This invention relates to imaging elements use- ful in photography and to processes for producing images employing such elements.

In producing coatings suitable for forming photographic images, a typical approach is to coat onto one or both surfaces of a planar support a radiation-sensitive material alone or in combination with other image-forming materials. Such coatings undergo a change in optical density as a function of exposure and if required, photographic processing. Coatings prepared, exposed and processed in this way tend to have reduced image definition by reasons of lateral image spreadin —that is, spreading in a direction parallel to the surfaces of the support. Lateral image spreading can be the result of radiation scattering during exposure, halation, or lateral re- actant migration during photographic processing. The effects of lateral image spreading can be seen as a loss in sharpness which can be mathematically analyzed in terms of modulation transfer function and as an increase in perceived graininess which can be math- ematically analyzed in terms of granularity. Grain¬ iness is particularly a problem in silver halide photography since it is directly related to and limits in many instances attainable photographic speeds. Typical approaches to reducing graininess in photographic images have involved some modification of" the imaging layers of photographic elements, their mode of processing or modification of the imaging layers after an image has been produced therein. An illustrative disclosure of this type is that of U.K. Patent 1,318,371, which recognizes the known fact

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that graininess is a function of the randomness of image distribution and therefore teaches to super¬ impose on the imaging layer a grid which subdivides the image either before or after its formation. In every embodiment of that patent planar photographic support surfaces are coated.

A non-planar support is employed in the Aluphoto . process in which silver halide is formed ±n situ in the random pores of an anodized aluminum plate. This is described by Wainer in "The Aluphoto Plate and Process", 1951 Photographic Engineering, Vol. 2, No. 3 PP- l6l-l ^β 9. Nonplanar supports intend to level out overlapping emulsion coating patterns are disclosed by U.S. Patents 2,983,606 and 3,019,124. U.S. Patent 3,138,459 discloses the use of a two color screen wherein two additive primary filter dyes are coated into grooves on opposite sides of a transparent support. The grooves on one side of the support are interposed between grooves on the opposite side of the support. The grooves prevent lateral spreading of the filter dyes into overlapping relation¬ ship. However, to accomplish this the grooves on each major surface of the support must be laterally spaced by at least the width of the grooves -on the opposite surface of the support.

U.S. Patent 2,599,542 discloses an electrophoto¬ graphic plate comprising a conductive backing plate having randomly or regularly spaced recesses or projections having a photoconductiye insulating layer coated thereon to obtain half-tone xerographic images . However, no significant halation has ever been observ¬ ed during exposure of xerographic photoconductive coatings. Also the optical density of photoconductive coatings are not altered during processing. According to the present invention there is

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provided an imaging element comprising a support and: (1) a radiation-sensitive imaging means which undergoes a change in mobility or optical density in forming a visible image; (2) a material capable of reducing the mobility of a diffusible photographic imaging mat¬ erial; or (3) at least three laterally positioned segment¬ ed filters of different spectral absorptions; the improvement comprising a support having a planar array of microvessels which individually open toward one of its surfaces, next adjacent of the microvessels being laterally spaced by less than the width of ad¬ jacent microvessels opening toward either of the surfaces of the support and the Imaging means, the mobility reducing material and/or the filters being present at least in part in the microvessels.

The non-planar microvessel-containing supports employed In the elements of the present invention lead to a number of advantages. Firstly, protection against halation can be obtained and this is accomplish¬ ed without competing absorption which is encountered with conventional antihalation layers . Exposing radiation can be redirected, and it can be caused to reencounter a radiation-sensitive component so that the opportunity for a speed increase is provided with¬ out loss of image definition.

Secondly, protection against loss of image definition during processing an exposed photographic element can be obtained. The invention is particular¬ ly well suited to achieving high, contrast images and permits, for example, high contrast and densities to be achieved through infectious development in image areas while inhibiting lateral spreading In background areas. Thirdly, the invention also permits extremely

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high photographic speeds without concomitant grain¬ iness, and in one embodiment of the invention this Is achieved by forming uniform densities within each . microvessel. Fourthly, the present invention offers the advantage of permitting greater absorption of expos¬ ing radiation. In one form this is accomplished by permitting the use of extended thicknesses of radiation-sensitive materials without loss of image definition usually associated with thick layers.

This invention is particularly advantageously applied to X-ray imaging, and the invention is compatible with providing radiation-sensitive material on both sides of the support. The present invention fifthly offers distinct and varied advantages in image transfer photography. The invention permits improved image definition and reduced graininess to be achieved for both retained and transfer images and offers protection against lateral image spreading in receiver layers. The invention is nevertheless compatible with, and in certain preferred forms directed to, image transfer materials which require deliberate lateral image spreading during transfer to obtain subtractive color images from additive color materials.

Sixthly, the present invention offers unexpected advantages in multicolor additive primary images of improved definition and reduced graininess. The invention is particularly well suited to forming multi- color additive primary filters of improved definition. A preferred class of elements according to the present invention comprise, as imaging means l) silver halide. A preferred class of such, elements are those in which the silver halide is located substantially wholly within the microvessels.

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The invention further provides a process for treating an element of the invention wherein the radiation-sensitive imaging means is adjacent to or present in the microvessels, which process comprises imagewise exposing the element and processing the exposed element to form a visible image.

In the drawings:

Figure 1A is a plan view of an element portion:

Figure IB is a sectional view taken along section lines IB-IB in Figure 1A;

Figures 2 to 5 are sectional views of alter¬ native pixel (defined below) constructions;

Figures 6 to 8 are plan views of alternative element portions; Figures 9 and 10 are sectional details of elements according to this invention;

Figure 11A is a plan view of an element portion according to this invention, and

Figures 11B, 11C and 12 through Iβ are sectional details of elements according to this invention.

A preferred embodiment of a photographic element constructed according to the present invention is a photographic element 100 schematically illustrated in Figures 1A and IB. The element is comprised of a support 102 having substantially parallel surfaces 104 and 106, and microvessels (tiny cavities) 108 which open toward surface 106., The microvessels are surrounded by an interconnecting network of lateral walls 110 which are integrally joined to an underlying portion 112 of the support so that the support acts as a barrier between adjacent microvessels. The underlying portion of the support defines the bottom wall 114 of each microvessel. Within each microvessel is provided a radiation-sensitive imaging material 116.

The dashed line 120 is a boundary of a pixel. The term "pixel" is employed herein to indicate a single unit of the photographic element which Is repeated to make up the entire imaging area of the element. This is consistent with the general use of the term in the imaging arts. The number of pixels is, of course, dependent on the size of the indi¬ vidual pixels and the dimensions of the photographic element. Looking at the pixels collectively, it is apparent that the imaging material in the reaction microvessels can be viewed as a segmented layer associated with the support.

The photographic elements of the present invention can be varied in their geometrical configurations and structural makeup. For example, Figure 2 schematically illustrates in section a single pixel of a photo¬ graphic element 200. The support 202 has two surfaces 204 and 206. A microvessel 208 opens toward surface 206. Contained within the microvessel is a radiation- sensitive material 216. The microvessels are form¬ ed so that the support provides inwardly sloping walls which perform the functions of both the lateral and bottom walls of the microvessels 108. Such Inwardly curving wall structures are more conveniently formed by certain techniques of manufacture, such as etching, and also are well suited to redirecting exposing radiation toward the interior of the re¬ action microvessels.

In Figure 3 a pixel of a photographic element 300 is shown. The element is comprised of a first support element 302 having surfaces 304 and 306. Joined to the first support element is a second support element 308 which is provided in each pixel with an aperture 310. The second support element is provided with an outer surface 312. The walls of

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the second support element forming the aperture 310 and surface 306 of the first support element together define a reaction microvessel. A radiation-sensitive material 316 ^" is located in the microvessel. Addition— ally, a relatively thin extension 314 of the radiation- sensitive material overlies the outer major surface of the upper support element and forms a continuous layer joining adjacent pixels. The lateral exten¬ sions of the radiation-sensitive material are some- times a byproduct of a specific technique of coating the radiation-sensitive material. One coating tech¬ nique which can leave extensions of the radiation- sensitive material is doctor blade coating. It Is generally preferred however, that the lateral exten- sions be absent or of the least possible thickness. In Figure 4 a pixel of a photographic element 400 is illustrated comprised of a support 402, which is of extended depth. The support is provided with surfaces 404 and 406 and microvessel 408 which is similar to microvessel 108 but is of extended depth. Two components 4l6 and 418 together form a radiation-sensitive imaging means. The first component 416, which in a continuous layer form would produce visually detectable lateral image spreading, forms a column of extended depth, as compared with the mat¬ erial 116 in the reaction microvessels 108. The second component 4l8 is in the form of a continuous layer overlying the second major surface of the support. In an alternative form the first component can be identical to the radiation-sensitive imaging material 116—that is, itself form the entire radiation-sensitive imaging means—and the second component 4l8 can be a continuous layer which per¬ forms another function, such as those conventionally performed by overcoat layers ^' .

In Figure 5 a pixel of a photographic element 500 is illustrated comprised, of a first support element 502 having surfaces- 504 and 506. Joined to the first support element is a transparent second support element 508 which is provided with, a net¬ work of lateral walls 510 integrally joined to an underlying portion 512 of the second support element. In one preferred form the first support element is a relatively nondeformable while the second support element is relatively deformable. An indentation 514 is formed in the second support element In each pixel area. The surfaces of the second support element ad¬ jacent its outer surface, are overlaid with a thin layer 515, which performs one or a combination of surface modifying functions. The portion of the coat¬ ing lying within the indentation defines the boun¬ daries of a microvessel 517. A first component 516 which lies within the microvessel and a second component 518 which overlies one entire surface of the pixel can be similar to the first and second components 4l6 and 4l8, respectively.

Each of the pixels shown in Figures 2 to 5 can be of a configuration and arranged in relation to other pixels so that the photographic elements 200, 300, 400 and 500 (ignoring any continuous material layers overlying the viewed major surfaces of the supports) appear identical In plan view to the photographic element 100. The pixels 120 shown in Figure 1 are hexagonal in plan view, but it Is appreciated that a variety of other pixel shapes and arrangements are possible. For example, in Figure 6 a photographic element βOQ is shown comprised of a support 602 provided with, microvessels 608, which are circular in plan view, ^" containing radiation-sensitive material 6l6. Microvessels which are circular in plan

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are particularly suited to formation by etching tech¬ niques, .although they can be easily formed by other techniques, as well. A disadvantage of the circular microvessels as compared with other configurations shown is that the lateral walls 610 vary continuously in width. Providing lateral walls of at least the minimum required width at their narrowest point inherently requires the walls in some portions of the pattern to be larger than that required minimum width. In Figure 7 a photographic element 700 is shown comprised of a support 702 provided with micro¬ vessels 708, which are square in plan view, contain¬ ing radiation-sensitive material 716. The lateral walls 710 are of uniform width. Figure 8 illustrates an element 800 comprised of a support 802 having an interlaid pattern of rectang¬ ular microvessels 808. Each of the microvessels con¬ tains a radiation-sensitive imaging material 8l6. The dashed line 820 identifies a single pixel of the ele- ment. In each of the elements 100 to 500, the surface of the support remote from the microvessels is illustrated as being planar. This is convenient for many photographic applications, but is not essential to the practice of this invention. Other element con- figurations are contemplated, particularly where the support is transparent to exposing radiation and/or viewing radiation.

For example, in Figure 9 a photographic element 900 is illustrated. The element is comprised of a support 902 having surfaces 90^ and 906. The support has a plurality of microvessels 908A and 90δB which, open toward top and bottom surfaces respectively. In the ^' preferred form, th-e microvessels 908A are aligned with the microvessels 908B along axes perpendicular to the surfaces. The ^' microvessels have lateral walls 910A and 910B which are integrally joined by an

underlying, preferably transparent, portion 912 of the support. Within each microvessel Is provided a radiation-sensitive material 916.

It can be seen that element 900 is essentially similar to element 100, except that the former element contains microvessels along both major surfaces of the support. It is apparent that similar variants of the photographic elements 200, 300, 400, 500, 600, 700 and 800 can be formed. In Figure 10 a photographic element 1000 is illustrated. The element is comprised of a support 1002 having a lenticular surface 1004 and a second surface 1006. Microvessels 1008 containing radiation- sensitive material 1016 having lateral walls 1010 of the support open toward the second surface. The element is made up of a plurality of pixels indicated in one occurrence by dashed line boundary 1020. Individual lenticules are coextensive with the pixel boundaries. For ease of illustration the drawings show the pixels greatly enlarged and with some deliberate distortions of relative proportions. For example, as is well known in the photographic arts, support thicknesses often range from about 10 times the thickness of the radiation-sensitive layers coated thereon up to 50 or even 100 times their thickness. Thus, in keeping with the usual practice in patent drawings in this art, the relative thicknesses of the supports have been reduced. This has permitted the microvessels to be drawn conveniently to a larger scale.

The microvessels preferably have widths within the range of from about 1 to 100 microns, preferably from 4 to 50 microns. For. ost imaging applications the microvessels are preferably sufficiently small

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In size that the unaided eye does not detect discrete image areas In viewing the photographic elements after they have been processed. - Approached in another way, the images produced by the photographic elements are similar to gravure images, and they are preferably made up of sufficiently small discrete images which are not distinguishable to the eye. For pictorial viewing of the images produced, optimum results are generally achieved with microvessels of less than 20 microns in width. The lower limit on the size of the microvessels is a function of the photographic speed desired for the element. As the areal extent of the microvessel is decreased, the probability of an imag¬ ing amount of radiation striking a particular reaction microvessel on exposure is reduced. Reaction micro¬ vessel widths of at least 7 microns, preferably at least 8 microns, optimally at least 10 microns, are preferred where the reaction microvessel contains radiation-sensitive material. At widths below 7 microns, silver halide emulsions in the microvessels show a significant reduction in speed.

The microvessels are of sufficient depth to contain at least a major portion of the radiation- sensitive material. In one preferred form the micro- vessels are of sufficient depth that the radiation- sensitive materials are entirely contained therein when employed in conventional coating thicknesses, and the support element which forms the lateral walls of the microvessels efficiently divides the radiation- sensitive materials into discrete units or islands. In some forms the microvessels do not contain all, but _^ only a major portion, of the radiation-sensitive material.

The minimum depth of the microvessels is that which allows the support element to provide an

effective lateral wall barrier to image spreading. In terms of actual dimensions the minimum depth, of the microvessels can vary as a function of the radiation-sensitive material employed and the maximum density which Is desired to be produced. The depth of the microvessels can be less than, equal to or greater than their width. The thickness of the imag¬ ing material or the component thereof coated in the microvessels Is preferably at least equal to the thickness to which the material is conventionally continuously coated on planar support surfaces. This permits a maximum density to be achieved within the area subtended by the microvessel which approximates the maximum density that can be achieved In imaging a corresponding coating of the same radiation-sensitve material. It is recognized that reflected radiation from the microvessel walls during exposure and/or viewing can have the effect of yielding a somewhat different density than obtained in an otherwise comparable continuous coating of the radiation- sensitive material. For instance, where the micro¬ vessel walls are reflective and the radiation-sensitive material is negative-working, a higher density can be obtained during exposure within the microvessels than would be obtained with a continuous coating of the same thickness of the radiation-sensitive material.

Because the areas lying between adjacent micro¬ vessels are free of radiation-sensitive material (or contain at most a relatively minor proportion of the radiation-sensitive material), the visual effect of achieving a maximum density within the areas subtended by the microvessels equal to the maximum density in a corresponding conventional continuous coating of the radiation-sensitive material is that of a somewhat reduced density. The exact amount of the reduction in

density is a function of the thickness of any material lying within the microvessels as well as the spacing between adjacent microvessels. Where the continuous conventional coating produces a density substantially less than the--maximum density obtainable by increas¬ ing the thickness of the coating and the microvessel area is a larger fraction of the pixel area (.e.g., 90 to 99 percent), the comparative loss of density attributable to the spacing of microvessels can be compensated for by increasing the thickness of the imaging material or component in the microvessel. This, of course, means increasing the minimum depth of the microvessels. Where the photographic element is not intended to be viewed directly, but is to be used as an intermediate for photographic purposes, such as a negative which is used as a printing master to form positive images in a reflection print photo¬ graphic element, the effect of spacing between ad¬ jacent microvessels can be eliminated in the reflection print by applying known printing techniques, such as slightly displacing the reflection print with respect to the master during the printing exposure. Thus, in this instance, increase in the depth of the micro¬ vessels is not necessary to achieve conventional maximum density levels with conventional thicknesses of radiation-sensitive materials.

The maximum depth of the microvessels can be substantially greater than the thickness of the radiation-sensitive material to be placed therein. for certain coating techniques it is preferred that the maximum depth of the microvessels approximate or substantially equal the thickness of the radiation- sensitive material to be employed. In forming conventional continuous coatings of radiation-sensitive materials one factor which limits the maximum thick-

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ness of the coating material is acceptable lateral image spreading, since the thicker the coating, the greater is the tendency, in most instances, toward loss of image definition. In the present invention lateral image spreading is limited by the lateral walls of the support element defining the micro¬ vessels and is independent of the thickness of the radiation-sensitive material located in the micro¬ vessels. Thus, it is possible and specifically contemplated in the present invention to employ micro- vessel depths and radiation-sensitive material thick¬ nesses therein which are far in excess of those thick¬ nesses employed in conventional continuous coatings of the same radiation-sensitive materials. While the depth of the microvessels can vary widely, it is generally contemplated that the depth of the microvessels will fall within the range of from 1 to 1000 microns in depth or more. For exceptional radiation-sensitive materials, such as vacuum vapor deposited silver halides, conventional coating thick¬ nesses are typically in the range from 40 to 200 nano¬ meters, and very shallow microvessels of a depth of 0.5 micron or less can be employed. In one preferred form, the depth of the microvessels is in the range of from 5 to 20 microns. This is normally sufficient to permit a maximum density to be generated within the area subtended by the reaction microvessel correspond¬ ing to the maximum density obtainable with continuous¬ ly coated radiation-sensitive materials of conventional thicknesses. These preferred depths of the micro¬ vessels are also well suited to applications where the radiation-sensitive material is intended to fill the entire microvessels—-e.g., to have a thickness corresponding to the depth of the reaction microvessel. It is usually desirable and most efficient to form

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the microvessels so that they are aligned along at least one axis in the plane of the support surface. For example, microvessels in the configuration of hexagons, preferred for multicolor and other applica- tions, are conveniently aligned along three support surface axes which intersect at 120° angles. It Is recognized that adjacent microvessels can be varied in spacing to permit alterations in visual effects. Generally it is preferred that adjacent reaction microvessels be closely spaced, since this aids the eye in visually ^" combining adjacent image areas and facilities obtaining higher overall maximum densities. The minimum spacing of adjacent microvessels is limit¬ ed only by the necessity of providing intervening lateral walls in the support elements. Typical ad¬ jacent; microvessels are laterally spaced a distance (corresponding to lateral wall thickness) of from 0.5 to 5 microns, although both greater and lesser spacings are contemplated. Spacing of adjacent microvessels can be approach¬ ed in another way in terms of the percentage of each pixel area subtended by the microvessel. This is a function of the size and peripheral configuration of the microvessel and the pixel in which it is contained. Generally the highest percentages of pixel area sub¬ tended by microvessel area are achieved when the per¬ ipheral configuration of the pixel and the microvessel are Identical, such as a hexagonal microvessel in a hexagonal pixel (as in Figure 1A) or a square micro- vessel in a square pixel (as in Figure 7). For closely spaced patterns it is preferred that the sub¬ tended microvessel area account for from 50 to 99 percent of the pixel area, most preferably from 90 to 98 percent of the pixel area. Even with microvessel and pixel configurations which do not permit the

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closest and most efficient spacing the subtended microvessel area can readily account for 50 to 80 (preferably 90) percent of the pixel area.

Photographic elements of the invention can be formed by one or a combination of support elements which, alone, or in combination, are capable of reducing lateral image spread and maintaining spatial integrity of the pixels forming the elements. Where the photographic elements are formed by a single support element, the support element performs both of these functions. Where the photographic elements are formed by more than one support element, as in Figures 3 and 5, for example, only one of the elements (preferably the first support elements 302 and 502) need have the structural strength to retain the desir¬ ed spatial relationship of adjacent pixels. The second support elements can be formed of relatively deformable materials. They can, but need not, con¬ tribute appreciably to the ability of the photographic elements 300 and 500 to be handled as a unit without permanent structual deformation.

The support elements of the elements of this invention can be formed of the same types of materials employed in forming conventional photographic supports. Typical photographic supports include polymeric film, wood fiber, e.g., paper, metallic sheet and foil, glass and ceramic supporting elements provided with one or more subbing layers to enhance the adhesive, antistatic, dimensional, abrasive, hardness, frictional, ^■ antihalation and/or other properties of the support surface.

