYETHYLENE (HDPE)

If you are looking for superior material flow and a high resistance to impact, this is the resin for you. It is low-cost, low- strength and has fair resistance to shrinkage. HDPE is favored as it is easily processed and can safely contact food. Disadvantages include weak weather resistance and high thermal expansion. This resin is commonly used for buckets and toys.

POLYPROPYLENE  

Polypropylene has low strength but a high resistance to impact. It offers excellent material flow, moderate resistance to shrinkage but a poor resistance to flash. This is a low-cost resin with a low impact on mold (wear) that can safely contact food and is easily processed. However, it can be degraded by UV light. It is commonly used in injection molding to produce consumer goods.

POLYETHYLENE 

Polyethylene is low-strength, highly resistant to impact and offers acceptable material flow. It is especially resistant to warpage and shrinkage yet offers minimal resistance to flash. Its main advantages include being corrosion-resistant, lightweight, highly flexible and safe when contacting food. Disadvantages include its high thermal expansion and poor weatherability. Polyethylene is commonly used in buckets, bearings and toys.

POLYSTYRENE 

Polystyrene has low to moderate strength, offers moderate resistance to impact, good material flow and acceptable resistance to shrinkage. It can safely contact food, is expandable and has a fast cycle time. However, it has a few disadvantages in that it is a poor solvent and is not especially resistant to chemicals. Common uses for polystyrene include product casings, packaging, toys and cups.

POLYVINYL CHLORIDE (PVC)

PVC has a moderate resistance to impact, warpage and flash. It has a low-to-medium strength and a medium/high impact on mold. This low-cost resin is UV resistant, has high Gloss and is flame retardant. However, its high density and UV sensitivity are certainly drawbacks. PVC is used to add strength to materials. It is also used in containers, fencing and various soft/flexible parts.

STYRENE ACRYLONITRILE (SAN)

SAN has medium strength and a low resistance to impact. This resin has a medium resistance to warpage and flash. It is favored for its chemical resistance, considerable clarity, excellent weatherability and process-ability. It is regularly used in cosmetics packaging, containers, automotive applications and electrical applications.

ENGINEERING RESINS FOR INJECTION MOLDING

Are You Using The Best Resin For Your Plastic Part | GreenLeaf Industries | Lenoir City, TNACETAL

This engineering resin has moderate strength, a moderate resistance to impact, fair material flow and fair resistance to warpage/shrinkage. Though it degrades when exposed to a considerable amount of UV light and has poor resistance to acids, it is not especially sensitive to moisture, provides excellent chemical resistance and is low-fatigue. Acetal is used for valve parts, bearings and springs.

POLYBUTYLENE TEREPHTHALATE (PBT)

PBT offers excellent resistance to impact, fair resistance to flash, moderate overall strength and fair material flow. It has a medium/high cost, a low strength at elevated temperatures and minimal resistance to acid. Yet it is revered for its electrical properties. It is commonly used in electronic components, automotive connectors and housings.

PBT / PET (GLASS FILLED)

This high-strength resin offers fair-to-good material flow and fair resistance to flash. It is comparably expensive yet it has a high stiffness-to-weight ratio and excellent resistance to UV light. This resin is commonly used in automotive components, housings and structural parts.

POLYETHYLENE TEREPHTHALATE (PET)

PET is a resin with medium strength, high resistance to impact and good material flow. It is also quite resistant to shrinkage/warpage and flash. This moderately-priced resin has a low-to-medium impact on mold. It offers clarity, easy processing and excellent chemical resistance. Dishwasher parts, infant products and sterilizer lids are made with PET.

POLYCARBONATE (PC)

PC offers medium strength, even at elevated temperatures. It has a high resistance to impact, good resistance to flash and fair/good resistance to shrinkage. This resin is RoHS-compliant, processed with ease and dimensionally stable. However, it can degrade during extended periods of processing. PC is regularly used in light covers, lenses and single-use containers.

POLYETHER ETHER KETONE (PEEK)

PEEK is high-strength, highly resistant to impact, offers good material flow and medium resistance to shrinkage and flash. This fairly costly resin is commonly favored for its chemical resistance, abrasive resistance, lubricating properties and excellent mechanical strength. It is used in a number of different medical applications.

POLYETHER IMIDE (PEI) 

PEI is remarkably strong, offers high material flow and decent resistance to flash as well as shrinkage/warpage. Yet it has limited colorablity and is notch sensitive. It is commonly used in automotive, medical and aerospace parts.

POLYETHERSULFONE

Polyethersulfone is high-strength, even at lofty temperatures. It offers medium resistance to impact and shrinkage. Yet it is high in cost, difficult to process and has poor weatherability. Food service, medical products, engineering applications and automotive products contain polyethersulfone.

POLYETHYLENE ETHER (PPE)

PPE is a medium-to-high strength resin that is highly resistant to impact and shrinkage. It offers a high material flow yet it is comparably expensive. Its color degrades when exposed to UV light. Advantages include resistance to acids and superior electrical properties.

POLYAMIDE (NYLON)

This resin is regularly used in bearings and various medium-stress components. It has moderate strength, high resistance to impact but poor resistance to flash.  The glass-filled version has excellent material flow, considerable strength and is extremely resistant to chemicals and wear.

POLYPHENYLENE SULFIDE  

This high-strength resin is extremely resistant to flash and moderately resistant to impact and shrinkage. It is electrically conductive and won’t succumb to wear. It is used in healthcare, engineering and automotive applications.

THERMOPLASTIC ELASTOMER (TPE)

TPE is an affordable low-strength resin, with minimal resistance to shrinkage, excellent material flow, good weatherability and UV resistance. It is used in seals and bushings.

THERMOPLASTIC POLYURETHANE

This medium-strength resin is used in sporting goods, gaskets and surgical instruments. It has an extensive durometer range and offers good resistance to wear along with oil, hydrolysis and chemicals.

 

About GreenLeaf:

GreenLeaf Industries is an ISO 9001 registered manufacturer that consistently adheres to all its standards to provide our clients with consistent, reliable, quality automotive and industrial plastic parts.

We are an American injection molding company, unafraid to compete in the world market and determined to succeed. Established in 1999, we take pride in our high-quality craftsmanship and superior customer service. Contact us to discuss whether your injection molding project may be a candidate for reshoring.

GreenLeaf Industries
310 Bussell Ferry Road
Lenoir City, TN 37771
(865) 988-5661
www.greenleaf.biz