GB738080A - Improvements in or relating to the manufacture of regenerated cellulose films - Google Patents

Abstract

A regenerated cellulose film is treated with an aqueous dispersion of colloidal silica, the particles of which have been rendered electrically neutral by treatment with a water dispersible, non-ionic, colloidal reagent selected from one of the following classes: (1) a polyoxyethylene ether of an alkyl phenol or naphthol, (2) a polyethyleneglycol tertiary alkyl thioether, (3) a fatty acid amide, (4) a condensation product of a fatty acid amide or ethanolamide with ethylene oxide, (5) a condensation product of an aliphatic sulphonamide with ethylene oxide, (6) an acid amide formed by reacting a fatty acid with diethanolamine, or (7) a substance obtained by the alkylation of the imido nitrogen of a disulphimide with ethylene oxide. Examples of the various classes of reagents are given. The film may be treated in the gel state, as it comes from the casting machine, by-passing it through an aqueous solution of the treated silica which may also contain a softening agent, e.g. glycerine, or the solution may be applied to a film which has been dried and rewetted, or in either case the aqueous solution of silica and the softening agent may be applied separately. The aqueous bath may have a pH between 1.5 and 11.5 and a temperature between 20 DEG and 80 DEG C. and may contain a partially condensed urea- or thiourea-formaldehyde or urea- or thiourea-formaldehyde-aliphatic alcohol resin. The bath containing resin may be applied at a pH of 5.0 to 7.5 and the treated film dried by heat without curing the resin, or the bath may be applied at a pH of 3.5 to 5.0, in which case drying the film by heat condenses the resin to the insoluble stage. The resin particles normally carry a negative charge and may be applied to film treated with a cationic surface active agent. Alternatively, a positive charge may be induced upon the resin particles as described in Specifications 675,477 and 677,184. The film may be further coated with a moisture-proof composition having a basis of nitro-cellulose, ethyl cellulose, cyclized rubber or a vinyl chloride-vinyl acetate, vinylidene chlorideacrylonitrile or vinylidene chloride-methyl methacrylate copolymer. Such a composition may comprise a cellulose ester or ether, a gum or resin, a wax and a plasticizer, and where a resin-coated film has been dried without condensing the resin to its insoluble stage the further coating may also comprise phosphoric acid, maleic acid or sulphur dioxide to promote further condensation during or after application. In example 5, a gel-regenerated cellulose film is passed through an aqueous bath containing glycerine, colloidal silica, a water-dispersible fatty acid amide and a partially condensed ureaformaldehyde resin, a pH of 6.5 being obtained with lactic acid or caustic soda. After removing excess liquid the film is dried and further coated with a composition comprising nitrocellulose, dibutyl phthalate, tricresyl phosphate, dewaxed dammar, ester gum, citric acid, paraffin wax (mp. 60 DEG C.), ethyl acetate, toluene and water and then heated to a temperature above the melting point of the wax. Specifications 657,342 and 710,331 also are referred to. The Provisional Specification refers to the treatment of silica particles with polyoxyethylene glycol esters of long chain aliphatic monocarboxylic acids.