CA1045878A - Photothermographic element, composition and process - Google Patents

Abstract

ABSTRACT

A stabilizer precursor combination of (a) a blocked thione stabilizer precursor with (b) a halogen containing stabilizer precursor in a photothemographic element or composition provides improved post-processing stability upon heat processing of the element or composition. This stabilizer precursor combination is useful in photothermographic materials.
for example, comprising photosensitive silver salt and an oxidation-reduction image-forming combination comprising a heavy metal salt oxidizing agent with a reducing agent.

Description

~045~378 Background of the Invention .
Field of the Invention This invention relates to certain stabilizer pre-cursor combinations in photothermographic elements, com-positions and processes to provide improved stable images.
In one of its aspec-ts it relates to a heat stabilizable photothermographic element comprising photosensitive sil-ver halide and a stabilizer precursor combination as des-cribed. In another of its aspects it relates to a photo-thermographic omposition comprising the described stab-ilizer precusor combination. A further aspect relates to a method of stabilizing an image in a photothermo-graphic element comprising photosensitive silver halide and a stabilizer precursor combination as described by overall heating the exposed photothermographic element.
Description of the State of the Art It is known to ~btain an image in a photosensitive element by so-called dry processing with heat. The photothermographic element empIoyedfor providing such an image can contain a reducing agent, a light-insensitive silver salt of an organic acid, such as silver behenate, as an oxidizing agent and a low concentration of photo-graphic silver halide. Such photothermographic elements are described, for example, in U.S. Patent 3,457,075 of Morgan et al, issued July 22, 1969; U.S. Patent 3,152,904 of Sorensen et al, issued October 13, 1964; British Specification 1,161,777 published August 20, 1969; U.S.
Patent 3,707,377 of Tiers et al, issued December 26, 1972 and in Research Disclosure, January, 1973, pages 16-21.
In a photothermographic material one of the-;~main difficulties involves post-processing stability. Because heat developable photographic elements are suitable for so-called

- 2 -.
, 109~S878 dry processing with heat and are designed to eliminate a fixing step which normally would remove undeveloped silver, it is necessary that a means be provided for post-processing stabilization to enable room-light handling.
Several means have been proposed to answer the need for post-processing stability of photothermographic elements, such as (1) washing with water to remove undev-eloped silver salts, (2) heating to release Bronstead or Lewis acid such as HCl, fluoride or HF from incorporated compounds such as m-nitrobenzenesulfonylchloride, para-toluene sulfonic acid urea addition complex or ~-acetami-dobenzenediazonium fluoroborate and (3)chelation of the oxidizing agent with for example, salicylaldoxime or be~-otriazole as described in U.S. Patent 3,152,904 of Sorensen et al, issued October 13, 1964. Another method proposed for solving the porblem of post-processing instability is to provide a photothermographic combination is on one sheet of material and the latent image formi~
photographic silver halide is on a separate sheet. The sheets are separated after exposure such as described in U.S. Patent 3,152,904. A futher means proposed for stab-ilization involves swabbing a 1% solution of phenylmer-captotetrazole onto the surface of the overall heated photothermographic material or rubbing benzotriazole into the surface of the coating. These proposed means for stabilization are not useful for large volume handling of heat developable photographic materials.
It has also been proposed to provide stabilized images in heat developable materials by treating the dev- -eloped image with a soluti~ containing certain thiol or thione compound stabilizers. This is described, for example, in U.S. Patent 3,617,289 of Ohkubo et al, issued ~ ~
NOvember 2, 1971. One of the compounds proposed for this `
solution stabilization is . . . ' . ' ' - ' ', :- " ~ ' "' ',.,, ~. . ' ,: : - , ` . : :: ... . :
- . : . . . .... . . .:: .
.

l-phenyl-5-mercaptotetrazole. Unfortunately, the addition of this compound to photographic silver compositions provides undesired desensitization at concentrations which produce stabilization and toning of a developed image.
Another means of stabilization of an image in a photothermographic material is described in Belgian Patent 768,071 published Julvv 30, 1971. Certain stabilizer precursors which are azole thioethers or blocked azolinethiones are employed in photothermographic materials according to ;~
the description in this patent. An example of a stabilizer precursor proposed in photothermographic materials is 5-methoxycarbonylthio-1-phenyltetrazole. Unfortunately, this compound does not always provide the desired increased stability of a heat developed image.
Another means for post-processing stabili%ation of certain photothermographic materials is described in U.S.
Patent 3,707,377 of Tiers et al, issued December 26, 1972.
Certain polyhalogenated organic oxidizing agents, such as tetrabromobutane, are described in certain heat developable photographic materials to provide post-processing stabilization.
As illustrated in the following comparative examples, certain combinations of compounds can provide surprisingl~ improved stabilization without the adverse sensitometric effects which may be observed with certain polyhalogenated organic oxidizing agents.
Halogenated organic compounds have been emplo~ed in photographic materials for various purposes, such as antifoggants.
Monohalogenated organic antifoggants for photographic emulsions 10451~78 dre described, for example, in U.S. Patent 3,128,187 of Sagal et al, issued April 7, 1964; U.S. Patent 3,232,762 of Ford et al, issued February 1, 1966; U.S. Patent 2,732,303 of Morgan et al, issued January 24,1956; U.S.
Patent 2,835,581 of Tinker et al, issued May 20, 1958 and U.S. Patent 3,271,154 o~ Dersch, issued September 6, 1966. None of these patents, however, indicate that certain combinations of stabilizer:precursors can be em-ployed in photothermographic materials to p~ovide im-proved post-processing stability.
Also, while various 5-mercaptotetrazole compounds are known in photographic materials for vario~spurpose such as, known in photographic materials for various purposes, such as descri'bed in British Patent 1,238,928 published July 14, 1971, and other of the described patents, none of the art suggests a useful solution to the continuing need for improved heat-developable, thicne(-compound containing, photographic materials providing improved post-processing stability.
Accordingly, there has been a continuing need for heat-developable photographic materials, especially ph~o-thermographic materials comprising an image-forming com-bination containing a silver salt oxidizing agent, such as silver behenate, with a reducing agent, and photo-sensitive silver halide, which have improved post-pro-cissing image stability, that is reduced background density and more desired image tone, when employing a combination of stabilizer precursors.

Summary of the Invention The described improvements are provided in a photo-thermographic element or composition by~employing as astabilizer precursor, a $tabilizer PreCursor combination of (a) a blocked thione stabilizer precursor with (b) a halogen containing stabilizer precursor. This stabilizer precursor combination is especially useful ln a photo-~ ' .

.

thermographic material comprising phtosensitive silver halide and an oxidation-reduction .

~ .
~ ' ' ,.:
: ~ :

104587~3 image-forming combination comprising (i) a heavy metal silver salt oxidizing agent, such as silver behenate -and silver stearate, with (ii) a reducing agent.
The described improvements are provided, for example, in a photothermographic element comprising a support having thereon a layer comprising (A) photo-sensitive silver halide in association with (B) an oxi-dation-reduction image-forrning comb~nation comprising (i) a silver aalt of a long-chain fatty acid, such as a silver behenate and silver stearate with, (ii) an organic reducing agent, such as a sulfonamidophenol reducing agent, (C) a polymeric binder for the described layer, such as poly(vinyl butyral) and(D) a stabilizer precursor combination of (a) a blocked thione stabilizer -precursor as described herein with (b) a halogen con-taining stabilizer precursor, also as described herein.
Detailed Description of the Invention A variety of blocked thione stabilizer precursors can be emplyed in the practice of the invention to pro-vide improved post-processi~g stability without adversely affecting desired properties of the heat-developable photographic material.
A blocked thione stabilizer precrusor as employed herein is intended to mean a thione compound which con-tains a group or moiety which blocks or prevents the thione compound from reacting with silver ions in the photothermographic material prior to heating the photo-thermographic material. While the exact mechanism of stabilization according to the invention is not fully understood, it is believed that the blocked thione as-described remains in a state which does not adversely affect the photothermographic material containing the blocked thione prior to heating. Upon heating, it is believed that thione compound is changed from its bloc~ed state tola state which enables reaction with silver -ions in the unexposed areas of :. . . . , . . . , i : . . . ................................... ...

