Coating composition and coating film

Abstract

A coating composition containing (A) a polyol, (B) a blocked polyisocyanate, and (C) a blocking agent dissociation catalyst, wherein the acid value of component (A) is 3-30 mgKOH / g, and component (C) contains a quaternary ammonium salt.

Description

Paint composition and coating film

[0001] This disclosure relates to paint compositions and coating films.

[0002] A known paint composition for use on automobile bodies and other parts is one that combines a polyol and a polyisocyanate. A method for improving the workability of paints using polyisocyanate as a curing agent is known, which involves inactivating the polyisocyanate by reacting it with a blocking agent. The blocked polyisocyanate obtained by this method does not react with the main component (polyol, etc.) at room temperature, but when heated, the blocking agent dissociates, regenerating the isocyanate group, which then reacts with the main component to form a crosslink. Therefore, with this method, the pot life is not limited, and it is possible to pre-mix the main component and curing agent to form a paint.

[0003] In paints that use blocked polyisocyanates as a curing agent, catalysts such as quaternary ammonium salts (blocking agent dissociation catalysts) are sometimes used to reduce the thermal energy required for the dissociation of the blocking agent (see, for example, Patent Document 1).

[0004] Japanese Patent Publication No. 2014-084426

[0005] Conventionally, paint curing was performed at high temperatures of 150°C or higher. However, in recent years, there has been a demand to cure paint films at lower temperatures (for example, 140°C or lower) to reduce costs, carbon dioxide emissions, and thermal degradation of the coated object during the baking process. Therefore, it is important that the paint composition has good low-temperature curing properties, that is, that even when the baking process is performed at a lower temperature than before, it can sufficiently crosslink and form a paint film with a good gel fraction. In this regard, as described in Patent Document 1 above, the low-temperature curing properties of the paint composition can be improved by using a specific quaternary ammonium salt, but there is still room for improvement in its performance. Furthermore, quaternary ammonium salts can cause discoloration (yellowing) of the paint film, impairing its appearance.

[0006] One aspect of this disclosure aims to provide a coating composition that exhibits excellent low-temperature curing properties and excellent resistance to yellowing.

[0007] This disclosure provides at least the following [1] to

[13] .

[0008] [1] A paint composition comprising (A) a polyol, (B) a blocked polyisocyanate, and (C) a blocking agent dissociation catalyst, wherein the acid value of component (A) is 3 to 30 mg KOH / g, and component (C) contains a quaternary ammonium salt.

[0009] [2] The paint composition according to [1], wherein the component (A) comprises an acrylic polyol.

[0010] [3] The paint composition according to [2], wherein the acrylic polyol comprises structural units derived from one or more (meth)acrylic acids and structural units derived from one or more (meth)acrylic acid esters.

[0011] [4] The paint composition according to [3], wherein the (meth)acrylic acid ester comprises at least one selected from the group consisting of (meth)acrylate hydroxyalkyl esters and (meth)acrylate alkyl esters.

[0012] [5] The paint composition according to any one of [1] to [4], wherein the component (B) comprises a block polyisocyanate having a structure derived from an aliphatic polyisocyanate or a derivative thereof having an aliphatic hydrocarbon group having 4 to 6 carbon atoms.

[0013] [6] The paint composition according to any one of [1] to [5], wherein the component (C) comprises a quaternary ammonium salt having a cationic group represented by the following formula (1). [In formula (1), R １ R represents an alkyl group having 1 to 16 carbon atoms, which may have a hydroxyl group, an amino group, or an alkoxy group as a substituent. ２ ~R ４ Each of these independently represents an alkyl group having 1 to 8 carbon atoms.

[0014] [7] The paint composition according to any one of [1] to [6], wherein the component (C) has at least one cationic group selected from the group consisting of a group represented by the following formula (2) and a group represented by the following formula (3).

[0015] [8] The paint composition according to any one of [1] to [7], wherein the component (C) is a monoalkyl carbonate group or a hydroxyl group having an alkyl group having 1 to 8 carbon atoms.

[0016] [9] The paint composition according to any one of [1] to [8], wherein the content of component (C) is 1.1 to 25 moles per mole of acidic group contained in component (A).

[0017]

[10] The paint composition according to any one of [1] to [9], wherein the component (B) comprises a blocked polyisocyanate having isocyanate groups sequestered with an oxime-based blocking agent.

[0018]

[11] The paint composition according to any one of [1] to

[10] , wherein the component (B) comprises a blocked polyisocyanate having an isocyanate group encapsulated with methyl ethyl ketoxime.

[0019]

[12] The paint composition according to any one of [1] to

[11] , wherein the ratio of the total number of active isocyanate groups contained in component (B) to the total number of hydroxyl groups contained in component (A) is 0.7 to 1.5 in terms of equivalent weight.

[0020]

[13] A coating film formed from any of the coating compositions described in [1] to

[12] .

[0021] According to one aspect of this disclosure, it is possible to provide a coating composition that exhibits excellent low-temperature curing properties and excellent resistance to yellowing.

[0022] The following describes exemplary embodiments of this disclosure. However, this disclosure is not limited in any way to the embodiments described below. In this specification, numerical ranges indicated using "~" indicate a range that includes the numerical values ​​before and after "~" as the minimum and maximum values, respectively. Also, unless otherwise explicitly stated, the units of the numerical values ​​before and after "~" are the same. Furthermore, the upper and lower limits described individually can be combined in any way. Also, in this specification, room temperature means 5 to 35°C. In this specification, "(meth)acrylic acid" includes acrylic acid and / or methacrylic acid. The same applies to similar expressions such as "(meth)acrylate alkyl ester".

[0023] <Paint Composition> One embodiment of the present disclosure is a paint composition containing (A) a polyol (hereinafter also referred to as "component (A)"), (B) a blocked polyisocyanate (hereinafter also referred to as "component (B)"), and (C) a blocking agent dissociation catalyst (hereinafter also referred to as "component (C)"), wherein the acid value of component (A) is 3 to 30 mg KOH / g, and component (C) contains a quaternary ammonium salt.

[0024] The above paint composition contains components (A) to (C), and therefore has excellent low-temperature curing properties. Accordingly, with the above paint composition, a coating film with a good gel fraction can be formed when baking is performed at a lower temperature than conventional methods (for example, at a temperature of 140°C or lower). The above paint composition contains components (A) to (C), and therefore has excellent resistance to yellowing. Accordingly, with the above paint composition, yellowing of the coating film can be suppressed more effectively than conventional methods, and a coating film with excellent appearance can be formed.

[0025] (Component (A): Polyol) Examples of polyols include acrylic polyols, polyester polyols, polyether polyols, epoxy polyols, polycarbonate polyols, and polylactone polyols. One of these polyols may be used alone, or two or more may be used in combination.

