Diffusion transfer processes employing permanent laminate film units
United States Patent 91 Weed [451 Apr. 1, 1975 [75] Inventor: Lucretia J. Weed, Boston, Mass.  
 [73] Assignee: Polaroid Corporation, Cambridge,  
 Mass.  
 [22] Filed: Dec. 31, I969 [211 App]. No.: 889,466  
 [52] U.S. CI. 96/29 R, 96/76 R [51] Int. Cl G03C 5/54 [58] Field of Search 96/29, 48 PD, 64, 76  
 [56] References Cited UNITED STATES PATENTS 2,563,342 8/1951 Land 96/29 9 3,152,903 10/1964 Shepard et al 96/64 3,152,904 10/1964 Sorensen et a1. 1. 96/76 3,257,206 6/1966 de Haes 96/76 3,311,473 3/1967 Foster et a1 96/64 3,415,647 12/1968 Wyand et a1 96/76 3,453,639 7/1969 Berman 346/1 3,516,827 6/1970 Schreck 96/76 3,607,270 6/1968 de Haes 96/29 FOREIGN PATENTS OR APPLICATIONS 874,046 8/1961 United Kingdom OTHER PUBLICATIONS C.A. 54-24060 D.  
 Primary E.raminerNorman G. Torchin Assistant Examiner.lohn L. Goodrow Attorney, Agent, or Firm-Robert M. Ford; Philip G. Kiely [57] ABSTRACT The present invention is directed to a photographic film unit which comprises a permanent laminate including a common support carrying on one surface, in order, a first layer comprising silver precipitating nuclei, a layer comprising photosensitive silver halide crystals and a second layer comprising silver precipitating nuclei; and processes employing said film unit,  
 5 Claims, 1 Drawing Figure PATENTEBAPR 3.874.944  
  VENTOR. LUCR: A J. WEED ATTORNEYS DIFFUSION TRANSFER PROCESSES EMPLOYING PERMANENTLAMINATE FILM UNITS The present invention relates to photography and, more particularly, to photographic products and processes specifically adapted for direct positive image reproduction.  
  In general, photographic silver image reproduction may be provided by selective exposure of, for example, the preferred photoresponsive material, that is, photosensitive silver halide, and the resultant exposed material may be processed in the conventional manner. specifically, the photoexposed emulsion thus may be developed by any of the conventional developing procedures known in the art to be adapted to effect reduction of photoexposed silver halide crystals. In general, such development will be effected by contact of the photoexposed emulsion with a solution containing a conventional developing agent such as one or more of the conventional developing agents and compositions of same set forth in Chapter 14 of The Theory of the Photographic Process (revised edition 1954), C. E. K. Mees, the Macmillan Co., New York, New York and Chapters VI, VII, VIII and IX of Photographic Chemistry, Volume I, P. Glafkides, Foundation Press, London, England. The preferred 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, p-phenylene diamines, and their various known functional homologues and analogues. The developing composition containing the specific silver halide developing agents selected will generally comprise an aqueous solution additionally containing at least an alkaline material such as sodium hydroxide or sodium carbonate or the like and may be contacted with the photoexposed silver halide material according to any of the conventional tray, tank, or the like, procedures. The composition may additionally and optionally contain one or more specific silver halide developing agents, preservatives, alkalis, restrainers, accelerators, etc., other than those specifically denoted in the cited reference material. The concentration of the various components employed may be varied over a wide range and, where desn&#39;able, any one or more of such components may be disposed in the photosensitive element, prior to exposure, and m a separate permeable layer of such element and/or in the emulsion comprising the photosensitive silver halide material itself.  
  For the purpose of stabilizing the developed image, the emulsion may be fixed in any of the conventional fixing, washing, and/or drying procedures known in the art as, for example, those described in Chapter XI of Photographic Chemistry, Volume I, supra, and Chapter 17 of The Theory of the Photographic Process, supra. For example, the photosensitive material retaining the developed mage may be initially contacted with a stop bath adapted to terminate action of the developing agent on the photosensitive emulsion by converting the pH of the emulsion to that at which the selected silver halide&#39;dev&#39;eloping agent or agents exhibit substantially no developing potential. Specifically, wherethe silver halide&#39;developing agent is organic compound&#39;exhibiting its developing action at an alkaline pH, for&#39;example,  
 a hydroquinone, or the like, the emulsion may be subjected to an acid stop bath for a sufficient time interval as to effectively neutralize the silver halide developing potential of the selected developing agent.  
