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(11) | EP 0 536 955 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Photothermographic article for preparing multicolor images |
| (57) This invention relates to heat-developable photographic materials, i.e., photothermographic
materials. It has been described in the patent literature to transfer a dye image
formed in a photothermographic system by means of a transfer solvent. It would be desirable to provide a photothermographic material capable of producing multiple color images, wherein image development, including dye transfer, can be carried out without the use of liquids. This invention provides a photothermographic article comprising (a) an image-receiving element comprising a polymeric image-receiving layer, (b) strippably adhered to said image-receiving element, an imageable photothermographic element comprising a plurality of emulsion layers, each of which emulsion layers comprises a binder, a silver source material, photosensitive silver halide in catalytic proximity to the silver source material, and a leuco dye, and (c) interposed between each pair of said emulsion layers, a dye-permeable interlayer. The dyes formed in each emulsion layer, i.e., magenta dye in the green sensitive layer, yellow dye in the blue sensitive layer, and cyan dye in the red sensitive layer, migrate through the interlayers and the emulsion layers to the image-receiving layer as the photothermographic article is heated for development. Dye formation and dye transfer can be carried out without the aid of any transfer solvent or wet chemicals. After development by heat, the imageable photothermographic element, which is strippably adhered to the image-receiving layer, can be peeled away from the image-receiving layer and discarded. |
1. Field of the Invention
[0001] This invention relates to heat-developable photographic materials, i.e., photothermographic materials, and in particular, to a photothermographic article capable of providing a multicolored image by thermal diffusion of dyes.
2. Discussion of the Art
[0002] Photothermographic imaging materials that are classified as "dry silver" compositions or emulsions comprise a light insensitive, reducible silver source, a light sensitive material which generates silver when irradiated, and a reducing agent for the reducible silver source. The light sensitive material is generally photographic silver halide, which must be in catalytic proximity to the light insensitive, reducible silver source. Catalytic proximity requires an intimate physical association of these two materials so that when silver specks or nuclei are generated by the irradiation or light exposure of the photographic silver halide, those nuclei are able to catalyze the reduction of the reducible silver source by the reducing agent. It has been long understood that silver halide is a catalyst for the reduction of silver ions and the silver-generating light sensitive silver halide catalyst progenitor may be placed into catalytic proximity with the silver source in a number of different fashions, such as partial metathesis of the reducible silver source with a halogen-containing source (e.g., U.S. Patent No. 3,457,075), coprecipitation of silver halide and reducible silver source material (e.g., U.S. Patent No. 3,839,049), and other methods that intimately associate the silver halide and the silver source.
[0003] The reducible silver source is a material that contains silver ions. The preferred reducible silver source includes silver salts of long chain aliphatic carboxylic acids, usually having from 10 to 30 carbon atoms. The silver salt of behenic acid or mixtures of acids of similar 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.
[0004] In both photographic and photothermographic emulsions, exposure of the photographic silver halide to light produces small clusters of silver atoms. The imagewise distribution of these clusters is known in the art as a latent image, as 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 are in catalytic proximity to the silver halide grains bearing the latent image.
[0005] As the visible image is produced entirely by silver, one cannot readily decrease the amount of silver in the emulsion without reducing the available maximum image density. Reduction of the amount of silver is desirable in order to reduce the cost of raw materials used in the emulsion.
[0006] One conventional way of attempting to increase the image density of photographic and photothermographic emulsions without increasing or while decreasing the amount of silver in the emulsion layer is by the inclusion of dye forming materials into the emulsion. In this way a dye enhanced silver image can be produced.
[0007] It has been described in the patent literature to transfer a dye image formed in a photothermographic system by means of a transfer solvent. See, for example, U.S. Patent Nos. 3,985,565; 4,021,240; 4,022,617.
[0008] Japanese Patent Application No. 59-5239 discloses a photothermographic contact diffusion system wherein a chemical reaction occurs in an image receiving layer between a diffused leuco dye and an acidic color developing agent.
[0009] Heat developable photographic materials for providing dye images by the reaction of color couplers with the oxidants of an organic reducing agent have been described in U.S. Patent Nos. 3,531,286; 3,761,270; and 3,764,328. These materials suffer from the problem that the optical density of the background is increased on account of the presence of unreduced silver. Poor print stability is also a problem.
[0010] Dye formation by an oxidation-reduction reaction between a reducible silver source and a leuco dye to form a visible dye is disclosed in U.S. Patent Nos. 3,985,565; 4,022,617; and 4,460,681. However, in these processes, the materials provide turbid and hazy color images on account of the presence of the reduced silver image after heat development. Moreover, the image tends to suffer from background stain upon aging due to residual chemicals in the material.
[0011] The silver images can be removed by liquid processing and the dyes can be transferred to an image-receiving layer with the aid of a transfer solvent such as alcohol. Another process employing a heat developable photographic material to produce dye images by the oxidation-reduction reaction between an organic silver salt oxidizing agent and a dye releasing compound that releases a mobile dye when the material is heated is disclosed in Japanese Patent Application Nos. 58-58543; 58-79247; 58-149046; 58-149047; etc. This process requires that the dyes be transferred to an image-receiving sheet with the aid of a transfer solvent such as water.
[0012] U.S. Patent No. 4,594,307 discloses a heat developable photographic material that produces a pure and stable dye image by the oxidation-reduction reaction between a reducible organic silver salt and a leuco dye reducing agent wherein the dye formed is transferred to an image-receiving layer by continuing the heating for development in order to separate the dye formed from the silver images and other residual chemicals. However, this material is not capable of producing a multiple color or full color image on the same substrate.
[0013] It would be desirable to provide a photothermographic material capable of producing multiple color images, wherein image development, including dye transfer, can be carried out without the use of liquids.
