WO2025013801A1 - Coating composition, coating film, and method for forming coating film - Google Patents

Abstract

Disclosed is a coating composition which contains an acrylic polyol, a melamine resin, and a modified blocked polyisocyanate. The modified blocked polyisocyanate is a blocked polyisocyanate that is modified with a tertiary amino alcohol.

Description

Coating composition, coating film, and method for forming coating film

This disclosure relates to a paint composition, a coating film, and a method for forming a coating film.

A coating composition that combines an acrylic polyol, a melamine resin, and a blocked polyisocyanate is known as an automotive coating composition that is applied to automobile bodies, etc. For example, Patent Document 1 discloses a coating composition that contains (A) a secondary hydroxyl group-containing acrylic resin, (B) a melamine resin, (C) an azole-based blocked polyisocyanate compound, (D) a phosphoric acid group-containing compound, and (E) an organometallic compound.

JP 2015-28136 A

However, the coating films formed using the above conventional coating compositions do not necessarily have a good appearance, and there is room for improvement in terms of coating film gloss.

In addition, while conventional paints have been baked at high temperatures of 150°C or higher, in recent years, there has been a demand for curing the coating film at lower temperatures (for example, at temperatures of 140°C or lower) in order to reduce costs during baking, reduce carbon dioxide emissions, and suppress deterioration of the coated object due to heat. Therefore, it is important that the coating composition has good curing properties, that is, it is important that a coating film with good hardness and gel fraction can be formed when the coating is baked at a lower temperature than conventional. However, the above conventional coating compositions do not necessarily have good curing properties. In order to improve the curing properties of coating compositions containing blocked polyisocyanates, quaternary ammonium salts are sometimes used as blocking agent dissociation catalysts, but quaternary ammonium salts can cause the coating film to discolor (yellowing), impairing its appearance.

One aspect of the present disclosure aims to provide a coating composition that is capable of forming a coating film with good appearance and has excellent curing properties.

This disclosure provides at least the following [1] to [6].

[1]
The composition includes an acrylic polyol, a melamine resin, and a modified blocked polyisocyanate,
A coating composition, wherein the modified blocked polyisocyanate is a blocked polyisocyanate modified with a tertiary amino alcohol.

［式（Ｉ）中、Ｒ^１及びＲ^２は、それぞれ独立して、炭素数１～８の１価の炭化水素基を表し、Ｒ^３は、炭素数１～１６の２価の炭化水素基を表す。］

［式（ＩＩ）中、Ｒ^４～Ｒ^８は、それぞれ独立して、水素原子、炭素数１～４のアルキル基又は炭素数１～４のアルコキシ基を表し、ａ及びｂは、それぞれ独立して、０又は１であり、ａ＋ｂは１である。］ [2]
The coating composition according to [1], wherein the tertiary amino alcohol comprises at least one selected from the group consisting of a compound represented by the following formula (I) and a compound represented by the following formula (II).

[In formula (I), R ¹ and R ² each independently represent a monovalent hydrocarbon group having 1 to 8 carbon atoms, and R ³ represents a divalent hydrocarbon group having 1 to 16 carbon atoms.]

[In formula (II), R ⁴ to R ⁸ each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms, a and b each independently represent 0 or 1, and a+b represents 1.]

[3]
The coating composition according to [1] or [2], wherein the modified blocked polyisocyanate contains a structure derived from an aliphatic polyisocyanate having 4 to 6 carbon atoms or a derivative thereof.

[4]
The coating composition according to any one of [1] to [3], wherein the modified blocked polyisocyanate has at least one group selected from the group consisting of an isocyanate group blocked with an oxime-based blocking agent, an isocyanate group blocked with a pyrazole-based blocking agent, and an isocyanate group blocked with an imidazole-based blocking agent.

[5]
A coating film formed from the coating composition according to any one of [1] to [4].

[6]
A method for forming a coating film, comprising the steps of applying the coating composition according to any one of [1] to [4] to a substrate and heating the substrate at 120 to 140°C to cure the coating film made of the coating composition.

This disclosure makes it possible to provide a coating composition that is capable of forming a coating film with good appearance and has excellent curing properties.

Below, exemplary embodiments of the present disclosure are described. However, the present disclosure is not limited to the following embodiments. In this specification, a numerical range indicated using "~" indicates a range that includes the numerical values written before and after "~" as the minimum and maximum values, respectively. In addition, unless specifically stated otherwise, the units of the numerical values written before and after "~" are the same. In addition, the upper and lower limit values individually described can be combined in any combination. In addition, in this specification, "(meth)acrylic" means at least one of acrylic and the corresponding methacrylic.

<Paint composition>
One embodiment of the present disclosure is a coating composition that includes an acrylic polyol, a melamine resin, and a modified blocked polyisocyanate that is a blocked polyisocyanate modified with a tertiary amino alcohol.

The coating composition has excellent curing properties. That is, the coating composition can form a coating film with good hardness and gel fraction even when baked at a temperature of 140°C or less (e.g., 120 to 140°C). It has been confirmed that this effect is achieved by using the modified blocked polyisocyanate, and is not achieved by mixing a tertiary amino alcohol and a blocked polyisocyanate separately. In addition, the modified blocked polyisocyanate does not easily inhibit the gloss of the coating film, and is also less likely to cause discoloration (yellowing). Therefore, the coating composition can form a coating film with a good appearance (i.e., a coating film with excellent gloss and little discoloration).

(Acrylic polyol)
The acrylic polyol is a polymer that may be called a hydroxyl group-containing acrylic resin. The acrylic polyol contains a (meth)acrylic monomer as a monomer unit and has a plurality of hydroxyl groups. The hydroxyl groups of the acrylic polyol may be hydroxyl groups derived from the (meth)acrylic monomer.

(Meth)acrylic monomers include (meth)acrylic acid hydroxy compounds (acrylic acid hydroxy compounds or methacrylic acid hydroxy compounds). (Meth)acrylic acid hydroxy compounds are (meth)acrylic acid esters that have one or more hydroxy groups in the molecule that can serve as reaction sites. The hydroxy groups in (meth)acrylic acid hydroxy compounds may be primary hydroxy groups, secondary hydroxy groups, or tertiary hydroxy groups.

(Meth)acrylic acid hydroxy compounds are, for example, esters of (meth)acrylic acid and aliphatic polyhydric alcohols. Examples of aliphatic polyhydric alcohols include glycols having 1 to 20 carbon atoms (ethylene glycol, propylene glycol, butylene glycol, neopentyl glycol, pentaerythritol, etc.).

Examples of (meth)acrylic acid hydroxy compounds include acrylic acid hydroxy compounds such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, 3-hydroxy-2,2-dimethylpropyl acrylate, and pentaerythritol triacrylate; and methacrylic acid hydroxy compounds such as 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, 3-hydroxy-2,2-dimethylpropyl methacrylate, and pentaerythritol trimethacrylate. The (meth)acrylic acid hydroxy compounds may be used alone or in combination of two or more.

As the (meth)acrylic monomer, a (meth)acrylic acid ester (hereinafter simply referred to as "(meth)acrylic acid ester") that does not fall under the above-mentioned (meth)acrylic acid hydroxy compound can also be used. The (meth)acrylic acid ester may be a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms. Examples of (meth)acrylic acid esters include (meth)acrylic acid alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, and dodecyl (meth)acrylate; (meth)acrylic acid cycloalkyl esters (products of esterification reaction between (meth)acrylic acid and alicyclic alcohols) such as cyclohexyl (meth)acrylate; (meth)acrylic acid aryl esters such as phenyl (meth)acrylate and benzyl (meth)acrylate; and the like. The (meth)acrylic acid esters may be used alone or in combination of two or more.