Typical of useful polymeric film supports are films of cellulose nitrate and cellulose esters such as cellulose triacetate and diacetate, polystyrene, polyamides, homo- and co-polymers of vinyl chloride,

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poly(vinyl acetal), polycarbonate, homo- and co¬ polymers of olefins, such as polyethylene and poly¬ propylene, and polyesters of dlabasic aromatic carboxylic acids with divalent alcohols, such as poly(ethylene--terephthalate) .

Typical of useful paper supports are those which are partially acetylated or coated with baryta and/or a polyolefin, particularly a polymer of an« -olefin containing 2 to 10 carbon atoms, such as polyethylene, polypropylene, and copolymers of ethylene and propylene Polyolefins, such as polyethylene, polypropylene and polyallomers, e.g., copolymers of ethylene and propylene, as illustrated by Hagemeyer et al U.S. Patent 3,478,128, are preferably employed as resin coatings over paper, as illustrated by Crawford et al U.S. Patent 3,411,908 and Joseph et al U.S. Patent 3,630,740, over polystyrene and polyester film supports, as illustrated by Crawford et al U.S. Patent 3,630,7 2, or can be employed as unitary flexible reflection supports, as illustrated by Venor et al ^• U.S. Patent 3,973,963.

Preferred cellulose ester supports are cellulose triacetate supports, as illustrated by Fordyce et al U.S. Patents 2,492,977, '978 and 2,739,069, as well as mixed cellulose ester supports, such as cellulose acetate propionate and cellulose acetate butyrate, as illustrated by Fordyce et al U.S. Patent 2,739,070.

Preferred polyester film supports are comprised of linear polyester, such as illustrated by Alles et al U.S. Patent 2,627,088, Wellman U.S. Patent

■ 2,720,503, Alles U.S. Patent 2,779,684 and Kibler et al U.S. Patent 2,901,466. Polyester films can be forme'd by varied techniques, as Illustrated by Alles, cited above, Czerkas et al U.S. Patent 3,663,683 and

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Willlams et al U.S. Patent 3,504,075, and modified for use as photographic film supports, as illustrated by Van Stappen U.S. Patent 3,227,576, Nadeau et al ^• U.S. Patent 3,501,301, Reedy et al U.S. Patent 3,589,905, Babbitt et al U.S. Patent 3,850,640,

Bailey et al U.S. Patent 3,888,678, Hunter U.S. Patent 3,904,420 and Mallinson et al U.S. Patent 3,928,697.

The elements can employ supports which are resis¬ tant to dimensional change at elevated temperatures, Such supports can be comprised of linear condensation polymers which have glass transition temperatures above about 190°C, preferably 220°C, such as poly¬ carbonates, pol carbox lie esters, polyamides , poly- sulfonamides, polyethers, polylmides, polysulfonates and copoly er variants, as illustrated by Hamb U.S. Patents 3,634,089 and 3,772,405; Hamb et al U.S. Patents 3,725,070 and 3,793,249; Gottermeier U.S. Patent 4,076,532; Wilson Research Disclosure, Vol. 118, February 1974, Item 11833, and Vol. 120, April 1974, Item 12046; Conklln et al Research Disclosure, Vol. 120, April 1974, Item 12012; Product Licensing Index, Vol. 92, December 1971, Items 9205 and 9207; Research Disclosure, Vol. 101, September 1972, Items 10119 and 10148; Research Disclosure, Vol. 106, February 1973, Item 10613; Research Disclosure, Vol.

117, January 1974, Item 11709, and Research Disclosure, Vol. 134, June 1975, Item 13^55.

The second support elements which define the lateral walls of the microvessels can be selected from a variety of materials lacking sufficient structural strength to be employed alone as supports. It is specifically contemplated that the second support element ^' s can be formed using conventional photopoly- merizable or photocrosslinkable materials—e.g., photoresists. Exemplary conventional photoresists are

disclosed by Arcesi et al U.S. Patents 3,640,722. and 3,748,132, Reynolds et al U.S. Patents 3,696,072 and 3,748,131, Jenkins et al U.S. Patents 3,699,025 and '026, Borden U.S. Patent 3,737,319, Noonan et al U.S. Patent ^"" 3,748,133, Wadsworth et al U.S. Patent 3,779,989, DeBoer U.S. Patent 3,782,938, and Wilson U.S. Patent 4,052,367. Still other useful photopoly- merizable and photocrosslinkable materials are dis¬ closed by Kosar, Light-Sensitive Systems : Chemistry and Application of Nonsilver Halide Photographic Processes, Chapters 4 and 5, John Wiley and Sons, 1965. It is also contemplated that the second support elements can be formed using radiation- responsive colloid compositions, such as dichromated colloids— .g., dichromated gelatin, as illustrated by Chapter 2, Kosar, cited above. The second support elements can also be formed using silver halide emulsions and processing in the presence of transi¬ tion metal ion complexes, as illustrated by Bissonette U.S. Patent 3,856,524 and McGuckin U.S. Patent

3,862,855. The advantage of using radiation-sensitive materials to form the second support elements is that the lateral walls and microvessels can be simultaneous¬ ly defined by patterned exposure. Once formed the second support elements are not themselves further responsive to exposing radiation.

It is contemplated that the second support elements can alternatively be formed of materials commonly employed as vehicles and/or binders in radiation-sensitive materials. The advantage of using vehicle or binder materials is their known compatibility with the radiation-sensitive materials. The binders and/or vehicles can be polymerized or hardened to a somewhat higher degree than when employed in radiation-sensitive materials to insure

di ensional integrity of the lateral walls which they form. Illustrative of specific binder and vehicle materials are those employed in silver halide emul¬ sions, more specifically described below. The light transmission, absorption and reflection qualities of the support elements can be varied for different photographic applications. The support elements can be substantially transparent or re¬ flective, preferably white, as are the majority of conventional photographic supports. The support elements can be reflective, such as by mirroring the microvessel walls. The support elements can In some applications contain dyes or pigments to render them substantially light impenetrable. Levels of dye or pigment incorporation can be chosen to retain the light transmission characteristics in the thinner regions of the support elements— .g., in the micro- vessel regions—while rendering the support elements relatively less light penetrable in thicker regions— e.g., in the lateral wall regions between adjacent microvessels. The support elements can contain neutral colorant or colorant combinations. Alternatively, the support elements can contain radiation absorbing materials which are "selective to a single region of the electromagnetic spectrum—e.g., blue dyes. The support elements can contain materials which alter radiation transmission qualities, but are not visible, such as ultraviolet absorbers. Where two support elements are employed in combination, the light transmission, absorption and reflection qualities of the two support elements can be the same or different. The unique advantages of varied forms of the support elements can be better appreciated by reference to the illustrative embodiments described below.

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Where the support elements are formed of conven¬ tional photographic support materials they can be provided with reflective and absorbing materials by techniques well known ^' by those skilled in the art, such techniques being adequately illustrated in the various patents cited above in relation to support materials. In addition, reflective and absorbing materials can be employed of varied types conven¬ tionally incorporated directly in radiation-sensitive materials, particularly in second support elements formed of vehicle and/or binder materials or using photoresists or dichromated gelatin. The incorporation of pigments of high reflection index in vehicle mat¬ erials is illustrated, for example, by Marriage U.K. Patent 504,283 and Yutzy et al U.K. Patent 760,775.

Absorbing materials incorporated in vehicle materials are illustrated by Jelley et al U.S. Patent 2,697,037; colloidal silver (e.g., Carey Lea Silver widely used as a blue filter); super fine silver halide used to improve sharpness, as illustrated by U.K. Patent 1,342,687; finely divided carbon used to improve sharpness or for antihalation protection, as illustrat¬ ed by Simmons U.S. Patent 2,327,828; filter and anti¬ halation dyes, such as the pyrazolone oxonol dyes of Gaspar U.S. Patent 2,274,782, the solubilized diaryl azo dyes of Van Campen U.S. Patent 2,956,879, the solubilized styryl and butadinenyl dyes of Heseltine et al U.S. Patents 3,423,207 and 3,384,487, the merocyanine dyes of Silberstein et al U.S. Patent 2,527,583, the merocyanine and oxonol dyes of Oliver U.S. Patents 3,486,897 and 3,652,284 and Oliver et al U.S. Patent 3,718,472 and the enamino hemioxonol dyes of Brooker et al U.S. Patent 3,976,661 and ultra¬ violet absorbers, such as the cyanomethyl sulfone- derived erocyanines of Oliver U.S. Patent 3,723,154,

the thiazolldones, benzotrlazoles and thiazolothiazoles of Sawdey U.S. Patents 2,739,888, 3,253,921 and 3,250,617 and Sawdey et al U.S. Patent 2,739,971, the triazoles of Heller et al U.S. Patent 3,004,896 and the hemioxonpls of Wahl et al U.S. Patent 3,125,597 and Weber et al U.S. Patent 4,045,229- The dyes and ultraviolet absorbers can be mordanted, as illustrat¬ ed by Jones et al U.S. Patent 3,282,699 and Heseltine et al U.S. Patents 3,455,693 and 3,438,779. The radiation-sensitive portions of conventional photographic elements are typically coated onto a planar support surface in the form of one or more continuous layers of substantially uniform thickness. The radiation-sensitive portions of the photographic elements of this Invention are desirably selected from among such conventional radiation-sensitive portions which, when coated as one or more layers of substantially uniform thickness, exhibit the characteristics of undergoing (1) an imagewise change in mobility or optical density in response to image¬ wise exposure and/or photographic processing, and (2) visually detectable lateral image spreading in trans¬ lating an imaging exposure to a viewable form. Lateral image spreading has been observed in a wide variety of conventional photographic elements. Lateral image spreading can be a product of optical phenomena, such as reflection or scattering of exposing radiation; diffusion phenomena, such as lateral diffusion of radiation-sensitive and/or imaging materials in the radiation-sensitive and/or imaging layers of the photographic elements. Lateral image spreading is particularly common where the radiation-sensitive and/or other imaging materials are dispersed in a vehicle or binder intended to be penetrated by exposing radiation and/or processing fluids.

The radiation-sensitive portions of the photo¬ graphic elements of this invention can be of a type which contain within a single component, correspond¬ ing to a layer of a conventional photographic element, radiation-sensitive materials capable of directly producing or being processed to produce a visible image by undergoing a change in mobility or optical density or a combination of radiation-sensitive materials and imaging materials which together similarly produce directly or upon processing a view¬ able image. The radiation-sensitive portion can be formed alternatively of two or more components, corresponding to two or more layers of a conventional photographic element, which together contain radiation- sensitive and imaging materials. Where two or more components are present, only one of the components need be radiation-sensitive and only one of the components need be an imaging component. Further, either the radiation-sensitive component or the imag- ing component of the radiation-sensitive portion of the element can be solely responsible for lateral Image spreading when conventionally coated as a continuous, substantially uniform thickness layer. In one form, the radiation-sensitive portion can be of a type which permits a viewable Image to be formed directly therein. In another form, the image produc¬ ed is not directly viewable in the element itself, but can be viewed in a separate element. For example, the image can be of a type which is viewed as a transferred image in a separate receiver element.

In one form, the radiation-sensitive portion of the photographic element can take the form of a material which relies upon a dye to provide a visible coloration, the coloration- being created, destroyed or altered in its light absorption characteristic in

response to imagewise exposure and processing. A dye is typically either formed or destroyed in response to imaging exposure and processing. In an exemplary form, the radiation-sensitive portion can be formed of an Imaging composition containing a photoreduc-tant and an imaging material. The photo- reductant can be a material which is activated by imagewise light exposure alone or in combination with heat and/or a base (typically ammonia) to produce a reducing agent. In some forms, a hydrogen source is incorporated within the photoreductant itself (i.e., an internal hydrogen source) or externally provided. Exemplary photoreductants include materials such as 2H-benzimidazoles, disulfides, phenazinium salts, diazoanthrones, -ketosulfides, nitroarenes and quinones (particularly internal hydrogen source quinones), while the reducible Imaging materials include aminotriarylmethane dyes, azo dyes, xanthene dyes, triazine dyes, nitroso dye complexes, indigo dyes, phthalocyanine dyes, tetrazolium salts and triazolium salts. Such radiation-sensitive materials and processes for their use are more specifically disclosed by Bailey et al U.S. Patent 3,880,659, ^• Bailey U.S. Patents 3,887,372 and 3,917,484, Fleming et al U.S. Patent 3,887,374 and Schleigh U.S. Patents 3,894,874 and 3,880,659, the disclosures of which are here incorporated by reference.

In another form, the radiation-sensitive portion of the photographic element can include a cobalt (III) complex which can produce images In various known combinations. The cobalt(III) complexes are themselves responsive to imaging exposures in the ultraviolet portion of the spectrum. They can also be spectrally sensitized to respond to the visible portion of the spectrum. In still another variant form, they can

be.employed in combination with photoreductants, such as those described above, to produce images. The cobalt(III) complexes can be employed in compositions such as those disclosed by Hickman et al U.S. Patents 1,897,843 and- 1,962,307 and Weyde U.S. Patent 2,084,420 to produce metal sulfide images. The cobalt( _. III) complexes typically include ammine or amine ligands which are released upon exposure of the complexes to actinic radiation and, usually, heating. The radiation- sensitive portion of the photographic element can include in the same component as the cobalt(III) complex or in an adjacent component of the same ele¬ ment or a separate element, materials which are responsive to a base, particularly ammonia, to produce an image. For example, materials such as phthalaldehyde and ninhydrin printout upon contact with ammonia. A number of dyes, such as certain types of cyanine, styryl, rhodamine and azo dyes, are known to be cap¬ able of being altered in color upon contact with a base. Dyes, such as pyrylium dyes, capable of being rendered transparent upon contact with ammonia, are preferred. By proper selection of chelating compounds employed in combination with the cobalt(III) complexes internal amplification can be achieved. These and other imaging compositions and techniques employing cobalt(III) complexes to form images are disclosed in Research Disclosure, Vol. 126, Item 12617, publish¬ ed October, 1974; Vol. 130, Item 13023, published February, 1975; and Vol. 135, Item 13523, published July, 1975, as well as in DoMinh U.S. Patent

4,075,019, Enriquez U.S. Patent 4,057,427 and Adin U.S. Serial No. 865,275, filed December 28, 1977, the disclosures of which are here incorporated by reference. The radiation-sensitive portion of the photo-

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graphic element can include diazo imaging materials Diazo materials can initially incorporate both a diazonium salt and an ammonia activated coupler (commonly referred to as two component diazo systems) or can initially incorporate only the diazonium salt and rely upon subsequent processing to imbibe the coupler (commonly referred to as one-component diazo systems). Both one-component and two-component diazo systems can be employed in the practice of this in- vent±on. Typically, diazo photographic elements are first imagewise exposed to ultraviolet light to activate radiation-struck areas and then uniformly contacted with ammonia to printout a positive image. Diazo mat¬ erials and processes for their use are described in Chapter 6, Kosar, cited above.

Since diazo materials employ ammonia processing, it is apparent that diazo materials can be employed in combination with cobalt(III) complexes which release ammonia. Where the cobalt(III) complex forms one component of the radiation-sensitive portion of the photographic element, the diazo component can either form a second component or be part of a separate ele¬ ment which is placed adjacent the cobalt(III) complex containing component during the ammonia releasing step. Using combinations of visible and/or ultra¬ violet exposures, positive or negative diazo images can be formed, as is more particularly described in the publications and patents cited above in relation to cobalt(III) complex containing materials, particular- ly DoMinh U.S.. Patent 4,075,019.

The photographic elements of this invention can include those which photographically form-or inactivate a physical development catalyst in an imagewise manner. Following creation of the physical development catalyst image, solvated metal ions can be electrolessly plat-

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ed at the catalyst image site to form a viewable metallic image. A variety of metals, such as silver, copper, nickel,, cobalt, tin, lead and indium, have been employed in physical development imaging. In a positive-working form a uniform catalyst is imagewise inactivated. Such a system is illustrated by Hanson et al U.S. Patent 3,320,064, In which a mixture of a light-sensitive organic azide with a thioether coupler Is imagewise exposed to inactivate a uniform catalyst in exposed areas. Subsequent electroless plating produces a positive image.

Negative-working physical development systems which form catalyst images include those which form catalyst images by disproportionation of metal ions and those which form catalyst images by reduction of metal ions. A preferred disproportionation catalyst imaging approach is to imagewise expose a diazonium salt, such as used in diazo imaging, described above, to form with mercury or silver ions a metal salt which can be disproportionated to form a catalyst image, as is illustrated by Dippel et al U.S. Patent 2,735,773 and de Jonge et al U.S. Patents 2,764,484, 2,686,643 and 2,923,626. Disproportionation imaging to form copper nuclei for physical development is dis- closed by Hillson et al U.S. Patent 3,700,448. Dis¬ proportionation to produce a mercury catalyst image can also be achieved by exposing a mixture of mercuric chloride and an oxalate', as Illustrated by Slifkln U.S. Patent 2,459,136. Reduction of metal ions to form a catalyst can be achieved by exposing a dia¬ zonium compound in the presence of water to produce a phenol reducing agent, as illustrated by Jonker et al U.S. Patent 2,738,272, Zinc oxide and. titanium oxide particles can be dispersed in a binder to provide a catalytic surface for photoreduc ion, as

illustrated by Levlnos U.S. Patent 3,052,541. Silver halide photographic elements, discussed below, con- ^• stitute one specifically contemplated class of photo¬ graphic elements which can be used for physical development ^" Imaging. Physical development imaging systems useful in the practice of this invention are generally illustrated by Jonker et al, "Physical Development Recording Systems. I. General Survey and Photochemical Principles", Photographic Science and Engineering, Vol. 13, No. 1, January-February, 1969, pages 1 through 8,- the disclosure of 'which is here incorporated by reference.

The radiation-sensitive silver halide containing imaging portions of the photographic elements of this invention can be of a type which contain within a single component, corresponding to a layer of a con¬ ventional silver halide photographic element, radia¬ tion-sensitive silver halide capable of directly producing or being processed to produce a visible image or a combination of radiation-sensitive silver halide and imaging materials which together produce directly or upon processing a viewable image. The imaging portion can be formed alternatively of two or more components, corresponding to two or more layers of a conventional photographic element, which together contain radiation-sensitive silver halide and imaging materials. Where two or more components are present, only one of the components need contain radiation-sensitive silver halide and only one of the components need be an Imaging component. Further, either the radiation-sensitive silver halide contain¬ ing component or the imaging component of the im.aging portion of the element can be primarily responsible for lateral Image spreading when conventionally coat- ed as a continuous, substantially uniform thickness

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layer. In one form the radiation-sensitive silver halide containing portion can be of a type which permits a viewable image to .be formed directly therein. In another form the Image produced Is not directly viewable In the element itself, but can be viewed in a separate element. For example, the image can be of a type which is viewed as a trans¬ ferred image in a separate receiver element.

In a preferred form the radiation-sensitive silver halide containing imaging portions of the photographic elements are comprised of one or more silver halide emulsions. The silver halide emulsions can be comprised of silver bromide, silver chloride, silver iodide, silver chlorobromide, silver chloro- iodide, silver bromoiodide, silver chlorobromolodide or mixtures thereof. The emulsions can include coarse, medium or fine silver halide grains bounded by 100, 111, or 110 crystal planes and can be prepared by a variety of techniques—e.g., single-jet, double-jet (including continuous removal techniques), accelerat¬ ed flow rate and interrupted precipitation techniques, as disclosed in Research Disclosure, December 1978, Vol. 176, Item 17643 in paragraphs I, II, III, IV, VI, IX and X. The photographic elements can be imagewise exposed with various forms of energy, which encompass the ultraviolet and visible (e.g., actinic) and infra¬ red regions of the electromagnetic spectrum as well as electron beam and beta radiation, gamma ray, X-ray, alpha particle, neutron radiation and other forms of-corpuscular and wave-like radiant energy in either noncoherent (random phase) forms or coherent (in phase) forms, as produced by lasers. Exposures can be monochromatic, orthochromatic or panchromatic. Imagewise exposures at ambient, elevated or reduced

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temperatures and/or pressures, including high or low intensity exposures, continuous or intermittent exposures, exposure times .ranging from minutes to relatively short durations in the millisecond to microsecond .range and solarizing exposures, can be employed within the useful response ranges determined by conventional sensitometric techniques, as illustrat¬ ed by T. H. James, The Theory of the Photographic Process, 4th Ed., Macmillan, 1977, Chapters 4, 6, 17, 18 and 23.

Referring to photographic element 100 in Figures 1A and IB, in a simple, illustrative form of this invention the support 102 is formed of a reflective material, preferably and hereinafter referred to as a white reflective material, although colored reflective materials are contemplated. The radiation-sensitive material 116 is a silver halide emulsion of the type which is capable of producing a viewable image as a result solely of exposure and, optionally, dry processing. Such silver halide emulsions can be of the printout type—that is, they can produce a visible image by the direct action of light with no subsequent action required—or of the direct-print type—that is, they can form a latent image by high Intensity imagewise exposure and produce a visible image by subsequent low intensity light exposure. A heat stabilization step can be interposed between the exposure steps. In still another form the silver halide emulsion can be of a type which is designed for processing solely by heat.

