CA2101564A1 - Post-processing stabilizers for photothermographic articles - Google Patents

Abstract

Abstract of the Disclosure Photothermographic compositions comprising a photographic silver halide, an organic silver salt, and a reducing agent for the organic silver salt, display improved stabilty in the presence of a compound having a nucleus of the formula:

wherein:
A represents any monovalent group for which the corresponding compound AH functions as a post-processing stabilizer, L is a -CO2- or a -CH2O- group that is lost during or after the deblocking step, with A bonded to a carbon atom of this group, and n is 0 or 1.

Description

`` 210156~

.
POST-PROCESSING STABILIZERS FOR
PHOTOT~ERMOGRAPHIC ARTICLES

FIELD OF THE INVENIION
This invention relates to photothermographic materials and in particular to post-processing stabilization of photothermographic silver-containing 10 materials.

BACKGROI~ND OF THE ~VENI~ON
Silver halide containing photothermographic imaging materials processed with heat, and without liquid development have been known in the art for many 15 years. These materials generally comprise a support having thereon a photographic light-sensitive silver halide, a light-insensitive organic silver salt, and a reducing agent for the organic silver salt.
The light-sensitive silver halide is in catalytic proximity to the light-insensitive organic silver salt so that the latent image, forrned by 20 irradiaeion of the silver halide, ~erves as a caealyst nucleus for the oxidation-reduction ~eaction of the organic silver salt with the reducing agent when the emulsion is heated above about 80- C. Such media are described, for example, in U.S. Pat. Nos. 3,457,075, 3,839,049, and 4,260,677. The silver halide may also be generated in the media by a preheating step in which halide 25 ion is released to form silver halide.
A variety of ingredients may be added to these basic components to enhance performance. For example, toning agents may be inco~porated to improve the color of the silver image of the photothermographic emulsions, as described in U.S. Pat. Nos. 3,846,136; 3,994,732 and 4,021,249. Various 30 n~ethods to produce dye images and multicolor images with photographic color couplers and leuco dyes are hlown and described in U.S. Pat. Nos. 4,022,617;

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3,531,286; 3,180,731; 3,761,270; 4,460,681; 4,883,747 and Research Disclosure, March 1989, item 29963.
A common problem that exists with phototherrnographic systems is post-processing instability of the image. The photoactive silver halide still 5 present in the developed image may continue to catalyze print-out of metallic silver during room light handling. Thus, there exists a need for stabilization of the unreacted silver halide. The addition of separate post-processing image stabilizers have been used to impart post-processing stability. Most often theseare sulfur containing compounds such as mercaptans, thiones, and thioethers as 10 described in Research Disclosure, June 1978, item 17029. U.S. Pat. Nos.
4,245,033; 4,837,141 and 4,451,561 describe sulfur compounds that are development restrainers for photothermographic systems. Mesoionic 1,2,4-triazolium-3-thiolates as fixing agents and silver halide stabilizers are described in U.S. Pat. No. 4,378,424. Substituted 5-mercapto-1,2,4-triazoles 15 such as 3-amino-5-benzothio-1,2,4-triazole as post-processing stabilizers aredescribed in U.S. Pat. Nos. 4,128,557; 4,137,079; 4,138,265, and Research Disclosure, May 1978, items 16977 and 16979.
Problems ansing from the addition of stabilizers may include thermal fogging during processing and losses irl photographic speed, maximum density 20 or contrast at effective stabilizer concentrations.
Stabilizer precursors have blocking or rnodifying groups that are usually cleaved during processing with heat and/or alkali. This provides the primary active stabilizer which can combine with the photoactive silver halide in the unexposed and undeveloped areas of the photographic material. For example, 25 in the presence of a stabilizer precursor in which the sulfur atom is unblocked upon processing, the resulting silver mercaptide will be more stable ~an the silver halide to light, atmospheric, and ambient conditions.
Various blocking techniques have been utilized in developing the stabilizer precursors. U.S. Pat. No. 3,61$1617 describes acyl blocked 30 photographically useful stabilizers. U.S. Pat. Nos. 3,674,478 and 3,993,661 describe hydroxyarylmethyl blocking groups. Benzylthio releasing groups are ., - . . ;, , ~ -. :: . - .

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described in U.S. Pat. No. 3,698,898. Thiocarbonate blocking groups are described in U.S. Pat. No. 3,791,830, and thioether blocking groups in U.S.
Pat. Nos. 4,335,200, 4,416,977, and 4,420,554. Photographically useful stabilizers which are blocked as urea or thiourea derivatives are described in S U.S. Pat. No. 4,310,612. Blocked imidomethyl derivatives are described in U.S. Pat. No. 4,350,752, and imide or thioimide derivatives are described in U.S. Pat. No. 4,888,268. Removal of all of these aforementioned blocking groups from the photographically useful stabilizers is accomplished by an increase of pH during alkaline processing conditions of the exposed imaging 10 material.
Thermally sensitive blocking groups have also been utilized. These blocking groups are removed by heating the imaging material during processing. Photographically useful stabilizers blocked as thermally sensitive carbamate derivatives are described in U.S. Pat. Nos. 3,844,~97 and 15 4,144,072. These carbamate derivatives presumably regenerate the photographic stabilizer through loss of an isocyanate. Hydroxymethyl blocked photographic reagents which are unblocked through loss of formaldehyde duAng heating are described in U.S. Pat. No. 4,510,236. Development inhibitor releasing couplers releasing tetrazolythio moieties are descAbed in U.S. Pat.
20 No. 3,70û,457. Substituted benzylthio releasing group~ are described in U.S.
Pat. No. 4,678,735. U.S. Pat. Nos. 4,351,896 and 4,404,390 utilize carboxybenzylthio blocking groups for mesoionic 1,2,4-triazolium-3-thiolate stabilizers. Photogrdphic stabilizers that are blocked by a Michael-type addition to the carbon-carbon double bond of either acrylonitAle or alkyl acrylates are 25 descAb d in U.S. Pat. Nos. 4,009,û29 and 4,511,644, ~espectively. Heating of these blocked deAvatives causes unblocking by a retro-Michael reaction.
VaAous disadvantages attend these different blocking techniques.
Highly basic solutions, that are necessary to cause deblocking of the alkali sensitive blocked deAvatives, are corrosive and irritating to the skin. With 30 photographic stabilizers that are blocked with a heat removable group, it is ofte~ found that the liberated reagent or by-product can react with other , .
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components of the imaging construction and cause adverse effects. Also, inadequate or premature release of the stabilizing moiety during heat processingmay occur.
There has been a continued need for improved post-processing 5 stabi1izers or stabilizer precursors that do not fog or desensitize phototherrnographic materials, and for stabilizer precursors that release the stabilizing moiety at the appropriate time and do not have any detrimental effects on the photosensitive material or user of said material.
Blocking groups which are removed by actinic radiation are discussed in 10 the context of organic synthesis utility in Amit et al., Israel J. Chem. 1~74, 12, 103; and V. N. R. Pillai, Synthesis, 1980, 1-26. The o-nitrobenzyl group has been known as a photocleavable blocking group for some time (J. Barltrop et al, J. Chem. Soc. Chem. Comm. 196C, 822-823.) Various substituted analogues have been prepared in order to maximize the photochemical 15 efficiency and chemical yield, and to suppress colored products of the photolysis. The o-nitrobenzyl group has been used to protect many different functional groups, including carboxylic acids, amines, phenols, phosphates, and thiols.
The o-nitrobenzyl moiety has been used in various imaging and 20 photoac~ive constructions. It has been used to block surfactants for radiation-induced tape removal as described in U.S. Pat. Nos. 4,478,967;
4,599,273; and 4,740,600; and peel-apart imaging as described in U.S. Pat.
No. 4,554,238. Nitrobenzylated acids as sources of photogenerated acid for photoresists have been extensively studied, in for example F. M. Houlihan et 25 al, Proc. SPIE-ln~. Soc. Op~. Eng. Vol. 920 (Advances in Resist Technology and Processing V~ 1988, 67-74 and references therein. Otherphotoresist applications are as follows. Nitrobenzyl groups incorporated into polyme~ic structures are described in U.S. Pat. Nos. 4,108,839; 4,576,902; 4,465,760 and 4,456,679. Photoinhibitors for photopolymers are described in BAtish Pat.
30 No. 1,547,548; German Pat. No. 2,710,417, and U.S. Pat. No. 4,477,556.
- Nitrobenzyl compounds used as photoreductants and photoinhibitors for . .. . . - . . . :. - . ~

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non-silver based photothermographic systems are described in U. S. Pat. Nos.
4,284,704; 4,273,860 and 3,880,659.
o-Nitrobenzylidene dyes have been used as photobleachable sensitizers for nitrate ion based non-silver photothermographic systems as described in 5 co-pending cases U.S. Ser. Nos. 07/539,572 and 07/754,169, and U.S. Pat.
No. 5,077,178.
In U. S. Pat. Nos. 4,343,893 and 4,501,896 the ~nitrobenzyl protecting group has been used in photographic applicationsalong with other electron-poor benzyl protecting groups to mask development image modifier 10 compounds.
U.S. Pat. No. 4,416,981 descAbes substituted benzothiazolines as photographic antifoggants but no special advantage is noted for the ~nitrobenzyl substitution.
U. S. Pat. No. 4,187,110 also describes a development inhibitor releaser 15 (DIR) coupler for conventional silver halide emulsions containing the ~nitrobenzyl functionality. In those applications as well, a photographically useful group is released from the blocking group by ~he action of processing, specifically electron transfer.
Photolytically active stabilizer precursors for photothermographic silver 20 imaging compositions which apparently release bromine atoms are descAbed in U.S. Pat. No. 4,459,350 and references cited therein.
Stabilizer precursors of the present invention are deblocked to release a stabilizer by the action of actinic radiation. Additionally, stabilizer precursors of this type can be added to photothermographic formulations without the 25 necessi~y of rebalancing the formulation to compensate for effects on sensitometry, as is often the case with other stabilizers in the art.

