JP2009144111A - Coating composition and method for forming coating film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating composition capable of forming a cured coating film excellent in any of anti-abrasion property, acid resistance, and finish appearance. <P>SOLUTION: The coating composition comprises an acrylic resin (A); and a polyisocyanate compound (B); wherein the acrylic resin (A) is obtained by copolymerizing (a) 15-80 mass% of a particular secondary hydroxyl group-containing (meth)acrylate and (b) 20-85 mass% of another unsaturated monomer capable of being copolymerized therewith, and the acrylic resin (A) is mainly characterized in that the secondary hydroxyl group is arranged with a certain distance from the polymer main chain, the hydroxyl group value is 100-200 mg KOH/g, and the hydroxyl group value derived from the hydroxyl group-containing (meth)acrylate (a) is 15-85 mg KOH/g. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a coating composition excellent in scratch resistance, acid resistance and finished appearance.

  A coating material to be coated on an object such as an automobile body is required to have excellent coating film performance such as scratch resistance, acid resistance, and finished appearance.

  Conventionally, melamine curable coatings have been widely used as the coating materials for the objects to be coated. The melamine curable paint is a paint containing a hydroxyl group-containing resin and a melamine resin as a crosslinking agent, has a high crosslinking density at the time of heat curing, and is excellent in coating film performance such as scratch resistance and finish. However, this paint has a problem that the ether crosslinks formed by the reaction between the hydroxyl group of the hydroxyl group-containing resin and the melamine resin are easily hydrolyzed by acid rain and the acid resistance of the coating film is poor.

  Japanese Patent Application Laid-Open No. 6-220397 discloses a two-component urethane cross-linking coating composition comprising a hydroxyl group-containing acrylic resin, a hydroxyl group-containing oligoester and an isocyanate prepolymer. This paint is excellent in acid resistance of the coating film because urethane crosslinks are hardly hydrolyzed. However, the scratch resistance of the coating film is insufficient.

  JP-A-3-278868 discloses a hydroxyl group-containing (meth) acrylate ester having a specific structure including a secondary hydroxyl group in a 3-coat / 2-bake coating method as a method for forming a coating film having excellent scratch resistance and the like. Also disclosed is a method of forming a coating film using a second clear coat paint comprising an acrylic copolymer (and an alkyl etherified melamine resin) containing as a constituent component. However, this coating film formation method is insufficient in both scratch resistance and finished appearance.

Japanese Patent Laid-Open No. 6-220397 JP-A-3-278868

  An object of the present invention is to provide a coating composition capable of forming a cured coating film excellent in any of scratch resistance, acid resistance and finished appearance.

  As a result of intensive studies to solve the above problems, the present inventors have determined that the secondary hydroxyl group is located at a position more than a certain distance from the polymer main chain by using a specific secondary hydroxyl group-containing monomer as a copolymerization component. The present inventors have found that the above object can be achieved by a coating composition containing a secondary hydroxyl group-containing acrylic resin and a polyisocyanate compound, which are mainly characterized by the fact, and have completed the present invention.

That is, the present invention
(A) 15 to 80% by mass of a hydroxyl group-containing (meth) acrylic acid ester represented by the following formula (I),

Wherein R ₁ is a hydrogen atom or a methyl group, R ₂ is an alkylene group having 1 to 10 carbon atoms, R ₃ is an alkylene group having 1 to ₃ carbon atoms or a group represented by the following formula (II), R ₄ is an acyloxy group represented by R ₅ COO— (R ₅ is an arbitrary alkyl group, phenyl group or tolyl group) or a group represented by R ₆ O— (R ₆ is an arbitrary alkyl group, phenyl group or tolyl group). Represents.)

And (b) a hydroxyl group value obtained by copolymerizing 20 to 85% by mass of another copolymerizable unsaturated monomer and having a hydroxyl value of 100 to 200 mgKOH / g and represented by the above formula (I) ( The present invention provides a coating composition containing an acrylic resin (A) having a hydroxyl value derived from a (meth) acrylic acid ester of 15 to 85 mgKOH / g and a polyisocyanate compound (B).

  The present invention also relates to a method of forming a multilayer coating film by coating at least one layer of a colored base coat paint and at least one layer of a clear coat paint on an object to be coated. The present invention provides a method for forming a multilayer coating film characterized by coating the coating composition described above.

  Secondary hydroxyl groups are generally less reactive than primary hydroxyl groups and are therefore advantageous for improving the finished appearance of the coating film, improving interlayer adhesion, etc., but the coating film obtained by reacting with a crosslinking agent The coating film performance such as scratch resistance is reduced. In the coating composition of the present invention, the secondary hydroxyl group of the acrylic resin is located at a certain distance or more away from the polymer main chain, so that the reactivity can be improved and the curability is lowered by the secondary hydroxyl group. Can be suppressed. Moreover, since the secondary hydroxy group having a long-chain specific structure exists, it is possible to impart flexibility to the cured coating film.

  Furthermore, urethane cross-linking by reaction of a hydroxyl group-containing acrylic resin and a polyisocyanate compound is excellent in acid hydrolysis resistance and mechanical properties.

  From the above, according to the coating composition of the present invention, it is possible to produce an effect that a cured coating film having excellent scratch resistance, acid resistance and finished appearance can be formed.

  Hereinafter, the coating composition of the present invention (hereinafter sometimes referred to as “the present coating”) and the method for forming a multilayer coating film will be described in detail.

Coating Composition The coating composition of the present invention is obtained by copolymerizing (a) a specific hydroxyl group-containing (meth) acrylic acid ester represented by the above formula (I) and (b) another copolymerizable unsaturated monomer. An acrylic resin having a hydroxyl value in a specific range and having a hydroxyl value in a specific range, and a secondary hydroxyl group derived from a hydroxyl group-containing (meth) acrylic acid ester represented by the above formula (I) ( A coating composition containing A) and a polyisocyanate compound (B).
Acrylic resin (A)
The acrylic resin (A) used in the paint is an acrylic resin having a specific secondary hydroxyl group as a cross-linking functional group, and can be obtained by copolymerizing the monomers (a) and (b).
Hydroxyl group-containing (meth) acrylic acid ester (a)
As the hydroxyl group-containing (meth) acrylic acid ester (a), any hydroxyl group-containing (meth) acrylic acid ester represented by the general formula (I) can be used without particular limitation.

  Specifically, for example, the hydroxyl group-containing (meth) acrylic acid ester (a) is obtained by adding an acid anhydride of a dicarboxylic acid to a hydroxyl group-containing acrylic monomer, and further, a carboxyl group of this adduct and an epoxy group of a monoepoxy compound. Can be synthesized by reacting with.

  Examples of the hydroxyl group-containing acrylic monomer used in the above reaction include 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 5-hydroxypentyl (meth) acrylate, Acrylic acid or methacrylic such as 6-hydroxyhexyl (meth) acrylate, 7-hydroxyheptyl (meth) acrylate, 8-hydroxyoctyl (meth) acrylate, 9-hydroxynonyl (meth) acrylate, 10-hydroxydecyl (meth) acrylate Examples include primary hydroxyalkyl esters having 2 to 10 carbon atoms of the acid.

Of these, 2-hydroxyethyl (meth) acrylate, 4 from the viewpoint of scratch resistance
-Hydroxybutyl (meth) acrylate can be mentioned as a preferable thing.

  In the present specification, “(meth) acrylate” means “acrylate or methacrylate”. “(Meth) acrylic acid” means “acrylic acid or methacrylic acid”. “(Meth) acryloyl” means “acryloyl or methacryloyl”. “(Meth) acrylamide” means “acrylamide or methacrylamide”.

