EP0736200A1 - Emulsions photographiques a sensibilite renforcee - Google Patents

Emulsions photographiques a sensibilite renforcee

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Publication number
EP0736200A1
EP0736200A1 EP95935226A EP95935226A EP0736200A1 EP 0736200 A1 EP0736200 A1 EP 0736200A1 EP 95935226 A EP95935226 A EP 95935226A EP 95935226 A EP95935226 A EP 95935226A EP 0736200 A1 EP0736200 A1 EP 0736200A1
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EP
European Patent Office
Prior art keywords
silver
iodide
emulsion
tabular grains
dopant
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Application number
EP95935226A
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German (de)
English (en)
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EP0736200B1 (fr
Inventor
David Earl Fenton
Lucius Seiberling Fox
Donald Lee Black
Roger Anthony Bryant
Myra Toffoln Olm
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Eastman Kodak Co
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Eastman Kodak Co
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Priority claimed from US08/329,591 external-priority patent/US5476760A/en
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Definitions

  • the invention relates to photographic emulsions and to processes for their preparation.
  • Corben U.S. Patent 4,210,450 discloses the preparation of a shelled converted halide emulsion by alternately ammoniacally precipitating silver chloro- iodobromide and introducing ammonium iodide and then repeating the sequence.
  • the emulsions are stated to be useful in color diffusion transfer, but no performance advantages are stated or demonstrated.
  • Marchetti et al U.S. Patent 4,937,180 discloses an emulsion in which silver halide grains containing bromide and, optionally, iodide are formed in the presence of a hexacoordination complex of rhenium, ruthenium or osmium with at least four cyanide ligands.
  • Marchetti et al U.S. Patent 5,268,264 discloses an emulsion in which silver halide grains having ⁇ 111 ⁇ crystal faces containing bromide and, optionally, iodide contain a buried shell formed in the presence of a hexacoordination complex of iron and at least 3 cyanide ligands.
  • Bell et al U.S. Patent 5,132,203 discloses an emulsion in which tabular silver halide grains are formed of a host stratum containing at least 4 mole percent iodide and laminar strata containing less than 2 mole percent iodide. Each of laminar strata is comprised of surface layer forming one of the major faces and a subsurface immediately beneath the surface layer containing a hexacoordination complex of a Group VIII period 4 or 5 metal and at least three cyanide ligands.
  • the invention is directed to an emulsion of enhanced photographic sensitivity comprised of a dispersing medium and silver halide tabular grains having a face centered cubic crystal lattice of the rock salt structure and containing iodide adjacent surfaces forming edges and corners of said tabular grains characterized in that the tabular grains contain a maximum surface iodide concentration along their edges, a lower surface iodide concentration within their corners than elsewhere along their edges, and a dopant capable of providing shallow electron trapping sites present in an overall concentration of up to 500 molar parts per million, based on silver, and limited to a surface concentration of less than 100 molar parts per million, based on the last precipitated 5 percent of silver.
  • Figures 1 and 2 each show the iodide concen ⁇ tration profiles of a tabular grain where the profile is taken from edge-to-edge (see line E-E below) or from corner-to-corner (see line C-C below) , where
  • Figure 1 demonstrates profiles from a tabular grain emulsion satisfying the requirements of the invention
  • Figure 2 demonstrates iodide profiles from a conventional tabular grain.
  • the tabu ⁇ lar grains contain a maximum surface iodide concentra ⁇ tion along their edges and a lower surface iodide concentration within their corners than elsewhere along their edges.
  • surface iodide concentration refers to the iodide concentration that lies within 0.02 ⁇ of the tabular grain surface.
  • the starting point for the preparation of an emulsion satisfying the requirements of the invention can be any conventional tabular grain emulsion in which the tabular grains (1) exhibit a face centered cubic crystal lattice of the rock salt structure and (2) have a surface iodide concentration of less than 2 mole percent.
  • Both silver bromide and silver chloride exhibit a face centered cubic crystal lattice of the rock salt structure (also identified by the space group designation Fm3m) .
  • the starting tabular grains can be selected from among silver bromide, silver chloride, silver chlorobromide and silver bromochloride.
  • silver iodide does not form a face centered cubic crystal lattice of the rock salt structure (except under conditions not relevant to photography) , minor amounts iodide can be tolerated in the face centered cubic crystal lattice rock salt structures formed by silver chloride and/or bromide.
  • the starting tabular grains can additionally include silver iodobromide, silver iodochloride, silver iodochlorobromide, silver iodobromochloride, silver chloroiodobromide and silver bromoiodochloride composi ⁇ tions, provided surface iodide concentrations are limited to satisfy criterion (2) above.
  • tabular grain emulsions suitable for use as starting emulsions can be selected from among those having either ⁇ 111 ⁇ or ⁇ 100 ⁇ major faces.
  • Suitable tabular grain emulsions containing ⁇ 111 ⁇ major face tabular grains are illustrated by ey U.S. Patent 4,399,215, Maskasky U.S. Patents 4,400,463, 4,684,607, 4,713,320, 4,713,323, 5,061,617, 5,178,997, 5,178,998, 5,183,732, 5,185,239, 5,217,858 and 5,221,602, Wey et al U.S. Patent 4,414,306, Daubendiek et al U.S.
  • Patent 5,176,991 Maskasky et al U.S. Patent 5,176,992, Black et al U.S. Patent 5,219,720, Maruyama et al U.S. Patent 5,238,796, Antoniades et al U.S. Patent 5,250,403, Zola et al EPO 0 362 699, Urabe EPO 0 460 656, Verbeek EPO 0 481 133, EPO 0 503 700 and EPO 0 532 801, Jagannathan et al EPO 0 515 894 and Sekiya et al EPO 0 547 912.
  • Emulsions containing ⁇ 100 ⁇ major face tabular grains useful as starting emulsions are illustrated by Bogg U.S.
