CA2049595A1

CA2049595A1 - Borate coinitiators for photopolymerizable compositions

Info

Publication number: CA2049595A1
Application number: CA002049595A
Authority: CA
Inventors: Gregory C. Weed; Dietrich M. Fabricius
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1990-08-27
Filing date: 1991-08-21
Publication date: 1992-02-28
Also published as: KR940007797B1; JPH04271352A; KR920004904A; US5153100A; EP0475153A1; AU8271791A

Abstract

BORATE COINTIATORS FOR
PHOTOPOLYMERIZABLE COMPOSITIONS
ABSTRACT

Photopolymerizable compositions in which the photoinitiator system contains a hexaarylbisimidazole and/or a p-dialkyaminophenyl carbonyl compound in combination with a borate anion coinitiator are disclosed.

Description

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~ORATE COINITIATORS FOR
PHOTOPOLYMERIZABLE COMPOSITI~NS
SEield of the InventiQn This invention relates to lnltl~tor systems for photopolymerlzable compositlons. More partlcularly, this invention perta~ns to photopolymerlzable compositions in which the photolnltlator 3ystem contains a hexaarylbisimldazole and/or a ~-dialkyamlnophenyl carbonyl compound in comblnatlon wlth a borate anion coinitiator.
BaCkgrouDd of the Inven~iQn The use of photoinitiator systems to initiate lS photopolymerization ls well known. When lrradiated by actinic radiation, ~he photoinltiator system generates free radicals which initiate polymerization of the monomer or monomers. The photoinitiator system may be a single compound which absorbs actinic radiation and forms the initiating radicals or it may consist of several different materials which undergo a complex series of reactions to produce radicals. Added components, which do not absorb actinic radiation, but which increase the efficiency of the photoinitiator system, are known as coinitiators.
Borate anion coinitiator~ have recently been dlsclosed. Gottschalk et al., U.S. Patents 4,772,530 and 4,772,541, dlsclose photopolymerizable composltions containing a cationlc dye-borate anion complex in which the catlonic dye-borate anion complex is capable of absorbing actinlc radiatlon and produclng free radicals.
Cationic methlne, polymethine, trlarylmeth~ne, indollne, thlazine, xanthene, oxazlne, and acrldlne were disclosed. Trlaryl alkyl borate anlons were the preferred borate colnitiators.

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Yamaguchi et al., U.S. Patent 4,902,604, discloses photopolymerizable compositlons containlng a salt formed by an organic cationic dye compound and a borate anion.
In these salts the catlonic dye compound comprised an azulene ring having a nitrogen atom or a chalcogen atom in the 2- or 4-position.
Xoike et al., Federal Republic of Germany Patent Appl~cation 3,822,921, discloses photopolymerizable compositions containing an organlc dye and a triaryl butyl borate anion coinitiator. In these systems the dye did not contain a counter an~on. Merocyanine type dyes, coumarin type dyes, and xanthene and thi~xanthene dyes were disclosed.
Despite the many improvements made in photoinitiator systems, a need exists for photopolymerizable compositions with increased photospeed. With increased photospeed, shorter irradiation times are possible. The t~me and effort necessary to prepare an image ls reduced, and the capacity of existing equipment is lncreased. Since exposure times are reduced, increased photospeed frequently leads to improved image quality as well.
Summarv of the InventiQn The inventlon is a photopolymerizable composition with improved sensitivity to actinic radiation. In one embodiment this invention is a photopolymerizable composltion comprising:
(A) an ethylenically unsaturated monomer capable of free-radical initiated polymerization; and ~B) an inltlator system activatible by actinic radiatlon, said initiator system consistlng essentially of:
(1) at least one compound selected from the group consisting of (a) hexaarylbisimidazole and (b) ~-aminophenyl carbonyl compound of the followlng structure:

R2~ ~C-Rs where:
R1 and R2 are each lndependently hydrogen or alkyl from one to six carbon atoms and R3 and R4 are hydrogen, or Rl+R3 are -~CH2)2- or -(CH2)3- and R2+R4 are -(CH2)3-;
R~ is hydrogen, alkyl of one to six carbon atoms, unsubstltuted or substituted phenyl, or -oR6, where R6 ls alkyl of one to six carbon atoms or unsubstituted or substituted phenyl;

(2) a borate anion coinltlator represented by the formula:

BXlX2X3X4 -wherein X1, X2, X3, and X4, the same or different, are selected from the group consisting of alkyl, aryl, aralkyl, ~lkenyl, alkynyl, alicyclic, heterocyclic, and allyl groups, with the prOviQO that at least one of X1, X2, X3, and X4 i~ not Aryl.

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Preferred hexaarylbisimidazoles are 2-Q-chloro-phenyl-substituted derivatives in which the other positions of the phenyl radicals are either unsubstituted or substituted with chloro, methyl or methoxy groups. The most preferred ~-amlnophenyl carbonyl compounds are Michler~s ketone, ethyl Michler's ketone, bis-(9-~ulolidyl)ketone, methyl ~-dimethyamino-benzoate and ethyl ~-d$methyaminobenzoate. Preferred borate anion coinitiators are triaryl alkyl borate anions. In a preferred embodiment the photopolymerizable composition also comprises a binder.
DetaiLed De~cription of the Inven~iQn The novel compositions of this inventicn are photopolymerizable compositions in which polymerization is initiated by free radicals generated by actinic radiation. Photopolymesizat$on proceeds by free radical initiated addition polymerizatlon and/or crosslinking of ethylenically unsaturated monomeric compounds. These compositions comprise a photoinitiator system, at least one polymerizable monomer, and, in the preferred case at least one binder. The photoinitiator system consists essentially of (a) hexaarylbislmidazole and/or a ~-aminophenyl carbonyl compound and ~b) a borate anion coinitiator. These compositions may also comprioe other ingredients, such as plasticizers, stabilizers, adhesion promoters, coating aids, and the like.

