US 3833369 A
Photographic systems for forming images by diffusion transfer wherein an aqueous processing composition including a reflecting agent, e.g., a white pigment, is applied between an exposed photosensitive component or element including at least one light-sensitive layer and an image-receiving component to develop the exposed photosensitive component and, as a function of development, to form a transfer image on the image-receiving component which, due to the presence of the thus applied reflecting agent, is viewable without separation as a reflection print, the essence of the invention being "encapsulating" the reflecting agent in a polymeric "skin" or wall to obtain stated beneficial results; and aqueous compositions including such encapsulated reflecting agents.
Claims available in
Description (OCR text may contain errors)
United. States Patent [191 Chiklis a al.
[ Sept. 3, 1974 COLOR DIFFUSION TRANSFER FILMS AND PROCESSES WITH POLYMER ENCAPSULATED REFLECTING AGENTS  Inventors: Charles K. Chiklis, Lexington; Paul D. Lubin, Hudson, both of Mass.
 Assignee: Polaroid Corporation, Cambridge,
22 Filed: Dec.29, 1972  Appl. No.: 319,291
 Field of Search 96/77, 3, 29 D, 76 R, 84 R, 96/97; 117/100 B, 100 M; 252/316  References Cited UNITED STATES PATENTS 2,966,408 12/1960 Land 96/84 R 3,135,695 6/1964 York ..96/l.5 3,276,869 10/1966 McCune 96/97 3,330,693 7/1967 Rumberger 117/100 B 3,503,785 3/1970 Kruse 117/100 M 3,519,593 7/1970 Bolger ll7/l00 B 3,544,500 12/1970 Osmond et al. 117/100 B 3,647,437 3/1972 Land 96/3 Primary ExaminerR0nald H. Smith Assistant ExaminerRichard L. Schilling Attorney, Agent,'0r Firm-Alvin Isaacs; John P. Morley  ABSTRACT Photographic systems for forming images by diffusion transfer wherein an aqueous processing composition including a reflecting agent, e.g., a white pigment, is applied between an exposed photosensitive component or element including at least one light-sensitive layer and an image-receiving component to develop the exposed photosensitive component and, as a function of development, to form a transfer image on the image-receiving component which, due to the presence of the thus applied reflecting agent, is viewable without separation as a reflection print, the essence of the invention being encapsulating the reflecting agent in a polymeric skin or wall to obtain stated beneficial results; and aqueous compositions including such encapsulated reflecting agents.
21 Claims, 2 Drawing Figures I PPORT DYE IIVELOPER LAYER SILVER HALIDE YER DYE DEVELOPER LAYER SENSITIVE SILVER HALIDE LAYER YER DYE DEVELOPER LAYER sENsn'|vE siLvER HAUDE LAYER LAYER ALKALINE PROCESSING RECEIV|NG LAYER LAYER LAYER UPPORT PATENTED 31974 sum w 2 fsupom' j CYAN DYE IIVELOPER LAYER RED-SENSITIVE SILVER HALIDE EMULSION LAYER /-INTERLAYER /YELLOW DYE DEVELOPER LAYER BLUE-SENSITIVE SILVER HALIDE I EMULSION LAYER OVERCOAT LAYER AQUEOUS A LKALINE PROCESSING COMPOSITION /-IMAGERECEIVING LAYER /sPAcER LAYER /NEUTRALIZING LAYER r SUPPORT FIGI /-MAGENTA DYE DEVELOPER LAYER BACKGROUND or THE INVENTION Various photographic systems have heretofore been disclosed wherein an aqueous processing composition including a reflecting agent dispersed therein is applied between a photosensitive component which has been exposed to form a developable image and a superposed image-receiving component to form a transfer image viewable, without separation of the respective components, as a reflection print. The reflecting agent, usually a white pigment such as titanium dioxide, is selected for its ability to mask effectively the negative component and to provide the desired background for viewing'the transfer image formed in the image-receiving component as a reflection print. The print thus formed may be in silver or in color. The respective negative and imagereceiving components may be present initially as separate elements which are brought into superposition during development or they may be contained together initially, e.g., before exposure, such as in the so-called integral negative-positive film units. Of particular interest in the practice of this invention are these integral negative-positive film units for preparing color images by diffusion transfer.
Generally speaking, in these systems the processing composition develops the negative component and, as a function of development, forms an imagewise distribution of image-forming constituents which is transferred, at least in part, by diffusion, to the imagereceiving component to impart thereto the desired transfer image. The reflecting agent contained in the processing composition serves to mask effectively the negative component (including any remaining imageforming constituents) and to provide the desired background, usually a white background, for viewing the overlying transfer image. The image-forming constituents may be a soluble silver complex which is reduced to image silver in accordancewith known silver diffusion transfer techniques; or they 'may be dye imageproviding materials, in accordance with known techniques for forming color transfer images.
The dye image-providing materials employed in the latter processes generally may be characterized as either (I) initially soluble or diffusible in the processing composition but being selectively rendered nondiffusible in an imagewise pattern as a function of development; or (2) initially insoluble or non-diffusible in the processing composition but being selectively rendered diffusible in an imagewise pattern as a function of development. These materials may be complete dyes or dye intermediates, e.g., color couplers.
As examples of-initially soluble or diffusible materials and their application in color diffusion transfer, mention may be made of. those disclosed, for example, in U.S. Pat. Nos. 2,647,049; 2,661,293; 2,698,244; 2,698,798; 2,802,735; 2,774,668; and 2,983,606. As examples of initially non-diffusible materials and their use in color transfer systems, mention may be made of the materials and systems disclosed in U.S. Pat. Nos. 3,443,939; 3,443,940; 3,227,550; 3,227,551; 3,227,552; 3,227,554; 3,243,294 and 3,445,228.
In any of these systems, multicolor images are obtained by employing a film unit containing at least two selectively sensitized silver halide layers each having associated therewith a dye image-providing material exhibiting desired spectral absorption characteristics. The most commonly employed elements of this type are the so-called tripack structures employing a blue-,
a greenand a red-sensitive silver halide layer having associated therewith, respectively, ayellow, a magenta and a cyan dye image-providing material.
