Evans, Francis J. (Rochester, NY)
Mclaen, Donald F. (Rochester, NY)

05/272832

04/02/1974

07/18/1972

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Eastman Kodak Company (Rochester, NY)

430/448

430/965, 430/619, 430/566, 430/353

G03C1/498; G03C5/24; G03C1/02

96/114.1,66R,94,48HD 117/36.8

Torchin, Norman G.

Suro Pico, Alfonzo T.

Hampton, Robert W.

What is claimed is

1. In a photothermographic element comprising a support having thereon a photosensitive component, an oxidation-reduction image-forming combination comprising a heavy metal salt oxidizing agent with a reducing agent the improvement comprising a sulfonamidophenol reducing agent.

2. A photothermographic element as in claim 1 wherein said sulfonamidophenol reducing agent is a compound, selected from the group represented by the formula: ##SPC9##

3. A photothermographic element as in claim 1 wherein said sulfonamidophenol reducing agent is a compound of the formula: ##SPC12##

4. A photothermographic element as in claim 1 wherein said sulfonamidophenol is a compound of the formula: ##SPC13##

5. A photothermographic element as in claim 1 wherein said sulfonamidophenol reducing agent is 2,6-dichloro-4-benzene-sulfonamidophenol.

6. A photothermographic element as in claim 1 wherein said sulfonamidophenol reducing agent is 4-benzenesulfonamidophenol.

7. A photothermographic element as in claim 1 also comprising an activator-toning agent which is phthalazinone, phthalimide, succinimide or N-hydroxy-1,8-naphthalimide.

8. A photothermographic element as in claim 1 wherein said photosensitive component is photosensitive silver halide.

9. A photothermographic element comprising a support having thereon

10. A photothermographic element as in claim 1 comprising about 0.25 to about 4.0 moles of said sulfonamidophenol reducing agent per mole of said photosensitive component.

11. A photothermographic composition comprising

12. A photothermographic composition as in claim 11 comprising about 0.4 to about 2.0 moles of said sulfonamidophenol reducing agent per mole of said photosensitive component.

13. A photothermographic composition as in claim 11 also comprising an activator-toning agent which is phthalazinone, phthalimide, succinimide or N-hydroxy-1,8-naphthalimide.

14. A photothermographic composition comprising

15. A photothermographic composition comprising

16. A process of developing a latent image in an exposed photothermographic element comprising a support having thereon a photosensitive component, an oxidation-reduction image-forming combination comprising a heavy metal salt oxidizing agent with a sulfonamidophenol reducing agent and a polymeric binder, comprising heating said element from about 80°C. to about 250°C.

17. A process of developing a latent image as in claim 16 wherein said photothermographic element is heated from about 80°C. to about 250°C. for about 0.5 to about 60 seconds.

18. A process of developing a latent image in a photothermographic element comprising a support having thereon

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to certain reducing agents in photothermographic elements, compositions and processes to provide improved processing temperature latitude with improved neutral developed images. In one of its aspects it relates to photothermographic elements containing such reducing agents. In another of its aspects it relates to a photothermographic composition containing the described reducing agents. A further aspect relates to a method of developing a latent image in the described photothermographic elements by overall heating.

2. Description of the State of the Art

It is well known in the art to provide photothermographic materials containing reducing agents. Such photothermographic materials after exposure are heated overall to provide a developed image in the absence of separate processing solutions. Reducing agents which have been employed in photothermographic materials are described, for example, in Belgian Pat. No. 765,452 issued May 28, 1971; Belgian Pat. No. 765,602 issued May 28, 1971; Belgian Pat. No. 765,601 issued May 28, 1971; Belgian Pat. No. 766,590 issued June 15, 1971; Belgian Pat. No. 766,589 issued June 15, 1971; Belgian Pat. No. 772,371 issued Oct. 15, 1971; U.S. Pat. No. 3,152,904 of Sorenson et al. issued Oct. 13, 1964; U.S. Pat. No. 3,152,903 of Sorenson et al. issued Oct. 13, 1964; U.S. Pat. No. 3,457,075 of Morgan et al. issued July 22, 1969; U.S. Pat. No. 3,392,020 of Yutzy et al. issued July 9, 1968 and British Specification No. 1,161,777 published Aug. 20, 1969. Many of the reducing agents such as aminophenol reducing agents which have been useful for photographic silver halide development are overly active in photothermographic materials and produce undesired indiscriminate reduction when employed in such photothermographic materials resulting in undesired fog in certain areas of a developed image. This is demonstrated in following comparative Example 2. The exposed areas of a photothermographic element tend to rapidly fog if heating of the photothermographic element during processing is continued beyond a certain temperature. It has been desirable to provide a photothermographic element which reduces this tendency toward fogging and thus provides wider processing temperature latitude. It has also been desirable to provide a photothermographic element which provides results which are less dependent upon the presence of a so-called activator toning agent such as phthalazinone. Many of the reducing agents employed in photothermographic materials such as methylene-2,2'-bis(4-methyl-6-tertiary-butylphenol), as demonstrated in following comparative Example 24 are highly dependent upon the presence in the photothermographic material of a so-called activator toner also known as a toner accelerator.

