JPWO2015053397A1 - Photocationic curable coating composition, coating film forming method, and coated article thereof - Google Patents

Abstract

The problem to be solved by the present invention is to provide a photocationic curable coating composition and a method for forming a coating film, which are excellent in transparency and excellent in curling resistance and scratch resistance of the resulting cured coating film. The present invention is a photocationically curable coating composition comprising a silsesquioxane compound (a) and an iodonium salt photoacid generator (b), the photocationically polymerizable group-containing silsesquioxane. The compound (a) is a hydrolyzable silane compound represented by the formula (I), or a mixture of the hydrolyzable silane compound represented by the formula (I) and the hydrolyzable silane compound represented by the formula (II). Is obtained by hydrolytic condensation of the hydrolyzable silane compound represented by the formula (I) and the mixture ratio of the hydrolyzable silane compound represented by the formula (II). Based on the total amount of the hydrolyzable silane compound represented by I) and / or formula (II), 55-100 mol% of the hydrolyzable silane compound represented by formula (I) is represented by formula (II). The hydrolyzable silane compound is 0 to 45 mol% That provides an optical cationically curable coating composition.

Description

[Cross-reference of related applications]
This application claims priority based on Japanese Patent Application No. 2013-213328 filed on Oct. 11, 2013, the entire disclosure of which is incorporated herein by reference.

  The present invention relates to a photocationic curable coating composition, a method for forming a coating film, and a coated article thereof.

Silsesquioxane is a general term for a series of network-like polysiloxanes having a basic structural unit of T units and a ladder-type, cage-type, and three-dimensional network type (random type) structure. Since this silsesquioxane is soluble in a general organic solvent, unlike silica, which is a complete inorganic substance represented by the general formula SiO ₂ , it is easy to handle, processability such as film formation and the like. It has the feature of excellent moldability.

  On the other hand, surface effect technology using photocuring is a technology that modifies the surface of the substrate by irradiating and curing the viscous liquid applied to the substrate (metal, plastic, woodworking product, etc.) with light (for example, ultraviolet rays). is there. Photocuring is a technique that utilizes a chemical reaction initiated by light, and is classified into a radical polymerization system and a cationic polymerization system based on the difference in the initiation reaction mechanism. Compared to radical polymerization systems, cationic polymerization systems are less susceptible to cure inhibition by oxygen, cure shrinkage is small, and curing of areas where light irradiation does not reach because of the long life of active species and curing by heating gradually progress. In recent years, application to various fields has been studied.

  The inventions of Patent Documents 1 and 2 relate to a photocation curable resin composition containing a silsesquioxane compound having an oxetanyl group and a cationic polymerization initiator. This composition was excellent in surface hardness and compatibility, but was cured by being irradiated with ultraviolet rays 5 times, and when it was irradiated once with ultraviolet rays, its curability and scratch resistance were insufficient.

  The invention of Patent Document 3 relates to a composition comprising an ultraviolet curable epoxy functional organopolysiloxane with enhanced ability to solubilize an onium salt photoinitiator and an onium salt initiator. This composition was excellent in compatibility with the onium salt initiator, but the scratch resistance was insufficient.

  On the other hand, the inventions of Patent Documents 4 and 5 relate to a cationic polymerization initiator having cationic polymerization initiating ability. When this cationic polymerization initiator is used, it does not contain toxic elements such as arsenic and antimony, and has good compatibility with other cationic polymerizable compounds and excellent curability. However, this was a case where the curl resistance was insufficient.

JP-A-11-116682 Japanese Patent Laid-Open No. 11-199673 JP-A-1-297421 Japanese Patent Publication No. 2005-116038 JP 2012-22227 A

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a photocationic curable coating composition having excellent transparency and curling resistance and scratch resistance of the resulting cured coating film, and It is providing the coating-film formation method.

  As a result of intensive studies to solve the above problems, the present inventors have found that a silsesquioxane compound (a) containing a specific photocationically polymerizable group and an iodonium salt photoacid generator (b). It was found that the above-mentioned problems can be solved by using, and the present invention has been completed.

That is, the present invention
Item 1. A photocationic curable coating composition comprising a silsesquioxane compound (a) containing at least one photocationically polymerizable group and an iodonium salt photoacid generator (b),
The photocationically polymerizable group-containing silsesquioxane compound (a) is
It is obtained by hydrolytic condensation of a hydrolyzable silane compound represented by formula (I) and / or a hydrolyzable silane compound represented by formula (II). ) Based on the total amount with the hydrolyzable silane compound represented by
The hydrolyzable silane compound represented by the formula (I) is 55 to 100 mol%,
The photocationic curable coating composition whose hydrolyzable silane compound represented by Formula (II) is 0-45 mol%.

[In the formula (I), R ¹ represents a divalent alkylene group having 1 to 6 carbon atoms. X is a halogen element or an alkoxy group having 1 to 6 carbon atoms, and the three Xs may be the same or different. ]
R ² SiX ₃ (II)
[Formula (II) is a compound other than formula (I), and R ² represents an optionally substituted monovalent organic group having 1 to 18 carbon atoms. X is a halogen element or an alkoxy group having 1 to 6 carbon atoms, and the three Xs may be the same or different. ]
Item 2. Item 2. The photocationic curable coating composition according to Item 1, wherein the photoacid generator (b) is an iodonium salt photoacid generator represented by the following formula (III).

[In Formula (III), R ³ represents an organic group bonded to I (iodine atom), and two R ^{3 s} may be the same as or different from each other. [Y] ⁻ is a phosphate anion represented by the formula (IV) or a boron compound anion represented by the formula (V), and Rf in the formula (IV) is fluorine in which all or part of the hydrogen atoms are fluorine. An alkyl group which may be substituted with an atom is represented. b is an integer of 0-5. The b Rf's may be the same or different. ]
Item 3. Item 3. The photocationic curability according to item 1 or 2, further comprising 50 parts by mass or less of another photocationically polymerizable group-containing compound (c) with respect to 100 parts by mass of the silsesquioxane compound (a). Paint composition.

  Item 4. Furthermore, the photocation curable coating composition of any one of claim | item 1 -3 containing a sensitizer (d).

  Item 5. Item 5. The photocationically curable coating composition according to any one of Items 1 to 4, wherein the epoxy equivalent of the photocationically polymerizable group-containing silsesquioxane compound (a) is 10 to 500 g / equivalent.

Item 6. When the cured coating film having a film thickness of 5 μm is formed on the acrylic resin plate having a thickness of 3 mm, the Martens hardness measured by a super micro hardness tester at a temperature of 23 ° C. and a load of 20 mN is 0.5. Item 6. The photocationically curable coating composition according to any one of Items 1 to 5, wherein a coating film having a thickness of 350 N / mm ² can be formed.

  Item 7. A photocationically curable coating composition according to any one of Items 1 to 6 is applied on an object to be coated so that a dry film thickness is 1 to 10 μm, and setting and / or preheating is performed. A coating film forming method characterized by irradiating with light after applying.

Item 8. The present invention relates to an article having a film formed by the method for forming a coating film according to Item 7.

  When the photocationic curable coating composition of the present invention is used, a cured coating film having excellent transparency can be obtained. Furthermore, according to the photocationic curable coating composition of the present invention, it is possible to obtain a cured coating film that can be cured at a low dose and that is excellent in curling resistance and scratch resistance of the resulting cured coating film.

  The photocationic curable coating composition of the present invention contains a silsesquioxane compound (a) and an iodonium salt-based photoacid generator (b). This will be described in detail below.

(A) Silsesquioxane Compound as Component In the present specification, “silsesquioxane compound” means only a silsesquioxane compound having a structure in which all Si—OH groups (hydroxysilyl groups) are hydrolyzed and condensed. Instead, it can also include a ladder structure in which Si—OH groups remain, an incomplete cage structure, and a random condensate silsesquioxane compound.

  The proportion of the silsesquioxane compound having a structure in which all of the Si—OH groups are hydrolyzed and condensed is 80 mass in the silsesquioxane compound as the component (a). % Or more, preferably 90% by mass or more, and more preferably 100% by mass from the viewpoint of liquid stability and scratch resistance.

  In the present invention, the silsesquioxane compound (a) contains at least one cationic polymerizable group. In the present invention, the cation polymerizable group means a group that polymerizes in the presence of an initiator that gives a cation, and specifically includes, for example, an epoxy group (for example, an alicyclic epoxy group, a glycidyl group). Etc.), oxetane ring, vinyl ether group, methylol group, alkoxymethylol group, dioxolane group, trioxane group, styryl group and the like. In the present invention, the silsesquioxane compound (a) is obtained by hydrolytic condensation of a hydrolyzable silane represented by the formula (I) and / or a hydrolyzable silane represented by the formula (II). It is a thing.

[In the formula (I), R ¹ represents a divalent alkylene group having 1 to 6 carbon atoms. X is a halogen element or an alkoxy group having 1 to 6 carbon atoms, and the three Xs may be the same or different. ]
R ² SiX ₃ (II)
[Formula (II) is a compound other than formula (I), and R ² represents an optionally substituted monovalent organic group having 1 to 18 carbon atoms. X is a halogen element or an alkoxy group having 1 to 6 carbon atoms, and the three Xs may be the same or different. ].

