EP1094363B1

EP1094363B1 - Photographic element with excellent speed differential for digital and optical exposure devices

Info

Publication number: EP1094363B1
Application number: EP00203506A
Authority: EP
Inventors: Pamela Mccue C/O Eastman Kodak Company Ferguson; Donald Richard C/O Eastman Kodak Company Diehl
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1999-10-20
Filing date: 2000-10-10
Publication date: 2004-04-07
Anticipated expiration: 2020-10-10
Also published as: DE60009629D1; DE60009629T2; EP1094363A3; JP2001142173A; EP1094363A2

Description

This invention relates to a photographic element which may be exposed by either optical and digital exposure devices.
In the photographic art a latent image is formed by the exposure of a silver halide emulsion which has been spectrally sensitized to a particular wavelength region of light by a suitable exposure device. Such exposure devices may have a broad spectrum of light exposure ranging from wavelengths below 400 nanometers (nm) to above 700 nm for devices which are now in the trade as optical exposure devices, or the exposure devices may have a very narrow wavelength of exposure and such devices are known in the art as laser exposure devices.
It is a long standing problem in the manufacture of photographic elements to build a silver halide emulsion which has suitable exposure speed for a broad band optical exposure device as well as having good exposure speed at the much shorter wavelength of the laser exposure device.
Commonly in the preparation of silver halide emulsions which are sensitive to red light, the emulsion may be sensitized by a wide range of cyanine type spectral sensitizing dyes. Such cyanine dyes are well known in the art and patents describing those types of dyes are set forth in Section V (A) of Research Disclosure, September 1996, Number 389, Item 38957, which will be identified hereafter by the term "Research Disclosure I." The Sections referred to herein are Sections of the Research Disclosure I unless otherwise indicated. All Research Disclosures referenced are published by Kenneth Mason Publications, Ltd., Dudley Annex, 12a North Street, Emsworth, Hampshire PO10 7DQ, ENGLAND.
It is also common in the preparation of silver halide emulsions to add to the emulsions inorganic dopants to provide desirable exposure properties of the emulsion. Such dopants have been described in the art and patents describing those type of dopants are set forth in Section I (D) (3) of Research Disclosure I.
It is also well known in the photographic art to add photographic filter dyes to the emulsion layers in order to adjust the speed of the emulsions and to improve the sharpness of the silver image. Such photographic filter dyes have been described in the art and patents describing those types of filter dyes are set forth in Section VIII (B) of Research Disclosure I.
When one skilled in the art wishes to build a photographic element which is sensitive to two different exposure devices it is common to use silver halide emulsions which are spectrally sensitized to the different wavelengths of exposure light by adding two different cyanine type spectral sensitizing dyes to the emulsions. It may be necessary at those times to use two different dopants to adjust the emulsions exposure properties and to use two or more photographic filter dyes to adjust the speed of the emulsions to the maximum wavelength of the light exposing devices.
It would be advantageous to use a single silver halide emulsion, to provide a photographic element with excellent exposure speed at two different wavelengths.
The invention provides an imaging element comprising at least one silver halide emulsion wherein the silver halide emulsion grains incorporate:
dopant (i) which comprises a hexacoordination metal complex which satisfies the formula [ML₆]ⁿ wherein n is zero, -1, -2, -3 or -4; M is a filled frontier orbital polyvalent metal ion, other than iridium; and L₆ represents bridging ligands which can be independently selected, provided that at least four of the ligands are anionic ligands, and at least one of the ligands is a cyano ligand or a ligand more electronegative than a cyano ligand;
and wherein the emulsion has been spectrally sensitized with a sensitizing dye and contains a filter dye that
(a) has a wavelength of absorbance maximum which is less than 15 nm (preferably less than 10 nm and more preferably less than 5 nm) different than the maximum wavelength of emulsion sensitivity provided by the spectral sensitizing dye, and
(b) has a half band width that is equal to the half bandwidth of the sensitizing dye,
In preferred embodiments of the invention, the silver halide grains further comprise dopant (ii) which comprises an iridium coordination complex. In particularly preferred embodiments, dopant (ii) contains a thiazole or substituted thiazole ligand.
The sensitizing dye is preferably selected from Dye A, Dye B and mixtures thereof, wherein Dye A is of formula I or II:

wherein:
in formula I, the substituents W₁-W₈ are chosen such that J is greater than or equal to 0.0, where J is defined as the sum of he Hammet σ_p values of W₁-W₈, or in formula II, the substituents W₁-W₈ are chosen such that J is greater than or equal to 0.24;
R₁ and R₂ each independently represents an alkyl group or a substituted alkyl group;
Z₁ and Z₂ each independently represents a 1-8 carbon alkyl group.
X is a counterion, if needed, to balance the charge of the dye; and Dye B is of formula I or II wherein: in formula I, the substituents W₁-W₈ are chosen such that J is less than 0.10, or in formula II, the substituents W₁-W₈ are chosen such that J is less than -0.14; and
R₁ and R₂ each independently represents an alkyl group or a substituted alkyl group;
X is a counterion, if needed, to balance the charge of the dye;
Z is a hydrogen or halogen atom or an alkyl group or a substituted alkyl group.
The filter dye preferably is of the formula:
wherein:
G and G' independently represent oxygen, substituted nitrogen, or C(CN)₂;
R₃, R₃', R₄, R₄' independently represent H or a substituent, or R₃ and R₄, R₃' and R₄' may form a ring;
R₅ is an acyl, alkoxycarbonyl, amido, carbamoyl, alkyl, aryl, alkyloxy, aryloxy, amino, or heterocyclic, any of which may be substituted or unsubstituted;
m is 0, 1, 2, or 3;
all of the L" together define a methine chain each L" representing a methine any of which may be substituted or unsubstituted; and
M⁺ is a cation or proton.
The invention has numerous advantages over prior practices in the art. The invention imaging elements provide the ability to have an imaging element that may be exposed with substantially invariant results over a wide range of exposure times. The imaging element of the invention when digitally exposed at exposure times of about 125 nanoseconds produces a clear, bright, and sharp image while minimizing fringing or other undesirable artifacts. The photographic element when digitally exposed maintains an acceptable maximum density in dark areas of the print, while also having the ability to print white whites in the white areas.
The optical performance of the imaging element of the invention is exceptional with optical exposure resulting in bright, sharp prints. It is a feature of this invention that prints made either by optical or by digital exposure have substantially the same excellent characteristics.
A full color imaging element has at least one layer comprising a silver halide emulsion a cyan dye forming coupler and silver halide grains sensitized to red light, at least one layer comprising a silver halide emulsion a magenta dye forming coupler and silver halide grains sensitized to green light and at least one layer comprising a silver halide emulsion a yellow dye forming coupler and silver halide grains sensitized to blue light.
The emulsions can be spectrally sensitized with any of the dyes known to the photographic art, such as the polymethine dye class, which includes the cyanines, merocyanines, complex cyanines and merocyanines, oxonols, hemioxonols, styryls, merostyryls and streptocyanines. Use of low staining sensitizing dyes in a photographic element processed in a developer solution with little or no optical brightening agent (for instance, stilbene compounds such as Blankophor REU™) is specifically contemplated. Further, these low staining dyes can be used in combination with other dyes known to the art ( Research Disclosure I, Section V).
Useful sensitizing dyes include, but are not limited to, the following.
In accordance with a preferred embodiment of the invention, the red sensitizing dye is selected from Dye A, Dye B and mixtures thereof, wherein Dye A is of formula I or II:

wherein:
in formula I, the substituents W₁-W₈ are chosen such that J is greater than or equal to 0.0, where J is defined a s the sum of the Hammet σ_p values of W₁-W₈, or in formula II, the substituents W₁-W₈ are chosen such that J is greater than or equal to 0.24;
R₁ and R₂ each independently represents an alkyl group or a substituted alkyl group;
Z₁ and Z₂ each independently represents a 1-8 carbon alkyl group.
X is a counterion, if needed, to balance the charge of the dye;
in formula I, the substituents W₁-W₈ are chosen such that J is less that 0.10, or in formula II, the substituents W₁-W₈ are chosen such that J is less that -0.14; and
R₁ and R₂ each independently represents an alkyl group or a substituted alkyl group;
X is a counterion, if needed, to balance the charge of the dye;
Z is a hydrogen or halogen atom or an alkyl group or a substituted alkyl group.
In the above formulae (I) and (II), W₁-W₈ preferably each independently represent an alkyl, acyl, acyloxy, alkoxycarbonyl, carbonyl, carbamoyl, sulfamoyl, carboxyl, cyano, hydroxy, amino, acylamino, alkoxy, alkylthio, alkylsulfonyl, sulfonic acid, aryl, or aryloxy group, any of which may be substituted or unsubstituted, or a hydrogen or halogen atom, and provided further that adjacent ones of W₁-W₈ can be bonded to each other via their carbon atoms to form a condensed ring. Dye A has structure I and substituents W₁-W₈ are chosen such that J is ≥ 0.0, or, alternatively, Dye A can also have the structure II provided substituents W₁-W₈ are chosen such that J is ≥ 0.24 and Dye B has structure II and substituents W₁-W₈ are chosen such that J is ≤ 0.10, or, alternatively, Dye B can also have structure I provided substituents W₁-W₈ are chosen such that J is ≤ - 0.14. Hammett σ_p values are discussed in Advanced Organic Chemistry 3rd Ed., J. March, (John Wiley Sons, NY; 1985). Note that the "_p" subscript refers to the fact that the σ values are measured with the substituents in the para position.
Z is a hydrogen or halogen atom or an alkyl group or substituted alkyl group, for example a 1 to 8 carbon atom alkyl group or substituted alkyl group. Preferably Z is a relatively "flat" substituent, such as a hydrogen, halogen or a methyl (substituted or unsubstituted). More particularly Z may be a substituted or unsubstituted methyl or a hydrogen.
Z₁ and Z₂ are independently a 1 to 8 carbon alkyl group (for example, methyl, ethyl, propyl, butyl).
Preferably at least one of R₁ or R₂, or both, are alkyl of 1-8 carbon atoms, either of which alkyl may be substituted or unsubstituted. Examples of preferred substituents include acid or acid salt groups (for example, sulfo or carboxy groups). Thus, either or both R₁ or R₂ could be, for example, 2-sulfobutyl, 3-sulfopropyl, or sulfoethyl.
Examples of Dye A and Dye B used in materials of the present invention are listed below in Table A, but the present invention is not limited to the use of these dyes.
In a preferred embodiment of the invention a silver halide photographic material comprises a red sensitive silver halide emulsion layer which has a dye of formula (Ia) used in combinations with a dye for formula (IIa):

where:
R₁ and R₂ each independently represent an alkyl group or a substituted alkyl group;
V₂-V₇ are independently H or a 1 to 8 carbon alkyl;
Z is a hydrogen or methyl;
A is a counterion if needed to balance the charge.
Sensitizing dyes which are particularly valuable in red spectrally sensitized emulsions are shown below:
When reference in this application is made to a substituent "group", this means that the substituent may itself be substituted or unsubstituted (for example "alkyl group" refers to a substituted or unsubstituted alkyl). Generally, unless otherwise specifically stated, substituents on any "groups" referenced herein or where something is stated to be possibly substituted, include the possibility of any groups, whether substituted or unsubstituted, which do not destroy properties necessary for the photographic utility. It will also be understood throughout this application that reference to a compound of a particular general formula includes those compounds of other more specific formula which specific formula falls within the general formula definition. Examples of substituents on any of the mentioned groups can include known substituents, such as: halogen, for example, chloro, fluoro, bromo, iodo; alkoxy, particularly those with 1 to 6 carbon atoms (for example, methoxy, ethoxy); substituted or unsubstituted alkyl, particularly lower alkyl (for example, methyl, trifluoromethyl); alkenyl or thioalkyl (for example, methylthio or ethylthio), particularly either of those with 1 to 6 carbon atoms; substituted and unsubstituted aryl, particularly those having from 6 to 20 carbon atoms (for example, phenyl); and substituted or unsubstituted heteroaryl, particularly those having a 5 or 6-membered ring containing 1 to 3 heteroatoms selected from N, O, or S (for example, pyridyl, thienyl, furyl, pyrrolyl); and others known in the art. Alkyl substituents may specifically include "lower alkyl", that is having from 1 to 6 carbon atoms, for example, methyl, ethyl. Further, with regard to any alkyl group, alkylene group or alkenyl group, it will be understood that these can be branched or unbranched and include ring structures.
Emulsions can be spectrally sensitized with mixtures of two or more sensitizing dyes which form mixed dye aggregates on the surface of the emulsion grain. The use of mixed dye aggregates enables adjustment of the spectral sensitivity of the emulsion to any wavelength between the extremes of the wavelengths of peak sensitivities (λ-max) of the two or more dyes. This practice is especially valuable if the two or more sensitizing dyes absorb in similar portions of the spectrum (i.e., blue, or green or red and not green plus red or blue plus red or green plus blue). Since the function of the spectral sensitizing dye is to modulate the information recorded in the negative which is recorded as an image dye, positioning the peak spectral sensitivity at or near the λ-max of the image dye in the color negative produces the optimum preferred response. In addition, the combination of similarly spectrally sensitized emulsions can be in one or more layers.
As mentioned above, the filter dye preferably is of the formula:
wherein:
G and G' independently represent oxygen, substituted nitrogen, or C(CN)₂;
R₃, R₃', R₄, R₄' independently represent H or a substituent, or R₃ and R₄, R₃' and R₄' may form a ring;
R₅ is an acyl, alkoxycarbonyl, amido, carbamoyl, alkyl, aryl, alkyloxy, aryloxy, amino, or heterocyclic, any of which may be substituted or unsubstituted;
m is 0, 1, 2, or 3;
all of the L" together define a methine chain each L" representing a methine any of which may be substituted or unsubstituted; and
M⁺ is a cation or proton.
Filter dyes of the above formula are described in more detail in U.S. Patent No. 5,451,494.
Particularly preferred filter dyes are of the formula:
wherein
R₅ and R₆ each independently represents H or a substituent, or R₅ and R₆ may form a ring;
R₇ is an acyl, alkoxycarbonyl, amido, carbamoyl, alkyl, aryl, alkoxy, aryloxy, amino, or heterocyclic, any of which may be substituted or unsubstituted; and
M⁺ is a cation or proton.
Hereunder, the typical examples of the photographic filter dyes relating to the present invention are given in Table 1. However, the present invention shall not be limited to use thereto.

