CA1090188A - Heat-activated bleaching of silver images using activator sheet containing a diffusible acid and a agx complexing agent - Google Patents

Abstract

Abstract of the Disclosure A dry, activator sheet for a dry, thermal silver dye-bleach process comprises a support having thereon a nonvolatile, diffusible acid and a non-hydrolyzable polymeric vehicle having a pH of 6.0 or less, especially 4.0 or less, and a melting point lower than 200°C. The activator sheet is useful to bleach a silver image in an element containing a bleachable dye.

Description

lO~(J188 This invention relates to dry, activator sheets for use in bleaching photographic elements containing a silver image and a bleachable dye and to photographic elements and processes for bleaching silver images and dyes.
Many methods to produce positive color images with photographic silver halide materials have been described in the art. m ose which are successfully employed in today's color photographic art include the silver dye bleach process, as described, for example, in J. S. Friedman, History of Color Photo~raPhy~ (1944) pp. 405-429 and A. Meyer, The Journal of Photographic Science, Vol. 13, 90-97 (1965); the color imaging process, as described in U.S. Patent 2,252,718; and reversal processes which utilize the color development of photographic silver halide elements containing incorporated color-forming couplers, as described, for example, in U.S. Patents 2,944,900;

2,984,567 and 3,189,452. In each of these processes~ however, lengthy solution processing techniques are required which rely heavily on precision control and sophisticated techniques in order to produce color photographic images of high quali~y.
The silver dye bleach process involves developing a silver image in an exposed silver halide emulsion containing bleachable dye, and subsequently bleaching the dye in those areas where the silver has been developed. ~11 the silver ion is removed or rendered transparent and insensitive to light by the bleach action, leaving a positive dye image in the areas where no metallic silver was present.
In most color photographic processes utilizing the above silver dye bleach system, it has been necessary to subject the exposed film to a large number of processing baths to achieve the discernable image. The exposed element is first developed with a black-and-white developer solution to produce a metallic silver image containing overall dye and A ~

~ 090188 then subjected to a strongly acidic dye bleach bath which decolorizes the dye in just those areas where the developed silver is present. The residual silver and silver halide are then removed in a subsequent bleach and fix bath and a direct-positive color image is obtained.
Photothermographic elements, i.e., photographic elements which produce a silver image upon imagewise exposure and then heat development, are described, for example, in Evans and McLaen U.S Patent 3,801,321 issued April 2, 1974; Sullivan, Cole and Humphlett U.S. Patent 3,785,830 issued January 15, 1974;
and Haist et al. U.S. Patents 3,301,678 and 3,531,285. These elements are particularly desirable in that an image can be produced by a dry process.
Michel et al., U.S. Patent 3,414,411, issued December

3, 1968, discloses an "in-camera" type system employing a photo-graphic element comprising a support having thereon a silver halide emulsion containing the salt of an acid and a developed silver image having in association therewith a bleachable dye, or dye precursor. The exposed emulsion is contacted with a viscous alkaline processing solution and with a web having an acidic substi-- tuent which is capable of exchanging hydrogen ion with the cation of the salt of an acid which is present in the emulsion to lower the pH of the emulsion to a level at which imagewise bleaching of the dye in areas of metallic silver and in the presence of a silver complexing agent proceeds. The dye bleaching is described as being conducted in the presence of a catalyst and the web is delaminated to uncover the image.
The processing solution of Michel et al., U.S. Patent 3,414,411, however, requires the use of salts which upon drying render the coating translucent or substantially opaque due to crystallization and the web must be delaminated from the element for viewing pur-poses. The acid used in the processing web is non-diffusible and immobile. Thus, in order to bleach the silver metal, ion 1~018t~

exchange must take place and the web must be peeled apart from the element.
The use of conventional dye bleach solutions is in some ways undesirable in that it is difficult to control the composi-tion of the solution and the process is time consuming.
It has thus been desirable to provide a photographic and preferably photothermographic dye bleach process which is dry, stable and does not require removing the bleaching web to prod-uce a positive color image.
Summary of the Invention It has been discovered according to the present invention that an element comprising a silver image and at least one over-all bleachable dye, that is a dye that is capable of being bleached in a silver dye-bleach process, can provide a positive dye image, in the absence of solutions, by contacting the element at moderately elevated temperatures, e.g. about 50C to about 150C, with a dye activator sheet comprising a support having thereon a layer or layers comprising a nonvolatile, diffusible acid and a non-hydrolyzable polymeric vehicle wherein the layer has a pH of up to 6.0, especially up to 4.0, and a melting point lower than 200C.
Thus, in accordance with the present teachings, a dry, activator sheet for a dry, thermal silver dye-bleach process is provided comprising a support having thereon a layer or layers comprising a) a nonvolatile, diffusible acid selected from the group consisting of nonvolatile, diffusible mineral acids and organic acids containing up to 10 carbon atoms, the acid being nonvolatile at processing t~mperatures of 50 to 150C in the activator sheet, lQ90188 b) a silver halide complexing agent, and c) a non-hydrolyzable polymeric vehicle.
The layer or layers have a pH of up to 4.0 and a melting point lower than 200C.
In accordance with a further teaching, a silver dye-bleach process of thermally dye bleaching a photographic element is provided which comprises a silver image in reactive association with a dye that is bleached in a silver dye-bleach process com-prising contacting the image with a dry, activator sheet compris-ing a support having thereon a layer or layers comprising a) a nonvolatile diffusible acid selected from the group consisting of nonvolatile, diffusible mineral acids and organic acids containing up to 10 carbon atoms, the acid being nonvolatile at processing temperatures of 50 to 150C in the activator sheet, b) a silver halide complexing agent, and c) a non-hydrolyzable polymeric vehicle.
The layer or layers have a pH of up to 6.4 and a melting point lower than 200C and heating to a temperature of from about 50 to about 150C to laminate the sheet to the element and produce a dye image.
In accordance with yet a further teaching, a photographic element is provided comprising a support having thereon a first layer containing a silver metal image in reactive association with a dye that is bleached in a silver dye-bl~ach process and laminated to the first layer a transparent second layer which comprises a) a nonvolatile, diffusible acid selected from the group consisting of mineral acids and organic acids containing up 10 carbon atoms, the acid being nonvolatile at processing temperatures of 50 to 150C in the activator sheet, b) a silver halid complexing agent, and c) a non-hydrolyzable polymeric vehicle.

