Improvement of the Mold Releasing Properties by DLC Surface Modification for the Injection Processing

Abstract

This paper aims to evaluate the mold releasing properties of DLC (Diamond Like Carbon) film coating on the injection mold. The thin walled plastic products need bigger mold releasing force than the ordinary products in the opening stage of the plastics injection molding process. Reducing mold releasing force by the mold surface modification makes stable production. DLC film coating was performed on the injection mold for reducing the mold releasing force and compared with non-treatment and hard chromium electroplating. Furthermore, the sliding friction coefficient between the DLC film specimen and PMMA resin was measured under the different surface temperatures, and each surface property was investigated by SPM (Scanning Prove Microscope) from a microscopic standpoint. As the result of cross-section measurement and evaluating the bearing length ratios of two perpendicular axes, the surface of the DLC film coating was remarkably smooth and had no sharp edges or directionality that compared with nontreatment and hard chromium electroplating specimens. Such characteristics restrain the deformation and adhesion of the outer layer part when the product slides on a metal surface. DLC film coating has shown 27%-35% less releasing force than the ordinary surface treatments.