R ¹ in the formula (I) is bonded to a silicon atom constituting the silsesquioxane compound. Generally, a three-membered ring containing oxygen is generically called an oxirane ring or an epoxy group. Among them, the “alicyclic epoxy group” refers to those having an epoxy group in the ring of a cycloaliphatic group such as a cyclohexane ring and a cyclooctane ring, and the silsesquiquine component (a) of the present invention. When synthesizing an oxane compound, among the compounds having an alicyclic epoxy group, an alicyclic epoxy group-containing hydrolyzable silane having a structure represented by the formula (I) is used as an essential component.

  By having the alicyclic epoxy group, the silsesquioxane compound as the component (a) is excellent in compatibility and reactivity with the iodonium salt photoacid generator, and therefore in the presence of the photoacid generator. And cured by light irradiation. Therefore, the cured coating film obtained by the photocationic curable coating composition of the present invention is excellent in transparency.

  Among the cationic photopolymerizable groups of the silsesquioxane compound as the component (a), the alicyclic epoxy group is a part of the cationic photopolymerizable group of the silsesquioxane compound as the component (a) or From the viewpoint of scratch resistance of the cured coating film, the content is preferably 55 to 100 mol%, more preferably 75 to 100 mol%, and particularly preferably 90 to 100 mol%. .

R ¹ in the formula (I) is not particularly limited as long as it is a divalent hydrocarbon group having 1 to 6 carbon atoms. Specific examples include a methylene group, an ethylene group, a 1,2-propylene group, a 1,3-propylene group, a 1,2-butylene group, a 1,4-butylene group, and a hexylene group. Among these, a divalent hydrocarbon group having 2 to 4 carbon atoms is preferable from the viewpoint of scratch resistance of the resulting cured coating film.

  Although the silsesquioxane compound which is (a) component has an alicyclic epoxy group in a specific ratio, other organic groups are not specifically limited.

  Examples of other organic groups include organic groups such as alkyl groups such as methyl group and ethyl group, 3-glycidyloxypropyl group, glycidyl group, oxetanyl group, vinyl group, and phenyl group. Especially, it is preferable that a glycidyl group, an oxetanyl group, or a methyl group is included from a sclerosing | hardenable point.

  The weight average molecular weight of the silsesquioxane compound as the component (a) is from 1,000 to 100,000, more preferably from 1,000 to 100,000, from the viewpoint of the viscosity and paintability of the photocationic curable coating composition. Within the range of 10,000 is preferred.

  In this specification, the weight average molecular weight of the silsesquioxane compound as component (a) uses “HLC (registered trademark) -8120GPC” (trade name, manufactured by Tosoh Corporation) as a gel permeation chromatograph. , "TSKgel (registered trademark) G4000HXL", "TSKgel (registered trademark) G3000HXL", "TSKgel (registered trademark) G2500HXL" and "TSKgel (registered trademark) G2000HXL" (trade names, all manufactured by Tosoh Corporation) A total of four lines can be used, and a differential refractometer can be used as a detector, and measurement can be performed under conditions of mobile phase: tetrahydrofuran, measurement temperature: 40 ° C., and flow rate: 1 mL / min.

(A) Production method of silsesquioxane compound as component (a) The silsesquioxane compound as component (a) includes a production method used for production of general silsesquioxane and a conventionally known chemical reaction. For example, it can be produced using the following production method.

Manufacturing method p
Examples of the production method p include a production method using a hydrolyzable silane having a photocationically polymerizable group as a starting material.

  Specifically, for example, a hydrolyzable silane represented by the above formula (I) as a starting material is subjected to hydrolysis condensation in the presence of a catalyst to produce a silsesquioxane compound as component (a). Is mentioned.

In formula (I), R ¹ represents a divalent alkylene group having 1 to 6 carbon atoms. In the present invention, examples of the divalent alkylene group having 1 to 6 carbon atoms include a methylene group, an ethylene group, an n-propylene group, an isopropylene group, an n-butylene group, an n-pentylene group, and an n-hexylene group. Is mentioned. As said alkylene group, a C1-C3 alkylene group is preferable. X is a halogen element or an alkoxy group having 1 to 6 carbon atoms, and the three Xs may be the same or different. In the present invention, examples of the halogen atom include fluorine, chlorine, bromine, iodine and the like. In the present invention, examples of the alkoxy group having 1 to 6 carbon atoms include a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, an isobutoxy group, a tert-butoxy group, and an n-pentyloxy group. , N-hexyloxy group and the like. Specific examples of X include chlorine, methoxy group, ethoxy group, n-propoxy group, isopropoxy group, n-butoxy group, isobutoxy group, tert-butoxy group and the like.

  Specific examples of the hydrolyzable silane represented by the formula (I) include 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltriethoxysilane, 2 -(3,4-epoxycyclohexyl) ethyltrichlorosilane and the like.

  The hydrolyzable silane of the formula (II) other than the hydrolyzable silane represented by the formula (I) may be used, and hydrolytic condensation is performed together with the hydrolyzable silane represented by the formula (I). The silsesquioxane compound is not particularly limited as long as it can produce the compound.

In formula (II), it is a compound other than formula (I), and R ² represents an optionally substituted monovalent organic group having 1 to 18 carbon atoms. X is the same as described above.

R ² in the formula (II) is preferably a monovalent organic group having 1 to 18 carbon atoms from the viewpoint of scratch resistance, and may be linear or branched, and 1 to 3 (preferably 1). May have a cyclic structure and may contain a urethane bond, an ester bond, an ether bond, or the like. Accordingly, the organic group represented by R ² includes a hydrocarbon group (an alkyl group having 1 to 18 carbon atoms, an aryl group having 6 to 18 carbon atoms (such as a phenyl group), an alkenyl group having 2 to 18 carbon atoms, and the like), Examples thereof include hydrocarbon groups interrupted by the urethane bond, ester bond, ether bond and the like. When the organic group includes a urethane bond, an ester bond, an ether bond, etc., the number of these bonds is not limited. For example, the number of the above bonds per organic group is 1 to 3, preferably 1. Is mentioned. In the present invention, when the organic group includes a urethane bond, an ester bond, an ether bond, or the like, the number of carbon atoms in the organic group includes the number of carbons included in these bonds. Therefore, for example, the number of carbon atoms of the methylcarbamoylethyl group (CH ₃ —NH— (C═O) —O—C ₂ H ₄ —) is 4, and the propionyloxybutyl group (C ₂ H ₅ — (C═O)) The number of carbon atoms of —O—C ₄ H ₈ —) is 7, and the number of carbon atoms of the ethoxypropyl group (C ₂ H ₅ —O—C ₃ H ₆ —) is 5. Moreover, you may have substituents, such as an amino group, a glycidyl group, a (meth) acrylate group, and an oxetane ring, in the side chain and / or the terminal. When the organic group has a substituent, the number of substituents is not limited. For example, the number of the substituents per organic group is 1 to 3, preferably 1. In the present invention, when the organic group has a substituent, the carbon number of the substituent is not included in the carbon number of the “organic group”. Therefore, for example, a glycidyl butyl group ((C ₂ H ₃ O) —C ₄ H ₈ —) corresponds to a butyl group which is an organic group having 4 carbon atoms and one glycidyl group substituted. Methyl-4-oxo-hexo-5-en-1-yl group (CH ₃ — (C═CH ₂ ) — (C═O) —C ₃ H ₆ —) is propyl which is an organic group having 3 carbon atoms. This corresponds to a group in which one methacrylate group is substituted.

  Examples of the hydrolyzable silane represented by the formula (II) include alkyltrialkoxysilanes such as methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, and ethyltriethoxysilane; phenyltrimethoxysilane, phenyltrimethoxysilane, and the like. Phenyltrialkoxysilanes such as ethoxysilane; (meth) acryloyl such as 3- (meth) acryloyloxypropyltrimethoxysilane, 3- (meth) acryloyloxypropyltriethoxysilane, 3- (meth) acryloyloxypropyltrialkoxysilane Oxy group-containing alkyltrialkoxysilane; glycidyl group-containing alkyltrialkoxysilanes such as 3-glycidyloxypropyltrimethoxysilane and 3-glycidyloxypropyltriethoxysilane; Examples include vinyl group-containing trialkoxysilanes such as nyltrimethoxysilane and vinyltriethoxysilane; oxetane ring-containing alkyltrialkoxysilanes such as 3-[(3-ethyloxetane-3-yl) methoxy] propyltrimethoxysilane. .

  From the viewpoint of curability and scratch resistance, methyltrialkoxysilane, glycidyl group-containing alkyltrialkoxysilane, and oxetane ring-containing alkyltrialkoxysilane are particularly preferable.

As the silsesquioxane compound (a), those obtained by hydrolytic condensation of a hydrolyzable silane containing the hydrolyzable silane represented by the formula (I) are preferable. The hydrolyzable silane used as the raw material of the silsesquioxane compound (a) may further contain a hydrolyzable silane represented by the formula (II). In a preferred embodiment of the present invention, the containing silsesquioxane compound (a) is:
With respect to the total molar mass of the hydrolyzable silane represented by the formula (I) and the formula (II),
Hydrolyzable silane represented by the formula (I) 55 to 100 mol%,
Hydrolyzable silane represented by the formula (II) 0 to 45 mol%,
In particular, from the viewpoint of scratch resistance, the following range is preferable.

  The hydrolyzable silane represented by the formula (I) is particularly in the range of 80 to 100 mol%, more particularly 90 to 100 mol%, and the hydrolyzable silane represented by the formula (II) is 0 to 100 mol%. 20 mol%, more particularly in the range of 0-10 mol / g. The amount of the hydrolyzable silane represented by the formula (II) being 0 mol% means that the silane is not used at all.

