Patent GB-1012298-A (GB)
Title: Microporous materials and process of making the same
IPC: C09K23/00
Filed: 1961-12-15
Abstract: A porous material is composed of a base material having relatively large pores within which particulate material, including at least 5% of fibrous material, is deposited to diminish the pore diameter to less than 25 micros over part of the length of the pores.  The material may be used as filters, cold sterilizers and porous separators as in batteries and diaphragm cells.  It can also be used for shock absorbers, moulded cushioning, acoustical absorbers, and in heat and sound insulation.  The preferred base is paper, particularly an all cotton paper, but other materials suitable to provide a base are stated to be porous forms of metals and of natural or synthetic plastic materials such as aluminium and synthetic resins and cellulose derivatives, sponges or foams of polyurethane, polyvinyl, chloride, polyethylene and polypropylene, textile fabrics, and non-woven fibrous layers such as felts, mats and bats formed from the following materials in fibre form; glass, asbestos, potassium titanate, aluminium silicate, mineral wool, regenerated cellulose, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyacrylonitrile, polyethylene, polypropylene, rubber, polymers of terephthalic acid and ethylene glycol, polyamides, casein, zein, cellulose acetate, viscose rayon, hemp, jute, linen, cotton, silk, wool, mohair, paper and metallic fibres, such as iron, copper, aluminium, stainless steel, brass, Monel (Trade Mark), silver and titanium.  The particulate material to be deposited in the pores is preferably fibrous and any member of the above list of materials in fibre form may be used.  Where non-fibrous particulate materials are used it is necessary to mix them with at least 5%, or better at least 25% of fibrous materials.  Suitable particulate materials in non-fibrous form are diatomaceous earth, Fuller's earth, silicon, magnesia, silica, talc, silica gel, alumina, quartz, carbon, activated carbon, clays, synthetic resins and cellulose derivatives-such as polyethylene, polyvinyl chloride, polystyrene, polypropylene, urea-formaldehyde, phenol-formaldehyde, polytetrafluoroethylene, polymers of terephthalic acid and ethylene glycol, polyacrylonitrile, ethyl cellulose, polyamides, and cellulose acetate-propionate-aluminium, silver, platinium, iron, copper, nickel, chromium, titanium, brass, stainless steel, bronze, cupronickel, beryllium, copper and substances to which the Trade Marks "Monel", "Inconel" and "Hastelloy" apply.  The fluid used to suspend the particulate material and to convey it into the base may be water, polyalkylene glycols-such as polyethylene glycols, poly 1,2-propylene glycols, and mono and di-alkyl ethers of them, such as methyl, ethyl, butyl, and propyl mono- and di-ethers dialkyl esters of aliphatic dicarboxylic acids-such as di-2-ethylhexyl adipate and glutarate-mineral lubricating oils, hydraulic fluids, vegetable oils, and organic solvents such as xylene, silicones, chloro, bromo and fluoro hydrocarbons, and petroleum ethers.  A dispersing agent may be used to provide a stable slurry; such an agent may be as used in paper-making, such as the alkali metal polyphosphates, e.g. sodium hexametaphosphate, sodium pyrophosphate, sodium metasilicate, pentasodium tripolyphosphate and sodium metaphosphate, or any synthetic surfactant or organic emulsifier may be used.  Various steps may be taken to ensure deposition of particulate material within the base, such as impregnation with dispersant before application of particulate material, or blending of dispersant and slurry before impregnation followed by reduction in the proportion of dispersant as impregnation proceeds, or addition of a precipitating agent either to the impregnant or the base. Flocculating agents that may be employed to facilitate deposition are aluminium sulphate (used in the presence of a polysulphate) and sodium carbonate (used in absence of a polysulphate). Potassium titanate fibres may also be used as flocculant for asbestos fibres.  Wetting agents may in some circumstances be necessary.  Bonding agents or binders may be employed to anchor the particulate material to the base; these may be in the form of thermoplastic particles, e.g. fibrids, or fibres of polyvinyl chloride, nylon, polyacrylonitrile, esters of terephthalic acid and ethylene glycol, cellulose acetate and polyethylene.  Other possible thermoplastic binders are polypropylene, polymethylene, polyisobutylene, ethyl cellulose, copolymers of vinyl chloride and vinyl acetate, polyvinylidene chloride, polyvinyl butyral, polyacrylic resins such as polymethyl methacrylate, alkyd resins and synthetic rubbers such as butadiene-styrene polymers. Thermosetting binders that can be used include phenol-urea- and melamine-formaldehyde resins, polyester resins, and epoxy resins, such as polymers of ethylene chlorohydrin and bisphenol.  