The (meth)acrylic monomer contained as a monomer unit in the acrylic polyol may be one type or two or more types. In other words, the acrylic polyol may be a homopolymer formed by polymerization of one type of (meth)acrylic monomer (for example, a homopolymer of a (meth)acrylic acid hydroxy compound), or a copolymer formed by copolymerization of two or more types of (meth)acrylic monomers (for example, a copolymer of a (meth)acrylic acid ester and a (meth)acrylic acid hydroxy compound).

The acrylic polyol may contain monomers other than (meth)acrylic monomers as monomer units, or may contain only (meth)acrylic monomers as monomer units. Examples of monomers other than (meth)acrylic monomers include the polymerizable unsaturated monomers disclosed in the above-mentioned Patent Document 1 as other polymerizable unsaturated monomers.

Acrylic polyol can be obtained, for example, by polymerizing the (meth)acrylic monomer by applying energy (light energy such as ultraviolet light or electron beam, heat energy, etc.) to a mixture of a (meth)acrylic monomer (for example, the above-mentioned (meth)acrylic acid hydroxy compound, or a monomer mixture containing the above-mentioned (meth)acrylic acid hydroxy compound and the above-mentioned (meth)acrylic acid ester) and a polymerization initiator. In other words, the acrylic polyol can be a thermal polymer or a photopolymer. The acrylic polyol may be a thermal polymer in that it is likely to become a polymer in which the polymerization reaction and crosslinking reaction are completed.

Polymerization initiators include thermal polymerization initiators and photopolymerization initiators. The polymerization initiator is selected appropriately depending on the polymerization method.

Examples of thermal polymerization initiators include peroxydicarbonates such as di-2-ethylhexylperoxydicarbonate; peroxyesters such as t-butylperoxybenzoate, t-butylperoxy-2-ethylhexanoate, t-butylperoxyisopropylcarbonate, and t-hexylperoxyisopropylcarbonate; and peroxyketals such as di(t-butylperoxy)-2-methylcyclohexane, di(t-butylperoxy)-3,3,5-trimethylcyclohexane, and di(t-butylperoxy)cyclohexane.

Examples of photopolymerization initiators include acetophenones such as acetophenone, methoxyacetophenone, 2,2-diethoxyacetophenone, p-dimethylaminoacetophenone, 2,2-dimethoxy-2-phenylacetophenone, α-hydroxy-α,α'-dimethylacetophenone, 2-hydroxy-2-cyclohexylacetophenone, and 2-methyl-1[4-(methylthio)phenyl]-2-monopropanone-1; benzoin ethers such as benzoin methyl ether, benzoin ethyl ether, and benzoin isopropyl butyl ether; Ketones such as benzophenone, 2-chlorobenzophenone, p,p'-dichlorobenzophenone, N,N'-tetramethyl-4,4'-diaminobenzophenone, and 4-(2-hydroxyethoxy)phenyl(2-hydroxy-2-propyl)ketone; thioxanthones such as thioxanthone, 2-chlorothioxanthone, and 2-methylthioxanthone; phosphine oxides such as bisacylphosphine oxide and benzoylphosphine oxide; ketals such as benzyl dimethyl ketal; quinones such as camphane-2,3-dione and phenanthrenequinone; and the like.

The glass transition temperature (glass transition point, Tg) of the acrylic polyol is, for example, -30 to 80°C. When the glass transition temperature of the acrylic polyol is in the above range, a coating film with excellent contamination resistance is easily obtained. From the viewpoint of better contamination resistance, the glass transition temperature of the acrylic polyol may be 0°C or higher or 10°C or higher, and may be 70°C or lower or 60°C or lower. From the above viewpoint, the glass transition temperature of the acrylic polyol may be 0 to 70°C or 10 to 60°C. An acrylic polyol having a glass transition temperature in the above range can be synthesized by adjusting the type and blending ratio of the monomer components. For example, when the acrylic polyol is a copolymer, the glass transition temperature can be estimated by the Fox formula and the blending ratio of the monomer components can be set to obtain an acrylic polyol having a glass transition temperature in the above range. The glass transition temperature of the acrylic polyol can be determined by measuring the inflection point of DSC in accordance with JIS K7121.

The hydroxyl value of the acrylic polyol may be, for example, 60 to 250 mgKOH/g. When the hydroxyl value of the acrylic polyol is within this range, a coating film with excellent curing properties is likely to be obtained. From the same viewpoint, the hydroxyl value of the acrylic polyol may be 80 mgKOH/g or more or 100 mgKOH/g or more, and may be 220 mgKOH/g or less or 200 mgKOH/g or less. From the above viewpoint, the hydroxyl value of the acrylic polyol may be 80 to 220 mgKOH/g or 100 to 200 mgKOH/g. The hydroxyl value of the acrylic polyol is a value measured by a method conforming to JIS K1557.

The weight average molecular weight of the acrylic polyol may be, for example, 3,000 to 30,000. When the weight average molecular weight of the acrylic polyol is within this range, a coating film having a better appearance in terms of smoothness and image clarity tends to be obtained. From the same viewpoint, the weight average molecular weight of the acrylic polyol may be 3,500 or more or 4,000 or more, and may be 20,000 or less or 10,000 or less. The weight average molecular weight in this specification is a standard polystyrene equivalent value measured by gel permeation chromatography (GPC).

One type of acrylic polyol may be used alone, or two or more types may be used in combination.

The content of the acrylic polyol may be 45% by mass or more, 50% by mass or more, or 55% by mass or more, based on the total solid content of the coating composition, from the viewpoint of further improving the curability. The content of the acrylic polyol may be 75% by mass or less, 70% by mass or less, or 65% by mass or less, based on the total solid content of the coating composition, from the viewpoint of further improving the smoothness of the coating film. From these viewpoints, the content of the acrylic polyol may be 45 to 75% by mass, 50 to 70% by mass, or 55 to 65% by mass, based on the total solid content of the coating composition. In this specification, the "total solid content of the coating composition" means the amount obtained by excluding the amount of the solvent from the total amount of the coating composition when the coating composition contains a solvent, and means the total amount of the coating composition when the coating composition does not contain a solvent. In one embodiment, the content of the acrylic polyol based on the total amount (solid content) of the acrylic polyol, the melamine resin, and the modified blocked polyisocyanate may be in the above range.

(Melamine resin)
The melamine resin may be a resin obtained by reacting melamine with one or more aldehydes, such as formaldehyde, paraformaldehyde, acetaldehyde, and benzaldehyde.

The melamine resin may be a methylol melamine such as dimethylol melamine, trimethylol melamine, tetramethylol melamine, pentamethylol melamine, or hexamethylol melamine. The melamine resin may be a condensation product of these methylol melamines.

The melamine resin may be a reaction product (an alkyl ether of methylolmelamine) obtained by reacting the above-mentioned methylolmelamine with one or more types of alcohol. Examples of the alcohol include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, 2-ethylbutanol, and 2-ethylhexanol.

The reaction product (alkyl ether of methylolmelamine) has, for example, a structure represented by the following formula (1).

In formula (1), R ^1a to R ^6a each independently represent a hydrogen atom or an alkoxymethyl group, provided that at least one of R ^1a to R ^6a is an alkoxymethyl group. Examples of the alkoxymethyl group include a methoxymethyl group, an ethoxymethyl group, an n-propyloxymethyl group, an isopropyloxymethyl group, an n-butoxymethyl group, an isobutyloxymethyl group, a 2-ethylbutyloxymethyl group, and a 2-ethylhexyloxymethyl group.

The above reaction product (alkyl etherified product of methylol melamine) may be a product in which some of the methylol groups contained in methylol melamine have been alkyl etherified, or may be a product in which all of the methylol groups contained in methylol melamine have been alkyl etherified. The melamine resin may be a condensation product of the above reaction product.

