Patent ID: 7008578

Claim:
A method for the production of an extruded, polystyrene-based resin foam plate comprising the steps of heating and kneading a polystyrene-based resin together with a blowing agent, a flame retardant and 1.5 to 8% talc by weight based on the weight of said extruded foam plate, in an extruder to obtain a foamable molten composition, and extruding said foamable molten composition through a die attached to an end of said extruder into a lower pressure zone, wherein said blowing agent comprises: (a) not less than 25% by weight but not greater than 65% by weight, based on the total weight of said blowing agent, of an isobutane-containing saturated hydrocarbon; (b) not less than 5% by weight but not greater than 70% by weight, based on the total weight of said blowing agent, of a dimethyl ether-containing ether; (c) not less than 5% by weight but not greater than 55% by weight, based on the totai weight of said blowing agent, of carbon dioxide; (d) 0–25% by weight, based on the total weight of said blowing agent, of other blowing agent components; wherein said isobutane is at least 46.1% by weight of said blowing agent; and wherein said foam plate has a thermal conductivity of not greater than 0.030 W/m·K.