US 2719791 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
Oct. 4, 1955 2,719,791
E. H. LAND METHOD OF IMPROVING THE STABILIZATION OF FINISHED PHOTOGRAPHIC PRINTS BY APPLYING A LIQUID COMPOSITION THERETO Filed Aug. '5, 1952 1 I50 [5b Shipping Layerilver Precipifafing Layer ferproof Subcoal' Prin+ s Receiving Sl'ruham FIG. I
I7 I50 (5b7 law l77wf-profeciive Couling Silver Image INVENTOR WQZZ.
ATTORNFYS United States Patent 6) METHOD OF IMPROVING THEiSTABlLIZATION' OF FINISHED PHOTOGRAPHIC' PRINTS'BYAP PLYING A LIQUID COMPOSITION THERETO Application August =5, 1952,.Serial No. 302,746 1 4 Claims. (Cl. 95-88) This invention-relates to methods for improving the stabilization of a photographic print by removing photographic reagents which remain therein following the completion of photographic processing and by providing on the print a protective coatinggwhich is difficultly permeable to water and vapor.
Objects of theinvention are to provide a method for improving the stabilization of a-photographic print containing-a silver image by'washing the surface of said print=on the image side thereof with an aqueous composition containing a plastic material capable of being formed into at least a difiicultly waterand vapor-permeable coating and involving the procedure of rubbing said composition-over the surface of the print to wash photographic reagents from the print-in the water of the composition and to coat said surface with said composition,- and then drying the composition on said surface to provide the coatingof-plastic'material'in a substantiallydry condition; to provide a method 'of*the-character'set forth wherein the composition is rubbed over the surface-of the printwith an irregular motion at least until'said surface is covered 'with the composition and thereafter the rubbing is continued with a regular motion wherebyto even and smooth off the applied composition; and "to provide a method for improving-thestabilization of aphotographic printby coating the-surface of-the print with a compositionof "the character described byrubbing said surface with an absorbent member 'whichis' charged with said composition and from which said composition is dischargeable by movement of-said absorbent member in frictional contact over said surface.
Other objects of the invention are to provide a method for-improving 'the'stabilizationof photographic prints containing va silver image in a water-permeable stratum which includes one-surface of the print by washing said stratum with an aqueous composition of "the nature descrihed'and rubbing saidcompositio'n over said surface to cause water from the composition to penetrate into the stratum forrremoval of photographic-reagents from the stratum in said water andtocoat said surface with" said composition while restricting the penetration of the water d-said composition into said print to a depthsubstantially equalrto the thickness of the stratumand thereafter drying. the composition; toprovide stabilization methods of'the character. described which employan aqueous dispersion of I a high molecular weight polymer or=polymeric material capable of forming a continuous filmiwh'enspreadion'a-surface, and including-either an aqueous solution of said polymeric material or an aqueous suspension thereof; and to provide stabilization practices of' this nature which preferablyutilize an aqueous suspension of a plastic material 'and'wherein the suspension is characterized by the 'fact that the plastic material re mains in suspended condition'following the freezing and the thawing of the-composition.
Other objects of the=invention will-in part be "obvious and vwill in part appear hereinafter.
The invention accordingly comprises the r severalsteps reason of developer-remaining in the print.
by sulfide from residual thiosulfate.-
and the relation of one or more of such steps with respect to each of theothers, lowing detailed disclosure, and the scope of the applica tion of which will be indicated in the claims.
For a fuller understanding ofthe nature and objects of the invention, reference should be had tothe following detailed description-taken in connection with the accompanying drawing wherein:
Figure 1 is a diagrammatic, enlarged,-sectional view showing one embodiment of a print-receiving element for carrying out the invention, the thickness of the various materials beinggreatly exaggerated for the purpose of illustration; and l b Fig. 2 is a view similar to Fig. 1 and shows the print-- receiving element of Fig. 1 after it has beenphotographically processed to provide a silver-image therein 'and after it has been stabilized "by the practices of this invention. V a 7 As will'appear from the foregoing, this invent-ion is concerned with improvements in the stabilization of photographic prints which carry a silver image. I
A finished silver print invariably retains therein at least traces of photographic processing reagents, of whichadversely affects the stabilization of the print.- Sii'nilarly, oxidizing agents carried in the atmosphere can exert an undesirable effect uponthe stabilizationof the print. These reagents, which'from the standpoint of stabilization may be classified as impurities, may in' the course of time. cause the v to become fogged.