Summary of the Invention
[0014] This invention provides a photothermographic article comprising:
(a) an image-receiving element comprising a polymeric image-receiving layer; and
(b) strippably adhered to said image-receiving element, an imageable photothermographic element comprising a plurality of emulsion layers, each of which emulsion layers comprises a binder, a silver source material, photosensitive silver halide in catalytic proximity to the silver source material, and a leuco dye, and interposed between each pair of said emulsion layers, a dye-permeable interlayer.
[0015] A given dye-permeable interlayer must preserve the integrity of the immediate previously coated emulsion layer during the application of the immediate subsequently coated emulsion layer. Each interlayer must be insoluble in or impermeable to solvents used to coat the subsequently applied overlying adjacent emulsion layer. Otherwise the solvents of the subsequently applied, overlying emulsion layer would dissolve or swell the previously coated interlayer and cause mixing of the emulsion layers, which would result in poor color selectivity, which is commonly referred to as "crosstalk".
[0016] The interlayers and the emulsion layers must be permeable to thermally diffusible dyes so that the dyes formed in each emulsion layer can migrate through the interlayers and the emulsion layers to the image-receiving layer. In other words, each interlayer must act as a barrier layer between the emulsion layers during the application of subsequently coated overlying emulsion layers, yet allow diffusion of the dyes formed during heat development at the elevated temperatures.
[0017] Homopolymers and copolymers of vinyl chloride and blends containing homopolymers or copolymers of vinyl chloride are preferably used as interlayers for the multilayer photothermographic element of the present invention.
[0018] Preferably, dye-permeable polymers that are impermeable to alcohols are employed as the first interlayer and polymers that are soluble in ether alcohols, but impermeable to lower alcohols, are employed as the second interlayer. The emulsion layer overlying the first interlayer is preferably coated from either a lower alcohol or a lower ether alcohol and the emulsion layer overlying the second interlayer is preferably coated from lower alcohols. The most preferred binder for the latter emulsion layer is poly(vinyl butyral), which is soluble in lower alcohols, e.g., methanol, ethanol.
[0019] When the heat developable photographic material of this invention is imagewise exposed to light and developed by heat, an oxidation-reduction reaction occurs between the reducible silver source and the leuco dye in each emulsion layer.
[0020] The dyes formed in each emulsion layer, i.e., magenta dye in the green sensitive layer, yellow dye in the blue sensitive layer, and cyan dye in the red sensitive layer, migrate through the interlayers and the emulsion layers to the image-receiving layer as the photothermographic article is heated for development.
[0021] Dye formation and dye transfer can be carried out without the aid of any transfer solvent or wet chemicals. After development by heat, the imageable photothermographic element, which is strippably adhered to the image-receiving layer, can be peeled away from the image-receiving layer and discarded.
Brief Description of the Drawing
[0022] FIG. 1 is a schematic illustration of an end view of one embodiment of the article of this invention.
Detailed Description
[0023] As used herein, the term "emulsion layer" means the layer of the article of this invention that contains the light-sensitive silver salt and silver source material. The terms "dye-forming layer" and "photothermographic layer" are synonymous with the term "emulsion layer". The term "lower alcohol" means an aliphatic alcohol having from one to six carbon atoms.
[0024] Referring now to FIG. 1, a preferred embodiment, a heat developable photothermographic article 10 comprises an image-receiving layer 12 and overlying image-receiving layer 12, a first emulsion layer 14. Overlying first emulsion layer 14 is a first interlayer 16. Overlying first interlayer 16 is a second emulsion layer 18. Overlying second emulsion layer 18 is a second interlayer 20. Overlying second interlayer 20 is a third emulsion layer 22. Overlying third emulsion layer 22 is a protective coat 24. Beneath image-receiving layer 12 is a substrate 26.
[0025] The image-receiving layer can be made from any flexible or rigid, transparent (optically clear) thermoplastic resin. The thickness should preferably be at least 0.1 micrometer, preferably from about 1 to about 10 micrometers, and preferably having a glass transition temperature in the range of 20° to 200°C so that it can withstand the conditions expected in photothermographic processing. Any thermoplastic resin or combination of thermoplastic resins capable of absorbing and fixing the dyes can be used. The resin acts as a dye mordant. No additional fixing agents are required, although they can be used, if desired. Preferably, the polymeric resin in the image-receiving layer is impermeable to the solvent used for coating the first emulsion layer and incompatible with the material of the polymeric binder used for the first emulsion layer. Incompatible polymers will adhere poorly to each other and will provide good strippability of the emulsion layers from the image-receiving layer. Preferred thermoplastic resins that can be used to prepare the image-receiving layer include polyesters such as polyethylene terephthalate, cellulosics such as cellulose acetate, cellulose butyrate, cellulose propionate, polystyrene, poly(vinyl chloride), poly(vinyl acetate), copolymers of vinyl chloride and vinyl acetate, copolymers of vinylidene chloride and acrylonitrile, and copolymers of styrene and acrylonitrile.
[0026] The image-receiving layer can be applied to a support base or substrate by various coating methods known in the art, such as curtain coating, extrusion coating, dip coating, air-knife coating, hopper coating, or any other coating method used for solution coating. After coating, the image-receiving layer is dried (e.g., in an oven) to remove the solvent. Commonly used solvents include methyl ethyl ketone, acetone, and tetrahydrofuran.
