Costa, Lorenzo F. (Rochester, NY)
Van Allan, James A. (Rochester, NY)
Grum, Frank (Rochester, NY)

05/443892

04/01/1975

02/19/1974

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Eastman Kodak Company (Rochester, NY)

430/351

430/370, 430/566, 430/617

G03C1/498; G03C1/02; G03C5/34; G03C1/34

96/48HD,109,114.1,66R,114,114.6

Torchin, Norman G.

Suro Pico, Alfonso T.

Knapp R. E.

What is claimed is

1. In a photothermographic element comprising a support having thereon a layer comprising (a) photographic 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 the layer and (d) a bromine compound stabilizer precursor, the improvement wherein said bromine compound stabilizer precursor comprises a compound represented by the structure: ##SPC3##

2. A photothermographic element as in claim 1 wherein R³ is phenyl, naphthyl or benzothiazolyl.

3. A photothermographic element as in claim 1 wherein said bromine compound stabilizer precursor is 2-tribromomethylsulfonylbenzothiazole.

4. A photothermographic element as in claim 1 wherein said bromine compound stabilizer presursor is 2,4-bis(tribromomethyl)-6-methyltriazine.

5. A photothermographic element as in claim 1 wherein said bromine compound stabilizer precursor is 2,2-dibromo-2-phenylsulfonylacetamide.

6. A photothermographic element as in claim 1 comprising about 0.002 mole to about 0.75 mole of said bromine compound stabilizer precursor per mole of total silver in said photothermographic element.

7. A photothermographic element comprising a support having thereon a layer comprising

8. A photothermographic composition comprising photographic silver halide, a polymeric binder and a bromine compound represented by the formula: ##SPC4##

9. A photothermographic composition as in claim 8 wherein said bromine compound is 2-tribromomethylsulfonylbenzothiazole.

10. A photothermographic composition as in claim 8 comprising about 0.002 mole to about 0.75 mole of said bromine compound per mole of total silver in said composition.

11. In a photothermographic composition comprising (a) photographic silver halide in association with (b) an oxidation-reduction image-forming combination comprising (i) a heavy metal salt oxidizing agent with (ii) a reducing agent, (c) a polymeric binder and (d) a bromine compound stabilizer precursor, the improvement wherein said bromine compound stabilizer precursor comprises a compound represented by the structure: ##SPC5##

12. A photothermographic composition as in claim 11 wherein R³ is phenyl, naphthyl or benzothiazolyl.

13. A photothermographic composition as in claim 11 wherein said bromine compound stabilizer precursor is 2-tribromomethylsulfonylbenzothiazole.

14. A photothermographic composition as in claim 11 wherein said bromine compound stabilizer is 2,4-bis(tribromomethyl)-6-methyltriazine.

15. A photothermographic composition as in claim 11 wherein said bromine compound stabilizer precursor is 2,2-dibromo-2-phenylsulfonylacetamide.

16. A phototheimographic composition as in claim 11 comprising about 0.002 mole to about 0.75 mole of said bromine compound stabilizer precursor per mole of total silver in said composition.

17. A photothermographic composition comprising

18. A method of developing an image in a photothermographic element comprising a support having thereon a layer comprising (a) photographic silver halide in association with (b) an oxidation-reduction image-forming combination comprising (i) a silver salt oxidizing agent with (ii) a reducing agent, (c) a polymeric binder and (d) a bromine compound stabilizer precursor comprising a compound represented by the structure: ##SPC6##

19. A method as in claim 18 of developing an image in a photothermographic element comprising a support having thereon a layer comprising

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to certain photolytically active polybrominated stabilizer precursors and photothermographic elements, compositions and processes using said precursors to provide improved stable images. In one of its aspects it relates to a photothermographic element comprising (a) photographic 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 the layer and (d) a photolytically active polybrominated organic compound stabilizer precursor as described. In another of its aspects it relates to a photothermographic composition comprising photographic silver halide, a polymeric binder and a photolytically active polybrominated organic compound stabilizer precursor as described. A further aspect relates to such photographic compositions which are photothermographic materials. A further aspect relates to a method of developing a stable image in a photothermographic element comprising the described photographic silver halide in association with the oxidation-reduction image-forming combination and the described stabilizer precursors.