[0026] (A) Component may contain an acrylic polyol, from the viewpoint of easily obtaining a paint composition with superior low-temperature curing properties. An acrylic polyol is a polymer sometimes called a hydroxyl group-containing acrylic resin, and is a polyol containing at least one structural unit selected from the group consisting of structural units derived from (meth)acrylic acid and structural units derived from (meth)acrylic acid esters.

[0027] (Meth)acrylic acid esters may be (meth)acrylic acid esters having hydroxyl groups (hereinafter referred to as "hydroxyl group-containing (meth)acrylic acid esters") or (meth)acrylic acid esters not having hydroxyl groups (hereinafter referred to as "hydroxyl group-free (meth)acrylic acid esters").

[0028] Examples of hydroxyl group-containing (meth)acrylic acid esters include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 3-hydroxy-2,2-dimethylpropyl (meth)acrylate, and pentaerythritol tri(meth)acrylate.

[0029] Examples of hydroxyl group-free (meth)acrylic acid esters include alkyl (meth)acrylic acid 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, dodecyl (meth)acrylate, and cyclohexyl (meth)acrylate, as well as aryl (meth)acrylic acid esters such as phenyl (meth)acrylate and benzyl (meth)acrylate.

[0030] As the (meth)acrylic acid ester, at least one selected from the group consisting of (meth)acrylate hydroxyalkyl esters and (meth)acrylate alkyl esters may be used, from the viewpoint of easily obtaining a paint composition with superior low-temperature curing properties and easily improving the yellowing resistance of the acrylic polyol. The (meth)acrylate hydroxyalkyl ester is the hydroxyl group-containing (meth)acrylic acid ester described above, and the (meth)acrylate alkyl ester is the hydroxyl group-free (meth)acrylic acid ester described above.

[0031] From the viewpoint of easily obtaining a paint composition with superior low-temperature curing properties, the acrylic polyol may be a polyol containing structural units derived from one or more types of (meth)acrylic acid and structural units derived from one or more types of (meth)acrylic acid esters. From the viewpoint of easily obtaining a paint composition with even superior low-temperature curing properties, the polyol may be a polyol containing structural units derived from one or more types of (meth)acrylic acid, structural units derived from one or more types of hydroxyl group-containing (meth)acrylic acid esters and structural units derived from one or more types of hydroxyl group-free (meth)acrylic acid esters. In particular, when the acrylic polyol contains structural units derived from one or more types of (meth)acrylic acid, structural units derived from one or more types of hydroxyalkyl (meth)acrylic acid esters and structural units derived from one or more types of alkyl (meth)acrylic acid esters, a paint composition with particularly superior low-temperature curing properties is easily obtained.

[0032] The content of the structural unit derived from (meth)acrylic acid may be 0.3% by mass or more, 0.5% by mass or more, 0.6% by mass or more, 1% by mass or more, 1.7% by mass or more, 2.4% by mass or more, 3% by mass or more, or 3.6% by mass or more, based on the total mass of the acrylic polyol, and may be 4.5% by mass or less, 4.2% by mass or less, 3.5% by mass or less, 2.9% by mass or less, 2.2% by mass or less, 1.5% by mass or less, or 0.9% by mass or less, and may be 0.3 to 4.5% by mass, 0.5 to 4.2% by mass, 0.6 to 3.5% by mass, 1 to 2.9% by mass, 1.7 to 4.5% by mass, 2.4 to 4.5% by mass, 3 to 4.5% by mass, 3.6 to 4.5% by mass, 0.3 to 2.2% by mass, 0.3 to 1.5% by mass, or 0.3 to 0.9% by mass. When the above content is not less than the above lower limit value, it is easy to improve the yellowing resistance of the acrylic polyol, and when the above content is not more than the above upper limit value, it is easy to obtain a paint composition excellent in low-temperature curability.

[0033] The content of the structural unit derived from (meth)acrylate may be 90% by mass or more, 95% by mass or more, 95.8% by mass or more, 96% by mass or more, or 97% by mass or more, based on the total mass of the acrylic polyol, and may be 99.9% by mass or less, 99% by mass or less, or 98% by mass or less, and may be 90 to 99.9% by mass, 95 to 99% by mass, or 95.8 to 98% by mass. When the above content is not less than the above lower limit value, it is easy to improve the yellowing resistance of the acrylic polyol, and when the above content is not more than the above upper limit value, it is easy to obtain a paint composition excellent in low-temperature curability.

[0034] The content of structural units derived from hydroxyl group-containing (meth)acrylic acid ester may be 10% by mass or more, 15% by mass or more, or 20% by mass or more, 50% by mass or less, 40% by mass or less, or 30% by mass or less, or 10 to 50% by mass, 15 to 40% by mass, or 20 to 30% by mass, based on the total mass of the acrylic polyol. In one embodiment, the content of structural units derived from (meth)acrylate hydroxyalkyl ester may be within the above range. If the above content is above the lower limit, a coating composition with superior low-temperature curability is more likely to be obtained, and if the above content is below the upper limit, the dispersibility of the acrylic polyol is more likely to be improved.

[0035] The content of structural units derived from hydroxyl group-free (meth)acrylic acid esters may be 60% by mass or more, 72% by mass or more, 72.2% by mass or more, 73% by mass or more, 73.5% by mass or more, 74.2% by mass or more, 74.8% by mass or more, or 75.5% by mass or more, based on the total mass of the acrylic polyol, and may not be 80% by mass or less, 76% by mass or less, 75.4% by mass or less, or 74.7% by mass or less. The content may be 74% by mass or less, 73.4% by mass or less, or 72.7% by mass or less, and may be 60-80% by mass, 72-76% by mass, 72.2-75.4% by mass, 73-80% by mass, 73.5-80% by mass, 74.2-80% by mass, 74.8-80% by mass, 75.5-80% by mass, 60-74.7% by mass, 60-74% by mass, 60-73.4% by mass, or 60-72.7% by mass. In one embodiment, the content of structural units derived from alkyl (meth)acrylate may be within the above range. If the above content is above the lower limit, it is easier to improve the yellowing resistance of the acrylic polyol, and if the above content is below the upper limit, it is easier to obtain a coating composition with superior low-temperature curability.

[0036] The structural units constituting the acrylic polyol may include structural units derived from monomers other than (meth)acrylic acid and (meth)acrylic acid esters. Examples of other monomers include maleic acid, itaconic acid, acrylamide, N-methylolacrylamide, diacetoneacrylamide, styrene, vinyltoluene, vinyl acetate, and acrylonitrile.