The photoinitiator system generates the free radicals which initiate polymerization of the monomer or monomers. The photoinitlator system should have a high molar absorption coefficient in the desired absorption range and should have a generate radicals with high efficiency. In addition, the system should possess such other desirable propertles such a-Q dark stability, , ,~, s, /, I

shelf-life, absence of odor, low toxicity, and reasonable cost.
Photoi~itiator systems containing ~-aminophenyl carbonyl compounds are well known. ~-Aminophenyl carbonyl compounds require a coinitiator to efficiently initiate polymerization. Typical coinitiators are hydrogen abstracting ketones such as benzophenone or camphorquinone ~2,3-boranedione). Photoinit~ator sy~tems which contain Mlchler's ketone (4,4'-bls-~dimethylamino)benzophenone) in combination with ahydrogen abstractor are disclosed in Chang, U.S. Patent 3,756,827 and in G. S. Hammond, et al., J. am~ Chem.
Soc., 2~, 6362 (1970). Photoinitiator systems which contain ~-dimethylaminobenzaldehyde or an ester of ~-dimethylaminobenzoic acid in combination with a hydrogen abstractor are disclosed in Barzynski, et al., U.S. Patent 4,113,593.
It has been discovered that borate anions may be used as coinitiators with ~-aminophenyl carbonyl compounds. The borate anion may be used in place of the hydrogen abstracting ketone. Alternatively the borate anion may be added to a ~-aminophenyl carbonyl com-pounds - hydrogen abstracting ketone initiator system to produce an initiator system with increased speed. A
preferred hydrogen abstracting ketone is benzophenone.
~ -Aminophenyl carbonyl compounds of the following structure may be used:

\N~C-Rs where:
Rl and R2 are each independently hydrogen or alkyl from one to six carbon atoms and R3 and R4 are hydr~gen, or Rl+R3 are -(CH2~2- or - ~CH2) 3-, or R2+R4 are - ~CH2) 3-;
S R5 is hydrogen, alkyl from one to s~x carbon atoms, unsubstituted or substltuted phenyl, or -oR6, where R6 is alkyl of one to six carbon atoms or uns~bstituted or substituted phenyl.
In a preferred class of a-aminophenyl carbonyl compounds R1 and R2 are each independently alkyl from one to three carbon atoms and R3 and R4 are hydrogen, or Rl+R3 and R2+R4 are independently -(CH2)3-; RS is (1) hydrogen, (2) alkyl from one to four carbon atoms, ~3) -oR6, where R6 is alkyl of one to four carbon atoms or lS unsubstituted or substituted phenyl, or (4):

Rl where R7 and R8 are each independently alkyl from one to three carbon atoms and R9 and R10 are hydrogen, or R7+R9 and R8+R10 are independently -(CH2)3-.
In a more preferred class of ~-aminophenyl carbonyl compounds Rl, R2, R7, and R8 ~re the ~ame and equal to alkyl from one to three carbon atoms and R3, R4, R9, and R10 are hydrogen, or R1+R3, R2+R4, R7+R9, and R3+R10 are the ~ame and equal to -(CH2)3-; or R1 and R2 are the same and equal to alkyl from sne to three carbon atoms and R3 and Rq are hydrogen, or R1~R3 and R2+R4 are -(CH2~3-, R5 30 18 -oR6~ where R6 is alkyl of one to four carbon atoms.

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The most preferred ~-amlnophenyl carbonyl compounds are: Michler's ketone (Rl e R2 . R7 ~ RB ~ methyl; R3 =
R4 = R9 = R10 = hydrogen), ethyl Michler~s ketone (R1 =
R2 e R7 = R~ ; ethyl; R3 ~ R4 - R9 e Rl0 ~ hydrogen), bis-(9-~ulolidyl)ketone (R1~R3 - R2~R4 - R7+R8 _ R~+R
-(CH2)3-), methyl ~-dlmethyaminobenzoa~e (Rl ~ R2 methyl; R3 ~ R4 - hydrogen; R6 ~ methyl) and ethyl ~-dimethyaminobenzoate (Rl _ R2 , methyl; R3 ~ R4 e hydrogen; R6 ~ ethyl).
Borate anions useful as coinitlators with dyes are disclosed in Gottschalk et al., U.S. Patents 4,772,530 and 4,772,541 and Koike et al., Federal Republic of Germany Patent Application 3,822,921, the disclosures of which are incorporated by reference. The borate anions are represented by the following general formula:

BXlX2X3X4 where Xl, X2, X3, and X4, are independently selected from the group consisting of alkyl, aryl, aralkyl, alkenyl, alkynyl, heterocyclic, and allyl groups, with the proviso that at least one of X1, X2, X3, and X4 is not aryl.
Each group may contain up to twenty carbon atoms, but groups with about seven carbon atoms or less are preferred. The alkyl groups may be linear, branched or cyclic, and may be substituted or unsubstituted.
Representative alkyl groups which may be present are:
methyl, ethyl, ~-propyl and n-butYl. Representative cycllc alkyl groups include cyclobutyl, cyclopentyl, and cyclohexyl. Representative exampleQ of aryl groups include phenyl and naphthyl, which may be unQubstituted or 3ubstituted with group~ such as, for example, methyl and methoxy. Repreqentative alkenyl groups are propenyl and ethynyl.

