FACTORS AFFECTING SURFACE SMOOTHNESS AND THE ROLE OF UNSATURATED POLYESTER RESIN AND GLASS-FIBER

This paper covers an investigation to determine the factors affecting surface smoothness of SMC moldings. Many studies have been done at man y laboratories to improve the surface smoothness quality of SMC moldin gs. These studies are aimed at comparison with steel sheets. This goal has almost been realized, resulting in better SMC formulations and mo lding process conditions. However, the authors could not get sufficien t results even with these better formulations and conditions because t he surface smoothness values in the data did not show adequate consist ency among the locations measured. In addition, they got various smoot hness values in their moldings, even when using the same SMC productio n lot. The authors tried to solve this inconsistency problem by examin ing the effect of unsaturated polyester resin/low profile additive and glass fiber as main factors in surface smoothness. They found substan tial effects with actual limitation in surface smoothness that came fr om ''compatibility'' between unsaturated polyester resin and low profi le additive, as well as the ''fibrillation state'' of chopped glass fi bers.