GB334581A - Improvements in or relating to the manufacture of articles of rubber and similar substances from aqueous dispersions containing such substances - Google Patents

Abstract

334,581. Dunlop Rubber Co., Ltd., James, R. G., and Twiss, D. F. June 6, 1929. Addition to 301,100. Emulsions, making.-In the electrophoretic de,- position of rubber or other organic material from a dispersion the particles of which normally carry a negative charge, the hydrogen ion concentration is increased in the presence of formaldehyde to such a degree that the charge on the particles is reversed without coagulation occurring; deposition is then effected on the cathode or a porous or semi-permeable mould surrounding it. When depositing from natural or dialyzed ammoniated latex the addition of protective colloids is not necessary, but when treating latices which have been deprived of their natural protective colloids, e.g. by centrifuging, a small addition of a protective colloid such as blood albumen is desirable. In an example 100 parts of preserved natural latex containing 35 parts of rubber and 0.6 parts of ammonia are treated with 38 per cent formaldehyde until the pH value falls to 6. 50 parts of distilled water are then added. 100 parts of 40 per cent acetic acid are then added, whereupon reversal of charge takes place. In another example 100 parts of concentrated latex containing 60 parts of rubber and 0.5 parts of ammonia are treated with sufficient 38 per cent formaldehyde to produce a pH value, measured 10 to 15 minutes after the addition, of 7.5. 100 parts of a neutral aqueous solution containing 0.7 parts of casein previously dissolved in the minimum quantity of dilute ammonia is then added, and finally 100 parts of 60 per cent acetic acid rapidly poured into the well-stirred mixture. It is possible to reduce the pH value by addition of formaldehyde to 4.5 without coagulation, the particules retaining their negative charge. The dispersions treated may be of rubber, guttapercha, balata, or other vegetable resins analogous thereto, unvulcanized or vulcanized and may contain vulcanizing or compounding ingredients and mav be natural or artificial; they may also be of rubber reclaim or synthetic rubber. The dispersions may contain addition agents adapted to prevent formation of gas at the cathode. Specification 331,563 is referred to.