CA1210626A - Multicolor photographic elements containing silver iodide grains - Google Patents

Abstract

MULTICOLOR PHOTOGRAPHIC ELEMENTS CONTAINING
SILVER IODIDE GRAINS

Abstract of the Disclosure Multicolor photographic elements are disclosed each containing superimposed emulsion layers for separately recording blue and minus blue light including at least one emulsion layer compris-ed of a dispersing medium and silver halide grains, wherein at least 50 percent of the total projected area of the silver halide grains is provided by thin tabular silver iodide grains having a thickness of less than 0.3 micron and an average aspect ratio of greater than 8:1. The multicolor photographic elements show advantages in the minus blue recording emulsion layers directly attributable to the thin tabular silver iodide grains.

Description

lZ1~2t;

MULTICOLOR PHOTOGRAPHIC ELEMENTS CONTAINI~G
SILVER IODIDE GRAINS
Field of thD Invention The invention relates to silver halide photographic elements capable of producing multi-color images and to processes for their use.
Background of the Invention Kofron et al Canadian Patent 1,175,698, titled SENSITIZED HIGH ASPECT RATIO SILVER HALIDE
EMULSIONS AN~ PHOTOGRAPHIC ELEMENTS, commonly assigned, discloses multicolor photographic elements in which at least one of the blue, green, and red recording emulsion layers is comprised of a dispers-ing medium and silver halide grains, wherein at least 50 percent of the total projected area of the silver halide grains is provided by chemically and spectrally sensitized tabular silver halide grains having a thickness of less than 0.3 micron, a diameter of at least ~.6 micron, and an average aspect ratio of greater than ~:1. Kofron et al specifically discloses the use of high aspect ratio tabular grain emulsions in which the tPbular grains are comprised of silver bromoiodide (iodide being limited by its solubility in silver bromide to about 40 mole percent), silver bromide, silver chloride, silver chloride containing minor amounts of bromide and/or iodide, and silver chlorobromide. (Except as otherwise indicated, all references to halide percentages are based on silver present in the corresponding emulsion, grain, or grain region being discussed; e.g., a grain consisting of silver bromoiodide containing 40 mole percent iodide also contains 60 mole percent bromide.) Kofron et al ; contains no disclosure of high aspect ratio tabular grain silver iodide emulsions, and, because of the rarity with which silver iodide emulsions are employed in muiticolor photographic elements, ~2~6Z6 bases its teachings on the properties of the silver halides more commonly employed in multicolor photography. For example, Kofron et al teaches increasing the permissible maximum thickness of the tabular grains from 0.3 micron to 0.5 micron to increase blue light absorption, recognizing that the thicker tabular grains are better able to assist the blue spectral sensitizing dyes in absorbing blue light. Further, Kofron et al discusses multicolor photographic elements in which high aspect ratio tabular grain blue recording emulsion layers overlie minus blue (green and/or red) recording emulsion layers and discuæses the effects of blue light reaching these minus blue recording emulsion layers. Jones and Hill Canadian Patent 1,174,885, titled PHOTOGRAPHIC IMAGE TRANSFER FILM UNIT, commonly assigned, is essentially cumulative in its teachings, but is directed specifically to image transfer film units. Maskasky Canadian Patent 1,175,278, titled CONTROLLED SITE EPITAXI~L SENS~TI-ZATION, commonly assigned is essentially cumulPtive ; in its teachlngs, but is directed specifically to the sensitization of high aspect ratio tabular grains by silver salt epitaxy.
Radiation-sensitive silver iodide emul-sion~, though infrequently employed in photography, are known in the art. Silver halide emulsions which employ grains containing silver iodide as a separate and distinct phase are illustrated by Steigmann German Patent 505,012, issued August 12, 1930;
Steigmann, Photographische Industrie, "Green- and Brown-Developing Emulsions", Vol. 34, pp. 764, 766, and 872, published July 8 and August 5, 1938;
Maskasky U.S. Patents 4,094,6~4 and 4,142,900; and Koitabashi et al U.K. Patent Application 2,063,499A.
Maskasky Research Disclosure, Vol. 18153, May 1974, 12i~Z6 Item 18153~ reports silver iodide phosphate photo-graphic emulsions in which silver i~ coprecipitated with iodide and phosphate. A separate silver iodide phase i6 not reported.
The crystal structure of silver iodide has been ~tudied by crystallographers, particularly by those interested in photography. As illustrated by Byerley and Hirsch, "Dispergions of Metastable High Temperature Cubic Silver Iodide", Journal of Photo-10 ~raPhic Science, Vol. 18, 1970, pp. 53-59, it i~
generally recognized that silver iodide is capable of existing in three different crystal forms. The most commonly encountered form of silver iodide crystals is the hexagonal wurtzite type, designated 15 3 phase silver lodide. Silver iodide is also stable at room temperature in its face centered cubic crystalline form, designated y phase silver iodide. A third form of crystalline silver iodide, stable only at temperatures above about 147C, is 20 the body centered cubic form, designated ~ phase silver iodide. The B phase is the most stable form of silver iodide.
James, The Theory of the Photographic Process, 4th Ed., Macmillan, 1977, pp. 1 and 2, 25 contains the following summary of the knowledge of the art:
According to the conclusions of Kokmei~er and Van Hengel, which have been widely accepted, more nearly cubic AgI is precipitated when silver ions are in excess and more nearly hexagonal AgI when iodide ions are in excess.
More recent measurements indicate that the presence or absence of gelatin and the rate of addition of the reactants have pronounced effects on the amounts of cubic and hexagonal A8I. Entirely hexagonal material was produced only when gelatin was present and the solutions ~,~

21~Z6 were added slowly without an excess of either A~ or+I~. No condition was found where only cubic ma~erial was observed.
Tabular silver iodide crystals have been observed. Preparations with an excess of iodide ions, producing hexagonal crystal structures of predominantly ~ phase silver iodide are reported by Ozaki and Hachisu, "Photophoresis and Photo-agglomeration of Plate-like Silver Iodide Parti-cles", Science of Light, Vol. 19, No. 2, 1970, pp.59-71, and Zharkov, Dobroserdova, and Panfilova, "Crystallization of Silver Halides in Photographic Emulsions IV. Study by Electron Microscopy of Silver Iodide Emulsions", Zh. Nauch. Prikl. Fot. Kine, March-April, 1957, 2, pp. 102-105.
Daubendiek, "AgI Precipitations: Effects of pAg on Crystal Growth(PB), III-23", Papers from the 197~ International Congress of Photo~raphic Science, Rochester, New York, pp. 140-143, 1~7~, reports the formation of tabular silver iodide grains during double-jet precipitations at a pAg of 1.5. Because of the excess of silver ions during precipitation, it is believed that these tabular grains were of face centered cubic crystal struc-ture. However, the average aspect ratio of thegrains was low, being estimated at substantially less than 5:1.
Maskasky Can. Serial No. 440,119, filed concurrently herewith and co~monly assigned, titled GAMMA PHASE SILVER IODIDE EMULSIONS, PHOTOGRAPHIC
ELEMENTS CONTAINING THESE EMULSIONS, AND PROCESSES
FOR THEIR USE, discloses the first high aspect ratio tabular grain silver iodide emulsions in which the grsins are of a face centered cubic crystal struc-ture, as is characteristic of silver iodide.

Summary of the Invention In one aspect this invention is directed toa photographic element capable of producing a multicolor image comprised of a support and, located 5 on the support, superimposed emulsion layers for facilitating separate recording of blue, green, and red light, each comprised of a tispersing medium and silver halide grains. The improvement comprises at least 50 percent of the total pro~ected area of the 10 silver halide grains in at least one emulsion layer being provided by thin tabular silver iodide grains having a thickness of less than 0.3 micron and an average aspect ratio of greater than 8:1.
In another aspect, the invention iB direct-15 ed to protucing a visible photographic image byprocessing in an aqueous alkaline solution in the presence of a developing agent an imagewise exposed photographic element as described above.
The multicolor photographic elements of 20 this invention exhibit high efficiencies in the absorption of blue light. They can display reduced color contamination of minus blue (i.e., red and/or green) records by blue light. The multicolor photographic elements of this invention can elimi-25 nate yellow filter layers without exhibiting color contamination of the minus blue record. In addition the multicolor elements of this invention can exhibit improvements in image sharpness ant in speed-grain relationships of the minus blue records.
Although the invention has been described with reference to certain specific advanta~es, other advantages will become apparent in the course of the ~ detailed description of preferred embodiments.
;~ Brief DescriPtion of the Drawings Figures 1 through 6 are photomicrographs of high aspect ratio tabular grain emulsions;

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zla6z6 Figure 7 is a plot of speed versus ~ranularity;
and Figures 8 and ~ are schematic diagrams related to scattering.
Description of Preferred Embodiments -This invention is directed to photographic elements capable of producing multicolor images and to processes for their use~ The multicolor photo~
graphic elements of this invention each incorporate at least one silver halide emulsion layer comprised of u dispersing medium and silver halide grains. At least 50 percent of the total projected area of the silver halide grains in the blue recording emulsion layer ~s provided by thin tabular grain6 having a thickness of less than 0.3 micron and an average aspect ratio of greater than 8:1. This emulsion layer is preferably a blue recording emulsion layer and is for convenience described below with reference to this use.
In addition to at least one blue recording emulsion layer as described above the multicolor photographic elements additionally include at least one green recording silver halide emulsion layer and at least one red recording silver halide emulsion layer. The multicolor photographic elements can also optionally include one or more additional blue recording emulsion layers. All of these additional emulsion layers can be chosen from among conven-tional multicolor photographic element emulsion layers. In a preferred form at least one green recording emulsion layer and at least one red recording emulsion layer are also comprised of high aspect ratio tabular grain emulsions. In certain preferred forms of the invention all of the emulsion layers can be comprised of high aspect ratio tabular 12iQ~2~

grain emulsions. Tabular silver iodide grsins sstisfying the s~me general r~quirement~ as those of the blue recording emulsion layer described above can be present in any or all of these ~dditional emul~ion layers, or high aspect ratio tabular grain silver halide emulsions of other halide compositions can be present in any or all of these ~dditional emulsion layer6.
As appl~ed to the silver halide emulsions of the present lnvention the texm "high aspect ratio" i6 herein defined as requiring that the silver halide grains having a thickness of less than 0.3 micron have an average aspect ratio of greater than 8:1 and account for at lea6t 50 percent of the totsl proJected area of the silver halide grsins.
The preferred higH aspect ratio tabular grain eilver halide emulsions of the presen~ invention are those wherein the ~ilver halide grains having a thicknes~
of less than 0.3 micron (optimally less than 0.2 micron) have an average aspect ratio of at least 12:1 and optimally at least 20:1.
It is appreciated that the thinner the tabular grain~ accounting for a given percentage of the pro~ected area, the higher the average aspect

2~ ratio of the emulgion. Individual tabular silver iodide grains have been ob~erved having thickne~6es slightly in excess of 0.005 micron, suggesting that preparat~ons of tabular silver iodide grains accord-ing to this invention having average thicknesses down to that value or at lea~t 0.01 micron are feasible. It is a di~tinct advantage of h~gh aspect ratio tabulax silver iodide grains that they can be prepsred at thicknesses less than high aspect ratlo tabular grains of other halide compositions.
Minimum tabular 8rain thicknesses of 0.03 micron for high aspect ratio tabular grain emulsions are 6~6 generally contemplated, these being particularly readily achieved for silver bromide and ~ilver bromoiodide tabular grain emulsions.
The grain characteri6tics described above S of the high aspect ratio tabular grain emulsion6 can be readily ascertained by procedures well known to those skilled in the art. As employed herein the term "aspect ratio" refers to the rstio of the diameter of the grain to its thickness. The "diameter" of the gra~n is in turn defined as the diameter of a circle having an area equal to the pro~ected area of the grain as viewed in a photo-micrograph (or an electron microgrsph) of an emul-sion sample. From shadowed electron microgr~ph~ of emulsion ssmple6 it i8 possible to determlne the thickness and diaméter of each grain and to identify those tabular grain~ having ~ thickness of less than 0.3 micron. From this ~he aspect ratlo of each such tabular grain can be calculated, ~nd the aspect 2~ ratios of all the tabular grains in the ssmple meeting the less than 0.3 micron thickness criterion can be averaged to obtain their average aspect ratio. By this definitisn the average dspect ratio is the average of individual tabular grain aspect ratios. In practice it is usually simpler to obtain an average thickness and an average diameter of the tabular grains havlng a thicknesæ of less than 0.3 micron and to calculate the aver~ge aspect ratio as the ratio of these two averages. Whether the sveraged individual aspect ratios or the averages of thlckness and diameter are used to determine the average aspect ratio, within the tolerances of grain mea~urements contemplated, the average aspect ratios obtained do not significantly differ. The pro~ected areas of the silver iodide grains meeting the thicknes~ and diameter criteria can be ~ummed, the ~21~Z6 projected areas of the remaining silver iodide grains in the photomicrogr~ph can be summed sepa-rately, and from the two sums the percertage of the total projected area of the silver iodide grains provided by the grains meeting the thickness and diameter critera can be calculated.
In the above determinations a reference tabular grain thickness of less than 0.3 micron was chosen to distinguish the uniquely thin tabular grains herein contemplated from thicker tabular grains which provide inferior photographic proper-ties. At lower diameters it is not always possible to distinguish tabular and nontabular grains in micrographs. The tabular grains for purposes of this disclosure are those which are less than 0.3 micron in thickness and appear tabular at 2,500 times magnification. The term "projected area" is used in the same sense as the terms "projection area" and "projective area" commonly employed in the art; see, for example, James and ~iggins, ~undamen~
tals of Photo~raphic Theory, Morgan and Morgan, New York, p. 15.
In a preferred form offering a broad range of observed advantages the present invention employs, in addition to high aspect ratio silver iodide emulsions~ high aspect ratio silver bromo-iodide emulsions. High aspect ratio silver bromo-iodide emulsions and their preparation is the subject of Wilgus and Haefner Canadian Patent 1,175,6~3, commonly assigned, titled HIGH ASPECT
RATIO SILVER BROMOIODIDE EMULSIONS AND PROCESSES FOR
THEIR PREPARATION.
High aspect ratio tabular grain silver bromoiodide emulsions can be prepared by a precipi-tation process which forms a part of the Wilgus and -- 121~626 Haefner invention. Into a conventional reaction vessel for silver halide precipitstion, equipped with an efficient stirring mechanism, i8 introduced a dispersing medium. Typically the dispersing 5 medium initially introduced into the reac~ion vessel is at least about 10 percent, preferably 20 to 80 percent, by weight based on total weight of the dispersing medium present in the silver bromoiodide emulsion at the conclusion of grain precipitation.
10 Since dispersing medium can be removed from the reaction vessel by ultrafiltration during eilver bromoiodide grain precipitation, as taught by Mignot U.S. Patent 4,334,012, it is appreciated that the volume of dispersing medium initially pre~ent in the 15 resction vessel can equal or even exceed the volume of the silver bromoiodide emulsion present in the reaction ves~el at the conclusion of grain precip~-tation. The dispersing medium initially introduced into the reaction vessel is preferably water or a 20 dispersion of peptizer in water, optionally contain-ing other ingredients, such as one or more Rilver halide ripening agents and/or metal dopants, more specifically described below. Where a peptizer is initially present, it i8 preferably employed in a 25 concentr~tion of at least 10 percent, most prefer-ably at least 20 percent, of the total peptizer present at the completion of silver bromoiodide precipitation. Additional dispersing medium is added to the reaction vessel with the silver and 30 halide salts and can also be introduced through a separate ~e~. It is common practice to ad~ust the proportion of dispersing medium, particularly to increase the proportion of peptizer, after the completion of the salt introductions.

~Z~6Z6 A minor portion, typically less than lO
percent, of the bromide salt employed in forming the silver bromoiodide grains is init~ally present ~n the resction veRsel to ad~ust the bromide ~on concentration of the di~persing med~um at the outset of silver bromoiodide precipitation. Also, the dispersing medium in the reaction vessel iB initial-ly æubsthntially free of iodide ions, since the pre6ence of iodide ions prior to concurrent ~ntro-ducton of silver and bromlde salts favors theformation of thick and nontabular grains. A~
employed herein, the term "substantially free of iodide ions" as applied to the contents of the reaction vessel means that there are insufficient iodide ions present a~ compared to bromide ions to precipitate as a separate silver iodide phase. It i6 preferred to maintain the iodide concentration in the reaction vessel prior to silver salt introduc-tion at less than 0.5 mole percent of the total halide ion concentration present. If the pBr of the dispersing medium is initially too high, the tabular silver bromolodide grains produced will be compara-tively thick and therefore of low aspect ratios. It is contemplated to maintsin the pBr of the reaction vessel initially at or below 1.6, preferably below 1.5. On the other hand, lf the pBx is too low, the formation of nontabular gilver bromoiodide grains is favored. Therefore, it i8 contemplated to maintain the pBr of the reaction vessel at or above 0.6. (As herein employed, pBr is defined as the negative logarithm of bromide ion concentration. pH, pCl, pI, and pAg are similarly defined for hydrogen, chloride, iodide, and silver ion concentration~, re~pectively.) During precipitation silver, bromide, and iodide salts are added to the reaction vessel by ~ZlQG26 techniques well known in the precipitation of silver bromoiodlde grains. Typically an aqueous solution of a soluble silver salt, such aR silver nitrate, i8 introduced into the reaction vessel concurrently with the introduction of the bromide and iod~de salt6. The bromide and iodide salts are also typically introduced as aqueous ~alt solution~, such as aqueous ~olutions of one or more soluble ammonium, alkali metal (e.g., sodium or potassium), or alkaline earth metal (e.g , magnesium or calclum) halide salts. The silver salt is at least initially introduced into the reaction vessel separately from the iodide salt. The iodide and bromlde salts can be added to the reaction vessel ~eparately or as 8 mixture.
With the introduction of 8i lver salt in~o the reaction vessel the nucleation stage of grain formation i8 initiated. A popula~ion of grain nuclei is formed which i8 capable of serving as precipitation sltes for silver bromlde and silver iodide as the introduction of sllver, bromide, and iodide salts continues. The precipitation of silver bromide and 6ilver iodide onto existing grain nuclei constitutes the growth stage of grain formation.
The aspect ratios of the tabular grains formed according to this invention are less affected by iodide and bromide concentrations during the growth stage than during the nucleation stage. It i8 therefore possible during the growth stage to increase the permi6sible latitude of pBr during concurrent introduction of silver, bromide, and iodide salts above 0.6, preferably ln the r~nge of from about 0.6 to 2.2, most preferably from about 0.8 to about 1.6, the latter being particularly preferred where a substantial rate of grain nuclei formation continues throughout the introduction of ` ``` lZ~(~6Z~i silver, bromide, and iodide salt~, 6uch a~ in the preparation of highly polydispersed emulsions.
Raising pBr values above 2.2 dùring tabular grain growth re~ults in thickening of the grains, but csn be tolerated in many instances while gtill reali~ing an average aspect ratio of greater thsn 8:1.
As an alternative to the introduction of silver, bromide, and iodide ~alts as aqueous solu-tions, it is specifically contemplated to introduce the silver, bromide, and iodide galts, inltially or in the growth stage, in the form of fine silver halide grains suspended in dispersing medium. The grain size is such that they are readily Ostwald ripened onto lsrgex grain nuclei, if any are present, once introduced into the reaction vessel.
The maximum useful grain ~izes will depend on the specific conditions within the reaction vessel, such as temperature and the presence of solubllizing and ripening agents. Silver bromide, silver iodide, and/or silver bromoiodide gralns can be introduced.
(Since bromide and/or iodide is precipitated in preference to chloride, it is also possible to employ silver chlorobromide and silver chlorobromo-iodide grains.) The silver halide grains are preferably very fine--e.g., less than 0.1 micron in mean diameter.
Sub~ect ~o the pBr requirements set forth above, the concen~ratlons and rate~ of silver, bromide, and iodide salt introductions can take any convenient conventional form. The silver and halide salts are preferably introduced in concentrations of from 0.1 to 5 moles per liter, although broades conventional concentration ranges, such a8 from 0.01 mole per liter to saturation, for example, are ; 35 contemplated. Specifically preferred precipitation techniques are those which achieve shortened ~, ~2~6Z6 precipitation times by increa~ing the rate of silver and halide ~alt introduction during the run. The rate of silver and halide salt introduction can be increased either by increasing the rate at which the dispersing medium and the silver and halide ~alts are introduced or by increasing the concentrations of the 6~ lver and halide salts within the dispersing medium being introduced. It i8 specifically prefer-red to increase the rate of silver and halide salt introduction, but to maintain the rate of introduc-tion below the threshold level at which the forma-tion of new grsin nuclei is favored--i.e., to avoid renucleation, as taught by Irie U.S. Patent

