Catalyst composition, blocked polyisocyanate composition, coating material composition, coating film, and method for forming coating film

Abstract

This catalyst composition is used for dissociating a blocking agent from a blocked polyisocyanate, and contains a quaternary ammonium salt and at least one compound selected from the group consisting of hydroxylamine compounds and oxime compounds.

Description

Catalyst composition, blocked polyisocyanate composition, coating composition, coating film, and method for forming coating film

[0001] The present disclosure relates to a catalyst composition, a blocked polyisocyanate composition, a coating composition, a coating film, and a method for forming a coating film.

[0002] Polyisocyanates have been known as curing agents used in paints, etc. For example, polyurethane resin paints, which are a combination of polyol and polyisocyanate, are known to have excellent abrasion resistance, chemical resistance, and stain resistance.

[0003] Paints using polyisocyanate as a curing agent are generally two-component compositions, in which the base component (e.g., polyol) and polyisocyanate are stored separately and mixed before use. However, once mixed, the paint cures in a short time, resulting in a short usable time and a problem with workability during application. Furthermore, because polyisocyanate reacts easily with water, it was impossible to use the above-mentioned paints in water-based paints such as electrodeposition paints.

[0004] One known method for addressing these issues is to inactivate polyisocyanate by reacting it with a blocking agent. The blocked polyisocyanate obtained by this method does not react with the base resin (such as a polyol) at room temperature, but when heated, the blocking agent dissociates, regenerating the isocyanate group, which then reacts with the base resin to form crosslinks. Therefore, this method does not limit the usable time, and it is possible to mix the base resin and curing agent in advance to form a paint, making it possible to apply polyisocyanate to water-based paints.

[0005] As a catalyst for dissociating a blocking agent from a blocked polyisocyanate (blocking agent dissociation catalyst), for example, a quaternary ammonium salt is known (see Patent Document 1).

[0006] Japanese Patent Application Publication No. 08-170048

[0007] The quaternary ammonium salts described in Patent Document 1 can impart low-temperature curing properties to coating compositions containing blocked polyisocyanates. However, quaternary ammonium salts tend to change color (e.g., yellow) over time. Therefore, even if the color does not change during use, they may cause discoloration of the blocked polyisocyanate composition after mixing with the blocked polyisocyanate. While Patent Document 1 describes that certain quaternary ammonium salts also have excellent yellowing resistance, it does not describe the color change caused by quaternary ammonium salts over time, and the yellowing resistance effect is not sufficient.

[0008] Therefore, one aspect of the present disclosure is to provide a catalyst composition that can not only impart low-temperature curing properties to a coating composition containing a blocked polyisocyanate, but also suppress color change over time when the blocked polyisocyanate composition is formed. Another aspect of the present disclosure is to provide a blocked polyisocyanate composition, a coating composition, a coating film, and a method for forming a coating film that use the catalyst composition.

[0009] The present disclosure provides at least the following [1] to

[11] .

[0010] [1] A catalyst composition used to dissociate a blocking agent from a blocked polyisocyanate, the catalyst composition comprising a quaternary ammonium salt and at least one nitrogen-containing compound selected from the group consisting of hydroxylamine compounds and oxime compounds.

[0011] [2] The catalyst composition according to [1], wherein the ratio of the content of the nitrogen-containing compound to the content of the quaternary ammonium salt is 0.05 to 6.0 in mass ratio.

[0012] [3] The catalyst composition according to [1] or [2], wherein the quaternary ammonium salt contains a quaternary ammonium cation represented by the following formula (1):

[0013]

[0014] [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; R ２ ~R ４ each independently represents an alkyl group having 1 to 8 carbon atoms.

[0015] [4] The catalyst composition according to any one of [1] to [3], wherein the nitrogen-containing compound comprises a hydroxylamine compound represented by the following formula (2):

[0016]

[0017] [In formula (2), R ５ and R ６ each independently represents a hydrogen atom or a linear or branched hydrocarbon group having 1 to 16 carbon atoms which may have one or more substituents; R ５ and R ６ may be linked to each other to form a ring.

[0018] [5] A blocked polyisocyanate composition comprising a blocked polyisocyanate and the catalyst composition according to any one of [1] to [4].

[0019] [6] The blocked polyisocyanate composition according to [5], wherein the content of the quaternary ammonium salt is 0.0001 to 40 parts by mass per 100 parts by mass of the blocked polyisocyanate.

[0020] [7] The blocked polyisocyanate composition according to [5] or [6], wherein the blocked polyisocyanate contains a structure derived from an aliphatic polyisocyanate having an aliphatic hydrocarbon group having 4 to 6 carbon atoms or a derivative thereof.

[0021] [8] The blocked polyisocyanate composition according to any one of [5] to [7], wherein the blocked polyisocyanate has at least one group selected from the group consisting of an isocyanate group blocked with an oxime-based blocking agent and an isocyanate group blocked with a pyrazole-based blocking agent.

[0022] [9] A coating composition comprising a base agent and a curing agent, the coating composition comprising a blocked polyisocyanate and the catalyst composition according to any one of [1] to [4], or the blocked polyisocyanate composition according to any one of [5] to [8].

[0023]

[10] A coating film formed from the coating composition according to [9].

[0024]

[11] A method for forming a coating film, comprising the steps of applying the coating composition according to [9] or

[10] to a substrate and heating at 60 to 100°C to cure a coating film made of the coating composition.

[0025] According to one aspect of the present disclosure, there is provided a catalyst composition that not only can impart low-temperature curing properties to a coating composition containing a blocked polyisocyanate, but also can suppress color change over time when the blocked polyisocyanate composition is formed. In addition, according to another aspect of the present disclosure, there are provided a blocked polyisocyanate composition, a coating composition, a coating film, and a method for forming a coating film that use the catalyst composition.

[0026] Exemplary embodiments of the present disclosure are described below. However, the present disclosure is not limited to the following embodiments. In this specification, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. Furthermore, unless specifically stated otherwise, the units of the numerical values ​​before and after "to" are the same. Furthermore, the upper and lower limits individually stated can be arbitrarily combined. Furthermore, unless otherwise specified, the materials exemplified below may be used alone or in combination of two or more types. When multiple substances corresponding to each component are present in the composition, the content of each component in the composition means the total amount of the multiple substances present in the composition, unless otherwise specified.

[0027] <Catalyst Composition> One embodiment of the present disclosure is a catalyst composition containing a quaternary ammonium salt and at least one nitrogen-containing compound selected from the group consisting of hydroxylamine compounds and oxime compounds (hereinafter also referred to as "nitrogen-containing compound (A)"). The catalyst composition is used to dissociate a blocking agent from a blocked polyisocyanate.