[0027] The leuco dye can be any colorless or lightly colored compound that can be oxidized to a colored form, when heated, preferably to a temperature of from about 80°C to about 250°C (176° to 482°F) for a time period of from about 0.5 to about 300 seconds and can diffuse through emulsion layers and interlayers into the image-receiving layer of the article of the invention. Any leuco dye capable of being oxidized by silver ion to form a visible image can be used in the present invention. Compounds that are both pH sensitive and oxidizable to a colored state are useful but not preferred, while compounds sensitive only to changes in pH are not included within the term "leuco dyes" because they are not oxidizable to a colored form. Representative classes of leuco dyes suitable for use in the present invention include, but are not limited to, biphenol leuco dyes, phenolic leuco dyes, indoaniline leuco dyes, acrylated azine leuco dyes, phenoxazine leuco dyes, phenodiazine leuco dyes, and phenothiazine leuco dyes. Also useful are leuco dyes such as those disclosed in U.S. Patent Nos. 3,445,234; 4,021,250; 4,022,617; and 4,368,247; Japanese Patent Application No. 57-500352. Preferred dyes are described in U.S. Patent No. 4,460,681, incorporated herein by reference. The density of the dye image and even the color of the dye image in the image-receiving layer is very much dependent on the resin of the image-receiving layer, which acts as a dye mordant and as such is capable of absorbing and fixing the dyes. A dye image having a reflection optical density in the range of from 0.3 to 3.5 (preferably from 1.5 to 3.5) or a transmission optical density in the range of from 0.2 to 2.5 (preferably from 1.0 to 2.5) can be obtained with the present invention. The leuco dye can be present in an emulsion layer in the range of from about 1 to about 20% by weight, preferably from about 3 to about 15% by weight.
[0028] The reducible silver source material, as mentioned previously, can be any material that contains a reducible source of silver ions. Silver salts of organic aliphatic acids, particularly long chain aliphatic carboxylic acids (e.g., having from 10 to 30, preferably from 15 to 28, carbon atoms) 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 7 to about 70% by weight of each emulsion layer.
[0029] The silver halide can be any photosensitive silver halide, such as silver bromide, silver iodide, silver chloride, silver bromoiodide, silver chlorobromoiodide, silver chlorobromide, etc., and can be added to the emulsion layer in any manner so as to place it in catalytic proximity to the silver source. The silver halide is generally present at a concentration of from about 0.01 to about 15% by weight of the emulsion layer, although higher concentrations, e.g., up to 20 to 25% by weight, are useful. It is preferred to use from about 0.1 to about 10% by weight silver halide in the emulsion layer and more preferred to use from about 0.1 to about 2.0% by weight. The silver halide used in this invention can be chemically and spectrally sensitized in a manner similar to conventional wet process silver halide or state-of-the-art photothermographic materials.
[0030] A reducing agent for silver ion besides the leuco dye is not essential to the emulsion layer, but can be added into any emulsion layer as an accelerator of the development rate, if necessary. When present, the preferred reducing agent (developer) for silver ion in this invention is a biphenol derivative or a triarylimidazole that will reduce silver ion to metallic silver and produce a colored quinone. Conventional photographic developers such as phenidone, hydroquinones, and catechol are useful in minor amounts, and hindered phenol reducing agents can also be added. The reducing agent is preferably present in a concentration of from about 0.1 to about 10% by weight of the emulsion layer.
[0031] To modify the development rate or the color of the image itself, development modifiers, present at a concentration in a range of from about 0.01 to about 10% by weight of the emulsion layer can be used. Representative development modifiers include aromatic carboxylic acids and their anhydrides such as phthalic acid, 1,2,4-benzenetricarboxylic acid,
2,3-naphthalenedicarboxylic acid, tetrachlorophthalic acid, 4-methylphthalic acid, homophthalic acid, 4-nitrophthalic acid, phenylacetic acid, naphthoic acid, naphthalic acid, phthalic anhydride, naphthalic anhydride, tetrachlorophthalic anhydride, and the like.
[0032] Toners such as phthalazinone and both phthalazine and phthalic acid, or derivatives thereof and others known in the art, are not essential to the emulsion layer but can be used if desired. These materials can be present, for example, in concentrations ranging from about 0.01 to about 10% by weight of the emulsion layer.
[0033] The binder for the emulsion layer can be selected from well-known natural and synthetic resins such as gelatin, poly(vinyl acetals), poly(vinyl chloride), poly(vinyl acetate), cellulose acetate, ethyl cellulose, polyolefins, polyesters, polystyrene, polyacrylonitrile, polycarbonates, methacrylate copolymers, maleic anhydride ester copolymers, copolymers of butadiene and styrene, and the like. Copolymers, terpolymers, and blends of polymers that include the above-mentioned resins are also included in these definitions. The preferred binder for the emulsion layers is poly(vinyl butyral). The binders are generally used in a concentration ranging from about 10 to about 75% by weight of each layer, and preferably from about 30 to about 55% by weight.
[0034] The emulsion layer adjacent to the image-receiving layer can also include additives to improve the strippability of the photothermographic element, e.g., fluoroaliphatic polyesters dissolved in ethyl acetate ("FLUORAD" FC 431, Minnesota Mining and Manufacturing Company, St. Paul, Minnesota). These additives can be added in a concentration in the range of from about 0.02 to about 0.5% by weight of the emulsion layer, preferably from about 0.1 to about 0.3% by weight. Alternatively, an additive to enhance strippability can be added to the image-receiving layer in the same concentration range. No solvents need to be used in the stripping process. The layer of the strippable portion of the photothermographic element in contact with the image-receiving layer typically has a delaminating resistance of 1 to 50 g/cm (based on 180° peel) and a cohesive strength greater than, preferably at least two times greater than, its delaminating resistance.
[0035] Polymers that exhibit permeability to dyes at elevated development temperatures and solubility in some solvents, but impermeability to dyes at ambient temperatures and insolubility in other solvents, can be utilized to form the interlayers in the element of the present invention.
[0036] The selection of the interlayers and solvents for coating them when a three-color system is coated on the same major surface of an image-receiving layer will be explained below. The solvents for applying the first emulsion layer should preferably not dissolve the image-receiving layer, as this would inhibit strippability of the emulsion layer from the image-receiving layer. The first emulsion layer preferably contains stripping agents for enhancement of strippability. The image-receiving polymers described in U.S. Patent No. 4,594,307 are soluble in tetrahydrofuran or a ketone, e.g., acetone, methyl ethyl ketone. Therefore, these solvents are not preferred for the coating solution of the first emulsion layer. Alcohols and toluene are preferred for the application of the first emulsion layer by coating from a solution.
