The influencing factors that cause color instability during production

In injection molding production, color shifts may occur every few days, or multiple color deviations can even appear within a single day. There are many factors causing color inconsistency. Below are the main factors leading to unstable color, for reference and corrective action during production.(1) Unstable injection molding machine temperature, fluctuating up and down, will definitely result in inconsistent color. This is a major influencing factor and shall be checked first.(2) Unstable production cycles, intermittent start-stop operation, and excessive backpressure setting that causes heat buildup can all lead to color variation.(3) Material mixing operators fail to mix color pigments and base resin in accordance with the mixing process requirements. Examples include insufficient mixing time, incorrect feeding method or feeding sequence, which result in uneven dispersion of color pigments. This item also requires priority inspection.(4) Excessively high drying temperature or overly long drying duration. Each type of resin and pigment has its specified range of drying temperature and time. Severe deviation from this range will change the color of molded parts. Variable feed rates can also trigger color instability for heat-sensitive colors, such as formulations containing fluorescent materials or light-colored molded components. For heat-sensitive plastics, drying is preferably avoided or performed at low temperatures. The safest practice is to dry the resin first and then blend it with color pigments.(5) Inside the drying hopper, hot air flow may cause local accumulation of color pigments, making the color progressively darker. For molded parts designed for a speckled finish, excessive specks may also occur. In such cases, add a small amount of dispersing oil to help the pigments adhere firmly to the resin pellets.(6) Excessive moisture content in the base resin causes pigment agglomeration and poor dispersion.(7) Inaccurate pigment formulation. Significant deviations in the dosage of each component across different batches of pigment mastermix will create color mismatch when switching to a new pigment batch.(8) Variable addition ratio of regrind material, which has a notable impact on light-colored molded products.(9) Inconsistent resin grades. Different base resins carry different inherent base hues, so molded parts with identical pigment recipes will show color differences. Even resin from the same supplier may have slight base hue variations between lots. For products with strict color tolerance requirements, the base hue consistency of each incoming material batch needs to be controlled.(10) Poor-quality pigments with insufficient heat resistance, or misapplication of pigments incompatible with the base resin, will cause unstable color performance.