For example, the highlights of the print may turn yellowdue to the oxidation of "unexhausted developer- Which'has not been removed from the print; Additionally, many oxidized developers have the ability to oxidizesilver so that not only will'the highlights turn yellow, as previouslymoted; but the shadows will 'alsofade by Furthermore,- silver may be oxidized by other agents: as, fo"r example, Similar oxidation effects .on-thesilver of an image can also-arise from oxidizing-tagents as, for-example,-sulfur dioxide, which are presentin the atmosphere.
By the 'present invention, .improvements'in print'stabilization'arewachieved by'appiying, atleasttto the image surfacekof afinished print,2an aqueous composition containing a plastic material which is capable of forming at least a-diificultly waterand -vapor-permeablecoating or film over said surface. The'stabilizing compositionmay be a solution of the plastic materiaL'or-itmay-be a-suspension. The stabilizing composition: isintended to be spread ordistributedover the surface of-theprintby-a rubbing action and, after the print has been thoroughly covered, is-evened-off; i
A preferred manner of applying the composition is from antelongated absorbent member or applicator which has beenchargedwith the composition: This absorbent member is placed upon-the-surface of the print. and is designed so that when-frictionally moved in contact with theesurfaceof theprint it will cause the'discha'rge of liquid .onto said surface. Preferably, the applicator is moved over the print surface-firstusing an irregular mo tion,-for example a circular motion, and this is continued until the 'printis thoroughly .coated with the s stabilizing composition, following which a: few light-smoothing strokes with'a regular motion; for example, a-straightline movement of the applicatorfrom-endrto end'ofethe print, is employed to smooth'ofli-the coating.
As is well understood, the image-carrying (stratum-rot a print ispermeable to liquids. Consequently,.:the;-water of the aqueous stabilizing 1 composition twillpenetrate into thevstratumyinawhich thesilver-imageeis carriedt. Atithe same. time, the. act of. rubbing the composition: overzthe Patented Oct. 4, 1955 which are exemplified in the 1fol' the presence printto become yellow and/or print assures penetration of the water of the composition into the print and provides a scrubbing action which washes impurities in the nature of the heretofore mentioned photographic reagents from the image-carrying stratum as well as the surface of the print. Impurities of this character will either be dissolved in the water or otherwise carried off thereby.
The plastic material contained in the composition, upon drying, i. e., evaporation of the water of the composition, will form a substantially continuous coating or film over the treated surface of the print. Since by design this plastic material will be at least difficultly waterand vapor-permeable, it will be appreciated that the coating provided will protect the treated surface of the print from penetration by reagents which are carried in the atmosphere and which are of a nature deleterious to the print.
The processing just described is highly effective in in stances where the silver image is formed in an extremely thin image-receiving or image-carrying stratum. For example, an image-receiving stratum may be employed having a thickness of as little as one micron or less. When it is considered that the longest wavelength for visible light is about 0.7 micron, it will be appreciated that an image-carrying stratum of the nature described, as well as a stratum several microns thick, will have a dimension which approaches the order of magnitude ascribed to a wavelength of light. Because of the thinness of the image-carrying stratum, the water of the aqueous composition is readily penetrable substantially therethrough whereby not only can this water be used to wash away impurities at the surface of the stratum but also impurities which exist throughout the stratum.
A higher degree of print stabilization is achievable in instances where a thin image-carrying stratum of the nature just detailed is supported upon a waterproof layer, i. e., a layer which is at least difiicultly permeable to water and vapor and which is capable of restricting penetration of photographic processing solutions therein, at least for the time that these photographic processing solutions are in contact with the print. An advantage of this arrangement resides in the fact that by supporting the image-carrying stratum on a waterproof layer and by coating the image-carrying stratum with the print coating of this invention, the image-carrying stratum is literally sandwiched between two difficultly waterand vapor-permeable layers so that it is protected on two sides from penetration by undesired agents carried in the atmosphere.