  • Patent 4,063,951 Mignot U.S. Patent 4,386,156, Maskasky U.S. Patents 5,264,337 and 5,275,930, House et al U.S. Patent 5,314,798, House et al U.S. Patent 5,320,938, Saitou et al EPO 0 569 971 and Saito et al Japanese Patent Application 92/77261.
  • the starting tabular grains contain less than 2 mole percent iodide through- out.
  • the presence of higher levels of iodide within the interior of the tabular grains is compatible with the practice of the invention, provided a lower iodide shell is present that brings the starting tabu ⁇ lar grains into conformity with criterion (2) .
  • the surface iodide modification of the start ⁇ ing tabular grain emulsion to enhance sensitivity can commence under any convenient conventional emulsion precipitation condition. For example, iodide introduc ⁇ tion can commence immediately upon completing precipi ⁇ tation of the starting tabular grain emulsion.
  • Iodide is introduced as a solute into the reaction vessel containing the starting tabular grain emulsion. Any water soluble iodide salt can be employed for supplying the iodide solute.
  • the iodide can be introduced in the form of an aqueous solution of an ammonium, alkali or alkaline earth iodide.
  • R-I wherein R represents a monovalent organic moiety that provides a carbon to iodide bond.
  • the compounds are chosen to exhibit at least some water solubility.
  • the number of carbon atoms is preferably limited to 10 or fewer and, where 3 or more carbon atoms are present, preferably contain a polar substituent to promote water solubility.
  • An extensive listing of such compounds are provided by Kikuchi et al EPO 0 561 415.
  • Kikuchi et al reacts the R-I compounds with other addenda specifically provided to achieve very rapid release of iodide
  • slow release of iodide is contemplated. This can be achieved by the slow reaction of the R-I compound with gelatin or a gelatin derivative contained in the emulsion. Fortuitously the organic moiety released reacts with the gelatin.
  • a common alternative method in the art for introducing iodide during silver halide precipitation is to introduce iodide ion in the form of a silver iodide Lippmann emulsion.
  • the introduction of iodide in the form of a silver salt does not satisfy the requirements of the invention.
  • iodide ion is introduced without concurrently introducing silver. This creates condi ⁇ tions within the emulsion that drive iodide ions into the face centered cubic crystal lattice of the tabular grains.
  • the driving force for iodide introduction into the tabular grain crystal lattice structure can be appreciated by considering the following equilibrium relationship: (ID
  • Ksp [Ag + ] [X-] where Ksp is the solubility product constant of the silver halide. To avoid working with small fractions the following relationship is also widely employed: (IV)
  • the benefits of the invention are not real ⁇ ized if all of the more soluble halide ions in the crystal lattice structure of the starting tabular grains are replaced by iodide. This would destroy the face centered cubic crystal lattice rock salt struc ⁇ ture, since iodide can only be accommodated in a lattice structure to a limited degree, and the net effect would be to destroy the tabular configuration of the grains.
  • the iodide ion that enters the tabular grains by halide displacement is not uniformly or randomly distributed.
  • the surface of the tabular grains are more accessible for halide displacement.
  • halide displacement by iodide occurs in a preferential order. Assuming a uniform surface halide composition in the starting tabular grains, the crystal lattice structure at the corners of the tabular grains is most susceptible to halide ion displacement, followed by the edges of the tabular grains.
  • the major faces of the tabular grains are least susceptible to halide ion displacement.
  • the highest iodide concen ⁇ trations in the tabular grains occur in that portion of the crystal lattice structure forming the corners of the tabular grains.
  • the next step of the process of preparation is to remove iodide ion selectively from the corners of the tabular grains.
  • This is accomplished by introduc- ing silver as a solute. That is, the silver is intro ⁇ pokerd in a soluble form, analogous to that described above for iodide introduction.
  • the silver solute is introduced in the form of an .aqueous solution similarly as in conventional single-jet or double-jet precipitations.
  • the silver is preferably introduced as an aqueous silver nitrate solution. No additional iodide ion is introduced during silver introduction.
  • the amount of silver introduced is in excess of the iodide introduced into the starting tabular grain emulsion during the iodide introduction step.
  • the amount of silver introduced is preferably on a molar basis from 2 to 20 (most preferably 2 to 10) times the iodide introduced in the iodide introduction step.
  • halide ion When silver ion is introduced into the high corner iodide tabular grain emulsion, halide ion is present in the dispersing medium available to react with the silver ion.
  • One source of the halide ion comes from relationship (II) .
  • the primary source of halide ion is attributable to the fact that photographic emulsions are prepared and maintained in the presence of a stoichiometric excess of halide ion to avoid the inadvertent reduction of Ag + to Ag°, thereby avoiding elevating minimum optical densities observed following photographic processing.
  • the introduced silver ion As the introduced silver ion is precipitated, it removes iodide ion from the dispersing medium.
  • the silver iodide at the corners of the grains exports iodide ion from the corners of the grains into solution, where it then reacts with additionally added silver ion.
  • Silver and iodide ion as well as chloride and/or bromide ion, which was present to provide a halide ion stoichiomet- ric excess, are then redeposited.
  • the stoichiometric excess of halide ion is maintained and the concentration of the halide ion in the dispersing medium is maintained in those ranges known to be favor ⁇ able for tabular grain growth.
  • concentration of the halide ion in the dispersing medium is maintained in those ranges known to be favor ⁇ able for tabular grain growth.
  • the pBr of the dispersing medium is maintain at a level of at least 1.0.
  • chloride emulsions the molar concentration of chloride ion in the dispers ⁇ ing medium is maintained above 0.5 M.
  • the net result of silver ion introduction as described above is that silver ion is deposited at the edges of the tabular grains. Concurrently, iodide ion migrates from the corners of the tabular grains to their edges. As iodide ion is displaced from the tabu ⁇ lar grain corners, irregularities are created in the corners of the tabular grains that increase their latent image forming efficiency. It is preferred that the tabular grains exhibit a corner surface iodide concentration that is at least 0.5 mole percent, preferably at least 1.0 mole percent, lower than the highest surface iodide concentration found in the grain—i.e., at the edge of the grain.
