US3706559A - Methods for making positive full-color dye-transfer prints - Google Patents

Abstract

METHODS ARE DISCLOSED FOR MAKING POSITIVE FULL-COLOR DYE-TRANSFER PRINTS BY IMAGEWISE EXPOSURE, TO A COLOR NEGATIVE, OF PHOTOGRAPHIC IMAGING MEDIA COMPRISING A FINELY-DIVIDED PHOTOCONDUCTOR AS THE PHOTOSENSITIVE AGENT. THE EXPOSED IMAGING MEDIA ARE DEVELOPED, IN THE PRESENCE OF A REUCIBLE METAL ION, WITH COUPLERS AND DEVELOPERS FORMING CYAN, MAGENTA, OR YELLOW DYE IMAGES IN RADIATIONEXPOSED PORTIONS THEREOF. THESE DYE IMAGES COMBINE TO REPRODUCE THE ORIGINAL IMAGE IN A FULL-COLOR PRINT.

Description

Dec. 19, 1972 H. SPRAGUE 3,705,559

METHODS FOR MAKING POSITIVE FULL-COLOR DYE-TRANSFER PRINTS Filed Feb. 27, 1969 ORIGINAL IMAGE RED GREEN BLUE COLOR NEGATIVE CYAN MAGENTA YELLOW EXPOSURE RED SENSITIVE: X X

GREEN SENSITIVE X BLUE SENSITIVE X X DEVELOPMENT 0nd TRANSFER RED SENSITIVE CYAN CYAN GREEN SENSITIVE MAGENTA MAGENTA BLUE SENSITIVE YELLOW YELLOW DYE TRANSFER PRINT: RED GREEN BLUE RROTECT/VE COAT/N6 A/VD BALLASTED YELLOW COUPLER YELLOW F/LTEI? LAYER A/VO BALLASTED MAGENTA *COUPLER RED FILTER LAYER sup/ am LAYER COMPR/Sl/VG BLUE-SENS/T/ZED PHOTOCO/VOUCT OR LA YER COMPR/SV/VG GREE/V-SE/VS/T/ZED PHOT O6 O/VDUC 7' OR LA YER COMPR/Sl/VG RED-SEA/S/T/ZEO PHOTOCO/VOUCTOR :7 2 ROBE/P7 H. SPRAGL/E INVENTOR.

ATTORNEY.

United States Patent ()flice Patented Dec. 19, 1972 3,706,559 METHODS FOR MAKING POSITIVE FULL-COLOR DYE-TRANSFER PRINTS Robert H. Sprague, Chelmsford, Mass., assignor to Itek Corporation, Lexington, Mass. Filed Feb. 27, 1969, Ser. No. 802,954 Int. Cl. G03c 5/24 U.S. CI. 96-48 PD 9 Claims ABSTRACT OF THE DISCLOSURE Methods are disclosed for making positive full-color dye-transfer prints by imagewise exposure, to a color negative, of photographic imaging media comprising a finely-divided photoconductor as the photosensitive agent. The exposed imaging media are developed, in the presence of a reducible metal ion, with couplers and developers forming cyan, magenta, or yellow dye images in radiationexposed portions thereof. These dye images combine to reproduce the original image in a full-color print.

BACKGROUND OF THE INVENTION (1) Field of the invention This invention relates to methods for making positive full-color dye transfer prints and to multi-layer photo graphic imaging media for preparing such dye transfer prints.

(2) Description of the prior art US. Pat. No. 3,380,823 discloses photographic imaging media comprising a finely-divided photoconductor as the photosensitive agent. Exposure of such imaging media to actinic radiation such as visible or ultraviolet light activates the photoconductor, rendering it capable of efiecting chemical reactions which can be utilized to develop a visible image. As taught in this patent and known in the art, the photoconductors of greatest utility for use in such imaging media are compounds formed between metals and elements of Group VIA of the Periodic Table, e.g. oxides, sulfides, selenides and tellurides. Preferred materials from the point of view of color, light-sensitivity, ease of development, and the like are titanium dioxide and zinc oxide.