  The emulsion may then be subjected to at fixing bath in order to effect removal of unexposed photorespon sive silver halide from the emulsion in accordance with the conventional procedures known to the art as adapted to effect same and as further detailed in the last cited references.  
  In general, the fixing agent employed may comprise a bath of a silver halide solvent such as sodium thiosulfate which is effective to remove substantially all types of silver halides from disposition in the emulsion strata originally containing the photosensitive silver halide without deleterious attack upon the conformation of the developed silver image. Subsequent to fixation, all residual traces of the fixing agent may be removed by aqueous wash contact, in order to insure the permanency of the developed image.  
  Where positive silver image formation is desired, that is, an image provided in terms of unexposed portions of the emulsion, reversal processing may be employed in its conventional manner, or a direct positive emulsion may be employed, or the positive image may be provided by diffusion transfer processing.  
  In the first alternative denoted above, the reversal processing may be accomplished in the conventional manner by developing the photoexposed emulsion by any of the conventional procedures known in the art as adapted to effect development of the latent image resultant from photoexposure such as, for example, the procedures identified above. Subsequent to development of the latent image to a visible silver image, the resultant developed image may be effectively removed in the conventional manner by contact of the image with any of the conventional agents known in the art as adapted to effect removal of a photographic silver image without deleterious effect upon unexposed photosensitive silver halide. such as, for example, the bleaching agents and bleaching baths set forth in Chapter XXX of Photographic Chemistry, Volume II, supra. Subsequent to the removal of the developed image by, for example, bleaching, the photosensitive silver halide remaining in the emulsion structure may be converted to a developable state by physical fogging resultant from, for example, exposure of actinic radiation, and- /or chemical fogging, for example, by contact with a conventional fogging agent or the like, and, in turn, the resultant fogged silver halide may be developed and, where desired, stabilized, in the manner set forth above, to provide the requisite positive silver image formation.  
  In the second alternative denoted above, the requisite positive silver image formation may be provided by employment of a conventional direct positive silver halide emulsion which may be directly developed, in the presence of a fogging agent, according to the procedure described above, to provide the requisite positive silver image formation.  
  In the third alternative denoted above, the positive silver image formation may be provided by diffusion transfer processing wherein the latent image provided to the photosensitive silver halide emulsion by exposure is developed and, substantially contemporaneous with such development, a soluble complex is obtained, for example, by reaction of a silver halide solvent with unexposed and undeveloped silver halide of the emulsion. The resultant soluble silver complex may be, at least in part, transported in the direction of a suitable print-receiving element, and the silver of the complex precipitated in such element to provide the requisite positive silver image formation. The resultant positive silver image in this embodiment, a silver transfer image, may be viewed as a reflection printlor a transparency.  
  Of the three alternatives denoted above, production of the positive image by diffusion transfer processing is clearly preferable to that denoted by the first alternative in view of the effective simplicity of the processing involved and is clearly preferable to that of the second embodiment by reason of the higher photographic speeds practicably obtainable.  
  In British Pat. No. 874,046, it is disclosed that two separate silver diffusion transfer positive images may be simultaneously provided, respectively, by exposure of a film unit which comprises an image-receiving layer located on one major surface of a silver halide emulsion layer and an image-receiving element superposed on the opposite major surface of the silver halide emulsion layer during processing and, subsequent to processing, separating the image-receiving element from its superposed relationship with the emulsion and the emulsion from its contiguous relationship with the imagereceiving layer.  
  However, for a plurality of reasons set forth in detail hereinafter, it would be particularly desirable to possess the wherewithal to fabricate an improved integral silver diffusion transfer film assemblage essentially comprising photoresponsive material directly providing positive image formation and possessing the sensitivity to incident electromagnetic radiation and acuity of image formation necessary to &#39;effectively provide photographic image reproduction.  
  Accordingly, it is a principle object of the present invention to provide new and improved photographic products, compositions and processes particularly adapted for the photographic reproduction of subject matter.  
  Other objects of the invention will in part be obvious and will in part appear hereinafter.  