Examples of the acid anhydride of dicarboxylic acid include acid anhydrides of dicarboxylic acids such as hexahydrophthalic acid, succinic acid, pimelic acid, maleic acid, and fumaric acid.
These acid anhydrides of dicarboxylic acids can be used alone or in combination of two or more.

  Of these, succinic anhydride and hexahydrophthalic anhydride can be suitably used from the viewpoint of excellent scratch resistance, stain resistance and the like.

  The addition reaction between the hydroxyl group-containing acrylic monomer and the acid anhydride of dicarboxylic acid can be synthesized by a half esterification reaction.

  The optimum temperature for the half esterification reaction varies mainly depending on the melting point of the acid anhydride of the dicarboxylic acid used. For example, when hexahydrophthalic anhydride is used as the acid anhydride, the temperature is about 100 to 180 ° C. In the half esterification reaction, a catalyst can be used as necessary.

  In the above addition reaction, a desired adduct can be obtained by reacting a hydroxyl group-containing acrylic monomer and an acid anhydride of dicarboxylic acid in an equimolar amount.

A monoepoxy compound is a compound having one epoxy group in one molecule, for example,
A monoglycidyl ether compound, a monoglycidyl ester compound, etc. can be mentioned.
Examples of the monoglycidyl ether compound include methyl glycidyl ether, butyl glycidyl ether, 2-ethylhexyl glycidyl ether, sec-butylphenyl glycidyl ether, 2-methyloctyl glycidyl ether, octadecyl glycidyl ether, phenyl glycidyl ether, tolyl glycidyl ether, octyl Examples thereof include phenyl glycidyl ether.

Examples of monoglycidyl ester compounds include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, 2-ethylhexylic acid, neodecanoic acid, capric acid, undecanoic acid, lauric acid, tridecanoic acid And glycidyl ester compounds of monovalent carboxylic acids such as myristic acid, palmitic acid, isostearic acid, stearic acid, 12-hydroxystearic acid, benzoic acid and toluic acid.
Among the above monoepoxy compounds, 2-ethylhexyl glycidyl ether and neodecanoic acid glycidyl ester compounds can be preferably used from the viewpoints of scratch resistance, finish, and the like.

  The addition reaction of a hydroxyl group-containing acrylic monomer and an acid anhydride of a dicarboxylic acid and a monoepoxy compound involves the addition of a carboxyl group of the addition group of a hydroxyl group-containing acrylic monomer and an acid anhydride of a dicarboxylic acid and an epoxy group of the monoepoxy compound. It can be easily carried out by reacting.

  The above addition reaction is carried out by mixing an adduct of a hydroxyl group-containing acrylic monomer and an acid anhydride of a dicarboxylic acid and a monoepoxy compound and reacting at a temperature of about 100 to 150 ° C. for about 1 to 10 hours. it can. If necessary, an organic solvent can be further added.

Moreover, in the said addition reaction, a catalyst can be used as needed. Specifically, as an effective catalyst for a crosslinking reaction between a carboxyl group and an epoxy group, 4 such as tetraethylammonium bromide, tetrabutylammonium bromide, tetraethylammonium chloride, tetrabutylphosphonium bromide, triphenylbenzylphosphonium chloride, etc. Class salt catalysts; amines such as triethylamine and tributylamine can be exemplified. Of these, quaternary salt catalysts can be preferably used.
In the reaction of an adduct of a hydroxyl group-containing acrylic monomer and a dicarboxylic acid anhydride with a monoepoxy compound, the reaction ratio is determined between the carboxyl group and the monocarboxylic acid in the adduct of the hydroxyl group-containing acrylic monomer and the dicarboxylic acid anhydride. A desired adduct can be obtained by reacting the epoxy group in the epoxy compound at an equimolar ratio.

  In an actual synthesis reaction, since it takes a reaction time to be equimolar, it is preferable to slightly add an adduct of a hydroxyl group-containing acrylic monomer and an acid anhydride.

  Specifically, the reaction is preferably carried out at a molar ratio (addition of hydroxyl group-containing acrylic monomer and acid anhydride of dicarboxylic acid / monoepoxy compound) of 1/1 to 1.2 / 1.

  From the viewpoint of production efficiency of the acrylic resin (A), the reaction between the adduct of the hydroxyl group-containing acrylic monomer and the acid anhydride of dicarboxylic acid and the monoepoxy compound is performed simultaneously with the copolymerization reaction of the acrylic resin (A). You can also.

  Specifically, for example, a monoepoxy compound is preliminarily charged in a reaction vessel together with a solvent to be added appropriately, and after raising the temperature to a predetermined copolymerization reaction temperature, a hydroxyl group-containing acrylic monomer and an acid anhydride of a dicarboxylic acid, In the adduct of a copolymerization reaction and an acid anhydride of a hydroxyl group-containing acrylic monomer and a dicarboxylic acid by adding dropwise a mixture of the copolymerized other unsaturated monomer (b) and a polymerization initiator. The addition reaction between the carboxyl group and the epoxy group in the monoepoxy compound can be carried out simultaneously.

In the hydroxyl group-containing (meth) acrylic acid ester (a) represented by the above formula (I), the alkylene group R ₂ has 1 to 10 carbon atoms, and 2 from the viewpoint of scratch resistance and acid resistance of the coating film. It is preferable that it is -6, and it is more preferable that it is 2-4. R ₃ is preferably a group having a cyclohexyl ring represented by the above formula (II) from the viewpoint of scratch resistance and stain resistance. In addition, when R ₃ is an alkylene group, the number of carbon atoms is 1 to 3, and it is preferably 2 to 3 and more preferably 3 from the viewpoint of scratch resistance and contamination resistance.

When R ₄ is an acyloxy group represented by R ₅ COO— (R ₅ is an arbitrary alkyl group, phenyl group or tolyl group), the alkyl group represented by R ₅ is from the viewpoint of scratch resistance and finish. And preferably a neodecane group.

When R ₄ is a group represented by R ₆ O— (R ₆ is an arbitrary alkyl group, phenyl group or tolyl group), the alkyl group represented by R ₆ is, from the viewpoint of scratch resistance and finish, A 2-ethylhexyl group is preferred.

The molecular weight of the hydroxyl group-containing (meth) acrylic acid ester (a) is preferably about 300 to 700, more preferably about 400 to 600, from the viewpoint of finish.
The hydroxyl group-containing (meth) acrylic acid ester (a) can be used alone or in combination of two or more.
Other unsaturated monomers copolymerizable (b)
The unsaturated monomer (b) is another copolymerizable unsaturated monomer other than the hydroxyl group-containing (meth) acrylic acid ester (a), specifically, one polymerizable unsaturated bond per molecule. It is a compound which has this. Specific examples of the unsaturated monomer (b) are listed in the following (1) to (9).

(1) Hydroxyl group-containing (meth) acrylic acid ester other than hydroxyl group-containing (meth) acrylic acid ester (a) Hydroxyl group and unsaturated bond in each molecule other than hydroxyl group-containing (meth) acrylic acid ester (a) A compound having one.

  Specifically, monoesterified products of acrylic acid or methacrylic acid and a dihydric alcohol having 2 to 10 carbon atoms are suitable. For example, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate etc. can be mentioned.

  In addition, as a monoesterified product of the polyhydric alcohol and acrylic acid or methacrylic acid, a compound obtained by ring-opening polymerization of ε-caprolactone to a hydroxyl group-containing (meth) acrylic ester, for example, “Placcel FA-1”, “Plaxel FA-2”, “Plaxel FA-3”, “Plaxel FA-4”, “Plaxel FA-5”, “Plaxel FM-1”, “Plaxel FM-2”, “Plaxel FM-3”, “ Plaxel FM-4 "," Placcel FM-5 "(all of which are manufactured by Daicel Chemical Industries, Ltd., trade names) and the like.

