Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2002-01-30
2004-08-10
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S567000, C430S600000
Reexamination Certificate
active
06773876
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a tabular grain having a very small thickness, a high aspect ratio and a large equivalent-circle diameter; a silver halide emulsion comprising the tabular grain; a process for producing the silver halide emulsion; and a novel crystal phase-controlling agent compound suitable for the production of the tabular grain.
BACKGROUND OF THE INVENTION
The tabular silver halide grain (hereinafter referred to as a “tabular grain”) has the following photographic properties:
1) the ratio of surface area to volume (hereinafter referred to as a “specific surface area”) is large and a large amount of sensitizing dye can be adsorbed to the surface of the grain, so that the color sensitization sensitivity can be relatively high as compared with the intrinsic sensitivity;
2) when an emulsion containing tabular grains is coated and dried, the grains are oriented in parallel to the support surface, so that the coated layer can be reduced in the thickness and the photographic light-sensitive material obtained can have good sharpness;
3) in an X-ray photographic system, when a sensitizing dye is added to the tabular grain, the silver halide cross-over light can be extremely reduced and therefore, the deterioration of image quality can be prevented;
4) light scattering is reduced and therefore, an image of high resolution can be obtained; and
5) the sensitivity to blue light is low, so that when the tabular grain is used in a green-sensitive layer or a red-sensitive layer, a yellow filter can be removed from the emulsion.
By virtue of these advantageous properties, tabular grains have been heretofore used in commercially available light-sensitive materials.
JP-B-6-44132 (the term “JP-B” as used herein means an “examined Japanese patent publication”) and JP-B-5-16015 disclose a tabular grain emulsion having an aspect ratio of 8 or more. The aspect ratio as used herein means a ratio of the equivalent-circle diameter to the thickness of a tabular grain. The diameter of a grain as used herein means the diameter of a circle having an area equal to the projected area of a grain when the emulsion is observed through a microscope or an electron microscope. The thickness is shown by the distance between two parallel main surfaces constituting a tabular silver halide.
JP-B-4-36374 discloses a color photographic light-sensitive material which is improved in the sharpness, sensitivity and graininess by using tabular grains having a thickness of less than 0.3 &mgr;m and a diameter of 0.6 &mgr;m or more in at least one layer of green-sensitive emulsion layer and red-sensitive emulsion layer.
In recent years, with the progress of silver halide light-sensitive materials designed to have higher sensitivity and smaller format, a color light-sensitive material having higher sensitivity and improved image quality is keenly demanded. To meet this requirement, the silver halide emulsion is demanded to have higher sensitivity and more excellent graininess. Conventional tabular silver halide emulsions cannot cope with these requirements and more improvement of the performance is demanded.
As the aspect ratio of a tabular grain is larger, the specific surface area is larger and the above-described advantageous properties of a tabular grain can be more effectively utilized. In other words, a larger amount of a sensitizing dye is adsorbed to a larger surface area and a larger intensity of light is absorbed per one grain, whereby higher sensitivity can be obtained. Therefore, many studies have been heretofore made to prepare tabular grains reduced in the thickness. JP-B-5-12696 discloses a method of oxidizing and thereby ineffectuating a methionine group in gelatin and preparing thin tabular grains using the gelatin as a dispersion medium, JP-A-8-82883 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) discloses a method of ineffectuating the amino group and the methionine group in gelatin and preparing thin tabular grains using the gelatin as a dispersion medium, and JP-A-10-148897 discloses a method of chemically modifying the amino group in gelatin to introduce at least two or more carboxyl groups and preparing thin tabular grains using the gelatin as a dispersion medium.
As for a tabular grain having a very large equivalent-circle diameter and a very small thickness, U.S. Pat. No. 5,612,175 discloses the tabular grain. In Examples of this patent, silver bromide tabular grains having a thickness of less than 0.1 &mgr;m and an average equivalent-circle diameter of several &mgr;m are disclosed. In the Examples, the thinnest tabular grain had a thickness of 0.04 &mgr;m and an average equivalent-circle diameter of 3.9 &mgr;m. European Patent 896,245 discloses, in the Example, a tabular grain having a thickness of 0.048 &mgr;m and an average equivalent-circle diameter of 3.74 &mgr;m. The tabular grains disclosed in these patents are expected to ensure high sensitivity and good graininess because of their very small thickness and very large main surfaces, however, in order to satisfy the recent requirement for higher sensitivity, tabular grains are still demanded to have a smaller thickness and larger main surfaces.
A crystal phase-controlling agent is an effective material for forming thin tabular grains, however, only with known compounds, the demanded aspect ratio cannot be achieved. For obtaining yet higher sensitivity, a crystal phase-controlling agent having higher performance, namely, a crystal phase-controlling agent having higher selectivity for the (111) face of a silver halide grain is being demanded. On the other hand, the crystal phase-controlling agent itself disadvantageously inhibits the adsorption of a sensitizing dye or chemical sensitization and therefore, is preferred not to be present on a tabular grain at the time of adding a sensitizing dye or at the chemical sensitization. From these reasons, a step of removing the crystal phase-controlling agent by water washing or the like is generally provided after the grain formation or before or after the adsorption of a sensitizing dye, however, the crystal phase-controlling agent cannot be completely removed and at present, this problem cannot be satisfactorily solved. In this meaning, a crystal phase-controlling agent which can be easily removed after the grain formation is demanded.
It is a well-known fact in the art that a silver halide emulsion is gradually sensitized due to naturally occurring radiation and with the passage of a long time, fogging is already generated before the exposure for the image recording and seriously deteriorates the image quality obtained by the exposure. In a silver halide emulsion, a latent image is formed on a silver halide grain upon exposure and thereby an image is recorded. For achieving high sensitivity, the size of silver halide grain must be increased to elevate the intensity of light absorbed at the exposure. On other hand, the absorption of naturally occurring radiation is, as well known, proportional to the volume of a silver halide. Thus, a silver halide emulsion may have higher sensitivity but at the same time, suffers from the increase of fogging due to radiation. Many efforts have been heretofore made to solve this problem but a definite method for solving this problem is not yet discovered. For solving this difficult problem, the effective means is to realize a grain having a very small thickness and a very large main surface area. More specifically, it is obvious that the intensity of light absorbed into a silver halide at the recording of an image is proportional to the amount of a sensitizing dye adsorbed to the surface of a silver halide grain and the amount of a sensitizing dye is proportional to the surface of a silver halide grain. On the other hand, the absorption of radiation is, as described above, proportional to the volume of a silver halide.
Accordingly, the tabular grain having a very large main surface area and a very small thickness and thereby having a very small grain volume, disclosed in the present inv
Ichikawa Shin-ichi
Inaba Tadashi
Takahashi Kazutaka
Urabe Shigeharu
Fuji Photo Film Co. , Ltd.
Schilling Richard L.
Sughrue & Mion, PLLC
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