  The invention accordingly comprises the process of 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 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 FIG. 1 is a diagrammatic enlarged crosssectional view illustrating the asso ciation of elements constituting one embodiment of the present invention, the thickness of the various material being exaggerated.  
  As previously stated, a silver diffusion transfer reversal process may provide a positive silver transfer image by development of the latent image provided a photosensitive silver halide emulsion by exposure and, substantially contemporaneous with such development, a  
 soluble silver complex is obtained, by reaction of a silver halide solvent with unexposed and undeveloped silver halide of the emulsion. The resultant soluble silver complex is, at least in part, transported in the direction of a suitable print-receiving element and the silver of the complex there precipitated to provide the requisite positive silver image formation.  
 The silver receptive stratum employed may be so 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 emulsion, to possess an ex-.  
 traordinarily high covering power, that is, opacity per i t ceptive stratum in clusters possessing a diameter directly proportional to the mass of image silver to be deposited in situ by reduction. Such conformation can be 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. The image silver thus precipitated in situ in galaxies of chosen physical parameters provides image conformation in which the element silver of the print-receiving element may possess a very high order of covering power, for example,  
 5 to 15 or more times that of the negative elemental image silver in the silver halide element.  
  As disclosed in US. Pat. No. 2,861,885, desirable composite prints comprising both negative and positive images in superposition may be provided by simplified silver diffusion transfer reversal processes employing a photosensitive silver halide emulsion which upon 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 above. 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, accordingly, 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.  
  In accordance with the present invention, however, it has now been quite unexpectedly discovered that distinctly&#39;advantageous results may be achieved in the production of silver image formation, as a function of photosensitive silver halide stratum exposure, by the employment of a film unit assemblage which comprises a permanently fixed laminate which includes a support carrying on one surface, in order, a first layer comprising silver precipitating nuclei, a layer comprising photosensitive silver halide crystals, and a second layer comprising silver precipitating nuclei.  
  The silver precipitating nuclei are present in a concentration effective to provide a silver image to the film unit possessing optical density inversely proportional to exposure of photosensitive silver halide layer and, specifically, in a concentration adapted to provide a silver image derived from unexposed silver halide crystals possessing greater covering power than that of a corresponding silver image derived from an identical quantum of exposed silver halide crystals. 7  
  In particular, it has been unexpectedly discovered that improved image reproduction may be obtained by means of the improved silver image characteristics provided by reason of the present invention. Specifically, it has now been found 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 at least two separate and discrete layers containing silver precipitating nuclei and a photosensitive silver halide layer positioned intermediate two silver precipitating nuclei containing layers 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. There is thus provided and the present invention is, accordingly, specifically directed to a film unit assemblage structure which is a permanently fixed laminate and comprises a common support carrying, in order on one surface, a first silver precipitating nuclei containing layer, a photosensitive silver halide layer, and a second silver precipitating nuclei containing layer.  
  As stated, the silver precipitating nuclei present in the film unit are disposed in a concentration effective to provide a silver image possessing an optical density inversely proportional to exposure of the emulsion and in effect provide a silver image derived from unexposed silver halide crystals possessing greater covering power than a silver image derived from exposed silver halide crystals, by reason of the fact that the image silver derived from unexposed silver halide crystals comprises silver of a first physical character and image silver derived from exposed silver halide crystals comprises silver of a second physical character and that the first physical character silver possesses higher optical density that the second physical character silver per unit mass.  
  It has been specifically found that in the preferred embodiments of the present invention, the film unit is adapted as specifically detailed herein to provide a differential 1.0 and specifically 1.5 density units between the predetermined maximum image density of the developed negative silver image, i.e., D and the predetermined minimum image density of developed positive silver, i.e., D In a particularly preferred embodiment, the film unit is fabricated to provide a maximum silver image density 0.5 and, more particularly, 0.3 density units upon development of completely exposed areas of the silver halide stratum and the film unit will possess silver precipitating nuclei in a concentration effective to provide a minimum image density 1.0 and specifically 1.8, preferably, in excess of 2.0 and, most preferably, 3.0 density units derived from processing of unexposed silver halide grains. In such preferred embodiment, the silver halide stratum will ordinarily comprise panchromatically sensitized silver chloroiodobromide or silver iodobromide, particularly that containing 1 to 9 percent iodide by weight of silver, dispersed in a permeable colloidal binder which, in a preferred embodiment comprises gelatin sufficiently hardened to provide a hydration factor, upon contact of aqueous processing composition preferably possessing a pH in excess of l2,&#39;effective to prevent swelling in excess of a magnitude equal to its ambient size within a period of 15 seconds.  
