US3473924A - Novel photographic products and processes - Google Patents

Description

III 21, 1969 H. G. ROGERS 3,473,924

novsu PHOTOGRAPHIC PRODUCTS AND PROCESSES Filed Dec. 11, 1967 2 Sheets-Sheet 1 ///////////A- \\\\\\\\\\\\%F i l6" ////////////7-MAGENTA DYE DEVELOPER LAYER GREEN SENSITIVE SILVER HALIDE EMULSION LAYER |9'\:\\\\\\\\\\\\\\/I-YELLOW DYE DEVELOPER LAYER BLUE SENSITIVE SILVER HALIDE EMULSION LAYER 27K AQUEOUS ALKALINE PROCESSING COMPOSITION m I I FIG.

INVENTOR.

Maw

BY 61:01am, 5 W 25mm, WMM

ATTORNEYS REFLECTION DENSITY Get 21, 1969 H. G. ROGERS 3,473,924

NOVEL PHOTOGRAPHIC PRODUCTS AND PROCESSES Filed Dec. 11, 1967 2 Sheets-Sheet 2 ,FG-BROMO-5METHYL4-AZABEN2IMIDAZOLE .6CHLOR04-AZABENZIMIDAZOLE 2.6 6-METHYL-4-AZABENZIMIDAZOLE I 5-METHYL-4-AZABENZIMIDAZOLE 1 4-AZABENZIMIDAZOLE BENZOTRIAZOLE 3.0 2.8 as 2.4 2.2 270 L8 L6 1.4 |.2 L0 0.8 as 0.4 02 0 STEP WEDGE DENSITY FIG. 2

INVENTOR.

Mama-W6 BY @Jww/n WW4, @"fiafdon W M22201 ATTORNEYS U.S. Ci. 9629 24 Claims ABSTRACT 0F THE DISCLOSURE Azabenzimidazoles are used for the prevention of fog formation in photographic processes and particularly in diffusion transfer photographic processes.

The present invention relates to photography and more particularly to photographic products and processes.

It has been extensively reported in literature pertaining to photography that photosensitive silver halide emulsions, and particularly photosensitive gelatino-silver halide emulsions, have a tendency to lose sensitivity and to become spontaneously devel'opable without exposure to light. This phenomenon, characterized as chemical fog, may be defined as the density above base level that is developed in emulsion areas that have received no intentional exposure and, in general, is not uniformly distributed over a selectively photoexposed emulsion, being greatest in the unexposed areas and decreasing with increased exposure in a nonlinear manner.

In both silver and color photographic systems, the latter where silver halides are used to control image dye formation, fog results in a loss of image acuity.

Chemical fog may be divided into two classes: inherent fog, that is, fog which is emulsion initiated; and induced fog, that is, fog which is initiated during development. Induced fog apears to be due to physical development about extragranular centers and inherent fog is probably due to the presence of grains bearing a catalytic site sensitivity speck which is unavoidably introduced and which is equivalent in its properties to latent image. Induced fog accordingly may be unaffected by the level of inherent fog. Thus it will be readily appreciated that an emulsion susceptible to the development of chemical fog requires silver halide grains possessing a catalytic center of sufficient size to be spontaneously developable and/ or grains unprotected from nondiscriminatory development.

Various and sundry procedures and additives have been disclosed in the art to provide an increase in the stability of photosensitive silver halide emulsions by reducing the tendency of photosensitive compositions to fog. These procedures usually increase the speed-to-fog ratio; otherwise there would be no point in using them unless the requirement for a low fog level completely overrides that for sensitivity. In general, the methods available for the control of fog are to increase the bromide ion concentration during the emulsion fabrication process; select fog free gelatins, i.e., gelatins which are free of fogging contaminants and which have desirable ratios of restrainer to sensitizer; reduce the level of chemical sensitization; and add inorganic or organic fog retarding adjuncts.

This invention relates primarily to the latter item above, and more particularly to the use of a specified class of synthetic, organic antifoggants.

Accordingly, it is a primary object of the present invention to provide novel photographic products, and processes utilizing same, which exhibit decreased susceptibility to fog formation.

Another object of the present invention is to provide novel processes and products, particularly adapted for nited States Patent 0 3,473,924 Patented Oct. 21, 1969 'ice obtaining monochromatic and multichromatic images by diffusion transfer, which exhibit decreased fog formation throughout an extended temperature range.

A still further object of the present invention is to provide novel photographic elements comprising not less than one silver halide emulsion having associated therewith specified transfer image-forming components which exhibit increased effective processing temperature latitude.

Other objects of the instant invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the process involving the several steps and the relation and order of one or more of such steps with respect to each of the others and the product possessing the features, properties and the relation of the elements which are exemplified in the following detailed disclosure and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention reference should be had to the following detailed description taken in connection with the accompanying drawings wherein:

FIGURE 1 is a diagrammatic enlarge cross-sectional view of one embodiment of a film unit for obtaining multicolor images by a diffusion transfer photographic process illustrating the association of elements during one stage of the performance of a diffusion transfer process, the thickness of the various materials being exaggerated; and

FIG. 2 is a comparative graphical representation of exposure vs. density relationship for hereinafter detailed dif fusion transfer photographic systems employing specified antifoggant compounds, including those of the present invention.

In diffusion transfer processes for the formation of transfer images, an exposed photographic emulsion is developed and, substantially concurrently therewith, an imagewise distribution of transfer image-forming components is provided as a function of the point-to-point degree of development. At least part of that imagewise distribution is transferred by diffusion to a contiguous imagereceiving layer to provide the desired transfer image formation to that layer.

In diffusing transfer processes for the formation of silver transfer images, an exposed silver halide emulsion 0 is developed and, substantially concurrently therewith, an

imagewise distribution of soluble silver complex is obtained by reaction of a silver solvent with silver halide of the emulsion as a function of its point-to-point degree of exposure. Preferably, the photosensitive silver halide emulsion is developed with a viscous processing composition which is spread between an element comprising the silver halide emulsion and a print receving element comprising a suitable silver precipitating layer. The processing composition affects development of the emulsion and substantially contemporaneously therewith forms a soluble silver complex, for example, a thiosulfate or thiocyanate, as a function of the point-to-point degree of emulsion exposure. This soluble silver complex is, at least in part, transported in the direction of the print receiving element and the silver thereof is largely precipitated in the silver precipitating layer of said element to form a transfer image therein.

U.S. Patents Nos. 2,647,049; 2,661,293; 2,698,798; and 2,802,735 disclose subtractive color diffusion transfer processes wherein color coupling techniques are utilized which comprise, at least in part, reacting one or more developing agents and one or more color formers, as a function of the photoexposure of a photographic emulsion, to provide a color image to a superposed imagereceiving layer. US. Patent No. 3,019,124 discloses the manufacture of photographic color screen elements particularly adapted for employment in multicolor diffusion transfer processes; and U.S. Patents Nos. 2,968,554 and 2,983,606 disclose diffusion transfer processes wherein a color screen element is utilized to provide a multicolor transfer image to a superposed image-receiving layer. U.S. Patents Nos. 2,774,608; 2,983,606; and 3,345,163 disclose diffusion transfer processes wherein complete dyes are utilized to provide a color transfer image to a superposed image-receiving layer.