As is now understood by the art, a positive print is obtainable, by a transfer process and in a single step from a photosensitive element having a silver halide photosensitive layer containing a latent image, by permeating into said photosensitive element and a printreceiving element arranged in superposed relation to the photosensitive element a viscous liquid reagent comprising a photographic developer and a substance which forms a soluble silver complex, e. g, a thiosulfate, with undeveloped silver halide. The developer develops the latent image, and the silver complex is at least in part transported in solution in said liquid in the direction of the print-receiving element where the silver thereof may be largely precipitated in a stratum of said print-receiving element to form a positive image in silver. After formation of the positive silver image, the two elements are stripped apart. The processing reagent is viscous and one preferred form thereof employs a thickening agent such as a high molecular weight film-forming polymer. The reagent is adapted to form a film which can be stripped, with the photosensitive element, from the print-receiving element.
One embodiment of a print-receiving element 12 is illustrated herein in Fig. 1 and comprises a support 13 which carries a waterproof layer or subcoat 16 upon which is superposed a liquid-permeable print-receiving 4 image-carrying stratum 15. 15 is shown as comprising a stripping layer 15a, which constitutes the outer surface portion thereof, and a silver precipitating layer 15b. By this construction only a surface portion of the print-receiving element, namely the print-receiving stratum, is capable of being permeated to any appreciable extent by the ionic reagents contained in the processing liquid.
The outer surface of the print-receiving stratum 15 is adapted to come into contact with the layer of liquid reagent used in the transfer process and is so constituted as to have a lesser adhesion for the solid residue of the processing liquid than does a photosensitive element employed in carrying out the process. For this reason the photosensitive element, when stripped from the printreceiving element, carries with it the residue of the processing reagent. The entire print-receiving stratum 15 may be essentially formed of a material having the desired stripping properties or preferably a thin film of a suitable stripping composition may constitute the outer surface portion of said stratum, while the remainder of said print-receiving stratum is formed of a vehicle more suitable for carrying the silver precipitating agents.
Support 13 may be formed of a water-permeable material such as an uncoated or gelatin-coated paper, for example, baryta paper, or the support may comprise a substantially water-impermeable material such, for example, as unplasticized polymethacrylic acid or one of the cellulosic esters such as cellulose nitrate, cellulose acetate, cellulose butyrate, cellulose propionate, cellulose acetate butyrate or cellulose acetate propionate. Preferred, however, are the rubbery types of plastic such as polyvinyl butyral.
If support 13 is water permeable, layer 16 constitutes a separate film of one of the just-named water-impermeable materials and is coated on said support in sufficient thickness to prevent any appreciable penetration of the liquid processing reagent therein. If support 13 is substantially water impermeable, layer 16 may be just an integral extension of said support, in which case no line of demarcation, as shown in Fig. 1, actually exists between layer 16 and support 13. It is to be clearly understood, therefore, that unless specifically stated to the contrary, all future references, especially in the claims, to a water-impermeable layer and a support therefor do not preclude a structure wherein the layer and support are integral parts of a single Water-impermeable sheet material such as a sheet of one of the aforementioned plastic materials.
The copending applications of Edwin H. Land, Serial No. 727,385, filed February 8, 1947, for Photographic Product and Process, now Patent No. 2,698,245, Serial No. 7795, filed February 12, 1948, for Photographic Process, now Patent No. 2,647,056, and Serial No. 164,- 908, filedMay 29, 1950, for Photographic Silver Halide Transfer Product and Process, now abandoned. and replaced by application Serial No. 449,995, filed August 16, 1954, and issued as Patent No. 2,698,237 on December 28, 1954, teach that the presence of certain compounds and elements during the formation of silver transfer prints has a desirable effect on the amount and character of silver precipitated during image formation. Materials for this purpose are, for example, the metallic sultides and selenides, the thiooxalates, the thioacetamides and others disclosed in said just-mentioned applications.
