Blocked-polyisocyanate composition, coating composition, curing agent for aqueous coating material, aqueous coating composition, and coating film

Abstract

A blocked-polyisocyanate composition comprising a blocked polyisocyanate, a blocking-agent dissociation catalyst, and an emulsification aid, wherein the blocked polyisocyanate has a hydrophilic group, the blocking-agent dissociation catalyst includes a quaternary ammonium salt, and the emulsification aid includes an alcohol having an octanol / water partition coefficient of 2.5-7.0.

Description

Blocked polyisocyanate composition, coating composition, curing agent for water-based coating, water-based coating composition and coating film

[0001] The present disclosure relates to a blocked polyisocyanate composition, a coating composition, a curing agent for an aqueous coating, an aqueous coating composition, and a coating film.

[0002] A known method involves deactivating polyisocyanate by reacting it with an active hydrogen group-containing compound called a blocking agent. The blocked polyisocyanate obtained by this method does not react with the base compound (such as a polyol) at room temperature, but when heated, the blocking agent dissociates, regenerating the isocyanate group, which then reacts with the base compound to form crosslinks. Therefore, this method does not significantly limit the usable time, and it is possible to premix the base compound and curing agent to form a paint. Blocked polyisocyanates can also be used in water-based paints.

[0003] Meanwhile, in recent years, there has been a demand for blocked polyisocyanates that can cure coatings at lower temperatures than conventional ones, with the aim of reducing costs and carbon dioxide emissions during baking and enabling coating on plastic components. To this end, for example, Patent Document 1 discloses a polyurethane coating resin composition comprising a blocked polyisocyanate compound (A), a compound (B) having two or more active hydrogen atoms in the molecule, and a catalyst comprising a quaternary ammonium organic acid salt (C) of a specific structure. Patent Document 1 also describes that this polyurethane coating resin composition can be cured at low temperatures, has excellent coating film properties, is excellent in terms of yellowing resistance of the cured resin and storage stability of the coating, and is highly safe, with no risk of environmental pollution such as water contamination.

[0004] Japanese Patent Application Publication No. 08-170048

[0005] However, even the polyurethane coating resin composition using the blocking agent dissociation catalyst of Patent Document 1 does not fully satisfy the low-temperature curing property and storage stability in an aqueous coating composition.

[0006] Therefore, some aspects of the present disclosure aim to provide an aqueous coating composition having excellent low-temperature curing properties and storage stability, as well as a blocked polyisocyanate composition, a curing agent for aqueous coatings, and a coating composition that contribute to the preparation of the aqueous coating composition. Another aspect of the present disclosure aims to provide a coating film obtained from the aqueous coating composition.

[0007] Each aspect of the present disclosure provides at least the following [1] to

[11] .

[0008] [1] A blocked polyisocyanate composition comprising a blocked polyisocyanate, a blocking agent dissociation catalyst, and an emulsification aid, wherein the blocked polyisocyanate has a hydrophilic group, the blocking agent dissociation catalyst contains a quaternary ammonium salt, and the emulsification aid contains an alcohol having an octanol / water partition coefficient of 2.5 to 7.0.

[0009] [2] The blocked polyisocyanate composition according to [1], wherein the blocked polyisocyanate has at least one group selected from the group consisting of an isocyanate group blocked with an oxime compound and an isocyanate group blocked with an active methylene compound.

[0010] [3] The blocked polyisocyanate composition according to [1] or [2], 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.

[0011] [4] The blocked polyisocyanate composition according to any one of [1] to [3], wherein the hydrophilic group contains a group derived from a nonionic hydrophilic compound having a number average molecular weight of 600 to 2000.

[0012] [5] The blocked polyisocyanate composition according to any one of [1] to [4], wherein the content of the hydrophilic group is 5 to 30 parts by mass per 100 parts by mass of the blocked polyisocyanate.

[0013] [6] The blocked polyisocyanate composition according to any one of [1] to [5], wherein the quaternary ammonium salt contains a cationic group represented by the following formula (1):

[0014]

[0015] [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, or an aryl group having 6 to 16 carbon atoms; R ２ ~R ４ each independently represents an alkyl group having 1 to 8 carbon atoms.

[0016] [7] The blocked polyisocyanate composition according to any one of [1] to [6], wherein the alcohol includes a monohydric alcohol.

[0017] [8] A coating composition comprising a base agent and a curing agent, the coating composition comprising the blocked polyisocyanate composition according to any one of [1] to [7].

[0018] [9] A curing agent for aqueous coating materials, comprising the blocked polyisocyanate composition according to any one of [1] to [7].

[0019]

[10] An aqueous coating composition comprising a compound having two or more isocyanate-reactive groups, a blocked polyisocyanate, a blocking agent dissociation catalyst, an emulsification aid, and water, wherein the blocked polyisocyanate has a hydrophilic group, the blocking agent dissociation catalyst contains a quaternary ammonium salt, and the emulsification aid contains an alcohol having an octanol / water partition coefficient of 2.5 to 7.0.

[0020]

[11] A coating film formed from the aqueous coating composition according to

[10] .

[0021] According to some aspects of the present disclosure, it is possible to provide an aqueous coating composition having excellent low-temperature curing properties and storage stability, as well as a blocked polyisocyanate composition, a curing agent for aqueous coatings, and a coating composition that contribute to the preparation of the aqueous coating composition. Furthermore, according to another aspect of the present disclosure, it is possible to provide a coating film obtained from the aqueous coating composition.