As disclosed in the aforementioned U.S. Patent No. 2,983,606, a photosensitive element containing a dye developer and a silver halide emulsion is exposed and wetted by a liquid processing composition, for example, by emersion, coating, spraying, flowing, etc., in the dark, and the exposed photosensitive element is superposed prior to, during or after wetting on a sheet-like support element which may be utilized as an image-receiving element. In a preferred embodiment, the liquid processing composition is applied to the photosensitive element in a substantially uniform layer as the photosensitive element is brought into superposed relationship with the imagereceiving layer. The liquid processing composition permeates the emulsion to initiate development. The dye developer is immobilized or precipitated in, for example, exposed areas as a function of the development. Such immobilization is apparently, at least in part, due to a change in the solubility characteristics of the dye developer upon oxidation; particularly with regard to its solubility in alkaline solutions. It may also be due in part to a tanning effect on the emulsion by oxidized developing agent and in part to a localized exhaustion of alkali as a result of development. In the exposed and partially exposed areas of the emulsion, the dye developer, unreacted and diifusible, provides an imagewise distribution of unoxidized dye developer dissolve in a liquid processing composition as a function of the point-to-point degree of exposure of the silver halide emulsion. At least part of this imagewise distribution of unoxidized dye developer is transferred by imbibition to a superposed image-receiving layer or element. Under certain conditions the layer of liquid processing composition may be utilized as the image-receiving layer. The image-receiving element receives a depthwise diffusion of dye developer without appreciably disturbing the imagewise distribution thereof to provide the color transfer image. The imagereceiving element may contain agents adapted to mordant or otherwise fix dye developer. If the color of the transferred dye developer is affected by change in the pH of the image-receiving element, this pH may be adjusted to provide a pH affording the desired color. The desired dye image carried by the image-receiving layer may be separated from the photosensitive element by stripping at the end of a suitable imbibition period.

Dye developers are compounds which contain in the same molecule both 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 developing function is a hydroquinonyl group. Other suitable developing functions include ortho-dihydroxyphenyl and orthoand 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.

An extensive compilation of such compounds is set forth in the aforementioned U.S. Patent No. 2,983,606 and, in particular, in the various U.S. Patents and copending applications incorporated by reference therein.

In general, the preferred dye developers comprise monoazo and anthraquinone dyes which possess one or two hydroquinonyl groups attached to the auxochromophoric system of the dye by means of a conjugation-interrupting divalent group such as, for example, in alkylene group.

Multicolored images may be obtained using color image-forming components, such as, for example, the previously mentioned dye developers, in diffusion transfer processes, by several techniques. One such technique contemplates the use of a photosensitive silver halide stratum comprising at least two sets of selectively sensitize minute photosensitive elements arrange in the form of a photosensitive screen. Transfer processes of this type are disclose in the previously noted U.S. Patent No. 2,983.- 606. In such an embodiment each of the minute photosensitive elements has associated therewith an appropriate dye developer in or behind a silver halide emulsion portion. In general, a suitable photosensitive screen prepared in accordance with the disclosure of said patent comprises minute red sensitized emulsion elements, minute green sensitized emulsion elements and minute blue sensitized emulsion elements arranged in side-by-side relationship in a screen pattern and having assoicated therewith. respectively, a cyan dye developer, a magenta dye developer and a yellow dye developer.

Another process for obtaining multicolor transfer images utilizing dye developers employs an integral multilayer photosensitive element such as is disclosed in the aforementioned U.S. Patents Nos. 2,983,606 and 3,345,- 163, wherein at least two selectively sensitized photosensitive strata and associated dye developers are superposed on a single support and are processed simultaneously and without separation with a single common image-receiving layer. A suitable arrangement of this type comprises a support carrying a red-sensitive silver halide emulsion stratum, a green-sensitive silver halide emulsion stratum, and a blue-sensitive silver halide emulsion stratum, said emulsions having assoicated therewith respectively, for example, a cyan dye developer, a magenta dye developer and a yellow dye developer. The dye developer may be utilized in the silver halide emulsion layer, for example, in the form of particles, or it may be employed as a layer behind the appropriate silver halide emulsion stratum, for example, a layer of dye developer applied by the use of a coating solution containing about 0.5 to 8%, by weight, of the respective dye developer. Each set of silver halide emulsion and associated dye developer strata may be separated from other sets by suitable interlayers, for example, gelatin and the synthetic polymeric materials disclosed in copending application of Lloyd D. Taylor, Ser. No. 641,669, filed Feb. 7, 1967, and now abandoned. In certain instances it may be desirable to incorporate a yellow filter in front of the green-sensitive emulsion and such yellow filter may be incorporated in an interlayer. However, where desirable, a yellow dye developer of appropriate spectral characteristics which is present in a state capable of functioning as a yellow filter may be employed. In such instances a separate yellow filter may be omitted.

The preceding color image-forming components, that is, dye developers, are preferably selected for their ability to provide colors that are useful in carrying out subtractive color photography, i.e., cyan, magenta and yellow. It should be noted that it is within the scope of this invention to use mixtures of dye developers, for example, to obtain a desired color, e.g., black. Thus it is to be understood that the expression color as used herein is intended to include the use of a plurality of colors to obtain black, as well as the use of a single black dye developer.

Copending U.S. application Ser. No. 234,864, filed Nov. 1, 1962, and now U.S. Patent 3,362,819, disclosed image-receiving elements, particularly adapted for employrnent in color diffusion transfer processes, for example, of the type disclosed in aforementioned U.S. Patent No. 2,983,606, which comprise a support layer possessing on one surface thereof, in sequence, a polymeric acid layer, a timing layer or spacer layer in the preferred embodiment, and an image-receiving layer adapted to provide a visible image upon tarnsfer to said layer of diifusible dye image-forming substance.

As set forth in the last-mentioned application, the polymeric acid layer comprises polymers which contain acid groups, such as carboxylic acid and sulfonic acid groups, which are capable of forming salts with alkali metals, such as sodium, potassium etc., or with organic bases, particularly quaternary ammonium bases, such as tetramethyl ammonium hydroxide, or potentially acidyielding 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, nondirTusible from the acid polymer layer. In the preferred embodiments disclosed, the acid polymer contains free carboxyl groups and the transfer processing composition employed contains a large concentration of sodium and/ or potassium ions. The acid polymers stated to be most useful are characterized by containing free carboxyl groups, being insoluble in water in the free acid form, and by forming water-soluble sodium and/or potassium salts. One may also employ polymers containing carboxylic acid anhydride groups, at least some of which preferably have been converted to free carboxyl groups prior to imbibition. Whi e the most readily available polymeric acids are derivatives of cellulose or of vinyl polymers, polymeric acids from other classes of polymers may be used.

The acid polymer layer is disclosed to contain at least sufficient acid groups to effect a reduction in the pH of the image layer from a pH of about 12 to l4 to a pH of at least 11 or lower at the end of the imbibition period, and preferably to a pH of about 5 to 8 within a short time after imbibition. The pH of the processing composition employed preferably is of the order of at least 12 to 14.

It is, of course, necessary that the action of the polymeric acid be so controlled as not to interfere with either development of the negative or image transfer of unoxidized dye developers. For this reason, the pH of the image layer is kept at a level of pH 12 to 14 until the positive dye image has been formed after which the pH is reduced very rapidly to at least about pH 11, and preferably about pH 9 to 10, before the positive transfer image is separated and exposed to air. Unoxidized dye developers containing hydroquinonyl developing radicals diffuse from the negative to the positive as the sodium or other alkali salt. The diffusion rate of such dye imageforming components thus is at least partly a function of the alkali concentration, and it is desired that the pH of the image layer remain on the order of 12 to 14 until transfer of the necessary quantity of dye has been accomplished. The subsequent pH reduction, in addition to its desirable effect upon image light stability, serves a highly valuable photographic function by substantially terminating further dye transfer. The processing technique thus effectively minimizes changes in color balance as a result of longer imbibition times in multicolor transfer processes using multilayer negatives.

