CA1259845A - Reversal photographic elements containing tabular grain emulsions - Google Patents

Abstract

REVERSAL PHOTOGRAPHIC ELEMENTS
CONTAINING TABULAR GRAIN EMULSIONS
Abstract of the Disclosure Silver halide photographic elements are disclosed capable of producing reversal images including at least one emulsion layer comprised of a blend of tabular silver haloiodide grains and relatively fine grains consisting essentially of a silver salt more soluble than silver iodide.

Description

1~9~

REVERSAL PHOTOGRAPHIC ELEMENTS
CONTAINING TABULAR GRAIN EMULSIONS
Field of ~he Invention This invention relates to improved photo-graphic elements adapted for producing reversalimages. More specifically3 thls invemtion relates to reversal silver halide photographic elementæ
containing in at least one emulsion layer tabular haloiodide grains.
Back~round _ the Invention The term "silver haloiodide" i~ employed in its ~rt recognized usage to designate silver halide grains containing s~lver ions in combination with iodide ions and at least one of chloride and bromlde ions. The term "reversal photographic elemen~"
designates a photogrsphic element which produces a photographic image for v~ewing by being imagewise exposed and developed to produce a nega~ive of the image to be viewed, followed by uniform exposure and/or fogging of residual silver halide and process-ing to produce a second, viewable image. Color slides, such as those produ~ed from Kodachrome- and Ektachrome- films, constitute a popular example of reversal photographic elements.. In the overwhel~ing .
25 -majority of applications.the fir6t image i8 negative and the second image is positive. Groet U.S. P~tent 4,082,553 illustrates a conventional reversal p~otographic element containing silver haloiodide grains modified by the incorporation of a small proportion of fogged silver halide grains. Hayashi et al German OLS 3,402,840 is similar to Groet, bu~
describes the imaging silver halide grains in terms of those larger than and smaller th~n 0.3 micrometer and additionally requlres in additlon to the fogged silver halide grain6 or their metal or metal ~ulfide equivalent an organlc compound c~pable of forming silver salt of low solubility.
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_~_ Hlgh aspect ratio tabular grain silver haloiodide emulsions have been recognized to provide a variety of photographic advantages, such as improvements ln speed-granularity relationships, increased image sharpness, and reduced blue speed of minus blue recording e~ulsion ~ayers. High aspect ratio tabular grain silver haloiodide emulsions in reversal photographic elements are illustrated by Research Disclosure Vol. 225, January 1983, Item 22534; Wilgus et al U.S. Patent 4,434,226; Kofron et al U.S. Patent 4,439,520; Solberg et al U.S. Patent 4,43~,048; Maskasky U.S. Patent 4,400,463; and Maskasky U.S. Patent 4,435,501. Research Disclosure is published by Kenneth Mason Publications, Ltd., The Old Harbourmasterlg, 8 North Street, Emsworth, ~ampshire P010 7DD, England.
Brief Description of ~Q Drawin~
This invention can be better appreciated by reference to the following detailed descrlption considered in conjunction with the drawings, in which Figure 1 is a schematic diagram intended to compare qualitatitively the reversal characteristic curve 2 o~ a reversal photographic element according to this invention with the rever~al 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 exempli~y-ing this invention, identified by the prefix E before the element number, and comparative elements, identified by the prefix C before the element number.
Sum~larv of the Invention In one aspect this invention is directed to a photographic element capable of forming a reversal image comprising a support and, coated on the support, at least one image recording emulsion layer r~ ~?
.~

5 ~3 ~3 L~L 5 --3~
comprised of a dispersing medium and a blend of radiation sensitive tabular silver halolodide grainæ
having a thickness of less than 0.5 ~m, a diameter of at least 0.6 ~m, and an average aspect ratio of greatex than 8:1 accounting for at least 35 percent of the total grain projected area of said emulsion layer and relatively fine grains present in a concentration sufficient to improve re!versal photo-graphic imaging consisting essentially of a sllver salt more soluble than silver iodide.
It has been discovered that the addition of relatively fine grains consisting essentially of a silver salt more soluble than silver iodide to an emulsion layer containing tabular silver haloiodide grains can produce a combination of advantages in reversal imaging. 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 den~ity and contrast are observed, To permit the advantages o~ 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 salt more soluble than silver iodide is illustrated ~chematically in Figure 1. Curve 1 is the rever~al characteristic curve produced by an emulsion layer of a conventional reversal photographic element wherein radiation sensitive tabular silver haloiodide grains are pre~ent~ but the relatively fine grains are not present. Curve 2 illustrates the reversal charac-teristic curve produced by the same emulsion layerdiffering only by the incluaion of the relatively :,:
~: .

, . ' . .

