US 5,310,644 A · Process for preparing a photographic emulsion using excess halide during nucleation

Abstract

A process for preparing a photographic emulsion involves an initial nucleation step of reacting a first silver salt with a bromide in the presence of a first excess halide under conditions effective to nucleate AgBr crystals. The nuclei are then grown to form photosensitive grains by addition of a second silver salt and a second halide as growth salts. If excess chloride is used during nucleation, even without excess bromide and/or a growth modifier, the nuclei formed have twin planes, and the pAg level can be used to control the aspect ratio of the tabular grains obtained. If a relatively high silver concentration in the growth solution is maintained throughout the growth step, the resulting grains have a unique, twinned cubooctahedral or cubooctahedral-tabular shape. Unique tabular grains having alternating 1.1.1 and 1.0.0 edge faces can be formed by this process.

Claims37

Dependent claims

A process for preparing a photographic emulsion, comprising the steps of:

(A) reacting a first silver salt with a bromide in the presence of a first, excess halide in the presence of a peptizing medium and under conditions of silver and halide concentration and rate of addition, pH, temperature and reaction time effective to nucleate AgBr crystals having twin planes, the first halide remaining in solution;
and
then (B) growing the crystals in an aqueous solution to form photosensitive grains by addition of a second silver salt and a second halide while maintaining a silver concentration in the growth solution sufficiently high to produce twinned cubooctahedral or cubooctahedral tabular grains having 1.1.1 and 1.0.0 edge structure.

Dependencies are inferred from the claim text.

Process for preparing a photographic emulsion using excess halide during nucleation

Life of this patent

Process for preparing a photographic emulsion using excess halide during nucleation

Life of this patent

Abstract

Claims37