Various reducing agents have been employed in the photographic art for various purposes. Many of these reducing agents, however, have not been satisfactory in photothermographic materials because of undesired image discrimination provided by such reducing agents, undesired image tone, undesired processing temperature latitude and the like.

Phenolic reducing agents have been used in photographic materials for various purposes. Sulfonamidophenols, for example, have been used for different purposes in photographic materials such as described in Canadian Pat. No. 815,526 issued June 17, 1969; copending applications Ser. No. 176,684 of Loria and Salminen, filed Aug. 31, 1971; Ser. No. 176,751 of Fleckenstein and Figueras filed Aug. 31, 1971 now abandoned and Ser. No. 176,752 of Fleckenstein filed Aug. 31, 1971. Most phenolic reducing agents, however, have not provided improved processing temperature latitude or improved developed image discrimination.

Accordingly, there has been a continuing need to provide improved photothermographic elements, compositions and processes to provide improved processing temperature latitude and improved image discrimination.

SUMMARY OF THE INVENTION

It has been found according to the invention that improved processing temperature latitude with improved image discrimination upon processing with heat is provided in a photothermographic element and/or composition by a sulfonamidophenol reducing agent. The sulfonamidophenol reducing agent can be employed in a photothermographic material comprising an oxidation-reduction image-forming combination comprising a heavy metal salt oxidizing agent with the described sulfonamidophenol reducing agent. This image-forming combination is used with a catalyst for the oxidation-reduction combination, preferably photosensitive silver halide. Certain of the sulfonamidophenol reducing agents enable the omission of a so-called activator toning agent from the described photothermographic material.

DETAILED DESCRIPTION OF THE INVENTION

A range of sulfonamidophenol reducing agents is useful in photothermographic elements and compositions according to the invention. In photothermographic materials a sulfonamidophenol reducing agent is useful which can be used in combination with a heavy metal salt oxidizing agent to provide an oxidation-reduction image-forming combination and which provides improved processing temperature latitude and improved image discrimination. One test which can be used in determination of suitable sulfonamidophenol reducing agents is set out in following Example 1. Another test which can be used is set out in following Examples 29-33 wherein succinimide is used as an activator toning agent in place of phthalazinone. The term sulfonamidophenol reducing agent as employed herein includes sulfonamidonaphthol reducing agents and sulfonamidophenol reducing agents. Choice of an optimum sulfonamidophenol reducing agent will depend upon the particular photothermographic composition, desired image, processing conditions and the like. The sulfonamidophenol reducing agents useful according to the invention can be prepared employing known procedures in the art and include such compounds as described in Canadian Pat. No. 815,526 of Bard, issued June 17, 1969. A useful class of sulfonamidophenol reducing agents according to the invention which includes sulfonamidophenols and sulfonamidonaphthols is represented by the structure: ##SPC1##

wherein

R ¹ and R ² are each selected from the group consisting of hydrogen; chlorine; bromine; iodine; alkyl containing one to four carbon atoms, such as methyl, ethyl, propyl and butyl; aryl containing six to 12 carbon atoms such as phenyl and tolyl; arylsulfonyl containing six to 12 carbon atoms, such as phenylsulfonyl; amino; hydroxy; alkoxy containing one to four carbon atoms, such as methoxy and ethoxy; and atoms completing with R ¹ or R ² a naphthalene nucleus;

