US3301772A - Electrolytic color development - Google Patents

Description

Jan. 31, 1967 F. VIRO 3,301,772

ELECTROLYTIC COLOR DEVELOPMENT Filed April 21,1965 3 Sheets-Sheet 1 L/ B o A O b o b 0 A MONOLAYER, MONOCOLOR COLORFORMER DISPERSED m EMULSION FIG] ' RECEIVING SHEET wm-l MULTICOLOR MULTILAYER WITH COLORFORMER IN OIL DISPERSED IN EMULSION INVENTOR.

FELIX VIRO ATTORNEYS ,2 AGEN T Jan. 3l, 1967 Filed April 21, 1965 FIGAI F. VIRO 3,301,772

ELECTROLYTIC COLOR DEVELOPMENT I 3 Sheets-Sheet 2 BLUE RED CLEAR PATTERN OPAQUE AREA l2a If o 0 0 YELLOW l7 YELLOW FILTER 0 0 o MAGENTA llb AN IIC COLOR DEVELOPED IN A LOW pH PRIMARY AROMATIC AMINO DEVELOPER FOR I TO 5 MINUTES I 22 v COUPLER TRANSFER TO THE IMAGE RECEIVING LAYER OF RECEIVING SHEET OF FIGURE 2 BY CONTACTING EX OSED AND FIRST DEVELOPED MULTILA ER FOR ITO 2 MINUTES AT HIGH pH WIJH A PRIMARY AROMATIC AMINO DEVELOPER BLUE GREEN RED OPAQUE CLEAR IN VEN TOR.

FELIX VIRO til ATTORNEYS AGENT United States Patent 3,301,772 ELECTROLYTIC COLOR DEVELOPMENT Felix Viro, Apalachin, N.Y., assignor to General Aniline & Film Corporation, New York, N .Y., a corporation of Delaware Filed Apr. 21, 1965, Ser. No. 454,240 8 Claims. (Cl. 204-2) This application is a continuation-in-part of my application, Serial No. 92,017, filed February 27, 1961, now abandoned.

This invention relates to color photography and the production of colored photographic images. More particularly, the invention relates to certain improvements in the development of color reproductions, especially positive color prints, of the type formed by the imagewise transfer of colorants from an exposed original photographic element to a receiving layer.

The formation of positive colored photographic images can be effected in numerous ways and the prior art has been cognizant of these techniques for a long time. A method much practiced today is based on the silver halide system of photography, wherein the production of a black and white image is utilized in such a manner as to regulate or control a concomitant colored image. The source of the colored image may be a color forming component, commonly incorporated in the photographic element. Such a color process is referred to as color development and depends on the reaction of the oxidation product of a primary aromatic amino developing agent with a color coupler to yield a subtractively colored dye image in situ with a black and white image. After removal of the negative silver image, the resulting negative dye image is utilized as a pattern to form a second positive color image which corresponds to the original color aspects of the subject being photographed. In the above described system, it is, of course, necessary to carry out two exposures in order to obtain a positive colored reproduction.

A more direct method for achieving a positive color reproduction makes use of a reversal development technique. In this system of forming :a positive colored image, a multilayer color photographic film is exposed and developed with a black and white silver halide developer, such as hydroquinone. The so-obtained negative silver image is then dissolved or otherwise removed in the usual manner, thereby leaving a silver halide image. This is next subjected to a high intensity n'on-imagewise exposure followed by development using a primary aromatic amino type developing agent, whereby color development takes place, the density of which is proportional to the residual silver halide and inversely proportional to the original exposure. After removal of the second silver image, there remains on the original photographic element a colored positive reproduction corresponding to the color aspects of the initial or first exposure.

In the above described method for attaining colored positive photographic reproductions, lengthy processing operations involving chemical solutions are required. In the former method, two separate exposures and developments are required before the final print bearing the colored reproduction is obtained. In the latter, i.e., the reversal development method, while not requiring the production of an internegative, does, however, necessitate two separate developments which are undesirably time consuming and uneconomical. Furthermore, unless prints are produced therefrom as an extra step, the images obtained by reversal development must be on a transparent for viewing through the base since, otherwise, the image would be reversed.

