NL23368C - - Google Patents

Abstract

301,439. Spicers, Ltd., and Hands, H. J. Aug. 30, 1927. Electricity, discharging.-The electric charge carried by sheets or films formed by evaporation of the solvent from solutions of compositions containing cellulose esters or ethers, such as cellulose acetate, when stripped from the surface on which they are formed is removed by passing them through an electrically conducting aqueous bath, connected to earth. The bath may contain a dilute solution of caustic alkali, acid, or an acid salt, such as sodium hydrogen phosphate, which reduces an extremely thin layer of the film to cellulose and thereby more effectually removes the electrical charge on the film, or alternatively the bath may contain neutral salts, such as sodium chloride, ammonium sulphate or sodium sulphate. Last traces of solvent may subsequently be removed from the films by passing them through an aqueous oxidizing bath containing for example hydrogen peroxide, or both baths may be combined. The films are then passed through a neutralizing bath and finally washed with water and dried. Sheets or films made according to Specification 287,635 may be further treated in this manner. A softening agent such as ethyl alcohol or methylated spirit may be added to the electrolyte bath. Gelatine coatings adhere more readily to such sheets or films, the surface layers of which have been reduced to cellulose. In the apparatus shown, the film 10 stripped from an endless metal band passes over guide rollers through the necessary treatment baths, the first of which is earthed, and between squeegees 18, 24 and 34, water sprays 30 and hotair drying chamber 36 to the winding reel 42.