JPH08225768A - Thermosetting coating composition - Google Patents

Abstract

PURPOSE: To obtain the composition containing two kinds of specific acrylic copolymers, excellent in storage stability, low temperature curability, solvent resistance, abrasion resistance, weatherability and decorativity, and useful for top clear coats, etc. CONSTITUTION: This composition comprises (A) an acrylic monomer containing 0.5-40wt.% of monomer units wherein 50-98% (preferably 80-95%) of acid anhydride groups are half ester groups, (B) an epoxy group-containing acrylic polymer, and, if necessary, (C) a hydroxyl group-having acrylic polymer. The component A is obtained by polymerizing a polymerizable monomer mixture containing an acid anhydride group-having monomer which is converted into an α,β- dicarboxylic acid monoester, or by polymerizing a polymerizable monomer mixture containing a monomer having a dibasic acid anhydride group and subsequently half-esterifying the acid anhydride groups with an alkanol.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermosetting coating composition which is particularly useful for top clear coat paints for automobiles and the like, which are required to have high aesthetic properties and coating film performance.

[0002]

2. Description of the Related Art Acrylic-melamine resins are often used as top clear coat paints for automobiles because they have excellent weather resistance and cosmetic properties.
However, the acrylic-melamine-based resin has low acid resistance because the melamine resin is used as a curing agent, and when this is applied to a paint, rain stains occur on the coating film due to acid rain,
It has the drawback of a poor appearance.

In order to solve this problem, a new curing system in place of melamine is required, and a curing system utilizing a crosslinking reaction between an acid group and an epoxy group has been actively studied.

For example, Japanese Patent Laid-Open No. 63-84674 discloses a low-molecular weight polyepoxide, a low-molecular weight hydroxyl group-containing polyfunctional substance, an acid anhydride as a coating composition excellent in adhesiveness, gloss and image clarity. A high solid content curable composition containing a cross-linking agent consisting of and a curing catalyst has been proposed. Further, Japanese Patent Laid-Open No. 1-196553 discloses a coating composition excellent in acid resistance, solvent resistance, water resistance, and appearance of a coating film, that is, an acrylic copolymer having an acid group and an acrylic copolymer having an epoxy group. A thermosetting solvent-based coating composition composed of a copolymer has been proposed.

[0005]

However, JP-A-63-
When a cross-linking agent composed of an acid anhydride is used as disclosed in Japanese Patent No. 84674, the storage stability is poor due to the high reactivity between the composition components, and the entire composition components may be liquefied. It is difficult and has poor workability. Further, in the case of the thermosetting solvent-based coating composition as disclosed in Japanese Patent Application Laid-Open No. 1-139653, since it is inferior in low-temperature curability, when it is baked at a relatively low temperature that can be adopted in a car baking line. However, it has a defect that the coating film performance such as crack resistance, acid resistance and solvent resistance in a cold environment becomes insufficient.

In order to solve these problems, JP-A-2-45577, JP-A-3-287650 and JP-A-4-363374 disclose that an acid anhydride group as an acid group is a half ester. Curable composition, a thermosetting composition containing a hydroxy compound and an epoxy compound, a copolymer obtained by half-esterifying an acid anhydride group as an acid group, a heat containing a compound having an epoxy group and a hydroxyl group Curable compositions have been proposed. However, since these thermosetting compositions have a large content of monomer units having a half-esterified acid anhydride group, they are still insufficient in storage stability or the acid anhydride group remains. Therefore, there is a problem that the low temperature curability and the solvent resistance of the coating film are still insufficient.

The object of the present invention is thermostability which is excellent in storage stability and low-temperature curing property, and is also excellent in coating film performance represented by solvent resistance, acid resistance, abrasion resistance, weather resistance and cosmetics. It is to provide a coating composition.

[0008]

SUMMARY OF THE INVENTION The present inventors have accomplished the present invention as a result of earnestly studying a thermosetting coating composition in view of the above problems of the prior art. That is, the thermosetting coating composition of the present invention has an acid anhydride group content of 50 to 98.
% 0.5 to 4 half-esterified monomer units
It is characterized by containing 0% by weight of an acrylic copolymer (A) and an epoxy group-containing acrylic copolymer (B).

The acrylic copolymer (A) used in the thermosetting coating composition of the present invention is a polymerizable monomer mixture containing a monomer having an α, β-dicarboxylic acid monoesterified acid anhydride group. Or a dicarboxylic acid anhydride group obtained by polymerizing a polymerizable monomer mixture containing a monomer having a dibasic acid anhydride group and half-esterifying the acid anhydride group with an alkanol. The monomer unit having an acid monoesterified acid anhydride group is contained in the range of 0.5 to 40% by weight. This is because if the amount of the monomer unit having a dicarboxylic acid monoesterified acid anhydride group is less than 0.5% by weight, a sufficient effect for improving the low temperature curability cannot be obtained. This is because the storage stability of the curable coating composition decreases, and the range is preferably 5 to 30% by weight.

In the present invention, it is preferable that 50 to 98% of the acid anhydride groups in the acrylic copolymer (A) are half-esterified. This is because when the half-esterification rate of the acid anhydride group in the acrylic copolymer (A) is less than 50%, the viscosity of the coating composition remarkably increases and the storage stability of the coating composition decreases. This is because there is a tendency. If it exceeds 98%, the low temperature curability of the coating film decreases,
This is because the solvent resistance of the coating film tends to decrease. The range is more preferably 80 to 95%.

The acrylic copolymer (A) of the present invention has an acid value of 50 to 150 mgKOH / g (mg of potassium hydroxide required to neutralize 1 g of the acrylic copolymer).
The weight average molecular weight is preferably 5,000 to 50,000. This is because the acrylic copolymer (A) has an acid value of 5
When it is less than 0 mgKOH / g, the hardness and solvent resistance of the coating film tend to be lowered due to insufficient curability,
This is because when it exceeds mgKOH / g, the viscosity of the copolymer remarkably increases and the gloss, water resistance and weather resistance of the coating film tend to decrease, and more preferably 70 to 130 m.
It is in the range of gKOH / g. When the weight average molecular weight of the acrylic copolymer (A) is less than 5,000, the water resistance and weather resistance of the coating film tend to be lowered, and when it exceeds 50,000, the viscosity of the resin is remarkably increased, This is because the cosmetic appearance of the film and the storage stability of the coating composition tend to decrease, and the range of 8000 to 20000 is more preferable.

