Understanding the 10 Most Common Injection Molding Materials

When it comes to plastic materials for injection molding, the options are vast and varied. From common polymers to specialty plastics and polymer blends, each material has its unique characteristics and processing requirements. This comprehensive guide will walk you through the top 10 plastic injection molding materials, discussing their properties and applications.

Choosing the right plastic injection molding material is pivotal in achieving the desired characteristics for your products. Each type of plastic material offers unique properties, making it suitable for specific applications. These are the most common plastic materials for injection molding:

• acrylonitrile butadiene styrene (ABS)
• polyethylene (PE)
• polypropylene (PP)
• polystyrene (PS)
• polycarbonate (PC)
• poly (methyl methacrylate) (PMMA)
• polyvinyl chloride (PVC)
• nylon (polyamide, PA)
• polyoxymethylene (POM)
• bulk molding compound (BMC)

ABS plastic is a type of thermoplastic engineering plastic known for its excellent mechanical properties, reasonable cost, rigidity, dimensional stability, and ease of molding. It finds wide application in various fields.

ABS is an amorphous polymer without a distinct melting point. It comes in many grades, so parameters should be adjusted accordingly during the injection process, typically above 160°C for molding. ABS exhibits good thermal stability during molding and has a limited range of usable temperatures, which helps prevent degradation or decomposition. However, high temperatures can harm the rubber phase in ABS, so care must be taken. ABS typically starts to decompose above 270°C.

PE (Polyethylene) exhibits good flow characteristics during molding and is hydrophilic, meaning it doesn't require special attention to thermal stability. However, its high molecular compatibility makes it susceptible to deformation.

High-density PE has a specific crystallization temperature, so it's recommended to increase injection pressure and speed. This is especially crucial for thick-walled products, as higher injection speeds can enhance surface gloss, prevent warping, and reduce molding shrinkage. Achieving this requires precise screw design and coordination of backflow.

Loss or damage to the material can lead to a slowdown in feeding during the molding process.

Polypropylene is a crystalline polymer known for its light weight, affordability, non-toxicity, and lack of odor. It offers advantages like corrosion resistance, high temperature tolerance, and strong mechanical strength. Similar to PE, it is also hydrophilic.

However, polypropylene begins to degrade at around 280°C, so it's best to operate at temperatures below 270°C to avoid issues. It exhibits strong molecular orientation, which can cause warping or distortion during low-temperature molding, so this aspect needs attention.

Polypropylene finds wide applications in industries such as medicine, food, chemicals, and daily life.

Polystyrene is one of the earliest plastics to be industrialized. It is valued for its transparency, water resistance, light resistance, chemical resistance, low moisture absorption, excellent electrical properties, affordability, easy dyeing, and ease of molding. As a result, it is widely used in instruments, meters, decoration, lighting, household items, and toys.

Polystyrene has a relative density of 1.05, making it a common choice for injection molding product series due to its close weight-to-volume ratio. It is an amorphous polymer without a distinct melting point, softening around 95°C, becoming fluid between 120 and 180°C, and decomposing above 300°C. Polystyrene has low specific heat capacity, allowing for rapid heating, flow, and cooling, which leads to quick solidification. Its moderate viscosity and good flowability make it easy to mold.

Polycarbonate (PC) is an advanced engineering plastic known for its exceptional properties. It boasts high transparency, outstanding impact toughness, resistance to creep, a broad operating temperature range, good dimensional stability, excellent electrical insulation, weather resistance, and non-toxicity. Because of these attributes, PC finds extensive use in instruments, lighting fixtures, electronic and electrical equipment, and various other fields.

However, PC products have some drawbacks. They are relatively sensitive to notches, making them prone to stress cracking. Additionally, they exhibit slightly lower fatigue resistance and chemical stability.

Polymethyl methacrylate (PMMA), also known as acrylic, is a modern type of plastic known for its excellent transparency, similar to regular glass. It allows about 90-92% of sunlight and 73.5% of ultraviolet rays to pass through. Because of this, PMMA is widely used in many areas such as aircraft, automobiles, buildings, optical and electronic devices, advertising signs, medical equipment, and more.