The spacer layer of the last-mentioned copending application, for example, an inert spacer layer comprising polyvinyl alcohol or gelatin or a temperature inversely permeable polymeric material as disclosed in copending US. application Ser. No. 447,100, filed Apr. 9, 1965, and now abandoned, acts to time control the pH reduction by the polymeric acid layer. This timing is disclosed to be a function of the rate at which the alkali diffuses through the spacer layer. It was stated to have 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 interlayer, but the pH drops quite rapidly once the alkali diffuses through the spacer layer.

As examples of materials, for use as the image-receiving layer, mention may be made of solution dyeable polymers such as, for example, nylon, N-methoxymethyl polyhexamethylene adipamide; partially hydrolyzed polyvinyl acetate; polyvinyl alcohol with or without plastid cizers; cellulose acetate with fillers, as, for example, onehalf cellulose acetate and one-half oleic acid; gelatin; and other materials of a similar nature. Preferred materials comprise polyvinyl alcohol or gelatin containing a dye mordant such as polyl-vinylpyridine, as disclosed in US. Patent No. 3,148,061.

As has been alluded toabove, the presence of an antifoggant in a photographic system may be responsible for reducing both inherent and induced fog and will, therefore, produce a more attractive end product, both from aesthetic and technological points of view. Such products doubtless have a competitive advantage over other photographic products not quite as attractive or technologically efficient. The antifoggant composition is particularly helpful in minimizing or preventing reaction of a dye developer with unexposed silver halide and may be added to the processing composition and/or to one or more processing composition permeable layers of the photosensitive and/or image-receiving elements. The pertinent art has recognized many compounds which have fog inhibiting characteristics, such as sodium and potassium bromide and iodide, 6-nitrobenzimidazole, benzotriazole, chlorobenzotriazole, S-methyl-benzimidazole, Z-aminobenzimidazole, thio acetanilide, etc.

At low temperatures, when processing composition is distributed upon the contact surface of a selectively exposed photosensitive element, of the aforementioned tripack configuration, development begins first in the bluesensitive emulsion, since it contacts the processing composition before the other layers. Temperature-retarded development, however, is slowed up even more by the restraining properties of antifoggant present and results, for example, in increased uncontrolled yellow dye developer transfer from the blue-sensitive emulsion to the image-receiving layer before complete developmental control has been established. This causes what may be termed yellow stain. It will be evident that at high temperatures the precise opposite happens, that is, the development rate is accelerated to a point where the restraining effect of the antifoggant is of insufiicient consequence. The blue-sensitive emulsion will then be developed and the properly developed silver, combined with the fog present, will cause an overcontrol and thereby hold back the desired imagewise yellow dye diffusion and result in an undesired shift in color balance of the transfer image.

It has unexpectedly been discovered that a certain class of compounds act as uniquely excellent antifoggants particularly adapted for advantageous employment in diffusion transfer photographic processes to provide improved latitude in the temperatures at which such process may be carried out. It has also been unexpectedly found that, in addition to their unique antifogging characteristics, compounds forming the class designated may be incorporated into photographic systems with substantially no sacrifice of the effective speed of the transfer process.

Generically speaking, the class of compounds which may be utilized in accordance with the present invention comprise azabenzimidazoles of the formula:

where R is selected from the group consisting of hydrogen, and lower alkyl groups, i.e., containing less than six carbon atoms; R and R are selected from the group consisting of hydrogen, halogen, lower alkyl, i.e., containing less than six carbon atoms, nitro, amino, hydroxy, lower alkoxy, i.e., containing less than six carbon atoms, aryl, sulfonamido, and carboxamido groups; it being understood that R and R may together constitute the atoms necessary to complete a cyclic structure, for example,

R, R and R are specifically intended to encompass equivalents thereof, including R and R taken together to form an annulated hydrocarbon ring system.

Illustrative of the compounds which may be utilized in the present invention are:

It is theorized that in the compounds displaying the strongest antifoggant activity, R and/or R are Weak electron donor moieties.

It has been found that the antifoggant compositions of the present invention may be used alone or in conjunction with other antifoggants. For example, with respect to a typical color film processing composition containing a conventional antifoggant such as benzotriazole and the like, generally in the order of about 2%, the antifoggants of the present invention may be added to the system with a concomitant reduction in the percentage of or elimination of the benzotriazole. In a preferred embodiment, the antifoggants of the present invention are utilized in conjunction with a conventional antifoggant compound, such as benzotriazole, whose effectiveness responds normally to changes in temperature, to provide to the system development and control characteristics satisfactory over a greater temperature range than that achieved by the teachings set forth in the art.

In a preferred embodiment of the present invention, a photosensitive element is employed which is specifically adapted to provide for the production of a multicolor dye transfer image and comprises a dimensionally stable support layer carrying at least two selectively sensitized silver halide emulsion strata each having a dye developer material of predetermined color associated therewith which as soluble and dilfusible in alkali at a first pH.

The preferred photosensitive image-receiving element comprises an alkaline solution permeable polymeric layer dyeable by the dye developer; a polymeric spacer layer comprising a polymer possessing decreasing alkaline solution permeability with increasing temperature; an alkaline solution permeable polymeric acid layer containing sufficient acidifying groups to effect reduction, subsequent to substantial multicolor transfer dye image formation, of the image-receiving element from the first pH to a second pH, at Which the dye image-providing material is insoluble and nondilfusible; and a dimensionally stable support layer.

The silver halide emulsions comprising the multicolor photosensitive laminate preferably possess predominant spectral sensitivity to separate regions of the spectrum and each has associated therewith 'a dye, which is a silver halide developing agent and is, most preferably, substantially soluble in the reduced form only at the first pH, possessing a spectral absorption range substantially complementary to the predominant sensitivity range of its associated emulsion. In the preferred embodiment each of the emulsion strata, and its associated dye, is separated from the remaining emulsion strata, and their associated dye, by separate alkaline solution permeable polymeric interlayers.

In such preferred embodiment of the invention, the silver halide emulsion comprises photosensitive silver halide dispersed in gelatin and is about 0.6 to 6 microns in thickness; the dye itself is dispersed in a aqueous alkaline solution polymeric binder, preferably gelatin, as a separate layer about 1 to 7 microns in thickness; the alkaline solution permeable polymeric interlayers, preferably gelatin. are about 1 to 5 microns in thickness; the alkaline solution permeable and dyeable polymeric layer is transparent and about 0.25 to 0.4 mil in thickness; the polymeric spacer layer intermediate the dyable polymeric layer and the polymeric acid layer is transparent and about 0.1 to 0.7 mil in thickness; the alkaline solution permeable polymeric acid layer is transparent and about 0.3 to 1.5 mils in thickness; and each of the dimensionally stable support layers are alkaline solution impermeable and about 2 to 6 mils in thickness. It will be specifically recognized that the relative dimensions recited above may be appropriately modified, in accordance with the desires of the operator, with respect to the specific product to be ultimately prepared.

In the preferred embodiment of the present inventions film unit for the production of a multicolor transfer image, the respective silver halide/dye developer units of the photosensitive element will be in the form of a tripack configuration which will ordinarily comprise a cyan dye developer/red-sensitive emulsion unit contiguous the dimensionally stable support layer, the yellow dye developer/blue-sensitive emulsion unit most distant from the support layer and the magenta dye developer/green-sensitive emulsion unit intermediate those units, recognizing that the relative order of such units may be varied in accordance with the desires of the operator.

Reference is now made to FIGURE 1 of the drawings wherein there is illustrated a preferred film unit of the present invention.

