US3833370A - Color diffusion transfer with development controlling polymeric salt - Google Patents

Abstract

Color diffusion transfer processes are carried out in the presence of a salt whose anion is derived from an immobile polymeric acid and whose cation is derived from a reagent adapted to control the development of silver halide.

Description

United States Patent Sahatjian [451 Sept. 3, 1974 [54] COLOR DIFFUSION TRANSFER WITH 3,575,699 4/1971 Bloom et all 96/3 DEVELOPMENT CONTROLLING 3,598,600 8/1971 Tuites et al. 96/109 3,754,910 8/1973 Taylor 96/3 POLYMERIC SALT Ronald A. Sahatjian, Bedford, Mass.

Polaroid Corporation, Cambridge, Mass.

Filed: Jan. 5, 1973 Appl. No.: 321,289

Inventor:

Assignee:

US. Cl 9673, 96/29 D, 96/77, 96/95, 96/109, .96/119 R Int. Cl. G03c 7/00, G03c 5/54, G03c 1/40, GO3C 1/06, G03c l/34 Field of Search 96/3, 29 D, 77, 95, 109

'- References Cited UNITED STATES PATENTS 10/1969 Rogers 96/3 Primary Examiner-Ronald H. Smith, I Assistant Examiner-Richai'd L. Schilling' Attorney, Agent, or Firm-Mart C. Matthews [57] ABSTRACT Color diffusion transfer processes are carried out in the presence of a salt whose'anion is derived from an immobile polymeric acid and whose cation is derived from a reagent adapted to control the development of silver halide.

46 Claims, No Drawings COLOR DIFFUSION TRANSFER WITH DEVELOPMENT CONTROLLING POLYMERIC SALT BACKGROUND OF THE INVENTION Various diffusion transfer systems for forming color images have heretofore been disclosed in the art and need not be described in detail in this application. Generally speaking, such systems rely for color image formation upon a differential in mobility or solubility of a dye image-providing material obtained as a function of development of exposed silver halide so as to provide an imagewise distribution of such material which is more diffusible and which is therefore selectively transferred, at least in part, by diffusion, to a superposed dyeable stratum to impart thereto the desired color transfer image. The differential in mobility or solubility may, for example, be obtained by a chemical action such as a redox reaction or a coupling reaction.

In any of these systems, multicolor iamges are obtained by employing a film unit containing at least two selectively sensitized silver halide emulsions each having associated therewith a dye image-providing material exhibiting desired spectral absorption characteristics. The most commonly employed elements of this type are the so-called tripack structures employing a blue-, a greenand a red-sensitive silver halide layer having associated therewith, respectively, a yellow, a magenta and a cyan dye image-providing material.

A particularly useful system for forming color images by diffusion transfer is that described in U.S. Pat. No. 2,983,606, employing dye developers (dyes which are also silver halide developing agents) as the dye imageproviding materials. In such systems, a photosensitive element comprising at least one silver halide layer having a dye developer associated therewith (in the same or in an adjacent layer) is developed by applying an aqueous alkaline processing composition. Exposed and developable silver halide is developed by the dye developer which in turn becomes oxidized to provide an oxidation product which is appreciably less diffusible than the unoxidized dye developer, thereby providing an imagewise distribution of diffusible dye developer in terms of unexposed areas of the silver halide layer, which imagewise distribution is then transferred, at least in part, by diffusion, to a dyeable stratum to impart thereto a positive dye transfer image. Multicolor images may be obtained with a photosensitive element having two or more selectively sensitized silver halide emulsions and associated dye developers, a tripack structure of the type described above and in various patents including the aforementioned U.S. Pat. No. 2,983,606 being especially suitable for accurate color recordation of the original subject matter.

A number of diffusion transfer photographic processes have been proposed wherein the resulting photograph comprises the developed silver halide emulsions retained with the dye-image carrying layer as part of a permanent laminate. The image-carrying layer is separated from the developed silver halide emulsions in said laminate by a light-reflecting layer, preferably a layer containing titanium dioxide. Illustrative of patents describing such products and processes are the aforementioned US. Pat. No. 2,983,606 issued Mar. 9, 1961 to Howard G. Rogers, US. Pat. Nos. 3,415,644, 3,415,645 and 3,415,646 issued Dec. 10, 1968 to Edwin H. Land, US. Pat. Nos. 3,594,164 and 3,594,165 issued July 20, 1971 to Howard G. Rogers,

and US. Pat. No. 3,647,347 issued Mar. 7,, 1972 to Edwin H. Land.

In the course of the above-described diffusion transfer processes, it is frequently desirable to have certain reagents present so as to modify the photographic and other properties of the transfer image, In particular, for example, one may wish to include a reagent which controls or modifies the development of developable silver halide to obtain advantageous photographic results. As examples of these reagents, mention may be made of the various development restrainers or arrestors, antifoggants, etc., known to the art. Such development controlling reagents, however, may be capable of having additional and undesired effects if they are available too early in the process cycle or at too high a concentration, since these reagents frequently form relatively insoluble products with silver halide and could interfere with the desired development of the exposed silver halide. While some reagents of this type are most effective for their intended purpose if used in relatively larger quantities at higher temperatures than at room temperature, efforts to incorporate such larger quantities initially in the processing composition frequently result in a reduction in the sensitivity or speed of the photosensitive element or other undesirable consequences.

Methods have been proposed in the art for employment with multi-layered diffusion transfer film units employing a common processing composition wherein the particular reagent is made available or released to the silver halide only after a predetermined period of time has elapsed from the application of the processing composition. As disclosed in US. Pat. No. 3,265,498, a reagent may be employed in a chemical form or in a physical location such that its availability to the developable silver halide is limited or restricted, e. g., as a result of the distance through which it must diffuse to reach the developing silver halide, or as a consequence of a significantly lower diffusion rate than the developing agents. Thus, for example, US. Pat. Nos. 3,265,498

and 3,575,699 and copending applications of Bloom et al., Ser. No. 60,272, filed Aug. 3, 1970 and Rickter, Ser. No. 214,665 filed Jan. 3, 1972 all teach the use of hydrolyzable reagents, i.e., reagent precursors which are substantially non-diffusible or at least substantially less diffusible in their unhydrolyzed form than in their hydrolyzed form. The reagent is therefore made available after the predetermined period by hydrolysis of the precursor by the aqueous processing composition. However, this reliance on hydrolysis for reagent release has certain disadvantages, especially in high humidity environments where unintentional hydrolysis and undesirable migration may occur or in extremes of temperature where the rate of hydrolysis may be effected.

It has been proposed in the art, for example, in the copending application of Dec. et al., Ser. No. 263,539, filed June 16, 1972, to incorporate an onium salt of a polymeric anion in the film unit, preferably in the photosensitive element, in order to make the onium compound available immediately, yet avoid deleterious interaction with other components in the system during storage. However, it should be noted that the purposes of the processes described in the last-mentioned application are quite different from the present invention in that no delay in the release of the reagent is desired or suggested.

