JP2012066235A - Method of forming multilayer coating film and coated article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of forming a multilayer coating film which provides an environmental responsiveness of a CO-reduction, etc. accompanying shorter hours taking for coating-film curing, a miniaturization of a painting equipment or the like, and shorter hours of baking, and which is excellent in scratch resistance, weather resistance, acid resistance, and finishing property, and a coated article.SOLUTION: The method includes steps of forming a colored coating film by coating an object to be coated with a colored coating (B), of forming a clear coating film by coating a clear paint (A) on the colored coating film, and of irradiating it with an active energy ray. The clear paint (A) includes a compound (a1) which has a weight-average molecular weight of 250 to less than 1,500, water tolerances of five or more, and an average of two or more acryloyl groups in the molecule, a compound (a2) which has a weight-average molecular weight of 1,500 or more and an average of two or more acryloyl groups in the molecule, and a photopolymerization initiator (a3), and a difference of the water tolerances of the compound (a1) and the compound (a2) is 1.0-10.0.

Description

The present invention is excellent in scratch resistance, weather resistance, acid resistance and finish, with environmental measures such as shortening the time required for curing the coating film, reducing coating equipment, etc., and reducing CO ₂ due to shortened baking time. The present invention relates to a method for forming a multilayer coating film and a coated article.

  A clear coating film is formed on an automobile body such as a motorcycle, an automobile, or a container after an electrodeposition coating film, an intermediate coating film, a base coating film, and the like are formed as necessary. Clear coatings generally contain a thermosetting coating composition containing a thermosetting functional group-containing resin such as a hydroxyl group-containing acrylic resin and a crosslinking agent such as a melamine resin, an acid group-containing resin, and an epoxy group-containing resin. It is formed by a coating film forming method in which a thermosetting coating composition or the like is applied and then heated and cured. According to this coating film forming method, a coating film excellent in coating film performance such as adhesion and coating film hardness can be formed.

  In recent years, energy saving and productivity improvement are required in the painting process. Accordingly, coating compositions that can be cured at a low temperature and coating compositions that can be cured in a short time are expected. However, the thermosetting coating composition usually requires a heating temperature of 140 ° C. and a heating time of 20 minutes to 40 minutes in a general coating process, and satisfies the requirements for energy saving and productivity improvement. It is not a thing.

  Patent Document 1 discloses that a surface coater is applied to an article pre-coated with an undercoat layer and / or a further coating layer, and then a top coat comprising a color-imparting and / or special-effect-giving base lacquer layer and a transparent clear lacquer layer, Or a method of multi-layer lacquering with a topcoat consisting of a pigmented single-layer top lacquer, comprising a paint comprising a binder curable by free radical and / or cationic polymerization, surfacer, base lacquer and clear lacquer and monolayer top Disclosed is a method characterized in that it is used as a lacquer and the binder is cured by high energy radiation.

Further, in Patent Document 2, although the clear paint soaks into the colored layer or in some cases near the surface of the base material, light having a wavelength necessary for curing the paint does not sufficiently pass through the colored layer or near the base material surface. A method for producing a coating material for curing a clear paint by irradiating light to a clear paint layer containing a photopolymerization initiator having a maximum absorption wavelength of 350 nm or more formed on a colored layer with respect to improvement of a coating film defect. It is disclosed.
However, these methods have failed in any of curability at low temperature in a short time, scratch resistance, weather resistance, acid resistance, and finish, and could not be satisfied in all coating film performances.

JP-T-2001-523571 Japanese Patent Laid-Open No. 2006-7202

  This invention is made | formed in view of the said situation, and makes it a subject to provide the coated article which is excellent in sclerosis | hardenability in low temperature and a short time, scratch resistance, a weather resistance, acid resistance, and finish.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have applied a colored paint on the object to be coated to form a colored paint film, and then applied a specific clear paint to apply a clear coating. It has been found that the above problems can be solved by a method of forming a film, and the present invention has been completed.

That is, the present invention
1. Applying a colored paint (B) to the object to be coated to form a colored paint film, applying a clear paint (A) on the colored paint film to form a clear paint film, and active energy rays A method comprising a step of irradiating, wherein the clear paint (A) has a weight average molecular weight of 250 to less than 1500, a water tolerance of 5 or more and a compound having an average of two or more acryloyl groups in the molecule (a1), a weight average molecular weight The difference in water tolerance between the compound (a1) and the compound (a2) is 1,500 or more and contains an average of two or more acryloyl groups in the molecule (a2) and a photopolymerization initiator (a3). A method for forming a multilayer coating film, characterized by being from 0 to 10.0;
2. The method for forming a multilayer coating film according to item 1, wherein the compound (a1) is a compound having a urethane bond,
3. The method for forming a multilayer coating film according to Item 1 or 2, wherein the compound (a2) is urethane acrylate having a weight average molecular weight of 1,500 to 30,000, or acrylic acrylate,
4). The method for forming a multilayer coating film according to any one of items 1 to 3, wherein the water tolerance of the compound (a2) is 0.5 to 4.5,
5. The method for forming a multilayer coating film according to any one of items 1 to 4, wherein the photopolymerization initiator (a3) is liquid at 20 ° C,
6). The method for forming a multilayer coating film according to any one of 1 to 5, wherein the light source of the active energy ray is a pulse xenon lamp,
7). The multilayer coating film forming method according to any one of 1 to 6, wherein the clear paint (A) comprises a hydroxyl group-containing resin (a4),
8). The multilayer coating film forming method according to any one of 1 to 7, wherein the clear paint (A) comprises a polyisocyanate compound (a5),
9. The clear paint (A) is obtained by reacting a caprolactone-modified hydroxyalkyl (meth) acrylate with a polyisocyanate compound, and a radical polymerizable unsaturated group-containing compound (a6) having an isocyanate equivalent weight in the range of 300 to 3,800. The method for forming a multilayer coating film according to any one of items 1 to 8,
10. The multilayer coating film forming method according to any one of 1 to 9, wherein the clear paint (A) contains colloidal silica (a7),
11. The multilayer coating film forming method according to any one of 1 to 10, wherein the clear paint (A) contains a silsesquioxane compound (a8),
12 Colored paint (B) contains a photoinitiator (a3), The coating-film formation method of any one of 1-11 characterized by the above-mentioned,
13. The coated article by the coating-film formation method of any one of 13.1-10.

According to the present invention, a coated article having excellent scratch resistance, weather resistance, acid resistance and finish can be provided. Furthermore, it is possible to cope with the environment such as lowering the heating temperature for curing the coating film, reducing coating equipment, etc., and reducing CO ₂ due to shortened baking time.
In the method for forming a multilayer coating film of the present invention, the compound (a1) penetrates from the coating layer of the clear paint into the lower colored coating film, and the multilayer coating film can be simultaneously cured by irradiation with active energy rays.
In particular, since the difference in water tolerance between the compound (a1) and the compound (a2) is 1.0 to 10.0, the penetration of the compound (a1) in the clear paint (A) into the lower layer coating film and the lower layer Migration of the compound (a2) to the coating film can be suppressed.
Curing is promoted in the lower layer coating by inhibiting the penetration of the compound (a1) in the clear coating (A) into the lower layer coating and the migration of the compound (a2) to the lower layer coating, and the upper layer coating. Then, because the components that contribute to weather resistance and acid resistance are retained,
A multilayer coating film excellent in scratch resistance, weather resistance, acid resistance and finish is obtained.
Furthermore, the coating film which is excellent in abrasion resistance and acid resistance can be obtained by mix | blending colloidal silica (a7) and / or a silsesquioxane compound (a8) in a clear paint (A).

The present invention relates to a multilayer coating film forming method and a coated article in which a colored coating is formed on an object to be coated to form a colored coating, and then a specific clear coating (A) is applied to form a clear coating. About. Details will be described below.

Clear paint (A):
The clear paint (A) is a compound (a1) having a weight average molecular weight of 250 to 1,500 and a water tolerance of 5 or more and an average of 2 or more acryloyl groups in the molecule (hereinafter abbreviated as “compound (a1)”). A compound (a2) having a weight average molecular weight of 1,500 or more and having an average of two or more acryloyl groups in the molecule (hereinafter sometimes abbreviated as “compound (a2)”), and a photopolymerization initiator The difference in water tolerance between the compound (a1) and the compound (a2) is 1.0 to 10.0.

Compound (a1) having a water tolerance of 5 or more and an average of 2 or more acryloyl groups in the molecule:
The compound (a1) having a water tolerance of 5 or more and an average of 2 or more acryloyl groups in the molecule is not particularly limited. For example, (1) an acrylic monomer obtained by reacting a polyol and acrylic acid, (2 ) Urethane acrylate obtained by adding a compound having a hydroxyl group and an acryloyl group to a polyisocyanate compound having a terminal isocyanate group in the molecule, and (3) a compound having at least two epoxy groups or glycidyl groups in the molecule and acrylic acid. And epoxy acrylate obtained by reacting with.

  In the acrylic monomer of the above (1), the polyol is not particularly limited. For example, ethylene glycol, diethylene glycol, triethylene glycol, dipropylene glycol, glycerin, trimethylolpropane, dimethylolpropane, pentaerythritol, dipentaerythritol and Tripentaerythritol and the like, and alkylene oxide (2 to 3 carbon atoms) addition polyol (3 to 12 mol adduct of glycerin ethylene oxide, 3 to 12 mol adduct of propylene oxide of glycerin, 3 to 12 mol adduct of ethylene oxide of trimethylolpropane , Propylene oxide 3-12 mol adduct of trimethylolpropane, ethylene oxide 4-16 mol adduct of ditrimethylolpropane, dimethylolpropane propylene. 4-16 mol adduct of pyrene oxide, 4-16 mol adduct of ethylene oxide of pentaerythritol, 4-16 mol adduct of propylene oxide of pentaerythritol, 6-24 mol adduct of ethylene oxide of dipentaerythritol, propylene oxide of dipentaerythritol 4-24 mole adduct, ethylene oxide 8-32 mole adduct of tripentaerythritol, propylene oxide 8-32 mole adduct of tripentaerythritol, ethylene oxide 3-12 mole adduct of isocyanuric acid and propylene oxide of isocyanuric acid 3-12 mol adduct) and the like are used.

  Specific examples of the acrylic monomer (1) include, for example, ethylene glycol diacrylate, diethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, propylene glycol diacrylate, dipropylene glycol diacrylate, and polypropylene. Glycol diacrylate, butylene glycol diacrylate, neopentyl glycol diacrylate, 1,6-hexanediol diacrylate, glycerin diacrylate, pentaerythritol diacrylate, hydroxypivalic acid-modified neopentyl glycol diacrylate, etc. Monomers]; trimethylolpropane triacrylate, pentaerythritol triac Rate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, tri methacryloyloxy ethoxy trimethylolpropane [more, 3 or more functional acrylic monomer], and.

In the urethane acrylate of the above (2), as the compound having a terminal isocyanate group in the molecule, for example, a polyisocyanate or a polyol exemplified in the compound of the above (1) is reacted with a polyisocyanate. Can be mentioned.
The polyisocyanate in the above (2) is, for example, a compound having two or more isocyanate groups in one molecule. For example, aliphatic polyisocyanate compounds such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, dimer acid diisocyanate, lysine diisocyanate, and burette type adducts or isocyanurate cycloadducts of these polyisocyanates; isophorone diisocyanate, 4,4 ′ -Methylenebis (cyclohexyl isocyanate), methylcyclohexane-2,4-diisocyanate, methylcyclohexane-2,6-diisocyanate, 1,3-di (isocyanatomethyl) cyclohexane, 1,4-di (isocyanatomethyl) cyclohexane, 1 , 4-cyclohexane diisocyanate, 1,3-cyclopentane diisocyanate, 1,2-cyclohexane diisocyanate, etc. Nate compounds and burette-type adducts and isocyanurate cycloadducts of these polyisocyanates; xylylene diisocyanate, metaxylylene diisocyanate, tetramethyl xylylene diisocyanate, tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, 1, 5-naphthalene diisocyanate, 1,4-naphthalene diisocyanate, 4,4′-toluidine diisocyanate, 4,4′-diphenyl ether diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4′-biphenylene diisocyanate, 3,3 ′ -Dimethyl-4,4'-biphenylene diisocyanate, bis (4-isocyanatophenyl) sulfone, isopropylidenebis (4-phenylisocyanate) Aromatic biisocyanate compounds, such as poly (isocyanates) and the like, and burette-type or isocyanurate cycloadducts of these polyisocyanates; triphenylmethane-4,4 ′, 4 ″ -triisocyanate, 1,3,5-tri Polyisocyanate having three or more isocyanate groups in one molecule such as isocyanatobenzene, 2,4,6-triisocyanatotoluene, 4,4′-dimethyldiphenylmethane-2,2 ′, 5,5′-tetraisocyanate Isocyanate compounds and burette type adducts or isocyanurate cycloadducts of these polyisocyanates; ethylene glycol, propylene glycol, 1,4-butylene glycol, dimethylolpropionic acid, polyalkylene glycol, trimethylolpropane, hexanetriol, etc. Polyols And a hydroxyl group in the urethane adduct isocyanate groups obtained by reacting a polyisocyanate compound in a ratio to be excess and biuret type adducts of these polyisocyanate or isocyanurate ring adducts.