~598 fine grains. It is to be understood that exposure and processing producing both curves are identlcal.
In the toe region 2a of the characteristic curve 2 it can be seen that density is lower than in the corresponding toe region la of the characteristic curve 1. Thus the inventive reversal photographic element produces images having hrighter highlights.
Comparing the mid-portions lb and 2b of the charac-teristic curves, it can be seen that the character-istic curve of the photographic element according tothe invention exhibits significantly higher contrast. Comparing the shoulder portions lc and 2c of the characteristic curves, it can be ~een that the shoulder portion 2c o~ the characteristic curve of the reversal photographic element sat;sfying this invention is of much higher density. In comparing the shoulder portions lc 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 o~
curve 1, where reversal threshold speed is defined as the exposure Ievel corresponding to the thre~hold (first detectable) decline from maximum density of the reversal characteristic curve. Shifting from the language o~ the photographic scientist to that of the ultimate user, the photographer, the present inven-tion adds speed~and "snap" to reversal photographicelements 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 8'~

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 ~ in maximum density, a loss of contrast, and an increase in toe region and minimum densities. If a conventional nontabular silver haloiodide 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 ~urther, advantageous modifications of reversal characteristic curve shape have been realized only when the radiation sensitive tabular grains are silver haloiodide grains as opposed to tabular silver halide grains lacking iodide as a constituent.
Description of Preferred Embodiments 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 record-ing 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 haloiodide 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 , ~
~, ~ s 5 ~

o which is cle~rly larger than any other single erystal 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 ~han 0.5 um and 8 diameter of at least 0.6 ~I have an average aspect ratio of 8reater than 8:1 and account for at least 35 percent of the to~al grain projected area of the blended grain emulsion layer in which they are present.
A convenient ~pproach 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 de~ined as requiring that the tabular silver halide grains having a thickness of less thsn 0.3 ~m ~nd a diameter of at least 0.6 ~ have an average ~spect ratio of greater than B:l and account for a~ least 50 percent of the total proje~ted area of the grain~
present in the emulsion. The term is thus defined in conformity with the usage of thls term in the patent~
25 relating to tabular grain emulsions cited above.
In general tabul~r grains are preferred having 3 thickness of less than 0.3 ~m. Where the emulsion layer is intended to record blue light as opposed to green or red light, it ~s advantageous to increase the thickness criter~on of the tabular grains to less ~han 0.5 ~m, instead of less than O.3 ~m. Such an increase in tabular grain thick-ness is also contemplated for applications in which the reversal image is to be viewed w~thout enlarge-35 ment or where granularity is of little importance,al~hough ~hese lat~er applic~tions are relatively ~ ~ S ~ 8~

rare in reversal imaging, reversel images being most co~monly viewed by projection. Tabul~r grain emulsions wherein the tabular grairs have a thickness of less than 0.5 ~ intended for recording blue S light are disclosed by Kofron et al U.S. Patent 4,439,520, cited above.
While the tabular grains satisfying ~he O . 3 ~m thickness and 0.6 ~m diameter criteria account for at least 50 percent o the total ?rojected area of the grains in high aspect ratio tabular grain emulsions, it is appreci~ted that in blending &
second grain population ~he tabular grain percentage of the tot~l grein projected area is decreased. The tabular grain emulsions contemplated for preparing blended grain emulsion layers satisfying the require-ments of this invention must be capable of providing tabul~r grains satisfying the thickness and diameter criteria which also provide at least 35 percent of the total grain projected ares in the blended 8rain emulsion l~yer. Thus, although the tabular graln emulsions employed in the practice of this invcntion preferably provide at least~50 percent of the total grain projected area, at least before blending with the second grain population, this i6 not essential if . . 25 the 3.5 percent of the total gr~in projected are~
condition noted above in the blended grain emulsion : layer is satisfied.
Thus, i~ is apparent that while high ~spect ratio tabular grain emulsions are preferred for prepsring the blended grain emulsions and in a highly preferre~ form the blended gr~ln emulsions are themselves high aspect rstio tabular 8r~in emulsions, this is not necessary in ~11 instance~, and departures can actually be advantageous for specific applications. However, for simplicity the ensuing discussion rel~ting to radiation sensitive t~bular s grain emulsions is directed to the preferred hlgh aspect ratio tabular grain emulsions, it belng appreciated that ~he teachings are g~nerally applic-able to tabular grain emulsions as herein defined.
The preferred high ~spect ratio tabular grain silver haloiodide emulsions are those wherein the silver haloiodide grains having a thickness of less th~n 0.3 ~m (optimally less than 0.2 ~m) and a diameter of at least 0.6 ~ have ~n aver~ge 10 aspect ratio of at least 12:1 and optimally at least 20:1. In a preferred form of the invention these silver haloiodide 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 ~rains. In a highly preferred form of the inventio~ the blended grain emulsions required by this invention al~o satisfy the parameters set out for the preferred high aspect ratio tabular grain emulsions.
It is appreciated that the thinner the tabulsr grains accounting for a given percentage of the projected area, the hig~er the average aspect ratio of the emulsion. Typically the tabular gr~in~
have an average thickness of ~t least 0.03 ~, al~hough even thlnner tabular gr~ins can in principle be employed.
High aspect ratio tabular grain emulsion6 useful in the practice of this invention can have extremely high average ~spect ratios. Tabular gr~in average aspect raeios can be increased by increasing average grain diameters. This can produce sharpness advantages, bu~ maximum average grain diameters are generally limited by granularity requirements for a specific photographic application. Tabular grain average aspect ratios can also or alternat~vely be increased by decreasing average grain thicknesses.