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

the photothermographic material to form a stable silver mercaptide in the unexposed areas. This is believed to prevent undesired decreased stability to room-light ex-posure.
A test c~n be used to determine whether or not a thione compound is a useful blocked thione image stabi-lizer precursor as described. While different tests can be employed to determine useful image stabilizer percursors depending upon the particular photothermogra-phic element and composition, desired image, processing conditions and the like, one test which can be employed for certain photothermographic elements is described in following Example 4. The compound tested in the described combination, after incorporation with the described halogen containing compound in the photothermographic element and after imagewise exposure and overall heating of the element as described in Example 1, should pre-vent the buildup of background density or minimum den-sity above O.10 density unit more than the original minmum density without undesired stain and without sig-ni~icantly adversely affecting maximum density.
One class of especially useful blocked thione stabilizer precursors is a 4-aryl-1-carbamoyl-2-tetrazo-line-5~ thione represented by the formula:

N N - C ,- NH R

~ R I n wherein R is aryl, sùch as aryl containing 6 to 12 carbon atoms, including phenyl and naphthyl; and nl i~
alkyl containing l to 12 carbon atoms, such as methyl, propyl, butyl and hexyl, aryl, such as aryl containing 6 to 12 carbon 1~45878 atoms, includin~ phenyl and naphthyl, cycloalkyl containing

3 to 8 carbon atoms, such as cyclohexyl and cyclopropyl, when n is 1, or alkylene containing 1 to 10 carbon atoms when n is 2, such as alkylene containing 1 to 6 carbon atoms including methylene and ethylene; and n is 1 or 2. These blocked thione stabilizer precursors are described in U.S. Patent 3,893,859 of D~ M. Burness et al, issued July 8, 1975.
Useful blocked thione stabilizer precursors within the described formula (I) include, for instance:

4-phenyl-1-phenylcarbamoyl-2-tetrazoline-5-thione, l-cyclohexylcarbamoyl-4-phenyl-2-tetrazoline-5-thione, l-methylcarbamoyl-4-phenyl-2-tetrazoline-5-thione, 4-hexylcarbamoyl-1-phenyl-2-tetrazoline-5-thione, N,N-hexamethylenebis(l-carbamoyl-4-phenyl-2-tetrazoline-5-thione), 4-butylcarbamoyl-1-phenyl-2-tetrazoline-5-thione, and di-2-(1-phenyl-5-thione-2-tetrazolin-4-ylcarbonylamino-ethyl fumarate.
Other useful classes of blocked stabilizer precursors are described, for example, in Belgian Patent 768,071 published July 30, 1971. Useful blocked thione and blocked ~:
thiol stabilizer precursors within these classes are:

5-Acetyl-2-benzoylthio-4-methylthiazole, 4-Benzoylmethyl-2-benzoylthiothiazole, 2-(2-~uroylthio)-4-hydroxymethylthiazole, ~ -2-Benzoylthio-4-hydroxymethylthiazole, 2-Benzoylthio-4-tert.-butylthiazole, 5-Carbethoxy-4-methyl-2-(3-oxobutylthio)thiazole, 5-Acetyl-2-(2-benzoylethylthio)-4-methylthiazole, ,.

., .' :, 1~4S878 2-(3-Oxobutylthio)thiazole, 4,5-Dimethyl-2-(3-oxobutylthio)thiazole, 2-(3-Oxobutylthio)-4-phenylthiazole, 4-Carboxy-2-(3-oxobutylthio)thiazole, 4-Carboethoxy-2-(3-oxobutylthio)thiazole, 4-(4-Methoxyphenyl)-2-(3-oxobutylthio)thiazole, 4-(4-Methoxyphenyl)-2-(3-oxobutylthio)thiazole, ~ -4-(4-Nitrophenyl)-2-(3-oxobutylthio)thiazole, 4-Tert.-butyl-2-(3-oxobutylthio) thiazole, 5-Acetyl-4-methyl-2-(3-oxobutylthio)thiazole, 5-Acetyl-2-furoylthio-4-methylthiazole, 4-Furoyl-3-(3-oxobutylthio)1,2,4-thiadiazoline-5-thione, 3-Methylthio-4-benzoyl-1,2,4-thiadiazoline-5-thione, :
4-Acetyl-3-methylthio-1,2,4-thiadiazoline-5-thione, :~
4-Acetyl-3-furoylethylthio-1,2,4-thiadiazoline-5-thione, 4-Furoyl-3-methylthio-1,2,4-thiadiazoline-5-thione, ~ ~:
5~(~enzoylethylthio)-]-phenyltetrazole, 5-(2-Acetylethylthio)-l-phenyltetrazole, 5-Methoxycarbonylthio-l-phenyltetrazole, 5-(4-Nitrobenzyloxycarbonylthio)phenyltetrazole, 5-(Ethoxycarbonylthio-l-phenyltetrazole 5-Benzoylthio-l-phenyltetrazole, ~. .
5-Acetyl-3-benzoyl-4-methylthiazoline-2-thione, 4-Benzoylmethyl-3-benzoylthiazoline-2-thione 3-Furoyl-4-hydroxymethylthiazoline-2-thione, 3-Benzoyl-4-hydroxymethylthiazoline-2-thione, 3-Benzoyl-4-tert.-butylthiazoline-2-thione, and 5-Carboethoxy-4-methyl-3-(3-oxobutyl)-thiazoline-2-thione The listed compounds have also in some cases been known as azole thioethers and blocked azolinethiones. These compounds can be prepared by methods known in the art For example, they can be prepared by the Michael addition of alpha, _ 9 _ ' :,, .

.. : , : . :

- lO~S878 beta-uns~turated ketones such as methyl vinyl ketone to 4-thiazonline-2-thione. This is descrived in the Journal of Heterocyclic Chemistry, 6, pages 397-401 (1969) by Humphlett.
The blocked thione stabilizer precursors which are tetrazoline-5-thione compounds can be prepared by reacting l-phenyl-2-tetrazoline-5-thione in a suitable solvent in the presence of a catalyst such as heptamethylisobigua-nide, with a suitable isocyanate compound. The prepara-tion of l-cyclohexylcarbamoyl-4-phenyl-2-tetrazoline-5-thione is typical of a useful preparation. It is pre-ferred that the resulting product be purified such as by treatment with solvents and other typical purification ~ means.
- A variety of halogen containing stabilizer precur~r can be employed accord~ng to the invention to prdvide im-proved post-processing stability without adversely affect-ing desired properties of the photothermographic material.
A test can be emplyed to determine useful halogen containing compounds or materials such as described in the following example 4. In this test, the halogen com-pound, after incorporation with the described blocked thione compound in the photothermographic element and after imagewise exposure and overall heating of the ele ment as described in Example 4, should prevent buildup of background density or minimum density above 0.10 density unit more than the original minimum density without undesired stain and without significantly advers-ely affecting maximum density.
It is believed that the describ-ed halogen containing stabilizer precursors are precursors to the moiety, com-pound or material which, is formed upon heating and com-bines with silver ions or atoms to prevent undesired in- - -stability due to room-light exposure. However, the exact ' ~ - 10 - ,. . ..

