US3685991A - Novel photographic products and processes - Google Patents

Abstract

THE PRESENT INVENTION RELATES TO AN INTEGRAL PHOTOGRAPHIC SILVER DIFFUSION TRANSFER FILM UNIT WHICH COMPRISES AN ADDITIVE MULTICOLOR SCREEN, SILVER PRECIPITATING NUCLEI, AND A LAYER COMPRISING PHOTOSENSITIVE SILVER HALIDE CRYSTALS, WHEREIN A SILVER HALIDE SOLVENT IS DISPOSED IN THE FILM UNIT IN A INACTIVE SPECIES, I.E., AS A SILVER HALIDE SOLVENT PROCURSOR, ADAPTED TO BE CONVERTED TO THE ACTIVE FORM BY THE APPLICATION OF A LIQUID PROCESSING COMPOSITION. PREFERABLY, A COMPOUND WHICH RELEASES A SILVER HALIDE SOLVENT IN THE PRESENCE OF ALKALI IS EMPLOYED, MORE PREFERABLY, A QUINONE-OR NAPHTHOQUINONE-METHIDE PRECURSOR CONTAINING THE SILVER SOLVENT MOIETY. IN A PARTICULARY PREFERRED EMBODIMENT, THE FILM UNIT ALSO CONTAINS A DEVELOPER OR DEVELOPER PRECURSOR.

Description

Aug. 22, 1972 J. M. GRASSHOFF ETAL 3,685,991

NOVEL PHOTOGRAPHIC PRODUCTS AND PROCESSES Filed March 8, 1971 I //l l I V E E 7 E INVENTORS J MICHAEL GRASSHOFF on y LLOYD 0. TAYLOR Ilwwn run/l m wrwL United States Patent Oflice Patented Aug. 22, 1972 US. Cl. 96--26 31 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to an integral photographic silver difiusion transfer film unit which comprises an additive multicolor screen, silver precipitating nuclei, and a layer comprising photosensitive silver halide crystals, wherein a silver halide solvent is disposed in the film unit in an inactive species, i.e., as a silver halide solvent precursor, adapted to be converted to the active form by the application of a liquid processing composition. Preferably, a compound which releases a silver halide solvent in the presence of alkali is employed, more preferably, a quinone-or naphthoquinonemethide precursor containing the silver solvent moiety. In a particularly preferred embodiment, the film unit also contains a developer or developer precursor.

BACKGROUND OF THE INVENTION (1) Field of the invention The present invention is directed to providing new and improved silver and additive color diffusion transfer process photographic film units which preferably comprise a composite photosensitive element adapted to provide, as a function of the point-to-point degree of the elements photoexposure, integral negative and positive silver images which include a negative silver image in superposed relationship with a positive silver image.

(2) Description of prior art As disclosed in US. Pat. No. 2,861,885, desirable composite prints comprising both negative and positive images in superposition may be provided by a silver diffusion transfer reversal process employing a photosensitive silver halide emulsion which upon substantially full development of its exposed areas, as a function of exposure, provides a relatively low maximum density negative silver image with relation to the high maximum density positive silver image provided by a silver precipitating environment of the type detailed below. In a composite print produced in accordance with the disclosure of the cited patent, the covering power of a given mass of image silver in the print-receiving element is there stated to range from 14 to 15 times that of an equal mass of image silver in the silver halide element and, that for transparency employment, a maximum negative density of as high as 1.0 density units may be permissible where the maximum positive density is about four or more times as great.

The image-receiving element so employed is disclosed to be constituted as to provide an unusually effective silver precipitating environment which causes the silver deposited therein, in comparison with negative silver developed in the silver halide layer, to possess an extraordinarily high covering power, that is, opacity per given mass of reduced silver; see Edwin H. Land, One Step Photography, Photographic Journal, Section A., pp. 7-15, January 1950.

Specifically, to provide such environment, silver precipitation nuclei are disclosed to be disposed within the silver receptive stratum in clusters possessing a diameter directly proportional to the mass of image silver to be deposited in situ by reduction. Such conformation is employed to cause image silver to precipitate, in association with the silver precipitation nuclei clusters, with the required density and of a size directly related to the physical parameters of the clusters and the image silver thus precipitated, in situ, in galaxies of chosen physical parameters to provide image conformation in which the elemental silver of the image-receiving element may possess a very high order of covering power, for example, five to fifteen or more times that of the negative image silver in the silver halide layer.

In accordance with the disclosures of US. Pats. Nos. 2,726,154 and 2,944,894 additive multicolor reproduction may be accomplished by a diffusion transfer reversal process which specifically includes exposure of an integral multilayer film assemblage through an optical screen comprising a plurality of minute optical elements and carrying photosensitive and image-receptive layers. As disclosed, diffusion transfer processing may be accomplished by permeation 'of the photoexposed integral film unit with a fluid processing composition and the image-receptive layer retained in permanent fixed rela tionship to the screen during, and subsequent to, formation of the requisite transfer image, with the operators option of separating the photosensitive layer from the remainder of the film unit, subsequent to transfer image formation, in film unit structures possessing the imagereceiving layer intermediate the screen and emulsion components.

Integral additive color diffusion transfer film assemblages, essentially comprising photoresponsive material directly providing positive image formation and possessing the sensitivity to incident electromagnetic radiation and acuity of image formation necessary to effectively provide color photographic image reproduction, are disclosed and claimed in the following copending applications, which are directed, in general, to film unit assemblages which comprise a permanently fixed laminate including a support carrying on one surface an additive color screen, photosensitive silver halide and silver precititating nuclei:

Application Serial Nos: Filing date 736,796 June 13, 1969 now US. Pat. 3,536,488. 889,656 Dec. 31, 1969 now US. Pat. 3,615,427. 889,657 Dec. 31, 1969 now US. Pat. 3,615,428. 889,660 Dec. 31, 1969 now US. Pat. 3,615,429. 889,636 Dec. 31, 1969 now US. Pat. 3,615,426.

The aforementioned applications are incorporated by reference herein in their entirety.

In the above-indicated film assemblages the silver precipitating nuclei are present in a concentration effective to provide a silver image to the film unit possessing opti cal density inversely proportional to exposure of the photosensitive silver halide layer, and specifically, in a concentration adapted to provide a silver imiage derived from unexposed silver halide crystals possessing greater covering power than that of corresponding silver image derived from identical quantum of exposed silver halide crystals.

As set forth in the above-indicated applications, improved image reproduction may be obtained by means of the improved silver image characteristics provided therein. Specifically, the above-indicated applications state that composite negative/positive silver image formation possessing an optical density inversely proportional to photoexposure of a photosensitive silver halide layer, characterized by improved silver image minimum and maximum optical densities and image acuity may be achieved by a process which includes exposing a photographic film unit, which comprises a permanent laminate containing a support carrying on one surface silver precipitating nuclei and photosensitive silver halide, and processing the film unit by contact, simultaneous with, or subsequent to exposure, with an aqueous processing composition, containing a silver halide developing agent and a silver halide solvent, to provide to the film unit the direct formation of a silver image possessing particularly desired low minimum silver image optical density, in terms of exposed areas of the film unit, and high maximum silver image optical density, in terms of unexposed areas of the film unit, as a function of exposure and development of the film unit.