BRIEF SUMMARY OF THE INVENTION The present invention makes it possible to control and preferably delay the availability of a reagent which controls the development of silver halide during the above-described color diffusion transfer processes. This result is achieved by carrying out the processes in the presence of a salt comprising an anion derived from a polymeric acid which is not diffusible from its location in the film unit and a cation derived from the development-controlling reagent. Upon contact with the processing composition, the reagent cation is rendered free to participate in the process. In accordance with this invention, a delay in the availability of a reagent may be effected, which delay is particularly valuable in the use of reagents tending to adversely affect image characteristics if made available in too large a quantity or too early in the process.

In a preferred embodiment, the polymeric acid anion is contained in a neutralizing layer of the imagereceiving element whose function is to lower the environmental pH of the film unit after a predetermined period of time, thereby taking advantage of the timing mechanisms already available in the film unit to control the timing of pH reduction. The salts of the present invention are not prone to the deficiencies of the hydrolyzable development restrainers with respect to high humidity and storage contamination in unitary film structures and have been found to be effective at high processing temperatures, for example, above 75 F. and especially over 100 F.

DESCRIPTION OF THE PREFERRED EMBODIMENT As indicated above, the present invention is directed to carrying out the color diffusion transfer processes previously described in the presence of a salt which comprises an anion derived from an immobile polymeric acid and a cation derived from a reagent adapted to control the development of silver halide.

It has been stated that the employment of such a development controlling reagent in.color diffusion transfer processes is particularly desirable if the reagent is made available in a controlled manner at a predetermined time. By means of the present invention, an advantageous and controlled release of the reagent may be accomplished, yet this reagent is provided in such a chemical form that it can be conveniently disposed in the film unit, particularly an integral positive-negative film unit, in a photographically inactive or unavailable state as a consequence of its non-diffusible polymeric anion, thus insuring the desired stability and sensitivity of the film unit upon prolonged storage. The active development controlling function is effectively rendered unavailable in the salt form with respect to premature interaction with the silver halide, i.e., what is referred to as contamination effects are avoided. However, the cation of the salt is made readily available to diffuse in the processing composition to the silver halide upon contact with the alkali of the processing composition.

Generally speaking, the salts of the present invention comprise the reaction product of an immobile polymeric acid and a development controlling reagent, both of which are described in greater detail hereinbelow.

These salts are believed to be formed as a result of the loss of the acid hydrogen of one or more of the pendant acid groups of the polymeric acid to form a negatively charged radical, i.e., an anion, and the subsequent replacement of that hydrogen by a positively charged radical, i.e., a cation, derived from the protonation of the development restrainer.

Reagents which are suitable for forming cations within the scope of this invention are derived from a wide variety of known compounds which control the development of silver halide. In general, these reagents will form products or complexes with undeveloped silver halide, whether exposed or unexposed, which products are substantially less developable either photolytically or by a silver halide developing agent, e.g., by a dye developer, and which are substantially insoluble,

and hence essentially non-diffusible, i.e., diffusible only with difficulty. Illustrative examples of such reagents are the so-called development arrestors, antifoggants,

etc.

The selected reagent must also be capable of protonation at a pH provided by the polymeric acid employed, i.e., a pH below 7, and most preferably in the range of about 2 to about 5, in order to form a salt within the context of this invention.

Particularly useful reagents described in the art as performing development controlling functions may be characterized as azole compounds, i.e., compounds having a 5-membered ring containing at least one atom of nitrogen. As examples of such azole compounds mention may be made of the various imidazoles, triazoles and tetrazoles known to the art and, especially in diffusion transfer systems, the 4-azabenzimidazoles such as disclosed in US. Pat. Nos. 3,473,924 and 3,687,660. Numerous examples of such reagents are described in the diffusion transfer art and those skilled in this art may readily select compounds which may be usefully employed by following the teachings of this invention.

One group of preferred reagents for the practice of this invention is disclosed in the copending application of Land et al, Ser. No. 246,669, filed Apr. 24, 1972 and its parent application Ser. No. 211,718, filed Dec. 23, 1971, now US. Pat. No. 3,785,814. These reagents may be generically described as 6-alkylamino purines of the formula:

LNJLN/ wherein R is an alkyl group, it being understood that alkyl is intended to include aralkyl, such as OCH:

Where the alkyl group is a simple alkyl group, better results are generally obtained when the alkyl group contains more than one or two carbons. As will be apparent from the above, the alkyl group may be substituted, e.g., by halogen, alkoxy, etc.

The above compounds have found advantageous employment with sulfur-free silver solvents such as 6- methyl uracil to prevent undesired reactions in integral film units, such as photolytic darkening of white areas, as described in detail in the application Ser. No. 21 1,718 mentioned above. In addition, the 6- alkylamino purines also have been found to be extremely effective in maintaining maximum dye density in dye developer transfer images, particularly when processing is conducted at temperatures above room temperature, i.e., at temperatures above 75 F. These reagents are soluble in alkaline media and have been advantageously disposed in the processing composition. They have been found to be useful without conventional antifoggants also being present, although such antifoggants may be useful in varying the sensitometry of a given photographic system.

The compound providing the anion in the present invention may be selected from a variety of immobile or non-diffusible polymeric organic acids, that is, those acids having a polymeric backbone with pendant acid groups thereon such as carboxyl groups, sulfonic acid groups, and the like. Most preferably, as will be described in more detail hereinafter, the salt comprising an anion of the polymeric acid and a cation of a reagent described above is employed as an acid-reacting reagent in a layer of the film unit which is adapted to lower the environmental pH after a predetermined period of time. An extensive listing of polymeric acids suitable for this pH reduction function and contemplated as useful in the practice of this invention may be found, for example, in U.S. Pat. No. 3,362,819. The most useful acid polymers are characterized as providing free acid groups, for example, carboxyl groups, and as being substantially non-diffusible in an aqueous medium, yet having solubility in a solvent which is sufficiently polar to allow the formation of a salt with one of the abovedescribed reagents. The polymeric acid selected should provide a pH sufficient to protonate the reagent, Le, a pH below 7 and most preferably a pH in the range from about 2 to about 5. As examples of specific polymeric acids contemplated as suitable for use in this invention, mention may be made of polystyrene sulfonic acid, polyacrylic acid, and acid derivatives of methyl vinyl ether/maleic anhydride and poly (ethylene/maleic anhydride).

The present invention is applicable to a wide variety of color diffusion transfer processes and the arrangement and order of the individual layers of the film used in such color processes may vary in many ways as is known in the art. For convenience, however, the more specific description of the invention may be by use of the preferred dye developer diffusion transfer color processes and of integral negative-positive film units of the type contemplated in the previously mentioned U.S. Pat. No. 3,415,644.