  Among the above, the hydroxyl group-containing (meth) acrylic acid ester (b-1) having a hydroxyalkyl group having 4 or more carbon atoms can be suitably used from the viewpoint of improving the scratch resistance of the coating film. By using (b-1) as a constituent component, it is possible to increase the cross-linking density of the resulting coating film, so that the effect of improving the scratch resistance of the coating film can be obtained. When (b-1) is used as a constituent component, the blending ratio is preferably 3 to 50% by mass, particularly 10 to 40% by mass based on the total amount of (a) and (b). .

  Examples of the hydroxyl group-containing (meth) acrylic acid ester having a hydroxyalkyl group having 4 or more carbon atoms include monoesterified products of acrylic acid or methacrylic acid and dihydric alcohols having 4 to 10 carbon atoms, acrylic acid or methacrylic acid. And a compound obtained by ring-opening polymerization of ε-caprolactone to a monoesterified product of a dihydric alcohol having 2 to 10 carbon atoms.

Specific examples of the monoesterified product of acrylic acid or methacrylic acid and a dihydric alcohol having 4 to 10 carbon atoms include 4-hydroxybutyl (meth) acrylate among those described above.

  Specific examples of the compound obtained by ring-opening polymerization of ε-caprolactone to a monoesterified product of acrylic acid or methacrylic acid and a dihydric alcohol having 2 to 10 carbon atoms include “Placcel FA-2”, “ Plaxel FM-3 "(all of which are trade names, manufactured by Daicel Chemical Industries, Ltd.).

(2) Acid group-containing monomer The acid group-containing monomer is a compound having one acid group and one polymerizable unsaturated bond in one molecule. Examples of the monomer include carboxyl group-containing monomers such as (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid and maleic anhydride; sulfonic acid group-containing monomers such as vinyl sulfonic acid and sulfoethyl (meth) acrylate; 2 Acidic phosphoric acid such as-(meth) acryloyloxyethyl acid phosphate, 2- (meth) acryloyloxypropyl acid phosphate, 2- (meth) acryloyloxy-3-chloropropyl acid phosphate, 2-methacryloyloxyethylphenyl phosphate Examples include ester monomers.
Further, an adduct of a hydroxyl group-containing acrylic monomer and an acid anhydride of dicarboxylic acid, which is an intermediate product in the synthesis of the hydroxyl group-containing (meth) acrylic acid ester (a), can also be used as the acid group-containing monomer.

  The acid group-containing monomer can also act as an internal catalyst when the acrylic resin (A) undergoes a crosslinking reaction with the crosslinking agent.

(3) Monoesterified product of acrylic acid or methacrylic acid and C1-C20 monohydric alcohol Specifically, methyl (meth) acrylate, ethyl acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n -Butyl (meth) acrylate, iso-butyl (meth) acrylate, tert-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, isomyristyl (meth) acrylate, isostearyl acrylate (Osaka Organic) Chemical Industry, trade name), cyclohexyl (meth) acrylate, lauryl (meth) acrylate, isobornyl (meth) acrylate, tricyclodecanyl (meth) acrylate, adamantyl (meth) acrylate, 3,5-dimethyl Adamantyl (meth) acrylate, 3-tetracyclododecyl methacrylate, tridecyl (meth) acrylate, stearyl (meth) acrylate, 4-methylcyclohexylmethyl (meth) acrylate, 4-ethylcyclohexylmethyl (meth) acrylate, 4-methoxycyclohexyl Examples thereof include methyl (meth) acrylate, tert-butylcyclohexyl (meth) acrylate, cyclooctyl (meth) acrylate, cyclododecyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, and the like.

  Among the above, unsaturated monomers having a bridged alicyclic hydrocarbon group having 10 to 20 carbon atoms and / or unsaturated monomers having an alicyclic hydrocarbon group having 3 to 12 carbon atoms (b-2- 1) can be suitably used from the viewpoint of improving the stain resistance of the coating film. By using the monomer (b-2-1) as a constituent component, the Tg of the resulting resin is increased and the polarity is decreased. Therefore, the finish is improved by smoothing the surface, and the water resistance and stain resistance are improved. The effect of can be obtained. Typical examples of the bridged alicyclic hydrocarbon group having 10 to 20 carbon atoms include isobornyl group, tricyclodecanyl group and adamantyl group.

  Specific examples of the unsaturated monomer having a bridged alicyclic hydrocarbon group having 10 to 20 carbon atoms include, for example, isobornyl (meth) acrylate, tricyclodecanyl (meth) acrylate, adamantyl ( Examples include meth) acrylate, 3,5-dimethyladamantyl (meth) acrylate, and 3-tetracyclododecyl methacrylate.

  Specific examples of the unsaturated monomer having an alicyclic hydrocarbon group having 3 to 12 carbon atoms include, for example, cyclohexyl (meth) acrylate, 4-methylcyclohexylmethyl (meth) acrylate, 4-ethyl among those described above. Examples include cyclohexylmethyl (meth) acrylate, 4-methoxycyclohexylmethyl (meth) acrylate, tert-butylcyclohexyl (meth) acrylate, cyclooctyl (meth) acrylate, cyclododecyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, and the like. be able to.

  Moreover, among the above, the unsaturated monomer (b-2-2) which has a C8 or more hydrocarbon group which has a branched structure can be used conveniently from a viewpoint of improving the abrasion resistance of a coating film. . By using the monomer (b-2-2) as a constituent component, the Tg and polarity of the resulting resin are reduced, so that the improvement in scratch resistance of the coating film by imparting flexibility and the finish by smoothing the surface. An improvement effect can be obtained. In addition, since it has a branched structure, a decrease in the Tg of the coating film can be suppressed as compared with a case where a unsaturated monomer having a linear hydrocarbon group having 8 or more carbon atoms is used as a constituent component. Therefore, it is advantageous from the viewpoint of improving acid resistance.

  Specific examples of the unsaturated monomer having a branched hydrocarbon structure having 8 or more carbon atoms include, for example, 2-ethylhexyl acrylate, isooctyl (meth) acrylate, isomyristyl (meth) acrylate, Examples include stearyl acrylate (trade name, manufactured by Osaka Organic Chemical Industry Co., Ltd.).

  When the monomer (b-2-2) is used as a constituent component, the blending ratio is 3 to 50% by mass, particularly 10 to 40% by mass based on the total amount of (a) and (b). Is preferred.

(4) alkoxysilyl group-containing unsaturated monomer For example, vinyltrimethoxysilane, vinyltriethoxysilane, acryloxyethyltrimethoxysilane, methacryloxyethyltrimethoxysilane, acryloxypropyltrimethoxysilane, methacryloxypropyltrimethoxysilane, Examples thereof include acryloxypropyltriethoxysilane, methacryloxypropyltriethoxysilane, and vinyltris (β-methoxyethoxy) silane. Among these, preferable alkoxysilane group-containing unsaturated monomers include vinyltrimethoxysilane, γ-acryloxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, and the like.

By using an alkoxysilyl group-containing unsaturated monomer as a constituent component, in addition to the crosslinking bond between a hydroxyl group and an isocyanate group, a condensation reaction between alkoxysilyl groups and a crosslinking bond due to a reaction between an alkoxysilyl group and a hydroxyl group can be generated. . Thereby, since the crosslinking density of the obtained coating film improves, the effect of an improvement in acid resistance and stain resistance can be obtained.
When the alkoxysilyl group-containing unsaturated monomer is used as a constituent component, the blending ratio is 3 to 50% by mass, particularly 5 to 35% by mass based on the total amount of (a) and (b). preferable.

(5) Aromatic vinyl monomer Specific examples include styrene, α-methylstyrene, vinyltoluene and the like.