Z ¹ and Z ³ are each selected from the group consisting of hydrogen; bromine; chlorine; alkyl containing one to four carbon atoms, as described; aryl containing six to 10 carbon atoms, such as phenyl and tolyl; arylsulfonyl containing six to 12 carbon atoms, as described; amino; hydroxy; alkoxy containing one to four carbon atoms, such as methoxy and ethoxy; and R ⁶ SO ₂ NH- wherein R ⁶ is alkyl containing one to four carbon atoms, such as methyl, ethyl, propyl and butyl, aryl containing 6 to 10 carbon atoms, such as phenyl and tolyl and hetero ring substituents, such as thienyl, quinolinyl and thiazyl, ##SPC2##

or ##SPC3##

wherein R is p-hydroxyphenyl, p-hydroxy-3,5-dichlorophenyl or p-hydroxy-3,5-dibromophenyl;

Z ² is hydrogen, alkyl containing one to four carbon atoms, such as methyl, ethyl, propyl and butyl, chlorine, bromine or R ⁶ SO ₂ NH-- when R ¹ and R ² are atoms completing a naphthalene nucleus;

Z ² is hydrogen, alkyl containing one to four carbon atoms such as methyl, ethyl, propyl or butyl, chlorine and bromine when R ¹ and R ² are other than atoms completing a naphthalene nucleus; at least one of Z ¹ , Z ² and Z ³ is R ⁶ SO ₂ NH--.

The described groups such as alkyl, alkoxy and aryl include such groups containing substituents which do not adversely affect the reducing properties and desired sensitometric properties of the described photothermographic elements and compositions. Examples of substituent groups which can be present are alkyl containing one to three 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.

One especially useful class of sulfonamidophenol reducing agents within the described structure are compounds of the formula: ##SPC4##

wherein

R ³ is phenyl, naphthyl, methylphenyl, thienyl, quinolinyl, thiazyl, or alkyl containing one to four carbon atoms, as described;

R ⁴ is hydrogen, R ³ SO ₂ NH--, alkoxy containing one to four carbon atoms, hydroxy, alkyl containing one to four carbon atoms, bromine or chlorine;

R ⁵ is hydrogen, bromine, chlorine, alkyl containing one to four carbon atoms, such as methyl, ethyl, propyl or butyl, or alkoxy containing one to four carbon atoms, such as methoxy, ethoxy and propoxy. R ³ , R ⁴ and/or R ⁵ 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. These substituent groups are the same as described for generic structure I.

Another class of sulfonamidophenol reducing agents which are useful in photothermographic elements and compositions of the invention are sulfonamidonaphthols of the formula: ##SPC5##

The sulfonamidophenol group in the described sulfonamidonaphthols can be in the ortho, meta or para position. The sulfonamidonaphthols and sulfonamidophenols which contain three sulfonamidophenol groups are more active compounds within the sulfonamidophenol reducing agent class. These sulfonamidophenols 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 sulfonamidonaphthols and trifunctional sulfonamidophenols is less than that provided by other of the described sulfonamidophenols.

Combinations of sulfonamidophenol reducing agents, as described, can be employed in photothermographic materials and elements according to the invention. Examples of useful sulfonamidophenol reducing agents in photothermographic materials and elements according to the invention are listed in the following examples. Especially useful sulfonamidophenol reducing agents include benzenesulfonamidophenol reducing agents, such as 2,6-dichloro-4-benzenesulfonamidophenol and/or 4-benzenesulfonamidophenol.

One embodiment of the invention is in a photothermographic element comprising a support having thereon a photosensitive component, an oxidation-reduction image-forming combination comprising a heavy metal salt oxidizing agent with a reducing agent; the improvement comprising a sulfonamidophenol reducing agent, as described.

The described photothermographic element comprises a photosensitive component which is typically a photosensitive salt, such as a photosensitive silver salt. It is believed that the photosensitive component acts as a catalyst for the described oxidation-reduction image-forming combination. A typical concentration range of photosensitive component, especially photosensitive silver salt, is from about 0.01 to about 20 moles of photosensitive component per mole of heavy metal salt oxidizing agent, for example, per mole of silver salt of organic acid. An especially useful photosensitive component is photosensitive silver halide. Useful photosensitive silver salts, however, include silver dye complexes and combinations of photosensitive silver halide with other photosensitive silver salts. Preferred photosensitive silver halides are silver chloride, silver bromide, silver bromoiodide, silver chlorobromoiodide or mixtures thereof. The photosensitive silver halide can be coarse or fine grain, very fine grain photosensitive silver halide being especially useful. The photosensitive 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 9232, pages 107-110, paragraph I. The photosensitive silver halide employed according to the invention can be unwashed or washed, can be chemically sensitized, can be protected against the production of fog and/or stabilized against loss of sensitivity during keeping, as described in the above Product Licensing Index reference.