[0037] The first interlayer must be impermeable to solvents to be used for applying the subsequent coating; however, the polymer for forming the first interlayer can be applied from any organic solvent. The polymer of the first interlayer is preferably a thermoplastic polymer. Homopolymers of vinyl chloride or copolymers of vinyl chloride, preferably having a glass transition temperature greater than 80°C, for example, a copolymer of vinyl chloride (96%) and vinyl acetate (4%), a blend of poly(vinyl chloride) (90%) and poly(vinyl acetate) (10%), can be used to form the first interlayer. These polymers are impermeable to lower alcohols, such as methanol, ethanol, propanol, isopropyl alcohol, butyl alcohol, and ether alcohols, such as methoxypropanol, ethoxypropanol, etc.
[0038] The second emulsion layer is coated onto the first interlayer. Both the second emulsion layer and subsequent emulsion layers, if used, contain the same classes of ingredients as does the first emulsion layer; the specific identity of these ingredients can vary.
[0039] Dye-permeable polymers that are soluble in some of the above-mentioned solvents, e.g., ether alcohol, but still impermeable to other of these solvents, e.g., lower alcohol, can be used as the second interlayer. The polymer for the second interlayer is preferably a thermoplastic polymer. For example, copolymers of vinyl chloride, particularly terpolymers containing hydroxyl groups, such as a terpolymer of vinyl chloride, vinyl acetate, and hydroxyalkyl acrylate, preferably having 1 to 6 carbon atoms in the alkyl portion thereof, or a terpolymer of vinyl chloride, vinyl acetate, and maleic acid, are soluble in ether alcohols, such as methoxypropanol, ethoxypropanol, etc., but are impermeable to lower alcohols, such as methanol, ethanol, propanol, etc., and can be utilized as the second interlayer.
[0040] The third emulsion layer is coated onto the second interlayer. The solvent used for coating this emulsion layer can be an alcohol that will not permeate the second interlayer, for example, a lower alcohol, such as methanol, ethanol, propanol, etc.
[0041] Polymers that are soluble in alcohol can be used to prepare the protective topcoat layer and the binder for the emulsion layers, particularly the binder for the second and third emulsion layers. Poly(vinyl butyrals) in which the poly(vinyl alcohol) content is greater than 9% by weight are soluble in methanol or ethanol and are the most preferable binders for the emulsion layers. Alcohol-soluble polymers having melting points greater than 180°C, for example, cellulose acetate propionate, copolymers of styrene and maleic anhydride, etc., can be used as the material for the protective topcoat. The interlayers and the protective topcoat may contain additives such as development modifiers, accelerators, etc.
[0042] The following table sets forth the solvents that are preferred for coating each layer of the photothermographic element of this invention.
| Layer | Solvent |
| First emulsion | Alcohols, toluene, other aromatic solvents |
| First interlayer | Any solvent |
| Second emulsion | Lower alcohols or ether alcohols |
| Second interlayer | Ether alcohols |
| Third emulsion | Lower alcohols |
| Topcoat | Lower alcohols |
[0043] Optional support bases or substrates of the photothermographic article of this invention can be any supporting material, such as paper, polymeric film, glass, or metal. Transparent or opaque polymeric films are particularly useful. Preferably, the support comprises a thermoplastic resin, e.g., polyesters such as polyethylene or poly(ethylene terephthalate); cellulosics such as cellulose acetate, cellulose butyrate, cellulose acetate butyrate, cellulose propionate; polyolefins such as polystyrene; polyvinyl resins such as poly(vinyl chloride) and poly(vinyl acetate); copolymerics of vinyl resins, such as copolymers of vinyl chloride and vinyl acetate, copolymers of vinylidene chloride and acrylonitrile, and copolymers of styrene and acrylonitrile. It is also desirable to employ a support that can also function as an image-receiving layer. Combinations of resins (binders) are also useful. It is preferred that the image-receiving layer and optional support base be flexible to allow for stripping.
[0044] The photothermographic article of this invention preferably employs a three-color system of yellow, magenta, and cyan. Dyes of these colors are formed by the heat-induced oxidation-reduction reaction between a reducible silver source and a chromogenic leuco dye reducing agent for the silver ion by means of light-exposed silver halide. Various constructions for producing full-color images are possible with the photothermographic article of the present invention. For example, a two-color system can be coated on one side and a third color can be coated on the other side of a transparent or translucent substrate. In this case, one interlayer is needed to separate two dye-forming emulsion layers.
[0045] However, a three-color system coated on the same surface of a substrate is preferable in most applications. In this case, two interlayers are needed to separate three dye-forming emulsion layers.
[0046] While not required, it is often desirable to modify the emulsion layer and/or the interlayers with additional ingredients, such as, for example, antihalation dyes, accutance dyes, coating aids, stabilizers, surfactants.
[0047] The photothermographic articles of the present invention can be used to form colored images by first exposing the article to actinic radiation to provide latent silver images, then developing the exposed article by heating the exposed article to form diffusible dyes in the emulsion layers, which dyes transfer by diffusion to the image-receiving layer, and then stripping at least one of the emulsion layers, and preferably two, three or more of the emulsion layers, away from the image-receiving layer. The developing and transfer step is preferably conducted at a temperature of from about 60°C to 160°C, preferably from about 80°C to about 140°C, for a time period of from about 1 second to about 60 seconds.
[0048] In another method of forming colored images by means of the photothermographic article of the present invention, the image-receiving element and the imageable photothermographic element are provided separately. The image-receiving element is preferably in contact with a first support. The photothermographic element is preferably in contact with a second support. The first and second supports are typically selected from paper, thermoplastic polymer, glass, or metal. The photothermographic element is first exposed to actinic radiation to provide latent silver images. Then the exposed photothermographic element is placed in face-to-face contact with the image-receiving layer of the image-receiving element to form a photothermographic article in which the photothermographic element is strippably adhered to the image-receiving element. The composite is then heated to develop the exposed article. During the development step, diffusible dyes that are formed in the emulsion layers are transferred by diffusion to the image-receiving layer to form a colored image on the image receiving layer. Then, at least one, and preferably two or more of the emulsion layers, can be stripped away from the image-receiving layer. Development and transfer conditions can be the same as those set forth previously.