  In accordance with the unexpected discovery which constitutes the present invention, the presence of silver precipitating nuclei contiguous both major surfaces of a photosensitive silver halide layer during processing effectively acts to facilitate advantageous production of a silver image inversely proportional to exposure of the silver halide layer by geometrically maximizing the effective concentration of nuclei next adjacent the photosensitive layer so that there is provided, in comparison with the structures of the prior art, decreased transport time and distance to ultimate image disposition of reduced soluble silver complex, derived from unexposed silver halides and constituting the ultimate image constituents. Such decreased transport time and distance as is achieved decreases lateral diffusion or deviation of image components and thereby provides the increased image acuity and resolution required for most effective image reproduction. In addition, it has also been further discovered that the resultant geometric maximization of effective silver precipitating nuclei concentration in adjacent spacial relationship to both major surfaces of the silver halide crystal containing layer enhances, to a maximum extent, image silver mordant sink capacity and, accordingly, efficiency, information content and acuity of the resultant silver image formation. The close spacial proximity of silver precipitating nuclei next adjacent the major surface boundaries of the photosensitive layer in effect provides silver precipitating nuclei substantially contiguous the silver halide crystals of the relatively thin, e.g., 1 micron, photosensitive layer and has been found to substantially obviate, when compared with prior art film unit structures, substantial fiber or filamentary silver image formation, during processing, as a function of the chemical development of exposed silver halide crystals, and the thereby resultant increased covering power derived from such image silver conformation.  
  In general, in accordance with the teachings of the photographic art, physically developed silver is directly reduced from a fluid phase during development and essentially comprises relatively compact grains. In contradistinction, chemically developed silver, in all known conventional processes, is directly furnished from exposed silver halide crystals and essentially includes image silver in the general form of fibers of filaments. The covering power, that is, the optical density per gram of silver per square meter, of the resultant silver image, in each instance, is a function of the aggregation and conformation of developed silver and, in general, may be considered to be inversely purportional to the diameter of the particles, or grains as aggregated, in the absence of considerations with respect to aggregate conformation.  
  In accordance with the present invention, however, a film unit assemblage may be fabricated, as detailed above, to provide as a function of exposure, upon de velopment in the presence of a silver halide solvent, silver image conformation, derived from development of photoexposed silver halide crystals, restricted to a major extent to elemental silver grains or particles possessing a diameter substantially equal to the original diameter of the unexposed photosensitive crystals constituting the silver halide stratum. The negative image silver is thus characterized by decreased fiber or filamentary conformation when compared with prior art type film unit structures. Amplification of the thus produced negative silver image, to provide an optical density beyond that provided by elemental silver image particles or grains of a diameter directly comparable to the silver halide stratum crystal diameters and resultant from increased image grain diameter pursuant to crystal area growth, directly or by reason of elemental silver fiber or filament production, is effectively prevented to a substantial magnitude.  
  Photosensitive silver halide emulsions of the high speed type generally employed for photographic reproduction are characterized by the presence of photoresponsive silver halide crystals possessing active sensitivity centers or sites which are believed to comprise minute aggregates of silver sulfide, the sulfide of which is derived from active sulfur naturally present initially in a polymeric matrix, for example, a gelatin matrix, or added to the formulation during fabrication. For optimum sensitivity there should be a limited but effective number of sensitivity sites in each crystal, particularly at the surface of the crystals. Upon exposure to incident electromagnetic radiation actinic to the crystals, it is understood that photons absorbed by the crystals provide photoelectrons within the crystals which are capable of diffusion to the sensitivity sites which possess a lower conductivity bond level and, in effect, provide such sites with a negative charge which precipitates, at the sites, as elemental silver, free silver ions originally disposed within the crystal lattice. During development of the exposed silver halide crystals, the silver halide developing agent, a reducing agent, provides additional electrons which serve to effect precipitation of additional silver ion of the crystals resulting in the extrusion of fiberous or filamentary elemental silver at surface sensitivity sites and which continues until reduction of the crystals is complete.  