[0022] Illustrative embodiments of each aspect of the present disclosure are described below. However, each aspect of 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 ​​written before and after "to" as the minimum and maximum values, respectively. Furthermore, unless specifically stated otherwise, the units of the numerical values ​​written before and after "to" are the same. Furthermore, the upper and lower limit values ​​individually stated can be combined in any combination.

[0023] <Blocked Polyisocyanate Composition> A blocked polyisocyanate composition according to one embodiment of the present disclosure comprises a blocked polyisocyanate (hereinafter also referred to as "blocked polyisocyanate (a)"), a blocking agent dissociation catalyst (hereinafter also referred to as "blocking agent dissociation catalyst (b)"), and an emulsification aid (hereinafter also referred to as "emulsification aid (c)"), wherein the blocked polyisocyanate (a) contains a hydrophilic group (hereinafter also referred to as "hydrophilic group (a1)"), the blocking agent dissociation catalyst (b) contains a quaternary ammonium salt (hereinafter also referred to as "quaternary ammonium salt (b1)"), and the emulsification aid (c) contains an alcohol having an octanol / water partition coefficient of 2.5 to 7.0 (hereinafter also referred to as "alcohol (c1)").

[0024] The blocked polyisocyanate (a) has hydrophilic properties due to the presence of the hydrophilic group (a1), and therefore, can also be called an aqueous blocked polyisocyanate.

[0025] According to the above embodiment, it is possible to provide a blocked polyisocyanate composition that contributes to the preparation of an aqueous coating composition having excellent low-temperature curing properties and storage stability. That is, the blocked polyisocyanate composition can impart excellent low-temperature curing properties to the aqueous coating composition, and can also impart excellent storage stability over time to the coating composition.

[0026] Here, "excellent low-temperature curing properties" means that a coating film that is difficult to dissolve in a solvent (e.g., methyl ethyl ketone) can be formed even when cured at a low temperature (e.g., a temperature of 100°C or less). The reason for this effect is not clear, but it is thought that the reason is that the composition contains an alcohol having an octanol / water partition coefficient of 2.5 to 7.0 as an emulsification aid, which allows the blocked polyisocyanate (a) and the blocking agent dissociation catalyst (b) to be mixed in a well-dispersed state, making it easier to exhibit the blocking agent dissociation effect, and also makes it possible to suppress coalescence with the base agent (e.g., polyol), thereby improving the coating stability.

[0027] <Blocked Polyisocyanate (a)> The blocked polyisocyanate (a) is a compound having one or more hydrophilic groups (a1) and one or more blocked isocyanate groups (hereinafter also referred to as "blocked polyisocyanate groups (a2)"). Here, the hydrophilic group refers to a functional group having hydrophilic properties, and the blocked isocyanate group refers to a group formed by blocking an isocyanate group with a blocking agent. The main skeleton of the blocked polyisocyanate (a) to which the hydrophilic group (a1) and the blocked isocyanate group (a2) are bonded is a skeleton derived from the polyisocyanate component, and has, for example, a structure in which some or all of the isocyanate groups have been removed from the polyisocyanate component.

[0028] The blocked isocyanate (a) may be a compound having a structure derived from the polyisocyanate component, a structure derived from the hydrophilic compound, and a structure derived from the blocking agent, and may be a reaction product of a polyisocyanate component, a hydrophilic compound having a hydrophilic group (a1), and a blocking agent (blocking agent for isocyanate groups). The hydrophilic compound is, for example, a compound having an octanol / water partition coefficient of less than 1 and having the hydrophilic group (a1). The hydrophilic compound is, for example, a compound having an isocyanate-reactive group, and the hydrophilic group (a1) is introduced into the structure of the polyisocyanate component by reaction of the isocyanate-reactive group with the isocyanate group of the polyisocyanate component. When the isocyanate-reactive group is a hydroxy group, the blocked polyisocyanate (a) has a structure in which the hydrophilic group (a1) is bonded directly or indirectly to the polyisocyanate component via a urethane group, and at least a portion of the isocyanate groups in the polyisocyanate component are blocked with a blocking agent.

[0029] The blocked polyisocyanate (a) may have isocyanate groups that are not blocked with a blocking agent (hereinafter referred to as "free isocyanate groups"). However, from the viewpoint of storage stability, it is preferable that the blocked polyisocyanate (a) does not have free isocyanate groups. For example, all of the available isocyanate groups in the blocked polyisocyanate (a) may be blocked isocyanate groups (a2). Here, the available isocyanate groups refer to both free isocyanate groups and blocked isocyanate groups.

[0030] (Polyisocyanate Component) The polyisocyanate component is composed of polyisocyanate. Polyisocyanate is a compound having a plurality of isocyanate groups (free isocyanate groups). Examples of polyisocyanates include aromatic polyisocyanates, aliphatic polyisocyanates, alicyclic polyisocyanates, and polyisocyanate derivatives thereof. Examples of derivatives include isocyanurates, allophanates, and biurets. The polyisocyanate component may be composed of one or more types of polyisocyanates.

[0031] The 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 polyisocyanate may be a non-aromatic polyisocyanate, from the viewpoint of improving the yellowing resistance of the cured coating film. Examples of non-aromatic polyisocyanates include aliphatic polyisocyanates such as hexamethylene diisocyanate, tetramethylene diisocyanate, 2-methyl-pentane-1,5-diisocyanate, 3-methyl-pentane-1,5-diisocyanate, lysine triisocyanate, and trioxyethylene diisocyanate; alicyclic polyisocyanates such as isophorone diisocyanate, cyclohexyl diisocyanate, hydrogenated diphenylmethane diisocyanate, norbornane diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated xylene diisocyanate, and hydrogenated tetramethylxylene diisocyanate, and derivatives thereof.