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Preferably, at least one, but not more than three, of Xl, X2, X3, and X4 iS an alkyl group. More preferred are anions in which xl-x4 is a combination of three aryl groups and one alkyl ~roup. The phenyl and ~-methoxy-phenyl groups are preferred aryl groups. A preferredanion is triphenylbutyl borate.
It is pre~erred that the cation as~oc~ated with the borate anion not absorb a si~niflcant amount of actinic radiation since this would decrease photospeed.
Representative cations are alkali metal cations and quaternary ammonium cations.
Quaternary ammonlum cations containing four alkyl groups are preferred. The alkyl groups may be linear, branched or cyclic, and may be substituted or unQubstituted. Representative quaternary ammonium cations are tetramethyl ammonium, tetraethyl ammonium, tetrabutylammonium, benzyl trimethyl ammonium, benzyl dimethyl tetradecylammonium, and (2-hydroxyethyl)-trimethylammonium.
Cations with larger alkyl groups may be used So advantage since t~e solubillty of the borate salt in the coating solvent is generally lncreased. Cations in which the alkyl groups together contain up to a total about thirty carbon atoms are preferred. Hydroxyl substitution may improve solubility and/or photospeed.
Particularly preferred cations are (2--hydroxyethyl)-trimethylammonium and benzyl dimethyl tetradecyl-ammonium.
Photoinitiator systems containing 2,2',4,4',5,5'-hexaarylbisimidazoles, or HABIs, are well known. Thesecompounds, which are described in: Chambers, U.S.
Patent 3,479,185; Cescon, U.S. Patent 3,784,557;
Dessauer~ U.S. Patent 4,252,887 and U.S. Patent 4,311,783; Tanaka et al., U.S. Patent 4,459,349, Wada et al., U.S. Patent 4,410,621, and Sheets, U.S. Patent ~., ~ . ' `

4,662,286, the disclosures of which are incorporated by reference, can be represented by the following general formula, in which Ar repre~ents an aryl group.

[ AAUu ~ N

A preferred class of hexaarylbisimidazoles are 2-Q-chlorophenyl-substituted derivatives in which the other positlons o~ the phenyl radicals are either unsubstituted or substituted with chloro, methyl or methoxy groups. Preferred HABXs include: Q-Cl-HABI, 2,2'-bis(~-chlorophenyl)-4,4,'5,5'-tetraphenyl-1,1'-biimidazole; CDM-HABI, 2-(Q-chlorophenyl)-4~5-bis(m-methoxyphenyl)imidazole dimer; TCTM-HABI, 2,5-bis(Q-chlorophenyl)-4-[3,4-dimethoxyphenyl]-lH-imidazole dimer; and TCDM-~ABI, the product of the oxidative coupling of 2-(Q-chlorophenyl)-4,5-diphenylimldazole and 2,4-bis-(~-chlorophenyl)-5-l3,4-dimethoxyphenyl~-imidazole disclosed in Sheets, U.S. Patent 4,662,286.
As disclosed in Chambers, V.S. Patent 3,479,185, HABIs requlre a chain transfer agent o:e hydrogen donor to efficiently in~tiate photopolymerizat~on. Without added chain transfer agent or hydrogen donor, little or no photopoiymerization occurs. Thlols, such as 2-mercaptobenzthiazole or 2-mercaptobenzoxzole, are typically added to HABI containing initiator systems for this purpo~e. The~e compounds may oxidize to disulfides or react with other components of the composition during manufacture and storage of the photopolymer. Photospeed is lost.

