Preparation of silver halide tabular emulsions in the presence of non-aqueous polar aprotic solvents and/or protic solvents having a dissociation constant smaller than that of water

摘要

A method has been found for the preparation of tabular silver halide emulsions, wherein crystals in said emulsion have a tabularity, defined as the ratio between the aspect ratio and the thickness of the emulsion crystals, of at least 25 and a homogeneity of said crystals in said emulsion, defined as a hundred times the ratio between the standard deviation and the average projective crystal diameter of said crystals of less than 30, characterised by the steps of forming silver halide grain nuclei by introduction of an aqueous silver salt solution and an aqueous halide salt solution, both solutions optionally comprising at least one non-aqueous solvent, in a reaction vessel containing water, a protective colloid and at least one non-aqueous aprotic solvent or a protic solvent having a dissociation constant smaller than that of water in a ratio by weight of solvent versus water from 5 to 60 %; adding an aqueous silver salt solution and an aqueous halide salt solution to said reaction vessel containing silver halide grain nuclei at a pBr value higher than 2.0; flocculating grown silver halide emulsion grains; washing and redispersing.