Diez materiales de moldeo por inyección más comunes

The name of injection molding materials sounds like a term in chemistry class. The abbreviation for polypropylene (PP) is similar to polystyrene (PS). Choosing the right injection molding material also means understanding your application requirements, which may vary between prototyping and production.

Fortunately, you don't need a PhD in chemistry to make the right material choices. Of course, there are many factors to consider, but everything starts from the basics: the names and abbreviations of the main materials, their advantages and disadvantages, typical applications, and common brands and grades.

There are ten commonly used injection molding materials:
● Acrylic (PMMA)
Acrylonitrile butadiene styrene (ABS)
Nylon polyamide (PA)
● Polycarbonate (PC)
● Polyethylene (PE)
● Polyoxymethylene (POM)
● Polypropylene (PP)
Polystyrene (PS)
● Thermoplastic elastomers (TPE)
● Thermoplastic polyurethane (TPU)

For each type of injection molded plastic, the following section explains what you need to know.

Acrylic (PMMA)
PMMA or acrylic, which is a sturdy, transparent thermoplastic, is a lighter weight, shatterproof alternative to glass. Because PMMA is transparent and has excellent optical clarity, it allows for a high percentage of light to pass through.

Advantages and disadvantages of acrylic
Acrylic resin has high tensile strength, can withstand loads, does not absorb odors, and can maintain strict tolerances during injection molding. This material can also resist sunlight and weather, making it suitable for outdoor use. Because it does not degrade when in contact with water, PMMA does not release bisphenol A (BPA), a chemical substance that has adverse effects on human health in many plastics.

Acrylic resin has some important limitations. They are more expensive than glass and more prone to scratches. They are also easily stained by grease and oil. In addition, for some industrial applications, the usage temperature of PMMA is too low. The acrylic resin used for injection molding lacks strong solvent resistance and is prone to stress cracking under particularly heavy loads.

PMMA application and level
Acrylic resin is used in windows, greenhouses, solar panels, bathroom casings, and other transparent components for building and lighting applications.

Universal acrylic acid is the cheapest type of PMMA used for commercial purposes rather than engineering applications. Label grade acrylic is 10 times stronger than general acrylic, providing excellent transparency for outdoor signage. Marine grade acrylic acid can resist damage from continuous exposure to water and is often used by shipbuilders.

Acrylonitrile butadiene styrene (ABS)
ABS is an engineering grade thermoplastic with a relatively low melting point and easy molding. This opaque polymer supports the use of colorants and provides different textures and surface treatments. ABS is known for its strength and impact resistance.

Advantages and disadvantages of ABS
ABS is tough, relatively inexpensive, and has good heat resistance, oil resistance, acid resistance, and alkali resistance. Its styrene content gives injection molded parts a glossy and aesthetically pleasing appearance, while its butadiene content can provide excellent toughness even at low temperatures.

Due to its weak resistance to sunlight or weather, ABS is not a good choice for outdoor applications. ABS combustion also produces a large amount of smoke, which has poor resistance to high friction and lacks resistance to solvents such as water.

ABS application and grade
Injection molded ABS is used for electronic components and keyboard buttons, protective headgear, plastic wall panels for power sockets, and automotive components such as instrument panels, wheel covers, and automotive body parts. Other applications include consumer goods, sports equipment, and industrial accessories.

ABS can also be combined with glass fillers to increase strength, or with polycarbonate to improve low-temperature impact resistance. Some suppliers produce filled and unfilled ABS plastics.

Nylon polyamide (PA)
Polyamide (PA) is a large class of materials that can be natural or synthetic. However, nylon, a polyimide, is always synthesized. Nylon injection molding is challenging because this type of polyamide is prone to shrinkage and insufficient filling.

Advantages and disadvantages of nylon
The advantages of nylon PA include toughness and high heat resistance. They also have high wear resistance, good fatigue resistance, and noise reduction performance. With its low coefficient of friction, injection molded nylon is suitable for high friction and wear applications.
Although nylon does not provide inherent flame retardancy and can burn quickly, flame retardant versions can be used. Similarly, although nylon can be degraded by sunlight, UV stabilizers can be added to improve performance. In addition, the material has poor resistance to strong acids and bases.