3,650,757, Kurz U.S. Pstent 3,672,900, Saito U.S.
Patent 4,242,445, Wilgus German OLS 2,107,118, Teitscheid et al European Patent Application 80102242, and Wey "Growth Mechanism of AgBr Cry6tal6 in Gelatin Solutlon", Photo~raphic Science and ~ineerin~, Vol. 21, No. 1, January/February 1977 p. 14, et. seq. By svoiding the formation of additional grain nuclei after pa6sing into the growth stage of precipitation, relatively monodis-persed tabular silver bromoiodide grain populations can be obtained. Emulsions having coefficients of variation of less than about 30 percent can be prepared. (As employed herein the coefficient of variation is defined as 100 times the standsrd deviation of the grain diameter divided by the average grain diameter.) By intentionally favoring renucleation during the growth stage of precipita-tion, it is, of course, possible to produce polydis-persed emulsions of substantially higher coeffi-cient6 of variation.
The concentration of iodide in the ~ilver bromoiodide emulsions can be controlled by the introduction of iodide salts. Any conventional .~

iodide concentration can be employed. Even very small amounts of iodide--e.g., as low as 0.05 mole percent--are recognized in the art to be benef~-cial, In their preferred form the emulsions of the present invention incorporate at least about 0.1 mole percent iodlde. Silver iodide can be incorpo-rated into the tabular silver bromoiodide grains up to its solubility limit in silver bromide at the temp~rature of grain formation. Thus, silver iodide concentrations of up to about 40 mole percent in the tabular silver bromoiodide grains can be achieved at precipitation temperatures of 90C. In practice precipitation temperatures can range down to near ambient room temperatures--e.g., about 30C. It is generally preferred that precipitation be undertaken at temperatures in the range of from 40 to 80C.
The relative proportion of iodide and bromide salts introduced into the reaction vessel during precipitation can be maintained ~n a fixed ratio to form a substantially uniform iodide profile in the tabular silver bromoiodide grains or varied to achieve differing photographic effects. Solberg et al Canadian Patent 1,175,697~ commonly assigned, titled RADIATION-SENSITIVE SILVER BROMOIODID~
EMULSlO~S, PHOTOGRAPHIC ELE~JENTS, AND PROCESSES FOR
THEIR USE, has recognized specific photographic advantages to result from increasing the proportion of iodide 1n annular or otherwise laterally displaced regions of high aspect ratio tabular grain silver bromoiodide emulsions as compared to central regions of the tabular grains. Solberg et al teaches iodide concentrations in the central regions of from 0 to 5 mole percent, with at least one mole percent higher iodide concentrations in the laterally surrounding annular regions up to the solubility limit of silver io~ide in silver bromide, preferably up to about 20 mole percent and optimally up to about 15 mole percent. Solberg et al constitutes a preferred species of high aspect ratio tabular grain silver bromoiodide emulsions.
In a variant form it is specifically contemplated to terminate iodide or bromide and iodide salt addition to the reaction vessel prior to the termination of silver salt addition so that excess halide reacts with the silver salt. This results in a shell of silver bromide being formed on the tabular silver bromoiodide grains. Thus, it is apparent that the tabular silver bromoiodide grains can exhibit substantially uniform or graded iodide concentration profiles and that the gradation can be controlled, as desired, to favor higher iodide concentrations internally or at or near the surfaces of the ~abular silver brsmoiodide grains.
; 20 Although the preparation of the high aspect ratio tabular grain silver bromoiodide emulsions has been described by reference to the process of Wilgus and Haefner, which produces neutral or nonammoniacal emulsions, these emulsions and their utility are not limited by any particular process for their prepara-tion. A process of preparing high aspect ratio tabular grain silver bromoiodide ~mulsions discovered subsequent to that of Wilgus and Haefner is described by Daubendiek and Strong Canadian Patent 1,175,701a commonly assigned, titled METHOD
OF PREPARING HIGH ASPECT RATIO GRAINS. Daubendiek and Strong teaches an improvement over the processes of Maternaghan, U.S. Patents 4,150,994, 4,184,877, and 4,184,878, wherein in a preferred form the silver iodide concentration in the reaction vessel is reduced below 0.05 mole per liter and the maximum size of the silver iodide grains initially present in the reaction vessel is reduced below 0.05 micron.
High aspect ratio tabular grain silver bromide emulsions lacking iodide are also useful in th~ multicolor photographic elements of this invention and can be prepared by the process described by Wilgus and Haefner modified to exclude iodide. High aspect ratio tabular grain silver bromide emulsions can alternatively be prepared following a procedure similar to that employed by deCugnac and Chateau, "Evolution of the Morphology of Silver Bromide Crystals During Physical Ripen-ing", Science et Industries Photographiques, Vol.
33, No. 2 ~lg62), pp. 121-125. High aspect ratio silver bromide emulsions containing square and rectangular grains can be prepared as taught by Mignot Canadian Patent 1,175,699, commonly assigned, titled SILVER BROMIDE EMULSIONS OF NARROW GRAIN SIZE
DISTRIBUTION AND PROCESSES ~OR THEIR PREPARATION.
In this process cubic seed grains having an edge length of less than 0.15 micron are employed. While maintaining the pAg of the seed grain emulsion in the range of from 5.0 to 8.0, the emulsion is ripened in the substantial absence of nonhalide silver icn complexing agents to produce tabular silver bromide grains having an average aspect ratio of at least 8.5:1. Still other preparations of high aspect ratio tabular grain silver bromide emulsions lacking iodide are illustrated in the examples.
To illustrate the diversity of high aspect ratio tabular grain silver halide emulsions which , ~

2~6~6 can be employed in addition to the high aspect ratio tabular grain silver iodide emulsions in the multicolor photographic elements of this invention, attention is directed to Wey Canadian Patent 1,175,691, commonly assigned~ titled IMPROVED
DOUBLE-JET PRECIPITATION PROCESSES AN~ PRODUCTS
THEREOF, which discloses a process of preparing tabular ~ilver chloride grains which are substan-tially internally free of both silver bromide and silver iodide. Wey employs a double-jet precipita-tion process wherein chloride and silver salts are concurrently introduced into a reaction vessel containing dispersing medium in the presence of ammonia. During chloride salt introduction the pAg within the dispersing medium is in the range of from 6.5 to 10 and the pH in the range of from 8 to 10.
The presence of ammonia at h~gher temperatures tends to cause thick grains to form, therefore precipita-tion temperatures are limited to up to 60C. The process can be optimized to produce high aspect ratio tabular grain silver chloride emulsions.
Maskasky Canadian Patent 1,175,693, commonly assigned, titled SILVER CHLORI~E EMULSIONS
OF MODIFIED C~YSTAL HABIT AND PROCESSES FOP~ T~EIR
PREPARATION, discloses a process of preparing tabular grains of at least 50 mole percent chloride having opposed crystal faces lying in {111}
cry~tal planes and, in one preferred form, at least one peripheral ed~e lying parallel to a <Zll>
crystallographic vector in the plane of one of the major surfaces. Such tabular grain emulsions can be prepared by reacting aqueous silver and chloride-containing halide salt solutions in the presence of a crystsl habit modifying amount of an amino-substi-tuted azaindene and a peptizer having a thioetherlinkage.
'~

lZ1~626 Wey and Wilgus Canadian Patent 1,175,698, commonly assigned, titled NOVEL SILVER CH~OROBROMIDE
~MULSIONS AND PROCESS~S FOR THEIR PREPARATION, discloses tabular grain emulsions wherein the silver halide grains contain chloride and bromide in at least annular grain regions and preferably through-out. The tabular grain regions containing silver, chloride, and bromide are formed by maintainin8 a molar ratio of chloride aDd bromide ions of from 1.6:1 to about 260:1 and the total concentration of halide ions in the reaction vessel in the range of from 0.10 to 0.90 normal during introduction of silver, chloride, bromide, and, optionally, iodide salts into the reaction vessel. The molar ratio of silver chloride to silver bromide in the ~abular gr~ins can range from 1:99 to 2:3.
Silver halide emulsions containing high aspect ratio silver iodide tabular grains of face centered cubic crystal structure are disclosed by Maskasky Can. Serial No. 44~,019, filed concurrently herewith, titled GAMMA PHASE SILVER IODIDE EMUL-SIONS, PHOTOGRAPHIC ELEMENTS CONTAINING THESE
EMULSIONS, AND PROCESSES FOR THEIR USE, cited above. Such emulsions can be prepared by modifying conventional double-jet silver halide precipitation procedures. As noted by James, The Theory of the Photographic Proces6, cited above, precipitation on the silver side of the equivalence point (the point at which æilver and iodide ion concentrations are equal) is important to achievin~ face centered cubic crystal structures. For example, it is preferred to precipitate at a pAg in the vicinity of 1.5, as undertaken by Daubendiek, cited above. (As employed herein pAg is the negative logarithm of silver ion concentration.) Second, in comparing the processes `` 12~626 employed in preparing the high aspect ratio tabular grain silver iodide emulsions with the unpublished details of the process employed by ~aubendiek, 'IAgI
Precipitations: Effects of pAg on Crystal Growth (PB)", cited above, to achieve relatively low aspect ratio silver iodide grains, the flow rates for silver and iodide salt introductions in relation to the final reaction veæsel volume are approximately an order of magnitude lower than those of Daubendiek (<0.003 mole/minute/liter as compared to <0.02 mole/minute/liter employed by Daubendiek).
Silver halide emulsions containing high aspect ratio silver iodide tabular grains of a hexagonal cry6tal structure, as exhibited by B phase silver iodide, can be prepared by double-jet precipitation procedures on the halide side of the equivalence pointO Useful parameters for precipita-tion are illustrsted in the Examples below. Zharkov et al, cited above, discloses the preparation of silver iodide emulsions containing tabular gralns of ~ phase crystal structure by ripening in the presence of a ammonia and an excess of potassium iodide~
High aspect ratio tabular grain emulsions u~eful in the practice of this invention can have extremely high average aspect ratios. Tabular grain average aspect ratios can be increased by increaæing average grain diameters. This can produce ~harpness advantageæ, but maximum average grain diameteræ are generally limited by granularity requirements for a specific photographic application. Tabular grain average aæpect ratios can also or alternatively be increased by decreasing average grain thicknesses.

`~ ~Z1~62~

When silver coverages are held con~tant, decreasing ~he 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 employed in the multicolor photographic elements of this invention are a function of the maxlmum average grain diameters acceptable for the specific photo-graphic application and the minimum attainable tabular grain thicknesses which can be produced.
Maximum average aspect ratios have been observed to vary, depending upon the precipitation technique employed and the tabular grain halide composition.
The highest observed average aspect ratios, 500:1, for tabular grains with photographically useful average grain diameters, have been achieved by Ostwald ripening preparations of silver bro~ide grains, with aspect ratios of 100:1, 200:1, or even higher being obtainable by double-jet precipitation procedures. The presence of iodide generally decreases the maximum average aspect ratios realized in silver bromoiodide tabular grains, but the preparation of silver bromoiodide tabular grain emulsions having average aspect ratios of 100:1 or even 200:1 or more is feasible. Average aspect ratios as high as 50:1 or even 100:1 for silver chloride tabular grains, optionally containing bromide and/or iodide, can be prepared as taught by Maskasky Can. Patent 1,175,6~3, cited above.
Because of the exceptionally thin silver iodide tabular grains which can be obtained, high average aspect ratios ranging up to 100:1 can be readily achieved, regardless of whether the silver iodide is in a face centered cubic (y phase) or hexagonal (~ phase) crystal structure. Emulsions containing silver iodide tabular grains of hexagonal crystal structure of even higher average ``` lZ~26 aspect ratios, ranging up to 200:1, or even 500:1, are contemplated.
Modifying compounds can be present during tabular grain precipitation. Such compounds can be 5 initially in the reaction vessel or can be added along with one or more of the salts according to conventional procedures. Modifying compounds, such as compounds of copper, thallium, lead 9 biRmuth cadmium, zinc, middle chalcogens (i.e., sulfur9 10 selenium, and tellurium), gold, and Group VIII noble metals, can be present during silver halide precipi-tation, as illu~trated by Arnold et al U.S. Patent 1,195,432, Hochstetter U.S. Patent 1,951,933, Trivelli et al U.S. Patent 2,448,060, Overman U.S.
15 Patent 2,628,167, Mueller et al UOS. Patent 2,950,972, Sidebotham U.S. Patent 3,488,709, Rosecrants et al U.S. Patent 3,737,313, Berry et al U.S. Patent 3,772,0319 Atwell U.S. Patent No.

4,269,927, and Research Disclosure, Vol. 134, June 20 1975, Item 13452. Research Disclosure and its predecessor, Product Licensing Index, are publica-t~ons of Kenneth Ma~on Publications Limited;
Emsworth; Hampshire P010 7DD; United Kingdom. The tabular grain emulsions can be internally reduction 25 gensitized during precipitation, as illustrated by Moisar et al, Journal of PhotograPh~c Science, Vol.
25, lg77, pp. 19-27.
The individual silver and halide salts can be added to the reaction vessel through surface or 3~ subsurface delivery tubes by gr~vi~y feed or by delivery apparatus for maintaining control of the rate of delivery and the pH9 pBr, and/or pAg of the reaction vessel contents, as illustrated by Culhane et al U.S. Patent 3,821,002, Oliver U.S. Patent 35 3,031,304 and Claes et al, Photographische Korres-pondenz, Band 102, Number 10, 1967, p. 162. In .;

~` 121~6Z~

order to obta~n rapid distribution of the reactants within the reaction vessel, specially constructed mixing devices can be employed, as illustrated by Audran U.S. Patent 2,996,287, McCros6en et al U.S.
Patent 3,342,605, Frame et al U.S. Patent 3,415,650, Porter et al U.S. Patent 3,785,777, Finnicum et al U.S. Patent 4,147,551, Verhille et al U.S. Patent 4,171,224, Calamur U.K. Patent Application 2,022,431A, Saito et al German OLS 2,5i5,364 and 2,556,885, and Research Disclosure, Volume 166, February 1978, Item 16662.
In forming the tabular grain emulsions a dispersing medium is initially contained in the reaction vessel. In a preferred form the dispersing medium is comprised on an aqueous peptizer suspen-sion. Peptizer concentrations of from 0.2 to about 10 percent by weight, based on the total weight of emulsion components in the reaction vessel, can be employed. It is common practice to maintain the concentration of the peptizer in the reaction vessel in the range of below about 6 percent, based on the total weight, prior to and during silver halide formation and to ad3ust the emulsion vehicle concen-tration upwardly for optimum coating characteristics by delayed, supplemental vehicle additions. I~ is contemplated that the emulsion as initially formed will contain from about 5 to 50 grams of peptizer per mole of æilver hal~de, preferably about 10 to 30 grams of peptizer per mole of silver halide.
Additional vehicle can be added later to bring the concentratlon up to as high as 1000 grams per mole of silver halide. Preferably the concentration of vehicle in the finished emulsion is above 50 grams per mole of silver halide. When coated and dried in forming a photographic element the vehicle prefer-ably forms about 30 to 70 percent by weight of the emulsion layer.

~2~6Z6 Vehicles (which include both binders and peptizer 8 ) can be chosen from among those conven-tionally employed in silver halide emulsions.
Preferred peptizer~ are hydrophilic colloids, which can be employed alone or in comb~nation wlth hydro-phobic materialsO Suitable hydrophilic materials include substances such as protein~, protein deriva-tives, cellulose derivative6--e.g~, cellulose esters, gelatin--e.g., alkali-tseated gelatin (cattle bone or hide gelatin) or acid-treated gelatin (pigskin gelat~n), gelatin derivative~--e.g., acetylated gelatin, phthalated gelatin and the like, polysaccharides such as dextran, gum arabic, zeinS casein, pectin, collagen derivative6, agar-agar, arrowroot, albumin and the like as describedin Yutzy et al U.S. Patents 2,614,928 and '929, Lowe et al U.S. Patents 2,691,582, 2,614,930, '931, 2,327,808 and 2,448,534, Gates et al U.S. Patents 2,787,545 and 2 9 956,880, Himmelmann e~ al U.S.
Patent 3,061,436, Farrell et al U.S. Patent 2,816,027, Ryan U.S. Patents 3,132,945, 3,138,461 and 3,186,846, Dersch et al U.R. Patent 1,167,159 and U.S. Patent 8 2,960,405 and 3,436,220, Geary V.S.
Patent 3,486,896, Gazzard U.K. Patent 793,549, Gates et al U.S. Patents 2,992,213, 3,157,506, 3,184,312 and 3,539,353, M~ller et al U.S. Patent 3,227,571, Boyer et al U.S. Patent 3,532,502, Malan U.S. Patent 3,551,151, Lohmer et al U.S. Patent 4,018,609, Luciani et 81 U.K. Patent 1,186,790, Hori et al U.R.
Patent 1,489,080 and Belgian Patent 856,631, U.K.
Patent 1,490~644, V.K. Patent 1,483,551, Arase et al U.K. Patent 1,459,906, Salo U.S. Patents 2,110,491 and 2,311,086, Fallesen U.S. Patent 2,343,650, Yutzy U.S. Patent 2,322,085, Lowe U.S. Patent 2,563,791, Talbot et al U.S. Patent 2,725,293, Hilborn U.S.
Patent 2,748,022, DePauw et al U.S. Patent ~.Z~ ~26 2,956,883, Ritchie U.K. Patent 2,095, DeStubner U.S.
Patent 1,752,069, Sheppard et al U.S. Patent 2,127,573, Lierg U.S. Patent 2,256,720~ Ga~par U.S.
Patent 2,361,936, Farmer U.K. Patent 15,727, Stevens U.K. Patent 1,062,116 and Yamamoto et al U.S. Patent 3,~23,517.
Other materials commonly employed in combination wlth hydrophilic colloid peptizers as vehicles (including vehicle extenders--e.g., mater-ials in the fo~m of latices) include synthetic polymeric peptizers, carriers and/or binders such es poly(vinyl lactams~, acrylamide polymers, polyvinyl alcohol and its derivatives, polyvinyl acetal6, polymer B of alkyl and sulfoalkyl acrylate6 and meth~cryl~tes, hydrolyzed polyvinyl acetate6, polyamides, polyvinyl pyridine, acrylic acid poly-mers, maleic anhydride copolymer6, polyalkylene oxides, methacryl~mide copolymers, polyvinyl oxazolidinone6, maleic acid copolymers, vlnylamine copolymers, methacrylic acid copolymers, acryloyl-oxyalkylsulfonic acid copolymers, sulfoalkylacryl-amide copolymers, polyalkyleneimine copolymers, polyamines, N,N-dialkylaminoalkyl acrylates, vinyl imidazole copolymer~, vinyl sulfide copolymers, halogenated styrene polymers, amineacrylamide polymers, polypeptldes and the like as deRcribed in Hollister et al U.S. Patents 3,679,425, 3,706,564 and 3,813,251, Lowe U.S. Patents 2,253,078, 2,276,322, '323, 2,281,703, 2,311,058 and 2,414,207, Lowe et al U.S. Patents 2,484,456, 2,541,474 and 2,632,704, Perry et al U.S. Patent 3,425,836, Smith et al U.S. Patents 3,415,653 and 3,615,624, Smith U.S. Patent 3,488,708, Whiteley et al U.S. Patents 3,392,025 and 3,511,818, Fitzgerald U.S. Patents 3,681,079, 3,721,565, 3,852,073, 3,861,918 and 3,925,083, Fitzgerald et al U.S. Patent 3,879,205, 2~

Nottorf U.S. Patent 3,142,568, Houck et al U.S.
Patents 3,062,674 and 3,220,844, Dann et al U.S.
Patent 2,882,161, Schupp U.S. Patent 2,579,016, Weaver U.S. Patent 2,829,053, Alles et al U.S.
Patent 2,698,240, Priest et al U.~. Patent 3,003,879, Merrill et al U.S. Patent 3,~19,397, Stonham U.S. Patent 3,284,207, Lohmer et al U.S.
Patent 3,167,430, Williams U.S. Pstent ~,957,767, Dawson et al U.S. Patent 2,893,867, Smith et al U.S.
Patents 2,860,986 and 2,904,539, Ponticello et al U.S. Patentæ 3,929,482 and 39860,428, Ponticello U.S. Patent 3,939,130, Dykstra U.S. Patent 3,411,911 and Dykstra et al Canadian Patent 774,054, Ream et al U.S. Patent 3,287,289, Smith U.K. Patent 1~466,600~ Stevens U.K. Patent 1,062,116, Fordyce U.S. Patent 2,211,323, Martinez U.S. Patent 2,284,877, Watkins U.S. Patent 2,420,455, Jones U.S.
Patent 2,533,166, Bolton U.S Patent 2,495,918, Graves U.S. Patent 2,289,775, Yackel U.S. Patent 27565,418, Unruh et al U.S~ Patents 2,865,893 and 2,875,059, Rees et al U.S. Patent 3,536,491, Broadhead et al U.K. Patent 1,348,815, Taylor et al U.S. Patent 3,479,186, Merrill ~t al U.S. Patent 3,520,857, Bacon et al U.S. Patent 3,690,888, Bowman U.S. Patent 3,748~143, Dickinson et al U.K. Patents 808,227 and '228, Wood U.K. Patent 822,192 and Iguchi et al U.K. Patent 1,398,055. These addi~
tional materials need not be present in the ~eaction vessel during silver halide precipitation, but rather are conventionally added to the emulsion prior to coating. The vehicle materials, including particularly the hydrophilic colloids, as we~l as the hydrophobic materials useful in combination therewith can be employed not only in the emulsion layers of the photographic elements of this inven-tion, but also in other layers, such as overcoat layers, interlayers and layers positioned beneath the emulsion layers.
It is specifically contemplated that grain ripening can occur during the preparation of high