Typical radiation-sensitive imaging means are disclosed in Research Disclosure, Vol, 17, 6 December 1978, Item 17643, paragraphs XXVI and XXVIIj and in Research Disclosure, Vol. 170, June 1978, Item 17029,

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Silver halide photographic elements can exhibit lateral Image spreading solely as a result o.f lateral reflection of exposing radiation within an emulsion layer. Lateral image spreading of this type is referred to in the art as halation, since the visual -effect can be to produce a halo around a bright object, such as an electric lamp, which is photographed. Other objects which are less bright are not surrounded by halos, but their photographic definition is sign- ificantly reduced by the reflected radiation. To overcome this difficulty conventional photographic elements commonly are provided with layers, commonly referred to as antihalation layers, of light absorb- - ing materials on a support surface which would other- wise reflect radiation to produce halation in an emul¬ sion layer. Such antihalation layers are commonly recognized to have the disadvantage ₍ that they must be entirely removed from the photographic element prior to viewing In most practical applications. A more fundamental disadvantage of antihalation layers which is not generally stated, since it is considered in¬ escapable, is that the radiation which is absorbed by the antihalation layer cannot be available to expose the silver halide grains within the emulsion. Another approach to reducing lateral image spread¬ ing attributable to light scatter in silver halide emulsions is to incorporate intergrain absorbers. Dyes or pigments similar to those described above for incorporation in the second support elements are commonly employed for this purpose. The disadvantage of. intergrain absorbers is that they significantly reduce the photographic speed of silver halide emul ^' sions. They compete with the silver halide grains in absorbing photons, and many dyes have a significant

desensitizing effect on silver halide grains. Like the absorbing materials in antihalation layers, it is also necessary that the Intergrain absorbers be removed from the silver halide emulsions for most practical applications, and this can also be a sign¬ ificant disadvantage.

When light strikes the photographic element 100 so that it enters one of the microvessels 108, a portion of the light can be absorbed immediately by the silver halide grains of the emulsion 116 while the remaining light traverses the microvessel without be¬ ing absorbed. If a given photon penetrates the emulsion without being absorbed, it will be redirect¬ ed by the white bottom wall 114 of the support 102 so that the photon again traverses at least a portion of the microvessel. This presents an additional opportunity for the photon to strike and be absorbed by a silver halide grain. Since it is recognized that the average photon strikes several silver halide grains before being absorbed, at least some of the exposing photons will be laterally deflected before they are absorbed by silver halide. The white lateral walls 110 of the support act to redirect laterally deflected photons so that they again traverse a portion of the silver halide emulsion within the same microvessel. This avoids laterally directed photons being absorbed by silver halide in adjacent microvessels. Whereas, in a conventional silver halide photographic element having a continuous emulsion coating on a white support, redirection of photons back into the emulsion by a white support is achieved only at the expense of significant lateral image spreading—e.g., halation, in the photographic element 100 the white support enhances the opportunity for photon absorption by the emulsion contained within the ^' microvessels while

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at the same time achieving a visually acceptable predefined limit on lateral image spread. The result can be seen photographically both in terms of improved photographic speed and contrast as well as sharper image definition. Thus, the advantages which can be gained by employing antihalation layers and intergrain absorbers in conventional photographic elements are realized in the photographic elements of the present invention without their use and with the additional surprising advantages of speed and contrast increase. Further, none of the disadvantages of anti¬ halation layers and intergrain absorbers are encounter¬ ed. For reasons which will become more apparent in discussing other forms of this invention, it should be noted, however, that the photographic elements of the present invention can employ antihalation layers and intergrain absorbers, if desired, while still retain¬ ing distinct advantages.

Most commonly silver halide photographic elements are intended to be processed using aqueous alkaline liquid solutions. When the silver halide emulsion contained in the microvessel 108 of the element 100 is of a developing out type rather than a dry process¬ ed printout, direct-print or thermally processed type, as illustrated above, all of the advantages describ¬ ed above are retained. In addition, having the emulsion within microvessels offers protection against lateral image spreading as a result of chemical re¬ actions taking place during processing. For example, microscopic inspection of silver produced by develop¬ ment reveals filaments of silver. The silver image in emulsions of the developing out type can result from chemical (direct) development in which image silver is provided by the silver halide grain at the

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site of silver formation or from physical develop¬ ment in which silver Is provided from adjacent silver halide grains or silver or other metal is provided from other sources. Opportunity for lateral image spreading in the absence of microvessels is particular¬ ly great when physical development is occurring. Even under chemical development conditions, such as where development is occurring In the presence of a silver halide solvent, extended silver filaments can be found. Frequently a combination of chemical and physical development occurs during processing. Having the silver developed confined within the microvessels circumscribes the areal extent of silver image spread¬ ing. The light-sensitive silver halide contained In the photographic elements can be processed following exposure to form a visible image by associating the silver halide with an aqueous alkaline medium in the presence of a developing agent contained in the medium or the element. Processing formulations and tech¬ niques are described in Research Disclosure, December 1978, Vol. 176, Item 17643, Paragraphs XIXA-B and XXA.

The developing agent can be Incorporated in the photographic element 100 in the silver halide emulsion 116. In other forms of the photographic elements, more specifically discussed below, the developing agent can be present in other hydrophilic colloid layers of the element adjacent to the silver halide emulsion. The developing agent can be added to the emulsion and hydrophilic colloid layers in the form of ^' a dispersion with a film- orming polymer in a water immiscible solvent, as illustrated by Dunn et al U.S. Patent 3,518,088, or as a dispersion with a polymer latex, as illustrated by Chem Research. Disclosure, Vol. 159, July 1977, Item 15930, and

Pupo et al Research Disclosure, Vol. 148, August 1976, Item 14850.

In a similar manner the photographic elements can contain development modifiers in the silver halide emulsion and other processing solution perme¬ able layers to either accelerate or restrain develop¬ ment as described in Research Disclosure, December 1978, Vol. 176, Item 17643, Paragraph XXI.

The photographic elements can contain or be processed to contain, as by direct development, an imagewise distribution of a physical development cat¬ alyst as described in Research Disclosure, December 1978, Vol. 176, Item 17643, Paragraph XXII.

In one specifically preferred form of the in- vention the photographic element is infectiously developed. The term "infectious" is employed in the art to indicate that silver halide development is not confined to the silver halide grain which provides the latent image site. Rather, adjacent grains which lack latent image sites are also developed because of- their proximity to the initially develop¬ able silver halide grain.

Infectious development of continuously coated silver halide emulsion layers is practiced in the art principally in producing high contrast photographic images for exposing lithographic plates. However, care must be taken to avoid unacceptable lateral image spreading because of the infectious development. In practicing the present invention the microvessels provide boundaries limiting lateral image spread. Since the vessels control lateral image spreading, the infectiousness or tendency of the developer to laterally spread the image can be as great and is, preferably, greater than in conventional infectious developers. In fact, one of the distinct advantages

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of infectious development Is that it can spread or integrate silver image development over the ^" entire area of the microvessel. This avoids silver image graininess within the microvessel and permits the microvessel ^' to be viewed externally as a uniform density unit rather than a circumscribed area, exhibit¬ ing an internal range of point densities.

The combination of microvessels and infectious development permits unique imaging results. For example, very high densities can be obtained in micro¬ vessels in which development occurs, since the infec¬ tious nature of the development drives the develop¬ ment reaction toward completion. At the same time, in other microvessels where substantially no develop- ment is initiated, very low density levels can be maintained. The result is a very high contrast photo¬ graphic image. It is known in the art to read out photographic images electronically by scanning a photographic element with a light source and a photo- sensor. The density sensed at each scanning location on the element can be recorded electronically and reproduced by conventional means, such as a cathode ray tube, on demand. It is well known also that digital electronic computers employed in recording and reproducing the information taken from the picture employ binary logic. In electronically scanning the photographic element 100, each microvessel can provide one scanning site. By using infectious development to produce high contrast, the photo- graphic image being scanned provides either a sub¬ stantially uniform dark area or a light area in each microvessel. In other words, the information taken from the photographic element is already in a binary logic form, rather than an analog form produced by continuous tone gradations. The photographic ele-

ments are then comparatively simple to scan electron¬ ically and are very simple and convenient to record and reproduce using digital electronic equipment. Techniques for infectious development as well as specific compositions useful in the practice of this invention are disclosed by James, The Theory of the Photographic Process, 4th Ed., Macmillan, pp. 420 and 421 (1977); Stauffer et al, Journal Franklin Institute, Vol. 238, p. 291 (.1944); and Beels et al, Journal Photographic Science, Vol. 23, p. 23 (.1975). In a preferred form a hydrazine or hydrazide is incorporated in the microvessel and/or in a developer and the developer containing a developing agent having a hydroxy group, such as a hydroquinone. Preferred developers of this type are disclosed in Stauffer et al U.S. Patent 2,419,974, Trivelli et al U.S. Patent 2,419,975 and Takada et al Belgian Patent 855,453.

The foregoing discussion of the use and advantages of the photographic element 100 has been by reference to preferred forms in which the support 102 is a white, reflection print. It can be used to form an image to be scanned electronically as has been described above. The element in this form can be used also as a master for reflection printing.

It is also contemplated that the support 102 can be transparent. In one specifically preferred form the underlying portion 112 of the support is trans¬ parent and colorless while the integral lateral walls contain a colorant therein, such as a dye, so that a substantial density is presented to light transmission through the lateral walls between surfaces 104 and 106

and between adjacent microvessels. In this form, the dyed walls perform the. function of an intergrain absorber or antihalation layer, as described above, while avoiding certain disadvantages which these - present. For ^' example, since the dye is in the lateral walls and not in the emulsion, dye desensitization of the silver halide emulsion is minimized, if not eliminat¬ ed. At the same time, It Is unnecessary to decolorize or remove the dye, as is normally undertaken when an anti- halation layer is provided.

In addition, this form of the support element 102 has unique advantages in use that have no direct counter¬ part in photographic elements having continuous silver halide emulsion layers. The photographic element when formed with a transparent underlying portion and dyed lateral walls is uniquely suited for use as a master in transmission printing. That is, after processing to form a photographic image, the photographic element can be used to control exposure of a photographic print element, such as a photographic element accord¬ ing to this invention having a white support, as described above, or a conventional photographic ele¬ ment, such as a photographic paper. In exposing the print element through the image bearing photographic element 100 the density of the lateral walls confines light transmission during exposure to the portions of the support 102 underlying the reaction microvessels. Where the microvessels are relatively transparent— i.e., minimum density areas, the print exposure is higher and in maximum density areas of the master, print exposure is lowest. The effect is to give a print in which highly exposed areas of the print element are confined to dots or spaced microareas. Upon subsequent processing t.o form a viewable print image the eye can fuse adjacent dots or micro-areas

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to give the visual effect of a continuous tone image. The effects of the nontransmission of exposing light through the lateral walls has been adequately described further above in connection with the support elements and the materials from which they can be formed. Since the eye is quite sensitive to small differences in minimum density, it is generally preferred that the lateral walls be substantially opaque. However, it is contemplated that some light can be allowed to pen- etrate the lateral walls during printing. This can have the useful effect, for instance, of bringing up the overall density in the print image. As mentioned above, it is also contemplated to displace the print element with respect to the master during printing so that a continuous print image is produced and any reduced density effect due to reduced transmission through the lateral walls is entirely avoided. Similar¬ ly, when the photographic element in this form is used to project an image, the lateral spreading of light during projection will fuse adjacent microvessel areas so that the lateral walls are not seen.

To illustrate still another variant form of the invention, advantages can be realized when the support element is entirely ^' transparent and colorless. In applications where the silver halide emulsion Is a developing out emulsion and is intended to be scanned pixel by pixel, as in the infectiously developed electron beam scanned application described above, control of lateral image spreading during development is, of course, independent of the transparency or coloration of the support element. However, even when the lateral walls are transparent and colorless, the proteotion against' light scattering between adjacent microvessels can still be realized in some instances, as discussed below in connection with

photographic element 200.

The photographic elements 200 through 1O00 share structural similarities with photographic elements 100 and are similar in terms of both uses and advantages. Accordingly,--the uses of these elements are discussed only by reference to differences which further illus¬ trate the invention.

The photographic element 200 differs from the element 100 in that the microvessels 208 have curved walls rather than separate bottom and side walls. This wall configuration is more convenient to form by certain fabrication techniques. It also has the advantage of being more efficient in redirecting exposing radiation back toward the center of the microvessel. For example, when the photographic element 200 is exposed from above (in the orientation shown), light striking the curved walls of the micro¬ vessels can be reflected inwardly so that it again traverses the emulsion 216 contained in the micro- vessel. When the support Is transparent and the ele¬ ment is exposed from below, a higher refraction index for the emulsion as compared to the support can cause light to bend inwardly. This directs the light toward the emulsion 216 within the microvessel and avoids scattering of light to adjacent microvessels.

A second significant difference in the construc¬ tion of the photographic element 200 as compared to the photographic element 100 is that the upper surface of the emulsion 216 lies substantially below the second major surface 206 of the support 202. The recessed position of the emulsion within the support provides it with mechanical protection against abrasion", kinking, pressure induced defects and matting. Although the element 100 brings the emulsion up to surface 106, it also affords protection

for the emulsion 116. In all forms of the photo¬ graphic elements of this invention, at least one component of the radiation-sensitive portion of the element is contained within the microvessels and add- itional protection is afforded against at least abrasion. It is specifically contemplated that the lateral walls of the support can perform the function of matting agents and that these agents can there¬ fore be omitted without encountering disadvantages to use, such as blocking. However, conventional , matting agents, such as illustrated by Paragraph XIII, Product Licensing Index, Vol. 92, Dec. 1971, Item 9232, can be employed, particularly In those forms of the photographic elements more specifically discussed below containing at least one continuous hydrophilic colloid layer overlying the support and the reaction microvessels thereof.

The photographic element 300 differs from photo¬ graphic element 100 in two principal respects. First, relatively thin extensions 314 of emulsion can extend between and connect adjacent pixels. Second, the support is made up of two separate support ele¬ ments 302 and 306. The photographic element 300 can be employed identically as photographic element 100. The imaging effect of the extensions 314 are in most instances negligible and can be ignored in use. In the form of the element 300 in which the first support element 302 is transparent and the second support element 308 is substantially light impenetrable exposure of the element through the first support element avoids exposure of the extensions 314. Where the _. emulsion is negative-working, this results in no silver density being generated between adjacent micro¬ vessels. Where the extensions are not of negligible thickness and no steps are taken to avoid their

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exposure, the performance of the photographic ele¬ ment combines the features of a continuously coated silver halide emulsion layer and an emulsion con¬ tained within a microvessel. The photographic element 00 differs from photo¬ graphic element 100 in two principal respects. First, the microvessel 408 is of relatively extended depth as compared with the microvessels 108, and, second, the radiation-sensitive portion of the element is divided into two separate components 4l6 and 418. These two differences can be separately employed. That is, the photographic element 100 could be modified to provide a second component like 4l8 over¬ lying surface 106 of the support, or the depth of the microvessels could be increased. These two differ¬ ences are shown and discussed together, since in certain preferred embodiments they are particularly advantageous when employed in combination.

While silver halide absorbs light, many photons striking a silver halide emulsion layer pass through without being absorbed. Where the exposing radiation is of a more energetic form, such as X-rays, the efficiency of silver halide In absorbing the expos¬ ing radiation is even lower. While increasing the thickness of a silver halide emulsion layer increases its absorption efficiency, there is a practical limit to the thickness of silver halide emulsion layers since thicker layers cause more lateral scattering of exposing radiation and generally result in greater lateral image spreading.

In a preferred form a radiation-sensitive silver halide emulsion forms the component confined within the microvessel 408. Thus lateral spreading is con¬ trolled not by the thickness of the silver halide or the depth of the microvessel, but by the lateral

walls of the microvessel. It is then possible to extend the depth of the microvessel and the thickness of the silver halide emulsion that is presented to the exposing radiation as compared to the thickness of continuously coated silver halide emulsion layers without encountering a penalty in terms of lateral image spreading. For example, the depth of the micro¬ vessels and the thickness of the silver halide emulsion can both be substantially greater than the width of the microvessels. In the case of a radiographic ele¬ ment intended to be exposed directly by X-rays it is then possible to provide relatively deep microvessels and to improve the absorption efficiency—i.e., speed, of the radiographic element. As discussed above, microvessel depths and silver halide emulsion thick¬ nesses can be up to 1000 microns or more. Microvessel depths of from about 20 to 100 microns preferred for this application are convenient to form by the same general techniques employed in forming shallower micro- vessels.

In one preferred form, the component 4l8 is an internally fogged silver halide emulsion. In this form, the components 4l6 and 4l8 can correspond to the surface-sensitive and internally fogged emulsions, respectively, disclosed by Luckey et al U.S. Patents

2,996,382, 3,397,987 and 3,705,858; Luckey U.S. Patent 3,695,881; Research Disclosure, Vol. 134, June 1975, Item 13452; Millikan et al U.S. Patent Office Defensive Publication T-0904017, April 1972 and Kurz Research Disclosure, Vol. 122, June 1974, Item 12233, all cited above. In a. preferred form, the surfa,ce-sensitive silver halide emulsion contains at least 1 mole per¬ cent iodide, typically from 1 to 10 mole percent iodide, based on total halide present as silver halide. The surface-sensitive silver halide is preferably a

silver bromoiodide and the internally fogged silver halide Is an internally fogged converted-halide which is at least 50 mole percent bromide and up to 10 mole percent Iodide (the remaining halide being chloride) based on total halide. Upon exposure and development of the Iodide containing surface-sensitive emulsion forming the component 416 with a surface developer, a developer substantially incapable of revealing an internal latent image Cquantitatively defined in the Luckey et al patents), iodide ions migrate to the component 4l8 and render the internally fogged silver halide grains developable by the surface developer. In unexposed pixels surface-sensitive silver halide is not developed, therefore does not release iodide ions, and the Internally fogged silver halide emulsion component in these pixels cannot be developed by the surface developer. The result is that the silver Image density produced by the radiation-sensitive emulsion component 4l6 is enhanced by the additional density produced by the development of the internally fogged silver halide grains without any significant effect on minimum density areas. It is, of course, unnecessary that the component 4l6 be of extended thickness in order to achieve an increase n density using the component 4l8, but when both features are present in combination a particularly fast and efficient photographic element is provided which is excellently suited to radiographic as well as other photographic applications. In variant forms of the invention the surface-sensitive and. internally fogged emulsions can be blended rather than coated in separate layers. When blended, It is preferred that the emulsions be located entirely within the microvessels. In one preferred form of the photographic element 500, the first support element 502 Is both transparent

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and colorless. The second support element 508 is relatively defor able and contains a dye, such as a yellow dye. The components 516 and 518 can correspond to the surface-sensitive and internally fogged silver halide emulsion components 4l6 and 4l8, respectively, described above. For this specific embodiment only, the spectral sensitivity of the surface-sensitive ^* emulsion is limited to the blue region of the visible spectrum. The layer 515 can be one or a combination of transparent, colorless conventional subbing layers. Conventional subbing layers and materials are dis¬ closed in the various patents cited above in connection with conventional photographic support materials. In one exemplary use the radiation-sensitive emulsion component 1 can be exposed through the transparent first support element 502 and the under¬ lying portion 512 of the second support element 508. While the second support element contains a dye to prevent lateral light scattering through the lateral walls 510, the thickness of the underlying portion of the second support element is sufficiently thin that it offers only negligible absorption of incident light. As another alternative the element in this form can be exposed through the second emulsion compon- ent 518 instead of the support, if desired.

In an alternative form of the photographic element 500 the emulsion component 516 can correspond to the emulsion component 4l8 and the emulsion component 518 can correspond to the emulsion component 4l6, In this form the radiation-sensitive silver haϋde emulsion is coated as a continuous layer while the internally fogged silver halide emulsion is present in the micro¬ vessel 514. Exposure through the support exposes only the portion of the radiation-sensitive emulsion component 518 overlying the microvessel, since the

dye in the lateral walls 510 of the second support element effectively absorbs light while the under¬ lying portion 12 of the second support element is too thin to absorb light effectively. Lateral image spreading in the continuous emulsion component is controlled by limiting its exposure to the area subtended by the microvessel. Lateral image spread¬ ing by the internally fogged emulsion is limited by the walls of the microvessel. In still another form of the photographic element 500 the first and second support elements can be form¬ ed from any of the materials, including colorless transparent, white and absorbing materials. The layer 515 can be chosen to provide a reflective surface, such as a mirror surface. For example, the layer 515 can be a vacuum vapor deposited layer of silver or another photographically compatible metal which is preferably overcoated with a thin transparent layer, such as a hydrophilic colloid or a film-forming polymer. ^> χhe components 516 and 518 correspond to the components 416 and 4l8, respectively, so that the only radiation- sensitive material is confined within the microvessel 514.