, . .: - . . , . . . .: .

~ 1045878 mechanism of stabilization is not fully understood.
The stabilizer precursors according to ~ ' ' ' ' ~ ' , .

.
' . . .. ...

';
~ ;'''.,' - lOa -the invention are compounds which do not prevent a redox reaction upon imagewise exposure o~ the descri~ed photothermographic materials. :-One class of useful halogen containing stabilizer precursors according to the invention comprises a compound repre-sented by the formula:

: 3 R - C - X
: l4 R

: - 2 3 4 ~herein X is chloro, bromo or iodo; R , R and R are individually selected from the group consisting or hydrogen; alkyl, such as alkyl containing 1 to 10 carbon atoms including methyl, ethyl, propy~ or octyl; hydroxyalkyl, such as hydroxyalkyl containing 1 to 10 carbon atoms, including hydroxymethyl, hydroxyethyl and hydroxyhexyl; acyloxyalkyl, such as acyloxyalkyl containing 2 to 10 carbon atoms; nitro; nitroalkyl, such as nitroalkyl contain~ng 1 to 10 carbon atoms; mm~uding nitromethyl, nitroethyl and nitropropyl; aryl, such as aryl containing 6 to 12 carbon atoms, including phenyl and naphthyl; acyl, such as acyl of the formula R"-CO-wherein R" is alkyl containing 1 to 5 carbon atoms including me~hyl, ethyl, propyl and butyl, or aryl containing 6 to 12 carbon atoms, such as phenyl and naphthyl; amido, such as amido represènted by the formula .: :
R ~ O ~ :
~ N-C .~:
; R

wherein R and R individually selected from the group consis.tin~
of hydrogen, alkyl containing 1 to 5 carbon atoms, such as methyl, .
ethyl and propyl, phenyl and naphthyl; sulfonyl represented by .

the formula R - SO - wherein R is alkyl con.~aining 1 to 5 -carbon atoms, such as methyl, ethyl and propyl or aryl, such as aryl containing 6 to 12 carbon atoms, such as phenyl, .:
-: . .

1~45878 napthyl or tolyl; bromo; chloro; and iodo; and wherein ~:
at least one of R , R , and R is hydroxyalkyl, acylox-yalkyl, acyl, amido or sulfonyl as defined. Alkyl, aryl, hydroxyalkyl, acyloxyalkyl, acyl, amido and sulfonyl as employed herein include substituents on the defined grcups which do not adversely affect stabilization or desired properties of photothermographic materials according to the invention. Suitable substituents include, for example, .
chloro, bromo, methoxy, phenyl, hydroxy, nitro and the like.
Another class of useful stabilizer precursors accord-ing to the--invention comprises a monohalogentaed organic compound having at least one carbonyl or sulfonyl group bonded to the carbon atom having the halogen substitu~nt, such as an alpha-monohaloketone represented by the for-mula: 5 6 R - CH - C - R
..
X O
wherein X is chloro, bromo or iodo; R is hydrogen, alkyl containing 1 to 10 carbon atoms, such as methyl,ethyl, propyl,butyl, ~pentyl or octyl, acyl containing 1 to 5 carbon atoms, such as acetyl and CH3CH2CO-, sulfamyl and aryl containing 6 to 12 carbon atoms, such as phenyl and `
naphthyl; R is amino, alkyl containing 1 to 10 carbon atoms, as described, and aryl containing 6 to 12 carbon atoms, such as phenyl and naphthyl. The described sub-stituent groups onthe alpha-monohaloketone compounds can contain substituents which do not adversely affect the stabilizing action of the alpha-monohaloketone, such as methyl, ethyl and the like. ~::
Useful halogenated organic compound stabilizer pre ~ ~.
cursors within the described classes include the follow-ing compounds: :
~-bromo-2,5-dimethoxyacetophenone ~-bromo-~- nitrol-~- phenylbutyrophenone ~2 ~:

. , . . ~. .
..

1~45878 2-bromo-2-~-tolylsulfonylacetamide ~-iodo-~~nitro-l)-phenylbutyrophenone - 12a -~ " ' -lO~S878 a-bromo-_-nitrotoluene 2-bromo-4'-phenylacetophenone 2-chloro-4'-phenylacetophenone Q-bromo-m-nitrotoluene 2-bromo-2-nitro-1,3-propanediol 1,3-dibenzoyloxy-2-bromo-2-nitropropane 2,2-dibromo-2-phenylsulfonylacetamide 2-bromo-2-~~tolylsulfonylacetamide 2-bromoacetophenone ~-chloro-~-nitrotoluene 2-bromo-2-phenylacetophenone 2-bromc-1,3-diphenyl-1,3-propanedione tetrabromobutane hexabromocyclohexane hexabromoethane 2-tribromonethylsulfonylbenzothiazole 2-bromo-2-nitro-1,3-di-(4-nitrobenzoyloxy)propane --2-bromo-1,3-di-(4-methoxybenzoyloxy)-2-nitropropane The described halogen containing organic stabilizer precursors can be prepared by methods known in the art.
For example, the parent organic compound can be halogen-ated employing, for example, bromine or chlorine. The -~
resulting halogenated compounds can be purified empl~ing purification procedures known in the art. Some organic ~:~
compound impurities can be present in the resulting com-position. In some cases it is necessary to separate the organic compound impurities before mixing the halogenated organic stabilizer precursors with the described photo-thermographic materials.
The useful concentration of the combination of stab-ilizer precursors according to the invention will depend upon different factors such as the particular photothermo-graphic .

.. .. .

element, processing temperatures, particular components of the photographic element, desired image and the like.
A useful concentration of the combination of stab-ilizer precursors according to the invention is (a) about 0.00~ to about 0.035 mole of the described blocked thione stabilizer precursor per mole of total silver with (b) about ô.OOl to about 1.0 mole of the described;,halogen containing stabilizer precursor per mole of total silver in the describ~ photothermographic material. The optimum concentration useful can be determined based on the des cribed factors.
The described halogen stabilizer precursors are also observed to provide desired, incubation antifoggant acti-vity in photothermographic materials according to the ~ -invention at a concentration within the range of about 0.001 mole to about 0.025 mole of the described halogen stabilizer precursor per mole of total silver in the photothermographic material. The optimum concentration of the halogen stabilizer precursor for incubation anti-foggant activity will depend upon such factors as the particular halogen compound, the particular photothermo-graphic material, desired image and the like.
Typical photothermographic elements in which the stabilizer precursor combination of the invention is use-ful are described, for example, in U.S. Patent 3,457,075 of Morgan et al, issued July 22, 1969; U.S. Patent 3,152, 904 of Sorensen et al, issued October 13, 1964; U.S.
Patent 3,429,706 of Shepard et al, issued February 25, 1969; U.S. Patent 3,672,904 of deMauriac, issued June 27, 1972 and Research Disclosure, January, 1973, pages 16-21.

The stabilizer precursor combination of the inven-tion is especially useful in photothermographic materials comprising , . , , . , , , , ~ , . . . . . . . . . .

