Black specks and brown streaks are among the most common reasons parts get rejected, especially in clear and light colors. Most of the time they come from inside your own equipment, but sometimes they arrive in the resin.
Where specks come from
| Source | Clues | Fix |
|---|---|---|
| Degraded material in the barrel or hot runner | Specks appear after a shutdown, a color change or a long cycle; worse at high melt temperature. | Purge thoroughly, lower melt temperature, reduce residence time, clean the screw and check for dead spots. |
| Dirty dryers, loaders and hoppers | Specks come and go; dust or fines visible in the system. | Clean the material-handling system; empty and clean dryers between materials. |
| Contaminated regrind | Specks rise as regrind percentage rises. | Screen and inspect regrind; lower the percentage. |
| Contaminated virgin resin | Specks follow a specific lot; visible in pellets before molding. | Inspect incoming pellets on a white tray; hold the lot and contact the supplier. |
| Colorant agglomerates | Specks are the color of the concentrate, not black. | Check concentrate dispersion and carrier compatibility. |
A quick way to find the source
- Spread a sample of pellets straight from the bag or box on a white tray. If specks are visible, it’s the resin.
- If the pellets are clean, take a sample from the hopper throat. If it’s dirty there, it’s your handling system.
- If both are clean, it’s inside the barrel, screw or hot runner.
Color problems · Prime vs. off-grade · Tell us the grade you run now →