JP2003301028A - Curable resin composition, clear coating composition and method of forming multilayer coating film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a curable resin composition which forms a coating film having properties excellent both in scratch resistance and in acid resistance, a clear coating composition, and to provide a method of forming a multilayer coating film. <P>SOLUTION: The curable resin composition is composed of (1) an acrylic copolymer containing a half ester acid group, (2) an acrylic copolymer containing an epoxy group and (3) a polyester polymer containing a carboxy group. The acrylic copolymer (1) containing a half ester acid group is obtained from an acrylic monomer containing a long chain carboxy group. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a curable resin composition, a clear coating composition and a method for forming a multilayer coating film.

[0002]

2. Description of the Related Art As a binder used in a top coating for automobiles, a curable resin composition obtained by combining a hydroxyl group-containing polymer and a melamine resin curing agent is generally used. However, a cured coating film obtained by using such a melamine resin as a curing agent,
Since it is inferior in acid resistance, it is easily deteriorated by acid rain and causes a defect in appearance. The reason why the coating film obtained by using the melamine resin as the curing agent is inferior in acid resistance is due to the triazine ring in the melamine resin, so that the disadvantage of inferior in acid resistance cannot be eliminated as long as the melamine resin is used as the curing agent.

In order to solve such drawbacks, Japanese Patent Application Laid-Open Nos. 2-45577 and 3-287650 disclose coating compositions which do not use a melamine resin. A similar coating composition is described in US Pat.
No. 4, No. 3,399,109 and No. 3,528,935. Since such a coating composition has an ester bond formed by reacting a carboxylic acid group and an epoxy group as a crosslinking point, it has good acid resistance and also has sufficient weather resistance as an overcoat film for automobiles.

However, such a coating composition has a drawback that it is easily scratched by a brush when washing an automobile using a car washing machine or the like. Further, in this curing system, a hard and brittle coating film is easily formed when only the crosslinking density is increased in order to impart scratch resistance to the coating film during car washing. A hard and brittle coating film is liable to be scratched when rubbed, and when coated on a sealer, it is difficult to deal with expansion and contraction of the sealer and cracks easily occur. Therefore, the coating film with only the increased crosslink density does not have sufficient scratch resistance even in the case of car washing and the like, and it is difficult to use it as a top coating film.

A coating composition capable of improving such scratch resistance improvement is described in JP-A-7-224146 and JP-A-9-71706.
However, although such a coating composition can improve the scratch resistance, the acid resistance may decrease in some cases.

[0006]

In view of the above situation, the present invention is a curable resin composition and a clear coating composition capable of forming a coating film having excellent properties in both scratch resistance and acid resistance. It is intended to provide a product and a method for forming a multilayer coating film.

[0007]

The present invention is a curable composition comprising a half ester acid group-containing acrylic copolymer (1), an epoxy group-containing acrylic copolymer (2) and a carboxyl group-containing polyester polymer (3). A resin composition,
The above half ester acid group-containing acrylic copolymer (1)
Is the following general formula (A);

[0008]

[Chemical 3]

(In the formula, n represents a natural number of 1 to 5.)
A long-chain carboxyl group-containing acrylic monomer represented by and / or the following general formula (B);

[0010]

[Chemical 4]

(In the formula, m represents a natural number of 1 to 5.)
A curable resin composition obtained by using a long-chain carboxyl group-containing acrylic monomer represented by:

The half ester acid group-containing acrylic copolymer (1) is represented by the long chain carboxyl group-containing acrylic monomer represented by the general formula (A) and / or the general formula (B). The monomer (a) composed of a long-chain carboxyl group-containing acrylic monomer is used in an amount of 1 to 50 based on the total amount of the monomer.
Mass%, acid anhydride group-containing ethylenically unsaturated monomer (b)
10 to 40% by mass with respect to the total amount of the monomer, and 10 to 85% by mass of the other copolymerizable ethylenically unsaturated monomer (c) with respect to the total amount of the monomer. The acid anhydride group-containing acrylic copolymer (X) obtained by polymerizing the compound and the monoalcohol (Y) having 1 to 12 carbon atoms have an acid anhydride group / hydroxyl group of 1/1 to 1/0. A half-ester group-containing acrylic copolymer (2) obtained by reacting the epoxy group-containing ethylenic unsaturated monomer (d) with the epoxy group-containing ethylenic unsaturated monomer (d). 10 to 60 mass% with respect to the total amount of monomers, 5 to 60 mass% of the hydroxyl group-containing ethylenically unsaturated monomer (e) with respect to the total amount of monomers, and other copolymerizable ethylenic unsaturated monomers A monomer containing 0 to 85% by mass of the saturated monomer (f) with respect to the total amount of the monomer. It is preferably a copolymer obtained by polymerizing the body composition.

The half ester acid group-containing acrylic copolymer (1) is 10 to 80% by mass relative to the solid mass of the curable resin composition, and the epoxy group-containing acrylic copolymer (2) is It is 20 to 80 mass% with respect to the solid content mass of the curable resin composition, and the carboxyl group-containing polyester polymer (3) is 10 to 85 mass% with respect to the solid content mass of the curable resin composition. It is preferable.

The acid anhydride group-containing ethylenically unsaturated monomer (b) is preferably at least one selected from the group consisting of itaconic anhydride, maleic anhydride and citraconic anhydride.

The C1-12 monoalcohol (Y) is preferably at least one selected from the group consisting of acetol, allyl alcohol, propargyl alcohol, methanol and ethanol.

The half ester acid group-containing acrylic copolymer (1) has a solid content resin acid value of 25 to 300 mg KO.
It is preferable that H / g and the number average molecular weight are 500 to 1300. The above epoxy group-containing acrylic copolymer (2)
Has an epoxy equivalent of 100 to 800 and a hydroxyl value of 40 to
It is preferably 300 mgKOH / g.

The curable resin composition of the present invention preferably further contains a quaternary ammonium salt compound (4). The curable resin composition of the present invention preferably further contains an organotin compound (5).

The present invention is also a clear coating composition containing a curable resin composition as a binder, wherein the curable resin composition is also a clear coating composition which is the curable resin composition.

The present invention comprises a step (I) of applying a base coating composition to a base material coated with the undercoat and / or an intermediate coating to obtain an uncured base coating, and the above step (I). (I) A step of applying a clear coating composition on the uncured base coating film obtained in (1) to obtain an uncured clear coating film (I
I), and a multilayer coating film comprising a step (III) of simultaneously heating and curing the uncured base coating film obtained in the step (I) and the uncured clear coating film obtained in the step (II) A method for forming a multilayer coating film, wherein the clear coating composition is the above-mentioned clear coating composition. The present invention will be described in detail below.

