Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2001-12-26
2004-03-09
Letscher, Geraldine (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S569000, C430S449000
Reexamination Certificate
active
06703194
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Present Invention
The present invention relates to silver halide grains, a silver halide emulsion and a silver halide color photographic photosensitive material. More specifically, it relates to silver halide grains, a silver halide emulsion and a silver halide color photographic photosensitive material which are excellent for high-intensity exposure use, capable of being processed at a high speed and suited for obtaining high-quality images.
2. Description of the Related Art
In recent years, methods for forming images by exposing a recording material with a laser or LED light source in accordance with digital image information for a short period of time (high intensity) have increasingly become more widespread in the field of silver halide photosensitive materials. In particular, high-quality images are offered using color photographic printing paper as a laser recorded material.
It has been well known in the field that it is necessary for photosensitive materials to have satisfactory gradation with high sensitivity in high-intensity exposure from a low-density area to a high-density area when conducting superhigh-intensity exposure for less than 10
−4
seconds.
Because rapid processability has always been demanded of such photosensitive materials, silver chloride exhibiting high solubility, high-speed development and high-speed bleach-fixation has been widely used. Silver chloride has high ionic crystallinity and low ionic conductivity. This high ionic crystallinity allows a state in which an electron is trapped in an electron-trapping center to be easily stabilized by electron-lattice interaction.
Accordingly, in many cases, electron residence time in an electron-trapping center is prolonged, which poses a problem in that a phenomenon called latent image sensitization occurs with time after exposure, and hence it becomes difficult to obtain a stable image.
Further, since the silver chloride has low ionic conductivity, problems arise in that, during a sensitizing process, silver ions are not satisfactorily supplied when forming a latent image, whereby inefficiency such as latent image dispersion or recombination is triggered, thus leading to occurrence of low sensitivity or soft gradation enhancement.
In order to solve the problems described above, a primary electron-trapping center is utilized. However, there has been the problem that, in many cases, latent image sensitization described above cannot be suppressed.
In order to increase the ionic conductivity of silver chloride, a method using silver chloroiodide or silver chlorobromide has been widely used. However, there has been the problem that use of these materials in large amounts not only impairs rapid processing, but also induces low sensitivity and soft gradation enhancement due to introduction of crystal defects caused by formation of junction among different kinds of silver halides, whereby good photographic performance cannot be obtained.
Because of the aforementioned problems, silver halide grains in which the ionic conductivity thereof has been increased by at least 100 times relative to a silver chloride base have not yet been actually used as a photographic photosensitive material.
SUMMARY OF THE PRESENT INVENTION
An object of the present invention is to offer a solution to the above problems associated with the related art and to achieve the following goals.
That is, an object of the present invention is to provide silver halide grains, a silver halide emulsion and a silver halide color photographic photosensitive material, which are suitable for high-intensity exposure (digital exposure), have high pressure resistance during development, are capable of being processed at a high speed (mass processing), and with which can be realized a high-image-quality print system.
Means for solving the aforementioned problems are as follows.
<1> Silver halide grains, wherein a difference in ionic conductivity between a region exhibiting highest ionic conductivity and a region exhibiting lowest ionic conductivity is at least 100 times.
<2> A silver halide emulsion containing the silver halide grains described in <1>.
<3> A silver halide color photographic photosensitive material containing the silver halide emulsion described in <2>.
Silver Halide Grains and Silver Halide Emulsion
High-intensity reciprocity law failure of a silver halide photographic emulsion occurs when a large number of photoelectrons is generated within silver halide grains during high-intensity exposure and latent image dispersion is caused. High-intensity reciprocity law failure can be reduced by making silver halide grains to exhibit such a function within the grains that a large number of photoelectrons generated by high-intensity exposure are temporally escaped from a conduction band, and after a certain period of time of residence are re-released in a conduction band. This process corresponds to changing the condition within silver halide grains during high-intensity exposure to the same condition during low-intensity exposure.
The function of temporally escaping the photoelectrons, namely the function of temporally trapping photoelectrons, can be realized by doping a transition metal complex into silver halide grains. Such a dopant is referred to as an electron slowly-releasing dopant or an illumination-conversion dopant.
Hexachloroiridium has been so far used as a transition metal complex capable of reducing high-intensity reciprocity law failure. When hexachloroiridium is used, photoelectrons generated by exposure are trapped in the lowest vacant orbit of iridium serving as a central metal, and after a certain period of time of residence are re-released into the conduction band. The time from the commencement of exposure to re-release of the trapped photoelectrons is defined as an electron residence time.
The electron residence time can be determined by a reciprocity curve or a double flash photoconduction method. In the present invention, it was determined by a reciprocity curve which can be created as described on page 297 of “
Kaitei Shashin Kogaku no Kiso: Gin
-
en Shashin
-
hen
(Fundamentals of Photographic Science and Engineering (Revised): Silver Photography)”, edited by the Society of Photographic Science and Technology of Japan, Corona Publishing Co., Ltd., 1998.
When an ordinary silver halide emulsion (specifically, a silver chloride emulsion) is used, higher sensitivity occurs approximately at an intermediate illumination intensity region, with a reduced sensitivity both at a low illumination intensity region and a high illumination intensity region, thereby creating a convex curve with respect to the bottom of the graph. In contrast, if an emulsion which has reduced high-intensity reciprocity law failure by doping an electron slowly-releasing dopant is used, sensitivity does not decrease in regions higher than a certain exposure intensity and a reciprocity curve is flattened in the regions. That is, another reciprocity curve is obtained with an emulsion in which a dopant is not contained. The exposure illumination intensity at which the flattening starts, namely an exposure time at the intensity at which a difference occurs from the curve obtained with another emulsion without doping, is defined as electron residence time.
Since the effect of electron slowly-releasing (photoelectron re-releasing) emerges upon termination of the exposure, the time at which the effect of electron slowly-releasing appears photographically can be defined as the time at which electron re-releasing starts, namely, as electron residence time.
When a light source for exposure is fixed, an electron residence time corresponding to only a certain exposure intensity may be set. However, in order to obtain an emulsion that always achieves the same photographic characteristics even when different light sources are used, it is necessary to introduce dopants having appropriate electron residence times in accordance with the intensity of respective light sources for exposure into silv
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