5 aspect ratio tabular gra~n silver hallde emulsions u~eful in the practice of the present invention, and it iB preferred that grain ripening occur within the reaction vessel during at least silver bromoiodide grain formation. Known silver halide solvents are 10 u~eful in promoting ripening. For example, an excess of bromide ions, when present in the reaction vessel, is known to promote ripening. It ~8 there-fore app~rent that the bromide salt solution run into the reaction vessel can itself promote ripen-15 ing. Other ripening agents can also be employed andcan be e~tirely contained within the dispersing medium ~n the reaction ves~el before silver and halide salt addition, or they can be introduced in~o the reaction ves~el along with one or more of the 20 halide salt, silver ~alt, or peptizer. In ~till another variant the ripening agent can be introduced independently during halide and silver salt additions.
Among preferred ripen~ng agents are those 25 containing ~ulfur. Thiocyanate salts can be used, such as alkali metal, most commsnly sodium and pota~s~um, and ammonium thiocyanate salts. While any conventional quantity of the thiocyanate salts can be introduced~ preferred concentrations are 30 gener&lly from about 0.1 to 20 grams of thiocyanate salt per mole of silver halide. Illustrative prior teachings of employing thiocyanate ripening agents are found in Nietz et al, U.S. Patent 2,2~2,264, cited above; Lowe et al U.S. Patent 2,448,534 and 35 Illingsworth U.S. Patent 3,320,069. Alternatively, -- ~LZ~ 2~i conventional thioether ripening agents, such as those disclosed in McBride U.S. Patent 3,2719157, Jones U.S. Patent 3,574,628, and Ro~ecrants et al U.S. Patent 3,737,313~ can be employed.
The high aRpect ratio tabular grsin emul-sions are preferably washed to remove soluble salts. The soluble sslts can be removed by decanta-tion, filtrat~on, and/or chill setting and leaching, as illustrated by Craft U.S. Patent 2,316,B45 and 10 McFall et al U.S. Patent 3,396,027; by coagulation washing, a~ illustrated by Hewitæon et al U.S.
Patent 2,618,556, Yutzy et al U.S. Patent 2,614,928, Yackel U.S. Patent 2,565,418, Hart et al U.S. Patent 3,241,969, Waller et al U.S. Patent 2,489,341, 15 Klinger U.K. Patent 1,305,409 and ~ersch et al U.K.
Patent 1,167,159; by centrifugation and decantation of a coagulated emulsion, as illustrated by Murray U.S. Patent 2,463,794, U~ihara et al U.S. Patent 37707,378, Audran U.S. Patent 2,996,287 and Timson 20 U.S. Pa~ent 3,498,454; by employing hydrocyclones alone or in combination wi~h centrifugeæ, as illus-trated by U.K. Patent 1,336,692, Claes U.K. Patent 1,356,573 and Ushomirskii et al Soviet Chemical Industry, Vol. 6, No. 3, 1974, pp. 181-185; by 25 diafiltration with a semipermeable membrane, as illustrated by Research Disclosure, Vol. 102, October 1972, Item 10208, Hagemaier et al Research Disclosure, Vol. 1319 March 1975, Item 13122, Bonnet Research Disclosure, Vol. 135, July 1975, Item 30 13577, Berg et al German OLS 2,436,461, Bolton U.S.
Patent 2,495,918, and Mignot U.S. Patent 4,334,012, cited above, or by employing an ion exchange resin, as illustrated by Maley U.S. Patent 3,782,953 and Noble U.S. Patent 2,827,428. The emulsions, with or 35 without senæitizers, can be dried and stored prior ~ ., to use as illustrPted by ~esearch Disclosure, Vol.
101, September 1972, Item 10152. Washing is particularly advantageous in terminating ripening of the tabular ~rains after the completion of precipi-tation to avoid increasing their thickness and reducing their aspect ratio.
Once the high aspect ratio tabular grain emulsions have been formed they can be shelled to produce core-shell emulsions by procedures well known to those skilled in the art. Any photograph-ically useful silver salt c~n be employed in forming æhells on the high aspect ratio tabular grain emulsions prepared by the present process. Tech-niques for forming silver salt shells are illus-trated by Berriman U.S. Patent 3,367,778, Porter et al U.S. Patents 3,2~6,313 and 3,317,322, Morgan U.S.
Patent 3,917,485, and Maternaghan, cited above.
Since conventional techniques for shelling do not favor the formation of high aspect ratio tabular grains, as shell growth proceeds the average aspect ratio of the emulsion declines. If conditions favorable for tabular grain formation are present in the reaction vessel during shell formation, shell growth can occur preferentially on the outer edges of the grains so that aspect ratio need not declin~. Wey and Wilgus, cited above, specifically teach procedures for shelling tabular grains without necessarily reducing the aspect ratios of the resulting core-shell grains as compared to the tabular grains employed as cor~ grains. Evans, Daubendiek, and Raleigh Canadian Patent 1,175,692, commonly assigned, titled DIRECT REVERSAL EMULSIONS
AND PHOTOGRAPHIC ELEMENTS USEFUL IN IMAGE TRANSFER
FI~M UNITS, specifically discloses the preparation of high aspect ratio ~`

-` ~Z~6Z6 -3~
core-shell tabular grain emulsions for use ~n forming direct reversal imageæ.
Although thé procedures for preparing tabular silver halide grains described above will 5 produce high sspect ratio tabular grain emulsions in which tabular grains satisfying the thickness and diameter criteria for aspect ratio account for at leaæt 50 percent of the total pro~ected area of the total silver halide grain population) it is recog-10 nized that further advantages can be realized byincreasing the proportion of such tabulsr grains present. Preferably at lea~t 70 percent (optimally at least 90 percent) of the total pro~ected area is provided by tabular silver halide grains meeting the 15 thickness and diameter criteria. While minor amounts of nonta~ular grains are fully compatible with many pho~ographic applications, to achieve the full ad~antages of tabular grains the proportion of tabular grains can be increa~ed. Larger tabular 20 silver halide grains can be mechanically ~eparated from smaller, nontabular grains in a mixed popula-tion of grains using conventional separation tech-niques--e.g., by using a centrifuge or hydro-cyclone. An illustrative teaching of hydrocyclone 25 separation ig provided by Audran et al U.S. Patent 3,3~6,641.
To the extent that radiation-sensitive silver halide emulsions other than high aspect ratio tabular grain emulsions are employed in the multi-30 color photographic elements of this invention, theycan be chosen from any conventional emulsion hereto-fore employed in multicolor photographic elements.
Illustrative emulsions, their preparation and chemical sens~tization are disclosed in Research 35 Disclosure, Vol. 176, December 1978, Item 17643, Paragraph I, Emulsion preparation and types and Para~raph III, chemical sensitization.

121~i26 Silver iodide emulsions other than high aspect ratio tabular grain emulsions to the extent el~ployed in various forms of the multicolor photo-graphic elements of this invention can be precipi-tated by procedures generally similar to those forpreparing the high aspect ratio tabular grain silver iodide emulsions, described above, but without taking the precautions indicated to produce high average aspect ratios. For example, such emulsions can be prepared by the techniques disclosed by Byerley and Hirsch, Zharkov et al, and Daubendiek, "AgI Precipitations: Effects of pAg on Crystal Growth (PB)", each cited above.
The silver iodide emulsions employed in the multicolor photographic elements of this invention can be senæitized by conventional techniques. A
preferred chemical sensitization technique iB to deposit a silver salt epitaxially onto the tabular silver iodide grains. The epitaxial deposition of silver chloride onto silver iodide host grains is taught by Maskasky ~.S. Patents 4,094,684 and 4,142,900, and the analogous deposition of silver bromide onto silver iodide host grains is taught by Koitabashi et al U.K. Patent Application 2,063,499A, each cited above.
It is specifically preferred to employ the high aspect ratio tabular ilver iodide grains as host grains for epitaxial deposition. The terms "epitaxy" and "epitaxial" are employed in their art recognized sense to indicate that the silver salt is in a crystalline form having its orientation controlled by the host tabular grains. The tech-niques described in Maskasky Can. Patent 1,175,693, cited above, are directly applicable to , , , ~
, ~^

" lZ~6~6 ~32-epitaxlal deposition on the silver iodide host grains of this inven~ion. The silver ~alt epitaxy is substantially excluded in a controlled manner from at least a portion of the major crystal faces 5 of the tabular hoæt grains. The tabular ho~t grains direct epitaxial deposition of silver aalt to their edges and/or corners.
By confin~ng epitaxial deposition to selected sites on the tabular grains an improvement 10 in sensitivity can be achieved as compared to allowing the silver salt to be epitaxially deposited randomly over the major faces of the tabular grains~ The degree to which the silver salt is confined to selected sensitization sites, leaving at 15 least a portion of the major crystal faces substan-tially free of epitaxially deposited silver salt, can be varied widely without departing from the invention. In general, larger increases in sen~i-tivity are realized as the epitaxial coverage of the 20 ma~or crystal faces decreases. It is specifically contemplated to confine epitaxially deposited silver salt to less than half the area of the ma~or Grystal faces of the tabular grains, preferably less than 25 percent, and in certain forms, such as corner 25 epitaxial 6ilver salt deposits, optimally to less than 10 or even 5 percent of the area of the ma~or cry~tal faces of the ~abular grains. In some embodiments epitaxial deposition has been observed to commence on the edge surfaces of the tabular 30 ~rains. Thus, where epitaxy is limited, it may be otherwise confined to selected edge sensitization ~ites and effectively excluded from the major crystal faces.
The epitaxially deposited silver salt can 35 be used to provide sensitization sites on the ,.~

--~ 121~Z6 tabular host grains. By controlling the sltes of epitaxial deposition, it is possible to achieve selective site sensitization of the tabular host grains. Sensitization can be achieved ~ one or 5 more ordered sites on the tabular host grains. By ordered it is meant that the sensitization site~
bear a predictable, nonrandom relationship to the ma~or crystal faces of the tabular gr~ins and, preferably, to each other. 8y controlling epitaxlal deposition with respect to the ma~or crystal faces of the tabular grains it is possible to control both the number and lateral spacing of sensitization ~ites.
In some instances selective site sen6itiza-tion can be detected when the silver ~odide 8rain6 are exposed to radiation to which they are ~ensitive and surface latent image centers are produced at sensitization sites. If the grAins bearing latent image centers sre entirely developed, the location and number of the latent image centers cannot be determined. However, if development is arrested before development has spread beyond the immediate vicinity of the latent image center, and the partially developed grain is then viewed under magnification, the partial development 6ites are clearly visible. They correspond generally to the sites of the latent image centers which in turn generally correspond to the sites of sensitizaton.
The sensitizing silver salt that is deposited onto the host tabular grains at selected ~ites can be generally chosen from among any silver salt cap*ble of being epitaxially grown on a silver halide grain and heretofore known to be useful in photography. The anion content of the silver salt and the tabular silver halide grains differ suffi-ciently to permit differences in the re~pective , crystMl ~tructures to be detected. It i8 6pecifi-cally contemplated to choo~e the silver salts from among those heretofore known to be useful in forming 6hells for core-shell silver halide emul6ion~. In addition to all the known photographically useful silver halides, the silver salts can include other silver salt6 known to be capable of precipitstlng onto silver halide grains, such a6 silver thio-cyanate, silver cyanide, ~ilver carbonate, sllver ferricyanide, silver arsenate or arsenite, and silver ch~omate. Silver chloride is a specifically prefer~ed sensitizer. Depending upon the silver salt chosen and the intended applicat~on, the ~llver salt can usefully be deposi~ed in the pre~ence of any of the modifying compounds described above in connection with the tabular gilver halide gralns.
Some iodide from the host grain~ may enter the ~ilver salt epitaxy. It is also contemplated that the host grains can contain anions other than iodide up to their solubility limit in silver iodide, and, as employed herein, the term "silver iodide grains"
is intended to include such host grains.
Conventional chemical sensitizstion can be undertaken prior to controlled site epitsxial deposition of silver salt on the host tabulQr grain or a8 a following step. When silver chloride and/or silver th~ocyanate is deposited~ a large increase in sensitivity i8 realized merely by selective site depo6ition of the silver ~alt. Thus, further chemical sensitization steps of a conventional type need not be undertaken to obtain photographic speed. On the other hand, an additional increment ln speed can generally be obtained when further chemical sensitization is undertaken, and it i8 a distinct advantage that neither elevated temperature nor extended holding times are required in finishing 21~62~

the emulsion. The quantity of sensitizers can be reduced, if desired, where (1) epitaxial deposition itself improves sensitivity or (2) sen6itization is directed to epitaxial deposition sites. Sub6tan-tially optimum sensitization of tabular silveriodide emulsions ha~ been achieved by the epitaxial deposition of silver chloride without further chemical sens~tization.
Any conventional technique for chemical sensitization following controlled g~te epitaxial deposition can be employed. In general chemical sensitization should be undereaken based on the composition of the gilver salt deposited rather than the composition of the host tabular graing, since chemical senBitization i8 believed to occur primar-ily at the silver salt deposition site6 or perhap6 immediately ad~acent thereto. Conventional tech-niques for achieving noble metal ~e.g., gold) middle chalcogen (e.g., sulfur, selenium, andJor tellur-ium), or reduction sensitization as well a~ combina-tions the~eof are disclosed in Research Disclosure, Item 17643, Paragraph III, cited above.
High aspect ratio tabular grain emulsions other ~han the silver iod~de emulsions discussed above can be chemically sensitized by procedures similar to those employed in chemically sensitizing emulsions conventionally employed in multicolor photographic elements, described above. Extremely high speeds and highly improved speed-granularity relationshipR can be achieved when the emul~ions are substantially optimally sensitized following the teachings of Kofron et al, cited above. In one preferred form chemical sensitization is undertaken after spectral ~ensitization. Similar resultg have also been achieved in some instances by introducing other adsorbable materials, such as f~nish modi-` ~21~626 fiers, into the emulsion prior to chemical sensiti-zation. Independent of the prior incorporation of adsorbable materials, it is preferred to employ thiocyanates during chemical sensitization in concentrations of from about 2 X 1~- 3 to 2 mole percent, based on silver, as taught by Damschroder U.S. Patent 2,462,361. Other ripening agents can be used during chemical sensitization. Still a third approach, capable of being practiced independently of, but compatible with, the two approaches described above, is to deposit silver salts epitax-ially on the high aspect ratio tabular grains, as is taught by Maskasky Can. Patent 1,175,278, cited above.
The silver iodide emulsions intended to record blue light exposures can, but need not, be spectrally sensitized in the blue portion of the spectrum. Silver bromide and silver bromoiodide emulsions containing nontabular grains and relative-ly thick tabular grains can be employed to record blue light without incorporating blue sensitizers, although their absorption efficiency is much higher when blue sensitizers are present. The silver halide emulsion~, regardless of composition, intended to record minus blue light are spectrally sensitized to red or green light by the use of spectral sensitizing dyes.
The silver halide emulsions incorporated in the multicolor photographic elements of this invention can be spectrally sensitized with dyes from a variety of classes, including the polymethine dye class, which classes include the cyanines, merocyanines, complex cyanines and merocyanines (i.e., tri-, tetra-, and poly-nuclear cyanines and merocyanines), oxonols, hemioxonols, styryls, ; merostyryls, and streptocyanines.

lZl~Z6 The cyanine spectral sens~tizing dyes include, ~oined by a methine linkage, two basic heterocyclic nuclei, such as those derived from quinolinium, pyridinium, isoquinolinium, 3H-indo-lium, benzte]lndolium, oxazolium, oxazolinium,thiazolium, thiazolinlum, selenazolium, selenazolin-ium, imidazolium, imidazolinium, benzoxa~olium, benzothiazolium, benzoselenazolium, benzimidazolium, naphthoxazolium, naphthothiazolium, naphtho~elena-zolium, dihydronaphthothiazolium, pyrylium, andimidazopyrazinium quaternary salts.
The merocyanine spectral sensitizing dyes include, ~oihed by a double bond or a methine linkage, 8 basic heterocyclic nucleus of the cyanine dye type and an acidic nucleus, such 8B can be derived from barbituric acid, 2-thiobarbituric acid, rhodanine, hydantoin, 2-thiohydantoin, 4-thiohydan-toin, 2-pyrazolin-5-one, 2-lsoxazolin-5-one, indan-1,3-dione, cyclohexane-1,3-dione, 1,3-dioxane-4,6-dione, pyrazolln-3,5-dione, pentene-2,4-dione, alkylsulfonylacetonitrile, malononitrile, isoquino-lin-4-one, and chroman-2,4-dione.
One or more spectral sensi~izing dyes may be used. Dyes with sensitizing maxima at wave-lengths throughout the visible spectrum and with agreat variety of spectral sensitivity curve shapes are known. The choice and relative proportions of dyes depends upon the region of the spectrum to which æensitivity is desired and upon the shape of the spectral sensitivity curve desired. Dyes with overlapping spectral sensitivity curves will often yield in combination a curve in which the sensi-tivity at each wavelength in the area of overlap is approximately equal to the sum of the sensitivities of the individual dye~. Thus, it is possi~le to use combinations of dyes with different maxima to .,, .......

~Z~ iZ6 achieve a spectral sen6itivity curve with a maximum intermedi~te to the ~ensitizing maxima of the individual dye 8 .
Combinations of spectral sen6itizing dyes can be u~ed which result in supersensitization--that is, spectral sensitization that i8 greater in some spectral region than that from any concentration of one of the dyes alone or that which would re6ult from the additive effect of the dyes. Supersensiti-zation can be achieved with selected combinations ofspectral sensitizing dyes and other addenda, such aR
~tabilizers snd antifoggants, development accele-rators or inhibitors, coating aids, brighteners and antistatic agents. Any one of several mechanisms a6 well as compounds which can be responsible for supersensitizatioff sre discussed by Gilman, "Review of the Mechanisms of Supersensitization", Photo-graphic Science snd Engineering, Vol. 18, 1974, pp.
418-430.
Spectral gensitizing dyes also affect the emulsions in other ways. Spectral sensitizing dyes can also function as antifoggants or stabilizers, development ~ccelerators or inhibltors, and halogen acceptors or electron acceptors, as disclosed in Brooker et al U.S. Patent 2,131,038 and Shiba et al U.S. Patent 3,930,860.
Sensitizing action can be correlated to the position of molecular energy levels of a dye with respect to ground state and conduction band energy levels of the silver hslide crystals. These energy levels csn in turn be correlated to polarographic oxidation snd reduction potentisls~ a8 discussed in Photographic Science and EngineerinR, Vol. 18, 1974, pp. 49-53 ~Sturmer et al), pp. 175-178 (Leubner~ and pp. 475-485 (Gilman). Oxidatlon and reduction potentisls can be measured as described by R. F.

