Abstract:
A photocurable composition comprising an ultraviolet radical polymerization initiator, a cationic dye with absorptions in the visible light region, a quaternary boron salt and optionally a polymerization accelerator, is irradiated with ultraviolet light and visible light either simultaneously or separately, to achieve adequate hardening in air of both the surface and the interior of the cured product, and to provide a cured product with an excellent appearance and without production of coloring substances derived from the polymerization initiator.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a photocurable composition and a curing process therefor. In particular, the present invention relates to a photocurable composition which can be cured not only on the curing surface but also to the interior of the cured product with notably minimized coloration of the cured product resulting from the polymerization initiator, by irradiation with ultraviolet light in the range of 200-400 nm and visible light in the range of 400-740 nm, even when using materials which exhibit poor light transmittance as a result of containing pigments and coloring dyes with strong hiding powers or having large thicknesses, as well as to a process for curing the photocurable material. 
     2. Description of the Related Art 
     Photopolymerization has been conventionally employed for a wide range of multifaceted uses, including curing and printing of coatings, resin relief-printing, printed board construction, resist and photo masking, black-and-white and color transfer coloring sheets and coloring sheet preparation, etc., and the recent focus on environmental issues, energy conservation and labor-saving means to counter increasing labor costs has stimulated active development with an emphasis on polymerization at normal temperature, rapid curing and the ability to be used without a solvent, which are features of photopolymerization. 
     In the area of printing ink, research has been progressing an ultraviolet photocuring inks for the purpose of elimination of solvents, improving productivity through achieving more rapid curing, or provision of superior physical characteristics for cured coatings (For example, Japanese Unexamined Patent Publications No. 1-229084 and No. 2-22370). In Japanese Unexamined Patent Publication No. 2-22370 there is disclosed an ultraviolet photocuring ink with an excellent-curing rate and coating hardness, which is characterized by containing a poly(meth)acrylic acid ester and an ultraviolet photopolymerization initiator. 
     Also, while research in the area of coating paints continues with respect to rapid curing and curing of colored coatings (for example, Japanese Unexamined Patent Publications No. 52-135341, No. 52-152436, No. 2-296875 and No. 3-6265), curing with ultraviolet light results in rapid curing of polymerizable monomers when cationic polymerization or radical polymerization is performed with irradiation of ultraviolet light of 200-400 nm, and therefore penetration of ultraviolet light has been a problem with colored coatings containing pigments or dyes with strong hiding powers. 
     For example, when a pigment or a coloring dye with a strong hiding power is added to give a colored coating with the aforementioned superior hiding power, the light transmittance is impaired by absorption or reflection of light by the pigment or coloring dye, resulting in a problem in which the coating surface cures but the interior of the coating fails to sufficiently harden. Also, even in transparent compositions containing no pigments or coloring dyes, if the curing composition thickness is increased or the curing composition contains a material with poor ultraviolet transmittance, the same problem occurs in which the interior of the curing composition fails to sufficiently harden. 
     In order to overcome this problem, an attempt has been made in Japanese Unexamined Patent Publication No. 6-75374 to increase the interior curability of photocurable compositions containing pigments, by adding a near-infrared radical polymerization initiator comprising a near-infrared light absorbing cationic dye and an organic boron salt sensitizer to an ultraviolet radical polymerization initiator. However, this composition has had a disadvantage in that the ultraviolet decomposition product of the near-infrared light absorbing cationic dye has caused coloration of the material after photocuring. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a photocurable composition which can be adequately cured not only on the surface but also in the interior by simultaneous or separate irradiation of ultraviolet light of 200-400 nm and visible light of 400-740 nm, and which gives cured products having an excellent appearance without coloring caused by the polymerization initiator, even with curing compositions comprising coloring materials with strong hiding powers such as pigments and coloring dyes and including materials with poor ultraviolet light transmittance, which compositions have presented difficulties for conventional ultraviolet curing, as well as a photocuring process therefor. 
     In order to overcome these problems, the present inventors have conducted diligent research on photocurable compositions employing ultraviolet radical polymerization initiators with absorptions between 200-400 nm, cationic dyes with visible light absorptions between 400-740 nm and quaternary boron salts as sensitizers, and on photocuring processes, and as a result the inventors have completed the present invention upon the discovery of a photocurable composition and a photocuring process therefor, whereby adequate hardening can be achieved both on the surface and in the interior of the cured product even when the composition contains pigments or coloring dyes with strong hiding powers, and whereby a cured product with an excellent outer appearance can be achieved without the production of coloring substances derived from the polymerization initiator. 
     In other words, according to the invention it is possible to obtain a photocurable composition with which adequate photocuring can be achieved both on the surface and in the interior even when the composition contains additives with strong hiding powers, and which gives cured products with an excellent appearance without coloring derived from the polymerization initiator, prepared by combining an ultraviolet radical polymerization initiator with a cationic dye represented by general formula (1): 
     
         D.sup.+ ·A.sub.1.sup.-                            (1) 
    
     wherein D +  is a cationic dye with absorptions in the visible light regions of 400-740 nm and A 1   -  is an anion, and a quaternary boron salt sensitizer represented by general formula (2): ##STR1## wherein R 1 , R 2 , R 3  and R 4  each independently represent an alkyl group which may have a substituent, an aryl group which may have a substituent, an allyl group which may have a substituent, an aralkyl group which may have a substituent, an alkenyl group which may have a substituent, an alkynyl group which may have a substituent, a silyl group which may have a substituent, a heterocyclic group or a halogen atom, and Z +  represents a quaternary ammonium cation, quaternary pyridinium cation, quaternary quinolinium cation, phosphonium cation, sulfonium cation, oxosulfonium cation, iodonium cation or metal cation, and mixing these with a compound which has a radical polymerizable unsaturated group. Furthermore, according to the present invention it is possible to further improve the interior curability of the coating by adding to the above-mentioned photocurable composition one or more polymerization accelerators selected from compounds represented by general formulas (3) to (8). ##STR2## wherein R 5  and R 6  each represent an aryl group which may have a substituent, R 7  represents an alkyl group which may have a substituent, an alkenyl group which may have a substituent, an alkynyl group which may have a substituent, an alicyclic group which may have a substituent, an aryl group which may have a substituent or an aralkyl group which may have a substituent, and A 2   -  represents an anion. 
     
         R.sub.8 --I.sup.+ --R.sub.9 ·A.sub.3.sup.-        (4) 
    
     wherein R 8  and R 9  represents aryl groups which may have substituents, and A 3   -  represents an anion. ##STR3## wherein R 10 , R 11 , R 12 , R 13  and R 14  each represent a hydrogen atom, halogen atom, cyano group, an alkyl group which may have a substituent, an alkoxy group which may have a substituent, an aryl group which may have a substituent or a heterocyclic group represented by general formula (5), R 15  represents an alkyl group which may have a substituent, and A 4   -  represents an anion. ##STR4## wherein R 16  represents an aryl group which may have a substituent, and each R 17  represents a halogen atom. ##STR5## wherein R 18  represents an aryl group which may have a substituent, and R 19  represents an alkyl group which may have a substituent, an aryl group which may have a substituent or a benzoyl group which may have a substituent. ##STR6## wherein R 20 , R 21  and R 22  each represent a trihalomethyl group, an alkyl group which may have a substituent, an alkenyl group which may have a substituent or an aryl group which may have a substituent, provided that at least one thereof is a trihalomethyl group. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     When the cationic dye of general formula (1) and the quaternary boron salt sensitizer of general formula (2) are used together according to the construction of the present invention, decomposition occurs with light of wavelength between 400 and 740 nm, and polymerization is initiated concurrently with loss of the color of the cationic dye. When no quaternary boron salt sensitizer is present, the decoloration reaction of the cationic dye fails to proceed sufficiently, thus impeding the polymerization reaction; however, the presence of the sensitizer according to the invention results in complete decoloration reaction of the cationic dye, and thus efficient progress of the polymerization initiation. Also, by the further addition of a polymerization accelerator represented general formulas (3) to (8), the polymerization initiation proceeds even more efficiently. These polymerization accelerators may be compounds which produce radicals by receiving electrons from the dye radical which are generated by irradiation of light of wavelength between 400 and 740 nm, and are thus able to notably improve the interior curability of the cured product. 
     In the cationic dye of general formula (1), which has absorptions between 400-740 nm, preferred cations (D + ) may include, for example, cationic portions of polymethine-, xanthene-, acridine-, azine-, oxazine-, thiazine-, diarylmethane- and triarylmethane cationic dyes, of which some concrete ones are listed in Table 1, but the present invention is not limited to these examples. 
     
