Patent ID: 8715543

Claim:
A molding compound comprising a thermosetting resin and a microencapsulated curing agent for curing the thermosetting resin, the microencapsulated curing agent comprising an organic peroxide curing agent and a polyurethane resin encapsulating the organic peroxide curing agent, wherein the polyurethane resin is made from (i) at least one isocyanate selected from the group consisting of xylylene diisocyanate, hydrogenated xylylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate and polyisocyanates obtained from these diisocyanates, (ii) a polyol comprising a polyethylene glycol having molecular weight of 200 to 20,000, and (iii) about 20 to 48 wt. % of a polyamine, the percent being based on the combined amounts of polyol and polyamine, wherein the microencapsulated curing agent is made by a process comprising (a) dissolving the organic peroxide curing agent and the isocyanate forming the polyurethane in an organic solvent which is essentially immiscible with water and a non-solvent for the polyol and polyamine forming the polyurethane, (b) emulsifying the organic solution so formed in an aqueous composition comprising water and a colloid-forming agent by vigorous mixing, and then (c) adding the polyol and optional polyamine to the emulsion so formed with continuous mixing to cause the polyurethane to form at the interface of the emulsified particles, wherein the microencapsulated curing agent when heated to 100° C. for 30 minutes exhibits a loss of weight of no greater than 10 wt. %, and further wherein the microencapsulated curing agent when heated to 140° C. for 5 minutes exhibits a loss of weight of at least 4 wt. %.