Among the above, when a compound obtained by alkylating methylol melamine with n-butyl alcohol or a condensate thereof (melamine resin having a butyl ether group) is used, the weather resistance of the coating film tends to improve. From the viewpoint of obtaining such an effect more significantly, all of the alkyl ether groups in the melamine resin may be butyl ether groups. From the same viewpoint, the number of butyl ether groups contained in each triazine ring of the melamine resin may be 3 to 4.

The weight average molecular weight of the melamine resin may be, for example, 400 to 6000, 500 to 5000, or 800 to 4000. When the weight average molecular weight of the melamine resin is within the above range, a coating film that is excellent in gloss and weather resistance is easily obtained.

　Commercially available melamine resins can also be used. Examples of commercially available products that can be used include "Cymel 202", "Cymel 203", "Cymel 211", "Cymel 238", "Cymel 251", "Cymel 303", "Cymel 323", "Cymel 324", "Cymel 325", "Cymel 327", "Cymel 350", "Cymel 385", "Cymel 1156", "Cymel 1158", "Cymel 1116", and "Cymel 1130" manufactured by Allnex Japan Co., Ltd., and "U-Ban 120", "U-Ban 20HS", "U-Ban 20SE60", "U-Ban 2021", "U-Ban 2028", and "U-Ban 28-60" manufactured by Mitsui Chemicals, Inc.

Melamine resins may be used alone or in combination of two or more types.

The content of the melamine resin may be 1% by mass or more, 3% by mass or more, or 5% by mass or more, based on the total solid content of the coating composition, from the viewpoint of further improving the curability. The content of the melamine resin may be 20% by mass or less, 15% by mass or less, or 10% by mass or less, based on the total solid content of the coating composition, from the viewpoint of further improving the smoothness of the coating film. From these viewpoints, the content of the melamine resin may be 1 to 20% by mass, 3 to 15% by mass, or 5 to 10% by mass, based on the total solid content of the coating composition. In one embodiment, the content of the melamine resin based on the total amount (solid content) of the acrylic polyol, the melamine resin, and the modified blocked polyisocyanate may be in the above range.

(Modified blocked polyisocyanate)
The modified blocked polyisocyanate is a blocked polyisocyanate modified with a tertiary amino alcohol.

Modified blocked polyisocyanates, for example, have a structure derived from unblocked polyisocyanates, isocyanate groups blocked with a blocking agent (hereinafter also referred to as "blocked isocyanate groups"), and isocyanate groups modified with a tertiary amino alcohol (hereinafter also referred to as "modified isocyanate groups").

[Unblocked polyisocyanate]
The unblocked polyisocyanate is a polyisocyanate that does not have the above-mentioned blocked isocyanate group. The unblocked polyisocyanate has a plurality of isocyanate groups (free isocyanate groups). Examples of the unblocked polyisocyanate include aromatic polyisocyanates, aliphatic polyisocyanates, alicyclic polyisocyanates, and polyisocyanate derivatives thereof. Examples of the derivatives include isocyanurates, allophanates, biurets, and the like.

The unblocked polyisocyanate may be a polyisocyanate that does not have an aromatic ring, i.e., a non-aromatic polyisocyanate, from the viewpoint of improving the yellowing resistance of the cured coating film. Examples of non-aromatic polyisocyanates include aliphatic polyisocyanates such as hexamethylene diisocyanate, tetramethylene diisocyanate, 2-methyl-pentane-1,5-diisocyanate, 3-methyl-pentane-1,5-diisocyanate, lysine triisocyanate, and trioxyethylene diisocyanate; alicyclic polyisocyanates such as isophorone diisocyanate, cyclohexyl diisocyanate, hydrogenated diphenylmethane diisocyanate, norbornane diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated xylene diisocyanate, and hydrogenated tetramethylxylene diisocyanate, and derivatives thereof. Examples of derivatives include isocyanurates, allophanates, and biurets. The derivative may be an isocyanate group-containing prepolymer obtained by reacting the polyisocyanate with a polyol, or may be a derivative of the prepolymer (e.g., an isocyanurate, an allophanate, a biuret, etc.). As the polyol, for example, a diol having 2 to 9 carbon atoms is used. Examples of such diols include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, and 1,5-pentanediol.

The unblocked polyisocyanate may contain an aliphatic polyisocyanate having 4 to 6 carbon atoms or a derivative thereof from the viewpoint of further improving the curing property, and may contain hexamethylene diisocyanate or a derivative thereof from the viewpoint of further improving the curing property. In other words, the modified blocked polyisocyanate may have a structure derived from an aliphatic polyisocyanate having 4 to 6 carbon atoms or a derivative thereof, or may have a structure derived from hexamethylene diisocyanate or a derivative thereof. The derivative of an aliphatic polyisocyanate having 4 to 6 carbon atoms (e.g., hexamethylene diisocyanate) may be at least one selected from the group consisting of an isocyanurate, an allophanate, and a biuret. These derivatives may be derivatives of the above-mentioned isocyanate group-containing prepolymer. Among these, when the derivative of hexamethylene diisocyanate is an isocyanurate, a higher coating hardness tends to be obtained. When the unblocked polyisocyanate contains an isocyanurate, from the viewpoint of further improving the hardness of the coating film, the content of the isocyanurate trimer (isocyanurate trimer content) based on the total mass of the unblocked polyisocyanate may be 50 mass% or more, and the content of the isocyanurate group (isocyanurate group content) relative to the total (100 mol%) of the isocyanurate group and allophanate group in the unblocked polyisocyanate may be more than 80 mol%. The upper limit of the isocyanurate trimer content may be 80 mass%, and the upper limit of the isocyanurate group content may be 99 mol%.

[Blocked isocyanate group]
The blocked isocyanate group is an isocyanate group blocked with a blocking agent and has a structure derived from the blocking agent. In other words, the blocked isocyanate group can be defined as a group formed by the reaction between the blocking agent and an isocyanate group.

Examples of blocking agents include alcohol-based blocking agents such as methanol, ethanol, n-butanol, isobutanol, 2-ethylhexanol, butyl cellosolve, propylene glycol monomethyl ether, ethylene glycol, and benzyl alcohol; phenol-based blocking agents such as phenol, cresol, ethylphenol, butylphenol, and 2-hydroxypyridine; lactam-based blocking agents such as ε-caprolactam, δ-valerolactam, and γ-butyrolactam; oxime-based blocking agents such as formaldoxime, acetaldoxime, acetoneoxime, methylethylketoxime, methylisobutylketoxime, and cyclohexanoneoxime; imidazole, 2-methylimidazole, 4-methylimidazole, 2,4-dimethylimidazole, Examples of the blocking agent include imidazole-based blocking agents such as imidazole, 2-ethylimidazole, 2-propylimidazole, 2-isopropylimidazole, 4-methyl-2-propylimidazole, 2-phenylimidazole, 4-phenylimidazole, 5-phenylimidazole, 2-methyl-4-phenylimidazole, 2-ethyl-4-methylimidazole, 2-undecylimidazole, and 2-heptadecylimidazole; pyrazole-based blocking agents such as 3,5-dimethylpyrazole, 3-methylpyrazole, and pyrazole; amine-based blocking agents such as diphenylamine, diisopropylamine, and isopropylethylamine; and triazole-based blocking agents such as triazole, 1,2,4-triazole, and 3,5-dimethyl-1,2,4-triazole. From the viewpoint of storage stability, an oxime-based blocking agent may be used. As the oxime-based blocking agent, methyl ethyl ketoxime is preferable. From the viewpoint of curability, pyrazole-based blocking agents and imidazole-based blocking agents may be used. As a pyrazole-based blocking agent, 3,5-dimethylpyrazole is preferred. As an imidazole-based blocking agent, 2-ethyl-4-methylimidazole is preferred.