A particularly useful system for forming color images by diffusion transfer is that described in U.S. Pat. No. 2,983,606, employing dye developers (dyes which are also silver halide developing agents) as the dye imageproviding materials. In such systems, a photosensitive element comprising at least one silver halide layer having a dye developer associated therewith (in the'same or in an adjacent layer) is developed by applying an aqueous alkaline processing composition. Exposed and developable silver halide is developed by the dye developer'which in turn becomes oxidized to provide an oxidation product which is appreciably less diffusible than the unreacted dye developer, thereby providing an imagewise distribution of diffusible dye developer in terms of unexposed areas of the silver halide layer, which imagewise distribution is then transferred, at least in part, by diffusion, to a dyeable stratum to impart thereto a positive dye transfer image. Multicolor images may be obtained with a photosensitive element having two or more selectively sensitized silver halide layers and associated dye developers, a tripack structure of the type described above and in various patents including the aforementioned U.S. Pat. No. 2,983,606 being especially suitable for accurate color recordation of the original subject matter.
In color diffusion transfer systems of the foregoing description, color images are obtained by exposing a photosensitive element-or negative component comprising at least a light-sensitive layer, e. g., a gelatino silver halide emulsion layer, having a dye imageproviding material associated therewith in the same or in an adjacent layer, to form a developable image; developing this exposed element with-a processing composition to form an imagewise distribution of a'soluble and diffusible image-providing material; and transferring this imagewise distribution, at least in part, by diffusion, to a superposed receiving element or positive component comprising at least a dyeable stratum to impart to this stratum a color transfer image. The negative and positive components may be separate elements which are brought together during processing and thereafter either retained together as the final print; or they may together comprise a unitary structure, e.g., integral negative-positive film units wherein the negative and positive components are laminated and/or otherwise physically retained together at least prior to image formation. I
Of particular interest are those integral negativepositive film units adapted for forming color transfer images viewable without separation, i.e., wherein the positive component containing the dye transfer image and any remaining associated dye image-providing material and to provide a background for viewing the color image formed in the dyeable stratum, without separation, by reflected light. The essential layers of such film units are preferably contained on a transparent dimensionally stable layer or support member positioned closest to the dyeable stratum so that the resulting transfer image is viewable through this transparent layer. Most preferably another dimensionally stable layer which may be transparent or opaque is positioned on the opposedsurface of the essential layers so that the aforementioned essential layers are sandwiched or confined between a pair of dimensionally stable layers or support members, at least one of each is transparent to permit viewing therethrough of a color transfer image obtained as a function of development of the exposed film unit in accordance with the known color diffusion transfer system such as will be detailed hereinafter. In a particularly preferred form such film units are employed in conjunction with a rupturable container of known description containing the requisite processing composition and adapted upon application of pressure of applying its contents to develop the exposed film unit, e.g., by applying the processing composition in a substantially uniform layer between the dyeable stratum and the negative component. It will be appreciated that the film unit may optionally contain other layers performing specific desired functions, e.g., spacer layers, pI-I-reducing layers, etc.
In addition to the reflecting agent employed to permit formation of a composite print viewable without separation, the processing composition generally will contain other reagents required in the particular photographic system employed. Accordingly, the processing composition comprises at least. an aqueous dispersion of a reflecting agent and'in most systems will also include at least an alkaline material to provide the requisite pH for development and image formation and a viscous film forming reagent. Where development of the film unit in the light is contemplated and the reflecting agent does not provide sufficient opacity against fogging for this purpose, the processing composition may include additional opacifying agent to prevent fogging of the photosensitive layeror layers by light passing through the applied layer of processing composition. Particularly useful processing compositions of the latter description include at least one optical filter agent which is highly colored at the pH of the processing composition but is substantially colorless or transparent at a subsequent pH for viewing purposes. Such processing compositions and opacifying agents useful therein are disclosed, for example, in US. Pat. No. 3,647,437 issued to Edwin H. Land.
As examples of photographic systems of the forego ing description for forming composite prints viewable, without separation,as reflection prints, mention may be made of those described in US. Pat. Nos.
3,690,879; 3,694,206; 3,697,269 and others.
Upon development of film units of the foregoing description with a processing reagent including a disper- 4 sion comprising one or more organic light-absorbing materials and a light-reflecting agent, e.g., a composition of the type defined in the aforementioned US. Pat. No. 3,647,437 including one or more optical filter agents or indicator dyes and a white pigment, certain visual problems have been observed in the color transfer image so formed, whether it'be developed in the dark in known manner or in the presence of actinic light. These visual problems, manifested as raindroplike streaks are believed to be caused by a phase separation whereby certain random areas of the spread composition suffer a loss or reduction of light- 'refiecting agent, e.g., white pigment. Where the film unit is developed in the dark, these streaks take the form of dark streaks of enhanced dye density, apparently caused by faster or greater dye transfer in these random areas of reduced pigment, during the development period, in tum causing greater dye density in these areas of the developed print. On the other hand, if the film unit is developed in the presence of actinic light, e.g., outside the camera in accordance with the procedures contemplated in the foregoing description, fogging of the negative in these random areas is caused by the presence of insufficient pigment (the reduction or loss of pigment may, for example, lower the optical density of the spread reagent from about 6 to about 2), thereby resulting in immobilization of I dye in these areas where dye should normally be free to diffuse, in turn causing white streaks to be present in the shadow (dye-containing) areas of the developed print. It will be appreciated that the white streaks so appearing in the print developed in the light correspond areawise to the dark streaks appearing in the print developed in the dark. In either instance, the resulting streaks adversely affect the quality of the color print.
As was mentioned previously, this problem is believed to be caused by a phase separation of the dispersion-containing processing reagent. In any event, that the phase separation does in fact occur has been documented both qualitatively with photomicrographs and quantitatively with Cary transmission spectra. This phase separation is most pronounced when the processing fluid contains a quaternary, salt of the type described in US. Pat. No. 3,173,786, e.g., an onium compound such as N-benzyl-a-picolinium bromide.
The present invention is directed to this phase separation stability problem.
SUMMARY OF THE INVENTION In addition to the aforementioned increased stability,
the present invention makes it conceptually possible to achieve further significant advantages including less tendency for stain and dirty highlight areas, as will be discussedhereinafter. I
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an enlarged, fragmentary, diagrammatic, sectional view of a film unit contemplated by this invention; and
FIG. 2 is a graph indicating quantitatively the rate of pigment settling and the improvement against settling obtained in accordance with this invention, the ordinate (y-axis) being the marking in milliliters on a graduated cylinder, the abscissa (x-axis) being the time in hours after pouring the freshly prepared aqueous dispersion into the cylinder.