  • the minimum level of iodide in the resulting emulsion can be as low as 0.4 mole percent.
  • Preferred emulsions according to the invention contain overall iodide levels of up to 20 mole percent, most preferably, up to 15 mole percent.
  • a preferred minimum overall iodide concentration is 1.0 mole percent, with higher overall iodide concentrations being preferred for photographic applications depending upon iodide release for photographic advantages, such as reliance upon iodide to increase native blue sensi ⁇ tivity or reliance upon iodide ions released in devel- opment for interimage effects.
  • overall concentrations are preferably maintained at less than 5 mole percent, optimally at less than 3 mole percent.
  • the tabular grains account for greater than 50 percent of total grain projected area.
  • the tabular grains most preferably account for at least 70 percent, optimally at least 90 percent, of total grain projected area. Any proportion of tabular grains satisfying the iodide profile requirements noted above can be present that is capable of observably enhancing photographic sensitivity.
  • at least 25 percent of the tabular grains exhibit the iodide profiles described above.
  • tabular grains accounting for at least 50 percent of total grain projected area exhibit the iodide profiles required by the invention.
  • Preferred emulsions according to the inven ⁇ tion are those which are relatively monodisperse.
  • COV coefficient of variation
  • ECD's equivalent circular diameters
  • the COV of ECD is also referred to as COVJJCD- BV employing a highly monodisperse starting tabular grain emulsion, such as an emulsion having a COV ⁇ CD .. °f less than 10 percent (disclosed, for example, by Tsaur et al U.S.
  • Patent 5,210,013 it is possible to prepare emulsions according to the invention in which COVECD °f tne final emulsion is also less than 10.
  • the silver bromide and iodobromide tabular grain emulsions of Tsaur et al U.S. Patents 5,147,771, '772, '773, and 5,171,659 represent a preferred class of starting tabular grain emulsions.
  • Sutton et al U.S. Patent 5,334,469 discloses improve ⁇ ments on these emulsions in which the COV of tabular grain thickness, COV ⁇ , is less than 15 percent.
  • the average tabular grain thicknesses (t) , ECD's, aspect ratios (ECD/t) and tabularities (ECD/t 2 , where ECD and t are measured in micrometers, ⁇ m) of the emulsions of the invention can be selected within any convenient conventional range.
  • the tabular grains preferably exhibit an average thickness of less than 0.3 ⁇ .
  • Ultrathin ( ⁇ 0.07 ⁇ m mean thickness) tabular grain emulsions are specifically contemplated.
  • Photo ⁇ graphically useful emulsions can have average ECD's of up to 10 ⁇ m, but in practice they rarely have average ECD's of greater than 6 ⁇ m.
  • any minimum mean ECD of the emulsions of the invention that is compatible .with average aspect ratio requirements can be employed. It is preferred to require individual grains to have parallel major faces and to exhibit an average aspect ratio of at least 2 to be considered tabular.
  • the average aspect ratio of the emulsions is always greater than 2, preferably greater than 5 and most preferably greater than 8. Extremely high average aspect ratios of 100 or more are contemplated, although typically tabular grain emulsion average aspect ratios are less than 75.
  • a photoelectron When a photon is absorbed by a silver halide grain, an electron (hereinafter referred to as a photoelectron) is promoted from the valence band of the silver halide crystal lattice to its conduction band, creating a hole (hereinafter referred to as a photohole) in the valence band.
  • a plurality of photoelectrons produced in a single imagewise exposure must reduce several silver ions in the crystal lattice to form a small cluster of Ag° atoms.
  • the photographic sensitivity of the silver halide grains is reduced. For example, if the photoelectron returns to the photohole, its energy is dissipated without contributing to latent image forma ⁇ tion.
  • the silver halide it is contemplated to dope the silver halide to create within it shallow electron traps that contribute to utilizing photoelectrons for latent image formation with greater efficiency. This is achieved by incorporating in the face centered cubic crystal lattice a dopant that exhibits a net valence more posi ⁇ tive than the net valence of the ion or ions it displaces in the crystal lattice.
  • the dopant can be a polyvalent
  • (+2 to +5) metal ion that displaces silver ion (Ag + ) in the crystal lattice structure The substitution of a divalent cation, for example, for the monovalent Ag + cation leaves the crystal lattice with a local net positive charge. This lowers the energy of the conduc ⁇ tion band locally. The amount by which the local energy of the conduction band is lowered can be esti ⁇ mated by applying the effective mass approximation as described by J. F. Hamilton in the journal Advances in Physics, Vol. 37 (1988) p. 395 and Excitonic Processes in Solids by M. Ueta, H. Kanzaki, K. Kobayashi, Y. Toyozawa and E.
  • photoelectrons When photoelectrons are generated by the absorption of light, they are attracted by the net positive charge at the dopant site and temporarily held (i.e., bound or trapped) at the dopant site with a binding energy that is equal to the local decrease in the conduction band energy.
  • the dopant that causes the localized bending of the conduction band to a lower energy is referred to as a shallow electron trap because the binding energy holding the photoelectron at the dopant site (trap) is insufficient to hold the electron permanently at the dopant site. Nevertheless, shallow electron trapping sites are useful. For example, a large burst of photoelectrons generated by a high intensity exposure can be held briefly in shallow electron traps to protect them against immediate dissi ⁇ pation while still allowing their efficient migration over a period of time to latent image forming sites.
  • a dopant to be useful in forming a shallow electron trap it must satisfy additional criteria beyond simply providing a net valence more positive than the net valence of the ion or ions it displaces in the crystal lattice.
  • a dopant When a dopant is incorporated into the silver halide crystal lattice, it creates in the vicinity of the dopant new electron energy levels (orbitals) in addition to those energy levels or orbitals which comprised the silver halide valence and conduction bands.
