Visualization Analysis on a Transcription Molding Process of Cavity the Surface State for Cyclic Olefin Copolymer

Abstract

When injection molding is carried out using cyclic olefin copolymer (COC) under inappropriate molding conditions, various external defects are known to be generated on the molded product surface. The shapes of these defects are unique to COC, and their generation mechanism has not been clarified to date. In this study, the authors propose a new method for visualizing the contact state between a transparent material and glass surface using a glass-inserted mold, to analyze a generation process of the various external defects in the use of COC. The results clarified the followings;(1) By tilting the metal side cavity surface opposite the glass surface, it was ascertained that black and white areas on the contact and non-contact areas between the glass and transparent resin can be obtained at high contrast.(2) Using this method, the authors also observed the generation process of external defects including phenomena unique to COC such as spot dimple shapes and shapes with large protrusions at the center of the dimple according to changes in the injection rate and mold temperature. It was confirmed that these external defects occur when the resins contact the glass surface.(3) Assuming that high viscosity component is unevenly distributed in the fluid, the generation of external defects, which is unique to COC, is thought to be caused by transcription inhibition due to the high viscosity component.(4) These results clarify that injection molding conditions such as high mold temperature and high injection rate are effective for preventing external defects.