SVMMARY OF THE INVENIION
In one aspect this invention relates to phototherrnographic articles 30 comprising a photothermographic composition coated on a substrate wherein thephotothermographic composition comprises a photographic silver salt, an - - . - - ~ , , - . : ., . ~ .

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, 21~15'6g organic silver salt, and a reducing agent for the organic silver salt, and a stabilizer having a central nucleus of the formula:

H ,., S A--(L)n )~3 The dashed line (---) on the bridging methine group is defined as indicating that 10 the valence of the ~arbon atom of the methine group is satisfied by any conveniently selected chemical group covalently bonded to that carbon.

or a central nucleus of the formula:

~,Y
A--(L)n or a compound havirg the formula:

H~ ,y Rl A--(L)n ~/R2 2~ 3 ~4 ~ .

-. ~ . - - - . - . - . . - - .

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wherein:
A represents any monovalent group for which the corresponding compound AH functions as a post-processing stabilizer having from 1 to 50 carbon atoms, and S Y, R', R2, R3, and R4 independently represent a group selected from hydrogen, alkyl, alkoxycarbonyl, alkenyl, aryl, hydroxy, mercapto, amino, amido, thioamido, carbamoyl, thiocarbamoyl, cyano, nitro, sulfo, carboxyl, fluoro, forrnyl, sulfoxyl, sulfonyl, hydrodithio, ammonio, phosphonio, silyl, and silyloxy groups having up to 18 carbon atoms, and wherein any two of R', o R2, R3, and R4 may together form a fused ring structure with the central benzene ring, and L is a -CO2- or -CH20- group wherein A is bonded to the carbon atom of L, and wherein L is lost during or after the deblocking step, and nisOor 1.
The stabilizer precursors of the present invention may also be described as having the general formula A-T-M-Z
wherein:
A is as previously defined, and T represents a covalent bond, or a -CO2- or -CH20- group, (wherein A
is bonded to the carbon atom of this group), and M represents a carbon atom having at least one hydrogen atom, and bonded thereto Z represents an aromatic group having at least one nitro group 25 substituent in the position ortho- to the substituent A-T-M-.
Preferred stabilizer precursors are o-nitrobenzyl blocked derivatives of heterocyclic compounds that stabilize silver images. They typically comprise from about 0.01 wt% to 10 wt% of the dry photothermographi composition.
They may be incorporated directly into the silver cont~ining layer or into an 30 adJacent layer. The stabilizer precursors of the inven~on are especially useful in .
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articles and compositions for the preparation of photothermographic color and black and white images.
Photothermographic articles of the present invention are useful for color and black and white imaging applications.
S o-Nitrobenzyl blocked stabilizers of the present invention stabiliæ silver halide and/or minimize untimely leuco oxidation for improved post-processing stabilization without desensitization or fogging during heat processing.
As used herein, the term ~nitrobenzyl refers to a 2-nitrobenzyl moiety having at least one hydrogen on the benzylic carbon and one other substituent 10 which may be hydrogen, and optionally having substituents on the aromatic ring, including ring fusions, or having the benzene ring replaced by a substituted or unsubstituted polycyclic aromatic moiety.
Where the term group is used in describing substituents, substitution is anticipated on the substituent for example, alkyl group includes ether groups 15 (e.g., CH3-CH2-CH2-O-CH2-), haloalkyls, nitroalkyls, carboxyalkyls, hydroxyallyls, sulfoalkyls, etc. while the terrn alkyl includes only hydrocarbons. Substituents which react with active ingredients, such as very strongly electrophilic or oxidizing substituents, would of course be excluded asnot being inert or harmless.
As used he.ein the symbol "~" means phenyl.
The stabilizer precursors of this invention are deblocked to release the parent stabilizer by the action of actinic radiation and therefore offer the advantage over unprotected stabilizers and heat-releasable stabilizers of being inert and inactive during the processing step, and resistant to thermal release 25 during shelf aging. They are only released when they are needed. They are useful in a wide range of photothermographic media and processing conditions, since they do not appear to have specific requirements for release that attend most other masking groups in the art such as heating, acids or bases, or coupling with a reduction step.

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DETAILED DESCRIPrION OF THE INVENTION
Photothermographic articles of the present invention comprise aphotothermographic composition coated on a substrate wherein the photothermographic construction comprises a photographic silver salt, an S organic silver salt, a reducing agent for the organic silver salt, and a stabilizer having the formula:

H~ ,Y

A--(L)n ~3 or a compound of the formula:

~, y Rl A--(L)n '~/R2 02N~`~3 ~0 wherein:
A represents any monovalent group for which the corresponding compound AH functions as a post-processing stabilizer having from I to 50 carbon atoms.
Y, R1, R2, R3, and R4 independently represent a group selected from 25 hydrogen, alkyl, alkoxycarbonyl, alkenyl, aryl, hydroxy, mercapto, arnino, amido, thioamido, carbamoyl, thiocarbamoyl, cyano, nitro, sulfo, carboxyl, fluoro, chloro, bromo, formyl, sulfoxyl, sulfonyl, hydrvdithio, ammonio, phosphonio, silyl, and silyloxy groups having up to 18 carbon atoms, and wherein any two of R', R2, R3, and R~ may together form a fused ring 30 structure with the ~entral benzene ring. Preferably, Rl, R~7 R3, and R4 are 2101~

hydrogen. Y is preferably selected from hydrogen, alkyl, and alkoxycarbonyl.
More preferably Y is hydrogen.
L is a -CO2- or -CH2O- group wherein A is bonded to the carbon atom of L, and wherein L is lost during or after the deblocking step.
n is 0 or 1. Preferably n is 0.
The stabilizer precursors of the present invention may also be described as having the general for nula A-T-M-Z
wherein:
A is as previously defined, and T represents a covalent bond, or a -CO2- or -CH20- group, (with A
bonded to a carbon atom of this group) and M represents a carbon atom having at least one hydrogen atom, and bonded thereto Z represents an aromatic group having at least one nitro group substituent in the position ortho- to the substituent A-T-M-.
In photothermographic articles of the present invention the layer(s) that contain the photographic silver salt are referred to herein as emulsion layer(s).
According to the present invention the o-nitrobenzyl blocked stabilizer is added20 either to one or more emulsion layers or to a layer or layers ad3acent to one o~
more emulsion layers. Layers that are adjacent to emulsion layers may be for example, primer layers, image-receiving layers, interlayers, opacifying layers, antihalation layer, banier layer, auxiliary layers, etc.
The o-nitrobenzyl group acts as a blocking group to block the activity of 25 the primary stabilizer AH. If AH is left unblocked and added to the photothermographic emulsion at the same molar equivalent concentration as the blocked compound, AH desensitizes or fogs the emulsion. Unblocking to release the active stabili7er occurs after exposure and development, during exposure to ambient light or to light in an accelerated aging device. Thus, the 30 blocked stabilizers of the present invention overcome the problems of . . .. .
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desensitization and fogging that occur when the stabilizers are use in their unblocked form.
The substituents Y, R', R2, R3, and R4 are chosen so that the compound or a model compound in which A is replaced by H passes the S following test for photoreactivity and low background stain.
To a solution of 3 g of 7.5 weight percent polyvinyl butyral in ethanol is added a solution of 8.5 millimoles of the compound in question in 0.5 mL of ethanol or tetrahydrofuran. The resulting solution is knife-coated 3 mil thick wet on unprimed opaque polyethylene terephthalate film and dried in a 70 C convection oven for 3 minutes. Samples of the coated film are exposed to 1200 foot-candle intensity fluorescent lights in a constant temperature 26C and constant humidity (65% relative humidity~
chamber for zero, one, and six hours. The polyvinylbutyral films are peeled from the polyester. If the infrared spectra of the films show greater than ten percent loss of intensity of the nitro band at about 1520 to 1540 cm~' after light exposure for one to six hours the compound is suitable for use in the present invention. 0 Preferably o-nitrobenzyl moieties that are used in the present invention show little or no color formation in the abovementioned film after light exposure for several hours.
A is preferably attached through a nitrogen atom. Post-processing 25 stabilizing groups for stabilizing silver ion AH usually have a heteroatom such as nitrogen available for complexing silver ion. The compounds are usually ring structures with the heteroatom within the ring or external to the ring.
These compounds are well known to one ordinarily skilled in the photographic art. Examples of AH include nitrogen-containing heterocycles, substituted or 30 unsubstituted, including but not limited to benzimidazole, benzotriazole, t~iazoles, tetrazoles, phenylmercaptotetra~oles, imidazoles, pyr~olidinones or .
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any such compound that stabilizes the emulsion layer, and particularly those that have deleterious effects on the initial sensitometry or excessive fog if used unblocked. Non-limiting examples of A~ include imidazoles such as benzimidazole and benzimidazole derivatives; triazoles such as benzotriazole, 5 1 ,2,4-triazole, 3-amino-1 ,2,4-triazole, and 2-thioalkyl-5-phenyl-1 ,2,4-triazoles;
tetrazoles such as 5-amino tetrazole; triazines such as mercaptotetrahydrotriazine; piperidones; tetraazaindans; 8-azaguanine; thymine;
thiazolines such as 2-amin~2-thiazoline, indazoles; hypoxanthines;
2H-pyridooxazin-3(4H)-one and other nitrogen containing heterocycles. Many 10 of such compounds are summarized in Research Disclosure, March 1989, item 29963. AH may also be a compound which stabiliæs a leuco dye, usually a reducing agent which has an active hydrogen which can be masked by replacement with the nitrobenzyl group. An example of a useful reducing agent is l-phenyl-3-pyrazolidinone (described in U.S. Pat. No. 4,423,139 for 15 stabilizing leuco dyes). Masking of such reducing agents during the processing step is usually necessary since they may act as developers or development accelerators to cause unacceptable fogging.
In another preferred embodiment of the invention, Y represents a hydrogen, alkyl, or an alkoxycarbonyl group; Rl-R4represent hydrogen, n is 0, 20 and AH is a post-processing stabilizer identified to be most advantageous for a given photothermographic construction; for instance, l-phenyl-3-pyra~olidinone, benzotriazole, or 3-(n-hexylthio)-5-phenyl-1,2,4-triazole.
Photothermographic articles of the invention may contain other post-processing stabilizers or stabilizer precursors in combination with the 25 compounds of the invention, as well as other additives in combination with the compound of the invention such as shelf-life stabilizers, toners, development accelerators and other image modifying agents.
Non-limiting examples of o-nitrobenzyl protected stabilizer precursors are:

