Donald J Novak

US Patent:

41475518, Apr 3, 1979

Filed:

Feb 28, 1975

Appl. No.:

5/554226

Inventors:

Loren T. Finnicum - Newark DE
Stanley H. Munger - Rumson NJ
Donald P. Novak - Eatontown NJ

Assignee:

E. I. Du Pont de Nemours and Company - Wilmington DE

International Classification:

G03C 102

US Classification:

96 94R

Abstract:

A process for preparing a photographic emulsion having a controlled grain size, structure and size distribution, wherein precipitation of first silver halide grains is accomplished in a stream, and partial substitution in the first silver halide grains of a second soluble halide is accomplished in a vessel by halide conversion to form mixed crystal silver halide grains. The initially formed mixed crystal silver halide grains are recycled in the stream wherein additional precipitation of the first silver halide occurs on the surfaces of the mixed crystals, which are enlarged. The enlarged crystals are fed from the recycle stream to a vessel wherein additional substitution by halide conversion is accomplished. Continuous or intermittent recycling of the mixed crystal silver halide grains, control of recycle flow rates, control of addition flow rates of silver salts and soluble halides to the process and control of excess halide concentration in the conversion vessel and recycle stream yields mixed crystal silver halide grains having a controlled grain size, structure and distribution.