WO1991012566A1

WO1991012566A1 - Photographic silver halide material and process for forming reversal images

Info

Publication number: WO1991012566A1
Application number: PCT/US1991/000759
Authority: WO
Inventors: Spencer Alan Pugh; Kenneth Joseph Reed; Jacob Issac Cohen
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1990-02-08
Filing date: 1991-02-04
Publication date: 1991-08-22
Anticipated expiration: 1992-08-08
Also published as: DE69123188D1; DE69123188T2; EP0466919A1; JPH04506271A; EP0466919B1

Abstract

A photographic silver halide emulsion comprises a dispersing medium and photographic silver haloiodide that (a) is a negative-working, core-shell silver haloiodide; (b) contains total iodide (It) within the range of 0.5 to 8 mole percent; and, (c) wherein the sivler haloiodide has a volume fraction of the shell (Vs) that is greater than 0.05 but less than or equal to a constant (A) times the total iodidie in mole percent (It) wherein A is a unitless parameter equal to 0.15 plus or minus 0.05; wherein upon exposure and two-step reversal processing of a photographic element comprising the emulsion a decrease in granularity is produced. Such a photographic silver halide emulsion is useful in a photographic silver halide element designed to form reversal images to provide a decrease in granularity of the image.

Description

-1- PHOTOGRAPHIC SILVER HALIDE MATERIAL AND PROCESS FOR FORMING REVERSAL IMAGES This invention relates to photographic silver haloiodide emulsions, photographic silver halide elements, particularly elements designed for forming reversal images, incorporating these emulsions, and processes for the use of the photographic elements.

Photographic emulsions useful in photography typically comprise a dispersing medium, such as gelatin, containing grains of photographic silver halide. Photographic ^■silver halide emulsions, particularly photographic silver bromoiodide emulsions and their preparation are described in, for example, such standard texts as Duffin, Photographic Emulsion Chemistry, Focal Press, 1966 and Mees and James, The Theory of the Photographic Process, Macmillan Publishing Co., 4th Edition, 1977.

Photographic silver halide emulsions having various grain sizes and shapes are also known in photography. Such photographic silver halide emulsions can be monodisr/ersed or polydispersed. The photographic silver halide emulsions include core—shell emulsions. Illustrative emulsions are described in, for example, U.S. Patents 4,692,400; 4,670,375; 4,636,461; 4,668,614; 4,665,012;and 4,477,564 and European Patent Application 147,868.

A particular problem has been encountered in core-shell photographic silver halide emulsions and processes designed with such emulsions for formation of reversal images. This problem is that conventional core-shell photographic silver halide emulsions that have been acceptable for forming reversal images, particularly color reversal photographic images, have been found not to provide the desired granularity when processed in a color reversal process, such as the known E—6 process of Eastman Kodak Company, U.S.A., that has a high degree of silver halide solvency in the black-and-white development step. This is illustrated by the comparative examples that follow. Core-shell silver bromoiodide emulsions, particularly such emulsions designed for negative photographic materials, that were considered as answers to this problem do not provide a useful reduction in granularity. Such emulsions include core—shell emulsions described in U.S. Patent 3,505,068. No answer to this problem in formation of color reversal images, particularly in camera speed color reversal photographic silver haloiodide elements, was clear from the description of core-shell photographic silver halide emulsions in these references.

It has been found that such requirements for reduced granularity without adversely affecting other sensitometric properties are satisfied by a photographic silver halide emulsion comprising a dispersing medium, preferably gelatin or a gelatin derivative, and photographic silver haloiodide, preferably silver bromoiodide, that (a) is a negative—working, core—shell silver haloiodide; (b) contains total iodide (I.) within the range of 0.5 to 8 mole percent; and, (c) wherein the silver haloiodide has a volume fraction of the shell (Vs) that is greater than 0.05 but less than or equal to a constant (A) times the total iodide in mole percent (I. ) wherein A is a unitless parameter equal to 0.15 plus or minus 0.05. Upon exposure and reversal processing of a photographic silver halide element comprising such an emulsion a decrease in granularity is produced.