The latent image of activated photoconductor formed in such imaging media by imagewise exposure thereof can be suitably developed by applying image-forming materials to the media. Suitable image-forming materials include redox systems, for example systems containing reducible metal ions such as silver ions or other ions of noble metals at least as easily reducible as ionic copper. U.S. Pats. Nos. 3,227,551 and 3,243,294 teach color photographic diffusion-transfer processes employing ballasted couplers, present in silver halide imaging media, which form and/ or release diffusible dyes during development.

SUMMARY OF THE INVENTION According to the present invention, a photographic imaging medium comprising a finely-divided photoconductor as the photosensitive agent, said photoconductor suitably being dispersed in a binder to form a photosensitive layer coated on a supporting substrate such as of paper, metal, glass, plastic, or the like, is exposed to imaging radiation which activates the photoconductor in radiation-exposed areas. Those portions of the photographic medium containing activated photoconductor are next developed by contacting the exposed medium, in the presence of reducible metal ions, with a color-forming coupler and a photographic developer which in its oxidized form is reactive with said color coupler to form a dye. In those portions of the imaging medium in which the photoconductor has been activated by radiation, metal ions are reduced to form a deposit of free metal whereas the developer is oxidized and reacts With the coupler to form a dye.

For forming full color prints, three separate imaging media may be used respectively sensitized to red, green, and blue light and respectively forming cyan, magenta, and yellow dye images which are transferred in register to a receptor sheet to form a dye transfer print. In another embodiment of the invention, these photosensitive colorproducing entities may form three layers of a single multi-layer medium.

Where separate media are employed to produce a full color print, the dye-forming developer and coupler may be present in the same development bath. They react to form dye when contacted with irradiated portions of the imaging medium in the presence of metal ion.

If the plural photosensitive entities necessary to produce a full color print comprise different layers of a single multi-layer imaging medium, appropriate ballasted couplers are suitably incorporated within the various layers. These couplers react with developer, at photo-activated sites and in the presence of a metal ion, to form and/or release diffusible dyes which are then transferred to a receptor sheet to form a positive dye transfer image.

To decrease fog which may appear in unexposed portions of a printing medium by reaction of metal ion with developer, a competing coupler may advantageously be incorporated into the radiation-sensitive layer or layers thereof. The competing coupler is capable of reacting with oxidized developer to form a non-diffusing compound. In unexposed areas, the competing coupler removes unwanted oxidized developer by formation of a non-diffusing compound, thus inhibiting fog formation. In exposed areas, where oxidized developer is plentifully present, the competing coupler does not consume enough of the developer to interfere with the production of a quality print by reaction of the oxidized developer with the regular coupler.

DESCRIPTION OF PREFERRED EMBODIMENT A better understanding of the present invention will be had by referring to the accompanying drawing, in which FIG. 1 is a schematic plan showing image and imagecopy color relationships at various stages of a process for producing a dye transfer print according to the present invention; and FIG. 2 is an enlarged side view, in section, of a typical multi-layer photographic medium useful for the preparation of full-color dye transfer prints according to the present invention.

FIG. 1 shows that an original image comprising red, green and blue portions is reproduced in a color negative, e.g. a conventional silver halide color negative such as a Kodacolor negative, as a dye image respectively comprising cyan, magenta, and yellow portions.

As further suggested by the Exposure plan shown in FIG. 1, according to the present invention, a first, redsensitive, photographic imaging medium comprising a finely-divided photoconductor sensitized to red light is exposed to white light through such as color negative. The magenta and yellow portions of the negative transmit red light and expose the medium correspondingly (as indicated by X in the figure), but the medium remains unexposed wherever red-absorbing cyan dye is present in the color negative (i.e. wherever red was present in the original image).

A second medium comprising green-sensitized photoconductor is exposed to the color negative using white light. This activates the photoconductor in those portions of the medium corresponding to the green-transmitting cyan and yellow portions of the color negative.

Exposure of a third, blue-sensitive, imaging medium to white light through the color negative activates the photosensitive photoconductor of the medium only in those portions corresponding with cyan and magenta areas of the color negative, i.e. those areas of the negative which transmit blue light.

