Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2000-05-23
2001-07-10
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S569000
Reexamination Certificate
active
06258522
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to photographic silver halide core-shell emulsions. More particularly, the invention relates to a silver bromoiodide emulsion having grains comprising several phases with different iodide content, which emulsion shows better granularity and sensitometric properties.
BACKGROUND OF THE ART
There have been more strict requirements for silver halide emulsions for photographic use, which has increased the demands for the high level photographic characteristics such as, for example, high speed, excellent graininess, high sharpness, low fog, wider exposure latitude range and so on.
The above mentioned requirements have been satisfied by well-known silver bromoiodide grain emulsions having a high silver iodide content in the inner part of the grains and a specific core-shell structure in the grains thereof. It is well known in the photographic art that light absorbing increases in the order of silver chloride, silver bromide and silver iodide, but development activity correspondingly decreases in the same order. By using the above described core-shell silver bromoiodide emulsions, a good balance between light sensitivity and development activity has been obtained.
Examples of core-shell silver bromoiodide emulsion are described in many patent and literature references. For example, U.S. Pat. No. 4,668,614 and U.S. Pat. No. 4,728,602 describe a monodispersed core-shell silver bromoiodide emulsion having a core part comprising a silver iodide content of 10 to 45 mol % and a shell part comprising a silver iodide content lower than 5 mol %., with an average silver iodide content higher than 7 mol %. When examined by X-ray diffractometry, two peaks are evidentiated. The first one corresponding to the high iodide core part, the second one to the low iodide shell part. According to the claimed invention it is preferred to have a ratio between the diffraction intensity of the two peaks in the range of from 1/10 to 3/1, more preferably 1/3 to 3/1.
Similarly, European application EP 299,719 discloses a core-shell silver halide emulsion having a core comprising not less than 10 mol % of silver iodide, at least one shell consisting of silver bromide or silver bromoiodide, the outermost of which has a silver iodide content not higher than 5 mol %, and an average silver iodide content of not less than 10 mol %.
EP 309,119 discloses a core-shell silver halide emulsion having at least three silver bromide or silver bromoiodide phases of different composition. According to a preferred embodiment of the claimed emulsion, the innermost phase has a silver iodide content of at least 10 mol %, the outermost phase has a silver iodide content of not more than 6 mol %, and the intermediate phase has a silver iodide content difference with the outermost or innermost phase of at least 3 mol %. When examined by X-ray diffraction, the claimed emulsion shows three or more diffraction peaks, each corresponding to a phase containing a different percentage of iodide.
EP 202,784 describes a core-shell type silver halide emulsion having an inner core essentially consisting of silver bromide or silver bromoiodide and a plurality of shells. The outermost shell has a silver iodide content ranging from 0 to 10 mol %, the innermost shell has a silver iodide content at least 6 mol % higher than that of the outermost shell, and an intermediate shell has a silver iodide content is at least 3 mol % lower than that of the innermost shell and at least 3 mol % higher than that of the outermost shell.
U.S. Pat. No. 4,477,564 describes a multiphase bromoiodide emulsion having an average silver iodide content higher than 12%.
U.S. Pat. No. 4,614,711 describes silver bromoiodide grains with a core shell structure with a core of silver bromide or bromiodide and a first layer composed of silver bromoiodide, exterior to said core and containing more iodide than said core by 10 mol % or more.
U.S. Pat. No. 5,780,216 discloses a color negative silver halide photographic material with a core shell emulsion having a plurality of shells comprising an inner core consisting essentialy of silver bromide or bromoiodide and a plurality of shells of silver bromide or silver bromoiodide comprising a high iodide shell interposed between two shells consisting essentially of silver bromide.
SUMMARY OF THE INVENTION
The present invention relates to a light-sensitive emulsion comprising silver bromoiodide grains of a core shell structure comprising:
a) an inner core consisting essentially of silver bromide or silver bromoiodide, the silver iodide content of said inner core being within the range of 0 to 10 mole %, and
b) a plurality of shells consisting essentially of silver bromide or silver bromoiodide,
wherein a pure silver iodide phase representing from 0.1 to 5 mole % of the total silver halide grain content is interposed between two adjacent shells, and wherein at least one of said adjacent shells has a silver iodide content higher than 5 mole %.
DETAILED DESCRIPTION OF THE INVENTION
The light-sensitive emulsion of the present invention comprises silver bromoiodide grains having an inner core and a plurality of shells. The inner core consists essentially of silver bromide or silver bromoiodide. The plurality of shells consists essentially of silver bromide or silver bromoiodide having different compositions.
The silver iodide content of the inner core is in the range of from 0 to 20 mol % relative to the total silver halide content of the inner core phase, preferably from 0 to 10 mol %, and more preferably from 0 to 5 mol %. According to the most preferred aspect of the present invention the inner core consists essentially of silver bromide.
The silver iodide content of each shell is in the range of from 0 to 40 mol %, preferably from 0 to 20 mol % relative to the total silver halide content of the shell. The plurality of shells comprises at least two shells having different silver halide composition.
The minimal core-shell structure of the silver halide grains according to the present invention consists in an inner core and two shells surrounding the inner core. The number of shells surrounding the inner core preferably ranges from two to four. Accordingly, the core-shell structure of the silver halide grains according to the present invention consists in an inner core, an innermost shell adjacent the inner core, an outermost shell, and, optionally, one or more intermediate shells interposed between the innermost shell and the outermost shell. Preferably, the innermost shell adjacent to the inner core has a silver bromoiodide composition, with a silver iodide content of from 2 to 20 mol %, most preferably from 3 to 10 mol % relative to the total silver halide content of the shell, and the outermost shell has a silver bromide composition. The intermediate shells can have a silver bromide or silver bromoiodide composition, with a silver iodide content ranging from 0 to 40 mol %, preferably from 0 to 20 mol % relative to the total silver halide content of the shell.
The silver content of the core and the plurality of shells relative to the total silver content of the grain can have different values depending on the number of shells representing the plurality of shells. Preferably, the silver content of the inner core represents from 20 to 70 mol %, more preferably from 30 to 60 mol % relative to the total silver content of the grain. Preferably, the silver content of the plurality of shells represents from 30 to 80 mol %, more preferably from 40 to 70 mol % relative to the total silver content of the grain. Each shell can have a silver content ranging from 5 to 40 mol %, preferably from 10 to 25 mol % relative to the total silver content of the grain.
According to the essential aspect of the present invention, a pure silver iodide phase is interposed between two adjacent shells The pure silver iodide phase has a silver content of from 0.1 to 5 mol %, preferably from 1 to 3 mol % relative to the total silver content of the grain.
According to the second essential aspect of the present invention, at
Astengo Ezio
Avidano Mauro
Ghirardo Stefania
Gunnella Alessandro
Mariotti Mario
Baxter Janet
Ferrania S.p.A.
Litman Mark A.
Mark A. Litman & Assoc.
Walke Amanda C.
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