As was mentioned previously, the present invention relates to photographic systems wherein an aqueous processing composition having dispersed therein a reflecting agent, e.g., an inorganic white pigment, is applied as a layer between an exposed photosensitive element or component containing a developable image and an image-receiving component or element to provide a photographic image viewable without separation as a reflection print. The invention is primarily directed towards improving the stability of such compositions against settling or phase separation of the reflecting agent.
Since particularly preferred film units contemplated by this invention are those so-called integral negativepositive film units for preparing color transfer images, the invention will be further described by reference thereto for purposes of illustration.
As shown in FIG. 1, such a film unit may comprise, as the essential layers, a layer 11 of cyan dye developer, red-sensitive silver halide emulsion layer 12, interlayer 13, a layer of magenta dye developer 14, greensensitive silver halide emulsion layer 15, interlayer 16, yellow dye developer layer 17, blue-sensitive silver halide emulsion layer 18,auxiliary layer 19, image receiving layer or dyeable stratum 21, spacer layer 22, and a pH-reducing or neutralizing layer 23. Layers 11-19 comprise the negative component25 and layers 2123 comprise the positive'component 26. These essential layers are shown to be confined between a dimensionally stable layer or support member which is preferably opaque so as to permit development in the light and dimensionally stable layer or support member 24.
which is effectively transparent to permit viewing of a color transfer image formed as a function of development in receiving layer or dyeable stratum 21.
Materials which may be employed in the preparation of the various layers described above are well known, described in the aforementioned patents, and therefore per se comprise no part of the present invention. Accordingly, they need not be described in further detail.
The film unit may be exposed through transparent layer 24 to form a developable image and thereafter developed by applying an aqueous alkaline processing composition including at least one organic lightabsorbing material, e.g., one or more indicator dyes which are highly colored at the pH of the alkaline processing composition and hence provide the necessary protection against'actinic radiation incident thereon, and a suitable reflecting agent, e.g., a white inorganic material which will effectively mask the negative component and provide a suitable background for viewing the color transfer image formed in stratum 21 as a reflection print through transparent layer 24.
A preferred processing composition of this description is one of those described in the aforementioned US. Pat. No. 3,647,437 including an inorganic lightreflecting pigment dispersion containing reflecting pigment in a concentration per se insufficient, distributed as a layer intermediate the reception layer and next adjacent silver halide layer, to effectively prevent transmission of radiation actinic to the silver halide layer therethrough and at least one optical filter agent, at a pH above the pKa of the optical filter agent, in a concentration per se also insufficient to prevent transmission of actinic radiation therethrough, which concentrations individually and additively are together insuffcient to prevent transmission of incident actinic radiation but in admixture are synergistically effective to provide a barrier to such transmission. Specifically, the inorganic light-reflecting pigment'dispersion containing the optical filter agent may be formulated to exhibit an optical transmission density 6.0 density units and an optical reflection density 1.0 density units at a pH above the pKa of the optical filter agents included.
In accordance with that patent, the optical filter agent will be employed in a concentration, itself ineffective to provide the required transmission density alone or, theoretically, in combination witli the inorganic light-reflecting pigment, as projected'by Beers Law, that is, D ECl wherein D is transmission density, E is the epsilon of the optical filter agent, C is the concentration and l is the radiation path length, but empirically effective in combination with the pigment to prevent transmission of radiation actinic to the silver halide layers incident on the layer comprising the dispersion, during processing in the presence of actinic radiation, and sufficiently low to provide substantially immediate viewing of transfer image formation against the background provided by the reflecting pigment. Such effective minimal concentration of filter agent specifically facilitates the acceleration of theclearing time involved in discharging from visual observation the filter agent employed by reduction of the environmental pH as detailed above from-above to below, the pKa of the filter agent selected.
The film unit assemblage constructed in accordance with that discovery is specifically adapted for process ing in the presence of actinic radiation by reason of the protection afforded the silver halide layers exposure surface by the presence of the pigment dispersion protecting from exposure such surface, and for the simul-v taneous viewing of the transfer image carried by the reception layer by reason of the minimal optical reflection density exhibited by the light-reflecting pigment layer, subsequent to photoexposure of the silver halide layer and formation of the pigment layer. There is thus provided substantially immediate viewing of transfer image formation against a reflecting pigment layer background exhibiting minimal contamination provided by the minor concentration of substantially masked optical reflecting agent now discovered to be necessary to prevent transmission of fog producing actinic radiation through the reflecting layer and thus protecting the silver halide layer during transfer processing. The de minimus concentration of optical filter agent unexpectedly discovered to be capable of effective employment to prevent light transmission when dispersed in intimate relationship with reflecting pigment optimizes discharge of the minimal reflectivity contamination as is so provided by the agent upon decrease of the environmental pH from that at which the optical filter agent absorbs radiation to that at which such agent is substantially innocuous optically.
A particularly preferred reflecting agent comprises titanium dioxide due to its highly effective reflection properties. In general, in such preferred embodiment, based upon percent titanium dioxide'(weight/volume) reflecting layers provided by processing compositions containing titanium dioxide dispersed in water in a concentration to give about 1,500 to 4,000 mgs./ft of titanium dioxide when solidified will provide a percent reflectance of about 85 to 90 percent. In the most preferred embodiments, the percent reflectance particularly desired will be in the order of -85 percent.
In embodiments wherein the dispersion comprises a preformed layer positioned intermediate the reception layer and next adjacent silver halide layer, the pigment layer will be sufficiently transparent to allow'transit of exposing radiation through the pigment layer and may comprise titanium dioxide reflecting agent processing a particle size distribution averaging 0.2 micron in diameter and preferably 0.05 micron in diameter as initially present preceding exposure of the film unit, which preferred materials, upon contact with aqueous alkaline processing composition, preferably aggregate to provide particles possessing a diameter in excess of 0.2 micron in diameter and will be coated at a coverage of 200 to 1,000 mgs./ft. Specifically, the 'reflecting agent will be present in a quantity insufficient to prevent exposure of the emulsion layers by actinic radiation incident on'the dimensionally stable transparent layer of the film unit but in a concentration sufficient, subsequent to processing, to mask dye developer associated with the silver halide emulsion strata from the dye transfer image. In the preferred construction of such embodiment, the pigment, such as titanium dioxide will be initially present in a relatively small particle size to provide unexpectedly efficient transit of radiation through the reflecting layer during exposure which upon contact with an alkaline processing composition and aggregation of the'pigment particles provides efficient light reflectivity and masking capacity subsequent to such aggregation.