Examples of the monomer unit having a dicarboxylic acid monoesterified acid anhydride group contained in the acrylic copolymer (A) of the present invention include, for example, monomethyl maleate, monoethyl maleate, monobutyl maleate,
Monooctyl maleate, monomethyl itaconate, monoethyl itaconate, monobutyl itaconate, monooctyl itaconate, mono-2-ethylhexyl itaconate, monomethyl fumarate, monoethyl fumarate, monobutyl fumarate, monooctyl fumarate, monoethyl citracone, etc. Is mentioned.

Other polymerizable monomers used in the acrylic copolymer (A) of the present invention include, for example, methyl (meth) acrylate, ethyl (meth) acrylate,
n-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate,
t-butyl (meth) acrylate, Sec-butyl (meth) acrylate, n-pentyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, etc. (Meth) acrylic acid esters having a hydrocarbon substituent of styrene, styrene derivatives such as styrene, vinyltoluene and α-methylstyrene, ethylenically unsaturated nitriles such as acrylonitrile and methacrylonitrile, N-methoxymethylacrylamide, N -Ethoxymethyl acrylamide, N
-N-alkoxy substituted amides such as butoxymethyl acrylamide, ethylenically unsaturated basic monomers such as dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, glycidyl (meth) acrylate, methylglycidyl (meth) ) Acrylate,
Epoxy group-containing monomers such as 3,4-epoxycyclohexyl (meth) acrylate and allyl glycidyl ether, methacrylic acid, acrylic acid, crotonic acid, vinylbenzoic acid, fumaric acid, itaconic acid, maleic acid, citraconic acid, maleic acid Acid anhydrides, itaconic anhydrides, fumaric anhydrides, monobasic or dibasic acids such as citraconic anhydride, β-carboxyethyl (meth) acrylate, β-carboxypropyl (meth) acrylate, β
-(Meth) acryloxyethyl acid succinate,
β- (meth) acryloxyethyl acid maleate,
β- (meth) acryloxyethyl acid phthalate,
β- (meth) acryloxyethyl acid hexahydrophthalate, β- (meth) acryloxyethyl acid methyl hexahydrophthalate, γ- (meth) acryloxypropyl acid succinate, ε to 2-hydroxyethyl (meth) acrylate -Caprolactone or γ-caprolactone to γ-butyrolactone succinic acid monoester or 2-hydroxyethyl (meth) acrylate in which the terminal hydroxyl group of the ring-opening adduct is esterified with succinic anhydride to introduce a carboxyl group at the terminal Phthalic acid monoester obtained by esterifying the terminal hydroxyl group of a ring-opening adduct of butyrolactone (eg, Praxel F monomer manufactured by Daicel Chemical Co., Ltd., Tone M monomer manufactured by UCC) with phthalic anhydride or hexahydrophthalic anhydride. Ester, hexahydrophthalic anhydride monoe Caprolactone-modified hydroxyl group-containing, such as ether (meth) half-ester reaction products of acrylic acid ester and an acid anhydride, 2-hydroxyethyl (meth)
Acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 4-
(Meth) acrylic acid esters having hydroxyalkyl groups such as hydroxybutyl (meth) acrylate and 4-hydroxyhexyl (meth) acrylate, γ-butyrolactone ring-opening addition product to 2-hydroxyethyl methacrylate, and 2-hydroxyethyl acrylate To
Caprolactone ring-opening adduct, ethylene oxide ring-opening adduct to methacrylic acid, propylene oxide ring-opening adduct to methacrylic acid, 2-hydroxyethyl (meth) acrylate or 2-hydroxypropyl (meth) acrylate dimer A long-chain carboxyl group-containing monomer such as (meth) acrylic acid esters having a hydroxyl group at the terminal of a vinyl ester or trimer, other hydroxy group-containing vinyl monomers such as 4-hydroxybutyl vinyl ether and p-hydroxystyrene The body etc. are mentioned. These may be used alone or in combination of two or more as required.

In the present invention, as the other polymerizable monomer, the above-mentioned monobasic acid or dibasic acid monomers, long-chain carboxyl group-containing monomers, hydroxyl group-containing monomers, epoxy group-containing monomers are used. The monomers are used alone or in combination of two or more, and the acrylic copolymer (A) contains a carboxyl group, a long-chain carboxyl group, a hydroxyl group and an epoxy group together with an α, β-dicarboxylic acid monoester group. By doing so, it becomes possible to further increase the reactivity of the coating composition without impairing storage stability, further improve the low temperature curability, and further improve the scratch resistance, solvent resistance and hardness of the coating film. Can be made.

In this case, the acrylic copolymer (A) has an acid value of 50 to 150 mgKOH / g, and the acrylic copolymer (A) has a hydroxyl group equivalent (the number of grams of the resin containing 1 gram equivalent of hydroxyl group) is 300 g. / Eq or more, epoxy equivalent (1
The number of grams of resin containing gram equivalent of epoxy groups is 1
It is preferable that the amount is 000 g / eq or more.
This is because the acid value of the acrylic copolymer (A) is 50 mgK.
When it is less than OH / g, the hardness and solvent resistance of the coating film are deteriorated due to insufficient curability, and when it exceeds 150 mgKOH / g, the viscosity of the copolymer is remarkably increased, and further, the gloss of the coating film, Water resistance and weather resistance tend to decrease, and when the hydroxyl group equivalent of the acrylic copolymer (A) is less than 300 g / eq, the viscosity of the coating composition remarkably increases and the gloss of the coating film,
This is because water resistance and weather resistance tend to decrease, and when the epoxy equivalent is less than 1000 g / eq, the coating composition tends to thicken and gel easily.

The acrylic copolymer (B) used in the thermosetting coating composition of the present invention is obtained by copolymerizing a monomer having an epoxy group in a specific ratio.

