Patent ID: 6100019
Filing Date: 2000-08-08
Classification: G03C

Abstract:
A process of emulsion preparation comprised of(1) precipitating an emulsion containing an aqueous dispersing medium and silver halide grains comprised of greater than 50 mole percent bromide, based on silver, greater than 50 percent of total grain projected area being accounted for by tabular grains having {111} major faces, and(2) selectively depositing on the tabular grains at their edges silver halide epitaxy comprised of greater than 50 mole percent chloride, based on silver,WHEREIN, while performing steps (1) and (2) in a single reaction vessel,(a) the emulsion precipitated in step (1) accounts for 0.05 to 1.5 moles of silver per liter of the dispersing medium,(b) any iodide at the major faces of the tabular grains is uniformly distributed and any iodide in a surface region accounting for 40 percent of total silver amounts to less than 7 mole percent, based on silver in the surface region,(c) after step (1) and through completion of subsequent steps (d)-(h) below, the pH of the emulsion is maintained in a range of from 3 to 8,(d) gelatino-peptizer in an amount of from 1 to 40 g per Ag mole is added to the emulsion,(e) chloride ion in a range of from 0.03 to 0.15 mole per liter is dispersed in the emulsion,(f) through completion of steps (g) and (h) below, the emulsion is confined to a pBr in a range of from 3.0 to 3.8,(g) iodide ion in a concentration of from 5.times.10.sup.-6 to 1.times.10.sup.-4 mole per square meter of grain surface area is uniformly adsorbed to the major faces of the tabular grains, and(h) silver ion is added to the emulsion at a rate of at least 0.02 mole per minute per mole of total silver in the emulsion to deposit the silver halide epitaxy in an amount of 0.1 to 50 percent of total silver.