POST-PROCESSING STABILIZATION OF PHOTOTHERMOGRAPHIC EMULSIONS

Field of the Invention

This invention relates to photothermographic materials and in particular to post-processing stabiliza¬ tion of dry silver systems.

Background of the Art

Silver halide photothermographic imaging materials, especially "dry silver" compositions, processed with heat and without liquid development have been known in the art for many years. Such materials"S_re a mixture of light insensitive silver salt of an organic acid (e.g. silver behenate), a minor amount of catalytic light sensitive silver halide, and a reducing agent for the silver source.

The light sensitive silver halide is in catalytic proximity to the light insensitive silver salt such that the latent image formed by the irradiation of the silver halide serves as a catalyst nucleus for the oxidation-reduction reaction of the organic silver salt with the reducing agent when heated above 80 ^β C. Such media are described in U.S. Pat. Nos. 3,457,075; 3,839,049; and 4,260,667. Toning agents can be incorporated to improve the color of the silver image of photothermographic emulsions as described in U.S. Pat. Nos. 3,846,136; 3,994,732 and 4,021,249. Various methods to produce dye images and multicolor images with photographic color couplers and leuco dyes are well known in the art as represented by U.S. Pat. Nos. 4,022,617; 3,531,286; 3,180,731; 3,761,270; 4,460,681; 4,883,747 and Research Disclosure 29963.

SHEET

A common problem that exists with these photothermographic systems is the instability of the image following processing. The photoactive silver halide still present in the developed image may continue to catalyze print-out of metallic silver even during room light handling. Thus, there exists a need for stabilization of the unreacted silver halide with the addition of separate post-processing image stabilizers or stabilizer precursors to provide the desired post-processing stability. Most often these are sulfur containing compounds such as mercaptans, thiones, thioethers and development inhibitor releasing compounds as described in Research Disclosure 17029 and U.S. Pat No. 3,700,457. Examples of stabilizer precursors in photothermographic materials are described in U.S. Pat. Nos. 3,839,041 and 3,301,678. U.S. Pat. Nos. 4,351,896 and 4,404,390 describe the use of blocked mesoionic l,2,4-triazolium-3-thiolates as silver halide stabilizer precursors in which the sulfur atom is blocked by an appropriate blocking group which is cleaved upon processing at processing temperatures to provide a moiety that combines with the photoactive silver halide in the unexposed and undeveloped areas of the photographic material. The resulting silver mercaptide is more stable than silver halide to light, atmospheric and ambient conditions. However, one of the problems with stabilizer precursors is the inadequate release of the stabilizing moiety within the desired time frame during processing.

Specifically, in connection with this invention, U.S. Pat. No. 4,245,033 describes sulfur compounds of the mercapto-type that are development restrainers of photothermographic systems. The use of substituted 5-mercapto-l,2,4-triazoles with immobilizing groups that are of a ballasting polymer type or hydrophilic in nature such as sulfo, hydroxyl, carboxyl or sulfinic acid as development restrainers are also described in U.S. Pat. No. 4,837,141. 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-mβrcapto-l,2,4-triazoleε such as

3-amino-5-benzothio-l,2,4-triazole as post-processing stabilizers are described in U.S. Pat. No. 4,128,557; 4,137,079; 4,138,265, and Research Disclosures 16977 and 16979. U.S. Pat. No. 4,451,561 describes amido derivatives of 5-mercapto-l,2,4-triazoles as development restrainers.

Some of the problems with these stabilizers include thermal fogging during processing or losses in photographic sensitivity, maximum density or contrast at stabilizer concentrations in which stabilization of the post-processed image can occur. Thus, there has been a continued need for improved post-processing stabilizers which stabilize the photoactive silver halide for post-processing stabilization without desensitizing or fogging the photographic materials.

Summary of the Invention

According to this invention, the incorporation of 3-substituted-5-alkylthio-l,2,4-triazoles to the photothermographic emulsion layer or layer adjacent to the emulsion layer stabilizes the photoactive silver halide for improved post-processing stabilizing without desensitizing or fogging the heat developable photographic material and process. These compounds are described in Formula I:

wherein R ¹ is H, an alkyl group, an electron withdrawing group such as halogen or as a substituted or unsubstituted aryl containing 6 to 14 carbons, preferably a phenyl or alkyl containing 1 to 20 carbons preferably 1 to 15 carbon atoms. The alkyl may be highly substituted as with N0 ₃ , F, Cl, Br, OH and the like, with highly fluorinated or perfluorinated alkyl being particularly desirable and n - 0 to 20, preferably n « 1 to 15.

It is another aspect of the present invention that excellent preservability occurs in both developed post-processed image and the unexposed photothermographic layer (shelf-aging) in the photothermographic element without desensitization of the element or the processed image.

Detailed Description of the Invention

The addition of the 3-substituted-5-alkylthio-l,2,4-triazoles present in a silver halide photothermographic emulsion or the adjacent layer to the emulsion provides the emulsion with improved post-processing stability and unprocessed Dmin stability without fogging or desensitizing said emulsion.

