Silver halide photographic light-sensitive material with high-sensitivity and improved fog and granularity and method of its production

Abstract: There is disclosed a silver halide light-sensitive material having a high sensitivity, reduced fog and excellent granular­ ity. The light-sensitive material contains monodispersed sil­ ver halide emulsion consisting mainly of twinned silver halide grains, wherein the twinned silver halide 9rains comprise: a. a high silver iodide content phase in the center thereof; b. an aspect ratio of less than 3; c. mainly {111} planes; and d. parallel twinned planes of an even number in a ratio of 50 % or more by number based on the total twinned grains.

Description: FIELD OF THE INVENTION The present invention relates to a silver halide photographic light-sensitive material and a method of its production, more specifically to a light-sensitive material with high sensitivity, reduced and excellent granularity and a production method thereof. BACKGROUND OF THE INVENTION In recent years, there have been increasing demands for improvements in the sensitivity and image quality of silver halide photographic light-sensitive materials. In response to these demands, there have been proposed various methods for controlling a shape, a size distribution and a composition of a silver halide grain. Japanese Patent Publication Open to Public Inspection No. 113934/1983 discloses a method of improving color photographic light-sensitive materials wherein a tabular silver halide emulsion having a diameter/thickness ratio of a grain (aspect ratio) exceeding 8 is applied to a green or red-sensitive layer. However, the emulsions having high aspect ratios exceeding 8 does not have satisfactory improvement in sensitivity or granularity since its latent image-forming efficiency is not necessarily high while having an excellent photoreceptive efficiency. Further, investigations have been made to prepare core/shell type tabular grains having a high silver iodide content phase in the core as well as to increase a monodispersion degree thereof. Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) Nos. 14636/1986, 112142/1986 and 163451/1988 disclose monodispersed twinned tabular grains having a core-shell structure. In the above disclosures, the grains having the aspect ratios of 3 to 8 show good performance but have insufficient improvement in sensitivity and granularity. SUMMARY OF THE INVENTION The object of the present invention is to provide a silver halide photographic light sensitive material (hereinafter referred to as a light-sensitive material) with high sensitivity, improved fog and excellent granularity and a production method thereof, more specifically to a light-sensitive material containing an improved core/shell type twinned silver halide grains and a production method thereof. The above object of the invention is accomplished by a silver halide photographic light-sensitive material comprising a support and provided thereon photographic component layers including at least one light-sensitive emulsion layer containing a monodispersed silver halide emulsion consisting mainly of twined halide grains, characterised in that the silver halide grains comprise: (a) a high silver iodide core; (b.) an aspect ratio of not less than 1.3 to less than 2; (c.) mainly [111] planes; and (d.) parralel twin planes of an even number in a ratio of 50% or more by number based on the total twinned grains. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1 and 2 are X ray diffraction patterns at (420) of emulsions Em-1 and emulsion Em-2 prepared in Examples 2 and 4, respectively, both having two peaks corresponding to high and low silver iodide contents. Fig. 3 is a schematic diagram of the twinned silver halide grain of the present invention, in which a-a', b-b' and c-c' each represent parallel twinned planes. (A) and (B) show twinned crystals comprising {111} planes alone, and (C) shows a twinned crystal comprising about 95% {111} planes and about 5% {100} planes. DETAILED DESCRIPTION OF THE INVENTION It has been found that improvements in sensitivity and image quality can be accomplished with an emulsion having such a low aspect ratio as described above, while emulsions having higher aspect ratios are popular. In the present invention, a monodispersion of a silver halide emulsion is defined by that the silver halide grains falling within the range of 80 to 120% of an average grain diameter d accounts for not less than 70%, preferably not less than 80%, more preferably not less than 90% by weight of the total silver halide grains. The average grain size d is defined by the grain size di in which the product of ni x di 3 is maximized, wherein ni is the number of the grains having the size di (the significant figure is calculated down to the third decimal place and the forth digit is rounded to the nearest whole number). A diameter of a twinned grain is defined by a diameter of the circle having the same area as that of the projected grain. Grain size can be determined by taking an electron micrograph of the grain at a magnifying rate of 10000 to 50000 and measuring the diameters of the printed grain images or the area of the projected images of more than 1000 grains selected arbitrarily. The silver halide emulsion used in the invention has a monodispersion degree of not more than 20%, preferably not more than 15%, wherein the monodispersion degree is defined by the following equation: (standard deviation of grain size/average grain size) x 100 = monodispersion degree (%) The grain size is determined by the method described above, and the average grain size is a simple average value calculated by the following equation: average grain size = Σdini/Σni In the invention, the silver halide emulsion is prepared preferably by precipitating a high iodide content phase on a monodispersed seed grain, more preferably by the method described in Japanese Patent O.P.I. Publication No. 6643/1986, in which monodispersed, twinned spherical seed grains are grown. The silver halide emulsion of the invention has mainly an even number of parallel twinned planes, preferably two twinned planes. The silver halide emulsion of the invention comprises a silver iodobromide having an average silver iodide content of 4 to 20 mol%, preferably 5 to 15 mol%. The concentration of an aqueous solution of silver nitrate used to grow the high silver iodide content phase present in the center of a grain is not more than 1 N, preferably 0.3 to 0.8 N. The twinned silver halide grains of the invention comprise mainly {111} planes in a ratio of not less than 60%, preferably 70 to 100%, more preferably 75 to 98% based on the whole grain. The average ratio of a diameter of a circle having the same area as that of the projected major plain to a distance (thickness) between two grain surfaces parallel to the twinned planes (aspect ratio) is less than 1.3 to less than 2.0. The method of producing a silver halide emulsion of the invention by adding an aqueous silver salt solution and an aqueous halide solution in the presence of protective colloid is characterized by taking the following steps: (a) forming nuclear grains having a silver iodide content of 0 to 5 mol% while pBr of the mother liquid is maintained at 2.0 to -0.7 during at least the first half of the time necessary for forming the nuclear grains; (b) forming monodispersed seed grains of a spherical twinned crystal by ripening the nuclear grains in the presence of a silver halide solvent of 10 -5 to 2.0 mol per mol silver halide; and (c) growing the seed grains by adding the water-soluble silver salt and halide solutions and/or fine silver halide grains. The two or more twinned planes may be or may not be parallel to each other. The grains may comprise {111} planes, {100} planes or combination thereof. In the formation