In the past few years, there has been a sharp increase in the demand for color prints which are of reasonably 3,301,772 Patented Jan. 31, 1967 good qualit but at the same time, modestly priced. As a consequence, considerable effort is being devoted to formulating inexpensive techniques for achieving positive colored photographic reproductions, particularly colored prints. One method which has been investigated for producing colored photographic prints utilizes a diffusing technique in combination with a transfer material for receiving the diffused image. According to this method, a colored positive image is formed by transferring residual or unused color developer and color coupler from an orig inal sensitive layer to a suitable receiving sheet after which coupling between the coupler and color former is caused to take place. The receiving layer is provided with an oxidizing agent, the purpose of which is to catalyze or bring about the color forming reaction. If this same process is utilized for producing multicolor positive images, a plurality of receiving sheets must be used, since a color separation dye image is formed in each receiving sheet, with the result that such sheets must be superimposed in order to produce the final colored reproduction. Although of academic interest, such a system is too complex for the commercial market, primarily because of the plurality of receiving sheets which make for a rather unwieldy and uneconomical operation. A later and improved color ditfusion process dispenses with the plurality of receiving sheets and substitutes a single light sensitive photographic element capable of recording all of the color aspects of the subject. The basis of the improved diffusion system is the utilization of color forming components, which are non-difi'usible during coating and negative development, but are rendered diff-usible under conditions of positive development. The colorless migrating coupler image is then converted into a visible dye image at the receiving sheet. For this purpose, the receiving sheet is conveniently provided with an oxidizing agent which oxidizes the paraphenylenediamine developer to the active coupling form for producing the aforedescribed positive dye image.

One of the primary disadvantages inherent in the color diffusion processes as above described is the high degree of discoloration due to the stain produced when excess color developer is decomposed by the oxidizing agent. As a consequence, the so-obtained color prints are poor in quality because of high background stain caused by oxidation of excess developer in these areas.

I have now discovered that colored positive photographic images can be produced utilizing the color dif fusion process without the need for an oxidizing agent which, as above pointed out, has the deleterious property of causing stain and discoloration in the final color prints and the provision of such an improved color diffusion process and compositions therefore constitute the principal object of this invention.

Another important object of the invention is a provision of a color diffusion transfer process utilizing color former components, the dilfusibility of which can be controlled by adjustments in pH.

Other objects and purposes will become manifest as the description proceeds.

In its broadest aspects, my invention is based on the finding that a diffusible colorant positive image remaining after negative development can be transformed by electrolytic oxidation into a visible colored positive image, thereby reproducing the primary colored aspects of the original subject. This new electrolytic process can be substituted or is applicable to any process which utilizes chemical oxidation in order to transform a diifusible positive image into a colored visible image. It can be used in the color transfer process in which a color former image diffuses imagewise to a transfer sheet whereby a visible positive image is produced by color coupling of the diffused coupler image with oxidized color developer.

Alternately, the diffusing positive image can be a leuco dye which on migrating to the transfer receiving material is transformed into a positive image by oxidation. In some cases, it is desirable to effect imagewise migration of a developer or a developing agent to a transfer layer having coupling components incorporated therein, whereby a colored image is produced by color development. My process is admirably suited for this latter system since the electric current is capable of bringing about coupling between the couplers and the transfer layer and the diffusing image of the developing agent. In all of these processes, wherein the diffusing positive image is chemically oxidized to produce a visible positive image, the chemical oxidizer can be replaced or substituted by the electrolytic oxidation method as herein described. The process requires a relatively low potential or voltage and is, therefore, adaptable for operating within a camera since the voltage can be provided by small dry cells of the type used in small flashlights.

The process as described herein can be operated with either direct current or alternating current at a potential of only a few volts. I prefer to employ direct current since the migrating positive image is accelerated to some extent when located in the direct current field, since it accelerates or hastens transfer of the diffusing image to the receiving material. The electrodes which are placed in direct contact with a layer which is to receive the diffusing image rnust be made of an element, the oxidation potentials of which are below the potential of the developer or leuco dye. For this purpose, I have found copper, platinum, carbon and similar materials to be suitable. In case it is desired to use direct current the anode or positive terminal is placed in contact with the receiving layer. Since the oxidation of color developer is an irreversible reaction, it is possible to employ a low voltage A.C. current to bring about oxidation of the color developer.