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

photosensitive silver halide in association with an oxi-dation-reduction irnage-forming combination comprising (i) silver behenate, with (ii) a phenolic reducing agent, such as a sulfonamidophenol reducing agent, a poly (viryl butyral) binder, a spectral sensitizing dye, and a toning agent (also known as an activator-toning agent) comprising succinimide, N-hydroxynaphthalimide or phthalazinone.
Such a photothermographic material is described, for ex-ample, in Research Disclosure, January, 1973, pages 16-21.
An especially useful embodiment of the invention is a photothermographic element comprising a support having thereon a layer comprising (a) photosensitive sil-ver halide in association with (b) an oxidation-reduction image-forming combination comprising (i) silver behene-nate, with (ii) a phenolic reducing agent, such as a sulfonamidophenol reducing agent, (c) a poly (vinyl but-yral)binder, (d) a spectral sensitizing dye, (e) a toning ~ :
agent, such as succinimide or N-hydroxy-1,8-naphthalimide, and a stabilizer precursor combination comprising (f) l-cyclohexylcarbamoyl-4-phenyl-2-tetrazoline-5-thione with (g) a halogen containing stabilizer precursor sel-ected from tetrabromobutane,~ -bromo-gamma-nitro-~
phenylbutyrophenone, 2-bromo-2-~-tolylsulfonylacetamide, ~, 2-tribromomethylsulfonyl-benzothiazole, 2,2-dibromo-2-phenylsulfonylacetamide, 1,3-dibenzoyloxy-2-bromo-2-nitropropane, 2-bromo-2-nitro-1,3-propanediol and combin-ations thereof.
The described photographic materials according to the invention comprise a photosensitive component which comprises photosensitive silver halide. In the photo-thermographic materials comprising the described oxida-tion-reduction image-forming combination, it is believed that the photosensitive silver halide or a component re sulting--from the photosensitive silver halide acts as a catalyst for the described oxidation-reduction image-.''~

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

forming combination. A typical concentration range of photosensitive silver halide is from about 0.01 mole to about 20.0 moles of photosensitive silver halide per mole of heavy metal salt oxidizing agent, for example, per mole of silver salt oxidizing agent. Other photo~
sensitive components can be useful in combination with photosensitive silver halide. Useful photosensitive sil-ver salts include silver-dye complexes and other photo-sensitive silver salts. Preferred photosensitive silver halides are silver chloride, silver bromide, silver "~
bromoiodide, silver chlorobromoiodide or mixtures there-of. Very fine-grain photosensitive silver halide is especially useful although coarse or fine-grain photo-sensitive silver halide can be employed if desired.iThe photosensitive silver halide can be prepared by any of the proàedures known in the photographic art. Such procedures and forms of photosensitive silver halide are described, for example, in the Product Licensing Index, Volume 92~,~ December, 1971, publication 9232 at page 107, paragraph I. The photosensitive silver halide according to the invention can be unwashed or washed, can be chemically sensitized, can be protected a~ainst the production of fog and and stabilized again$t loss of sensitivi~ty during keeping, as described in the Product Licensing Index, Voiume 92, December, 1971, publication 9232, pages 107-110.
The photothermographic elements and compositions according to the invention typically comprise an oxida-tion-reduction image-forming combination which contains an oxidizing agent, preferably a heavy metal salt oxidi-zing agent. The heavy heavy metal salt oxidizing agent can be a heavy metal salt of an organic acid such as a fatty acid which is resistant to darkening upon illumin-ation. An especially useful class of heavy metal salts of organic acids is represented by the water insolub~e -silver salts of long-chain fatty acids which are : . - : . . :

stable to light. Compounds which are suitable silver ;
slat oxidizing agent include: silver behenate, silver stearate, silver oleate, silver laurate, silver hydroxy-stearate, silver caparate, silver myristate and silver palmitate. Silver salts can be employed as the heavy metal salt oxidizing agent which are not silver salts of long-chain fatty acids. Such silver salt oxidizing agents which are useful include, for example, silver benzoate, silver benzotriazole, silver terephthalate, silver phthalate and the like.
The described photothermographic elements a~d com-positions can comprise various reducing agents. Suitable reducing agents which can be employed with the described stabilizer precursors include substituted phenols and naphthole, for example, bis-beta-napthols. Suitable bis-beta-naphthols include, for exampl~e,2,2'-dihydroxy-1,1' binaphthyl,6,6'-dibromo-2,2'-dihydroxy-1,1'-binaphthyl,

6,6'-dinitro-2,2'-dihydroxy-1,1'-binaphthyl and bis-(2-hydroxy-1-maphthyl)methane. Other reducing agents which can be employed in photothermographic elements, according to the invention, include polyhydroxybenzenes such as hydroquinone, alkyl-substituted hydroquinones such as tertiary butylhydroquinone, methyl-hydroquinone, 2,5-dimethylhydroquinone and 2,6-dimethylhydro-quinone;
catechols and pyrogallols, chloro-substituted hydro-quinones such as chlorohydroquinone or dichlorohydroqui-none;alkoxy-substituted hydroquinone such as methoxyhy-droquinone or ethoxyhydroquinone; aminophenol devel~ping agents, such as 2,4-diaminophenols and methylaminophenols;
ascorbic acid developing agents such as ascorbic acid, ascorbic acid ketals and ascorbic acid derivatives; hy-droxylamine developing agents; 3-pyrazolidone developing agents such as l-phenyl-3pyrazolidone and 4-methyl-4-hydroxymethyl-l-phenyl-3-pyrazolidone and the like. Com-binations of reducing agents can be employed if desired.

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

lQ~5878 Especially useful reducing agents which can be employed in the photothermographic materials according to the invention are sulfonamidophenol reducing agents as described in Research Disclosure~ January, 1973, pages 16-21. One especially useful class of sulfonamidophenol reducing agents is represented by the formula:
OH
8 ~ R7 wherein R is phenyl, naphthyl, methylphenyl, thienyl, quinolinyl, thiazyl, or alkyl containing 1 to 4 carbon atoms, such as methyl, ethyl, propyl or butyl; R7 is hydrogen, R SO2NH-, alkoxy containing 1 to 4 carbon atoms, such as methoxy, ethoxy, propoxy and butoxy, bromo or chloro;
R is hydrogen, bromo, chloro, alkyl containing 1 to 4 carbon atoms, as described, or alkoxy containing 1 to 4 carbon atoms~
such as methoxy~ ethoxy and propoxy. R7, R8 and/or R9 can contain substituent groups which do not adversely affect the reducing properties of the described sulfonamidophenol reducing agents or the desired sensitometric properties of the photo-thermographic elements and materials of the lnvention. Examples of substituent groups which can be present are alkyl containing 1 to 3 carbon atoms such as methyl, ethyl and propyl, chloro, bromo and phenyl. In some cases, it is desirable to avoid an amino group as a substituent. The amino group, in some cases, provides an overly active reducing agent. 5ulfonamidophenol reducing agents, as described, include sulfonamidonaphthols.
A sulfonamidonaphthol which is useful is represented by the formula:
OH