[0032] From the viewpoint of further improving curability, the polyisocyanate may contain an aliphatic polyisocyanate having an aliphatic hydrocarbon group having 4 to 6 carbon atoms or a derivative thereof. In other words, from the viewpoint of further improving curability, the blocked polyisocyanate (a) may contain a structure derived from an aliphatic polyisocyanate having an aliphatic hydrocarbon group having 4 to 6 carbon atoms or a derivative thereof. As the aliphatic polyisocyanate having an aliphatic hydrocarbon group having 4 to 6 carbon atoms, hexamethylene diisocyanate is preferred. In other words, the structure derived from an aliphatic polyisocyanate having an aliphatic hydrocarbon group having 4 to 6 carbon atoms or a derivative thereof is preferably a structure derived from hexamethylene diisocyanate or a derivative thereof. As the derivative of hexamethylene diisocyanate, an isocyanurate, an allophanate, or a biuret is preferred.

[0033] (Hydrophilic Group (a1)) The hydrophilic group (a1) may be a functional group derived from a hydrophilic compound, or may be a reaction residue of a hydrophilic compound formed by reacting an isocyanate-reactive group of a hydrophilic compound having an isocyanate-reactive group with an isocyanate group of a polyisocyanate component.

[0034] Examples of the hydrophilic compound include a nonionic hydrophilic compound, an anionic hydrophilic compound, a cationic hydrophilic compound, etc. These hydrophilic compounds may be used alone or in combination of two or more.

[0035] [Nonionic Hydrophilic Compound] Examples of the nonionic hydrophilic compound include poly(oxyalkylene) glycol and poly(oxyalkylene) monoalkyl ether.

[0036] The hydrophilic group derived from poly(oxyalkylene) glycol is, for example, a hydroxypolyethylene oxide group (formula: -(OR ａ ) ｎ The hydrophilic group derived from the poly(oxyalkylene) monoalkyl ether is an alkoxypolyalkyleneoxide group (a group represented by the formula: -(OR ａ ) ｎ OR ｂ In the above formula, n is an alkylene oxide unit (OR ａ ) and R ａ represents an alkylene group, and R ｂ represents an alkyl group.

[0037] Alkylene group (R ａ The alkylene group (R) may be linear, branched, or cyclic. ａ The number of carbon atoms in the alkylene group (R ａ Specific examples of the alkylene group (R ) include an ethylene group, an ethyl group, an isopropylene group, and an n-butylene group. ａ When the hydroxypolyethylene oxide group and the alkoxypolyalkylene oxide group are ethylene groups, the low-temperature curing properties of the aqueous coating composition are more likely to be improved. In other words, the hydroxypolyethylene oxide group and the alkoxypolyethylene oxide group may be hydroxypolyethylene oxide groups and alkoxypolyethylene oxide groups, respectively, from the viewpoint of further improving the low-temperature curing properties of the aqueous coating composition.

[0038] Alkyl group (R ｂ The alkyl group (R) may be linear, branched, or cyclic.ｂ The number of carbon atoms in the alkyl group (R) is, for example, 1 to 18, and may be 1 to 12, 1 to 6, or 1 to 2. ｂ Specific examples of the alkyl group (R ) 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, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, and an octadecyl group. ｂ When the alkyl group is a methyl group or an ethyl group, the low-temperature curing properties of the aqueous coating composition are more likely to be improved.

[0039] The lower limit of the number average molecular weight of the nonionic hydrophilic compound may be 200, 400, or 600. When the number average molecular weight is equal to or greater than the above lower limit, the water dispersibility of the block polyisocyanate composition tends to be better. The upper limit of the number average molecular weight of the nonionic hydrophilic compound may be 4,000, 3,000, or 2,000. When the number average molecular weight is equal to or less than the above upper limit, the curability of the aqueous coating composition containing the block polyisocyanate composition tends to be better. From the above viewpoint, the number average molecular weight of the nonionic hydrophilic compound, particularly the poly(oxyalkylene) monoalkyl ether, may be 200 to 4,000, 400 to 3,000, or 600 to 2,000. In particular, the above effect tends to be more pronounced when the number average molecular weight of the nonionic hydrophilic compound is 600 to 2000, that is, when the hydrophilic group (a1) contains a group derived from a nonionic hydrophilic compound having a number average molecular weight of 600 to 2000. The number average molecular weight is measured using gel permeation chromatography (GPC) and determined using polystyrene as a standard substance.

[0040] [Anionic Hydrophilic Compound] Examples of the anionic hydrophilic compound include carboxyl group-containing compounds and sulfonic acid group-containing compounds. Among these, using a carboxyl group-containing compound as the anionic hydrophilic compound improves ease of production and compatibility with aqueous coating compositions. Examples of the carboxyl group-containing compound include monohydroxycarboxylic acids, dihydroxycarboxylic acids, and derivatives thereof. Among these, monohydroxycarboxylic acids or dihydroxycarboxylic acids are preferred as the carboxyl group-containing compound, with monohydroxycarboxylic acids being more preferred. When a carboxyl group-containing compound or a sulfonic acid group-containing compound is used as the anionic hydrophilic compound, the blocked polyisocyanate composition may be neutralized with a neutralizing agent after production. Examples of the neutralizing agent include alkali metals, alkaline earth metals, ammonia, and tertiary amines such as trimethylamine, triethylamine, and dimethylethanolamine.