In practicing the invention, I prefer to utilize a color diffusion transfer system of the type described in U.S. application Serial No. 816,521, filed May 28, 1959, in the name of Andre K. Schwerin and Dewey M. Dumers. According to this application, a negative colored image is first formed by color forming development. The residual positive image composed of uncoupled color former is then caused to diffuse at elevated pH to a receiving sheet wherein the presence of a color developer the migrating positive color former image is converted to a positive colored dye image. The receiving sheet contains an oxidizing agent which oxidizes the color developer and thus provides the oxidized or reactive species of the developer which couples with the color former image. In the color diffusion transfer process as described herein, I employ, in lieu of the chemical oxidizers of the application, a low voltage electric potential applied to the receiving layer. The color developing agent is quickly and easily oxidized to the reactive form which then reacts with the diffused color former image with concomitant production of a positive colored photographic reproduction.

The color formers which are used in practicing the color diffusion process as described in the aforementioned application are especially designed for this system, it being particularly important that the couplers diffuse at higher pH, i.e., 12.5-13.0, but remain relatively immobile at lower pH values. Specifically, the color formers which are used in this diffusion process must possess the following attributes:

(1) Medium molecular weight (2) Freedom from water-solubilizing groups such as carboxy or sulfonic acid functions (3) Sufficient oil solubility to \be incorporated in resinous or oily packets (4) Contain such groups as phenolic or enolic hydroxy which form coupler salt at a high pH (12.5-13.0) which metal salt renders the color former molecules diffusible in aqueous medium (5) Produce non-diffusible dyes with conventional primary aromatic amino developing agents such as N-diethylp-phenylenediamine; N-ethyl-N-fi-hydroxy-ethyl-p-phenylenediamine and N-diethyl-3-methyl-p-phenylenediarnine, and the like Examples of couplers which can be utilized in connection with the above described color diffusion process can be formulistically depicted as follows:

(1 olrn o o H I o- NHC 0 H30 \N/ (II/- I occurs after the positive image is formed, the production of stain and discoloration is minimized. The instant technique, therefore, represents -a decided advance over the prior art in presenting a simplified method of producing positive colored photographic images without the need for several stages or processing. As has previously been pointed out, such conditions are especially important if colored prints are to be produced by development within the camera itself.

The invention will be more fully understood by reference to the accompanying drawings in which:

FIGURE 1 discloses in section an elevational view of a mono-layer containing on a clear film or paper support a coating of a gelatino silver halide emulsion having uniformly dispersed therein oily packets containing dissolved color former according to the invention;

FIGURE 2 shows in section an elevational view of a transfer sheet consisting of a conducting support having coated on one of its surfaces a receiving layer of gelatin or a similar photographic colloid carrier;

FIGURE 3 depicts in section an elevational view of a multilayer coating in which each of the layers contain a differently sensitized silver halide emulsion having uniformly dispersed therein oily packets of dissolved color former;

FIGURE 4 is a flow sheet illustrating the steps of: (A) Exposing,

(B) Color developing to a negative image the multilayer coating of FIGURE 3,

(C) Transferring the unreacted color former from the first development to the transfer sheet,

(D) Forming the colored positive photographic image produced by the coupling of the diffused color formers with electrolytically oxidized color developer,

FIGURES 5, 6 and 7 are schematic views, partly in cross-section, depicting various forms of electrodes in contact with the receiving sheet undergoing development.

' FIGURES 1 and 3 of the drawings are believed to be self-explanatory when his understood that reference character ltl'represents the base of the sensitized elements of FIGURES land 3. Reference character 11 represents the light-sensitive emulsion layers having distributed through the colloid carrier 14 oily packets of dissolved color former 12 and silver halide grains 13. FIGURE 2 depicts the receiving sheet 25 comprising the base 10a which carries thereon the receiving layer 15.