Examples of the compound (2) having a hydroxyl group and an acryloyl group include pentaerythritol triacrylate, dipentaerythritol pentaacrylate, 2-hydroxyethyl acrylate, glycerol diacrylate, and ethylene oxide, propylene oxide, and ε- Examples include alkylene oxide-modified or lactone-modified compounds obtained by adding caprolactone, γ-butyrolactone, and the like, and compounds obtained by adding polyisocyanates to these compounds can also be used.
Examples of the compound having at least two epoxy groups or glycidyl groups in the molecule (3) include ethylene glycol diglycidyl ether diacrylate, diethylene glycol diglycidyl ether diacrylate, phthalic acid diglycidyl ester diacrylate, and glycerin poly A glycidyl ether polyacrylate is mentioned.

  The compound (a1) having an average of two or more acryloyl groups in the molecule can be used alone or in combination of two or more. As the compound (a1), for example, a urethane acrylate obtained by adding a compound having a hydroxyl group and an acryloyl group to a polyisocyanate compound having a terminal isocyanate group in the molecule can be used, and a coating film excellent in scratch resistance and acid resistance can be used. Obtainable. The compound (a1) is not limited to the above urethane acrylate.

In addition, the compound (a1) has a weight average molecular weight of 250 to less than 1,500, preferably 300 to 1,300. Further, the water tolerance is 5 or more, preferably 5.0 to 10.0, and the average functional group number is 2.0 to 10.0, preferably 2.1 to 9.0.
Being within the above range is significant in terms of the penetration of the compound (a1) into the lower layer coating film and the water resistance of the resulting multilayer coating film when the coating film is formed. Further, the compound (a1) is substantially a compound having no isocyanate group.

  In this specification, the weight average molecular weight uses tetrahydrofuran as a solvent, “HLC-8120GPC” (trade name, manufactured by Tosoh Corporation) as a gel permeation chromatograph, and one “TSKgel G4000HXL” as a column. , Using a total of four “TSKgel G3000HXL” and one “TSKgel G2000HXL” (trade names, all manufactured by Tosoh Corporation), using a differential refractometer as a detector, and a mobile phase: Tetrahydrofuran, measurement temperature: 40 ° C., flow rate: 1 mL / min.

  In this specification, the water tolerance is obtained by the following measurement. A solid content of 0.5 g of each compound was dissolved in 10 mL of acetone, and deionized water was added dropwise with stirring at 23 ° C., and the turbidity according to JIS-K0101 (industrial water test method) was 100 ° C. as a formazine turbidity standard. The amount of deionized water dropped (mL).

  In this specification, the average number of functional groups is determined by adding dodecyl mercaptan to a radical polymerizable unsaturated group and back titrating the remaining dodecyl mercaptan with an iodine solution, and calculating the average functionality according to the following formula (1). The cardinality was calculated.

Average number of functional groups = unsaturated group concentration (mol / kg) × weight average molecular weight (g / mol) ÷ 1000 Formula (1)
Compound (a2) having a weight average molecular weight of 1,500 or more and having an average of two or more acryloyl groups in the molecule:
The compound (a2) having a weight average molecular weight of 1,500 or more and having an average of two or more acryloyl groups in the molecule is a weight average molecular weight of 1,500 or more, preferably 1,700 to 30,000, more preferably 1,700. ~ 25,000. In addition to the above conditions, a water tolerance of 0.5 to 9.0, preferably 0.5 to 4.5 is also preferable from the viewpoint of leaving the compound (a2) in the clear coating film. Further, the compound (a2) is substantially a compound having no isocyanate group.

  Specific examples of the compound (a2) having a weight average molecular weight of 1,500 or more and having an average of two or more acryloyl groups in the molecule include polyester acrylate, urethane acrylate, and acrylic acrylate. It is preferable to use urethane acrylate and / or acrylic acrylate from the viewpoint of scratch resistance and weather resistance.

The urethane acrylate is obtained by, for example, (1) adding a compound having a hydroxyl group and an acryloyl group to a polyisocyanate compound having a terminal isocyanate group in the molecule.
(2) What is manufactured by the method of making an isocyanate group containing (meth) acrylate monomer react with the polyurethane polyol obtained by making a polyisocyanate compound and a polyol react is mentioned.

Examples of the polyisocyanate compound used for the production of urethane acrylate include aliphatic diisocyanates such as hexamethylene diisocyanate, trimethylene diisocyanate, 1,4-tetramethylene diisocyanate, pentamethylene diisocyanate, lysine diisocyanate, isophorone diisocyanate, 4,4. Examples thereof include alicyclic diisocyanates such as' -methylenebis (cyclohexyl isocyanate), burette type adducts and isocyanurate ring type adducts of these diisocyanates.
Examples of the compound having a hydroxyl group and an acryloyl group used in the production of urethane acrylate include pentaerythritol triacrylate, dipentaerythritol pentaacrylate, 2-hydroxyethyl acrylate, glycerol diacrylate, and ethylene oxide and propylene oxide. , [Epsilon] -caprolactone, [gamma] -butyrolactone, and the like, can be mentioned alkylene oxide-modified or lactone-modified compounds, and compounds obtained by adding polyisocyanates to these compounds can also be used.

  Examples of the polyol used for the production of urethane acrylate include ethylene glycol, propylene glycol, butylene glycol, neopentyl glycol, 1,6-hexanediol, trimethylolpropane, glycerin, pentaerythritol, polycaprolactone diol, polyester polyol, Examples include ether polyols.

  Examples of the isocyanate group-containing (meth) acrylate monomer include unsaturated compounds obtained by adding a polyisocyanate compound such as hexamethylene diisocyanate to an active hydrogen-containing polymerizable monomer such as isocyanate ethyl acrylate, isocyanate propyl acrylate, or hydroxyethyl acrylate. Etc.

  The above acrylic acrylate is an acrylic resin containing an acryloyl group. Specifically, a compound obtained by adding acrylic acid to an acrylic resin copolymerized with glycidyl methacrylate, 2-hydroxyethyl acrylate, 4-hydroxybutyl acrylate, pentaerythritol triacrylate on an acrylic resin copolymerized with 2-acryloyloxyethyl isocyanate And a compound obtained by adding 2-acryloyloxyethyl isocyanate to an acrylic resin copolymerized with a hydroxyl group-containing monomer. These may be used alone or in combination of two or more.

  Furthermore, in the present invention, the difference in water tolerance between the compound (a1) and the compound (a2) is 1.0 to 10.0, preferably 1.0 to 7.0. The water tolerance of the compound (a2) is lower than the water tolerance of the compound (a1), and the difference is 1.0 or more, thereby suppressing the transfer of the compound (a2) to the lower layer coating film, and the compound (a1) Is meaningful in that it soaks selectively.

Photopolymerization initiator (a3):
The photopolymerization initiator (a3) used for the clear paint (A) can be used without particular limitation as long as it is an initiator that absorbs active energy rays and generates radicals. 1 type (s) or 2 or more types can also be used together.

  Examples of the photopolymerization initiator include α-diketones such as benzyl and diacetyl; acyloins such as benzoin; acyloin ethers such as benzoin methyl ether, benzoin ethyl ether and benzoin isopropyl ether; thioxanthone and 2,4-diethyl Thioxanthones such as thioxanthone, 2-isopropylthioxanthone and thioxanthone-4-sulfonic acid; Benzophenones such as benzophenone, 4,4′-bis (dimethylamino) benzophenone and 4,4′-bis (diethylamino) benzophenone; Michler's ketones; Acetophenone, 2- (4-toluenesulfonyloxy) -2-phenylacetophenone, p-dimethylaminoacetophenone, α, α′-dimethoxyacetoxybenzophenone, 2,2′-dimeth Ci-2-phenylacetophenone, p-methoxyacetophenone, 2-methyl [4- (methylthio) phenyl] -2-morpholino-1-propanone, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) Acetophenones such as -butan-1-one, α-isohydroxyisobutylphenone, α, α′-dichloro-4-phenoxyacetophenone, 1-hydroxycyclohexyl-phenyl-ketone; 2,4,6-trimethylbenzoyldiphenylphosphine Acyl phosphine oxides such as oxide and bis (acyl) phosphine oxide; quinones such as anthraquinone and 1,4-naphthoquinone; phenacyl chloride, trihalomethylphenyl sulfone, tris (trihalomethyl) -s-triazine, etc. Gen compounds; peroxides such as di -t- butyl peroxide and the like. These can be used as one or a mixture of two or more.

  Examples of commercially available photopolymerization initiators (a3) include IRGACURE-184, IRGACURE-261, IRGACURE-819, IRGACURE-500, IRGACURE-651, IRGACURE-907, IRGACURE-CGI-1700, DAROCURE ( Darocur) -1173, Darocur-1116, Darocur-127, Darocur-TPO, Darocur-2959, Darocur-1664, Darocur-4043 (trade name, manufactured by Ciba Specialty Chemicals), Kayacure-MBP, Kayacure- DETX-S, Kayacure-DMBI, Kayacure-EPA, Kayacure-OA (trade name, manufactured by Nippon Kayaku Co., Ltd.), VICURE-10, Vicure 55 (trade name, manufactured by STAUFFER Co., LTD., Product name) ], Trigonal (T RIGONAL) P1 [manufactured by AKZO Co., LTD., Trade name], Sandray 1000 (manufactured by SANDOZ Co., LTD., Trade name), Deep (DEAP) [APGEON ( APJOHN Co., LTD., Product name], CANTACURE-PDO, CANTACURE-ITX, CANTACURE-EPD [manufactured by WARD BLEKINSOP Co., LTD., Product name] be able to.

  It is preferable that the photopolymerization initiator (a3) is in a liquid state at 20 ° C. in that when a multilayer coating film is formed, the photopolymerization initiator (a3) is infiltrated into the coating film of the lower colored coating. The photopolymerization initiator (a3) may be liquid as a mixture of a photopolymerization initiator that is solid at 20 ° C. and a photopolymerization initiator that is liquid at 20 ° C. (for example, Irgacure-500).

Hydroxyl-containing resin (a4):
The clear coating material (A) can contain a hydroxyl group-containing resin (a4) having at least one hydroxyl group in one molecule, if necessary. Examples of the hydroxyl group-containing resin (a4) include resins having a hydroxyl group, such as polyester resins, acrylic resins, polyether resins, polycarbonate resins, polyurethane resins, epoxy resins, and alkyd resins. These can be used alone or in combination of two or more. Especially, it is preferable that a hydroxyl-containing resin (a4) is a hydroxyl-containing acrylic resin from the point of the weather resistance of the obtained multilayer coating film.

  The hydroxyl group-containing acrylic resin is usually prepared by a hydroxyl group-containing polymerizable unsaturated monomer and other polymerizable unsaturated monomers copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer in a manner known per se, for example, in an organic solvent. It can manufacture by making it copolymerize by methods, such as the solution polymerization method of this, and the emulsion polymerization method in water.

  The hydroxyl group-containing polymerizable unsaturated monomer is a compound having at least one hydroxyl group and one polymerizable unsaturated bond in one molecule. Specifically, for example, 2-hydroxyethyl (meth) acrylate, 2 A monoesterified product of (meth) acrylic acid such as hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate and a dihydric alcohol having 2 to 8 carbon atoms; Ε-caprolactone modified product of monoesterified product of (meth) acrylic acid and dihydric alcohol having 2 to 8 carbon atoms; N-hydroxymethyl (meth) acrylamide; allyl alcohol, and polyoxyethylene chain whose molecular terminal is a hydroxyl group (Meth) acrylate etc. which have can be mentioned.