[0028] The catalyst composition can impart low-temperature curing properties to a coating composition containing a blocked polyisocyanate. Furthermore, the catalyst composition can inhibit color change over time when used in a blocked polyisocyanate composition. This reduces color change during the production of a coating film (before and after curing), contributing to the formation of a coating film with less coloration. The catalyst composition itself may be resistant to color change over time. Surprisingly, some catalyst compositions, although they themselves undergo color change equivalent to or greater than that observed when the nitrogen-containing compound (A) is not used, have been found to exhibit the effect of inhibiting color change over time when used in a blocked polyisocyanate composition.

[0029] (Quaternary Ammonium Salt) The quaternary ammonium salt contains a quaternary ammonium cation as a cationic group. As the quaternary ammonium salt, a compound known as a blocking agent dissociation catalyst can be used.

[0030] The quaternary ammonium cation is represented, for example, by the following formula (1):

[0031]

[0032] In formula (1), R １ ~R ４ R each independently represents a hydrocarbon group. １ ~R ４ may be the same or different from each other.

[0033] The hydrocarbon group may be an aliphatic hydrocarbon group (e.g., an alkyl group or a cycloalkyl group) or an aromatic hydrocarbon group (e.g., an aryl group). From the viewpoint of enhancing the effect of improving low-temperature curing properties and enhancing the effect of reducing color change over time of the blocked polyisocyanate composition and coloration of the coating film, the hydrocarbon group may be an aliphatic hydrocarbon group. In particular, when the aliphatic hydrocarbon group is an alkyl group, the above effects tend to be further enhanced.

[0034] When the hydrocarbon group is an aliphatic hydrocarbon group, it has, for example, 1 to 16 carbon atoms. The aliphatic hydrocarbon group may have 3 or more or 6 or more carbon atoms, and may have 12 or less or 8 or less carbon atoms. When the hydrocarbon group is an aromatic hydrocarbon group, it has, for example, 6 to 16 carbon atoms. The aromatic hydrocarbon group may have 8 or more or 10 or more carbon atoms, and may have 14 or less or 12 or less carbon atoms.

[0035] The hydrocarbon group may have a substituent. Examples of the substituent include a hydroxy group, an amino group, and an alkoxy group. The number of carbon atoms in 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 a methoxy group, an ethoxy group, a butoxy group, a propyloxy group, a pentyloxy group, and a hexyloxy group. The number of substituents may be, for example, 0 to 3. The number of carbon atoms in the substituent is counted as the number of carbon atoms in the hydrocarbon group.

[0036] In one embodiment, R in formula (1) １ represents 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 ~R ４ each independently represents an alkyl group having 1 to 8 carbon atoms. When such a quaternary ammonium salt is used, a coating composition having excellent low-temperature curing properties is likely to be obtained.

[0037] R １Specific examples of the alkyl group represented by the formula (I) 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, a 2-ethylhexyl group, a 2-propylheptyl group, a nonyl group, a decyl group, an isodecyl group, a dodecyl group, a hexadecyl group, etc. These groups may be substituted with one or more substituents (for example, a hydroxy group, an amino group, or an alkoxy group).

[0038] From the viewpoint of making it easier to obtain a coating composition with even better low-temperature curing properties, R １ may be an unsubstituted alkyl group or hydroxyalkyl group having 1 to 16 carbon atoms. １ When the unsubstituted alkyl group having 1 to 16 carbon atoms is an unsubstituted alkyl group having 1 to 16 carbon atoms, the effect of improving low-temperature curing tends to be even greater. From the viewpoint of further enhancing this effect, the unsubstituted alkyl group may be an alkyl group having 1 to 10 carbon atoms. Furthermore, when the unsubstituted alkyl group having 1 to 16 carbon atoms is an alkyl group having 6 to 8 carbon atoms, the effect of improving low-temperature curing and the effect of reducing color change over time of the blocked polyisocyanate composition and coloration of the coating film tend to be even greater. This tendency is particularly pronounced when the alkyl group is an alkyl group having 8 carbon atoms (particularly an n-octyl group).

[0039] R ２ ~R ４ Specific examples of the alkyl group represented by the formula (I) 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.

[0040] From the viewpoint of making it easier to obtain a coating composition with even better low-temperature curing properties, R ２ ~R ４ may be an alkyl group having 1 to 4 carbon atoms. From the viewpoint of further enhancing the effect of improving low-temperature curing properties, the alkyl group having 1 to 4 carbon atoms is preferably an alkyl group having 1 to 2 carbon atoms, and more preferably a methyl group.

[0041] In view of the above, the quaternary ammonium cation is represented by R １ is an alkyl group having 1 to 10 carbon atoms, and R ２ ~R ４ may be a cation in which R is an alkyl group having 1 to 4 carbon atoms. Specific examples of such a cation include trimethylmono-n-octylammonium cation, trimethylmono-n-butylammonium cation, tetramethylammonium cation, and tetrabutylammonium cation. In particular, when the quaternary ammonium cation is trimethylmono-n-octylammonium cation, there tends to be a greater effect in improving low-temperature curing properties and in reducing color change over time of the blocked polyisocyanate composition and coloration of the coating film.

[0042] The anionic group of the quaternary ammonium salt may be a group consisting of an anion derived from an acid such as an organic acid group or an inorganic acid, or may be a group consisting of an anion derived from an ester such as a carbonate ester. The anionic group of the quaternary ammonium salt may also be a group that does not fall into any of these categories (for example, a hydroxyl group (hydroxide ion)).

[0043] Examples of groups consisting of anions derived from organic acids (organic acid groups) include fatty acid groups. The number of carbon atoms in the 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 a formic acid group, an acetic acid group, a 2-ethylhexanoic acid group (octylic acid group), a lauric acid group, a cyclohexanecarboxylic acid group, and a pivalic acid group.

[0044] Examples of groups consisting of anions derived from inorganic acids (inorganic acid groups) include halogen groups (fluoro, chloro, bromo, etc.), hydrogen carbonate groups, and carbonate groups.

[0045] 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 group, ethyl carbonate group, propyl carbonate group, and butyl carbonate group.

[0046] The anionic group of the quaternary ammonium salt may be a fatty acid group having 1 to 12 carbon atoms, a monoalkyl carbonate group having an alkyl group having 1 to 8 carbon atoms, or a hydroxyl group, from the viewpoint of easily obtaining a coating composition with excellent low-temperature curing properties. From the viewpoint of further enhancing the effect of improving low-temperature curing properties, the anionic group may be a fatty acid group having 1 to 7 carbon atoms or a monoalkyl carbonate group having an alkyl group having 1 to 4 carbon atoms, and from the viewpoint of further enhancing this effect, it may be a monoalkyl carbonate group having an alkyl group having 1 to 2 carbon atoms.