[0041] [Cationic Hydrophilic Compound] Examples of the cationic hydrophilic compound include hydroxyl group-containing amino compounds. When a hydroxyl group-containing amino compound is used, it may be neutralized with a neutralizing agent after production of the blocked polyisocyanate composition. Examples of the neutralizing agent include organic acids such as acetic acid, propionic acid, butanoic acid, and 2-ethylhexanoic acid.

[0042] Among the above, the use of at least one hydrophilic compound selected from the group consisting of nonionic hydrophilic compounds and anionic hydrophilic compounds facilitates the production of the blocked polyisocyanate (a), and the use of a nonionic hydrophilic compound not only facilitates production but also has the effect of making it easier to improve low-temperature curing properties.Furthermore, among the nonionic hydrophilic compounds, the use of a poly(oxyalkylene) monoalkyl ether facilitates the improvement of the dispersibility of the blocked polyisocyanate (a) and can further reduce the viscosity of the blocked polyisocyanate composition.

[0043] From the viewpoint of achieving superior low-temperature curing properties, the content of the nonionic hydrophilic compound based on the total mass of the hydrophilic groups (a1) possessed by the blocked polyisocyanate (a) may be 90 mass% or more, 95 mass% or more, or 100 mass%. From the same viewpoint, the content of the alkoxy polyalkylene oxide group based on the total mass of the hydrophilic groups possessed by the component (B) may be in the above-mentioned range, and the content of the alkoxy polyethylene oxide group based on the total mass of the hydrophilic groups possessed by the component (B) may be in the above-mentioned range.

[0044] The content of the hydrophilic group (a1) may be 1% by mass or more, 3% by mass or more, or 5% by mass or more, based on the total amount of isocyanate compounds in the isocyanate composition obtained by dissociating the blocking agent from the blocked polyisocyanate (a), from the viewpoint of easily obtaining an aqueous coating composition having excellent low-temperature curing properties. The content of the hydrophilic group (a1) may be 50% by mass or less, 40% by mass or less, or 30% by mass or less, based on the total amount of isocyanate compounds in the isocyanate composition obtained by dissociating the blocking agent from the blocked polyisocyanate (a), from the viewpoint of easily obtaining an aqueous coating composition having excellent storage stability. From these viewpoints, the content of the hydrophilic group (a1) may be 1 to 50% by mass, 3 to 40% by mass, or 5 to 30% by mass, based on the total amount of isocyanate compounds in the isocyanate composition obtained by dissociating the blocking agent from the blocked polyisocyanate (a).

[0045] The content of the hydrophilic group (a1) may be 5 parts by mass or more, 7 parts by mass or more, or 9 parts by mass or more per 100 parts by mass of the blocked polyisocyanate (a), from the viewpoint of easily obtaining an aqueous coating composition having excellent low-temperature curing properties. The content of the hydrophilic group (a1) may be 30 parts by mass or less, 20 parts by mass or less, or 15 parts by mass or less per 100 parts by mass of the blocked polyisocyanate (a), from the viewpoint of easily obtaining an aqueous coating composition having excellent storage stability. From these viewpoints, the content of the hydrophilic group (a1) may be 5 to 30 parts by mass, 7 to 20 parts by mass, or 9 to 15 parts by mass per 100 parts by mass of the blocked polyisocyanate (a).

[0046] (Blocked Isocyanate Group (a2)) The blocked isocyanate group (a2) has a structure derived from a blocking agent. As the blocking agent, a known active hydrogen group-containing compound known as a blocking agent for an isocyanate group can be used. Examples of the blocking agent include blocking agents (alcohol-based blocking agents) made of alcohol compounds such as methanol, ethanol, n-butanol, isobutanol, 2-ethylhexanol, butyl cellosolve, propylene glycol monomethyl ether, ethylene glycol, and benzyl alcohol; blocking agents (phenol-based blocking agents) made of phenol compounds such as phenol, cresol, ethylphenol, butylphenol, and 2-hydroxypyridine; blocking agents (lactam-based blocking agents) made of lactam compounds such as ε-caprolactam, δ-valerolactam, and γ-butyrolactam; blocking agents (oxime-based blocking agents) made of oxime compounds such as formaldoxime, acetaldoxime, acetoneoxime, methyl ethyl ketoxime, methyl isobutyl ketoxime, and cyclohexanoneoxime;Blocking agents (imidazole-based blocking agents) consisting of imidazole compounds such as 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, 2-undecylimidazole, and 2-heptadecylimidazole; blocking agents (amine-based blocking agents) consisting of amine compounds such as diphenylamine, diisopropylamine, and isopropylethylamine; Meldrum's 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, and malonic acid. Blocking agents (active methylene-based blocking agents) consisting of active methylene compounds such as methyl t-butyl, ethyl t-butyl malonate, dibenzyl malonate, diphenyl malonate, benzyl methyl malonate, ethyl phenyl malonate, t-butylphenyl malonate, isopropylidene malonate, alkyl acetoacetates such as methyl acetoacetate, ethyl acetoacetate, n-propyl acetoacetate, isopropyl acetoacetate, n-butyl acetoacetate, t-butyl acetoacetate, benzyl acetoacetate, and phenyl acetoacetate, 2-acetoacetoxyethyl methacrylate, acetylacetone, and ethyl cyanoacetate, pyrazole, 3,5-dimethylpyrazole, 3,5-diisopropylpyrazole, 3,5-diphenylpyrazole, 3,5-di-t-butylpyrazole, 3-methylpyrazole, 4-benzyl-3,5-dimethylpyrazole, 4-nitro-3,5-dimethylpyrazole, 4-bromo-3,5-dimethylpyrazole,Examples of suitable blocking agents include blocking agents (pyrazole-based blocking agents) composed of pyrazole compounds such as 5-dimethylpyrazole and 3-methyl-5-phenylpyrazole. These blocking agents may be used singly or in combination of two or more. Among these, when at least one compound selected from the group consisting of oxime compounds and active methylene compounds is used, i.e., when the blocked polyisocyanate (a) has, as the blocked isocyanate group (a2), at least one group selected from the group consisting of an isocyanate group blocked with an oxime compound and an isocyanate group blocked with an active methylene compound, storage stability tends to be further improved. This effect is more pronounced when an oxime compound is used, and more pronounced when methyl ethyl ketoxime is used.