The curable resin composition of the present invention is suitable for use as a binder component of a clear coating composition for automobiles, and comprises the above half ester acid group-containing acrylic copolymer (1) and the above epoxy. It comprises a group-containing acrylic copolymer (2) and the carboxyl group-containing polyester polymer (3).

The curing system for the curable resin composition of the present invention comprising the polymers (1) to (3) is as follows. First, a carboxyl group and a carboxylate group in the half ester acid group-containing acrylic copolymer (1) react with each other by heating to generate an acid anhydride group in the half ester acid group containing acrylic copolymer (1). , Free monoalcohol is produced. The above monoalcohol is removed from the system by evaporation. The acid anhydride group formed in the half ester acid group-containing acrylic copolymer (1) reacts with the hydroxyl group contained in the epoxy group-containing acrylic copolymer (2) to form a cross-linking point, and to re-carboxyl. Form a group. This carboxyl group reacts with the epoxy group present in the epoxy group-containing acrylic copolymer (2) to form a crosslinking point. The carboxyl group in the carboxyl group-containing polyester polymer (3) also forms a crosslinking point by reacting with the epoxy group present in the epoxy group-containing acrylic copolymer (2) by the same reaction mechanism. As described above, the three types of polymers react with each other to promote curing and provide a high crosslink density.

The half ester acid group-containing acrylic copolymer (1) is an acrylic copolymer having in its molecule a half ester acid group obtained by half-esterifying an acid anhydride group with a hydroxyl group, and has the above general formula (A ) A long-chain carboxyl group-containing acrylic monomer and / or a long-chain carboxyl group-containing acrylic monomer represented by the general formula (B). . The half ester group is composed of a carboxyl group and a carboxylate group, and the carboxyl group and the carboxylate group react with each other by heating to give an acid anhydride group in the half ester acid group-containing acrylic copolymer (1). Must be something that you generate.

The above-mentioned monomer (a) has a long-chain carboxyl group as a side chain, but since the above-mentioned long-chain carboxyl group functions as a soft segment, it is obtained from the curable resin composition of the present invention. The cured film has excellent scratch resistance. Further, the carboxyl group at the terminal of the side chain in the monomer (a) causes a reaction with the epoxy group-containing acrylic copolymer (2) in a crosslinking reaction to form a crosslinked chain. By the crosslinking reaction, the soft segment portion is included in the crosslinking chain, so that good scratch resistance can be obtained.

In both the compound represented by the general formula (A) and the compound represented by the general formula (B), the monomer (a) has a specific n or m. It may be a single compound having a value of or a mixture of a plurality of compounds having different n or m. From the viewpoint of easy production of the monomer (a), a mixture of a plurality of components having different values of n or m is preferable. Further, it may be a mixture of the compound represented by the general formula (A) and the compound represented by the general formula (B). Examples of the mixture of the long-chain carboxyl group-containing acrylic monomer represented by the general formula (A), in which n is 1 to 5 and the main monomer (a) is, for example, Aronix M-5300 manufactured by Toagosei Co., Ltd. (Trade name), represented by the general formula (B),
As a mixture of the long-chain carboxyl group-containing acrylic monomer mainly composed of the monomer (a) in which m is 1 to 5, for example, Aronix M-5600 (trade name) manufactured by Toa Gosei Co., Ltd. can be mentioned. When a long chain carboxyl group-containing acrylic monomer consisting of only n or m of 6 or more is used, the above half ester group-containing acrylic copolymer (1)
Since the molecular weight of is too high, the curability deteriorates.

The half ester acid group-containing acrylic copolymer (1) contains the monomer (a) in an amount of 1 to 50% by mass based on the total amount of the monomer, and an acid anhydride group-containing ethylenically unsaturated monomer. 10 to 40% by mass of the body (b) with respect to the total amount of monomers, and 10 to 85% by mass of the other copolymerizable ethylenically unsaturated monomer (c) with respect to the total amount of monomers. Acid anhydride group-containing acrylic copolymer (X) obtained by copolymerizing a monomer composition and a monoalcohol (Y) having 1 to 12 carbon atoms have an acid anhydride group / hydroxyl group of 1/1 ~ 1 / 0.5
It is preferable that the half-ester group-containing acrylic copolymer (1) is obtained by reacting at a ratio of.

The acid anhydride group-containing acrylic copolymer (X) is a monomer having the monomer (a) within the range of 1% by mass for the lower limit and 50% by mass for the upper limit. It is preferably obtained from the composition. When the amount of the monomer (a) is less than 1% by mass, the effect of scratch resistance is not sufficiently obtained, which is not preferable. When the amount of the monomer (a) exceeds 50% by mass, the effect cannot be improved beyond a certain level even if the amount is increased, which is not preferable. The lower limit is more preferably 3% by mass, further preferably 5% by mass. The upper limit is more preferably 35% by mass, further preferably 30% by mass.

The acid anhydride group-containing ethylenically unsaturated monomer (b) is an acid anhydride group-containing radically polymerizable ethylenically unsaturated monomer. The acid anhydride group-containing ethylenically unsaturated monomer (b) is not particularly limited,
For example, itaconic anhydride, maleic anhydride, citraconic anhydride, etc. can be mentioned. The acid anhydride group-containing ethylenically unsaturated monomer (b) may be a combination of two or more components.

The acid anhydride group-containing acrylic copolymer (X) has a lower limit of 10% by mass and an upper limit of 4% based on the total amount of the acid anhydride group-containing ethylenically unsaturated monomer (a).
It is preferably obtained from a monomer composition having a content of 0% by mass. When the acid anhydride group-containing ethylenically unsaturated monomer (b) is less than 10% by mass, a sufficient crosslink density cannot be obtained and the physical properties of the film may deteriorate. When the upper limit exceeds 40% by mass, the viscosity is extremely increased, and it becomes difficult to obtain a curable resin composition having a high solid content. The lower limit is more preferably 15% by mass, and further preferably 20% by mass. The upper limit is more preferably 35% by mass, further preferably 30% by mass.

The other copolymerizable ethylenically unsaturated monomer (c) is not particularly limited, and examples thereof include styrenes such as styrene and α-methylstyrene; methyl acrylate, ethyl acrylate, propyl acrylate. , Acrylic acid-n, i and t-butyl, acrylic acid esters such as 2-ethylhexyl acrylate and lauryl acrylate; methyl methacrylate, ethyl methacrylate, propyl methacrylate, methacrylic acid-n, i and t-. Examples thereof include methacrylic acid esters such as butyl, 2-ethylhexyl methacrylate, and lauryl methacrylate; amides such as acrylamide and methacrylamide. These may be used alone or in combination of two or more.

