REVERSAL PHOTOGRAPHIC ELEMENTS CONTAINING TABULAR GRAIN EMULSIONS

Abstract: Silver halide photographic elements are disclosed cap­ able of producing reversal images including at least one emulsion layer comprised of a blend of tabular silver haloiodide grains and relatively fine grains consisting essen­ tially of a silver salt more soluble than silver iodide.

Description: This invention relates to improved multicolor photographic elements adapted for producing viewable reversal dye images. More specifically, this invention relates to such reversal silver halide photographic elements containing in at least one emulsion layer tabular bromoiodide grains. The term "silver bromoiodide" is employed in its art recognized usage to designate silver halide grains containing silver ions in combination with iodide ions and bromide ions. The term "reversal photographic element" designates a photographic element which produces a photographic image for viewing by being imagewise exposed and developed to produce a negative of the image to be viewed, followed by uniform exposure and/or fogging of residual silver halide and processing to produce a second, viewable image. Color slides, such as those produced from Kodachrome® and Ektachrome® films, constitute a popular example of reversal photographic elements. In the overwhelming majority of applications the first image is negative and the second image is positive. U.S. Patent 4,082,553 illustrates a conventional reversal photographic element containing silver haloiodide grains modified by the incorporation of a small proportion of fogged silver halide grains. German OLS 3,402,840 is similar to U.S. Patent 4,082,553, but describes the imaging silver halide grains in terms of those larger than and smaller than 0.3 micrometer and additionally requires in addition to the fogged silver halide grains or their metal or metal sulfide equivalent an organic compound capable of forming a silver salt of low solubility. High aspect ratio tabular grain silver bromoiodide emulsions have been recognized to provide a variety of photographic advantages, such as improvements in speed-granularity relationships, increased image sharpness, and reduced blue speed of minus blue recording emulsion layers. High aspect ratio tabular grain silver bromoiodide emulsions in reversal photographic elements are illustrated by Research Disclosure Vol. 225, January 1983, Item 22534; and U.S. Patents 4,434,226; 4,439,520 (DE-A-3 241 635, corresponding); 4,433,048; 4,400,463; and 4,435,501. Research Disclosure is published by Kenneth Mason Publications, Ltd., The Old Harbourmaster's, 8 North Street, Emsworth, Hampshire PO10 7DD, England. DE-A-3 241 635 at page 84, lines 20-28 discloses that, when a relatively fine grain silver chloride emulsion is blended with or coated adjacent the tabular grain silver bromoiodide emulsions, a further increase in the contrast and/or sensitivity-i.e., speed-granularity relationship-of the emulsion can result. DE-A-3 347 215 has as its purpose to improve the covering power of a negative silver image by blending an internally fogged emulsion with a tabular grain emulsion. The covering power of a silver image is the ratio of maximum density divided by the coating coverage of silver. Thus, in comparing coatings of equal silver coating coverages, increases in covering power can be demonstrated by comparing maximum densities. When maximum density is increased without increasing fog, the necessarily increased slope of the characteristic curve joining minimum and maximum density exposure regions produces increases in measured contrast and speed, which is the reason that careful speed comparisons can only be undertaken at a matched contrast. Since increased silver covering power can be entirely a function of the physical form of the developed silver rather than any increase in the amount of silver developed, it is impossible to predict increased dye image densities from increased silver covering power. It is an object of this invention to provide a multicolor photographic element capable of forming a viewable reversal dye image comprising a support and, coated on the support, a blue recording yellow dye image forming layer unit, a green recording magenta dye image forming layer unit, and a red recording cyan dye image forming layer unit, at least one layer unit containing an recording emulsion layer comprised of a dispersing medium and a blend of radiation sensitive tabular silver bromoiodide grains having a thickness of less than 0.5 µm, a diameter of at least 0.6 µm, and an average aspect ratio of greater than 8:1 accounting for at least 35 percent of the total grain projected area of said emulsion layer, said reversal photographic element exhibiting increased reversal threshold speed. It is a further object to provide reversal photographic elements as described above which exhibit reduced toe region density in the reversal image as well as increases in maximum density and contrast. These objects are achieved by the improvement characterized in that blended with the radiation sensitive tabular silver bromoiodide grains are relatively fine silver bromide or silver thiocyanate grains present in a concentration of at least 0.5 mole percent, based on total silver in said emulsion layer. It has been discovered that the addition of relatively fine grains consisting essentially of a silver bromide or thiocyanate salt to an emulsion layer containing tabular silver bromoiodide grains can produce a combination of advantages in reversal dye imaging. (Except as otherwise noted, all images referred to are dye images.) The reversal threshold speed of the reversal photographic elements can be increased. At the same time, reduced toe region density in the reversal image as well as increases in maximum density and contrast are observed. To permit the advantages of the present invention to be visualized more easily, the relative reversal imaging performance of a photographic element according to the present invention and a conventional reversal photographic element differing solely by the absence of the relatively fine grains consisting essentially of a silver bromide or thiocyanate salt is illustrated schematically in Figure 1. Curve 1 is the reversal characteristic curve produced by an emulsion layer of a conventional reversal photographic element wherein radiation sensitive tabular silver bromoiodide grains are present, but the relatively fine grains are not present. Curve 2 illustrates the reversal characteristic curve produced by the same emulsion