FIELD OF THE INVENTION
The invention is in the area of photopolymer compositions and photoimaging media (elements) and associated processes that can be photoimaged and/or photopolymerized by actinic radiation in the near-IR range (˜770-1500 nm) of the electromagnetic spectrum.
BACKGROUND OF THE INVENTION
Various dyes are known to the art that are infrared (IR) absorbers and which can act as photothermal sensitizers for various reactions that are initiated using near IR radiation. Examples include the SQS and related squarylium dyes disclosed in U.S. Pat. No. 5,019,549 which are useful dyes for use in donor elements for laser-induced thermal imaging processes.
The hexaarylbiimidazoles (HABIs) are a very useful class of photoinitiators that are widely known to those skilled in the art and which are used in many photopolymer products. Some key HABI review articles include the following: “Photoinitiators for Free-Radical-Initiated Photoimaging Systems”, B. Monroe and G. Weed, Chem. Rev., 93, p. 435-448 (1993), see p. 440-441 for the section on HABIs; and “Photopolymers: Radiation Curable Imaging Systems” by B. M. Monroe, Chapter 10 in Radiation Curing: Science and Technology, edited by S. P. Pappas, Plenum Press, New York, (1992), see p. 407-412 for the section on HABIs.
There are various compounds known that are sensitizers of HABIs for photopolymer processes effected with actinic radiation in the ultraviolet and visible regions of the electromagnetic spectrum. It would be very desirable to have efficient sensitizers of HABIs for photopolymer processes in the near infrared (˜770-1500 nm) of the electromagnetic spectrum, particularly since this type of actinic radiation is readily available from inexpensive diode lasers that can be employed for direct digital imaging. Efficient sensitizers of HABIs active in the near infrared are not currently known to the art, and there is a strong need to have efficient sensitizers of HABIs with sensitization in the near infrared region of the electromagnetic spectrum.
In Japanese patent publication 08-297364, there are disclosed some near infrared cationic dyes present in photosensitive image-forming sheets that sensitize HABIs. All of these dyes though have a borate anion, which is a well-known coinitiator of HABI(s), present as counterion. Since borate anion is present in these compositions, the dyes would sensitize HABIs. Having a borate anion present as counterion can be disadvantageous, since this anion is relatively large tending to impart limited solubility to the dye and hence likely making it difficult to tailor properties of compositions comprising these dyes. These compositions are comprised of three essential components—near IR dye, borate anion, and HABI. A two component composition—near IR dye and HABI-of the present invention obviates the need for the large borate anion.
SUMMARY OF THE INVENTION
Novel photopolymer compositions and photoimaging media (elements) are disclosed which contain dyes that absorb strongly in the near infrared (near IR) region of the electromagnetic spectrum. These dyes are useful as efficient photosensitizers in sensitizing photoinitiators that can initiate photopolymerization and other photoimaging reactions. These photopolymer compositions and photoimaging media are sensitive in the near infrared (near IR) region of the electromagnetic spectrum and are characterized in undergoing polymerization of ethylenically unsaturated monomer components or other photopolymerizable materials, preferably in negative-acting photopolymer systems, and/or other photoimaging reactions that are initiated by exposure to near IR actinic radiation. These compositions and photoimaging media, in a first embodiment, comprise a near IR dye photochemical sensitizer, which is substantially free of borate anion, a hexaarylbiimidazole (HABI) compound as photoinitiator, a chain transfer agent, and a photopolymerizable material, which preferably is an ethylenically unsaturated monomer. These compositions and photoimaging media, in a second embodiment, comprise a near IR dye photochemical sensitizer, which is substantially free of borate anion, a hexaarylbiimidazole (HABI) compound as photoinitiator, and a leuco dye. Additional embodiments involve processes using the compositions of this invention and elements containing the compositions of this invention. These compositions and photoimaging media are useful in a variety of photopolymer products, including photoresists, solder masks, proofing films, flexographic printing products, and holographic recording films.
DETAILED DESCRIPTION OF THE INVENTION
A key aspect of the present invention is the discovery that certain dyes that absorb in the near infrared and which are substantially free of a borate anion are efficient sensitizers of hexaarylbiimidazoles (HABIs), which as a class of photoinitiators are well known to those skilled in the art to be difficult to sensitize especially in the longer wavelength regions. Furthermore, in sharp contrast to many known photosensitizers, the photosensitizers of this invention are effective in bringing about polymerization upon exposure in a photopolymerizable film over a considerably larger film thickness in comparison to what the known sensitizers can do. While not being bound by any theory, the photosensitizers of this invention are believed to act via a photochemical mechanism that involves, after excitation of the photosensitizer to an excited state upon exposure to actinic radiation, electron transfer from the excited photosensitizer to the HABI and then subsequent cleavage of the HABI to give a triarylimidazole radical (lophyl radical). The lophyl radical may either serve as the initiator directly or may indirectly afford via reaction with a hydrogen donor other radical(s) that serve to initiate photopolymerization and/or photoimaging. If the oxidation potential of the near IR photosensitizer is too high in relation to the reduction potential of the HABI, then electron transfer will be inefficient or may not occur at all, and the near IR photosensitizer will not be a photochemical sensitizer of the HABI. If, on the other hand, the oxidation potential of the near IR photosensitizer is suitably low in relation to the reduction potential of the HABI, then according to the well-known Marcus theory for electron transfer, the donation of an electron from the dye to the HABI should be efficient and the dye may be an efficient photochemical sensitizer of the HABI initiator.
The present invention, therefore, relates to a method for generating HABI radicals which act as photoinitiators in photochemical compositions comprising exposing a composition comprising a near IR dye; a HABI photoinitiator; and a photoactivatable compound to near infrared radiation wherein the near IR dye is activated to an excited state IR dye* which subsequently transfers an electron to the HABI photoinitiator which leads to the formation of HABI radicals. In a specific embodiment the near infrared absorbing dye is free of borate anion in which regard the invention may be considered to consist essentially of the near infrared absorbing dye and the HABI together with the other ingredients.