2. Description of the State of the Art

It is known to obtain an image in a photosensitive element by so-called dry processing with heat. The photothermographic element employed for providing such an image can contain a reducing agent, a light-sensitive silver salt of an organic acid, such as silver behenate, as an oxidizing agent and a low concentration of photographic silver halide. Such photothermographic materials are described, for example, in U.S. Pat. No. 3,457,075 of Morgan, et al., issued July 22, 1969; U.S. Pat. No. 3,152,904 of Sorensen, et al., issued Oct. 13, 1964; British Specification No. 1,161,777 published Aug. 20, 1969; U.S. Pat. No. 3,392,020 of Yutzy, et al., issued July 9, 1968; U.S. Pat. No. 3,707,377 of Tiers, et al., issued Dec. 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 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. These include, for example, (1) washing the element with water to remove undeveloped silver salts, (2) heating the element to release Bronstead or Lewis acid such as HCl, borontrifluoride or HF from compounds such as m-nitrobenzenesulfonyl chloride, para-toluenesulfonic acid urea addition complex or p-acetamidobenzenediazonium fluoroborate and (3) chelation of the oxidizing agent with, for example, salicylaldoxime or benzotriazole as described in U.S. Pat. No. 3,152,904 of Sorensen, et al., issued Oct. 13, 1964. Another method proposed for solving the problem of post-processing instability is to provide a photothermographic combination in which the oxidation-reduction image-forming combination is on one sheet of material and the latent image-forming photographic silver halide on a separate sheet. The sheets are separated after imagewise exposure such as described in U.S. Pat. No. 3,152,904. A further means proposed for stabilization involves swabbing a 1% solution of phenylmercaptotetrazole onto the surface of the overall heated photothermographic material or rubbing benzotriazole into the surface of the photothermographic element. 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, photographic materials by treating the developed image with a solution containing certain thiol or thione compound stabilizers. This is described, for example, in U.S. Pat. No. 3,617,289 of Ohkubo, et al., issued Nov. 2, 1971. One of the compounds proposed for this solution stabilization is 1-phenyl-5-mercaptotetrazole. Unfortunately, the addition of this compound to unexposed photographic silver halide 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 copending U.S. application Ser. No. 249,260 of Hiller, filed May 1, 1972 which is a continuation-in-part application of U.S. Ser. No. 43,171 of Hiller, filed June 3, 1970, now abandoned and corresponding to Belgian Pat. No. 768,071 published July 30, 1971. Certain stabilizer precursors which are azole thioethers or blocked azoline thiones are employed in photothermographic materials according to the description in the applications. 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 in the developed image.

Another means for post-processing stabilization of certain photothermographic materials is described in U.S. Pat. No. 3,707,377 of Tiers, et al., issued Dec. 26, 1972. Certain polyhalogenated organic oxidizing agents such as tetrabromobutane and tribromoquinalidine are described in certain heat developable photographic materials to provide post-processing stabilization. Unfortunately, tetrabromobutane and tribromoquinaldine do not provide the desired stabilization in certain photothermographic materials. For instance, photothermographic elements containing tribromoquinaldine cannot be expected to be processable above about 50°C. without undesired decomposition of the tribromoquinaldine. As illustrated in the following comparative examples, the photolytically active polybrominated organic compound stabilizer precursors according to the invention provide surprisingly improved stabilization without significantly adversely affecting maximum density and without undesired decomposition.

Halogenated organic compounds have been employed in photographic materials for various purposes, such as antifoggants. Halogenated organic antifoggants for photographic emulsions are described, for example, in U.S. Pat. No. 3,128,187 of Segal, et al., issued Apr. 7, 1964; U.S. Pat. No. 3,232,762 of Ford, et al., issued Feb. 1, 1966; U.S. Pat. No. 2,732,303 of Morgan, et al., issued Jan. 24, 1956; U.S. Pat. No. 3,835,581 of Tinker, et al., issued May 20, 1958 and U.S. Pat. No. 3,271,154 of Dersch, issued Sept. 6, 1966. None of these patents, however, indicate that the photolytically active polybrominated organic compound stabilizer precursors according to the invention can be employed in photothermographic materials to provide improved post-processing stability.

Photographic materials which do not contain photographic silver halide and comprising tribromomethylsulfonyl derivatives of certain heterocyclic compounds such as benzothiazole compounds and benzimidazole compounds are described in Canadian Pat. No. 831,465 issued Jan. 6, 1970. This patent, however, does not described photothermographic materials containing photographic silver halide.

There has been a continuing need for photothermographic materials comprising an image-forming combination containing photographic silver halide which have improved post-processing image stability, that is reduced background density and no significant decrease in desired maximum density when employing a halogen-containing stabilizer precursor.

SUMMARY OF THE INVENTION

It has been found according to the invention that the described improvements are provided in a photothermographic element or composition as described by employing as a bromine containing organic stabilizer precursor a polybromo compound represented by the formula: ##SPC1##

wherein

R is alkyl containing 1 to 6 carbon atoms,

R ¹ is hydrogen or a bromine atom,

R ² is a bromine atom or a carbamoyl group, and

R ³ is an aromatic chromophore group which has the property of imparting to said bromine compound stabilizer precursor the ability to absorb electromagnetic radiation having a wavelength between about 250 and 385 nm; and at least one of R ¹ , R ² and R ³ is or contains a bromine atom.