In view of the above, in one embodiment, the modified blocked polyisocyanate may have at least one group selected from the group consisting of an isocyanate group blocked with an oxime-based blocking agent, an isocyanate group blocked with a pyrazole-based blocking agent, and an isocyanate group blocked with an imidazole-based blocking agent.

[Modified isocyanate group]
The modified isocyanate group is an isocyanate group modified with a tertiary amino alcohol. The modified isocyanate group can also be described as a group formed by the reaction of a tertiary amino alcohol with an isocyanate group. The modified isocyanate group has, for example, a structure represented by the formula: *-NH-C(O)O-X-NR ₂ (wherein R represents a monovalent hydrocarbon group, X represents a divalent linking group, and * represents a bond).

　A tertiary amino alcohol is a compound having at least one tertiary amino group and at least one hydroxyl group. The number of tertiary amino groups and hydroxyl groups that a tertiary amino alcohol has may each be one or more. The number of tertiary amino groups may be one or two, and the number of hydroxyl groups may be one.

Examples of the tertiary amino alcohol having one tertiary amino group include compounds represented by the following formula (I).

In formula (I), ^R1 and ^R2 each independently represent a monovalent hydrocarbon group having 1 to 8 carbon atoms, and ^R3 represents a divalent hydrocarbon group having 1 to 16 carbon atoms. ^R1 and ^R2 may be the same or different.

The monovalent hydrocarbon groups represented by ^R1 and ^R2 may be aliphatic hydrocarbon groups (e.g., alkyl groups or cycloalkyl groups) or aromatic hydrocarbon groups (e.g., aryl groups). When the hydrocarbon group is an aliphatic hydrocarbon group, it may have, for example, 1 to 8 carbon atoms. The aliphatic hydrocarbon group may have, for example, 1 to 4 or 1 to 2 carbon atoms. When the hydrocarbon group is an aromatic hydrocarbon group, it may have, for example, 6 to 16 carbon atoms. The aromatic hydrocarbon group may have, for example, 6 to 14 or 6 to 12 carbon atoms.

The monovalent hydrocarbon group represented by ^R1 and ^R2 may be an aliphatic hydrocarbon group from the viewpoint of further improving the curability, or may be an alkyl group from the viewpoint of further improving the curability. Specific examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, and a 2-ethylhexyl group. As the alkyl group, a linear alkyl group is preferable, and a linear alkyl group having 1 to 4 carbon atoms (a methyl group, an ethyl group, an n-propyl group, and an n-butyl group) is more preferable.

The divalent hydrocarbon group represented by ^R3 may be an aliphatic hydrocarbon group (for example, an alkylene group or a cycloalkylene group) or an aromatic hydrocarbon group (for example, an arylene group). When the hydrocarbon group is an aliphatic hydrocarbon group, the number of carbon atoms is, for example, 1 to 16. The number of carbon atoms of the aliphatic hydrocarbon group may be 2 to 8 or 2 to 6. When the hydrocarbon group is an aromatic hydrocarbon group, the number of carbon atoms is, for example, 6 to 16. The number of carbon atoms of the aromatic hydrocarbon group may be 6 to 14 or 6 to 12.

The divalent hydrocarbon group represented by ^R3 may be an aliphatic hydrocarbon group from the viewpoint of further improving the curability, and may be an alkylene group from the viewpoint of further improving the curability. Specific examples of the alkylene group include a methylene group, an ethylene group, an n-propylene group, an isopropylene group, an n-butylene group, an isobutylene group, a t-butylene group, an n-pentylene group, an n-hexylene group, an n-heptylene group, an n-octylene group, and a 2-ethylhexylene group. As the alkylene group, a linear alkylene group is preferable, and a linear alkylene group having 2 to 6 carbon atoms (ethylene group, n-propylene group, n-butylene group, n-pentylene group, and n-hexylene group) is more preferable.

Specific examples of compounds represented by formula (I) include 6-(dimethylamino)-1-hexanol, 2-(dimethylamino)ethanol, 2-(dibutylamino)ethanol, 2-(diethylamino)ethanol, 2-(dipropylamino)ethanol, 2-(diisopropylamino)ethanol, 2-(diisobutylamino)ethanol, 2-(dipentylamino)ethanol, 2-(dihexylamino)ethanol, 2-(dioctylamino)ethanol, and 8-(dimethylamino)-1-octanol.

An example of a tertiary amino alcohol having two tertiary amino groups is a compound represented by the following formula (II).

In formula (II), R ⁴ to R ⁸ each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms, a and b each independently represent 0 or 1, and a+b represents 1. ^{R 4} to R ⁸ may be the same or different.

Examples of the alkyl group having 1 to 4 carbon atoms represented by R ⁴ to R ⁸ include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, an s-butyl group, and a t-butyl group. Examples of the alkoxy group having 1 to 4 carbon atoms represented by R ⁴ to R ⁸ include a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, an s-butoxy group, and a t-butoxy group.

In particular, when R ⁴ is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms, R ⁵ to R ⁷ are each independently a hydrogen atom or a methyl group, and R ⁸ is a hydrogen atom, the curability tends to be further improved, when R ⁴ to R ⁷ are each independently a hydrogen atom or a methyl group, and R ⁸ is a hydrogen atom, the curability tends to be further improved, and when R ⁴ to R ⁸ are all hydrogen atoms, the curability tends to be particularly improved.

Specific examples of the compound represented by formula (II) above include compounds represented by formulas 1 to 24 below.

The tertiary amino alcohol may contain at least one compound selected from the group consisting of the compounds represented by formula (I) and the compounds represented by formula (II) from the viewpoint of further improving the curing properties. That is, the blocked polyisocyanate may have at least one group selected from the group consisting of the isocyanate group modified with the compound represented by formula (I) and the isocyanate group modified with the compound represented by formula (II). The tertiary amino alcohol may contain a compound selected from the compounds shown in the above specific examples from the viewpoint of further improving the curing properties, and may contain at least one compound selected from the group consisting of 6-(dimethylamino)-1-hexanol, 2-(dimethylamino)ethanol, 2-(dibutylamino)ethanol, and 1,4-diazabicyclo[2,2,2]octane-2-methanol.

The molecular weight of the tertiary amino alcohol is, for example, 80 to 250. From the viewpoint of improving compatibility with polyisocyanate, the molecular weight of the tertiary amino alcohol may be 100 or more or 130 or more. From the viewpoint of further improving curing properties, the molecular weight of the tertiary amino alcohol may be 230 or less or 200 or less.

The content of the modified isocyanate group may be 0.1 to 30 mass%, 0.5 to 20 mass%, or 1 to 10 mass%, based on the total mass of the compound obtained by dissociating the blocking agent from the modified blocked polyisocyanate.

The modified blocked polyisocyanate may have free isocyanate groups, but when the blocked polyisocyanate does not have free isocyanate groups, the storage stability can be further improved. From the viewpoint of further improving the storage stability, all of the effective isocyanate groups in the modified blocked polyisocyanate may be blocked isocyanate groups. Here, effective isocyanate groups refer to both free isocyanate groups and blocked isocyanate groups.

The effective isocyanate group content of the modified blocked polyisocyanate (hereinafter referred to as the "effective NCO content") may be 4 to 28 mass%, 5 to 25 mass%, or 6 to 22 mass%, from the viewpoint of further enhancing the curing property of the coating material. Here, the effective NCO content is the isocyanate group present in the modified blocked polyisocyanate that can participate in a crosslinking reaction, expressed in mass %. The effective NCO content can be said to be the content (free NCO content) of free isocyanate groups in the compound obtained by dissociating the blocking agent from the modified blocked polyisocyanate relative to the total mass of the modified blocked polyisocyanate. The free NCO content can be determined by reacting the isocyanate groups in the measurement sample (the compound obtained by dissociating the blocking agent from the modified blocked polyisocyanate) with an excess of secondary amine, and then back titrating the unreacted secondary amine with hydrochloric acid.