  When manufacturing the silsesquioxane compound which is (a) component, a catalyst can be used. As the catalyst, a basic catalyst is preferably used. Specific examples of the basic catalyst include alkali metal hydroxides such as potassium hydroxide, sodium hydroxide and cesium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, benzyltrimethyl Examples thereof include ammonium hydroxide salts such as ammonium hydroxide and ammonium fluoride salts such as tetrabutylammonium fluoride.

  The amount of the catalyst used is not particularly limited, but if it is too much, there are problems such as high cost and difficulty in removal, and if it is too small, the reaction may be slow. Therefore, Preferably it is 0.0001-1.0 mol with respect to 1 mol of hydrolysable silane, More preferably, it is the range of 0.0005-0.1 mol.

  When hydrolyzing and condensing a hydrolyzable silane, water is usually used. The quantity ratio of hydrolyzable silane and water is not particularly limited. The amount of water used is from 0.1 to 100 mol, and further from 0.5 to 3 mol, per mol of hydrolyzable silane, in terms of the yield and purity of the silsesquioxane compound having the desired structure. It is preferable to be within the ratio. Moreover, when using a basic catalyst as aqueous solution, the water to be used may be substituted with the water, and water may be added separately.

  In the hydrolysis condensation, an organic solvent may be used. It is preferable to use an organic solvent from the viewpoint of preventing gelation and adjusting the viscosity during production. As the organic solvent, polar organic solvents and nonpolar organic solvents can be used alone or as a mixture.

  As the polar organic solvent, lower alcohols such as methanol, ethanol and 2-propanol, ketones such as acetone and methyl isobutyl ketone, and ethers such as tetrahydrofuran are used. Particularly, acetone and tetrahydrofuran have a low boiling point and the system is uniform. And the reactivity is improved. As the nonpolar organic solvent, a hydrocarbon solvent is preferable, and an organic solvent having a boiling point higher than that of water such as toluene and xylene is preferable. In particular, an organic solvent azeotropic with water such as toluene efficiently removes water from the system. This is preferable because it is possible. In particular, mixing a polar organic solvent and a nonpolar organic solvent provides the above-described advantages, so that it is preferably used as a mixed solvent.

  As reaction temperature at the time of hydrolysis condensation, it is 0-200 degreeC normally, Preferably it is 10-190 degreeC, More preferably, it is 10-120 degreeC. Moreover, although this reaction can be implemented irrespective of a pressure, the pressure range of 0.02-0.2 MPa is preferable, and the pressure range of 0.08-0.15 MPa is especially preferable. The reaction is usually completed in about 1 to 15 hours.

  In the hydrolysis-condensation reaction, the condensation reaction proceeds with hydrolysis, and most of the hydrolyzable group of the hydrolyzable silane [specifically, for example, X in the formula (I), preferably 100% is hydroxyl. It is possible to condense liquid stability and scratch resistance by hydrolysis to a group (OH group) and further condensing most of the OH group, preferably 80% or more, more preferably 90% or more, and particularly preferably 100%. To preferred.

  The alcohol, solvent, and catalyst generated by the reaction may be removed from the mixed solution after hydrolysis condensation by a known method. The obtained product may be further purified by removing the catalyst by various purification methods such as washing, column separation, and adsorption with a solid adsorbent according to the purpose. From the viewpoint of efficiency, it is preferable to remove the catalyst by washing with water.

  Here, when 100% condensation does not occur in the hydrolysis condensation, the product obtained by the present production method includes a silsesquioxane compound having a structure in which all of the Si—OH groups (hydroxysilyl groups) are hydrolyzed and condensed. In addition to this, there may be a ladder structure in which Si-OH groups remain, an incomplete cage structure and / or a silsesquioxane compound of a random condensate, which is the component (A) obtained by this production method. The silsesquioxane compound may contain these ladder structures, incomplete cage structures, and / or random condensates. In addition, the ratio of the silsesquioxane compound having a structure in which all of the Si—OH groups are hydrolyzed and condensed is preferably 80% by mass or more in the silsesquioxane compound as the component (a) obtained by the above production method. More preferably, it is 90% by mass or more from the viewpoint of liquid stability and scratch resistance.

Iodonium salt photoacid generator (b)
The photocationic curable coating composition of the present invention contains an iodonium salt photoacid generator (b).
The iodonium salt-based photoacid generator (b) is a compound that generates a cation (acid) by light and can serve as an initiator for cationic polymerization.

  In particular, from the viewpoint of transparency and scratch resistance, the photoacid generator (b) is preferably an iodonium salt photoacid generator represented by the following formula (III).

In formula (III), R ³ represents an organic group bonded to I (iodine atom), and two R ^{3 s} may be the same or different from each other. [Y] ⁻ is a phosphate anion represented by the formula (IV) or a boron compound anion represented by the formula (V), and Rf in the formula (IV) is fluorine in which all or part of the hydrogen atoms are fluorine. An alkyl group which may be substituted with an atom is represented. b is an integer of 0-5. The b Rf's may be the same or different.

R ³ includes an aryl group having 6 to 30 carbon atoms, a heterocyclic group having 4 to 30 carbon atoms, an alkyl group having 1 to 30 carbon atoms, an alkenyl group having 2 to 30 carbon atoms, or an alkynyl group having 2 to 30 carbon atoms. Which represent alkyl, hydroxy, alkoxy, alkylcarbonyl, arylcarbonyl, alkoxycarbonyl, aryloxycarbonyl, arylthiocarbonyl, acyloxy, arylthio, alkylthio, aryl, heterocycle, aryloxy, alkylsulfinyl, arylsulfinyl, alkylsulfonyl , Arylsulfonyl, alkyleneoxy, amino, cyano, nitro groups, halogen and the like.

  In the above, the aryl group having 6 to 30 carbon atoms includes monocyclic aryl groups such as phenyl groups and condensed naphthyl, anthracenyl, phenanthrenyl, pyrenyl, chrysenyl, naphthacenyl, benzanthracenyl, anthraquinolyl, fluorenyl, naphthoquinone, anthraquinone, etc. And a polycyclic aryl group.

  Examples of the heterocyclic group having 4 to 30 carbon atoms include cyclic groups containing 1 to 3 hetero atoms such as oxygen, nitrogen and sulfur, which may be the same or different. Are monocyclic heterocyclic groups such as thienyl, furanyl, pyranyl, pyrrolyl, oxazolyl, thiazolyl, pyridyl, pyrimidyl, pyrazinyl and indolyl, benzofuranyl, isobenzofuranyl, benzothienyl, isobenzothienyl, quinolyl, isoquinolyl, quinoxalinyl, quinazolinyl A condensed polycyclic heterocyclic group such as carbazolyl, acridinyl, phenothiazinyl, phenazinyl, xanthenyl, thianthenyl, phenoxazinyl, phenoxathinyl, chromanyl, isochromanyl, dibenzothienyl, xanthonyl, thioxanthonyl, dibenzofuranyl It is below.

  Examples of the alkyl group having 1 to 30 carbon atoms include linear alkyl groups such as methyl, ethyl, propyl, butyl, hexadecyl, okdadecyl, isopropyl, isobutyl, sec-butyl, tert-butyl, isopentyl, neopentyl, tert-pentyl, isohexyl, etc. And a cycloalkyl group such as cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl. Examples of the alkenyl group having 2 to 30 carbon atoms include linear, branched, and the like such as vinyl, allyl, 1-propenyl, isopropenyl, 1-butenyl, 2-butenyl, 3-butenyl, 1-methyl-1-propenyl, and the like. Can be mentioned. Further, examples of the alkynyl group having 2 to 30 carbon atoms include linear or branched ethynyl, 1-propynyl, 2-propynyl, 1-butynyl, 2-butynyl, 3-butynyl, 1-methyl-2-propynyl and the like. Things.