Another aspect of the invention is a photographic element, particularly a reversal color photographic element, comprised of a support bearing at least one photographic silver haloiodide emulsion layer, as described herein.

A further aspect of the invention is a method of forming a reversal image, particularly a color reversal image, by exposure and reversal processing a photographic element as described herein.

The described invention enables unique and unexpected advantages. The described emulsion, element and process enable the reduction of granularity of a color reversal image. The described emulsions are particularly advantageous when chemically sensitized and spectrally sensitized and in color reversal photographic materials designed to produce reversal color images. The described core-shell photographic silver bromoiodide emulsions, in addition to enabling reduced granularity, also enable improved spectral sensitization, improved control of densitometric curve shape.

The term two—step reversal processing herein mean process involving a black-and-white development step followed by a chromogenic development step, such as in the well known E-6 process (See, for example, British Journal of Photography Annual, 1988, pages 194 to 196.). The term volume fraction of the shell (Vs) herein means the volume of the shell of the described emulsion grain divided by the total volume of the emulsion grain (sum of the volume of the core plus the volume of the shell). Because the densities (also known as specific gravities) of regions with different haloiodide compositions are nearly the same, V is also equal to the number of moles of silver haloiodide in the shell of the emulsion grain divided by the total number of moles of silver haloiodide in the emulsion grain (sum of the number of moles in the core plus the number of moles in the shell). The parameter V can be related to shell thickness, but the relationship depends upon the morphology of the emulsion grain and the size of the emulsion. For example, the emulsion can be a cubic emulsion with a cubic core. If the total edge length of the emulsion is L and the core edge length is s, then from simple geometry the total volume of the

3 grain is L and the volume of the shell is L 3-s3. Consequently, the volume fraction of the shell (Vs is (L³-s³)/L³. The shell thickness (t) of this emulsion, measured from the face of the cubic core to the face of the cubic grain is (L-s)/2. Using these relationships, Vs can be expressed in terms of L and t as follows:

Similar relationships can be derived for other emulsion morphologies. The shell thickness alone is not enough to define Vs. The emulsion morphology as well as the total grain size or the core size should be considered.

For the emulsions described herein, the volume fraction of the shell (Vs) is greater than

0.05 but does not exceed the value calculated by the equation V = A x It wherein A is a unitless constant equal to 0.15 plus or minus 0.05, and I ^■,t is the total iodide (in mole percent) in the silver haloidide grain. The constant A is defined within a range of plus or minus 0.05 because the exact value of A can vary depending upon the subsequent surface treatments of the emulsion.

The total bulk iodide of the silver haloiodide can be determined by procedures and means known in the photographic art. When the volume fraction of the shell is outside the described range the described core—shell photographic silver halide does not provide decreased granularity with other desired properties of a core-shell photographic silver halide. The optimum volume fraction of the shell will depend upon such factors as the desired image, the particular photographic element, the optimum chemical sensitization of the emulsion, the optimum spectral sensitization of the emulsion, and the particular reversal process for forming the image in the photographic element. The value of A can also vary within its defined range (0.15 plus or minus 0.05) with such factors. The grain size and the characteristics of the silver haloiodide, particularly the silver bromoiodide, as described can be readily ascertained by procedures well known in the photographic art. The shape and size of the silver haloiodide grain can be any shape and size that are known in the photographic art. The grain size is typically within the range of 1.0 to 0.3 microns, preferably within the range of 0.7 to 0.4 microns. The shape of the grain is typically cubic, -octahedral or cubooctahedral, but other grain shapes known in the photographic art are useful, such as tabular grains.