In exposing the element in this form from the emulsion side the reflective surface redirects light within the microvessel so that light is either absorbed by the emulsion component 516 on its first pass through the microvessel or is redirected so that it traverses the microvessel one or more additional times, thereby increasing its chances of absorption. Upon develop¬ ment image areas appear as dark areas on a reflective background. If a dye image is produced, as discussed below, the developed silver and silver mirror can be concurrently removed by bleaching so that a dye image on a typical white reflective or colorless transparent

support is produced.

A very high contrast photographic element can be achieved by selectively converting the reflecting surface within the microvessels to a light absorbing form. For Instance, if a developer inhibitor releas¬ ing (DIR) coupler of the type which releases an organic sulfide is incorporated in the emulsion within the microvessels and development Is undertaken with a color developing agent, the color developing agent can react with exposed silver halide to form silver and oxidized color developing agent. The oxidized color developing agent can then couple with the DIR coupler to release an organic sulfide which is capable of reacting with the silver reflecting surface in the microvessels to convert silver to a black silver sulfide. This Increases the maximum density obtainable in the microvessels to convert silver to a black silver sulfide. This increases the maximum density obtainable in the microvessels while leaving the reflecting surface unaffected in minimum density areas. Thus, an increased contrast can be achieved by this approach. Specific DIR couplers and color developing agents are described below in connection with dye imaging. Metals other than silver which will react with the released organic sulfide to form a metal sulfide can be alternatively employed.

In the foregoing discussion of elements 400 and 500 two component radiation-sensitive means 4l6 and 4l8 or 516 and 518 are described in which the com- ponents work together to increase the maximum density obtainable. In another form the components can be chosen so that they work together to minimize the density ^' obtained in areas where silver halide is the radiation-sensitive component developed, For example, If one of the components is a light-

sensitive silver halide emulsion which contains a DIR coupler and the other component is a spontaneously developable silver halide emulsion (e.g., a surface or internally fogged emulsion) , imagewise exposure and processing causes the light-sensitive emulsion to begin development as a function of light exposure. As this emulsion is developed It produces oxidized developing agent which couples with the DIR coupler, releasing development inhibitor. The inhibitor reduces further development of adjacent portions of the otherwise spontaneously developable emulsion. The spontaneously developable emulsion develops to a maximum density in areas where development inhibitor is not released. By using a relatively low covering power light-sensitive emulsion (e.g., a relatively coarse, high-speed emulsion), and a high covering power spontaneously developable emulsion, it is possible to obtain images of increased contrast. The DIR coupler can be advantageously coated in the micro- vessels or as a continuous layer overlying the micro¬ vessels along with the radiation-sensitive emulsion, and the spontaneously developable emulsion can be located in the alternate position. In this arrange¬ ment the layer 515 is not one which is darkened by reaction with an inhibitor, but can take the form, if present, of a subbing layer, if desired. The radiation-sensitive emulsion can be either a direct- positive or negative-working emulsion. The developer chosen is one which is a developer for both the radiation-sensitive and spontaneously developable emulsions. Instead of being coated in a separate layer, the two emulsions can be blended, if desired, and ^' both coated in the microvessels.

It is conventional to form photographic elements with continuous emulsion coatings on opposite sur-

faces of a planar transparent film suppor . For example, radiographic elements are commonly prepared in this form. In a typical- radiographic application fluorescent screens are associated with the silver halide emulsion layers on opposite surfaces of the support. Part of the X-rays incident during exposure are absorbed by one of the fluorescent screens. This stimulates emission by the screen of light capable of efficiently producing a latent image in the adjacent emulsion layer. A portion of the incident X-rays pass through- the element and are absorbed by the remaining screen causing light exposure of the adjacent emulsion layer on the opposite surface of the support. Thus two superimposed latent images are formed in the emulsion layers on the opposite surfaces of the support. When light from a screen causes exposure of the emulsion layer on the opposite surface of the support, this is referred to in the art as crossover. Crossover is generally minimized since it results in loss of image definition.

The photographic element 900 is well suited for applications employing silver halide emulsion layers on opposite surfaces of a transparent film support. The alignment of the reaction microvessels 908A and 908B allows two superimposed photographic images to be formed.

As an optional feature to reduce crossover, selective dying of the lateral walls 910A and 910B can be employed as described above. This can be relied upon to reduce scattering of light from one microvessel to adjacent microvessels on the same side of the support and adjacent, nonaligned microvessels on the opposite side cf the support . Another tech¬ nique to reduce crossover is to color the entire support -902 with a dye which can be bleached after

exposure and/or processing to render the support substantially transparent and colorless. Bleachable dyes suited to this application are illustrated by Stur er U.S. Patent 4,028,113 and Krueger U.S. Patent ^• 4,111,699. A..conventional approach in the radio¬ graphic art is to undercoat silver halide emulsion layers to reduce crossover. For instance Stappen U.S. Patent 3,923,515 teaches to undercoat faster silver halide emulsion layers with slower silver halide emulsion layers to reduce crossover. In applying such an approach to the present invention a slower silver halide emulsion 916 can be provided in the microvessels. A faster silver halide emulsion layer can be positioned in an overlying relationship either in the microvessels or continuously coated over the reaction microvessels on each major surface 904 and 906 of the support. Instead of employing a slower silver halide emulsion in the microvessels an internally fogged silver halide emulsion can be placed in the microvessels as is more specifically described above. The internally fogged silver halide emulsion is capable of absorbing crossover exposures while not being affected in its photographic performance, since It is not responsive to exposing radiation. To illustrate a diverse photographic application the photographic element 900 can be formed so that the silver halide emulsion in the microvessels 908B is an imaging emulsion while another silver halide emulsion can be Incorporated in the microvessels 908A. The two emulsions can be chosen to be oppositely working. That is, if the emulsion in the microvessels 908B is negative-working, then the emulsion in the micro¬ vessels 908A is positive-working. Using an entirely trans¬ parent support element 902, exposure of the element from above, in the orientation shown in Figure 9, results in forming a primary photographic latent image in the emulsion contained In the

908B. The emulsion contained in the microvessels 908A is also exposed, but to some extent the light exposing it will be scattered in passing through the overlying emulsion, microvessels and support portions. Thus, the emulsion in the microvessels

9θ8B in-this instance can be used'to form an unsharp mask for the overlying emulsion. In one optional form specifically contemplated an agent promoting in¬ fectious development can be incorporated in the emulsion providing the unsharp mask. This allows image spreading within the microvessels, but the lateral walls of the microvessels limits lateral image spreading. Misalignment of the reaction vessels 90δA and 908B can also be relied upon to de- crease sharpness in the underlying emulsion. An add¬ itional approach is to size the microvessels 908A so that they are larger than the microvessels 908B. Any combination of these three approaches can, if desired, be used. It is recognized in the art that unsharp masking can have the result of increasing image sharpness, as discussed in Mees and James, The Theory of the Photographic Process, 3rd Ed. , Mac illan, 1966, p. 495. Where the photographic element is used as a printing master, any increase in minimum density attributable to masking can be eliminated by adjustment of the printing exposure.

In the photographic element 1000 the lenticular surface 1004 can have the effect of obscuring the lateral walls 1010 separating adjacent microvessels 1008. Where the lateral walls are relatively thick, as where very small pixels are employed, the lenticular surface can laterally spread light passing through the microvessel portion of each pixel so that the walls are either not seen or appear thinner than they actually are. In this use the support 1002 is

colorless and transparent,, .although the lateral walls 1010 can be dyed, if desired. It is, of course, recognized that the use of lenticular surfaces on supports of photographic elements having continuously coated radiation-sensitive layers have been employed to obtain a variety of effects, such as color separa¬ tion, restricted exposure and stereography, as illust¬ rated by Cary U.S. Patent 3,316,805, Brunson et al U.S. Patent 3,148,059, Schwan et al U.S. Patent 2,856,282, Gretener U.S. Patent 2,794,739, Stevens U.S. Patent 2,543,073 and Winnek U.S. Patent 2,562,077. The photographic element 1000 can also provide such conventional effects produced by len¬ ticular surfaces, if desired. The photographic elements and the techniques described above for producing silver images can be readily adapted to provide a colored image through the use of dyes. In perhaps the simplest approach to obtaining a projectable color image a conventional dye can be incorporated in the support of the photo¬ graphic element, and silver image formation under¬ taken as described above. In areas where a silver image is formed the element is rendered substantially incapable of transmitting light therethrough, and in the remaining areas light is transmitted correspond¬ ing in color to the color of the support. In this way a colored image can be readily formed. The same effect can also be achieved by using a separate dye filter layer or element with a transparent support element. Where the support element or portion defining the lateral walls is capable of absorbing light used for projection, an image pattern of a chosen color can be formed by light transmitted through microvessels in inverse proportion to the silver present therein.

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The silver halide photographic elements can be used to form dye images therein through the selective destruction or formation of dyes as described in Research Disclosure, December 1978, Vol. 176, Item 17643, Paragraph VII.

Dye images can be formed or amplified by processes which employ in combination with a dye-image generating reducing agent an inert transition metal ion complex oxidizing agent, as illustrated by Bissonette U.S. Patents 3,748,138, 3,826,652, 3,862,842 and 3,989,526 and Travis U.S. Patent 3,765,891 and/or a peroxide oxidizing agent, as illustrated by Matejec U.S. Patent 3,674,490, Research Disclosure, Vol. 116, December 1973, Item II66O, and Bissonette Research Disclosure, Vol. 148, August 1976, Items 14836, 14846 and 14847. The photographic elements can be particularly adapted to form dye images by such processes, as illustrated by Dunn et al U.S. Patent 3,822,129, Bissonette U.S. Patents 3,834,907 and 3,902,905, Bissonette et al U.S. Patent 3,847,619 and Mowrey U.S. Patent 3,904,413.

It is common practice in forming dye images in silver halide photographic elements to remove the silver which is developed by bleaching. In some instances the amount of silver formed by development is small in relation to the amount of dye produced, particularly in dye image amplification referred to above, and silver bleaching is omitted without sub¬ stantial visual effect. In still other applications the silver image is retained and the dye image is intended to enhance or supplement the density provided by the image silver. In the case of dye enhanced silver imaging it is usually preferred to form a neutral dye. Neutral dye-forming couplers useful for this purpose are disclosed' in Research Disclosure, vol. 162, October 1977, Item 16226. The enhancement

of silver images with dyes in photographic, elements intended for thermal processing is disclosed In Research Disclosure, Vol. 173, September 1973, Item 17326, and Houle U.S. Patent 4,137,079. In the -photographic elements described above the dye image supplements or replaces the silver image by employing in combination with the photo¬ graphic elements conventional color photographic element components and/or processing steps. For example, dye images can be produced in the micro¬ vessels of the elements 100 through 1000 or in the imaging components 4l8 and 18 by modifying the pro¬ cedures for use described above in view of current knowledge in the field of color photography. Accord- ingly, the following detailed description of dye image formation is directed to certain unique, illustrative combinations, particularly those In which the radiation-sensitive portion of the photo¬ graphic element is divided into two components. In one highly advantageous form of the Invention having unique properties the photographic element 400 can be formed so that a radiation-sensitive silver halide emulsion component 416 is contained within the microvessel while a dye image providing component _. 418 overlies the microvessel. The dye image providing component is chosen from among conventional components capable of forming or destroying a dye in proportion to the amount of silver developed in the microvessel. Preferably the dye image providing component contains a bleachable dye useful in a silver-dye-bleach process or an incorporated dye-forming coupler. In an alter¬ native form the bleachable dye or dye-forming coupler can' ^" be present in the emulsion component 4l6, and the separate imaging component 4l8 can be omitted, When a photon is absorbed by a silver halide

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grain a hole-electron pair is created. Both the electron and hole can migrate through the crystal lattice, but they are generally precluded in an emulsion from migrating to an adjacent .silver halide grain . While holes are employed in surface fogged emulsions to provide direct-positive images, in the more typical negative-working silver halide emulsions which are initially unfogged the electrons generated by the absorbed photons are relied upon to produce an image. The electrons provide the valence electrons given up by silver in the crystal lattice to form metallic silver. It has been post¬ ulated that when four or more metallic silver atoms are formed at one location within the crystal a developable latent image site is created.

It is known in silver halide photography and is apparent from the mechanism of latent image form¬ ation described above that the speed of silver halide emulsions generally increases as a function of the average silver halide grain size. It is also known that larger silver halide grains produce images exhibiting greater graininess. Ordinary silver halide photographic elements employ silver halide grains whose size is chosen to strike the desired balance between speed and graininess for the intended end use. For example, in forming photographic images intended to be enlarged many times, graininess must be low. On the other hand, radiographic elements generally employ coarse silver halide grains in order to achieve the highest possible speeds consistent with necessary image resolution. It is further known in the photographic arts that techniques which increase the speed of a photographic element without increasing image graininess can be used to decrease

image graininess or can be traded off in element design to improve some combination of speed and grain¬ iness. Conversely, techniques which improve Image graininess without decreasing photographic speed can be used to improve speed or to improve a combination of speed and graininess.

It has been recognized and reported in the art that some photodetectors exhibit detective quantum efficiencies which are superior to those of silver halide photographic elements. A study of the basic properties of conventional silver halide photographic elements shows that this is largely due to the binary, on-off nature of individual silver halide grains, rather than their low quantum sensitivity. This is discussed, for example, by Shaw, "Multilevel Grains and the Ideal Photographic Detector", Photographic Science and Engineering, Vol. 16, No. 3, May-June 1972, pp. 192-200. What is meant by the on-off nature of silver halide grains is that once a latent image site is formed on a silver halide grain, it becomes entire¬ ly developable. Ordinarily development is Independent of the amount of light which has struck the grain above a threshold, latent image forming amount. The silver halide grain produces exactly the same product upon development whether it has absorbed many photons and formed several latent image sites or absorbed only the minimum number of photons to produce a single latent image site.

The silver halide emulsion component 4l6 can employ very large, very high speed silver halide grains. Upon exposure by light or X-rays, for instance, latent image sites are formed in and on the silver halide grains. Some grains may have only one latent image site, some many and some none. However, the number of latent Image sites formed within a single

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microvessel 4.08 is related to the amount of expos¬ ing radiation. Because the silver halide grains are relatively coarse, their speed is relatively high. Because the number of latent Image sites within each microvessel'-Is directly related to the amount of exposure that the microvessel has received, the pot¬ ential is present for a high detective quantum efficiency, provided this information is not lost in development. in a preferred form each latent image site is then developed to increase its size without complete¬ ly developing the silver halide grains. This can be undertaken by interrupting silver halide development at an earlier than usual stage, well before optimum development for ordinary photographic applications has been achieved. Another approach is to employ a DIR coupler and a color developing agent. The in¬ hibitor released upon coupling can be relied upon to prevent complete development of the silver halide grains. In a preferred form of practicing this step self inhibiting developers are employed. A self- inhibiting developer is one which initiates develop¬ ment of silver halide grains, but itself stops development before the silver halide grains have been entirely developed. Preferred developers are self-inhibiting developers containing p-phenylene- diamines, such as disclosed by Neuberger et al, "Anomalous Concentration Effect: An inverse Relation¬ ship Between the Rate of Development and Developer Concentration of Some p_-Fhenylenediamines", Photo¬ graphic Science and Engineering, Vol. 19, No, 6, Nov-Dec 1975, pp. 327-332. Whereas with interrupted development and development in the presence of DIR couplers silver halide grains having a longer develop- ment induction period than adjacent developing grains can be entirely precluded from development, the use

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of a self-inhibiting developer has the advantage that development of an individual silver halide grain is not inhibited until after some development of that grain has occurred. After development enhancement of the latent image sites, there is present in each microvessel a plurality of silver specks. These specks are proportional in size and number to the degree of exposure of each microvessel. The specks-, however, present a random pattern within each microvessel and are further too small to provide a high density. The next objective is to produce in each pixel a dye density which is substantially uniform over the entire area of Its microvessel. Inasmuch as the preferred self-inhibiting developers contain color developing agents, the oxidized developing agent produced can be reacted with a dye-forming coupler to create the dye image. However, since only a limited amount of silver halide is developed, the amount of dye which can be formed in this way is also limited. An approach which removes any such limitation on -maximum dye density formation, but which retains the proportionality of dye density in each pixel to the degree of exposure is to employ a silver catalyzed oxidation-reduction reaction using a peroxide or transition metal ion complex as an oxidizing agent and a dye-image-generat¬ ing reducing agent, such as a color developing agent, as illustrated by the patents cited above of Bissonette, Travis, Dunn et al, Matejec and Mowrey and the accompany- Ing publications. In these patents it is further dis¬ closed that where the silver halide grains form sur¬ face latent Images the- latent images can themselves provide ^* sufficient silver to catalyze a dye image amplification reaction. Accordingly, the step of en- hancing the latent image by development is not absolute¬ ly essential, although it is preferred. In the prefer-

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red form any visible silver remaining in the photo¬ graphic element after forming the dye image is removed by bleaching, as is conventional in color photography. The resulting photographic image is a dye image in which each ^" pixel in the array exhibits a dye density which is internally uniform and proportional to the amount of exposing radiation which has been supplied to the pixel. The regular arrangement of the pixels serves to reduce the visual sensation of grain¬ iness. The pixels further supply more information about the exposing radiation than can be obtained by completely developing the silver halide grains contain¬ ing latent image sites. The result is that the detective quantum efficiency of the photographic element is quite high. Both high photographic speeds and low graininess are readily obtainable. Where the dye is formed in the microvessels rather than in an overcoat, as shown, further protection against lateral image spreading is obtained. All of the advantages described above in connection with silver imaging are, of course, also obtained in dye imaging and need not be described again in detail. Further, while this preferred process of dye imaging has been discussed referring specifically to the photographic element 400, it is appreciated that it can be practiced with any of the photographic elements shown ^" and described above.

Referring to the photographic element 500, in one preferred form the component 518 can be a silver halide emulsion layer and the component 516 can be a dye image-forming component. In conventional color photo¬ graphic elements the radiation-sensitive portion of the element is commonly formed of layer units, each comprised of a silver halide emulsion layer and an adjacent hydrophilic colloid layer containing an incorporated dye-forming coupler or bleachable dye.

The components 518 and 516 in terms of composition can be identical to these two conventional color photographic element layer unit coatings.

A significant difference between the photo- graphic element 500 and a photographic element having a continuously coated dye image component is that the microvessel 514 limits lateral image spreading of the imaging dye. That is, it can laterally limit the chemical reaction which is forming the dye, where a coupler is employed, or bleaching the dye, in the case of a silver-dye-bleach process. Since the silver image produced by exposing and developing the element can be bleached from the element, it is less impor¬ tant to image definition that silver development is not similarly laterally restrained. Further, it is recognized by those skilled in the art that greater lateral spreading typically occurs in dye imaging than when forming a silver image in a silver halide photo¬ graphic element. The advantages of this component relationship is also applicable to photographic element 400.

It has been recognized in the art that additive multicolor images can be formed using a continuous, panchromatically sensitized silver halide emulsion layer which is exposed and viewed through an array of additive primary (blue, green and red) filter areas. Exposure through an additive primary filter array allows silver halide to be selectively develop¬ ed, depending upon the pa tern of blue, green and red light passing through the overlying filter areas.

If a negative-working silver halide emulsion is employ¬ ed, the multicolor image obtained is a negative of the exposure image, and if a direct-positive emulsion is employed, a positive of the exposure image is obtained. Additive primary dye multicolor images can

be reflection viewed, but .are best suited for project- Ion viewing, since they require larger amounts of light than conventional subtractive primary multi¬ color images to obtain comparable brightness. Dufay ^' U.S. Patent 1,003,720 teaches forming an additive multicolor filter by alternatively print¬ ing two-thirds of a filter element with a greasy material to leave uncovered an array of areas . An additive primary dye is imbibed into the filter element in the uncovered areas. By repeating the sequence three times the entire filter area is covered by an interlaid pattern of additive primary filter areas. Rogers U.S. Patent 2,681,857 illustrates an improvement on the Dufay process of forming an additive primary multicolor filter by printing. Rheinberg U.S. Patent 1,191,034 obtains essentially a similar effect by using subtractive primary dyes (yellow, magenta and cyan) which are allowed to laterally diffuse so that two subtractive primaries are fused in each area to produce an additive primary dye filter array.

More recently, in connection with semiconductor sensors, additive primary multicolor filter layers have been developed which are capable of defining an interlaid pattern of areas of less than 100 microns on an edge and areas of less than 10 4 cm2. One approach is to form the filter layer so that it contains a dye mordant. In this way when an inter¬ laid pattern of additive primary dyes is introduced to complete the filter, mordanting of the dyes reduces lateral dye spreading. Filter layers comprised of mordanted dyes and processes for their preparation are disclosed in Research Disclosure, Vol. 157, May 1977, Item 15705. Examples of mordants and mordant layers useful In preparing such filters are described in the following: Sprague et al U.S.

