CA1051250A - Spectral sensitization of transition metal complexes - Google Patents

Abstract

Abstract of the Disclosure A photographic element is disclosed comprised of a support and a radiation-sensitive layer having as its sole photolytically active component a cobalt(III)complex which is free of a sensitizable anion and which has at least two monodentate ligands and, in intimate association with the cobalt(III)complex, a spectral sensitizer capable of absorbing radiation longer than 300 nanometers in wavelength. The cobalt(III)complex and the spectral sensitizer are chosen such that the cobalt-(III)complex exhibits a reduction potential which lies between the ground state oxidation and reduction potentials of the spectral sensitizer.

Description

~051250 This invention is directed to a process and an element capable of reducing in response to actinic radiation in excess of 300 nanometers in wavelength a cobalt(III)complex. More specifically, this inven-tion is directed to a photographic process and element which is capable of the selective reduction of a cobalt(III)complex through the incorporation of a sensitizer therefor. The present invention ~s further concerned with a photographic element and process capable of forming a photographic image either in a photographic element or layer containing the cobalt(III)complex or in a separate photographic element or layer.
Classically, photographic elements have incorporated silver halide as a radiation-sensitive material. Upon exposure and processing the silver is reduced to its metallic form to produce an image. Processing, with its use of successive aqueous baths, has become increasingly objectionable to users desiring more immediate availability of a photographic image.
Despite the processing required silver halide photography has remained popular, since it offers a number of distinct advan-tages. For example, although silver halide is itself photo-responsive only to blue and lower wavelength radiation, spectral sensitizers have been found which, without directly chemically interacting, are capable of transferring higher waveleng-th radiation energy to silver halide to render it ` panchromatic. Additionally, silver halide photography is ; attractive because of its comparatively high speed. Frequently silver halide is referred to as exhibiting internal amplifica-tion -- i.e. the amount of silver atoms reduced in imaging is a large multiple of the number of photons received.

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A variety of nonsilver photographic systems have been considered by those skilled in the art. Typically these systems have been chosen to minimize photographic processing and to provide usable photographic images with less delay than in silver halide photography. Characteristically these systems require at least one processing step to either print-out or fix the photographic image. For example, ammonia or heat pro-cessing has been widely used. While advantageously simple in terms of processing, these systems have, nevertheless, exhibited significant disadvantages. For example, many nonsilver systems are suitable for producing only negative images (or only positive images). Further, these systems have been quite slow, since they have generally lacked the internal amplification capability of silver halide. Many systems have also suffered from diminishing image-background contrast with the passage of time.
The use of cobalt(III)complex compounds in photo-graphic elements is generally known in the art. For example, ,~ .
-~ Shepard et al U.S. Patent 3,15?,903 teaches imaging through ; 20 the use of an oxidation-reduction reaction system that requires a photocatalyst. The solid reducing agent is taught to be any ` one of a number of hydroxy aromatic compounds including dihydro-phenols, such as hydroquinone. The oxidant is taught to be chosen from a variety of metals, such as silver, mercury, lead, gold, ~j manganese, nickel, tin, chromium, platinium and copper. Shepard ;il et al does not specifically teach the use of cobalt(III)complexes as oxidants. Instead Shepard et al teaches that photochromic complexes, such as cobalt ammines, can be employed as photo-~ catalysts to promote the oxidation-reduction reaction.
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Cobalt(III)compl~xes are known to be directly responsive to electromagnetic radiation when suspended in solution. While most cobalt(III)complexes are preferentially responsive to ultraviolet radiation below about 300 nanometers, a nurnber of cobalt(III)complexes have been observed in solution to be responsive to electromagnetic radiation ranging well into the visible spectrum. Unfortunately, these same complexes when incorporat`ed into photographic elements lose or are diminished in their ability to respond directly to lower wavelength radia-tion. For example, Hickman et al in U.S. Patent 1,897,843teaches mixing thio-acetamide with hexamino cobaltic chloride to form a light-sensitive complex capable of interacting with lead acetate to produce a lead sulfide image. Hickman et al U.S. Patent 1,962,307 teaches mixing hexammine cobaltic chloride and citric acid to form a light-sensitive complex capable of bleaching a lead sul~ide image. Weyde in U.S.
Patent 2,084~420 teaches producing a latent image by exposing Co(NH3)2(N02)4NH4 to light or an electrical current. A visible image can be formed by subsequent development with ammonium sulfide. None of these patents teach the incorporation of a sensitizer to extend the spectral response of the cobalt(III)-complex.
Borden in U.S. Patent 3,567,453, issued March 2, 1971, and in his article "Review of light-sensitive tetraarylborates", :
Photographic Science and Engineering, Volume 16, No 4, July-August 1972, discloses that aryl borate saltS incorporating a wide variety of cations can be altered in solvent solubility upon exposure to actinic radiation. Borden demonstrates the general utility of aryl borate salts as radiation-sensitive compounds useful in forming differentially developable coatings, . .

~osiz50 as is typical of lithography, by evaluating some 4Q0 different cations ranging from organic cations, such as diazonium, acridinium and pyridinium salts, to inorganic cations, i such as cobalt hexammine. Borden discloses that the aryl borate salts can be spectrally sensitized with a variety of sensitizers, including quinones. In its unsensitized form the cobalt hexaamine tetraphenyl borate of Borden is reported to be light-sensitive in the range of from 290 to 430 nanometers.
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Borden in his report notes that hexaammino cobalt chloride, 10 although bright orange and therefore absorptive in the visible spectrum, is not useful in the lithographic system discussed in his article. Thus, Borden relies upon the light-sensitive aryl borate anionic moiety to provide radiation sensitivity above ~' 300 nanometers.
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`, ' Sun~ary of the Invention It is an ob~ect of this lnvention to provide a radiation-sensitive element and process capable of imagewise reducing a cobalt(III) complex. It is a more specific ob~ect to provide elements and processes capable of produclng positive or negative photographic images either ln a radiation-sensltive layer or within a separate internal or external imaging layer.
It is another ob~ect of this invention to provide photographic elements useful with only thermal processing.
These and other objects of this invention can be achieved in one aspect by providing a radiation-sensitive element comprising a support and, as a coating thereon, a radiation-sensitive layer comprised of a spectral sensitizer and, as the sole photolytically active component, a cobalt(III) complex which is free of a sensitizable anion and whlch has at least two monodentate ligands. The spectral sensltizer is capable of absorbing radiation longer than 300 nanometers in wavelength.
The cobalt(III) complex and the spectral sensitizer are chosen such that the cobalt(III) complex exhibits a reduction potential which lies between the ground state oxidation and reduction potentials of the spectral sensitizer.
In another aspect of this invention is directed to a process comprising exposing to electromagnetic radiation of a wavelength longer than 300 nanometers a layer comprised of a spectral sensitizer capable of absorbing radiation longer than 300 nanometers in wavelength and a cobalt(III~ complex which is free of a sensitizable anion and has at least two monodentate ligands. An image-recording layer which is visibly responsive to at least one of the monodentate ligands contalned 30 within the cobalt(III) complex is associated with the radiation-sensitive layer. At least one monodentate ligand is then transferred from the cobalt(III) complex to the image recordlng layer.

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This invention can be better understood by reference to the following detailed description considered in conjunction with the drawings, in which Fig. 1 is a schematic diagram of a radiation-sensitive element according to this invention;
Fig. 2 is a schematic diagram of the radiation-sensit;ive element in combination with an original image bearing element receiving a reflex exposure;
Fig. 3 is a schematic diagram of the radiation-; 10 sensitive element in combination with a copy sheet receivingthermal processing;

Fig. 4 is a schematic dlagram of the imaged copy sheet, ;~
Fig, 5 is a schematic diagram of a composite radiation-sensitive imaging element;
i' Figs. 6 and 7 are schematic diagrams of an original image bearing element and an image bearing radiation-sensitive ~ composite J Fig, 8 is a schematic diagram of a multi-layer, , 20 multi-color image recording radiation-sensitive element; and Fig, 9 is a plot of cobalt(III)complex ground state reduction potentials in volts versus the logarithm of the rate of dye fade in optical density units.

lQ~5lZ50 Cobalt(III)Complexes The cobalt(III)complexes employed in the practice of this invention are those which feature a molecule having a cobalt atom or ion surrounded by a group of atoms, ions or other molecules which are generically referred to as ligands.
The cobalt atom or ion in the center of these complexes is a Lewis acid- while the ligands are Lewis bases. While it is known that cobalt is capable of forming complexes in both its divalent and trivalent forms, trivalent cobalt complexes--i.e. cobalt(III)complexes--are employed in the practi~e of this invention, since the ligands are tenaciously held in these complexes as compared to corresponding cobalt(II)complexes.
~; Preferred cobalt(III)complexes are those which are inert.
Inert complexes are defined as those which, when a test sample thereof is dissolved at 0.1 molar concentration at 20C in an ; inert solvent solution also containing a 0.1 molar concentration of a tagged uncoordinated ligand of the same species as the coordinated ligand, exhibits essentially no exchange of unco-ordinated and coordinated ligands for at least one minute, and preferably for at least several hours, such as up to five hours or more. This test is advantageously conducted under the con-ditions existing within the radiation-sensitive elements of this invention. Many cobalt(III)complexes show essentially no change of uncoordinated or coordinated ligands for several days.
The definition of inert complexes, and the method of measurïng j ligand exchange using radioactive isotopes to tag ligands are well known in the art. See, for example, Taube, Chem. Rev., Vol. 50, p. 69 (1952) and Basolo and Pearson, Mechanisms of Inorganic Reactions, A Study of Metal Complexes and Solutions, ., ~ .

- lOS1250 2nd Edition, 1967~ published by John Wiley and Sons, page 141.
~urther details on measurement of ligand exchange appear in articles by Adamson et al, J. Am. Chem., Vol. 73, p. 4789 (1951).
Cobalt(III)complexes useful in the practice of this invention include those having coordination numbers of 6.
A wide variety of ligands can be used with cobalt(III) to form cobalt(III)complexes. Nearly all Lewis bases (i.e. substances having an -unshared pair of electrons) can be ligands in cationic cobalt(III)complexes. Some typical useful ligands include halides (e.g. chloride, bromide, fluoride), nitrate, nitrite, superoxide, water, amine (e.g. ethylenediamine, diethylene-triamine, triethylenetetramine, diaminodiacetate, ethylene-diaminetetraacetic acid, etc.), ammine, azide, glyoxime, thio-cyanide, cyanide, carbonate, and similar ligands, including those referred to on page 44 of Basolo et al, supra. The - cobalt(III)complexes of this invention incorporate at least two monodentate ligands.
The preferred cobalt(III)complexes for use in the practice of this invention are those in which the cobalt(III) atom and the ligands associated therewith form a cationic moiety--hereinafter referred to as a cationic cobalt(III) complex--having a net positive charge of +3. To form a com-plete compound one or more nonsensitizable anions are asso-ciated with the cationic cobalt(III)complex as determined by the charge neutralization rule. Anions are considered to be nonsensitizable for purposes of this invention if their use in combination with known sensitizers for silver halide emulsions does not stimulate their photographic response upon exposure to electromagnetic radiation longer than 300 nanorneters in wave-length. Such anions can, of course, be readily identified to _g_ 1~)51ZSO

be nonsensitizable by observing their behavior in combination with photolytically inactive cations with and without known spectral sensitizers being present. No photographic activity is exhibited by the anions employed in the practice of this invention. The photographic activlty of the compounds in which they are incorporated is provided by the cationic cobalt(III)-complex. Espécially useful with cationic cobalt(III)complexes are nonsensitizable anions, such as halides (e.g. chloride, bromide, fluoride, etc.), sulfite, sulfate, alkyl or aryl sul-fonates, nitrate, nitrite, perchlorate, carboxylate (e.g. halo-alkylcarboxylate, acetate, hexanoate, etc.), hexafluorophos-phate, tetrafluoroborate and other similar anions.
While a variety of anions can be used in the practice of this invention, we have observed that those anions which are relatively acid--i.e., exhibit an acid dissociation constant of 3 5 or less--produce cobalt(III)complexes which are less easily reduced. This can result in reduced photographic speed, however, in systems of the type disclosed by Thap DoMinh in commonly ; assigned U.S. Patent No. 4,075,019, titled High Gain Transition Metal Complex Imaging, cobalt(III)complexes incorporating anions having acid dissociation constants of 3.5 or less (preferably from 3.0 to 0.0), when employed with certain compounds capable of forming Co(III) ligands, exhibit remark-able increases in imaging capabilities, probably due to catalysis of irnage-producing cobalt(III)complex generation which more than offsets any resistance to initial reduction.
Since the spectral sensitizers employed in the practice of this invention can bear a negative charge site, it is con-templated that the spectral sensitizer can itself form an anionic moiety associated with a cationic cobalt(III)complex. The !~

spectral sensitizer quali~ies as a nonsensitive anion, since its response on exposure is not dependent upon the presence of conven-tional spectral sensitizers for silver halide emulsions. One or more cations, as determined by the charge neutralization rule, can alsc be included in addition to the cationic cobalt(III)complex to complete the compound. Preferred cations are those which produce readily solubilizable compounds, such as alkali and quaternary ammonium cations.
Most cobalt(III)complexes are preferentially respon~
sive to electromagnetic radiation of a wavelength shorter than 300 nanometers. A number of cobalt(III)complexes are known which can be directly photoreduced in solution by electro-magnetic radiation of a wavelength longer than 300 nanometers.
However, there is a very marked decrease in direct reduction capabilities when these cobalt(III)complexes are present as or in coatings. Most cobalt(III)complexes are not directly reducible at wavelengths longer than 300 nanometers in photo-graphic coatings, It is a surprising discovery of this invention that known spectral sensitizers for silver halide can improve the photolytic response of cobalt(III)complexes to electromagnetic radiation of wavelengths longer than 300 nanometers. It is even more surprising that cobalt(III)complexes which are not directly responsive to wavelengths longer than 300 nanometers can be photolytically activated--i.e. reduced--when employed in combination with the spectral sensitizers of this invention.
Exemplary preferred cobalt(III)complexes useful in the practice of this invention are those set forth in Table I.

