Dull Surface (Lack of Gloss):
Due to poor mold surface finish, inadequate contact between the molten material and the mold surface, or improper material and mold temperatures, the molded product fails to exhibit the natural gloss of the resin. Instead, the surface appears whitish, cloudy, or dull.
| 21.1 Causes | 21.2 Solutions |
|---|---|
| 21.1.1 Poor mold surface finish; presence of scratches, moisture, or oil contamination. | 21.2.1 Repair or clean the mold surface and wipe the cavity dry. |
| 21.1.2 Excessive or improper use of mold release agent. | 21.2.2 Choose a suitable release agent, apply sparingly, and wipe the cavity if necessary. |
| 21.1.3 Moisture or excessive volatiles in the plastic. | 21.2.3 Dry the material according to process requirements; if necessary, increase drying temperature or extend drying time. |
| 21.1.4 Decomposition or deterioration of plastic or pigment. | 21.2.4 Replace with qualified material. |
| 21.1.5 Poor plastic flowability. | 21.2.5 Use a material with better flowability or increase mold temperature and injection pressure appropriately. |
| 21.1.6 Low material temperature, low mold temperature, or slow injection speed. | 21.2.6 Increase material temperature, mold temperature, and injection speed. |
| 21.1.7 Excessive air in the melt or poor mold venting. | 21.2.7 Increase back pressure appropriately and add venting slots in suitable mold locations. |
| 21.1.8 Injection speed too fast and small gate size causing melt vaporization, resulting in a milky thin layer. | 21.2.8 Reduce injection speed and enlarge gate size to prevent melt vaporization. |
| 21.1.9 Material and mold temperatures too high or too low (each plastic type has an optimal temperature range for gloss; deviations reduce gloss). | 21.2.9 Adjust material and mold temperatures according to the specific resin requirements. |
| 21.1.10 Insufficient feeding or poor plasticization. | 21.2.10 Adjust feed volume to ensure uniform plasticization. |
| 21.1.11 Mixed or incompatible materials. | 21.2.11 Replace with qualified material. |
| 21.1.12 Insufficient draft angle causing poor demolding. | 21.2.12 Increase draft angle to ensure easy ejection of parts. |
| 21.1.13 Low surface hardness of molded parts, prone to scratching and abrasion. | 21.2.13 Design and choose proper packaging to protect product surfaces from friction. |
| 21.1.14 Uneven or oversized pellets. | 21.2.14 Use uniform pellets or adjust processing conditions for even plasticization. |
| 21.1.15 Exposed filler or non-oriented silver flake filler. | 21.2.15 Increase mold temperature to ensure filler is not exposed. |
| 21.1.16 Presence of silver streaks or uneven coloration. | 21.2.16 Ensure proper drying of material, identify cause of color unevenness, and take corrective measures. |
| 21.1.17 Hot runner temperature too high or too low; heater or thermocouple damaged. | 21.2.17 Adjust hot runner temperature or replace heater and thermocouple. |
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