GB638457A - Improvements in or relating to photographic emulsions - Google Patents

Abstract

638,457. Photographic emulsions. DU. PONT DE NEMOURS & CO., E. 1. Feb. 5. 1948, No. 3405. Convention date, Feb 6, 1947. [Class 98 (ii)] Water-soluble salts are removed from a silver-halide emulsion made with a non- gelling, hydrophilic polymeric colloid by dialysis. The silver halide is precipitated into a solution of the colloid in water, or water with a miscible solvent, in the same way as for gelatin emulsions, and then, since these colloids cannot be alternately set or gelled and melted by temperature changes like gelatin, dialysis replaces the customary chilling, shredding and washing procedure. Suitable polymeric colloids include partially hydrolysed polyvinyl lower fatty acid esters, lower alkyl ethers and acetals ; hydrolysed vinyl ester copolymers with ethylenically unsaturated compounds such as methyl acrylate, methyl methacrylate and ethylene, especially the ethylene/vinyl acetate copolymers described in Specification 600,023 ; colour former polymers as described in Specifications 535,341, 593,088, 598,475, 627,353, and 635,294, partially hydrolysed cellulose acetate, methyl cellulose, sodium cellulose glycollate, polyamides as described in Specifications 595,375 and 619,553, and polydioxolanes as described in U.S.A. Specification 2,436,138. The semi-permeable membrane may be uncoated regenerated cellulose film, gelatin, chromated gelatin, parchment paper, denitrated nitrocellulose, collodion, animal membranes and various synthetic resin and superpolymer membranes.. Dialysis may be effected by placing the emulsion containing either all or a part only of the colloid in a cell or bag of regenerated cellulose, arranging this in a perforated frame with walls about a quarter inch apart and shaking the frame while it is surrounded by water, or by continuous flow of emulsion through such narrow plate-supported cells. Diminution of the electrolyte content of the emulsion may be followed by conductivity measurements. When the emulsion includes a solvent such as alcohol, additions of solvent may be made during the dialysis to prevent precipitation of the colloid. Eight examples detail the process and indicate its superiority over acetone or sodium sulphate coagulation and washing processes such as those described in Specification 600,023.