The modified blocked polyisocyanate can be obtained, for example, by reacting a polyisocyanate having free isocyanate groups, such as an unblocked polyisocyanate, with a blocking agent and a tertiary amino alcohol. That is, the modified blocked polyisocyanate can be a reaction product of a polyisocyanate having free isocyanate groups, a blocking agent and a tertiary amino alcohol. The polyisocyanate having free isocyanate groups, the blocking agent and the tertiary amino alcohol may each be used alone or in combination of two or more. However, from the viewpoint of improving the yellowing resistance of the cured coating film, it is not necessary to use an aromatic polyisocyanate as the polyisocyanate having free isocyanate groups.

The order in which the polyisocyanate having a free isocyanate group, the blocking agent, and the tertiary amino alcohol are reacted is not particularly limited. For example, the polyisocyanate having a free isocyanate group may be reacted with the tertiary amino alcohol to obtain an isocyanate-terminated precursor, and then the obtained isocyanate-terminated precursor may be reacted with the blocking agent.

The reaction between the polyisocyanate having a free isocyanate group and the tertiary amino alcohol may be carried out, for example, in the presence of a solvent. Examples of the solvent that can be used include aromatic solvents such as toluene and xylene, ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, ester solvents such as ethyl acetate and butyl acetate, and glycol ether solvents such as ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, and diethylene glycol diethyl ether. The reaction temperature may be 20 to 200°C. The reaction time may be, for example, 1 to 10 hours. The amount of polyisocyanate and tertiary amino alcohol used may be adjusted so that the content of modified isocyanate groups falls within the above range. For example, 0.1 to 60 mol% of the tertiary amino alcohol may be used relative to the total number of moles of free isocyanate groups in the polyisocyanate. The above reaction proceeds without a catalyst, but the reaction can also be accelerated by using a known urethane reaction catalyst.

The reaction between the isocyanate-terminated precursor and the blocking agent can be carried out according to the reaction conditions for a typical blocking reaction. The reaction between the isocyanate-terminated precursor and the blocking agent can be carried out at room temperature or with heating. Regardless of whether or not heating is carried out, the temperature of the reaction liquid can be, for example, 20 to 200°C.

The modified blocked polyisocyanate may be a compound derived from a reaction product of a polyisocyanate having a free isocyanate group, a blocking agent, and a tertiary amino alcohol. The modified blocked polyisocyanate may be, for example, a compound obtained by reacting a reaction product of a polyisocyanate having a free isocyanate group, a blocking agent, and a tertiary amino alcohol with a compound that can react with the free isocyanate group in the reaction product (e.g., an active hydrogen group-containing compound, etc.).

The modified blocked polyisocyanates may be used alone or in combination of two or more. For example, two or more modified blocked polyisocyanates derived from different types of unblocked polyisocyanates may be used in combination.

The content of the modified blocked polyisocyanate may be 20% by mass or more, 25% by mass or more, or 30% by mass or more, based on the total solid content of the coating composition, from the viewpoint of easily obtaining a coating composition with excellent curability. The content of the modified blocked polyisocyanate may be 45% by mass or less, 40% by mass or less, or 35% by mass or less, based on the total solid content of the coating composition, from the viewpoint of improving the storage stability of the coating. From these viewpoints, the content of the modified blocked polyisocyanate may be 20 to 45% by mass, 25 to 40% by mass, or 30 to 35% by mass, based on the total solid content of the coating composition. In one embodiment, the content of the modified blocked polyisocyanate based on the total amount (solid content) of the acrylic polyol, the melamine resin, and the modified blocked polyisocyanate may be in the above range.

(Other ingredients)
The coating composition may further contain other components other than the acrylic polyol, melamine resin, and modified blocked polyisocyanate, such as additives such as pigments, dispersion stabilizers, viscosity regulators, leveling agents, antigelling agents, light stabilizers, antioxidants, ultraviolet absorbers, heat resistance improvers, inorganic and organic fillers, plasticizers, lubricants, antistatic agents, reinforcing materials, and catalysts.

The coating composition may contain a solvent as another component. Examples of the solvent include benzene, toluene, xylene, cyclohexane, acetone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, n-butyl acetate, cellosolve acetate, propylene glycol monomethyl ether acetate, diethylene glycol dimethyl ether, 1,4-dioxane, and the like. These solvents may be used alone or in combination of two or more. The content of the solvent may be 0 to 95 mass%, 5 to 90 mass%, or 10 to 80 mass%, based on the total mass of the coating composition.

The coating composition may contain an unblocked polyisocyanate (e.g., a polyisocyanate remaining as an unreacted product), a blocking agent (e.g., a blocking agent remaining as an unreacted product), or a tertiary amino alcohol (e.g., a tertiary amino alcohol remaining as an unreacted product). The content of the unblocked polyisocyanate contained in the coating composition may be 5% by mass or less, or may be 0% by mass, based on the total solid content of the coating composition. The content of the blocking agent contained in the coating composition may be 5% by mass or less, or may be 0% by mass, based on the total solid content of the coating composition. The content of the tertiary amino alcohol contained in the coating composition may be 5% by mass or less, or may be 0% by mass, based on the total solid content of the coating composition.

The equivalent ratio of active hydrogen groups (e.g., hydroxyl groups in acrylic polyol) to available isocyanate groups contained in the coating composition ([isocyanate-reactive groups]/[available isocyanate groups]) may be 1/9 to 9/1, or may be 2/8 to 8/2. When the ratio is within the above range, better curing properties are obtained.

The coating composition may be a one-liquid type composition in which all of the components are contained in one liquid. A one-liquid type coating composition can be, for example, a mixture prepared by mixing an acrylic polyol, a melamine resin, a modified blocked polyisocyanate, and other optional components.

The coating composition may be a multi-liquid composition in which the components are present in multiple liquids. The multi-liquid coating composition may, for example, comprise a first liquid containing an acrylic polyol and a melamine resin, and a second liquid containing a modified blocked polyisocyanate.

The coating composition can be used as an automobile topcoat paint, anti-chipping paint, electrocoating paint, paint for automobile parts, paint for automobile repair, pre-coated metal and rust-resistant steel plate for metal products such as home appliances and office equipment, paint for construction materials, paint for plastics, adhesive, adhesion promoter, sealant, etc.

<Coating film and method for forming the coating film>
Another embodiment of the present disclosure is a coating film formed from the coating composition of the above embodiment. Also, another embodiment of the present disclosure is a method for forming a coating film, comprising the steps of applying the coating composition of the above embodiment to a substrate and curing the coating film (uncured coating film) made of the coating composition.

The coating film may be an uncured coating film made of the paint composition of the above embodiment, or may be a coating film (cured coating film) formed by curing the uncured coating film. The thickness of the coating film is, for example, 5 to 40 μm. The coating film may be a thin film with a thickness of less than 20 μm.

The coating composition may be applied by known methods such as roll coating, curtain flow coating, spray coating, electrostatic coating, bell coating, and electrochemical coating. The amount of coating composition applied and the thickness of the coating film may be determined appropriately depending on the material of the surface to be coated, etc.

The coating film (uncured coating film) made of the paint composition may be cured by heating the coating film. The heating temperature (baking temperature) may be, for example, 200°C or lower, and the heating time (baking time) may be, for example, 10 to 180 minutes. Conventionally, baking of paint compositions has been carried out at high temperatures of 150°C or higher, but with the paint composition of this embodiment, a good cured coating film can be obtained even when baking is carried out at 140°C or lower (for example, 120 to 140°C).

