GB703416A - Improvements in or relating to the manufacture of regenerated cellulose film - Google Patents

Abstract

Two purified regenerated cellulose films in the gel state are brought into continuous intimate contact and while in contact they are treated with an aqueous dispersion containing hydrophilic colloidal particles of a partially condensed condensation product dispersed in a substantially neutral aqueous medium (pH6-7.5), dried without curing the condensation product and finally separated. The condensation product may be a partially condensed urea- or thiourea-formaldehyde resin reacted, if desired, with methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, ethylene glycol, propylene glycol, diethylene glycol or glycerine. Preferably the hydrophilic colloidal particles of the condensation product carry an electrical charge opposite to that developed by the gel films in contact with water. The colloidal particles usually carry a negative charge, and this may be changed to positive by treating, before or during the partial condensation, with a dilute aqueous solution of a quaternary ammonium or phosphonium or ternary sulphonium compound containing a straight chain alkyl group of at least 8 carbon atoms or a branched chain alkyl group of at least 12 carbon atoms directly attached to the nitrogen, phosphorus or sulphur atom. The normal negative charge on the regenerated cellulose gel film in contact with water may be changed to positive by treatment with a dilute aqueous solution, e.g. 1 per cent., of a cationic surface-active agent such as cetyl trimethyl ammonium bromide or cetyl pyridinium bromide. In addition to the condensation product the impregnating bath may contain glycerine or other softening agent for regenerated cellulose, and/or an anti-blocking agent such as colloidal silica or alumina. The negative charge on these silica or alumina particles may be changed, if desired, to positive by treatment with a dilute aqueous solution of a cationic surface-active agent; in any event the sign of the electric charge on these particles should be the same as that carried by the partially condensed condensation product. The silica or alumina particles may be deposited on the two films before they are brought into continuous intimate contact if desired. That surface of the regenerated cellulose film treated with colloidal resinous material may be coated with a pressure-sensitive adhesive (rubber, or polyisobutylene together with hydrogenated rosin or a soft alkyd resin) and an acidic substance. The adhesive is preferably applied from a solution or dispersion in a volatile organic solvent such as toluene or trichlorethylene (containing a proportion of a polar solvent such as ethyl acetate if desired), brought to a pH of 3 or less by the addition of phosphoric acid, maleic acid, citric acid or sulphur dioxide. Evaporation of the solvent at a temperature between 60 and 90 DEG C. will also insolubilize the resin. The treated regenerated cellulose film may also be used to make laminated sheet material by applying a thermoplastic adhesive to the coated side to secure a cellulosic or metallic sheet thereto (see Group VIII). The cellulosic sheet may be regenerated cellulose, cellulose acetate or paper. The adhesive may have a base of polyvinyl acetate, natural or synthetic resins, rubber, nitrocellulose or ethyl cellulose. The sheet coated with the partially condensed condensation product may also be printed with a printing ink containing an acidic substance (phosphoric acid, citric acid or sulphur dioxide) and if desired a polar solvent such as ethyl acetate. The printed sheet is then heated to cure the resin. In an example two gel-regenerated cellulose films are brought into continuous intimate contact and passed through an aqueous solution containing 5.0 per cent. of glycerine, 0.1 per cent. of colloidal silica (as an aqueous colloidal dispersion treated with cetyl pyridinium bromide) and 0.2 per cent. of a partially condensed urea-formaldehyde resin. The films are dried while in contact and then separated. To the treated side is applied an adhesive coating comprising 10 per cent. of crepe rubber, 14.0 per cent. of hydrogenated rosin, 2.0 per cent. of ester gum, 0.2 per cent. of antioxidant, 0.1 per cent. of citric acid and 73.7 per cent. of pool rubber solvent. The solvent is evaporated at 70 DEG C. and the film is wound up and slit to form pressure-sensitive adhesive tape. Specifications 423,365, 663,736, 675,477 and 677,184 are referred to.