Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2000-02-28
2001-10-02
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S581000, C430S583000, C430S584000, C430S587000, C430S600000, C430S607000, C430S611000, C430S610000, C430S614000, C430S615000, C430S944000
Reexamination Certificate
active
06297001
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to photothermographic materials with superior storage stability and in particular to black-and-white thermally developable silver salt photothermographic materials with superior storage stability of silver images.
BACKGROUND OF THE INVENTION
In the field of medical treatment and graphic arts, there have been problems in working property with respect to effluents produced from wet-processing of image forming materials, and recently, reduction of the processing effluent is strongly demanded in terms of environment protection and space saving.
Accordingly, there are needed techniques regarding photothermographic materials for photographic use and which are capable of forming black images exhibiting high sharpness, enabling efficient exposure by means of a laser imager or laser image setter. As such a technique is known a thermally developable photosensitive material, which comprises a support having thereon an organic silver salt, light-sensitive silver halide grains and a reducing agent, as described in U.S. Pat. Nos. 3,152,904 and 3,487,075; and D. Morgan “Dry Silver Photographic Material” (Handbook of Imaging Materials, Marcel Dekker, Inc., page 48, 1991). No processing solution is used in this thermally developable photosensitive material (hereinafter, also referred to as a photothermographic material), enabling a simple system friendly to the environment and operators.
Since this thermally developable photothermographic material contains an organic silver salt, light-sensitive silver halide grains and a reducing agent, there are problems such that the photothermographic material not only tends to cause fogging before or during thermal development but also easily produces fog or photolytic silver (or print-out silver). Specifically, this photothermographic material, after exposure, is subjected only to thermal development at a temperature of 80 to 250° C., without being further subjected to fixing so that there was such problems that silver images causes discoloring upon exposure to light or heat during storage under the concurrent presence of the silver halide, organic silver salt and reducing agent which remained in unexposed areas.
A technique for solving these problems is disclosed in JP-A 6-208192 and 8-267934 (herein, the term, JP-A means a unexamined and published Japanese Patent Application) and references cited therein. Although these disclosed techniques were effective to some extent, they were not sufficiently so as a technique to satisfy levels required by the market.
SUMMARY OF THE INVENTION
In view of the foregoing problems, an object of the present invention is to provide a thermally developable photothermographic material which produces little fog when allowed to stand for a long period of time and producing silver images superior in storage stability, and an image forming method by use thereof.
The object of the invention can be accomplished by the following constitution:
1. A photothermographic material comprising a non-photosensitive organic silver salt, a photosensitive silver halide, a reducing agent, a binder and a cross-linking agent; the photothermographic material further comprising a compound capable of generating a labile species other than a halogen atom upon exposure to ultraviolet radiation or visible radiation to deactivate the reducing agent;
2. An image forming method comprising exposure of the photothermographic material described above to laser light by using a laser exposure apparatus, wherein scanning laser light is not exposed at an angle substantially vertical to the exposed surface of the photosensitive material;
3. An image recording method comprising exposure of the photothermographic material described above to laser by using a laser exposure apparatus, wherein scanning laser light is longitudinally multiple; and
4. An image recording method, wherein the photothermographic material described described above is thermally developed in a state containing an organic solvent of 5 to 1,000 mg/m
2
.
DETAILED DESCRIPTION OF THE INVENTION
The photothermographic material comprises a) a non-photosensitive organic silver salt, b) a photosensitive silver halide, c) a reducing agent capable of reducing a silver ion of the organic silver salt when activated upon heating, d) a binder and e) a cross-linking agent for the binder. Concurrent presence of silver halide as a photoreceptor, the organic silver salt as a silver source and the reducing agent deteriorates pre-exposure storage stability of the photothermographic material. No fixation subsequent to development produces disadvantages in stability after being developed, such as occurrence of marked print-out when exposed to light. Such disadvantages are contemplated to be due to the fact that the presence of a reducing agent in the photosensitive material easily causes thermal fogging upon reaction with an organic silver salt and the reducing agent functions not only as reduction of a silver ion but also as a hole trap when exposed, after development, to light in the wavelength region different from that of the image recording light, promoting print-out of silver halide and the organic silver salt.
It was discovered that problems such as described above could be solved by incorporating a compound capable of generating a labile species, which deactivated the reducing agent on exposure to ultraviolet or visible radiation after thermal development to inhibit reduction of the silver halide and the organic silver salt. As a reducing agent used in photothermographic materials are employed reducing agents containing a proton, such as bisphenols and sulfonamidophenols. Accordingly, a compound generating a labile species which is capable of abstracting a proton to deactivate the reducing agent is preferred. More preferred is a compound as a non-colored photooxidizing substance, which is capable of generating a free radical as a labile species on exposure. Any compound having such a function is applicable. However, a halogen radical, which easily forms silver halide is not preferred. An organic free radical composed of plural atoms is preferred. Any compound having such a function and exhibiting no adverse effect on the photothermographic material is usable irrespective of its structure.
Of such free radical generation compounds, a compound containing an aromatic, and carbocyclic or heterocyclic group is preferred, which provides stability to the generated free radical so as to be in contact with the reducing agent for a period sufficient to react with the reducing agent to deactivate it. Representative examples of such compounds include biimidazolyl compounds and iodonium compounds. The imidazolyl compounds generate two imidazolyl radicals as a free radical upon exposure to ultraviolet or visible radiation, which are capable of oxidizing a reducing agent remaining after development, thereby inhibiting reduction of silver salts. It is surprising that the imidazolyl compound is photo-active and capable of oxidizing a reducing agent effective in heat-promoted reduction of a substantially non-photosensitive organic silver salt.
Of such imidazolyl compounds, a compound represented by the following formula [1] is preferred:
wherein R
1
, R
2
and R
3
(,which may be the same or different) each are an alkyl group (e.g., methyl, ethyl, hexyl), an alkenyl group (e.g., vinyl, allyl), an alkoxyl group (e.g., methoxy, ethoxy, octyloxy), an aryl group (e.g., phenyl, naphthyl, tolyl), hydroxy, a hydrogen atom, a halogen atom, an aryloxyl (e.g., phenoxy), an alkylthio group (e.g., methylthio, butylthio), an arylthio group (e.g., phenylthio), a heterocyclic group (e.g., pyridyl, triazyl), an acyl group (e.g., acetyl, propionyl, butylyl, valeryl), a sulfonyl group (e.g., methylsulfonyl, phenylsulfonyl), an acylamino group, sulfonylamino group, an acyloxy group (e.g., acetoxy, benzoxy), carboxy, cyano, a sulfo group, or an amino group. Of these groups are preferred an aryl group, a heterocyclic group, an alkenyl group and cyano group.
The biimidazolyl compound
Hirai Katsura
Takiguchi Hideki
Bierman Jordan B.
Bierman, Muserlian and Lucas
Chea Thorl
Konica Corporation
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