[0049] The following non-limiting examples will further illustrate the invention of this application. In these examples, all percentages are by weight unless indicated otherwise.
Example 1
[0050] This example describes a photothermographic article having two photothermographic emulsion layers on one major surface of the image-receiving layer.
[0051] A 15% solution of a copolymer of vinyl chloride (90%) and vinyl acetate (10%) in methyl ethyl ketone was coated at a wet thickness of 0.08 mm onto an opaque polyester film and dried in an oven at a temperature of 80°C for five minutes to form an image-receiving layer.
[0052] A dispersion of silver behenate half soap (1 mole of silver behenate to 1 mole of behenic acid, 10% solids) in toluene was made by a homogenization process. A portion of the 10% half soap dispersion (110 g) was diluted with ethyl alcohol (380 g). Then poly(vinyl butyral) (0.4 g) was added to the dilute dispersion and dissolved.
[0053] Mercurous bromide (10 cc of a solution containing 1.8 g HgBr in 100 cc of methyl alcohol) was added to the dispersion with stirring. Additional poly(vinyl butyral) (26 g) having a poly(vinyl alcohol) content in the range of 17-21%, was added to the dispersion. This dispersion will hereinafter be referred to as Dispersion A. Benzoyl leuco bis-trifluoroethyl dimethyl diazine (0.20 g), a green sensitizing dye (2 cc of a solution containing 0.01 g of dye in 100 cc methyl alcohol), and 3 drops of a fluorocarbon coating additive were added to 25 g of Dispersion A and the resulting dispersion mixed. The resulting mixed dispersion was coated over the image-receiving layer at a wet thickness of 0.08 mm and dried in an oven at a temperature of 78°C for five minutes to form a magenta emulsion layer.
[0055] A 10% solution of a terpolymer of vinyl chloride (83%), vinyl acetate (16%), and maleic acid (1%) in a solvent mixture of acetone (50%) and toluene (50%) was prepared. 4-Methylphthalic acid (0.1 g) was added to 25 g of the solution and the resulting solution mixed thoroughly. The solution was coated onto the previously coated magenta emulsion layer at a wet thickness of 0.05 mm (2 mils) to form an interlayer. The interlayer was dried in an oven at a temperature of 78°C for five minutes.
[0056] A cyan emulsion layer was prepared in a manner similar to that used to prepare the magenta emulsion layer described previously, except that the leuco dye and the sensitizing dye were changed. 3,6-Bis(diethylamino)-9-benzoylphenoxazine (0.30 g), which had been pre-dissolved in 3 cc of toluene, and a red sensitizing dye (1 cc of a solution containing 0.005 g of dye in 200 cc of methyl alcohol) were added to 25 g of Dispersion A and the resulting dispersion mixed. The resulting mixed dispersion was coated over the interlayer at a wet thickness of 0.10 mm and dried in an oven at a temperature of 80°C for five minutes to form a cyan emulsion layer.
[0057] A 10% solution of cellulose acetate butyrate (hydroxyl content of 4.8%) in ethyl alcohol was prepared. 4-Methylphthalic acid (0.1 g) was added to 25 g of the solution and the resulting solution mixed thoroughly. The mixed solution was coated over the cyan emulsion layer at a wet thickness of 0.8 mm (3 mils) and dried in an oven at a temperature of 80°C for five minutes to form a protective coating.
[0058] Sheets cut from the resulting article were then exposed to an EG&G sensitometer through a "WRATTEN 58" or a "WRATTEN 25" filter for 10⁻³ second to produce heat-developable latent images in the emulsion layers, and the images heat-developed at a temperature of 138°C on a heat blanket for 30 seconds. An image having a dark rust color and an image having a blue color were formed on the light exposed area of the sheets. Each image consisted of a dye and a silver image. The portion of the element containing the photothermographic emulsion layers, the interlayer, and the protective coating was then stripped away from the image-receiving layer.
[0059] Clear magenta and cyan dye images corresponding to the green and red light exposed areas of the sheet, respectively, were observed to have been transferred to the image-receiving layer. Good color separation was observed. The following sensitometric data were obtained from the sample.
| Magenta | Cyan | |
| D min | 0.17 | 0.08 |
| D max | 1.19 | 1.81 |
| Ergs/cm² at 0.6 + D min | 31 | 64 |
[0060] As used herein, "D min" means the minimum image optical density in exposed regions; "D max" means the maximum image optical density in exposed regions.
Example 2
[0061] This example describes a photothermographic article capable of providing three colors and having two photothermographic emulsion layers on one major surface of the image-receiving layer and one photothermographic emulsion layer on the other major surface of the image-receiving layer.
[0062] Formulations for the image-receiving layer, magenta emulsion layer, cyan emulsion layer, and interlayer between the magenta emulsion layer and the cyan emulsion layer, similar to those of Example 1, were coated on a transparent polyester substrate in a manner similar to that employed in Example 1, except that the coating orifice for the emulsion layers was changed. The magenta emulsion was coated over the image-receiving layer at a wet thickness of 0.10 mm and the cyan emulsion was coated over the interlayer at a wet thickness of 0.13 mm. A second image-receiving layer was also prepared on the reverse side of the transparent substrate.
[0063] A yellow emulsion layer was prepared by adding 2,6,2′,6′-tetramethylbiphenol (0.2 g), a blue sensitizing dye (1 cc of a solution containing 0.02 g of dye in 100 cc of methyl alcohol), and 3 drops of a fluorocarbon coating additive to 25 g of Dispersion A as described in Example 1 and the resulting dispersion mixed. The resulting mixed dispersion was coated over the second image-receiving layer at a wet thickness of 0.10 mm and dried in an oven at a temperature of 80°C for five minutes to form a yellow emulsion layer.
