Plastic Selection guide
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.
Material Selection Guide for Commodity and Engineered Resins
Offering superior toughness, strength, impact resistance, and temperature resistance, acrylonitrile butadiene styrene (ABS) is used in a wide range of industries and applications, from automotive to piping and is RoHS compliant. ABS combines the strength and rigidity of acrylonitrile and styrene polymers with the toughness of polybutadiene rubber. ABS is easily molded and provides a colorfast, glossy effect with a high-quality surface finish. This plastic polymer has no exact melting point.
ABS materials can be processed using any of the standard thermoplastic processing methods. It easily adheres to itself, similar plastics, and metal coatings, making it well-suited for a range of different products.
For instance, it’s frequently used in appliances, telephone handsets, computer and other office equipment housings. ABS can also be used in musical instruments, golf club heads, medical devices, lawn mower covers, motorcycle helmets, canoes, toys, enclosures for electronics and electronic assemblies, luggage, interior and exterior automobile trim and interiors, shower heads, and handles. When extruded into a filament, ABS is ideal for use in 3D printers.
ABS does not have good chemical resistance, however, and should not be used in applications requiring electrical insulation or UV resistance.
Benefits: ABS/PC combines the strength and heat resistance of polycarbonate with the flexibility of ABS. ABS/PC also provides improved processing during injection molding, increased toughness and dimensional stability, higher heat resistance than ABS, and improved low temperature impact resistance than PC.
Applications: These blends are typically used in the automotive, electronic, and telecommunications industries among others applications.
Considerations: ABS/PC materials oftentimes can minimize thick molding concerns found in ABS or PC materials when molded alone. It is frequently used when increased mechanical properties are required when using ABS or when a lower cost PC is required.
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.
LOW DENSITY POLYETHYLENE (LDPE)
The most flexible type of polyethylene, low-density polyethylene (LDPE) offers superior moisture resistance, high-impact strength, good chemical resistance, and translucence. A low-cost option, LDPE is also weatherproof and can be easily processed with most methods.
Low-density polyethylene is used in a wide range of everyday products and applications. It can be found in many consumer goods and housewares, for example, as well as medical products, agricultural products, and electronic wiring. This versatile resin is found in shopping bags, plastic film and packaging, bottles and containers, lids and caps, six-pack rings, computer components, juice boxes, and toys. And with more and more people recycling bags and wraps, LDPE products often get a second life in items such as shipping envelopes, garbage can liners, floor tile, paneling, furniture, compost bins, trash cans, and landscape timber.
However, LDPE is difficult to bond and should not be used in harsh weather or high-temperature applications.
Polypropylene (PP) is one of the most widely produced plastics in the world. It’s known for its chemical resistance, elasticity and toughness, fatigue resistance, insulation properties, and transmissivity. Polypropylene (PP) is food grade, microwave and dishwasher safe. Although flammable and vulnerable to UV radiation, polypropylene still offers good resistance to chemical solvents and electricity.
A diverse range of applications makes use of polypropylene, as it can be easily customized by introducing special additives or altering the manufacturing process. In fact, this versatile material is sometimes referred to as the “steel” of plastics since PP can be tailored to so many different uses.
Polypropylene is well-suited for applications within the packaging, electrical and equipment manufacturing, household appliance, automotive, and construction industries. More specifically, PP is used for packaging solutions, buckets and bowls, plastic parts, living hinges, toys, medical components, washing machine drums, bottle caps, and textiles, among many other items. Polypropylene has a relatively slippery surface, so it’s possible to use PP as a substitute for other plastics, like acetal, in low-friction applications, such as gears and furniture contact points.
Most grades of polypropylene are flammable and subject to degradation by UV radiation.
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 weather ability. Polyethylene is commonly used in buckets, bearings and toys.
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.
HIGH IMPACT POLYSTYRENE (HIPS)
High-impact polystyrene (HIPS) provides good impact resistance, excellent machinability, fine dimensional stability, outstanding aesthetic qualities, and highly customizable surfaces. HIPS can be printed, glued, bonded, and decorated easily. It’s also very cost-efficient.
High-impact polystyrene is used in many print applications, such as promotional signs, display materials, garden stakes and tags, posters, and retail packaging, as well as 3D lenticular or moving images. In fact, HIPS is specially formulated for use in graphic arts applications. HIPS is also ideally suited for high-speed digital printing equipment. Other common uses include appliance components, TV and audiovisual (AV) equipment parts, bicycle trailers, toys, gasoline tanks, hot and cold drinking cups, and computer housings.
Although HIPS is flammable, flame-retardant varieties are available.
ENGINEERING RESINS FOR INJECTION MOLDING
Celcon® is a common brand name for acetal, also known as polyoxymethylene (POM), polyacetal, or polyformaldehyde. This thermoplastic offers outstanding toughness, excellent wear, creep resistance and chemical solvent resistance, easy colorization, good heat distortion, and low moisture absorption. Celcon® also provides high stiffness and excellent dimensional stability.
Ideal for food and beverage, mechanical, automotive, and household applications, this is our resin of choice for manufacturing toy parts, as well as various gears and bearings. It works especially well for plastic gears, as it greatly minimizes the friction resulting from contact.
Celcon® is frequently used in “point-of-contact” pieces, parts that physically touch another surface. Common point-of-contact pieces include those used on the bottom of couches to allow for smooth sliding across the floor, as well as guitar picks, pinch valves, and plastic buckles. This versatile thermoplastic is also used in bearings and bushings, pump and valve parts, manifolds, jigs and fixtures, wear pads, and electrical components.
It should not be used for applications in high-heat environments, however, and is subject to UV degradation.
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.
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.
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.
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 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.
ALIPHATIC POLYAMIDES (PA or PPA)
This Nylon 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.
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.
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.