(The red, green, and blue-sensitive media mentioned above are suitably prepared by dispersing a finely-divided photoconductor such as finely-divided titanium dioxide in a binder such as gelatin, and coating a support layer such as paper or cellulose acetate with the mixture. The photoconductor is suitably sensitized to red, green, or blue light with cyanine and hemi-cyanine dyestuffs like those taught in Belgian Pat. 714,080.)

The exposed media, now containing radiation-activated photoconductor, are next developed in the presence of a reducible metal ion. Suitably, the exposed media are first contacted with an aqueous solution of an appropriate metal ion e.g. a solution of silver nitrate, and are then developed in a developing bath comprising a photographic developer and a coupler capable of reacting with oxidized developer to form a cyan, magenta, or yellow dye.

Thus, the exposed red-sensitive medium discussed above is suitably first contacted with a solution of aqueous silver nitrate and then developed in a bath comprising a photographic developer and a coupler reacting with oxidized developer to form a cyan dye. Where the photoconductor has been activated by exposure, metal ion is reduced and developer is oxidized and combines with the coupler to form cyan dye as shown in FIG. 1.

The exposed green-sensitive layer is developed with a second developing solution containing developer and a coupler forming a magenta dye, and the exposed blue-sensitive layer is separately developed with still another developer-coupler solution with formation of a yellow dye image in exposed areas.

As further suggested in FIG. 1, when the cyan, magenta, and yellow images respectively formed in the now-developed media are transferred in register to a receptor sheet, a positive print reproducing the pattern of reds, greens, and blues of the original image is obtained.

FIG. 2 of the accompanying drawing shows a photographic printing medium according to the present invention in which red-sensitive, green-sensitive, and blue-sensitive layers are present in a single multi-layer structure. The photosensitive layers in such a multi-layer medium function in principle like the separate media discussed just above in connection with FIG. 1. That is, each layer contains finely-divided photoconductor selectively sensitized to red, green, or blue light. On exposure to radiation such as white light passing through a color negative, the photoconductor is activated in image patterns like those shown in FIG. 1. However, in the multi-layer structure, a different coupler is incorporated into each layer in ballasted form so that a diiferent color is produced within each layer when the exposed medium is contacted with a photographic developer in the presence of a reducing metal ion.

The oxidized developer may react with a ballasted coupler in one of two ways. First, the developer may react with the ballasted coupler to form a dilfusible dye, leaving a non-migrating ballast residue in the layer. Second, a diffusible pre-formed dye, held in a layer by attachment to a ballasting group, may be rendered mobile by reaction of the developer and the ballasting group to release the dye.

Thus, the red-sensitive layer of such a structure may comprise a ballasted coupler forming or releasing a diffusible cyan dye when the coupler is treated with a developer in the presence of metal ion. The green-sensitive layer comprises a ballasted coupler forming or releasing a diifusible magenta dye on reaction with oxidized developer, and the blue-sensitive layer comprises a coupler forming or releasing a ditfusible yellow dye on reaction with oxidized developer. The cyan, magenta, and yellow dyes released each diffuse through the layers and are then simultaneously transferred to a receptor sheet by contact processes to form a full-color dye transfer positive print.

The drawing of FIG. 2 shows a multi-layered structure of this type including a support layer suitably of a material such as paper, glass, plastic, or the like. A solutionpermeable red-sensitive layer immediately thereover comprises a binder such as gelatin in which is dispersed a finely-dividd photoconductor, such as titanium dioxide, which is sensitized to red light with a dye such as taught in Belgian Pat. 714,080. Ballasted couplers forming and/or releasing a cyan dye on development and suitable for inclusion in such a red-sensitive layer are taught, for example, in US. Pats. 3,227,551 and 3,243,294.

The red filter layer shown in the structure of FIG. 2 protects the red-sensitive layer from exposure to green and blue light by screening out wavelengths shorter than red.

The green-sensitive layer of the structure of FIG. 2 again comprises a photosensitive photoconductor material such as titanium dioxide, but in combination with a ballasted coupler forming and/or releasing a difiusible magenta dye on reaction with developer in the presence of metal ion at an activated site. Suitable couplers are again those described in US. Pats. 3,227,551 and 3,243,- 294, for example.

