Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2001-09-19
2004-05-04
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C264S531000, C264S607000, C264S631000
Reexamination Certificate
active
06730470
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a photothermographic material, in particular, a novel photothermographic material showing high sensitivity, high developing speed and little performance fluctuation due to variation of heat development temperature.
RELATED ART
A large number of photosensitive materials are known which have a photosensitive layer on a support and form images by exposing imagewise. As an example of a system that contributes to environmental protection or enables simplification of image formation means, there is a technique of forming an image by heat development.
Methods for forming images by heat development are described in, for example, U.S. Pat. Nos. 3,152,904, 3,457,075 and D. Klosterboer, Imaging Processes and Materials, “Thermally Processed Silver Systems” A, 8th ed., Chapter 9, page 279, compiled by J. Sturge, V. Walworth and A. Shepp, Neblette (1989). Such a photothermographic material contains a reducible non-photosensitive silver source (e.g., silver salt of an organic acid), 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. The photosensitive 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 shows black color and this presents a contrast to the non-exposed region to form an image.
Density of images to be formed is controlled by heat development temperature and time. However, since the image density is influenced by heating methods and means, development characteristics of photothermographic material and so forth, uniform images of a certain level are not always obtained. For this reason, it has been one of major problems of photothermographic materials that uneven density is more likely to be caused compared with the case where a material is immersed into a development solution at a constant temperature like in the wet type development. To solve this problem, it is effective to use a sufficient development temperature and take sufficient time until the image formation is saturated. However, when a sufficient development temperature and sufficient time are used, there is caused problems of degradation of quality such as increase of fog and change of silver color tone and reduction of productivity such as decrease of developing speed.
There has been proposed use of a highly active reducing agent as a development enhancer in order to increase the speed of the heat development treatment. For example, Japanese Patent Laid-open Publication (Kokai, hereinafter referred to as JP-A) 10-221806 discloses use of hindered phenol compounds and bisphenol compounds as a reducing agent and use of sulfonamidophenol compounds as a development enhancer. The development enhancer used in this case is a reducing agent showing higher activity than the main reducing agent, and it can accelerate advance of development in an early stage of development. However, since use of such a development enhancer in a larger amount relative to the main reducing agent causes problems such as fog, it can actually be used only in a limited amount. Therefore, its effect is also limited.
Meanwhile, JP-A-58-198038 and JP-A-58-229556 disclose photothermographic materials using a heat-fusible solvent with the aid of a hydrophilic binder such as gelatin as a binder. As the heat-fusible solvent, these patent documents disclose urea derivatives, amide derivatives, polyethylene glycols and polyhydric alcohols.
However, these photothermographic materials suffer from bad storability before light exposure. Therefore, sensitivity is decreased and fog is increased during storage. Furthermore, they also suffer from a problem of significant fluctuation of developing speed due to change of humidity in an environment for heat development. For example, under high humidity, the developing speed becomes high, whereas it will be lowered under low humidity.
SUMMARY OF THE INVENTION
In view of the aforementioned problems of the prior art, an object of the present invention is to provide a photothermographic material showing high sensitivity, high developing speed and little performance fluctuation due to variation of heat development temperature.
The inventors of the present invention assiduously studied in order to achieve the aforementioned object. As a result, they found that a photothermographic material providing the desired effects can be obtained by adding a heat-fusible solvent that is solid at an ordinary temperature and can be fused at a heat development temperature to a photothermographic material comprising at least (a) a photosensitive silver halide, (b) a silver salt of an organic acid, (c) a reducing agent and (d) a hydrophobic and thermoplastic organic binder on a support, and thus accomplished the present invention.
The photothermographic material of the present invention preferably further contains a halogen-releasing precursor and/or an ultrahigh contrast agent. Further, the photothermographic material of the present invention is preferably produced through a step of coating and drying a coating solution containing latex dispersed in water as the organic binder. Furthermore, the photothermographic material of the present invention is preferably produced through a step of coating and drying a coating solution containing microparticles of the reducing agent solid-dispersed in water and/or microparticles of the halogen-releasing precursor solid-dispersed in water.
The photothermographic material according to the present invention is characterized by high sensitivity, high developing speed and little performance fluctuation due to variation of heat development temperature.
PREFERRED EMBODIMENTS OF THE INVENTION
The photothermographic material of the present invention will be explained in detail hereinafter.
The photothermographic material of the present invention comprises at least (a) a photosensitive silver halide, (b) a silver salt of an organic acid, (c) a reducing agent and (d) a hydrophobic and thermoplastic organic binder on a support, and it is characterized by further containing a heat-fusible solvent that is solid at an ordinary temperature and can be fused at a heat development temperature.
Therefore, the heat-fusible solvent used for the photothermographic material of the present invention will be explained first.
The heat-fusible solvent used for the photothermographic material of the present invention is an organic material that is solid at an ordinary temperature but melts or shows a mixed melting point together with other components at a heat development temperature to be used or a temperature lower than that and is liquefied upon heat development to accelerate the heat development. The scope of the heat-fusible solvent includes compounds that can be a solvent for a developing agent, compounds having a high dielectric constant and known to promote physical development of silver salt and so forth.
Preferred examples of the heat-fusible solvent include urea derivatives, amide derivatives, sulfonamide derivatives, polyhydric alcohols and polyethylene glycols.
Specifically, the urea derivatives include urea, dimethylurea, phenylurea, diethyleneurea, diisopropylurea, dimethoxyethylurea, tetramethylurea, tetraethylurea and so forth. The amide derivatives include acetamide, stearylamide, p-toluamide, p-propanoyloxyethoxybenzamide, propionamide, butanamide, benzamide, diacetamide, acetanilide, ethylacetamide acetate, 2-chloropropionamide, phthalimide, succinimide, N,N-dimethylacetamide and so forth. The sulfonamide derivatives include phenylsulfonamide, p-toluenesulfonamide, p-chlorophenylsulfonamide, o-aminophenylsulfona
Birch & Stewart Kolasch & Birch, LLP
Chea Thorl
Fuji Photo Film Co. , Ltd.
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