Patent 2,548,564; We.yerts U.S. Patent 2,5.48,575; Carroll et al U.S. Patent 2,675,316; Yutzy et al U.S. Patent 2,713,305; Saunders et al U.S. Patent 2,756,149; Reynolds et al U.S. Patent 2,768,078; Grey et al U.S. Patent 2,839 _* 01; Minsk U.S. Patents 2,882,156 and 2,945,006; Whitmore et al U.S. Patent 2,940,849; Condax U.S. Patent 2,952,566; Mader et al U.S. Patent 3,016,306; Minsk et al U.S. Patents 3,048,487 and 3,184,309; Bush U.S. Patent 3,271,147; Whitmore U.S. Patent 3,271,148; Jones et al U.S. Patent 3,282,699; Wolf et al U.S. Patent 3, 08,193; Cohen et al U.S. Patents 3,488,706, 3,557,066, 3,625,694, 3,709,690, 3,758,445, 3,788,855, 3,898,088 and 3,944,424; Cohen U.S. Patent 3,639,357; Taylor U.S. Patent 3,770,439; Campbell et al U.S. Patent 3,958,995; and Ponticello et al Research Disclosure, Vol. 120, April 1974, Item 12045. Preferred mordants for forming filter layers are more specifically disclosed by Research Disclosure, Vol. 167, March 1978, Item 16725. Another approach to forming an additive primary multicolor filter array is to incorporate photobleach- able dyes In a filter layer. By exposure of the element with an image pattern corresponding to the filter ^" areas to be formed dye can be selectively bleached in exposed areas leaving an interlaid pattern of additive primary filter areas. The dyes can thereafter be treated to avoid subsequent bleach¬ ing. Such an approach is disclosed by Research Dis¬ closure, Vol. 177, January 1979, Item 17735. While it is recognized that conventional additive primary multicolor filter layers can be employed in connection with the photographic elements 1Q0 through 1000 to form additive multicolor images in accordance with this invention, it Is preferred to form additive primary multicolor filters comprised of an interlaid

pattern of additive primary dyes in an array of micro¬ vessels. The microves.sels offer the advantages of providing a physical barrier between adjacent additive primary dye areas thus avoiding lateral spreading, edge commingling of the dyes and similar disadvantages. The microvessels can be identical in size and con¬ figuration to those which have been described above. In Figures 11A and 11B an exemplary filter ele¬ ment 1100 of this type is illustrated which is similar to the photographic element 100 shown in Figures 1A and IB, except that instead of radiation-sensitive material being contained in the microvessels 1108, an interlaid pattern of green, blue and red dyes is provided, indicated by the letters G, B and R, respectively. The dashed line 1120 surrounding an adjacent triad of green, blue and red dye-containing microvessels defines a single pixel of the filter element which is repeated to make up the interlaid pattern of the element. It can be seen that each microvessel of a single pixel is equidistant from the two remaining microvessels thereof. Looking at an area somewhat larger than a pixel, it can be seen that each microvessel containing a dye of one color is surrounded by microvessels containing dyes of the remaining two colors. Thus, it is easy for the eye to fuse the dye colors of the adjacent microvessels or, during projection, for light passing through adjacent microvessels to fuse. The underlying portion 1112 of the support 1102 must be transparent to permit projection viewing. While the lateral walls 1110 of the support can be transparent also, they are preferably opaque (e.g., dyed), particularly for -proj-ection viewing,: as has been discussed above in connection with element 100. An exemplary filter element has been illustrated as a variant of photo-

graphic element 100, but it is appreciated that corresponding filter element variants of photographic elements 200 -through 1000 are also contemplated. Placing the red, green and blue additive primary dyes in microvessels offers a distinct advantage in achieving the desired lateral relationship of individual filter areas. Although lateral dye spreading can occur in an individual microvessel which can be advantageous in providing a uniform dye density within the micro- vessel, gross dye spreading beyond the confines of the microvessel lateral walls Is prevented.

In Figure 11C the use of filter element 1100 in combination with photographic element 100 is illustrat¬ ed. The photographic element contains in the reaction microvessels 108 a panchromatically sensitized silver halide emulsion 116. The microvessels 1108 of the filter element are aligned (i.e. registered) with the microvessels of the photographic element. Exposure of the photographic element occurs through the blue, green and red dyes of the aligned filter element.

The filter element and the photographic element can be separated for processing and subsequently realigned for viewing or further use, as in forming a photographic print ^' . The second alignment can be readily accomplish- ed by viewing the image during the alignment procedure. It is possible to join the filter element and photo¬ graphic element by attachment along one or more edges so that, once positioned, the alignment between the two elements is subsequently preserved. Where the filter and photographic elements remain In alignment processing fluid can be dispensed between the elements in the-same manner as in in-camera image transfer processing. In order to render less exacting the process of initial alignment of the filter and photo- graphic element microvessels, the microvessels of

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the filter element can be substantially larger in area than those of the photographic element and can, if desired, overlie more than one of the microvessels of the photographic element. Complementary edge con- figurations, ^" riot shown, can be provided on the photo¬ graphic and filter elements to facilitate alignment. A variant form which insures alignment of the silver halide and the additive primary dye microvessels is achieved by modifying element 900 so that silver halide remains in microvessels 908A, but additive primary dyes are present in microvessels 908B.

By combining the functions of the filter and photographic elements in a single element any in¬ conveniences of registering separate filter and photo- graphic element microvessels can be entirely obviated. Photographic elements 1200, 1300 and 1400 illustrate forms of the invention in which both silver halide emulsion and filter dye are positioned in the same element microvessels. These elements appear in plan view identical to element 1100 In Figure 11A. The views of elements 1200, 1300 and 1400 shown in Figures 12, 13 and 14, respectively, are sections of these elements which correspond to the section shown in Figure 11B of the element 1100. The photographic element 1200 is provided with microvessels 1208. In the bottom portion of each microvessel is provided a filter dye, indicated by the letters B, G and R. A panchromatically sensitized silver halide emulsion 1216 is located in the micro- vessels so that it overlies the filter dye contained therein.

The photographic element 1300 is provided with microvessels 1308. In the microvessels designated B a blue filter dye is blended with a blue sensitized silver halide emulsion. Similarly in the micro-

vessels designated G and R a green filter dye is blended with a green sensitized silver halide emulsion and a red filter dye is blended with a red sensitized silver halide emulsion, respectively. In this form the silver ha-lide emulsion is preferably chosen so that it has negligible native blue sensitivity, since the blended green and red filter dyes offer substantial, but not complete, filter protection against exposure by blue light of the emulsions with which they are associated. In a preferred form silver chloride emulsions are employed, since they have little native sensitivity to the visible spectrum.

The photographic element 1400 is provided with a transparent first support element 1402 and a yellow second support element l4θδ. The microvessels B extend from the outer major surface 1412 of the second support element to the first support element. The microvessels G and R have their bottom walls spaced from the first support element. The contents of the microvessels can correspond to those of the photo¬ graphic element 1300, except that the silver halide emulsions need not be limited to those having negligible blue sensitivity in order to avoid unwanted exposure of the G and R microvessels. For example, iodide containing silver halide emulsions, such as silver bromoiodides, can be employed. The yellow color of the second support element allows blue light to be filtered so that it does not reach the G and R micro¬ vessels in Objectionable amounts when the photographic element is exposed through the support. The yellow color of the support can be imparted and removed for viewing using materials and techniques conventionally employed in connection with yellow filter layers, such as Carey Lea silver and bleachable yellow filter dye layers, in multilayer multicolor photographic elements.

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The yellow color of the support can also be incorporat¬ ed by employing a photobleachable dye. Photobleaching is substantially slower than imaging exposure so that the yellow color remains present during imagewise exposure, but .after processing handling in roomlight or intentional uniform light exposure can be relied upon to bleach the dye. Photobleachable dyes which can be incorporated into supports are disclosed, for example, by Jenkins et al U.S. Reissue Patent 28,225 and the Sturmer and Kruegor U.S. Patents cited above. The optimum approach for imparting and removing yellow color varies, of course, with the specific support element material chosen.

While the elements 1100 and 1400 illustrated in connection with additive primary multicolor Imaging confine both the imaging and filter materials to the microvessels, it is appreciated that continuous layers can be used in combination in various ways . For example, the filter element 1100 can be overcoated with a panchromatically sensitized silver halide emulsion layer. Although the advantages of having the emulsion in the microvessels are not achieved, the advantages of having the filter elements in microvessels are retained. In the photographic elements 1200, 1300 and 1400 it is specifically contemplated that the radiation-sensitive portion of the photographic element can be present as two components, one contained in the microvessels and one in the form of a layer overlying the microvessels, as has been specifically discussed above in connection with photographic elements 400 and 50 ^" 0.

In one preferred additive primary multicolor imag¬ ing application one or a combination of bleachable leuco dyes are incorporated in the silver halide emulsion or a contiguous component. Suitable bleach-

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able leuco dyes useful In silver-dye-bleach processes have been identified above in connection with dye imaging. The leuco dye or combination of leuco dyes are chosen to yield a substantially neutral density. In a specifically preferred form the leuco dye or dyes are located in the reaction microvessels . The silver halide emulsion that is employed ^' in combination with the leuco dyes is a negative-working emulsion. Upon exposure of the silver halide emulsion through the filter element silver halide is rendered developable in areas where light penetrates the filter elements. The silver halide emulsion can be developed to produce a silver Image which can react with the dye to destroy it using the silver-dye-bleach process, described above. Upon contact with alkaline developer solution, the leuco dyes are converted to a colored form uniformly within the element. The silver-dye- bleach step causes the colored dyes to be bleached selectively in areas where exposed silver halide has been developed to form silver. The developed silver which reacts with dye is reconverted into silver halide and thereby removed, although subsequent silver bleaching can be undertaken, if desired. The colored dye which is not bleached is of sufficient density to prevent light from passing through the filter elements with which it Is aligned.

When exposure and viewing occur through an add¬ itive primary filter array, the result is a positive additive primary multicolor dye image. It is advan- tageous that a direct-positive multicolor image is obtained with a single negative-working silver halide emulsion. Having the dye in its leuco form during silver halide exposure avoids any reduction of emulsion speed by reason of competing absorption by the dye. Further, the use of a negative-working emulsion permits

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very high emulsion speeds to be readily obtained. By placing both the imaging and filter dyes in the micro¬ vessels registration is assured and lateral image spreading is entirely avoided. Another-preferred approach to additive primary multicolor imaging is to use as a redox catalyst an image-wise distribution of silver made available by silver halide emulsion contained in the microvessels to catalyze a neutral dye Image producing redox re- action in the microvessels. The formation of dye images by such techniques are described above in connection with dye imaging. This approach has the advantage that very low silver coverages are required to ^' produce dye images. The silver catalyst can be sufficiently low in concentration that it does not limit transmission through the filter elements. An advantage of this approach is that the redox reactants can be present in either the photographic element or the processing solutions or some combination thereof. So long as redox catalyst is confined to the micro¬ vessels lateral image spreading can be controlled, even though the dye-forming reactants are- coated in a continuous layer overlying the microvessels. In one form a blend of three different subtractive primary dye-forming reactants are employed. However, only a single subtractive primary dye need be formed in a microvessel in order to limit light transmission through the filter and microvessel. For example, forming a cyan dye in a microvessel aligned with a red filter element is sufficient to limit light transmission.

To illustrate a specific application, in any one of the arrangements illustrated in Figures 11C, 12., 13 and 1 ^" 4, the silver halide emulsion contained in the microvessels is exposed through the filter elements. Where the silver halide emulsion forms a surface latent

Image, this can be enough silver to act as a redox catalyst. It is generally preferred to develop the latent image to form additional catalytic silver. The silver, acting as a redox catalyst, permits the selective reaction of a dye-image-generating reducing agent and an oxidizing agent at its surface. If the emulsion or an adjacent component contains a coupler, for example, reaction of a color developing agent, acting as a dye-image-generating reducing agent, with an oxidizing agent, such as a peroxide oxidizing agent (e.g., hydrogen peroxide) or transition metal ion complex (e.g., cobalt(III) hexammine), at the silver surface can result in a dye-forming reaction occurring. In this way a dye can be formed in the microvessels. Dye image formation can occur during and/or after silver halide development. The transition metal ion complexes can also cause dye to be formed in the course of bleaching silver, if desired. In one form the microvessels each contain a yellow, magenta or cyan dye-image-generating reducing agent and the blue, green and red filter areas are aligned with the microvessels so that subtractive and additive primary color pairs can be formed in alignment capable of absorbing throughout the visible spectrum. In the foregoing discussion additive primary multicolor imaging is accomplished by employing blue, green and red filter dyes preferably contained in microvessels. It is also possible to produce add¬ itive multicolor images according to the present invention by employing subtractive primary dyes in combination. For example, it is known that if dyes, of any two subtractive primary colors are mixed the result is an additive primary color. In the present invention, if two microvessels in transparent supports are aligned, each containing a different sub-

tractive primary dye, only light of one additive primary color can pass through the aligned microvessels. For example, a filter which- is the equivalent of filter 1100 can be formed by employing in the microvessels 90δA and 90δB.of the element 900 subtractive primary dyes rather than silver halide. Only two subtractive primary dyes need to be supplied to a side to provide a multicolor filter capable of transmitting red, green and blue light in separate areas. By modifying the elements 1100, 1200, 1300 and 1400 so that aligned microvessels are present on opposite surfaces of the support, it is possible to obtain additive primary filter areas with combinations of subtractive primary dyes. Multicolor images formed by laterally displaced green, red and blue additive primary pixel areas can be viewed by reflection or, preferably, projection to reproduce natural Image colors. This is not possible using the subtractive primaries-yellow, magenta and cyan. Multicolor subtractive primary dye images are most commonly formed by providing superimposed silver halide emulsion layer units each capable of forming a subtractive primary dye image.

Photographic elements according to the present invention capable of forming multicolor images employ- ^• ing subtractive primary dyes can be in one form similar in structure to corresponding conventional photographic elements, except that in place of at least the image- forming layer unit nearest the support, at least one image-forming component of the layer unit is located in' the microvessels, as described above in connection with dye imaging. The microvessels can be overcoated with additional image-forming layer units according to conventional techniques.

It is possible in practicing the present invention to form each of the three subtractive dye images which together form the multicolor dye images in the micro¬ vessels. By one preferred approach this can be achiev- ed by employing three silver halide emulsions, one sensitive to blue exposure, one sensitive to green exposure and one sensitive to red exposure. Silver halide emulsions can be employed which have negligible native sensitivity in the visible portion of the spectrum, such as silver chloride, and which are separately spectrally sensitized. It is also possible to employ silver halide emulsions which have substantial native sensitivity in the blue region of the spectrum, such as silver bromoiodide. Red and green spectral sensitizers can be employed which substantially desen¬ sitize the emulsions in the blue region of the spectrum. The native blue sensitivity can be relied upon to provide the desired blue response for the one emulsion intended to respond to blue exposures or a blue sen- sitizer can be relied upon. The blue, green and red responsive emulsions are blended, and the blended emulsion introduced into the microvessels. The result¬ ing photographic element can, in one form, be identical to photographic element 100. The silver halide emul- sion 116 can be a blend of three emulsions, each responsive to one third of the visible spectrum. By employing spectral sensitizers which are absorbed to the silver halide grain surfaces and therefore non- wandering any tendency of the blended emulsion to become panchromatically sensitized is avoided.

Following imagewise exposure, the photographic element is black-and-white developed. No dye is formed. Thereafter the ^" photographic element is successively exposed uniformly to blue, green and red light, in any desired order. Following monochromatic

exposure and before the succeeding exposure, the photo¬ graphic element is processed in a developer contain¬ ing a color developing agent and a soluble coupler capable of forming with oxidized color developing agent a yellow, magenta or cyan d ^' ye. The result is that a multicolor image is formed by subtactive primary dyes confined entirely to the microvessels. Suitable processing solutions, including soluble couplers, are illustrated by Mannes et al U.S. Patent 2,252,718, Schwan et al U.S. Patent 2,950,970 and Pilato U..S. Patent 3,547,650, cited above. In a preferred form negative-working silver halide emulsions are employed and positive multicolor dye images are obtained.

In another form of the invention mixed packet silver halide emulsions can be placed in the reaction microvessels to form subtractive primary dye multi¬ color images. In mixed packet emulsions blue responsive silver halide is contained In a packet also contain¬ ing a yellow dye-forming coupler, green responsive silver halide in a packet containing a magenta dye- forming coupler and red responsive silver halide in a packet containing a cyan dye-forming coupler. Imag¬ ing exposure and processing with a black-and-white developer is performed as described above with refer- ence to the blended emulsions. However, subsequent exposure and processing is comparatively simpler. The element is uniformly exposed with a white light source or chemically fogged and then processed with a color developer. In this way a single color develop- g step is required in place of the three successive color developing steps employed with soluble couplers. A suitable process is illustrated by the Ektachrome E4 and ^" E6 and Agfa processes described in British Journal of Photography Annual, 1977, PP. 194-197, and British Journal of Photography, August 1974, pp. 668-669.

Mixed packet silver halide emulsions which can be employ¬ ed in the practice of this invention are illustrated by Godowsky U.S. Patents 2,6.98,974 and 2,843,488 and Godowsky et al U.S. Patent 3,152,907. It is well recognized in the art that transferred silver images can be formed. This is typically accom¬ plished by developing an exposed silver halide photo¬ graphic element with a developer containing a silver halide solvent. The silver halide which is not develop- ed to silver is solubilized by the solvent. It can then diffuse to a receiver bearing a uniform distribu¬ tion of physical development nuclei or catalysts. Physical development occurs in the receiver to form a transferred silver image. Conventional silver image transfer elements and processes (including processing solutions) are generally discussed in Chapter 12, "One Step Photography", Neblette's Handbook of Photo¬ graphy and Reprography Materials, Processes and Systems, 7th Ed. (1977) and in Chapter 16, "Diffusion Transfer and Monobaths", T. H. James, The Theory of the Photographic Process, 4th Ed. (1977).

The photographic elements 100 through 1000 des¬ cribed above in connection with silver imaging can be readily employed for producing transferred silver images. Illustrative of silver halide solvent contain¬ ing processing solutions useful in providing a trans¬ ferred silver image in combination with these photo¬ graphic elements are those disclosed by Rott U.S. Patent 2,352,014, Land U.S. Patents 2,543,181 and 2,861,885, Yackel et al U.S. Patent 3,020,155 and

Stewart et al U.S. Patent 3,769,014. The receiver to which the silver image is transferred is comprised of a conventional photographic support (or cover sheet) onto which is coated a reception layer comprised of silver halide physical developing nuclei or other silver precipitating agents. In a preferred form the

receiver and photographic element are initially related so that the emulsion and silver image-forming surfaces of the photographic element and receiver, respectively, are juxtaposed and the processing solution is contained in a rupturable pod to be released between the photographic element and receiver after imagewise exposure of the silver halide emulsion. The photographic element and receiver can be separate elements or can be joined along one or more edges to form an integral element. In a common preferred separate element or peel-apart form the photographic element support is initially transparent and the receiver is comprised of a reflective (e.g , white) support. In a common integral format both the receiver and photographic element supports are transparent and a reflective (e.g., white) background for viewing the silver image is provided by overcoating the silver image-forming reception layer of the receiver with a reflective pigment layer or incorporating the pigment in the processing solution.

A wide variety of nuclei or silver precipitating agents can be utilized in the reception layers used in silver halide solvent transfer processes. Such nuclei are incorporated into conventional photographic organic hydrophilic colloid layers such as gelatin and poly- vinyl alcohol layers as include such physical nuclei or chemical precipitants as (a) heavy metals, especially in colloidal form and salts of these metals, (.b) salts, the anions of which form silver salts less soluble than the silver halide of the photographic emulsion to ^' be processed, and (c) nondiffusible polymeric materials with functional groups capable of combining with and insolubilizing silver ions.

Typical useful silver precipitating agents in- elude sulfides, selenides, polysulfides, polyselenides,

thiourea and Its derivatives, mercaptans, stannous halides, silver, gold, platinum, palladium, mercury, colloidal silver, aminoguanidine sulfate, amino- guanidine carbonate, arsenous oxide, sodium stannite, substituted hydrazines, xanthates, and the like. Poly (vinyl mercaptoacetate) is an example of a suitable nondiffusing polymeric silver precipitant. Heavy metal sulfides such as lead, silver, zinc, aluminum, cadmium and bismuth sulfides are useful, particular- ly the sulfides of lead and zinc alone or in an admix¬ ture or complex salts of these with thioacetamide, dithio-oxamide or dithiobiuret. The heavy metals and the noble metals particularly In colloidal form are especially effective. Other silver precipitating agents will occur to those skilled In the present art. Instead of forming the receiver with a hydro¬ philic colloid layer containing the silver halide precipitating agent, it Is specifically contemplated to form the receiver alternatively with microvessels. The microvessels can be formed of the same size and configuration as described above. For example, referring to Figure 11C, if instead of employing red, green and blue filter dyes in the microvessels 1108, silver precipitating agent suspended in a hydrophilic colloid is substituted, an arrangement useful in silver image transfer results. The same alignment considerations discussed above in connection with Figure 11C also apply. In this form the support 1102 is preferably reflective (e.g., white) rather than transparent as shown, although both types of supports are useful. By confining silver image-forming physical development to the microvessels protection against lateral image spreading is afforded.