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The second layer has a pH of up to 4.0 and melting point lower than 200C.
Detailed Description of the Invention The term "dry" as used herein is intended to refer to materials that are dry to the touch.
The support for the dry, activator sheet or web can be any material which retains dimensional stability at bleaching tempera-tures. Examples of suitable supports are paper, poly-olefins such as polyethylene or polypropylene, polycarbonate, high temperature-resistant film supports such as supports from 1,1,3-trimethyl-5-carboxy-3-(p-carboxyphenyl)indan polymers, cellulose acetate butyrate, polyethylene terephthalate, and the like. The preferred support materials are those which are transparent so that the positive color image can be viewed through the activator sheet.
The support has thereon, either in a layer or layers, the nonvolatile, diffusible acid and the polymeric vehicle. The support and layer or layers containing the above substituents can also be separated by an intermediate layer such as a timing layer, such as a Tio2 layer, which allows the silver image to be heat developed and bleached in a single heating step, and wherein the timing layer allows the development of the silver image prior to the bleaching by the activator sheet.
The acid used must be nonvolatile to avoid release of un-desired materials and must be mobile and diffusible in the photographic laminate comprising the described activator sheet and the photographic element so that the silver image can be effectively bleached in a short period of time. The acid can be selected from the group consisting of nonvolatile, diffusible ~j~ -6-lQ~0188 mineral acids and organic acids containing up to 10 carbon atoms.
Nonvolatile mineral acids useful herein include sulfuric acid, sulfamic acid, phosphoric acid, and the like.
Examples of nonvolatile, diffusible organic acids useful herein are those acids containing up to 10 carbon atoms including carboxylic acids such as citric acid, acetic acid, and other acids such as p-toluenesulfonic acid, phenylphosphonic acid, phenylphosphoric acid, phenylphosphinic acid, benzene-sulfonic acid, p-toluene sulfinic acid, and the like.
me term "nonvolatile" as used herein is intended to mean that no significant concentration of the acid, as described, is releasable from the activator sheet or element according to the invention at processing temperature.
It is critical that the acid be diffusible. By the term "diffusible acids" it is meant that the acids in themselves are mobile within the photographic laminant at the processing temperatures employed or they can be rendered mobile by the use of a suitable thermal solvent.
m e acid incorporated in the activator sheet is generally strongly acidic and/or present in sufficient proportions to provide a pH of 6.o or lower, especially up to 4.0, in the layer or layers on the support. Acids which are unable even at large proportions to reduce t~e pH in the layer or layers to a value below 6.o would not be suitable for use according to the invention.
me polymeric vehicle useful in this invention is a film-forming polymeric material containing organic residues which are non-hydrolyzable or slow to hydrolyze such as poly(vinyl alcohol), poly(acrylic acid), poly(styrene sulfonic acid), poly(vinyl pyrrolidone), poly(ethylene oxide), and 1(~30188 the like. It is critical that the vehicle be non-hydrolyzable or slow to hydrolyze because hydrolyzable vehicles such as gelatin compete for hydrogen ions and become hydrolyzed and denatured by the presence of the acid in the layer. The resulting layers then would be effective for only a short period of time after coating.
By the term "non-hydrolyzable vehicle'r it is meant that a coating containing said vehicle and said diffusible acid, when kept at room temperature, i.e. about 19C, 50~ relative humidity for about 4 weeks, shows no appreciable loss in activity due to pH changes caused by, for example, trans esterification or transamidation reactions.
Examples of non-hydrolyzable vehicles useful herein are sulfonated polystyrene, poly(acrylic acid), poly(acrylamide), poly(vinyl alcohol), poly(vinylpyrrolidone), poly(ethylene oxide), and active methylene containing polymers such as copolymers of acrylamide and ethyl 5-(m- and p-vinylphenyl)-3-oxo-pentanoate, copolymers of acrylamide and 6-(m- and p-vinylbenzyl)-2,4-hexanedione and the like.

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A silver halide complexing agent generally known in the art as a ~ixing agent must be present in either the activator sheet o~ the invention or it must be incorporated in the photographic element employed. As used herein, the term "complexing agent" refers to compounds which either (1) dissolve and remove silver ion from the emulsion layer or (2) are stabilizing compounds which react with the silver ion to render it insensitive to light and transparent.
The complexing agent employed herein in one form can be that of a conventional silver halide solvent. Silver halide solvents are defined as compounds which, when employed in an aqueous solution (60C), are capable of dissolving more than ten times the amount (by weight) of silver halide which can be dissolved in water at 60C.
Typical useful silver halide solvents include water-soluble thiosulfates (e.g., sodium thiosulfate, potassium thiosulfate, ammonium thiosulfate~ and the like), thiourea, ethylene-thiourea, a water-soluble thiocyanate (e.g., sodium thio-cyanate, potassium thiocyanate and ammonium thiocyanate), and a water-soluble sulfur-containing dibasic acid. ~ater-soluble diols used to advantage include those having the formula:
- HO(CH2CH2Z)pCH2CH20H, wherein p is an integer of from 2 to 13, and Z represents oxygen or sulfur atoms such that at least one third of the Z atoms are sulfur and there are at least two consecutive Z~s in the structure of the compound which are sulfur atoms. The diols advantageously used are also included in compounds having the formula: H0(-CH2CH2X)c_l-2CH2X )d-l(-cH2cH2x)e-l(cH2cH2xl)f l~CH2CH2X)g l-CH2CH20H, wherein X and X represent oxygen or sulfur, such that when X represents oxygen, Xl represents sulfur, and when X
represents sulfur, X represents oxygen; and each of c, d, e, f and g represents an integer of from 1 to 15, such that the ~(~g~

sum of c+d~e~f~g represents an integer of from 6 to 19, and such that at least one third of the total of all the X's plus all the Xl's represents sulfur atoms and at least two consecutive X's and/or X 's in the structure of the compound are sulfur atoms.
Typical diols include the following:
1) 3,6-dithia-1,8-octanediol 2) 3,6,9-trithia-1,11-undecanediol HocH2cH2scH2cH2scH2cH2scH2cH2oH
3) 3,6,9,12-tetrathia-1,14-tetradecanediol H(CH2CH2S)4CH2CH2H

4) 9-oxo-3,6,9,12,15-tetrathia-1,17-heptadecane-diol HO(cH2cH2s)2cH2cH2o(cH2cH2s)2cH2cH2oH

5) 9,12-dioxa-3,6,15,18-tetrathia-1,20-eicosanediol H0(CH2CH2S)2(CH2CH20)2(CH2CH2S)2( 2

6) 3,6-dioxa-9,12-dithia-1,14-tetradecanediol Ho(cH2cH2o)2(cH2cH2s)2cH2cH2oH

7) 3,12-dioxa-6,9-dithia-1,14-tetradecanediol 2cH2o(cH2cH2s)2cH2cH2ocH2cH2oH

8) 3,18-dioxa-6,9,12,15-tetrathia-1,20-eicosanediol HocH2cH2o( cH2cH2s)4cH2cH2ocH2cH2oH
: 9) 12,18-dioxa-3,6,9,15,21,24,27-heptathia-1,29-nonacosanediol (CH2CH2S)3CH2CH2CH2CH2SCH2CH2(CH2 2 )3 10) 6,9,15,18-tetrathia-3,12,21-trioxo-1,23-tricosanediol HocH2cH2o(cH2cH2s)2cH2cH2o(cH2cH2s)2 : Water-soluble sulfur-containing dibasic acids which can be used include those having the formula: HOOCCH2-(SCH2CH2)qSCH2COOH~ in which q represents an integer of from 10~01~