                                           TABLE 1__________________________________________________________________________                             Maximum    absorption wavelength  No. Chemical structure (type of solvent)__________________________________________________________________________  1                               428 nm  (chloroform)   - 2                               522 nm  (acetonitrile)   - 3                               528 nm  (chloroform)   - 4                               528 nm  (ethanol)   - 5                               544 nm  (acetonitrile)   - 6                               559 nm  (acetonitrile)   - 7                               613 nm  (acetonitrile)   - 8                               632 nm  (acetonitrile)   - 9                               658 nm  (chloroform)   - 10                               527 nm  (acetonitrile)   - 11                               534 nm  (acetonitrile)   - 12                               549 nm  (acetonitrile)   - 13                               560 nm  (acetonitrile)   - 14                               589 nm  (acetonitrile)__________________________________________________________________________ 
    
     Since these dyes have a short or no polymethine skeleton in the molecule, they are resistant to oxidation by oxygen in the air during ultraviolet irradiation, resulting in minimal production of cationic dye oxides which impair the color phase of the cured product, and are thus able to give cured products with excellent appearances. 
     The counter anion (A 1   - ) of the cationic dye of general formula (1) may be any desired anion, and as examples there may be mentioned halide anions such as chloride, bromide and iodide anions; sulfonate anions such as benzenesulfonate anion, p-toluenesulfonate anion and methanesulfonate anion; borate anions such as tetraphenyl borate, tetraanisyl borate, n-butyltriphenyl borate, n-butyltri (4-t-butylphenyl)borate, tetrabenzyl borate and tetrafluoroborate; and other types of anions such as ClO 4   - , PF 6   -  and SbF 6 . The present invention, however, is not limited to these examples. Two or more of these cationic dyes may also be used in any desired proportion as necessary. 
     The quaternary boron salt sensitizer of the invention is represented by general formula (2). ##STR21## wherein R 1 , R 2 , R 3 , R 4  and Z +  are as defined above. 
     As concrete examples of the anion portion of the compounds with the structure represented by general formula (2) there may be mentioned n-butyltriphenyl borate, n-octyltriphenyl borate, n-dodecyltriphenyl borate, sec-butyltriphenyl borate, t-butyltriphenyl borate, benzyltriphenyl borate, n-butyltrianisyl borate, n-octyltrianisyl borate, n-dodecyltrianisyl borate, n-butyltri(4-tolyl)borate, n-butyltri(2-tolyl)borate, n-butyltri(4-t-butylphenyl)borate, n-butyltri(4-fluoro-2-methylphenyl)borate, n-butyltri(4-fluorophenyl)borate, n-butyltrinaphthyl borate, triphenylsilyltriphenyl borate, diphenylmethylsilyltriphenyl borate, dimethylphenylsilyltriphenyl borate, trimethylsilyltriphenyl borate, tetra-n-butyl borate, di-n-butyldiphenyl borate and tetrabenzyl borate. 
     As concrete examples of the cation portion there may be mentioned tetramethylammonium, tetraethylammonium, tetra-n-butylammonium, tetraoctylammonium, methylquinolinium, ethylquinolinium, methylpyridinium, ethylpyridinium, tetramethylphosphonium, tetra-n-butylphosphonium, trimethylsulfonium, triphenylsulfonium, trimethylsulfoxonium, diphenyliodonium, di(4-t-butylphenyl)iodonium, lithium cation and sodium cation. These anion portions and cation portions may be used for the invention in any desired combination. Also, the present invention is not limited to these examples. There is also no problem with using 2 or more quaternary boron salt sensitizers in combination. 
     Concrete examples of polymerization accelerators are given below. As the cation portion of the sulfonium salt represented by general formula (3) there may be mentioned triphenylsulfonium, diphenylanisylsulfonium, diphenyl(4-tolyl)sulfonium, diphenyl(4-fluorophenyl)sulfonium, diphenyl[4-(phenylthio)phenyl]sulfonium, diphenylbenzylsulfonium, diphenyl(4-chlorobenzyl)sulfonium, diphenyl(4-bromobenzyl)sulfonium, diphenyl(4-cyanobenzyl)sulfonium, di(4-t-butylphenyl)benzylsulfonium, dianisyl(4-bromobenzyl)sulfonium, diphenylphenacylsulfonium, diphenyl(4-chlorophenacyl)sulfonium, diphenyl(4-cyanophenacyl)sulfonium, diphenylallylsulfonium, diphenylmesylsulfonium, diphenyl-p-toluenesulfonylmethylsulfonium, diphenyl(dimethylsulfoniumylmethyl)sulfonium, and diphenyl[4-(diphenylsulfoniumyl)phenyl]sulfonium. As the anion portion there may be mentioned BF 4   - , PF 6   - , AsF 6   - , SbF 6   - , ClO 4   - , Cl - , Br - , tetraphenyl borate, tetrakis(pentafluorophenyl) borate, benzenesulfonate anion, p-toluenesulfonate anion and trifluoromethanesulfonate anion, and these anion portions and cation portions may be used for the invention in any desired combination. 
     As the cation portion of the iodonium salt represented by general formula (4) there may be mentioned diphenyliodonium, anisylphenyliodonium, di(4-t-butylphenyl)iodonium, di(4-chlorophenyl)iodonium, ditolyliodonium and di(3-nitrophenyl)iodonium, and as the anion portion there may be mentioned BF 4   - , PF 6   - , AsF 6   - , SbF 6   - , ClO 4   - , Cl - , Br - , tetraphenyl borate, tetrakis(pentafluorophenyl)borate, benzenesulfonate anion, p-toluenesulfonate anion and trifluoromethanesulfonate anion. These anion portions and cation portions may be used for the invention in any desired combination. 
     As the cation portion of the pyridinium salt represented by general formula (5) there may be mentioned N-methoxypyridinium, N-ethoxypyridinium, N-methoxy-2-picolinium, N-methoxy-3-picolinium, N-ethoxy-2-picolinium, N-ethoxy-3-picolinium, N-methoxy-4-bromopyridinium, N-methoxy-3-bromopyridinium, N-methoxy-2-bromopyridinium, N-ethoxy-4-bromopyridinium, N-ethoxy-3-bromopyridinium, N-ethoxy-2-bromopyridinium, N-ethoxy-4-chloropyridinium, N-ethoxy-3-chloropyridinium, N-ethoxy-2-chloropyridinium, N-methoxy-4-methoxypyridinium, N-methoxy-3-methoxypyridinium, N-methoxy-2-methoxypyridinium, N-ethoxy-4-methoxypyridinium, N-ethoxy-3-methoxypyridinium, N-ethoxy-2-methoxypyridinium, N-methoxy-4-phenylpyridinium, N-methoxy-3-phenylpyridinium, N-methoxy-2-phenylpyridinium, N-ethoxy-4-phenylpyridinium, N-ethoxy-3-phenylpyridinium, N-ethoxy-2-phenylpyridinium, N-methoxy-4-cyanopyridinium, N-ethoxy-4-cyanopyridinium, N,N&#39;-dimethoxy-4,4&#39;-bipyridinium, N,N&#39;-diethoxy-4,4&#39;-bipyridinium, N,N&#39;-dimethoxy-2,2&#39;-bipyridinium and N,N&#39;-diethoxy-2,2&#39;-bipyridinium. As the anion portion there may be mentioned BF 4   - , PF 6   - , AsF 6   - , SbF 6   - , Cl - , Br - , tetraphenyl borate, tetrakis(pentafluorophenyl) borate, benzenesulfonate anion, p-toluenesulfonate anion and trifluoromethanesulfonate anion. These anion portions and cation portions may be used for the invention in any desired combination. 
     As concrete examples of the halogenated sulfone compound represented by general formula (6) there may be mentioned trichloromethylphenylsulfone, tribromomethylphenylsulfone, trichloromethyl-4-chlorophenylsulfone, tribromomethyl-4-nitrophenylsulfone, 2-trichloromethylbenzothiazolesulfone, 2,4-dichlorophenyltrichloromethylsulfone, 2-methyl-4-chlorophenyltrichloromethylsulfone and 2,4-dichlorophenyltribromomethylsulfone. 
     As concrete examples of peroxides represented by general formula (7) there may be mentioned benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, t-butylperoxybenzoate, di(t-butylperoxy)isophthalate, di(t-butylperoxy)terephthalate, di(t-butylperoxy)phthalate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane and 3,3&#39;,4,4&#39;-tetra(t-butylperoxycarbonyl)benzophenone. 
     As concrete examples of triazine compounds represented by general formula (8) there may be mentioned 2,4,6-tris(trichloromethyl)-s-triazine, 2,4,6-tris(tribromomethyl)-s-triazine, 2,4-bis(dichloromethyl)-6-trichloromethyl-s-triazine, 2-propionyl-4,6-bis(trichloromethyl)-s-triazine, 2-benzoyl-4,6-bis(trichloromethyl)-s-triazine, 2-(4-cyanophenyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(4-nitrophenyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(4-chlorophenyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(4-cumenyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(4-aminophenyl)-4,6-bis(trichloromethyl)-s-triazine, 2,4-bis(4-methoxyphenyl)-6-trichloromethyl-s-triazine, 2,4-bis(3-chlorophenyl)-6-trichloromethyl-s-triazine, 2-(4-methoxystyryl)-4,6-bis(trichloromethyl)-s-triazine, 2-(4-chlorostyryl)-4,6-bis(trichloromethyl)-s-triazine, 2-(4-aminophenyl)-4,6-bis(trichloromethyl)-s-triazine, 2,4-bis(4-methoxyphenyl)-6-trichloromethyl-s-triazine, 2,4-bis(3-chlorophenyl)-6-trichloromethyl-s-triazine, 2-(4-methoxystyryl)-4,6-bis(trichloromethyl)-s-triazine, 2-(4-chlorostyryl)-4,6-bis(trichloromethyl)-s-triazine, 2-(4-aminostyryl)-4,6-bis(dichloromethyl)-s-triazine, 2-(4&#39;-methoxy-1&#39;-naphthyl)-4,6-bis(trichloromethyl)-s-triazine and 2-(6&#39;-nitro-1&#39;-naphthyl)-4,6-bis(trichloromethyl)-s-triazine. The above-mentioned polymerization accelerators of general formulas (3) to (8) may be used alone, but there is absolutely no problem with adding 2 or more. 
     The ultraviolet radical polymerization initiator used for the invention is a common photopolymerization initiator of the type which generates free radicals when excited by irradiation of ultraviolet light. Compounds with the structure represented by general formula (9) may be mentioned as examples thereof. ##STR22## wherein Ar represents an aryl group which may have a substituent, and X represents an alkyl group, hydroxy-substituted alkyl group, halogen-substituted alkyl group, alkoxy-substituted alkyl group, morpholino-substituted alkyl group, amino-substituted alkyl group, benzyl group, hydroxy-substituted benzyl group, alkoxy-substituted benzyl group, alkoxycarbonyl group, an aryl group which may have a substituent or a phosphinoyl group with a substituent. 
     As concrete examples of compounds represented by the structure of general formula (9) there may be mentioned benzoin compounds such as benzoin alkyl ethers, e.g., benzoin isobutyl ether, benzoin isopropyl ether and benzoin ethyl ether, and benzyl dimethyl ketal; acetophenone compounds such as α-hydroxyalkylphenone compounds, α,α-dialkoxyalkylphenone compounds and α-amino-alkylphenone compounds, e.g., diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 1-hydroxycyclohexyl phenyl ketone, 4-t-butyltrichloroacetophenone and 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropanone-1,2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1; glyoxy ester compounds such as methylphenyl glyoxylate; acylphosphine oxide compounds such as 2,4,6-trimethylbenzoyldiphenylphosphine oxide and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide; and benzophenone compounds such as benzophenone, benzoylbenzoic acid, methyl benzoylbenzoate, hydroxybenzophenone, 4-phenylbenzophenone and acrylate benzophenone. 
     Generally, compounds known as P1-type photoinitiators, such as benzoin compounds, acetophenone compounds, glyoxy ester compounds and acylphosphine oxide compounds, may also be used alone, but ultraviolet radical polymerization initiators such as benzophenone compounds which are so called P2-type photoinitiators are used together with a hydrogen donating compound. 
     A hydrogen donating compound is one which can donate hydrogen to the initiator which has been excited by light, and as examples thereof there may be mentioned aliphatic amines such as triethanolamine and methyldiethanolamine, and aromatic amines such as 2-dimethylaminoethylbenzoic acid, ethyl 4-dimethylaminobenzoate, isobutyl 4-dimethylaminobenzoate and 4,4-dimethylaminobenzophenone. These ultraviolet radical polymerization initiators may be used alone or in combinations of 2 or more. 
     The compound with an ethylenically unsaturated bond to be used for the invention may be any one which is a compound having at least one radical polymerizable ethylenically unsaturated bond in the molecule, and which has the chemical form of a monomer, oligomer or polymer. One of these may be used alone, or 2 or more may be combined in any desired proportion for improvement in the intended characteristics. The following may be mentioned as examples of such compounds with radical polymerizable ethylenically unsaturated bonds. 
