Injection molding can process a wide range of materials. In addition to metals and thermosets, injection molding is suited to a large number of thermoplastic polymers, from commodity polymers like ABS to high-performance materials like PEEK.

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Engineers will select a thermoplastic based on the requirements of the molded part. Some moldings need to be impact-resistant, some need to be food-safe, while others need to be flexible. Another property that engineers and product designers often require is heat resistance. Heat-resistant molded parts can be used in a range of situations, such as near engines, within powerful electronic parts, and in extreme outdoor environments.

So which are the best heat-resistant thermoplastics for injection molding? This article discusses some of the most popular thermally resistant injection molding materials, noting their respective advantages and applications, as well as discussing the complexities of using such materials during the injection molding process.

Premium temperature-resistant plastics

The most temperature-resistant injection molding plastics come at a high cost but exhibit excellent thermal performance, both in terms of their continuous service temperature (CST) &#; how much heat they can withstand over long periods of time &#; and their resistance to even higher temperatures in short bursts.

1. PEEK

Maximum CST: 260 °C

Polyether ether ketone (PEEK) is a high-performance polymer used for engineering purposes. With a melting temperature of 343 °C, it is as robust and strong as it is difficult to process. Its extremely high CST makes it suitable for applications in demanding industries like aerospace. Example PEEK parts include bearings, pumps, and compressor plate valves.

2. PPS and PPSU

Maximum CST: 220 °C and 210 °C

Polyphenylene sulfide (PPS) is another high-performance polymer with engineering applications. As well as having a high CST, it exhibits excellent UV and chemical resistance, making it suitable for outdoor use. PPS parts include gaskets, seals, and electrical insulation. Polyphenylsulfone (PPSU) is slightly weaker and less thermally resistant, but exhibits greater hardness.

3. PEI

Maximum CST: 170 °C

Polyetherimide (PEI), often known by the brand name Ultem, is a high-performance polymer often used as a slightly more affordable alternative to PEEK. As well as performing well in high temperatures, it offers good strength, ductility, and chemical resistance. Applications of PEI include medical components, throttle bodies, and thermostat housings.

Affordable temperature-resistant plastics

Engineers sometimes need temperature-resistant moldings that do not need to be of aerospace-grade quality. In these cases, they can choose from more affordable temperature-resistant polymers with good engineering properties. (For the lowest possible budgets, engineers might select a commodity polymer like ABS, which has a reasonable CST of 90 °C but which is also sold in various &#;high heat&#; ABS formulations resisting up to 110 °C.)

1. PC

Maximum CST: 140 °C

Polycarbonate (PC) is often used for its high-quality appearance &#; especially for transparent parts &#; and good impact resistance, but the thermoplastic also offers good heat resistance. PC can be molded for uses in electronics, automotive, and aerospace. It is also used for optical and lighting components like headlamp lenses.

2. PA 66

Maximum CST: 140 °C

Nylon 66 is one of the more heat-resistant polyamides (PA) that is widely used in injection molding. With good mechanical strength and rigidity, nylon 66 has applications in the automotive industry for under-the-hood components like air intake manifolds. Glass-filled PA66 has a slightly higher CST, while PA46 is another good choice for high-temp applications.

3. POM

Maximum CST: 105 °C

Polyoxymethylene (POM) or acetal is another engineering thermoplastic in a lower price bracket than ultra-premium materials like PEEK. It provides good stiffness and low friction, with a relatively high CST. Molded POM can be made into various engineering parts like gears and fasteners, as well as automotive and electronics parts.

Molding considerations

Because the injection molding machine must melt down pellets of the chosen thermoplastics, high-temperature materials are necessarily more difficult to process. However, with the right setup, it is still possible to achieve high-quality moldings using these engineering materials.

For an ultra high-temp plastic like PEEK, the injection molding machine barrel will reach temperatures above 400 °C, with the molds around 160 °C. These high temperatures can pose certain issues, such as residue getting stuck in the barrel feeder areas. High-temp materials like PEEK often necessitate purging of the machine before use of a subsequent molding material.

Another molding consideration with high-temperature plastics is unwanted freezing off of the nozzle or mold gates. If temperatures are not quite high enough, gates or the machine nozzle can freeze off before the mold cavity is completely filled. Larger gates may mitigate this issue if it persists.

Molding high-temperature plastics with 3ERP

3ERP has many years of experience making prototypes and production parts via injection molding, and we can mold parts in the above materials and many more besides. Request a free quote for your next batch of high-temperature plastic parts.

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Types of Plastic Overview

What are the Materials Used in Plastic Injection Molding?

Injection molding is considered to be one of the fastest and most optimized methods of producing large numbers of identical plastic components at one time. Injection molding is used for nearly every consumer plastic product and is the most common plastic manufacturing method around. Because of the wide range of applications and industries where plastics are used, different chemical formulations are required for the plastic injection molding process.

The professionals at Retlaw Industries use a wide variety of plastics when manufacturing our molded products, depending on what type of plastic product our customers need.

Our expert plastic part designers will work on your new or existing design concept to find the best material for your particular application. Whether you need electronic enclosures molded from ABS or pull-out drawer handles made from acetal (POM), our experts will address your needs and help you build the best part possible out of the best materials available.

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Here are some of the plastic materials our experts use in plastic injection molding:

Also known as Plexiglas, acrylic is a hard transparent plastic material often used in electronics and automotive parts. Other forms of acrylic are also used in everyday products due to its natural transparency and coloring properties, everything from eyewear lenses, acrylic paint, and even acrylic nails. Acrylic can also be colorized to be either translucent or opaque.