  The aryl group having 6 to 30 carbon atoms, the heterocyclic group having 4 to 30 carbon atoms, the alkyl group having 1 to 30 carbon atoms, the alkenyl group having 2 to 30 carbon atoms, or the alkynyl group having 2 to 30 carbon atoms is at least 1 It may have a kind of substituent, and examples of the substituent include a linear alkyl group having 1 to 18 carbon atoms such as methyl, ethyl, propyl, butyl, okdadecyl; isopropyl, isobutyl, sec-butyl, tert-butyl A branched alkyl group having 1 to 18 carbon atoms; a cycloalkyl group having 3 to 18 carbon atoms such as cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl; a hydroxy group; methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy, straight-chain or branched alkoxy groups having 1 to 18 carbon atoms such as tert-butoxy and dodecyloxy; C2-C18 linear or branched alkylcarbonyl groups such as pionyl, butanoyl, 2-methylpropionyl, heptanoyl, 2-methylbutanoyl, 3-methylbutanoyl, octanoyl; benzoyl, naphthoyl, etc. Arylcarbonyl group; methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, isopropoxycarbonyl, butoxycarbonyl, isobutoxycarbonyl, sec-butoxycarbonyl, tert-butoxycarbonyl, etc., a straight or branched alkoxycarbonyl group having 2 to 19 carbon atoms; phenoxy Aryloxycarbonyl groups having 7 to 11 carbon atoms such as carbonyl and naphthoxycarbonyl; arylthiocarbonyl groups having 7 to 11 carbon atoms such as phenylthiocarbonyl and naphthoxythiocarbonyl; A linear or branched acyloxy group having 2 to 19 carbon atoms such as xyl, ethylcarbonyloxy, propylcarbonyloxy, isobutylcarbonyloxy, sec-butylcarbonyloxy, tert-butylcarbonyloxy, octadecylcarbonyloxy; phenylthio, biphenylylthio, Methylphenylthio, chlorophenylthio, bromophenylthio, fluorophenylthio, hydroxyphenylthio, methoxyphenylthio, naphthylthio, 4- [4- (phenylthio) benzoyl] phenylthio, 4- [4- (phenylthio) phenoxy] phenylthio, 4 -[4- (phenylthio) phenyl] phenylthio, 4- (phenylthio) phenylthio, 4-benzoylphenylthio, 4-benzoyl-chlorophenylthio, 4-benzoyl-methyl Thiophenylthio, 4- (methylthiobenzoyl) phenylthio, 4- (p-tert-butylbenzoyl) phenylthio, etc. arylthio groups having 6 to 20 carbon atoms; methylthio, ethylthio, propylthio, tert-butylthio, neopentylthio, dodecylthio, etc. Straight or branched alkylthio group having 1 to 18 carbon atoms; aryl group having 6 to 10 carbon atoms such as phenyl, tolyl, dimethylphenyl, naphthyl; thienyl, furanyl, pyranyl, xanthenyl, chromanyl, isochromanyl, xanthonyl, thioxanthonyl, dibenzofuran A heterocyclic group having 4 to 20 carbon atoms such as nyl; an aryloxy group having 6 to 10 carbon atoms such as phenoxy and naphthyloxy; methylsulfinyl, ethylsulfinyl, propylsulfinyl, tert-pentylsulfinyl, octylsulfur A linear or branched alkylsulfinyl group having 1 to 18 carbon atoms such as nyl; an arylsulfinyl group having 6 to 10 carbon atoms such as phenylsulfinyl, tolylsulfinyl, naphthylsulfinyl; methylsulfonyl, ethylsulfonyl, propylsulfonyl, isopropylsulfonyl, butylsulfonyl A linear or branched alkylsulfonyl group having 1 to 18 carbon atoms such as octylsulfonyl; an arylsulfonyl group having 6 to 10 carbon atoms such as phenylsulfonyl, tolylsulfonyl (tosyl group) and naphthylsulfonyl; an alkyleneoxy group; a cyano group; Nitro group; halogen such as fluorine, chlorine, bromine and iodine.

  Specific examples of iodonium cations include diphenyliodonium, di-p-tolyliodonium, bis (4-dodecylphenyl) iodonium, bis (4-methoxyphenyl) iodonium, bis (4-ethoxyphenyl) iodonium, (4-octyloxy Phenyl) phenyliodonium, bis (4-decyloxy) phenyliodonium, 4- (2-hydroxytetradecyloxy) phenylphenyliodonium, 4-isopropylphenyl (p-tolyl) iodonium, 4-isobutylphenyl (p-tolyl) iodonium, etc. Iodonium ion.

  In the formula (IV), Rf represents an alkyl group in which all or part of the hydrogen atoms may be substituted with fluorine atoms. Specific examples of the alkyl group include linear alkyl groups such as methyl, ethyl, propyl, butyl, pentyl and octyl; branched alkyl groups such as isopropyl, isobutyl, sec-butyl and tert-butyl; and cyclopropyl, cyclobutyl and cyclopentyl. And a cycloalkyl group such as cyclohexyl and the like, and a preferable carbon number is 1-4. In the alkyl group, all or part of the hydrogen atoms may be substituted with fluorine atoms, and the substitution ratio is 80% or more, more preferably 90% or more, particularly 100% from the viewpoint of polymerization curability and scratch resistance. It is preferable that

Particularly preferred Rf is a linear or branched alkyl group having 1 to 4 carbon atoms and a fluorine atom substitution rate of 100%. Specific examples include CF ₃ , CF ₃ CF ₂ , (CF ₃ ) ₂ CF _{, CF 3 CF 2 CF 2,} CF 3 CF 2 CF 2 CF 2, (CF 3) 2 CFCF 2, CF 3 CF 2 (CF 3) CF, include _{(CF 3)} 3 C.

In another embodiment, particularly preferred Rf is a linear or branched unsubstituted alkyl group having 1 to 4 carbon atoms, and specific examples include CH ₃ , CH ₃ CH ₂ , (CH ₃ ) _{2. CH, CH 3 CH 2 CH 2} , CH 3 CH 2 CH 2 CH 2, (CH 3) 2 CHCH 2, CH 3 CH 2 (CH 3) CH, include _{(CH 3)} 3 C.

In formula (III), from the viewpoint of transparency, [Y] ⁻ is preferably a phosphate anion represented by formula (IV).

  In the formula (IV), the number b of Rf is an integer of 0 to 5, more preferably 1 to 4, and particularly preferably 2 or 3 from the viewpoint of scratch resistance. The b Rf's may be the same or different.

Specific examples of preferable phosphate anions include ([PF ₆ ] ⁻ ), [(CF ₃ CF ₂ ) ₃ PF ₃ ] ⁻ , and [(CF ₃ CF ₂ CF ₂ ) ₃ PF, which are fluorinated phosphate anions. ₃ ] ⁻ , [((CF ₃ ) ₂ CF) ₃ PF ₃ ] ⁻ , [((CF ₃ ) ₂ CF) ₂ PF ₄ ] ⁻ , [((CF ₃ ) ₂ CFCF ₂ ) ₃ PF ₃ ] ⁻ and Fluorinated alkyl phosphate anions such as [((CF ₃ ) ₂ CFCF ₂ ) ₂ PF ₄ ] ^— and the like can be mentioned. From the viewpoints of curability, transparency of the coating film and scratch resistance, the anionic species is particularly preferably a fluorinated alkyl phosphate anion.

In another embodiment, specific examples of particularly preferred phosphate anions include ([PF ₆ ] ⁻ ) and [(CH ₃ CH ₂ ) ₃ PF ₃ ] ⁻ , [(CH ₃ CH ₂ CH ₂ ) ₃ PF ₃ ] ⁻ , [((CH ₃ ) ₂ CH) ₃ PF ₃ ] ⁻ , [((CH ₃ ) ₂ CH) ₂ PF ₄ ] ⁻ , [((CH ₃ ) ₂ CHCH ₂ ) ₃ PF _3] ^- and _{[((CH 3) 2 CHCH} 2) 2 PF 4] - , and the like fluorinated alkyl phosphate anion, such as.

  As the iodonium salt-based photoacid generator (b), a commercially available product can be used. For example, Irgacure (registered trademark) 250 (trade name, fluorinated iodonium phosphate salt manufactured by BASF), IK-1 ( San Apro, trade name, fluorinated alkyl phosphate iodonium salt), PI-2074 (Rhone Plan, trade name, fluorinated phenyl borate iodonium salt), and the like.

  The photoacid generator may be dissolved in advance in a solvent that does not inhibit cationic polymerization.

  Solvents include carbonates such as propylene carbonate, ethylene carbonate, 1,2-butylene carbonate, dimethyl carbonate, and diethyl carbonate; ketones such as acetone, methyl ethyl ketone, cyclohexanone, methyl isoamyl ketone, and 2-heptanone; ethylene glycol, ethylene glycol Multivalents such as monoacetate, diethylene glycol, diethylene glycol monoacetate, propylene glycol, propylene glycol monoacetate, dipropylene glycol, and dipropylene glycol monoacetate monomethyl ether, monoethyl ether, monopropyl ether, monobutyl ether, or monophenyl ether Alcohols and derivatives thereof; cyclic ethers such as dioxane Class: ethyl formate, methyl lactate, ethyl lactate, methyl acetate, ethyl acetate, butyl acetate, methyl pyruvate, methyl acetoacetate, ethyl acetoacetate, ethyl pyruvate, ethyl ethoxyacetate, methyl methoxypropionate, ethyl ethoxypropionate, Methyl 2-hydroxypropionate, ethyl 2-hydroxypropionate, ethyl 2-hydroxy-2-methylpropionate, methyl 2-hydroxy-3-methylbutanoate, 3-methoxybutyl acetate, 3-methyl-3-methoxybutyl acetate And esters such as aromatic hydrocarbons such as toluene and xylene.

  The blending ratio of the photoacid generator (b) is preferably in the range of 0.1 to 15 parts by mass, and more preferably 0.5 to 8 parts by mass with respect to 100 parts by mass of the total weight of the component (a).

Other photocationically polymerizable compounds (c)
The photocationic curable coating composition of the present invention may further contain other photocationically polymerizable group-containing compound (c).

  The other photocationically polymerizable group-containing compound (c) is a compound other than the component (a), which is ionically polymerized using a cation as a chain carrier (growth seed). Among them, from the viewpoint of curability and cost balance, a compound having one or more photocationically polymerizable groups, particularly an epoxy group-containing compound and / or an oxetane compound in which the photocationically polymerizable group is an epoxy group and / or an oxetane ring. It is preferable that Examples of the epoxy group include an oxiranyl group, a glycidyl group, and an alicyclic epoxy group (such as an epoxycycloalkyl group). Specific examples of the compound include a glycidyl group-containing compound having one or more glycidyl groups, and an oxetane ring. An oxetane compound having one or more, an epoxy group-containing oxetane compound having at least one oxetane ring and an epoxy group (hereinafter referred to as an epoxy group-containing oxetane compound), and an alicyclic epoxy having at least one alicyclic epoxy group It is preferably at least one selected from the group-containing compound group.