  By using an aromatic vinyl monomer as a constituent, the Tg of the resulting resin is increased, and a hydrophobic coating film with a high refractive index can be obtained. The effect of improving water resistance and acid resistance can be obtained.

  When an aromatic vinyl monomer is used as a constituent component, the blending ratio is preferably in the range of 3 to 50% by mass, particularly 5 to 40% by mass based on the total amount of (a) and (b). .

(6) Polymerizable unsaturated bond-containing amide compounds For example, acrylic acid amide, methacrylic acid amide, dimethylacrylamide, N, N-dimethylpropylacrylamide, N-butoxymethylacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, And diacetone acrylamide.

(7) Other vinyl compounds For example, vinyl acetate, vinyl propionate, vinyl chloride, versatic acid vinyl ester and the like can be mentioned. Examples of the versatic acid vinyl ester include “Veoba 9” and “Veoba 10” (trade names, manufactured by Japan Epoxy Resin Co., Ltd.), which are commercially available products.

(8) Polymerizable unsaturated bond-containing nitrile compound Examples include acrylonitrile and methacrylonitrile.

(9) Epoxy group-containing vinyl monomer The epoxy group-containing vinyl monomer is a compound having one epoxy group and one polymerizable unsaturated bond in one molecule. Specific examples thereof include glycidyl acrylate and glycidyl methacrylate. be able to.

  The epoxy group-containing vinyl monomer is an adduct of a hydroxyl group-containing acrylic monomer and an acid anhydride of a dicarboxylic acid in the synthesis of the hydroxyl group-containing acrylic ester (a) from the viewpoint of production efficiency of the acrylic resin (A). When the reaction with the monoepoxy compound is carried out simultaneously with the copolymerization reaction of the acrylic resin (A), it is preferably not used.

  As unsaturated monomer (b), the monomer shown by said (1)-(9) can be used by 1 type, or in combination of 2 or more types.

  The acrylic resin (A) can be synthesized by copolymerizing a monomer mixture comprising the hydroxyl group-containing (meth) acrylic acid ester (a) and another copolymerizable unsaturated monomer (b).

  The copolymerization method for copolymerizing the monomer mixture to obtain the acrylic resin (A) is not particularly limited, and a copolymerization method known per se can be used. Thus, a solution polymerization method in which polymerization is carried out in the presence of a polymerization initiator can be preferably used.

  Examples of the organic solvent used in the solution polymerization method include aromatic solvents such as toluene, xylene, and swazole 1000 (trade name, high-boiling petroleum solvent) manufactured by Cosmo Oil; ethyl acetate, 3-methoxybutyl Ester solvents such as acetate, ethylene glycol ethyl ether acetate, propylene glycol methyl ether acetate; ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, methyl amyl ketone, propyl propionate, butyl propionate, ethoxy ethyl propionate, etc. Can be mentioned.

  These organic solvents can be used alone or in combination of two or more. However, since the acrylic resin used in the coating material has a high hydroxyl value, it has a high boiling point from the viewpoint of the solubility of the resin. It is preferable to use a system solvent. Further, a higher boiling aromatic solvent may be used in combination.

  Examples of the polymerization initiator that can be used in the copolymerization of the acrylic resin (A) include 2,2′-azobisisobutyronitrile, benzoyl peroxide, di-t-butyl peroxide, and di-t-amyl peroxide. , T-butyl peroctoate, 2,2′-azobis (2-methylbutyronitrile) and the like radical polymerization initiators known per se.

  The hydroxyl value of the acrylic resin (A) is 100 to 200 mgKOH / g from the viewpoint of the curability of the coating composition finally obtained and the coating film performance such as scratch resistance and water resistance of the resulting coating film. Preferably, it is about 110-170 mgKOH / g, More preferably, it is about 130-160 mgKOH / g. When the hydroxyl value is less than 100 mgKOH / g, the scratch resistance of the coating film obtained from the coating composition of the present invention may be insufficient. On the other hand, when it exceeds 200 mgKOH / g, the water resistance of the coating film decreases. There is a case.

  The hydroxyl value derived from the hydroxyl group-containing (meth) acrylic acid ester (a) is 15 to 85 mgKOH / g, preferably about 25 to 75 mgKOH / g, more preferably about 30 to 70 mgKOH / g. When the hydroxyl value derived from the hydroxyl group-containing (meth) acrylic acid ester (a) is less than 15 mgKOH / g, the scratch resistance of the coating film obtained from the coating composition of the present invention may be insufficient, while 100 mgKOH If the amount exceeds / g, the acid resistance or water resistance of the coating film may decrease.

  The weight average molecular weight of the acrylic resin (A) is preferably about 2000 to 30000 from the viewpoint of the curability of the finally obtained coating composition and the coating performance such as scratch resistance and water resistance of the resulting coating. More preferably, it is about 3000-20000, and more preferably about 4000-15000.

  In this specification, the weight average molecular weight of the resin is a value measured by gel permeation chromatography (GPC) with reference to standard polystyrene. Measurements in the following production examples and the like are as follows: “HLC8120GPC” (trade name, manufactured by Tosoh Corporation) as a GPC device, “TSKgel G-4000HXL”, “TSKgel G-3000HXL”, “TSKgel G-2500HXL” Using “TSKgel G-2000HXL” (both manufactured by Tosoh Corporation, trade name), mobile phase: tetrahydrofuran, measurement temperature: 40 ° C., flow rate: 1 cc / min, detector: RI It was.

  The glass transition temperature of the acrylic resin (A) is preferably about −40 to 30 ° C., more preferably about −30 to 10 ° C., from the viewpoint of the hardness of the obtained coating film and the smoothness of the coating surface. .

  In this specification, the glass transition temperature is a value measured by DSC (Differential Scanning Calorimeter) at a heating rate of 10 ° C./min based on JISK7121 (Plastic transition temperature measurement method). The measurement in the following production examples, etc., uses “SSC5200” (trade name, manufactured by Seiko Denshi Kogyo Co., Ltd.) as a DSC. I did it.

  The mixing ratio of the hydroxyl group-containing (meth) acrylic acid ester (a) and the other copolymerizable unsaturated monomer (b) is such that the hydroxyl group-containing (meth) acrylic acid ester (a) is 15 with respect to the total monomer amount. It is -80 mass%, Preferably it is about 20-70 mass%, More preferably, it is about 30-65 mass%. The other copolymerizable unsaturated monomer (b) is 20 to 85% by mass, preferably about 30 to 80% by mass, and more preferably about 35 to 70% by mass.

When the amount of the hydroxyl group-containing (meth) acrylic acid ester (a) is less than 15% by mass, the resulting coating film may have insufficient scratch resistance, and when it exceeds 80% by mass, the coating film has an acid resistance. May be insufficient. When the amount of the other unsaturated monomer (b) that can be copolymerized is less than 20% by mass, the resulting coating film may have insufficient acid resistance, and when it exceeds 85% by mass, the resulting coating film is obtained. In some cases, the scratch resistance is insufficient.
Polyisocyanate compound (B)
The polyisocyanate compound (B) is a crosslinking agent of the present coating composition, and is a compound having two or more isocyanate groups in one molecule. Examples of the polyisocyanate compound (B) include those known for polyurethane production, such as aliphatic polyisocyanates, alicyclic polyisocyanates, araliphatic polyisocyanates, aromatic polyisocyanates, and derivatives of these polyisocyanates. be able to.

  Examples of the aliphatic polyisocyanate include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3- Aliphatic diisocyanates such as butylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, 2,6-diisocyanatomethylcaproate, such as lysine ester triisocyanate, 1,4,8- Triisocyanatooctane, 1,6,11-triisocyanatoundecane, 1,8-diisocyanato-4-isocyanatomethyloctane, 1,3,6-triisocyanatohexane, 2 5,7 and aliphatic triisocyanates such as trimethyl-1,8-diisocyanato-5-isocyanatomethyl octane and the like.