layer differing only by the inclusion of the relatively fine grains. It is to be understood that exposure and processing producing both curves are identical. In the toe region 2a of the characteristic curve 2 it can be seen that density is lower than in the corresponding toe region 1a of the characteristic curve 1. Thus the inventive reversal photographic element produces images having brighter highlights. Comparing the mid-portions 1b and 2b of the characteristic curves, it can be seen that the characteristic curve of the photographic element according to the invention exhibits significantly higher contrast. Comparing the shoulder portions 1c and 2c of the characteristic curves, it can be seen that the shoulder portion 2c of the characteristic curve of the reversal photographic element satisfying this invention is of much higher density. In comparing the shoulder portions 1c and 2c of the characteristic curves it can be seen that curve 2 is already declining from maximum density at minimum exposure level shown while the threshold decline from maximum density of the curve 1 occurs well within the density scale. Thus, it can be seen that the reversal threshold speed exhibited by curve 2 exceeds that of curve 1, where reversal threshold speed is defined as the exposure level corresponding to the threshold (first detectable) decline from maximum density of the reversal characteristic curve. Shifting from the language of the photographic scientist to that of the ultimate user, the photographer, the present invention adds speed and "snap" to reversal photographic elements employing radiation sensitive tabular grain emulsions. The inventive character of the reversal photographic elements herein disclosed is underscored when it is appreciated that highly analogous reversal photographic elements differing in one or more essential features of this invention do not exhibit even qualitatively predictable similarities in performance when the relatively fine grain silver salts are introduced into the reversal photographic elements. Specifically, when the relatively fine grains of silver salt are placed in layers adjacent to rather than in the radiation sensitive tabular grain emulsion layer, the result is a loss in maximum density, a loss of contrast, and an increase in toe region and minimum densities. If a conventional nontabular silver bromoiodide emulsion is substituted for the tabular grain emulsion layer, the result is marked reversal desensitization, which necessarily increases toe region density at comparable exposure levels. If relatively fine grain silver iodide is substituted for relatively fine grains exhibiting a higher level of solubility, no enhancement of the characteristic curve shape is observed. Still further, advantageous modifications of reversal characteristic curve shape have been realized only when the radiation sensitive tabular grains are silver bromoiodide grains as opposed to tabular silver halide grains lacking iodide as a constituent. This invention can be better appreciated by reference to the following detailed description considered in conjunction with the drawings, in which Figure 1 is a schematic diagram intended to compare qualitatitively the reversal characteristic curve 2 of a reversal photographic element according to this invention with the reversal characteristic curve 1 of a reversal photographic element differing only in lacking a second grain population; Figures 2 through 10 present and compare reversal characteristic curves of elements exemplifying this invention, identified by the prefix E before the element number, and comparative elements, identified by the prefix C before the element number. This invention relates to an improvement in silver halide photographic elements useful in reversal imaging. The photographic elements are comprised of a support and one or more image recording silver halide emulsion layers coated on the support. At least one of the image recording emulsion layers contains a dispersing medium and radiation sensitive tabular silver bromoiodide grains blended with relatively fine grains consisting essentially of a silver salt more soluble than silver iodide. Tabular grains are herein defined as those having two substantially parallel crystal faces, each of which is clearly larger than any other single crystal face of the grain. The tabular grains employed in the blended grain emulsion layers forming one or more layers of the reversal photographic elements of this invention are chosen so that the tabular grains having a thickness of less than 0.5 µm and a diameter of at least 0.6 µm have an average aspect ratio of greater than 8:1 and account for at least 35 percent of the total grain projected area of the blended grain emulsion layer in which they are present. A convenient approach for preparing blended grain emulsion layers satisfying the requirements of this invention is to blend with the relatively fine second grain population a radiation sensitive high aspect ratio tabular grain emulsion. The term "high aspect ratio tabular grain emulsion" is herein defined as requiring that the tabular silver halide grains having a thickness of less than 0.3 µm and a diameter of at least 0.6 µm have an average aspect ratio of greater than 8:1 and account for at least 50 percent of the total projected area of the grains present in the emulsion. The term is thus defined in conformity with the usage of this term in the patents relating to tabular grain emulsions cited above. In general tabular grains are preferred having a thickness of less than 0.3 µm. Where the emulsion layer is intended to record blue light as opposed to green or red light, it is advantageous to increase the thickness criterion of the tabular grains to less than 0.5 µm, instead of less than 0.3 µm. Such an increase in tabular grain thickness is also contemplated for applications in which the reversal image is to be viewed without enlargement or where granularity is of little importance, although these latter applications are relatively rare in reversal imaging, reversal images being most commonly viewed by projection. Tabular grain emulsions wherein the tabular grains have a thickness of less than 0.5 µm intended for recording blue light are disclosed by U.S. Patent 4,439,520, cited above. While the tabular grains satisfying the 0.3 µm thickness and 0.6 µm diameter criteria account for at least 50 percent of the total projected area of the grains in high aspect ratio tabular grain emulsions, it is appreciated that in blending a second grain population