In such color diffusion transfer systems, color transfer images are obtained by exposing a photosensitive element, sometimes referred to as a negative component, comprising at least a light-sensitive layer, e.g., a gelatino silver halide emulsion layer, having an image dye-providing material associated therewith in the same or in an adjacent layer, to form a developable image; developing this exposed element with a processing composition to form an imagewise distribution of a diffusible image dye-providing material; and transferring this imagewise distribution, at least in part, by diffusion, to a superposed image-receiving element, sometimes referred to as a positive component, comprising at least a dyeable stratum to provide a color transfer image. The negative and positive components initially may be carried on separate supports which are brought together during processing and thereafter retained together as the final integral negative-positive reflection print, or preferably they may initially comprise a unitary structure, e.g., integral negative-positive film units wherein the negative and positive components are part of a photosensitive laminate or they may otherwise be physically retained together in superposed relationship prior to, during and after image formation. (Procedures for forming such film units wherein the positive and negative components are temporarily laminated together prior to exposure are described, for example in U.S. Pat. No. 3,652,281 to Albert J. Bachelder and Frederick J. Binda and in U.S. Pat. No. 3,652,282 to Edwin H. Land, both issued Mar. 28, 1972). In the preferred embodiments, the positive component is not removed from the negative component for viewing purposes, although this invention is'contemplated as suitable for those diffusion transfer processes where this occurs. The preferred film units comprise a plurality of layers including a negative component comprising at least one light-sensitive silver halide and associated dye-developer as the dye image-providing material and a positive component comprising at least a dyeable stratum. As indicated above, these components may be laminated together or otherwise secured together in physical juxtaposition as an essentially integral structure. Film units intended to provide multicolor images comprise two or more selectively sensitized silver halide layers each having associated therewith an appropriate dye-developer providing an image dye spectral absorption characteristics substantially complementary to the light by which the associated silver halide is exposed. The most commonly employed negative components for forming multicolor images are of the tripack structure and contain blue-, greenand red-sensitive silver halide layers each having associated therewith in the same or in a contiguous layer a yellow, a magenta and a cyan dye-developer respectively. Interlayers or spacer layers may, if desired, be provided between the respective silver halide layers and associated dyedevelopers or between other layers.

In addition to the aforementioned layers, such film units further include means for providing a reflecting layer between the dyeable stratum and the negative component in order to mask effectively the silver image or images formed as a function of development of the silver halide layer or layers and also to mask image dyeproviding material which is not transferred, thereby providing a background, preferably white, for viewing the color image formed in the dyeable stratum, without separation, by reflected light. This reflecting layer may comprise a preformed layer of a reflecting agent included in the film unit or the reflecting agent may be provided after photoexposure, e. g., by including the reflecting agent in the processing composition. The dye transfer image is then viewable through a dimensionally stable protective layer or support. Most preferably another dimensionally stable layer or support, which may be transparent or opaque, is positioned on the opposed surface so that the aforementioned layers are between a pair of dimensionally stable layers or support members, one of which is transparent to permit viewing therethrough of the color transfer image.

The liquid processing composition referred to for effecting multicolor diffusion transfer processes comprises at least an aqueous solution of an alkaline material, for example, sodium hydroxide, potassium hydroxide, and the like, and preferably possessing a pH in excess of 12, and most preferably includes a viscosityincreasing compound constituting a film-forming material of the type which, when the composition is spread and dried, forms a relatively firm and relatively stable film. The preferred film-forming materials disclosed comprise high molecular weight polymers such as polymeric, water-soluble ethers which are inert to an alkaline solution such as, for example, a hydroxyethyl cellulose or sodium carboxymethyl cellulose. Other filmforming materials or thickening agents whose ability to increase viscosity is substantially unaffected if left in solution for a long period of time are also capable of utilization. As stated, the film-forming material is preferably contained in the processing composition in such suitable quantities as to impart to the composition a viscosity in excess of 100 cps. at a temperature of approximately 24 C. and preferably in the order of 100,000 cps. to 200,000 cps. at that temperature.

A rupturable container of known description contains the requisite processing composition and is adapted upon application of pressure to release its contents for development of the exposed film unit, e.g., by distributing the processing composition in a substantially uniform layer between a pair of predetermined layers. In film units providing an integral negativepositive reflection print, a processing composition containin g a white pigment may be distributed between the dyeable stratum and the negative component to provide the light-reflecting layer.

A preferred opacification system to be contained in the processing composition to effect processing outside of a camera is that described in the above-mentioned U.S. Pat. No. 3,647,437, and comprises a dispersion of an inorganic light-reflecing pigment which also contains at least one light-absorbing agent, i.e., optical filter agent, at a pH above the pKa of the optical filter agent in a concentration effective when the processing composition is applied, to provide a layer exhibiting optical transmission density greater than about 6.0 density units with respect to incident radiation actinic to the photosensitive silver halide and optical reflection density greater than about 1.0 density units with respect to incident visible radiation.

In lieu of having the light-reflecting pigment in the processing composition, the light-reflecting pigment used to mask the photosensitive strata and to provide the requisite background for viewing the color transfer image formed in the receiving layer may be present initially in whole or in part as a preformed layer in the film unit. As an example of such a preformed layer, mention may be made of that disclosed in U.S. Pat. No. 3,165,421 issued Oct. 26, 1971 and in U.S. Pat. No. 3,620,724 issued Nov. 16, 1971, both in the name of Edwin H. Land. The reflecting agent may be generated in situ as is disclosed in U.S. Pat. Nos. 3,647,434 and 3,647,435, both issued Mar. 7, 1972 to Edwin H. Land.

The dye developers (or other image dye-providing substances) are preferably selected for their ability to provide colors that are useful in carrying out subtractive color photography, that is, the previously mentioned cyan, magenta and yellow. They may be incorporated in the respective silver halide emulsion or, in the preferred embodiment, in a separate layer behind the respective silver halide emulsion. Thus a dye developer may, for example, be in a coating or layer behind the respective silver halide emulsion and such a layer of dye developer may be applied by use of a coating solution containing the respective dye developer distributed, in a concentration calculated to give the desired coverage of dye developer per unit area, in a filmforming natural, or synthetic, polymer, for example, gelatin, polyvinyl alcohol, and the like, adapted to be permeated by the processing composition.

Dye developers are compounds which contain the chromophoric system of a dye and also a silver halide developing function. By a silver halide developing function is meant a grouping adapted to develop exposed silver halide. A preferred silver halide development function is a hydroquinonyl group. Other suitable developing functions include ortho-dihydroxyphenyl and ortho-and para-amino substituted hydroxyphenyl groups. In general, the development function includes a benzenoid developing function, that is, an aromatic developing group which forms quinonoid or quinone substances when oxidized.