In FIGURE 4,,the multilayer coating depicted in FIG- 3 is exposed to a pattern representing the primary colored aspects'of a subject. Referring to the flow sheet, for FIGURE 4, A depicts the exposure step and the re cording of the latent primary images in the three sensitized layers. 16 represents a blue latent image, 17 the green and 18 the red. The opaque area of the pattern forms no images in the sensitized layer; under the clear area of the pattern, latent images are formed in each layer.

In accordance with the invention, the exposed photographic element of A is developed in a low pH primary aromatic amino developer for 1-5 minutes, whereby a negative colored image and a negative silver image is recorded at 20, the green image 21 and the red at 22. These are the subtractively dyed images of negative development and as dye images are non-diffusing under pH conditions of the first development. The exposed and first developed layer is then developed in a second developer containing a primary aromatic amino developing' agent under elevated pH conditions, whereby the couplers not utilized for dye formation in first development are rendered diffusible in the higher alkaline medium of the second development. After allowing second development to proceed for 1-2 minutes, the receiving sheet of FIGURE 2 is placed in contact with the upper layer of the exposed 3-layer coating whereby the migrating coupler image is imbibed on the image receiving layer of the receiving sheet. The receiving sheet, which now contains the diffused color former image in addition to imbibed c-olor developer, is placed between the electrodes of a low voltage potential wherein the anode is connected to the image receiving sheet and the cathode is connected to the support of the receiving sheet. Under the action of the low voltage current, the primary aro matic amino developing agent is oxidized to the reactive coupling form which reacts with the diffused color forming image to form on the receiving layer of visible positive colored reproduction of the original subject matter being photographed.

In carrying out the electrolytic development of the receiving sheet, the electrodes may consist of a pair of rollers 26 and 27 as shown in FIGURE 5, having electroconductive surfaces which are pressed against the opposite sides of the receiving sheet 25. The latter passes between the rollers as the latter rotate, the conductive surface of roller 26 being connected to the anode and that of roller 27 to the cathode of a source 28 of low DC. voltage. The sheet 25 has its base 10A in contact with the cathode roller 27, and its receiving layer 15 in contact with the anode roller 26.

Alternatively, as shown in FIGURE 6, the cathode roller 27 may be replaced by a cathode-connected plate 29 on which the receiving sheet 25 is supported with its base 10A in contact with plate 29. An anode-connected roller 30, similar to roller 26, is passed over the receiving surface 15 of the receiving sheet 25 to effect development thereof.

Instead, if desired, both rollers can be replaced by electrically conductive plates 31 and 32, connected respectively to anode and cathode of a low voltage D-.C. source, and pressed respectively against the receiving side 15 and the base 10A of the receiving sheet 25.

The rollers of FIGURES 5 and 6 are of such length, and the plates of FIGURES 6 and 7' of such dimensions, as to contact (progressively in the case of the rollers, and simultaneously in the case of the plates) the entire image-bearing area of the receiving sheet 25 when the latter is passed between or under the rollers or lies in contact with the plates.

The following examples will further explain the invention, although it is to be understood that the invention is not restricted to such examples.

Example I One coating was prepared in which the average size of the oily packet Was less than 1 micron. This coating was prepared by dissolving ten millimoles of a cyan color former of the following formula:

In 30 g. of tricresylphosphate and dispersing this solution in 120 ml. of a 6% aqueous gelatin solution to which had been added 0.5 ml. of lauryl sulfate (25% solution). Homogenation of the oily coupler solution was affected by agitation in a Waring Blendor. The dispersion obtained in this manner was then mixed by the gentle stirring with 300 g. of a gelatino silver chlorobromide emulsion containing 6% silver halide and the mixture coated on a clear filmbase such as cellulose triacetate. The usual coating finals known to the art can be incorporated at this point.

& After drying the coating was exposed in a step-wedge sensitometer and developed to maximum density for 5 minutes at 20 C. in the following developer:

Sodium hexametaphosphate 'g 1 Sodium sul-fite g 8 N-ethyl-N-fi-hydroxyethy1-p phenylene diann'ne -g 5 Sodium carbonate, monohydrate ..g 10 Sodium bromide g 1 Water to make cc 1000 This developer has a pH of 10.7.