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P~--N/~o Ph--N~o Ph--N/ ~ ~o 02N o2N~3~NO2 ~3 Pn--N~o Ph N/~o ~--N~o H3C~ ~OCH3 02N 02N OCH3 02N ~3 N ~N ~--SC6H,3 N `N ~SC6HI3 H~c~3 o2N~3 ,N ¢~ N~,N

~ o2N

The amounts of the above described ingredients that are added to the emulsion layer according to the present invention may be varied depending upon the particular compound used and upon the type of emulsion layer ~i.e., black and white or color). However, the ingredients are preferably added in an S amount of 0.01 to 100 mol, and more preferably from 0.1 to 5û mol per mol of silver halide in the emulsion layer.

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The photothermographic dry silver emulsions of this invention may be constructed of one or more layers on a substrate. Single layer constructions must contain the silver source material, ~he silver halide, the developer and binder as well as optional additional materials such as toners, coating aids, and 5 other adjuvants. Two-layer constructions must contain the silver source and silver halide in one emulsion layer (usually the layer adjacent to the substrate) and some of the other ingredients in the second layer or both layers, although t~vo layer constructions compAsing a single emulsion layer containing all the ingredients and a protective topcoat are envisioned. Multicolor 10 photothermographic dry silver constructions may contain sets of these bilayers for each color, or they may contain all ingredients within a single layer as described in U.S. Pat. No. 4,708,928. In the case of multilayer multicolor photothermographic articles the various emulsion layers are generally maintained distinct from each other by the use of functional or non-functional 15 barrier layers between the various photosensitive layers as described in U.S. Pat. No. 4,460,681.
While not necessary for practice of the present invention, it may be advantageous to add mercury aI) salts to the emulsion layer(s) as an antifoggant. Preferred mercury (II) salts for this purpose are mercuric acetate 20 and mercuric bromide.
The light sensitive silver halide used in the present invention may typically be employed in a range of 0.75 to 25 mol percent and, preferably, from 2 to 20 mol percent of organic silver salt.
The silver halide may be any photosensitive silver halide such as silver - -25 bromide, silver iodicle, silver chloride, silver bromoiodide, silver chlorobromoiodide, silver chlorobromide, etc. The silver halide may be in any form which is photosensitive including, but not limited to cubic, orthorhombic, tabular, tetrahedral, etc., and may have epita~ial growth of crystals thereon.
The silver halide used in the present invention may be employed without 30 modification. However, it may be chemically sensitized with a chemical sensitizing agent such as a compound containing sulfur, selenium or tellurium ..
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etc., or a compound containing gold, platinum, palladium, rhodium or iridium, etc., a reducing agent such as a tin halide, etc., or a combination thereof. Thedetails of these procedures are described in T.N. James "The Theory of the Photographic Process", Fourth Edition, Chapter 5, pages 149 to 169.
S The silver halide may be added to the emulsion layer in any fashion which places it in catalytic proximity to the silver source. Silver halide and the organic silver salt which are separately formed or "prefonned" in a binder can be mixed prior to use to prepare a coating solution, but it is also effective to blend both of them in a ball mill for a long period of time. Further, it is 10 effective to use a process which comprises adding a halogen-containing compound in the organic silver salt prepared to partially convert the silver of the organic silver salt to silver halide.
Methods of preparing these silver halide and organic silver salts and manners of blending them are known in the art and described in Research Disclosure, June 1978, item 17029, and U.S. Pat. No. 3,700,458.
The use of preformed silver halide emulsions of this invention can be unwashed or washed to remove soluble salts. In the latter case the soluble saltscan be removed by chill-setting and leaching or the emulsion can be coagulation washed, e.g., by the procedures described in U.S. Pat. Nos. 2,618,5S6;
2,614,928; 2,565,418; 3~241,969; and 2,489,341. The silver halide grains may have any crystalline habit including, but not limited to cubic, tetrahedral,orthorhombic, tabular, laminar, platelet, etc.
The organic silver salt may be any organic material which contains a reducible source of silver ions. Silver salts of organic acids, particularly long chain (10 to 30 preferably 15 to 28 carbon atoms) fatty carboxylic acids are preferred. Complexes of organic or inorganic silver salts wherein the ligand has a gross stability constant between 4.0 and 10.0 are also desirable. The silver source material should preferably constitute from about 5 to 30 percent by weight of the imaging layer.
The organic silver salt which can be used in the present invention is a silver salt which is comparatively stable to light, but forms a silver image when .
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heated to 80 C or higher in the presence of an exposed photocatalyst (such as photographic silver halide) and a reducing agent.
Preferred organic silver salts include silver salts of organic compounds having a carboxy group. Non-limiting examples thereof include silver salts of 5 an aliphatic carboxylic acid and a silver salt of an aromatic carboxylic acid.Preferred examples of the silver salts of aliphatic carboxylic acids include silver behenate, silver stearate, silver oleate, silver laurate, silver caproate, silver myristate, silver palmitate, silver maleate, silver fumarate, silver tartrate, silver linolea~e, silver butyrate and silver camphorate, mixtures thereof, etc.
10 Silver salts with a halogen atom or a hydroxyl on the aliphatic carboxylic acid can also be effectively used. Preferred examples of the silver salts of aromaticcarboxylic acids and other carboxyl group-containing compounds include silver benzoate, a silver substituted benzoate such as silver 3,5-dihydroxybenzoate, silver o-methylbenzoate, silver m-methylbenzoate, silver p-methylbenzoate, 15 silver 2,4-dichlorobenzoate, silver acetamidobenzoate, silver p-phenyl benzoate, etc., silver gallate, silver tannate, silver phthalate, silver ~erephthalate, silver salicylate, silver phenylacetate, silver pyromellitate, a silver salt of 3-carboxymethyl~-methyl-4-thiazoline-2-thione or the like as described in U.S.
Pat. No. 3,785,830, and silver salt of an aliphatic carboxylic acid containing a20 thioether group as described in U.S. Pat. No. 3,330,663, etc.
Silver salts of compounds containing mercapto or thione groups and derivatives thereof can also be used. Preferred examples of these compounds include a silver salt of 3-mercapto-4-phenyl-1,2,4-triazole, a silver salt of 2-mercaptobenzimidazole, a silver salt of 2-mercapto-5-aminothiadiazole, a 25 silver salt of 2-1ethylglycolamido) benzothiazole, a silver salt of thioglycolic acid such as a silver salt of an S-allyl thioglycolic acid (wherein the alkyl group has from 12 to 22 carbon atoms), a silver salt of a dithiocarboxylic acid such as a silver salt of dithioacetic acid, a silver salt of a thioamide, a silver salt of 5-carboxylic-1-methyl-2-phenyl-4-thiopyridine, a silver salt of mercaptotriazine, 30 a silver salt of 2-mercaptobenzoxazole, a silver salt as described in U.S. Pat.
No. 4,123,274, for example, a silver salt of 1,2, 4-mercaptothiazole derivative - . , - . . . . .