PMMA is tough but doesn't flow easily, so it's typically processed at low temperatures. To process it effectively, the screw design should increase the compression ratio, creating high material pressure. The rod diameter should be minimized to balance light turning force and strong injection force, ensuring smooth quality and flatness. Slow rotation is advised to prevent the temperature of the material from rising too much.

PMMA is a precise material that requires careful technical processing. During operation, it should be kept in a dust-free environment, with clean funnels and molds, and operators should wear white gloves to maintain cleanliness. PMMA is an amorphous polymer with a glass transition temperature of 105°C, a melting temperature above 160°C, and a decomposition temperature over 270°C, allowing for a wide range of molding temperatures.

Polyvinyl chloride (PVC) is among the most widely used thermoplastics globally. It offers excellent chemical stability, high dielectric strength, oil resistance, flame resistance, moderate mechanical strength, and affordability. These qualities make it a popular choice in agriculture, chemical industry, electronics, construction, light industry, and other sectors.

However, hard PVC is prone to scorching and acid concentration. To avoid these issues, the internal temperature of the pipe should be kept between 170°C to 190°C, with short residence times. The mold temperature should be maintained between 50°C to 60°C, and injection pressure should be maximized. Slow rotation feeding helps prevent temperature rise inside the pipe, and slow injection aids in gas discharge from the mold, requiring enlarged mold vent holes. The screw should be electroplated, and a check valve device is unnecessary. The nozzle hole is typically doubled in size, and each injection should reach the bottom to avoid material stagnation.

Polyvinyl chloride has poorer thermal stability compared to other thermoplastics. It tends to decompose with prolonged exposure to high temperatures, especially in contact with certain metals. Therefore, strict control of molding temperature is crucial. PVC is commonly used to manufacture connectors or pipes for faucets.

Polyamide, often referred to as nylon (PA), is a polymer compound with multiple recurring amide groups on its main chain. It is primarily employed as a load-bearing thermoplastic and stands as one of the most extensively utilized plastics in various industries. Nylon's melt exhibits low viscosity and excellent flowability.

Polyoxymethylene (POM) boasts exceptional mechanical properties, remarkable resistance to creep and stress relaxation, the highest fatigue resistance, and self-lubricating properties among plastics. Its elastic modulus surpasses that of nylon 66, ABS, and polycarbonate. POM features a wide operating temperature range (-40 to 100°C), outstanding abrasion resistance, good resistance to chemical agents and pesticides, low water absorption, dimensional stability, excellent electrical insulation properties, and can be processed through various methods. Additionally, it comes with a relatively low raw material cost. These qualities have led to a rapid expansion in the development and application of polyoxyethylene.

Bulk Molding Compound (BMC) is a thermosetting resin made primarily of special unsaturated polyester. It exhibits excellent electrical insulation properties, heat resistance, flame resistance, high mechanical strength, dimensional stability, corrosion resistance, water resistance, and shrinkage stability. Among various thermosetting molding materials, BMC is considered the highest grade. It finds wide application in various electrical products, components for communication and information equipment, automotive parts, insulation coatings for electric tools, ultra-quiet motors, food utensils, and more.

Here's a table comparing the properties of the above 10 common plastic injection molding materials:

Choosing the right plastic injection molding material for your high-quality products is a critical decision that can significantly impact their overall quality, durability, and performance. By considering factors such as application requirements, material properties, cost considerations, and environmental impact, you can make an informed decision that meets your specific needs. Conducting thorough research, consulting with suppliers, and implementing testing and quality control measures will further enhance the success of your injection molding process.

Injection Molding Machine Supplier

Huarong Group understands the importance of selecting the right materials for injection molding processes. As a leading injection molding machine manufacturer, we are committed to providing comprehensive solutions to meet your manufacturing needs. Contact Huarong today to discover how we can help you achieve exceptional results in your injection molding endeavors.

• Group Name: Huarong Group
• Brand: Huarong, Yuhdak, Nanrong
• Service Offerings: Injection Molding Machine, Vertical Injection Molding Machine, Injection Molding Automation
• Tel: +886-6-7956777  #521
• Address: No.21-6, Zhongzhou, Chin An Vil., Xigang Dist., Tainan City 72351, Taiwan
• Official Website: https://www.huarong.com.tw/

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