  Examples of the alicyclic polyisocyanate include 1,3-cyclopentene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (common name: Isophorone diisocyanate), 4,4'-methylenebis (cyclohexyl isocyanate), methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 1,3-bis (isocyanatomethyl) cyclohexane, 1,4-bis (Isocyanatomethyl) cycloaliphatic diisocyanates such as cyclohexane, norbornane diisocyanate, for example 1,3,5-triisocyanatocyclohexane, 1,3,5-trimethylisocyanate Natocyclohexane, 2- (3-isocyanatopropyl) -2,5-di (isocyanatomethyl) -bicyclo (2.2.1) heptane, 2- (3-isocyanatopropyl) -2,6-di ( Isocyanatomethyl) -bicyclo (2.2.1) heptane, 3- (3-isocyanatopropyl) -2,5-di (isocyanatomethyl) -bicyclo (2.2.1) heptane, 5- (2 -Isocyanatoethyl) -2-isocyanatomethyl-3- (3-isocyanatopropyl) -bicyclo (2.2.1) heptane, 6- (2-isocyanatoethyl) -2-isocyanatomethyl-3- (3-isocyanatopropyl) -bicyclo (2.2.1) heptane, 5- (2-isocyanatoethyl) -2-isocyanatomethyl-2- (3-isocyanatopropyl) -bicyclo (2 2.1) -Heptane, 6- (2-isocyanatoethyl) -2-isocyanatomethyl-2- (3-isocyanatopropyl) -bicyclo (2.2.1) heptane, etc. Can be mentioned.

  Examples of the araliphatic polyisocyanate include 1,3- or 1,4-xylylene diisocyanate or a mixture thereof, ω, ω′-diisocyanato-1,4-diethylbenzene, 1,3- or 1,4-bis ( 1-isocyanato-1-methylethyl) benzene (common name: tetramethylxylylene diisocyanate) or an aromatic aliphatic diisocyanate such as a mixture thereof, for example, an araliphatic triisocyanate such as 1,3,5-triisocyanatomethylbenzene And so on.

  Examples of the aromatic polyisocyanate include m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4′-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 2,4′- or 4,4′-diphenylmethane diisocyanate or a mixture thereof. 2,4- or 2,6-tolylene diisocyanate or mixtures thereof, aromatic diisocyanates such as 4,4′-toluidine diisocyanate, 4,4′-diphenyl ether diisocyanate, for example, triphenylmethane-4,4 ′, 4 Aromatic triisocyanates such as '' '-triisocyanate, 1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene, such as 4,4'-diphenylmethane-2,2', 5 , 5'-Tetraisocyanate And aromatic tetraisocyanates such bets can be mentioned.

  Examples of the polyisocyanate derivative include various derivatives such as dimer, trimer, biuret, allophanate, carbodiimide, uretdione, uretoimine, isocyanurate, and iminooxadiazinedione of the above-described polyisocyanate compound.

  These polyisocyanates can be used alone or in combination of two or more. Among these polyisocyanates, aliphatic diisocyanates, alicyclic diisocyanates and derivatives thereof are preferable from the viewpoint of excellent weather resistance of the cured coating film, and hexamethylene diisocyanate (HMDI), hexamethylene diisocyanate derivatives, isophorone diisocyanate (IPDI). And derivatives of isophorone diisocyanate are more preferred.

  Moreover, the blocked polyisocyanate compound which is the compound which blocked the isocyanate group of the polyisocyanate compound which has a 2 or more free isocyanate group in 1 molecule mentioned above with the blocking agent as a polyisocyanate compound can also be used.

  The blocking agent blocks free isocyanate groups. When the blocked polyisocyanate compound is heated to, for example, 100 ° C. or higher, preferably 130 ° C. or higher, the isocyanate group is regenerated and can easily react with the hydroxyl group. Examples of such blocking agents include phenols such as phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxydiphenyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, and hydroxybenzoic acid methyl; ε-caprolactam, δ-valerolactam, Lactams such as γ-butyrolactam, β-propiolactam; aliphatic alcohols such as methanol, ethanol, propyl alcohol, butyl alcohol, amyl alcohol, lauryl alcohol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono Butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether Ethers such as propylene glycol monomethyl ether and methoxymethanol; benzyl alcohol; glycolic acid; glycolic acid esters such as methyl glycolate, ethyl glycolate, and butyl glycolate; lactic acid esters such as lactic acid, methyl lactate, ethyl lactate, and butyl lactate; Alcohols such as methylol urea, methylol melamine, diacetone alcohol, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate; oximes such as formamide oxime, acetamide oxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, benzophenone oxime, cyclohexane oxime System: Dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, acetylacetone Which active methylene series; mercaptans such as butyl mercaptan, t-butyl mercaptan, hexyl mercaptan, t-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol, methylthiophenol, ethylthiophenol; Acid amides such as amides, acetic acid amides, stearic acid amides, benzamides; imides such as succinic acid imides, phthalic acid imides, maleic acid imides; Amines such as butylamine, dibutylamine and butylphenylamine; imidazo such as imidazole and 2-ethylimidazole Pyrazoles such as 3,5-dimethylpyrazole; Ureas such as urea, thiourea, ethylene urea, ethylene thiourea and diphenyl urea; Carbamate esters such as phenyl N-phenylcarbamate; Ethyleneimine and propyleneimine Examples thereof include blocking agents such as imine series; sulfite series such as sodium bisulfite and potassium bisulfite.

When blocking (reacting the blocking agent), a solvent can be added as necessary. As the solvent used for the blocking reaction, those not reactive to isocyanate groups are preferable. For example, ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate, and solvents such as N-methylpyrrolidone (NMP). Can give.
A polyisocyanate compound (B) can be used individually or in combination of 2 or more types.

  In the coating composition of the present invention, the equivalent ratio (NCO / OH) of the hydroxyl group in the acrylic resin (A) and the isocyanate group in the polyisocyanate compound (B) is excellent in the curability and coating stability of the composition. Therefore, it is preferably about 0.5 to 2.0, and more preferably about 0.8 to 1.5.

The amount of the acrylic resin (A) and the polyisocyanate compound (B) in the coating composition of the present invention is an acrylic resin (A) and a non-volatile component based on the total solid content of the component (A) and the component (B). It is suitable that A) is in the range of 40 to 80% by mass, preferably 45 to 70% by mass, and the polyisocyanate compound (B) is in the range of 20 to 60% by mass, preferably 30 to 55% by mass.
Other Components Known pigments such as color pigments, extender pigments, glitter pigments, and rust preventive pigments can be blended in the coating composition of the present invention as necessary.

  Examples of the coloring pigment include titanium oxide, zinc white, carbon black, cadmium red, molybdenum red, chromium yellow, chromium oxide, Prussian blue, cobalt blue, azo pigment, phthalocyanine pigment, quinacridone pigment, isoindoline pigment, selenium pigment, Examples include perylene pigments. Examples of extender pigments include talc, clay, kaolin, barita, barium sulfate, barium carbonate, calcium carbonate, silica, and alumina white. Examples of the bright pigment include aluminum powder, mica powder, and mica powder coated with titanium oxide.

  Various resins such as an acrylic resin, a polyester resin, an alkyd resin, a silicon resin, and a fluororesin can be added to the coating composition of the present invention as necessary. It is also possible to use a small amount of a crosslinking agent such as a melamine resin or a blocked polyisocyanate compound. Furthermore, if necessary, general paint additives such as a curing catalyst, an ultraviolet absorber, a light stabilizer, an antioxidant, a surface conditioner, and an antifoaming agent can be blended.