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It has been discovered that borate anions may be used as coinitiators for HABIs. When a borate anion is present, efficient photopolymerization is obtained, even in the absence of 8 chain transfer agent or hydrogen donor. Borate anions which may be uqed ln combination with HABIs are described above.
HABIs absorb strongly in the 255-275 nm region of the spectrum and usually have somewhat lesser absorption in the 300-375 nm region. As described in Chang, U.S.
Patent 3,549,367, and Anderson et al., U.S. Patent 4,535,052, sensitivity to the 300-375 nm region may be increased by using a hexaarylbisimidazole in combination with a ~-amlnophenyl carbonyl compound.
When a borate anion ls added to a photoinitiator system containing a HABI and ~-aminophenyl carbonyl compound, photospeed iQ increased. The ~-aminophenyl carbonyl compounds described above may be used in combination with HABI and borate coinitiators. Addition of a chain transfer agent or hydrogen donor is unnecessary. ~he most preferred ~-aminophenyl carbonyl compounds are Michler's ketone, ethyl Michler's ketone, bis-~9-~ulolidyl)ketone, methyl ~-dlmethyaminobenzoate and ethyl ~-dimethyaminobenzoate.
~Qn~
The composition contains at least one ethylenically unsaturated compound whlch undergoes free-radical initiated polymerization, generally known as a monomer.
The composition contains at leaQt one ~uch material and may contain a mixture of such materials.
Typical monomers are: unsaturated esters of alcohols, preferably polyols, ~uch as, diethylene glycol diacrylate, glycerol triacrylate, ethylene glycol dimethacrylate, pentaerythritol tri- ~nd tetraacrylate and methacrylate; unsaturated amides, such 1,6-hexamethylene bis-acrylamide; vinyl esters such as dlvinyl succinate, divlnyl phthalate, and dlvlnyl benzene-1,3-disulfonate; styrene and derlvatives thereof; and N-vinyl compounds, such as N-vinyl carbazole. Numerous other unsaturated monomers polymerizable by free-radical ~nitlated polymerization and useful in photopolymerlzable compositions are known to those skilled in the art. For photoresist applications the preferred monomers are trimethylol propane triacrylate, the triacrylate ester of ethoxylated trimethylolpropane, tetraethylene glycol diacrylate, and tetraethylene glycol dimethacrylate ~ he composition contains at least one preformed macromolecular polymeric material, generally know as a binder. The composition contains at least one such material and may contain a mixture of such materials.
In general, the binder should be soluble or swellable in the coating solvent and compatible with the other components of the photopolymerizable system.
Although the borate anion is generally unstable in the presence of strong acid, the use of acidic binders ln the practlce of thls lnventlon ls not precluded. It 18 preferred, however, that the binder contain weakly acldlc monomers, such as acrylic acld and methacrylic acid, and/or the binder have a low acid number.
Representative binder-~ are poly(methyl methacrylate) and copolymers of methyl methacrylate with other alkyl acrylates, alkyl methacrylates, methacrylic acid, and/or acrylic acid; poly~vinyl acetate3 and its partially hydrolyzed derivatives; gelatln; cellulose esters and ethers, such as cellulose acetate butyrate;
and polyethylene oxides. Numerou-~ other binders useful in photopolymerizable compositions are known to those skilled in the art. For photoresist applications the preferred blnders are copolymers of methyl methacrylate, ~ r ethyl acrylate, and methacrylic ac~d. Copolymers of methyl methacrylate, ethyl acrylate, and methacrylic acid copolymerized with a small amount of allyl methacrylate may also be used to advantage.
LSIA~ 2V~ le~
Other components conventionally added to photopolymerizable compositlons can be present to modify the physical properties of the fllm. Such components include: plasticizers, thermal stabillzers, optical brighteners, ultraviolet radlation absorbing materials, adhesion modifiers, coating aids, and release agents.
~ plasticizer may be present to modify adhesion, flexibillty, hardness, and other mechanical properties of the film in a conventional fashion. When a binder is present, a plasticizer would be selected which i9 compatible with the binder as well as the monomer and other components of the compositlon. With acrylic binders, for example, plasticizers can include dibutyl phthalate and other esters of aromatic acids; esters of aliphatic polyacids, such as diisooctyl adipate;
aromatic or aliphatic acid esters of glycols, polyoxyalkylene glycols, aliphatic polyols; alkyl and aryl phosphates; and chlorinated paraffins. In general, water insoluble plasticizers are preferred for greater high humidity storage stability, but are not necessary to get improved latitude.
Many ethylenically unsaturated monomers are sub~ect to thermal polymerization, especlally when stored for long periods or at elevated temperatures. ~ormally a conventional thermal polymerization inhibitor will be present to ~mprove the storage ~tability the photopolymerlzable compositlon. The nitroso dimers described in Pazos, U.S. Patent 4,168,982, are also useful. Since monomers generally contain thermal polymerization inhibitors added by their manufacturers, it is frequently unnecessary to add additional inhibitor.
Nonionic surfactants may be added to the photopolymerizable composition AS coating alds. Typical coating aids are polyethylene oxides, such as Polyox~
WShN, and fluorlnated nonionlc surfactants, such as Fluorad~ FC-430 and Fluorad~ FC 431.
Depending on the application, other inert additives can be employed such as dyes, pigments and fillers.
These additives are generally present in minor amounts so as not to interfere with the exposure of the photopolymerizable layer.
ComDos i~Qn While the composition of the photopolymerizable composition will depend on the intended application, when the composition is to be u~ed as a dry film, in general, the binder should be at least about 25% and the monomer should not exceed about 60%, based on the total weight of the composition. ~f the amount of binder is below approximately 25%, or the amount of monomer exceeds approximately 60%, the composition has insufficient ~iscosity to form a solld film. While the amount of initiator system present will depend on the thickness of the layer and the desired optical density for the intended application, in general, about 0.1% to about 10% by weiqht will be present.
Typical compositions are by weight: binder(s) 25 to 90%, preferably 45 to 75%; monomer (-Q) ~ 5 to 60%, preferably, 15 to 50%; plasticizer, 0 to 25%, preferably, 0 to 15%; photoinitiator system, 0.1 to 10~, preferably 1 to 7%; and other inqredients, 0 to 5~, typically 0 to 4%.
The amount of borate salt present is limited by its solubility. Although as much as 1% or more borate salt by weight may be added in fa~orable cases, additlon of too much borate salt may adversely affect the dark stability and shelf life of the photopolymer. In general, the concentrat~on of borate salt should be between about 0.05 and about 14. A preferred range is about 0.1 to about 1.0%.