1 to 3, and the alkali metal and ammonium salts of said acids. Typical illustrative examples include:
1) ethylene-bis-thioglycolic acid OccH2scH2cH2scH2cooH
2) 3,6,9-trithiahendecane dioic acid HOOCCH2 ( SCH2CH2 )2SCH2COOH
3) 3,6,9,12-tetrathiatetradecanedioic acid HOOCCH2 ( SCH2C~2 ) 3SCH2COOH
4) ethylene-bis-thioglycolic acid disodium salt 105) ethylene-bis-thioglycolic acid dipotassium salt 6) ethylene-bis-thioglycolic acid diammonium salt 7) 3,6,9-trithiahendecane dioic acid disodium salt 8) 3,6,9,12-tetrathiatetradecanedioic acid disodium salt The complexing agent, if included in the emulsion, must not desensitize the emulsion. Various complexing agents which can be incorporated in the emulsion layers of the ` photographic element without adversely affecting the element include thiouronium and isothiouronium salts, such as 2,2'-methylsulfonylimino bls(ethyl isothiouronium para toluene sulfonate), 3,5-thiouronium-1-methyl-1-propane sulfonate, 3,5-thiouronium-l-propane sulfonate~ and the like as described in U.S. Patents 3,531,285 and 3,301,678; aminothiazolines such as 2-amino-2-thiazolium trichloroacetate and the like, azo thio-ethers and blocked azolinethiones such as those described, for example, in U.S. Patent 3,824,103 and complexing agents such as those described in U.S. Patent 3,785,830.
If the complexing agent is incorporated in the activator sheet, any of the above complexing agents can be used in addition to other complexing agents such as thiourea and the like.
The activator sheet can also contain a thermal solvent, if desired, to aid the acid in diffusing to the -- 10 _ emulsion layer. The thermal solvent should be added if the depressed melting point of the mixture of the diffusible acid and the complexing agent, if any, is 200C or higher. The thermal solvents can, at any rate, accelerate the rate of bleaching by depressing the melting point of the mixture.
By the term 'rthermal solvent" it is meant a non-hydrolyzable organic material which is a solid at ambient temperatures, but which has a mixed melting point with the other ingredients at or below the temperature of the thermal process employed. Preferred thermal solvents for this invention include a variety of ethers, sugars and alcohols which act as solvents for the incorporated materials functioning in the process.
Examples of useful thermal solvents can be found in U.S. Patent 3,667,959 issued June 6, 1972; U.S. Patent 3,347,675 issued October 17, 1967 and U.S. Patent 3,438,776 issued April 15, 1969 and include non-hydrolyzable polar solvents containing up to 10 carbon atoms such as ethylene glycol, and low molecular weight polyethylene glycol and poly-ethylene oxide, l,10-decanediol, 1,6-hexanediol, sorbitol and the like.
In accordance with the invention, a catalyst may be incorporated in the photographic emulsion, the acidic processing web, or in both of these materials to aid in obtaining an optimum dye image. The presence of a catalyst is needed in the activator sheet if the pH is above 4Ø Advantageously, the bleaching of the image dye is conducted in the presence of a suitable catalyst, such as a phenazine, a quinoxaline, an anthra-quinone, or a pyrazine. A number of catalysts useful herein - are described in U.S. Patent 2,183,395 and 2,270,118. These compounds oxidize the metallic silver to silver ion, and in 1()~01~
so doing are reduced. m e reduced catalyst then cross-oxidizes with the image dye. mis cross-oxidation decolorizes, i.e.
bleaches, the image dye and oxidizes the catalyst back to its original state.
If the activator sheet is at a pH of about 4.0 to about 6.o, a catalyst must be included in the activator sheet.
If the pH of the activator sheet is 4.0 or lower, the use of a catalyst is optional.
Other addenda such as bleaching compounds, dye bleach competers and fixing compounds known in the art can be incorporated into the activator sheet of this invention.
In order to satisfactorily bleach out the silver image with a brief heating step, the activator sheet must have a pH not greater than 6.0, especially not greater than 4.0, and must have a melting point sufficiently low to enable the acid at processing temperatures to diffuse to the emulsion layer, i.e. a melting point below about 200C, such as within the range of about 50C to about 150C. mus, the strength and proportion of the acid can be adjusted to achieve the low pH values and the use of-the thermal solvent can lower the melting point of acids having higher melting points in order to achieve these properties.
It is pointed ou~ that if gelatin is used as a binder in the emulsion layers, since it is a buffer, more acid should be used~ Binders which are not buffers may require the use of less acid.
m e acid component as described can be present in a range of concentration in the activator sheet so long as the pH
of the layer or layers in the sheet is 6.o or less, especially not greater than 4Ø Preferably the acid is present from about 3 1.0 g/m2 to about 50.0 g/m2 in the activator sheet. m e polymeric vehicle preferably is present from about 1.0 g/m2 to about 50.0 g~m2 in the activator sheet. Typical concentrations for complexing agents are from about 1.0 g/m2 to about 50.0 g/m2 or (about 1 mole to about 5 mole/mole of silver halide). mermal solvents can be present from about 1.0 g/m2 to about 50.0 g/m2 1()~3()18~

while catalysts such as phenazine are preferably pre~ent from about 0 to about 100 mg/ft2 in the activator sheet, depending upon the pH of the activator sheet.
The activator sheet can be prepared by coatlng onto a suitable support a coating solution comprising the acid, the vehicle, optionally the complexing agent, the thermal solvent, and catalyst if the pH is above 4.0, and then drying. m e various components are coated from a solvent such as methanol, ethanol, acetone, water or the like. me various components can be coated ln one layer or in different ad~acent layers.
A typlcal activator sheet or web comprises the following components thiourea 5.4 g/m 1,6-hexanediol 5.4 g/m p-toluenesulfonic acid 5.4 g/m poly(vinylpyrrolidone) 2.7 g/m Triton TX-100 (m is is a 1.25 ml (10% ~olution) surfactant which is a sodium salt of an alkyl aryl polyether sulfonate and is a trademark of Rohm and Haas Co., U.S.A.).
in methanol/distilled water (50:50 parts by volume) This activator sheet or web has an effective p~ of 4.0 or less.
m e s~lver and dye images are bleached by merely placing the activator sheet over the image and laminating by applying heat at the melting point of the components in the activator sheet and lightly pressing the two sheets together, such as with a roller or other suitable means. A positive dye lmage is produced in the element by bleaching upon briefly heating the laminate, preferably to a temperature of about 50C to about 150C and more preferably from about 90C to about 120C over a time period ranging from about 2 to about 300 seconds, preferably from about 15 to 30 seconds. The temperature and length of heating can be varied widely depending on the thickness of the emulsion, activator chemistry layers, desired B

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lmage, and the llke.
Any sultable means can be useful to provide thedeslred processing temperature. The heating means can be a slmple hot plate, lron, roller, oven or the like.
Processing is usually carried out under atmospheric condltions of pressure and humidity. Conditions outside normal atmospherlc pressures and humidlty can be employed if desired.
In a preferred embodiment, the support for the actlvator sheet is transparent so that the image is vislble through the activator sheet. It ls a partlcular advantsge of thls lnvention that the activator sheet need not be del~mlnated from the image. The resultlng photographic element comprises a support having thereon a first layer containing a silver metal image and overall bleachable dye and laminated to the dye image a transparent second layer comprising a) a nonvolatile, diffusible acld selected from the group consisting of nonvolatile, diffusible mineral acids and organic acids containlng up to 10 carbon atoms and b) a nonhydrolyzable polymeric vehicle whereln said second layer or layers have a pH of up to 6.o, especlally up to 4.0, and a melting point lower than 200C.
Alternatlvely, the resultlng photographic element can comprise a support havlng thereon a first layer containing a sllver metal image and overall bleachable dye and laminated thereon a transparent second layer or layers comprising - a) a nonvolatile diffusible acid selected from the group consisting of nonvolatile, diffusible mineral acids and organic acids containing up to 10 carbon atoms b) a silver halide complexing agent and c) a nonhydrolyzable polymeric vehicle wherein said second layer or layers have a pH of up to 6.o, especially up to 4.0, and a melting point lower :~ than 200C.

