Patent GB-756649-A (GB)
Title: Improvements in or relating to a process for the manufacture of closed-cell cellular material of natural and/or synthetic rubber
Filed: 1954-09-14
Abstract: In a method of manufacturing a closed cell cellular article of natural and/or synthetic rubber comprising preparing a vulcanizable mix containing a blowing agent, shaping the mix to the desired shape in miniature size and confining in a mould, heating so that the blowing agent generates gas and vulcanization is effected, releasing the vulcanized material while still hot, and allowing it to expand and cool to assume its final size, the mix includes a vulcanization accelerator capable of causing the vulcanization to proceed after a particular time interval without substantial change in tensile strength and modulus of elasticity of the natural and/or synthetic rubber, and the heating is continued for at least said time interval, whereby the expansion and shrinkage of the article when released from the mould is determined only by the amount of blowing agent used, and is substantially independent of the exact period of vulcanization. The vulcanisation accelerator may comprise benzothiazyl disulphide admixed with tetramethyl thiuram disulphide, cyclohexyl-2-benzothiazole sulphenamide admixed with tetramethyl thiuram disulphide, and either alone or in combination, benzyl hexamethylene tetra-ammonium - 2 - benzothiazyl sulphide, dibenzo-thiazyl dimethyl thiourea, diorthotolyl guanidine, and tetra-ethyl thiuram disulphide.  In an example, a mixture of GRS synthetic rubber, polystyrene, calcium silicate, coumarone resin, light oil, paraffin wax, stearic acid, zinc oxide, benzothiazyl disulphide, tetramethyl thiuram disulphide, sulphur, and dinitrosopentamethylene tetramine (blowing agent) is formed into shaped pieces and vulcanized in moulds of the same internal size and shape for periods up to 24 minutes.  The degrees of expansion and subsequent shrinkage of the vulcanized articles when released from the moulds are found to be substantially constant after a period of 12 minutes.ALSO:In a method of manufacturing a closed-cell cellular article of natural and/or synthetic rubber material in which a vulcanizable mix of the material is prepared containing a blowing agent shaping the mix to the desired shape in minature size and confining in a mould heating the material so that the blowing agent generates gas and vulcanization is effected releasing the vulcanized material while still hot, and allowing it to expand and cool to assume its final size, the mix includes a vulcanization accelerator capable of causing the vulcanization to proceed after a particular time interval without substantial change in tensile strength and modulus of elasticity of the natural and/or synthetic rubber material, and the heating is continued for at least said time interval, whereby the expansion and shrinkage of the article when released from the mould is determined only by the amount of blowing agent used, and is substantially independent of the exact period of vulcanization.  The vulcanization accelerator may comprise benzothiazyl disulphide admixed with tetramethyl thiuram disulphide, cyclohexyl-2-benzo-thiazole sulphenamide admixed with tetramethyl thiuram disulphide, and either alone or in combination, benzyl hexamethylene tetra-ammonium-2-benzothiazyl sulphide, dibenzo-thiazyl dimethyl thiourea, diorthotolyl guanidine, example a mixture in parts by weight of GRS synthetic rubber 100, high styrene and tetraethyl thiuram disulphide.  In an example a mixture in parts by weight of GRS synthetic rubber 100, high styrene resin 50, calcium silicate 75, coumarone resin 5, light oil 5, paraffin wax 1.5, stearic acid 2, zinc oxide 5, benzothiazyl disulphide 2, tetramethyl thiuram disulphide 0.3 sulphur 3, and dinitroso-pentamethlylene tetramine (blowing agent) 4 is formed into shaped pieces and vulcanized in moulds of the same internal size and shape for periods up to 24 minutes.  The degrees of expansion and subsequent shrinkage of the vulcanized articles when released from the moulds are found to be substantially constant after a period of 12 minutes.