Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
1999-09-02
2001-04-17
Le, Hoa Van (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S567000
Reexamination Certificate
active
06218098
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a new preparation process for a silver halide photographic emulsion with high silver chloride content and cubic grains, and to the emulsion thus obtained.
BACKGROUND OF THE INVENTION
Silver halide emulsions have always been used in photographic light-sensitive materials. The preparation of silver halide grains comprises two conventional steps, a nucleation step and a growth step.
For the nucleation step, there are various conventional processes. The single-jet process comprises adding a silver halide aqueous solution into a stirred reactor containing a colloid, usually gelatin, and a halide aqueous solution. In the double-jet processes, the silver salt and halide solutions are added simultaneously or alternately from two separate sources into a stirred reactor containing the colloid. In both cases, growth is generally obtained by a double-jet precipitation.
In the conventional processes, it may be difficult to correlate the number of nuclei obtained with the final number of grains, especially because of the Ostwald ripening which favors the growth of large grains rather than small grains, due to their different solubility. For a given number of nuclei, the number of grains after growth will usually be less than the number of nuclei.
There is a third process which comprises carrying out the nucleation step inside a first reactor by simultaneously adding the silver salt solution, the halide solution and the colloid solution, and in carrying out the growth step in a second reactor by adding a silver salt solution and one or more halide solutions.
In the prior art, the preparation process for ultra-thin silver halide emulsions is well known and comprises using, for example, growth inhibitors. The Patent Application EP 431 584 describes a preparation process for an ultra-thin grain emulsion with grain size less than or equal to 0.05 &mgr;m. The preparation process for such an emulsion includes adding a silver salt solution and a halide solution into a stirred reactor containing at least one high molecular weight compound and a compound capable of adsorbing on the silver halide grains, given that the high molecular weight compound and the growth inhibitor both have a retarding effect.
U.S. Pat. No. 5,254,454 describes a preparation process of silver halide grains for photographic emulsion, wherein the nucleation step is carried out in a strongly stirred mixer (10,000 rpm) by adding a silver salt solution, a halide solution and a colloid solution. According to U.S. Pat. No. 5,254,454, a first emulsion is thus obtained which contains fine silver halide grains (size less than or equal to 0.01 &mgr;m). This first emulsion is then transferred to a reactor in which the pAg is modified. The modified emulsion is then transferred to a second reactor containing a second emulsion composed of nuclei. The nuclei contained in the second reactor will encourage, after dissolution, the growth of the fine grains of the first emulsion.
Considering the variety of silver halide photographic emulsions used in photographic materials, it would be highly preferable to have a preparation process, using a single nucleation step, of emulsions that exhibit identical or different silver halide grain size or grain size diversity.
SUMMARY OF THE INVENTION
This is the object of the present invention which relates to a preparation process for silver halide emulsion wherein at least 50% of the projected area of the emulsion grains is accounted for by high chloride cubic grains. The process comprises:
i) precipitating an intermediate emulsion comprising high chloride content cubic nuclei having an average edge length that is less than or equal to 0.07 &mgr;m, by adding to an external continuous reaction vessel at least one silver salt aqueous solution, one chloride salt aqueous solution and one hydrophilic colloid aqueous solution, under conditions where (Qgel.TGel)/(QAg.CAg) is more than 100, wherein Qgel is the flow rate of the hydrophilic colloid aqueous solution, Tgel is the hydrophilic colloid content in the hydrophilic colloid solution (g/l), QAg is the silver salt aqueous solution flow rate, CAg is the silver content of the silver salt aqueous solution (mole/l), CAg being between 0.01 and 5 mole/l, with average pCl in the external reaction vessel of between 1.7 and 3.5,
ii) continuously transferring the intermediate emulsion containing the nuclei from the external continuous reaction vessel to a storage vessel,
iii) stabilizing the nuclei by adding growth inhibitor in a quantity so that the coverage of the nuclei by the growth inhibitor is at least 20%, and
iv) growing the nuclei of the intermediate emulsion to obtain a high chloride emulsion comprising cubic grains.
The flow rate of hydrophilic colloid aqueous solution Qgel and the flow rate of silver salt aqueous solution QAg must be expressed in the same unit.
Using the process of the present invention, it is possible to obtain an intermediate emulsion comprising stabilized cubic nuclei having an average edge length less than or equal to 0.07 &mgr;m, which after growth allows a photographic emulsion to be obtained comprising larger cubic grains with high chloride content.
It is especially advantageous to be able to divide the intermediate emulsion obtained in step ii) into several parts and to carry out on each part a specific growth step. In this way from a single nucleation step several emulsions are obtained comprising cubic grains with a high silver chloride content that have various sizes and/or size variations and/or compositions.
The process of the present invention exhibits a high reproducibility and has improved robustness compared with the existing processes, because it is well known that the most delicate step for obtaining grains with a particular morphology is the nucleation step.
It is also desirable to obtain a preparation process for silver halide emulsions that has high productivity, i.e. a process capable of producing at least 0.6 moles of silver halide per liter of emulsion and per operation.
REFERENCES:
patent: 5254454 (1993-10-01), Mimiya et al.
patent: 5264338 (1993-11-01), Urabe et al.
patent: 5709990 (1998-01-01), Jezequel et al.
patent: 5723279 (1998-03-01), Jezequel
patent: 6048683 (2000-04-01), Mehta et al.
patent: 431 584 A1 (1991-06-01), None
James et al, The theory of the Photographic Process, Machi Ken Publishing Co, U.S.A. p. 1, 1977.
Jezequel Pierre-Henri
Schmuckle Christian S.
Anderson Andrew J.
Eastman Kodak Company
Le Hoa Van
Walke Amanda C.
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