Causes and solutions of color imbalance in injection mold processing

Uneven color processing of injection mold is the color of the surface of the product is not the same, which can be near and far from the material head, and occasionally will appear in the material flow area of the sharp edge. Uneven color is caused by uneven distribution of pigments, especially by adding color through master, powder, or liquid color. At temperatures below the recommended processing temperature, the master material or color material cannot be completely homogenized. When the molding temperature is too high, or the residual time of the cylinder is too long, it is also easy to cause the thermal degradation of pigments or plastics, resulting in uneven color.

Reasons related to processing parameters and improvement measures:

1, the material is not evenly mixed, reduce the speed of the screw; Increase the barrel temperature and screw back pressure

2, the melting temperature is too low, increase the cylinder temperature, increase the screw back pressure

3, screw back pressure is too low, increase the screw back pressure

4, screw speed is too high, reduce screw speed

Design related reasons and improvement measures:

1, screw stroke is too long, with large diameter or long diameter cylinder

2. The residence time of the molten material in the cylinder is short, and the cylinder with large diameter or long diameter is relatively large

3, screw L: D is too low, the use of large diameter cylinder

4, screw compression ratio is low, using high compression ratio screw

5. Without shear segment and/or mixing segment, provide shear segment and/or mixing segment

When the material is plasticized or homogenized at the correct temperature, if it is injected too quickly through the cross section of the head, friction heat may be generated, resulting in pigment degradation and color change. Injection molding usually in the use of color masterbatch, should ensure the pigment and its solution to color the resin in chemical and physical characteristics of the compatibility.