In another variation of the invention it is contemplated that a conventional photographic element

containing at least one continuous silver halide emulsion layer can be employed in combination with a receiver as described above in which the silver pre¬ cipitating agent is confined within microvessels. Where the silver precipitating agent Is confined in the microvessels, their depth can be the same as or significantly less than the depth of microvessels which contain a silver halide emulsion, since the peptizers, binders and other comparatively bulky components characteristic of silver halide emulsions can be greatly reduced in amount or eliminated. Generally microvessel depths as low as those contemplat¬ ed for vacuum vapor deposited imaging materials, such as silver halide, described above, can be usefully employed also to contain the silver precipitating agents.

A variety of approaches are known in the art for obtaining transferred dye images. The approaches can be generally categorized in terms of the initial mobility of the dyes or dye precursors, hereinafter also referred to as dye image providing compounds. (Initial mobility refers to the mobility of the dye image providing compounds when they are contacted by the processing solution. Initially mobile dye image providing compounds as coated do not migrate prior to contact with processing solution). Dye image providing compounds are classified as either positive- working or negative-working. Positive-working dye image providing compounds are those which produce a positive transferred dye image when employed in combination with a conventional, negative-working silver halide emulsion. Negative-working dye Image provid¬ ing ^' compounds are those which produce a negative trans¬ ferred dye image when employed in combination with conventional, negative-working silver halide emulsions.

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Image transfer systems, which include both the dye image providing compounds and the silver halide emulsions, are positive-working when the transferred dye image is positive and negative-working when the transferred -dye image is negative. When a retained dye image is ^" formed, it is opposite in sense to the transferred dye image. (The foregoing definitions assume the absence ©f special image reversing tech¬ niques, such as those referred to in Research Dls- closure, Vol. 176, December 1978 Item 17643, para¬ graph XXIII-E) .

A variety of dye image transfer systems have been developed and can be employed in the practice of this Invention. One approach is to employ ballast- ed dye-forming (chromogenic) or nondye-forming (non- chromogenic) couplers having a mobile dye attached at a coupling-off site. Upon coupling with an oxidized color developing agent, such as a para-phenylenediamine, the mobile dye is displaced so that it can transfer to a receiver. The use of such negative-working dye image providing compounds is illustrated by Whitmore et al U.S. Patent 3,227,550, Whitmore U.S. Patent 3,227,552 and ^" Fujiwhara et al U.K. Patent 1,445,797- In a preferred image transfer system employing as negative-wor ing dye image providing compounds redox dye-releasers, a cross-oxidizing developing agent (electron transfer agent) develops silver halide and then cross-oxidizes with a compound contain¬ ing a dye linked through an oxidizable sulfonamido ^' group, such as a sulfonamidophenol, sulfonamidoaniline, sulfonamidoanilide, sulfonamidopyrazolobenzimidazole, sulfonamidoindole or sulfonamidopyrazole. Following cross-oxidation hydrolytic deamidation cleaves the mobile dye with the sulfonamido group attached. Such systems are illustrated by Fleckenstein U.S. Patents

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3,928,312 and 4,053,312, Fleckenstein et al U.S. Patent 4,076,529, Meltzer et al U.K. Patent 1,489,694, Degauchi German OLS 2,729,820, Koyama et al German OLS 2,613,005, Vetter et al German OLS 2,505,248 and Kestner et al Research Disclosure, Vol. 151, November 1976, Item 15157. Also specifically contemplated are otherwise similar s stems which employ an immobile, dye-releasing (a) hydroquinone, as illustrated by Gompf et al U.S. Patent 3,698,897 and Anderson et al U.S. Patent 3,725,062, (b) para-phenylenediamine, as illustrated by Whitmore et al Canadian Patent 602,607, or (c) quaternary ammonium compound, as illustrated by Becker et al U.S. Patent 3,728,113.

Another specifically contemplated dye image trans- fer system which employs negative-working dye image providing compounds reacts an oxidized electron trans¬ fer agent or, specifically, in certain forms, an oxidiz¬ ed para-phenylenediamine with a ballasted penolic coupler having a dye attached through a sulfonamido linkage. Ring closure to form a phenazine releases mobile dye. Such an imaging approach is illustrated by Bloom et al U.S. Patents 3,443,939 and 3,443,940.

In still another image transfer system employing negative-working dye image providing compounds, ballast- ed sulfonylamidrazones, sulfonylhydrazones or sulfonyl- carbonylhydrazides can be reacted with oxidized para- phenylenedia ine to release a mobile dye to be trans¬ ferred, as illustrated by Puschel et al U.S. Patents 3,628,952 and 3,844,785. In an additional negative- working system a hydrazide can be reacted with silver halide having a developable latent image site and there¬ after decompose to release a mobile, transferrable dye, as -illustrated by Rogers U.S. Patent 3,245,789, Kohara et al Bulletin Chemical Society of Japan. Vol. 43, pp. 2433-37, and Lestina et al Research Disclosure,

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Vol. 28, December 1974, Item 12832.

The foregoing image transfer systems all employ negative-working dye image providing compounds which are initially immobile and contain a performed dye which is split off during imaging. The released dye is mobile and _. can be transferred to a receiver. Positive-working, initially immobile dye image provid¬ ing compounds which split off mobile dyes are also known. For example, it is known that when silver halide is imagewise developed the residual silver ions associated with the undeveloped silver halide can react with a dye substituted ballasted thiazolidine to release a mobile dye imagewise, as illustrated by Cieciuch et al U.S. Patent 3,719,489 and Rogers U.S. Patent 3,443,941.

Preferred positive-working, initially immobile dye image providing compounds are those which release mobile dye by anchimeric nucleophillc displacement reactions. The compound in its initial form is hydro- lyzed to its active form while silver halide develop¬ ment with an electron transfer agent is occurring. Cross-oxidation of the active dye-releasing compound by the oxidized electron transfer agent prevents hydro- lytic cleaving of the dye moiety. Benzisoxazolone precursors of hydroxylamine dye-releasing compounds are illustrated by Hinshaw et al U.K. Patent 1,464,104 and Research Disclosure, Vol. 144, April 1976, Item 1-4-447. N-Hydroquinonyl carbamate dye releasing com¬ pounds are illustrated by Fields et al U.S. Patent 3,980,479. It is also known to employ an immobile re¬ ducing agent (electron donor) in combination with an immobile ballasted electron-accepting nucleophilic dis¬ placement (BEND) compound which, on reduction, anch- imetrically displaces a diffusible dye. Hydrolysis of the electron donor precursor to its active form

occurs simultaneously with silver halide development by an electron transfer agent. Cross-oxidation of the electron donor with the oxidized electron transfer agent prevents further reaction. Cross-oxidation of the BEND--compound with the residual, unoxidized electron donor then occurs. Anchimeric displacement •of mobile dye from the reduced BEND compound occurs as part of a ring closure reaction. An image transfer system of this type is illustrated by Chasman et al U.S. Patent 4,139,379-

Other positive-working systems employing initially immobile, dye releasing compounds are illustrated by Rogers U.S. Patent 3,185,567 and U.K. Patents 880,233 and 880,234. A variety of positive-working, initially mobile dye image providing compounds can be imagewise immobiliz¬ ed by reduction of developable silver halide directly or indirectly through an electron transfer agent. Systems which employ mobile dye developers, including shifted dye developers, are illustrated by Rogers U.S. Patents 2,774,668 and 2,983,606, Idelson et al U.S. Patent 3,307,947, Dershowitz et al U.S. Patent 3,230,085, Cieciuch et al U.S. Patent 3,579,334, Yutzy U.S. Patent 2,756,142 and Harbison U.S. Patent Office Defensive Publication T889,017. In a variant form a dye moiety can be attached to an initially mobile coupler. Oxidation of a para-phenylenediamine or hydro- quinone developing agent can result in a reaction be¬ tween the oxidized developing agent and the dye contain- ing a coupler to form an immobile compound. Such systems are illustrated by Rogers U.S. Patents 2,774,668 and 3,087,817, Greenhalgh et al U.K. Patents 1,157,501 and 1,157,502, Puschel et al U.S. Patent 3,844,785, Stewart et al U.S ^" . Patent 3,653,896, Gehin et al French Patent 2,287,711 and Research Disclosure,

Vol. 145, May 1976, Item 14521.

Other image transfer systems employing positive- working dye image providing compounds are known in which varied immobilization or transfer techniques are employed.-- For example, a mobile developer-mordant can be imagewise immobilized by development of silver halide to imagewise immobilized an initially mobile dye, as illustrated by Haas U.S. Patent 3,729,314. Silver halide development with an electron transfer agent can produce a free radical intermediate which causes an initially mobile dye to polymerize in an imagewise manner, as illustrated by Pelz et al U.S. Patent 3,585,030 and Oster U.S. Patent 3,019,104. Tanning development of a gelatino-silver halide emulsion can render the gelatin impermeable to mobile dye and thereby imagewise restrain transfer of mobile dye as illustrated by Land U.S. Patent 2,543,181. Also gas^ bubbles generated by silver halide develop¬ ment can be used effectively to restrain mobile dye transfer, as illustrated by Rogers U.S. Patent

2,774,668. Electron transfer agent not exhausted by silver halide development can be transferred to a receiver to imagewise bleach a polymeric dye to a leuco form, as illustrated by Rogers U.S. Patent 3,015,561. A number of image transfer systems employing positive-working dye image providing compounds are known in which dyes are not initially present, but are formed by reactions occurring in the photographic element or receiver following exposure. For example, mobile coupler and color developing agent can be imagewise reacted as a function of silver halide development to produce an immobile dye while residual developing agent and coupler are transferred to the receiver and the developing agent is oxidized to form on coupling a transferred immobile dye image, as

illustrated by Yutzy U.S. Patent 2,756,142, Greenhalgh et al U.K. Patents 1,157,501 to 1,157,506 and Land U.S. Patents 2,559,643, 2,647,049, 2,661,293, 2,698,244 and 2,698,798. In a variant form of this system the coupler can be reacted with a solubilized diazonium salt (or azosulfone precursor) to form a diffusible azo dye before transfer, as illustrated by Viro et al U.S. Patent 3,837,852. In another variant form a single, initially mobile coupler-developer compound can participate in intermolecular self-coupling at the receiver to form an immobile dye image, as illustrat¬ ed by Simon U.S. Patent 3,537,850 and Yoshiniobu U.S. Patent 3,865,593- In still another variant form a mobile amidrazone is present with the mobile coupler and reacts with it at the receiver to form an immobile dye image, as illustrated by Janssens et al U.S. Patent 3,939,035. Instead of using a mobile coupler, a mobile leuco dye can be employed. The leuco dye reacts with oxidized electron transfer agent to form an immobile product, while unreacted leuco dye is transferred to the receiver and oxidized to form a dye image, as illus¬ trated by Lestina et al U.S. Patent 3,880,658, Cohler et al U.S. Patent 2,892,710, Corley et al U.S. Patent 2,992,105 and Rogers U.S. Patents 2,909,430 and 3,065,074. Mobile quinone-heterocyclammonium salts can be immobilized as a function of silver halide development and residually transferred to a receiver where conversion to a cyanine or merocyanine dye occurs, as illustrated by Bloom U.S. Patents 3,537,851 and 3,537,852.

Image transfer systems employing negative- working _, dye image providing compounds are also known in which dyes are not initially present, but are form¬ ed by reactions occurring In the photographic element or receiver following exposure. For example, a ballast-

ed coupler can react with color developing agent to form a mobile dye, as illustrated by Whitmore et al U.S. Patent 3,227,550, Whitmore U.S. Patent 3,227,552, Bush et al U.S. Patent 3,791,827 and Viro et al U.S. Patent 4,036,643. An immobile compound containing a coupler can react with oxidized para-phenylene-diamine to release a mobile coupler which can react with addi¬ tional oxidized para-phenylenediamine before, during or after release to form a mobile dye, as illustrated by Figueras et al U.S. Patent 3,734,726 and Janssens et al German OLS 2,317,134. In another form a ballasted amidrazone reacts with an electron transfer agent as a function of silver halide development to release a mobile amidrazone which reacts with a coupler to form a dye at the receiver, as illustrated by Ohyama et al U.S. Patent 3,933,493.

Where mobile dyes are transferred to the receiver a mordant is commonly present in a dye image providing layer. Mordants and mordant containing layers are described in the following: Sprague et al U.S. Patent 2,548,564; Weyerts U.S. Patent 2,548,575; Carroll et al U.S. Patent 2,675,316; Yutzy et al U.S. Patent 2,713,305; Saunders et al U.S. Patent 2,756,149; Reynolds et al U.S. Patent 2,768,078; Gray et al U.S. Patent 2,839,401; Minsk U.S. Patents 2,882,156 and 2,945,006; Whitmore et al U.S. Patent 2,940,849; Condax U.S. Patent 2,952,566; Mader et al U.S. Patent 3,016,306; Minsk et al U.S. Patents 3,048,487 and 3,184,309; Bush U.S. Patent 3,271,147; Whitmore U.S. Patent 3,271,148; Jones et al U.S. Patent 3,282,699; Wolf et al U.S. Patent 3,408,193; Cohen et al U.S. Patents 3,488,706, 3,557,066, 3,625,694, 3,70-9,690, . 3,758,445, 3,788,855, 3,898,088 and 3,944,424; Cohen U.S. Patent 3,639,357; Taylor U.S. Patent 3,770,439; Campbell et al U.S. Patent 3,958,995;

Ponticello et al Research Disclosure, Vol. 120, April 1974, Item 12045; and Research Disclosure, Vol. 167, March 1978, Item I6725.

The disclosures of the patents and publications cited above ^" as illustrating image transfer systems employing positive and negative-working dye image providing compounds are here incorporated by reference. Any one of these systems for forming transferred dye images can be readily employed in the practice of this invention. Photographic elements according to this invention capable of forming transferred dye images are comprised of at least one image-forming layer unit having at least one component located In the reaction microvessels, as described above in connection with dye imaging. The receiver can be in a conventional form with a dye image providing layer coated continuous¬ ly on a planar support surface, or the dye image provid¬ ing layer of the receiver can be segmented and located In microvessels, similarly as described in connection with silver image transfer. The dye not transferred to the receiver can, of course, also be employed In most of the systems identified to form a retained dye image, regardless of whether an image is formed by transfer. For instance, once an imagewise distribution of mobile and immobile dye is formed in the element, the mobile dye can be washed and/or transferred from the element to leave a retained dye image.

It is known in the art to form multicolor trans¬ ferred dye images using an additive primary multicolor imaging photographic element in combination with trans¬ ferable subtractive primary dyes. Such arrangements are illustrated by Land U.S. Patent 2,968,554 and Rog ^' ers U.S. Patents 2,983,606 and 3,019,124. According to these patents an additiye primary multicolor imaging photographic element is formed by successively coating

onto a support three at least partially laterally displaced imaging sets each comprised of a silver halide emulsion containing an additive primary filter dye and a selectively transferable subtractive primary dye or dye precursor. One set is comprised of a red- sensitized silver halide emulsion containing a red filter dye and a mobile cyan dye providing component, another set is comprised of a green-sensitized silver halide emulsion containing a green filter dye and a mobile magenta dye providing component, and a third set is comprised of a blue sensitive silver halide emulsion containing a blue filter dye and a mobile yellow dye providing component. Upon imagewise exposure the spectral sensitization and filter dyes limit response of each set to one of the additive primary colors, blue, green or red. Upon subsequent development mobile sub¬ tractive primary dyes are transferred selectively to a receiver as a function of silver halide development. In passing to the receiver the subtractive primary dye being transferred from each set laterally diffuses so that it can overlap subtractive primary dyes migrating from adjacent regions of the remaining two sets. The result is a viewable transferred subtractive primary multicolor image. Conventional photographic elements of this type suffer a number of disadvantages. First, protection against lateral Image spreading between sets, before transfer, is at best incomplete. In the configurations disclosed by Land and Rogers in U.S. Patents 2,968,554, 2,983,606 and 3,019,124 at least one imaging set over¬ lies in its entirety one or more additional imaging sets. Further, at least one of the imaging sets is laterally extended in at least one areal dimension. In one form a first imaging set is in the form of a continuous coating covering the entire imaging area.

In other forms at least one Imaging set takes the form of continuous stripes. Second, the thickness of the silver halide emulsion portion of the photographic ele¬ ments is inherently variable, presenting disadvantages in an otherwise planar element format. Since in some areas as many as three sets are superimposed while in other areas only one set is present, either the emulsion portion surface nearest the receiver is nonplanar (leading to nonunifor ity in diffusion distances and possible nonunifor ities in the receiver and other element portions), or the support is embossed to render the receiver surface of the emulsion portion planar. If the support is embossed, a disadvantage is presented in registering the embossed pattern of the support surface with the set patterns. Third, to the extent that the sets overlap, the silver halide emulsions are not effic¬ iently employed. Finally, the retained dye image is of limited utility. Where the emulsion sets overlap black areas are formed because of the additive primary filter dyes present. The dye retained after transfer there¬ after cannot form a projectable image, nor would it form an acceptable or useful image by reflection. Also, the dye retained is wrong-reading. The photographic elements then fail to provide a retained multicolor dye negative which can be conveniently transmission print¬ ed or enlarged corresponding to a transferred multi¬ color dye positive image.

A preferred photographic element capable of form¬ ing multicolor transferred dye images according to the present invention is illustrated in Figure 15. The photographic element 1500 is of the integral format type. A transparent support 1502 is provided which can be identical to transparent support 1102 described above,. The support is provided with microvessels 1508 separated by lateral walls 1510. The lateral walls

are preferably dyed or opaque for reasons which have been discussed above. In each microvessel there is provided a negative-working silver halide emulsion containing a filter dye. ' The microvessels form an interlaid pattern, preferably identical to that shown in Figure HA, of a first set of microvessels contain¬ ing red-sensitized silver halide and a red filter dye, a second set of microvessels containing green-sensitiz¬ ed silver halide and a green filter dye and a third set of microvessels containing blue-sensitized or blue sensitive silver halide and a blue filter dye. (In an alternative form, not shown, a panchromatically sen¬ sitized silver halide emulsion can be coated over the microvessels rather than incorporating silver halide within the microvessels.) In each of the emulsions there Is also provided an initially mobile subtractive primary dye precursor. In the red-sensitiz¬ ed emulsion containing microvessels R, the green- sensitized emulsion containing microvessels G and the blue-sensitized emulsion containing microvessels B are provided mobile cyan, magenta and yellow dye precursors, respectively. The support 1502 and emul¬ sions together form the image-generating portion of the photographic element. An image-receiving portion of the photographic element is comprised of a transparent support (or cover sheet) 1550 on which is coated a conventional dye mordant layer 1552. A reflection and spacing layer 1554, which is preferably white, is coated over the mordant. A silver reception layer 1556, which can be identical to that described in connec ^' tion with silver image transfer, overlies the reflection and spacing layer.

-In the preferred integral construction of the photographic element the image-generating and Image-

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receiving portions are joined along their edges and lie in face-to-face relationship. After imagewise exposure a processing solution is released from a rupturable pod, not shown, integrally joined to the image-generating and receiving portions along one edge thereof. A space 1558 is indicated between the- image-generating and receiving portions to indicate the location of the -processing solution when present after exposure. The processing solution contains a silver halide solvent, as has been described above in connection with silver image transfer. A silver halide developing agent is contained in either the processing solution or a processing solution permeable layer which is contacted by the processing solution upon its release from the rupturable pod, for example. The developing agent or agents can be incorporated in the silver halide emulsions. Incorporation of develop¬ ing agents has been described above.

The photographic element 1500 Is preferably a positive-working image transfer system in which dyes are not initially present (other than the filter dyes), but are formed by reactions occurring in the image generating portion or receiver of the photographic element during processing following exposure, described above in connection with the dye image transfer.

Specific combinations for use as emulsions, processing solutions and mordant layers are illustrated by Yutzy U.S. Patent 2,756,142, Greenhalgh et al U.K. Patents 1,157,501-506, Land U.S. Patents 2,559,643, 2,647,049, 2,661,293, 2,698,244 and 2,698,798, Viro et al U.S.

Patent 3,837,852, Simon U.S. Patent 3,537,850, Yoshiniobu U.S. Patent 3,865,593, Lestina U.S. Patent 3,880,658, Cohler et al U.S. Patent 2,892,710, Corley et al U.S. Patent 2,-992,105, Rogers U.S. Patents 2,909,430 and 3,065,074 and Bloom U.S. Patents 3,537,851

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and 3,537,852. The red, green and blue filter dyes can be chosen from among conventional, substantially inert filter dyes, such as those illustrated by Land U.S. Patent 2,968,554 and Rogers U.S. Patents 2,983,606 and ^' 3,019,124. Useful filter dyes can be selected from _. azo, oxonol, merocyanine and arylmethane dye classes, among others.