The above-mentioned film units are disclosd to be particularly desirable for employment as a cine film for motion picture projection by reason of the inherent ability to simply and effectively process such a film, employing relatively simple and stable processing compositions, without the necessity of providing a process and apparatus specifically adapted to effect stripping of a separate emulsion stratum from the remainder of the film unit to provide information recordation possessing the image integrity in reproduction characteristics required for effective employment of the film.

Such film assemblages are suitable employed in a cine film system such as that described in application Scr. No. 755,901, filed Aug. 28, 1968, which includes a compact cine film cassette or container adapted to allow exposure of a film assemblage as retained therein, subsequent processing of the film to provide the desired image record and projection of the resultant image record or other presentation for viewing purposes. Thus, the film assemblage may be exposed, processed, dried if necessary, and projected without transferring the film from its original container to any other container or even in effect removing the film from the original container. The cine film system of application Ser. No. 755,901 includes a film processing station whereupon the exposed film strip is transported from a first storage reel, past an applicator where a moist processing composition to develop to a visible condition iml'ages recorded on the film is applied and thence to a second storage reel.

The processing composition may be applied to the film assemblage by a variety of methods such as, for example, doctor blades, extrusion heads, capillary applicators, wicks, and the like. The amount of processing composition applied to the assemblage should be controlled within relatively narrow limits, however, sufiicient processing composition must be applied to adequately and completely permeate the assemblage to the depth necessary and in the quantity necessary to provide the desired image conformation.

The processing composition employed will generally include an alkaline material, for example, sodium hydroxide, potassium hydroxide, sodium carbonate, or the like, and most preferably, in a concentration providing a pH to the processing composition in excess of about 12. The processing composition may, if desired, contain the sole silver halide developing agent or agents and/or solvent or solvents employed or silver halide developing agent and/or solvent in addition to that disposed as in the film unit. The relative proportions of the agents comprising the developing composition may be altered to suit the requirements of the operator. Thus, the developing composition may be modified by the employment of preservatives, alkalis, silver halide solvents, etc., other than those specifically mentioned herein. When desirable it is also contemplated to include in the developing composition components such as restrainers, accelerators, and the like, and the concentration of such agents may be varied over relatively wide range commensurate With the art.

In the film units and processes set forth in the aboveindicated U.S. Pats. Nos. 2,726,154 and 2,944,894, and the above-indicated copending applications, a quantity of processing composition and reactants will inevitably be retained within the film unit, particularly if the imagereceiving layer is maintained in permanent relationship with the emulsion as well as the screen, and this residuum may possess the capacity to deleteriously effect image quality over an extended period of time, in addition to conventional environmental degradation of image silver.

SUMMARY OF THE INVENTION The present invention is directed to novel integral photographic silver diffusion transfer process film units of enhanced image quality, particularly with respect to projected images, which film units comprise, in essence, an additive multicolor screen, silver precipitating nuclei, photosensitive silver halide, and a silver halide solvent disposed therein in an inactive species, adapted to be converted to an active form upon contact with a liquid processing composition. Preferably, the inactive solvent species or solvent precursor is converted to the active species in the presence of alkali. Particularly preferred is a quinoneor naphthoquinone-methide precursor containing the solvent moiety. An alternative film unit also includes a silver halide developer or developer precursor.

In a preferred embodiment, a film unit of the present invention comprises a support carrying, in order, on one surface an additive multicolor screen, a layer containing silver precipitating nuclei, 9. layer containing photosensitive silver halide, and, disposed in the layer containing the photosensitive silver halide, a compound adapted to provide sodium thiosulfate in the presence of alkali and a silver halide developer.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an enlarged cross-sectional view of a preferred film unit within the scope of the present invention; and

FIG. 2 is an enlarged cross-sectional view of an alternative construction of a film unit within the scope of the present invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to an integral photographic film unit particularly suited for a silver diffusion transfer process which comprises an additive multicolor screen, silver precipitating nuclei, a photosensitive silver halide layer, and a silver solvent in an inactive species, e.g., a silver halide solvent precursor adapted to be converted to the active form in the presence of liquid processing composition. Preferably, a silver halide developing agent or precursor therefor is also disposed in said film unit.

As previously characterized, a silver diffusion transfer process may be employed to provide a silver transfer image which may comprise an integral negative silver image in superposed relationship to a positive silver image adapted to exhibit greater covering power than the negative image by development of the latent image provided a photosensitive silver halide element by exposure, and substantially contemporaneous with such development, formation of a soluble silver complex by reaction of a silver halide solvent with unexposed and undeveloped silver halide of the element. The silver of the resultant soluble silver complex is at least in part precipitated in the presence of silver precipitating nuclei to provide the requisite positive silver image formation, which may optionally be retained in contiguous relationship to a negative silver image resulting from development of the latent image carried by exposed silver halide, and the concomitant reduction of exposed silver halide to negative silver or separated therefrom subsequent to substantial transfer image formation.

In the present invention, it has been found that employing a silver halide solvent in an inactive species, adapted to be activated by contact with a liquid processing composition, initially disposed in the film unit, provides greater flexibility and latitude in processing conditions since carefully controlled predetermined amounts of silver halide solvent can be made available to the system without regard to permeability of the film unit to the silver halide solvent or necessity for precise metering of the silver halide solvent. It is only necessary that the film unit be sufficiently wetted with a liquid adapted to convert the silver halide solvent to its active form. Any variation in the amount of activating liquid applied or method of application to the film unit would not be critical since only enough is required to convert the silver halide solvent to its active species.

The particular location of the inactive species of the silver halide solvent in the present invention is not critical. The silver halide solvent precursors may be disposed in a separate layer, i.e., in a polymeric matrix permeable to liquid processing composition or it may be disposed directly in one of the above-mentioned layers in the film unit. In a preferred embodiment, the inactive species of the silver halide solvent is disposed in the layer containing the photosensitive silver halide crystals.

The silver halide solvent may be disposed in the film unit in any form provided it is prevented from functioning as a silver halide solvent until activated, as by contact with the processing composition subsequent to exposure of the film unit. In one embodiment, inorganic salts such as lead salts, e.g., lead thiosulfate which can be converted to sodium thiosulfate upon contact with alkali, is employed.

The particularly preferred inactive species are compounds which may be defined as quinone-methide or naphthoquinone-methide precursors containing the silver halide solvent moiety. They may also be defined as phenols or naphthols (including protected derivatives thereof) having the desired silver halide solvent bonded to a nuclear carbon atom through a methylene (CH substituent in a position ortho or para to the hydroxyl group.