Comparison Filter Dyes:

The absorbance maximum and half band width of the dyes used in this invention in a photographic coating are shown in Table 2.

Absorbance maximum and half band width of filter dyes
Dye	Absorbance maximum (gelatin coating)	Ratio of Absorbance Density O.D.(λmax-50nm) /O.D.(λmax)	Half Band Width
Invention FD1	694 nm	0.58	95 nm
Invention FD7	702 nm	0.60	100 nm
Invention FD8	703 nm	0.65	100 nm
Invention FD10	701 nm	0.59	96 nm
Invention FD11	687 nm	0.64	100 nm
Invention FD12	687 nm	0.62	100 nm
Invention FD13	686 nm	0.63	98 nm
Comparison CFD1	671 nm	0.59	100 nm
Comparison CFD2	638 nm	0.60	102 nm
Comparison CFD3	725 nm	0.71	192 nm
Comparison CFD4	718 nm	0.61	120 nm

In accordance with a preferred embodiment of the invention the silver halide contains dopant (i) which is a hexacoordination metal complex which satisfies the formula: [ML₆]ⁿ wherein
n is zero, -1, -2, -3 or -4;
M is a filled frontier orbital polyvalent metal ion, other than iridium; and
L₆ represents bridging ligands which can be independently selected, provided that at least four of the ligands are anionic ligands, and at least one of the ligands is a cyano ligand/or a ligand more electronegative than a cyano ligand.
Any remaining ligands can be selected from among various other bridging ligands, including aquo ligands, halide ligands (specifically, fluoride, chloride, bromide and iodide), cyanate ligands, thiocyanate ligands, selenocyanate ligands, tellurocyanate ligands, and azide ligands. Hexacoordinated transition metal complexes of which include six cyano ligands are specifically preferred as dopant (i).
Illustrations of specifically contemplated for use as dopant (i) are hexacoordination complexes for inclusion in the high chloride grains are provided by Olm et al U.S. Patent 5,503,970 and Daubendiek et al U.S. Patents 5,494,789 and 5,503,971, and Keevert et al U.S. Patent 4,945,035, as well as Murakami et al Japanese Patent Application Hei-2[1990]-249588, and Research Disclosure Item 36736 (November, 1994). Useful neutral and anionic organic ligands for dopant (i) hexacoordination complexes are disclosed by Olm et al U.S. Patent 5,360,712 and Kuromoto et al U.S. Patent 5,462,849.
Dopant (i) is preferably introduced into the high chloride grains after at least 50 (most preferably 75 and optimally 80) percent of the silver has been precipitated, but before precipitation of the central portion of the grains has been completed. Preferably dopant (i) is introduced before 98 (most preferably 95 and optimally 90) percent of the silver has been precipitated. Stated in terms of the fully precipitated grain structure, dopant (i) is preferably present in an interior shell region that surrounds at least 50 (most preferably 75 and optimally 80) percent of the silver and, with the more centrally located silver, accounts for the entire central portion (99 percent of the silver), most preferably accounts for 95 percent, and optimally accounts for 90 percent of the silver halide forming the high chloride grains. Dopant (i) can be distributed throughout the interior shell region delimited above or can be added as one or more bands within the interior shell region.
Dopant (i) can be employed in any conventional useful concentration. A preferred concentration range is from 10^-8 to 10^-3 mole per silver mole, most preferably from 10^-6 to 5 X 10^-4 mole per silver mole.

The following are specific illustrations of dopant (i):

(i-1)	[Fe(CN)₆]^-4
(i-2)	[Ru(CN)₆]^-4
(i-3)	[Os(CN)₆]^-4
(i-4)	[Rh(CN)₆]^-3
(i-5)	[Co(CN)₆]^-3
(i-6)	[Fe(pyrazine)(CN)₅]^-4
(i-7)	[RuCl(CN)₅]^-4
(i-8)	[OsBr(CN)₅]^-4
(i-9)	[RhF(CN)₅]^-3
(i-10)	[In(NCS)₆]^-3
(i-11)	[FeCO(CN)₅]^-3
(i-12)	[RuF₂(CN)₄]^-4
(i-13)	[OsCl₂(CN)₄]^-4
(i-14)	[RhI₂(CN)₄]^-3
(i-15)	[Ga(NCS)₆]^-3
(i-16)	[Ru(CN)₅(OCN)]^-4
(i-17)	[Ru(CN)₅(N₃)]^-4
(i-18)	[Os(CN)₅(SCN)]^-4
(i-19)	[Rh(CN)₅(SeCN)]^-3
(i-20)	[Os(CN)Cl₅]^-4
(i-21)	[Fe(CN)₃Cl₃]^-3
(i-22)	[Ru(CO)₂(CN)₄]^-1

When dopant (i) have a net negative charge, it is appreciated that they are associated with a counter ion when added to the reaction vessel during precipitation. The counter ion is of little importance, since it is ionically dissociated from the dopant in solution and is not incorporated within the grain. Common counter ions known to be fully compatible with silver chloride precipitation, such as ammonium and alkali metal ions, are contemplated. It is noted that the same comments apply to Dopant (ii), otherwise described below.
In another preferred embodiment of the invention, the silver halide further comprises dopant (ii), which is an iridium coordination complex. Particularly preferred are iridium coordination complex containing at least one thiazole or substituted thiazole ligand. Careful scientific investigations have revealed Group VIII hexahalo coordination complexes to create deep electron traps, as illustrated R. S. Eachus, R. E. Graves and M. T. Olm J. Chem. Phys., Vol. 69, pp. 4580-7 (1978) and Physica Status Solidi A, Vol. 57, 429-37 (1980) and R. S. Eachus and M. T. Olm Annu. Rep. Prog. Chem. Sect. C. Phys. Chem., Vol. 83, 3, pp. 3-48 (1986). Dopant (ii) employed in the practice of this invention are believed to create such deep electron traps. In dopant (ii), the ligand can be any photographically acceptable ligand. Preferably dopant (ii) contains a thiazole or substituted thiazole, wherein the substituent(s) can be any photographically acceptable substituent which does not prevent incorporation of dopant (ii) into the silver halide grains. Exemplary substituents include lower alkyl (e.g., alkyl groups containing 1-4 carbon atoms), and specifically methyl. A specific example of a substituted thiazole ligand which may be used in accordance with the invention is 5-methylthiazole. Dopant (ii) preferably is an iridium coordination complex having ligands each of which are more electropositive than a cyano ligand. In a specifically preferred form the remaining non-thiazole or non-substituted-thiazole ligands of the coordination complexes forming dopant (ii) are halide ligands.
Particularly preferred dopant (ii) contains a coordination complex containing organic ligands disclosed by Olm et al U.S. Patent 5,360,712, Olm et al U.S. Patent 5,457,021 and Kuromoto et al U.S. Patent 5,462,849.
In a preferred form it is contemplated to employ as dopant (ii) a hexacoordination complex satisfying the formula: [IrL¹ ₆]^n' wherein
n' is zero, -1, -2, -3 or -4; and
L¹ ₆ represents six bridging ligands which can be independently selected, provided that at least four of the ligands are anionic ligands, each of the ligands is more electropositive than a cyano ligand, and preferably at least one of the ligands comprises a thiazole or substituted thiazole ligand. In a specifically preferred form at least four of the ligands are halide ligands, such as chloride or bromide ligands.
Dopant (ii) is preferably introduced into the high chloride grains after at least 50 (most preferably 85 and optimally 90) percent of the silver has been precipitated, but before precipitation of the central portion of the grains has been completed. Preferably dopant (ii) is introduced before 99 (most preferably 97 and optimally 95) percent of the silver has been precipitated. Stated in terms of the fully precipitated grain structure, dopant (ii) is preferably present in an interior shell region that surrounds at least 50 (most preferably 85 and optimally 90) percent of the silver and, with the more centrally located silver, accounts the entire central portion (99 percent of the silver), most preferably accounts for 97 percent, and optimally accounts for 95 percent of the silver halide forming the high chloride grains. Dopant (ii) can be distributed throughout the interior shell region delimited above or can be added as one or more bands within the interior shell region.
Dopant (ii) can be employed in any conventional useful concentration. A preferred concentration range is from 10^-9 to 10^-4 mole per silver mole. Iridium is most preferably employed in a concentration range of from 10^-8 to 10^-5 mole per silver mole.

Preferably dopant (ii) is of the formula:

(ii-1)	[IrCl₅(thiazole)]^-2
(ii-2)	[IrCl₄(thiazole)₂]^-1
(ii-3)	[IrBr₅(thiazole)]^-2
(ii-4)	[IrBr₄(thiazole)₂]^-1
(ii-5)	[IrCl₅(5-methylthiazole)]^-2
(ii-6)	[IrCl₄(5-methylthiazole)₂]^-1
(ii-7)	[IrBr₅(5-methylthiazole)]^-2
or
(ii-8)	[IrBr₄(5-methylthiazole)₂]^-1