of the nuclear grains, pBr is maintained at -0.7 to 2.0, preferably -0.7 to 1.5 during at least a half of the time necessary for forming the grains. The nuclear grains may be monodispersed or polydispersed. Polydispersion is defined by the monodispersion degree of not less than 25%. The nuclear grains contain twinned grains in a ratio of not less than 50%, preferably not less than 70%, and more preferably not less than 90% based on the total grains. Substantially monodispersed spherical grains are prepared by adding the silver salt and halide solutions to the nuclear grains in the presence of a silver halide solvent of 10 -5 to 2.0 mol per mol silver halide. Substantially monodispersed grains are defined by the grains having the monodispersion degree of less than 25%. Substantially spherical grains are defined by the grains which are round to such extent that {111} and {100} planes are not clearly recognizable via electron micrographic observation and have a L/ℓ ratio of 1.0 to 2.0, preferably 1.0 to 1.5, wherein L and ℓ represent the maximum and minimum grain diameters, respectively. The spherical grains account for not less than 60%, preferably not less than 80%, and more preferably almost all of the total seed grains. Examples of the silver halide solvent used in the seed grain formation are (a) organic thioethers described in US Patent Nos. 3,271,157, 3,531,289 and 3,574,628, Japanese Patent O.P.I. Publication Nos. 1019/1979 and 158917/1979 and Japanese Patent Examined Publication No. 30571/1983; (b) thiourea derivatives described in Japanese Patent O.P.I. Publication Nos. 82408/1978, 29829/1980 and 77737/1980; (c) AgX solvents having a thiocarbonyl group located between an oxygen or sulfur atom and a nitrogen atom described in Japanese Patent O.P.I. Publication Nos. 144319/1978; (d) imidazoles described in Japanese Patent Publication No. 100717/1979; (e) sulfites; (f) thiocyanates, (g) ammonia; (h) hydroxylalkyl-substituted ethylenediamines described in Japanese Patent O.P.I. Publication No. 196228/1982; (i) substituted mercaptotetrazoles described in Japanese Patent O.P.I. Publication No. 202531/1982; (j) water-soluble bromides; and (k) benzimidazole derivatives described in Japanese Patent O.P.I. Publication No. 54333/1983. Examples of these silver halide solvents (a) to (k) are given below. (e) K 2 SO 3 , Na 2 SO 3 (f) NH 4 SCN, KSCN (g) NH 3 (j) NaBr, NH 4 Br, KBr These solvents may be used in combination. Preferred solvents are thioethers, thiocyanates, thioureas, ammonia and bromides, more preferably a combination of ammonia and bromide. pH is 3 to 13, preferably 6 to 12, and the temperature is 30 to 70°C, preferably 35 to 50. In one mode of preferred embodiment of the present invention, the seed grains are prepared by ripening for 30 seconds to 10 minutes using 0.4 to 1.0 mol/ℓ ammonia and 0.03 to 0.5 mol/ℓ potassium bromide in combination at pH of 10.8 to 11.2 and a temperature of 35 to 45°C. A water-soluble silver salt may be added for adjustment of ripening during the seed grain formation. The seed grains are grown by adding the silver salt and halide solutions by the double jet method with the addition speed varied gradually so that the new grains are not formed and Ostwald ripening does not occur, as described in Japanese Patent O.P.I. Publication Nos. 39027/1976, 142329/1980, 113928/1983, 48521/1979 and 49938/1983. The seed grains can be grown by another method described in the proceeding of the 1983 annual meeting of the Society of Photographic Science and Technology of Japan, p. 88, in which fine silver halide grains coexist in the emulsion for recrystallization on the nuclear grains. In the preparation of the high silver iodide content silver halide emulsion of the present invention, pAg is maintained at 5 to 11, preferably 6.0 to 9.5; the temperature is 40 to 85°C, preferably 60 to 80°C; and pH is 1.5 to 5.8, preferably 1.8 to 3.0. In the present