Method of preparation of a monodispersed tabular silver halide grain emulsion

摘要

The present invention relates to a method for the preparation of a tabular silver halide grain emulsion, wherein said silver halide emulsion comprises tabular grains having a thickness lower than 0.5 µm and an average aspect ratio of at least 2:1 accounting for at least 50% of the total projected area, and shows a coefficient of variation lower than 30%, said method comprising the steps of (a) forming silver halide nuclei by adding from 5% to 15% by weight of total silver nitrate to a reaction vessel comprising a dispersing medium and bromide aqueous solution at a pBr ranging from 0 to 2 and a pH ranging from 2 to 5, (b) performing a first addition of a silver halide solvent after at least 50% by weight of silver nitrate used during nucleation has been added, (c) ripening the silver halide nuclei, (d) growing said silver halide nuclei by double jet addition of a soluble silver salt and a soluble bromide salt aqueous solutions at pBr between 1 and 2 to obtain tabular silver halide grains, (e) adjusting the pBr to a value ranging from 4.5 and 7 by single jet addition of a soluble silver salt aqueous solution, (f) performing a second addition of silver halide solvent, and (g) thickening said tabular silver halide grains by double jet addition of a soluble silver salt and a soluble bromide salt aqueous solutions at pBr between 1.0 and 3.0.