The other ethylenically unsaturated monomer (c) is represented by the above general formula (A) or (B) within a range that does not impair the effects of the present invention, and n or m is a natural number of 6 or more. It may have a monomer that is That is, in the synthesis of the monomer (a), n or m may have a component of 6 or more, but even in such a case, the component of n or m of 6 or more is not removed, It can be used as it is as a raw material.

When the monomer represented by the general formula (A) has a natural number of 6 or more, the number average molecular weight of all the monomers represented by the general formula (A) has a lower limit of 150. The upper limit is preferably within the range of 400. When the monomer represented by the general formula (B) has a natural number of 6 or more, the number average molecular weight of all the monomers represented by the general formula (B) has a lower limit of 150 and an upper limit of 500. It is preferably within the range.

The acid anhydride group-containing acrylic copolymer (X) is the above-mentioned other ethylenically unsaturated monomer (c).
It is preferable that it is obtained from a monomer composition having a lower limit of 10% by mass and an upper limit of 85% by mass with respect to the total amount of monomers. The other ethylenically unsaturated monomer (c) may not be contained at all. When the other ethylenically unsaturated monomer (c) exceeds 85% by mass, the amount of the monomer (a) and the acid anhydride group-containing ethylenically unsaturated monomer (b) to be blended is Since it is decreased, sufficient curability and scratch resistance cannot be obtained, which is not preferable. The lower limit is more preferably 20% by mass, further preferably 30% by mass. The upper limit is more preferably 80% by mass and even more preferably 75% by mass.

The method for copolymerizing the acid anhydride group-containing acrylic copolymer (X) is not particularly limited, and examples thereof include:
Examples of the method include solution polymerization such as ordinary radical polymerization.

The radical polymerization initiator used in the above polymerization reaction is not particularly limited, and examples thereof include t-butylperoxy-2-ethylhexanoate and dimethyl-2,2 '.
-Azobisisobutyrate etc. can be mentioned. These may be used alone or in combination of two or more. The radical polymerization initiator is preferably used in a ratio of the lower limit of 3 mass% and the upper limit of 15 mass% with respect to the total amount of the above-mentioned monomers. A chain transfer agent or the like may be added as an additive to the above copolymerization.

The acid anhydride group-containing acrylic copolymer (X) preferably contains at least two acid anhydride groups in one molecule. If it is less than 2, the curability will be insufficient. It is more preferable that the lower limit is 2 and the upper limit is 15.

The half-esterifying agent used for half-esterifying the acid anhydride group of the acid anhydride group-containing acrylic copolymer (X) is a monoalcohol (Y) having 1 to 12 carbon atoms. preferable. The above-mentioned monoalcohol is preferable because it has good reactivity and has a low boiling point, so that it has good evaporativity at the time of heat curing, and that the curing reaction can proceed satisfactorily. The C1-12 monoalcohol (Y) is not particularly limited, and examples thereof include methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, t-butanol, methylcellosolve, and ethylcellosolve. , Dimethylaminoethanol, diethylaminoethanol, acetol, allyl alcohol, propargyl alcohol and the like. These may be used alone or in combination of two or more. Among these, acetol, allyl alcohol, propargyl alcohol, and methanol are more preferable.

The reaction method of the above half esterification is not particularly limited, and for example, it can be carried out in the presence of a catalyst at a temperature of room temperature to 120 ° C. according to a usual method.
The catalyst is not particularly limited, and examples thereof include tertiary amines such as triethylamine and tributylamine; quaternary ammonium salts such as benzyltrimethylammonium chloride, benzyltrimethylammonium bromide, benzyltributylammonium chloride and benzyltributylammonium bromide. Is mentioned. These may be used alone or in combination of two or more.

In the above half esterification reaction,
The molar ratio of the acid anhydride group and the hydroxyl group is lower limit 1/1 and upper limit 1
It is preferable to react the acid anhydride group-containing polymer (X) with the monoalcohol (Y) having 1 to 12 carbon atoms so that the ratio is within the range of /0.5. The above ratio is 1
If it is less than / 1, the excess alcohol may be too much and cause cracking during curing. If the above ratio exceeds 1 / 0.5, unreacted anhydride groups remain and storage stability may deteriorate, which is not preferable. The above lower limit is 1 /
1. The upper limit is preferably 1 / 0.7.

The number average molecular weight (Mn) of the acrylic ester group-containing half ester acid group (1) is preferably in the range of 500 as the lower limit and 20000 as the upper limit. The lower limit is more preferably 1000, and the upper limit is 10
It is more preferably 000. When the number average molecular weight (Mn) is less than 500, the curability is insufficient and
When it exceeds 20,000, the viscosity of the copolymer becomes high and it is difficult to form a curable resin composition having a high solid content, which is not preferable. In the present specification, the number average molecular weight (Mn)
Is a polystyrene-equivalent number average molecular weight measured by GPC (gel permeation chromatography).

The half ester acid group-containing acrylic copolymer (1) has a solid resin acid value of 25 mgKOH at the lower limit.
/ G, the upper limit is preferably 300 mgKOH / g. When the acid value is less than 25 mgKOH / g, a sufficient crosslink density cannot be obtained, and the curability is not sufficient. When the acid value exceeds 300 mgKOH / g,
There may be a problem that the viscosity becomes high and it becomes difficult to form a curable resin composition having a high solid content. The above lower limit is 60
It is preferably mgKOH / g, and the upper limit is 2
It is preferably 00 mgKOH / g.

The half ester acid group-containing acrylic copolymer (1) is contained in a ratio of lower limit of 10% by mass and upper limit of 80% by mass with respect to the mass of solid content contained in the curable resin composition. preferable. If less than 10% by mass, 8
Even if it exceeds 0% by mass, there is a problem that the curability becomes insufficient, which is not preferable. The above lower limit is more preferably 15% by mass, and further preferably 20% by mass. The upper limit is more preferably 50% by mass, and further preferably 40% by mass.

The epoxy group-containing acrylic copolymer (2) is an acrylic polymer having an epoxy group in its molecule, and contains the epoxy group-containing ethylenically unsaturated monomer (d) and other ethylenic unsaturated monomers. Saturated monomer (f)
It is preferably a copolymer obtained by copolymerizing a monomer composition comprising

The epoxy group-containing ethylenically unsaturated monomer (d) is not particularly limited, and examples thereof include glycidyl (meth) acrylate and 3,4-epoxycyclohexanylmethyl methacrylate. You may use together 2 or more types of the said monomer. The epoxy group-containing ethylenically unsaturated monomer (d) is preferably contained in the above monomer composition at a ratio within a range of a lower limit of 30% by mass and an upper limit of 70% by mass. If it is less than 30% by mass, sufficient curability may not be obtained, and if it exceeds 70% by mass, the flexibility of the coating film may be deteriorated and scratch resistance may be deteriorated.

