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Plastic injection molding is a widely used manufacturing process that involves injecting molten plastic material into a mold to create a specific shape or product. One of the key factors that determine the success of this process is the choice of the right plastic material for the desired application. With so many options available, it can be overwhelming to select the right material for your project. In this blog, we will discuss the 10 common plastic injection molding materials, their properties, and their applications. Whether you are a product designer, engineer, or manufacturer, this blog will provide you with valuable insights into the different plastic materials available and help you make informed decisions. So, let's dive in and explore the world of plastic injection molding materials!
There are 10 commonly used injection molding materials:
● Acrylic (PMMA)
● Nylon poly (PA)
● Polycarbonate (PC)
● Polyethylene (PE)
● Polyoxymethylene (POM)
● Polypropylene (PP)
● Polyethylene soft (PS)
● Thermoplastic Elastomer (TPE)
● Thermoplastic polyethylene oxide (TPU)
PMMA, or acrylic, is a strong, clear thermoplastic that is a lighter weight, shatterproof alternative to glass. Because PMMA is transparent and has excellent optical clarity, it allows a high percentage of light to pass through.
Acrylonitrile Butadiene Styrene (ABS)
ABS is an engineering-grade thermoplastic with a relatively low melting point that makes it easy to shape. This opaque polymer supports the use of colorants and offers different textures and finishes. ABS is known for its strength and impact resistance.
ABS is tough, relatively cheap, and has good resistance to heat, oil, acids, and alkalis. Its styrene content gives injection molded parts a glossy, aesthetic appearance, while its butadiene content provides excellent toughness even at low temperatures.
Since ABS is not very resistant to sunlight or weather, it is not a good choice for outdoor applications. ABS also produces a lot of smoke when it burns, has poor resistance to high friction, and has little resistance to solvents such as water.
Injection molded ABS is used in electronic components and keyboard keys, protective headgear, plastic wall panels for electrical outlets, and automotive components such as dashboards, wheel housings, and auto body parts. Other applications include consumer goods, sports equipment and industrial accessories.
ABS can also be combined with glass fillers for strength, or polycarbonate for low temperature impact resistance. Some suppliers make filled and unfilled ABS plastic.
Nylon polyamide (PA)
Polyamides (PA) are a large class of materials that can be either natural or synthetic. However, nylon, a type of polyimide, is always synthetic. Injection molding nylon is challenging because this polyamide tends to shrink and be underfilled.
It has good toughness and high heat resistance. They also have high wear resistance, good fatigue resistance and noise dampening properties. With its low coefficient of friction, injection molded nylon is suitable for high friction and wear applications.
While nylon doesn't offer inherent flame resistance and can burn quickly, flame retardant versions are available. Also, while nylon is degraded by sunlight, UV stabilizers can be added to improve performance.
The material is less resistant to strong acids and bases.
Nylon is commonly used in strong mechanical components such as bearings, bushings, gears and slides. It is also ideal for housings and snap closures, threaded inserts, power snaps, jigs and fixtures. Other applications range from toothbrushes and wheels to medical implants and electrical connectors.
There are four main grades of nylon: Nylon 66, 11, 12 and 46. Each grade has slightly different mechanical properties.
Has a higher melting point and greater acid resistance for use in chemical processing applications.
Has higher resistance to dimensional changes due to its higher moisture resistance. It is used for outdoor applications.
Has the lowest melting point and relatively good resistance to water absorption.
It operates at higher temperatures than other grades of nylon. Applications include engines and transmissions.
Nylon grades can be glass filled for increased mechanical strength.
Polycarbonate (PC) plastic is a strong, tough material that is naturally transparent. Their properties are similar to PMMA, but polycarbonate maintains its physical properties over a wider temperature range. Once tinted, PC retains its color and retains its strength over time.
Polycarbonate is extremely durable and is 250 times stronger than glass. With its predictable and uniform mold shrinkage, this injection molding material provides precise dimensional control. PC plastic is also lightweight and has excellent optical properties to support light transmission.
Because it contains BPA, injection molded polycarbonate is not recommended for food preparation or storage. It also requires higher processing temperatures, which makes molding more expensive. Polycarbonate is also scratch-resistant.