[0047] (Production Method) The blocked polyisocyanate (a) can be obtained, for example, by reacting a polyisocyanate component, a hydrophilic compound having a hydrophilic group (a1), and a blocking agent. The polyisocyanate component, hydrophilic compound, and blocking agent may each be used alone or in combination of two or more. Details of the polyisocyanate component, hydrophilic compound, and blocking agent are as described above. By not using an aromatic polyisocyanate as the polyisocyanate component, the yellowing resistance of the cured coating film can be improved.

[0048] The order in which the polyisocyanate component, the hydrophilic compound, and the blocking agent are reacted is not particularly limited. From the viewpoint of easily adjusting the amount of hydrophilic group to be introduced, the polyisocyanate component and the hydrophilic compound may be reacted to obtain an isocyanate group-terminated precursor, and then the obtained isocyanate group-terminated precursor may be reacted with the blocking agent.

[0049] The reaction between the polyisocyanate component and the hydrophilic compound may be carried out in the presence of a solvent such as an aromatic solvent such as toluene or xylene, a ketone solvent such as acetone, methyl ethyl ketone or methyl isobutyl ketone, an ester solvent such as ethyl acetate or butyl acetate, or a glycol ether solvent such as ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate or diethylene glycol diethyl ether. The reaction temperature may be 20 to 200°C. The reaction time may be, for example, 1 to 10 hours. Although the reaction proceeds even without a catalyst, the reaction can be accelerated by using a known urethanization reaction catalyst.

[0050] The reaction between the isocyanate-terminated precursor and the blocking agent can be carried out under reaction conditions for a typical blocking reaction. The reaction between the isocyanate-terminated precursor and the blocking agent can be carried out at room temperature or with heating. Regardless of whether heating is performed or not, the temperature of the reaction solution can be, for example, 20 to 200°C.

[0051] The method for producing the blocked polyisocyanate (a) is not limited to the above. For example, after reacting a polyisocyanate component, a hydrophilic compound, and a blocking agent, if the resulting reaction product has free isocyanate groups, the blocked polyisocyanate (a) 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.

[0052] When the polyisocyanate component has an alkoxypolyethylene oxide group, a blocked polyisocyanate (a) can also be obtained by reacting a polyisocyanate having an alkoxypolyethylene oxide group with a blocking agent.

[0053] Alternatively, the blocked polyisocyanate (a) can be obtained by using a blocked polyisocyanate instead of the polyisocyanate component. For example, the blocked polyisocyanate (a) can be obtained by reacting a blocked polyisocyanate having no alkoxypolyethylene oxide group with the poly(oxyethylene)glycol monoalkyl ether.

[0054] 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 polyisocyanates may be used in combination.

[0055] The content of the blocked polyisocyanate (a) may be 40% by mass or more, 60% by mass or more, or 80% by mass or more, based on the total solid content of the blocked polyisocyanate composition, from the viewpoint of easily obtaining an aqueous coating composition having excellent low-temperature curing properties. The content of the blocked polyisocyanate (a) may be 99% by mass or less, 95% by mass or less, or 90% by mass or less, based on the total solid content of the blocked polyisocyanate composition, from the viewpoint of improving the storage stability of the aqueous coating composition. From these viewpoints, the content of the blocked polyisocyanate (a) may be 40% by mass to less than 99% by mass, 60 to 95% by mass, or 80 to 90% by mass, based on the total solid content of the blocked polyisocyanate composition. The total amount of solids in the block polyisocyanate composition means the amount obtained by excluding the amounts of the solvent and emulsification aid from the total amount of the block polyisocyanate composition when the block polyisocyanate composition contains a solvent, and means the amount obtained by excluding the amount of the emulsification aid from the total amount of the block polyisocyanate composition when the block polyisocyanate composition does not contain a solvent.

[0056] <Blocking agent dissociating catalyst (b)> The blocking agent dissociating catalyst (b) contains a quaternary ammonium salt (b1). As the quaternary ammonium salt (b1), any quaternary ammonium salt known as a blocking agent dissociating catalyst can be used without particular limitation, but from the viewpoint of easily obtaining an aqueous coating composition with excellent low-temperature curing properties, a quaternary ammonium salt containing a cation group represented by the following formula (1) may also be used.

[0057]

[0058] 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, or an aryl group having 6 to 16 carbon atoms; R ２ ~R ４ are each independently an alkyl group having 1 to 8 carbon atoms.

[0059] R １ The number of carbon atoms in the alkyl group represented by R may be 1 to 10, or may be 6 to 8. １ 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, a 2-ethylhexyl group, a 2-propylheptyl group, a nonyl group, a decyl group, an isodecyl group, a dodecyl group, and a hexadecyl group. These groups may be substituted with one or more hydroxy groups, one or more amino groups, or one or more alkoxy groups. 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.