NNSO~

The sulfonamido group in the described sulfonamidonaphthols can be in the two, three, or four position. The sulfonamidonaphthols and sulfonamidophenols which contain two sulfonamido groups are more active compounds within the sulfonamido reducing agent class. The sulfonamidophenols containing two or more sulfon-amido groups are employed for shorter developing times or with heavy metal salt oxidizing agents which are less active than silver behenate. In some cases, image~:discrimination provided by photothermographic materials containing the sulfonamido-naphthols and trifunctional suIfonamidophenols is less than that provided by other of the described sulfonamidophenols.
It is desirable, in some cases, to employ a so-called -toning agent, also known as an accelerator-toning agent or activator-toning agent, in the photothermographic materials of the invention. Useful toning agents are described, for example, in Belgian Patent 766,590 issued June 15, 1971 and in Research Disclosure~ January~ 1973, pages 16-21. Combinations of toning agents can be employed in the photothermographic materials according to the invention if desired. Typical toning agents include, for example, phthalimide, 2,3-naphthalimide, N-hydroxyphthalimide, N-potassium phthalimide, -succinimide, N-hydroxy-1,8-naphthalimide and/or N-hydroxy-succinimide. In some cases~ other toning agents can be employed such as 1-(2H)-phthalazinone and 2-acetylphthalazinone and the like.
A photothermographic element or composition as described according to the invention can contain various -colloids alone or ln combination as vehicles~ binding agents and in various layers. Suitable materials can be hydrophobic or hydrophilic. They are transparent or translucent and include both naturally-occurring substances such as proteins, for example, gelatin, gelatin derivatives, cellulose derivatives, .. , . . ~ . ..

lV45878 polysaccharides such as dextran, gum arabic and the like; and synthetic polymeric substances such as water soluble polyvinyl compounds like poly(vinylpyrrolidone), acrylamide polymers and the like. Other synthetic polymeric compounds which can be employed include dispersed vinyl compounds such as in latex form and particularly those which increase dimensional stability of photographic materials. Effective polymers include water-insoluble polymers of alkyl acrylates and methacrylates, acrylic acid, sulfoalkyl acrylates, methacrylates and those which have crosslinking sites which facilitate hardening or curing as well as those have recurring sulfobetaine units as described in Canadian Patent 774,054. Especially useful high molecular weight materials and resins include poly(vinyl butyral), cellulose acetate butyrate, poly(methyl methacrylate~, poly(vinylpyrrolidone), ethylcellulose, polystyrene, poly(vinyl chloride), chlorinated rubber, polyisobutyleDe, butadiene-styrene copolymers vinyl chloride-vinyl acetate copolymers, copolymers of vinyl acetate, vinyl chloride and maleic acid and poly(vinyl alcbhol).
The useful concentration of reducing agent according to the invention will vary depending upon the particular ~-photographic element, desired image, processing conditions, particular stabilizer precursor combination employed and the like.
A suseful concentration of reducing agent is typically from about 0,2 mole to about 2.0 moles of reducing agent per mole of photosensitive silver halide. A suseful concentration of reducing agent in relationship to oxidizing agent, such as silver behenate or silver stearate, is typically from about 0.01 mole to about 20 moles of reducing agent per mole of oxidizing agent such as per mole of silver behenate in the photothermographic material. Combinations of reducing agents can be employed if desired. When combinations are employed, the total concentration of reducing agent is typically within the ' ' ' . : :

. . .. .

described concentration range.
Pho~othenmographic materials according to the invention can contain development modifiers that function as speed-increasing compounds, hardeners, antistatic layers, plasticizers and lubricants, coating aids, brighteners, spectral sensitizing dyec, absorbing and filter dyes, also as described in the Product Licensin~ Index, Volume 92, December, 1971J publication 9232, pages 107-110.
The photothermographic elements according to the invention can comprise a wide variety of supports. Typical supports include cellulose nitrate film, cellulose ester film, poly(vinyl acetal) film, polystyrene film, poly(ethylene -terephthalate) film, polycarbonate film and related films or resinous materials, as well as glass " paper, metal and the like.
The support chosen should withstand the processing temperatures employed according to the invention. Typically, a flexible support is employed.
The photothermographic compositions and other compositions according to the invention can be coated on a suitable support by various coating procedures including dip coating, air knife coating, curtain coating or extrusion coating using hoppers such as described in U.S. Patent 2,681,294 of Beguin, issued June 15, 1954. If desired, two or more layers can be coated simultaneously such as described in U.S. Patent 2,761,791 of Russell, issued September 4, 1956 and British Patent 837,095.
Spectral sensitizing dyes can be used in the described photothermographic elements and compositions of the invention to con~er additional sensitivity to the elements and compositions of the invention. Useful sensitizing dyes are described, for example, in the Product Licensing Index, Volume 92, December, 1971, publication 9232, paragraph XV.

After imagewise exposure of the photographic element according to the invention, typically to visible light, the resulting latent image can be developed merely by overall heating the~element to moderately elevated temperatures.
This overall heating merely involves heating the described element overall in the range from about 80C. to about 250 C. such as for about 0.5 to about 60 seconds. By increasing or decreasing the length of time of heating, a higher or lower temperature within the described range can be employed depending upon the desired image, particular stabilizer precursor, particular reducing agent, and the like. Typically, a lower processing temperature is desired. A preferred processing temperature range is from about 115C. to about 175C. A developed and stabilized image is typically produced within several seconds, such as from about 0.5 seconds to about 60 seconds.
Any suitable means can be used for providing the desired processing temperature range. The heating means can be a simple hot plate, iron, roller or the like. ;
Processing is usually carried out under ambient conditions of pressure and humidity. Conditions outside normal atmospheric pressure and humidity can be employed if desired.
The described stabilizer precursors according to the invention can be in any suitable location in the photographic material ~according to the invention which provides the desired stabilized image. If desired, one or more of the components of the photothermographic element according to the invention can be in one or more layers of the element. For example, in some cases~ it can be desirable to~?include certain percentages of the reducing agent, toner, image stabilizer precursors and/or other addenda in a proteceive layer over the photothermo-: : : . , . . .: . . ' .
.
.. , .. - . ' : :

1(;~45878 graphic element. This in some cases can reduce migration of certain addenda in the layers of the photothermographic element.
Another embodiment of the invention comprises a photothermographic composition or element comprising (a) photo-sensitive silver halide in association with (b) a photo-sensitive silver halide developing agent, as described, (c) a stabilizer precursor combination, also as described, (d) a base-release agent, and (e) a polymeric binder for the composition or element.
A further embodiment of the invention comprises a photographic silver halide image stabilizer precursor composition comprising (a) a polymeric binder for said-composition with (b) a blocked thione, silver halide image stabilizer precursor and (c) a halogen containing stabilizer precursor as described.
A variety of base-release agents can be employed in the photographic materials according to the invention depending upon the particular photographic cQmponent, the 0 particular stabilizer precursor~ the desired image, processing temperature range, and the like. A base-release agent as employed herein is intended to mean a compound which releases base upon heating to a desired temperature to/ provide activation of st least one of the components of the photographic material, such as activation of the reducing agent. Typical base-release agents include those described, for example, iD U.s. Patent 3,531,285 of Haist et al, issued September 29, 1970. Useful - base-release agents include~ for example, guanidinium salts, such as guanidinium trichloroacetate, quaternary ammonium malonates~ ce~tain amino acids, heat cleavable hydrzides, ~ -and oxazolidones, as described in U.S. Patent 3,531,285.