These preferred compounds may be represented by the formula:

(ANCHOR)|1-1 GHQ-SOLVENT 5 wherein:

CH -SOLVENT substituent being ortho or para to the Y substituent;

ANCHOR represents an anchoring or ballasting substituent such as is described, for example, in US. Pat. No. 3,443,940, e.g., an alkyl containing at least ten carbon atoms, such as decyl, dodecyl, stearyl, oleyl, etc., linked directly to the aromatic nucleus or indirectly through an appropriate linking group such as a CONH, -alkyleneCONH or substituent, an aromatic ring, e.g., of the benzene or naphthalene series, or a heterocyclic ring, which rings may be either bonded to a single carbon atom of the aromatic nucleus formed by the X atoms or fused thereto by being bonded to a pair of adjacent carbon atoms; a polymeric substituent, e.g., high polymer backbone; or ANCHOR may be a plurality of short chain radicals which together provide the anchoring moiety; and

n is 1 or 2.

If desired, the benzene or naphthalene nucleus of the compounds may contain other substituents providing particular desired functions, e.g., a substituent which will retard or slow down the hydrolysis rate and hence control the rate or time of release of the silver halide solvent, as will be described hereinafter.

As examples of compounds suitable for use in this invention, mention may be made of the following:

( (|)OCCH3 I CHzSSOaNQ sodium S-(p-acetoxybenzyl) thiosulfate l CH2 S S OaNa sodium S'(p-hydroxybenzyl) thiosulfate CH2S SO Na sodium S-(o-acetoxybenzyl) thiosulfate Other conventional silver halide solvents may also be employed as the SOLVENT moiety of Formula A.

The preparation of compounds Within the scope of Formula A is set forth in greater detail in US. application 'Ser. No. 99,310, filed on Dec. 17, 1970, which is incorporated herein in its entirety.

As stated above, a particularly preferred alternative embodiment includes a silver halide developing agent disposed in the film unit in addition to the silver solvent precursor. Employment of the developing agent as well as the silver solvent in the film unit permits processing of the exposed film unit to be accomplished with a minimum of externally applied processing reagent. In the case of alkali releasable silver halide solvent species, processing may be effected with an aqueous alkaline solution, e.g., sodium or potassium hydroxide.

The developing agent may be disposed in the receiving layer, photosensitive layer or in a separate permeable polymeric layer and further may be disposed in the same layer as the silver halide solvent precursor. The developer may be employed in its active form or it may be disposed in the film unit as a developing agent precursor releasable in the presence of aqueous processing composition, such as those disclosed and claimed in aforementioned U.S. application Ser. No. 99,310.

Referring now to the drawings, FIG. 1 is an enlarged cross-sectional view of an integral film unit within the scope of the present invention which comprises transparent film base or support 10 carrying on one surface, in order, additive multicolor screen 11 comprising geo metrically repetitive plurality of primary red color filter elements, a plurality of primary green color filter elements and a plurality of blue color filter elements arranged in a repetitive distribution in side-by-side relationship in substantially a single plane, substantially photoinsensitive layer 12 carrying silver precipitating nuclei, photosensitive layer 13 containing silver halide crystals and a silver halide solvent precursor.

FIG. 2 illustrates an alternative embodiment of the present invention wherein the film unit comprises transparent support member carrying on a first side, in order, additive multicolor screen 11, substantially photoinsensitive layer 12 carrying silver precipitating nuclei, photosensitive layer 14 containing silver halide crystals, permeable polymeric layer 15 containing silver halide solvent precursor and silver halide developing agent.

As will be readily recognized, additional layers may optionally be included in the film unit such as, for example, separate layers retaining processing reagents, spatial layers, barrier layers, protective layers and support layers.

In the practice of the present invention, the silver precipitating nuclei may be disposed within the photosensitive silver halide stratum of the film unit assemblages, in a separate layer or layers or element contiguous one or both surfaces of the silver halide stratum and the silver halide stratum may comprise two or more silver halide strata, each optionally retaining silver precipitating nuclei, and may include a separate silver precipitating nuclei layer positioned intermediate separate silver halide strata.

For the purpose of insuring the production of a positive image possessing a high covering power, the silver precipitating nuclei will be disposed within the film unit in a concentration per unit area effective to cause image silver derived from unexposed silver halide crystals to possess the desired opacity per given mass of in situ reduced silver.

In general, silver precipitating nuclei comprise a specific class of adjuncts well known in the art as adapted to effect catalytic reduction of solubilized silver halide specifically including heavy metals and heavy metal compounds such as the metals of Groups I-B, II-B, IV-A, VIA, and VIII and the reaction products of Groups I-B, II-B, IV-A, and VIII metals with elements of Groups VIA, and may be effectively employed in the conventional concentrations traditionally employed in the art, preferably in a relatively low concentration in the order of about 1-25 l0- moles/ft.

Especially suitable as silver precipitating agents are those disclosed in US. Pat. No. 2,698,237 and specifically the metallic sulfides and selenides, there detailed, these terms being understood to include the selenosulfides, the polysulfides, and the polyselenides. Preferred in this group are the so-called heavy metal sulfides. For best results it is preferred to employ sulfides whose solubility products in an aqueous medium at approximately C. vary between 10 and 10- and especially the salts of zinc, copper, cadmium and lead. Also particularly suitable as precipitating agents are heavy metals such as silver, gold, platinum, palladium, etc., and in this category the noble metals illustrated are preferred and are generally provided in the matrix as colloidal particles.

In particular, it has been discovered that improved color reproduction in accordance with the principles of additive color photography may be obtained by means of the improved image characteristics provided by reason of the present invention. Specifically, it has been found that composite negative/positive silver image formation, particularly adapted for additive color reproduction and characterized by improved silver image minimum and maximum optical densities and image acuity may be achieved by a process which includes exposing a photographic film unit, which comprises a color screen in association with a photosensitive silver halide layer fabricated to conform to the parameters previously set forth and having associated therewith silver precipitating nuclei, and a silver halide solvent in an inactive species, wherein the exposure of the emulsion is effected by radiation traversing through the color screen and the processing of the film is accomplished by contact, simultaneous with, or subsequent to, exposure, with an aqueous processing composition containing a silver halide developing agent, to provide to the film unit the direct formation of a silver image possessing required low silver image optical density, in terms of exposed areas of the film unit, and required high silver image optical density, in terms of unexposed areas of the film unit, as a function of exposure and development of the film unit.

Color photographic reproduction may thus be provided by exposing the above described photoresponsive silver halide stratum, to selected subject matter, through an optical screen element possessing filter media or screen elements of selected radiation modulating characteristics such as filter media selectively transmitting predetermined portions of the electromagnetic radiation spectrums visible segment. The color information thus re corded is read out by viewing resultant image conformation through the same or a similar screen element in appropriate registration with the image. The individual filter media or screen elements constituting the optical screen will be constructed to effect selective filtration of predetermined portions of the visible electromagnetic spectrum substantially corresponding to its red, blue and green regions and color information recordation will be accomplished by point-to-point incidence of radiation actinic to the selected photoresponsive material as modulated by such screen element. Visual reproduction of the information content recorded is accomplished by read out of the impressed image as modulated by the original or a substantially identical screen element in accurate registration with the image record.

