Under normal circumstances, the gloss of the surface of an injection molded part is mainly determined by the type of plastic, the colorant and the finish of the mold surface. However, due to some other reasons, the surface color and gloss defects of the product and the dark color of the surface are often caused. The reasons for this and the solution are as follows:
(1) The mold has poor finish, the surface of the cavity has rust, etc., and the mold is poorly exhausted.
(2) The casting system of the mold is defective. The cold material well should be enlarged, the flow channel should be enlarged, the main flow channel should be polished, the runner and the gate should be polished.
(3) The material temperature and the mold temperature are low, and the local heating method of the gate can be used if necessary.
(4) The processing pressure is too low, the speed is too slow, the injection time is insufficient, and the back pressure is insufficient, resulting in poor compactness and darkening of the surface.
(5) The plastic should be fully plasticized, but the degradation of the material should be prevented, the heat should be stable, and the cooling should be sufficient, especially thick-walled.
(6) Prevent cold material from entering the part, and if necessary, use a self-locking spring or lower the nozzle temperature.
(7) Excessive recycled materials are used, plastic or colorant is of poor quality, mixed with water vapor or other impurities, and the quality of the lubricant used is poor.
(8) The clamping force should be sufficient.