[0060] Examples of the aryl group having 6 to 16 carbon atoms include a phenyl group, a naphthyl group, an anthryl group, a tolyl group, a xylyl group, a cumenyl group, a vinylphenyl group, a biphenylyl group, and a phenanthryl group.

[0061] R １ R may be an unsubstituted alkyl group or hydroxyalkyl group from the viewpoint of easily obtaining an aqueous coating composition with excellent low-temperature curing properties. １ When the alkyl group is an alkyl group having no substituent, it is easier to obtain an aqueous coating composition having even better low-temperature curing properties. Among the alkyl groups having no substituent, alkyl groups having 1 to 10 carbon atoms are preferred, alkyl groups having 6 to 8 carbon atoms are more preferred, alkyl groups having 8 carbon atoms are even more preferred, and an n-octyl group is particularly preferred.

[0062] R ２ ~R ４The number of carbon atoms in the alkyl group represented by R may be 1 to 4, or may be 1 to 2. ２ ~R ４ Specific examples of the alkyl group represented by R 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. ２ ~R ４ may all be methyl groups.

[0063] From the viewpoint of making it easier to obtain an aqueous coating composition having even better low-temperature curing properties, the quaternary ammonium salt (b1) may contain at least one compound selected from the group consisting of compounds represented by the following formula (2) and compounds represented by the following formula (3): In particular, when the quaternary ammonium salt (b1) contains a compound represented by formula (2), it is easier to obtain an aqueous coating composition having even better low-temperature curing properties.

[0064]

[0065]

[0066] The anionic group of the quaternary ammonium salt (b1) may be, for example, an organic acid group or an inorganic acid group. Examples of organic acid groups include fatty acid groups. Examples of inorganic acid groups include halogen groups (e.g., fluoro, chloro, bromo, etc.), hydrogen carbonate groups, and carbonate groups. The anionic group may be a group consisting of an anion derived from an ester such as a carbonate ester, or may be a group that does not fall into any of these categories (e.g., a hydroxyl group).

[0067] 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 the fatty acid group include a formic acid group, an acetic acid group, octylic acid, lauric acid, cyclohexanecarboxylic acid, and pivalic acid.

[0068] The number of carbon atoms in the monoalkyl carbonate group may be, for example, 1 to 8, 1 to 4, or 1 to 2. Specific examples of the monoalkyl carbonate group include a methyl carbonate group, an ethyl carbonate group, a propyl carbonate group, and a butyl carbonate group.

[0069] From the viewpoint of making it easier to obtain an aqueous coating composition with excellent low-temperature curing properties, the anionic group of the quaternary ammonium salt (b1) may contain at least one group selected from the group consisting of a fatty acid group having 1 to 12 carbon atoms, a monoalkyl carbonate group having 1 to 8 carbon atoms, and a hydroxyl group. Of these, it is preferable for the anionic group to contain at least one group selected from the group consisting of a fatty acid group having 1 to 7 carbon atoms and a monoalkyl carbonate group having 1 to 4 carbon atoms, and it is more preferable for the anionic group to contain a monoalkyl carbonate group having 1 to 2 carbon atoms.

[0070] From the above viewpoint, the quaternary ammonium salt (b1) may include a salt formed from a combination of a cationic group represented by any one of the above formulae (1) to (3) and a fatty acid group having 1 to 12 carbon atoms, a monoalkyl carbonate group having 1 to 8 carbon atoms, or a hydroxyl group.

[0071] Specific examples of the quaternary ammonium salt (b1) include trimethyl n-octylammonium hydrogen carbonate, trimethyl n-octylammonium monomethyl carbonate, trimethyl n-octylammonium carbonate, tetramethylammonium acetate, hexadecyltrimethylammonium hydroxide, trimethyl(2-hydroxypropyl)ammonium 2-ethylhexanoate, tetramethylammonium hydrogen carbonate, tetraethylammonium hydrogen carbonate, tetra n-propylammonium hydrogen carbonate, tetra n-butylammonium hydrogen carbonate, triethylmonomethylammonium hydrogen carbonate, tri n-propylmonomethylammonium hydrogen carbonate, tri n-butylmonomethylammonium hydrogen carbonate, tri n-butylmonoethylammonium hydrogen carbonate, 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. The quaternary ammonium salt (b1) may be used alone or in combination of two or more.

[0072] The blocked polyisocyanate composition may contain a blocking agent dissociation catalyst other than the quaternary ammonium salt (b1), and the proportion of the quaternary ammonium salt (b1) in the total blocking agent dissociation catalyst (b) may be 0.0001 to 100 mass%, 0.001 to 100 mass%, or 0.01 to 100 mass%.

[0073] The content of the blocking agent dissociating catalyst (b) may be 0.0001 parts by mass or more, 0.001 parts by mass or more, or 0.01 parts by mass or more, relative to 100 parts by mass of the blocked polyisocyanate (a), from the viewpoint of improving low-temperature curing properties. The content of the blocking agent dissociating catalyst (b) may be 40 parts by mass or less, 30 parts by mass or less, or 20 parts by mass or less, relative to 100 parts by mass of the blocked polyisocyanate (a), from the viewpoint of improving the storage stability of the coating material. From these viewpoints, the content of the blocking agent dissociating catalyst (b) may be 0.0001 to 40 parts by mass, 0.001 to 30 parts by mass, or 0.01 to 20 parts by mass, relative to 100 parts by mass of the blocked polyisocyanate (a).

