Color difference / discoloration

Fiber colors are inconsistent between different spinning positions or different time periods at the same spinning position; after fabric dyeing, fabric surface color difference or streaks appear. Roots of spinning color difference include uneven masterbatch metering, spinning temperature fluctuation causing colorant thermal stability changes, and chip batch color differences. Color difference is most obvious in dark colors and sensitive colors (such as navy blue, coffee) varieties, and is the primary control indicator of textile appearance quality.

1. Equipment factors: Inaccurate colorant metering causes colorant mixing ratio fluctuation. 2. Comprehensive factors: Plastication temperature fluctuation causes color change. 3. Operational factors: Incomplete cleaning when changing material varieties. 4. Comprehensive factors: Poor colorant dispersion forms color spots. 5. Roll gap adjustment factors: Crown and cross-angle compensation of calender rolls is the core means of controlling the transverse thickness distribution of the film. Crown design is based on roll deflection calculations; if it does not match the actual process load, it will cause abnormal transverse distribution of film thickness — thicker in the middle and thinner at both ends, or an inverse bow-shaped distribution.

1. Process parameter optimization and adjustment: Use a precise colorant metering system. 2. Mold/tooling improvement and maintenance: Stabilize processing temperature. 3. Equipment inspection and system maintenance: Thoroughly clean equipment and pipelines when changing materials. 4. Material/formulation optimization: Ensure colorant fully dispersed (pre-dispersed color masterbatch recommended). 6. Preventive management: Establish standardized process parameter cards and quality control limits for each mold/product, and regularly conduct process capability index (CPK) evaluations. For recurring problems, use fishbone diagrams or 5Why analysis to trace the root cause, and solidify countermeasures as PFMEA control points. Establish a regular equipment maintenance system and implement life management for key tooling such as dies/spinnerets/calender rolls/coating heads.

This problem is a typical manifestation of color difference / discoloration in calender molding. The core of the solution lies in precise adjustment of roll gap compensation, uniform control of roll temperature distribution, and assurance of feed system stability. It is recommended to start troubleshooting from roll system parameters and gradually go deeper into the equipment and formulation levels.