Matched die molding of fiber reinforced plastic articles

摘要

Lightweight glass fiber reinforced plastic articles are produced in matched dies by combining fibrous reinforcing materials, such as glass fibers, with a foamable unsaturated polyester resin composition. The matched dies are closed and compressed so that the resin composition fills the mold cavity and wets the fibrous reinforcing material. Thereafter the matched dies are separated to increase the volume of the mold cavity by at least 50 percent greater than the closed volume. The matched dies are retained in this relationship until the unsaturated polyester resin composition has cured and expanded to fill the mold cavity. The resulting product has a density less than 67 percent of the density of a corresponding reinforced plastic article fabricated from the same composition (unsaturated polyester resin, fillers and reinforcement), which is not foamed. The unsaturated polyester resin composition preferably includes 0.5 to 3 percent by weight (based on the weight of unsaturated polyester resin) of an azo blowing agent to accomplish resin cure and foaming.