  • new electron energy levels orbitals
  • For a dopant to be useful as a shallow electron trap it must satisfy these additional criteria: (1) its highest energy electron o_ccupied molecular o_rbital (HOMO, also commonly refer ⁇ red to as the frontier orbital) must be filled--e.g.
  • HOMO highest energy electron o_ccupied molecular o_rbital
  • the orbital if the orbital will hold two electrons (the maximum possible number) , it must contain two electrons and not one and (2) its lowest energy unoccupied molecular o_rbital (LUMO) must be at a higher energy level than the lowest energy level conduction band of the silver halide crystal lattice. If conditions (1) and/or (2) are not satisfied, there will be a local, dopant- derived orbital in the crystal lattice (either an unfilled HOMO or a LUMO) at a lower energy than the local, dopant-induced conduction band minimum energy, and photoelectrons will preferentially be held at this lower energy site and thus impede the efficient migra ⁇ tion of photoelectrons to latent image forming sites.
  • LUMO lowest energy unoccupied molecular o_rbital
  • Metal ions satisfying criteria (1) and (2) are the following: Group 2 metal ions with a valence of +2, Group 3 metal ions with a valence of +3 but excluding the rare earth elements 58-71, which do not satisfy criterion (1) , Group 12 metal ions with a valence of +2 (but excluding Hg, which is a strong desensitizer, possibly because of spontaneous reversion to Hg + 1) , Group 13 metal ions with a valence of +3, Group 14 metal ions with a valence of +2 or +4 and Group 15 metal ions with a valence of +3 or +5.
  • metal ions satisfying criteria (1) and (2) those preferred on the basis of practical convenience for incorporation as dopants include the following period 4, 5 and 6 elements: lanthanum, zinc, cadmium, gallium, indium, thallium, germanium, tin, lead and bismuth.
  • Specifically preferred metal ion dopants satisfying criteria (1) and (2) for use in forming shallow electron traps are zinc, cadmium, indium, lead and bismuth.
  • Specific examples of shallow electron trap dopants of these types are provided by DeWitt, Gilman et al, Atwell et al, Weyde et al and Murakima et al EPO 0 590 674 and 0 563 946, each cited above.
  • Group VIII metal ions Metal ions in Groups 8, 9 and 10 that have their frontier orbitals filled, thereby satisfying criterion (1) , have also been investigated. These are Group 8 metal ions with a valence of +2, Group 9 metal ions with a valence of +3 and Group 10 metal ions with a valence of +4. It has been observed that these metal ions are incapable of forming efficient shallow elec ⁇ tron traps when incorporated as bare metal ion dopants. This is attributed to the LUMO lying at an energy level below the lowest energy level conduction band of the silver halide crystal lattice. However, coordination complexes of these
  • the requirement of the frontier orbital of the metal ion being filled satisfies criterion (1) .
  • criterion (2) At least one of the ligands forming the coordination complex must be more strongly electron withdrawing than halide (i.e., more electron withdrawing than a fluoride ion, which is the most highly electron withdrawing halide ion) .
  • the spectrochemical series places the ligands in sequence in their electron withdrawing properties, the first (I ⁇ ) ligand in the series is the least electron withdrawing and the last (CO) ligand being the most electron withdrawing.
  • the underlining indicates the site of ligand bonding to the polyvalent metal ion.
  • the efficiency of a ligand in raising the LUMO value of the dopant complex increases as the ligand atom bound to the metal changes from Cl to S to 0 to N to C.
  • the ligands C_N ⁇ and QO are especially preferred.
  • N_CS ⁇ thiocyanate
  • Se ⁇ seleno- cyanate
  • N 0 ⁇ cyanate
  • N.CTe ⁇ tellurocyanate
  • azide N3
  • spectrochemical series can be applied to ligands of coordination complexes, it can also be applied to the metal ions.
  • the following spectrochemical series of metal ions is reported in
  • the metal ions in boldface type satisfy frontier orbi ⁇ tal requirement (1) above.
  • this listing does not contain all the metal ions which are specifically contemplated for use in coordination complexes as dopants
  • the position of the remaining metals in the spectrochemical series can be identified by noting that an ion's position in the series shifts from Mn +2 , the least electronegative metal, toward Pt +4 , the most electronegative metal, as the ion's place in the Periodic Table of Elements increases from period 4 to period 5 to period 6.
  • the series position also shifts in the same direction when the positive charge increases.
  • Os +3 a period 6 ion, is more elec ⁇ tronegative than Pd 4 " 4 , the most electronegative period 5 ion, but less electronegative than Pt +4 , the most electronegative period 6 ion.
  • Ir +3 , Os +3 and Pt + are clearly the most electro-nega ⁇ tive metal ions satisfying frontier orbital requirement (1) above and are therefore specifically preferred.
  • the filled frontier orbital polyvalent metal ions of Group VIII are incorporated in a coordination complex containing ligands, at least one, most prefer ⁇ ably at least 3 , and optimally at least 4 of which are more electronegative than halide, with any remaining ligand or ligands being a halide ligand.
  • the metal ion is itself highly electronegative, such Os +3 , only a single strongly electronegative ligand, such as carbonyl, for example, is required to satisfy LUMO requirements. If the metal ion is itself of relatively low electronegativity, such as Fe +2 , choosing all of the ligands to be highly electronegative may be required to satisfy LUMO requirements.
  • Fe(II) (CN) 6 is a specifically preferred shallow elec ⁇ tron trapping dopant.
  • coordination complexes containing 6 cyano ligands in general represent a convenient, preferred class of shallow electron trap ⁇ ping dopants.
  • Ga +3 and In "1"3 are capable of satisfying HOMO and LUMO requirements as bare metal ions, when they are incorporated in coordination complexes they can contain ligands that range in electronegativity from halide ions to any of the more electronegative ligands useful with Group VIII metal ion coordination complexes.
