Light-sensitive,heat developable copy-sheets for producing color images



United States Patent C ABSTRACT OF THE DISCLOSURE Color images are formed by dry photography using a sheet or film containing a phenolic or acive methylene color coupler component in conjunction with a photosensitive silver halide catalyst progenitor in catalytic proximity with major amounts of a catalyzable heat-sensitive light-stable silver salt and a p-phenylenediamine reducing agent. This invention relates to the recording of light-images, and has particular reference to sheet materials which, when merely exposed to a light-image and then uniformly briefly heated, display a colored corresponding visible image. Among other applications, sheet materials formulated in accordance with the principles of the invention are useful in preparing full-color reproductions of multi-colored originals, e.g. vfrom color separation negative transparencies thereof. A light pattern from each negative is impressed on a transparent copy-sheet capable of being developed to a corresponding color; the sheets are heated to develop the colored reproduction; and the several sheets, either before or after heating, are laid up in registry. Treatment with aqueous solutions or chemical vapors is avoided, the color images being rapidly developed by simple brief heating of the exposed integral sheet. Light-sensitive copy-sheets which are heat-developable have previously been described, for example in Belgian Pat. No. 663,112 of Oct. 27, 1965. The sheet contains small amounts of light-sensitive silver halide catalytically associated with much larger amounts of a silver soap and a reducing agent. Exposure to a light-pattern followed by moderate over-all heating results in a black image. Color-forming systems are known in the photographic art in which light-struck silver halide is reacted with a mild reducing agent, e.g. a p-phenylenediamine developer, to form an oxidized intermediate which when the n reacted with a coupler yields a colored dye. The process is described in Mees, Theory of the Photographic Process, 3rd ed., p .384 et seq. The reducing agent is introduced as a component of an aqueous alkaline developer solution at a high pH; the coupler components may also form a part of the solution. Diffusion of the several components into and out of the gelatin-silver halide stratum is a major problem in such systems. It has now been found possible to produce colored image patterns in sensitive sheet materials in the absence of water and merely open exposure to a light-image followed by moderate heating, by incorporating in the copysheet a catalytically small amount of photosensitive silver halide in close catalytic association with much larger amounts of a light-stable silver salt and in conjunction with both a p-phenylenediamine developer and a phenolic or active methylene coupler, preferably in the presence of a film-forming polymeric binder. The following specific examples, in which all proportions are in parts by weight unless otherwise indicated, will serve further to illustrate but not to limit the invention. ice EXAMPLE 1 A first coating composition is prepared, by prolonged mixing in a ball mill, of Parts Silver behenate:behenic acid (equimolar mixture) 94 Ethyl cellulose 13 2-cyanoacetylcoumarone (M-31 coupler) 2 Toluene 404 The mixture is coated onto transparent polyester film using a knife coater at an orifice of 2 mils (.002 inch) and permitted to dry. Over the dry coating is then applied, by lightly swabbing with a saturated cotton pledget and undar darkroom conditions, a solution containing Parts N N -diethyl 3 methyl-p-phenylene diamine hydrochloride (CD-2 color developing agent) 2 Aqueous hydriodic acid 2 Methanol 600' and the sheet is again dried, the increase in weight being within the range of about .01.04 gram per square foot. The treated surface is exposed to a light-image from a projection lamp, for example from five to 20 seconds, and then heated uniformly for a few seconds at C. A somewhat muddy magenta image pattern appears at the light-struck areas. The incorporation of another source of halide ion, such as the hydriodic acid employed here, permits the substitution of a soluble non-halide salt of the developer, such for example as the oxalic acid salt, for the hydrogen halide salt if desired. In a series of further examples, other specific couplers are substituted in equal weight proportions for the M 31. The composition and procedure is otherwise identical. The image color is as indicated. Ex. Coupler Image color 4-(p-toluenesullonamldo)-benzoylacetanilide Yellow. 2,6-dibromo1,5-dihydroxynaphthalene Cyan. Acetoacet-o-anisidide 2,4-dichloro-l-naphthol 3-Inethyl1-phenylpyrazolone 2,4-dibromo-1-naphtl1ol EXAMPLE 8 The first coating composition contains three parts by weight of 2,4-dichloro-1-naphthol in place of the two parts of M-3l, being otherwise prepared and applied as in Example 1. The second coating, applied by swabbing, consists of methanol containing approximately .4 percent of N ,N -dimethyl-p-phenylenediamine hydrochloride. The initially white coating is converted to a dull cyan at exposed areas by exposure to light followed by brief over-- all heating at 110 C. Additional examples are prepared in the same manner but with substitution of other coupler components for the naphthol, with results as tabulated. Ex. Coupler Image color 9. 