The dyeable stratum, or image-receiving layer, may comprise one of the materials known in the art, such as polyvinyl alcohol, gelatin, etc. It may contain agents adapted to mordant or otherwise fix the transferred image dye(s). Preferred materials comprise polyvinyl alcohol or gelatin containing a dye mordant such as poly-4-vinylpyridine, as disclosed in U.S. Pat. No. 3,148,061, issued Sept. 8, 1964 to Howard C. Haas. If the color of the transferred image dye (s) is affected by changes in pH, the pH of the image layer may be adjusted to provide a pH affording the desired color.

The nature of the chemical form in which the development controlling reagent is provided in the present invention allows for great flexibility in its utilization and placement in the film unit. This flexibility enables the operator to vary substantially the timing of the release of development controlling reagent, and the quantity made available to the silver halide, in accordance with, for example, the sensitometry desired or the processing temperatures to be encountered.

In the various color diffusion transfer systems which have previously been described and which employ an aqueous alkaline processing fluid, it is well known to employ an acid-reacting reagent in a layer of the film unit to lower the environmental pH following substantial dye transfer in order to increase the image stability and/or to adjust the pH from the first pH at which the image dyes are diffusible to a second (lower) pH at which they are not. For example, the previously mentioned U.S. Pat. No. 3,415,644 discloses systems wherein the desired pH reduction may be effected by providing a polymeric acid layer adjacent the dyeable stratum. These polymeric acids may be polymers which contain acid groups, e.g., carboxylic acid and sulfonic acid groups, which are capable of forming salts with alkali metals, such as sodium, potassium, etc., or with organic bases, or potentially acid-yielding groups, such as anhydrides or lactones, or other groups which are capable of reacting with bases to capture and retain them. The acid-reacting group is, of course, non-diffusible from the acid polymer layer.

As previously indicated, the salt of the present invention is preferably disposed in this neutralizing layer, and most preferably the above-mentioned polymeric acid of the neutralizing layer serves to provide the anion of the salt. Preferably, all of the free acid groups of the selected polymeric acid are not converted to the salt form in this embodiment of the invention. However, essentially all of the acid groups may be so converted, if desired, since the acid groups neutralized by salt formation are still available to capture alkali ion from the processing composition by cation exchange to accomplish the pH reduction function of the neutralizing layer. The acid salts are preferably formed by reacting somewhat less than a stoichiometric quantity of the selected reagent with the polymeric acid of the neutralizing layer. For convenience, this reaction may be carried out in the medium which serves as the coating solution for the neutralizing layer prior to its coating. As previously noted, it is contemplated that the salt of this invention may be disposed in a variety of locations in the film unit, in which case the salt may be formed apart from a coating solution and subsequently'distributed in the coating solution of any appropriate layer.

It will be appreciated that in the preferred embodiment described above the amount or degree to which the active hydrogens of the polymeric acid are replaced with the reagent cation will be at least in part dependent upon the amount of reagent needed in the particular film unit and system in which these salts are employed. The lesser the amount of this replacement the fewer the reagent cations which will be present for a given coverage of the acid salt. It will be readily apparent that the appropriate amount of reagent needed may be determined by routine experimentation.

The pH of the processing composition may be of the order of at least 12 to 14, and it preferably contains a larger concentration of sodium and/or potassium ions. The neutralizing layer should therefore contain at least sufficient acid groups to effect a reduction in the pH of the image layer from a pH of about 12 to 14 to a pH of at least 1 l or lower at the end of the imbibition period, and preferably to a pH of about to 8 within a short time after imbibition, thus requiring, of course, that the acidic action of the salt of this invention be accurately so controlled as not to interfere with either development of the negative or image transfer of the color-providing material. For this reason, the pH of the image layer should be kept ata functional transfer level until dye image has been formed. Where the colorproviding material is not diffusible at the lower pH obtained by the polymeric acid layer, the subsequent pH reduction, in addition to its desirable effect upon image light stability, also serves a highly valuable photographic function by substantially terminating further dye transfer.

In order to prevent premature pH reduction during transfer processing, or premature release of the devel opment controlling reagent cation, the acid groups may be so distributed in the neutralizing layer that the rate of their availability to the alkali is controllable, e.g., as a function of the rate of swelling of the polymer layer which rate in turn has a direct relationship to the diffusion rate of the alkali ions. The desired distribution of the acid groups in the acid polymer layer may be effected by mixing the acid polymer with a polymer free of acid groups, or lower in concentration of acid groups, and compatible therewith, or by using an acid polymer having a relatively lower proportion of acid groups.

The layer containing the polymeric acid may also contain a water-insoluble polymer, preferably a cellulose ester, which acts to control or modulate the rate at which the alkali reacts with the acid groups, free or neutralized by salt formation. As examples of cellulose esters contemplated for use, mention is made of cellulose acetate, cellulose acetate butyrate, etc. The particular polymers and combinations of polymers employed in any given embodiment are, of course, selected so as to have adequate wet and dry strength and when necessary or desirable, suitable subcoats are employed to help the various polymeric layers adhere to each other during storage and use.

in addition, an inert interlayer or spacer layer also may be and is preferably disposed between the neutralizing layer and the dyeable stratum in order to control or time the pH reduction so that it is not premature and interfere with the development process. Suitable spacer or timing layers for this purpose are described with particularity in U.S. Pat. Nos. 3,362,819; 3,415,644; 3,419,389; 3,421,893; 3,455,686; and 3,575,701. v

This timing is disclosed as being a function of the rate at which alkali diffuses through the inert spacer layer. It has been found that the pH does not drop until the alkali has passed through the spacer layer, i.e., the pH is not reduced to any significant extent by the mere diffusion into the timing layer, but the pH drops quite rapidly once the alkali diffuses through this spacer layer. The timing layer preferably comprises a permeable polymeric film-forming material whose permeability characteristics may be either directly or inversely dependent on changes in temperature as described in detail in the aforementioned U.S. Patents.

In the context of the present invention, the permeability characteristics exhibited by the timing layer as a function of temperature is a matter of choice for one practicing the invention, depending in a large part on the intended function of the development controlling reagent being introduced. To illustrate, a reagent may be desired to be made available in increasingly larger quantities as the processing temperature increases so as to reduce the fog associated with the higher temperatures, and thus maintain transfer image density. Such a high temperature antifoggant may require the selection of a timing layer whose permeability increases in direct relation with the processing temperature so as to make more of the reagent available at higher temperatures. On the other hand, if the reagent introduced into the process is for another purpose, for example, for arresting all development of silver halide after a predetermined period of time, increased permeability of the timing layer with temperature would most likely result in the premature introduction of the reagent thereby interfering with the desired imagewise development of silver halide. With such a development arrestor, therefore, one may desire a temperature-inverting timing layer whose permeability decreases under conditions of increasing temperature.