It has been disclosed in the'just-noted applications that the precipitation and aggregation of silver obtained by using silver precipitating agents, including the above-mentioned materials, are very greatly improved by providing in the print-receiving element as a vehicle for said agents a macroscopically continuous matrix consisting essentially of submacroscopic agglomerates of particles of a water-insoluble, inorganic, chemically inert, adsorbent substance. The word submacroscopic refers to a class of sizes which includes as a subclass those sizes known as The print-receiving stratum submicroscopic. The substance preferably has a. low" c.0- eflicient of absorption .forlightas compared to silver and the matrix formed therefrom is essentially free of-protective colloid action for silyier. One example of such a matrix is a layer of silica such: as is. formed by drying a layer of the dispersion of theasili'ca aerogel available under the trade name Santocel C.
Layer 15b constitutes a silicamatrix formed by drying an aqueous dispersion: of. silica aerogclin which has: been incorporated one or more of the heretofore mentioned silver precipitatingagents as,,for example, a sulfideand/ or a sclenide. Whenone or more of; the heavy metallic sulfides or selenides are employed, it is desirable, for the purpose of obtaining optimum results, to add one or'more ion-capturing salts to the: silica. dispersion, such, for example, as one or more saltsxfrom. the class consisting of salts of cadmium, cerium(ious.)1, cobalt(ous),v iron, lead, nickel, manganese. and thorium. The silica. dispersion is coated ontothe waterproof subcoat 16', following which it is dried.
Compositions of the: character just described for providing silver precipitating layers are disclosed in the foregoing applications. One example of a suitable coating composition for providing an; image-receiving layer is. as
1% solution of sodium sulfide cc 280 Silica aerogel grams '30 Solution containing 30 g. cadmium acetate, I g. neutral lead acetate and 30v g. zinc nitrate dissolved in 100 cc. of water ;cc 92 Inasmuch as the presence of silver precipitating agents and the use of a silicamatrix' greatly enhance the precipitation and aggregation of silver from the transferred silver complex, it is possible to make the layer 15b of an extremely thin character. For example, the layer 15b of the print-receiving stratummayhave: a thickness of' from less than one micron to three microns or more. The relative thinness of the layer 15b becomes impressive when considering the fact that the wavelength range for visible light is from approximately 0.4 to 0.7 micron. In any event, the thickness dimension noted for the layer 1517 will clearly illustrate its thinness and the ability of the layer to be penetrated by the aqueous coating composition with which this invention is. concerned.
Stripping layer 15a may be formed, for example, of gum arabic, sodium alginate, pectin, cellulose acetate-hydrogen phthalate, polyvinyl alcohol, hydroxyethyl' cellulose or polymethacrylic acid and, when kept very thin, may be of plastici-zedmethyl; cellulose, ethyl cellulose, methyl methacrylate or butyl methacrylate. The layer 15a may be formed by roll-coating. a: suitable solution of one of the just-noted materials on the layer 1512 and may be applied to a thickness of from approximately one to three microns.
A print structure suchas that utilized in the element 12 offers certain features which favor print stabilization- For example, the waterproof layer 16 restricts penetration of a liquid photographic reagent applied onto the image surface of the print to a thickness which is substantially equal to the image stratum 15. This limits the distribution of the photographic reactants to the image stratum of the print and also exerts a control over the quantity of the reactants which can be introduced into the print for image processing purposes. Consequently, reactants introduced. into the image stratum 15 for print processing are able to be readily removed or washed out of the stratum by reason of its extreme thinness.
it will thus be appreciated that print structure such as that described herein readily lends itself to improved; stabilization by-the methods which have heretofore been set forth. The thinness of the image stratum permits traces of reagents which may remain therein after completion of photographic processing for forming an image tobe easily removed by a limited mass-or volume of water,
especially when. the water. is applied .vvitha-an accompanying rubbing action in the manner described. Significantly, theability of a limitedquantity of water torem'ove traces of reactants permits relatively quick drying of the stabilizing composition, as wellasthe use of a.stabilizing. composition which has ahigh solids content, whereby to assure a coating of a continuous'character on. the surface of the print. 1
Additionally, a stabilizing composition ,of the character described lendsitself to -retentionfiin an absorbent applicator device for discharge uponthefri'ctional movement of the applicator device over the-su-rface of the print. Furthermore, since the stabilizing: composition will retain its usefulness if kept from: contact with the atmosphere, an absorbent'applicatormeans which has been charged with the Stabilizing composition-may beindefinitely stored in a condition ready for use if kept. in a hermetically scalable container when-not employed. It will be appreciated that under-these circumstances-it is possible toemploy an absorbent applicator'means which has been impregnated or charged with a s-uificient quantity of the stabilizingcomp'osition to coata plurality of prints.