The described improvements are provided, for example, in a photothermographic element comprising a support having thereon a layer comprising (a) photographic silver halide in association with (b) an oxidation-reduction image-forming combination comprising (i) a heavy metal salt oxidizing agent, preferably a silver salt oxidizing agent, with (ii) an organic reducing agent, (c) a polymeric binder for the layer and (d) a bromine compound stabilizer precursor as described.

A latent image in the described photothermographic element or composition can be developed by overall heating the element or composition to moderately elevated temperatures.

DETAILED DESCRIPTION OF THE INVENTION

A variety of bromine compound stabilizer precursors, as described within the above formulas, can be employed according to the invention to provide improved post-processing stability without significantly adversely affecting desired properties of the photothermographic material.

Different tests can be employed to determine whether compounds or materials are useful as stabilizer precursors as described depending upon the particular photothermographic element, composition, desired image, processing conditions and the like. One test which can be employed for certain photothermographic elements is as follows:

A silver behenate-behenic acid dispersion (A) is prepared by ball-milling the following components for 72 hours:

silver behenate 168.0 g behenic acid 64.0 g poly(vinyl butyral) 120.0 g lithium stearate 16.4 g acetone-toluene (1:1 parts by volume) 2.01 l

A photothermographic element is prepared by combining 141 ml of the described dispersion (A) with the following addenda, mixing thoroughly and coating at 0.63 g of composition per square decimeter on a suitable paper support:

acetone solution containing 0.01% 18.0 ml by weight 3-ethyl-5[(3-ethyl-2- benzothiazolinylidene)-1-methyl- ethylidene]-2-thio-2,4-oxazolidinedione acetone solution containing 10% by 24.0 ml weight 2,6-dichloro-4-benzenesulfon- amidophenol poly(vinyl butyral)-silver 22.0 ml bromoiodide emulsion (6 l./mole Ag., 6 mole % I, 100 g. polymer/mole Ag) acetone-toluene (1:1 by volume) 44.0 ml organic solvent solution, typically 11.0 ml acetone, containing polybromo stabilizer precursor according to the invention (typically organic solvent solution containing about 3% by weight of stabilizer precursor according to the invention)

The resulting photographic element is permitted to dry. It is then imagewise exposed to tungsten light for 1 second and then overall heated by contacting the exposed photothermographic element for about 2 to 4 seconds with a metal block heated to 150°C. Preferred stabilizer precursors according to the invention should prevent buildup of background density or minimum density above 0.10 density unit more than the original minimum density of a developed image without significantly adversely affecting maximum density.

It is believed that the described brominated organic compounds according to the invention are precursors to the moiety which upon combination with silver ions or atoms prevents instability due to roomlight exposure. The exact mechanism of stabilization is not fully understood. It is believed, however, that upon imagewise exposure of a photothermographic material containing photographic silver halide to actinic radiation, latent image specks of metallic silver are formed in the photographic silver halide remaining in the background areas of the photothermographic element to produce unwanted background printup, especially after subsequent overall heating. It is believed that the bromine from the described stabilizer precursors of the invention is at least in part released photolytically and attacks and destroys the latent image metallic silver sites before they produce printup, that is before background fog is produced, without attacking the developed silver image to any significant degree. It is believed that the photolytically released bromine comprises free radicals which reoxidize the latent image silver atoms in the photographic silver halide to silver ions.

An advantage of the bromine containing stabilizer precursors according to the invention is that they have sufficient thermal stability for use in the described photothermographic materials. This is illustrated in the following comparative examples.

One useful class of stabilizer precursors according to the invention within the described formulas comprises a compound wherein described R ¹ and R ² are each bromine atoms and R ³ is phenyl, naphthyl or benzothiazole.

The term "aromatic chromophore group" as employed herein is intended to mean a group which imparts to the bromine compound stabilizer precursor containing the group the ability to release at least one bromine atom when exposed to electromagnetic radiation having a wavelength between about 250 and 385 nm. A variety of aromatic chromophore groups can provide this desired property. Especially useful aromatic chromophore groups include phenyl, naphthyl or benzothiazole. These groups can contain substituent groups which do not adversely affect the stabilizing action of the stabilizer precursors according to the invention, such as methyl, ethyl and the like.

The term "polybromo" or "polybrominated" compound as employed herein is intended to mean a compound as described containing two or more bromine atoms.