     As polymerizable monomers there may be mentioned ester compounds of (meth)acrylic acid and monohydric alcohols, such as for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, propyl (meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate, lauryl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, stearyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, benzyl (meth)acrylate, butoxyethyl (meth)acrylate and phenoxyethyl (meth)acrylate. 
     Other monomers which may be used include vinylbenzenes such as styrene, vinylstyrene, methylstyrene, chlorostyrene and divinylstyrene; vinyl ethers such as isobutyl vinyl ether, methyl vinyl ether and 2-ethylhexyl vinyl ether; (meth)acrylic compounds such as (meth)acrylonitrile, (meth)acrylamide and methylene bis(meth)acrylamide; vinyl esters such as vinyl acetate, vinyl propionate and vinyl benzoate; and allyl group-containing monomers such as allyl alcohol, allyl acetate, diallyl phthalates and triallyl trimellitate, as well as other vinyl compounds. 
     Other monomers which may be used include carboxyl group-containing monomers such as (meth)acrylic acid; hydroxyl group-containing monomers such as 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate; addition products of isocyanate compounds such as butyl isocyanate and phenyl isocyanate with the aforementioned hydroxyl-containing monomers; and nitrogen-containing unsaturated monomers such as N-vinylpyrrolidone, N-vinylcarbazole, N-vinylacetamide and vinylpyridine. 
     Other monomers which may be used include polyfunctional vinyl compounds such as diethyleneglycol di(meth)acrylate, triethyleneglycol di(meth)acrylate, polyethyleneglycol di(meth)acrylate, propyleneglycol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, neopentylglycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate and dipentaerythritol hexa(meth)acrylate; products of reacting (meth)acrylic acid with addition products of polyhydric alcohols and ethylene oxide or propylene oxide; products of reacting (meth)acrylic acid with addition products of polyhydric alcohols and ε-caprolactone; phosphorus-containing polymerizable monomers, (meth)acrylic polyfunctional polyorganosilsesquioxanes, etc. 
     Polymerizable oligomers include ethylenically unsaturated bond-containing resins, among which there may be mentioned the following as concrete examples. (Meth)acryloyl group-containing polyester resins, unsaturated polyester resins, (meth)acryloyl group-containing polyurethane resins, (meth)acryloyl group-containing epoxy resins, (meth)acryloyl group-containing phosphorous epoxy resins, (meth)acryloyl group-containing acrylic resins, (meth)acryloyl group-containing polybutadiene resins and (meth)acryloyl group-containing silicone resins. 
     The cationic dye represented by general formula (1) may be used in an amount of 0.001-5 parts by weight to 100 parts by weight of the compound with an ethylenically unsaturated bond, to achieve the object of the present invention. At less than 0.001 part by weight the polymerization fails to proceed sufficiently, which can result in inadequate curing. At greater than 5 parts by weight the characteristics of the cured product are impaired while the cured product also undergoes coloration, making it impossible to achieve the object of the invention. The amount is preferred to be 0.01-2 parts by weight. 
     The quaternary boron salt sensitizer represented by general formula (2) may be used in an amount of 0.005-10 parts by weight to 100 parts by weight of the compound with an ethylenically unsaturated bond, to achieve the object of the present invention. At less than 0.005 part by weight the polymerization fails to proceed sufficiently, which can result in inadequate curing while also causing coloration of the cured product as the decoloration reaction of the cationic dye fails to proceed to a sufficient degree. At greater than 10 parts by weight, the characteristics of the cured product are impaired. The amount is preferred to be 0.05-5 parts by weight. 
     The polymerization accelerators represented by general formulas (3) to (8) may be used in an amount of 0.005-10 parts by weight to 100 parts by weight of the compound with an ethylenically unsaturated bond, to achieve the object of the present invention. At less than 0.005 part by weight the effect of the polymerization accelerator is not apparent. At greater than 10 parts by weight, the characteristics of the cured product are impaired, and the stability of the photocurable composition is notably reduced. The amount is preferred to be 0.01-5 parts by weight. 
     The ultraviolet radical polymerization initiator may be used in an amount of 0.01-10 parts by weight to 100 parts by weight of the compound with an ethylenically unsaturated bond, to achieve the object of the invention. At less than 0.01 part by weight the curing becomes impossible in air, and at greater than 10 parts by weight there are disadvantages of impaired characteristics of the cured product, as well as deterioration and yellowing of the cured product due to residual ultraviolet radical polymerization initiator. The amount is preferred to be 0.1-5 parts by weight. 
     One or more coloring materials selected from coloring pigments, coloring dyes and bright pigments may be used with the photocurable composition of the invention. Coloring pigments which may be used include known organic and inorganic pigments described in &#34;Updated Pigment Handbook&#34; (ed. Association of Japan Pigment Technology, 1976), including white pigments such as titanium white and zinc oxide and black pigments such as carbon black and titanium black. Coloring dyes which may be used include known ones described in &#34;Dye Handbook&#34; (ed. The Society of Synthetic Organic Chemistry, 1970). Bright pigments which may be used include aluminum powder, aluminum paste, silver powder, titanium oxide-coated mica, mica-like iron oxide and the like. These coloring materials may be added in an amount of 0-200 parts by weight to 100 parts by weight of the compound with an ethylenically unsaturated bond. 
     Various different extender pigments may also be added to the photocurable composition of the invention, among which there may be mentioned powders of silica, silica-alumina, alumina, aluminum hydroxide, quartz, calcium carbonate, kaolin, talc, mica, aluminum sulfate and calcium phosphate, as well as powders having the particle surfaces coated with a polyfunctional (meth)acrylic monomer or silane coupling agent. There is no problem with separate addition of 2 or more different types of extender pigments, or their addition after admixture. 
     The photocurable composition of the invention may be mixed with a binder, such as an organic polymer, and applied onto a glass plate, an aluminum or other metal plate, or a polyethylene terephthalate or other polymer film. As polymers which may be used in admixture with the photocurable composition of the invention there may be mentioned polymers and copolymers of polyacrylates, poly-α-alkylacrylates, polyamides, polyvinylacetals, polyurethanes, polycarbonates, polystyrenes and polyvinyl esters, and specifically there may be mentioned polymethacrylate, polymethyl methacrylate, polyethyl methacrylate, polyvinyl carbazole, polyvinyl pyrrolidone, polyvinyl butyral, polyvinyl acetate, novolac resins, phenol resins, epoxy resins and alkyd resins. 
     The photocurable composition of the invention may be used as a solventless composition, as a contribution toward improvement of the earth environment. It may, of course, also be used in a form diluted with a conventional solvent. The solvent used in such cases may be any common solvent used for conventional coating, etc., examples of which are aromatic hydrocarbons such as toluene and xylene, alcohols such as ethanol, 2-propanol and 1-butanol, ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, ethers such as diethyleneglycol dimethyl ether and triethyleneglycol dimethyl ether, esters such as ethyl acetate, n-butyl acetate and amyl acetate, and monoethers of ethylene glycol such as methyl cellosolve and ethyl cellosolve. These solvents may be used alone or in mixtures of 2 or more. An organic solvent lowers the viscosity of the composition and improves the workability and adhesion to the substrates for the cured product. 
     A thermal polymerization inhibitor may also be added to the photocurable composition of the invention, for the purpose of preventing polymerization during periods of storage. As concrete examples of thermal polymerization inhibitors to be added to the photocurable composition of the invention there may be mentioned p-methoxyphenol, hydroquinone, alkyl-substituted hydroquinone, catechol, t-butylcatechol and phenothiazine. 
     The photocurable composition of the invention may also employ, depending on the purpose, an anti-fogging agent, an anti-discoloring agent, a fluorescent brightener, a surfactant, a plasticizer, a flame-retardant, an antioxidant, an ultraviolet absorber, a foaming agent, an anti-fungal agent, an antistatic agent, a magnetic substance, a conductive material, etc. 
     The photocuring process of the invention is accomplished by curing of the aforementioned photocurable composition of the invention after it has been coated onto the substrate, by simultaneous or separate irradiation of ultraviolet light of wavelength 200-400 nm and visible light of wavelength 400-740 nm. Examples of light sources for emission of the ultraviolet light of 200-400 nm include high pressure mercury lamps, super high pressure mercury lamps, metal halide lamps, short arc metal halide lamps, xenon lamps and excimer lasers. 
     Examples of light sources for emission of visible light of 400-740 nm include high pressure mercury lamps, super high pressure mercury lamps, metal halide lamps, short arc metal halide lamps, xenon lamps, sodium lamps, halogen lamps, incandescent lamps, sunlight and semiconductor lasers. Complete curing with a single light source is possible if the light source used is one which simultaneously emits a high output of ultraviolet light of 200-400 nm and visible light of 400-740 nm, such as a high pressure mercury lamp, super high pressure mercury lamp, metal halide lamp, short arc metal halide lamp or xenon lamp. 
     Of the above-mentioned light sources, high pressure mercury lamps, super high pressure mercury lamps, metal halide lamps, short arc metal halide lamps and xenon lamps are ones from which light is emitted by heating a substance with an atomic structure which tends to radiate electromagnetic waves including light to a vapor state in a bulb or emission tube, and then externally applying a large amount of energy by electric discharge or the like. A detailed description may be found in &#34;Ultraviolet Curing Systems&#34; (Kiyomi Kato, Gakkai Publishing Center, 1989), p.375-394 and &#34;Optical Engineering Handbook&#34; (Asakura Shoten, 1986), p.465-469. 
     On the other hand, incandescent lamps and halogen lamps are light sources of the type from which light is irradiated by heating a heating element in a bulb or emission tube to an incandescent state using an electric current. A tungsten filament is usually used as the heating element. A detailed description may be found in &#34;Optical Engineering Handbook&#34; (Asakura Shoten, 1986), p.462-463. 
     The photocurable composition and photocuring process according to the present invention may be applied not only to coatings, adhesives and tackifiers, but also to various types of recording media which include microcapsules and photosensitive materials such as inks and electron photographic and holographic materials which are applied onto substrates together with binders. 
     The present invention will now be explained by way of the following examples. These examples, however, are not intended to restrict the invention. 
     [Preparation of Coatings] 
     Coating compositions were prepared containing the coloring pigments with the compositions listed in Table 2. Clear coating paints were also prepared with the compositions listed in Table 3. 
     [Preparation of Samples and Comparative Samples] 
     Photocuring samples were prepared by mixing different paints, visible light absorbing cationic dyes, quaternary boron salt sensitizers and ultraviolet radical polymerization initiators, with the mixing compositions listed in Table 4. Comparative samples for Table 4 were also prepared in the same manner with the compositions listed in Table 5. 
     Photocuring samples were prepared by mixing different paints, visible light absorbing cationic dyes, quaternary boron salt sensitizers, polymerization accelerators and ultraviolet radical polymerization initiators, with the mixing compositions listed in Table 6. The compositions listed in Table 5 were used as comparative samples for Table 6. 
     
