GB1114152A - Foamed products - Google Patents

Abstract

A drawn extruded foamed product is obtained by drawing an extruded foamed thermoplastic material so that it becomes orientated essentially in one direction to give a product having a width of at least 1/2 -inch and a strength improvement in the direction of production. The thermoplastic material may be a polymer or copolymer obtained by polymerization of ethylenically unsaturated monomers. Such a monomer is a hydrocarbon, nitrile, vinyl halide, vinyl or acrylate ester, a mono-olefin, diene, or a vinyl-substituted benzene. Suitable comonomers are a vinyl halide, vinyl pyrollidone or a vinyl pyridine. A copolymer can involve two or more of the above monomers. The thermoplastic material can also consist of a mixture of two or more polymers or copolymers. Other suitable polymers are natural and synthetic rubbers, polyamides, polyurethanes, polylactams and polyesters. The thermoplastic material may also be rayon or a cellulose ester. The blowing agent may be a low-boiling substance or a chemical agent. The foam is extruded through a slit or annular die to form a sheet or board of thickness 0.05 to 2 inches and density 1-10 lb./cu. ft. The extruded foamed material is drawn, usually at an elevated temperature, using a draw-down ratio of between 20:1 and 2:1. The extruded foamed material may be heated by passing it through hot gas or a bath of a heated liquid. Nylon materials can be drawn at room temperature. In the examples polystyrene, polyethylene, polypropylene and a nylon are used.