. ,, `` ~2~:!6Z6 Large in Photographic Sensitivity, Academic Press, 1973, Chapter 15.
The chemistry of cyanine and related dyes is illustrsted by Weisæberger and Taylor, Topics _ Heterocyclic Chemistry, John Wiley and Sons, New York, 1977, Chapter VIII; Venkataraman, The Chemistry of Synthetic Dyes, Acsde~ic Press, New York, 1971, Chapter V; James, The _ eorv of the Photographic Process, 4th Ed., Macmillan, 1977~
Chapter 8, and F. M. Hamer, Cyanine Dyes and Related Compounds, John Wiley and Sons, 1964.
Among useful spectral sensitizing dyes for sensitizing silver halide emulsions are those found in U.K. Patent 742,112, Brooker U.S. Patents 1,846,300, '301, '302, '303, '304, 2,078,233 a~d 2,089,729, B~ooker et al U.S. Patents 2,165,338, 2,213,238, 2,231,658, 2,4g3,747, '748, 2,526,632, 2,739,964 (Reissue 24,292), 2,778,823, 2,917,516, 3,352,857, 3,411,916 and 3,431,111, Wilmanns et al U.S. Patent 2,295,276, Sprague U.S. Patents 2,481,698 and 2,503,776, Carroll et al U.S. Patent6 2,688,545 and 2,704,714~ Larive et al U.S. Patent 2,921,067, Jones U.S. Patent 2,945,763, Nys et al U.S. Patent 3,282,933, Schwan et al U.S. Patent 3,397,060, Riester U.S. Patent 3,660,102, Kampfer et al U.S. Patent 3,660,103, Taber et al U.S. Patents 3,335,010, 3,352,680 and 3,384,486, Lincoln et al U.S. Patent 3,397,981, Fumia et al U.S. Patent~
3,482,978 and 3,623,881, Spence et al U.S. Patent 3,718,470 and Mee U.S. Patent 4,025,349. Example~
of useful dye combinations, including supersensitiz-ing dye comb~nations, are found in Motter U.S.
Patent 3,506,443 and Schwan et al U~S. Patent 3,672,898. As examples of supersensitizing combina-tions of spectral sensitizing dyes and non-light absorbing addenda, it is specifically contemplated .~J

12~¢~Z6 to employ thiocyanates during spectral sensitiza-tion, as taught by Leermakers U.S. Patent 2,221,805;
bis-triazinylaminostilbenes, as taught by McFall et al U.S. Patent 2,933,390; sulfona~ed aromatic compounds, as taught by Jones et al U.S. Paten~
2,937,089j mercapto-~ubstituted heterocycles, a~
taught by Riester U.S. Patent 3,457,078; iodlde, as taught by U.K. Patent 1,413,826; and still other compounds, such as those disclosed by Gilman, "Review of ~he Mechanisms of Supersensitization'~, cited above.
Conventional amount~ of dyes can be employed in spectrally sensitizing the emulsion layers contain~ng nontabular or low aspect ratio lS tabular silver halide grains. To realize the full advantages of this invention it is preferred to adsorb spectral sensitizing dye to the grain surfaces of the high aspect ratio tabular grain emulsions in a substantially optimum amount--that is, in an amount sufficient to realize at least 60 percent of the maximum photographic speed attainable from the grains under contemplated conditions of exposure. The quantity of dye employed will vary with the specific dye or dye combination chosen as well as the size and aspect ratio of the grains. It is known in the photographic art that optimum spectral sensitization is obtained with organic dyes at about ~5 to 100 percent or more of monolayer coverage of the total available surface area of surface sensitive silver halide grains, as disclosed, for example, in West et al, "The Adsorp-tion of Sensitizing Dyes in Photographic Emulsions", Journal of Phys. Chem., Vol 56, p. 1065, 1952;
Spence et al, "Desensitization of Sensitizing Dyes", Journal of Physical and Colloid Chemistry, Vol. 56, No. 6, June 1948, pp. 1090-1103; and Gilman et al `` ~21(~6Z6 --~1--U.S. Patent 3,979,213. Optimum dye concentration levels can be chosen by procedure~ taught by Mees, Theory of the Photographic Process, Macmi}lan, 1942, pp. 1067-1069.
Although native blue sensitivity of silver bromide or bromoiodide is usually relied upon in the art in emulsion layers intended to record expo6ure to blue light, it i8 gpecifically recognized that advantages can be realized from ~he use of blue 10 spectral se~sitizing dyes. When the blue recording emulsion~ in such emulsion layer~ are high aspect ratio tabular grain silver bromide and silver bromoiodide emulsions, very large increases in speed are realized by the use of blue spectral sensitizing 15 dye8.
Useful blue spectr~l ~ensitizing dyes for high a6p~ct ratio tabular grain silver bromide and silver bromoiodide emulsions can be selected from any of the dye classes known to yield spectral 20 sensitizers. Polymethine dyes, ~uch a~ cyanines, merocyanines, hemicyMnines, hemioxonols, and mero-styryls, are preferred blue spectral sensitizers ; Generally useful blue spectral sensitizers can be selected from among these dye classes by their 25 absorption characteristics--i.e., hue. There are, however, general structural correlations that can serve as a guide in selecting useful blue sensi-tizers. Generally the shorter the methine chain, the shorter the wavelength of the 6ensitizing 30 maximum. Nuclei also influence absorption. The addition of fused rings to nuclei tends to favor longer wavelengths of absorption. Substituents ca~
also alter absorption characteristics. In the formulae which follow, unles~ othewise specified, alkyl groups and moieties contain from 1 to 2~
carbon atoms, preferably from 1 to 8 carbon atoms.
. , .~

~21~6Z6 Aryl groups and moieties contain from 6 to 15 carbon atoms and are preferably phenyl or naphthyl group~
or moieties.
Preferred cyanine blue spectral sensitizers are monometh~ne cyanines; however, u~eful cyanine blue spectral sensitizers can be selected from among those of Formula 1.
1- -Z~- -I R3 R4 Rs 1- _z2_ _ I
10 Rl~N~CH-CH~pC-C~~C~C)m~C~CH~CH~qN~R2 Formula 1 k Q
where zl and Z2 may be the same or different and each represents the elements needed to complete a cyclic nucleus dérived from basic heterocyclic nitrogen compounds such as oxazoline, oxazole, benzoxazole, the naphthoxazoles (e.g., naphth-[2,1-d]oxazole, naphth[2,3-d]oxazole, and naphth-~1,2-d]oxazole), thiazoline, thiazole, benzothia-zole, the naphthothiazoles (e.g., naphtho~2,1-d]-thiazole), the thiazoloquinolines (e.g., thiazolo-[4,5-b]quinoline), selenazollne, selenazole, benzo-selenazole, the naphthoselenazoles (e.g., naphtho-tl,2-d~selenazole), 3H-indole (e.g., 3,3-dimethyl-3H-indole), the benzindoles (e.g., l,l-dimethylbenz-[e]indole), imidazoline, imidazole, benzimidazole, the naphthimidazoles (e.g., naphth~2,3-d]imidazole), pyridine, and quinoline, which nuclei may be substi-tuted on the ring by one or mose of a wide varietyof substituents such as hydroxy, the halogens (e.g., fluoro, chloro, bromo, and iodo), alkyl groups or substituted alkyl groups (e.g., methyl, ethyl, propyl, isopropyl, butyl, octyl, dodecyl, octadecyl, 2-hydroxyethyl, 3-sulfopropyl, carboxymethyl, 2-cyanoethyl, and trifluoromethyl), aryl groups or ` " lZ~626 substituted aryl groups (e.g., phenyl, l-naphthyl, 2-naphthyl, 4-sulfophenyl, 3-carboxyphenyl, and 4-biphenyl), aralkyl group~ (e.g., benzyl and phenethyl), alkoxy groups (e.g., methoxy, ethoxy, and isopropoxy), aryloxy groups (e.g., phenoxy and l-naphthoxy), alkylthio groups (e.g., methylthio and ethylthio), arylthio groups (e.g., phenylthio, ~-tolythio, and 2-naphthylthio), methylenedioxy, cyano, 2-thienyl, styryl, amino or substituted amino groups (e.g., anilino, dimethylamino, diethylamino, and morpholino), acyl groups, such as carboxy (e.g., acetyl and benzoyl) and sulfo;
Rl and R2 can be the game or different and reprefient ~lkyl groups, aryl groups, alkenyl groups, or aralkyl groups, with or without substituents, (e.g., carboxymethyl, 2-hydroxyethyl, 3-fiulfopropyl, 3-sulfobutyl, 4-sulfobutyl, 4-sulfophenyl, 2-meth-oxyethyl, 2-sulfatoethyl, 3-thiosulfatopropyl, 2-phosphonoethyl, chlorophenyl, and bromophenyl);
R3 represents hydrogen;
R~ and R5 represents hydrogen or alkyl of from 1 to 4 carbon atoms;
p and q are 0 or 1, except that both p and q pre~erably are not l;
m i~ 0 or 1 except that when m is 1 both p and q are 0 and at leaRt one of Z~ and Z2 represents imidazoline, oxazoline, thiazoline, or selenazoline;
A is an anionic group;
B is a cstionic group; and k and ~ may be 0 or 1, depending on whether ionic substituents are present. Variants are, of course, possible in which Rl and R3, R2 and R5, or Rl and R2 (particularly when m, p, and q are 0) together represent the atoms necessary to complete an alkylene bridge.
Some representative cyanine dyes useful a~
blue sensitizers are listed in Table I.
. .,J

~Z$~;~iZ6 Table I
l. 3,3'-Diethylthiacyanine b~omide ~ CH-- ~+ ;l ;
S
I I Br~
C2Hs C2Hs 2. 1-Ethyl-3'-methyl-4'-phenylnaphtho[1,2-d]thiazolothiazolinocyanine bromide ~-~ ,S~ ~
CH--~ ~ J

\-~ C2Hs CHa ~-~ B~
lS3. 1',3-Diethyl-4-phenyloxazolo-2'-cyanine iodlde \ .~ \./ ~.
. Il / ~CH-l~+/ll\ ~l 20~./ C2Hs C2Hs I-4. Anhydro 5-chloro-5'-methoxy-3,3'-bi B -(~-6ulfoethyl)thiacyanine hydroxide, triethylamine s~lt ~-\ /s\ /s\ /-~
C~!~-/Y\N/ ~ bCH
(CH2) 2 (CHz) 2 (CzH5)3NH+
SOa S03 5. 3,3'-Bis(2-carboxyethyl3thiazolino-carbocyanine iodide \ /s\
CH-CH-CH--~ ~ ~

(CH~)2 (CH2)2 COOH COOH

6. 1,1'-Diethyl-3,3'-ethylenebenzimida-zolocyanine iodide ~ ? \\N+/ \ ~

7. 1-(3-E~hyl-2-benzothiazolinylidene)-1,2,3,4-tetrahydro-2-methylpyrido-~2,1-b]-benzothiazolinium iodide / 5\ /-~

~-/ ~ \ ~ I-C 2Hs ~ H3

8. Anhydro-5,5'-dimethoxy-3,3'-bl 8 (3-sulfopropyl)thiscyanine hydroxide, sodium salt I 1l \ -CH--/\ + ¦l i NaS03(CH2) 3 (CH2~3S03- Ns +
Preferred merocyanine blue spectral sensi-tizers are zero methine merocyanine~; however, -46 ~
u~eful me~ocyanine blue spectral ~ensitizer~ can be selected from among those of Formula 2.
o _ _z _ _ R/~ 11 -G
5R-N~cH-cH~rc~(c-cR )n \G2 Formula 2 where Z represent~ the Rame elements as either Zl or 0 Z2 of Formula 1 above;
R represents the same group~ a~ e~ther Rl or R2 of Formula 1 above;
R4 and Rs represent hydrogen, an alkyl group of 1 to 4 carbon fltoms~ or an aryl group (e.g., phenyl or naphthyl) 3 Gl repre~ents an slkyl group or 6ub6tituted alkyl group, an aryl or sub~t~tuted aryl group, an aralkyl group, ~n alkoxy group, ~n aryloxy group, a hydroxy group~ an amino group, a subRtituted amino group wherein ~pecific group~ are of the types in Formula l;
G2 can represent eny one of the groups listed for Gl and in addition can repre~ent a cyano group, an alkyl, or arylsulfonyl group, or a group represented by -C-Gl, or G2 taken together with o can represent the elements needed to complete a syclic acidic nucleus such a6 those derived from 2,4-oxazolidinone (e.g., 3-ethyl-2,4-oxazolidin-dione), 2,4-thiazolidindione (e.g., 3-methyl-2,4-ehiazolidlndione), 2-thio-2~4-oxazolidindione (e.g., 3-phenyl-2-thio-2,4-oxazolidindione), rhodanine, Euch as 3-ethylrhodanlne, 3-phenylrhodanine, 3~(3-dimethylaminopropyl)rhodanine, and 3 calboxy-~LZ1~6Z~-47-methylrhodanine, hydantoin (e.g., 1,3-diethylhydan-toin and 3-ethyl-1-phenylhytantoin), 2-thiohydantoin (e.g., l-ethyl-3-phenyl-2-thiohydantoin, 3-heptyl-l-phenyl-2-thiohydantoin, and 1,3-diphenyl-2-thio-hydantoin), 2-pyrazolin-5-one, such as 3-methyl-1-phenyl-2-pyrazolln-5-one, 3-methyl-1-(4-carboxy-butyl)-2-pyrazolin-5-one, and 3-methyl-2-(4-sulfo-phenyl)-2-pyrazolin-5-one, 2-isoxazolin-5-one (e.g., 3-phenyl-2-isoxazolin-5-one), 3,5-pyrazolidindione (e.g., 1,2-diethyl-3,5-pyrazolidindione and 1,2-di-phenyl-3,5-pyrazolidindione), 1,3-indandione, 1,3-dioxane-4,6-dione, 1,3-cyclohexanedione, barbi-turic acid (e.g., l-ethylbarbituric acid and 1,3-di-ethylbarbituric acid), and 2-thiobarbiturlc acid (e.g., 1,3-diethyl-2-thiobarbituric acid and 1,3-bi B (2-methoxyethyl)-2-thiobarbituric BCi d);
r and n each can be 0 or 1 except that when n is 1 then generally either Z is restricted to imidazo-line, oxazoline, selenazoline, thiazoline, imidazo-line, oxazole, or benzoxazole, or Gl and G2 donot repre6ent a cyclic sy6tem. Some representative blue 6ensitizin~ merocyanine dyes are listed below in Table II.
Table II
1. 5-(3-Ethyl-2-benzoxazolinylidene)-3-phenylrhodanine 1 ll ~ ~ II-N/ ~.
~ S

C2Hs ~2~ 26 2. 5-tl-(2-Carboxyethyl) 1,4-dihydro-4-pyridinyl~dene]-l-ethyl-3-phenyl-2-thio-. hydantoin S i i ~ ! -N/ ~.
HOOCCH2CH~ S
'-- \N/

C2Hs 3. 4-(3-Ethyl-2~benzothiazolinylidene)-3-methyl-l-(~-~ulfophenyl)-2-pyrazolin-5-one, Pota~ium Salt . i iI_SO3 K~
.~ ~./S~ ll-N/ ~.
~N

C2Hs ~H3 4. 3-Carboxymethyl-5-(5-chloro-3-ethyl-2-benzothiflzolinylidene)rhodanine Cl/ ~-/ ~ \S/
C2Hs 5. 1,3-Diethyl-5-t3,4,4-trimethyloxazoli-dinylidene)ethylidene]-2-thiobarbituric acid H C ~ CH-CH.~ S
H3C I ~ \C2Hs ~Z~ i2~

~49-Useful blue sensitizing hemicyanine dyes include those represented by Formul~ 3.
l l G3 R-N~CH-CH~pC~CLI~CL2(~CL3CL4) ~N~ 4 Formula 3 (A)k where Z, R, and p repre~ent the same element6 aæ in Formula 2; G 3 and G4 may be the same or differ-10 ent and may represent alkyl, substituted alkyl,aryl, substituted aryl, or aralkyl, as illustrated for ring substituents in Formula 1 or G3 and G4 taken together complete a ring sy~tem derived from a cycl~c secondary amine, such as pyrrolidine, 3-pyr-15 roline, p~peridine, piperazine (e.g., 4-methylpiper-azine and 4-phenylpiperazlne), morpholine, 1,2,3,4-tetrahydroquinoline, decahydroquinoline, 3~azabi-cyclo[3,2,2]nonane, indoline, azetidine, and hexa-hydroazepine;
Ll to L4 repre~ent hydrogen, alkyl of 1 to 4 carbon~, aryl, substituted aryl, or any two of Ll, L2, L3, L4 can represent the elements needed to complete an alkylene or carbocyclic bridge;
n is O or l; and A and k have the same definition as in Formula 1.
Some representative blue Rensitizin~
hemicyanine dyes are ll~ted below in Table III.

~21~2~
-so -Table III
1. 5,6-Dichloro-2-[4-(diethylamino)-1,3-butadien-l-yl~-1,3-diethylbenzimidazolium iodide C2 ~s l~C~ N" C2Hs - CH-CH-CH-CH-N~

C2Hs I-2. 2-{2-[2-(3-Pyrrolino)-l-cyclopenten-l-yl~ethenyl}3-ethylthiazolinium perchlorate i ~ -CH-CH~-C-C/ ~

I Cl-04 C2Hs 0 3. 2-(S,S-Dimethyl-3-piperidino-2-cyclohexen-l-yldenemethyl)-3-ethylbenzoxazolium perchlorate (CH3 )2 i \~/ \ CH=~ /. Cl-04 C2 Hs Useful blue sensitiz~ng hemioxonol dyes 30 include those represented by Formula 4.
G~- ~ 0 G3 C'CLl ( -CL2 -CL3 ) -~
Formula 4 where "` ~Z1~62 G~ and G2 represent the same elements as in Formula 2;
G3, G4, Ll, L2, and L3 represent the same elements as in Formula 3; and n is O or 1.
Some representative blue ~ensitizing hemioxonol dyes are listed in Table IV.
Table IV
1. 5-(3-Anilino-2-propen-1-ylidene)-1,3-diethyl-2-thiobarbituric acid C2 Hs /N-C~ H
S'-~ ,~ ~CH-CH-CH-N-C2Hs 2. 3-Ethyl-5-(3-piperidino-2-propen-1-ylidene)rhodanine o 2 0 ~ /- -CH-CH~=CH-~ /-g \S/ -3.3-Allyl ~5-[5,5 -dimethyl-3-(3-pyrrolino)-2-cyclohexen-1-ylidene]rhodanine O Hs C\ /CH3 CH2~CH-CH2\~ \ ./ \ ~< \

Useful blue sensitiz~ng merostyryl dyes ~nclude those represented by Formula 5.

G ~--CH-~CH~CH)n--~ ~ ~ G4 Formula 5 ~ \

lZ~L~62~ --~2 -where Gl, G2, G3, G4, and n are as defined in Formula 4.
Some representative blue sensitizing 5 merostyryl dyes are listed in Table V.
Table V
1. 1-Cyano-1-~4-dimethylaminobenzylidene)-2-pentanone ~C-CH-~

2. 5-(4-Dimethylaminobenzylidene-2~3-diphenylthiazolidin-4-one-1-oxide .\ O
./ ~ \ / \ CH3 ~./ O
3. 2-(4-Dimethylaminocinnamylidene)thiazolo-[3,2-a]benzimldazol-3~one ._. O
\N-~ / ZcH-cHzcH-.~

Spectral sensitization can be undertaken at any stage of emulsion preparation heretofore known 30 to be useful. Most commonly spectral sensitization is undertaken ln the art subsequent to the comple-tion of chemical sensitization. However, it is specifically recognized that spectral sensitization can be undertaken alternatively concurrently with 35 chemical sensitizat~on, can entirely precede chemi-cal sensitization, and can even commence prior to lZ~;6 -s3-the completion of silver halide grain precipitation, as taught by Philippaerts et al U.S. Patent 3,628,960, and Lock-r et al U.S. Patent 4,225,666.
As taught by Locker et al, it is specifically contemplated to distribute introduction of the spectral sensitizing dye into the emulsion so that a portion of the spectral sensitizing dye is present prior to chemical sensitization and a remaining portion is in~roduced after chemical sensitization.
Unlike Locker et al, it is specifically contemplated that the spectral sensitizing dye can be added to the emulsion after 80 percent of the silver halide has been precipitated. Sensitization can be enhanced by pAg adjustment, including variation in pAg which completes one or more cycles, during chemical and/or spectral sensitization. A specific example of pAg adjustment is provided by Research Disclosure, Vol. 181, May 1979, Item 18155.
Multicolor Photographic ~lement and Processing Features In addition to the radiation-sensitive emulsions described above the multicolor photo-graphic elements of this invention can include a variety of features which are conventional in multicolor photographic elements and therefore require no detailed description. For example, the multicolor photographic elements of this invention can employ conventional features, such as disclosed in Research Disclosure, Item 17643, cited above.
Optical brighteners can be introduced, as disclosed by Paragraph V. Antifoggants and sensitizers can be incorporated, as disclosed by Paragraph VI.
Absorbing and scattering materials can be employed in the emulsions of the invention and in separate layers of the photographic elements, as described in Paragraph VIII. Hardeners can be incorporated, as disclosed in Paragraph X.

lZ~6Z6 Coating aids, as described in Paragraph XI, and plasticizers and lubricants, as des~ribed in Para-graph XII, can be present. Antistatic layers, as described in Paragraph XIII, can be present.
5 Methods of addition of addenda are described in Paragraph XIV. Matting agents can be incorporated, as described in Paragraph XVI. Developing agents and development modifiers can, if desired, be incorporated, as described in Paragraphs XX and 10 XXI. Silver halide emulsion layers as well as interlayers, overcoats, and subbing layer6, if any, present in the photographic elements can be coated and dried as described in Paragraph XV.
The layers of the photographic elements can 15 be coated on a variety of supports~ Typical photo-graphic supports include polymeric film, wood fiber--e.g., paper, metallic sheet and foil, glass and ceramic supporting elements provided with one or more subbing layers to enhance the adhesive, anti-20 static~ dimensional, abrasive, hardness, frictional, antihalation and/or other properties of the support surface. Typical of useful paper and polymeric film supports are those disclosed in Research Disclosure, Item 17643, cited above, Paragraph XVII.
The multicolor photographic elements can be used to form dye images therein through the selec-tive destruction or formation of dyes. The photo-graphic elements can be used to form dye images by emplo~ing developers containing dye image formers, 30 such as color couplers, as illustrated by U.K.
Patent 478,984, Yager et al U.S. Patent 3,113,864, Vittum et al U.S. Patents 3,002,836, 2,271,238 and 2,362,598, Schwan et al U.S. Patent 2,950,970, Carroll et al U.S. Patent 2,592,243, Porter et al 35 U.S. Patents 2,343,703, 2,376,380 and 2,369,489, Spath U.K. Patent 886,723 and U.S. Patent 2,899,306, Tuite U.S. Patent 3,152,896 and Mannes et al U.S.