The other ethylenically unsaturated monomer (f) is not particularly limited, and for example, the copolymerizable ethylenic unsaturated monomer (f) used in the polymerization of the half ester acid group-containing acrylic copolymer (1) is used. A monomer that can be used as the saturated monomer (c) can be used. The other ethylenically unsaturated monomer (f) has a lower limit of 30.
It is preferably contained in the above-mentioned monomer composition in a proportion of mass% and an upper limit of 70 mass%.

The above epoxy group-containing acrylic copolymer (2) is a copolymer obtained by further copolymerizing a monomer composition having a hydroxyl group-containing ethylenically unsaturated monomer (e). It is preferable. By having the above-mentioned hydroxyl group-containing ethylenically unsaturated monomer (e), the curability of the entire resin composition is improved, which is preferable. The hydroxyl group-containing ethylenically unsaturated monomer (e) is not particularly limited, and examples thereof include 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and Praxel FM-1 (commodity). Name, manufactured by Daicel Chemical Industries, Ltd.),
Praxel FA-1 (trade name, manufactured by Daicel Chemical Industries, Ltd.)
Etc. can be mentioned. The hydroxyl group-containing ethylenically unsaturated monomer (e) has a lower limit of 10 in the monomer composition.
It is preferable to have a ratio within the range of 50% by mass and the upper limit of 50% by mass. If it is less than 10% by mass, the effect of improving the curability cannot be sufficiently exerted, and if it exceeds 50% by mass, the viscosity may increase.

The copolymerization method is not particularly limited,
For example, a solution polymerization method such as radical polymerization can be used. The number average molecular weight (Mn) of the above copolymer is
It is preferable that the lower limit is 500 and the upper limit is 20,000. More preferably, the lower limit is 1000 and the upper limit is 18000. When the number average molecular weight (Mn) is less than 500,
The curability is not sufficient, and when it exceeds 20,000, the viscosity of the copolymer becomes high and it becomes difficult to form a curable resin composition having a high solid content. As the radical polymerization initiator used in the above-mentioned polymerization reaction, the same one as in the reaction of the above half ester acid group-containing acrylic copolymer (1) can be used.

The epoxy group-containing acrylic copolymer (2) preferably has an epoxy equivalent in the range of 100 as the lower limit and 800 as the upper limit. The epoxy equivalent is 10
When it is less than 0, there may be a problem that the flexibility of the coating film is lowered. When the epoxy equivalent exceeds 800, the number of epoxy groups is small, and thus sufficient curability may not be obtained. The lower limit is more preferably 250. The upper limit is more preferably 600.

The epoxy group-containing acrylic copolymer (2) preferably has a hydroxyl value within the range of a lower limit of 40 mgKOH / g and an upper limit of 300. When the hydroxyl value is less than 40, there may be a problem that curability is lowered. If the hydroxyl value exceeds 300, the viscosity may increase.

The epoxy group-containing acrylic copolymer (2) is preferably contained in a ratio of the lower limit of 20% by mass and the upper limit of 80% by mass based on the mass of the solid content contained in the curable resin composition. If it is out of the above range, there is a problem that curability becomes insufficient, which is not preferable. The above lower limit is more preferably 30% by mass, and further preferably 40% by mass. The upper limit is more preferably 70% by mass, and further preferably 60% by mass.

The carboxyl group-containing polyester polymer (3) is a polyester polymer having a carboxyl group in the molecule. The carboxyl group-containing polyester polymer (3) preferably has, as the carboxyl group, a carboxyl group generated by an addition reaction of an acid anhydride group and a hydroxyl group.

The carboxyl group-containing polyester polymer (3) includes a polyester polyol obtained by adding a lactone compound (h) to a polyhydric alcohol (g) and carrying out a chain extension reaction, and an acid anhydride group-containing polyester polyol. It is preferable to use a polymer obtained by the reaction with the compound (i).

Since the carboxyl group-containing polyester polymer (3) obtained by the above reaction has a sharp molecular weight distribution, the curable resin composition of the present invention can be highly solidified (high solidification), It is preferable because a cured film having excellent weather resistance and water resistance can be obtained, and at the same time, a cured film having excellent chipping resistance and skin appearance can be obtained.

The polyhydric alcohol (g) is a compound having at least 3 hydroxyl groups in one molecule. The polyhydric alcohol (g) is not particularly limited, and, for example,
Trimethylolpropane, trimethylolethane, 1,
2,4-butanetriol, ditrimethylolpropane, pentaerythritol, dipentaerythritol,
Examples thereof include glycerin. These may be used alone or in combination of two or more.

The lactone compound (h) is not particularly limited as long as it is a lactone compound capable of causing a ring-opening addition reaction with the polyhydric alcohol compound. The lactone compound (h) preferably has 4 to 7 carbon atoms because it easily causes the ring-opening addition reaction.

The lactone compound (h) is not particularly limited and includes, for example, ε-caprolactone, γ-caprolactone, γ-valerolactone, δ-valerolactone and γ.
-Butyrolactone and the like can be mentioned. These may be used alone or in combination of two or more. Among these, ε-caprolactone is more preferable from the viewpoint of reactivity and the like.

The above chain extension reaction can be carried out under the same conditions as in ordinary ring-opening addition reaction. For example, the polyester polyol in which the polyhydric alcohol (g) is chain-extended can be obtained by reacting in a suitable solvent or without solvent at a temperature of 80 to 200 ° C. for 5 hours or less. In the above reaction, a tin catalyst or the like may be used.

In the chain extension reaction, the ratio of the hydroxyl groups of the polyhydric alcohol (g) to the lactone compound (h) is such that the lactone compound (h) is relative to the hydroxyl groups of the polyhydric alcohol (g). Is the lower limit of 0.2 in molar ratio,
It is preferable to use it in a ratio within the range of the upper limit of 10. If the ratio is less than 0.2, the coating film becomes hard and the impact resistance of the coating film decreases, and if it exceeds 10, the hardness of the coating film decreases. The lower limit is more preferably 0.25,
More preferably, it is 0.3. The upper limit is more preferably 5, still more preferably 3.

The acid anhydride group-containing compound (i) is not particularly limited, and examples thereof include phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, 4-methylhexahydrophthalic anhydride, trimellitic anhydride, Examples thereof include succinic anhydride. The acid anhydride group-containing compound (i) is more preferably a compound having 8 to 12 carbon atoms, and further preferably hexahydrophthalic anhydride, 4-methylhexahydrophthalic anhydride or trimellitic anhydride. preferable. These may be used alone or in combination of two or more.

The method of addition reaction between the polyester polyol and the acid anhydride group-containing compound (i) is not particularly limited. For example, the half ester carried out in the half ester acid group-containing acrylic copolymer (1) is used. The reaction can be carried out under the same reaction conditions as in the above.

