Patent GB-700619-A (GB)
Title: Improvements in or relating to the production of moistureproof regenerated cellulosefilms
Inventor: BERRY WILLIAM
IPC: C08J7/052
Filed: 1950-09-18
Abstract: 700,619. Moistureproof regenerated cellulose films. BRITISH CELLOPHANE, Ltd. Sept. 14, 1951 [Sept. 18, 1950], No. 22893/50. Class 140 Moistureproof regenerated cellulose film with a moistureproof coating on one side only is produced by bringing a pair of purified gel regenerated cellulose films into intimate contact, drying the pair of films in continuous intimate contact to form two optically adhered plies of a single web, coating the dried single web on both sides with a moistureproof coating, and then separating the two plies of the coated web. The films may be produced on the same casting machine as in Specification 423,365, [Group IV], from viscose of the same ageing and composition characteristics and may have the same thickness. The drying may be effected by passage under tension over heated drying rolls at, e.g. 90 C. Before being brought into contact the films may be treated with an aqueous dispersion of a colloidal anti-sticking agent, e.g. silica, sodium silicate, waterinsoluble amide, or soap, and on contact the films' are further treated to ensure a substantially greater amount, e.g. 1.5-3 times, of the agent on the outer film faces than is held between the inner faces. Before drying the contacted films may be treated with an aqueous solution of a regenerated cellulose softening agent, e.g. glycerine, or urea, with suspended therein, colloidal matter, e.g. an anti-sticking agent such as silica, particles of a partial condensate of melamine and formaldehyde in an acidified aqueous medium, or hydrophilic particles of a partial condensate of urea and formaldehyde in a neutral aqueous medium. An aqueous dispersion of silica may be added to the aqueous liquid containing the urea-formaldehyde partial condensate, in which case the particles of silica and condensate carry the same electric charge, e.g. positive, which is opposite to that of the film, due to the addition of a cationic surface active agent, e.g. cetyl trimethyl ammonium bromide, tetradecyl pyridinium bromide, or cetyl triethanol ammonium iodide. Before the colloidal material treatment the films may be treated together or singly with an aqueous solution of softening agent. The coating liquid may be an aqueous dispersion of a co-polymer, e.g. vinylidene chloride/acrylonitrile or /methylmethacrylate, a solution of nitrocellulose, high melting point paraffin wax, and gum dammar in an organic solvent, e.g. toluene, a mixture of cellulose ether or ester, gum or resin, wax and plasticizer, an organic solvent, e.g. methyl ethyl ketone/toluene, solution of a vinylidene chloride co-polymer, e.g. with vinyl chloride, or molten mixtures of ethyl cellulose, non-heat convertible resin (natural or modified gum or resin such as rosin, or a polyhydric alcohol-polbasic acid resin such as rosin modified glycerol maleate), plasticizer, and wax. If the film is treated before coating with a urea-formaldehyde partial condensate, the coating composition may contain an acidic substance, e.g. citric acid or sulphur dioxide, which catalyses further condensation.