In a first embodiment which entails photopolymerization of a photopolymerizable (photohardenable) material to afford photopolymerized (photohardened) photopolymer, the compositions are comprised of the following components:
1) a photoinitiator system; which comprises:
A) a near IR dye photochemical sensitizer; and
B) a hexaarylbiimidazole (HABI) compound as photoinitiator;
2) a chain transfer agent; and
3) a photopolymerizable material, which preferably is an ethylenically unsaturated monomer,
with the proviso that the near IR dye photochemical sensitizer is substantially free of borate anion.
In a second embodiment which entails photoimaging of a photoimageable material to afford an image comprising photoimaged photopolymer, the photoimageable compositions are comprised of the following components:
1) a photoinitiator system; which comprises:
A) a near IR dye photochemical sensitizer; and
B) a hexaarylbiimidazole (HABI) compound as photoinitiator; and
2) a leuco dye,
with the proviso that the near IR dye photochemical sensitizer is substantially free of borate anion.
Both the compositions of the first embodiment and the compositions of the second embodiment may contain additional components, such as other components that are typically present in photopolymer compositions. The additional components include but are not limited to polymeric binder(s), additional components of the types named above (e.g., additional HABI initiator(s), additional leuco dye(s), additional monomer(s), etc.), as well as other optional components such as fillers, pigments, surfactants, adhesion modifiers, scum formation modifiers, and the like. Furthermore, the compositions of the first embodiment may contain but are not required to contain leuco dye(s), and the compositions of the second embodiment may contain but are not required to contain photopolymerizable (photohardenable) material(s).
Unless specifically indicated otherwise, the discussion presented below on the component specifications and details applies equally to both the first and second embodiments of this invention.
HABI Photoinitiator/Near IR Photosensitizer Photoinitiator System
The photoinitiator or photoinitiating system includes one or more hexaarylbiimidazole (HABI) compounds which directly furnish free-radicals when activated by actinic radiation. By “actinic radiation” is meant radiation which allows formation of the free-radicals necessary to initiate polymerization of the monomer. This photoinitiating system can also include a plurality of compounds, one or more of which yields the free-radicals after having been caused to do so by another compound, a photosensitizer or sensitizer, which is activated by the radiation. The photosensitizer in this invention extends spectral response into the near infrared (near-IR) spectral region. Also radiation employing a laser can be employed in specific situations.
Substituted 2,4,5,2′,4′,5′-hexaarylbiimidazole dimers (HABIs) useful in the invention are disclosed in: Chambers, U.S. Pat. No. 3,479,185;-Cescon, U.S. Pat. No. 3,784,557; Dessauer, U.S. Pat. No. 4,311,783; and Sheets, U.S. Pat. No. 4,622,286. Preferred dimers of this class are 2-o-chlorosubstituted hexaphenylbiimidazoles in which the other positions on the phenyl radicals are unsubstituted or substituted with chloro, methyl or methoxy, such as: CDM-HABI, i.e., 2-(o-chlorophenyl)-4,5-bis(m-methoxyphenyl)-imidazole dimer; o-Cl-HABI, i.e., biimidazole, 2,2′-bis (o-chlorophenyl)-4,4′5,5′-tetraphenyl-; and TCTM-HABI, i.e., 1H-imidazole, 2,5-bis(o-chloro-phenyl)-4-[3,4-dimethoxyphenyl]-, dimer, each of which is typically used with a hydrogen donor or chain transfer agent. Especially preferred initiators of this class for this invention are ortho-Cl-HABI, i.e., 1,1′-biimidazole, 2,2′-bis(ortho-chlorophenyl)-4,4′,5,5′-tetraphenyl-imidazole dimer and 2,3,5-TCl-HABI, i.e., 2,2′-bis(2,3,5-trichlorophenyl)-4,4′,5,5′-tetraphenyl-1,1′-biimidazole.
The near infrared photosensitizers of this invention are those having the generic formula shown in Table 1 following the examples or the specific formula described herein or shown in Table 2.
As shown in Table 1, the infrared sensitive dye is chosen from a compound of Formula I wherein substituent A is chosen from
(1) a 5-6 membered heterocyclic ring system having 1-3 ring heteroatoms selected from N which are substituted with H, C1-C6 alkyl, (CH2)mCO2H or (CH2)mCO2(C1-C6 alkyl) and a C atom of the heterocyclic ring system may be substituted with oxygen to form a carbonyl or enolate anion and m is 0-4;
(2) A 5-6 membered carbocyclic moiety substituted with H, C1-C6 alkyl wherein a carbon atom of the carbocyclic moiety may be substituted with oxygen to form a carbonyl or enolate anion;
(3) quinoline or isoquinoline wherein the nitrogen is directly bonded to the carbocyclic moiety of formula I;
(4) N,N-bisaryl or bis(C1-C6 alkyl) or bisaryl(C1-C6 alkyl) amine wherein the aryl group is chosen from napthyl or phenyl which is unsubstituted or substituted with substituents chosen from F, Br, Cl, OCH3, CF3, OH, C1-C6 alkyl or aryl C6-C10, such as phenyl or naphthyl;
(5) a heterocyclic ring system having at least one nitrogen bonded directly to the carbocyclic ring of formula I and a group Z selected from C, NR8, O or S wherein R8 is chosen from H, C1-C6 alkyl, CO2H or CO2-C1-C6 alkyl;
substituent D1 is chosen from a 9-15 membered heterocyclic system such as a heteroaryl ring system having at least one heteroatom (U) chosen from NR3, O, S or PR3 which is directly bonded to the aryl portion of the heteroaryl ring system and wherein R3 is chosen from C1-C6 alkyl which may be unsubstituted or substituted with CO2II, SO3II or salts thereof and wherein the aryl ring may be unsubstituted or substituted with substituents selected from OCH3, CF3, Br, Cl, F, C1-C6 alkyl, OH or substituent D1 may be a fused ring heterocyclic system such as when heterocyclic rings are fused to form a polycyclic structure;
substituent D2 has the identical heterocyclic ring system as D1, which may be heteroaryl or fused ring heterocyclic system, except that when U is NR3, the nitrogen is quaterinized to form an amine salt which is neutralized by an enolate anion from A when A is a substituted pyrimidine like moiety or by a discrete (non intra-molecular) anion;
n is chosen from 1-2.
