Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2000-07-14
2004-08-31
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S598000, C430S613000, C430S617000, C430S620000
Reexamination Certificate
active
06783925
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a thermally processed image forming material, and more particularly to the material suitable for photographic printing plate making using a scanner or image setter, or for medical purposes, and still more particularly to the material for photographic printing plate making or medical purposes having an excellent coated surface property and being capable of producing images with a low fog and high Dmax (maximum density).
RELATED ART
There are a variety of known photosensitive materials having on a support a photosensitive layer and producing an image by image exposure. Of these, a technique for producing image by heat development is worth a particular mention in that allowing environmental preservation and simplifying the image producing means.
A strong need for reducing the volume of waste process solution has arisen in recent fields of photographic printing plate making or medical diagnosis from viewpoints of environmental preservation and space saving. Thus a technology related to a photothermographic material for photographic printing plate making or medical diagnosis has been desired, the material being such that affording efficient laser exposure and providing a clear black image with high resolution and sharpness. Such photothermographic material can provide the user with a more simple and environment-conscious heat development and processing system using no solution-base process chemical.
The image producing method based on heat development is disclosed, for example, in U.S. Pat. Nos. 3,152,904 and 3,457,075 and “Thermally Processed Silver Systems” written by D. Morgan and B. Shely, Imaging Processes and Materials, Neblette's 8th ed., edited by Sturge, V. Walworth and A. Shepp, Chapter 9, p.279, (1989). Such photosensitive material contains an reducible non-photosensitive silver source (e.g., organic acid silver salt), a catalytic amount of photocatalyst (e.g., silver halide) and a reducing agent for silver, all of which being generally dispersed in an organic binder matrix. While the photosensitive material is stable at the room temperature, it will produce silver through a redox reaction between the reducible silver source (which serves as an oxidizing agent) and the reducing agent when heated to a high temperature (80° C. or above, for example) after light exposure. The redox reaction is promoted by a catalytic action of the latent image produced by the light exposure. That is, the silver generated by the reaction of the reducible silver within the exposed area provides a black spot, which makes a contrast with the non-exposed area and is recognizable as an image.
The silver source employed by such system generally refers to a silver salt of a fatty acid, and a variety of methods for producing thereof have been known. Examples of the methods include such that preparing an organic acid silver salt in a concomitant solution of water and water-insoluble solvent as disclosed for example in JP-A-49-93310 (the code “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-49-94619 and JP-A-53-68702; such that preparing an organic acid silver salt in an aqueous solution as disclosed in JP-A-53-31611, JP-A-54-4117 and JP-A-54-46709; and such that preparing an organic acid silver salt in an organic solvent as disclosed in JP-A-57-186745, JP-A-47-9432 and U.S. Pat. No. 3,700,458. In principle, the organic acid silver salt is obtained by dissolving a fatty acid into water under heating to a temperature of the melting point thereof or above, adding sodium hydroxide or an alkali metal salt under vigorous stirring, and further adding silver nitrate to convert an alkali soap into a silver soap.
The alkali soap forms micell in the aqueous solution, which appears as a milky liquid. The conversion reaction from such micellar state to silver salt, however, often suffers from a problem in production stability. Thus as a measure for obtaining a homogeneous solution of alkali soap, use of a mixed solution of water and alcohol as a solvent is disclosed in JP-A-55-40607.
Now the alkali soap shows alkalinity as its name suggests, so that the silver soap is prepared under a high pH environment. Adding silver nitrate to an alkali solution, however, not only produces silver oxide as a by-product but also results in an undesirable production of silver nucleus by an action of a trace amount of contaminant which inevitably generates during the production and exhibits a high reducing activity under such high-pH environment. Such by-product is quite disadvantageous in that degrading property of the thermally processed photographic material, and more specifically in that causing undesirable fog and degrading the coated surface quality. From this viewpoint, a method for obtaining a homogeneous solution to suppress the generation of the by-product is disclosed in JP-A-55-40607, in which fog still remains unsolved.
In JP-A-9-127643, disclosed is a method for producing silver salt based on simultaneous measuring and addition of an alkali metal salt solution and silver nitrate solution, and is specified as simultaneous addition of an aqueous sodium behenate solution and isopropyl alcohol. While the method is successful in at least lowering the high pH during the reaction to the medium range and thereby in suppressing the generation amount of salver oxide, fog still cannot thoroughly be cleared and the coated surface quality still cannot be improved due to a weak reducibility of isopropyl alcohol.
As described above, preparation of fatty acid silver salt needs special accounts such that eliminating as possible reducible substances during the formation of fatty acid silver salt, controlling the grain size and controlling the grain form, where all these requirements cannot be satisfied at a time by the conventional method.
In the conventional production of a thermally processed material using the fatty acid silver salt, a photosensitive layer thereof is often formed by coating a coating liquid containing an organic solvent such as toluene, methyl ethyl ketone or methanol. Using an organic solvent as the solvent, however, is not only disadvantageous in terms of safety in the production processes, adverse effects on human body, and high cost ascribable to the solvent recovery or the like, but is also inappropriate in terms of providing an environment-conscious photothermographic material.
Thus a method for forming, using a water-base coating liquid, the photosensitive layer (also referred as “water-base photosensitive layer”hereinafter) is proposed. For example, JP-A-49-52626 and JP-A-53-116144 disclose cases using gelatin as a binder. In JP-A-50-151138, a case using polyvinyl alcohol as a binder is described.
A case with a combined use of gelatin and polyvinyl alcohol is found in JP-A-60-61747. As another exemplary case, the photosensitive layer using a water-soluble polyvinyl acetal as a binder is described in JP-A-58-28737.
Using a water-soluble binder allows the photosensitive layer to be formed with a water-base coating liquid and is beneficial from environmental and economic viewpoints. The water-soluble polymer binder is, however, less compatible with the fatty acid silver salts, and may interact with the photographic additives other than the organic silver salt, which are usually dissolved or dispersed also in a water-base solvent, to produce an undesirable agglomeration and thereby to make it difficult to obtain a good surface quality.
In order to obtain practically agreeable quality of the coated surface using the water-base coating liquid containing a fatty acid silver salt, the fatty acid silver salt must be kept in a finely dispersed state in the water-base solution without causing agglomeration. Discovery of a method for finely dispersing the fatty acid silver salt is thus desired. One method generally accepted relates to such that producing a hydrophobic grain dispersion of a fatty acid silver salt, separating the grain therefrom by filtration to obtain a solid matter, and re-dispersing the solid matter after be
Chea Thorl
Fuji Photo Film Co., LTD
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