The term "dopant" is used in this application to mean a component that is added to a silver halide emulsion as it is precipitated such that the dopant is incorporated into the emulsion grains.
The silver halide grains preferably contain greater than 50 mole percent chloride, based on silver. Preferably the grains contain at least 70 mole percent chloride and, optimally at least 90 mole percent chloride, based on silver. Iodide can be present in the grains up to its solubility limit, which is in silver iodochloride grains, under typical conditions of precipitation, about 11 mole percent, based on silver. It is preferred for most photographic applications to limit iodide to less than 5 mole percent iodide, most preferably less than 2 mole percent iodide, based on silver.
Silver bromide and silver chloride are miscible in all proportions. Hence, any portion, up to 50 mole percent, of the total halide not accounted for chloride and iodide, can be bromide. For color reflection print (i.e., color paper) bromide is typically limited to less than 10 mole percent based on silver and iodide is limited to less than 1 mole percent based on silver.
In a widely used form high chloride grains are precipitated to form cubic grains--that is, grains having {100} major faces and edges of equal length. In practice ripening effects usually round the edges and comers of the grains to some extent. However, except under extreme ripening conditions substantially more than 50 percent of total grain surface area is accounted for by {100} crystal faces.
High chloride tetradecahedral grains are a common variant of cubic grains. These grains contain 6 {100} crystal faces and 8 {111} crystal faces. Tetradecahedral grains are within the contemplation of this invention to the extent that greater than 50 percent of total surface area is accounted for by {100} crystal faces.
Although it is common practice to avoid or minimize the incorporation of iodide into high chloride grains employed in color paper, it is has been recently observed that silver iodochloride grains with {100} crystal faces and, in some instances, one or more {111} faces offer exceptional levels of photographic speed. In these emulsions iodide is incorporated in overall concentrations of from 0.05 to 3.0 mole percent, based on silver, with the grains having a surface shell of greater than 50 Å that is substantially free of iodide and a interior shell having a maximum iodide concentration that surrounds a core accounting for at least 50 percent of total silver. Such grain structures are illustrated by Chen et al EPO 0 718 679.
In another embodiment the high chloride grains can take the form of tabular grains having {100} major faces. Preferred high chloride {100} tabular grain emulsions are those in which the tabular grains account for at least 70 (most preferably at least 90) percent of total grain projected area. Preferred high chloride {100} tabular grain emulsions have average aspect ratios of at least 5 (most preferably at least >8). Tabular grains typically have thicknesses of less than 0.3 µm, preferably less than 0.2 µm, and optimally less than 0.07 µm. High chloride {100} tabular grain emulsions and their preparation are disclosed by Maskasky U.S. Patents 5,264,337 and 5,292,632, House et al U.S. Patent 5,320,938, Brust et al U.S. Patent 5,314,798 and Chang et al U.S. Patent 5,413,904.
Once high chloride grains having predominantly {140} crystal faces have been precipitated in the presence of dopant (i) or a combination of dopant (i) and dopant (ii) described above, chemical and spectral sensitization, followed by the addition of conventional addenda to adapt the emulsion for the imaging application of choice can take any convenient conventional form. These conventional features are illustrated by Research Disclosure I, cited above, particularly:
III. Emulsion washing;
IV. Chemical sensitization;
V. Spectral sensitization and desensitization;
VII. Antifoggants and stabilizers;
VIII. Absorbing and scattering materials;
IX. Coating and physical property modifying addenda; and
X. Dye image formers and modifiers.
Some additional silver halide, typically less than 1 percent, based on total silver, can be introduced to facilitate chemical sensitization. It is also recognized that silver halide can be epitaxially deposited at selected sites on a host grain to increase its sensitivity. For example, high chloride {100} tabular grains with comer epitaxy are illustrated by Maskasky U.S. Patent 5,275,930. For the purpose of providing a clear demarcation, the term "silver halide grain" is herein employed to include the silver necessary to form the grain up to the point that the final {100} crystal faces of the grain are formed. Silver halide later deposited that does not overlie the {100} crystal faces previously formed accounting for at least 50 percent of the grain surface area is excluded in determining total silver forming the silver halide grains. Thus, the silver forming selected site epitaxy is not part of the silver halide grains while silver halide that deposits and provides the final {100} crystal faces of the grains is included in the total silver forming the grains, even when it differs significantly in composition from the previously precipitated silver halide.
In the simplest contemplated form a imaging element contemplated for use in the electronic or optical printing method used in the invention can consist of a single emulsion layer satisfying the emulsion description provided above coated on a conventional photographic support, such as those described in Research Disclosure I, Section XVI. In one preferred form the support is a white reflective support, such as photographic paper support or a film support that contains or bears a coating of a reflective pigment. To permit a print image to be viewed using an illuminant placed behind the support, it is preferred to employ a white translucent support, such as a Duratrans™ or Duraclear™ support.
Image dye-forming couplers may be included in the element such as couplers that form cyan dyes upon reaction with oxidized color developing agents which are described in such representative patents and publications as: U.S. Patent Nos. 2,367,531; 2,423,730; 2,474,293; 2,772,162; 2,895,826; 3,002,836; 3,034,892; 3,041,236; 4,883,746 and "Farbkuppler - Eine Literatur Ubersicht," published in Agfa Mitteilungen, Band III, pp. 156-175 (1961). Preferably such couplers are phenols and naphthols that form cyan dyes on reaction with oxidized color developing agent. Also preferable are the cyan couplers described in, for instance, European Patent Application Nos. 491,197; 544,322; 556,700; 556,777; 565,096; 570,006; and 574,948.
Typical cyan couplers are represented by the following formulas:

wherein R₇, R₁₁ and R₁₄ each represents a hydrogen or a substituent; R₈ represents a substituent; R₉, R₁₀ and R₁₃ each represents an electron attractive group having a Hammett's substituent constant σ_para of 0.2 or more and the sum of the σ_para values of R₉ and R₁₀ is 0.65 or more; R₁₂ represents an electron attractive group having a Hammett's substituent constant σ_para of 0.35 or more; X represents a hydrogen or a coupling-off group; Z₁ represents nonmetallic atoms necessary for forming a nitrogen-containing, six-membered, heterocyclic ring which has at least one dissociative group; Z2 represents ―C(R₁₃)= and ―N=; and Z₃ and Z₄ each represent ―C(R₁₄)= and ―N=.
For purposes of this invention, an "NB coupler" is a dye-forming coupler which is capable of coupling with the developer 4-amino-3-methyl-N-ethyl-N-(2-methanesulfonamidoethyl) aniline sesquisulfate hydrate to form a dye for which the left bandwidth (LBW) of its absorption spectra upon "spin coating" of a 3% w/v solution of the dye in di-n-butyl sebacate solvent is at least 5 nm. less than the LBW for a 3% w/v solution of the same dye in acetonitrile. The LBW of the spectral curve for a dye is the distance between the left side of the spectral curve and the wavelength of maximum absorption measured at a density of half the maximum.
The "spin coating" sample is prepared by first preparing a solution of the dye in di-n-butyl sebacate solvent (3% w/v). If the dye is insoluble, dissolution is achieved by the addition of some methylene chloride. The solution is filtered and 0.1-0.2ml is applied to a clear polyethylene terephthalate support (approximately 4cm x 4cm) and spun at 4,000RPM using the Spin Coating equipment, Model No. EC101, available from Headway Research Inc., Garland TX. The transmission spectra of the so prepared dye samples are then recorded.
Preferred "NB couplers" form a dye which, in n-butyl sebacate, has a LBW of the absorption spectra upon "spin coating" which is at least 15 nm, preferably at least 25 nm, less than that of the same dye in a 3% solution (w/v) in acetonitrile.
In a preferred embodiment the cyan dye-forming "NB coupler" useful in the invention has the formula (NBC-1A)
wherein
R₁₅ and R₁₆ are substituents selected such that the coupler is a "NB coupler", as herein defined; and
Z is a hydrogen atom or a group which can be split off by the reaction of the coupler with an oxidized color developing agent.
The coupler of formula (IA) is a 2,5-diamido phenolic cyan coupler wherein the substituents R' and R" are preferably independently selected from unsubstituted or substituted alkyl, aryl, amino, alkoxy and heterocyclyl groups.
In a further preferred embodiment, the "NB coupler" has the formula (NBC-1):
wherein
R₁₉ and R₂₀ are independently selected from unsubstituted or substituted alkyl, aryl, amino, alkoxy and heterocyclyl groups and Z is as hereinbefore defined;
R₁₇ and R₁₈ are independently hydrogen or an unsubstituted or substituted alkyl group; and
Typically, R₁₉ is an alkyl, amino or aryl group, suitably a phenyl group. R'" is desirably an alkyl or aryl group or a 5-10 membered heterocyclic ring which contains one or more heteroatoms selected from nitrogen, oxygen and sulfur, which ring group is unsubstituted or substituted.
In the preferred embodiment the coupler of formula (NBC-I) is a 2,5-diamido phenol in which the 5-amido moiety is an amide of a carboxylic acid which is substituted in the alpha position by a particular sulfone (-SO₂-) group, such as, for example, described in U.S. Patent No. 5,686,235. The sulfone moiety is an unsubstituted or substituted alkylsulfone or a heterocyclyl sulfone or it is an arylsulfone, which is preferably substituted, in particular in the meta and/or para position.
Couplers having these structures of formulae (NBC-I) or (NBC-IA) comprise cyan dye-forming "NB couplers" which form image dyes having very sharp-cutting dye hues on the short wavelength side of the absorption curves with absorption maxima (λ_max) which are shifted hypsochromically and are generally in the range of 620-645 nm, which is ideally suited for producing excellent color reproduction and high color saturation in color photographic papers.
Referring to formula (NBC-I), R₁₇ and R₁₈ are independently hydrogen or an unsubstituted or substituted alkyl group, preferably having from 1 to 24 carbon atoms and in particular 1 to 10 carbon atoms, suitably a methyl, ethyl, n-propyl, isopropyl, butyl or decyl group or an alkyl group substituted with one or more fluoro, chloro or bromo atoms, such as a trifluoromethyl group. Suitably, at least one of R₁₇ and R₁₈ is a hydrogen atom and if only one of R₁₇ and R₁₈ is a hydrogen atom then the other is preferably an alkyl group having 1 to 4 carbon atoms, more preferably one to three carbon atoms and desirably two carbon atoms.
As used herein and throughout the specification unless where specifically stated otherwise, the term "alkyl" refers to an unsaturated or saturated straight or branched chain alkyl group, including alkenyl, and includes aralkyl and cyclic alkyl groups, including cycloalkenyl, having 3-8 carbon atoms and the term 'aryl' includes specifically fused aryl.
In formula (NBC-I), R₁₉ is suitably an unsubstituted or substituted amino, alkyl or aryl group or a 5-10 membered heterocyclic ring which contains one or more heteroatoms selected from nitrogen, oxygen and sulfur, which ring is unsubstituted or substituted, but is more suitably an unsubstituted or substituted phenyl group.
Examples of suitable substituent groups for this aryl or heterocyclic ring include cyano, chloro, fluoro, bromo, iodo, alkyl- or aryl-carbonyl, alkyl- or aryl-oxycarbonyl, carbonamido, alkyl- or aryl-carbonamido, alkyl- or arylsulfonyl, alkyl- or aryl-sulfonyloxy, alkyl- or aryl-oxysulfonyl, alkyl- or arylsulfoxide, alkyl- or aryl-sulfamoyl, alkyl- or aryl-sulfonamido, aryl, alkyl, alkoxy, aryloxy, nitro, alkyl- or aryl-ureido and alkyl- or aryl-carbamoyl groups, any of which may be further substituted. Preferred groups are halogen, cyano, alkoxycarbonyl, alkylsulfamoyl, alkyl-sulfonamido, alkylsulfonyl, carbamoyl, alkylcarbamoyl or alkylcarbonamido. Suitably, R₁₉ is a 4-chlorophenyl, 3,4-di-chlorophenyl, 3,4-difluorophenyl, 4-cyanophenyl, 3-chloro-4-cyanophenyl, pentafluorophenyl, or a 3- or 4-sulfonamidophenyl group.
In formula (NBC-I), when R₂₀ is alkyl it may be unsubstituted or substituted with a substituent such as halogen or alkoxy. When R''' is aryl or a heterocycle, it may be substituted. Desirably it is not substituted in the position alpha to the sulfonyl group.
In formula (I), when R''' is a phenyl group, it may be substituted in the meta and/or para positions with one to three substituents independently selected from the group consisting of halogen, and unsubstituted or substituted alkyl, alkoxy, aryloxy, acyloxy, acylamino, alkyl- or aryl-sulfonyloxy, alkyl- or aryl-sulfamoyl, alkyl- or aryl-sulfamoylamino, alkyl- or aryl-sulfonamido, alkyl- or aryl-ureido, alkyl- or aryl-oxycarbonyl, alkyl- or aryl-oxy-carbonylamino and alkyl- or aryl-carbamoyl groups.
In particular each substituent may be an alkyl group such as methyl, t-butyl, heptyl, dodecyl, pentadecyl, octadecyl or 1,1,2,2-tetramethylpropyl; an alkoxy group such as methoxy, t-butoxy, octyloxy, dodecyloxy, tetradecyloxy, hexadecyloxy or octadecyloxy; an aryloxy group such as phenoxy, 4-t-butylphenoxy or 4-dodecyl-phenoxy; an alkyl- or aryl-acyloxy group such as acetoxy or dodecanoyloxy; an alkyl- or aryl-acylamino group such as acetamido, hexadecanamido or benzamido; an alkyl- or aryl-sulfonyloxy group such as methyl-sulfonyloxy, dodecylsulfonyloxy or 4-methylphenyl-sulfonyloxy; an alkyl- or aryl-sulfamoyl-group such as N-butylsulfamoyl or N-4-t-butylphenylsulfamoyl; an alkyl- or aryl-sulfamoylamino group such as N-butyl-sulfamoylamino or N-4-t-butylphenylsulfamoyl-amino; an alkyl- or aryl-sulfonamido group such as methane-sulfonamido, hexadecanesulfonamido or 4-chlorophenyl-sulfonamido; an alkyl- or aryl-ureido group such as methylureido or phenylureido; an alkoxy- or aryloxy-carbonyl such as methoxycarbonyl or phenoxycarbonyl; an alkoxy- or aryloxy-carbonylamino group such as methoxy-carbonylamino or phenoxycarbonylamino; an alkyl- or aryl-carbamoyl group such as N-butylcarbamoyl or N-methyl-N-dodecylcarbamoyl; or a perfluoroalkyl group such as trifluoromethyl or heptafluoropropyl.
Suitably the above substituent groups have 1 to 30 carbon atoms, more preferably 8 to 20 aliphatic carbon atoms. A desirable substituent is an alkyl group of 12 to 18 aliphatic carbon atoms such as dodecyl, pentadecyl or octadecyl or an alkoxy group with 8 to 18 aliphatic carbon atoms such as dodecyloxy and hexadecyloxy or a halogen such as a meta or para chloro group, carboxy or sulfonamido. Any such groups may contain interrupting heteroatoms such as oxygen to form e.g. polyalkylene oxides.
In formula (NBC-I) or (NBC-IA), Z is a hydrogen atom or a group which can be split off by the reaction of the coupler with an oxidized color developing agent, known in the photographic art as a 'coupling-off group' and may preferably be hydrogen, chloro, fluoro, substituted aryloxy or mercaptotetrazole, more preferably hydrogen or chloro.
The presence or absence of such groups determines the chemical equivalency of the coupler, i.e., whether it is a 2-equivalent or 4-equivalent coupler, and its particular identity can modify the reactivity of the coupler. Such groups can advantageously affect the layer in which the coupler is coated, or other layers in the photographic recording material, by performing, after release from the coupler, functions such as dye formation, dye hue adjustment, development acceleration or inhibition, bleach acceleration or inhibition, electron transfer facilitation, color correction.
Representative classes of such coupling-off groups include, for example, halogen, alkoxy, aryloxy, heterocyclyloxy, sulfonyloxy, acyloxy, acyl, heterocyclylsulfonamido, heterocyclylthio, benzothiazolyl, phosophonyloxy, alkylthio, arylthio, and arylazo. These coupling-off groups are described in the art, for example, in U.S. Patent Nos. 2,455,169; 3,227,551; 3,432,521; 3,467,563; 3,617,291; 3,880,661; 4,052,212; and 4,134,766; and in U.K. Patent Nos. and published applications 1,466,728; 1,531,927; 1,533,039; 2,066,755A, and 2,017,704A. Halogen, alkoxy and aryloxy groups are most suitable.
Examples of specific coupling-off groups are -Cl, -F, -Br, -SCN, -OCH₃, - OC₆H₅, -OCH₂C(=O)NHCH₂CH₂OH, -OCH₂C(O)NHCH₂CH₂OCH₃, - OCH₂C(O)NHCH₂CH₂OC(=O)OCH₃, -P(=O)(OC₂H₅)₂, -SCH₂CH₂C00H,
Typically, the coupling-off group is a chlorine atom, hydrogen atom or p-methoxyphenoxy group.
It is essential that the substituent groups be selected so as to adequately ballast the coupler and the resulting dye in the organic solvent in which the coupler is dispersed. The ballasting may be accomplished by providing hydrophobic substituent groups in one or more of the substituent groups. Generally a ballast group is an organic radical of such size and configuration as to confer on the coupler molecule sufficient bulk and aqueous insolubility as to render the coupler substantially nondiffusible from the layer in which it is coated in a photographic element. Thus the combination of substituent are suitably chosen to meet these criteria. To be effective, the ballast will usually contain at least 8 carbon atoms and typically contains 10 to 30 carbon atoms. Suitable ballasting may also be accomplished by providing a plurality of groups which in combination meet these criteria. In the preferred embodiments of the invention R₁₇ in formula (NBC-I) is a small alkyl group or hydrogen. Therefore, in these embodiments the ballast would be primarily located as part of the other groups. Furthermore, even if the coupling-off group Z contains a ballast it is often necessary to ballast the other substituents as well, since Z is eliminated from the molecule upon coupling; thus, the ballast is most advantageously provided as part of groups other than Z.
The following examples further illustrate preferred couplers used in the invention.

