PHOTOTHERMOGRAHIC ACCELERATORS FOR LEUCO DIAZINE, OXAZINE, AND THIAZINE DYES

Abstract: A photothermographic construction comprises a light-­ sensitive color-forming element on a support base, the element comprising a silver source, optionally silver halide, a binder, and an oxidizable leuco phenazine, phenoxazine, or phenothiazine dye, and as development accelerator a car­ boxylic acid, Lewis acid, or Bronsted acid.

Description: PHOTOTHERMOGRAPHIC CONSTRUCTION CONTAINING M & J 4 z 6 PHENAZINE, PHENOXAZINE, AND PHENOTHIAZINE DYES Field of the Invention The present invention relates to silver halide photothermographic color constructions. In another aspect, it relates to two-or three-color separation photothermographic recording systems utilizing certain classes of leuco dyes as color formers. Background Art Photothermographic imaging systems are those imaging materials which, upon first being exposed to light in an imagewise fashion, produce an image when subsequently heated. The exposure to light or other radiation photoactivates or photodeactivates a component in the imageable element and subsequent heating causes an image forming reaction to differentially occur in exposed and unexposed regions. Silver halide photothermographic imaging materials, often referred to as "dry silver' compositions because no liquid development is necessary to produce the final image, have been known in the art for many years. These imaging material basically comprise a lightinsensitive, reducible silver source, a light-sensitive material which generates silver when irradiated, and a reducing agent for silver ion in the silver source. The light-sensitive material is generally photographic silver halide which must be in catalytic proximity to the light-insensitive silver source. Catalytic proximity is an intimate physical association of these two materials which enables catalysis of the reduction of the silver source by silver specks formed on the silver halide. Exposure of the silver halide to light produces small clusters of silver atoms. The imagewise distribution of these clusters is known in the art as the latent image. This latent image generally is not visible by ordinary means and the light-sensitive article must be further processed in order to produce a visual image. The visual image is produced by the catalytic reduction of silver ions which, as already noted, are in catalytic proximity to the specks of the latent image. The silver source used in this area of technology is a material which contains a reducible source of silver ions. The earliest and still preferred source comprises silver salts of long chain carboxylic acids, usually of from 10 to 30 carbon atoms. The silver salt of behenic acid or mixtures of acids of like molecular weight have been primarily used. Salts of other organic acids or other organic materials such as silver imidazolates have been proposed, and U.S. Patent No. 4,260,677 discloses the use of complexes of inorganic or organic silver salts as image source materials. Color-forming, "dry silver" imaging systems are known in the photographic art. Color-formation is based on the oxidation/reduction reaction between the light-exposed silver salt of a fatty acid which has been halidized and dye-sensitized to a specific wavelength and is used with a chromogenic developer in the presence of elevated temperature. For example, U.S. Patent No. 3,531,286 teaches the inclusion of color coupler components such as a p-phenylenediamine developer and a phenolic or active methylene coupler in close proximity to the light-sensitive emulsion. J. W. Carpenter and P.W. Lauf, Research Disclosure No. 17029, issued June 1978, review prior art relating to photothermographic silver halide systems which include color formation. U.S. Patent No. 4,021,240 discloses the use of sulfonamidophenol reducing agents and four equivalent photographic color couplers in thermographic and photothermographic emulsions to produce dye images including multicolor images. U.S. Patent No. 3,985,565 discloses the use of certain class of phenolic type photographic color couplers in photothermographic emulsions to provide a color image. U.S. Patent No. 4,021,250 discloses the use of 0.0025 percent leuco thiazine dye as a shelf life extender in a photothermographic system comprising an organic silver salt, a catalytic amount of a photosensitive silver halide, a reducing agent, and a binder. The example disclosed used 1.87 percent chlorothymol and 0.126 percent phthalazinone as the image producing reactants. Leuco methylene blue, a thiazine dye, is known to be useful in recording systems. U.S. Patent No. 2,646,367 discloses a carbonless copy system using, for example, benzoyl leuco methylene blue as the color forming agent. U.S. Patent No. 3,447,944 discloses a thermographic copy system utilizing leuco methylene blue and its derivatives as color former. U.S. Patent No. 4,309,255 relates to leuco methylene blue in electrochromic recording paper. Japanese laid-open patent document 59-5239 discloses a 2-sheet, positive-acting, light-sensitive, heat-developablet diffusion, image transfer construction. Summary of the Invention Briefly, the present invention comprises a single-sheet, negative-acting photothermographic construction having a light-sensitive color-forming element on a support base, the element comprising a light-sensitive and non light-sensitive silver source, optionally silver halide, a binder, and an oxidizable leuco phenazine, phenoxazine, or phenothiazine dye, and as development accelerator a carboxylic acid, Lewis acid or Bronsted acid. Any oxidizable leuco phenazine, phenoxazine, or phenothiazine dye known in the art is useful in the present invention. The oxidized forms can have colors ranging from turquoise to yellow. The photothermographic portion of the element can be any imageable layer or layers which are photosensitive and developable by being heated (e.g., on a heated drum roll or by exposure to infrared radiation), preferably in the tempeature range of 150 to 3500F (approximately 65 to 180 C). Particularly important are silver halide photothermographic systems comprising silver halide, a silver source material in catalytic proximity to the silver halide, and a reducing agent for silver ion in a binder, these systems being commonly known as 'dry silver' construction. These systems may be in a single layer or in a plurality of layers as is well known in the art. The color-forming element of the present invention can be useful in a two or three color separation photothermographic recording system. In such a system it may be required to provide in a topcoat layer a "barrier polymer" which is impervious to an upper adjacent color layer. Such constructions are described, for example, in U.S. Patent Nos. 4,460,681 and 4,452,883. In the present application: "leuco dye" means a colorless or lightly colored dye which can be oxidized to a colored form; "aryl" means phenyl or naphthyl; "arylene" means phenylene or naphthylene; "lower alkyl" means alkyl containing 1 to 4 carbon atoms: "lower alkoxy" means alkoxy containing 1 to 4 carbon atoms; "aliphatic" means a straight-chain or branched-chain hydrocarbon; "halogen" means fluorine, chlorine, bromine or iodine; and in association with" means in the same layer or in a layer contiguous thereto. For example, the location of the photosensitive silver halide in the photothermographic element or composition of the invention is such that will enable catalytic action. The described photosensitive silver halide can accordingly be in the same layer as or in a layer contiguous to the described oxidation-reduction imageforming combination (i.e., the silver salt oxidizing agent such as silver behenate or silver stearate and the reducing agent and development modifier of the present invention). Detailed Description The present invention comprises a single-sheet, negative-acting, photothermographic element on a support base, said element comprising a silver source, optionally silver halide, a leuco dye as reducing agent for silver ion, a binder, and a development accelerator, wherein a) said leuco dye comprises a phenazine, phenothiazine, or phenoxazine leuco dye having the formula EMI5.1 wherein X can be -S-, -0-, or -NQ-: : each R can be the same or different and is independently selected from 1) hydrogen, 2) an unsubstituted aryl or alkyl group or these groups substituted by up to four groups selected from alkyl, alkoxy, cyano, hydroxy, halogen, nitro, mercapto, alkylsulfonyl, arysulfonyl, and Z, where Z is as defined below, wherein all alkyl and alkoxy groups have 1 to 20 carbon atoms, and preferably are lower alkyl and alkoxy, and 3) Z, wherein Z can be EMI5.2 wherein each Q can be the same or different and is independently selected from 1) hydrogen, 2) an unsubstituted aryl or alkyl group or these groups substituted by up to four groups selected from alkyl, alkoxy, cyano, hydroxy, halogen, nitro, mercapto, alkylsulfonyl, arysulfonyl, and Z, where Z is as defined above, wherein all alkyl and alkoxy groups have 1 to 20 carbon atoms, and preferably are lower alkyl and alkoxy: and R' is the same or different and can be indepen dently selected from hydrogen, halogen, alkyl or alkoxy of 1 to 6 carbon atoms or by these groups substituted by up to 3 halogen atoms; and L can be Z or hydrogen: with the proviso that R and L can have up to a total of 5 carbonyl and sulfonyl groups, preferably up to 3 carbonyl and sulfonyl groups; and b) said development accelerator comprises at least one aliphatic or aromatic carboxylic acid or anhydrides thereof, Lewis acid, or Bronsted acid selected from 1) a carboxylic acid having the formula R10(COOH)n wherein n is an integer having the value 1 to 4, preferably 1 to 3, R10 is a group which is unsubstituted or substituted by at least one group selected from amino, hydroxyl, aryl, lower alkyl, lower alkoxy, cyano sulfonyl, mercapto, nitro, halogen, and Z, wherein Z is as defined above, wherein when n is 1, R10 is selected from the group consisting of alkyl, alkenyl, aryl, and phenylalkyl, all having up to 10 carbon atoms, and when n is 2, 3, or 4, R10 is selected from the group consisting of alkenylene, alkylene, and arylene, all having up to 14 carbon atoms; ; 2) a Lewis acid preferably selected from halide, nitrate, sulfate, sulfonate, and carboxylate salts such as ammonium and alkyl-substituted ammonium nitrates, nitrates of Ni, Zn, Al, Cu, and Hg, and chloride of mercury II; and 3) Bronsted acid preferably selected from sulfonic and sulfinic acids, phenols, phosphonic and phosphinic acids, and sulfimides. The above-defined leuco dyes can have a molecular weight up to 2000, preferably up to 700, and the carboxylic acids can have a molecular weight up to 500, preferably up to 400. The preferred photothermographic construction of the present invention is of the "dry silver" type. The color-forming element which can provide an image ranging from cyan to yellow, including, magenta, red, violet, purple or blue can be of unitary construction or the light-sensitive layer may be in association with the leuco dye, i.e., in a bilayer construction. Single layer constructions must contain the silver source material, the silver halide, the developer, and the development accelerator in the same layer. In a bilayer construction the light-sensitive layer has a topcoat layer which comprises the leuco dye and acid material. Dry silver bilayer constructions must contain the silver source and silver halide in one emulsion layer (usually the layer adjacent the substrate). The other ingredients can be in the same layer, a second layer, or both layers. Optional additional materials include toners, coating aids, and other adjuvants. Photothermographic color constructions of the present invention incorporate at least one spectrallysensitized color-forming element according to the present invention to produce a single or multi-color photothermographic color recording system. When at least two color forming elements are present, the spectral sensitization may be to a pair of colors such as two of black, yellow, red, green, blue, and purple provided that each colorforming element is sensitized to a portion of the spectrum at least 60 nm different from the other color-forming element(s), and each color-forming layer forms a visible dye having a maximum absorbance at least 60 nm different from that of the dye formed in the other color-forming element(s). Preferred pairs of colors to which the construction may be sensitized are yellow-cyan, yellow-magenta, and cyan-magenta. Preferably, a barrier polymer which is impervious to the solvent system of a color construction above it is coated between each pair of color-forming layers. Such a barrier polymer or barrier polymers are essential for the production of good color separation. The test for determining if a barrier polymer is impermeable to the solvent of the next layer can be simply performed. Such a test is described in U.S. Patent No. 4,452,883 and is incorporated herein by reference. The photothermographic color construction may comprise three different monocolorforming layers to provide a 3-color forming system. The oxazine and thiazine leuco dyes and dyes of the invention can be prepared as is known in the art by acylation of an unsubstituted phenoxazine or phenothiazine compound to provide an N-acylated phenoxazine or phenothiazine compound. Nitration, in acetic acid, as is known in the art provides, after recrystallization, the 3,7-dinitro phenoxazine or phenothiazine compound. Hydrogenation catalyzed by platinum metal gives the corresponding diamino compounds. Treatment of the diamino compound with the appropriate alkylating or acylating reagent at room temperature in the presence of a base such as pyridine, triethylamine, or sodium hydroxide, gives the diamino substituted leuco dye. To prepare leuco phenazine dyes useful in the present invention a phenylene diamine compound, e.g., N,N-dimethyl p-phenylenediamine and an aniline compound, e.g., N,N-dimethylaniline are combined in a solvent, preferably water, in a reaction vessel and stirred, preferably at room temperature. It is preferred that the reaction be conducted in an aqueous acidic environment. A second aniline compound, e.g., 4-methylaniline is then added to the mixture. The resulting mixture is then stirred and heated for a sufficient period of time to bring about formation of the dye product in free form. To the solution is added an ionizable halide salt, e.g., KI, Nail, to precipitate the dye product. The solution is then cooled, and the dye collected by filtration and dried in air. Reduction in water in the presence of a water-soluble reducing agent, e.g., sodium dithionite, provides a hydrogen leuco dye. Extraction in a non-reactive water-insoluble solvent (e.g., methylene dichloride) and treatment of the organic portion with a reactive halide compound (e.g., benzoyl chloride) gives the leuco dye. In a preferred embodiment wherein the photothermographic construction is of the dry silver type, the silver source material, as mentioned above, may be any material which contains a reducible source of silver ions. Silver salts of organic acids, particularly long chain (10 to 30, preferably 15 to 28, carbon atoms) fatty carboxylic acids are preferred. Complexes of organic