[0037] The method for obtaining the acrylic polyol is not particularly limited. For example, it may be a method of mixing at least one selected from the group consisting of (meth)acrylic acid and (meth)acrylic acid esters with a polymerization initiator and subjecting them to a polymerization reaction.

[0038] There is no particular limitation on the polymerization initiator, and generally used ones can be used. Examples of the polymerization initiator include azobisisobutyronitrile, 1,1'-azobis(cyclohexanecarbonitrile), di-tert-butyl peroxide, tert-butyl hydroperoxide, hydrogen peroxide, potassium peroxodisulfate, benzoyl peroxide, triethylborane, diethylzinc, tert-butyl 2-ethylperoxyhexanoate, and the like. The content of the polymerization initiator may be 1 to 5 parts by mass with respect to 100 parts by mass of the polymerizable monomer.

[0039] The polymerization reaction for obtaining the acrylic polyol may be carried out, for example, in the presence of a solvent. Examples of the solvent 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, for example, 20 to 200°C. The reaction time may be, for example, 1 to 10 hours.

[0040] From the viewpoint of obtaining a paint composition with superior low-temperature curability, the acrylic polyol content may be 30% by mass or more, 40% by mass or more, 50% by mass or more, or 58% by mass or more, based on the total solid content of the paint composition. From the viewpoint of easily improving the dispersibility of the acrylic polyol, the acrylic polyol content may be 80% by mass or less, 75% by mass or less, 70% by mass or less, or 65% by mass or less, based on the total solid content of the paint composition. From these viewpoints, the acrylic polyol content may be 30 to 80% by mass, 40 to 75% by mass, 50 to 70% by mass, or 58 to 65% by mass, based on the total solid content of the paint composition. In this specification, "total solid content of the paint composition" means the amount obtained by subtracting the amount of solvent from the total amount of the paint composition if the paint composition contains a solvent, and the total amount of the paint composition if the paint composition does not contain a solvent.

[0041] From the viewpoint of obtaining a paint composition with superior low-temperature curing properties, the content of component (A) may be 30% by mass or more, 40% by mass or more, 50% by mass or more, or 58% by mass or more, based on the total solid content of the paint composition. From the viewpoint of easily improving the dispersibility of the polyol, the content of component (A) may be 80% by mass or less, 75% by mass or less, 70% by mass or less, or 65% by mass or less, based on the total solid content of the paint composition. From these viewpoints, the content of component (A) may be 30 to 80% by mass, 40 to 75% by mass, 50 to 70% by mass, or 58 to 65% by mass, based on the total solid content of the paint composition.

[0042] The hydroxyl value of component (A) may be 50 mg KOH / g or more, 60 mg KOH / g or more, 70 mg KOH / g or more, 80 mg KOH / g or more, or 90 mg KOH / g or more, from the viewpoint of easily obtaining a paint composition with superior low-temperature curing properties. The hydroxyl value of component (A) may be 150 mg KOH / g or less, 140 mg KOH / g or less, 130 mg KOH / g or less, 120 mg KOH / g or less, or 110 mg KOH / g or less, from the viewpoint of easily improving the dispersibility of the polyol. From these viewpoints, component (A) may be 50 to 150 mg KOH / g, 60 to 140 mg KOH / g, 70 to 130 mg KOH / g, 80 to 120 mg KOH / g, or 90 to 110 mg KOH / g. The hydroxyl value is measured in accordance with JIS K1557-1. If component (A) contains multiple types of polyols, "hydroxyl value of component (A)" means the hydroxyl value of all polyols contained in component (A) (a mixture of all polyols). From the viewpoint of obtaining the above-mentioned effects more significantly, component (A) may contain an acrylic polyol having a hydroxyl value within the above range.

[0043] Component (A) has an acidic group. The acidic group of component (A) can deactivate quaternary ammonium salts remaining in the paint composition, thereby suppressing yellowing of the cured coating film caused by the quaternary ammonium salts. The acid value of component (A) is 3 to 30 mg KOH / g, and from the viewpoint of easily improving the yellowing resistance of the cured coating film, it may be 4 mg KOH / g or more, 5 mg KOH / g or more, 8 mg KOH / g or more, 13 mg KOH / g or more, 18 mg KOH / g or more, 23 mg KOH / g or more, or 28 mg KOH / g or more. From the viewpoint of easily obtaining a paint composition with superior low-temperature curability, it may be less than 30 mg KOH / g, 29 mg KOH / g or less, 28 mg KOH / g or less, 27 mg KOH / g or less, 22 mg KOH / g or less, 17 mg KOH / g or less, 12 mg KOH / g or less, or 7 mg KOH / g or less. In particular, when the acid value of component (A) is 22 mg KOH / g or less, the low-temperature curing properties of the paint composition tend to improve significantly. From these viewpoints, the acid value of component (A) may be 3 mg KOH / g or more and less than 30 mg KOH / g, 3 to 29 mg KOH / g, 3 to 28 mg KOH / g, 4 to 27 mg KOH / g, 5 to 22 mg KOH / g, 8 to 17 mg KOH / g, 13 to 30 mg KOH / g, 18 to 30 mg KOH / g, 23 to 30 mg KOH / g, 28 to 30 mg KOH / g, 3 to 12 mg KOH / g, or 3 to 7 mg KOH / g. The acid value is measured in accordance with JIS K1557-5. When component (A) contains multiple types of polyols, "the acid value of component (A)" means the acid value of all polyols contained in component (a mixture of all polyols). From the viewpoint of obtaining the above-mentioned effects more significantly, component (A) may contain an acrylic polyol having an acid value within the above range.

[0044] The glass transition temperature (Tg) of component (A) may be 35°C or higher, 40°C or higher, or 42°C or higher from the viewpoint of obtaining a paint composition with superior low-temperature curability, and may be 55°C or lower, 50°C or lower, or 47°C or lower from the viewpoint of improving the flexibility of the cured coating film. From these viewpoints, the glass transition temperature (Tg) of component (A) may be 35-55°C, 40-50°C, or 42-47°C. The glass transition temperature is determined by measuring the inflection point of the DSC in accordance with JIS K7121. When component (A) contains multiple types of polyols, "the glass transition temperature (Tg) of component (A)" means the glass transition temperature (Tg) of the entire polyol mixture (all polyols) contained in component (A). From the viewpoint of obtaining the above-mentioned effects more significantly, component (A) may contain an acrylic polyol having a glass transition temperature (Tg) within the above range.