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TABLE I
_emplary Preferred Cobalt(III)Complexes (Reduction Potentials in Volts Parenthetically Indicated) C- 1 hexa-,~mmine cobalt(III) acetate(-0.35) C- 2 hexa-ammine cobalt(III) chloride(-0.315) -C- 3 hexa-ammine cobalt(III) trifluoroacetate C- 4 chloropenta-ammine cobalt(III) bromide C- 5 bromopenta-ammine cobalt(III) bromide C- 6 aquopenta-ammine cobalt(III) chloride(-0.44) C- 7 bis(ethylenediamine) di-ammine cobalt-(III) perchlorate C- 8 bis(ethylenediamine) diacetato cobalt-(III) chloride C- 9 triethylenetetramine dichloro cobalt(III) ' acetate :-7~ C-10 bis(methylamine) tetra-ammine cobalt(III) hexafluorophosphate ) ~0 C-11 aquopenta(methylamine) cobalt(III) nitrate C-1.2 chloropenta(ethylamine) cobalt(III) butanoate C-13 trinitrotris-ammlne cobalt(III)~ methyl-sulfonate I C-14 trinitrotris(methylamine) cobalt(III) fluoride C-15 acetatopenta-ammine cobalt(III) nitrate (-0-285) 3 C-16 bis(trimethylenediamine) dichloro -- cobalt(III) trifluoroacetate - C-17 bis(dimethylglyoxime) bispyridine cobalt-- (III) trichloroacetate I C-18 N,N'-ethylenebis(salicylideneimine) bis-! ammine cobalt(III) bromide C-19 bis(dimethylglyoxime) ethylaquo cobalt-(II~) sulfate C-20 J~-superoxodeca-ammine dicobalt(III) perchlorate C-21 sodi~n dichloro ethylenediamine diaceto cobalt(III) chloroacetate iO51250 ~`
TABL~ I Cont. -- Exem~lary Preferred Cobalt(III)Complexes C-22 penta-ammine carbonato cobalt(III) nitrate (-.44) C-23 trans~bis(ethylenediamine) diazido cobalt(III)] sulfate C-24 cis[bis(ethylenediamine) azidothiocyanato ~:
cobalt(III)] dithionate (-0.50) -i C-25 cis[bis(ethylenediamine) diazido cobalt(III)] perchlorate (-0.67) .
C-26 cisrethylenediamine nitro azido cobalt(III)] perchlorate (-0.70) : C-27 cis[bis(ethylenediamine) dichloro cobalt- ~ -I)] chloride (-0.40) C-28 trans[bis(ethylenedic~mine) dichloro cobalt(III)] chloride (_0.40) C-29 trans[bis(ethylenediamine) dibromo 1 cobalt(III)] bromide (-0.13) i C-30 trans~bis(ethylenediamine) thiocyanato-j 20 chloro cobalt(III)] thiocyanate (-0.40) .. .... . .. ... ... .
C-31 triethylenetetramine dinitro cobalt(III) ~ i_dide . --- -3 C-32 trans[dinitrotetra-ammine cobalt(III)]
nitrate (-0.225) C-33 ci~[bis(ethylenediamine) amminochloro ! cobalt(III)] chloride (-0.54) t C-34 trans[bis(ethylenediamine) dith1'ocyanato ' cobalt(III)] chloride (-0.150) 1, .
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Spectral Sensitizers Any compound known to be a spectral sensitizer for negative-working silver halide emulsions can be employed as a spectral sensitizer in the practice of this invention, provided certain relationships are satisfied. First, the spectral sensitizer should be chosen to exhibit a ground state oxidation potential that is unfavorable for the reduction of the cobalt(III)complex. This relationship is preferable to avoid the spontaneous reduction of the cobalt(III)complex in the absence of actinic radiation. It is generally preferred ; that the ground state oxidation potential of the spectral sensi-tizer be related to the reduction potential of the cobalt(III)-complex such-that for an electron to be transferred from the spectral sensitizer to the cobalt(III)complex it must exhibit a net energy gain. The adverse energy gradient then insures against reduction of the cobalt(III)complex in the absence of externally supplied energy.
The spectral sensitizers are, of course, chosen to reverse the energy gradient relationship upon exposure to 20 actinic radiation. That is, the spectral sensitizers are chosen to be capable of absorbing radiation having a wavelength longer than 300 nanometers. The absorbed radiant energy then converts the spectral sensitizer to an excited state favorable for f reduction of a cobalt(III)complex. In other words, the energy gradient between the excited spectral sensitizer and cobalt(III)-co~lplex is reversed by irradiation so that if an electron is transferred from the excited spectral sensitizer to the cobalt-(III)complex, it exhibits a net energy loss. Thus, a favorable energy gradient for reduction of the cobalt(III)complex is 30 provided.

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We have observed that the required energy relation-ships can be satisfied by employing in combination a cobalt(III)-comp:Lex which exhibits a reduction potential intermediate the ground state oxidation and reduction potentials of the spectral sensLtizer, with the further provision, in the case of reversibly reducible complexes, that the reduction potential of the cobalt-(III)complex more nearly approach the ground state oxidation potential ~han the ground state reduction potential of the spectral sensitizer. While it is difficult to measure accurately the excited state oxidation potentials of spectral sensitizers, it is known that upon excitation the oxidation potential of the spectral sensitizer approaches its ground state reduction potential. This then reverses the energy gradient between the spectral sensitizer and the cobalt(III)complex. Another advan-~age of this relationship is that by choosing the potentlal di~erence between the reduction potential of the cobalt(III)-complex and the ground state reduction potential of the spectral sensitizer to be large as compared to the potential difference between the ground state oxidation potential of the spectral 20 sensitizer and the reduction potential of the cationic cobalt-(III)complex, a more favorable energy gradient is obtained for electron transfer to the cobalt(III)complex from the excited spectral sensitizer than for re-transfer of an electron back to the oxidized spectral sensitizer at its ground state. This relationship is particularly pertinent where the cobalt(III)-complex reduction reaction is readily reversed. It is, of course, recognized that in a number of cationic cobalt(III)-complexes reduction generates cobalt(II) species with concomit-tant ligand release. Reversal of the reaction is not then pos-3 sible, and the a~ailable potential gradient for regenerationof the cobalt(III)complex is of no consequence.

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Both the cobalt(III)complexes and the spectral sensitizers employed in the practice of this invention can be neutral compounds lacking ionizable components. Since it is important that the spectral sensitizer and cobalt(III)complex be intimately associated, we prefer to employ cationic cobalt-(III)complexes in combination with spectral sensitizers bearing a negative charge. In one form the negatively charged spectral sensitizer can even be incorporated into the cobalt(III)complex as an anionic moiety associated with a cationic cobalt(III)complex.
Enhanced spectral sensitization has been obtained where the negative charge site is located in the vicinity of the chromo-phore of the spectral sensitizer. The negative charge site can be vicinally located either by being located within a few bond lengths of the chromophore (preferably within five bond lengths) or by the steric configuration of the molecule. Generally negative charge sites have been incorporated into spectral sensitizers by those skilled in the art through the incorporation of ionizable oxy or sulfur substituents, such as hydroxy, carboxy, sulfonic acid, mercapto and similar substituents. Any one of 20 these charge site providing substituents can be employed in the practice of this invention.
Preferred spectral sensitizers for use in the practice - of this invention are those having an anodic polarographic half-wave potential (also referred to as a ground state oxidation potential) which is less than one volt. It is further preferred that the spectral sensitizers be chosen so that the sum of the cathodic polarographic half-wave potential (also referred to as a ground state reduction potential) and the anodic polarographic - half-wave potential is more negative than -0 50 volt.

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As used herein and in the claims, polarographic measurements are made in accordance with the following procedure. Cathodic polarographic half-wave values are obtained against an aqueous silver-silver chloride reference electrode for the electrochemical reduction of the test compound using controlled-potential polarographic techniques.
A 1 x 10 4 M methanol solution of the test compound is pre-pared. The solvent is 100 percent methanol, if the compound is soluble therein. In some instances, it is necessary to use mixtures of methanol and another solvent, e.g., water, acetone, dimethylformamide, etc., to prepare the 1 x 10 M solution of the test compound. There is present in the test solution, as supporting electrolyte, Q.l M lithium chloride. Only the most ' positive (least negative) half-wave potential value observed is I considered, and it ~s designated herein as the ground state I reduction potential or simply the reduction potential. Anodic ; half-wave values are determined against an aqueous silver-silver chloride reference electrode for the electrochemical oxidation of the tested compounds at a pyrolytic graphite n~ electrode, and are obtained by controlled-potential voltammetry using solutions identical to those used to determine the cathodic polarographic values. Only the most negative (least positive) half-wave potential observed is utilized, and it is designated herein as the ground state oxidation potential. In both ; measurements, the reference electrode (a~ueous silver-silver chloride) is maintained at 20C. Signs are given according to the recommendation of IUPAC at the Stockholm Convention, 1953. The well known general principles of poiarographic measurements are used. See Kolthoff and Lingane, "polarography" second edition, Interscience Publishers, New York (1952). The principles of controlled-potential electrochemical instrumentation which . .
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lOSi2SOallows precise measurements in solvents of low conductivity is described by Kelley5 Jones and Fisher, Anal. Chem., 31, 1475 (1959). The theory of potential sweep voltammetry such as that employed in obtaining the anodic determinations is described by Delahay, "New Instrumental Methods in Electrochemistry" Inter-science Publishers, New ~ork (1954) and Nicholson and Shain, Anal. Chem., 36, 706 (1964). Information concerning the utility and characteristicæ of the pyrolytic graphite electrode is des-cribed by Chuang, Fried and Elving, Anal. Chem., 36, (1964). It should be noted that the spectral sensitizers and cobalt(III)-complexes operable in this invention include those which contain oxidizable ions, such as iodide. For example, many tested compounds which are iodide salts are useful herein. However, the polarographic measurements referred to above cannot be determined in the presence of oxidizable ions. Therefore, such compounds are converted, just for purposes of making polaro-graphic determinations, to an anion such as chloride or ~-toluenesulfonate, which do not interfere in making accurate polarographic measurements. Hence, compounds containing ' 20 oxidizable ions are included within the scope of the useful compounds defined herein and in the claims.
The spectral sensitizers useful in the practice of this invention can be chosen from among those classes of spectral sensitizers known to sensitize negative silver halide emulsions. The spectral sensitizers can take the form of sensitizing dyes, such as acridines, anthrones, azo dyes, azo-methines, cyanines, merocyanines, styryl and styryl base dyes, polycyclic hydrocarbon dyes, ketone dyes, nitro dyes, oxonols (including hemi-oxonols), sulfur dyes, 30 triphenylmethane dyes, xanthene dyes, etc.

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~ yanine dyes have been found to be particularly advantageous. The term "cyanine dye"~ as used herein, is to be construed broadly as inclusive of simple cyanines, carbo-cyanines, dicarbocyanines, tricarbocyanines, rhodacyanines, etc. Cyanine dyes can contain such basic nuclei as the thiazolines, oxaolines, pyrrolines, pyridines, oxazoles, thiazoles, selenazoles and imidazoles. Such nuclei can contain alkyl, alkylene, hydroxyalkyl, sulfoalkyl, carboxyalkyl, aminoalkyl and enamine groups and can be fused to carbocyclic or heterocyclic ring systems either unsubstituted or substituted - with halogen, phenyl, alkyl, haloalkyl, cyano, or alkoxy groups.
The cyanine dyes can be symmetrical or unsymmetrical and can contain alkyl, phenyl, enamine or heterocyclic substituents on the methine or polymethine chain. Cyanine dyes include complex(tri- or tetra-nuclear) cyanines.
Merocyanine dyes can be employed which are generally ' 'I
comparable to the cyanine dyes discussed above. The merocyanine dyes can contain the basic nuclei noted above as well as acid nuclei such as thiohydantoins, rhodanines, oxazolidenediones, 20 thiazolidenediones, barbituric acids, thiazolineones, and malononitriles. These acid nuclei can be substituted with alkyl, alkylene, phenyl, carboxyalkyl, sulfoalkyl, hydroxyalkyl, alkoxyalkyl, alkylamino groups or heterocyclic nuclei.
As examples of useful spectral sensitizers in addition to sensitizing dyes for negati~e silver halide emulsions, con-ventional optical brighteners which otherwise satisfy the criteria of this invention can be employed to spectrally sensitize cobalt(III)complexes. Exemplary categories of known optical brighteners useful in sensitizing cobalt(III)complexes include stilbenes, triazenes, naphthylene sulfonates, oxazoles '' -19-lOS~ZSO
and coumarins. Particularly preferred optical brighteners useful in the practice of this invention are bis-triazinyl-aminostilbenes, particularly bis-triazinylaminostilbene disul,fonates. Exemplary preferred sensitizers of this type are discl,osed in U.S. Patents 2,875,058; 3,012,971 and 3,025,242.
In addition to the foregoing, it has been observed that hematoporphyrin acts as a spectral sensitizer for cobalt(III)complexes. For example, it has been observed that hexa-ammine cobalt(III) can be selectively spectrally sensitized , ' to the red portion of the visible spectrum employing hematoporphyrin as a spectral sensitizer.
Exemplary spectral sensitizers preferred for use in the practice of this invention ere set forth in Table II.

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TABLE II
Exemplary Preferred Spectral Sensitizers = Carbon atom and sufficient hydrogen atoms, if any, to satisfy unspecified bonds Et = Ethyl group Ph = Phenyl group Bu = n-Butyl group ; - Ground State Potentials Oxidation Reduction SS-l ~o.58 -1.11 I 1,1~-diethyl-2,2~-carbocyanine iodide , SS-2 +0.27 -0.98 . I ~
1,1'-diethyl-2,2'-dicarbocyanine iodide SS-3 + 4 -1.03 $ Br ~
[ ~4-b~benzOthiaZyolo~c4yH-[l 4]thiaz no-' ' .

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TABL~` 11 (Contil~ued) E;~cm~lary Preferrcd Spectral Sensiti%ers Grouncl St~tc I`ot~ntials (volts) O~i.dation ~eduction , SS-4 + 5 -1,4 s 3-carboxymethyl-5-[(3-ethyl-2-benzothia-zolinylidene)ethylidene]rhodanine ~, . I
SS-5 +0.37 -1.16 l, q ` Ph--~ `I=.-.=.-I~ ~-Ph N= -- --=N

i bis[3-methyl-1-phenyl-2-pyrazoline- - j 5-one-(4)]trimethinoxonol ss-6 +o. 27 wl . 1 Ph-~ -Ph N=-- ~_ ., .
bis[3-methyl-1-phenyl-2-pyrazoline-5-one-(4)]pentamethinoxonol SS-7_ + ~ -1.2 ', ! ~--~. ~I I
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Oxadicarbocyanine2-hadbcxyeth~

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~051Z50 TABL~ ll (Cont:inued) ~em~lary Preferreù Spectl~al Sensitizers Ground Stat;e ~otentials Oxidation Reduction SS-~ +o.6 -1.26 iI t ~ ,--S03H
N-Et ~ =~

2SpPrPYl d ene ] - 3-metthhalolinylidene) -. .. , .. ., _ . . .. , . .... .

