United States Patent (19) (11) Patent Number: 4,859,572 Farid et al. (45) Date of Patent: Aug. 22, 1989

54 DYE SENSTIZED PHOTOGRAPHIC IMAGING SYSTEM FOREIGN PATENT DOCUMENTS 0223587A 5/1987 European Pat. Off, . (75) Inventors: Samir Y. Farid; Roger E. Moody, 2083832A 3/1982 United Kingdom . both of Rochester, N.Y. OTHER PUBLICATIONS (73) Assignee: Eastman Kodak Company, Volman et al., Advances in Photochemistry, vol. 13, in the Rochester, N.Y. chapter titled "Dye Sensitized Photopolymerization' 21 Appl. No.: 189,002 by D. F. Eaton, pp. 427 to 488, John Wiley & Sons (1986). 22) Filed: May 2, 1988 Farid et al., U.S. Ser. Nos. 933,712, 933,658,933,660, 51 Int. Cl." ...... G03C 1/68 and 933,657, all filed Nov. 21, 1986, and commonly (52) U.S. Cl...... 430/281; 430/914; assigned (Now issued as Farid et al U.S. Pat. Nos. 430/915; 430/916; 522/25; 522/26; 522/27; 4,743,528; 4,743,529; 4,743,530; and 4,743,531). 522/28; 522/31 Primary Examiner-Paul R. Michl (58) Field of Search ...... 430/915, 281, 916,914; Assistant Examiner-C. D. R. Dee 522/25, 28, 63, 27, 26, 31 Attorney, Agent, or Firm-Carl O. Thomas 56) References Cited (57) ABSTRACT U.S. PATENT DOCUMENTS A photographic imaging system is disclosed comprised 4,050,934 9/1977 Turner ...... 96/1 R of a hardenable organic component containing ethyl 4,289,842 9/1981 Tan et al...... 430/270 enic unsaturation sites and an initiator system for ethyl 4,307,182 12/1981 Dalzell et al...... 430/339 enic addition. The initiator system is comprised of an 4,353,787 10/1982 Alexander et al. . ... 204/159.15 electron acceptor activator, an electron donor activa 4,399,209 8/1983 Sanders et al...... 430/138 tor, and, acting as a photosensitizer, a dye capable of 4,440,846 4/1984 Sanders et al...... 430/138 absorbing imaging radiation. The dye has a reduction 4,497,889 2/1985 Fuerniss ...... 430/260 potential related to that of the electron acceptor activa 4,571,377 2/1986 McGinniss et al...... 430/31 tor and an oxidation potential related to that of the 4,590,147 5/1986 Lindley ...... 430/286 electron donor activator to permit each to release a free 4,743,528 5/1988 Farid et al...... , 430/281 radical upon excitation of the photosensitizer by expo

4,743,529 5/1988 Farid et al...... 430/281 4,743,530 5/1988 Farid et al...... 430/28 sure to actinic radiation. 4,743,531 5/1988 Farid et al...... 430/281 4,772,541 9/1988 Gotschalk ...... 430/339 15 Claims, No Drawings 4,859,572 1. 2 the latter by photon capture, causing release of a free DYE SENSITIZED PHOTOGRAPHIC IMAGING radical which in turn induces immobilizing addition SYSTEM reactions at sites of ethylenic unsaturation. Imaging systems which rely on a combination of an FIELD OF THE INVENTION activator and a photosensitizer are typically exposed in This invention relates to photography. More specifi the ultraviolet or blue portion of the spectrum. The cally, this invention relates to an imaging system which necessity of using shorter imaging wavelengths places relies upon the hardening of organic component con constraints on the master or pattern employed for imag ing. For example, a master which presents a longer taining ethylenic unsaturation to produce an image 10 pattern. m wavelength visible dye image, but exhibits little vari ance in ultraviolet or blue transmittance is not well BACKGROUND OF THE INVENTION suited for imagewise exposing an imaging system which A variety of photographic imaging systems are responds only to ultraviolet or blue radiation. Further, known wherein a hardenable organic component con such imaging systems are disadvantageous and have taining ethylenic unsaturation sites is relied upon for 15 found limited acceptance in producing multicolor im image formation. The organic component undergoes ages, photoinduced addition reactions, typically either poly Activators are recognized in the art to fall into two merization or crosslinking, at the ethylenic unsaturation distinct classes. One class of activator is referred to as sites which produce hardening and allow image dis electron acceptor activators. These activators liberate a crimination to be achieved. 20 free radical capable of initiating ethylenic addition by A simple illustration of such an imaging system is a negative working photoresist which contains an imag accepting an electron from a photosensitizer in its ex ing dye. Imagewise exposure of the photoresist fol cited state. The reactions can be diagrammed as fol lowed by development leaves a dye image in exposed lows: areas. While there are a plethora of known negative 25 working photoresists which might be cited, Tan et al (I) U.S. Pat. No. 4,289,842 illustrates photoresist employ Sens - A seSens' (a) ing crosslinkable copolymers containing ethylenic un saturation in pendant groups, Lindley U.S. Pat. No. b 4,590,147 illustrates photoresists including vinyl oligo 30 Sens* -- A+-R-G-Senst + A-R (b) mers, and Fuerniss U.S. Pat. NO. 4,497,889 illustrates photoresists containing vinyl monomers. (c) Illustrative of more elaborate imaging systems capa ble of producing transferred dye images are Sanders et al. U.S. Pat. Nos. 4,399,209 and 4,440,846. A dye pre 35 where cursor and a hardenable organic component containing Sens represents a photosensitizer, ethylenic unsaturation sites are coated together on a N represents exposure to actinic radiation, support in rupturable microcapsules. Imagewise expo * indicates the excited state produced by light absorp sure to actinic radiation hardens the organic component tion on exposure, by inducing addition at its ethylenic unsaturation sites. At-R represents the electron acceptor activator, Upon subsequent rupture of the microcapsules only the At represents the electron accepting moiety of the dye precursor in unexposed microcapsules have the activator before an electron is accepted, mobility to transfer to a receiving sheet where a view A represents the electron accepting moiety of the able dye image is formed. activator after an electron is accepted, R represents the Since the hardenable organic components containing 45 moiety that is ultimately cleaved as a free radical, ethylenic unsaturation exhibit only limited direct re Sens shows the photosensitizer converted to a cat sponse to exposing radiation, it is common practice to ion radical by loss of an electron, and include an initiator of the ethylenic addition reaction. In denotes a radical. practice negative working photoresists are typically The reaction sequence described above is an ideal one imagewise exposed using radiation wavelengths in the 50 in which the electron acceptor activator radical pro near ultraviolet region of the spectrum. While Sanders duced by step (b) reacts further as indicated in step (c) et all recognize that imaging exposures are possible with to provide a free radical. ignored in this reaction se various forms and wavelengthss of radiation, the pre quence is a possible recombination of the photosensi ferred wavelengths of exposure are limited to the ultra tizer cation radical with the electron acceptor activator violet and the blue, up to about 480 nm, with the initia 55 radical to regenerate the electron acceptor activator in tors for the ethylenic addition reaction disclosed being its initial form and to transform the photosensitizer those which are responsive at these wavelengths of cation radical into an unexcited dye molecule. This exposure. reaction sequence can be diagrammed as follows: In order to achieve higher levels of sensitivity (i.e., higher imaging speeds) than can be achieved with a 60 single initiator, it is common practice in preparing imag a. ing compositions to employ coinitiators. One of the Sens - As Sens' (a) coinitiators is a photosensitizer. Photosensitizers are relied upon to capture photons of exposing radiation. Sens* + A*-R-G-Senst + A-R (b)b The remaining coinitiator is referred to as an activator. 65 The activator is not relied upon to respond directly to d exposing radiation, but rather adjacent activator and Senst + A-R-G-Sens + At-R (d) photosensitizer molecules react, following excitation of 4,859,572 3 w 4 Photon6. energy is internally dissipated in this reaction cationic dyes include Methylene Blue, Safranine O, sequence, since no free radical is produced and the Malachite Green, and various cyanine and rhodamine photosensitizer produced is no longer in an excited dyes. state. More efficient imaging systems are those in which reaction step (c) is favored over reaction step (d). Related Patent Applications Another class of activator is referred to as electron Farid et al U.S. Ser. Nos. 933,712, 933,658,933,660, donor activators. These activators liberate a free radical and 933,657, all filed Nov. 21, 1986, and commonly capable of initiating ethylenic addition by donating an assigned, disclose hardenable compositions comprised electron to a photosensitizer in its excited state. The of an organic compound containing ethylenic unsatura reactions can be diagrammed as follows: O tion, an azinium salt activator, and, acting as a photosen sitizer, a dye having a reduction potential which is at III most 0.1 volt more positive than the reduction potential of the azinium salt activator. Sens - A seSens' Farid et al U.S. Ser. No. 933,657 discloses the combi 15 (f) nation of a photosensitizer, an alkoxy azinium electron Sens" + D--R-G-Sens + D-R' acceptor activator, and benzene substituted with an electron donating amino group, acting as an imaging D-R -GD + R' (g) enhancer. Although amines are known to be electron donor acceptors, the aminobenzene enhancers require 20 where one or more benzene ring substituents having a Ham D-R' represents the electron donor activator, mett sigma value electron withdrawing characteristic of D- represents the electron donating moiety of the at least -0.20 volt. This substitution renders these com activator before donating an electron, pounds ineffective as electron donor activators, as D represents the electron donating moiety of the shown by inability to produce an image when combined activator after donating an electron, 25 with a dye in the absence of the electron acceptor acti Sens shows the photosensitizer converted to a anion Vator. by loss of an electron, and the remaining symbols are as indicated above. SUMMARY OF THE INVENTION Again, reaction sequence (III) is an ideal one in In one respect this invention is directed to a photo which the electron donor radical produced by step (f) 30 graphic imaging system comprised of a hardenable or reacts further as indicated in step (g) to provide a free ganic component containing ethylenic unsaturation radical. Ignored in this reaction sequence