The near infrared photosensitizers within the scope of this invention include, but are not limited to, the following dye compounds as defined in the glossary: DF-15131, DF-15118, DF-1668, DF-15132, DF-1413, DF-1419, DF-1429, DF-1422, NK-2268, NK-3877, GW-826, DF-12124, GW-976, GW-436, GW-186, and GW-776. Dye compounds that are preferred as photosensitizers include, but are not limited to, the following: DF-15132, NK-3877, KF-634, DF-1668, DF-1413, DF-15118, DF-15131, GW-826, GW-976, and GW-186. Dye compounds that are most preferred as photosensitizers according to the invention are the following: DF-1413, DF-15118, DF-15131, GW-826, GW-976, and GW-186. The basis for the above preferences is relative efficacy of the dye as a near IR photosensitizer.
The solubility characteristics of the dye provide another basis for preferences in dye selection. In this regard, zwitterion dyes that are charge neutral are preferred in coating photopolymer compositions from an organic solvent(s), such as methyl ethyl ketone or methanol, since these zwitterionic dyes have significantly higher (better) solubility characteristics in organic solvents and are less prone toward crystallization of solids in the compositions during coating and/or use. In some cases, these zwitterionic dyes can lead to other performance advantages of the compositions of this invention. For compositions coated from organic solvents, dyes having the zwitterionic bartituric acid moiety (i.e., 2-[2,4,6-trioxo-1,3-pyrimidin-5-yl]) or related zwitterionic moieties are preferred. Such dyes are charge neutral and do not contain a counterion, such as a halide anion, that is present in other dyes that are not charge neutral. Dyes within the scope of the invention having the bartituric acid moiety and which are preferred on the basis of solubility characteristics include, but are not limited to, DF-1413, DF-1419, DF-1422, DF-1668, DF-1429, DF-15118, DF-15131, and DF-15132.
Dye compounds that were tested (see comparative examples) and found to be inoperable and which are consequently outside the scope of the invention include the following: SQS.
The quantity of photoinitiator system (including photosensitizer(s) and photoinitiator(s) to comprise the photoinitiator system) in a photopolymerizable composition of this invention is typically from 0.5 to 10 parts by weight relative to the total components, preferably is from about 1 to about 5 parts by weight relative to the total components, and most preferably is from about 2 to about 3 parts by weight relative to the total components. The ratio of photosensitizer(s) to photoinitiator(s) in parts by weight of the total photoinitiator system of this invention is typically from about 0.02 to about 1.0, preferably is from about 0.03 to about 0.5, and most preferably is from about 0.04 to about 0.2.
Chain Transfer Agent
Hexarylbiimidazole (HABI) photoinitiators are known to those skilled in the art to be generally ineffective toward initiating photopolymerization of an ethylenically unsaturated monomer unless there is present in the photo-polymerizable composition a chain transfer agent (hydrogen donor). When a suitable chain transfer agent is present in the composition, then a HABI photoinitiator is very effective and efficient in initiating the polymerization of ethylenically unsaturated monomer(s) to afford photopolymerized photopolymer. For this reason, a suitable chain transfer agent is a necessary and required component in the photopolymerizable (photohardenable) compositions of the first embodiment of this invention. The chain transfer agent generally must be present in an amount in the range from about 0.1 to about 2 parts by weight based on the total composition. Preferably, the chain transfer agent is present in an amount in the range from about 0.5 to about 1.0 parts by weight based on the total composition.
In sharp contrast, HABI photoinitiators are known to be effective during photoimaging in oxidizing a leuco dye to the corresponding colored dye form to form an image even in the absence of a chain transfer agent. Thus, for the compositions of the second embodiment of this invention, a chain transfer agent is not required since there is effective photoimaging in its absence, but it is nevertheless an optional component in these compositions.
Suitable chain transfer agents according to this invention include, but are not limited to, the following: N-arylglycine, such as for example, N-phenylglycine; julolidine; N,N-dialkylamino aromatics, where the alkyl groups are independently C1-C6 alkyl, and representative examples include Michler's Ketone, leuco crystal violet and other aminotriarylmethane leuco dyes, and 2,6-diisopropyl-N,N-dimethylaniline; 2-mercaptobenzoxazole; 1,1-dimethyl-3,5-diketocyclohexane, or organic thiols, e.g., 2-mercaptobenzothiazole; 2-mercaptobenzoxazole; 2-mercaptobenzimidazole; pentaerythriotol tetrakis (mercaptoacetate); 4-acetamidothiophenol; mercaptosuccinic acid; dodecanethiol; beta-mercaptoethanol; beta-mercaptoethanol; or other organic thiol. Preferred chain transfer agents for this invention include N-phenylglycine, 2,6-diisopropyl-N,N-dimethylaniline, and julolidine.
The first embodiment of this invention involves compositions that contain a photopolymerizable material that undergoes photopolymerization upon exposure to near infrared actinic radiation to afford a polymerized photopolymer. In general, the invention scope is considered to include any photopolymer systems known in the art which undergo photopolymerization upon exposure to actinic radiation to afford polymerized photopolymer. Suitable photopolymer systems include, but are not limited to, negative working systems in which at least one ethlenically unsaturated monomer is photopolymerized to photopolymerized photopolymer, negative working systems, such as poly(vinyl cinnamate) that involve cycloaddition reactions to afford photopolymerized photopolymer, and positive working systems, such as those of the diazaquinone type that afford acid functionality that is developable in aqueous alkali upon exposure to actinic raidation. Discussion of these different photopolymer systems can be found in many references, such as, for example, Photoreactive Polymers The Science and Technology of Resists, by Arnost Reiser, John Wiley & Sons, New York, 1989.