  Examples of the other polymerizable unsaturated monomer copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl ( (Meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, tert-butyl (meth) acrylate, n-hexyl (meth) acrylate, n-octyl (meth) acrylate, 2-ethylhexyl (meth) Acrylate, nonyl (meth) acrylate, tridecyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, “isostearyl acrylate” (trade name, manufactured by Osaka Organic Chemical Industry Co., Ltd.), cyclohexyl (meth) acrylate , Methylcyclohexyl Alkyl or cycloalkyl (meth) acrylates such as (meth) acrylate, t-butylcyclohexyl (meth) acrylate, cyclododecyl (meth) acrylate; polymerizability having an isobornyl group such as isobornyl (meth) acrylate Unsaturated monomer; polymerizable unsaturated monomer having adamantyl group such as adamantyl (meth) acrylate; vinyl aromatic compound such as styrene, α-methylstyrene, vinyltoluene; vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (2 Polymerizable unsaturated monomers having an alkoxysilyl group such as -methoxyethoxy) silane, γ- (meth) acryloyloxypropyltrimethoxysilane, γ- (meth) acryloyloxypropyltriethoxysilane; Perfluoroalkyl (meth) acrylates such as chill (meth) acrylate and perfluorooctylethyl (meth) acrylate; polymerizable unsaturated monomers having a fluorinated alkyl group such as fluoroolefin; and photopolymerizable functional groups such as maleimide groups Polymerizable unsaturated monomers having: vinyl compounds such as N-vinylpyrrolidone, ethylene, butadiene, chloroprene, vinyl propionate and vinyl acetate; carboxyl groups such as (meth) acrylic acid, maleic acid, crotonic acid and β-carboxyethyl acrylate Containing polymerizable unsaturated monomer: (meth) acrylonitrile, (meth) acrylamide, N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide, glycidyl (meth) acrylate and amine Nitrogen-containing polymerizable unsaturated monomers such as adducts with 2 or more polymerizable unsaturated groups such as allyl (meth) acrylate and 1,6-hexanediol di (meth) acrylate in one molecule Polymerizable unsaturated monomer having: glycidyl (meth) acrylate, β-methylglycidyl (meth) acrylate, 3,4-epoxycyclohexylmethyl (meth) acrylate, 3,4-epoxycyclohexylethyl (meth) acrylate, 3,4- Epoxy group-containing polymerizable unsaturated monomers such as epoxycyclohexylpropyl (meth) acrylate and allyl glycidyl ether; (meth) acrylate having a polyoxyethylene chain whose molecular terminal is an alkoxy group; 2-acrylamido-2-methylpropanesulfonic acid Allyl sulfonic acid, styrene sulfonic acid sodium Polymerizable unsaturated monomers having a sulfonic acid group such as an um salt, sulfoethyl methacrylate and its sodium salt and ammonium salt; 2-acryloyloxyethyl acid phosphate, 2-methacryloyloxyethyl acid phosphate, 2-acryloyloxypropyl acid phosphate, Polymerizable unsaturated monomers having a phosphate group such as 2-methacryloyloxypropyl acid phosphate; 2-hydroxy-4- (3-methacryloyloxy-2-hydroxypropoxy) benzophenone, 2-hydroxy-4- (3-acryloyloxy) -2-hydroxypropoxy) benzophenone, 2,2′-dihydroxy-4- (3-methacryloyloxy-2-hydroxypropoxy) benzophenone, 2,2′-dihydroxy-4 Polymerizable unsaturated monomers having an ultraviolet-absorbing functional group such as (3-acryloyloxy-2-hydroxypropoxy) benzophenone, 2- (2′-hydroxy-5′-methacryloyloxyethylphenyl) -2H-benzotriazole; 4 -(Meth) acryloyloxy-1,2,2,6,6-pentamethylpiperidine, 4- (meth) acryloyloxy-2,2,6,6-tetramethylpiperidine, 4-cyano-4- (meth) Acryloylamino-2,2,6,6-tetramethylpiperidine, 1- (meth) acryloyl-4- (meth) acryloylamino-2,2,6,6-tetramethylpiperidine, 1- (meth) acryloyl-4 -Cyano-4- (meth) acryloylamino-2,2,6,6-tetramethylpiperidine, 4-crotono Luoxy-2,2,6,6-tetramethylpiperidine, 4-crotonoylamino-2,2,6,6-tetramethylpiperidine, 1-crotonoyl-4-crotonoyloxy-2,2,6,6- UV-stable polymerizable unsaturated monomers such as tetramethylpiperidine; acrolein, diacetone acrylamide, diacetone methacrylamide, acetoacetoxyethyl methacrylate, formylstyrol, vinyl alkyl ketones having 4 to 7 carbon atoms (eg, vinylmethyl Examples thereof include polymerizable unsaturated monomer compounds having a carbonyl group such as ketone, vinyl ethyl ketone, and vinyl butyl ketone, and these can be used alone or in combination of two or more.

  The hydroxyl group-containing resin (a4) is 30 to 300 mgKOH / g, particularly 40 to 250 mgKOH / g, more particularly 50 to 200 mgKOH / g, from the viewpoint of thermosetting at low temperature and the water resistance of the resulting coating film. It preferably has a hydroxyl value.

  The hydroxyl group-containing resin (a4) has an acid group such as a carboxyl group from the viewpoint of increasing the reactivity with the polyisocyanate compound (a5) and the radical polymerizable unsaturated group-containing compound (a6) described later. preferable. The acid value of the hydroxyl group-containing resin (a4) is preferably in the range of 1 to 25 mgKOH / g, particularly 1 to 20 mgKOH / g. The hydroxyl group-containing resin (a4) generally has a weight average molecular weight within the range of 3,000 to 100,000, particularly 4,000 to 50,000, more particularly 5,000 to 30,000.

Polyisocyanate compound (a5)
The clear paint (A) can contain a polyisocyanate compound (a5). The polyisocyanate compound (a5) is a compound having an isocyanate group in the molecule, and examples thereof include the polyisocyanate compounds exemplified in the description of the compound (a1) and the compound (a2). Of these, isocyanurate cycloadducts of aliphatic polyisocyanates are preferred from the viewpoint of the weather resistance of the coating film, and isocyanurate cycloadducts of hexamethylene diisocyanate are particularly preferred.

Radical polymerizable unsaturated group-containing compound (a6)
The radical polymerizable unsaturated group-containing compound (a6) is obtained by reacting a caprolactone-modified hydroxyalkyl (meth) acrylate (a61) with a polyisocyanate compound (a62), and has an isocyanate equivalent weight in the range of 300 to 3,800. A compound.

  This compound (a6) is excellent in curability by irradiation with active energy rays and excellent in curability at a low temperature (specifically, normal temperature to 100 ° C.). This makes it possible to lower the heating temperature and shorten the heating time in the painting process. Moreover, the coating film obtained from the coating composition containing this compound (a6) is excellent in scratch resistance and weather resistance. Further, the water tolerance is preferably 0.5 to 4.0 from the viewpoint of leaving the compound (a6) in the clear coating film.

Caprolactone-modified hydroxyalkyl (meth) acrylate (a61)
Caprolactone-modified hydroxyalkyl (meth) acrylate (a61) represents a compound represented by the following general formula.

(In the formula, R ¹ represents a hydrogen atom or a methyl group, R ² represents an alkylene group having 2 to 6 carbon atoms, m represents an integer of 3 to 8, and n represents an integer of 1 to 5)
Examples of the caprolactone-modified hydroxyalkyl (meth) acrylate (a61) include compounds represented by the following general formula (I).

(In formula (I), R ¹ represents a hydrogen atom or a methyl group, R ² represents an alkylene group having 2 to 6 carbon atoms, and n is 1 to 5).

Specifically, the caprolactone-modified hydroxyalkyl (meth) acrylate includes “Placcel FA-1”, “Placcel FA-2”, “Placcel FA-2D”, “Placcel FA-3”, “Placcel FA-4”, “Placcel FA-5”, “Plaxel FM-1”, “Plaxel FM-2”, “Plaxel FM-2D”, “Plaxel FM-3”, “Plaxel FM-4”, “Plaxel FM-5” (any Can also be mentioned by Daicel Chemical Industries, trade name). Among these, caprolactone-modified hydroxyethyl acrylate in which R ¹ is a hydrogen atom and R ² is an ethylene group is preferable from the viewpoint of curability.

Polyisocyanate compound (a62)
On the other hand, the polyisocyanate compound (a62) is a compound having two or more isocyanate groups in one molecule, and examples thereof include the polyisocyanate compounds exemplified in the description of the compound (a1) and the compound (a2).
Among these, from the viewpoint of the weather resistance of the coating film, an isocyanurate cycloadduct of an aliphatic polyisocyanate compound is preferable, and an isocyanurate cycloadduct of hexamethylene diisocyanate is particularly preferable.

  The reaction of the caprolactone-modified hydroxyalkyl (meth) acrylate (a61) and the polyisocyanate compound (a62) can be performed by a known method for reacting the hydroxy group-containing compound with the polyisocyanate compound.

  The blending ratio of the caprolactone-modified hydroxyalkyl (meth) acrylate (a61) and the polyisocyanate compound (a62) is not particularly limited as long as the isocyanate equivalent of the resulting radical polymerizable unsaturated group-containing compound (a6) is within the above range. .

  The above reaction can usually be carried out in an organic solution. Examples of organic solvents include aromatic hydrocarbon solvents such as toluene and xylene, ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, and ester solvents such as ethyl acetate, propyl acetate, isobutyl acetate, and butyl acetate. Can be mentioned. These can be used as one or a mixture of two or more. The reaction temperature is preferably from room temperature to 100 ° C., and the reaction time is preferably from 1 to 10 hours.

  In the above reaction, a catalyst such as dibutyltin dilaurate, dibutyltin diethylhexoate or dibutyltin sulfite may be used as necessary. The addition amount of the catalyst is preferably 0.01 to 1 part by mass and more preferably 0.1 to 0.5 part by mass with respect to 100 parts by mass of the total amount of reaction raw materials. A polymerization inhibitor such as hydroquinone monomethyl ether may be used. It is preferable that the addition amount of a polymerization inhibitor is 0.01-1 mass part with respect to 100 mass parts of total amounts of a reaction raw material.

  Since the radically polymerizable unsaturated group-containing compound (a6) has an isocyanate group, the mixing ratio of both in the reaction of caprolactone-modified hydroxyalkyl (meth) acrylate with the polyisocyanate compound is usually that of the isocyanate group of the polyisocyanate compound. The mixing ratio is an excess (isocyanate group / hydroxykyl group> 1.0) in an equivalent ratio with respect to the hydroxyl group of caprolactone-modified hydroxyalkyl (meth) acrylate. And the isocyanate equivalent of a radically polymerizable unsaturated group containing compound (a6) can be adjusted by adjusting a mixing ratio.

  The radical polymerizable unsaturated group-containing compound (a6) has an isocyanate equivalent weight in the range of 300 to 3,800. When the radically polymerizable unsaturated group-containing compound (a6) has an isocyanate group within the above range, the coating composition of the present invention is excellent in curability at low temperatures. The isocyanate equivalent of the radically polymerizable unsaturated group-containing compound (a6) is preferably in the range of 500 to 2,500 from the viewpoint of scratch resistance of the coating film.

  Here, in this specification, the isocyanate equivalent is an isocyanate equivalent determined by back titration using dibutylamine. The reverse titration is carried out by adding excess dibutylamine to the sample for reaction, and titrating the remaining dibutylamine with an aqueous hydrochloric acid solution using bromophenol blue as a titration indicator.

  Further, the radical polymerizable unsaturated group-containing compound (a6) preferably has an unsaturated group equivalent of 300 to 2,000. More preferably, it is 500-1,000. When the unsaturated group equivalent is within these ranges, it is possible to obtain a coating film having more excellent scratch resistance and weather resistance.

  Here, in this specification, the unsaturated group equivalent is determined by adding dodecyl mercaptan to a radically polymerizable unsaturated group and back titrating the remaining dodecyl mercaptan with an iodine solution.

Colloidal silica (a7)
Colloidal silica (a7) blended as necessary contains. Colloidal silica (a7) can impart scratch resistance to the resulting coating film, and also contributes to improvement of scratch resistance and impact resistance. The average particle diameter of the colloidal silica (a7) is 20 to 350 nm, more preferably 40 to 300 nm.