Polycarbonates are used in mechanical guards, clear or tinted windows, diffusers and light pipes for light-emitting diodes (LEDs) and clear pipes. This material can also be used to produce clear molds for polyurethane and silicone castings.
Polycarbonate can be filled with glass and compounded with ABS for improved impact resistance. Some grades contain relatively small percentages of stainless-steel fibers.
Polyethylene is the most commonly used plastic in the world. There are mainly three types:
● High density (HDPE, PEHD)
● Low Density (LDPE)
● Polyethylene terephthalate (PET, PETE)
PE is the only commercial polymer that can be selected based on its density, so this measurement is important because it controls other material properties. Both HDPE and LDPE have useful properties such as chemical resistance, but they differ in their hardness, flexibility, melting point and optical clarity. PET plastic is not defined by density.
HDPE, LDPE, and PET are all low-cost plastics that resist both moisture and chemicals. LDPE is softer and more flexible than HDPE, which is an opaque material. Like LDPE, PET can be as clear as glass. Engineers and designers love these materials because they offer a variety of options in terms of optical clarity and other properties.
PE plastics are limited by poor UV resistance and cannot withstand high service temperatures. HDPE parts less than 0.020 inches thick are difficult to form. Tight tolerances are difficult to achieve with injection molded LDPE. PET absorbs a lot of water and requires the resin to dry, which increases production costs.
PE plastic is best known for use in baby bottles (HDPE), plastic film (LDPE) and water bottles (PET); however, these products are not injection molded. They are made using a different type of molding called blow molding. Examples of injection molded PE include children's toys, tool boxes, wire and cable insulation, and medical device components.
PE plastics have numbered grades, with higher numbers generally indicating higher density. For example, HDPE 500 is denser than HDPE 300. Both grades are denser than LDPE, which also uses a grade numbering system.
Polyoxymethylene (POM) is an engineering plastic also known as acetal. It can be injection molded into parts requiring low friction, high stiffness and excellent dimensional stability. Because of their highly crystalline structure, POM plastics are naturally opaque and white.
Injection molded POM combines excellent rigidity, thermal stability and low coefficient of friction. It also has low water absorption and good chemical resistance. There are two main types of POM plastics available: homopolymers and copolymers. This allows engineers and designers to choose acetal materials with different properties.
In its pure form, POM has low impact strength and very high thermal expansion. Mold shrinkage is relatively high, and acetal is not resistant to UV rays. POM plastic as a homopolymer offers higher stiffness and tensile strength. However, all POM plastics (homopolymers and copolymers) are not fire rated according to standards such as UL 94.
Due to its low coefficient of friction, injection molded POM is suitable for bearings, gears, conveyor belts and pulleys. Other applications include fasteners, eyeglass frames, knife and firearm parts, locking systems and high-performance engineered components.
POM comes in glass fiber or mineral reinforced grades for strength and stiffness. Compounds reinforced with these two materials offer an excellent balance of mechanical properties.
Polypropylene (PP) has similar properties to polyethylene (PE), but is stiffer and more heat resistant. It is the second most commonly used plastic in the world. Although the density of polypropylene varies with the filler, pure PP is the lowest density commercial plastic.
Polypropylene plastic offers good chemical resistance and retains its shape after twisting or bending. PP also has a high melting point and will not degrade when exposed to moisture or water. Injection molded polypore, as this plastic is sometimes called, is also recyclable up to four times. Furthermore, recycled PP can be combined with other plastic materials.
Injection molded polypropylene degrades under UV light and is extremely flammable. At temperatures above 100° C (212° F), it dissolves into aromatic hydrocarbons such as benzene and toluene, which are harmful to human health. PP is difficult to color because it is difficult to bond; however, pigments can be added to color the material.
Injection molded polypropylene has a variety of consumer, commercial and industrial applications. Examples include children's toys, storage containers, sporting goods, packaging, appliances, and power tool bodies.
PP plastics can be filled with glass fibers for dimensional stability, stiffness, strength and resistance to warping. Grades include high crystalline polypropylene (HcPP), which has higher stiffness than ordinary polypropylene.