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4-[(1-ethyl-2-naphtho[l 3 2-d]thiazolinylidene)-isopropylidene]-3-methyl-1-(p-sulfophenyl)-2-pyrazoline-5-one '. . , I

SS-10 +0.56 -1.16 ---COzH

ethylidene]rhoydanin(3-ethyl-2-benzox ' .

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~o~zso TABL'., ll (Continue~
~xem~lary Preferred Spectral Sensiti~r~
Ground State Potentials (volts) Oxidal;ion ~.eauction SS~ .63 -1.48 Et ~ -S
3-carboxymethyl-5-[(3-ethyl-2-benzo-xazolinylidene)-ethylidene]-2-thio-J 2,4-oxazolidenedione _ .. . . .
SS-l~ '33 -1~47 r ~ C02 --N-- S -S

Ylidene)-iso5p[o3~1iedthYl~2~th azo_ ~ 1 1 - !
;, SS-13 +.28 -1.50 t/ ~b-~--~=S
~ ~- Et \~
l-carboxymethyl-5-[(3-ethyl-2-benzoxaz-olinylidene)-ethylidene-3-phenyl-2-thiohydantoin ~ !

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, , lOS1250 TABLE ll ~Continued) Exem~la~y Preferrecl Spectr~l Sensitizers Ground State Potentials (volts) 0,cidation Reduction SS-14 +.42 -1.70 H03S~ -- N; ~ S ~--S

3-ethyl-5~[1-(4-sulfobutyl)-4(1H)-pyridylidene]rhodanine sodium salt SS-15 +.89 -1.76 ~---t - ~ -C0=H

3-carboxymethyl-5-(3-methyl-2-benzoxazolinylidene)rhodanine SS-16 +.56 -1.68 Et-N~ -Et 3-ethyl-5-(1-ethyl-4(1H)-pyridyliden SS-17 +0.60 -1.3 ~6; ~ so~

,Na +l 4 5y4ro5~9-ditbhyl-3 3~_ . !
.
i~
i -25-.

:,~
~ . . .

~051Z50 TABLE II (Continued) Exer,~plary Preferred Spectral Sensitizers . Ground Sta~e Potentials (volts) Oxidation Reduction ~ ss-18 +o . 60 -1 . 37 -t ~-E5t 3-ethyl-5-~(3-ethyl-2-benzoxazolinylidene)-ethylidene] rhodanine 7 . . ~S-l9 +0.57 -1.27 , Et t ~ ESt ..
1 3-ethyl-5-~(3-ethyl-2-benzothiazolinylidene)-.~ ethylidene~ rhodanine , l;

SS-20 +0.58 -1.50 l~t Ft C~ J~ ,t~ ~ -Cl !:
r? c~ Et-~ T c~

~1 t . ~ C l -1 . benZimidazolo carbocyanil '3 3'~tetraethYl SS-2l +0.73 -1.28 1.
/S~ I ~S\
~-Et ~+, .;
~-. thiaCarboCyaniYne9hymderthyid3 ~ ~ (3-sul~obutyl) , -26_ ~ . ' ,: ' .
... ., ., . _, . . , , . , . . , _, _ . , , ..

~05~Z50 T~BLE 1' (Continuecl~ .
~xem~lary Preferred Spectral Sensiti~.ers Ground State Potentials (volts) Oxidation Reduc'fion SS-22 +0.72 -1.28 - ~ .

anhydro-9-methyl-3,3~-di(3-~ulfobutyl)-thiacarbocyanine hydroxide f ~, ' ', SS-2~ +-4g -1.47 ~',' ' . ' '.

Et ~

3-ethyl-5-[(3-ethyl-2-benzoxazolinylldene)-ethylidene]-l-phenyl-2-thiohydantoin ', SS-24 ~o.63 -1.14 Et E;~
Br ~
:( 3,3'-diethyl-4'-methyloxathiazolo-l' carbocyanine bromide - ." ' ~ ~ .

~'.'' ., ~

~' ' ', . . . . ..... . . . .

lOS1250 : `ABLE II (Continued) ~,;emplary .'referred S~ectral Sensitizers Ground State Potentials (volts) Oxidation Redllction +o.64 -1.54 I~ -Et 2-p_diethylaminostyrylbenzothiazole , ss-26 +o . 87 -1 . o6 Cl~ Et Et- ~ !_CI

5, 5 ~ - dichloro-3,3'-9-triethylthiacarbo-cyanine bromide ~ SS-27 +0. 86 -1 . 15 Cl--~ --Et ~ -CI

anhydro-5,5'-dichloro-3,9-diethyl-3'-(3-sulfobutyl) thiacarbocyanine hydroxide ', . , ~, , ', .

. _ lOSiZSO

TABL~ II (Continued) ~xemplary Prefer-~cd S~ectral Sensiti7.e-r Ground State Potentials (volts) Oxidation Reduction ss-28 +0.51 -1.48 1~ ph 2-diphenylamino-5-[(3-ethyl-2-benzoxazolinyl-idene)ethylidene]-2-thiazolin-4-one SS-29 +o.46 -1.36 =I~ Ph _N-Et ~5/ ~ !
2-diphenylamino-5-[(3-ethyl-2-benzothiazolinyl-idene)ethylidene]-2-thiazolin-4-one I~ b~ -S

H
~ -carboxyphenyl-5-~(3-ethyl-2-benzoxazolinyl-Z~ idene)-ethylidene]-3-phenyl-2-thiohydantoin .

'' ~ ,' ~ -29-- .. .. .. .. ..... ~ ... . . .

~O5~Z50 TABL~ Il (Continued) Exe~plary Preferred S~ectral Sensitizers Ground State Potentials (volts) Oxidation Reduction ~Oz o~ . .= $ - ~N- - - - -So~ ~

-Na 4-(2,4-dinitrobenzylidene)-1,4-dihydro-1-(4-sulfobutyl) quinoline, sodiùm salt " .
, , .
~ SS-32 , _ 5-~(3-ethylnaphthr2,1-d]oxazolin-2-ylidene)-ethylidene]-3-heptyl-1-phenyl-2-thiohydantoin ,, , SS-33 ~0.21 -1.22 -~-~ ~S~ =t tjJ~ Bu t n ~=---=---=-~=s h-Et ~h 5-r4-(3-ethyl-2-benzothiazolinylidene)-2-butenylidene]-3-heptyl-1-phenyl-2-thiohydantoin , j , , I
~; i .
'~ ' , !
!
"

, . .
!
. !

lOS1250 TABL~ Il (Contlnued) Exem~lary Preferred Saectral Sensitizers Ground State Potentials (volts) Oxidation P~eduction - . ..

SS-3LI ~o.63 -l.29 Br 1 3,3'-dimethyl-9-phenyl-4,5-4'-5'-dibenzothia- :
carbocyanine bromide .
, . .
ss-35 +o. 8 tmivee thagn , -1 . 90 =tso H~
7 HO-~ OH 2 4Na +
11 N,N'-di[2-p-sodiosulfoanilino-4-diethanolamino-. l?3,5-triazyinyl(6)]-diaminostilbene-2,2~-dlsulfonic acid, sodium salt more nega-- SS-~6 +o.83 tive than , -1 . 90 50~ ~ SD~
~ ~ Et-~-Et 2 :l 6Na+
l1 N,N'-di [ 4- diethylamino-6-(2,5-disulfoanilino)]-:.1 2-s-triazinylamino - 2,~'-stilbene disulfonic ~1 acid, hexasodium salt ., .

'', :

.. . .

. .

lOSlZSO
TABLE II (Continued) Exc~plary Preferrecl Spectral Sensitizers : Ground State Potentials - ( volts ) Oxidation Reduction SS-~7 , -OH

HO5~ zH
hematoporphyrin ;, .' , .
.. , . ~ -.
., ' ,'' ,, ' :
., .

.~ , .j ' '' .

., ' I , r f !
, . -32-..

.

.~ . .

-., . - . : .

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The spectral sensitizers employed in the practice of this invention are to be distinguished from the photoreductants disclosed by Adin and Fleming in commonly assigned, concurrently filed Canadian patent application Serial No. 221,819, titled TR~NSITION METAL PHOTOREDUCTION SYSTEMS AND PROCESSES. It is not; presently understood whether the spectral sensitizers of this invention enter into an oxidation-reduction reaction with cobalt(III)complexes or merely transfer energy to the cobalt(III)-complex to promote its reduction. It is then possible that both ~
spectral sensitizers and photoreductants form reducing agents for ~ -cobalt(III)complexes. The definitive distinction between spectral sensitizers and photoreductants is that spectral sensi-tizers must be intimately associated with a cobalt(III)complex at the time of exposure to radiation in order to promote .j reduction of the cobalt(III)complex. By contrast when a photo-reductant is first exposed to actinic radiation and thereafter associated with a cobalt(III)complex, reduction of the ' cobslt(III)complex sti11 occurs.

':

,, ~
,~ :

'' .. ..

iOS1250 Radiation-Sensitive Composition, Layer and Element To form a radiation-sensitive coating useful in the present invention it is merely necessary to bring together the sensitizer and the cobalt(III)complex. The resulting composition can then be brought into a spatially fixed relation-ship, as by coating the composition onto a support to form a radiation-sensitive element according to the present invention.
The components of the composition, particularly the sensitizer ~`
and the cobalt(III)complex, are intimately associated. This can be readily achieved, for example, by dissolving the react-ants in a solvent system.
The solvent system can be a common solvent or a com-bination of miscible solvents which together bring all of the reactants into solution. Typical preferred solvents which can be u~ed alone or in combination are lower alkanols, such as methanol, ethanol, isopropanol, t-butanol and the like;
ketones, such as methylethyl ketone, acetone and the like;
water; liquid hydrocarbons; chlorinated hydrocarbons, such as , chloroform, ethylene chloride, carbon tetrachloride and the ~ 20 like; ethers, such as diethyl ether, tetrahydrofuran, and the j like; acetonitrile; dimethyl sulfoxide and dimethyl formamide.
For ease of coating and to assure the desired intimate relationship of the spectral sensitizer and cobalt(III)complex it is preferred that they be incorporated into the radiation-sensitive layer along with a conventional photographic vehicle.
The vehicle can take the form of a hydrophilic colloid, latex or ! resinous binder, for example. Generally any vehicle known to have utility in photographic elements and, particularly, diazo photographic elements can be used in the practice of this in-vention. Such vehicles are well known to those skilled in ., .
' -34-~ ~ .
, .

.

~OSlZSO ~;

the art so that no useful purpose would be served by including an extensive catalogue of representative binders in this spècification. Any of the vehicles disclosed in Produc-~Lice~sin~ Index, Vol. 92, December, 1971, publication 9232, at page 108, can be used as vehicles in the radiation-sensitive elements of this invention. For most applications gelatin is a preferred vehicle. `~
The cobalt(III)complex and spectral sensitizer forming the radiation-sensitive layer can be varied widely and still produce useful results. For example, while a 1 to 1 molar ratio of cobalt(III)complex to spectral sensitizer pro-duces excellent results, very satisfactory performance is achieved when from 0.1 to 10 moles of the cobalt(III)complex are employed per mole of the sensitizer. Still further, useful results can be obtained employing from 0.01 to 100 moles of the cobalt(III)complex per mole of sensitizer. The concentration of sensitizer is a function of its density at its maximum absorption wavelength above 300 nanometers. Sufficient sen-sitizer is employed to provide a net optical density in the range of from 0.1 to 3Ø At lower densities a very high proportion of available radiation is not absorbed within the radiation-sensitive layer while at higher densities the sen-sitizer adjacent the surface of the radiation-sensitive layer tends to selectively absorb most of the available radiation.
The sensitizer is preferably present in an amount sufficient to provide a net optical density in the range of from 0.5 to 2Ø The vehicle can account for up to 99~ by weight of the radiation-sensitive layer, but is typically employed in proportions of from 50 to 90~ by weight of the radiation-sensitive layer. It is, of course, recognized that the vehicle ~,,, :
;

., .. . , , ,, . . . ~

-105125~

can be omitted entirel~ from the radiation-sensitive layer.
Typically the radiation-sensitive layer can vary widely in thickness depending on the characteristics desired for the radiation-sensitive layer--e.g. image density, flexibility, etc. For most photographic applications coating thicknesses in the range of from 2 to 20 microns are preferred.
Any conventional photographic support can be used in the practice of this invention. Typical supports include transparent supports, such as film supports and glass supports lO as well as opaque supports, such as metal and photographic paper supports. The support can be either rigid or flexible.
Preferred supports for most applications are paper or film supports. The support can incorporate one or more subbing layers for the purpose of altering its surface properties Typlcally sub~ing layers are employed to enhance the adherency of the radiation-sensitive coating to the support. Suitable exemplary supports are disclosed in Product Licensing Index, Vol. 92, December, 1971, publication 9232, at page 108.
The radiation-sensitive layer can be formed on the 20 support using any conventional coating technique. Typically the reactants, the vehicle (if employed) and any desired addenda are dissolved in a solvent system and coated onto the support by such means as whirler coating, brushing, doctor blade coating, hopper coating and the like. Thereafter the solvent is evaporated. Other exemplary coating procedures are set forth in the Product Licensing Index publication cited above, s at page 109. Coating aids can be incorporated into the coating composition to facilitate coating as disclosed on page 108 of the Product Licensing Index publication. It is also possible 30 to incorporate antistatic layers and/or matting agents as disclosed on this page of the Product Licensing Index publi-cation.