Although for color information recordation purposes, the photoresponsive material and optical screen may comprise separate and distinct elements appropriately registered during periods of exposure and viewing and the optical screen element may be temporarily or permanently positioned on the surface of a transparent carrier opposite that retaining the photoresponsive material, for practical purposes, it is preferred to permanently position the photoresponsive material in direct contiguous relationship to the color screen during exposure, in order to maximize the acuity of the resulting image record.

Subsequent to exposure of the photoresponsive material to actinic radiation transmitted through and filtered by the optical screen, the resultant photoexposed element may be further processed in accordance with the materials selected and generally without regard to the filter screen when the latter element is stable with respect to and/or protected from contact with the processing compositions and components selected. Such protection and stability will ordinarily be enhanced and facilitated by disposition of the filter screen between a transparent, processing composition impermeable carrier and the photoresponsive material, and, in particular, where such configuration additionally includes the presence of a processing composition barrier element or layer intermediate the screen and the photoresponsive material.

The preferred film assemblages will comprise a panchromatically sensitized silver halide stratum possessing the parameters previously set forth positioned contiguous a surface of the multicolor additive color screen which, in the preferred assemblage denoted above, may also possess the image-receiving component intermediate a silver halide stratum and the color screen, to allow exposure of the emulsion to be accomplished through a cplor screen, including through a transparent supporting member, if present, and formation of the requisite positive silver image in immediate, contiguous relationship to the color screen employed during exposure. Such embodiment obviates the necessity of registering the color screen with the resultant positive silver image, for viewing purposes, in that the screen employed for exposing may also be employed for viewing and is in automatic registration with the positive silver image.

Thus a preferred embodiment of the present invention for the reproduction of color information in accordance with the principles of additive color photography may comprise a film unit assemblage which contains an additive multicolor screen comprising a geometrically repetitive plurality of actinic radiation-filtering colored elements including a set of primary blue-colored filtered elements, a set of primary green-colored filter elements and a set of primary red-colored filter elements arranged in a repetitive distribution in side-by-side relationship in a substantially single plane positioned intermediate a transparent support member and a photosensitive silver halide stratum conforming to the parameters set forth above and having silver precipitating nuclei associated therewith in any of the manners previously detailed.

It will be specifically recognized, however, that in embodiments of the invention which employ a separate photo-insensitive silver precipitating nuclei containing layer, intermediate a color screen and a photosensitive silver halide layer, such nuclei containing layer should most preferably possess a thickness of less than about a wavelength of light so that for all practical optical purposes the photosensitive silver halide emulsion layer will be effectively located next adjacent the color screen whereby minimizing to a maximum extent any possible optical parallex problems during radiation transmission, as well as any substantial laterial diffusion of silver imageforming components during processing of the film unit.

The photoresponsive silver halide materials employed in the practice of the present invention will, as previously described, comprise a crystal of a compound of silver, for example, one or more of the silver halides, such as photosensitive silver chloride, silver iodide, silver bromide, and preferably, mixed silver halides, such as silver chlorobromide, silver iodochloride, silver iodobromide or silver iodochlorobromide, of varying halides ratios and the silver concentrations dispersed in a processing composition permeable binder material such as gelatin and the like, most preferably silver iodobromide and iodochlorobromide, particularly that comprising -1 to 9% iodide by weight of silver.

The preferred silver halide type photosensitive layers employed for the fabrication of the photographic film unit, may be prepared by reacting a Water-soluble silver halide, such as ammonium, potassium or sodium chloride, preferably together with corresponding iodide and bromide, in an aqueous solution of a peptizing agent such as colloidal gelatin solution; digesting the dispersion at an elevated temperature, to provide increased crystal growth; Washing the resultant dispersion to remove undesirable reaction products and residual Water-soluble salts, for example, employing the preferred gelatin matrix material, by chilling the dispersion, noodling the set dispersion, and washing the noodles with cold water, or, alternatively, employing any of the various floe systems, or procedures, adapted to effect removal of undesired components, for example, the procedures described in US. Pats. Nos. 2,614,928; 2,614,929; 2,728,662, and the like; after ripening the dispersion at an elevated temperature in combination with the addition of gelatin or such other polymeric material as may be desired and various adjuncts, for example, chemical sensitizing agents and the like; all according to the traditional procedures of the art, as described in Neblette, C. B., Photography-Its Materials and Processes, 6th ed., 1962.

Optical sensitization and preferably panchromatic sensitization of the emulsions silver halide crystals may then be accomplished by contact with optical sensitizing dye or dyes; all according to the traditional procedures of the art, or described in Hamer, F. M. The Cyanine Dyes and Related Compounds.

Subsequent to optical sensitization, any further desired 10 additives, such as coating aids and the like, may be incorporated in the emulsion and the mixture coated according to the conventional photographic emulsion coating procedures known in the art.

As the binder for the photoresponsive material, the aforementioned gelatin may be, in wvhole or in part, replaced with some other natural and/or synthetic processing composition permeable polymeric material such as albumin; casein; or zein or resins such as cellulose derivative, as described in US. Pats. Nos. 2,322,085 and 2,541,- 474; vinyl polymeric such as described in an extensive multiplicity of readily available US. and foreign patents or the photoresponsive material may be present substantially free of interstitial binding agent as described in US. Pats. Nos. 2,945,771; 3,145,566; 3,142,567; Newman, Comment on Non-Gelatin Film, B. J. O. P., 434, Sept. 15, 1961; and Belgian Pats. Nos. 642,557 and 642,558.

One procedure particularly useful for the production of one preferred gelatino silver halide emulsion comprises the formulation, in the manner previously detailed, of a silver iodochlorobromide emulsion containing in order of -l% iodide by initially forming a silver chloride emulsion, adding to the emulsion the requisite bromide and iodide, separating from the formulation undesired reaction products, and after-ripening the resultant silver iodochlorobromide emulsion in combination with the selected auxiliary sensitizing, speed increasing, etc., adjuncts elected.

Specifically, the specified emulsion may be formulated by a conventional double jet addition, over a period of 3 minutes and 25 seconds, at a rate of 1800 cc. per minute of 1026 gms. of potassium chloride in 5336 gms. of distilled water at 60 C. to a solution at C. comprising 205 gms. of potassium chloride, 5750 gms. of distilled water and 2560 gms. of a solution formed by dissolving 800 gms. of gelatin in 8800 mls. of distilled water, adjusting the pH to 10:01 with 50% sodium hydroxide, adding over a 30 minute period and at 40 C. with stirring 88 gms. of phthalic anhydride in 616 mls. of acetone, and after 30 minutes at 40 C. adjusting the pH to 6 with 50% sulfuric acid. After a digestion period of 5 minutes at 80 C., 60 gms. of potassium iodide and 1337 gms. of potassium bromide in 5336 gms. of water is added to the formulation, over a period of 3 minutes and 25 seconds, at a rate of 1800 cc. per minute and at 60 C. and the resultant emulsion digested for 'a further period of 35 minutes at 80 C. The resultant silver iodochlorobromide emulsion is precipitated at 20 C. by reduction of the pH to about 2.7 with sulfuric acid, the precipitate separated from the supernatant liquid and washed with chilled distilled Water until the Wash water exhibits a conductivity of -50 to ,umhos/cm, the volume adjusted with distilled water for the addition of 950 gms. of gelatin, and the emulsion then after ripening for 210 minutes at a temperature of 54 C. and a pH of 5.7.

