Appeal No. 1998-1732
Application 08/608,321
THE INVENTION
The appellants’ claimed invention is directed toward a
method for making a light sensitive silver halide emulsion
comprising tabular grains having colloidal silica sol as a
protective colloid. Claim 1 is illustrative:
1. 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 Fm, 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
Fm to 0.30 Fm as a protective colloid, in the presence as an
onium compound 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 redispensing the silver
halide obtained;
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