In commercial applications, acrylic falls under #7 (OTHER). This can include other types of plastics including polycarbonate, polylactic fibers, nylon, and fiberglass. 

Advantages of Acrylic:

• Transparency &#; among the clearest plastics available today
• Weather Resistance &#; resists moisture and ultraviolet discoloration
• Chemical Resistance &#; unaffected by water and weak acids and alkaline solutions
• Surface Hardness &#; good impact strength and rigidity
• Dimensional Stability &#; lends to a predictable final product

ABS plastic is one of the most commonly used plastics in injection molding due to its wide temperature range, good stability, and insulating properties. ABS is commonly found in plastic toys such as Lego bricks, but it&#;s also often used in many types of electronics, tools, and home repair equipment.

Advantages of ABS:

• Impact Resistance &#; rubberlike formulations make ABS resilient to impact
• Surface hardness &#; high rigidity in certain formulations
• Chemical Resistance &#; not affected by alkalis, water, and most inorganic acids
• Uniform Shrinkage &#; good dimensional stability
• Wide Temperature Range &#; resists heat and won&#;t shatter in cold
• Machinability &#; easy to form after cooling

When in need of rigid, heat-resistant plastic, HDPE is the best material to use. Since polyethylene is a food-grade plastic &#; meaning it is safe to use around food &#; this material is commonly manufactured in storage containers, kitchenware, and refrigerator shelving. HDPE is also a good plastic for holding chemical-based products such as cleaning agents, laundry detergent, bleach, and shampoo.

In commercial applications, HDPE falls under #2 (HDPE). 

Advantages of HDPE:

• Sustainable &#; made of 100% recyclable material
• Chemical Resistance &#; resistant to corrosion, rust, and other chemicals
• Heat Resistance &#; doesn&#;t melt or corrode in high temperatures
• Food Grade &#; safe to use as food packaging and equipment
• Inexpensive &#; can be mass-produced at a low price

Nylon is one of the most versatile materials used in plastic injection molding. It&#;s commonly combined with a range of other materials to enhance its characteristics. Thanks to its high melting temperature and low friction properties, it&#;s useful for a wide range of products such as nylon rope, reinforced automotive parts, and even clothing.

Advantages of Nylon:

• Low Friction &#; doesn&#;t heat up under high friction
• Chemical Resistance &#; resistant to corrosion from chemicals
• Abrasion Resistance &#; useful for elastic and clothing applications
• Adaptable &#; can be combined with many other types of plastic materials

Polycarbonate is a useful plastic material for applications needing transparency or high impact resistance. For this reason, polycarbonate is most commonly used in eyewear applications, but it&#;s also used in pipes for LED lights, clear windows, and sporting equipment.

In commercial applications, polycarbonate falls under #7 (OTHER). This can include other types of plastics including acrylic, polylactic fibers, nylon, and fiberglass.

Advantages of Polycarbonate:

• Impact Resistance &#; doesn&#;t scratch or dent under impact
• UV Resistance &#; doesn&#;t corrode or discolor in ultraviolet light
• Transparency &#; can be made into windows and eyewear lenses
• Chemical Resistance &#; doesn&#;t corrode from chemicals
• Rigidity &#; makes for good eyewear and window applications

Polyetherimide, also known as Ultem, is an amorphous material with extremely high heat resistance compared to other plastics. Due to its rigidity and high heat performance, polyetherimide is most commonly used in medical devices, electronics, and industrial plastic parts.

Advantages of Polyetherimide:

• Rigidity &#; hard plastic useful for high-impact industrial applications
• Heat Resistance &#; doesn&#;t melt or warp under high temperatures
• High Tensile Strength &#; resists cracking or breaking in hard environmental conditions
• Flame Resistance &#; isn&#;t flammable and generates low smoke

Also known as Acetal, polyoxymethylene is a semi-crystalline polymer which is very rigid and has a naturally glossy surface, making it a useful material for a wide range of industries. Acetal is most commonly found in automotive applications, household appliances, and electronics.

Advantages of Polyoxymethylene:

• Rigidity &#; stays strong and doesn&#;t bend easily
• Impact Resistance &#; strong and stable enough to resist strong impacts
• Solvent Resistance &#; doesn&#;t corrode or rust due to chemicals and solvents
• Glossy surface &#; smooth, reflective properties

Much like Acetal, polypropylene is a plastic with a naturally glossy surface when properly manufactured. Its chemical resistance and elastic properties make it useful for a wide variety of food-related applications, including plastic kitchenware, dishwasher-safe plates, and storage containers. Polypropylene is also commonly used to make toys, hard luggage containers, and even external car parts.

In commercial applications, polypropylene falls under #5 (PP).

Advantages of Polypropylene:

• Chemical Resistance &#; doesn&#;t react with most bases and acids
• Fatigue Resistance &#; retains its shape after a lot of bending and flexing
• Electrical Resistance &#; strong insulation properties
• Elasticity &#; can bend, flex and deform without actually breaking

Polystyrene is a polymer used in a wide variety of plastic and foam applications across a range of industries. Due to its bending and flexing properties, polystyrene is often used in hinged applications, such as disposable food containers and bottles. It&#;s also widely used to make rigid foam insulation and sheeting for laminate floors.

In commercial applications, polystyrene falls under #6 (PS). 

Advantages of Polystyrene:

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• Optical Clarity &#; transparent resin can be useful for see-through plastic products
• FDA Grade &#; safe to use when packaging food and consumable materials
• Stability &#; rigid material useful for packaging
• Inexpensive &#; can be mass-produced at a low cost

Whatever type of molded plastic you need, the experts at Retlaw Industries can help! Contact us today to get a quote on our professional molding services.