JP2018193508A - Clear coating composition and method of forming clear film - Google Patents

Abstract

To provide a clear coating composition that allows curing of a film under a low-temperature heating condition, with the obtained film having excellent hardness, and the film having excellent chemical resistance, solvent resistance and weather resistance.SOLUTION: A clear coating composition contains an acrylic resin (A) having an oxidation polymerizable functional group having 2-4 double bonds, an acrylic resin (B) having a reactive double bond group and a metal dryer (C). There is also provided a method of forming a clear film having a film containing the clear coating composition.SELECTED DRAWING: None

Description

  The present invention relates to a clear coating composition and a method for forming a clear coating film.

  As a clear coating composition, patent document 1 (Unexamined-Japanese-Patent No. 2012-92232) is mentioned, for example. Patent Document 1 discloses an aqueous two-component clear coating material, wherein (a) an acrylic resin having both a carboxyl group and a hydroxyl group having a solid content hydroxyl value of 80 to 200 mgKOH / g and a solid content acid value of 10 to 50 mgKOH / g A clear paint containing (b) an amine compound, (c) a polyisocyanate compound, and (d) a hindered phenol compound is disclosed (Claim 1). Such a clear coating can be suitably used for coating many objects to be coated, and a coating film excellent in coating film performance is formed.

  In recent years, there has been a demand for shortening the coating line process, reducing carbon dioxide, and saving energy during coating film formation. From such a viewpoint, for example, when a clear coating composition is applied to a substrate to form a clear coating film, it is required to cure the clear coating composition under low-temperature heating conditions.

  However, the clear coating composition according to Patent Document 1 is cured at a high temperature, for example, at a temperature of 160 ° C. as described in the paragraph “0061”. There is a need for clear coating compositions that can be cured.

  On the other hand, a clear coating composition containing an alkyd resin can be cured at room temperature, but the resulting clear coating film is inferior in weather resistance, and the physical properties such as hardness of the cured coating film are not suitable for a clear coating film. It is enough.

  In addition, the two-component clear paint as disclosed in Patent Document 1 has a technical problem that the workability of coating is poor because the pot life is short. Therefore, there is a need for a paint that can ensure the workability of painting for a longer time.

  Therefore, the coating film can be cured under low-temperature heating conditions, and good film hardness can be obtained even when the coating film is cured under low-temperature heating conditions. Furthermore, chemical resistance and solvent resistance are obtained. There is a need for clear coating compositions that can form excellent coatings. Further, there is a need for a clear coating composition having excellent coating workability.

JP 2012-92232 A

  The present invention solves the above-mentioned conventional problems, and its object is a clear coating composition capable of curing a coating film under low-temperature heating conditions, and the obtained coating film hardness is good Providing a clear coating composition excellent in chemical resistance, solvent resistance and weather resistance of the coating film, and a method for forming a clear coating film having a coating film containing the clear coating composition ,It is in.

［式中、Ｒ_１は、結合手、置換基を有してもよい炭素数１〜１０のアルキレン基、又は、置換基を有してもよい、１又はそれ以上の不飽和二重結合を含む炭素数２〜１０の炭化水素基であり、および
Ｒ_２は、水素、置換基を有してもよい炭素数１〜１０のアルキル基、又は、置換基を有してもよい、１又はそれ以上の不飽和二重結合を含む炭素数２〜１０の炭化水素基である。］
で表される、
上記［１］から［３］のいずれか１に記載のクリヤー塗料組成物。
［５］前記アクリル樹脂（Ａ）のヨウ素価が３０〜１３０である、［１］から［４］のいずれか１に記載のクリヤー塗料組成物。
［６］前記クリヤー塗料組成物に含まれる前記アクリル樹脂（Ａ）と前記アクリル樹脂（Ｂ）の全樹脂固形分１００質量部に対して、前記アクリル樹脂（Ａ）の量は１０〜９０質量部である、［１］から［５］のいずれか１に記載のクリヤー塗料組成物。
［７］前記酸化重合性官能基は、炭素数４〜３０である、［１］から［６］のいずれか１に記載のクリヤー塗料組成物。
［８］被塗物上に、［１］〜［７］のいずれか１に記載のクリヤー塗料組成物を塗装して、未硬化のクリヤー塗膜を形成する工程；並びに
未硬化のクリヤー塗膜を焼き付け硬化させ、クリヤー塗膜を形成する工程；
を含み、
前記焼き付け硬化を行う温度が、６０℃以上１２０℃以下である、
クリヤー塗膜の形成方法。 In order to solve the above problems, the present invention provides the following aspects.
[1] A clear coating composition comprising an acrylic resin (A) having an oxidative polymerizable functional group having 2 to 4 double bonds, an acrylic resin (B) having a reactive double bond group, and a metal dryer (C) .
[2] The clear coating composition according to [1], wherein the acrylic resin (B) having a reactive double bond group is a non-aqueous dispersion resin.
[3] The clear coating composition according to [1] or [2], wherein the reactive double bond group is at least one selected from an acryloyl group and a methacryloyl group.
[4] The oxidative polymerizable functional group is represented by the following chemical formula (I) or (II):

[Wherein R ₁ represents a bond, an alkylene group having 1 to 10 carbon atoms which may have a substituent, or one or more unsaturated double bonds which may have a substituent. A hydrocarbon group having 2 to 10 carbon atoms, and R ₂ is hydrogen, an alkyl group having 1 to 10 carbon atoms which may have a substituent, or 1 or It is a C2-C10 hydrocarbon group containing a further unsaturated double bond. ]
Represented by
The clear coating composition according to any one of [1] to [3] above.
[5] The clear coating composition according to any one of [1] to [4], wherein the iodine value of the acrylic resin (A) is 30 to 130.
[6] The amount of the acrylic resin (A) is 10 to 90 parts by mass with respect to 100 parts by mass of the total resin solids of the acrylic resin (A) and the acrylic resin (B) contained in the clear coating composition. The clear coating composition according to any one of [1] to [5].
[7] The clear coating composition according to any one of [1] to [6], wherein the oxidative polymerizable functional group has 4 to 30 carbon atoms.
[8] A step of coating the clear coating composition according to any one of [1] to [7] on an object to form an uncured clear coating; and an uncured clear coating Baking and curing to form a clear coating film;
Including
The temperature for performing the bake hardening is 60 ° C. or higher and 120 ° C. or lower.
A method for forming a clear coating film.

  By using the clear coating composition of the present invention, even when the cured coating film is formed under low-temperature heating conditions, for example, at a temperature of 120 ° C. or less, it has good coating film hardness, and also has chemical resistance. There is an advantage that a clear coating film having excellent properties, solvent resistance and weather resistance can be formed.

Background of the Invention First, the background to the present invention will be described. For example, the present inventors have studied to cure a coating composition containing a melamine resin, a urethane resin, an acrylic resin or the like under a low-temperature heating condition.
However, if an attempt is made to cure a coating composition containing such a resin simply under low-temperature heating conditions, for example, at 120 ° C. or lower, problems such as a problem that the curing time becomes long and physical properties of the coating film are inferior are caused.
Therefore, the present inventors tried to cure under low-temperature heating conditions, for example, 120 ° C. or less, while even under such low-temperature heating conditions, the curing time was comparable to that of the prior art, A clear coating composition having excellent coating film properties was examined. And if it is a clear coating composition containing the acrylic resin (A) and acrylic resin (B) which have a specific structure, and a metal dryer, even if it hardens | cures on low temperature heating conditions, hardening time will be extended significantly. In addition, it was found through experiments that a coating film having excellent coating film hardness and excellent coating properties such as chemical resistance, solvent resistance and weather resistance was obtained, and the present invention was completed. It came to do.

The present invention includes an acrylic resin (A) having an oxidative polymerizable functional group having 2 to 4 double bonds, an acrylic resin (B) having a reactive double bond group, and a metal dryer (C). It is a clear coating composition.
Even if the cured coating film is formed at a temperature of 120 ° C. or less by the clear coating composition according to the present invention, it has a good coating film hardness, and in addition, it has chemical resistance, solvent resistance and weather resistance. An excellent clear coating film can be formed. Furthermore, a coating film excellent in chemical resistance, solvent resistance and weather resistance can be provided. The clear coating composition according to the present invention is a one-pack type clear coating composition, has a long pot life, and is excellent in workability and storage stability. Moreover, a smooth coating film appearance can be formed.