The triazole may be generally represented by the formula II

wherein R represents an alkyl group (preferably of 1 to 20 carbon atoms, more preferably 1 to 15 carbon atoms) and Q is H, an alkyl group or an electron-withdrawing group, and even halogen. Q preferably is an alkyl group (preferably 1 to 20 carbon atoms, more preferably 1 to 15 carbon atoms), aryl group (up to 25 carbon atoms, e.g., phenyl

group), and these alkyl or aryl groups may be substituted with various moieties such as nitro, amino, hydroxyl, ^" fluorine, chlorine, bromine, carboxyl, carboxyl ester and the like. The Q group is preferably at least as electron withdrawing as CH ₃ (CH ₂ ) _i9 -. Q may be represented by the formula:

(H) _# (CX ₃ ),(CH ₂ ) _b (CH ₃ ) _C (CH ₂ ) _d -

wherein

X comprises halogen atoms, a is 0 or 1, b is 0 or between 1 and 6, c is 0 or between 1 and 20, d is 0 or between 1 and 6, e is 0 when a is 1 and e is 1 when a is 0, a plus c is at least 1, and b plus d is no more than 6 and wherein X may be F, Cl, or Br, preferably at least 50% of X is F, more preferably at least 90% is F, and most preferably all X is F. The tauto eric form of structural formula II is also included within the formula. In that structure the external hydrogen is shifted to the adjacent nitrogen atom and the double bonds shift to accommodate the positioning of the hydrogen atom.

Specific examples of the 3-substituted-5- alkylthio-l,2,4-triazoles are shown by the formulae below, which, however does not limit the compounds to be used in the present invention.

H

/

N-N

H ₅ C ₆ -^ _/ )—SC ₁₂ H ₂ I-B

¹ 25

N

H

H ₅ C ₆ -^ Λ—SC ₂ H ₅ I-C

N

H

N-N ^/ I-D

N

These exemplified compounds may be readily synthesized by the reaction of 3-substituted-5-mercapto- 1,2,4 triazoles with an alkylbromide as shown below.

Synthesis of Compound I-A (3-phenyl-5-hexylthio-1,2,4-lH-triazole)

0.1 moles (9.1 g) of thiosemicarbazide were put in 24 ml of sodium methylate (30%) and 75 ml of methanol were added.

0.1 moles (15 g) of ethyl benzoate were added and the mixture was refluxed for 16 hours.

The solvent was distilled and the mixture was added with 150 ml of water; after 10 minutes stirring, concentrated hydrochloric acid was added to pH-1, and the mixture was stirred for 3 hours.

The product was filtered off, dried and crystallized with methanol/water mixture (50/50);

yield-85% of 3-phenyl-5-mercapto-l,2, -lH-triazole.

0.03 moles (5.31 g) of 3-phenyl-5-mercapto-l,2,4-triazole were put in 50 ml of methanol with 0.03 moles of KOH; the mixture was stirred until a clear solution.

0.03 moles (4.23 ml) of hexyl bromide were added and the mixture was refluxed for 24 hours; the salt was filtered off, and the solvent was distilled to obtain a dry oil. 40 ml of methanol was added and the mixture was heated for 20 minutes.

After cooling under stirring for 10 hours, the precipitate was filtered off to obtain 6.1 g of pure compound; yield was 80%.

The amounts of the above described compounds (I-A, I-B, I-C and I-D) according to the present invention which are added can be varied depending upon the particular compound used and upon the photothermographic emulsion type. However, they are preferably added in an amount of 10 ^"3 to 10 mol, and more preferably from 10 ^"2 to 5 mol, per mol of silver halide in the emulsion laye.r.

The photothermographic dry silver emulsions of this invention may be constructed of one or more layers on a substrate. Single layer constructions may contain the silver source material, the silver halide, the developer and binder as well as optional additional materials such as toners, coating aids and other adjuvants. Two-layer constructions must contain the silver source and silver halide in one emulsion layer (usually the layer adjacent the substrate) and some of the other ingredients in the second layer or both layers.

Multicolor photothermographic dry silver constructions contain sets of these bilayers for each color. Color forming layers are maintained distinct from each other by the use of functional or non-functional barrier layers between the various photosensitive layers as described in U.S. Pat. No. 4,460,681.

E SHEET

The silver source material, as mentioned above, may be any 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 constitutes from about 5 to 30 percent by weight of the imaging layer. The second layer in a two layer construction or in the bilayer of a multi-color construction would not affect the percentage of the silver source material desired in the photosensitive single imaging layer.

The organic silver salt which carfΗ_e used in the present invention is a silver salt which is comparatively stable to light, but forms a silver image when heated to 80 ^β C or higher in the presence of an exposed photocatalyst (such as silver halide) and a reducing agent.

