Dual functional additive

Claim 1

In a maturated moldable sheet molding compound suitable for molding under pressure, said molding compound having fillers and reinforcing materials dispersed in a thermosetting resin composition said resin being comprised primarily of an unsaturated polyester resin said resin including an aliphatically unsaturated monomer, a free radical polymerization catalyst and an internal mold release agent, said resin composition further containing a dual thickening system for modifying the viscosity of the resin composition, said dual thickening system comprising an oxide or hydroxide of magnesium or calcium and a polyisocyanate; the improvement comprising: using as the polyisocyanate an isocyanate terminated prepolymer having an NCO to OH ratio of from about 1.2/1 to 5/1 said isocyanate terminated prepolymer being the reaction product of one equivalent of a polyol having an average molecular weight of about 600 to 4000 and an average functionality between 2 and 6 with from 1.1 to 5 equivalent weights of a polyisocyanate selected from the group consisting of toluene diisocyanate, ethylene diisocyanate, phenyl diisocyanate, 4,4'-dipenyl methane diisocyanate (MDI), a mixture of 4,4'-diphenyl isocyanate and its trifunctional cyclic adduct container carbondiimide linkages, 1,5-naphtalene diisocyanate, xylene diisocyanate, tetramethylene diisocyanate, and hexamethylene diisocyanate; whereby sheet molding compounds containing the improved dual thickening system have improved shrink characteristics and better viscosity index properties enhancing the moldability of the resin and quality of the products made using the improved resin.