Thermally processed image recording material

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

Reexamination Certificate

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C430S531000

Reexamination Certificate

active

06391536

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a thermally processed image recording material. In particular, the present invention relates to a thermally processed image recording material that shows superior image storability after heat development.
RELATED ARTS
There are known many photosensitive materials having a photosensitive layer on a support, with which image formation is attained by imagewise light exposure. Those materials include those utilizing a technique of forming images by heat treatment as systems that can contribute to the environmental protection and simplification of image forming means.
In recent years, reduction of amount of waste processing solutions is strongly desired in the field of films for medical use and the field of photographic art films from the standpoints of environmental protection and space savings. Therefore, development of techniques relating to thermally processed image recording materials for medical diagnosis films and photographic art films are required, which materials enables efficient exposure by a laser image setter or laser imager and formation of a clear black image having high resolution and sharpness. Such thermally processed image recording materials can provide users with a simple and non-polluting heat development processing system that eliminates the use of solution-type processing chemicals.
Among such thermally processed image recording materials, those materials for medical images are required to provide high quality of images excellent in sharpness and graininess, since such images are required to be very fine images. In addition, for easy diagnosis, cold monochromatic images are preferred. At present, various types of hard copy systems using pigments and dyes, for example, ink jet printers and electrophotographic systems, are available as ordinary imaging systems. However, no satisfactory image-forming system is available for medical images.
Methods for forming images by heat development are described in, for example, U.S. Pat. Nos. 3,152,904 and 3,457,075 and Klostervoer, “Thermally Processed Silver Systems”, Imaging Processes and Materials, Neblette, 8th ed., compiled by J. Sturge, V. Walworth and A. Shepp, Chapter 9, p. 279, (1989). Such photothermographic materials comprise a reducible non-photosensitive silver salt (e.g., silver salt of an organic acid), a photocatalyst (e.g., silver halide) in a catalytically active amount and a reducing agent for silver, which are usually dispersed in an organic binder matrix. While the photosensitive materials are stable at an ordinary temperature, when they are heated to a high temperature (e.g., 80° C. or higher) after light exposure, silver is produced through an oxidation-reduction reaction between the reducible silver salt (which functions as an oxidizing agent) and the reducing agent. The oxidation-reduction reaction is accelerated by catalytic action of a latent image of silver halide generated upon exposure. The silver resulted from the reaction of the reducible silver salt in the exposed areas shows black color that provides contrast with respect to the non-exposed areas, and thus images are formed. Thermally processed image recording materials and systems therefor based on the above principle are disclosed in many references including U.S. Pat. No. 2,910,377 and Japanese Patent Publication (Kokoku, hereinafter referred to as JP-B) 43-4924.
However, since such thermally processed image recording materials are not subjected to a fixation treatment after the heat development, they suffer from a problem that the silver salt of an organic acid, and possibly a photosensitive silver halide, when the materials are photothermographic materials, are left as they are in the materials even after the heat development, and thus white portions are colored when the materials are left at a high temperature for a long period of time after the heat development.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a thermally processed image recording material that shows improved image storability after the heat development, i.e., that shows improved coloration of white portions observed when the material is left at a high temperature. Another object of the present invention is to provide a thermally processed image recording material that comprises a transparent layer showing low haze and superior brittleness.
The inventors of the present invention assiduously studied in order to achieve the aforementioned objects. As a result, they found that an excellent thermally processed image recording material that provides the desired effects could be obtained by using a dispersion of polymer microparticles having a core/shell structure which satisfies particular requirements as a binder, and thus accomplished the present invention.
That is, the present invention provides a thermally processed image recording material having an image-forming layer that contains a non-photosensitive silver salt of an organic acid, a reducing agent for silver ions and a binder on a support, wherein the binder is coated as a dispersion of polymer microparticles having a core/shell structure, glass transition temperature of shell part of the core/shell structure is higher than glass transition temperature of core part, and the binder shows a minimum film-forming temperature of 30° C. or lower.
The glass transition temperature of the core part of the core/shell structure is preferably 10° C. or lower, and the glass transition temperature of the shell part is preferably 40° C. or higher. Further, the dispersion of polymer microparticles is preferably latex prepared by emulsion polymerization. Furthermore, the image-forming layer preferably contains a photosensitive silver halide.
According to the present invention, there can be provided thermally processed image recording materials that provide improved image storability after heat development, i.e., improved coloration of white portions when the materials are left at a high temperature, and have transparent coated films with low haze that are also excellent in brittleness.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be explained in detail hereafter.
The thermally processed image recording material of the present invention has an image-forming layer that contains a non-photosensitive silver salt of an organic acid, a reducing agent for silver ions and a binder on a support. The aforementioned image-forming layer preferably further contains a photosensitive silver halide. In this case, the image-forming layer is a photosensitive layer, and the thermally processed image recording material of the present invention includes a photothermographic material.
The binder used for the image-forming layer of the thermally processed image recording material of the present invention is characterized in that it is provided by coating a dispersion of polymer microparticles that have a core/shell structure, the glass transition temperature of the shell part of the core/shell structure is higher than that of the core part, and the minimum film forming temperature of the binder is 30° C. or lower. The image-forming layer is preferably formed by coating and drying the coating solution which is prepared by mixing a dispersion of the aforementioned polymer microparticles with other ingredients.
The binder of the image-forming layer serves as a field of the image formation by the heat development, and provides a storage environment for the picture elements during image storage. The aging stability of the images formed by the development is greatly affected by the environment surrounding the silver grains that can be picture elements. Thermally processed materials, in particular, do not undergo a fixation reaction process as described above, and therefore non-imagewise development may occur even after the image formation. In the thermally processed materials, in general, significant improvement in storage stability can be obtained by reducing diffusibility of the compounds involved in the development process which present arou

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