The silver haloiodide emulsion can be polydispersed or monodispersed. The term monodispersed herein means that at least 95% (such as 95 to 99.97.) by weight of the silver haloiodide grains less than the mean grain diameter and at least 957, (such as 95 to 99.97o) by number of the silver haloiodide grains larger than the mean grain diameter must be within 407. of the mean grain diameter. The mean grain diameter means the diameter of a circle equal in area to the mean projected area of the silver haloiodide grains, especially viewed in a photomicrograph or an electronmicrograph of an emulsion sample. e silver haloiodide grains which may be any shape known in the photographic art may have rounded corners and rounded edges . The core of the silver haloiodide grain as described can have various shapes as known in the photographic art. The core shape can be essentially round, cubic, octahedral, cubooctahedral or other shape.

The silver haloiodide grains as described can be formed by conventional double jet emulsion preparation techniques and methods known in the photographic art. In a process of preparing a silver bromoiodide as described typically a dispersing medium, preferably an aqueous gelatin or gelatin derivative composition, is introduced into a conventional reaction vessel designed for silver halide precipitation equipped with a stirring mechanism. Typically the dispersing medium is introduced into the reaction vessel in a concen¬ tration that is at least .017,, preferably .057. to 57., by weight based on the total weight of the dispersing medium present in the silver haloiodide emulsion at the conclusion of grain precipitation. The volume of dispersing medium initially present in the reaction vessel can equal or exceed the volume of the silver haloiodide emulsion present in the reaction vessel at the conclusion of the grain precipitation. The dispersing medium introduced into the reaction vessel is preferably a dispersion of peptizer in water, particularly gelatin in water, optionally containing other ingredients, such as silver halide ripening agents and/or metal dopants. The peptizer, particularly gelatin or a gelatin derivative, is preferably initially present in a concentration of at least 10%, preferably at least 207., of the total peptizer present at the completion of the silver haloiodide precipitation. Additional dispersing medium can optionally be added to the reaction vessel with the silver salts and the alkali bromide and iodide salts and also can be introduced through a separate inlet means, such as a separate jet. The proportion of dispersing medium can be adjusted after the completion of the salt introductions or after washing.

During precipitation silver salts, particularly silver nitrate, bromide salts, preferably alkali metal bromide salts, and iodide salts, preferably alkali metal iodide salts, are added to the reaction vessel by techniques known in the photographic art. Typically an aqueous silver salt solution, preferably a silver nitrate solution, is introduced concurrently with the introduction of bromide and iodide salts. The bromide and iodide salts are typically introduced as aqueous salt solutions, preferably as aqueous salt solutions or one or more alkali metal such as potassium or sodium, salts. Alkaline earth metal salts can also be useful, such as calcium and magnesium salts. The silver salt is introduced into the reaction vessel separately from the halide salts. The iodide and bromide salts can be added to the reaction vessel separately or as a mixture.

With the introduction of the silver salts into the reaction vessel the nucleation stage of the grain formation is initiated. A population of grain nuclei are formed that aie capable of serving as precipitation sites for silver halodόdide as the introduction of silver, bromide ajnd iodide salts continues. The precipitation of the silver halide onto the existing grain nuclei constitutes the growth step of grain formation. The permissible latitude of pBr during the growth stage of the precipitation is is within the range of 1 to 4. A highly preferred pBr is about 3. The pBr can be regulated during the precipitation. The pBr herein is the negative logarithm of bromide concentration and is measured by methods known in the photographic art. Subject -to the requirements of the process as described, the concentration and rates of silver salt, bromide salt and iodide salt introductions can take any convenient and conventional form useful for forming core-shell silver haloiodide grains. The rate of silver and halide salt introduction can be constant or optionally increased either by increasing the rate at which the silver and halide salts are introduced or by increasing the concentrations of the silver and halide salts being introduced. It is preferred to increase the rate of the silver and halide salt introductions, but to maintain the rate of introduction below that at which the formation of new grain nuclei is favored to avoid renucleation. The concentration of iodide can be varied in each step as desired to form the desired core-shell grain.

The process of preparing the silver haloiodide is preferably carried out at a temperature within the range of 25° to 80^βC, such as about 45°C. The core of the silver haloiodide can be measured and observed by methods known in the photographic art, such as by x-ray diffraction techniques known in the art.

