Patent GB-829912-A (GB)
Title: Apparatus and process for making cellular rubber
Filed: 1956-11-07
Abstract: A continuous sheet of gas-expanded cellular rubber is produced by continuously forming a rubber composition containing a blowing agent into a sheet, heating the sheet to cause the blowing agent to evolve a gas and expand the rubber composition, intermittently breaking contact between the composition and the surface supporting it during expansion, and vulcanizing the expanded composition.  In one form of apparatus (not shown), the extruded rubber composition is conveyed continuously into a first heating chamber where it is partially vulcanized below a temperature high enough to cause the blowing agent to evolve a gas.  It then passes on to a vibrator conveyer and advances through a second heating chamber where the composition, whilst bouncing on the vibrating conveyer to break contact therewith, is expanded and vulcanization completed.  If desired expansion and vulcanization can be effected in different chambers.  Instead of a vibrator conveyer, a series of air jets positioned below an open mesh conveyer belt can be employed to direct streams of air against the underside of the rubber composition thereby causing it to break contact with the conveyer.  Partial vulcanization before expansion is omitted when an open cell rather than a closed cell sponge is required. Rubbers employed may be natural, e.g. caoutchouc, or synthetic, e.g. polymers and copolymers of butadiene-1,3; 2,3-dimethyl butadiene-1,3; and 1,4-dimethyl butadiene-1,3; copolymers thereof with styrene, methyl and ethyl acrylate, methyl and ethyl methacrylate, acrylonitrile and isobutylene, and polychloroprene. Blowing agents specified are sodium bicarbonate, ammonium carbonate, diazoaminobenzene, dinitrozo pentamethylenetetramine, 1,3-bis-(o-zenyl)-triazene, and p,p1-oxybis-(benzene sulphonyl hydrazide).  In examples, the following compositions are blown and vulcanized: (1) and (3) natural rubber, carbon black, hydrocarbon oil; (2) GR-S rubber, natural rubber, paraffin oil, zinc oxide stearic acid, carbon black, naphthenic hydrocarbon plasticizer, finely-divided urea; (4) butadiene-acrylonitrile polymer, coumarone-indene polymer, naphthenic hydrocarbon plasticizer, carbon black, zinc oxide; (5) polychloroprene, natural rubber, GR-S, paraffin oil, naphthenic hydrocarbon plasticizer, carbon black, zinc oxide, magnesia, stearic acid.  Proportions of the various ingredients are given. Both open and closed cell products are produced.ALSO:A continuous sheet of gas-expanded cellular rubber is produced by continuously forming a rubber composition containing a blowing agent into a sheet, heating the sheet to cause the blowing agent to evolve a gas and expand the rubber composition, intermittently breaking contact between the composition and the surface supporting it during expansion, and vulcanizing the expanded composition.  In one form of apparatus, (not shown), the extruded rubber composition is conveyed continuously into a first heating chamber where it is partially vulcanized below a temperature high enough to cause the blowing agent to evolve a gas. It then passes on to a vibrator conveyer and advances through a second heating chamber where the composition, whilst bouncing on the vibrating conveyer to break contact therewith, is expanded and vulcanization completed.  If desired expansion and vulcanization can be effected in different chambers.  Instead of a vibrator conveyer, a series of air jets positioned below an open mesh conveyer belt can be employed to direct streams of air against the underside of the rubber composition thereby causing it to break contact with the conveyer. Partial vulcanization before expansion is omitted when an open cell rather than a closed cell sponge is required. Rubbers employed may be natural, e.g. caoutchouc, or synthetic, e.g. polymers and copolymers of butadiene-1, 3; 2, 3- dimethyl butadiene -1, 3; and 1, 4- dimethyl butadiene -1, 3; copolymers thereof with styrene, methyl and ethyl acrylate, methyl and ethyl methacrylate, acrylonitrile and isobutylene, and polychloroprene. Blowing agents specified are sodium bicarbonate, ammonium carbonate, diazoaminobenzene, dinitrozo pentamethylenetetramine, 1, 3- bis (o - zenyl) -triazene, and p, p1 oxybis (benzene sulphonyl hydrazide).  In examples the following compositions are blown and vulcanized: (1) and (3) natural rubber, carbon black, hydrocarbon oil; (2) GR-S, natural rubber, paraffin oil, zinc oxide, stearic acid, carbon black, naphthenic hydrocarbon plasticizer finely divided urea; (4) butadiene-acrylonitrile polymer, coumarone-indene polymer, naphthenic hydrocarbon plasticizer, carbon black, zinc oxide; (5) polychloroprene, natural rubber, GR-S, paraffin oil, naphthenic hydrocarbon plasticizer, carbon black, zinc oxide, magnesia, stearic acid. Proportions of the various ingredients are given.  Both open and closed cell products are produced.