The photopolymerizable compo-~tlons can be coated onto a wide variety of substrates. By "substrate" is meant any natural or synthetic support, prefer~bly one which is capable of existing ln ~ flexlble or rigid form. For example, ~he substrate can be a metal sheet or foil, a sheet or film of synthetic organic resin, cellulose paper, fiberboard, and the like, or a composite of two or more of these materials.
The particular substrate will generally be determined by the intended application. For example, when prlnted circuits are produced, the substrate may be a plate which is a copper coating on fiberboard; in the preparation of lithoqraphic printlng plates, the substrate may be anodized aluminum. Specific substrates include alumina-blasted aluminum, anodized aluminum, alumina-blasted polyethylene terephthalate film, polyethylene terephthalate film, e.g., resin-subbed polyethylene terephthalate film, polyvinyl alcohol-coated paper, crosslinked polyester-coated paper, nylon, glass, cellulose acetate film, heavy paper such as lithographic papcr, and the like.
The photopolymerizable layer may prepsred by mixing the ingredients of the photopolymerizable composition in a solvent, such as dichloromethane, usually in the weight ratlo of about 15:85 to 25:75 (solids to solvent), coating on the substrate, and evaporating the solvent. Coatings should be unlform. While the thickness of the layer wlll depend on the intended application, for dry fllm photoresists the coating ~J ~ J .. ' should have a thickness of about 0.2 to 4 mil ~5 to 100 microns), preferably 0.5 to 2 mil (13 to 50 microns), when dry. For protection, a release film, such as polyethylene or polypropylene, may be placed over the photopolymerizable layer after the solvent evaporates.
~ lternatively, since photopolymer composltlons are quickly and efficiently coated onto polymer films using continuous web coating techniques, it may be convenient to coat the photopolymerizable composition onto a polymer film support, ~uch as polyethylene terephthalate film, and laminate the resulting photopolymerizable layer to the substrate prior to exposure. The photopolymerizable layer may be protected until it is ready for use by, preferably, a release film, such as polyethylene or polypropylene, applied as the coated polymer film emerges from the drier. After removal of the release fllm, the photopolymerizable layer can then be laminated to the support. The polymer film support then acts as a coversheet which is removed after exposure.
Ex~osure/Imaae Formation Any convenient source or sources of actinic radiation providing wavelengths in the region of the spectrum that overlap the absorption bands of the sensitizer can be used to activate photopolymerization.
8y "actinic radiation" is meant radiation which is active to produce the free-radical~ necessary to initiate polymerization of the monomer (8) . The radiation can be natural or artificial, monochromatic or polychromatic, incoherent or coherent, and for h~gh efficiency should correspond cloQely to in wavelength to the absorptlon of the inltiator Qyqtem.
Conventional llght sources include fluorescent lamps, mercury, metal additive and arc lamps. Coherent light sources are xenon, ~rgon ion, and ionized neon ~ er lasers, as well as tunable dye lasers and the frequency doubled neodymium:YAG laser, whose emissions fall within or overlap the visible absorptlon bands of the sensitizer.
The photopolymerizable compositions of this invention have good photospeed. They are useful in printlng plates for offset and letter press, englneering drafting films, holographic recording films, photoresists, solder masks, and varlous proofing applications, such as prepress color proofing. Other specific uses will be evident to those skilled in the art.
In photoresist applications, resists prepared from the compositions of this invention are useful for the preparation of microcircuits. The resist can be either solvent soluble or aqueous developable. Solder masks are protective coatings which are selectively applied to portions of a printed circuit board to confine solder to pad areas on the board and to prevent bridging between conductors durlng tinning operations and during soldering of components. A solder mask also functions to prevent or minimize corrosion of the baQe copper conductors and as a dielectric to insulate certain components ln ad~acent circuitry.
The advantageous properties of this lnvention can be observed by reference to the following examples which illustrate, but do not limit, the lnvention.

~a:~
~L~SE~8Y
BDTB Benzyl dlmethyl tetradecylammonium triphenylbutyl borate BPTMAB ~3-Bromopropyl)trimethyl ammonlum triphenylbutyl borate BTMAB Benzyltrimethyl ammonium triphenylbutyl borate BZ Benzophenone; CAS 119-61-9 Carboset~ 1034 Poly(methyl methacrylate/ethyl acrylate/methacrylic acid) ~44/35/21);
MW 50,000; Tg 87C; Union Carbide, Danbury, CT
Q-Cl-HABI l,1'-Biimidazole, 2,2'-bis~Q-chlorophenyl]-4,4',5,5' tetraphenyl-;

CDM-~ABI 2-(~-chlorophenyl~-4,5-b$s(m-methoxy-phenyl)imidazole dimer; CAS 29777-36-4 EMK Ethyl Michler's ketone; 4,4'-Bis-(diethylamino~benzophenone; CAS 90-93-7 15 EPD Quantacure~ EPD; Ethyl ~-dimethyamino-benzoate;
HTMAP (2-Hydroxyethyl)trimethylammonium tetraphenylbutyl borate ITX Quantacure~ ITX; 2-iso-Propyl-thioxanthone;
TBAB Tetrabutylammonlum trlphenylbutyl borate TCDM-HABI Product of the oxidative coupllng of 2-~-chlorophenyl)-4,5-dlphenylimidazole and 2,4-bis-(Q-chlorophenyl)-5-[3,4-dimethoxyphenyl]imidazole TCTM-HABI 2,5-bis(Q-chlorophenyl)-4-t3,4-d~methoxyphenyl]-lH-imidazole dimer;
TMAOAc Tetrabutylammonium acetate TMAB Tetramethylammonium triphenylbutyl borate TMABr Tetramethylammonium bromide TMACl Tetramethylammonlum chlorlde TMAPF6 Tetramethylammonium hexa1uorsphosphate TMABF4 Tetramethylammonlum tetra~luoroborate 35 TEAB Tetraethylammonlum triphenylbutyl borate .' . :