is a possible sites and an initiator system for ethylenic addition com reaction of the photosensitizer anion radical with the prised of an electron acceptor activator chosen from the electron donor activator radical to regenerate the elec class of activators that liberate a free radical capable of tron donor activator in its initial form and to transform 35 initiating ethylenic addition by accepting an electron the photosensitizer cation radical into an unexcited dye from a photosensitizer in its excited state, an electron molecule. This reaction sequence can be diagrammed as donor activator chosen from the class of activators that follows: liberate a free radical capable of initiating ethylenic addition by donating an electron to a photosensitizer in (IV) its excited state, and, as a photosensitizer, a dye capable e of absorbing imaging radiation. The dye has a reduction Sens - A >Sens' (e) potential more cathodic, equal to, or up to 0.1 volt less cathodic than that of the electron acceptor activator Sens* + D--R' --Gesens + D-R' (f) 45 and an oxidation potential equal to or more anodic, equal to, or up to 0.1 volt less anodic than that of the Sens + D-R' - GSens + D-R' (h)h electron donor activator. It has been discovered that an initiator system com Photon energy is internally dissipated in this reaction prised of both an electron acceptor and an electron sequence, since no free radical is produced and the 50 donor activator in combination with a dye photosensi regenerated photosensitizer is no longer in an excited tizer produces distinct advantages. First, the incorpora state. More efficient imaging systems are those in which tion of activators from both the electron acceptor and reaction step (g) is favored over reaction step (h). electron donor classes approximately doubles the speed A survey of useful electron acceptor and electron of the imaging system, even in systems in which recom donor activators useful with photosensitizers is set forth 55 bination reactions, such as (d) and (h) above are mini in Volman et al, Advances in Photochemistry, Vol. 13, in mal. In systems in which these recombination reactions the chapter titled “Dye Sensitized Photopolymeriza are significant, even larger increases in speed can be tion' by D. F. Eaton, pp. 427 to 488, John Wiley & Sons realized. The presence of a dye photosensitizer over (1986). comes a variety of problems in imaging applications, Specht and Farid published U.K. Specification No. 60 particularly in forming multicolor imaging systems, 3,083,832A discloses photopolymerization coinitiators encountered with photosensitizers absorbing at shorter including an azinium electron acceptor activator and, wavelengths. acting as a photosensitizer, an amino-substituted ketocoumarin. DEFINITION OF TERMS Gottschalk et al published European Patent Applica 65 The terms "alkyl (sometimes shortened to the prefix tions No. 0,223,587 discloses a polymerization system alk)' and “aryl (sometimes shortened to the prefix ar) including as an initiator a zwitterion consisting of an are employed throughout to indicate substituents and undissociated borate anion and a dye cation. Disclosed moieties that can be widely varied. Unless otherwise 4,859,572 5 6 stated, the carbon atom content of alkyl and aryl substit A represents exposure to actinic radiation, uents and moieties can be assumed to conform to the * indicates the excited state produced by light expo following norms: It is preferred to choose alkyl substitu Sure, ents from among those that contain l to 10 carbon A-R represents the electron acceptor activator, atoms. Aryl substituents preferably contain from 6 to 10 A represents the electron accepting moiety of the carbon atoms-e.g., phenyl or naphthyl. To minimize activator before an electron is accepted, molecular bulk lower alkyl groups (those containing A represents the electron accepting moiety of the from 1 to 5 carbon atoms-e.g., methyl, ethyl, propyi, activator after an electron is accepted, butyl, and pentyl) and phenyl groups are optimum sub Sens shows the photosensitizer converted to a stituent choices satisfying the alkyl and aryl substituent 10 cation radical by loss of an electron, definitions, respectively. References to alkenyl and al D-R represents the electron donor activator, kynyl substituents are to be understood as containing at D- represents the electron donating moiety of the least 2 carbon atoms, but otherwise having similar num activator before donating an electron, bers of carbon atoms as the alkyl groups. D represents the electron donating moiety of the The terms "more anodic' and "less anodic' are em 15 activator after donating an electron, ployed in their art recognized usage to mean more posi R and R' represent the moieties that are ultimately tive and less positive, respectively. cleaved as free radicals, and The terms "more cathodic' and "less cathodic' are donates a radical. employed in their art recognized usage to mean more It is also possible for the photosensitizer after being negative and less negative, respectively. 20 excited by photon capture from actinic radiation to react with the electron donor activator to produce a DESCRIPTION OF PREFERRED free radical. The photosensitizer anion radical then EMBODIMENTS reacts with the electron acceptor activator to produce a The present invention is directed to a photographic second free radical. Again, a single captured photon imaging system comprised of an organic component 25 produces two free radicals as opposed to only one in a which is hardened (i.e., significantly increased in molec conventional system and an approximate doubling of ular weight through polymerization or crosslinking, the speed of the photographic system of the invention resulting in an alteration of its physical characteristics, results. The alternative reaction sequence can be dia particularly viscosity and/or solubility) by undergoing grammed as follows: an addition reaction at sites of ethylenic unsaturation. 30 To facilitate hardening the imaging system includes an - (V) - initiator system for ethylenic addition comprised of an electron acceptor activator, an electron donor activa Sens - A seSens' (n) tor, and a dye capable of acting as a photosensitizer. The initiator system is believed to function in one or 35 both of the following ways, depending upon the specific choice of photosensitizer and activators. (p) According to one reaction scheme the photosensi tizer, after being excited by photon capture from actinic (q) radiation, reacts with the electron acceptor activator to 40 produce a free radical as described above. In other words, reaction sequence I described above occurs. (r) This produces a free radical. The photosensitizer cation radical, which is an unused reaction product of reaction sequence I, then reacts with the electron donor activa 45 where tor to produce a second free radical. Thus, a signal Sens shows the photosensitizer converted to an captured photon produces two reactive free radicals as anion by reduction and opposed to only one in a conventional system. This all the remaining notations are as indicated above. results in an approximate doubling of the photographic In looking at reaction sequences IV and V it can be 50 seen that no matter which activator the photosensitizer system of the invention. The reaction sequence can be in its excited state reacts with first, the photosensitizer diagrammed as follows: ion radical is produced which then reacts with the re maining activator. The reaction of the photosensitizer (IV) ion radical with the remaining activator removes the Sens - A seSens" (i) 55 photosensitizer ion radical from the system as it is formed and thereby minimizes the possibility of the (j) energy dissipating recombination reactions (d) and (h) Sens* + A*-R-G-Sensh - A-R occurring. Thus, as compared to conventional systems (k) in which recombination reactions (d) or (h) are signifi A-R-GA + R 60 cant, the present invention offers the potential of imag ing speeds more than twice as large. ---s f (l) When the dye acting as a photosensitizer is exposed Senst + D--R" - Gesens + D-R to actinic radiation and absorbs a photon, an electron in (m) the highest occupied molecular orbital of the dye is 65 lifted to a higher energy level-namely the lowest un occupied molecular orbital of the dye, and a vacancy is where left behind in the molecular orbital it initially occupied. Sens represents a photosensitizer, The electron acceptor activator can accept the electron 4,859,572 7 8 from the higher energy level orbital within the dye, and propylamine, triethylamine, benzylamine, N-methyl the electron donor activator can donate an electron to piperidine, quinuclidine, piperidine, pyrrollidine, dieth fill the vacancy in the originally occupied orbital, pro ylamine, triethanolamine, aniline, 4-bromoaniline, N vided certain relative energy relationships are satisfied. methylaniline, N,N-dimethylaniline, 2-anilinoacetic If the reduction potential of the electron acceptor acid, 2-(3-indolyl)acetic acid, and triphenylamine (and activator is more cathodic than that of the dye, an elec its triphenylphosphine and triphenylarsine analogs); tron in the higher energy orbital of the dye is readily sulfur compounds, such as arylsulfinates (e.g., tolylsulfi transferred from the dye to the highest unoccupied nates); enolates of diketones, such as acetylacetone and molecular orbital of the electron acceptor activator, 5,5-dimethyl-1,3-cyclohexanedione (also known as since this represents an exothermic process. Even if the O dimedone); acetic acid derivatives, such as 2-(3,4-dime process is instead slightly endothermic-i.e., even if the thoxyphenoxy)acetic acid and 2-(4-methoxyphenylthi reduction potential of the dye is up to 0.1 volt less ca o)acetic acid; allylthiourea; N-phenylglycine; and vari thodic than that of the electron acceptor activator, ous azoles, including imidazole, oxazole, and thiazole; ambient thermal activation readily overcomes such a and various organiometallic compounds, such as SnR4 small barrier. 