The silver precipitating nuclei and/or discrete nuclei layer or layers may be realized by the application of, location of, and/or in situ generation of, the nuclei, which may be similar or dissimilar, directly or indirectly in or as the respective layer and in the presence or absence of binder or matrix material and, in the latter instance, may comprise one or more adjacent or separate strata of a premeable material containing one or more nuclei types disposed in one or more such layers. Matrix materials adapted for such employment may comprise both inorganic and organic materials, the latter type preferably comprising natural or synthetic, processing composition permeable, polymeric materials such as protein materials, for example, glues, gelatins, caseins, etc.; carbohydrate materials, for example, chitins, gums, starches, alginates, etc.; synthetic polymeric materials, for example, of the vinyl or cellulosic types such as vinyl alcohols, amides and acrylamides, regenerated celluloses and cellulose ether and esters, polyamides and esters, etc., and the like; and the former type preferably comprising submacroscopic agglomerates of minute particles of a water-insoluble, in-

11 organic, preferably siliceous material such, for example, as silica aerogel as disclosed in US. Pat. No. 2,698,237.

Where the silver precipitating agent is one or more of the heavy metal sulfides or selenides, it may be preferable to prevent the diffusion and wandering of the sulfide or selenide ions, as the case may be, by also including, in the silver precipitating layers or in separate layers closely adjacent thereto, at least one metallic salt which is substantially more soluble in the processing agent than the heavy metal sulfide or selenide used as the silver precipitating agent and which is irreducible in the processing agent. This more soluble salt has, as its cation, a metal whose ion forms sulfides or selenides which are difiicultly soluble in the processing agent and which give up their sulfide or selenide ions to silver by displacement. Accordingly, in the presence of sulfide or selenide ions the metal ions of the more soluble salts have the effect of immediately precipitating the sulfide or selenide ions from solution. These more soluble or ion-capturing salts may be soluble salts of any of the following metals: cadmium, cerium(ous), cobalt(ous), iron, lead, nickel, manganese, thorium and tin. Satisfactory soluble and stable salts of the above metals may be found, for example, among the following groups of salts: the acetates, the nitrates, the borates, the chlorides, the sulfates, the hydroxides, the formates, the citrates and the dithionates. The acetates and nitrates of zinc, cadmium, nickel, and lead are preferred. In general, it is also preferable to use the white or lightly colored salts although for certain special purposes the more darkly colored salts may be employed.

The previously mentioned ion-capturing salts may also serve a function of improving the stability of the positive image provided they possess, in addition to the aforementioned characteristics, the requisites specified in US. Pat. No. 2,584,030. For example, if the ion-capturing salt is a salt of a metal which slowly forms insoluble or slightly soluble metallic hydroxides with the hydroxyl ions in the alkaline processing liquid, it will suitably control the alkalinity of the film unit to substantially, if not totally, prevent the formation of undesirable developer stains.

In accordance with a particularly preferred embodiment of the present invention, photosensitive and image-receiving strata carrying the image silver are fabricated to substantially prevent microscopic distortion of the image conformation by preventing microscopic migration or diffusion of image elements within the polymeric matrix. In general, conventional photographic image elements may ordinarily comprise a microscopically dynamic system without seriously noticeable disadvantages to the conventional employment of the image. However, for particularly accurate color reproduction in accordance with the principles of additive color photography, microscopic distortion of image elements is preferably obviated to insure maximization of the accuracy of image registration with the appropriate individual optical filter elements of the additive color screen associated with the image-carrying element. Specifically, it has been found that a photosensitive film unit comprising photosensitive emulsion containing silver halide crystals and silver precipitating nuclei dispersed in a polymeric binder and where employed photoinsensitive image-receiving layers containing silver precipitating nuclei dispersed in a polymeric binder, the binders of which possess a lattice effective to substantially prevent microscopic migration or diffusion of image silver, provide color reproduction acuity particularly described for effective color reproduction in the manner previously described.

The desired polymeric binder lattice property may be readily achieved by selection of a polymeric material possessing the property of sufficiently fixing specially image components, or a polymeric material, otherwise desired, may be modified, for example, by crosslinking and/or hardening, to the extent necessary to provide the desired spacial maintenance of image components, that is, a rigidity effective to maintain positive image components in registration with the individual optical filter elements of the color screen through which the photosensitive emulsion was exposed. For example, a preferred polymeric binder material, that is, gelatin, may be hardened by contact with conventional hardening agents to the extent necessary to provide the desired rigidification of the photographic image. Where desired discrete particulate materials facilitating increased processing composition penetration of the photosensitive element, without deleterious effect on the polymeric matrixs lattice, may be advantageously incorporated in the photosensitive element for the purpose of expediting processing of the element.

Production of color screen, in accordance with the art may be prepared by totally mechanical means, as for example, by printing or ruling a dyeable substrate, for example, with a greasy ink formulation, in accordance with the desired filter pattern, subjecting the substrate to suitable coloration, in areas which do not possess the repellant ink mask, effecting removal of the mask, and repeating this procedure, in accordance with the geometrical pattern of filter elements desired, a sufficient number of times to provide the desired multiplicity of diversely colored filter element; directly printing a carrier substrate with the desired dye formulations in accordance with the predetermined filter pattern and repeating this printing procedure a sufficient number of times to provide the multiplicity of colored filter elements desired, or depositing, as an irregular filter screen pattern, a thin layer comprising a random distribution of small grains, such as starch grains, which have been independently colored with the colors desired for optical filtering effects. Alternatively, color screen may be prepared by photomechanical methods of the type initially proposed by, for example, Ducos Du Hauron in the nineteenth century, which comprise, in general, coating a suitable support or film base with an adhesive composition having coated thereon a photosensitive colloid composition, as for example, dichromated gelatin, effecting exposure of the sensitive gelatin layer by incident actinic radiation, through a suitable mask which provides an exposure pattern devised in accordance with the desired optical filter element arrangement, effecting differential hardening of the sensitized material as a function of the point-to-point degree of exposure, removing unexposed unhardened material by solvent contact, subjecting the remaining hardened material to a suitable dyeing procedure in order to provide a firstcolored optical filter element series, and repeating this procedure, employing appropriate masks, as often as necessary to provide the number of optical filter element types desired in the final color screen element.