Examples of the epoxy group-containing monomer used in the acrylic copolymer (B) of the present invention include glycidyl (meth) acrylate and methylglycidyl (meth).
Acrylate, 3,4-epoxycyclohexylmethyl (meth) acrylate, allyl glycidyl ether and the like can be mentioned, and these can be used alone or in combination of two or more as required. The amount of these epoxy group-containing monomers used is preferably in the range such that the epoxy equivalent of the acrylic copolymer (B) is 200 to 1500 g / eq, and for example, 15 to 60% by weight. It is more preferably in the range of 20 to 50% by weight.

Other polymerizable monomers used in the acrylic copolymer (B) of the present invention include, for example, methyl (meth) acrylate, ethyl (meth) acrylate,
n-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate,
t-butyl (meth) acrylate, Sec-butyl (meth) acrylate, n-pentyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, etc. (Meth) acrylic acid esters having a hydrocarbon substituent of styrene, styrene derivatives such as styrene, vinyltoluene and α-methylstyrene, ethylenically unsaturated nitriles such as acrylonitrile and methacrylonitrile, N-methoxymethylacrylamide, N -Ethoxymethyl acrylamide, N
-N-alkoxy substituted amides such as butoxymethyl acrylamide, ethylenically unsaturated basic monomers such as dimethylaminoethyl (meth) acrylate and diethylaminoethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2 -Hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-
(Meth) acrylic acid esters having a hydroxyalkyl group such as hydroxyhexyl (meth) acrylate,
Γ-Butyrolactone ring-opening adduct to 2-hydroxyethyl methacrylate, ε-caprolactone ring-opening adduct to 2-hydroxyethyl acrylate, ethylene oxide ring-opening adduct to methacrylic acid, and propylene oxide ring-opening to methacrylic acid. (Meth) acrylic acid esters having a hydroxyl group at the end of an adduct, a dimer or trimer of 2-hydroxyethyl (meth) acrylate or 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl vinyl ether, p -Other hydroxyl group-containing vinyl monomers such as hydroxystyrene, methacrylic acid, acrylic acid, crotonic acid, vinylbenzoic acid, fumaric acid,
Monobasic or dibasic acid monomers such as itaconic acid, maleic acid, citraconic acid, monomethyl maleate, monoethyl maleate, monobutyl maleate, monooctyl maleate, monomethyl itaconate, monoethyl itaconate, monobutyl itaconate , Monooctyl itaconate, mono-2-ethylhexyl itaconate, monomethyl fumarate, monoethyl fumarate, monobutyl fumarate, monooctyl fumarate, monoesters of acid anhydride monomers such as monoethyl citracone, etc., β-carboxyethyl (meth) acrylate, β-carboxypropyl (meth) acrylate, β- (meth) acryloxyethyl acid succinate, β- (meth) acryloxyethyl acid maleate, β- (meth) acryloxyethyl Acid lid Rate, β- (meth) acryloxyethyl acid hexahydrophthalate, β- (meth) acryloxyethyl acid methyl hexahydrophthalate, γ- (meth) acryloxypropyl acid succinate, 2-hydroxyethyl (meth) acrylate Ε-caprolactone or γ-butyrolactone ring-opened adduct of succinic acid monoester in which the terminal hydroxyl group is esterified with succinic anhydride to introduce a carboxyl group at the terminal or ε-caprolactone to 2-hydroxyethyl (meth) acrylate or A phthalate obtained by esterifying the terminal hydroxyl group of a ring-opening adduct of γ-butyrolactone (for example, Praxel F monomer manufactured by Daicel Chemical Co., Ltd. and Tone M monomer manufactured by UCC) with phthalic anhydride or hexahydrophthalic anhydride. Acid monoester, hexahydrophthalic anhydride Caprolactone-modified hydroxyl group-containing (meth) long chain carboxyl group-containing monomers such as half-ester reaction products of acrylic acid esters and acid anhydrides such as monoesters and the like. These may be used alone or in combination of two or more as required.

In the present invention, a hydroxyl group-containing monomer or a carboxyl group-containing monomer is used as the other polymerizable monomer, and the acrylic copolymer (B) is combined with the epoxy group together with the hydroxyl group or the carboxyl group. By containing, it becomes possible to increase the reactivity of the coating composition without impairing the storage stability, further improve the low temperature curability, and further improve the solvent resistance and hardness of the coating film. it can. This effect can be further enhanced by using a hydroxyl group-containing monomer and a carboxyl group-containing monomer and incorporating an epoxy group, a hydroxyl group and a carboxyl group in the acrylic copolymer (B). .

In the present invention, the epoxy equivalent of the acrylic copolymer (B) is 200 to 1500 g.
/ Eq and the weight average molecular weight is preferably 1000 to 20000. This is because when the epoxy equivalent of the acrylic copolymer (B) exceeds 1500 g / eq, the curability is insufficient, so that the hardness and solvent resistance of the coating film tend to decrease, and when it is less than 200 g / eq, the coating This is because the composition tends to thicken and gel easily, and more preferably in the range of 250 to 950 g / eq.

When the weight average molecular weight of the acrylic copolymer (B) is less than 1000, the water resistance and weather resistance of the coating film tend to be lowered, and when it exceeds 20,000, the viscosity of the resin is remarkably increased. However, this is because the cosmetic properties and solvent resistance of the coating film tend to decrease, and more preferably 3000
The range is from 10,000 to 10,000.

Further, when the acrylic copolymer (B) contains a hydroxyl group or a carboxyl group, the hydroxyl equivalent of the acrylic copolymer (B) is 400 to 6000 g /
The range of eq is preferable. This has a hydroxyl equivalent of 400g
/ Eq is less than 6000 g / eq
This is because the non-sand recoating property tends to be deteriorated when it exceeds 1.0, more preferably 500 to 3000 g / e.
q, more preferably 800 to 3000 g / eq. The acid value of the acrylic copolymer (B) is 50 m.
It is preferably gKOH / g or less. This has an acid value of 50 mg
This is because when the content exceeds KOH / g, the coating composition tends to thicken or gel easily.