[0045] The number-average molecular weight (Mn) of component (A) may be 10,000 or more, 12,000 or more, or 14,000 or more from the viewpoint of obtaining a paint composition with superior low-temperature curability, and may be 20,000 or less, 18,000 or less, or 16,000 or less from the viewpoint of improving paint stability. From these viewpoints, the number-average molecular weight (Mn) of component (A) may be 10,000 to 20,000, 12,000 to 18,000, or 14,000 to 16,000. The number-average molecular weight is measured using gel permeation chromatography (GPC) and refers to the value determined using polystyrene as a standard substance. If component (A) contains multiple types of polyols, "the number-average molecular weight (Mn) of component (A)" means the number-average molecular weight (Mn) of all polyols contained in component (A) (a mixture of all polyols). From the viewpoint of obtaining the above-mentioned effects more significantly, component (A) may contain an acrylic polyol having a number-average molecular weight (Mn) within the above range.

[0046] (Component (B): Blocked Polyisocyanate) Blocked polyisocyanate is a compound that can be derived from polyisocyanate that does not have isocyanate groups blocked by a blocking agent (hereinafter also referred to as "unblocked polyisocyanate"). Blocked polyisocyanate has, for example, a structure derived from unblocked polyisocyanate and isocyanate groups blocked by a blocking agent (hereinafter also referred to as "blocked isocyanate groups").

[0047] [Unblocked Polyisocyanates] Unblocked polyisocyanates are compounds that have multiple isocyanate groups (free isocyanate groups) and do not have isocyanate groups blocked by a blocking agent. Examples of unblocked polyisocyanates include aromatic polyisocyanates, aliphatic polyisocyanates, alicyclic polyisocyanates, and their polyisocyanate derivatives. Examples of polyisocyanate derivatives include isocyanurates, allophanates, and biuretes.

[0048] The polyisocyanate derivative may be an isocyanate group-containing prepolymer obtained by the reaction of the above-mentioned polyisocyanate with a polyol, or a derivative of the prepolymer (e.g., isocyanurate, allophanate, biuret, etc.). As the polyol, for example, a diol having 2 to 9 carbon atoms can be used. Examples of such diols include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, 3-methyl-1,5-pentanediol, and 2-ethyl-1,3-hexanediol.

[0049] Unblocked polyisocyanates do not need to have aromatic rings, from the viewpoint of improving the yellowing resistance of the cured coating film. In other words, unblocked polyisocyanates may be non-aromatic polyisocyanates. Examples of non-aromatic polyisocyanates include aliphatic polyisocyanates such as hexamethylene diisocyanate, tetramethylene diisocyanate, 2-methylpentane-1,5-diisocyanate, 3-methylpentane-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.

[0050] The unblocked polyisocyanate may contain an aliphatic polyisocyanate or derivative thereof having an aliphatic hydrocarbon group having 4 to 6 carbon atoms, from the viewpoint of further improving curability, and may also contain a hexamethylene diisocyanate or derivative thereof, from the viewpoint of further improving curability. In other words, component (B) may contain a blocked polyisocyanate having a structure derived from an aliphatic polyisocyanate or derivative thereof having an aliphatic hydrocarbon group having 4 to 6 carbon atoms, and may also contain a blocked polyisocyanate having a structure derived from a hexamethylene diisocyanate or derivative thereof. As a derivative of hexamethylene diisocyanate, at least one selected from the group consisting of isocyanurate, allophanate, and biuret may be used. In particular, when an isocyanurate is used, the gel fraction of the coating film can be further improved. The isocyanurate may be an isocyanurate of hexamethylene diisocyanate, or an isocyanurate of an isocyanate group-containing prepolymer obtained by the reaction of hexamethylene diisocyanate with a polyol (for example, the diol mentioned above).

[0051] When using unblocked polyisocyanate containing isocyanurate compounds, from the viewpoint of further improving the gel fraction of the coating film, the isocyanurate trimer content (isocyanurate trimer content) based on the total mass of the unblocked polyisocyanate may be 50% by mass or more, and the isocyanurate group content (isocyanurate group content) relative to the total of isocyanurate groups and allophanate groups in the unblocked polyisocyanate (100 mol%) may be greater than 80 mol%. The upper limit of the above isocyanurate trimer content may be 80% by mass, and the upper limit of the above isocyanurate group content may be 99 mol%.

[0052] [Blocked Isocyanate Group] A blocked isocyanate group is an isocyanate group that has been sealed with a blocking agent and has a structure derived from the blocking agent.

[0053] 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; formaldehyde oxime, acetaldehyde oxime, acetone oxime, and Oxime-based blocking agents such as ethyl ketoxime, methyl isobutyl ketoxime, and cyclohexanone oxime; imidazole, 2-methylimidazole, 4-methylimidazole, 2,4-dimethylimidazole, 2-ethylimidazole, 2-propylimidazole, 2-isopropylimidazole, 4-methyl-2-propylimidazole, 2-phenylimidazole, 4-phenylimidazole, 5-phenylimidazole, 2-methyl-4-phenylimidazole, 2-ethyl-4-methylimidazole, and 2-undecylimidazole Imidazole-based blocking agents such as 2-heptadecylimidazole, amine-based blocking agents such as diphenylamine, diisopropylamine, isopropylethylamine, meldramic acid, dimethyl malonate, diethyl malonate, di-n-butyl malonate, di-t-butyl malonate, di-2-ethylhexyl malonate, methyl n-butyl malonate, ethyl n-butyl malonate, methyl s-butyl malonate, ethyl s-butyl malonate, methyl t-butyl malonate, ethyl t-butyl malonate, dibenzyl malonate, diphenyl malonate, benzyl malonate Active methylene-based blocking agents such as ethylphenyl malonate, t-butylphenyl malonate, isopropylidene malonate, alkyl acetoacetate (methyl acetoacetate, ethyl acetoacetate, n-propyl acetoacetate, isopropyl acetoacetate, n-butyl acetoacetate, t-butyl acetoacetate), benzyl acetoacetate, phenyl acetoacetate, 2-acetoacetoxyethyl methacrylate, acetylacetone, ethyl cyanoacetate, pyrazole, 3,5-dimethylpyrazole, 3,5-diisopropylpyrazole, 3,5-diphenylpyrazole, 3,Examples of pyrazole-based blocking agents include 5-di-t-butylpyrazole, 3-methylpyrazole, 4-benzyl-3,5-dimethylpyrazole, 4-nitro-3,5-dimethylpyrazole, 4-bromo-3,5-dimethylpyrazole, and 3-methyl-5-phenylpyrazole. The blocking agent may be an oxime-based blocking agent from the viewpoint of improving storage stability, and may be a methyl ethyl ketoxime from the viewpoint of further improving storage stability.

[0054] Blocked polyisocyanates may have free isocyanate groups, and may not have free isocyanate groups from the viewpoint of improving storage stability. For example, all of the active isocyanate groups in a blocked polyisocyanate may be blocked isocyanate groups. Here, active isocyanate groups mean both free isocyanate groups and blocked isocyanate groups.