The photothermographic elements and/or compositions according to the invention comprise an oxidation-reduction image-forming combination which contains an oxidizing agent, preferably a heavy metal salt oxidizing agent. The 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 illumination. An especially useful class of heavy metal salts of organic acids is represented by the water insoluble silver salts of long-chain fatty acids which are stable to light. Compounds which are suitable silver salt oxidizing agents include silver behenate, silver stearate, silver oleate, silver laurate, silver hydroxystearate, silver caprate, 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. In most cases, however, only the more reactive sulfonamidophenol reducing agents are useful with a silver benzotriazole as the heavy metal salt oxidizing agent.

The described sulfonamidophenol reducing agents can be employed in combination with other reducing agents in the described oxidation-reduction image-forming combination. Suitable reducing agents which can be employed in combination with the sulfonamidophenol reducing agents include substituted phenols and naphthols, for example, bis-β-naphthols. Suitable bis-β-naphthols include, for example, 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/or bis-(2-hydroxy-1-naphthol)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 butyl hydroquinone, methyl hydroquinone, 2,5-dimethyl hydroquinone and 2,6-dimethyl hydroquinone; catechols and pyrogallols, chloro-substituted hydroquinones such as chloro hydroquinone or dichloro hydroquinone; alkoxy substituted hydroquinone such as methoxy hydroquinone or ethoxy hydroquinone; aminophenol developing agents, such as 2,4-diaminophenols and methylaminophenols; ascorbic acid developing agents such as ascorbic acid, ascorbic acid ketals and ascorbic acid derivatives; hydroxylamine developing agents; 3-pyrazolidone developing agents such as 1-phenyl-3-pyrazolidone and 4-methyl-4-hydroxymethyl-1-phenyl-3-pyrazolidone and the like. Combinations of these reducing agents can be employed if desired.

It is often desirable to employ a so-called activator toning agent, also known as an accelerator-toning agent, in the photothermographic elements according to the invention to obtain a desired image. The activator toning agent is typically useful in a range of concentration, such as a concentration of about 0.10 moles to about 1.1 moles of activator toning agent per mole of oxidizing agent in the photothermographic element. A typical suitable activator toning agent is a heterocyclic activator toning agent containing at least one nitrogen atom as described in Belgian Pat. No. 766,590 issued June 15, 1971. Typical activator toning agents include, for example, phthalimide, N-hydroxyphthalimide, N-hydroxy-1,8-naphthalimide, N-potassium phthalimide, N-mercury phthalimide, succinimide and/or N-hydroxysuccinimide. Other activator toning agents which can be employed include phthalazinone, 2-acetylphthalazinone and the like.

It is desirable, in some cases, to employ an image stabilizer and/or image stabilizer precursor in the described elements of the invention. Typical image stabilizers or stabilizer precursors are described, for example, in Belgian Pat. No. 768,071 issued July 30, 1971. Typical stabilizer precursors include, for example, azothioethers and blocked azoline thione stabilizer precursors as described in this Belgian Patent.

A photothermographic element, as described according to the invention can contain various compounds 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 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 having 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, polymethyl methacrylate, poly(vinyl pyrrolidone), ethylcellulose, polystyrene, polyvinyl chloride, chlorinated rubber, polyisobutylene, butadiene-styrene copolymers, vinyl chloride-vinyl acetate copolymers, copolymers of vinyl acetate, vinyl chloride and maleic acid and polyvinyl alcohol.

If desired, the photosensitive silver halide employed in the described photothermographic elements can be prepared in situ such as described in U.S. Pat. No. 3,457,075 of Morgan et al. issued July 22, 1969.

An especially useful photothermographic element according to the invention comprises a support having thereon (a) photosensitive silver halide, (b) an oxidation-reduction image-forming combination comprising (i) silver behenate and/or silver stearate, with (ii) 2,6-dichloro-4-benzenesulfonamidophenol and/or 4-benzenesulfonamidophenol, (c) succinimide and/or N-hydroxy-1,8-naphthalimide, and (d) a polymeric binder, such as poly(vinyl butyral).

