Appeal No. 1998-1732
Application 08/608,321
EP ‘092 discloses a method for making a light sensitive
silver halide emulsion comprising grains which contain
colloidal silica sol as a protective colloid and which may be
tabular grains (abstract; page 4, line 26). The size of the
grains may be 0.01 to 7 µm (page 4, lines 36-37). In an
example, the aspect ratio of the grains is up to 12 (page 9,
line 56). The degree of coverage by silica sol particles is
50-100% (page 5, line 55).
The method includes precipitating silver halide in a
reaction medium comprising an aqueous solution of silver
nitrate and a halide salt in colloidal silica, by means of a
technique which can be a double-jet method (page 4, lines 18-
19) (page 6, lines 41-46). Suitable colloidal silicas include
Syton , Ludox , Nalco , Nalcoag , and Kieselsol Types 100, 200® ® ® ® ®
and 600 (page 4, lines 2-5), which are among the colloidal
silicas used by the appellants (specification, page 5, lines
10-18) and, therefore, include particles within the average
particle size limitation of claim 29. The precipitation takes
place in the presence of an onium compound which can be a
phosphonium compound (page 3, lines 25-54). The teaching that
in the precipitation “the protective colloid can comprise
-4-
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