The preferred choice for the photopolymerizable material is an ethylenically unsaturated monomer. Suitable monomers useful herein are well known in the prior art and typically undergo free radical initiated polymerization. In the compositions of this invention that contain an ethylenically unsaturated monomer, the composition contains at least one or a mixture of such components. In general, preferred monomers for photopolymer applications have boiling points greater than 100° C. (at 760 mm Hg, 1 atmosphere), more preferably, greater than 150° C. (at 760 mm Hg, 1 atmosphere). Numerous unsaturated monomers polymerizable by free-radical initiated polymerization and useful in photopolymerizable compositions are known to those skilled in the art.
The monomer provides the capability of the photopolymer coating composition to photopolymerize and contributes to overall properties. In order to effectively do so, the monomer should contain at least one ethylenically unsaturated group capable of undergoing polymerization on exposure to actinic radiation.
The preferred monomeric compounds are polyfunctional, but monofunctional monomers, such as (meth)acrylate esters of polycaprolactone, can also be used. Suitable monomers which can be used as the sole monomer or in combination with others include the following: diethylene glycol diacrylate, tripropylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, ethoxylated trimethylolpropane tri(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate and similar compounds as disclosed in U.S. Pat. No. 3,380,831, triethylene glycol dimethacrylate, bisphenol-A di(meth)-acrylate, di-(2-methacryloxyethyl) ether of bisphenol-A, di-(3-acryloxy-2-hydroxypropyl) ether of bisphenol-A, di-(2-acryloxyethyl)ether of bisphenol-A, di-(3-methacryloxy-2-hydroxypropyl) ether of tetrachloro-bisphenol-A, di-(2-methacryloxyethyl) ether of tetrachloro-bisphenol-A, di-(3-methacryloxy-2-hydroxypropyl) ether of tetrabromo-bisphenol-A, di-(2-methacryloxyethyl) ether of tetrabromo-bisphenol-A, ethoxylated bisphenol-A di(meth)acrylate, propoxylated bisphenol-A di(meth)-acrylate, diacrylate of bisphenol-A diglycidyl ether and poly-caprolactone diacrylate.
A particularly preferred class of monomers or comonomers is tripropylene glycol diacrylate, trimethylolpropane triacrylate, ethoxylated trimethylolpropane triacrylate, propoxylated trimethylolpropane triacrylate, ethoxylated Bisphenol A dimethacrylate, and triethylene glycol dimethacrylate. The polymerizable material can be present in any amount from 0 to about 70 weight percent. For the first embodiment, it is normally present in an amount from 20 to 70 weight percent.
The compositions of this invention most often preferably contain one or more binder polymer as optional component(s).
The binder polymers present in the compositions of this invention are not required to but preferably do contain acid functionality for aqueous processability (aqueous development), which is preferably achieved by incorporating one or more carboxyl-containing comonomers into the binder polymer. Preferred polymers for the instant invention also contain styrene as a comonomer. Suitable polymers for the instant invention contain 0-50 weight percent styrene as comonomer, have an acid number in the range 90-160, have a molecular weight (weight average) in the range 20,000-300,000, and have a glass transition temperature in the range 50-120° C. Preferably, the binders contain 5-40% styrene as comonomer, have an acid number in the range 110-140, have a molecular weight (weight average) in the range 40,000-200,000, and have a glass transition temperature in the range 60-110° C. Most preferably, the polymers contain 10-30% styrene as comonomer, have an acid number in the range 125-135, have a molecular weight (weight average) in the range 60,000-100,000, and have a glass transition temperature in the range 70-100° C.
Preferred polymer binders are acid-containing copolymers or homopolymers comprised of at least one acid-containing monomer of structural unit:
in which Ra is H, phenyl, or alkyl; Rb is CO2Rc, SO3Rd, or other acidic functional group; and Rc and Rd are H or alkyl, which is unsubstituted or hydroxyl-substituted. Alkyl groups can contain one to twelve carbon atoms and preferably one to eight. Comonomers, which are suitable for forming the binder copolymer, are styrene and unsaturated carboxylic acids and their derivatives, such as (meth)acrylic acid and (meth)acrylates. Acrylic acid, methacrylic acid, methyl methacrylate, styrene, ethyl acrylate, ethyl methacrylate, butyl methacrylate, butyl acrylate, maleic anhydride, 2-hydroxyethyl methacrylate, and 2-ethylhexyl methacrylate are preferred.
Suitable binder copolymers can be formed by direct copolymerization of one or more ethylenically unsaturated dicarboxylic acid anhydrides, or the corresponding alkyl diesters, with one or more of the above comonomers.
Suitable ethylenically unsaturated dicarboxylic acid anhydrides are, for example, maleic anhydride, itaconic acid anhydride and citraconic acid anhydride and alkyl diesters such as the diisobutyl ester of maleic anhydride. The copolymer binder containing acid anhydride functionality can be reacted with primary aliphatic or aromatic amines to produce acid and amide functionality.
A preferred acid-containing binder for aqueous processability in use as well as aqueous coatability in dry film manufacture is a carboxylic acid-containing copolymer, such as those disclosed in U.S. Pat. Nos. 3,458,311 and 4,273,857, and which can be prepared by any of the addition polymerization techniques known to those skilled in the art such as described therein. The level of carboxylic acid groups is determined for a given composition by optimizing the amount needed for good development in aqueous alkaline developer.