[0047] From the above viewpoint, the quaternary ammonium salt is a quaternary ammonium cation represented by the above formula (1), and R １ represents 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 ~R ４ may be a combination of a quaternary ammonium cation, each of which independently represents an alkyl group having 1 to 8 carbon atoms, and a fatty acid group having 1 to 12 carbon atoms, a monoalkyl carbonate group having an alkyl group having 1 to 8 carbon atoms, or a hydroxyl group. １ is an alkyl group having 1 to 10 carbon atoms, and R ２ ~R ４ is a C1-4 alkyl group and a monoalkylcarbonate group or hydroxyl group having an alkyl group having 1-8 carbon atoms, and １ is an alkyl group having 4 to 8 carbon atoms, and R ２ ~R ４ A combination of a cation in which is an alkyl group having 1 to 2 carbon atoms and a monoalkylcarbonate group having an alkyl group having 1 to 8 carbon atoms is more preferred.

[0048] Specific examples of quaternary ammonium salts include trimethylmono-n-octylammonium hydrogen carbonate, trimethylmono-n-octylammonium methyl carbonate, trimethylmono-n-octylammonium carbonate, trimethylmono-n-butylammonium methyl carbonate, trimethylmono-n-butylammonium acetate, tetramethylammonium acetate, hexadecyltrimethylammonium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, trimethyl(2-hydroxypropyl)ammonium 2-ethylhexanoate, tetramethylammonium hydrogen carbonate, tetraethylammonium hydrogen carbonate, tetra-n-propylammonium Examples of the carbonate-soluble ammonium carbonate include ammonium bicarbonate, tetra-n-butylammonium bicarbonate, triethylmonomethylammonium bicarbonate, tri-n-propylmonomethylammonium bicarbonate, tri-n-butylmonomethylammonium bicarbonate, tri-n-butylmonoethylammonium bicarbonate, tetramethylammonium monomethyl carbonate, tetraethylammonium monoethyl carbonate, tetra-n-butylammonium monobutyl carbonate, triethylmonomethylammonium monomethyl carbonate, tri-n-propylmonomethylammonium monomethyl carbonate, tri-n-butylmonomethylammonium monomethyl carbonate, tri-n-butylmonoethylammonium monoethyl carbonate, tetramethylammonium carbonate, and tetra-n-butylammonium carbonate.

[0049] The catalyst composition may contain one or more types of quaternary ammonium salts.

[0050] The content of the quaternary ammonium salt may be 10% by mass or more, 20% by mass or more, or 30% by mass or more, based on the total mass of the catalyst composition, from the viewpoint of more easily obtaining a coating composition with excellent low-temperature curing properties. The content of the quaternary ammonium salt may be 99% by mass or less, 95% by mass or less, or 90% by mass or less, based on the total mass of the catalyst composition, from the viewpoint of further reducing color change over time of the blocked polyisocyanate composition and coloration of the coating film. From these viewpoints, the content of the quaternary ammonium salt may be, for example, 10 to 99% by mass, based on the total mass of the catalyst composition.

[0051] (Nitrogen-containing compound) [Hydroxylamine compound] The hydroxylamine compound is, for example, a compound represented by the following formula (2).

[0052]

[0053] In formula (2), R ５ and R ６ each independently represents a hydrogen atom or a linear or branched hydrocarbon group having 1 to 16 carbon atoms which may have one or more substituents. ５ and R ６ may be linked to each other to form a ring.

[0054] The hydrocarbon group may be a saturated or unsaturated aliphatic hydrocarbon group (e.g., an alkyl group, an alkylene group, a cycloalkyl group, or a cycloalkylene group), or an aromatic hydrocarbon group (e.g., an aryl group or an arylene group). From the viewpoint of further reducing color change over time of the blocked polyisocyanate composition and coloration of the coating film, the hydrocarbon group may be an aliphatic hydrocarbon group. As the aliphatic hydrocarbon group, a saturated aliphatic hydrocarbon group is preferred.

[0055] When the hydrocarbon group is an aliphatic hydrocarbon group, it has, for example, 1 to 16 carbon atoms. The aliphatic hydrocarbon group may have 1 or more or 2 or more carbon atoms, and may have 12 or less or 8 or less carbon atoms. When the hydrocarbon group is an aromatic hydrocarbon group, it has, for example, 6 to 16 carbon atoms. The aromatic hydrocarbon group may have 8 or more or 10 or more carbon atoms, and may have 14 or less or 12 or less carbon atoms.

[0056] The hydrocarbon group may have a substituent. Examples of the substituent include a hydroxy group, an amino group, and an alkoxy group. The number of carbon atoms in 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 a methoxy group, an ethoxy group, a butoxy group, a propyloxy group, a pentyloxy group, and a hexyloxy group. The number of substituents may be, for example, 0 to 3.

[0057] In one embodiment, R in formula (2) ５ and R ６ are each independently an alkyl group having 1 to 16 carbon atoms. When such a hydroxylamine compound is used, the color change over time of the blocked polyisocyanate composition and the coloration of the coating film can be further reduced.

[0058] R ５ and R ６ The aliphatic saturated hydrocarbon group may be an alkyl group. 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, a 2-ethylhexyl group, a 2-propylheptyl group, a nonyl group, a decyl group, an isodecyl group, a dodecyl group, and a hexadecyl group.

[0059] R ５ and R ６ The saturated aliphatic hydrocarbon groups may be linked to each other to form an alkylene group. ５ and R ６ Specific examples of the alkylene group formed by linking together include an ethylene group, a 1,2-propylene group, a 1,2-butylene group, and a 2,3-butylene group.

[0060] From the viewpoint of further reducing the color change of the blocked polyisocyanate composition over time and the coloring of the coating film, R ５ and R ６ may each independently be an alkyl group having 1 to 4 carbon atoms. The alkyl group having 1 to 4 carbon atoms is preferably an alkyl group having 1 to 2 carbon atoms, and more preferably a methyl group.

[0061] Specific examples of the hydroxylamine compound include hydroxylamine, N,N-diethylhydroxylamine, N-isopropylhydroxylamine, N,N-dibutylhydroxylamine, and Nt-butylhydroxylamine.

[0062] The catalyst composition may contain one or more types of hydroxylamine compounds.

[0063] The content of the hydroxylamine compound may be 1% by mass or more, 5% by mass or more, or 10% by mass or more, based on the total mass of the catalyst composition, from the viewpoint of further reducing color change over time of the blocked polyisocyanate composition and coloration of the coating film. The content of the hydroxylamine compound may be 90% by mass or less, 80% by mass or less, or 70% by mass or less, based on the total mass of the catalyst composition, from the viewpoint of more easily obtaining a coating composition with excellent low-temperature curing properties. From these viewpoints, the content of the hydroxylamine compound may be, for example, 1 to 90% by mass, 5 to 80% by mass, or 10 to 70% by mass, based on the total mass of the catalyst composition.

