Manufacture of asbestos products by electrophoretic deposition

Articles containing substantial proportions of both chrysotile asbestos fibres and organic polymeric material are produced by forming a mixed colloidal anionic aqueous dispersion of chrysotile asbestos fibres and particles of the polymeric material, applying a voltage between two electrodes immersed in the dispersion whereby the fibres and particles migrate towards the anode and form a deposit on it or on an ion-permeable membrane, e.g. a fine mesh cloth, in the path to the anode, and when a deposit of the required thickness has been formed removing the anode or membrane and the deposit as a unit from the dispersion. Typically the deposit is subsequently stripped from the anode or membrane either before or after drying. The dispersion may also contain additional fibres not colloidally dispersed as well as other finely divided material, these additional materials being co-deposited with the asbestos and polymeric material, and may contain a water-soluble soap so that if the anode is of a metal that corrodes during the process a water-insoluble soap is also included in the deposit, thereby improving its wet-strength. To maintain the composition of the dispersion constant, the dispersion which preferably is continuously or periodically circulated in a separate circuit through a reservoir from which dispersion is fed by a metering pump to and through the electro-deposition bath is replenished periodically or continuously, e.g. with undispersed constituents which are dispersed by a pump in the reservoir circulation. The organic polymeric material may be synthetic rubbers, thermoplastic resins such as polythene, polyvinyl chloride, polystyrene or polyester resins, thermosetting resins or mixtures thereof. The additional fibres employed may be amosite or crocidolite asbestos or undispersed chrysotile asbestos, slag wool, or chopped glass fibre rovings while finely divided particles of metal, graphite, colloidal silica, clay, or lentonite may also be included in the dispersion, bentonite acting as a subsidiary dispersion agent. Examples of anionic dispersing agents are alkyl aryl sulphonates, alkyl sulphosuccinates or sulphated higher alcohols. The anode may be of Al, Zn, Cu, Pb, or Fe or of non-corrodible materials such as Pt or carbon, and may be a plate or cylinder. Several anodes may be employed simultaneously and a diaphragm may be disposed close to the cathode to prevent cathodically evolved gas contaminating the dispersion.