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me photographic element can be prepared using any source for the silver image. For example, the silver image can be provided by imagewise exposing a photographic emulsion containing a silver salt such as silver behenate, silver laurate, silver trifluoroacetate and silver halide such as silver chloride, silver chlorobromide, or the like to provide a latent image and chemically developing or physically developing the latent image in a conventional developer bath or by heat if using a photothermographic element.
In yet another embodiment, a silver image with an overall dye covering can be obtained by simply depositing silver through a mask and overall depositing the bleachable dye.
The bleachable dyes used herein are well known in the art. m e term "bleachable dyes" as used herein includes compounds which are dye precursors, i.e., colorless compounds which become colored during processing of the photographic materials and shifted dyes which shift hypsochromically or bathochromically to the desired image hues when sub~ected to a different environment such as a change in pH, reaction with a material to form a complex, etc. The term "non-diffusible" as used herein refers to bleachable dyes which in themselves are non-diffusible in the emulsion, or dyes which are rendered non-diffusible by the use of a suitable mordant, such as those described in U.S. Patent 2,882,156. The elements of this invention can have a single emulsion coating for monochrome dye images formed from either one or a mixture of bleachable dyes, which dye images are either colored or neutral (e.g., black and white) images. Primarily, azo dyes are used in silver dye-bleach systems because the bleaching process cleaves the -N=N- double bond to give two aromatic fragments. Typical azo dyes which can be used in the practice of this invention are listed in numerous patents, ~j l~Y0~8 some of which are U.S. Patent Nos. 923,265; 999,996; 1,042,300;1,077,628; and U.S. Patent Nos. 3,178,290; 3,178,291; 3,183,225 and 3, 211, 556.
Bleachable dyes include those known in the art and dyes such as disclosed in the Color Index (third edition) published by the Society of Dyers and Colourists, copyright 1971, printed by Lund Humphreys, Bradford and London, provided they are bleachable as herein described. m is includes bleachable dyes such as azo dyes, formazan dyes, azoxy dyes, xanthene dyes, azine dyes, phenylmethane dyes, nitroso dyes, indigo dyes, quinones, nitro-substituted dyes, phthalocyanines, and others known to one skilled in the art. Precursors to these dyes as known in the art, such as, hydrazo or diazonium compounds to yield azo dyes, tetrazolium salts to yield formazan dyes, etc., are also useful herein.
me bleachable dyes are defined as those dyes which in the presence of a photographic image comprised of silver metal and an aqueous solution of a silver complexing agent such as thio-urea and an electron transport agent such as phenazine at pH
20 values up to 4.0 suffer discharge of their color proportionate to the amount of silver metal present. Further examples of these dyes may be found in U.S. Patent 3,202,511; 3,493,372 and U.K. Patents 1,146,118 and 1,255,857.
The elements of this invention may have a plurality of coatings each containing a different bleachable dye for providing multicolor images. Especially useful arrangements are those in which at least three light-sensitive emulsion layers are provided which are respectively sensitized to blue, green and red radiation, and contain, respectively, non-30 diffusible yellow, magenta and cyan dyes. me emulsions usedin this invention can contain the bleachable dyes. However, it is also possible, and sometimes preferabl~, to incorporate ~, 10~0188 the bleachable dye in an alkaline-permeable layer contiguous to the emulsion layer. This arrangement provides increased speed, especially when the bleachable dye containing layer is coated adjacent to the emulsion layer. mus, in one useful arrangement, a support has coated thereon, in the following order, layers containing, respectively, blue-sensitive silver halide, bleachable yellow dye; green-sensitive silver halidej bleachable magenta dye; red-sensitive silver halide and bleachable cyan dye.
m e dyes can be added by any of the conventional methods known in the art, for example, as dispersions in which ballasted dyes are rendered partially soluble by use of a sulfonic acid or carboxylic acid substituentj or as dispersions wherein an oil soluble dye is dispersed alone or in the presence of a high boiling solvent in the photographic binder.
In the silver dye-bleach system, photographically developed silver is used to reduce a dye from a colored to a colorless form. m is dye bleaching step is usually carried out in an acidic solution in the presence of a silver ion complexing agent and a dye bleach catalyst. In this invention, a dry sheet is provided to carry out the bleach step. This step can be carried out at a pH up to 4.0 without the need of a silver dye-bleach catalyst.
me bleachable dyes are preferably used at a concentration ranging from about 0.1 g/m2 to about 3.oo g/m2 to achieve a discernible image, depending on the molar extinction coefficient of the dye, and whether a reflection -- 1~ --.

~(~90188 print or transparency ls deslred.
In the preferred embodlment the photographlc element ls completely dry processed. The sllver lmage ls produced by a photothermographlc process uslng a photothermographlc element.
Typlcal photothermographlc elements to which the bleachable dyes are added are descrlbed ln U.S. Patent 3,785,830 of Sulllvan, Cole and Humphlett, U.S. Patent No. 3,301,678 and U.S. Patent 3,531,285 both by Halst, Humphlett and Johnson and U.S. Patent 3,801,321 of Evans and McLaen.
Other photothermographlc elements which are processed by heat lnclude those containing a silver salt and a base precursor such as the salt of trlfluoroacetic acid, and an amine, or bis-isothiuronlum compound such as those described in U.S. Patents3,669,670; 3,301,678 and 3,531,285.
The photothermographic element can comprise a support havlng thereon a reduclng agent, a silver salt oxldlzlng agent, and a photosensltlve sllver hallde composltlon. Typlcally, preferred photothermographic elements are described in U.S.
Patents 3,785,830 and 3,801,321.
Various reducing agents useful in photothermographic compositions containing bleachable dyes and optlonally sllver complexlng agents are for example, polyhydroxybenzenes such as hydroqulnone developing agents lncludlng, for lnstance, hydro-quinone, alkyl substituted hydroqulnones, exempllfied by - tertiarybutylhydroquinone, methylhydroquinone, 2,5-dlmethyl-hydroquinone and 2,6-dimethylhydroqulnone; catechols and pyrogallol; halo-substltuted hydroqulnones such as chlorohydro-qulnone or dlchlorohydroquinone; alkoxy substituted hydroquinones such as methoxyhydroquinone or ethoxyhydroquinone and the like. Other reducing agents which can be employed include reductone developing agents such as anhydro dihydro piperidino hexose reductone; hydroxytetronic acid reducing agents and - 18 _ 1~0~

hydroxy~etronimide developlng agents; 3-pyrazolidinone developing ag-ents such as l-phenyl-3-pyrazolidinone and 4-methyl-4-hydroxymethyl-l-phenyl-3-pyrazolidlnone and those described in British Patent 930,572 published July 3, 1963; certain hydroxylamine developlng agents; ascorbic acid developing agents such as ascorbic acid, ascorbic acid ketals, and other ascorbic acid derivatives, phenylenediamine developing agents; certain aminophenol developing agents and the like. Combinations of reducing agents can also be employed. Preferred reducing agents are sulfonamido-phenols such as 2,6-dichloro and 2,6-dibromo-4-benzenesulfon-; amidophenols as described in U.S. Patent 3,801,321 and bis-Deta-naphthols such as described in U.S. Patent 3,751,249.
The silver salt oxidizing agent can be a silver salt of a long chain fatty acid such as silver behenate, silver stearate, silver oleate, silver laurate, silver hydroxystearate, silver caprate, silver myristate and silver palmitate as well as silver benzoate, silver phthalate, silver acetate, silver phthalazinone, silver benzotriazole and silver saccharin.
A particularly useful silver salt herein is a silver salt of a thione. The silver salt of the thione can be prepared in situ in the photothermographic materials by combining a source of silver, such as silver trifluoroacetate, with the thione compound in the compositlon. The thione compound is a compound represented by the formula:

Rl__ __~
N - C=S

ZCOOH

~ 01~8 wherein Rl represents atoms completing a 5 member hetero-cyclic nucleus, such as a thiazoline nucleus, and Z is alkylene, such as alkylene containing 1 to 3O carbon atoms, typically 1 to lO carbon atoms. Examples of suitable 5 member heterocyclic nuclei are thiazoline-2-thione, benzo-thiazoline-2_thione, imidazoline-2-thione or similar hetero-cyclic thione nucleus. The heterocyclic nucleus can contain substitutent groups which do not adversely affect the described photothermographic nlaterials such as alkyl containing 1 to 3 carbon atoms, or phenyl. Alkylene as employed herein includes so called branched chain alkylene such as -CH--An especially suitable silver salt formin~ thione com--pound is a thiazoline-2-thione represented by the formula:

R21C > =S
Z COOH

wherein zl is alkylene containing 1 to 4 carbon atoms, typically methylene, R2 and R3 are each selected from the group consist-ing of hydrogen, alkyl containing 1 to 4 carbon atoms, and aryl containing 6 to lO carbon atoms, or taken together are atoms completing a benzo group. The alkyl, aryl and benzo groups can be substituted with groups which do not adversely affect the described photothermographic materials.