3-methyl-l-phenylpyrazolone Magenta. l0 Acetoacet-o-anisidide Yellow. EXAMPLE 11 the precipitated silver, for example by brief washing with a solvent for the silver. As an illustration, the magenta image areas of the copy formed as described under Example 1 are clarified and brightened by soaking of the imaged sheet for a short time in a five-percent solution of potassium cyanide in water, followed by washing and drying. The background areas are at the same time rendered essentially white or clear. Where a washing step is contemplated, a binder component must be selected Which permits effective washing without being itself dissolved or otherwise rendered ineffective. The addition of inert fillers or pigments is sometimes helpful for these or other purposes. The clarity of the colored image may also be improved by holding the silver soap content of the coating to a minimum, by selecting particular combinations of substituted p-phenylenediamine developer components and active methylene or phenolic coupler components capable of producing dyes of maximum tint intensity, and by otherwise compounding and proportioning to cause the reduction and precipitation of minimal amounts of silver and in as nearly colloidal state as possible. The formation of colored images by the simple procedures and with the simple coatings hereinbefore described is particularly surprising in view of the presence of the relatively large proportions of free behenic acid, since color coupling by conventional photographic techniques ordinarily requires an alkaline medium. Even in the ab sence of free behenic acid in the original coating, it might be supposed that any chemical reducing action on the silver soap would liberate the acid and thus prevent the color coupling reaction. Nevertheless the reaction in either case proceeds smoothly upon mere heating of the exposed area, with formation of a colored image as already described. Silver salts of other high molecular weight organic acids, and particularly the silver soaps of other long chain fatty acids, e.g. stearic acid, are also useful for the purposes of the invention. Commercial behenic acid from which the silver behenate-behenic acid mixture is prepared is itself a mixture of long chain fatty acids of which not more than about three-fourths is behenic acid. The presence of free fatty acid increases the opacity and water-resistance of the coating, but free acid is not essential and may be omitted where a transparent coating is desired. EXAMPLE 12 A mixture of 240 grams of silver behenate-behenic acid, 88 grams of polyvinylbutyral resinous binder, 508 grams of toluene and 753 grams of methylethyl ketone is homogenized by milling in a ball mill. To 15 grams of the mixture is added a solution of one-half gram of the color coupler 1-(p-phenylsulfonylphenyl)-3-(2 phenoxymyristoylamido)-2-pyrazolin-5-0ne in 5 ml. of methylethylketone. The composition is thoroughly mixed and is smoothly coated on transparent polyester film. After drying, the residual coating is microns thick. A second layer is then applied and dried, to a dry thickness of 6 microns; the solution as applied contains 0.5 gram of N ,N -diethyl-pphenylenediamine hydrobromide and 2.5 grams of polyvinylpyrrolidone in grams of methanol. The sheet is maintained under darkroom conditions during and following application of the second coating. Exposure of the sheet through a photographic negative transparency followed by contact for about one second with a smooth metal plate at a temperature of 100 C. results in a magenta image conforming to the light-struck areas. Substitution of the same amount of dodecyl 4-(benzoylacetamido)-benzoate for the 1-(p-phenylsulfonylphenyl)- 3-(2 phenoxymyristoylamido)-2-pyrazolin-5-one gives a yellow image. 2,4-dichloro 6 (p-nonylphenoxyacetamido)-m-cresol similarly gives a cyan image. Essentially the same results are obtained by adding the color coupler compound with the second coating rather than with the first coating, using a slightly different solvent mixture to assure complete solution of all components. The second coating composition may then consist of one-half gram of color coupler, one-half gram of N ,N diethyl-p-phenylenediamine hydrobromide, 2.5 grams of polyvinylpyrrolidone, 5 ml. of acetone, and 39 ml. of methanol. Other color couplers of equal effectiveness include 3- (p-(p-nonylphenoxyacetamido) *benzamido)-1-phenyl-2- pyrazolin-S-one and 2 (p-(p-benzoylacetamidobenzenesulfonamido) phenyl) 1 stearylbenzimidazole-S-sulfonic acid giving magenta and yellow images respectively in the composition of Example 12. In each of the several examples the formation of photosensitive silver halide occurs by reaction between the silver