Acrylic resin (A) having an oxidation polymerizable functional group having 2 to 4 double bonds
In oxidative polymerizable functional group present invention having 2-4 double bonds, oxidation polymerization functional group is a functional group bonded directly or through other binding group in the main chain of the acrylic resin, the air at room temperature It is a functional group that undergoes oxidative polymerization with oxygen therein. When oxidative polymerization through such oxidative polymerizable functional groups proceeds, a three-dimensional network structure can be formed. Moreover, if it is the oxidation polymerizable functional group which has 2-4 double bonds based on this invention, a crosslinking reaction position can be increased and it can bridge | crosslink more effectively. In addition, since the reaction proceeds even at room temperature, it can contribute to reduction of carbon dioxide and energy saving.
The oxidatively polymerizable functional group in the present invention has 2 to 4 double bonds. When the oxidative polymerizable functional group has 2 to 4 double bonds, crosslinking between the acrylic resin (A) and the acrylic resin (B) having a reactive double bond group can be promoted. Furthermore, even if the acrylic resin (A) and the acrylic resin (B) are baked under low temperature heating conditions, sufficient hardness, chemical resistance, solvent resistance, weather resistance, scratch resistance, and the like are provided. A coating film can be formed.

The oxidatively polymerizable functional group has 2 to 4 double bonds, preferably 2 to 3 double bonds, for example, 2 double bonds. The number of carbon atoms of the oxidative polymerizable functional group is, for example, 3 or more and 30 or less, and in some embodiments, 4 or more and 30 or less, for example, 5 or more and 22 or less, and in some embodiments, 8 or more and 22 or less. is there.
In some embodiments, the oxidative polymerizable functional group is linear. Preferably, the oxidative polymerizable functional group may be a non-conjugated dienyl group or a conjugated dienyl group.

Examples of the oxidatively polymerizable functional group having two double bonds include propadienyl group, 1,2-butadienyl group, 1,3-butadienyl group, 1,2-pentadienyl group, 1,3-pentadienyl group, 1,4- Pentadienyl group, 2,3-pentadienyl group, 2,4-pentadienyl group, 1,2-hexadienyl group, 1,3-hexadienyl group, 1,4-hexadienyl group, 1,5-hexadienyl group, 2,3-hexadienyl group Group, 2,4-hexadienyl group, 2,5-hexadienyl group, 3,4-hexadienyl group, 3,5-hexadienyl group, 4,5-hexadienyl group, 1,2-heptadienyl group, 1,3-heptadienyl group 1,4-heptadienyl group, 1,5-heptadienyl group, 1,6-heptadienyl group, 2,3-heptadienyl group, 2,4- Ptadienyl group, 2,5-heptadienyl group, 2,6-heptadienyl group, 3,4-heptadienyl group, 3,5-heptadienyl group, 3,6-heptadienyl group, 4,5-heptadienyl group, 4,6-heptadienyl group Group, 5,6-heptadienyl group, 1,2-octadienyl group, 1,3-octadienyl group, 1,4-octadienyl group, 1,5-octadienyl group, 1,6-octadienyl group, 1,7-octadienyl group 2,3-octadienyl group, 2,4-octadienyl group, 2,5-octadienyl group, 2,6-octadienyl group, 2,7-octadienyl group, 3,4-octadienyl group, 3,5-octadienyl group, 3,6-octadienyl group, 3,7-octadienyl group, 4,5-octadienyl group, 4,6-octadienyl group 4,7-octadienyl group, 5,6-octadienyl group, 5,7-octadienyl group, can be exemplified 6,7-octadienyl group. Similarly, an oxidatively polymerizable functional group having 9 or more carbon atoms such as nonadienyl group and decadienyl group may be used. Moreover, the oxidation polymerizable functional group having two double bonds may appropriately have a functional group that R ₁ and R ₂ described later may have.

As oxidative polymerizable functional groups having three double bonds, butatrienyl group, 1,2,3-pentatrienyl group, 1,2,4-pentatrienyl group, 1,2,3-hexatrienyl group 1,2,4-hexatrienyl group, 1,2,5-hexatrienyl group, 2,3,4-hexatrienyl group, 2,3,5-hexatrienyl group, 1,2,3 -Heptatrienyl group, 1,2,4-heptatrienyl group, 1,2,5-heptatrienyl group, 1,2,6-heptatrienyl group, 1,3,4-heptatrienyl group, 1,3,5-heptatrienyl group, 1 , 3,6-heptatrienyl group, 2,3,4-heptatrienyl group, 2,3,5-heptatrienyl group, 2,3,6-heptatrienyl group, 2,4,5-heptatrienyl group, 2,4,6- Heptatrienyl group, 3,4,5-heptatrienyl group, 3,4,6-heptatrienyl group, 1,2,3-octatrienyl group, 1,2,4-octatrienyl group, 1,2,5-octatrienyl group 1,2,6-octatrienyl group, 1,2,7 octatrienyl group, 2,3,4-octatrienyl group, 2,3,5-octatrienyl group, 2,3,6- Octatrienyl group, 2,3,7-octatrienyl group, 3,4,5-octatrienyl group, 3,4,6-octatrienyl group, 3,4,7-octatrienyl group,
1,2,3-nonatrienyl group, 1,2,4-nonatrienyl group, 1,2,5-nonatrienyl group, 1,2,6-nonatrienyl group, 1,2,7-nonatrienyl group, 1,2,8 -Nonatrienyl group, 1,3,4-nonatrienyl group, 1,3,5-nonatrienyl group, 1,3,6-nonatrienyl group, 1,3,7-nonatrienyl group, 1,3,8-nonatrienyl group, 1 , 4,5-nonatrienyl group, 1,4,6-nonatrienyl group, 1,4,7-nonatrienyl group, 1,4,8-nonatrienyl group, 1,5,6-nonatrienyl group, 1,5,7- Nonatrienyl group, 1,5,8-nonatrienyl group, 1,6,7-nonatrienyl group, 1,6,8-nonatrienyl group, 1,7,8-nonatrienyl group, 2,3,4-nonatrienyl group, 2, 3 5-nonatrienyl group, 2,3,6-nonatrienyl group, 2,3,7-nonatrienyl group, 2,3,8-nonatrienyl group, 2,4,5-nonatrienyl group, 2,4,6-nonatrienyl group, 2,4,7-nonatrienyl group, 2,4,8-nonatrienyl group, 2,5,6-nonatrienyl group, 2,5,7-nonatrienyl group, 2,5,8-nonatrienyl group, 2,6,7 -Nonatrienyl group, 2,6,6-nonatrienyl group, 3,4,5-nonatrienyl group, 3,4,6-nonatrienyl group, 3,4,7-nonatrienyl group, 3,4,8-nonatrienyl group, 3 , 5,6-nonatrienyl group, 3,5,7-nonatrienyl group, 3,5,8-nonatrienyl group, 3,6,7-nonatrienyl group, 3,6,8-nonatrienyl group, 4,5,6- Examples include natrienyl group, 4,5,7-nonatrienyl group, 4,5,8-nonatrienyl group, 5,6,7-nonatrienyl group, 5,6,8-nonatrienyl group, and 6,7,8-nonatrienyl group. . Moreover, the oxidative polymerizable functional group having three double bonds may appropriately have a functional group that R ₁ and R ₂ described later may have.

As an oxidatively polymerizable functional group having four double bonds, a pentatetraenyl group, a hexatetraenyl group, for example, 1,2,3,4-hexatetraenyl group, 1,2,3,5-hexatetra, An enyl group, a 1,2,4,5-hexatetraenyl group, a heptatetraenyl group, such as a 1,2,3,4-heptatetraenyl group, a 1,2,3,5-heptatetraenyl group, 1,2,3,6-heptatetraenyl group, 1,2,4,5-heptatetraenyl group, 1,2,4,6-heptatetraenyl group, 1,2,5,6-heptatetraenyl group Group, 1,3,4,5-heptatetraenyl group, 1,3,4,6-heptatetraenyl group, 1,3,5,6-heptatetraenyl group, 2,3,4,5-hepta Octatetraenyl group such as tetraenyl group, for example 1,2,3 4-octatetraenyl group, 1,2,3,5-octatetraenyl group, 1,2,3,6-octatetraenyl group, 1,2,3,7-octatetraenyl group, 1,2, 4,5-octatetraenyl group, 1,2,5,6-octatetraenyl group, 1,2,6,7-octatetraenyl group, 1,3,5,7-octatetraenyl group, 2, Examples thereof include 3,4,5-octatetraenyl group, 2,3,4,6-octatetraenyl group and 2,3,5,6-octatetraenyl group. Moreover, the oxidative polymerizable functional group having four double bonds may appropriately have a functional group that R ₁ and R ₂ described later may have.