In general, the reflecting agents to be employed are those which remain substantially immobile within their respective compositions during and subsequent to photographic processing and particularly those which comprise insoluble and nondiffusible inorganic pigment dispersions within the layer in which they are disposed.
The optical filter agent selected should be one exhibiting, at a pH above its pKa, maximum spectral absorption of radiation at the wavelengths to which the film units photosensitive silver halide layer or layers are sensitive and should be substantially immobile or nondiffusible within the pigment dispersion, during performance of its radiation filtration function, in order to maintain and enhance the optical integrity of the dispersion as a radiation filter unit functioning in accordance with the present invention, and to prevent its diffusion into and localized concentration within the image-receiving layer thereby decreasing the efficiency of the reflecting pigment dispersion as a background against which image formation may be immediately viewed, during the initial stages in the diffusion transfer processing of the film unit, by filter agent absorption of dispersion reflected visible radiation prior to reduction in the. environmental pH below the pKa of the agent. Commensurate with the spectral sensitivity range of the associated silver halide layer or layers, the optical filter agent selected may comprise one or more filter dyes possessing absorption complementary to such silver halide layers in order to provide effective protection against fog-providingradiation during processing. Recognizing that the filter agent absorption will derogate from image-viewing characteristics by contaminating reflecting pigment background, the selected agents must'be those exhibiting major spectral absorption at the pH at which processing is effected and minimal absorption at a pH below that which obtains during transfer image formation. Accordingly, the selected optical filter agent or agents must possess a pKa below that of the processing pH and above that of the environmental pI-I subsequent to transfer image formation, and will be selected for employment in'the minimum concentration necessary to provide an optical transmission density 6.0, at wavelengths at which the silver halide layer is maximally responsive, and in no instance an optical reflection density 1.0 at such wavelengths.
Many such optical filter agents are disclosed in US. Pat. No. 3,647,437 as well as in U.S.- Pat. Nos. 3,702,244 and 3,702,245.
In addition to the reflecting agent and opacifying agent, processingcompositions for use in the aforementioned film units for preparing color transfer images may, and usually will, contain other reagents performing specific desired functions, e.g., a viscosityincreasing reagent such as hydroxyethyl cellulose, sodium carboxymethyl cellulose, etc.; an alkaline material such as sodium, lithium or potassium hydroxide, antifoggants, development restrainers, and the various other photographic reagents heretofore employed in such processing compositions. The presence or absence of such reagents is immaterial for purposes of this invention.
To further illustrate the practice of this invention, a film unit of thetype shown in FIG. 1 maybe prepared, for example, bytcoating, in succession, on a gelatin subbed, 4 mil. opaque polyethylene terephthalate film base, the following layers:
1. a layer of cyan dye developer dispersed in gelatin and coated at a coverage of about mgs/ft. of dye and about 80 mgs./ft. of gelatin;
2. a red-sensitive gelatino silver iodobromide emulsion coated at a coverage of about mgs./ft. of silver and about 70 mgs./ft. of gelatin;
3. a layer of a 60-30-4-6 copolymer of butylacrylate, diacetone acrylamide, styrene and methacrylic acid and polyacrylamide coated at a coverage of about mgs./ft. of the copolymer and about 5 mgs./ft. of polyacrylamide;
4. a layer of magenta dye developer dispersed in gelatin and coated at a coverage of about 100 mgs./ft. of dye and about 100 mgs./ft. of gelatin;
7 5. a green-sensitive gelatino silver iodobromide emulsion coated at a coverage of about 100 mgs./ft. of silver and about 50 mgsJft. of gelatin;
6. a layer containing the copolymer referred to above in layer 3 and polyacrylamide coated at a coverage of about 100 mgs./ft. of copolymer and about 12 mgs./ft. of polyacrylamide;
7. a layer of yellow dye developer dispersed in gelatin and coated at a coverage of about 70 mgslft. of dye and about 56 mgs./ft. of gelatin;
8. a blue-sensitive gelatino silver iodobromide emulsion layer including the auxiliary developer 4- methylphenyl hydroquinone coated at a coverage of about 120 mgs./ft. of silver, about 60 mgs./ft. of gelatin and about 30 mgsjft. of auxiliary developer; and 9. a layer of gelatin coated at a coverage of about 50 mgsjft. of gelatin.
The three dye developers employed above may be the following:
smain a cyan dye developer;
a magenta dye developer; and
.a yellow dye developer.
Then a transparent'4 mil. polyethylene terephthalate film base may be coated, in succession, with the following illustrative layers:
l. the partial butyl ester of polyethylene/maleic anhydn'de copolymer prepared by refluxing, for 14 hours, 300 grams of high viscosity poly-(ethylene/maleic anhydride), 140 grams of n-butyl alcohol and 1 cc; of 85 percent phosphoric acid to provide a polymeric acid layer at a coverage of about 2,500 mgs./ft.
2. a timing layer containing about a 40:1 ratio of a 60-30-4-6 copolymer of butylacrylate, diacetone acrylamide, styrene and methacrylic acid and polyacrylamide at a coverage of about 500 mgs./ft.; and
3. a 2:1 mixture, by weight, of polyvinyl alcohol and poly-4-vinylpyridine, at a coverage of about 400 mgs./ft. and including about mgs./ft. of a development restrainer, l-phenyl-5-mercaptotetrazole, to provide a polymeric image-receiving layer containing development restrainer.
The two components may then be laminated together to provide the desired integral film unit. I
A rupturable container comprising an outerlayer of lead foil and an inner liner or layer of polyvinyl chloride retaining an aqueous alkaline processing solution may then be fixedly mounted on the leading edge of each of the laminates, by'pressure-sensitive tapes, in-
. terconnecting the respective container and laminates so that, upon application of compressive pressure to the container to rupture the containers marginal seal, its contents may be distributed between the dyeable stratum (layer 3 of the positive component) and the gelatin layer (layer 9) of the negative component.
An illustrative processing composition to be employed in the rupturable container may comprise the following proportions of ingredients:
Water".-. cc. Potassium hydroxide 11.2 gms. Hydrox ethyl cellulose (high viscosity) [commercially 3.4 gins.
availa 1e from Hercules Powder 00., Wilmington, Delawere, under the trade name Natrasol 250]. N -phenethyi-a-pico1inium bromide 2.7 gms.