[0064] The ratio of the hydroxylamine compound content to the quaternary ammonium salt content (hydroxylamine compound content / quaternary ammonium salt content) may be 0.05 to 6.0 by mass. When this ratio is 0.05 or more, coloration of the coating film tends to be further reduced, and when this ratio is 6.0 or less, a coating composition with excellent low-temperature curing properties tends to be obtained. From these viewpoints, the ratio may be 0.1 or more, 0.3 or more, 1.0 or more, 2.0 or more, 3.0 or more, or 4.0 or more; and may be 5.5 or less, 5.0 or less, 4.5 or less, 3.0 or less, 1.0 or less, or 0.2 or less; 0.1 to 6.0, 0.3 to 6.0, 1.0 to 6.0, 2.0 to 6.0, 3.0 to 6.0, or 4.0 to 6.0; or 0.05 to 5.5, 0.05 to 5.0, 0.05 to 4.5, 0.05 to 3.0, 0.05 to 1.0, or 0.05 to 0.2.

[0065] [Oxime Compound] The oxime compound is, for example, a compound represented by the following formula (3).

[0066]

[0067] In formula (3), R ７ and R ８ each independently represents a hydrogen atom or a linear or branched hydrocarbon group having 1 to 16 carbon atoms which may have one or more substituents. ７ and R ８ may be linked to each other to form a ring. ７ and R ８ The hydrocarbon group represented by R ５ and R ６ is the same as the hydrocarbon group represented by R ５ and R ６ The same effects can be expected due to the same characteristics as the hydrocarbon group represented by the formula:

[0068] Specific examples of the oxime compound include methyl ethyl ketoxime, acetaldoxime, acetoxime, 2-butanone oxime, cyclohexanone oxime, acetone oxime, diacetyl monooxime, benzophenone oxime, 2,2,6,6-tetramethylcyclohexanone oxime, diisopropyl ketone oxime, methyl t-butyl ketone oxime, diisobutyl ketone oxime, methyl isobutyl ketone oxime, methyl isopropyl ketone oxime, methyl 2,4-dimethylpentyl ketone oxime, methyl 3-ethylheptyl ketone oxime, methyl isoamyl ketone oxime, n-amyl ketone oxime, 2,2,4,4-tetramethyl-1,3-cyclobutanedione monooxime, 4,4'-dimethoxybenzophenone oxime, and 2-heptanone oxime.

[0069] The catalyst composition may contain one or more types of oxime compounds.

[0070] The content of the oxime compound may be 1% by mass or more, 5% by mass or more, or 10% by mass or more, based on the total mass of the catalyst composition, from the viewpoint of further reducing color change over time of the blocked polyisocyanate composition and coloration of the coating film. The content of the oxime compound may be 90% by mass or less, 80% by mass or less, or 70% by mass or less, based on the total mass of the catalyst composition, from the viewpoint of more easily obtaining a coating composition with excellent low-temperature curing properties. From these viewpoints, the content of the oxime compound may be, for example, 1 to 90% by mass, 5 to 80% by mass, or 10 to 70% by mass, based on the total mass of the catalyst composition.

[0071] The ratio of the oxime compound content to the quaternary ammonium salt content (oxime compound content / quaternary ammonium salt content) may be 0.05 to 6.0 by mass. When this ratio is 0.05 or more, coloration of the coating film tends to be further reduced, and when this ratio is 6.0 or less, a coating composition with excellent low-temperature curing properties tends to be obtained. From these viewpoints, the ratio may be 0.1 or more, 0.3 or more, 1.0 or more, 2.0 or more, 3.0 or more, or 4.0 or more; and may be 5.5 or less, 5.0 or less, 4.5 or less, 3.0 or less, 1.0 or less, or 0.2 or less; 0.1 to 6.0, 0.3 to 6.0, 1.0 to 6.0, 2.0 to 6.0, 3.0 to 6.0, or 4.0 to 6.0; or 0.05 to 5.5, 0.05 to 5.0, 0.05 to 4.5, 0.05 to 3.0, 0.05 to 1.0, or 0.05 to 0.2.

[0072] The content of the nitrogen-containing compound (A) may be 1% by mass or more, 5% by mass or more, or 10% by mass or more, based on the total mass of the catalyst composition, from the viewpoint of further reducing color change over time of the blocked polyisocyanate composition and coloration of the coating film. The content of the nitrogen-containing compound (A) may be 90% by mass or less, 80% by mass or less, or 70% by mass or less, based on the total mass of the catalyst composition, from the viewpoint of more easily obtaining a coating composition with excellent low-temperature curing properties. From these viewpoints, the content of the nitrogen-containing compound (A) may be, for example, 1 to 90% by mass, 5 to 80% by mass, or 10 to 70% by mass, based on the total mass of the catalyst composition.

[0073] The ratio of the content of the nitrogen-containing compound (A) to the content of the quaternary ammonium salt (content of nitrogen-containing compound (A) / content of quaternary ammonium salt) may be 0.05 to 6.0 by mass. When this ratio is 0.05 or more, coloration of the coating film tends to be further reduced, and when this ratio is 6.0 or less, a coating composition with excellent low-temperature curing properties tends to be obtained. From these viewpoints, the ratio may be 0.1 or more, 0.3 or more, 1.0 or more, 2.0 or more, 3.0 or more, or 4.0 or more; and may be 5.5 or less, 5.0 or less, 4.5 or less, 3.0 or less, 1.0 or less, or 0.2 or less; 0.1 to 6.0, 0.3 to 6.0, 1.0 to 6.0, 2.0 to 6.0, 3.0 to 6.0, or 4.0 to 6.0; or 0.05 to 5.5, 0.05 to 5.0, 0.05 to 4.5, 0.05 to 3.0, 0.05 to 1.0, or 0.05 to 0.2.

[0074] (Other Components) The catalyst composition may further contain components other than the quaternary ammonium salt and the nitrogen-containing compound (A). The content of the components other than the quaternary ammonium salt and the nitrogen-containing compound (A) in the catalyst composition may be 5% by mass or less, 1% by mass or less, or 0.1% by mass or less, based on the total mass of the catalyst composition.

[0075] The catalyst composition may contain, for example, a blocking agent dissociation catalyst other than a quaternary ammonium salt. The content of the blocking agent dissociation catalyst other than a quaternary ammonium salt in the catalyst composition may be 5% by mass or less, 1% by mass or less, or 0.1% by mass or less, based on the total mass of the catalyst composition.

[0076] (Preparation Method) The catalyst composition can be prepared by mixing the quaternary ammonium salt, the nitrogen-containing compound (A), and any other components that may be optionally included.

[0077] <Blocked Polyisocyanate Composition> One embodiment of the present disclosure is a blocked polyisocyanate composition comprising a blocked polyisocyanate and the catalyst composition of the above embodiment. In other words, the blocked polyisocyanate composition of one embodiment of the present disclosure comprises a blocked polyisocyanate, a quaternary ammonium salt, and a nitrogen-containing compound (A).

[0078] The blocked polyisocyanate composition contains the catalyst composition of the embodiment, and therefore can impart low-temperature curing properties to the coating composition. For the same reason, the blocked polyisocyanate composition can provide a coating composition that is less likely to undergo color change during the production of a coating film (before and after curing of the coating film).