The photographic element 1500 is imagewise expos¬ ed through the transparent support 1502. The red, green and blue filter dyes do not interfere with imagewise exposure, since they absorb in each instance primarily only outside that portion of the spectrum to which the emulsion in which they are contained is sen¬ sitized. The filter dyes can,- however, perform a use- ful function in protecting the emulsions from exposure outside the intended portion of the spectrum. For instance, where the emulsions exhibit substantial native blue sensitivity, the red and green filter dyes can be relied upon to absorb light so that the red- and green-sensitized emulsions are not Imaged by blue light. Other approaches which have been dis¬ cussed above for minimizing blue sensitivity of silver halide emulsions can also be employed, if •desired. Upon release of processing solution between the Image-forming and receiving portions of the element, silver halide development is initiated in the micro¬ vessels containing exposed silver halide. Silver halide development within a microvessel results in a selective immobilization of the initially mobile dye precursor present. In a preferred form the dye precursor is both immobilized and converted to a sub- tractive ^" primary dye. The residual mobile imaging dye precursor, either in the form of a dye or a pre- cursor, migrates through the silver reception layer

1556 and the reflection and spacing layer 1554 to the mordant layer 1552. In passing through the silver reception and spacing layers the mobile subtractive primary dyes or precursors are free to and do spread laterally. Referrring to Figure 11A, it can be seen that each microvessel containing a selected subtractive primary dye precursor is surrounded by microvessels containing precursors of the remaining two subtractive primary dyes. It can thus be seen that lateral spreading results in overlapping transferred dye areas in the mordant layer of the receiver when mobile dye or precursor is being transferred from adjacent micro- vessels. Where three subtractive primary dyes overlap in the receiver, black image areas are formed, and where no dye is present, white areas are viewed due to the reflection from the spacing layer. Where two of the subtractive primary dyes overlap at the receiver an additive primary image area is produced. Thus, it can be seen that a positive multicolor dye image can be formed which can be viewed through the transparent support 1550. The positive multi-color transferred dye image so viewed is right-reading.

It is recognized in forming multicolor dye images in conventional photographic elements having super- imposed color forming layer units that oxidized color developing agent produced in one layer can, unless restrained, wander to an adjacent layer unit to produce dye stain. Accordingly, it is conventional practice to incorporate antistain agents (oxidized developing agent scavengers) in Interlayers between adjacent colorforming layer units. Such antistain agents include ballasted or otherwise nondiffusing (.immobile) antioxidants, as illustrated by Weissberger et al U.S. Patent 2,336,327, Loria et al U.S. Patent 2,728,659, Vittum et al U.S. Patent 2,360,290, Jelley et al

U.S. Patent 2,403,721 and Thirtle et al U.S. Patent 2,701,197- To avoid authooxidation the antistain agents can be employed in combination with other antioxidants, as illustrated by Knechel et al U.S. Patent 3,700,-453.

In the multicolor photographic elements accord¬ ing to this invention the risk of stain attributable to wandering oxidized developing agent is substantially reduced, since the lateral walls of the support ele- ment prevent direct lateral migration between adjacent reaction microvessels. Nevertheless, the oxidized developing agent in some systems can be mobile and can migrate with the mobile dye or dye precursor toward the receiver. It is also possible for the oxidized developing agent to migrate back to an adjacent micro- vessel. To minimize unwanted dye or dye precursor immobilization prior to its transfer to the mordant layer of the receiver it is preferred to incorporate in the silver reception layer 1556 a conventional antistain agent. Specific antistain agents as well as appropriate concentrations for use are set forth in the patents cited above as illustrating con¬ ventional antistain agents, the disclosures of which are here incorporated by reference. Since the processing solution contains silver halide solvent, the residual silver halide not develop¬ ed In the microvessels is solubilized and allowed to diffuse to the adjacent silver reception layer. The dissolved silver is physically developed in the silver reception layer. In addition to providing a useful transferred silver image this performs an unexpected and useful function. Specifically, solubilization and transfer of the silver halide from the micro¬ vessels operates to limit direct or chemical develop- ment of silver halide occurring therein. It is well

recognized by those skilled In the art that extended contact between silver halide and a developing agent under development conditions (e.g., at an alkaline pH) can result in an increase in fog levels. By solubiliz- ing and trans'ferring the silver halide a mechanism is - provided for terminating silver halide development in the microve-ssels. In this way production of oxidiz¬ ed developing agent is terminated and immobilization of dye in the microvessels is also terminated. Thus, a very simple mechanism Is provided for terminating silver halide development and dye immobilization.

It is, of course, recognized that other conven¬ tional silver halide development termination tech¬ niques can be employed in combination with that describ- ed above. For example, a conventional polymeric acid layer can be overcoated on the cover sheet 1550 and then overcoated with a timing layer prior to coating the dye mordant layer 1552. Illustrative acid and timing layer arrangements are disclosed by Cole U.S. patent 3,635,707 and Abel et al U.S. Patent 3,930,684. In variant forms of this invention it is contemplated - that such conventional development termination layers can be employed as the sole means of terminating silver halide development, if desired. In addition to obtaining a viewable transferred multicolor positive dye image a. useful negative multi¬ color dye image is obtained. In microvessels where silver halide development has occurred an immobilized subtractive primary dye is present. This immobilized imaging dye together with the additive primary filter dye offer a substantial absorption throughout the visible spectrum, thereby providing a high neutral density to these reaction microvessels. For example, where-an immobilized cyan dye is formed in a micro- vessel also containing a red filter dye, it is

apparent that the cyan dye absorbs red light while the red filter dye absorbs in the blue and the green regions of the spectrum. The developed silver present in the microvessel also increases the neutral density. In microvessels in which silver halide development has not occurred, the mobile dye precursor, either before or after conversion to a dye, has migrated to the receiver. The sole color present then is that provided ^' by the filter dye. If the image-generating portion of the photographic element 1500 is separated from the image-receiving portion, it is apparent that the image- generating portion forms in itself an additive primary multicolor negative of the exposure image. The add-, itive primary negative image can be used for either transmission or reflection printing to form right- reading multicolor positive images, such as enlarge¬ ments, prints and transparencies, by conventional photographic techniques.

It is apparent that transferred multicolor subtractive primary positive images and retained multicolor additive primary negative images can also be obtained as described above by employing direct- positive silver halide emulsions in combination with negative-working dye image providing compounds. Dyes (other than filter dyes) are not initially present, but are formed by reactions occurring in the photo¬ graphic element or receiver following exposure, as described above In connection with—dye image transfer. As can be readily appreciated from the foregoing description, the photographic element 1500 possesses a .number of unique and unexpected advantages. In comparing the image-generating portion of the photo¬ graphic "element to those of Land and Rogers discussed above, it _. can be seen that this portion of the photo- graphic element is of a simple construction and

thinner than the image-receiving portion .of the ele¬ ment, which is the opposite of conventional Integral receiver multicolor image transfer photographic ele- ents. The emulsions contained in the microvessels all lie in a--common plane and they do not present an uneven or noήplanar surface configuration either to the support or the image-receiving portion of the ele¬ ment. The emulsions are not wasted by being in over¬ lapping arrangements, and they are protected against lateral image spreading by being uniformly laterally confined. Further, the microvessels confining the emulsions can be of identical configuration so that any risk of dye imbalances due to differing emulsion configurations are avoided. Whereas Land and Rogers obtain a wrong-reading retained dye pattern which is at best of questionable utility for reflection imaging, the image-generating portion of the photographic element of this invention provides a right-reading multicolor additive primary retained image which can be conveniently used for either reflective or trans¬ mission photographic applications.

Instead of incorporating subtractive primary dye precursors in the microvessels, as described above, / it is possible to use subtractive primary dyes direct- ly. If the dye is blended with the emulsion, a photographic speed reduction can be expected, since the subtractive primary dye is competing with the silver halide grains in absorbing red, green or blue light. This disadvantage can be obviated, however, by forming the image-generating portion of the photo¬ graphic element so that the filter dye and silver halide emulsion are blended together and located in the-'lower portion of the microvessels while the sub- tractive _^ primary dye, preferably distributed in a suitable vehicle, such as a hydrophilic colloid, is

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located in the microvessels to overlie the silver halide emulsion. In this way when the photographic - element is exposed through the support 1502, expos- . Ing radiation is received by the emulsion and competitive -absorption by the subtractive primary dy of incident radiation is not possible. It Is also specifically contemplated that -instead of mixing the filter dye with the emulsion the filter dye can be placed in the microvessels before the emulsion, as- is illustrated in Figure 12. The advantages of such an arrangement have been discussed in connection with photographic element 1200. Finally, it is contemplated that the reaction microvessels can be filled in three distinct tiers, with the filter dyes being first intro- duced, the emulsions next and the subtractive primary dyes overlying the emulsions. It is thus apparent that any of the conventional positive-working or negative-working image transfer systems which employ performed subtractive primary dyes, described above in connection with dye image transfer, can be employed in the photographic element 1500.

Figure 16 illustrates a photographic element l600 which can be substantially simpler in construction than the photographic element 1500. The image-generat- ing portion of the photographic element 1600 can be identical to the image-generating portion of the photo¬ graphic element 1500. Reference numerals 1602, l6θ8 and l6l0 identify structural features which correspond to those identified by reference numerals 1502, 1508 and 1510, respectively. In a simple preferred form the microvessels l6θ8 contain silver halide emulsions and filter dyes as described in connection with, photo¬ graphic- element 1500, but they do not contain an imag¬ ing -dye .or dye precursor.

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The image-receiving portion of the photographic element l600 is comprised of a transparent support 1650 onto which is coated a silver reception layer 1656 which can be identical to silver reception layer' 1556. A reflective layer 165 is provided on the surface of the silver reception layer remote from the support 1650.. The reflection layer is preferably thinner than the imaging and spreading layer 1554, since it is not called upon to perform an intentional spreading function. The reflection layer is prefer¬ ably white.

Upon exposure through the support 1602 negative- working silver halide is rendered developable in the exposed microvessels. Upon introducing a processing solution containing a silver halide developing agent and a silver halide solvent in the space 1658 indicat¬ ed between the image-receiving and image-generating portions, silver halide development is initiated in the exposed microvessels and silver halide solubiliza- tion is initiated in the unexposed microvessels. The solubilized silver halide is transferred through the reflection layer 1654 and forms a silver image at the silver reception layer I656. In viewing the silver image in the silver reception layer through the support 1650 against the background provided by the reflection layer a right-reading'positive silver image is provided. The photographer is thus able to judge the photographic result obtained, although a multicolor positive image is not immediately viewable. The image-generating portion of the photographic element, however, contains a multicolor additive primary negative image. This image can be used to provide multicolor positive images by known photographic tech¬ niques when the image-generating portion Is separated from the image-receiving portion. The photographic

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element 1600 offers the user advantage of rapid information as to the photographic result obtained, but avoids the complexities and costs inherent in multicolor dye image transfer. As described above the photographic element 1600 relies upon silver halide development In the microvessels to provide the required increase in neutral 'density to form a multicolor additive primary negative image in the image-generating portion of the element. Since it is known that silver reception layers can produce silver images of higher density than those provided by direct silver halide development, it -is possible that at lower silver halide coating coverages a satisfactory transferred silver image can be obtained, but a less than desired silver density obtained in the microvessels. The neutral density of the microvessels can be increased by employing any one of a variety of techniques. For example redox process¬ ing of the image-generating portion of the photographic element after separation from the image-receiving portion can be undertaken. In redox processing the silver developed In the microvessels acts as a catalyst for dye formation which can increase the neutral density of the microvessels containing silver can also be employed as a catalyst for physical, development to enhance the neutral density of the silver containing microvessels. These techniques have been discussed above in greater detail in connection with multicolor additive primary imaging. In the foregoing discussion of the photographic elements 1500 and l600 silver halide emulsion is positioned in the microvessels 1508 and I608 and silver precipitating agent is located in the silver reception layers 1556 and I656. Unique and unexpected advantages can be achieved by reversing this relation-

ship. For example, the layers 1556 and 16 can be comprised of a panchromatically sensitized silver halide emulsion while the microvessels 1508 and lβOδ

(or a layer overlying the microvessels, not shown) can contain -a- silver precipitating agent, the remain-, ing components of the microvessels being unchanged.

Assuming-for purposes of illustration a negative- working silver halide emulsion In a positive-working image transfer system, upon imagewise exposure through the supports 1502 and l602, silver halide is rendered developable in the lightstruck areas of the emulsion layers. Upon release of the aqueous alkaline process- ing solution containing silver halide solvent unexposed silver halide is solubilized and migrates to the adjacent microvessels where silver precipitation occurs. In the photographic element l600 a projectable positive additive primary dye image is obtained in the support l602 (which is now an image-receiving rather than the image-generating portion of the element). In the photographic element 1500 a similar result is obtained in the support 1502, but a portion of the imaging dye -can be retained in the microvessels to supplement the precipitated silver in providing a neutral density in the unexposed microvessels. The portion of the imaging dye not retained in the microvessels is, of course, immobilized by the mordant layer 1552 and forms a multicolor subtractive primary positive transferred dye image. Oxidized developing agent scavenger is preferably located in the microvessels 1608 to reduce dye stain and facilitate dye trans¬ fer. • In the photographic element 1500 the emulsion layer 1556, the support 1502 and the contents of the microvessels together form the image generating portion of the element. In the photographic element 1600 if a direct-positive silver halide emulsion is substituted for the negative-working emulsion, a

positive silver image is viewable in the layer 1656 while a projectable negative additive primary multi¬ color image is formed in the support 1602.

One advantage of continuously coating the silver halide emulsion and positioning the silver precipitat¬ ing agent in -the microvessels Is that a single, pan¬ chromatically sensitized silver halide emulsion can be more' efficiently employed than in the alternative arrangement, since the emulsion is entirely located behind the filter dyes during exposure. Another important advantage is that the microvessels in the supports 1502 and 1602 contain no light-sensitive materials in this form. This allows the relatively more demanding steps of filling the microvessels to be performed in roomlight while the more conventional fabrication step of coating the emulsion as a continuous layer is performed in the dark. For the reasons dis¬ cussed above in connection with silver Image transfer it is also apparent that the microvessels can be shallower when they contain a silver precipitating agent than when they contain silver halide emulsion, although this is not essential.

Numerous additional structural modifications of the photographic elements 1500 and l600 are possible. For example, while the supports 1502 and 1602 have been shown, it is appreciated that specific features of other support elements described above containing microvessels can also be employed in combination, particularly pixels of the type shown in Figures 2, 3, 4 and 5, microvessel arrangements as shown in

Figures 6 and 7 and lenticular support surfaces, as shown in Figure 10. Instead of the image-receiving portion disclosed In connection with element 1500 any conventional image-receiving portion can be sub- stituted which contains a spacing layer to permit

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lateral diffusion of mobile subtractive primary dyes, such as those of the Land and Rogers patents, cited above. Instead of the image-receiving portion disclos¬ ed in connection with element 1600 an image-receiving ^' portion from-any conventional silver image transfer photographic element can be substitued. The dye mordant layer- 1552 and the silver reception layer 1656 can both be modified so that the materials thereof are located In microvessels, if desired. The aqueous alkaline processing solution can be introduced at any desired location between the supports 1502 and 1550 or l602 and I650, and one or more of the layers associat¬ ed with support 1550 and I650 can be associated with support 1502 and 1602 instead. Any of the photographic elements discussed above In connection with dye transfer imaging can be adapted to transfer multicolor dye images by overcoating the one image-forming layer unit required and specifically described with one or, preferably, two additional image-forming layer units each capable of transferring a different subtractive primary dye. Finally, it is recognized that numerous specific features well known in the photographic arts can be readily applied or adapted to the practice of this invention and for this reason are not specifically redescribed.

One preferred technique according to this inven¬ tion for preparing microvessel containing supports is to expose a photographic element having a transparent support in an imagewise pattern, such as illustrated in Figures 1A, 6, 7 and 8. In a preferred form the photographic element is negative-working and exposure corresponds to the areas intended to be subtended by the" ^' microvessel areas while the areas intended to be subtended by the lateral walls are not exposed. By conventional photographic techniques a pattern is

formed in the element In which the areas to be sub¬ tended by the microvessels are of a substantially uniform maximum density while the areas intended to be subtended by the lateral walls are of a substantially uniform minimum density.

The photographic element bearing the Image pattern is next coate-d with a radiation-sensitive composition capable of forming the lateral walls of the support element arid thereby defining the side walls of the microvessels. In a preferred form the radiation- sensitive coating is a negative-working photoresist or dichromated gelatin coating. The coating can be on the surface of the photographic element bearing the image pattern or on the opposite surface, e.g., for a silver halide photographic element, the photoresist or dichromated gelatin can be coated on the support or emulsion side of the element. The photoresist or dichromated gelatin coating is next exposed through the pattern in the photographic element, so that the areas corresponding to the intended lateral walls are exposed. This results in hardening to form the lateral wall structure and allowing the unexposed material to be removed according to conventional procedures well known to those skilled in the art. For instance, these procedures are fully described in the patents cited above in connection with the description of photoresist and dichromated gelatin support materials.

The image pattern Is preferably removed before the element is subsequently put to use. For example, where a silver halide photographic element is exposed and processed to form a silver image pattern, the silver can be bleached by conventional photographic techniques after the microvessel structure Is formed by the radiation-sensitive material.

If a positive-working photoresist Is employed, it is initially in a hardened form, but is rendered selectively removable in areas which receive, exposure.. Accordingly, with a positive-working photoresist or other radiation-sensitive material either a positive- ^• working photographic element Is employed or the sense of the exposure pattern is reversed. Instead of coat¬ ing the radiation-sensitive material onto a support bearing an image pattern, such as an image-bearing photographic element, the radiation-sensitive material can be coated onto.any conventional support and image¬ wise exposed directly rather than through an image pattern. It is, of course, a simple matter to draw the desired pixel pattern on an enlarged or macro-scale and then to photoreduce the pattern to the desired scale of the microvessels for purposes of exposing the photoresist.

Another technique which can be used to form the microvessels in the support is to form a plastic de- formable material as a planar element or as a coating on a relatively nondeformable support element and then to form the microvessels in the relatively deformable material by embossing. An embossing tool is employed hich contains projections corresponding to the desir- ed shape of the microvessels. The projections can be formed on an initially plane surface by conventional techniques, such as coating the surface with a photo¬ resist, imagewise exposing in a desired pattern and removing the photoresist in the areas corresponding to the spaces between the intended projections (which also correspond to the configuration of the lateral walls to be formed in the support). The areas of the embossing tool surface which are not protected by photoresist are then etched to leave the projections.

Upon removal of the photoresist overlying the projec¬ tions and any desired cleaning step, such as washing with a mild acid, base or other solvent, the emboss¬ ing tool is ready for use. In a preferred form the embossing tool Is formed of a metal, such as copper, and Is given a.mirror metal coating, such as by vacuum vapor depositing chromium or silver. The mirror metal coating results In smoother walls being formed during embossing. Still another technique for preparing supports containing microvessels Is to form a planar element, such as a sheet or film, of a material which can be locally etched by radiation. The material can form the entire element, but is preferably present as a continuous layer of a thickness corresponding to the desired depth of the microvessels to be formed, coated on a support element which is formed of a material which is not prone to radiation etching. By irrlda- tion etching the planar element surface in a pattern corresponding to the microvessel pattern, the un¬ exposed material remaining between adjacent micro¬ vessel areas forms a pattern of interconnecting lateral walls. It is known that many dielectric materials, such as glasses-and plastics, can be radiation etched. Cellulose nitrate and cellulose esters (e.g., cellulose acetate and cellulose acetate butyrate) are illustrative of plastics which are particularly preferred for use. For example, coatings of cellulose nitrate have been found to be virtually insensitive to ultraviolet and visible light as well as infrared, beta, X-ray and gamma radiation, but cellulose nitrate can be readily etch¬ ed .by alpha particles and similar fission fragments. Techniques for forming cellulose coatings for radiation etching are known in the art and disclosed, for example, by Sherwood U.S. Patent 3,501,636, here in-

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corporated by reference. ^■

The foregoing techniques are well suited to forming transparent microvessel containing supports, a variety of transparent materials being available 5 satisfying the requirements for use. Where a white support is desired, white materials can be employed or- the transparent materials can be loaded with white pigment, such as titania, baryta and the like. Any of the whitening materials employed in conjunction

10 with conventional reflective photographic supports can be employed. Pigments to impart colors rather .than white to the support can, of course, also be employed, if desired. Pigments are particularly well suited to forming opaque supports which are white or

15 colored. Where it is desired that the support be transparent, but tinted, dyes of a conventional nafcy are preferably incorporated in the support form¬ ing materials. For example, in one form of the support described above the support is preferably yellow to

20 absorb blue light while transmitting red and green.