  • Group VIII metal ions and ligands of intermediate levels of electronegativity it can be readily determined whether a particular metal coordina- tion complex contains the proper combination of metal and ligand electronegativity to satisfy LUMO require ⁇ ments and hence act as a shallow electron trap. This can be done by employing electron paramagnetic resonance (EPR) spectroscopy.
  • EPR electron paramagnetic resonance
  • Electron EPR signals are commonly characterized by a parameter called the g factor.
  • the method for calcu ⁇ lating the g factor of an EPR signal is given by C. P. Poole, cited above.
  • the g factor of the electron EPR signal in the silver halide crystal lattice depends on the type of halide ion(s) in the vicinity of the elec ⁇ tron.
  • R. S. Eachus, M. T. Olm, R. Janes and M. C. R. Symons in the journal Physica Status Solidi (b) , Vol. 152 (1989), pp. 583-592 in a AgCl crystal the g factor of the electron EPR signal is 1.88
  • a coordination complex dopant can be identi ⁇ fied as useful in forming shallow electron traps in the practice of the invention if, in the test emulsion set out below, it enhances the magnitude of the electron
  • the undoped control emulsion is a 0.45 ⁇ 0.05 ⁇ edge length AgBr octahedral emulsion precipitated, but not subsequently sensitized, as described for Control IA of Marchetti et al U.S. Patent 4,937,180.
  • the test emulsion is identi ⁇ cally prepared, except that the metal coordination complex in the concentration intended to be used in the emulsion of the invention is substituted for Os(CNg) 4 " in Example IB of Marchetti et al.
  • test and control emulsions are each prepared for electron EPR signal measurement by first centrifuging the liquid emulsion, removing the supernatant, replacing the supernatant with an equivalent amount of warm distilled water and resuspending the emulsion. This procedure is repeated three times, and, after the final centrifuge step, the resulting powder is air dried. These procedures are performed under safe light conditions.
  • the EPR test is run by cooling three, differ ⁇ ent samples of each emulsion to 20, 40 and 60°K, respectively, exposing each sample to the filtered output of a 200 W Hg lamp at a wavelength of 365 nm, and measuring the EPR electron signal during exposure. If, at any of the selected observation temperatures, the intensity of the electron EPR signal is signifi- cantly enhanced (i.e., measurably increased above signal noise) in the doped test emulsion sample rela ⁇ tive to the undoped control emulsion, the dopant is a shallow electron trap.
  • Hexacoordination complexes are preferred coordination complexes for use in the practice of this invention. They contain a metal ion and six ligands that displace a silver ion and six adjacent halide ions in the crystal lattice. One or two of the coordination sites can be occupied by neutral ligands, such as carbonyl, aquo or ammine ligands, but the remainder of the ligands must be anionic to facilitate efficient incorporation of the coordination complex in the crystal lattice structure. Illustrations of specif ⁇ ically contemplated hexacoordination complexes for inclusion in the protrusions are provided by McDugle et al U.S. Patent 5,037,732, Marchetti et al U.S.
  • Useful neutral and anionic organic ligands for hexacoordination complexes are disclosed by Olm et al U.S. Patent 5,360,712.
  • Careful scientific investigations have revealed Group VIII hexahalo coordination complexes to create deep (desensitizing) 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) .
  • M is filled frontier orbital polyvalent metal ion (preferably Fe +2 , Ru +2 or Os +2 );
  • Ls represents six coordination complex ligands which can be independently selected, provided that at least four of the ligands are anionic ligands and at least one (preferably at least 3 and optimally at least 4) of the ligands is more electronegative than any halide ligand (i.e., more electron withdrawing than a fluoride ion, which is the most electronegative halide ion) ; and n is a negative integer having an absolute value of less than 5 (preferably, -2, -3 or -4).
  • the SET dopants are effective in overall concentrations ranging from 1 X 10 " ⁇ to 5 X 10 ⁇ 4 mole per silver mole or, alternatively stated, from 1 to 500 molar parts per million (mppm) of silver.
  • Preferred overall SET dopant concentrations are from 10 to 300 mppm of silver (1 X 10 ⁇ 5 to 3 X 10 ⁇ 4 mole per silver mole) .
  • less than optimum results are obtained when the SET dopant is located too close to the surface of the grain. It is therefore contemplated to limit the surface concentra ⁇ tion of the SET dopant to less than 100 mppm of silver forming the outer (last precipitated) 5 percent of the grain structure.
  • the outer (last precipi- tated) 30 percent of the grain structure contains an SET dopant concentration of less than 100 mppm.
  • concentration of the SET dopant in the surface portions of the tabular grains includes, of course, entirely eliminating the SET dopant from the surface regions of the grains. That is, it is specifically contemplated and preferred to withhold the addition of SET dopant while the final, surface portion of the tabular grains are formed.
  • the SET dopant can be confined to a narrow band or distributed in any desired manner within the interior of the grains.
  • SET dopants can be employed effectively in emulsions according to the invention that are not spectrally sensitized, it has been observed quite unexpectedly that SET dopants provide comparatively large increases in photographic speed when employed in combination with one or more cyanine spectral sensitizing dyes exhibiting an oxidation potential (Eox) less positive than +0.87 volt and difference between dye oxidation and reduction potentials (Eox-Ered) of less than 2.10 volts.
  • Eox oxidation potential
  • Eox-Ered difference between dye oxidation and reduction potentials
  • Oxidation and reduction potentials of cyanine dyes have been extensively studied and hence the selection of specific cyanine dyes that satisfy these Eox and Eox-Ered preferences is well within the capability of the art. Oxidation and reduction potentials of cyanine dyes are extensively discussed in Photographic Science and Engineering, Vol. 18, 1974, pp. 49-53 (Sturmer et al) , pp. 175-185 (Leubner) and pp. 475-485 (Gilman) and by Gilman in Vol. 19, 1975, p. 333. Oxidation and reduction potentials can be measured as described by R. J. Cox, Photographic Sensitivity , Academic Press, 1973, Chapter 15.
