CA1284740C - Photosensitive materials containing ionic dye compounds as initiators - Google Patents

Abstract

Abstract of the Disclosure A photohardenable composition comprising a free radical addition polymerizable or crosslinkable compound and an ionic dye counter ion compound, said compound being capable of absorbing actinic radiation and producing free radicals which initiate free radical polymerization or crosslinking of said compound; and photosensitive materials incorporating the same.

Description

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P~OTOS ENS I T I VE MATERIALS
CONTA}NING IONIC DYE COMPOUNDS AS INITIATORS

Back~round of ~he Invention The present invention relates to noYel photohardenable compositions and to photosensitive materials employing them. More particularly, it relates to free radical ad~ition polymerizable compositions containing an ionic dye-counter ion complex such as a ca~ionic dye-borate anion complex or an anionic dye-iodonium ion complex as a photoinitiator.
~.S. Patents 4,399,20g and 4,440,84S to The Mead Corporation desctibe imaging materials and imaging processes in which amages are formed through exposure controlled release of an image-~orming agent from a microcapsule containing a photohardenable composition.
The imaging ~aterial is exposed image-wise to actinic radiation and ~ubjected ~o a uniform rupturing force.
Typically the image-forming agent i~ a color precursor which is released image-wise from the microcapsules whereupon it reacts wi~h a developer to form a visible i~age.
One of ~the problems which has ~een encoun~ered in designing commercially accep~able panchromatic, ~ull color imaging materials employing these ~echniques has been the relatively short wavelengths band to which most ~' .

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photohardenable compositions ~re 6ensitive to actinic radiation. In most cases, the compositions are only sensitive to ultraviolet radiation or blue light, e.g., 350 to ~80 n~.
Full color pho~osensi~ive materials ~re described in U.S. Patent No. a,842,976, issued June 27, 1989, an~ ~I,S. Paten~ Mo. a,57~,8~1, issued March 1~, 1~86. ~)ese imaging materials include a photosens~tive laye~ which contains three sets of microcapsules. Each set of microcapsules is sensitive to a different band ~f radiation in the ultraviolet or blue spectrum and contains a cyan, ~agenta or yellow image-forming agen~. The absorption spectra o~ the initiators employed in t~ese microcapsules are never perfectly distinct. ~here is always some degree of overlap in the absorption curves and sometimes it is ~ubstantial. Exposure conditions therefore must be controlled carefully to avoid cross-exposure.
It would be desirable to extend the sensitivi~y of the photohardenable compositions used in these imaging materials to longer wav21engths. By extending the sensitivity o~ the photohardenable compositions to longer wavelengths, the amount of overlap in ~he absorption spectra of ~he initiators and the concommitant incidence of cross-ex~osure can be reduced~ It would be particularly desirable if compositions could be designed with sensitivities to selected wavelength bands throughout the visible ~pectrum (~00 to 700 nm) since thi~ would provide a visible light-sensitive material which could be exposed by direct re~lection or transmission imaging and withou~ i~age processing.

Summary of the Invention It has been found that ionic dye-counter ion compounds, such as cationic dye-borate anion compounds, ~re useful photoinitiators of free radical addition reactions. Such compounds consist of a visible light absorber (the ionic dye) ionically bonded to a reac~ive counter ion. The coun~er ion is reactive in the sense that upon excitation of ~he dye the counter ion donates an electron to or accepts an electron from the excited dye.
This electron transfer process generates radicals capable of initiating polymerization of a monomer.
The mechanism whereby the compounds absorb energy - and generate free radicals is not entirely clear. It is believed that upon exposure to actinic radiation, the dye ion is excited to a singlet state in which it accepts an electron from or donates an electron to the counter ion.
For a cationic dye borate anion compound, this can be illustrated by the following equation:

BR4 D+ ~ D + BR4.

The lifetime of the dye singlet state is extremely short by comparison to the lifetime of the triplet state. The quenching rate constants which have been observed suggest that the ionic compounds experience a very efficient electron transfer via the singlet state.
In solution in the polymerizable compound, tight ionic pairing of the counter ion and the dye is believed to provide favorable spacial dis~ribution promoting electron transfer to ~uch an extent that the transfer occur~ even ~8~

MDX l88 P2 -4-though the lifetime of the singlet sta~e is very short.
Of course, t~is does not mean that electron transfer is restricted to the singlet state. Ionic dyes which have siynificant populations of triple~ state may undergo electron transfer ~hrough the singlet state, triplet state, or both singlet and triplet states.
Upon transfer of the electron, a radical is formed. The ionic compounds used as initiators in the present invention do not appear to exhibit back electron transfer. It is believed ~hat following electron transfer, the dye and counter ion become disassociated such that back electron transfer does not occur.
The ionic compounds used in the present inven~ion are different than the collision generated species encountered in other photosensitive systems such as collision complexes which yield encounter complexes, exciplexes and/or contact ion pairs. See for example, Ravarnos, George J. and Turrol Nicholas J., ~Photosensitization by Reversible Electzon Transfer~, Chem. Rev. 1986, 40l-449.
In accordance with the present invention the ionic dye and the counter ion are present in the photo~olymerizable composition as a stable, non-transient compound, and not as a dissociated ion pair. Formation of the compound is not dependent upon diffusion and collision. As distinguished from photographic materials and compositions containing collision dependent complexes essentially all of the sensitizing dye present in the photosensitive materials of the present invention prior to exposure is ionically bonded to the the counter ion.
The ionic compounds used as initiators in the present invention can also be characterized in that they are soluble in nonpolar solvents such as TMPTA and the like. They are soluble in an amount of at least about 0.1% and perferably at least about 0.3%. While these amounts are not large, they are substantial considering the normally lower solublity of ionic materials in polar solvents. While the compounds are soluble, the dye and the counter ion do not dissociate in solution. They remain ionically bonded to each other.
In dye-sensitized photopolymerizable compositions, visible light is absorbed by a dye having a comparable absorption band, the dye is raised to its excited electronic state, the lifetime of which may be 10 9 to 10-3 second, depending upon the nature (singlet or triplet) of the excited state. During this time, absorbed energy in the form of an electron must be transferred to or from the dye molecule to produce the free radical. In prior initiator systems, this ~ransfer is diffusion controlled. The excited dye must interact (collide) with another molecule in the composition which quenches the dye and generates a free radical. In ~he present invention, the transfer is not diffusion (collision~ controlled. Electron transfer occurs a~
greater than diffusion controlled rates. In terms of Stern-Volmer kinetics, this means the quenching constant (Kq) of the excited dye is greater than 101 and, more particularly, greater than 1012 have been observed for the ionic compounds. A~ these rates, electron transfer can occur through the singlet state.
Thus, the present invention provides a means for generating free radicals from the excited state of an ionic dye and insodoing provides photohardenable compositions which are sensitive at longer wavelengths~