In the addition reaction, the number of the acid anhydride (i) with respect to the hydroxyl group of the polyhydric alcohol (g) is in the range of lower limit 0.2 and upper limit 1.0 in terms of molar ratio. preferable. When the above molar ratio is less than 0.2, the curability of the paint may be insufficient. The lower limit of the molar ratio is more preferably 0.5, and the upper limit of the molar ratio is more preferably 0.9.

It is not necessary to modify all the hydroxyl groups of the above polyester polyol to carboxyl groups, and hydroxyl groups may remain. That is, since the above-mentioned carboxyl group-containing polyester polymer (3) having a hydroxyl group simultaneously provides a coating film surface with a carboxyl group and a hydroxyl group, for example, when recoated, the above-mentioned carboxyl group-containing polyester having no hydroxyl group. Excellent adhesion can be provided as compared with the polymer (3).

The carboxyl group-containing polyester polymer (3) has an acid value of 50 mgKOH / g as the lower limit and 3 as the upper limit.
It is preferably within the range of 50 mgKOH / g. When the acid value is less than 50 mgKOH / g, curability may be insufficient, and when the acid value exceeds 350 mgKOH / g, the carboxyl group-containing polyester polymer (3)
In some cases, the viscosity becomes too high and it becomes difficult to obtain a curable resin composition having a high solid content. The above lower limit is 100 mgKOH
/ G is more preferable, and 120 mgKOH / g
Is more preferable. The upper limit is 300 mg KO
More preferably H / g, 250 mg KOH /
More preferably, it is g.

The number average molecular weight (Mn) of the carboxyl group-containing polyester polymer (3) is preferably in the range of lower limit 400 and upper limit 3500. Molecular weight is 40
If it is less than 0, the curability may be insufficient or the water resistance of the cured film may be reduced. If the molecular weight exceeds 3500, the carboxyl group-containing polyester polymer (3) will have too high a viscosity and will be difficult to handle. Therefore, it may be difficult to obtain a curable resin composition having a high solid content. The lower limit is more preferably 500, and even more preferably 700. More preferably, the upper limit is 3000,
It is more preferably 2500.

The above carboxyl group-containing polyester polymer (3) has a mass average molecular weight (Mw) / number average molecular weight (M
It is preferable that n) is 1.8 or less. If the mass average molecular weight (Mw) / number average molecular weight (Mn) exceeds 1.8, the water resistance or weather resistance of the coating film may decrease. The mass average molecular weight (Mw) / number average molecular weight (Mn) is more preferably 1.5 or less, further preferably 1.4 or less.

When the carboxyl group-containing polyester polymer (3) has a hydroxyl group, the carboxyl group-containing polyester polymer (3) preferably has a hydroxyl value of 150 mgKOH / g or less. If the hydroxyl value exceeds 150 mgKOH / g, the water resistance of the coating film may decrease. Preferably lower limit 5 mg KOH
/ G and the upper limit is 100 mgKOH / g. The lower limit is more preferably 10 mg, and the upper limit is more preferably 80 mgKOH / g.

The carboxyl group-containing polyester polymer (3) is preferably contained in the curable resin composition in an amount of 10% by mass as the lower limit and 85% by mass as the upper limit. If it is less than 10% by mass, a curable resin composition having a high solid content is unlikely to be formed, and if it exceeds 85% by mass, the weather resistance of the cured film is deteriorated, which is not preferable. The lower limit is more preferably 15% by mass, further preferably 18% by mass. The upper limit is more preferably 50% by mass, and further preferably 40% by mass.

In the curable resin composition of the present invention, [total number of epoxy groups in epoxy group-containing acrylic copolymer (2)] / [half ester acid group-containing acrylic copolymer (1) and carboxyl group-containing polyester polymer] (3) Total number of half-esterified acid anhydride groups and carboxyl groups] = 0.5 to 1.5 is preferable. The lower limit of the total number of epoxy groups in the epoxy group-containing acrylic copolymer (2) is more preferably 0.6, and the upper limit of the total number of epoxy groups in the epoxy group-containing acrylic copolymer (2) is It is more preferably 1.3. Further, [total number of hydroxyl groups of the above epoxy group-containing acrylic copolymer (2)] / [total number of half-esterified acid anhydride groups of the above half ester acid group-containing acrylic copolymer (1)] = 0.1 It is preferably 1.5.
The lower limit of the total number of hydroxyl groups of the epoxy group-containing acrylic copolymer (2) is more preferably 0.3, and the upper limit of the total number of hydroxyl groups of the epoxy group-containing acrylic copolymer (2) is 1. More preferably, it is 2.

The compounding amount of the epoxy group-containing acrylic copolymer (2) giving the above ratio is, for example, that of the half ester acid group-containing acrylic copolymer (1) and the carboxyl group-containing polyester polymer (3). It is preferable that the lower limit is 50% by mass and the upper limit is 250% by mass with respect to 100% by mass in total. The lower limit is more preferably 80% by mass, and the upper limit is preferably 150% by mass. When the compounding amount of the epoxy group-containing acrylic copolymer (2) is less than 50% by mass, sufficient curing may not be performed, and the cured film may have reduced water resistance, weather resistance, etc. If it exceeds, unreacted carboxyl groups may remain and the chemical resistance may decrease.

The curable resin composition may have, for example, a curing catalyst. Examples of the curing catalyst include quaternary ammonium salt compound (4). The quaternary ammonium salt compound (4)
Is not particularly limited, and examples thereof include benzyltriethylammonium chloride and bromide; tetrabutylammonium chloride, bromide, salicylate, glycolate, paratoluenesulfonate, nitrate, dibutylphosphate and di-2-ethylhexylphosphate; trimethylbenzylammonium dibutylphosphate. Trimethyl cetyl ammonium butyl phosphate; octyl trimethyl ammonium dimethyl phosphate; dodecyl trimethyl ammonium diphenyl phosphate and the like. These catalysts may be used alone or as a mixture of two or more of the above. The blending amount of the quaternary ammonium salt compound is preferably within the range of the lower limit of 0.1% by mass and the upper limit of 2.0% by mass with respect to the solid mass of the curable resin composition.

The curable resin composition may contain the organotin compound (5). The organic tin compound (5) is not particularly limited, and examples thereof include dimethyltin bis (methylmalate), dimethyltin bis (ethylmalate), dimethyltin bis (butylmalate), dibutyltin bis (butylmalate), dibutyltin bis (dodecylbenzene sulfonate). Etc. When the quaternary ammonium salt compound (4) and the organic tin compound (5) are used in combination, the compounding amount is a total amount of these with respect to the solid content of the curable resin composition, and the lower limit is 0.1% by mass, The upper limit is preferably 3.0% by mass. The organotin compound (5) is more preferably used in combination with the quaternary ammonium salt compound. The combined use of the quaternary ammonium salt compound (4) and the organic tin compound (5) is preferable in that good curability can be obtained.