Nylon application and grade
Nylon is commonly used for sturdy mechanical components such as bearings, bushings, gears, and rails. It is also an ideal choice for shell and snap closure, threaded inserts, power filming, fixtures, and fixing devices. Other applications range from toothbrushes and wheels to medical implants and electrical connectors.

Although nylon is the name for a specific type of polyamide developed by DuPont, this nylon polyamide can also be obtained from other companies. Today, there are four main grades of nylon: nylon 66, 11, 12, and 46. The mechanical performance varies slightly for each level.
Nylon 66 has a higher melting point and stronger acid resistance, making it suitable for chemical processing applications.
Nylon 11 has higher resistance to dimensional changes due to its higher moisture resistance. It is used for outdoor applications.
Nylon 12 has the lowest melting point and relatively good water resistance.
Nylon 46 operates at a higher temperature than other grades of nylon. Applications include engines and transmissions
Nylon grade can be filled with glass to improve mechanical strength.

Polycarbonate (PC)
Polycarbonate (PC) plastic is a naturally transparent, sturdy, and tough material. Their characteristics are similar to PMMA, but polycarbonate maintains its physical properties over a wider temperature range. After coloring, the PC will maintain its color and strength over time.

Advantages and disadvantages of polycarbonate
Polycarbonate is very durable, 250 times stronger than glass. With its predictable and uniform mold shrinkage, this injection molding material can provide precise dimensional control. PC plastic is also lightweight and has excellent optical properties to support light transmission.

Because it contains BPA, it is not recommended to use injection molded polycarbonate for food preparation or storage. It also requires a higher processing temperature, which will increase the molding cost. Polycarbonate is also not scratch resistant.

PC application, level
Polycarbonate is used for mechanical protective devices, transparent or colored windows, diffusers, light tubes for light-emitting diodes (LEDs), and transparent tubes. This material can also be used to produce transparent molds for polyurethane and silicone castings.
Polycarbonate can fill glass and composite with ABS to improve impact resistance. Some grades contain relatively small percentages of stainless steel fibers.

Polyethylene (PE)
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, as it controls other material properties, so this measurement is important. HDPE and LDPE both have useful properties such as chemical resistance, but they differ in their respective hardness, flexibility, melting point, and optical transparency. PET plastic is not defined by density.

Advantages and disadvantages of polyethylene
HDPE, LDPE, and PET are all low-cost plastics that can prevent moisture and chemicals. LDPE is softer and more flexible than HDPE, which is an opaque material. Like LDPE, PET can be as transparent as glass. Engineers and designers like these materials because they offer multiple choices in terms of optical clarity and other properties.

PE plastic is limited by its poor UV resistance and cannot withstand high usage temperatures. HDPE parts with a thickness less than 0.020 inches are difficult to form. It is difficult to achieve tight tolerances for injection molded LDPE. PET will absorb a large amount of water and require resin drying, which will increase production costs.

PE application and grade
PE plastic is famous for its use in milk bottles (HDPE), plastic films (LDPE), and water bottles (PET); However, these products are not injection molded. They are made using different types of molding called blow molding. Examples of injection molded PE include children's toys, toolboxes, wire and cable insulators, and medical equipment components.
PE plastics have numbered grades, and larger numbers usually indicate higher density. For example, HDPE 500 has a higher density than HDPE 300. Both grades have a higher density than LDPE, which also uses a grade numbering system.

Polyoxymethylene (POM)
Polyoxymethylene (POM) is an engineering plastic, also known as acetal. It can be injection molded into parts that require low friction, high stiffness, and excellent dimensional stability. Because they have a highly crystalline structure, POM plastics are naturally opaque and white.

Advantages and disadvantages of polyoxymethylene
Injection molded POM combines excellent rigidity, thermal stability, and low friction coefficient. It also has low water absorption and good chemical resistance. There are two main types of POM plastics to choose from: homopolymers and copolymers. This allows engineers and designers to choose acetal materials with different characteristics.