the tabular grain percentage of the total grain projected area is decreased. The tabular grain emulsions contemplated for preparing blended grain emulsion layers satisfying the requirements of this invention must be capable of providing tabular grains satisfying the thickness and diameter criteria which also provide at least 35 percent of the total grain projected area in the blended grain emulsion layer. Thus, although the tabular grain emulsions employed in the practice of this invention preferably provide at least 50 percent of the total grain projected area, at least before blending with the second grain population, this is not essential if the 35 percent of the total grain projected area condition noted above in the blended grain emulsion layer is satisfied. Thus, it is apparent that while high aspect ratio tabular grain emulsions are preferred for preparing the blended grain emulsions and in a highly preferred form the blended grain emulsions are themselves high aspect ratio tabular grain emulsions, this is not necessary in all instances, and departures can actually be advantageous for specific applications. However, for simplicity the ensuing discussion relating to radiation sensitive tabular grain emulsions is directed to the preferred high aspect ratio tabular grain emulsions, it being appreciated that the teachings are generally applicable to tabular grain emulsions as herein defined. The preferred high aspect ratio tabular grain silver bromoiodide emulsions are those wherein the silver bromoiodide grains having a thickness of less than 0.3 µm (optimally less than 0.2 µm) and a diameter of at least 0.6 µm have an average aspect ratio of at least 12:1 and optimally at least 20:1. In a preferred form of the invention these silver bromoiodide grains satisfying the above thickness and diameter criteria account for at least 70 percent and optimally at least 90 percent of the total projected area of the silver halide grains. In a highly preferred form of the invention the blended grain emulsions required by this invention also satisfy the parameters set out for the preferred high aspect ratio tabular grain emulsions. It is appreciated that the thinner the tabular grains accounting for a given percentage of the projected area, the higher the average aspect ratio of the emulsion. Typically the tabular grains have an average thickness of at least 0.03 µm, although even thinner tabular grains can in principle be employed. High aspect ratio tabular grain emulsions useful in the practice of this invention can have extremely high average aspect ratios. Tabular grain average aspect ratios can be increased by increasing average grain diameters. This can produce sharpness advantages, but maximum average grain diameters are generally limited by granularity requirements for a specific photographic application. Tabular grain average aspect ratios can also or alternatively be increased by decreasing average grain thicknesses. When silver coverages are held constant, decreasing the thickness of tabular grains generally improves granularity as a direct function of increasing aspect ratio. Hence the maximum average aspect ratios of the tabular grain emulsions of this invention are a function of the maximum average grain diameters acceptable for the specific photographic application and the minimum attainable tabular grain thicknesses which can be conveniently produced. Maximum average aspect ratios have been observed to vary, depending upon the precipitation technique employed and the tabular grain halide composition. High aspect ratio tabular grain silver bromoiodide emulsions with average aspect ratios of 100:1, 200:1, or even higher are obtainable by double-jet precipitation procedures. The tabular bromoiodide grains employed in the practice of this invention exhibit higher photographic speeds and are for this reason the preferred and most commonly employed emulsions for candid photography. Iodide must be present in the tabular silver bromoiodide grains in a concentration sufficient to influence photographic performance. It is thus contemplated that at least about 0.5 mole percent iodide will be present in the tabular silver bromoiodide grains. However, high levels of iodide are not required to achieve the advantages of this invention. Generally the tabular silver bromoiodide grains contain less than 8 mole percent iodide. Preferred iodide levels in the tabular silver bromoiodide grains are from 1 to 7 mole percent and optimally are from 2 to 6 mole percent. All of the above iodide mole percentages are based on total silver present in the tabular grains. The radiation sensitive tabular bromoiodide grains required for the practice of this invention are preferably provided by selecting from among the various high aspect ratio tabular grain emulsions disclosed in Research Disclosure Vol. 225, January 1983, Item 22534; and U.S. Patents 4,434,226; 4,439,520; 4,433,048; and 4,435,501; each cited above. The blended grain emulsion required for the practice of this invention can be conveniently provided by blending with a tabular grain silver bromoiodide emulsion as described above a second grain population consisting essentially of silver bromide or thiocyanate salt. It is preferred that the silver salt forming the relatively fine grains be at least as soluble as the most soluble silver halide present in the radiation sensitive tabular grains. For example, using radiation sensitive tabular silver bromoiodide grains, the relatively fine grains consist essentially of silver bromide, silver thiocyanate, or a combination of both. Advantages have been realized when silver bromide and silver thiocyanate grains are employed in combination. Although the relatively fine grains consist essentially of silver bromide or thiocyanate salt, it is appreciated that less soluble silver salts in small quantities that do not interfere with effectiveness can be present. For example, it is common to treat silver halide emulsions with soluble iodide salt solutions in conjunction with spectral sensitization and to employ as antifoggants and stabilizers compounds which form highly insoluble silver salts. While such conventional treatments can result in the adsorption of small quantities of silver iodide or one or more other highly insoluble silver salts to the surfaces of the relatively fine grains, such conventional emulsion treatments are not normally incompatible with the practice of this invention. The grains consisting essentially of a silver bromide or thiocyanate salt are fine as compared to