Photothermographic material

#The present invention relates to a photothermographic material, in particular, a photothermographic material that realizes higher sensitivity. More precisely, the present invention relates to a photothermographic material useful for use in image setters suitable for photomechanical processes, medical diagnosis and so forth.

#In recent years, reduction of amount of waste processing solutions is strongly desired in the fields of films for medical diagnosis, photomechanical processes and so forth from the standpoints of environmental protection and space savings. Therefore, photothermographic materials are noted as films for medical diagnosis and photomechanical processes that can be efficiently exposed by using a laser image setter or laser imager and can form clear black images with high resolution and sharpness. Such photothermographic materials can provide a simpler and non-polluting heat development processing system that does not require use of solution-type processing chemicals. Photothermographic materials contain a silver salt of an organic acid, photosensitive silver halide grains, reducing agent and binder on a support, and described in, for example, U.S. Pat. Nos. 3,152,904, 3,457,075 and D. Klosterboer, Imaging Processes and Materials, “Thermally Processed Silver Systems”, 8th ed., Chapter 9, page 279, compiled by J. Sturge, V. Walworth and A. Shepp, Neblette (1989).

#However, since the photosensitive silver halide contained in photothermographic materials is not fixed and remains in films even after image formation, grain size and amount thereof are limited in order to prevent degradation of printed out conditions. That is, the grain size and amount of photosensitive silver halide are designed so as to be as small as possible. Therefore, photothermographic materials have a problem of lower sensitivity compared with photosensitive materials for wet processing.

#FIG. 1 is a side view of an exemplary heat development apparatus used for heat development of the photothermographic material of the present invention. In the figure, there are shown a photothermographic material 10, taking-in roller pairs 11, taking-out roller pairs 12, rollers 13, a flat surface 14, heaters 15, and guide panels 16. The apparatus consists of a preheating section A, a heat development section B, and a gradual cooling section C.

#The photothermographic material of the present invention will be explained in detail hereafter. In the present specification, ranges indicated with “−” mean ranges including the numerical values before and after “−” as the minimum and maximum values.

#The photothermographic material of the present invention contains a silver salt of an organic acid, a photosensitive silver halide, a reducing agent and a binder on a support. Further, the photothermographic material of the present invention is characterized by containing at least one compound selected from compounds of the aforementioned Types (i) to (iv). Therefore, the compounds of Types (i) to (iv) used in the present invention will be explained first.

#Type (i)