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such as a silver salt of 3-amino-5-benzylthio-1,2,4-thiazole, a silver salt of thione compound such as a silver salt of 3-(2-carboxyethyl)-4-methyl-4-thiazoline-2-thioneas disclosed in U!S. Pat. No.
3,301,678.
S Furthermore, a silver salt of a compound containing an imino group may be used. Preferred examples of these compounds include silver salts of benzothiazole and derivatives thereof, for example, silver salts of benzothiazoles such as silver methylbenzotriazolate, etc., silver salt of halogen-substituted benzotriazoles, such as silver S-chlorobenzotriazolate, etc., 10 silver salts of carboimidobenzotriazole, etc., silver salt of 1,2,4-triazoles or l-H-tetrazoles as described in U.S Pat. No. 4,220,709, silver salts of imidazoles and imidazole derivatives, and the like. Various silver acetylide compounds can also be used, for instance, as described in U.S. Pat. Nos. 4,761,361 and 4,775,613.
It is also found convenient to use silver half soaps, of which an equimolar blend of silver behenate and behenic acid, prepared by precipitation from aqueous solution of the sodium salt of commercial behenic acid and analyzing about 14.5 percent silver, represents a prefelTed example.
Transparent sheet materials made on transparent film backing require a 20 transparent coating and for this purpose the silver behenate full soap, containing not more than about four or five percent of free behenic acid and analyzing about 25.2 percent silver may be used.
The method used for making silver soap dispersions is well known in the art and is disclosed in Research Disclosure, April 1983, item 22812, Research 25 Disclos~lre, October 1983, item 23419 and U.S. Pat. No. 3,985,565.
The light-sensitive silver halides may be advantageously spechally sensitized with various l~own dyes including cyanine, merocyanine, styryl, hemicyanine, oxonol, hemioxonol and xanthene dyes. Useful cyanine dyes include those having a basic nucleus, such as a thiazoline nucleus, an o~azoline30 nucleus, a pyrroline nucleus, a pyridine mlcleus, an oxazole nucleus, a thiazole nucleus, a selenazole nucleus and an imidazole nucleus. Useful merocyanine .- -- . . . .- ~

' ' . ' ' - ' : - - ' -. .-.:
, ~- .

2 101 ~ ~

dyes which are preferred include those having not only the above described basic nuclei but also acid nuclei, such as a thiohydantoin nucleus, a rhodanine nucleus, an oxazolidinedione nucleus, a thiazolidinedione nucleus, a barbituric acid nucleus, a thiazolinone nucleus, a malononitrile nucleus and a pyrazolone 5 nucleus. In the above described cyanine and merocyanine dyes, those having imino groups or carboxyl groups are particularly effective. Practically, the sensitizing dyes to be used in the present invention may be properly ælected from known dyes such as those described in U.S. Pat. Nos. 3,761,279, 3,719,~95, and 3,877,943, British Pat Nos. 1,466,201, 1,469,117 and 10 1,422,057, and can be located in the vicinity of the photocatalyit according to known methods. Spectral sensitizing dyes may be typically used in amounts of about 10~ mol to about 1 mol per 1 mol of silver halide.
The reducing agent for the organic silver salt may be any material, preferably organic material, that can reduce silver-ion to metallic silver.
15 Conventional photographic developers such as phenidone, hydroquinones, and catechol are useful but hindered phenol reducing agents are preferred. The reducing agent should be present as 1 to 10 percent by weight of the imaging layer. In multilayer constructions, if the reducing a~ent is added to a layer other than an emulsion layer, slightly higher proportions, of from about 2 to 1520 percent tend to be more desirable.
A wide range of reducing agents has been disclosed in dry silver systems including amidoximes such as phenylamidoxime, 2-thienylamidoxime and p-phenoxyphenylamidoxime, azines (e.g., 4-hydroxy-3,5-dimethoxybenzaldehydeazine); a combination of aliphatic 25 carboxylic acid aryl hydrazides and ascorbic acid, such as 2,2'-bis(hydroxymethyl)propionyl-,B-phenylhydrazide in combination with ascorbic acid; a combination of polyhydroxybenzene and hydroxylamine, a reductone and/o~ a hydrazine (e.g., a combination of hydroquinone and bis(ethoxyethyl)hydroxylarnine, piperidinohexose reductone or 30 fonnyl-4-methylphenylhydrazine); hydroxamic acids such as phenylhydroxamic acid, p-hydroxyphenylhydroxamic acid, and ~B-alaninehydroxamic acid; a : . . ... - . . . .. .
: .. , . - -, ,, ~ ' -, . .-. - : -., ~
- : . . - : - - . ~ .
. ~ . ' -'~ ~ " ' ::, -- ' ' '" : ' - ' ' . ' ' - .' ' ' . ' ' .' . . :
.

- 210~5~

combination of azines and sulfonamidophenols, (e.g., phenothiazine and 2,6-dichloro-4-benzenesulfonamidophenol); cY-cyanophenylacetic acid derivatives such as ethyl-~-cyano-2-methylphenylacetate, ethyl a-cyanophenylacetate;
bis-,B-naphthols as illustrated by 2,2'-dihydroxyl-1-binaphthyl, 5 6,6'-dibromo-2,2'-dihydroxy-1,1'-binaphthyl, and bis(2-hydroxy-1-naphthyl)methane; a combination of bis-,B-naphthol and a 1,3-dihydroxybenzene derivative, (e.g., 2,4-dihydroxybenzophenone or 2,4-dihydroxyacetophenone); 5-pyrazolones such as 3-methyl-1-phenyl-5-"razolone; reductones as illustrated by 10 dimethylaminohexose reductone, anhydrodihydroaminohexose reductone, and anhydrodihydropiperidonehexose reductone; sulfonamido-phenol reducing agents such as 2,6-dichloro-4-benzensulfonamidophenol, and p-benzenesulfonamidophenol; 2-phenylindane-1,3-dione and the like; chromans such as 2,2-dimethyl-7-t-butyl-6-hydroxychroman; 1,4-dihydropyridines such as 15 2,6-dimethoxy-3,5-dicarboethoxy-1,4-dihydrowridine; bisphenols (e.g., bis(2-hydroxy-3-t-butyl-5-methylphenyl)methane, 2,2-bis(4-hydroxy-3-methylphenyl)propane, 4,4-ethylidene-bis(2-t-butyl-6-methylphenol), and 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane); ascorbic acid derivatives (e.g., 20 1-ascorbyl palmitate, ascorbyl stearate); and unsaturated aldehydes and ketones, such as benzil and biacetyl; 3-pyrazolidones and certain indane-1,3-diones.
In addition to the aformementioned ingredients it may be advantageous to include additives known as "toners" that improve the image. Toner materials may be present, for example, in amounts from 0.1 to 10 percent by weight of 25 all silver bearing components. Toners are well known materials in the photothermographic art as shown in U.~. Pat. Nos. 3,080,254; 3,847,612 and 4,123,282.
Examples of toners include phthalimide and N-hydroxyphthalimide;
cyclic imides such as succinimide, pyrazoline-S-ones, and a quinazolinone, 30 3-phenyl-2- pyrazoline-S-one, 1-phenylurazole, quinazoline, and 2,4-thiazolidinedione; naphthalimides (e.g., N-hydroxy-1,8-naphthalimide); cobalt - ~ .
- - , -- ~

21~15~

complexes (e.g., cobaltic hexammine trifluoroacetate); mercaptans as illustratedby 3-mercapto-1,2,4-triazole, 2,4-dimercaptopyrimidine, 3-mercapto-4,5-diphenyl-1,2,4-triazole and 2,5-dimercapto-1 ,3,4-thiadiazole;
N-(aminomethyl)aryldicarboximides, (e.g., 5 (N,N-dimethylaminomethyl)phthalimide, and N,N-(dimethylaminomethyl)naphthalene-2,3-dicarboximide); and a combination of blocked pyrazoles, isothiuronium derivatives and certain photobleaching agents (e.g., a combination of N,N'-hexarnethylene bis(l-carbamoyl-3,5-dimethylpyrazole), 1,8-(3,~diazaoctane)bis(isothiuronium 10 trifluoroacetate) and 2-(tribromomethylsulfonyl)benzothiazole); and merocyanine dyes such as 3-ethyl-5[(3-ethyl-2-benzothiazolinylidene)-l-methylethylidenq-2-thio-2~4-oxazolidinedione; phthalazinone and phthalazinone derivatives or metal salts or these derivatives such as 4-(1-naphthyl)phthalazinone, 6-chlorophthalazinone, 15 5,7-dimethoxyphthalazinone, and 2,3-dihydr~1,4-phthalazinedione; a combination of phthalazinone plus sulfinic acid derivatives (e.g., phthalic acid, 4-methylphthalic acid, 4-nitrophthalic acid, and tetrachlorophthalic anhydride);quinazolinediones, benzoxazine or naphthoxazine derivatives; rhodium complexes functioning not only as tone modifiers, but also as sources of halide 20 ion for silver halide formation in situ, such as ammonium hexachlororhodate (III), rhodium bromide, rhodium nitrate and potassium hexachlororhodate (III);
inorganic peroxides and persulfates (e.g., ammonium peroxydisulfate and hydrogen peroxide); benzoxazine-2,4-dîones such as 1,3-benzoxazine-2,4-dione, 8-methyl-1,3-benzoxazine-2,4-dione, and ~nitro-1,3-benzoxazine-2,4-dione;
25 pyrimidines and asymmetric triazines (e.g., 2,4-dihydroxypynmidine, 2-hydroxy-4-aminopyrimidine), azauracils, and tetrazapentalene derivatives (e.g, 3,~dimercapt~1 ,4-diphenyl-lN,4H-2,3a,5,6a-tetraz~pentalene, and 1,4-di(o-chlorophenyl)-3,~dimercapto-lH,4H-2,3a,5,6a-tetrazapentalene).
A number of methods are known in the art for obtaining color images 30 with dry silver systems including: a combination of silver benzotriazole, well known magenta, yellow and cyan dye-forming couplers, aminophenol -, - . ' ' ' ':

