Patent GB-1178472-A (GB)
Title: Fluid-Permeable Fibrous Multilayer Materials and Process of Making the Same
IPC: B01D53/02
Filed: 1967-02-27
Abstract: 1,178,472. Micro-porous multilayer filter. LLOYD & HILLMAN Ltd. 27 Feb., 1967 [28 Feb., 1966], No. 9171/67. Heading D2B. A multi-layer fluid-permeable material used to remove micro-organisms or particles from fluids or as semi-permeable membranes for gases and liquids is made by flowing (under the influence of gravity or a pressure differential of less than 12" of water) over and through a foraminous support an aqueous dispersion containing at least 25% of fibres agitating at first (optionally with a deflocculating agent) to separate the fibres and deposit a 0.0005 to 0.01 inch layer of maximum pore diameter less than 25 microns of separate fibres each parallel to the plane of the support, reflocculating (by settling or adding a flocculating agent) before drawing through the remaining liquid (at least 80% of the whole) to deposit a thicker (e.g. 0.003 to 0.5 inch) coarser layer of clumps and single fibres of average pore diameter less than 150 microns and voids volume of at least 75%, in which some of the fibres are at 30‹ or more to the plane of the support and their layer. At the interface, fibres in the two layers interlock. The support may later be stripped off, or left as part of the filter, which may be plane or corrugated. Preferred fibres include asbestos, glass, quartz, potassium titanate, colloidal aluminium oxide, aluminium silicate, mineral wool, regenerated cellulose, microcrystalline cellulose, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyacrylonitrile, polyethylene, polypropylene, rubber, polymers of terephthalic acid and ethylene glycol, polyamides, casein or zein fibres cellulose acetate, viscose rayon, hemp, jute, linen, cotton, silk, wool, mohair, paper, metallic fibres and needle-shaped clays. Non-fibrous particles, such as diatomaceous earth, magnesia, silica, talc, silica gel, alumina, quartz, carbon, activated carbon, clays, synthetic resins and cellulose derivatives such as polyethylene, polyvinyl chloride, polystyrene, polypropylene, ureaformaldehyde, phenol-formaldehyde, polytetrafluoroethylene, polytrifluorochloroethylene, polymers of terephthalic acid and ethylene glycol, polyacrylonitrile, ethyl cellulose, polyamides, cellulose acetate propionate, and metal particles may be added to the dispersion. Dispersing media other than water are specified. Examples of binding agents include thermosetting resins, such as polyepoxide resins, polyester resins and phenol (or urea or melamine)-formaldehyde resins, used with curing agents such as organic amines and quaternary, ammonium compounds, acidic organic orthophosphates, sulphonic acid or sulphonyl halides or acid anhydrides; thermoplastic solid binders such as polyethylene, polypropylene, polymethylene, polyisobutylene, polyamides, cellulose acetate, ethyl cellulose, copolymers of vinyl chloride and vinyl acetate polyvinyl chloride, polyvinylidene chloride, polyvinylidene fluoride, polyvinyl butyral, polytetrafluoroethylene polytrichlorofluoro ethylene, lignin-sulfonate resins, starch binders, casein binders, terpene resins and polyacrylic resins; elastomeric binders such as natural or synthetic rubbers, especially neoprene, with curing agents such as metallic oxides, zinc salts of, 2-mercapto-benzo-thiazole, and zinc dibutyl dithiocarbamate. Precipitating agents for the binder include magnesium chloride, hydrated aluminium sulphate, aluminium nitrate and calcium salts. Dispersing agents of any known type may be used. Anionic, non ionic and cationic wetting agents may be added. Reference has been directed by the Comptroller to Specification 1,066,480.