Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2002-03-18
2003-08-12
Le, Hoa Van (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
Reexamination Certificate
active
06605422
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for producing a silver halide photographic emulsion for photosensitive materials.
BACKGROUND OF THE INVENTION
Silver halide photographic emulsions are usually produced by charging silver ions and halide ions in a reaction vessel equipped with a stirrer. Initial charging causes nucleation, while further addition causes crystal growth. Stirring is effected by various methods as described in Japanese Patent Application (Laid-Open) Nos. 219092/1995, 171156/1996 and 283741/1992, Japanese Patent Publication 22739/1996, and U.S. Pat. No. 3,782,954. When nucleation is caused by such methods, however, circulation of the emulsion in the reaction vessel causes nucleus formation and nucleus growth simultaneously even by adopting any one of the above-described stirring methods, thereby making it difficult to form a mono-disperse nucleus.
In the silver halide photographic fields, tabular silver halide grains having a large light receiving area as a photosensitive element have been used widely. Use of tabular silver halide grains having a small thickness is preferred in order to heighten the light receiving efficiency. The above-described process is however accompanied by such a drawback that tabular silver halide grains during growth pass through a supersaturated region in the vicinity of the adding port of silver ions or halide ions, leading to an increase in the thickness of the tabular grains.
In Japanese Patent Publication No. 82208/1995 or 23218/1995, disclosed is a countermeasure against such a drawback by disposing an external mixer outside the reaction vessel, forming silver halide fine grains in the external mixer and using them for the nucleus formation or growth step. In this process, an aqueous solution of a silver salt, an aqueous solution of a halide salt and an aqueous solution of a dispersion medium are charged in the external mixer to form fine grains continuously. These fine grains can be used for nucleus formation and/or growth. This external mixer is desired to be able to completely mix the added solutions as fast as possible. Necessity of long hours for mixing or circulation of the added solutions in the external mixer is not preferred.
As the reaction vessel, various types are usable. In U.S. Pat. No. 5,250,403 or Japanese Patent Application (Laid-Open) No. 43570/1998, mixing is conducted by a stirring blade equipped in a mixer having a small capacity. In such a process, however, the added solutions circulate inside of the mixer.
In Japanese Patent Application (Laid-Open) No. 139440/1992 or International Patent Publication No. 507255/1994, mixing is conducted without mechanical stirring so that this process is free from the problem of circulation of added solutions. This process is however insufficient in mixing power, because it does not include stirring. In order to maintain a sufficient mixing power even without mechanical stirring, a process of mixing the added solutions by making use of the kinetic energy of their jet stream has been proposed. In Japanese Patent Application (Laid-Open) No. 334848/1996, disclosed is a process for producing a silver halide photographic emulsion by using such a kinetic energy of a jet stream. This however relates to a process for producing a silver halide photographic emulsion by a single jet method and entirely differs from the process using an external mixer. Moreover, the kinetic energy used here is insufficient for complete mixing of the solutions in the reaction vessel and mechanical stirring is used in combination. In Japanese Patent Application (Laid-Open) 2000-338620, disclosed is a process of mixing an aqueous solution of a silver salt and an aqueous solution of a halide within a short time by forming at least one of these solutions into a high-speed linear jet stream. By this process, a high kinetic energy contributes to mixing and the problems of the circulation of the added solutions can be overcome, but this process involves such a drawback as unstable flow rate because high pressure is necessary for the formation of a jet stream.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a process for producing a silver halide emulsion capable of producing mono-disperse silver halide grains by using, as nuclei, small-sized, mono-disperse silver halide grains continuously formed. Another object of the present invention is to provide a process for producing a silver halide emulsion by using these mono-disperse silver halide grains for crystal growth, thereby forming thin tabular silver halide grains.
These objects can be attained by the below-described processes.
[1] A process for producing a silver halide emulsion, which comprises disposing a mixer equipped with a first channel and a second channel brought into partial contact therewith; and allowing a silver salt solution (Fluid 1) and a halide solution (Fluid 2) to pass through said first channel and said second channel, respectively, to thin said two fluids into lamellae having an open interface therebetween and having a thickness of 1 to 500 &mgr;m in a normal line direction on the contact interface, thereby diffusing, transferring and reacting silver ions and halogen ions between said two thin layers, and thus forming silver halide grains continuously.
[2] The process as described in [1], wherein the first channel and the second channel are disposed in parallel and alternately and the number of the channels is 3 or greater.
[3] A process for producing a silver halide emulsion, which comprises feeding a fine-grain silver halide emulsion prepared by a process as described in [1] or [2] to a reaction vessel for causing nucleation and/or grain growth, and thereby causing nucleation and/or grain growth in the reaction vessel.
[4] A process for preparing a silver halide emulsion, which comprises disposing at least one mixer as described in [1], in circulating loop for circulating a dispersion medium solution in a reaction vessel to the reaction vessel and outside the reaction vessel, and charging a silver salt solution and/or a halogen salt solution in mixer, thereby inducing nucleation and/or grain growth.
[5] The process as described in [3], wherein the fine grains of the silver halide emulsion has an aspect ratio of 5 or greater.
The preparation process of the present invention makes it possible to form a silver halide photographic emulsion made of tabular grains having a high aspect ratio and narrow grain size distribution.
DETAILED DESCRIPTION OF THE INVENTION
As the halide salt solution of the present invention, an aqueous solution of potassium bromide, sodium bromide, potassium chloride, sodium chloride, potassium iodide or sodium iodide or mixture thereof is generally used. When silver halide grains available by the process of the present invention are used as a nucleus, the aqueous solution preferably has a concentration of 4 mol/L or less, more preferably 1 mol/L less, with 0.2 mol/L or less being most preferred. When they are used for crystal growth, a highly concentrated aqueous solution is preferred from the viewpoint of productivity. A concentration of 0.5 mol/L or greater but not greater than 4 mol/L, more preferably 1.0 mol/L or greater is preferred. The temperature of the aqueous solution is preferably 5° C. or greater but not greater than 75° C.
It is preferred that at least one of the silver salt solution and halide salt solution of the present invention contains gelatin as a protective colloid. Gelatin has a large influence on the probability of twin crystal formation in the resulting silver halide grains so that a preferred concentration of the aqueous gelatin solution varies, depending on the using purpose of the fine silver halide grains thus formed. When continuously formed silver halide grains are used as a nucleus for the preparation of tabular silver halide grains, parallel double twin nuclei are necessary so that the concentration of the aqueous gelatin solution mus
Fuji Photo Film Co. , Ltd.
Le Hoa Van
Sughrue & Mion, PLLC
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