15 compounds, where R is independently in each occur In an analogous manner, if the oxidation potential of rence chosen from among alkyl, aralkyl (particularly, the electron donor activator is more anodic than that of the dye, an electron moving from the highest occupied benzyl)(aryl, and alkaryl Substituents--e.g., n molecular orbital of the electron donor activator to the C3H7Sn(CH3)3, (allyl)Sn(CH3)3, and (benzyl)Sn(n- orbital vacancy in the dye is moving from a higher to a 20 C4H9)3. lower potential, which again represents an exothermic Another class of electron donor activators are bo process. Even if the process is slightly endother rates. Such activators can be generally represented by mic-i.e., even if the oxidation potential of the dye is up the formula: to 0.1 volt less anodic than that of the electron donor activator, ambient thermal activation readily over 25 R1 R4 (V) comes such a small barrier. Slightly endothermic reactions in which the reduc Y tion potential of the dye is up to 0.1 volt less cathodic than that of the electron acceptor activator or the oxida tion potential of the dye is up to 0.1 less anodic than that 30 where of the electron donor activator, occur in every instance, R, R2, R3, and R are independently selected from regardless of whether the electron acceptor activator or the group consisting of alkyl, aryl, allyl, aralkyl, alke the electron donor activator first reacts with the dye in nyl, alkynyl, alicyclic (preferably 5 to 7 membered cy its excited state. When the activator is reacting with the cloalkyl) groups, and saturated and unsaturated hetero dye in its excited state, it is preferred that the reaction 35 cyclic groups, such as those completing 5 or 6 mem be exothermic or only slightly endothermic. When the bered rings having up to three heteroatoms selected activator is reacting with the dye ion radical, as indi from among oxygen, chalcogen (e.g., sulfur, selenium, cated in reactions (1) and (q) above exothermic reac or tellurium), or nitrogen; and tions are still preferred, but still more endothermic reac Y is any convenient counterion. When the remaining tions can be expected in many instances occur. Thus, substituents are charge neutral, Y is a cation, such as the reduction potential of the dye can be up to 0.2 volt ammonium or an alkali metal. The borate electron (or more) less cathodic than that of a second to react donor activators can be selected from among any those electron acceptor activator or the oxidation potential of disclosed by Gottschalk et al published European Pa the dye can be up to 0.2 volt (or more) less anodic than tent Application 0,223,587, cited above and here incor that of a second to react electron donor activator. 45 porated by reference. Thus, by choosing combinations of a dye intended to In a specifically preferred form the borate is an alkyl act as a photosensitizer, an electron acceptor activator, triarylborate. The three aryl moieties are preferably and an electron donor acceptor based on comparisons chosen from among phenyl and lower alkyl substituted of their oxidation and reduction potentials, it is possible phenyl groups, such as tolyl and xylyl. The alky moiety to select specific three member combinations for initia 50 tor systems satisfying the requirements of this invention. is preferably a lower alkyl moiety. The oxidation and reduction potentials of many com The electron acceptor activator can be chosen from pounds have been published. If not published, oxidation the class of activators that liberate a free radical capable and reduction potentials can be measured by textbook of initiating ethylenic addition by accepting an electron procedures. For example, oxidation and reduction po 55 from a photosensitizer in its excited state. A variety of tentials can be measured as described by R. J. Cox, known electron acceptor activators useful in the imag Photographic Sensitivity, Academic Press, 1973, Chapter ing system of this invention are disclosed by Volman et 15. al, cited above and here incorporated by reference, at The electron donor activator can be chosen from the pp. 475-478. Disclosed classes of electron acceptor class of activators that liberate a free radical capable of 60 activators include cationic onium activators, such as initiating ethylenic addition by donating an electron to ammonium, diazonium (e.g., phenyldiazonium salts a photosensitizer in its excited state. A variety of known optionally substituted with groups such as alkyl, alkoxy, electron donor activators useful in the imaging system halo, or nitro groups), sulfonium (e.g., optionally alkyl of this invention are disclosed by Volman et al, cited or alkoxy substituted triarylsulfonium salts including above and here incorporated by reference, at pages pp. 65 adjacent aryl nuclei with 2,2' oxy bridging groups), 439-475. Disclosed classes of electron activators in Selenium salt analogues of the sulfonium activators, and clude amines, such as triethanolamine, hydrazine, 1,4- iodonium salts (e.g., diphenyl and 2,2'-biphenyl iodo diazabicyclo[2.2.2 octane, tri-n-butylamine, tri-n- nium salts optionally alkyl substituted). 4,859,572 10 Preferred electron acceptor activators are azinium other than the one required amine substituent) the net activators, such as those disclosed by Heseltine etal and Hammett value derived electron withdrawing charac Jenkins et al U.S. Pat. Nos. Re. 27,922 and 27,925, teristic of the ring substituents can be determined. Specht and Farid U.K. No. 3,083,832A, and Research The dyes employed as photosensitizers in the practice Disclosure, Vol.200, Dec. 1980, Item 20036. The azinium activators include an azinium nucleus, of the this invention can be selected from among known such as a pyridinium, diazinium, or triazinium nucleus. dye classes. Preferred dyes are those which exhibit an The azinium nucleus can include one or more aromatic absorption peak within the visible spectrum-i.e., from rings, typically carbocyclic aromatic rings, fused with about 390 to 700 nm. Dyes are contemplated for use as an azinium ring. In other words, the azinium nuclei O photosensitizers which have absorption peaks in spec include quinolinium, isoquinolinium, benzodiazinium, tral regions ranging from the near ultraviolet to the near and naphthodiazonium nuclei. To achieve the highest infrared. Specific dye absorption characteristics can be attainable activation efficiencies per unit of weight it is chosen based on the radiation source employed for preferred to employ monocyclic azinium nuclei. exposure. For broad spectrum exposure sources, dyes A quaternizing substituent of a nitrogen atom in the 15 azinium ring is capable of being released as a freeradical with broad absorption peaks are preferred. For narrow upon electron transfer from the photosensitizer to the band exposures, including laser exposure sources, it is anzinium activator. In one preferred form the quaterniz preferred that the absorption peak of the dye exactly ing substituent is an oxy substituent. The oxy substituent match the maximum emission wavelength of the expo (-O-T) which quaternizes a ring nitrogen atom of the 20 sure source. It is generally preferred to employ a sub azinium nucleus can be selected from among a variety tractive primary dye as a photosensitizer, particularly, of synthetically convenient oxy substituents. The moi when producing multicolor images. A subtractive pri ety T can, for example, be an alkyl radical, such as methyl, ethyl, butyl, etc. The alkyl radical can be substi mary dye has a principal absorption peak in one of the tuted. For example, arakyl (e.g. benzyl and phenethyl) 25 blue (400 to 500 nm), green (500 to 600 nm), or red (600 and sulfoalkyl (e.g. sulfomethyl) radicals are contem to 700 nm) regions of the spectrum and appears yellow, plated. In another form T can be an acyl radical, such as magenta, or cyan. an -C(O)-T radical, where T can take any of the Among specifically contemplated dye classes from varied forms of alkyl and aralkyl radicals described which dyes can be selected are coumarin (including above. In addition T can be an aryl radical, such as 30 ketocoumarin and sulfonocoumarin) dyes, merocyanine phenyl or naphthyl. The aryl radical can in turn be dyes, merostyryl dyes, oxonol dyes, and hemioxonol substituted. For example, T can be a tolyl or xylyl radical. T typically contains from 1 to 18 carbon atoms, dyes. Dyes from each of the foregoing classes all con with alkyl moieties in each instance above preferably tain a keto group in the blue absorbing chromophore being lower alkyl moieties and aryl moieties in each 35 and are all therefore designated keto dyes. In addition, instance preferably containing 6 to 10 carbon atoms. it is a specific recognition of this invention that a dye Highest activity levels have been realized when the oxy photosensitizer useful in the practice of this invention substituent (-O-T) contains 1 or 2 carbon atoms. need not be a keto dye. That is, a keto group in the The azinium nuclei need include no substituent other chromophore of the dye is not essential. Non-keto dyes than the quaternizing substituent. However, the pres embrace a variety of dye classes, including non-keto ence of other substituents is not detrimental to the activ polymethine dyes, anthracene dyes, rhodamine dyes, ity of the activators. While it is known to include azinium nuclei substituents to increase blue light absorp acridine dyes, aniline dyes, and azo dyes. Non-keto tion by the activator directly, substituents capable of polymethine dyes include cyanine, hemicyanine, and performing this function are not required, since the 45 styryl dyes. photosensitizer can be relied upon for light absorption. In one preferred form of the invention the dye photo it is specifically contemplated to employ in combina sensitizers are chosen from the polymethine dye class, tion with the azinium electron acceptor activator an which includes the cyanines, merocyanines, complex aniline enhancer of the type disclosed in U.S. Ser. No. cyanines and merocyanines (i.e., tri-, tetra- and poly 933,657, filed Nov. 21, 1986, commonly assigned and 50 nuclear cyanines and merocyanines), oxonols, hemiox cited above, titled ENHANCED IMAGING COM onols, styryls, merostyryls, and streptocyanines. POSITION CONTAINING AN AZINUM ACTI VATOR. The anilines contemplated for use as enhanc The cyanine dyes include, joined by a methine link ers are those which are ring substituted with one or age, two basic heterocyclic nuclei, such as azolium or more groups capable of imparting a net Hammett sigma 55 azinium nuclei, for example, those derived from pyri derived electron withdrawing characteristic of at least dinium, quinolinium, isoquinolinium, oxazolium, + 0.20 to the benzene ring. A positive Hammett sigma thiazolium, selenazolium, indazolium, pyrazolium, pyr value is indicative of a substituent which is capable of rolium, indolium, 3H-indolium, imidazolium, ox rendering a phenyl ring electron withdrawing while a adiazolium, thiadioxazolium, benzoxazolium, benzothi negative Hammett sigma value is indicative of a substit 60 azolium, benzoselenazolium, benzotellurazolium, ben uent which is capable of rendering a phenyl ring elec zimidazolium, 3H- or 1H-benzoindolium, naphthox tron donating. Hydrogen is assigned a Hammett sigma azolium, naphthothiazolium, naphthoselenazolium, value of zero. Lange's Handbook of Chemistry, 12th Ed., McGraw-Hill, 1979, Table 3-12, pp. 3-135 to naphthotellurazolium, carbazolium, pyrrolopyridinium, 3-138, lists Hammett sigma values for a large number of 65 phenanthrothiazolium, and acenaphthothiazolium qua commonly encountered substituents. By algebraically ternary salts. summing the Hammett sigma values of the various ring Exemplary of the basic heterocyclic nuclei are those substituents of the aniline (that is, the ring substituents satisfying Formulae 1 and 2. 