  • spectral sensitizing dyes The properties of spectral sensitizing dyes, together with extensive examples, are provided in Research Disclosure , Item 36544, cited above, Section V. Spectral sensitization and desensitization, A. Sensitizing dyes. Section V as well as Hamer The Cyanine Dyes and Related Compounds, John Wiley & Sons, 1964, illustrate the various forms of cyanine dyes, including simple (monomethine) cyanines, carbocyanines (trimethinecyanines) , dicarbocyanines (pentamethine- cyanines) , tricarbocyanines (heptamethine cyanines, and complex (trinuclear) cyanines.
  • Eox-Ered 1.145(hv - 2.225) + 1.858
  • h the Planck constant
  • v the light frequency (which is the reciprocal of the wavelength) .
  • nmJ 1.44(nmSol - 500) + 555
  • Eox-Ered of 1.40 volts the corresponding nmSol and nmJ are 679 nm and 813 nm, respectively.
  • Eox-Ered of the cyanine spectral sensitizing dyes employed will be at least 1.10 volts, with most applications employing cyanine dyes with Eox-Ered values of at least 1.20 volts and, most commonly, at least 1.40 volts.
  • spectral sensitizing dyes exhibiting oxidation potentials less positive than +0.87 volts and for this reason preferred for use in the emulsions of the invention:
  • Eox-Ered 1.90 v
  • Eox-Ered 1.98 v
  • the emulsions of the invention can optionally contain other dopants.
  • a summary of other conventional dopants is provided by Research Disclosure , Item 36544, cited above, I. Emulsion grains and their preparation, D. Grain modifying conditions and adjustments, paragraph (3) . It has, for example, been observed that the selenium sensitization of emulsions is enhanced when selenium is introduced as a dopant--hereinafter also referred to as a Se dopant.
  • Preferred selenium dopants are of the type disclosed by Wu U.S. Patent 5,166,045.
  • a selenium donating substance is present.
  • the selenium can be incorporated in an elemental form--i.e., Se°—or in a divalent form in either an organic or inorganic compound.
  • Specif ⁇ ically preferred inorganic compounds can take the following form: (VIII)
  • M is a monovalent metal, such as an alkali metal, and L is halogen or pseudohalogen.
  • the halogen can be selected from among fluoride, chlo ⁇ ride and bromide.
  • the term "pseudohalogen" is employed in its art recognized usage to indicate ligands that are reactively similar to halogen and are at least as electronegative as halogen.
  • L completes with Se a selenocyanate or isoselenocyanate moiety.
  • Carbon, nitrogen or phosphorus bonds not satisfied by selenium can be satisfied by hydrogen or organic moieties, such as substituted or unsubstituted alkyl or aryl moieties containing up to about 10 carbon atoms.
  • Lower alkyl ( ⁇ 6 carbon atoms and optimally ⁇ 4 carbon atoms) are preferred while preferred aryl moieties are those containing from 6 to 10 carbon atoms, such as phenyl lower alkyl substituted phenyl moieties.
  • selenium dopant source materials for inclusion during precipitation include the following:
  • Preferred concentrations of the selenium dopants are in the range of from 1 X 10 _ € > to 7 X 10" 5 mole per silver mole or, alternatively stated, from 1 to 70 mppm.
  • Selenium concentrations are based on total silver, even when the Se dopant is introduced during precipitation of only a portion of the grain.
  • the Se dopant can be introduced during any convenient portion of or throughout grain formation, but is preferably introduced prior to halide conversion, resulting in the location of edge and corner iodide profiles, discussed above.
  • SET and Se dopants it is preferred to introduce these dopants into separate portions of the tabular grains. Preferably at least 10 mole percent of the total silver is precipi ⁇ tated between completion of introduction of one of the dopants and commencement of introduction of the remain ⁇ ing dopant.
  • the dopants can be introduced in either order, it is preferred to complete introduction of the SET dopant before introducing the Se dopant.
  • An iridium dopant capable of reducing low intensity reciprocity failure is preferably incorpo- -31- rated in the tabular grains of the emulsions of the invention. Specific examples of iridium dopants employed to reduce low intensity reciprocity failure are contained in Kim U.S.
  • a more general survey of iridium dopants employed to reduce reciprocity failure and for other purposes is provided by B. H. Carroll, Iridium Sensitization: A Literature Review", Photographic Science and Engineering, Vol. 24, No. 6, Nov/Dec 1980, pp. 265-267.
  • a still more general survey of dopants, including iridium dopants intended to reduce reciprocity failure is provided in Research Disclosure , Item 36544, Section I. Emulsion grains and their prepa ⁇ ration, D. Grain modifying conditions and adjustments, paragraphs (3) and (4) . Any conventional iridium dopant known to reduce low intensity reciprocity fail ⁇ ure can be employed in any amount known to be useful for this purpose in the practice of the invention.
  • the iridium dopant is incorporated in the crystal lattice structure of the grain in the form a hexacoordination complex satisfying the formula: (IX)
  • X is a halide ligand
  • L' is any bridging ligand, and m is -2 or -3.
  • a convenient counter ion such as ammonium or alkali metal
  • ammonium or alkali metal is associated with the hexacoordination complex, but only the anionic portion of formula IX is actually incorporated within the crystal lattice structure.
  • the iridium can be in a +4 valence state, as illustrated, for example by Leubner et al
  • U.S. Patent 4,902,611 the +4 iridium reverts to the +3 valence state upon incorporation.
  • Chloride and bromide are preferred halide ligands.
  • the bridging ligand L' can also be a halide ligand or, alternative ⁇ ly, can take any convenient conventional form, includ ⁇ ing any of the various individual ligand forms disclosed in McDugle et al U.S. Patents 4,933,272, 4,981,781 and 5,037,732, Marchetti et al U.S. Patent 4,937,180, Keevert et al U.S. Patent 4, 945, 035 * and Olm et al U.S. Patent 5,360,712.