Examples of the substrates include molded articles made of materials such as stainless steel, phosphate-treated steel, galvanized steel, iron, copper, aluminum, brass, glass, acrylic polyol, polycarbonate resin, polyethylene terephthalate resin, polyethylene naphthalate resin, polybutylene phthalate resin, polystyrene resin, AS resin, ABS resin, polycarbonate-ABS resin, 6-nylon resin, 6,6-nylon resin, MXD6 nylon resin, polyvinyl chloride resin, polyvinyl alcohol resin, polyurethane resin, phenolic resin, melamine resin, polyacetal resin, chlorinated polyolefin resin, polyolefin resin, polyamide resin, polyether ether ketone resin, polyphenylene sulfide resin, NBR resin, chloroprene resin, SBR resin, and SEBS resin, as well as surface-treated articles of such molded articles. Surface-treated articles may be molded articles (surface-treated molded articles) made of olefin resins such as polyethylene and polypropylene that have been subjected to surface treatment such as corona discharge treatment.

The contents of this disclosure will be explained in more detail below using examples and comparative examples, but this disclosure is not limited to the following examples.

In the following examples and comparative examples, the following tertiary amino alcohols, tertiary amines, and organometallic compounds were used.
Tertiary amino alcohol (1): 6-(dimethylamino)-1-hexanol (product name: Kao Raiser No. 25, manufactured by Kao Corporation)
Tertiary amino alcohol (2): 1,4-diazabicyclo[2,2,2]octane-2-methanol (product name: RZETA ("RZETA" is a registered trademark), manufactured by Tosoh Corporation)
Tertiary amino alcohol (3): 2-(dimethylamino)ethanol (product name: Amino Alcohol 2MabS, manufactured by Nippon Nyukazai Co., Ltd.)
Tertiary amino alcohol (4): 2-(dibutylamino)ethanol (product name: Amino Alcohol 2MB, manufactured by Nippon Nyukazai Co., Ltd.)
Tertiary amine (1): N,N-dimethyloctylamine (Tokyo Chemical Industry Co., Ltd.)
Organometallic compound (1): dioctyltin dilaurate (DOTDL, manufactured by Kyodo Pharmaceuticals)
Quaternary ammonium salt (1): Trimethylmono-n-octylammonium monomethyl carbonate (manufactured by Tosoh Corporation)

<Synthesis Example>
(Synthesis Example 1: Synthesis of Polyisocyanate A-1)
A four-neck flask equipped with a stirrer, a thermometer, a heating device, a nitrogen seal tube, and a cooling tube was charged with 995 g of hexamethylene diisocyanate (hereinafter referred to as HDI), 5.0 g of 1,3-butanediol (manufactured by Tokyo Chemical Industry Co., Ltd.), and 0.3 g of phenol (manufactured by Tokyo Chemical Industry Co., Ltd.), and a urethane reaction was carried out for 2 hours at 80 ° C. under a nitrogen stream. Then, 0.04 g of potassium 2-ethylhexanoate (manufactured by Tokyo Chemical Industry Co., Ltd.), which is an isocyanurate catalyst, was added, and an isocyanurate reaction was carried out for 2 hours at 70 ° C. After the NCO content reached 40.0 mass%, 0.15 g of JP-508 (manufactured by Johoku Chemical Industry Co., Ltd.) was added, a termination reaction was carried out, and the reaction liquid was cooled to room temperature. The reaction liquid was subjected to thin-film distillation at a temperature of 130 ° C. and a pressure of 0.04 kPa to remove unreacted HDI, and a purified polyisocyanate A-1 was obtained. The NCO content of Polyisocyanate A-1 was 21.8% by mass, and the viscosity at 25° C. was about 2,500 mPa·s.

( ^1H -NMR: Measurement of Isocyanurate Group Content)
Polyisocyanate A-1 was subjected to ¹ H-NMR measurement to determine the isocyanurate group content (the content of isocyanurate groups relative to the total of isocyanurate groups and allophanate groups (100 mol%)). Specifically, the isocyanurate group content was calculated from the area of the signal of the hydrogen atom of the methylene group adjacent to the nitrogen atom of the isocyanurate group at around 3.7 ppm and the signal of the hydrogen atom bonded to the nitrogen atom of the allophanate group at around 8.5 ppm. The isocyanurate group content was 89 mol%. The ¹ H-NMR measurement was performed under the following measurement conditions.
[Measurement conditions]
(1) Measuring device: ECX400M (manufactured by JEOL Ltd., ^1H -NMR)
(2) Measurement temperature: 23℃
(3) Sample concentration: 0.1 g/1 ml
(4) Number of times accumulated: 16
(5) Relaxation time: 5 seconds (6) Solvent: deuterium dimethyl sulfoxide (7) Chemical shift reference: hydrogen atom signal of methyl group in deuterium dimethyl sulfoxide (2.5 ppm)

<Preparation Example: Preparation of Blocked Polyisocyanate Composition>
(Preparation Example 1)
In a four-neck flask equipped with a stirrer, a thermometer, a heating device, a nitrogen seal tube, and a cooling tube, 510 g of polyisocyanate A-1 and 27 g of tertiary amino alcohol (1) were charged, the flask was replaced with nitrogen, and the reaction temperature was heated to 80° C. while stirring, and the reaction was allowed to proceed for 2 hours at the same temperature. 250 g of butyl acetate was charged into the resulting reaction liquid and stirred for 30 minutes, and then 213 g of methyl ethyl ketoxime (manufactured by Ube Industries, Ltd., "MEKO" in the table) was charged in three separate portions so that the temperature did not exceed 80° C. Thereafter, the reaction was allowed to proceed for 2 hours at 70° C., and when the peak of the NCO group (near 2270 cm ⁻¹ ) disappeared in the infrared absorption spectrum (IR measurement), the mixture was cooled to room temperature to obtain a blocked polyisocyanate composition (1) containing a modified blocked polyisocyanate. The solid content (content of modified blocked polyisocyanate) was 75% by mass.

(Preparation Example 2)
In a four-neck flask equipped with a stirrer, a thermometer, a heating device, a nitrogen seal tube, and a cooling tube, 509 g of polyisocyanate A-1 and 27 g of tertiary amino alcohol (2) were charged, the flask was replaced with nitrogen, and the reaction temperature was heated to 80° C. while stirring, and the reaction was allowed to proceed for 2 hours at the same temperature. 250 g of butyl acetate was charged into the resulting reaction liquid and stirred for 30 minutes, after which 214 g of methyl ethyl ketoxime (manufactured by Ube Industries, Ltd., “MEKO” in the table) was charged in three separate portions so that the temperature did not exceed 80° C. Then, the reaction was allowed to proceed for 2 hours at 70° C., and when the peak of the NCO group (near 2270 cm ⁻¹ ) disappeared in the infrared absorption spectrum (IR measurement), the mixture was cooled to room temperature to obtain a blocked polyisocyanate composition (2) containing a modified blocked polyisocyanate. The solid content (content of modified blocked polyisocyanate) was 75% by mass.

(Preparation Example 3)
In a four-neck flask equipped with a stirrer, a thermometer, a heating device, a nitrogen seal tube, and a cooling tube, 516 g of polyisocyanate A-1 and 27 g of tertiary amino alcohol (3) were charged, the flask was replaced with nitrogen, and the reaction temperature was heated to 80° C. while stirring, and the reaction was allowed to proceed for 2 hours at the same temperature. 250 g of butyl acetate was charged into the resulting reaction liquid and stirred for 30 minutes, after which 207 g of methyl ethyl ketoxime (manufactured by Ube Industries, Ltd., “MEKO” in the table) was charged in three separate portions so that the temperature did not exceed 80° C. Then, the reaction was allowed to proceed for 2 hours at 70° C., and when the peak of the NCO group (near 2270 cm ⁻¹ ) disappeared in the infrared absorption spectrum (IR measurement), the mixture was cooled to room temperature to obtain a blocked polyisocyanate composition (3) containing a modified blocked polyisocyanate. The solid content (content of modified blocked polyisocyanate) was 75% by mass.

