Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2001-05-23
2002-07-30
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S607000, C430S619000, C430S959000
Reexamination Certificate
active
06426181
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to photothermographic capture films. More specifically, it relates to photographic capture films that are intended to be developed to yield an image by the application of heat, preferably without the addition of processing solutions. Subsequent processing steps may employ liquid processing.
BACKGROUND OF THE INVENTION
Photothermographic films do not require processing solutions and instead contain within them all the chemistry required for development of a photographic image. These film chemistries are designed so that at room temperature they are inactive, leading to good raw stock keeping but at elevated temperatures (greater than 120° C.) the film chemistries become functionally active. A problem in designing such photothermographic films is that the exposure of silver halide grains at these elevated temperatures during processing can lead to fog growth and poor or unacceptable image formation.
Typical antifoggants from traditional systems when included at levels used in conventional systems are not capable of effectively restraining this fog. For example, the compound 1-phenyl-5-mercapto-tetrazole (PMT) has been extensively used in the photographic system to control fog formation and to inhibit development of silver halide crystals while in processing solution. Typical levels of PMT incorporation in conventional photographic systems are in the range of 1 to 50 mg per mole of imaging silver.
There remains a need for inhibiting fog in chromogenic photothermographic systems.
SUMMARY OF THE INVENTION
The present invention is directed to a color photothermographic element comprising at least three imaging layers comprising a blocked developer, a coupler, silver halide, and a mixture of at least two organic silver salts. In one embodiment, the first organic silver ligand exhibits a cLogP of 0.1 to 10 and a pKsp of 7 to 14 and wherein the second organic silver ligand exhibits a cLogP of 0.1 to 10 and a pKsp of 14 to 21. Both organic silver salts are present at levels above 5 g/mol of imaging silver halide. Preferably, the first organic silver salt, which may be referred to as the silver donor, which is its primary function, is present, at levels in the range of 5 to 3,000 g/mol of imaging silver halide. Preferably, the second organic silver salt, which may be referred to as the thermal fog inhibitor, which is its primary function, is present at levels in the range of 5 to 3,000 g/mol of imaging silver halide. These ranges are on the order of 250 to 150,000 times higher than levels used in conventional photographic systems.
In one embodiment of the invention, the second organic silver salt is the silver salt of a mercapto-functional compound, preferably a mercapto-heterocyclic compound at levels in the range of 5 to 3,000 g/mol of imaging silver, where it can effectively inhibit fog during thermal processing of chromogenic photothermographic films comprising a silver donor.
The use of the second organic silver salt according to the present invention has been found to (a) prevent desorption of sensitizing dyes from the imaging silver halide grains, which otherwise can lead to speed losses; (b) prevent defects in the film coatings such as surface roughness, which otherwise might occur in the presence of high levels of the mercapto-functional compound not in the form of a silver salt; and (c) allow conventional wet processing of the photothermographic material to proceed. The second organic silver salt tends to be present in the film as a solid particle dispersion.
Thus, it has been found that if the specified quantities of a mercapto-functional compound is incorporated into the photothermographic elements in the form of a dispersion of fine particles of the silver salt, a similar antifogging effect to that of the a mercapto-functional compound alone is obtained. In addition, imaging elements are obtained exhibiting higher speed and reduced coating surface roughness. Thus it is possible to obtain fog suppression with higher photographic speed as well as improved coating quality compared to equivalent quantities of the a mercapto-functional compound not present in the form of a silver salt.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to a color photothermographic element comprising at least three imaging layers comprising a blocked developer, a coupler, silver halide, and a mixture of at least two organic silver salts, wherein the first organic silver ligand exhibits a cLogP of 0.1 to 10 and a pKsp of 7 to 14 and wherein the second organic silver ligand exhibits a cLogP of 0.1 to 10 and a pKsp of 14 to 21. Both organic silver salts are present at levels above 5 g/mol of silver halide in the emulsion or imaging layer. Preferably, the first organic silver salt, which may be referred to as the silver donor, which is its primary function, is present, at levels in the range of 5 to 3,000 g/mol of imaging silver. Preferably, the second organic silver salt, which may be referred to as the thermal fog inhibitor, which is its primary function, is present at levels in the range of 5 to 3,000 g/mol of imaging silver.
The log of the partition coefficient, clogP, characterizes the octanol/water partition equilibrium of the compound in question. Partition coefficients can be experimentally determined. As an estimate, clogP values can be calculated by fragment additivity relationships. These calculations are relatively simple for additional methylene unit in a hydrocarbon chain, but are more difficult in more complex structural variations. An expert computer program, MEDCHEM, Pomona Medchem Software, Pomona College, California (ver. 3.54), permits consistent calculation of partition coefficients as the log value, clogP, from molecular structure inputs and is used in the present invention to calculate these values as a first estimate.
The activity solubility product or pK
sp
of an organic silver salt is a measure of its solubility in water. Some organic silver salts are only sparingly soluble and their solubility products are disclosed, for example, in Chapter 1 pages 7-10 of
The Theory of the Photographic Process,
by T. H. James, Macmillan Publishing Co. Inc., New Your (fourth edition 1977). Many of the organic silver salts consist of the replacement of a ligand proton with Ag+. The silver salts derived from mercapto compounds are relatively less soluble. The compound PMT has a pK
sp
of 16.2 at 25° C. as reported by Z. C. H. Tan et al.,
Anal. Chem.,
44, 411 (1972); Z. C. H. Tan,
Phototgr. Sci. Eng.,
19, 17 (1975). In comparison, benzotriazole, for example, has a pK
sp
of 13.5 at a temperature of 25° C. as reported by C. J. Battaglia,
Photogr. Sci. Eng.,
14, 275 (1970).
In the present invention, the organic silver donor is a silver salt of a nitrogen acid (imine) group, which can optionally be part of the ring structure of a heterocylic compound. Aliphatic and aromatic carboxylic acids such as silver behenate or silver benzoate, in which the silver is associated with the carboxylic acid moiety, are specifically excluded as the organic silver donor compound. Compounds that have both a nitrogen acid moiety and carboxylic acid moiety are included as donors of this invention only insofar as the silver ion is associated with the nitrogen acid rather than the carboxylic acid group. The donor can also contain a mercapto residue, provided that the sulfur does not bind silver too strongly, and is preferably not a thiol or thione compound.
Preferably, a silver salt of a compound containing an imino group can be used. Preferably, the compound contains a heterocyclic nucleus. Typical preferred heterocyclic nuclei include triazole, oxazole, thiazole, thiazoline, imidazoline, imidazole, diazole, pyridine and triazine.
The first organic silver salt may also be the derivative of a tetrazole. Specific examples include but are not limited to 1H-tetrazole, 5-ethyl-1H-tetrazole, 5-amino-1H-tetrazole, 5-4′methoxyphenyl-1H-tetrazole, and 5-4′carboxyphenyl-1H-tetrazole.
The first organic silver salt may also be a derivati
Irving Lyn M.
Irving Mark E.
Levy David H.
Chea Thorl
Eastman Kodak Company
Konkol Chris P.
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