Preferred couplers are IC-3, IC-7, IC-35, and IC-36.
Couplers that form magenta dyes upon reaction with oxidized color developing agent are described in such representative patents and publications as: U.S. Patent Nos. 2,311,082, 2,343,703, 2,369,489, 2,600,788, 2,908,573, 3,062,653, 3,152,896, 3,519,429, 3,758,309, and "Farbkuppler-eine Literatur-Übersicht," published in Agfa Mitteilungen, Band III, pp. 126-156 (1961). Preferably such couplers are pyrazolones, pyrazolotriazoles, or pyrazolobenzimidazoles that form magenta dyes upon reaction with oxidized color developing agents. Especially preferred couplers are 1H-pyrazolo [5,1-c]-1,2,4-triazole and 1H-pyrazolo [1,5-b]-1,2,4-triazole. Examples of 1H-pyrazolo [5,1-c]-1,2,4-triazole couplers are described in U.K. Patent Nos. 1,247,493; 1,252,418; 1,398,979; U.S. Patent Nos. 4,443,536; 4,514,490; 4,540,654; 4,590,153; 4,665,015; 4,822,730; 4,945,034; 5,017,465; and 5,023,170. Examples of 1H-pyrazolo [1,5-b]-1,2,4-triazoles can be found in European Patent applications 176,804; 177,765; U.S Patent Nos. 4,659,652; 5,066,575; and 5,250,400.
Typical pyrazoloazole and pyrazolone couplers are represented by the following formulas:
wherein R_a and R_b independently represent H or a substituent; R_c is a substituent (preferably an aryl group); R_d is a substituent (preferably an anilino, carbonamido, ureido, carbamoyl, alkoxy, aryloxycarbonyl, alkoxycarbonyl, or N-heterocyclic group); X is hydrogen or a coupling-off group; and Z_a, Z_b, and Z_c are independently a substituted methine group, =N―, =C―, or ―NH―, provided that one of either the Z_a―Z_b bond or the Z_b―Z_c bond is a double bond and the other is a single bond, and when the Z_b―Z_c bond is a carbon-carbon double bond, it may form part of an aromatic ring, and at least one of Z_a, Z_b, and Z_c represents a methine group connected to the group R_b.
Specific examples of such couplers are:
Couplers that form yellow dyes upon reaction with oxidized color developing agent are described in such representative patents and publications as: U.S. Patent Nos. 2,298,443; 2,407,210; 2,875,057; 3,048,194; 3,265,506; 3,447,928; 3,960,570; 4,022,620; 4,443,536; 4,910,126; and 5,340,703 and "Farbkuppler-eine Literaturübersicht," published in Agfa Mitteilungen, Band III, pp. 112-126 (1961). Such couplers are typically open chain ketomethylene compounds. Also preferred are yellow couplers such as described in, for example, European Patent Application Nos. 482,552; 510,535; 524,540; 543,367; and U.S. Patent No. 5,238,803. For improved color reproduction, couplers which give yellow dyes that cut off sharply on the long wavelength side are particularly preferred (for example, see U.S. Patent No. 5,360,713).
Typical preferred yellow couplers are represented by the following formulas:

wherein R₁, R₂, Q₁ and Q₂ each represents a substituent; X is hydrogen or a coupling-off group; Y represents an aryl group or a heterocyclic group; Q₃ represents an organic residue required to form a nitrogen-containing heterocyclic group together with the >N―; and Q₄ represents nonmetallic atoms necessary to form a 3- to 5-membered hydrocarbon ring or a 3- to 5-membered heterocyclic ring which contains at least one hetero atom selected from N, O, S, and P in the ring. Particularly preferred is when Q₁ and Q₂ each represent an alkyl group, an aryl group, or a heterocyclic group, and R₂ represents an aryl or tertiary alkyl group.
Preferred yellow couplers can be of the following general structures
Unless otherwise specifically stated, substituent groups which may be substituted on molecules herein include any groups, whether substituted or unsubstituted, which do not destroy properties necessary for photographic utility. When the term "group" is applied to the identification of a substituent containing a substitutable hydrogen, it is intended to encompass not only the substituent's unsubstituted form, but also its form further substituted with any group or groups as herein mentioned. Suitably, the group may be halogen or may be bonded to the remainder of the molecule by an atom of carbon, silicon, oxygen, nitrogen, phosphorous, or sulfur. The substituent may be, for example, halogen, such as chlorine, bromine or fluorine; nitro; hydroxyl; cyano; carboxyl; or groups which may be further substituted, such as alkyl, including straight or branched chain alkyl, such as methyl, trifluoromethyl, ethyl, t-butyl, 3-(2,4-di-t-pentylphenoxy) propyl, and tetradecyl; alkenyl, such as ethylene, 2-butene; alkoxy, such as methoxy, ethoxy, propoxy, butoxy, 2-methoxyethoxy, sec-butoxy, hexyloxy, 2-ethylhexyloxy, tetradecyloxy, 2-(2,4-di-t-pentylphenoxy)ethoxy, and 2-dodecyloxyethoxy; aryl such as phenyl, 4-t-butylphenyl, 2,4,6-trimethylphenyl, naphthyl; aryloxy, such as phenoxy, 2-methylphenoxy, alpha- or beta-naphthyloxy, and 4-tolyloxy; carbonamido, such as acetamido, benzamido, butyramido, tetradecanamido, alpha-(2,4-di-t-pentyl-phenoxy)acetamido, alpha-(2,4-di-t-pentylphenoxy)butyramido, alpha-(3-pentadecylphenoxy)-hexanamido, alpha-(4-hydroxy-3-t-butylphenoxy)-tetradecanamido, 2-oxo-pyrrolidin-1-yl, 2-oxo-5-tetradecylpyrrolin-1-yl, N-methyltetradecanamido, N-succinimido, N-phthalimido, 2,5-dioxo-1-oxazolidinyl, 3-dodecyl-2,5-dioxo-1-imidazolyl, and N-acetyl-N-dodecylamino, ethoxycarbonylamino, phenoxycarbonylamino, benzyloxycarbonylamino, hexadecyloxycarbonylamino, 2,4-di-t-butylphenoxycarbonylamino, phenylcarbonylamino, 2,5-(di-t-pentylphenyl)carbonylamino, p-dodecyl-phenylcarbonylamino, p-toluylcarbonylamino, N-methylureido, N,N-dimethylureido, N-methyl-N-dodecylureido, N-hexadecylureido, N,N-dioctadecylureido, N,N-dioetyl-N'-ethylureido, N-phenylureido, N,N-diphenylureido, N-phenyl-N-p-toluylureido, N-(m-hexadecylphenyl)ureido, N,N-(2,5-di-t-pentylphenyl)-N'-ethylureido, and t-butylcarbonamido; sulfonamido, such as methylsulfonamido, benzenesulfonamido, p-toluylsulfonamido, p-dodecylbenzenesulfonamido, N-methyltetradecylsulfonamido, N,N-dipropyl-sulfamoylamino, and hexadecylsulfonamido; sulfamoyl, such as N-methylsulfamoyl, N-ethylsulfamoyl, N,N-dipropylsulfamoyl, N-hexadecylsulfamoyl, N,N-dimethylsulfamoyl; N-[3-(dodecyloxy)propyl]sulfamoyl, N-[4-(2,4-di-t-pentylphenoxy)butyl]sulfamoyl, N-methyl-N-tetradecylsulfamoyl, and N-dodecylsulfamoyl; carbamoyl, such as N-methylcarbamoyl, N,N-dibutylcarbamoyl, N-octadecylcarbamoyl, N-[4-(2,4-di-t-pentylphenoxy)butyl]carbamoyl, N-methyl-N-tetradecylcarbamoyl, and N,N-dioctylcarbamoyl; acyl, such as acetyl, (2,4-di-t-amylphenoxy)acetyl, phenoxycarbonyl, p-dodecyloxyphenoxycarbonyl, methoxycarbonyl, butoxycarbonyl, tetradecyloxycarbonyl, ethoxycarbonyl, benzyloxycarbonyl, 3-pentadecyloxycarbonyl, and dodecyloxycarbonyl; sulfonyl, such as methoxysulfonyl, octyloxysulfonyl, tetradecyloxysulfonyl, 2-ethylhexyloxysulfonyl, phenoxysulfonyl, 2,4-di-t-pentylphenoxysulfonyl, methylsulfonyl, octylsulfonyl, 2-ethylhexylsulfonyl, dodecylsulfonyl, hexadecylsulfonyl, phenylsulfonyl, 4-nonylphenylsulfonyl, and p-toluylsulfonyl; sulfonyloxy, such as dodecylsulfonyloxy, and hexadecylsulfonyloxy; sulfinyl, such as methylsulfinyl, octylsulfinyl, 2-ethylhexylsulfinyl, dodecylsulfinyl, hexadecylsulfinyl, phenylsulfinyl, 4-nonylphenylsulfinyl, and p-toluylsulfinyl; thio, such as ethylthio, octylthio, benzylthio, tetradecylthio, 2-(2,4-di-t-pentylphenoxy)ethylthio, phenylthio, 2-butoxy-5-t-octylphenylthio, and p-tolylthio; acyloxy, such as acetyloxy, benzoyloxy, octadecanoyloxy,p-dodecylamidobenzoyloxy, N-phenylcarbamoyloxy, N-ethylcarbamoyloxy, and cyclohexylcarbonyloxy; amino, such as phenylanilino, 2-chloroanilino, diethylamino, dodecylamino; imino, such as 1 (N-phenylimido)ethyl, N-succinimido or 3-benzylhydantoinyl; phosphate, such as dimethylphosphate and ethylbutylphosphate; phosphite, such as diethyl and dihexylphosphite; a heterocyclic group, a heterocyclic oxy group or a heterocyclic thio group, each of which may be substituted and which contain a 3 to 7 membered heterocyclic ring composed of carbon atoms and at least one hetero atom selected from the group consisting of oxygen, nitrogen and sulfur, such as 2-furyl, 2-thienyl, 2-benzimidazolyloxy or 2-benzothiazolyl; quaternary ammonium, such as triethylammonium; and silyloxy, such as trimethylsilyloxy.
If desired, the substituents may themselves be further substituted one or more times with the described substituent groups. The particular substituents used may be selected by those skilled in the art to attain the desired photographic properties for a specific application and can include, for example, hydrophobic groups, solubilizing groups, blocking groups, releasing or releasable groups, etc. Generally, the above groups and substituents thereof may include those having up to 48 carbon atoms, typically 1 to 36 carbon atoms and usually less than 24 carbon atoms, but greater numbers are possible depending on the particular substituents selected.
Representative substituents on ballast groups include alkyl, aryl, alkoxy, aryloxy, alkylthio, hydroxy, halogen, alkoxycarbonyl, aryloxcarbonyl, carboxy, acyl, acyloxy, amino, anilino, carbonamido, carbamoyl, alkylsulfonyl, arylsulfonyl, sulfonamido, and sulfamoyl groups wherein the substituents typically contain 1 to 42 carbon atoms. Such substituents can also be further substituted.

