GB414234A - Improvements in or relating to the manufacture of porous rubber - Google Patents

Abstract

An aqueous rubber, gutta, or like dispersion is coagulated in the presence, in distribution through the mass, of grains of a pore-forming core material, which material is capable of remaining solid at normal temperatures and is soluble or colloidally dispersible by action of hot water or prolonged action of cold water upon it, and thereafter extracting the core material. The process is particularly applicable to the production of moulded articles. The dispersions may be natural or artificial, and may be in the form of concentrated or diluted latex. The core material may be a reversible colloid, e.g. glue, gum arabic, agar-agar, gelatine, gum tragacanth, or dextrin, or molasses or other sugar substances; or a product of the partial hydrolysis of starch or cellulose such as that obtainable from bleaching residues. Or the grains may be formed partly of these materials and partly of an inert powder, e.g. talc, kaolin, calcium carbonate. The dispersion may contain vulcanizing agents, accelerators, antioxidants, and minerals or other softeners. The grains may contain or be coated with a coagulant, e.g. a heat-destabilizing agent such as magnesium or calcium sulphate, or di-substituted aromatic guanidines, or ammonium salts in conjunction with zinc oxide, or heat-destabilizing agents may be added to the dispersion. The rubber dispersion may be unvulcanized or pre-vulcanized. Vulcanization may occur when the temperature is raised to cause coagulation, or the temperature may be further raised after coagulation, or the hot water used to extract the core material may effect vulcanization. The dispersion may be poured into a mould containing the core material, or the latter may be mixed with the dispersion before application to the mould. The mould may be made of material incapable of withstanding the usual high temperatures of vulcanization, e.g. wood or plaster of paris. Examples are given illustrating the making of the grains or pellets and the treatment of mixtures of pellets and dispersions; according to Example III, the latex may be mixed with an aqueous emulsion of mineral oil.