Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2002-03-25
2003-09-23
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S569000, C430S599000, C430S604000
Reexamination Certificate
active
06623917
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to silver halide photographic emulsions exhibiting enhanced sensitivity and superior graininess.
BACKGROUND OF THE INVENTION
Silver halide photographic light sensitive materials (hereinafter, also denoted simply as photographic materials) are said to be mature products having a high level of completeness, while various performance factors such as high sensitivity, enhanced image quality and improved storage stability are required and recently the requirements have become higher levels. Specifically with regard to high sensitivity and enhanced image quality, further enhanced performance is required to maintain superiority of silver halide photographic materials in view of recent technical progress in digital cameras.
To achieve higher sensitivity and enhanced image quality, there has been studied a technique for enhancing the ratio of sensitivity to grain size for respective grains in a silver halide emulsion (hereinafter, also denoted simply as an emulsion).
It is commonly known that silver halide grains contained in a silver halide emulsion have, in general, various shapes. Examples thereof include regular crystal silver halide grains such as cubic, octahedral or tetradecahedral grains, tabular silver halide grains having a single twin plane or plural parallel twin planes, and tetrapod-like or needle-like silver halide grains having non-parallel twin planes. Specifically, tabular silver halide grains (hereinafter, also denoted simply as tabular grains) are supposed to have the following advantages as photographic performance:
1. the ratio of grain volume to grain surface area (hereinafter, also denoted as a specific surface area) is relatively high, causing a large amount of a sensitizing dye to be adsorbed onto the surface so that spectral sensitivity is high relative to intrinsic sensitivity;
2. when a tabular grain containing emulsion is coated and dried, the tabular grains are arranged in parallel to the support surface and thereby, the coating layer thickness can be reduced, leading to an enhancement of sharpness of the photographic material;
3. light scattering due to silver halide grains is relatively low, resulting in images with high resolution;
4. sensitivity to blue light (intrinsic sensitivity) is relatively low so that when used in a green-sensitive or red-sensitive layer, the yellow filter density can be reduced or the yellow filter can be removed from the constitution of a photographic material; and
5. In cases when having achieved the same sensitivity as commonly known other type grains, the characteristic grain shape results in a reduced silver coating amount, leading to an enhancement of sensitivity/graininess ratio and superior resistance to natural radiation.
As prior art relating to tabular grains, preparation methods and utilizing techniques thereof are described in U.S. Pat. Nos. 4,434,226, 4,439,520, 4,414,310, 4,433,048, 4,414,306 and 4,459,353; JP-B Nos. 6-43605, 6-43606, 6-214331 and 6-222488 (hereinafter, the term, JP-B refers to published Japanese Patent); JP-A Nos. 6-43605, 6-43606, 6-214331, 6-2224888, 6-230493 and 6-258745 (hereinafter, the term, JP-A means unexamined and published Japanese Patent Application).
To effectuate the foregoing advantages of tabular grains, it is effective to employ tabular grains having a higher aspect ratio. However, practical use of tabular grains having an aspect ratio of 12 or more produced the following problems.
1. Intended sensitivity was not achieved due to latent image dispersion. Theoretically, in proportion to an increase of the grain surface area absorbing light, the number of adsorbed photons was increased, leading to enhanced photographic sensitivity. In practice, however, the absorbed photons are dispersed onto a number of latent image specks formed on the major faces having a large area, resulting in lowering the probability of forming developable latent image specks. As a result, desired sensitivity cannot be obtained.
2. Adsorption of a sensitizing dye was actually insufficient so that light absorption expected from an increased grain surface area was not obtained and enhanced photographic sensitivity was not achieved.
3. Techniques of dislocation lines described in JP-A No. 63-220238, 1-102547, 6-27564 and 6-11781 are a sensitivity enhancing technique frequently employed in the photographic art. In fact, it is indispensable to have this technique combined with a high aspect ratio grain emulsion. However, the combination of tabular grains having an aspect ratio of 12 or more with the dislocation lines produced problems in that introduction of iodide ions resulted in lowering of the aspect ratio. It was also proved by the inventors of this application that even in an attempted to increase the aspect ratio by the adjustment of grain growth conditions, problems arose such a deteriorating the grain size distribution.
To overcome the foregoing problems in high aspect ratio grain emulsions, there have been proposed some compositions including an epitaxial grain emulsion described in U.S. Pat. No. 5,497,789. However, none of such proposals solved the foregoing three problems in practical use of high aspect ratio grain emulsions. Thus, merits achieved by tabular grains having a higher aspect ratio were not satisfactorily achieved.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to provide a high aspect ratio-having tabular grain emulsion exhibiting enhanced sensitivity and improved graininess.
The object of the invention can be achieved by the following constitution:
A silver halide photographic emulsion comprising silver halide grains wherein at least 80% of a total grain projected area is accounted for by tabular grains, the tabular grains having an average aspect ratio of at least 12, a variation coefficient of grain diameter of less than 30%, an average overall surface iodide content of 5 to 15 mol % and an average surface iodide content in the vicinity of corners of the respective grains of less than 3 mol %; and the tabular grains further having a shallow electron trap in the peripheral region of the respective grains.
Furthermore, in preferred embodiments of the invention,
(1) less than 30% by number of the tabular grains is accounted for by grains having at least 10 dislocation lines in each of edges of the grain;
(2) at least 60% by number of the tabular grains is accounted for by grains having at least 10 dislocation lines at edges at respective edges of the grain and said dislocation lines being a non-iodide-gap type;
(3) the emulsion contains a compound having a function of injecting at least two electrons into silver halide through photoexcitation by a single photon;
(4) the emulsion contains a sensitizing dye in an amount exceeding a monolayer adsorption amount; and
(5) the tabular grains each have an epitaxial growth phase in the vicinity of corners of the grain.
DETAILED DESCRIPTION OF THE INVENTION
Silver halide emulsions relating to the invention are those containing tabular grains. The tabular grains are crystallographically classified into twinned crystal grains. The twinned crystal grain refers to a crystal grain having at least one twinned plane within the grain. Classification of silver halide twinned crystal grains is described in Klein & Moisar's report (Photographishe Korrespondenz, vol. 99, page 99, and vol. 100, page 57) Tabular grains relating to the invention are those having at least two twinned planes parallel to the major faces.
The twin plane can be observed by a transmission electron microscope. Thus, a photographic emulsion is coated on a support to prepare a sample so that the major face of tabular grains contained are arranged parallel to the support surface. The thus prepared sample is cut using a diamond cutter to obtain ca. 0.1 &mgr;m thick slices. The presence of twin plane(s) can be confirmed through observation of this slice using a transmission electron microscope. In the invention, the spacing between two twin planes of the tabular grains is determined in such
Ishikawa Sadayasu
Suzuki Katsuhiko
Takada Hiroshi
Konica Corporation
Muserlian Lucas and Mercanti
Schilling Richard L.
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