One of the particular advantages of using ionic dye-counter ion compounds as initiators of free radical addition reactions is the ability to select from a wide variety of dyes which absorb at substantially different wavelengths. The absorption characteristics of the compound are principally determined by the dye. Thus, by selecting a dye which absorbs at 400 nm or greater, the sensitivity of the photosensitive material can be extended well into the visible range. Furthermore, compounds can be selected which are respectively sensitive to red, green and blue light without substantial cross-talk.
The ionic dye-counter ion compounds are particularly useful in providing $ull color photosensitive materials. In these materials, a layer including three sets of microcapsules having distinct sensitivity charac~eristics is provided on a support. Each set of microcapsules respectively contains a cyan, magenta, and yellow color-forming agent.
The absorption characteristics of the three sets of microcapsules in a full color photosensitive material must be sufficiently different that the cyan-forming capsules can be differentially hardened at a predetermined wavelength or over a predetermined wavelength range without hardening the magenta or yellow-forming capsules and, likewise~ the magenta~forming and yellow-forming capsules can be selectively hardened upon exposure respectively to second and third wavelengths without hardening the cyan-forming capsules or hardening the other of the yellow-forming or magenta-forming -~;~8~
MDX l8~ P2 -7-capsules. Microcapsules ~aving ~his characteristic (i.e., cyan-, magenta- and yellow-~orming capsules which can be selectively hardened by exposure at distinct wavelengths without cross-exposure) are referred to herein as having ~distinctly different sensitivities. a As indicated above, because most photohardenable compositions are sensitive to ultraviolet radiation or blue light and they tend not to be sensitive to wavelengths greater than about 480 nm, it has been difficult to achieve microcapsules having distinct sensitivities at three wavelengtbs. Often it can only be achieved by carefully adjusting the exposure amounts so as not to cross-expose the capsules.
The present invention facilitates the achievement of distinct sensitivities by shi~ting the peak absorption of at least one of the initiators to higher wavelengths, such as wavelengths greater ~han about 400 nm. In this manner~ instead of attempting to establish distinct - sensi~ivities at three wavelengths within the narrow wavelength range of, for example, 350 nm to 480 nm, sensitivity can be established over a broader range of, for example, 350 to 550 nm or higher. In accordance with the invention, the sensitivity of the microcapsules can be extended well into the visible spectrum to 600 nm and in some cases to about 700 nm. In the preferred case compounds are provided which are respectively sensitive to red, green and blue light.
A principal object of the present invention is to provide photohardenable compositions which are sensitive to visible light, e.g., wavelengths greater than about 400 nm.

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A further object of ~he present invention i~ to provide visible light-sensitive photohardenable compositions which are useful in the imaging materials described in U.S. Patents ~,399,209 and 4,~40,846.
Another object of the present invention is to provide photohardenable compositions which are sensitive at greater than about 400 nm and which are useful as photoresists or in forming polymer images.
These and other objects are accomplished in accordance with the present invention which, in one embodiment, provides:
A photohardenable composition comprising a free radical addition polymerizable or crosslinkable compound and a ionic dye-counter ion compound, said ionic dye-counter ion compound being capable of absorbing actinic radiation and producing free radicals which initiate free radical addition polymerization or crosslinking of said addition polymerizable or crosslinkable compound.
Another embodiment of the present invention resides in a photosensitive material comprising a support having a layer of photosensitive microcapsules on the surface thereof, said microcapsules containing an internal phase including a photohardenable composition comprising a free radical addition polymerizable or crosslinkable compound and a an ionic dye-counter ion compound.
Still another embodiment of the present invention resides in a photosensitive material useful in forming full color images comprising a support having a layer of photosensitive microcapsules on the surface thereof, said . .~

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photosensitive microcapsules comprising a first set of microcapsules having a cyan image-forming agent associa~ed therewith, a second set of microcapsules having a magenta image-forming agent associa~ed therewith, and a third set of microcapsules having a yellow image-forming ayent associated therewith, at least one of said first, second, and third sets of microcapsules containing an internal phase which includes a photohardenable composition including a free radical addition polymerizable or crosslinkable compound and an ionic dye-counter ion compound~
A further embodimen~ of the present invention resides in a photosensitive material comprising a support having a layer of a photohardenable composition on the surface thereof, said photohardenable composition comprising a free radical addition polymeriæable or crosslinkable compound and an ionic dye-counter ion compound which provides a quenching constant (~q) which is greater than lolO and preferably greater than 10~
In accordance with more particular embodiments of the invention, the ionic compound is a cationic dye-borate anion compound and still more particularly a cyanine dye-borate anion compound or an anionic dye compound such as ionic compounds of xanthene dyes with iodonium or pyryllium ions.

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Det~iled Description of the Invention Cati~nic dye-borate anion compounds ~re known in the art. Their preparation and use in imaging systems is described .in U.S. Patents 3,567,453; 4,307,1B2; 4,343,8gl;
S 4,447,521; and 4,45~,227. The ~ompounds used in the present invention can be represented by ~he general formula !I)~

~ ~R4 ~I) R2~ ~ R3 where D~ is a ca~ionic dye; and Rl, R2, R3, and R4 are indepen~ently selected from the group consisting of alkyl, aryl, alkaryl, allyl, aralkyl, alkenyl, alkynyl, alicyclic ~nd saturated or unsaturated heterocyclic groups.
Useful dyes form photoreducible but dark stable complexes with borate anions and can be cationic methine, polymethine, ~riarylmethane, indoline, thiazine, ~anthene, oxazine and acridine dyes. ~ore specifically, ~he dyes may be cationic cyanine, carbocyanine, hemicyanine/
rhodamine and azomethine dyes. In addition to being cationic, the dyes should not contain ~roups which would neutlalize or desensitize the complex or render the complex poorly ~ark stable. Examples of groups which generally ~hould not be present in the dye are acid groups such as free carboxylic or ~ulphonic acid groups.

