Experimental analysis of generation process of white tree-ring-like surface defects in injection molding

Molding defects such as silver streaks, weld-lines, and flow-marks are problems faced in injection molding. In the case of molded products with mirror surface, one such external defect is the white tree-ring-like surface defects appearing on the surface. From experience, we know that this defect occurs conspicuously with PBT/PET when the mold temperature is high. Although this molding defect is thought to occur in the demolding process, the mechanism by which it occurs is not clear. For this reason, in this study, we investigated the conditions by which white tree-ring-like surface defects occur and reviewed the generation mechanism by visualizing the demolding process. We found that when the mold is forcibly separated from the molded product while they are still tightly adhered together, the surface of the molded product that is tightly adhered to the mold wall deforms, causing demolding to progress intermittently, resulting in the white surface defects. In addition, characteristic tree-ring-like pattern...