Small 3D emulsions with enhanced photographic response

Abstract

 A silver halide photographic element comprises at least one silver halide emulsion layer comprising 3D emulsion grains having an equivalent spherical diameter of less than or equal to 0.35 µm and said layer further comprises a fragmentable electron donor compound of the formula X-Y' or a compound which contains a moiety of the formula -X-Y'; wherein

X is an electron donor moiety, Y' is a leaving proton H or a leaving group Y, with the proviso that if Y' is a proton, a base, β^-, is covalently linked directly or indirectly to X, and wherein:

1) X-Y' has an oxidation potential between 0 and about 1.4 V; and

2) the oxidized form of X-Y' undergoes a bond cleavage reaction to give the radical X* and the leaving fragment Y'; and

3) the radical X* has an oxidation potential ≤-0.7V (that is, equal to or more negative than about -0.7V).

Description

[0001] This invention relates to the use of a fragmentable two electron donor with light-sensitive, nontabular silver halide emulsions having equivalent spherical diameters less than or equal to 0.35 µm..

[0002] Fragmentable two electron donors are compounds that have been designed to undergo a bond fragmentation reaction after capturing the photohole created by absorption of light in a silver halide emulsion. The radical resulting from this bond fragmentation reaction is designed to be sufficiently energetic so as to inject an electron into the silver halide emulsion. Consequently, absorption of one photon by a silver halide emulsion containing a fragmentable two electron donor results in creation of two electrons in the silver halide emulsion, the first resulting from the initial absorption of the photon and the second resulting from the sequence of reactions caused by capture of the photohole at the fragmentable two electron donor. The production of this second electron leads to increased photographic speed. Fragmentable two electron donors have been described in U.S. Patents Nos. 5,747,235, 5,747,236, 5,994,051, and 6,010,841, and published European Patent Applications 893,731 and 893,732. These references disclose speed gains associated with the use of fragmentable two-electron donors in a wide variety of silver halide emulsions. However, it is also frequently found that addition of a fragmentable two-electron donor to an emulsion increases the fog, so that it becomes necessary to limit the amount of fragmentable two-electron donor used in order to avoid excessive fog. In such cases, the extent of practical speed gain obtainable from the fragmentable two-electron donor may be reduced.

[0003] Small 3D emulsions (i.e. nontabular emulsions with equivalent spherical diameters (ESD) < 0.35 µm) are particularly useful in photographic elements where excellent image structure is required. These emulsions offer low granularity owing to their small volume and high sharpness (acutance) owing to their reduced propensity to scatter light. Consequently, such emulsions are frequently used as slow components in camera-speed color negative multilayer films. They are also used to supply most of the range of emulsions, fast to slow, required for duplicating films used in photo labs and the motion picture industry. Such emulsions are also useful in microfilm. However, the small size of the emulsions limits the speed of photographic materials based on these emulsions. Higher speed at small grain size would allow shorter exposure times and/or lower intensity exposures which could be translated into improved throughput in high speed film printers or lower cost exposure sources.

[0004] There is a need to find emulsions that have a reduced propensity for fog in the presence of fragmentable two-electron donors. In addition, methods for improving the speed of small 3D emulsions are desirable.

[0005] One aspect of this invention comprises a silver halide photographic element comprising at least one silver halide emulsion layer comprising 3D emulsion grains having an equivalent spherical diameter of less than or equal to 0.35 µm and said layer further comprises a fragmentable electron donor compound of the formula X-Y' or a compound which contains a moiety of the formula -X-Y'; wherein
   X is an electron donor moiety, Y' is a leaving proton H or a leaving group Y, with the proviso that if Y' is a proton, a base, β^-, is covalently linked directly or indirectly to X, and wherein:

1) X-Y' has an oxidation potential between 0 and about 1.4 V; and

2) the oxidized form of X-Y' undergoes a bond cleavage reaction to give the radical X^• and the leaving fragment Y'; and

3) the radical X^• has an oxidation potential <-0.7V (that is, equal to or more negative than about -0.7V).

[0006] This invention provides 3D emulsions of small size with enhanced photographic speed. Such emulsions are particularly useful in photographic elements where excellent image structure (i.e. low granularity and high sharpness) is required.

[0007] We have unexpectedly found that application of fragmentable two-electron donors to small (less than 0.35 µm equivalent spherical diameter) 3D emulsions can yield substantial speed without egregious accompanying fog. A 3D emulsion is one in which at least 50 percent of total grain projected area is accounted for by 3D grains. As used herein, the term "3D grain" refers to nontabular morphologies, for example cubes, octahedra, rods and spherical grains, and to tabular grains having an aspect ratio of less than 2. In our experiments, emulsion size has been measured by turbidimetric techniques as described in Particle Characterization, vol. 2, pages 14-19, 1985. The measurement yields an equivalent spherical volume/turbidity mean diameter. These measurements will be described herein as "equivalent spherical diameters" or ESD. Particles having morphologies other than spherical will be related to this measurement by having a volume equivalent to a sphere having a diameter equal to the ESD. Emulsions with ESD's less than or equal to 0.25 µm are preferred for our invention and emulsions with ESD's less than or equal to 0.15 µm are particularly preferred. High acutance and low graininess associated with these small 3D emulsions are much sought after for slow record components in camera-speed films, for all the components in a duplicating film, and in microfilms.

[0008] In the following discussion of silver halide emulsions and their preparation, reference will be made to Research Disclosure, September 1996, Number 389, Item 38957, which will be identified hereafter by the term "Research Disclosure I." This and all other Research Disclosures referenced herein are published by Kenneth Mason Publications, Ltd., Dudley Annex, 12a North Street, Emsworth, Hampshire P010 7DQ, ENGLAND. The Sections hereafter referred to are Sections of the Research Disclosure I unless otherwise indicated.

[0009] The silver halide emulsions employed in the photographic elements of the present invention may be negative-working, such as surface-sensitive emulsions or unfogged internal latent image forming emulsions, or positive working emulsions of the internal latent image forming type (that are fogged during processing). Suitable emulsions and their preparation as well as methods of chemical and spectral sensitization are described in Research Disclosure I, Sections I through V. Color materials and development modifiers are described in Sections V through XX. Vehicles which can be used in the photographic elements are described in Section II, and various additives such as brighteners, antifoggants, stabilizers, light absorbing and scattering materials, hardeners, coating aids, plasticizers, lubricants and matting agents are described, for example, in Sections VI through XIII. Manufacturing methods are described in all of the sections, layer arrangements particularly in Section XI, exposure alternatives in Section XVI, and processing methods and agents in Sections XIX and XX.

[0010] With negative working silver halide a negative image can be formed. Optionally a positive (or reversal) image can be formed although a negative image is typically first formed.

[0011] The morphology of the 3D silver halide grains may be octahedral, cubic, or polymorphic. Emulsions with cubic morphology are preferred. The silver halide used in the photographic elements may be silver iodobromide, silver bromide, silver chloride, silver chlorobromide, silver iodochloride, silver iodobromochloride, and the like. Silver bromide or silver iodobromide emulsions are preferred and silver iodobromide emulsions are particularly preferred. In referring to silver halide grains containing two or more halides, the halides are named in their order of ascending concentrations.

[0012] The silver halide grains to be used in the invention may be prepared according to methods known in the art, such as those described in Research Disclosure I and James, The Theory of the Photographic Process. These include methods such as ammoniacal emulsion making, neutral or acidic emulsion making, and others known in the art. These methods generally involve mixing a water soluble silver salt with a water soluble halide salt in the presence of a protective colloid, and controlling the temperature, pAg, pH values, etc, at suitable values during formation of the silver halide by precipitation.

[0013] In the course of grain precipitation one or more dopants (grain occlusions other than silver and halide) can be introduced to modify grain properties. For example, any of the various conventional dopants disclosed in Research Disclosure I, Section I. Emulsion grains and their preparation, subsection G. Grain modifying conditions and adjustments, paragraphs (3), (4) and (5), can be present in the emulsions of the invention. In addition it is specifically contemplated to dope the grains with transition metal hexacoordination complexes containing one or more organic ligands, as taught by Olm et al U.S. Patent 5,360,712.

[0014] It is specifically contemplated to incorporate in the face centered cubic crystal lattice of the grains a dopant capable of increasing imaging speed by forming a shallow electron trap (hereinafter also referred to as a SET) as discussed in Research Disclosure Item 36736 published November 1994.

[0015] The SET dopants are effective at any location within the grains. Generally better results are obtained when the SET dopant is incorporated in the exterior 50 percent of the grain, based on silver. An optimum grain region for SET incorporation is that formed by silver ranging from 50 to 85 percent of total silver forming the grains. The SET can be introduced all at once or run into the reaction vessel over a period of time while grain precipitation is continuing. Generally SET forming dopants are contemplated to be incorporated in concentrations of at least 1 X 10^-7 mole per silver mole up to their solubility limit, typically up to about 5 X 10^-4 mole per silver mole.

