Patent ID: 6312882
Filing Date: 2001-11-06
Classification: G03C,Y10S

Abstract:
Method for preparing a light-sensitive silver halide emulsion comprising tabular grains containing colloidal silica sol as a protective colloid, said tabular grains having an average grain thickness of not more than 0.3 .mu.m, an average aspect ratio of more than 12:1, a total projective area of said tabular grains of at least 90% and a coverage degree by silica sol particles within the range from 50 to 2000%, comprising the following steps:precipitating in a reaction medium silver halide by means of a double-jet or triple-jet technique applied to aqueous solutions of silver nitrate and halide salts in colloidal silica having an average particle size in the range from 0.003 .mu.m to 0.30 .mu.m as a protective colloid, in the presence of a phosphonium compound; but in the absence of gelatin, wherein a ratio by weight of said colloidal silica to said phosphonium compound is obtained between 3 and 400;controlling nucleation and growth steps by means of variable flow rate(s) of aqueous solutions of silver nitrate and halide salts and/or by means of constant pAg-Values during said steps;subjecting the reaction medium to at least one physical ripening step;desalting the reaction medium and redispersing the silver halide obtained;chemically ripening the silver halide andadjusting a ratio by weight of colloidal silica sol to amount of silver halide, expressed as an equivalent amount of silver nitrate, to a value of at least 0.03 at all tines during precipitation in a reaction vessel.