1.18 gms. H CH:
This film unit may then be exposed in known manner to forma' developable image and the thus exposed element may then be developed by applying compressive pressure to the rupturable container in order to distribute the aqueous alkaline processing composition, thereby forming a multicolor transfer image which is viewable through the transparent polyethylene terephthalate. film base as a positive reflection print.
From the foregoing discussion and illustrative example of the type of film units to which this invention is directed, it will be seen that theprocessing composition performs two essential functions: (1) supplying at least certain of the photographic reagents required for development and image formation in the particular photographic system employed; and (2) providing a reflecting layer to mask effectively the negative image and to form a suitable background for viewing the positive color image by reflected light. In themost preferred systems employing such film units, development in the light is contemplated and the processing composition when applied during development further serves as a part of the light-tight envelope necessary to protect the exposed negative from fogging during such development in the light. This last-mentioned function is obtained in the illustrative example by the opacifying property of the combination of reflecting agent (titanium dioxide) and opacifying agent (the three indicator dyes).
To accomplish these objectives at optimum efficiency, it will be appreciated that the processing compositions must be stable during the period between manufacture and usage. This may, for example, be on the order of several weeks or longer. It has been found, however, that during this shelf life period, there is a tendency for settling or phase separation of the reflecting agent dispersion, causing the problems heretofore noted in the ability of the processing composition to perform its masking and opacifying functions.
In accordance with this invention it has been found that this problem may be markedly reduced if not eliminated altogether by encapsulating the reflecting agent within a polymeric skin. The preferred polymers employed for this purpose are derived from acrylic monomers and thus may be referred to simply as acrylic polymers. As examples of acrylic polymers as well as others which may be employed in accordance with this invention, mention may be made of polymers and multicomponent systems of acrylic acid, methacrylic acid, derivatives of acrylic and methacrylic acid, styrene/maleic anhydride copolymers, styrene, isoprene, acrylamide. styrene sulfonic acid, 4-vinyl phthalic acid, vinyl sulfonic acid, soluble salts of carboxymethyl cellulose, etc.
The methods of encapsulation are per se well known in the art and include: (a) emulsion polymerization method; (b) polymer precipitation; -(c) cationic polymerization from-the reflecting agent surface using adsorbed BF as catalyst; and (d)- ceric (IV) ion initiated grafting from polyvinyl alcohol skins.
In general, a particularly useful procedure for encapsulating the reflecting agent comprises the steps of first polymerizing to form a polymeric skin on the core particles, whether by homopolymerization or copolymerization, and thereafter by emulsion polymerization techniques building on to the thus formed polymeric skin to form the desired polymeric wall encapsulating the reflecting agent.
Since procedures for encapsulation are well known in the art and per se comprise no part of the present invention, they need not be described in further detail. However, for further reference to the art of encapsulation, attention may be invited, for example, to US. Pat. Nos; 2,800,457; 2,800,458; 3,041,289; and 3,533,958.
Below is listed various polymeric coatings which may be employed, the ratios'and percent polymer to encapsulated reflecting agent being by weight. In most of these it will be noted that the total polymeric coating includes the initial polymeric skin and the major polymeric composition (referred to simply as Major Composition), it being understood that the polymeric coating thus formed can in fact be a chemical graft or physical mixture or both of the skin and major polymeric composition.
Skin Major Composition Total Polymer l. GRAFT (STY) (ISO);, 34 2. STY/MAH (STY),(1SO) 34 3. GRAFT (STY),'(1SO) 25 4. AA MMA 5.8 '5. AA (MMA) (MAA), 9.2
6. STY/MAH (STY) (BUT) 34 7. STY/MAH (STY),(BUT) 13 8. STY/MAH (STY),(BUT) 13 9. STY/MAH (STY),(BUT) 13 10. STY/MAH (STY) (ISO) 25 1 1. STY/MAH (STY) (ISO) 13 12. STY/MAH (STY) (ISO) 34 13. STY/MAH (STY) (ISO) 34 14. STY/MAl-I ISO 34 15. STY/MAH (STY), (lSO) 13 16. STY/MAH (STY).(ISO), 13 17. STY/MAH ISO 13 18. PVA (MMA),,(MAA) 14.6 19. PVA (nBuMA) (MMA) 17.4
, U1 20. PVA 5.3 21. PVA (nBuMA),,(MMA) 13.4
)1 22. AA (STY) (SSA), 6.25 23. AA (STY) (SSA) 8.0 24. PVA 4.7 25. AA (MMA) (MAA), 6.12 26. AA (nBuMA) (MAA) 4.92 27. AA (ST oo(SSA) 6.1 28. AA (STY) (SSA) 10.2 29. AA (MMA), (MAA) 10.6 30. AA (STY) (SSA) 9.9 31. AA (S'IY), ,(SSA) 9.3 32. AA (nBuMA) (MAA) 8.0 33. AA (STY), (SSA), 10.0 34. AA (STY) (SSA) 5.0 35 A (MMAiaiMA iitt 22-9 -Cont1nued Skin Major Composition Total Polymer 36. AA (NBuMA) (MAA) 11.6 37. AA MAA 5.1 38. AA (nBuMA), (MAA), 10.9 39. AA VBTAC 5.4 40. AA '(MMA) (MAA), 8.6 41. AA (MMA) (MAA) 13.2 42. AA VBTAC 2.3 43. AA MAA 0.8 44. AA (nBuMA) (MAA) 14.3 45. AA (nBuMA) (MAA) 11.0 46. AA (MMA) (MAA) 9.5 47. AA (MMA) (MAA) 5.0 48. AA (MMA) (MAA) 9.6 49. AA (MMA) (MAA), 10.1 50. AA MMA 9.7 51. AA MMA 10.0 52. AA (nBuMA) (MAA), 15.0 53. AA nBuMA 13.9 54. AA MMA 5.0 55. AA MMA 4.3
* A graft polymer ol'a terpolymer of methyl acrylate) (methacrylic acid and (2-5ulfoethylmethacrylate) on hydroxyethyl cellulose.
