Generally, the gloss on the surface of injection molded parts is mainly determined by the type of plastic, colorant, and finish of the mold surface. But there are some other reasons. The reasons and solutions are as follows:
(1) Poor mold finish, rust on the surface of the cavity, and poor mold exhaust.
(2) The gating system of the mold is defective. Then, we should enlarge the cold slug well and the runner, polish main runner, runner and gate.
(3) The material temperature and mold temperature are low. Then, the local heating of the gate can be used if necessary.
(4) The overly slow processing pressure and speed, the insufficient injection time and back pressure, these can result in poor compactness and dark surface.
(5) Plastics must be fully plasticized. But we need to prevent degradation of the material, stablize heating and adequately cooled, especially thick-walled ones.
(6) Prevent cold material from entering the part, use self-locking spring or lower nozzle temperature when necessary.
(7) Too much recycled materials are used. Plastics or colorants and lubricants are of poor quality. And water vapor or other impurities are mixed.
(8) The clamping force should be sufficient.