1. Field of the Invention
The present invention relates to a photothermographic material (this may be hereinafter referred to as “photographic material”), in particular to that favorable for medical diagnosis, industrial analysis, industrial photography, printing or COM.
2. Description of the Related Art
Reduction of the amount of waste after development and fixing of films for medical diagnostics and photographic printing has been strongly demanded in recent years in view of environmental preservation and for saving work space. Accordingly, technologies related to photothermographic materials are urgently required for providing films for medical diagnosis and photographic printing, by which efficient exposure is possible using a laser image setter or laser imager to form clear monochromatic images with high resolution and sharpness. No liquid chemicals are needed for development and fixing when the photothermographic materials is used, making it possible to supply to customers a photothermographic systems that is more simple and friendly to the environment.
The same applies to the field of general purpose image forming materials, which, however, differ from those in the field of medical diagnosis. Specifically, photo-images for medical diagnosis must clarify the details of body parts and therefore must have sharp and good image quality with fine graininess.
To photosensitive materials, dye is generally added and it serves as a filter dye or acts for antihalation or anti-irradiation. In general, the dye added to photosensitive materials functions while the photographic materials are exposed to have an image thereon, and it is completely removed while the materials are developed. After developed, therefore, the images formed on the photosensitive materials should not be stained with the dye that is not removed but has still remained therein after development. If having still remained in the processed photographic materials, the dye absorbs some visible light to thereby stain the images formed on the processed photosensitive materials.
In conventional wet development, it is relatively easy to remove the dye from the processed photosensitive materials into the processing solutions. However, in dry development such as heat development, the dye is difficult to remove. To overcome the problem, a method of decolaring the dye by heat during heat development has been proposed. For example, JP-A No. 11-352626 discloses a technique of decolaring the dye in processed photothermographic materials, which comprises controlling the melting point of a base precursor in the materials and decolaring the dye in the processed materials by the action of the base formed during the step of heat-developing the materials.
However, this technique does not satisfy some customers' demand for more rapid heat development of photothermographic materials. The drawback of the technique is that dye erasure in developed photothermographic materials is unsatisfactory and some dye still remains in the processed materials.
In the technique proposed, if an excess amount of a base precursor is in the photothermographic materials in order to improve the dye erasure in the processed materials, it causes another problem in that water drops given to the images of the processed materials leave their traces thereon, or that is, the water resistance of the processed materials worsens.