Modifying compounds can be present during the silver haloiodide precipitation. Such compounds can be initially in the reaction vessel or can be added with one or more of the salts according to conventional emulsion making procedures. Modifying compounds, such as compounds of copper, iridium, thallium, lead, bismuth, cadmium, zinc, middle chalcogens , such as sulfur, selenium, and tellurium, gold, Group VIII noble metals, can be present during the precipitation.

The individual silver and halide salts can be added to the reaction vessel through surface or subsurface delivery tubes, by gravity feed or delivery apparatus for maintaining control of the rate of delivery and the pH, pBr, and/or pAg of the reaction vessel contents as is used in the art of photographic emulsion making.

In forming the silver haloiodide emulsions a dispersing medium preferably comprises in the reaction vessel initially an aqueous peptizer suspension. The peptizer concentration is typically within the range of that used in preparation of conventional core-shell photographic emulsions. The emulsion vehicle concentration is typically adjusted upward for optimum coating characteristics by delayed, supplemental vehicle additions. Typically the emulsion as initially formed contains peptizer within the range of about 5 to 50 grams of peptizer per mole of silver halide, preferably within the range of about 10 to about 30 grams of peptizer per mole of silver halide. Additional vehicle can be added later to bring the concentration up to as high as 1000 grams per mole of silver halide. Preferably the concentration of vehicle in the finished emulsion is about 50 grams per mole of silver halide. When coated and dried on a support forming the photographic element, the vehicle preferably comprises about 30 to about 707. by weight of the emulsion layer.

Vehicles, including both binders and peptizers, can be selected from those conventionally employed in photographic Isilver halide emulsions. Preferred peptizers are hydrophilic colloids, that can be used alone or in combination with hydrophobic materials. Useful hydrophilic materials include both naturally occurring substances, such as proteins, protein derivatives, cellulose derivatives, such as cellulose esters, gelatin* such as alkali treated gelatin or acid treated gelatin, gelatin derivatives, such as acetylated gelatin and phthalated gelatin, polysaccharides, such as dextran, gum arabic, zein, casein, pectin, collagen derivatives, agar-agar, arrowroot and albumin and other vehicles and binders known in the photographic art. Gelatin is highly preferred.

Other materials commonly used in combination with hydrophilic colloid peptizers as vehicles, including for example vehicle extenders such as materials in the form of latices, are also useful in the emulsions of the invention, such as synthetic polymeric peptizers, carriers and/or binders, such as poly(vinyl lactams), acrylamide polymers, poly(vinyl alcohol) and its derivatives, poly(vinyl acetals), polymers of alkyl and sulfoalkyl acrylates and methacrylates, hydrolyzed poly(vinyl acetates), polyamides, poly(vinyl pyridine), acrylic acid polymers, maleic acid copolymers, vinyl amine copolymers, methacrylic acid copolymers, acryloyloxyalkylsulfonic acid copolymers, sulfoacrylamide copolymers, polyalkyleneimine copolymers, polyamines, N,N—dialkylaminoalkyl acrylates, vinyl imidazole polymers and copolymers, vinyl sulfide copolymers, halogenated styrene polymers, amineacrylamide polymers, polypeptides and other vehicles and binders known to be useful in the photographic art, such as described in U.S. Patent 4,433.048. These added materials need not be present in the reaction vessel during the silver halide precipitation, but rather are typically added to the emulsion prior to coating on the support. The vehicles and binders, including the hydrophilic colloids, as well as the hydrophobic materials, can be employed alone or in combination, not only in the emulsion layers of the photographic element, but also can be used alone or in combination in other layers, such as overcoat layers, interlayers, and layers positioned between the emulsion layers and the support. The silver bromoiodide emulsions are preferably washed to remove soluble salts . Any of the processes and compositions known in the photographic art for this purpose are useful for washing the silver bromoiodide emulsions of the invention. The soluble salts can be removed by decantation, filtration, and/or chill setting and leaching, coagulation washing, by centrifugation, and by other methods and means known in the photographic art. if desired the silver bromoiodide emulsion of the invention can be blended or otherwise combined with other photographic silver halide emulsions if required. The photographic silver bromoiodide emulsion can be, for example, combined with a tabular grain silver halide emulsion, such as one described in U.S. Patent 4,433,048.