As illustrated in FIGURE 1, film unit 10 comprises a photosensitive laminate 11 including, in order, dimensionally stable support layer 12, preferably a fiexible sheet material; cyan dye developer layer 13; red-sensitive silver halide emulsion layer 14; interlayer 15, magenta dye developer layer 16; green-sensitive silver halide emulsion layer 17; interlayer 18; yellow dye developer layer 19; blue-sensitive sliver halide emulsion layer 20; auxiliary layer 21, which may contain an auxiliary silver halide developing agent; and an image-receiving element 22 including image-receiving layer 23; spacer layer 24; neutralizing layer 25; and dimensionally stable support layer 26, preferably a flexible sheet material.

As shown in the drawing, the multilayer exposed photosensitive element 11 is shown in processing relationship with an image-receiving element 22 and a layer 27 of processing solution distributed intermediate elements 11 and 22.

In the performance of a difiusion transfer multicolor process employing film unit 10, the unit is exposed to radiation, actinic to photosensitive laminate 11.

Subsequent to exposure, film unit may be processed by being passed through opposed suitably gapped rolls in order to apply compressive pressure to a frangible container in order and to effect rupture of the container and distribution of alkaline processing composition 27, having a pH at which the cyan, magenta and yellow dye developers are soluble and difiusible, intermediate dyeable polymeric layer 23 and auxiliary layer 21.

Alkaline processing solution 27 permeates emulsion layers 14, 17 and to initiate development of the latent images contained in the respective emulsions. The cyan, magenta and yellow dye developers, of layers 14, 17 and 20, are immobilized, as a function of the development of their respective associated silver halide emulsions, preferably substantially as a result of their conversion from the reduced form to their relatively insoluble and nondiifusible oxidized forrn, thereby providing imagewise distributions of mobile, soluble and diifusible cyan, magenta and yellow dye developer, as a function of the point-to-point degree of their associated emulsions exposure. At least part of the imagewise distributions of mobile cyan, magenta and yellow dye developer transfers, by diffusion, to aqueous alkaline solution perm able polymeric layer 23 to provide a multicolor dye transfer image to that layer. Subsequent to substantial transfer image formation, a sufiicient portion of the ions comprising aqueous alkaline solution 27 transfers, by diffusion, through permeable polymeric layer 23, permeable spacer layer 24 and to permeable polymeric acid layer whereby alkaline solution 27 decreases in pH, as a function of neutralization, to a pH at which the cyan, magenta and yellow dye developers, in the reduced form, are insoluble and nondiffusible, to provide thereby a stable multicolor dye transfer image.

Subsequent to substantial transfer image formation, print-receiving element 22 may be manually dissociated from the remainder of the film unit, for example, by strip- Y ping.

The following examples describe the preparation of typical azabenzimidazole antifoggants of the present invention. These examples are considered to be exemplary and should not be taken in a limiting sense.

EXAMPLE 1 The compound 6-nitro-5-amino-4-azabenzimidazole was prepared by the following procedure:

11.4 g. of S-amino-4-azabenzimidazole-dihydrochloride (prepared according to the procedure set forth i Example 3, infra), was dissolved in 20 ml. of sulfuric acid, specific gravity 1.42. While the temperature was main- 10 tained at 5 to 10 C., 8 ml. of a 50% solution of nitric acid, specific gravity 1.84, in concentrated sulfuric acid,

was added slowly with stirring. The mixture was gradually warmed to 35 C. whereupon the reaction occurred. The temperature rose to 67 C. After the exotherm subsided the .mixture was heated at 50 C. for 1 /2 hours. It was then cooled, poured into ice and neutralized with concentrated ammonium hydroxide. The orange-yellow solid was filtered, washed With water and air dried. The dry solid was taken up in hot methanol, the insoluble salts were filtered off, and the methanol was concentrated. Enough water was added to effect crystallization. The melting point of the recovered 6-nitro-5-amino-4-azabenzimidazole is 294-296 C.

EXAMPLE 2 The compound diimidazo-4-azabenzimidazole I I was prepared according to the following procedure:

6.7 g. of 6-nitro-5-amino-4-azabenzimidazole (prepared according to the procedure set forth in Example 1, supra) was placed in a flask containing 100 ml. of water, 25 ml. of ethanol, 0.8 g. of platinum on carbon catalyst and 0.05 g. of platinum oxide. The reduction was carried out in a hydrogenator under 40 pounds per square inch pressure. When the theoretical amount of hydrogen was taken up the reduction was discontinued, the catalyst filtered from the solution under nitrogen and the solvent evaporated under vacuum. An excess of 97% formic acid was then added to the mixture which was refluxed overnight. The excess formic acid was removed by evaporation under vacuum and the residue was taken up in water and made only slightly acid with 10% sodium hydroxide. The resulting solid was filtered and taken up in hot water and treated with decolorizing charcoal. The resultant 5diimidazo-4-azabenzimidazole is a white solid which separated from the water on cooling. It has a melting point of from 385405 C.

EXAMPLE 3 The compound 5-arnino-4-azabenzimidazole dihydrochloride \N N .2HOl

was made according to the following procedure:

19 g. of 2,3,6-triaminopyridine dihydrochloride was added to 200 ml. of 98-100% formic acid and the solution was refluxed for 10 hours and evaporated to dryness on a rotary evaporator. The residue was treated with ml. of concentrated hydrochloric acid, heated on a steam bath for about 15 minutes, treated with charcoal and filtered hot. The volume was reduced to about 25 ml. on a rotary evaporator and to the hot solution was added 5075 ml. of ethanol. Upon cooling, light tan needles of 5-amino-4-azabenzimidazole dihydrochloride formed. The melting point of the product was found to be 285-288 C.

The 2,3,6-triaminopyridine dihydrochloride employed above was made by the following procedure:

A mixture of 25 gms. of 2,6-diamino-3-phenylazopyri dine hydrochloride, 200 ml. of water, 50 ml. of concentrated hydrochloric acid and 2 spatulas full of 5% platinum on charcoal was reduced at 40 pounds per square inch of pressure at room temperature until theoretical EXAMPLE 4 The compound 6-chloro-4-azabenzimidazole was prepared according to the following procedure:

A solution of gms. of 5-chloro-2,3-diaminopyridine in 50 ml. of 98100% formic acid was refluxed gently for one hour. The solution was evaporated to dryness using a rotary evaporator. The residue, a tan colored solid, was dissolved in about 800 ml. of boiling water, treated with charcoal and filtered hot. The charcoal residue was extracted with about 500 ml. of boiling water and filtered hot. The filtrates were combined and evaporated to about 300 ml. and cooled. The product was filtered and dried. Yellowish-white crystals of 6-chloro-4- azabenzimidazole with a melting point of 238241 C. were recovered.

EXAMLE 5 The compound 5-hydroxy-4-azabenzimidazole was prepared according to the following procedure:

12.7 gms. of 5-amino-4-azabenzimidazole dihydrochloride (Example 3, supra) were added to ml. of concentrated sulfuric acid in 400 ml. of water. The solution was cooled to 510 C. and a solution comprising 7.2 gms. of NaNO in 75 ml. of water was added dropwise with stirring. After stirring an additional 2 hours after the addition of the nitrite at 5-10 C., the solution was carefully neutralized with 10% sodium hydroxide. The product slowly crystallized on stirring in the ice bath was filtered and washed with a few milliliters of cold water. On recrystallization from 300-400 ml. of water yellowish needles with a melting point of 318324 C. were recovered.