:, :' ~ ' ' '' " ''. . -1~587&~

When a base-release agent is employed in a photographic material according to the invention, a range of concentration can be employed as described. A useful concentration is typically about 0.25 mole to about 10 moles of the base-release agent per mole of the photosensitive silver salt in the photographic material. A photothermographic composition or element according to the invention can accordingly comprise (a) photosensitive silver halide in association with (b) about 1 to about 4 moles of a silver halide developing agent per mole of such silver halide, (c) a blocked thione stabilizer precursor, as described, (d) a halogen containing stabilizer precursor, also as described, (e) about 0.25 to about 10 moles of a base-release agent per mole of such silver halide, and (f) a pol~meric binder for the composition or element.
If desired, the described stabilizer precursors, according to the invention, can be used in combination with other stabilizers or stabilizer precursors, such as with S-carbamoyl stabilizer precursors in photographic elements and compositions such as photothermographic materials. Useful S-carbamoyl stabilizer precursors are described in U.S.
Patent 3,824,103 of Z. R. Pierce et al, issued Jul~ 16, 1974.
The following examples are included for a further understanding of the invention.
~: :
Example 1 mis is a comparative example.
A silver behenate-behenic acid dispersion (I) is prepared by ball-milling the following components for 64 hours:
silver behenate 168 g behenic acid 64 g lithium stearate 16.8 g poly(vinylbut~ral) 120 g acetone-toluene (1:1 by volume)2 liters A~ - 24 _ . ...

The following addenda are combined with 71 ml of the above-identified dlspersion (I), mixed thoroughly and then coated on a suitable paper support at 0.86 g Ag/m2 and 2.5 g poly(vinylbutyral)/m2.
Poly(vinylbutyral)-silverbro~oiodide11 ml emulsion (3 l./mole Ag, 100 g polymer/mole Ag, 6 mole % iodide) Acetone-methanol solution (33:1 by 6 ml volume) containing 0.01% by weight 3-carboxy~methyl-5-C(3-methyl-2-thiazolinylidene)-l-methylethylidene~-rhodanine and 0.03% ~y volume triethylamine Acetone solution containing 10% by12 ml weight 2,6-dichloro-4-benzenesulfon-amidophenol Acetone-toluene-methanol solution 11 ml (1:1:1 by volume) containing 0.5%
by weight N-hydroxy-1,8-naphthalimide Acetone 12 ml The material is also overcoated with the following composition at 0.95 g cellulose acetate/m2.
cellu~lose acetate 20.0 g acetone-dichloromethane (1:1 by volume) 800 ml The dried element is exposed imagewise to tungsten light for 4 seconds and then heat-processed by contacting the element with a metal block heated to 140C. for 2 seconds.
After a sensitometric curve is obtained of the freshly processed sample, the coating is sub~ected to roomlight (about 50-60 ft.-candles from a white fluorescent bulb) for 1~ 2~ ~ 24~ 48~ and 120 hours, respectively. After each time interval, a new sensitometric curve is plotted from the processed sample. The ~min a~d Dmax values are lis~ed in following Table I.

Example 2 This is a comparative example This example is like Example 1 except that the composition now contains 2.5 ml of an acetone solution containing 3% by weight of 1-cyclohexylcarbamoyl-4-phenyl-2-tetrazoline-- , . : . , . ~, . . - ~ : : .

1~4S878 5-thione, designated Compound A, corresponding to 0.017 molelmole Ag. The thione compound is added to the described photothermographic composition prior to coating on the paper support. The sample is exposed, heat processed and subjected to roomlight handling as described in Example 1. The results are given in following Table I.
Example 3 This is a comparative example.
This example is like Example 1 except that the composition now contains 20 ml of an acetonesolutlon~
containing 10~/o by weight of ~-bromo-2-nitro-~-phenyl-butyrophenone, designated as Compound B, corresponding to 0.35 mole/mole Ag. The bromo compound is added to the described photothermographic composition prior to coating on the paper support. The samp~e is exposed, heat processed and subjected to the roomlight handling as described in ;
Example 1. The results are given in~ollowing Table I.

Example 4 The procedure in Example 1 is repeated except that the element contains the blocked thione and the ~haloketone -of Examples 2 and 3 at the concentrations specified in Table I.
The photothermographic element is exposed, heat processed and subjected to the roomlight handling as described in Example 1. The results are given in following Table I.

.. . . . . . . . . . . . .

X ,~ ~ o , . ~
~o .c , o o o o U) ~ ~ C~
o o o o ~ 0 ~ ~ ~ 0 oo U~ ~ ~ C~l .
~ ~ o o o o a 0 .
e ~ ~ O
~ ~ O O O O
~ .
.. U~
~ ~ U~ O
~ P~ ~J O O O O
~
U~
O
~ 1 _ N CO O
,~; I ~r) ~r) U 1 -I o o o o ~ ' ~1~ ~ 0 ~
,C
O O O O O ' ' ro , O
~¢ O 1` 1~, .
C~ O ~
O O t~ O ' ~1 0 X ' _~ ~
XO p~

.., . ~ ~
~ , .

- 2 7_ :

: .- - , . , ,. ,: - ., -, ., , ~ , 1~)4S87~3 Examples_5-19 Similar results are obtained when the following halogen containing stabilizer precursors are employed in the photothermographic element according to Example 4 in place of Compound B:
Example 5 Tetrabromobutane Example 6 2-tribromomethylsulfonylbenzothiazole Example 7 2,2-dibromo-2-phenylsulfonylacetamide ~~ S2 CBr2 CONH2 Example 8 2-bromoacetophenone ~ COCH2Br ,.

Example 9 ~-chloro-p-nitrotoluene . ' CH2Cl ~ .
.' Example 10 2,4'-dibromoacetophenone COC323r Br "' 109~587~
Example 11 2-bromo-2-phenylac~tophenone ~ CHBrCO
Exam~ e 12 2-bromo-1,3-diphenyl-1,3-propanedione ~ COCHBrCO

Example 13 ~_bromo-2,5-dimethoxyacetophenone H3CO~ ~ COCH2Br OCH
Example 14 2-bromo-2-~-tolylsulfonylacetamide CH3 ~ SO2CHBrCONH2 Example 15 ~-iodo-r-nitro-~-phenylbutyrophenone No2CH2-CHCHICOC6H5 Example 16 ~-bromo-p-nitrotoluene ;; CH2Br 2 ~ :

' - - - :: :
- . : : ' ' - . .:

Example 17 2-bromo-4'-phenylacetophenone ~)_ COCH2Br Example 18 ~-bromo~m-nitrotoluene Br ~l ' .

Example 19 2-bromo-2-nitro-1,3-propanediol H0 H2 , 2 Br Example l9-A

1,3-dibenzoyloxy-2-bromo-2-nitropropane : 0 N0 0 C6H5C OCH2 - ,C - CH2 - - C - C6H5 Br Another advantage which the described halogen contain~ng stabilizer precursors provide in silver halide - photothermographic materials is that they provide enhanced shelf-life or incubation stability at elevated temperatures o~ long-term keeping at ambient room conditions as described.
Examples 20-23 Similar results are obtained when the following blocked thione stabilizer precursors are employed in the photothermographic element according to Example 4 in place of Compound A:

.',:

: 30 16~145878 Example 20 l-methylcarbamoyl-4-phenyl-2-tetrazoline-5-thione Example 21 4-hexylcarbamoyl-1-phenyl-2-tetrazoline-5-thione Example 22 N,N'-hexamethylenebis(l-carbamoyl-4-phenyl-2-tetrazoline-5-thione Example 23 4-phenyl-1-phenylcarbamoyl-2-tetrazoline-5-thione Example 24 The following example illustrates a photothermographic material according to the invention comprising a base-release agent as described: a composition is prepared by mixing hydroquinone, 4-methyl-4-hydroxymethyl-1-phenyl-3-pyrazolidone, guanidinium trichloroacetate, poly(vinyl alcohol) binder in alcohol and water as described in Example 1 of U.S. Patent 3,531,285 of Haist et al, issued September 29, 1970.
l-Cyclohexylcarbamoyl-4-phenyl-tetrazoline-5-thione and tetrabromobutane also are added to the composition. The composition is coated on a photographic paper containing a gelatino, silver bromide photographic layer. Upon imagewise exposure to light followed by overall heating the element to about 190C. for a few sedonds, a developed and stabilized image results.
The invention has been described in detail with ~-particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

~': ':.