The salts of this invention may be applied in accordance with conventional coating techniques. It is most preferable to employ polymeric salts which are watersoluble and which may therefore be formed in aqueous coating solutions, thereby obviating the need for organic solvents and the obvious manufacturing disadvantages inherent in the use of organic coating solutions, e.g., the need for special equipment to handle these solvents which are typically volatile, including the storage thereof before use, and the involved danger in the use of such solvents. However, the coating disadvantages do not preclude the use of water-insoluble polymeric salts which need be coated from organic solutions, and from a photographic standpoint, these water-insoluble salts may be equally applicable and are therefore contemplated by the present invention. It should be apparent that whether water-soluble or water-insoluble salts are employed, the salt itself is not diffusible from its location in the film unit, whereas the free reagent cation is characterized as being soluble and diffusible in the alkaline processing composition, at least while the pH is basic, e.g., above about pH 9.

As was heretofore mentioned, the neutralizing layer of this invention is useful in systems wherein the photosensitive strata and the dyeable stratum are contained on separate elements; and in systems wherein they are contained together as a unitary film unit, e.g., in the integral negative-positive film units previously described. In the former type, the neutralizing layer is most preferably contained in association with the dyeable stratum, e.g., in an image-receiving element comprising a support carrying the neutralizing layer and the dyeable stratum with a spacer or timing layer preferably being disposed therebetween. It may however be contained as a layer in the photosensitive element, i.e., in the element containing the photosensitive strata, as is disclosed in US. Pat. No. 3,362,821. In like manner, in the integral negative-positive film units, the neutralizing layer is preferably associated with the dyeable straturn, e.g., on the side of the dyeable stratum opposed from the negative component, and most preferably a timing layer is disposed between the neutrailizing layer and dyeable stratum. I

A particularly useful embodiment of this invention employs a salt comprising the reaction product of 6- benzylamino purine:

@w N fl A and the half butyl ester of the poly (ethylene/maleic anhydride) copolymer having the repeating units:

The salt is preferably disposed in a neutralizing layer which is positioned on the side of the dyeable stratum of the preferred integral negative-positive film units just described which is opposed to the photosensitive strat. The 6-benzylamino purine salt has been found to be uniquely suited for such placement without exhibiting the contamination effects which result from the undesirable diffusion of a development controlling reagent from the image-receiving element to the photosensitive element upon storage. The preferred salt is characterized as being soluble in the aqueous acidic medium of the neutralizing layer, i.e., about pH 2, with all the attendant coating benefits described above, and also provides a soluble and diffusible cation upon contact with the alkaline processing composition (pH about 13 to 14). The cation remains soluble and diffusible in the processing composition while the environmental pH is maintained at a level above about pH 9. However, the 6-benzylamino purine is substantially insoluble and non-diffusible at neutral pH levels, i.e., around pH 7.

It is to be remembered that the polymeric acid anion is non-diffusible from the neutralizing layer and therefore prevents migration of the salt, as such, from the neturalizing layer. Thus, the'6-benzylamino purine is immobilized and made unavailable until contacted by the processing composition. As described before, this reagent is particularly useful in maintaining transfer image density, especially at temperatures above F., e.g. 100 F. or above. Since the entire quantity needed to provide an acceptable density at such high temperatures, if included solely in the processing composition, may cause a reduction in photographic speed at room temperature, the present invention may be conveniently employed to meter out the required supplemental amount of reagent at a controlled rate under conditions of increasing temperature. 9

The present invention will be further illustrated by the following examples; however, it is understood that the scope of this invention is not limited to the details therein set forth.

EXAMPLE 1 The polymeric saltof 6-benzylamino purine was prepared by adding to an aqueous acidic (about pH 2) coating solution comprising the half butyl ester of poly (ethylene/maleic anhydride), about mg. of 6- benzylamino purine per gram of said ester. The resultant solution was coated at a coverage of about 2,500 mgs/ft. on a transparent 4 mil polyethylene terephthlate film base to provide the neutralizing layer of an image-receiving element. Over this layer, were coated, in succession:

l. a timing layer containing about a 40:1 ratio of a 60-30-4-6 copolymer of butylacrylate, diacetone acrylamide, styrene and methacrylic acid, and polyacrylamide, at a coverage of about 500 mgs./ft. and

2. a polymeric image-receiving layer containing a 2:1 mixture, by weight, of polyvinyl alcohol and poly-4- vinylpyridine, at a coverage of about 300 mgs./ft.

The element so prepared was immersed in an aqueous alkaline solution of potassium hydroxide at a pH of about 9 for about 3 minutes at room temperature. The release of 6-benzylamino purine from the element into the solution was confirmed by a UV. spectrum of the solution, which indicated the presence of 6- benzylamino purine.

EXAMPLE 2 An additional image-receiving layer was prepared as described in Example 1 without forming the salt of the 6-benzylamino purine in the coating solution for the neutralizing layer, to serve as a control for the test image-receiving element of Example 1.

An aqueous laminating solution was prepared comprising about 5 parts of water to 1 part (by weight) of polyethylene glycol having a molecular weight range of about 6,000 to 7,500 (commerically available from Union Carbide Corp. under the tradcname Carbowax 6000) The test and control image-receiving elements were then each bonded to photosensitive elements of identical structure to form a laminate by distributing the above-prepared laminating solution between the top layers of said elements at a coverage of about 25 mg./ft. as they were brought face-to face at the nip of pressure-applying rollers, all according to the teachings of the copending application of E. H. Land, Ser. No. 247,023, filed Apr. 24, 1972, now US. Pat. No. 3,793,023. The laminates thus formed were stored for 5 days at 100 F. and 90 percent relative humidity, exposed to an analytical target andprocessed with an aqueous alkaline processing composition. The sensitometric results showed essentially no deleterious effects from the storage of the test element when compared with the control, thereby indicating the absence of an undesired migration of the 6-benzylamino purine from the test image-receiving element during storage.

EXAMPLE 3 The test and control image-receiving elements described in Example 2 were each taped together with a photosensitive element to form an integral film unit. Each photosensitive element comprised the following, in sequence, on an opaque film base:

1. A layer comprising the cyan dye developer:

2. A red-sensitive gelatino silver iodobromide emulsion.

3. An interlayer of a 60-30-4-6 copolymer of butylacrylate, diacetone acrylamide, styrene and metacrylic acid, and polyacrylamide.

4. A layer comprising the magenta dye developer:

5. A green-sensitive gelatino silver iodobromide emulsion layer.

6. A layer containing the copolymer referred to above in layer 3 and polyacrylamide.

7. A layer comprising the yellow dye developer:

8. A blue-sensitive gelatino silver iodobromide emulsion layer; and

9. A layer of gelatin.

Each film unit was provided with a rupturable container retaining an aqueous alkaline processing solution and fixedly mounted on the leading edge thereof so that, upon application of compressive pressure to the container to rupture the containers marginal seal, its contents were distributed in a layer approximately 0.0028 inch thick between the image-receiving layer and the gelatin overcoat layer of the photosensitive component. The aqueous alkaline processing composition comprised:

-0001. Hood-f 2. U

CIBIISTOK/ and, water to make 100 g.