  The presence of an effective concentration of silver precipitating nuclei contiguous both surfaces of the thin silver halide layer during the development process effectively acts to facilitate prevention of microscopic elemental silver filament or fiber extrusion beyond the crystal surface with the concomitant result of restricting image grain size to that of the crystal. Accordingly, the covering power of the resultant negative image in each instance is limited to that provided by elemental silver grains or particles possessing a diameter substantially equal to that of the original crystals dispersed in the photosensitive matrix and absent amplification due to the diameter increase of conventional negative image elements resultant from filamentary image silver;  
  There is thus provided by means of the present invention photosensitive silver halide crystals or grains dispersed in an environment containing silver precipitating nuclei or agents which in the presence of a solvent developer composition cause exposed grains to be reduced to opaque structures smaller in presented area than the area of the same grains developed in an identical developer composition absent such precipitating nuclei. Silver image masses derived from exposed silver 8 l halide grains developed in accordance with the present invention, accordingly, possess low optical covering power as compared with the covering power provided by identical grains developed in the same solvent developer absent the presence of the precipitating environ? ment. Specifically, the present invention provides forj the production of a direct positive silver image in which the transmissivity of silver image is a function of the quantity of actinic radiation which exposed the photosensitive silver halide. The exposed silver halide grains are reduced as compact masses possesing low covering power simultaneously with reduction of unexposed silver halide grains as colloidal dispersions possessing high covering power. The direct positive silver image thus produced in situ by means of the present invention possesses extraordinary high sharpness when compared with the silver transfer processes&#39;of the prior art.  
 For the purpose of insuring the production of a positive image possessing a high covering power, the silver precipitation nuclei will be disposed within the film unit in a concentration per unit area effective to cause image silver derived from unexposed silver halide crys tals to possess the desired opacity per given mass of in situ reduced silver.  
  It will be specifically recognized, however, that in a preferred embodiment of the invention the photoinsensitive silver precipitating nuclei containing layer should most preferably possess a thickness of less than about a wavelength of light, whereby minimizing to a maximum extent any substantial lateral diffusion of silver image-forming components during processing of the film unit.  
  Referring to FIG. 1, there is shown a diagrammatic enlarged cross-sectional view of a film unit constructed in accordance with a preferred embodiment of the present invention. The film unit is shown to specifically comprise a flexible transparent film base or support member 10 carrying on one surface, in order, a first substantially photoinsensitive layer 11 comprislngsilver precipitating nuclei; a photosensitive silver halide I emulsion 12; and a second substantially photoinsensitive layer 11 comprising silver precipitating nuclei.  
 The photoresponsive material of photographic emulsion 12 will,.as previously described, preferably comprise a crystal of a compound of silver, for example,  
 In general, silver precipitating nuclei comprise a spe-.  
 cific 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 IB, IIB, IVA,  
 VIA, and VIII and the reaction products of Groups IE, I  
 IIB, IVA, and VIII metals with elements of Group 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 X 10&#39; moles/ft Especially suitable as silver precipitating agents are those disclosed in U.S. Pat. No. 2,698,237 and spe cifically&#39; 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 20 C. vary between and 10 and especially the salts of zinc, copper, cadium and lead. Also particularly suitable as precipitating agents are heavy metals such as silver, gold, platinum and palladium and in this category the noble metals illustrated are preferred and are generally provided in the matrix as colloidal particles.  
  The preferred silver halide type photographic emulsion 12, employed for the fabrication of the photographic film unit, may be prepared by reacting a watersoluble silver halide, such as ammonium, potassium or sodium bromide, preferably together with a corresponding iodide, 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 floc systems, or procedures, adapted to effect removal of undesired components, for example, the procedures described in U.S. Pat. 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 l-lamer, F. M., The Cyanine Dyes and Related Compounds.  