[0064] A coating solution for a topcoat was prepared by adding phthalazinone (0.2 g) to a mixture of resins (50 g) containing 25 parts by weight 25% alkyl monoester of poly(methyl vinyl ether-co-maleic acid) ("GANTREZ ES-225", GAF Corporation) in ethanol and 75 parts by weight of 10% poly(vinyl pyrrolidone) (PVP K90, GAF Corporation) in methanol. The solution was coated over the yellow emulsion layer at a wet thickness of 0.08 mm (3 mils) and dried in an oven at a temperature of 80°C for five minutes.
[0065] Sheets cut from the resulting article were then exposed to an EG&G sensitometer through a "WRATTEN 47B", a "WRATTEN 58", or a "WRATTEN 25" filter for 10⁻³ second to produce heat-developable latent images in the emulsion layers, and the images heat-developed at a temperature of 138°C on a heat blanket for 40 seconds. The portions of the element containing the emulsion layers were then stripped away from the image-receiving layers on both sides of the transparent sheet.
[0066] Clear yellow, magenta, and cyan dye images corresponding to the blue, green, and red light exposed areas of the sheet, respectively, were observed to have been transferred to the image-receiving layers. Good color separation was observed. The following sensitometric data were obtained from the sample.
| Yellow | Magenta | Cyan | |
| D min | 0.10 | 0.10 | 0.05 |
| D max | 1.30 | 1.20 | 0.90 |
| Ergs/cm² at 0.6 + D min | 150 | 200 | 400 |
Example 3
[0067] This example describes a photothermographic article capable of providing two colors and having two photothermographic emulsion layers on one major surface of the image-receiving layer.
[0068] The formulation for the image-receiving layer was applied to an opaque polyester film in the same manner as was described in Example 1. Ethyl syringketazine (0.12 g), phthalazinone (0.05 g), a green sensitizing dye (1 cc of a solution containing 0.01 g of dye in 100 cc of methyl alcohol), and 3 drops of a fluorocarbon coating additive were added to 25 g of Dispersion A as described in Example 1 and the resulting dispersion mixed. The resulting mixed dispersion was coated over the image-receiving layer at a wet thickness of 0.08 mm and dried in an oven at a temperature of 80°C for five minutes to form a magenta emulsion layer.
[0069] An 8% solution of a copolymer of vinyl chloride (86%) and vinyl acetate (14%) in a solvent mixture of methyl ethyl ketone (50%) and toluene (50%) was prepared. Phthalazinone (0.1 g) was added to 25 g of the solution and the resulting solution mixed thoroughly. The resulting solution was coated onto the previously coated magenta emulsion layer at a wet thickness of 0.05 mm (2 mils) to form an interlayer. The interlayer was dried in an oven at a temperature of 80°C for five minutes.
[0070] A dispersion of silver behenate half soap (1 mole of silver behenate to 1 mole of behenic acid, 10% solids) in toluene was made by a homogenization process. A portion of the 10% half soap dispersion (205 g) was diluted with ethyl alcohol (285 g). Then poly(vinyl butyral) (0.4 g) was added to the dilute dispersion and dissolved. Mercurous bromide (6 cc of a solution containing 1.8 g HgBr in 100 cc of methyl alcohol) was added to the dispersion with stirring and the resulting dispersion mixed for three hours. Zinc bromide (8 cc of a solution containing 2.25 g ZnBr₂ in 100 cc of methyl alcohol) was then added to the dispersion with stirring and the resulting dispersion was mixed for an hour. Additional poly(vinyl butyral) (26 g) was added to the dispersion and dissolved. This dispersion will hereinafter be referred to as Dispersion B. 2-(3,5-Di -tert-butyl-4-hydroxyphenyl)-4-phenyl-5-(3-nitro-4-ethoxyphenyl)imidazole (0.3 g), phthalazinone (0.25 g), and a blue sensitizing dye (1 cc of a solution containing 0.02 g of dye in 100 cc of methyl alcohol) were added to 25 g of Dispersion B and the resulting dispersion mixed. The resulting mixed dispersion was coated over the interlayer at a wet thickness of 0.10 mm and dried in an oven at a temperature of 80°C for five minutes to form a yellow emulsion layer.
[0071] Sheets cut from the resulting article were then exposed to an EG&G sensitometer through a "WRATTEN 47B" or a "WRATTEN 58" filter for 10⁻³ second to produce heat-developable latent images in the emulsion layers, and the images heat-developed at a temperature of 138°C on a heat blanket for 30 seconds. The portion of the element containing the emulsion layers was then stripped away from the image-receiving layer.
[0072] Clear magenta and yellow dye images corresponding to the green and blue light exposed areas of the sheet, respectively, were observed to have been transferred to the image-receiving layer. Good color separation was observed. The following sensitometric data were obtained from the sample.
| Yellow | Magenta | |
| D min | 0.13 | 0.11 |
| D max | 1.28 | 1.92 |
| Ergs/cm² at 0.6 + D min | 53 | 76 |
Example 4
[0073] This example describes a photothermographic article capable of providing three colors and having two photothermographic emulsion layers on one major surface of the image-receiving layer and one photothermographic emulsion layer disposed between the other major surface of the image-receiving layer and a substrate.
[0074] 3,6-Bis(diethylamino)-9-(4-methylbenzoyl)phenoxazine (0.2 g) and a red sensitizing dye (0.5 cc of a solution containing 0.005 g of dye in 200 cc of methyl alcohol) were added to 25 g of Dispersion A as described in Example 1 and the resulting dispersion mixed. The resulting mixed dispersion was coated over an opaque polyester film at a wet thickness of 0.08 mm and dried in an oven at a temperature of 80°C for five minutes to form a cyan emulsion layer.