4,859,572 . 11 12 atoms or phenyl when the methine group is substituted; and -- Z- - Formula 1 q is 0 or 1. =C-(L=L)-N-R Cyanine dyes can contain two heterocyclic nuclei of the type shown in Formula 1 joined by a methine link age containing an uneven number of methine groups or can contain a heterocyclic nucleus according to each of -- z-- Formulae 1 and 2 joined by a methine linkage contain -C=(L-L)=N-R ing an even number of methine groups, where the meth Formula 2 O ine groups can take the form -CR=as described above. The greater the number of the methine groups linking nuclei in the polymethine dyes in general and the cyanine dyes in particular the longer the absorption wavelengths of the dyes. For example, dicarbocyanine O 15 dyes (cyanine dyes containing five methine groups link ing two basic heterocyclic nuclei) exhibit longer ab sorption wavelengths than carbocyanine dyes (cyanine dyes containing three methine groups linking two basic where heterocyclic nuclei) which in turn exhibit longer ab Z represents the elements needed to complete a cyc 20 sorption wavelengths than simple cyanine dyes (cya lic nucleus derived from basic heterocyclic nitrogen nine dyes containing a single methine group linking two compounds such as oxazoline, oxazole, benzoxazole, the basic heterocyclic nuclei). Carbocyanine and dicarbo naphthoxazoles (e.g., naphth 2,1-d-oxazole, cyanine dyes are longer wavelength dyes while simple naphth 2,3-dioxazole, and naphth 1,2-dioxazole), oxadi cyanine dyes are typically yellow dyes, but can exhibit azole, thiazoline, thiazole, benzothiazole, the naphtho 25 absorption maxima up to about 550 nm in wavelength thiazoles (e.g., naphtho2,1-dthiazole), the with proper choice of nuclei and other components thiazoloquinolines (e.g., thiazolo.4,5-d-quinoline), capable of bathochromically shifting absorption. phenanthrothiazole, acenaphthothiazole, thiadioxazole, One of the techniques for bathochromically shifting selenazoline, selenazole, benzoselenazole, the naph the absorption maxima of polymethine dyes in general thoselenazoles (e.g., naphtho1,2-d-selenazole), ben 30 and cyanine dyes in particular is to include in the meth zotellurazole, naphthotellurazoles (e.g., naptho(1,2-d- ine linkage an oxocarbon bridging nucleus. Exemplary tellurazole), imidazoline, imidazole, benzimidazole, the oxocarbon bridging nuclei can take any of the forms naphthimidazoles (e.g., naphth 2,3-dimidazole), 2- or indicated by Formula 3. 4-pyridine, 2- or 4-quinoline, 1- or 3-isoquinoline, ben zoquinoline, 3H-indole, 1H- or 3H-benzoindole, and 35 Formula 3 pyrazole, which nuclei may be substituted on the ring by one or more of a wide variety of substituents such as C-(C) hydroxy, the halogens (e.g., fluoro, chloro, bromo, and iodo), alkyl groups or substituted alkyl groups (e.g., - / methyl, ethyl, propyl, isopropyl, butyl, octyl, dodecyl, C octadecyl, 2-hydroxyethyl, 3-sulfopropyl, carboxy methyl, 2-cyanoethyl, and trifluoromethyl), aryl groups O or substituted aryl groups (e.g., phenyl, 1-naphthyl, 2-naphthyl, 4-sulfophenyl, 3-carboxyphenyl, and 4 45 C biphenylyl), aralkyl groups (e.g., benzyl and phenethyl), O O alkoxy groups (e.g., methoxy, ethoxy, and isopropoxy), | || aryloxy groups (e.g., phenoxy and 1-naphthoxy), alkyl C-(C) thio groups (e.g., methylthio and ethylthio), arylthio groups (e.g., phenylthio, p-tolylthio, and 2-mapht hylthio), methylenedioxy, cyano, 2-thienyl, styryl, 50 amino or substituted amino groups (e.g., anilino, di methylamino, diethylamino, and morpholino), acyl groups, (e.g., formyl, acetyl, benzoyl, and benzenesulfo wherein n is the integer 0, 1 or 2. nyl); 55 Merocyanine dyes link one of the cyanine dye type Q represents the elements needed to complete a cyc basic heterocyclic nuclei described above to an acidic lic nucleus derived from basic heterocyclic nitrogen keto methylene nucleus through a methine linkage as compounds such as pyrrole, indole, carbazole, benzin described above, but containing zero, two, or a higher dole, pyrazole, indazole, and pyrrolopyridine; even number of methine groups. Zero methine dyes, R represents alkyl groups, aryl groups, alkenyl those containing no methine groups in the linkage be groups, or aralkyl groups, with or without substituents, tween nuclei, exhibit a double bond linkage between the (e.g., carboxy, hydroxy, sulfo, alkoxy, sulfato, thiosul nuclei in one resonance form and a single bound linkage fato, phosphono, chloro, and bromo substituents); in another resonance form. In either resonance form the L is in each occurrence independently selected to linkage sites in the nuclei are formed by methine groups represent a substituted or unsubstituted methine 65 forming a part of each nucleus. Zero methine polymeth group-e.g., -CR = groups, where R represents hy ine dyes are yellow dyes. drogen when the methine group is unsubstituted and Exemplary acidic nuclei are those which satisfy For most commonly represents alkyl of from 1 to 4 carbon mula 4. 4,859,572 13 14 in Formula 5 joined by a methine linkage as previously Formula 4 described containing one or a higher uneven number of methine groups. Useful merostyryl dyes exhibit a keto methylene nu cleus as shown in Formula 4 and a nucleus as shown in Formula 6 joined by a methine linkage as described above containing one or a higher uneven number of where methine groups. Gl represents an alkyl group or substituted alkyl group, an aryl or substituted aryl group, an aralkyl 10 Formula 6 group, an alkoxy group, an aryloxy group, a hydroxy group, an amino group, or a substituted amino group, wherein exemplary substituents can take the various forms noted in connection with Formulae 1 and 2; 15 G2 can represent any one of the groups listed for Gl where and in addition can represent a cyano group, an alkyl, or G3 and G' are as previously defined. arylsulfonyl group, or a group represented by The cyanine, merocyanine, hemicyanine, hemiox onol, and merostyryl dyes described above are intended -C-G1, 20 to be illustrative of the simpler structural forms of useful O polymethine dyes. It is generally recognized that sub stituents can join the nuclei and methine linkages to or G2 taken together with G can represent the elements form additional cyclic structures. Further, the dyes can needed to complete a cyclic acidic nucleus such as those contain three or more nuclei. For example, by substitut derived from 2,4-oxazolidinone (e.g., 3-ethyl-2,4- 25 ing a merocyanine dye in its methine linkage with a oxazolidindione), 2,4-thiazolidindione (e.g., 3-methyl second basic heterocyclic nucleus of the cyanine dye 2,4-thiazolidindione), 2-thio-2,4-oxazolidindione (e.g., type an allopolar cyanine dye can be formed. Further, 3-phenyl-2-thio-2,4-oxazolidindione), rhodanine, such the various substituents not forming a part of the dye as 3-ethylrhodanine, 3-phenylrhodanine, 3-(3-dime chromophore can be varied as desired to tailor dye thylaminopropyl)rhodanine, and 3-carboxymethylr 30 physical properties, particularly hydrophobicity and hodanine, hydantoin (e.g., 1,3-diethylhydantoin and hydrophillicity, to suit the particular film forming com 3-ethyl-1-phenylhydantoin), 2-thiohydantoin (e.g., 1 ponents employed. By choosing as the aliphatic moi ethyl-3-phenyl-2-thiohydantoin, 3-heptyl-1-phenyl-2- eties of the dyes hydrocarbon groups having more car thiohydantoin, and arylsulfonyl-2-thiohydantoin), 2 bon atoms (e.g., from about 6 to 20 carbon atoms) the pyrazolins-one, such as 3-methyl-1-phenyl-2-pyrazolin 35 dyes can be rendered more oleophilic while hydrocar 5-one, 3-methyl-1-(4-carboxybutyl)-2-pyrazolin-5-one, bon groups containing fewer numbers of carbon atoms and 3-methyl-2-(4-sulfophenyl)-2-pyrazolin-5-one, 2 (e.g., 1 to 5 carbon atoms) and particularly those bear isoxazolin-5-one (e.g., 3-phenyl-2-isoxazolin-5-one), 3,5- ing polar substituents render the dyes more hydrophilic. pyrazolidindione (e.g., 1,2-diethyl-3,5-pyrazolidindione The aromatic moieties of the dyes typically contain and 1,2-diphenyl-3,5-pyrazolidindione), 1,3-indandione, from 6 to 10 carbon atoms. 1,3-dioxane-4,6-dione, 1,3-cyclohexanedione, barbituric In addition to the initiator system described above the acid (e.g., 1-ethylbarbituric acid and 1,3-diethylbarbitu imaging system includes a hardenable organic compo ric acid), and 2-thiobarbituric acid (e.g., 1,3-diethyl 2 nent containing ethylenic unsaturation sites. Depending thiobarbituric acid and 1,3-bis(2-methoxyethyl)-2-thi upon the application an imaging dye or dye precursor obarbituric acid). 45 can also be included. In a simple illustrative form the Useful hemicyanine dyes are essentially similar to the hardenable organic component can take the form of an merocyanine dyes described above, differing only in organic film forming component of a negative-working substituting for the keto methylene group of Formula 4 photoresist optionally having the imaging dye or its the group shown below in Formula 5. precursor blended therewith. 