Introduction
Injection molding is one of the most popular manufacturing processes for producing plastic parts and products at scale in China. The process involves injecting molten plastic material into a mold cavity where it cools and solidifies into the final part shape.
With such a versatile process, the material selection plays a crucial role in determining the characteristics and quality of the final product. There are several types of plastics that can be used for China injection molding, each with their unique properties, advantages and limitations.
This article provides a comparative analysis of the most common injection molding materials used in the Chinese manufacturing industry – thermoplastics, thermosets and elastomers. We will examine the key characteristics, benefits and applications of each material type to help you make an informed decision for your product requirements.
Overview of Injection Molding Materials
The three broad categories of plastics used for injection molding in China are:
Thermoplastics
Thermoplastics are the most common type of injection molding material. They become pliable or moldable above a specific temperature and solidify upon cooling. This property allows thermoplastics to be reheated, reshaped and recycled repeatedly.
Common thermoplastics used in China include polyethylene (PE), polypropylene (PP), polystyrene (PS), acrylonitrile butadiene styrene (ABS), polyamide (nylon), polyethylene terephthalate (PET) and polycarbonate.
Thermosets
Unlike thermoplastics, thermoset plastics can only be heated and shaped once. They undergo a permanent chemical change during the curing process to form an irreversible, highly cross-linked polymer structure. As a result, thermosets cannot be recycled or remolded after the initial forming.
Common thermosetting materials include phenolic, epoxy resin, unsaturated polyester resin and silicone.
Elastomers
Elastomers exhibit rubber-like elasticity and flexibility. They can stretch under tension and quickly regain their original shape once the load is removed. Thermoplastic elastomers (TPE) and vulcanized rubber are the two types commonly processed via injection molding.
Now that we have an overview of the different material categories, let’s examine the key characteristics and applications of each type in closer detail. This will provide helpful insights for selecting the right injection molding plastic based on your product requirements.
Properties and Applications of Thermoplastics
Thermoplastics account for over 90% of all injection molded plastics produced in China due to their versatility, recyclability and wide range of beneficial properties. Let’s look at some of the most commonly used thermoplastic polymers:
Polyethylene (PE)
Polyethylene is a lightweight, low friction plastic with excellent chemical resistance and electrical insulating properties. It also has good impact strength even at colder temperatures.
Key applications of PE in injection molding include:
- Food and liquid containers
- Toys
- Automotive and appliance parts
- Packaging film and bags
The high molecular weight HDPE and UHMW grades are commonly used in China for large size containers and drums, crates, bins, pails, caps and lids.
Polypropylene (PP)
Polypropylene has high rigidity and heat resistance with a waxy surface texture. It’s chemically inert, has good fatigue resistance and low moisture absorption.
Common applications of PP in injection molding:
- Packaging containers
- Automotive components
- Appliance housings
- Industrial fibers
- Syringes, medical devices
The high impact copolymer variation allows PP to be modified for improved cold temperature performance.
Polystyrene (PS)
Polystyrene is an inexpensive, transparent and easily colored/tinted material. It has good dimensional stability but is more prone to cracking under stress.
Typical injection molded products using PS:
- Packaging boxes and trays
- Consumer electronics casings
- Housewares and kitchenware
- Toys and novelty goods
The high impact (HIPS) and super high impact (SHIPS) grades are modified for improved ductility and fracture resistance.
Acrylonitrile Butadiene Styrene (ABS)
ABS combines the strength and rigidity of acrylonitrile and styrene polymers with the toughness and durability of polybutadiene rubber. It has excellent dimensional stability.
Common injection molded applications include:
- Automotive body panels and trims
- Appliance housings
- Office equipment casings
- Piping and fittings
ABS is widely used as an engineering thermoplastic in China due to its superior mechanical properties.
Polyamide (Nylon)
Polyamides exhibit high strength and thermal stability. Nylon is inherently flexible, abrasion resistant and has good chemical resistance.
Typical uses include:
- Gears, cams, bearings
- Automotive engine parts
- Food processing equipment
- Plumbing supplies
- Appliance components
Nylon grades like Nylon 6 and Nylon 66 containing glass fiber reinforcement have very high rigidity, strength and heat resistance.
Polyethylene Terephthalate (PET)
PET is stiff, strong and transparent. It exhibits good gas and moisture barrier properties. It is also recyclable and FDA approved.
Common injection molded PET applications:
- Beverage bottles
- Food packaging
- Clamshell packaging
- Microwave oven trays
Amorphous PET is popular for transparent injection molded containers and parts requiring high stiffness.
Polycarbonate (PC)
Polycarbonate has extremely high impact and heat resistance. It also demonstrates good dimensional stability across a wide temperature range.
Typical uses include:
- Eyeglasses, face shields
- Automotive lenses
- Electronics housings
- Medical devices and labware
Polycarbonate grades are available with UV protection for outdoor applications. Metal plated PC resins provide an attractive chrome-like finish for decorative parts.
