Process for preparing a photographic emulsion comprising silver halide grains with high silver chloride content

摘要

A process for the preparation of a high chloride silver halide grain emulsion in which at least 50% of the projected area of the emulsion grains is accounted for by cubic grains, said process comprising:;i) precipitating an intermediate emulsion containing high chloride cubic nuclei having an average edge length less than or equal to 0.07 &mgr;m, by adding to an external continuous reactor at least one silver salt aqueous solution, a chloride salt aqueous solution and a hydrophilic colloid aqueous solution, in conditions so that (Qgel*Tgel)/(Qag*CAg) is more than 100, wherein Qgel is the flow rate of the hydrophilic colloid aqueous solution, Tgel is the hydrophilic colloid content of the hydrophilic colloid solution (g/l), QAg is the flow rate of the silver salt aqueous solution, CAg is the silver concentration of the silver salt aqueous solution (mole/l) and is comprised between 0.01 and 5 moles/l, the average pCl in the external reactor being between 1.7 and 3.5,;ii) continuously transferring the intermediate emulsion containing the cubic nuclei from the external continuous reactor to a storage vessel,;iii) stabilizing the nuclei by the addition of a growth inhibitor in an amount such as the nuclei coverage by the growth inhibitor is at least 20%, and;iv) growing the nuclei of the intermediate emulsion to obtain a high chloride emulsion comprising cubic grains by adding a silver salt aqueous solution and a halide salt aqueous solution provided that the silver salt solution is added with a flow rate that does not lead the formation of new stable nuclei.