Method of preparing urethane foam articles

Abstract

In a method of preparing a urethane foam article having a high density outer surface layer, of the type wherein a plastic liquid containing isocyanates, polyols, a catalyst, a blowing agent, an assistant and other additives is poured into a mold through a one-shot molding process, while maintaining the mold at a temperature in the range of from 15.degree. to 40.degree. C., a temperature sensitive catalyst is added for causing the isocyanates and the blowing agent to create a difference in chemical reaction between an outer portion of the plastic liquid contacting the mold surface and an inner portion of the plastic liquid held out of contact with the mold surface, thereby retarding the foaming of the outer portion than that of the outer portion. Subsequently, a evolved gas is allowed to expand under exothermic heat of the inner portion of the plastic liquid while at the same time the evolved gas is taken up by gelation of the plastic liquid, thereby increasing the blowing pressure rapidly until the mold is over-packed with a foaming plastic mass. Finally, an outer portion of the foaming plastic mass extending along the mold surface is gelled while inhibiting the foaming of the last-mentioned outer portion, thus forming a high density layer on the outer surface of a urethane foam article.