  The glycidyl group-containing compound is a compound having at least one glycidyl group in the molecule, and examples of the compound having one glycidyl group include phenyl glycidyl ether and butyl glycidyl ether, and a compound having two or more epoxy groups. Contains ethylene glycol diglycidyl ether, hexanediol diglycidyl ether, tetraethylene glycol diglycidyl ether, trimethylolpropane triglycidyl ether, bisphenol A diglycidyl ether, hydrogenated bisphenol A diglycidyl ether, novolac type epoxy compound, glycidyl group An acrylic resin etc. are mentioned.

  The glycidyl group-containing acrylic resin is, for example, a glycidyl group-containing polymerizable unsaturated monomer (hereinafter sometimes abbreviated as “glycidyl monomer”) and, if necessary, other polymerizable monomers copolymerizable with these monomers. It is obtained by copolymerizing a saturated monomer (hereinafter, sometimes abbreviated as “other monomer”).

  As the glycidyl monomer, any polymerizable unsaturated monomer containing a glycidyl group can be used without particular limitation. Typical examples thereof include glycidyl acrylate, glycidyl methacrylate, methyl glycidyl acrylate, methyl glycidyl methacrylate, and allyl glycidyl. Examples thereof include ether and vinyl glycidyl ether. Of these, glycidyl acrylate and glycidyl methacrylate are preferably used.

  The other monomer copolymerizable with the glycidyl monomer is a monomer that is appropriately used as required according to the intended performance of the resulting glycidyl group-containing acrylic resin, such as methyl acrylate, methyl methacrylate, ethyl Acrylate, ethyl methacrylate, n-, i- or t-butyl acrylate, n-, i- or t-butyl methacrylate, hexyl acrylate, hexyl methacrylate, octyl acrylate, octyl methacrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate, stearyl C1-C24 alkyl or cycloalkyl ester of acrylic acid or methacrylic acid such as methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate and the like; -Hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, etc. acrylic acid or methacrylic acid having 1 to 8 carbon atoms in hydroxy Alkyl ester; α, β-ethylenically unsaturated carboxylic acid such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, crotonic acid; acrylamide, methacrylamide, N-methylacrylamide, N-ethylmethacrylamide, diacetoneacrylamide, Acrylamide or methacrylate such as N-methylolacrylamide, N-methylolmethacrylamide, N-methoxymethylacrylamide, N-butoxymethylacrylamide Luamide or derivatives thereof; aromatic vinyl monomers such as styrene, vinyltoluene, α-methylstyrene; vinyl propionate, vinyl acetate, acrylonitrile, methacrylonitrile, vinyl pivalate, veova monomer (made by Shell Chemical Co., vinyl of branched fatty acid) Ester), Silaplane (registered trademark) FM0711, FM0721, FM0721 (all of which are manufactured by Chisso Corp., polydimethylsiloxane macromonomer having a methacryloyl group at the end). . Of these monomers, styrene and methyl methacrylate are particularly preferred.

  The glycidyl group-containing acrylic resin is a solution polymerization, bulk polymerization, emulsion polymerization, suspension polymerization of the monomer component consisting of the above glycidyl monomer and other monomers as required, for example, in the presence or absence of a radical polymerization initiator. It can obtain by superposing | polymerizing by the polymerization method known per se. The glycidyl group-containing acrylic resin preferably has a weight average molecular weight of generally 1,000 to 100,000, particularly 2,000 to 50,000.

  The blending ratio of each monomer component in the polymerization of the glycidyl group-containing acrylic resin is preferably in the following range with respect to 100 parts by mass of the total amount of monomer components.

Glycidyl monomer: 10 to 100 parts by mass, preferably 20 to 80 parts by mass,
Other monomers: 0 to 90 parts by mass, preferably 20 to 80 parts by mass.

  In the glycidyl group-containing acrylic resin, the concentration of the glycidyl group is generally in the range of 0.1 to 7.0 equivalent / kg, particularly 0.2 to 5.0 equivalent / kg.

  The oxetane compound is a compound having at least one oxetane ring in the molecule, and is preferably a compound having 1 to 3 oxetane rings.

  Compounds having one oxetane ring include 3-ethyl-3-methoxymethyloxetane, 3-ethyl-3-ethoxymethyloxetane, 3-ethyl-3-butoxymethyloxetane, 3-ethyl-3-hexyloxymethyloxetane, 3-methyl-3-hydroxymethyloxetane, 3-ethyl-3-hydroxymethyloxetane, 3-ethyl-3-allyloxymethyloxetane, 3-ethyl-3- (2'-hydroxyethyl) oxymethyloxetane, 3- Ethyl-3- (2'-hydroxy-3'-phenoxypropyl) oxymethyloxetane, 3-ethyl-3- (2'-hydroxy-3'-butoxypropyl) oxymethyloxetane, 3-ethyl-3- [2 '-(2 "-ethoxyethyl) oxymethyl] oxetane, 3-ethyl- -(2'-butoxyethyl) oxymethyloxetane, 3-ethyl-3-benzyloxymethyloxetane, 3-ethyl-3- (p-tert-butylbenzyloxymethyl) oxetane, 3-ethyl-3- (phenoxymethyl) ) Oxatan, 3-ethyl-3- (2-ethylhexyloxymethyl) oxetane and the like.

  The compound having two or more oxetane rings (for example, 2 to 3, preferably 2) is a compound having at least two oxetane rings capable of photocationic polymerization (hereinafter referred to as a polyoxetane compound). For example, di [1-ethyl (3-oxetanyl)] methyl ether; xylylene bisoxetane; reaction product of 3-lower alkyl-3-hydroxyoxetane and polyisocyanate compound; 3-lower alkyl-3-hydroxyoxetane and alcohol A reaction product of 3-lower alkyl-3-hydroxyoxetane and polycarboxylic acid, and the like. Examples of the 3-lower alkyl-3-hydroxyoxetane include 3-methyl-3-hydroxymethyloxetane and 3-ethyl-3-hydroxymethyloxetane.

  The epoxy group-containing oxetane compound is a compound having one or more oxetane rings and epoxy groups in the molecule (hereinafter referred to as an epoxy group-containing oxetane compound), preferably including a compound having a molecular weight of less than 1,000, Specific examples include compounds represented by the following formula (VI).

In formula (VI), R ⁴ represents a hydrogen atom, a fluorine atom, a linear or branched alkyl group having 1 to 6 carbon atoms, a linear or branched fluoroalkyl group having 1 to 6 carbon atoms, or an allyl group, R ⁵ represents an epoxy group.

A representative example of the epoxy-containing oxetane compound is a compound in the case where R ⁴ is an ethyl group and R ⁵ is a glycidyl group or a 3,4-epoxycyclohexylmethyl group in the above formula (VI).

  The alicyclic epoxy group-containing compound is a compound having at least one such alicyclic epoxy group in the molecule and a compound other than the compound (a), and preferably has 2 to 3 alicyclic epoxy groups. And a compound having a weight average molecular weight of less than 2,000 and more preferably 100 to 1,500. In addition, the alicyclic epoxy group-containing compound preferably has an epoxy equivalent of 50 to 500 g / equivalent, particularly 100 to 300 g / equivalent, from the viewpoint of reaction rate. Here, the epoxy equivalent is the number of grams of a resin containing 1 gram equivalent of an epoxy group measured by a method according to JIS K7236.

  Specific examples of the alicyclic epoxy group-containing compound include dicyclopentadiene dioxide, bis (2,3-epoxycyclopentyl) ether, epoxycyclohexenecarboxylic acid ethylene glycol diester, bis (3,4-epoxycyclohexylmethyl) adipate. Bis (4,5-epoxy-2-methylcyclohexylmethyl) adipate, ethylene glycol-bis (3,4-epoxycyclohexanecarboxylate), 3 ', 4'-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate 3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxy-6-methylcyclohexanecarboxylate, 1,2,5,6-diepoxy-4,7-methanoperhydroindene, 2- (3, 4-D Poxycyclohexyl) -3 ', 4'-epoxy-1,3-dioxane-5-spirocyclohexane, 1,2-ethylenedioxy-bis (3,4-epoxycyclohexylmethane), di-2,3-epoxycyclopentyl Examples include ether, 4 ′, 5′-epoxy-2′-methylcyclohexylmethyl-4, 5-epoxy-2-methylcyclohexanecarboxylate, 4-oxiranyl-1, 2-epoxycyclohexane and the like.

  Commercially available products can be used as the alicyclic epoxy group-containing compound. For example, Celoxide (registered trademark) 2000, Celoxide (registered trademark) 2021P, Celoxide (registered trademark) 2081, Celoxide (registered trademark) 3000 (all , Trade name, manufactured by Daicel Chemical Industries, Ltd.).