[0055] Blocked polyisocyanates can be obtained, for example, by reacting the above-mentioned unblocked polyisocyanate with the above-mentioned blocking agent. That is, blocked polyisocyanates can be reaction products of unblocked polyisocyanate and a blocking agent. Unblocked polyisocyanates and blocking agents may be used individually or in combination of two or more. When aromatic polyisocyanates are not used as unblocked polyisocyanates, the yellowing resistance of the cured coating can be improved.

[0056] The reaction between the unblocked polyisocyanate and the blocking agent can be carried out according to the reaction conditions of a normal blocking reaction. The reaction between the unblocked polyisocyanate and the blocking agent may be carried out at room temperature or with heating. Regardless of whether heating is used, the temperature of the reaction solution may be, for example, 20 to 200°C.

[0057] The method for producing blocked polyisocyanates is not limited to the above. For example, if the reaction product obtained after reacting an unblocked polyisocyanate with a blocking agent has free isocyanate groups, blocked polyisocyanates can also be obtained by reacting the free isocyanate groups of the reaction product with a modifying agent such as an active hydrogen group-containing compound.

[0058] Blocked polyisocyanates may be used individually or in combination of two or more types. For example, two or more blocked polyisocyanates derived from different types of unblocked polyisocyanates may be used in combination.

[0059] From the viewpoint of obtaining a paint composition with superior low-temperature curing properties, the content of component (B) may be 10% by mass or more, 15% by mass or more, 20% by mass or more, or 25% by mass or more, based on the total solid content of the paint composition. From the viewpoint of improving the storage stability of the paint, the content of component (B) may be 60% by mass or less, 50% by mass or less, 40% by mass or less, or 35% by mass or less, based on the total solid content of the paint composition. From these viewpoints, the content of component (B) may be 10 to 60% by mass, 15 to 50% by mass, 20 to 40% by mass, or 25 to 35% by mass, based on the total solid content of the paint composition.

[0060] (B) The effective isocyanate group content of component (hereinafter referred to as "effective NCO content") may be 4 to 28% by mass, 5 to 22% by mass, or 6 to 16% by mass, from the viewpoint of further improving the curability of the paint. Here, the effective NCO content is expressed in mass percent as the isocyanate groups present in the blocked polyisocyanate that can participate in the crosslinking reaction. The effective NCO content can be rephrased as the content of free isocyanate groups in the polyisocyanate obtained by dissociating the blocking agent from the blocked isocyanate, relative to the total mass of the blocked polyisocyanate (free NCO content). The free NCO content can be determined by reacting the isocyanate groups in the measurement sample (polyisocyanate obtained by dissociating the blocking agent from the blocked isocyanate) with an excess of secondary amine, and then back titrating the unreacted secondary amine with hydrochloric acid.

[0061] The ratio of the total number of active isocyanate groups in component (B) to the total number of hydroxyl groups in component (A) ([NCO / OH]) may be 0.7 or more, 0.8 or more, or 0.9 or more in terms of equivalent weight, from the viewpoint of obtaining a paint composition with superior low-temperature curability. The ratio of the total number of active isocyanate groups in component (B) to the total number of hydroxyl groups in component (A) may be 1.5 or less, 1.4 or less, or 1.3 or less in terms of equivalent weight, from the viewpoint of improving the storage stability of the paint. From these viewpoints, the ratio of the total number of active isocyanate groups in component (B) to the total number of hydroxyl groups in component (A) may be 0.7 to 1.5, 0.8 to 1.4, or 0.9 to 1.3 in terms of equivalent weight.

[0062] (Component (C): Blocking agent dissociation catalyst) Component (C) contains a quaternary ammonium salt. Any quaternary ammonium salt known as a blocking agent dissociation catalyst can be used without particular restriction. In particular, when using a quaternary ammonium salt having a cationic group represented by the following formula (1), a paint composition with superior low-temperature curability is more likely to be obtained.

[0063] In formula (1), R １represents an alkyl group having 1 to 16 carbon atoms, which may have a hydroxy group, an amino group or an alkoxy group as a substituent, and R ２ to R ４ each independently represents an alkyl group having 1 to 8 carbon atoms.

[0064] The alkyl group represented by R １ may have 1 to 10 carbon atoms, may have 1 to 8 carbon atoms, or may have 6 to 8 carbon atoms. The specific examples of the alkyl group represented by R １ include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, 2-ethylhexyl group, 2-propylheptyl group, nonyl group, decyl group, isodecyl group, dodecyl group, hexadecyl group, etc. These groups may be substituted with one or more hydroxy groups, may be substituted with one or more amino groups, or may be substituted with one or more alkoxy groups. The carbon number of the alkoxy group may be, for example, 1 to 8, 1 to 6, 1 to 4 or 1 to 2. Examples of the alkoxy group include methoxy group, ethoxy group, butoxy group, propyloxy group, pentyloxy group, hexyloxy group, etc.

[0065] R １ may be an alkyl group having no substituent from the viewpoint that a coating composition excellent in low-temperature curability can be easily obtained. The alkyl group having no substituent may have 1 to 10 carbon atoms, may have 1 to 8 carbon atoms, or may have 6 to 8 carbon atoms. Among them, when the carbon number of the alkyl group is 8, the low-temperature curability of the coating composition is more likely to be improved. When R １ is an n-octyl group, the low-temperature curability of the coating composition is more likely to be further improved.

[0066] R ２ to R ４ represented by may have 1 to 4 carbon atoms, or may have 1 to 2 carbon atoms. R ２ to R ４Specific examples of alkyl groups represented include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, 2-ethylhexyl group, etc. From the viewpoint of obtaining a paint composition with superior low-temperature curability, R ２ ~R ４ All of them may be methyl groups. From the viewpoint of obtaining a paint composition with superior yellowing resistance, R １ ~R ４ All of them may be methyl groups.

[0067] The quaternary ammonium salt may have at least one cationic group selected from the group consisting of the group represented by the following formula (2) and the group represented by the following formula (3). That is, component (C) may contain at least one quaternary ammonium salt selected from the group consisting of the quaternary ammonium salt having the cationic group represented by the following formula (2) and the quaternary ammonium salt having the cationic group represented by the following formula (3). In particular, when the quaternary ammonium salt has the cationic group represented by the following formula (2), a paint composition with even better low-temperature curability is more likely to be obtained, and when the quaternary ammonium salt has the cationic group represented by the following formula (3), a paint composition with even better yellowing resistance is more likely to be obtained.

[0068]

[0069]

[0070] The anionic group of a quaternary ammonium salt may be a group consisting of an anion derived from an acid such as an organic acid or an inorganic acid, or a group consisting of an anion derived from an ester such as a carbonate ester. The anionic group of a quaternary ammonium salt may be a group that does not fall into any of these categories (for example, a hydroxyl group (a group consisting of a hydroxide ion)).

