Photographic element containing a high-dye-yield coupler for...

Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Two or more radiation-sensitive layers containing other than...

Reexamination Certificate

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C430S543000, C430S557000, C430S950000, C430S359000, C430S955000, C430S226000

Reexamination Certificate

active

06569612

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a color photographic element containing a silver-halide emulsion layer and an associated high-dye-yield coupler that comprises a parent coupler that forms a first dye with an oxidized developer and, linked to the coupling site, a releasable second dye, wherein the parent coupler contains one or more electron-withdrawing groups such that the pKa at the coupling site is less than 8.7.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 4,840,884 by Mooberry and Singer discloses high-dye-yield (HDY) couplers that react with oxidized color developer, typically in a conventional wet, alkaline, photographic process, to form one dye from the coupler parent and release a second dye or precursor of a second dye, usually a high extinction methine dye. Coupler coating loads can be decreased and/or density increases can be achieved by the use of such HDY couplers compared to ordinary two equivalent couplers. This patent (U.S. Pat. No. 4,840,884) discloses examples of hydrophilic sulfonamide solubilization of yellow couplers. In addition to incorporation of a sulfonamide in the coupler to enhance reactivity, the patent also discloses carboxyl solubilization in the dye moiety. It has been found, nevertheless, that couplers of this type, particularly those containing a coupler portion capable of forming a yellow dye upon coupling with oxidized developer, are often unsatisfactory from the standpoint of activity. Activity improvements can be obtained in couplers of this type when containing timing groups as disclosed in U.S. Pat. No. 5,447,819. These couplers have the general formula COUP— (T)
m
—L—DYE and particular solubilizing groups are incorporated in the timing group (T) to enhance reactivity. It has been found, however, that such couplers containing a timing group present other problems. In particular, such couplers have been found to cause dark-keeping problems, wherein the disclosed HDY coupler can be unstable during keeping and can be oxidized in ambient surroundings, resulting in the premature release of the DYE portion of the coupler.
U.S. Pat. No. 5,457,004 describes high dye yield couplers having methine dye chromophores. Several of the described couplers (I-4, I-5, I-46, I-57 and I-60) disclose acyloxy links between the COUP and DYE groups. All contain sulfonamide-solubilized coupler moieties. Example I-60 incorporates a carboxyl group in the dye moiety as well. The sulfonamide couplers have proved to be less active than desired toward color developer.
Improved HDY couplers have been disclosed by Mooberry et al. in U.S. Pat. No. 6,132,944. This patent discloses HDY couplers that contain a release dye bonded through an acyloxy group at the coupling site where the coupler contains an arylhydroxy, sulfamoyl or sulfonamido group of pKa less than 8.8.
PROBLEM TO BE SOLVED BY THE INVENTION
A problem to be solved is to provide a silver halide photographic element containing a HDY yellow coupler that will exhibit improved activity. By improved activity is meant an improvement in Dmax, Gamma, Drange, and/or the ratio of Drange to the laydown of coupler, wherein Drange is equal to Dmax minus Dmin. Improved activity is especially relevant to color photothermographic systems, where achieving adequate yellow dye density has been a recurrent problem. Photothermographic systems involve heat processable photosensitive elements that are constructed so that after exposure they can be processed in a substantially dry state by applying heat.
Another problem is to provide light-sensitive imaging elements having yellow, magenta and cyan dye records of comparable density-forming ability and consistent stability in all three color records. Again, this is especially relevant to color photothermographic systems, where the dye images require the reaction of a developer released from a blocked developer and a dye-forming coupler within substantially dry gelatin. It has been found that, with conventional couplers, the yellow dye records have tended to provide less density than the magenta records.
In order to solve the above-mentioned problems and thereby improve the color recording quality of photographic systems, there is a need for a photographic element containing a stable HDY yellow coupler that will exhibit a higher activity than couplers heretofore discovered. Improving the color recording quality of color photothernographic systems has been particularly challenging.
SUMMARY OF THE INVENTION
These and other problems may be overcome by the practice of our invention. Applicants have found certain HDY yellow couplers with improved activity, which couplers therefore provide dye density enhancement. In particular, Applicants have found that HDY yellow couplers that are acetanilide compounds containing one or more electron-withdrawing groups, such that the pKa at the coupling site is less than 8.7 provide improved activity, such as dye density enhancement.
In one particular embodiment of the invention, such couplers are benzoylacetanilide compounds that contain, at the coupling site, a carbamyloxy group connected to a methine releasable dye.
In another particular embodiment, it has been found advantageous to use such HDY yellow couplers in the yellow record of a photothermographic element, in association with a blocked para-phenylenediamine developer.
The invention is also directed to a new class of yellow couplers. Finally, the invention is also directed to an imaging method comprising exposing a color photographic element of the invention to light and thereafter developing the element, either by conventional photoprocessing, with a developer solution, or by heating the element in the absence of an externally applied developing agent.
DETAILED DESCRIPTION OF THE INVENTION
As indicated above, an object of the present invention is to provide improved image dye formation in color photographic elements. In one embodiment, in particular, the invention provides a chromogenic (color) photothermographic element comprising radiation sensitive silver halide, a blocked developing agent, at least one yellow coupler that forms an image dye upon reaction of said compound with the oxidation product of the unblocked developing agent, and a hydrophilic binder, wherein the yellow coupler is selected as described below, such that the pKa at the coupling site is less than the pKa at the coupling site of the the following prior art compound:
As described in the examples, the pKa at the coupling site of this compound CY-12 is 8.7, according to standard measurement. This compound is the same as compound I-4 in column 8 of U.S. Pat. No. 5,457,004, hereby incorporated by reference in its entirety. Preferably, the pKa of the present HDY coupler at the coupling site is less than or equal to 8.6 (at least 0.1 units less than the pKa at the coupling site of CY-12), preferably less than or equal to 8.5 (at least 0.2 units less than the pKa at the coupling site of CY-12), more preferably less than or equal to 8.0 (at least 0.7 units less than the pKa at the coupling site of CY-12), and most preferably less than or equal to about 7.7 (at least 1.0 unit less than the pKa at the coupling site of CY-12).
In a color photothermographic element, a blocked developer decomposes (i.e., unblocks) on thermal activation to release a developing agent that reacts with the coupler, wherein thermal activation is at a temperature of at least 60° C., preferably at least 80° C., more preferably at least 100° C. In dry processing embodiments, thermal activation preferably occurs at temperatures between about 80 to 180° C., preferably 100 to 160° C. In not completely dry development (“substantially dry”) systems, thermal activation preferably occurs at temperatures between about 60 and 140° C. in the presence of added water, which however is used in an amount that is insufficient to well fully all the imaging layers. Preferably, any added water is neither highly acidic nor highly basic, with pH between 5 and 9. In one preferred embodiment of the invention, the photothermographic element comprises at least one organic

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