  Examples of the curing catalyst include tin octylate, dibutyltin di (2-ethylhexanoate), dioctyltin di (2-ethylhexanoate), dioctyltin diacetate, dibutyltin dilaurate, dibutyltin oxide, and dioctyltin. Examples thereof include oxides, organometallic catalysts such as lead 2-ethylhexanoate, and tertiary amines.

These compounds described above as the curing catalyst may be used alone or as a mixture of two or more. The amount of the curing catalyst varies depending on the type thereof, but is usually 0 to 5 parts by mass, preferably about 0.1 to 4 parts by mass with respect to 100 parts by mass of the total solids of the component (A) and the component (B). .
Known ultraviolet absorbers can be used, and examples thereof include ultraviolet absorbers such as benzotriazole absorbers, triazine absorbers, salicylic acid derivative absorbers, and benzophenone absorbers. By blending the ultraviolet absorber, the weather resistance, yellowing resistance and the like of the coating film can be improved.

As content in the coating composition of a ultraviolet absorber, it is about 0-10 mass parts normally with respect to 100 mass parts of resin solid content total measurement. Moreover, it is preferable that content of a ultraviolet absorber is about 0.2-5 mass parts, and it is more preferable that it is about 0.3-2 mass parts.
A conventionally well-known thing can be used as a light stabilizer, For example, a hindered amine light stabilizer can be mention | raise | lifted. By blending a light stabilizer, the weather resistance, yellowing resistance and the like of the coating film can be improved.

  As content in the coating composition of a light stabilizer, it is about 0-10 mass parts normally with respect to 100 mass parts of resin solid content total measurement. Further, the content of the light stabilizer is preferably about 0.2 to 5 parts by mass, and more preferably about 0.3 to 2 parts by mass.

Although the form of the coating composition of the present invention is not particularly limited, it is usually used as an organic solvent type coating composition. As the organic solvent used in this case, various organic solvents for paints such as aromatic or aliphatic hydrocarbon solvents; alcohol solvents; ester solvents; ketone solvents; ether solvents and the like can be used. As the organic solvent to be used, those used at the preparation of the component (A), the component (B) and the like may be used as they are, or may be added as appropriate.
Preparation method of coating composition The coating composition of the present invention comprises an acrylic resin (A), a polyisocyanate compound (B), and a curing catalyst, a pigment, various resins, an ultraviolet absorber, a light stabilizer, used as necessary, An organic solvent or the like can be prepared by mixing by a known method.

  When the isocyanate group of the polyisocyanate compound which is the component (B) is not blocked, the coating composition of the present invention has an acrylic resin (A) and a polyisocyanate compound (B) because of storage stability. Are two-component paints separated from each other, and it is preferable to mix the two before use.

  The solid content concentration of the coating composition of the present invention is preferably about 30 to 70% by mass, and more preferably about 40 to 60% by mass.

Coating method The coating composition of the present invention can be suitably used in various coating methods described below.

Examples of the object to be coated include bodies such as automobiles and motorcycles, or parts thereof. Further, cold rolled steel sheets, galvanized steel sheets, zinc alloy plated steel sheets, stainless steel sheets, tin plated steel sheets, etc., metal base materials such as aluminum plates and aluminum alloy plates; various plastic base materials, etc. May be.

  Moreover, as a to-be-coated article, the metal surface of the said vehicle body, components, and a metal base material may be subjected to chemical conversion treatment such as phosphate treatment, chromate treatment, and complex oxide treatment. Furthermore, as the object to be coated, an undercoat film and / or an intermediate coat film such as various electrodeposition paints may be formed on the vehicle body, metal base material, or the like.

Coating and curing method The coating method of the coating composition of the present invention is not particularly limited. For example, a wet coating film is formed by a coating method such as air spray coating, airless spray coating, rotary atomization coating, or curtain coat coating. be able to. In air spray coating, airless spray coating, and rotary atomization coating, electrostatic application may be performed as necessary. Of these, air spray coating and rotary atomization coating are particularly preferred. In general, the coating film thickness is preferably about 10 to 50 μm as the cured film thickness.

  In the case of air spray coating, airless spray coating, and rotary atomization coating, the viscosity of the coating is adjusted to a viscosity range suitable for the coating, usually Ford Cup #No. In a 4-viscosity meter, it is preferable to adjust appropriately using a solvent such as an organic solvent so that the viscosity is within a range of about 15 to 60 seconds at 20 ° C.

  The wet coating film is cured by heating. Heating can be performed by a known heating means. For example, a drying furnace such as a hot air furnace, an electric furnace, or an infrared induction heating furnace can be applied.

  The heating temperature is usually about 100 to 180 ° C, preferably about 120 to 160 ° C. The heating time is usually in the range of about 5 to 60 minutes.

Multilayer coating film forming method According to the coating composition of the present invention, a coating film having excellent coating performance such as scratch resistance, acid resistance, and finished appearance can be formed. In the coating film forming method to be used, it is preferably used as a clear coating composition for forming a top clear coat.

  Accordingly, the multilayer coating film forming method of the present invention is a method of forming a multilayer coating film by applying at least one colored base coat paint and at least one clear coat paint, and comprises the uppermost clear coat. The paint composition described above is used as the paint.

  As an object to which the multilayer coating film forming method of the present invention is applied, an automobile body and its parts are particularly preferable.

  More specifically, examples of the method for forming a multilayer coating film include a method of using the coating composition of the present invention for forming a top clear coat in the multilayer coating film forming method of the following methods a to c. Can do.

  Method a: A method of forming a top coat multilayer coating film in which a colored base coat and a top clear coat are sequentially formed on an object to be coated.

  Method b: A method of forming a top coat multilayer coating film in which a colored base coat, a clear coat, and a top clear coat are sequentially formed on an object to be coated.

  Method c: A three-coating multi-layer coating film forming method in which a first colored base coat, a second colored base coat, and a top clear coat are sequentially formed on an object to be coated.

  Each top coat film forming step of these methods a, b and c will be described in detail.

  In each method, as a method for applying the colored base coating composition and the clear coating composition, a coating method such as airless spray, air spray, or rotary atomization coating can be employed. In these coating methods, electrostatic application may be performed as necessary.

In the method a, as the coating composition for forming the colored base coat, a known colored coating composition can be used.
As the colored base coating composition, it is preferable to use a coating composition that is used when painting an automobile body or the like.

  The colored base coating composition is an organic solvent-type or aqueous coating composition containing a base resin, a crosslinking agent, a colored pigment, a metallic pigment, a light interference pigment, an extender pigment and the like.

  As the base resin, for example, at least one of acrylic resin, vinyl resin, polyester resin, alkyd resin, urethane resin, and the like can be used. The base resin has, for example, a crosslinkable functional group such as a hydroxyl group, an epoxy group, a carboxyl group, or an alkoxysilyl group. As the crosslinking agent, for example, at least one of alkyl etherified melamine resin, urea resin, guanamine resin, polyisocyanate compound, blocked polyisocyanate compound, epoxy compound, carboxyl group-containing compound and the like can be used. The base resin and the crosslinking agent are preferably used in a proportion of 50 to 90% by weight of the base resin and 50 to 10% by weight of the crosslinking agent based on the total amount of both components.

  In method a, the colored base coating composition is applied to an object to be coated so that the cured film thickness is about 10 to 50 μm. The coated base coating composition is cured by heating at about 100-180 ° C., preferably about 120-160 ° C. for about 10-40 minutes, or left at room temperature for several minutes without curing after coating, or about 40 Preheat at ~ 100 ° C for about 1-20 minutes.