EXAMPLE 6 The compound 6-bromo-4-azabenzimidazole \NAN 12 EXAMPLE 7 The compound 2-methyl-6-chloro-4-azabenzimidazole was prepared according to the following procedure:

5 gms. of 2,3-diamino-5-chloropyridine was refluxed with 50 ml. of acetate anhydride for 5 hours. The solution was evaporated to dryness on a vacuum rotary dryer. Several crystallizations were made from toluene which re sulted in white crystals of 2-methyl-6-chloro-4-azabenzimidazole with a melting point of 2l02l1.5 C.

EXAMPLE 8 The compound 6-bromo-5-methyl-4-azabenzimidazole was prepared according to the following procedure:

A solution of 10.6 gms. of 2-amino6-methylpyridine in 47 gms. of 20% sulfuric acid was cooled in ice water and 18.7 gms, of bromine was added dropwise over 15 minutes with continuous stirring. It was stirred for an additional half hour at room temperature until a colorless solution resulted. It was then cooled again in ice water and made alkaline by adding gms. of ice cold aqueous 20% sodium hydroxide dropwise. A white solid resulted, which was filtered and dried in a vacuum desiccator. The product, 2-amino-5-bromo-6 methylpyridine, was recrystallized from ligroin and was found to have a melting point between 70 and 71 C.

14- gms. of Z-amino-5-bromo-6-methylpyridine was slowly added with stirring to 60 ml. of concentrated sulfuric acid which had been cooled to 20 C. The resultant solution was warmed to 55 C, and 4.7 cc. of concentrated nitric acid was added dropwise at such a rate that the temperature remained at about 5560 C. The solution was stirred for one hour and then poured over 150 gms. of cracked ice and treated with 40% sodium hydroxide to precipitate 2-amino-3-nitro-5-bromo-6-methylpyridine which was recrystallized from butanol. The melting point of the 2-amino-3-nitro-5-bromo-6-methylpyridine was found to be 207209 C.

2.4 gms. of 2-amino-3-nitro-5-bromo-6-methylpyridine and 150 cc. of ethyl acetate were hydrogenated in the presence of Raney nickel. The resultant clear solution was filtered and the catalyst washed with ethyl acetate. Without heating ethyl acetate was evaporated on a rotary dryer. An off-white solid was produced and recrystallized from water. The resultant 2,3-diamino-5-bromo-6-rnethylpyridine was found to have a melting point of 128 C.

3.8 gms. of 2,3-diamino-5-bromo-6-methylpyridine was heated with 130 cc. of 96100% formic acid in a 250 cc. round bottom flask equipped with a stirrer and condenser for 19 hours at a reflux temperature. The mixture was cooled to room temperature and half of the formic acid was removed by evaporation. The remainder of the solution was poured into cc. of water and neutralized to pH 7 with concentrated ammonium hydroxide. A tan, solid 6-bromo-5-methyl-4-azabenzimidazole was recovered. The material was purified from ethyl acetate and was found to have a melting point between 205 and 206 C.

13 EXAMPLE 9 The compound S-methyl-4-azabenzimidazole EXAMPLE 10 The compound methane sulfonamido-4-azabenzimidazole hemihydrate i I 1/2Hfl0 HaCOzSN N was prepared according to the following procedure:

A solution of 2.5 m1. of 50% sodium hydroxide was added dropwise to a stirred solution of 7.21 gms. of 5- amino-4-azabenzimidazole dihydrochloride (Example 3, supra). To the resulting suspension 4.8 grns. of methanesulfonyl chloride was added dropwise and then followed with an additional 3.4 ml. of a 50% solution of sodium hydroxide. The precipitate was filtered and washed with isopropanol yielding 6.7 gms. of solid material with a melting point of 167-169 C. Recrystallization from a methanol-isopropanol mixture gave yellow needles of 5- methane-sulfonamido-4 azabenzimidazole hemihydrate with a melting point of 181-183" C.

EXAMPLE 11 The compound 5-bromo-4-azabenzimidazole was prepared according to the following procedure:

A solution of 10.35 gms. of 5 amino 4 azabenzimidazole dihydrochloride (Example 3, supra) in 25 ml. of 48% solution of hydrobromic acid was cooled to C. and 7.8 ml. of bromine was added under stirring over a period of 35 minutes. A solution of 8.7 grns. of sodium nitrite in 13 ml. of water was added at 0 C. over a period of 30 minutes and the stirring was con tinued at 10 C. for 15 minutes. A solution of sodium hydroxide was then added at the same temperature. The solution was filtered and then extracted continuously with ethyl acetate. Evaporation of the solvent gave 4.66 grns. of solid material having a melting point of 223-227 C. which, on crystallization from ether gave 5-bromo-4- azabenzimidazole crystals with a melting point of 229- 233 C.

The present invention will be illustrated in greater de tail in conjunction with the following specific examples which set out representative photographic products and processes which, however, are also intended to be illustrative and not of limiting effect. The examples clearly show not only the excellent antifoggant properties of the compounds of the present invention, particularly at low 14 temperatures, but also illustrate the speed stability of photographic systems employing the compounds.

EXAMPLE 12 An image-receiving element was prepared by coating a cellulose nitrate subcoated baryta paper with the partial butyl ester of polyethylene/maleic anhydride copolymer prepared by refluxing, for 14 hours, 300 gms. of DX- 84031 resin [trade name of Monsanto Chemical Co., St. Louis, Mo., for high viscosity poly(ethylene/maleic anhydride)], 140 grns. of n-butyl alcohol and 1 cc. of phosphoric acid to provide a polymeric acid layer approximately 0.3 mil thick. The external surface of the acid layer was coated with a 4% solution of partial acetaldehyde acetal of polyvinyl alcohol in water-methanol-isopropanol to provide a polymeric spacer layer approximately 0.15 mil thick. The external surface of the spacer layer was then coated with a 2:1 mixture, by weight, of polyvinyl alcohol and poly-4-vinylpyridine, at a coverage of approximately 600 mgs. per square foot, to provide a polymeric image-receiving layer approximately 0.40 mil thick. The thus-prepared image-receiving element was then baked at 180 F. for 30 minutes and then allowed to cool.

A multicolor, multilayer photosensitive element was prepared in a manner similar to that disclosed in the aforementioned U.S. Patent No. 3,345,163 and detailed hereinbefore. In general, the photosensitive elements comprised a support carrying a red-sensitive silver halide emulsion stratum, a green-sensitive silver halide emulsion stratum and a blue-sensitive silver halide emulsion stratum. In turn, the emulsions had dispersed behind them in water-immiscible organic solvents and contained in separate gelatin polymeric layers, respectively, a cyan dye developer, a magenta dye developer and a yellow dye developer. A gelatin interlayer was positioned between the yellow dye developer layer and the green-sensitive emulsion stratum, and also between the magenta dye developer layer and the red-sensitive emulsion stratum. The particular dye developers employed in the photosensitive elements were 1,4-bis (a-methyl-{i-hydroquinonyl-ethylamino) 5,8 dihydroxyanthraquinone (a cyan dye developer) 2-(p-[2,5'-dihydroxyphenethyl] -phenylazo)-4- isopropoxy-l-naphthol (a magenta dye developer); and 1 phenyl 3 n hexyl carbamyl 4 (p-[hydroquinonylethyl]-phenylazo)-5-pyrazolone (a yellow dye developer). The last-mentioned yellow and magenta dye developers are disclosed in U.S. Patent- No. 3,134,764 and the cyan dye developer is disclosed in U.S. Patent No. 3,135,606.