The photographic silver bromoiodide can be chemically sensitized by procedures and by compounds known in the photographic art. For example, the silver bromoiodide can be chemically sensitized with active gelatin, or with sulfur, selenium, tellurium, gold, platinum, palladium, iridium, osmium, rhodium, rhenium, or phosphorous sensitizers or combinations of these sensitizers, such as at pAg levels within the range of 5 to 10 and at pH levels within the range of 5 to 8 at temperatures within the range of 30 to 80°C. The silver bromoiodide can be chemically sensitized in the presence of finish, also known as chemical sensitization, modifiers, such as compounds known to suppress fog and increase speed during chemical sensitization, such a azaindenes, azapyridazines, azapyrimidines, benzothiazolium salts, and sensitizers having one or more heterocyclic nuclei. Optionally the silver bromoiodide can be reduction sensitized, such as with hydrogen, or through the use of reducing agents, such a stannous chloride, thiourea dioxide, polyamines or amineboranes .

The photographic silver bromoiodide emulsion can be spectrally sensitized by methods and compounds known in the photographic art. The photographic silver bromoiodide emulsion can be spectrally sensitized by, for example, dyes of a variety of classes, including the polymethine dye class, including cyanines, merocyanines, complex cyanines and merocyanines, oxonols, hemioxonols, styryls, merostyryls and streptocyanines. Combinations of spectral sensitizers are also useful.

The photographic silver bromoiodide emulsion of the invention can be used in many ways, in photographic element formats and for purposes that core-shell silver bromoiodide emulsions have been used in the photographic art.

Photographic silver halide elements comprising a photographic silver bromoiodide emulsion as described can be either single color or multicolor elements. In a multicolor element, a cyan dye-forming coupler is typically associated with a red-sensitive emulsion, a magenta dye-forming coupler is typically associated with a green—sensitive emulsion and a yellow dye-forming coupler is associated with a blue—sensitive emulsion. Multicolor elements typically contain dye-forming units sensitive to each of the three primary regions of the spectrum. Each unit can comprise a single emulsion layer or multiple emulsion layers. The layers of the element and the image-forming units can be arranged in various orders as known in the photographic art.

The photographic element can contain added layers, such as filter layers, interlayers, overcoat layers, subbing layers and other layers known in the art.

In the following discussion of illustrative materials that are useful in elements of the invention reference will be made. to Research Disclosure. December 1978, Item 17643, published by Kenneth Mason Publications Ltd., The Old Harbourmaster's, 8 North Street, Emsworth, Hampshire P010 7DD, England, the disclosures of which are incorporated by reference. The publication will be identified hereafter by the term "Research Disclosure".

Silver halide emulsions that can be employed in combination with the silver bromoiodide emulsion of the invention can be comprised of silver bromide, silver chloride, silver iodide, silver chloroiodide, silver chlorobromide or mixtures thereof. These silver halide emulsions ^can include silver halide grains of any convention l shape or size. Specifically the emulsions can be coarse, medium or fine grain. Tabular grain silver, halide emulsions are useful in a photographic element as described. The silver halide emulsions that are useful with the silver bromoiodide emulsions of the invention can be polydisperse or monodisperse as precipitated. The grain size distribution of these emulsions can be controlled by silver halide grain separation techniques or by blending silver halide emulsions of differing grain sizes. For example, silver bromo¬ iodide or silver bromides,of different sizes of the same type and shape can be blended. Any coupler known in the photographic art can be used with the silver bromoiodide emulsions as described. Examples of useful couplers are described in, for example, Research Disclosure Section VII, paragraphs D,E,F and G and in U.S. Patent 4,433,048 and the publications cited therein. The couplers can be incorporated as described in Research Disclosure Section VII and the publications cited therein.