  Further, as other photocationically polymerizable group-containing compound (c), in addition to the above compound group, for example, butyl vinyl ether, isobutyl vinyl ether, octadecyl vinyl ether, cyclohexyl vinyl ether, butanediol monovinyl ether, butanediol divinyl ether, cyclohexanedimethanol Divinyl ether, cyclohexanedimethanol monovinyl ether, diethylene glycol divinyl ether, ethylene glycol divinyl ether, ethylene glycol monovinyl ether, diethylene glycol monovinyl ether, triethylene glycol divinyl ether, triethylene glycol monovinyl ether, tetraethylene glycol divinyl ether, tetraethylene glycol monovinyl ether , Tert-butyl vinyl ether, tert-acyl vinyl ether, ethyl hexyl vinyl ether, dodecyl vinyl ether, ethylene glycol butyl vinyl ether, hexanediol divinyl ether, hexanediol monovinyl ether, trimethylolpropane trivinyl ether, trimethylolpropane divinyl ether, trimethylolpropane monovinyl ether, Neopentyl glycol divinyl ether, neopentyl glycol monovinyl ether, glycerol divinyl ether, glycerol trivinyl ether, diglycerol trivinyl ether, sorbitol tetravinyl ether, allyl vinyl ether, 4-vinyl ether styrene, hydroquinone divinyl ether, phenyl vinyl ether Compounds such as tellurium, alcohol adducts of oxiranyl group-containing epoxycyclohexane, monomers or polymers whose hydroxyl groups are modified with vinyl ether, other monomers having cationic polymerization properties such as styrene, α-methylstyrene, divinylbenzene, polybutadiene-based polymers, vinylcarbazole Alternatively, a polymer or the like may be used alone or in combination.

  The content of the other photocationically polymerizable compound (c) is preferably 50 parts by mass or less and 30 parts by mass or less with respect to 100 parts by mass of the component (a) from the viewpoint of curling resistance.

  The photocationic curable coating composition of the present invention may be solventless or may further contain an organic solvent.

  Examples of the organic solvent include alcohol solvents such as methanol, ethanol, butanol, methyl isobutyl carbinol, 2-ethylhexanol, and benzyl alcohol; ketone solvents such as acetone and methyl isobutyl ketone; ethyl acetate, butyl acetate, methyl benzoate, Ester solvents such as methyl propionate; ether solvents such as cyclohexanone, tetrahydrofuran, dioxane, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, isopropyl glycol; diethylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, 3 -Glycol ether aromatic hydrocarbon solvents such as methoxybutyl acetate, aliphatic hydrocarbon solvents And the like. These can be used in appropriate combination depending on the purpose such as adjustment of viscosity and adjustment of coating property.

  Among the above organic solvents, it is preferable to use an organic solvent having a boiling point of 100 ° C. or less from the viewpoint of finish and curability. Among them, methanol, ethanol, acetone, methyl ethyl ketone, ethyl acetate, It is preferable to use at least one selected from dimethoxyethane.

  The composition of the present invention may further contain a sensitizer (d). The sensitizer (d) usually absorbs at a wavelength longer than the maximum absorption wavelength indicated by the iodonium salt photoacid generator (b), and initiates polymerization by the iodonium salt photoacid generator (b). It is a compound that promotes.

  The sensitizer (d) is preferably a compound that absorbs light having a wavelength longer than 350 nm. The iodonium salt-based photoacid generator (b) usually exhibits maximum absorption at a wavelength near or shorter than 300 nm, generates a cationic species or a Lewis acid in response to light at a wavelength near the iodonium salt photoacid generator, Cationic polymerization of the oxan compound (a) is initiated, but if the sensitizer (d) as described above is added, it will be sensitive to light having a longer wavelength, particularly longer than 350 nm. .

  Examples of the sensitizer (d) include anthracene sensitizers and thioxanthone sensitizers.

Specific examples of the anthracene sensitizer include, for example,
9,10-dimethoxyanthracene,
9,10-diethoxyanthracene,
9,10-dipropoxyanthracene,
9,10-diisopropoxyanthracene,
9,10-dibutoxyanthracene,
9,10-dipentyloxyanthracene,
9,10-dihexyloxyanthracene,
9,10-bis (2-methoxyethoxy) anthracene,
9,10-bis (2-ethoxyethoxy) anthracene,
9,10-bis (2-butoxyethoxy) anthracene,
9,10-bis (3-butoxypropoxy) anthracene,
2-methyl- or 2-ethyl-9,10-dimethoxyanthracene,
2-methyl- or 2-ethyl-9,10-diethoxyanthracene,
2-methyl- or 2-ethyl-9,10-dipropoxyanthracene,
2-methyl- or 2-ethyl-9,10-diisopropoxyanthracene,
2-methyl- or 2-ethyl-9,10-dibutoxyanthracene,
2-methyl- or 2-ethyl-9,10-dipentyloxyanthracene,
2-methyl- or 2-ethyl-9,10-dihexyloxyanthracene,
Etc.

  Examples of the thioxanthone sensitizer include 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2,4-diethylthioxanthone, and chloropropoxythioxanthone.

A commercial item can be used as said sensitizer (d). As a commercial item of the said anthracene type sensitizer, "Anthracure (trademark) UVS-1331", "Anthracure (trademark) UVS-1221" (above, the Kawasaki Kasei Kogyo company make) etc. are mentioned, for example. .
Examples of commercially available thioxanthone-based sensitizers include “KAYACURE (registered trademark) DETX-S” (manufactured by Nippon Kayaku Co., Ltd.), “Speedcure (registered trademark) ITX”, “Speedcure (registered trademark) DETX. "Speedcure (registered trademark) CPTX" (manufactured by LAMBSON).

  In the coating composition of the present invention, an anthracene sensitizer is preferably used as the sensitizer (d).

  When the coating composition of the present invention contains the above sensitizer, the solid content of the sensitizer is selected from the above-mentioned sills from the viewpoint of the scratch resistance of the formed coating film and the storage stability of the coating composition. 0.01 to 10 parts by mass, preferably 0.05 to 8 parts by mass, and more preferably 0.1 to 5 parts by mass with respect to 100 parts by mass of the solid content of the sesquioxane compound (a). Is preferred.

  The composition of the present invention may further contain an auxiliary sensitizer (e). The auxiliary sensitizer (e) is a compound that further promotes the action of the sensitizer.

The auxiliary sensitizer (e) is not particularly limited, and various types can be used. For example, a naphthalene-based auxiliary sensitizer can be preferably used. Specific examples of the naphthalene-based auxiliary sensitizer include, for example,
4-methoxy-1-naphthol,
4-ethoxy-1-naphthol,
4-propoxy-1-naphthol,
4-butoxy-1-naphthol,
4-hexyloxy-1-naphthol,
1,4-dimethoxynaphthalene,
1-ethoxy-4-methoxynaphthalene,
1,4-diethoxynaphthalene,
1,4-dipropoxynaphthalene,
1,4-dibutoxynaphthalene and the like can be mentioned.

  When the coating composition of the present invention contains the auxiliary sensitizer (e), the solid content of the auxiliary sensitizer (e) depends on the scratch resistance of the formed coating film and the storage of the coating composition. From the viewpoint of stability, 0.01 to 10 parts by mass, preferably 0.05 to 8 parts by mass, more preferably 0.1 to 0.1 parts by mass with respect to 100 parts by mass of the solid content of the silsesquioxane compound (a). It is preferable to be within the range of 5 parts by mass.

The composition of the present invention may further contain various additives, saturated resins and the like. Examples of the additive include a thermal acid generator, an ultraviolet absorber, a light stabilizer, a polymerization inhibitor, an antioxidant, an antifoaming agent, a surface conditioner, a flow conditioner, a plasticizer, and a colorant. Examples of the saturated resin include a saturated acrylic resin, a saturated polyester resin, a saturated urethane resin, these gel particles, and fine particle powder.
The non-volatile content of the photocationic curable coating composition of the present invention is not particularly limited, but is 20 to 100% by mass, and further 25 to 70% from the viewpoint of smoothness of the coating film and shortening of the drying time. Within the range of mass% is preferable. In addition, the non volatile matter of the cation curable coating composition of this invention is the value which totaled the mass of all the components mix | blended except a solvent.

The photocationic curable coating composition of the present invention has a coating film surface when a cured coating film having a thickness of 5 μm is formed on an acrylic resin plate having a thickness of 3 mm. A coating film having a Martens hardness measured under 20 mN of 0.5 to 350 N / mm ² can be formed. In this embodiment, the “acrylic resin plate having a thickness of 3 mm” means a plate made by Mitsubishi Rayon Co., Ltd. and Acrylite (registered trademark) L001 having a thickness of 3 mm.

Further, from the viewpoint of scratch resistance, it is preferable that the Martens hardness is 150 to 340 N / mm ² and the elastic recovery rate of the coating film is 70% or more. The elastic recovery rate is preferably 74% or more, more preferably 83% or more from the viewpoint of scratch resistance.

  “Martens hardness (HM)” in the present invention is the hardness of the coating film obtained from the test load and the indentation surface area when indented from the surface of the coating film by the Vickers indenter, and is an index of the hardness of the object surface.

Specifically, it is a value calculated by substituting the value of the test load and the indentation depth into the following equation.
Formula HM = F / (26.43 × h ² )
F: Test load (mN)
h: Indentation depth (μm).

The “elastic recovery rate (ηIT)” in the present invention is a numerical representation of how much the recessed coating film returns, and is the ratio of elastic work (elastic deformation / total deformation). The ratio of the elastic work amount can also be stopped by (W _elast / W _total ) × 100. Here, W _elast is the work of elastic recovery [ _Nmm ], and W _total is the _total indentation work [Nmm]. The numerical value of each work amount can be measured and determined together with the Martens hardness measurement. A coating film having a large “elastic recovery rate” has elasticity and good scratch resistance.

  A coating film having a Martens hardness of the coating film formed by the present coating composition, and more preferably an elastic recovery rate in the above range or more, has an appropriate balance between hardness and elasticity, and scratched the coating film. Sometimes, even if the scar is recovered, it is easy to return to the original coating state, and the scratch resistance is extremely excellent.

