GB1039540A - Improvements in or relating to coating methods - Google Patents

Abstract

A surface of a web of paper or board is coated by forming a foam of a liquid coating composition comprising at least one coating component with a gas or vapour, applying the foam to a surface and mechanically disintegrating substantially all of the foam to form a continuous surface coating over the coating area. The surface of the web may be coated on the paper or board-making machine as an integral part of the manufacturing process. The coating component may be a vinyl polymer or copolymer, e.g. polyethylene, polyvinyl chloride or acetate, polyvinylidene chloride, chlorinated polyvinyl chloride, polymethyl methacrylate, polyacrylic acid, butadiene-styrene or -acrylonitrile, acrylonitrile-butadiene-styrene terpolymers, natural rubber, synthetic polyisoprene, polybutadiene, and butyl rubber, and may be in the form of a latex. The vinyl polymer may be polyvinyl alcohol and is used in the form of an aqueous solution in the coating composition. The coating component may be a condensation polymer e.g. aminoplasts such as urea or melamine-formaldehyde, phenoplasts such as phenol-formaldehyde, polyesters and polyamides, polysaccharide or derivative thereof e.g. starch, cellulose, cellulose acetate, carboxymethyl cellulose, ethyl cellulose, a plant gum e.g. mannan, locust bean, guar gum, an animal or vegetable protein e.g. casein or gelatine, an organo silicon polymer, or an inorganic polymer e.g. silicates of alkali metals and alkaline earth metals, clays, waxes, synthetic and natural e.g. paraffin, microcrystalline, halo, bees and carnauba wax; rosin and rosin derivatives e.g. hydrogenated rosin; siccative and semi-siccative oils e.g. linseed, dehydrated castor, tung, siticica oil and penta erythrityl tetra linoleate; and potentially reactive compositions e.g. epoxy resins in combination with polyamides, polyamines or polyesters. The coating composition may contain one or more of surface active agents, pigments, fillers, dyestuffs, and vapour phase corrosion inhibitors. The composition may be foamed to at least twice e.g. four or ten times its original volume. The foam may be p substantially immobile. The foam may be applied to the surface and disintegrated by means of a knife or edge extending across the surface or by air knife, rolls, rod or reciprocating brush coater. The foam may be supplied to the coating means via a manifold. The composition may contain one or more thickening agents e.g. polyvinyl alcohol and gums. The gas may be air, nitrogen, carbon dioxide, fluoro- and chlorofluoro-alkanes and -cycloalkanes, or may be formed in situ by reaction of two or more substances.ALSO:A surface of a web of paper or board is coated by forming a foam of a liquid coating composition comprising at least one coating component with a gas or vapour, applying the foam to a surface and mechanically disintegrating substantially all of the foam to form a continuous surface coating over the coating area. The surface of the web may be coated on the paper or board-making machine as an integral part of the manufacturing process. The coating component may be a vinyl polymer or copolymer, e.g. polyethylene, polyvinyl chloride or acetate, polyvinylidene chloride, chlorinated polyvinyl chloride, polymethyl methacrylate, polyacrylic acid, butadiene-styrene or -acrylonitrile, acrylonitrilebutadienet-styrene terpolymers, natural rubber, synthetic polysoprene, polybutadiene, and butyl rubber, and may be in the form of a latex. The vinyl polymer may be polyvinyl alcohol and is used in the form of an aqueous solution in the coating composition. The coating component may be a condensation polymer e.g. aminoplasts such as urea or melamine-formaldehyde, phenoplasts such as phenol-formaldehyde, polyesters and polyamides, a polysaccharide or derivative thereof e.g. starch, cellulose, cellulose acetate, carboxymethyl cellulose, ethyl cellulose, a plant gum e.g. mannan, locust bean, guar gum, an animal or vegetable protein e.g. casein or gelatine, an organo silicon polymer, or an inorganic polymer e.g. silicates of alkali metals and alkaline earth metals, clays, waxes, synthetic and natural e.g. paraffin, microcrystalline, halo, bees and carnauba wax; rosin and rosin derivatives e.g. hydrogenated rosin; siccative and semi-siccative oils e.g. linseed, dehydrated castor, tung, siticica oil and penta erythrityl tetra linoleate; and potentially reactive compositions e.g. epoxy resins in combination with polyamides, polyamines or polyesters. The coating composition may contain one or more of surface active agents, pigments, fillers, dyestuffs, and vapour phase corrosion inhibitors. The composition may be foamed to at least twice e.g. four or ten times its original volume. The foam may be substantially immobile. The foam may be applied to the surface and disintegrated by means of a knife or edge extending across the surface or by air knife, rolls, rod or reciprocating brush coater. The foam may be supplied to the coating means via a manifold. The composition may contain one or more thickening agents e.g. polyvinyl alcohol and gums. The gas may be air, nitrogen, carbon dioxide, fluoro- and chlorofluoro-alkanes and -cycloalkanes, or may be form in situ by reaction of two or more substances.