Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
1999-12-09
2001-06-05
Letscher, Geraldine (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S569000, C430S570000, C430S599000, C430S603000, C430S604000, C430S605000
Reexamination Certificate
active
06242171
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to sliver halide photography. More specifically, the invention relates to a method for the preparation of a high bromide tabular grain emulsion and to the emulsion prepared by the method.
DEFINITION OF TERMS
The term “equivalent circular diameter” or “ECD” is employed to indicate the diameter of a circle having the same projected area as a silver halide grain.
The term “aspect ratio” designates the ratio of grain ECD to grain thickness (t).
The term “tabular grain” indicates a grain having two parallel crystal faces which are clearly larger than any remaining crystal face and having an aspect ratio of at least 2.
The term “tabular grain emulsion” refers to an emulsion in which tabular grains account for greater than 50 percent of total grain projected area, and preferably more than 70 percent of total grain projected area.
The term “high bromide” in referring to grains and emulsions indicates that bromide is present in a concentration greater than 50 mole percent, based on total silver.
In referring to silver halide grains and emulsions containing two or more halides, the halides are named in order of descending concentrations.
The term “fine grain” indicates a grain having an edge length of less than about 0.5 micrometer.
The term “coefficient of variation” or “COV” is defined as 100 times the standard deviation (sigma) of grain ECD divided by average grain ECD.
Pluronic 31R1 is the BASF trademark for
HO—[CH(CH
3
)CH
2
O]
x
—(CH
2
CH
2
O)
y
—[CH
2
(CH
3
)CHO]x′—H
where x=25, x′=25 and y=7.
Research Disclosure
is published by Kenneth Mason Publications, Ltd., Dudley House, 12 North St., Emsworth, Hampshire P010 7DQ, England.
BACKGROUND OF THE INVENTION
The ability to differentiate between an exposed area and an unexposed area of a film or paper is essential in a photographic product. The exposed photographic product is developed by a chemical developer that affords a high amplification by the production of metallic silver resulting from the catalytic action of latent image centers formed by the exposure. The silver formed makes up the final image in black-and-white products. In color photographic products, the oxidized developer resulting from the reduction of the silver halide to metallic silver reacts with couplers to form a dye image. In a negative-working emulsion, the ability of the emulsion to differentiate an exposed area and an unexposed area of a photographic element depends on the possibility that this emulsion silver halide is reduced in exposed areas only while there is no unwanted formation of metallic silver in unexposed areas not meant to be developed during processing. However, metallic silver can be formed in unwanted areas as a result of oversensitization e.g. with gold and sulfur, or of the presence of traces of metals such as Fe, Ni, Pb, Sn, Cu, or Ni. The result of this is a density build up (or fog) in Dmin areas.
Many methods have been proposed to minimize the increase of Dmin in negative-type emulsion coatings. These methods include adding, at various stages in the preparation of a photographic emulsion, stabilizers, antifoggants, antikinking agents, latent image stabilizers, prior to coating. Examples of addenda for this purpose are disclosed in Research Disclosure, September 1994, publication No 36544, Chapter VII, page 515.
It should be noted that the differentiation between an exposed area and an unexposed area on a film or paper is not the sole criterion used to evaluate the performance of a photographic material. The photographic industry seeks to improve the speed of the emulsions without increased fogging, or even with decreased fogging, without incurring a granularity penalty.
It is, however, well-known that increasing the speed of a photographic emulsion can favor fogging and result in an increase of granularity.
Currently, most photographic materials are based on emulsions containing silver halide grains of tabular form, because it is recognized that the use of such tabular grains provides high performance silver halide photography in terms of advantages such as for instance covering power, developability, separation of native and spectral sensitivities, or speed/granularity relation. However, it is still desirable to increase the speed of the emulsion without at the same time incurring a fog and granularity penalty.
SUMMARY OF THE INVENTION
The present invention provides a method of preparing novel emulsions that exhibit an improved relationship between imaging speed and minimum density (fog).
In one aspect this invention is directed to a method of preparing a silver halide tabular grain emulsion comprising (a) providing an emulsion in which silver halide tabular grains containing greater than 50 mole percent bromide, based on silver, account for greater than 50 percent of total grain projected area, (b) adding to the emulsion of step (a) emulsion containing non-sensitized silver halide grains which (i) contain greater than 80 mole percent bromide, based on silver, (ii) exhibit {100} crystal faces, and (iii) exhibit a mean grain edge length of less than about 0.5 micrometers, and (c) chemically sensitizing the emulsion resulting from step (b).
In another aspect, this invention is directed to a novel emulsion prepared by the method of the invention.
REFERENCES:
patent: 4520098 (1985-05-01), Dickerson
patent: 4812390 (1989-03-01), Giannesi
patent: 5176990 (1993-01-01), Kim
patent: 5514517 (1996-05-01), Waki
patent: 5726006 (1998-03-01), Gourlaouen et al.
patent: 5879873 (1999-03-01), Gourlaouen et al.
patent: 6080536 (2000-06-01), Elst et al.
patent: 645 668 (1995-03-01), None
Anderson Andrew J.
Eastman Kodak Company
Letscher Geraldine
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