The present invention relates to a silver halide photographic material. More particularly, the present invention relates to a silver halide photographic material capable of providing a high-contrast and sensitivity photographic image in a rapid and consistent way.
High-contrast photographic image is usually employed in forming characters or halftone image in photomechanical processes, or forming fine-line image in ultra-high-precision photomechanical processes. Certain kinds of silver halide photographic materials are known to be capable of forming photographic image with very high contrast. In one conventional method, a light-sensitive material composed of a silver chlorobromide emulsion that has an average grain size of 0.2 .mu.m, that has a narrow grain size distribution, that comprises uniformly shaped grains and that has a high silver chloride content (at least 50 mol %) is processed with an alkaline hydroquinone developer of low sulfite ion concentration to form an image of high sharpness and high resolution, for example, a halftone image or a fine-line image. Silver halide light-sensitive materials of a type to be processed by this method are known as "lithographic" light-sensitive materials.
The photomechanical process involves a step of converting the original of continuous tone to be reproduced into a halftone image, or a step in which the continuous change in the density of the original is converted to a set of dots having areas proportional to the varying densities. To form a halftone image, the original is imaged onto a "lithographic" light-sensitive material via a crossline screen or a contact screen and subsequently developed. However, development of a lith-type light-sensitive material (i.e., a silver halide photographic material containing a silver halide emulsion consisting of fine grains of uniform size and shape) with an ordinary black-and-white developer results in the formation of a lower quality image than when it is developed with a lith-type developer. Thus, the lith-type light-sensitive material is conventionally processed with a lith-type developer that has a very low concentration of sulfite ions and which contains hydroquinone as the sole developing agent. However, developers of the lith type are very low in storage stability because they are highly sensitive to autooxidation. Hence, there is a strong need for controlling them to provide consistent quality of development in their continuous use and substantial efforts have been made to improve the storage stability of lith-type developers.
One of the methods proposed so far to attain object is replenishment with two separate liquids, one being a replenisher intended to compensate for the deterioration in developer's activity during development (compensation for process fatigue) and the other being a replenisher intended to compensate for the oxidative deterioration over time (compensation for aging fatigue). This method of using two types of replenishers is commonly adopted with automatic processors in photomechanical processes. However, because of the need to control the balance in replenishment with two liquids, this method suffers the problem of complexity in both equipment and operations.
Another problem with the use of lith-type developers is that they have a long induction period (i.e., the time required for an image to appear upon development) and hence are incapable of providing rapid access to image.
Methods are known that are capable of rapid formation of high-contrast image without using developers of the lith type. They are characterized by containing hydrazine compounds in silver halide light-sensitive materials [see U.S. Pat. No. 2,419,975 and JP-A-51-16623 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-51-20921, etc.]. According to these methods, the concentration of sulfite ions in developers can be held high enough to accomplish development with their storage stability being maintained at enhanced levels. However, in order to obtain a contrasty image by these methods, a developer with fairly high pH is necessary, which presents a problem in keeping the developer stable to produce a photographic image rapidly and with high sensitivity. The high pH of the developer tends to cause fogging and to prevent it, various organic restrainers must be contained in high concentrations but then sensitivity is compromised. A further problem is that a contrasty image is susceptible to defects such as pinholes if dust particles or other foreign substances are deposited on the light-sensitive material.