[0016] SET dopants are known to be effective to reduce reciprocity failure. In particular the use of iridium hexacoordination complexes or Ir⁺⁴ complexes as SET dopants is advantageous.

[0017] Iridium dopants that are ineffective to provide shallow electron traps (non-SET dopants) can also be incorporated into the grains of the silver halide grain emulsions to reduce reciprocity failure.

[0018] To be effective for reciprocity improvement the Ir can be present at any location within the grain structure. A preferred location within the grain structure for Ir dopants to produce reciprocity improvement is in the region of the grains formed after the first 60 percent and before the final 1 percent (most preferably before the final 3 percent) of total silver forming the grains has been precipitated. The dopant can be introduced all at once or run into the reaction vessel over a period of time while grain precipitation is continuing. Generally reciprocity improving non-SET Ir dopants are contemplated to be incorporated at their lowest effective concentrations.

[0019] The contrast of the photographic element of can be further increased by doping the grains with a hexacoordination complex containing a nitrosyl or thionitrosyl ligand (NZ dopants) as disclosed in McDugle et al U.S. Patent 4,933,272.

[0020] The contrast increasing dopants can be incorporated in the grain structure at any convenient location. However, if the NZ dopant is present at the surface of the grain, it can reduce the sensitivity of the grains. It is therefore preferred that the NZ dopants be located in the grain so that they are separated from the grain surface by at least 1 percent (most preferably at least 3 percent) of the total silver precipitated in forming the silver iodochloride grains. Preferred contrast enhancing concentrations of the NZ dopants range from 1 X 10^-11 to 4 X 10^-8 mole per silver mole, with specifically preferred concentrations being in the range from 10^-10 to 10^-8 mole per silver mole.

[0021] Although generally preferred concentration ranges for the various SET, non-SET Ir and NZ dopants have been set out above, it is recognized that specific optimum concentration ranges within these general ranges can be identified for specific applications by routine testing. It is specifically contemplated to employ the SET, non-SET Ir and NZ dopants singly or in combination. For example, grains containing a combination of an SET dopant and a non-SET Ir dopant are specifically contemplated. Similarly SET and NZ dopants can be employed in combination. Also NZ and Ir dopants that are not SET dopants can be employed in combination. Finally, the combination of a non-SET Ir dopant with a SET dopant and an NZ dopant. For this latter three-way combination of dopants it is generally most convenient in terms of precipitation to incorporate the NZ dopant first, followed by the SET dopant, with the non-SET Ir dopant incorporated last.

[0022] The photographic elements of the present invention, as is typical, provide the silver halide in the form of an emulsion. Photographic emulsions generally include a vehicle for coating the emulsion as a layer of a photographic element. Useful vehicles include both naturally occurring substances such as proteins, protein derivatives, cellulose derivatives (e.g., cellulose esters), gelatin (e.g., alkali-treated gelatin such as cattle bone or hide gelatin, or acid treated gelatin such as pigskin gelatin), deionized gelatin, gelatin derivatives (e.g., acetylated gelatin, phthalated gelatin, and the like), and others as described in Research Disclosure I. Also useful as vehicles or vehicle extenders are hydrophilic water-permeable colloids. These include synthetic polymeric peptizers, carriers, and/or binders such as poly(vinyl alcohol), poly(vinyl lactams), acrylamide polymers, polyvinyl acetals, polymers of alkyl and sulfoalkyl acrylates and methacrylates, hydrolyzed polyvinyl acetates, polyamides, polyvinyl pyridine, methacrylamide copolymers, and the like, as described in Research Disclosure I. The vehicle can be present in the emulsion in any amount useful in photographic emulsions. The emulsion can also include any of the addenda known to be useful in photographic emulsions.

[0023] The silver halide to be used in the invention may be advantageously subjected to chemical sensitization. Compounds and techniques useful for chemical sensitization of silver halide are known in the art and described in Research Disclosure I and the references cited therein. Compounds useful as chemical sensitizers, include, for example, active gelatin, sulfur, selenium, tellurium, gold, platinum, palladium, iridium, osmium, rhenium, phosphorous, or combinations thereof. Chemical sensitization is generally carried out at pAg levels of from 5 to 10, pH levels of from 4 to 8, and temperatures of from 30 to 80°C, as described in Research Disclosure I, Section IV (pages 510-511).

[0024] The silver halide may be sensitized by sensitizing dyes by any method known in the art, such as described in Research Disclosure I. The dye may be added to an emulsion of the silver halide grains and a hydrophilic colloid at any time prior to (e.g., during or after chemical sensitization) or simultaneous with the coating of the emulsion on a photographic element. The dyes may, for example, be added as a solution in water or an alcohol. The dye/silver halide emulsion may be mixed with a dispersion of color image-forming coupler immediately before coating or in advance of coating (for example, 2 hours). Typical sensitizing for use with fragmentable electron donors are described in U.S. Patent No. 5,747,236.

[0025] In accordance with this invention the silver halide emulsion contains a fragmentable electron donating (FED) compound which enhances the sensitivity of the emulsion. The fragmentable electron donating compound is of the formula X-Y' or a compound which contains a moiety of the formula -X-Y'; wherein
   X is an electron donor moiety, Y' is a leaving proton H or a leaving group Y, with the proviso that if Y' is a proton, a base, β^-, is covalently linked directly or indirectly to X, and wherein:

1) X-Y' has an oxidation potential between 0 and about 1.4 V; and

2) the oxidized form of X-Y' undergoes a bond cleavage reaction to give the radical X^• and the leaving fragment Y';
   and, optionally,

3) the radical X^• has an oxidation potential ≤-0.7V (that is, equal to or more negative than about -0.7V).

[0026] Compounds wherein X-Y' meets criteria (1) and (2) but not (3) are capable of donating one electron and are referred to herein as fragmentable one-electron donating compounds. Compounds which meet all three criteria are capable of donating two electrons and are referred to herein as fragmentable two-electron donating compounds.

[0027] In this patent application, oxidation potentials are reported as "V" which represents "volts versus a saturated calomel reference electrode".

[0028] In embodiments of the invention in which Y' is Y, the following represents the reactions that are believed to take place when X-Y undergoes oxidation and fragmentation to produce a radical X^•, which in a preferred embodiment undergoes further oxidation.

where E₁ is the oxidation potential of X-Y and E₂ is the oxidation potential of the radical X^•.

[0029] E₁ is preferably no higher than about 1.4 V and preferably less than about 1.0 V. The oxidation potential is preferably greater than 0, more preferably greater than about 0.3 V. E₁ is preferably in the range of about 0 to about 1.4 V, and more preferably from about 0.3 V to about 1.0 V.

[0030] In certain embodiments of the invention the oxidation potential, E₂, of the radical X^• is equal to or more negative than -0.7V, preferably more negative than about - 0.9 V. E₂ is preferably in the range of from about -0.7 to about -2 V, more preferably from about -0.8 to about -2 V and most preferably from about-0.9 to about -1.6 V.

[0031] The structural features of X-Y are defined by the characteristics of the two parts, namely the fragment X and the fragment Y. The structural features of the fragment X determine the oxidation potential of the X-Y molecule and that of the radical X^•, whereas both the X and Y fragments affect the fragmentation rate of the oxidized molecule X-Y^•+.

[0032] In embodiments of the invention in which Y' is H, the following represents the reactions believed to take place when the compound X-H undergoes oxidation and deprotonation to the base, β^-, to produce a radical X^•, which in a preferred embodiment undergoes further oxidation.

[0033] Preferred X groups are of the general formula:





or

The symbol "R" (that is R without a subscript) is used in all structural formulae in this patent application to represent a hydrogen atom or an unsubstituted or substituted alkyl group. In structure (I):

m = 0, 1;

Z = O, S, Se, Te;

Ar = aryl group (e.g., phenyl, naphthyl, phenanthryl, anthryl); or heterocyclic group (e.g., pyridine, indole, benzimidazole, thiazole, benzothiazole, thiadiazole, etc.);

R₁ = R, carboxyl, amide, sulfonamide, halogen, NR₂, (OH)_n, (OR')_n, or (SR)_n;

R' = alkyl or substituted alkyl;

n = 1-3;

R₂ = R, Ar';

R₃ = R, Ar';

R₂ and R₃ together can form 5- to 8-membered ring;

R₂ and Ar = can be linked to form 5- to 8-membered ring;

R₃ and Ar = can be linked to form 5- to 8-membered ring;

Ar' = aryl group such as phenyl, substituted phenyl, or heterocyclic group (e.g., pyridine, benzothiazole, etc.)

