Problem:
Differences in color or colored streaks on the surface of the moulding. The cause is usually due to non uniform distribution of the pigments during plasticisation but can also be due to non compatibility of the polymer and master batch.

Solution:

1. Check compatibility of the master batch with the base polymer.
2. Check the metering unit for defects.
3. Increase the speed of injection.
4. Reduce and increase the screw speed. Evaluate the effects on streak formation.
5. Increase the back pressure to improve mixing.
6. Confirm the temperature of the melt is within specification.
7. Confirm the temperature is within limits of the master batch.
8. Check the control and temperature sensor of the hot runner system.
9. Check whether the shot weight, barrel volume and residence time is within guidelines.
10. Check suitability of the screw L/D ratio, shear and/or mixing section.

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