Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2001-06-29
2004-05-18
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S631000
Reexamination Certificate
active
06737231
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods for efficiently preparing grains of silver salt of an organic acid by reacting a solution containing silver ions and a solution containing an alkali metal salt of an organic acid. The present invention also relates to apparatuses for preparing grains of silver salt of an organic acid that require low facility cost and show high productivity. The present invention further relates to a method for producing a thermally processed image recording material that utilizes the methods for preparing grains of silver salt of an organic acid.
BACKGROUND OF THE INVENTION
In recent years, reduction of amount of waste processing solutions is strongly desired in the field of medical diagnosis from the standpoints of environmental protection and space savings. Therefore, techniques relating to photothermographic materials for use in photographic-art processes and medical diagnosis are required which enables efficient exposure by a laser image setter or laser imager and formation of a clear black image having high resolution and sharpness. Such photothermographic material scan provide users with a simple and non-polluting heat development processing system that eliminates the use of solution-type processing chemicals.
The same is demanded in the field of ordinary image-forming materials. However, photo-images for medical use, in particular, require high image 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.
Meanwhile, methods for forming an image by heat development are described in, for example, U.S. Pat. Nos. 3,152,904 and 3,457,075 and D. Klosterboer, “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). Among these, the photothermographic material generally contains a photocatalyst (e.g., silver halide) in a catalytically active amount, a reducing agent, a reducible silver salt (e.g., organic acid silver salt), and optionally a toning agent for controlling silver color tone, which are usually dispersed in an organic binder matrix. In this photothermographic material when the material is heated at a high temperature (e.g., 80° C. or higher) after light exposure, black silver images are produced through an oxidation-reduction reaction between the silver halide or 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 the silver halide generated upon exposure. Therefore, the monochromatic silver images are formed in exposed areas of the materials (U.S. Pat. No. 2,910,377, Japanese Patent Publication (Kokoku, hereinafter referred to as JP-B) 43-4924 etc.). These thermal image-forming systems utilizing silver salts of organic acids can achieve image quality and color tone required for images for medical use.
The silver source used in these systems is generally a silver salt of an organic acid, and various methods for producing it have been known. For example, there can be mentioned the method of preparing a silver salt of an organic acid under coexistence of water and a hardly water-soluble solvent as disclosed in Japanese Patent Laid-open Publication (Kokai, hereinafter referred to as JP-A) 49-93310, JP-A-49-94619 and JP-A-53-68702, the method of preparing a silver salt of an organic acid in an aqueous solution as disclosed in JP-A-53-31611, JP-A-54-4117 and JP-A-54-46709, the method of preparing a silver salt of an organic acid in an organic solvent as disclosed in JP-A-57-186745, JP-A-47-9432 and U.S. Pat. No. 3,700,458 and so forth. Basically, the preparation is carried out by heating an organic acid to a temperature higher than its melting point to melt it in water, adding sodium hydroxide or an alkali metal salt with vigorous stirring, and then adding a solution containing silver ions in order to convert the alkali soap into silver soap.
Such alkali soap forms micelles in an aqueous solution, and gives a solution of whitely turbid appearance. The reaction from such a micelle state to the silver soap often suffers from problems concerning production stability. Therefore, as a method for obtaining the alkali soap as a uniform solution, a method of using a mixed solution of water and alcohol as the solvent is disclosed in JP-A-55-40607.
Further, since alkali soap presents alkalinity, the silver soap will be prepared under a high pH condition in the above case. However, addition of a solution containing silver ions into an alkaline solution produces silver oxide as a by-product. Further, it also generates unintended silver nuclei produced by a trace amount of reducing contaminants, which are unavoidable in view of production process and exhibit high reducing property due to the high pH. Such by-products are extremely disadvantageous from the viewpoint that they degrade performance of photothermographic materials, in particular, they cause undesired fog. In this respect, the aforementioned problems are not solved even in the method disclosed in JP-A-55-40607, which aims at obtaining a uniform solution in order to suppress the generation of the by-products.
Further, JP-A-9-127643 discloses a method for producing a silver salt by simultaneous addition of measured amounts of an alkali metal salt solution and a silver nitrate solution, and refers to simultaneous addition of a solution of sodium behenate in a mixture of water and isopropyl alcohol and a solution of silver nitrate. This method can at least shift the pH of the reaction from the high pH region to a neutral region, and thus it is a preferred method for reducing the generation amount of silver oxide. However, isopropyl alcohol shows weak reducing property, and this makes the method insufficient as a method for completely solving the problem of fog.
Further, JP-A-9-127643 discloses a method for producing a silver salt by simultaneous addition of measured amounts of an alkali metal salt solution and a silver nitrate solution, and refers to simultaneous addition of a solution of sodium behenate in a mixture of water and isopropyl alcohol and a solution of silver nitrate. This method can at least shift the pH of the reaction from the high pH region to a neutral region, and thus it is a preferred method for reducing the generation amount of silver oxide. However, isopropyl alcohol shows weak reducing property, and this makes the method insufficient as a method for completely solving the problem of fog.
Moreover, the silver behenate grains formed by this method are two-dimensionally and anisotropically grown acicular grains having a size of 0.04 &mgr;m to 0.05 &mgr;m, and no description is found concerning control of the grain size or grain morphology.
JP-A-11-349325 disclose a method for forming scaly grains, which show morphology different from that of the conventional acicular grains, by using a low temperature in a reaction field for the simultaneous addition of measured amounts of alkali metal salt solution and solution containing silver ions. In this method, scaly grains can be obtained in a low temperature region, and acicular grains can be obtained in a high temperature region by controlling the temperature of the reaction field. However, this method still cannot provide such high degree of freedom that the grain morphology and grain size can be independently controlled.
In order to obtain a uniform dispersion practically usable as a coating solution containing a silver salt of an organic acid, it is necessary to obtain a state that the silver salt of an organic acid is finely dispersed in a solvent without aggregation. For this reason, it is necessary to develop a method for dispersing the silver s
Ando Takashi
Kawanishi Naoyuki
Nagai Yoichi
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