This layer is protected from wavelengths shorter than green by an overlying yellow filter layer, shown in FIG. 2.

The blue-sensitive layer of FIG. 2 similarly comprises a photoconductive sensitized to blue light with a cyanine or hemicyanine dye like those taught in Belgian Pat. 714,080 and a ballasted coupler forming and/or releasing a difi'usible yellow dye at activated sites on reaction with oxidized developer in the presence of metal ion. Such couplers are disclosed, for example, in the US. patents mentioned earlier.

The multi-layer structure is suitably provided with an abrasion resistant top coat, such as of hardened gelatin, which also controls the difl'usion rate of dye from the structure.

After exposure of the multi-layered medium of FIG. 2 to activating radiation, e.g. to white light through a color negative, the exposed medium is suitably developed by first sensitizing it with a reducible metal ion, such as by moistening it with an aqueous solution of silver nitrate. The exposed metal-sensitized medium is then contacted with a developer which, when oxidized, will react with the couplers contained in the diiferent layers of the medium. A variety of alkaline color developing solutions useful for the color development of silver halide media and containing aromatic primary amino color developing agents can be utilized. Particularly useful materials include the p-phenylene diamine color developers.

Alternatively the image-forming materials, e.g., solution of metal ions and/or reducing agent therefor may development step proceeds optimally under acid conditions, that is high densities of metallic silver are formed using an acid phenylene diamine solution. However, color coupling does not take place at acid pHs. If the developed medium is next immersed in an alkaline bath, the coupling reaction proceeds with formation of good dye densities.

Some fogging in photographic imaging media of the type discussed above in explanation of FIGS. 1 and 2 may result from an unwanted reaction of metal ion and de veloper in non-exposed areas of the printing medium, i.e. in the absence of activated photoconductor. Oxidized developer produced in this way may then react with coupler to form or release dye in non-exposed areas.

A technique for reducing fog, particularly in the multilayer printing medium shown in FIG. 2 of the present invention, involves the incorporation of a competing coupler into the photosensitive layers. Such a competing coupler typically reacts with oxidized developer at a rate faster than that of the couplers forming or releasing a difiusible dye. In areas of the medium in which the photoconductor has not been activated by exposure, small quantities of oxidized developer produced by non-photolytic reaction of developer with metal ion immediately react with the competing coupler to form a non-diffusing coupling product. Since the competing coupler is more reactive than the ballasted coupler, the small quantity of oxidized developer present in these areas is immediately depleted without the formation of diffusible fogging dye. In those portions of the printing medium which have been exposed with activation of the photoconductor, the supply of oxidized developer is sufiiciently great that oxidized developer not consumed by the competing coupler couples with ballasted couplers to form or release diffusible dyes. A dye image suitable for transfer to a receptor sheet is thus produced while fog is decreased in non-exposed areas.

Receptor materials for dye transfer processes are known in the art and are commercially available. The receptor sheets, if desired, may comprise a mordant such as pyridine polymer metho-p-toluene sulfonate described in US. Pat. 2,484,430.

A better understanding of the present invention will be had by referring to the following specific examples, given by way of illustration.

EXAMPLE 1 Preparation of a photographic imaging medium adaptable to the transfer of dye images 50 grams of an aqueous slurry containing 25 percent by weight of finely-divided titanium dioxide (about 0.3- 0.4 micron) were diluted with 42.6 ml. of distilled water and 3.4 ml. of a percent solution of a commercial wetting agent (Tiwet). The resulting mixture was heated to about 100 F. and then combined with 100 grams of a 10 percent aqueous solution of gelatin swelled and heated to 100 "F. 2.6 ml. of a 50 percent aqueous solution of glycerine were added to the resulting slurry as a humectant and anti-foaming agent. The resulting slurry was then uniformly poured onto a flat piece of subbed triacetate film and drawn down with a hot wire rod. The resulting gelatin coating was dried for minutes at room temperature and for another 20 minutes at about 50 C. in a circulating hot air oven.