The weight ratio of the acrylic copolymers (A) and (B) in the thermosetting coating composition of the present invention is 1/3 ≦ (A).
It is preferable that / (B) ≦ 10/3. This is because the weight ratio of acrylic copolymers (A) and (B) is 1 /
When it is less than 3, the storage stability and the water resistance of the coating film tend to decrease, and when it exceeds 10/3, the solvent resistance and hardness of the coating film tend to decrease, and more preferably 1 /
The range is 2 ≦ (A) / (B) ≦ 4/2.

The molar ratio of the carboxyl group to the epoxy group of the thermosetting coating composition of the present invention is preferably 1 / 2≤carboxyl group / epoxy group≤1 / 0.5. Outside of this range, unreacted functional groups tend to reduce the water resistance and weather resistance of the coating film, which is not preferable. More preferably, the range is 1 / 1.8 ≦ carboxyl group / epoxy group ≦ 1 / 0.7.

The thermosetting coating composition of the present invention also comprises
In order to further improve yellowing resistance and non-sand recoatability, the acrylic copolymer (C) having a hydroxyl group is added to the total amount of the acrylic copolymers (A) and (B).
It can be added in the range of 0.5 to 30% by weight. This is because when the addition amount of the acrylic copolymer (C) is less than 0.5% by weight with respect to the total amount of the acrylic copolymers (A) and (B), yellowing resistance of the coating film and This is because the effect of improving the non-sand recoatability is not sufficient, and if it exceeds 30% by weight, the hardness and solvent resistance of the coating film tend to decrease, and the range of 5 to 20% by weight is more preferable.

Examples of the hydroxyl group-containing monomer used in the acrylic copolymer (C) of the present invention include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate and 3-hydroxypropyl. (Meth) acrylate, 2-hydroxybutyl (meth)
(Meth) acrylic acid esters having a hydroxyalkyl group such as acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, γ to 2-hydroxyethyl methacrylate
-Butyrolactone ring-opening adduct, ε-caprolactone ring-opening adduct to 2-hydroxyethyl acrylate, ethylene oxide ring-opening adduct to methacrylic acid, propylene oxide ring-opening adduct to methacrylic acid, 2-hydroxyethyl ( (Meth) acrylate or 2-hydroxypropyl (meth) acrylate dimer or trimer having (meth) acrylic acid ester having a hydroxyl group at the terminal, 4-
Other hydroxyl group-containing vinyl monomers such as hydroxybutyl vinyl ether and p-hydroxystyrene are listed,
These may be used alone or in combination of two or more as required. The amount of the hydroxyl group-containing monomer used is preferably in the range such that the hydroxyl group equivalent of the acrylic copolymer (C) is 250 to 1000 g / eq, and for example, 10 to 50% by weight. It is more preferably in the range of 15 to 40% by weight.

This is because when the hydroxyl group equivalent of the acrylic copolymer (C) exceeds 1000 g / eq, the non-sand recoating property and solvent resistance of the coating film tend to decrease, and 250 g
This is because if it is less than / eq, the water resistance of the coating film tends to decrease.

Other polymerizable monomers used in the acrylic copolymer (C) of the present invention include, for example, methyl (meth) acrylate, ethyl (meth) acrylate,
n-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate,
t-butyl (meth) acrylate, Sec-butyl (meth) acrylate, n-pentyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, etc. (Meth) acrylic acid esters having a hydrocarbon substituent of styrene, styrene derivatives such as styrene, vinyltoluene and α-methylstyrene, ethylenically unsaturated nitriles such as acrylonitrile and methacrylonitrile, N-methoxymethylacrylamide, N -Ethoxymethyl acrylamide, N
-N-alkoxy substituted amides such as butoxymethyl acrylamide, ethylenically unsaturated basic monomers such as dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, methacrylic acid, acrylic acid, crotonic acid, vinyl Monobasic or dibasic acid monomers such as benzoic acid, fumaric acid, itaconic acid, maleic acid, citraconic acid, monomethyl maleate, monoethyl maleate, monobutyl maleate, monooctyl maleate, monomethyl itaconate, itacone Acid monoethyl, itaconic acid monobutyl, itaconic acid monooctyl,
Monoesters of dibasic acid or acid anhydride monomer such as mono-2-ethylhexyl itaconate, monomethyl fumarate, monoethyl fumarate, monobutyl fumarate, monooctyl fumarate, and monoethyl citracone, β-carboxyethyl (meta ) Acrylate, β-carboxypropyl (meth) acrylate, β- (meth) acryloxyethyl acid succinate, β- (meth) acryloxyethyl acid maleate, β- (meth) acryloxyethyl acid phthalate, β- ( (Meth) acryloxyethyl acid hexahydrophthalate, β- (meth)
Acryloxyethyl acid methyl hexahydrophthalate, γ- (meth) acryloxypropyl acid succinate, 2-hydroxyethyl (meth) acrylate to ε-caprolactone or γ-butyrolactone ring-opening adduct, the terminal hydroxyl group is succinic anhydride. Ε-to succinic acid monoester or 2-hydroxyethyl (meth) acrylate which is esterified with carboxylic acid to introduce a carboxyl group at the terminal
Ring-opening addition product of caprolactone or γ-butyrolactone (for example, Praxel F monomer manufactured by Daicel Chemical Industries, Ltd.,
Caprolactone modified hydroxyl group-containing (meth) acrylic acid ester such as phthalic acid monoester obtained by esterifying terminal hydroxyl group of UCC Tone M monomer) with phthalic anhydride, hexahydrophthalic anhydride, or hexahydrophthalic anhydride monoester And long-chain carboxyl group-containing monomers such as half-ester reaction products of acid anhydrides, glycidyl (meth) acrylate, methylglycidyl (meth) acrylate,
Examples thereof include epoxy group-containing monomers such as 3,4-epoxycyclohexyl (meth) acrylate and allyl glycidyl ether. These may be used alone or in combination of two or more as required.

The acrylic copolymer (A) of the present invention,
(B) and (C) can be produced by a known polymerization method such as a solution polymerization method, a bulk polymerization method and an emulsion polymerization method, but a solution polymerization method is preferable. When producing the acrylic copolymer by a solution polymerization method,
The mixture of monomers is copolymerized in the presence of an organic solvent and a polymerization initiator. As the organic solvent, isopropanol,
Common ones such as n-butanol, toluene and xylene can be selected. The polymerization initiator can be selected from commonly used polymerization initiators such as azobisisobutyronitrile, benzoyl peroxide and cumene hydroperoxide. If necessary, a chain transfer agent such as 2-mercaptoethanol or n-octyl mercaptan can be used.