The developed strip without washing is pressed into contact for 3 minutes with a transfer sheet of b aryta coated paper which had been previously presoaked for 5 minutes in a 2% solution of sodium hydroxide. Contact between the developed strip and transfer sheet is conveniently effected by means of power driven pressure rollers as is well known in the art. The purpose of presoaking the transfer sheet with alkali is to provide the necessary high pH :to effect diffusion of the coupler image. After aprpoximately 1 minute contact with the receiving layer, transfer of the coupler to the receiving sheet has reached equilibrium and the image receiving sheet is separated and brought in contact with {the electrodes connected to a low voltage D.C. source in such a manner that the anode is in immediate contact with the gel layer of the image receiving sheet. As electrodes there may be used any of the arrangements shown in FIGURES 5, 6 and 7. Under the action of the low voltage current, electrolytic oxidation of the developer takes place with immediate coupling mm the diffused color former image resulting in the production of a positive cyan colored image.

Example II Utilizing the procedure as given in Example I, a positive magenta image was produced by substituting a magenta color former of the following (formula:

The procedure and results paralleled those of Example I with the exception that the positive colored image was magenta.

Example III A yellow image was produced by following the procedure of Example I except the cyan color former of the first example was replaced by yellow color former of the following structure:

The results and procedure paralleled those of the first example with the exception that the positive color image was yellow.

Example IV This example i lustrates the utilization of a three-layer coating as illustrated in FIGURE 3 which is composed of three diiferently sensitized silver halide coatings on a base each coating sensitized one of the primary color regions of the visible spectrum. In preparing a multilayer color reproduction photographic element, a baryta treated paper base is coated with the composition described in Example I in which the silver bromo chloride emulsion containing 6% silver halide, is sensitized with a red sensitizer of the following structure:

S H300 I I OCHs t H t i l moo -o=oo 1 00113 On top of the red sensitive layer is applied a green sensitive layer which is the composition described in Example II wherein the silver halide is sensitized with a sensitizer for the green of the type described in US. Patent 2,295,- 276. On top of the green sensitive layer is applied a 3% gela-tino separation layer containing yellow colloidal silver as a yellow filter. The upper blue sensitive layer is formed by coating over the filter layer the silver halide yellow color former dispersion described in Example III. The resulting multilayer coating is illustrated in FIGURE 4 of the drawing. The dried coating is exposed to an image or a stepwedge sensitometer and processed in the following manner:

The exposed negative image was developed for 5 minutes at 25 C. in the solution of the following composition:

2-amino-S-diethylaminotoluene g 4.0 Sodium sulfite g Borax g 5 Sodium hydroxide g 1.5 Benzyl alcohol cc 3.0 Sodium bromide g 0.5 Water 1000 cc.

The developed image was then brought in contact with the receiving sheet in the following high pH developer:

2-amino-S-diethylaminotoluene g 4.0 Sodium sulfite g 20 Sodium hydroxide g Sodium iodide g 80 Water 1000 cc.

After three minute contact the receiver was separated and the positive image was developed electrolytically as described in Example I.

Example V Light-sensitive materials are prepared as in Examples I-IV, with the only exception of keeping silver halide and color former ratio in the emulsion to 8:1. In this case, the light-sensitive material, after receiving an imagewise exposure, was developed for 90 seconds in the following high pH developer, after which it was brought in contact with image receiving sheet and then was processed as described in Examples I-IV:

2-amino-5-diethylaminotoluene g 4.0 Sodium sulfite g Sodium hydroxide g 15 Sodium bromide g 2.5

Water 1000 cc.

A full colored reproduction of the original subject is reproduced on the receiving layer. It will be evident that the process contemplated herein can be brought about in a camera or similar copying device. The only requirements are the ability to expose the sensitized material, develop the same, and to contact the developed material at a high pH with a transfer sheet.

