| 摘要 |
A method is disclosed 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 mum, an average aspect ratio of more than 12:1, a total projective area of said tabular grains of at least 50% and a coverage degree by silica sol particles within the range from 50 to 2000%, comprising 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 mum to 0.30 mum as a protective colloid, in the presence of at least one onium compound, selected from the group consisting of a phosphonium compound, a iodonium compound and an ammonium compound, except for an ammonium compound containing NH4+-ions; but in the absence of gelatin, wherein a ratio by weight of said colloidal silica to said onium compound(s) 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 every moment throughout precipitation in a reaction vessel.
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