2101~

developing agents, a base release agent such as guanidinium trichloroacetate andsilver bromide in poly(vinyl butyral) as described in U.S. Pat. Nos. 4,847,188 and 5,064,742; preformed dye release systems such as those described in U.S.
Pat. No. 4,678,739; a combination of silver bromoiodide, sul~onamidophenol 5 reducing agent, silver behenate, poly(vinyl butyral), an amine such as n~octadecylamine and 2-equivalent or 4-equivalent cyan, magenta or yellow dye-forming couplers; leuco dye bases which oxidize to form a dye image ~e.g., Malachite Green, Crystal Violet and para-rosaniline); a combination of in situ silver halide, silver behenate, 3-methyl-1-phenylpyrazolone and 10 N,N'-dimethyl-p-phenylenediamine hydrochloride; incorporating phenolic leuco dye reducing agents such as 2(3,5-di-(t-butyl)-4-hydroxyphenyl)-4,5-diphenylimidazole, and bis(3,5-di-(t-butyl)-4- hydroxyphenyl)phenylmethanç, incorporating azomethine dyes or azo dye reducing agents; silver dye bleach processes (for example, an 15 element comprising silver behenate, behenic acid, poly(vinyl butyral), poly(vinyl-butyral)peptized silver bromoiodide emulsion, 2,~dichloro-4-benzçnesulfonamidophenol, 1,8-(3,~diazaoctane)bis(isothiuronium-p-toluenesulfonate) and an azo dye can be exposed and heat processed to obtain a negative silver image with a uniform 20 distribution of dye, and then laminated to an acid activator sheet comprisingpolyacrylic acid, thiourea and p-toluenesulfonic acid and heated to obtain well defined positive dye images); and amines such as aminoacetanilide (yellow dye-forming), 3,3'-dimethoxybenzidine (blue dye-forming) or sulfanilide (magenta dye forming) that react with the oxidized form of incorporated 25 reducing agents such as 2,6-dichloro-4-benænesulfonamidophenol to form dye images. Neutral dye images can be obtained by the addition of amines such as behenylamine and p-anisidine.
Leuco dye oxidation in such silver halide systems for color formation is disclosed in U.S. Pat. Nos. 4,021,240, 4,374,821, 4,460,681 and 4,883,747.
Silver halide emulsions containing the stabilizers of this inventiori can be protected further against the additional production of fog and can be stabilized -~ , - -.: ~ ', '- ', - ~ ' ' , ~

. - ~ .. . - . .
... : - -- - . . .-: , 2101.~

against loss of sensitivity during shelf storage. Suitable antifoggants, stabiliærs, and stabilizer precursors which can be used alone or in combination, include thiazolium salts as described in U.S. Pat. Nos. 2,131,038 and 2,694,716;
azaindenes as descAbed in U.S. Pat. Nos. 2,886,437and 2,444,605; mercury S salts as described in U.S. Pat. No. 2,728,663; urazoles as described in U.S.
Pat. No. 3,287!135; sulfocatechols as descAbed in U.S. Pat. No. 3,235,652;
oximes as described in BAtish Pat. No. 623,448; nitrones; nitroindazoles;
polyvalent metal salts as descAbed in U.S. Pat. No. 2,839,405; thiouronium salts as descAbed in U.S. Pat. No. 3,220,839; and palladium, platinum and gold salts descAbed in U.S. Pat. Nos. 2,566,263 and 2,597,915;
halogen-substituted organic compounds as descAbed in U.S. Pat. Nos.
4,108,665 and 4,442,202; tAazines as descAbed in U.S. Pat. Nos. 4,128,557;
4,137,079; 4,138,265; and 4,459,350; and phosphorous compounds as descrAbed in U.S. Pat. No. 4,411,985.
Stabilized emulsions of the invention can contain plasticizers and lubricants such as polyalcohols (e.g., glyceAn and diols of the type described in U.S. Pat. No. 2,960,404); fatty acids or esters SUC}I as those descAbed in U.S.
Pat. No. 2,588,765 and U.S. Pat. No. 3,121,060; and silicone resins such as those descAbed in BAtish Pat. No. 955,061.
The photothermographic elements of the present invention may include image dye stabiliærs. Such image dye stabilizers are illustrated by British Pat.No. 1,326,889; U.S. Pat. Nos. 3,432,300; 3,698,909; 3,574,627; 3,573,050;
3,764,337 and 4,042,394.
Photothermographic elements containing emulsion layers stabili~ed 25 according ~o the present invention can be used in photographic elements whichcontain light absorbing mateAals and filter dyes such as those descAbed in U.S.
Pat. Nos. 3,253,921; 2,274,782; 2,527,583 and 2,~56,879. If desired, the dyes can be mordanted, for example, as described in U.S. Pat. No. 3,282,699.
Photothermographic elements containing emulsion layers stabilized as 30 descAbed herein can contain matting agents such as starch, titanium dioxide, .

:, ' .:" ':

2 1 ~

zinc oxide, silica, polymeric beads including beads of the type described in U.S. Pat. No. 2,992,101 and U.S. Pat. No. 2,701,245.
Emulsions stabilized in accordance with this invention can be used in photothermographic elements which contain antistatic or conducting layers, such.5 as layers that comprise soluble salts (e.g., chlorides, nitrates, etc.), evaporated metal layers, ionic polymers such as those described in U.S. Pat. Nos.
2,861,056 and 3,206,312 or insoluble inorganic salts such as those described in U.S. Pat. No. 3,428,451.
The binder may be selected from any of the well-known natural or 10 synthetic resins such as gelatin, polyvinyl acetals, polyvinyl chloride, polyvinyl acetate, cellulose acetate, polyolefins, polyesters, polystyrene, polyacrylonitrile, polycarbonates, and the like. Copolymers and terpolymers are of course included in these definitions. The preferred phototherrnographic silver containing polymers are polyvinyl butyral, butyl ethyl cellulose, methacrylate 15 copolymers, maleic anhydride ester copolymers, polystyrene, and butadiene-styrene copolymers.
Optionally, these polymers may be used in combinations of two or more thereof. Such a polymer is used in an amount sufficient to carry the components dispersed therein, that is, within the effective range of the action 20 as the binder. The effective range can be appropriately determined by one skilled in the art. As a guide in the case of carrying at least an organic silver salt, it can be said that a preferable ratio of the binder to the organic silver salt ranges from 15:1 to 1:2, and particularly from 8:1 to 1:1.
Photothermographic emulsions containing a stabilizer according to the 25 present invention may be coated on a wide variety of supports. Typical supports include polyester film, subbed polyester film, poly(ethylene terephthalate)film, cellulose nitrate film, cellulose ester film, poiy(vinyl acetal) film, polycarbonate film and related or resinous materials, as well as glass, paper metal and the like. Typically, a flexible support is employed, especially 3Q a paper support, which may be partially acetylated or coated with baryta and/or an a-olefin polymer, particularly a polymer of an a-olefin containing 2 to 10 :

2~0~6 ~

carbon atoms such as polyethylene, polypropylene, ethylene-butene copolymers and the like. Substrates may be transparent or opaque.
Substrates with a backside resistive heating layer may also be used in color phototherrnographic imaging systems such as shown in U.S. Pat. Nos.
5 4,460,681 and 4,374,921.
Photothermographic emulsions of this invention can be coated by various coating procedures including dip coating, air hlife coating, curtain coating, orextrusion coating using hoppers of the type described in U.S. Pat. No.
2,681,294. If desired, two or more layers may be coated simultaneously by the 10 procedures described in U.S. Pat. No. 2,761,791 and British Pat. No. 837,095.Additional layers may be incorporated into photothermographic articles of the present invention such as dye receptive layers for receiving a mobile dyeimage, an opacifying layer when reflection prints are desired, a protective topcoat layer and a primer layer as is known in the photothermographic art.
15 Additionally, it may be desirable in some instances to coat different emulsion layers on both sides of a transparent substrate, especially when it is desirable to isolate the imaging chemistries OI the different emulsion layers.
The present invention will be illustrated in detail in the following examples, but the embodiment of the present invention is not limited thereto.
EXAMPLES
The first three examples are typical synthetic procedures for compounds of the invention. E~amples 4 through 8 illustrate the utility of the invention in photothermographic imaging constructions. The scope of the invention is not 25 limited to the examples herein.
TLC means "thin layer chromatographyn.
All materials used in the following examples were readildy available from standard commercial sources such as Aldrich Chemical Co. (Milwaukee, WI) unless otherwise noted.