the tabular silver bromoiodide grains. In general, the permissible size of this second grain population blended with the radiation sensitive tabular grains is a direct function of the solubility of the silver salt forming these grains. The second grain population in all instances exhibits an average grain diameter of less than 0.5 µm and preferably exhibits an average grain diameter of less than 0.3 µm. Optimally the second grain population exhibits an average grain diameter of less than 0.1 µm. Thus, the second grain population is optimally provided by blending a conventional Lippmann emulsion with the radiation sensitive tabular grain emulsion to produce the blended grain emulsion required for the practice of this invention. The minimum average diameter of the second grain population is limited only by synthetic convenience, typically being at least about 0.05 µm. Any concentration of the second grain population can be employed that is capable of enhancing the photographic properties of the reversal photographic elements. Minimum second grain population concentrations can range from as low as about 0.5 mole percent, based on total silver in the blended grain emulsion layer, with concentrations. above about 1 mole percent being preferred and concentrations above about 5 mole percent being optimum for maximizing photographic benefits. To avoid inefficient use of silver salts maximum concentrations of the second grain population are generally maintained below the concentrations of the silver bromoiodide forming the radiation sensitive tabular grains-that is, below 50 mole percent, based on total silver in the blended grain emulsion layer, with most efficient utilization of silver occurring at second grain concentrations below about 40 mole percent. It is generally most convenient to prepare the emulsions required for the practice of this invention by blending a tabular silver bromoiodide grain emulsion and a separately prepared emulsion containing the relatively fine second grain population-for example, a relatively fine grain silver bromide or silver thiocyanate emulsion, the preparations of which are well known to those skilled in the art and form no part of this invention. As previously, noted the relatively fine grain emulsion is optimally a Lippmann emulsion. So long as the grain requirements identified above are satisfied, either or both of the tabular grain containing and relatively fine grain containing emulsions can themselves be the product of conventional grain blending. Apart from the blended grain emulsion features specifically described above the reversal photographic elements of this invention can take any convenient conventional form. The reversal photographic elements can take the form of either black-and-white or color reversal photographic elements. In a very simple form the reversal photographic elements according to this invention can be comprised of a conventional photographic support, such as a transparent film support, onto which is coated a blended grain emulsion layer as described above. Although conventional overcoat and subbing layers are preferred, only the blended grain emulsion layer is essential. Following imagewise exposure, silver halide is imagewise developed to produce a first silver image, which need not be viewable. The first silver image can be removed by bleaching before further development when a silver or silver enhanced dye reversal image is desired. Thereafter, the residual silver halide is uniformly rendered developable by exposure or by fogging. Development produces a reversal image. The reversal image can be either a silver image, a silver enhanced dye image, or a dye image only, depending upon the specific choice of conventional processing techniques employed. The production of silver reversal images is described by Mason, Photographic Processing Chemistry , 1966, Focal Press Ltd., pp. 160-161. If a dye only image is being produced, silver bleaching is usually deferred until after the final dye image is formed. The reversal photographic elements of this invention are in a preferred form color reversal photographic elements capable of producing multicolor images--e.g., images that at least approximately replicate subject colors. Illustrative of such color reversal photographic elements are those disclosed by U.S. Patents 4,439,520 and 4,082,553, each cited above. In a simple form such a color reversal photographic element can be comprised of a support having coated thereon at least three color forming layer units, including a blue recording yellow dye image forming layer unit, a green recording magenta dye image forming layer unit, and a red recording cyan dye image forming layer unit. Each color forming layer unit is comprised of at least one radiation sensitive silver halide emulsion layer. In a preferred form of the invention at least one radiation sensitive emulsion layer in each color forming layer unit is comprised of a blended grain emulsion as described above. The blended grain emulsions in each color forming layer unit can be chemically and spectrally sensitized as taught by U.S. Patent 4,439,520. In a preferred form chemical and spectral sensitization of the tabular grain emulsion is completed before blending with the second grain population, which therefore remains substantially free of sensitizing materials. One or more dye image providing materials, such as couplers, are preferably incorporated in each color forming layer unit, but can alternatively be introduced into the photographic element during processing. The following constitutes a specific illustration of a color reversal photographic element according to this invention: I. Photographic Support Exemplary preferred photographic supports include cellulose acetate and poly(ethylene terephthalate) film supports and photographic paper supports, especially a paper support which is partially acetylated or coated with baryta and/or α-olefin polymer, particularly a polymer of an α-olefin containing 2 to 10 carbon atoms, such as polyethylene, polypropylene, and ethylenebutene copolymers. II. Subbing Layer To facilitate coating on the photographic support it is preferred to provide a gelatin or other conventional subbing layer. III. Red Recording Layer Unit At least one layer comprised of a red sensitized blended grain high aspect ratio tabular grain silver bromoiodide emulsion layer, as described in detail above. In an emulsion layer or in a layer adjacent thereto at least one conventional cyan dye image forming coupler is included, such as, for