  • Typical ligands other than chloride and bromide ligands include H2O, F ⁇ , NCS ⁇ , SCN “ , CN “ , NCO ⁇ , I " , N3-, N0 3 _ , N0 ⁇ , and organic ligands, such as substituted or unsubstituted pyrazine, pyrimidine, thiazole, oxazole, pyridine, acetonitrile and pyridazine ligands.
  • the iridium dopant is preferably introduced following precipitation of at least 20 (most preferably 60) percent of the silver forming the tabular grains and before 90 (most preferably 80) of the silver form ⁇ ing the tabular grains has been precipitated.
  • the ideal location for the iridium dopant is in a band formed just before precipitation of the surface portion of the tabular grains, from which iridium is excluded.
  • Preferably at least 20 (optimally at least 60) percent of total silver is precipitated before iridium is introduced.
  • Preferred concentrations of the iridium dopant can range up to about 800 (most preferably 140) molar parts per billion (mppb) or, alternately stated, 8 X 10 ⁇ mole per silver mole, based on total silver. Minimum effective iridium concentrations of 2.8 mppb have been reported, although concentrations of at least about 15 mppb are usually more convenient to use.
  • an intervening band between completion of the SET dopant introduction and commencement of iridium doping.
  • the intervening band preferably accounts for at least 10 percent of total silver and optimally at least 20 percent of total silver.
  • Selenium and iridium dopants do not exhibit any unwanted interactions and can be introduced entirely concurrently, entirely sequentially or in any desired manner between these extremes.
  • tabular grain emulsions of the invention can take any convenient conventional form.
  • conventional emul ⁇ sion preparation techniques specifically contemplated to be compatible with the present invention are those disclosed in Research Disclosure, Vol. 365, Sept. 1994, Item 36544, I. Emulsion grains and their preparation, A. Grain halide composition, paragraph (5) ; C. Precipita ⁇ tion procedures; and D. Grain modifying conditions and adjustments, paragraphs (1) and (6) .
  • the emul ⁇ sions of the invention can be prepared for photographic use as described by Research Disclosure , 36544, cited above, I. Emulsion grains and their preparation, E. Blends, layers and performance categories; II. Vehicles, vehicle extenders, vehicle-like addenda and vehicle related addenda; III. Emulsion washing; IV. Chemical sensitization; and V. Spectral sensitization and desensitization, A. Spectral sensitizing dyes.
  • the emulsions or the photographic elements in which they are incorporated can additionally include one or more of the following features illustrated by Research Disclosure, Item 36544, cited above: VII. Antifog- gants and stabilizers; VIII. Absorbing and scattering materials; IX.
  • Coating physical property modifying addenda X. Dye image formers and modifiers; XI. Layers and layer arrangements; XII. Features applicable only to color negative; XIII. Features applicable only to color positive; XIV. Scan facilitating features; and XV. Supports.
  • the exposure and processing of photographic elements incorporating the emulsions of the invention can take any convenient conventional form, illustrated by Research Disclosure, Item 36544, cited above, XVI. Exposure; XVIII. Chemical development systems; XIX. Development; and XX. Desilvering, washing, rinsing and stabilizing.
  • Example 1 This example has as its purpose to demon ⁇ strate the improvement in photographic speed that is realized by the iodide placement within the tabular grains, independent of dopant addition.
  • Emulsion A This demonstrates an emulsion exhibiting an overall similarity to the emulsions of the invention, but lacking the specific iodide placement features of the invention.
  • aqueous gelatin solution (composed of 1 liter of water, 0.56 g of alkali-processed low methionine gelatin, 3.5 ml of 4N nitric acid solution, 1.12 g of sodium bromide and having a pAg of 9.38 and 14.4 wt%, based on total silver used in nucleation, of PLURONIC-31R1 TM (a surfactant satisfying the formula:
  • aqueous silver nitrate containing 1.27 g of silver nitrate
  • 32 mL of aqueous sodium bromide containing 0.66 g of sodium bromide
  • 49 mL of aqueous silver nitrate (contain- ing 13.3 g of silver nitrate) and 48.2 mL of aqueous sodium bromide (containing 8.68 g of sodium bromide) were added simultaneously at linearly accelerated rates starting from respective rates of 0.67 mL/min and 0.72 mL/min for the subsequent 24.5 minutes.
  • This emulsion demonstrates the speed advantages of the iodide placement required by the invention.
  • Emulsion A The procedure used to prepare Emulsion A was employed up to the step at which iodide was introduced. From that point the precipitation proceeded as follows: Then 16.6 mL of an aqueous potassium iodide solution (containing 10.45 g of potassium iodide) were added over a three minute period at constant flow rate. The solution was delivered to a position in the kettle such that mixing was maximized. After a 10 minute hold, 220.8 mL of an aqueous silver nitrate solution
  • This emulsion satisfied the iodide placement required by the invention, but did not contain an SET dopant.
  • a vessel equipped with a stirrer was charged with 6 L of water containing 3.4 g of oxidized bone gelatin, 6.7 g of sodium bromide, 0.5 g of surfactant Pluronic 31R1 TM (see formula X above) and sufficient nitric acid to achieve a pH of 1.85 at 45°C.
  • aqueous silver nitrate containing 1146 of silver nitrate
  • 2784 mL of aqueous sodium bromide containing 716.9 g of sodium bromide
  • an aqueous potassium iodide solution (containing 62.4 g of potassium iodide) were added over a two minute period at a constant flow rate.
  • the solution was delivered to a position in the kettle such that mixing was maximized.
  • 1325 mL of an aqueous silver nitrate solution (containing 540.6 g of silver nitrate) were added over a 26.5 minute period at a constant flow rate.
  • 985 mL of an aqueous silver bromide solution (containing 253.6 g of sodium bromide) were added over a 20 minute period at a constant rate.