Stabilizers and scavengers that can be used in these photographic elements include, but are not limited to, the following.

Examples of solvents which may be used in the invention include the following:

Tritolyl phosphate	S-1
Dibutyl phthalate	S-2
Diundecyl phthalate	S-3
N,N-Diethyldodecanamide	S-4
N,N-Dibutyldodecanamide	S-5
Tris(2-ethylhexyl)phosphate	S-6
Acetyl tributyl citrate	S-7
2,4-Di-tert-pentylphenol	S-8
2-(2-Butoxyethoxy)ethyl acetate	S-9
1,4-Cyclohexyldimethylene bis(2-ethylhexanoate)	S-10

The dispersions used in photographic elements may also include ultraviolet (UV) stabilizers and so called liquid UV stabilizers such as described in U.S. Patent Nos. 4,992,358; 4,975,360; and 4,587,346. Examples of UV stabilizers are shown below.
The aqueous phase may include surfactants. Surfactant may be cationic, anionic, zwitterionic or non-ionic. Useful surfactants include, but are not limited to, the following:
Further, it is contemplated to stabilize photographic dispersions prone to particle growth through the use of hydrophobic, photographically inert compounds such as disclosed by Zengerle et al in U.S. Patent No. 5,468,604.
The photographic elements of this invention can be single color elements or multicolor elements. Multicolor elements typically contain dye image-forming units sensitive to each of the three primary regions of the visible 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 the following discussion of suitable materials for use in the emulsions and elements of this invention, reference will be made to Research Disclosure L
The silver halide emulsions employed in the elements of this invention can be either negative working or positive working. Suitable emulsions and their preparation are described in Research Disclosure I, Sections I and II and the publications cited therein. Suitable vehicles for the emulsion layers and other layers of elements of this invention are described in Research Disclosure I, Section IX and the publications cited therein.
The elements of the invention can include couplers as described in Research Disclosure I, Section VII, paragraphs D, E, F, and G and the publications cited therein. These couplers can be incorporated in the elements and emulsions as described in Research Disclosure I, Section VII, paragraph C and the publications cited therein.
The photographic elements of this invention or individual layers thereof, can contain brighteners (see Research Disclosure I, Section V), antifoggants and stabilizers (see Research Disclosure I, Section VI), antistain agents and image dye stabilizers (see Research Disclosure I, Section VII, paragraphs I and J), light absorbing and scattering materials (see Research Disclosure I, Section VIII), hardeners, (see Research Disclosure I, Section IX), plasticizers and lubricants (see Research Disclosure I, Section XII), antistatic agents (see Research Disclosure I, XIII), matting agents (see Research Disclosure I, Section XVI) and development modifiers (see Research Disclosure I, Section XXI).
The photographic elements can be coated on a variety of supports as described in Research Disclosure I, Section XVII and the references described therein. In a preferred embodiment of the invention comprises a reflective support. The reflective support preferably includes a resin layer with a stabilizing amount of hindered amine extruded on the top side of the imaging layer substrate. Hindered amine light stabilizers (HALS) originate from 2,2,6,6-tetramethylpiperidine. The hindered amine should be added to the polymer layer at 0.01- 5% by weight of said resin layer in order to provide resistance to polymer degradation upon exposure to UV light. The preferred amount is at 0.05-3% by weight. This provides excellent polymer stability and resistance to cracking and yellowing while keeping the expense of the hindered amine to a minimum. Examples of suitable hindered amines with molecular weights of less than 2300 are Bis(2,2,6,6-tetramethyl-4-piperidinyl)sebacate; Bis(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate; Bis(1,2,2,6,6-pentamethyl-4-piperidinyl)2-n-butyl-(3,5-di-tert-butyl-hydroxy-benzyl)malonate; 8-Acetyl-3-dodecyl-7,7,9,9-tetramethyl-1.3,8-triazaspiro(4,5)decane-2,4-dione; Tetra(2,2,6,6-tetramethyl-4-piperidinyl)1,2,3,4-butanetetracarboxylate; 1-(-2-[3,5-di-tert-butyl-4-hydroxyphenyl-propionyloxyl]ethyl)-4-(3,5-di-tert-butyl-4-hydroxyphenylpropionyloxy)-2,2,6,6-tetramethylpiperidine; 1,1'-(1,2-ethenediyl)bis(3,3,5,5-tetramethyl-2-piperazinone); The preferred hindered amine is 1,3,5-triazine-2,4,6-triamine,N,N'''-[1,2-ethanediylbis[[[4,6-bis(butyl(1,2,2,6,6-pentamethyl-4-piperidinyl)amino]-1,3,5-triazine-2-yl]imino]-3,1 propanediyl]]-bis[N',N"-dibutyl-N',N"-bis(1,2,2,6,6-pentamethyl-4-piperidinyl) which will be referred to as Compound A. Compound A is preferred because when mixtures of polymers and Compound A are extruded onto imaging paper the polymer to paper adhesion is excellent and the long term stability of the imaging system against cracking and yellowing is improved.
Suitable polymers for the resin layer include polyethylene, polypropylene, polymethylpentene, polystyrene, polybutylene, and mixtures thereof. Polyolefin copolymers, including copolymers of polyethylene, propylene and ethylene such as hexene, butene, and octene are also useful. Polyethylene is most preferred, as it is low in cost and has desirable coating properties. As polyethylene, usable are high-density polyethylene, low-density polyethylene, linear low density polyethylene, and polyethylene blends. Other suitable polymers include polyesters produced from aromatic, aliphatic or cycloaliphatic dicarboxylic acids of 4-20 carbon atoms and aliphatic or alicyclic glycols having from 2-24 carbon atoms. Examples of suitable dicarboxylic acids include terephthalic, isophthalic, phthalic, naphthalene dicarboxylic acid, succinic, glutaric, adipic, azelaic, sebacic, fumaric, maleic, itaconic, 1,4-cyclohexanedicarboxylic, sodiosulfoisophthalic and mixtures thereof. Examples of suitable glycols include ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, 1,4-cyclohexanedimethanol, diethylene glycol, other polyethylene glycols and mixtures thereof. Other polymers are matrix polyesters having repeat units from terephthalic acid or naphthalene dicarboxylic acid and at least one glycol selected from ethylene glycol, 1,4-butanediol and 1,4-cyclohexanedimethanol such as poly(ethylene terephthalate), which may be modified by small amounts of other monomers. Other suitable polyesters include liquid crystal copolyesters formed by the inclusion of suitable amount of a co-acid component such as stilbene dicarboxylic acid. Examples of such liquid crystal copolyesters are those disclosed in U.S. Patent Nos. 4,420,607; 4,459,402; and 4,468,510. Useful polyamides include nylon 6, nylon 66, and mixtures thereof. Copolymers of polyamides are also suitable continuous phase polymers. An example of a useful polycarbonate is bisphenol-A polycarbonate. Cellulosic esters suitable for use as the continuous phase polymer of the composite sheets include cellulose nitrate, cellulose triacetate, cellulose diacetate, cellulose acetate propionate, cellulose acetate butyrate, and mixtures or copolymers thereof. Useful polyvinyl resins include polyvinyl chloride, poly(vinyl acetal), and mixtures thereof. Copolymers of vinyl resins can also be utilized.
Any suitable white pigment may be incorporated in the polyolefin layer, such as, for example, zinc oxide, zinc sulfide, zirconium dioxide, white lead, lead sulfate, lead chloride, lead aluminate, lead phthalate, antimony trioxide, white bismuth, tin oxide, white manganese, white tungsten, and combinations thereof. The preferred pigment is titanium dioxide because of its high refractive index, which gives excellent optical properties at a reasonable cost. The pigment is used in any form that is conveniently dispersed within the polyolefin. The preferred pigment is anatase titanium dioxide. The most preferred pigment is rutile titanium dioxide because it has the highest refractive index at the lowest cost. The average pigment diameter of the rutile TiO₂ is most preferably in the range of 0.1 to 0.26 µm. The pigments that are greater than 0.26 µm are too yellow for an imaging element application and the pigments that are less than 0.1 µm are not sufficiently opaque when dispersed in polymers. Preferably, the white pigment should be employed in the range of from 10 to 50 percent by weight, based on the total weight of the polyolefin coating. Below 10 percent TiO₂, the imaging system will not be sufficiently opaque and will have inferior optical properties. Above 50 percent TiO₂, the polymer blend is not manufacturable. The surface of the TiO₂ can be treated with an inorganic compounds such as aluminum hydroxide, alumina with a fluoride compound or fluoride ions, silica with a fluoride compound or fluoride ion, silicon hydroxide, silicon dioxide, boron oxide, boria-modified silica (as described in US Patent 4,781,761), phosphates, zinc oxide, ZrO₂, etc. and with organic treatments such as polyhydric alcohol, polyhydric amine, metal soap, alkyl titanate, polysiloxanes, silanes. The organic and inorganic TiO₂ treatments can be used alone or in any combination. The amount of the surface treating agents is preferably in the range of 0.2 to 2.0% for the inorganic treatment and 0.1 to 1% for the organic treatment, relative to the weight of the weight of the titanium dioxide. At these levels of treatment the TiO₂ disperses well in the polymer and does not interfere with the manufacture of the imaging support.
The polymer, hindered amine light stabilizer, and the TiO₂ are mixed with each other in the presence of a dispersing agent. Examples of dispersing agents are metal salts of higher fatty acids such as sodium palmitate, sodium stearate, calcium palmitate, sodium laurate, calcium stearate, aluminum stearate, magnesium stearate, zirconium octylate, zinc stearate, higher fatty acids, higher fatty amide, and higher fatty acids. The preferred dispersing agent is sodium stearate and the most preferred dispersing agent is zinc stearate. Both of these dispersing agents give superior whiteness to the resin-coated layer.
For photographic use, a white base with a slight bluish tint is preferred. The layers of the waterproof resin coating preferably contain colorants such as a bluing agent and magenta or red pigment. Applicable bluing agents include commonly know ultramarine blue, cobalt blue, oxide cobalt phosphate, quinacridone pigments, and a mixture thereof. Applicable red or magenta colorants are quinacridones and ultramarines.
The resin may also include a fluorescing agent, which absorb energy in the UV region and emit light largely in the blue region. Any of the optical brighteners referred to in U.S. Patent 3,260,715 or a combination thereof would be beneficial.
The resin may also contain an antioxidant(s) such as hindered phenol primary antioxidants used alone or in combination with secondary antioxidants. Examples of hindered phenol primary antioxidants include pentaerythrityl tetrakis [3-(3,5-di-tert-butyl-4-hydroxyphenyl)proprionate] (such as Irganox 1010), octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)proprionate (such as Irganox 1076 which will be referred to as compound B), benzenepropanoic acid 3,5-bis(1,1-dimethyl)-4-hydroxy-2[3-[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl)-1-oxopropyl)hydrazide (such as Irganox MD1024), 2,2'-thiodiethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)proprionate] (such as Irganox 1035), 1,3,5-trimethyl-2,4,6-tri(3,5-di-tert-butyl-4-hydroxybenzyl)benzene (such as Irganox 1330), but are not limited to these examples. Secondary antioxidants include organic alkyl and aryl phosphites including examples such as triphenylphosphite (such as Irgastab TPP), tri(n-propylphenyl-phophite) (such as Irgastab SN-55), 2,4-bis(1,1-dimethylphenyl) phosphite (such as Irgafos 168).
The hindered amine light stabilizer, TiO₂, colorants, slip agents, optical brightener, and antioxidant are incorporated either together or separately with the polymer using a continuous or Banburry mixer. A concentrate of the additives in the form of a pellet is typically made. The concentration of the rutile pigment can be from 20% to 80% by weight of the masterbatch. The master batch is then adequately diluted for use with the resin.
The support to which the waterproof resin layer is laminated may be a polymeric, a synthetic paper, cloth, woven polymer fibers, or a cellulose fiber paper support, or laminates thereof. The base also may be a microvoided polyethylene terephthalate such as disclosed in U.S. Patent Nos. 4,912,333; 4,994,312; and 5,055,371. The preferred support is a photographic grade cellulose fiber paper.
To form the water-proof resin coating according to the present invention, the pellet containing the pigment and other additives is subjected to hotmelt coating onto a running support of paper or synthetic paper. If desired, the pellet is diluted with a polymer prior to hot melt coating. For a single layer coating the resin layer may be formed by lamination. The die is not limited to any specific type and may be any one of the common dies such as a T-slot or coat hanger die..An exit orifice temperature in heat melt extrusion of the water-proof resin ranges from 260-349°C (500-660°F). Further, before coating the support with resin, the support may be treated with an activating treatment such as corona discharge, flame, ozone, plasma, or glow discharge.
In preferred embodiments of the invention the resin layer is a biaxially oriented polyolefin sheet as described in U.S. Patent No. 5,853,965 or a microvoided biaxially oriented polyolefin sheet as described in U.S. Patent No. 5,866,282.
The thickness of the resin layer which is applied to a base paper of the reflective support used in the present invention at a side for imaging, is preferably in the range of 5 to 100 µm and most preferably in the range of 10 to 50 µm.
The thickness of the resin layer applied to a base paper on the side opposite the imaging element is preferably in a range from 5 to 100 µm and more preferably from 10 to 50 µm.
The surface of the waterproof resin coating at the imaging side may be a glossy, fine, silk, grain, or matte surface. On the surface of the water-proof coating on the backside which is not coated with an imaging element may also be glossy, fine, silk, or matte surface. The preferred water-proof surface for the backside away from the imaging element is matte.
In a preferred embodiment the invention employs imaging elements which are constructed to contain at least three silver halide emulsion layer units. A suitable full color, multilayer format for a imaging element used in the invention is represented by Structure I.
wherein the red-sensitized, cyan dye image-forming silver halide emulsion unit is situated nearest the support; next in order is the green-sensitized, magenta dye image-forming unit, followed by the uppermost blue-sensitized, yellow dye image-forming unit. The image-forming units are separated from each other by hydrophilic colloid interlayers containing an oxidized developing agent scavenger to prevent color contamination. Silver halide emulsions satisfying the grain and gelatino-peptizer requirements described above can be present in any one or combination of the emulsion layer units. Additional useful multicolor, multilayer formats for an element of the invention include structures as described in U.S. Patent 5,783,373. Each of such structures in accordance with the invention preferably would contain at least three silver halide emulsions comprised of high chloride grains having at least 50 percent of their surface area bounded by {100} crystal faces and containing dopants from classes (i) and (ii), as described above. Preferably each of the emulsion layer units contains emulsion satisfying these criteria.
In a more preferred embodiment, the invention employs imaging elements which are constructed as described in U.S. Patent No. 5,948,601. In this embodiment, the invention employs imaging elements which are constructed to contain at least three silver halide emulsion layer units and an interlayer adjacent to the blue sensitive emulsion layer
Conventional features that can be incorporated into multilayer (and particularly multicolor) imaging elements contemplated for use in the method of the invention are illustrated by Research Disclosure I, cited above:

XI.

Layers and layer arrangements

XII.

Features applicable only to color negative

XIII.

Features applicable only to color positive

B. Color reversal
C. Color positives derived from color negatives

XIV.

Scan facilitating features.

It is specifically contemplated that the imaging element of the invention comprises a multilayer full color imaging element have at least one layer comprising a silver halide emulsion a cyan dye forming coupler and silver halide grains sensitized to red light, at least one layer comprising a silver halide emulsion a magenta dye forming coupler and silver halide grains sensitized to green light and at least one layer comprising a silver halide emulsion a yellow dye forming coupler and silver halide grains sensitized to blue light.
Illustrative multilayer structures are given below. These structures are illustrative only and do not limit use of the invention in other multilayer formats.

MULTILAYER STRUCTURE I

Blue Sensitive Emulsion (Blue EM-1). A high chloride silver halide emulsion is precipitated by adding approximately equimolar silver nitrate and sodium chloride solutions into a well stirred reactor containing glutaryldiaminophenyldisulfide, gelatin peptizer and thioether ripener. Cesium pentachloronitrosylosmate(II) dopant is added during the silver halide grain formation for most of the precipitation, followed by the addition of potassium hexacyanoruthenate(II), potassium (5-methylthiazole)-pentachloroiridate, a small amount of KI solution, and shelling without any dopant. The resultant emulsion contains cubic shaped grains having edge length of 0.6 µm. The emulsion is optimally sensitized by the addition of a colloidal suspension of aurous sulfide and heat ramped to 60°C during which time blue sensitizing dye BSD-4, potassium hexchloroiridate, Lippmann bromide and 1-(3-acetamidophenyl)-5-mercaptotetrazole were added.
Green Sensitive Emulsion (Green EM-1): A high chloride silver halide emulsion is precipitated by adding approximately equimolar silver nitrate and sodium chloride solutions into a well stirred reactor containing, gelatin peptizer and thioether ripener. Cesium pentachloronitrosylosmate(II) dopant is added during the silver halide grain formation for most of the precipitation, followed by the addition of potassium (5-methylthiazole)-pentachloroiridate. The resultant emulsion contains cubic shaped grains of 0.3 µm in edgelength size. The emulsion is optimally sensitized by the addition of glutaryldiaminophenyldisulfide, a colloidal suspension of aurous sulfide and heat ramped to 55°C during which time potassium hexachloroiridate doped Lippmann bromide, a liquid crystalline suspension of green sensitizing dye GSD-1, and 1-(3-acetamidophenyl)-5-mercaptotetrazole were added.
Red Sensitive Emulsion (Red EM-1): A high chloride silver halide emulsion is precipitated by adding approximately equimolar silver nitrate and sodium chloride solutions into a well stirred reactor containing gelatin peptizer and thioether ripener. During the silver halide grain formation, potassium hexacyanoruthenate(II) and potassium (5-methylthiazole)-pentachloroiridate are added. The resultant emulsion contains cubic shaped grains of 0.4µm in edgelength size. The emulsion is optimally sensitized by the addition of glutaryldiaminophenyldisulfide, sodium thiosulfate, tripotassium bis{2-[3-(2-sulfobenzamido)phenyl]-mercaptotetrazole} gold(I) and heat ramped to 64°C during which time 1-(3-acetamidophenyl)-5-mercaptotetrazole, potassium hexachloroiridate, and potassium bromide are added. The emulsion is then cooled to 40°C, pH adjusted to 6.0 and red sensitizing dye RSD-1 is added.
Coupler dispersions were emulsified by methods well known to the art and the following layers were coated on the following support:

The following light sensitive silver halide imaging layers were utilized to prepare photographic print materials for the invention. The following imaging layers were coated utilizing curtain coating.

Layer	Item	Laydown (g/m²)
Layer 1	Blue Sensitive Layer
	Gelatin	1.3127
	Blue sensitive silver (Blue EM-1)	0.2399
	Y-1	0.4143
	ST-23	0.4842
	Tributyl Citrate	0.2179
	ST-24	0.1211
	ST-16	0.0095
	Sodium Phenylmercaptotetrazole	0.0001
	Piperidino hexose reductone	0.0024
	5-chloro-2-methyl-4-isothiazolin-3-one/2-methyl-4-isothiazolin-3-one(3/1)	0.0002
	SF-1	0.0366
	Potassium chloride	0.0204
	Dye-1	0.0148
Layer 2	Interlayer
	Gelatin	0.7532
	ST-4	0.1076
	S-3	0.1969
	5-chloro-2-methyl-4-isothiazolin-3-one/2-methyl-4-isothiazolin-3-one(3/1)	0.0001
	Catechol disulfonate	0.0323
	SF-1	0.0081
Layer 3	Green Sensitive Layer
	Gelatin	1.1944
	Green sensitive silver (Green EM-1)	0.1011
	M-4	0.2077
	Oleyl Alcohol	0.2174
	S-3	0.1119
	ST-21	0.0398
	ST-22	0.2841
	Dye-2	0.0073
	5-chloro-2-methyl-4-isothiazolin-3-one/2-methyl-4-isothiazolin-3-one(3/1)	0.0001
	SF-1	0.0236
	Potassium chloride	0.0204
	Sodium Phenylmercaptotetrazole	0.0007
Layer 4	M/C Interlayer
	Gelatin	0.7532
	ST-4	0.1076
	S-3	0.1969
	Acrylamide/t-Butylacrylamide sulfonate copolymer	0.0541
	Bis-vinylsulfonylmethane	0.1390
	3,5-Dinitrobenzoic acid	0.0001
	Citric acid	0.0007
	Catechol disulfonate	0.0323
	5-chloro-2-methyl-4-isothiazolin-3-one/2-methyl-4-isothiazolin-3-one(3/1)	0.0001
Layer 5	Red Sensitive Layer
	Gelatin	1.3558
	Red Sensitive silver (Red EM-1)	0.1883
	IC-35	0.2324
	IC-36	0.0258
	UV-2	0.3551
	Dibutyl sebacate	0.4358
	S-6	0.1453
	FD-13	0.0229
	Potassium p-toluenethiosulfonate	0.0026
	5-chloro-2-methyl-4-isothiazolin-3-one/2-methyl-4-isothiazolin-3-one(3/1)	0.0001
	Sodium Phenylmercaptotetrazole	0.0005
	SF-1	0.0524
Layer 6	UV Overcoat
	Gelatin	0.8231
	UV-1	0.0355
	UV-2	0.2034
	ST-4	0.0655
	SF-1	0.0125
	S-6	0.0797
	5-chloro-2-methyl-4-isothiazolin-3-one/2-methyl-4-isothiazolin-3-one(3/1)	0.0001
Layer 7	SOC
	Gelatin	0.6456
	Ludox AM™ (colloidal silica)	0.1614
	Polydimethylsiloxane (DC200™)	0.0202
	5-chloro-2-methyl-4-isothiazolin-3-one/2-methyl-4-isothiazolin-3-one(3/1)	0.0001
	SF-2	0.0032
	Tergitol 15-S-5™ (surfactant)	0.0020
	SF-1	0.0081
	Aerosol OT™ (surfactant)	0.0029

Dye-1, Dye-2 are conventional filter dyes of the following formulae which are used in the blue and green sensitive layers, respectively: The red sensitive layer contains filter dye FD-13.

