A common problem encountered with molded polyurethane foams blown with water, especially high quantities of water exceeding 3.0 weight percent based on the total weight of the polyol composition, is that the foam will drastically shrink unless crushed with mechanical means while hot. Efforts have been made to chemically manipulate the polyurethane foam system to obviate the need for mechanical crushing means. The various attempts made to reduce foam shrinkage included using low activity surfactants, reducing the amount of ethylene oxide termination on the polyether polyol to slow its reactivity, or using a graft polymer dispersion prepared by the continuous process rather than by the semi-batch process. A wider particle size distribution is thought to aid in opening up more cells in the foam, which in turn reduces foam shrinkage. It is desirable, however, to obtain a polyurethane foam by using a graft polymer dispersion which is effective to reduce foam shrinkage without regard to its particle size distribution or its method of manufacture.
USPTO Backgrounds
USPTO Backgrounds