GB1300929A - Production of foamed thermoplastics - Google Patents

Abstract

1300929 Extruded expanded thermoplastics BRITISH PETROLEUM CO Ltd 10 June 1970 [9 June 1969] 29076/69 Heading B5A [Also in Division C3] A heat softened thermoplastics containing a mixture of n-pentane and methyl chloride blowing agents, is extruded as a foamed product which is of lower density than is obtainable by the use of either agent alone. The thermoplastics may comprise a polymer or co-polymer of an ethylenically unsaturated monomer, e.g. ethylene, propylene, 4-methyl pentene-1 or styrene, or a substituted monomer such as acrylonitrile, vinyl chloride, vinyl acetate or methyl methacrylate. Preformed expandable beads may be extruded, or one agent may be incorporated in the beads and the other injected therein during extrusion. or both may be injected during extrusion. The thermoplastics is preferably polystyrene, and preferably 3 to 30% by weight of the thermoplastics comprises blowing agent, the weight ratio of pentane to methyl chloride being 5 : 1 to 0À2 : 1 and preferably 0À2 : 1 to 0À4 : 1. A nucleating agent such as mixed sodium bicarbonate and citric acid may be employed. In an example, methyl chloride was injected into polystyrene containing nucleating agent and n-pentane, at 2,500 p.s.i. into the mixing zone of an extruder at 115‹ to 210‹ C., the temperature being reduced in a following cooling extruder to 110‹ C. to yield an extruded rod of overall density 2À0lbs cu.ft. having apolystyrene skin of 0À002 inch thickness and with a foamed core of average cell size 0À026 by 0À022 inch. In further examples, the separate agents produced foams of 3 lbs. (n-pentane), and 2-3 lbs. cu.ft. (methyl chloride).