Light-sensitive silver halide grain and silver halide emulsion

#The present invention relates to a silver halide photographic material, and particularly to a silver halide photographic material using dopant technology, which has high sensitivity, high gradation and no reciprocity failure.

#As one of techniques for modifying silver halide grains to improve the entire performance of silver halide photographic materials so as to be expected, there is a technique of incorporating silver ions and materials other than halide ions (dopants) into the silver halide grains (a doping technique). In particular, many investigations have been conducted for the doping technique of transition metal ions. When the transition metal ions are introduced into the silver halide grains as dopants, it has generally been observed that the transition metal ions effectively change photographic properties even though they are added in an extremely slight amount.

#In order to improve the photographic properties of silver halide emulsions more effectively, a technique has also been known in which the silver halide grains are doped with not only the transition metal ions but also transition metal complexes. Effects obtained by the doping technique are (1) increase of sensitivity, (2) improvement in reciprocity failure and (3) increase of contrast. For the purpose of obtaining a highly sensitized emulsion, a group VIII metal complex having a cyanide ion as a ligand is used as a dopant, as disclosed in Japanese Patent Laid-Open No. 20854/1990 and Japanese Patent Publication No. 113743/1995. A hexacyano complex having iron or aluminum as a central metal is an effective sensitizing dopant among others. In order to obtain a high gradation emulsion, there is used a technique using hexachlororuthenium, hexachlororhodium or hexachlororhenium as disclosed in Japanese Patent Laid-Open Nos. 184740/1988, 285941/1989, 20852/1990 and 20855/1990, or a technique using nitrosyl or thionitrosyl as a ligand of a transition metal complex as disclosed in European Patents 033642, 0606895 and 0610670.

#A 3% aqueous solution of lime-treated gelatin (1000 ml) was adjusted to pH 5.5 and pCl 1.7, and an aqueous solution containing 2.12 mol of silver nitrate and an aqueous solution containing 2.2 mol of sodium chloride were concurrently added thereto at 66° C. with vigorous stirring. From the time when the addition of silver nitrate reached 80% to the time when it reached 90%, potassium chloride was added with vigorous mixing so as to give a content of 2 mol % per mol of silver halide in a final product. At the time when the addition of silver nitrate reached 90%, an aqueous solution of potassium iodide was added with vigorous mixing in an amount to give an I content of 0.2 mol % permol of silver halide in the final product. After desilvering treatment was carried out at 40° C., 168 g of lime-treated gelatin was added to adjust the pH and the pCl to 5.5 and 1.8, respectively. Thus, an emulsion of cubic silver iodobromochloride grains having a equivalent sphere diameter of 0.75 μm and a coefficient of variation of 11% was obtained.

#This emulsion was dissolved at 40° C., and sodium thiosulfonate was added thereto in an amount of 2×10−5 mol per mol of silver halide. Then, using sodium thiosulfate pentahydrate as a sulfur sensitizer, and gold (I) borate tetrafluoride bis(1,2,5-trimethyl-1,2,4-triazolium-3-thiolate as a gold sensitizer, ripening was conducted at 60° C. so as to give optimum results. After the temperature was lowered to 40° C., sensitizing dye A was added in an amount of 2×10−4 mol per mol of silver halide, sensitizing dye B in an amount of 1×10−4 mol per mol of silver halide, 1-phenyl-5-methylureidephenyl-5-mercaptotetrazole in an amount of 2×10−4 mol per mol of silver halide, and potassium bromide in an amount of 2×10−3 mol per mol of silver halide. The emulsion thus obtained was named emulsion 1-1. 8

#Emulsion 1-2 was prepared in the same manner as with emulsion 1-1 with the exception that hexachloroiridium was added to a layer of 92% to 98% from the center of the grain by the grain volume, in an amount of 2×10−8 mol based on the total amount of silver added.