Photothermographic material

Details Photothermographic material Photothermographic material

2000-08-24

2002-04-09

Chea, Thorl (Department: 1752)

Radiation imagery chemistry: process, composition, or product th

Radiation sensitive product

Silver compound sensitizer containing

C430S568000, C430S607000, C430S613000, C430S614000

Reexamination Certificate

active

06368782

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a photothermographic material.
BACKGROUND OF THE INVENTION
In recent years, reduction of amount of waste processing solutions is strongly desired in the medical diagnosis field and the photographic art field from the standpoints of environmental protection and space savings. Techniques relating to photothermographic materials for use in medical diagnosis and photographic-art processes are required which enables efficient exposure by a laser image setter or a laser imager and formation of a clear black image having high resolution and sharpness. The photothermographic materials can provide users with a simple and non-polluting heat development processing system that eliminates the use of solution-type processing chemicals including a developing solution.
The same applies to the field of ordinary image-forming materials. However, photo-images for medical use require high quality excellent in sharpness and graininess as they need very fine images. In addition, for easy diagnosis, cold monochromatic images are preferred. At present, various types of hard copy systems using pigment and dye, for example, ink jet printers and electrophotographic systems are available as ordinary imaging systems. However, no satisfactory image-forming system is available for medical use.
Methods utilizing a silver salt of an organic acid for forming an image by heat development are described, for example, in U.S. Pat. Nos. 3,152,904 and 3,457,075 and B. Shely, Imaging Processes and Materials, “Thermally Processed Silver Systems”, Neblette, 8th ed., compiled by J. Sturge, V. Walworth and A. Shepp, Chapter 9, p.279, (1989). The photothermographic material, in particular, comprises a image-forming layer (photosensitive layer) containing a photocatalyst (e.g., silver halide) in a catalytically active amount, a reducing agent, a reducible silver salt (e.g., silver salt of an organic acid), and optionally a toning agent for controlling tone of silver, which are usually dispersed in a binder matrix. When the photothermographic material is heated at a high temperature (e.g., 80° C. or higher) after light exposure, a monochromatic black silver image is produced through an oxidation-reduction reaction between the silver halide or 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. Therefore, the monochromatic silver images are formed in exposed areas of the materials. This technique is 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. The photothermographic systems using a silver salt of an organic acid can achieve image quality and tones that satisfy the needs in the medical filed.
In the aforementioned photothermographic systems utilizing a silver salt of an organic acid, it has been found that a smaller silver halide grain size provides higher sensitivity due to the increase of starting points of development. However, when a smaller grain size is chosen, a problem arises in that sensitivity is significantly reduced after storage of a photothermographic material at an elevated temperature (e.g., for 7 hours at 60° C.).
SUMMARY OF THE INVENTION
An object of the present invention is to provide a means to solve those problems of the related art. More specifically, the object of the present invention is to provide a photothermographic material for use in medical imaging, photomechanical process and so forth, which has high sensitivity and superior storability before development (especially, storability at elevated temperatures).
The inventors of the present invention conducted intensive studies to achieve the aforementioned object, and as a result, they achieved the present invention.
The present invention provides a photothermographic material comprising, on one side of a support, at least one photosensitive silver halide, a non-photosensitive silver salt of an organic acid, a reducing agent for silver ions, and a binder, wherein the photosensitive silver halide has an average grain size of from 0.001 &mgr;m to 0.06 &mgr;m and the material comprises at least two kinds of organic polyhalogenated compounds wherein at least one of said organic polyhalogenated compounds is represented by the following formula (1):
wherein Z
1
and Z
2
independently represent a halogen atom, X
1
represents a hydrogen atom or an electron withdrawing group, Y
1
represents —CO— group or —SO
2
— group, Q represents an arylene group or a divalent heterocyclic group, L represents a linking group, W
1
and W
2
independently represent a hydrogen atom, an alkyl group, an aryl group, or a heterocyclic group, and n represents 0 or 1.
According to a preferred embodiment of the present invention, there is provided the aforementioned photothermographic material, wherein a layer containing the organic polyhalogenated compound represented by the formula (1) is formed by using an aqueous coating solution and the organic polyhalogenated compound represented by the formula (1) is added to the aqueous coating solution as an aqueous dispersion.
According to the present invention, photothermographic materials can be provided which have high sensitivity and high image quality, as well as superior storage stability before development, for example, extremely small decrease in sensitivity during storage at an elevated temperature. Therefore, the photothermographic materials of the present invention are useful for use in medical imaging, photomechanical process and so forth.
PREFERRED EMBODIMENT OF THE INVENTION
The photothermographic material of the present invention comprises at least two kinds of organic polyhalogenated compounds, and at least one of said compounds is an organic polyhalogenated compound represented by the formula (1). As organic polyhalogenated compounds other than the aforementioned compounds, an organic polyhalogenated compound represented by the following formula (II) is preferred.
In the formula (II), symbol “A” represents an alkyl group, an aryl group, or a heterocyclic group, Z
3
and Z
4
independently represent a halogen atom, X
2
represents a hydrogen atom or an electron withdrawing group, Y represents —C(═O)—, —SO— or —SO
2
—, and symbol “n” represents 0 or 1.
The aryl group represented by the symbol “A” may be monocyclic, or may have a condensed ring structure. Preferably, the aryl group is a monocyclic or bicyclic aryl group having from 6 to 30 carbon atoms (e.g., phenyl, naphthyl, etc.). More preferred examples include a phenyl group or a naphthyl group, and a further preferred example includes a phenyl group.
The heterocyclic group represented by the symbol “A” is a 3-membered to 10-membered, saturated or unsaturated heterocyclic group having at least one of N, O or S atoms. The heterocyclic group may be monocyclic or may form a condensed ring structure with any other rings. The heterocyclic group is preferably a 5- or 6-membered unsaturated heterocyclic group optionally having a condensed ring structure, more preferably a 5- or 6-membered aromatic heterocyclic group optionally having a condensed ring structure. A nitrogen-containing 5- or 6-membered aromatic heterocyclic group optionally having a condensed ring structure is more preferred, and a 6-membered aromatic heterocyclic group having from 1 to 4 nitrogen atoms and optionally having a condensed ring structure is most preferred.
Specific examples of the hetero ring in the heterocyclic group include pyrrolidine, piperidine, piperazine, morpholine, thiophene, furan, pyrrole, imidazole, pyrazole, pyridine, pyrimidine, pyrazine, pyridazine, triazole, triazine, indole, indazole, purine, thiadiazole, oxadiazole, quinoline, phthalazine, naphthyridine, quinoxaline, quinazoline, cinnoline, pteridine, acridine, phenanthroline, phenazine, tetrazole, thiazole, oxazole, benzimidazole, benzoxazole, benzthiazole, benzoselenazole, indolenine, tetrazaindene and t

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