Patent ID: 6087085
Filing Date: 2000-07-11
Classification: G03C

Abstract:
Method for preparing an emulsion having grains rich in silver bromide in the presence of gelatin as a protective colloid in a reaction vessel wherein a yield of more than 250 g, expressed as amount of silver nitrate, equivalent with the amount of precipitated silver halide per liter of reaction vessel mixture is attained, wherein at least 70% of a total projected area of all grains is provided by {111} tabular grains having an average aspect ratio of more than 2:1 and an average thickness of from 0.05 up to 0.30 .mu.m and wherein a ratio by number of hexagonal tabular grains to triangular tabular crystals present is more than 10:1, said method comprising following steps:preparing in a reaction vessel a gelatinous dispersion medium containing an initial amount of gelatin corresponding with less than 50% of a total amount of gelatin used in the said method, said initial amount of gelatin having an average methionine content of less than 30 .mu.moles per mole and said dispersion medium having a volume of less than 2 liter per 500 g, expressed as amount of silver nitrate, equivalent with the amount of precipitated silver halide;precipitating therein silver halide crystal nuclei by double-jet precipitation of an aqueous silver nitrate and an aqueous solution comprising halide ions, wherein less than 10% by weight of a total amount of silver nitrate used is consumed;adding to said reaction vessel gelatin in an amount of more than 50% of a total amount of gelatin used in the said method;growing said silver halide crystal nuclei by further precipitation of silver halide by means of double-jet precipitation of an aqueous silver nitrate solution and an aqueous solution comprising halide ions, wherein more than 90% by weight of a total amount of silver nitrate is consumed; andconcentrating by ultrafiltration the said reaction mixture volume in the said reaction vessel obtained during precipitation growth steps.