[0071] Examples of groups consisting of anions derived from organic acids (organic acid groups) include fatty acid groups. The number of carbon atoms in a fatty acid group (aliphatic monocarboxylic acid group) may be, for example, 1 to 12, 1 to 7, or 1 to 3. Specific examples of fatty acid groups include formic acid, acetate, octic acid, lauric acid, cyclohexanecarboxylic acid, and pivalic acid.

[0072] Examples of groups consisting of anions derived from inorganic acids (inorganic acid groups) include halogen groups (fluoro groups, chloro groups, bromo groups, etc.), bicarbonate groups, and carbonate groups.

[0073] Examples of groups consisting of anions derived from esters (ester groups) include monoalkyl carbonate groups. The number of carbon atoms in the alkyl group in the monoalkyl carbonate group may be, for example, 1 to 8, 1 to 4, or 1 to 2. Specific examples of monoalkyl carbonate groups include methyl carbonate groups, ethyl carbonate groups, propyl carbonate groups, and butyl carbonate groups.

[0074] The anionic group of the quaternary ammonium salt may be a monoalkyl carbonate group having an alkyl group with 1 to 8 carbon atoms, from the viewpoint of easily obtaining a paint composition with superior low-temperature curability. The anionic group of the quaternary ammonium salt may also be a hydroxyl group, from the viewpoint of easily obtaining a paint composition with superior yellowing resistance.

[0075] From the above-mentioned viewpoint, the quaternary ammonium salt may be composed of a combination of a cationic group represented by formula (1) and a monoalkyl carbonate group or hydroxyl group having an alkyl group having 1 to 8 carbon atoms. In particular, when a quaternary ammonium salt having a cationic group represented by formula (2) and a monoalkyl carbonate group having an alkyl group having 1 to 8 carbon atoms is used, a paint composition with even better low-temperature curability is more likely to be obtained, and when a quaternary ammonium salt having a cationic group represented by formula (3) and a hydroxyl group is used, a paint composition with even better yellowing resistance is more likely to be obtained.

[0076] Specific examples of quaternary ammonium salts include trimethyl n-octylammonium bicarbonate, tetramethylammonium hydroxide, trimethyl n-octylammonium monomethyl carbonate, trimethyl n-octylammonium carbonate, tetramethylammonium acetate, hexadecyltrimethylammonium hydroxide, trimethyl(2-hydroxypropyl)ammonium 2-ethylhexanoic acid, tetramethylammonium bicarbonate, tetraethylammonium bicarbonate, tetran-propylammonium bicarbonate, tetran-butylammonium bicarbonate, triethylmonomethylammonium bicarbonate, trin-propylmonomethylammonium bicarbonate, trin-butylmonomethylammonium bicarbonate, trin-butylmonoethylammonium bicarbonate, tetramethylammonium monomethyl carbonate, tetraethylammonium monoethyl carbonate, tetran-butylammonium monobutyl carbonate, triethylmonomethylammonium monomethyl carbonate, trin-propylmonomethylammonium monomethyl carbonate, trin-butylmonomethylammonium monomethyl carbonate, trin-butylmonoethylammonium monoethyl carbonate, tetramethylammonium carbonate, tetran-butylammonium carbonate, and tetran-butylammonium carbonate. Among these, when at least one selected from the group consisting of trimethyl n-octylammonium monomethyl carbonate and tetramethylammonium hydroxide is used, a paint composition with superior low-temperature curability and yellowing resistance is easily obtained. When trimethyl n-octylammonium monomethyl carbonate is used, a paint composition with particularly excellent low-temperature curability is easily obtained. When tetramethylammonium hydroxide is used, a paint composition with particularly excellent yellowing resistance is easily obtained. A quaternary ammonium salt may be used alone, or two or more may be used in combination.

[0077] The blocking agent dissociation catalyst may contain blocking agent dissociation catalysts other than quaternary ammonium salts. The proportion of quaternary ammonium salts in the total blocking agent dissociation catalyst may be 0.0001 to 100% by mass, 0.001 to 100% by mass, or 0.01 to 100% by mass.

[0078] From the viewpoint of easily improving low-temperature curability, the content of the quaternary ammonium salt may be 1 part by mass or more, 3 parts by mass or more, 5 parts by mass or more, 10 parts by mass or more, 20 parts by mass or more, 25 parts by mass or more, or 30 parts by mass or more per 100 parts by mass of block polyisocyanate. From the viewpoint of improving the storage stability of the paint, the content of the quaternary ammonium salt may be 60 parts by mass or less, 50 parts by mass or less, 40 parts by mass or less, or 35 parts by mass or less per 100 parts by mass of block polyisocyanate. From these viewpoints, the content of the quaternary ammonium salt may be, for example, 1 to 60 parts by mass, 3 to 60 parts by mass, 5 to 60 parts by mass, 10 to 60 parts by mass, 20 to 50 parts by mass, 25 to 40 parts by mass, or 30 to 35 parts by mass per 100 parts by mass of block polyisocyanate.

[0079] From the viewpoint of easily improving low-temperature curing properties, the content of quaternary ammonium salt may be 1.1 moles or more, 1.15 moles or more, 1.3 moles or more, 1.6 moles or more, 2.1 moles or more, 3 moles or more, or 6 moles or more per mole of acidic groups contained in component (A). That is, the molar ratio (mc / ma) of the content of quaternary ammonium salt mc to the amount ma of acidic groups contained in component (A) may be 1.1 or more, 1.15 or more, 1.3 or more, 1.6 or more, 2.1 or more, 3 or more, or 6 or more. From the viewpoint of easily improving the yellowing resistance of the cured coating film, the content of quaternary ammonium salt may be 25 moles or less, 20 moles or less, 15 moles or less, 10 moles or less, 5 moles or less, 3 moles or less, 2.1 moles or less, 1.6 moles or less, or 1.3 moles or less per mole of acidic groups contained in component (A). From these perspectives, the content of the quaternary ammonium salt may be 1.1 to 25 moles, 1.15 to 20 moles, 1.3 to 15 moles, 1.6 to 10 moles, 2.1 to 25 moles, 3 to 25 moles, 6 to 25 moles, 1.1 to 5 moles, 1.1 to 3 moles, 1.1 to 2.1 moles, 1.1 to 1.6 moles, or 1.1 to 1.3 moles per mole of acidic groups contained in component (A). The number of moles of acidic groups contained in component (A) is calculated from the content of component (A) and the acid value of component (A).