Suitable organic silver salt include silver salts of organic compounds having a carboxy group. Preferred examples thereof include a silver salt of 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 caprate, silver myristate, silver pal itate, silver maleate, silver fumarate, silver tartarate, silver furoate, silver linoleate, silver butyrate and silver camphorate, mixtures thereof, etc. Silver salts which are suitable with a halogen atom of a hydroxyl group can also be effectively used. Preferred examples of the silver salts of aromatic carboxylic acid 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, silver 2,4-dichlorobenzoate , silver aceta idobenzoate, silver

p-phenyl benzoate, etc., silver gallate, silver tannate, silver phthalate, silver terephthalate, silver salicylate, silver phenylacetate, silver pyromellitate, a silver salt of 3-carboxymethyl-4-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 a thio- ether 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 be used. Preferred examples of these compounds include a silver salt of 3-mercapto-4-phenyl-l,2,4-triazole, a silver salt of 2-mercaptobenzimidazole, a silver salt of 2-mercapto-5- aminothiadiazole, a silver salt of 2-( s-ethylglycolamido) benzothiazole, a silver salt of thioglycoTfc acid such as a silver salt of a S-alkyl thioglycolic acid (wherein the alkyl group has from 12 to 22 carbon atoms) as described ^• in Japanese patent application No. 28221/73, a silver salt of a dithiocarboxylic acid such as a silver salt of dithioacetic acid, a silver salt of thioamide, a silver salt of 5-carboxylic-l-methyl-2-phenyl-4-thiopyridine , a silver salt of mercaptotriazine, a silver salt of 2-roercaptobenzoxazole, a silver salt as described in U.S. Pat. No. 4,123,274, for example, a silver salt of 1,2,4-mercaptothiazole derivative such as a silver salt of 3-amino-5-benzylthio-l,2, 4-thiazole, a silver salt of thione compound such as a silver salt of 3-(2-carboxyethyl )-4-methyl-4-thiazoline-2-thione as disclosed in U.S. Pat. No. 3,301,678.

Furthermore, a silver salt of a compound containing an iraino group can be used. Preferred examples of these compounds include a silver salt of benzothiazole and a derivative thereof as described in Japanese patent publications Nos. 30270/69 and 18146/70, for example, a silver salt of benzothiazole such as silver salt of methylbenzotriazole, etc., a silver salt of a halogen substituted benzotriazole , such as a silver salt of 5-chlorobenzotriazole, etc., a silver salt of

TE SHEET

carboimidobenzotriazole, etc., a silver salt of 1,2,4-triazole, of 1-H-tetrazole as described in U.S. Pat. No. 4,220,709, a silver salt of imidazole and an imidazole derivative, and the like.

It is also found convenient to use silver halfsoaps, 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 preferred example. Transparent sheet materials made on transparent film backing require a transparent coating and for this purpose the silver behenate full soap, containing not more than about four or 5 percent of free behenic acid and analyzing about 25.2 percent silver mayHse used.

The method used for making silver soap dispersions is well known in the art and is disclosed in Research Disclosure April 1983 (22812), ibid October 1983 (23419) and U.S. Pat. No. 3,985,565.

The light sensitive silver halide used in the present invention can be employed in a range of 0.0005 mol to 5 mol and, preferably, from 0.0005 mol to 1.0 mol per mol of organic silver salt.

The silver halide may be any photosensitive silver halide such as silver bromide, silver iodide, silver chloride, silver bromoiodide, silver chlorobromoiodide, silver chlorobromide, etc.

The silver halide used in the present invention may be employed without modification. However, it may be chemically sensitized with a chemical sensitizing agent such as a compound containing sulphur, selenium or tellurium 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. The details of these procedures are described in T.H. James "The Theory of the Photographic Process", Fourth Edition, Chapter 5, pages 149 to 169.

The silver halide may be added to the emulsion layer in any fashion which places it in catalytic proximity to the silver source.

The silver halide and the organic silver salt which are separately formed 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 effective to use a process which comprises adding a halogen-containing compound in the organic silver salt prepared to partially convert convert the silver of the organic silver salt to silver halide.

Methods of preparing these silver halide and organic silver salts and manners of blendirg them are described in Research Disclosures, No. 170-29, Japanese patent applications No. 32928/75 and 42529/76, U.S. Pat. No. 3,700,458, and Japanese patent applications Nos. 13224/74 and 17216/75.

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 salts can be removed by chill-setting and leaching or the emulsion can be coagulation washed, e.g., by the procedures described in Hewitson, et al., U.S. Pat. No. 2,618,556; Yutzy et al., U.S. Pat. No. 2,614,928; Yackel, U.S. Pat. No. 2,565,418;; Hart et al., U.S. Pat. No. 3,241,969; and Waller et al., U.S. Pat. No. 2,489,341. The silver halide grains may have any crystalline habit including, but not limited to cubic, tetrahedral, orthorhombic, tabular, laminar, platelet, etc.