, 5 ~
_9_ When silver coverages are held cons~ant, decreasing the thickness of tabular grains generally improves granularity as a dir ct function of increasing aspect ratio. Hence the maximum average aspect ratios of the tabular grain emulsions of thiE; invention ~re a function of the maximum aver~ge grain diameters acceptable for the specifie pho~ogrsphic application and the minimum a~tainable tabular grain thicknesses which can be conveniently produced. Maximum average 1~ aspect ratios have been observed to vary, depending upon the precipi~a~ion technique employed and the tabular grain halide composition. High aspect r~tio tabular grain silver haloiodide emulsions with average aspect r~tios of 100:1, 200:1, or even higher ~re obt~inable by double-jet precipitation procedures.
The tabular haloiodide gr~ins employed in the practice of this invention contain in add~tion to iodide at least one of bromide and chloride. Thus, the silver haloiodides speciflcally contemplated are silver bromoiodides, silver chlorobromoiodides, and silver chloroiodides. Silver bromoiodide emulsions generally exhibit higher ph~otographic speeds and are ; for this reason the preferred and most commonly employed emulsions for candid photogr~phy.
Iodide must be present in the tabula-r silver haloiodide grains in a concentration sufficient to influence photographic performance. It is thu~
contempla~ed that at least about 0.5 mole percent iodide will be present in the tabular silver halo-iodide grains. However, high levels of iodide are not required to achieve the advantages of this invention. Generally the t~bular silver haloiodide grains contain less ~han 8 mole percent iodide.
Preferred iodide levels in ~he tabular silver hsloiodide grains are from 1 to 7 mole percen~ ~nd optimally are from 2 to 6 mole percent. All of the ~L2: 5 ~3 8 L~

above iodide mole percentages are based on ~otel silver present in the tabular grains.
The r~diation sensitive tabul~r h~loiodide grains required for the practice of this invention are preferably provided by selecting from amon~ the various high aspect ratio tabular grain emulsions disclosed in Research Disclosure Yol. 225, January 1983, Item 22534; Wilgus et al U.S. Patent 4,434,226;
Kofron et al UOS. Patent 4,43~,520; Solber~ et al lu U.S. Patent 4,433,048; Maskasky U.S. Patent 4,40~,463; and Maskasky U.S. Pa~ent 4,435,501; each cited above.
The blended grain emulsion required for the practice of this invention can be convenien~ly : 15 provided by blending with a tabul~r gr~in silver h~loiodide emulsion as described above a second grain population consisting essentially of silver salt which is more soluble than silver iodide. The silver salt should be sufficiently insoluble that it is capable of forming a grain rather than being present in a solubilized-form. Useful silver salts can be chosen from among those ha~ng a solubility product constant in the range 9.5 to less than 16. Preferred silver s~l~s are those having a solubility product constant in the range of from 9.75 to 15.5, op~imally from ll to 13. Unless otherwise stated9 all solu-bility product constants are referenced to a temp~ra-ture of 20~C. A discussion and listing of solubility product constsnts for exemplary silver salts is presented by James, Theory of the Photo&raphic : Process, 4th Ed., Macmillan, 1977, Chapter 1, Sections F~ G, and Hs pp. 5-lO.
It is preferred th~t the silver salt forming the relatively fine grains be at least as soluble as the mos~ soluble silver halide present ~n the rsdiation sensi~ive tabul~r grains. For example, L~L 5 when the tabular grains consist essentially of silver chlorobromoiodide, ~he rela~ively fine grains preferably consist essentially of sllver chloride or silver chlorobromide as opposed to s.ilver bromide.
5 When radiation sensitive tabular silver bromoiodide grains are employed 5 the relstively fine grfllns preferably consist essentially of silver bromide, silver thiocyanate, or a combination of both.
Advantages have been realized when silver bromide and 1~ silver thiocyanate grains are employed in combination.
Although ~he relatively fine grains consist essentially of silver salt more soluble than silver iodide, it is appreciated that less soluble silver salts in small quantities that do not interfere with 15 effectiveness can be presen~. For example, it is common to treat silver halide emulsions with soluble iodide salt solutions in conjunction with spectral sensitiza~ion and to employ 8S antifoggAn~s and stabilizers compounds which form highly insoluble silver salts. While such conventional treatments can result in the adsorp~ion of small quan~ities of silver iodide or one or more other highly in601uble silver salts to the surfaces of the relatively fine grains, such conventional emulsion treatments are not ~5 normally incompatible with the practice of this invention.
The grains consistlng essentially of a silver salt more soluble than silver isdide are fine as compared ~o the tabular silver haloiodide grains.
In general, the permissible si~e of this second grain popul~tion blended with the radiation sensitive tabular grains is a direc~ function of the solubility of the silver salt forming these grain6. The sesond gra~n population in all ins~ances exhibi~s an average grain diameter of less than 0.5 ~m and preferably exhibits an average grain diameter of less than 0.3 ~L~ 5 ~ 8 L~