TMPEOTA Triacrylate ester of ethoxylated trimethylolpropane; CAS 2B961-43-5 TMPTA Trimethylolpropane triacrylate;2-ethyl-2-(hydroxymethyl)-1,3-propanediol triacrylate; CAS 15625-89-5 ~neral P~ocedures In the Examples whlch follow it should be understood that "coating ~olution" refers to the mixture of solvent and additives whlch is coated, even though some of the addltives may be in suspension rather than in solution, and that "total solids" refers to the total amount of nonvolatile material in the coating solution even though ~ome of the additives may be nonvolatile liquids at ambient temperature. All parts are by weight unless otherwise indicated.
All operations were carried out under yellow lights. A st~ck solution containing Carboset~ 1034 (65.0%), ~MPEOTA (26.0%), and TMPTA ~9.0%) was prepared by dissolving the ingredients in 2-butanone ~54.5% total solids). The lndicated initiators were added to aliquots of the stoc~ solution prior to coating. The indicated percentage of added initlator i8 the weight added ~nitiator in gm relative to 100 gm of solids in the stock solution.
Solutions were board coated on 23 m~cron thick clear polyethylene terephthalate film with a 200 micron doctor blade to give a dry film thickneqs of approximately 38 mlcrons. The coat~ng solvent was 2-butanone. In ~ome cases about 5~ of l-propanol or 2-propanol was added to increase the solubility of the lngredients ln the co~ting solution.
Fllms were hot roll laminated to copper, exposed under a Stouffer-41 target (Stouffer Industries, South Bend, IN) using a PC-130 printer (Du Pont, Wilmington, DE). The polyethylene terephthalate was left in place as a coversheet during exposure. The Stouffer-41 target contains forty one sixth root of two steps. The polyethylene terephthalate film was removed and the exposed samples developed at 50% breakpolnt (29C, 1%
aqueous Qodium carbonate) using a Chemcut aqueous processor (Chemcut, State College, PA).
All exposed films which were capable of holding steps were also capable of imaging at least an about 250 micron line and space pattern. Those exposed films which were incapable of holding steps were also incapable of holding the line and Qpace pattern.
Control Exam~le A
Thls example illustrates that tetramethyl ammonium chloride (TMACl), tetramethyl ammonium bromide (TMABr), tetramethyl ammonium acetate ~TMAOAc), and tetramethyl ammonium hexafluorophosphate ~TMAPF6) are not coinitiators for hexaarylbisimidiazoles.
Samples containing the indicated initiators were prepared and exposed as described in the general procedures. An initiator system containing 0.20% EMK
and 2.00% Q-Cl HABI was added to each sample. The results are shown in Table 1.

Table 1 Exposure (2) 1/6 Relative Added Salt~ ~mJ/cm2) Steps Held Photospeed None 94 26 lb 0.04% TMACl 94 26 1.0 O . 06% TMABr 94 27 . 1.1 0.18% TM~Br 94 26 1.0 O.05% TMAOAc 94 26 1.0 0.06% TMAPF6 94 26 1.0 ~Initiator system: 0.20% EMX and 2.00% Q-Cl HABI.
bReference.
~m~
This example illustrates that tetramethyl ammonium triphenyl butyl borate ~TMAB) is a coinitiator for hexaarylbisimidiazoles.
Samples containing (13 2.00% the indicated HABI and (2) 2.00% the indicated HABI plus 0.12% TMAB were prepared and exposed as described in the general procedures. The results are shown in Table 2.

Expo~ure (2) l/6 Inltiator Sy~tem ~mJ/cm2) Step~ Held Incre~e 2.00% Q-Cl-HABI 1620 6 2.00~ Q-Cl-~ 0.124 TMAB 110 26 150 X
2.00% CDM-~ABI 161 21 2.00~ CDM-~A~I + 0.12% TMAB34 22 5.3 X
2.00~ TCTM-HABI 797 15 2.00~ TCTM-HABI + 0.12~ ~MAB 17 22 105 X
2.00~ TCDM-HABI 17 14 2.00 TCDM-HABI I 0.124 TMAB17 21 2.2 X

Example 2 and Control Examnle B
This example illustrates that the triphenyl butyl borate an$on is a coinitiator for hexaarylbisimidazole initiated photopolymerization but that tetramethyl ammonium tetrafluoroborate (TMABF4) is not.
Samples containing 0.20% EMK and 2.00% Q-Cl HABI
were prepared and exposed as described in the general procedures. The results are given in Table 3.

~able 3 Exposure ~2) 1/6 Relative Added Salt~ ~mJ/cm2) Steps Held Photospeed None 110 25 lb O.124 TMAB 110 29 1.6 O.05% TMABF4 110 24 0.9c 0.12% T~ABF4 110 14 o.gc Inltiator system: 0.20% EMK and 2.00% Q-Cl HABI.
bReference.
CDecrease ln photospeed.