50 The organic film forming component can take the G3 Formula 5 form of any containing ethylenic unsaturation and capa / ble of selective immobilization by undergoing an addi mN tional reaction at the site of the ethylenic unsaturation. Yg: Hardening of the film forming component and thus 55 immobilization of the blended imaging dye or dye pre where cursor can be imparted by initiating polymerization of G3 and G' may be the same or different and may monomers containing ethylenic unsaturation or by initi represent alkyl, substituted alkyl, aryl, substituted aryl, ating crosslinking of linear polymers or oligomers con or aralkyl, as illustrated for ring substituents in Formula taining ethylenic unsaturation. For example, any of the 1 or G and G' taken together complete a ring system monomeric or crosslinkable polymeric film forming derived from a cyclic secondary amine, such as pyrroli components disclosed in Jenkins etal and Heseltine et al dine, 3-pyrroline, piperidine, piperazine (e.g., 4-methyl U.S. Reissue 27,925 or 27,922, respectively, are suitable piperazine and 4-phenylpiperazine), morpholine, for use in the photoresists of this invention and are here 1,2,3,4-tetrahydroquinoline, decahydroquinoline, 3 incorporated by reference. Tan et al U.S. Patent azabicyclo(3,2,2lnonane, indoline, azetidine, and hex 65 4,289,842, here incorporated by reference, discloses ahydroazepine. negative working photoresists containing light sensitive Useful hemioxonol dyes exhibit a keto methylene acrylate copolymers containing pendant groups, such as nucleus as shown in Formula 4 and a nucleus as shown alkenyl groups with ethylenic unsaturation. Lindley 4,859,572 15 16 U.S. Patent 4,590,147, here incorporated by reference, To achieve highest levels of sensitivity it is generally discloses vinyl oligomers which can be employed as preferred to choose the imaging dye or its precursor to film forming components in the photoresists of this avoid competition or interaction with the photosensi invention. Useful film forming components containing tizer. For example, with an imaging dye present in the vinyl monomers are disclosed in Fuerniss U.S. Patent imaging system during imagewise exposure if the imag 4,497,889 and Anderson et al U.S. Patent 4,535,052, ing dye absorbs at the same wavelength as the photosen both here incorporated by reference. Kosar Light-Sensi sitizer, the speed of the system is reduced to the extent tive Systems, John Wiley & Sons, 1965, further describes that the imaging dye captures photons which would a variety of useful film forming components for use in otherwise be captured by the photosensitizer. There the practice of this invention, including ethylenically O fore, it is apparent that the imaging dye, where present unsaturated monomers and polymers. during imagewise exposure, is preferably chosen to Preferred film forming components are comprised of exhibit a maximum absorption peak in a different por at least one addition polymerizable ethylenically unsat tion of the spectrum than the photosensitizer. For in urated compound having a boiling point above 100 C. stance a cyan (red absorbing) photosensitizer employed 15 with a yellow (blue absorbing) imaging dye exhibits at normal pressure which is preferably employed in higher levels of sensitivity than when the imaging dye is combination with a polymeric binder. The ethylenically also a cyan dye. Further, to reduce the possibility of unsaturated compound (typically a monomer) and the interactions between the photosensitizer and the imag polymeric binder can be employed together in widely ing dye, it is preferred that the imaging dye have an varying proportions, including ethylenically unsatu absorption peak at a shorter wavelength than the photo rated compound ranging from 3 to 97 percent by weight sensitizer. With such a relationship the imaging dye is of the film forming component and polymeric binder responding to higher energy (shorter wavelength) radi ranging from 97 to 3 percent by weight of the film ation than the photosensitizer and therefore not likely to forming component. A separate polymeric binder, interfere with the interaction of the photosensitizer and though preferred, is not an essential part of the film 25 activator. forming component and is most commonly omitted Subject to the above considerations imaging dyes can when the ethenically unsaturated compound is itself a be selected from among the various known classes of polymer. dyes. The imaging dyes are preferably selected from Chang U.S. Pat. No. 3,756,827, here incorporated by among the more light stable dyes, such as azo dyes, reference, discloses in column 2, line 36 to column 3, 30 anthracene dyes, and the like. The imaging dyes are line 30, a variety of suitable organic monomers for use preferably selected to remain substantially inert during in the photoresists of this invention. Specifically illus the photohardening step. trated in the examples below are ester monomers con In a specific preferred form of the invention, instead taining ethylenic unsaturation. Similar monomers in of incorporating an imaging dye in the photoresist an clude ethylenically unsaturated diester polyhydroxy 35 imaging dye precursor, such as a leuco dye or other polyethers, described in Chambers U.S. Pat. No. chromogenic material described more specifically 4,245,031, here incorporated by reference. below in connection with more elaborate imaging sys Organic polymeric binders which can form a part of tems, can be employed. The use of a dye precursor the film forming component of the photoresist include: which is substantially colorless at the stage of image (1) polyesters, including those based on terephthalic, 40 wise exposure has the advantage that the dye precursor isophthalic, sebacic, adipic, and hexahydroterephthalic does not absorb exposing radiation and hence does not acids; (2) nylons or polyamides; (3) cellulose ethers and compete with the photosensitizer. In other words, esters; (4) polyaldehydes; (5) high molecular weight higher levels of sensitivity can be realized when a dye ethylene oxide polymers-e.g., poly(ethylene glycols), precursor is employed for imaging as compared with an having weight average molecular weights from 4000 to 45 imaging dye. For example, an image dye which absorbs 4,000,000; (6) polyurethanes; (7) polycarbonates; (8) at the same wavelength as the photosensitizer does not synthetic rubbers-e.g., homopolymers and copolymers compete with the photosensitizer for photons when a of butadienes; and (9) homopolymers and copolymers dye precursor is employed so that the image dye chro formed from monomers containing ethylenic unsatura mophore is not formed until after imagewise exposure tion, such as polymerized forms of any of the various 50 has occurred. ethylenically unsaturated monomers, such as polyalk In addition to the film forming component, the initia ylenes-e.g. polyethylene and polypropylene; poly(vi tor system, and, optionally, the imaging dye or dye nyl alcohol); poly(vinyl esters)--e.g., poly(vinyl ace precursor the photoresists can contain any one or com tate); polystyrene; poly(acrylic and methacrylic acids bination of known addenda, such as thermal inhibitors, and esters)--e.g., poly(methyl methacrylate) and poly 55 supplemental colorants (e.g., pigments), plasticizers, (ethyl acrylate), as well as copolymer variants. fillers, etc. To facilitate coating on a substrate the pho In addition to the film forming component and the toresist is usually dispersed in a solvent to create a solu coinitiators the negative-working photoresist can con tion or slurry, the liquid being evaporatively removed tain an imaging dye or an imaging dye precursor. The after coating. Any solvent can be employed for this imaging dye or its precursor can be present in any con 60 purpose which is inert toward the film forming compo centration which imparts a visually discernable color nents and addenda of the photoresist. Solvents can be ation to the photoresist when coated on a substrate, chosen from among a wide variety of organic liquids, exposed to imaging radiation, and then developed. Use including N,N-dimethylformamide; N,N-dime ful imaging dye concentrations can vary widely, de thylacetamide; alcohols, such as methanol, ethanol, pending upon a variety of factors, such as the extinction 65 butanol, etc.; ketones, such as acetone, cyclohexanone, coefficient of the dye, the degree of color saturation and butanone; esters, such as ethyl acetate and ethyl desired, the manner in which the dye is dispersed, and benzoate; ethers, such as tetrahydrofuran and dioxane; the dispersing medium. chlorinated aliphatic hydrocarbons, such as methylene 4,859,572 17 18 chloride and 1,2-dichloroethane; aromatic hydrocar The liquid developer can be any convenient liquid bons, such as benzene and toluene; and other common which is capable of selectively removing the photoresist solvents, such as dimethyl sulfoxide, chlorobenzene, in unexposed areas. The coated photoresist can be and various mixtures of solvents. sprayed, flushed, swabbed, soaked, or otherwise treated Any conventional ratio of each activator to film 5 with the developer to achieve selective removal. In its forming component can be present in the photoresists of simplest form the liquid developer can be the same this invention. Activator concentrations are as a practi liquid employed as a solvent in coating the photoresist. cal matter most conveniently specified in terms of moles Methoxyethyl acetate and ethoxyethyl acetate are com of activator per gram of dry solids, the latter constiting mon developers. Also aqueous developers are com of the film forming component and the minor amounts 10 monly employed, such as miscible combinations of of various addenda, but excluding any liquid component water and alcohols, with proportions in the range of introduced to facilitate coating. Typically from about from 20 to 80 percent water and 80 to 20 percent alco 5X10-7 to 3x 10-4, preferably from about 2x 10-5 to hol being common. Exemplary water miscible alcohols 2x 10-mole of each activator is present per gram of include glycerol, benzyl alcohol, 1,2-propanediol, sec 15 butyl alcohol, and ethers derives from glycols, such as dry solids. Increases in photographic response can be dihydroxy poly(alkylene oxides). Lactone developers, realized when a minimal concentration of the electron such as those disclosed by Martinson et al U.S. Pat. No. acceptor activator is combined with any of the above 3,707,373, can be employed. Optimum developer concentrations of the electron donor activator or vice choices for specific photoresists are disclosed in the versa. It is, however, generally preferred to employ the 20 various patents cited above illustrating the specific film two activators in a ratio of from 1:10 to 10:1, preferably forming components. 25:75 to 75:25 on a mole basis. Following development a retained dye image is pres In the practice of the present invention the enhancer ented by the photoresist coating remaining on the sub is an optional coinitiator, meaning that it need not be strate. The colored areas correspond to the areas of present or need not be present in en effective amount. 25 exposure. Multicolor images, such as images employed However, it is generally preferred to incorporate the for color proofing, can be produced by superimposing enhancer in any convenient effective amount. Typically three elements each comprised of a transparent support from about 0.1 to 10 moles per mole of azinium electron and a photoresist image, where each image is formed by acceptor activator are employed. The use of larger a different additive or subtractive primary dye. amounts is, of course, possible. 