As the colloidal silica (a7), those dispersed and stabilized in a solvent can be suitably used. Commercial products of such colloidal silica (a7) include SNOWTEX MPA-ST, SNOWTEX IPA-ST, SNOWTEX IPA-ST-UP, SNOWTEX IPA-ST-ZL, SNOWTEX EG-ST, SNOWTEX NPC-ST-30, Snowtex DMAC-ST, Snowtex MEK-ST, Snowtex MEK-ST-UP, Snowtex MEK-ST-L, Snowtex MIBK-ST, Snowtex XBA-ST, Snowtex PMA- ST, Snowtex PGM-ST (above, manufactured by Nissan Chemical Industries, Ltd.), NANOBYK-3650, NANOBYK-3651, NANOBYK-3652 (above, manufactured by Big Chemie Japan), and the like can be mentioned.
In addition, it is preferable to modify the colloidal silica surface in order to impart stability in the clear paint (A) and crosslinkability by irradiation with active energy rays. As such a modification method, the above colloidal silica may be added to 3-methacryloyloxypropyltrimethoxysilane, 3-acryloyloxypropyltrimethoxysilane, 2-acryloyloxyethyl isocyanate, 2-methacryloyloxyethyl isocyanate, 1,1-bis ( Examples include a method of reacting acryloyloxymethyl) ethyl isocyanate. The said colloidal silica may be used independently and may use 2 or more types together.
Silsesquioxane compound (a8)
If the silsesquioxane compound (a8) mix | blended as needed is a silsesquioxane compound which has an organic group directly couple | bonded with the silicon atom, it can be conveniently used without a restriction | limiting especially. By having an organic group, the stability in the clear paint becomes good.

  Here, in the present specification, the “silsesquioxane compound” does not mean only a silsesquioxane compound having a structure in which all Si—OH groups (hydroxysilyl groups) are hydrolyzed and condensed, but Si—OH A ladder structure in which groups remain, an incomplete cage structure, and a silsesquioxane compound of a random condensate can also be included.

In the silsesquioxane compound (a8), the ratio of the silsesquioxane compound having a structure in which all Si—OH groups are hydrolyzed and condensed is preferably 80% by mass or more, more preferably 90% by mass or more, and particularly preferably. Is preferably 100% by mass from the viewpoint of liquid stability and weather resistance.
Furthermore, a silsesquioxane compound in which at least one of the organic groups directly bonded to the silicon atom is an organic group having a urethane bond and one (meth) acryloyloxy group can be more preferably used.

  As the silsesquioxane compound (a8), for example, a cissesquioxane compound in which the organic group having the urethane bond and one (meth) acryloyloxy group is an organic group represented by the following general formula (A) Can be mentioned.

  Here, as a silsesquioxane compound (a8), even if it has one type among the organic groups represented by the said general formula (A), it may have multiple types of organic groups. .

  In other words, as the silsesquioxane compound (a8), for example, the organic group having the urethane bond and one (meth) acryloyloxy group is represented by the following general formulas (I) to (III). The silsesquioxane compound which is at least 1 type selected from the group which consists of can be mentioned.

The R ² is not particularly limited as long as it is a divalent hydrocarbon group having 1 to 10 carbon atoms. Specifically, for example, methylene group, ethylene group, 1,2-propylene group, 1,3-propylene group, 1,2-butylene group, 1,4-butylene group, hexylene group and other alkylene groups; cyclohexylene group And aralkylene groups such as a phenylene group, a xylylene group, and a biphenylene group. Among them, a divalent hydrocarbon group having 1 to 6 carbon atoms, particularly an ethylene group, a 1,2-propylene group, and a 1,4-butylene group, have high heat resistance, scratch resistance, and high polarity polymerization. It is preferable from the viewpoint of better compatibility with unsaturated compounds.

The R ³ is not particularly limited as long as it is a divalent hydrocarbon group having 1 to 10 carbon atoms. Specifically, for example, methylene group, ethylene group, 1,2-propylene group, 1,3-propylene group, 1,2-butylene group, 1,4-butylene group, hexylene group and other alkylene groups; cyclohexylene group And aralkylene groups such as a phenylene group, a xylylene group, and a biphenylene group. Among them, a divalent hydrocarbon group having 1 to 6 carbon atoms, particularly an ethylene group or a 1,3-propylene group, is compatible with heat-resistant, scratch-resistant and highly polar polymerizable unsaturated compounds. Is preferable from the viewpoint of more excellent.

  The n is not particularly limited as long as it is an integer of 0 to 9. n is preferably an integer of 0 to 5, more preferably an integer of 0 to 3, particularly preferably 0 or 1.

The R ⁴ is not particularly limited as long as it is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 6 carbon atoms. Specifically, for example, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, sec-butyl group, n-pentyl group, isopentyl group, neopentyl group, cyclopentyl An acyclic aliphatic monovalent hydrocarbon group or a cyclic aliphatic monovalent hydrocarbon group such as a linear or branched alkyl group such as a group, n-hexyl group, isohexyl group, cyclohexyl group; trifluoromethyl group, 3, And fluorine-containing alkyl groups such as 3,3-trifluoro-n-propyl group. In particular, a methyl group is preferable from the viewpoint of better compatibility with a highly polar polymerizable unsaturated compound.

The R ⁵ is not particularly limited as long as it is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 6 carbon atoms. Specifically, for example, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, sec-butyl group, n-pentyl group, isopentyl group, neopentyl group, cyclopentyl An acyclic aliphatic monovalent hydrocarbon group or a cyclic aliphatic monovalent hydrocarbon group such as a linear or branched alkyl group such as a group, n-hexyl group, isohexyl group, cyclohexyl group; trifluoromethyl group, 3, And fluorine-containing alkyl groups such as 3,3-trifluoro-n-propyl group. In particular, a methyl group is preferable from the viewpoint of better compatibility with a highly polar polymerizable unsaturated compound.

As the organic group represented by the general formula (I), R ¹ is hydrogen from the viewpoint that heat resistance, scratch resistance, compatibility with a highly polar polymerizable unsaturated compound and active energy ray curability are more excellent. An organic group which is an atom, R ² is an ethylene group or a 1,4-butylene group, R ³ is an ethylene group or a 1,3-propylene group, and n is 0 is preferable.

As the organic group represented by the general formula (II), R ⁴ is methyl from the viewpoint of better heat resistance, scratch resistance, compatibility with a highly polar polymerizable unsaturated compound and active energy ray curability. And an organic group in which R ³ is an ethylene group or a 1,3-propylene group, R ¹ is a hydrogen atom, and R ² is an ethylene group.

Examples of the organic group represented by the general formula (III) include heat resistance, scratch resistance, compatibility with a highly polar polymerizable unsaturated compound, and active energy ray curability, so that R ⁵ is methyl. And an organic group in which R ³ is an ethylene group or a 1,3-propylene group, R ¹ is a hydrogen atom, and R ² is an ethylene group.

The silsesquioxane compound (a8) may be a compound having a single composition or a mixture of compounds having different compositions. The weight average molecular weight of the silsesquioxane compound (a8) is not particularly limited. The weight average molecular weight is preferably 1,000 to 100,000, more preferably 1,000 to 10,000. These ranges are significant in terms of improving the scratch resistance of the coating film obtained by blending the silsesquioxane compound (a8).
If necessary, the clear paint (A) includes a curing catalyst, a thickener, an ultraviolet absorber, a light stabilizer, an antifoaming agent, a rust inhibitor, a plasticizer, an organic solvent, a surface conditioner, an anti-settling agent, etc. Ordinary paint additives can be contained alone or in combination of two or more.
The clear paint (A) may be either an organic solvent-type paint composition or an aqueous paint composition, but is preferably an organic solvent-type paint composition from the viewpoint of storage stability and the like. In the present specification, the water-based coating composition is a coating in which the main component of the solvent is water, and the organic solvent-type coating composition is a coating that does not substantially contain water as a solvent.

  The organic solvent used in the case of the organic solvent type paint is not particularly limited. Specific examples include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methyl amyl ketone, ethyl isoamyl ketone, diisobutyl ketone, and methyl hexyl ketone; ethyl acetate, butyl acetate, methyl benzoate, methyl propionate Ester solvents such as tetrahydrofuran, dioxane, dimethoxyethane and the like; glycol ether solvents such as propylene glycol monomethyl ether acetate and 3-methoxybutyl acetate; aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, etc. Is mentioned.

In the clear paint (A), the content of each component should be as follows:
The present invention is suitable for achieving the object.
Content of the compound (a1) which has an acryloyl group is 4-95 mass parts with respect to 100 mass parts of solid content of a clear coating material (A), Preferably it is 10-90 mass parts. These ranges are significant in terms of reactivity to active energy rays.
Content of a compound (a2) is 4-95 mass parts with respect to 100 mass parts of solid content of a clear coating material (A), Preferably it is 10-90 mass parts. These ranges are significant in terms of scratch resistance, weather resistance and acid resistance.

  Content of a photoinitiator (a3) is 1-8 mass parts with respect to 100 mass parts of solid content of a clear coating material (A), Preferably it is 1.5-6 mass parts. These ranges are significant in terms of reactivity to active energy rays.

  In addition, content of the hydroxyl-containing resin (a4) mix | blended as needed is less than 40 mass parts with respect to 100 mass parts of solid content of a clear coating material (A), Preferably it is 10-30 mass parts. These ranges are significant in terms of low-temperature curability.

In addition, content of the polyisocyanate compound (a5) mix | blended as needed is less than 30 mass parts with respect to 100 mass parts of solid content of a clear coating material (A), Preferably it is 10-25 mass parts. is there. These ranges are significant in terms of low-temperature curability.
In addition, the radically polymerizable unsaturated group containing compound (a6) mix | blended as needed
The content of is less than 70 parts by mass, preferably 10 to 55 parts by mass with respect to 100 parts by mass of the solid content of the clear paint (A). These ranges are preferable from the viewpoint of scratch resistance and weather resistance.

  In addition, content of the colloidal silica (a7) mix | blended as needed is 30 mass parts or less with respect to 100 mass parts of solid content of a clear coating material (A), Preferably it is 1-25 mass parts. . These ranges are significant in terms of improving scratch resistance and impact resistance.

  In addition, content of the silsesquioxane compound (a8) mix | blended as needed is 30 mass parts or less with respect to 100 mass parts of solid content of a clear coating material (A), Preferably it is 1-25 masses. Part. These ranges are significant for interlayer adhesion.

  The clear paint (A) further contains usual paint additives such as a curing catalyst, a thickener, an antifoaming agent, a rust preventive, a plasticizer, an organic solvent, a surface conditioner, and an anti-settling agent. Each can be contained alone or in combination of two or more.

  The clear paint (A) may be either an organic solvent-type paint composition or an aqueous paint composition, but is preferably an organic solvent-type paint composition from the viewpoint of storage stability and the like. In the present specification, the water-based coating composition is a coating in which the main component of the solvent is water, and the organic solvent-type coating composition is a coating that does not substantially contain water as a solvent.

The organic solvent used in the case of the organic solvent type paint is not particularly limited. Specifically, for example, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methyl amyl ketone, ethyl isoamyl ketone, diisobutyl ketone, methyl hexyl ketone; ethyl acetate, butyl acetate, methyl benzoate, methyl propionate, etc. Esters such as tetrahydrofuran, dioxane and dimethoxyethane; glycol ethers such as propylene glycol monomethyl ether acetate and 3-methoxybutyl acetate; aromatic hydrocarbons and aliphatic hydrocarbons.
Next, the colored paint (B) will be described.

Colored paint (B):
The colored paint (B) may be either an organic solvent-type paint composition or an aqueous paint composition. In the present specification, the water-based coating composition is a coating in which the main component of the solvent is water, and the organic solvent-type coating composition is a coating that does not substantially contain water as a solvent.
As the coloring paint (B), a coloring pigment and / or a metallic pigment usually used for coloring the base resin and the coating, and a coating containing a crosslinking agent as required can be suitably used.
As the base resin, for example, a resin such as an acrylic resin, a polyester resin, an alkyd resin, an epoxy resin, or a polyurethane resin having a functional group capable of crosslinking reaction can be suitably used. Examples of the functional group capable of crosslinking reaction include a hydroxyl group, a carboxyl group, an epoxy group, and a carbonyl group.