R = a hydrogen atom or an unsubstituted or substituted alkyl group.

In structure (II):

Ar = aryl group (e.g., phenyl, naphthyl, phenanthryl); or heterocyclic group (e.g., pyridine, benzothiazole, etc.);

R₄ = a substituent having a Hammett sigma value of -1 to +1, preferably -0.7 to +0.7, e.g., R, OR, SR, halogen, CHO, C(O)R, COOR, CONR₂, SO₃R, SO₂NR₂, SO₂R, SOR, C(S)R, etc;

R₅ = R, Ar'

R₆ and R₇ = R, Ar'

R₅ and Ar = can be linked to form 5- to 8-membered ring;

R₆ and Ar = can be linked to form 5- to 8-membered ring (in which case, R₆ can be a hetero atom);

R₅ and R₆ can be linked to form 5- to 8-membered ring;

R₆ and R₇ can be linked to form 5- to 8-membered ring;

Ar' = aryl group such as phenyl, substituted phenyl, heterocyclic group;

R = hydrogen atom or an unsubstituted or substituted alkyl group.

A discussion on Hammett sigma values can be found in C. Hansch and R. W. Taft Chem. Rev. Vol 91, (1991) p 165.
In structure (III):

W = O, S, Se;

Ar = aryl group (e.g., phenyl, naphthyl, phenanthryl, anthryl); or heterocyclic group (e.g., indole, benzimidazole, etc.)

R₈ = R, carboxyl, NR₂, (OR)_n, or (SR)_n (n = 1-3);

R₉ and R₁₀ = R, Ar';

R₉ and Ar = can be linked to form 5- to 8-membered ring;

Ar' = aryl group such as phenyl substituted phenyl or heterocyclic group;

R = a hydrogen atom or an unsubstituted or substituted alkyl group.

In structure (IV):
"ring" represents a substituted or unsubstituted 5-, 6- or 7-membered unsaturated ring, preferably a heterocyclic ring.

[0034] The following are illustrative examples of the group X of the general structure I:

[0035] In the structures of this patent application a designation such as-OR (NR₂) indicates that either -OR or -NR₂ can be present.

[0036] The following are illustrative examples of the group X of general structure II:









Z₁ = a covalent bond, S, O, Se, NR, CR₂, CR=CR, or CH₂CH₂.

Z₂ = S, O, Se, NR, CR₂, CR=CR, R₁₃, = alkyl, substituted alkyl or aryl, and
R₁₄ = H, alkyl substituted alkyl or aryl.

[0037] The following are illustrative examples of the group X of the general structure III:



n = 1-3

[0038] The following are illustrative examples of the group X of the general structure IV:

Z₃ = O, S, Se, NR

R₁₅ = R, OR, NR₂

R₁₆ = alkyl, substituted alkyl

[0039] Preferred Y' groups are:

(1) X', where X' is an X group as defined in structures I-IV and may be the same as or different from the X group to which it is attached

(2)

(3)

   where M = Si, Sn or Ge; and R' = alkyl or substituted alkyl

(4)

   where Ar" = aryl or substituted aryl

(5)

[0040] In preferred embodiments of this invention Y' is -H, -COO- or -Si(R')₃ or-X'. Particularly preferred Y' groups are -H, -COO^- or -Si(R')₃.

[0041] In embodiments of the invention in which Y'is a proton, a base, β^-, is covalently linked directly or indirectly to X. The base is preferably the conjugate base of an acid of pKa between about 1 and about 8, preferably about 2 to about 7. Collections of pKa values are available (see, for example: Dissociation Constants of Organic Bases in Aqueous Solution, D. D. Perrin (Butterworths, London, 1965); CRC Handbook of Chemistry and Physics, 77th ed, D. R. Lide (CRC Press, Boca Raton, Fl, 1996)). Examples of useful bases are included in Table I.

[0042] Preferably the base, β^- is a carboxylate, sulfate or amine oxide.

[0043] In some embodiments of the invention, the fragmentable electron donating compound contains a light absorbing group, Z, which is attached directly or indirectly to X, a silver halide absorptive group, A, directly or indirectly attached to X, or a chromophore forming group, Q, which is attached to X. Such fragmentable electron donating compounds are preferably of the following formulae:

        Z-(L-X-Y')_k



        A-(L-X-Y')_k



        (A-L)_k-X-Y'



        Q-X-Y'



        A-(X-Y')_k



        (A)_k-X-Y'



        Z-(X-Y')_k

   Or

        (Z)_k -X-Y'

Z is a light absorbing group;

k is 1 or 2;

A is a silver halide adsorptive group that preferably contains at least one atom of N, S, P, Se, or Te that promotes adsorption to silver halide;

L represents a linking group containing at least one C, N, S, P or O atom; and

Q represents the atoms necessary to form a chromophore comprising an amidinium-ion, a carboxyl-ion or dipolar-amidic chromophoric system when conjugated with X-Y'.

[0044] Z is a light absorbing group including, for example, cyanine dyes, complex cyanine dyes, merocyanine dyes, complex merocyanine dyes, homopolar cyanine dyes, styryl dyes, oxonol dyes, hemioxonol dyes, and hemicyanine dyes.

[0045] Preferred Z groups are derived from the following dyes:













and

[0046] The linking group L may be attached to the dye at one (or more) of the heteroatoms, at one (or more) of the aromatic or heterocyclic rings, or at one (or more) of the atoms of the polymethine chain, at one (or more) of the heteroatoms, at one (or more) of the aromatic or heterocyclic rings, or at one (or more) of the atoms of the polymethine chain. For simplicity, and because of the multiple possible attachment sites, the attachment of the L group is not specifically indicated in the generic structures.

[0047] The silver halide adsorptive group A is preferably a silver-ion ligand moiety or a cationic surfactant moiety. In preferred embodiments, A is selected from the group consisting of: i) sulfur acids and their Se and Te analogs, ii) nitrogen acids, iii) thioethers and their Se and Te analogs, iv) phosphines, v) thionamides, selenamides, and telluramides, and vi) carbon acids.

[0048] Illustrative A groups include:







        -CH₂CH₂SH

and

[0049] The point of attachment of the linking group L to the silver halide adsorptive group A will vary depending on the structure of the adsorptive group, and may be at one (or more) of the heteroatoms, at one (or more) of the aromatic or heterocyclic rings.

[0050] The linkage group represented by L which connects the light absorbing group to the fragmentable electron donating group XY by a covalent bond is preferably an organic linking group containing a least one C, N, S, or O atom. It is also desired that the linking group not be completely aromatic or unsaturated, so that a pi-conjugation system cannot exist between the Z and XY moieties. Preferred examples of the linkage group include, an alkylene group, an arylene group, -O-, -S-, -C=O, -SO₂-, -NH-, -P=O, and -N=. Each of these linking components can be optionally substituted and can be used alone or in combination. Examples of preferred combinations of these groups are:

where c = 1-30, and d = 1-10

[0051] The length of the linkage group can be limited to a single atom or can be much longer, for instance up to 30 atoms in length. A preferred length is from about 2 to 20 atoms, and most preferred is 3 to 10 atoms. Some preferred examples of L can be represented by the general formulae indicated below:





e and f = 1-30, with the proviso that e + f < 31

[0052] Q represents the atoms necessary to form a chromophore comprising an amidinium-ion, a carboxyl-ion or dipolar-amidic chromophoric system when conjugated with X-Y'. Preferably the chromophoric system is of the type generally found in cyanine, complex cyanine, hemicyanine, merocyanine, and complex merocyanine dyes as described in F. M. Hamer, The Cyanine Dyes and Related Compounds (Interscience Publishers, New York, 1964).

[0053] Illustrative Q groups include:

[0054] Particularly preferred are Q groups of the formula:

wherein:

X₂ is O, S, N, or C(R₁₉)₂, where R₁₉ is substituted or unsubstituted alkyl.

each R₁₇ is independently a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, or substituted or unsubstituted aryl group;

a is an integer of 1-4;
and

R₁₈ is substituted or unsubstituted alkyl, or substituted or unsubstituted aryl.