~m. Op~imally the second gra~n population exhibits an average grain diameter of less than 0.1 ~.
Thus, the second grain population is optimally provided by blending a conventional Lippmann emulsion S with the radi~tion 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 popul~tlon is limlted only by synthetic convenience, typically being at least about 0~05 ~m.
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 popula-tion concentr~tions can range from as low 8S about0.5 mole percent; b~sed on total silver in the blended gr~in emulsion layer~ with concentrations above about 1 mole percent being preferred and concentrations above about 5 mole percent belng optimum for maximizing photographic benefits. To svoid inefficient use of silver salts m~ximum concentrations of the seco~d grain population are generally maintained below the concen~rations of the silver haloiodide forming the radia~ion sensitlve tabular grains--that ls, below SO mole percent, ba6ed 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 requ~red for the practice of this invention by blending a tabular silver haloiodide grain emulsion and a separfltely prep~red emulsion containing the relatiYely fine second grain popula-tion. The relatively fine grain emulsion c n, for example, take the form of a relatively fine grain silver chloride, silver bromide, or silver thio-cyanate emulsion, the preparation~ of whish are well known to those skilled in the art and form no p~r~ of this invention. As prev~ously, no~ed the relatively S fine grain emulsion is optimally a Lippmann emul-sion. So long as the grain requ~remen~s identified above are satisfied, either or both of the tabular grain containing and reletively fine grain cont~ining emulsions can themselves be ehe product of conven-tional grain blending.
Apar~ from the blended grsin emulsionfeatures specifically described above ~he reversal photographic elements of this invention can take any convenient conventional form. The reversal photo-graphic elements can t~ke the form of e~ther black-and-white or color reversal photographic elements.
In a very simple form the reversal photo-graphic elements according ~o this inven~ion can be comprised of a conventional photographic support, such ~s a transparent film support, onto which i6 coated a blended grain emulsion layer as described aboYe. Although conventio~al overcoat snd subbing layers are pre~erred, only the blended grsin emulsion layer is essential. Following im~gewlse exposure, - 25 silver halide is imagewlse developed to produce a fLrs~ silver image, which need not be view~ble. The firs~ silver image can be removed by bleaching before further development when ~ silver or silver enhanced dye reversal image is desired. There~fter, the residual silver halide ls uniformly rendered develop-able by exposure or by fogging. Developmen~ produce6 reversel image. The revers~l image can be ei~her silver image, a silver enh~nced dye image, or a dye image only, depending upon the specific choice of conventional processing technique6 employed. The production of silver reversal images i5 described by s ;;9 8L~ 5 Mason, Photographic Processin~ ChemistrY, 1966, Fooal Press Ltd., pp. 160-161. If a dye only image i6 being produced, silver bleaching is ususlly deferred until after the final dye image is formed.
The reversal photographic elements of thls in~ention are in a preferred form color reversal photographic elements capable of producing multicolor images - -e . g ., images th~t at least approxim~tely replicate subject colors. Illustrstive of such color 1~ reversal photographic ele~ents are those disclosed by Kofron et al U.S. Patent 4,439,520 and ~roet U.S.
Patent 4,082,553, each cited above. In ~ simple form such a color reversal photographic element can be comprised of a support having coa~ed thereon at least three color forming layer units, including a blue recording yellow dye image forming layer unit, a green recording magent~ dye image forming layer unit, and a red recording cyan dye image forming layer unit. Each color forming layer unit is comprised of a~ least one radia~ion sensitive silver halide emulsion layer. In a preferred form of the inven~ion at least one radiation sens~itive emulsion layer in each color forming layer unit is comprised of a blended grain emulsion as described above. The 25 blen~ed grain emulsions in each color forming layer unit cRn be chemic~lly and spectrally sensitized as taught by Kofron et al U.S. Patent 4,43~,520. In a preferred form chemical and spectral sensitization of the tsbular grain emulsion is completed before 30 blending with the second grain population~ which therefore remains ~ubst~ntially free of sensitiæing materials. One or more dye im~ge providing mater-i~ls, such as couplers, ~re prefer~bly incorporated in each color forming layer unit, but c~n alterna-tively be introduced into the photographic elementduring processing.

9 ~3 L`L 5 The following constitutes a specific illustration of a color reversal photogr~phic element according ~o this invention:
I. Photographic Suppor~
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 eoated with bary~a and/or ~-olefin polymer, particularly a polymer of an ~-olefin containing 2 to 10 carbon atoms, such as polyethyl-ene, polypropylene, and ethylenebutene copolymers.
II. Subbing Layer To facili~ate 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 haloiodide emulsion layer~ as described in detail above. In an emulsion layer or in a layer adjacent thereto at least one conven~ional 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; 3,034~92;
~; 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 leas~ one hydrophilic colloid interlayer, preferably ~ gelatin interlayer which includes a reducing agent, 6uch a~ an aminophenol or an ~lkyl subseituted hydroquinone, i~ provided to act as an oxidized developing agent seavenger.

1~2 5 ~3 8 L~ 5;

V. Green Recording Layer Unit At least one layer comprised of a green sensi-ti7ed blended gr~in high aspect ra~io tabul~r grain silver haloiodide emulsion layer, as described ~n detail abo~e. In an emulsion layer or in ~ layer adjacen~ there~o at least one conventional magenta dye image forming coupler is include~d, such as, for example, one of the magenta dye image forming couplers disclosed in U.S. Pa~en~s 2,725,292;
1~ 2,772,161; 2,895,826; 2,908,573; 2,920,~61;
2,933,391; 2,983,608; 3,005,712; 3,006,759;
3,062,653; 3,148~062; 3,152,896; 3,214,437;
39227,554, 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 lsyer can take ~ny convenient conventionAl form, such as a gelatino-yellow colloidal silver layer (i.e., a Carey 20 Lea silver layer) or a yellow dye cont~ining gelatin layer. In addition the filter layer contains ~
reducing agent ac~ing as a~ oxidized developing agent scavenger, as described above in connection with ~he Interlayer IV.
VII. Blue Recording Layer Unit At least one layer comprised of a blue sensitized blended gr~in high aspect r~tio tabular grain silver haloiodide emulsion l~yer, as described in detail above. In an alternative form the tabular grains can 30 be thicker than high aspect r~tio tabul2r grains-~that is, the thickness criteria for the gr~ins can be incre~sed from O . 3 ~m to less th~n 0.5 ~m, 86 described above. In this lnstance the grains exhibit more na~ive blue speed, whlch preferably is augmented 35 by the use of blue spectral sensitizers, although this is not essen~clal, except for the highest 5 ~ 'B L'9~

attainable blue ~peeds. In an emulsion layer or in a layer adjacent thereto at least one conventional yellow dye image f orming coupler is included, such as, for example, one of the yellow dye image forming couplers disclosed in U.S. Patents 2,875,057;
2,895,826; 2,908,573; 2,920,961; 3,14~,0~2;
3,227,55~; 3,253,924; 3,265,506; 3,277,155;
3,369,~95; 3,384,657; 3,408,194; 3,415,652; and 3,~7,928.
VIII. Overcoat Layer At least one overcoat layer is provided. Such layers are typically transparent gela~in layers and contain known addenda for enhancing coating, handl-ing, and photographic properties, such as matting agents, surfactants, antistatic agents, ultraviolet absorbers, and similar addenda.
As disclosed by Ko~ron et al U.S. Patent