~ Z6 Patents 2,115,394, 2,252,718 and 2,108,602, and Pilato U.S. Patent 3,547,650. In this form the developer contains a color-developing agent (e.g., a primary aromatic amine) which in its oxidized form 5 is capable of reacting with the coupler (coupling) to form the image dye.
The dye-forming couplers can be incorpo-rated in the photographic elements, as illu~trated by Schneider et al, Die Chemie, Vol. 57, 1944, p.
10 113, Mannes et al U.S. Patent 2,304,940, Martinez U.S. Patent 2,269,158, Jelley et al U.S. Patent 2,322,027, Frolich et al U.S. Patent 2,376,679, Fierke et al U.S. Patent 2,801,171, Smith U.S.
Patent 3,748,141, Tong U.S. Patent 2,772,163, 15 Thirtle et al U.S. Patent 2,835,579, Sawdey et al U.S. Patent 2,533,514, Peterson U.S. Patent 2,353,754, Seidel U.S. Patent 3,409,435 and Chen Research Disclosure, Vol. 159, July 1977, Item 15930. The dye-forming couplers can be incorporated 20 in different amounts to achieve differing photo-graphic effects. For example, U.K. Patent 923,045 and Kumai et al U.S. Patent 3,843,369 teach limiting the concentration of coupler in relation to ~he silver coverage to less than normally employed 25 amounts in faster and intermediate speed emulsion layers.
The dye-forming couplers are commonly chosen to form sub~ractive primary (i.e., yellow, magenta and cyan) ~mage dyes and are nondiffusible, 30 colorles6 couplers, such as two and four equivalent couplers of the open chain ketomethylene, pyra-zolone, pyrazolotriazole, pyrazolobenzlmidazole, phenol and naphthol type hydrophobically ballasted for incorporation in high-boiling organic (coupler) 35 solvents. Such couplers are illustrated by Salminen et al U.S. Patents 2,423,730, 2,772,162, 2,895,826, 2,710,803, 2,407,207, 3,737,316 and 2,367,531, Loria -lZ~6Z6 ~56 -et al U.S. Patents 2,772,161, 2,600,788, 3,006,759, 3,214,437 and 3,253,924, McCrossen et al U.S. Patent 2,875,057, Bush et al U.S. Patent 2,908,573, Gledhill et al U.S. Patent 3,034,892, Weissberger et 5 al U.S. Patents 2,474,293, 2,407,210, 3,062,653, 3,265,506 and 3,384,657p Porter et al U.S. Patent 2,343,703, Greenhalgh et al U.S. Patent 3,127,269, Feniak et al U.S. Patents 2,865,748, 2,933,391 and 2,865,751, Bailey et al U.S. Patent 3,725,067, 10 Beavers et al U.S. Patent 3,758,308, Lau U.S. Patent 3,779,763, Fernandez U.S. Patent 3,785,829, U.K.
Patent 969,921, U.K. Patent 1,241,069, U.K. Patent 1,011,940, Vanden Eynde et al U.S. Patent 3,762,921, Beavers U.S. Patent 2,983,608, Loria U.S. Patent~
15 3,311,476, 3 9 408,194, 3,458,315, 3,447,928, 3,476,563, Cressman et al U.S. Patent 3,419,390, Young U.S. Patent 3,419,391, Lestina U.S. Patent 3,519,429, U.K. Patent 975,928, U.K. Patent 1,111,554, Jaeken U.S. Patent 3,222,176 and Canadian 20 Patent 726,651, Schulte et al U.K. Patent 1,248,924 and Whitmore et al U.S. Patent 3,227,550. Dye-form-ing couplers of differing reaction rates in single or separate layers can be employed to achieve desired effect~ for specific photographic 25 aPPlications.
The dye-forming couplers upon coupl~ng can release photographically useful fragments, such as development inhibitors or accelerators, bleach accelerators, developing agents, silver halide 30 solvents, toners, hardeners, fogging agents, anti-foggants, competing couplers, chemical or spectral sensitlzers and desensitizers. Development inhibi-tor-releasing (DIR) couplers are illu~trated by Whitmore et al U.S. Patent 3,143,062, Barr et al 35 U.S. Patent 3,227,554, Barr U.S. Patent 3,733,201, Sawdey U.S. Patent 3,617,291, Groet et al U.S.
Patent 3,703,375~ Abbott et al U.S. Patent -- lZlr~Z6 3,615,506, Weissberger et al U.S. Patent 3,265,506, Seymour U.S. Patent 3,620,745, Marx et ~1 U.SO
Patent 3,632,345, Mader et al U.S. Patent 3,869,291, U.K. Patent 1,201,110, Oishi et al U.S. Patent 5 3,642,485, Verbrugghe U.K. Patent 1,236,767, Fu~iwhara et al U.S. Patent 3,770,436 and Matsuo et al U.S. Patent 3,808,945. Dye-forming couplers and nondye-forming compounds which upon coupling release a variety of photographically useful groups &re described by Lau U.S. Patent 4,248,962. DIR
compounds which do not form dye upon reaction with oxidized color-developing ~gents can be employed, a~
illustrated by Fujiwhara et al German OLS 2,529,350 and U.S. Patents 3,928,041, 3,958,993 and 3,961,959, 15 Odenwalder et al German OLS 2,448,063, Tanaka et al German OLS 2,610,546, Kikuchi et al U.S. Patent 4,049,455 and Credner et al U.S. Patent 4,052,213.
DIR compounds which oxidatively cleave can be employed, as illu~trated by Porter et al U.S. Patent 20 3,379,529, Green et al U.S. Patent 3,043,690, Barr U.S. Patent 3,364,022, Duennebier et al U.S. Patent 3,297,445 and Rees et al U.S. Patent 3,287,129.
Silver halide emulsions which are relatively light insensitive, such ~s Lippmann emulsions, have been 25 utili~ed as interlayer6 and overcoat layer~ to prevent or control the migration of development inhibitor fragments as described in Shiba et al U.S.
Patent 3,892,572.
The photographic elements can incorporate 30 colored dye-forming couplers, such as those employed to form integral masks for negative color images, as illustrated by Hanson U.S. Patent 2,449,966, Glass et al U.S. Patent 2,521,908, Gledhill et al U.S.
Patent 3,034,892, Loria U.S. Patent 3,476,563, 35 Lestina U.S. Patent 3,519,429, Friedman U.S. Patent 2,543,691, Puschel et al U.S. Patent 3,028,238, Menzel et al U.S. Patent 3,061,432 and Greenhalgh . ..-~ 6Z~
-5~-U.K. Patent 1,035,959, and/or competing couplers, as illustrated by Murin et al U.S. Patent 3,876,428, Sakamoto et al U.S. Patent 3,580,722, Puschel U.S.
Patent 2,998,314, Whitmore U.S. Patent 2, 808,329, 5 Salminen U.S. Patent 2,742,832 and Weller et al U.S.
Patent 2, 689, 793.
The photographic element6 can include image dye stabilizers. Such image dye stabilizers are illustrated by U.K. Patent 1,326,889, Lestina et al 10 U.S. P~tents 3,432,300 and 3,69~,909, Stern et al U.S. Patent 3,574,627, Brannock et al U.S. Patent 3,573,050, Arai et al U.S. Patent 3,764,337 and Smith et al U.S. Patent 4,042, 394.
Dye images can be formed or ~mplified by 15 proce~ses which employ in combination with a dye~
image-generating reducing agent an inert transition metal ion complex oxidizing agent, as illustrated by Bissonette U.S. Patents 3,748,13~, 3,826,652, 3,862,842 and 3,989,526 and Travis U.S. Patent 20 3,765,891, and/or a peroxide oxidizing agent, as illu~trated by Mate~ec U.S. Patent 3,674,490, Research Disclosure, ~ol. 116, December 1973, I~em 11660, and Bissonette Research Disclo~ure, Vol. 148, August 1976, Items 14836, 14846 and 14847.
The photographic elements can produce dye images through the selective destruction of dyes or dye precursors, such as silver-dye-bleach processes, as illustr~ted by A. Meyer, The Journal of Photo-graphic Science, Vol. 13, 1965, pp. 90-97. Bleach-30 able azo, azoxy, xanthene, azine, phenylmethane, nitroso complex, indigo, quinone~ nitro-substituted, phthalocyanine and formazan dyes, as illustrated by Stauner et al U.S. Patent 3,754,923, Piller et al U.S. Patent 3,749,576, Yoshida et al U.S. Patent 35 3,738,839, Froelich et al U.S. Patent 3,716,368, Piller U.S. Patent 3,655,388, Williams et al U.S.
Patent 3,642,482, Gilman U.S. Patent 3,567,448, ~Z~J62~

Loeffel U.S. Patent 3,443,953, Ander~u U.S. Pstents 3,443,952 and 3,211,556, Mory et al U.S. Patents 3,202,511 and 3,178,291 and Anderau et ~1 U.S.
Patents 3,178,285 and 3,178,290, as well as their 5 hydrazo, diazonium and tetrazolium precursors and leuco and shifted derivative6, ns ~llu6trated by U.K. Patents 923,265, 999,996 and 1,042,300, Pelz et al U.S. Patent 3,684,513, Watanabe et al U.S. Patent 3,615,493, Wilson et al U.S. Patent 3,503,741, Boes 10 et al U.S. Patent 3,340,059, Gompf et al U.S. Patent 3,493,372 snd Puschel et al U.S. Patent 3~561,970, can be employed.
It is common practice in forming dye images in silver halide photographic elements to remove the 15 developed silver by bleaching. Such removal can be enhanced by incorporation of a bleach accelerator or a precursor thereof in a proce6sing solution or in a layer of the element. In some instances the amount of silver formed by development is small in relation 20 to the amount of dye produced, particularly in dye image amplification, as described above, and silver bleaching is omitted without substantial visual effect.
The photographic el~ments can be processed 25 to form dye images which correspond to or are reversals of the silver halide rendered selectively developable by imagewise exposure. Reversal dye images can be formed in photographic elements having differentlally spectrally sensitized silver halide 30 layers by black-and-white development followed by i) where the elements lack incorporated dye image formers, sequential reversal color development with developers containing dye image former~, such as color couplers, as illustr~ted by Mannes et al U.S.
35 Patent 2,252,718~ Schwan et al U.S. Patent 2,950,970 and Pilato U.S. Patent 3,547,650; ii) where the elements contain incorporated dye image formers, :;

z~

such as color couplers, a single color development step, as illustrated by the Kodak Ektachrome~ E4 and E6 and Agfa processes described in British Journal of Pho~ography Annual, 1977, pp. 194-197, and British Journal of Photography, August 2, 1974, pp. 668-669; and iii) where the photographic elements contain bleachable dyes, silver-dye-bleach processing, as illustrated by the Cibachrome P-10 and P-18 processes described in the British Journal of Photography Annual, 1977, pp. 204-212.
The photographic elements can be adapted for direct color reversal processing (i.e., produc-tion of reversal color images without prior black-and-white development), as illustrated by U.K.
Patent 1,075,385, Barr U.S. Patent 3,243,294, Hendess et al ~.S. Patent 3,647,452, Puschel et al German Patent 1,257,570 and U.S. Patents 3,457,077 and 3,467,520, Accary-Vene~ et al U.K. Patent 1,132,736, Schranz et al German Patent 1,259,700, Marx et al German Patent 1,259,701 and Muller-Bore German OLS 2,005,091.
Dye images which correspond to the silver halide rendered selectively developable by imagewise exposure, typically negative dye images, can be produced by processing, as illustrated by the Kodacolor~ C-22, the Kodak Flexicolor'~ C-41 and the Agfacolor processes described in British Journal of PhotogrPphy Annual, 1977, pp. 201~205. The photographic elements can also be processed by the Kodak Ekt~print-3 and -300 processes as described in Kodak Color Dataguide, 5th Ed., 1975, pp. 18-19, and the Agfa color process as described in British Journal of Photography Annual, 1977, pp. 205-206, such processes being particularly suited to process-ing color print materials, such as resin-coated photographic papers, to form positive dye images.
The multicolor photographic elements of this invention produce multicolor images from combinations of subtractive primary imaging dyes.
Such photographic elements are comprised of a support and typically at least a triad of super-impo~ed silver halide emul~ion layers ~or separately 5 recording blue, green, and red exposures as yellow, magenta, and cyan dye images, respectively. (Expo-6ure~ can be of any conventional nature and are illustrated by Research Disclosure, 17643, cited above, Paragraph XVIII.) Although the present 10 invention generally embraces any mul~icolor photo-graphic eleme~t of this type including at least one silver halide emulsion layer containing high aspect ratio silver iodide tabular grains, additional advantages can be realized when additional high 15 aspect ratio tabular grain emulsion layer6 are employed.
Multicolor photographic elements are often described in terms of color-forming layer units.
Most commonly multicolor photographic element~
20 contain three superimposed color-forming layer units each containing at least one silver halide emulsion layer capable of recording expogure to a different third of the spectrum and capable of producing a complementary subtractive primary dye image. Thus, 25 blue, green) and red recording color-forming layer units are used to produce yellow, magenta, and cyan dye image~, respectively. Dye imaging materials need not be present in any color-forming layer unit, but can be entirely supplied from processing 30 solutions~ When dye imaging materials are incorporated in the photographic element, they can be located in an emulsion layer or in a layer located to receive oxidized developing or electron transfer agent from an ad~acent emulsion layer of 35 the same color-forming layer unit.
To prevent migration of oxidized developing or electron transfer agents between color-forming ' .i ~Z~i2~i layer units with resultant color degradation, it is common practice to employ scavengers. The scaven-gers can be located in the emulsion layer~ them-selves ~ as taught by Yutzy et al U-S- Pstent 5 2,937,086 and/or in interlayers between adjacent color-formin~ layer units, as illustrated by Weissberger et al U.S. Patent 2,336,327. It is also contemplated to employ Lippmann emulRions, particu-larly silver chloride and silver bromide emulsions 1~ of grain diameters of less than 0.1 micron, blended with the silver iodide emulsions or in separate interlayers separating the silver iodide emulsion layers from the silver halide emulsion layers ~o act as scavengers for iodide ion6 released on develop-15 ment. Suitable Lippmann emulsions are disclosed byShiba et al U.S. Patent 3,892,572, cited above, and Nicholas et al U.S. Patent 3,737~317.
Although each color-forming layer unit can contain a single emulsion layer, two, three, or more 20 emulsion layers differing in photographic speed are often incorporated in a single color-forming layer unit. Where thP desired layer order arrangement does not permit multiple emulsion layers differing in speed to occur in a single color-forming layer 25 unit, it i~ common practice to provide multiple (usually two or three) blue, green, and/or red recording color-forming layer units in a single photographic element.
The multicolor photographic elements of this invention can take any convenient form consis-tent with the requirements indicated above. Any of the six possible layer arrangements of Table 27a, p.
211, disclosed by Gorokhovskii, Spectral Studies of Ib-_lh~55~0~ Y ~ ec~, Focal Press, New York, can 35 be employed. To provide a simple, specific illus-tration, it is contemplated to add to a conventional multicolor silver halide photographic element during lZl~Z~i its preparation one or more blue recording emulsion layers containing high aspect ratio tabular silver iodide grains positioned to receive e~po~ing radia-tion prior to the remaining emul~ion layers.
5 However, in most instances it is preferrred to sub6titute one or more blue recording emulsion layers containing high aspect ratio tabular silver iodide grain~ for con~entional blue recording emul~ion layers, optionally in combination with 10 layer order srrangement modifications.
The invention can be better appreciated by reference to the following di6cus~ion of distinctive features exhibited by the multicolor photographic elements of thi6 invention, particularly those 15 contributed by th presence of 8 ilver iodide and/or high average aspect ratio tabular grain~.
a. ~lue light ab60rbing capabilitie6 The multicolor photographic elements of this invention u6e at least one emul6ion layer 20 containing high aspect ratio tabular ~ilver iodide grain6 to record imagewise exposures to the blue portion of the visible spectrum. Since silver iodide possesses a very high level of absorption of blue light in the 6pectral region of les6 than about 25 430 nanometer6, in one application of this invention the 6ilver iodide grains can be relied upon to absorb blue light of 430 nanometers or less in wavelength without the use of a blue spectral sensitizing dye. A silver iodide tabular grain is 30 capable of absorbing mo t of the less than 430 nanometer blue light incident upon it when it is at least about 0.1 ~icron in thicknes6 and 6ubstan-tially all of such light when it is at lea~t about 0.15 micron in thickness. (In coating emulsion 35 layers containing high aspect ratio tabular grains the grains spontaneously align themselves so that thPir ma~or crystal faces are parallel to the support ~urface and hence perpendicular to the direction of exposing radi~tion. Hence exposing radiation seeks to tr~verse the thickness of the t~bular grains.) The blue light abgorbing capability of tabular silver iodide grains i~ in direct contra~t to the light absorbing capability of the high sspect ratio tabular grain emulsion~ of other silver hslide compositions, such as those disclosed by Kofron et 10 al, cited above. The latter exhibit markedly lower levels of blue light absorption even at thicknesses up to 0.3 micron. Kofron et al, for instance, specifically teaches ~o increase tabular grain thicknesses up to 0.5 micron to increase blue light 15 absorption. Further, it should be noted that the tabular grain thicknesses taught by Kofron et al take into account that the emulgion layer will normally be coated with a conventional silver coverage, which i~ sufficient to prov~de many layers 20 of superimposed tabular grains, whereas the 0.1 and 0.15 micron thicknesses above are for a single grain. It is therefore apparent that not only can tabular silver iodide grainæ be used without blue spectral sensitizers, but they permit blue recording 25 emulsion layers to be reduced in thickness (thereby increasing sharpness) and reduced in silver cover-age. In considering this application of the inven-tion further it can be appreciated that tabular gra~n silver iodide emulsions, provided minimal 30 grain thicknesses are satisfied, absorb blue light as a function of the pro~ected area which they present to exposing radiation. Thi~ is a funda-mental distinction over other silver halides, such as silver bromide and silver bromoiodide, which, 35 without the assi~tance of spectral sensitizers, absorb blue light as a function of their volume.
Not only are the high aspect ratio tabular grain silver iodide emulsions more efficient in -~Zl~Z6 absorbing blue light than high aspect ratio tabular grains of differing halide composition, they are more efficient than conventional silver iodide emulsion~ containing nontabular gr~ins or lower 5 average aspect ratio tabular grains. At a 8 ilver coverage chosen to employ the blue light absorbing capability of the high a~pect ratio tabular silver iodide grain~ efficiently conventional silver iodide emulsions present lower pro~ected areas and hence 10 are capable of reduced blue light absorption. They also capture fewer photons per grain and are of lower photographic speed than the high aspect ratio tabular silver iodide grain emulsions, other parame-ters being comparable. If the average diameters of 15 the conventional silver ~odide grains are increased to match the pro~ected area6 presented by the high aspect ratio tabular grain silver iodide emulions, the conventional grains become much thicker than the high aspect ratio tabular silver iodide grains, 20 require higher silver coverages to achieve compar-able blue absorption, and are in general less efficient.
Although high aspect ratio tabular silver iodide grain emulsions can be used to record blue 25 light exposures without the use of spectral ~enstiz-ing dyes, it is appreciated that the native blue absorption of silver iodide is not high over the entire blue region of the ~pectrum. To achieve a photographic respon6e over the entlre blue region of 30 the spectrum it is specifically contemplated to employ in combinat~on with such emulsion6 one or more blue sensitizing dyes. The dye preferably exhibits an absorption peak of a wavelength longer than 430 nanometers so that the absorption of the 35 silver iodide forming the tabular grains and the blue sensitizing dye together extend over a larger wavelength range of the blue spectrum.
-~ZlQ6Z~

While silver iodide and a blue sensitizing dye can be employed in combination to provide a photographic response over the entire blue portion of the spectrum, lf the ~lver iodide grains are 5 cho~en as described above for recording blue light efficiently in the absence of spectral æens~tizing dye, the result is a highly unbalanced sensitivity.
The silver iodide grains absorb substantially all of the blue light of a wavelength of less than 430 10 nanometers while the blue sensitizing dye absorbs only a fractlon of the blue light of a wavelength longer than 430. To obtain a balanced sensitivity over the entire blue portion of the spectrum it is contemplated to reduce the effic~ency of the silver 15 iodide grains in absorbing light of less than 430 nanometers in wavelength. This can be accomplished by reducing the average thicknes~ of the tabular grains 8 o that they are less than 0.1 micron in thickness. The optimum thicknes6 of the tabular 20 grains for a specific ~pplication is selected 80 that absorption above and below 430 nanometers iB
substantlally matched. This will vary as a function of the spectral sensitizing dye or dyes employed.
b. CaPabili~ies related to epitaxy ~s indicated above, there are distinct advantages to be realized by epitax~ally depositing silver chloride onto the silver halide host grains.
~nce the silver chloride is epitaxially deposited, however, it can be altered in halide content by 30 substituting le~s soluble halide ions in the silver chloride crystal la~tice. Using a conventional halide conversion process bromide and/or halide ions can be introduced into the orig~nal silver chloride cry~tal lattice. Halide conversion can be achieved merely by bringing the emulsion comprised of silver halide host grains bearing silver chloride epitaxy into contact with an aqueous solution of bromide ' :

lZiQ626 and/or iodide salts. An advantage is achieved in extending the halide compositions available for use while retaining the advantages of silver chloride epitaxial deposition. Additionally, the converted 5 halide epitaxy forms an internal latent image. This permits the emulsions to be applied to photographic applications requiring the formation of an internsl latent image, such as direct positive imaBing.
Further advantages and features of this form of the 10 invention can be appreciated by reference to Maskasky U.S. Patent 4,142,900.
When the silver salt epitaxy is much more readily developed than the host grains, it i~
possible to control whether the 8 ilver salt epitaxy 15 alone or the entire composite grain develops merely by controlling the choice of developing a8ents and the conditions of development. With vigorous developing agents, such as hydroquinone, catechol, halohydroquinone, N-methylaminophenol 6ul fate, 20 3-pyrazolidinone, and mixtures thereof, complete development of the composite silver halide grains can be schieved. Maskasky U.S. Patent 4,094,684, cited above, illustrates that under certain mild development conditions it is possible to selectively 25 develop silver chloride epitaxy while not developing silver iodide host grains. Development can be specifically optimized for maximum silver develop-ment or for selective development of epitaxy, which can re6ult in reduced graininess of the photographic 30 image. Further, the degree of silver iodide devel-opment can control the release of iodide ions, which can be used to inhibit development.
c. CaPabilities imparted by iodide ion release In a 6pecific application of this invention a multicolor photographic element can be constructed incorporating a uniform distribution of a redox catalyst in addition to at least one layer contain-~-- ~2~ Z6 ing high aspect ratio tabular 6ilver iodide grains.When the silver iodide grains are imagewise devel-oped, iodide ion iB released which locally poisons the redox catalyst. Thereafter a redox reaction can 5 be catalyzed by the unpoisoned catalyst remaining.
Bissonette U.S. Patent 4,089,685, specifically illustrate~ a useful redox system in which a perox-ide oxidizing agent and a dye-image-generating reducing agent, such as a color developing agent or 10 redox dye-releasor, react imagewise at available, unpoisoned catalyst sites within a photographic element. Maskasky U.S. Patent 4,158,565, di~closes the use of silver iodide host grains bearing silver chloride epitaxy in such a redox amplification 15 system.
d. Speed-granularity capabilitieR
An important advantage of the multicolor photographic elements of this invention is their improved speed-granularity relationship. As taught 20 by Kofron et al, cited above, substantially opti-mally chemically and spectrally sensitized high aspect ratio tabular grain silver halide emul~ions can exhibit unexpected improvements in the speed-granularity relationships of multicolor photographic 25 elements.
Within the range of silver halide grain sizes normally encountered in photographic element~
the maximum speed obtained at optimum sensitization incresses linearly with increasing grain size. The 30 number of absorbed quanta necessary to render a grain developable is ~ubstantially independent of grain size, but the density that a given number of grains will produce upon development is directly related to their size. If the aim is to produce a maximum den~ity of 2, for example, fewer grains of 0.4 micron as compared to 0.2 micron in average diameter are required to produce that density. Less . . .