Since the polymer used in the present invention has an acidic group as a functional group, it can be neutralized with an amine to
It is also possible to make an aqueous polymer composition using water as a medium.

The present invention is also a clear coating composition containing the curable resin composition as a binder component. In the clear coating composition, in addition to the binder component, an additive that can be used in the clear coating composition such as an ultraviolet absorber, a hindered amine light stabilizer, an antioxidant, a crosslinked resin particle, and a surface modifier. You may mix. When the crosslinked resin particles are used, the lower limit is 0.01% by mass and the upper limit is 1 with respect to the resin solid content of the curable resin composition of the present invention.
It is preferable to mix it in a proportion of 0 mass%. The lower limit is more preferably 0.1% by mass, and the upper limit is more preferably 5% by mass. When the amount of the crosslinked resin particles added exceeds 10% by mass, the appearance of the coating film obtained deteriorates, and when it is less than 0.01% by mass, the rheology control effect cannot be obtained.

The clear coating composition of the present invention can be applied by spray coating, brush coating, dip coating, roll coating, flow coating or the like.

The clear coating composition of the present invention can be applied to any substrate such as wood, metal, glass, cloth, plastic,
Foams, etc., especially plastic and metal surfaces, eg
It can be advantageously used for steel, aluminum and alloys thereof. Particularly, it is preferably used as a clear coating for automobiles.

According to the method for forming a multilayer coating film of the present invention, a base paint is applied to an object to be coated to form an uncured base film, and then the clear coating composition is applied onto the uncured base film. It is applied to form a clear uncured coating film, and the base uncured coating film and the clear uncured coating film are simultaneously heated and cured.

The above-mentioned article to be coated can be used for various base materials such as metal molded articles, plastic molded articles, foams, etc., but as the article to be coated for forming a multilayer coating film for automobiles, Examples thereof include metal molded products such as iron, aluminum and alloys thereof, and plastic molded products. It is preferably applied to a metal molded product that can be subjected to cationic electrodeposition coating. It is preferable that the surface of the article to be coated is subjected to chemical conversion treatment. Further, the object to be coated may have an electrodeposition coating film formed thereon. As the above electrodeposition paint, a cation type and anion type can be used, but from the viewpoint of anticorrosion property, the cation type electrodeposition paint is preferable.

Further, if necessary, an intermediate coating film may be formed. An intermediate coating material is used for forming the intermediate coating film. The intermediate coating material is not particularly limited, and examples thereof include water-based or organic solvent-based coating materials well known by those skilled in the art.

The base paint is not particularly limited,
For example, a coating film-forming resin, a curing agent, a coloring pigment such as an organic-based, inorganic-based or bright material, and an extender pigment may be included. The form of the base paint is not particularly limited, and examples thereof include an aqueous or organic solvent type.

The method of applying the base paint to the article to be coated is not particularly limited, and spray coating,
Examples thereof include rotary atomization coating, and from the viewpoint of improving the appearance, multistage coating using these methods or a coating method combining these is preferable.

In the method for forming a multilayer coating film of the present invention, the coating film thickness of the above base paint is a lower limit of 10 μm in dry film thickness,
The upper limit is preferably 20 μm.

In the method for forming a multilayer coating film of the present invention, when the above base coating material is water-based, in order to obtain a good finished coating film, the base uncured coating is applied before coating the above clear coating composition. It is desirable to heat the membrane at 40-100 ° C for 2-10 minutes. Specific examples of the method of applying the clear coating composition in the method for forming a multilayer coating film of the present invention include a micro-microbell and a coating method using a rotary atomization type electrostatic coating machine called microbell. You can

The coating film thickness of the above clear coating composition in the method for forming a multilayer coating film of the present invention has a lower limit of 30 μ as a dry film thickness.
m, and the upper limit is preferably 45 μm.

The base uncured coating film and the clear uncured coating film formed by the above method are simultaneously heated and cured to form a multilayer coating film. The heating temperature has a lower limit of 10
It is preferable to perform the treatment at 0 ° C. and the upper limit of 180 ° C. It is more preferable that the lower limit is 120 ° C and the upper limit is 160 ° C. The heat curing time varies depending on the curing temperature etc.,
When it is carried out at the above-mentioned heat curing temperature, it is suitable to be 10 to 30 minutes.

The film thickness of the multilayer coating film thus obtained is preferably within the range of the lower limit of 40 μm and the upper limit of 65 μm. The multilayer coating film obtained by the above method has excellent coating film physical properties such as scratch resistance, acid resistance, and solvent resistance.

[0085]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the examples, "parts" means "parts by mass" unless otherwise specified.

Synthesis Example 1 Acrylic Copolymer Containing Half Ester Acid Group (1) (K-1) 1050 parts of xylene in a 3 liter reaction vessel equipped with a thermometer, a stirrer, a cooling tube, a nitrogen introducing tube and a dropping funnel. Was charged and the temperature was raised to 130 ° C. Then, here, with stirring, 300 parts of styrene and 25 parts of 2-ethylhexyl acrylate.
0 part, isobutyl methacrylate 100 parts, long chain carboxyl group-containing monomer (A-1) [represented by the general formula (A),
n = 1; Aldrich reagent] 100 parts, maleic anhydride 250 parts, propylene glycol monomethyl ether acetate 300 parts and t-butyl peroxy 2-.
A monomer composition consisting of 150 parts of ethylhexyl hexanoate and an initiator solution were added dropwise over 3 hours. 2 more
125 parts of methanol was added to the copolymer obtained by continuing stirring for an hour, and reacted at 70 ° C. for 20 hours,
Acid value 150mgKOH / g (solid content conversion), nonvolatile content 4
A half ester group-containing acrylic copolymer (1) (K-1) having a 3% number average molecular weight of 2,200 was obtained.

Synthesis Examples 2 to 7 Half-ester group-containing acrylic copolymer (1) (K) was prepared in the same manner as in Synthesis Example 1 except that the formulations shown in Table 1 were used.
-2) to (K-7) were obtained. In Table 1, monomer (B-1)
[Aronix M-5600 (trade name) manufactured by Toagosei Co., Ltd.] is represented by the general formula (B), and m = 1, 2, 3, 4
And a number average molecular weight of 2
00. The monomer (A-2) [Aronix M-5300 (trade name) manufactured by Toagosei Co., Ltd.] is represented by the general formula (A), and n = 1, 2, 3, 4, and 5. And has a number average molecular weight of 200.