A concentration range of reducing agent can be employed in the described photothermographic element and/or composition of the invention. A useful concentration of reducing agent is typically from about 0.25 mole to about 4 moles of sulfonamidophenol reducing agent per mole of photosensitive component, such as silver halide in the photothermographic element and/or composition. In relation to the oxidizing agent employed, a useful concentration of reducing agent is typically from about 0.10 mole to about 20.0 moles of reducing agent per mole of oxidizing agent, such as silver behenate or silver stearate. If other reducing agents are employed in combination with the described sulfonamidophenol reducing agent, the total concentration of reducing agent is typically within the described concentration range for sulfonamidophenol.

Photothermographic elements 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, paragraph I.

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 supports which can withstand the processing temperatures employed according to the invention. Typically a flexible support is employed.

Another embodiment of the invention is a photothermographic composition comprising (a) a photosensitive component, typically a photosensitive silver salt such as photosensitive silver halide, with (b) an oxidation-reduction image-forming combination comprising (i) a heavy metal salt oxidizing agent with (ii) a sulfonamidophenol reducing agent, as described, and (c) a polymeric binder, also as described, such as poly(vinyl butyral). An example of such a photothermographic composition comprises (a) photosensitive silver halide, (b) an oxidation-reduction image-forming combination comprising (i) silver behenate or silver stearate, with (ii) a sulfonamidophenol reducing agent, as described, such as 2,6-dichloro-4-benzene-sulfonamidophenol and/or 4-benzenesulfonamidophenol, (c) an activator-toning agent which is phthalazinone, phthalimide, succinimide, and/or N-hydroxy-1,8-naphthalimide, and (d) a polymeric binder, such as poly(vinyl butyral).

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. 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. 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 exposure of the described photothermographic 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 merely involves heating the described photothermographic element overall from about 80°C. to about 250°C. such as for about 0.5 seconds 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. A developed image is typically produced within several seconds, such as about 0.5 seconds to about 60 seconds. A processing temperature of about 110°C. to about 165°C. is especially useful.

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.

If desired, one or more components of the photothermographic element 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, activator toner, image stabilizer and/or stabilizer precursor 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 following examples are included for a further understanding of the invention.

EXAMPLE 1

A dispersion is prepared by ball-milling the following components for about 12 hours:

poly(vinyl butyral) 1.25 g behenic acid 3.2 g silver behenate 3.9 g sodium bromide 0.2 g 1-(2H)phthalazinone 0.9 g acetone-toluene (1:1 parts by volume) 50 ml

The resulting dispersion, in the absence of a reducing agent, is coated on a polyethylene coated paper support at 0.6 millimoles of silver per square foot. A 0.02 molar solution of 4-(N-Methylsulfonamido)phenol in acetone-alcohol is coated onto the resulting element at 6 milligrams per square decimeter. The resulting photothermographic element is permitted to dry. It is then sensitometrically exposed to tungsten light and then overall heated by contacting a heated metal block for 2 seconds at 115°C.

A dense black image having a maximum density of 0.63 and a minimum density of 0.18 is obtained.

EXAMPLE 2

This is a comparative example.

The procedure set out in Example 1 is repeated with the exception that 4-aminophenol is employed as a reducing agent in place of 4-(N-methylsulfonamido)phenol. The concentration of 4-aminophenol is 0.02 molar. The coating coverage of 4-aminophenol is 5 milligrams per square decimeter. Upon sensitometric exposure of the photothermographic element and overall heating at 115°C. as described in Example 1, an image appears in less than one second followed by rapid formation of dense fog. The resulting image is brown in color.

EXAMPLES 3-17

The procedure set out in Example 1 is repeated with the exception that the sulfonamidophenol reducing agents listed in the following Table I are employed in place of the described 4-(N-methylsulfonamido)phenol. Heating time of the photothermographic element after sensitometric exposure is listed in Table I as well as the degree of image discrimination and fog formation. A single plus indicates a low density (under 0.2), two pluses indicate an image of moderate density (0.2 - 0.8) and three pluses indicate an image of high density (over 0.8). Zero indicates no image fog.