example, one of the cyan dye image forming couplers disclosed in U.S. Patents 2,423,730; 2,706,684; 2,725,292, 2,772,161; 2772,162; 2,801,171; 2,895,826; 2,908,573; 2,920,961; 2,9767,146; 3,002,836; 3,034,892; 3,148,062, 3,214,437; 3,227,554; 3,253,924; 3,311,476; 3,419,390; 3,458,315; and 3,476,563. IV. Interlayer At least one hydrophilic colloid interlayer, preferably a gelatin interlayer which includes a reducing agent, such as an aminophenol or an alkyl substituted hydroquinone, is provided to act as an oxidized developing agent scavenger. V. Green Recording Layer Unit At least one layer comprised of a green sensitized blended grain high aspect ratio tabular grain silver bromoiodide emulsion layer, as described in detail above. In an emulsion layer or in a layer adjacent thereto at least one conventional magenta dye image forming coupler is included, such as, for example, one of the magenta dye image forming couplers disclosed in U.S. Patents 2,725,292; 2,772,161; 2,895,826; 2,908,573; 2,920,961; 2,933,391; 2,983,608; 3,005,712; 3,006,759; 3,062,653; 3,148,062; 3,152,896; 3,214,437; 3,227,554, 3,253,924; 3,311,476; 3,419,391; 3,432,521; and 3,519,429. VI. Yellow Filter Layer A yellow filter layer is provided for the purpose of absorbing blue light. The yellow filter layer can take any convenient conventional form, such as a gelatino-yellow colloidal silver layer (i.e., a Carey Lea silver layer) or a yellow dye containing gelatin layer. In addition the filter layer contains a reducing agent acting as an oxidized developing agent scavenger, as described above in connection with the Interlayer IV. VII. Blue Recording Layer Unit At least one layer comprised of a blue sensitized blended grain high aspect ratio tabular grain silver bromoiodide emulsion layer, as described in detail above. In an alternative form the tabular grains can be thicker than high aspect ratio tabular grains-that is, the thickness criteria for the grains can be increased from 0.3 µm to less than 0.5 µm, as described above. In this instance the grains exhibit more native blue speed, which preferably is augmented by the use of blue spectral sensitizers, although this is not essential, except for the highest attainable blue speeds. In an emulsion layer or in a layer adjacent thereto at least one conventional magenta dye image forming coupler is included, such as, for example, one of the magenta dye image forming couplers disclosed in U.S. Patents 2,875,057; 2,895,826; 2,908,573; 2,920,961; 3,148,062; 3,227,554; 3,253,924; 3,265,506; 3,277,155; 3,369,895; 3,384,657; 3,408,194; 3,415,652; and 3,447,928. VIII. Overcoat Layer At least one overcoat layer is provided. Such layers are typically transparent gelatin layers and contain known addenda for enhancing coating, handling, and photographic properties, such as matting agents, surfactants, antistatic agents, ultraviolet absorbers, and similar addenda. As disclosed by U.S. Patent 4,439,520, the high aspect ratio tabular grain emulsion layers show sufficient differences in blue speed and green or red speed when substantially optimally sensitized to green or red light that the use of a yellow filter layer is not required to achieve acceptable green or red exposure records. It is appreciated that in the absence of a yellow filter layer the color forming layer units can be coated in any desired order on the support. While only a single color forming layer unit is disclosed for recording each of the blue, green, and red exposures, it is appreciated that two, three, or even more color forming layer units can be provided to record any one of blue, green, and red. It is also possible to employ within any or all of the blue, green, and red color forming layer units multiple radiation sensitive emulsion layers any, some, or all of which satisfy the blended grain emulsion requirements of this invention. In addition to the features described above the reversal photographic elements can, of course, contain other conventional features known in the art, which can be illustrated by reference to Research Disclosure , Vol. 176, December 1978, Item 17643. For example, the silver halide emulsions other than the blended grain emulsions described can be chosen from among those described in Paragraph I; the silver halide emulsions can be chemically sensitized, as described in Paragraph III; the silver halide emulsions can be spectrally sensitized, as described in Paragraph IV; any portion of the elements can contain brighteners, as described in Paragraph V; the emulsion layers can contain antifoggants and stabilizers, as described in Paragraph VI; the color forming layer units can contain color image forming materials as described in Paragraph VII; the elements can contain absorbing and scattering materials, as described in Paragraph VIII; the emulsion and other layers can contain vehicles, as described in Paragraph IX; the hydrophilic colloid and other layers of the elements can contain hardeners, as described in Paragraph X; the layers can contain coating aids, as described in Paragraph XI; the layers can contain plasticizers and lubricants, as described in Paragraph XII; the layers, particularly the layers coated farthest from the support, can contain matting agents, as described in Paragaph XVI; and the supports can be chosen from among those described in Paragraph XVII. This exemplary listing of addenda and features is not intended to restrict or imply the absence of other conventional photographic features compatible with the practice of the invention. The photographic elements can be imagewise exposed with any of various forms of energy, as illustrated by Research Disclosure , Item 17643, cited above, Paragraph XVIII. For multicolor imaging the photographic elements are exposed to visible light. Multicolor reversal dye images can be formed in photographic elements according to this invention having differentially spectrally sensitized silver halide emulsion layers by black-and-white development followed by color development. Reversal processing is demonstrated below employing conventional reversal processing compositions and procedures. Examples The invention can be better appreciated by reference to the following specific examples. Coverages in parenthesis are expressed in grams per square meter. The elements described were in each instance, except as otherwise stated, exposed through a step tablet for 0.02 second by a 500 watt 2850°K light source through a Wratten 8® filter and reversal processed with a 3 minute first development step using the Kodak E-6® process. The