In the present invention, the cured coating film is a cured and dried state specified in JIS K 5600-1-1 (2004), that is, the center of the coating surface is strongly sandwiched between the thumb and the index finger, and the coating surface is dented by a fingerprint. It is a coating film in which the movement of the coating film is not felt, the center of the coating surface is rapidly rubbed with a fingertip, and the coating surface is not rubbed. On the other hand, an uncured coating film is a state in which the coating film has not reached the above-mentioned cured and dried state, and includes a dry-to-touch state and a semi-cured and dried state defined in JIS K 5600-1-1.

Coating film formation method The coating film formation method of the photocationic curable coating composition of the present invention is such that the photocationic curable coating composition is applied on the object to be coated so that the dry film thickness is 1 to 10 μm. After setting and / or preheating, light irradiation is performed.

  This step of setting and / or preheating is performed to reduce or remove the volatile content of the coating film immediately after coating, and can be performed by an air blow, an IR furnace, or the like. The setting can be usually performed by leaving the coated article to stand in a dust-free atmosphere for 30 seconds to 600 seconds at room temperature. Preheating (preheating) can be usually performed by heating the coated object in a drying furnace at a temperature of 40 to 90 ° C, preferably 50 to 70 ° C for 1 to 30 minutes. Moreover, when performing an air blow, it can carry out by spraying the air heated to normal temperature or the temperature of 25 to 80 degreeC normally on the coating surface of to-be-coated object. The preheating time can be usually 30 seconds to 600 seconds.

  The heating temperature condition at the time of performing the preheating is not particularly limited, but the component that volatilizes by heat, for example, the other photocationically polymerizable compound (c) contains a low boiling point compound ( When it contains less than 150 ° C), the heating temperature is preferably less than 70 ° C, more preferably 40 ° C to 70 ° C.

  Further, when heating and light irradiation are performed in combination, heat from a light irradiation source (for example, heat generated by a lamp) may be used as the heat source. Further, when light irradiation is performed after heating, the light irradiation may be performed in a state where the object to be coated is heated (a state having residual heat).

  The article to be coated is not particularly limited. Specific examples include metals, ceramics, glass, plastics, wood, and the like. In addition, a primer layer, an electrodeposition coating layer, an intermediate coating layer, a top coating layer, etc. are formed in advance by applying a primer coating, a cationic electrodeposition coating, an intermediate coating, a top coating, etc. May be.

  The dry film thickness is preferably in the range of 1 to 10 μm, more preferably 1 to 8 μm, from the viewpoint of the appearance and curability of the coating film, scratch resistance, and curl resistance.

  The curling property can be observed in terms of the degree of cure shrinkage of the coating composition. For example, the coating plate after the photocationic curable coating composition is formed on the surface of the plastic substrate is placed on a horizontal table with the coating surface facing up. Then, the distance (lifting distance) between the four corners of the test piece and the horizontal table can be measured and evaluated by the total length. The smaller the shrinkage during curing, the smaller the total length and the better the curl resistance.

The light irradiation source in the light irradiation step is not particularly limited, and is an ultrahigh pressure, high pressure, medium pressure, low pressure mercury lamp, chemical lamp, KrF excimer laser, ArF excimer laser, extreme ultraviolet (EUV: Extreme). Examples include an Ultra Violet lamp, an X-ray, and an electron beam (e-beam), a carbon arc lamp, a xenon lamp, a metal halide lamp, a fluorescent lamp, an LED (light emitting diode) lamp, a tungsten lamp, and the sun. The said irradiation source can be used individually or in combination of 2 or more types.
The light referred to in the present invention includes sunlight, laser light, radiated light (infrared rays, visible rays, ultraviolet rays, β rays, γ rays, X rays) and the like, and is not particularly limited to visible rays. The light has a function of activating a compound that generates a cation (acid) by light irradiation and advancing a cation polymerization reaction.

Irradiation amount varies depending radiation source, for example, when using a high pressure mercury lamp, 10 to 500 mJ / cm ² in the integrated irradiation dose, it is possible to further curing in the range of 50~120mJ / cm ^2.

  The light irradiation may be performed in an air atmosphere or in an inert gas atmosphere.

  Moreover, you may provide the process of heating a coating film after light irradiation. By post-heating, the distortion of the coating film generated by curing the coating film by light irradiation can be alleviated. Further, the heating may improve the hardness or adhesion of the coating film. The heating temperature is preferably within the temperature range shown above.

  The product form of the article in which the film is formed with the photocationic curable coating composition of the present invention is not particularly limited. However, since it has excellent transparency and scratch resistance, it can be particularly suitably used as a hard coat agent. .

Hereinafter, the present invention will be described in more detail with reference to examples. “Part” and “%” indicate “part by mass” and “% by mass” unless otherwise specified. The structural analysis and measurement in this example were performed by the following analyzer and measurement method in addition to the analyzer described in this specification.
⁽²⁹ Si-NMR)
Apparatus: FT-NMR EX-400 manufactured by JEOL
Solvent: CDCl ₃
Internal standard: Tetramethylsilane.

(Production Example 1)
In a separable flask equipped with a reflux condenser, a thermometer, an air inlet tube, and a stirrer, 800 parts of methyl ethyl ketone, 22 parts of deionized water, and 0.5 part of tetrabutylammonium fluoride were blended and dissolved while stirring. . 200 parts of 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane was added thereto and reacted at 40 ° C. for 12 hours. The product was concentrated by a rotary evaporator to obtain a 50% non-volatile solution of the product (A-1).

As a result of ²⁹ Si-NMR analysis of the product (A-1), only a peak around −70 ppm derived from the T3 structure in which all three oxygen atoms bonded to Si were bonded to other Si was confirmed.

  As a result of GPC measurement of the product (A-1), the weight average molecular weight was 1,500.

  The epoxy equivalent of the product (A-1) was 178 g / eq.

From the results of the ²⁹ Si-NMR, the weight average molecular weight, and the epoxy equivalent for the product (A-1), all of the organic groups in which the product (A-1) was directly bonded to the silicon atom were represented by the following formula (P Organic group represented by -I)

It was confirmed to be a silsesquioxane compound having

(Production Examples 2-9)
In Production Example 1, the products (A-2) to (A-9) having a non-volatile content of 50% in Examples 2 to 9 were used in the same manner as in Production Example 1 except that the composition of each component is shown in Table 1. ) The compounding ratio of each component shown in Table 1 is a molar ratio, and the weight average molecular weight and epoxy equivalent of each product are also shown.

Article to be coated (a) an acrylic resin plate: 100 × 150 mm having a thickness of 3mm was cut into an acrylic resin plate (Mitsubishi Rayon Co., Ltd. ACRYLITE (R) L001, a methacrylic resin plate [polymethyl methacrylate and methyl methacrylate The product (a) was degreased with n-butyl acrylate copolymer content of 88% or more] with isopropyl alcohol.

  (B) PET resin sheet: A4 size, 100 μm thick polyethylene terephthalate resin sheet (manufactured by Toyobo Co., Ltd., trade name “Cosmo Shine (registered trademark) A4100”) was used as the article to be coated (b).

  (C) Glass plate: A glass plate 100 × 150 mm thick 3 mm degreased with isopropyl alcohol and subjected to excimer treatment was used as the article to be coated (c).

Coating film formation method (A) After coating each cationic curable coating composition on a coated material with a bar coater under a condition that the film thickness after curing is 5 μm, and preheating at 60 ° C. for 30 seconds to remove the solvent. Then, ultraviolet rays (peak top wavelength 365 nm) were irradiated with an ultraviolet irradiation device under the condition of an integrated irradiation amount of 100 mJ / cm ² to obtain a cured coating film.
・ Ultraviolet irradiation device: belt conveyor type UV irradiation device ・ Lamp: 240 W / cm ² high-pressure mercury lamp (1 lamp number)
(Heraeus Noblelight Fusion Ubuy Co., Ltd.)
・ Lamp output: 60%
Illuminance (measured with UV integrated light meter UIT (registered trademark) -250, photoreceiver UVD-C365 (manufactured by USHIO INC.)): 140 mW / cm ²
・ Irradiation distance: 10cm
・ Integrated irradiation amount (measured with UV integrated light meter UIT (registered trademark) -250, photoreceiver UVD-C365), adjusted by conveyor speed Speed 10 m / min = Total irradiation amount equivalent to 100 mJ / cm ² (b) Formation of the above coating film Curing was carried out in the same manner as in the coating film forming method (a) except that the lamp used, the irradiation distance, and the integrated irradiation amount were as follows.
・ Lamp: 192W 365nm UV-LED (96 lamps)
Illuminance (measured with UV integrated light meter UIT-250, receiver UVD-C365): 630 mW / cm ²
・ Irradiation distance: 1cm
・ Integrated irradiation dose (measured with UV integrated light meter UIT-250, photoreceiver UVD-C365) Adjusted by conveyor speed Speed 2 m / min = Total irradiation dose equivalent to 500 mJ / cm ² .

Example (Example 1) Photocationic curable coating composition No. 1
A 50% nonvolatile solution of the product (A-1) obtained in Production Example 1, a photoacid generator (Note 1) of the following formula (B-1), and BYK-333 (Note 10) in a mass ratio of 100 5: 0.1, diluted with methyl ethyl ketone to a non-volatile content of 40%, stirred, and photocationic curable coating composition No. 1 was produced. Table 2 shows the blending amount of each component by mass ratio.