Monomer:H E 0:3 :1
STY Styrene MAl-l maleic anhydride ISO isoprene DMS dimethyl siloxane SlL silicone BUT butadiene PVA polyvinyl alcohol MMA methyl methacrylate MAA methacrylic acid nBuMA n-butyl methacrylate SSA styrene sulfonic acid VBTAC paravinyl benzyl trimethyl ammonium chloride The preferred reflecting agents to be encapsulated in accordance with this invention are white, pigments such as titanium dioxide, zinc oxide, lead oxide, barium sulfate, etc. While such reflecting agents arepreferred in the foregoing photographic systems, it will be appreciated that the invention is not limited thereto and is applicable to other reflecting agent dispersions in alkali as well. In any event, these pigment particles are generally quite small, typically having a mean particle size on the order of about 0.2 p" I To achieve at least some significant advantage, the amount of encapsulating polymer employed should be at least two percent by total weight of the encapsulated reflecting agent. While theoretically there is no upper limit in the amount which can be employed for purposes of encapsulation, .it will be appreciated that unnecessary amounts should obviously be avoided as should amounts which might adversely affect the'masking and opacifying functions contemplated in the particular photographic system employed. A preferred range of polymer is on the order of from about 2-25 percent by weight, although it will be noted from the list of illustrative polymers appearing previously that greater amounts have also been employed.
While the preferred polymers are obtained from acrylic monomers, other hydrophobic polymers may also be employed and illustrative other polymers of this description were also recited in the list of illustrative polymers.
The polymer coating encapsulating the reflecting agent particle may be of a uniform or of a non-uniform thickness. One skilled in the art will readily understand the various methods by which the uniformity can be varied and such procedures in polymer technique need not be described in detail. Generally speaking, however, depending on how the polymer coating is applied (polymerization process or sequence of addition of monomers) one can alter the physical nature of the coated particle to range from a uniform coating to a case where it was not particularly uniformly coated but the coating possessed strands of interconnecting tissue which'bridged many particles in a web-like structure.
While the present invention contemplates both uniform and non-uniform coatings, the latter type with interconnecting tissue providing the web-like structure has been found to be preferred in the prevention of settling in alkali. Although not wishing to be restricted to any particular theory for this'phenomenon, it is believed to be due to the fact that the web-like structure provides a reduced effective density over that of a dispersion of uniformly coated and dispersed particles, and this reduced effective density in turn affords increased resistance to settling.
If this theory is in fact correct, it would also be theoretically'possible to obtainreduced effective density and, in turn, improved resistance to settling by selecting a polymer skin which swells many times in alkali. However, this has been neither proven nor disproved.
The following two illustrative examples show how the polymerization process for encapsulation may be varied to provide either a uniform coating or aweb-like structure.
Example 1 liters of demineralized water, 19 kg. of titanium dioxide (mean particle size 0.211.), and 132 g. of acrylic acid were placed in a reactor and stirred for one-half hour. Nitrogen was then bubbled through the resulting dispersion for about two hours, after which time the mixture was pressurized to 12 psi with nitrogenand the temperature was raised to 60C. When the temperature reached 60C, 10.6 g. of ammonium persulfate polymerization catalyst were added. After a half an hour, 1,860 g. of methyl methacrylate and 98 g. of divinyl benzene (cross-linking agent) were added. After an additional two hours, 21.1 g. of methacrylic acid were added and the temperature was maintained for an additional 16 hours at 60C to provide, in the form of a nonsettling slurry, titanium dioxide particles encapsulated within a skin of mainly poly(acrylic acid) onto or into which the other two monomers were polymerized to form a terpolymer of acrylic acid, methyl methacrylate and methacrylic acid. It may be oven dried, pulverized and used as required, or itmay be employed as a paste to prepare the photographic processing compositions. Electron photomicrographs confirmed the web-like structure of interconnecting tissue described above.
Example 2 I Example 3 100 g. of titanium dioxide were dispersed withvigorous stirring in a solution of g. of the graft polymer of methyl acrylate, methacrylic acid and 2-sulfoethylmethacrylate on hydroxyethyl cellulose noted in the foregoing list of illustrative formulations in 150 ml. of water. The pH was then lowered slowly to about 3 to precipitate the polymer on the pigment surface. After purging with nitrogen for about 30 minutes, 37 g. of distilled isoprene, 13 g. of distilled styrene and l g. of acrylic acid were added, followed by 0.05 g. each of ammonium persulfate and sodium bisulfite. The emulsion polymerization was allowed to run overnight at room temperature and the dispersion which settled was washed three'times with water and isolated as a paste, the encapsulated pigment of formulation 1.
Example 4 Under a blanket of nitrogen, 2 g. .of styrene/maleic anhydride in 150 cc. of boiled distilled water were slurried on a steam cone. 50 percent sodium hydroxide was added to raise the pH to about8. 100 g. of titanium dioxide were then added with agitation, after which glacial acetic acid was slowly added to lower the pH to about 5, at which point the copolymer precipitates out onto the pigment surface, 30 cc. of water, 12.5 g. ofstyrene, 0.25- g. of dodecyl mercaptan, 0.15 g.- of potas-' 16 dried in a vacuum oven at 30C overnight to yield the encapsulated pigment of formulation 18.
Example 7 42 g. of titanium dioxide having a skin coating of polyvinyl alcohol were slurried for 10 minutes'in 500 cc. of distilled water. 4.7 g. of n-butyl methacrylate and 2.6 g. of methyl methacrylatewere then added, after which the temperature was raised to 50C and the pH adjusted to 1.5 with concentrated nitric acid. 0.4 g. of ceric ammonium nitrate in 10 cc. of water were then added. After about 10 minutes, 0.6 g. of methacrylic acid was added dropwise and the resulting mixture was stirred for about 2 hours at 50C,'washed three times sium persulfate and 37.5 g. of isoprene were added v under a blanket of nitrogen. The resulting mixture was placed into a tumbling bath at 50C for about 21 hours and washed thoroughly with water to yield the encapsulated pigment of formulation 2.
Example 5 Under a blanket of nitrogen, 100 g. of titanium dioxide in 150 cc. of boiled distilled water containing 5 g. of styrene/maleic anhydride copolymer at pH 9 were slurried. Glacial acetic acid was added to lower the pH to about 5. While under a blanket of nitrogen, 30 cc. of boiled distilled water, 0.05 g. of l-dodecanethiol, 0.03 g. of potassium persulfate, 9 g. of butadiene and l g. of freshly distilled styrene were added. The resulting mixture was placed in a tumbling oil bath at 50C for about 20 hours and then washed well with water to yield the encapsulated pigment of formulation 7.