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

Claims (25)

WHAT IS CLAIMED IS:

1. A photothermographic element comprising a support having thereon at least one layer comprising photosensitive silver halide and a stabilizer precursor combination of (a) a blocked thione stabilizer precursor which contains a moiety which prevents the thione stabilizer precursor from reacting with silver ions in the photothermographic element prior to heating the photothermographic element, with (b) a halogen containing stabilizer precursor.

2. A photothermographic element as in Claim 1 comprising a support having thereon at least one layer comprising photosensitive silver halide and a combination of (a) a blocked thione stabilizer precursor which is a compound represented by the formula:

wherein R is aryl containing 6 to 12 carbon atoms and R1 is alkyl containing 1 to 6 carbon atoms, aryl containing 6 to 12 carbon atoms, cycloalkyl containing 3 to 8 carbon atoms when n is l; or R1 is alkylene containing 1 to 6 carbon atoms when n is 2; n is 1 or 2; with (b) a halogen containing stabilizer precursor which is a compound represented by the formula:

wherein X is chloro, bromo or iodo; R2, R3 and R4 are individually selected from the group consisting of hydrogen;
alkyl containing 1 to 10 carbon atoms; hydroxyalkyl containing 1 to 10 carbon atoms; acyloxyalkyl containing 2 to 10 carbon atoms; nitro; nitroalkyl containing 1 to 10 carbon atoms, aryl containing 6 to 12 carbon atoms; acyl of the formula R" - CO - wherein R" is alkyl containing l to 5 carbon atoms, or aryl containing 6 to 12 carbon atoms; amido represented by the formula wherein R7 and R8 are individually selected from the group consisting of hydrogen, alkyl containing 1 to 5 carbon atoms, phenyl and naphthyl; sulfonyl represented by the formula wherein R9 is alkyl containing 1 to 5 carbon atoms, or aryl containing 6 to 12 carbon atoms; bromo; chloro; and iodo;
and wherein at least one of R2, R3 and R4 is hydroxyalkyl, acyloxyalkyl, acyl, amido or sulfonyl as defined.

3. A photothermographic element as in Claim l wherein said blocked thione stabilizer precursor is l-cyclohexyl-carbamoyl-4-phenyl-2-tetrazoline-5-thione.

4. A photothermographic element as in Claim l wherein said halogen containing stabilizer precursor is a compound selected from the group consisting of (a) tetrabromobutane, (b) .alpha.-bromo-gamma-nitro-.beta.-phenylbutyrophenone, (c) 2-bromo-2-p-tolylsulfonylacetamide, (d) 2-tribromomethylsulfonylbenzothiazole, (e) 2,2-dibromo-2-phenylsulfonylacetamide, (f) 1,3-dibenzoyloxy-2-bromo-2-nitropropane, (g) 2-bromo-2-nitro-1,3-di-(4-nitrobenzoyloxy)propane, (h) 2-bromo-1,3-di-(4-methoxybenzoyloxy)-2-nitropropane, and combinations thereof.

5. A photothermographic element as in Claim 1 wherein said stabilizer precursor combination comprises (a) about 0.005 to about 0.035 mole of said blocked thione stabilizer per mole of total silver with (b) about 0.001 to about 1.0 mole of said halogen containing stabilizer precursor per mole of total silver.

6. In a photothermographic element comprising a support having thereon a layer comprising (A) photosensitive silver halide in association with (B) an oxidation-reduction image-forming combination comprising (i) a heavy metal salt oxidizing agent with (ii) an organic reducing agent, (C) a polymeric binder for said layer, and (D) a stabilizer precursor, the improvement wherein said stabilizer precursor comprises a stabilizer precursor combination of (a) a blocked thione stabilizer precursor which contains a moiety which prevents the thione stabilizer precursor from reacting with silver ions in the photothermographic element prior to heating the photo-thermographic element, with (b) a halogen containing stabilizer precursor.

7. A photothermographic element as in Claim 6 wherein said stabilizer precursor comprises a stabilizer precursor combination of (a) about 0.005 to about 0.035 mole of a blocked thione stabilizer precursor per mole of total silver with (b) about 0.001 mole to about 1.0 mole of a halogen containing stabilizer precursor per mole of total silver in said element.

8. A photothermographic element as in Claim 6 com-prising a support having thereon a layer comprising (A) photosensitive silver halide in association with (B) an oxidation-reduction image-forming combination comprising (i) silver behenate with (ii) a sulfonamidophenol reducing agent, (C) a poly(vinyl butyral) binder for said layer, (D) a stabilizer precursor combination comprising (I) l-cyclohexyl-carbamoyl-4-phenyl-2-tetrazoline-5-thione with (II) 2-bromo-2-p-tolylsulfonylacetamide, (E) a spectral sensitizing dye, and (F) a toner comprising succinimide, N-hydroxy-1,8-naphthalimide or phthalazinone.

9. In a photothermographic element comprising a support having thereon a layer comprising (A) photosensitive silver halide, (B) a silver halide developing agent, (C) a development activator precursor, (D) a polymeric binder for said layer and (E) a stabilizer precursor, the improvement wherein said stabilizer precursor comprises a combination of (a) a blocked thione stabilizer precursor which contains a moiety which prevents the thione stabilizer precursor from reacting with silver ions in the photothermographic element prior to heating the photothermographic element, with (b) a halogen containing stabilizer precursor.

10. A photographic composition comprising photo-sensitive silver halide, a polymeric binder for said composition and a stabilizer precursor combination comprising (a) a blocked thione stabilizer precursor which contains a moiety which prevents the thione stabilizer precursor from reacting with silver ions in the photothermographic element prior to heating the photothermographic element, with (b) a halogen containing stabilizer precursor.

11. A photographic composition as in Claim 10 also comprising a silver halide developing agent.

12. A photographic composition as in Claim 10 wherein said stabilizer precursor combination comprises (a) a blocked thione stabilizer precursor represented by the formula:

wherein R is aryl containing 6 to 12 carbon atoms and R1 is alkyl containing 1 to 6 carbon atoms, aryl containing 6 to 12 carbon atoms, cycloalkyl containing 3 to 8 carbon atoms when n is l; or R1 is alkylene containing 1 to 6 carbon atoms when n is 2; n is 1 or 2; with (b) a halogen containing stabilizer precursor which is a compound represented by the formula:

wherein X is chloro, bromo or iodo; R2, R3 and R4 are individually selected from the group consisting of hydrogen;
alkyl containing 1 to 10 carbon atoms; hydroxyalkyl containing 1 to 10 carbon atoms; acyloxyalkyl containing 2 to 10 carbon atoms; nitro; nitroalkyl containing 1 to 10 carbon atoms;
aryl containing 6 to 12 carbon atoms; acyl of the formula R" - CO - wherein R" is alkyl containing 1 to 5 carbon atoms, or aryl containing 6 to 12 carbon atoms; amido represented by the formula wherein R7 and R8 are individually selected from the group consisting of hydrogen, alkyl containing 1 to 5 carbon atoms, phenyl and naphthyl; sulfonyl represented by the formula wherein R9 is alkyl containing 1 to 5 carbon atoms, or aryl containing 6 to 12 carbon atoms; bromo; chloro; and iodo;
and wherein at least one of R2, R3 and R4 is hydroxyalkyl, acyloxyalkyl, acyl, amido or sulfonyl as defined.