In various forms of the supports described above the portion of the support forming the bottom walls of at least one set of microvessels, generally all of the microvessels, is transparent, and the portion of the

25 support forming the lateral walls is either opaque or dyed to intercept light transmission therethrough. As has been discussed above, one technique for achiev¬ ing this result Is to employ different support materials to form the bottom and lateral walls of the supports.

30 A preferred technique for achieving dyed lateral walls and transparent bottom walls in a support form¬ ed of a single material Is as follows: A transparent film is- employed which is Initially unembossed and relatively nondeformable with an embossing tool. Any

35 of the transparent film-forming materials more

specifically described above and known to be useful in forming conventional photographic film supports, such as cellulose nitrate or ester, polyethylene, polystyrene, poly(ethylene terephthalate) and similar polymeric films, can be employed. One or a combination of dyes capable of imparting the desired color ^' to the lateral walls to be formed Is dissolved in a solution capable of softening the transparent film. The solution can be a conventional plasticizing solution for the film. As the plasticizing solution migrates into the film from one major surface, it carries the dye along with it, so that the film is both dyed and softened along one surface. Thereafter the film can be embossed on Its softened and therefore relatively deformable surface. This produces microvessels In the film support which have dyed lateral walls and trans¬ parent bottom walls.

Once the support with microvessels therein is formed, material forming the radiation-sensitive portion of the photographic element, or at least one component thereof, can be introduced into the microvessels by doctor blade coating, solvent casting or other con¬ ventional coating techniques. Identical or analogous techniques can be used In forming receiver or filter elements containing microvessels. Other, continuous layers, If any, can be coated over the microvessels, the opposite support surface or other continuous layers, employing conventional techniques as disclosed in Research Disclosure, December 1978, Vol. 176, item 17643, paragraph XV.

Materials to facilitate coating and handling can be employed In accordance with conventional techniques, as illustrated by -Product Licensing Index, Vol. 92, December 1971, Item 9232, paragraphs XI and XII and Research Disclosure, Vol. 176, December 1978, Item

17643, paragraphs XI and XII.

In some of the embodiments of the invention described above a multicolor photographic element or filter element is to be formed which requires an inter- laid pattern--of microvessels which are filled to differ one from the other. Usually it is desired to form an interlaid pattern of at least three different microvessel-confined materials. In order to fill one microvessel population with one type of material while filling another remaining microvessel population with another type of material at least two separate coating steps are usually employed and some form of masking is employed to avoid filling the remaining microvessel population with material Intended for only the first microvessel population.

A useful technique for selectively filling microvessels to form an interlaid pattern of two or more differing microvessel populations is to fill the microvessels on at least one surface of the support with a material which can be selectively removed by localized exposure without disturbing the material contained in adjacent microvessels. A preferred mat¬ erial for this purpose is one which will undergo a phase change upon exposure to light and/or ^' heating, preferably a material which is readily sublimed upon moderate heating to a temperature well below that at which any damage to the support occurs. Sublimable organic materials, such as naphthalene, and para- dichlorobenzene are well suited for this use. Certain epoxy resins are also recognized to be suitable. How¬ ever, it is not necessary that the material s.ublime. For_ example, the support microvessels can b.e initially filled with water which' is frozen and selectively thawed. -It is also possible to fill the microvessels with a positive-working photoresist which is select-

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ively softened by exposure. Thus, a wide range of materials which sublime, melt or exhibit a marked reduction in viscosity upon exposure can be employed. According to a preferred exposure technique a 5 laser beam is- sequentially aimed at the microvessels forming one population of the interlaid pattern. This is typically done by known laser scanning techniques, such as illustrated by Marcy U.S. Patent 3,732,796, Dillon et al U.S. Patent 3,864,697 and Starkweather 0 et al U.S. published patent application B309,86θ.

When a first laser scan is completed, the support is left with one exposed microvessel population while the remaining microvessels are substantially undis¬ turbed. Instead of sequentially laser exposing -5 the microvessels in the manner indicated, exposure through a mask can be undertaken, as is well known. Laser scanning exposure offers the advantages of eliminating any need for mask preparation and align¬ ment with respect to the support prior to exposure. Where sublimable material is employed as an ini¬ tial filler, the microvessels are substantially emptied during their exposure. Where the filler mat¬ erial is converted to a liquid form, the exposed microvessels can be emptied after exposure with a vacuum pickup. The empty microvessel population can be filled with imaging and/or filter materials using conventional coating techniques, as have been describ¬ ed above. The above exposure and emptying procedure is then repeated at least once, usually twice-, on different microvessels. Each time the microvessels emptied are filled with a different material. The result is two, usually three, or more populations of microvessels arranged in an interlaid pattern of any desired configuration. An Illustrative general tech- nique, applied to filling cells in a gravure plate,

Is described in an article by D. A. Lewis, "Laser Engraving of Gravure Cylinders", Technical Association of the Graphic Arts, 1977, pp. 34-42, here incorporat¬ ed by reference. The practice of this invention can be further illustrated by. reference to the following examples. Example 1

Sample reaction microvessels were prepared in the following manner: A. A pattern of hexagons 20 microns in width and approximately 10 microns high was formed on a copper plate by etching. Using the etched plate having hexagon projections, dichloromethane and ethanol (80:20 volume ratio) solvent containing 10 grams per 100 ml of Gen- acryl Orange-R, a yellow azo dye, was placed in contact with a cellulose acetate photographic film support for six seconds. Hexagonal depressions were embossed in the softened support, forming reaction microvessels. The yellow dye was absorbed in the cellulose acetate film support areas laterally surrounding, but not beneath, the microvessels, giving a blue density.

B. Using an alternative technique, the desired hexagon pattern for the reaction microvessels was developed in a fine grain gelatino-silver bromoidide emulsion coated on a cellulose acetate photographic film support. The pattern was spin overcoated first with a very thin layer of a negative photoresist comprised of a cyclized polyisoprene solubilized in 2-ethoxyethanol and sensitized with diazobenzilidene- 4-methylcyclohexanone. The pattern was then spin over¬ coated with an approximately 10 micron layer of a positive photoresist comprised of a cresylformaldehyde resin esterfied with 6-diazo-5,6-dihydro-5-oxo-l- naphthalene sulfonyl chloride solubilized in 2-ethoxy- ethyl acetate together with a copolymer of ethyl

acrylate and methacrylate acid, the resist being stabilized with glacial acetic acid. The ^" thin layer of negative photoresist provided a barrier between the incompatible gelatin and positive photoresist . layers. To .prevent nitrogen bubble formation In the . negative photoresist, an overall exposure was given before the positive photoresist layer was added. Exposure through the film pattern and development produced microvessels in the positive photoresist. C. Using still another method, an aqueous mixture of 12.5 by weight percent bone gelatin plus 12 percent by weight of a 2 weight percent aqueous solution of ammonium dichromate (to which was added 1 1/2 ml cone. NH _j ,OH/100 ml of the aqueous mixture) was coated (200 micron wet coating) on a cellulose acetate photographic film support with a doctor coat¬ ing blade. Exposure was made with a positive hexagon pattern using a colllmated ultraviolet arc source. Development was for 30 seconds with a hot (4l°C) water spray. Microvessels with sharp, well defined walls were obtained.

By each of the above techniques, microvessels were formed ranging from 10 to 20 micron in average diameter and from 7 to 10 microns in depth with 2 micron lateral walls separating adjacent microvessels.

Example 2

A fast, coarse grain gelatino-silver bromoiodide emulsion was coated with a doctor blade (.50 micron wet coating) onto a sample of an embossed film support having microvessels prepared according to Example 1A and dried at room temperature so that the emulsion is substantially wholly within the microvessels. A comparison coating sample was made with the same blade on an une bossed film support. Identical test

-Ill-

exposures of the embossed and unembossed elements were processed for 3 minutes in a surface black-and- white developer, as set forth in Table I.

. Table 1

Black-and-White Developer

Water (50°C) 500 cc p-Methylaminophenol sulfate • 2 _t 0 g

Sodium sulflte, desiccated 90.0 g Hydroquinone 8.0 g

Sodium carbonate, monohydrated 52.5 g

Potassium bromide 5.0 g . Water to 1 liter

in a comparison of 7X enlarged prints made from the embossed and unembossed elements, the image made from the embossed element was visibly sharper. Example 3

A coarse grain gelatino-silver bromoiodide emul- sion was coated with a doctor blade (50 micron wet coating) onto a sample of an embossed film support having microvessels prepared according to Example 1A. The silver bromoiodide emulsion was then overcoated with a gelatino emulsion of fine grain, internally fogged converted halide silver bromide grains.

Exposure and development (in D19b developing solution) of the coarse grains released iodide which diffused to the fine grain emulsion, disrupting the grains and making them imagewise developable in the surface developer. Increased contrast and Dmax of the emboss¬ ed film over a comparable planar film, was obtained. Example 4

A coarse grain gelatino-silver bromoiodide emulsion was coated with a doctor blade (.50 micron wet coating) onto a sample of an embossed film support having microvessels prepared according to Example 1A

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and dried at room temperature so that the emulsion is substantially wholly within the microvessels. After exposure the sample was developed in a lith developer of the composition .set forth in Table II In which parts A and B were mixed in a volume ratio of 1:1 just prior to use. Increased contrast was obtained without -loss of sharpness.

Table II Lith Developer

A) Hydroqulnone 28.6 g Sodium sul ite, desiccated 8.0 g Sodium formaldehyde bisulfite 134 g Potassium bromide 2.4 g Water to 1 liter

B) Sodium carbonate H-0 IδO g Water to 1 liter

Example 5

A high speed, coarse grain gelatino-silver bromo- iodide emulsion was coated with a doctor blade (50 micron wet coating) onto a sample of the film support having microvessels prepared according to Example IB. The emulsion on drying was substantially wholly within the microvessels. A first sample- of the element was imagewise exposed and was then developed in a black- and-white developer, as set forth in Table III.

Table III Black-and-White Developer Water 0 ml

Sodium sulfite 2 g l-Phenyl-3-pyrazoli _d one 1 . 5 g

Sodium carbonate 0 g Potassium bromide 2 g 6-Nitro-benzimidazole nitrate

(as 0.1 percent solution) 40 mg Water to 1 liter

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The _. first sample was washed In water and Immersed in a fix bath of the composition set forth in Table IV.

Table TV Fix Bath

Water (5D ^' °C) 600 cc

Sodium thiosulf te 360.0 g

Ammonium chloride 50.0 g

Sodium sulfite, desiccated 15.0 g

Acetic acid, 28 percent 48.0 cc

Boric acid, crystals 7.5 g

Potassium alum 15.0 g Water to 1 liter

The first sample was washed in water and allowed to dry. The sample was then immersed in a rehalogen- izing bath of the composition set forth in Table V.

Table V Rehalogenizing Bath Potassium ferricyanide 50 g

Potassium bromide 20 g

Water to 1 liter

The first sample was washed in water and was then developed in the color developer set forth in Table VI.

Table VI

Color Developer Sodium sulfite 2.0 g

4-(p_-Toluenesulfonamido)-ω-benzoyl- aeetanilide a yellow dye-form¬ ing coupler (dissolved in alcoholic sodium hydroxide) 0.8 g N,N-diethyl-p-phenylenediamine HC1 2.5 g

Sodium carbonate H~0 20 g

2, -Dihydroxy-p-benzene disulfonic acid (dissolved in alcoholic sodium hydroxide) 7.5 g . Water to 1 liter, pH 11.2

The first sample was washed in water and immersed in a bleach bath of the composition set forth in Table VII.

Table VII

Bleach Bath Potassium ferricyanide 50 g

Potassium bromide 20 g

Water to 1 liter

The first sample was immersed in a fix bath of the composition set forth above in Table IV after which it was washed in water.

A second sample was similarly exposed and pro- cessed through the step of immersion in the fix bath

(first occurrence) washed and dried. The images obtain¬ ed using the first and second samples were enlarged 10X onto a light-sensitive commercial black-and-white photographic paper containing a gelatino-silver bromide emulsion. Graininess, due to the silver grain, was very apparent in the enlargement prepared from the second sample but was not visible in the enlargement prepared from the first sample. In the first sample, no grain was evident within the individual micro- vessels. Rather, a substantially uniform intra- mlcrovessel dye density was observed. Example 6

Coatings were made as follows: A magenta coupler, l-(2,4-dimethyl-6-chlorophenyl)-3-[(3-πl-

pentadecylphenoxy)-butyramlde]-5-pyrazolone, was dis¬ persed in tricresyl phosphate at a weight ratio of 1:1/2. This dispersion was mixed with a fast gelatino- silver bromoiodide emulsion and coated with a doctor blade (50 micron wet coating) onto a sample of a film support having a pattern of 20 micron average diameter microvessels prepared as discussed in Example 1A. The emulsion was substantially wholly within the micro- vessels. For comparison, a coating with the same mix- ture, but without microvessels was made. Identical line test exposures on each coating were processed in the following manner:

The coatings were developed for 3 minutes in a black-and-white developer of the composition set forth in Table I.

The coatings were then immersed in a fix bath of the composition set forth in Table VIII.

Table VIII Fix Bath

Water (50°C) 600 cc

Sodium thiosulfate 360.0 g

Ammonium chloride 50.0 g

Sodium sulfite, desiccated 15.0 g Acetic acid, 28 percent 48.0 cc

Boric acid, crystals 7.5 g

Potassium alum 15.0 g

Water to 1 liter

The coatings thereafter were washed in water. They were then reactivated 15 minutes in 25 weight percent aqueous potassium bromide and was washed for 10- minutes in running water, followed by development for ^' 3 minutes in a peroxide oxidizing agent contain¬ ing color developer of the .composition set forth in Table IX.

Table IX Color Developer Potassium carbonate 20. g

Potassium sulfite, desiccated 2 g 4-Amino-3-methyl-N-ethyl-N-?- (Methanesulfonamido)ethyl- aniline sulfate hydrate 5 g Sodium hexametaphosphate 1.5 g Hydrogen peroxide ( _. 40 percent) 10 ml Water to liter

The coatings were then washed in water. Large amounts of dye were formed in both coatings. The comparison coating without the microvessels show¬ ed gross spreading of dye and image degradation. The microvessel coating spread was confined by the micro- vessels and showed no signs of inter-vessel spreading. Example 7

A cellulose acetate photographic film support was embossed with a pattern of microvessels approximately 20 microns in average diameter and 8 microns deep prepared according to Example 1A. A fast gelatino- silver bromoiodide emulsion was doctor-coated (50 micron wet coating) onto the film support having microvessels and dried at room temperature so that the emulsion was substantially wholly within the micro¬ vessels. The coating was image-wise exposed. An image of a line object was developed for two minutes in a black-and-white developer of the composition set forth in Table I. The sample was then immersed in a fix bath of the composition set forth in Table IV.

The sample was thereafter washed in water and dried. It was overcoated with a gelatin dispersion of 2- \ t\- (2, -di-tert-amylphenoχ )butyramido]- ,6-dichloro-5- ethylph.enol in a high boiling coupler solvent harden- _e d for two minutes In formalin hardener and was then washed in water. The sample was activated as a dye

- -

image amplification catalyst for 15 minutes in 25 percent by weight aqueous solution of potassium bromide and was washed for 10 minutes In water, follow¬ ed by development for 5 minutes in a peroxide color developer of--the composition set forth in Table IX.

Within the exposed microvessels a random pattern - of silver spe ^' cks were formed by development in the black-and-white developer. Subsequent development in the color developer produced a cyan dye within areas subtended by the microvessels containing the silver specks. The cyan dye was uniformly distributed within these microvessel subtended areas and produced greater optical density than the silver specks alone. The result was to convert a random distribution of silver specks within the microvessels into a uniform dye pattern. Example 8

Two donor elements for image transfer were pro¬ vided, each having a diffusible cyan coupler, 2,6- dibromo-l,5-naphthalenediol, on a photographic planar film support. A receiving element was prepared by coating a cellulose acetate film support embossed according to Example 1, paragraph A, so that the microvessels in the support were filled with gelatin. To provide a control-receiving element, a second, planar cellulose acetate film support was coated with the same gelatin to provide a continuous planar coat¬ ing having a thickness corresponding to that of the gelatin in the microvessels. Each of the receiving elements was immersed in the color developer of Table X and then laminated to one of the donor sheets.

Table X Color Developer " Ben ^' zyl alcohol 12 ml Sodium sulfite, desiccated 2.0 gm

4-Amino-3-methyl-N,n- diethylaniline monohydro- chloride 2.5 gm

Sodium hydroxide 5.0 gm Water to.1 liter

After diffusion of the cyan coupler to the receiv¬ ing elements,- he receiving and donor elements were peeled apart. The receivers were then _^ treated with ^' a saturated aqueous solution of potassium periodate to oxidize the color developer and to form the cyan dye. _. The cyan dye image formed in the receiving element having the microvessels was perceptibly sharper than the one formed in the control receiving element with the planar support and continuous gelatin layer. Example 9

A pattern of hexagons 20 microns in width and approximately 7 microns high was formed on a copper plate by etching. Using the etched plate having hex¬ agon projections, an embossing solvent solution con- sisting of 48 parts by volume dichloromethane, 52 parts by volume methanol and 0.51 parts by volume Sudan Black B (Color Index No. 26150), was placed in contact with a cellulose acetate photographic film support. Hexagonal depressions were embossed in the • softened support, forming microvessels. The black dye was absorbed in the cellulose acetate film support areas laterally surrounding, but not beneath the microvessels, giving a neutral density.

The microvessels were filled to form a triad of blue, green and red interlaid segmented filters, such that the blue, green and red filter segments occupied alternating parallel rows of the microvessels. The-blue filter was formed of a blue pigment and an alkali-soluble yellow dye-forming coupling agent, 2-(p-carboxyphenoxy)-2-pivalyl-2' ,4'-dichloroacetamide,

-119-

suspended in a transparent polymeric photographic vehicle. The green filter was formed of a green pig¬ ment and an alkali-soluble-magenta dye-forming coupling agent, l-(2-benzothlazolyl)-3-amino-5-pyrazolone, slm- ilarly suspended. The red filter was formed of a red- violet pigment and an alkali-soluble cyan dye-forming coupler, 2,6-dibromo-l,5-naphthalenediol, similarly suspended. The microvessels can be suitably selectively filled to form the triad of filter and coupler mat- erials by initially filling the microvessels with a sublimable material such as l-amino-4-hydroxy-2- phenoxy anthraquinone coated in a dichloromethane solvent, selectively subliming the sublimable material from one third of the microvessels with a laser scan, filling the emptied microvessels with one filter and coupler combination, and sequentially repeating these steps twice more with different laser scans and different filter and coupler combinations. The filled microvessels were overcoated with a mixed silver sulfide and silver iodide silver nucleating agent dispersed in 2 percent by weight gelatin using a 50-micron coating doctor blade spacing.

A commercially available black-and-white photo¬ graphic paper having a panchromatically sensitized gelatino-silver chlorobromide emulsion layer was attached along an edge to the cellulose acetate film support with the emulsion layer of the photographic paper facing the microvessel containing surface of the cellulose acetate. The photographic paper was imagewise exposed through the cellulose acetate film support (and therefore through the filters) with the elements in face-to-face contact. After exposure, the elements were separated, but not detached, and immersed for 3 seconds in the color developer of Table XI.

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Table XI Color Developer Benzyl alcohol 12 ml

Sodium sulfite, desiccated 2.5 m 4-Amino-3-methyl-N,N- diethylaniline monohydro- chloride 2.5 gm

Sodium hydroxide 5.0 gm

Sodium thiosulfate 10.0 gm 6-Nitrobenzimidazole nitrate 20 mg

Water to 1 liter Thereafter, the elements were restored to face-to- face contact for 1 minute to permit development of the imagewise exposed silver halide and Image transfer to occur. The elements were then separated, and the silver image was bleached from the photographic paper. A three-color negative image was formed by subtractive primary dyes in the photographic paper while a three- color screened image was formed by the additive primary filters and the transferred silver image on the cell¬ ulose acetate film support. Example 10

Example ^' 9 was repeated, but with a silver halide emulsion layer coated over the filled microvessels and the silver nucleating agent layer being coated on a separate planar ilm support. The emulsion layer was a high-speed panchromatically sensitized gelatino- silver halide emulsion layer coated with a doctor blade (150 micron wet thickness) spacing. The color developer was of the composition set forth in . Table XII.

Table XII Color Developer Benzyl alcohol 12 ml

Sodium sulfite, desiccated 2.5 gm

4-Amino-3-methyl-N,N- dlethylaniline monohydro- chloride 2.5 gm Sodium"hydroxide 7-5 gm

Sodium -thiosulfate 60.0 gm

6-Nitrob ^" enzimIdazole nitrate 20 mg

Potassium bromide 2.0 gm l-Phenyl-3-pyrazolidone 0.2 gm

Water to 1 liter Both elements were Immersed In the color developer for 5 seconds and thereafter held in face-to-face contact for 2 minutes. A screened three-color negative was obtained on the cellulose acetate film support and a transferred positive silver and multicolor dye image was obtained on the planar support.