  Next, as a paint for forming a top clear coat, the clear paint composition of the present invention is applied so that the film thickness is about 10 to 70 μm in terms of the cured film thickness, and is heated to cure the multilayer coating film Can be formed. Heating is about 100 to 180 ° C., preferably about 120 to 160 ° C., and preferably about 10 to 40 minutes.

  In the above-mentioned two-coat system, the base paint composition is applied and the clear paint composition is applied without being heated and cured, and when these two-layer coating films are cured simultaneously, the two-coat one-bake system is used. When the composition is applied and cured by heating, and then the clear coating composition is applied and the clear coating film is cured, the 2-coat 2-bake method is used.

  As the colored base coating composition in method b, the same colored base coating composition as described in the section of method a can be used. Further, the first clear paint composition for forming the clear coat may be a paint for forming a transparent coating film, for example, a paint composition that does not contain most or all of the pigment in the above-mentioned known colored base paint composition. Things can be used. And the coating composition of this invention is used as a 2nd clear coating composition which forms a top clear coat. In addition, as the first clear paint composition, the clear coat and the top clear coat formed from the clear paint composition of the present invention may be formed using the clear paint composition of the present invention.

  In method b, in the same manner as in method a, the colored base coating composition is applied to the object to be coated and heat-cured, or left to stand at room temperature for several minutes or preheated without being cured, and then the colored base coating composition is coated. The first clear coating composition is applied onto the film so that the film thickness is about 10 to 50 μm as a cured film thickness, and is about 100 to 180 ° C., preferably about 120 to 160 ° C., for about 10 to 40 minutes. Heat to cure or leave or preheat at room temperature for several minutes without curing.

  Next, as the second clear paint composition, the paint composition of the present invention is applied so that the film thickness is about 10 to 50 μm as a cured film thickness, and heated to form a cured multilayer coating film. can do. The heating conditions are the same as in method a.

  Without applying and curing the base coating composition, the first clear coating composition is applied, the second clear coating composition is applied without curing, and the three-layer coating film is simultaneously cured. In this case, the 3 coat 1 bake method is used. When the first clear paint composition is applied without applying the base paint composition and heat-curing, these coating films are simultaneously heat-cured, and the second clear paint composition is applied and cured. Is a 3-coat 2-bake system. In addition, when a base coating composition is applied and heated and cured, a first clear coating composition is applied, this is cured, a second clear coating composition is applied, and this is cured, a 3 coat 3 bake system It is.

  In the method c, as the first colored base coating composition, the same colored base coating composition as described in the method a can be used.

  In the method c, in the same manner as in the method a, the first colored base coating composition is applied to the object to be coated and heat-cured, or left to stand for several minutes at room temperature without being cured or pre-heated. On the colored base coating film, the second colored base coating composition is applied so that the film thickness is about 10 to 50 μm as a cured film thickness, and about 100 to 180 ° C., preferably about 120 to 160 ° C. Heat for 10 to 40 minutes to cure, or leave or preheat at room temperature for several minutes without curing.

  Next, as a coating composition for forming the top clear coat, the coating composition of the present invention is applied so that the film thickness is about 10 to 50 μm in terms of the cured film thickness, and heated to form a cured multilayer coating. A film can be formed. The heating conditions are the same as in method a.

  Without applying the first base coating composition and curing by heating, the second base coating composition is applied, and without being cured, the clear coating composition is applied, and these three-layer coating films are simultaneously cured. In this case, the 3-coat 1-bake method is used. In addition, when the first base coating composition is applied and heated and cured, the second base coating composition is applied, the clear coating composition is applied without curing, and these coating films are simultaneously cured. This is a 3-coat 2-bake method. When the first base coating composition is applied and heat-cured, the second base coating composition is applied, this is cured, and the clear coating composition is applied and cured. It is.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the following examples. In the following, “part” and “%” are both based on mass, and the film thickness of the coating film is based on the cured coating film.
Production Examples 1-6 of Adduct (a-1) of Hydroxyl-Containing Acrylic Monomer and Dicarboxylic Acid Anhydride
A four-necked flask equipped with a stirrer, a thermometer, a cooling tube, and an air inlet was charged with an acid anhydride in an amount (part by mass) shown in Table 1 below, and the temperature was raised to 100 ° C. in an air atmosphere. After reaching 100 ° C., 0.3 part of methoxyphenol was added, and an amount (parts by mass) of a hydroxyl group-containing acrylic monomer shown in Table 1 below was dropped over 2 hours. Thereafter, by aging for 2 hours, No. of the adduct (a-1) of the hydroxyl group-containing acrylic monomer and the acid anhydride of dicarboxylic acid was obtained. 1-6 were obtained. The special values of the obtained adducts (a-1) are shown together in Table 1 below.

Production and production examples 7-18 of hydroxyl group-containing (meth) acrylic acid ester (a)
A four-necked flask equipped with a stirrer, a thermometer, a cooling tube, and an air inlet was charged with an amount (part by mass) of a monoepoxy compound shown in Table 2 below, and the temperature was raised to 130 ° C. in an air atmosphere. After reaching 130 ° C., 0.5 part of tetrabutylammonium bromide was added, and the amount (mass part) of the adduct (a-1) obtained in the above production example shown in Table 2 below was added dropwise over 5 hours. Thereafter, by aging for 4 hours, the hydroxyl group-containing (meth) acrylic acid ester (a) No. 1-12 were obtained. The special values of the respective hydroxyl group-containing (meth) acrylic acid esters (a) obtained are shown together in Table 2 below. The epoxy group content of each hydroxyl group-containing (meth) acrylic acid ester (a) is 0 mmol / g.

  In Table 2, (Note 1) and (Note 2) are as follows.

Cardura E-10P (Note 1): Trade name, manufactured by Japan Epoxy Resin, Neodecanoic acid monoglycidyl ester Denacol EX-121 (Note 2): Trade name, manufactured by Nagase ChemteX Corporation, 2-ethylhexyl glycidyl ether

Production Examples of Acrylic Resin (A) Production Examples 19 to 41
A four-necked flask equipped with a stirrer, thermometer, condenser, and nitrogen gas inlet was charged with 310 parts of Swazol 1000 (trade name, manufactured by Cosmo Oil Co., Ltd., hydrocarbon solvent) and heated to 125 ° C under a nitrogen atmosphere. The mixture of the monomer and the polymerization initiator in the amount (parts by mass) shown in Table 3 below was added dropwise over 4 hours. Next, after aging for 30 minutes while flowing nitrogen gas at 125 ° C., a mixture of 320 parts of SWAZOL 1000 and 5 parts of 2,2′-azobisisobutyronitrile was added dropwise over 1 hour, and then for 1 hour. By aging, each acrylic resin (A) No. 1 to 23 solutions were obtained. Each of the obtained acrylic resins (A) No. The special values of the solutions 1 to 23 are shown together in Table 3 below.

Production Examples 1-20 and Comparative Examples 1-4 of Coating Composition
Using the acrylic resin (A) obtained in Production Examples 19 to 41 and the raw materials described in Table 4 below, each paint composition was stirred and mixed using a disper in the formulation shown in Table 4 below. Items 1 to 24 were obtained. In addition, the mixing | blending of each coating composition shown in Table 4 is solid content mass ratio of each component.

In Table 4, (* 1) to (* 4) have the following meanings.
(* 1) N-3300: manufactured by Sumika Bayer Urethane Co., Ltd., hexamethylene diisocyanate, solid content 100%, NCO content 21.8%.
(* 2) UV1164: UV absorber manufactured by Ciba Geigy.
(* 3) HALS292: Ciba Geigy, light stabilizer.
(* 4) BYK-300: trade name, manufactured by Big Chemie, surface conditioner Each coating composition 1-24 obtained in the above Examples 1-20 and Comparative Examples 1-4 was added with butyl acetate to Cup #No. 4 was adjusted to a viscosity of 25 seconds at 20 ° C.