  In the present invention, the oxidatively polymerizable functional group may be a group introduced by an unsaturated fatty acid having 2 to 4 double bonds.

［式中、Ｒ_１は、結合手、置換基を有してもよい、直鎖または分枝状の炭素数１〜１０のアルキレン基、又は、置換基を有してもよい、１又はそれ以上の不飽和二重結合を含む、直鎖または分枝状の炭素数２〜１０の炭化水素基であり、および
Ｒ_２は、水素、置換基を有してもよい、直鎖または分枝状の炭素数１〜１０のアルキル基、又は、置換基を有してもよい、１又はそれ以上の不飽和二重結合を含む、直鎖または分枝状の炭素数２〜１０の炭化水素基である。］
で示される。 In some embodiments, the oxidatively polymerizable functional group has the following chemical formula (I) or (II):

[Wherein, R ₁ may have a bond, a substituent, a linear or branched alkylene group having 1 to 10 carbon atoms, or a substituent, or 1 A straight-chain or branched hydrocarbon group having 2 to 10 carbon atoms containing the above unsaturated double bond, and R ₂ may have a hydrogen or a substituent, straight-chain or branched Linear or branched hydrocarbon having 1 to 10 carbon atoms, or one or more unsaturated double bonds which may have a substituent It is a group. ]
Indicated by

Examples of substituents that R ₁ and R ₂ may have include, for example, alkyl groups, alkenyl groups, alkynyl groups, alkoxy groups, alkyl ester groups, nitrile groups, hydroxyl groups, cyano groups, sulfonyl groups, carboxyl groups, and aromatic hydrocarbons. The group can be mentioned. R ₁ and R ₂ may have the same or different substituents.
Preferably, R ₁ and R ₂ are linear groups. More preferably, R ₁ is a linear alkylene group having 1 to 10 carbon atoms, and R ₂ is a linear alkyl group having 1 to 10 carbon atoms.

  When the main chain of the acrylic resin (A) having an oxidation polymerizable functional group is acrylic, compatibility with the acrylic resin (B) is improved. Furthermore, the coating film formed from the clear coating composition of the present invention has excellent coating hardness even under low-temperature heating conditions, and is excellent in chemical resistance, solvent resistance and weather resistance.

Specific examples of the oxidative polymerizable functional group represented by the formula (I) include a case where R ₁ is a bond or an aspect such as an alkylene group, a 1,4-heptadienyl group, a 2,5-heptadienyl group, 1,4-octadienyl group, 1,4-octadienyl group, 2,5-octadienyl group, 1,4-nonadienyl group, 2,5-nonadienyl group, 1,4-decadienyl group, 2,5-decadienyl group, etc. Can be mentioned.

Specific examples of the oxidatively polymerizable functional group represented by the formula (II) include a case where R ₁ is a bond or an aspect such as an alkylene group, a 1,3-hexadienyl group, a 2,4-hexadienyl group, 1,3-heptadienyl group, 2,4-heptadienyl group, 1,3-octadienyl group, 2,4-octadienyl group, 1,3-nonadienyl group, 2,4-nonadienyl group, 1,3-decadienyl group, 2 , 4-decadienyl group and the like.
In the present invention, the oxidatively polymerizable functional group may be a group introduced by an unsaturated fatty acid having 2 to 4 double bonds.
By having such an oxidatively polymerizable functional group, even when the acrylic resin (A) and the acrylic resin (B) are cured under low-temperature heating conditions, good coating film hardness, chemical resistance, A coating film having solvent resistance, weather resistance, scratch resistance and the like can be formed.

  The preparation method of the acrylic resin (A) having an oxidatively polymerizable functional group having 2 to 4 double bonds is not particularly limited. For example, it is prepared by introducing an oxidatively polymerizable functional group into the acrylic resin. be able to. The starting material used when the oxidative polymerizable functional group is introduced into the acrylic resin is not particularly limited as long as it is a compound that can form the above structure by introduction into the acrylic resin.

The structure of the acrylic resin used for the preparation of the acrylic resin (A) having an oxidative polymerizable functional group having 2 to 4 acrylic resin double bonds is not particularly limited as long as it can form a clear coating film. For example, the acrylic resin includes an alkyl ester group-containing monomer (1), a hydroxyl group-containing acrylic monomer (2), a carboxyl group-containing acrylic monomer (3), an epoxy group-containing acrylic monomer (4), and other acrylic monomers ( It can be prepared by introducing the oxidatively polymerizable functional group into a polymer obtained by polymerizing at least one monomer selected from 5).

In one embodiment, the acrylic resin (A) according to the present invention is at least one selected from an acrylic monomer (2) having a hydroxyl group, an acrylic monomer (3) having a carboxyl group, and an acrylic monomer (4) having an epoxy group. The above oxidatively polymerizable functional group is introduced into a copolymer obtained by polymerizing the monomer with at least one monomer selected from the monomer (1) having an alkyl ester group and the other acrylic monomer (5). Can be prepared.
In the present invention, the total amount of the acrylic monomer (2) having a hydroxyl group, the acrylic monomer (3) having a carboxyl group, and the acrylic monomer (4) having an epoxy group is used when the acrylic resin (A) is synthesized. It is preferably used in the range of 5 to 70 parts by mass, and more preferably in the range of 10 to 50 parts by mass with respect to 100 parts by mass of the total amount of all monomers.

Acrylic monomer having alkyl ester group (1)
The acrylic monomer (1) having an alkyl ester group may preferably contain an alkyl ester group having 1 to 20 carbon atoms, preferably 1 to 12 carbon atoms.
Specific examples of the monomer include (meth) acrylate esters such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, and (meth) acrylic. Isobutyl acid, t-butyl (meth) acrylate, hexyl (meth) acrylate, phenyl acrylate, cyclohexyl methacrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, Dodecyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, isobornyl (meth) acrylate, t-butylcyclohexyl (meth) acrylate, dicyclopentadienyl (meth) acrylate or the like Of the mixture.
In the present specification, “(meth) acryl” is a term representing both acrylic and methacrylic.

Acrylic monomer having a hydroxyl group (2)
Examples of the acrylic monomer (2) having a hydroxyl group include, for example, 4-hydroxybutyl (meth) acrylate, 5-hydroxypentyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, and (meth) acrylic acid. 7-hydroxyheptyl, 8-hydroxyoctyl (meth) acrylate, 7-methyl-8-hydroxyoctyl (meth) acrylate, 2-methyl-8-hydroxyoctyl (meth) acrylate, and ( Examples thereof include lactone-modified acrylic monomers obtained by reacting 1 to 5 moles of lactones such as ε-caprolactone with hydroxyethyl methacrylate.

Further, examples include 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, and the like.
Furthermore, among the acrylic monomers (2) having a hydroxyl group, 4-hydroxybutyl (meth) acrylate, a reaction product of hydroxyethyl (meth) acrylate and ε-caprolactone, Plaxel FM-1, FM-2, FA- A hydroxyl group-containing monomer consisting of 1 and FA-2 may be used.

Specific examples of commercial products of acrylic monomers modified with caprolactone include, for example, trade names manufactured by Daicel Chemical Industries, Plaxel FA-1, Plaxel FA-2, Plaxel FA-3 (hydroxyethyl acrylate with ε-caprolactone 1 mol, 2 mol and 3 mol monomers), Plaxel FM-1, Plaxel FM-2, Plaxel FM-3 (1 mol of ε-caprolactone to 1 mol of hydroxyethyl methacrylate, 2 mol, 3 mol, respectively) And a monomer manufactured by The Dow Chemical Company (USA), TONE m-100 (a monomer obtained by adding 2 mol of ε-caprolactone to 1 mol of hydroxyethyl acrylate).
Moreover, the monoester of polyether glycol and (meth) acrylic acid and the monoether of polyether glycol and hydroxyalkyl of (meth) acrylic acid are mentioned. For example, “Blemmer AP-150” manufactured by Nippon Oil & Fats Co., Ltd. can be mentioned.

