The main reasons and solutions for the uneven color of injection molded products are as follows:
(1) The colorant is poorly diffused, which tends to cause a pattern near the gate.
(2) The plastic or colorant has poor thermal stability. To stabilize the color tone of the part, it is necessary to strictly fix the production conditions, especially the material temperature, the amount of material and the production cycle.
(3) For crystalline plastics, try to make the cooling speed of each part of the parts consistent. For parts with large difference in wall thickness, coloring agent can be used to mask the chromatic aberration. For the parts with uniform wall thickness, the temperature and mold temperature should be fixed. .
(4) The shape of the part and the form of the gate. The position has an influence on the filling condition of the plastic, so that some parts of the part are subject to chromatic aberration and should be modified if necessary.
Under normal circumstances, the gloss of the surface of an injection molded article is mainly determined by the type of plastic, the colorant and the finish of the die face. However, due to some other reasons, the surface color and gloss defects of the product, dark surface and other defects. The reasons for this and the solution are as follows:
(1) The mold finish is poor, the surface of the cavity is rusted, and the mold is poorly exhausted.
(2) The casting system of the mold is defective. The cold 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 if necessary, the gate can be locally heated.
(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, if necessary, use a self-locking spring or reduce the nozzle temperature.
(7) Excessive use of recycled materials, poor quality of plastic or colorant, mixed with water vapor or other impurities, the quality of the lubricant used is poor.