[0075] 4-Methylphthalic acid (0.1 g) was added to 25 g of a 7% solution of poly(vinyl alcohol) in water (50%) and methyl alcohol (50%) and mixed. The solution was coated over the cyan emulsion layer at a wet thickness of 0.08 mm (3 ( mils) to form an interlayer. The interlayer was dried in an oven at a temperature of 80°C for five minutes.
[0076] An image-receiving layer, a magenta emulsion layer, an interlayer, and a yellow emulsion layer were prepared and coated over the poly(vinyl alcohol) layer in the same manner as was described in Example 3. The image-receiving layer was in face-to-face contact with the poly(vinyl alcohol) layer.
[0077] Sheets cut from the resulting article were then exposed to an EG&G sensitometer through a "WRATTEN 47B", "WRATTEN 58", or "WRATTEN 25" filter for 10⁻³ second to produce heat-developable latent images in the emulsion layers, and the images heat-developed at a temperature of 138°C on a heat blanket for 30 seconds. The portion of the element containing the magenta and yellow emulsion layers was then stripped away from the image-receiving layer.
[0078] Clear yellow, magenta, and cyan dye images corresponding to the blue, green, and red light exposed areas of the sheet, respectively, were observed to have been transferred to the image-receiving layer. Good color separation was observed. The following sensitometric data were obtained from the sample.
| Yellow | Magenta | Cyan | |
| D min | 0.18 | 0.13 | 0.16 |
| D max | 1.03 | 1.50 | 1.62 |
| Ergs/cm² at 0.6 + D min | 82 | 27 | 132 |
Example 5
[0079] This example describes a photothermographic article capable of providing three colors and having three photothermographic emulsion layers on one major surface of the image-receiving layer.
[0080] A 15% solution of a copolymer of vinyl chloride (90%) and vinyl acetate (10%) in a solvent mixture containing methyl ethyl ketone (50%) and toluene (50%) was prepared. Isobutyl syringketazine (1.12 g) was added to 25 g of the solution and the resulting solution mixed. The resulting mixed solution was coated at a wet thickness of 0.08 mm (3 mils) onto an opaque polyester film and dried in an oven at a temperature of 80°C for five minutes to form an image-receiving layer.
[0081] A magenta emulsion layer was prepared and coated over the image-receiving layer in a manner similar to that described in Example 3.
[0082] A 5% solution of a high molecular weight homopolymer of vinyl chloride in tetrahydrofuran was prepared. Phthalazinone (0.1 g) was added to 25 g of the solution and mixed. The resulting mixed solution was coated over the magenta emulsion layer at a wet thickness of 0.05 mm (2 mils) to form an interlayer. The interlayer was dried in an oven at a temperature of 80°C for five minutes.
[0083] A yellow emulsion layer was prepared and applied over the first interlayer in a manner similar to that described in Example 3.
[0084] A 7% solution of terpolymer of vinyl chloride (81%)/vinyl acetate(4%)/hydroxy containing alkyl acrylate (15%) in 1-methoxy-2-propanol was prepared. Phthalazinone (0.1 g) was added to 25 g of the solution and the resulting solution mixed. The resulting mixed solution was coated over the second emulsion layer at a wet thickness of 0.05 mm (2 mils) to form a second interlayer. This interlayer was dried in an oven at a temperature of 80°C for five minutes.
[0085] 3,6-Bis(diethylamino)-9-(4-methylbenzoyl)phenoxazine (0.3 g), 4-methylphthalic acid (0.1 g), and a red sensitizing dye (a 0.5 cc of a solution containing 0.005 g of dye in 200 cc of methyl alcohol) were added to 25 g of Dispersion A as described in Example 1 and the resulting dispersion mixed. The resulting mixed dispersion was coated over the second interlayer at a wet thickness of 0.10 mm and dried in an oven at a temperature of 80°C for five minutes to form a cyan emulsion layer.
[0086] Sheets cut from the resulting article were then exposed to an EG&G sensitometer through a "WRATTEN 47B", "WRATTEN 58", or "WRATTEN 25" filter for 10⁻³ second to produce heat-developable latent images in the emulsion layers, and the images heat-developed at a temperature of 138°C on a heat blanket for 40 seconds. The portion of the element containing the emulsion layers was then stripped away from the image-receiving layer.
[0087] Clear, yellow, magenta, and cyan dye images corresponding to the blue, green, and red light exposed areas of the sheet, respectively, were observed to have been transferred to the image-receiving layer. Good color separation was observed. The following sensitometric data were obtained from the samples.
| Yellow | Magenta | Cyan | |
| D min | 0.10 | 0.10 | 0.14 |
| D max | 1.24 | 1.61 | 0.85 |
| Ergs/cm² at 0.6 + D min | 132 | 129 | 250 |
Example 6
[0088] This example describes a photothermographic article capable of providing three colors and having three photothermographic emulsion layers on one major surface of the image-receiving layer.
[0089] Example 5 was repeated, with the exception that the first interlayer was replaced with a layer prepared in the following manner:
A 3.5% by weight solution of a blend of poly(vinyl chloride) (95%) and poly(vinyl acetate) (5%) in tetrahydrofuran was coated onto the magenta emulsion layer as the first interlayer at a wet thickness of 0.08 mm (3 mils) and dried in an oven at a temperature of 80°C for five minutes.
[0090] Sheets cut from the resulting article were then exposed to an EG&G sensitometer through a "WRATTEN 47B", a "WRATTEN 58", or a "WRATTEN 25" filter for 10⁻³ second to produce heat-developable latent images in the emulsion layers, and the images heat-developed at a temperature of 138°C on a heat blanket for 40 seconds. The portion of the element containing the emulsion layers was then stripped away from the image-receiving layer.