Although color screen may be produced by traditional contact printing or projection type photomechanical processes, a particularly preferred process for the production of color screen comprises the process set forth in US. Pat. No. 3,284,208 which includes, in essence, successively coating the smooth surface of a lenticular film with a plurality of photoresponsive layers and sequentially subjecting the coatings to selectively displaced radiation incident on, and focused by, the lenticules receiving same, in order to provide selective exposure of the coating. Subsequent to each exposure, unexposed coating is removed and the resultant resist dyed in order to provide a series of chromatic filter elements, prior to the deposition of the next succeeding photoresponsive layer. Each such exposure is derived from electromagnetic radiation incident on the lenticular film at an angular displacement specifically adapted to provide the desired plurality of chromatic filter element series in substantial side-by-side or screen relationship and adapted to filter predetermined wavelengths of light.

For the preparation of the preferred trichromatic additive screens, the exposed area of each photoresponsive area will generally comprise about one-third of the layer contiguous each lenticule receiving exposing radiation. Although all three exposures may be accomplished by radiation incident on the lenticules of the lenticular film at three separate angles each adapted to provide exposure about one-third of the area contiguous each lenticule receiving radiation, it will be recognized that the terminal chromatic filter formation may also be provided by exposing the terminal photoresponsive layer to diffuse radiation traversing through the lenticular film and masked by the previously formed chromatic filter elements.

At a stage subsequent to formation of the first and second series of filter elements, the lenticular configuration will be constituted as a continuous smooth surface. In the instances where the lenticules comprise a separate stratum temporarily affixed to the surface of a support on which the color screen is formed, such separate stratum may be stripped from the support. Alternatively, where the lenticules comprise an integral component of the film base or support and have been provided to the base by pressure and/ or solvent deformation of the base, a continuous smooth surface may be reconstituted by application of suitable solvent and the deformation pressures produced during the manufacturing of lenticular film base released to provide reconstitution of the bases original configuration. Where desired, for example, for optical transmission purposes, the reconstituted surface may be polished, for example, by surface contact with an appropriate rotating polishing cylinder or drum, for the time interval necessary to provide the desired optical characteristics to the film base surface.

Optionally the external surface of the color screen may be overcoated with a protective polymeric composition, such as nitrocellulose, cellulose acetate, and the like, for the purpose of protecting the screen from processing composition deformation during employment of the resultant film unit. The external surface of the color screen may then have applied thereto the remaining layers constituting the film assemblage as detailed hereinbefore.

Apparatus particularly adapted to facilitate effecting exposure of the lenticular film in accordance with the aforementioned U.S. Pat. No. 3,284,208 is disclosed and claimed in U.S. Pat. No. 3,318,220.

The support or film base employed may comprise any of the various types of transparent rigid or flexible supports, for example, glass, polymeric films of both the synthetic type and those derived from naturally occurring products, etc. Especially suitable materials, however, comprise fiexible transparent synthetic polymers such as polymethacrylic acid, methyl and ethyl esters; vinyl chloride polymers; polyvinyl acetals; polyamides such as nylon; polyesters such as the polymeric films derived from ethylene glycol terephthalic acid; polymeric cellulose derivatives such as cellulose acetate, triacetate, nitrate, propionate, butyrate, acetate-butyrate, or acetate propionate; polycarbonates; polystyrenes; and the like.

The present invention will be illustrated in greater detail in conjunction with the. following illustrative constructions which set forth representative embodiments and photographic utilizations of the film units of the present invention, which however, are not limited to the details therein set forth but are intended to be illustrative only.

The smooth surface of a lenticular film comprising a polyester film base may have bonded to one surface a cellulose acetate butyrate layer comprising 550 lenticules per inch, each of which may possess a plano-convex con" figuration for condensing the incident radiation into con verging rays and a focal length generally in the order of about 100 microns in air and, as a result of this short focal length, imaging objects over about one inch from the lens surface at infinity, may be coated on the opposite surface with an adhesive composition comprising 70 cc. of methanol, 1.25 grams of nitrocellulose, and 30 cc. of butyl alcohol. A first layer of gelatin sensitized by the addition of weight percent potassium dichromate (based on dry gelatin), may then be coated on the external surface of the first adhesive layer. The first gelatin layer may then be exposed to ultraviolet radiation, in ac- 14 cordance with the previously detailed explanation, and the resultant photoexposed carrier subjected to a water wash in order to provide removal of unexposed sensitized gelatin, in accordance with the exposure pattern contained in the first gelatin layer. The web may then be treated with an acid dyeing bath comprising 1.17% Direct Red Cl. 81; 0.32% Direct Yellow Cl. 4; and 2.95% glacial acetic acid, rinsed to effect removal of excess dye, dried and a second adhesive composition containing 70 cc. of methanol, 30 cc. of butyl alcohol, and 1.25 grams of nitrocellulose overcoated thereon. A second layer of gelatin sensitized by the addition of 15 weight percent potassium dichromate may be coated on the second adhesive layer. The second photosensitized gelatin layer may also be exposed to ultraviolet radiation in accordance with the previously detailed description. The second gelatin layer may then be washed with water to effect removal of unexposed photosensitive gelatin, in the manner previously detailed, and the remaining gelatin resist dyed by contact with an acid dyeing bath containing 0.83% Acid Green Cl. 7; 0.32% Direct Yellow Cl. 4; and 2.86% glacial acetic acid. The Web may then be rinsed to effect removal of any residual excess dye, dried and coated with a third adhesive composition comprising 30 cc. butanol, 1.25 grams of nitrocellulose, and 70 cc. of methanol. A third layer of gelatin sensitized with 15 weight percent potassium dichromate may then be coated on the external surface of the third adhesive layer and the third photosensitive gelatin layer subjected to exposure by ultraviolet radiation, in accordance with the description detailed previously. The third layer of photosensitive gelatin may then be washed in order to provide the desired resist formation and the resultant resist dyed by contact with a solution containing 1.0% Blue T Pina and 18% glacial acetic acid, washed to effect removal of residual dye and dried. A protective overcoat layer may be provided by coating the external surface of the multicolor screen element with a composition comprising 70 cc. methanol, 30 cc. butanol, and 5 grams of nitrocellulose.

Subsequent to formation of the color screen, the lenticulated cellulose acetate butyrate may be removed from the polyester base and the external surface of the polymeric protective coating may be coated with a composition comprising deacetylated chitin and copper sulfide at a coverage of about 4.4 mgs./ft. deacetylated chitin and 0.25 mg./ft. copper sulfide. On the external surface of the silver precipitating agent containing layer may then be coated a hardened gelatino silver iodobromide emulsion coated at a coverage of mgs./ft. gelatin and 104 mgs./ft. silver and containing 7.4 mgs./ft. propylene glycol alginate, 2.9 mgs./ft. sodium dioctylsulfosuccinate; and 75 mg./ft. sodium S-(p-acetoxybenzyl) thiosulfate and 50 mgs./ft. of phenyl hydroquinone (oil dispersion).