As is illustrated in Fig. 1, in a simple form the radiation-sensitive element 100 can be formed entirely of a support 102 and a radiation-sensitive layer 104. In this form the radiation-sensitive element need not exhibit an image recording capability, rather the radiation-sensitive element merely exhibits a selective response to actinic radiation. This selective response can be usefully employed, as in recording the image in a separate photographic element. In a preferred radiation-sensitive element of this type the co~alt(III)complex ' 10 incorporates one or more ligands which can be volatilized upon ¦ reduction of the complex. For example, the cobalt(III)complex can incorporate one or more ammine ligands which are liberated ? as ammonia upon imagewise reduction of the cobalt(III)complex.
For such an application it is preferred to choose a cobalt(III)~omplex which incorporates a large number of ammine ligands, as are present in cobalt hexa-ammine and cobalt penta-ammine complexes.

! Separate Image-Recording Layers and Elements ¦ Where the radiation-sensitive layers employed in 20 the practice of this invention do not incorporate an image recording capability, it is contemplated that a separate image-recording layer be used with the radiation-sensitive layer. In a simple form a separate image-recording element can be used in combination with a radiation-sensitive element such as element 100. In this way reaction products released upon imagewise exposure of the radiation-sensitive element can be transferred in an image pattern to produce an image printout or bleachout in the image-recording layer. In one form of the invention it is contemplated that ammonia will be imagewise transferred from : ~ .

', . .- .. . .

iOSlZSO
the radiation-sensitive layer to a separate image-recording ; element. In such instance the image-recording element can take the form of any conventional element containing a layer capable of producing an image as a result of ammonia receipt, or, rnore generally, contact with a base.
In a simple form the image-recording element can con-sist of a support bearing thereon a coating including a material capable of either printout or bleachout upon con-tact with ammonia. For example, materials such as phthalalade-hyde and ninhydrin printout upon contact with ammonia and aretherefo~ useful in forming negative images. A number of dyes, such as certain types of cyanine dyes, styryl dyes, rhodamine dyes, azo dyes, etc., are known to be altered in color upon contact with a base. Particularly preferred for ~, forming positive images are dyes which are bleached by contact with a base, such as ammonia to a substantially transparent form. Pyrylium dyes have been found to be particularly suited for such applications While the image-recording layer can consist essentially of a pH or ammonia responsive imaging material, in most instances it is desirable to include a binder - or vehicle for the imaging material. The image-recording element can be formed using bhe same support and photographic vehicles employed in forming the radiation-sensitive element or in any other convenient, conventional manner.
To record an image using separate radiation-sensitive and image-recording elements, the radiation-sensitive layer of the radiation-sensitive element is first imagewise exposed to radiation of from 300 to about 900 nanometers, preferably to radiation of from 300 to 700 nm. This can be accomplished ., .

-iOSlZ5Vusing a mercury arc lamp, carbon arc lamp, photoflood lamp, laser or the like. Upon exposure to actinic radiation the sensitizer present in the radiation-sensitive layer is activated by energy absorption to stimulate reduction of the cobalt(III)-complex. It is desirable to have the image-recording layer of the image-recording element closely associated with the radiation-sensitive layer at the time of exposùre. In those instances where it is desirable to drive out released ammonia ligands by the application of heat, the image-recording element 10 can be associated with the radiation-sensitive element before or after exposure. For example, in one form the radiation-sensitive element can be exposed and thereafter associated with the image-recording element, as by feeding the elements with the radiation-sensitive and image-recording layers juxtaposed between heated rolls After the radiation-sensitive element has been used to produce an image in the image-recording element, it can be discarded To facilitate transfer of released ligands to the image-recording element it is preferred to heat the radiation-sensitive layer to a temperature in the range of from 80 to 150C. Heating can, if desired, be performed con-currently with exposure.
Where a cobalt(III)complex is employed which contains ammine ligands, it is contemplated that the ammonia given off upon reduction of the complex can, by proper choice of reactants, stimulate further imagewise release of ammine ligands. For example, ~-superoxodecammine dicobalt(III)compounds can be decomposed by contact with free ammonia. Hence, when a radiation-sensitive layer is formed using this type of cobalt(III)complex~ exposure of the spectral sensitizer and the , .

.. . ~` .
~ . ~ . . .

~OS12SO
ammine ligand containing cobalt(III)complex initiates reduction ' of the complex, but thereafter the ammonia released can further reduce the ~-superoxodecammine dicobalt(III)compound in irradiated areas.
-An illustrative practice of this invention employing separate radiation-sensitive and image-recording elements can be appreciated by reference to Figs. 2 through 4 of the drawings.
In Fig. 2 the radiation-sensitive element 100 comprised of support 102, which in this instance is a substantially trans-10~ parent support, and radiation-sensitive layer 104 is placed , in contact with an image-recording element 106 comprised of a support 108 and an image-recording layer 110. In the form shown the image-recording layer is initially colored--i.e. possesses a uniform visible optical density--but is capable of being bleached. An initially colorless image-~ecording layer that ? iS capable of being colored could be alternatively employed.
With the elements 100 and 106 associated in face-to-j face relationship (that is, the image-recording and radiation-sensitive layers are adjacent and not separated by a support) 20 as illustrated the radiation-sensitive element is imagewise exposed to actinic radiation, indicated schematically by arrows 114, through support 102. Substantially all of the radiation reaches the radiation-sensitive layer 104. The radiation activates the spectral sensitizer in the layer 104 causing it to promote reduction of the cationic cobalt(III)-complex. This is confined to irradiated areas 112a and 112b.

4 o lOS12SO
The liberated ligands of the cationic co~alt(III)-complex migrate to the image-recording layer. Ligand transfer can be accelerated by the uniform application of heat, as is schematically illustrated by arrows 116 in Fig. 3. The released and transferred ligands cause the image-recording layer to become bleached in the areas 118a and 118b. Thus, upon stripping away the radiation-sensitive element an image-recording element remains, as shown in Fig. 4, which provides a positive copy of the original exposure pattern. By employing --lO an initially colorless image-recording layer that is colored by receipt of reaction products from the radiation-sensitive layer a negative copy of the exposure pattern can be formed.
Instead of employing separate radiation-sensitive and image-recording elements, separate radiation-sensitive and image-recordin~ layers can be incorporated within a ~ingle element. This can be illustrated by reference to Fig. 5. An element 200 is schematically shown comprised of a support 202 and a radiation-sensitive layer 204, which can be identical to support 102 and radiation-sensitive layer 104, described above. Overlying the 20 radiation-sensitive layer is a separation layer 206. An image-recording layer 208, which can be identical to the separate image-recording layers previously discussed, overlies the separation layer. If desired, the relationship of the image-recording and radiation-sensitive layers can be interchanged.
The separation layer is an optional component of the element 200, since in most instances the image-recording and ~, radiation-sensitive layers are chemically compatible for sub-stantial time periods. However, to minimize any degradation of properties of either of the active layers due to migration `' 30 of chemical components from one layer to the other, as could conceivably occur during extended periods of storage before use, it ~s preferred to incorporate the separation layer.

.

~051Z50 The separation layer is chosen to be readily permeable by the reaction product(s) to be released from the radiation-sensitive layer upon exposure while impeding unwanted migration of initially present components of the radiation-sensitive and image-recording layers. For example, the separation layer can be chosen to be readily permeable to ammonia, but relatively impermeable to liquid components. It has been found that a wide-range of polymeric layers will permit diffusion of gaseous ammonia from the radiation-sensitive layer to the image-recording layer while otherwise inhibiting interaction of the components of these layers.
It is generally preferred to employ hydrophobic polymer layers as separation layers where the radiation-sensitive and image-recording layers incorporate polar reactants whose migration is sought to be inhibited. Most preferred are linear hydrocarbon polymers, such as polyethylene, polypropylene, polystyrene and the like. It is generally preferred that the separation layer exhibit a thickness of less than about 200 microns in order to allow image definition to be retained in the image-recording layer. For most appli-cations separation layers of 20 or fewer microns are preferred.

Photoresponsive Separate Image-Recording Layers While the separate image-recording layers heretofore described need not themselves be radiation responsive, image-recording layers which are responsive both to reaction pro-ducts released by the radiation-sensitive layers and also directly responsive to actinic radiation are recognized to be useful in the practice of this invention. For example, a 1 conventional diazo recording element can be used as an image-; 30 recording element in the practice of this invention. Typically ; ' '-' lOS~ZSO
diazo recording elements are first imagewise exposed to ultra-violet light to inactivate radiation-struck areas and then uniformly contacted with ammonia to printout a positive image.
Diazo recording elements can initially incorporate both a diazonium salt and an amrnonia activated coupler (commonly referred to as two-component diazo systems) or can initially incorporate only the diazonium salt and rely upon subsequent processing to imbibe the coupler (commonly referred to as one-component diazo systems). Both one component and two component diazo systems can be employed in the practice of this invention. Subsequent discussions, although directed to the more common two component diazo systems, should be recognized to be applicable to both systems. The photoresponsive image-recording layers can be incorporated in separate image-recording elements or can ~e incorporated directly within the radiation-sensitive elements of this invention, such as illustrated in Fig 5. In this instance it is generally preferred that the separation layer 206 be chosen to be impermeable to ultraviolet light. If the support is chosen to be opaque the separation 20 layer is chosen to be transparent to light of a wavelength long enough to activate the radiation-sensitive layer without activating the image-recording layer.
The use of a radiation-sensitive layer and a separate photoresponsive image-recording layer in combination offers a versatility in imaging capabilities useful in forming either positive or negative images. The production of a positive image with such a combination can be readily appreciated by reference to Fig 6. In this figure a radiation-sensitive , layer 302 and a photoresponsive image-recording layer, such as a conventional diazo recording layer, are associated in face-to-face relationship. The layers together with a support and separation layer can, if desired, form a single element, such .:
-lOS~250 as element 200, or, in the alternative, the separate layers can be provided by placing a conventional diazo recording element and the radiation-sensitive element 100 in face-to-face relationship To form a positive image the photosensitive image-recording layer 304 is first imagewise exposed to ultraviolet radiation, as is schematically indicated by transparency 306 bearing the image 308. This photolytically destroys the diazonium salt in the exposed areas of the image-recording layer. The radiation-sensitive layer 302 is preferably uniformly exposed to actinic radiation before it is associated with the layer 304, where separate image-recording and radiation-sensitive elements are employed. Aiternately, where a single element is employed incorporating layers 302 and 304, the radiation-~ensitive layer is uniformly exposed using radiation in the visible spectrum so as not to destroy the diazonium salt in image areas. Exposures through either major outer surface are preferred where the layers 302 and 304 form a single element.
Transparent or opaque supports can be used with either single or 20 plural element arrangements. Heating of the layers 302 and 304 in face-to-face relationship results in ammonia being released from the radiation-sensitive layer for migration to the diazo - ;
.
layer, thereby activating the coupler in the diazo layer to produce a dye image 310, which is a positive copy of the image 308. If an element bearing a negative image is substituted for transparency 306, the negative image will be reproduced in the layer 304 i The identical photosensitive image-recording and separate radiation-sensitive layer combination employed to form a positive image in Fig. 6 can also be used to form a negative image, as illustrated in Fig. 7. To form a negative image the radiation-, . . _ . _ .

~051250 sensitive layer is first imagewise exposed, as indicated by the transparency 306 bearing the image 308. Where the layers 302 and 304 are in separate elements the radiation-sensitive element is preferably exposed before association with the imag~-recording element. Where the layers are in a single element, the radiation-sensitive layer is preferably exposed with visible radiation to avoid deactivating the diazo layer.
With the layers associated as shown, they are uniformly heated.
This imagewise releases ammonia from the radiation-sensitive 10 layer which migrates to the diazo layer, causing imagewise printout. The area of the diazo layer defining the negative image 312 can then be deactivated by exposure to ultraviolet light, if desired, although this is not required. The image 312 is a negative copy of the image 308. If an element bearing a negative image is substituted for transparency 306, the image ~ill be reversed in the layer 304.
While the foregoing describes certain illustrative, preferred approaches for employing a photoresponsive image-recording layer and a separate radiation-sensitive layer in combination, it is appreciated that a number of variations are contemplated. For example, the sensitizer in the radiation-sensitive layer and the photoresponsive image-recording layer can be variously chosen to be responsive to different portions of the spectrum. Instead of the sensitizer being responsive to visible light and the diazo layer being responsive to ultraviolet light, as noted above, a diazonium salt can be chosen which is selectively responsive to visible light and , a sensitizer chosen that is selectively respon<;ive to ultraviolet light of a wavelength longer than 300 nm. In still another varia-30 tion, where uniform ammonia release is employed to develop the ; diazo image, a supplementary base treatment can be used to enhance the diazo image, if desired. Still other variations will be readily apparent to those skilled in thé art.

I~adiation-Sensitive Layers with Visible Image-Recording Capabilities __ In employing a radiation-sensitive layer to also perform the function of image-recording, a radiation-sensitive element, such as element 100, can be employed having a radiation-sensitive layer containing only a cobalt(III)complex and a spectral sensitizer as active components. To record images with a radiation-sensitive element of this type the cobalt(III)complex is employed as an oxidant for a leuco dye which is convertible to a colored form upon oxidation. Alter-natively, conventional dye-forming components (e.g. an oxidizable organic color developing agent and a coupler) can be employed which are converted to a colored dye upon oxidation of the organic color developer and coupling. In this approach the radiation-sensitive layer is initially ima~ewise exposed to reduce the cobalt(III)complex to a cobalt(II)compound in radiation-struck areas. Heating can accompany or follow exposure, if desired, , to assure that maximum reduction occurs. Thereafter, the ;~ radiation-sensitive layer is brought into contact with a 20 leuco dye or the dye-forming components are brought together within the radiation-sensitive layer. The cobalt(III)complex remaining in the non-irradiated areas then oxidizes the leuco 1 dye or the organic color developing agent so that a colored image is formed in the non-irradiated areas of the radiation-sensitive layer. The organic color developing agent and coupler therefor can be introduced into the radiation-sensitive layer together or separately. As is well understood in the art, both the coupler and the oxidizable organic color developing agent can be contained in a common solution and concurrently introduced 30 into the radiation-sensitive layer. In a preferred form a ballasted coupler is employed which is initially contained within . , the radiation-sensitive layer with the organic color developing - agent being later introduced. A wide variety of conventional "

lOSlZSO

techniques for introducing the dye image forming components into the radiation-sensitive layer can be used ranging from bathing the radiation-sensitive element, after exposure and heating, in dye-forming component solutions to releasing the dye-forming components from pressure rupturable containers such as pods or micro-encapsulation layers contained in the radiation-sensitive element or a separate element abutted therewith A wide variety of oxidizable leuco dyes and oxi-dizable dye-forming component combinations are known to the art that can be readily employed in the practice of this i invention. Exemplary leuco dyes include aminotriarylmethanes, aminoxanthenes, aminothioxanthenes, amino-9,10-dihydroacri-dines, aminophenothiazines, aminodihydrophenazines, aminodi-` phenylmethanes, aminohydrocinnamic acids (cyanoethanes), leuco-!~ indigold dyes, 1,4-diamino-2,3-dihydroanthraquinones, etc. In addition to these general categories of useful leuco dyes there are numerous other types of amines which can be oxidized to a colored species, such as those set forth in U.S. Patents 3,042,515 and 3,042,517--e.g 4,4~-ethylenedianiline, diphenyl-amine, N,N-dimethylaniline, 4,4'-methylenedianiline, triphenyl-; amine, N-vinylcarbazole, and the like. Certain hydrazones and ~`
acyl derivatives of these hydrazones can be oxidized to diazonium compounds which will then couple with any of a large number of . coupling agents to produce an azo dye. Exemplary compounds of this type are disclosed in U.S. Patent 3,076,721. Exemplary of couplers useful with such hydrazones and acyl derivatives thereof are N,N-diethylaniline, N,N-dimethyl-m-toluidine and N-(2-cyanoethyl)-N-methyl-2-naphthylamine. Aromatic primary amines in combination with a coupling agent can produce upon oxidation azomethine, indoaniline and indophenol dyes.