Useful stabilizer precursors as described include, for example, the following compounds:

2-tribromomethylsulfonylbenzothiazole

2,4-bis(tribromomethyl)-6-methyltriazine

2,2-dibromo-2-phenylsulfonylacetamide

The described polybrominated organic compounds can be prepared by methods known in the art. For example, the parent organic compound can be brominated employing conventional bromination processes. An example preparation is the preparation of 2-tribromomethylsulfonylbenzothiazole which comprises adding dropwise at 5° to 10°C. 150 milliliters of bromine to a stirred solution of 240 grams of sodium hydroxide in 2.5 liters of water. Upon completion of the addition, a solution of 110 grams of 2-carboxymethylmercaptobenzothiazole and 50 grams of sodium bicarbonate in 1.25 liters of water is added dropwise. Stirring is continued for 3 hours and the resulting white mixture is allowed to stand overnight at room temperature. The resulting white solid can be collected by filtration and recrystallized from acetic acid to provide the desired 2-tribromomethylsulfonylbenzotriazole having a melting point of 168°-170°C.

Another example of a useful preparation is the preparation of 2,4-bis(tribromomethyl)-6-methyltriazine in which a mixture of 140 grams of 2,4,6-trimethyltriazine and 520 grams of sodium acetate dispersed in 2,300 milliliters of acetic acid is heated to 70°C. while adding 520 milliliters of bromine slowly with stirring over a 2-hour period. The temperature is raised to 90°C. for one hour and the mixture is allowed to stand about 16 hours. After standing, 2 liters of water is added and the solid mixture resulting is collected by filtration and recrystallized from acetonitrile. The desired 2,4-bis(tribromomethyl)-6-methyltriazine has a melting point of 153°-155°C.

Some halogenated organic compound impurities can be present in the resulting compositions. These impurities can be separated, if desired, before mixing the desired brominated compound stabilizer precursor with the described photothermographic materials.

The described polybrominated stabilizer precursors according to the invention are useful in a variety of silver halide photothermorgaphic materials.

The useful concentration of stabilizer precursor according to the invention will depend upon different factors such as the particular photothermographic element, particular components of the photothermographic material, desired image, desired image stability and the like. A useful concentration of stabilizer precursor according to the invention is about 0.002 mole to about 0.75 mole of the described stabilizer precursor per mole of total silver in the photothermographic material. An especially useful concentration is about 0.01 mole to about 0.5 mole of the described stabilizer precursor per mole of total silver in the photothermographic material. When combinations of stabilizer precursors are employed according to the invention, the total concentration of stabilizer precursors is within the described concentration range. The optimum concentration useful can be determined based on the described factors.

Typical photothermographic materials in which the stabilizer precursors of the invention are useful are described, for example, in U.S. Pat. No. 3,457,075 of Morgan, et al., issued July 22, 1969; U.S. Pat. No. 3,152,904 of Sorensen, et al., issued Oct. 13, 1964; U.S. Pat. No. 3,429,706 of Shepard, et al., issued Feb. 25, 1969; U.S. Pat. No. 3,672,904 of deMauriac, issued June 27, 1972 and Research Disclosure, January, 1973, pages 16-21. The stabilizer precursors of the invention are especially useful in photothermographic materials comprising (a) photographic silver halide in association with (b) an oxidation-reduction image-forming combination comprising (i) a silver salt of a long-chain fatty acid, such as silver behenate, with (ii) a phenolic reducing agent, (c) a poly(vinyl butyral) binder for the layer, (d) a toner, also known as an activator-toning agent or known as a toner-accelerator, comprising 1-(2H)-phthalazinone, succinimide or N-hydroxy-1,8-naphthalimide, and (e) a spectral sensitizing dye.

An especially useful embodiment of the invention is a photothermographic element comprising a support having thereon a layer comprising (a) photographic 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 the layer, (d) a toner comprising 1-(2H)-phthalazinone, succinimide or N-hydroxy-1,8-naphthalimide, and (e) a stabilizing concentration of 2-tribromomethylsulfonylbenzothiazole, 2,4-bis(tribromomethyl)-6-methyltriazine or 2,2-dibromo-2 -phenylsulfonylacetamide.

The described photothermographic materials according to the invention comprise a photosensitive component which is photographic silver halide. In the photothermographic materials it is believed that the latent image silver resulting from the photosensitive salt acts as a catalyst for the described oxidationreduction image-forming combination. A typical concentration range of photographic silver halide is from about 0.01 mole to about 20.0 moles of photographic silver halide per mole of silver salt oxidizing agent, for example, per mole or silver behenate. Other photosensitive silver salts can be used in combination with the photographic silver halide if desired. Useful photosensitive silver salts include silver-dye complexes. Preferred photographic silver halides are silver chloride, silver bromide, silver bromoiodide, silver chlorobromoiodide or mixtures thereof. Very fine-grain photographic silver halide is especially useful although coarse or fine-grain photosensitive silver halide can be employed if desired. The photographic silver halide can be prepared by any of the procedures 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 9,232 on page 107, paragraph I. The photographic silver halide according to the invention can be unwashed or washed, can be chemically sensitized, can be protected against the production of fog and stabilized against loss of sensitivity during keeping, as described in the above Product Licensing Index publication.

