Abstract
This investigation clarifies the relationship between the composition of unsaturated polyester compounds and the mold shrinkage or low-profile property, which substantially controls the surface smoothness of SMC moldings.
The surface smoothness corresponded well to the mold shrinkage, to which the contribution of thermal shrinkage during cooling was larger than that of polymerization shrinkage during curing. The thermal shrinkage was found to be closely related to the microstructure of the moldings, consisting of a low-profile additive and an unsaturated polyester resin. There was less thermal shrinkage when the compound with a well compatible low-profile additives was molded under a lower molding pressure.
