Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2001-04-18
2003-07-15
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S523000, C430S567000, C430S604000, C430S620000, C430S630000, C430S935000
Reexamination Certificate
active
06593076
ABSTRACT:
FIELD OF THE INVENTION
The present invention related to photothermographic material, and an image recording method and image forming method by the use thereof.
BACKGROUND OF THE INVENTION
In the field of graphic arts and medical treatment, there have concerns in processing of photographic films 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 environmental protection and space saving. There has been desire a photothermographic material for photographic use, capable of forming distinct black images exhibiting high sharpness, enabling efficient exposure by means of a laser imager or a laser image setter.
Known as such a technique is a thermally developable photothermographic material which comprises on a support an organic silver salt, light sensitive silver halide grains, reducing agent and a binder, as described in U.S. Pat. Nos. 3,152,904 and 3,487,075, and D. H. Klosterboer “Thermally Processed Silver Systems” (Imaging Processes and Materials) Neblette, 8th Edition, edited by Sturge, V. Walworth, and A. Shepp, page 279, 1989), etc.
Such a photothermographic material is characterized in that light sensitive silver halide grains and an organic silver salt are incorporated in a light sensitive layer as a photosensor and a silver ion source, respectively, which are thermally developed by an included reducing agent at a temperature of 8− to 140° C. to form images, without being fixed. To achieve smoothly supplied silver ions to silver halide and prevent lowered transparency caused by light scattering, there have been made attempts to improve the shape of organic silver salt grains capable of being optimally arranged in the light sensitive layer and having little adverse effect on light scattering.
However, problems arose with attempts to form fine particles simply by dispersion or pulverization at high energy using a dispersing machine, due to the fact that silver halide grains or organic silver salt grains were damaged, resulting in not only increased fogging and reduced sensitivity but also deteriorated image quality. Accordingly, there have been desired techniques of achieving enhanced photosensitivity, higher density and reduced fogging without an increase of a silver coverage.
Further, problems arose with pre-exposure storage of photothermographic materials such that variation in sensitivity, fog density or contrast occurred and problems also arose with post-process storage that the fogging or image color tone was varied. There have been made various attempts but they are still insufficient, therefore, further enhanced improvement is desired.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a photothermographic material exhibiting enhanced sensitivity and reduced fogging, causing no deterioration in image quality due to a white spots or coagula and also improved in raw stock stability (i.e., pre-exposure stock keeping) and silver image lasting quality; and an image recording method and image forming method by the use of the same.
The above object of the invention can be accomplished by the following constitution:
1. A photothermographic material comprising an organic silver salt and a light sensitive silver halide, wherein the photothermographic material contains a hydrophilic binder of 0.5 to 2 g per mol of the organic silver salt and the organic silver salt being formed in the presence of the silver halide of 7×10
15
to 3×10
17
grains per mol of the organic silver salt;
2. A method of preparing a photothermographic material comprising the steps of:
(a) preparing a light sensitive layer composition and
(b) coating the light sensitive layer composition to form a light sensitive layer,
wherein the photothermographic material comprises an organic silver salt, a light sensitive silver halide and a hydrophilic binder, step (a) comprising forming the organic silver salt in the presence of the silver halide of 7×10
15
to 3×10
17
grains per mol of the organic silver salt and the photothermographic material containing the hydrophilic binder of 0.5 to 2 g per mol of the organic silver salt.
DETAILED DESCRIPTION OF THE INVENTION
In this invention, the photothermographic material containing an organic silver salt, a light sensitive silver halide, a reducing agent, binder and a cross-linking agent, in which the photothermographic material contains a hydrophilic binder of 0.5 to 2.0 g per mol of the organic silver salt, and during the stage of formation of the organic silver salt, 7×10
15
to 3×10
17
grains of the light sensitive silver halide per mol of the organic silver salt are mixed to form the organic silver salt, thereby leading to a photothermographic material exhibiting enhanced sensitivity and reduced fogging, causing no deterioration in image quality due to a white spots or coagula and also improved in raw stock stability (i.e., pre-exposure stock keeping) and silver image lasting quality. In this invention, the light sensitive silver halide is preferably contained in amount of 0.8 to 2.0 g/m
2
, based on silver.
It is contemplated that such effects of this invention are attributed to that adjustment of a hydrophilic binder surrounding the light sensitive silver halide grains to a specified quantity leads to efficient dispersion, thereby preventing coagulation of silver halide grains and efficient supply of silver ions from the organic silver salt at the stage of thermal development.
Silver halide used in the invention functions as light sensor. Silver halide grains are preferably small in size to prevent milky-whitening after image formation and obtain superior images. The grain size is preferably not more than 0.1 &mgr;m, more preferably, 0.01 to 0.1 &mgr;m, still more preferably, 0.03 to 0.07 &mgr;m, and most preferably 0.04 to 0.07 &mgr;m. The form of silver halide grains is not specifically limited, including cubic or octahedral, regular crystals and non-regular crystal grains in a spherical, bar-like or tabular form. Halide composition thereof is not specifically limited, including any one of silver chloride, silver chlorobromide, silver iodochlorobromide, silver bromide, silver iodobromide, and silver iodide.
In this invention, silver halide grains are used in an amount of 7×10
15
to 3×10
17
grains per mol of organic silver salt. The silver halide grains less than this range by number results in insufficient densities and the number exceeding this range leads to deteriorated image quality.
In this regard, the number of silver halide grains can be determined based on the density, specific gravity and size of the silver halide grains. The grain size can be determined by an electron microscope.
Silver halide used in this invention preferably occludes ions of metals belonging to Groups 6 to 11 of the Periodic Table. Preferred as the metals are W; Fe, Co, Ni, Cu, Ru, Rh, Pd, Re, Os, Ir, Pt and Au. Of these preferred are Fe, Co, Ru, Rh, Re, Os, and Ir. These metals may be introduced into silver halide in the form of a complex. In the present invention, regarding the transition metal complexes, six-coordinate complexes represented by the general formula described below are preferred:
Formula: (ML
6
)
m
:
wherein M represents a transition metal selected from elements in Groups 6 to 11 of the Periodic Table; L represents a coordinating ligand; and m represents 0, 1-, 2-, 3-or 4-. Exemplary examples of the ligand represented by L include halides (fluoride, chloride, bromide, and iodide), cyanide, cyanato, thiocyanato, selenocyanato, tellurocyanato, azido and aquo, nitrosyl, thionitrosyl, etc., of which aquo, nitrosyl and thionitrosyl are preferred. When the aquo ligand is present, one or two ligands are preferably coordinated. L may be the same or different. Particularly preferred examples of M include rhodium (Rh), ruthenium (Ru), rhenium (Re), iridium (Ir) and osmium (Os).
Exemplary examples of transition metal ion complexes are shown below.
1: [RhCl
6
]
3−
Goan Kazuyoshi
Maeda Keiko
Shima Tetsuo
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