30 In the foregoing imaging systems only a single coated The photosensitizer can be present in any concentra layer is required for imaging. However, it is recognized tion capable of increasing the response of the photore that the imaging systems of the invention can employ sist to visible light. While the photosensitizer concentra multiple layers. For example, instead of blending the tion can vary widely, it is generally contemplated to imaging dye with the film forming component as de photosensitize in concentrations ranging from about 35 scribed above, a separate imaging dye layer can be 5X 10-7 to 3x 10-4 mole per gram of dry solids. Pre coated between the substrate and the photoresist layer. ferred photosensitizer concentrations are in the range of Upon imagewise exposure and development the photo from 10-6 to 5X105 mole per gram of dry solids, with resist is removed in exposed areas. When the photoresist optimum concentrations generally being in the range of remains the underlying image dye remains in its initial from about 2X 10-6 to 2X 10-5 mole per gram of dry 40 immobilized condition, while in other areas the dye can solids. be removed or decolorized by washing or any other The substrate onto which the photoresist is coated convenient technique. can take any convenient conventional form. For imag Instead of forming retained dye images with photore ing, transparent and white reflective substrates are par sist coatings as described above, it is specifically con ticularly advantageous; however, any substrate which 45 templated to form transferred dye images. For example, does not exactly match the hue of image dye can be instead of removing the film forming component of the employed. Substrates such as glass, ceramic, metal, photoresist layer in unexposed areas by development cellulose paper, fiberboard, semiconductor, or polymer following imagewise hardening, the unhardened areas substrates are illustrative. Specific substrates include of the photoresist layer or only the imaging dye or dye alumina-blasted aluminum, anodized aluminum, alumi 50 precursor contained in these areas can be selectively na-blasted poly(ethylene terephthalate) film, poly(ethy transferred to a receiver. For example, the greater tacki lene terephthalate) film, flame or electrostatic discharge ness of the unhardened areas can be relied upon to per treated poly(ethylene terephthalate) film, poly(vinyl mit their transfer by first laminating the imagewise ex alcohol)-coated paper, crosslinked polyester-coated posed layer to a receiver sheet and then stripping. In paper, nylon, glass, cellulose acetate film, heavy paper, 55 another approach, the hardened portions of the image such as lithographic paper, and the like. wise exposed layer can be relied upon to reduce the In perhaps their most commonly used form photore mobility of the image dye or dye precursor so that sists are coated in a fluid form on a substrate and evapo imaging dye is transferred to or formed in the receiver ratively dried, usually with heating, to produce a uni only in areas corresponding to unexposed areas of the form coating. Often, particularly in the manufacture of 60 photoresist layer. Other variant approaches of forming semiconductor devices, the substrate is spun, thereby transferred images should be apparent from the descrip employing centrifugal forces to assure the uniformity of tion of other imaging systems below. the photoresist coating before drying. After exposure to In the foregoing description of photoresists the hard visible radiation causes addition to occur at the ethyl enable organic component containing ethylenic unsatu enic unsaturation sites of the film forming component, a 65 ration sites is a film forming component. However, in liquid developer is brought into contact with the coated certain preferred imaging systems of the invention the substrate to remove selectively the photoresist in areas hardenable organic component can be present as a dis which were not exposed to actinic radiation. continuous or internal phase forming microcapsules 4,859,572 19 20 which can be in contact with a surrounding continuous produced, are located within the microcapsules. For phase or separated therefrom by intervening rupturable simplicity subsequent discussion is directed to chromo encapsulating walls. While it is possible to coat micro genic materials contained in the microcapsules with capsules each containing the hardenable organic con developer being located in the receiver layer, but the ponent, coinitiators, and imaging dye or dye precursor converse arrangement is possible, except as specifically to form a single color image, the present invention noted. The receiver layer can be similar to the receiver makes possible the formation of multicolor images em for a preformed imaging dye, differing only by the ploying a single layer of microcapsules coated on a additional inclusion of a developer. support. Since the microcapsules form discrete packets Transferred dye image systems can be similar to the of materials, it is possible to mix in the same layer micro 10 retained dye image systems described above, but differ capsules containing dye photosensitizers which absorb in the location of the receiver layer. Instead of coating at differing locations in the visible spectrum and imag the receiver layer on the same support as the microcap ing dyes (or their precursors) of differing imaging hues. sules, the receiver layer is coated on a separate support. For example, it is contemplated to coat as a single layer In integral format arrangements the receiver layer and on a substrate (a) microcapsules containing a yellow 15 its support can be associated with the microcapsule dye photosensitizer and a yellow or blue imaging dye or layer and its support at the time of exposure as well as its precursor, (b) microcapsules containing a magenta at the time transfer to the receiver from the microcap dye photosensitizer and a magenta or green imaging dye sules occurs. Alternatively, the receiver layer and its or its precursor, and (c) microcapsules containing a support need not be associated with the microcapsule cyan dye photosensitizer and a cyan or red imaging dye 20 layer until rupture of the microcapsules occurs. In ei or its precursor. Except for the choice of dye photosen ther arrangement the receiver layer and its support can sitizer and imaging dye the microcapsules can be other be employed alone as the image bearing element or can wise identical. Thus, merely by blending three differing be retained with the microcapsule layer and its support. populations of microcapsules it is possible to obtain in the latter instance the decolorization of the photosen multicolor images with the same ease and facility as 25 sitizer by room light in the image bearing element and monochromic dye images are obtained. Except for hue the initially colorless form of the chromogenic material selection of components and blending of microcapsule are particularly advantageous. populations prior to coating, monochromic and multi In general similar materials can be employed in form color imaging according to this invention are identical. ing the microcapsule systems described above as have Therefore, for simplicity the description which follows 30 been previously described in connection with negative is in terms of monochromic imaging, but the description working photoresists, the principal difference being in is applicable to both monochromic and multicolor im the physical continuity of the iamging layer. However, aging, except as specifically noted. certain materials described below have been found to be The microcapsules can be employed to produce ei particularly well suited to use in microcapsule imaging ther a retained or a transferred dye image. Further, 35 systems and constitute preferred materials. either a preformed dye or, preferably, a dye precursor Preferred hardenable organic components containing can be contained in the microcapsules. ethylenic unsaturation include compounds containing at In the retained imaging system a receiver layer is least one terminal ethylenic group per molecule and coated on a substrate and is overcoated by a layer of preferably two or more terminal ethylenic groups per microcapsules. Within each coated microcapsule expo 40 molecule. Typically they are liquid and can also double sure to light which is absorbed by the dye photosensi as a carrier oil for the chromogenic material in the tizer results in release of free radicals by the activators internal phase. Representative examples of these com which in turn results in hardening of the organic com pounds include ethylenically unsaturated acid esters of ponent containing ethylenic unsaturation. Subsequent polyhydric alcohols such as trimethylol propane tri uniform rupture of all the coated microcapsules, as by 45 acrylate. Another preferred hardenable component can passing the exposed element between pressure rollers, include an acrylate prepolymer derived from the partial results in migration of imaging dye or its precursor from reaction of pentaerythritrol with acrylic acid or acrylic the microcapsules which were not exposed and hence acid esters. Such materials are available from Richard were not internally hardened. son Company, Melrose Park, Ill. -e.g., R1-1482 and The released dye or dye precursor diffuses into the 50 R1-1483. Also useful are isocyanate modified acrylate, received layer. Where an imaging dye is contained in methacrylate, and itaconic acid esters of polyhydric the microcapsules, the receiver layer can be formed of alcohols, such as disclosed by Carlick et al U.S. Pat. any convenient transparent dye penetrable material. Nos. 3,825,479; 3,759,809; and 3,783,151. For example, the dye can enter a hydrophilic colloid The chromogenic materials used in the present inven layer or film forming polymer layer. Preferably a mor 55 tion are preferably oil soluble color formers which pro dant is present in the receiver layer to immobilize the duce a dye upon reaction with a developer in the pres iamge dye on receipt. ence of a carrier oil. Representative examples of such When the microcapsules contain a dye precursor, the chromogenic materials include substantially colorless dye image forming layer contains a second component compounds including a lactone, lactam, sultone, spiro capable of interacting with the dye precursor to form 60 pyran, ester, or amido structure. Specifically preferred the image dye. One of the two components is hereinaf chromogenic materials are triarylmethane, bis