When a negative-working aqueous processable photoresist, solder mask, proofing film, or flexographic plate is laminated to a substrate and photoprinted, development of the photoresist, solder mask, proofing film, or flexographic plate composition may require that the binder material should contain sufficient carboxylic acid groups to render the photoresist, solder mask, proofing film, or flexographic plate coating composition processable in aqueous alkaline developer. The photoresist, solder mask, proofing film, or flexographic plate coating layer will be removed in portions which are not exposed to radiation but will be substantially unaffected in exposed portions during development by aqueous alkaline liquids such as wholly aqueous solutions containing 1% sodium carbonate by weight at a temperature of 30° C. for 1-2 minutes.
For those applications where the development is effected using solvent development with an organic liquid developer or semiaqueous development with a liquid mixture containing water and organic solvent(s), it is not required that the binder(s) have acid-containing functionality, such as carboxylic acid functionality. In these cases, all of the comonomers for the binder(s) can be non-acid containing comonomers.
The leuco form of the dye which comprises one component of a photoimaging composition of the present invention is the reduced form of the dye having one or two hydrogen atoms, the removal of which together with an additional electron in certain cases produces the dye. Such dyes have been described, for example, in U.S. Pat. No. 3,445,234, column 2, line 49 to column 8, line 55. The following classes are included:
(d) amino-9, 10-dihydroacridines
(i) leuco indamines
(j) aminohydrocinnamic acids (cyanoethanes, leuco methines)
(l) leuco indigoid dyes
Of these leuco forms, (a) through (i) form the dye by losing one hydrogen atom, while the leuco forms (j) through (p) lose two hydrogen atoms to produce the parent dye. Aminotriarylmethanes are preferred. A general preferred aminotriarylmethane class is that of the acid salts of aminotriarylmethanes wherein at least two of the aryl groups are phenyl groups having (a) an ReRfN-substituent in the position para to the bond to the methane carbon atom wherein Re and Rf are each groups selected from hydrogen, C1 to C10 alkyl, 2-hydroxyethyl, 2-cyano-ethyl, or benzyl and, optionally, (b) a group ortho to the methane carbon atom which is selected from lower alkyl (C is 1 to 4), lower alkoxy (C is 1 to 4), fluorine, chlorine or bromine; and the third aryl group may be the same as or different from the first two, and when different is selected from
(a) Phenyl which can be substituted with lower alkyl, lower alkoxy, chloro, diphenylamino, cyano, nitro, hydroxy, fluoro or bromo;
(b) Naphthyl which can be substituted with amino, di-lower alkylamino, alkylamino;
(c) Pyridyl which can be substituted with alkyl;
(e) Indolinylidene which can be substituted with alkyl.
Preferably, R1 and R2 are hydrogen or alkyl of 1-4 carbon atoms. Leuco dye is present in 0.1 to 5.0 percent by weight of solids in the photoimaging composition.
With the leuco form of dyes which have amino or substituted amino groups within the dye structure and which are characterized as cationic dyes, an amine salt-forming mineral acid, organic acid, or an acid from a compound supplying acid is employed. The amount of acid usually varies from 0.33 mol to 1 mol per mol of amino nitrogen in the dye. The preferred quantity of acid is about 0.5 to 0.9 mol per mol of amino nitrogen. Representative acids which form the required amine salts are hydrochloric, hydrobromic, sulfuric, phosphoric, acetic, oxalic, p-toluenesulfonic, trichloroacetic, trifluoroacetic and perfluoroheptanoic acid. Other acids such as acids in the “Lewis” sense or acid sources which may be employed in the presence of water or moisture include zinc chloride, zinc bromide, and ferric chloride. Representative leuco dye salts include tris-(4-diethylamino-o-tolyl) methane zinc chloride, tris-4-diethylamino-o-tolyl) methane oxalate, tris-(4-diethylamino-o-tolyl) methane p-toluene-sulfonate and the like.
Aminotriarylmethanes and salts thereof are preferred leuco dyes in this invention. Especially preferred aminotriarylmethane leuco dyes according to this invention include, but are not limited to, LCV, LECV, LPCV, LBCV, LV-1, LV-2, LV-3, aminotriarylmethane leuco dyes having different alkyl substituents bonded to the amino moieties wherein each alkyl group is independently selected from C1-C4 alkyl, and aminotriarylmethane leuco dyes comprising any of the preceding named structures that are further substituted with one or more alkyl groups on the aryl rings wherein the latter alkyl groups are independenly selected from C1-C3 alkyl. The most preferred aminotriarylmethane leuco dyes according to this invention are LCV, LECV, LV-1, LV-2, and LV-3. The leuco dye can be present in the compositions in any amount from 0 to about 20 weight percent. In embodiment 2, it will normally be present in an amount from 0.5 to about 10 weight percent.
Other compounds conventionally added to proofing films, flexographic printing plates, photoresist, solder mask, and other related photopolymer compositions may also be present in the coating to modify the physical properties of the film. Such components include: adhesion modifiers, thermal stabilizers, a printout image system comprising colorants such as dyes and pigments, viscosity control agents, coating aids, wetting agents, surfactants, release agents, fillers, crosslinking agents, and the like.
Examples of suitable printout image systems are the following: 2,2′-bis(o-chlorophenyl)-4,4′,5,5′-tetraphenyl-1,1 ′-biimidazole and Leuco Crystal Violet (LCV); 1,2-dibromotetrachloroethane and LCV; tribromomethyl phenylsulfone (BMPS) and LCV; and 2,3-dibromo-3-phenylpropiophenone (BPP) and LCV.
Some heterocyclic compounds improve adhesion of the coating to copper-clad substrates or prevent residue formation during processing in a resist or related application. Suitable heterocyclic components include materials such as those disclosed in Hurley et al., U.S. Pat. No. 3,622,334, Jones, U.S. Pat. No. 3,645,772, and Weed, U.S. Pat. No. 4,710,262. Preferred heterocyclic components include benzotriazole, 5-chloro-benzotriazole, 1-chloro-benzotriazole, 4-and 5-carboxy-benzotriazole, 1-hydroxy-benzotriazole, 2-mercapto-benzoxazole, 1 H-1,2,4-triazole-3-thiol, 5-amino-1,3,4-thiodiazole-2-thiol, and mercapto-benzimidazole.