  Subsequent to optical sensitization, any further desired 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 whole 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 U.S. Pat. Nos. 2,322,085 and 2,541,474; vinyl polymers such as described in an extensive multiplicity of readily available U.S. and foreign patents or the photoresponsive material may be present substantially free of interstitial binding agent as described in U.S. Pat. Nos. 2,945,771; 3,145,566; 3,142,567; Newman, Comment on Non- Gelatin Film, B. J. O. P., 534, Sept. 15, 19 61; and Belgian Pat. Nos. 642,557 and 642,558. I  
  The discrete silver precipitating nuclei layer or layers 11 may be realized by the application of, location of, and/or in situ generation of, the nuclei directly or indirectly contiguous one or both surfaces of the photosensitive layer in the presence or absence of&#39;binde r or matrix material and, in the latter instance, may comprise one or more adjacent or separated strata of a permeable material contiguous either or both surfaces 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, ploymeric 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 ethers and esters, polyamides and esters, etc., and the like; and the former type preferably comprising submacroscopic agglomerates of minute particles of a water-insoluble, inorganic, preferably siliceous material such, for example, as silica aerogel as disclosed in U.S. Pat. No. 2,698,237.  
  Where the silver precipitating agent is one or more of the heavy metal sulfides or selenides, it may be preferably 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 difficulty 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 ahve 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 preferably 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 U.S. Pat. No. 2,584,030. For example, if the ioncapturing 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 substantial1y,&#39;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 is fabricated to substantially prevent microscopic distortion of the image conformation by preventing microscopic migration or diffusion of image elements within the poly- &#39;meric matrix. In general, conventional photographic image elements may ordinarily comprise a microscopically dynamic system without seriously noticeable disadvantage to the conventional employment of the image. However, for particularly accurate information recordation, microscopic distortion of image elements is preferably obviated to insure maximization of the accuracy of image reproduction. Specifically, it has been found that a photosensitive film unit comprising photosensitive emulsion containing silver halide crystals dispersed in a polymeric binder and a photoinsensitive image-receiving layer containing silver precipitating nuclei dispersed in a polymeric binder and a photoinsensitive image-receiving layer 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 image reproduction acuity particularly desired for effective information recordation 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 spacially 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 spacially maintain positive image components. 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 elementfor the purpose of expediting processing of the element.  
  Support or film base may comprise any of the various types of transparent ridged 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 flexible transparent synthetic polymers such as polymethacrylic acid, methyl and ethyl esters; vinyl chloride polymers; polyvinvl 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 specific example which sets forth a representative fabrication of the film units of the present invention, which however, is not limited to the detailed description herein set forth but is intended to be illustrative only.  
  A gelatin subbed cellulose triacetate film base may be coated with a composition comprising deacetylated chitin and copper sulfide at a coverage of 3 mgs./ft. deactylated chitin and 2 mgs./ft. copper sulfide. On the external surface of the preceding layer a hardened gelatino silver iodobromide emulsion may then be coated at a coverage of 200 mgsJft. gelatin, 100  
 mgs./ft. silver and 4.0 mgs./ft. algin. The resultant film unit may then be overcoated with a layer comprising deacetylated chitin and copper sulfide ata coverage of 6 mgs ./ft. deacetylated chitin and 4 mgs./ft. copper in 61.6 cc. of acetone added to the solution over a period of 30 minutes. Subsequent to addition of the phthalic anhydride the reaction mixture may be maintained at the stated temperature and pH for a period of about 30 minutes and then adjusted to a final pH of about 6.0.  
  To a solution comprising 226 grams of the gelatin phthalic anhydride derivative, prepared as above, 161 grams of potassium bromide, 2 grams of potassium iodide, and 1200 grams of water may be added a solution comprising 200 grams of silver nitrate in 1600 grams of water, at a rate of about cc. per minute, for a period of about 3 minutes, held 10 minutes and the addition continued for a period of about 9 minutes. The resulting emulsions may then be precipitated by reducing the pH to about 2.5-3.0 with sulfuric acid. The precipitate may then be separated from the supernatant liquid and washed until the wash water is essentially free of excess potassium bromide. Ninety-five grams of gelatin may then be added to the precipitate, the volume adjusted with water to 845 cc., and dissolved by heating to about 38 C., for about 20 minutes, at a pH of about 5-6, and about 1.0 cc. of l N potassium bromide added to the emulsion. To the reaction mixture, at about 56 C., may be added 5 cc. of a solution containing 0.1  
 grams of ammonium thiocyanate in 9.9 cc. of water and 0.4 cc. of a solution containing 0.097 grams of gold chloride in 9.9 cc. of water, and the mixture ripened at i that temperature for about 37 hours. The resultant emulsion may then be panchromatically sensitized by the sequential addition of 0.1 percent, by weight, methanol solutions of anhydro 5,5 &#39;-diphenyl-3,3 &#39;-bis-(4- sulfobutyl)-9-ethyl-oxacarbocyanine hydroxide and anhydro 5 ,5 &#39;-dimethyl-3 ,3 &#39;-bis-( 3-sulfopropyl)-9-ethylthiacarbocyanine hydroxide in optionally effective concentrations. The copper sulfide silver precipitating agent may be provided, prior to coating, by the in situ addition of substantially equimolar quantities of copper acetate and sodium sulfide solutions.  