If it is desired to increase the rate of diffusion of the colorant image while effecting simultaneous development thereof, it is necessary to have in contact with the image receiving layer a material, the oxidation potential thereof being less than that of the oxidizable colorant. Specifically, a layer, having an oxidation potential as above described, can be interpolated between the image receiving layer and the support. Alternately, the support itself may be made of a material having the required oxidation potential Whereas most of the examples as described herein specify gelatin as the colloid carrier, it will be understood that other gelatin substitutes can be used and, in this connection, mention is made of polyvinyl alcohol, methyl cellulose, casein, and other gelatin substitutes well known to those skilled in the art. a

It may be added that the color formers which are employed are those which are capable of forming nondiffusing quinonimine or azomethine dye images upon color development with a primary aromatic amino developer. These color formers are pyrazolones, phenolic derivatives, or straight chain keto methylene compounds. They must not only possess such structural features but must also meet the attributes previously specified. By using a leuco dye, which is non-diffusing in the oxidized form, but diffusing in the leuco form at high pH,a color positive image could be obtained by a process similar to Example 1.. However, the developer solution would not include the color developer since the diffusing leuco image itself would be the source of a final colored positive image.

My electrolytic development process could be utilized to produce an image in light sensitive layers by the use of conventional color formers or leuco dyes if the light sensitive layers are capable of causing imagewise change in conductivity of the colloid layer, upon exposure to light, heat or other source of radiant energy.

Modifications of the invention will occur to persons skilled in the art and I, therefore, do not intend to be limited in the patent granted except as necessitated by the appended claims.

. I claim:

1. A process of forming a positive multicolor photographic reproduction which comprises exposing to the color aspects of a subject a photographic material comprising a suitable support carrying at least one light sensitive photographic silver halide emulsion layer, containing a coupler compound capable of forming a dye when reacted with the oxidation products of a primary aromatic amino silver halide developing agent, and said coupler compound being characterized by relatively high diffusibility at elevated pH, developing the exposed emulsion layers in the presence of said developing agent at a pH below 12.5, to form non-dilfusible dye images in those areas corresponding to light-exposure, transferring the diffusible invisible positive image of color coupler by imbibition at an elevated pH above 12.5 to a receiving layer having therein a primary aromatic amino silver halide developing agent, applying a relatively low voltage electrical potential to the total moist surface of said receiving layer, the potential of which is sufiicient to bring about electrolytic oxidation of the developing agent to form oxidized developing agent which reacts with the positive image of diffusing color former to produce a positive dye image corresponding to the color aspects of the subject.

2. A process of forming a positive multicolor photographic reproduction which comprises exposing to the color aspects of a subject, a photographic material comprising a suitable support carrying at least two superhuposed silver halide emulsion layers sensitized to different regions of the electromagnetic visible spectrum, each layer being further provided with a different coupler compound capable of forming a dye when reacted with the oxidation products of a primary aromatic amino silver halide developing agent, and said coupler compound being characterized by relatively high dilf-usibility at elevated pH, developing the exposed emulsion layers in the presence of said developing agent at a pH below 12.5, to form non-difliusible dye images in those areas corresponding to light exposure, transferring the difl usible invisible positive images of the color couplers by imbibition at an elevated pH above 12.5 to a receiving layer having therein a primary aromatic amino silver halide developing agent, applying a relatively low voltage electrical potential to the moist imbibed surface of said receiving layer, the potential of which is sulficient to bring about electrolytic oxidation of the developing agent to form oxidized developing agent which reacts with the positive image of the diffusing color formers to produce a positive dye image corresponding to the color aspects of the subject.