Photothermographic emulsions containing preformed silver halide in accordance with this invention can be sensitized with chemical sensitizers, such as with reducing agents; sulfur, selenium or tellurium compounds; gold, platinum or palladium compounds, or combinations of these. Suitable chemical sensitization procedures are described in Shepard, U.S. Pat. No. 1,623,499; Waller,

U.S. Pat. No._ 2,399,083; McVeigh, U.S. Pat. No. 3,297,447; and Dunn, U.S. Pat. No. 3,297,446.

The light-sensitive silver halides can be spectrally sensitized with various known dyes include cyanine, styryl, hemicyanine, oxonol, hemioxonol and xanthene dyes. Useful cyanine dyes include those having a basic nucleus, such as a thiazoline nucleus, an oxazoline nucleus, a pyrroline nucleus, a pyridine nucleus, an oxazole nucleus, a thiazole nucleus, a selenazole nucleus and an imidazole nucleus. Useful merocyanine 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 thiazolidinediohe nucleus, a barbituric acid nucleus, a thiazolinone nucleus, a malonitrile nucleus and a pyrazolone 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 is properly selected from known dyes as described in U.S. Pat. No. 3,761,279, 3,719,495 and 3,877,943, British Pat Nos. 1,466,201, 1,469,117 and 1,422,057, Japanese Patent Application (OPI) Nos. 27924/76 and 156424/75, and so on, and can be located in the vicinity of the photocatalyst according to known methods used in the above-described examples. These spectral sensitizing dyes are used in amounts of about 10 ^{" 4} mol to about 1 mol per 1 mol of photocatalyst.

The reducing agent for silver ion may be any material, preferably organic material, which will reduce silver ion and metallic silver. 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 a two-layer construction, if the reducing agent is in the second layer, slightly high proportions, of from about 2 to 15 percent tend to be more desirable.

A wide range of reducing agents have been disclosed in dry silver systems including amidoximes such as phenylamidoxime, 2-thienylamidoxime and p-phenoxy- phenylamidoxime, azine, e.g., 4-hydroxy-3 , 5-dimethoxy- benzaldehyde azine; a combination of aliphatic carboxylic acid aryl hydrazides and ascorbic acid, such as 2,2-bis(hydroxymethyl )propionyl-beta-phenyl hydrazide in combination with ascorbic acid; a combination of polyhydroxybenzene and hydroxylamine, a reductone and/or a hydrazine, e.g., a combination of hydroquinone and bis(ethoxyethyl)hydroxylamine, piperidinohexose reductone or formyl-4-methylphenyl hydrazine, hydroxamic acids such as phenylhydroxamic acid, p-hydroxyphenyl hydroxamic acid, and beta-alanine hydroxamic acid; a combination of azines and sulphonamidophenols, e.g., phenothiazine and 2,6-dichloro-4-benzenesulphonamidophenol; alpha-cyanophenylacetic acid derivatives such as ethyl-alpha-cyano-2-methylphenylacetate, ethyl alpha-cyanophenylacetate; bis-beta-naphthols as illustrated by 2,2'-dihydroxy-1,l'-binaphthyl, 6,6'-dibromo-2,2'-dihydroxy-l,1'-binaphthyl, and bis(2-hydroxy-l-naphthyl)methane; a combination of bis-beta-naphthol and a 1,3-dihydroxybenzene derivative, e.g., 2,4-hydroxy-benzophenone or 2'4'-dihydroxyacetophenone; 5-pyrazolones such as 3-methyl-l-phenyl-5-pyrazolone; reductones as illustrated by dimethylamino hexose reductone, anhydro dihydro amino hexose reductone, and anhydro dihydro piperidone hexose reductone; sulphonamidophenol reducing agents such as 2,6-dichloro-4-benzensulphonoamidophenol , and p-benzenesulphonamidophenol; 2-phenylindane-l , 3-dione and the like; chromans such as 2,2-dimethyl-7-t-butyl-6-hydroxychroman; 1 , 4-dihydro-pyridines such as

2,6-dimethoxy-3, 5-dicarbethoxy-l , 4-dihydropyridine ; bisphenols e.g. , bis( 2-hydroxy-3-t-butyl-5-methylphenyl )methane ,

2,2-bis(4-hydroxy-3-methylphenyl) ropane, 4,4-ethylidene-bis(2-tert-butyl~6-methylphenol) , and 2,2-bis(3,5-dimethyl-4~._ydroxyp_.?nylJpropane; ascorbic acid derivatives, e.g., 1-ascorbylpalmitate, ascorbylεtearate and unsaturated aldehydes and ketones, such as benzyl and diacetyl; 3-pyrazolidones and certain indane-1,3-diones.

The literature discloses additives, "toners", which improve the image.

The materials may be present, for example, in amounts from 0.1 to 10 percent by weight of all silver bearing components. Toners are well known materials in the photothermographic art as shown in U.S. Pat. No. 3,080,254; 3,847,612 and 4,123,282.