Monomer having a carboxyl group (3)
As the monomer (3) having a carboxyl group, acrylic acid, methacrylic acid, acrylic acid dimer, crotonic acid, 2-acryloyloxyethylphthalic acid, 2-acryloyloxyethyl succinic acid, isocrotonic acid, maleic acid, fumaric acid , Itaconic acid, 3-vinylsalicylic acid, 3-vinylacetylsalicylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and the like. Among these, acrylic acid and methacrylic acid are preferable.

Acrylic monomer having epoxy group (4)
The acrylic monomer (4) having an epoxy group is not particularly limited as long as it has an epoxy group and a polymerizable unsaturated double bond in the molecule. For example, glycidyl (meth) acrylate, β-methylglycidyl (meta ) Acrylate, glycidyl ether of 4-hydroxybutyl (meth) acrylate, and (meth) acrylate of 3,4-epoxycyclohexanemethanol. From the viewpoint of reactivity, it is preferable to use glycidyl ether of glycidyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate.

Other acrylic monomers (5)
Other acrylic monomers (5) are other than acrylic monomers (1) having alkyl ester groups, acrylic monomers (2) having hydroxyl groups, acrylic monomers (3) having carboxyl groups, and monomers (4) having epoxy groups. And monomers copolymerizable with these acrylic monomers.

  For example, polymerizable amide compounds such as (meth) acrylamide, N-methylol (meth) acrylamide, N-butoxymethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N, N-dibutyl (meth) acrylamide N, N-dioctyl (meth) acrylamide, N-monobutyl (meth) acrylamide, N- (2-hydroxyethyl) acrylamide, N- (2-hydroxyethyl) methacrylamide, and the like, for example, styrene , Α-methylstyrene, vinyl ketone, t-butylstyrene, parachlorostyrene, vinylnaphthalene, etc., polymerizable nitriles such as acrylonitrile, methacrylonitrile, vinyl esters such as vinyl acetate, vinyl propionate, dienes such as The Dienes, isoprene, polymerizable aromatic compounds, polymerizable nitriles, alpha-olefin, and vinyl esters, and dienes. These can be selected according to the paint design.

  The above monomers can be polymerized by, for example, solution polymerization using a radical polymerization catalyst by a usual method.

The acrylic resin (A) can be prepared by introducing an oxidatively polymerizable functional group having 2 to 4 double bonds into the copolymer of the monomer mixture.
As a method for introducing an oxidatively polymerizable functional group having 2 to 4 double bonds, for example,
A monomer mixture containing a monomer having a carboxyl group is copolymerized, and then the epoxy group and a compound having an oxidatively polymerizable functional group having 2 to 4 double bonds are reacted to have 2 to 4 double bonds. A method for preparing an acrylic resin (A) having an oxidatively polymerizable functional group;
Oxidation having 2 to 4 double bonds by copolymerizing a monomer mixture containing a monomer having a hydroxyl group, and then reacting an epoxy group and a compound having an oxidative polymerizable functional group having 2 to 4 double bonds A method for preparing an acrylic resin (A) having a polymerizable functional group;
A monomer mixture containing a monomer having an epoxy group is copolymerized, and then a compound having a carboxyl group and an oxidative polymerizable functional group having 2 to 4 double bonds is reacted to have 2 to 4 double bonds. A method for preparing an acrylic resin (A) having an oxidatively polymerizable functional group;
Etc.
Examples of the compound having an oxidatively polymerizable functional group having 2 to 4 epoxy groups and double bonds include cardanol-modified glycidyl ether. A commercially available product may be used as the compound having an oxidative polymerizable functional group having 2 to 4 epoxy groups and double bonds.
Examples of the compound having an oxidative polymerizable functional group having 2 to 4 carboxyl groups and double bonds include unsaturated fatty acids having 2 to 4 double bonds. Specific examples of the compound having an oxidative polymerizable functional group having 2 to 4 carboxyl groups and double bonds include, for example, α-linolenic acid, stearidonic acid, linoleic acid, γ-linolenic acid, dihomo-γ-linolenic acid, Examples include arachidonic acid.
The above reaction can be carried out under reaction conditions usually used by those skilled in the art.

  In one embodiment, the hydroxyl value of the produced acrylic resin (A) is preferably 0 to 200 mgKOH / g, more preferably 1 to 200 mgKOH / g, and further preferably 20 to 150 mgKOH / g. .

  The acid value of the acrylic resin (A) is preferably from 0 to 100 mgKOH / g, for example, preferably from 1 to 100 mgKOH / g, and more preferably from 2 to 70 mgKOH / g.

The number average molecular weight (M _n ) of the acrylic resin (A) is preferably in the range of 300 to 50000, more preferably 500 to 30000, for example. If it is less than the lower limit, the coating film hardness may be insufficient, and if it exceeds the upper limit, the appearance of the coating film may be deteriorated.
The value of the number average molecular weight in the present specification is a value obtained by converting a measured value by gel permeation chromatogram (GPC) with a polystyrene standard.

  The iodine value of acrylic resin (A) is 30-130, for example, Preferably it is 80-120. When the iodine value of the acrylic resin (A) is within such a range, sufficient curability can be obtained, and further excellent weather resistance can be provided.

  The glass transition temperature (Tg) of the acrylic resin (A) is, for example, −50 to 80 ° C., and preferably −30 to 50 ° C. When the glass transition temperature (Tg) of the acrylic resin (A) is within such a range, the clear coating film is excellent in mechanical strength, and further, the coating film can be prevented from being hard and brittle.

  The said acrylic resin (A) may be used individually by 1 type, and may use 2 or more types together.

  The amount of the acrylic resin (A) is 10 to 90 parts by mass with respect to 100 parts by mass of the total resin solids of the acrylic resin (A) and the acrylic resin (B) contained in the clear coating composition. Is preferable, and it is more preferable that it is 25-75 mass parts.

Acrylic resin having reactive double bond group (B)
The acrylic resin (B) having a reactive double bond group in the present invention can be crosslinked with the acrylic resin (A), and is applied, for example, to a clear coating film formed from the clear coating composition of the present invention. Film strength can be provided. By using together the acrylic resin (A) and acrylic resin (B) according to the present invention, the crosslinking density can be improved without impairing the weather resistance.

The reactive double bond group in the acrylic resin (B) according to the present invention includes, for example, alkenes such as vinyl group and allyl group, unsaturated carboxylic acids such as acryloyl group and methacryloyl group, and aromatic groups having vinyl group such as styrene. Group hydrocarbons and the like.
The reactive double bond group according to the present invention can be easily initiated and cross-linked by a radical or a cation, for example, an acrylic resin (B) having a reactive double bond group and an oxidative polymerizable functional group. Since the acrylic resin (A) can be cross-linked, the coating film can be cured under low-temperature heating conditions, the resulting coating film hardness is good, and the solvent resistance, chemical resistance, and weather resistance are excellent. An excellent clear coating composition can be obtained.

  The number average molecular weight of the acrylic resin (B) is preferably in the range of 250 to 100,000,000. For example, when the acrylic resin (B) is a non-aqueous dispersion resin, the number average molecular weight is more preferably in the range of 3,000 to 100,000,000. By using such a non-aqueous dispersion resin as the acrylic resin (B), it becomes possible to include a resin component having a high molecular weight in the clear coating composition without deteriorating the coating stability. There is an advantage that a high coating strength can be imparted to the clear coating obtained. In addition, the number average molecular weight of such an acrylic resin (B) can be calculated by a known method.

In one embodiment, the acrylic resin (B) having a reactive double bond group may be a non-aqueous dispersion resin. The “non-aqueous dispersion” means a non-aqueous dispersion type resin, which is obtained by dispersing and stabilizing the resin using an organic solvent as a medium.
In one embodiment, the acrylic resin (B) having a reactive double bond group has a core-shell structure. By having the core-shell structure, for example, the core portion has a crosslinked structure, and a desired hardness can be imparted to the clear coating film formed from the clear coating composition of the present invention. Moreover, by having a shell part, it is a clear coating composition which can perform crosslinking | crosslinking with an acrylic resin (A) more effectively, and can perform coating-film hardening on low-temperature heating conditions, Comprising: A clear coating film having good hardness and excellent chemical resistance, solvent resistance and weather resistance can be obtained.