Exemplary of N,N-dialkylphenylenediamines and p-aminophenols, which are preferred for use in the practice of this invention, are 10512S0 ~ ~

N,N-dimethyl-p-phenylenediamine~ N,N-dimethyltoluene-2,5-diamine, 2,6 dibromo-4-aminophenol, 2-chloro-4-aminophenol, etc. These amines are useful with couplers such as open chain keto-methylenes, phenols, naphthols, 5-pyrazolones ænd indazolones. Further speciflc illustrations of oxidizable leuco dyes and dye-forming component combinations useful in the practice of this invention are provided in U.S. Patent 3,383,212.
Instead of utilizing the residual cobalt(III)complex . ., ~ .
~ remaining after exposure and heating to form an imaging colora- ~
. . -tion, it is recognized that the reaction products formed on imaging and/or heating can be employed to form an image within the radiation-sensitive layer, if desired. This approach has the advantage of requiring no additional processing. Any compound can be incorporated which is compatible with the remaining components of the radiation-sensitive layer and which ` is capable of either being bleached or darkened upon contact with or further reaction with one or more of the reaction products formed on imaging and/or heating. In one form such a component can be identical to one of the components pre-viously described for incorporation in a separate image-recording layer. For example, a component such as ninhydrin or o-phthalaldehyde can be incorporated which generates a color upon contact with ammonia released as a reaction product :~ upon imaging and/or heating of the radiation-sensitive layer.
Alternatively, bleachable dyes, such as the pyrylium, styryl, cyanine, rhodamine and similar conventional dyes known to exhibit color alterations upon contact with a base can be incorporated into the radiation-sensitive layer.
,,, :, ~ -48-.

. ~ .
.`'' .

........

A cobalt(II)compound produced as a reaction product ; in the course of reducing a cationic cobalt(III)complex in the radiation-sensitive layer can, if desired, be used to record images. To be useful in forming an image~within the radiation-sensitive layer it is merely necessary that any cobalt(II)-compound formed in exposed areas be visibly distinguishable from the original cobalt(III)complex present in unexposed areas. Typically cobalt(II)compounds produced as reaction pro-ducts tend to range from colorless to yellow, so that they are 10 best suited to forming image backgrounds. By choosing an optically dense cobalt(III)complex which is reducible to a - colorless to yellow cobalt(II)compound, useful positive images can be formed within the radiation-sensitive layer.
In a preferred form of the invention the cobalt(III)complex as well as the spectral sensitizer are chosen to be of a lower optical density or distinctly different color than the cobalt-(II)compounds which are imagewise generated.
In one form of the invention a com~ound can be included within the radiation-sensitive layer to facilitate 20 the formation of optically dense cobalt sulfide images upon - exposure to actinic radiation and heating. This is accomplished .j .
in a preferred embodiment of the invention merely by incorporating into the radiation-sensitive layer in intimate association with the cobalt(III)complex and spectral sensitizer a compound con-. S
~- taining a thioamide (-C-N-) functional group (or a tautomer thereof). The compound is, of course, chosen to be chemically compatible with the remaining components of the radiation-sensitive layer prior to exposure and heating. Preferred thio-amide compounds are thiourea and thioacetamide as well as 30 substituted and/or cyclized derivatives thereof. Alkyl, aryl, alkaryl and aralkyl substituted thioureas and thioacetamides : ~ -49 ;, 105iZS0 are particularly contemplated. The aryl substituents and substituent moieties can include groups, such as phenyl, naphthyl, anthryl, etc. The alkyl substituents and substituent moieties can include branched and straight chain acyclic and cyc].ic alkyl groups having from l to 20 carbon atoms, preferably from l to 6 carbon atoms. To increase the image densities obtainable with thioamide compounds it has been found useful to increase their maximum solubilities within the radiation-sensitive layer. This can be accomplished by employing combina-tions of thioamides or thioamides in combination with other solubilizing compounds. For example, thioacetamide and sul-famide are good solubilizing agents for thiourea in gelatin.
It has been discovered that the use of a transparent overlayer incorporating one or more thioamide compounds will increase the optical density o~ images obtained. The overlayer offers ; the advantage of allowing greater concentrations of the thio-amides to be employed. It has also been observed that superior results are obtained using thioamides to produce images if the radiation-sensitive layer is heated concurrently with exposure.
s 20 It is recognized that th~ use of a cobalt(III)complex and a spectral sensitizer in combination can be used to enhance the ~ .
radiation sensitivity and spectral response of radiation-sensitive systems such as those disclosed in U.S. Patents - 1,897,843; 1,962,307; and 2,084,420, cited above.
Exemplary preferred thioamide compounds useful in the practice of this invention are set forth in Table III.
TABLE III

Exemplary Thioamides for Producing Cobalt Sulfide Ima~es ` 30 TA-l N,N-dimethylthioformamide TA-2 thioacetamide TA-3 thiobutanamide -_50_ :' . A I ~;

~oSlZSO

TABLE III (Continued) TA-4 thiohexanamide TA-5 2-phenylthioacetamide TA-6 N,N-dimethylthioacetamide TA-7 N,N-dihexylthioacetamide TA-8 4-ethyl-3-thiosemicarbazide TA-9 thio~rea TA-10 N-methylthiourea TA-ll N,N'-diphenylthiourea TA-12 ethanedithioamide TA-13 propylene thiourea ~j TA-14 1-phenyl-2-thiourea TA-15 diallylthiourea TA-16 3-allyl-1,1-diethyl-2-thiourea ; TA-17 thiobenzamide TA-l~ thiobenzanilide TA-l9 thiocarbanilide TA-20 thioacetanilide TA-21 dithiobiurea In another form of the invention optically dense cobalt(II) images can be formed by incorporating into the radiation-sensitive layer a compound capable of forming a visibly colored cobalt(II)complex as a ligand thereof. It . . .
is possible to produce optically dense cobalt(II)compounds ~ useful in forming negative images by incorporating into the ;;~ radiation-sensitive layer a compound capable of chelating with the cobalt(II) atom formed on reduction of the cobalt(III)complex. In the preferred practice of this , ~ .
invention the chelating compound is initially present with and chemically compatible with the cobalt(III)complex and ~ the spectral sensitizer within the radiation-sensitive layer.
': ' ~; -51-. ~ . ... " ..
~ .... . .. . ~. ~ .

~051250 While a variety of compounds are known to be capable of forming optically dense chelates with cobalt(II) atoms and can be employed in the practice of this invention, preferred chelating compounds include formazan dyes, dithio-oxamides, nitrosarols, azo compounds, hydrazones and Schiff bases. As is well understood by those skilled in the art all formazan dyes are capable of forming bidentate chelates and are therefore useful in the practice of this invention.
Preferred formazan dyes are those having a ring-bonded, i 10 aromatic substituent in the 1 and 5 positions. In formazan dyes it is unnecessary that either of these aromatic sub-stituents exhibit a ligand-forming capability in order for the dye to exhibit a bidentate chelate-forming capability, I but chelate ligand-forming, aromatic substituents can be i chosen, if desired, to produce additional chelate ligands.
~ithiooxamide is a preferred chelating compound as well as derivatives thereof having one or both nitrogen atoms sub-J stituted with an alkyl, alkaryl, aryl or aralkyl group.
Preferred nitrosarol compounds are those in which the nitroso 2~ and hydroxy substituents are adjacent ring position substituents (e.g., 2-nitrosophenols, 1-nitroso-2-naphthols, 2-nitroso-1-naphthols, etc.). Preferred azo compounds capable of forming at least bidentate chelates with cobalt(II) are those of the ' general formula:
"A~ Zl-N=N-z2.
Preferred hydrazones capable of forming at least bidentate - chelates with cobalt(II) are those of the general formula:
;j Z3-CH=N-NH-Z4 -1~ Preferred Schiff bases capable of forming at least bidentate 1 30 chelates with cobalt(II) are those of the general formula:
Z5 -cH=N-z6 -.

, . . .

~OSlZ50 In the foregoing formulas each of the Z substituents are chosen to be ring-bonded, aromatic substituents and at least z2, z , Z4, Z5 and z6 are chosen to be capable of forming ; a chelate ligand. The aromatic substituents of the ligand-forming compounds can take the form of either homocyclic or heterocyclic single- or multiple-ring substituents, such as phenyl, naphthyl, anthryl, pyridyl, quinolinyl, azolyl, etc.
In one form the aromatic substituent can exhibit a ligand forming capability as a result of being substituted in the ring position adjacent the bonding position with a substituent which is susceptible to forming a ligand, such as a hydroxy, carboxy or amino group. In another form the aromatic substituent can be chosen to be an N-heterocyclic aromatic substituent which contains a ring nitrogen atom adjacent the azo bonding position--e g. a 2-pyridyl, 2-quinolinyl, or 2-azolyl (e.g. 2-thiazolyl, Z-benzothiazolyl, 2~oxazolyl, 2-benzoxazolyl, etc.) substituent.
The aromatic substituents can, of course, bear substituents which do not interfere with chelating, such as lower alkyl (i.e., one to six carbon atoms), benzyl, styryl, phenyl, bi-20 phenyl, naphthyl, alkoxy (e.g., methoxy, ethoxy, etc.), aryloxy ~j (e.g., phenoxy), carboalkoxy (e.g., carbomethoxy, carboethoxy, etc.), carboaryloxy (e.g., carbophenoxy, carbonaphthoxy), acyloxy (e.g., actoxy, benzoxy, etc.), acyl (e.g., acetyl, benzoyl, etc.), halogen (i.e., fluoride, chloride, bromide, iodide), cyano, azido, nitro, haloalkyl (e.g., trifluoromethyl, trifluoroethyl, etc.), amino (e.g., dimethylamino), amido (e.g., acetamido, benzamido), ammonium (e.g., trimethylammonium), azo (e.g., phenylazo), sulfonyl (e.g., methylsulfonyl, phenyl-sulfonyl), sulfoxy (e.g., methylsulfoxy), sulfonium (e.g., di-methyl sulfonium), silyl (e.g., trimethylsilyl) and thioether ~! (e.g., methylthio) substituents. It is generally preferred that the alkyl substituents and substituent moieties have 20 .1 , . . ~
: ` , lOS~ZSO

or fewer carbon atoms, most preferably six or fewer carbon atoms. The aryl substituents and substituent moieties are preferably phenyl or napht,hyl groups. Exemplary preferred chelste forning cornpowlds ere set forth in T~ble IV.

, ~

,-:
:'.', .~

,~f . , ' .

'i ,, .

. ' '''~' -, ., , :.~
, ~.... - - .

TABLE IV
Exemplary Chelate-Forming compounds CH-l 1,3,5-triphenylformazan CH-2 1-~4-chlorophenyl)-3,5-diphenylformazan CH-3 1-(4-iodophenyl)-3,5-diphenylformazan CH-4 1,5-diphenylformazan CH-5 1,5-diphenyl-3-methylformazan CH-6 1,5-diphenyl-3-(3-iodophenyl)formazan CH-7 1,5-(2-carboxyphenyl)-3-cyanoformazan ~-CH-8 1,5-diphenyl-3-acetylformazan CH-9 1,3-diphenyl-5-(4-diphenyl)formazan ;
CH-10 1-(2-hydroxyphenyl)-3,5-diphenylformazan :
CH-ll 1-(2-carboxyphenyl)-3,5-diphenylformazan CH-12 1-phenyl-3-(3,4-dimethoxyphenyl)-5-(4-nitrophenyl)formazan CH-13 1,5-diphenyl-3-(2-naphthyl)formazan CH-14 1-phenyl-3-undecyl-5-(4-nitrophenyl)-formazan CH-15 1-(2-hydroxy-5-sulfophenyl)-3-phenyl-5-(2-carboxyphenyl)formazan CH-16 1,5-diphenyl-3-carbohexoxyformazan CH-17 1-(4-methylthiophenyl)-3-(3-nitrophenyl)-5-(3,5-dichlorophenyl)formazan . CH-18 1-(2-naphthyl)-3-(4-cyanophenyl)-5-(3--, nitro-5-chlorphenyl)formazan CH-ls 1-(3-pyridyl)-3-(4-chlorophenyl)-5-phenylformazan CH-20 1-(2,4,5-trichlorophenyl)-3-phenyl-5-- (4-nitrophenyl)formazan ~, CH-21 1-(4-pyridyl)-3-phenyl-5-(2-trifluoro-methylphenyl)formazan ~ CH-22 1-(2-nitro-4-chlorophenyl)-3-(4-chloro-- phenyl-5-(4-phenylazophenyl)formazan CH-23 1,3-diphenyl-5-(2-pyridyl)formazan CH-24 1-(2,5-dimethylphenyl)-3-phenyl-5-(2-pyridyl)formazan . . .