MULTILAYER STRUCTURE II

Blue Sensitive Emulsion (Blue EM-1a). A high chloride silver halide emulsion is precipitated by adding approximately equimolar silver nitrate and sodium chloride solutions into a well stirred reactor containing p-glutaryldiaminophenyldisulfide, gelatin peptizer and thioether ripener. Cesium pentachloronitrosylosmate(II) dopant is added during the silver halide grain formation from 3.9% to 70% of the making process, followed by the addition of potassium hexacyanoruthenate(II) at 75-80% of the make and potassium (5-methylthiazole)-pentachloroiridate from 92-95% of the make. In addition, potassium iodide was added at 90% +/-3% of the making process to form a band of silver iodide at 0.2% +/-0.1% of the silver in the grain. The resultant emulsion contains cubic shaped grains having edge length of 0.64 µm. The emulsion is optimally sensitized by the addition of p-glutaryldiaminophenyldisulfide followed by a colloidal suspension of aurous sulfide and heat ramped to 60°C. After the temperature reached 60°C, blue sensitizing dye BSD-4, potassium hexchloroiridate, Lippmann bromide and 1-(3-acetamidophenyl)-5-mercaptotetrazole were added.
Green Sensitive Emulsion (Green EM-1a): A high chloride silver halide emulsion is precipitated by adding approximately equimolar silver nitrate and sodium chloride solutions, the silver nitrate solution containing p-glutaryldiaminophenyldisulfide, into a well stirred reactor containing gelatin peptizer and thioether ripener. Cesium pentachloronitrosylosmate(II) dopant is added from 1.5% to 75% of the silver halide grain formation, followed by the addition of potassium (5-methylthiazole)-pentachloroiridate from 90-95% of the precipitation. The resultant emulsion contains cubic shaped grains of 0.34 µm in edgelength size. The emulsion is optimally sensitized by the addition of a liquid crystalline suspension of green sensitizing dye GSD-1 and a colloidal suspension of aurous sulfide followed by heating to 60°C. for 35 minutes. After cooling to 40°C., an antifoggant 1-(3-acetamidophenyl)-5-mercaptotetrazole, potassium bromide and potassium chloride were added.
Red Sensitive Emulsion (Red EM-1a): A high chloride silver halide emulsion is precipitated by adding approximately equimolar silver nitrate and sodium chloride solutions into a well stirred reactor containing gelatin peptizer and thioether ripener. During the silver halide grain formation, cesium pentachloronitrosylosmate, potassium hexacyanoruthenate(II) and potassium (5-methylthiazole)-pentachloroiridate are added from 3-75%, 80-85% and 90-95% of the precipitation, respectively. The resultant emulsion contains cubic shaped grains of 0.38 µm in edgelength size. The emulsion is optimally sensitized by the addition of glutaryldiaminophenyldisulfide, sodium thiosulfate and Bis(1,4,5-trimethyl-1,2,4-triazolium-3-thiolate)gold(I)fluoroborate. After heating to 65°C. this emulsion was held for 28 minutes and then the following were added: 1-(3-acetamidophenyl)-5-mercaptotetrazole, potassium hexachloroiridate and potassium bromide. The emulsion is then cooled to 40°C and red sensitizing dye RSD-1 is added.

The following light sensitive silver halide imaging layers can be coated on a support to form an imaging element.

	Item	Laydown g/m²
Layer 1	Blue Sensitive Layer
	Gelatin	1.3885
	Blue Sensitive silver (Blue EM-1a)	] 0.2799
	Y-5	0.4521
	ST-6	0.0775
	ST-7	0.0258
	S-3	0.1981
	Piperidino hexose reductone	0.0023
	Sodium phenylinercaptotetrazole	0.0001
	DYE-1	0.0323
Layer 2	Split Yellow Interlayer
	Gelatin	0.3229
	Y-5	0.1938
	ST-6	0.0332
	ST-7	0.0111
	S-3	0.0849
Layer 3	Interlayer
	Gelatin	0.7535
	ST-4	0.0660
	S-2	0.1884
	Acrylamide/t-Butylacrylamide sulfonate copolymer	0.1281
	Bis-vinylsulfonylmethane	0.0151
Layer 4	Green Sensitive Layer
	Gelatin	1.3498
	Green Sensitive silver (Green EM-1a)	] 0.1076
	M-1	0.2142
	S-2	0.0761
	S-3	0.0326
	ST-8	0.0560
	ST-21	0.1636
	ST-22	0.5436
	DYE-2	0.0075
	Sodium phenylmercaptotetrazole	0.0003
Layer 5	UV Interlayer
	Gelatin	0.7136
	UV-1	0.0312
	UV-2	0.1722
	ST-4	0.0527
	S-10	0.0344
	S-2	0.0344
Layer 6	Red Sensitive Layer
	Gelatin	1.3563
	Red sensitive silver (Red EM-1 a)	0.1938
	C-1	0.4004
	S-2	0.3918
	UV-2	0.2573
	S-9	0.0328
	ST-4	0.0033
	DYE-3	0.0151
	Potassium tolylthiosulfonate	0.0027
	Potassium tolylsulfinate	0.0003
Layer 7	UV Overcoat
	Gelatin	0.5350
	UV-1	0.0229
	UV-2	0.1301
	st-4	0.0384
	S-10	0.0255
	S-2	0.0255
Layer 8	SOC
	Gelatin	0.6458
	Ludox AM™ (colloidal silica)	0.1615
	Polydimethylsiloxane (DC200™)	0.0202

It is particularly advantageous for the multilayer imaging element to have the following exposure characteristics : an exposure range of between 1000 nanoseconds and 0.5 seconds when there is a density loss of no more than 10 percent as a function of the red shoulder color record, wherein said photographic element has an exposure range of between 1000 nanoseconds and 0.5 seconds when there is a density loss of no more than 8 percent as a function of the green shoulder color record, wherein said photographic element has an exposure range of between 1000 nanoseconds and 0.5 seconds when there is a density loss of no more than 5 percent as a function of the blue shoulder color record, wherein said photographic element has an exposure range of between 1000 nanoseconds and 0.5 seconds when there is a density loss of no more than 6 percent as a function of the red Dmax color record, wherein said photographic element has an exposure range of between 1000 nanoseconds and 0.5 seconds when there is a density loss of no more than 9 percent as a function of the green Dmax color record, wherein said photographic element has an exposure range of between 1000 nanoseconds and 0.5 seconds when there is a density loss of no more than 5 percent as a function of the blue Dmax color record, wherein said photographic element has an exposure range of between 1000 nanoseconds and 0.5 seconds when there is a density loss of no more than 9 percent as a function of the red inmax color record, wherein said photographic element has an exposure range of between 1000 nanoseconds and 0.5 seconds when there is a density loss of no more than 10 percent as a function of the green inmax color record, and wherein said photographic element has an exposure range of between 1000 nanoseconds and 0.5 seconds when there is a density loss of no more than 5 percent as a function of the blue inmax color record.
The imaging elements comprising the radiation sensitive high chloride emulsion layers according to this invention can be conventionally optically printed, or in accordance with a particular embodiment of the invention can be image-wise exposed in a pixel-by-pixel mode using suitable high energy radiation sources typically employed in electronic printing methods. Suitable actinic forms of energy encompass the ultraviolet, visible and infrared regions of the electromagnetic spectrum as well as electron-beam radiation and is conveniently supplied by beams from one or more light emitting diodes or lasers, including gaseous or solid state lasers. Exposures can be monochromatic, orthochromatic or panchromatic. For example, when the imaging element is a multilayer multicolor element, exposure can be provided by laser or light emitting diode beams of appropriate spectral radiation, for example, infrared, red, green or blue wavelengths, to which such element is sensitive. Multicolor elements can be employed which produce cyan, magenta and yellow dyes as a function of exposure in separate portions of the electromagnetic spectrum, including at least two portions of the infrared region, as disclosed in the previously mentioned U.S. Patent No. 4,619,892. Suitable exposures include those up to 2000 nm, preferably up to 1500 nm. Suitable light emitting diodes and commercially available laser sources are known and commercially available. Imagewise exposures at ambient, elevated or reduced temperatures and/or pressures can be employed within the useful response range of the imaging element determined by conventional sensitometric techniques, as illustrated by T.H. James, The Theory of the Photographic Process, 4th Ed., Macmillan, 1977, Chapters 4, 6, 17, 18 and 23.
The quantity or level of high energy actinic radiation provided to the recording medium by the exposure source is generally at least 10^-4 ergs/cm², typically in.the range of about 10^-4 ergs/cm² to 10^-3 ergs/cm² and often from 10^-3 ergs/cm² to 10² ergs/cm². Exposure of the recording element in a pixel-by-pixel mode as known in the prior art persists for only a very short duration or time. Typical maximum exposure times are up to 100 µ seconds, often up to 10 µ seconds, and frequently up to only 0.5 µ seconds. Single or multiple exposures of each pixel are contemplated. The pixel density is subject to wide variation, as is obvious to those skilled in the art. The higher the pixel density, the sharper the images can be, but at the expense of equipment complexity. In general, pixel densities used in conventional electronic printing methods of the type described herein do not exceed 10⁷ pixels/cm² and are typically in the range of about 10⁴ to 10⁶ pixels/cm². An assessment of the technology of high-quality, continuous-tone, color electronic printing using silver halide photographic paper which discusses various features and components of the system, including exposure source, exposure time, exposure level and pixel density and other recording element characteristics is provided in Firth et al., A Continuous-Tone Laser Color Printer, Journal of Imaging Technology, Vol. 14, No. 3, June 1988. As previously indicated herein, a description of some of the details of conventional electronic printing methods comprising scanning a recording element with high energy beams such as light emitting diodes or laser beams, are set forth in Hioki U.S. Patent 5,126,235, European Patent Applications 479 167 A1 and 502 508 Al.
Once imagewise exposed the imaging element can be processed as described in Research Disclosure I, Section XVIII, and then processed to form a visible dye image as described in Research Disclosure I, Section XIX. Processing to form a visible dye image includes the step of contacting the element with a color developing agent to reduce developable silver halide and oxidize the color developing agent. Oxidized color developing agent in turn reacts with the coupler to yield a dye.
With negative working silver halide, the processing step described above gives a negative image. To obtain a positive (or reversal) image, this step can be preceded by development with a non-chromogenic developing agent to develop exposed silver halide, but not form dye, and then uniformly fogging the element to render unexposed silver halide developable. Or, a direct positive emulsion can be employed to obtain a positive image.
Development is followed by the conventional steps of bleaching, fixing, or bleach-fixing, to remove silver and silver halide, washing and drying.
The following examples illustrates the practice of the present invention in a silver halide photographic element and the advantage in differential red speed of emulsions exposed at the peak sensitivity of the emulsion compared to emulsions exposed at approximately 25 to 50 nm shorter than the peak sensitivity when using dopants, and dyes used in this invention as compared to the comparison filter dyes shown above.

Preparation of Photographic Elements

The photographic elements were prepared as follows:

Preparation of Blue Sensitive Emulsion (Blue EM-1b). A high chloride silver halide emulsion was precipitated by adding approximately equimolar silver nitrate and sodium chloride solutions into a reactor vessel containing a gelatin peptizer and a thioether ripener. Cesium pentachloronitrosylosmate(II) dopant was added during the silver halide grain formation for most of the precipitation followed by addition of potassium hexacyanoruthenate(II), a small amount of KI solution and shelling without any dopant. The resultant emulsion contained cubic shaped grains of 0.64 µm in edge length size. The emulsion was optimally sensitized by the addition of a colloidal suspension of aurous sulfide followed by a heat ramp, and addition of blue sensitizing dye, BSD-1, 1-(3-acetamidophenyl)-5-mercaptotetrazole, an optimal amount of glutaryldiaminophenyl disulfide and Lippmann bromide, iridium hexachloroiridate.
Preparation of green sensitive emulsion (Green EM-1b). A high chloride silver halide emulsion was precipitated by adding approximately equimolar silver nitrate and sodium chloride solutions into a reactor vessel containing a gelatin peptizer and a thioether ripener. Cesium pentachloronitrosyl osmate(II) dopant was added during the silver halide grain formation for most of the precipitation followed by shelling without dopant. The resultant emulsion contained cubic shaped grains of 0.34 µm in edge length size. The emulsion was optimally sensitized by the addition of a colloidal suspension of aurous sulfide followed by a heat ramp, and addition of an iridium dopant, Lippmann bromide and 1-(3-acetamidophenyl)-5-mercaptotetrazole, green sensitizing dye, GSD-2, and further 1-(3-acetamidophenyl)-5-mercaptotetrazole.
Preparation of red sensitive emulsion (Red EM-1b). A high chloride silver halide emulsion was precipitated by adding approximately equimolar silver nitrate and sodium chloride solutions into a reactor vessel containing a gelatin peptizer and a thioether ripener. The resultant emulsion contained cubic shaped grains of 0.38 µm in edge length size. The emulsion was optimally sensitized by the addition of a colloidal suspension of aurous sulfide followed by a heat ramp, and addition of 1-(3-acetamidophenyl)-5-mercaptotetrazole, potassium bromide and red sensitizing dye, RSD1. In addition, iridium and ruthenium doctors were added during the sensitization process.
Preparation of red sensitive emulsion (Red EM-2). A high chloride silver halide emulsion was precipitated by adding approximately equimolar silver nitrate and sodium chloride solutions into a reactor vessel containing a gelatin peptizer and a thioether ripener. The resultant emulsion contained cubic shaped grains of 0.38 µm in edge length size. The emulsion was optimally sensitized by the addition of a solution of sensitizer Z' followed by a heat ramp, and addition of 1-(3-acetamidophenyl)-5-mercaptotetrazole, potassium bromide and red sensitizing dye, RSD1. In addition, iridium and ruthenium dopants were added during the precipitation process.
Preparation of red sensitive emulsion (Red EM-3) An AgClBr cubic grain emulsion, 0.60%Br, 0.21 micron, spectrally sensitized with SD-2, 0,043mmole/Ag mole, laid down at 68.9 mg/sq.m. An AgClBr cubic grain emulsion,0.87% Br, 0.15 micron, spectrally sensitized with SD-2, 0.051 mmole/ag mole and laid down at 346.6 mg/sq. m. An AgClBr cubic grain emulsion, 1.12% Br, 0.11 micron, spectrally sensitized with SD-2, 0.045 mmole/Ag mole, and laid down at 79.7 mg/sq.m.