                       TABLE 2______________________________________Compositions for coloring paints______________________________________  Type and composition of paint    White      White    White  Metallic   paint 1 paint 2 paint 3 paint______________________________________  Type and AT-600*.sup.1 Aronix M- Ripoxy AT-600  content of 46.7 pts/wt 8030*.sup.3 SP-1509*.sup.5 60.0 pts/wt  compound with 9EG-A*.sup.2 42.0 49.0 PTMGA-250*.sup.6  ethylenically 14.0 pts/wt pts/wt pts/wt 18.0 pts/wt  unsaturated isobornyl 14EG-A*.sup.4 dicyclo- isobornyl  bond acrylate 28.0 pentanyl acrylate   14.0 pts/wt pts/wt acrylate 18.0 pts/wt21.0pts/wt  Type and CR-90*.sup.7 same as same as 561PS*.sup.8  content of 30.0 pts/wt left left 15.4 pts/wt  pigment  Type and butyl same as same as butyl  content of acetate left left acetate  solvent 18.0 pts/wt   30.0 pts/wt  Type and Homogenol L- same as same as Polyflow  content of 18*.sup.12 left left No.75  additives 1.0 pt/wt   1.0 pt/wt   Polyflow   No.75*.sup.13   1.0 pt/wt______________________________________  Type and composition of paint    Yellow paint                Red paint   Blue paint______________________________________  Type and AT-600 same as left same as left  content of 60.0 pts/wt  compound with PTMGA-250  ethylenically 18.0 pts/wt  unsaturated isobornyl  bond acrylate   18.0 pts/wt  Type and benzimida- quinacridone red phthalo-cyanine  content of zolone yellow pigment*.sup.10 blue pigment*.sup.11  pigment pigment*.sup.9 10.0 pts/wt 10.0 pts/wt   10.0 pts/wt  Type and butyl acetate same as left same as left  content of 10.0 pts/wt  solvent xylene   10.0 pts/wt  Type and Solsperse*.sup.14 same as left same as left  content of 24000GR  additives 1.0 pt/wt   Polyflow No.75   1.0 pt/wt______________________________________ *.sup.1 urethane acrylate, Kyoeisha Chemical Co., Ltd. *.sup.2 polyether acrylate, Kyoeisha Chemical Co., Ltd. *.sup.3 polyester acrylate, Toagosei Chemical Industry Co., Ltd. *.sup.4 polyether acrylate, Kyoeisha Chemical Co., Ltd. *.sup.5 epoxy acrylate, Showa Highpolymer Co., Ltd. *.sup.6 polyether acrylate, Kyoeisha Chemical Co., Ltd. *.sup.7 titanium oxide, Ishihara Sangyo Kaisha Ltd. *.sup.8 aluminum paste, Showa Aluminum Powder K.K. *.sup.9 Dainichiseika Color &amp; Chemicals Mfg. Co., Ltd. *.sup.10 Dainichiseika Color &amp; Chemicals Mfg. Co., Ltd. *.sup.11 Dainichiseika Color &amp; Chemicals Mfg. Co., Ltd. *.sup.12 dispersing agent, Kao Corporation *.sup.13 levelling agent, Kyoeisha Chemical Co., Ltd. *.sup.14 dispersing agent, Zeneca 
    