' . ! ,~
. . ~ .
,, .': . ' .

lOSlZ5~
TABLE IV ' (continued) : .
Exemplary Chelate-Forming Compounds ~ ..
:~ CH-25 1-(2-pyridyl)-3-(4-cyanophenyl)-5-(2- ~:
~ tolyl)formazan : ' " . ,;
' CH-26 1-(2-benzothiazolyl)-3-phenyl-5-(2 '~ pyridyl)formazan , ~ .
CH-27 1-(4,5-dimethylthiazol-3-yl)-3-(4- '-:
bromophenyl)-5-(3-trifluoropethyl- . ::' ' phenyl)formazan ' ~:
CH-28 1,3-diphenyl-5-(banzothiazol-2-yl)-, formazan ~ CH-29 1-(benzoxazol-2-yl)-3-phenyl-5-(4--~ chlorophenyl)formazan CH-30 1,3-diphenyl-5-(2-quinolinyl)formazan CH-31 1-phenylazo-2-phenol , CH-32 1-phenylazo-4-dimethylamino-2-phenol .:
CH-33 2-hydrophenylazo-2-phenol CH~34 1-(2-hydroxyphenylazo)-~-naphthol CH-35 1-(2-pyridylazo)-2-naphthol ~ CH-36 1-(2-pyridylazo)-2-phenol : CH-37 1-(2-pyridylazo)-4-resorcinol ,.
. CH-38 1-(2-quinolylazo)-2-naphthol ~ CH-39 1-(2-thiazolylazo)-2-naphthol .~ CH-40 1-(2-benzothiazolylazo)-2-naphthol .~ CH-41 1-(4-nitro-2-thiazolylazo)-2-naphthol '''~ CH-42 1-(2-thiazolylazo)-4-resorcinol ., , CH-43 2,2-azodiphenol .~ :
.~l CH-44 1-(3,4-dinitro-2-hydroxyphenylazo)-2,5-'.~ phenylene-diamine ;~ CH-45 1-(2-benzothiazolylazo)-2-aclnaphthol ,~ .
:~ CH-46 1-(1-isoquinolylazo)-2-aclnaphthol ::- CH-47 2-pyridinecarboxaldehyde-2-pyxidyl-.~. hydrazone '~ CH-48 2-pyridinecarboxaldehyde-2-benzothia-'~i zolylhydrazone .

.. ~ .

. ~.
. ., iOS~250 TABLE IV (Continued) Exemplary Chelate-Forming Compounds CH-49 2-thiazolecarboxaldehyde-2-benzoxa-zolylhydrazone CH-50 2-pyridinecarboxaldehyde-2-quinolyl-hydrazone CH-Sl 1-(2-pyridylmethyleneamino)-2-naphthol :~
CH-52 1-(2-quinolylmethyleneamino)-2-naphthol CH-53 1-(2-thiazolylmethyleneamino)-2-' naphthol CH-54 2-(2-benzoxazolylmethyleneamino)-2-phenol :-;', CH-5S 2-(2-pyridylmethyleneamino)-2- ~ :, phenol CH-56 2-(2-pyridylmethyleneamino)-2-~' pyridine . -' CH-57 2-(2-pyridylmethyleneamino)-2-' quinoline :~ CH-58 2-(4-nitro-2-pyridylmethyleneamino)-1 2-thiazole CH-5g 2-(2-benoxazolylmethyleneamino)-2-oxazole , CH-60 1-nitroso-2-naphthol ,~ CH-61 ' 2-nitroso-1-naphthol .' CH-62 1-nitroso-3,6-disulfo-2-naphthol CH-63 disodium 1-nitroso-2-naphthol-3,6-di sulfonate : .
~ . CH-64 4-nitrosoresorcinol ;,~ CH-65 2-nitroso-4-methoxyphenol ~,, CH-66 dithiooxamide `l .j CH-67 N,N'-dimethyldithiooxamide ,I CH-68 N,N'-diphenyldithiooxamide CH-69 N,N'-di-n-hexyldith~ooxamide :l CH-70 N,N'-di-p-tolyldithiooxamide ,~, -57-:~' iO51;~50 All of the chelating compounds added to the radiation-sensitive layer can be introduced similarly as the leuco dye or leuco dye precursor-coupler combinations. That is, these image-forming compounds can be added to the radia-tion-sensitive layer by conventional procedures after imagewise exposure, if desired. To minimize processing it is generally preferred to incorporate the image-forming compounds capable of reacting with the reaction products formed on exposure directly into the radiation-sensitive layer at the time it is formed. This can be conveniently accomplished by dissolving the image-forming compound within the coating composition used to form the radiation-sensitive layer. While the proportions of the image-forming compounds incorporated within the radiation-sensitive layer can be widely varied, it is generally .
preferred that the image-forming compound be present in a concentra-tion of from 0.1 to 10 parts per part by weight of cobalt(III~-complex initially present in the radiation-sensitive layer.
lj ~
' Physically Altered Radiation-Sensitive Layers and Elements I

In the foregoing discussion it is pointed out that radiation-sensitive layers and elements can have utility apart from separate image-recording elements or layers through the inclusion of visible image producing components within the radiation-sensitive layer itself. It is, however, not j essential that a visible change occur in the radiation-sensitive ~, layer for it to be useful for image-recording purposes. Any 3,~ readily detectible physical alteration of a radiation-sensitive layer according to this invention on exposure and/or processing ~, can be employed in imaging.
i In one such application it is contemplated that a polymer having functional groups capable of interacting with reaction products produced in reduction~of the sensitized ;`

. ,.. . . -.. `- . . ..
. .

~OSlZ50 cobalt(III)complex be employed as a photographic vehicle in the radiation-sensitive layer. In one form the polymer can include groups capable of forming coordination ligands with the cobalt-(II)atoms produced on reduction of the cobalt(III)complex. In this way the polymer can be selectively modified in exposed and, optionally, héat processed areas to vary its physical properties.
In a preferred form the polymer can be crosslinked by the cobalt(II)atoms to render the polymer selectively insoluble and oleophilic.
The unique advantages afforded by the present invention can, perhaps, be best appreciated by reference to a specific illustrative embodiment. It is well known to those skilled in the art that gelatin coatings are substantially opaque to near ultraviolet radiation. At the same time unsensitized cobalt(III)-complexes when incorporated into coatings are typically insensi-tive to radiation of a wavelength longer than 300 nanometers and, in the overwhelming majority of instances, to radiation of a wavelength longer than 400 nanometers. Cobalt(III)complexes, ~;, such as cobalt hexa-ammines and cobalt penta-ammines, when incorporated into gelatin coatings without employing a spectral , .
sensitizer as taught by this invention do not selectively physi-;~ cally alter the gelatin in exposed areas in any useful way. On the other hand, when a spectral sensitizer is included in com-'~ bination with the cobalt(III)complex which extends its sensitivity into the visible spectrum, exposure of the gelatin j coating containing the sensitized cobalt(III)complex leads to a physical alteration of the gelatin which is both readily detected and useful.
Since gelatin is well known to incorporate carboxy groups, it is believed that the cobalt(II)atoms released upon ;~j exposure and/or processing form ligands with each of two car-boxy groups to crosslink the gelatin in exposed areas. The ~- -59-gelatin in exposed areas can be selectively rendered insoluble and comparatively oleophilic. This permits the gelatin in unexposed areas to be selectively removed, as by washing with water, leaving behind an oleophilic exposed image area. By placing the gelatin coating on a supporting surface which is comparatively hydrophilic, the crosslinked gelatin will i selectively adsorb oleophilic printing inks, and a lithographic printing plate can be formed in a manner not possible prior to this invention. Where a comparatively thick gelatin coating of 10 more than about 100 microns is employed together with a high degree of crosslinking, a relief printing plate can be pro- -duced. It is also recognized that it is possible to uniformly harden gelatin coatings, if desired. Further, it is recognized that any conventional polymer having crosslinking sites available for forming ligands with cobalt(II)atoms can be substituted for gelatin Multi-Color Elements In the foregoing description the radiation-sensitive ~ and image recording elements have been described for simplicity `j 20 in terms of a single radiation-sensitive or image-recording layer being employed capable of producing an image by increasing or reducing optical density with respect to a back-ground or by producing a visibly distinguishable coloration 1:
with respect to the background area. It is to be recognized i that the present invention is fully applicable to forming multi-color images, as by the use of plural radiation-sensitive ! layers each sensitized to a different portion of the visible . j .
- electromagnetic spectrum.

An exemplary multi-color image forming radiation-3 sensitive element according to this invention is shown in Fig. 8.

The element 400 is comprised of a support 402. A conventional subbing layer or layer combination 404 is interposed between the .
.. , ~.. . . .
.
..... .

support and a first radiation-sensitive layer 406. Separated from the first radiation-sensitive layer by a first transparent interlayer 408 is a second radiation-sensitive layer 410.
Simi:Larly a second transparent interlayer 412 separates the second radiation-sensitive layer and a third radiation-sensitive layex 1~14. A protective transparent overlayer 416 overlies the ; third radiation-sensitive layer. In a simple, preferred form of the invention the interlayers, the overlayer and the photo-graphic vehicles for the radiation-sensitive layers can be gelatin or a combination of gelatin and synthetic polymer. Both the interlayers and overlayer are optional and can be omitted, if desired. In a preferred form the spectral sensitization of the third radiation-sensitive layer extends only through the blue region of the spectrum while the second radiation-sensitive layer is sensitized only through the blue and green regions of the ~pectrum and the sensitization of the first radiation-sensitive layer extends through the entire visible spectrum.
By choosing spectral sensitizers that are responsive to different portions of the visible electromagnetic spectrum for inclusion in each of the radiation-sensitive layers a multi-color image can be recorded. For example, in one form of the invention a color coupler can be selectively incorporated in each radiation-sensiti~e layer to produce a subtractive primary color which absorbs electromagnetic radiation corres-ponding to the range of the spectrum to which the layer has been sensitized. By processing the radiation-sensitive element ) after exposure with conventional color development solutions a multi-color image can be produced which is a negative of the multi-color imaging exposure. This element can be used to print a positive of the multi-color imaging exposure, if desired.
' ~OSi250 In another form chelating compounds can be included in the radiation-sensitive layers which will produce colored i images in each layer of any desired color. Such chelating t compounds can be chosen to produce subtractive primaries in each of the radiation-sensitive layers so that a colored negative of the original multi-color imaging exposure can be achieved. It is to be noted that the choice of color image to -be formed within the radiation-sensitive layers can be indepen-dent of the portion of the electromagnetic spectrum to which the 10 layer is sensitized. Hence, it is possible to produce images which are either positive or negative reproductions of the exposure image or which form the exposure image in a different color combination altogether.

.
~' ,, ,:

''~
.' 1 , ~OSlZ50 Examples 1 throu~h 48 A variety of spectral sensitizers chosen from Table II were employed to sensitize the photoreduction of cobalt(III)complexes C-2 and C-6. The cobalt(III)complexes and spectral sensitizers were each dissolved to saturation in separate portions of an equal parts by volume of ethanol and water which was brought to a pH of 5 with sodium acetate.
After mixi~g the solutions were either imbibed into filter paper or mixed with gelatin and coated onto a support. The coatings were exposed for a few seconds with a 1000 watt quartz -~
iodine lamp at a distance of 12 inches. Portions of the coatings were panchromatically exposed and found to be responsive. Portions of the coatings were also exposed within the visible spectrum only to light of a wavelength in the third of the visible spectrum corresponding to the maximum wavelen~th of absorption of the spectral sensitizer. All coatings set forth in Table V were found to be responsive to light in the portion of the visible spectrum covering the maximum absorption wavelength of the spectral sensitizers.
The spectral sensitizers were all chosen to be stable to light in the absence of the cobalt(III)complexes. Spectral sensitivity was then observed as a function of the degree to which the spectral sensitizer faded on exposure. Dye fade observations were confirmed in several instances by employing -CH-36 to provide a printout indicative of cobal,t(II) generation. In all instances the coatings were found to be sensitive to panchromatic light and to light corresponding to the wavelength of maximum absorption of the sensitizer.
The spectral results are summarized below in Table V.

. P.

o Xl o ::

, :, (U * ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~ ~ 0 ~ 0 ~ ~ 0~ 0 ,f ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~I ~ ~ ~ ~ P~ ~ ~ ~ ~ ~ ~ ~ ~f ~ P~ ~ ~L

H
3 ~1H a1 H H N N ~D ~ N N ~D ~D N N ~ D C'J N ~D ~O N N ~ D N N '.D ~D c`~
'( C~; ~ l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l ~1 V~ VVVVVVVC~VVVVUUVVVVVVUUUUUVUUUV
V
. :

. ~ 0 N ~_ t~
:? ~ ~ I I I I I I I I s c~ ~" u~ ~q n M n u} n u~ n n n ~ Q n v~ n n n n n n u2 n u~
nnnu2nnnnnnnnul nnu2nu2nnnnnn,nnv2nrn,n :-~CQ
; '?
: ~' . :1 .
1 o i -~ a) f ~ ~ rl C`J ~)~ 1~ ~CO ~ 0 ~I N ~f)J IS~D ~) (r, O ~I C~ ) ~0 :~ 0 '~ ~

1,: O N

: ~ -64-.;
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CO rl ~, o o ~ ~ o ~ L~ o 3 ~ co ~D ~1 0 ~ .=t ~O ~ t~
_ ~ ~t ~ ' ~ ~ ~O ~O U~ ~ ~ O
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a~ o ~ o~
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V ~ ~ ~ ,s ¢, C~ ¢, ~s .
,., ~
~s O
V
'' H X
,_~ H r~l ~D ~O ~O ~O ~O ~O ~O ~O ~ ~ ~O C~ O ~O ~O ~O ~O
p~l H ~ 4 O~g VVVVUVVV~)VVVVVV~VV
V V
,~
h ,: ~ a) N r-l ~I N N t~ ~f) ~ ~15~ CO CO ~
r~l ~1 ~1 ~1 ~1 ~ r-l r-l r~l ~1 ~1 ~1 ~ ~ ~f) ~N N
1 ~ IIIIIIIIIIIIIIIIII
rl U~ n U2 U~ U~ tQ U~ U~ Ul r,f~
,,,u~ a) ~:4 ~' :;' ~
., ~1 .-.' ~i "~, a) :: l~ r-l N ~)~ IS~D ~CO C~ O ~I CN ~)~ I~D ~CO P~

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., N
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By comparing Tables II and V it is apparent that spectral sensitizers exhibiting a ground state oxidation poterltial of less than l.00 volt and summed ground state oxidation and reduction potentials which are more negative than -0.50 volt are well suited for use in the practice of this invention. A preferred class of spectral sensi,tizers are merocyanine dyes bearing a negative charge which exhibit a ground state oxidation potential of less than 1.00 volt and summed ground state oxidation and reduction potentials more negative than -0.50 volt. In the foregoing examples the most effective spectral sensitizers were merocyanine dyes ' SS-l, SS-ll, SS-12, SS-13 and SS-18, each of which had a , carboxymethyl solubilizing group on the acidic ring and , which exhibited ground state oxidation potentials in the range of from 0.5 to o.89 volt and reduction potentials in the range of from -1.40 to -1.70 volts.
The oxonol dyes SS-5 and SS-6 were found to be effective only when coated in a basic medium, since their reduction potentials are considerably increased in acidic media. The oxonol coating solutions were rendered basic by dropwise addition of sodium hydroxide. The oxonol dyes in basic , coatings were somewhat less effective than the merocyanine dyes noted above, but more effective than the other spectral sensitizers listed in Table V.
3`
i Example 49 ~ }
~, Part A

A sample of a supported single-layer gelatin i coating containing 50.0 mg of gelatin per square dm was ¦ treated in the following sequence:

.

