GB1228828A - - Google Patents

Abstract

1,228,828. High contrast photographic silver halide materials. EASTMAN KODAK CO. Aug. 15, 1968 [Aug. 18, 1967], No. 39113/68. Heading G2C. A high contrast photographic material comprises a support bearing a layer of a high contrast silver halide emulsion (i.e. one in which the halide comprises at least 50 mole per cent chloride and less than 5 mole per cent iodide, the remainder being bromide, said emulsion when exposed on a sensitometer and developed for 2 minutes at 20‹C. in a developer of the composition: - sodium sulphite (anhy.) 30 g., paraformaldehyde 7À5 g., potassium metalisulphite 2À6 g., boric acid (Cryst.) 7À5 g., hydroquinone 22À5 g., potassium bromide 1À6 g., and water to 1000 ml has a gamma of at least 4 measured between a density of 0À3 and 3À0) comprising at least 85 mole per cent silver halide which emulsion layer itself bears an overcoat layer comprising a water-permeable colloid, preferably gelatine, in an amount of at least 130 mg per square foot. The silver halide emulsion preferably comprises 90 mole per cent chloride, 1 mole per cent iodide and 9 mole per cent bromide, The overcoat may have a vinyl polymer dispersed therein and may be a water-insoluble vinyl polymer containing units derived from an alkyl acrylate or alkyl methacrylate. The invention also comprises a method of processing the material defined above in which the imagewise exposed material is inserted into a continuous transport processing machine in which the developer (e.g. hydroquinone) is one capable of infectious development and preferably contains a carbonyl bisulphite-amine condensation product e.g. a formaldehyde bisulphite-amine condensation product or sodium bis(2-hydroxyethyl) aminomethane sulphonate. The concentration of the developing agent is preferably from 0À05 to 0À50 mole per litre and the concentration of the condensation product is preferably from 0À10 to 1À0 mole per litre of developer. The heavy overcoat layer provides the material during processing with an ample supply of unexhausted developer or other processing solution while the material is not actually immersed in the processing solution such as occurs when the material in travelling through the air while being transferred from one processing tank to the next. The occurrence of drag lines is virtually eliminated.