The photothermographic elements and compositions according to the invention comprise an oxidation-reduction image-forming combination which contains a heavy metal salt oxidizing agent, preferably a silver salt oxidizing agent, especially a silver salt of a long-chain fatty acid. Such silver salt oxidizing agents are resistant to darkening upon illumination. Typically useful silver salts of long-chain fatty acids are those containing about 17 to 30 carbon atoms. Compounds which are useful silver salt oxidizing agents include: silver behenate, silver stearate, silver oleate, silver laurate, silver hydroxystearate, silver caprate, silver myristate and silver palmitate. Silver salts which are not silver salts of long-chain fatty acids can be employed in combination with the 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. Examples of other heavy metal salt oxidizing agents are gold stearate, mercury behenate and gold behenate. Combinations of oxidizing agents are also useful.

The described photothermographic elements and compositions can comprise various organic reducing agents. Useful reducing agents which can be employed with the described stabilizer precursors include substituted phenols and naphthols, for example, bis-beta naphthols. Suitable bis-beta-naphthols include, for example, 2,2'-dihydroxy-1,1'-binaphthyl, 6,6'-dibromo-2,2'-dihydroxy-1,1'-binaphthyl or 6,6'-dinitro-2,2'-dihydroxy-1,1'-binaphthyl. 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, methylhydroquinone, 2,5-dimethylhydroquinone and 2,6-dimethylhydroquinone; catechols and pyrogallols, chloro-substituted hydroquinones such as chlorohydroquinone or dichlorohydroquinone; alkoxy-substituted hydroquinone such as methoxyhydroquinone or ethoxyhydroquinone; aminophenol reducing agents, such as 2,4-diaminophenols and methylaminophenols; ascorbic acid reducing agents such as ascorbic acid, ascorbic acid ketals and ascorbic acid derivatives; hydroxylamine reducing agents; 3-pyrazolidone reducing agents such as 1-phenyl-3-pyrazolidone and 4-methyl-4-hydroxymethyl-1-phenyl-3-pyrazolidone and the like. Combinations of reducing agents can be employed if desired.

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: ##SPC2## wherein R ⁶ is phenyl, naphthyl, methylphenyl, thienyl, quinolinyl, thiazyl, or alkyl containing 1 to 4 carbon atoms, such as methyl, ethyl, propyl or butyl; R ⁴ is hydrogen, R ⁶ SO ₂ NH--, alkoxy containing 1 to 4 carbon atoms, such as methoxy, ethoxy, propoxy and butoxy, bromine or chlorine; R ⁵ is hydrogen, bromine, chlorine, alkyl containing 1 to 4 carbon atoms, as described, or alkoxy containing 1 to 4 carbon atoms, such as methoxy, ethoxy and propoxy. R ⁴ , R ⁵ and/or R ⁶ 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 photothermographic elements and materials of the invention. Examples of substituent groups which can be present are alkyl containing 1 to 3 carbon atoms such as methyl, ethyl and propyl, chlorine, bromine 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.

It is desirable, in some cases, to employ a so-called toning agent, also known as an activator-toning agent or a toner-accelerator, in the photothermographic materials of the invention. Useful toning agents are described, for example, in Belgian Pat. No. 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, N-hydroxyphthalimide, N-potassium phthalimide, succinimide, N-hydroxy-1,8-naphthalimide and N-hydroxysuccinimide. In some cases other toning agents can be employed such as 1-(2H)-phthalazinone, 2-acetylphthalazinone and the like.

It is desirable, in some cases, to employ a combination of stabilizer precursors in the photothermographic materials of the invention.

In addition to combinations of stabilizers within the described formula according to the invention, other image stabilizers or stabilizer precursors can in some cases be employed with the stabilizer precursors of the invention. Typical stabilizer precursors which can be employed in combination with the stabilizer precursors of the invention include, for example, azole thioethers and blocked azoline thione stabilizer precursors as described in Belgian Pat. No. 768,071 issued July 30, 1971, and in copending U.S. application Ser. No. 435,806 of Burness, et al., filed concurrently herewith.

A photothermographic element or composition as described according to the invention can contain various colloids and polymers alone or in 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, polysaccharides such as dextran, gum arabic and the like; and synthetic polymeric substances such as water soluble polyvinyl compounds like poly(vinyl pyrrolidone), 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 waterinsoluble 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 having recurring sulfobetaine units as described in Canadian Pat. No. 774,054. Especially useful high molecular weight materials and resins include poly(vinyl butyral), cellulose acetate butyrate, poly(methyl methacrylate), poly(vinyl pyrrolidone), ethylcellulose, polystyrene, poly(vinyl chloride), chlorinated rubber, polyisobutylene, butadiene-styrene copolymers, vinyl chloride-vinyl acetate copolymers, copolymers of vinyl acetate, vinyl chloride and maleic acid and poly(vinyl alcohol).