In the case of an aqueous coating material, the base resin has a sufficient amount of hydrophilic groups to make the resin water-soluble or water-dispersed in addition to the functional group capable of undergoing a crosslinking reaction with the crosslinking agent. Examples of the hydrophilic group include a carboxyl group, a hydroxyl group, a methylol group, an amino group, a sulfonic acid group, and a polyoxyethylene bond. Depending on the type of these hydrophilic groups, the base resin can be water-soluble or water-dispersed, for example, by neutralization with a basic substance or acid. Further, when the base resin is produced by polymerization, the base resin can be dispersed in water by emulsion polymerization of the monomer component in the presence of a surfactant or a water-soluble polymer substance. As the base resin, among them, an acrylic resin or a polyester resin having a hydroxyl group and a carboxyl group is preferable.
The acrylic resin having a hydroxyl group and a carboxyl group usually has a hydroxyl value in the range of about 50 to 600 mgKOH / g, an acid value in the range of about 10 to 100 mgKOH / g, and a number average molecular weight in the range of about 1,000 to 100,000. It is preferable that The polyester resin having a hydroxyl group and a carboxyl group usually has a hydroxyl value in the range of about 20 to 800 mgKOH / g, an acid value in the range of about 4 to 200 mgKOH / g, and a weight average molecular weight in the range of about 500 to 500,000. It is preferable that

As the base resin, when the article to be coated is a plastic material such as polypropylene resin, chlorinated polyolefin and / or polyolefin can be used in combination from the viewpoint of the adhesion of the coating film.
The chlorinated polyolefin is a chlorinated polyolefin, and as the chlorinated polyolefin, for example, a radical homopolymer or copolymer of at least one olefin selected from ethylene, propylene, butene, methylbutene, isoprene and the like And radical copolymers of the olefins with vinyl acetate, butadiene, acrylic esters, methacrylic esters and the like.
The chlorinated polyolefin and / or polyolefin can generally have a weight average molecular weight in the range of 30,000 to 200,000, in particular 50,000 to 150,000, and the chlorination rate is 50% by weight or less. , Preferably 10 to 45% by mass, more preferably 10 to 35% by mass.

  As the chlorinated polyolefin, chlorinated polyethylene, chlorinated polypropylene, chlorinated ethylene-propylene copolymer, chlorinated ethylene-vinyl acetate copolymer and the like are particularly suitable. Moreover, what graft-polymerized the polymerizable monomer to the chlorinated polyolefin can also be used.

  Examples of the polymerizable monomer to be graft-polymerized include (meth) acrylic acid alkyl ester, (meth) acrylic acid alkoxyalkyl ester, glycidyl (meth) acrylate, an adduct of glycidyl (meth) acrylate and monocarboxylic acid, and hydroxyalkyl. (Meth) acrylate, acrylic acid, methacrylic acid and the like can be mentioned.

  In the case of imparting water dispersibility to chlorinated polyolefin and / or polyolefin, at least one hydrophilic monomer such as polymerizable unsaturated dicarboxylic acid or anhydride thereof may be graft-polymerized by a known method. it can. A polymerizable unsaturated dicarboxylic acid or an anhydride thereof is a compound having one polymerizable unsaturated bond and two or more carboxyl groups or an anhydride group in one molecule. For example, maleic acid and an anhydride thereof , Itaconic acid and its anhydride, citraconic acid and its anhydride, and the like. The amount of these hydrophilic monomers used is preferably in the range of 90 to 10% by mass, particularly 80 to 30% by mass based on the total amount with the chlorinated polyolefin.

  As the crosslinking agent, polyisocyanate compounds, melamine resins, carbodiimide resins, polyhydrazide compounds, glycidyl group-containing compounds, and the like can be used.

  Examples of the polyisocyanate compound include aromatic diisocyanates such as tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, xylylene diisocyanate, and metaxylylene diisocyanate; aliphatic diisocyanates such as hexamethylene diisocyanate; isophorone diisocyanate, hydrogenated 4, A compound having at least two isocyanate groups in one molecule such as alicyclic diisocyanate such as 4′-diphenylmethane diisocyanate and various derivatives of these diisocyanate compounds can be used.

  As the melamine resin, in particular, a methylolated melamine resin having an average of 3 or more methylol groups per triazine nucleus; a part obtained by reacting a methylolated melamine resin with a monoalcohol having 1 to 10 carbon atoms or full etherification Melamine resin can be used. As these melamine resins, those having an imino group can also be used. These can be either hydrophobic or hydrophilic.

  As the carbodiimide resin, a water-soluble or water-dispersible polycarbodiimide compound is preferably used as the polycarbodiimide compound from the viewpoint of the smoothness of the resulting coating film. The water-soluble or water-dispersible polycarbodiimide compound can be used without particular limitation as long as it is a polycarbodiimide compound that can be stably dissolved or dispersed in an aqueous medium. Specific examples of the water-soluble polycarbodiimide compound include “Carbodilite SV-02”, “Carbodilite V-02”, “Carbodilite V-02-L2”, and “Carbodilite V-04” (all manufactured by Nisshinbo Co., Ltd.). , Product name), etc. can be used. Moreover, as said water dispersible polycarbodiimide compound, "Carbodilite E-01", "Carbodilite E-02" (all are the Nisshinbo Co., Ltd. make, brand name) etc. can be used, for example. These polycarbodiimide compounds react with the hydroxyl group of the base resin.

The polyhydrazide compound has at least two hydrazide groups per molecule. Specific examples of polyhydrazide compounds include dihydrazides of saturated aliphatic carboxylic acids having 2 to 18 carbon atoms such as oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, sebacic acid dihydrazide; Diolefins of monoolefinically unsaturated dicarboxylic acids such as acid dihydrazide, fumaric acid dihydrazide, itaconic acid dihydrazide; phthalic acid, terephthalic acid or isophthalic acid dihydrazide; pyromellitic acid dihydrazide, trihydrazide or tetrahydrazide; nitrilotriacetic acid trihydrazide, Citric acid trihydrazide, 1,2,4-benzenetrihydrazide; ethylenediaminetetraacetic acid tetrahydrazide, 1,4,5,8-naphthoic acid tetrahydrazide; carbo Examples thereof include polyhydrazide obtained by reacting a low polymer having an acid lower alkyl ester group with hydrazine or hydrazine hydrate (hydrazine hydride), and these can be used alone or in combination of two or more. .
The glycidyl group-containing compound is a compound having one or more, preferably two or more glycidyl groups in one molecule. In addition to the glycidyl group, the glycidyl group-containing compound is a cationically polymerizable group or ring (for example, a cationically polymerizable group such as an alicyclic epoxy group, a vinyl group, a bicycloorthoester group, a spiroorthocarbonate group; an oxetane ring, etc. A cationically polymerizable ring).

  Specific examples of the glycidyl group-containing compound include, for example, glycidyl ether compounds such as diglycidyl ether, 2-glycidylphenyl glycidyl ether, and 2,6-diglycidylphenyl glycidyl ether; bisphenol A type epoxy resins, bisphenol F type epoxy resins, Epoxy resin having glycidyl ether group or glycidyl ester group such as cresol novolac type epoxy resin and phenol novolak type epoxy resin; glycidyl group-containing polymerizable unsaturated such as glycidyl (meth) acrylate, methyl glycidyl (meth) acrylate, allyl glycidyl ether Examples include (co) polymers of monomers and other polymerizable unsaturated monomers as required.

  The mixing ratio of the base resin and the cross-linking agent is 60 to 95 parts by weight, preferably 70 to 90 parts by weight, and 5 to 40 parts by weight of the cross-linking agent with respect to 100 parts by weight of the total solid content of both components. , Preferably it can be used in the ratio of 10-30 mass parts.

  Examples of the color pigment include aluminum pigments, pearl powder, graphite, bright pigments such as MIO, titanium white, phthalocyanine blue, and carbon black. If necessary, extender pigments may be blended. Although the compounding quantity of a coloring pigment is not specifically limited, For example, the range of 1-150 mass parts is preferable with respect to 100 mass parts of resin non volatile matters of a colored paint (B), More preferably, it is the range of 1-100 mass parts. is there.

In the colored paint (B), as a curing catalyst for promoting the crosslinking reaction, for example, tin octylate, dibutyltin di (2-ethylhexanoate), dioctyltin di (2-ethylhexanote), Organometallic compounds such as dioctyltin diacetate, dibutyltin dilaurate, dibutyltin oxide, monobutyltin trioctate, lead 2-ethylhexanoate, and zinc octylate can be appropriately blended.
The blending amount of these curing catalysts is usually within the range of 0.005 to 5 parts by mass, preferably 0.01 to 3 parts by mass, per 100 parts by mass in total of the base resin and the crosslinking agent.
If necessary, the colored paint (B) further includes an ultraviolet absorber, a light stabilizer, an acid addition agent, a surface conditioner, a pigment dispersant, a curing catalyst, an extender pigment, an antisettling agent, an antifoaming agent, and an increase. You may mix | blend a sticky agent, a rust preventive agent, etc. suitably.

The colored paint (B) can be prepared by dissolving or dispersing each of the above-described components in a solvent by a known method to form a paint. As the solvent, an organic solvent or water can be used, and among these, usual organic solvents such as hydrocarbon solvents, ester solvents, ether solvents, alcohol solvents, and ketone solvents can be used. The colored paint (B) is Ford Cup No. It is preferable that the solid content concentration is adjusted so as to be within a range of about 20 to 60% by mass so as to obtain a viscosity in a range of about 10 to 40 seconds at 4 (20 ° C.).
The photopolymerization initiator (a3) used for the clear paint (A) can be blended with the colored paint (B). By containing the photopolymerization initiator (a3), the compound (a1) soaked from the clear paint (A) can be cured by irradiation with active energy rays.

[Multilayer coating film forming method]
The method for forming a multi-layer coating film of the present invention includes a step of applying a colored paint (B) to an object to form a colored paint film, and applying a clear paint (A) on the colored paint film. And a step of irradiating active energy rays to simultaneously cure the colored coating and the clear coating. Next, a preferred embodiment will be described.
The object to be coated is not particularly limited. For example, metal materials such as iron, aluminum, brass, copper, stainless steel, tinplate, galvanized steel, alloyed zinc (Zn-Al, Zn-Ni, Zn-Fe, etc.) plated steel; polyethylene resin, polypropylene resin, acrylonitrile -Butadiene-styrene (ABS) resin, polyamide resin, acrylic resin, vinylidene chloride resin, polycarbonate resin, polyurethane resin, epoxy resin and other plastic materials such as FRP; glass, cement, concrete and other inorganic materials; wood A fiber material (paper, cloth, etc.) and the like, among which a metal material and a plastic material are suitable.

  In addition, the use of the object to which the coating film forming method is applied is not particularly limited. For example, an outer plate portion of an automobile body such as a passenger car, a truck, a motorcycle, or a bus; an automobile part; a mobile phone, an audio device, etc. And the like. Among them, the outer plate portion of an automobile body and automobile parts are preferable.

  The object to be coated may be obtained by subjecting the metal surface of the metal material or the vehicle body formed from the metal material to a surface treatment such as phosphate treatment, chromate treatment, zirconium treatment, or complex oxide treatment. Good. In addition, the object to be coated may be various electrodeposition coatings on the metal material or the vehicle body, or an uncured or cured coating of an aqueous or organic solvent type intermediate coating, and further preheated as necessary. (Preheating) may be performed.

Further, the object to be coated may be an uncured or cured film of an aqueous or organic solvent-type primer coating on the plastic material, and further preheat (preheat) the uncured coating as necessary. It may be what you did.

Here, from the viewpoint of saving process and energy saving to reduce the number of times of baking in the heat drying oven and energy consumption, the primer coating is not preheated (preheated) using an organic solvent type primer and is applied on the primer coating. It is desirable to use a water-based paint as the colored paint.
The colored paint (B) can be applied by a method known per se, for example, air spray, airless spray, electrostatic coating, etc., and the coating film thickness is usually 10 to 100 μm, preferably 10 by dry coating. It can be in the range which becomes -35 micrometers.
The coated film is usually preheated (preheated) directly or indirectly at a temperature of 60 to 120 ° C., preferably 70 to 110 ° C. for 1 to 60 minutes in a drying furnace. Alternatively, the setting can be performed on the coated surface of the object to be coated at room temperature or in an atmosphere at a temperature lower than 25 to 70 ° C.