Specific examples of useful cationic dyes are Methylene Blue, Safranine 0, Malachite Green, cyanine dyes of the general for~ula (II) and rhodamine dyes of the formula (III):

5 ~ ~/ ~ ' ~
1 ~ (II) n = O, 1, 2, 3, R = alkyl Y = CH=C~, N-CH3, C(CH3)2, O, ~, Se co,R' (III) ~0 R', R = alkyl, aryl, and any combination thereof While they have not been tested, the cationic cyanine dyes disclosed in U.S. Pa~ent 3,495,9~7 should be useful in the present invention.
The borate anion is designed such that the borate radical generated upon exposure to light and after elec-tron transfer ~o the dye (Eq. 1) readily dissociates with the formation of a radical as follows:

BR4 _~ BR3 ~ R- (Eq. 2) ~'~8~7~

For example particularly preferred anions are triphenylbutylborate and trianisylbutylborate anions because they readily dissociate to triphenylborane or trianisylborane and a butyl radical. On the other hand tetrabutylborate anion does not work well presumably because the tetrabutylborate radical is not stable and it readily accepts an electron back from the dye in a back electron transfer and does not dissociate efficiently.
Likewise, tetraphenylborate anion is very poor because the phenyl radical is not easily formed.
Preferably, at least one but not more than three of Rl, R2, R3, and R4 is an alkyl group. Each of Rl, R2, R3, and R4 can contain up tc 20 carbon atoms, and they typically contain 1 to 7 carbon atoms.
More preferably Rl-R4 are a combination of alkyl group(s~ and aryl group(s) or aralkyl group(s~ and still more preferably a combination of three aryl groups and one alkyl group.
Representative examples of alkyl groups repre-sented by Rl-R4 are methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl, stearyl, etc. The alkyl group~ may be substituted, for example, by one or more halogen, cyano, acyloxy, acyl, alkoxy or hydroxy groups.
Representative examples of aryl groups repre-sented by Rl-R4 include phenyl, naphthyl and substi-tuted aryl groups such as anisyl. Alkaryl groups include methylphenyl, dimethylphenyl, etc. Representative examples of aralkyl groups represented by Rl-R4 groups include benzyl. Representative alicyclic groups include cyclobutyl~ cyclopentyl, and cyclohexyl groups~ Examples -~Z~7~

of an alkynyl group are propynyl and ethynyl, and examples of alkenyl groups include a vinyl group.
As a general rule, useful ionic dye compounds must be identified empirically, however, potentially useful dye and counter ion combinations can be identified by reference to the Weller equa- tion (Rehm, D. and Weller, A., Isr. J Chem. ~1970), 8, 259-271), which can be simplified as follows.

~G = EOx-Ered E~' ~Eq. 3) where G is the change in the Gibbs free energy, EoX is the oxidation potential of the borate anion B~4, Ered is the reduction potential of the cationic dye, and Eh ~ is the energy of light used to excite the dye.
Useful compounds will have a negative free energy change.
Similarly, the difference between the reduction potential of the dye and the oxidation potential of the borate must be negative for the compounds to be dark stable, i.e., Eox - Ered > O.
As indicated, E~. 2 is a simplification and it does not absolutely predict whether a compound will be useful in the present invention or not. There are a number of othex factors which will influence this determination. One such factor is the effect of the monomer on the complex. Another factor is the radial distance between the ions. It is also known that if the Weller equation produces too negative a value, deviations from the equation are possible. Furthermore~ the Weller equation only predicts electron transfer, it does not ~'Z8~

predict whether a particulae dye complex is an efficient initiator of polymerization. The equation is a useful first approximation.
Specific examples of cationic dye-borate anion compounds useful in the present invention are shown in the following table with their ~ max.

~2~
hl)X 188 P2 14A--- Table Compound No. Structure ~\ ma~ (TMPTA) 1. ~ 5 5 2 nm C ~ ~2~3 Ph3~ H~

2. 0~5 5~0 568 nm 4~15 ~ 4N15 Ph3~ 4H~

3 0~0 ~ 4 92 nm ~C6H13 1l-S6Hl3 4 C~ sx~ 428 nm 3 a 3 Ph3~ R-C,~Hg ,o~ N ~ 658 nm (CH~ )~ 5, 11(Q'3)2 . ~.
Ph38 V ~-~C4Hg 6. a~3 X~ N ~,CN 528 rlm ~H2 N~112 ~h3~ 6~C~Hg ~ Z 8 ~

s NO ~ I ~ ~50nm H3CN2~ U12C~3 Ar3B-R ' No. R' Ar 7A n-butyl phenyl 7~ n~hs%yl phenyl 7C n butyl anlsyl B. 55Onm R . R

Ar3_B_R~

No. ' R ~r 8A methyl n-~utyl phenyl 8B methyl n-hexyl phenyl 8C n-butyl n-~utyl phenyl 8~ n ~utyl n-~xyl ph~nyl 8E n-heptyl n-butyl phenyl 8~ n-hep~yl n-hexyl phenyl 8G ethyl n-butyl phenyl ~28~7~
MDX lB8 P2 -16-9- ~ ~ ~ 570 nm Sys~em ~1* C~
( 3 ~ 4 9 10. ~ ~ ~ 590 nm System (~ ~ C

11. ~ 640nm R A~ 3~!- ~ ' ~

. No~ R R'` Ar llA methyl n-butyl phenyl llB methyl n-hexyl phenyl llC n-butyl n-butyl phenyl llD n-butyl n-hexyl phenyl llE n-pentyl n-butyl phenyl llF n-pentyl n-hexyl phenyl llG n-heptyl n-butyl phenyl llH n-heptyl n-hexyl phenyl 11I methyl n-butyl anisyl ~3 ~3 a33 740 nm System (~3~3 C4~9 .. . . .