Another suitable silver salt formlng thione compound is an imldazoline-2-thione represented by the formula:

' 411 ~ =S

)18~

wherein z2 is alkylene containing 1 to 4 carbon atoms~
typically ethylene; R6 is alkyl, typically alkyl contain-ing 1 to 3 carbon atoms, such as methyl, ethyl or propyl, aryl containing 6 to 10 carbon atoms, such as phenyl, or carboxyalkyl, such as carboxyethyl and carboxymethyl;
R4 and R are each selected from the group consisting of hydrogen, alkyl containing 1 to 4 carbon atoms, such as methyl, ethyl and propyl, aryl containing 6 to 10 carbon atoms, such as phenyl or tolyl, or R4 and R5 taken together are atoms completing a benzo group.
A further suitable silver salt forming thione compound is an oxazoline-2-thione represented by the formula:

R7ll _ o 811 ~>

wherein z2 is as described; R7 and R8 are each selected from the group consisting of hydrogen~ alkyl containing 1 to 4 carbon atoms, such as methyl, ethyl, and propyl, aryl contain-: ing 6 to lO carbon atoms, such as phenyl or tolyl, or R7 and R taken together are atoms completing a benzo group.
Examples of suitable thione compounds within the deecribed formulas include:
3-(2-carboxyethyl)-4-methyl-4-thiazoline-2-thione, 3-(2-carboxyethyl)benzothiazoline-2-thione, 3-(2-carboxyethyl)-5-phenyl-1,3,4-oxadiazoline-2-thione, 3-(2-carboxyethyl)-5-phenyl-1,3,4-thiadiazoline-2-thione, 3-(carboxymethyl)_4_methyl-4-thiazoline-2-thione~

3-(2-carboxyethyl)-1-phenyl-1,3,4-triazoline-2-thione, 1,3-bis(2-carboxyethyl)imidazoline-2-thione, 1,3-bis(2-carboxyethyl)benzimidazoline-2-thione, 3-(2-carboxyethyl)-1-methylimidazoline-2-thione, 3-(2-carboxyethyl)benzoxazoline-2-thione, and 3-(1-carboxyethyl)-4-methyl-4-thiazoline-2-thione.

1(~90188 The described thione compounds can be prepared employing processes known in the art. The described silver complexes of the thione compounds can be prepared in situ, as described, or the silver complexes can be isolated.
The photosensitive silver halide useful herein can include, for example, silver chloride, silver bromide, silver bromoiodide, silver chlorobromoiodide, or mixtures thereof.
For the purposes of the invention, silver iodide is also included as a photosensitive silver halide. While the photo-sensitive silver halide can be prepared in situ in thephotothermographic material, this is not necessary according to the invention. 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 well-known procedures employed in the photographic art. The silver halide can be prepared, for example, employing single-~et preparation techniques, double-~et preparation techniques, such as techniques employed in preparing Lippmann emulsions and the like. Surface image or internal image ~ilver halide materials can be used. If desired, mixtures of surface and internal image silver halide materials can be used. Negative type silver halide is typically employed.
The silver halide materials can be regular grain such as described in Klein and Moisar, Journal of Photographic Science, Volume 12, No. 5, September-October (1964), pages 242-251.
The photosensitive silver halide can be chemically sensitized employing techniques known in the photographic arts.
Although a binder is not essential with the photo-thermographic materials described, a binder is typically em-ployed. The binders which are useful with the describedphotothermographic materials include various colloids employed alone or in combination as vehicles and/or bindlng agents which do not adversely affect the desired photothermo-graphic propertles of the described compositions and in varlous layers of a photothermographic element. Suitable materials can be hydrophilic or hydrophoblc. The binders whlch are suitable are transparent or translucent and include both naturally-occurring substances such as protelns, for example, gelatln, gelatin derlvatlves, cellulose derlvatlves, poly-saccharldes such as dextran, gum arabic and the like; and synthetic polymeric substances such as water soluble polyvinyl compounds llke poly(vinylpyrrolidone), acrylamide polymers and the llke. 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 photothermographic materials. Suitable binders include polymers such as water insoluble polymers of alkyl acrylates or methacrylates and those whlch have cross-linking sites which facilltate hardenlng or curing as well as those having recurring sulfobetaine unlts. Especlally sultable bindlng agents include high molecular weight materials and reslns such as poly(vinyl butyral), cellulose acetate butyrate, poly(methyl methacrylate), poly(vinylpyrrolldone), ethyl cellulose, poly(styrene), poly-(vinyl chloride), chlorinated rubber, poly(isobutylene), butadiene-styrene copolymers, vinyl chlorlde-vinyl acetate copolymers, copolymers of vlnyl acetate, vinyl chloride and maleic acid, poly(vinyl alcohol), high molecular weight ethylene oxide polymers and active methylene polymers such as those described in U.S. Patent 3,904,418 by Ponticello and Mowrey.
The photothermographic compositio~ can be coated on a wide varlety of supports. Useful supports include those which can withstand the processing temperatures employed such as cellulose ester film, poly(vinyl acetal) film, polystyrene film, ` -`` 1(~90~8~il poly(ethylene terephthalate) film, polycarbonate film and re-lated fllms or resinous materials, as well as glass, paper, metal and the like. Typically a flexible support is employed.
Hardenable layers of a photothermographic element, as described, can be hardened by various organic or inorganic hardeners alone or in combination, such as aldehydes, ketones, vinyl sulfones, aziridines, mucrochloric acid and the like which do not adversely affect the sensitometric properties of the photothermographic materials. Hardeners which cause adverse reduction of the described compositlon should be avoided.
The photothermographic elements and materials according to the invention can contain addenda and layers commonly employed in photo~hermographic elements, such as antistatic and/or conducting layers, plasticizers and/or lubricants, surfactants, matting agents, brightening agents, light-absorbing materials, filter dyes, antihalation dyes and absorbing dyes, and the like.
The various components of the photothermographic materials of the invention can be added from water solutions, or suitable organic solvent solutions can be used. The components can be added using various procedures known in the photographic art.
If desired, an agent, sometimes referred to as a toning agent or activator-toning agent, can be employed with the photother-mographic materials according to the invention to provide an increase in density at certain processing temperatures. Suitable toning agents, also known as activator-toning agents, include cyclic imide toning agents such as phthalimide, N-hydroxyphthalimide, succinimide, and N-hydroxysuccinimide, and the like. These are described, for instance, in Belgian Patent 766,590, issued June 15, 1971. Sulfolane in some instances can provide improved results in the described photothermographic compositions.
Some photothermographic elements and compositions described according to the invention do not need a toning agent.
Spectral sensitizing dyes can be used conveniently to confer additional sensitivity to the light sensitive silver halide employed according to the invention. For instance, additional spectral sensitization can be obtained by treating the silver halide with a solution of a sensitizing dye in an organic solvent or the dye can be added in the form of a dispersion. Spectral sensitizers which can be used include the cyanines, merocyanines, complex(trinuclear or tetranuclear) merocyanines, complex(trinuclear or tetranuclear) cyanines, holopolar cyanines, styryls, hemicyanines, such as enamines, oxonols, and hemioxonols.
A range of concentrations of each component in the photothermographic material can be employed. Typically, each light sensitive layer of a photothermographic element according to the invention can comprise a) from about 0 to about l.0 x lO l moles of silver as the described complex and b) about l.0 x lO 3 to about l.0 x lO 2 moles of the described photosensitive silver halide per square meter of support and c) a reducing agent in at least molar equivalency to conduct development based on reducible silver ions and up to lO times equivalent in excess.
An optimum concentration of each component will depend upon the particular components, the desired image, processing temperature and the like.
The bleachable dye can be added directly to the photothermographic composition prior to coating or can be added after the composition is applied to the support.

A

The photothermographic layer and/or other layers of a photothermographic element according to the invention can be coated by various coating procedures including dip coating, airkni~e coating, curtain coating or extrusion coating using hoppers of the type described in U.S. Patent 2,681,294 of Beguin, issued June 15, 1954. If desired, two or more layers can be coated simultaneously by procedures known in the art.
The silver image on the photothermographic element can be produced after imagewise exposure within a short time by merely moderately overall heating the photothermographic element.
For instance, a visible image on a photothermographic element according to the invention can typically be produced within a few seconds, e.g. about 1 to about 60 seconds after exposure by heating the element to about a temperature within the range of 100C to about 250C, typically about 130C to about 180C.
Usually, the time of heating is less than about 20 seconds, such as about 2 to 5 seconds at a temperature of about 180C.
Optimum time of heating and optimum temperature of heating can be determined employing test procedures well known in the art.
One embodiment of the invention accordingly is a method of developing and stabilizing an image in an exposed photothermographic element comprising a support having thereon (a) a reducing agent, as described, (b) a silver salt of a thione compound, also as described, (c) a photosensitive component consisting essentially of photosensitive silver halide, (d) a bleachable dye and, if desired, (e) a binder, comprising heating the photothermographic element to a temperature within the range of about 100C to about 250C.
In developing an image in a photothermographic element according to the invention, increasing or decreasing the length of time of heating can enable use of a higher or lower temperature within the described range.