[0079] (Blocked Polyisocyanate) A blocked polyisocyanate is a compound derived from a polyisocyanate that does not have an isocyanate group blocked with a blocking agent (hereinafter also referred to as an "unblocked polyisocyanate"), and has at least a structure derived from the unblocked polyisocyanate and an isocyanate group blocked with a blocking agent (hereinafter also referred to as a "blocked isocyanate group").

[0080] [Unblocked Polyisocyanate] The unblocked polyisocyanate is a compound having 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 derivative may be an isocyanate group-containing prepolymer obtained by reacting the above-mentioned polyisocyanate with a polyol, or a derivative of the prepolymer (e.g., an isocyanurate, allophanate, biuret, and the like). As the polyol, for example, a diol having 2 to 9 carbon atoms is used. Such diols include, for example, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, and 1,5-pentanediol.

[0081] The unblocked polyisocyanate does not need to have an aromatic ring, from the viewpoint of improving the yellowing resistance of the cured coating film. That is, the unblocked polyisocyanate may be a non-aromatic polyisocyanate. 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.

[0082] From the viewpoint of further improving low-temperature curing properties, the unblocked polyisocyanate may contain an aliphatic polyisocyanate having an aliphatic hydrocarbon group having 4 to 6 carbon atoms or a derivative thereof. In other words, the blocked polyisocyanate may have a structure derived from an aliphatic polyisocyanate having an aliphatic hydrocarbon group having 4 to 6 carbon atoms or a derivative thereof. When the aliphatic polyisocyanate having an aliphatic hydrocarbon group having 4 to 6 carbon atoms is hexamethylene diisocyanate, the effect of improving low-temperature curing properties tends to be further enhanced. From this viewpoint, the unblocked polyisocyanate may contain hexamethylene diisocyanate or a derivative thereof, and the blocked polyisocyanate may have a structure derived from hexamethylene diisocyanate or a derivative thereof. The derivative of hexamethylene diisocyanate may be at least one selected from the group consisting of isocyanurates, allophanates, and biurets. These derivatives may also be derivatives of the above-mentioned isocyanate group-containing prepolymers. Among these, when the hexamethylene diisocyanate derivative is an isocyanurate, higher coating hardness tends to be obtained. When the unblocked polyisocyanate contains an isocyanurate, from the viewpoint of further improving coating hardness, 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 groups and allophanate groups 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%.

[0083] [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.

[0084] Examples of the blocking agent 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, methyl ethyl ketoxime, methyl isobutyl ketoxime, and cyclohexanone oxime; imidazole, 2-methylimidazole, 4-methylimidazole, and 2,4-dimethylimidazole. Examples of suitable blocking agents 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. Methyl ethyl ketoxime is preferred as the oxime-based blocking agent. From the viewpoint of curability, a pyrazole-based blocking agent may be used. The pyrazole-based blocking agent is preferably 3,5-dimethylpyrazole.

[0085] In view of the above, in one embodiment, the blocked polyisocyanate may have at least one group selected from the group consisting of an isocyanate group blocked with an oxime-based blocking agent and an isocyanate group blocked with a pyrazole-based blocking agent.

[0086] The blocked polyisocyanate may have a free isocyanate group, but when the blocked polyisocyanate does not have a free isocyanate group, storage stability can be further improved. From the viewpoint of further improving storage stability, all of the available isocyanate groups in the blocked polyisocyanate may be blocked isocyanate groups. Here, the available isocyanate groups refer to both free isocyanate groups and blocked isocyanate groups.

[0087] The blocked polyisocyanate can be obtained, for example, by reacting a polyisocyanate having free isocyanate groups, such as the unblocked polyisocyanate, with the blocking agent. That is, the blocked polyisocyanate can be a reaction product of a polyisocyanate having free isocyanate groups and the blocking agent. The polyisocyanate having free isocyanate groups and the blocking agent may each be used alone or in combination of two or more. However, when an aromatic polyisocyanate is not used as the polyisocyanate having free isocyanate groups, the yellowing resistance of the cured coating film can be further improved.

[0088] The blocked polyisocyanate may be a compound derived from a reaction product of a polyisocyanate having a free isocyanate group and a blocking agent, or may be a compound obtained by reacting the reaction product of a polyisocyanate having a free isocyanate group and a blocking agent with a compound capable of reacting with the free isocyanate group in the reaction product (e.g., an active hydrogen group-containing compound, etc.).

[0089] The reaction between the polyisocyanate having free isocyanate groups and the blocking agent can be carried out according to the reaction conditions for a typical blocking reaction. The reaction can be carried out at room temperature or with heating. Regardless of whether heating is performed or not, the temperature of the reaction solution can be, for example, 20 to 200°C.

[0090] The blocked polyisocyanates may be used singly or in combination of two or more. For example, two or more blocked polyisocyanates derived from different types of unblocked polyisocyanates may be used in combination.

[0091] The content of the block polyisocyanate may be 40% by mass or more, 60% by mass or more, or 80% by mass or more, based on the total solids content of the block polyisocyanate composition, from the viewpoint of easily obtaining a coating composition with excellent low-temperature curing properties. The content of the block polyisocyanate may be less than 100% by mass, or 95% by mass or less, or 90% by mass or less, based on the total solids content of the block polyisocyanate composition, from the viewpoint of improving the storage stability of the coating. From these viewpoints, the content of the block polyisocyanate may be, for example, 40% by mass or more but less than 100% by mass, or 60 to 95% by mass, or 80 to 90% by mass, based on the total solids content of the block polyisocyanate composition. Note that, when the block polyisocyanate composition contains a solvent, the total solids content of the block polyisocyanate composition refers to the amount obtained by excluding the amount of the solvent from the total amount of the block polyisocyanate composition. When the block polyisocyanate composition does not contain a solvent, the total solids content of the block polyisocyanate composition refers to the amount obtained by excluding the amount of the solvent from the total amount of the block polyisocyanate composition.

[0092] (Catalyst Composition) The catalyst composition is as described in the above embodiment and contains a quaternary ammonium salt and a nitrogen-containing compound (A). The ratio of the content of the nitrogen-containing compound (A) to the content of the quaternary ammonium salt in the blocked polyisocyanate composition may be in the same range as the range exemplified for the ratio of the content of the nitrogen-containing compound (A) to the content of the quaternary ammonium salt in the catalyst composition. The same applies to the ratio of the content of the hydroxyamine compound to the content of the quaternary ammonium salt and the ratio of the content of the oxime compound to the content of the quaternary ammonium salt.

[0093] The content of the catalyst composition in the blocked polyisocyanate composition may be adjusted so that the content of the quaternary ammonium salt falls within the following range. From the viewpoint of more easily obtaining a coating composition with excellent low-temperature curing properties, the content of the quaternary ammonium salt may be 0.0001 parts by mass or more, 0.001 parts by mass or more, or 0.01 parts by mass or more, per 100 parts by mass of the blocked polyisocyanate. From the viewpoint of improving the storage stability of the coating, the content of the quaternary ammonium salt may be 40 parts by mass or less, 30 parts by mass or less, or 20 parts by mass or less, per 100 parts by mass of the blocked polyisocyanate. From these viewpoints, the content of the quaternary ammonium salt may be, for example, 0.0001 to 40 parts by mass, per 100 parts by mass of the blocked polyisocyanate.