-2~-- ~ .. .

`' ` 1 ~ ' `
~: . . .
. : ' ': ~ ' . ' ' "

2 ~

Densitometry measurements were made on a custom built computer scanned densitometer and are believed to be comparable to measuremnts obtainable from commercially av~ilable densitometers.
The structure of compounds I-A and I-B; lI, IIA, and IIB; IIIA, IIIB, 5 and mc are shown below:

[~N [~--11 O N ~3 I-A I-B
1~

:.:
.

. .: ~ ~ -, 2101V~

HO~

Se~tizing Dye A

10 1~,o~

Leuco Dys B

N~Nl$C H N N~\SC6H~3 `NlSC6Hl3 02N f 3,No2 Il II-A II-B

. . . , . ~ ~ . . . . . . .. . . . . .

:. . . , - . : . . .
- . . , ~ . . - - ~. :
-; . -- : - - - - -:

2101~

'I) ~N ~o '1) ~ ~I) o/N~O

02N~ H3Co~;X3 CH3OC~,3 m-A m-s m-c ~tCH3)3 ,,~,,OH
O~ C(cH ) CH3CH2~ HO2CH~C~S

H~ \~

D

.. .~ .- ~ ` . .

- . - : . . .: ,-- , : : :
, ; . ~ : - :

2101~ ~

Example 1 This examp!e describes a preparation generally useful for this class of compounds and particularly shown as the preparation of 1- and 2-(o-nitrobenzyl)benzotriazole (I-A and I-B, respectively) S 2-Nitrobenzyl bromide (9.1 g) and 5 g benzotriazole were stirred together with 4.24 g triethylamine in 25 mL dichloromethane . The reaction mixture was allowed to stir for 5 hours, then extracted with dilute sodium carbonate solution and dried with magnesium sulfate, filtered, and evaporated.
The crude product (8.1 g) was recrystaUized from methanol/ethyl acetate. TLC
10 (on silica) showed two components, I-A (minor) and I-B (major). The crude product was used for examples that follow.

Example 2 This example demonstrates the preparation of compounds ~-A and II-B.
To a stirred solution of 5.00 g 3-(n-hexylthio)-5-phenyl-1,2,4-triazole (Il), 4.13 g o-nitrobenzyl bromide, and 0.310 g tetra-n-butylammonium bromide in 200 mL dichloromethane was added a solution of 4.57 g sf potassium carbonate in water. After vigorous stirring for five days, the layers were separated. The aqueous layer was washed with dichloromethane and the 20 combined organic layers washed with brine (3xlO0 mL) and dried with sodium sulfate, filtered and concentrated in vacuo ~o give 7.4 g of a light yellow oil.Chromatography on a silica gel flash column (4.6 x 15 cm dry packed and eluted with 50:50 dichloromethane-hexane) gave 4.45 g II-A and 1.22 g of a mix~ure of II-A and I~-B containing ca. 18~6 II-A. As the isomers II-A and 25 II-B were equally effective, separation was not necessary.

Example 3 This example demonstrates ~e preparation of compound m-A.
To a suspension of 4.32 g 1-phenyl-3-pyrazolidinonè in 30 mL
30 anhydrous ethanol under nitrogen was added 19 mL of 1.07 M sodium ethoxide in ethanol, and 3.08 g 2-nitrobenzyl bromide was added. After about 100 . ~; . ' . :
.... : .

2:101~g'~

minutes, TLC (in ether) showed the reaction complete. The solvent was removed in vacuo overnight. The residue was taken up in ethyl acetate, washed with aqueous sodium bicarbonate and water, and evaporated. A viscous oil (5.74 g) was obtained. The crude product was flash chromatographed with S silica gel in ether. After evaporation of solvent, 3.75 g III-A was obtained, which crystallized on standing.

Exarnple 4 A silver premix was prepared as follows: a dispersion of silver behenate 10 half soap was made at 10% solids in toluene and acetone by homogenization.
To 223.3 g of the silver half soap dispersion was added 0.34 g of polyvinyl butyral. After 15 minutes of mixing, 7.6 mL of a solution of 0.963 g mercuric acetate in 19.0 g methanol, and 21.2 mL of a solution of l.0 g calcium bromide in 49.0 g ethanol were added. Then 14.5 mL of a solution of 15 1.45 g calcium bromide in 48.5 g e~hanol was added 60 minutes later. After 60 minutes of mixing 41.2 g of polyvinylbuty~l was added.
To 29.3 g of the silver premi~ described above was added 1.47 mL of a solution of 0.021 g sensitizing dye A in 50 mL methanol.
After 30 minutes a magenta color-forming leuco dye B solution was 20 added as shown below.
C~mponent Amount LeucD Dye B 0.61 g Phthalazinone 0.916 g Tetrahydrofuran 22.4 g Methyl Ethyl Ketone 33.6 g VAGH~ (IJnion Carbide) 2.2 g ~a vinyl acetate/vinyl chloride copolymer) P~lyvinylbutyral 9.8 g .
3~

-, . . , - . . : :. , - . -- . - --,- : - .: - . - . - . . -2101~

The leuco dye B is disclosed in U.S. Pat. No. 4,795,697.
A topcoat solution was prepared consisting of 23% by weight polystyrene resin, and 3.1 wt % Acryloid B-66 (Monsanto) in approximately 50:50 mixture of toluene and methyl ethyl ketone.
To lO.Og of the magenta silver coating solution was added 0.4 mL or 0.9 mL of the mixture of I-A and I-B from Example 1, at a concentration of 0.25 g mixture in 5.0 mL of tetrahydrofuran, or 0.3 mL of benzotriazole ~BZT) at a concentration of 0.34 g in 5 mL ethanol, or 0.4 mL or 0.9 mL of o-nitrobenzyl alcohol (BA) at a concentration of 0.14 g in 5.0 mL ethanol.
The magenta silver layer and topcoat were each coated at a wet thickness of 2 mils, and dried for 5 minutes at 82C. The samples were exposed for 10-3 seconds th~ough a 58 Wratten filter and a 0 to 3 continuous wedge and developed by heating to approximately 138C for 6 seconds.
The density of magenta color for each sample was measured using a 15 green filter of a computer densitometer.
The initial sensitometric data were:

Stabilizer D""" D",~,~ Speedl Cont~ast2 ~ ~ ~
Control (0.0 mL) 0.10 1.68 2.19 1.25 0.3 mL BZT 0.10 0.11 ** **
0.4 mL BA 0.10 1.72 2.20 1.24 0.9 mL BA 0.10 1.78 2.22 1.31 0.4 mLI-A + I-B3 0.10 1.77 2.16 1.26 0.9 mLI-A + I-B 0.10 1.73 2.20 1.31 *~ In this and subsequent tables, means the value was not obtainable (i.e., no image) I Log exposure corresponding to densi~ of 0.6 above D"" ,.
~ Average contrast measured by the slope of the line joining density points 0.3 and 0.9 above D,......
3 This iS an approximate molar equivalent of the BZT parent stabilizer.

.
- . ~ -. . - . .
.. . .. .
' ~

: ,' . . ' :
..
- .

21~1~6 -~

Post-processing stability was measured by exposing imaged sarnples to 1200 ft-candles of illumination (daylight fluorescent bulbs) for 6 and 24 hours at 655'0 relative humidity and 26.7 C.

6 hours 24 hours Stabilizer D~ ""' t~D,~ D"""' ~D""~' Con~ol (0.0 mL) +.17 -.19 +.24 -.54 0.3 mL BZT +.11 ** +.11 **
0.4 mL BA +.13 -.25 +.22 -.66 0.9 mL BA +.11 -.23 +.21 -.78 0.4mLI-A + I-B +.11 -.23 +.11 -.66 0.9 mL I-A + I-B +.09 -.21 +.08 -.77 - -I ~D = DF;~ - D~,;". D values represent reflectance optical density through a green filter.

At this concentration of the primary stabilizer benwtriazole, D",~, 20 post-processing improvements were obs~rved, but significan~ desensitization of the silver halide emulsion had occurred. With the use of the masked benzotriazoles I-A ~t I-B, ~e benzotria~ole activity was adequately blocked to minimize any initial desensitization effects and yet release of BZT occurred at the appropriate time for D""" post processing improvements similar to the 25 unblocked BZT stabilizer. 2-Nitrobenzyl alcohol alone (BA) also contributes some post processing stabilization at 6 hours, but the effect is minimal after prolonged exposure to 24 hours illumination.