ZS

radiation is required to render fewer grains developable.
Unfortunately, because the density produced with the larger grains is concentrated at fewer 5 sites, there are greater point-to-point fluctuations in density. The viewer's perception of point-to-point fluctuations in densi~y is termed "graini-ness". The objective measuremen~ of point-~o-point fluctuations in density iB termed "granularity".
10 While quantitative measurements of granularity have taken different forms, granularity is most commonly measured as rms (root mean square) granularity, which is defined as the standard deviation of density within a viewing microaperture (e g~, 24 to 15 48 microns). Once the maximum permissible granu-larity (also commonly referred to as grain, but not to be confused w~th silver halide gra~ns) for a specific emulsion layer iB identified, the maximum speed which can be realized for that emulsion layer 20 is also effectively limited.
From the foregoing it can be appreciated that over the years intensive investigat~on in the photographic art has rarely been directed toward ob~aining maximum photographic speed in an absolute 25 sense, but, rather, has been directed toward obtain-ing maximum fipeed at optlmum sensitization while satisfying practical granularity or grain criteria.
~rue improvements in silver halide emulsion sensi-tivity allow speed to be increased without increas-30 ing granularity, granularity to be reduced withoutdecreasing speed 9 or both speed and granularity to be simultaneously improved. Such sensitivity improvement is commonly and succinctly referred to in the art as improvement in the speed-granularity 35 relationship of an emulsion.
In Figure 7 a schematic plot of speed versus granularity is shown for five silver halide ` 12~z~

emulsion6 1 ~ 2, 3, 4, and 5 of the æame composition, but differing in grain size, each similarly sens~-tized, identically coated, and identically processed. While the indiv~dual emulsions differ in 5 maximum speed and granularity, there is a predict-able linear relationship between the emulsions, as indicated by the speed-granularity line A. All emulsions which can be ~oined along the line A
exhibit the same speed-granularity relationship.
10 Emulsions which exhibit true improvements in sensi-tivity lie above the speed-granularity line A. For example, emulsions 6 and 7, which lie on the common speed-granularity l~ne B, are superior in their 6peed-granularity relationship6 to any one of the 15 emulsions 1 through 5. Emulsion 6 exhibits a higher speed than emulsion 1, but no higher granularity.
Emulsion 6 exhibits the same speed as emulsion 2, but at a much lower granularity. Emulsion 7 is of higher speed than emulsion 2, but is of a lower 20 granularity than emulsion 3, which is of lower speed than emulsion 7. Emulsion 8, which falls below the speed-granularity line ~, exhibits the poorest speed-grunularity relationship shown in Figure 7.
Although emulsion 8 exhibits the highest photo-25 graphic speed of any of the emulsions, its speed isrealized only at a disproportionate increase in granularity.
The importance of speed-granularity rela-tionship in photography has led to extensive efforts 30 to quantify and generalize speed-granularity deter-minations. It is normally a simple matter to compare precisely the speed-granularity relation-ships of an emulsion series differing by a single characterist~c, such as silver halide grain size.
35 The speed-granularity relationships of photographic products which produce similar characteristic curves are often compared. For elaboration of granularity ., ~6Z~;

measurement~ in dye imaging attention is directed to "Understanding Grainines~ and Granularity", Kodak Publication No. F-20, Revised 11-79 (a~ailable from Eastman Kodak Company, Rochester, New York 14650);
5 Zwick, "Quantitative Studie6 of Factors Affecting Granularity", PhotograPhic Science and Engineering, Vol. 9, No. 3, May-June, 1965; Eric60n and Marchant, "RMS Granularity of Monodisperse Photo~raphic Emulsions", Photographic Science and Engineering, 10 Vol- 16, No. 4, July-August 1972, pp. 253-257; and Trabka, "A Random-Sphere Model for ~ye ~louds", Photographic Science and Engineering, Vol. 21, No.
4, July-August 1977, pp. 183-192.
To achieve the highest attainable speed-15 granularity relationships in the multicolor photo-graphic elements 4f this invention lt is specifi-cally preferred that the emulsions contained in the multicolor elements be sub6tantially op~imally chemically and spectrally sensitized, although, 20 sub~ect to the con6iderations discussed above, the silver iod~de emulsion6 need not be 6pectrally 6en6itized. By "6ub6tantially optimally" it is meant that the emulsions preferably achieve speed6 of at least 60 percent of the maximum log speed 25 attainable from the grains in the spectral region of 6ensitization under the contemplated conditions of use and processing. Log speed is herein defined as lOOtl-log E), where E is measured in meter-candle-seconds at a density of 0.1 above fog. Sub6tan-30 tially optimum chemical and spectral ~ensitizationof high aspect ratio tabular grain silver halide emulsion6, particularly silver bromoiodide emul-sions, is generally taught by Kofron et al. Such emulsion6 can exhibit 6peed-granularity relation-35 ship6 superior to conventional (low aspect ratiotabular grain or nontabular grain) emulsion~. It is generally preferred to employ silver bromoiodide /

~Zl~ 26 emulsions in com~ination with the high aspect ratio tabular grain silver iodide emulsions to achieve the highest attainable speed-granularity relationship6.
Illingsworth U.S. Patent 3,320,069 particularly 5 illustrates conventional silver bromoiodide emul-sions of outstanding speed-granularity relat~onship contemplated for use in the multicolor photographic elements of ~his invention.
e. Sharpness capabilities While granularity, because of its relation-ship to speed, is often a focal point of discussion relating to image quality, image sharpneRs can be addressed independently. Some factors which influ-ence image sharpness, such a8 lateral diffusion of 15 imaging materials during processing (~ometimes termed "image smearing'l), are more closely related to imaging and processing materials ~han the silver halide grains. On the other hand, because of their light scattering properties, 6ilver halide grains 20 themselves primarily affect sharpne~s during image-wise exposure. It is known in the ~rt that silver halide grains having diameters in the range o~ from 0.2 to 0.6 micron exhibit maximum scattering of visible light.
Loss of image ~harpness resulting from light scattering generally increaseg with increasing ~hickness of a silver halide emulsion layer. The reason for this can be appreciated by reference to Figure 8. If a photon of light 1 i8 deflected by a 30 silver halide grain at a point 2 by an angle r measured as a declination from its original path and is thereafter absorbed by a second silver halide grain at a point 3 after traversing a thickness t_ of the emulsion layer, the photographic record of 35 the photon is di6placed laterally by a distance x.
~f, instead of being absorbed within a thickness t=, the photon traverses a second equal thickness ~æ~a~626 t3 and is absorbed at a point 4, the photographic record of the photon is displaced laterally ~y twice the distance x. It i8 therefore apparent that the greater the thickne~s displacement of the silver 5 halide grains in a photographic element, the greater the risk of reduction in image sharpness attribut-able to light scatter~ng. (Although Figure 8 illustrates the principle in a very 6imple situa-tion, it is appreciated that in actual practice a 10 photon is typically reflected from ~everal grains before actually being absorbed and statistical methods are requ~red to predict it~ probable ulti-mate point of sbsorption.) In multicolor photographic elementg 15 containing three or more superimposed silver halide emulsion layer6 an lncreased risk of reduction in image sharpness can be presented, since the ~ilver halide grains are distributed over at least three layer thlcknesses. In some applications thickness 20 displacement of the 6ilver halide grains ~8 further increased by the presence of additional materials that either (1) increAse the thicknesses of the emulsion layers themselves--a~ where dye-image-pro-viding materials, for example, are incorporated in 25 the emulsion layers or (~) form additional layers separating the silver halide emulsion layers, thereby increasing their thickness displacement--as where separate scavenger and dye-image-providing material layers separate ad~acent emulsion layers.
30 Further, in multicolor photographic elements there are st least three superimposed layer units, each containing at least one silver halide emulsion layer. Thus, there is a substantial opportunity ~or loss of image shsrpness attributable to scattering.
35 Because of the cumulative scattering of overlying silver halide emulsion layers, the emulsion layer~
farther removed from the exposing radiation source - can exhibit very significant reductions in sharpness.

~2~ L16Z~

The high aspect ratio tabular grain silver halide emul~ions employed in the multicolor photo-graphic elements of the p~esent invention a~e advantageous becnuse of their reduced high angle 5 light scattering as compared to nontabular and lower aspect ratio tabular grain emulsions. As discussed above with reference to Figure 8, the art has long recognized that image sharpness decreases with increasing thickness of one or more silver halide 10 emulsion layers. ~owever from Figure 8 it i8 al80 apparent that the lateral component of light scat-tering (x and 2x) increases directly with the angle . To the extent that the angle y remains small, the lateral displacement of scattered light 15 remains ~mall and image sharpnes~ remains high.
Advantageous sharpness characterlstics obtainable with high aspect ratio tabular grain emulsions of the present invention are attributable to the reduction of high angle scattering. This can 20 be quantitatively demonstrated. Referring to Figure ~, a sample of an emulsion 1 according to the present invention is coated on a transparent (spec-ularly transmissive3 support 3 at a silver coverage of 1.08 g/m3. Although not shown, the emulsion 25 and support are preferably immersed in a liquid having a substantially matched refractive index to minimize Fresnel reflections at the surfaces of the support and the emulsion. The emulsion coating is exposed perpendicular to the support plane by a 30 collimated light source 5. Light from the source following a path indicated by the dashed line 7, which forms an optical axis, strikes the emulsion coating at point A. Light which passes through the support and emulsion can be sensed at a constant 35 distance from the emulsion at a hemispherical detection surface 9. At a point B, which lies at the intersection of the extension of the initial 6 Z ~ -light path and the detection surface, light of a maximum intensity level is detected.
An arbitrarily selected point C is shown in Figure 9 on the detection surface. The dashed line 5 between A and ~ forms an angle ~ with the emulsion coating. By moving point C on the detection surface it is possible to vary ~ from 0 to 90. By measuring the intensity of the light scattered 8~ a function of the angle ~ it i~ possible (because of 10 the rotational symmetry of light scattering about the optical axis 7) to determine the cumulative light distribution as a function of the angle ~.
(For a background description of the cumulMtive light distribution see DePalma and Gasper, "Deter-15 mlning the Optical Properties of PhotographicEmulsions by the Monte Carlo Method", Photo~raphic Sclence and Engineering, Vol. 16, No. 3, May-June 1971, pp. 181-191.) After determining the cumulative light 20 distribution as a function of the angle ~ at values from 0 to 90 for the emulsion 1 according to the present invention, the same procedure is repeated, but with a conventional emul~ion of the same average grain volume coated at the same silver 25 coverage on another portion of support 3. In comparing the cumulative light distribution as a function of the angle ~ for the two emulsions, for values of ~ up to 70 (and in some instances up to 80 and higher) the amount of scattered light is 30 lower with the emulsions according to the present invention. In Figure 9 the angle y is shown as the complement of the angle ~. The angle of scattering is herein discussed by reference to the angle y. Thus, the high aspect ratio tabular 35 grain emulsions of this invention exhibit less high-angle scattering. Since it is high-angle scattering of light that contributes dispropor-z~

tionately to reduction in image ~harpness, it follows that ~he high a6pect r~tio tabular grain emul~lons of the pre~ent invention are in each instance capable of producing sharper images.
As herein defined the term "collection angle" i~ the value of the angle ~ at which half of the light striking he detection ~urface lies within an area subtended by a cone formed by rota-tion of line AC about the polar axis at the angle lO Y while half of the light strikes the detection surface within the remaining area.
While not wi6hing to be bound by any particular theory to account for the reduced high angle scattering properties of high aspect ratio 15 tabular 8rain emulsions according to the present invention, it is bel~eved that the large flat ma~or crystal faces presented by the high aspect r&tio tabular grains as well as the orientation o$ the grains in the coating account for the improvements 20 in 6harpness observed. Specifically 3 it has been observed that the tabular grains present in a silver halide emulsion coating are substantially aligned with the planar support ~urface on which they lie.
Thus, light directed perpendicular to the photo-25 graphic element striking the emulGion layer tends tostrike the tabular grains substantlally perpen~
dicular to one ma~or crystal face. The thinness of tabular grains as well as their orientation when coated permits the high aspect ratio tabular grain 30 emulsion layers of this invention to be substan-tially thinner than conventional emulsion coatings, which can also contribute to sharpness. The tabular silver iodide grains can be even thinner th~n tabular grains of other silver halide compositions 35 and be coated at lower silver coverages while still exhibiting efficient blue absorption. Thus high aspect ratio tabular grain silver iodide elements ~,' ~L21~6Z6 often are capable of permitting significant improve-ments in sh~rpness in the multi~olor elements of this invention.
In a specific preferred form of the inven-5 tion the high aspect ratio tabular grain emulsionlayers exhibit a minimum average grain diameter of at least 1.0 micron, most preferably at least 2 microns. Both improved 6peed and sharpnes~ are attainable as average grain diameters are 10 increased. While maximum useful average grain diameters will vary with the graininess that can be tolerated for a specific imaging application, the maximum average grain diameters of high aspect ratio tabular grain emulsions according to the present 15 invention are in all in6tances les6 than 30 microns, preferably less than 15 microns, and optimally no greater than 10 microns.
Although it i8 possible to obtain reduced high angle scattering with ~ingle layer coatings of 20 high aspect ratio tabular grain emulsions according to the present invention, it does not follow that reduced high angle scattering is necessarily real-ized in multicolor coatings. In certain multicolor coating formats enhanced sharpne6s can be achieved 25 with the high aspect ratio tabular grain emulsions of this invention, but in other multicolor coating formats the high a6pect ratio tabular grain emul-sions of this invention can actually degrade the sharpne~s of underlying emulsion layers. If the 30 emulsion layer of the multicolor photographic element lying nearest the exposing radiation source contains grains having an average diameter in the range of from 0.2 to 0.6 micron, as is typical of many nontabular emulsions, it will exhibit maximum 35 scattering of light passing through it to reach the underlying emulsion layers. Unfortunately, if light has already been scattered before it reaches a high 6~Ç;
`, ~
aspect ratio tabular grain emulsion layer, the tabular gr~ins can scatter the light pa~sing through to one or more underlying emul~ion layer~ to an even greater degree than a conventional emulsion. Thufi, 5 this particular choice of emulsions and layer arrangement results in the sharpness of the emulsion layer or layer~ underlying the high aspect ratio tabular grain emulsion layer being ~ignlficantly degraded to an extent greater than would be the case 10 if no high aspect ratio tabular grain emulsion~ were pre6ent in the layer order arrangement.
In order to realize fully the sharpness advantages in an emulsion layer that underlies a high aspect ratio tabular grain emulsion layer it is 15 preferred that the the tabular grain emulsion layer be positioned ~o receive light that is free of significant scattering (preferably positioned to receive substantially specularly transmitted light). Stated another way, in the multicolor 20 photographic elements of this invention improvements in sharpnes B in emulsion layers underlying tabular grain emulsion layers are best realized only when the tabular grain emulsion layer doe6 not itself underlie a ~urbid layer. For example, if a high 25 aspect ratio tabular grain green recording emulsion layer overlie6 a red recording emulsion layer and underlies a Lippmann emulsion layer and/or a high aspect ratio tabular grain blue recording emulsion layer according to this invention, the sharpness of 30 the red recording emulsion layer w~ll be improved by the presence of the overlying tabular grain emulsion layer or layers. Stated in quantitative terms, if the collection angle of the layer or layers over-lying the high aspect ratio tabular grain green 35 recording emulsion layer is less than about 10~, an improvement in the sharpness of the red recording emulsion layer can be realized. It is, of cour~e, ."~' $

immaterial whether the red recording emulsion layer is itself a high aspect ratio tabular grain emulsion layer insofar as the effect o~ the overlying layers on its sharpness is concerned.
In a multicolor photographic element containing superimposed color-forming units it is preferred that at least the emulsion layer lying nearest the source of exposing radiation be a high aspect ratio tabulsr grain emulsion in order to 10 obtain the advantages of sharpnesR offerred by this invention. In a specifically preferred form of the invention each emulsion layer which lies nearer the expo~ing radiation ~ource than another image record-ing emulsion layer iB a high aspect ratio tabular 15 grain emulsion layer.
f. Blue and minus-blue speed separation Silver bromide and silver bromoiodide emulsions possess sufficient native sensitivity to the blue portion of the spectrum to record blue 20 radiation without blue spectral ~ensitization. When these emulsions are employed to record green and/or red ~minus blue) light exposures, ~hey are corre-spondingly spectrally sensitized. In multicolor photography, the native sensitivity of silver 25 bromide and silver bromoiodide in emulsions intended to record blue light iB advantageous. However, when these silver halides are employed in emulsion layers intended to record exposure~ in ~he green or red portion of the spectrum, the native blue sensitivity 30 iB an inconvenience, since response to both blue and green light or both blue and red light in the emulsion layers will falsify the hue of the multi-color image sought to be reproduced.
In constructing multicolor photographic 35 elements using silver bromide or silver bromoiodide emulsions the color falsification can be analyzed as two distinct concerns. The first concern is the ~2~
--~u--difference between ~he blue ~peed of the green or red recording emulsion layer and its green or red speed. The second concern is the difference between the blue speed of each blue recording emulsion layer 5 and the blue speed of the corresponding green or red recording emulsion layer. Generally in preparing a multicolor photographic element intended to record accurately image colors under daylight exposure conditions (e.g., 5500K) the aim is to achieve a 10 difference of about an order of magnitude between the blue speed of each blue recor~ing emulsion layer and the blue speed of the corresponding green or red recording emulsion layer. The art has recognized that ~uch aim speed differences are not realized 15 using silver bromide or silver bromoiodide emul~ions unless employed in combination with one or more approachés known to ameliorate color falsification.
Even then, full order of magnitude speed differences have not always been realized in product. However, 20 even when such aim speed differences are realized, further increasing the separation between blue and minus blue ~peeds will further reduce the recording of blue exposures by layers intended to record minus blue exposures.
By far the most common approach to reducing exposure of red and green spectrally sensitized silver bromide and silver bromoiodide emulsion layers to blue light, thereby effectlvely reducing their blue speed, i8 to locate these emulsion layers 30 behind a yellow (blue absorbing) filter layer. Both yellow filter dye~ and yellow colloidal silver are commonly employed for this purpose. In a common multicolor layer format all of the emulsion layers are silver bromide or bromoiodide. The emulsion 35 layers intended to record green and red exposures are located behind a yellow filter while the emul-sion layer or layers intended to record blue l~ght ' are located in front of the filter layer.