This covers some of the major thermoplastic materials injection molded in high volumes across China. Each material has specific mechanical, thermal, electrical and chemical properties that make it suitable for certain applications.
Now let’s look at two other plastic resin categories – thermosets and elastomers, which also serve important roles in injection molding manufacturing.
Properties and Uses of Thermosets
While thermoplastics are the most widely used, thermosets make up around 5% of all plastic fabrication in China. Their cross-linked structure and high thermal stability lend unique advantages:
Phenolic Resin
Phenolic or phenol-formaldehyde resins are known for heat, flame and chemical resistance. They have very low moisture absorption. Phenolics are commonly used in:
- Motor and generator insulation
- Electrical switchgear components
- Automotive brake and clutch pads
Phenolics can withstand prolonged high temperature exposure above 150°C without deforming.
Epoxy Resin
Epoxies demonstrate very low shrinkage and excellent adhesion to inserts and substrates. They are inherently flame retardant with good chemical resistance.
Typical injection molded epoxy applications:
- Electrical insulators, bushings
- Automotive and aerospace composites
- Adhesives, coatings, primers
- Casting and tooling compounds
Epoxies have very high flexural strength and are dimensionally stable across a wide temperature range.
Unsaturated Polyester Resin
UPR resins are versatile, economical and widely used in China. They cure quickly with low shrinkage when combined with styrene. UPR has good chemical resistance and weatherability.
Common injection molded parts made from UPR:
- Bathroom fixtures
- Electrical components
- Automotive body filler
- Fiberglass boat hulls
UPR resins can be reinforced with glass fibers for significantly improved structural rigidity.
Silicone Rubber
Silicones have exceptionally high heat resistance, ranging up to 300°C. They are inherently flexible and compressible with excellent electrical insulation.
Typical injection molded silicone applications:
- Oven mitts, pot holders
- Medical parts and gaskets
- Spark plug boots
- Electronic potting compounds
Platinum-cured silicone grades are commonplace for injection molding food contact and medical components in China.
As we’ve seen, each thermoset plastic has unique properties suited for niche applications that involve high temperatures, corrosion resistance or electrical insulation.
Finally, let’s examine the key characteristics of elastomeric injection molding materials.
Advantages of Elastomers
Making up around 5% of plastics injection molding in China, elastomers provide enhanced flexibility and resilience. The two main types used are:
Thermoplastic Elastomers (TPE)
TPEs combine the processability of thermoplastics with the elastic performance of rubbers. They can be customized for hardness and flexural modulus.
Common injection molded applications for TPEs:
- Automotive seals and gaskets
- Consumer goods and sporting gear
- Medical equipment housing
- Appliance parts and cables
TPEs allow products to be designed with both rigid and soft, flexible sections.
Vulcanized Rubber
Vulcanized rubber compounds provide high tear and abrasion resistance with good tensile strength. They can withstand repetitive flexing.
Typical injection molded rubber products:
- O-rings, seals, grommets
- Bumpers, pads, feet
- Automotive body seals
- Jar rings, lid seals
Adding reinforcing fillers like carbon black improves rubber hardness, modulus and chemical resistance.
This concludes our broad overview comparing the different categories of injection molding materials commonly used for manufacturing in China.
Key Considerations for Selecting an Injection Molding Material
Now that we’ve examined the properties and applications of the most popular injection molding plastics, here are some key factors to consider when selecting your ideal material:
- Operating temperature range – Heat deflection temperature and thermal stability are critical
- Chemical resistance – Depending on fluids and environment the parts are exposed to
- Structural rigidity vs. flexibility – Based on strength, impact resistance and elasticity needs
- Colorability, clarity and finish – Aesthetic qualities and ability to match your product branding
- Flammability rating – According to UL94 and oxygen index standards
- Moisture absorption – For applications exposed to condensation, humidity and water
- Electrical properties – Dielectric strength and insulating capability
- UV and weathering resistance – For outdoor exposure and long-term durability
- FDA compliance – For food contact, medical devices and pharmaceutical needs
Additionally, factors like cost, production volume and ease of processing also affect the suitability of a given plastic resin for your specific application. Prototyping and testing of different materials is highly recommended during the design phase.
Conclusion
We have explored the broad range of injection molding materials available for manufacturing in China along with their key characteristics and typical applications. Thermoplastics make up the vast majority of injection molded plastics owing to their ease of processing, recyclability and diverse mechanical properties. But engineered thermosets and elastomers also serve important roles where high heat, chemical or electrical resistance is needed.
There are many factors that ultimately determine the optimum injection molding material for your product – operating conditions, strength, appearance, regulatory compliance and cost considerations all play a role. We hope this detailed comparison will help provide a firm basis for making an informed material selection, as you develop parts and products leveraging the extensive injection molding capabilities available in China.