- - . - .. . . . . . - .
- ~
~ . . .
., -. . . - , . , . - . .: . .. . . . .
.. . .
- - - . -2101~

Example 5 To lO.Og of a magenta silver halide coating solution similar in component composition as described in Example 4, was added 0.8 mL of an isomer mixture, compounds II-A and II-B at a concentration of 0.3 g in 5.0 5 mL ethanol, or 0.8 mL of the primary stabilizer 3-(n-hexylthio)-5-phenyl-1,2,4-triazole (Il) at a concentration of 0.2 g in 5.0 mL ethanol. The silver solutions and topcoats were coated, exposed, and processed as described in Exarnple 4. The density of magenta color for each sample was measured using a green filter of a computer densitometer. The 10 initial sensitometric data are shown below.

Stabilizer D"", D""" Speedl Contrast2 Contrast3 Control (0.0 mL) .08 1.73 1.85 1.60 1.80 15 0.8 mLIIA + IIB .08 1.54 1.86 1.63 1.43 0.8 mL II .08 1.09 2.72 1.11 ~**

' Log e~posure corresponding to density of 0.6 above D~"",. -2 Average contrast me~sured by the slope of the line joining density points 0.3 and 0.9 ~bove D, 3 Average contrast measured by the slope of the liDe joining density points 0.6 and 1.20 above D . .
The post-processing print stabili~ was measured as described in 25 Example 4, and the results are shown below.
6 hours 24 hours ~D""~, AD",," D",~, aD"",~

Control (O.O mL) +.16 -.14 +.21 -.50 0.8 mL II-A + II-B +.12 -.11 +.13 -.48 0.8 mL II +.13 -.19 +.14 -.48 At this ~ncentra~on of the primary stabilizer II, D""" post-processing improvements were observed wi~ significant desensitization of the silvor halide : .
- - . , - - ~ ~ . . .

2101.~

emulsion. With the addition of an equivalent molar amount of II-A + II-B, the parent compound was adequately blocked to minimize most desensitization and yet release of the primary stabilizer II occurred at the appropriate time after processing for D~ post-processing stabilization similar to the unblocked 5 II stabilizer.

Example 6 A silver premix was prepared as follows: a dispersion of silver behenate half soap was made at 10% solids in toluene and ethanol by homogenization 10 and contained 1.5% by weight polyvinyl butyral. To 71g of this silver half soap dispersion was added 200g of ethanol. After lS minutes of mixing, 2.6 mL of a mercuric bromide solution (0. l9g in 10 mL methanol) was added.
Then an additional 2.6 mL of mercuric bromide solution(0.19g in lQ rnL
methanol) was added lS minutes later. After 60 minutes of mixing 25g of 15 polyvinyl butyral was added.
To 82.7g of the prepared silver premix described above was added a cyan color-forming leuco dye solution as shown below.

Component Amount Leuco Dye C 0. 82g Toluene 11.7g Ethyl methacrylate copolymer 2.3g (Acryloid~ B72, Rohm and Haas) FC-431~ (a fluorocarbon surfactant, 3M) 0.2 ~
Ethanol 1.21 g Preparation of leuco dye C is disclosed in U.S. Pat. No. 4,782,010.
After the addition of ~e leuco dye premix solution, 1.2 rnL of the sensitizing dye D (0.016g / 13 mL methanol + 37 mL toluene), shown above, 3Q was- added and aliQwed to sensitize for 30 minu~s.

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A topcoat solution was prepared containing approximately 17% Scripset 640~ (Monsanto, styrene/maleic anhydride copolymer), 1.1% Syloid 244~
(Monsanto, colloidal silica), 1.37% phthalic acid, 0.14% benzotriazole, and 0.44% of a fluorocarbon surfactant in an approximate 50:50 mixture of 5 methanol and ethanol.
To 15.0 g aliquots of the topcoat solution described above was added 0.182% or 0.455% by weight compound m-A, or 0.1% or 0.25% by weight l-phenyl-3-pyrazolidinone (P).
The cyan silver layer and topcoat were each coated at a wet thickness of 10 2 mils and 1.5 mils, respectively and dried for 3 minutes at 82 C. The samples were exposed for 10-3 seconds through a 25 Wratten filter and a 0 to 3 continuous wedge and developed by heating to approximately 138- C for 6 seconds.
The density of the cyan color for each sample was measured using a red 15 filter of a computer densitometer. Post-processing stability was measured by exposing imaged samples to 1200 ft. candles of illumination for 6 and 24 hours at 65% relative humidity and 26.7 C. The initial sensitometric data are shown below.

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D" ", Dmax Speed' Contrast2 ContrasP

Control (0.0) .17 2.08 1.57 1.44 1.37 S 0.1% P .77 ** ** ** **
0.25% P 1.14 ** ~* ** **
0.182% m-A .18 1.93 1.58 1.43 1.42 0.455% m-A .19 2.10 1.47 1.62 1.69 ' Log e~posure co~TespondiDg to density of 0.6 above D, 2Ave~age contrast measured by the slope of the line joiniDg density points 0.3 and 0.9 above D
3 Ave~uge contrast measured by the slope of the line joining densi~ points 0.6 and 1.20 above D . .
The post-processing print stability results are shown below.
6 hours 24 hours~D~ D""" ~D""~
Control (0.0) +.32 -.05 + .76 -.02 0.182% m-A +.30 +.04 +.69 +.08 0.455% m-~ +.30 +.04 +.67 +.03 -The addition of l-phenyl-3-pyrazolidinone increased the initial D,.....
significantly, but the addition of the blocked l-phenyl-3-pyrazolidinone m-A, at a molar amoun~ e:quivalent to the parent compound g~ve negligible effects on initial sensitometry . Small D~ o post-processing improvements were observed 30 with m-A, though l-phenyl-3-pyrazolidinone alone did not significan~y stabilize the post-processed irnage.

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Example 7 To l5.0g aliquots of the topcoat solution described in Example 6 was added 0.192% or 0.67% by weight compound m-B, which has the structure shown above.
S The silver solutions and topcoats were coated, exposed, and processed as described in Example 6. The initial sensitometric data are shown below.

Stabilizer D""~, D,~ Speedl Contrast2 Control (0.0) .15 1.81 1.90 1.43 0.192% m-B .15 1.92 1.78 1.69 0.67% m-B .15 1.90 1.74 1.90 ' Log e~posure co~espond~ng to a density of 0.6 above D
2 Average contrast messured by the slope of the l~ne joiniDg density poi~ts 0.3 and 0.9 ~bove D,.~..

The post-processing print stability was measured at 100 ft. candles of illumination for 7 and 14 days at 73% relative humidi~y and 70 C. These results are shown below.

7 days ` 14 days ~D""" ~D"",~ ~D""" ~D, _ ~
Control (0.0) +.43 +.12 +.64 +.16 0.192% m-B +.36 +.07 +.50 +.07 0.67% m-B +.35 +.Og +.50 +.06 As described in Example 6 the parent compound l~henyl-3-py~azolidinor~e greatly increased initial D~""" but an equivalent molar - 35 amount of the blocked 1-phenyl-3-pyrazolidinone m-B adequately blocked the ., ~ ..
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activity of the l-phenyl-3-pyrazolidinone to minimize initial sensitometry effects. Modest post-processing D""" improvements were observed.

.
Example 8 To a 15.0 g aliquot of topcoat solution described in Example 6 was added 0.77% by weight compound m-c.
The silver solutions and topcoats were coated, exposed and pr~cessed as described in Example 6. The initial sensitometric data are shown below.

10 Stabilizer D,~", D"",~ Speedl Contrast2 ~ . ... _ _ Control (0.0) .16 2.33 1.91 3.23 0.77~0 m-c .17 2.21 1.84 3.25 ' Log e~posure corre~ponding to density of 0.6 above D,.....
2 Average contrast malsured by the dope of the line joining 0.3 and 0.9 above D~o ".

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The post-processing stability was measured as described in Example 7 and the results are shown below.

.
Stabiliær /~D"", ~D, 1200 foot-candles 6 hours 24 hours Control (0.0) +.29 +.70 0.77%m-C +.27 +.67 100 foot-candles 7 days 14 days Control (0.0) +.45 +.67 0.77% m-c +.37 +.51 --- _ As described in Example 6 the parent compound 1-phenyl-3-pyrazolidinone greatly increased initial D",~" but an equivalent molar amount of the blocked l-phenyl-3-py~azolidinone, III-C, adequately blocked the acti~ity of the parent compound to give minimal effects on the initial 20 sensitometry. Modest post-processing D""" improvements were observed at both intensities of illumination.

Example 9 This example illustrates the effectiveness of a nitrobenzyl-protected 25 stabilizer in a mercury-free formulation.
To 200 g of a silver half soap dispersion containing preformed silver bromide crystals at 55 C was added 32 g of polyvinyl butyral. Aher 30 minutes of mixing, three portions of 55 mg of pyridinium hydrobromide perbromide in 2 mL ethanol each were added at 60 minute intervals. Finally, 30 1.3 mL 10 wt % calcium bromide in ethanol was added 30 minutes later. The mixture was incubated overnight, then 17 mL of a solution of 21 mg of sensiti~ing dye A in 100 mL metllanol was added and stinred for 30 minutes.

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To 7.0 g of the above silver dispersion was added 12.5 g of the below described magenta color-forming leuco dye B.