4,439,520, the high aspect ratio tabular graln 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 tha~ in the absence of a yello~ 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 sensi-tive emulsion layers any, some, or all o$ which satisfy the blended grain emulsion requirements of this invention.

~, ~' 3L2 ~3 8L~5 In addition to the features described above ~h~ reversal photographic elemen~s can~ of coursel contain other conventiona' features l~nown in the art, which can be illustrated by reference to Rese~rch Disclosure, Vol. 176, December 1978, Item 17643. For example, the silver halide emulsions other than the blended gr&in emulsions described can be ~hosen from among those described in Paragraph I; the silver halide emulsions can be chemically sensitiæed, as 1~ described in Paragraph III; the silver halide emulsions can be spectrally sensitized, ~s described in Paragraph IV; any portion of ~he elements can con~ain brighteners, as described in Paragraph V; the emulsîon l~yers can contain antlfoggants and stabilizers, as described in Paragraph VI~ the color forming layer units can contain color image Eorming materials as described in Paragraph VII; the elements can contain absorbing and scattering materi~ls, as described in Paragraph VIII; the emulsion and other layers can contain vehicles, as described in Para-graph IX; the hydrophilic colloid and other layers of the elements can contain ha'rdeners, as described in P~ragraph X9 the layers. can contain coatîng aids~ 8S
described in Paragraph XI; the layers can contain 2S plasticizers and lubricants, as.described in.Para-graph XII; the layers, particularly the layers coated farthest from the support, can contain matting agents, as described in Paragaph XVI; and the suppor~s can be chosen from among those described in 30 Paragraph XVII. This exempl~ry listing of addenda and features is not intended to restrict or imply the absence of other conventional photographic features compatible with ~he practice of ~he invention.
The photographic elements can be imagewise 35 exposed with any of various forms of energy, B~
illustrated by Resear~h Disclosure, Item 17643, cited 1~598~

above, Paragraph XVIII. For multicolor imaging the photographic elements are exposed eo visible light.
Multicolor reversal dye images can be formed in photographic elements according to this lnvention

5 having differentially spectrally se~sitized silver halide emulsion layers by black-and-white development followed by color development. Reversal processin~
is demonstrated below employing conven~ional 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 lS instance, except ~s otherwise stated, exposed through a step tablet for 0.02 second by a 500 watt 2850K
light source ~hrough a Wrstten 8- filter and reversal processed wlth 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 ~he 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 sonsisting of (8) high aspect ratio tabular bromoiodide grains (1.08) havlng an aver~ge aspect r~tiv of 18~ n average tabul~r graln thickness of 0.1 ~m, and 8 bromide to iodide mole ratio of 97:3; (b) 0.08 ~m silver bromide gr~ins (0.86) provided by blending Lippmann emul 6 ion with a high aspect ratio tabular grain silver bromoiodide emulsion providlng the ~2S~345 grains for (a); (c) gelatin (2.16); and (d) a msgenta dye forming coupler, 1~(2,4,6~trichlorophenyl)-3-{3-[~-(2,4,-di-tert-amylphenoxy)acetamido]benz-amido}-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 ~o 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, bu~ was partitioned into ~wo equal parts blended into Layers 1 and 3.
The photographic performsnce of the color revers~l photographic elements can be compared by r~ference ~o Figure 2, which shows the characteristic 20 curves for Elements 1, 2, and 3 as curves El, C2, and C3, respectively. In comparing curve El with curves ; C2 and C3 it can be seen t~at a higher maximum : - density and contrast is realized and that a lower density in the toe reg~on of the curve El is realized. Ie is surprising th~t the psrtitioning o the silver bromide Lippmann emulsion between the overcoat and undercoat layers degrades photographic performance so that lower maximum density and contrast as well as ~ higher minimum density are observed than when the Llppmann emulsion i8 entirely absent. Further, it is highly surprising that the partitioned Lippma~n 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.

