GB809749A - Improvements in or relating to the production of moisture-proof sheet wrapping materials - Google Patents

Abstract

809,749. Coating webs; water-sensitive sheet materials. BRITISH CELLOPHANE Ltd. May 23, 1957 [May 28, 1956], No. 16459/56. Drawings to Provisional Specification. Class 140. Water-sensitive sheet material is coated with synthetic organic film-forming polymer by applying a thin coating of a liquid aqueous dispersion and, when the coating is still wet, bringing the coated surface of the sheet into contact with the barrel of a water-wet smoothing roller in such a way that at the zone of contact the barrel of the smoothing roller is moving in a direction opposite to that of the movement of the sheet. The method of the invention is particularly applied to coating organic non- fibrous material such as regenerated cellulose with polymers and copolymers of ethylenically unsaturated compounds, but sheets of paper or films of alginic acid derivatives, of protein such as gelatin or casein, of lowly substituted cellulose ester or ether, or of polyvinyl alcohol may be coated. The coating materials may comprise polyvinylidene chloride, polyvinyl chloride or copolymers of ( 1 ) vinylidene chloride plus at least one other ethylenically unsaturated compound such as acrylonitrile; (2) vinylidene chloride plus a mixture of one or more vinyl or substituted vinyl compounds such as methacrylonitrile, a monomeric alkyl ester of acrylic or methacrylic acid having 1 to 5 carbon atoms in the alkyl group (e.g. methyl methacrylate), monomeric vinyl chloride, vinyl acetate or styrene and with or without one or more of such acidic ethylenic compounds as itaconic or citraconic acid or their anhydrides or mesaconic acid and with or without acrylonitrile in addition to the vinyl or substituted vinyl compound or compounds or in substitution for one of the vinyl or substituted vinyl compounds when another is present; (3) vinylidene chloride, acrylonitrile and one or more of the acidic ethylenic compounds such as above ; (4) vinyl chloride and vinyl acetate. The water-wetted roller may be partially immersed in a water bath and excess water may be removed therefrom by a doctor blade. A stationary pad, pressed into contact with the surface of the roller below the surface of the water in the bath, frees the barrel from deposits of polymer. After leaving the smoothing roller the base sheet may be heat-dried and its opposite surface similarly coated, the coatings then being consolidated by further heat treatment. A pair of base sheets may be coated simultaneously in the nip of a pair of horizontal rollers, and may then be separated for subsequent treatment. Jockey rollers mounted on pivoted arms may be provided to vary the arc of contact of the separated base sheets with their smoothing rollers. Specifications 663,645 and 756,851 are referred to.