     
                       TABLE 3______________________________________Compositions for clear coatings    Type of clear coating        Clear     Clear   Clear   Clear  coating 1 coating 2 coating 3 coating 4______________________________________Type and AT-600    AT-600    Ripoxy SP-                                Aronix M-  content of 66.7 pts/wt 66.7 pts/wt 1529X*.sup.1 8030  compound with PTMGA-250 9EG-A 60.0 pts/wt 70.0 pts/wt  ethylenically 20.0 pts/wt 40.0 pts/wt 9EG-A 14EG-A  unsaturated isobornyl  20.0 pts/wt 30.0 pts/wt  bond acrylate  dicyclo-   20.0 pts/wt  pentanylacrylate20.0 pts/wt______________________________________ *.sup.1 epoxy acrylate, Showa Highpower Co., Ltd. 
    
     
                                           TABLE 4__________________________________________________________________________Compositions for photocuring samples      Type and content         Anion portion of   of ultraviolet   quaternary boron salt Quaternary  Type and radical Visible light-  sensitizer (cation boron salt  content of polymerization absorbing cationic dye Cationic portions all                                         tetra-n- sensitizerpaint      initiator              cation                   anion dye content                               butylammonium)                                         content__________________________________________________________________________Sample 1white paint 1      Irgacure 184*.sup.1              Table 1-5                   chloride                         0.02 pt/wt                               n-butyltriphenyl                                         0.20 pt/wt   100 pts/wt 2.0 pts/wt  anion  borate  Sample 2 white paint 2 Irgacure 184*.sup.1 Table 1-4 iodide 0.02 pt/wt                                         n-butyltri(4-t- 0.40 pt/wt                                           100 pts/wt 2.0 pts/wt                                         anion  butylphenyl) borate                                          Sample 3 white paint 3                                         Darocur 1173*.sup.2 Table                                         1-1 tetraphenyl 0.03 pt/wt                                         n-butyltri(2-tolyl) 0.30                                         pt/wt   100 pts/wt 2.0 pts/wt  borate  borate  Sample 4 metallic Irgacure 651*.sup.3 Table 1-2 perchlorate 0.03 pt/wt                                         n-butyltri(4-tolyl) 0.50                                         pt/wt   paint 2.0 pts/wt  anion  borate   100 pts/wt  Sample 5 yellow paint Irgacure 1700*.sup.4 Table 1-6 tetraphenyl 0.05                                         pt/wt n-butyltriphenyl 0.50                                         pt/wt   100 pts/wt 2.5 pts/wt  borate  borate  Sample 6 red paint Irgacure 184 Table 1-8 tetraphenyl 0.04 pt/wt                                         n-butyltriphenyl 0.50 pt/wt   100 pts/wt 2.0 pts/wt  borate  borate  Sample 7 blue paint Darocur 1173 Table 1-7 tetraphenyl 0.05 pt/wt                                         n-butyltri(4-fluoro-2- 0.70                                         pt/wt   100 pts/wt 2.0 pts/wt  borate  methylphenyl) borate    Lucirin TPO*.sup.5    0.5 pt/wt__________________________________________________________________________ *.sup.1 1hydroxycyclohexyl phenyl ketone, CibaGeigy *.sup.2 2hydroxy-2-methyl-1-phenylpropan-1-one, CibaGeigy *.sup.3 benzyldimethyl ketal, CibaGeigy *.sup.4 mixture of 2hydroxy-2-methyl-1-phenylpropan-1-one:bis(2,6-dimethoxybenzoyl)-2,4,4-trmethylpentylphosphine oxide = 3:1, CibaGeigy *.sup.5 2,4,6trimethylbenzoyldiphenylphosphine oxide, BASF The above samples were prepared by dissolving the visible lightabsorbing cationic dye, quaternary boron salt sensitizer and ultraviolet radical polymerization initiator in 5 parts by weight of Nmethylpyrrolidone, and then adding the paint. 
    