[0055] Illustrative fragmentable electron donating compounds include:

[0056] The fragmentable electron donors of the present invention can be included in a silver halide emulsion by direct dispersion in the emulsion, or they may be dissolved in a solvent such as water, methanol or ethanol for example, or in a mixture of such solvents, and the resulting solution can be added to the emulsion. The compounds of the present invention may also be added from solutions containing a base and/or surfactants, or may be incorporated into aqueous slurries or gelatin dispersions and then added to the emulsion. The fragmentable electron donor may be used as the sole sensitizer in the emulsion. However, in preferred embodiments of the invention a sensitizing dye is also added to the emulsion. The compounds can be added before, during or after the addition of the sensitizing dye. The amount of electron donor which is employed in this invention may range from as little as 1 x 10^-8 mole per mole of silver in the emulsion to as much as about 0.1 mole per mole of silver, preferably from about 5 x 10^-7 to about 0.05 mole per mole of silver. Where the oxidation potential E₁ for the XY moiety of the electron donating sensitizer is a relatively low potential, it is more active, and relatively less agent need be employed. Conversely, where the oxidation potential for the XY moiety of the electron donating sensitizer is relatively high, a larger amount thereof, per mole of silver, is employed. In addition, for XY moieties that have silver halide adsorptive groups A or light absorptive groups Z or chromophoric groups Q directly or indirectly attached to X, the fragmentable electron donating sensitizer is more closely associated with the silver halide grain and relatively less agent need be employed. For fragmentable one-electron donors relatively larger amounts per mole of silver are also employed. Although it is preferred that the fragmentable electron donor be added to the silver halide emulsion prior to manufacture of the coating, in certain instances, the electron donor can also be incorporated into the emulsion after exposure by way of a pre-developer bath or by way of the developer bath itself.

[0057] Fragmentable electron donating compounds are described more fully in U.S. Patents 5,747,235, 5,747,236, 5,994,051, and 6,010,841, and published European Patent Applications 893,731 and 893,732.

[0058] Various compounds may be added to the photographic material of the present invention for the purpose of lowering the fogging of the material during manufacture, storage, or processing. Typical antifoggants are discussed in Section VI of Research Disclosure I, for example tetraazaindenes, mercaptotetrazoles, polyhydroxybenzenes, hydroxyaminobenzenes, combinations of a thiosulfonate and a sulfinate, and the like.

[0059] For this invention, polyhydroxybenzene and hydroxyaminobenzene compounds (hereinafter "hydroxybenzene compounds") are preferred as they are effective for lowering fog without decreasing the emulsion sensitvity. Examples of hydroxybenzene compounds are:

[0060] In these formulae, V and V' each independently represent -H, -OH, a halogen atom, -OM (M is alkali metal ion), an alkyl group, a phenyl group, an amino group, a carbonyl group, a sulfone group, a sulfonated phenyl group, a sulfonated alkyl group, a sulfonated amino group, a carboxyphenyl group, a carboxyalkyl group, a carboxyamino group, a hydroxyphenyl group, a hydroxyalkyl group, an alkylether group, an alkylphenyl group, an alkylthioether group, or a phenylthioether group.

[0061] More preferably, they each independently represent -H, -OH, -Cl, -Br,-COOH, -CH₂CH₂COOH, -CH₃, -CH₂CH₃, -C(CH₃)₃, -OCH₃, -CHO, -SO₃K,-SO₃Na, -SO₃H, -SCH₃, or -phenyl.

[0062] Especially preferred hydroxybenzene compounds follow:

[0063] Hydroxybenzene compounds may be added to the emulsion layers or any other layers constituting the photographic material of the present invention. The preferred amount added is from 1 x 10^-3 to 1 x 10^-1 mol, and more preferred is 1 x 10^-3 to 2 x 10^-2 mol, per mol of silver halide.

[0064] The emulsion layer of the photographic element of the invention can comprise any one or more of the light sensitive layers of the photographic element. The photographic elements made in accordance with the present invention can be black and white elements, single color elements or multicolor elements. Multicolor elements contain dye image-forming units sensitive to each of the three primary regions of the spectrum. Each unit can be comprised of a single emulsion layer or of multiple emulsion layers sensitive to a given region of the spectrum. The layers of the element, including the layers of the image-forming units, can be arranged in various orders as known in the art. In an alternative format, the emulsions sensitive to each of the three primary regions of the spectrum can be disposed as a single segmented layer.

[0065] A typical multicolor photographic element comprises a support bearing a cyan dye image-forming unit comprised of at least one red-sensitive silver halide emulsion layer having associated therewith at least one cyan dye-forming coupler, a magenta dye image-forming unit comprising at least one green-sensitive silver halide emulsion layer having associated therewith at least one magenta dye-forming coupler, and a yellow dye image-forming unit comprising at least one blue-sensitive silver halide emulsion layer having associated therewith at least one yellow dye-forming coupler. The element can contain additional layers, such as filter layers, interlayers, overcoat layers, subbing layers, and the like. All of these can be coated on a support which can be transparent or reflective (for example, a paper support).

[0066] Photographic elements of the present invention may also usefully include a magnetic recording material as described in Research Disclosure, Item 34390, November 1992, or a transparent magnetic recording layer such as a layer containing magnetic particles on the underside of a transparent support as in US 4,279,945 and US 4,302,523. The element typically will have a total thickness (excluding the support) of from 5 to 30 microns. While the order of the color sensitive layers can be varied, they will normally be red-sensitive, green-sensitive and blue-sensitive, in that order on a transparent support, (that is, blue sensitive furthest from the support) and the reverse order on a reflective support being typical.

[0067] The present invention also contemplates the use of photographic elements of the present invention in what are often referred to as single use cameras (or "film with lens" units). These cameras are sold with film preloaded in them and the entire camera is returned to a processor with the exposed film remaining inside the camera. Such cameras may have glass or plastic lenses through which the photographic element is exposed.

[0068] The photographic elements of the present invention may also use colored couplers (e.g. to adjust levels of interlayer correction) and masking couplers such as those described in EP 213 490; Japanese Published Application 58-172,647; U.S. Patent 2,983,608; German Application DE 2,706,117C; U.K. Patent 1,530,272; Japanese Application A-113935; U.S. Patent 4,070,191 and German Application DE 2,643,965. The masking couplers may be shifted or blocked.

[0069] The photographic elements may also contain materials that accelerate or otherwise modify the processing steps of bleaching or fixing to improve the quality of the image. Bleach accelerators described in EP 193 389; EP 301 477; U.S. 4,163,669; U.S. 4,865,956; and U.S. 4,923,784 are particularly useful. Also contemplated is the use of nucleating agents, development accelerators or their precursors (UK Patent 2,097,140; U.K. Patent 2,131,188); development inhibitors and their precursors (U.S. Patent No. 5,460,932; U.S. Patent No. 5,478,711); electron transfer agents (U.S. 4,859,578; U.S. 4,912,025); antifogging and anti color-mixing agents such as derivatives of hydroquinones, aminophenols, amines, gallic acid; catechol; ascorbic acid; hydrazides; sulfonamidophenols; and non color-forming couplers.

[0070] The elements may also contain filter dye layers comprising colloidal silver sol or yellow and/or magenta filter dyes and/or antihalation dyes (particularly in an undercoat beneath all light sensitive layers or in the side of the support opposite that on which all light sensitive layers are located) either as oil-in-water dispersions, latex dispersions or as solid particle dispersions. Additionally, they may be used with "smearing" couplers (e.g. as described in U.S. 4,366,237; EP 096 570; U.S. 4,420,556; and U.S. 4,543,323.) Also, the couplers may be blocked or coated in protected form as described, for example, in Japanese Application 61/258,249 or U.S. 5,019,492.

[0071] The photographic elements may further contain other image-modifying compounds such as "Development Inhibitor-Releasing" compounds (DIR's). Useful additional DIR's for elements of the present invention, are known in the art and examples are described in U.S. Patent Nos. 3,137,578; 3,148,022; 3,148,062; 3,227,554; 3,384,657; 3,379,529; 3,615,506; 3,617,291; 3,620,746; 3,701,783; 3,733,201; 4,049,455; 4,095,984; 4,126,459; 4,149,886; 4,150,228; 4,211,562; 4,248,962; 4,259,437; 4,362,878; 4,409,323; 4,477,563; 4,782,012; 4,962,018; 4,500,634; 4,579,816; 4,607,004; 4,618,571; 4,678,739; 4,746,600; 4,746,601; 4,791,049; 4,857,447; 4,865,959; 4,880,342; 4,886,736; 4,937,179; 4,946,767; 4,948,716; 4,952,485; 4,956,269; 4,959,299; 4,966,835; 4,985,336 as well as in patent publications GB 1,560,240; GB 2,007,662; GB 2,032,914; GB 2,099,167; DE 2,842,063, DE 2,937,127; DE 3,636,824; DE 3,644,416 as well as the following European Patent Publications: 272,573; 335,319; 336,411; 346,899; 362,870; 365,252; 365,346; 373,382; 376,212; 377,463; 378,236; 384,670; 396,486; 401,612; 401,613.

[0072] DIR compounds are also disclosed in "Developer-Inhibitor-Releasing (DIR) Couplers for Color Photography," C.R. Barr, J.R. Thirtle and P.W. Vittum in Photographic Science and Engineering, Vol. 13, p. 174 (1969).