~q~8~7~Ln The cationic dye-borate anion compounds can be prepared by reacting a borate salt with a dye in a coun-terion exchange in a known manner. See Hishiki, Y., Repts. Scio Research Inst. (1953), 29, pp 72-79. Useful bora~e sal~s are sodium salts sucb as sodium tetraphenyl-borate, sodium triphenylbutylborate, sodium trianisyl-butylborate and ammonium salts such as tetra0thylammonium tetraphenylborate.
Anionic dye compounds are also useful in the present invention. Anionic dye-iodonium ion compounds of the formula ¦IV):

IR5-I-R~]n D~n (IV) where D- is an anionic dye and R5 and R6 are independently selected from the group consisting of aromatic nucleii such as phenyl or naphthyl and n is 1 or 2; and anionic dye~pyryllium compounds of the formula (V):
D-n L~ n (V) where D- and n are as defined above are typical examples of anionic dye complexes.
Representative examples of anionic dyes include xanthene and oxonols. In addition to iodonium and pyryllium ions) other compounds of anionic dyes and sulfonium cations are potentially useful.

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As in the case of the cationic dye compounds, usef ul dye-cation combinations can be identif ied through the Weller equation as having a negative free energy.
Selected examples o~ anionic dye rompounds are shown in Table 2 ~ max. ca. 570 nm in TMPTA).

~2~
~DX 1~8 P2 -lg-Tabl e 2 ~a ~6, ` o~ ,~.

(~I

C ~0~ 0 ~Z8~74~
MD% 188 P2 -20-The most typical exa~ples of a free radical addition polymerizable or crosslinkable compound useful in the present invention is an ethylenically unsaturated com-pound and, more specifically/ a polyethylenically unsatu-rated compound. These compounds include bo~h monomers having one or more ethylenically unsaturated groups, such as vinyl or allyl groups, and polymers having terminal or pendant ethylenic unsaturation. Such compounds are well known in the art and include acrylic and methacrylic tO esters of polyhydric alcohols such as trimethylolpropane, pentaerythri~ol, and the like; and acrylate or methacry-late terminated epoxy resins, acrylate or methacrylate terminated polyesters, etc. RepresentatiVe examples include ethylene glycol diacrylate, ethylene glycol dimethacrylate, trimethylolpropane triacrylate (TMPTA), pentaerythritol tetraacrylate, pentaerythritol tetra-methacrylate, dipentaerythritol hydroxypentacrylate (DPHPA), hexanediol-1,6-dimethacrylate, and diethyl-eneglycol dimethacrylate.
The ionic dye compound is usually used in an amount up to about 1% by weight based on the weight of the photopolymerizable or crosslinkable species in the photohardenable composition. More typically, the compound is used in an amount of about 0.2~ to O.S~ by weight.
While the compound can be used alone as the initiator, film speeds tend to be quite low and oxygen inhibition is observed. It has been found that it is preferable to use the compound in combination with an autoxidizer. ~n autoxidizer is a compound which is capable of consuming oxygen in a free radical chain process.

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Examples of useful autoxidizers are N,~-dialkylanilines. Examples of preferred N,N-dialkylanilines are dialkylanilines substituted in one or more of the ortho-, meta-, or ~ - position by the following group~: methyl, ethyl, isopropyl~ t-butyl~
3,4-tetramethylene, phenyl, trifluoromethyll acetyl, ethoxycarbonyl, carboxy, carboxylate, trimethylsilymethyl, trimethylsilyl, triethylsilyl, trimethylgermanyl, triethylgermanyl, trimethylstannyl, triethylstannyl, n-butoxy, n-pentyloxy, phenoxy, hydroxy, acetyl-oxy, methylthio, ethylthio, isopropylthio, thio-(mercapto-), acetylthio, fluoro, chloro, bromo and iodo.
Representative examples of N,N-dialkylanilines useful in the present invention are 4-cyano-Nr N-dimethyl-aniline, 4-acetyl-N,N-dimethylaniline, 4-bromo-N, N-dimethylaniline, ethyl 4-(N,N-dimethylamino) benzoate, 3-chloro-N,N-dimethylaniline, 4-chloro-N,N-dimethylaniline, 3-ethoxy-N,N-dimethylaniline, 4-fluoro-N,N-dimethylaniline, 4-methyl-N,N-dimethylaniline, 4-ethoxy-N,N-dimethylaniline, N,N-dimethylthioanicidine, 4-amino- N,N-dimethylaniline, 3-hydroxy-N,N-dimethylaniline, N,N,N',N'-tetramethyl-1,4-dianiline, 4-acetamido-N, N-dimethylaniline, etc.
Preferred N,N-dialkylanilines are substituted with an alkyl group in the ortho-position and include 2,6-diisopropyl-N,N-dimethylaniline, 2,6-diethyl-N,N-dimethyl-aniline, ~,N,2,4,6-pentamethylaniline (PMA) and p~t-butyl-N,N-dimethylaniline.
The autoxidizers are preferably used in the present invention in concentrations of about 4-5% by weight.

:, .:. , 8 ~7 The photohardenable composi~ions o~ the present invention c~n be coated upon a ~upport in a conYentional manner and used as a photoresist ~r in ph~tolithography to form a polymer image or they can be encapsulated as ~escribed in U.S. Paten~s 4,399,209 and ~,~40,846 and used to control the release of ~n image-forming agent. The latter processes typically involve image-wise exposing the photosensitive ma~erial to actinic radia~ion and subjecting the layer of ~icrocapsules to a uniform rupturing force such as pressure, abrasion, or ultrasonic energy whereupon the image-forming agent is released from ~he microcapsules for reaction with a developer.
Several processes can be used to form color images as explained in U.~. Patent ~,842,~76, issued July 27, 1989. If the microcapsules contain photosensitive compositions which lS are sensitive to red, green and blue light, images can be formed by direct transmission or reflection imaging or by image processing. Image processing may involve forming color ~eparations (color-seps) corresponding to the red, green and blue component images and sequen~ially exposing the photosensitive ~aterial ~o three distinct bands of radiation hereinaf~er designated ~ -2, and ~ -3 through each color separation. ~therwise, it may involve electronic processing in which the image or subject to be recorded i~ view~d through a Dunn or matrix camera and ~he output ~rom the camera electronically ~rives three exposure ~ources corresponding to ~ -2, And ~-3.
Alternatively, the image may be produced synthetically, e.g., a computer-generated image.