~, . .

105~250 Step_l Imbibition of the sample for one minute with a solution composed of 0.1 gram of SS-37, 2.0 grams of Na2C03, and 100 ml of distilled water.
Step 2 (a) Exposure of a first area of the sample for 15 seconds to a 1000 watt quartz iodine lamp at a distance of 30.5 cm through filters commercially available under the trademark Kodak Wratten 29 and 2.4* so that only red light reaches the coating.
tb) Exposure of a second area of the sample for 15 seconds to the same light source through filters commercially available under the trademark Kodak Wratten 98 and 2A* so that only blue light reaches the coating.
~;'! (c) Exposure of a third area of the sample for 15 seconds to U.V. radiation emitted by a 1000 watt quartz ~i iodine lamp at a distance of 30.5 cm with no filter being used.
, Step 3 Imbibition of the sample for one minute with a solution :, .i consisting of 0.1 gram of 1-(2-hydroxy-5-sodiosulfo phenyl)-3-phenyl-5-(2-carboxyphenyl) formazan dye, 2.0 grams of Na2C03, and 100 ml of distilled water.
, Step 4 Rinsing of the sample for one minute with a 0.2%
, aqueous solution of Na2C03.
. ~
j Step 5 Washing of the sample for 2 minutes with tap water.
,'1 .
No image was formed in any one of the three exposed i ~ areas.

) * See "Kodak Filters for Scientific and Technical Uses", Kodak Publication No. B-3 , ' , ' "

...:

, . . .

lOS1250 Part B
The procedure described in Part A was repeated with the exception that the hematoporphyrin solution in Step 1 was replaced with a cobalt hexammine solution of the following composition:

C-2 0.5 g Na~C03 2.0 g H2~ 100 ml A blue image of low density was recorded in the third area of the sample which had been exposed without a filter. No image was formed as the result of blue, green or red light exposure. The blue image was produced by the formazan dye chelating with cobalt(II) produced by ultraviolet light reduction of C-2. The result of this test confirmed the known native sensitivity of C-2 to ultraviolet light less than 300 nm in wavelength.
Part C
The procedure described in Part A was repeated with the exception that the SS-37 solution in Step 1 contained, in addition, 0.5 grams of C-2.
The density of the blue image in the third area of the sample (U.V. radiation, no filter) was much higher than the density in the comparable area in the sample described in -~ Part B, and a blue image was formed also in the first area of ~; the sample exposed only to red light. No image was formed as the result of either the green or blue light exposure. It is then ~i apparent that the SS-37!has optically sensitized the photo-:d reduction of cobalt(III)complex to red light and that it has - chemically sensitized the photoreduction of cobalt(III)complex to ultraviolet radiation.

.
. - . ., 105~Z50 Example 50 A. A sample of a supported single~layer gelatin coating containing per square dm of coating 40.0 mg gelatin and 15.0mg of the cyan-dye-forming coupler 5-[a -(2,4-di-tert-amylphenoxy)hex anamido]-2-heptafluorobutyramidophenol dissolved inl5.0 mg dibutyl phthalate was imbibed for one minute with a solution consisting of 0.1 gram of ss-38, 2.0 grams of Na2C03, and 100 ml of distilled water. The sample was then exposed for ten seconds to a 1000 watt quartz iodine lamp through a -~
graduated-density test sample at a distance of 30.5 cm, - developed for one minute in the following color developing solution:

~-amino-N-ethyl-N- ~ -hydroxyethyl-aniline sulfate 2.0 g C03 2.0 g Na~S03 0.1 g .' $ H20 100 ml and washed for 2 minutes.
No image was recorded in the so treated test sample.
B. A faint image consisting of one visible step was ' produced when the above procedure was repeated in a similar sequence wherein the SS-37 imbibition solution was replaced with a solution consisting of 0.5 gram of C-2~ 2.0 grams of Na2C03, and 100 ml of distilled water.
The image probably was produced by a complex of ~l photolytically produced Co(II) and the coupler.
~` C. A good cyan image consisting of 3 steps was ; produced when the procedure described in Section A was repeated in a similar sequence wherein the SS-37~imbibition solution contained, in addition, 0.5 grams of C-2.

., , 105~250 Examples 51 through 5~
The procedures of the previous Example 1 were repeated using (ss-6) as a spectral sensitizer and, in each coating, one of the cobalt(III)complexes C-24, C-25, C-26, C-27, C-28, C-29, C-30 and C-33. The ground state reduction potential of each cobalt(III)complex together with the initial optical density of its coating were measured. The coatings were then exposed panchromatically for 15 seconds and the coating densities again measured. A general relationship was noted to exist in that those cobalt(III)complexes having less negative reduction potentials were more easily sensitized as determined by measurements of spectral sensitizer fading. This relationghip i5 shown in Fig. 9. Because of their greater ease of ~ r~duction it is preferred to employ cobalt(III)complexes having ;1 ground state reduction potentials more positive than -0.50 volt in the practice of this invention.

Example 59 A piece of filter paper, commercially available under the trademark Whatman, No. 2 filter paper was imbibed , 2G with a portion of Solution A and dried.
Solution A
1.0 g C-2 in 10 ml water 0.13 g TA-2 in 10 ml water 17 ml 12-1/2~ gelatin solution 2.5 mlsaponin A uniform exposure of different parts of the imbibed - paper to radiation at wavelengths shorter than 3000 A, followed by heating at 100C, yielded cobalt sulfide images. Table VI
; lists background and image densities obtained by this procedure ~ 30 and with radiation below 3000 ~ filtered , ' ,' ~ -70-.. . , -- . .. .. ..

lOS~250 a~

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: ~ e ~

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:' o o 105iZ50 These data show that no images are obtained with heat alone or with radiation at wavelengths greater than 3000 ~, A 1~ by weight aqueous solution of SS-35 was imbibed into a sample Whatman No. 2 filter paper and dried. The paper was then coated with solution A and dried. The conditions under which this coating was exposed to yield cobalt sulfide images are listed in Table VII. . ~:

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The data related to Step c in Table VII shows that the spectral response of the radiation sensitive material can be extended beyond 3000 A in the presence of an optical brightener, The data related to Step d in Table VII shows that the optical sensitivity of the material also was extended into a region beyond 4000 R, i.e., into the region of the visible spectrum.

Example 60-A poly(ethylene terephthalate) film support was coated with a portion of Solution B at a thickness of 300 microns and dried.
Solution B
0.5 g C-2 1.0 g TA-9 0.1 g TA 2 5 ml water 32 ml 12-1/2~ gelatin (aqueous solution) 2.5 ml saponin 5 mg SS-4 in 5 ml ethanol 2.5 ml 5~ formaldehyde The film gave a cobalt sulfide image of relatively ` low density upon exposure through a test object to a quartz iodine lamp for 15 seconds. The film was heated at a temperature of 125C during the exposure.
The film was overcoated with Solution C at the same ,, i thickness and air-dried. When the film was again thermally developed for 5 seconds at 125C, a cobalt sulfide image of a density greater than 1.0 was produced, .
:

Solution C
0.1 g TA-2 : ~
1.0 g TA-9 `
ml 12-1/2~ gelatin (aqueous solution) , 2.5 ml sapdnin Example61 ~, .
Similar results were obtained when the procedures described in the preceding example were repeated using Solution D as the overcoat. ~
Solution D . ~ :
0.1 g TA-2 - -1.0 g TA-9 ~.
0.5 g C-2 ml gelatin ~l 2.5 ml saponin ., .
Example 6~
A coating having a thickness of 300 microns was ~ formed on a poly(ethylene terephahalate) film support using $: : a melt of Composition E.
Composition E
0.5 g C 2 0.5 g TA-9 ~ 0.1 g TA-2 ¦ : 2.5 g glycerol 0.5 ml ss-36 32 ml poly[(N-isopropylacrylamide)-co-(3-methacryloyloxypropane-1-sulfonic acid, sodium salt)-co-(2-acetoacetoxy-ethyl methacrylate)] formed from a 7:2:1 mole ratio of monomers 105~Z50 A thin, transparent overcoat of cellulose acetate butyrate was formed over the radiation-sensitive layer. The radiation-sensitive layer was imagewise exposed with a quartz i,odide lamp at a distance of 16 cm. The exposed radiation-sensitive element was then placed in face-to-face contact with a conventional two-component diazo recording element and uniformly heated to a temperature of 120C for 25 seconds. A
positive c-opy of the original image was recorded in the diazo recording element.

Example 63 Following the procedures of the preceding example except as noted, a radiation-sensitive element was prepared with the coating densities of active components as noted below:
Coating Densities 20 mg/dm2 C-2 4 mg/dm2 TA-2 20 mg/dm TA-9 20 mg/dm SS-36 Further, poly~N-isopropylacrylamide)-co-(3-acryloxyloxypropane-l-sulfonic acid, sodium salt)-co-(2-acetoacetoxyethyl meth-acrylate)] forrned t'rom a 7:2:0.25 mole ratio of monomers was substituted as the photographic vehicle. In this case the con-, ventional diazo recording element and the radiation-sensitive ', element were placed in face-to-face contact before exposure, and heating. A negative image was formed in the diazo recording element.

Examples ~l through 77 1051Z50 Various radiation-sensitive coatings containing thiourea were identically formed on the non-gelatin side of a photographic paper support having SS-35 imbibed therein7 but with additional thioamides and other solubilizing agents being varied. The coating employed in each instance without the solubilizing agents was of Composition F.
Composition F
1.37 grams TA-9 0 1.0 gram C-2 17 ml 12-1/2~ by weight gelatin in water 2.5 ml saponin 200 mg. of each solubilizing agent was incorporated.
The coatings were in each instance exposed with a 1000 watt quartz iodide lamp. Varied exposure conditions, solubilizing sgent~ and results re set forth in Tsb:e VIII.

, "

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105~250 Example7~
A portion of a coating composition consisting of 64 grams of a 12.5~o aqueous solution of gelatin, 1 ~ram of C-2, 1 gram of a 14~ aqueous solution of the SS-35, 6 ml of a 7.5'~ solution of the spreading agent saponin, and 28 ml of water, and whose pH had been adjusted to 8.o with NaOH, was applied onto a transparent hydrophilic support at a rate to produce a dry coverage of 650 mg of gelatin, 80 mg of C-2 and 13.5 mg of SS-35 per square foot of coating. Upon drying, 10 a sample of the so produced coating was exposed across a test pattern with a low output U.V. lamp of 1 minute.
To render the crosslinked image visible, a methylene blue dye was imbibed into the coating. The sample was then washed in warm water for 1 minute to dissolve the unexposed, hence uncrosslinked gelatin. The result was a dyed relie~
image on a clear support.
The sample was tested for its lithographic characteristics by using it as a printing master in the following manner: upon the application onto the surface of the sample of water and a black printing ink in a conventional printing press, the sample~s surface was contacted with printing paper. The crosslinked areas of the sample proved to be sufficiently oleophilic to provide a lithographic reproduction ; of the image pattern.
; Additional samples of the coating were processed and evaluated similarly as above with essentially the same results.
Among the samples were strips which, upon exposure, were washed, unwashed, dyed, and undyed. The substitution of C-22 and C-6 (bu-t with a perchlorate anion) produced no change in result.
Samples in which poly[(N-isopropylacrylamide)-co-(3-methacryloyl-oxypropane-l-sulfonic acid, sodium salt)-co-(2-acetoacetoxyethyl methacrylate)]

.

.~

-` 105125~) and polyacrylic acid were substituted for gelatin also were useful but performed somewhat less effectively than gelatin.
Washing the strips prior to inking appeared to be helpful, but not essential. Dyeing seemed to have little effect on ink receptivity. The coatings proved to be most sensitive when a small amount of H20 was present in the coating. A 10-second dip of the coating into water followed by wiping dry to the touch introduced sufficient moisture to insure maximum sensitivity.

Examples 79 through 95 To a solution of 10 mg of a spectral sensitizer in 1 ml of an appropriate solvent was added 2.5 grams of the following standard formulation:
C-3 0 7 gram TA-9 0.4 gram Polyvinylpyrrolidone 0.9 gram 2-Methoxyethanol 8.o grams This was coated at a wet thickness of 160 microns on a transparent film support he].d on a coating block maintained at 30C. The temperature of the block was raised to 60C, held there for 5 minutes and then readjusted to 30C. An overcoat of a 10% by weight solution of poly(methyl methacrylate) in toluene having a wet thickness of 160 microns was applied and the coating cured at 60C for 5 minutes.
The dye coating was laminated face-to-face to a ~ recording layer containing a 2,4-diphenyl-6-( ~-methyl-3,4--' diethoxystyryl)pyrylium fluoroborate, an ammonia-sensitive dye and the cobalt(III)complex containing layer was exposed through the support on a spectrograph, the light of which h P
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105~2S0 was modulated with a step tablet having steps differing in dens-Lty by 0 3 lOge. The exposed element was then passed twice at 45 cm/min through heated rollers maintained at 120C and the laminate separated. A negative dark image, believed to be cobalt sulfide, was obtained in the cobalt(III)-complex contalning coating while a positive image of bleached dye was obtained in the receiving layer.
The results are summarized in Table IX, page 81.
The invention has been defined in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

__.

Claims (52)

WE CLAIM:

1. A radiation-sensitive element comprising a support and, as a coating thereon, a radiation-sensitive layer comprised of a spectral sensitizer and, as the sole photolytically active component, a cobalt(III)complex which is free of a sensitizable anion and which has at least two monodentate ligands, the spectral sensitizer being capable of absorbing radiation longer than 300 nanometers in wavelength and said cobalt(III)complex exhibiting a reduction potential which lies between the ground state oxidation and reduction potentials of the spectral sensitizer.