or inorganic silver salts wherein the ligand has a gross stability constant for silver ion of between 4.0 and 10.0 are also desirable. The silver source material should constitute from about 5 to 70 and preferably from 7 to 30 percent by weight of the imaging layer. The second layer in a two-layer construction would not affect the percentage of the silver source material desired in the single imaging layer. The silver halide may be any photosensitive silver halide such as silver bromide, silver iodide, silver chloride, silver bromoiodide, silver chlorobromoiodide, silver chlorobromide, etc., and may be added to the emulsion layer in any fashion which places it in catalytic proximity to the silver source. The silver halide is generally present as 0.75 to 15 percent by weight of the imaging layer; although larger amounts up to 20 or 25 percent are useful. It is preferred to use from 1 to 10 percent by weight silver halide in the imaging layer and most preferred to use from 1.5 to 7.0 percent. Where the construction has more than one color-forming element, the dyes formed from the leuco dyes in the various color-forming layers should of course be different. A difference of at least 60 nm in reflective or transmissive maximum absorbance is required. Preferably the absorbance maximum of dyes formed will differ at least 80 or 100 nm. When three dyes are to be formed1 two should differ by at least these minimums, and the third should differ from at least one of the other dyes by at least 150 nm and preferably at least 200 or even at least 250 nm. This will provide a good, full color range for the final image. In the present invention, the reducing agent (developer) for silver ion is the leuco phenazine, phenoxazine, or phenothiazine dye defined above which will reduce silver ion to metallic silver and produce a colored dye. Many representative examples of these dyes are given below in TABLES I and II. The reducing agent should be present as 0.1 to 10 percent by weight of the imaging layer. In a two-layer construction, if the reducing agent is in the second layer, slightly higher proportions, of from about 2 to 15 percent, tend to be more desirable. Additional reducing agents can be useful. Conventional photographic developers such as phenidone, hydroquinones, and catechol are useful in minor amounts, and hindered phenol reducing agents may also be added. Other leuco dyes not specified above (e.g., Crystal Violet) may be useful as an additional reducing agent in minor amounts (up to about one-half the amount of the primary reducing agent). Toners such as phthalazinone and phthalazine and others known in the art are not essential to the construction, but may be desirable. These materials may be present, for example, in amounts of from t.001 to 1 percent by weight. The binder for the silver coating is selected from well-known natural and synthetic resins such as gelatin, polyvinyl acetals, polyvinyl chloride, polyvinyl acetate, cellulose acetate, ethyl cellulose, polyolefins, polyesters, polystyrene, polyacrylonitrile, polycarbonates, methacrylate copolymers, maleic anhydride ester copolymers, and butadiene-styrene copolymers, and the like. When simultaneous coating of layers is used, the binder is selected to coordinate with the solvent used. Copolymers and terpolymers which include the above-stated binders are of course included in these definitions. The preferred photothermographic silver containing binder is polyvinyl butyral. The binders are generally used in a range of from 20 to 75 percent by weight of each layer, and preferably about 30 to 55 percent by weight. Development modifiers which can be useful in the present invention have been defined above. The acid chosen for a particular light-sensitive element depends on the activity of the leuco diazine, oxazine, or thiazine dye, i.e., upon its tendency to become oxidized to a colored form. More reactive leuco dyes require less acidic materials than to less readily oxidized leuco dyes. For example, Pergascript Turquoise" (a more reactive leuco dye) requires phthalic acid whereas Copikem II" (a less reactive leuco dye) requires a more reactive acid such as 4-nitrophthalic acid. Representative and preferred development modifiers include aromatic carboxylic acids and their anhydrides such as phthalic acid, benzoic acid, chlorinated and nitro-substituted benzoic acids, l,2,4-benzenetricar- boxylic acid, 2,3-naphthalene dicarboxylic acid, tetrachlorophthalic acid, 4-methyl phthalic acid, homophthalic acid, 4-nitrophthalic acid, o-phenylacetic acid, naphthoic acid, naphthalic acid, phthalic anhydride, naphthalic anhydride, tetrachlorophthalic anhydride, 3-nitrophthalic acid; aliphatic carboxylic acids such as malic acid, chloracetic acid, itaconic acid, tartaric acid, benzoylformic acid, and thiodiacetic acid; Bronsted acids, e.g., sulfonic acids such as p-toluene sulfonic acid, phosphonic and phospninic acids, phenols such as 2,4-dinitrophenol, 2,6-dinitrophenol, and pentachlorophenol, and other acidic materials such as sulfimides (e.g., saccharin); or Lewis acids including nitrate salts such as nickel nitrate, copper nitrate, mercury nitrate, zinc nitrate, aluminum nitrate, or ammonium nitrate. Sensitizing dyes useful in the present invention include many compounds known in the art, as well as 454 (prepared as in U.S. Patent No. 2,493,748) EMI12.1 Erythrosin (Aldrich Chemical Co., Milwaukee, WI) EMI12.2 563 (prepared as in U.S. Patent No. 3,719,495) EMI13.1 421 (prepared as in U.S. Patent No. 3,719,495) EMI13.2 The support base or substrate is a transparent or opaque polymeric film. Preferably it is made of such materials as polyester [ e.g., poly(ethyleneterephthalate) ] , cellulose ester (e.g., cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate), polyolefins, polyvinyl resins, and the like. The coatings can either be made as single layers, as for example by knife-coating or extruding, and dried before the next layer is applied or each monocolor can be dual coated, as for example by dual slide-coating or dual extrusion, i.e., each of the sensitized silver layers with its respective topcoat, which may contain a barrier resin, can be coated together to reduce the number of passes through the coater. Representative examples of useful leuco diazine, oxazine, and thiazine dyes are given in TABLES I and II below with the Dmin and Dmax values for the bilayer element which was prepared as follows: Silver Solution silver behenate 1.7 g toluene 9.3 g methyl ethyl ketone (MEK) 3.1 g These 3 components were homogenized. Separately added were: toluene 71.1 g ethanol 6.5 g polyvinyl butyral resin (Butvar B-76, 8.3 g Monsanto Corp.) Mixing was continued until the Butvar dissolved. Then 1 ml of a solution of 4.3 g ZnC12 dissolved 100 ml ethanol was added and mixing continued for 1 hour. The dispersion was coated at 76 micrometer (3 mil) orifice (wet thickness) on a super calendered 691B Simplon" photographic paper (Simpson Paper Co., Vicksburg, MI) using a knife coater. The coating was dried 4 minutes at 850C (1850F). Topcoat Preparation ethanol 50.0 g acetone 42.5 g Butvar B-76 7.5 g UV absorber (Cyasorb" UV 5411 0.1 g American Cyanamid) phthalic acid 0.5 g The five components were mixed until dissolution occured. To individual samples (8 g) of the topcoat solution 0.05 g of each of the leuco dyes listed in TABLES I and II below were added with mixing. All coatings were at 76 micrometer (3 mil) wet thickness using a Bird applicator over individual samples of the above-described dried silver coating. The construction was dried either at 15 min. at room temperature (210C), designated condition A, or 3 min. at 85'C (185eF), designated condition B. The construction was exposed 20 sec. to approximately 3800 fc using a 3M Model 636 tungsten lamp and then developed at 1240C (2550F) for the specified time on a heated blanket processor. TABLE I EMI16.1 EMI16.2 <SEP> Drying <SEP> Processing <tb> Sample <SEP> R1 <SEP> R2 <SEP> R3 <SEP> R4 <SEP> R5 <SEP> R6 <SEP> Color <SEP> Dmin <SEP> Dmax <SEP> condition <SEP> time <SEP> (sec) <tb> <SEP> # <tb> 1 <SEP> # <SEP> C2H5 <SEP> C2H5 <SEP> C2H5 <SEP> C2H5 <SEP> H <SEP> purple <SEP> 0.82 <SEP> 1.19 <SEP> A <SEP> 10* <tb> <SEP> O <tb> <SEP> # <SEP> # <SEP> # <tb> 2 <SEP> # <SEP> C2H5 <SEP> C2H5 <SEP> H <SEP> C-# <SEP> H <SEP> magenta <SEP> 0.09 <SEP> 0.28 <SEP> A <SEP> 10* <tb> 3 <SEP> #-CN <SEP> C2H5 <SEP> C2H5 <SEP> C2h5 <SEP> C2H5 <SEP> H <SEP> purple <SEP> high <SEP> A <SEP> 10 <tb> EMI17.1 <SEP> Drying <SEP> Processing <tb> Sample <SEP> R1 <SEP> R2 <SEP> R3 <SEP> R4 <SEP> R5 <SEP> R6 <SEP> Color <SEP> Dmin <SEP> Dmax <SEP> condition <SEP> time <SEP> (sec) <tb> <SEP> O <tb> <SEP> # <tb> 4 <SEP> #-S-# <SEP> CH3 <SEP> CH2CF3 <SEP> CH3 <SEP> CH2CF3 <SEP> CH3 <SEP> magenta <SEP> 0.17 <SEP> 0.19 <SEP> A <SEP> 60 <tb> <SEP> # <tb> <SEP> O <tb> 5 <SEP> # <SEP> CH3 <SEP> CH2CF3 <SEP> CH3 <SEP> CH2CF3 <SEP> CH3 <SEP> magenta <SEP> 0.56 <SEP> 1.21 <SEP> A <SEP> 10 <tb> 6 <SEP> # <SEP> CH3 <SEP> CH2CF3 <SEP> CH3 <SEP> CH2CF3 <SEP> H <SEP> magenta <SEP> 0.82 <SEP> 1.31 <SEP> A <SEP> 10 <tb> 7 <SEP> OC2H5 <SEP> CH3 <SEP> CH2CF3 <SEP> CH3 <SEP> CH2CF3 <SEP> CH3 <SEP> purple <SEP> 0.43 <SEP> 0.96 <SEP> B <SEP> 30 <tb> 8 <SEP> #-Cl <SEP> CH3 <SEP> CH2CF3 <SEP> CH3 <SEP> CH2CF3 <SEP> OCH3 <SEP> magenta <SEP> 0.55 <SEP> 2.55 <SEP> A <SEP> 10 <tb> 9 <SEP> # <SEP> CH3 <SEP> CH3 <SEP> CH3 <SEP> CH3 <SEP> OCH3 <SEP> purple <SEP> 0.21 <SEP> 1.02 <SEP> A <SEP> 9 <tb> <SEP> / <tb> <SEP> Cl <tb> 10 <SEP> #-Cl <SEP> CH3 <SEP> CH3 <SEP> CH3 <SEP> CH3 <SEP> OCH3 <SEP> purple <SEP> 1.05 <SEP> 1.92 <SEP> A <SEP> 5 <tb> EMI18.1 <SEP> Drying <SEP> Processing <tb> Sample <SEP> R1 <SEP> R2 <SEP> R3 <SEP> R4 <SEP> R5 <SEP> R6 <SEP> Color <SEP> Dmin <SEP> Dmax <SEP> condition <SEP> time <SEP> (sec) <tb> 11 <SEP> # <SEP> CH3 <SEP> CH3 <SEP> CH3 <SEP> CH3 <SEP> CH3 <SEP> purple <SEP> 0.38 <SEP> 1.84 <SEP> A <SEP> 9** <tb> <SEP> / <tb> <SEP> Cl <tb> 12 <SEP> # <SEP> CH3 <SEP> CH3 <SEP> CH3 <SEP> CH3 <SEP> CH3 <SEP> purple <SEP> 0.68 <SEP> 1.88 <SEP> A <SEP> 2 <tb> <SEP> / <tb> <SEP> F <tb> <SEP> Cl <SEP> Cl <tb> <SEP> \/ <tb> 13 <SEP> # <SEP> CH3 <SEP> CH3 <SEP> CH3 <SEP> CH3 <SEP> OCH3 <SEP> purple <SEP> 0.30 <SEP> 1.51 <SEP> A <SEP> 2 <tb> <SEP> Cl <tb> <SEP> \ <tb> 14 <SEP> # <SEP> CH3 <SEP> CH2CF3 <SEP> CH3 <SEP> CH2CF3 <SEP> OCH3 <SEP> purple <SEP> 0.20 <SEP> 0.58 <SEP> B <SEP> 2-1/2 <tb> <SEP> min. <tb> * <SEP> 135 C <SEP> (275 F) <tb> ** <SEP> 116 C <SEP> (240 F) <tb> TABLE II EMI19.1 EMI19.2 Sample <SEP> R7 <SEP> R8 <SEP> R9 <SEP> X <SEP> Color <SEP> Dmin <SEP> Dmax <SEP> Drying <SEP> Time <tb> <SEP> O <tb> <SEP> # <tb> 15 <SEP> H <SEP> H <SEP> COO <SEP> S <SEP> magenta <SEP> 0.70 <SEP> 1.88 <SEP> A <SEP> 10* <tb> 16 <SEP> CH3 <SEP> H <SEP> H <SEP> O <SEP> green <SEP> 0.29 <SEP> 0.50 <SEP> A <SEP> 6 <tb> 17 <SEP> NH-# <SEP> CH3 <SEP> CH3 <SEP> S <SEP> green <SEP> - <SEP> - <SEP> A <SEP> 10 <tb> <SEP> O <tb> <SEP> # <tb> 18 <SEP> H <SEP> H <SEP> ONHCH2CH2CH <SEP> S <SEP> blue-gray <SEP> - <SEP> - <SEP> A <SEP> 10 <tb> 19 <SEP> # <SEP> H <SEP> H <SEP> O <SEP> green <SEP> 0.21 <SEP> 0.84 <SEP> A <SEP> 10 <tb> <SEP> O <tb> <SEP> # <tb> 20 <SEP> CH3 <SEP> H <SEP> CNHC4H9 <SEP> O <SEP> green <SEP> - <SEP> - <SEP> A <SEP> 20 <tb> EMI20.1 Sample <SEP> R7 <SEP> R8 <SEP> R9 <SEP> X <SEP> Color <SEP> Dmin <SEP> Dmax <SEP> Drying <SEP> Time <tb> 21 <SEP> CH3 <SEP> H <SEP> COOC2H5 <SEP> S <SEP> magenta <SEP> - <SEP> - <SEP> A <SEP> 20 <tb> 22 <SEP> # <SEP> H <SEP> COOC2H5 <SEP> O <SEP> red <SEP> - <SEP> - <SEP> A <SEP> 30 <tb> 23 <SEP> NHC4H9 <SEP> H <SEP> COOC2H5 <SEP> O <SEP> purple <SEP> 0.57 <SEP> 0.98 <SEP> A <SEP> 5 <tb> <SEP> O <tb> <SEP> # <tb> 24 <SEP> H <SEP> H <SEP> CCF3 <SEP> O <SEP> - <SEP> 1.50 <SEP> 1.78 <SEP> A <SEP> 2 <tb> <SEP> O <tb> <SEP> # <tb> 25 <SEP> NHC4H9 <SEP> H <SEP> CCF3 <SEP> O <SEP> red-orange <SEP> 0.35 <SEP> 1.07 <SEP> A <SEP> 30 <tb> 26 <SEP> H <SEP> H <SEP> SO2CH3 <SEP> O <SEP> orange <SEP> 1.89 <SEP> 2.09 <SEP> A <SEP> 3 <tb> <SEP> O <tb> <SEP> # <tb> 27 <SEP> NHC4H9 <SEP> H <SEP> CCCl3 <SEP> O <SEP> pink <SEP> 0.29 <SEP> 0.50 <SEP> A <SEP> 15 <tb> <SEP> O <tb> <SEP> # <tb> 28 <SEP> NHC4H9 <SEP> H <SEP> CCH2Cl <SEP> O <SEP> orange <SEP> 0.34 <SEP> 1.20 <SEP> A <SEP> 20 <tb> <SEP> O <tb> <SEP> # <tb> 29 <SEP> NHC4H9 <SEP> CH3 <SEP> CCF3 <SEP> 0 <SEP> purple <SEP> 0.35 <SEP> 0.64 <SEP> B <SEP> 25 <tb> EMI21.1 Sample <SEP> R7 <SEP> R8 <SEP> R9 <SEP> X <SEP> Color <SEP> Dmin <SEP> Dmax <SEP> Drying <SEP> Time <tb> 30 <SEP> NHC4Hg <SEP> H <SEP> CCHCl2 <SEP> O <SEP> pink <SEP> 0.40 <SEP> 0.48 <SEP> A <SEP> 20 <tb> 31 <SEP> CH3 <SEP> H <SEP> CH2CF3 <SEP> O <SEP> blue <SEP> 0.18 <SEP> 0.57 <SEP> B <SEP> 3 <SEP> min <tb> 32 <SEP> # <SEP> CH3 <SEP> CH3 <SEP> CH3 <SEP> S <SEP> blue-green <SEP> 0.53 <SEP> 2.19 <SEP> A <SEP> 80 <tb> * <SEP> 135 C <SEP> (275 F) <tb> Objects and advantages of this invention are further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples1 as well as other conditions and details, should not be construed to unduly limit this invention. In the examples the dyes used have the structure: EMI22.1 Pergascript Turquoise" Copikem II" (leuco oxazine) (leuco thiazine) S-2G (Hilton-Davis) (Ciba-Geigy) CYAN CAN EMI22.2 *Leuco Diazine A (3M) MAGENTA Preparation of Leuco Diazine A lOg of Heliotrope B dye EMI22.3 (Pfaltz and Bauer Chemical Co., Stamford, CT) was dissolved in 250 ml of water under a nitrogen blanket. Sufficient sodium dithiohite was added until all of the color was discharged. 200 ml of methylene chloride was added and the solution was stirred vigorously with a mechanical stirrer. 8g of benzoyl chloride was added and the pH of the aqueous phase was adjusted to 10 while stirring was maintained for 3 hours. At this time the methylene chloride layer was separated, washed with water, diluted with potassium carbonate solution and again with water. The solution was dried over MgSO4 and the solvent removed under vacuum yielding a crude product. This material was tecrystallized from acetone to give the product leuco diazine A. EXAMPLE 1 The leuco oxazine dye, Pergascript Turquoise S-2G, was tested for photothermographic imaging using it in a silver soap system in the absence of a metal halide with a Lewis acid as development accelerator. Silver Soap Dispersion 1A Grind charge Material Amount A silver behenate full soap 8.0 g B Butvar B76 0.1 g C ethanol 17.99g D toluene 37.89 g ballmill time 23 hours Let Down charge E toluene 36.02g ballmill time 1 hour The above solution was milled in an 240-ml glass jar half filled with 12.7 mm glass balls. Finished Silver Soap Coating Solution 1B The following materials were mixed together and coated onto a baryta coated paper at 0.1016 mm (4 mils) and air dried. Charge Material Amount A silver soap dispersion 1A 69.6 g B toluene 98 ml C ethanol 15 ml D Butvar B76 15 g E fluorochemical surfactant 0.2 g (FC 431, 3M) Topcoat Formulation The following solution was prepared to evaluate some acid development modifiers. Master solution 1C Charge Material Amount A Pergascript Turquoise S-2G 0.625 g B Cyasorb UV 5411" (UV absorber, 0.125 g American Cyanamid) C ethanol 12.50 ml D 10 wt. % Butvar B76 in acetone 50.0 g Effect of Nickel Nitrate A 0.5 ml solution of 0.1 g of nickel nitrate dissolved in 5 ml of methanol and 5 ml of n-methylpyrrolidone was added to 5 g of example master solution 1C (no