POM has low impact strength and very high thermal expansion rate in its pure form. The shrinkage rate of the mold is relatively high, and acetal is not resistant to ultraviolet rays. POM plastics, as homopolymers, provide higher hardness and tensile strength. However, all POM plastics (homopolymers and copolymers) cannot meet the fire resistance rating of UL 94 and other standards.

POM application, level
Due to its low friction coefficient, injection molded POM is suitable for bearings, gears, conveyor belts, and pulleys. Other applications include fasteners, eyeglass frames, cutting tools and gun parts, locking systems, and high-performance engineering components.
POM uses glass fiber or mineral reinforced grades to improve strength and stiffness. Compounds reinforced with these two materials can provide excellent mechanical performance balance.

Polypropylene (PP)
Polypropylene (PP) has similar characteristics to polyethylene (PE), but is harder and more heat-resistant. It is the second most commonly used plastic in the world. Although the density of polypropylene varies with the variation of fillers, pure PP is the lowest density commercial plastic.

Advantages and disadvantages of PP
Polypropylene plastic provides good chemical resistance and maintains 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 polypro (sometimes also known as this type of plastic) can be recycled up to four times. In addition, recycled PP can be used in combination with other plastic materials.

Injection molded polypropylene degrades under ultraviolet light and is highly flammable. At temperatures above 100 ° C (212 ° F), it dissolves into aromatic hydrocarbons that are harmful to human health, such as benzene and toluene. Because it is difficult to bond, PP is difficult to color; However, pigments can be added to color the material.

PP application, grade
Injection molded polypropylene has various consumer, commercial, and industrial applications. Examples include children's toys, storage containers, sports equipment, packaging, appliances, and power tool bodies.

PP plastic can be filled with fiberglass to improve dimensional stability, stiffness, strength, and resistance to warping. The grades include high crystalline polypropylene (HcPP), which has higher stiffness than ordinary polypropylene.

Polystyrene (PS)
Polystyrene (PS) is a commercial plastic with two basic types used for injection molding:
● General purpose polystyrene (GPPS)
High impact polystyrene (HIPS)

GPPS is brittle and has lower dimensional stability than HIPS. HIPS is compounded with butadiene rubber to enhance its material properties. GPPS also has a glass like transparency, while HIPS is opaque. Both types of polystyrene are very suitable for injection molding because they have predictable and uniform shrinkage rates.

Advantages and disadvantages of PS
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 disinfect medical equipment. Injection molded polystyrene also has good chemical resistance to diluted acids and bases.

Polystyrene is flammable, susceptible to UV degradation, and is susceptible to erosion by hydrocarbon solvents such as benzene and kerosene. Because it is brittle, GPPS is prone to cracking. Although injection molded polystyrene is recyclable, it is not biodegradable.

PS application, level
Polystyrene is used in medical, optical, electrical, and electronic applications. Due to its higher impact strength, HIPS is often used in conjunction with electrical appliances and equipment. Injection molded GPPS is used for plastic toys, boxes, containers, and pallets.
Polystyrene can be filled with glass to increase strength, or copolymerized with acrylic acid to enhance transparency and improve 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 properties of rubber, its processing method is the same as plastic. The elasticity of TPR is part of its appeal to designers and engineers. TPE is also recyclable and can be recycled six times. In addition, other recycled materials can be mixed together to produce TPE.

Advantages and disadvantages of TPE
Thermoplastic elastomers can be stretched to moderate elongation. After eliminating this pressure, they almost returned to their original shape. TPE also has a shorter molding cycle, supports secondary molding options, and is easier to shape and cheaper than liquid silicone rubber (LSR).

However, under continuous pressure, TPE is prone to creep, which is a trend of permanent deformation of solid materials. This material often loses its rubber properties at higher temperatures and is much more expensive than other injection molding materials.

TPE application, level
Injection molded TPE is used in footwear, medical devices, automotive parts, and pet products. Automotive applications include wind and rain seals and shock and dust covers. Medical applications include breathing tubes, valves, catheters, and ventilation masks.