3. A process of torming a positive multicolor photographic reproduction which comprises exposing imagewise to a col-or object a photographic material comprising a suitable support, three superimposed silver halide emulsion layers sensitized to dilferent regions of the visible spectrum, each layer containing a color ttormer capable of forming when reacted with the oxidation products of a primary aromatic amino silver halide developing agent, a dye image complementary in color to that color to which silver halide emulsion layer is sensitized, and wherein the lowest emulsion layer is sensitized to red light and contains a color former capable of forming a cyan image, a middle layer sensitized to green light and containing a color former capable of forming a magneta image, and a top layer sensitive to blue light and containing a color former capable of forming a yellow image, said color tiormers being characterized by a relatively high diffusibility at a pH above 12.5; developing the exposed emulsion layers in the presence of said developing agent or a pH ibelow 12.5 to form non-diffusible dye images in those areas exposed by light, transferring by imbibition in a medium having a pH above 12.5 the ditEusi-ble residual color formers in the unexposed areas to the total wet surface a receiving layer having therein a primary aromatic amino silver halide developing agent; applying uniformly a relatively low voltage electrical potential to the imbided moist surface of said receiving layer, the potential of which is sufficient to bring about electrolytic oxidation of the developing agent to 'form the 12 oxidized developing agent which reacts with the difi'used color formers to produce a positive multicolor dye image corresponding to the color aspects of the subject in the receiving layer.

4. The prcess according to claim 2 wherein the photographic element comprises three superimposed silver halide photographic layers each sensitized to one of the primary colors of the electromagnetic visible spectrum, and each emulsion layer having a color coupler compound capable of forming substractively color dye images on first development.

5. A process as defined Iby claim 3, wherein a yellow filter layer is interposed between the green sensitive layer and the blue .sensitive layer.

6. A process as defined in claim 2, wherein the low voltage electrical potential is provided by a direct current source.

7. A process as defined in claim 6, wherein the anode of that direct current source is applied to that side of the image receiving sheet which faces the multilayer material and to which the diffused color formers are transferred.

8. A process as defined by claim 2, wherein the low voltage electrical potential is provided by an alternating current source.

References Cited by the Examiner UNITED STATES PATENTS 2,43 0,254 ll/ 1947 Solomon 204Z 2,756,142 7/ 1956 Yutzy 96--3 3,220,836 11/ 1965 Fair-bank 96-29 FOREIGN PATENTS 3 ,47 8 11/ 1960 Great Britain.

NORMAN G. TORCHIN, Primary Examiner.

J. TRAVIS BROWN, Examiner.

Claims (1)

1. A PROCESS OF FORMING A POSITIVE MULTICOLOR PHOTOGAPHIC REPRODUCTION WHICH COMPRISES EXPOSING TO THE COLOR ASPECTS OF A SUBJECT A PHOTOGRAPHIC MATERIAL COMPRISING A SUITABLE SUPPORT CARRYING AT LEAST ONE LIGHT SENSITIVE PHOTOGRAPHIC SILVER HALIDE EMULSION LAYER, CONTAINING A COUPLER COMPOUND CAPABLE OF FORMING A DYE WHEN REACTED WITH THE OXIDATION PRODUCTS OF A PRIMARY AROMATIC AMINO SILVER HALIDE DEVELOPING AGENT, AND SAID COUPLER COUMPOUND BEING CHARACTERIZED BY ELATIVELY HIGH DIFFUSIBILITY AT ELEVATED PH, DEVELOPING THE EXPOSED EMULSION LAYERS IN THE PRESENCE OF SAID DEVELOPING AGENT AT A PH BELOW 12.5, TO FORM NON-DIFFUSIBLE DYE IMAGES IN THOSE AREAS CORRESPONDING TO LIGHT-EXPOSURE, TRANSFERRING THE DIFFUSIBLE INVISIBLE POSITIVE IMAGE OF COLOR COUPLER BY IMBIBITION AT AN ELEVATED PH ABOVE 12.5 TO A RECEIVING LAYER HAVING THERIN A PRIMARY AROMATIC AMINO SILVER HALIDE DEVELOPING AGENT, APPLYING A RELATIVELY LOW VOLTAGE ELELCTRICAL POTENTIAL TO THE TOTAL MOIST SURFACE OF SAID RECEIVING LAYER, THE POTENTIAL OF WHICH IS SUFFICIENT TO BRING ABOUT ELECTROLYTIC OXIDATION OF THE DEVELOPING AGENT TO FORM OXIDIZED DEVELOPING AGENT WHICH REACTS WITH THE POSITIVE IMAGE OF DIFFUSING COLOR FORMER TO PRODUCE A POSITIVE DYE IMAGE CORRESPONDING TO THE COLOR SPECTS OF THE SUBJECT.

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