In more detail, the stabilizing composition is a. solidliquid composition wherein the solidcontent thereof is provided by a plastic material, i.- e., ahigh molecular weight polymer or polymeric material. capable of forming, when spread on a support surface, a continuous film which isat least difiicultly permeable towater and vapor.
The liquid of the composition is preferably water, although an aqueous-solution of an organic solvent or solvents-may be employed. It is to be notedyhowever, thatiin generate print will tolerate limited useof. organic solvents and that in the case of a print-receiving element, such'as the element 12 (Fig. 1), the use of organic solvents: which could seriously harm the. waterproof layerlflshoul'd be avoided. The solid or plastic material may be-of a watersoluble or water-insoluble character. Thus, the stabilizing composition. will constitute a'dispersion of the-plastic material in an aqueousmedium. 'By this definition, the term dispersion? is employed todesignate solution or'a suspension.
Preferably the stabilizing composition comprises a suspension of a water-insoluble 'plastic' material. Ai-suspension is preferred because it permi-ts th'eformulation of a stabilizing composition having ahiglr sol-id. content with low viscosity which perm-its'the application of a uniformly thin, relatively dry coat. onto the print surface, i-. e., a coating which will dry within a; relatively few seconds following. completion of its application. In comparison,
a solution with a high solid content produces-a composition of high viscosity and results in the formation of. a relatively wet and thick coating with increased time requirement for drying. Additionally it is diflicult to evenly apply a viscous composition so asto obtain a. uniformand smooth print coating. v I
The thickness of the dry coating. provided bythe stabilizing composition will be influenced by the type of composition employed, the solidcontent of the composition and the quantity of the composition applied tothe-print surface. In general, the minimum thickness. for the dried protective coating should be of a-. magnitude not less thanthat. which will giverise. toloworder iinterference colors, while. the maximum thickness of the dried coating will be determined by its ability to withstand cracking, as for example in the handling of the coated: print or in the aging of the coating under various. storage and display conditionsof the print. The invention may be practiced with a composition having. a solid-content 'ofas low as 10%, while the viscosity ofv the compositiontwill exert a control, as indicated above, uponthe upper limit for the solid content of thecomposition. Thus, when asatisfactory viscosity is obtained, it is-possible-to employ a composition having asolidcontent of 50% and even higher.
Certain other characteristics are required of the:.plascomprising water and a water-miscible solvent.
7 tie material used in the stabilizing composition. For example, this plastic should provide a continuous coating or film having relatively good transparency and preferably a high gloss. Reference to a continuous coating as used herein means that the particles of the material forming the coating may overlie one another or that one particle is a part of the particle next to it. Additionally and preferably, the plastic material should be able to provide an abrasion-resistant coating. As another characteristic, the composition should preferably remain substantially unaffected when frozen and then thawed. For example, there should preferably be substantially no coagulation of a suspension when it thaws from a frozen condition.
A preferred stabilizing composition comprises an aqueous suspension of a polymer of vinyl acetate. The expression a polymer of vinyl acetate is intended to include copolymers and interpolymers thereof. A vinyl acetate polymer of this nature is available in the form of an aqueous suspension under the trade name of Darex Polymer Y. A specific example of a suitable stabilizing composition in the form of a suspension makes use of 29 grams of vinyl acetate polymer and 71 grams of water.
If desired, a small quantity of wetting agent may be added to this just-mentioned composition, for example, .003 gram of dioctyl sodium sulfosuccinate which is commercially available under the trade name of Aerosol OT.
The solid content of this stabilizing composition may be varied as previously indicated. Also, the quantity of wetting agent employed may be varied as, for example, from .001% to .l%. The specific just-described suspension of a vinyl acetate polymer possesses a viscosity which permits easy application and provides a composition which remains substantially unaffected by the freezing and thaw- 'ing thereof.