acid) and also to 5 g of example master solution 1C containing m-nitrobenzoic acid (0.075 g per 12.1 g master solution IC). These solutions were coated at 0.1016 mm onto silver soap coating 1B and air dried. The results are shown in TABLE III. TABLE III UV exposure Dev. time Sample Time (sec.) 1240C (sec.) Dmin Dmax 1. no acid 10 20 0.12 0.32 30 10 0.11 0.43 90 10 0.12 0.62 2. m-nitrobenzoic 30 1.5 0.42 0.76 acid The data of TABLE III show nickel nitrate acts as a development catalyst without the use of an additional carboxylic acid catalyst. EXAMPLE 2 Silver Soap Solution 2A A halide sensitized silver soap solution was prepared using the example 2A silver soap homogenate as follows: Charge Material Amount A silver soap coating solution 1B 60 g B 4.32 g zinc chloride dissolved in 0.6 ml 100 ml of ethanol This was coated at 0.0762 mm onto 0.0508 mm (2 mil) thick titanium oxide filled polyester film and air dried. Topcoat Master Solution 2B A topcoat master solution was made as follows: Charge Material Amount A 15 wt. 8 Butvar B-76 in acetone 100 g B ethanol 127 cc C Cyasorb UV 5411 0.2 g Run using Pergascript Turquoise Then 0.125 grams of Pergascript Turquoise S2G was added to 10 grams of topcoat master solution 2B. The development modifiers were added and the resulting solutions were coated at 0.1524 mm (6 mils) onto silver soap coating 2A and air-dried. The resulting coated material was then exposed to UV light and developed at 124 C. The results are shown in TABLE IV below. TABLE IV Development Wexposure Dev. Time Image Sample modifier time (sec.) 1240C (sec.) Dmin Dmax color 1 0.05 g phthalic acid 40 20 0.25 0.16 green 2 0.05 g 4-nitro- 40 2 0.25 1.52 green phthalic acid 3 5 mg nickel nitrate 40 2.5 0.32 1.02 blue dissolved in 0.5 ml methanol 4 0.5 mg nickel nitrate 40 30 0.16 0.36 green dissolved in 0.5 ml methanol Run using Copikem-II and Leuco Diazine A Using the same procedure runs using Copikem-Il or Leuco Diazine A in place of the Pergascript Turquoise-S2G were made. The results are shown in TABLE V below. TABLE V Dev. time Development UV exposure 124"C Image Sample Leuco dye modifier time(sec.) (sec.) Dmin Dmax color 1 0.125 g 0.05g 4-nitro- 40 20 0.16 1.07 blue Copikem-II phthalic acid green 2 0.06g Leuco 0.05g phthalic 40 15 0.47 1.64 maroon Diazine A acid 3 0.06g Leuco 0.05g 4-nitro- 40 10 0.76 1.24 maroon Diazine A phthalic acid The data of TABLES IV and V demonstrate the usefulness of various acids as development accelerators with oxazine, thiazine, and diazine leuco dyes in a silver halide-containing photothermographic system. EXAMPLE 3 Silver Behenate Premix 3A A silver behenate half soap dispersion was prepared by dispersing 300 grams in 2696 ml of ethanol and 347 ml of toluene by rapid mixing. This dispersion was then homogenized on a Manton-Gaulin Model 15M.8TBA SND homogenizer (Manton-Gaulin Co.) using two passes at 550 kg/cm2 (8000 psi) and 225 kg/cm2 (4000 psi). Then 389.8 grams of this material were diluted with 113 ml of ethanol. Mixing in 34.7 grams of polyvinyl butyral polymer (Butvar-B76) for 1 hour finished this premix. Pergascript Turquoise-S2G Plus Acid in Silver Soap Coating 3B Evaluation was made of the effect of acid on the oxidation-reduction reaction between Pergascript Turquoise and silver behenate half soap. The following formulation was used for this evaluation. Ingredient Amount A. Silver Behenate Premix 3A 30.0 g B. ethanol 6.0 ml C. 5.72 g calcium bromide in 100 ml ethanol 0.4 ml D. 5 g acid (see TABLE VI) in 100 ml acetone 3.0 ml E. 10 g Pergascript Turquoise-S2G in 100 ml toluene 3.0 ml These solutions were coated at 0.1016 mm onto 0.0508 mm thick titanium oxide filled polyester (3M) and air dried 3 minutes plus 3 minutes 820C (18O0F). Then exposed for 120 seconds to the "Violite" (Allied Litho Supply Co., San Francisco, CA) UV light source (General Electric 15 watt blacklight) through a continuous step tablet. Then processed at 1270C (2600F) on a 3M Model 70 heat blanket processor for 1 to 120 seconds. The densities were measured on a Macbeth densitometer using a red filter. The acids tested are listed in following TABLE VI below. TABLE VI Development Time Red Filter Image Acid &commat; 1270C (sec.) Dmin Dmax color 1. phthalic 75 0.22 1.32 green 2. 4-nitrophthalic 1 0.52 1.36 blue The 4-nitrophthalic acid was re-evaluated with the addition of 0.4 ml of 0.57 g of mercuric chloride per 100 ml of ethanol and the same repeated with the addition of 3.0 ml of 5 g of Ionoxt (R) 201 antioxidant (Shell Chemical Company) to the test solution formulation. These solutions were coated and tested in the same manner as previous samples. The results are listed in TABLE VII below. TABLE VII Development Time Red Filter Image Sample Q 1270C (sec.) Dmin Dmax) color 1. control 1 0.52 1.36 blue 2. with mercuric chloride 2 0.18 1.44 blue 3. with mercuric chloride 2 0.31 1.66 blue and "lonox 201N The data of TABLE VII show that mercuric chloride can be used as a Lewis acid type development accelerator and as an antifoggant in the present invention with or without an antioxidant. Copikem-II Plus Acid In Silver Behenate Coating Evaluation of the effect of different acids on the oxidation-reduction reaction between Copikem-If and silver behenate half soap was made. The following formulation was used for this evaluation: Ingredient Amount A. silver behenate premix 3A 30.0 g B. ethanol 3.0 ml C. 5.72 g calcium chloride in 100 ml ethanol 0.4 ml D. acid 0.15 g E. acetone 3.0 ml F. 5 g Copikem-II in 100 ml toluene 6.0 ml These solutions were coated, dried, and processed as described in Example 3B. The acids are listed in TABLE VIII below. TABLE VIII Development time Red filter Image Acid &commat; 1270C (sec.) Dmin Dmax) color 1. phthalic 90 0.19 0.27 yellow 2. 4-nitrophthalic 20 0.64 0.97 blue 3. 4-chlorophthalic 55 0.22 0.48 green Leuco Diazine A Plus Acids and Toners in Silver Behenate Coating Evaluation was made of the effect of acid on the oxidation-reduocton reaction using Leuco Diazine A and silver behenate half soap. The following formulation was used for this evaluation: Leuco Diazine A Plus Acid and Toners in Silver Behenate Coating Ingredient Amount A. silver behenate premix 3A 30.0 g B. ethanol 4.0 ml C. 0.57 g mercuric chloride in 100 ml ethanol 0.4 ml D. 5.7 g calcium chloride in 100 ml ethanol 0.4 ml E. 5 grams acid in 100 ml ethanol 3.0 ml F. 6 grams Leuco Diazine A in 100 ml acetone 3.0 ml plus 1.2 ml NMP (N-methylpyrrolidone) These solutions were coated, dried, and processed as described in 3B. The materials evaluated are listed in TABLE IX below. Measurements were made using a green filter. TABLE IX Development Green filter Image Test Material Time 1270C (sec.) Dmin Dmax Color 1. phthalic acid 15 0.16 1.28 Magenta 2. *phthalazinone plus 10 0.15 1.38 Magenta phthalic' acid * (used 1.5 ml of 2.5 g phthalazinone in 100 ml methanol) The data of TABLE IX shows that a combination of phthazinone plus phthalic acid gave a higher image density than phthalic acid alone. EXAMPLE 4 - metal nitrate evaluation with leuco oxazine dye Silver Behenate Premix 4A A silver behenate premix was prepared to use in evaluating use of metal nitrate with oxazine and thiazine leuco dyes in a dye sensitized, silver halide containing silver behenate half soap system. The silver behenate homogenate 4A was used. Ingredients Amount A. silver behenate homogenate 4A 389.8 g B. N-methylpyrrolidone (NMP) 2.4 ml C. toluene 6.0 ml D. ethanol 104.0 ml E. 0.5 g Butvar-B76 in 100 ml ethanol 0.9 ml F. Butvar-B76 34.6 g Sensitized Silver Behenate Premix 4B and 4C The solution premix 4A was halidized and dye sensitized to green light using the following formulation: Amount Ingredients 4B 4C A. silver behenate premix 4A 50 g 50 g B. ethanol 20 ml 20 ml C. 0.57 g mercuric bromide in 100 ml ethanol 0 0.7 ml D. 5.72 g calcium bromide in 100 ml ethanol 0.7 ml 0.7 ml E. 0.1 g RP 421 dye in 100 ml ethanol 1.3 ml 1.3 ml This solution was coated at 0.0508 mm onto 0.0508 mm thick titanium oxide filled polyester (3M) and dried for 3 minutes at 770C (1700F). This was used to evaluate the metal nitrates used in a topcoat containing the leuco dye, phthalic acid, and a polymer. Topcoat Master Solution 4D A topcoat master solution containing Pergascript Turquoise for Lewis acid (nitrate) evaluation was prepared using the following: Ingredients Amount A. 10 wt. percent CAB-553-0-4 in ethanol 120.0 g (Eastman-alcohol soluble cellulose acetate butyrate) B. phthalic acid 0.6 g C. *Pergascript Turquoise-S2G 1.2 g D. N-methylpyrrolidone 12.234 g *The leuco dye was predissolved in the N-methylpyrrolidone before mixing it with the polymer solution. Topcoat Solution 4E The nitrate salts were predissolved in methanol at a concentration of 1 gram per 100 ml. These were added to topcoat master solution 4D to give an equivalent concentration of 2.34 x 10-5 moles of metal nitrate per 30 grams of solution. The nitrates which were evaluated are shown in TABLE X with the amounts used in milligrams. TABLE X Compound Amount (1 g/100 ml methanol) (mg/30 grams topcoat) nickel nitrate 6.8 aluminum nitrate 8.8 ammonium nitrate 1.9 These topcoat solutions were individually coated on top of silver behenate coatings 4B and 4C at an orifice setting of 0.1016 mm and dried for 5 minutes at 770C (1700F). They were exposed for 10-3 seconds to Xenon flash (EG & sensitometer) through a continuous tone wedge, then heat developed for 20 seconds at 1240C (2550F) on 3M Model 70 Heat Blanket Processor. The resulting wedges were measured on a computer densitometer using a red filter. The results are shown in TABLES XI and XII below. TABLE XI (Silver Behenate Premix 4B) sensitivity at Sample Gamma 0.4 density/fog nitrate Dmin Dmax angle (ergs/cm2) 1 none .06 0.60 210 782 2 nickel .11 1.53 410 250 3 aluminum .16 1.44 270 140 4 ammonium .08 1.22 310 174 TABLE XII (Silver Behanate Premix 4C) 5 none .07 1.40 400 873 6 nickel .06 2.16 570 449 7 aluminum .09 2.04 530 252 8 ammonium .07 2.16 550 659 The data of TABLE XI show that the Lewis acid (nitrate) improved the thermal reactivity of the system resulting in higher image densities, gamma angles, and light sensitivity. The image color of the above systems was blue to cyan. EXAMPLE 5 - nickel nitrate and nickel bromide evaluation as development accelerator with leuco thiazine dye Sensitized Silver Behenate Premix 5A The solution premix 4A prepared in EXAMPLE 4 was halidized and dye sensitized to green light using the following formulation: Ingredients Amount A. silver behenate premix 4A 200.0 g B. 0.57 g mercuric bromide in 100 ml ethanol 2.8 ml C. 5.72 g calcium bromide in 100 ml ethanol 2.8 ml D. 1.79 g mercuric acetate in 28 ml methanol 2.8 ml E. 0.10 g * 421 dye in 100 ml ethanol 5.2 ml This solution was coated at 0.0508 mm onto 0.508 mm thick titanium oxide filled polyester and dried for 3 minutes at 770C (170 F). Topcoat Master Solution 5B A topcoat master solution containing Copikem-Il for metal nitrate evaluation was prepared using the following formulation: Ingredients Amount A. 10 wt. percent CAB-553-0-4 in ethanol 160.0 g B. 4-nitrophthalic acid 0.8 g C. Copikem-II 1.6 g D. N-methylpyrrolidone 16.43g (Predissolve Copikem-Il in (D) before addition to (A)). Nickel Nitrate Evaluation Nickel nitrate and phthalic acid were individually predissolved in methanol at a concentration of 1 gram per 100 ml. Then 0.5 ml of these solutions were added to individual 22.354 gram portions of topcoat master solution 5B. These topcoat solutions were coated over a sensitized silver behenate coating 5A at an orifice setting of 0.1016 mm and dried for 5 minutes at 770C (170 F). They were exposed, processed, and tested as in EXAMPLE 4. The results are shown in TABLE XIII below: TABLE XIII Development Sends.&commat;0.4 Sample time &commat;1240C Gamma insity/fog No. Additive (sec.) Dmin Dmax angle (ergs/cm2) 1 phthaiic acid 90 0.14 0.93 25 3,818 2 nickel nitrate 90 0.16 1.35 44 1,000 The data demonstrate the effectiveness of a nitrate salt as development accelerator. EXAMPLE 6 - combination of other leuco dyes with leuco oxazine and thiazine dyes Topcoat Master Solution 6A A topcoat master solution containing 4-nitrophthalic acid and leuco crystal violet was made to evaluate the effect of combining the oxazine and thiazine leuco dyes with nickel nitrate. The following formulation was used: Ingredients Amount A. 10 wt. percent CAB-553-0-4 in ethanol 200.0 g B. 4-nitrophthalic acid 1.0 g C. leuco Crystal Violet (Aldrich Chemical Co.) 0.2 g The Pergascript Turquoise, Copikem-II, and nickel nitrate were predissolved in solvents then added to 20.12 grams of the example topcoat master solution 4G. The following solutions were prepared: Amounts Ingredients 1 2 3 4 A. master solution 6A 20.12g 20.12g 20.129 20.12g B. 1.09 Pergascript Tur- 1.2 ml 1.2 ml 1.8 ml 0 quoise-S2G per 6 ml N-methylpyrrolidone C. 1.0g Copikem-II per 1.0 ml 1.0 ml 0 3.0 ml 10 ml N-methylpyrrolidone D. 1.0g nickel nitrate 0 0.5 ml 0.5 ml 0.5 ml per 100 ml methanol These solutions were coated at 0.0762 mm onto silver behenate coating 5A and dried for 5 minutes at 770C (170 F). They were exposed, processed, and tested as in Example 4. The results are shown in TABLE XIV below. TABLE XIV Combination Development Sens.&commat;0.4 Sample with leuco time &commat;124 C Gamma density/fog No. crystal violet (sec.) Dmin Dmax angle (ergs/cm2) 1 Pergascript Turquoise 20 0.26 1.63 58 960 and Copikem-II 2 Pergascript Turquoise 20 0.27 2.01 690 580 and Copikem-II nickel nitrate 3 Pergascript Turquoise 20 0.43 1.62 490 480 nickel nitrate 4 Copikem-II 60 0.22 1.05 33 1260 nickel nitrate All images were bluish-green in color. The data of TABLE XIV show that the combination of the leuco dyes of the invention in combination with other leuco dyes and nickel nitrate gave useful systems. EXAMPLE 7 Effect of Phthalazine The effect of phthalazine was evaluated using the following formulations 7A and 7B: Amounts Ingredients 7A 7B A. 10 wt.% CAP-553-0.4 in ethanol 29.9 g 29.9 9 B. l.2g Pergascript Turquoise-S2G in 3.0 ml 3.0 ml 12 ml N-methylpyrrolidone C. phthalic acid 0.30g 0.30g D. 4-nitrophthalic acid 0.05g 0.05g E. tetrachlorophthalic acid 0.03g 0.03g F. phthalazine 0 0.03g These solutions were coated 0.1016 mm thick onto Silver Behenate Coating 4C and dried for 5 minutes at 770C (1700F). They were exposed, processed, and tested as in Example 4. The results are shown in TABLE XV below. TABLE XV Development solution Time 1240C Gamma density/fog no. Description (sec.) Dmin Dmax angle (ergs/cm2) 7A control 15 0.11 2.13 580 163 7B with phthalazine 60 0.08 1.68 380 1422 The samples were aged for two hours using 2152 milliphots (2000 foot candles), 270C (80 F), and 60 percent relative humidity. The changes in Dmin are shown in TABLE XV. TABLE XVI Solution Initial 2 Hour Delta no. Dmin Dmin Dmin 7A 0.13 0.93 +0.80 7B 0.12 0.49 +0.37 The data of TABLES XV and XIV show that conventional development modifiers used in dry silver are also useful in this system. Although phthalazine reduces the thermal reactivity it improves the print stability. The use of phthalazine with nickel nitrate and Pergascript Turquoise was evaluated in the following formulation. Amounts Ingredients ¯ 7C 7D A. 10 wt.