  The method for applying the clear paint (A) is not particularly limited. For example, it can be applied by air spray, airless spray, rotary atomizing coater, dip coating, brush or the like. Electrostatic application may be performed during coating. The coating film thickness is usually 10 to 100 μm, preferably 10 to 50 μm in terms of cured film thickness.

  After coating, preliminary heating (preheating) and air blowing can be performed to reduce the volatile content of the coating film immediately after coating or to remove the volatile content. The preheating can be usually performed by directly or indirectly heating the coated object to be coated in a drying furnace at a temperature of 50 to 110 ° C., preferably 60 to 90 ° C. for 1 to 30 minutes. Moreover, an air blow can be normally performed by spraying the air heated to normal temperature or the temperature of 25 to 80 degreeC on the coating surface of the to-be-coated object.

When the clear paint (A) is cured, it is irradiated with active energy rays and heated as necessary.
When heating, the order of active energy ray irradiation and heating is not particularly limited. Active energy ray irradiation may be performed after heating, heating may be performed after active energy ray irradiation, or heating and active energy rays. Irradiation may be performed simultaneously.

  Moreover, when performing said heating and active energy ray irradiation simultaneously, it is good also considering the heat (For example, the heat | fever which a lamp | ramp emits) from the irradiation source of an active energy ray as a heat source. Further, when the active energy ray irradiation is performed after the heating, the active energy ray irradiation may be performed in a state where the object to be coated is heated (a state having a residual heat).

Examples of the active energy ray include ultraviolet light, visible light, and laser light (near infrared light, visible light laser, ultraviolet laser, etc.). Its dose is usually 100~5,000mJ / cm ^2, preferably preferably in the range of 300~3,000mJ / cm ^2. As the active energy ray irradiation source, conventionally used ones such as ultra-high pressure, high pressure, medium pressure, low pressure mercury lamp, FusionUV electrodeless lamp, chemical lamp, carbon arc lamp, xenon lamp, metal halide A light source obtained from each light source such as a lamp, a fluorescent lamp, a tungsten lamp, and sunlight, a light beam in a visible region cut by an ultraviolet cut filter, and various lasers having an oscillation line in the visible region can be used. Further, a pulse emission type pulse xenon lamp can also be used. The reaction initiating component generated by pulsed light emission often disappears in a short time, and the reaction initiating component can be stably supplied into the system by performing the next light emission within a certain time after light irradiation. Among these light emission sources, a pulse emission type xenon lamp excellent in short-time emission is preferable. By using a pulse light emission type xenon lamp, it is possible to irradiate a strong energy ray in a short time, so that inhibition of surface hardening by oxygen can be suppressed, and as a result, the scratch resistance of the coating film is improved.
In addition, as the lamp emission characteristics, a wavelength showing a wide range of wavelength distribution, but showing a maximum emission intensity in an emission wavelength distribution of 200 to 800 nm is defined as a peak wavelength, and this peak wavelength is particularly preferably 250 to 600 nm. If it is 300-500 nm, hardening will progress favorably.

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.
[Clear paint (A)]
Production Production Example 1 of Compound (a1) Compound No. 1 Production Example of 1 Solution In a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser and air blowing device, 210 parts of trimethylhexamethylene diisocyanate, 232 parts of 2-hydroxyethyl acrylate, 0.2 part of dibutyltin dilaurate, While charging 111 parts of butyl acetate and 0.7 parts of hydroquinone monomethyl ether and blowing air into the reaction vessel, the temperature was raised to 80 ° C. and maintained at that temperature for 5 hours, and substantially all of the added trimethylhexamethylene diisocyanate reacted. It was confirmed that compound No. 80 having a nonvolatile content of 80% was obtained. One solution was obtained.
Compound No. The water tolerance was 11.3, the weight average molecular weight was 450, and the average number of functional groups was 2.1.

Production Example 2 Compound No. 2 Solution Production Example In a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser and air blowing apparatus, 222 parts of isophorone diisocyanate, 704 parts of pentaerythritol triacrylate, 0.2 part of dibutyltin dilaurate, 232 of butyl acetate And 0.7 part of hydroquinone monomethyl ether were charged, and the temperature was raised to 80 ° C. and kept at that temperature for 5 hours while blowing air into the reaction vessel, and it was confirmed that substantially all of the added isophorone diisocyanate had reacted. Compound No. 80 having a non-volatile content of 80%. Two solutions were obtained.
Compound No. The water tolerance was 6.5, the weight average molecular weight was 1,000, and the average number of functional groups was 6.0.

Production Example 3 Compound No. 3 Example of production of solution In a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser and air blowing device, 168 parts of hexamethylene diisocyanate, 704 parts of pentaerythritol triacrylate, 0.2 part of dibutyltin dilaurate, butyl acetate 218 parts and 0.7 part of hydroquinone monomethyl ether were charged, and while blowing air into the reaction vessel, the temperature was raised to 80 ° C. and maintained at that temperature for 5 hours, and all the added hexamethylene diisocyanate had reacted. Confirmed, compound No. 80 having a non-volatile content of 80%. Three solutions were obtained.
Compound No. The water tolerance was 5.7, the weight average molecular weight was 800, and the average number of functional groups was 6.0.

Production Example of Compound (a2) Production Example 4 Compound No. 4 4. Example of production of solution In a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser and air blowing device, 841 parts of hexamethylene diisocyanate nurate pentamer, 704 parts of pentaerythritol triacrylate, dibutyltin dilaurate 0 .2 parts, 386 parts of butyl acetate and 0.7 parts of hydroquinone monomethyl ether were added, and the temperature was raised to 80 ° C. and kept at that temperature for 5 hours while blowing air into the reaction vessel. It was confirmed that compound No. 80 having a nonvolatile content of 80% was obtained. Four solutions were obtained.
Compound No. The water tolerance was 3.1, the weight average molecular weight was 2500, and the average number of functional groups was 5.8.

Production Example 5 Compound No. 5 Production Example of Solution In a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, and a dropping device, 95 parts of xylene was charged and stirred at 100 ° C. while blowing nitrogen gas, and 15 parts of isobornyl methacrylate was added thereto. A mixture of 15 parts of n-butyl methacrylate, 70 parts of glycidyl methacrylate and 4 parts of 2,2′-azobisisobutyronitrile was added dropwise at a uniform rate over 3 hours, and further aged at the same temperature for 2 hours. Thereafter, a mixture of 5 parts of xylene and 0.5 part of 2,2′-azobisisobutyronitrile was added dropwise to the reaction vessel over 1 hour. After completion of the addition, the mixture was aged for 1 hour to obtain a glycidyl group-containing acrylic resin solution. Obtained.
Further, a solution prepared by dissolving 29.6 parts of acrylic acid and 0.5 part of t-butylammonium bromide in 10.9 parts of butyl acetate was added to the glycidyl group-containing acrylic resin solution and reacted for 8 hours. Compound No. Five solutions were obtained.
Compound No. The water tolerance was 5, the weight average molecular weight was 20,000, and the average number of functional groups was 63.4.

Production Example 6 Compound No. 6 Solution Production Example 95 parts of xylene was charged into a reaction vessel equipped with a stirrer, thermometer, reflux condenser, and dropping device, and stirred at 100 ° C. while blowing nitrogen gas, and 15 parts of isobornyl acrylate was added therein. A mixture of 15 parts of n-butyl methacrylate, 70 parts of glycidyl methacrylate and 5 parts of 2,2′-azobisisobutyronitrile was added dropwise at a uniform rate over 3 hours, and further aged at the same temperature for 2 hours.
Thereafter, a mixture of 5 parts of xylene and 0.5 part of 2,2′-azobisisobutyronitrile was added dropwise to the reaction vessel over 1 hour. After completion of the addition, the mixture was aged for 1 hour to obtain a glycidyl group-containing acrylic resin solution. Obtained.
Further, a solution prepared by dissolving 29.6 parts of acrylic acid and 0.5 part of t-butylammonium bromide in 10.9 parts of butyl acetate was added to the glycidyl group-containing acrylic resin solution and reacted for 8 hours. Compound No. 6 solutions were obtained.
Compound No. The water tolerance was 6, the weight average molecular weight was 15,000, and the average number of functional groups was 47.6.

Production Example 7 Compound No. 7 Solution Production Example A reaction vessel equipped with a stirrer, thermometer, reflux condenser, and dropping device was charged with 95 parts of xylene and stirred at 100 ° C. while blowing nitrogen gas. A mixture of 70 parts of glycidyl methacrylate and 6 parts of 2,2′-azobisisobutyronitrile was added dropwise at a uniform rate over 3 hours, and further aged at the same temperature for 2 hours. Thereafter, a mixture of 5 parts of xylene and 0.5 part of 2,2′-azobisisobutyronitrile was added dropwise to the reaction vessel over 1 hour. After completion of the addition, the mixture was aged for 1 hour to obtain a glycidyl group-containing acrylic resin solution. Obtained.
Further, a solution prepared by dissolving 29.6 parts of acrylic acid and 0.5 part of t-butylammonium bromide in 10.9 parts of butyl acetate was added to the glycidyl group-containing acrylic resin solution and reacted for 8 hours. Compound No. 7 solutions were obtained.
Compound No. The water tolerance was 7, the weight average molecular weight was 7,000, and the average number of functional groups was 22.2.
Production of hydroxyl group-containing resin (a4) Production Example 8 Hydroxyl group-containing acrylic resin no. Production of one solution
In a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, and a dropping device, 80 parts of xylene were charged and stirred at 100 ° C. while blowing nitrogen gas, and 10 parts of styrene, 40 parts of methyl methacrylate, i- A mixture of 8 parts of butyl methacrylate, 20 parts of n-butyl acrylate, 20 parts of 2-hydroxyethyl acrylate, 2 parts of acrylic acid and 4 parts of 2,2′-azobisisobutyronitrile was dropped at a uniform rate over 3 hours. The mixture was further aged for 2 hours at the same temperature. Thereafter, a mixture of 10 parts of xylene and 0.5 part of 2,2′-azobisisobutyronitrile was added dropwise to the reaction vessel over 1 hour, and aged for 1 hour after completion of the addition, containing a hydroxyl group having a solid content of 55%. Acrylic resin no. One solution was obtained.
The obtained hydroxyl group-containing acrylic resin No. The acid value of 1 was 15.6 mgKOH / g, the hydroxyl value was 96.6 mgKOH / g, and the weight average molecular weight was 20,000.

Production Example 9 Hydroxyl group-containing acrylic resin 2. Preparation of solution In a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, and a dropping device, 80 parts of xylene were charged and stirred at 100 ° C. while blowing nitrogen gas. A mixture of 8 parts i-butyl methacrylate, 10 parts n-butyl acrylate, 30 parts 2-hydroxyethyl acrylate, 2 parts acrylic acid and 4 parts 2,2′-azobisisobutyronitrile over 3 hours. The solution was added dropwise at a rate and aged at the same temperature for 2 hours. Thereafter, a mixture of 10 parts of xylene and 0.5 part of 2,2′-azobisisobutyronitrile was added dropwise to the reaction vessel over 1 hour, and aged for 1 hour after completion of the addition, containing a hydroxyl group having a nonvolatile content of 55%. Acrylic resin no. Two solutions were obtained. The obtained hydroxyl group-containing acrylic resin No. 2 had an acid value of 15.6 mgKOH / g, a hydroxyl value of 144.9 mgKOH / g, and a weight average molecular weight of 20,000.

Production Production Example 10 of Radical Polymerizable Unsaturated Group-Containing Compound (a6) Production of Radical Polymerizable Unsaturated Group-Containing Compound (a6) Solution In a reaction vessel equipped with a stirrer, thermometer, reflux condenser, and dropping device, methoxy was added. A mixture of 25.3 parts of propyl acetate, 50.0 parts of isocyanurate cycloadduct of hexamethylene diisocyanate (NCO content 21%), 0.02 part of dibutyltin dilaurate, and 0.2 part of hydroquinone monomethyl ether was charged. The mixture was heated to 50 ° C. with stirring. Subsequently, 51.1 parts of Plaxel FA-2D (trade name, manufactured by Daicel Chemical Industries, Ltd., caprolactone-modified hydroxyethyl acrylate) was added dropwise over 8 hours while keeping the temperature of the mixture not exceeding 60 ° C. The mixture was further stirred for 1 hour at 0 ° C. to obtain a radically polymerizable unsaturated group-containing compound (a6) solution having a nonvolatile content of 80%. The obtained radical polymerizable unsaturated group-containing compound had an isocyanate equivalent of 681, an unsaturated group equivalent of 681, and a weight average molecular weight of 1,021.