~L~59~3~5 Element 4 ~not satisfy~ng the invention) An element identic~l to Element 1 w~6 prepared, except th~t instead of blending a hlgh aspect rstio tabular grain emulsion with the silver 5 bromlde Lippmann emulsion (a) a single ~et precipi-t~ted, ammonia diges~ed silver bromoiodide emulsion containing non~abular gr~ins of 0.54 1~ in mean diameter Pnd a bromide to iodide mol,e r&~lo of 96.5:3.4 was substituted for the high aspect ratio tabular grain silver bromoiodide emulsion and tb) the coating coverage of the silver bromide grains was reduced to 0.43 g/m 2 .
_lement 5 (not satisfying the invention) : Element S was identical to Element 4, except that no Lippmann emulsion w~s blended to form Layer 2.
Element 6 (not s~tisfyin~ the invention) Element 6 was identical to Element 4, except th~t the Lippmann emulsion cover~ge was increased to 0.86 g/m 2 and was not blended in Layer 2, but was partitioned into two equsl p~rts blended into Layers . 1 and 3.
: The photogr~phic p~rformance of the color reversal photographlc elements can be compared by reference to Figure 3, which shows the ch~racteristic 25 curves for.Elemen~s 4, 5, and 6 as curves C4, CS, and C6, respec~lvely. In comparing ~he performance of the elements it is appsrent that the blending of the Lippman silver bromide grain6 in the nontabular - silver bromoiodide emulsion h~d the effect of markedly reduclng the speed of Element 4 as compared to Elemen~ 1, presented by the dashed line curve El~
or Elements 5 and 6, represented by curves C5 ~nd C6. It can be seen that lnclusion of the Lippmann silver bromide emulsion in L&yer 2 of Element 4 resulted in an increase in maximum density end ~
slight increase in contrast ~s compared to Element 5, ~L25~5 but the large loss of speed prevented any decrease in ~oe region density from being obtained. It is to be further noted that the relationship of rurves C5 and C6 is reversed from that expected from the relation-5 ship of curves C2 and C3.
Element 7 ~not satisfyin~ the invention) Element 7 was identical to ~Lement 4, except that the single je~ ~mmonia digested silver bromo-iodide emulsion exhibited a bromide to iodide mole ratio of 93.7:6.3 and a mean grain diameter of 0.70 ~m .
Element 8 (no~ satisfying the invention~
Element 8 was identical to Element 7, Pxcept that no Lippmann emulsion W85 blended to form Layer 2.
Element 9 (not satisfyin~ the inven ion) Element 9 was identical to Element 7, except that the Lippmann emulsion coverage was increased to 0.86 g/m 2 and was not blended in Layer 2, but was p~rtitioned into two equal parts blended into Layers 1 and 3.
The performance of Elements 7, 8, and 9 is represented by curves C7, C~, 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 ~o that of E~ements 4, 5, and 6, respectively.
Element 10 (not satisfying the invention) The following layer6 were coated on a transparent film support in the order recited:
Lsyer 1 A very high speed green sensitized high aspect ratio tabular grain silver bromoiodide emulsion consi~ting of ~a) high aspect ratio tabular bromoiodide grains having an sversge aspect ratio of 18:1, an aversge tabular grain thickness of 0.1 ~m, and a bromide to iodide mole ratio of 97:3 (1.08); (b) gelatin (2.16);

~,~ 5~3 8L~L5 and (c~ a cyan dye forming coupler, 3~ (2,4,-di-t rt-amylphenoxy)hexanamido]-2-heptafluorobutyr-smidophenol (0.97).
Layer 2 Gelatin (0.97) and bis(vinylsulfonyl)methane hardener at 1.75% by weight, based on total g~elatin in both layers.
Element_ll (satisfy~g the invention) Element 11 was identical to Element 10, 10 except that 0.054 g/m 2 of 0.08 ~m silver bromide grRins in the form of a Lippmann emulsion were blended with the high aspect ratio tabular gr~in silver bromoiodide emulsion.
Element 12 (satisfying the invention) -Element 12 was identical to Element 11, except that the coatlng coverage of the silver bromide grains was approximately doubled to 0.11 g/ m 2 .
Element 13 (satisfying the invention) 2~ Element 13 was identical to Element 12, except thae the coating coverage of the silv~r bromide grains was doubled ~o 0.22 g/m2.
The performances of Element 10, represeneed 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 in~ermediate between those of Elements 10 and 13, except that Element 11 exhib~ted a lower maximum density ~nd no higher contrast th~n Element 10.
However, when the characteristie curves were ~ran~
lated to a superposed position at minimum exposure (at the left hand edge of the plot) 3 it w~s apparen~
that the threshold speed and contrase increased progressively as a dirsct function of Lippmann ~25~3~

emulsion inclusion, with Element lO exhibiting ~he lowest ~hreshold ~peed and contrast and Element 13 exhibitin~ the highest threshold speed and contr~st.
Elements 14 through 17 The comparison described above with refer~
ence to Elements 10 through 13 was repeated, but with O.2 to 0.4 ~m silver ~hiocyanate grains being substituted for the silver b-romide grains. Silver thiocyan~e concentr&tions are lis~ed in Table I.
lU The results for Element 14, represented by curv~ C14, and Element 17, represented by curve E17, are ~hown in Figure 6. Intermediate perform~nces were exhibited by Elements 15 and 16. Element 14 does not satisfy the requirements of the invention while elements 15 through 17 do s~tisfy the requirements of the invention.
Table I
Element Curve A~CN (g/m 2) 14 C14 None 2015 --- 0.055 16 --- 0.11 17 E17'~ 0.22 Element 18 (not satisfying the invention~
The following layers were coated on a . 25 transp~rent film support in the orde~ recited:
Layer l A very high speed green sensitized high ~spect ra~io tabular grsin silver bromoiodide emulsion con~isting of (a) high aspect ratio tabular bromoiodide grains 30 having an aver~ge aspect ratio of 18:1, an sver~ge tabular grain ~hicknes 6 of 0.1 ~m, and ~ bromide to iodide mole ratio of 97:3 (1.08); (b) gelatin (2.16~;
and (c) a cyan dye formlng coupler, 3-~ ~(2,4,-di-tert-amylphenoxy)hexanamido]-2-heptafluorobutyr-35 amidophenol (0.97).

