Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Antihalation or filter layer containing
Reexamination Certificate
2002-08-02
2004-12-14
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Antihalation or filter layer containing
C430S517000, C430S617000, C430S619000
Reexamination Certificate
active
06830879
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a photothermographic material, more precisely, a photothermographic material that shows little residual color in the absence of substantial decoloration and provides an image of high definition.
RELATED ART
Photothermographic materials have been proposed since old days and described in, for example, U.S. Pat. Nos. 3,152,904, 3,457,075, and B. Shely, “Thermally Processed Silver Systems” in Imaging Processes and Materials, Neblette, 8th Ed., Ed. by Sturge, V. Walworth and A. Shepp, page 2, 1969. Photothermographic materials generally have a photosensitive layer containing a catalytic amount of photocatalyst (e.g., silver halide), a reducing agent, a reducible silver salt (e.g., silver salt of an organic acid) and a toning agent for controlling silver color tone, which are typically dispersed in a binder matrix. After being exposed imagewise, photothermographic materials are heated at an elevated temperature (e.g., 80° C. or higher) and thereby an oxidation/reduction reaction is caused between the silver halide or the reducible silver salt (functioning as an oxidizing agent) and the reducing agent to form a black silver image. The oxidation/reduction reaction is promoted by the catalytic action of a latent image of silver halide produced by the exposure. Therefore, the black silver image is formed in the exposed area.
Heat development has an advantage of easy and quick processing because it does not require processing solutions as used in the wet development processing. In recent years, simple and quick development processing is desired in the field of photographic techniques, in particular, photography for medical and printing use. Since wet development processing has substantially reached the limit of improvements, image formation methods based on the heat development are noted in the technical fields of, in particular, photography for medical use and printing use.
However, the heat development suffers from various problems that never occur with the wet development.
One of the problems is the problem concerning decoloration of dye. A dye is often added to photographic light-sensitive materials as a filter or for anti-halation or anti-irradiation purpose. A dye is usually added to a non-photosensitive layer and exerts its function upon imagewise exposing. If the dye remains in the photographic light-sensitive material thereafter, the formed image may be colored with the dye. Therefore, the dye is preferably removed from the photographic light-sensitive material during development after the exposure. In the wet development process, the dye can be readily removed from the photographic light-sensitive material with processing solutions. By contrast, it is very difficult (or substantially impossible) to remove the dye in heat development. For light-sensitive materials exposed with near infrared, infrared or red laser rays, in particular, it is necessary to sufficiently prevent irradiation and halation during exposure in order to obtain an image of high definition, and therefore a dye is usually contained in light-sensitive materials to prevent such a phenomenon. However, because it is difficult to remove a dye in heat development, the coloration of image due to the remaining dye particularly causes a problem.
As one class of methods for solving such a problem, there have been proposed methods of decoloring a dye by heating during heat development. For example, U.S. Pat. No. 5,135,842 discloses a method of decoloring a polymethine dye having a particular structure by heating. U.S. Pat. Nos. 5,314,795, 5,324,627 and 5,384,237 disclose methods of decoloring polymethine dyes by using carbanion generators. As another class of methods, Japanese Patent Laid-open Publication (Kokai, henceforth referred to as JP-A) No. 9-146220, JP-A-11-223898 and so forth propose methods of solving the problem by using an invisible dye that has an absorption peak having a narrow half band width in the near infrared region and shows little absorption in the visible region, substantially without providing a decoloration mechanism.
However, there is no effective means for preventing residual color due to a dye with respect to light-sensitive materials exposed with a red laser ray except for use of a complicated decoloration mechanism, and no effective solution has been proposed yet. Therefore, use of the images must be limited, for example, the images are not used as images for appreciation as visible images as described in JP-A-13294, or the images must be changed to those that can be used as images for appreciation as visible images by delaminating the antihalation layer after exposure (even with increase of waste materials). When the coloration with a dye is prevented by utilizing a decoloration mechanism in a light-sensitive material exposed with a red laser ray, mentioned as problems are insufficient decoloration of the dye, decoloration of the dye during storage of photothermographic materials due to insufficient stability of the dye and so forth. For example, when a polymethine dye is used for the purpose of prevention of irradiation etc., the polymethine dye decomposes during heat development after light exposure and decolored to some extent. However, since the decomposition products of the polymethine dye have light-absorbing property to a certain extent, the docoloration becomes insufficient and thus residual color of images (especially in highlight portions) poses a problem. Furthermore, there is also a problem that a dye once decolored may recolor due to contact with an acid or the like. When decoloration of dye is attained by using a complicated reaction mechanism, there is also caused a problem that there should be various by-products in the light-sensitive material due to the complicated reaction mechanism and they degrade handling property of the light-sensitive material after the heat development.
SUMMARY OF THE INVENTION
The present invention was accomplished in view of the aforementioned various problems, and its object is to provide a photothermographic material suitable for light exposure with a red laser ray that can provide an image having sufficient definition without residual color after development and superior handling property.
The inventors of the present invention assiduously studied about dyes and as a result, they obtained a finding that irradiation upon exposure with a red laser ray could be sufficiently prevented by using a dye in an aggregated state showing sharp absorption (having a narrow half band width), and such a dye showed markedly little absorption for lights within the visible region and thus causes no practical problem of remaining color tint. They accomplished the present invention based on this finding.
That is, in order to achieve the aforementioned object, the present invention provides a photothermographic material having a support, at least one photosensitive layer containing a silver halide and a reducing agent and a non-photosensitive layer containing aggregates of a dye, wherein a transmission absorption spectrum of the aggregates has a maximum absorption wavelength within the range of 600-750 nm. The photothermographic material of the present invention preferably further contains a non-photosensitive silver source (more preferably, silver salt of an organic acid). Further, the photothermographic material of the present invention preferably contains the aggregates of a dye in the form of aqueous microparticles containing hydrophilic colloid in the non-photosensitive layer.
As preferred embodiments of the present invention, there are provided the aforementioned photothermographic material, wherein the maximum absorbance peak in the transmission absorption spectrum of the aggregates has a half band width of 100 nm or less; the aforementioned photothermographic material, wherein the aggregates show a maximum absorbance of 0.15 or less for a light having a wavelength of 400-600 nm before and after heat treatment; and the aforementioned photothermographic material, wherein the aggregates show an absorbance of 0.2
Suzuki Keiichi
Suzuki Ryo
Yabuki Yoshiharu
Birch & Stewart Kolasch & Birch, LLP
Fuji Photo Film Co. , Ltd.
Schilling Richard L.
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