behenate and the source of halide ions present in the second coating. Thus in Example 8 the dimethyl-p-phenylenediamine hydrochloride serves as a source of chloride ions; in Example 1 there is additionally included a source of iodide ions. The procedure employed makes certain that full catalytic effectiveness is achieved at the light-struck areas during subsequent reduction of the silver behenate. The amount of silver halide which must be formed to yield adequate photosensitivity is surprisingly small due to its essentially catalytic function, and substantially all of the oxidation of substituted p-phenylenediamine occurring at the image is by reaction with silver behenate rather than with silver halide. The halide ion may equally well be introduced in other ways, for example by subjecting the coated silver soap to the action of hydrogen halide vapors, or by pre-reaction of the silver soap particles with halide ion. Organic as well as inorganic sources of halide ion are useful. Mixtures of halides may be used. Silver iodide is itself sensitive mainly to blue light. Where exposure to radiations of other restricted wavelength ranges and for minimum time is contemplated, the use of silver bromide in conjunction with various sensitizing dyes is indicated. Images of any desired color may be produced, as already noted in conjunction with the illustrative examples, by selection of appropriate color couplers. Thus the use of acylacetanilides as color formers or couplers results in yellow images; couplers such as 3-methyl-1- phenylpyrazolone and 2-cyanoacetylcoumarone give magenta images; and cyan images are obtained with phenolic and naphtholic couplers. Combinations of these classes of color-forming components may also be used; a particularly effective formulation includes a blend of appropriate members from all three classes to produce a black image, thereby adding to the density of the silver image and permitting an economically attractive reduc tion in the total amount of both silver soap and reducing agent for a desired image density. Multi-color products may also be provided using the principles of this invention. The combination in registry of a plurality of different monocolor transparencies has already been indicated. Multiple color layers in an integral sheet are also contemplated, the structure typically including, on a transparent film base and in the order named, a first layer sensitized to red light and containing a coupler and developer combination suitable for producing a cyan dye, a second layer sensitized to green light and producing a magenta dye, a filter layer for preventing the passage of blue and ultraviolet, and an outer layer sensitive to blue light and producing a yellow dye. In another multi-color structure the three color-sensitive and color-producing coatings are applied as separate side-by-side microscopic dot areas, together with appropriate filters where necessary. Exposure of either structure to a color image, as from a multi-color transparency either by contact printing or through suitable projection apparatus, followed by simple overall heating, is suflicient in either case to provide a multicolor reproduction. What is claimed is as follows: 1. Method of making a record in color of a lightpattern, comprising: exposing to said light-pattern a sheet material including a photosensitive layer comprising photosensitive silver halide catalytically associated with light-stable high molecular weight organic acid silver salt oxidizing agent, p-phenylenediamine developer as reducing agent for said silver salt, and phenolic or active-methylene color-forming coupler, to form an invisible latent image; and briefly uniformly heating said layer in the absence of water to produce a visible colored image at areas corresponding to said light-pattern. 2. Sheet material useful in making a record by the method defined in claim 1 and including a photosensitive layer comprising photosensitive silver halide catalytically associated with light-stable high molecular weight organic acid silver salt oxidizing agent, a p-phenylenediamine developer as reducing agent for said silver salt, and at least one phenolic or active-methylene color-forming coupler. 3. In the method of making a photosensitive colorforming sheet material having photosensitive silver halide in catalytic association with light-stable high molecular Weight organic acid silver salt oxidizing agent and in- UNITED STATES PATENTS 3,457,075 7/1969 Morgan et al. 96l02 3,409,457 11/1968 MenZel 1l736.8 FOREIGN PATENTS 663,112 1 0/1965 Belgium. J. TRAVIS BROWN, Primary Examiner



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Patent Citations (3)

    Publication numberPublication dateAssigneeTitle
    BE-663112-AOctober 27, 1965
    US-3409457-ANovember 05, 1968Agfa AgThermographic copying sheet
    US-3457075-AJuly 22, 1969Minnesota Mining & MfgSensitized sheet containing an organic silver salt,a reducing agent and a catalytic proportion of silver halide

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