~5 L~yer 2 A yellow filter layer co~prised of gelatin (O.S0~;
~-cyano-4-[N,N-bis(isopropoxycarbonyl~ethyl)]-amino-2-methyl-4'-methanesulfonamidochalcone ~0.11);
and ~-cyano-4-~N-ethyl-N-(2,2,2-trifluoroethoxy-carbonylmethyl~amino-2-methyl-41-propanes~lfonamido-chalcone (0.08).
Layer 3 A very high speed blue sensitized high aspect r~tio 1~ tabular grain ~ilver bromoiodide emulsion consisting of (a) high aspect ratio tsbular bromoiodide grains (1.08) heving an average aspect ratio of 11.7:19 an average tHbular grain thickness of 0.12 ~m, and a bromide to iodide mole ratio of 97:3; ~b) gelatin (2.16); and (c) a yellow dye forming coupler, ~-~4-(4-benæyloxyphenylsulfonyl)phenoxy]-~-pivalyl-2-chloro-5-hexadecylsulfonamidoacetan~lide (1 . ~1) .
Lsyer 4 20 Ultraviolet absorbers 3-(di-n-hexylamino)allylidene-malonitrile (0.11) ~nd n-propyl-~-cyano-~-methoxy-cinnamate (0.11), 0.08 ~m silver bromide grains (0.12), gelatin ~1.36), and bis(vinylsulfonyl)me~hane hardener at 1.75~h by weight, based on total gelatin -25 in all layers.
Elements 19 and 20 (satisfyin~ the invention) Elements 19 and 20 were identical to Element 18, except that the green sensieized high aspect rstio tabular grsin emulsion forming Layer 1 ~lso contained 0.11 and 0.22 g/m29 respect~vely, of 0.0 ~m silver bromide gr~ins9 introduced by blending a Lippmann emulsion. The time of development wa four minutes 30 seconds.
The performances of Element 18, represented 35 by reversal charact2ristlc curve C18, and Element 20, represented by reversal chr~cterist~c curve E20~ are compared in Figure 7. A very pronounced increa~e in maxim~m density, threshold speed, and contrast and a very pronounced decease in toe region density is observed for Elemene 20. The perform~nce of Element 19 was intermediate between that of Elements 18 and 20~ but nearer to tha~ of Element 20.
Elements 21 and 22 (satisfying ~he invention) Elements 21 and 2Z were identical to Element 18, except that the green sensitized high aspect lU ratio tabul~r grain emulsion forming Layer 1 also contained 0.054 and 0.11 g/m2, respectively, of 0.2-0.4 ~m average diameter silver ~hiocyanate grains.
In Figure 8 the reversal characteris~ic 15 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 2U than Element 18.
Elemen~ 22, which contained approximately twice the coating coverage~of silver thiocyanate grains exhibited differences from Element 18 that were qualitatlvely similar to those exhibited by 25 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 ehat the green sensltized high sspect ratio tabular grain emulsion forming Layer 1 al~o contained 0.11 glm2 of 0.2-0.4 ~m average diameter silYer thlocyan~te grain~ and 0.22 g/m 2 of 0.08 ~m sllver bromide grains.
The reversal characteristic curve E23 35 obtained for Element 23 is plotted in Figure 8. It can be seen that a higher maximum den6ity and contrast is realized ~s comp~red to corresponding curves C18 and E21 representing Flements 18 ~nd 21, respec~ively. Also a lower toe region density i6 refllized~
Element 24 (not satisfyan~ the invention) An element similar to Element 14 was prepared, exposed, and processed, except that the emulsion layer additionally~con~ained silver iodide grains of less than 0.1 ~m in av~rage diameter 1~ (0.11) as a result of blending in a Lippmann silver iodide emulsion.
The chara~teris~ic curves from Element 14, Curve C14, and Elemen~ 24, Curve C24, are comp~red in Figure 9. From Figure 9 it is apparent that the addi~ion of the fine silver iodide grains resulted ~n an incre~ent~l incre~se in density at all levels of exposure. Reduced toe region density was not obtained, contrast incre~se was m~rginAl, ~nd minimum density was increased. Thus, the ~dvantages of the inven~ion are not realized by substituting silver iodide grains.
Element 25 (not satisfyhn~ ~he inven~ion) A control element w~s made by coating &
sulfur and gold chemically sensitized high speed red spectr~lly sensitized high aspect r~tio tab~l~r gr&in silver bromoiodide emulsion on a gelatin (4.89) subbed film support. The tabular silver bromoiodide grains had an average diameter of 1.6 ~m ~nd an average thickness of 0.11 ~m. The silver coverage w~s 1.46 g/m 2 and the gelatin coverage of the emulsion lsyer was 2.15 g/m 2. The emulslon layer W&S overco~ted with gel~tin (0.98), and ~he element WR8 hardened with 1.57 percent by weight, based on total gelatin, bis~vinylsulfonyl)meth~ne~ The film support had a process removable carbon containing antihalation lsyer of the type disclosed in Simmons U.S. Pstent 2,327,828~