Each film unit was exposed to an analytical target through the transparent support and the layers thereon. The processing of the film units was accomplished by passing each film unit between a pair of pressureapplying rollers into a lighted room at room temperature. The laminate obtained by distribution of the processing composition was maintained intact to provide an integral negative-positive reflection print.

The reflection densities to red, green and blue light were measured about 60 minutes after processing by an automatic recording densitometer which plotted the characteristic positive H+D curves relating the logarithm of the original exposure of the negative to the reflection densities of the positives. The following table summarizes the results obtained for the maximum reflection density (D obtained with each color, the log exposure value determined at a density of 0.75 (0.75 speed) for each color and the algebraic differences obtained when the green speed values as just defined were subtracted from the red speed values (red balance) and from the blue speed values (blue balance):

Table 1 shows that when the sole source of the 6- benzylamino purine was the salt disposed in the test image-receiving element, about 0.15 to 0.20 more D than the control without the salt was obtained at room temperature, with more acceptable sensitometric speed and balance.

16 EXAMPLE 4 Test and control film units were fabricated and exposed as described in Example 3. The processing of the film units was accomplished by passing each film unit between the aforementioned pair of pressure-applying rollers into a lighted area at temperatures of 40 F F (room temperature), F. and into a 1 15 F. water bath. The film units were then sensitometrically evaluated as described in Example 3.

6-benzy1amino purine was included in the processing composition employed for both test and control film units, in addition to including the polymeric salt of 6- benzylamino purine in the neutralizing layer of the test image-receiving element. The processing composition comprised:

ethyl-N,N-ethylcne glycine COOH HOOC-A 2.71g. CXSHWO g/ and water to make 100 g.

. The following table summarizes the sensitometric results:

It can be seen from the data in Table 2 that additional 6-benzylamino purine located in the neutralizing layer of the image-receiving element as a salt of the polymeric acid in accordance with this invention, was made available to the photosensitive element at temperatures above 75 F especially at 1 15 F., to give significantly less D loss and balance shift than shown by the control with o-benzylamino purine disposed only in the processing composition. The data also indicate that the TABLE 2 Control lma c-rcccivin Elemcnt Temp. 40F 75F 100F 1 F Color R G B R G B R G B R G B D,,,,, 2.50 2.32 2.05 2.55 2.40 2.02 1.90 1.54 1.40 1.30 1.34 1.24 A from 0.05 0.08 +0.03 0.65 0.86 0.62 l.25 l.06 0.78 75F 0.75 0.71 0.97 1.06 1.25 1.37 1.45 1.53 1.78 1.78 1.89 1.64, 1.66 Speed A from 0.54 0.40 0.39 +0.28 +0.41 +0.33 +0.64 +0.27 +0.21 75F Balance 0.26 +0.09 0. 12 +0.08 0.25 0.00 +0.25 +0.02 A from 0.14 +0.01 0.l3 0.08 +0.37 0.06 75F Test lmugc-rccciving Element Temp. 40F 75F 100F 1 15F Color R G B R G B R G B R G B 1),, 2.37 2.26 1.97 2.35 2.33 1.94 1.88 1.64 1.42 1.85 1.87 1.57 A from +0.02 0.07 +0.03 0.47 0.29 -0.52 0.50 0.46 0.37 75F 0.75 0.70 0.95 1.00 1.21 1.31 1.37 1.46 1.68 1.67 1.54 1.48 1.49 Speed A from 0.51 0.36 0.37 +0.25 +0.37 +0.30 +0.33 +0.17 +0.12 75F Balance 0.25 +0.05 0. 10 +0.06 0.22 0.01 +0.06 +0.01 A from 0.15 0.01 0.12 0.07 +0.16 0.05 75F 6-benzylamino purine was released from the salt faster as the temperature was increased, thus making this particular embodiment of the present invention especially useful in minimizing sensitometric changes resulting from elevated processing temperatures.

Since certain changes may be made in the above product and process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description and examples shall be interpreted as illustrative and not in a limiting sense.

What is claimed is: l. A process for fonning a diffusion transfer dye image which comprises:

applying an aqueous alkaline processing composition to an exposed photosensitive element which includes a silver halide emulsion layer having associated therewith a dye image-providing material, thereby initiating development of exposed silver halide; and forming as a function of said development an imagewise distribution of mobile dye image-providing material which is transferred, at least in part, to a superposed image-receiving layer to impart thereto a dye image;

said process being performed in the presence of a non-diffusible salt incorporated within the film unit comprising said photosensitive element and said image-receiving layer, said salt having an anion derived from an immobile polymeric acid and a cation derived from an azole compound capable of protonation at a pH below 7 and adapted to control the development of silver halide, said cation being rendered diffusible to said silver halide when said salt is contacted by said processing composition.

2. A process as defined in claim 1 wherein said salt is contacted by said processing composition after a predetermined period of time has elapsed from the application of said processing composition, thereby delaying the introduction of said development controlling reagent.

3. A process as defined in claim 1 wherein said processing composition initially includes said development controlling reagent in its active form.

4. A process as defined in claim 1 carried out at a temperature above F.

5. A process as defined in claim 1 wherein said azole compound is a 4-azabenzimidazole.

6. A process as defined in claim 1 wherein said azole compound is a 6-alkylamino purine of the formula:

N//\H/N 'W/ wherein R is an alkyl group.

7. A process as defined in claim 7 wherein said 6- alkylamino purine is 6-benzylamino purine.

8. A process as defined in claim 1 wherein said polymeric acid provides a pH in the range of about 2 to about 5.

9. A process as defined in claim 1 wherein said salt is an acid salt which is employed as an acid-reacting reagent for lowering the environmental pH of said film unit following processing with said alkaline processing composition.

10. A process as defined in claim 1 wherein said dye image-providing material is a dye developer.

11. A process as defined in claim 1 wherein a redsensitive silver halide emulsion, a green-sensitive silver halide emulsion and a blue-sensitive silver halide emulsion are present in said photosensitive element, said silver halide emulsions having associated therewith, respectively, a cyan dye developer, a magenta dye developer and a yellow dye developer, and said dye image is a multicolorimage.

12. A photographic product for forming a diffusion transfer dye image which comprises:

a film unit comprising a photosensitive element including at least one silver halide emulsion layer having associated therewith a dye image-providing material; and an image-receiving element including at least an image-receiving layer;

means providing an aqueous alkaline processing composition for initiating development of said silver halide emulsion after photoexposure to form thereby an imagewise distribution of mobile dye image-providing material which is transferred, at least in part, to said image-receiving layer to impart thereto a dye image; and

incorporated within said film unit, a non-diffusible salt having an anion derived from an immobile polymeric acid and a cation derived from an azole compound capable of protonation at a pH below 7 and adapted to control the development of silver halide, said cation being rendered diffusible to said silver halide when said salt is contacted by said processing composition.

13. A photographic product as defined in claim 12 wherein said non-diffusible salt layer is disposed in said image-receiving element.