The gelatino silver iodochlorobromide emulsion employed may be prepared as previously detailed and chemically sensitized, at about 56 C., by the addition of a sensitizing amount of a solution containing 0.1 gram of ammonium thiocyanate in 9.9 cc. of water and 1.2 cc. of a solution containing 0.097 gram of gold chloride in 9.9 cc. of water. The resultant emulsion may then be panchromatically sensitized by the sequential addition of 0.1%, by weight, methanol solutions of anhydro 5,5'-dipheny1-3,3-bis-(4-sulfobutyl)-9-ethyloxacarbocyanine hydroxide and anhydro 5,5'-dimethyl-3,3-bis-(3-sulfopropyl)-9-ethyl thiacarbocyanine hydroxide in optionally effective concentrations.

The copper sulfide silver precipitating agent may be provided in situ by the addition of substantially equimolar quantities of copper nitrate and sodium sulfide solutions to the deacetylated chitin coating solution prior to application of the composition to the color base support.

The film unit, fabricated either substantially as detailed above or in accordance with any one or more of the structural embodiment denoted above, may be subjected to exposing electromagnetic radiation incident on the transparent base and developed by temporary contact of the film unit, for about 60 seconds, with a processing composition, which for illustrative purposes may comprise 111 cc. of water, 6.2 grams of sodium hydroxide, 6.48 grams of sodium sulfite, 0.42 gram of 6-nitrobenzimidazole, 3.5 cc. of surfactant (reaction product of nonyl phenol and glycidyl), to provide a positive silver image possessing the optical characteristics described hereinbefore and the acuity required for additive color reproduction.

As denoted above, the photosensitive silver halide stratum and/or the silver precipitating nuclei containing stratum may have advantageously incorporated therein discrete particulate materials providing increased porosity to the film unit, without deleterious effect on the dimensional stability of the binder lattice, in particular, those materials which additionally act as an antiswelling agent for the binder material and, accordingly, act to facilitate the prevention of the carried images microscopic distortion, particularly, with respect to an associated color screen, such as discrete silica particles dispersed, for example, in a concentration of about 0.3 to 1.5 silica per part binder, for the purpose of facilitating processing composition permeation of the film units silver halide crystal and silver precipitating nuclei containing layer or layers. In addition, the silver halide or silver precipitating nuclei containing stratum may be advantageously overcoated with a processing composition permeable polymeric material such as a hardened gelatin pad or the like to advantageously promote uniformity in processing composition permeation of such stratum, by modulating any wave front resultant from initial surface contact with the liquid employed and to thereby promote uniform maintenance of the polymeric binders physical characteristics.

Although chrome alum and particularly algin have been advantageously employed as hardening agents for the polymeric gelatin emulsion binder, it will be recognized that substantially any hardening or crosslinking agent may be employed, where necessary and with respect to any one or more layers of the film unit, which does not provide deleterious photographic effects, to the extent required to provide a binder lattice which effectively inhibits to a substantial effect, migration of image silver. An extensive collection of hardening agents are disclosed in the art as specifically adapted to effect hardening or crosslinking of photographic polymeric binder material compositions and by reason of their innocuous photographic effects are to be preferred in the practice of the present invention. The sole requirement for effective operation of the film unit is that the emulsions polymeric lattice be constructed to provide the optical image parameters denoted hereinbefore. Thus, substantially any conventional hardening and crosslinking agent may be selected from those set forth throughout, for example, the pertinent patent literature regarding such agents, and the concentration employed, as known in the art, will be dependent upon the relative activity of the selected agent, or agents, and the relative amount of hardening or crosslinking to be effected. The specific concentration of a selective hardening or crosslinking agent, to be contacted with a selected polymeric binder, may be readily determined empirically, within the specific context of ultimate photographic employment, by screening. It will be further recognized that any of the various processing composition permeable, synthetic or natural polymeric materials, possessing the physical characteristics required to provide the results denoted above, may be substituted in replacement of the specifically illustrated polymeric materials provided that such selected polymer provides a matrix which is not deleterious to photosensitive silver halide crystals and possesses a lattice allowing processing in the manner previously described.

Suitable silver halide solvents for employment in the practice of the present invention include conventional fixing agents such as the previously noted sodium thiosulfate, sodium thiocyanate, ammonium thiocyanate, the additional agents described in US. Pat. No. 2,543,181, and the associations of cyclic imides and nitrogenous bases such as associations of barbiturates or uracils and ammonia or amines and other associations described in US. Pat. No. 2,857,274.

Where desired conventional silver toning agent or agents may be disposed within the emulsion composition in a concentration effective to provide a positive image toned in accordance with the desires of the operator.

In the preferred embodiment of the present invention, the processing composition will include an alkaline material, for example, sodium hydroxide, potassium hydroxide or sodium carbonate, or the like, and most preferably in a concentration providing a pH to the processing composition in excess of about 12. The processing composition may, where desired, contain the sole silver halide developing agent or agents employed, or a silver halide developing agent in addition to that disposed within the film unit; however, disposition of one or more developing agents in the emulsion and/or a permeable layer directly associated therewith, intermediate the emulsion and a color screen, is a particularly preferred embodiment, for the purpose of providing enhanced image acuity, by more readily facilitating directly initiated development at radiation exposed areas of the emulsion without the necessity of diffusing such agents to such sites by means of the processing composition selected.

The preferred silver halide developing agents generally comprise organic compounds and, in particular, comprise organic compounds of the aromatic series containing at least two hydroxyl and/or amino groups wherein at least one of such groups is in one of ortho or para positions with respect to at least one other of such groups such as, for example, the various known hydroquinones, p-aminophenols, and their various known functional homologues and analogues.

It will be apparent that the relative proportions of the agents comprising the processing composition set forth herein may be altered to suit the requirements of the operator, however, the processing composition solvent employed will generally comprise water and will possess a solvent capacity which does not deleteriously hydrate the selected binder lattices beyond that required to provide the preferred image formation. Accordingly, no adjunct should be included within such composition which deleteriously effects the lattice parameters required for such image formation.

In the description herein, each color series of filter elements has been described as covering that part of the total area in proportion to the total number of colors used, i.e., in the tricolor system, each color occupies onethird of the total area. This may vary quite widely before having a noticeable effect to the observer and, in fact, may be compensated by changing the intensity of the colors. In actual practice, if one dye is of greater intensity than the others, a deliberate compensation may be made by reducing the total relative area of the intense color. The aspect of relative areas is well known in the art so that when relative areas are used in this application, it is intended to include the variances which the art would recognize as being successful.

Various colors and numbers of colors may be used in this invention but the preferred system, as previously mentioned, is a tricolor arrangement of the three primary colors, red, green and blue.

It will be recognized, however, that, in accordance with the instant disclosure, a plurality of chromatic filter element series may be provided, the number of series being solely determined by the optical parameters of the resultant color screen desired.

For example, a four-color system such as red, green, violet-blue and orange-yellow could also be efiectively 17 employed in accordance with the teachings of the instant disclosure.

In the practice of the present invention, additive trichromatic color screens possessing 550, 756, and 1125 triplets/inch may be readily employed and it has been found that image resolution obtained by means of the present invention exceeds that obtainable in prior art processes. Such increased resolution specifically facilitates the acuity of color reproduction to be achieved by the practice of the invention and the silver halide stratum will be panchromatically sensitized to provide equal image production, as a direct function of incident exposing radiation, throughout the response portion of the radiation spectrum to further enhance the acuity of color information recordation by the emulsion.