~2~626 This arrangement has a number of art-recog-nized disadvantages. Wh~le blue light expo~ure of green and red recording emulsion layer~ i~ reduced to tolerable level~, a less than ideal layer order 5 arrangement is imposed by the use of a yellow filter. The green and red emulsion layer~ receive light that haR already pa~sed through both the blue emulsion layer or layers and the yellow filter.
This light hAs been scattered to Rome extent, and 10 image sharpness can therefore be degraded. Further, the yellow filter is it~elf imperfect and actually absorbs to a slight extent in the green por~ion of the spectrum, which results in a 10R~ of green speed. The yellow filter material, particularly 15 where it is yellow colloidal silver, increaseR
materials cost and accelerates required replacement of processing solutions, 6uch as bleaching and bleach-fixing solutions.
Still another disadvantage associated with 20 separating the blue emulsion layer or layer6 of a photographic element from the red and green emulsion lsyers by interposing a yellow filter ls that the speed of the blue emulsion layer is decreased. This is because the yellow filter layer absorbs blue 25 light passing through the blue emulsion layer or layers that might otherwise be reflected to enhance exposure .
A number of approaches have been suggested for avoiding the disadvantages of yellow filters in 30 multicolor photographic elements, as illustrated by Lohmann U.K. Patent 1,560,963, which teache6 relo-cating the yellow filter layer; Gaspar U.S. Patent 2,344,084, which teaches using silver chloride and silver chlorobromide emulsions; and Mannes et al 35 U-S- Patent 2,388,859, and Knott et al U.S. Patent 2,456,954~ which teach introducing an order of magnitude difference between the blue and minus blue , ~z~

speeds of the blue and minus blue recording emulsion layers; but each has introduced other significant disadvantages. For example, Lohmann incur6 blue light contamination of the minus blue recording 5 emulsions lying above the yellow filter; Gaspar incurs the reduced speeds and lower speed-granu-larity rel~tionships of silver chloride and silver chlorobromide emulsions; and Mannes et al and Knott et al require large grain size differences to obtain 10 an order of magnitude speed difference in the blue and minus blue recording emulsion layers, which requires either increasing granularity or signifi-cantly reducing ~peed in at least one emulsion layer.
Kofron et al, cited above~ has recognized 15 that the blue light absorption of high aspect ratio tabular grain silver bromide and silver bromoiodide emulsions can be sufficiently reduced so that yellow filter l~yers can be eliminated. However, the multicolor photographic elements of Kofron et al 20 show significantly larger increases in the separa-tion of blue and minus blue speeds when yellow filter layers are incorporated in the multicolor photograph~c elements to receive blue light prior to minus blue recording emulsion layers. Fur~her, when 25 Kofron et al employs high aspect ratio tabular grains of increased thickness ~up to 0.5 micron) or higher iodide concentrations, significant color falsification of minus blue recording emul6ion layers is possible in the absence of yellow filter 30 protection.
In the practice of the present invention locating at least one high aspect ratio tabular grain silver iodide blue recording emulsion layer between the source of exposing radiation and the 35 minus blue recording emulsion layers of the multi-color photographic element protects the minus blue recording emulsion layers from blue light exposure even more efficiently than most conventional yellow filter layers incorporated in multicolor photo-graph~c elements. Thus, conventional yellow filter layers can be entirely eliminated from multicolor 5 photographic elements according to the present invention while avoiding color falsiflcation by t~e minus blue recording emulsion layers. Further, this can be accomplished while employing any sil~er halide composition or grain configuration in the 10 minus blue recording emulsion layers 3 while employ-ing color forming layer units which are substan-tially matched in speed and contrast, and/or while exposing the multicolor photographic element to substantially neutral (5500K) light. Still 15 further, achieving multicolor photographic elements of such capabilities are in no way incompatible with achieving the highest levels of sharpness and the highest speed-granularity capabilities of the multicolor photographic elements of this invention.
20 Rather, the use of a blue recording high aspect ratio tabular grain silver ioidide emulsion in the multicolor photographic elements according to the present invention both avoids color falsification by ~lue light exposure of the minus blue recording 25 emulsion layers and allows addit~onal improvements in sharpness and speed-granularity relationships to be realized.
g. Examples of ~pecific layer order arrange-ments Layer Order Arrangement I
Exposure TB (AgI) IL
35 G (AgX) __IL
R (AgX) lZ~ Z6 Layer Order Arran~ment II
Expo~ure TG (AgX) IL

IL (AgX) _ _ TB _ (A~I) Layer Order Arrangement III
Expo~ure TB (~gI) IL
TG (Agl) _ TR (AgI) Layer Order Arrangeme~t IV
Exposure TFB (A~X) IS

IL (AgI3 _ G (AgX) IL
R

.,.~, Layer Order Arran~ement V
Exposure TFG_ (AgX) IL
TFR (AgX) IL
FB (AgX) TB (AgI) ~ IS
IL
FG _~gX) FR (AgX) IL
SG (AgX) IL
SR

20 where B, G, and R designate blue, green, and red recording color-forming layer units, respectively;
T appearing before the color-forming layer unit B, G, or R indicates that the emul6ion layer or 25 layers contain a high aspect ratio tabular grain emulsion, as more 6pec~fically described above, F appearing before the color-forming layer unit B, G, or R indica~es that the color-forming layer unit is faster in photographic speed than at least 30 one other color-forming layer unit which records light exposure in the same third of the spectrum in the same Layer Order Arrangement;
S appearing before the color-forming layer unit B~ G, or R indicates that the color-forming layer 35 unit is slower in photographic speed than at least one other color-forming layer unit which records light exposure in the same third of the spectrum in the same Layer Order Arrangement;

lZR~6Z6 AgI indicates that the emul~ion layer or layers of the color-forming layer unit con~ains ~ silver iodide emulsion;
AgX indicates that the emul~ion layer or layer6 5 of the color-forming layer unit contains a ~ilver halide emulsion which permits most of the blue light striking it to pass through unabsorbed--e.g., silver chloride, silver bromide, or silver bromoiodide;
IL designates an interlayer containing an oxidized developing agent or electron transfer agent scavenger and, where the interlayer ~eparates AgI
and AgX containing color-forming layer units, preferably also an iodide ion scavenger; and IS designates an interlayer containing an iodide 15 ion scavenger without necessarily including any additional scavenger.
Each faster or slower color-forming layer unit can differ in photographic speed from another color-forming layer unit which records light expo-20 sure in the same third of the spectrum as a resultof its position in the Layer Order Arrangement, its inherent speed properties, or a combination of both.
In Layer Order Arrangements I through V, the location of the support is not shown. Following 25 customary practice, the ~upport will in most instances be positioned ~arthest from the Rource of exposing radiation--that is, beneath the layers as shown. If the support is colorless and 6pecularly transmissive--i.e., transparent, it can be located 30 between the exposure source and the indicated layers. Stated more generally, the support can be located between the exposure source and any color-forming layer unit intended to record light to which the support i8 transparent.
Turning first to Layer Order Arrangement I, the blue recording color-forming layer unit is . positioned to receive exposing radiation first.

~ .~
~2~6Z6 This color-forming layer unit contains one or more silver halide emulsions comprised of high average aspect ratio silver iodide grains. This emulsion very efficiently absorbs the blue light and 6ubstan-S tially none of the minus blue light inciden~ uponit. As diseussed above, the tabular silver iodide grain6 can be relied upon to absorb most or substan-tially all of the blue light of a wavelength less than 430 nm even in the absence of a blue spectral 10 sen~itizing dye. When a blue spectral sensitizing dye iB present, blue light ab60rption by the color-forming layer unit can be extended to longer blue wavelengths. If desired to obtain a more nearly balanced blue absorption over portions of the blue 15 spectrum longer and shorter than 430 nm in wave-length, the ~hickness of the tabular silver iodide grains can be reduced below about ~.1 micron down to the minimum grain thicknesses attainable.
Since the silver iodide tabular grains in 20 the blue recording color-forming layer unit can be quite thin (0.01 micron or les~) and the halide composition and pro~ected area of the tabular silver iodide grains render them quite efficient in absorb-ing blue light, the blue-recording color-forming 25 layer unit can be thinner than conventional emulsion layers or even high aspect ratio tabular grain emulsion layers of differing silver halide content, such as silver bromide or silver bromoiodide emul-sion layers. The fact that the blue recording 30 color-forming layer unit contains high aspect ratio tabular gralns allows a sharper image to be produced in this color-forming layer unit. Further, the fact that the blue recording color-forming layer unit is positioned to receive imaging radiation that is 35 substantially specular, contributes to improving the sharpnes6 of the minus blue recording color forming . layer units.
....

Another unexpected advantage of Layer Order Arrangement I attributsble to the presence and location of the ta~ular grain 6ilver iodide emul6ion layer i6 the increased speed and ~peed-granularity 5 relationship of each underlying radiation-6en6itive emulsion layer. Since the tabular grain fiilver iodide emulsion layer requires less silver halide to absorb blue light efficiently, there iB le~s reflec-tion of minus blue (green and/or red) light by the 10 6ilver iodide grains than would be the case if comparable blue ab~orption were achieved uging a non-tabular emul~ion or a high a~pect ratio tabular grain emulsion of another halide composition. ThUB, a higher percentage of minu6 blue light reaches the 15 minus blue recording emulsion l~yers, thereby enhancing their photographic efficiency.
In any of the varied forms described above blue light, if any, contained in the light emerging from the blue-recording color-forming layer unit can 20 be sufficiently attenuated that it i8 unnece~sary to employ a yellow filter layer in the multicolor photographic element to protect the underlying green and red-recording color-forming layer unit~ from blue light exposure. Hence the green and red-25 recording color-forming layer unit6 can contain emulsions of any silver halide composition, includ-ing silver bromide and/or silver bromoiodide emul-sions, without exhibiting color fal~ification. The green and red recording color-forming layer units 30 can be of any conventional silver halide composition (including silver iodide) or grain configuration (includlng high aspect ratio tabular grain configu-ration).
In developing imagewise exposed Layer Order 35 Arrangement I iodide ion can, but need not be released by the blue recording color-forming layer unit. Where the tabular silver iodide grains are sensitized by epitaxial deposition of a silver halide other than iodide, 6uch as silver chloride, it is possible to develop the ~ er chloride selectively, as described above. In this case few, 5 if any, iodide ions are released by development.
Where the tabular 6ilver iodide grain6 are developed, at least to some extent, iodide ion6 can be allowed to migrate to the adjacent color-forming unit to produce useful interimage effects. It is 10 known in the art that useful lnterimage effects can be realized by the migration of iodide ions to adjacent color-forming layer units. Attention i6 drawn to Groet U.S. Patent 4,082,553 for an illus-trative upplication. However, it is generally 15 preferred to reduce the iodide ions released to an adjacent color-forming layer unit. This can be accomplished by incorporating an iodide sc~venger, such as a silver chloride or s~lver bromide Lippmann emulsion, in the blue recording color-forming layer 20 unit and/or in the interlayer separating the adja-cent color-forming layer unit. Because of it small grain size the Lippmann emulsion is sub~tantially light insensitive in relation to the blue recording emulsion layer or layer6.
To avoid repetition, only features that distinguish subsequent Layer Order Arrangements from previous Layer Order Arrangement6 are 6pecifically discu66ed. In Layer Order ~rrangement II the green and red recording color-forming layer units are 30 comprised of high average aspect ratio tabular silver halide grains which permit most of the blue light striking the grains to pass through unabsorbed. This can be permitted by the composi-tion of the grains (i.e., the absence of or low 35 concentrations of iodide) and/or diminished thick-nes6es of the grains. In a particularly preferred `f form of Layer Order Arrangement II the blue record-` -~ Z~ 26 -so -ing color-forming layer unit is coated on a reflec-tive support, such as a white support. It is well appreciated that both initially incident radiation and initially unabsorbed reflected radiation 5 contribute to exposure of emulsion layers coated on white reflective supports. In Layer Order Arrange-ment II the tabular silver iodide grains absorb blue light initially incident upon them and, if any blue light is not initially absorbed, these grains also 10 absorb blue light reflected by the support. Thus the green and red recording color-forming layer units are protected from blue light exposure by reflection. The ùse of the silver iodide tabular grains in the blue recording color-forming layer 15 unit signlficantly reduces the blue exposure of the minus blue recording emulsion layers even though the blue recording color-forming layer unit is not interposed between the radiation source and the minus blue recording color-forming layer units.
Since each of the color-forming layer units in Layer Order Arrangement II are compri6ed of high average aspect ratio silver halide grains, very high levels of sharpness are possible. Further, Layer Order Arrangement II offers a significant advantage 25 in that the green recording color-forming layer unit is positioned nearest the source of exposing radia-tion. This allows a sharper image to be produced in the green color-forming layer unit as well as permitting its speed-granularity relationship to be 30 improved. Since the human eye i8 more sensitive to the green recording color-forming layer unit image than the images produced in the remaining color-forming layer units, the advantages realized in the green recording color-forming layer unit are highly 35 advantageous in achieving the best overall multi-color photographic image.
Layer Order Arrangment III differs from Layer Order Arrangement I in that the green and red ~.2~(~626 recording color-forming layer units both contain high aspect ratio tabular grain silver iodide emulsions. In view of the capability of producing extremely thin tabular silver iodide grains, this 5 allows the color-forming layer units to be sub~tan-tially reduced in th~ckness. This in turn allows sharper photographic image~ to be produced, particu-larly in the red recording color-forming layer unit~
although where a white reflective ~upport i8 1~ employed, significant improvements in sharpne~R may be realized in each of the color-forming layer units. Although the minus blue color-forming layer units are highly efficient in recordlng blue light, they are protected from blue light exposure by the 15 overlying tabular silver iodide grains in the blue recording color-forming lsyer unit.
L~yer Order Arrangement IV dif~ers from Layer Order Arrangement I by the addition of an additional blue recording color forming leyer unit 2~ containing a fast high aspect ratio tabular grain 6ilver halide emulsion the halide of which need not be silver iodide. By containing high aspect ratio tabular gra~ns the additional blue color-forming layer unit avoids ~cattering incident radiation 25 which would degrade the sharpness of imaging records in underlying emul~on layers. The fast blue-recording layer unit i8 relied upon to achieve a blue speed which matches the green and red speeds of the underlying emulsion layers. The high aspect 30 ratio tabular silver iodide emulsion can be used ~o extend the exposure latitude of the fast blue recording color-forming layer unit while at the same time more efficiently protecting the underlying color-forming layer units from blue light exposure.
35 Since the two blue recording color-forming layer units are ad;acent each other, there is no need to provide an interlayer for oxidized developing agent scavenger. However, since the blue recording color-forming layer units are of differing halide composition, the inclusion of an iodide 6cavenger in an interlayer between the color-forming layer units 5 i~ shown, although ne~ther the u~e of an interlayer or an iodide scavenger is essential. The iodide scavenger can be incorporated in either or both blue recording color-forming layer unit~, but iB prefer-ably incorporated in the one con~aining tabular 10 silver iodide grains. Iodide scavenger can also be present in the interlayer separating the tabular silver iodide grain containing blue recording color-forming layer unit from the green recording color-forming layer unit.
Layer Order Arrangement V illustrates the application of the invention to a multicolor photo-graphic element containing multiple blue, green, and red color-forming layer units. Incident radiation initially strikes a green recording color-forming 20 layer unit comprised of a substantially optimally 6ensitized high Aspect ratio tabular grain 6ilver halide emulsion, preferably a silver bromoiodide emulsion. The light then passes through to an underlying red recording color-forming layer unit, 25 which can be identical to the green recording color-forming layer unit above, except that the silver halide emulsion is sensitized to red light.
These two minus blue recording color-forming layer units by reason of their favored location for 30 receiving exposing radiation and because of the exceptional speed-granularity relationships of substantially optimally sen6itized high aspect ratlo tabular grain emulsions can exhibit exceptionally high speeds. Since speed is normally measured near 35 the toe of a negative-working emulsion character-i~tic curve, typically at a density of about 0.1 above fog, it is not necessary that the two upper -` lZ~26 minus blue recording color-forming layer units be capable of producing by themselves high dye densities in order to increase the minus blue speed of the photographic element. Therefore it i8 5 specifically contemplated that these minus blue recording color-forming layer units can be excep-tionally thin. The use of thin coatings i8, 0~
course, compatible with the use of tabular grain emulsions.
After paæsing through the upper two minus blue recording color-forming layer units, light is received by a fast blue recording color-forming layer unit. Although the fast blue recording color-forming layer unit can coDtain one or more 15 silver halide emulsion layers of any conventional type, this color-forming layer unit is preferably identical to the fast blue color-forming layer unit described in connection with Layer Order Arrangement IV. To protect the underlying minus blue recording 20 color-forming layer units from blue light exposure, a second blue recording color-forming layer unit is ~hown co~taining a high aspect rat~o tabular grain silver iodide emulsion. An iodide scavenger is also shown in this color-forming layer unit. It is 25 appreciated that the blue recording silver halide emulsions can be present, if desired, in the same color-forming layer unit, either blended or, prefer-ably, coated as separate layers.
Immediately beneath the blue recording 30 color-forming layer units are two fast minus blue recording color-forming layer units, a green and a red color-forming layer unit in that order. Since the emulsions of these color-forming layer units are protected from blue light exposure by the high 35 aspect ratio tabular silver iodide grains in the overlying blue recording color-forming layer unit, the silver halide emulsions in these two fast minus ~Z~6Z4 blue recording color-forming layer units can be from among any green or red sensitized emulsions hereto-fore described. In a preferred form the green snd red sen~itized ~ilver halide emulsions are identical S to those of the outermo~t two color-forming layer units. That is, these minu~ blue record~ng color-forming layer units preferably also contain sub~tan-tially optimally sensitized high aspect ratio tabular grain emulsions, most preferably silver 10 bromoiod~de emulsion~.
The two minus blue recording color-forming layer units farthest from the expo~ing radiation source are labeled slow color-forming green and red recording color-formin~ layer unit~. Their unction 5 i8 to extend the exposure latitude of the photo-graphic element and to contribute additional den~ity for achieving maximum dye densities ~n ~he case of a negatlve-working photographic element. The emul-sions employed can be of any conventional type.
20 They can be identical to the silver halide emulsions employed in the other minus blue-recording color-forming layer units, relying on their less favored layer order arrangement to reduce their effective speed. Speed-granularity advantages are realized by 25 coating faster and slower emulsions in geparate layers a~ opposed to blending the emulsions.
The multicolor photographic elements of the present invention can, if desired, be applied to image transfer applications. For example, a multi-30 color photographic element~ can form a part of amulticolor image transfer film unit. When the photographic elements are employed in image transfer film units they incorporate dye image providing material~ which undergo an alteration of mobil~ty as 35 a function of silver halide development. An image dye receiver can form a part of the image transfer film unit or be separate therefrom. Useful image lz~a6z6 transfer film unit features are disclosed in Research Disclosure~ Item 17643, cited above, Paragraph XXIII; Research Disclosure, Vol. 152, November 1976, Item 15162; and Jones and Hill Can.
Patent 1,175,278, cited above. The image transfer film units disclosed by Jones and Hill are particu-larly preferred for image transfer applications of the photographic elementæ of this invention.
Examples The preparation and sensitization of high aspect ratio tabular grain silver iodide emulsions is illustrated by the following specific examples:
Emulsion Preparation and Sensitization Examples In each of the examples the contents of the reaction vessel were stirred vigorously throughout silver and iodide salt introductions; the term "percent" means percent by weight, unless otherwise indicated; and the term "M" stands for a molar concentration, unless otherwise stated. All solutions, unless otherwise stated, are aqueous emulsions.
Example Emulsions 1 through 4 relate to silver halide emulsions in which the tabular silver iodide grains are of a face centered cubic crystal structure.
Example Emulsion 1 Tabular Grain Silver lodide Emulsion 6.0 liters of a 5 percent deionized bone gelatin aqueous solution were placed in a precipita-tion vessel and stirred at pH 4.0 and pAg calculatedat 1.6 at 40C. A 2.5 molar potassium iodide solution and a 2.5 molar silver nitrate solution were added for 5 minutes by double-jet addition at a constant flow rate consuming 0.13 percent of the silver used. Then the solutions were added for 175 minutes by accelerated flow (44X from start to ,~

lZ1~6Z6 f~nish) consuming 99.87 percent of the silver used.
Silver iodide in the amount of 5 moles WAS
precipitated.
The emulsion was centrifuged, resuspended 5 in distilled water, centrifuged, re6uspended in 1.0 liters of a 3 percent gelatin solution and adju~ted to pAg 7.2 measured at 40C. The resul~cant tabular grain silver iodide emulsion had an average grain diameter of 0.84 l~m, an average grain thickness of 10 0.0661lm, an aspect ratio of 12.7:1, and greater than 80 percent of the grains were tabular based on projected area. Using x-ray powder diffraction analysis greater than 90 percent of the silver iodide was estimated to be present in the y 15 phase. See Figure 1 for a carbon replica electron micrograph of a sample of the emul~ion.
Example Emulsion 2 Epitaxial AgCl on Tabular Grain AgI Emulsion 29.8 g of the tabular grain AgI emulsion 20 (0.04 mole) prepared in Example 1 was brought to a final weight of 40.0 g with distilled water and placed in a reaction vessel. The pAg was measured as 7.2 at 40C. Then 10 mole percent silver chloride was precipitated onto the AgI host emulsion 25 by double-,~et addition for approximately 16 minutes of 0.5 molar NaCl solution and a 0.5 molar AgN03 solution at 0.5 ml/minute. The pAg was maintained at 7.2 throughout the run. See Figure 2 for a carbon replica photomicrograph of a sample of the 30 emulsion-Example Emulsion 3 Epitaxial AgCl plu8 Iridiumon Tabular Grain AgI Emulsion Emulsion 3 was prepared similarly to the epitaxial AgCl tabular grain AgI emulsion of Example 35 2 with the exception that 15 seconds after the start of the silver salt and halide salt solutions 1.44 mg of an iridium compound/Ag mole was added to the - reaction vessel.

