GB1272129A - Press-moulded cross-linked polymeric foams and a process for producing the same - Google Patents

Abstract

1,272,129. Compressed cross-linked polymer foamed sheets. TORAY INDUSTRIES Inc. 27 Aug., 1969 [28 Aug., 1968; 7 Nov., 1968], No. 42737/69. Headings C3C and C3P. A foam sheet comprises a cross-linked polymer of an aliphatic C 2-6 α-olefin, a chlorinated product thereof, a cross-linked copolymer containing more than 50% by weight of an aliphatic α-olefin, a mixture thereof, or a mixture thereof with not more than 30% by wt. of another thermoplastic resin or rubber, the foam sheet having closed cells, the gel percentage as defined of the foam being at least 10% by weight, the ratio of the mean cell diameter in the thickness direction of the foam sheet to the mean cell diameter in the length direction of the foam sheet being less than 2/5, the mean cell diameter in the length direction being 15-800 microns, the mean cell diameter in the thickness direction being 1-250 microns, and the apparent density of the foam being 0À1- 0À8 g./ml. The polymer may be polyethylene, polypropylene, an ethylene-propylene or -vinyl acetate copolymer and may be mixed with butyl rubber. The foam sheet may be made by heating a foam comprising the above crosslinked polymers having closed cells and a foaming expansion factor of 3-20 times, a mean cell diameter of less than 500 microns, and a gel percentage as defined of at least 10% by weight to a temperature of at least the softening point thereof to render the foam plastic, compressing the heated foam to a thickness less than ¢ of the original thickness to form a sheet having an apparent density from 0À1 to 0À8 g./ml., cooling the foam to a temperature at least 30‹ C. lower than the softening point of the polymer, and then releasing the compressive pressure.