The photosensitive element was then exposed through a step wedge to selectively filtered radiation and processed by spreading an aqueous liquid control processing composition comprising:

Water cc Potassium hydroxide gms 10 Hydroxyethyl cellulose gms- 3.8 0.1% aqueous solution of potassium iodide gms 5 1-benZyl-2-pic0linium bromide gmS 2.5 Potassium thiosulfate gm 0.45

between said image-receiving element and said exposed multicolor element as they were brought into superposed relationship in the absence of actinic radiation. After an imbibition period of 1 minute, the image receiving element was separated from the remainder of the film assembly.

A second control was formulated as above with the addition of 3.5 grns. of benzotriazole antifoggant to the processing composition.

A test was formulated as above employing 7.8 grns. of 5-methyl-6-bromo-4-azabenzimidazole in lieu of the benzotriazole antifoggant. The results are set out in tabular form below, and concisely present comparisons of the silver and fog build-up at intervals of 5, 10 and 60 seconds.

15 Silver and fog buildup were individually measured on a develograph instrument which utilizes the infrared attenuation characteristic of developed silver to monitor the dynamics of the development process. Under-developed silver halides are relatively transparent and infrared inerties of a -methyl-4-azabenzimidazole containing processing composition as compared to the primary control processing composition and to a secondary control processing compsition containing an equimolar amount of benzotriazole. As before, the data indicates that the resensitive, while developed silver grains attenuate in the 5 straining properties of the instant test compound are infrared--the infrared density of the developed metallic secondary to its antifoggant properties.

Exposed Silver Buildup Fog Buildup A Processing Time in Seconds Processing Composition 5 60 5 10 60 5 10 i0 Primarycontrol 0.69 0.76 0.86 0.25 0.31 0.33 0.44 0.45 0.53

Primary control containing 1.4% benzotriazole Primary control containing 1.56% 5-111ethyl-4-aZabenzimidazole EXAMPLE 15 The procedure of Example 13 was again carried out utilizing as an antifoggant 6-methyl-4-azabenzimidazole.

Exposed Silver Buildup Fog Buildup A Processing Time in Seconds Processing Composition 5 10 60 5 10 60 5 10 60 Control 2.15 2.55 3.20 0.90 1.40 2.35 1 115 0.85 Control Plus Benzotriazole... 1.93 2.43 3.23 0.23 0.38 1.40 1.70 2 05 1.83 Control Plus 5-methy1-6-brom 1.60 1.90 3.03 0.15 0.35 0.85 1.45 1.60 2.18

The high reduction in fog buildup as compared with the modest reduction in silver buildup with the desired 60 seconds processing evidences the fact that the restraining properties of the preferred test composition are clearly secondary to its antifoggant properties, i.e., there is no substantial retardation in development.

EXAMPLE 13 The procedure of Example 12 was followed utilizing a primary control processing composition comprising:

Water cc 100 Potassium hydroxide gms 9 Hydroxyethyl cellulose gms 3.8 Methylphenyl hydroquinone gm 0.6

with a typical gelatino silver halide (black and white) negative sheet material such as, for example, that found in type 107 film packs, sold by Polaroid Corporation, Cambridge, Mass, and a secondary control processing composition and a test processing composition containing equimolar amounts of benzotriazole and 6-chloro-4-azabenzimidazole, that is, 0.7 and 0.9%, respectively. The fog buildup, at 5, 10 and 60 seconds processing time, comprised 0.15, 0.18, 0.23; 0.3, 0.5, 0.8; and 0.00, 0.00, 0.05, respectively.

The preceding comparative testing was repeated utilizing 6-chloro-4-azabenzimidazole and the identical processing compositions as above with 1.2% l-benzyl-u-picolim'um bromide added in each instance, and 1.4% benzotriazole added to the secondary control formulation. The corresponding fog buildup was 0.23, 0.33, 0.35; 0.03, 0.08, 0.10; and 0.00, 0.00, 0.05.

EXAMPLE 14 The procedure of Example 13 was carried out using as the primary control procesing composition the following:

The following tabulation depicts the antifoggant prop- The primary control processing composition comprised:

A processing composition containing 0.783% G-methyl- 4-azabenzimidazole was compared with the primary control processing composition and a secondary control processing composition containing an equimolar amount (0.7%) of benzotriazole. The fog buildup, at 5, l0 and 60 seconds processing time, comprised 0.15, 0.20 and 0.20 for the primary control; 0.02, 0.05 and 0.05 for the secondary control; and 0.00, 0.00 and 0.05 for the test composition.

Similar experiments with this compound were carried out using a primary control processing composition similar to the composition above except that it contained 1.2% of 1 benzyl on picolinium bromide. The corresponding fog build-up was 0.20, 0.25, 0.25; 0.05, 0.10. 0.10; and 0.00, 0.00, 0.02.

It is well worth noting that both with and without the quaternary salt, the test compound, 6-methyl-4-azabenzimidazole, shows an almost negligible fog level.

EXAMPLE 16 In order to demonstrate the unusual low temperature antifogging effect of the compounds utilized in the instant invention, photosensitive sheet material of Example 12 was selectively exposed to blue light and processed according to the procedure of that example employing processing compositions containing illustrative antifoggant compositions of the present invention. The following formulation was utilized as a control processing composition:

Water cc Potassium hydroxide gms l0 Hydroxyethyl cellulose gms 3.8 1-benzyl-2-picolinium bromide gms 2.5 Benzotriazole gms 3.5 1% aqueous solution of potassium iodide gms Potassium thiosulfate gm 0.5

In performing the following comparative tests, the The lower stain points and speed stability may be eascompositions containing the antifoggants of the present ily appreciated by referring to FIG. 2 of the drawings, invention were modified slightly in the following manwhich depicts log exposure vs. density for the blue curve, ner: In lieu of 0.5 gm. of potassium thiosulfate, 0.45 gm. i.e., yellow dye density, for diffusion transfer processof potassium thiosulfate was utilized; and in lieu of the ing at 50 F. utilizing the specified antifoggants of the 3.5 gms. of benzotriazole, 1.5 gms. of benzotriazole was present invention, as compared with difiusion transfer utilized. Additionally, in lieu of the 3 gms. of a 1% processing utilizing benzotriazole as the antifoggant. aqueous potassium iodide solution, 5 grns. was utilized. In general, the optimum concentration of the agents The antifoggant-containing processing compositions to be employed should be determined empirically for of the instant invention contained the following amounts each specific photographic system. In general, such conof antifoggant, respectively centration range is between 0.005 to 5.0 mgs. per milli- Test 1: 0.1% 4-azabenzimidazole; Test 2: 0.173% 5- mole of silver halide present in the silver halide emulamino 4 azabenzimidazole hydrochloride; Test 3; sion of concern, depending on the fogging characteris- 0.111% 5 methyl 4 azabenzimidazole; Test 4: tics of the silver halide emulsion. In a preferred embodi- 0.l29% 6 chloro 4 azabenzimidazole; Test 5: 0.111% merit, the incorporation of from about 0.02 to 1.0% of G-methyl 4 azabenzimidazole; and Test 6: 0.177% 6- the compounds of the present invention, based on the bromo-5-methyl-4-azabenzimidazole. weight of the processing composition utilized in the dif- The following tabulation displays a comparison of fusion transfer photographic process, provides particuyellow stain point and blue 0.3 speed, and illustrates larly desirable results. Although concentrations in excess that good speed stability results from the use of the antiof the first mentioned range may be employed, an infoggants of the present invention. The 0.3 speed is taken crease in the concentration beyond the designated limfrom the blue curves on a standard log exposure-density its generally provides no additional beneficial results.

graph. Conversely, concentrations below that of the designated Stain point as applied to the instant invention is synrange merely decrease fog control below the effective onymous with D of the receiving sheet after process levels generally sought, but do not negate the achieveing, which is a measure of the dye density in the receivment of some beneficial fog control.