(Preparation Example 4)
In a four-neck flask equipped with a stirrer, a thermometer, a heating device, a nitrogen seal tube, and a cooling tube, 508 g of polyisocyanate A-1 and 27 g of tertiary amino alcohol (4) were charged, the flask was replaced with nitrogen, and the reaction temperature was heated to 80° C. while stirring, and the reaction was allowed to proceed for 2 hours at the same temperature. 250 g of butyl acetate was charged into the resulting reaction liquid and stirred for 30 minutes, after which 216 g of methyl ethyl ketoxime (manufactured by Ube Industries, Ltd., “MEKO” in the table) was charged in three separate portions so that the temperature did not exceed 80° C. Then, the reaction was allowed to proceed for 2 hours at 70° C., and when the peak of the NCO group (near 2270 cm ⁻¹ ) disappeared in the infrared absorption spectrum (IR measurement), the mixture was cooled to room temperature to obtain a blocked polyisocyanate composition (4) containing a modified blocked polyisocyanate. The solid content (content of modified blocked polyisocyanate) was 75% by mass.

(Preparation Example 5)
In a four-neck flask equipped with a stirrer, a thermometer, a heating device, a nitrogen seal tube, and a cooling tube, 494 g of polyisocyanate A-1 and 26 g of tertiary amino alcohol (1) were charged, the flask was replaced with nitrogen, and the reaction temperature was heated to 80° C. while stirring, and the reaction was carried out at the same temperature for 2 hours. 250 g of butyl acetate was charged into the resulting reaction liquid and stirred for 30 minutes, and then 230 g of 3,5-dimethylpyrazole (manufactured by Tokyo Chemical Industry Co., Ltd., "DMP" in the table) was charged in three separate portions so that the temperature did not exceed 80° C. Then, the reaction was carried out at 70° C. for 2 hours, and when the peak of the NCO group (near 2270 cm ⁻¹ ) disappeared in the infrared absorption spectrum (IR measurement), the mixture was cooled to room temperature to obtain a blocked polyisocyanate composition (5) containing a modified blocked polyisocyanate. The solid content (content of modified blocked polyisocyanate) was 75% by mass.

(Preparation Example 6)
In a four-neck flask equipped with a stirrer, a thermometer, a heating device, a nitrogen seal tube, and a cooling tube, 473 g of polyisocyanate A-1 and 26 g of tertiary amino alcohol (1) were charged, the flask was replaced with nitrogen, and the reaction temperature was heated to 80° C. while stirring, and the reaction was allowed to proceed for 2 hours at the same temperature. 250 g of butyl acetate was charged into the resulting reaction liquid and stirred for 30 minutes, after which 252 g of 2-ethyl 4-methylimidazole (manufactured by Tokyo Chemical Industry Co., Ltd., “2E4MZ” in the table) was charged in three separate portions so that the temperature did not exceed 80° C. Then, the reaction was allowed to proceed for 2 hours at 70° C., and when the peak of the NCO group (near 2270 cm ⁻¹ ) disappeared in the infrared absorption spectrum (IR measurement), the mixture was cooled to room temperature to obtain a blocked polyisocyanate composition (6) containing a modified blocked polyisocyanate. The solid content (content of modified blocked polyisocyanate) was 75% by mass.

(Preparation Example 7)
A blocked polyisocyanate composition (7) was obtained in the same manner as in Preparation Example 1, except that the tertiary amino alcohol (1) was not used.

(Preparation Example 8)
A blocked polyisocyanate composition (8) was obtained in the same manner as in Preparation Example 5, except that the tertiary amino alcohol (1) was not used.

(Preparation Example 9)
A blocked polyisocyanate composition (9) was obtained by adding a tertiary amino alcohol (1) as an additive (blocking agent dissociation catalyst) to the blocked polyisocyanate composition (7) obtained in Preparation Example 7. The amount of the tertiary amino alcohol (1) added was 27 g per 510 g of polyisocyanate A-1.

(Preparation Example 10)
A blocked polyisocyanate composition (10) was obtained by adding a tertiary amine (1) as an additive (blocking agent dissociation catalyst) to the blocked polyisocyanate composition (7) obtained in Preparation Example 7. The amount of the tertiary amino alcohol (1) added was 27 g per 510 g of polyisocyanate A-1.

(Preparation Example 11)
Blocked polyisocyanate composition (11) was obtained by adding organometallic compound (1) as an additive (blocking agent dissociation catalyst) to blocked polyisocyanate composition (7) obtained in Preparation Example 7. The amount of organometallic compound (1) added was 27 g per 510 g of polyisocyanate A-1.

(Preparation Example 12)
A blocked polyisocyanate composition (12) was obtained by adding a quaternary ammonium salt (1) as an additive (blocking agent dissociation catalyst) to the blocked polyisocyanate composition (7) obtained in Preparation Example 7. The amount of the quaternary ammonium salt (1) added was 27 g per 510 g of polyisocyanate A-1.

Example 1
(Preparation of Coating Composition)
56 g of ACRYDIC A-801 (trade name, manufactured by DIC Corporation, acrylic polyol, solid content concentration: 50 mass%, hydroxyl value: 50 mgKOH/g), 3 g of CYMEL 303LF (trade name, manufactured by Allnex Japan Co., Ltd., melamine resin, solid content concentration: 100 mass%), 19 g of the blocked polyisocyanate composition (1), and 21 g of butyl acetate (manufactured by Kishida Chemical Co., Ltd.) were mixed to obtain a coating composition of Example 1.

(Cureability Evaluation)
[Martens hardness measurement]
The coating composition prepared above was applied to a color steel plate (white) so that the thickness before drying was 100 μm. The obtained coating film was left at room temperature for 60 minutes, and then baked by heating for 20 minutes in a thermostatic chamber at 130° C. The indentation strength of the coating film after baking (cured coating film) was measured under the following conditions in accordance with ISO 14577. The results are shown in Table 1.
〔conditions〕
Test equipment: Fischerscope HM2000 (manufactured by Fisher Instruments)
Indenter: Vickers diamond Test load: 5 mN
Test temperature: 25°C

[Gel fraction measurement]
The coating composition prepared above was applied to a release paper so that the thickness before drying was 200 μm. The obtained coating film was left at room temperature for 60 minutes, and then baked by heating for 20 minutes in a thermostatic chamber at 130 ° C. The coating film after baking (cured coating film) was immersed in methyl ethyl ketone at room temperature for 24 hours to determine the gel fraction. The gel fraction was calculated from the following formula. The results are shown in Table 1.
Gel fraction (unit: mass %)=mass of coating film after immersion (mass of undissolved part)/mass of coating film before immersion×100

[MEK rubbing test]
The coating composition prepared above was applied to an SPCC-SB steel plate so that the thickness before drying was 100 μm. The resulting coating film was left to stand at room temperature for 60 minutes, and then baked by heating for 20 minutes in a thermostatic chamber at 130° C. The baked coating film (cured coating film) was rubbed with absorbent cotton soaked in methyl ethyl ketone under a load of 500 g, and the number of rubbings until damage was observed was measured. The results are shown in Table 1.