Synthetic Example 8 Epoxy Group-Containing Acrylic Copolymer (2) (L) A 2 liter reaction vessel equipped with a thermometer, stirrer, cooling tube, nitrogen introducing tube and dropping funnel was charged with 640 parts of xylene. The temperature was raised to ° C. 380 parts of glycidyl methacrylate, 4-hydroxybutyl acrylate 1 in a dropping funnel
A monomer and initiator solution consisting of 28 parts, 292 parts of isobutyl acrylate and 100 parts of t-butylperoxy 2-ethylhexanoate was added dropwise over 3 hours. After the dropping was completed, the temperature was kept at 130 ° C. for 30 minutes, and then a solution containing 5 parts of t-butylperoxy 2-ethylhexanoate and 50 parts of xylene was added dropwise over 30 minutes. After completion of the dropwise addition, the reaction was continued for another 2 hours at 130 ° C. to obtain an epoxy group-containing acrylic copolymer (L) having a nonvolatile content of 59%, a number average molecular weight of 2700, a hydroxyl value of 85 mgKOH / g and an epoxy equivalent of 400.

Synthetic Example 9 Carboxyl Group-Containing Polyester Polymer (3) (M-1) 136 parts of pentaerythritol and 456 parts of ε-caprolactone were placed in a 2 L reaction tank equipped with a thermometer, a stirrer, a cooling tube and a nitrogen introducing tube. And 0.1 part of dibutyltin oxide to 1 part
The temperature was raised to 70 ° C. and kept at 170 ° C. for 3 hours.
Then, hexahydrophthalic anhydride 5 dissolved by heating
After adding 39 parts and holding at 150 ° C. for 1 hour, 464 parts of ethyl 3-ethoxypropionate was added to give a number average molecular weight of 1700, an acid value of 174 mgKOH / g (solid content conversion),
Hydroxyl value 25 mgKOH / g (solid content conversion), nonvolatile content 71% carboxyl group-containing polyester polymer (M
-1) was obtained.

Synthesis Example 10 Carboxyl Group-Containing Polyester Polymer (3) (M-2) In a 2 L reaction vessel equipped with a thermometer, a stirrer, a cooling tube and a nitrogen introducing tube, 136 parts of pentaerythritol and 912 parts of ε-caprolactone. And 1 part of 0.2 parts of dibutyltin oxide
The temperature was raised to 70 ° C. and kept at 170 ° C. for 3 hours.
Then, hexahydrophthalic anhydride 5 dissolved by heating
After adding 38 parts and holding at 150 ° C. for 1 hour, 444 parts of ethyl 3-ethoxypropionate was added to give a number average molecular weight of 2500, an acid value of 130 mgKOH / g (solid content conversion) and a hydroxyl value of 19 mgKOH / g (solid content conversion). ), And a carboxyl group-containing polyester polymer (M-2) having a nonvolatile content of 75% was obtained.

[0091]

[Table 1]

Synthesis Example 11 Acrylic Copolymer (N) for Base Coating Composition 76 parts of ethylene glycol monobutyl ether was charged into a 1 L reaction vessel equipped with a stirrer, a temperature controller, and a cooling tube, and 15 parts of styrene and methyl methacrylate were further charged. 63
Part, 2-hydroxyethyl methacrylate 48 parts, n-
Butyl acrylate 117 parts, methacrylic acid 27 parts, acrylamide 30 parts and azobisisobutyronitrile 3
61 parts of a monomer solution of 100 parts was added and the temperature was raised to 120 ° C. with stirring. After adding 245 parts of the above monomer solution in 3 hours, stirring was continued for 1 hour. Further, 28 parts of dimethylethanolamine and 200 parts of deionized water were added to obtain an acrylic copolymer (N) for a base coating composition having a volatile content of 50% and a resin number average molecular weight of 12,000. The above polymer had an OH value of 70 and an acid value of 58.

Synthesis Example 12 Urethane Group-Containing Water Dispersion (O) for Base Coating Composition 40.2 parts of dimethylolpropionic acid, 30 parts of triethylamine and N-methyl were placed in a 100 ml reaction vessel equipped with a thermometer, a stirrer and a condenser. Pyrrolidone (312 parts) was added, and the mixture was heated and dissolved at 90 ° C. Next, 290 parts of isophorone diisocyanate and 700 parts of polypropylene glycol (molecular weight: 1000) were added, and after stirring for 10 minutes, 1.03 parts of dibutyltin dilaurate was added. Next, the temperature was raised to 95 ° C. and the reaction was carried out for 1 hour. Then a thermometer, a stirrer,
15000 parts of deionized water and hydrazine hydrate 9.2 in a 5000 ml reaction vessel equipped with a condenser and a dropping funnel.
Parts were added and the urethane prepolymer solution obtained above was added under stirring. Then, the mixture was stirred for 30 minutes to obtain a urethane machine-containing water dispersion (O) for a base coating composition. The urethane group-containing water dispersion (O) for the base coating composition is
It was a cloudy and stable aqueous dispersion. The urethane machine-containing water dispersion (O) for the base coating composition had an acid value of solid content of 16.2 and a nonvolatile content of 33%.

Examples 1 to 5 By preparing clear coating compositions having the curable resin composition of the present invention obtained by using the polymers prepared in Synthesis Examples 1 to 10 as a binder component and measuring the physical properties, An evaluation was made.

Example 1 A clear coating composition was prepared by mixing the components in the composition shown in Table 2. The clear composition was diluted to a coating viscosity with a solvent consisting of butyl acetate / xylene = 1/1 to obtain a clear coating. Water-based base paint (Nippon Paint Co., Ltd. super rack) M260) and then dried at 60 ° C for 5 minutes, and then the above clear coating is applied wet-on-wet at 140 ° C ×
It was baked for 30 minutes to form a cured coating film. The cured coating film was evaluated by the following evaluation methods. The results are shown in Table 2. At that time, the dry film thickness of the clear coating was 40 μm.

(Paint Stability) After leaving the obtained clear coating for 1 week at room temperature, the presence or absence of turbidity and separation was visually determined. When there was no turbidity or separation, it was designated as "OK".

(Pencil hardness) JIS K5600-5-4
Evaluation was performed according to the method described in 1.

(Warm water resistance) The obtained cured coating film was immersed in warm water of 40 ° C. for 10 days, and then the surface of the coating film was visually evaluated. When no change was observed, it was designated as "OK".

(Acid resistance) The above cured coating film and 0.1N H ₂
After contact with 0.2 ml of SO ₄ aqueous solution at 60 ° C. for 2 hours, the coating film surface was visually evaluated according to the following criteria. ◎ No change was observed ○ Slight traces were seen △ Clearly traces were seen.