2. A radiation-sensitive element according to claim 1 in which said cobalt(III)complex is comprised of at least one ammine ligand.

3 A radiation-sensitive element according to claim 2 in which said cobalt(III)complex is comprised of at least five ammine ligands.

4. A radiation-sensitive element according to claim 3 in which said cobalt(III)complex is comprised of a hexa-ammine cobalt(III) cationic moiety.

5. A radiation-sensitive element according to claim 1 in which said cobalt(III)complex contains at least one ligand selected from the group consisting of ammine, aquo, halo, alkylene-diamine, azido, thiocyanato, and nitro ligands.

6. A radiation-sensitive element according to claim 5 in which said cobalt(III)complex includes a cationic moiety chosen from the class consisting of hexa-ammine cobalt(III), aquopenta-ammine cobalt(III), cis[bis(ethylenediamine)azidothio-cyanato cobalt(III)], cis[bis(ethylenediamine)diazido cobalt(III)], cis[bis(ethylenediamine)nitroazido cobalt(III)], cis[bis(ethylene-diamine) dichloro cobalt(III)], trans[bis(ethylenediamine) dichloro cobalt(III)], trans[bis(ethylenediamine) dibromo cobalt(III)], bis(ethylenediamine) thiocyanato chloro cobalt(III), and cis[bis(ethylenediamine) amminochloro cobalt(III)] cationic moieties.

7. A radiation-sensitive element according to claim 1 in which said cobalt(III)complex includes a cationic cobalt(III) moiety.

8. A radiation-sensitive element according to claim 1 in which said cobalt(III)complex exhibits a ground state reduc-tlon potential which is less negative than -0.50 volt.

9. A radiation-sensitive element according to claim 1 in which said spectral sensitizer exhibits a ground state oxida-tion potential of less than 1.00 volt.

10. A radiation-sensitive element according to claim 9 in which said spectral sensitizer has ground state oxidation and reduction potentials the sum of which is more negative than -0.50 volt.

11. A radiation-sensitive element according to claim 1 in which said spectral sensitizer is chosen from the class consisting of cyanine, merocyanine, styryl base and oxonol dyes.

12. A radiation-sensitive element according to claim 9 in which said spectral sensitizer is hematoporphyrin.

13. A radiation-sensitive element according to claim 9 in which said spectral sensitizer is a bis(triazinyl-amine)stilbene.

14. A radiation-sensitive element according to claim 13 in which said spectral sensitizer is a bis(triazinyl-amine)stilbene disulfonic acid or salt thereof.

15. A radiation-sensitive element according to claim 1 in which said spectral sensitizer is chosen from the class consisting of (1) 1,1'-diethyl-2,2'-carbocyanine iodide (2) 1,1'-diethyl-2,2'-dicarbocyanine iodide (3) 1,1',2,2'-tetrahydro(4H-[1,4]thiazino[3,4-b]-benzothiazolo)cyanine bromide (4) 3-carboxymethyl-5-[(3-ethyl-2-benzothiazolinylidene)-ethylidene]rhodanine (5) bis[3-methyl-1-phenyl-2-pyrazoline-5-one-(4)]-trimethinoxonol (6) bis[3-methyl-1-phenyl-2-pyrazoline-5-one-(4)]-pentamethinoxonol (7) anhydro-3,3'-di(2-carboxyethyl )oxadicarbocyanine hydroxide (8) 4-[(3-ethyl-2-benzothiazolinylidene)isopropylidene]-3-methyl-1-(p-sulfophenyl)-2-pyrazoline-5-one (9) 4-[(1-ethyl-2-naphtho[1,2-d]thiazolinylidene) isopropylidene]-3-methyl-1-(p-sulfophenyl)-2-pyrazoline-5-one (10) 3-carboxymethyl-5-[(3-ethyl-2-benzoxazolinylidene)-ethylidene]rhodanine (11) 3-carboxymethyl-5-[(3-ethyl-2-benzoxazolinylidene)-ethylidene]-2-thio-2,4-oxazolidenedione (12) 3-carboxymethyl-5-[(3-methyl-2-thiazolidinylidene)-isopropylidene]rhodanine (13) 1-carboxymethyl-5-[(3-ethyl-2-benzoxazolinylidene)-ethylidene-3-phenyl-2-thiohydantoin (14) 3-ethyl-5-[1-(4-sulfobutyl)-4(1H)-pyridylidene]-rhodanine sodium salt (15) 3-carboxymethyl-5-(3-methyl-2-benzoxazolinylidene)-rhodanine (16) 3-ethyl-5-(1-ethyl-4(1H)-pyridylidene rhodanine (17) anhydro-9-ethyl-3,3'-(3-sulfopropyl)-4,5,4',5'-dibenzothiacarbocyanine hydroxide sodium salt (18) 3-ethyl-5-[(3-ethyl-2-benzoxazolinylidene)-ethylidene]rhodanine (19) 3-ethyl-5-[(3-ethyl-2-benzothiazolinylidene)-ethylidene]rhodanine (20) 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethyl-benzimidazolo carbocyanine chloride (21) anhydro-3-ethyl-9-methyl-3'-(3-sulfobutyl)-thiacarbocyanine hydroxide (22) anhydro-9-methyl-3,3'-di(3-sulfobutyl)-thiacarbocyanine hydroxide (23) 3-ethyl-5-[(3-ethyl-2-benzoxazolinylidene)-ethylidene]-1-phenyl-2-thiohydantoin (24) 3,3'-diethyl-4'-methyloxathiazolocarbocyanine bromide (25) 2-p-diethylaminostyrylbenzothiazole (26) 5,5'-dichloro-3,3',9-triethylthiacarbocyanine bromide (27) anhydro-5,5'-dichloro-3,9-diethyl-3'-(3-sulfobutyl)thiacarbocyanine hydroxide (28) 2-diphenylamino-5-[(3-ethyl-2-benzoxazolinylidene) ethylidene]-2-thiazolin-4-one (29) 2-diphenylamino-5-[(3-ethyl-2-benzothiazolinylidene)-ethylidene]-2-thiazolin-4-one (30) 1-p-carboxyphenyl-5-[(3-ethyl-2-benzoxazo-linylidene)ethylidene]-3-phenyl-2-thiohydantoin (31) 4-(2,4-dinitrobenzylidene)-1,4-dihydro-1-(4-sulfobutyl)quinoline, sodium salt (32) 5-[(3-ethylnaphth[2,1-d]oxazolin-2-ylidene)-ethylidene]-3-heptyl-1-phenyl-2-thlohydantoin (33) 5-[4-(3-ethyl-2-benzothiazolinylidene)-2-butenylidene]-3-heptyl-1-phenyl-2-thiohydantoin (34) 3,3'-dimethyl-9-phenyl-4,5,4',5'-dibenzothia-carbocyanine bromide (35) 2-diphenylamine- 5-[(3-ethyl-2-benzoxazo-linylidene)ethylidene-2-thiazolin-4-one (36) N,N'-di[2-p-sodiosulfoanilino-4-diethanol-amino-1,3,5-triazmyl(6)]-diaminostilbene-2,2'-disulfonic acid, sodium salt (37) N,N'-di {[4-diethylamino-6-(2,5-disulfonilino)]-2-s-triazinylamino} -2,2'-stilbene disulfonic acid, hexasodium salt, and (38) hematoporphyrin.

16. A radiation-sensitive element according to claim 1 in which said cobalt(III)complex is a cationic moiety arld said spectral sensitizer is an anionic moiety.

17. A radiation-sensitive element according to claim 1 in which said spectral sensitizer is present in an amount sufficient to impart an optical density of from 0.1 to 3.0 to said coating.

18. A radiation-sensitive element according to claim 17 in which said spectral sensitizer is present in an amount sufficient to impart an optical density of from 0.5 to 2.0 to said coating.

19. A radiation-sensitive element according to claim 1 in which said cobalt(III)complex is present in a concentration of from 0.01 to 100 moles per mole of spectral sensitizer.

20. A radiation-sensitive element according to claim 19 in which said cobalt(III)complex is present in a concentration of from 0.1 to 10 moles per mole of spectral sensitizer.

21. A radiation-sensitive element according to claim 20 in which said cobalt(III)complex and said spectral sensitizer are present in approximately equal molar concen-trations.

22. A radiation-sensitive element according to claim 1 in which said coating additionally includes a binder in a concentration of up to 99 percent by weight, based on the total weight of said coating.

23. A radiation-sensitive element according to clairn 22 in which said binder is present in a concentration of from 50 to 9° percent by weight, based on the total weight of said coating.

24. A radiation-sensitive element according to claim 1 in which said radiation-sensitive layer additionally includes a compound capable of forming a ligand of an optically dense cobalt(II)compound upon reduction of said cobalt(III)complex.

25. A radiation-sensitive element according to claim 24 in which said ligand forming compound is a chelating agent.

26. A radiation-sensitive element according to claim 24 in which said ligand forming compound is capable of forming at least bidentate chelates with cobalt.

27. A radiation-sensitive element according to claim 26 in which said chelating compound is chosen from the group consisting of formazan dyes, dithiooxamide, nitrosarol, azo, hydrazones and Schiff base chelating agent.

28. A radiation-sensitive element according to claim 1 additionally including within said radiation-sensitive layer a thioamide.

29. A radiation-sensitive element according to claim 28 in which said thioamide is a thiourea or thio-acetamide.

30. A radiation-sensitive element according to claim 29 in which said thiourea and said thioacetamide include at least one alkyl, aryl, alkaryl, or aralkyl substituent.

31. A radiation-sensitive element according to claim 30 in which each alkyl moiety contains from 1 to 20 carbon atoms.

32. A radiation-sensitive element according to claim 30 in which each aryl moiety is chosen from the class consisting of phenyl and naphthyl groups.

33. A radiation-sensitive element according to claim 28 in which said thioamide is a mixture of a thiourea and a thioacetamide.

34. A radiation-sensitive element according to claim 33 in which said thioamide is a mixture of thiourea and thioacetamide.

35. A radiation-sensitive element according to claim 1 and, in combination therewith, image recording means overlying said radiation-sensitive layer.

36. A combination according to claim 35 in which said image recording means includes an ammonia responsive layer and said cobalt(III)complex includes at least one ammine ligand.

37. A combination according to claim 36 in which said ammonia responsive layer is additionally radiation responsive.

38. A combination according to claim 37 in which said ammonia responsive layer is a diazonium salt containing layer.

39. A combination according to claim 36 and, in combination therewith, at least one ammonia permeable layer interposed between said radiation-sensitive layer and said ammonia responsive layer.

40. A radiation-sensitive element comprising a support and, as a coating thereon, a radiation-sensitive layer comprised of a spectral sensitizer capable of absorbing radia-tion longer than 300 nanometers in wavelength which exhibits a ground state oxidation potential of less than 1.00 volt and summed ground state oxidation and reduction potentials more negative than -0.50 volt and, as the sole photolytically active component a cobalt(III)complex which is free of a sensitizable anion and which has at least two monodentate ligands, said cobalt(III)complex exhibiting a ground state reduc-tion potential intermediate between the ground state oxidation and reduction potentials of said spectral sensitizer and less negative than -0.50 volt.

41. A process comprising exposing to electromagnetic radiation of a wavelength longer than 300 nanometers a radiation-sensitive layer comprised of a spectral sensitizer capable of absorbing radiation longer than 300 nanometers in wavelength and a cobalt(III)complex which is free of a sensitizable anion and has at least two monodentate ligands, associating with the layer an image-recording layer which is visibly responsive to at least one of the mono-dentate ligands contained within the cobalt(III)complex, and transferring at least said one monodentate ligand to said image-recording layer.

42. A process according to claim 41 in which the radiation-sensitive layer is imagewise exposed and an image recorded within the image recording layer.

43. A process according to claim 41,in which the radiation-sensitive layer is heated.

44. A process according to claim 43 in which the radiation-sensitive layer is heated to a temperature in the range of from 80 to 150°C.

45. A process according to claim 43 in which heating is undertaken after exposure.

46. A process according to claim 43 in which exposure occurs while the radiation-sensitive layer is heated above ambient temperature.

47, A process according to claim 43 in which the cobalt(III)complex includes an ammine ligand and ammonia is liberated from the radiation-sensitive layer.

48. A process according to claim 47 in which the radiation-sensitive layer is substantially uniformly exposed and heated so that ammonia is substantially uniformly liberated from the radiation-sensitive layer.

49. A process according to claim 47 in which the radiation-sensitive layer is imagewise exposed and substan-tially uniformly heated so that ammonia is imagewise liberated from the radiation-sensitive layer.

50. A process of forming a positive image comprising associating a diazo image recording means with a radiation-sensitive layer containing a spectral sensitizer capable of absorbing radiation longer than 300 nanometers in wavelength and a cobalt(III)complex free of a sensitizable anion and containing at least two monodentate ligands at least one of which is an ammine ligand, imagewise exposing the diazo image recording means to actinic radiation, uniformly exposing the radiation-sensitive layer to radiation of a wavelength longer than 300 nanometers, and heating the radiation-sensitive layer to stimulate release of ammine ligands through the reduction of the cobalt-(III)complex and transfer of released ammonia to the diazo image recording means to form a positive image therein.

51. A process of forming a negative image comprising associating a diazo image recording means with a radiation-sensitive layer containing a spectral sensitizer capable of absorbing radiation longer than 300 nanometers in wavelength and a cobalt(III)complex free of a sensitizable anion and containing at least two monodentate ligands at least one of which is an ammine ligand, imagewise exposing the radiation-sensitive layer to radiation of a wavelength longer than 300 nanometers, and heating the radiation-sensitive layer to stimulate release of ammonia from the cobalt(III)complex and transfer of the ammonia to the image recording means to permit the formation of a negative diazo image.

52. A process according to claim 51 in which the diazo image recording means is uniformly exposed to actinic radiation after the negative image is formed therein to stabilize the diazo image recording means against printout in negative image areas.