.

lQ30188 In some cases it may be convenient to produce the positive dye image using only a single heating step. This can be accomplished by placing a timing layer between the photo-thermographic element and the activating sheet and exposing and heat processing whereby the bleaching is delayed until the silver image is developed.
If moisture is present in the activator sheet, the sheet should be preheated to a molten state prior to laminating to release excess moisture and prevent gas bubbles when the dry ~activator sheet is laminated to the silver dye image.
The activator sheet described herein is stable in the dry condition and can be kept on a shelf for long periods of time prior to use.
; m e invention is further illustrated by the following examples.
Example 1 A heat-developable photographic element was prepared by combining the following components and coating on a suitable paper support:
A. A sulfur and gold sensitized, cubic-grained silver bromide emulsion (0.4 gAg/m2) B. l-Phenyl-3-pyrazolidone ~1.08 g/m2) C. 1,8-(3,6-Dioxaoctane)-bis-isothiuronium-p-toluene-sulfonate (3.24 g/m2) D. a,a-bis[4-(3',6'-disulfo-8'-heptoyl~mino-1'-naphthol-2'-yl)azo-2,5'-dimethylphenyl]toluene, tetrasodium salt (0.2 g/m2) E. Gelatin (6.75 g/m2) A sample of the above prepared element was imagewise exposed to tungsten light through a graduated-density test object to provide a latent image which was then thermally developed by contacting the sample for 5 seconds with a heated metal block ,~

l~g~188 having a temperature of 200C. A negative silver scale was produced. Two samples were then laminated in contact with the following activator sheet for 15 seconds at 100C both freshly coated and after one hour. The activator sheet comprised a film support having coated thereon Sulfonated polystyrene 1.8 g/m2 Thiourea 10.8 g/m p-Toluenesulfonic acid 10.8 g/m2 l,10-Decanediol 10.8 g~m Positive magenta dye images were observed which gave excellent uniform bleaching and good minimum densities. The equivalent results indicated fresh activity of the activator sheet and activity after 1 hour were equal~
In a similar manner, 1,6-hexanediol and ethyleneglycol were used as replacements for l,10-decanediol and similar results were obtained.
Effective silver halide solvents which replaced thiourea were also shown, including:
A.
H
~N> =S

B. HO-CH2-CH2-S-CH2-CH2 S CH2 2 3 \ " / CH3 C N - C - N
CH3 / \ CH4 105~0188 Example 2 - comParative Exam~le A photographic element containing a cellulose acetate support having coated thereon 2.90 g of AgBr/m2 and the azo dye having the structure CH3 OH NH-C-(CH2)5cH3 ~N - N~OS03Na H-C

\

O
\ CH3 OH NH-C-(CH2)5cH3 CH3 S~3 ~ S03Na was imagewise exposed and processed for 3 minutes in Kodak Developer Dl9, fixed and dried. m e dried negative silver image was bleached by laminating it to an activator web coated on a polyethylene terephthalate support for 20 seconds at 90C.
The preparation contained the following compounds coated thereon (per square meter~:
Thiourea 5.4 g Distilled water 54 ml Sulfonated polystyrene 10.8 ml (18.3% solution ln water) Polyacrylic acid (Acrysol10.8 ml A-3 which is a trademark of Rohm and Haas Co., U.S.A.) (25% solution) Hydrochloric acid 10.8 ml Distilled water containing5.4 ml 6% saponin A positive dye image was formed. However, the acid was too volatile.
Example 3 A sample of photothermographic element was prepared B by combining the following components and coating on a suitable paper support: 29 - _ ~ _ 18l~
A. A sulfur and gold sensitized cubic grained silver bromide emulsion (0.43 gAg/m2).
B. l-phenyl-3-pyrazolidone (1.08 g/m2) C. Dimethyldodecylammonium hydrogen malonate (3.24 g/m2) D. a,a-bis[4-(3',6'-disulfo-8'-heptoylamino-1'-naphthol-2'-yl) azo-2,5'-dimethylphenyl]toluene, tetrasodium salt (0.21 g/m2) E. Gelatin (6.75 g/m2) F. 2,2'-methyl sulfonyl imino bis(ethyl isothiouronium para-toluene sulfonate) (3.24 g/m2) A sample was exposed with tungsten light through a graduated density test object to provide a latent image which was thermally developed as in Example 1 for 30 seconds at 150C. The element was then laminated with an activator she~t comprising a polyester film support having coated thereon a layer containing polyacrylic acid at 2.7 g/m2 and p-toluenesulfonic acid at 5.4 g/m2. The complexing agent was the isothiouronium salt in the emulsion layer. The laminated structure was then heated to 100C and after 1 minute a well-defined positive magenta dye image was obtained.

Example 4 A sample of the photothermographic element described in Example 3, but with a poly(ethylene terephthalate) film support, was exposed through a graduated-density test object and directly laminated with an acid activator sheet comprising a polyester film support comprising (a) a first layer containing titanium dioxide at 21.6 g/m2 and gelatin at 2.16 g/m2 and overcoated with (b) a second layer containing polyacrylic acid at 2.7 g/m2, p-toluene sulfonic acid at 5.4 g/m2 and thiourea at 5.4 g/m . m e laminated structure was then thermally 1()301~

processed by contact for one minute with a metal block heatedto 150C. A reflectlon prlnt comprlslng a well-deflned, posltlve magenta dye lmage resulted whlch lndlcated that sllver development and bleachlng were carrled out ln a slngle heatlng : step, presumably due to the volumlnous T102 layer acting as a timing layer for the silver-dye bleach reaction.

Example 5 This example illustrates the use of a photothermo-graphlc materlal, such as described in Evans and McLaen U.S.
Patent 3,801,321, to produce a dye image according to the practice of thls lnventlon:
A sllver behenate/behenlc acld dlsperslon was pre-pared by ball-mllllng the followlng components for 72 hours:

Sllver behenate 33.6 g Behenlc acid 25.4 g Poly(vinyl butyral)12.0 g Acetone/toluene (1:1 by volume) 675 ml Photothermographic elements were then prepared by comblning the followlng addenda and coating the compositlon at o.oo6 lnch on a polyethylene terephthalate film support both -with and wlthout a titanium dloxide reflectlve layer:

Sllver behenate dlsperslon (as prepared above) 2.0 ml Silver bromoiodide emulslon peptized in poly(vinyl butyral) (3.0 l/mole Ag, 100 g polymer/mole Ag, 6 mole % iodlde) 2.0 ml Poly(vlnyl butyral) (2-1/2 wt. %
of an acetone/toluene solution) 2.0 ml Azo dye havlng the structure 40 mg 1(?5~0188 OH
~,CO~ tC~ > 4Q~C5Hl l-t 2~N~N~CH3 2,6-Dichloro-4-benzenesulfonamido- 60 mg 1,8-(3,~-Dioxaoctane)bis-iso-thiuronium-p-toluene sulfonate 100 mg Samples of the coatings were exposed through a graduated-density test ob~ect and thermally developed for 30 : seconds at 150C. The developed samples, which contained a negatlve silver lmage and a uniform distribution of dye, were 10 then laminated with an acid activator sheet prepared by coating the following composition on a polyethylene terephthalate film support at a wet thickness of 0.006 inch:
Polyacrylic acid (Acrysol A-3) 10 ml (25 wt. % aqueous solution) Thiourea 5 g p-Toluene sulfonic acid 5 g Ethanol/water (1:1 by volume to : total volume of 81 ml The laminated structures were heated to 120C for 30 seconds and well-defined, positive dye images were obtained.