13. A photographic composition as in Claim 10 wherein said blocked thione stabilizer precursor is 1-cyclohexyl-carbamoyl-4-phenyl-2-tetrazoline-5-thione.

14. A photographic composition as in Claim 10 wherein said halogen containing stabilizer precursor is a compound selected from the group consisting of (a) tetrabromobutane, (b) .alpha.-bromo-gamma-nitro-.beta.-phenylbutyrophenone, (c) 2-bromo-2-p-tolylsulfonylacetamide, (d) 2-tribromomethylsulfonylbenzothiazole, (e) 2,2-dibromo-2-phenylsulfonylacetamide, (f) 1,3-dibenzoyloxy-2-bromo-2-nitropropane, (g) 2-bromo-2-nitro-1,3-di-(4-nitrobenzoyloxy)propane, (h) 2-bromo-1,3-di-(4-methoxybenzoyloxy)-2-nitropropane, and combinations thereof.

15. In a photothermographic composition comprising (A) photosensitive silver halide in association with (B) an oxidation-reduction image-forming combination comprising (i) a heavy metal salt oxidizing agent with (ii) an organic reducing agent, (C) a polymeric binder for said layer, and (D) a stabilizer precursor, the improvement wherein said stabilizer precursor comprises a stabilizer precursor combination of (a) a blocked thione stabilizer precursor which contains a moiety which prevents the thione stabilizer precursor from reacting with silver ions in the photothermographic composition prior to heating the photothermographic composition, with (b) a halogen containing stabilizer precursor.

16. A photographic composition as in Claim 15 wherein said stabilizer precursor combination comprises (a) about 0.005 to about 0.035 mole of said blocked thione stabilizer precursor per mole of total silver with (b) about 0.001 to about l.0 mole of said halogen containing stabilizer precursor per mole of total silver in said composition.

17. A photothermographic composition comprising (A) photosensitive silver halide in association with (B) an oxidation-reduction image-forming combination comprising (i) a silver salt of a long-chain fatty acid with (ii) an organic reducing agent, (C) a polymeric binder for said composition, and (D) a stabilizer precursor, the improvement wherein said stabilizer precursor comprises a stabilizer precursor combination of (a) about 0.005 to about 0.035 mole of a blocked thione stabilizer precursor which contains a moiety which prevents the thione stabilizer precursor from reacting with silver ions in the photothermographic composition prior to heating the photo-thermographic composition, per mole of total silver with (b) about 0.001 mole to about 1.0 mole of a halogen containing stabilizer precursor per mole of total silver in said composition.

18. A photothermographic composition as in Claim 17 comprising (A) photosensitive silver halide in association with (B) an oxidation-reduction image-forming combination comprising (i) silver behenate with (ii) a sulfonamidophenol reducing agent, (C) a poly(vinyl butyral) binder for said composition, (D) a stabilizer precursor combination comprising (I) l-cyclo-hexylcarbamoyl-4-phenyl-2-tetrazoline-5-thione with (II) 2-bromo-2-p-tolylsulfonylacetamide, (E) a spectral sensitizing dye, and (F) a toner comprising succinimide, N-hydroxy-1,8-naphthalimide or phthalazinone.

19. A photothermographic composition comprising (a) photosensitive silver halide in association with (b) a silver halide developing agent, (c) a development activator precursor, (d) a polymeric binder for said composition and (e) a stabilizer precursor for said silver halide, the improvement wherein said stabilizer precursor comprises a combination of (i) a blocked thione stabilizer precursor which contains a moiety which prevents the thione stabilizer precursor from reacting with silver ions in the photothermographic composition prior to heating the photothermographic composition, with (ii) a halogen containing stabilizer precursor.

20. A process of stabilizing an image in a photo-thermographic element comprising a support having thereon at least one layer comprising a photosensitive silver halide and a stabilizer precursor combination of (a) a blocked thione stabilizer precursor which contains a moiety which prevents the thione stabilizer precursor from reacting with silver ions in the photothermographic element prior to heating the photo-thermographic element, with (b) a halogen containing stabilizer precursor for said silver salt, comprising heating said element to about 80°C to about 250°C.

21. A process as in Claim 20 wherein said element is heated at about 80°C to about 250°C for about 0.5 to about 60 seconds.

22. A process of developing and stabilizing an image in a photothermographic element comprising (A) photosensitive silver halide in association with (B) an oxidation-reduction image-forming combination comprising (i) a silver salt of a long-chain fatty acid with (ii) an organic reducing agent, (C) a polymeric binder for said layer, and (D) a stabilizer precursor comprising a combination of (a) a blocked thione stabilizer precursor which contains a moiety which prevents the thione stabilizer precursor from reacting with silver ions in the photothermographic element prior to heating the photothermo-graphic element, with (b) a halogen containing stabilizer precursor, comprising heating said element to about 80°C
to about 250°C.

23. A process of developing and stabilizing an image in a photothermographic element comprising a support having thereon a layer comprising (A) photosensitive silver halide in association with (B) an oxidation-reduction image-forming combination comprising (i) silver behenate with (ii) a sulfonamidophenol reducing agent, (C) a poly(vinyl butyral) binder for said layer, (D) a stabilizer precursor combination comprising (I) l-cyclohexylcarbamoyl-4-phenyl-2-tetrazoline-5-thione with (II) 2-bromo-2-p-tolylsulfonylacetamide, (E) a spectral sensitizing dye and (F) a toner comprising succinimide, N-hydroxy-1,8-naphthalimide or phthalazinone; comprising heating said element to about 120°C to about 160°C for about 0.5 to about 30 seconds.

24. A photographic silver halide image stabilizer precursor composition comprising (a) a polymeric binder for said composition with (b) a blocked thione silver halide image stabilizer precursor which contains a moiety which prevents the thione stabilizer precursor from reacting with silver ions in the photothermographic composition prior to heating the photothermographic composition, and (c) a halogen containing stabilizer precursor.

25. A photographic silver halide image stabilizer precursor composition comprising (a) a poly(vinyl butyral) binder for said composition with (b) l-cyclohexylearbamoy1-4-phenyl-2-tetrazoline-5-thione, and (c) a halogen containing stabilizer precursor which is a compound selected from the group consisting of (i) tetrabromobutane, (ii) .alpha.-bromo-gamma-nitro-.beta.-phenylbutyrophenone, (iii) 2-bromo-2-p-tolylsulfonylacetamide, (iv) 2-tribromomethylsulfonylbenzothiazole, (v) 2,2-dibromo-2-phenylsulfonylacetamide, (vi) 2-bromo-2-nitro-1,3-propanediol, (vii) 1,3-dibenzoyloxy-2-bromo-2-nitropropane, (viii) 2-bromo-2-nitro-1,3-di-(4-nitrobenzoyloxy)propane, (ix) 2-bromo-1,3-di-(4-methoxybenzoyloxy)-2-nitropropane, and combinations thereof.