Polystyrene (PS) is a commodity plastic that comes in two basic types for injection molding:
● General Purpose Polystyrene (GPPS)
● High Impact Polystyrene (HIPS)
GPPS is brittle and has lower dimensional stability than HIPS, and HIPS is compounded with butadiene rubber to enhance its material properties. GPPS also has glass-like transparency, while HIPS is opaque. Both types of polystyrene are well suited for injection molding because of their predictable and uniform shrinkage.
PS plastic is inexpensive, lightweight, and resistant to moisture and bacterial growth. They also have excellent resistance to gamma radiation and can be used to sterilize medical equipment. Injection molded polystyrene also has good chemical resistance to diluted acids and bases.
Polystyrene is flammable, susceptible to UV degradation, and attacked by hydrocarbon solvents such as benzene and kerosene. Because it is brittle, GPPS cracks easily. Although injection molded polystyrene is recyclable, it is not biodegradable.
Polystyrene is used in medical, optical, and electrical and electronic applications. Due to its higher impact strength, HIPS is often used with appliances and equipment. Injection molded GPPS is used in plastic toys, boxes, containers and trays.
Polystyrene can be glass-filled for strength or copolymerized with acrylic for clarity and improved chemical and UV stability.
Thermoplastic Elastomer (TPE)
Thermoplastic Elastomer (TPE) or Thermoplastic Rubber (TPR) is a mixture of rubber and plastic materials.
Although TPE has the characteristics and performance of rubber, it is processed in the same way as plastic.
The flexibility of TPR is part of what makes it attractive to designers and engineers. TPE is also recyclable and can be recycled six times. Additionally, other recycled materials can be blended together to produce TPE.
Thermoplastic elastomers can be stretched to moderate elongations. When this stress is removed, they almost return to their original shape. TPE also offers shorter molding cycles, supports overmolding options, and is easier and less expensive to mold than liquid silicone rubber (LSR).
Under sustained stress, however, TPE is prone to creep, the tendency of a solid material to deform permanently. This material also tends to lose its rubbery properties at higher temperatures and is much more expensive than other injection molding materials.
Injection molded TPEs are used in footwear, medical devices, auto parts and pet products. Automotive applications include weather sealing and shock and dust covers. Medical applications include breathing tubes, valves, catheters and ventilation masks.
Thermoplastic Polyurethane (TPU)
Thermoplastic polyurethane (TPU) is a thermoplastic elastomer (TPE) that, like other TPEs, has rubber-like elasticity; however, injection molded TPU has a higher hardness and can be used as a replacement for hard rubber. TPU is often chosen over TPE because TPU is better suited for temperature extremes and chemical resistance. TPE, on the other hand, is softer and more flexible.
Compared to other TPEs, TPU has higher resistance to abrasion, chemicals, grease, oil and high temperature performance. Injection molded TPU also has good load-bearing capabilities and is suitable for use in environments where the material is exposed to ozone.
TPU can be too stiff or lack the required flexibility for some injection molded parts. TPU also tends to be more costly and requires drying before processing.
Injection molded TPU is used in footwear, gaskets, casters and sporting goods. Applications also include enclosures or enclosures for electronic and medical equipment. In medical applications, TPU is sometimes used in place of polyvinyl chloride (PVC), a plastic that can cause skin irritation.
TPU is available in commercial, medical and industrial grades. TPU materials are mainly divided into three categories: polyester, polyether and polycaprolactone.
By understanding the key differences between these materials, product designers, engineers, and manufacturers can make informed decisions and select the best material for their specific application. Whether you are producing consumer goods, automotive parts, medical devices, or any other type of product, the right material can help you achieve the desired performance, aesthetics, and cost-effectiveness.
Overall, plastic injection molding continues to be a widely used and practical manufacturing process, thanks to its versatility, efficiency, and ability to produce high-quality products. With the knowledge gained from this blog, you can confidently choose the right plastic material for your next injection molding project and bring your product to life.
Alpine mold has been committed to solving all problems related to the injection molding industry for customers. Whether it is the choice of materials or the problems that may arise in injection molding, we have good solutions to escort your projects.