  In this specification, the core means a layer including the central part of the particle, and often includes a region generated during nucleation. The shell is a layer that exists adjacent to the outside of the core and covers at least a part of the core.

Preferably, the acrylic resin (B) having a reactive double bond group according to the present invention is a non-aqueous dispersion resin having a core-shell structure.
In this embodiment, it is preferable that more reactive double bond groups exist in the shell portion. For example, the reactive double bond group can be introduced into the acrylic resin (B) by modifying the functional group of the resin contained in the shell of the acrylic resin (B) with a known material and method.

The non-aqueous dispersion resin having a core-shell structure is obtained by polymerizing a polymerizable monomer in a specific organic solvent in the presence of a dispersion stable resin soluble in the organic solvent. Here, as the specific organic solvent, for example, an organic solvent that dissolves a polymerizable monomer and does not dissolve a polymer formed from the monomer can be used.
For example, a so-called non-aqueous dispersion (NAD) dispersion using a polymer containing a polymerizable monomer as a core and a dispersion-stable resin as a shell can be suitably used.

The dispersion stable resin is not particularly limited as long as it is a resin that can stably synthesize a non-aqueous dispersion resin in an organic solvent.
As the dispersion stable resin, for example, an acrylic resin can be used. The acrylic resin that can be used as the dispersion stabilizing resin preferably has a hydroxyl value (solid content) of 0 to 300 mgKOH / g, more preferably 10 to 250 mgKOH / g, for example 20 to 180 mgKOH / g. Is more preferable. The acid value (solid content) is preferably 0 to 100 mgKOH / g, and more preferably 0 to 50 mgKOH / g. The number average molecular weight is preferably from 800 to 100,000, more preferably from 1,000 to 20,000.

The method for synthesizing the dispersion stable resin is not particularly limited, and preferred examples include a method obtained by radical polymerization in the presence of a radical polymerization initiator, a method obtained by a condensation reaction or an addition reaction, and the like. Furthermore, the monomer used for obtaining the dispersion-stable resin can be appropriately selected according to the characteristics of the resin, but it is preferable to use a monomer having a linear alkyl group having 8 to 12 carbon atoms. The monomer having a linear alkyl group having 8 to 12 carbon atoms can be used in an amount of preferably 5 to 50 parts by mass, more preferably 5 to 20 parts by mass with respect to 100 parts by mass of the total amount of monomers. Furthermore, you may use what has functional groups, such as a glycidyl group and an isocyanate group, as needed.
For example, a dispersion stable resin may be prepared from a monomer used for preparing the acrylic resin (A).

The non-aqueous dispersion resin can be obtained by polymerizing a polymerizable monomer in a mixed solution of a dispersion stable resin and an organic solvent. As the polymerizable monomer, a radical polymerizable monomer can be used.
The organic solvent used for polymerization dissolves the dispersion-stable resin but does not dissolve resin particles obtained by polymerizing the polymerizable monomer, and can be appropriately selected from various organic solvents.

  As the polymerizable monomer used for the synthesis of the non-aqueous dispersion resin, it is preferable to use a monomer having a functional group. Typical examples of the polymerizable monomer having a functional group are as follows. Examples of the polymerizable monomer having a hydroxyl group include hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, hydroxymethyl methacrylate, allyl alcohol, and hydroxyethyl (meth) methacrylate. Examples include adducts with ε-caprolactone.

  On the other hand, examples of the polymerizable monomer having an acidic group include polymerizable monomers having a carboxyl group, a sulfonic acid group and the like. Examples of those having a carboxyl group include (meth) acrylic acid, crotonic acid, ethacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconic acid, maleic anhydride, fumaric acid and the like. Examples of the polymerizable monomer having a sulfonic acid group include t-butylacrylamide sulfonic acid. When using the polymerizable monomer which has an acidic group, it is preferable that a part of acidic group is a carboxyl group.

  In addition, glycidyl group-containing unsaturated monomers such as glycidyl (meth) acrylate, isocyanate group-containing unsaturated monomers such as m-isopropenyl-α, α-dimethylbenzyl isocyanate, isocyanatoethyl acrylate, and the like are functional groups. As a polymerizable monomer having

  Other polymerizable monomers include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, T-butyl (meth) acrylate, isobutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, methacrylic acid (Meth) acrylic acid alkyl ester such as tridecyl, addition reaction product of oil fatty acid and acrylic acid or methacrylic acid ester monomer having oxirane structure (for example, addition reaction product of stearic acid and glycidyl methacrylate), having 3 or more carbon atoms Oxirane compounds containing alkyl groups and acrylic acid or methacrylic Addition reaction product, styrene, α-methyl styrene, o-methyl styrene, m-methyl styrene, p-methyl styrene, pt-butyl styrene, benzyl (meth) acrylate, itaconic acid ester (dimethyl itaconate, etc.) ), Maleic acid esters (such as dimethyl maleate), fumaric acid esters (such as dimethyl fumarate), acrylonitrile, methacrylonitrile, methyl isopropenyl ketone, vinyl acetate, Veova monomer (trade name, manufactured by Shell Chemical Co., Ltd.), Examples thereof include polymerizable monomers such as vinyl propionate, vinyl pivalate, ethylene, propylene, butadiene, N, N-dimethylaminoethyl acrylate, N, N-dimethylaminoethyl methacrylate, acrylamide, and vinyl pyridine.

  In addition to such a monomer, a monomer used for preparing the acrylic resin (A) may be selected as a polymerizable monomer according to the composition of the acrylic resin (A).

  In the preparation of the non-aqueous dispersion resin, the composition ratio of the dispersion stable resin and the polymerizable monomer can be arbitrarily selected according to the purpose. For example, the dispersion stable resin is 3 to 80 mass based on the total mass of these two components. %, Particularly 5 to 60% by mass, and the polymerizable monomer is preferably 97 to 20% by mass, particularly 95 to 40% by mass. Furthermore, the total concentration of the dispersion stabilizing resin and the polymerizable monomer in the organic solvent is preferably 30 to 80% by mass, particularly 40 to 60% by mass, based on the total mass.

  The polymerization reaction for obtaining the non-aqueous dispersion resin is preferably performed in the presence of a radical polymerization initiator. Examples of the radical polymerization initiator include azo initiators such as 2,2′-azobisisobutyronitrile and 2,2′-azobis (2,4-dimethylvaleronitrile), benzoyl peroxide, lauryl peroxide, Examples include t-butyl peroctoate. These initiators are used in an amount of 0.2 to 20 parts by mass, preferably 0.5 to 10 parts by mass, per 100 parts by mass of the polymerizable monomers. In general, the polymerization reaction for obtaining a non-aqueous dispersion in an organic solvent containing a dispersion-stable resin is preferably performed in a temperature range of about 60 to 160 ° C. for about 1 to 15 hours.

  The non-aqueous dispersion resin thus obtained has a hydroxyl value (solid content) of preferably 0 to 300, for example 1 to 200, and in some embodiments, 20 to 150. The acid value (solid content) is 0 to 200 mgKOH / g, preferably 0 to 50 mgKOH / g, and the average particle diameter (D50) is 0.05 to 10 μm, preferably 0.1 to 2 μm. The average particle diameter (D50) can be measured by a dynamic light scattering method. Specifically, it can be measured using a nanotrack particle size distribution measuring apparatus UPA (manufactured by Nikkiso Co., Ltd.).

  Since the non-aqueous dispersion resin is in the form of particles in the clear coating composition, by using the non-aqueous dispersion resin, it is possible to obtain a low-viscosity coating composition despite its high molecular weight. .

  As the acrylic resin (B) having a reactive double bond group, in addition to the non-aqueous dispersion resin, for example, a (meth) acrylate compound having one or more reactive double bond groups, one or more reactions (Meth) acrylate oligomers or polymers having an ionic double bond group can be used. Commercial products may be used for these. Examples of commercially available products include Aronix series manufactured by Toagosei Co., Ltd. and Unidic series manufactured by DIC Corporation.

  The said acrylic resin (B) may be used individually by 1 type, and may use 2 or more types together.