~xam~le_~
This example illustrateQ that catlons other than the tetramethyl ammonium cation may be used with the borate anion. A large increase in photospeed was observed w~th ~2-hydroxyethyl)trimethylammonlum tr~phenylmethyl borate (HTMAP ) .
Samples containing 0.204 EMR and 2.00% Q-Cl HABI were prepared and exposed as described in the general procedures. The results are Qhown in Table 4.

Table 4 Exposure ~2) l/6 Relative Added Salta (mJ/cm2) Steps Held Photospeed None 68 18 lb 0.13~ HTMAP 68 29 3.6 O.65% HTMAP 28 37 22.4 20 0.20% BDTB 68 25 2.2 0.50% BDTB 68 28 3.2 1.00% BDTB 68 31 4.5 ~Initlator system: 0.20% EMX and 2.00% ~-Cl HABI.
bReference.

This example illustrates that borate salts with various catlons may be used as colnltlators for an lnltlator system contalning an amlne and a hexaarylbisimldazole.
Samples containing the indicated lnitiators were prepared 2nd exposed as described ln the general procedures. The results ~re glven in Table 5.

~ ~ ? ~ ~ ~. r ~, ., .. . ~ ~.,;

Exposure (2) 1/6 Relative Added Salta ~mJ/cm2) Steps Held Photospeed 5 Nonea 120 24 lb 0.12% TMAB 120 30 2.0 0.24% TMAB 120 33 . 2.8 0.14% TEAB 120 28 1.6 0.17% TBAB 120 31 2.2 10 020% BDTAB 120 32 2.5 0.13% BTMAB 120 33 2.8 0.15% BPTMAB 120 31 2.2 0.18% TTP 120 29 1.8 0.16% BTAB 120 29 1.8 aInitiator system: 0.20% EMK and 2.00% Q-Cl HABI.
bReference.

This example illustrates that TMAB ls a coinitiator for various initiators of photopolymerization.
Samples containing the indicated initiators were prepared and exposed as described in the general procedures. The results are shown in Table 6.

' Table 6 Rela-tive Initiator Exposure (2) 1/6 Steps Held Photo-System (mJJcm2) No Borate ~oratea speed None 1620 0 0 c 0.20% EMK 815 18 39 9.0 2.00% ~Z408 14 21 2.2 0.20% ITX 408 20 34 5.0 2.00% EPD 1620 0 8 d ao.12% TMAB added.
bPhotospeed of composition with borate added relatiYe to the same composition without borate.
CControl - no photopolymerization with or without added borate.
dNot calculable. Greater than 2.5.

;~mDL~ fi This example illustrates that tetramethyl ammonium triphenyl butyl borate (TMAB) 19 a coinitiator for an lnitiator system containing benzophenone (BZ) and a bis-[~-(N,N-dialkylamino)phenyl]ketone.
Samples containing (1) 2.00% BZ and 0.20% EMK and ~2) 2.00% BZ and 0.20% EMK plus 0.12% TMAB were prepared and exposed as described in the general procedures. The results are shown in Table 7. Addition of borate to the initiator system increased photospeed about 60%.

~5 ,able~l Initiator Sy~temExpo~ure ~2) 1/6 Init$ator Sy3tem(mJ/cm2) Step~ Held _ 2.004 BZ I 0.204 E~R 70 25 2.00% ~Z + 0.20% EMX + 0.124 TMA~ 44 25

Claims

1. A photopolymerizable composition with improved sensitivity to actinic radiation comprising:
(A) an ethylenically unsaturated monomer capable of free-radical initiated polymerization; and (B) an initiator system activatible by actinic radiation, said initiator system consisting essentially of:
t least one compound selected from the group consisting of (a) hexaarylbisimidazole and (b) p-aminophenyl carbonyl compound of the following structure:

where:
R1 and R2 are each independently hydrogen or alkyl from one to six carbon atoms and R3 and R4 are hydrogen, or R1+R3 is -(CH2)2-, or -(CH2)3- and R2+R4 is -(CH2)3-;
R5 is hydrogen, alkyl of one to six carbon atoms, unsubstituted or substituted phenyl, or -OR6, where R6 is alkyl of one to six carbon atoms or unsubstituted or substituted phenyl;
(2) a borate anion coinitiator represented by the formula:

wherein X1, X2, X3, and X4, the same or different, are selected from the group consisting of alkyl, aryl, aralkyl, alkenyl, alkynyl, alicyclic, heterocyclic, and allyl groups, with the proviso that at least one of X1, X2, X3, and X4 is not aryl.

2. A photopolymerizable composition of Claim 1 wherein said compound is a hexaarylbisimidazole.

3. A photopolymerizable composition of Claim L wherein said compound is a p-aminophenyl carbonyl compound.

4. A photopolymerizable composition of Claim 3 wherein R1 and R2 are each independently alkyl from one to three carbon atoms and R3 and R4 are hydrogen, or R1+R3 and R2+R4 are independently -(CH2)3-; R5 is (1) hydrogen, (2) alkyl from one to four carbon atoms, (3) -OR6, where R6 is alkyl of one to four carbon atoms or unsubstituted or substituted phenyl, or (4):

where R7 and R8 are each independently alkyl from one to three carbon atoms and R9 and R10 are hydrogen, or R7+R9 and R9+R10 are independently be -(CH2)3-.

