Method of producing hard foamed materials

Claim 1

In the method of producing hard foamed objects of expanded vinyl chloride resin which comprises forming a mixture comprised of said vinyl chloride resin and a blowing agent; introducing the mixture into a mold; pressurizing the mold while heating the mold to cause the blowing agent to partially expand the resulting resin mixture to fill said mold; cooling said mold; removing the resulting object from said mold and then heating the object to further expand its size without changing its shape, the improvement which comprises: forming a dry mixture of said resin with about 0.4 to about 40 times by weight of the resin of a powdery inorganic filler, adding to the dry mixture at least about 30 parts by weight of said mixture of a solvent selected from toluene and xylene, kneading the solvent, resin and inorganic filler containing mixture in a closed kneader at about 40° to about 100° C. until the outer surfaces of the particles of said inorganic filler are covered with said resin and are adhered to each other by said resin, adding a blowing agent comprised of liquid butane, and an additional amount of about 30 to about 40 parts by weight of said solvent, thoroughly mixing the resulting mixture so that all the ingredients including the liquid butane are thoroughly dispersed and then introducing said mixture into said mold.