Examples of toners include phthalimide and N-hydroxyphthalimide; cyclic imides such as succinimide, pyrazoline-5-ones, and a quinazolinone,

3-phenyl-2-pyrazoline-5-one, 1-phenylurazole, quinazoline, and 2,4-thiazolidinedione; naphthalimides, e.g., N-hydroxy-l,8-naphthalimide; cobalt complexes, e.g., cobaltic hexamine trifluoroacetate; ercaptans as illustrated by 3-mercapto-l,2,4-triazole, 2,4-dimercaptopyrimidine,

3-mercapto- ,5-diphenyl-l,2,4-triazole and 2,5-dimercapto-l,3,4-thiadiazole; N-(aminomethyl)aryl dicarboximides, e.g. (N-dimethylaminomethyl)-phthalimide, and N-(dimethy1aminomethy1)naphthalene-2,3-dicarbo imide; and a combination of blocked pyrazoles, isothiuronium derivatives and certain photobleach agents, e.g., a combination of N,N'-hexamethylene bis(l-carbamoyl-3,5-dimethylpyrazole) , l,8-(3,6-diazaoctane)bis( isothiuronium trifluoroacetate) and 2-(tribromomethylsulphoπyl)benzothiazole) ; and merocyanine dyes such as

3-ethyl-5[ (3-ethyl-2-benzothiazolinylidene)-l- methylethylidene]-2-thio-2, -oxazolidinedione; phthalazinone, phthalazinone derivatives or metal salts cr

these derivatives such as 4-( 1-naphthyl )p_thalazino_ e , 6-chlorophthalazinone, 5,7-dimethoxyphthalazinone , and 2, 3-dihydro-l,4-phthalazinedione; a combination of phthalazinone plus sulphinic 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 ion for silver halide formation in situ, such as ammonium hexachlororhodate (III), rhodium bromide, rhodium nitrate and potassium hexachlororhodate (III); inorganic peroxides and persulphates, e.g., ammonium peroxydisulphate and hydrogen peroxide; benzoxazine-2, 4-diones ' ^" such as 1,3-benzoxazine-2, -dione, 8-methyl-l ,3-benzoxazine-2, 4-dione, and 6-nitro-l,3-benzoxazine-2, -dione; pyrimidines and asym-triazines, e.g., 2,4-dihydroxypyrimidine, 2-hydroxy-4-aminopyrimidine , and azauracil, and tetrazapentalene derivatives, e.g, 3,6-dimercapto-l,4-diphenyl-lH,4H-2,3a,5,6a- tetrazapentalene, and

1,4-di(o-chloro-phenyl )3,6-dimercapto-lH, 4H-2,3a,5,6a- tetrazapentalene.

A number of methods have been proposed for obtaining colour images with dry silver systems. Such methods include incorporated coupler materials, e.g., a combination of silver benzotriazole, well known magenta, yellow and cyan dye-forming couplers, aminophenol developing agents, a base release agent such as guanidinium trichloroacetate and silver bromide in poly(vinyl butyral); a combination of silver bro oiodide, sulphonamidophenol 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; incorporating leuco dye bases which oxidizes to form a dye image, e.g., Malechite Green,

Crystal Violet and pararosani 1ine; a combination of in situ silver halide, silver behenate, 3-methyl-l-phenylpyrazolone and N,N'-dimethy1-p-phenylenediamine hydrochloride; incorporating phenolic leuco dye reducing agents such as 2-(3 ,5-di-tert-butyl-4-hydroxyphenyl)-4,5- diphenylimidazole, and bis(3,5-di-tert-butyl-4-hydroxyphenyl)phenylmethane, incorporating azomethine dyes or azo dye reducing agents; silver dye bleach process, e.g., an element comprising silver behenate, behenic acid, poly(vinyl butyral), poly(vinyl-butyral)peptized silver bromoiodide emulsion, 2,6-dichloro-4-benzenesulphonamidophenol, 1,8-(3,6-diazaoctane)bis-isothiuronium-p-toluene sulphonate and an azo dye was exposed and heat processed to obtain a negative silver image with a uniform distribution of dye which was laminated to an acid activator sheet comprising polyacrylic acid, thiourea and p-toluene sulphonic acid and heated to obtain well defined positive dye images; and incorporating amines such as aminoacetanilide (yellow dye-forming), 3,3'-dimethoxybenzidine (blue dye-forming) or sulphanilanilide (magenta dye forming) which react with the oxidized form of incorporated reducing agents such as 2,6-dichloro-4-benzene-sulphonamido-phenol 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 are disclosed in U.S. Pat. No. 4,021,240, 4,374,821, 4,460,681 and 4,883,747.

Silver halide emulsions containing the stabilizers of this invention can be protected further against the additional production of fog and can be stabilized against loss of sensitivity during keeping. Suitable anti-foggants and stabilizers nich can be used alone or in combination, include the thiazolium salts described in Staud, U.S. Pat. No. 2,131,038 and Allen U.S.

