Injection Molding Process Scheme for Stable Low-Gloss Appearance of Plastic Parts
Low-gloss plastic components are widely adopted in consumer electronics, automotive interior and home appliance industries. The core challenge of low-gloss molding lies in maintaining uniform matte texture on product surfaces during continuous mass manufacturing, while avoiding local bright spots, gloss discrepancy, flow marks and other appearance defects. Multiple factors including process parameters, mold surface status and raw material performance will affect the final surface effect. A complete control system covering mold, material, process and on-site management needs to be established to guarantee consistent appearance in batch production.
Raw Material Selection and Preprocessing
The raw material selection prioritizes base materials with inherent low-gloss characteristics, or modified plastics blended with matte masterbatch and matte fillers. The dispersion performance of fillers directly decides the uniformity of matte texture. Batch-to-batch fluctuation in filler content of raw materials may trigger gloss inconsistency. For moisture-absorbing materials, drying operation should be carried out in accordance with specifications. Excess moisture will produce silver streaks and bubbles on the product surface and destroy the matte outer layer. Drying temperature and duration should be properly controlled. Over-drying may result in material degradation, and degraded melt tends to form bright areas and color difference on surfaces. The material barrel must be fully cleaned before material switching. Raw materials of different batches should be stored separately. Sampling tests shall be implemented before mass production to confirm the gloss meets standards.
Mold Surface Texture Control
The matte effect of low-gloss plastic parts is reproduced through the etched texture on mold cavity. The depth and uniformity of mold etching texture form the fundamental condition for low-gloss molding. After etching processing, inspect the mold surface to check for polished bright spots, as local polished regions will form bright patches on molded products. During production, mold cavities tend to accumulate release agent and plastic precipitates inside texture grooves, which gradually weaken the three-dimensional sense of texture and make plastic surfaces brighter. The cavity needs regular cleaning before and after production. Soft cleaning tools should be used to prevent scratches on etched texture. Mold steel with stable etching performance is preferred. Evaluate the wear resistance before mass production for steel grades whose texture is easy to wear.
Gating System and Gate Design
Gate positions are preferably arranged on non-appearance surfaces. Melt will generate shear heat when flowing through gates. Excessive shear force can change the surface structure of melt and leave obvious gate marks. For multi-cavity molds, balanced runner layout should be adopted to ensure consistent filling speed and pressure in every cavity and avoid gloss difference among molded parts. Optimize the cross-section of runners to reduce melt shear rate and local overheating. Cold slug wells with sufficient volume are required to trap cold material at the front of melt flow. Cold material entering the cavity will lead to flow marks and uneven gloss. Appropriately enlarge the gate cross-section when necessary to lower injection shear and prevent excessive stretching of surface melt.
Mold Temperature Control
Mold temperature is one of the most critical process variables affecting low-gloss appearance. Higher mold temperature allows melt to fully fit the mold surface and raises the gloss of finished parts. Lower mold temperature enables rapid solidification of surface melt to achieve matte effect, yet excessively low temperature easily brings weld lines and short shot defects. Mold temperature machines are used for closed-loop temperature control. Even cooling runner layout reduces temperature difference on cavity surfaces. Conduct mold temperature range test in trial molding to lock appropriate parameters. Random adjustment of temperature settings is prohibited during mass production.
Injection and Packing Parameter Setting
High injection speed increases melt shear, which readily forms bright bands and flow marks on product surfaces. Segmented injection mode is recommended. Reduce injection speed near the end of filling to cut shear heat at weld areas. Excessive packing pressure squeezes melt into mold texture grooves and lifts local gloss, while insufficient packing pressure will cause sink marks. Set packing time according to product wall thickness, and control the upper limit of packing pressure on the premise of qualified dimensions. Narrow the fluctuation range of injection and packing pressure to stabilize gloss performance across batches.
Venting and Demolding Control
Trapped gas inside the cavity will cause burning spots and bright patches. Set vent slots at weld lines and melt terminal positions. The depth of vent slots matches material characteristics to balance vent performance and flash prevention. Carbon deposits accumulate inside vent slots during production, requiring regular cleaning. Minimize the usage of release agent, because residual release agent fills texture grooves and brightens plastic surfaces. If release agent has to be used, spray a tiny amount in mist form or select raw materials with built-in release agent. Arrange ejector pins away from major appearance surfaces and guarantee even ejection force to avoid white marks and appearance color difference induced by local deformation.
On-line Monitoring and Defect Adjustment in Mass Production
Take samples regularly and test gloss values with gloss meters during mass production, and establish qualified gloss control range. When local bright areas appear, check cavity dirt accumulation first, then verify mold temperature and injection speed. Reduce mold temperature if the overall gloss is too high. Check runner balance and venting status for uneven gloss. Re-verify product appearance after raw material batch replacement and mold maintenance before continuous production to lower batch nonconformity risks.