5. A photopolymerizable composition of Claim 4 wherein R1, R2, R7, and R8 are the same and equal to alkyl from one to three carbon atoms and R3, R4, R9, and R10 are hydrogen, or R1+R3, R2+R4, R7+R9, and R8+R10 are the same and equal to -(CH2)3-; or R1 and R2 are the same and equal to alkyl from one to three carbon atoms and R3 and R4 are hydrogen, or R1+R3 and R2+R4 are -(CB2)3-, R5 is -OR6, where R6 is alkyl of one to four carbon atoms.

6. A photopolymerizable composition of Claim 3 wherein the a-aminophenyl carbonyl compound is selected from the group consisting of Michler's ketone, ethyl Michler's ketone, bis-(9-julolidyl)ketone, methyl p-dimethyaminobenzoate and ethyl p-dimethyaminobenzoate.

7. A photopolymerizable composition of Claim 3 wherein a hydrogen abstracting ketone is also present.

8. A photopolymerizable composition of Claim 7 wherein said hydrogen abstracting ketone is benzophenone.

9. A photopolymerizable composition of Claim 1 wherein at least one hexaarylbisimidazole and at least one p-aminophenyl carbonyl compound are present.

10. A photopolymerizable composition of Claim 1 wherein said borate anion contains a combination of three aryl groups and one alkyl group.

11. A photopolymerizable composition of Claim 1 wherein the cation associated with said borate anion is a quaternary ammonium cation containing four alkyl groups, said alkyl groups together containlng fewer than thirty carbon atoms.

12. A photopolymerizable composition of Claim 11 wherein said cation is benzyl dimethyl tetradecyl-ammonium or (2-hydroxyethyl)trimethylammonium.

13. A photopolymerizable composition or Claim 1 additional comprising a binder.

14. A photopolymerizable composition of Claim 13 wherein said compound is a hexaarylbisimidazole.

15. A photopolymerizable composition of Claim 14 wherein said hexaarylbisimidazole is 2-o-chlorophenyl-substituted and the other positions on the phenyl radicals are either unsubstituted or substituted with chloro, methyl or methoxy groups.

16. A photopolymerizable composition of Claim 14 wherein said hexaarylbisimidazole is selected from the group consisting of 2,2'-bis(o-chlorophenyl)-4,4,'5,5'-tetrapheny-1,1'-biimidazole; 2-(o-chlorophenyl)-4,5-bis (m-methoxyphenyl)imidazole dimer; 2,5-bis(o-chloro-phenyl)-4-[3,4-dimethoxyphenyl]-1H-imidazole dimer;
and the product of the oxidative coupling of 2-(o-chloro-phenyl)-4,5-diphenylimidazole and 2,4-bis-(o-chloro-phenyl)-5-[3,4-dimethoxyphenyl]imidazole.

17. A photopolymerizable composition of Claim 13 wherein said compound is a p-aminophenyl carbonyl compound.

18. A photopolymerizable composition of Claim 17 wherein R1 and R2 are each independently alkyl from one to three carbon atoms and R3 and R4 are hydrogen, or R1+R3 and R2+R4 are independently -(CH2)3-; R5 is (1) hydrogen, (2) alkyl from one to four carbon atoms, (3) -OR6, where R6 is alkyl of one to four carbon atoms or unsubstituted or substituted phenyl, or (4):

where R7 and R8 are each independently alkyl from one to three carbon atoms and R9 and R10 are hydrogen, or R7+R9 and R8+R10 are independently be -(CH2)3-.

19. A photopolymerizable composition of Claim 18 wherein R1, R2, R7, and R8 are the same and equal to alkyl from one to three carbon atoms and R3, R4, R9, and R10 are hydrogen, or R1+R3, R2+R4, R7+R9, and R8+R10 are the same and equal to -(CH2)3-; or R1 and R2 are the same and equal to alkyl from one to three carbon atoms and R3 and R4 are hydrogen, or R1+R3 and R2+R4 are -(CH2)3-, R5 is -OR6, where R6 is alkyl of one to four carbon atoms.

20. A photopolymerizable composition of Claim 19 wherein the p-aminophenyl carbonyl compound is selected from the group consisting of Michler's ketone, ethyl Michler's ketone, bis-(9-julolidyl)ketone, methyl p-dimethyaminobenzoate and ethyl p-dimethyaminobenzoate.

21. A photopolymerizable composition of Claim 17 wherein a hydrogen abstracting ketone is also present.

22. A photopolymerizible composition of Claim 21 wherein said hydrogen abstracting ketone 15 benzophenone.

23. A photopolymerizible composition of Claim 13 wherein at least one hexaarylbisimidazole and at least one p-aminophenyl carbonyl compound are present.

24. A photopolymerizable composition of Claim 13 wherein said borate anion contains at least one, but not more than three, aryl groups.

25. A photopolymerizable composition of Claim 24 wherein said borate anion contains a combination of three aryl groups and one alkyl group.

26. A photopolymerizable composition of Claim 13 wherein the cation associated with said borate anion is a quaternary ammonium cation containing four alkyl groups, said alkyl groups together containing fewer than thirty carbon atoms.

27. A photopolymerizable composition of Claim 26 wherein said cation is benzyl dimethyl tetradecy-ammonium or (2-hydroxyethyl)trimethylammonium.

28. A photopolymerizable composition of Claim 13 wherein said photopolymerizable composition is a photoresist.