Use of solvent mixtures in making foamable compositions

Abstract

A process for rapidly producing a substantially uniform, solid, cellular thermoplastic article comprising the steps of: (a) charging a vessel with (1) a solid thermoplastic polymer, (2) a solvent mixture the amount of which in the range of from about 25-50% by weight of said polymer boils at or below 0.degree.C. and to prevent shrinkage the minor amount of which in the range of from about 3-30% by weight of said polymer boils at or near 20.degree.C., said solvent mixture being capable of forming a gel with the polymer when subjected to super-atmospheric pressure, (3) water in sufficient amount to lubricate the flow of the gel from the vessel as specified in step (c) below, and (4) for homogeneous polymer solutions a nucleating agent selected from the group consisting of spherical polyethylene powder, glass hollow spheres, phenolic hollow spheres and mixtures thereof; (b) subjecting the contents of the vessel to super-atmospheric pressure at a temperature in the range of room temperature to below the critical temperature of said solvent mixture for a time sufficient to form a flowable gel; and, (c) thereafter rapidly opening an outlet at the bottom of the vessel to cause the gel to flow from the vessel and form the cellular article. Foamable compositions usable in the process to make the cellular articles are described. Major means more than 50% by weight of the solvent mixture and minor means less than 50% by weight of the solvent mixture as the terms imply.