Color that drifts from one lot to the next leads to rejected parts and customer complaints. The cause is usually one of a few things, and most of them can be controlled.
Common causes
| Cause | What to check |
|---|---|
| Base resin color varies | “Natural” resin isn’t always the same shade. A different lot, grade or source can be yellower or grayer. |
| Letdown ratio drifts | Feeder calibration, and whether the ratio is set by weight or by volume. |
| Carrier doesn’t match the resin | A concentrate in the wrong carrier resin may not disperse well. |
| Poor dispersion | Streaks or specks of color point to mixing: screw design, back pressure, or the concentrate itself. |
| Regrind | Regrind has extra heat history and can shift color, especially in light shades. |
| Process temperature | Some pigments shift with melt temperature or residence time. |
How to lock in color
- Use one consistent base resin source and approve it like any other spec.
- Match the concentrate to your exact resin, with a carrier that’s compatible.
- Consider pre-colored compound for critical colors: the color is built into every pellet, so there’s no letdown to drift.
- Approve color against a physical standard plus a measured target, not by eye alone.