Black and white photothermographic material and method for...

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

Reexamination Certificate

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C430S611000, C430S617000, C430S620000

Reexamination Certificate

active

06472138

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photothermographic material and a method for fabricating thereof.
2. Description of Related Art
A strong need for reducing the volume of the waste of processsing solution has arisen in recent medical diagnosis field from viewpoints of environmental preservation and space saving. Thus a technology related to a photothermographic material for medical diagnosis and photographic purposes has been desired, in which the material is expected to allow efficient light exposure with a laser image setter or laser imager, and to provide a black image with a high resolution and sharpness. Such photothermographic material can provide the user with a more simple and environment-conscious image producing system using no solution-base process chemical.
While a similar need has been occurring in the field of general image forming materials, images used in the medical diagnosis field specifically require a high image quality such as excellent sharpness and graininess for fine depiction, and prefer a blue-black tone for facilitating diagnoses. Although various hard copy system using pigment or dye, exemplified as an inkjet printer and electronic photograph system, are prevailing as a general image forming system, none of which is satisfactory as an output system for medical images.
Other type of photothermographic system using an organic silver salt is known, for example, in U.S. Pat. Nos. 3,152,904 and 3,457,075 and “Thermally Processed Silver Systems” by D. Klosterboer, Imaging Processes and Materials, Neblette's 8th ed., edited by J. Sturge, V. Walworth and A. Shepp, Chapter 9, p. 279, (1989). In particular, the photothermographic material generally has a photosensitive layer comprising a catalytic amount of a photocatalyst (e.g., silver halide), a reducing agent, a reducible silver salt (e.g., organic silver salt), and an optional toner for controlling color tone of silver image, all of which being dispersed in a binder matrix. The photothermographic material produces a black silver image when heated, after light exposure, to a high temperature (e.g., 80.C. or above) through redox reaction of the silver halide or reducible silver salt with the reducing agent. Since the redox reaction is promoted by a catalytic action of silver halide composing a latent image, which is produced by the light exposure, that the blacked silver image is formed in the exposed area. Such heat-assisted image producing system is disclosed in numbers of literatures typified by U.S. Pat. No. 2,910,377 and JP-B-43-4924 (the code “JP-B-” as used in this specification means an “examined Japanese patent publication”), and recently Fuji Medical Dry Imager FM-DPL was launched as a medical image producing system using such photothermographic material.
Such black and white photothermographic material utilizing the non-photosensitive fatty acid silver salt and the photosensitive silver halide can achieve a higher maximum optical density (Dmax) by employing smaller silver halide grains to enhance the covering power. A problem, however, resides in that the adsorption of a sensitizing dye onto the silver halide grains becomes weaker as the silver halide grains become smaller, which is causative of increased desensitization during a long-term storage. Solving means therefor is thus eagerly desired.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to solve the foregoing problem in the prior art.
That is, an object of the present invention is to provide a black and white photothermographic material for laser exposure affording a large covering power and thus affording a high Dmax, and capable of suppressing desensitization in the course of the storage.
The present inventor found out, after extensive studies, that an excellent photothermographic material exhibiting desired function can be fabricated by using a photosensitive silver halide grains having an average grain size of 10 nm to 50 nm, and also by using a compound expressed by the formula (1) as defined in this specification, which led the inventor to propose the present invention.
That is, the present invention provides a black and white photothermographic material containing on one side of a support a reducing agent for reducing silver ion, a binder, a non-photosensitive fatty acid silver salt and a photosensitive silver halide, wherein such photosensitive silver halide forms grains with an average grain size of 10 nm to 50 nm prepared independently from such non-photosensitive fatty acid silver salt; and wherein a compound expressed by the formula (1) below is further contained:
[(Z)
m
L]
n
ASM
1
  formula (1)
[where, in the formula (1),
Z represents —SO
3
M
2
, —COOR
1
, —OH or —NHR
2
; in which M
2
being a hydrogen atom or an alkali metal atom, R
1
being a hydrogen atom, an alkali metal atom or an alkyl group having 1 to 6 carbon atoms, R
2
being a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, —COR
4
, —COOR
4
or —SO
2
R
4
, in which R
4
being a hydrogen atom, an aliphatic group or an aromatic group;
m is an integer not less than 1, and for the case of m≧2, the groups Z in a number of m may be same or different with each other;
L represents a single bond or a linkage group;
n is an integer not less than 1, and for the case of n≧2, the groups (Z)
m
L in a number of n may be same or different with each other;
A is a heterocyclic group which may be substituted; and
M
1
is a hydrogen atom or an alkali metal atom.]
The compound expressed by the formula (1) is preferably contained as being adsorbed on the non-photosensitive fatty acid silver salt.
The average grain size of the photosensitive silver halide is preferably 10 nm to 45 nm, and more preferably 10 nm to 40 nm.
Another aspect of the present invention is to provide a method for fabricating a black and white photothermographic material containing on one side of a support a reducing agent for reducing silver ion, a binder, a non-photosensitive fatty acid silver salt and a photosensitive silver halide, comprising:
a step for preliminarily making a compound expressed by the formula (1) below adsorb to grains of the non-photosensitive fatty acid silver salt:
[(Z)
m
L]
n
ASM
1
  formula (1)
 [where, in the formula (1), Z represents —SO
3
M
2
, —COOR
1
, —OH or —NHR
2
; in which M
2
being a hydrogen atom or an alkali metal atom, R
1
being a hydrogen atom, an alkali metal atom or an alkyl group having 1 to 6 carbon atoms, R
2
being a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, —COR
4
, —COOR
4
or —SO
2
R
4
, in which R
4
being a hydrogen atom, an aliphatic group or an aromatic group;
m is an integer not less than 1, and for the case of m≧2, the groups Z in a number of m may be same or different with each other;
L represents a single bond or a linkage group;
n is an integer not less than 1, and for the case of n≧2, the groups (Z)
m
L in a number of n may be same or different with each other;
A is a heterocyclic group which maybe substituted; and
M
1
is a hydrogen atom or an alkali metal atom.];
a step for preparing the photosensitive silver halide grains having an average grain size of 10 nm to 50 nm; and
a step for mixing the non-photosensitive fatty acid silver salt grains having the compound expressed by the formula (1) adsorbed thereon with the photosensitive silver halide grains.
The present invention is the first to provide a photothermographic material high in Dmax and at the same time less in sensitivity degradation (desensitization) during the storage.
DETAILED DESCRIPTION OF THE INVENTION
Mode of implementation and embodiment of the black and white photothermographic material of the present invention will be detailed hereinafter.
The photothermographic material of the present invention contains on one side of a support a reducing agent for reducing silver ion, a binder, a non-photosensitive fatty acid silver salt and a photosensitive silver halide, such photosensitive silver halide forms

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