Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Identified backing or protective layer containing
Reexamination Certificate
2002-09-17
2004-05-04
Wilson, D. R. (Department: 1713)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Identified backing or protective layer containing
C525S057000, C525S061000
Reexamination Certificate
active
06730464
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a polyvinyl acetal resin for use in a heat-developable photosensitive material and to a heat-developable photosensitive material.
BACKGROUND ART
A heat-developable photosensitive material comprises a support and a composition applied thereto which is obtained by dispersing mainly a fatty acid silver salt and an organic reducing agent, optionally together with a small amount of a photosensitive silver halide, in a polymer binder.
The silver halides so far used widely are excellent in photographic characteristics, hence are utilized in high quality image forming materials. However, they have problems; the procedures in the steps of development and fixation are complicated and, since the above steps each involves wet treatment, not only troubles are caused by the complicated treatment works but also chemical waste liquid is discharged in large amounts.
For avoiding such problems, heat-developable photosensitive materials have been developed so that the development step may be carried out not in the manner of wet process but in the manner of heat-development, and have partly been put to practical use.
Thus, for example, Japanese Kokoku Publication Sho-43-004924 discloses a heat-developable photosensitive sheet material which comprises an organic silver salt containing, within the molecule, a group of associated silver ions, a silver halide catalytically contacting with the silver ions, and a slow reducing agent.
In the above-cited publication, it is described that the heat-developable photosensitive sheet material is formed by incorporating a photosensitive material comprising such organic silver salt, silver halide and slow reducing agent in a film or a fibrous product almost free of any binder, which serves as a transparent self-support, or by incorporating the above material in a coat layer of a film-forming binder, such as polyvinyl butyral, polymethyl methacrylate, cellulose acetate, polyvinyl acetate, cellulose acetate propionate or cellulose butyrate, and applying the resulting composition to a heat-resistance support, such as a paper sheet, plastic film, metal foil or glass sheet; and polyvinyl acetal resins are used and alleged to be most suitable as the above film-forming binder.
However, for reasons of production process, the conventional polyvinyl acetal resins contain minute amounts of impurities, and these impurities cause the film-forming binder itself to have photosensitivity, so that the following defects may be caused: the coat layer of the film-forming binder prepared may be colored unreasonably or, after application, images may undergo or show fog, poor gradation or deficient sensitivity, or the photosensitive sheet material may have poor storability before image forming. Depending on the glass transition temperature of the polyvinyl acetal resin, the film may undergo heat deformation in the step of heat-development, or images after application may show fog, poor gradation or deficient sensitivity, or cracking may occur during film handling, among others.
As means for solving the above problems of deterioration of image characteristics, the use of a thione compound represented by a general formula as the silver salt oxidizing agent in a thermal photographic composition containing a photosensitive silver halide, a reducing agent and a silver salt oxidizing agent is described in Japanese Kokai Publication Sho-49-052626, for instance, by which stable images can be formed without causing any independent stabilizer or stabilizer precursor to exist in the system. However, the use of such thione compound as the silver salt oxidizing agent can never solve the above-mentioned problems which the conventional polyvinyl butyral resins have.
Further, for improving image characteristics, it is said to be necessary that the fatty acid silver salt, organic reducing agent, photosensitive silver halide and other ingredients be dispersed more uniformly. However, when a polyvinyl acetal resin with a low degree of polymerization is used for making a point of the dispersibility, the resulting coat will be weak in strength and problems such as fog may arise. When, conversely, a polyvinyl acetal resin with a high degree of polymerization is used for satisfying the coat strength requirement, it becomes difficult to uniformly disperse the fatty acid silver salt, organic reducing agent and photosensitive silver halide therein.
Furthermore, among heat-developable photosensitive materials, heat-developable silver salt films are inferior in image characteristics, in particular image density and visibility of gradated portions, to the conventional X-ray sensitive films in which gelatin is used and which is processed by the wet method. Therefore, it is strongly demanded that the heat-developable silver salt films be improved with respect to these image characteristics. For that purpose, it is necessary to strictly control the nuclear growth of silver in the step of heating.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a polyvinyl acetal resin for heat-developable photosensitive materials as well as a heat-developable photosensitive material while solving such problems as coating solution pot life, coloration of heat-developable photosensitive material, fog, poor gradation, insufficient sensitivity and poor undeveloped film storability and making it possible for the materials to acquire good image characteristics.
The present invention provides
a polyvinyl acetal resin for heat-developable photosensitive materials
which is a polyvinyl acetal resin synthesized by the acetalization reaction between a polyvinyl alcohol and an aldehyde and
which comprises having a degree of polymerization of 200 to 3,000, a residual acetyl group content of 0 to 25 mole percent and a residual hydroxyl group content of 17 to 35 mole percent, as calculated while regarding one acetal group as two acetalized hydroxyl groups, a water content of not more than 2.5% by weight and a residual aldehyde content of not more than 10 ppm and is free of any antioxidant.
In another aspect, the invention provides
a polyvinyl acetal resin for heat-developable photosensitive materials
which comprises two polyvinyl acetal resin species differing in degree of polymerization by at least 300 and
which comprises having an apparent degree of polymerization of 200 to 1,000, an apparent residual acetyl group content of 0 to 25 mole percent and an apparent residual hydroxyl group content of 17 to 35 mole percent, as calculated while regarding one acetal group as two acetalized hydroxyl groups, a water content of not more than 2.5% by weight and a residual aldehyde content of not more than 10 ppm and is free of any antioxidant.
The polyvinyl acetal resin for heat-developable photosensitive materials according to the present invention preferably has a glass transition temperature of 55 to 110° C.
In a further aspect, the invention provides a heat-developable photosensitive material in which the polyvinyl acetal resin for heat-developable photosensitive materials according to the present invention is used.
DETAILED DISCLOSURE OF THE INVENTION
In the following, the present invention is described in detail.
The present inventor made intensive investigations concerning the causes of coloration of a heat-developable photosensitive material in which a polyvinyl acetal resin is used, and of the occurrence of fog, poor gradation, insufficient sensitivity and other troubles with images after coating and found that these troubles are caused by the structure of the polyvinyl acetal resin and the minute amounts of impurities resulting from the production. Based on such findings, the present invention has now been completed.
The polyvinyl acetal resin for heat-developable photosensitive materials according to the first aspect of the invention is synthesized by the acetalization reaction between a polyvinyl alcohol and an aldehyde.
The mode of the above acetalization reaction is not particularly restricted but the reaction may be carried out using an acid catalyst i
Sekisui Chemical Co. Ltd.
Sughrue & Mion, PLLC
Wilson D. R.
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