Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2000-08-03
2002-11-19
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S567000, C430S569000, C430S604000, C430S607000, C430S611000, C430S613000, C430S614000, C430S615000
Reexamination Certificate
active
06482583
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a photothermographic material.
BACKGROUND OF THE INVENTION
In the field of medical diagnosis, these days much desired is reducing the wastes of processing solutions for environmental protection and space saving. In that situation, required are techniques with photothermographic materials for medical diagnosis and ordinary photography capable of being efficiently exposed with laser image setters or laser imagers to form sharp and clear monochromatic images of high resolution. Such photothermographic materials could provide users with simple photothermographic systems not requiring solution-type processing chemicals and therefore not polluting the environment.
The same applies to the field of ordinary image-forming materials, which, however, shall differ from those in the field of medical diagnosis. Specifically, photo-images for medical diagnosis must clarify the details of body parts and therefore must have sharp and good image quality with fine graininess. In addition, for easy diagnosis thereon, preferred are cold monochromatic images in the field of medical diagnosis. At present, various types of hard copy systems with pigment and dye, for example, ink jet printers and electrophotographic systems are available for ordinary imaging systems. However, No satisfactory systems for forming photo-images enough for medical diagnosis are available.
On the other hand, photothermographic systems with silver salts of an organic acid used therein are described, for example, in U.S. Pat. Nos. 3,152,904 and 3,457,075, and in D. Klosterboer, 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). In general, photothermographic materials have a photosensitive layer which contains a catalytically active amount of a photocatalyst (e.g., silver halide), a reducing agent, a reducible silver salt (e.g., silver salt of an organic acid), and optionally a color tone adjustor for controlling silver tones, all of which are dispersed in a binder matrix in the layer. Photothermographic materials of that type are, after having been imagewise exposed, heated at a high temperature (for example, at 80° C. or higher) to form monochromatic silver images through oxidation-reduction reaction between the silver halide or the reducible silver salt (which serves as an oxidizing agent) and the reducing agent therein. The oxidation-reduction reaction is accelerated by the catalytic action of the latent image of the exposed silver halide. Therefore, the monochromatic silver images are formed in the exposed area of the materials. This technique is disclosed in many references such as typically U.S. Pat. No. 2,910,377 and Japanese Patent Publication (hereinafter referred to as JP-B) 4924/1968. The photothermographic systems with a silver salt of an organic acid could realize good image quality and tones enough for photo-images for medical diagnosis applications.
Silver halide grains are used for the photosensitive elements in the photothermographic materials. Silver halide grains having a grain size of 0.01 &mgr;m or larger can be produced according to a specifically controlled method for producing them in photographic gelatin. However, fine silver halide grains having a grain size of from 0.005 &mgr;m to 0.1 &mgr;m have a problem that, after a while, smaller grains often dissolve and aggregate to be large grains through physical ripening. To that effect, such fine silver halide grains are unstable.
One method for preventing silver halide grains from growing large is known, in which is used a stabilizer for stabilizing photographic performances of the grains. The stabilizer includes, for example, tetrazaines and mercaptothiazoles. However, in case where such a stabilizer is added to silver halide grains to such a degree that it can fix the size of the grains, the grains could hardly receive a spectral sensitizing dye to be adsorbed onto their surfaces. As a result, photographic materials containing the thus-stabilized silver halide grains could not ensure desired sensitivity. In the method, therefore, it is difficult to well control the size of silver halide grains without interfering with the photographic performance. If the size of silver halide grains can be controlled, some advantages can be obtained. For example, emulsions of the grains could be stored more stably, and the number of the grains produced from a predetermined amount of silver could be increased.
One problem of photothermographic materials of the type mentioned above is that they are often fogged and desensitized while stored at high temperatures in high humidity before image formation.
One technique known in the art for stabilizing photographic performances of such photothermographic materials comprises adding a mercapto-heterocyclic compound or a tetrazaine compound to the materials, as described in Japanese Patent Laid-Open (hereinafter referred to as JP-A) 225445/1995. However, even though containing such a compound, the photothermographic materials are still significantly fogged and desensitized while stored at high temperatures in high humidity before image formation, and are therefore not satisfactory.
Given that situation, it is desired to provide photothermographic materials which are fogged little and have good photographic performances and which, even stored at high temperatures in high humidity before image formation, are still fogged little and desensitized little.
SUMMARY OF THE INVENTION
The object of the present invention is to solve the problems in the related art mentioned above. Specifically, the object of the present invention is to provide a high-sensitivity photothermographic material which is fogged little and gives good images and which has improved storage stability before processed for image formation.
Having assiduously studied so as to solve the problems mentioned above, the present inventors have found that, when silver halide grains having a hexacyano-metal complex in their outermost surfaces are used in a photothermographic material and when a mercaptobenzimidazole compound is added thereto, then excellent photothermographic materials having desired advantages can be obtained. On the basis of this finding, the present inventors have completed the present invention.
According to the invention, there is provided a photothermographic material having, on one surface of its support, at least one type of photosensitive silver halide grains, a non-photosensitive silver salt of an organic acid, a reducing agent for silver ions, and a binder; which contains a compound of the following general formula (I) and in which the silver halide grains have a hexacyano-metal complex of the following general formula (II) in their outermost surfaces:
wherein R
11
, R
12
, R
13
and R
14
may be the same or different, and each independently represents a hydrogen atom, a halogen atom, a hydroxyl group, an amino group, a nitro group, a cyano group, a carboxyl group or its salt, a sulfo group or its salt, an alkyl group, an alkenyl group, an alkynyl group, an aryl group, a heterocyclic group, or a group of R
15
—D—; where R
15
represents a hydrogen atom, a halogen atom, a hydroxyl group, an amino group, a nitro group, a cyano group, a carboxyl group or its salt, a sulfo group or its salt, an alkyl group, an alkenyl group, an alkynyl group, an aryl group, or a heterocyclic group; and D represents —SO
2
—, —O—, —S—, —CO—, —COO—, —OCO—, —CONH—, —NHCO—, —NHCONH—, —SO
2
NH— or —NHSO
2
—;
[M(CN)
6
]
n−
(II)
wherein M represents Fe, Ru, Os, Co, Rh, Ir, Cr or Re; and n indicates 3 or 4.
Preferably in the photothermographic material of the invention, the silver halide grains contain, in its inside, a coordination metal complex having a metal of an element of Groups III to XIV in the Periodic Table and/or a metal ion of an element of Groups III to XIV in the Periodic Table.
More preferably, the coordination metal complex contained in the inside of silver ha
Birch & Stewart Kolasch & Birch, LLP
Chea Thorl
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