[0074] <Emulsifier> The emulsifier (c) contains an alcohol (alcohol (c1)) having an octanol / water partition coefficient (hereinafter referred to as logPow) of 2.5 to 7.0. The logPow of the alcohol (c1) may be 3.0 or more, 6.0 or less, or may be 3.0 to 6.0, in order to achieve both coating film curability and pot life. In this embodiment, when the alcohol (c1) is a mixed alcohol containing two or more alcohols, the logPow of the alcohol (c1) can be a weighted average of the logPow of each alcohol constituting the mixed alcohol.

[0075] In this specification, log Pow is measured and calculated by the following method in accordance with the flask shaking method described in JIS Z7260-107. [Measurement of log Pow] 10 g of ion-exchanged water and 10 g of 1-octanol are placed in a 50 mL separatory funnel and equilibrated by shaking at 25°C. 1 g of emulsification aid is added thereto and, after thorough shaking, the 1-octanol phase and the water phase are separated by centrifugation. The amount of crosslinker dissolved in each phase is quantified by gas chromatography, and the value obtained by taking the common logarithm of the partition coefficient P between the two phases is taken as log Pow.

[0076] The alcohol (c1) as an emulsification aid aids the dispersibility of the blocked polyisocyanate (a) in water, thereby stabilizing the dispersed state of the blocked polyisocyanate (a) in water. From the viewpoint of enhancing the above effect, the alcohol (c1) may be a monohydric alcohol.

[0077] The alcohol (c1) may be any of a primary alcohol, a secondary alcohol, and a tertiary alcohol. Specific examples of primary alcohols include n-octanol, 2-ethyl-1-octanol, n-decanol, n-tridecanol, and 2-butyloctanol. Specific examples of secondary alcohols include menthol, 2-octanol, and 7-ethyl-2-methyl-4-undecanol. Specific examples of tertiary alcohols include adamantane alcohol.

[0078] The content of alcohol (c1) may be 5 parts by mass or more or 10 parts by mass or more, 60 parts by mass or less or 40 parts by mass or less, or 5 to 60 parts by mass or 10 to 40 parts by mass, per 100 parts by mass of blocked polyisocyanate (a). When the content is 5 parts by mass or more, the effect of supporting the dispersibility of blocked polyisocyanate (a) in water is even more excellent. Furthermore, when the content is 5 parts by mass or more, the effect of supporting the film-forming properties of the blocked polyisocyanate composition during film formation is even more excellent, and film formation proceeds more easily, resulting in a coating film with higher strength. Furthermore, when the content is 60 parts by mass or less, VOCs (volatile organic compounds) can be further suppressed.

[0079] The emulsification aid (c) may contain an emulsification aid other than the alcohol (c1). For example, the emulsification aid (c) may contain an alcohol other than the alcohol (c1). In this case, the weighted average value of the log Pow of each alcohol contained in the emulsification aid (c) (i.e., the log Pow of all the alcohols contained in the emulsification aid (c)) may be 2.5 or more or 3.0 or more, and may be 7.0 or less or 6.0 or less, or may be 2.5 to 7.0 or 3.0 to 6.0. The weighted average value of the log Pow of each alcohol contained in the blocked polyisocyanate composition (i.e., the log Pow of all the alcohols contained in the blocked polyisocyanate composition) may be within the above-mentioned range.

[0080] The amount of emulsifier other than the alcohol (c1) contained in the emulsifier (c) may be 5% by mass or less, 1% by mass or less, or 0% by mass based on the total mass of the emulsifier (c).

[0081] The content of the emulsification aid (c) may be 5 parts by mass or more or 10 parts by mass or more, 60 parts by mass or less or 40 parts by mass or less, or 5 to 60 parts by mass or 10 to 40 parts by mass, per 100 parts by mass of the blocked polyisocyanate (a). When the content is 5 parts by mass or more, the effect of supporting the dispersibility of the blocked polyisocyanate (a) in water is even more excellent. Furthermore, when the content is 5 parts by mass or more, the effect of supporting the film-forming properties of the blocked polyisocyanate composition during film formation is even more excellent, and film formation proceeds more easily, resulting in a coating film with higher strength. Furthermore, when the content is 60 parts by mass or less, VOCs (volatile organic compounds) can be further suppressed.

[0082] <Other Components> The blocked polyisocyanate composition may contain a solvent. As the solvent, a hydrophilic solvent is preferably used. Examples of the solvent include water, ethylene glycol, propylene glycol, 1,4-butanediol, methyl ethyl ketone, acetone, ethyl acetate, propylene glycol monomethyl ether acetate, diethylene glycol dimethyl ether, N-methylpyrrolidone, ethylene glycol monoethyl ether acetate, and diethylene glycol diethyl ether. These solvents may be used alone or in combination of two or more.

[0083] The content of the solvent 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 blocked polyisocyanate composition.

[0084] The blocked polyisocyanate composition may contain a polyisocyanate that does not have a blocked isocyanate group (e.g., a polyisocyanate component remaining as an unreacted product), or may contain an unreacted blocking agent. The content of the 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 the 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.

[0085] The blocked polyisocyanate composition may further contain additives such as pigments, dispersion stabilizers, viscosity modifiers, leveling agents, antigelling agents, light stabilizers, antioxidants, ultraviolet absorbers, heat resistance improvers, inorganic and organic fillers, plasticizers, lubricants, antistatic agents, reinforcing materials, and catalysts.