[0080] From the viewpoint of easily improving low-temperature curability, the content of the blocking agent dissociation catalyst may be 1 part by mass or more, 3 parts by mass or more, 5 parts by mass or more, 10 parts by mass or more, 20 parts by mass or more, 25 parts by mass or more, or 30 parts by mass or more per 100 parts by mass of blocked polyisocyanate. From the viewpoint of improving the storage stability of the paint, the content of the blocking agent dissociation catalyst may be 60 parts by mass or less, 50 parts by mass or less, 40 parts by mass or less, or 35 parts by mass or less per 100 parts by mass of blocked polyisocyanate. From these viewpoints, the content of the blocking agent dissociation catalyst may be, for example, 1 to 60 parts by mass, 3 to 60 parts by mass, 5 to 60 parts by mass, 10 to 60 parts by mass, 20 to 50 parts by mass, 25 to 40 parts by mass, or 30 to 35 parts by mass per 100 parts by mass of blocked polyisocyanate.

[0081] (Other components) The paint composition may contain other components besides polyols, blocked polyisocyanates, and blocking agent dissociation catalysts. For example, the paint composition may contain a solvent. Suitable solvents 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.

[0082] The solvent content may be 0 to 90% by mass, 5 to 80% by mass, or 10 to 70% by mass, based on the total mass of the paint composition.

[0083] The paint composition may contain unblocked polyisocyanate (for example, polyisocyanate remaining as unreacted material) and may contain unreacted blocking agent. The content of unblocked polyisocyanate in the paint composition may be 5% by mass or less, or 0% by mass, based on the total solid content of the paint composition. The content of unreacted blocking agent in the paint composition may be 5% by mass or less, or 0% by mass, based on the total solid content of the paint composition.

[0084] The paint composition may further contain additives such as pigments, dispersion stabilizers, viscosity modifiers, leveling agents, gelling inhibitors, light stabilizers, antioxidants, ultraviolet absorbers, heat resistance improvers, inorganic and organic fillers, plasticizers, lubricants, antistatic agents, reinforcing materials, and catalysts.

[0085] The paint composition may be a one-component composition in which all constituent components are contained in one liquid, or it may be a multi-component composition in which the constituent components exist separately in multiple liquids. The multi-component paint composition may comprise a first liquid (main component) containing a polyol and a second liquid (curing agent) containing a blocked polyisocyanate. In this case, other constituent components (blocking agent dissociation catalyst and other components) may be contained in the first liquid, in the second liquid, or in liquids different from the first and second liquids.

[0086] The ratio of available isocyanate groups to the total number of hydroxyl groups in the paint composition ([available isocyanate groups] / [hydroxyl groups]) may be 0.7 to 1.5, 0.8 to 1.4, or 0.9 to 1.3 in terms of equivalent ratio.

[0087] The paint composition can be used as a top coat or intermediate coat paint for automobiles, chipping-resistant paint, electrodeposition paint, paint for automobile parts, paint for automobile repair, pre-coated metal and rust-resistant steel sheets for metal products such as home appliances and office equipment, paint for building materials, paint for plastics, adhesive, adhesion promoter, sealant, etc.

[0088] <Coating Film> Another embodiment of the present disclosure is a coating film formed from the coating composition of the above embodiment.

[0089] The above-mentioned coating film includes a cured product of the paint composition of the above embodiment. The above-mentioned coating film can be formed by applying the paint composition onto a substrate using a known method and curing the coating film (uncured coating film) made of the paint composition. Examples of known methods include roll coating, curtain flow coating, spray coating, electrostatic coating, bell coating, electrodeposition coating, etc. The amount of paint composition applied, the thickness of the coating film, etc., may be appropriately determined according to the material of the surface to be coated, etc.

[0090] The coating film made from the paint composition may be cured by heating the coating film. The heating temperature (baking temperature) may be, for example, 200°C or less. The heating time (baking time) may be, for example, 10 to 180 minutes. According to the paint composition of this embodiment, even when baking is performed at a low temperature of 100°C or less (for example, 60 to 100°C), a cured coating film with a good gel fraction can be obtained.

[0091] The contents of this disclosure will be described in more detail below using examples and comparative examples, but this disclosure is not limited to the following examples.

[0092] <Example 1> (Production of Acrylic Polyol) 400 g of butyl acetate was placed in a reaction vessel equipped with a four-necked flask containing a stirrer, thermometer, heating device, nitrogen sealing tube, and condenser, and the temperature was raised to 120°C while stirring. Next, a monomer mixture consisting of 113.8 g of methyl methacrylate (MMA), 259.3 g of butyl methacrylate (BMA), 116.2 g of 2-hydroxyethyl methacrylate (HEMA), and 3.2 g of acrylic acid (AA) was mixed with 7.5 g of the peroxide-based polymerization initiator "Perbutyl O (manufactured by NOF Corporation)" and added dropwise over 2 hours to carry out the polymerization reaction. Next, 2.0 g of the above peroxide-based polymerization initiator "Perbutyl O (manufactured by NOF Corporation)" and 100 g of butyl acetate were added dropwise to the reaction vessel over 1 hour to obtain a solution containing acrylic polyol (1) (solid content: 50% by mass). Acrylic polyol (1) had a hydroxyl value of 100 mg KOH / g, an acid value of 5 mg KOH / g, a glass transition temperature (Tg) of 45°C, and a number-average molecular weight (Mn) of 15,000. The hydroxyl value was measured in accordance with JIS K1557-1, and the acid value was measured in accordance with JIS K1557-5. The number-average molecular weight (Mn) was determined using gel permeation chromatography (GPC) with polystyrene as the standard substance.

[0093] (Production of Block Polyisocyanate) In a reaction vessel equipped with a four-necked flask containing a stirrer, thermometer, heating device, nitrogen sealing tube, and condenser, 517 g of Coronate HXR (manufactured by Tosoh Corporation, hexamethylene diisocyanate trimer, NCO content 21.8% by mass, trade name) and 250 g of butyl acetate were charged. Next, 233 g of methyl ethyl ketoxime (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was charged, keeping the temperature below 80°C, and the reaction was carried out at 70°C for 2 hours. Subsequently, the peak of the NCO group (2270 cm⁻¹) was identified by infrared absorption spectroscopy (IR measurement). －１ Once the surrounding area had disappeared, the mixture was cooled to room temperature to obtain a solution containing blocked polyisocyanate (1) (solid content 75% by mass).