invention, a stirring condition is an important factor. The stirring apparatus disclosed in Japanese Patent O.P.I. Publication No. 160123/1988 is preferably used, in which a nozzle for adding a solution is placed near the mother liquid inlet so that the nozzle is dipped in the liquid. It is preferable that the rotating rate of the stirrer be 400 to 1200 rpm. The silver halide emulsion used in the present invention may be subjected to chemical sensitization by an ordinary method and to spectral sensitization to the prescribed wavelength regions with sensitizing dyes. The silver halide emulsion may contain an antifogging agent, a stabilizer and other additives. Gelatin is preferably used as a binder. The emulsion layers and other hydrophilic colloid layers may be hardened and contain a plasticizer and a latex. The present invention is applied preferably to color photographic light-sensitive materials such as color negative films and color reversal films. The emulsion layers of the color photographic light-sensitive materials contain couplers. There may be added a colored coupler having a corrective effect, a competitive coupler and a compound that releases photographically useful fragments such as a development accelerator, a bleaching accelerator, a developer, a silver halide solvent, a toning agent, a hardener, a fogging agent, an antifogging agent, a chemical sensitizer, a spectral sensitizer and a desensitizer by coupling with the oxidation product of a developing agent. The light-sensitive material may be provided with supplementary layers such as a filter layer, an antihalation layer and an anti-irradiation layer. These layers and/or emulsion layers may contain a dye that elutes from the light-sensitive material or is bleached during development. The light-sensitive material may contain a formalin scavenger, a fluorescent brightening agent, a matting agent, a lubricant, an image stabilizer, a surfactant, an anti-fogging agent, a development accelerator, a development retarder and a bleaching accelerator. Examples of the supports are polyethylene-laminated paper, polyethylene terephthalate film, baryta paper and cellulose triacetate film. The light-sensitive material is subjected to conventional processing after exposure. EXAMPLE The present invention is hereinafter described in more detail by means of the following examples. Example 1 Preparation of spherical seed emulsion A monodispersed spherical seed emulsion was prepared by the method described in Japanese Patent O.P.I. Publication No. 6643/1986. Solution A 1 Ossein gelatin 150 g Potassium bromide 53.1 g Potassium iodide 24 g Water was added to the total quantity of 7.2 ℓ. Solution B 1 Silver nitrate 1.5 kg Water was added to the total quantity of 6ℓ. Solution C 1 Potassium bromide 1327 g 1-phenyl-5-mercaptotetrazole in methanol solution 0.3 g Water was added to the total quantity of 3ℓ. Solution D 1 Aqueous ammonia (28%) 705 mℓ To solution A 1 stirred vigorously at 40°C, solutions B 1 and C 1 were added by the double jet method at pBr of 1.09 to 1.15 in 30 seconds to prepare nuclear grains. One minute and 30 seconds later, solution C 1 was added in 20 seconds, followed by ripening for 5 minutes, wherein the KBr and ammonia concentrations were 0.071 mol/ℓ and 0.63 mol/ℓ, respectively. Then, pH was adjusted to 6.0, and the emulsion was immediately desalted and washed with water. Observation via an electron microscope revealed that this seed emulsion contained the monodispersed spherical grains having an average grain size of 0.36 µm and a monodispersion degree of 18%. Example 2 Preparation of emulsion of the present invention An emulsion of the present invention having an average silver iodide content of 6.0% was prepared as follows: Solution A 2 Ossein gelatin 76.8 g Seed emulsion of Example 1 0.191 mol eq. Water was added to the total quantity of 4ℓ. Solution B 2-1 Silver nitrate 206.4 g Water was added to the total