When an acrylic copolymer is produced by a solution polymerization method, in general, in order to control the molecular weight,
It is preferable to carry out the polymerization in the range of 80 to 160 ° C.,
More preferably, it is in the range of 100 to 140 ° C. As the acrylic copolymer, in the case of containing a carboxyl group and an epoxy group, when trying to copolymerize a monomer having a carboxyl group and a monomer having an epoxy group at the same time, The reaction causes a marked increase in viscosity during the polymerization and a tendency to cause gelation, so that the content of the carboxyl group and the epoxy group in the copolymer is limited to an extremely small amount. Therefore, when the acrylic copolymer (A) of the present invention contains an epoxy group, first, a monomer having a carboxyl group (including a monomer having a hydroxyl group if necessary) is 100 ° C. or higher. It is preferable to use a two-step polymerization method in which the monomer having an epoxy group is polymerized by lowering the polymerization temperature to 75 ° C. or lower after the copolymerization at the temperature of 1. Similarly, in the case where the acrylic copolymer (B) contains a carboxyl group, first, a monomer having an epoxy group (including a monomer having a hydroxyl group if necessary) is heated at a temperature of 100 ° C. or higher. It is preferable to use a two-step polymerization method in which the monomer having a carboxyl group is polymerized by lowering the polymerization temperature to 75 ° C. or lower.

If necessary, a melamine resin or a blocked isocyanate resin may be added to the thermosetting coating composition of the present invention as an auxiliary curing agent. These can be added in an appropriate amount so as not to impair the storage stability and coating performance of the coating composition, and the addition amount is based on the total amount of the acrylic copolymers (A) and (B). 20% by weight or less is preferable. This is because the amount of auxiliary curing agent added is 20
This is because if the content exceeds 5% by weight, the acid resistance of the coating film tends to decrease and the coating film tends to yellow. Examples of auxiliary curing agents other than the above include epoxy compounds such as glycidyl ether, glycidyl ester, and alicyclic epoxy compounds, and alkyl diols, alkyl polyols, acrylic polyols, polyester polyols, polyurethane polyols, hydroxy compounds, and the like. it can.
You may use these auxiliary hardening agents in mixture of 2 or more types.

The thermosetting coating composition of the present invention may contain a catalyst to accelerate curing. The curing catalyst may be a known one used in the esterification reaction of an acid group and an ester group, and for example, a quaternary ammonium salt or a phosphonium salt is preferable. Specific examples thereof include benzyltrimethylammonium chloride, benzyltrimethylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium hydroxide, benzyltriphenylphosphonium chloride and benzyltriphenylphosphonium bromide.

Further, in order to improve the stability, an acidic compound represented by a sulfonic acid type or a phosphoric acid type can be added if necessary. Specific examples thereof include paratoluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid and amine blocked products thereof, monoalkylphosphoric acid, dialkylphosphoric acid and monoalkylphosphorous acid.

Further, the thermosetting coating composition of the present invention contains a rheology modifier such as organic benton, polyamide, microgel, fibrin resin, a surface modifier represented by silicone, an ultraviolet absorber, and the like. Additives such as a light stabilizer, an antioxidant, and an anti-sagging agent can be appropriately blended as necessary using known means.

When the thermosetting coating composition of the present invention is used as a clear coat paint for automobile coating, the thermosetting coating composition of the present invention can be used as the base coat layer in contact with the clear coat layer. However, a known curable resin can be appropriately used if necessary. These thermosetting resins include diluents composed of volatile organic solvents, curing agents composed of amino resins or polyisocyanate compounds, aluminum pastes, mica, brightening agents such as flake iron oxide, titanium oxide, carbon black. , Inorganic pigments such as quinacridone and organic pigments, polyester resins, epoxy resins, addition resins such as cellulose resins, surface modifiers, ultraviolet absorbers, antioxidants and other additives using known means as necessary. It can be blended appropriately.

[0036]

EXAMPLES The present invention will be specifically described below with reference to examples. All parts and percentages in the examples are by weight. -Definition of physical properties of copolymer Viscosity: Value measured by Gardner-Holt foam viscometer (25 ° C) Nonvolatile matter: Nonvolatile matter when 1 g of resin is sampled on an aluminum dish and dried at 150 ° C for 1 hour. Ratio of hydroxyl group: 1 gram of resin containing 1 gram equivalent of hydroxyl group Acid value: mg of potassium hydroxide required to neutralize 1 g of acrylic copolymer Epoxy equivalent: Resin containing 1 gram equivalent of epoxy group Weight average molecular weight: measured by gel permeation chromatography-half-esterification rate of acid anhydride group The value of the weight part of the α, β-dicarboxylic acid monoester monomer unit in the copolymer is the acid anhydride monomer. Unit and α, β-
The value (%) divided by the sum of the weight parts of dicarboxylic acid monoester monomer units is shown.

Definition of physical properties of paint Coating viscosity: No. 4 Seconds until all the paint in the Ford cup falls and flows out (20 ° C) -Definition of coating film performance Visual appearance: Judgment based on gloss and smoothness Gloss: Digital bending angle manufactured by Suga Test Instruments Co., Ltd. Measured using a gloss meter uGV-4D (60G) Hardness: Mitsubishi Pencil Uni used (scratch coating at 45 degree angle to measure hardness) Acid resistance: 40% sulfuric acid aqueous solution spotted, 50
After leaving it at ℃ for 1 hour, wash it with water and visually judge the spot mark Water resistance: After immersing in warm water of 40 ℃ for 10 days, visually judge the appearance Solvent resistance: Soak methyl ethyl ketone in gauze,
Visual appearance after 50 reciprocating rubbing tests Weather resistance: After 1000 hours evaluation with Sunshine Weather Ometer manufactured by Suga Test Instruments, visually judge appearance of coating film immersed in hot water at 50 ° C for 24 hours Scratch resistance: Daiei Using a friction fastness tester manufactured by Kagaku Seiki Co., Ltd., gauze was applied to the contact point of the coated surface, 10 reciprocating rubbing tests were performed with a load of 1 kg, and the scratches were visually determined. Storage stability: 72 at 30 ° C The state of the paint after leaving for a time is shown.