[0094] (Preparation of Paint Composition) In a reaction vessel, 49.6 g of a solution containing the acrylic polyol (1) prepared above (solid content: 50% by mass), 16.4 g of a solution containing the blocked polyisocyanate (1) prepared above (solid content: 75% by mass), 7.1 g of a trimethyl-n-octylammonium monomethyl carbonate solution (manufactured by Tosoh Corporation, solid content: 55% by mass, "TMOA-MC" in Table 1), which is a blocking agent dissociation catalyst, and 26.9 g of butyl acetate were sequentially charged and thoroughly mixed to obtain a paint composition. The amount of the solution containing the blocked polyisocyanate (1) was adjusted so that the ratio of the total number of active isocyanate groups in the blocked polyisocyanate (1) to the total number of hydroxyl groups in the acrylic polyol (1) ([NCO / OH]) was 1.0 in terms of equivalent ratio. The amount of trimethyl-n-octylammonium monomethyl carbonate solution was adjusted so that the molar ratio (mc / ma) of the amount of trimethyl-n-octylammonium monomethyl carbonate to the acidic group ma contained in acrylic polyol (1) was 7.1 moles.

[0095] <Examples 2-6 and Comparative Examples 1-3> (Production of Acrylic Polyols) Solutions containing acrylic polyols (2) to (9) were obtained in the same manner as in Example 1, except that the amounts of MMA and AA were changed as shown in Table 1 (solid content: 50% by mass). The hydroxyl value, acid value, glass transition temperature (Tg), and number average molecular weight (Mn) of the obtained acrylic polyols (2) to (9) were measured in the same manner as in Example 1. As a result, the hydroxyl value was 100 mg KOH / g, the acid value was as shown in Table 1, the glass transition temperature (Tg) was 45°C, and the number average molecular weight (Mn) was 15,000.

[0096] (Preparation of paint composition) A paint composition was obtained in the same manner as in Example 1, except that a solution containing any of the acrylic polyols (2) to (9) prepared above was used instead of the solution containing acrylic polyol (1) (solid content: 50% by mass). The molar ratio (mc / ma) of the amount of trimethyl-n-octylammonium monomethyl carbonate added (mc) to the amount of acidic groups ma contained in acrylic polyols (2) to (9) is shown in Table 1.

[0097] <Example 7> (Preparation of paint composition) In a reaction vessel, 49.6 g of a solution containing the acrylic polyol (2) prepared above (solid content: 50% by mass), 16.4 g of a solution containing the blocked polyisocyanate (1) prepared above (solid content: 75% by mass), 7.2 g of a tetramethylammonium hydroxide solution (manufactured by Tokyo Chemical Industry Co., Ltd., solid content: 10% by mass, "TMA-OH" in Table 1), which is a blocking agent dissociation catalyst, and 26.8 g of butyl acetate were sequentially charged and thoroughly mixed to obtain a paint composition. The amount of the solution containing the blocked polyisocyanate (1) was adjusted so that the ratio of the total number of active isocyanate groups in the blocked polyisocyanate (1) to the total number of hydroxyl groups in the acrylic polyol (2) ([NCO / OH]) was 1.0 in terms of equivalent ratio. The amount of tetramethylammonium hydroxide solution was adjusted so that the molar ratio (mc / ma) of the amount of tetramethylammonium hydroxide to the acidic group ma contained in acrylic polyol (2) was 3.6 moles.

[0098] <Evaluation> (Low-temperature curing performance evaluation) The paint composition prepared above was applied to release paper so that the thickness before drying was 200 μm. The resulting coating film was left to stand at room temperature for 60 minutes, and then baked by heating in a constant temperature bath at 80°C for 20 minutes. The baked coating film (cured coating film) was immersed in methyl ethyl ketone at room temperature for 24 hours, and the gel fraction was determined. The gel fraction was calculated using the following formula: Gel fraction (unit: mass%) = Mass of coating film after immersion (mass of undissolved portion) / Mass of coating film before immersion × 100 If the gel fraction measured above was 70% by mass or more, it was evaluated as having excellent low-temperature curing performance. The results are shown in Table 1.

[0099] (Yellowing Resistance Evaluation) The paint composition prepared above was applied to a color steel plate substrate (manufactured by Yutaka Panel Service Co., Ltd.) using a bar coater to a thickness of 100 μm before drying. The resulting coating film was left to stand at room temperature for 60 minutes, and then baked by heating in a constant temperature bath at 80°C for 20 minutes. The b* value of the resulting coating film was measured using a Spectrum II Guide 60 / 0 Gross (manufactured by BYK-Gardner). If b* was 0.4 or less, it was evaluated as having excellent yellowing resistance. The results are shown in Table 1.

[0100]

Claims

1. A paint composition comprising (A) a polyol, (B) a blocked polyisocyanate, and (C) a blocking agent dissociation catalyst, wherein the acid value of component (A) is 3 to 30 mg KOH / g, and component (C) contains a quaternary ammonium salt.

2. The paint composition according to claim 1, wherein component (A) comprises an acrylic polyol.

3. The paint composition according to claim 2, wherein the acrylic polyol comprises structural units derived from one or more (meth)acrylic acids and structural units derived from one or more (meth)acrylic acid esters.

4. The paint composition according to claim 3, wherein the (meth)acrylic acid ester comprises at least one selected from the group consisting of (meth)acrylate hydroxyalkyl esters and (meth)acrylate alkyl esters.

5. The paint composition according to claim 1, wherein component (B) comprises a blocked polyisocyanate having a structure derived from an aliphatic polyisocyanate or a derivative thereof having an aliphatic hydrocarbon group having 4 to 6 carbon atoms.

6. The paint composition according to claim 1, wherein the component (C) comprises a quaternary ammonium salt having a cationic group represented by the following formula (1). [In formula (1), R １ R represents an alkyl group having 1 to 16 carbon atoms, which may have a hydroxyl group, an amino group, or an alkoxy group as a substituent. ２ ~R ４ Each of these independently represents an alkyl group having 1 to 8 carbon atoms.

7. The paint composition according to claim 1, wherein component (C) has at least one cationic group selected from the group consisting of a group represented by the following formula (2) and a group represented by the following formula (3).

8. The paint composition according to claim 1, wherein component (C) has a monoalkyl carbonate group or a hydroxyl group having an alkyl group having 1 to 8 carbon atoms.

9. The paint composition according to claim 1, wherein the content of component (C) is 1.1 to 25 moles per mole of acidic group contained in component (A).

10. The paint composition according to claim 1, wherein component (B) comprises a blocked polyisocyanate having isocyanate groups encapsulated with an oxime-based blocking agent.

11. The paint composition according to claim 1, wherein component (B) comprises a blocked polyisocyanate having an isocyanate group encapsulated with methyl ethyl ketoxime.

12. The paint composition according to claim 1, wherein the ratio of the total number of active isocyanate groups contained in component (B) to the total number of hydroxyl groups contained in component (A) is 0.7 to 1.5 in terms of equivalent weight.

13. A coating film formed from the coating composition according to any one of claims 1 to 12.

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