quantity of 2209 mℓ. Solution C 2-1 Ossein gelatin 88.4 g Potassium bromide 101.2 g Potassium iodide 60.5 g Water was added to the total quantity of 2209 mℓ. Solution B 2-2 Silver nitrate 961.2 g Water was added to the total quantity of 5143 mℓ. Solution C 2-2 Ossein gelatin 179 g Potassium bromide 667 g Potassium iodide 9.4 g Water was added to the total quantity of 3800 mℓ. Each six nozzles for supplying the B 2 and C 2 solutions were disposed under a stirring propeller of the mixing apparatus disclosed in Japanese Patent O.P.I. Publication No. 160128/1988. Solutions B 2-1 and C 2-1 were added to solution A 2 stirred at a high speed of 1000 rpm at 75°C by the double jet method with an addition rate increased gradually from 8.57 mℓ/min at the beginning to 24.16 mℓ/min at the final stage over a period of 135 minutes, during which pAg and pH were maintained at 8.0 and 2.0, respectively. Subsequently, solutions B 2-2 and C 2-2 were added by the double jet method over a period of 73.5 minutes. The initial and final addition rates of solution B 2-2 were 43.1 mℓ/min and 97.0 mℓ/min, respectively, and the initial and final addition rates of solution C 2-2 were 31.8 mℓ/min and 71.6 mℓ/min, respectively. pAg and pH were maintained at 9.0 and 2.0 during the addition. After completion of the addition, pH was adjusted to 6.0, and the emulsion was desalted by a conventional method. Observation via an electron microscope revealed that the grains were monodispersed and 100% twinned and that the monodispersion degree was 13% and the ratio of the grains having twinned planes of an even number was 85%. Measurement by X ray diffraction revealed that the grains had two peaks and that there existed a clear border between a high silver iodide content phase (core) and a low silver iodide content phase. The grains were found to comprise mainly {111} planes. The average aspect ratio of the grains having an even number of twinned planes was 1.9. This emulsion is designated as Em-1. Example 3 Preparation of spherical seed emulsion A monodispersed spherical seed emulsion having an average grain size of 0.34 µm and a monodispersion degree of 21% was prepared in the same manner as in Example 1 except that ripening time was changed from 5 minutes to 1 minute. Example 4 An emulsion of the present invention having an average silver iodide content of 6.0 mol% was prepared as follows: Solution A 4 Ossein gelatin 74.1 g Seed emulsion of Example 3 0.306 mol eq. Water was added to the total quantity of 4000 mℓ. Solution B 4-1 Silver nitrate 206.4 g Nitric acid (1.38) 5.5 mℓ Water was added to the total quantity of 1105 mℓ. Solution C 4-1 Ossein gelatin 44.2 g Potassium bromide 101 g Potassium iodide 60.8 g Water was added to the total quantity of 1105 mℓ. Solution B 4-2 Silver nitrate 941 g Nitric acid (1.38) 6.6 mℓ Water was added to the total quantity of 1582 mℓ. Using the same apparatus as in Example 2, an emulsion was prepared. To solution A 4 stirred at a high speed of 1000 rpm at 75°C, solutions B 4-1 and C 4-1 were added by the double jet method. The initial and final addition rates were 12.21 mℓ/min and 26.03 mℓ/min, respectively, and the addition time was 58 minutes. pAg and pH were maintained at 8.0 and 2.0, respectively, during the addition. Then, solutions B 4-2 and C 4-2 were added by the double jet method. The initial and final addition rates were 19.44 mℓ/min and 44.0 mℓ/min, respectively, and the addition time was 50 minutes. pAg and pH were maintained at 8.0 and 2.0, respectively during the addition. After completion of addition, pH was adjusted to 6.0, followed by desalting and washing. Observation via an electron microscope revealed that the grains were monodispersed and 100% twinned and that a monodispersion degree was 14% and the ratio of the grains having twinned planes of an even number was 82%. The grains having an even number of twinned planes consisted of 95% {111} planes and 