◎: No abnormality ○: Viscosity slightly increased, no problem in practical use △: Thickened, problem in practical use ×: Gelation, unusable Low temperature curability: Using xylene on a coated plate baked at 120 ° C Conduct the above solvent resistance test and visually judge the appearance of the coating film after the test. ・ Non-sand recoating property A zinc electrophosphate coated steel plate (30 cm * 90 cm) is coated with a cationic electrodeposition paint for automobiles at 180 ° C. Bake for 30 minutes. Further, an amino alkyd resin-based intermediate coating material was applied and baked at 160 ° C. for 30 minutes, then the coating film was sanded and dried to obtain a test piece.

First, a base coat paint and a clear coat paint were overcoated on the test piece by a wet-on-wet method, baked for 25 minutes in a hot-air dryer at 160 ° C., and allowed to cool, and the same base coat paint was further applied without sanding. Overcoat the clear coat paint with the wet-on-wet method and apply 2 with a hot air dryer at 120 ° C.
After baking for 5 minutes, a multilayer coating film for evaluation was formed. 1 cm square of this laminated coating film was scratched at 1 mm intervals to make 100 cross-cuts. After sticking cellophane tape on top of this, peel it off at a stretch, and check the adhesiveness from the number of cross-cuts left without peeling. evaluated.

⊚: Area remaining without peeling is 90/100
Above Δ: Area remaining without peeling is 50/100 or more 90/1
Less than 00 x: less than 50/100 remaining area without peeling-Cold-heat crack resistance Steel sheet (30 cm * 90 cm) treated with zinc phosphate is coated with a cationic electrodeposition coating for automobiles and baked at 180 ° C for 30 minutes It was Further, an amino alkyd resin-based intermediate coating material was applied and baked at 160 ° C. for 30 minutes, then the coating film was sanded and dried to obtain a test piece.

First, a base coat paint and a clear coat paint were overcoated on the test piece by a wet-on-wet system, and baked for 25 minutes with a hot air dryer at 120 ° C. to form a multilayer coating film for evaluation. This coated plate at 40 ℃ 3
After leaving it in the hot air drier for 0 minutes, it is put in a methanol bath containing dry ice at -40 ° C and rapidly cooled. After leaving in a methanol bath for 30 minutes, cracks in the coating film were evaluated. The same operation is repeated for 5 cycles. (The number represents the number of cycles in which cracks did not occur on the coated plate. ⊚ indicates 5 cycles without cracks.) ・ Criteria for visual judgment ◎: The coating quality after the performance test did not change from that before the test and was excellent. Judged that the coating performance was maintained. ◯: The coating quality after the performance test was slightly lower than that before the test, but was judged to have sufficient practical performance. Δ: The coating quality after the performance test was Decreased from before the test and judged to be practically problematic x: The coating film quality after the performance test is significantly deteriorated compared to before the test,
Judgment as practically unusable (1) Manufacturing example of base coat paint (M-1) 10 parts of n-butanol and 90 parts of toluene were added as a solvent to a container equipped with a stirrer, a temperature controller, and a condenser, and the mixture was stirred. After heating to 100 ° C., vinyl consisting of 40 parts of methyl methacrylate, 30 parts of ethyl acrylate, 15 parts of n-butyl acrylate, 12 parts of 2-hydroxyethyl methacrylate, 3 parts of methacrylic acid and 0.6 part of azobisisobutyronitrile. After the mixture of the system monomer and the polymerization initiator was dropped into the solvent over 4 hours, the mixture was polymerized at the same temperature for 3 hours to synthesize an acrylic copolymer (B-1). The resulting acrylic copolymer (B-1) had a nonvolatile content of 50% and a weight average molecular weight of 40,000. Further, 100 parts of this acrylic copolymer (B-1), 25 parts of U-Van 20SE-60 (manufactured by Mitsui Toatsu Chemicals, Inc., butylated melamine resin, solid content 60%), Alpaste #
14 parts of 1700 NL (manufactured by Toyo Aluminum Co., Ltd., aluminum paste, solid content 65%) were mixed to obtain a base coat coating composition. This base coat coating composition was diluted with a mixed solvent consisting of ethyl acetate / toluene / Solvesso # 150 (produced by Esso Co., aromatic hydrocarbon) = 40/30/30 (% by weight), and the viscosity of the base coat coating composition was adjusted to Ford. Prepare in cup # 4 for 13 seconds,
A silver metallic base coat paint (M-1) was obtained.

(2) Synthesis of acrylic copolymer (P-1) 50 parts of butyl acetate as a solvent in a container equipped with a stirrer, a temperature controller, and a condenser, Solvesso # 100 (Aromatic petroleum derivative manufactured by Esso Co.) After adding 50 parts and heating to 100 ° C. with stirring, 15 parts of methacrylic acid, 5 parts of monobutyl fumarate, 10 parts of styrene, 49.5 parts of n-butyl methacrylate, 20 parts of 2-ethylhexyl acrylate, azobisisobutyrate. A mixture of a vinyl monomer consisting of 3 parts of ronitrile and a polymerization initiator was added dropwise to the solvent over 4 hours, and the internal temperature of the flask was maintained at 100 ° C. to sufficiently increase the addition rate to the resin. By the way, the reaction was terminated and an acrylic copolymer (P-1) was synthesized. The characteristic values of the obtained acrylic copolymer are shown in Table 1.

(3) Acrylic copolymer (P-2)
(P-3), (P-5) to (P-7), (P-10) to
Synthesis of (P-12), (P-15) to (P-16) Each of the vinyl-based monomers shown in Table 1 is polymerized by the same operation as in the method of synthesizing the acrylic copolymer (P-1). , Acrylic copolymers (P-2) to (P-3), (P-5) to
(P-7), (P-10) to (P-12), (P-1
5) to (P-16) were synthesized. The characteristic values of the obtained copolymer are shown in Table 1.

