Patent GB-760569-A (GB)
Title: Manufacture of sponge rubber from natural and/or synthetic rubber latex
Inventor: BETHE EUGENE JOHN
IPC: C08L21/00
Filed: 1954-12-23
Abstract: In a method of making latex foam rubber a foamed vulcanizable compounded synthetic rubber latex containing a non-gaseous gelling agent is shaped before gelling takes place, the shaped foam is gelled in the presence of a gas containing at least 50 per cent by volume of carbon dioxide, and the gelled foam is vulcanized.  The synthetic rubber latex may be that of butadiene-1,3, isoprene, chloroprene, piperylene, 2,3-dimethylbutadiene-1,3, or a mixture of such butadienes-1,3, or one or more butadienes-1,3 copolymerized with an aryl olefine, e.g. styrene, a-methyl styrene, parachlorostyrene, dichlorostyrene, or vinyl naphthalene, or with an a-methylene carboxylic acid, ester, nitrile, or amide, e.g. acrylic acid methyl, acrylate, methyl methacrylate, crylonitrile, methacrylonitrile, or methacrylamide, or with isobutylene, methyl vinyl ether, methyl vinyl ketone, or vinylidene chloride.  A mixture of such synthetic rubber latex and natural rubber latex may also be used.  The gas, which functions as an auxiliary gelling agent to accelerate the gelling of the foam, may consist of substantially pure carbon dioxide and be provided as an atmosphere surrounding the moulds or other shaping devices for the foam.  Alternatively or additionally the gas may be forced through the foam.  The non-gaseous gelling agent may comprise sodium silicofluoride, or a combination of zinc oxide with ammonium salts.  An amount of sodium silicofluoride which is 0.5 to 4 per cent by weight of the rubber in the latex is preferably used.ALSO:In a method of making latex foam rubber a foamed vulcanizable compounded natural and or synthetic rubber latex containing a non-gaseous gelling agent is shaped before gelling takes place, the shaped foam is gelled in the presence of a gas containing at least 50 per cent by volume of carbon dioxide, and the gelled foam is vulcanized.  The said gas which functions as an auxiliary gelling agent to accelerate the gelling of the foam, may consist of substantially pure carbon dioxide and be provided as an atmosphere surrounding the moulds or other shaping devices for the foam.  Alternatively or additionally the gas may be forced through the foam.  The non-gaseous gelling agent may comprise sodium silicofluoride, or a combination of zinc oxide with ammonium salts.  An amount of sodium silicofluoride which is 0,5 to 4 per cent by weight of the rubber in the latex is preferably used.  The latex may be that of natural rubber or of a butadiene polymer or copolymer, or a mixture of such latices.  In an example natural rubber latex (60 per cent solids) is compounded in a vulcanizable composition comprising in parts by weight, rubber 100, potassium ferro-cyanide (stabilizer) 0,1, potassium oleate 0,9, castor-oil soap 1, triethyl-trimethylene-triamine (for improving the physical properties of the foam rubber) 0,5, and vulcanizing and filler ingredients.  The compounded latex is whipped into a foam and an aqueous slurry containing 0,75 parts by weight of sodium silicofluoride added.  The foam is then poured into a mould and allowed to gel at room temperature in an atmosphere of carbon dioxide, when the gelling is completed in 3 minutes.  If the same foam composition is gelled in air at room temperature the gelling period is 55 minutes.  Triethyl trimethylene-triamine may be added to the sodium silicofluoride slurry.