[0091] Clear yellow, magenta, and cyan dye images corresponding to the blue, green, and red light exposed areas of the sheet, respectively, were observed to have been transferred to the image-receiving layer. Good color separation was observed. The following sensitometric data were obtained from the sample.
| Yellow | Magenta | Cyan | |
| D min | 0.14 | 0.10 | 0.10 |
| D max | 1.74 | 1.87 | 0.96 |
| Ergs/cm² at 0.6 + D min | 42 | 63 | 166 |
[0092] The green sensitizing dyes used in Examples 1-6 is disclosed in U.S. Patent No. 4,476,220 and has the following structural formula:
[0093] The blue sensitizing dye used in Examples 2-6 is disclosed in U.S. Patent No. 4,123,282 and has the following structural formula:
[0094] The red sensitizing dye used in Examples 1, 2, 4-6 is disclosed in U.S. Patent No. 3,719,495 and has the following structural formula:
[0095] The fluorocarbon coating additive used in the foregoing examples has the trademark "FLUORAD FC 431" and is available from Minnesota Mining and Manufacturing Company, St. Paul, Minnesota.
[0096] 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.
1. A heat developable photothermographic article comprising:
(a) an image-receiving element comprising a polymeric image-receiving layer; and
(b) strippably adhered to said image-receiving element, an imageable photothermographic element comprising a plurality of emulsion layers, each of which emulsion layers comprises a binder, a silver source material, photosensitive silver halide in catalytic proximity to the silver source material, and a leuco dye, and interposed between each pair of said emulsion layers, a dye-permeable interlayer.
2. The article according to Claim 1, further comprising a support.
3. The article according to Claim 1, wherein said image-receiving element is in contact
with a support.
4. The article according to Claim 2, wherein said support is selected from the group
consisting of paper, thermoplastic polymer, glass, and metal.
5. The article according to Claim 3, wherein said support is selected from the group
consisting of paper, thermoplastic polymer, glass, and metal.
6. The article according to Claim 1, wherein said leuco dye is selected from the group
consisting of biphenol leuco dyes, phenolic leuco dyes, indoaniline leuco dyes, acrylated
azine leuco dyes, phenoxazine leuco dyes, phenodiazine leuco dyes, and phenothiazine
leuco dyes.
7. The article according to Claim 1, wherein said image-receiving layer comprises a polymeric
thermoplastic polymer selected from the group consisting of polyesters, cellulosics,
and polyolefins.
8. The article according to Claim 7, wherein said polymer is selected from the group
consisting of polyvinyl resins, copolymers of vinyl resins, poly(vinyl acetate), poly(vinyl
chloride), and copolymers of vinyl chloride and vinyl acetate.
9. The article according to Claim 1, wherein the binder for at least one of said emulsion
layers comprises a poly(vinyl butyral).
10. The article according to Claim 1, wherein said at least one dye-permeable interlayer
comprises a thermoplastic polymer.
11. The article according to Claim 10, wherein said thermoplastic polymer comprises a
polymer selected from the group consisting of terpolymers formed from vinyl chloride,
vinyl acetate, and maleic acid, copolymers formed from vinyl chloride and vinyl acetate,
homopolymers of vinyl chloride, terpolymers formed from vinyl chloride, vinyl acetate,
and hydroxyalkyl acrylate, and blends of poly(vinyl chloride) and poly(vinyl acetate).
12. The article according to Claim 1, wherein said photothermographic element further
comprises a development modifier.
13. The article according to Claim 5, wherein said support is made from a thermoplastic
polymer.
14. The article according to Claim 1, wherein said photothermographic element further
comprises a stripping agent.
15. The article according to Claim 14, wherein said stripping agent is a fluorocarbon
compound.
16. A method of providing a colored image comprising the steps of:
(1) providing a photothermographic article according to Claim 1;
(2) imagewise exposing said emulsion layers of said photothermographic article to actinic radiation to provide latent silver images;
(3) developing the exposed article by heating said exposed article to form diffusible dyes and allowing said dyes to transfer by diffusion to said image-receiving layer to provide a colored image on said image-receiving layer; and
(4) stripping at least one of said emulsion layers away from said image-receiving layer.
17. The method according to Claim 16, wherein said image-receiving layer is in contact
with a support.
18. The method according to Claim 17, wherein said support is selected from the group
consisting of paper, thermoplastic polymer, glass, and metal.
19. The method according to Claim 18, wherein said support for said image-receiving layer
is a thermoplastic polymer.
20. The method according to Claim 16, wherein said article includes a stripping agent.
21. The method according to Claim 16, wherein said developing and transfer step is conducted
at a temperature of from about 60°C to about 160°C for a time of from about 1 second
to about 60 seconds.
22. A method of providing a colored image comprising the steps of:
(1) providing an image-receiving element comprising a polymeric image-receiving layer;
(2) providing an imageable photothermographic element comprising a plurality of emulsion layers, each of which emulsion layers comprises a binder, a silver source material, photosensitive silver halide in catalytic proximity to the silver source material, and a leuco dye, and interposed between each pair of said emulsion layers, a dye-permeable interlayer;
(3) imagewise exposing said emulsion layers of said photothermographic article to actinic radiation to provide latent silver images;
(4) placing said exposed photothermographic element in face-to-face contact with the image-receiving layer of the image-receiving element to form a photothermographic article in which the photothermographic element is strippably adhered to the image-receiving element;
(5) developing the exposed article by heating said exposed article to form diffusible dyes and allowing said dyes to transfer by diffusion to said image-receiving layer to provide a colored image on said image-receiving layer; and
(6) stripping at least one of said emulsion layers away from said image-receiving layer.
23. The method according to Claim 22, wherein said image-receiving layer is in contact
with a support.
24. The method according to Claim 22, wherein said photothermographic element is in contact
with a support.
25. The method according to Claim 22, wherein said developing and transfer step is conducted
at a temperature of from about 60°C to about 160°C for a time of from about 1 second
to about 60 seconds.