Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2001-12-26
2003-02-25
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
Reexamination Certificate
active
06524784
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to photothermographic materials and an image forming method, and in particular to photothermographic materials suitable for use in printing plate making and an image forming method by use thereof.
BACKGROUND OF THE INVENTION
In the field of graphic arts and medical treatment, there have been concerns in processing of photographic film 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 desired 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, and reducing agent, as described in U.S. Pat. Nos. 3,152,904 and 3,487,075, and D. Morgan, “Dry Silver Photographic Materials” (Handbook of Imaging Materials, Marcel Dekker, Inc. page 48, 1991).
Such a photothermographic material contains a reducible light-insensitive silver source (such as organic silver salts), a light-sensitive silver halide and a reducing agent, which are dispersed in a binder matrix. The photothermographic materials are stable at ordinary temperature and forms silver upon heating, after exposure, at a relatively high temperature (e.g., 80° C. to 140° C.) 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 produced by exposure. Silver formed through reaction of the reducible silver salt in exposed areas provides a black image, which contrasts with non-exposes areas, leading to image formation. Such photothermographic materials meet requirements for simplified processing and environmental protection.
Such photothermographic materials have been mainly employed as photographic materials mainly for use in micrography and medical radiography, but partly for use in graphic arts. This is due to the fact that the maximum density (also denoted as Dmax) of obtained images is still low and the contrast is relatively low so that desired quality levels for graphic arts have not yet been achieved. To overcome such problems, there have been attempted incorporation of hydrazine derivatives as a contrast-increasing agent into the photothermographic material to form high contrast halftone dot images but satisfactory levels have not yet achieved. In general, when the foregoing contrast-increasing agent promotes thermal development of the halftone dot-exposed photothermographic material, halftone dots often tend to be abruptly formed so that intermediate-size and large-size dots become larger than intended their dot sizes, leading to deteriorated linearity of halftone dot images.
In the laser image setter described above, coherent light such as green laser of 500 to 600 nm and long wave laser having an emission wavelength in the near-infrared region are usually employed so that photothermographic materials used therein contain sensitizing dyes sensitive to such light are employed in the photothermographic material. After subjected to thermal processing, the sensitizing dyes remain on the halftone dot images, producing problems that dot image quality or linearity is lowered, resulting to so-called deterioration due to remaining dye stain. It was found that the use of recently developed short wave laser having an emission at 350 to 450 nm to halftone dot images on the photothermographic material resulted in superior images to those obtained by commonly known long wave laser, without causing dye stains. However, satisfactory levels were not necessarily attained.
SUMMARY OF THE INVENTION
In view of the foregoing facts, the present invention was achieved. Thus, it is an object of the invention to provide a photothermographic material exhibiting superior halftone dot quality, an enhanced maximum density and superior linearity and forming high contrast images, without causing dye stain, and an image forming method by the use thereof.
The above object of the invention can be achieved by the following constitution:
1. A photothermographic material comprising on a support an organic silver salt, silver halide grains, a reducing agent, a contrast-increasing agent and a binder, which has been prepared by using an organic solvent as a main solvent in coating, wherein the photothermographic material has a residual organic solvent content of 30 to 500 mg/m
2
and exhibits a sensitivity maximum at a wavelength of 350 to 450 nm; and
2. An image forming method comprising exposing the photothermographic material described above to light using a light source having a maximum emission within the wavelength region of 350 to 450 nm.
Furthermore, preferred effects of the invention were achieved by the following embodiments.
3. The photothermographic material described in 1, wherein the silver halide grains have an average grain size of not more than 0.03 &mgr;m;
4. The photothermographic material described in 1 or 2, wherein the photothermographic material comprises a compound represented by the following formula (I) to (III):
wherein R
1
through R
4
are each a hydrogen atom, halogen atom, nitro group, hydroxy group, alkyl group, alkoxy group, aryl group, aryloxy group, acylamino group, carbamoyl group, sulfo group, alkylthio group or arylthio group, provided that R
1
and R
2
, or R
3
and R
4
may combine with each other to form a ring, and R
1
through R
4
may be substituted by any substituent group;
wherein R
5
and R
6
are each a hydrogen atom, alkyl group or acyl group; X is —CO— or —COO—; m, n and p are each an integer of 1 to 4, R
5
and R
6
may be substituted by any substituent group;
wherein A, B and C are each a substituted or unsubstituted alkyl group, aryl group, alkoxy group, aryloxy group or heterocyclic group, provided that at least one of A, B and C is represented by the following formula (IV):
wherein R
7
and R
8
are each a hydrogen atom, or a substituted or unsubstituted alkyl group, aryl group, alkoxy group or aryloxy group; and
5. The image forming method described in 2, wherein the light is incoherent light.
DETAILED DESCRIPTION OF THE INVENTION
Photothermographic Material
The thermally developable photothermographic material relating to the invention (hereinafter, also denoted simply as photothermographic material) comprises on a support a light-sensitive silver halide layer and a light-insensitive layer, the light-sensitive layer containing a hydrophilic or hydrophobic binder, an organic silver salt, silver halide grains, a reducing agent and a contrast-increasing agent; and such ingredient compounds are dissolved or dispersed in an organic solvent or water, and preferably an organic solvent as a main solvent and coated on the support such as PET (i.e., polyethylene terephthalate) to obtain the photothermographic material. The photothermographic material preferably contains a UV absorbent.
Binder
Binders suitable for the light-sensitive layer or light-insensitive layer of the photothermographic material relating to the invention is are transparent or translucent, and generally colorless. The binders are natural polymers, synthetic resins, and polymers and copolymers, other film forming media; Examples thereof include gelatin, gum arabic, poly(vinyl alcohol), hydroxyethyl cellulose, cellulose acetate, cellulose acetatebutylate, poly(vinyl pyrrolidone), casein, starch, poly(acrylic acid), poly(methyl methacrylic acid), poly(vinyl chloride), poly(methacrylic acid), copoly(styrene-maleic acid anhydride), copoly(styrene-acrylonitrile, copoly(styrene-butadiene, poly(vinyl acetal) series [e.g., poly(vinyl formal)and poly(vinyl butyral), polyester series, polyurethane series, phenoxy resins, poly(vinylidene chloride), po
Bierman, Muserlian and Lucas
Chea Thorl
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