A stabilizing composition such as that just set forth and employing a polymer of vinyl acetate as the solid thereof will provide a relatively hard, transparent coating of high gloss on the print-receiving stratum 15, as well as a coating which is substantially water-insoluble and hence substantially waterand vapor-impermeable. In Fig. 2, the print element 12 of Fig. i has been illustrated following its photographic processing to form, by transfer, a silver image 18 therein and also following the application of a stabilizing composition of the above character thereon to provide a protective coating 17 on the printrcceiving stratum 15. It will be appreciated, in the element 12, that the protective coating 17 in conjunction With the waterproof subcoat 16 will operate to restrict the penetration into the print-receiving stratum 15 of agents which are carried by the atmosphere and which are harmful to the print.
As mentioned, there may be employed as the solid material for the stabilizing composition any high molecular weight polymer capable of forming a continuous film which is at least difficultly permeable to water and vapor and which possesses the other properties heretofore mentioned. Other examples of a suitable plastic material which will supply a substantially waterand vapor-impermeable coating include acrylic polymers including the methacrylatcs and acrylates, butadiene-styrene copolymers, vinyl chloride and various natural and synthetic waxes and resins. It may be noted that the just-mentioned plastic materials are generally water insoluble and are incorporated as a suspension in an aqueous medium. As a consequence, they will produce a substantially waterand vapor-impermeable coating when dried.
Examples of water-soluble materials which are useful. to provide a protective coating 17 include polyvinyl alcohol, sodium carboxymethyl cellulose, hydroxymethvl cellulose and the sodium salts of polymethacrylic acid and polyacrylic acid. These materials, being water soluble, are employed in aqueous solution.
Additional polymericmaterials are available for coating purposes when they may be incorporated in a carrier Where the water-miscible solvent is of a character which is harmful to the print, the ratio between the water and the solvent must be chosen so that the latter will not harm the print and especially the subcoat 16. For example, the carrier may comprise a mixture of water and an alcohol or water and acetone or water and dioxane. In this regard, a modified resin such as that commercially available under the trade name Amberol 750" may be dispersed in an aqueous alcoholic ammoniacal solution. Furthermore, certain organic solvents miscible in water may be utilized to improve the drying qualities of the stabilizing composition. For example, methanol and ethanol are added to water in which polyvinyl alcohol is dissolved to speed up the drying of the composition.
It should be kept in mind, in connection with the use of water-soluble plastics, that the coating 17 functions to protect the image surface of the print from harmful agents carried in the atmosphere and that ordinarily the print will have limited contact with water and vapor. Obviously, the immersion of the finished print in water is not to be expected as a part of its treatment under normal or usual circumstances involved in its handling, storage and display. Rather, any contact of moisture with the finished print will be from sources such as water and vapor in the atmosphere or dampness from the hands. The limited volume of water which can be applied from these sources is generally insufficient to entirely dissolve the entire protective coating on the print, and the difficulty of permeating such moisture through the coating Will increase with the thickness of the coating. Consequently, water-soluble plastics are available to provide a stabilizing coating which is sufiiciently diflicultly perme able to Water and vapor to provide worthwhile print protection under usually encountered conditions. The aqueous solutions of plastics with high plastic content will be sufiiciently viscous so that coatings of a watersoluble plastic of the thickness needed to provide print protection are obtainable.
In carrying out a photographic transfer process with the element 12, it is to be particularly noted that during the stripping of the photosensitive element from the element 12, stripping layer 5a is cleaved and a thin portion thereof is stripped away with the photosensitive layer and the film formed by the photographic processing reagent. This cleavage has the further effect of diminish ing the thickness of the print-receiving stratum i5 of the finished print and augments the ability of the print to be stabilized by the practices of this invention. For this purpose, the layer 15a is illustrated in Fig. 2 follow ing the cleavage thereof after photographic processing and consequently is shown as being thinner than its initia condition prior to processing.
As previously noted, the coating composition is intended to be impregnated into a suitable applicator device having an absorbent member made of a textile material such as wool or cotton. To impart a pleasing appearance to the absorbent member and the applicator device as a whole, it may be desirable to add a dye to the coating composition. Such a dye should be substantive to the material of the absorbent member so that the coating composition when applied to the print will contain substantially no dye in solution and will provide the desired transparent coating. One such suitable dye is Congo red.