Example 6 A photothermographic material was prepared by the following steps:

(l) A silver thiazoline thione complex was prepared by combining the following addenda and blending for 45 minutes ~t 48.9C:

1()90188 3-(2-carboxyethyl)benzo-thiazoline-2-thione 14.8 g Silver trifluoroacetate 5.25 g Isopropyl alcohol 27 ml Distilled water (2) A developer toner solution was prepared as follows:
` Methanol 30 ml t-Butylhydroquinone 3 g 3-Mercapto-l-H-1,2-4-triazole 20 ml Methanol to a total volume 35 ml (3) A final coating composition was prepared by combining the above-identi~ied mixtures in the following proportlons:

S,ilve,r com~lex disper,sion 105 ml ~as aescrl~ed unde~ ~1) above) Developer-toner mixture 35 ml Solution containing 10~ by weight 1 ml saponin Gelatin peptized silver iodide emulsion 6 ml Azo dye 380 ml ' The final composition was coated at 0.94 milliliters per square decimeter on a polyethylene coated paper support. The photothermographic material was exposed imagewise for 4 seconds and then thermally developed by contact for 15 seconds with a metal block heated to 140C. A negative silver image and a uniform distribution of magenta dye was observed. The sample was then laminated in contact with a sample of an activator sheet and heated to 70C for 60 seconds. The activator sheet consisted of a polyethylene terephthalate film support having coated thereon a layer comprising 10.8 grams per square meter thiourea, 5.4 grams per square meter ethylene glycol~ 1.9 grams lQ5~0188 per square meter sulfonated polystyrene, and 0.001 llter per square meter sulfuric acld.
After heating, the elements were left lamlnated and a well-defined positive magenta dye image was observed.
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 inventlon.

Claims (37)

WHAT IS CLAIMED IS:

1. A dry, activator sheet for a dry, thermal silver dye-bleach process comprising a support having thereon a layer or layers comprising (a) a nonvolatile, diffusible acid selected from the group consisting of nonvolatile, diffusible mineral acids and organic acids containing up to 10 carbon atoms, said acid being nonvolatile at processing temperature of 50°
to 150°C in said activator sheet, (b) a silver halide complexing agent; and (c) a non-hydrolyzable polymeric vehicle wherein said layer or layers have a pH of up to 4.0 and a melting point lower than 200°C.

2. A dry, activator sheet as in claim 1 wherein the non-hydrolyzable polymeric vehicle is a member selected from the group consisting of poly(styrene sulfonic acid), poly-(ethylene oxide), poly(acrylamide), poly(acrylic acid), poly(vinylpyrrolidone), poly(vinyl alcohol) and active methylene containing polymers.

3. A dry, activator sheet as in claim 1 wherein said layer or layers also contain thiourea as said silver halide complexing agent.

4. A dry, activator sheet as in claim 1 wherein said nonvolatile, diffusible acid is selected from the group consisting of sulfuric acid, acetic acid, citric acid, para-toluenesulfonic acid, benzenesulfonic acid, phenylphos-phonic acids, phenylphosphoric acids, phenylphosphinic acids, and carboxylic acids containing up to 10 carbon atoms.

5. A dry, activator sheet as in claim 1 wherein said layer or layers also contain a non-hydrolyzable thermal solvent containing up to 10 carbon atoms.

6. A dry, activator sheet as in claim 1 wherein said layer or layers also contain a non-hydrolyzable thermal solvent selected from the group consisting of polyethylene glycol, poly(ethylene oxide), decanediol and hexanediol.

7. A dry, activator sheet as in claim 1 wherein said layer or layers also contain a silver halide complexing agent comprising from about 1.0 g/m2 to about 50 g/m2 of the mineral or organic acid, from about 1.0 g/m2 to about 50 g/m2 of the silver halide complexing agent, and from about 1.0 g/m2 to about 50 g/m2 of the non-hydrolyzable polymeric vehicle.

8. A dry, activator sheet as in claim 1 wherein an intermediate layer separates the support and the layer or layers comprising the diffusible acid, silver halide complexing agent and non-hydrolyzable polymeric vehicle.

9. A dry, activator sheet for a dry, thermal silver dye-bleach process comprising a support having thereon a layer or layers comprising (a) para-toluene sulfonic acid, (b) a poly(vinyl pyrrolidone) vehicle, (c) a thiourea silver halide complexing agent, and (d) a thermal solvent, wherein said layer or layers have a pH of up to 4.0 with a melting point lower than 200°C.

10. A silver dye-bleach process of thermally dye bleaching a photographic element comprising a silver image in reactive association with a dye that is bleached in a silver dye-bleach process comprising contacting said image with a dry, activator sheet comprising a support having thereon a layer or layers comprising (a) a nonvolatile diffusible acid selected from the group consisting of nonvolatile, diffusible mineral acids and organic acids containing up to 10 carbon atoms, said acid being nonvolatile at processing temperature of 50° to 150°C in said activator sheet;
(b) a silver halide complexing agent; and (c) a non-hydrolyzable polymeric vehicle wherein said layer or layers have a pH of up to 4.0 and a melting point lower than 200°C and heating to a temperature from about 50°C to about 150°C to laminate the sheet to the element and produce a dye image.

11. The process of claim 10 wherein the activator sheet also contains a non-hydrolyzable thermal solvent containing up to 10 carbon atoms.

12. The process of claim 10 wherein said dye is an azo dye.

13. The process of claim 10 wherein the non-hydrolyzable polymeric vehicle is selected from the group consisting of poly(styrene sulfonic acid), poly(acrylamide), poly(acrylic acid), poly(vinyl alcohol), poly(ethylene oxide), poly(vinylpyrrolidone) and active methylene containing polymers.

14. The process of claim 10 wherein the silver halide complexing agent is thiourea.

15. The process of claim 10 wherein the nonvolatile diffusible mineral or organic acid is selected from the group consisting of phenylphosphoric acid, phenylphosphonic acid, phenylphosphinic acid, sulfuric acid, acetic acid, citric acid, para-toluenesulfonic acid, benzenesulfonic acid, and carboxylic acids containing up to 10 carbon atoms.

16. The process of claim 10 wherein the activator sheet also contains a thermal solvent which is selected from the group consisting of polyethylene glycol, poly(ethylene oxide) decanediol and hexanediol.

17. The process of claim 10 wherein the activator sheet comprises from about 1.0 g/m2 to about 50 g/m2 of a mineral or organic acid, from about 1.0 g/m2 to about 50 g/m2 of a silver halide complexing agent, and from about 1.0 g/m2 to about 50 g/m of a non-hydrolyzable polymeric vehicle.

18. A silver dye-bleach process of thermally dye bleaching a photographic element comprising a silver image in reactive association with a dye that is bleached in a silver dye-bleach process and a silver halide complexing agent comprising contacting said image with a dry, activator sheet, said activator sheet comprising a support having coated thereon a layer or layers comprising (a) a nonvolatile, diffusible acid selected from the group consisting of nonvolatile, diffusible mineral acids and organic acids containing up to 10 carbon atoms, said acid being nonvolatile at processing temperature of 50° to 150°C in said activator sheet; and (b) a non-hydrolyzable polymeric vehicle wherein said layer or layers having a pH up to 4.0 and a melting point lower than 200°C and heating to a temperature from about 50°C to about 150°C to laminate the sheet to the element and produce a dye image.

19. The process of claim 18 wherein the silver halide complexing agent is an isothiuronium salt.

20. A photographic element comprising a support having thereon a first layer containing a silver metal image in reactive association with a dye that is bleached in a silver dye-bleach process and laminated to said first layer a transparent second layer comprising:
(a) a nonvolatile, diffusible acid selected from the group consisting of mineral acids and organic acids containing up to 10 carbon atoms, said acid being nonvolatile at processing temperature of 50° to 150°C in said activator sheet;
(b) a silver halide complexing agent, and (c) a non-hydrolyzable polymeric vehicle wherein said second layer has a pH up to 4.0 and a melting point lower than 200°C.

21. The photographic element of claim 20 wherein the second layer also comprises a non-hydrolyzable thermal solvent.

22. The photographic element of claim 20 wherein the non-hydrolyzable polymeric vehicle is a member selected from a group consisting of poly(styrene sulfonic acid), poly-(acrylamide), poly(acrylic acid), poly(ethylene oxide), poly(vinyl alcohol), poly(vinylpyrrolidone) and active methylene containing polymers.