The useful concentration of reducing agent according to the invention will vary depending upon the particular photothermographic element, desired image, processing conditions, particular stabilizer precursor employed and the like. A useful concentration of reducing agent is typically from about 0.2 mole to about 2.0 moles of reducing agent per mole of photographic silver halide. A useful 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 silver salt of a long-chain fatty acid, such as per mole of silver behenate, in the photothermographic material. Reducing agents can be employed in combination. When combinations are employed, the total concentration of reducing agent is typically within the described concentration range.

Photothermographic 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 dyes, absorbing and filter dyes, also as described in the Product Licensing Index, Volume 92, December, 1971, 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, film supports as described in U.S. Pat. No. 3,634,089 of Hamb, issued Jan. 11, 1972 and U.S. Pat. No. 3,725,070 of Hamb, et al., issued Apr. 3, 1973 and related films or resinous materials, as well as glass, paper, metal and the like supports which can 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. Pat. No. 3,681,294 of Beguin issued June 15, 1954. If desired, two or more layers can be coated simultaneously such as described in U.S. Pat. No. 2,761,791 of Russell, issued Sept. 4, 1956 and British Pat. No. 837,095.

Spectral sensitizing dyes can be used in the described photothermographic elements and compositions of the invention to confer 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, pages 107-110, paragraph XV.

After imagewise exposure of a photothermographic element according to the invention, typically a 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 to a temperature within the range of from about 80°C. 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 reducing agent, and the like. Typically, a lower processing temperature is desired. A preferred processing temperature range is from about 115°C. to about 175°C. 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 precursor according to the invention can be in any suitable location in the photothermographic 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 precursor and/or other addenda in a protective layer over the photothermographic element. This in some cases can reduce migration of certain addenda in the layers of the photothermographic element.

The described stabilizer precursors according to the invention can be used in, for example, photothermographic materials comprising photographic silver halide as described in U.S. Pat. No. 3,679,426 of Youngquist, issued July 25, 1972; U.S. Pat. No. 3,667,958 of Evans, issued June 6, 1972; U.S. Pat. No. 3,667,959 of Bojara and deMauriac, issued June 6, 1972; Belgian Pat. No. 766,590 issued June 15, 1971; U.S. Pat. No. 3,672,904 of deMauriac, issued June 27, 1972; Belgian Pat. No. 772,371 issued Oct. 15, 1971 and U.S. application Ser. No. 272,832 of Evans and McLaen, filed July 18, 1972.

A variety of methods of incorporating a stabilizer precursor according to the invention into photothermographic materials as described can be employed. A typical method of preparing a photothermographic material according to the invention is described in U.S. application Ser. No. 275,582 of Simons, filed July 27, 1972. The described stabilizer precursor can be incorporated in the described photothermographic materials at various stages in preparation.

The following examples are included for a further understanding of the invention.

EXAMPLE 1

This is a comparative example.

A silver behenate-behenic acid dispersion A is prepared by ball-milling the following components for 72 hours: silver behenate 168.0 g behenic acid 64.0 g poly(vinyl butyral) 120.0 g lithium stearate 16.4 g acetone-toluene (1:1 parts by volume) 2.0 l.

A photothermographic element is prepared by combining 141 ml. of the above-described dispersion (A) with the following addenda, mixing thoroughly and coating at 0.63 g of composition/dm ² on a suitable paper support:

Acetone solution containing 0.01% 18.0 ml by weight 3-ethyl-5-[(3-ethyl-2- benzothiazolinylidene)-1-methyl- ethylidene]-2-thio-2,4-oxazolidinedione Acetone solution containing 10% by 24.0 ml weight 2,6-dichloro-4-benzenesulfon- amidophenol Poly(vinyl butyral)-silver bromoiodide 22.0 ml emulsion, (6 l./mole Ag, 6 mole % I, 100 g polymer/mole Ag) Acetone-toluene (1:1 by volume) 44.0 ml

The following composition is coated over the element at a coverage of 0.43 g/dm ² , thereby providing a protective layer containing approximately 10.76 mg cellulose acetate/dm ² of support.

cellulose acetate 5.0 g acetone-dichloromethane (1:1 parts by volume) 200.0 ml

The resulting photothermographic element is imagewise exposed for 1 second to tungsten light and then overall heated by contacting the photothermographic element for 2 seconds on a metal block heated to 150°C. The sensitometric results for the resulting developed image are given in following Table I. The processed element is then subjected to 1,500 ft. candles of light for 72 hours. The sensitometric data resulting from this stability test are also given in following Table I.