Kodak E-6® process is described in the British Journal of Photography Annual , 1982, pp. 201-203. Element 1 (satisfying the invention) The following layers were coated on a film support in the order recited: Layer 1 Gelatin (1.08) Layer 2 A very high speed green sensitized high aspect ratio tabular grain silver bromoiodide emulsion consisting of (a) high aspect ratio tabular bromoiodide grains (1.08) having an average aspect ratio of 18:1, an average tabular grain thickness of 0.1 µm, and a bromide to iodide mole ratio of 97:3; (b) 0.08 µm silver bromide grains (0.86) provided by blending a Lippmann emulsion with a high aspect ratio tabular grain silver bromoiodide emulsion providing the grains for (a); (c) gelatin (2.16); and (d) a magenta dye forming coupler, 1-(2,4,6-trichlorophenyl)-3-{3-[α-(2,4,-di- tert -amylphenoxy)acetamido]benzamido}-5-pyrazolone (0.86). Layer 3 Gelatin (1.08) and bis(vinylsulfonyl)methane hardener at 1.75% by weight, based on total gelatin in all layers. Element 2 (not satisfying the invention) Element 2 was identical to Element 1, except that no Lippmann emulsion was blended to form Layer 2. Element 3 (not satisfying the invention) Element 3 was identical to Element 1, except that the Lippmann emulsion was not blended in Layer 2, but was partitioned into two equal parts blended into Layers 1 and 3. The photographic performance of the color reversal photographic elements can be compared by reference to Figure 2, which shows the characteristic curves for Elements 1, 2, and 3 as curves E1, C2, and C3, respectively. In comparing curve E1 with curves C2 and C3 it can be seen that a higher maximum density and contrast is realized and that a lower density in the toe region of the curve E1 is realized. It is surprising that the partitioning of the silver bromide Lippmann emulsion between the overcoat and undercoat layers degrades photographic performance so that lower maximum density and contrast as well as a higher minimum density are observed than when the Lippmann emulsion is entirely absent. Further, it is highly surprising that the partitioned Lippmann emulsion produces a result just the opposite of that produced by blending the Lippmann emulsion with the high aspect ratio tabular grain silver bromoiodide emulsion. Element 4 (not satisfying the invention) An element identical to Element 1 was prepared, except that instead of blending a high aspect ratio tabular grain emulsion with the silver bromide Lippmann emulsion (a) a single jet precipitated, ammonia digested silver bromoiodide emulsion containing nontabular grains of 0.54 µm in mean diameter and a bromide to iodide mole ratio of 96.5:3.4 was substituted for the high aspect ratio tabular grain silver bromoiodide emulsion and (b) the coating coverage of the silver bromide grains was reduced to 0.43 g/m². Element 5 (not satisfying the invention) Element 5 was identical to Element 4, except that no Lippmann emulsion was blended to form Layer 2. Element 6 (not satisfying the invention) Element 6 was identical to Element 4, except that the Lippmann emulsion coverage was increased to 0.86 g/m² and was not blended in Layer 2, but was partitioned into two equal parts blended into Layers 1 and 3. The photographic performance of the color reversal photographic elements can be compared by reference to Figure 3, which shows the characteristic curves for Elements 4, 5, and 6 as curves C4, C5, and C6, respectively. In comparing the performance of the elements it is apparent that the blending of the Lippman silver bromide grains in the nontabular silver bromoiodide emulsion had the effect of markedly reducing the speed of Element 4 as compared to Element 1, presented by the dashed line curve E1, or Elements 5 and 6, represented by curves C5 and C6. It can be seen that inclusion of the Lippmann silver bromide emulsion in Layer 2 of Element 4 resulted in an increase in maximum density and a slight increase in contrast as compared to Element 5, but the large loss of speed prevented any decrease in toe region density from being obtained. It is to be further noted that the relationship of curves C5 and C6 is reversed from that expected from the relationship of curves C2 and C3. Element 7 (not satisfying the invention) Element 7 was identical to Element 4, except that the single jet ammonia digested silver bromoiodide emulsion exhibited a bromide to iodide mole ratio of 93.7:6.3 and a mean grain diameter of 0.70 Element 8 (not satisfying the invention) Element 8 was identical to Element 7, except that no Lippmann emulsion was blended to form Layer 2. Element 9 (not satisfying the invention) Element 9 was identical to Element 7, except that the Lippmann emulsion coverage was increased to 0.86 g/m² and was not blended in Layer 2, but was partitioned into two equal parts blended into Layers 1 and 3. The performance of Elements 7, 8, and 9 is represented by curves C7, C8, and C9 in Figure 4. In comparing the curves of Figures 3 and 4, it is apparent that the relative performance of Elements 7, 8, and 9 is similar to that of Elements 4, 5, and 6, respectively. Element 10 (not satisfying the invention) The following layers were coated on a transparent film support in the order recited: Layer 1 A very high speed green sensitized high aspect ratio tabular grain silver bromoiodide emulsion consisting of (a) high aspect ratio tabular bromoiodide grains having an average aspect ratio of 18:1, an average tabular grain thickness of 0.1 µm, and a bromide to iodide mole ratio of 97:3 (1.08); (b) gelatin (2.16); and (c) a cyan dye forming coupler, 3-[α-(2,4,-di- tert -amylphenoxy)hexanamido]-2-heptafluorobutyramidophenol (0.97). Layer 2 Gelatin (0.97) and bis(vinylsulfonyl)methane hardener at 1.75% by weight, based on total gelatin in both layers. Element 11 (satisfying the invention) Element 11 was identical to Element 10, except that 0.054 g/m² of 0.08 µm silver bromide grains in the form of a Lippmann emulsion were blended with the high aspect ratio tabular grain silver bromoiodide emulsion. Element 12 (satisfying the invention) Element 12 was identical to Element 11, except that the coating coverage of the silver bromide grains was approximately doubled to 0.11 g/m². Element 13 (satisfying the invention) Element 13 was identical to Element 12, except that the coating coverage of the silver bromide grains was doubled to 0.22 g/m². The performances of Element 10, represented by curve C10, and Element 13, represented by curve E13, are compared in Figure 5. It is apparent that curve E13 demonstrates a higher