ter referred to as a chromogenic material and the other phenylmethane, xanthene, thiazine, spiropyran, and is referred to as a developer. Either or both can be similar compounds. Also useful as chromogenic materi viewed as a dye precursor and either can be located als are organic compounds capable of complexing with within the microcapsules with the other located in the 65 heavy metals to form dyes-e.g., copper phthalocya dye image forming layer in monochromic imaging. nine. Specific chromogenic materials, including specific However, for multicolor imaging the chromogenic . additive and subtractive primary dye forming chromo materials, which differ based on the hue of the dye to be genic materials, are disclosed in U.S. Pat. Nos. 4,859,572 21 22 3,920,510; 4,399,209; and 4,440,846, here incorporated In preferred forms the microcapsules each include in by reference. addition to the internal phase a rupturable surrounding In addition to the hardenable organic component, the encapsulating wall. Encapsulation can be undertaken in initiator system, and the chromogenic material, the any convenient conventional manner. Oil soluble chro discrete phase or microcapsules can also contain a car- 5 mogenic materials have been encapsulated in hydro rier oil. Preferred carrier oils are weekly polar solvents philic wall forming materials, such as gelatin and gelatin having boiling points above 170° C. and preferably in derivatives (e.g., phthalated gelatin), gum arabic, poly(- the range of from 180° C. to 300° C. Exemplary carrier vinyl alcohol), and carboxymethylcellulose wall form oils include alkylated biphenyls (e.g., monoisopropyl ing materials, as illustrated by Green et al U.S. Pat. Nos. biphenyl), polychorinated biphenyls, caster oil, mineral 10 2,730,456 and 2,800,457; resorcinol-formaldehyde wall oil, deodorized kerosene, naphthenic mineral oils, dibu formers, as illustrated by Vassiliades U.S. Pat. No. tyl phthalate, dibutyl fumerate, brominated paraffin, 3,914,511; isocyanatepolyol wall formers, as illustrated and mixtures thereof. Alkylated biphenyls are preferred by Kiritani et al U.S. Pat. No. 3,796,669; urea-formalde on the basis of low toxicity while brominated paraffins hyde wall formers, particularly urea-resorcinol-for employed in combination with trimethylol propane 15 maldehyde wall formers, as illustrated by Foris et al triacrylate are particularly preferred for halftone imag U.S. Pat. Nos. 4,001,140, 4,087,376, and 4,089,802; 1Ilg. melamineformaldehyde resin wall formers; and hydrox Carrier oils are not required. As previously noted the ypropyl cellulose wall formers, as illustrated by Shackle hardenable organic component can in many instances U.S. Pat. No. 4,025,455; all of the foregoing patents 20 being here incorporated by reference. The wall formers perform the mobility providing function of a carrier oil, must, of course, be capable of transmitting exposing particularly where the hardenable organic component radiation. Preferred wall formers are gelatin and gelatin is a monomer. The choice of carrier oil will depend to derivatives as well as urea-resorcinolformaldehyde wall some extent on the chromogenic material to be trans formers. Microencapsulation can be accomplished by ported on rupture of the microcapsule. Carrier oils are 25 any convenient conventional technique, including coac chosen on the basis of their ability to impart mobility to ervation, interfacial polymerization, polymerization of the chromogenic material in the absence of hardening of one or more monomers in oil, as well as various melting the organic component containing ethylenic unsatura dispersing, and cooling methods. tion as well as being nonreactive with the various com The microcapsules normally are chosen to be of a size ponents of the microcapsules. 30 too small to be individually discerned by the unaided The internal phase forming the microcapsules is then eye. The microcapsules preferably range from about 1 comprised of the hardenable organic component, an to 25 micrometers (um) in diameter, more typically optional carrier oil, a chromogenic material, coinitia from about 3 to 15 um in diameter, depending upon the tors, and any of a variety of optional components in sharpness of the image desired, the smoothness of the tended to offer improvement in imaging properties, is support surface, and the technique used for rupturing such as light scattering materials, stabilizers, and the the microcapsules. Generally the sharpness of the dye like. image increases as the size of microcapsules decreases. The materials forming the internal phase of the mi However, smaller microcapsules are less easily coated crocapsules can be present in generally similar concen on rough surface supports and less easily ruptured uni tration ranges as previously described in connection 40 formly by mechanical techniques. with photoresists. In general the hardenable organic The microcapsules are normally coated at a density component constitutes at least about 40 percent by sufficient to at least cover the surface of the support. weight of the internal phase and typically constitutes That is, based on the average diameter of the microcap from about 50 to 99 percent by weight of the internal sules the coating coverage is chosen to provide at least phase. The chromogenic material can be present in any 45 a monolayer coverage of microcapsules on the support. concentration compatible with providing a visible dye Instead of forming the microcapsules with discrete image. In general useful concentrations range from walls, it is appreciated that microcapsule containing about 0.5 to 20.0 percent by weight, based on the weight compositions suitable for coating on a substrate can be of the internal phase. A preferred range of chromogenic produced by forming an emulsion in which the micro material for monochromic imaging is from about 2 to 750 capsules constitute the discontinuous or internal phase percent by weight of the internal phase. in multicolor of a binder analogous to the wall formers above constit imaging a somewhat higher concentration of chromo uents the continuous phase. For example, such micro genic material is preferred, since only a third of the capsule coatings can be formed employing hydrophilic microcapsules are available to provide a maximum binders, such as hardened gelatin and gelatin deriva image dye density of any primary hue. For example, a 55 tives. maximum density magenta image must be formed using Reacting with the chromogenic material (or first dye only the one third of the microcapsules containing the precursor) is a developer (or second dye precursor). chromogenic material which forms a magenta dye. A The developer can take the form of any material capa preferred range of chromogenic material for multicolor ble of reacting with the chromogenic material to pro imaging is from about 5 to 15 percent by weight of the 60 duce a dye. For the preferred classes of chromogenic internal phase. Carrier oils are not required, but can be materials identified above illustrative developers in present in concentrations of up to about 50 percent by clude clay minerals, such as acid clay, and active clay weight of the internal phase, preferably in concentra attapulgite; organic acids such as tannic acid, gallic tions of from about 10 to 40 percent of the internal acid, and propyl gallate; acid polymers, such as phenol phase. The coinitiators can be present in the same con- 65 formaldehyde resins; condensates of carboxylic acids centrations set out above for the photoresists, where the containing at least one hydroxy group and formalde dry solids percent bases correspond to internal phase hyde; metal salts of aromatic carboxylic acids, such as percentage bases for the microcapsule utility. zinc salicylate, tin salicylate, zinc 2-hydroxynaphtheno 4,859,572 23 24 ate, zinc 3,5-di-tert-butylsalicylate; oil soluble metal It is specifically contemplated to modify the imaging salts of phenol-formaldehyde novolak resins (more spe systems disclosed by Gottschalk et al published Euro cifically illustrated by U.S. Pat. Nos. 3,672,935; pean Patent Application No. 0,223,587, here incorpo 3,732,120; and 3,737,410), zinc carbonate, and mixtures rated by reference, by substituting the initiator system of the above. of this invention for that disclosed therein. When the developer is coated on a substrate, as is While the invention has been described above in preferred, the developer is typically dispersed in a terms of forming dye images, it is appreciated that nega binder. The binder is chosen to be a relatively dye per tive-working photoresist compositions often include no meable inert material, such as poly(vinyl alcohol), gela colorant or colorant precursor, since their primary pur tin or a gelatin derivative, maleic anhydride-styrene O pose is to define a protective image rather than an image copolymer, starch, gum arabic, or a cellulose ester. In that is intended for viewing. general well known film forming binders are useful. As An illustration of a negative-working resist applica mentioned above, a mordant can be incorporated in the tion of the invention which requires no incorporated binder for the developer to assist in immobilizing the image dye or image dye precursor is provided by a tape dye once it is formed. A variety of mordants particu 15 assisted bonding application of the invention. As dis larly compatible with gelatin and gelatin derivatives are closed by Guild U.S. Pat. No. 4,247,623, a useful inter disclosed by Hartman U.S. Pat. No. 4,315,978. mediate article for packing integrated circuits is a a tape While the microcapsule containing imaging system having a metal layer laminated between a positive has been described above in terms of employing a chro working photoresist layer and a negative-working pho mogenic material and a developer, it is appreciated that 20 toresist layer. Since the negative-working photoresist mobile imaging dyes can be substituted for the the chro acts as a support for beam leads for the integrated cir mogenic material, if desired. The advantage of employ cuit package formed from the metal layer, it is chosen to ing chromogenic materials is that the chromogenic exhibit desirable dimensional stability and hardness at material need contain no chromophore to compete with temperatures of 200 C. and higher. Binders are there the dye photosensitizer for photon dye capture. Fur 25 fore chosen for the photoresist having a glass transition ther, the chromogenic material minimizes coloration of temperature of at least 150° C. Examples of useful poly the imaging system in areas where no image dye is meric binders known to have thermal properties com formed. patible with the above requirements include polyacryl While the preferred microcapsule imaging systems ates, polyamides, polycarbonates, polyesters, polyester above have been described in terms of forming a discon 30 amides, polyimides. preferred binders are those dis tinuous oleophilic phase in a continuous hydrophilic closed in U.S. Pat. No. 4,322,490. Further details of phase, it is appreciated that the reverse relationship is preferred negative-working photoresists for this appli also possible. It is specifically contemplated to form cation are set out in Klein et al U.S. Ser. No. 77,714, microcapsules containing dyes or chromogenic materi filed July 24, 1987, commonly assigned, now U.S. Pat. als which are more hydrophilic and to rely on the rela 35 No. 4,792,517, tive hydrophobicity if not impermeability of the micro capsule walls to initially confine the dyes. Where micro EXAMPLES capsule wall formers are present, the same relatively The invention can be better appreciated by reference hydrophilic binders described above can still be em to the following specific examples. ployed. The important point to note is that an extremely broad range of imaging dyes and chromogenic materials EXAMPLE are available for use. Hartman U.S. Pat. No. 4,315,978 Control l illustrates a variety of yellow, magenta, and cyan dyes An photographic imaging composition PI-1 was pre containing polar substituents to impart mobility in more hydrohpilic media. pared, formulated as follows:

2.34 g Binder A 1.17 g Monomer A 1.17 g Monomer B 0.012 g Inhibitor A 0.02 mmol Activator A 0.02 mmol Photosensitizer A 10.32 g Solvent (Dichloromethane) Binder A exhibited the following structure

O O C! (> C --CH O O

Monomer A exhibited the following structure 4,859,572 25 d 26 -continued R

R O O R = -C-O-CH2-CH-O-C-CH=CH2

R Monomer B exhibited the following structure

C-O-CH-CH-O-C-CH=CH2;

Inhibitor A exhibited the following structure H3C CH3

HO / N S OH and

(CH3)3C C(CH3)3 Activator A was 1-methoxy-4-phenylpyridinium tetra fluoroborate. Control 3 Photosensitizer A was 1,1",9-triethylbenzo thiazolocarbocyanine trifluroacetate. A second imaging composition PI-2 was prepared PI-1 was coated on a copper sheet using a 0.3 mm identical to P-1, but with Activator B in a concentra coating knife and dried for 10 minutes at about 70° C. A tion of 0.02 mmol substituted for Activator A. transparent polypropylene cover sheet was then placed Activator B was tetrabutylammonium butyltri over the coating. phenylborate. PI-2 was clearly inferior to PI-1 in its Since PI-1 without PHotosensitizer A responds to 35 imaging response. The concentration of Activator B ultraviolet exposures, shorter wavelengths were re was chosen after running a concentration series indicat moved during exposure using a W-16 Wratten (R) filter ing that further increases in concentration were produc capable of filtering 99.9 percent of radiation of less than ing little, if any, further increases in imaging speed. 510 nm in wavelength. EXAMPLE 1. To determine the degree of effectiveness of the initia 40 tor system exposure of a coated sample was undertaken A third imaging composition PI-3 was prepared iden through a Kodak T-14 (R) step tablet having 14 equal tical to PI-1, but with Activator B added. That is, this increment density steps ranging in density from essen imaging composition contained Activator A, Activator tially zero to 2.1. A three minutes exposure was under B, and Photosensitizer A as a three member initiator taken using a Nu-arc FT32L (R) flip-top platemaker 45 system. The imaging speed of the composition PI-3 was equipped with a 4000 watt pulsed Xenon lamp. After between 1.5 times and 2.0 times faster than the imaging exposure the sample was baked for 10 minutes at 70° C. speed of PI-1 and faster by an even greater amount than and spray developed for two minutes. Development P-2. & was undertaken using 1,1,1-trichloroethane as a devel This result demonstrates that the combination of an oper. Response was measured in terms of the number of 50 electron acceptor activator, such Activator A, and an stepped exposure areas (steps) in which the photoresist electron donor activator, such as Activator B, in a pho was retained following exposure. For example, a sample tographic imaging system in combination with a dye which was retained following exposure and develop photosensiter produces a synergistic initiator System ment on 10 steps, but was absent from the remaining that unexpectedly increases imaging response. four steps was assigned a step rating of 10. If partial 55 EXAMPLE 2 retention of the photoresist was observed on the elev enth step, this was indicated by assigning a plus ratin Control 3 g-i.e., 10--. On the other hand, where the photoresist A photographic imaging system PI-4 was prepared retention was deemed just barely adequate to merit the and tested similarly as PI-1, except that Photosensitizer Step rating, this was indicated by assigning a minus 60 B, 1,1'-diphenylbenzoxazolocarbocyanine iodide, was rating-i.e., 10-. substituted for Photosensitizer A. The dye exhibited an PI-1 exhibited a step rating of 10. absorption peak of 499 nm. Since PI-4 without Photosensitizer B responds to Control. 2 ultraviolet exposures, shorter wavelengths were re Control 1 was repeated as described, except that the 65 moved during exposure using a W-2A Wratten (R) filter concentration Activator A was doubled. No observable capable of filtering 99.9 percent of radiation of less than increase in speed was observed. 400 nm in wavelength. 4,859,572 27 28 membered heterocyclic rings having up to three Control 4 heteroatoms selected from the group consisting of Another imaging composition PI-5 was prepared oxygen, nitrogen, and a middle chalcogen chosen identical to PI-4, but with Activator B substituted for from the group consisting of sulfur, selenium, and Activator A. PI-4 was clearly inferior to PI-3 in its tellurium, and, image response. as a photosensitizer, a dye capable of absorbing imag ing radiation to achieve an excited state, said dye EXAMPLE 2 having a reduction potential more cathodic, equal An additional imaging composition PI-5 was pre to, or up to 0.1 volt less cathodic than that of the pared identical to PI-4, but with Activator B added. 10 electron acceptor activator and an oxidation poten That is, this imaging composition contained Activator tial more anodic, equal to, or up to 0.1 volt less A, Activator B, and Photosensitizer B. The imaging anodic than that of the electron donor activator. speed of the composition PI-5 was between 1.7 times 2. A photographic imaging system according to claim and 2.2 times faster than the imaging speed of PI-3 and 1 in which said hardenable organic component is com faster by an even greater amount than PI-4. 15 prised of at least one addition polymerizable ethyleni This result further demonstrates that the combination cally unsaturated compound having a boiling point of an electron acceptor activator, such Activator A, and above 100° C. at normal pressure. an electron donor activator, such as Activator B, in a 3. A photographic imaging system according to claim photographic imaging system in combination with a dye 2 in which said polymerizable ethylenically unsaturated photosensiter produces a synergistic initiator system 20 compound is a monomer. that unexpectedly increases imaging response. 4. A photographic imaging system according to claim The invention has been described in detail with par 2 in which said polymerizable ethylenically unsaturated ticular reference to preferred embodiments thereof, but compound is an oligomer. it will be understood that variations and modifications 5. A photographic imaging system according to claim can be effected within the spirit and scope of the inven 25 2 in which said polymerizable ethylenically unsaturated tion. compound is a crosslinkable polymer. What is claimed is: 6. A photographic imaging system according to claim 1. A photographic imaging system comprised of 1 in which said photosensitizer exhibits a reduction a hardenable organic component containing ethyl potential that is more cathodic than the reduction po enic unsaturation sites and 30 tential of said electron acceptor activator. an initiator system for ethylenic addition comprised 7. A photographic imaging system according to claim of an activator pair and a photosensitizer consisting 1 in which said photosensitizer exhibits an oxidation of potential that is more anodic than the oxidation poten a cationic onium electron acceptor activator chosen tial of said electron donor activator. from the class of activators that liberate a free radi 35 8. A photographic imaging system according to claim cal capable of initiating ethylenic addition by ac 1 in which said photosensitizer is a rhodamine, anthra cepting an electron from a photosensitizer in its cene, azo, aniline, or acridine dye. excited state, 9. A photographic imaging system according to claim an electron donor activator chosen from the class of 1 in which said photosensitizer is a polymethine dye. activators that liberate a free radical capable of 40 10. A photographic imaging system according to initiating ethylenic addition by donating an elec claim 9 in which said photosensitizer is a cyanine, mero tron to a photosensitizer in its excited state, said cyanine, oxonol, hemioxonol, styryl, merostyryl, or electron donor activator including aborate anionic streptocyanine dye. moiety that satisfies the formula: 11. A photographic imaging system according to 45 claim 1 in which said photosensitizer is a subtractive primary dye. Rl 12. A photographic imaging system according to claim 1 additionally including an imaging dye or a pre R^ Yr cursor thereof. 50 13. A photographic imaging system according to where claim 2 in which said imaging dye is an additive or R, R2, R3, and R4 are independently selected from subtractive primary dye. the group consisting of alkyl of from 1 to 18 carbon 14. A photographic imaging system according to atoms, aryl of from 6 to 18 carbon atoms, allyl, claim 1 in which said electron acceptor activator is an aralkyl in the aryl moiety contains from 6 to 18 55 azinium salt activator. carbon atoms and the alkyl moiety contains 1 to 5 15. A photographic imaging system according to carbon atoms, alkenyl of from 2 to 10 carbon claim 14 in which said azinium salt activator is an N atoms, alkynyl of from 2 to 18 carbon atoms, cyclo alkoxypyridinium salt. alkyl of from 5 to 7 carbon atoms, and 5 and 6 k k t sk xx 60

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