Element 26 (satisyin~ the inventlon) An element was prepared ~imil~r to Element 25, ex~ept tha~ ~he silver coverage was increa6ed S
percen by weight by blending into the silver 5 bromoiodide emulsion before coating a Lippmann emulsion h~ving silver bromide grains of 0.08 ~m average diame~er.
Element 27 (satisfying the invention) An element was prepared similar to Element 1~ 25, except that the silver coverage was increased 10 percent by weight by blending into the silver bromoiodide emulsion befQre coating ~ Lippmann e~ulsion having silver bromide gr~ins of 0.08 average diameter.
Element 28 (satisfylng the invention) An element was prepared simil~r to Element 25, except that the silver coverage WA6 increa6ed 20 percent by weight by blending into the silver bro~oiodide emulsion before coating a Lippm~nn emulsion h~ving silver bromide gr~ins of 0.08 ~m average diameter.
Elements 25, 26, 27, and 28 were ideneically exposed ~nd proce~sed. The dried elements were exposed (1/50 second 9 500 watts/2850K) through a - 25 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 Battagl;ni et al U.S. Patent 3,607,263, 30 Example 1, w~shed, exposed uniformly to red ligh~, and processed in color developer sontaining a cyan coupler, following ~ procedure like that of Example 1 of Schwan et al U.S. Patent 2,959,970.
The characteristis curves obtained for Elemen~s 25 and 28 sre shown in Figure 10 as curves C25 and E28, respectively. It can be seen that curYe 2 5 ~

E28 has a higher maximum density and con~rast than . curve C25 and exhibits reduced density in the toe region of the c~aracteristic curve. The ch&rac~er-istic curves for Elements 26 and 27, not shown, fell 5 between the characteristic curves C25 and E28, but nearer to E28.
The invention has been described with par~icular reference to preferred embodlments thereof~ but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

Claims (21)

WHAT IS CLAIMED IS

1. A photographic element capable of forming a reversal image comprising a support and, coated on said support, at least one image recording emulsion layer comprised of a dispersing medium and a blend of radiation sensitive tabular silver haloiodide 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 and relatively fine grains present in a concentration sufficient to improve reversal imaging consisting essentially of a silver salt more soluble than silver iodide.

2. A photographic element capable of forming a reversal image according to claim 1 wherein said radiation sensitive tabular silver haloiodide 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.

3. A photographic element capable of forming a reversal image according to claim 1 wherein said tabular silver haloioidide grains contain less than 8 mole percent iodide, based on silver.

4. A photographic element capable of forming a reversal image according to claim 1 wherein said relatively fine grains consist essentially of a silver salt having a solubility product constant less than 16 at 20°C.

5. A photographic element capable of forming a reversal image according to claim 4 wherein said relatively fine grains consist essentially of a silver salt having a solubility equal to or greater than that of silver bromide.

6. A photographic element capable of forming a reversal image according to claim 1 wherein said relatively fine grains-have an average diameter of less than 0.5 µm.

7. A photographic element capable of forming a reversal image according to claim 1 wherein said relatively fine grains are present in a concen-tration of at least 0.5 mole percent, based on total silver present in said image recording emulsion layer.

8. A photographic element capable of forming a reversal image according to claim 1 wherein said photographic element is capable of producing a dye image.

9. 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 units and a red recording cyan dye image forming layer unit, at least one of said dye image forming layer units being comprised of an image recording emulsion layer comprised of a dispersing medium and a blend of 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 and grains consisting essentially of a silver salt having a solubility product constant of 15.5 or less having an average diameter of less than 0.5 µm present in a concentration of at least 0.5 mole percent, based on total silver in said image recording emulsion layer.

10. 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 an image recording emulsion layer comprised of a dispersing medium and a blend of radiation sensitive tabular silver haloiodide 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 and grains consisting essentially of a silver salt having a solubility product constant of 15.5 or less having an average diameter of less than 0.5 µm present in a concentration of at least 0.5 mole percent, based on total silver in said image recording emulsion layer.

11. A multicolor photographic element capable of forming a viewable reversal dye image according to claim 9 wherein said tubular grains have an average aspect ratio of at least 12:1.

12. A multicolor photographic element capable of forming a viewable reversal dye image according to claim 9 wherein said tabular grains contain from 1 to 7 mole percent iodide, based on silver.

13. 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.

14. A multicolor photographic element capable of forming a viewable reversal dye image according to claim 9 wherein said grains having a solubility product constant of 15.5 or less have an average diameter of less than 0.3 µm.

15. A multicolor photographic element capable of forming a viewable reversal dye image according to claim 14 wherein said grains having an average diameter of less than 0.3 µm have a solubility product constant at 20°C in the range of from 11 to 13.

16. A multicolor photographic element capable of forming a viewable reversal dye image according to claim 15 wherein said grains having an average diameter of less than 0.3 µm are present in a concentration of at least 1 mole percent, based on total silver present in said image recording emulsion layer.

17. A multicolor photographic element capable of forming a viewable reversal dye image according to claim 16 wherein said grains having an average diameter of less than 0.3 µm are present in a concentration in the range of from 5 to 50 mole percent, based on total silver present in said image recording emulsion layer.

18. A multicolor photographic element capable of forming a viewable reversal dye image according to claim 15 wherein said grains having an average diameter of less than 0.3 µm consist essentially of silver thiocyanate.

19. A multicolor photographic element capable of forming a viewable reversal dye image according to claim 15 wherein said grains having a solubility product constant in the range of from 11 to 13 have an average diameter of less than 0.1 µm.

20, A multicolor photographic element capable of forming a viewable reversal dye image according to claim 19 wherein said grains having an average diameter of less than 0.1 µm consist essentially of at least one of silver bromide and silver chloride.

21. A multicolor photographic element capable of forming a viewable reversal dye image according to claim 19 wherein said grains having an average diameter of less than 0.1 µm consist essentially of silver bromide.