Patent GB-954296-A (GB)
Title: Improvements in or relating to diaphragms
IPC: H01M50/454
Filed: 1959-09-29
Abstract: 954,296. Coated fabrics. BRITISH FIBRAK SEPARATOR CO. Ltd., M. P. LATHAM, and A. HARDY. Sept. 1, 1960 [Sept. 29, 1959], No. 33096/59. Heading B2E. A permeable diaphragm material comprises a first layer 27 of a porous base material and a second layer 25 of porous sintered thermoplastic powder having a first average particle diameter, there being provided between the first and second layers a sintered thermoplastic powder 26 comprising particles having a second average particle diameter which is smaller than the first average particle diameter, and maintaining the first and second layers in intimate contact across substantially their whole surface to form a porous but effectively continuous bond between the layers. The diaphragm material may be an electric battery separator in which the first layer consists of a fibrous sheet which may comprise cellulose or glass, or a mixture thereof, e.g. about 10% glass fibre and 90% cellulose pulp, impregnated with cured acid-resisting resin, e.g. a water-soluble phenolic resin or polyvinyl chloride latex, which may contain a wetting agent. The second layer may be a layer of sintered powder having an average particle diameter of about 10 microns, and the sintered thermoplastic powder which provides the effectively continuous bond between the first and second layers may be a sintered mixture of a powder having an average particle diameter of from 0À5-1 micron and a powder having an average particle diameter of about 10 microns. A wetting agent may be incorporated in the sintered thermoplastic powder. Layer 25 may have ribs 28 in its surface. The face of the sintered layer and/or the non-coated face of the base material may have pores of predetermined size constituted by the interstices of a continuous lace-like network of thermoplastic extending over the face, the network comprising abutting finely divided particles of the thermoplastic sintered together at their points of contact and adhering to the face. The thermoplastic may be polyvinyl chloride, polyvinyl acetate, polyethylene or polymethyl methacrylate, which may be sintered at 220-230 C. The diaphragm material may be produced by coating a face of a porous base material with a mixture of finely divided particles of a thermoplastic containing at least two constituents of different average particle size such that the particles penetrate into the base material, covering the coating with a layer of finely divided particles of thermoplastic having an average particle size substantially the same as the larger of the constituents, and then sintering the thermoplastic to form a porous membrane which is continuously bonded to the base material by the sintered coating. In the production of an electric battery separator, the base material is a fibrous sheet impregnated with an acid-resisting resin which is partially or wholly cured, e.g. if a water soluble phenolic resin at 230-260 C., prior to the application of the particulate coating; the completion of the curing being effected after sintering. The coating may be effected by brushing the mixture of finely divided particles over the face to be coated or, as shown, the base material in the form of a continuous web may be advanced through a falling curtain of the mixture 9 from vibrating hopper 8, prior to brushing with brush 10, advanced through a falling curtain of particles 12 from vibrating hopper 11, and under a forming roller 13 which may be ribbed or flat. The coated material is then passed through oven 14 to "case harden" the particulate layer, under finishing roller 15, which may be ribbed or flat, and through oven 16 to sinter the particles. Finely divided particles 19 from vibrating hopper 18 may be applied to the face of the sintered layer or to the non-coated face of the base material and after passing under brush 20, sintered, e.g. at 150-250 C., in oven 21, to form an adherent continuous lace-like network of abutting particles having interstices which constitute pores of regulated size. The diaphragm or separator may be impregnated with a wetting agent from spray 22 and dried in oven 23 prior to being cut by guillotine 24. Specification 843,452 is referred to.