Patent ID: 6214532
Filing Date: 2001-04-10
Classification: G03C

Abstract:
Method of preparing a photosensitive element containing a silver halide emulsion with homogeneous and thin tabular crystals having an aspect ratio of at least 2, a thickness between 0.07 and 0.22 .mu.m and a variation coefficient of not more than 30%, comprising the steps of:(1) forming silver halide nuclei by simultaneously adding an aqueous silver salt and a halide salt solution to a reaction vessel (a), containing an aqueous solution of a protective colloid,(2) transferring the dispersion of silver halide nuclei formed in vessel (a) to a mixing chamber (b) and diluting said dispersion,(3) growing in a growth chamber (c) at a controlled potential value said nuclei of the diluted dispersion by adding and mixing an aqueous silver salt and a halide salt solution and collecting the grown crystals in reaction vessel (a) which is a part of a closed circuitry together with the mixing and growth chambers (b) and (c),(4) transferring said silver halide crystal dispersion to mixing chamber (b) and diluting the dispersion,(5) further growing the silver halide crystals in growth chamber (c) at a controlled potential value and collecting the silver halide crystals in reaction vessel (a),(6) concentrating the emulsion of silver halide crystals simultaneously with the step of growing in order to keep the emulsion level in reaction vessel (a) controlled;wherein the steps of growing proceed at an enhanced potential value (expressed in mV) during growth as compared to during forming said silver halide nuclei, said enhanced potential value being chosen as a function of emulsion dilution, with a dilution factor expressed as volume of demineralized water:volume of emulsion, to obtain less thickness growth (expressed in nm/mV) than in an absence of dilution.