Black / Brown Specks or deposits are visible on the surface of the moulding, normally caused by contamination or degradation of the material.
1. Reduce the temperature of the polymer melt.
2. Reduce the screw speed and / or the back pressure.
3. Clean the moulding machine thoroughly - full purge.
4. Check for any impurities, leaks or dirt deposits in the feed stock hopper supply.
5. Check the shot weight. The entire shot weight should not be less than 15 to -25% of the maximum capacity of the machine.
6. Check compatibility of pigment or master-batch with the base polymer.
7. Reduce the time in which the material is openly exposed to the ambient conditions.