Photothermographic material

Details Photothermographic material Photothermographic material

2000-09-15

2002-07-02

Chea, Thorl (Department: 1752)

Radiation imagery chemistry: process, composition, or product th

Radiation sensitive product

Silver compound sensitizer containing

C430S531000

Reexamination Certificate

active

06413712

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a photothermographic material.
RELATED ARTS
A strong need for reducing the volume of waste process solution has arisen in recent particular diagnosis field from viewpoints of environmental preservation and space saving. Thus a technology related to a thermally processed image forming material for particular diagnosis and photographic purposes has been desired, the material being such that allowing efficient light exposure with a laser image setter or laser imager, and providing a black image with a high resolution and sharpness. Such thermally processed image forming material can provide the user with a more simple and environment-conscious image producing system using no solution-base process chemical.
While a similar need has been occurring in the field of general image forming materials, images used in the particular diagnosis field specifically require a high image quality such as excellent sharpness and graininess for fine depiction, and prefer a blue-black tone for facilitating diagnoses. Although various hard copy system using pigment or dye, exemplified as an inkjet printer and electronic photograph system, are prevailing as a general image forming system, none of which is satisfactory as an output system for particular images.
Other type of thermally processed image forming material using an organic silver salt is known, for example, in U.S. Pat. Nos. 3,152,904 and 3,457,075 and“Thermally Processed Silver Systems” by D. Klosterboer, Imaging Processes and Materials, Neblette's 8th ed., edited by J. Sturge, V. Walworth and A. Shepp, chapter 9, p.279, (1989). In particular, the photothermographic material generally has a photosensitive layer comprising a catalytic amount of a photocatalyst (e.g., silver halide), a heat developing agent, a reducible silver salt (e.g., organic silver salt), and an optional toning agent for controlling tone of silver image, all of which being dispersed in a binder matrix. The photothermographic material produces a blackened silver image when heated, after light exposure, to a high temperature (e.g., 80° C. or above) through redox reaction of the silver halide or reducible silver salt with the reducing agent. Since the redox reaction is promoted by a catalytic action of silver halide composing a latent image, which is produced by the light exposure, that the blackened silver image is formed in the exposed area. Such heat-assisted image producing system is disclosed in numbers of literatures typified by U.S. Pat. No. 2,910,377 and JP-B-43-4924 (the code “JP-B-” as used in this specification means an“examined Japanese patent publication”), and recently Fuji Particular Dry Imager FM-DPL was launched as a particular image producing system using such photothermographic material.
In the photothermographic material, o-bisphenol-base reducing agents as expressed by the formula (I) are effectively used by virtue of their high activity. These compounds are disclosed, for example, in European Pat. No. 803,764, JP-A-51-51933 (the code“JP-A-” as used in this specification means an“unexamined published Japanese patent application”), and JP-A-6-3793. A problem, however, resides in that such photothermographic material is likely to tint in the white background region during a long term storage after the processing, since such photosensitive material is not subjected to fixation treatment after the processing and thus heat-sensitive organic acid silver salt and the reducing agent will remain intact within the photosensitive material. While decreasing the amount of use of the o-bisphenol-base reducing agent will be necessary to solve such problem of the tint in the white background, this may contradict the primary goal of the present invention to achieve a sufficient image density, so that it has been difficult to obtain a sufficient image density while suppressing the tint.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to solve the foregoing problem in the prior art. That is, an object of the present invention is to provide a photothermographic material affording a sufficient image density under general image producing conditions and capable of suppressing the time-dependent tint of the white background after the development processing.
The present inventors found out, after extensive studies, that a preferable photothermographic exhibiting desired function can be fabricated by using, as a reducing agent, specific compounds in combination, which led us to propose the present invention.
That is, the present invention provides
(1) a photothermographic material containing in elsewhere on one side of a support at least one species of photosensitive silver halide, a non-photosensitive organic silver salt, a reducing agent for reducing silver ion and a binder, in which the reducing agent comprises a combination of at least one species of o-polyphenol compound and at least one species of hindered phenol; and
(2) a photothermographic material containing in elsewhere on one side of a support at least one species of photosensitive silver halide, a non-photosensitive organic silver salt, a reducing agent for reducing silver ion and a binder, in which the reducing agent comprises a combination of at least one species of compound expressed by the formula (I) below and at least one species of compound expressed by the formula (II) below:
(where in the formula (I), R
1
to R
4
independently represent a hydrogen atom or a group substitutable on a benzene ring; L represents an -S- group or a —CHR
5
— group; said R
5
representing a hydrogen atom or an alkyl group); and
(where in the formula (II), R
1
represents an alkyl group whereas excluding 2-hydroxyphenylmethyl group; R
2
represents a hydrogen atom or an acylamino group; R
3
represents a hydrogen atom or an alkyl group; and R
4
represents a group substitutable on a benzene ring).
According to the present invention, concomitant improvement both in the development density and image storability can be achieved by using o-polyphenol-base reducing agents [compounds expressed by the formula (I)] and the hindered phenol-base reducing agents [compounds expressed by the formula (II)] in combination. It is thus possible according to the present invention to provide a photothermographic material affording a sufficient image density under general image producing conditions while suppressing the time-dependent tint of the white background after the development processing.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be detailed hereinafter.
The photothermographic material of the present invention contains in elsewhere on one side of a support at least one species of photosensitive silver halide, a non-photosensitive organic silver salt, a reducing agent for reducing silver ion and a binder. Such photothermographic material according to the first aspect of the present invention is characterized in that containing as the reducing agent at least one species of o-polyphenol compound and at least one species of hindered phenol used in combination.
As has previously been described in the specification, the o-polyphenol compound expressed by the formula (I) is a known reducing agent for use in the photothermographic-material. The hindered phenol compound expressed by the formula (II) is also disclosed in European Pat. No. 803,764, JP-A-50-22135, JP-A-50-36110, JP-A-52-84727, and JP-A-6-3793. The hindered phenol-base reducing agent was, however, low in heat-developing activity while causing less tint in the white background, so that it was difficult to obtain an image with a sufficient density at a practical reaction temperature and within a practical reaction time. The present inventors found after extensive studies that using these compounds, independently known as a reducing agent, in combination resulted in amazing effects in that the image density was dramatically increased beyond expectation as compared with that obtainable in the case of independent use of such compounds, and in that the storability

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