  • the silver halide emulsion thus obtained contained 3.6 mole percent iodide.
  • Table IV The properties of the grains of this emulsion are shown in Table IV below.
  • Emulsion D This emulsion was prepared similarly as
  • Emulsion C except that an SET dopant was additionally added.
  • the emulsions listed in Table IV were optimally sulfur and gold sensitized and red sensitized with a combination of SS-1 and SS-2 in a 9:1 molar ratio, as the sensitizing dyes present in the.finish.
  • Single layer coatings on a transparent film support employed cyan dye-forming coupler (CC-l) at a coating coverage of 9.69 mg/dm 2 and a silver coating coverage of 10.76 mg/dm 2 .
  • a sample of each coating was exposed by a tungsten light source through a graduated density test object and a Wratten 23ATM filter, which permits significant transmission at wavelengths longer than 560 nm. Processing was conducted using the Eastman Flexicolor TM color negative processing chemicals and procedures .
  • This example demonstrates the effect of varied levels and placements of the SET dopant.
  • Dopant Profile % refers to the interval of dopant introduction, referenced to the percent of total silver present in the reaction vessel at the start and finish of dopant introduction.
  • This example has as its purpose to demon- strate the enhanced sensitivity of an emulsion accord ⁇ ing to the invention when spectrally sensitized to the blue and green regions of the spectrum.
  • This emulsion is provided for purposes of comparison. Unlike the emulsion of the invention, described below, it does not contain an SET dopant.
  • a vessel equipped with a stirrer was charged with 6 liters of water containing 6.8 g of oxidized bone gelatin, 6.7 g of sodium bromide, 2 g of surfac- tant PLURONIC 31R1 TM (see formula VIII above for formu ⁇ la) , and sufficient nitric acid to achieve a pH of 1.85 at 45°C. While keeping the temperature at 45°C, 42.4 mL of an aqueous solution of silver nitrate (containing 3.60 g of silver nitrate) and 42.7 mL of an aqueous solution of sodium bromide (containing 2.29 g of sodium bromide) were simultaneously added over a period of 1 minute at a constant rate.
  • the mixture was held and stirred for 1 minute during which 86 mL of an aqueous sodium bromide solution (containing 8.82 g of sodium bromide) was added. Thereafter, the temperatur of the mixture was raised to 60°C over a period of 9 minutes. Then, 101 mL of an aqueous solution of ammonium sulfate (containing 10.2 g of ammonium sulfate) were added, and the pH of the mixture was adjusted to 9.5 with aqueous sodium hydroxide. The mixture thus prepared was stirred for 9 minutes.
  • aqueous potassium selenocyan ⁇ ate containing 0.305 g of potassium selenocyanate
  • 143.5 mL of an aqueous potassium iodide solution containing 65.5 g of potassium iodide
  • the solution was delivered to a position in the kettle such that mixing was maximized.
  • 1337 mL of an aqueous silver nitrate solution (contain ⁇ ing 545.0 g of silver nitrate) were added over a 26.5 minute period at constant flow rate.
  • This emulsion demonstrates an emulsion according to the invention containing an SET dopant.
  • Emulsion M An emulsion was prepared following the same procedure as for Emulsion M, except as follows: The potassium selenocyanate solution was omitted and 61 mL of an aqueous solution containing 0.22 gram (corre ⁇ sponding to 50 mppm, based on total silver) of potassium hexacyanoruthenate was added to the mixture during the time corresponding to the addition of 66 to 68 percent of the total silver.
  • emulsions listed in Table VII were optimally spectrally and chemically sensitized.
  • Chemi ⁇ cal sensitizers were conventional sulfur and gold sensitizers.
  • Spectrally sensitizers included either green or blue dyes.
  • the green sensitizing dyes were used in a molar ratio of 4.5 to 1.
  • the green sensitizing dye present in the larger amount was SS-11, and the green sensitizing dye present in the smaller amount was SS-12.
  • the sensitized emulsions were combined with a cyan-dye forming coupler (CC-l) and coated on a photo ⁇ graphic film support with a silver coverage of 807 mg/m 2 (75 mg/ft 2 ) . A sample of each coating was exposed with a tungsten light source for l/50th second.
  • Blue-sensitized film samples were exposed through a Wratten 2B TM filter, which transmits at wavelengths longer than 390 nm. Green-sensitized film samples were exposed through a Wratten 9 TM filter. Exposed film samples were developed for 3 minutes and 15 seconds using Kodak Flexicolor TM C-41 color negative processing.
  • Example 5 This example as its purpose to demonstrate that cyanine dyes Eox-Ered of ⁇ 2.10 volts produce in the SET doped emulsions of the invention an unexpected larger increase in speed than cyan dyes that fail to satisfy this relationship. Except as otherwise stated the details of emulsion features, film construction, exposure and processing are found in the preceding examples.
  • Emulsion Dye (volts) (volts) Speed

Landscapes

  • Silver Salt Photography Or Processing Solution Therefor (AREA)

Abstract

L'invention concerne des émulsions à grains tabulaires présentant une sensibilité photographique renforcée. Les grains tabulaires présentent une concentration d'iodure en surface maximale, le long de leurs arêtes, et une concentration d'iodure en surface moins importante dans les coins qu'en d'autres endroits le long de leurs arêtes. Les grains contiennent un dopant capable de produire des pièges à électrons peu profonds.
EP95935226A 1994-10-26 1995-10-13 Emulsions photographiques a sensibilite renforcee Expired - Lifetime EP0736200B1 (fr)

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US08/329,591 US5476760A (en) 1994-10-26 1994-10-26 Photographic emulsions of enhanced sensitivity
US329591 1994-10-26
US72395P 1995-06-30 1995-06-30
US723 1995-06-30
PCT/US1995/012521 WO1996013757A1 (fr) 1994-10-26 1995-10-13 Emulsions photographiques a sensibilite renforcee

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JP3597538B2 (ja) 2004-12-08

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