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While the discussion herein relates to forming 3-color full color images, 4-color images are also possible. For example, microcapsules containing cyan, mayneta, yellow, an~ black image-forming agen~s can be provided which have distinct sensitivities at four wavelengths, e.g., A -1, /\-~ 3, and A-4.
In accordance with the invention, at least one set of the microcapsules in a full color system contains an ionic dye compound. The other sets also may contain an ionic dye compound, or they may contain a different type of photoinitiator.
In accordance with the preferred embodiments of the invention, a full color imaging system is provided in which the microcapsules are sensitive to red, green, and blue light respectively. The photosensitive composition in at least one and possibly all three microcapsules are sensitized by an ionic dye compound. For optimum color balance, the microcapsules are sensitive (~ max) at about 450 nm, 550 nm, and 650 mn, respectively. Such a system is useful with visible ligbt sources in direct transmission or reflection imaging. Such a material is useful in making contact prints or projected prints of color photographic slides. They are also useful in electronic imaging using lasers or pencil light sources of appropriate wavelengths.
Because the ionic dye compounds absorb at wavelengths greater than 400 nm, they are colored.
Typically, the unexposed dye compound is present with the image-forming agent in the image areas and, thus~ the color of the compound must be considered in determining the color of the image. However, the compound is used in very small ~28~74L~

amoun~s compared to the image-forming agent and exposure sometimes bleaches the compound.
The photohardenable compositions of the present invention can be encapsulated in various wall formers using techniques known in the area o~ carbonless paper including coacervation, interfacial polymerization, polymerization of one or more monomers in an oil, as well as various melting/
dispersing, and cooling methods. To achieve maximum sensi-tivities, it is important that an encapsulation technique be used which provides high quality capsules which are responsive to changes in the internal phase viscosity in terms of their ability to rupture. Because the borate tends to be acid sensitive, encapsulation procedures conducted at hiyher pH ~e.~.~ greater than about 67 are lS preferred.
Oil soluble materials have been encapsulated in hydrophilic wall-forming materials such as gelatin-type materials (see U.S. Patent Nos. 2,730,456 and 2,800,457 to Green et al) including gum arabic, polyvinyl alcohol, carboxy-me~hylcellulose; resorcinol-formaldehyde wall formers (see U.S. Patent No. 3,755,190 to ~art, et al):
isocyanate wall-formers (see U.S. Patent ~o. 3,914,511 to Vassiliades) isocyanate-polyol wall-formers (see U.S.
Patent No. 3,796,669 to Ririntani et al), urea-formaldehyde wall-formers, particularly urea-resorcinol-formaldehyde in which oleophilicity is enhanced by the addition of resorci-nol tsee U.S. Patent Nos. 4~001,140; 4,087,376 and 4,089!802 to Foris et al) and melamine-formaldehyde resin and hydroxypropyl cellulose (see commonly assigned U.S.
Patent No. 4,025,455 to Shackle).

Urea-resorcinol-formaldehyde and melamine-~ormaldehyde capsules with low oxygen permeability are preferred. In some cases to reduce oxygen permeability it is desirable to ~orm a double walled capsule by conducting encapsulation in two stages.
A capsule size sbould be selected which minimizes light attenuation. The mean diameter of the capsules used in this invention typically ranges from approx}mately 1 to 25 microns. As a general rule, image resolution improves as the capsule size decreases. If the capsules become too small, they may become inaccessible in ~he pores or the fiber of the substrate. These very small capsules may therefore be screened from exposure by the substrate~ They may also fail to rupture when exposed to pressure or other rupturing means. In view of these problems, it has been determined that a preferred mean capsule diameter range is from approximately 10 microns. Technically, however, the capsules can range in size up to the point where they become visible to the human eye.
An open phase system may also be used in accordance with the invention instead of an encapsulated one. This can be done by dispersing what would otherwise be the capsule contents throughout the coating on the substrate as discrete droplets. Suitable coatings for this embodiment include polymer binders whose viscosity has been adjusted to match the dispersion required in the coating.
Suitable binders are gelatin, polyvinyl alcohol, polyacrylamide, and acrylic lattices. Whenever reference is made to ~capsules" and ~encapsulation~ without reference to a discrete capsule wall in this specification or the ~28~

appended claims, those terms are intended to include the alternative of an open phase system.
The photosensitive material of the present inven-tion can be used to control the interaction of various image-forming agents.
In one embodiment of the present invention the capsules may contain a benign visible dye in the internal phase in which case images are formed by contacting the exposed imaging material under pressure with a plain paper or a paper treated to enhance its affinity for the visible dye. A benign dye is a colored dye which does not interfere with the imaging photochemistry, for example, by relaxing the excited state of the initiator or detrimen~ally absorbing or attenuating the exposure radiation.
In a preferred embodiment of the invention, images are formed through the reaction of a pair of chromogenic materials such as a color precursor and a color developer, either of which may be encapsulated with the photohardenable compos.ition and function as the image forming agen~. In general, these materials include colorless electron dona~ing type compounds and are well known in the art. Representative examples of such color formers include substantially colorless compounds having in their partial skeleton a lactone~ a lactam, a sultone, a spiropyran, an ester or an amido structure such as triarylmethane compounds, bisphenylmethane co~pounds, xanthene compounds, fluorans, thiazine compounds, spiropyran compounds and the like. Crystal Violet Lactone and Copikem X, IV and XI are often used. The color formers can be used alone or in combination.

