GB766319A - Improvements in or relating to the manufacture of foam rubber - Google Patents

Abstract

In a method of manufacturing shaped articles of foam rubber, fresh natural rubber latex of a strength of not more than 4,5 lbs. rubber content per gallon is treated with ammonia to effect maturing thereof, the treated latex is frothed with a frothing agent when an average maturity of not more than 5 days has been attained, a mould of the required shape filled with the frothed latex, and the latex gelled in the presence of sodium silicofluoride and ammonium sulphate and with the application of heat insufficient to vulcanize the latex, thereafter covering the mould and heating the latex with moist steam to effect vulcanization. The amount of ammonia used is preferably between 0,25 and 0,068 per cent by weight of the latex, the ammonia treatment being effected at 75 DEG to 95 DEG F. A stabilizing agent such as sodium sulphite or bisulphite may be added to the latex prior to the treatment with ammonia. The gelling is preferably effected in two or more stages, by partly filling the mould and gelling the latex therein, and adding and gelling latex in further stages or a further stage until the mould is filled. The water evolved during the gelling is allowed to drain into recesses in the bottom of the mould, whilst some evaporates and escapes around the mould cover. In an example 4 gallons of latex having a rubber content of 3,5 lbs. per gallon, and 48 hours after treatment with ammonia, has its ammonia concentration adjusted to not more than 0,2 per cent by weight, and is divided into two portions of 3 gallons and 1 gallon respectively. Sulphur accelerators, antioxidants, colouring pastes, and ammonium sulphate are then added to each portion. The 3 gallon portion is then admixed with soap solution and frothed, zinc oxide powder added, and then sodium silicfluoride. The mix is beaten, poured into a mould of the construction described in Specification 766,320, and gelled at 110 DEG to 130 DEG F. The gelled latex is then allowed to cool to room temperature, and the 1 gallon portion frothed with soap solution, admixed with zinc oxide and sodium silicofluoride, and then poured into the mould to fill the latter. The gelling is completed at 150 DEG F. and steam vulcanizing effected at 212 DEG F.