Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Identified radiation sensitive composition with color...
Reexamination Certificate
1999-11-18
2001-02-13
Letscher, Geraldine (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Identified radiation sensitive composition with color...
C430S543000, C430S377000, C430S449000
Reexamination Certificate
active
06187526
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to color photography, and more particularly to a method to prevent the growth of micro-organisms in dispersions used to incorporate additives, in particular couplers, in silver halide photographic materials.
BACKGROUND OF THE INVENTION
In practice, color images are obtained by exposing silver halides layers, and then developing these layers using developing agents of the paraphenylenediamine type. When these agents are oxidized, in proportion to the development of the silver halides, they react with couplers to form dyes of the azomethane type. Each layer of emulsion in a color photographic material is associated with a coupler that by reaction with an oxidized paraphenylenediamine will produce a primary subtractive color, yellow, magenta or cyan, complementary to the area of sensitivity of the emulsion layer (blue, green or red, respectively). The couplers are added to the emulsion layers or to adjacent layers as solutions in heavy or oily solvents with high boiling point, dispersed in hydrophilic colloids such as gelatin or gelatin derivatives, for example phthalylated gelatin.
Additives other than couplers, for example dyes, or substituted hydroquinones such as dioctyl hydroquinone, can be added to the photographic layers by the same method. These conventional methods for the inclusion of additives are disclosed in Research Disclosure, publication 36544, September 1994, page 527.
The incorporation of some additives, such as couplers, requires auxiliary solvents that are useful during the preparation of the dispersion, but which have subsequently to be removed by any of various known means. This invention relates to dispersions in which the auxiliary solvents are removed by washing.
In general, the introduction of additives involves:
preparation of a fluid dispersion in the high boiling point solvent, the hydrophilic colloid and an auxiliary solvent;
congealing and subdivision of the chilled dispersion to obtain a high contact surface area, and the washing of this dispersion to remove the auxiliary solvent;
storage of the washed subdivided congealed dispersion; and
remelting of the dispersion for use in the preparation of a photographic layer.
Although the dispersion is stored at low temperature (below 10° C.), the presence of a hydrophilic colloid of the gelatin type favors the proliferation of micro-organisms. Such microbial growth, which is especially prevalent in summer, can spoil whole batches of dispersion. To prevent such spoilage, biocides and anti-bacterial agents have been employed. However, the use of such biocides meets the following difficulty: the biocide can be added at the time of the preparation of the dispersion, when this is fluid, but it is liable to be removed at the washing stage, leaving the dispersion unprotected during storage. If the biocide is added after washing, the dispersion has to be remelted specially for that purpose. Addition of a further step to an already complex process is not desirable.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a method to prevent the growth of micro-organisms in dispersions intended for the preparation of photographic materials. It is another object of this invention to provide a method which unexpectedly allows the biocide to be permanently incorporated in the subdivided chilled dispersion with no additional remelting step being required.
According to this invention the above objects are met by providing a method which comprises the steps of:
(1) forming a fluid dispersion that comprises a hydrophilic colloid, a high-boiling solvent, an auxiliary solvent and a photographic reagent;
(2) chilling, dividing and washing the dispersion to remove the auxiliary solvent from the dispersion.
(3) Additing an aqueous solution of at least one biocide to the washed chilled dispersion.
DETAILED DESCRIPTION OF THE INVENTION
The biocides used in this invention are hydrophilic compounds soluble in water or aqueous solvents. Aqueous solvents are here defined as mixtures containing predominantly water (more than 80% and preferably more than 90%), together with other hydrophilic constituents such as alcohols, glycols, or surfactants. Biocides meeting this criterion include for example isothiazolones, such as N-alkylisothiazolones, dithiocarbamates, the sodium salt of 1 -hydroxypyridine-2-thione, N-alkyl-4-isothiazolidones, and chlorobenzenesulfonates. The concentration of the biocides is adjusted to prevent the proliferation of micro-organisms but without adversely affecting the properties of the photographic materials.
The biocides are generally used in small amounts, from 5 to 50 ppm or more according to the biocide selected, based on the mass of the dispersion. In practice, the biocide is added in the form of a few ml of a dilute solution of biocide per kg of dispersion. In step (2) of the method, the chilled and solidified dispersion is divided into particles or noodles to obtain a large contact surface area allowing efficient washing and subsequent impregnation by the biocide solution. This division can be achieved by extruding the chilled dispersion through a perforated plate, to obtain noodles, or by any other appropriate means.
As indicated, once prepared, the dispersion comprises a permanent solvent with a high boiling point together with an auxiliary solvent, which is removed at the washing step. The auxiliary solvent is for example a solvent soluble in water, or that can be removed in an aqueous medium, and with a boiling point between 70 and 250° C., for example beta-ethoxyethyl acetate, ethyl acetate, ethyl propionate, butoxyethoxyethyl acetate, and solvents such as those defined in U.S. Pat. No. 2,949,360.
The high-boiling solvent (having a boiling point higher than about 200° C.) is for example tricresyl phosphate, dibutyl phthalate, triphenyl phosphate, n-butyl phthalate, or high-boiling point solvents of the crystalloidal type. References concerning high boiling point solvents include for example U.S. Pat. Nos. 2,322,027, 2,801,170, 3,748,141.
REFERENCES:
patent: 3396027 (1968-08-01), McFall et al.
patent: 4075022 (1978-02-01), Van Wignsberghe
patent: 4224403 (1980-09-01), Toda et al.
patent: 4490462 (1984-12-01), Kawaguchi et al.
patent: 4997752 (1991-03-01), Sasaki et al.
patent: 5055381 (1991-10-01), Abe et al.
patent: 5059516 (1991-10-01), Sato et al.
patent: 5153116 (1992-10-01), Metoki et al.
patent: 5346809 (1994-09-01), Takada et al.
patent: 5726003 (1998-03-01), Zengerle et al.
patent: 331 319 (1994-01-01), None
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Research Disclosure No. 36544, Sep. 1994, Kenneth Mason Publication, Ltd., Dudley House, 12 North Sreet, Emsworth, Hampshire P010 7DQ, England.
Japanese Abstract 9329862.
Japanese Abstract 10011739.
Japanese Abstract 9133977.
Japanese Abstract 2843867.
Research Disclosure No. 37026, vol. 370, Feb. 1995.
Fernandez-Puente Laurent G.
Paris Christian
Eastman Kodak Company
Letscher Geraldine
Meeks Roberts Sarah
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