5% {100} planes. The average aspect ratio of the grains having an even number of twinned planes was 1.7. Measurement by X ray diffraction revealed that the grains had two peaks corresponding to a high silver iodide content phase (core) and a low silver iodide content phase and that there existed a clear border between the two phases. This emulsion is designated as Em-2. Example 5 Silver ioidobromide emulsion Em-3 having an average silver iodide content of 9.0% was prepared in the same manner as in Example 4 except that the volume of the high iodide content phase was increased. Em-3 consisted of 100% twinned grains having a monodispersion degree of 14% and the ratio of the grains having twinned planes of an even number was 80%. The grains having an even number of twinned planes had an average aspect ratio of 1.9 and consisted of 93% {111} planes and 7% {100} planes. Example 6 The layers having the following compositions were formed on a triacetyl cellulose film support in the order from the support to prepare comparative light-sensitive material sample No. 1. In the examples below, the addition amounts are expressed in grams per m 2 unless otherwise stated. The amounts of silver halide and colloid silver are converted to silver, and those of sensitizing dyes are expressed in mole per mol of silver. Layer 1: Antihalation layer Black colloidal silver 0.2 Gelatin 0.4 UV absorber UV-1 0.3 High boiling organic solvent Oil-1 0.3 Layer 2: Interlayer Gelatin 1.0 Layer 3: First red-sensitive emulsion layer Silver iodobromide emulsion (AgI 7 mol%, octahedron, 0.3 µm) 0.6 Gelatin 1.2 Sensitizing dye S-1 8 x 10 -4 Sensitizing dye S-2 5 x 10 -4 Sensitizing dye S-3 3 x 10 -5 Coupler C-1 0.10 Coupler C-3 0.25 Colored coupler CC-1 0.04 DIR coupler D-2 0.05 High boiling organic solvent Oil-1 0.45 Layer 5: Third red-sensitive emulsion layer Em-A shown below 1.6 Gelatin 1.6 Sensitizing dye S-1 1 x 10 -4 Sensitizing dye S-2 1 x 10 -4 Sensitizing dye S-3 1 x 10 -5 Coupler C-1 0.20 Coupler C-2 0.10 Colored coupler CC-1 0.02 DIR coupler D-2 0.05 High boiling organic solvent Oil-1 0.40 Layer 6: Interlayer Gelatin 0.80 Additive SC-1 0.03 Additive SC-2 0.02 High boiling organic solvent Oil-2 0.05 Layer 7: First green-sensitive emulsion layer Silver iodobromide emulsion (AgI 7 mol%, octahedron, 0.3 µm) 0.4 Gelatin 0.8 Sensitizing dye S-4 6 x 10 -4 Sensitizing dye S-5 1 x 10 -4 Sensitizing dye S-6 1 x 10 -4 Coupler M-1 0.05 Coupler M-3 0.25 Colored coupler CM-1 0.04 DIR coupler D-1 0.06 High boiling organic solvent Oil-2 0.40 Layer 8: Second green-sensitive emulsion layer Silver iodobromide emulsion (AgI 8 mol%, octahedron, 0.7 µm) 0.8 Gelatin 1.1 Sensitizing dye S-4 3 x 10 -4 Sensitizing dye S-5 5 x 10 -5 Sensitizing dye S-6 5 x 10 -5 Coupler M-1 0.05 Coupler M-3 0.20 Colored coupler CM-1 0.03 DIR coupler D-1 0.05 High boiling organic solvent Oil-2 0.30 Layer 9: Third green-sensitive emulsion layer Em-A 1.2 Gelatin 1.1 Sensitizing dye S-4 2 x 10 -4 Sensitizing dye S-5 5 x 10 -4 Sensitizing dye S-6 5 x 10 -4 Coupler M-2 0.05 Coupler M-3 0.10 Colored coupler CM-1 0.02 DIR coupler D-1 0.02 High boiling organic solvent Oil-2 0.30 Layer 10: Yellow filter layer Yellow colloidal silver 0.05 Gelatin 1.0 Additive SC-1 0.03 Additive SC-2 0.02 High boiling organic solvent Oil-2 0.05 Layer 11: First blue-sensitive emulsion layer Silver iodobromide emulsion (AgI 7 mol%, octahedron 0.7 µm) 0.20 Gelatin 1.30 Sensitizing dye S-7 1 x 10 -3 Coupler Y-1 0.80 DIR coupler D-2 0.10 High boiling organic solvent Oil-2 0.28 Layer 12: Second blue-sensitive emulsion layer Silver iodobromide emulsion (AgI 8 mol%, octahedron, 0.7 µm) 0.50 Gelatin 0.50 Sensitizing dye S-7 5 x 10 -4 Coupler Y-1 0.60 DIR coupler D-2 0.08 High boiling organic solvent Oil-2 0.25 Layer 13: Third blue-sensitive emulsion layer Em-B shown below 0.70 Gelatin 0.70 Sensitizing dye S-7 2 x 10 -4 Coupler Y-1 0.20 DIR coupler D-2 0.01 High boiling organic solvent