 The film unit, fabricated as detailed above, may be grams of -nitrobenzimidazole, and 5 grams of.  
 2,6-dimethylhydroquinone, to provide production of a positive silver image possessing the optical characteristics described hereinbefore and the acuity required for effective image reproduction.  
 A film unit fabricated and processed in the general manner detailed above exhibited a D silver coverage of 96 mgs./ft. and a D,,,,,, silver coverage of 96 mgs./ft. and an optical density of 2.80 and 0.31, respectively.  
 Comparison of a film unit fabricated and processed in the general manner detailed above, verses a film unit fabricated and processed in substantially the same manner with the significant exception that the lastmentioned copper sulfide layer was absent clearly illustrates the unexpectedly improved results provided by means of the present invention. Specifically, a film unit fabricated to be directly comparative with the film unit detailed above and possessing no separate layer containing silver precipitating nuclei overlying the photosensitive silver halide emulsion layer, exhibited a D silver coverage of 98.4 mgs./ft. and a D,,,,,, silver coverage of 98.4 mgs./ft. and an optical density of 2.50 and 0.42, respectively.  
  Additional film units may be fabricated and processed in the manner detailed above and optimized to exhibit a D of 3.3 and a D,,,,,, of 0.3 and to thus provide a differential of 3.0 density units and, in effect, a percent transmission ratio of about 1,000 1, and, where desired, for example, by reason of selected color screen parameters, a D of 4.0 and a D,,,,,, of 0.3 to provide a differential of 3.7 density units and thus a percent transmission ratio of about 5,000 l.  
  The film units of the present invention are particularly desirable for employment as a cine&#39;film for motion picture projection, in addition to slide transparency film, by reason of the inherent ability to simply and effectively process such film employing relatively simple and stable processing compositions, immediately subsequent to exposure, without the necessity of providing a process and apparatus adapted to effect stripping of a separate emulsion stratum from the remainder of the film unit, to provide information recordation possessing the image integrity and reproduction characteristics required for effective employment of the film.  
  As previously stated, the photosensitive silver halide emulsion and/or the silver precipitating nuclei containing layer 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 emulsion s 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 emulsion and silver precipitating nuclei containing layers. in addition, the silver precipitating nuclei containing stratum distal the color screen 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 intial 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 support, is a particularly preferred embodiment, for the purpose of providing unexposed image acuity, which more readily facilitates 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.  
  It will be apparent that the relative proportions of the agents comprising the developing composition set forth herein may be altered to suit the requirements of the operator. Thus, it is within the scope of this invention to modify the herein described developing compositions by the situation of preservatives, alkalis, silver halide solvents, etc., other than those specifically mentioned. When desirable, it is also contemplated to include, in the developing composition, components such as restrainers, accelerators, etc. The concentration of such agents may be varied over a relatively wide range commensurate with the art.  
  The processing composition solvent employed, however, 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 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 described 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 s illustrate and not in a limiting sense.  
 What is claimed is:  
  1. A photographic process which comprises, in combination, the steps of exposing a photographic film unit comprising a permanent laminate which contains a common transparent support carrying on one surface,  
 in order, a first layer comprising silver precipitating nuclei; a layer comprising a photosensitive silver halide; and a second layer comprising silver precipitating nuclei, contacting said exposed silver halide layer with an aqueous processing composition containing a silver halide developing agent and a silver halide solvent thereby providing a visible silver image to said film unit in terms of the unexposed areas of said silver halide layer as the function of the point-to-point degree of exposure thereof, and maintaining said laminate intact subsequent to processing.  