EXAMPLE 2

The procedure described in Example 1 is repeated with the exception that the described composition contained 11 milliliters of an acetone solution containing 3% by weight of 2-tribromomethylsulfonylbenzothiazole; and, the acetone-toluene solvent mixture was reduced to 33 milliliters.

The resulting photothermographic element was imagewise exposed and then overall heated as described in Example 1. It was then exposed to 1,500 ft. candles of light for 72 hours also as described in Example 1. The resulting sensitometric data are given in following Table I.

TABLE I ____________________________________________________________ ______________ Fresh 72 Hour Print-Up Relative* Relative* Example Stabilizer Speed Contrast Dmin Dmax Speed Contrast Dmin Dmax ____________________________________________________________ ______________ 1 no 100 1.87 0.01 1.24 78 1.62 0.22 1.24 2 yes 52 1.49 0.01 1.22 52 1.29 0.01 1.13 ____________________________________________________________ ______________ *measured at 0.3 above Dmin The above results demonstrate that compounds such as 2-tribromomethylsulfonyl-benzothiazole are extremely efficient image stabilizers for photothermographic materials. Note that print-out density due to roomlight handling is prevented over a 72 hour period.

EXAMPLE 3

A silver behenate dispersion is prepared by ballmilling the following components for 100 hours:

silver behenate 50.0 g poly(vinyl butyral) 15.0 g methyl isobutyl ketone 500 ml

A photothermographic element is prepared by combining the following addenda in the order indicated, mixing thoroughly and coating the resulting composition on an unsubbed poly(ethylene terephthalate) film support at 0.74 milliliters per square decimeter:

poly(vinyl butyral)-silver bromide 200.0 ml emulsion (6 liters of emulsion per mole of silver, 100 g. of polymer per mole of silver) acetone solution containing 0.66 60.0 ml milligrams of 2-(5,5-dicyano- 4-phenyl-2,4-pentadienylidene)- 1-ethylnaphtho[1,2-d]-thiazoline (hold one hour at room temperature) silver behenate dispersion as 500.0 ml described above acetone solution containing 50.0 ml 10% by weight succinimide (hold one hour at room temperature) acetone solution containing 180.0 ml 14% by weight poly(vinyl butyral) acetone solution containing 180.0 ml 6.3% by weight 4-benzenesulfon- amidophenol acetone solution containing 50.0 ml 5% by weight 2,4-dihydroxy- benzophenone acetone-toluene solution 30.0 ml (1:1 by volume) containing 2% by volume silicone surfactant (Silicone AF-70 which is a trade name of the General Electric Co., U.S.A.) acetone solution containing 20.0 ml 2.28% by weight anhydrous lithium iodide (hold one hour at room temperature)

The resulting photothermographic element is also overcoated with the following composition at 0.25 milliliters per square decimeter:

poly[4,4'-(hexahydro-4,7-methano- 5.0 g indan-5-ylidene)diphenylene carbonate] dichloroethane 95.0 ml acetone 4.0 ml silicone surfactant (L-522 sold 0.5 ml by the Union Carbide Co., U.S.A.)

After drying, the photothermographic element is separated into several equal parts. One part is maintained as a control and the remaining parts are dipped quickly into a solution of 30 grams per liter of tribromoquinaldine, referred to herein as TBQ, in 2-butanone and air dried. Control and comparative examples of the described photothermographic element are also prepared in the same manner by dipping film strips into the solvents alone or into a solution of 2-tribromomethylsulfonylbenzothiazole, also referred to herein as TSB, respectively. Each film sample is exposed imagewise for 5 minutes to red light from the zero order light of a calibrated monochromator when protected with a filter combination that permits only radiation of wavelengths longer than 590 nanometers to pass. The respective samples are then overall heated as indicated in the following Table II employing the listed time and temperature conditions. In Table II the term "con" is used to identify untreated film samples used as controls and the term "S-C" is used to identify solvent treated control samples.

The described polylerominated organic compounds according to the invention are useful in the photothermographic element according to Example 3 as an incubation antifoggant. An incubation antifoggant is intended to mean a compound according to the invention which increases stability in the photothermographic material prior to imagewise exposure.

TABLE II ____________________________________________________________ ______________ Compound Development Development Descriptor Time (Min.) Temperature (°C) Observations ____________________________________________________________ ______________ TBQ 5 53 A weak image is formed TBQ 5 60 No image TBQ 5 70 No image TBQ 5 80 No image TBQ 2 90 No image S-C 2 90 A poor negative image is formed Con 2 90 A negative image is formed TBQ 2 100 No image TSB 2 100 A good negative image is formed S-C 2 100 A good negative image is formed Con 2 100 A good negative image is formed TBQ 2 110 No image TSB 2 110 Good negative image (better than control) S-C 2 110 Good negative image Con 2 110 Good negative image ____________________________________________________________ ______________

The data in Table II indicates that the TBQ treated coatings do not provide useful images with the described element, processing time and temperature listed. It is believed that the undesired results with TBQ are due at least in part to undesired decomposition of TBQ at temperatures above 50°C. This is demonstrated in the following examples. Photolytic efficiency of stabilizer precursors according to the invention can also be tested employing the procedure in the following examples.