Thermoplastic polyurethane (TPU)
Thermoplastic polyurethane (TPU) is a type of thermoplastic elastomer (TPE) that, like other TPEs, has elasticity similar to rubber; However, injection molded TPU has higher hardness and can be used as a substitute for hard rubber. TPU is usually chosen instead of TPE because TPU is more suitable for extreme temperatures and chemical resistance. On the other hand, TPE is softer and more flexible.

Advantages and disadvantages of TPU
Compared with other TPEs, TPU has higher wear resistance, chemical resistance, grease, oil, and high temperature performance. Thermoplastic polyurethane produced by injection molding also has good load-bearing capacity, making it suitable for materials exposed to ozone environments.

TPU may be too hard or lack the required flexibility for certain injection molded parts. Thermoplastic polyurethane is often more expensive and requires drying before processing. Due to the short shelf life of certain brands, injection molding companies may have to dispose of them before use.

TPU application, level
Injection molded TPU is used for footwear, washers, casters, and sports equipment. Applications also include casings or casings for electronic and medical devices. In medical applications, TPU is sometimes used instead of polyvinyl chloride (PVC), which is a plastic that may cause skin irritation.

Thermoplastic polyurethane has commercial grade, medical grade, and industrial grade. TPU materials are mainly divided into three categories: polyester, polyether, and polycaprolactone.

Mixed injection molding materials
Although they are the most common types, the materials listed above are not your only choice. According to your specific requirements, you can also choose a mixed plastic that combines the best performance of two different polymers. There are multiple mixtures to choose from, but the most common types are PC/ABS, PC/PBT, and PPE/PS.

PC/ABS
PC/ABS is a mixture of polycarbonate (PC) plastics and acrylonitrile butadiene styrene (ABS). It is sturdy, hard, heat-resistant, and has a low shrinkage rate, which can reduce injection molding defects. This mixture is used for glove boxes in the automotive industry and laptop display cases in the electronics industry.

PC/PBT
PC/PBT is a mixture of PC plastic and polybutylene terephthalate (PBT), which is an engineering polymer used for insulation in the electrical and electronic industries. PC/PBT combines chemical resistance, temperature resistance, and mechanical strength very well. Its performance can be further enhanced by providing flame retardant or UV resistant additives.

PPE/PS
PPE/PS is a mixture of polyphenylene ether (PPE) and polystyrene (PS). It has excellent dimensional stability, low mold shrinkage, low water absorption, and excellent stability in hot and cold water. Injection molded PPE/PS is used in fluid engineering, environmental engineering, and drinking water applications.

Special injection molding materials
In addition to blending materials, injection molding also uses various special materials. The most common types are PEI, PBT, PEEK, LCP, and PVC.

PEI
Polyetherimide (PEI) is a heat-resistant thermoplastic that combines stiffness and stability, as well as low flammability and low smoke generation. The environmental resistance and high impact strength of PEI make it an ideal choice for medical components and parts in automotive transmission and lighting systems.

PBT
Polybutylene terephthalate (PBT) has low melt viscosity and is an excellent material for forming thin section parts. PBT also exhibits excellent creep resistance, which describes the trend of slow deformation of materials after prolonged exposure to high levels of stress. The applications of PBT include keyboards, switches, and distribution boxes.

PEEK
Polyether ether ketone (PEEK) is an engineering plastic commonly used in medical applications because it can resist gamma radiation and high-pressure sterilization, both of which are used for sterilization. PEEK has excellent mechanical properties, resistance to chemicals and thermal degradation, and can withstand long-term liquid immersion.

LCP
Liquid crystal polymers (LCP) are used for injection molding of thin-walled and very small components. LCP can also resist gamma radiation, steam high-pressure sterilization, and most chemical disinfection methods. In addition to medical equipment, these special plastics are also used for injection molded sockets in integrated circuits (ICs).

PVC
Polyvinyl chloride (PVC) is a lightweight, recyclable, and relatively inexpensive plastic that combines environmental resistance with excellent tensile strength. This sturdy and hard specialty plastic is used for automotive parts, pipes, windows, and spools. PVC also has excellent dimensional stability and good color retention.

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