[0073] It is also contemplated that the concepts of the present invention may be employed to obtain reflection color prints as described in Research Disclosure, November 1979, Item 18716. The emulsions and materials to form elements of the present invention, may be coated on pH adjusted support as described in U.S. 4,917,994; with epoxy solvents (EP 0 164 961); with additional stabilizers (as described, for example, in U.S. 4,346,165; U.S. 4,540,653 and U.S. 4,906,559); with ballasted chelating agents such as those in U.S. 4,994,359 to reduce sensitivity to polyvalent cations such as calcium; and with stain reducing compounds such as described in U.S. 5,068,171 and U.S. 5,096,805. Other compounds which may be useful in the elements of the invention are disclosed in Japanese Published Applications 83-09,959; 83-62,586; 90-072,629; 90-072,630; 90-072,632; 90-072,633; 90-072,634; 90-077,822; 90-078,229; 90-078,230; 90-079,336; 90-079,338; 90-079,690; 90-079,691; 90-080,487; 90-080,489; 90-080,490; 90080,491; 90-080,492; 90-080,494; 90-085,928; 90-086,669; 90-086,670; 90-087,361; 90-087,362; 90-087,363; 90-087,364; 90-088,096; 90-088,097; 90-093,662; 90-093,663; 90-093,664; 90-093,665; 90-093,666; 90-093,668; 90-094,055; 90-094,056; 90-101,937; 90-103,409; 90-151,577.

[0074] Photographic elements of the present invention are preferably imagewise exposed using any of the known techniques, including those described in Research Disclosure I, section XVI. This typically involves exposure to light in the visible region of the spectrum, and typically such exposure is of a live image through a lens, although exposure can also be exposure to a stored image (such as a computer stored image) by means of light emitting devices (such as light emitting diodes, CRT and the like). Where photographic elements of the present invention are intended as duplicating films or as print materials, the exposure is typically made by passing light in the visible region through a color negative or positive image and appropriate focussing lenses.

[0075] Photographic elements comprising the composition of the invention can be processed in any of a number of well-known photographic processes utilizing any of a number of well-known processing compositions, described, for example, in Research Disclosure I, or in T.H. James, editor, The Theory of the Photographic Process, 4th Edition, Macmillan, New York, 1977. In the case of processing a negative working element, the element is treated with a color developer (that is one which will form the colored image dyes with the color couplers), and then with a oxidizer and a solvent to remove silver and silver halide. In the case of processing a reversal color element, the element is first treated with a black and white developer (that is, a developer which does not form colored dyes with the coupler compounds) followed by a treatment to fog silver halide (usually chemical fogging or light fogging), followed by treatment with a color developer. Preferred color developing agents are p-phenylenediamines. Especially preferred are:

4-amino N,N-diethylaniline hydrochloride,

4-amino-3-methyl-N,N-diethylaniline hydrochloride,

4-amino-3-methyl-N-ethyl-N-(β-(methanesulfonamido) ethylaniline sesquisulfate hydrate,

4-amino-3-methyl-N-ethyl-N-(β-hydroxyethyl)aniline sulfate,

4-amino-3-β-(methanesulfonamido)ethyl-N,N-diethylaniline hydrochloride and

4-amino-N-ethyl-N-(2-methoxyethyl)-m-toluidine di-p-toluene sulfonic acid.

[0076] Dye images can be formed or amplified by processes which employ in combination with a dye-image-generating reducing agent an inert transition metal-ion complex oxidizing agent, as illustrated by Bissonette U.S. Patents 3,748,138, 3,826,652, 3,862,842 and 3,989,526 and Travis U.S. Patent 3,765,891, and/or a peroxide oxidizing agent as illustrated by Matejec U.S. Patent 3,674,490, Research Disclosure, Vol. 116, December, 1973, Item 11660, and Bissonette Research Disclosure, Vol. 148, August, 1976, Items 14836, 14846 and 14847. The photographic elements can be particularly adapted to form dye images by such processes as illustrated by Dunn et al U.S. Patent 3,822,129, Bissonette U.S. Patents 3,834,907 and 3,902,905, Bissonette et al U.S. Patent 3,847,619, Mowrey U.S. Patent 3,904,413, Hirai et al U.S. Patent 4,880,725, Iwano U.S. Patent 4,954,425, Marsden et al U.S. Patent 4,983,504, Evans et al U.S. Patent 5,246,822, Twist U.S. Patent No. 5,324,624, Fyson EPO 0 487 616, Tannahill et al WO 90/13059, Marsden et al WO 90/13061, Grimsey et al WO 91/16666, Fyson WO 91/17479, Marsden et al WO 92/01972. Tannahill WO 92/05471, Henson WO 92/07299, Twist WO 93/01524 and WO 93/11460 and Wingender et al German OLS 4,211,460.

[0077] Development is followed by bleach-fixing, to remove silver or silver halide, washing and drying.

[0078] The following examples illustrate the preparation of emulsions and photographic elements in accordance with this invention.

Precipitation of emulsions for green sensitization:

Emulsion E-1

[0079] A silver iodobromide cubic emulsion (Emulsion E-1) was prepared containing 3.5 % total iodide distributed as a homogeneous run iodide phase. The following solutions were made:

A: 6.1 liters water, 118 g of bone gelatin, 2.7 grams of NaBr, 0.58 grams of PLURONIC 31R1® (a polyalkylene oxide block copolymer surfactant available from BASF), 0.86 grams of thioether (Ethanol, 2,2'-(1,2-ethanediylbis(thio))bis-)

B: 4.0 liters of 1.425 molar AgNO3

C: 4.5 liters of 1.430 molar total NaBr/KI (3.5 molar percent in KI)

D: 1.60 mg K₂IrCl₆ dissolved in 30 ml of water

[0080] Solution A was placed in a 20 liter reaction vessel and heated to 44 degrees C. Solutions B and C were added in a double jet fashion at a constant rate while the pAg for the solution was held at 9.00 by adjusting the flow of solution C. After one minute, solution D was added for a period of one minute. One minute after Solution D addition stopped, the flow of solution C was controlled such that pAg was reduced to 7.65 over a period of three minutes. After another 24.5 minutes, addition was stopped and the solution was cooled to 40 degrees and subjected to ultrafiltration. The monodispersed cubic emulsion grains had an average ESD of 0.15 µm as determined by discrete wavelength turbidimetry.

Emulsion E-2

[0081] A silver iodobromide cubic emulsion (Emulsion E-2) was prepared containing 3.4 % total iodide distributed as a homogeneous run iodide phase. The following solutions were made:

A: 9.1 liters water, 202.8 g of bone gelatin, 4.79 grams of NaBr, 2.25 grams of PLURONIC 31R1®, 1.57 g of thioether (Ethanol, 2,2'-(1,2-ethanediylbis(thio))bis-)

B: 3.92 liters of 2.96 molar AgNO3

C: 4.59 liters of 2.65 molar total NaBr/KI (3.4 molar percent in KI)

D: 1.59 mg K₂IrCl₆ dissolved with 7.98 g of 4.0 molar HNO₃ and 41.2 ml of water.

[0082] Solution A was placed in a 20 liter reaction vessel and heated to 50 degrees C. 34 ml of solutions B and C were added in a double jet fashion at an equal and constant rate for 30 seconds. During the next three minutes the addition rate for solution B was held at 42.6 ml/min and the flow of solution C was controlled such that pAg was raised to 7.73. After achieving pAg of 7.73 the flow rate for solution B was reduced to 21.3 ml/min and then ramped to a rate of 23 ml/min over a two minute period, during which Solution D was added at a constant rate, and solution C flow rates were adjusted to control pAg at 7.73. After that, the flow rate for solution B was set to 45.9 ml/min and, over the next 33.1 minutes, linearly ramped to 155.5 ml/min, while solution C flow rates were controlled to maintain a constant pAg at 7.73. After this, addition was stopped and the solution was cooled to 40 degrees and subjected to ultrafiltration. The monodispersed cubic emulsion grains had an average ESD of 0.33 µm as determined by discrete wavelength turbidimetry.

Emulsion E-3

[0083] Emulsion E-3 was made in a manner identical to E-2 except that solution A was changed to the following:
A: 9.1 liters water, 202.8 g of bone gelatin, 4.79 grams of NaBr, 2.25 grams of PLURONIC 31R1®, 2.13 g of thioether (Ethanol, 2,2'-(1,2-ethanediylbis(thio))bis-)

[0084] The monodispersed cubic emulsion grains thus made had an average ESD of 0.40 µm as determined by discrete wavelength turbidimetry.