(4) Synthesis of acrylic copolymer (P-4) 50 parts of butyl acetate as a solvent in a container equipped with a stirrer, a temperature controller, and a condenser, Solvesso # 100 (Aromatic petroleum derivative manufactured by Esso Co.) After adding 50 parts and heating to 100 ° C. with stirring, 5 parts of methacrylic acid, 0.5 part of maleic anhydride, 2 parts of monomethyl maleate, β-methacryloxyethyl acid hexahydrophthalate 15
Part, 2-hydroxyethyl methacrylate 14 parts, styrene 26 parts, n-butyl methacrylate 9 parts, lauryl methacrylate 18.5 parts, azobisisobutyronitrile 3 parts of a mixture of a vinyl-based monomer and a polymerization initiator. It dripped in the solvent over 4 hours. Then, the internal temperature of the flask was lowered to 75 ° C., and further 2 parts of glycidyl methacrylate, 1 part of 2-hydroxyethyl methacrylate, 4 parts of styrene, 1 part of n-butyl methacrylate, 2 parts of lauryl methacrylate, 1 part of azobisdimethylvaleronitrile. The mixture of the vinyl-based monomer and the polymerization initiator was dropped into the solvent over 2 hours. After the dropping, the internal temperature of the flask was maintained at 75 ° C. and the reaction was terminated when the addition rate to the resin was sufficiently increased to synthesize an acrylic copolymer (P-4). The characteristic values of the resulting acrylic copolymer are shown in Table 1.
It was shown to.

(5) Synthesis of acrylic copolymer (P-8) 50 parts of butyl acetate as a solvent in a container equipped with a stirrer, a temperature controller, and a condenser, Solvesso # 100 (Aromatic petroleum derivative manufactured by Esso Co.) After adding 50 parts and heating to 100 ° C. with stirring, maleic anhydride 5 parts, methacrylic acid 10 parts, butyl acetate 20 parts, n-butyl methacrylate 10 parts, styrene 40 parts, 2-ethylhexyl acrylate 33.5 parts , Azobisisobutyronitrile 2
Part, a mixture of a vinyl-based monomer composed of 4 parts of t-butyl isopropyl carbonate and a polymerization initiator was added dropwise to the solvent over 4 hours, and the internal temperature of the flask was maintained at 100 ° C. Was raised sufficiently. Then, the internal temperature of the flask was lowered to 70 ° C., and methanol 1.47 was added.
And 0.2 part of triethylamine were added and reacted at 70 ° C. for 7 hours, the reaction was terminated when the reduction of acid anhydride groups was confirmed by IR, and the acrylic copolymer (P- 8) was synthesized. The characteristic values of the obtained acrylic copolymer are shown in Table 1. The resulting acrylic copolymer (P-8) had 6.0 parts of monomethyl maleate monomer units and 0.5 parts of maleic anhydride monomer units, where the total of monomer units was 100 parts. Had.

(6) Synthesis of acrylic copolymer (P-9) 50 parts of butyl acetate as a solvent in a container equipped with a stirrer, a temperature controller and a condenser, Solvesso # 100 (Aromatic petroleum derivative, manufactured by Esso Co.) After adding 50 parts and heating to 100 ° C. with stirring, maleic anhydride 8 parts, methacrylic acid 5 parts, butyl acetate 20 parts, n-butyl methacrylate 14.8 parts, styrene 30 parts, 2-ethylhexyl acrylate 40 parts. , Azobisisobutyronitrile 2
Part, a mixture of a vinyl-based monomer composed of 2 parts of t-butyl isopropyl carbonate and a polymerization initiator was added dropwise to the solvent over 4 hours, and the internal temperature of the flask was maintained at 100 ° C. Was raised sufficiently. After that, the inner temperature of the flask was lowered to 80 ° C., and further, 2.22 of methanol was added.
And 0.17 parts of triethylamine were added, and the mixture was reacted at 80 ° C. for 7 hours, and when the reduction of acid anhydride groups was confirmed by IR, the reaction was terminated, and the acrylic copolymer (P -9) was synthesized. The characteristic values of the obtained acrylic copolymer are shown in Table 1. The resulting acrylic copolymer (P-9) contains 9.0 parts of monomethyl maleate monomer units and 1.2 parts of maleic anhydride monomer units, when the total amount of the monomers is 100 parts. Had (half-esterification rate of acid anhydride was 85%
Is).

(7) Acrylic copolymer (P-13)
Synthesis of (P-14) The vinyl-based monomers shown in Table 1 were polymerized by the same operation as in the method for synthesizing the acrylic copolymer (P-9) to obtain an acrylic copolymer (P-13) to (P-14) was synthesized.
The characteristic values of the obtained copolymer are shown in Table 1.

[0048]

[Table 1]

* 1: The number in parentheses is the content of the dicarboxylic acid monoester introduced into the polymer structure by copolymerizing the corresponding acid anhydride monomer and dicarboxylic acid monoesterification with an alkanol, and finally remaining. Content of maleic anhydride.

(8) Synthesis of Acrylic Copolymer (P-17) 20 parts of n-butanol as a solvent and Solvesso # 100 in a container equipped with a stirrer, a temperature controller and a condenser.
(Esso Co., aromatic petroleum derivative) 80 parts was added, and after heating to 120 ° C. with stirring, 30 parts of glycidyl methacrylate, 30 parts of styrene, 23 parts of 2-ethylhexyl methacrylate, 7 parts of 2-hydroxyethyl acrylate, n -A mixture of a vinyl-based monomer consisting of 10 parts of butyl methacrylate, 3 parts of azobisisobutyronitrile, and 7 parts of t-butyl isopropyl carbonate and a polymerization initiator was added dropwise to the solvent over 4 hours, and then the content in the flask was increased. The temperature was kept at 120 ° C., the reaction was terminated when the addition rate to the resin was sufficiently increased, and the acrylic copolymer (P-1
7) was synthesized. The characteristic values of the obtained acrylic copolymer are shown in Table 2.

(9) Acrylic copolymer (P-18),
Synthesis of (P-20) to (P-23) The vinyl-based monomers shown in Table 2 are polymerized by the same operation as in the method of synthesizing the acrylic copolymer (P-18) to obtain an acrylic copolymer. (P-18), (P-20) to (P-2)
3) was synthesized. The characteristic values of the obtained copolymer are shown in Table 2.

