Analysis of Color Problems of Injection Molded Products

Ⅰ. Analysis of the causes of uneven color of injection molded products

The main reasons and solutions for the uneven color of injection molded products are as follows:

1. Poor diffusion of the colorant, which often causes patterns near the gate.

2. Plastics or colorants have poor thermal stability. To stabilize the color tone of the parts, the production conditions must be strictly fixed, especially the material temperature, material quantity and production cycle.

3. For crystalline plastics, try to make the cooling speed of each part of the part consistent. For parts with large wall thickness differences, colorants can be used to mask the color difference. For parts with relatively uniform wall thickness, the material temperature and mold temperature should be fixed.

4. The shape of the part, the form of the gate, and the position have an impact on the filling of the plastic, causing color differences in some parts of the part, which must be modified if necessary.

Ⅱ. The cause analysis of color and gloss defects

Under normal circumstances, the gloss on the surface of injection molded parts is mainly determined by the type of plastic, the colorant and the smoothness of the mold surface. However, it is often caused by some other reasons to cause defects such as surface color and gloss defects, surface dark color, etc. of the product. The reasons and solutions for this are analyzed as follows:

1. The finish of the mold is poor, there is rust on the surface of the cavity, etc., and the exhaust of the mold is poor.

2. If the gating system of the mold is defective, the cold slug well should be increased, the runners, polished main runners, runners and gates should be increased.

3. The material temperature and mold temperature are low, if necessary, local heating of the gate can be used.

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 plastic must be prevented, the heating must be stable, and the cooling must be sufficient, especially for thick-walled ones.

6. To prevent cold material from entering the workpiece, use self-locking springs or lower the temperature of the nozzle if necessary.

7. Too much recycled material is used, the quality of plastic or colorant is poor, mixed with water vapor or other impurities, and the quality of lubricant used is poor.

8. The clamping force should be sufficient.

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