14. A photographic product as defined in claim 13 wherein said development controlling reagent is also disposed in its active form in said processing composition.

15. A photographic product as defined in claim 12 wherein said dye image-providing material is a dye developer.

16. A photographic product as defined in claim 13 wherein said azole compound is a 4-azabenzimidazole.

17. A photographic product as defined in claim 13 wherein said azole compound is a 6-alkylamino purine of the formula:

' R-NH Ill I where R is an alkyl group.

18. A photographic product as defined in claim 17 wherein said 6-alkylamino purine is 6-benzylamino punne.

19. A photographic product as defined in claim 17 which includes a sulfur-free silver solvent in said processing composition.

20. A photographic product as defined in claim 12 wherein said polymeric acid provides a pH in the range of about 2 to about 5.

21. A photographic product as defined in claim 12 which further comprises a neutralizing layer for lowering the environmental pH upon contact with said aqueous alkaline processing composition, said neutralizing layer including a polymeric acid having a plurality of acid groups.

22. A photographic product as defined in claim 21 wherein said non-diffusible salt is disposed in said neutralizing layer.

23. A photographic product as defined in claim 22 wherein said neutralizing layer is disposed in said image-receiving element.

24. A photographic product as defined in claim 22 wherein the anion of said salt is derived from the polymeric acid of said neutralizing layer to provide the acid-reacting reagent of said neutralizing layer.

25. A photographic product as defined in claim 24 wherein said polymeric acid is the half butyl ester of poly (ethylene/maleic anhydride).

26. A photographic product as defined in claim 12 wherein said photosensitive element and said imagereceiving element are retained together as an integral positive-negative film unit including means providing a light-reflecting layer between said image-receiving layer and said silver halide emulsion (s) sufficient to mask effectively said silver halide emulsion (s) after development thereof and provide a background for viewing said dye image, and a transparent support through which said dye image may be viewed.

27. A photographic product as defined in claim 26 wherein said means providing a light-reflecting layer comprises a white pigment dispersed in said processing composition, and said processing composition is contained in a rupturable container positioned to distribute said processing composition containing said pigment between said image-receiving layer and said silver halide emulsion (s).

28. An image-receiving element for use in diffusion transfer processes, comprising an image-receiving layer having associated therewith a non-diffusible salt with an anion derived from an immobile polymeric acid and a cation derived from a reagent adapted to control the development of silver halide.

29. An image-receiving element as defined in claim 28 wherein said non-diffusible salt is disposed in a separate layer adjacent to said image-receiving layer.

30. An image-receiving element as defined in claim 29 wherein said separate layer is a neutralizing layer for lowering the environmental pH upon contact with an aqueous alkaline processing composition, said neutralizing layer including a polymeric acid having a plurality of acid groups.

31. An image-receiving element as defined in claim 30 wherein the anion of said salt is derived from the polymeric acid of said neutralizing layer to provide the acid-reacting reagent in said neutralizing layer.

32. An image-receiving element as defined in claim 30 further comprising a polymeric timing layer disposed between said image-receiving layer and said neutralizing layer.

33. An image-receiving element as defined in claim 28 wherein said polymeric acid provides a pH in the range of about 2 to about 5.

34. An image-receiving element as defined in claim 33 wherein said polymeric acid is the half butyl ester of poly (ethylene/maleic anhydride).

35. An image-receiving element as defined in claim 33 wherein said development controlling reagent is an azole compound capable of protonation in said pH range.

36. An image-receiving element as defined in claim 35 wherein said azole compound is a 4- azabenzimidazole.

37. An image-receiving element as defined in claim 35 wherein said azole compound is a 6'-alkylamino purine of the formula:

wherein R is an alkyl group.

38. An image-receiving element as defined in claim 37 wherein said 6-alkylamino purine is 6-benzylamino purine.

39. An integral positive-negative film unit comprising in sequence,

a first dimensionally stable support;

a red-sensitive silver halide emulsion having associated therewith a cyan dye-developer;

a green-sensitive silver halide emulsion having associated therewith a magenta dye-developer;

a blue-sensitive silver halide emulsion having associated therewith a yellow dye-developer;

a dyeable polymeric layer;

a neutralizing layer comprising a non-diffusible salt having an anion derived from an immobile polymeric acid and a cation derived from an azole compound adapted to control the development of silver halide, said cation being rendered diffusible to at least one of said silver halide emulsions upon contact with an aqueous alkaline processing composition, said salt effecting a reduction of the pH of said processing composition from a first pH at which said dye developers and said cation are soluble and diffusible to at least a second lower pH at which said dye developers are substantially insoluble and non-diffusible;

a second dimensionally stable support which is transparent;

means securing at least the side edges of said layers in fixed relationship; and

a rupturable container retaining said aqueous alkaline processing composition having said first pH and containing dispersed therein a white inorganic pigment in a quantity sufficient to mask effectively said silver halide layers and any dye developer associated therewith after development and to provide a background for viewing by reflected light, through said transparent layer, a diffusion transfer image is said dyeable layer formed by development of said film unit, said rupturable container being fixedly positioned to distribute said processing composition containing said pigment between said dyeable layer and said silver halide emulsions.

40. A film unit as defined in claim 39 wherein said dye developers are disposed in separate layers adjacent their respective silver halide emulsion layers.

41. A film unit as defined in claim 40 further comprising an aqueous polymeric timing layer disposed between said dyeable layer and said neutralizing layer.

42. A film unit as defined in claim 43 wherein said azole compound is a 6-alkylamino purine of the formula:

maleic anhydride).

Claims (45)