' The developer materials conventionally employed in carbonless paper technology are also useul in the present invention. Illustrative examples are clay minerals such as acid clay, active clay, attapulgite, etc~ organic acids such as tannic acid, gallic acid, propyl gallate, etc.;
acid polymers such as phenol-formaldehyde resins, phenol acetylene condensation resins, condensates between an organic carboxylic acid having at least one hydroxy group and formaldehyde, etc.; metal salts or aromatic carboxylic acids such as zinc salicylate, tin salicylate, zinc 2-hydroxy naphthoate, zinc 3,5 di-tert butyl salicylate~
zinc 3,5-di~ methylbenzyl)salicylate, oil soluble metal salts or phenol-formaldehyde novolak resins (e.g., see U.S.
Patent Nos. 3,672,935; 3,732,120 and 3,737,410) such as zinc modified oil soluble phenol-formaldehyde resin as disclosed in ~.S. Patent No. 3,732,12n, zinc carbonate etc.
and mixtures thereof.
As indicated in U.S. Patents 4,3g9,209 and 4,440,846, the developer may be present on the photo-sensitive sheet (providing a so-called self-contained system) or on a separate developer sheet.
In self-contained systems, the developer may be provided in a single layer underlying the microcapsules as disclosed in ~.S. Patent No. 4,440,846. Alternatively, the color former and the color developer may be individually encapsulated in photosensitive capsules and upon exposure both capsule sets image-wise rupture releasing color former and developer which mix to form the image. Alternatively, the developer can be encapsulated in non-photosensitive capsules such that upon processing all developer capsules rupture and release developer but ~he color former containing capsules rupture in only the unexposed or under-exposed area which are the only areas where the color former and developer mix. Still another alternative is to encapsulate the developer in photosensitive capsules and the color former in non-photosensitive capsules.
The present invention is not necessarily limited to embodiments where the image-formlng agent is present in the internal phase. Rather, this agent may be present in the capsule wall of a discrete capsule or in the binder of an open phase system or in a binder or coating used in combination with discrete capsules or an open phase system designed such that the image-wise ruptured capsules release a solvent for the image-forming agent. Embodiments are also envisioned in which a dye or chromogenic material is fixed in a capsule wall or binder and is released by interaction with the internal phase upon rupturing the capsules.
The most common substrate or this invention is a transparent film since it assist in obtaining uniform development characteristics, however, paper may also be used. The paper may be a comrnercial impact raw stock, or special grade paper such as cast-coated paper or chrome-rolled paper. Transparent films such as polyethylene terephthalate can be used. Translucent substrates can also be used in this invention.
Synthesis Examples 1 and 2 respectively illustrate the preparation of borates and dye-borate compounds.

SY~THESIS ~XAMPLE 1 Dissolve triphenylborane in 150 ml dry benzene (lM) under nitrogen atmosphere. Place flask in a cool water bath and, while stirring, add n-BuLi, ~1~1 eg.) via syringe. A white precipitat~ soon formed after addition was s~arted. Stirring is continued about 45-60 min.
Dilute with 100 ml hexane ancl filter, washing with hexane.
Thi~ resultant Li salt is slightly air unstable. Dissolve the white powder in about 200 ml distilled water and, with vigorous stirring, add aqueous solu~ion of tetramethyl ammonium chloride ~1.2 eg. of theoretical in 200 ml). A
thick white precipitate forms. Stir this aqueous mixture about 30 min. at room temperature, then filter. Wash collected white solid with distilled water.
As an alternative synthesis, to a l.OM solution of 2.0 equivalents of l-butene in dry, oxygen-free dichlor~methane, under inert atomosphere, was added slowly dropwise with stirring, 1.0 equivalents of a lnOM solution of dibromethane-methylsulfide complex in dichloromethane.
The reaction mixture stirred at reflux for 36 hours and the dichloromethane and excess l-butene were removed by simple distillation. Vacuum distillation of the residue afforded 0.95 equivalents of a colorless mobile oil (Bp 66-7 0~35 mm Hg, ~BNMR;bs (4.83PPM~. ~nder inert atmosphere, ~his oil was dissolved in dry, oxygen-free tetrahydrofuran to give a l.OM solution and 3.0 equivalents of a 2.0M solution of phenylmagnesium chloride in tetrahydrofuran were added dropwise with stirring. After stirring 16 hours, ~he resultant solution was added slowly with vigorous stirriny to 2 equivalents of tetramethylammonium chloride, as a 0.2 ~2~3~7~

M solution, in water. The resulting white floccula~e solid was filtered and dried to afford a near quantitative amounk of t~e desired product Mp 250-2C, ~BNMR:bs ~-3.70PPM)~

Sonicate a suspension of a borate salt (1 g/10 ml) in MeO~, to make a very fine suspension. Protect flask from light by wrapping with aluminum foil then add 1 equivalent of dye. Stir this solution with low heat on a hot plate for about 30 min. Let cool to room temperature then dilute with 5-10 volumes of ice waterO Filter the resultant solid and wash with water un~il washings are colorless. Suction filter to dryness. Completely dry initiator compound by low heat (about 50C) in a vacuum drying oven. Initiator is usually formed quantitatively.
Analysis by H-NMR indicates 1:1 compound formation typically greater than 90%.
The present invention is illustrated in more detail by the following non-limiting Exampl~s.

Exam~le 1 Capsule Preparation 1. Into a 600 ml stainless steel beaker, 104 g water and 24.8 g isobutylene maleic anhydride copolymer (18%) are weighed.
2. The beaker is clamped in place on a hot plate under an overhead mixer. A six-bladed, 45 pi~ch~ turbine impeller is used on the mixer.

~Z~3~L7~0 3. After thoroughly mixing, 3.1 g pectin (polygalacturonic acid methyl ester) is slowly sif~ed into the beaker. This mixture is stirred for 20 minutes.
4. The pH is adjusted to 4.0 using a 20~ solution of H2SO4, and 0.1 g Quadrol (2-hydroxypropyl ethylenediamine with propylene oxide from BASF) is added.

5. The mixer is turned up to 3000 rpm and the internal phase is added over a period of 10-15 seconds.
Emulsification is continued for 10 minutes.

