Factors Affecting Surface Smoothness and the Role of Unsaturated Polyester Resin and Glass Fiber

This paper covers an investigation to determine the factors affecting sur face smoothness of SMC moldings. Many studies have been done at many laboratories to improve the surface smoothness quality of SMC moldings. These studies are aimed at comparison with steel sheets. This goal has almost been realized, resulting in better SMC formulations and molding process conditions. However, the authors could not get suffi cient results even with these better formulations and conditions because the surface smoothness values in the data did not show adequate consistency among the locations mea sured. In addition, they got various smoothness values in their moldings, even when using the same SMC production lot. The authors tried to solve this inconsistency problem by examining the effect of un saturated polyester resin/low profile additive and glass fiber as main factors in surface smoothness. They found substantial effects with actual limitation in surface smoothness that came from "compatibility" between unsaturated polyester resin and low profile addi tive, as well as the "fibrillation state" of chopped glass fibers.