Metal dryer The clear coating composition of the present invention comprises a metal dryer. This metal dryer serves to crosslink unsaturated bonds. As the above-mentioned metal dryer, any one can be used as long as it is usually used for paints. Among them, cobalt, barium, vanadium, manganese, cerium, lead, iron, calcium, zinc are particularly representative. , Naphthenates and octylates such as zirconium, cerium, nickel or tin.

A metal dryer can be set to the metal amount of the range of 0.01-3.0 mass parts with respect to 100 mass parts of resin solid content of a clear coating composition. When the amount of metal in the metal dryer is less than 0.01% by mass, the reaction does not proceed sufficiently, and the adhesion to the object to be coated forming a clear coating film may be deteriorated. Furthermore, the acrylic resin (A) and acrylic (B) according to the present invention are also insufficiently crosslinked, and the desired coating film hardness may not be obtained.
On the other hand, if the amount of metal in the metal dryer is more than 3.0 parts by mass, the basic performance such as paint skin may be deteriorated. Moreover, there exists a possibility that the high weather resistance requested | required of a clear coating film may not be satisfy | filled.
The metal dryer is blended in an amount of preferably 0.01 to 2.9% by mass, more preferably 0.02 to 2.8% by mass with respect to 100 parts by mass of the resin solid content of the clear coating composition.

Additives The clear coating composition of the present invention may contain additives usually used by those skilled in the art, such as ultraviolet absorbers, hindered amine light stabilizers, antioxidants, rheology control agents, and surface conditioners.

Solvent The clear coating composition of the present invention can be of a one-part type. For example, since the pot life can be made longer than that of the two-pack type clear coating composition, the workability is excellent. Furthermore, since it is a one-pack type coating composition, the baking process can be performed under low-temperature heating conditions, and energy consumption and CO ₂ emission can be reduced. Moreover, it is excellent also in storage stability and drying property.

  Examples of the organic solvent used in the clear coating composition of the present invention include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, n-pentanol, and isopentane. Alkyl alcohol solvents such as ethanol; methyl cellosolve, ethyl cellosolve, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, etc. Glycol ether solvents; aromatic hydrocarbon solvents such as benzene, toluene, xylene, and ethylbenzene; Click Son aromatic naphtha No. Mixed hydrocarbon solvent containing aromatic hydrocarbon such as 2 (manufactured by Exxon USA); aliphatic hydrocarbon solvent such as n-pentane, n-hexane and n-octane; Isopar C, Isopar E, Exol DSP100 / 140, Exol D30 (all manufactured by Exxon USA), mixed solvent containing aliphatic hydrocarbon such as IP Solvent 1016 (Idemitsu Petrochemical Co., Ltd.); cyclopentane, cyclohexane, methylcyclohexane, ethylcyclohexane, etc. Alicyclic hydrocarbon solvents such as: tetrahydrofuran, dioxane, diisopropyl ether, di-n-butyl ether and other ether solvents; acetone, methyl ethyl ketone, methyl isobutyl ketone and other ketone solvents; methyl acetate, ethyl acetate, n-propyl acetate , Isopropyl acetate, n acetate Butyl, isobutyl acetate, n- amyl, isoamyl acetate, hexyl acetate, ethyl propionate, and ester solvents such as butyl propionate. A small amount of water may be used in combination with these organic solvents.

The clear coating composition of the present invention has an advantage that the temperature for baking and curing can be set to 60 ° C. or higher and 120 ° C. or lower. That is, the clear coating composition according to the present invention can be cured under a lower temperature heating condition than before. Moreover, the clear coating composition of the present invention has a good coating film hardness even when the coating film is cured under low-temperature heating conditions, and additionally has chemical resistance, solvent resistance and weather resistance. There is an advantage that an excellent clear coating film can be formed.
Preferably, the temperature for performing the baking and curing is 60 ° C. or higher and 110 ° C. or lower. For example, the temperature for performing the baking and curing is 70 ° C. or higher and 90 ° C. or lower.
For example, if the temperature for baking and curing is less than 60 ° C., the solvent resistance and weather resistance may be inferior.

  As described above, the clear coating composition of the present invention is characterized in that a clear coating film having a good coating film hardness can be formed even when curing is performed under low-temperature heating conditions. On the other hand, the clear coating composition of the present invention can be heat-cured under general baking curing conditions such as 120 to 180 ° C., if necessary.

Method for Forming Clear Coating Film The present invention further provides a method for forming a clear coating film.
The method for forming a clear coating film according to the present invention comprises a step of coating the clear coating composition according to the present invention on an object to be formed to form an uncured clear coating film; and an uncured clear coating film Baking and curing to form a clear coating;
Including
The temperature for performing the bake hardening is 60 ° C. or higher and 120 ° C. or lower.

In some embodiments,
There is provided a method for forming a multi-layer coating film on a coating material, which comprises sequentially applying a base coating composition and a clear coating composition on the coating material by wet-on-wet.
In one embodiment, the method for forming a multilayer coating film comprises:
Applying a base coating composition on an object to form an uncured base coating;
Applying the clear coating composition according to the present invention on an uncured base coating to form an uncured clear coating; and simultaneously baking and curing the uncured base coating and the clear coating. A step of forming a multilayer coating film,
The temperature for performing the bake hardening is 60 ° C. or higher and 120 ° C. or lower.

  If it is the clear coating composition in this invention, as mentioned above, the temperature which performs baking hardening can be set to 60 to 120 degreeC. Preferably, the temperature for performing the bake curing is 60 ° C. or higher and 110 ° C. or lower, for example, the temperature for performing the bake curing is 60 ° C. or higher and 90 ° C. or lower, and in one embodiment, 70 ° C. or higher and 90 ° C. or lower.

  The clear coating composition of the present invention can be baked and cured, for example, under conditions of 120 ° C. or higher, if necessary.

In the method for forming a multilayer coating film of the present invention, a base coating composition and a clear coating composition can be sequentially applied by wet-on-wet on various objects to be coated.
In an embodiment, the article to be coated may be an automobile body on which an electrodeposition coating film is formed. The electrodeposition coating film is formed by applying an electrodeposition coating composition to an automobile body and baking and curing it. The automobile body to be coated is not particularly limited as long as it is a metal product capable of cationic electrodeposition coating. For example, iron, copper, aluminum, tin, zinc, an alloy containing these metals, and the like can be given.
In one embodiment, the article to be coated is a resin product used in the vehicle field. Since the clear coating composition according to the present invention can be cured under low-temperature heating conditions, a clear coating film excellent in coating film hardness and various physical properties described above can be formed on resin products.
Further, the article to be coated may have both a metal product and a resin product.

  The electrodeposition coating composition is not particularly limited, and known cationic electrodeposition coating compositions and anionic electrodeposition coating compositions can be used. Electrodeposition coating and baking may be performed by a method and conditions usually used for electrodeposition coating of automobile bodies.

  In one embodiment, the method includes a step of applying an intermediate coating composition on an article on which an electrodeposition coating has been formed to form an uncured intermediate coating, and then applying the base coating composition. May be. As the intermediate coating composition, known ones can be used, and for example, an aqueous intermediate coating composition can be used.

  The intermediate coating composition can be applied by spraying using, for example, an air electrostatic spray, a rotary atomizing electrostatic coater or the like.

  The coating amount is adjusted so that the film thickness of the cured coating film is 10 to 40 μm, preferably 15 to 30 μm. If the film thickness is less than 10 μm, the appearance and chipping resistance of the resulting coating film may be reduced, and if it exceeds 40 μm, problems such as sagging during coating and pinholes during baking hardening may occur.

The applied intermediate coating composition is preheated (pre-dried) by heating or blowing air before applying the base coating composition. In the present specification, “preheating” means that the applied coating composition is dried by heating under conditions such as temperature and time at which curing does not occur. By performing preheating, a smooth coating film appearance can be formed without causing a problem that water remaining in the coating film causes bumping in the step of baking the multilayer coating film and causes a crack.
In addition, by performing preheating, even if the base coating composition is applied immediately after forming an uncured intermediate coating film, it can be avoided that these two coating layers are mixed (mixed layer), The resulting multilayer coating film can have a very excellent coating film appearance.