Prints which have been coated with the preferred com position comprising a polymer of vinyl acetate have some tendency to stick to each other, at least when placed in face-to-face contact. This tendency may be avoided by applying to the outer surface of the stabilizing coating 17 a thin stratum of a waxlike substance, for example either a natural wax or a synthetic wax, which is preferably substantially colorless. Additionally, waxing improves the luster of the print. The wax may be applied byrubbing a coating pad over the outer surface of the protective layer. This pad, which may comprise a small square of flannel, preferably mapped on both sides, is impregnated with a suspension of the wax as, for example, by immersing the pad in the suspension and then drying the pad.
While the practices of this invention to provide improved print stabilization have been illustrated in connection with the stabilization of a silver image obtained by carrying out a photographic silver halide transfer process, it should be realized that these practices are employable to achieve improvements in the stabilization of a silver print having an image formed in the photosensitive layer thereof by exposure and conventional development and fixation of the print. However, optimum stabilization of a silver print produced by the classical procedures of exposure, development and fixation is obtainable when the print structure utilizes a photosensitive layer which is relatively thin and at least approaches an order of thickness such as that indicated for the stratum 15 and when this photosensitive layer is supported upon a Waterproof layer or subcoat such as the layer 16 illustrated in the drawing.
Since certain changes may be made in the above process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.
What is claimed is:
1. A method of producing a stable photographic print, said method comprising the steps of spreading, in a thin layer, between a siliceous silver-receptive stratum of an image-receptive sheet and an exposed gelatino silver halide stratum of a photosensitive sheet, an aqueous alkaline solution of a silver halide developer and a silver halide solvent, whereby exposed silver halide in the silver halide stratum is reduced to silver and unreduced silver halide from the silver halide stratum forms a water-soluble, complex silver salt which diffuses through the layer of solution to the silver-receptive stratum where it is reduced to silver to form a visible print, stripping the silver-receptive stratum from the silver halide stratum, whereby the print retains a residue of the solution, swabbing the print with an absorbent applicator charged with a composition containing an aqueous dispersion of a plastic material, which yields a ditficultly waterand vapor-permeable coating on drying, to wash the residue from the print into the applicator and to permeate the dispersion into the image-receptive sheet only through the silver-receptive stratum, and
drying the dispersion retained by the print to produce a protective, ditficultly waterand vapor-permeable coating containing the plastic material.
2. A method of producing a stable photographic print comprising, in sequence, a support, a water-impermeable stratum, and a siliceous silver-receptive stratum, said method comprising the steps of spreading, between said silver-receptive stratum and a photoexposed gelatino silver halide stratum, an aqueous alkaline solution of a silver halide developer and a silver halide solvent, whereby exposed silver halide in the silver halide stratum is reduced to silver and unreduced silver halide from the silver halide stratum forms a water-soluble, complex silver salt which diffuses through the layer of solution to the silverreceptive stratum where it is reduced to silver to form a visible print, stripping the print from the gelatino silver halide stratum whereby the silver-receptive stratum retains a residue of the solution, swabbing the silver-receptive stratum with an absorbent applicator charged with a composition containing an aqueous dispersion of an organic plastic material, which yields a diflicultly waterand vapor-permeable coating on drying, to wash the residue from the silver-receptive stratum into the applicator and to permeate the print through the silver-receptive stratum to the water-impermeable stratum, and drying the dispersion retained by the print to produce on the silver-receptive stratum a protective, diflicultly waterand vaporpermeable coating containing the plastic material.
3. The method of claim 2 wherein the water-impermeable stratum is composed of a rubbery plastic.
4. The method of claim 3 wherein the thickness of the silver-receptive stratum is of the order of 1 micron.
References Cited in the file of this patent UNITED STATES PATENTS 1,411,677 Trivelli Apr. 4, 1922 2,173,480 Jung Sept. 19, 1939 2,259,009 Talbot Oct. 14, 1941 2,331,746 Talbot Oct. 12, 1943 FOREIGN PATENTS 553,438 Great Britain May 21, 1943 894,225 France Mar. 6, 1944