     
                       TABLE 5______________________________________Composition for comparative photocuring samples                Type and   content   of ultraviolet  Type and radical  content polymerization  of paint initiator Remarks______________________________________Comparative    white paint 1                Irgacure 184                            comparison for  sample 1 100 pts/wt 2.0 pts/wt samples 1, 8, 9  Comparative white paint 2 ditto comparison for  sample 2 100 pts/wt  samples 2, 10, 11  Comparative white paint 3 Darocur 1173 comparison for  sample 3 100 pts/wt 2.0 pts/wt samples 3, 12, 13  Comparative metallic paint Irgacure 651 comparison for  sample 4 100 pts/wt 2.0 pts/wt samples 4, 14, 15  Comparative yellow paint Irgacure 1700 comparison for  sample 5 100 pts/wt 2.5 pts/wt samples 5, 16, 17  Comparative red paint Irgacure 184 comparison for  sample 6 100 pts/wt 2.0 pts/wt samples 6, 18, 19  Comparative blue paint Darocur 1173 comparison for  sample 7 100 pts/wt 2.0 pts/wt samples 7, 20, 21    Lucirin TPO    0.5 pt/wt______________________________________ 
    
     
                       TABLE 6______________________________________Compositions for photocurlng samples (paints,  ultraviolet radical polymerization initiators  and visible light-absorbing cationic dyes)            Type/content of   ultraviolet Visible light-  Type and radical absorbing Cationic  content of polymerization cationic dye dye  paint     initiator   cation                              anion content______________________________________  Sample 8 white paint 1 Irgacure 184*.sup.1 Table chloride 0.020                                      100 pts/wt 2.0 pts/wt 1-5                                    anion pt/wt  Sample 9 white paint 1 Irgacure 184*.sup.1 Table chloride 0.020                                      100 pts/wt 2.0 pts/wt 1-5                                    anion pt/wt  Sample 10 white paint 2 Irgacure 184*.sup.1 Table iodide 0.020   100 pts/wt 2.0 pts/wt 1-4 anion pt/wt  Sample 11 white paint 2 Irgacure 184*.sup.1 Table iodide 0.020   100 pts/wt 2.0 pts/wt 1-4 anion pt/wt  Sample 12 white paint 3 Darocur 1173*.sup.2 Table tetra- 0.030   100 pts/wt 2.0 pts/wt 1-1 phenyl pt/wt borate  Sample 13 white paint 3 Darocur 1173*.sup.2 Table tetra- 0.030   100 pts/wt 2.0 pts/wt 1-1 phenyl pt/wt borate  Sample 14 metallic Irgacure 651*.sup.3 Table per- 0.030   paint 2.0 pts/wt 1-2 chlorate pt/wt   100 pts/wt   anion  Sample 15 metallic Irgacure 651*.sup.3 Table chlorate 0.030   paint 2.0 pts/wt 1-2 anion pt/wt   100 pts/wt  Sample 16 yellow paint Irgacure 1700*.sup.4 Table tetra- 0.050   100 pts/wt 2.5 pts/wt 1-6 phenyl pt/wt borate  Sample 17 yellow paint Irgacure 1700*.sup.4 Table tetra- 0.050   100 pts/wt 2.5 pts/wt 1-6 phenyl pt/wt borate  Sample 18 red paint Irgacure 184 Table tetra- 0.040   100 pts/wt 2.0 pts/wt 1-8 phenyl pt/wt borate  Sample 19 red paint Irgacure 184 Table tetra- 0.040   100 pts/wt 2.0 pts/wt 1-8 phenyl pt/wt borate  Sample 20 blue paint Darocur 1173 Table tetra- 0.050   100 pts/wt 2.0 pts/wt 1-7 phenyl pt/wt    Lucirin TPO*.sup.5  borate    0.5 pt/wt  Sample 21 blue paint Lucirin TPO*.sup.5 Table tetra- 0.050   100 pts/wt 0.5 pt/wt 1-7 phenyl pt/wt borate______________________________________Compositions for photocuring samples (quaternary boron  salt sensitizers, polymerization accelerators)     Quaternary boron   salt sensitizer   anion (cation Quaternary  Poly-   portions are all boron salt  merization   tetra-n- sensitizer Polymerization accelerator   butylammonium) content accelerator content______________________________________  Sample n-butyltriphenyl 0.20 pt/wt triphenyl- 0.30 pt/wt  8 borate  sulfonium triflate  Sample n-butyltriphenyl 0.20 pt/wt diphenyliodonium 0.30 pt/wt  9 borate  hexafluoro-phosphate  Sample n-butyltri(4-t- 0.40 pt/wt N-ethoxy-4- 0.30 pt/wt  10 butylphenyl)  phenyl   borate  pyridinium hexa-fluorophosphate  Sample n-butyltri(4-t- 0.40 pt/wt trichloromethyl- 0.30 pt/wt  11 butylphenyl)  phenylsulfone   borate  Sample n-butyltri(2- 0.30 pt/wt t-butylperoxy- 0.40 pt/wt  12 tolyl) borate  benzoate  Sample n-butyltri(2- 0.30 pt/wt 2,4,6-tris(tri- 0.30 pt/wt  13 (tolyl) borate  chloromethyl)-s-triazine  Sample n-butyltri(4- 0.50 pt/wt diphenyl(4-fluoro 0.40 pt/wt  14 tolyl) borate  phenyl)sulfoniumtriflate  Sample n-butyltri(4- 0.50 pt/wt bis(4-t-butyl- 0.50 pt/wt  15 tolyl) borate  phenyl)iodoniumhexafluoro-antimonate  Sample n-butyltriphenyl 0.50 pt/wt N,N                                   &#39;-diethoxy- 0.50 pt/wt  16 borate  4,4&#39;-bipyridiniumbis-(hexafluoro-phosphate)  Sample n-butyltriphenyl 0.50 pt/wt tribromomethyl- 0.50 pt/wt  17 borate  phenylsulfone  Sample n-butyltriphenyl 0.50 pt/wt 3,3&#39;,4,4&#39;-tetra(t- 0.30 pt/wt                                    18 borate  butylperoxy-carbonyl)-benzophenone  Sample n-butyltriphenyl 0.50 pt/wt 2-(4-methoxy- 0.30 pt/wt  19 borate  styryl)-4,6-bis(tri-chloromethyl)-s-triazine  Sample n-butyltri(4- 0.70 pt/wt diphenylbenzyl- 0.50 pt/wt  20 fluoro-2-methyl  sulfonium hexa-   phenyl) borate  fluoroantimonate  Sample n-butyltri(4- 0.70 pt/wt N-ethoxy- 0.50 pt/wt  21 fluoro-2-methyl  pyridinium hexa-   phenyl) borate  fluorophosphate______________________________________ The above samples were prepared by dissolving the visible light absorbing cationic dye, quaternary boron salt sensitizer, polymerization accelerato and ultraviolet radical polymerization initiator in 5 parts by weight of Nmethylpyrrolidone, and then adding the paint. 
    