A second coating of gelatin was applied over the dried photosensitive coating from a 6 percent aqueous solution at a wet thickness of 3 mils. This coating prevents unwanted loss of dye from the developed underlayer during wet processing.

EXAMPLE 2 Dye sensitization of a photographic imaging medium A first sheet of the film prepared in Example 1 was dye sensitized to red light by dip-dyeing for two minutes in a dilute aqueous solution of N-hydroxyethyl-4-[3-(3- ethyl 2(3H) benzothiazolylidene)propenyl]quinolium chloride, covered by Belgian Pat. 714,080.

For sensitizing to green light and blue light, respectively, separate pieces of film are dip-dyed in dilute aqueous solutions of 2-(p-climethylaminostyryl)-4-methylthiazolium methochloride,

and Z-(p-dimethylaminophenyl)-6-methylbenzothiazolium methochloride (Thioflavine). Dye sensitization using these dyes is also taught in Belgian Pat. 714,080. After dip-dyeing, each sample of sensitized film is dried for about 30 minutes at C. in a circulating hot air oven. The sensitized films are suitably dark-adapted overnight.

EXAMPLE 3 Exposure and processing Because of variations which will be encountered in the sensitivity of the various available dyes employed for preparing sensitized films as in Example 2, and because of difierences in filter factors and the like, the details of exposure and development of different imaging media will vary, but in principle are the same for each of the three images being prepared.

So, for example, a green-sensitive film like that described in Example 2 was exposed for 15 seconds through a Koda-color negative using light from a 200-Watt bulb at a distance of 10 inches.

Redand blue-sensitized films like those in Example 2 were similarly exposed through the same negative.

EXAMPLE 4 Development and transfer of color images The exposed green-sensitive medium was next dipped in a 1 N aqueous solution of silver nitrate for 10 seconds and drained for 10 seconds. A silver image was developed by contacting the film for seconds with a 0.1% aque one solution of 2-amino-5-diethylamino toluene developer, 2.5 grams of the commercially available coupler 3- methyl-l-(p-sulfophenyl) pyrazalone,

and dilute acetic acid to give pH of 5.

The film was then rinsed for 5 seconds in a 0.05 N solution of NH OH to promote color coupling.

In those portions of the green-sensitive medium which had been exposed to imaging radiation, a magenta dye was formed. The film was then rinsed for 10 seconds in a dilute acetic acid stop bath containing 0.5% formaldehyde to harden the gelatin prior to transfer.

Finally, the film was rolled in contact with a strip of commercial dye transfer paper preconditioned by soaking in commercial paper conditioner (an aqueous solution of wetting agents). When the film and paper were separated, a stable magenta dye image remained in the paper.

The pyrazolone coupler may be replaced by cyanoacetylcoumarone sodium sulfate,

prepared by the sulfonation of cyanoacetylcoumarone with oleum.

NaSO

I o oar-@sonw was prepared as follows.

17.5 g. of N-methylsulfanilic acid sodium salt and 17.3 g. of 1-hydroXy-2-naphthoylchloride were combined in 190 cc. of dry pyridine and refluxed for 3 hours. The hot solution was filtered to remove a small amount of insoluble salt. The solution was cooled and 300 cc. of ether were added. A precipitate formed and the mixture was left standing over the weekend. The precipitate was filtered off and washed with acetone. After drying, 27 g. of white crystals were obtained, which were dissolved in 80 cc. of H 0. The solution was made alkaline with Na CO' solution and after addition of NaCl a heavy crystalline precipitate formed. After standing for onehalf hour in a refrigerator, the precipitate was filtered olf and washed first with salt water, followed by H 0, and finally with acetone. After drying, 19 g. of product were obtained and dissolved in 400 cc. of boiling methanol. The solution was filtered hot and concentrated to 300 cc. After standing in the refrigerator overnight the product was filtered off, washed with methanol and dried. Yield: 13 g. M.P. 317-318 C.

The resulting cyan image was transferred to the same receptor sheet in register with the magenta image.

Finally, the exposed blue-sensitized film was contacted with silver nitrate and then with a developer solution containing N,N-diethyl-p-phenylenediamine developer and sulfobenzoylacetanilide as the coupler.