Thermal polymerization inhibitors that can be used in the coating compositions are: p-methoxyphenol, hydroquinone, alkyl- and aryl-substituted hydroquinones and quinones, tert-butyl catechol, 2,6-di-tert-butyl-p-cresol, and phenothiazine. Also useful for thermal polymerization inhibitors are the nitroso compositions disclosed in U.S. 4,168,982.
Various dyes and pigments may be added to increase the visibility of the photopolymer image. Any colorant used, however, should preferably be transparent to the actinic radiation. Representative dyes include leuco crystal violet, Victoria green dye, Victoria blue dye, and Neozapon red dye.
In the case of a photoimageable solder mask composition, there will be in addition to the key components listed above a crosslinking agent present to provide for curing of the imaged resist. Suitable crosslinking agents include an adduct of a polyisocyanate compound and a isocyanate group blocking agent, and formaldehyde condensation resins with melamines, ureas, benzguanidines, and the like.
A suitable photodeactivation compound can be employed in this invention. Preferred are various quinone compounds. A quinone redox couple useful in the photoimaging composition is described in U.S. Pat. No. 3,658,543, column 9, lines 1 to 46, incorporated by reference. Preferred oxidants include 9,10-phenanthrenequinone alone or in admixture with 1,6-and 1,8-pyrenequinone which absorb principally in the 430 to 550 nm region. The reductant component of the redox couple is 100 to 10 percent of an acyl ester of triethanolamine of the formula:
where Rg is alkyl of 1 to 4 carbon atoms, and 0 to 90 percent of a C1, to C4 alkyl ester of nitrioltriacetic acid or of 3,3′,3″-nitrilotripropionic acid. Triethanolamine triacetate and dibenzylethanolamine acetate are preferred reductant components. The molar ratios of oxidants to biimidazole used ranges from 0.01:1 to 2:1, preferably 0.2:1 to 0.6:1. The molar ratios of reductant biimidazole used ranges from about 1:1 to about 90:1, preferably 10:1 to 20:1.
Materials of Construction
Any of the support films known for use as such for a photoimageable coating can be used as a temporary support for coating the photoimageable material onto in the application of the present invention. The temporary support film, which preferably has a high degree of dimensional stability to temperature changes, may be chosen from a wide variety of polyamides, polyolefins, polyesters, vinyl polymers, and cellulose esters, and may have a thickness of from about 6 to 200 microns. A particularly suitable support film is polyethylene terephthalate having a thickness of about 25 microns.
In a photoimageable film it is necessary or at least highly desirable to protect the photosensitive layer by a removable cover film in order to prevent blocking when it is stored in a roll form. The protective cover film is removed prior to lamination of the photoimageable element to a substrate.
The protective cover film may be selected from the same group of high polymer films described for the temporary support film, supra, and may have the same wide range of thicknesses; however, it is preferable to use a cover sheet that is relatively flexible under lamination conditions. A cover sheet of 25 microns thick polyethylene or polypropylene is especially suitable.
The preferred ranges of components for the photopolymerizable compositions of the first embodiment of this invention are about 30 to 80 parts by weight of the polymer(s) (binder(s), polymeric binder(s)); about 10 to 50 parts by weight of photopolymerizable material(s); and about 0.5 to 10 parts by weight of the photoinitiator system comprised of a near IR photosensitizer and a HABI photoinitiator. The preferred ranges of components for the photoimageable (2nd) embodiment of this invention are 0 to about 70 parts by weight of polymers, about 0.1 to about 10 parts by weight of leuco dye(s), and about 0.5 to 10 parts by weight of the photoinitiator system comprised of a near IR photosensitizer and a HABI photoinitiator. The preferred ratio range of photosensitizer to photoinitiator on a parts by weight basis is from about 0.04 to about 0.2.
The thickness of the photoimageable and/or photopolymerizable (photohardenable) layer will depend on the type of processing being done and is not limited.
The process of formation of a dry film is relatively simple and direct. The stable liquid photoimageable and/or photopolymerizable composition(s) of the present invention is coated onto a substrate which may be permanent or temporary. Various methods of coating can be employed which are well known in the art.
Substantially all solvent(s) in the liquid composition is removed which results in a dry film. Since a relatively high solids content is present in the liquid, under preferred conditions it is considered that a relatively small amount of liquid has to be removed in forming a dry film.
PROCESS OF USE
The photoimageable and/or photopolymerizable compositions of this invention may be used to prepare photoresists, soldermasks, printing plates, and proofing products. These compositions are applied to a substrate by coating or lamination if a dry film as described above is prepared. After drying, the coating is imagewise exposed to actinic radiation, generally through a process negative or positive transparency after a draw-down time of 30 seconds to 2 minutes. The transparency is an image bearing transparency consisting solely of substantially opaque and substantially transparent areas where the opaque areas are substantially of the same optical density. The compositions used in the process of the invention generally exhibit their maximum sensitivity in the near infrared (near-IR) range, therefore the radiation source should furnish an effective amount of this type of radiation. Suitable radiation sources include diode lasers which emit in the near-IR range. The radiation exposure time can vary from fractions of a second to minutes depending on the intensity, type of radiation source used and its distance from the photoimageable/photopolymerizable layer and the type of photoimageable/photopolymerizable layer. In general exposure times range from 10 seconds to 10 minutes or more using standard non-laser commercial radiation sources and can be much shorter (milliseconds or less) using laser sources.
