Material Classification and Application of Injection Molding Fillers

Injection molding fillers are non-reacting additives dispersed in plastic to modify performance, improve dimensional stability, reduce warpage, and lower production costs. They are widely used in PP, PE, ABS, PA, and other common resins, playing a key role in optimizing product quality and reducing manufacturing costs. The selection of fillers directly affects the mechanical properties, appearance, and processing performance of injection-molded parts. This article summarizes the main types, characteristics, and typical applications of common fillers, providing clear guidance for industrial selection and production, suitable for production managers and technical personnel.

Inorganic Mineral Fillers

Inorganic minerals are the most widely used fillers in injection molding, accounting for over 90% of applications, due to their low cost, wide availability, good compatibility with most resins, and easy processing. Calcium carbonate is the most common and lowest-cost filler, available in heavy (GCC) and light (PCC) types: GCC (100-1250 mesh) is used for cost reduction in general parts such as plastic basins, bags, and simple shells, with an addition ratio of 10%-50%. Talc powder is a flaky mineral that significantly improves product rigidity, reduces warpage, and enhances heat resistance, ideal for automotive parts, home appliance shells, and crates made of PP or PE, with an addition ratio of 5%-30%, which can increase flexural strength by 20%-50%. Kaolin enhances surface finish and electrical insulation, suitable for electronic and electrical shells and PVC pipes. Mica and barium sulfate improve dimensional stability and surface gloss, with barium sulfate also providing radiation shielding properties for medical and counterweight parts.

Fiber Reinforcing Fillers

Fiber reinforcing fillers act as a "skeleton" in plastics, significantly enhancing tensile strength, flexural strength, and impact resistance, making them suitable for load-bearing structural parts. Glass fiber (GF) is the most popular reinforcing filler, available in short (SGF) and long (LGF) types: SGF (5-15 μm diameter) is widely used in PA+GF, PP+GF, and PBT+GF modified plastics, with an addition ratio of 10%-50%, greatly improving mechanical properties and heat resistance, suitable for automotive structural parts, mechanical components, and electronic brackets. Carbon fiber (CF) offers ultra-high strength, low weight, and electrical conductivity, but its price is much higher than glass fiber, used in high-end products such as sports equipment, aerospace components, and conductive parts, with an addition ratio of 5%-30%. Mineral whiskers provide balanced performance and cost, replacing part of glass fiber in mid-to-low-end load-bearing parts.

Functional Fillers

Functional fillers are used in small amounts but impart special properties to injection-molded parts, enabling them to meet specialized industry requirements. Aluminum hydroxide (ATH) and magnesium hydroxide (MDH) are environmentally friendly halogen-free flame retardants, widely used in electrical shells, flame-retardant pipes, and other flame-retardant parts made of PVC, PE, and PP, with an addition ratio of 20%-60%. Graphite and carbon black provide electrical conductivity and anti-static performance, suitable for anti-static crates, electronic grounding parts, and conductive components. Thermal conductive fillers (such as copper powder, aluminum powder) improve heat dissipation, used in thermal conductive shells and heat dissipation components for electronic products. Other functional fillers include silica for thickening soft plastics and titanium dioxide for whitening and anti-aging.

Organic Fillers

Organic fillers such as wood flour, bamboo powder, and recycled plastic powder are mainly used for ultra-low-cost applications or wood-plastic composites (WPC). They are rarely used alone due to their limited mechanical performance, but can be blended with inorganic fillers to balance cost and basic processability. Wood flour and bamboo powder are used in WPC products such as imitation wood furniture and outdoor profiles, with an addition ratio of 30%-60%, achieving a natural wood-like appearance and texture. Recycled plastic powder and pulp powder are only used in disposable products and non-load-bearing parts such as plastic garbage bags and simple toys, with an addition ratio of 10%-40%, minimizing production costs.

Conclusion

Injection molding fillers are categorized by function and material: inorganic minerals for cost reduction and rigidity improvement, fiber reinforcing fillers for strength enhancement, functional fillers for special properties, and organic fillers for extreme cost savings. Correct selection based on resin type, product performance requirements, and processing conditions ensures balanced performance, product quality, and production costs, making filler selection a key practical link in injection molding modification and mass production.