Green-Sensitizations: Chemical and Spectral

[0085] Emulsions E-1, E-2 and E-3 were chemically and spectrally sensitized using:

a. Dyes G1 and G2

b. A benzolthiazolium finish modifier (Benzothiazolium, 5,6-dimethoxy-3-(3-sulfopropyl)-, inner salt),

c. Sodium aurous di-thiosulfate

d. Sodium thiosulfate pentahydrate

e. The azaindene compound [(1,2,4)Triazolo(1,5-a)pyrimidin-7-ol, 6-bromo-5-methyl- ] commonly known as bromo-TAI

f. The azaindene compound [(1,2,4)Triazolo(1,5-a)pyrimidin-7-ol, 5-methyl-, sodium salt commonly referred to as TAI

[0086] Additionally, the antifoggant and metal sequestrant, HB-3, was added prior to coating. For some experimental variations, the two electron donating sensitizing agent FED-2 was also added before coating.

Coating/Evaluation of Green-Sensitized Emulsions

[0087] Coatings were then prepared consisting of the green-sensitized silver halide emulsion at a laydown of 75 mg/ft² (0.825 g/m²), 150 mg/ft² (1.65 g/m²) of the cyan dye forming coupler C1, and a gelatin vehicle at 300 mg/ft² (3.3 g/m²). An overcoat of gelatin at 250 mg/ft² (2.75 g/m²) was subsequently applied containing bisvinylsulfonylmethyl ether hardener 1.8% wt/wt of gelatin.

[0088] For photographic evaluation, each of the coating strips was exposed for 0.01 sec to a 3000 K color temperature tungsten lamp filtered to give an effective color temperature of 5500K and further filtered a Kodak Wratten filter number 9 and a step wedge ranging in density from 0 to 4 density units in 0.2 density steps. The exposed film strips were processed in standard C-41 chemistry. Speed was metered at the point 0.15 density units above dmin and is reported in units of log relative sensitivity (log S).

[0089] For all of the coatings, the effects of the addition of FED-2 were assessed by comparing speed gained and dmin growth relative to a coating that had been treated identically except for the addition of the FED-2. A better result will have higher speeds and reduced dmin growth. In these experiments a dmin growth greater than 0.05 density units is considered unacceptable.

[0090] Table I summarizes the data for the green sensitized emulsions. For emulsion E-1, it can be seen that even the highest level of FED-2, which yielded a speed increase of 0.11 log S, gave a corresponding dmin increase of only 0.014. For Emulsion E-2, the lowest level of FED-2 gave a similar speed increase of 0.10 log S with a moderate (but acceptable) dmin increase of 0.047. However, for the largest emulsion, the lowest level of FED-2 gave a similar speed increase (0.13 log S) but with an unacceptable a dmin increase of 0.094 density units. The responses of the two smaller emulsions with FED-2 are advantaged compared to the largest emulsion in giving useful speed increases with acceptable dmin increases. The smallest emulsion, E-1, shows the best performance in this respect.

Table I

Delta dmin, and delta dyed Speed for various levels of FED-2 coated with green-sensitized Emulsions E-1, E-2, E-3
		Delta dmin/delta 0.15 speed
Emulsion Example	ESD (µm)	Level of FED-2 Per silver mole
		0.15 mg	0.30 mg	0.45 mg
E-1	0.15	0.000/0.03	0.006/0.07	0.014/0.11	Invention
E-2	0.33	0.047/0.10	0.170/0.20	0.298/0.25	Invention
E-3	0.40	0.094/0.13	0.280/0.26	0.383/0.35	Comparative

Precipitation of emulsions for blue sensitization:

Emulsion E-4

[0091] A silver iodobromide cubic emulsion (Emulsion E-4) was prepared containing 3.3 % total iodide distributed as a homogeneous run iodide phase. The following solutions were made:

A: 6.1 liters water, 118 g of bone gelatin, 2.7 grams of NaBr, 0.58 grams of PLURONIC 31R1®, 0.92 grams of thioether (Ethanol, 2,2'-(1,2-ethanediylbis(thio))bis-)

B: 4.0 liters of 1.425 molar AgNO3

C: 4.5 liters of 1.430 molar total NaBr/KI (3.3 molar percent in KI)

D: 1.60 mg K₂IrCl₆ dissolved in 30 ml of water

[0092] Solution A was placed in a 20 liter reaction vessel and heated to 46 degrees C. Solutions B and C were added in a double jet fashion at a constant rate while the pAg for the solution was held at 8.94 by adjusting the flow of solution C. After one minute, solution D was added for a period of one minute. One minute after Solution D addition stopped, the flow of solution C was controlled such that pAg was reduced to 7.60 over a period of three minutes. After another 24.5 minutes, addition was stopped and the solution was cooled to 40 degrees and subjected to ultrafiltration.

[0093] The monodispersed cubic emulsion grains had an average ESD of 0.17 µm as determined by discrete wavelength turbidimetry.

Emulsion E-5

[0094] A silver iodobromide cubic emulsion (Emulsion E-5) was prepared containing 3.3 % total iodide distributed as a homogeneous run iodide phase. The following solutions were made:

A: 6.1 liters water, 118 g of bone gelatin, 2.7 grams of NaBr, 0.58 grams of PLURONIC 31R1®, 0.86 grams of thioether (Ethanol, 2,2'-(1,2-ethanediylbis(thio))bis-)

B: 4.0 liters of 1.425 molar AgNO3

C: 4.5 liters of 1.430 molar total NaBr/KI (3.3 molar percent in KI)

D: 0.80 mg K₂IrCl₆ dissolved in 30 ml of water

[0095] Solution A was placed in a 20 liter reaction vessel and heated to 60 degrees C. Solutions B and C were added in a double jet fashion at a constant rate while the pAg for the solution was held at 8.55 by adjusting the flow of solution C. After one minute, solution D was added for a period of one minute. One minute after Solution D addition stopped, the flow of solution C was controlled such that pAg was reduced to 7.26 over a period of three minutes. After another 24.5 minutes, addition was stopped and the solution was cooled to 40 degrees and subjected to ultrafiltration.

[0096] The monodispersed cubic emulsion grains had an average ESD of 0.20 µm as determined by discrete wavelength turbidimetry.

Emulsion E-6

[0097] A silver iodobromide cubic emulsion (Emulsion E-4) was prepared containing 3.3 % total iodide distributed as a homogeneous run iodide phase. The following solutions were made:

A: 6.1 liters water, 118 g of bone gelatin, 2.7 grams of NaBr, 0.58 grams of PLURONIC 31R1®, 0.91 grams of thioether (Ethanol, 2,2'-(1,2-ethanediylbis(thio))bis-)

B: 4.0 liters of 1.425 molar AgNO3

C: 4.5 liters of 1.430 molar total NaBr/KI (3.3 molar percent in KI)

D: 0.50 mg K₂IrCl₆ dissolved in 30 ml of water

[0098] Solution A was placed in a 20 liter reaction vessel and heated to 79 degrees C. Solutions B and C were added in a double jet fashion at a constant rate while the pAg for the solution was held at 8.08 by adjusting the flow of solution C. After one minute, solution D was added for a period of one minute. One minute after Solution D addition stopped, the flow of solution C was controlled such that pAg was reduced to 6.86 over a period of three minutes. After another 24.5 minutes, addition was stopped and the solution was cooled to 40 degrees and subjected to ultrafiltration.

[0099] The monodispersed cubic emulsion grains had an average ESD of 0.27 µm as determined by discrete wavelength turbidimetry.

Blue-Sensitizations : Chemical and Spectral

[0100] Emulsions E-4, E-5 and E-6 were chemically and spectrally sensitized using:

a. Sodium Aurous di-thiosulfate

b. Sodium thiosulfate pentahydrate

c. 2-Benzoxazolamine, N-2-propynyl-

d. Dye B1

e. Benzothiazolium, 3,3'-(1,10-decanediyl)bis-, dibromide

f. The azaindene compound [(1,2,4)Triazolo(1,5-a)pyrimidin-7-ol, 6-bromo-5-methyl- ] commonly known as bromo-TAI

g. The azaindene compound [(1,2,4)Triazolo(1,5-a)pyrimidin-7-ol, 5-methyl-, sodium salt commonly referred to as TAI

[0101] Additionally, the antifoggant and metal sequestrant, HB-3, was added prior to coating. For some experimental variations, the two electron donating sensitizing agent FED-2 was also added before coating.

Coating/Evaluation of Blue-Sensitized Emulsions

[0102] Coatings were then prepared consisting of sensitized silver halide emulsion at a laydown of 75 mg/ft² (0.825 g/m²), 150 mg/ft² (1.65 g/m²) of the cyan dye forming coupler C1, and a gelatin vehicle at 300 mg/ft² (3.3 g/m²). An overcoat of gelatin at 250 mg/ft² (2.75 g/m²) was subsequently applied containing bisvinylsulfonylmethyl ether hardener 1.8% wt/wt of gelatin.