The photographic emulsions and elements can contain addenda known to be useful in the photographic art. The photographic emulsions and elements can contain brighteners (Research Disclosure Section V), antifoggants and stabilizers (Research Disclosure Section VI), antistain agents and image dye stabilizers (Research Disclosure Section VII, paragraphs I and J), light absorbing and scattering materials (Research Disclosure Section VIII), hardeners (Research Disclosure Section X), coating aids (Research Disclosure Section XI), plasticizers and lubricants (Research Disclosure Section XII), antistatic agents (Research Disclosure Section XIII), matting agents (Research Disclosure Section XVI) and development modifiers (Research Disclosure Section XXI). The photographic elements can be coated on a variety of supports as described in Research Disclosure Section XVII and the references described therein.

The photographic elements can be exposed to actinic radiation, typically in the visible region of the spectrum, to form a latent image as described in Research Disclosure Section XVIII and then processed in a reversal process to form a visible image using process steps and processing compositions known in the photographic art. A reversal color photographic silver haloiodide element as described is typically processed in a color reversal photographic process, such as the E-6 process of Eastman Kodak Company, U.S.A. A typical reversal process in which the photographic element comprises dye—forming couplers includes developing the exposed element in a first black-and-white developer; washing the element in water; processing the resulting element in a reversal processing solution or reversal exposure; developing the resulting element in a color developer; and bleaching and fixing the element. A typical reversal process and processing compositions are described in Japanese Published Patent Application 63-264753 published November 1, 1988; The British Journal of Photography Annual. 1982. pages 201-203; and The British Journal of Photography Annual. 1977, pages 194-197. In case the dye-forming couplers are not in the photographic element but in at least one of the processing solutions, a process as described in, for example, U.S. Patent 2,252,718 can be used.

The following examples further illustrate the invention. Examples 1 - 3:

A 12 liter reaction vessel was charged with 4 liters of distilled water, 50 gm/1 of photographic gel (57o) and .1212 gm/1 of NaBr (0.00118N). The reactor was then adjusted to a pH of 3.0 at 40^βC.

The temperature of the reactor was raised to 80^βC and the vAg was adjusted with NaBr to 93.5 mv (pBr=2.947). An initial nuclei population was established using a five minute double jet precipitation with .5 N ANOg and .526 N NaBr delivered at a constant flow rate of 15 cc/minute while controlling at a vAg of 93.5 mv (pBr=2.947). The flow rate was then accelerated to 45 cc/minute over a period of 10 minutes while still maintaining vAg control. The precipitation was then interrupted and a change was made to 3.0 N growth AgN0₃ and a mixed halide solution (3.1 N) which was 6.8 mole percent KI. The precipitation was then continued (for 57.73 minutes) along an accelerated flow profile starting from 4 and ending at 86.6 cc/minute. At this time a bromide shell was applied by adjusting the vAg to +65mv with NaBr solution and growing at this vAg with 3.1 N NaBr for 12.21 minutes. The final flow rate was 104.0 cc/minute. At this time the temperature was lowered to 40°C and 200 gm of phthalated gelatin were added to effect a 2X iso wash. Final pH 6.2 pAg 8.2 . 11.5 moles of AgBrl (containing 4.4 mole percent I) were precipitated with 60 gm/mole of gelatin. The procedure was repeated to provide a series of core-shell emulsions: A (comparison) having a Vs of 0.67;

B (invention) (Example 1) having a Vs of 0.50; and, C (Invention) having a Vs of 0.31.