TABLE I ##SPC6##

Time Example No. Substituents (seconds) Image/Fog ______________________________________ 3 R ⁸ =CH ₃ SO ₂ NH- 2 +++/+ 4 R ⁶ =CH ₃ SO ₂ NH- 4 +++/0 5 R ⁸ =C ₆ H ₅ SO ₂ NH- 3 ++/+ 6 R ⁸ =p-CH ₃ C ₆ H ₄ SO ₂ NH- 4 ++/+ 7 R ⁸ =p-NO ₂ C ₆ H ₄ SO ₂ NH- 5 ++/0 8 R ⁸ =p-BrC ₆ H ₄ SO ₂ NH- 4 ++/+ 9 R ⁶ =p-CH ₃ C ₆ H ₄ SO ₂ NH- 6 +++/0 10 R ⁶ =CH ₃ ;R ⁸ =CH ₃ SO ₂ NH- 2 ++/+ 11 R ⁶ =CH ₃ R ⁸ =C ₆ H ₅ SO ₂ NH- 2 +++/+ 12 R ⁷ =CH ₃ ;R ⁸ =C ₆ H ₅ SO ₂ NH- 4 +++/0 13 R ⁶ =Cl;R ⁸ =C ₆ H ₅ SO ₂ NH- 1 +++/0 14 R ⁶ =Cl;R ⁸ =p-BrC ₆ H ₄ SO ₂ NH- 2 ++/0 15 R ⁶ =R ¹⁰ =Cl;R ⁸ =C ₆ H ₅ SO ₂ 1H- ++/+ 16 R ⁶ =R ¹⁰ =Br;R ⁸ =C ₆ H ₅ SO ₂ 2H- ++/+ 17 R ⁸ =C ₄ H ₉ SO ₂ NH- 4 ++/+ ______________________________________

In each example, other substituents are hydrogen unless indicated otherwise.

Each photothermographic element in Examples 3-17 produced an image with acceptable image discrimination.

EXAMPLES 18-23

These examples demonstrate a photothermographic element according to the invention in the absence of an activator toning agent.

The procedure set out in Example 1 is repeated with the exception that phthalazinone is omitted. The procedure is also repeated employing a 0.02 molar concentration of phthalazinone in the photothermographic element. The results of Examples 18-23 with and without phthalazinone are set out in following Table II. In each instance the photothermographic element is heated for the designated time at 150°C.

Table II ____________________________________________________________ ______________ Without Toner With Phthalazinone ____________________________________________________________ ______________ Example Compound Time Time No. of (seconds) Image Hue (seconds) Image Hue ____________________________________________________________ ______________ 18 Example 5 1 +++ Neutral 5 +++ Neutral 19 Example 7 1 +++ Brown 3 +++ Neutral 20 Example 10 3 ++ Brown 3 ++ Brown 21 Example 12 2 +++ Brown 4 +++ Neutral 22 Example 13 2 +++ Neutral 2 +++ Neutral *23 1 +++ Neutral too active ____________________________________________________________ ______________ ##SPC7##

It should be noted in these examples that the image appears as rapidly in the absence of the toning agent as in its presence and that the images are equally dense although they are not as neutral in hue in each example.

EXAMPLE 24

This is a comparative example.

The procedure set out in Example 18 is repeated with the exception that methylene-2,2'-bis(4-methyl-6-tertiary-butylphenol) is employed in place of the described reducing agent. The results produced after sensitometric exposure and overall heating at 150°C. are set out in the following Table III.

Table III ____________________________________________________________ ______________ Without Toner With Phthalazinone ____________________________________________________________ ______________ Example Time: Time No. (seconds) Image Hue (seconds) Image Hue 24 11 + Tan 5 +++ Dark Brown ____________________________________________________________ ______________

EXAMPLES 25-28

Ten cc of a 2.5% by weight poly(vinyl butyral) solution in acetone/toluene containing 0.4 millimoles of the reducing agent designated in Table IV and 0.08 to 0.14 millimoles of 1-(2H)-phthalazinone is overcoated onto a photosensitive element containing behenic acid, silver behenate and silver bromide in a poly(vinyl butyral) binder. This photosensitive element is prepared by mixing the noted components and coating the resulting composition onto a film support at 0.60 millimoles of silver per square foot. The resulting photothermographic element is sensitometrically exposed to tungsten light through a high contrast image. The resulting latent image is developed by overall heating the photothermographic element by contacting it with a heated metal block at 115°C. or 150°C. for the time specified in following Table IV.

