Method of preparation of a photographic emulsion comprising grains of silver halide with a high degree of silver chloride

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 mu 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) stabilizating 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. IMAGE