Thermally developable photosensitive material

Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing

Reexamination Certificate

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C430S604000

Reexamination Certificate

active

06287755

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a thermally developable photosensitive material and specifically to the thermally developable photosensitive material having high sensitivity when exposed by a laser imager or a laser image setter with an excellent image stability after development.
BACKGROUND OF THE INVENTION
Conventionally, in the printing and plate-making field and the medical field, solution waste generated along with the wet process for image forming materials has caused problems regarding workability, and in recent years, a decrease in the processing solution waste has been strongly demanded in terms of environmental protection and room saving. Thus, a technique for light heat photographic material for a technical photographic use is demanded in which exposure can be sufficiently carried out using a laser image setter or a laser imager, and sharp and bright images with high resolving power can be achieved. As such techniques, methods are well known which are described, for example, in U.S. Pat. Nos. 3,152,904 and 3,487,075 and D. Morgan,
{circumflex over (l)}
Dry Silver Photographic Materials
{circumflex over (l)}
(Handbook of Imaging Materials, Marcel Dekker, Inc. page 48, 1991), etc. These photosentive materials are referred to as thermally developable photosensitive materials comprising a support having thereon an organic silver salt, a photosensitive silver halide and a reducing agent.
Conventionally, these thermally developable photosensitive materials are characterized in that they are thermally developed at temperature of 80 to 140° C. so as to obtain images without fixation, so that the silver halide and the organic silver salt in an unexposed portion are not removed and remain in the photosensitive materials.
Accordingly, the remaining silver halide and organic silver salt cause an increase of fog in the unexposed portion, staining the unexposed portion and discoloring an image tone of the developed silver into a warm black tone when storing the photosensitive materials for a long time. Specifically, in cases where an amount of silver is increased to obtain a sufficient image density available for a practical use, there exists a problem that diagnosis ability is lowered because of the increase of fog, so that the thermally developable photosensitive material with small amount of silver by which high light-sensitivity and high image density are attained has been desired.
SUMMARY OF THE INVENTION
Accordingly, in view of the foregoing, the present invention was accomplished. An object of the invention is to provide the thermally developable photosensitive material with high sensitivity when exposed and high image density.
DETAILED DESCRIPTION OF THE INVENTION
Above objects of the invention could be attained by the following constitution:
1. A thermally developable photosensitive material comprising photosensitive silver halide grains, an organic silver salt, a reducing agent and a binder, characterized in that a dispersibility ((standard deviation of circle equivalent diameter of cell)/(average value); cell centering each grain is obtained by processing an electron microscope image employing an extension method) of said photosensitive silver halide grains having grain size of not less than 0.02 &mgr;m, measured from an expopsing side of said thermally developable photosensitive material, is not more than 80%.
2. The thermally developable photosensitive material of item 1, wherein previously prepared photosensitive silver halide grains mixed with said organic silver salt are monodispersed silver halide grains.
3. The thermally developable photosensitive material of item 1, wherein a photosensitive layer contains zirconium in an amount of 0.005 to 0.5 mg per 1 g of silver.
4. The thermally developable photosensitive material of item 1, wherein said thermally developable photosensitive material contains 5 to 1000 mg/m
2
of solvent.
5. A thermally developable photosensitive material comprising photosensitive silver halide grains, an organic silver salt, a reducing agent and a binder, characterized in that not less than 95% of said photosensitive silver halide grains having grain size of not less than 0.02 &mgr;m is in contact with said organic silver salts.
6. The thermally developable photosensitive material of item 5, wherein previously prepared photosensitive silver halide grains mixed with said organic silver salt are monodispersed silver halide grains.
7. The thermally developable photosensitive material of item 5, wherein a photosensitive layer contains zirconium in an amount of 0.01 to 0.5 mg per 1 g of silver.
8. The thermally developable photosensitive material of item 5, wherein said thermally developable photosensitive material contains 5 to 1000 mg/m
2
of solvent.
The embodiments of the present invention are detailed below.
Silver halide grains of photosensitive silver halide in the present invention work as a light sensor. In order to minimize translucence after image formation and to obtain excellent image quality, the less the average grain size, the more preferred, and the average grain size is preferably less than 0.1 &mgr;m; is more preferably between 0.01 and 0.1 &mgr;m, and is most preferably between 0.02 and 0.08 &mgr;m. Herein, the grain size indicates a diameter of circle (circle equivalent diameter) having equal area to that of each grain image observed with a transmission electron microscope.
Furthermore, silver halide grains are preferably monodisperse grains. The monodisperse grains as described herein refer to grains having a monodispersibility obtained by the formula described below of less than 40%; more preferably less than 30%, and most preferably between 0.1 and 20%.
 Monodispersibility=(standard deviation of grain diameter)/(average of grain diameter)×100
There is no limitation as to the silver halide grain shape, but the silver halide grain shape in which a high ratio of a Miller index [100] plane occupies is preferred. This ratio is preferably at least 50%; is more preferably at least 70%, and is most preferably at least 80%. The ratio occupying the Miller index [100] plane can be obtained based on T. Tani, J. Imaging Sci., 29, 165 (1985) in which adsorption dependency of a [111] plane and a [100] plane is utilized.
Furthermore, another preferred silver halide shape is a tabular grain. The tabular grain as described herein is a grain having an aspect ratio represented by r/h of at least 3, wherein r represents a grain diameter in &mgr;m obtained as the square root of the projection area, and h represents thickness in &mgr;m in the vertical direction. Of these, the aspect ratio is preferably between 3 and 50.
The grain diameter is preferably not more than 0.1 &mgr;m, and is more preferably between 0.01 and 0.08 &mgr;m. These are described in U.S. Pat. Nos. 5,264,337, 5,314,789, 5,320,958, and others.
The composition of silver halide may be any of silver chloride, silver chlorobromide, silver chloroiodobromide, silver bromide, silver iodobromide, or silver iodide.
The photographic emulsion employed in the present invention can be prepared employing methods described in P. Glafkides,
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Chimie et Physique Photographique{circumflex over (l)} (published by Paul Montel Co., 1967), G. F. Duffin,
{grave over (l)}
Photographic Emulsion Chemistry
{circumflex over (l)}
(published by The Focal Press, 1966), V. L. Zelikman et al.,
{grave over (
1
)}
Making and Coating Photographic Emulsion{circumflex over (
1
)} (published by The Focal Press, 1964), etc. Namely, any of several acid emulsions, neutral emulsions, ammonia emulsions, and the like may be employed. Furthermore, when grains are prepared by allowing soluble silver salts to react with soluble halide salts, a single-jet method, a double-jet method, or combinations thereof may be employed.
Silver halide employed in the present invention is preferably comprised of ions of metals or complexes thereof, in transition metal belonging to Groups VIB, VIIB, VIII and IB of the Periodic Table. A

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