Preparation of test plate Using each of the coating compositions 1 to 24 having the viscosity adjusted, test plates were prepared as follows.

Electron GT-10 (trade name, thermosetting epoxy resin-based cationic electrodeposition paint, manufactured by Kansai Paint Co., Ltd.) has a thickness of 20 μm on a 0.8 mm-thick dull steel sheet subjected to zinc phosphate conversion treatment. Electrodeposited as described above, cured by heating at 170 ° C. for 30 minutes, and amylak TP-65-2 (trade name, polyester / melamine resin-based automotive intermediate coating) manufactured by Kansai Paint Co., Ltd. on the electrodeposited surface. The film was air spray coated to a film thickness of 35 μm and heated at 140 ° C. for 30 minutes to be cured. A water-based metallic base coat WBC713T # 202 (manufactured by Kansai Paint Co., Ltd., acrylic / melamine resin-based automotive top coat paint, black paint color) is applied on the intermediate coating surface to a film thickness of 15 μm and left at room temperature for 5 minutes. Then, after preheating at 80 ° C. for 10 minutes, each coating composition 1 to 24 was applied on the uncured base coat coating surface to a film thickness of 35 μm, and allowed to stand at room temperature for 10 minutes. A test plate was obtained by heating at 140 ° C. for 20 minutes to cure both coating films together. Each of the obtained test plates was allowed to stand at room temperature for 7 days and then subjected to the following coating film performance test.
Performance test results Scratch resistance: 20 degree specular reflectivity of test plate after car washer was washed 15 times in car wash machine under 20 ° C condition with test plate affixed to roof with water resistant tape made by Nichiban (20 ° gloss value) was measured and evaluated by the gloss retention (%) relative to the 20 ° gloss value before the test. The higher the gloss retention, the better the scratch resistance. As the car wash machine, “PO20 FWRC” manufactured by Yasui Industry Co., Ltd. was used.

  Acid resistance: 0.4 cc of 40% sulfuric acid was dropped on the coating film of each test plate, heated for 15 minutes on a hot plate heated to 60 ° C., and then the test plate was washed with water. The etching depth (μm) of the sulfuric acid dropping portion was cut off using a surface roughness meter (manufactured by Tokyo Seimitsu Co., Ltd., surface roughness profile measuring machine “Surfcom 570A”) with a cutoff of 0.8 mm (scanning speed: 0.3 mm / sec, The acid resistance was evaluated by measurement under the condition of 5000 times magnification. The smaller the etching depth, the better the acid resistance.

  Contamination resistance: Each test plate was tested for 600 hours under the conditions of JIS K5400 in a sunshine weatherometer (manufactured by Suga Test Instruments Co., Ltd., accelerated rust resistance tester). The substance was adhered to the nell and rubbed lightly on the surface of each test plate. This was left for 24 hours in a constant temperature and humidity chamber at 20 ° C. and 75% RH, and then the coated surface was washed with running water, and the degree of contamination of the coated film was evaluated according to the following criteria based on the lightness difference (ΔL) of the coated plate. The smaller the ΔL value, the better the stain resistance. ΔL was determined by the following equation.

ΔL = (L value before stain resistance test) − (L value after stain resistance test)
The L value was measured using CR400 manufactured by Konica Minolta (tristimulus value direct-reading color meter D65 light source 2 ° visual field diffuse illumination vertical light reception (d / 0)). The L value is a value based on the CIE 1976 L ^* a ^* b ^* color system.

  A: ΔL <0.2, O: 0.2 ≦ ΔL <0.5, OΔ: 0.5 ≦ ΔL <1, Δ: 1 ≦ ΔL <2, X: 2 ≦ ΔL.

  In addition, in the contamination resistance test, ELECRON GT-10 (trade name, manufactured by Kansai Paint Co., Ltd., thermosetting epoxy resin-based cationic battery) was formed on a 0.8 mm-thick dull steel sheet subjected to zinc phosphate conversion treatment. Electrodeposition coating to a film thickness of 20 μm, heated at 170 ° C. for 30 minutes to cure, and then Amirac TP-65-2 (manufactured by Kansai Paint Co., Ltd., trade name, polyester / melamine resin system) An automotive intermediate coating, white coating color) is applied by air spraying to a film thickness of 35 μm and heated and cured at 140 ° C. for 30 minutes as a coating, and each coating composition 1-24 is applied to the coating. A white test plate obtained by coating the film so as to have a film thickness of 35 μm, allowing it to stand at room temperature for 10 minutes, and then curing it by heating at 140 ° C. for 20 minutes was used. Similarly, each test plate was allowed to stand at room temperature for 7 days and then subjected to a stain resistance test.

Finishability (20 ° gloss): The 20-degree specular reflectance (20 ° gloss value) of each test plate was measured using HG-268 (manufactured by Handy Gloss Meter Suga Test Instruments Co., Ltd.).
The performance test results are also shown in Table 4.

Claims (11)

(A) 15 to 80% by mass of a hydroxyl group-containing (meth) acrylic acid ester represented by the following formula (I),

Wherein R ₁ is a hydrogen atom or a methyl group, R ₂ is an alkylene group having 1 to 10 carbon atoms, R ₃ is an alkylene group having 1 to ₃ carbon atoms or a group represented by the following formula (II), R ₄ is an acyloxy group represented by R ₅ COO— (R ₅ is an arbitrary alkyl group, phenyl group or tolyl group) or a group represented by R ₆ O— (R ₆ is an arbitrary alkyl group, phenyl group or tolyl group). Represents.)

And (b) a hydroxyl group value obtained by copolymerizing 20 to 85% by mass of another copolymerizable unsaturated monomer and having a hydroxyl value of 100 to 200 mgKOH / g and represented by the above formula (I) ( The coating composition containing the acrylic resin (A) whose hydroxyl value derived from a meth) acrylic acid ester is 15-85 mgKOH / g, and a polyisocyanate compound (B). The coating composition according to claim 1, wherein R ₂ is a tetramethylene group represented by (—CH ₂ —) ₄ . The coating composition according to claim 1 or 2, wherein R ₃ is a group represented by the formula (II). (B) As another copolymerizable unsaturated monomer, a hydroxyl group-containing unsaturated monomer having a hydroxyalkyl group having 4 or more carbon atoms is contained as a copolymerization component. Paint composition. (B) The unsaturated monomer which has a C3-C12 alicyclic hydrocarbon group as another copolymerizable unsaturated monomer is contained in any one of Claims 1-4 as a copolymerization component. The coating composition as described. (B) As another copolymerizable unsaturated monomer, an unsaturated monomer having a bridged alicyclic hydrocarbon group having 10 to 20 carbon atoms is contained as a copolymerization component. The coating composition according to Item. (B) The unsaturated monomer which has a C8 or more hydrocarbon group which has a branched structure as another copolymerizable unsaturated monomer is contained in any one of Claims 1-6 as a copolymerization component. The coating composition as described. (B) The coating composition of any one of Claims 1-7 which contains an alkoxy silyl group containing unsaturated monomer as a copolymerization component as another copolymerizable unsaturated monomer. The coating composition according to any one of claims 1 to 8, comprising an aliphatic diisocyanate and a derivative thereof as the polyisocyanate compound (B). Furthermore, the coating composition of any one of Claims 1-9 containing a coloring pigment. A method for forming a multi-layer coating film by coating at least one layer of a colored base coat paint and at least one layer of a clear coat paint on an object to be coated, the top layer being a clear coat paint. A method for forming a multilayer coating film, comprising coating the coating composition according to any one of the above.