GB675475A - Improvements in or relating to the production of moistureproof film - Google Patents

Abstract

In the production of moisture-proof solid films of water-sensitive non-fibrous organic material of types which normally develop when immersed in water, an electric charge of negative sign, but which may be so treated that they develop charges of positive sign under these conditions, an aqueous dispersion of a partially condensed urea-formaldehyde or thiourea-formaldehyde resin, of which the particles carry an electric charge of opposite sign to that developed by the base film in contact with water, is applied to the base film to form an anchor coating for a subsequently-applied moisture-proofing coating. In examples there are described (1) the treatment of purified gel regenerated cellulose film with an aqueous solution containing glycerol and "Beckamine" (Registered Trade Mark) L101, a urea-formaldehyde resin which can be diluted with water to give a dispersion of positively charged colloidal particles; (2) the restoration of the charge on the particles of "Beckamine" L101, which had become negative in the course of time, to positive, by treatment with cetyl pyridinium bromide, tetradecyl pyridinium bromide, and "Lissolamine" (Registered Trade Mark) A-50, a paste containing cetyl trimethyl ammonium bromide, and the use of the so-treated dispersions in admixture with aqueous solutions of glycerine; (3) the production of a partially condensed thiourea-formaldehyde resin by heating together thiourea, formalin, sodium acetate, glacial acetic acid and "Lissolamine" A-50, cooling and neutralizing with sodium hydroxide solution, the resulting resin being mixed with an aqueous solution of glycerol and urea and applied to a regenerated cellulose film, the charge on the dispersed resin particles being positive; (4) the production of an aqueous dispersion of a partially-condensed urea - formaldehyde resin having positively charged particles by heating together urea, formalin, sodium acetate, glacial acetic acid, adding cetyl ethyl methyl sulphonium bromide, or cetyl triethyl phosphonium bromide, and, after further heating and cooling, neutralizing with caustic soda solution; the resins are applied to a regenerated cellulose film in admixture with an aqueous solution of glycerol and urea. Acidic condensing agents for the insolubilization of the resin, including inorganic acids, e.g. phosphoric acid, organic acids, e.g. salicylic, gluconic or citric acids, salts which become acidic when heated under the conditions used, e.g. ammonium thiocyanate, acid esters and acid resins, may be added either to the partially condensed resin or to the subsequently applied moisture-proofing coating. Specifications 663,736 and 675,477 are referred to.