In addition to the described essential layers, it will be recognized that the film unit may also contain one or more subcoats or layers, which, in turn, may contain one or more additives such as plasticizers, intermediate essential layers for the purpose, for example, of enhancing adhesion, and that one or more of the descriped layers may comprise a composite of two or more strata which may be contiguous or separated from each other.

Since certain changes may be made in the above product, process and apparatus 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. An additive multicolor diffusion transfer photographic film unit which comprises a photosensitive element which includes an additive multicolor screen, a layer comprising photosensitive silver halide and having associated therewith silver precipitating nuclei, and a silver halide solvent in an inactive species adapted to be converted to the active form in the presence of alkaline liquid processing composition.

2. A film unit as defined in claim 1 wherein said inactive species comprises an insoluble salt of said silver halide solvent.

3. A film unit as defined in claim 1 wherein said inactive species comprises a non-difiusible compound which in the presence of alkali forms a quinone-methide of a naphthoquinone-methide and releases a silver halide solvent.

4. A film unit as defined in claim 3 wherein said compound is a phenol, a naphthol or a protected derivative thereof which in the presence of alkali forms a phenol or a naphthol, said compound further having said silver halide solvent bonded to a nuclear carbon atom of the aromatic nucleus through an alkylene substituent in a position ortho or para to the hydroxyl group or its protected derivative.

5. A film unit as defined in claim 4 wherein said compound is of the formula:

(ANCHOR)n-1 CHz-SOLVENT wherein ANCHOR is an anchoring substituent rendering said compound appreciably less difiusible than it would be without said ANCHOR substituent; and

n is 1 or 2.

6. A film unit as defined in claim 1 wherein said film unit comprises a laminate which includes a common support carrying on one surface an additive multicolor screen, a layer comprising silver precipitating nuclei and a layer comprising photosensitive silver halide crystals.

7. A film unit as defined in claim 6 wherein said silver halide solvent is disposed in said photosensitive layer.

8. A film unit as defined in claim 6 which includes a processing composition permeable layer adjacent said photosensitive layer having disposed therein said silver halide solvent.

9. A film unit as defined in claim 1 wherein said film unit includes a silver halide developing agent.

10. A film unit as defined in claim 9 wherein said developing agent is in an inactive species adapted to be converted to an active species in the presence of alkaline liquid processing composition.

11. A film unit as defined in claim 8 wherein said processing composition permeable layer is gelatin.

12. A film unit as defined in claim 1 wherein said silver precipitating nuclei and said photosensitive silver halide are disposed in the same layer.

13. A film unit as defined in claim 1 wherein said silver precipitating nuclei are present in a concentration effective to provide upon diffusion transfer processing of the film unit a silver image possessing an optical density inversely proportional to exposure of the photosensitive silver halide layer.

14. A film unit as defined in claim 13 wherein said silver precipitating nuclei are present in a concentration efiective to provide upon diffusion transfer processing of the film unit a silver image derived from unexposed silver halide crystals possessing greater covering power than a silver image derived from exposed silver halide crystals.

15. A film unit as defined in claim 13 wherein said silver image derived from unexposed silver halide crystals comprises silver of a first physical character, and said silver image derived from exposed silver halide crystals comprises silver of a second physical character, said first physical character silver possessing higher optical density than said second physical character silver per unit mass.

16. A film unit as defined in claim 1 wherein said silver halide solvent in an inactive species is sodium S- (p-acetoxybenzyl)thiosulfate.

17. A film unit as defined in claim 1 which is a permanently fixed laminate and comprises a transparent support carrying on a first surface an additive color screen, at least a first substantially photoinsensitive layer comprising silver precipitating nuclei, and at least a first photosensitive silver halide emulsion layer comprising photosensitive silver halide crystals, said silver precipitating nuclei present in a concentration etfective to provide, upon development, in the presence of a silver halide solvent, as a function of exposure, a silver image derived from the development of exposed silver halide crystals possessing a maximum image density at least 1.0 density unit less than the maximum density of silver image derived from development of unexposed silver halide crystals.

18. A film unit as defined in claim 17 wherein said silver precipitating nuclei and said silver halide crystals are disposed in processing composition permeable binders and at least one of said permeable polymeric binders comprises gelatin.

19. A film unit as defined in claim 18 wherein said gelatin binder contains dispersed therein silica.

20. A film unit as defined in claim 18 wherein said permeable binder of at least one of said photoinsensitive layers comprises deacetylated chitin.

21. A film unit as defined in claim 18 including a separate processing composition permeable polymeric layer containing a silver halide developing agent positioned intermediate said support and said photosensitive silver halide emulsion.

22. A film unit as defined in claim 1 wherein said silver precipitating nuclei comprises metallic sulfides, metallic selenides, or colloidal noble metals.

23. A film unit as defined in claim 22 wherein said silver precipitating nuclei are present in a concentration of about 1 to 25 10- moles/ft.

24. A film unit as defined in claim 1 wherein said silver halide comprises silver iodobromide crystals.

25. A film unit as defined in claim 24 wherein said silver iodobromide crystals comprise about 1 to 9%, by weight, iodide.

26. A film unit as defined in claim 1 wherein said photosensitive silver halide is panchromatically sensitized.

27. An additive multicolor silver diffusion transfer photographic process which comprises, in combination, the steps of:

(a) exposing an integral photographic film unit comprising an additive color screen, photosensitive silver halide, silver precipitating nuclei, and a silver halide solvent in an inactive species; and

(b) contacting said exposed film unit with a silver halide developing agent and an alkaline liquid processing composition adapted to convert said inactive species to an active species, thereby providing a visible silver image to said unit, as a function of the point-to-point degree of exposure thereof.

28. A process as defined in claim 27 which comprises,

in combination, the steps of:

(a) exposing a photographic film unit comprising a permanent laminate containing a transparent support carrying on a first surface an additive color screen, a substantially photoinsensitive layer comprising silver precipitating nuclei and a photosensitive silver halide layer comprising photosensitive silver halide crystals, and a silver halide solvent in an inactive species;

(b) contacting said silver halide emulsion with a silver halide developing agent and an alkaline aqueous processing composition adapted to convert said inactive species to an active species for a period of time effective to provide a visible silver image to said film unit, as a function of exposure; and

(c) maintaining said laminate intact subsequent to processing.

29. A difiusion transfer multicolor photographic process as defined in claim 28 wherein said color screen comprises a trichromatic additive color screen comprising red, green and blue optical filter elements in a screen pattern.

30. A process as defined in claim 28 wherein said inactive species comprises a compound which in the presence of alkali forms a quinone-methide or a naphthoquinone-methide and releases a silver halide solvent.

31. A process as defined in claim 28 wherein said developing agent is disposed in said film unit.

References Cited UNITED STATES PATENTS 6/1971 Haist et al. 9695 1/1970 Bredoux et al. 9661 U.S. Cl. X.R.

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