A cubic core—shell silver bromoiodide (Emulsion E) (Example 3) was prepared as follows: The core was precipitated by double—jet addition of 2.5 liters of 2.0M AgNOg and a 2.0M halide solution consisting of 0.159M KI and 1.841M NaBr into a kettle containing 7.5 liters deionized water, 2.25 g l,8-dihydroxy-3,6-dithia-octane and 240 g phthalated gelatin. The precipitation was carried out at 45°C at pAg controlled at 8.24 that corresponds to a pBr of 3.16. The AgN0~ flow was linearly accelerated from 40 to 81.24 cc/minute over 41.24 minutes . The final core-shell emulsion was prepared by double-jet precipitation onto the above described core. Conditions used were the same as those for the core except that a 2.0M NaBr solution replaced the solution of mixed NaBr and KI, and the AgN0~ flow was accelerated from 81 to 107.5 cc/minute over 26.5 ^•minutes . The emulsion was washed by conventional coagulation at pH 3.85.

Grain size by electron microscopy was 0.49 micron and the emulsion had a high degree of monodispersity. I- analysis by neutron activation gave 4.13 mole percent, within experimental error of the 4.0 aim, and x-ray powder diffraction indicated approximately equal amounts of 2 phases, 6.67, and 1.7% I-, suggesting that I- redistribution had occurred on shelling.

A second core-shell emulsion (Emulsion D) (comparative emulsion D) was prepared similarly except the core was precipitated with 1.25 liters of 2.0M AgN0₃ and a 2.0M halide solution consisting of 0.317M KI and 1.683M NaBr, and the AgN0₃ flow was accelerated linearly from 26 to 61.04 cc/minute over 28.72 minutes; and the shell was prepared with 3.75 liters of 2.0M AgN0₃ and about 3.8 liters 2.0M NaBr, the AgN0₃ being accelerated linearly from 51 to 104.52 cc/minute over 48.22 minutes. Grain size and width were the same as Emulsion E. I- was 4.0 mole percent and x-ray powder analysis indicated 2 phases, one at 12 and the other at 2 mole percent I-, again suggesting I- redistribution on shelling. The volume fraction of the shell of Emulsion D was 0.75. The volume fraction of the shell of Emulsion E was 0.50. Coating Format I

The silver haloiodide grains of Emulsions A, B and C described in the examples were coated on a cellulose triacetate support. The emulsion layer was comprised of octahedral silver haloiodide grains (0.807 g Ag/m²) and gelatin (3.23 g/m²) to which had been added the cyan-dye-forming coupler 2-[2,4-biε(1,1-dimethylpropyl)phenoxy]-N-{4-

[(2,2,3,3,4,4,4-heρtafluor-1-oxobutyl)amino]-3- hydroxyphenyl}-hexanamιde (2.69 g/m2 and

4-hydroxy-6-methyl-l,3,3a,7-tetraazaindene (1.75 g/Ag mole) .

Coating Format II The silver haloiodide grains of Emulsions D and E described in the examples were coated on a cellulose triacetate support. The emulsion layer was comprised of cubic silver haloiodide grains (1.08 g

Ag/m 2) and gelatin (3.23 g/m2) to which had been added the cyan dye forming coupler

2-[2,4-bis(1,l-dimethylpropyl)phenoxy]-N-{4-

[(2,2,3,3,4,4,4-heptafluor-1-oxobutyl)amino]-3-

2 hydroxyphenyl}-hexanamιde (2.69 g/m and

4-hydroxy-6-methyl-l,3,3a,7—tetraazaindene (1.75 g/Ag mole).

The resulting photographic films were exposed through a 0—3.0 density step tablet to a 5500K tungsten light source on a commercial sensitometer. Examples A, 1 and 2 were exposed for 1/10 second and examples B and 3 were exposed for 2 seconds. Processing was for 4 minutes in the KODAK E-6 process First Developer, followed by the rest of the E-6 process, as described in the British Journal of Photography Annual. 1977, pages 194-197. (KODAK is a trademark of Eastman Kodak Company, U.S.A.) The standard deviation of the density fluctuations of a uniformly exposed and developed patch of each photographic film was measured with a 48 micron diameter circular aperture, as described in James, The Theory of the Photographic Process. 4th Edition, MacMillan, 1977, Chapter 21. This standard deviation will be referred to as the RMS granularity. For the purposes of comparison, the RMS granularities were measured for all of the above coatings at an optical density of 1.0.