EXAMPLE 4

The thermal stability of proposed stabilizer precursors can be determined by dissolving about 5 milligrams of the proposed stabilizer precursor and about 5 milligrams of cadmium iodide in 5 milliliters of 2-butanone and immersing the sample in a thermostatically controlled water bath while raising the temperature of the water bath slowly from room temperature to 75°C. over a period of 6 hours of continuous observation. The temperature at which each sample produces color is recorded. Those proposed stabilizer precursors which provide a color below about 60°C. are considered insufficiently stable for purposes of the invention. The results are recorded in the following Table III.

The proposed stabilizer precursors can also be qualitively evaluated for relative photolytic efficiency by preparing solutions in the manner described for the thermal stability test in Example 4. The solution is exposed to actinic light from an unfiltered xenon arc lamp for 5 seconds at a distance of 10 centimeters. The density of the color produced in the solution is observed and an arbitrary reading of the density qualitatively is given to each solution of excellent, good, fair or poor. The relative photolytic efficiency ratings are given in the following Table III.

The following compounds are tested:

Compound A -- 2-tribromomethylsulfonylbenzothiazole (TSB) Compound B -- 1-methyl-2-(2-hydroxy-3,3-tri- chloropropyl)quinolinium p- toluenesulfonate Compound C -- 2,4-bis(tribromomethyl)-6-methyl- s-triazine (referred to herein as BMT) Compound D -- bis(tribromomethyl)sulfoxide Compound E -- bis(tribromomethyl)sulfone Compound F -- alpha,alpha,alpha-tribromoquinaldine (TBQ)

TABLE III ______________________________________ Decomposition Photolytic Compound Temperature (°C) Efficiency ______________________________________ A Above 75 Good B 50 Poor C Above 75 Excellent D 73 Excellent E 60 Excellent F 50 Good ______________________________________

The tests reported in the above table indicate that compounds A and C are especially useful because their decomposition temperature is above 75°C.

EXAMPLE 5

The procedure described in Example 2 is repeated with the exception that the compound 2,4-bis(tribromomethyl)-6-methyl-s-triazine (BMT) is employed in place of 2-tribromomethylsulfonylbenzothiazole (TSB). Results similar to those in Example 2 are obtained.

EXAMPLE 6

Five strips of a photothermographic paper, i.e., 3M Company Dry Silver Paper Type 7743, are treated as follows:

Sample No. 1 Untreated Original (Control 1) 2 Solvent treated (Control 2) 3 TBQ treated 4 BMT treated 5 TSB treated

The solvent treated sample is prepared by stroking the front surface of the 3M Company Dry Silver Paper Type 7743 once with a camel's hair brush which has been dipped into 2-butanone.

The TBQ and BMT treated samples are prepared in the same mannere as the solvent treated sample except, in place of the solvent, a solution is used comprising 20 grams per liter of the stabilizer precursor in the solvent.

The TSB treated sample is prepared as described above except that the concentration of the solution was only 9 grams of TSB per liter.

The samples are dried overnight in the dark and treated in a fadeometer the next day. The fadeometer is a standard testing apparatus which provides exposure to intense light. The total reflected densities were measured from each sample at 550 nanometers after 4 hours and after 28 hours fading in the high intensity xenon arc fadeometer. The measured densities are recorded in the following Table IV.

TABLE IV ______________________________________ Reflection density after Sample No. Fading Time (Hours) Compound ______________________________________ 0 4 28 1 0.10 0.26 1.04 Control 2 0.10 0.43 1.19 Solvent 3 0.09 0.17 0.16 TBQ 4 0.09 0.10 0.13 BMT 5 0.07 0.11 0.22 TSB* ______________________________________ *It is believed that these densities would be lower if the treating solution were as concentrated as the treating solutions of the other samples.

3M Company Dry Silver Paper Type 7743 comprises a paper support having thereon a photothermographic layer comprising a toner which is 1-(2H)-phthalazinone with 2,2'-methylenebis(4-methyl-6-tertiarybutylphenol), silver behenate, silver bromide, aluminum oxide, and tetrabromobutane. The photothermographic layer is overcoated with a vinylacetate and vinylacetate-vinyl chloride copolymer layer. Tetrabromobutane is employed as a stabilizer.

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.