maximum density, threshold speed, and contrast and a lower toe region density. Elements 11 and 12 exhibited performances intermediate between those of Elements 10 and 13, except that Element 11 exhibited a lower maximum density and no higher contrast than Element 10. However, when the characteristic curves were translated to a superposed position at minimum exposure (at the left hand edge of the plot), it was apparent that the threshold speed and contrast increased progressively as a direct function of Lippmann emulsion inclusion, with Element 10 exhibiting the lowest threshold speed and contrast and Element 13 exhibiting the highest threshold speed and contrast. Elements 14 through 17 The comparison described above with reference to Elements 10 through 13 was repeated, but with 0.2 to 0.4 µm silver thiocyanate grains being substituted for the silver bromide grains. Silver thiocyanate concentrations are listed in Table I. The results for Element 14, represented by curve C14, and Element 17, represented by curve E17, are shown in Figure 6. Intermediate performances were exhibited by Elements 15 and 16. Element 14 does not satisfy the requirements of the invention while elements 15 through 17 do satisfy the requirements of the invention. Element 18 (not satisfying the invention) The following layers were coated on a transparent film support in the order recited: Layer 1 A very high speed green sensitized high aspect ratio tabular grain silver bromoiodide emulsion consisting of (a) high aspect ratio tabular bromoiodide grains having an average aspect ratio of 18:1, an average tabular grain thickness of 0.1 µm, and a bromide to iodide mole ratio of 97:3 (1.08); (b) gelatin (2.16); and (c) a cyan dye forming coupler, 3-[α-(2,4,-di- tert -amylphenoxy)hexanamido]-2-heptafluorobutyramidophenol (0.97). Layer 2 A yellow filter layer comprised of gelatin (0.60); α-cyano-4-[N,N-bis(isopropoxycarbonylmethyl)]-amino-2-methyl-4'-methanesulfonamidochalcone (0.11); and α-cyano-4-[N-ethyl-N-(2,2,2-trifluoroethoxycarbonylmethyl]amino-2-methyl-4'-propanesulfonamidochalcone (0.08). Layer 3 A very high speed blue sensitized high aspect ratio tabular grain silver bromoiodide emulsion consisting of (a) high aspect ratio tabular bromoiodide grains (1.08) having an average aspect ratio of 11.7:1, an average tabular grain thickness of 0.12 µm, and a bromide to iodide mole ratio of 97:3; (b) gelatin (2.16); and (c) a yellow dye forming coupler, α-[4-(4-benzyloxyphenylsulfonyl)phenoxy]-α-pivalyl-2-chloro-5-hexadecylsulfonamidoacetanalide (1.61). Layer 4 Ultraviolet absorbers 3-(di- n -hexylamino)allylidenemalonitrile (0.11) and n -propyl-α-cyano- p -methoxycinnamate (0.11), 0.08 µm silver bromide grains (0.12), gelatin (1.36), and bis(vinylsulfonyl)methane hardener at 1.75% by weight, based on total gelatin in all layers. Elements 19 and 20 (satisfying the invention) Elements 19 and 20 were identical to Element 18, except that the green sensitized high aspect ratio tabular grain emulsion forming Layer 1 also contained 0.11 and 0.22 g/m², respectively, of 0.08 µm silver bromide grains, introduced by blending a Lippmann emulsion. The time of development was four minutes 30 seconds. The performances of Element 18, represented by reversal characteristic curve C18, and Element 20, represented by reversal chracteristic curve E20, are compared in Figure 7. A very pronounced increase in maximum density, threshold speed, and contrast and a very pronounced decease in toe region density is observed for Element 20. The performance of Element 19 was intermediate between that of Elements 18 and 20, but nearer to that of Element 20. Elements 21 and 22 (satisfying the invention) Elements 21 and 22 were identical to Element 18, except that the green sensitized high aspect ratio tabular grain emulsion forming Layer 1 also contained 0.054 and 0.11 g/m², respectively, of 0.2-0.4 µm average diameter silver thiocyanate grains. In Figure 8 the reversal characteristic curve E21 of Element 21 is compared with the reversal characteristic curve C18 of Element 18. It can be seen that maximum density and contrast are higher for Element 21 than for Element 18. Element 21 exhibits a much lower density in the toe region of the curve than Element 18. Element 22, which contained approximately twice the coating coverage of silver thiocyanate grains exhibited differences from Element 18 that were qualitatively similar to those exhibited by Element 21, but the differences were larger in the case of Element 22. Element 23 (satisfying the invention) Element 23 was identical to Element 18, except that the green sensitized high aspect ratio tabular grain emulsion forming Layer 1 also contained 0.11 g/m² of 0.2-0.4 µm average diameter silver thiocyanate grains and 0.22 g/m² of 0.08 µm silver bromide grains. The reversal characteristic curve E23 obtained for Element 23 is plotted in Figure 8. It can be seen that a higher maximum density and contrast is realized as compared to corresponding curves C18 and E21 representing Elements 18 and 21, respectively. Also a lower toe region density is realized. Element 24 (not satisfying the invention) An element similar to Element 14 was prepared, exposed, and processed, except that the emulsion layer additionally contained silver iodide grains of less than 0.1 µm in average diameter (0.11) as a result of blending in a Lippmann silver iodide emulsion. The characteristic curves from Element 14, Curve C14, and Element 24, Curve C24, are compared in Figure 9. From Figure 9 it is apparent that the addition of the fine silver iodide grains resulted in an incremental increase in density at all levels of exposure. Reduced toe region density was not obtained, contrast increase was marginal, and minimum density was increased. Thus, the advantages of the invention are not realized by substituting silver iodide grains. Element 25 (not satisfying the invention) A control element was made by coating a sulfur and gold chemically sensitized high speed red spectrally sensitized high aspect ratio tabular grain silver bromoiodide emulsion on a gelatin (4.89) subbed film support. The tabular silver bromoiodide grains had an average diameter of 1.6 µm and an average thickness of 0.11 µm. The silver coverage was 1.46 g/m² and the gelatin coverage of the emulsion layer was 2.15 g/m². The emulsion layer was overcoated with gelatin (0.98), and the element was hardened with 1.57 percent by weight, based on total gelatin, bis(vinylsulfonyl)methane. The film support had a process removable carbon containing antihalation