6. At the start of emulsification, the hot plate is turned up so heating continues during emulsification.

7. After 10 minutes, the mixing speed is reduced to 2000 rpm and 14.1 9 urea solution (50% w/w), 3~2 g resorcinol in 5 g water, 21.4 9 formaldehyde (37~), and 0.6 9 ammonium sulfate in 10 ml water are added at two-minute intervals.

8. The beaker is covered with foil and a heat gun is use~ to help bring the temperature of the preparation to 65C. When 65C is reached, the hot plate is adjusted to maintain this temperature for a two to three hour cure time during which ~he capsule walls are formed.

9. After curing~ the heat is turned off and the pH is adjusted to 9.0 using a 20~ NaO~ solution.

10. Dry sodium bisulfite (2.8 g) is added and the capsule preparation is cooled to room temperature.
Three batches of microcapsules were prepared for use in a full color imaging sheet using the three internal phase compositions set forth below. Internal Phase A
provides a yellow image-forming agent and is sensitive at 420 nm, Phase B provides a magenta image-forming agent and . . .

~2~3~7~) is 6ensitive at 480 nml and Phase C contains d cyan image-forming Agen~ and ~ cati~nic dye-bo~ate anion complex which is ~ensitive ~t 570 nm. ~he three bat~hes of microcapsules were mixed, coated on a support, and dried to provide a full color imaging ~heet.
Internal Phase A (420 nm) 3-Thenoyl-7-diethylamino coumarin15 g 2-Mercaptobenzoxazole ~BO) 2.0 g Pentamethylaniline (PM~) 1.0 9 Reakt Yellow (BAS~) 5.0 9 SF-5~ (Union Carbide Isocyanate)1.67 g N-10~ Desmodur Polyi~ocyanate Resin) 3.33 9 Internal Phase B (480 nm) ... . . .

DP~PA 15 9 9-(4'-Isopropylcinnamoyl)-1,2,4-te~rahydro-3~, 6~, lOH[l]-- benzopyrano[9, 9A,l-yllquinolazine-10-one 0.15 9 MBO 1.0 9 PMA 2.0 9 ~agenta Çolor Former ~D-5100~ilton Davis Chemical Co) 8.0 g SF-50 1.67 g N-100 3;33 9 Internal Phase C (570 nm) . .

Cationic Dye Compound No. 20.15 9 PMA 2.0 g Cyan Colo~ Pormer (S-29663~Hilton Davis Chemical Co.) 4.0 9 ~_50 1.67 g N-100 3.33 9 * Tx~de~ark ~., ~' ~

~Z8~

MDX 188 P~ -33~

Example 2 Capsule Preparation 1. Into a 600 ml stainless steel beakee, 110 g water and 4.6 9 isobutylene maleic anhydride copolymer (dry) are weighed.
2. The beaker is clamped in place on a hot plate under an overhead mixer. A six-bladed, 45 pitch~ turbine impeller is used on the mixer.
3. After thoroughly mixing, 490 9 pectin }0 (polygalacturonic acid methyl ester) is slowly sifted into the beaker. This mixture is stirred for 2 hours at room temperature (800-1200 rpm).
4. The pH is adjusted to 7.0 with 20~ sulfuric acid.
5. The mixer is turned up to 3000 rpm and the internal phase is added over a period of 10-15 seconds.
Emulsification is continued for 10 minutes. Magenta and yellow precursor phases are emulsified at 25-30C Cyan phase is emulsified at 45-50C (oil), 25-30~C (water).
6. At the start of emulsification, the hot plate is turned up so heating continues during emulsification.
7. After 10 minutes, the pH is adjusted to 8.25 with 20~ sodium carbo~ate, the mixing speed is reduced to 2000 rpm, and a solution of melamine-formaldehyde prepolymer is slowly added which is prepared by dispersing 3.9 g ~elamine in 44 g water, adding 605 g formaldehyde solution (37~) and heating at 60C until the solution clears plus 30 minutes.

.. . . .

~z~
MDX 18B P2 -34~

8. The pH is adjusted to 6.0, ~he beaker is covered with foil and placed in a water bath to bring the temperature of the preparation to 65C. When 65C is reached, the hot plate i5 adjuste~ ~o maintain this temperature for a two hour cure time during which the capsule walls are formed.
9. After curing, mixing speed is reduced to 600 rpm, formaldehyude scanvenger solution (7.7 g urea and 7.0 g water) is added and the solution was cured another 40 minutes.
10. The pH is adjusted to 9.5 using a 20~ NaOH
solution and stirred overnight at room temperature.
Three batches of microcapsules were prepared as above for use ~n a full color imaging sheet using the three internal phase compositions set forth below.

Yellow Forming Capsules (420 nm) DPHPA 15 g 3-Thenoyl-7-diethylamino coumarin15 9 2-Mercaptobenzoxazole (MBO) 2.0 9 2,6-Diisopropylaniline 1.0 g Reakt Yellow (BASF) 5.0 g N-lOO(Desmodur Polyisocyanate Resin) 3.33 9 Magenta Forming Capsules (550 nm)_ Compound 8A 0.2 9 2,6-Diisopropylaniline 2.0 9 HD51~0 (Magenta color precursor from ~ilton-Davis Chemical Co.) 12.0 9 8~

~yan ~ormin~ C~psules (S50 nm) TMPTA 50 g Compound 11 ~ 0.31 9 2,6-dii~opropylaniline~ 7.0 9 Cyan Precursor (CP-177 of ~ilton-Davis Chemical Co.)6 g The three batches of microcapsules were blended together and coated on a support to provide an imaging material in accordance with the present invention.
~aving described the invention in detail and by reference to preferred embodiments thereo, it will be apparent that ~odi~ications and variations are possible without departing from the ~cope of the invention defined in the appended claims.

* ~rade~mark ~''

Claims (37)

1. A photohardenable composition comprising a free radical addition polymerizable or crosslinkable compound and an ionic dye-reactive counter ion compound, said ionic dye-reactive counter ion compound being capable of absorbing actinic radiation and producing free radicals which initiate free radical polymerization or crosslinking of said polymerizable or crosslinkable compound and being a stable non-transient compound prior to exposure to said actinic radiation.

2. The photohardenable composition of claim 1 wherein said ionic dye-counter ion compound is soluble in said free radical addition polymerizable or crosslinkable compound.