~Z1~26 Example Emulsions 1, 2 and 3 were each coated on a polyester film support at 1.73 g sil~er/m2 and 3.58 g gelatin/m2. The coatings were overcoated with 0.54 g gelatin/m2 snd 5 contained 1.0 percent bis(vinylsulfonylmethyl)ether hardener based on tot~l gelatin content. The coatings were expoged for 1/2 second to a 600W
2850K tungsten light 60urce through a 0-6.0 den~ity ~tep tablet (0.30 step6) and processed for 6 minutes 10 at 20C in a total (surface + internal) developer of the type described by Weiss et al U.S. Pstent 3,826,654.
Sensitometric results reveal that for the tabular grain AgI host emulsion (Emulsion 1) no 15 discernible image was obtained. However, for the epitaxial AgCl (10 mole percent)/tabular grain AgI
emulsion (Emulsion 2), a significant negative image was obtained with a D-min of 0.17, a D-max of 1.40, and a contrast of 1.7. For the iridium sensitized 20 epitaxial AgCl (10 mole percent)/tabular grain AgI
emulsion (Emulsion 3) a negative image was obtained with a D-min of 0.19, a D-max of 1.40, a contrast of 1.2, and approximately 0.5 log E faster in threshold speed than Emulsion 2. 5 Example Emulsion 4 The Use of Phosphate to Increase the Size of AgI
Tabular Grains This emulsion was prepared similar to Example Emulsion 1 except that it contained 0.011 30 molar R2HP04 in the precipitation vessel and 0.023 molar K2HP04 in the 2.5 molar potas-sium iodide solution.
The resultant tabular grain emulsion was found to consist of silver iodide. No phosphorus 35 was detectable using x-ray microanalysis. The AgI
tabular grain emulsion had an average grain diameter of 1.65~m compared to 0.84~m found for Example lZ~626 Emulsion 1, an average grain thicknes6 of 0.20~m, an aspect ratio of 8.3:1, and ~reater than 70 percent of the grains were tabular based on projected area. Greater than 90 percent of the 5 silver iodide was present in the ~ phase as determined by x-ray powder diffraction analysis.
Example Emul~ions 5 through X relate to silver halide emulsions in which the tabular silver iodide grains are of a hexagonal crystal structure, 10 indicat~ng the silver iodide to be present predomi-nantly in the ~3 phase.
~:xample Emulsion 5 Tabular Grain AgI Emulsion 4.0 liters of a 2.0 percent deionized phthalated gelatin aqueous solution containil g 0.08 15 molar potassium iodide were placed in a precipita-tion vessel with stirring. The pH was adju~ted to 5.8 et 40C. The temperature was increased to 80C
and the pI was determined to be 1.2. Then a 1.0 molar potassium iodide solution a'c 45C and a 0.06 20 molar silver nitrate solution at 45C were run concurrently into the precipitation vesRel by double-jet addition. The silver salt solution was added for 138.9 minutes by accelerated flow (3.5X
from start to finish) utilizing 0.3 mole of silver.
25 The iodide salt solution was added at a rate suffi-cient to maintain the pI at 1.2 at 80C throughout the run. The emul~ion was cooled to 30C, washed by the coagulation method of Yutzy and Frame, U.S.
Patent 2,614,928, and stored at pH 5.8 and pAg 9.5 30 measured at 40C. The resultant tabular grain 6ilver iodide emulsion had an average grain diameter of 2.5 llm, an average thickne~s of 0.30 llm, an average aspect ratio of 8.3:1, and greater than 75 percent of the pro~ected area was provided by 35 tabulsr grains. See Figure 3 for a photomicrograph of Emulsion S.

~Z~6Z6 Example Emulsion 6 Tabular Grain AgI Host Emulsion 5.0 liters of a 2.0 percent deionized phthalated gelatin aqueous solution (Solution A) 5 containing 0.04 molar potassium iodide were placed in a precipitation ves~el with 6tirring and the pH
wss ad~usted to 5.8 at 409C. The temperature was increased to 90C and the pI Wa8 de~erm~ned to be 1.6. Then a 1.0 molar potass~wm iodide solution at 10 70C (Solution B) and a 6.95 x 10- 2 molar AgN03 solution at 70C (Solution C) were run concurrently into Solution A by double-~et addi-tion. Solution C was added for 125 minute by accelerated flow (2.23X from start to finish consum-15 ing 6.4 percent of the total silver used. SolutionC wa~ then added at accelerated flow rate6 in five intervals of 125 minutes, 150 minute~, 150 minutes, 150 minutes, and 20 minutes each consuming 13.7 percent, 20.8 percent, 25.3 percent, 29.7 percent, 20 and 4.0 percent, re~pectively, of the total silver used. Solution B was added concurrently throughout at flow rates sufficient to maintain the pI at 1.6 at 90C. The emulsion was cooled to 30C, washed by the coagulation method of Yutzy and Frame U.S.
25 Patent 2,614,928, and stored at pH 6.0 and pAg 9.5 measured at 40C. Approximately 7.6 x 10-1 mole of silver was used to prepare this emulsion. The resul~ant tabular grain sllver iodide emulsion had an average grain diameter of 7.7~m, an average 30 thlckness of 0.35~m, an aspect ratio of 22:1, and greater than 75 percent of the pro~ected area was provided by the tabular gra~ns.
Example Emuls~on 7 Silver Bromide (10 mole percent) Deposition on Tabular Grain AgI Emul~ion A total of 2.03 liters of a 0.98 percent deionized phthalated gelatin aqueous solution lZ1~6Z6 containing 444.0 g (0.44 mole) of Emulsion 6 were placed in a precipitation vessel with stirring. The pH wa~ ad~usted to approximately 6.2. The pAg was ad~usted to approximately 7.6 at 40C using a 1 x 5 10-3 molar potassium bromide solution. Then a 0.1 molar potassium bromide solution at 40C and a 0.1 molar silver nitrate solution at 40C were run concurrently into the precipitation vessel by double-~et addition. The silver 6alt solution was 10 added for 30 minutes at 14.8 ml/minute while the bromide salt solution was added at a rate ~ufficient to maintain the pAg at 7.6 at 40C. Approximately 10 mole percent silver bromide was added to the tabular 8rain silver iodide host emulsion. The 15 emulsion was cooled to 30C, washed by the coagula-tion method of Yutzy and Frame U.S. Patent 2,614,928, and stored at pH 5.8 and pAg 8.2 measured at 40C.
The silver bromide epitaxially deposited 20 was almost exclusively along the edges of the tabular silver iodide host crystals.
ExamPle Emulsion 8 Silver Chloride (10 mole percent) Deposition on Tabular Grain AgI Emulsion A total of 1.98 liters of a 1.26 percent deionized phthalated gelatin aqueous solution containing 486.0 g (0.44 mole) of an Emulsion 6 repeat were placed in a precipitation vessel with stirring. The pH was ad~usted to approximately 30 6Ø The pAg was ad~usted to approximately 6.9 at 40C using a 1.0 molar potassium chloride solution.
Then a 9.25 x 10- 2 molar potassium chloride solution at 40C and a 9.25 x 10- 2 molar silver nitrate solution at 40C were run concurrently into 35 the precipitation vessel by double-~et addition.
The silver salt solution was added for 60 minute~ at 8.0 ml/minute while the chloride salt solution was added at a rate such that the pAg changed from 6~9 to 6.7 at 40C throughout the run. Approximately 10 mole percent æilver chloride was added to the tabular grain silver iodide hoæt emulsion. The 5 emulsion was cooled to 30C, washed by the coagula-tion method of Yutzy and Frame U.S. Patent 2,614,928, and ~tored at pH 5.0 and p~g 7.2 measured at 40C.
The silver chloride epitaxially deposited 10 was almost exclusively along the edges of the tabular silver iodide host crystals.
Example Emulsion6 6, 7, and 8 were sepa-rately coated on polyester film support at 1.61 g silver/m2 and 5.38 g gelatin/m2. The coating 15 elements also contained 1.61 g yellow coupler ~-pivalyl-~4-(4-hydroxybenzenesulfonyl)-phenoxy]-2-chloro-5-(n-hexadecanesulfonamido)~
acetanilide/m2, 3.29 g 2-(2-octadecyl)-5-sulfo-hydroquinone, sodium salt/Ag mole and 1.75 g 4-hy-20 droxy-6-methyl-1,3,3a,7-tetraazaindene/Ag mole. The coating elements were overcoated with a 0.89 g gelatin/m2 layer that contained 1.75 percent by weight hardener bi6(vinylsul0nylmethylaether based on total gelatin content. Emulsion 8 was also 25 spectrally sensitized with 0.25 millimole anhydro-5,5'-dichloro-3,3'-bis(3-gulfopropyl)thiacyanine hydroxide trimethylamine salt/Ag mole and then chemically sensitized with 15 mg gold sulfide/Ag mole for 5 minutes at 55C and coated as described 30 above-The coatings were exposed for 1/10 secondto A 600 watt 3000K tungsten light source through a 0-6.0 density step tablet (0.30 steps) and processed for either 3 or 6 minutes at 37.7C in a color 35 developer of the type described in The British Journal of Photography Annual, 1979, pages 204-206.
Blue sensitometry was obtained. Sensito-metric results revealed that for Emulsion 6, the 2~ @

tabular grain AgI host emulsion, no d~scernible image was obtained at either 3 minutes or 6 minutes development time. Emulsion 7, the AgBr deposited on AgI host emulsion, resulted in a significant nega-5 tive image at 6 minutes development with a D-min of 0.13, a D-max of 0.74, and a contrast of 0.42.
Unsensitized Emulsion 8, the AgCl deposited on AgI
host emulsion, resulted in a substantial negative image a~ 3 minutes development with a D-min of 0.13, 10 a D-max of 0.74, and a contrast of 0.80. Further-more, the chemically and spectrally sensitized Emulsion 8 which had a D-min of 0.13, D-max of 0.80, and contrast of 0.65, was approximately 0.60 log E
faster in speed than unsensitized Emulsion 8. 5 Example Emulsion 9 Tabular Grain Agl Host Emulsion 5.0 liters of a 2.0 percent deionized gelatin aqueous solution containing 0.04 molar potassium iodide were placed in a precipitation 20 ves~el with stirring. The pH was ad~usted to 5.8 at 40C. The temperature was increased to 90C and the pI was determined to be 1.4. Then a 0.5 molar potassium ioodide solution and a 0.07 molar silver nitrate solution were run concurrently into the 25 precipitation vessel by double-jet addition. The silver salt solution was added in six increments according to the followlng flow profile.
Silver Salt Addition Profile Accelerated flow Percent of 30 Run Time (Start to Finish) Total S~lver . _ 125' 2.23x 6.1 125' 1.55x 10.8 150' 1.43x 19.2 150' 1.3 x 26.1 3515~' 1.23x 32.9 20' 1.03x 4.9 A total of approximately 0.8 mole of silver was utilized. The iodide salt solution was added at a rate sufficient to maintain the pI at approxi-mately 1.4 at 90C throughout the precipitation.
The emulsion was cooled to 30C and washed by the coagulation method of Yutzy and Frame U.S. Patent 5 2,614,928. The resultant tabular grain 6ilver iodide emulsion had an average grain diameter of 11.4 ~m, an average grain thickness cf 0.32 ~m, an average aspect r~tio of 35.6:1, and greater than 75 percent of the projected surface area was 10 contributed by the tabular silver iodide gr~ins.
See Figure 4 for a photomicrogr~phic of Emulsion 9.
Example Emulsion 10 Silver Chloride (10 mole percent) Deposition on Tabular Grain AgI Emul~ion A sample of Emulsion 9 in the amount of 1048 grams (1.3 mole AgI) prepared above wa6 placed in a precipitation vessel. Next 1.3 liters of di~tilled water were added and the emulsion wa~
ad~usted to pAg 7.0 at 40C using a 1.0 molar KCl 20 solution. Then a 1.0 molar KCl solut~on and a 0.46 molar AgNO3 solution were added over two hours by double-jet utilizing accelerated flow (2x from start to finish) at controlled pAg 7.0 at 40C. A
total of 10 mole percent silver chloride was 25 precipitated onto the silver iodide host Emulsion

9. Following precipitation the emulsion was cooled to 30C and washed by the coagulation method of Yutzy and Frame U.S. Patent 2,614,928. See Figure 5 for a photomicrogrsph of Emulsion 10.
30 Example Emulsion ll Silver Bromide (5 mole percent) Deposition on Tabular Grain AgI Emulsion A tabular grain AgI emulsion was prepared by a double-~et precipitation technique. The r 35 emulsion had an average grain diameter of 6.0 ~m, an average grain thickness of 0.23 ~m, an average aspect ratio of 26:1, and greater than 75 percent 121~6~6 of the pro~ected surface area was contributed by the tabular silver iodide grains.
The tabular grain ~ilver iodide emulsion in the amount of 600 grams (1.0 mole AgI) w~s plAced in 5 a precipitation vessel. Next 1.6 liters of distil-led water were added and the emul~ion was ad~usted to pAg 8.0 at 40C using a 1.0 molar KBr solution.
Then a l.0 molar KBr solution and a 0.037 molar AgNO3 solution were added over elght hours by

10 double-jet utilizing accelera~ed flow (Sx from start to finish) at controlled pAg 8.0 a~ 40C. A to$al of 5 mole percent silver bromide was precipitated onto the silver iodide host emulsion. Following precipitation the emulsion was cooled to 30C and 15 washed by the coagulation method o$ Yutzy and Frame ~.S. Patent 2,614,928. See Figure 6 for a photo-micrograph of Emulsion 11.
Multicolor Photographic Element Example Three silver halide emulsions of near 20 equivalent grain volumes were prepared by double-~et precipitation techniques. The emulsions were separately coated in the blue layer of multilayer elements and compared for the blue light absorption in the green recording layer. Emulsion A was a 25 three-dimensional grain silver iodide with an average grain size of 0.75~m and an average grain volume of 0.22(~m)3. Emulsion B was a tabular grain silver bromoiodide (97:3) emulsion with an average grain diameter of 1.8~m, an average grain 30 thickness of O.O99~m, an aspect ratio of 18:1, an average pro;ected area of greater than 80%, and an average grain volume of 0.25(~m)3. Emulsion C, satisfying the requirements of this invention, was a tabular grain silver iodide emulsion with an average 35 grain diameter of 1.7~m, an average grain thick-ness of 0.095~m, an average aspect ratio of 12~ Z6 17.9:1, a tabular grain projected area of greater than 50% of the total grain projected area, and an average grain volume of 0.21(~m)3.
Each emulsion was coated in the blue layer (Layer 9) at 0.97 g. silver/m2 and 1.51g.
gelatin/m2. Layer 9 also contained 2-(2-octa-decyl)-5-sulfohydro-quinone, sodium ~alt at 0.30 glm2 and 4-hydroxy-6-methyl-1,3,3~,7-tetraazain-dene at 2.27 g¦m2. No yellow filter layer was 10 present in the multilayer element.
The remaining film tructure coated on cellulose triacetate support is described b~low.
Layer 1: A slow cyan imaging component containing a blend of a red sensitized tabular grain (0.16~m thick x 5.3~m diameter) oeilver bromoiodide (97:3) emulsion and a red sensitized 0.55~m three-dimensional grain silver bromo~odide (97:3) emulsion in a 1.7:1 ratio coated at 2.48 g. ~ilver/m2 and 2.56 g. gelatin/m2. Also present were cyan dye-forming coupler at 0.94 g/m2, 2-(2-octadecyl)-5 -8ul fohydro-quinone, sodium salt at 0.08 g/m2 And 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene at 0.80 g/m2.
Layer 2: Gelatin lnterlayer at 0.61 g/m2.
Layer 3: A slow magenta imaging component containing a blend of a green sensitized tabulsr grain (0.16~m thick x 5.3~m diameter) silver bromoiodide (97:3) emulsion, A green sensitized 0.5S ~m three-dimensional gr in silver bromoiodide (97:3) emulsion, and a green sensitized 0.21~m three-dimensional green silver bromoiodide (95.2:4.8) emulsion in a ratio of 4.2:3.2:1 coated at 2.73 g. silver/m2 and 2.70 g.

~2~``626 gelatin/m2. Alæo present were magenta coupler at 0.82 g/m2, 2-(2-octadecyl)-S-sulfohydro-quinone, sodium salt at 0.11 g/m2, and 4-hydroxy-6-methyl-1,3,3a~7-tetraazaindene at 0.44 g/m2.
Layer 4: Gelatin interlayer at 0.61 g/m2 .
Layer 5: A fast cyan imaging component containing a red sensitized tabular grain (0.16~m thick x 5.3~m diameter) sllver bromo-iodide (97:3) emulsion coated at 1.83 g.
silver/m2 snd 1.83 g. gela~in/m2. Also present were cyan coupler 0.22 g/m2, 2-(2-octadecyl)-5-sulfohydroquinone, sodium salt at 0.06 g/m2 a and 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene at 1.25 g/m2 .
Layer 6: Gelat~n interlayer at 0.61 g/mZ.
Layer 7: A fast magenta imaging component con~aining a green sensit~zed tabular grain (0.16~m thick x 5.3~m diameter) silver bromo-iodide (97:3) emulsion coated at 1.83 g.
silver/m2 and2.09 g. gelatin/m2. Also present were magenta coupler at 0.16 g/m2, 2-(2-octadecyl)-5-sulfohydro-quinone, sodium ~alt at 0.06 g/m2, and 4-hydroxy-6-methyl-1,3,3a,7~tetraazaindene at 1025 g/m2.
Layer 8: Gelatin interlayer at 0.81 g/m2.
The multilayer element was overcoated with 30 1.36 g. gelatin/m2 and hardened with 2.0% bis-(vinylsulfonyl-methyl) ether based on the total gelatin content.
A control coating was also prepared with the exception that the silver halide emuls~on was 35 omitted from Layer 9. Gelatin was coated at 1.51 g/m2 in that layer. The remaining layers were the same as described above.

~Z~6Z6 Each coating was exposed for 1/10 second to a 600W 5500K tungsten light ~ource through a 0-6.0 density step tablet (0.30 steps) plus Wratten 36 +
38A filter (permitting only 350 to 460 nm wavelength 5 light to be transmitted) and processed for-2 1/2 minutes in a color developer of the type described in the British Journal of Photography Annual, 1979, pages 204-206.
To provide a measure of the blue light 10 transmitted through Layer 9> a characteristic curve of the magenta record was plotted for each multi-color element, and the ~peed of the magenta record was measured. Layer magenta ~peed~ indicate lower levels of blue light transmi~sion.
TABLE VI
Coating Relative Blue Speed Control 100 Emulsion A (three-dimensional 61 grain AgI) Emulsion B (tabular grain AgBrI) 92 Emul~ion C (tabular grain AgI) 51 30 relative speed units - 0.30 log E, where E is exposure measured in meter-candle-seconds.
As shown in Table VI the multicolor element 25 containing Emulsion C provided the lowest relative blue speed in the magenta record layer. This indicated that of the three emulsions of near equivalent grain volumes, the tabular grain silver iodide emul~ion ab~orbed the greatest amount of blue 30 light. The improvement of Emulsion C over Emulsion A demonstrated that blue light absorption by silver iodide occurred due to projected surface area rather than grain volume. These results show that by coating a high aspect ratio silver iodide emulsion 35 in a blue recording layer less unwanted blue light is transmitted to the underlying emulsion layers.

, ~21~6~6 The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be under~tood that variations and modifications can be effected within the spirit 5 and scope of the invention.

Claims (18)

WHAT IS CLAIMED IS

1. In a photographic element capable of producing a multicolor image comprised of a support and, located on said support, superimposed emulsion layers for facilitat-ing separate recording of blue, green, and red light, each comprised of a dispersing medium and silver halide grains, the improvement comprising at least 50 percent of the total projected area of said silver halide grains in at least one emulsion layer being provided by thin tabular silver iodide grains having a thickness of less than 0.3 micron and an average aspect ratio of greater than 8:1.

2. A photographic element according to claim 1 wherein said one emulsion layer is a blue recording emulsion layer.

3. A photographic element according to claim 1 wherein said tabular silver iodide grains have an average aspect ratio of at least 12:1.

4. A photographic element according to claim 1 wherein said tabular silver iodide grains account for at least 70 percent of the total projected area of said silver halide grains in said one blue recording emulsion layer.

5. A photographic element according to claim 1 wherein silver salt is epitaxially located on said tabular silver iodide grains.

6. A photographic element according to claim 4 wherein said silver salt is comprised of a silver halide.

7. A photographic element according to claim 5 wherein said silver salt is comprised of silver chloride.

8. A photographic element according to claim 5 wherein said silver salt is comprised of silver bromide.

9. A photographic element according to claim 4 wherein said silver salt is epitaxially located on less than 25 percent of the total surface area provided by the major crystal faces of said tabular silver iodide grains.

10. A photographic element according to claim 9 wherein said silver salt is epitaxially located on less than 10 percent of the total surface area provided by the major crystal faces of said tabular silver iodide grains.

11. A photographic element according to claim 1 wherein said tabular silver iodide grains have an average thickness greater than 0.005 micron.

12. A photographic element according to claim 1 wherein said tabular silver iodide grains have an average thickness greater than 0.01 micron.

13. A photographic element according to claim 1 wherein said tabular silver iodide grains have an average thickness of less than 0.1 micron and said emulsion additionally contains a blue spectral sensitizing dye having an absorption peak of a wavelength longer than 430 nanometers.

14. A photographic element according to claim 1 wherein said tabular silver iodide grains have an average thickness greater than 0.1 micron.

15. A photographic element according to claim 14 wherein said tabular silver iodide grains have an average thickness greater than 0.15 micron.

16. A photographic element according to claim 1 wherein said tabular silver iodide grains are positioned to receive exposing radiation prior to remaining of said silver halide grains.

17. A photographic element according to claim 1 wherein said tabular silver iodide grains are positioned to receive exposing radiation prior to said silver halide grains present in said red and green recording emulsion layers.

18. A photographic element according to claim 1 wherein said red and green recording emul-sion layers are comprised of high average aspect ratio tabular grain emulsions and are positioned to receive exposing radiation prior to said tabular silver iodide grains and said support is a white reflective support.