Table IV ____________________________________________________________ ______________ Example Toner- Temp Time No. Compound Accelerator (°C.) (seconds) Dmax Dmin ____________________________________________________________ ______________ 25 Butylsulfonamidophenol Phthalazinone 115° 2 1.05 .10 26 Butylsulfonamidophenol Phthalazinone 150° 1 1.60 .09 27 1,1'-Binaphthol (Comparative Example) Phthalazinone 115° 20 .88 .16 28 1,1'-Binaphthol (Comparative Example) Phthalazinone 150° 5 1.90 .19 ____________________________________________________________ ______________

It is concluded from the results in Examples 25-28 that the sulfonamidophenol reducing agent of Example 25 produces a desired maximum density in shorter processing time than the compound of Example 27. It is also observed that the compounds of Example 25 provides greater processing temperature latitude.

EXAMPLES 29-37

The procedure set out in Example 1 is repeated with the exception that phthalazinone is replaced with an equal molar concentration of succinimide and a concentration of one mole of the sulfonamidophenol reducing agent described in following Table V is employed for each 2 moles of silver behenate present in the photothermographic element. The photothermographic element is sensitometrically exposed to tungsten light and then overall heated at the temperatures and times described in following Table V. The results employing this procedure are set out in following Table V.

Table V ____________________________________________________________ ______________ Example Sulfonamidophenol Temp Time Image No. Compound (°C.) (seconds) Density Fog ____________________________________________________________ ______________ 29 Compound of 120° 2 1.14 0.06 Example 5 30 Compound of 125° 2 1.00 0.06 Example 5 31 Compound of 130° 2 1.40 0.15 Example 5 32 Compound of 135° 2 1.20 0.14 Example 5 33 Compound of 140° 2 1.28 0.16 Example 5 34 Compound of 125° 2 1.20 0.10 Example 17 35 Compound of 130° 2 1.22 0.05 Example 17 36 Compound of 130° 2 1.18 0.30 Example 3 37 Compound of 135° 2 1.08 0.20 Example 3 ____________________________________________________________ ______________

It is concluded from this data that satisfactory image density is obtained at a processing temperature of 120°C. and yet fog density is not excessive at temperatures as high as 140°C. This is increased processing temperature latitude which many reducing agents do not provide. With many reducing agents fog is observed almost as soon as desired image density is produced.

EXAMPLES 38-63

The procedure set out in Example 1 is repeated using the sulfonamidophenols of Table VI. Processing is carried out at 150°C. The time of processing and image density are given in following Table VI. Image discrimination is satisfactory in each case with the exception of the sulfonamidonaphthols and trifunctional sulfonamidophenols which are more desirably employed for very short processing times or with a different oxidizing agent than silver behenate. The results of Examples 38-63 are set out in the following Table VI. ##SPC8##

EXAMPLE 64

A silver behenate-behenic acid dispersion is prepared by ball-milling the following components for about 112 hours:

Silver behenate 168.0 g Behenic acid 64.0 g Lithium stearate 16.8 g Poly(vinyl butyral) 120.0 g Acetone-toluene (1:1 parts by volume) 2.01 l

63.0 ml. of this dispersion are mixed with 20.0 ml. of silver bromoiodide dispersed in poly(vinyl butyral) (6 liters/mole of silver) and with the following components:

Acetone-toluene-methanol (1:1:1 parts by volume)solution containing 0.5% by weight of N-hydroxy-1,8-naphthalimide 8.0 ml Acetone-methanol solution (33:1 parts by volume) containing 3-carboxy-methyl-5-[(3-methyl-2-thiazolidinylidene)-1-methyl ethylidene]rho danine and 0.01% by volume triethylamine 6.2 ml Acetone solution containing 10% by weight 2,6-dichloro-4-benzenesulfonamid ophenol 10.0 ml Acetone 18.0 ml

The resulting composition is coated and permitted to dry on a paper support at 8.61 mg. of silver per square decimeter to provide a photothermographic element. This photothermographic element is exposed sensitometrically to tungsten light for 0.5 seconds and then heated overall by contacting the element with a heated metal block for 2 seconds at 140°C. A developed image results. The element is then held in fluorescent room light under ambient conditions for 48 hours. The resulting image is black with a beige background.

It is often desirable to provide an overcoat on the described photothermographic elements. The overcoat can comprise polymeric materials which can protect the photothermographic element against undesired fingerprint marks and abrasion. One overcoat which is suitable comprises a combination of gelatin with a polyhydric alcohol plasticizer, such as 3-methyl-2,4-pentanediol and/or glycerin, or a polymeric latex comprising at least one 2-acetoacetoxyethyl methacrylate group, such as described in U.S. Pat. No. 2,960,404 of Milton et al. and/or U.S. Pat. No. 3,488,704 of Smith.

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.