23. The photographic element of claim 20 wherein the silver halide complexing agent is thiourea.

24. The photographic element of claim 20 wherein the mineral or organic acid is selected from the group consisting of phenylphosphoric acid, phenylphosphonic acid, phenyl-phosphinic acid, sulfuric acid, acetic acid, para-toluenesulfonic acid, benzenesulfonic acid, and carboxylic acids containing 10 carbon atoms or less.

25. The photographic element of claim 20 also comprising a non-hydrolyzable thermal solvent selected from the group consisting of polyethylene glycol, poly(ethylene oxide), decanediol, and hexanediol.

26. The photographic element of claim 20 wherein said second layer comprises from about 1.0 g/m2 to about 50 g/m2 of a mineral or organic acid, from about 1.0 g/m2 to about 50 g/m of silver halide complexing agent, and from about 1.0 g/m2 to about 50 g/m2 of a non-hydrolyzable polymeric vehicle.

27. A photographic element comprising a support having thereon a first layer containing a silver metal image in reactive association with a dye that is bleached in a silver dye-bleach process and laminated to said first layer a second layer comprising (a) para-toluenesulfonic acid, (b) a poly(vinyl pyrrolidone) vehicle, (c) a thiourea silver halide complexing agent, and (d) a thermal solvent, wherein said second layer has a pH of up to 4.0 with a melting point lower than 200°C.

28. A photographic element comprising a support having thereon a first layer containing a silver metal image in reactive association with a dye that is bleached in a silver dye-bleach process and silver halide complexing agent and laminated to said first layer a transparent second layer comprising (a) a nonvolatile, diffusible acid selected from the group consisting of nonvolatile, diffusible mineral acids and organic acids containing up to 10 carbon atoms, said acid being nonvolatile at processing temperature of 50° to 150°C in said activator sheet, and (b) a non-hydrolyzable polymeric vehicle wherein said second layer has a pH of up to 4.0 and a melting point lower than 200°C.

29. A photographic element of claim 28 wherein the second layer also comprises a non-hydrolyzable thermal solvent.

30. The photographic element of claim 28 wherein the silver halide complexing agent of the first layer is an isothiouronium salt.

31. A photothermographic element comprising a support having thereon, in reactive association, an image-forming combination comprising (i) an organic silver salt oxidizing agent, with (ii) a reducing agent for the organic silver salt oxidizing agent, (iii) a photosensitive silver halide and (iv) a dye that is bleached in a silver dye-bleach process, having thereon an activator sheet comprising a support having thereon a layer or layers comprising (a) a nonvolatile, diffusible acid selected from the group consisting of nonvolatile, diffusible mineral acids and organic acids containing up to 10 carbon atoms, said acid being nonvolatile at processing temperature of 50° to 150°C in said activator sheet; and (b) a non-hydrolyzable polymeric vehicle wherein said layer or layers have a pH of up to 4.0 and a melting point of lower than 200°C.

32. A photothermographic element comprising a support having thereon a first layer comprising a sulfonamido-phenol reducing agent, a silver behenate oxidizing agent, photosensitive silver halide, a polymeric binder, an azo dye that is bleached in a silver dye-bleach process, having thereon an activator sheet comprising a support having thereon a second layer comprising (a) para-toluenesulfonic acid, (b) a poly(vinyl pyrrolidone) vehicle, (c) a thiourea silver halide complexing agent, and (d) a thermal solvent, wherein said second layer has a pH of up to 4.0 with a melting point lower than 200°C.

33. A silver dye-bleach process of thermally dye bleaching a photographic element comprising a silver image in reactive association with a dye that is bleached in a silver dye-bleach process comprising contacting said image with a dry, activator sheet comprising a support having thereon a layer or layers comprising (a) a nonvolatile, diffusible acid selected from the group of nonvolatile, diffusible acids consisting of sulfuric acid, acetic acid, citric acid, para-toluenesulfonic acid, benzenesulfonic acid, phenylphosphonic acid, phenylphosphoric acid, phenylphosphinic acid and carboxylic acids containing up to 10 carbon atoms, said acid being nonvolatile at processing temperature of 50° to 150°C in said activator sheet, (b) a silver halide complexing agent, and (c) a non-hydrolyzable polymeric vehicle selected from the group consisting of poly(styrene sulfonic acid), poly(ethylene oxide), poly(acrylamide), poly(acrylic acid), poly(vinyl pyrrolidone), poly(vinyl alcohol) and active methylene non-hydrolyzable polymeric vehicles, wherein said layer or layers have a pH up to 4.0 with a melting point lower than 200°C and heating to a temperature from about 50°C to about 150°C to laminate the sheet to the element and produce a dye image.

34. A silver dye-bleach process of thermally dye-bleaching a photothermographic element comprising a silver image in reactive association with bleachable azo dye comprising contacting said image with a dry, activator sheet comprising a support having thereon a layer (A) comprising (a) para-toluenesulfonic acid, (b) a poly(vinyl pyrrolidone) vehicle, (c) a thiourea silver halide complexing agent, and (d) a thermal solvent, wherein said layer (A) has a pH up to 4.0 with a melting point lower than 200°C and heating to a temperature from about 50°C to about 150°C to laminate the sheet to the photothermo-graphic element and produce a dye image.

35. A silver dye-bleach process of thermally dye bleaching a photographic element comprising a silver image in reactive association with a dye that is capable of being bleached in a silver dye-bleach process and a silver halide complexing agent comprising contacting said image with a dry, activator sheet comprising a support having coated thereon a layer or layers comprising (a) a nonvolatile, diffusible acid selected from the group consisting of nonvolatile, diffusible acids consisting of sulfuric acid, acetic acid, citric acid, para-toluenesulfonic acid, phenylphosphonic acid, phenylphosphoric acid, phenylphosphinic acid and carboxylic acids containing up to 10 carbon atoms, said acid being nonvolatile at processing temperature of 50° to 150°C in said activator sheet and (b) a non-hydrolyzable polymeric vehicle selected from the group consisting of poly(styrene sulfonic acid), poly(ethylene oxide), poly(acrylamide), poly(acrylic acid), poly(vinyl pyrrolidone), poly(vinyl alcohol) and active methylene non-hydrolyzable polymeric vehicles, wherein said layer or layers have a pH up to 4.0 with a melting point lower than 200°C and heating to a temperature from about 50°C to about 200°C to laminate the sheet to the element and produce a dye image.

36. A photothermographic element comprising a support having thereon, in reactive association, in a binder an image-forming combination comprising (i) an organic silver salt oxidizing agent with (ii) a reducing agent for the organic silver salt oxidizing agent, (iii) photosensitive silver halide and (iv) a dye that is bleached in a silver dye-bleach process, having thereon an activator sheet comprising a support having thereon a layer or layers comprising (a) a nonvolatile, diffusible acid selected from the group of nonvolatile, diffusible acids consisting of sulfuric acid, acetic acid, citric acid, para-toluenesulfonic acid, benzenesulfonic acid, phenylphosphonic acid, phenylphosphoric acid, phenylphosphinic acid and carboxylic acids containing up to 10 carbon atoms, said acid being nonvolatile at processing temperature of 50° to 150°C in said activator sheet and (b) a non-hydrolyzable polymeric vehicle selected from the group consisting of poly(styrene sulfonic acid), poly(ethylene oxide), poly(acrylamide), poly(acrylic acid), poly(vinyl pyrrolidone), poly(vinyl alcohol) and active methylene non-hydrolyzable polymeric vehicles, wherein said layer or layers have a pH up to 4.0 with a melting point of lower than 200°C.

37. A photothermographic element comprising a support having thereon a first layer comprising a silver halide developing agent, photosensitive silver halide, a polymeric binder, a thermosensitive base-release agent and a dye that is bleached in-a silver dye-bleach process, having thereon an activator sheet comprising a support having thereon a layer (A) comprising (a) para-toluenesulfonic acid, (b) a poly(vinyl pyrrolidone) vehicle, (c) a thiourea silver halide complexing agent, and (d) a thermal solvent, wherein said layer (A) has a pH up to 4.0 with a melting point lower than 200°C.