[0094] (Other Components) The blocked polyisocyanate composition may further contain other components in addition to the above-described components that may be contained in the blocked polyisocyanate and catalyst composition. Examples of other components include additives such as pigments, dispersion stabilizers, viscosity modifiers, leveling agents, antigelling agents, light stabilizers, antioxidants, UV absorbers, heat resistance improvers, inorganic and organic fillers, plasticizers, lubricants, antistatic agents, reinforcing materials, and catalysts.

[0095] The blocked polyisocyanate composition may contain a solvent as another component. Examples of solvents 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, and 1,4-dioxane. These solvents may be used alone or in combination of two or more. The content of the solvent may be 0 to 95% by mass, 5 to 90% by mass, or 10 to 80% by mass, based on the total mass of the blocked polyisocyanate composition.

[0096] The blocked polyisocyanate composition may contain unblocked polyisocyanate (e.g., polyisocyanate remaining as an unreacted product) and may contain unreacted blocking agent. The content of unblocked polyisocyanate contained in the blocked polyisocyanate composition may be 5% by mass or less, or even 0% by mass, based on the total solid content of the blocked polyisocyanate composition. The content of unreacted blocking agent contained in the blocked polyisocyanate composition may be 5% by mass or less, or even 0% by mass, based on the total solid content of the blocked polyisocyanate composition.

[0097] The effective isocyanate group content (hereinafter referred to as "effective NCO content") of the blocked polyisocyanate composition may be 4 to 28% by mass, 5 to 22% by mass, or 6 to 16% by mass, from the viewpoint of further enhancing the curability of the coating material. Here, the effective NCO content refers to the isocyanate groups present in the blocked polyisocyanate composition that can participate in a crosslinking reaction, expressed in mass %, and can be rephrased as the content of free isocyanate groups in the polyisocyanate composition obtained by dissociating the blocking agent from the blocked polyisocyanate relative to the total mass of the blocked polyisocyanate composition (free NCO content). The free NCO content can be determined by reacting the isocyanate groups in a measurement sample (the polyisocyanate composition obtained by dissociating the blocking agent from the blocked polyisocyanate) with an excess of secondary amine, followed by back titration of the unreacted secondary amine with hydrochloric acid.

[0098] The above-described blocked polyisocyanate composition can be prepared by mixing the blocked polyisocyanate, the previously prepared catalyst composition, and other optional components. The blocked polyisocyanate composition can also be prepared by mixing the blocked polyisocyanate, a quaternary ammonium salt, a nitrogen-containing compound (A), and other optional components. The blocked polyisocyanate composition is used, for example, as a curing agent for a coating composition (e.g., a low-temperature curing coating composition). That is, another embodiment of the present disclosure is a curing agent for a coating (e.g., a low-temperature curing coating) comprising the blocked polyisocyanate composition.

[0099] <Paint Composition> Another embodiment of the present disclosure is a paint composition comprising a base agent and a curing agent. The paint composition comprises a blocked polyisocyanate and the catalyst composition of the above embodiment. In other words, the paint composition of one embodiment of the present disclosure comprises a base agent and a curing agent, and the base agent, curing agent, or other agent comprises a blocked polyisocyanate, a quaternary ammonium salt, and a nitrogen-containing compound (A). The paint composition may comprise the above-mentioned blocked polyisocyanate composition. Details of the blocked polyisocyanate contained in the paint composition are the same as those of the blocked polyisocyanate contained in the above-mentioned blocked polyisocyanate composition. Furthermore, the ratio of the content of the nitrogen-containing compound (A) to the content of the quaternary ammonium salt in the paint composition may be the same range as the exemplified range of the content of the nitrogen-containing compound (A) to the content of the quaternary ammonium salt in the catalyst composition. The same applies to the ratio of the content of the hydroxyamine compound to the content of the quaternary ammonium salt and the ratio of the content of the oxime compound to the content of the quaternary ammonium salt.

[0100] The coating composition may be a one-component composition in which all of the constituent components are contained in one component, or a multi-component composition in which the constituent components are present in multiple components. A multi-component coating composition may comprise a first component containing a base agent and a second component containing a curing agent. The blocked polyisocyanate is contained in the second component as a curing agent, but the catalyst composition may be contained in either the first or second component. Similarly, when the coating composition contains other components that can be contained in the blocked polyisocyanate composition, these components may be contained in either the first or second component. When the catalyst composition is contained in the second component, the blocked polyisocyanate composition of the above embodiment may be used as the second component.

[0101] The coating composition contains a blocked polyisocyanate and the catalyst composition of the embodiment, and therefore has excellent low-temperature curing properties. For the same reason, the coating composition is less likely to cause color change during the production of a coating film (before and after curing of the coating film). Therefore, the coating composition can easily form a coating film with little coloration.

[0102] The base agent contains, for example, an active hydrogen group-containing compound. Examples of active hydrogen groups include hydroxy groups and amino groups. The active hydrogen group-containing compound has an average number of functional groups (average number of active hydrogen groups) of 2 or more, for example, 2 to 50. Examples of active hydrogen-containing compounds having such an average number of functional groups include polyols, polyamines, and amino alcohols. In particular, when the base agent contains a polyol as the active hydrogen group-containing compound, it is easy to obtain better low-temperature curing properties and a coating film with less coloration.

[0103] The number-average molecular weight of the active hydrogen group-containing compound is, for example, 500 to 20,000, and may be 500 to 10,000. Examples of active hydrogen group-containing compounds having such a number-average molecular weight include polyurethane resins, polyamide resins, saturated or unsaturated polyester resins, alkyd resins modified with saturated or unsaturated fatty acids, acrylic resins, fluororesins, epoxy resins, and cellulose resins (all of which are resins containing active hydrogen groups). Furthermore, taking into consideration the coating film performance, such as gloss, thickness, hardness, durability, flexibility, and drying speed, as well as cost, at least one compound selected from the group consisting of saturated or unsaturated polyester resins, alkyd resins modified with saturated or unsaturated fatty acids, and acrylic resins may be used.

[0104] The blending ratio of the base agent and curing agent in the coating composition may be adjusted based on the ratio of the total amount of available isocyanate groups in the curing agent to the total amount of active hydrogen groups in the base agent. The ratio of the total amount of available isocyanate groups in the curing agent to the total amount of active hydrogen groups in the base agent may be 1 / 9 to 9 / 1, or 2 / 8 to 8 / 2, in molar ratio. When the molar ratio is within the above range, better curability can be obtained.

[0105] The content of the catalyst composition in the coating composition may be adjusted so that the content of the quaternary ammonium salt per 100 parts by mass of the blocked polyisocyanate falls within the above-mentioned range (e.g., 0.0001 to 40 parts by mass), similar to the content of the catalyst composition in the above-mentioned blocked polyisocyanate composition.