Pat. No. 2,694,716; the azaindenes described in Piper, U.S. Pat. No. 2,886,437 and Heimbach, U.S. Pat. No. 2,444,605; the mercury salts described in Allen, U.S. Pat. No. 2,728,663; the urazoles described in Anderson, U.S. Pat. No. 3,287,135; the sulfocatechols described in Kennard, U.S. Pat. No. 3,235,652; the oximes described in Carrol et. al., British Patent No. 623,448; nitron; nitroindazoles; the polyvalent metal salts described in Jones, U.S. Pat. No. 2,839,405; the thiuronium salts described by Herz, U.S. Pat. No. 3,220,839; and palladium, platinum and gold salts described in Trivelli, U.S. Pat. No. 2,566,263 and Damschroder, U.S. Pat. No. 2,597,915.

Stabilized emulsions of the invention can contain plasticizers and lubricants such as ^" **polyalcohols , e.g., glycerin and diols of the type described in Milton, U.S. Pat. No. 2,960,404; fatty acids or esters such as those described in Robins, U.S. Pat. No. 2,588,765 and Duane, U.S. Pat. No. 3,121,060; and silicone resins such as those described in DuPont British Patent No. 955,061.

The photothermographic elements can include image dye stabilizers. Such image dye stabilizers are illustrated by U.K. Patent No. 1,326,889; Lestina et al. U.S. Pat. Nos. 3,432,300 and 3,698,909; Stern et al. U.S. Pat. No. 3,574,627; Brannock et al. U.S. Pat. No. 3,573,050; Arai et al. U.S. Pat. No. 3,764,337 and Smith et al. U.S. Pat. No. 4,042,394.

Photothermographic elements containing emulsion layers stabilized according to the present invention can be used in photographic elements which contain light absorbing materials and filter dyes such as those described in Sawdey, U.S. Pat. No. 3,253,921; Gaspar U.S. Pat. No. 2,274,782; Carroll et al., U.S. Pat. No. 2,527,583 and Van Campen, U.S. Pat. No. 2,956,879. If desired, the dyes can be mordanted, for example, as described in Milton and Jones, U.S. Pat. No. 3,282,699. Photothermographic elements containing emulsion layers stabilized as described herein can contain matting

SUBSTITUTESHEET

agents such as starch, titanium dioxide, zinc oxide, silica, polymeric beads including beads of the type described in Jelley et al., U.S. Pat. No. 2,992,101 and Lynn, 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 as layers that comprise soluble salts, e.g., chlorides, nitrates, etc., evaporated metal layers, ionic polymers such as those described in Minsk, U.S. Pat. Nos. 2,861,056, and 3,206,312 or insoluble inorganic salts such as those described in Trevoy, U.S. Pat. No. 3,428,451.

The binder may be selected from any of the well- known natural or 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 photothermographic silver containing polymer is polyvinyl butyral, butethyl cellulose, methacrylate copolymers, maleic anhydride ester copolymers, polystyrene, and butadiene-styrene copolymers.

Optionally these polymers may be used in combination 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 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 the stabilizer of the invention can be coated on a wide variety of supp--ι;ts. Typical supports include polyester film, subbed polyester film, poly(ethylene terephthalate)film, cellulose nitrate film, cellulose

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ester film, poly(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 a paper support, which can be _ partially acetylated or coated with baryta and/or an alphaolefin polymer, particularly a polymer of an alpha-olefin containing 2 to 10 carbon atoms such as polyethylene, polypropylene, ethylenebutene copolymers and the like.

The substrate with backside resistive heating layer may also be used in color photothermographic imaging systems such as shown in U.S. Pat. No. 4,460,681 and 4,374,921.

Photothermographic emulsions of this invention can be coated by various coating procedures including dip coating, air knife coating, curtain coating, or extrusion coating using hoppers of the type descirbed in Benguin, U.S. Pat. No. 2,681,294. If desired, two or more layers may be coated simultaneously by the procedures described in Russell, U.S. Pat. No. 2,761,791 and Wynn British Patent No. 837,095.

The present invention will be illustrated in detail in reference to the following examples, but the embodiment of the present invention is not limited thereto.

Example 1

A dispersion of silver behenate half soap was made at 10% solids in toluene and acetone by homogeniza- tion. To 127g of this silver half soap dispersion vas added 252g methyl ethyl ketone, 104g isopropyl alcohol and 0.5g of polyvinylbutyral . After 15 minutes of mixing, 4 ml of mercuric bromide ( .36/10 ml methanol) were added. Then 8.0 ml of calcium bromide (.236g/10ml methanol) was added 30 minutes later. After two hours of mixing, 27.0 g of polyvinylpyrolidone was added, and 27.0 g of polyvinylbutyral was added one hour later.

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To 32.1 g of the prepared silver pre ix described above was added 2.0 ml of the sensitizing dye A (0.045g/50ml of methanol) shown below.

