Method for the preparation of styrene polymer foam

Claim 1

In a process for the preparation of an alkenyl aromatic thermoplastic resinous elongate foam body having a machine direction and a transverse direction, the body defining a plurality of closed noninterconnecting gas-containing cells therein, the steps of the method comprising heat plastifying an alkenyl aromatic synthetic resinous material, adding to the heat plastifying synthetic resinous material a volatile fluid foaming agent to provide a foaming agent resinous polymer mixture under a pressure sufficiently high that foaming is prevented, mixing the fluid foaming agent with the plastified resin to form a blowable resinous mixture, reducing the temperature of the mixture to a temperature such that when pressure is removed therefrom, a foam of desirable quality is obtained, reducing the pressure on the mixture to thereby cause the mixture to form a foam of desired quality, the foam having a minimal cross section of 8 square inches and a minimal thickness of 0.25 inch and water vapor permeability of not greater than 1.8 perm inches, the improvement which comprises employing a blowing agent selected from the group consisting of (1) a mixture of from about 5 to 20 weight percent isopropyl alcohol, from about 5 to 50 percent chlorodifluoromethane, and from about 30 to 70 percent dichlorodifluoromethane; (2) a mixture of from about 5 to 50 percent of an ethanol, methanol or mixtures thereof, from about 5 to 50 percent of chlorodifluoromethane, and about 30 to 70 percent dichlorodifluoromethane; and mixtures thereof, all percentages being by weight.