Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2000-05-12
2002-01-29
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S513000, C430S530000
Reexamination Certificate
active
06342343
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a photothermographic material.
BACKGROUND OF THE INVENTION
Reduction of waste solutions has been strongly desired in recent years in the medical field from the viewpoint of environmental protection and space saving. Accordingly, techniques concerning a thermographic photosensitive material for medical diagnosis and photographic technical use in which exposure can be performed efficiently with a laser/image setter or a laser/imager and can form a clear black image exhibiting high resolving power and sharpness have been required. Such a thermographic photosensitive material can offer to customers a simpler and environmentally benign thermographic processing system without the use of solution type processing chemicals.
There also arises the same requirement in the field of general image-forming materials but the medical image is characteristics in that a blue black tone image is preferably used because high image quality which is excellent in sharpness and graininess is necessitate as precise imaging is required, in addition, from the viewpoint of easiness of diagnosis. At present, various hard copy systems utilizing pigments and dyes such as ink jet printers and electrophotography prevail as general image-forming systems, however, none of these systems are satisfactory as a medical image output system.
On the other hand, thermal image-forming methods making use of organic silver salts are described, for example, in U.S. Pat. Nos 3,152,904 and 3,457,075, and B. Shely,
Thermally Processed Silver Systems
, “Imaging Processes and Materials”, compiled by J. Sturge, V. Walworth, A. Shepp, 8th Ed., Neblette, Chapter 9, p.279(1989). In particular, a photothermographic material generally has a-photosensitive layer comprising a catalytically active amount of photocatalyst (e.g., a silver halide), a reducing agent, a reducible silver salt (e.g., an organic silver salt), and a toner which controls the tone of silver according to necessity, having dispersed in a binder matrix. A photothermographic material forms a black silver image by heating at high temperature (e.g., 80° C. or more) after image exposure to cause an oxidation reduction reaction between a silver halide or a reducible silver salt (which functions as an oxidizing agent) and a reducing agent. The oxidation reduction reaction is accelerated by the catalytic action of the latent image of the silver halide generated by exposure. Therefore, the black silver image is formed in the exposed area. The above thermal image-forming methods are described in various literature including U.S. Pat. No. 2,910,377 and JP-B-43-4924 (the term “JP-B” as used herein means an “examined Japanese patent publication”) These thermal image-forming methods making use of organic silver salts can achieve satisfactory image quality and tone as a medical image.
However, for applying thermal image-forming methods to medical diagnosis, not only various photographic characteristics should be improved but also images should be those not adversely affecting medical diagnosis. Above all, there is an important problem that if dusts and the like adhere to the photographic material during photographing at medical site, the clear spots are generated in the area. There is also the case that dusts adhere to photographic materials during processing steps of cutting and packaging. The adhesion of dusts is liable to increase as the processing rate increases, therefore, economically disadvantageous.
It is important for medical diagnosis to improve such clear spot failure due to the adhesion of dusts while maintaining photographic characteristics, in particular, not causing unevenness of density by processing.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a photothermographic material which is free from clear spot failure and does not cause unevenness of density by processing.
The above object of the present invention has been achieved by the following means.
(1) A photothermographic material comprising on one surface side of the support at least one kind of photosensitive silver halide, a photo-insensitive organic silver salt, a reducing agent for a silver ion, and a binder, and having an electroconductive layer, wherein the surface resistivity (under the atmosphere of 25° C., 25% RH) of the material is 10
11
&OHgr; or less, and the optical density at the exposure wavelength of the surface side containing the photosensitive silver halide is from 0.2 to 3.0.
(2) The photothermographic material as described in the above item (1), wherein the electroconductive layer contains a metallic oxide.
(3) The photothermographic material as described in the above item (1) or (2), wherein the electroconductive layer is provided on the surface of the support opposite to the side which contains the photosensitive silver halide.
(4) The photothermographic material as described in any of the above items (1), (2) and (3), wherein the optical density at the exposure wavelength of the surface of the support opposite to the side which contains the photosensitive silver halide is from 0.2 to 3.0.
(5) The photothermographic material as described in any of the above items (1) to (4), wherein an antihalation layer which is decolored by the heat at thermal development is provided on the surface of the support opposite to the side which contains the photosensitive silver halide.
(6) The photothermographic material as described in any of the above items (1) to (5), wherein the total film thickness exclusive of the support is 15 to 38 &mgr;m.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail below.
The photothermographic material according to the present invention comprises a support having provided thereon an image-forming layer containing a photo-insensitive organic silver salt and a binder, and further contains on the same side of the support a photosensitive silver halide and a reducing agent for a silver ion. The image-forming layer is preferably a photosensitive layer containing a photosensitive silver halide. The photothermographic material further have an electroconductive layer, and the surface resistivity of either surface of the material (under the atmosphere of 25° C., 25% RH) is 10
11
&OHgr; or less. The optical density (i.e., an absorbance) at the exposure wavelength of the photosensitive layer side (exclusive of the support) is from 0.2 to 3.0, preferably from 0.2 to 2.0, and the optical density at the exposure wavelength of the back surface side (exclusive of the support) is preferably from 0.2 to 3.0, more preferably from 0.2 to 2.0, most preferably from 0.2 to 1.0. These optical densities are the optical densities at exposure time, i.e., before thermal development processing. By providing the above electroconductive layer to restrict the surface resistivity of the photothermographic material within the above range and regulating the optical density at the exposure wavelength of the photosensitive layer side within the above range, a clear spot failure due to adhesion of dusts to the material during producing and processing steps and density unevenness by processing can be prevented, while when the surface resistivity of the material exceeds 10
11
&OHgr;, dusts are liable to be adhered, as a result, a clear spot failure arises. On the other hand, when the optical density of the photosensitive layer side is less than 0.2, density unevenness by processing is generated and when exceeds 3.0, the sensitivity lowers. Concerning the clear spot failure, the total film thickness of the photothermographic material exclusive of the support (the total of both sides) is preferably 15 to 38 &mgr;m, particularly preferably from 18 to 35 &mgr;m, and when the processing rate is high, the clear spot failure is improved by limiting the total film thickness of the material The optical density of the back surface Within the above range is preferred to ensure sharpness.
The photothermographic material according to the present invention has an electroconductive layer. The electroconducti
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