     [Curing Process for Each Sample] 
     Curing conditions A: Curing with metal halide lamp 
     Samples 1-21 and comparative samples 1-7 were coated onto aluminum plates (150×70 mm) with a #50 bar coater to a film thickness of about 50 μm. The coatings of samples 1-21 and comparative samples 1-7 were then subjected to photocuring in air with a metal halide lamp (UVL-6000M2-N1, input power 120 W/cm, Ushio Inc.) which emits light of 200-740 nm. The metal halide lamp was incorporated in a belt conveyor-type light-irradiating apparatus (UVC-5033, product of Ushio Inc.), the distance between the metal halide lamp and the coatings was 25 cm, the belt conveyor speed was 1.7 m/min, and the irradiation was performed twice. 
     Curing conditions B: Curing with halogen lamp and high pressure mercury lamp 
     Samples 1-21 and comparative samples 1-7 were coated in the same manner to a film thickness of about 50 μm, after which they were irradiated with light in air for 20 seconds at an irradiation distance of 30 cm, using a 1.5 kW halogen lamp (RDS Corporation HG-100V-1.5 KWB) which emits light of 400 nm and greater. Photocuring was then performed in air with a high pressure mercury lamp (UVL-6000-O/N, input power 80 W/cm, Ushio Inc.) which emits light of 200-740 nm. The high pressure mercury lamp was incorporated in a belt conveyor-type light-irradiating apparatus as in curing conditions A, the distance between the high pressure mercury lamp and the coatings was 25 cm, the belt conveyor speed was 2 m/min, and the irradiation was performed twice. 
     Curing conditions C: Curing with short arc metal halide lamp and high pressure mercury lamp 
     Samples 1-7 and comparative samples 1-7 were coated in the same manner to a film thickness of about 50 μm, after which they were irradiated with light in air for 20 seconds at an irradiation distance of 1 m, using a 2.0 kW short arc metal halide lamp (Dynabeam 2, Toshiba Lighting &amp; Technology Corporation) which emits light of 300 nm and greater. Photocuring was then performed in air with a high pressure mercury lamp (UVL-6000-O/N, input power 80 W/cm, Ushio Inc.) which emits light of 200-740 nm. The distance between the high pressure mercury lamp and the coatings was 25 cm, the belt conveyor speed was 2 m/min, and the irradiation was performed twice. 
     Curing conditions D: Curing with xenon lamp and high pressure mercury lamp 
     Samples 1-7 and comparative samples 1-7 were coated in the same manner to a film thickness of about 50 μm, after which they were irradiated with light in air for 20 seconds at an irradiation distance of 50 cm, using a 1.0 kW xenon lamp (SUPERSOL-S 1003SR, Ushio U-tech Inc.) which emits light of 300 nm and greater. Photocuring was then performed in air with a high pressure mercury lamp (UVL-6000-O/N, input power 80 W/cm, Ushio Inc.) which emits light of 200-740 nm. The distance between the high pressure mercury lamp and the coatings was 25 cm, the belt conveyor speed was 2 m/min, and the irradiation was performed twice. 
     [Evaluation of Coatings] 
     Cured state 
     Designating samples 1-21 cured under curing conditions A as Examples 1-21 and comparative samples 1-7 as Comparative Examples 1-7, the cured states of the front and back surfaces of the coatings were evaluated using the evaluation method of &#34;JIS K-5400 (universal paint testing method), 6.5 hour drying time&#34;. 
     Also, about 0.5 g of the cured coating was peeled off the plate, and the coating was refluxed for one hour in about 100 ml of acetone to extract the acetone-soluble portion, after which the acetone-insoluble coating was dried and the acetone-insoluble resin content ratios before and after acetone reflux were measured. The acetone-insoluble resin content ratio is calculated with the following equation, with a larger value indicating greater polymerization/three-dimensional crosslinking of the coating, and thus better curability. 
     
         acetone-insoluble resin content ratio (%)=(acetone-insoluble resin portion of coating/total resin portion of coating)×100 
    
     The results are shown in Table 7. Likewise, samples 1-21 and comparative samples 1-7 cured under curing conditions B were evaluated as Examples 22-42 and Comparative Examples 8-14, respectively; samples 1-7 and comparative samples 1-7 cured under curing conditions C were evaluated as Examples 43-49 and Comparative Examples 15-21, respectively; and samples 1-7 and comparative samples 1-7 cured under curing conditions D were evaluated as Examples 50-56 and Comparative Examples 22-28, respectively. The results are shown in Tables 8, 9 and 10. 
     
                       TABLE 7______________________________________State of cured coatings photocured under curing conditions A                         Acetone-  State of cured insoluble resin  coating*.sup.1 content ratio    Sample   Front   Back    (%)______________________________________Example 1  sample 1   A       A     84  Example 2 sample 2 A A 93  Example 3 sample 3 A A 82  Example 4 sample 4 A A 81  Example 5 sample 5 A A 86  Example 6 sample 6 A A 84  Example 7 sample 7 A A 87  Example 8 sample 8 A A 91  Example 9 sample 9 A A 90  Example 10 sample 10 A A 94  Example 11 sample 11 A A 95  Example 12 sample 12 A A 94  Example 13 sample 13 A A 89  Example 14 sample 14 A A 89  Example 15 sample 15 A A 89  Example 16 sample 16 A A 94  Example 17 sample 17 A A 92  Example 18 sample 18 A A 91  Example 19 sample 19 A A 89  Example 20 sample 20 A A 94  Example 21 sample 21 A A 92  Comp. Example 1 comp. sample 1 A D 57  Comp. Example 2 comp. sample 2 A C 62  Comp. Example 3 comp. sample 3 A D 54  Comp. Example 4 comp. sample 4 A C 65  Comp. Example 5 comp. sample 5 A C 62  Comp. Example 6 comp. sample 6 A C 62  Comp. Example 7 comp. sample 7 A C 60______________________________________ *.sup.1 The extent of curing was evaluated with the following 4 grades: A: No finger imprint on coating surface or feeling of coating movement when center of coating film was firmly pressed between thumb and forefinger, and no abrasive damage to coating surface upon repeated rapid rubbing of center of coating film with fingertip. B: No rubbing scars on coating surface when center of coating film was gently rubbed with fingertip. C: No residue on fingertip when center of coating film was lightly touche with fingertip. D: Paint adhered to fingertip when center of coating film was lightly touched with fingertip. 
    
     
                       TABLE 8______________________________________State of cured coatings photocured under curing conditions B                         Acetone-  State of cured insoluble resin  coating*.sup.1 content ratio    Sample   Front   Back    (%)______________________________________Example 22 sample 1   A       A     80  Example 23 sample 2 A A 89  Example 24 sample 3 A A 79  Example 25 sample 4 A A 78  Example 26 sample 5 A A 80  Example 27 sample 6 A A 81  Example 28 sample 7 A A 83  Example 29 sample 8 A A 86  Example 30 sample 9 A A 90  Example 31 sample 10 A A 92  Example 32 sample 11 A A 93  Example 33 sample 12 A A 89  Example 34 sample 13 A A 91  Example 35 sample 14 A A 87  Example 36 sample 15 A A 90  Example 37 sample 16 A A 89  Example 38 sample 17 A A 89  Example 39 sample 18 A A 87  Example 40 sample 19 A A 90  Example 41 sample 20 A A 92  Example 42 sample 21 A A 92  Comp. Example 8 comp. sample 1 A D 52  Comp. Example 9 comp. sample 2 A C 59  Comp. Example 10 comp. sample 3 A D 50  Comp. Example 11 comp. sample 4 A D 52  Comp. Example 12 comp. sample 5 A D 52  Comp. Example 13 comp. sample 6 A D 54  Comp. Example 14 comp. sample 7 A D 52______________________________________ 
    