[0106] The coating composition can be used as an automotive topcoat paint, a chipping-resistant paint, an electrodeposition paint, a paint for automotive parts, a paint for automotive repair, pre-coated metals and rust-proof steel sheets for metal products such as home appliances and office equipment, a paint for building materials, a paint for plastics, an adhesive, an adhesion promoter, a sealant, etc.

[0107] <Coating film and method for forming 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.

[0108] The coating film may be an uncured coating film made from a mixture of the base agent and the curing agent in the coating 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.

[0109] The coating composition may be applied by known techniques such as roll coating, curtain flow coating, spray coating, electrostatic coating, bell coating, electrodeposition coating, etc. The amount of coating composition to be applied, the thickness of the coating film, etc. may be appropriately determined depending on the material of the surface to be coated, etc.

[0110] Curing of a coating film (uncured coating film) made of the coating composition may be carried out 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. According to the coating composition of this embodiment, a cured coating film having good hardness can be formed even when baking is carried out at a low temperature of 100°C or lower (e.g., 60 to 100°C).

[0111] Examples of substrates include molded articles made of materials such as stainless steel, phosphate-treated steel, zinc-coated 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 molded articles. The surface-treated article may also be a molded article (surface-treated molded article) made of an olefin resin such as polyethylene or polypropylene that has been subjected to a surface treatment such as corona discharge treatment.

[0112] The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited to the following examples.

[0113] Synthesis Example 1 Synthesis of Quaternary Ammonium Salt S-1 A 200 ml autoclave was charged with 15.4 g of dimethylmono-n-octylamine (manufactured by Tokyo Chemical Industry Co., Ltd.), 13.2 g of dimethyl carbonate (manufactured by Tokyo Chemical Industry Co., Ltd.), and 31.4 g of methanol (manufactured by Kishida Chemical Co., Ltd.), and the mixture was stirred at 110° C. for 12 hours to allow the reaction to occur. The reaction liquid was collected in a container (a single-necked recovery flask), and the pressure in the container was reduced to 30° C. to remove unreacted dimethyl carbonate and methanol, yielding 24.2 g of trimethylmono-n-octylammonium monomethyl carbonate (quaternary ammonium salt S-1).

[0114] Synthesis Example 2 (Preparation of Polyisocyanate A-1) 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.) were charged into a four-necked flask equipped with a stirrer, thermometer, heating device, nitrogen seal tube, and condenser, and a urethane-forming reaction was carried out at 80°C for 2 hours under a nitrogen stream. Thereafter, 0.04 g of potassium 2-ethylhexanoate (manufactured by Tokyo Chemical Industry Co., Ltd.), an isocyanuration catalyst, was added, and an isocyanuration reaction was carried out at 70°C for 2 hours. After the NCO content reached 40.0% by mass, 0.15 g of JP-508 (manufactured by Johoku Chemical Industry Co., Ltd.) was added to carry out a termination reaction, and the reaction solution was cooled to room temperature. This reaction solution was subjected to thin-film distillation at a temperature of 130°C and a pressure of 0.04 kPa to remove unreacted HDI, thereby obtaining purified Polyisocyanate A-1. Polyisocyanate A-1 had an NCO content of 21.8% by mass and a viscosity at 25°C of approximately 2,500 mPa s.

[0115] ( １ H-NMR: Measurement of isocyanurate group content) Polyisocyanate A-1 １ H-NMR measurement was carried out to determine the isocyanurate group content (the content of isocyanurate groups relative to the total (100 mol%) of isocyanurate groups and allophanate groups). 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%. １ H-NMR measurement was carried out under the following measurement conditions: [Measurement conditions] (1) Measurement equipment: ECX400M (manufactured by JEOL Ltd.) １ H-NMR) (2) Measurement temperature: 23°C (3) Sample concentration: 0.1 g / 1 ml (4) Number of accumulations: 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)

[0116] Examples 1 to 6 Preparation of catalyst compositions As the nitrogen-containing compound (A), N,N-diethylhydroxylamine (manufactured by Tokyo Chemical Industry Co., Ltd., indicated as "DEHA" in the tables), which is a hydroxylamine compound, and methyl ethyl ketoxime (manufactured by Ube Industries, Ltd., indicated as "MEKO" in the tables), which is an oxime compound, were prepared. The nitrogen-containing compound (A) and the quaternary ammonium salt S-1 were mixed in a mass ratio R (nitrogen-containing compound (A) / quaternary ammonium salt) shown in Table 1 below, to prepare catalyst compositions of Examples 1 to 6 (catalyst compositions 1 to 6).

[0117] (Evaluation of Discoloration Resistance) The catalyst compositions of Examples 1 to 6 were stored at 45°C for 48 hours, and the b* values ​​of the catalyst compositions according to the CIE Lab standard were measured before and after storage using a spectrophotometer COH7700 (manufactured by Nippon Denshoku Kogyo Co., Ltd.). Furthermore, the "rate of change in b* value" was calculated from the b* values ​​before and after storage (initial b* value and b* value after storage) using the following formula, and the resistance of the catalyst compositions to discoloration over time (discoloration resistance) was evaluated based on this rate of change. Rate of change in b* value (unit: %) = 100 × (b* value after storage - initial b* value) / initial b* value

[0118] The evaluation criteria are as follows. If the evaluation was B, the catalyst composition was evaluated to have sufficient discoloration resistance. A: The rate of change in b* value was 0% or more and less than 30%. B: The rate of change in b* value was 30% or more and less than 60%. C: The rate of change in b* value was 60% or more.

[0119] (Preparation of Blocked Polyisocyanate Compositions) Using the catalyst compositions of Examples 1 to 6, blocked polyisocyanate compositions (compositions containing a blocked polyisocyanate and a catalyst composition) of Examples 1 to 6 were prepared by the following method.

[0120] Into a four-neck flask equipped with a stirrer, a thermometer, a heating device, a nitrogen seal tube, and a condenser, 515 g of polyisocyanate A-1 and 250 g of butyl acetate were charged and stirred for 30 minutes, and then 234 g of methyl ethyl ketoxime (manufactured by Ube Industries, Ltd., "MEKO" in the table) (equivalent ratio relative to the amount of polyisocyanate A-1 mixed was 1.0) was charged in three divided portions so that the temperature did not exceed 80°C. Thereafter, the mixture was reacted at 70°C for 2 hours, and the infrared absorption spectrum (IR measurement) showed that the peak of the NCO group (2270 cm)－１ When the color (approximately 100%) disappeared, the mixture was cooled to room temperature, and 22.5 g of the catalyst composition was added and stirred for 30 minutes. By the above operations, the blocked polyisocyanate compositions of Examples 1 to 6 were obtained, respectively.

