Injection Molding Defects And Solutions -- Uneven Color Or Discoloration

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Injection Molding Defects and Solutions -- Uneven Color or Discoloration 2025-10-17

Uneven Color or Discoloration:
Uneven color on the surface of a plastic part may result from poor dispersion of pigments or fillers, or from discoloration of the plastic or pigments. If the entire plastic part shows uneven color, it is usually caused by poor thermal stability of the plastic. When the color is uneven at weld lines, it is related to the nature of the pigment.

	Causes		Solutions
17.1.1	When using dry pigments in a tumbling mixer, the pigment only adheres to the surface of the resin pellets, resulting in uneven color.	17.2.1	Use colored masterbatch or pre-dispersed granules to ensure uniform color.
17.1.2	Poor quality of pigments.	17.2.2	Replace with high-dispersibility, high-temperature-resistant pigments.
17.1.3	Poor dispersibility of the dispersing agent.	17.2.3	Replace with a dispersing agent that ensures uniform pigment dispersion.
17.1.4	Uneven plasticization.	17.2.4	Adjust processing: increase melt temperature, increase back pressure, reduce screw speed to achieve uniform plasticization.
17.1.5	Uneven distribution of fiber fillers, exposed fiber, or resin loss due to contact with solvents, leading to fiber exposure.	17.2.5	Reduce screw speed and increase back pressure to ensure even fiber distribution, prevent fiber exposure, and avoid resin loss from solvent contact.
17.1.6	Decomposition of the plastic or pigment.	17.2.6	Lower melt temperature, increase mold temperature, and use high-temperature-resistant pigments.
17.1.7	Mold surface has moisture, oil, or improper release agent.	17.2.7	Wipe off moisture and oil from the mold surface and use a suitable release agent.
17.1.8	Foreign materials mixed into the plastic or pigment.	17.2.8	Use clean material and strictly prohibit mixing different materials.
17.1.9	Uneven wall thickness or uneven crystallinity, affecting transparency and causing uneven color.	17.2.9	For crystalline products, apply post-heating treatment or increase mold temperature to ensure uniform crystallinity.
17.1.10	High temperature in the hot runner or malfunctioning thermocouple, causing high melt temperature and decomposition.	17.2.10	Lower hot runner temperature or replace the thermocouple.
17.1.11	Damaged barrel or screw, causing residual material.	17.2.11	Repair or replace the barrel and screw.