Com~onent Amount Leuco Dye B O.9g Phthalazir~one 1.8g Tetrahydrofuran 80.0g VAGH (Union Carbide) 2.7g (vinyl acetate/vinyl chloride copolymer~
Polyvinylbutyral 7.6g A topcoat solution was prepared consisting of lS g of 4.6% by weight cellulose acetate resin in approximately 11214 mixture of methanol, methyl ethylketone, and acetone, with 25 mg of 2,5-bis(tribromomethyl)-l-thia-3,4-diazole.
lS To 19.5g of the magenta silver coating solution was added 20 to S0 mg of the mixture of compounds I-A and I-B, as a methanol solution.
The magenta silver layer and topcoat were each coated at a wet thickness of 2 mils, and dried for 4 minutes at 77 C. The samples were exposed for 10-3 seconds through a 58 Wratten filter and a 0 to 3 continuous 20 wedge and develope~ by heating to ap~r~ximately 136 C for 14 seconds.
The density of magenta color for each sample was measured using a green filter of a cornputer densitometer. Post-processing stability was measuredby exposing imaged samples to 1200 ft-candles of illumination (daylight fluorescent bulbs) for 6 and 24 hours at 65% relative humidity and 26.7 C.
25 The initial sensitometric data a~e shown below.

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Do~n D"""~ S~eed' Contrast2 .
Control (0.0 mL) .. 11 2.19 1.23 3.90 520 mg I-A+I-B .12 2.20 1.22 3.89 30 mg I-A+I-B .11 2.20 1.20 3.76 40 mg I-A+I-B .13 2.22 1.22 4.01 50 mg I-A+I-B .12 2.21 1.22 3.84 ~ Log e~tposure corresponding to derlsity of 0.6 above D,......
2 Average contrast measured by the slope of the line joining density points 0.3 alld 0.9 above Dm 3 This iS Ul appro~ te molar equivalent of the BZT parent stAbilizer.

The post processing print stabili~ of these constructions was measured at 1200 ft candles and the results are shown below.

Stabilizer 6 hours 24 hours ~D"",1 %Fade /~D~,,,,,I %Fade ; ~ . ~ . _.
Control (0.0 mL) ~.16 11% +.26 40%
20 mg I-A+I-B +.10 13% +.14 44%
2S 30 mg I-A+][-B +.09 14% +.15 44%
40 mg I-A+]l-B +.07 12% +.11 46%
50 mg I-A+I-B +.08 15% +.11 46%

~ Final D",b, - ~iti~l D",b,. Refers to refleclance optical density throu~h a gree~ filter.

Substantial improvements in red and blue filter ~\D""" were also seen with I-A + I-B. Note that addition of this stabilizer gives no adverse effects on sensitometry.

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Examples 10-13 A silver halide-silver behenate dry soap was prepared by the procedures described in U.S. Pat. No. 3,839,049. The silver halide totalled 9~ of the total silver while silver behenate comprised 9% of the total silver. The silver 5 halide was a O.OSS micron silver bromoiodide emulsion with 2% iodide.
A photothermographic emulsion was prepared by homogenizing 300 g of the silver halide-silver behenate dry soap described above with 525 g toluene, 1675 g 2-butanone and S0 g poly(vinylbutyral) (13-76, Monsanto).
The homogenized photothermographic emulsion (500 g) and 100 g 10 2-butanone were cooled to 55F with stirring. Additional poly(vinylbutyral) 75.7 g ~76) was added and stirred for 20 minutes. Pyridinum hydrobromide perbromide (PHP, 0.45 g) was added and stirred for 2 hours. The addition of 3.25 ml of a calcium bromide solution (1 g of CaBr2 and 10 ml of methanol) was followed by 30 minutes of stirring. The temperature was raised to 70F
15 and the following were added in 15 minute increments with stirnng:
3.0 g (2-(4-chlorobenzoyl)benzoic acid, IR dye solution (D-l dye; 10.5 mg D-l in 6g dimethylformamide), 185 mg of 2-mercaptobenzimidazole in 5g methanol, 16.4 g of developer 1,1-bis(2-hydroxy-3,5-dimethylphenyl)-3,5,5-trimethylhexane, and 1.7 g 2-(tribromomethylsulfone)benzotlliazole.

(CH2)2COO- (cH2) The photothermographic emulsion wæ divided into 40g portions. The control was coated at this stage without any additions (cont~ol) as were Examples 12 and 13. Examples 10 and 11 contained equal molar levels of the 30 parent compound (BZI~ and the blocked denvative (I-A + I-B) respectively.

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The photothermographic emulsions were coated on 3 mil (0.76 x lO~m) polyester base by means of a knife coater and dried at 175F for four minutes.
The dry coating weight was 23 g/m2.
An active, protective topcoat solution-was prepared with the following 5 ingredients:
256.0 g acetone 123.0 g 2-butanone 50.0 g methanol 20.2 g cellulose acetate 2.89 g phthalazine 1.55 g 4-methylphthalic acid 1.01 g tetrachlorophthalic acid 1.50 g tetrachlorophthalic anhydride The bulk topcoat was split into 20 g portions. Equal molar levels of BZT and 15 I-A + I-B were added to the topcoat solutions for examples 12 and 13. The topcoat solutions were coated over the silver layer at a dry weight of 3.0 g/m2.The layer was dried at 175F for four minutes.
The coated materials were then exposed with a laser sensitometer incorporating a 780 nm diode. After exposure, the film strips were processed 20 at 260F for ten seconds. The images obtained were evaluated by a densitometer. Sensitometric results include Dmin, Dmax, Spd (relative speed at a density of 1.0 above Dmin versus a control wtih no added test compound set at 100) and average contrast (cont measured frorn a density of 0.25 to 2.0 above Dmin). The processed film strips were tested for print stability by 25 taping the strips to a view box (type employed by radiologists). The film strips were placed on the view box with the raw polyester side next to the view box and the silver and topcoat side out. The view box remained on during the four day test period. The Dmin values were read after the four day print stability test and are reportesl in Table 1.

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The results compiled in Table 1 show that both the parent compound BZT and the blocked version I-A + I-B greatly improve the print stability.
The blocked benzotriazole, I-A + I-B, would be preferred due to the smaller reduction in intial sensitivity.

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Claims (10)

1. A photothermographic composition comprising a photographic silver halide, an organic silver salt, and a reducing agent for the organic silver salt, and a stabilizer having a nucleus of the formula:

wherein:
A represents any monovalent group for which the corresponding compound AH functions as a post-processing stabilizer, L is a -CO2- or a -CH2O- group that is lost during or after the deblocking step, with A bonded to a carbon atom of this group, and n is 0 or 1.

2. The composition of Claim 1 wherein said stabilizer has a central nucleus of the formula and Y is selected from the group consisting of hydrogen, alkyl, alkoxycarbonyl, alkenyl, aryl, hydroxy, mercapto, amino, amido, thioamido, carbamoyl, thiocarbamoyl, cyano, nitro, sulfo, carboxyl, fluoro, formyl, sulfoxyl, sulfonyl, hydrodithio, ammonio, phosphonio, silyl, and silyloxy groups having up to 18 carbon atoms.

3. The composition of Claim 1 wherein AH is selected from the group consisting of benzimidazoles, triazoles, benzotriazoles, tetrazoles, triazines, thiazolines, 3-pyrazolidinones, indazoles, hypoxanthines, and imidazoles.

4. The composition of Claim 2 wherein AH is selected from the group consisting of benzimidazoles, triazoles, benzotriazoles, tetrazoles, 1-phenyl-3-pyrazolidinones and imidazoles.

5. The composition of Claim 2 wherein Y is selected from the group consisting of H, alkyl, and alkoxycarbonyl.

6. The composition of Claims 1, 2 or 3 adhered to a substrate is at least one layer.

7. A photothermographic composition comprising one layer or two adjacent layers coated on a substrate wherein the photothermographic composition comprises a photographic silver halide, an organic silver salt, and a reducing agent for the organic silver salt, and a compound having the formula:

wherein:
A represents any monovalent group for which the corresponding compound AH is a post-processing stabilizer, and Y, R1 R2, R3, and R4 independently represent a group selected from hydrogen, allyl, alkenyl, aryl, hydroxy, mercapto, amino, amido, thioamido, carbamoyl, thiocarbamoyl, cyano, nitro, sulfo, carboxyl, fluoro, chloro, bromo, formyl, sulfoxyl, sulfonyl, hydrodithio, ammonio, phosphonio, silyl, and silyloxy groups having up to 18 carbon atoms, and wherein any two of R', R2, R3, and R4 may together form a fused ring structure with the central benzene ring, and L is a -CO2- or a -CH2O- group, wherein A is bonded to the carbon atom of L, and n is 0 or 1.

8. The composition of Claim 7 wherein AH is selected from the group consisting of benzimidazoles, imidazoles, triazoles, benzotriazoles, piperidones, purines, indazoles, thiazolines, 3-pyrazolidinones, triazines, tetrazaindenes, hypoxanthines, and tetrazoles.

9. The composition of Claims 7 or 8 wherein Y is selected from the group consisting of hydrogen, alkyl, and alkoxycarbonyl.

10. The composition of Claims 2, 3 or 7 wherein n is 0.