After 20 minutes, a yellow color-forming leuco dye solution was added as shown below.

Component Amount Leuco Dye B .275 g Tribenzyla ine .24g Phthalazinone • 14g Tetrahydrofuran 6.0 ml

The leuco dye is disclosed in U.S. Pat. No. 4,883,747 and has the following formula:

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After sensitization with the dye an the addition of the leuco base dye solution. Compound I-A was added in the - amounts of 0.2 ml or 1.0 ml (.lg/5ml methanol) to a 9.9 g aliquot of the yellow coating solution. The resulting solutions were coated along with an unstabilized solution at a wet thickness of 3 mils and dried at 82 ^β C in an oven for 5 minutes onto a vesicular polyester base. A topcoat solution was coated at a wet thickness of 3 mils and dried at 82°C in an oven for 5 minutes over the silver halide layer. The topcoat solution consisted of 7% polyvinyl 0 alcohol in an approximate 50:50 mixture of water and methanol and 0.2% phthalazine.

The samples were exposed for 10 ^"3 seconds through a 47B Wratten filter and a 0 to 3 continuous wedge and developed by heating to approximately 138°C for 6 5 seconds.

The density of the dye for each sample was measured using a blue filter of a computer densitometer . Post-processing stability was measured by exposing imaged samples to 1200 ft-candles of illumination for 6 hours at 0 65% relative humidity and 26.7 ^β C. The initial sensitometric data are shown below:

Dmin Dmax S eed ¹ Contrast ²

5

Log exposure corresponding to density of 0.6 above Dmin

" ² Average contrast measured by the slope of the line joining density points 0.3 and 0.9 above Dmin.

The post-processing print stability results are shown below: 5

TE SHEET

At a concentration in which initial sensitometry is not affected (0.2 ml), a 66% Dmin post-processing improvement vs. the unstabilized control was observed.

Example 1A (Comparison)

This is for a comparative example. To 9.9 g of the yellow silver halide coating solution as described in Example 1 was added 0.25 ml or 0.75 ml of 3-phenyl-5- mercapto-1 ,2, 4 triazole (PMT) at a concentration of 0.05 g/5 ml methanol; or 0.2 ml or 1.0 ml of

5-mercapto-l,2, 4-triazole (MT) at a concentration of 0.1 g/5 ml methanol. The silver solutions and topcoats were coated, exposed and procesed as described in Example 1. The initial sensito etric data is shown below.

¹ Log exposure corresponding to density of 0.6 above Dmin.

2 Average contrast measured by the slope of the line joining density points 0.3 and 0.9 above Dmin.

The post-processing print stability was measured as described in Example 1 and the results are shown below.

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ΔDmin ΔDmax

At the 0.75 ml addition of PMT and at the 0.2 ml addition of MT, in which great desensitization of the silver halide emulsion has occured, very little post-processing Dmin improvement was observed.

Example 2

A two color formulation was tested with compound I-A. To 9.9 g of the yellow silver halilde dispersion described in Example 1 was added 0.2 ml or 0.5 ml of compound I-A at a concentration of 0.05 g/5 ml in methanol. The resulting solutions and an unstabilized silver halide dispersion were coated with a topcoat as described in Example 1. In addition to the yellow silver halide layer and topcoat layers, a third coating solution was prepared by using 502 g of the silver half soap dispersion of Example 1 and adding 0.4 g of polyvinylbutyral. After 15 minutes of mixing, a 0.05 g/9.75 g mercuric acetate in methanol solution and a 0.55 g/18.4 g calcium bromide in methanol solution were added 30 minutes later. After 45 minutes of mixing, 49.8 g cf polyvinylbutyral was added.

SUBSTITUTE SHEET

To 35.8 g of prepared silver pre ix described above was added 1.4 ml of the sensitizing dye C (0.021 ^* g/100 ml of methanol) shown below.

CH_

CH,

CH ₂ ^C = CH- : s

C ₂ H ₄ C0 ₂ H O 2H5

After 30 minutes, a magenta color-forming leuco dye solution was added as shown below.

Component Amount

Leuco Dye D. .593 g Phthalazinone .901 g Tetrahydrofur n 47.6 g VAGH (Union Carbide) 2.2 g Polyvinylbutyral 10.2 g

The leuco dye is disclosed in U.S. Patent No 4,795,697 and has the following formula:

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A fourth layer topcoat solution was prepared consisting of 24.0% polystyrene resin in approximately 52% tetrahydrofuran, 17% toluene, 2% acetone and 5% methanol.

The third and fourth layers are coated simultaneously onto the yellow topcoat at 2 mils wet thickness, respectively, and dried 5 minutes at 82°C. The samples were exposed and processed as described in Example 1. The initial sensitometric data is shown below for the bipack.