(Coating film appearance evaluation)
[Gloss Evaluation]
The coating composition prepared above was applied to a color steel plate (white) so that the thickness before drying was 100 μm. The obtained coating film was left at room temperature for 60 minutes, and then baked by heating for 60 minutes in a thermostatic chamber at 160 ° C. The gloss at 60 ° of the coating film (cured coating film) after baking was measured using a haze-gloss reflectometer (manufactured by BYK-Additives & Instruments) in accordance with JIS Z8741. The results are shown in Table 1.

[Coloring evaluation]
The coating composition prepared above was applied to a color steel plate (white) so that the thickness before drying was 100 μm. The resulting coating film was left at room temperature for 60 minutes, and then baked by heating for 60 minutes in a thermostatic chamber at 160° C. Using a BYK-GARDNER colorimeter (product name: SPECTRO2GUIDE), the b* value of the coating film (cured coating film) after baking was measured according to the CIE Lab standard. The results are shown in Table 1.

Example 2
(Preparation of Coating Composition)
55 g of ACRYDIC A-801, 3 g of CYMEL 303LF, 20 g of the blocked polyisocyanate composition (2), and 21 g of butyl acetate were mixed to obtain a coating composition of Example 2. Next, the curability of the obtained coating composition and the appearance of the coating film made of the coating composition were evaluated in the same manner as in Example 1. The results are shown in Table 1.

Example 3
(Preparation of Coating Composition)
55 g of ACRYDIC A-801, 3 g of Cymel 303LF, 21 g of the blocked polyisocyanate composition (3), and 21 g of butyl acetate were mixed to obtain a coating composition of Example 3. Next, the curability of the obtained coating composition and the appearance of the coating film made of the coating composition were evaluated in the same manner as in Example 1. The results are shown in Table 1.

Example 4
(Preparation of Coating Composition)
55 g of ACRYDIC A-801, 3 g of Cymel 303LF, 20 g of the blocked polyisocyanate composition (4), and 21 g of butyl acetate were mixed to obtain a coating composition of Example 4. Next, the curability of the obtained coating composition and the appearance of the coating film made of the coating composition were evaluated in the same manner as in Example 1. The results are shown in Table 1.

Example 5
(Preparation of Coating Composition)
55 g of ACRYDIC A-801, 3 g of Cymel 303LF, 20 g of the blocked polyisocyanate composition (5), and 21 g of butyl acetate were mixed to obtain a coating composition of Example 5. Next, the curability of the obtained coating composition and the appearance of the coating film made of the coating composition were evaluated in the same manner as in Example 1. The results are shown in Table 1.

Example 6
(Preparation of Coating Composition)
55 g of ACRYDIC A-801, 3 g of Cymel 303LF, 20 g of the blocked polyisocyanate composition (6), and 21 g of butyl acetate were mixed to obtain a coating composition of Example 6. Next, the curability of the obtained coating composition and the appearance of the coating film made of the coating composition were evaluated in the same manner as in Example 1. The results are shown in Table 1.

<Comparative Example 1>
(Preparation of Coating Composition)
56 g of ACRYDIC A-801, 3 g of Cymel 303LF, 19 g of the blocked polyisocyanate composition (7), and 21 g of butyl acetate were mixed to obtain a coating composition of Comparative Example 1. Next, the curability of the obtained coating composition and the appearance of the coating film made of the coating composition were evaluated in the same manner as in Example 1. The results are shown in Table 2.

<Comparative Example 2>
(Preparation of Coating Composition)
56 g of ACRYDIC A-801, 3 g of CYMEL 303LF, 19 g of the blocked polyisocyanate composition (8), and 21 g of butyl acetate were mixed to obtain a coating composition of Comparative Example 2. Next, the curability of the obtained coating composition and the appearance of the coating film made of the coating composition were evaluated in the same manner as in Example 1. The results are shown in Table 2.

<Comparative Example 3>
(Preparation of Coating Composition)
56 g of ACRYDIC A-801, 3 g of Cymel 303LF, 19 g of the blocked polyisocyanate composition (9), and 21 g of butyl acetate were mixed to obtain a coating composition of Comparative Example 3. Next, the curability of the obtained coating composition and the appearance of the coating film made of the coating composition were evaluated in the same manner as in Example 1. The results are shown in Table 2.

<Comparative Example 4>
(Preparation of Coating Composition)
56 g of ACRYDIC A-801, 3 g of Cymel 303LF, 19 g of the blocked polyisocyanate composition (10), and 21 g of butyl acetate were mixed to obtain a coating composition of Comparative Example 4. Next, the curability of the obtained coating composition and the appearance of the coating film made of the coating composition were evaluated in the same manner as in Example 1. The results are shown in Table 2.

<Comparative Example 5>
(Preparation of Coating Composition)
56 g of ACRYDIC A-801, 3 g of Cymel 303LF, 19 g of the blocked polyisocyanate composition (11), and 21 g of butyl acetate were mixed to obtain a coating composition of Comparative Example 5. Next, the curability of the obtained coating composition and the appearance of the coating film made of the coating composition were evaluated in the same manner as in Example 1. The results are shown in Table 2.

<Comparative Example 6>
(Preparation of Coating Composition)
56 g of ACRYDIC A-801, 3 g of CYMEL 303LF, 19 g of the blocked polyisocyanate composition (12), and 21 g of butyl acetate were mixed to obtain a coating composition of Comparative Example 6. Next, the curability of the obtained coating composition and the appearance of the coating film made of the coating composition were evaluated in the same manner as in Example 1. The results are shown in Table 2.

<Comparative Example 7>
A coating composition of Comparative Example 7 was obtained in the same manner as in Example 1, except that Cymel 303LF was not used. Then, the curability of the obtained coating composition and the appearance of the coating film made of the coating composition were evaluated in the same manner as in Example 1. The results are shown in Table 3.

<Comparative Example 8>
A coating composition of Comparative Example 8 was obtained in the same manner as in Example 1, except that ACRYDIC A-801 was not used. Then, the curability of the obtained coating composition and the appearance of the coating film made of the coating composition were evaluated in the same manner as in Example 1. The results are shown in Table 3.

<Comparative Example 9>
A coating composition of Comparative Example 9 was obtained in the same manner as in Example 1, except that the blocked polyisocyanate composition (1) was not used. Then, the curability of the obtained coating composition and the appearance of the coating film made of the coating composition were evaluated in the same manner as in Example 1. The results are shown in Table 3.

Claims (6)

The composition includes an acrylic polyol, a melamine resin, and a modified blocked polyisocyanate,
A coating composition, wherein the modified blocked polyisocyanate is a blocked polyisocyanate modified with a tertiary amino alcohol. The coating composition according to claim 1, wherein the tertiary amino alcohol comprises at least one selected from the group consisting of a compound represented by the following formula (I) and a compound represented by the following formula (II):

[In formula (I), R ¹ and R ² each independently represent a monovalent hydrocarbon group having 1 to 8 carbon atoms, and R ³ represents a divalent hydrocarbon group having 1 to 16 carbon atoms.]

[In formula (II), R ⁴ to R ⁸ each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms, a and b each independently represent 0 or 1, and a+b represents 1.] The coating composition according to claim 1, wherein the modified blocked polyisocyanate contains a structure derived from an aliphatic polyisocyanate having 4 to 6 carbon atoms or a derivative thereof. The coating composition according to claim 1, wherein the modified blocked polyisocyanate has at least one group selected from the group consisting of an isocyanate group blocked with an oxime-based blocking agent, an isocyanate group blocked with a pyrazole-based blocking agent, and an isocyanate group blocked with an imidazole-based blocking agent. A coating film formed from the coating composition according to any one of claims 1 to 4. A method for forming a coating film, comprising the steps of applying the coating composition according to any one of claims 1 to 4 to a substrate and heating the coating film to 120 to 140°C to cure the coating film made of the coating composition.