Comp. B D 4.0 0.75 0.19

(Comparison)

3 E 4.0 0.50 0.13 (Invention)

Comp. C D 4.0 0.75 0.19

(Comparison)

E 4.0 0.50 0.13

(Comparison)

In comparative example A, lower granularity numbers for emulsions B and C compared to emulsion A illustrate the improved granularity provided by the invention. When the A value of the emulsion is less than 0.15 ± 0.05, significant improvements in granularity are observed. The lower granularity number of emulsion E compared to emulsion D in comparative example B also illustrates the improved granularity provided by the invention. The advantage provided by this invention is only apparent when the emulsions are developed in a reversal process in which the black-and-white developer contains silver halide solvents, such as the E6 process. When the silver halide solvents are not present, as illustrated in comparative, example C, then no distinction is made between the two emulsions The processing for examples C (no solvent case) is relevant because'color negative development (such as conventional C—41 developer) is a low solvent developer.

The examples in the above table that use no solvent (example C) are processed in the same E-6 process as the other examples with the exception that potassium sulfite and sodium thiocyanate (two silver halide solvents that are typically present in the first developer of the E—6 process) are not included in the composition of the first developer of the E-6 process .

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

Claims

WHAT IS CLAIMED IS:

1. A photographic silver halide emulsion comprising a dispersing medium and photographic silver haloiodide that (a) is a negative—working, core—shell silver haloiodide;

(b) contains total iodide within the range of 0.5 to 8 mole percent; and

(c) wherein the silver haloiodide has a volume fraction of the shell (V ) that is greater than 0.05 but less than or equal to a constant (A) times the total iodide in mole percent (I. ) wherein A is a unitless parameter equal to 0.15 plus or minus 0.05; wherein upon exposure and two—step reversal processing of a photographic silver halide element comprising the emulsion a decrease in granularity is produced.

2. A photographic 'silver haloiodide emulsion as in claim 1 wherein the silver haloiodide is silver bromoiodide.

3. A photographic silver haloiodide emulsion as in claim 1 wherein the silver haloiodide comprises octahedral silver bromoiodide grains.

4. A photographic silver haloiodide emulsion as in claim 1 Wherein the silver haloiodide has an average grain size within the range of 1.0 to 0.3 microns.

5. A photographic silver haloiodide emulsion as in claim l*^** wherein the silver haloiodide is silver bromoiodide containing total iodide within the range of 2 to 6 mole percent.

6. A photographic silver haloiodide emulsion as in claim 1 wherein the dispersing medium is gelatin or a gelatin derivative.

7. A reversal photographic silver halide element comprising a support bearing at least one photographic silver halide emulsion layer comprising a photographic silver haloiodide emulsion as defined in claim 1.

8. A reversal photographic silver halide element as in claim 7 that is a color reversal photographic silver halide element.

9. A reversal multicolor photographic silver halide element comprising a support bearing emulsion layers for separately recording blue, green and red light wherein at least one of the layers comprises a photographic silver haloiodide emulsion as defined in claim 1.

10. A reversal multicolor photographic silver halide element as in claim 9 comprising at least one blue-sensitive layer containing at least one yellow dye image—forming coupler, at least one green-sensitive layer containing at least one magenta dye image—forming coupler, and at least one red-sensitive layer containing at least one cyan dye image-forming coupler.

11. A reversal process for forming an image in an exposed reversal photographic silver halide element as defined in claim 7 comprising, in sequence, developing the element in a first black-and—white developer; washing the element in water; processing the resulting element in a reversal processing solution to render unexposed silver halide developable; developing the resulting element in a color developer; and, bleaching and fixing the element.

12. A reversal process for forming an image in an exposed reversal photographic silver halide element as defined in claim 10 comprising, in sequence, developing the element in a first black-ahd-white developer; washing the element in water; processing the resulting element in a reversal processing solution; developing the resulting element in a color developer; and, bleaching and fixing the elemen .