Production Example of Colloidal Silica (a7) Production Example 11 Modified Colloidal Silica Production of one solution
In a reaction vessel equipped with a thermostat, a stirrer, a reflux condenser and an air blowing device, 333.3 parts (100 parts solids) of Snowtex PMT-ST (Nissan Chemical Industries, trade name, colloidal silica, 30%), 5 parts of 3-acryloyloxypropyltrimethoxysilane was charged, and the temperature was raised to 80 ° C. while blowing dry air into the reaction vessel. The temperature was maintained for 3 hours, and after confirming that substantially all of the charged 3-acryloyloxypropyltrimethoxysilane had reacted with PMT-ST, the mixture was cooled and modified colloidal silica No. 31 having a solid content of 31%. One solution was obtained.

Production Example of Silsesquioxane Compound (a8) Production Example 12 Product (a8-1)
A separable flask equipped with a reflux condenser, a thermometer, an air introduction tube, and a stirrer was charged with 685 parts of 3-isocyanatopropyltriethoxysilane, 315 parts of 2-hydroxyethyl acrylate, and 1 part of p-methoxyphenol, and dried air was added. The mixture was reacted at 100 ° C. for 12 hours while blowing to obtain a product (P1).
Next, 728 parts of the product (P1) and 2800 parts of tetrahydrofuran were placed in a separable flask equipped with a reflux condenser, a thermometer, and a stirrer, and stirred at room temperature. 4 parts of tetrarabutylammonium fluoride trihydrate was dissolved in 54 parts of deionized water and charged into a flask, and reacted at 20 ° C. for 24 hours. After adding 500 parts of 1-methoxy-2-propanol and removing volatiles by distillation under reduced pressure, 500 parts of 1-methoxy-2-propanol was further added and distilled under reduced pressure, and the solvent was exchanged. The product was adjusted to 1000 parts to obtain 1000 parts of a product (a8-1) solution having a solid content of 50%.
As a result of ²⁹ Si-NMR analysis of the product (a8-1), only a peak around −70 ppm derived from T3 structure in which all three oxygen atoms bonded to Si were bonded to other Si was confirmed. , T1 and T2 peaks were not observed.
Further, as a result of ¹ H-NMR analysis of the product (a8-1), a peak of 0.6 ppm derived from a methylene group bonded to Si was confirmed. In addition, 5.9 ppm, 6.1 ppm, and 6.4 ppm peaks derived from the carbon-carbon unsaturated bond of the acryloyloxy group were confirmed. The molar ratio of the carbon-carbon unsaturated bond of the acryloyloxy group to the methylene group bonded to Si calculated from these peak intensity ratios was 1.01.
Moreover, as a result of conducting FT-IR analysis about the product (a8-1), the peak of 1540cm < ^-1 > vicinity attributed to a urethane bond was confirmed.
Moreover, as a result of performing a gel permeation chromatograph (GPC) analysis about the product (a8-1), the weight average molecular weight was 2,500.
From the results of ²⁹ Si-NMR, ¹ H-NMR, FT-IR, and GPC for the product (a8-1), all of the organic groups in which the product (a8-1) was directly bonded to the silicon atom were found to be Organic group represented by the following formula (1)

Formula (1)
It is confirmed that the silsesquioxane compound is a silsesquioxane compound having a weight average molecular weight of 2,500, wherein the silsesquioxane compound has a structure in which almost all Si—OH groups are hydrolyzed and condensed. It was done.

Production Example 13 Product (a8-2)
A separable flask equipped with a reflux condenser, thermometer, air inlet tube, and stirrer was charged with 100 parts of Glycidyl POSS cage mixture (trade name, manufactured by Hybrid Plastics) and 140 parts of butyl acetate, and dissolved while stirring at 60 ° C. I let you. 40 parts of acetic acid, 0.5 part of p-methoxyphenol, and 10 parts of tetrabutylammonium bromide were added thereto, and reacted at 120 ° C. for 12 hours while blowing dry air. After cooling to 80 ° C. and adding 85 parts of 2-isocyanatoethyl acrylate and reacting at 80 ° C. for 10 hours, the volatile matter was removed by distillation under reduced pressure, and 500 g of 1-methoxy-2-propanol was added and further distillation under reduced pressure. As a result, a product (a8-2) solution having a solid content of 50% was obtained.
The Glycidyl POSS cage mixture used as a raw material was a 3-glycidoxypropyl group-containing cage-type polysilsesquioxane, the weight average molecular weight was 1,800, and the epoxy equivalent was 168 g / eq.
As a result of ²⁹ Si-NMR analysis of the product (a8-2), only a peak around −70 ppm derived from T3 structure in which all three oxygen atoms bonded to Si were bonded to other Si was confirmed. A peak derived from the T1 or T2 structure indicating the presence of a silyl group was not confirmed.
As a result of ¹ H-NMR analysis of the product (a8-2), a peak of 0.6 ppm derived from a methylene group bonded to Si was confirmed. In addition, 5.9 ppm, 6.1 ppm, and 6.4 ppm peaks derived from the carbon-carbon unsaturated bond of the acryloyloxy group were confirmed. The molar ratio of the carbon-carbon unsaturated bond of the acryloyloxy group to the methylene group bonded to Si calculated from these peak intensity ratios was 1.00. Moreover, the peak attributed to an epoxy group was not confirmed. The epoxy equivalent determined by titration was 10,000 g / eq or more.
Further, as a result of FT-IR analysis of the product (a8-2), a broad peak in the vicinity of 1540 cm ⁻¹ attributable to urethane bonds that was not confirmed in the raw material Glycidyl POSS cage mixture was confirmed.
Further, GPC analysis of the product (a8-2) revealed that the weight average molecular weight was 4,000.
From the ²⁹ Si-NMR, ¹ H-NMR, FT-IR, and GPC results for the product (a8-2), all of the organic groups in which the product (a8-2) was directly bonded to the silicon atom were found to be Organic group represented by the following formula (2)

式（２）
を有するシルセスキオキサン化合物であって、該シルセスキオキサン化合物の５５％以上がＳｉ−ＯＨ基の全てが加水分解縮合した構造である重量平均分子量４，０００のシルセスキオキサン化合物であることが確認された。

Formula (2)
A silsesquioxane compound having a weight average molecular weight of 4,000 in which at least 55% of the silsesquioxane compound has a structure in which all Si—OH groups are hydrolyzed and condensed. It was confirmed.

Production and production example 14 of clear paint (A) Production of Compound No. 1 obtained in Production Example 1 1 in 25 parts (solid content 20 parts), the compound No. 1 obtained in Production Example 4. No. 4 100 parts (solid content 80 parts), Darocur 1173 (Note 5) 3.0 parts, and butyl acetate 129.5 parts were uniformly mixed. 1 was obtained.
Clear paint No. Compound No. 1 1 and compound No. 1 The difference in water tolerance of 4 was 8.2.

Production Examples 15 to 51 Clear Paint No. 2-No. Production of clear paint No. 38 in the same manner as in Production Example 14 except that the composition of each component is as shown in Tables 1 to 3. 2-No. 38 was obtained.

(Note 1) PETA: Pentaerythritol triacrylate, average functional group number 3, water tolerance 15.8
(Note 2) TMPTA: Trimetrole propane triacrylate, average functional group number 3, water tolerance 7.2
(Note 3) UN-901T: manufactured by Negami Kogyo Co., Ltd., trade name, urethane acrylate, average functional group number 9, water tolerance 1.5

（注４）ダロキュアＴＰＯ：チバ スペシャルティ ケミカルズ社製、商品名、光重合開始剤
（注５）ダロキュア１１７３：チバ スペシャルティ ケミカルズ社製、商品名、光重合開始剤
（注６）イルガキュア５００：チバ スペシャルティ ケミカルズ社製、商品名、光重合開始剤
（注７）スノーテックスＭＰＡ−ＳＴ：日産化学社製、商品名、コロイダルシリカ、固形分４０％。

(Note 4) Darocur TPO: Ciba Specialty Chemicals, trade name, photopolymerization initiator (Note 5) Darocur 1173: Ciba Specialty Chemicals, trade name, photopolymerization initiator (Note 6) Irgacure 500: Ciba Specialty Chemicals Product name, photopolymerization initiator (Note 7) Snowtex MPA-ST: Product name, colloidal silica, solid content 40%.

Comparative Production Examples 1-7 Clear Paint No. 39-No. Production of clear paint No. 45 in the same manner as in Production Example 11 except that the composition of each component was as shown in Table 4. 39-No. 45 was obtained.

Production of colored paint (B) Production Example 52 Colored paint No. 1
Add 50 parts of Retan PG Eco thinner 30 (mixed thinner, manufactured by Kansai Paint Co.) to 50 parts of Retan PG Hybrid Eco Sun Metallic paint (trade name, lacquer type paint manufactured by Kansai Paint Co., Ltd.) Paint No. One solution was obtained.

Production Example 53 Colored Paint No. 2
Lettan PG Hybrid Eco Sun Metallic (Kansai Paint Co., Ltd., trade name, lacquer type paint), 50 parts of Retan PG Eco Thinner 30 (Kansai Paint Co., Ltd., mixed thinner), Darocur TPO (Note 4) 1 part of the mixture was added and stirred. Two solutions were obtained.

Production Example 54 Production of hydroxyl group-containing acrylic resin emulsion 130 parts of deionized water and 0.52 parts of Aqualon KH-10 (Note 8) were charged into a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser and dropping device. The mixture was stirred and mixed in a nitrogen stream and heated to 80 ° C. Next, 1% of the total amount of the following monomer emulsion (1) and 5.3 parts of a 6% aqueous ammonium persulfate solution were introduced into the reaction vessel and maintained at 80 ° C. for 15 minutes. Then, the remaining monomer emulsion (1) was dripped in reaction container hold | maintained at the same temperature over 3 hours, and it age | cure | ripened for 1 hour after completion | finish of dripping. Thereafter, the following monomer emulsion (2) was added dropwise over 1 hour, and after aging for 1 hour, the mixture was cooled to 30 ° C. while gradually adding 40 parts of 5% dimethylethanolamine aqueous solution to the reaction vessel, and 100 mesh nylon The sample was discharged while being filtered with a cloth, and the average particle size was 100 nm [submicron particle size distribution analyzer “COULTER N4 type” (manufactured by Beckman Coulter, Inc.), diluted with deionized water, and measured at 20 ° C. A hydroxyl group-containing acrylic resin emulsion having a nonvolatile content of 30%, an acid value of 33 mgKOH / g, and a hydroxyl value of 25 mgKOH / g was obtained.

(Note 8) Aqualon KH-10: Polyoxyethylene alkyl ether sulfate ester ammonium salt: 97% active ingredient manufactured by Daiichi Kogyo Seiyaku Co., Ltd.
Monomer emulsion (1): 42 parts of deionized water, 0.72 part of Aqualon KH-10 (see Note 7), 2.1 parts of methylenebisacrylamide, 2.8 parts of styrene, 16.1 parts of methyl methacrylate, ethyl acrylate 28 parts and 21 parts of n-butyl acrylate were mixed and stirred to obtain a monomer emulsion (1).
Monomer emulsion (2): 18 parts deionized water, 0.31 part Aqualon KH-10 (see note 7), 0.03 part ammonium persulfate, 5.1 parts methacrylic acid, 5.1 parts 2-hydroxyethyl acrylate Then, 3 parts of styrene, 6 parts of methyl methacrylate, 1.8 parts of ethyl acrylate and 9 parts of n-butyl acrylate were mixed and stirred to obtain a monomer emulsion (2).

Production Example 54 Production of hydroxyl group-containing polyester resin solution (PE1) In a reaction vessel equipped with a thermometer, thermostat, stirring device, reflux condenser and water separator, 109 parts of trimethylolpropane, 141 parts of 1,6-hexanediol, First, 126 parts of hexahydrophthalic anhydride and 120 parts of adipic acid were charged, the temperature was raised between 160 ° C. and 230 ° C. over 3 hours, and then a condensation reaction was performed at 230 ° C. for 4 hours. Next, in order to add a carboxyl group to the obtained condensation reaction product, 38.3 parts of trimellitic anhydride was further added, reacted at 170 ° C. for 30 minutes, and then diluted with 2-ethyl-1-hexanol. Thus, a hydroxyl group-containing polyester resin solution (PE1) having an acid value of 46 mgKOH / g, a hydroxyl value of 150 mgKOH / g, a solid content of 70%, and a weight average molecular weight of 6,400 was obtained.