Following imagewise exposure to form imaged and non-imaged areas in the photoimageable/photopolymerizable composition, and removal of the cover sheet, if present, the exposed layer is developed to form an image on the first substrate. Developing of the exposed layer having imaged and non-imaged areas to form an image on the first substrate can be a dry development step, as in certain proofing applications, or it can be a wet development step, as in other proofing applications and as typical for photoresist, solder mask, and flexographic printing plate applications. The exposed layer may be developed using an aqueous alkaline developer, a semiaqueous developer, or a solvent developer which will remove the non-imaged areas leaving a relief image. If the first substrate is a copper-clad epoxy glass substrate, then the image formed is a resist image which may be used as a mask for etching or plating the copper exposed areas of the first substrate. If the first substrate is a metal substrate, such as anodized aluminum, then a printing plate results. The photoimageable layer may be pigmented resulting in a proofing product after wash-off development.
The exposed layer may also be developed by toning with a toning foil or film or by dusting with a powdered toner. Useful toning films are described in Froehlich, U.S. Pat. No. 3,625,014, issued Jul. 6, 1987. The films, which are comprised of a support and a low cohesive strength, pigmented polymer layer, are laminated to the exposed layer having imaged and non-imaged areas. The support is peeled off along with the pigmented polymer adjacent the imaged areas on the first substrate. In general, it is necessary to apply the toning film more slowly than usual lamination rates and some experimentation may be required to determine optimum rates and temperatures for laminating each different toning film.
Dry non-electroscopic toners, their method of production, as well as improved surface coatings, are well known in the art as, for example, in Chu and Manger, U.S. Pat. No. 3,620,726; Gray, U.S. Pat. No. 3,909,382; Fickes et al., U.S. Pat. No. 4,215,193; Fickes, U.S. Pat. No. 4,397,941; and Matrick, U.S. Pat. No. 4,546,072. The toner is applied to the exposed layer having non-tacky, imaged areas and tacky non-imaged areas. Excess toner is wiped off, providing a toner image on the first substrate.
The exposed layer having imaged and non-imaged areas may also be developed by peel-apart development. In this embodiment the photoimageable layer may be pigmented. A second substrate may be laminated to the photoimageable layer prior to the exposure step or after formation of the imaged and non-imaged areas in the exposed layer. The second substrate is then peeled off, resulting in the imaged areas remaining on the first substrate and the non-imaged areas being removed on the second substrate. If the photo-imageable/photopolymerizable layer is unpigmented, the tacky non-imaged areas that are removed with the second substrate may be treated with dry particulate toners or toning films as described above.
Photopolymerization done under the compositions and processes of this invention is defined to be effective when the compositions, upon imagewise exposure to actinic radiation, are substantially unaffected by an aqueous (developer) solution (1% sodium carbonate by weight), a semiaqueous (developer) solution, or a solvent (developer) solution at a temperature of 30° C. for 1-2 minutes in portions exposed to actinic radiation but removed in portions not exposed to actinic radiation.
Photoimaging done under the compositions and processes of this invention, when not involving photopolymerization, is defined to be effective when the compositions, upon imagewise exposure to actinic radiation, undergo an increase in optical density of at least 0.2 optical density units in portions exposed to actinic radiation but undergo an increase of at most 0.1 optical density units in portions not exposed to actinic radiation. For photoimaging involving photopolymerization and washout, effective photoimaging is defined in the same manner as effective photopolymerization as given above.
Near Infrared (Near IR) Sensitive Dye
This is a dye which absorbs in the near infrared (near-IR) range (˜770-1500 nm) of the electromagnetic spectrum and which is capable of activating a HABI photoinitiator to initiate photopolymerization of a photopolymerizable material and/or to initiate photoimaging of a photoimageable material via formation of a colored dye from a colorless or lightly colored dye precursor. An example of such color formation is the oxidation of a leuco dye to the colored dye form to generate the photoimage.
A Pair of Corresponding Heterocyclic Ring Structures
A pair of corresponding heterocyclic ring structures is defined to be two heterocyclic ring structures having the same number of atoms of each type and in which each atom is bonded to the same number and types of other atoms in each paired structure. The only difference between pairs is that some of the chemical bonds are different between the paired members (C-C single bond versus a C═C double bond) and that a heteroatom is quatemized in one member (D2) of a given pair and not quaternized in the other member (D1) of the given pair. Some illustrative examples of D1 and D2 paired members of different heterocyclic ring structures are given below in Table 2.