  In the method of the present invention, the coated intermediate coating composition is preheated at 60 to 90 ° C., preferably 70 to 90 ° C. for 3 to 10 minutes.

  The base coating composition is applied wet-on-wet on an object to be coated on which an electrodeposition coating film has been formed, and in some embodiments, on an uncured intermediate coating film. A known base coating composition can be used. For example, an aqueous base coating composition can be used.

  The coating amount of the base coating composition is usually adjusted so that the film thickness after curing of the coating film is 10 to 20 μm. If the film thickness after curing is less than 10 μm, the masking of the underlayer may be insufficient or color unevenness may occur. If the film thickness exceeds 20 μm, sagging may occur during painting and pinholes may occur during heat curing. There is a risk of doing so.

If desired, the base coating composition is preheated to form an uncured base coating.
For example, the preheating temperature is 60 to 90 ° C., preferably 70 to 90 ° C., and preheating is performed for 3 to 10 minutes. By performing preheating, even if a clear coating composition is applied immediately after forming an uncured base coating film, these two coating layers can be prevented from being mixed (mixed), and the resulting composite coating can be avoided. An extremely excellent coating film appearance can be provided to the layer coating film.
Furthermore, sagging of the base coating composition can be effectively prevented by preheating the aqueous base coating composition.

  On this coating film, the clear coating composition of the present invention can be applied to form an uncured clear coating film.

  The coating amount of the clear coating composition is usually adjusted so that the film thickness after drying and curing of the coating film is 15 to 60 μm. When the film thickness after curing is less than 15 μm, the appearance such as glossiness of the multilayer coating film is deteriorated.

  Then, the uncured intermediate coating film, base coating film and clear coating film formed as desired are baked and cured simultaneously. The baking is usually performed by heating to a temperature of 60 ° C. or higher and 120 ° C. or lower, preferably 60 to 110 ° C., for example, 70 to 90 ° C. Thereby, a cured coating film having a high degree of crosslinking can be obtained. If the heating temperature is less than 60 ° C, curing tends to be insufficient, and if it exceeds 120 ° C, the resulting coating film may be hard and brittle. Although the time to heat can be suitably set according to the said temperature, for example, when temperature is 60-120 degreeC, it is 10 to 60 minutes.

  EXAMPLES Hereinafter, although an Example is hung up and demonstrated in more detail about this invention, this invention is not limited only to these Examples. In the examples, “parts” means “parts by mass” unless otherwise specified.

(Production Example A-1) Preparation Example of Acrylic Resin (A-1) Having Oxidation-Polymerizable Functional Group In a 1 liter Kolben equipped with a stirring blade, a temperature controller, a reflux tube, a nitrogen inlet, and a dropping funnel, 329.70 parts by mass of butyl acetate was charged, the temperature was raised to 110 ° C., and a monomer / initiator mixture having the composition shown in Table 1 was dropped for 3 hours, followed by aging for 0.5 hour. After the initiator, a post shot was dropped for 0.5 hour, and then aged for 1 hour to obtain an acrylic resin as a main chain. The period from the dropping to the end of aging was performed under a nitrogen atmosphere at 110 ° C. and a stirring speed of 150 rpm.

Next, in the same Kolben from which the nitrogen inlet was removed, an acrylic resin as a main chain, a polymerization inhibitor and a catalyst were charged in the amounts shown in Table 1, and the temperature was raised to 110 ° C. Thereafter, 130.88 parts by mass of linoleic acid was added dropwise over 0.5 hours as a raw material for the oxidative polymerizable functional group and aged until no decrease in the acid value was observed. A-1) was obtained. All of the series of operations were performed under an air atmosphere at a stirring speed of 150 rpm.
The obtained resin (A-1) had a number average molecular weight of 4700, a weight average molecular weight of 9400, and a nonvolatile content (hereinafter also referred to as “NV”) of 50% by GPC.

(Production Example B-1) Preparation Example of Acrylic Resin (B-1) Having Reactive Double Bond Group As an acrylic resin having a reactive double bond group, a non-aqueous dispersion (hereinafter also referred to as NAD) is used. It was. Below, the preparation example of NAD which concerns on manufacture example B-1 is demonstrated.

Shell synthesis A solvent is charged into a 0.5 liter Kolben equipped with a stirring blade, a temperature controller, a reflux tube, a nitrogen inlet, and a dropping funnel, and blended as shown in Table 2 under a nitrogen atmosphere at 110 ° C. and 150 rpm. The monomer and the initiator were dropped for 3 hours and then aged for 0.5 hour, followed by a subsequent shot for 0.5 hour, and further aged for 1 hour to prepare an acrylic resin. The temperature was lowered to 100 ° C., a polymerization inhibitor (hydroquinone monomethyl ether; MEHQ) and a catalyst (dibutyltin dilaurate; DBTDL) were added, and then 0.25 mol Karenz AOI with respect to 1.0 mol of the main chain synthesized in an air atmosphere. (Showa Denko Co., Ltd., 2-isocyanatoethyl acrylate) was added dropwise over 0.5 hours. Thereafter, aging was performed for 2 hours, and a double bond for core-shell graft was introduced into the shell.

NAD synthesis Next, in another Kolben equipped with a 1 liter stirring blade, temperature controller, reflux tube, nitrogen inlet, and dropping funnel, the above prepared shell resin with a double bond and butyl acetate / A mixture of Isopar E was charged, and the temperature and the temperature were increased to 110 rpm and 110 ° C. in a nitrogen atmosphere, and then the monomers and initiators shown in Table 3 were added dropwise for 3 hours. After aging for 0.5 hour, a post shot was dropped for 0.5 hour and then further aged for 1 hour to obtain NAD.

Modification of NAD (introduction of reactive double bond group)
Next, the obtained NAD and DBTDL (catalyst, 100 ppm with respect to resin solid content) were charged into another 0.5 liter Kolben equipped with a stirring blade, a temperature controller, a reflux tube, and a dropping funnel, and 80 ° C. The temperature was raised to. Thereafter, Karenz AOI (manufactured by Showa Denko KK, 2-isocyanatoethyl acrylate) described in Table 4 and a solvent were mixed and dropped into Kolben over 10 minutes. The solvent used had the same composition as the NAD internal solvent, and the NV increased by the addition was adjusted to be the same as the original NAD. After aging until the end of the addition reaction, the mixture was cooled to room temperature to prepare an acrylic resin (B-1) having a reactive double bond group.
Note that the completion of the reaction was determined by confirming the disappearance of the peak of the NCO group using FT-IR.

Example 1 Preparation of Clear Coating Composition In Production Example (A-1), except that an oxidation-polymerizable acrylic resin was prepared with the formulation shown in Table 1, the same as in Production Example (A-1), An acrylic resin (A-2) having an oxidative polymerizable functional group was prepared.
Into the reaction container, the acrylic resin (B-1) having a reactive double bond group, a solvent, and an acrylic resin (A-2) having an oxidizable polymerizable functional group were added in the order shown in Table 5, After stirring well, a catalyst (metal dryer) was added and stirred to prepare a clear coating composition.
Since the amount of the catalyst added was small, it was diluted with the solvent shown in Table 5 and added.

Formation of Clear Coating Film For the evaluation of solvent resistance and coating film haze, the clear coating composition prepared above was applied onto a glass plate using a 4 mil film applicator to form an uncured clear coating film. The uncured clear coating film was baked at a temperature of 80 ° C. for 30 minutes to form a clear coating film.
Moreover, the laminated coating-film board was produced for weather resistance evaluation. SPCC-SD steel plate (dull steel plate) that has been treated with zinc phosphate and washed with water is coated with “Power Top U-80”, a cationic electrodeposition paint made by Nippon Paint Automotive Coatings Co., Ltd. The coating was coated with “Orga P-2”, an intermediate coating material manufactured by Nippon Paint Automotive Coatings Co., Ltd., and baked and dried. A base plate “AQUAREX AR-2000 Blue Mica” manufactured by Nippon Paint Automotive Coatings Co., Ltd. was applied to the test plate after the intermediate coating was applied, and then preheated at 80 ° C. for 3 minutes. Thereafter, the clear coating composition prepared above was spray-coated to a dry film thickness of 35 μm and baked at 80 ° C. for 30 minutes to form a laminated coating film.