ing sheet, after 60 seconds imbibition, corresponding to The agents themselves may be initially disposed in any a fully exposed section of the photosensitive element. one or more processing composition permeable layers of Stain, for the present purposes, may be characterized as the film units photosensitive and/or image-receiving elethe level of transfer image dye density achieved, at total ments, for example, at any stage during its manufacture,

exposure of the photosensitive element, in a diffusion in supplementation of, or in replacement of, the previtransfer process. ously illustrated disposition as a compound of the proc- The following tabulation compares the antlfoggant essing composition. properties of the compounds of the instant invention The liquid processing composition referred to for efwith a control processing composition, as described fectmg monochromatic and multicolor transfer processes above, at 50 F. comprises at least an aqueous solution of an alkaline Yellow 0.3 Test Stain Blue No. Processing Composition Point Speed Primary controL.. 0.26 0.25 1 Composition containing .1% 4-azabenzim1dazole 0.20 0. 2 Composition containing 173% of 5amino-4-azabenzimidazole 0 20 0.57 3 Composition containing .111% 5-methyl-4-azabenzirnidazole 0.22 0. 46 4 Composition containing .129% of 6chloro-4-azabenzimidazole 0. 21 O. 40 5 Composition containing .111% of S-methyl-Qazabenzimidazol 0. 21 0. 42 6 r. Composition containing .111% G-bromo-o-methyli azabenzimid zole- 0.17 0. 46

The following tabulation compares the antifoggant compound, for example, diethylamine, sodium hydroxproperties of the compounds of the instant invention ide or sodium carbnoate and possesses a pH in excess of with a control processing composition, as described 50 12 preferably. If the liquid processing composition is to above, at F. be applied to the emulsion by being spread thereon, pref- Yellow 0.3 Test Stain Blue No. Processing Composition Point Speed Primarycontrol. 0.16 0.82 1 Composition containing 0.1% 4-azabenzimidazole- 0 12 0. 2. Composition containing 173% fi-amino-azabenz' 0.14 0. 82 3. Composition containing .111% 5-methyl-4azabenzirnidazole- 0. 12 0.85 4. Composition containing .12Q% trchloroA-azabenzimidazolm- 0.13 0. 78 5 Composition containing 111% fi-methyl-iazabenzimidazole- 0.13 0.78 6 Composition containing 0.177% of 6br0mo-5methyl4 azabenzimidazole 0.10 0.75

The following tabulation compares the antifoggant erably in a relatively thin uniform layer, it includes a activities of the compounds of the present invention with a viscosity-increasing compound constituting a film-formprocessing composition control, as described above, at 65 ing material of the type which, when said composition 100 F. 1s spread and dried, forms a relatively firm and relatively Yellow 0.3 Test Stain Blue No. Processing Composition Point Speed Primary control- 0.13 96 1 Composition containing 0.1% i-azabenzim dazole 0. 11 0. 99 2. Composition containing 0.173% of 5-amino-4-azabenzimidazole dihydrochloride 0. 12 95 3 Composition containing 0.111% 5-methyl-4azabenzimidazole 0.12 97 4. i- Composition containing 0.129% 6-chloro4-azabenzimidazole 0.12 93 5- Composition containing 0.111% fi-methyl-q-azabenzimidazole 0. l2 6 Composition containing 0.177% 6-bromo-5methyl-4azabenzimidazole 0. 12 90 stable film. A preferred film-forming material is a high molecular weight polymer such as a polymeric, watersoluble ether which is inert to an alkaline solution such as, for example, a hydroxyethyl cellulose or sodium carboxymethyl cellulose. Other film-forming materials or thickening agents whose ability to increase viscosity is substantially unafiected if left in solution for a long period of time may also be used. The film-forming material is preferably contained in the processing composition in suitable quantities to impart to said composition a viscosity in excess of 1,000 centipoises at a temperature of approximately 24 C. and preferably of the order of 1,000 to 200,000 centipoises at said temperature. Illustrations of suitable liquid processing compositions may be found in the several patents and copending applications herein mentioned and also in examples herein given. Under certain circumstances, it may be desirable to apply a liquid processing composition to the photosensitive element prior to exposure, in accordance with the technique described in U.S. Patent No. 3,087,816, issued Apr. 30, 1963.

It will be noted that the liquid processing composition employed may contain an auxiliary or accelerating developing agent, such as p-methylaminophenol, 2,4-diaminophenol, p-benzylaminophenol, hydroquinone, toluhydroquinone, phenylhydroquinone, 4-methylphenylhydroquinone, etc. It is also contemplated to employ a plurality of auxiliary or accelerating developing agents, such as a 3-pyrazolidone developing agent and a benzenoid developing agent, as disclosed in U.S. Patent No. 3,039,- 869, issued June 19, 1962. As examples of suitable combinations of auxiliary developing agents, mention may be made of 1-phenyl-3-pyrazolidone in combination with p-benzylaminophenol and l-phenyl 3 pyrazolidone in combination with 2,5 bis-ethyleneimino hydroquinone. Such auxiliary developing agents may be employed in the liquid processing composition or they may be initially incorporated, at least in part, in one or more permeable strata of the film unit. It may be noted that at least a portion of the dye developer oxidized during development may be oxidized and immobilized as a result of a reaction, e.g., an energy-transfer reaction, with the oxidation product of an oxidized auxiliary developing agent, the latter developing agent being oxidized by the development of exposed silver halide. Such a reaction of oxidized developing agent with unoxidized dye developer would regenerate the auxiliary developing agent for further reaction with the exposed silver halide.

In addition, development may be desirably effected in the presence of an onium compound, particularly a quaternary ammonium compound, in accordance with the processes disclosed in U.S. Patent No. 3,173,786.

The support layers referred to may comprise any of the various types of conventional rigid or flexible supports, for example, glass, paper, metal, and polymeric films of both synthetic types and those derived from naturally occurring products. Suitable materials include paper; aluminum; polymethacrylic acid, methyl and ethylesters; vinyl chloride polymers; polyvinyl acetal; polyamides such as nylon; polyesters such as polymeric films derived from ethylene glycol terephthalic acid and cellulose derivatives such as cellulose acetate, triacetate, nitrate, propionate, butyrate, acetate-propionate, or acetatebutyrate.

It will be understood that silver halides of varying halide concentrations may be advantageously employed and that the silver halide emulsions employed may be sensitized chemically and optically by any of the accepted procedures.

While a rupturable container provides a convenient means for spreading a liquid processing composition between layers of a film unit whereby to permit the processing to be carried out within a camera apparatus, the practices of this invention may be otherwise effected. For example, a photosensitive element, after exposure in suitable apparatus and while preventing further exposure thereafter to actinic light, may be removed from such apparatus and permeated with the liquid processing composition, as by coating the composition on said photosensitive element or otherwise wetting said element with the composition, following which the permeated, exposed photosensitive element, still, without additional exposure to actinic light, is brought into contact with the imagereceiving element for image formation in the manner heretofore described.

In all examples of this specification, percentages of components are given by weight unless otherwise indicated.

Throughout the specification and appended claims, the expression positive image has been used. This expression should not be interpreted in a restrictive sense since it is used primarily for purposes of illustration, in that it defines the image produced on the image-carrying layer as being reversed, in the positive-negative sense, with respect to the image in the photosensitive element. As an example of an alternative meaning for positive image." assume that the photosensitive element is exposed to actinic light through a negative transparency. In this case, the latent image in the photosensitive element Wlll be a positive and the image produced on the image-carrying layer will be a negative. The expression positive image is intended to cover such an image produced on the image-carrying layer.