The red sensitive emulsion was combined with dispersion using techniques known in the art and the resulting light-sensitive silver halide components were applied to polyethylene resin coated paper support as described in COATING FORMAT 1 to provide Examples 1-4. The amount of absorber dye filter dyes FD 1-13 in Examples 1-5 was adjusted to give approximately equal speed attenuation as the comparison dyes. For Example 5, the red, blue and green sensitive emulsions were combined with dispersions using techniques known in the art and the resulting light-sensitive silver halide components were applied to polyethylene resin coated paper support to give a multilayer coating COATING FORMAT 2:

COATING FORMAT 1
Layer 1	g/m²
Gelatin	1.198
Silver (Red EM-1b, or EM-3)	0.19
C-1	0.365
S-1	0.358
UV-2	0.235
S-3	0.03
D-6	0.02
Layer 2
Gelatin	0.697
Surfactant	0.04
Lubricant	0.027

COATING FORMAT 2
Layer 1	g/m²
Gelatin	1.321
Silver (Blue EM-1b)	0.203
Y1	0.418
S-1	0.285
ST-1	1.393
D-4	0.008
Layer 2
Gelatin	0.65
scavenger	0.057
S-1	0.163
Layer 3
Gelatin	1.087
Silver (Green EM-1b)	0.172
M-1	0.365
S-2	0.635
S-3	0.059
ST-2	0.404
scavenger	0.037
D-5	0.006
Layer 4
Gelatin	0.849
UV-1	0.062
UV-2	0.353
scavenger	0.085
S-4	0.138
Layer 5
Gelatin	1.198
Silver (Red EM-2)	0.19
C-1	0.365
S-1	0.358
UV-2	0.235
S-3	0.03
D-6	0.02
Layer 6
Gelatin	0.645
UV-1	0.048
UV-2	0.277
scavenger	0.067
S-4	0.108
Layer 7
Gelatin	0.697
Surfactant	0.04
Lubricant	0.027

Evaluation Examples

The samples were exposed through a step wedge and processed using conventional processing solutions and conditions.
The processed color photographic paper strips were measured for spectral sensitivity maximum (λ max), density at wavelength of sensitivity maximum (Speed1) and density at wavelength of sensitivity [maximum - 50 nm] (Speed2). The percent ratio of Speed2/Speed1 is shown as DIFSP and represents the differential speed between an optical exposure device and a digital exposure device operating with a 50 nm shorter exposing wavelength maximum. The data are shown in Tables 3-7.

Example 1

A coated element was prepared to examine the effect of filter dyes with absorbance maximum greater than 15 nm different than the spectral sensitization maximum upon the differential speed factor DIFSP. In this example, the red emulsion used was Red EM-Ib.

Element	Filter Dye	Filter Dye λ max	Spec Sens λ max	Speed 1	Speed2	DIFSP
101	Comparison CFD2	638nm	710nm	227	135	59.5%
102	Comparison CFD4	718nm	700nm	199	154	77.4%
103	for Invention FD8	703nm	700nm	200	165	82.5%
104	for Invention FD12	687nm	700nm	197	160	81.2%

The data in Table 3 show that the comparison filter dyes, CFD2 and CFD4, which have an absorbance maximum more than 15 nm different than the wavelength of sensitization maximum do not provide as good short red speed for use in digital exposure devices applications as do the dyes used in the invention FD8 and FD12. Additionally, it was found that Comparison Filter Dye CFD4 gave unwanted processing stain in the processed element.

Example 2

A coated element was prepared to examine the effect of minor variations in the structure of the filter dyes upon the differential speed factor DIFSP. In this example, the red emulsion used was Red EM-1b.

Element	Filter Dye	Filter Dye λ max	Spec Sens λ max	Speed1	Speed2	DIFSP
201	Comparison CFD1	671nm	710nm	153	95	62.1%
202	for Invention FD7	702nm	700nm	160	110	68.7%
203	for Invention FD8	703nm	700nm	153	108	70.6%
204	for Invention FD10	701nm	700nm	154	110	71.9%
205	for Invention FD11	687nm	700nm	145	98	67.6%
206	for Invention FD12	687nm	700nm	145	95	65.5%
207	for Invention FD13	686nm	700nm	150	100	66.6%

The data in Table 4 show that the dyes FD7, FD8 and FD10 with an absorbance maximum nearly identical with the spectral sensitization maximum provide the best short red speed for digital exposure applications. Also, invention dyes FD11, FD12, and FD13 show that minor modifications of the substituent on the pyrazolone portion of the filter dye may be changed and the good short red speed may be maintained.

Example 3

A coated element was prepared to examine the effect of different substitution in the polymethine chain of the filter dyes upon the differential speed factor DIFSP. In this example, the red emulsion used was Red EM-1b

Element	Filter Dye	Filter Dye λ max	Spec Sens λ max	Speed1	Speed2	DIFSP
301	Comparison CFD1	671nm	710nm	163	105	64.4%
302	for Invention FD1	694nm	700nm	146	106	72.6%
303	for Invention FD8	703nm	700nm	151	112	74.1%

The data in Table 5 shows for FD1 which has a chain methyl substituent that the structure of the substituent on the pentamethine chain of the dyes used in the invention may be changed to provide dyes with an absorbance maximum nearly identical with the spectral sensitization maximum and, therefore, excellent short red speed suitable for use with both optical and digital exposure devices.

Example 4

A coated element was prepared to examine the effect of the half band width of the filter dyes upon the differential speed factor (DIFSP). In this example, the red emulsion used was Red EM-3

Element Filter Dye Filter Dye λ max Spec Sens λ max Speed1 Speed2 DIFSP

401 Comparison CFD3 725nm 700nm 250 150 60%

402 for Invention FD13 686nm 700nm 250 175 70%
The data in Table 6 show for Comparison Filter Dye 3 which has an absorbance maximum near the spectral sensitization maximum but has a broad half band width, see Table 2, does not provide good short red speed and would not provide a method of manufacturing a photographic element suitable for use in both a optical and digital exposure device.

Example 5

A coated element was prepared to examine the effect of the invention dye in a full multilayer embodiment where all three color records plus typical interlayers and overcoats are included. In this example the green emulsion used was green EM-1b, the blue emulsion used was blue EM 1b and the red emulsion used was Red EM-2.

Element Filter Dye Filter Dye λ max Spec Sens λ max Speed1 Speed2 DIFSP

401 Comparison CFD1 671nm 700nm 180 119 66%

403 for Invention FD13 686nm 700nm 182 130 71%

The data in Table 7 show for Comparison Filter Dye 1 coated in a full multilayer embodiment vs Filter Dye 13 that the speed advantages at positions hypsochromic to the spectral sensitivity peak are retained.
While the working examples are directed to imaging elements in which it is the red sensitive layer that contains the combination of dopant, sensitizing dye and filter dye in accordance with this invention, it is to be understood that the same principles apply to the green and blue sensitive layers when it is desired to increase the speed at a wavelength lower than the wavelength of maximum sensitivity of the sensitizing dye.

Claims

An imaging element comprising at least one silver halide emulsion wherein the silver halide emulsion grains incorporate dopant (i) which comprises a hexacoordination metal complex which satisfies the formula [ML₆]ⁿ wherein n is zero, -1, -2, -3 or -4; M is a filled frontier orbital polyvalent metal ion, other than iridium; and L₆ represents bridging ligands which can be independently selected, provided that at least four of the ligands are anionic ligands, and at least one of the ligands is a cyano ligand or a ligand more electronegative than a cyano ligand;
and wherein the emulsion has been spectrally sensitized with a sensitizing dye and contains a filter dye that

(a) has a wavelength of absorbance maximum which is less than 15 nm different than the maximum wavelength of emulsion sensitivity provided by the spectral sensitizing dye, and

(b) has a half band width that is equal to the half bandwidth of the sensitizing dye,

thereby resulting in an emulsion which has a sensitivity at a wavelength of 50 nm shorter than the maximum wavelength of sensitization which is 65% or greater of the emulsion speed at the maximum wavelength of spectral sensitivity.
An imaging element according to claim 1, wherein the sensitizing dye is selected from Dye A and Dye B, or mixtures thereof, wherein Dye A is of formula I or II:

wherein:

in formula I, the substituents W₁-W₈ are chosen such that J is greater than or equal to 0.0, where J is defined a s the sum of the Hammet σ_p values of W₁-W₈, or in formula II, the substituents W₁-W₈ are chosen such that J is greater than or equal to 0.24;

R₁ and R₂ each independently represents an alkyl group or a substituted alkyl group;

Z₁ and Z₂ each independently represents a 1-8 carbon alkyl group.

X is a counterion, if needed, to balance the charge of the dye;

and Dye B is of formula I or II wherein:

in formula I, the substituents W₁-W₈ are chosen such that J is less that 0.10, or in formula II, the substituents W₁-W₈ are chosen such that J is less that -0.14; and

R₁ and R₂ each independently represents an alkyl group or a substituted alkyl group;

X is a counterion, if needed, to balance the charge of the dye;

Z is a hydrogen or halogen atom or an alkyl group or a substituted alkyl group.
An imaging element according to claim 1, wherein the sensitizing dye is a dye of formula (Ia), and/or a dye for formula (IIa):

where:

R₁ and R₂ each independently represent an alkyl group or a substituted alkyl group;

V₂-V₇ are independently H or a 1 to 8 carbon alkyl;

Z is a hydrogen or methyl;

A is a counterion if needed to balance the charge.
An imaging element according to any preceding claim, wherein the filter dye is of the formula:
wherein:

G and G' independently represent oxygen, substituted nitrogen, or C(CN)₂;

R₃, R₃', R₄, R₄' independently represent H or a substituent, or R₃ and R₄, R₃' and R₄' may form a ring;

R₅ is an acyl, alkoxycarbonyl, amido, carbamoyl, alkyl, aryl, alkyloxy, any of which may be substituted or unsubstituted;

m is 0, 1, 2, or 3;

all of the L" together define a methine chain each L" representing a methine any of which may be substituted or unsubstituted; and

M⁺ is a cation or proton.
An imaging element according to claim 4, wherein the filter dye is of the formula:
wherein

R₅ and R₆ each independently represent H or a substituent, or R₅ and R₆ may form a ring;

R₇ is an acyl, alkoxycarbonyl, amido, carbamoyl, alkyl, aryl, alkoxy, aryloxy, amino, or heterocyclic, any of which may be substituted or unsubstituted; and

M⁺ is a cation or proton.
An imaging element according to claim 5, wherein the filter dye is a dye of formula:
where M is a cation.
An imaging element according to any preceding claim, wherein L₆ represents bridging ligands which can be independently selected, provided that least four of the ligands are anionic ligands, and at least one of the ligands is a cyano ligand or a ligand more electronegative than a cyano ligand; and any remaining ligands are selected from aquo ligands, halide ligands, cyanate ligands, thiocyanate ligands, selenocyanate ligands, tellurocyanate ligands, and azide ligands.
An imaging element according to claim 7, wherein each L₆ is a cyano ligand.
An imaging element according to any preceding claim, which further comprises dopant (ii) which is an iridium complex.
An imaging element according to claim 9, wherein dopant (ii) comprises a hexacoordination complex satisfying the formula: [IrL¹ ₆]^n' wherein

n' is zero, -1, -2, -3 or -4; and

L¹ ₆ represents six bridging ligands which can be independently selected, provided that at least four of the ligands are anionic ligands, each of the ligands is more electropositive than a cyano ligand.