[0103] For photographic evaluation, samples from each of the coatings was exposed for 0.01 sec to a 3000 K color temperature tungsten lamp filtered to give an effective color temperature of 5500K and further filtered a Kodak Wratten filter number 2B and a step wedge ranging in density from 0 to 4 density units in 0.2 density steps. The exposed film strips were processed in standard C-41 chemistry. Speed was metered at the point 0.15 density units above the minimum density and reported in units of log relative sensitivity (log S).

[0104] The effects of the addition of FED-2 were assessed by comparing speed gained and dmin growth relative to a coating that had been treated identically except for the addition of FED-2. A better result will have higher speeds accompanied with lower dmin growth.

[0105] Table II summarizes the data for the blue sensitized emulsions. For the smallest emulsion, E-4, it can be seen that even the highest level of FED-2 (48 mg/Ag-mole), which yielded a speed increase of 0.24 log S, gave a corresponding dmin increase of only 0.06 density units. For the same dmin increase, emulsion E-5, with an ESD of 0.20 µm, gave a speed increase of 0.18 log S when treated with 24 mg/mole Ag of FED-2. The largest emulsion, treated with a substantially lower level of FED-2 (6mg/Ag-mole), gave a small speed increase (0.04 log S) and a dmin increase of 0.12 density units. These data indicate that emulsions with ESD's of 0.25 µm or less are advantaged for speed gain with relatively low dmin increases.

Table II

Delta dmin, and delta dyed speed for various levels of FED-2 coated with blue-sensitized emulsions E-4, E-5, E-6
		Delta dmin / delta 0.15 speed
		Level of FED-2 per silver mole
Emulsion Example	ESD (µm)	3 mg	6 mg	12 mg	24 mg	48 mg
E-4	0.17	****	0.02/0.11	0.03/0.16	0.04/0.21	0.06/0.24
E-5	0.20	****	0.04/0.11	0.05/0.15	0.06/0.18	0.08/0.20
E-6	0.27	0.10/0.0	0.12/0.04	0.14/0.09	0.16/0.10	****

**** indicates no test performed

Precipitation of emulsions for red sensitization:

Emulsion E-7

[0106] A silver iodobromide cubic emulsion (Emulsion E-7) was prepared containing 3.3 % total iodide distributed as a homogeneous run iodide phase. The following solutions were made:

A: 6.0 liters water, 118 g of bone gelatin, 2.5 grams of NaBr, 0.48 grams of PLURONIC 31R1®.

B: 4.6 liters of 1.425 molar AgNO3

C: 4.6 liters of 1.430 molar total NaBr/KI (3.3 molar percent in KI)

D: 9.60 mg K₂IrCl₆ dissolved in 46.5 ml of water

[0107] Solution A was placed in a 20 liter reaction vessel and brought to 36 degrees C. Solutions B and C were added in a double jet fashion at a constant rate while the pAg for the solution was held at 9.23 by adjusting the flow of solution C. After one minute, solution D was added for a period of one minute. One minute after Solution D addition stopped, the flow of solution C was controlled such that pAg was reduced to 7.85 over a period of three minutes. After another 24.1 minutes, addition was stopped and the solution was warmed to 40 degrees and subjected to ultrafiltration.

[0108] The monodispersed cubic emulsion grains had an average ESD of 0.07 µm as determined by discrete wavelength turbidimetry.

Emulsion E-8

[0109] A silver iodobromide cubic emulsion (Emulsion E-8) was prepared containing 3.3 % total iodide distributed as a homogeneous run iodide phase. The following solutions were made:

A: 6.0 liters water, 118 g of bone gelatin, 2.4 grams of NaBr, 0.48 grams of PLURONIC 31R1®, 0.40 grams of thioether (Ethanol, 2,2'-(1,2-ethanediylbis(thio))bis-)

B: 4.6 liters of 1.425 molar AgNO3

C: 4.6 liters of 1.430 molar total NaBr/KI (3.3 molar percent in KI)

D: 1.44 mg K₂IrCl₆ dissolved in 28.6 ml of water

[0110] Solution A was placed in a 20 liter reaction vessel and heated to 41.5 degrees C. Solutions B and C were added in a double jet fashion at a constant rate while the pAg for the solution was held at 9.06 by adjusting the flow of solution C. After one minute, solution D was added for a period of one minute. One minute after Solution D addition stopped, the flow of solution C was controlled such that pAg was reduced to 7.70 over a period of three minutes. After another 24.1 minutes, addition was stopped and the solution was cooled to 40 degrees and subjected to ultrafiltration.

[0111] The monodispersed cubic emulsion grains had an average ESD of 0.11 µm as determined by discrete wavelength turbidimetry.

Emulsion E-9

[0112] A silver iodobromide cubic emulsion (Emulsion E-9) was prepared containing 3.3 % total iodide distributed as a homogeneous run iodide phase. The following solutions were made:

A: 6.0 liters water, 118 g of bone gelatin, 2.4 grams of NaBr, 0.48 grams of PLURONIC 31R1®, 0.575 grams of thioether (Ethanol, 2,2'-(1,2-ethanediylbis(thio))bis-)

B: 4.6 liters of 1.425 molar AgNO3

C: 4.6 liters of 1.430 molar total NaBr/KI (3.3 molar percent in KI)

D: 3.3 mg K₂IrCl₆ dissolved in 46.5 ml of water

[0113] Solution A was placed in a 20 liter reaction vessel and heated to 40 degrees C. Solutions B and C were added in a double jet fashion at a constant rate while the pAg for the solution was held at 9.11 by adjusting the flow of solution C. After one minute, solution D was added for a period of one minute. One minute after Solution D addition stopped, the flow of solution C was controlled such that pAg was reduced to 7.74 over a period of three minutes. After another 24.1 minutes, addition was stopped, the solution was maintained at 40 degrees and subjected to ultrafiltration.

[0114] The monodispersed cubic emulsion grains had an average ESD of 0.13 µm as determined by discrete wavelength turbidimetry.

Emulsion E-10

[0115] A silver iodobromide cubic emulsion (Emulsion E-10) was prepared containing 3.3 % total iodide distributed as a homogeneous run iodide phase. The following solutions were made:

A: 6.0 liters water, 118 g of bone gelatin, 2.4 grams of NaBr, 0.48 grams of PLURONIC 31R1®, 0.86 grams of thioether (Ethanol, 2,2'-(1,2-ethanediylbis(thio))bis-)

B: 4.6 liters of 1.425 molar AgNO3

C: 4.6 liters of 1.430 molar total NaBr/KI (3.3 molar percent in KI)

D: 1.24 mg K₂IrCl₆ dissolved in 28.5 ml of water

[0116] Solution A was placed in a 20 liter reaction vessel and heated to 51.5 degrees C. Solutions B and C were added in a double jet fashion at a constant rate while the pAg for the solution was held at 8.77 by adjusting the flow of solution C. After one minute, solution D was added for a period of one minute. One minute after Solution D addition stopped, the flow of solution C was controlled such that pAg was reduced to 7.44 over a period of three minutes. After another 24.1 minutes, addition was stopped, the solution was cooled to 40 degrees and subjected to ultrafiltration.

[0117] The monodispersed cubic emulsion grains had an average ESD of 0.18 µm as determined by discrete wavelength turbidimetry.

Red-Sensitizations : Chemical and Spectral

[0118] Emulsions E-7 through E-10 were chemically and spectrally sensitized using:

a. Sodium Aurous di-thiosulfate

b. Sodium thiosulfate pentahydrate

c. 2-Benzoxazolamine, N-2-propynyl-

d. Dye R1

e. Benzothiazolium, 3,3'-(1,10-decanediyl)bis-, dibromide

f. The azaindene compound [(1,2,4)Triazolo(1,5-a)pyrimidin-7-ol, 6-bromo-5-methyl- ] commonly known as bromo-TAI

g. (except for E-10) a 10-to-1 weight-ratio-mixture of benzenesulfonothioic acid, 4-methyl-, potassium salt and benzenesulfinic acid, 4-methyl-, sodium salt

Additionally, the antifoggant and metal sequestrant, HB-3, was added prior to coating. For some experimental variations, the two electron donating sensitizing agent FED-2 was also added before coating.

Coating/Evaluation of Red-Sensitized Emulsions

[0119] Coatings were then prepared consisting of sensitized silver halide emulsion at a laydown of 40 mg/ft² (0.44 g/m²), 60 mg/ft² (0.66 g/m²) of the cyan dye forming coupler C1, and a gelatin vehicle at 300 mg/ft² (3.3 g.m²). An overcoat of gelatin at 50 mg/ft² (0.55 g/m²) was subsequently applied containing bisvinylsulfonylmethane hardener 1.4% wt/wt of gelatin.