Throughout the specification and claims, the expression superposing has been used. This expression is 1ntended to cover the arrangement of two layers in overlying relation to each other either in face-to-face contact or in separated condition and including between them at least one layer or stratum of a material which may be a viscous liquid.

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

What is claimed is:

1. In a process for forming a photographic silver image which comprises the step of developing an ex posed photosensitive element containing a silver halide emulsion with an aqueous processing composition, the improvement which comprises conducting said process in the presence of an effective amount of an antifoggant of the formula:

wherein:

R and R are each a hydrogen, halogen, lower alkyl.

lower alkoxy, nitro, amino, hydroxy, aryl, carboxamido, or sulfonamido group;

R and R when taken together, are

and

R is a hydrogen or lower alkyl group.

2. A process as defined in claim 1, wherein said process is conducted at a temperature within the range of about 50-100 F.

3. A process as defined in claim 1, wherein said antifoggant is selected from the group consisting of S-methyi- 6-bromo-4-azabenzimidazole, 6 chloro-4-azabenzimida- 21 zole, -methyl-4-azabenzimidazole, 6-bromo-4-azabenzimidazole and 6-methyl-4-azabenzimidazole.

4. A process as defined in claim 1 which includes the steps of developing said exposed photosensitive element with an aqueous alkaline difiusion transfer processing composition; forming thereby an imagewise distribution of image-forming components in said photosensitive element, as a function of the point-to-point degree of exposure thereof; and transferring at least part of said imagewise distribution, by diffusion, to a contiguous imagereceiving layer to provide thereto a photographic diffusion transfer image.

5. A process as defined in claim 4, wherein said antifoggant is selected from the group consisting of 5-methyl- 6-bromo-4-azabenzimidazole, 6 chloro-4-azabenzimidazole, 5-methyl-4-azabenzimidazole, 6-bromo-4-azabenzimidazole and 6-methyl-4-azabenzimidazole.

6. A process as defined in claim 4, wherein said imageforming components comprise soluble silver complex.

7. A process as defined in claim 4, wherein said imageforming components comprise color image-forming components.

8. A process as defined in claim 7, wherein said color image-forming components comprise a dye which is a silver halide developing agent.

9. A process for forming transfer images in color, as defined in claim 8, which includes, in combination, the steps of exposing a photosensitive element which comprises at least two selectively sensitized silver halide emulsion layers each having a dye of predetermined color associated therewith, which dye is a silver halide developing agent and is soluble and diifusible in alkali; contacting said exposed photosensitive element with an aqueous alkaline processing composition; effecting thereby development of the latent images contained in each of said silver halide emulsions; immobilizing the dye associated with each of said emulsions as a result of development; forming thereby an imagewise distribution of mobile dye, as a function of the point-to-point degree of exposure thereof; and transferring, by imbibition, at least a portion of each of said imagewise distributions of mobile dye to a superposed image-receiving element to provide thereto a multicolor dye transfer image.

10. A process of forming transfer images in color, as defined in claim 9, which includes, in combination, the steps of exposing a photosensitive element comprising blue-sensitive, green-sensitive and red-sensitive gelatino silver halide emulsion layers mounted on a common support, said blue-sensitive, green-sensitive and red-sensitive silver halide emulsion layer having associated therewith, respectively, yellow, magenta and cyan dyes, each of said dyes being a silver halide developing agent soluble and diifusible in alkali; contacting said exposed photosensitive element with an aqueous alkaline processing composition; effecting thereby development of the latent image contained in each silver halide emulsion; immobilizing said yellow, magenta, and cyan dye, as a function of development of their respective associated silver halide emulsion; forming thereby an imagewise distribution of mobile yellow, magenta and cyan dye; and transferring, by imbibition, at least a portion of each of said imagewise distributions of mobile dye to a superposed image-receiving element to provide thereto a multicolor dye transfer image.

11. A process as defined in claim 10, wherein said antifoggant is selected from the group consisting of S-methyl- 6-bromo-4-azabenzimidazole, 6 chloro-4-azabenzimidazole, 5-methyl-4-azabenzimidazole, 6-bromo-4-azabenzimidazole and 6-methyl-4-azabenzimidazole.

12. A process as defined in claim 10, wherein said process is conducted at a temperature within the range of about 50-100 F.

13. As a product, a photosensitive element which comprises a support layer carrying a photosensitive silver halide emulsion having associated therewith an antifoggant of the formula:

and R is a hydrogen or lower alkyl group.

14. As a product, a photosensitive element as defined in claim 13, wherein said antifoggant is selected from the group consisting of S-methyl-6-bromo-4-azabenzimidazole, 6 chloro-4-azabenzimidazole, 5-methyl-4-azabenzimidazole, 6-bromo-4azabenzimidazole and 6-methyl-4- azabenzimidazole.

15. As a product, a photosensitive element as defined in claim 13, wherein said silver halide emulsion has a dye, which dye is a silver halide developing agent, associated therewith.

16. As a product, a photosensitive element as defined in claim 15, wherein said dye is disposed in a separate layer intermediate said silver halide emulsion and said support.

17. As a product, a photosensitive element as defined in claim 13, wherein said support layer carries on one surface at least two selectively sensitized silver halide emulsion layers each having a dye, which dye is a silver halide developing agent, of predetermined color associated therewith.

18. As a product, a photosensitive element as defined in claim 17, wherein each of said selectively sensitized photosensitive emulsion layers has predominant spectral sensitivity to separate regions of the spectrum and the dye associated with each of said emulsion layers possesses a spectral absorption range substantially complementary to the predominant sensitivity range of its associated emulsion layer.

19. As a product, a photosensitive element as defined in claim 18, wherein said photosensitive silver halide 50 emulsion layers comprise, in sequence, a red-sensitive silver halide emulsion layer, a green-sensitive silver halide emulsion layer, and a blue-sensitive silver halide emulsion layer, having associated therewith, respectively, cyan, magenta and yellow dyes, each of said dyes being silver halide developing agents.

20. As a product, a photographic film unit as defined in claim 13, including a diffusion transfer image-receiving element affixed at least one edge of said photosensitive element. 60 21. As a product, a photographic film unit as defined in claim 20 including a rupturable container retaining an aqueous alkaline processing composition affixed one edge of one of said photosensitive and said image-receiving elements and adapted upon rupture to distribute its contents intermediate said photosensitive element and said image-receiving element upon super-positioning of said elements.

22. As a product, a photographic film unit as defined in claim 21, wherein said antifoggant is disposed in said processing composition.

23. As a product, a photographic film unit as defined in claim 19 including a diffusion transfer image-receiving element afiixed one edge of said photosensitive element and a rupturable container retaining an aqueous alkaline processing composition containing said antifoggant af- 23 fixed one edge of one of said photosensitive and said image-receiving elements and adapted upon rupture to distribute its contents intermediate said photosensitive element and said receiving element upon super-positioning of said elements.

24. As a product, a photographic film unit as defined in claim 23, wherein said antifoggant is selected from the group consisting of 5-methyl-6-brom0-4-azabenzimidazole, 6 chloro-4-azabenzimidazole, 5-methyl-4-azabenzimidazole, 6-bromo-4-azabenzimidazole and 6-methyl-4- azabenzimidazole.

References Cited UNITED STATES PATENTS 2,324,123 7/1943 Weissberger 96-56 Peterson 96-456 Spath 96-22 Green et a1. 96-3 Salminen 96-55 Rogers et a1. 96-3 Dersch et a1. 96-66..5 Idelson et a1. 96-29 US. Cl. X.R.

Images