Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2002-03-27
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
06605423
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for preparing a silver halide emulsion.
BACKGROUND AND PROBLEM TO BE SOLVED
An essential component of a photographic film is a silver halide emulsion, comprised of a dispersion of silver halide crystals dispersed in a protective colloid. To prepare this light-sensitive dispersion, the first step is to precipitate the silver halide crystals by the reaction of an aqueous solution of a silver salt (silver nitrate in most cases) with an aqueous solution of an alkali metal halide (chloride, bromide or iodide of an alkali metal). This reaction is generally carried out with an excess of halide in the presence of a hydrophilic colloid (generally gelatine or a derivatives thereof) to obtain a stable dispersion without agglomeration of the crystals so formed.
To favor this dispersion, a vigorous mechanical stirring is generally used, the effect of which is to generate foams. To avoid the generation of foam, which is troublesome when emulsions are prepared in industrial quantities, antifoaming agents are commonly used. It is now recognized that some of these antifoaming agents can interact with gelatine and lead to undesirable reactions such as the agglomeration of silver halide grains. U.S. Pat. No. 5,681,692 mentions this agglomeration effect. It is also known that certain antifoaming agents, when they are present in a photographic silver halide emulsion, can affect the sensitometric characteristics of this emulsion. In other cases, they can also affect the physical uniformity of the emulsion and so generate physical defects when the silver halide emulsion is coated on the support.
Because of the need to eliminate foaming during the precipitation of silver halide emulsions, it is not possible to avoid the use of antifoaming agents. However, after the silver halide grain precipitation stage, it would be desirable to rid the emulsion of these agents, but without creating additional complex steps in the photographic emulsion manufacturing process.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a method for preparing a silver halide photographic emulsion that overcomes the problem stated above.
The present invention relates to a method for preparing a silver halide photographic emulsion that comprises the steps of:
a) providing a nucleation medium comprising an aqueous composition based on a hydrophilic colloid and a non-ionic antifoaming agent;
b) precipitating silver halide nuclei in said nucleation medium;
c) growing said silver halide nuclei to form a silver halide photographic emulsion; and
d) removing the non-ionic antifoaming agent from the nucleation medium by contacting the silver halide photographic emulsion resulting from step c) with a material that has surface lipophilic functions.
DESCRIPTION OF PREFERRED EMBODIMENTS
The nucleation medium comprises a peptizing agent that is typically a hydrophilic colloid such as gelatine, modified gelatine, for example phthalylated gelatine, or oxidized gelatine, i.e., gelatine containing less than 30 micromoles of methionine per gram. The hydrophilic colloids that can be used in the invention are described in Research Disclosure, September 1996, n° 38957, Chapter II-A pages 598-599.
Non-ionic antifoaming agents include poly(dimethylsiloxane) derivatives, for example those cited in U.S. Pat. No. 5,837,439, polyethylene glycol dioleate (Emerest 2648®, manufactured by Henkel), polyethylene glycol ditallate (4-5 EO MAPEG 200 DT®, manufactured by PPG Specialty Chemicals), polyethylene glycol dilaurate (4-5 EO MAPEG DL®, manufactured by PPG Specialty Chemicals), SILWET L-720® (manufactured by OSI Specialties), SILWET L-722® (manufactured by OSI Specialties), together with those cited in Research Disclosure, January 1995, n° 36929, page 29.
Conventionally, the term “nucleation” designates the step between the beginning of the introduction of the reagents and the end of the introduction of the reagents, in which the nuclei of silver halide are precipitated. During this step, a significant part of the silver consumed thus serves to precipitate further grains, rather than to grow the grains already formed. Various conventional methods can be used to carry out the nucleation of silver halide grains. In single jet processes, an aqueous solution of silver salt is introduced in a stirred reactor containing a colloid, generally gelatine or one of its above-mentioned equivalents, and an aqueous solution of halides. In double jet processes, the solutions of silver and halide salts are introduced simultaneously or alternately from separate sources in a stirred reactor containing the colloid. The formation of nuclei can be carried out by simultaneous or alternate double jets or successive simple jets of silver nitrate followed by halide. In either case the growth step immediately follows, and is typically carried out by a double-jet precipitation. Growth may also be performed by the addition and ripening-out of preformed fine silver halide grains. A third type of process exists comprising first a nucleation step carried out in a first reactor by simultaneously introducing solutions of silver and, halide salts and colloid, and a growth step in a second reactor by introducing a solution of silver salt and one or more halide solutions.
The nucleation step is carried out in the presence of a mechanical stirring that in certain mixers can reach rotation rates of the order of 10,000 r.p.m. Examples of stirrers are described in Research Disclosure n° 38213, February 1996, pages 111-114 and Research Disclosure n° 38957, September 1996, Chapter I, Part C-3, page 595.
In accordance with the invention, the material that bears lipophilic functions on its surface is able to dissolve the non-ionic antifoaming agent, thereby removing it from the nucleation medium. It is theorized that the antifoaming agent is trapped by the material owing to the presence of lipophilic functions on its surface and despite the presence of a peptizing agent in the nucleation medium.
After use, the material bearing lipophilic functions on its surface can be washed with a solvent that dissolves the antifoaming agent, thereby allowing the antifoaming agent to be recovered and the material to be re-used.
In a specific embodiment of the invention, the material comprises an inert support on which lipophilic functions have been grafted by means of covalent Si—O— bonds. In this case, a support is selected that possesses active groups on its surface that will participate in the grafting of lipophilic functions thereby forming a lipophilic layer on that surface. Active groups can be created on the surface of a support by chemical treatment of the support, for example by treating the support with a base or an acid. The support can also be treated with a silicon or aluminum halide. These active groups can be acid or hydroxyl groups, preferably hydroxyl groups. To graft lipophilic functions onto this support, the support bearing the active groups on its surface is placed in contact with a compound able to both react with the active groups and supply lipophilic functions. The active groups on the support will react with this compound and so permit the grafting of lipophilic functions that will form a lipophilic layer on the surface of the support.
In one embodiment of the invention, the grafting of the layer onto the support is achieved by the “self-assembly” method, i.e., using the ability that certain chemical compounds have to self-assemble when they react on a surface. This method was described by Abraham Ulman in “Formation and Structure of self-assembled Monolayers” Chem. Rev. 1996, 96, 1553-1554.
According to the invention, the support can be organic and (or) inorganic. The organic supports that can be used are polyethylene, poly ethylene terephthalate, polyvinyl chloride, cellulosic materials, etc. The inorganic supports that can be used are for example clays, hydrotalcite, pumice, imogolite, phyllosilicates, vermiculite, glass, metals, etc. These supports can take various forms, for example films, particle
Guilment Jean
Poncelet Olivier J.
Anderson Andrew J.
Eastman Kodak Company
Le Hoa Van
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