1. 2. A process as defined in claim 1 wherein said salt is contacted by said processing composition after a predetermined period of time has elapsed from the application of said processing composition, thereby delaying the introduction of said development controlling reagent.
2. 3. A process as defined in claim 1 wherein said processing composition initially includes said development controlling reagent in its active form.
3. 4. A process as defined in claim 1 carried out at a temperature above 75* F.
4. 5. A process as defined in claim 1 wherein said azole compound is a 4-azabenzimidazole.
5. 6. A process as defined in claim 1 wherein said azole compound is a 6-alkylamino purine of the formula:
6. 7. A process as defined in claim 7 wherein said 6-alkylamino purine is 6-benzylamino purine.
7. 8. A process as defined in claim 1 wherein said polymeric acid provides a pH in the range of about 2 to about 5.
8. 9. A process as defined in claim 1 wherein said salt is an acid salt which is employed as an acid-reacting reagent for lowering the environmental pH of said film unit following processing with said alkaline processing composition.
9. 10. A process as defined in claim 1 wherein said dye image-providing material is a dye developer.
10. 11. A process as defined in claim 1 wherein a red-sensitive silver halide emulsion, a green-sensitive silver halide emulsion and a blue-sensitive silver halide emulsion are present in said photosensitive element, said silver halide emulsions having associated therewith, respectively, a cyan dye developer, a magenta dye developer and a yellow dye developer, and said dye image is a multicolor image.
11. 12. A photographic product for forming a diffusion transfer dye image which comprises: a film unit comprising a photosensitive element including at least one silver halide emulsion layer having associated therewith a dye image-providing material; and an image-receiving element including at least an image-receiving layer; means providing an aqueous alkaline processing composition for initiating development of said silver halide emulsion after photoexposure to form thereby an imagewise distribution of mobile dye image-providing material which is transferred, at least in part, to said image-receiving layer to impart thereto a dye image; and incorporated within said film unit, a non-diffusible salt having an anion derived from an immobile polymeric acid and a cation derived from an azole compound capable of protonation at a pH below 7 and adapted to control the development of silver halide, said cation being rendered diffusible to said silver halide when said salt is contacted by said processing composition.
12. 13. A photographic product as defined in claim 12 wherein said non-diffusible salt layer is disposed in said image-receiving element.
13. 14. A photographic product as defined in claim 13 wherein said development controlling reagent is also disposed in its active form in said processing composition.
14. 15. A photographic product as defined in claim 12 wherein said dye image-providing material is a dye developer.
15. 16. A photographic product as defined in claim 13 wherein said azole compound is a 4-azabenzimidazole.
16. 17. A photographic product as defined in claim 13 wherein said azole compound is a 6-alkylamino purine of the formula:
17. 18. A photographic product as defined in claim 17 wherein said 6-alkylamino purine is 6-benzylamino purine.
18. 19. A photographic product as defined in claim 17 which includes a sulfur-free silver solvent in said processing composition.
19. 20. A photographic product as defined in claim 12 wherein said polymeric acid provides a pH in the range of about 2 to about 5.
20. 21. A photographic product as defined in claim 12 which further comprises a neutralizing layer for lowering the environmental pH upon contact with said aqueous alkaline processing composition, said neutralizing layer including a polymeric acid having a plurality of acid groups.
21. 22. A photographic product as defined in claim 21 wherein said non-diffusible salt is disposed in said neutralizing layer.
22. 23. A photographic product as defined in claim 22 wherein said neutralizing layer is disposed in said image-receiving element.
23. 24. A photographic product as defined in claim 22 wherein the anion of said salt is derived from the polymeric acid of said neutralizing layer to provide the acid-reacting reagent of said neutralizing layer.
24. 25. A photographic product as defined in claim 24 wherein said polymeric acid is the half butyl ester of poly (ethylene/maleic anhydride).
25. 26. A photographic product as defined in claim 12 wherein said photosensitive element and said image-receiving element are retained together as an integral positive-negative film unit including means providing a light-reflecting layer between said image-receiving layer and said silver halide emulsion (s) sufficient to mask effectively said silver halide emulsion (s) after development thereof and provide a background for viewing said dye image, and a transparent support through which said dye image may be viewed.
26. 27. A photographic product as defined in claim 26 wherein said means providing a light-reflecting layer comprises a white pigment dispersed in said processing composition, and said processing composition is contained in a rupturable container positioned to distribute said processing composition containing said pigment between said image-receiving layer and said silver halide emulsion (s).
27. 28. An image-receiving element for use in diffusion transfer processes, comprising an image-receiving layer having associated therewith a non-diffusible salt with an anion derived from an immobile polymeric acid and a cation derived from a reagent adapted to control the development of silver halide.
28. 29. An image-receiving element as defined in claim 28 wherein said non-diffusible salt is disposed in a separate layer adjacent to said image-receiving layer.
29. 30. An image-receiving element as defined in claim 29 wherein said separate layer is a neutralizing layer for lowering the environmental pH upon contact with an aqueous alkaline processing composition, said neutralizing layer including a polymeric acid having a plurality of acid groups.
30. 31. An image-receiving element as defined in claim 30 wherein the anion of said salt is derived from the polymeric acid of said neutralizing layer to provide the acid-reacting reagent in said neutralizing layer.
31. 32. An image-receiving element as defined in claim 30 further comprising a polymeric timing layer disposed between said image-receiving layer and said neutralizing layer.
32. 33. An image-receiving element as defined in claim 28 wherein said polymeric acid provides a pH in the range of about 2 to about 5.
33. 34. An image-receiving element as defined in claim 33 wherein said polymeric acid is the half butyl ester of poly (ethylene/maleic anhydride).
34. 35. An image-receiving element as defined in claim 33 wherein said development controlling reagent is an azole compound capable of protonation in said pH range.
35. 36. An image-receiving element as defined in claim 35 wherein said azole compound is a 4-azabenzimidazole.
36. 37. An image-receiving element as defined in claim 35 wherein said azole compound is a 6-alkylamino purine of the formula:
37. 38. An image-receiving element as defined in claim 37 wherein said 6-alkylamino purine is 6-benzylamino purine.
38. 39. An integral positive-negative film unit comprising in sequence, a first dimensionally stable support; a red-sensitive silver halide emulsion having associated therewith a cyan dye-developer; a green-sensitive silver halide emulsion having associated therewith a magenta dye-developer; a blue-sensitive silver halide emulsion having associated therewith a yellow dye-developer; a dyeable polymeric layer; a neutralizing layer comprising a non-diffusible salt having an anion derived from an immobile polymeric acid and a cation derived from an azole compound adapted to control the development of silver halide, said cation being rendered diffusible to at least one of said silver halide emulsions upon contact with an aqueous alkaline processing composition, said salt effecting a reduction of the pH of said processing composition from a first pH at which said dye developers and said cation are soluble and diffusible to at least a second lower pH at which said dye developers are substantially insoluble and non-diffusible; a second dimensionally stable support which is transparent; means securing at least the side edges of said layers in fixed relationship; and a rupturable container retaining said aqueous alkaline processing composition having said first pH and containing dispersed therein a white inorganic pigment in a quantity sufficient to mask effectively said silver halide layers and any dye developer associated therewith after development and to provide a background for viewing by reflected light, through said transparent layer, a diffusion transfer image is said dyeable layer formed by development of said film unit, said rupturable container being fixedly positioned to distribute said processing composition containing said pigment between said dyeable layer and said silver halide emulsions.
39. 40. A film unit as defined in claim 39 wherein said dye developers are disposed in separate layers adjacent their respective silver halide emulsion layers.
40. 41. A film unit as defined in claim 40 further comprising an aqueous polymeric timing layer disposed between said dyeable layer and said neutralizing layer.
41. 42. A film unit as defined in claim 43 wherein said azole compound is a 6-alkylamino purine of the formula:
42. 43. A film unit as defined in claim 42 wherein said 6-alkylamino purine is 6-benzylamino purine.
43. 44. A film unit as defined in claim 43 which includes an additional amount of said 6-benzylamino purine in said processing composition.
44. 45. A film unit as defined in claim 43 wherein said polymeric acid provides a pH of about 2.
45. 46. A film unit as defined in claim 45 wherein said polymeric acid is the half butyl ester of poly (ethylene/maleic anhydride).