Black Spot
Dark spots include black spots and black stripes. Black spots are when the product has the correct color fading but occasionally black or dark spots are visible; Black stripes are strips of different colors. This is usually due to material decomposition. Screw cleaning is not clean. It's caused by impurities in the material.
| Cause | Cuntermeasure | |
| Forming condition |
1. The material of injection molding machine is not clean 2. High temperature of the material will cause material degradation 3. Excessive injection pressure will increase the shear and decompose the material 4. Excessive shear caused by excessive injection molding speed 5. The thermal pause time of materials is too long |
1. Clean the material and screw with cleaning machine material, pull out screw when necessary to clean 2. Reduce the forming temperature 3. Reduce injection pressure and screw speed 4. Reduce injection speed 5. Reduce buffer margin and replace small machine so that the delay time is less than the retention time required by the material |
| Die |
1. Impurities are produced in the nozzle or hot runner 2. There is oil in the mold 3. Hot runner is not cleaned |
1. Clean the nozzle or hot runner 2. Clean the mold 3. Clean hot runner
|
| Material | The raw material itself has impurities and black spots |
Change of material
|
| Other | The hopper is not cleaned | Re-clean the hopper |