layer of the type disclosed in Simmons U.S. Patent 2,327,828. Element 26 (satisfying the invention) An element was prepared similar to Element 25, except that the silver coverage was increased 5 percent by weight by blending into the silver bromoiodide emulsion before coating a Lippmann emulsion having silver bromide grains of 0.08 µm average diameter. Element 27 (satisfying the invention) An element was prepared similar to Element 25, except that the silver coverage was increased 10 percent by weight by blending into the silver bromoiodide emulsion before coating a Lippmann emulsion having silver bromide grains of 0.08 µm average diameter. Element 28 (satisfying the invention) An element was prepared similar to Element 25, except that the silver coverage was increased 20 percent by weight by blending into the silver bromoiodide emulsion before coating a Lippmann emulsion having silver bromide grains of 0.08 µm average diameter. Elements 25, 26, 27, and 28 were identically exposed and processed. The dried elements were exposed (1/50 second, 500 watts/2850°K) through a 0.61 neutral density filter and a Daylight V filter plus a Wratten 23A® filter. After removal of the antihalation layer, the elements were processed for 80 seconds in a black-and-white developer of the type disclosed by Battaglini et al U.S. Patent 3,607,263, Example 1, washed, exposed uniformly to red light, and processed in color developer containing a cyan coupler, following a procedure like that of Example 1 of Schwan et al U.S. Patent 2,959,970. The characteristic curves obtained for Elements 25 and 28 are shown in Figure 10 as curves C25 and E28, respectively. It can be seen that curve E28 has a higher maximum density and contrast than curve C25 and exhibits reduced density in the toe region of the characteristic curve. The characteristic curves for Elements 26 and 27, not shown, fell between the characteristic curves C25 and E28, but nearer to E28.

Claims: A multicolor photographic element capable of forming a viewable reversal dye image comprising a support and, coated on said support, a blue recording yellow dye image forming layer unit, a green recording magenta dye image forming layer unit, and a red recording cyan dye image forming layer unit, at least one layer unit containing an image recording emulsion layer comprised of a dispersing medium and radiation sensitive tabular silver bromoiodide grains having a thickness of less than 0.5 µm and a diameter of at least 0.6 µm have an average aspect ratio of greater than 8:1 and account for at least 35 percent of the total grain projected area of said emulsion layer, characterized in that blended with said radiation sensitive tabular silver bromoiodide grains are relatively fine silver bromide or silver thiocyanate grains present in a concentration of at least 0.5 mole percent, based on total silver in said emulsion layer. A multicolor photographic element capable of forming a viewable reversal dye image according to claim 1 wherein said radiation sensitive tabular silver bromoiodide grains having a thickness of less than 0.3 µm, a diameter of at least 0.6 µm, and an average aspect ratio of greater than 8:1 account for at least 50 percent of the total grain projected area of said emulsion layer. A multicolor photographic element capable of forming a viewable reversal dye image according to claims 1 and 2 wherein said tabular silver bromoiodide grains contain less than 8 mole percent iodide, based on silver. A multicolor photographic element capable of forming a viewable reversal dye image according to claims 1 through 3 wherein said relatively fine grains consist essentially of silver thiocyanate. A multicolor photographic element capable of forming a viewable reversal dye image according to claim 4 wherein said relatively fine grains consist essentially silver bromide. A multicolor photographic element capable of forming a viewable reversal dye image according to claims 1 through 5 wherein said relatively fine grains have an average diameter of less than 0.5 µm. A multicolor photographic element capable of forming a viewable reversal dye image according to claim 6 wherein said relatively fine grains have a diameter of less than 0.3 µm and consist essentially of silver thiocyanate. A multicolor photographic element capable of forming a viewable reversal dye image according to claim 6 wherein said relatively fine grains have a diameter of less than 0.1 µm and consist essentially of silver bromide. A photograpic element according to claims 1 through 8 which is a multicolor photographic element capable of forming a viewable reversal dye image wherein each of said blue recording yellow dye image forming layer unit, said green recording magenta dye image forming layer unit, and said red recording cyan dye image forming layer unit, are comprised of a blend of said radiation sensitive tabular silver bromoiodide grains and said relatively fine grains. A multicolor photographic element capable of forming a viewable reversal dye image according to claim 9 wherein said green and red recording dye image forming layer units each contain radiation sensitive tabular silver bromoiodide grains containing less than 8 mole percent iodide, having a thickness of less than 0.3 µm, a diameter of at least 0.6 µm, and an average aspect ratio of greater than 8:1 accounting for at least 50 percent of the total grain projected area of said emulsion layer. A multicolor photographic element capable of forming a viewable reversal dye image according to claims 9 and 10 wherein said tabular grains have an average aspect ratio of at least 12:1. A multicolor photographic element capable of forming a viewable reversal dye image according to claims 9 through 11 wherein said tabular grains contain from 1 to 7 mole percent iodide, based on silver. A multicolor photographic element capable of forming a viewable reversal dye image according to claim 12 wherein said tabular grains contain from 2 to 6 mole percent iodide, based on silver. A multicolor photographic element capable of forming a viewable reversal dye image according to claims 1 through 13 wherein said relatively fine grains are not intentionally internally fogged. A multicolor photographic element capable of forming a viewable reversal dye image according to claims 1 through 14 wherein said relatively fine grains are grains from a Lippmann emulsion.

Inventors: SHUMAN, DAVID CLAYTON, SOWINSKI, ALLAN FRANCIS
Applicants: EASTMAN KODAK COMPANY
Application year: 1986
Main classification: G03C1
IPC codes: G03C1, G03C5