  2. A photographic process as defined in claim 1 which comprises, in combination, the steps of exposing a photographic film unit comprising a permanent laminate containing a transparent support carrying on one surface, in order, a first substantially photoinsensitive layer comprising silver precipitating nuclei, a photosensitive silver halide emulsion comprising photosensitive silver halide crystals dispersed in a processing composition permeable polymeric binder, and a second substantially photoinsensitive layer comprising silver precipitating nuclei, said silver precipitating nuclei present in a concentration effective to provide a silver image derived from unexposed silver halide crystals possessing greatercovering power than a silver image derived from exposed silver halide crystals, contacting said silver halide emulsion with an aqueous processing composition containing a silver halide developing agent and a silver halide solvent for a period of time effective to provide a visible silver image to said film unit, as a function of emulsion exposure, derived from unexposed silver halide crystals possessing greater covering power than the silver image derived from exposed silverhalide crystals, and maintaining said laminate intact subsequent to processing.  
 3. A photographic process as defined in claim 2 l which comprises, in combination, the steps of exposing a photographic film unit which comprises a permanent fixed laminatecontaining a transparent support carrying on one surface, in order, a first substantially photoinsensitive layer comprising silver precipitating nuclei dispersed in a processing composition permeable matrix, a photosensitive silver halide emulsion comprising photosensitive silver halide crystals dispersed in a processing composition permeable polymeric binder, and a second substantially photoinsensitive layer comprising silver precipitating nuclei dispersed in a pro cessing composition permeable matrix, said silver precipitating nuclei present in a concentration effective to provide upon development, as a function of exposure,  
 a silver image derived from development of unexposed silver halide crystals possessing a maximum image density at least 1.0 density units greater than the maximum density of the silver image derived from development of exposed silver halide crystals, contacting said silver halide emulsion with an aqueous processing composi-. tion containing a silver halide developing agent and a silver halide solvent for a period of time effective to provide a visible silver image to said film unit in terms I of the unexposed areas of said emulsion as a function r of the point-to-point degree of emulsion exposure, said visible silver image derived from development of unexposed silver halide crystals and possessing a maximum image density at least 1.0 density units possessing a maximum image density at least 1.0 density units greater than the maximum density of developed silver derived from development of exposed silver halide crystals, and maintaining said laminate intact subsequent to said processing.  
  4. A photographic process as defined in claim 3 which comprises, in combination, the steps of exposing a photographic film unit which is a permanently fixed laminate and comprises a transparent support carrying on one surface, in order, a first substantially photoinsensitive layer comprising silver precipitating nuclei dispersed in a processing composition permeable poly meric binder, a photosensitive silver halide emulsion comprising photosensitive silver halide crystals dis-.  
 persed in a processing composition permeable polymeric binder, and a second substantially photoinsensitive layer comprising silver precipitating nuclei dispersed in a processing composition permeable polymeric binder, said silver precipitating nuclei present in a sufficient time to provide a silver image to said film unit comprising a maximum density of image silver derived from development of unexposed silver halide crystals of not less than about 1.5 and a maximum density of image silver derived from development of exposed silver halide crystals not in excess of about 0.5, and maintaining said laminate intact subsequent to processing.  
  5. A photographic process as defined in claim 4 which comprises, in combination, the steps of exposing a photographic film unit which comprises a permanent laminate containing a transparent support carrying on one surface, in order, a first substantially photoinsensitive layer comprising silver precipitating nuclei dispersed in a processing composition permeable polymeric binder, a photosensitive silver halide emulsion comprising panchromatically sensitized silver iodobromide crystals dispersed in a processing composition permeable gelatin binder, and a second substantially photoinsensitive layer comprising silver precipitating nuclei dispersed in a processing composition permeable polymeric binder, said binders possessing a lattice effective to substantially prevent microscopic diffusion of image silver components, said silver precipitating nuclei present in a concentration effective to provide, upon development in the presence of a silver halide solvent and as a function of exposure, image silver derived from development of exposed silver iodobromide crystals possessing a maximum silver image density less than about 0.3 and a maximum silver image density derived from unexposed silver iodobromide crystals greater than about 1.8, contacting said exposed emulsion with an aqueous processing composition containing a silver halide developing agent and a silver halide solvent for a time sufficient to provide a silver image to said film unit in terms of the unexposed areas of said emulsion possessing a maximum silver image density of not less than about 1.8 and a silver image to said emulsion in terms of the exposed areas of said emulsion possessing a maximum silver image density not in excess of about 0.3; and maintaining said laminate intact subsequent to processing.