Example 6 i 42 g. of titanium dioxide having a skin coating of polyvinyl alcohol were slurried for 10 minutes in 500 cc. of distilled water. 7.2 g. of methyl methacrylate were added and nitrogen was bubbled through the mixture for one hour after which time the temperature was raised to 50C andthe pH was adjusted to about 1.5 by adding concentratednitn'c acid. 0.4 g. of ceric ammonium nitrate in 10 cc. of water were then added. After 10 minutes 0.8 g. of methacrylic acid was added dropwise and the resulting mixture was stirred for 2 hours at 50C, washed three times with distilled water and with distilled water and dried overnight in a vacuum oven at 30C to yield the encapsulated pigment of formulation 19.
Example 8 150 g. of titanium dioxide and l g.' of acrylic acid were dispersed using dispersator for 30 minutes in 750 cc. of water. The resulting mixture was then poured into a flask and purged with nitrogen for 30 minutes, after which time 0.03 g. of ammonium persulfate was added and the temperature was raised to 60C. After 30-minutes, 10 g. of styrene were added dropwise with continued stirring for about 2 hours. 0.1- g. of styrene sulfonic acid in water-were added dropwise and the resulting mixture was maintained at about 60C for an additional hour. It was then washed well with water, filtered, washed with methanol and dried in an oven over- .night to yield the encapsulated pigment of formulation -22. l
- Example 9 -150 g. of titanium dioxide and l g. of acrylic acid were added to 750 cc. of water and the resulting mixture was dispersed in a dispersator and nitrogen was bubbled through the resulting dispersion for about one hour. 0.03 g. of ammonium persulfate was added at 60C. After about 20 minutes, 10 g. of n-butyl methacrylate were added and the temperature was maintained at 60C for 2 hours, after which time 0.1 g. of
methacrylic acid was added toyield the encapsulated pigment of formulation 26'.
Example 1 10 Example 1 l To a mixture of 25.5 g. of acrylic acid and 200 cc. of distilled water, 3,640 g. of titanium dioxide were added with high agitation and the resulting mixture was stirred for about 2% hours under nitrogen. 1.27 g. of ammo- I nium persulfate were added and the temperature was raised to 60C and maintained at this temperature for about 30 minutes. 455 cc. of methyl methacrylate and 29 cc. of divinyl benzene were then added. .The resulting mixture was then pressurized to 35 psi with nitrogen. After one hour, 5.1 cc. of methacrylicacid were added and the reaction was run overnight, filtered, washed and micronized to yield the encapsulated pigmerit of formulation 40.
The encapsulated reflecting agents of this invention, e. g., the encapsulated titanium dioxides prepared in the foregoing examples, have been found to offer increased stability against phase separation in the alkaline processing compositions in which they are employed. Quantitative measurements of this increased stability were most expeditiously obtained by forming a dispersion of the encapsulated and non-encapsulated pigments in an aqueous alkaline solution approximating the pH of the processing fluid, pouring 100 ml. of this dispersion in a graduated cylinder and observing the settling of the pigment over a period of hours. Specifically, 30 grams of the pigment were dispersed thoroughly in 100 ml. of 2N KOH which were then poured into the graduated cylinder. FIG. 2 compares the settling of a control non-encapsulated titanium dioxide dispersion (designated as A) with the same titanium dioxide encapsulated within a 5 percent by weight coating of largely polymethyl methacrylate (designated as .B) and the same encapsulated within a percent by weight coating of largely poly-methyl methacrylate (designated as C). Settling was determined visually at various time intervals, simply by observing the separation point on the graduate between the clear aqueous supernatant and the white dispersion. The graph of FIG. 2 shows dramatically the quantitative comparison between the control (non-encapsulated) and encapsulated pigments of this invention. For example, with the control (A), after 10 hours, the pigment had settled from the 100 ml. level to-the point where the aqueous supernatant was clear above about the 34 ml. mark; as compared with about the 68 ml. mark of the 5 percent by weight coating (B), and about the 98 ml. mark of the 10 percent by weight coating (C). Comparable significant improvement is observed throughout the remaining time intervals on the graph.
It will be appreciated that the quantitative data evidenced on the graph depicting degree of settling in a graduated cylinder does not necessarily represent the magnitude and comparative rates of settling in actual use in the contemplated processing compositions. However, the relative pigment instability in viscous reagents such as the formulation previously given in the description of an illustrative film unit and process and the significant improved results of the encapsulated pigments of this invention have been repeatedly determined. Accordingly, the laboratory test illustrated in the graph is a useful tool in observing and demonstrating quantitatively the relative differences in stability against settling. For example, if no difference between a control and test is observable in the graduated cylinder, one would anticipate no difference or advantage in actual usage. Conversely, if significant or dramatic differences are so demonstrated in the cylinder, one would expect at least significant improvement in actual usage. This has infact been proven to be correct.
It will be noted thatthe g. of encapsulated pigment employed in pigment B in fact contains 47.5 g. of pigment and 2.5 g. of polymer; and the one in pigment C contains 45 g. of pigment and 5 g. of polymer. One may query whether the lesser amounts of pigment in B and C in any way decreases the ability of the processing compositions employing same, e.g., whether there is a print. No such loss is observable, and the encapsulated pigments are in fact as good or better, even though less pigment is employed. In a sense, therefore, one could say that the present invention affords increased efficiency in the use of pigment.
. This latter point may be explained in another way. It is possible to obviate the photographic problems of settling by increasing the quantity of pigment in the processing composition to an amount sufficient, even with settling, to perform the desired masking and opacifying functions. However, these increased amounts will necessarily make dye transfer therethrough to the receiving layer correspondingly more difficult, causing loss of dye density and/or longer development times before the reflection print is obtained. The present invention makes it possible to obtain the same results with less pigment and without the above-noted problems inherent in the use of greater quantities of pigment. In this sense, it can again be reasoned that the present invention makes more efficient use of the pigment while avoiding the problems inherent in the use of greater quantities of pigment.
While the present invention is directed essentially to improving shelf life stability against settling or phase separation, the present invention theoretically can provide other advantages.
One problem in obtaining color images of maximum quality in the described systems is that of staining and- /or dirty D caused by the unwanted transfer of dye or contaminants from the negative following substantial image formation. It is conceptually possible to minimize if not eliminate this problem by selecting an encapsulating polymer which will coalesce substantially to fuse the coated particles, each to the other, thereby providing a highly reflective hydrophobic barrier after dye image formation to further unwanted transfer of contaminating materials from the negative.
Other conceptually possible advantages include (a) encapsulated pigments which offer improved reflectance; (b) modifying the surface charge to minimize unwanted pigment-charged specie interaction; (c) employment of polymers having specific desired rheological properties, e.g., self-thickening pigments, etc. It is to be understood, however, that these are only theoretically possible additional advantages contemplated by the present invention which have neither been proved nor disproved.