[0120] For photographic evaluation, samples from each of the coatings was exposed for 0.01 sec to a 3000 K color temperature tungsten lamp filtered to give an effective color temperature of 5500K and further filtered a Kodak Wratten filter number 2B and a step wedge ranging in density from 0 to 4 density units in 0.2 density steps. The exposed film strips were processed in standard C-41 chemistry. Speed was metered at the point 0.15 density units above the minimum density and reported in units of log relative sensitivity (log S).

[0121] The effects of the addition of FED-2 were assessed by comparing speed gained and dmin growth relative to a coating that had been treated identically except for the addition of FED-2. A better result will have higher speeds accompanied with lower dmin growth.

[0122] Table III summarizes the data for the red sensitized emulsions. For the smallest emulsion, E-7, it can be seen that even the highest level of FED-2 (25 mg/Ag-mole), which yielded a speed increase of 0.33 log S, gave no significant dmin increase. Emulsion E-8, with an ESD of 0.11 µm, gave a speed increase of 0.10 log S when treated with 2 mg/mole Ag of FED-2. Interpolating, one would expect that a speed increase of about 0.20 log S could be achieved with a dmin increase of about 0.05. Emulsion E-9, with an ESD of 0.13 µm, gave results similar to E-8 but at about half the FED-2 level. The largest emulsion would exceed the acceptable dmin growth with an FED-2 level between 0.1 and 0.25 mg per silver mole. These data indicate that emulsions with ESD's of 0.15 µm or less are particularly advantaged for speed gain with relatively low dmin increases.

Precipitation and red sensitization of additional emulsions:

Emulsion E-11:

[0123] A silver iodobromide cubic emulsion (Emulsion E-11) was prepared exactly like emulsion E-7 as the check for making variations in the amounts of K₂IrCl₆ used in the precipitations and N-2-propynyl-2-benzoxazolamine used in the sensitizations.

Emulsion E-12:

[0124] This emulsion was identical to emulsion E-11 except that no N-2-propynyl-2-benzoxazolamine was used in the sensitization step.

Emulsion E-13:

[0125] A silver iodobromide cubic emulsion (Emulsion E-13 ) was prepared exactly like emulsion E-11 except that Solution D had the following composition:
D: 19.2 mg K₂IrCl₆ dissolved in 46.5 ml of water - i.e., twice the amount in emulsion E-11.

Emulsion E-14:

[0126] This emulsion was identical to emulsion E-13 except that no N-2-propynyl-2-benzoxazolamine was used in the sensitization step.

Emulsion E-15:

[0127] A silver iodobromide cubic emulsion (Emulsion E-15 ) was prepared exactly like emulsions E-11 and E-13 except that Solution D was omitted - i.e., emulsion E-15 contained no K₂IrCl₆.

Emulsion E-16:

[0128] This emulsion was identical to emulsion E-15 except that no N-2-propynyl-2-benzoxazolamine was used in the sensitization step.

[0129] Emulsions E-11 through E-16 were coated and evaluated like emulsions E-7 through E-10.

[0130] Table IV shows, first, that there was a relatively small effect due to variations in the amount of K₂IrCl₆ used in the precipitations. Indeed, there was a small speed loss associated with increasing amounts of K₂IrCl₆. The slightly greater effect of FED-2 with higher levels of K₂IrCl₆ almost exactly compensated for the speed loss associated with the K₂IrCl₆ such that emulsions E-11, E-13 and E-15 all had the same speed with FED-2, within experimental uncertainty.

[0131] Table IV also shows that, although omission of N-2-propynyl-2-benzoxazolamine from the sensitization caused some speed loss, in these cases the speed gain realized from the use of FED-2 in coating was substantially greater and, in fact, largely offset the loss from the change in sensitization procedure.

[0132] Overall, Table IV illustrates that the advantageous effect of FED-2 in this small cubic emulsion can be seen in both the presence and absence of Ir dopant as well as in the presence or absence of the N-2-propynyl-2-benzoxazolamine.

Table IV

Delta dmin, and delta dyed speed for FED-2 coated with red-sensitized emulsions E-11 through E-16
Emulsion Example	ESD (µm)	K2IrCl6	2-benzoxazolamine, N-2-propynyl-	dmin/ 0.15 speed **	Delta dmin / delta 0.15 speed for 5 mg FED-2 per silver mole
E-11	0.07	Same as E-7	Same as E-7	0.05/1.00	0.00/0.09
E-12	0.07	Same as E-7	NONE	0.04/0.64	0.00/0.22
E-13	0.07	Double E-7	Same as E-7	0.05/0.97	0.00/0.11
E-14	0.07	Double E-7	NONE	0.04/0.59	0.00/0.28
E-15	0.07	NONE	Same as E-7	0.05/1.00	0.00/0.06
E-16	0.07	NONE	NONE	0.04/0.66	0.00/0.25

** 0.15 speed for E-11 set equal to 1.00 log S.

Claims

1. A silver halide photographic element comprising at least one silver halide emulsion layer comprising 3D emulsion grains having an equivalent spherical diameter of less than or equal to 0.35 µm and said layer further comprises a fragmentable electron donor compound of the formula X-Y' or a compound which contains a moiety of the formula -X-Y'; wherein
   X is an electron donor moiety, Y' is a leaving proton H or a leaving group Y, with the proviso that if Y' is a proton, a base, β^-, is covalently linked directly or indirectly to X, and wherein:

1) X-Y' has an oxidation potential between 0 and about 1.4 V; and

2) the oxidized form of X-Y' undergoes a bond cleavage reaction to give the radical X^• and the leaving fragment Y'; and

3) the radical X^• has an oxidation potential ≤-0.7V.

2. A photographic element according to claim 1, wherein the morphology of the 3D emulsion grains is cubic.

3. A photographic element according to claim 1 or claim 2, wherein the silver halide comprises silver bromide or silver iodobromide.

4. A photographic element according to claim 3, wherein the silver halide comprises silver iodobromide.

5. A photographic element according to any preceding claim, wherein X is of structure (I) (II), (III) or (IV):

R₁ = R, carboxyl, amide, sulfonamide, halogen, NR₂, (OH)_n, (OR')_n, or (SR)_n;

R' = alkyl or substituted alkyl;

n= 1-3;

R₂ = R, Ar';

R₃ = R, Ar';

R₂ and R₃ together can form 5- to 8-wherein:

m = 0, 1;

Z = O, S, Se, Te;

R₂ and Ar = can be linked to form 5- to 8-membered ring;

R₃ and Ar = can be linked to form 5- to 8-membered ring;

Ar' = aryl groupor heterocyclic group.
and

R = a hydrogen atom or an unsubstituted or substituted alkyl group;

wherein:

Ar = aryl group or heterocyclic group

R₄ = a substituent having a Hammett sigma value of -1 to +1,

R₅ = R or Ar'

R₆ and R₇ = R or Ar'

R₅ and Ar = can be linked to form 5- to 8-membered ring;

R₆ and Ar = can be linked to form 5- to 8-membered ring (in which case, R₆ can be a hetero atom);

R₅ and R₆ can be linked to form 5- to 8-membered ring;

R₆ and R₇ can be linked to form 5- to 8-membered ring;

Ar' = aryl group or heterocyclic group;
and

R = hydrogen atom or an unsubstituted or substituted alkyl group;

wherein:

W = O, S, Se;

Ar = aryl group or heterocyclic group;

R₈ = R, carboxyl, NR₂, (OR)_n, or (SR)n (n = 1-3);

R₉ and R₁₀ = R, Ar';

R₉ and Ar = can be linked to form 5- to 8-membered ring;

Ar' = aryl group or heterocyclic group;
and

R = a hydrogen atom or an unsubstituted or substituted alkyl group;

wherein:
   "ring" represents a substituted or unsubstituted 5-, 6- or 7-membered unsaturated ring.

6. A photographic element according to any preceding claim, wherein Y' is:

(1) X', where X' is an X group as defined in structures I-IV and may be the same as or different from the X group to which it is attached

(2)

(3)

   where M = Si, Sn or Ge; and R' = alkyl or substituted alkyl

(4)

   where Ar" = aryl or substituted aryl

(5)

7. A photographic element according to claim 1, wherein the fragmentable electron donor compound is selected from compounds of the formulae:

        Z-(L-X-Y')_k



        A-(L-X-Y')_k



        (A-L)_k-X-Y'



        Q-X-Y'



        A-(X-Y')_k



        (A)_k-X-Y'



        Z-(X-Y')_k

   Or

        (Z)_k-X-Y'

wherein:

Z is a light absorbing group;

k is 1 or 2;

A is a silver halide adsorptive group;

L represents a linking group containing at least one C, N, S, P or O atom; and

Q represents the atoms necessary to form a chromophore comprising an amidinium-ion, a carboxyl-ion or dipolar-amidic chromophoric system when conjugated with X-Y'.