Patent GB-1087790-A (GB)
Title: Process for the production of black colloidal-silver dispersion
IPC: G03C1/825
Filed: 1965-10-20
Abstract: A silver halide emulsion in a hydrophilic protective colloid is reacted with 0.0001 to 0.1 mol of borohydride per 1 mol of the silver halide in the emulsion and subsequently is reduced with a reducing agent for silver halide, other than borohydride, which can be used as a developer for silver halide photographic materials to produce a black colloidal silver dispersion. The protective colloid may be gelatin, polyvinyl alcohol or a water-soluble cellulose and the borohydride may be sodium, potassium or ammonium borohydride.  The photographic developer may be hydroquinone, toluhydroquinone, catechol, monomethylaminophenol, 1 - phenyl - 3 - pyrazolidone, phenylenediamine, ascorbic acid or hydrazine and the reaction product may have added to it a thiol compound or an organic compound capable of forming a thiol compound by decomposition, for instance 2-mercapto-benzimidazole to improve the storage stability.  A benzotriazole derivative such as 6-nitro-, 6-methyl-, 6-sulphobenzotriazole or 41-nitronaphtho-11,21-4,5-triazole may be added to the emulsion to give a colloidal silver dispersion having a higher red optical density.  As well as the developer a caustic alkali, sodium carbonate, potassium carbonate, borax, sodium metaborate, sodium phosphate or sodium sulphate may be used as an alkali agent, and the borohydride is preferably used as an aqueous alkali solution.  Excess developer and oxidation products thereof are removed by gelling or precipitating the dispersion and rinsing with water and the dispersion may be coated on to a support to provide a photographic sensitive element having an anti-halation layer containing the colloidal-silver dispersion.ALSO:A black colloidal-silver dispersion for coating a photographic film is produced by reacting a silver halide emulsion in a hydrophilic protective colloid with 0.0001 to 0.1 mol of borohydride per 1 mol. of silver halide in the emulsion and subsequently reducing it with a reducing agent for silver halide, other than borohydride, which can be used as a developer for silver halide photographic materials.  The protective colloid may be gelatin, polyvinyl alcohol or a water-soluble cellulose and the borohydride may be sodium, potassium or ammonium borohydride.  The photographic developer may be hydroquinone, catechol, monomethylamino-phenol, 1-phenyl-3-pyrazolidone, phenylenediamine, ascorbic acid or hydrazine and the reaction product may have added to it a thiol compound or an organic compound capable of forming a thiol compound by decomposition, for instance 2-mercapto-benzimidazole to improve the storage stability.  A benzotriazole derivative such as 6-nitro-, 6-methyl-, 6-sulpho-benzotriazole or 41 nitro naptho-11, 21-4, 5-triazole may be added to the emulsion to give a colloidal silver dispersion having a higher red optical density.  As well as the developer a caustic alkali, sodium carbonate, potassium carbonate, borax, sodium metaborate, sodium phosphate or sodium sulphate may be used as an alkali agent, and the borohydride is preferably used as an aqueous alkali solution.  Excess developer and oxidation products thereof are removed by gelling or precipitating the dispersion and rinsing with water and the dispersion may be coated onto a support to provide a photographic sensitive element having an antihalation layer containing the colloidal-silver dispersion.