Control (0.0 ml) 0.2 ml I-A 0.5 ml I-A

¹ Log exposure corresponding to density of 0.6 above Dmin,

2 Average contrast measured by the slope of the line joining density points 0.3 and 0.9 above Dmin.

The post processing print stability results as tested in Example 1 are shown below.

ΔDmin ΔDmax

The addition of I-A to the yellow silver layer had no effect on initial sensitometric responses cf the magenta-color forming layer, and a 60% Dmin post processing improvement vs. the unstabilized sample was observed for the yellow silver layer without any effects on the initial sensitometric responses.

Example 3

To 9.9 g of a yellow silver coating solution- similar to Example 1, was added 0.4 ml or 0.8 ml of compound I-A at a concentration of 0.1 g/5 ml of methanol, or 0.5 ml or 1.0 ml of 5-hexylthio-l ,2, 4 triazole (HT) at a concentration of 0.03 g/25 ml of methanol and coated as described in Example 1. The topcoat was coated over the yellow silver layer as described in Example 1 but contained less phthalazine (0.06%). A magenta silver layer and topcoat were coated as third and fourth layers, and are described in Example 3. The samples were exposed and processed as described in Example 1. The.initial sensitometric data is shown below for the bipack.

¹ Log exposure corresponding to density of 0,6 above Dmin,

² Average contrast measured by the slope of the line joining density points 0.3 and 0.9 above Dmin.

The post-processing print stability results as tested in Example 1 are shown below.

ΔD in ΔDmax

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A 44% Dmin post-processing improvement vs. the unstabilized sample was observed for compound I-A without any effects on the initial sensitometric responses. With the HT compound, desensitization occurs in the yellow silver layer before post-processing stabilization was observed.

Example 4

To 9.9 g of a similar yellow silver halide coating solution as described in Example 1 was added 0.35 ml or 1.0 ml of comound I-A at a concentration of 0.1 g/5 ml in ethanol, or 0.35 ml or 1.0 ml of compound I-B at a concentration of 0.13 g/5 ml in ethanol and coated as

___ described in Example 1. The yellow topcoat was the same as described in Example 3.

The layers were coated, exposed and processed as described in Example 1. The initial sensitometric data is shown below.

Control (0.0 ml) 0.35 ml I-A 1.0 ml I-A 0.35 ml I-B 1.0 ml I-B

² Average contrast measured by the slope of the line joining density points 0.3 and 0.9 above Dmin.

The post-processing print stability was measured as described in Example 1 and the results are shown below.

At the same molar concentrations, compounds I-A and I-B behave similarly for post-processing print stabilization. A greater than 70% Dmin post-processing Dmin improvement was observed with minimal effects on initial sensitometric response.

Example 5

To 9.9 g yellow silver halide solution as described in Example 1 was added 0.1 ml, or 0.35 ml or 1.0 ml of compound I-A at a concentration of 0.015 g/25 ml of tetrahydrofuran. A similar topcoat solution was prepared as in Example 1. A magenta silver halide coating solution and topcoat were also prepared as described in Example 3 for a two color formulation. The exposure and processing were the same as in Example 1, and the initial sensitometric response is shown below for the bipack.

Control (0.0 ml) 0.1 ml I-A 0.35 ml I-A 1.0 ml I-A

Log exposure corresponding to density of 0.6 above Dmin,

Average contrast meassured by the slope of the line joining density points 0.3 and 0.9 above Dmin.

SUBST _I TUTE SHEET

Post-proceεsing stability was tested by exposure of imaged samples to a xeno lamp at 1500 watts for 30 minutes, and unprocessed stability was tested by pre- equilibrating unexposed samples for 16 hours at 22°C and 50% relative humidity, then sealing the samples in a foil bag, and placing in a oven at 50°C for 8 hours. The results are shown below.

10

15

Print Stability

20

25

The results show an improvement in both the post-processed and unprocessed Dmin without any effects on the initial sensitometric responses.

Example 6

30 To 9.9 g of a yellow silver halide solution similar to that described in Example 1 was added 0.35 ml or 0.65 ml of compound I-C at a concentration of .039 g/5 ml of ethanol, or 0.35 ml or 0.65 ml of compound I-D at a concentration of 0.038 g/5 ml of ethanol and coated as " described in Example 1. The yellow topcoat was similar tc

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that described in Example 1. The layers were coated, exposed and processed as described in Example 1. The - initial sensitometric data is shown below.

Control (0.0 ml)

0.35 ml I-C

0.65 ml I-C

0.35 ml I-D

0.65 ml I-D

¹ Log exposure corresponding to density of 0.6 above Dmin.

² Average contrast measured by the slope of ^" he line joining density points 0.3 and 0.9 above Dmin.

The post-processing print stability was measured as described in Example 1 and the results are shown below.

ΔDmin ΔDmax

A 68% and 58% Dmin post-processing improvement vs. the unstabilized sample was observed for 0.65 ml addition of compound I-C and 0.35 ml addition of compound I-D, respectively, with little effect on the initial sensitometric response.