[0121] (Evaluation of Discoloration Resistance) The resistance of the blocked polyisocyanate compositions obtained in Examples 1 to 6 to discoloration over time was evaluated by storing the blocked polyisocyanate compositions at 45°C for one week, measuring the b* values ​​of the blocked polyisocyanate compositions according to the CIE Lab standard before and after storage, and calculating the rate of change in the b* values ​​(initial b* value and b* value after storage) before and after storage using the following formula. The b* values ​​were measured using a spectrophotometer COH7700 (manufactured by Nippon Denshoku Industries Co., Ltd.): Rate of change in b* value (unit: %) = 100 × (b* value after storage - initial b* value) / initial b* value

[0122] The evaluation criteria are as follows: A: The rate of change in b* value is 0% or more and less than 150%; B: The rate of change in b* value is 150% or more and less than 200%; C: The rate of change in b* value is 200% or more.

[0123] (Preparation of Coating Composition) The coating compositions of Examples 1 to 6 were prepared using the blocked polyisocyanate compositions of Examples 1 to 6, respectively. Specifically, the coating compositions were prepared by mixing 63.7 g of Acrydic A-801 (trade name, manufactured by DIC Corporation, acrylic polyol, solids concentration 50 mass%, hydroxyl value 50 mgKOH / g) as the base agent, 10.6 g of the blocked polyisocyanate composition as a curing agent, and 25.2 g of butyl acetate (manufactured by Kishida Chemical Co., Ltd.).

[0124] (Preparation of Coating Films) The coating compositions of Examples 1 to 6 were applied to substrates under the following conditions, and then cured to obtain the coating films (cured coating films) of Examples 1 to 6, respectively.

[0125] (Evaluation of low-temperature curing properties) [Gel fraction measurement] The coating composition prepared above was applied to release paper under the following coating conditions to a thickness of 200 μm before drying. The resulting coating film was left to stand at room temperature for 60 minutes, and then baked by heating in a thermostatic chamber 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. The results are shown in Table 1. Gel fraction (unit: mass %) = mass of coating film after immersion (mass of undissolved portion) / mass of coating film before immersion × 100 [Coating conditions] Coating method: using an applicator Humidity conditions: 50% RH Temperature conditions: 23°C Drying (curing) conditions: forced drying at 80°C for 20 minutes Film thickness: approximately 200 μm

[0126] Example 7 Preparation of Blocked Polyisocyanate Composition 500 g of Polyisocyanate A-1 and 250 g of butyl acetate were charged into a four-necked flask equipped with a stirrer, a thermometer, a heating device, a nitrogen seal tube, and a condenser, and the mixture was stirred for 30 minutes. Then, 249 g of 3,5-dimethylpyrazole (manufactured by Tokyo Chemical Industry Co., Ltd., "DMP" in the table) (equivalent ratio relative to the amount of Polyisocyanate A-1 mixed was 1.0) was charged in three divided portions so that the temperature did not exceed 80°C. The mixture was then reacted at 70°C for 2 hours, and the infrared absorption spectrum (IR measurement) showed a peak corresponding to an NCO group (at 2270 cm －１ When the color (approximately 100%) disappeared, the mixture was cooled to room temperature, and 22.5 g of the catalyst composition of Example 4 (catalyst composition 4) was added and stirred for 30 minutes. By the above operations, a blocked polyisocyanate composition of Example 7 was obtained. The discoloration resistance of the obtained blocked polyisocyanate composition was evaluated in the same manner as in Examples 1 to 6.

[0127] (Preparation of Coating Composition) The coating composition of Example 7 was prepared using the blocked polyisocyanate composition of Example 7. Specifically, the coating composition was prepared by mixing 63.6 g of ACRYDIC A-801 as the base agent, 10.9 g of the blocked polyisocyanate composition as a curing agent, and 25.5 g of butyl acetate.

[0128] (Preparation and Evaluation of Coating Film) A coating film (cured coating film) was prepared and evaluated for low temperature curing (measurement of gel fraction) in the same manner as in Example 1, except that the coating composition of Example 7 was used as the coating composition. The results are shown in Table 1.

[0129] Comparative Example 1 In Comparative Example 1, neither a hydroxylamine compound nor an oxime compound was used, and quaternary ammonium salt S-1 was used as the catalyst. The discoloration resistance of the catalyst (quaternary ammonium salt S-1) of Comparative Example 1 was evaluated in the same manner as in Examples 1 to 6, and then the preparation of a blocked polyisocyanate composition, evaluation of the discoloration resistance of the blocked polyisocyanate composition, preparation of a coating composition, production of a coating film, and evaluation of low-temperature curing properties were carried out in the same manner as in Examples 1 to 6 above, except that quaternary ammonium salt S-1 was used instead of the catalyst composition. The results are shown in Table 1.

[0130]

Claims

1. A catalyst composition used to dissociate a blocking agent from a blocked polyisocyanate, the catalyst composition comprising a quaternary ammonium salt and at least one nitrogen-containing compound selected from the group consisting of hydroxylamine compounds and oxime compounds.

2. The catalyst composition according to claim 1, wherein the ratio of the content of the nitrogen-containing compound to the content of the quaternary ammonium salt is 0.05 to 6.0 by mass.

3. The catalyst composition according to claim 1, wherein the quaternary ammonium salt contains a quaternary ammonium cation represented by the following formula (1): [In formula (1), R １ represents 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; R ２ ~R ４ each independently represents an alkyl group having 1 to 8 carbon atoms.

4. The catalyst composition according to claim 1, wherein the nitrogen-containing compound comprises a hydroxylamine compound represented by the following formula (2): [In formula (2), R ５ and R ６ each independently represents a hydrogen atom or a linear or branched hydrocarbon group having 1 to 16 carbon atoms which may have one or more substituents; R ５ and R ６ may be linked to each other to form a ring.

5. A blocked polyisocyanate composition comprising a blocked polyisocyanate and the catalyst composition according to any one of claims 1 to 4.

6. The blocked polyisocyanate composition according to claim 5, wherein the content of the quaternary ammonium salt is 0.0001 to 40 parts by mass per 100 parts by mass of the blocked polyisocyanate.

7. The blocked polyisocyanate composition according to claim 5, wherein the blocked polyisocyanate contains a structure derived from an aliphatic polyisocyanate having an aliphatic hydrocarbon group having 4 to 6 carbon atoms or a derivative thereof.

8. The blocked polyisocyanate composition according to claim 5, wherein the blocked polyisocyanate has at least one group selected from the group consisting of an isocyanate group blocked with an oxime-based blocking agent and an isocyanate group blocked with a pyrazole-based blocking agent.

9. A coating composition comprising a base agent and a curing agent, the coating composition comprising a blocked polyisocyanate and the catalyst composition according to any one of claims 1 to 4.

10. A coating film formed from the coating composition according to claim 9.

11. A method for forming a coating film, comprising the steps of applying the coating composition according to claim 9 to an object to be coated and heating the applied coating at 60 to 100°C to cure the coating film made of said coating composition.

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