Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2001-03-29
2004-03-16
Ashton, Rosemary (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S567000, C430S374000, C430S376000
Reexamination Certificate
active
06706469
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a silver halide emulsion, a silver halide color photographic light-sensitive material, and a color image-forming method, both of which latter two use said silver halide emulsion. In particular, the present invention relates to a silver halide emulsion containing high silver chloride tabular grains having {111} major faces, a silver halide color photographic light-sensitive material, and a color image-forming method, both of which latter two use said silver halide emulsion.
BACKGROUND OF THE INVENTION
It is well known that color photography is a process of forming dye images, achieved by subjecting a light-sensitive material, comprising a support, having thereon dye-forming couplers and a silver halide emulsion, to a color development processing with an aromatic primary amine color-developing agent, resulting in the formation of an oxidation product of the developing agent, followed by a reaction of the oxidation product and the dye-forming coupler (hereinafter referred to as a coupler).
Nowadays, such silver halide color photographic light-sensitive materials are extensively used, because they are highly sensitive and excellent in gradation. Recently, however, demands for photographic properties, such as further enhancement of photographic speed, processing stability, image quality, and development processing speed, have become stronger than ever. Therefore, various studies are carried out. As to advances in processing speed, light-sensitive materials using silver halide grains having a high silver chloride content (a silver chloride content of 90 mole % or more is referred to as high silver chloride) have become mainly used, from the viewpoint of rapid color development, particularly in a color photographic printing paper. For example, International Patent Publication WO 87/04534 discloses that a high silver chloride emulsion is preferably used as a photographic emulsion. However, it is also known that, if the silver chloride content of the silver halide emulsion to be used is increased, developing speed is greatly improved, but, on the other hand, silver chloride emulsions have a disadvantage that generally they exhibit low sensitivity. Accordingly, overcoming this disadvantage is a task to be solved in order to put a high silver chloride emulsion to practical use.
Further, the stability to a processing solution is enumerated as one of important properties which are required for a color photographic printing paper. Generally, a high silver chloride emulsion raises the problem that, as the silver chloride content increases, silver halide grains are easily dissolved into a processing solution. In a practical color development processing as an example, a light-sensitive material passes through successive baths that include a developing solution, a fixing/bleaching solution, and a washing solution, in this order. It is known that, if a bleach-fixing solution is mixed in a developing solution in the foregoing processing steps, dissolution of the grains is accelerated, and dissolution physical development advances, so that an image obtained by the development processing exhibits higher sensitivity and higher contrast, thereby causing a fluctuation of the gradation, compared with the sensitivity and contrast obtained by a normal processing, in which mixing of the bleach-fixing solution in the developing solution does not occur. Such a situation is rare but occurs at a definite frequency. Further, it is known that activities of the developing solution change due to a difference between frequencies in the use of running processing. Consequently there is a problem that a difference in activities of the developing solution changes photographic properties.
As to the foregoing problem, when dissolution of grains occurs more easily, a greater change in photographic properties due to the difference in activities of the developing solution is likely to occur. It is considered important, from the viewpoint of providing a highly reliable color photographic printing paper, that an image of definite quality is regularly formed, even by the foregoing development processing in which impurities are mixed, or when some degree of change in activities of the developing solution arise. Further, in fact, demand for improvement of the above-mentioned processing stability is also strong in the market, and improvement in the toughness of development processing steps using a high silver chloride emulsion is desired. Herein, the expression “an image of definite quality” used herein refers to an image obtained without fogging, sensitization, and fluctuation of gradation, due to the above-mentioned change of the processing solution.
When tabular silver halide emulsion grains are employed in a photographic light-sensitive material, generally the proportion by which rays of light incident upon a light-sensitive layer, pass through the light-sensitive layer, is lower, and the capture efficiency of light increases, and moreover enhancement of photographic speed (sensitivity) can be achieved, in comparison with non-tabular silver halide emulsion grains. It is known that tabular silver halide grains therefore can be made smaller than non-tabular grains, resulting in improved image quality (covering power, sharpness, granularity), development progress characteristics, spectral sensitization characteristics, and the like.
On the other hand, it was found that, when tabular grains are compared to non-tabular grains having a photographic speed equivalent thereto, the tabular grains cause a more serious problem in solubility, since they have a larger ratio of surface area to volume. U.S. Pat. No. 5,543,281 discloses that a certain type of phenylmercaptotetrazole derivatives is effective in preventing grains from being dissolved. However, these compounds were insufficient to solve the foregoing problem.
As a result of studies aimed at solving the problems of sensitization and fluctuation of gradation due to mixing of a bleach-fixing solution in a developing solution, the present inventor has found that it is useful in solution of the problems to control the ratio (b/a) of grain thickness (b) to the distance (a) between parallel twin planes of the tabular grains, so that the ratio (b/a) would be less than 5, and further preferably to increase the degree of monodispersion of the ratio (b/a).
JP-A-6-308644 (“JP-A” means unexamined published Japanese patent application) describes a method of producing tabular grains, which comprises controlling the distance between twin planes and the ratio of the thickness of tabular grains to the distance between twin planes. However, this patent publication relates to a method of producing high silver bromide {111} tabular grains, and there is no mention of high silver chloride grains.
In order to produce high silver chloride {111} tabular grains, a special measure is needed. For example, U.S. Pat. Nos. 4,400,463, 5,185,239, and 5,176,991, JP-A-63-213836, U.S. Pat. Nos. 5,176,992, and 5,691,128, disclose a method of forming grains in the presence of a crystal habit-controlling agent, such as aminoazaindene, triaminopyrimidine, hydroxylaminoazine, thiourea, xanthonoid, or a pyridinium salt, respectively. JP-A-9-197594 discloses a method of producing tabular grains having a ratio (b/a) of grain thickness (b) to the distance (a) between twin planes of 5 or more. Thus, generally, as the silver chloride content increases, a {111} plane is predominantly formed on the outermost surface. Consequently, when high silver chloride {111} tabular grains are formed, the grains are apt to grow in the thickness direction (b), and to ordinarily exhibit a ratio (b/a) of 5 or more.
SUMMARY OF THE INVENTION
The present invention is a silver halide emulsion which comprises silver halide grains having a silver chloride content of at least 90 mole %, wherein tabular grains satisfying the following conditions {circle around (1)} and {circle around (2)} account for at least 70% of the total projected area of a
Ashton Rosemary
Fuji Photo Film Co. , Ltd.
Walke Amanda C.
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