Other binders are polytetrafluoroethylene, polytrifluorochloroethylene, starch, casein, terpene, resins, and ligninsulphonate resins. Binding may also be brought about by means of heat, or solvent and pressure. Examples are given using an all-cotton paper base and various proportions of short and long fibred asbestos with and without fibrous glass and diatomaccous earth or potassium titanate fibres; pore diameters from 0.15 to 0.89 micron are given for the products of the examples.  In order to ensure that the particulate material remains in the pores, the surface of the base opposite to that from which impregnation took place may be partially coated with plastic material.  Alternatively, the porous material can be backed by a layer having finer pores as by bonding to form a laminate.ALSO:A porous material is composed of a base material having relatively large pores within which particulate material, including at least 5% of fibrous material, is deposited to diminish the pore diameter to less than 25 microns over part of the length of the pores.  The material may be used as filters, cold sterilizers and porous separators as in batteries and diaphragm cells.  It can also be used for shock absorbers, moulded cushioning, acoustical absorbers, and in heat and sound insulation.  The preferred base is paper, particularly an all cotton paper, but other materials suitable to provide a base are stated to be porous forms of metals and of natural or synthetic plastic materials, such as aluminium and synthetic resins and cellulose derivatives, sponges or foams of polyurethane, polyvinyl chloride, polyethylene and polypropylene, textile fabrics, and non-woven fibrous layers such as felts, mats and bats formed from the following materials in fibre form: glass, asbestos, potassium titanate, aluminium silicate, mineral wool, regenerated cellulose, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyacrylonitrile, polyethylene, polypropylene, rubber, polymers of terephthalic acid and ethylene glycol, polyamides, casein, zein, cellulose acetate, viscose rayon, hemp, jute, linen, cotton, silk, wool, mohair, paper and metallic fibres, such as iron, copper, aluminium, stainless steel, brass, "Monel" (Trade Mark), silver and titanium.  The particulate material to be deposited in the pores is preferably fibrous and any member of the above list of materials in fibre form may be used.  Where non-fibrous particulate materials are used it is necessary to mix them with at least 5%, or better at least 25% of fibrous materials.  Suitable particulate materials in non-fibrous form are diatomaceous earth, Fuller's earth, silicon, magnesia, silica, talc, silica gel, alumina, quartz, carbon, activated carbon, clays, synthetic resins and cellulose derivatives-such as polyethylene, polyvinyl chloride, polystyrene, polypropylene, urea-formaldehyde, phenol-formaldehyde, polytetrafluoroethylene, polymers of terephthalic acid and ethylene glycol, polyacrylonitrile, ethyl cellulose, polyamides, and cellulose acetate-propionate-aluminium, silver, platinum, iron, copper, nickel, chromium, titanium, brass, stainless steel, bronze, cupronickel, beryllium, copper and substances to which the Trade Marks "Monel", "Inconel" and "Hastelloy" apply.  The fluid used to suspend the particulate material and to convey it into the base may be water, polyalkylene glycols-such as polyethylene glycols, poly 1,2-propylene glycols, and mono- and di-alkyl ethers of them, such as methyl, ethyl, butyl, and propyl mono- and di-ethers-dialkyl esters of aliphatic dicarboxylic acids-such as di-2-ethylhexyl adipate and glutarate-mineral lubricating oils, hydraulic fluids, vegetable oils, and organic solvents such as xylene, silicones, chloro, bromo and fluoro hydrocarbons, and petroleum ethers.  A dispersing agent may be used to provide a stable slurry; such an agent may be as used in paper-making, such as the alkali metal polyphosphates, e.g. sodium hexametaphosphate, sodium pyrophosphate, sodium metasilicate, pentasodium tripolyphosphate and sodium metaphosphate, or any synthetic surfactant or organic emulsifier may be used.  Various steps may be taken to ensure deposition of particulate material within the base, such as impregnation with dispersant before application of particulate material, or blending of dispersant and slurry before impregnation followed by reduction in the proportion of dispersant as impregnation proceeds, or addition of a precipitating agent either to the impregnant or the base. Flocculating agents that may be employed to facilitate deposition are aluminium sulphate (used in the presence of a polysulphate) and sodium carbonate (used in the absence of a polysulphate). Potassium titanate fibres may also be used as a flocculant for asbestos fibres.  Wetting agents may in some circumstances be necessary.  Bonding agents or binders may be employed to anchor the particulate material to the base; these may be in the form of thermoplastic particles, e.g. fibrids, or fibres of polyvinyl chloride, nylon, polyacrylonitrile, esters