Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2000-12-07
2003-03-18
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C554S074000
Reexamination Certificate
active
06534258
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for producing grains of aliphatic acid silver salt and a thermally processed image recording material which utilizes grains of aliphatic acid silver salt produced by the production method. The thermally processed image recording material of the present invention is characterized in that, in particular, it causes low fog and provides good images for diagnosis.
BACKGROUND OF THE INVENTION
A large number of photosensitive materials are known which have a photosensitive layer on a support and form image by imaging exposure. Examples of a system that enables environmental conservation or simplification of image formation includes a technique of forming an image by heat development.
In recent years, reduction of amount of waste processing solutions is strongly desired in the photographic art field and the medical diagnosis field from the standpoints of environmental protection and space savings. Therefore, techniques relating to thermally processed image recording materials (photothermographic materials) for use in photographic-art processes and medical diagnosis are required which enables efficient exposure by a laser beam and formation of a clear black image having high resolution and sharpness. The thermally processed image recording materials can provide users with a simple and non-polluting heat development processing system that eliminates the use of solution-type processing chemicals.
Methods for forming an image by heat development are described, for example, in U.S. Pat. Nos. 3,152,904 and 3,457,075 and 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). The thermally processed image recording material contains a reducible light-insensitive silver source (e.g., organic silver salt), a photocatalyst (e.g., silver halide) in a catalytically active amount, and a reducing agent for silver, which are usually dispersed in an organic binder matrix. This thermally processed image recording material is stable at an ambient temperature, but when the material is heated at a high temperature (e.g., 80. C. or higher) after light exposure, silver is produced through an oxidation-reduction reaction between the reducible silver source (which functions as an oxidizing agent) and the reducing agent. The oxidation-reduction reaction is accelerated by catalytic action of a latent image generated upon exposure. The silver produced by the reaction of the reducible silver salt in the exposed region provides a black image and this presents a contrast to the non-exposure region to form an image.
The silver source used in these systems is generally an aliphatic acid silver salt, and various methods for producing it are 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 aliphatic acid to a temperature higher than its melting point to dissolve it in water, adding sodium hydroxide or an alkali metal salt with vigorous stirring, and then adding silver nitrate 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 alkali soap in 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 silver nitrate into an alkaline solution not only produces silver oxide as a byproduct, but 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 a byproduct is extremely disadvantageous from the viewpoint that it degrades performance of photothermographic materials, in particular, it causes undesired fog and degrades coated surfaces. 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 byproduct.
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.
Furthermore, upon preparation of non-photosensitive organic acid silver salt, viscosity of reaction mixture becomes extremely high, and therefore it is very difficult to dilute a liquid added during the preparation.
SUMMARY OF THE INVENTION
In view of the problems of the prior art, an object of the present invention is to provide a method for producing grains of aliphatic acid silver salt, which show excellent fog prevention ability, in addition, excellent fog prevention ability even after time lapse, and a thermally processed image recording material which utilizes grains of aliphatic acid silver salt produced by such a method.
The inventors of the present invention assiduously studied in order to achieve the aforementioned object. As a result, they found that an excellent effect to be sought was obtained by the following method. Thus, the present invention has been accomplished.
That is, the present invention provides a method for producing grains of aliphatic acid silver salt by mixing a solution containing silver ions and a solution of aliphatic acid alkali metal salt to attain reaction of them, wherein (1) 95-100% of the total molar number to be added of the aliphatic acid alkali metal salt is added under a condition that dilution factor of the solution of aliphatic acid alkali metal salt becomes 10-fold or higher at 1 second after the addition, (2) 95-100% of the total amount to be added of silver in the solution containing silver ions is added under a condition that dilution factor of the solution containing silver ions becomes 20-fold or higher at 1 second after the addition, and (3) 50-100% of the total amount to be added of the solution of aliphatic acid alkali metal salt is added simultaneously with the solution containing silver ions.
In the production method of the present invention, it is preferred that the solution containing silver ions and the solution of aliphatic acid alkali metal salt are added to a closed mixing means to attain the reaction. Further, it is also preferred that the dilution factor of the solution of aliphatic acid alkali metal salt is 15-fold or higher, and the dilution factor of the solution containing silver ions is 50-fold or higher.
The present invention also provides a thermally processed image recording material comprising a reducing agent, binder, and grains of aliphatic acid silver salt on a support, wherein the grains of aliphatic acid silver salt are produced by the aforement
Kawanishi Naoyuki
Oyamada Takayoshi
Chea Thorl
Fuji Photo Film Co. , Ltd.
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