% CAB-553-0.4 in ethanol 18.55 g 18.55 g B. phthalic acid 0.093g O.O93g C. 4-nitrophthalic acid 0.028g 0.028g D. 1.2 g Pergascript Turquoise-S2G in 1.10 ml 1.10 ml 7.2 ml NMP E. 2.0 g nickel nitrate in 100 ml 0 0.46 ml methanol F. 5.0 g phthalazine in 100 ml ethanol 0 0.24 ml These solutions were coated at 0.1016 mm onto Silver Behenate Coating 4C and dried for 5 minutes at 770C (170µF). They were exposed, processed, and tested as in EXAMPLE 4D. The results are shown in TABLE XVII below. TABLE XVII 2 hour Development Sens. &commat; 0.4 print Solution time &commat;124 C Sens.&commat;0.4 Gamrn density/fog stability no. Description (sec.) Dmin Dmax Angle (ergs/cm2) Dmin delta 7C control 20 0.20 2.44 600 122 0.55 7D nickel nitrate 60 0.19 2.25 620 242 0.33 plus phthalazine The data of TABLE XVII show the increased density and sensitivity of the nickel nitrate/phthalazine containing construction. When compared to phthalazine alone, the addition of nickel nitrate was not detrimental to print stability but did improve sensitometry. EXAMPLE 8 - Acids with Oxazine Dye Cyan Silver Coating 8A (below) was prepared and coated at 3.6 g/m2 (0.32 grams per square foot) onto 0.076 mm thick polyester film MELINEX" TYPE 329 (ICI) using a laboratory hand knife coater. Various acids were used in the construction with the leuco oxazine dye, Pergascript Turquoise S-2G. Cyan Silver Coating 8A Charge Material Amount A Cyan Silver Coating 3B (Example 3) 90 grams B ethanol 36 cc C 0.36 g mercuric bromide in 2 cc 100 cc methanol D 4.0 g calcium bromide in 1.8 cc 100 cc methanol E 0.017 g MSD 563 Dye (see above) in 2.9 cc 50 cc methanol 0.064 mm (2.5 mil) orifice; dried 5 min at 820C (1800F) The following formulation was used to evaluate acids in a topcoat over the precoated red sensitive silver coating (8A). Cyan Topcoat Solution 8B Charge Material Amount A 10% by weight CAB-553-0 25 g B acid to be tested 0.3 or 0.4 g C (FC431, 3M) fluorochemical surfactant 1 drop The topcoat was coated at a 0.076 mm orifice and dried for 5 minutes at 829C (180 F). The material was then exposed for 10-3 seconds to an EG & xenon flash sensitometer. No filter was used. The samples were processed at l240C (255 F) on a 3M Model 70 heated blanket processor. The dwell times, Dmin and Dmax, are noted with the acid tested in TABLE XX below. TABLE XX I. AROMATIC MONOCARBOXYLIC ACIDS Conc. Dwell g/25g time Acid Topcoat (sec) Dmin Dmax 1 benzoic 0.3 60 0.08 0.10 2. salicylic 0.4 20 0.45 1.75 3. 3-chlorobenzoic 0.4 60 0.27 0.39 4. 2-chloro-4-nitrobenzoic 0.4 10 0.33 2.36 20 0.73 3.05 5. 2,4-dichlorobenzoic 0.4 10 0.17 1.67 20 0.23 2.08 II. AROMATIC DICARBOXYLIC ACIDS Conc. Dwell g/25g time Acid Topcoat (sec) Dmin Dmax 1. phthalic 0.3 20 0.08 2.00 2. homophthalic 0.4 60 0.08 0.98 3. phthalic anhydride 0.4 20 0.08 2.03 4. 4-methylphthalic 0.4 20 0.09 2.47 5. 4-nitrophthalic 0.4 20 0.10 1.76 6. 3-nitrophthalic 0.4 60 0.08 0.63 7. tetrachlorophthalic 0.4 20 0.11 0.51 acid 8. tetrachlorophthalic 0.4 60 1.59 slight anhydride image high fog 9. saccharin 0.4 60 0.10 0.55 III. ALIPHATIC DICARBOXYLIC ACIDS Conc. Dwell g/25g time Acid Topcoat (sec) Dmin Dmax 1. maleic 0.4 20 0.18 2.23 2. itaconic 0.3 60 0.08 0.76 3. glutaconic 0.4 60 0.10 0.43 4. dichloromaleic 0.4 20 0.10 2.65 5. malic 0.3 60 0.10 0.98 6. tartaric 0.3 60 0.08 0.48 IV. ALIPHATIC POLYCARBOXYLIC ACIDS Conc. Dwell g/25g time Acid Topcoat (sec) Dmin Dmax 1. citric 0.4 60 0.09 1.04 V. NITRATE SALTS Conc. Dwell g/25g time Nitrate Topcoat (sec) Dmin Dmax 1. zinc 0.006 60 0.28 0.87 2. ammonium 0.006 60 0.20 0.45 VI. POLYAROMATIC DICARBOXYLIC ACIDS Conc. Dwell g/25g time Acid Topcoat (sec) Dmin Dmax 1. 2,3-naphthalene 0.4 60 0.12 1.32 dicarboxylic acid The data of TABLE XX show the usefulness of various acids as development accelerator with Pergascript Turquoise S-2G in color constructions. EXAMPLE 9 Cyan Oxazine Leuco Dye Developer in Magenta/6yan Bipack A dispersion of a silver behenate half soap was made at 10% by weight in a solvent mixture of 90% toluene and 10% ethanol using two passes with a Manton-Gaulin homogenizer, Model l5M, at 550 kg/cm2 and 225 kg/cm2 (8000 and 4000 psi). This silver soap dispersion is then prepared for coating by the addition of dilution solvents, halide, polymer, and sensitizing dye in a selected sequence of time and mixing. Magenta Silver Coating 9A Add time Charge Material Amount (min.) A 108 Ag half soap homogenate 177 g (90 toluene/10 ethanol) B toluene 175 g C Butvar B-76 (polyvinyl butyral) 0.1 g 10 D mercuric acetate solution 3 cc 20 (4 g/100 cc methanol) E mercuric bromide solution 3 cc 30 (0.36 g/100 cc methanol) F calcium bromide solution 3 cc 35 (4 g/100 cc methanol) G C 0.1 g 75 H E 3 cc 95 I F 3 cc 100 J C 78 g 220 K 10% by weight Butvar B76 in 335 g 280 toluene Stop mixing at 340 minutes. 90 grams of EXAMPLE 1 were dye sensitized with 2.7 cc of a 8534 dye (green light sensitizer) solution with a concentration of 0.013 g dye/50 cc methanol. This solution was coated on top of a 0.05 mm (2 mil) thick titanium dioxide filled polyester film (3M) using a 0.076 mm 3 mil orifice on a laboratory hand knife coater. This coating was dried at 810C (177 F) for 5 minutes. Magenta Topcoat 9B The following topcoat solution was prepared to coat on top of Magenta Silver Coating 9A. Charge Material Amount A toluene 34 cc B ethanol 10 cc C phthalazinone 0.16 g D tetrabromophthalic anhydride 0.16 g E 30% by weight Acryloid-A21t 25 9 (polyme thylme thacryla te, Union Carbide) F 30% by weight Acryloid-B44" 25 g (polymethylmethacrylate, Union Carbide) G magenta leuco indoaniline dye 0.52 g EMI43.1 H ethanol 10 cc * 8.15g of 2,6 dichlorophenol and 15.9g sodium carbonate were dissolved in 300 ml water; then, 150 ml chloroform were added. A solution of 65.9g potassium ferricyanide in 300 ml water was added and the solution was stirred for 1 hour. The chloroform layer was separated, washed with 5% aqueous sodium hydroxide, dried with MgSo4 and stripped to yield a dye. One gram of this dye was dissolved in 200 ml diethylether and 0.58 g of t-butyl hydroquinone was added. The mixture was allowed to stand for 3 hours. The ether was extracted with 5% aqueous sodium hydroxide. The aqueous layer was separated and acidified with 10% hydrochloric acid. A precipitate formed. This suspension was extracted with ether. The ether was evaporated giving a tan material, the magenta leuco indoaniline dye. This solution was coated on top of coating 9A using a 0.076 mm (3 mil) orifice and drying at 810C (1770F) for 5 minutes. A different dispersion of a silver behenate half soap was made similar to 9A, except that a solvent mixture of 90% ethanol and 10% toluene was used. This silver soap dispersion was used in preparing a red light sensitive coating for the cyan color system which was to be coated on top of the pre-coated magenta color forming system. Cyan Silver Premix 9C Charge ¯ Material Amount A 10% Ag half soap homogenate 390 g (90 ethanol/10 toluene) B ethanol 104 cc C Butvar-B76 34 g Cyan Silver Coating 9D Charge Material Amount A cyan silver premix 9C 90 g B ethanol 36 cc C mercuric bromide solution 2 cc (0.36 g/100 cc methanol) D calcium bromide solution 1.8 gg (4.0 g/100 cc methanol) 50 grams of Cyan Silver Premix 9C solution were dye sensitized with 1.2 cc of MSD 563 dye (red light sensitizer) solution having a concentration of 0.017 grams/50 cc methanol. This was coated on top of the precoated 9A and 9B layers at an orifice of 0.05 mm (2 mils). The coating was dried at 810C (1770F) for 5 minutes. Cyan Color Topcoat 9D The following topcoat solution was prepared to coat on top of Cyan Silver premix 9C to finish the magenta/cyan color bipack. Charge Material Amount A ethanol 40 cc B phthalic acid 0.50 g C 4-nitrophthalic acid 0.24 g D 15% by weight of CAB-553-O in ethanol 