(Scratch resistance) 1 g of 50% aqueous dispersion of cleanser (New Homing Cleanser (trade name; manufactured by Kao Corporation, polishing agent 87%, surfactant 5%, and other components blended) was applied 2 ×. A 2 cm flannel cloth was attached to a Gakushin type dyeing friction fastness tester (manufactured by Daiei Kagaku Seiki Co., Ltd.), and the resulting cured coating film was rubbed 10 times with a load of 500 g. Sample Suga Tester Co., Ltd.
The 20 ° gloss measured by using a gloss meter manufactured by a company is measured, and the retention rate with respect to the value of 20 ° gloss of the sample before the treatment is shown in%. The correspondence between the retention rate and visual evaluation is shown below. > 90 No change 80-90 Scratches are slightly visible but not noticeable 70-80 Scratches are slightly visible 70> Scratches are clearly visible

Examples 2-5, Comparative Examples 1 and 2 The clear coating compositions of Examples 2-5 and Comparative Examples 1 and 2 were prepared in the same manner as in Example 1 except that the formulations shown in Table 2 were used. Then, after diluting, a cured coating film was prepared and the coating film performance was evaluated. The evaluation results are shown in Table 3.

[0102]

[Table 2]

[0103]

[Table 3]

As is clear from the results of Table 3, Example 1
The clear coating compositions of Nos. 5 to 5 provide coatings with better scratch resistance than those of the Comparative Examples. It is also excellent in acid resistance. Furthermore, high solidification of clear paint is possible.

[0105]

The cured film obtained from the curable resin composition of the present invention has excellent acid resistance and abrasion resistance. A clear coating composition having excellent acid resistance and scratch resistance can be formed by the clear coating composition using the curable resin composition as a binder.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C09D 135/00 C09D 135/00 167/00 167/00 (72) Inventor Hisashi Tanabe Ikeda, Neyagawa, Osaka Nakamachi 19-17, Japan Paint Co., Ltd. (72) Inventor Shinya Yamada 19-17 Ikeda Nakamachi, Neyagawa-shi, Osaka F-Term (Japan) 4P075 AE12 BB26Z CA02 CA13 CA32 CA38 CA44 CB06 DA06 DA25 DB02 DB07 DB13 DB20 DB21 DB31 DC11 EA07 EA43 EB14 EB20 EB22 EB33 EB35 EB38 EB52 EB55 EB56 EC07 EC08 EC37 4J036 AK10 AK11 FB03 FB11 GA02 GA09 JA01 JA04 KA01 4J038 CG061 CG141 CH141B06 NACH CH161 CH151 CH161 CH161 CH161

Claims (11)

[Claims] 1. A curable resin composition comprising a half ester acid group-containing acrylic copolymer (1), an epoxy group-containing acrylic copolymer (2) and a carboxyl group-containing polyester polymer (3), The half ester acid group-containing acrylic copolymer (1) has the following general formula (A); (In the formula, n represents a natural number of 1 to 5.) and / or a long chain carboxyl group-containing acrylic monomer and / or the following general formula (B); (In the formula, m represents a natural number of 1 to 5.) A curable resin composition obtained from a long chain carboxyl group-containing acrylic monomer represented by the formula. 2. The half ester acid group-containing acrylic copolymer (1) is a long chain carboxyl group-containing acrylic monomer represented by the general formula (A) and / or the general formula (B).
1-50 mass% of the monomer (a) consisting of a long-chain carboxyl group-containing acrylic monomer represented by the following formula, acid anhydride group-containing ethylenically unsaturated monomer (b) 10 to 40% by mass with respect to the total amount of the monomer, and 10 to 85% by mass of the other copolymerizable ethylenically unsaturated monomer (c) with respect to the total amount of the monomer. Acid anhydride group-containing acrylic copolymer (X) obtained by polymerizing a product
And a monoalcohol (Y) having 1 to 12 carbon atoms so that a half ester group-containing acrylic copolymer obtained by reacting acid anhydride group / hydroxyl group in a ratio of 1/1 to 1 / 0.5 The epoxy group-containing acrylic copolymer (2) is a polymer, and the epoxy group-containing ethylenically unsaturated monomer (d) is 10 to 60 mass% with respect to the total amount of the monomer, and the hydroxyl group-containing ethylenically unsaturated monomer. 5 to 60% by mass of the monomer (e) based on the total amount of the monomer, and 0 to 85% of the other copolymerizable ethylenically unsaturated monomer (f) based on the total amount of the monomer.
The curable resin composition according to claim 1, which is a copolymer obtained by polymerizing a monomer composition having a mass%. 3. A half ester acid group-containing acrylic copolymer (1) is used in an amount of 1 relative to the mass of the solid content of the curable resin composition.
0 to 80% by mass, and the epoxy group-containing acrylic copolymer (2) has a content of 2 with respect to the solid content of the curable resin composition.
The curable resin composition according to claim 1 or 2, wherein the content is 0 to 80% by mass, and the carboxyl group-containing polyester polymer (3) is 10 to 85% by mass based on the mass of the solid content of the curable resin composition. . 4. The acid anhydride group-containing ethylenically unsaturated monomer (b) is at least one selected from the group consisting of itaconic anhydride, maleic anhydride and citraconic anhydride. The curable resin composition described. 5. A monoalcohol having 1 to 12 carbon atoms (Y)
The curable resin composition according to claim 1, 2, 3 or 4, wherein is at least one selected from the group consisting of acetol, allyl alcohol, propargyl alcohol, methanol and ethanol. 6. The half ester acid group-containing acrylic copolymer (1) has a solid content resin acid value of 25 to 300 mgKOH.
/ G, number average molecular weight is 500-1300, The curable resin composition according to claim 1, 2, 3, 4 or 5. 7. An epoxy group-containing acrylic copolymer (2)
Has an epoxy equivalent of 100 to 800 and a hydroxyl value of 40 to
It is 300 mgKOH / g.
Or the curable resin composition according to item 6. 8. A quaternary ammonium salt compound (4)
Curable resin composition of Claim 1, 2, 3, 4, 5, 6 or 7 containing. 9. The curable resin composition according to claim 1, further comprising an organic tin compound (5). 10. A clear coating composition comprising a curable resin composition as a binder, wherein the curable resin composition is any one of claims 1, 2, 3, 4, 5, 6, 7, 8 or 9. A clear coating composition which is the curable resin composition of. 11. A step (I) for obtaining an uncured base coating film by applying a base coating composition to a base material coated with an undercoat and / or an intermediate coating, and obtained by the step (I). (II) to obtain an uncured clear coating film by applying a clear coating composition on the obtained uncured base coating film, and the uncured base coating film and step (II) obtained by the step (I) A multilayer coating film forming method comprising the step (III) of simultaneously heating and curing the uncured clear coating film obtained by the above, wherein the clear coating composition is the clear coating composition according to claim 10. And a method for forming a multilayer coating film.