Common Plastics for Thin-Wall Injection Molding
Thin-wall injection molding typically refers to parts with a wall thickness ranging from 0.2 to 1.5 mm. This process imposes stringent requirements on the plastic's melt flow rate (MFR), mechanical strength, and molding shrinkage rate. The ideal material must balance rapid mold filling, good dimensional stability, and resistance to deformation. Below is a professional translation of the simplified guide, covering general purpose, engineering, and modified plastics commonly used in the industry.
1. General Purpose Plastics
General purpose plastics are cost-effective with excellent flow properties, making them the foundation for thin-wall applications, particularly in low-stress scenarios such as packaging and daily necessities.
Polypropylene (PP)
PP exhibits excellent flowability (MFR ranging from 10 to 100 g/10min) and low melt viscosity, enabling rapid filling of thin cavities. It also offers a stable molding shrinkage rate (1.0%~2.5%), ensuring controllable dimensional accuracy. With its low density and good chemical resistance, PP is suitable for disposable thin-wall food containers, beverage cups, and packaging trays. Modified with nucleating agents, PP's rigidity and heat resistance can be further enhanced to meet higher performance requirements.
Low-Density Polyethylene (LDPE)
LDPE possesses extremely high melt flow and low viscosity, minimizing filling resistance. It is particularly suited for ultra-thin parts (thickness < 0.5 mm) such as plastic films, thin shopping bags, and food packaging liners. While it offers good flexibility and resistance to brittleness, its low rigidity limits its use to non-load-bearing structural components.
Polystyrene (PS)
As an amorphous plastic, PS features excellent flowability (MFR 5~30 g/10min) and transparency, resulting in parts with a smooth, glossy surface. It is ideal for thin-wall transparent packaging boxes, stationery casings, and electronic component trays. Standard PS is relatively brittle, so High-Impact Polystyrene (HIPS) is often used for thin-wall appliance housings that require resistance to minor impacts.
2. Engineering Plastics
Engineering plastics offer superior mechanical properties and heat resistance, making them suitable for load-bearing, precision thin-wall structural components used in electronics, automotive, and medical devices.
Acrylonitrile-Butadiene-Styrene (ABS)
ABS balances rigidity, toughness, and flowability (moderate MFR 1~10 g/10min), making it a common choice for thin-wall engineering parts. It provides good dimensional stability and can be easily post-processed (e.g., electroplating, painting). ABS is suitable for thin-wall appliance housings, automotive interior parts, and electronic connector shells. When reinforced with glass fiber, it gains additional strength for use in complex structural components.
Polycarbonate (PC)
PC offers high impact resistance, transparency, and heat resistance. Although the flowability of pure PC is moderate (MFR 2~10 g/10min), copolymerization or flow modifiers can optimize it for thin-wall molding. PC thin-wall parts are strong and weather-resistant, ideal for mobile phone cases, laptop housings, and optical components. However, its low shrinkage rate (0.5%~0.8%) demands precise control over mold temperature and holding pressure to prevent warpage.
Polyamide (PA, Nylon)
PA is a crystalline engineering plastic. Common grades like PA6 and PA66 have excellent flowability (MFR 5~50 g/10min) and low melt viscosity, allowing for fast filling. They also offer high strength and wear resistance. PA thin-wall parts are used in electronic connectors, automotive thin-wall gears, and medical devices. A critical consideration is PA's high water absorption rate; thorough drying is mandatory to avoid defects like silver streaks and bubbles.
Polyoxymethylene (POM)
POM is known for its high rigidity and exceptional wear resistance, combined with good flowability (MFR 1~20 g/10min) and stable shrinkage (1.5%~3.0%). It is suitable for thin-wall precision mechanical parts such as gears, snaps, and connectors. POM exhibits good fatigue resistance for cyclic loading but has limited heat resistance, making it unsuitable for high-temperature environments.
3. Modified Plastics
Modified plastics are engineered through filling, copolymerization, or toughening to optimize specific properties for the unique demands of thin-wall injection molding.
Glass Fiber Reinforced Plastics
Glass fiber reinforced PP, ABS, and PA are preferred for structural thin-wall parts. The addition of glass fibers significantly enhances rigidity, strength, and heat resistance while reducing shrinkage to prevent deformation. For example, glass-filled PA is used in automotive thin-wall bumper brackets, and glass-filled PP is used in structural components for home appliances.
PC/ABS Alloy
PC/ABS alloys combine the high impact resistance of PC with the superior flowability of ABS. They are easier to mold than pure PC and are widely used for complex thin-wall parts like automotive interior trim and electronic device housings.
High-Flow Modified Plastics
Chemically modified plastics with ultra-high MFR (2 to 3 times that of standard grades), such as high-flow PP and ABS, enable the molding of ultra-thin parts (wall thickness < 0.5 mm) with fast cycle times. These materials produce parts with a smooth surface and minimal weld lines, making them ideal for high-volume production of thin-wall packaging and electronic components.