The coupler,

is prepared from ethyl benzoylacetate and sodium sulfanilate.

EXAMPLE 5 Preparation of a multi-layered copy medium A multi-layered copy medium like that shown in FIG. 2 is prepared by coating a sheet of subbed cellulose triacetate with a first photosensitive layer comprising a ballasted cyan-forming coupler in combination with a finelydivided photoconductor, titanium dioxide, appropriately sensitized to red light.

Specifically, a gelatin layer containing photosensitive titanium dioxide, like the layer described in Example 1 herein, was prepared and deposited on a support layer. The gelatin layer was sensitized to red light by incorporating thereinto a red-sensitizing dyestutf of the type taught in Example 2. Also incorporated in the gelatin was a non-diffusing cyan coupler capable of reaction with oxidized color developer to release a dilfusible preformed cyan dye.

In particular, the non-diffusing cyan coupler had the following structure:

ClHal:

Alternatively, one of the ballasted couplers taught in columns 17-20 of U .5. Pat. 3,227,551 can be incorporated in this layer. These couplers, however, react with oxidized developer to form a dilfusible cyan dye rather than to release a pre-formed dye.

A gelatin filter layer containing a water-soluble nondiifusing red azo dye of the formula was next applied over the red-sensitive layer.

A green-sensitive layer is then applied over the red filter layer. The green-sensitive layer is prepared from a gelatin solution containing finely-divided green-sensitized titanium dioxide and a non-diffusing coupler capable of reacting with oxidized developer to release a pre-formed magenta dye.

Specifically, the coupler used had the following formula:

/S (RH OH i \N/ SO Na QOSOJNQ SOaNa Alternatively, one of the ballasted couplers taught in column 21 or 22 of US. Pat. 3,227,551 can be incorporated into this layer. These couplers react with oxidized developer to form a diffusible magenta dye rather than to release a preformed dye.

H NH:

A blue-sensitive layer containing gelatin and finelydivided titanium dioxide as earlier described herein, is next applied. The photoconductor pigment is sensitized to blue light with a dye as described in Example 2, and the layer additionally contains a non-diffusing coupler releasing a preformed diifusible yellow dye or forming a diffusible yellow dye on reaction with oxidized developer. US. Pat. 3,227,551 teaches ballasted couplers releasing a difiusible pre-formed yellow dye in columns 12-15, for example, and couplers forming a diffusible yellow dye in column 23.

Finally, an abrasion-resistant gelatin topcoat is applied over the blue-sensitive layer.

"A full color positive print is made by exposing the above-described copying medium to a source of white light through the negative image to be copied,

The exposed medium is then contacted with aqueous silver nitrate and a conventional color developing solution containing an aromatic primary amino developing agent, preferably under acid conditions which promote maximum silver densities but inhibit color coupling. For example, the developing solution can comprise a mixture of silver nitrate and a developer such as 4-amino- N-ethyl-N-fl-hydroxy-ethyl aniline sulfate, acidified with acetic acid. In each of the light-sensitive layers of the exposed printing medium which have been struck by light, the activated photoconductor effects reduction of the silver ion to metallic silver and oxidation of the developer.

When the developed medium is next treated in an alkaline bath, the oxidized developer reacts with the ballasted couplers present in the various layers, and forms and/or releases diliusible cyan, magenta, and yellow dyes from these layers.

The diffusible dyes are transferred by contact of the developed multi-layer medium with an appropriate printing paper, for example a receptor sheet of the type earlier described herein.

EXAMPLE 6 Fog reduction by competing couplers To reduce fog-producing dye density in unexposed areas of the multi-layer medium described in the previous example, a fast-acting competing coupler such as a-naphthol may be included in the photosensitive layers with the ballasted couplers. For example, a-naphthol may be imbibed into the gelatin layers of the medium by one-minutes immersion in a weakly basic dilute (about 0.1%) solution of naphthol.