Oil-2 0.07 Layer 14: First protective layer Silver iodobromide (AgI 1 mol%, 0.08 µm) 0.3 Gelatin 1.0 UV absorber UV-1 0.1 UV absorber UV-2 0.1 Formalin scavenger HS-1 0.5 Formalin scavenger HS-2 0.2 High boiling organic solvent Oil-1 0.1 High boiling organic solvent Oil-3 0.1 Layer 15: Second protective layer Gelatin 0.7 Alkali-soluble matting agent (average grain size: 2 µm) 0.12 Polymethyl methacrylate (average grain size: 3 µm) 0.02 Lubricant WAX-1 0.04 Antistatic agent Su-1 0.004 In addition to these compositions, each layer contained coating aid Su-2, dispersion aids Su-2 and Su-3, hardeners H-1 and H-2, stabilizer Stab-1, antifogging agents AF-1 and AF-2 and preservative DI-1. Em-A: A monodispersed octahedral silver iodobromide emulsion having an average AgI content of 6 mol%, a high silver iodide content phase in the core, a monodispersion degree of 13% and an average grain size of 1.0 µm. Em-B: A monodispersed octahedral silver iodobromide emulsion having an average AgI content of 9 mol%, a high silver iodide content phase in the core, a monodispersion degree of 14% and an average grain size of 1.0 µm. Em-C: A tabular silver iodobromide emulsion having an average AgI content of 6 mol%, a high silver iodide content phase in the core, a monodispersion degree of 21%, an average aspect ratio of 6 and an average grain size of 1.8 µm. Em-D: A tabular silver iodobromide emulsion having an average AgI content of 9 mol%, a high silver iodide content phase in the core, a monodispersion degree of 19%, an average aspect ratio of 5 and an average grain size of 1.6 µm. The comparative light-sensitive material sample No. 2 was prepared in the same manner as in sample No. 1 except that Em-A and Em-B used in Layers 5, 9 and 13 were replaced with Em-C and Em-D as shown in Table 1. The inventive light-sensitive material samples No. 3 to 5 were prepared in the same manner as in comparative sample No. 1 except that the emulsions in Layers 5, 9 and 13 were replaced with Em-1, Em-2 and Em-3 of the invention each chemically sensitized with sodium thiosulfate, chloroauric acid and ammonium thiocyanate, as shown in Table 1. Sample Nos. 1 to 5 were each subjected to wedge exposure with white light and then to following processing: Processes (38°C) Color development 3 minutes 15 seconds Bleaching 6 minutes 30 seconds Washing 3 minutes 15 seconds Fixation 6 minutes 30 seconds Stabilization 1 minute 30 seconds Drying The compositions of the processing solutions used in the respective processes are as follows: Color developer 4-amino-3-methyl-N-ethyl-N-β-hydroxyethylaniline sulfate 4.75 g Sodium sulfite anhydrous 4.25 g Hydroxylamine 1/2 sulfate 2.0 g Potassium carbonate anhydrous 37.5 g Sodium bromide 1.3 g Trisodium nitrilotriacetate (monohydrate) 2.5 g Potassium hydroxide 1.0 g Water was added to the total quantity of 1ℓ (pH = 10.1). Water was added to the total quantity of 1ℓ, and pH was adjusted to 6.0 with aqueous ammonia. Fixer Ammonium thiosulfate 175.0 g Ammonium sulfite anhydrous 8.5 g Sodium metabisulfite 2.3 g Water was added to the total quantity of 1ℓ, and pH was adjusted to 6.0 with acetic acid. Stabilizer Formalin (37% aqueous solution) 1.5 mℓ Konidax produced by Konica Corporation 7.5 mℓ Water was added to the total quantity of 1ℓ. Fog and relative sensitivity of each sample were measured with blue, green and red light. Granularity (RMS) was determined by scanning an area having the density of fog + 0.3 with a microdensitometer having an opening scanning area of 250 µm2 and measuring a density variation. The results are shown in Table 2. As is evident from Table 2, the inventive light-sensitive materials showed remarkable improvements if fog, sensitivity and granularity in comparison with the comparative light-sensitive materials. Of the inventive light-sensitive materials, the light-sensitive materials containing the AgX grains having {100} planes had better performance.