(10) Acrylic copolymer (P-19)
Of n-butanol as a solvent in a container equipped with a stirrer, a temperature controller, and a condenser, Solvesso # 100
(Esso Co., aromatic petroleum derivative) 80 parts was added, and after heating to 120 ° C. with stirring, 40 parts of glycidyl methacrylate, 9 parts of 2-hydroxyethyl acrylate,
Styrene 18 parts, 2-ethylhexyl methacrylate 1
A mixture of a vinyl-based monomer consisting of 8 parts, 5 parts of n-butyl methacrylate, 3 parts of azobisisobutyronitrile and 7 parts of t-butyl isopropyl carbonate and a polymerization initiator was added dropwise to the solvent over 4 hours. After that, the internal temperature of the flask was lowered to 70 ° C., and further 4 parts of methacrylic acid, 2-
Ethylhexyl methacrylate 2 parts, styrene 2 parts, 2
A mixture of a vinyl-based monomer consisting of 1 part of hydroxyethyl acrylate, 1 part of n-butyl methacrylate and 1 part of azobisdimethylvaleronitrile and a polymerization initiator was added dropwise to the solvent over 2 hours. After dropping, increase the internal temperature of the flask to 7
The reaction was terminated when the temperature was kept at 0 ° C. to sufficiently increase the addition rate to the resin, and an acrylic copolymer (P-19) was synthesized. The characteristic values of the obtained acrylic copolymer are shown in Table 2.

[0053]

[Table 2]

(11) Acrylic copolymer (P-24)
Of n-butanol as a solvent in a container equipped with a stirrer, a temperature controller, and a condenser, Solvesso # 100
(Esso Co., aromatic petroleum derivative) 80 parts was added, and after heating to 120 ° C. with stirring, 20 parts of 2-hydroxyethyl methacrylate, 30 parts of styrene, 20 parts of n-butyl methacrylate, 29 parts of n-butyl acrylate. ,
A mixture of a vinyl monomer consisting of 1 part of methacrylic acid and 3 parts of azobisisobutyronitrile and a polymerization initiator was dropped into the solvent over 4 hours, and the internal temperature of the flask was 120 ° C.
The reaction was terminated when the addition rate to the resin was sufficiently increased, and the acrylic copolymer (P-24) was synthesized. The characteristic values of the obtained acrylic copolymer are shown in Table 3. In addition, the vinyl-based monomers shown in Table 3 were each polymerized by the same operation as in the method for synthesizing the acrylic copolymer (P-24) to synthesize the acrylic copolymer (P-25). The characteristic values of the obtained copolymer are shown in Table 3.

[0055]

[Table 3]

(12) Preparation of clear coat paint The acrylic copolymers shown in Tables 1, 2 and 3 were blended in the proportions shown in Tables 4 and 5, and mixed with stirring, and then mixed solvent (Solvesso # 100). / Cellosolve acetate = 50/50
(Weight ratio) was added and diluted so that the coating viscosity would be 25 seconds (using Ford cup No. 4, measurement temperature 20 seconds) to prepare a clear coat paint.

[0057]

[Table 4]

[0058]

[Table 5]

(All numbers in the table are based on solid content.) * 1) Surface modifier, manufactured by Monsanto * 2) Curing catalyst: benzyltributylammonium chloride * 3) manufactured by Mitsui Toatsu Chemicals, Inc. Butylated melamine resin (non-volatile content 60%) * 4) Butanediol diglycidyl ether manufactured by Nagase Kasei Co., Ltd. Examples 1 to 11 and Comparative Examples 1 to 13 Zinc phosphate-treated steel sheet (30 cm x 90 cm) on a car cation. The electrodeposition paint was applied and baked at 180 ° C. for 30 minutes. Further, an amino alkyd resin-based intermediate coating material was applied and baked at 160 ° C. for 30 minutes, and then the coating film was water-polished and dried. On this coating film, first, a base coat paint (M-1) was applied so that the dry film thickness was 15 μm, and after standing for 5 minutes, the clear coat paint shown in Table 4 or Table 5 was applied to the dry film thickness of 30 μm. Was repeatedly applied by the wet-on-wet method. After leaving the undried coating film for 15 minutes at room temperature, bake it for 30 minutes with a hot air dryer at 140 ° C (a sample for evaluation of cold and heat crack resistance is baked at 120 ° C x 25 minutes). 2 coat 1 bake multi-layer coating A film was formed. The coating performance of the obtained multilayer coating is shown in Tables 6 and 7.

[0060]

[Table 6]

[0061]

[Table 7]

The thermosetting coating compositions of Examples 1 to 11 of the present invention had excellent storage stability, low temperature curability, and coating film performance. On the other hand, the thermosetting coating compositions of Comparative Examples 1 to 13 which do not satisfy the conditions specified by the present invention,
Storage stability, low temperature curability, and coating performance were all low.

[0063]

As is apparent from the above examples, the thermosetting coating composition containing the acrylic copolymer of the present invention is excellent in storage stability and low temperature curability, and further, it should be used. By this, it is possible to provide a coating film excellent in coating film performance, which is very useful industrially.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhiko Hotta 4-chome Sunadabashi 1-chome, Higashi-ku, Nagoya, Aichi Mitsubishi Rayon Co., Ltd. Product Development Laboratory (72) Inventor Kunio Iwase 4-chome, Sunadabashi, Higashi-ku, Aichi No. 60 Mitsubishi Rayon Co., Ltd. Product Development Laboratory (72) Inventor Hiroshi Takeuchi 4-chome, Sunadabashi, Higashi-ku, Nagoya, Aichi Prefecture 60-60 Mitsubishi Rayon Co., Ltd. Product Development Laboratory

Claims (2)

[Claims] 1. An acrylic copolymer (A) containing 0.5 to 40% by weight of a monomer unit in which 50 to 98% of an acid anhydride group is half-esterified, and an acrylic copolymer having an epoxy group. A thermosetting coating composition containing the combination (B). 2. The thermosetting coating composition according to claim 1, which contains an acrylic copolymer (C) having a hydroxyl group.