A cured coating film obtained by curing the obtained photocationic curable coating composition by the coating film forming method (a) was allowed to stand for 1 hour in an atmosphere of 23 ° C. and 50% relative humidity within 30 minutes after curing. The plate was used as a test plate. The coating film had a Martens hardness (Note 11) of 245 N / mm ² and an elastic recovery rate (Note 12) of 81%.

  (Examples 2 to 18 and Comparative Examples 1 to 3) Photocationic curable coating composition No. 2-21 Photocationic curing with 40% non-volatile content of Examples 2 to 18 and Comparative Examples 1 to 3 in the same manner as in Example 1 except that the composition of each component shown in Table 2 in Example 1. Paint composition no. 2 to 21 were obtained. The composition of the coating composition shown in Table 2 is a mass ratio of each component.

Table 2 also shows the Martens hardness and the elastic recovery rate of the coating film obtained by curing the obtained photocationic curable coating composition. The notes in the table are as follows.
(Note 1)

Photoacid generator No. B-1: An iodonium salt-based photocationic polymerizable initiator represented by the above formula (B-1),
(Note 2)

Photoacid generator No. B-2: an iodonium salt-based photocationic polymerizable initiator represented by the above formula (B-2),
(Note 3)

Photoacid generator No. B-3: An iodonium salt-based photocationically polymerizable initiator represented by the above formula (B-3),
(Note 4)

Photoacid generator No. B-4: a sulfonium salt-based photocationically polymerizable initiator represented by the above formula (B-4),
(Note 5) Component C-1: Celoxide (registered trademark) 2012P (trade name, manufactured by Daicel Corporation, compound represented by the following formula C-1, epoxy equivalent of 118 to 145 g / equivalent.

(Note 6) Component C-2: Aron Oxetane (registered trademark) OXT-221 (trade name, manufactured by Toagosei Co., Ltd., compound represented by the following formula (C-2), boiling point 119 ° C./0.67 kPa ,

(Note 7) Component C-3: Aron Oxetane (registered trademark) OXT-101 (trade name, manufactured by Toagosei Co., Ltd., compound represented by the following formula (C-3), boiling point 105 ° C./0.93 kPa ,

(Note 8) Component D-1: Anthracure (registered trademark) UVS-1331 (trade name, manufactured by Kawasaki Kasei Co., Ltd., anthracene compound represented by the following formula (D-1), sensitizer,

(Note 9) Component D-2: “Anthracure (registered trademark) ET-2201” (trade name, manufactured by Kawasaki Kasei Co., Ltd., auxiliary sensitizer)
(Note 10) BYK (registered trademark) -333: trade name, manufactured by Big Chemie, polyether-modified dimethylpolysiloxane, surface conditioner (Note 11, 12) Martens hardness and elastic recovery rate:
<Measurement method>
The Martens hardness of each test plate was measured using a Fischerscope (registered trademark) HM200S (trade name, manufactured by Fisher Instruments Co., Ltd.) under a load of 20 mN / 25 seconds in an atmosphere of 23 ° C. and 50% relative humidity. And measured. A Vickers square pyramid (material: diamond) was used as the indenter, and the position of the sample was adjusted so that the vicinity of the center of one peak of the prism portion was the indenter action point.

<Measurement procedure>
(1-1) Load is applied until the load reaches 10 mN at a speed of 20 mN / 25 seconds.
(1-2) Unloading until the load reaches 0.4 mN at the same speed.
The above procedure was repeated while changing the measurement position, and three data points were taken for each sample.
<Calculation method>
The Martens hardness and the elastic recovery rate were determined from the relationship between the test force and the indentation depth obtained by the above measurement method. The Martens hardness (HM) and the elastic recovery rate (ηIT) were calculated using analysis software attached to the ultra micro hardness test system.

(Example 19)
On the object to be coated (b), the photocation curable coating composition No. 1 obtained in Example 1 was used. 1 was applied, and the coated sheet cured by the method of the coating film forming method (a) was left as it was for 1 hour in an atmosphere of 23 ° C. and 50% relative humidity within 30 minutes after curing as a test sample, It used for various evaluation. The evaluation results are shown in Table 3.

(Examples 20 to 39, Comparative Examples 4 to 6)
In Example 19, test samples were prepared and subjected to various evaluations in the same manner as in Example 19 except that the objects to be coated, the coating film forming method, and the cured film thickness were those described in Table 3. The evaluation results are shown in Table 3. The notes in the table are as follows.

(Note 13) <Adhesiveness>
According to JIS K 5600-5-6 (1990), make 100 1mm x 1mm gobangs on the coating film until it reaches the substrate, stick adhesive tape on the surface, and peel it off rapidly. The number of the remaining Gobanchi laminated films was evaluated.
S: Remaining number / total number = 100/100 and no edge defect AA: Remaining number / total number = 100/100 and no more than five edge defects B: Remaining number / total number = 99 to 90 Pieces / 100 pieces,
Alternatively, 100/100 and 6 or more edges are missing. C: Remaining number / total number = 89 or less / 100.

(Note 14) <Transparency>
The appearance (visual observation) and colorability of each test sample were evaluated. Appearance was checked for the presence or absence of abnormalities such as dirt and cracks in the coating film. A film having no abnormalities such as dust and cracks was designated as AA. A coating film having an abnormality such as dust and cracks is designated as B.

  Colorability (initial) [Δb]: The b value was measured with “CR-300” (trade name, manufactured by Konica Minolta). For each test sample, the difference (Δb) between the b value of the object to be coated and the b value of the test sample was measured, and the colorability was evaluated as follows. If Δb is 1.2 or less, it is at a level that causes no practical problems.

(Note 15) <Curl resistance>
A central portion of each coated sheet was cut into a 10 cm square and used as a measurement sample. In the evaluation, warping at four corners was measured with a ruler, and the total of the four points was taken as the curl value for each test sample.
The smaller the value, the better the value.
S: Less than 5 mm AA: 5 mm or more and less than 20 mm B: 20 mm or more and less than 50 mm C: 50 mm or more It is not measured when the object to be coated is a glass plate.

(Note 16) <Abrasion resistance>
Steel wool method: Commercial steel wool (# 0000) was rubbed 50 times with a load of 1000 g on the coating surface of each test sample, and the coating film was visually observed and evaluated according to the following criteria. Since scratch resistance is good, the number of scratches was evaluated.
S: No cracks, no peeling, or no scratches AA: No cracks, no peeling, or less than 5 scratches A: No cracks, no peeling, or 5 to less than 10 scratches B: No cracking or peeling, or 10 or more and less than 20 scratches are observed C: Cracking, peeling, or significant scratches are observed.

Claims (8)

A photocationic curable coating composition comprising a silsesquioxane compound (a) and an iodonium salt photoacid generator (b),
The silsesquioxane compound (a) is
Hydrolyzing and condensing the hydrolyzable silane compound represented by the formula (I) or the hydrolyzable silane compound represented by the formula (I) and the hydrolyzable silane compound represented by the formula (II) The blending ratio of the mixture of the hydrolyzable silane compound represented by the formula (I) and the hydrolyzable silane compound represented by the formula (II) is the formula (I) and the formula (II ) Based on the total amount with the hydrolyzable silane compound represented by
The hydrolyzable silane compound represented by the formula (I) is 55 to 100 mol%,
The photocationic curable coating composition whose hydrolyzable silane compound represented by Formula (II) is 0-45 mol%.

[In the formula (I), R ¹ represents a divalent alkylene group having 1 to 6 carbon atoms. X is a halogen element or an alkoxy group having 1 to 6 carbon atoms, and the three Xs may be the same or different. ]
R ² SiX ₃ (II)
[In Formula (II), R ² represents a monovalent organic group having 1 to 18 carbon atoms which may be substituted. X is a halogen element or an alkoxy group having 1 to 6 carbon atoms, and the three Xs may be the same or different. However, the compound represented by the formula (I) is excluded] The photocationic curable coating composition according to claim 1, wherein the photoacid generator (b) is an iodonium salt photoacid generator represented by the following formula (III).

[In Formula (III), R ³ represents an organic group bonded to I (iodine atom), and two R ^{3 s} may be the same as or different from each other. [Y] ⁻ is a phosphate anion represented by the formula (IV) or a boron compound anion represented by the formula (V), and Rf in the formula (IV) is fluorine in which all or part of the hydrogen atoms are fluorine. An alkyl group which may be substituted with an atom is represented. b is an integer of 0-5. The b Rf's may be the same or different. ] The photocationic curing according to claim 1 or 2, further comprising 50 parts by mass or less of the other photocationically polymerizable group-containing compound (c) with respect to 100 parts by mass of the silsesquioxane compound (a). Coating composition. Furthermore, the photocation curable coating composition of any one of Claims 1-3 containing a sensitizer (d). The photocationic curable coating composition according to any one of claims 1 to 4, wherein the epoxy equivalent of the silsesquioxane compound (a) is 10 to 500 g / equivalent. When the cured coating film having a film thickness of 5 μm is formed on the acrylic resin plate having a thickness of 3 mm, the Martens hardness measured by a super micro hardness tester at a temperature of 23 ° C. and a load of 20 mN is 0.5. ~350N / mm ² to become light cationically curable coating composition according to any one of claims 1 to 5, a coating film can be formed. A photocationic curable coating composition according to any one of claims 1 to 6 is applied on an object to be coated so that the dry film thickness is 1 to 10 µm, and setting and / or preheating is performed. Then, the method of forming a coating film is characterized by irradiating with light. An article on which a coating film is formed by the coating film forming method according to claim 7.