(Examples 2-9, Comparative Examples 1-8)
Except that the acrylic resin (A) having an oxidative polymerizable functional group was used in the composition shown in Table 1, and the solvent was added depending on the catalyst amount and conditions used in the preparation of the clear coating composition. In the same manner as in Example 1, a clear coating composition was prepared.
Further, a clear coating film was formed in the same manner as in Example 1 except that the baking temperature at the time of forming the coating film was described in Table 5.

(Reference Example 1)
The use of “McFlow O-1860 Clear” (produced by Nippon Paint Automotive Coatings Co., Ltd., acid / epoxy curable clear coating composition) as the clear coating, and the baking temperature after clear coating as shown in Table 6 And an evaluation coated plate was formed in the same manner as in Example 1 except that the baking time was 20 minutes.

(Reference Example 2)
“SP O-100 Clear” (manufactured by Nippon Paint Automotive Coatings Co., Ltd., melamine-curing clear coating composition) was used as the clear coating, and the baking temperature after clear coating was the temperature described in Table 6. A coated plate for evaluation was formed in the same manner as in Example 1 except that.

(Reference Example 3)
The use of “PU Excel O-2100 Clear” (manufactured by Nippon Paint Automotive Coatings Co., Ltd., two-component urethane-cured clear paint composition) as the clear paint, and the baking temperature after clear paint as shown in Table 6 And an evaluation coated plate was formed in the same manner as in Example 1 except that the baking time was 20 minutes.

  Evaluation was performed according to the following procedures using the coating compositions, coating films and evaluation coating plates prepared in the above Examples, Comparative Examples and Reference Examples. The evaluation results are shown in the following table.

(Paint stability evaluation)
700 g of the paint prepared with the formulation shown in Table 5 is put in a 1 liter round can and left in a constant temperature bath at −5 ° C., 20 ° C., and 40 ° C. for 30 days, and the viscosity, hue and particle size before and after standing. The change of was confirmed. Viscosity was measured at Ford Cup # 4, 25 ° C. As for the hue, the presence or absence of clear yellowing was visually determined. The particle size was confirmed with a 50 μm grind gauge (manufactured by Otsuka Equipment). The evaluation criteria are as follows. Table 5 shows the evaluation results of Examples and Comparative Examples, and Table 6 shows the evaluation results of Reference Examples.

Viscosity ○: Change before and after test ± 2 seconds or less ×: Change before and after test exceeds ± 2 seconds

Hue 3: No yellowing is observed 2: Yellowing is observed 1: Remarkably yellowed

Particle size ○: Particle size of less than 5 μm ×: Particle size of 5 μm or more

(Solvent resistance evaluation)
The prepared coating film was rubbed back and forth with a cloth soaked in xylene for 15 reciprocations to evaluate the solvent resistance. The evaluation criteria are as follows. Table 5 shows the evaluation results of Examples and Comparative Examples, and Table 6 shows the evaluation results of Reference Examples.
○: No trace after rubbing △: Traces such as whitening and rubbing traces ×: Dissolution of coating film

(Coating haze evaluation)
The produced coating film was subjected to haze evaluation with a haze meter NDH2000 (manufactured by Nippon Denshoku Industries Co., Ltd.). The evaluation criteria are as follows. Table 5 shows the evaluation results of Examples and Comparative Examples, and Table 6 shows the evaluation results of Reference Examples.
◯: Less than haze 1 ×: Haze 1 or more

(Weather resistance evaluation)
The prepared coating film was subjected to an accelerated weather resistance test using a sunshine weather meter (manufactured by Suga Test Instruments Co., Ltd.), and the discoloration before and after the test was evaluated visually. The operating conditions were based on JIS K5400, and the operating time was 1000 hours.
The evaluation criteria are as follows. Table 5 shows the evaluation results of Examples and Comparative Examples, and Table 6 shows the evaluation results of Reference Examples.
4: Discoloration is not recognized in the coating film 3: Discoloration of the coating film is slightly observed 2: The coating film is discolored 1: The coating film is remarkably discolored

  The coating films obtained in the examples were evaluated for chemical resistance (JIS K5600). As a result, they were not inferior to the clear coating films obtained in the reference examples using conventional clear coating compositions. It was confirmed that there was no problem.

  Thus, the clear coating composition of the present invention has a good coating film hardness even when the coating film is cured under low-temperature heating conditions (for example, 60 to 120 ° C.). A clear coating film excellent in chemical resistance, solvent resistance and weather resistance can be formed. Moreover, the coating film excellent also in the coating-film haze can be obtained.

On the other hand, in Comparative Example 1, the clear coating composition had a solvent resistance and a weather resistance because the acrylic resin (A) did not have the oxidation polymerizable functional group according to the present invention. It was a bad coating film.
In Comparative Example 2, since the acrylic resin (B) according to the present invention was not included, the obtained coating film had a place where traces such as whitening and scratching occurred, and the weather resistance was poor. It was a coating film.
In Comparative Example 3, since the acrylic resin (A) according to the present invention was not included, the obtained coating film had traces such as whitening and scratches, and the coating film had poor weather resistance. It was.
Comparative Example 4 is a clear coating composition using an alkyd resin instead of the acrylic resin (A) according to the present invention, and the obtained coating films are all paint stability, solvent resistance, coating film haze. The film was insufficient in both weather resistance and weather resistance.
Comparative Example 5 is a clear coating composition using a general-purpose acrylic resin instead of the acrylic resin (A) according to the present invention, and the obtained coating film was dissolved in the coating film in the solvent resistance test. In addition, the coating film had poor weather resistance.
Comparative Example 6 is a clear coating composition that does not contain the metal dryer (C) according to the present invention, and the obtained coating film was dissolved in the solvent resistance test, and in addition, the weather resistance was poor. It was a coating film.

  Reference Examples 1 to 3 are commercially available clear coating compositions that are designed to have a baking temperature of about 140 ° C. As is clear from the evaluation results of Reference Examples 1 to 3 and the evaluation results of Examples 1 to 9, the clear coating composition of the present invention has a baking temperature of 60 to 120 ° C. even under low temperature heat curing conditions. It can be seen that solvent resistance and weather resistance comparable to conventional clear coating films are obtained.

  The clear coating composition of the present invention has an advantage that the coating film can be cured under low temperature heat curing conditions. Further, even when heat curing is performed under low temperature heating conditions, a coating film having good coating film hardness can be obtained, and further, there is an advantage of excellent chemical resistance, solvent resistance and weather resistance. . The present invention can also provide a method for forming a multilayer coating film using the clear coating composition.

Claims (8)

  A clear coating composition comprising an acrylic resin (A) having an oxidatively polymerizable functional group having 2 to 4 double bonds, an acrylic resin (B) having a reactive double bond group, and a metal dryer (C).   The clear coating composition according to claim 1, wherein the acrylic resin (B) having a reactive double bond group is a non-aqueous dispersion resin.   The clear coating composition according to claim 1 or 2, wherein the reactive double bond group is at least one selected from an acryloyl group and a methacryloyl group. The oxidative polymerizable functional group is represented by the following chemical formula (I) or (II)

[Wherein R ₁ represents a bond, an alkylene group having 1 to 10 carbon atoms which may have a substituent, or one or more unsaturated double bonds which may have a substituent. A hydrocarbon group having 2 to 10 carbon atoms, and R ₂ is hydrogen, an alkyl group having 1 to 10 carbon atoms which may have a substituent, or 1 or It is a C2-C10 hydrocarbon group containing a further unsaturated double bond. ]
Represented by
The clear coating composition according to any one of claims 1 to 3.   The clear coating composition according to any one of claims 1 to 4, wherein the acrylic resin (A) has an iodine value of 30 to 130.   The amount of the acrylic resin (A) is 10 to 90 parts by mass with respect to 100 parts by mass of the total resin solids of the acrylic resin (A) and the acrylic resin (B) contained in the clear coating composition. The clear coating composition according to any one of claims 1 to 5.   The clear coating composition according to any one of claims 1 to 6, wherein the oxidative polymerizable functional group has 4 to 30 carbon atoms. A step of coating the clear coating composition according to any one of claims 1 to 7 on an object to be coated to form an uncured clear coating; and baking and curing the uncured clear coating Forming a clear coating film;
Including
The temperature for performing the bake hardening is 60 ° C. or higher and 120 ° C. or lower.
A method for forming a clear coating film.