In those portions of the medium irradiated during exposure, the amount of competing coupler is small in comparison with the amount of oxidized developer produced in the presence of radiation-activated photoconductor. Accordingly, the ballasted couplers react in normal fashion in these areas to produce difiusible dyes. In nonirradiated areas where, nevertheless, oxidized developer may be produced by an unwanted reaction of developer with silver ion, the competing coupler reacts quickly with any oxidized developer produced to form a non-diffusing product. The amount of oxidized coupler in inactivated areas is small and is consumed by reaction with the fastreacting competing coupler in preference to reaction with the ballasted coupler. The competing coupler thus ties up the oxidized developer, preventing dye production by its reaction with the ballasted couplers. In this way, a dye image is still produced in light-struck areas, while fog dye density in non-exposed areas is reduced by the formation of non-ditfusible substances.

What is claimed is:

1. A photographic imaging medium for making positive full-color dye-transfer prints, said medium comprising a support layer having thereon a plurality of radiation-sensitive layers each comprising a finely-divided reversibly activatable photoconductor, different of said radiation-sensitive layers being sensitized respectively to red, green and blue light and respectively including a different ballasted color coupler generating a cyan, magenta and yellow dye on development, each of said layers also containing a competing, faster-acting coupler forming a non-diffusible product with oxidized developer, and a top coat of hardened gelatin to control the diffusion rate of dye from the medium.

2. A method for forming a full-color, dye-transfer print consisting essentially of:

(a) exposing red-, green-, and blue-sensitized photographic imaging media to imaging radiation from a color master, said imaging media each comprising a finely-divided reversibly activatable photoconductor which is reversibly activatable by imaging radiation dispersed in a gelatin binder;

(b) developing under acidic conditions each of said imaging media in the presence of silver ions with a silver reducing agent and color coupler to thereby develop a silver image while simultaneously preventing color coupling;

(c) contacting said imaging medium with an alkaline solution to cause color coupling thereby generating diifusible cyan, magenta and yellow dye images in radiation-exposed portions of said respective media; and,

(d) transferring in register said cyan, magenta and yellow dye images to a receptor to form said full-color print.

3. A method of claim 2 wherein said imaging media contain color couplers in ballasted form, the couplers in said red-, .green-, and blue-media respectively generating difiusible cyan, magenta and yellow dyes upon reaction with developer under alkaline conditions.

4. A method of claim 3 wherein a second, competing, faster-acting color coupler which forms a non-ditfusible product upon reaction with developer is additionally present in said radiation-sensitive layers during development.

5. A method of claim 4 wherein said receptor comprises a mordanted receptor sheet.

6. A method of claim 5 including the additional step of hardening gelatin layers in said imaging media prior to transferring dye to said receptor sheet.

7. A method of claim 6 including the additional step of rinsing the imaging media in dilute acetic acid after color coupling but prior to transfer of the cyan, magenta and yellow dyes.

8. A method of claim 7 wherein said competing coupler comprises a-naphthol.

9. A method for forming a color dye-transfer print consisting essentially of:

(a) exposing a photographic imaging medium to actinic radiation, said imaging medium comprising a finelydivided reversibly activatable photoconductor which is reversibly activatable by actinic radiation;

(b) developing under acidic conditions the exposed portions of said medium in the presence of silver ions, a silver reducing agent and a color coupler to thereby develop a silver image while simultaneousl preventing color coupling;

(c) contacting exposed portions of said medium with an alkaline solution to cause color coupling thereby generating a diifusible dye image in radiation-exposed portions; and,

(d) transferring said dye image to a receptor to form a positive color print.

(References on following page) 12 OTHER REFERENCES Collins and Giles, The Journal of the Society of Dyers and Colourists, vol. 68, No. 11, p. 448, 1952.

l 1 References Cited UNITED STATES PATENTS 3:; Color Photography, Kirk-Othmer Encyclopedia of 10/1967 Land at 5 Chemical Technology, 2nd ed., vol. 5, p. 819.

5/1967 Land et a1. 963 8/1958 Whitmore CHARLES E. VAN HORN, Primary Examiner 12/1956 Rogers 9629 M. B. WITTENBERG, Assistant Examiner 7/1953 Land 95-2 10 U S C1 X R FOREIGN PATENTS 96 1 R 1 5 27 69 7;

Great Britain 9627

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