68 g E cyan leuco oxazine dye 1.0 g (Pergascript Turquoise-S-2G) E toluene 10 cc This was coated on top of Cyan Silver Premix 9C at an orifice of 0.1016 mm (4 mils) and dried for 5 minutes at 810C (1770F). The magenta/cyan bipack was now complete and had the following construction: Base - 0.05 mm thick (2 mil) Tio2 filled polyester 1st layer - green light sensitive silver 2nd layer - magenta color developer & development modifiers in barrier polymer 3rd layer - red light sensitive silver 4th layer - cyan color developer & development modifiers in hard topcoat polymer. This material was exposed to an EG & (EG & , Electrooptics Div., Salem, MA) xenon flash sensitometer using the proper light filtration to generate the mono-magenta and mono-cyan colors. A Wratten Number 58 and a Wratten Number 25 were used. The exposed material was then processed at 124 C (2550F) for 20 seconds. The sensitometry of the bipack is given in TABLE XVIII below. TABLE XVIII Filter f58 (Green) t25 (Red) Dmin 0.26 0.23 Dmax 1.57 2.20 gamma angle 54 65 ergs/cm2 at 0.6 density/fog 64 21 image color magenta cyan The data of TABLE XVIII shows that a good color separation was obtained and demonstrates the utility of a two-color system. EXAMPLE 10 Example of Cyan Oxazine Leuco Dye Developer in Yellow/Magenta/Cyan Tripack The following will illustrate a three color separation system employing the cyan oxazine leuco dye, pergascript Turquoise. Yellow Silver Coating 10A This solution was prepared by adding 1.5 cc of a &num;454 dye (blue sensitizer) solution having a concentration of 0.032 grams per 50 cc of methanol to 40 grams of Magenta Silver Coating 9A. This was coated at a 0.1016 mm (4 mil) orifice using a laboratory hadn knife coater onto a 0.0508 mm thick (2 mil) titanium dioxide filled polyester film (3M). The coating was dried for 5 minutes at 81 C (177 F). Yellow Topcoat Resin Premix 10B Charge Material Amount A 10% by weight PVP-K90 75 g (polyvinylpyrrolidone, GAF Corp.) in methanol B 25% by weight Gantrez-ES225 25 g (copolymer methyl vinyl ether/maleic acid, GAF Corp.) in 50% ethanol & 50% methanol C 2-amino-2-methyl-l-propanol 0.275 g Charges B and C were mixed together prior to addition to charge A. Yellow Topcoat Coating lOC Charge Material Amount A methanol 12 cc B 2t2',6,6'-tetramethyl-4t4'-biphenol 0.3 g prepared as described in U.S. Patent No. 4,374,921 C phthalic acid 0.04 g D 4-methyl-phthalic acid 0.08 g E tetrachlorophthalic acid 0.05 g F phthalazine 0.125 g G resin premix 10B 40 g Charges B through F were predissolved in charge A before addition of charge G. This solution was coated on top of precoated Yellow Silver Coating 9A at a 0.076 (3 mil) orifice and dried for 5 minutes at 790C (1750C). The magenta color forming systems 9A and 9B described in Example 8 were coated on top of the yellow color forming system described above. The resulting material was exposed and processed using the procedure of Example 9. A Wratten Number 47B (blue light) was used for the yellow color. The sensitometry of this yellow/magenta bipack is given in TABLE XIX below. TABLE XIX Filter t47B (Blue) &num;58 (Green) Dmin 0.30 0.31 Dmax 1.79 1.50 gamma angle 50o 53o ergs/cm2 at 0.6 density/fog 27 25 image color yellow magenta The cyan color forming system utilizing Cyan Silver premix 9C and Cyan Silver Coating 9D was coated on top of the yellow/magenta bipack. The sensitometry for the yellow, magenta, and cyan were obtained by the same methods just described. The results showed a good three color separation for copying in color. The sensitometry for the yellow did not change from the bipack and the magenta and cyan were the same as disclosed in the magenta/cyan bipack. Various modifications and alterations of this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention, and it should be understood that this invention is not to be unduly limited to the illustrative embodiments set forth herein.

Claims: CLAIMS: 1. A single-sheet, negative-acting, photothermographic construction comprising at least one light-sensitive color-forming element on a support base, the element comprising a light-sensitive and a non light-sensitive silver source, a binder, an oxidizable leuco phenazine, phenoxazine, or phenothiazine dye as reducing agent for said silver sources, and as development accelerator a carboxylic acid, Lewis acid, or Bronsted acid; wherein the image color is provided by the oxidized form of said leuco dye. 2. The construction according to Claim 1 wherein said light-sensitive silver source is silver halide. 3. The construction according to any preceding claim wherein a) said leuco dye comprises a phenazine, phenothiazine, or phenoxazine leuco dye having the formula EMI49.1 wherein each R is the same or different and is independently selected from 1) hydrogen, 2) an unsubstituted aryl or alkyl group or these groups substituted by up to four groups selected from alkyl, alkoxy, cyano, hydroxy, halogen, alkylsulfonyl, arylsulfonyl, and Z where Z is as defined below, wherein all alkyl and alkoxy groups have 1 to 20 carbon atoms, and 3) Z, wherein Z is EMI50.1 wherein each Q is the same or different and is independently selected from 1) hydrogen, 2) an unsubstituted aryl or alkyl group or these groups substituted by up to four groups selected from alkyl, alkoxy, cyano, hydroxy, halogen, alkylsulfonyl, arysulfonyl and z, where Z is as defined above, and wherein all alkyl and alkoxy groups have 1 to 20 carbon atoms: R' is the same or different and is independently selected from hydrogen, halogen, alkyl or alkoxy of 1 to 6 carbon atoms or these groups substituted by up to 3 halogen atoms; and X is -S-, -O-, or -NQ-; L is hydrogen or Z; with the proviso that R and L can have up to a total of 5 carbonyl and sulfonyl groups; and b) said development accelerator comprising at least one acid selected from 1) a carboxylic acid having the formula R10(COOH)n wherein n is an integer having the value 1 to 4, R10 is a group which is unsubstituted or sub stituted by at least one group selected from amino, hydroxyl, aryl, lower alkyl, lower alkoxy, cyano, sulfonyl, mercapto, nitro, halogen atom, and z, wherein Z is as defined above, wherein when n is 1, R10 is selected from the group consisting of alkyl, alkenyl, aryl, and phenylalkyl, having up to 10 carbon atoms, and when n is 2, 3, or 4, R10 is selected from the group consisting of alkenylene, alkylenet and arylene, having up to 14 carbon atoms: 2) a Lewis acid selected from halide, nitrate, sulfate, sulfonate, and carboxylate salts: : and 3) a Bronsted acid selected from sulfonic and sulfonic acids, phenols, phosphonic and phosphinic acids, and sulfimides, wherein the image color is provided by the oxidized form of said leuco dye. 4. The construction according to any preceing claim wherein said leuco dye is EMI51.1 EMI52.1 5. The construction according to any preceding claim wherein said carboxylic acid is selected from substituted benzoic or naphthoic acid. 6. The construction according to any preceding claim wherein said Lewis acid is selected from nitrates of Ni, Zn, All Cu, Hg, and NH4+. 7. The construction according to any preceding claim wherein said color-forming element has a unitary layer construction. 8. The construction according to any preceding claim wherein said color-forming element has a bilayer construction. 9. The construction according to any preceding claim which is part of a 2- or 3-color separation recording system.

Inventors: BELLUS, PETER A. MINNESOTA MINING AND, FRENCHIK, ROBERT A. MINNESOTA MINING AND
Applicants: MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1985
Main classification: G03C1
IPC codes: G03C1, G03C7, B41M5