Patent GB-1267215-A (GB)
IPC: G03C1/12
Filed: 1969-07-25
Abstract: 1,267,215. Electron-bombarded silver halide photographic material. EASTMAN KODAK CO. July 25, 1969 [July 29, 1968], No.37402/69. Heading G2C. A method of producing a photographic material comprises electron bombarding the surface of a hydrophobic support so that a silver halide emulsion will adhere to the bombarded surface and which comprises coating on the bombarded surface (i) a spectrally sensitized silver halide emulsion layer containing a colour forming coupler or (ii) a non- spectrally sensitized blue-sensitive silver halide emulsion layer containing a yellow-forming coupler and over the blue-sensitive silver halide emulsion layer a silver halide emulsion-layer which has been spectrally sensitized to a different region of the spectrum and which contains a different colour-forming coupler, the dye employed to spectrally sensitize the silver halide in the emulsion (i) coated on the support or over the bluesensitive silver halide emulsion layer (ii) being a cationic imidazolocyanine dye (i.e. a dye which has the amidinium ion chromophoric system - see Mees and James, "The Theory of the Photographic Process", page 201, 3rd Edition, 1965, published by the MacMillan Company, New York - and which features two imidazole nuclei joined together by a polyene chain containing an equal number of alternating single and double bonds, the terminal carbon atoms of the polyene chain being the 2-carbon atom of the respective imidazole nuclei. The term 'cationic' excludes betaine type dyes and dyes having anionic substituents (e.g. disulphoalkyl substituted cyanine dyes) and the nuclei and the methine chain of the imidazolocyamine dye is free from any group which is as acidic, or which is more acidic than carboxy, e.g. sulpho or sulphato. Preferred dyes have the formula: - wherein Z 1  and Z 2  each complete a fused aromatic hydrocarbon nucleus which may be substituted; L 1 , L 2  and L 3  each represents a methine group which may be substituted; n is an integer of 1 to 3; R 1 , R 2 , R 3  and R 4  each represents alkyl, cyclohexyl, alkenyl, acetoxyethyl or aryl; and X represents an acid anion. Coating (i) above may be a silver halide emulsion layer spectrally sensitized to red, green or blue light and containing a cyan-magenta- or yellow-forming coupler respectively. The hydrophobic support may be a poly (α-olefin)- coated paper where the poly (α-olefin) is preferably polyethylene or polypropylene, hardened gelatin-coated paper, or a stearato chromic chloride-coated paper or a poly (ethylene terephthalate), polyamide, polyacetal, polycarbonate, cellulose ester or cellulose ether support. The silver halide emulsions may contain dispersed therein a water-insoluble polymer of an alkyl acrylate or methacrylate, acrylic acid or sulphoalkyl methacrylate. Spectral sensitization of silver halide emulsions with the dyes of the type defined above permits the coating of the emulsion directly on to, or over another emulsion coated directly on to, a hydrophobic surface within 30 minutes after it has been electron bombarded, without adverse sensitometric effects. Preferably coating is effected in less than a second to thirty seconds.