GB1169879A - Porous Coatings - Google Patents

Abstract

1,169,879. Microporous coating. CARL FREUDENBERG K.G. 21 Dec., 1966 [31 Dec., 1965], No. 57147/66. Heading B2E. [Also in Division C3] A flexible microporous layer of vulcanised soft synthetic rubber having a transition temperature not below -25‹C, and having an elongation at break of at least 200% is made by applying to a porous support a viscous aqueous latex of a synthetic rubber which has carboxylic acid groups on the polymer chain containing a vulcanising agent in amount such as to give the above elongation, coagulating the latex on the support and vulcanising the coating. The porous support is generally a non-woven fleece or web. The rubber may be a copolymer of butadiene or chloroprene with acrylonitrile, styrene or methylmethacrylate and with 2-20% of a polymerisable carboxylic acid e.g. acrylic, methacrylic and itaconic acids. The amount of vulcanising agent does not exceed 2% in the case of sulphur or 5% in the case of ZnO. The latex may have a rubber concentration of from 20-60% by weight and a viscosity of between 2,000 and 20,000. Thickening agents such as protective colloids e.g. methyl cellulose alginates. P.V.A., soluble salts of polyacrylic acid, casein gelatins and tragacanth may be added to the latex. Accelerators and other additives such as fillers and pigments may be added. Less than 80% of air, based on the volume of fluid is stirred into the latex. The latex may be applied direct to the porous support, e.g. by a coating calender, such as swelling resistant paper or a silicone band or strip. Coagulation may be by dipping the coated porous support in a coagulating bath containing a solution in an organic solvent of suitable salts or acids, or by cooling or by heat sensitisation by including a suitable salt e.g. NH 4 Cl, NH 4 NO 3 or sodium silicofluoride. After coagulation vulcanisation may be effected with hot or steam. The surface may be buffed, or a grain pattern may be formed with a press or a graining calender. A suitable coating finish may be applied by spraying or with lacquering rollers. The finish may be of polyamide, polyurethane, or acrylic or methacrylic ester polymer.