Near IR Dyes Within Invention Scope
2-[2-[2-[2,4,6-trioxo-1,3-pyrimidin-5-yl]-3-[2-(1,3-dihydro-1-ethyl-3,3-dimethyl-2H-indol-2-ylidene)-ethylidene]-1-cyclopenten-1-yl]-ethenyl]-1-ethyl-3,3-dimethyl-3H-indolium, inner salt
2-[2-[2-[2,4,6-trioxo-1,3-pyrimidin-5-yl]-3-[2-(1,3-dihydro-1,3,3-trimethyl-5-methoxy-2H-indol-2-ylidene)-ethylidene]-1-cyclopenten-1-yl]-ethenyl]-1,3,3-trimethyl-5-methoxy-3H-indolium, inner salt
2-[2-[2-[2,4,6-trioxo-1,3-pyrimidin-5-yl]-3-[2-(1,3-dihydro-1,1,3-trimethyl-2H-benz[e]indol-2-ylidene)-ethylidene]-1-cyclopenten-1-yl]-ethenyl]-1,3-dihydro-1,1,3-trimethyl-2H-benz[e]indolium, inner salt
2-[2-[2-[2,4,6-trioxo-1,3-pyrimidin-5-yl]-3-[1-ethyl-naphtho[1,2-d]thiazol-2(1H)-ylidene)-ethylidene]-1-cyclopenten-1-yl]-ethenyl]-1-ethyl-2H-naphtho [1,2-d]thiazolium, inner salt
2-[2-[2-piperidino-3-[2-(1-ethyl-1,3-dihydrobenzothiazol-2-ylidene)-ethylidene]-1-cyclopenten-1-yl]ethenyl]-1-ethylbenzothiazolium, n-butyltriphenylboron salt
2-[2-[2-[2,4,6-trioxo-1,3-pyrimidin-5-yl]-3-[3-ethyl-6-methoxy-2(3H)benzothiazolylidene)-ethylidene]-1-cyclopenten-1-yl]-ethenyl]-3-ethyl-6-methoxy-2(3H)-benzothiazolium, inner salt
2-[2-[2-[2,4,6-trioxo-1,3-pyrimidin-5-yl]-3-[3-ethyl-2(3H)benzothiazolylidene)-ethylidene]-1-cyclopenten-1-yl]-ethenyl]-3-ethyl-2(3H)-benzothiazolium, inner salt
2-[2-[2-[2,4,6-trioxo-1,3-pyrimidin-5-yl]-3-[3-(sulfopropyl)-5-trifluoro-methyl-2(3H)benzothiazolylidene)-ethylidene]-1-cyclopenten-1-yl]-ethenyl]-3-(3-sulfopropyl)-5-trifluoromethyl-2(3H)-benzothiazolium, bis-triethylammonium salt
2-[2-[2-2-piperdino-3-[2-(1-ethyl-1,3-dihydrobenzothiazol-2-ylidene)-ethylidene]-1-cyclopenten-1-yl]ethenyl]-1-ethylbenzothiazolium, bromide salt
2-[2-[2-2-morpholino-3-[2-(1-ethyl-1,3-dihydrobenzothiazol-2-ylidene)-ethylidene]-1-cyclohexen-1-yl]ethenyl]-1-ethylbenzothiazolium, bromide salt
2-[2-[2-4-carboethoxyhexahydropyrazino-3-[2-(1-ethyl-1,3-dihydrobenzothiazol-2-ylidene)-ethylidene]-1-cyclopenten-1-yl]ethenyl]-1-ethylbenzothiazolium, bromide salt
2-[2-[2-(2 aza-1,2,3,4-tetrahydronaphthalenyl)-3-[2-(1-ethyl-1,3-dihydrobenzo-thiazol-2-ylidene)-ethylidene]-1-cyclohexen-1-yl]ethenyl]-1-ethylbenzothiazolium, bromide salt
2-[2-[2-4-methylhexahydropyrazino-3-[2-(1-ethyl-1,3-dihydrobenzothiazol-2-ylidene)-ethylidene]-1-cyclohexen-1-yl]ethenyl]-1-ethylbenzothiazolium, tetrafluoroborate salt
2-[2-[2-2-diphenylamino-3-[2-(1-ethyl-1,3-dihydrobenzothiazol-2-ylidene)-ethylidene]-1-cyclopenten-1-yl]ethenyl]-1-ethylbenzothiazolium, perchlorate salt
2-[2-[2-diphenylamino-3-[2-(1-ethyl-6-methoxy-1,3-dihydrobenzothiazol-2-ylidene)-ethylidene]-1-cyclopenten-1-yl]ethenyl]-1-ethyl-6-methoxy-benzothiazo-lium, perchlorate salt
| || |
| || |
| ||CDM-HABI ||2-(o-chlorophenyl)-4,5-bis(m-methoxyphenyl)- |
| || ||imidazole dimer |
| ||o-Cl-HABI ||2,2′-bis(o-chlorophenyl)-4,4′,5,5′-tetraphenyl- |
| || ||1,1′-biimidazole (CAS No. 1707-68-2) |
| ||2,3,5-TCl-HABI ||2,2′-bis(2,3,5-trichlorophenyl)-4,4′,5,5′- |
| || ||tetraphenyl-1,1′-biimidazole or |
| || ||1,1′-Bi-1H-imidazole, 4,4′,5,5′-tetraphenyl-2.2′- |
| || ||bis(2,3,5-trichlorophenyl)- (CA Index Name, |
| || ||CAS No. 154482-21-0) |
| ||TCTM-HABI ||1H-imidazole, 2,5-bis(o-chloro-phenyl)-4-[3,4- |
| || ||dimethoxyphenyl]-, dimer |
| || |
Name of Chain Transfer Agent(s)
|LBCV ||Leuco butyl crystal violet; the formal chemical name is |
| ||tris(N,N-dibutylaminophenyl)methane. |
|LCV ||Leuco crystal violet; the formal chemical name is |
| ||tris(N,N-dimethylaminophenyl)methane. |
|LECV ||Leuco ethyl crystal violet; the formal chemical name is |
| ||tris(N,N-diethylaminophenyl)methane. |
|LPCV ||Leuco propyl crystal violet; the formal chemical name is |
| ||tris(N,N-di-n-propylaminophenyl)methane. |
|LV-1 ||Bis(4-N,N-diethylaminophenyl)(2-methyl-4-N,N- |
| ||diethylaminophenyl)methane. |
|LV-2 ||(4-N,N-Diethylaminophenyl)bis(2-methyl-4-N,N- |
| ||diethylaminophenyl)methane. |
|LV-3 ||Tris(2-methyl-4-N,N-diethylaminophenyl)methane. |
|TMPEOTA ||Ethoxylated trimethylolpropane triacrylate |
| ||(= polyoxyethylated trimethylolpropane |
| ||triacrylate) |
|TMPTA ||Trimethylolpropane triacrylate |
| || |
| || |
| ||N—PhGly ||N-Phenylglycine |
| ||Jul ||Julolidine |
| ||DIDMA ||2,6-Diisopropyl-N,N-dimethylaniline |
| ||Binder Polymer ||MMA/EA/MAA (44/35/21 wt. %) where |
| || ||MMA = methyl methacrylate |
| || ||EA = ethyl acrylate |
| || ||MAA = methacrylic acid |
| ||PET ||Polyethylene terephthalate (Mylar ® film, |
| || ||DuPont, Wilmington, DE) |
| || |