3. The photohardenable composition of claim 1 wherein said ionic dye-counter ion compound is characterized in that following exposure of said compound to light, said dye is excited to a singlet state which is quenched by said counter ion.

4. The photohardenable composition of claim 3 wherein following exposure of said ionic dye-counter ion compound to light, an electron is transferred from said dye to said counter ion or from said counter ion to said dye and the rate of said electron transfer is greater than a diffusion controlled rate.

5. The photohardenable composition of claim 1 wherein said compound is an anionic dye compound.

6. The-photohardenable composition of claim 5 wherein said anionic dye is selected from the group consisting of xanthene and oxonol dyes.

7. The photohardenable composition of claim 1 wherein said polymerizable or crosslinkable compound is an ethylenically unsaturated compound.

8. The photohardenable composition of claim 5 wherein said ionic dye counter ion compound is an anionic dye-iodonium ion complex or an anionic dye-pyryllium ion complex.

9. The photohardenable composition of claim 8 wherein said dye is a xanthene dye.

10. A photosensitive material comprising a support having a layer of a photohardenable composition on the surface thereof, said composition comprising a free radical addition polymerizable or crosslinkable compound and an ionic dye-reactive counter ion compound, said ionic dye-reactive counter ion compound being capable of absorbing actinic radiation and producing free radicals which initiate free radical polymerization or crosslinking of said polymerizable or crosslinkable compound and being a stable non-transient compound prior to exposure to said actinic radiation.

11. The photosensitive material of claim 10 wherein said ionic dye-counter ion compound is soluble in said addition polymerization or crosslinkable compound.

12. The photosensitive material of claim 10 wherein said ionic dye-counter ion compound is further characterized in that following exposure of said compound to light, said dye is excited to a singlet state which is quenched by said counter ion.

13. The photosensitive material of claim 10 wherein following exposure of said ionic dye-counter ion compound to light, an electron is transferred from said dye to said counter ion or from said counter ion to said dye and the rate of said electron transfer is greater than a diffusion controlled rate.

14. The photosensitive material of claim 10 wherein said complex is an anionic dye complex.

15. The photosensitive material of claim 14 wherein said anionic dye is selected from the group consisting of xanthene and oxonol dyes.

16. The photosensitive material of claim 10 wherein said polymerizable or crosslinkable compound is an ethylenically unsaturated compound.

17. The photosensitive material of claim 14 wherein said ionic dye-counter ion compound is an anionic dye iodonium ion compound or an anionic dye pyryllium ion compound.

18. The photosensitive material of claim 17 wherein said dye is a xanthene.

19. A photosensitive material comprising a support having a layer of microcapsules on one surface thereof, said microcapsules having an image-forming agent associated therewith and containing an internal phase including a photohardenable composition, said composition comprising a free radical addition polymerizable or crosslinkable compound and an ionic dye-reactive counter ion compound, said ionic dye-reactive counter ion compound being capable of absorbing actinic radiation and producing free radicals which initiate free radical polymerization or crosslinking of said polymerizable or crosslinkable compound and being a stable non-transient compound prior to exposure to said actinic radiation.

20. The photosensitive material of claim 19 wherein said ionic dye-counter ion compound is soluble in said addition polymerizable or crosslinkable compound.

21. The photosensitive material of claim 19 wherein said ionic dye-counter ion compound is further characterized in that following exposure of said compound to light, said dye is excited to a singlet state which is quenched by said counter ion.

22. The photosensitive material of claim 19 wherein following exposure of said ionic dye-counter ion compound to light, an electron is transferred from said dye to said counter ion or from said counter ion to said dye and the rate of said electron transfer is greater than a diffusion controlled rate.

23. The photosensitive material of claim 19 wherein said ionic dye-counter ion compound is an anionic dye complex.

24. The photosensitive material of claim 23 wherein said anionic dye is selected from the group consisting of xanthene and oxonol dyes.

25. The photosensitive material of claim 19 wherein said polymerizable or crosslinkable compound is an ethylenically unsaturated compound.

26. The photosensitive material of claim 25 wherein said ionic dye-counter ion compound is an anionic dye-iodonium compound or an anionic dye pyryllium compound.

27. The photosensitive material of claim 26 wherein said image-forming agent is a substantially colorless chromogenic material.

28. The photosensitive material of claim 19 wherein said material is useful in forming full color images and said microcapsules include a first set of microcapsules having a cyan image-forming agent associated therewith, a second set of microcapsules having a magenta image-forming agent associated therewith and a third set of microcapsules having a yellow image-forming agent associated therewith, at least one of said first, second and third sets of microcapsules containing said photohardenable composition contain said ionic dye-counter ion compound,

29. The photosensitive material of claim 28 wherein said material is useful in forming images by a process which comprises the steps of image-wise exposing said microcapsules to three distinct wavelengths of actinic radiation which respectively harden said first, second and third sets of microcapsules and subjecting said microcapsules to a uniform rupturing force.

30. The photosensitive material of claim 29 wherein at least one of said wavelengths is greater than 400 nm.

31. The photosensitive material of claim 30 wherein said three distinct wavelengths are red, green and blue light.

32. The photohardenable composition of claim 1 wherein essentially all of said dye present in said composition is ionically bonded to said counter ion.

33. The photosensitive material of claim 10 wherein essentially all of said dye present in said composition is ionically bonded to said counter ion.

34. The photosensitive material of claim 19 wherein essentially all of said dye present in said composition is ionically bonded to said counter ion.

35. The photohardenable composition of claim 1 wherein said ionic dye-reactive counter ion compound is further characterized in that it is soluble in trimethyl-olpropane triacrylate in an amount of at least about 0.1%
by weight.

36. The photohardenable material of claim 10 wherein said ionic dye-reactive counter ion compound is further characterized in that it is soluble in trimethylolpropane triacrylate in an amount of at least about 0.1% by weight.

37. The photosensitive material of claim 19 wherein said ionic dye-reactive counter ion compound is further characterized in that it is soluble in trimethylolpropane triacrylate in an amount of at least about 0.1% by weight.