Article transparent to microwaves and process for making same

Claim 1

A molded burn-resistant article, for use in microwave ovens transparent to microwaves of 1915 to 2450 megahertz, said article having a maximum dielectric constant not greater than 5, having chemical resistance unaffected by detergents, having high abrasion resistance, and being essentially unbreakable under ordinary usage conditions in microwave ovens, and being obtained by molding a sheet molding composition consisting essentially of a mixture of an unsaturated cross linkable polyester of a dicarboxy acid and a dihydric alcohol, a cross linking inhibitor, a chemically inert powdered filler, a thermoplastic polymer, a cross linking monomer capable of cross linking with said polyester to form a thermosetting resin, cut bundles of glass filaments, a catalyst for the cross linking reactant, a thickening agent, and a mold release ingredient, said sheet molding composition containing 5% to 35% by weight of cut bundles of glass filaments 1/4 inch to 3 inches long, between solid smooth heated dies at pressures and temperatures sufficiently high to cause cross linking between said polyester and said cross linking monomer.