     
                       TABLE 9______________________________________State of cured coatings photocured under curing conditions C                         Acetone-  State of cured insoluble resin  coating content ratio    Sample   Front   Back    (%)______________________________________Example 43 sample 1   A       A     82  Example 44 sample 2 A A 91  Example 45 sample 3 A A 76  Example 46 sample 4 A A 77  Example 47 sample 5 A A 82  Example 48 sample 6 A A 81  Example 49 sample 7 A A 84  Comp. Example 15 comp. sample 1 A D 54  Comp. Example 16 comp. sample 2 A C 60  Comp. Example 17 comp. sample 3 A D 52  Comp. Example 18 comp. sample 4 A D 54  Comp. Example 19 comp. sample 5 A D 51  Comp. Example 20 comp. sample 6 A C 56  Comp. Example 21 comp. sample 7 A D 53______________________________________ 
    
     
                       TABLE 10______________________________________State of cured coatings photocured under curing conditions D                         Acetone-  State of cured insoluble resin  coating content ratio    Sample   Front   Back    (%)______________________________________Example 50 sample 1   A       A     82  Example 51 sample 2 A A 90  Example 52 sample 3 A A 81  Example 53 sample 4 A A 83  Example 54 sample 5 A A 80  Example 55 sample 6 A A 84  Example 56 sample 7 A A 82  Comp. Example 22 comp. sample 1 A D 52  Comp. Example 23 comp. sample 2 A C 60  Comp. Example 24 comp. sample 3 A D 51  Comp. Example 25 comp. sample 4 A D 53  Comp. Example 26 comp. sample 5 A D 51  Comp. Example 27 comp. sample 6 A C 56  Comp. Example 28 comp. sample 7 A D 52______________________________________ 
    
     State of coloration 
     Samples with the compositions listed in Table 11 were prepared. Here, the visible light-absorbing cationic dyes listed in Table 1 were used for samples 22-26, and the near infrared light-absorbing cationic dyes listed in Table 12 were used for comparative samples 8-12. Sample 22 and comparative sample 8, sample 23 and comparative sample 9, sample 24 and comparative sample 10, sample 25 and comparative sample 11 and sample 26 and comparative sample 12 were identical in all components except for the cationic dye, and were prepared with the purpose of comparing the colorability of the coatings with different cationic dyes. These were cured under curing conditions B, and the color phases of the coatings were compared visually. These were also compared against a standard color chart according to &#34;JIS Z 8721 (identification method by color-order system), and the color phases of the coatings were evaluated by selecting the chart color (expressed as HV/C) nearest to the color phase of the coating. The results are shown in Table 13. 
     
                                           TABLE 11__________________________________________________________________________Compositions for photocuring samples used for discoloration test of curedcoatings      Type and                                               content   Anion                                             portion of   of ultraviolet   quaternary boron salt Quaternary  Type and radical Type of  sensitizer (cation boron-based  content of polymerization cationic dye Cationic portions all tetra-n-                                             sensitizerpaint      initiator             cation                 anion dye content                             butylammonium)                                       content                                             Remarks__________________________________________________________________________Sample 22clear paint 1      Irgacure 184             Table                 perchlorate                       0.04  n-butyltriphenyl                                       0.50 pt/wt   100 pts/wt 2.0 pts/wt 1-2 anion pt/wt borate  Sample 23 clear paint 1 Darocur 1173 Table iodide anion 0.05 n-butyltri(                                             4-t- 0.50 pt/wt                                               100 pts/wt 2.0 pts/wt                                             1-4  pt/wt butylphenyl)                                             borate  Sample 24 clear paint 2 Darocur 1173 Table chloride 0.05 n-butyltripheny                                             l 0.50 pt/wt   100 pts/wt 2.0 pts/wt 1-5 anion pt/wt borate  Sample 25 clear paint 3 Darocur 1173 Table chloride 0.05 n-butyltri(4-to                                             lyl) 0.50 pt/wt                                               100 pts/wt 2.0 pts/wt                                             1-6 anion pt/wt borate                                              Sample 26 clear paint                                             4 Darocur 1173 Table                                             tetraphenyl 0.09                                             n-butyltri(2-tolyl)                                             0.50 pt/wt   100 pts/wt 2.0 pts/wt 1-7 borate pt/wt borate  Comp. clear paint 1 Irgacure 184 Table tetraphenyl 0.082 n-butyltripheny                                             l 0.50 pt/wt comparison  sample 8 100 pts/wt 2.0 pts/wt 12-1 borate pt/wt borate  for sample 22                                              Comp. clear paint 1                                             Darocur 1173 Table                                             n-butyltri- 0.111                                             n-butyltri(4-t- 0.50                                             pt/wt comparison                                              sample 9 100 pts/wt                                             2.0 pts/wt 12-2 phenyl                                             pt/wt butylphenyl)                                             borate  for sample 23                                                  borate  Comp. clear paint 2 Darocur 1173 Table tetraphenyl 0.100 n-butyltripheny                                             l 0.50 pt/wt comparison  sample 10 100 pts/wt 2.0 pts/wt 12-3 borate pt/wt borate  for sample 24  Comp. clear paint 3 Darocur 1173 Table p-toluene- 0.082 n-butyltri(4-tol                                             yl) 0.50 pt/wt compariso                                             n  sample 11 100 pts/wt 2.0 pts/wt 12-2 sulfonate pt/wt borate  for sample                                             25 anion  Comp. clear paint 4 Darocur 1173 Table p-toluene- 0.093 n-butyltri(2-tol                                             yl) 0.50 pt/wt compariso                                             n  sample 12 100 pts/wt 2.0 pts/wt 12-2 sulfonate pt/wt borate  for sample                                             26 anion__________________________________________________________________________ 
    
     
                                           TABLE 12__________________________________________________________________________                             Maximum    absorption wavelength  No. Chemical structure (type of solvent)__________________________________________________________________________  1                               820 nm  (trimethylolpropane  triacryla                             te) ## 820 nm  (trimethylolpropane  triacrylate)   - 3    ##STR25##                      830 nm  (trimethylolpropane  triacrylat                             e)__________________________________________________________________________ 
    
     
                       TABLE 13______________________________________Coloration state of coatings               Cationic dye used                    Near    Visible infrared Visually    light- light- determined Color    absorbing absorbing state of phase of   Sample cationic cationic coating coating   used dye dye coloration (HV/C)______________________________________Ex. 57 sample 22           table 1-2                    --      colorless                                    N8.8  Comp Ex. comp. -- table 12-1 yellow 5Y9/2  29 sample 8  Ex. 58 sample 23 table 1-4 -- colorless N8.9  Comp. Ex. comp. -- table 12-2 yellow- 5GY9/1  30 sample 9   green  Ex. 59 sample 24 table 1-5 -- colorless N8.8  Comp. Ex. comp. -- table 12-3 yellow 5Y9/2  31 sample 10  Ex. 60 sample 25 table 1-6 -- colorless N9.0  Comp. Ex. comp. -- table 12-2 yellow- 5GY9/1  32 sample 11   green  Ex. 61 sample 26 table 1-7 -- colorless N8.6  Comp. Ex. comp. -- table 12-2 yellow- 5GY9/1  33 sample 12   green______________________________________ 
    
     A photocurable composition according to the present invention comprising a compound with an ethylenically unsaturated group and a cationic dye of general formula (1), a quaternary boron salt sensitizer of general formula (2) and an ultraviolet radical polymerization initiator and optionally a polymerization accelerator of any of general formulas (3) to (8) can be adequately cured in air on the surface and to the interior of the cured product by irradiation of ultraviolet light of wavelength 200-400 nm and visible light of wavelength 400-740 nm, even if it contains a pigment or coloring dye with a strong hiding power. Moreover, the resulting cured product also undergoes no coloration by oxidation products of the cationic dye, thus providing a cured product with an excellent appearance. Consequently, this curable composition and process for photocuring it provide a material and curing process which can be satisfactorily applied in the fields of painting, adhesives, tackifiers, inks and holographic materials.