Production Example 55 Production of glitter pigment concentrate (P1) In a stirring and mixing vessel, 19 parts of aluminum pigment paste “GX-180A” (Asahi Kasei Metals Co., Ltd., metal content 74%), 2-ethyl-1-hexanol 35 Part, 8 parts of a phosphoric acid group-containing resin solution (Note 9) and 0.2 part of 2- (dimethylamino) ethanol were mixed uniformly to obtain a bright pigment concentrate (P1).

  (Note 9) Phosphate group-containing resin solution: put a mixed solvent of 27.5 parts of methoxypropanol and 27.5 parts of isobutanol into a reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser and a dropping device, 6. Heat to 110 ° C., 25 parts of styrene, 27.5 parts of n-butyl methacrylate, 20 parts of “isostearyl acrylate” (trade name, Osaka Organic Chemical Industries, Ltd., branched higher alkyl acrylate), 4-hydroxybutyl acrylate Mixture 121.5 consisting of 5 parts, 15 parts of a phosphoric acid group-containing polymerizable monomer (Note 10), 12.5 parts of 2-methacryloyloxyethyl acid phosphate, 10 parts of isobutanol and 4 parts of t-butylperoxyoctanoate Is added to the above mixed solvent over 4 hours, and 0.5 parts of t-butylperoxyoctanoate is added. A mixture of finely Isopropanol 20 parts was added dropwise for 1 hour. Thereafter, the mixture was aged and stirred for 1 hour to obtain a phosphate group-containing resin solution having a nonvolatile content of 50%. The acid value due to the phosphoric acid group of this resin was 83 mgKOH / g, the hydroxyl value derived from 4-hydroxybutyl acrylate was 29 mgKOH / g, and the weight average molecular weight was 10,000.

  (Note 10) Phosphoric acid group-containing polymerizable monomer: put 57.5 parts of monobutyl phosphoric acid and 41 parts of isobutanol in a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser and dripping device After warming, 42.5 parts of glycidyl methacrylate was added dropwise over 2 hours, followed by stirring and aging for another hour. Thereafter, 59 parts of isopropanol was added to obtain a phosphate group-containing polymerizable monomer solution having a nonvolatile content of 50%. The acid value due to the phosphate group of the obtained monomer was 285 mgKOH / g.

Production Example 56 Production of 3 150 parts of the hydroxyl group-containing acrylic resin emulsion obtained in Production Example 54, 64 parts of the hydroxyl group-containing polyester resin solution (PE1) obtained in Production Example 55, and the glitter pigment concentrate obtained in Production Example 56 (P1) ) 62 parts and 12.5 parts of “Cymel 202” (trade name, manufactured by Nippon Cytec Industries, Inc., melamine resin, non-volatile content 80%) are mixed uniformly, and further, deionized water and 2- (dimethylamino) ethanol are added. In addition, a colored paint No. having a pH of 8.0 and a solid content of 23% was used. 3 was obtained.

[How to create a test plate]
Preparation of article A Polypropylene NX-280AK (manufactured by Mitsubishi Oil Chemical Co., Ltd., plate thickness 3.2 mm) was subjected to trichloroethane vapor degreasing for 1 minute and then dried at 80 ° C. for 10 minutes. Next, “SOFLEX No. 1000” (manufactured by Kansai Paint Co., Ltd., polyolefin-containing conductive organic solvent primer primer) was applied as a primer with a dry film thickness of 15 μm, set at room temperature for 3 minutes, and “coated A” did.

Preparation of object B: Degreased and zinc phosphate-treated cold-rolled steel sheet (JISG3020, 400 × 300 × 0.8 mm) and cationic electrodeposition paint “Electron GT-10” (trade name: manufactured by Kansai Paint Co., Ltd., epoxy) A resin polyamine-based cationic resin using a block polyisocyanate compound as a curing agent) is electrodeposited so as to have a film thickness of 20 μm based on the cured coating film, and is heated at 170 ° C. for 20 minutes to be crosslinked and cured. A coated film was obtained.
On the obtained electrodeposition coating surface, an intermediate coating "TP-65-2 (white coating color)" (manufactured by Kansai Paint Co., Ltd., polyester resin / melamine resin type, organic solvent type) is applied to the cured coating film by air spray. On the basis of this, the coating plate was coated to have a film thickness of 30 μm, heated at 140 ° C. for 30 minutes to be crosslinked and cured, and the coated plate on which the intermediate coating film was formed was designated as “Coating object B”.

Example 1
In the above-mentioned “Substance A”, the colored paint No. 1 was coated using a rotary atomizing coater so that the dry film thickness was 15 μm, and preheated at 80 ° C. for 3 minutes.
Next, the clear paint No. 1 obtained in Production Example 14 was used. 1 was air spray coated so that the dry film thickness was 30 μm. Then, after preheating at 80 degreeC for 3 minute (s), the active energy ray was irradiated with the irradiation amount of 1,500 mJ / cm < ² > using D valve | bulb (note 17). Subsequently, it was heated and dried at 90 ° C. for 10 minutes to obtain a test plate.

  (Note 17) D bulb: manufactured by Fusion, trade name, metal halide lamp, UV irradiation lamp.

Examples 2-48
A test plate was obtained in the same manner as in Example 1 except that the type of clear paint was changed to those shown in Tables 5 to 7.

Examples 49-74
A test plate was obtained in the same manner as in Example 1 except that the types of the colored paint and the clear paint and the light source for light irradiation were changed to those shown in Tables 8 and 9.

(Note 18) H bulb: product name, high-pressure mercury lamp, UV irradiation lamp (Note 19) manufactured by Fusion Co., Ltd. Pulse: material name, product name, xenon pulse ultraviolet irradiation device.

Comparative Examples 1-7
A test plate was obtained in the same manner as in Example 1 except that the clear paint was changed to that shown in Table 10.

試験方法
（注１１）付着性：
試験板の塗膜面にＪＩＳ Ｋ ５６００−５−６（１９９０）に準じて塗膜に２ｍｍ×２ｍｍのゴバン目１００個を作り、その面に粘着テープを貼着し、急激に剥がした後に、塗面に残ったゴバン目塗膜の数を評価した。
◎：残存個数／全体個数＝１００個／１００個で縁欠けなし
○：残存個数／全体個数＝１００個／１００個で縁欠けあり
△：残存個数／全体個数＝９９個〜９０個／１００個
×：残存個数／全体個数＝８９個以下／１００個。

Test method (Note 11) Adhesion:
After making 100 2mm x 2mm gobang eyes on the coating film according to JIS K 5600-5-6 (1990) on the coating surface of the test plate, sticking an adhesive tape on the surface and peeling it off rapidly, The number of gobang eye coats remaining on the paint surface was evaluated.
A: Remaining number / total number = 100/100, no missing edges ○: Remaining number / total number = 100/100, no edges missing Δ: Remaining number / total number = 99 to 90/100 X: Remaining number / total number = 89 or less / 100.

(Note 12) Finishability:
Each test plate was evaluated for finish by gloss measurement.
The glossiness of each coated surface was measured according to the specular glossiness (60 degrees) of JIS K5600-4-7 (1999). The measured glossiness was evaluated according to the following criteria.
A: Specular gloss is 90 or more. B: Specular gloss is 70 or more and less than 90. Δ: Specular gloss is 50 or more and less than 70.

(Note 13) Scratch resistance 1:
Each test plate was subjected to a Taber abrasion test (abrasion wheel CF-10P, load 500 g, 100 revolutions) in accordance with ASTM D1044. About the coating film before and behind a test, the glossiness of each coating surface was measured according to the specular glossiness (60 degree | times) of JISK5600-4-7 (1999). The glossiness after the test with respect to the glossiness before the test was determined as a gloss retention (%) and evaluated according to the following criteria.
A: Gloss retention 90% or more B: Gloss retention 80% or more and less than 90% B: Gloss retention 60% or more and less than 80% X: Gloss retention 60% or less

(Note 14) Scratch resistance 2:
Steel wool # 0000 was placed on each test plate, and was reciprocated 10 times with a load of 1 kgf / cm ² using a Gakushin type friction fastness tester.
About the coating film before and behind a test, the glossiness of each coating surface was measured according to the specular glossiness (60 degree | times) of JISK5600-4-7 (1999). The glossiness after the test with respect to the glossiness before the test was determined as a gloss retention (%) and evaluated according to the following criteria.
◎: Gloss retention 90% or more ○: Gloss retention 80% or more but less than 90% △: Gloss retention 60% or more but less than 80% ×: Gloss retention 90% or less

(Note 15) Weather resistance:
Each test plate was subjected to a 2000-hour weather resistance test using a sunshine weatherometer in accordance with JIS K 5600-7-8 (1999). The adhesion of the test plate after the test was evaluated.
After making 100 2mm x 2mm gobangs on the coated surface according to JIS K 5600-5-6 (1990) on each coated surface, affixing adhesive tape to the surface and removing it rapidly, The number of remaining gobang eyes was evaluated:
◎: remaining number / total number = 100/100, no missing edges ○: remaining number / total number = 100/100, no edges missing Δ: remaining number / total number = 99 to 90 / 100 pieces x: remaining number / total number = 89 or less / 100 pieces.

(Note 16) Acid resistance:
0.5 mL of 1% sulfuric acid aqueous solution was dropped on the surface of each coating film and allowed to stand for 24 hours in an atmosphere having a temperature of 20 ° C. and a relative humidity of 65%. Then, the coating film surface was wiped with gauze and the appearance was visually evaluated.
◎: No abnormality on the surface of the coating film ○: Slight traces on the surface of the coating film but disappear when washed with water △: Some discoloration or whitening is observed on the coating film surface ×: The surface of the coating is significantly discolored or whitened.

Claims (13)

Applying a colored paint (B) to the object to be coated to form a colored paint film, applying a clear paint (A) on the colored paint film to form a clear paint film, and active energy rays A method comprising a step of irradiating, wherein the clear paint (A) has a weight average molecular weight of 250 to less than 1500, a water tolerance of 5 or more and a compound having an average of two or more acryloyl groups in the molecule (a1), a weight average molecular weight The difference in water tolerance between the compound (a1) and the compound (a2) is 1,500 or more and contains an average of two or more acryloyl groups in the molecule (a2) and a photopolymerization initiator (a3). It is 0-10.0, The multilayer coating-film formation method characterized by the above-mentioned. The method for forming a multilayer coating film according to claim 1, wherein the compound (a1) is a compound having a urethane bond. The method for forming a multilayer coating film according to claim 1 or 2, wherein the compound (a2) is urethane acrylate or acrylic acrylate having a weight average molecular weight of 1,500 to 30,000. The water tolerance of a compound (a2) is 0.5-4.5, The multilayer coating-film formation method of any one of Claims 1-3. The method for forming a multilayer coating film according to any one of claims 1 to 4, wherein the photopolymerization initiator (a3) is liquid at 20 ° C. The method for forming a multilayer coating film according to any one of claims 1 to 5, wherein the light source of the active energy ray is a pulse xenon lamp. The multilayer coating film forming method according to any one of claims 1 to 6, wherein the clear paint (A) contains a hydroxyl group-containing resin (a4). The multilayer coating film forming method according to any one of claims 1 to 7, wherein the clear paint (A) contains a polyisocyanate compound (a5). The clear paint (A) is obtained by reacting a caprolactone-modified hydroxyalkyl (meth) acrylate with a polyisocyanate compound, and a radical polymerizable unsaturated group-containing compound (a6) having an isocyanate equivalent weight in the range of 300 to 3,800. The method for forming a multilayer coating film according to any one of claims 1 to 8. The multilayer coating film forming method according to any one of claims 1 to 9, wherein the clear paint (A) contains colloidal silica (a7). The method for forming a multilayer coating film according to any one of claims 1 to 10, wherein the clear paint (A) comprises a silsesquioxane compound (a8). The method for forming a multilayer coating film according to any one of claims 1 to 11, wherein the colored paint (B) contains a photopolymerization initiator (a3). The coated article by the multilayer coating-film formation method of any one of Claims 1-12.