Since certain changes may be made in the above product and process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
What is claimed is: w
1. In a photographic film unit including a photosensitive element comprising at least one light-sensitive silver halide layer havinga dye image-providing material associated therewith, an image receiving element comprising a dyeable stratum, an aqueous alkaline processflecting agent is a white pigment.
3. A film unit as defined in claim 1 wherein said means comprises a container of said aqueous alkaline processing composition and said reflecting agent comprises a pigment.
4. In a photographic product comprising a photosensitive component including at least one light-sensitive silver halide layer having a dye image-providing material associated therewith; a positive component including a dyeable stratum and a quantity of an aqueous alkaline processing composition having a reflecting agent dispersed therein adapted to be applied as a layer between said positive and negative components to impart to said dyeable stratum a color transfer image viewable without separation of said components due tothe ability of said applied reflecting agent to mask effectively the negative component and to provide the background for viewing by reflected light the transfer image imparted to said dyeable stratum;
the improvement wherein said reflecting agent is encapsulated within a polymeric wall.
5. A product as defined in claim 4 whereinsaid reflecting agent is a white pigment.
6. A product as defined in claim 5 wherein said polymeric wall is characterized as being a coating encapsulating said pigment and having strands of interconnecting tissues bridging a plurality of the thus encapsulated pigment particles.
7. A product as defined in claim 6 wherein said poly mer is an acrylic polymer.
8. A product as defined in claim 6 wherein said pigment is titanium dioxide.
9. A product as defined in claim 4 wherein said processing composition includes at least one opacifying agent.
10. A product as defined in claim 9 in which the opacifying agent is an optical filteragent exhibiting major spectral absorption at the pH of said alkaline processing composition and which is substantially transparent at the lower pH obtained after transfer image formation.
1 1. In a photographic product comprising a transparent support; a dyeable stratum; a blue-sensitive silver halide layer having a yellow dye image-providing material associated therewith; a green-sensitive silver halide layer having a magenta dye image-providing material capsulating said agent and having strands of interconnecting tissues bridging a plurality of the thus encapsulated agent particles.
13. A product as defined in claim 11 wherein said polymer is an acrylic polymer.
14. A product as defined in claim 13 wherein said reflecting agent is titanium dioxide.
15. A product as defined in claim 14 wherein the amount of polymeric material encapsulating said titanium dioxide is at least 2 percent by. weight of said titanium dioxide. 1 I
16.'In a photographic film unit adapted to be processed by passing the unit between a pair of juxtaposed pressure-applying members and which comprises, in
an opaque support;
a layer of a cyan dye image-providing material;
a red-sensitive silver halide emulsion layer;
a layer of a magenta dye image-providing material;
a green-sensitive silver halide emulsion layer;
a layer of a yellow dye image-providing material;
a blue-sensitive silver halide emulsion layer;
1 a dyeable stratum;
a neutralizing layer for lowering the'environmental pH from a first pH of an alkaline processing composition employed to develop said film unit to a second pH;
and a transparent support,
each of said dye image-providing materials being adapted to form, as a function of development, an imagewise distribution of dye which is soluble and diffusible in alkali at said first pH but which is substantially nondiffusible at said second pH;
a rupturable container retaining an alkaline aqueous processing composition possessing the first pH and having dispersed therein titanium dioxide and at least one optical filter agent which is substantially non-diffusible from the processing composition and possessing a pKa'below the first pH and above the second pH and the titanium dioxide and filter agent are present in 'a'quantity sufficient, upon application of the alkaline processing composition as a layer between the dyeable'stratum and the bluesensitive emulsion layer, to provide sufficient opacity to protect the silver halide emulsion layers from fogging by actiniclight incident on the thus applied layer of processing composition at said first pH, whereby said applied layer of processing fluid cooperates with said opaque support to provide a lighttight envelope for said emulsion layers so that said film unit can be developed in the light, said titanium dioxide being present in an amount sufficient to mask effectively said silver halide emulsion layers and any remaining dye image-providing material following development of said film unit and to provide a white background for viewing through saidtransparent support a color transfer image imparted to said dyeable stratum by difiusion thereto of said imagewise distribution of soluble and diffusible dye formed as a function of development, said rupturable container being positioned and extending transverse an edge of said film unit to effect unidirectional discharge of its contents intermediate, the dyeable stratum and the blue-sensitive emulsion layer;
the improvement wherein the titanium dioxide is encapsulated within a polymeric wall to provide greater resistance against settling or phase separation of said dispersed titanium dioxide from the aqueous alkaline medium in said rupturable container.
17. A film unit as defined in claim 16 wherein said polymeric wall is characterized as being a coating encapsulating said pigment and having strands of interconnecting tissues bridging a plurality of the thus encapsulated pigment particles.
18. A film unit as defined in claim 16 wherein said polymer is an acrylic polymer.
19. A film unit as defined in claim 16 wherein the amount of polymer encapsulating said titanium dioxide is from about 2 to about 25 percent by weight of said encapsulated titanium dioxide.
20. In a photographic process wherein a film unit including a-negative component comprising at least one light-sensitive silver halide layer having a dye imageproviding material associated therewith and a positive component including a dyeable stratum is exposed to orm? de elop ble im e E EUlJSIQRE s iilmt unit is then developed by applying an aqueous alkaline processing composition in a layer between said negative and positive components to develop said image and to form, as a function of said development, a color diffusion transfer image viewable, without separation of said components, as a color reflection print;
22 the improvement wherein the composition employed to develop said image comprises an aqueous alkaline solution having dispersed substantially unifonnly therein a pigment encapsulated within a polymeric wall.
21. In a photographic process wherein a film unit including a negative component comprising at least one light-sensitive silver halide layer having a dye imageproviding material associated therewith and a positive component including a dyeable stratum is exposed to form a developable image and the thus exposed film unit is then developed by applying an aqueous alkaline processing composition in a layer between said negative and positive components to develop said image and to form, as a function of said development, a color diffusion transfer image viewable, without separation of said components, as a color reflection print;
the improvement wherein the composition employed to develop said image comprises an aqueous alkaline solution having dispersed substantially uniformly therein a titanium dioxide encapsulated within a polymeric wall and an optical filtering agent exhibiting major spectral absorption at a pH of said alkaline solution but which is substantially transparent at a lower pH. v