Claims: A silver halide photographic light-sensitive material comprising a support and provided thereon photographic component layers including at least one light-sensitive emulsion layer containing a monodispersed silver halide emulsion consisting mainly of twinned silver halide grains, characterised in that the silver halide grains comprise: a. a high silver iodide core; b. an aspect ratio of not less than 1.3 to less than 2; c. mainly [111] planes; and d. parallel twin planes of an even number in a ratio of 50% or more by number based on the total twinned grains. The light-sensitive material of claim 1, characterised in that the twinned grains consist of [111] and [100] planes. The light-sensitive material of claim 2, characterised in that 60 % or more of the twinned grains consist of [111] planes. The light-sensitive material of claim 3. characterised in that 70 % to 100% of the twinned grains consist of [111] planes. The light-sensitive material of claim 4, characterised in that 75 % to 98% of the twinned grains consist of [111] planes. The light-sensitive material of claim 1, characterised in that the silver halide emulsion has a monodispersion degree of 20 % or less. provided that the monodispersion degree is defined by the following equation: Monodispersion degree = (standard deviation of grain size/average grain size) X 100 The light-sensitive material of claim 6. characterised in that the monodispersion degree is 15 % or less. The light-sensitive material of claim 1, characterised in that the silver halide emulsion comprises silver bromoiodide grains having an average silver halide content of 4 to 20 mol %. The light-sensitive material of claim 8. characterised in that the average silver halide content is 5 to 15 mol %. The light-sensitive material of claim 3, characterised in that the twinned silver halide grains have two twinned planes. A process for forming a light-sensitive material according to claim 1, characterised in that the silver halide grains are prepared by the following three steps: Step 1: forming nuclear grains having a silver iodide content of 0 to 5 mol % by adding a water-soluble silver salt solution and a water-soluble halide solution to an aqueous protective colloid solution while maintaining the pBr of the mother liquid at - 0.7 to 2.0 during at least the first half of the time necessary for forming the nuclear grains; Step 2: forming monodispersed seed grains of a twinned spherical crystal by ripening the nuclear grains in the presence of a silver halide solvent of 10 -5 to 2.0 mol per mol of silver halide; and Step 3: growing the seed grains by adding a water-soluble silver salt solution and a water-soluble halide solution, or the same in the presence of fine silver halide grains. The process according to claim 11, characterised in that the pH of the mother liquid is maintained at 1.5 to 5.8 during the formation of any portion of at least 30 % by volume of the silver halide grains. The process according to claim 11, characterised in that the pBr in Step 1 is maintained at - 0.7 to 1.5. The process according to claim 11, characterised in that the ratio of twinned nuclear grains contained in the whole nuclear grains is 50 % or more. The process according to claim 14. characterised in that the ratio is 70 % or more. The process according to claim 15, characterised in that the ratio is 90 % or more. The process according to claim 11, characterised in that the ratio of spherical seed grains contained in the whole seed grains is 60 % or more. The process according to claim 17, characterised in that the ratio is 80 % or more. The process according to claim 14, characterised in that the the silver halide solvent is at least one selected from an organic thioether, a thiourea derivative, a compound having a thiocarbonyl group between an oxygen atom or a sulfur atom and a nitrogen atom, an imidazole derivative, a sulfite salt, a thiocyanate derivative. ammonia, an ethylene diamine derivative substituted with hydroxyalkyl, a substituted mercaptotetrazole derivative, a water-soluble bromide and a benzoimidazole derivative. The process according to claim 19, characterised in that the silver halide solvent is at least one selected from an organic thioether, a thiocyanate derivative, ammonia and a water-soluble bromide. The process according to claim 20, characterised in that the silver halide solvent is a combination of ammonia and a water-soluble bromide. The process according to claim 11, characterised in that the pH and temperature in Steps 2 and 3 are 3 to 13 and 30 to 70°C respectively. The process according to claim 22, characterised in that the pH and temperature in are 6 to 12 and 30 to 70° C respectively. The process according to claim 11, characterised in that the pAg, temperature and pH in Step 3 are 5 to 11, 40 to 85 °C and 1.8 to 3.0 respectively. The process according to claim 24, characterised in that the pAg, temperature and pH are 6.0 to 9.5. 60 to 80° C and 1.8 to 3.0 respectively.

Inventors: HEKI KATSUHIKO, HOSHINO HIROYUKI, KONDOU TOSHIYA, SUZUKI KATSUHIKO, YAGI TOSHIHIKO, HEKI, KATSUHIKO, HOSHINO, HIROYUKI, KONDOU, TOSHIYA, SUZUKI, KATSUHIKO, YAGI, TOSHIHIKO, HEKI, KATSUHIKO, KONICA CORPORATION, HOSHINO, HIROYUKI, KONICA CORPORATION, KONDOU, TOSHIYA, KONICA CORPORATION, SUZUKI, KATSUHIKO, KONICA CORPORATION, YAGI, TOSHIHIKO, KONICA CORPORATION
Applicants: KONISHIROKU PHOTO IND, KONICA CORPORATION
Application year: 1990
Main classification: G03C1
IPC codes: G03C1