[0086] The effective isocyanate group content (hereinafter referred to as "effective NCO content") of the blocked polyisocyanate composition may be 4 to 10% by mass, 3 to 20% by mass, or 3 to 28% by mass or more, from the viewpoint of further enhancing the curability of the coating material. Here, the effective NCO content is 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 isocyanate, 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 isocyanate) with an excess of secondary amine, followed by back titration of the unreacted secondary amine with hydrochloric acid.

[0087] The blocked polyisocyanate composition described above can be obtained by mixing the blocked polyisocyanate (a), the blocking agent dissociation catalyst (b), the emulsification aid (c), and the other components that may be included. The blocked polyisocyanate composition can be used as a curing agent component of an aqueous paint composition. That is, another embodiment of the present disclosure is a curing agent for an aqueous paint that contains the blocked polyisocyanate composition.

[0088] <Aqueous Coating Composition> Another embodiment of the present disclosure is an aqueous coating composition comprising a compound having two or more isocyanate-reactive groups (hereinafter referred to as an "isocyanate-reactive compound"), the blocked polyisocyanate (a), the blocking agent dissociation catalyst (b) containing the quaternary ammonium salt (b1), the emulsification aid (c) containing the alcohol (c1), and water.

[0089] The details (including preferred embodiments) of the blocked polyisocyanate (a), blocking agent dissociation catalyst (b), and emulsification aid (c) in the aqueous coating composition are the same as the details of the blocked polyisocyanate (a), blocking agent dissociation catalyst (b), and emulsification aid (c) contained in the blocked polyisocyanate composition of the above embodiment.

[0090] The aqueous coating composition contains a blocked polyisocyanate (a), a quaternary ammonium salt (b1), and an alcohol (c1), and therefore has excellent low-temperature curing properties and storage stability.

[0091] The isocyanate-reactive compound has two or more isocyanate-reactive groups (e.g., active hydrogen groups). Examples of the isocyanate-reactive group include a hydroxy group and an amino group. Examples of the isocyanate-reactive compound include polyols, polyamines, and amino alcohols. Among these, the use of a polyol can enhance the effects of the present disclosure. Examples of polyols include acrylic polyols, polyester polyols, polyether polyols, epoxy polyols, polycarbonate polyols, and polylactone polyols. The hydroxyl value of the polyol may be, for example, 10 to 300 mg KOH / g per solid content.

[0092] The isocyanate-reactive compound may be used in a state of being emulsified, dispersed, or dissolved in water. In other words, the aqueous coating composition may contain an isocyanate-reactive compound-containing liquid (solution, dispersion, emulsion, or suspension) obtained by emulsifying, dispersing, or dissolving the isocyanate-reactive compound in water. The isocyanate-reactive compound-containing liquid may contain a neutralizing agent such as ammonia or a water-soluble amino compound (e.g., a tertiary amine such as triethylamine or 2-(dimethylamino)ethanol).

[0093] The equivalent ratio of the isocyanate-reactive groups to the available isocyanate groups contained in the aqueous coating composition ([isocyanate-reactive groups] / [available isocyanate groups]) is determined based on the required coating film properties and is not particularly limited. The equivalent ratio may be, for example, in the range of 0.2 to 2.

[0094] The aqueous coating composition may contain other components that can be contained in the above-mentioned blocked polyisocyanate composition.

[0095] The aqueous 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. The multi-component aqueous coating composition may comprise a first component (main component) containing an isocyanate-reactive compound and a second component (curing agent) containing the blocked polyisocyanate (a). In this case, the other constituent components (blocking agent dissociation catalyst and other components) may be contained in the first component, the second component, or a component different from the first and second components.

[0096] The aqueous 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.

[0097] (Paint Composition) Yet another embodiment of the present disclosure is a paint composition comprising a base agent and a curing agent, the paint composition comprising the above-mentioned blocked polyisocyanate composition. The blocked polyisocyanate composition may be contained in either the base agent or the curing agent. When the blocked polyisocyanate composition is contained in the curing agent, the base agent contains an isocyanate-reactive compound. In this case, the curing agent may be the above-mentioned blocked polyisocyanate composition, or may further contain other polyisocyanate components. Details of the isocyanate-reactive compound and the equivalent ratio of isocyanate-reactive groups to available isocyanate groups contained in the paint composition are the same as those in the above-mentioned <Aqueous Paint Composition>.

[0098] The coating composition of this embodiment may be an aqueous coating composition containing water.

[0099] The coating composition may be a one-component composition in which all of the components are contained in one liquid, or a multi-component composition in which the components are present in multiple liquids. That is, the base agent and the curing agent may be present separately, or may be mixed in one liquid. A multi-component aqueous coating composition may contain agents other than the base agent and the curing agent.

[0100] <Coating Film> Another embodiment of the present disclosure is a coating film formed from the aqueous coating composition of the above embodiment.

[0101] The coating film includes, for example, a cured product of the aqueous coating composition of the above embodiment. The coating film can be formed by applying the above aqueous coating composition to a substrate by a known method and curing the coating film (uncured coating film) made of the aqueous coating composition. Known methods include, for example, roll coating, curtain flow coating, spray coating, electrostatic coating, bell coating, and electrodeposition coating. The amount of the aqueous coating composition applied, the thickness of the coating film, and the like may be appropriately determined depending on the material of the surface to be coated, etc.

[0102] The coating film made of the aqueous coating composition may be cured by heating the coating film. The heating temperature (baking temperature) may be, for example, 200°C or lower, and the heating time (baking time) may be, for example, 10 to 180 minutes. With the aqueous coating composition of this embodiment, a good cured coating film can be obtained even when baking is performed at a low temperature of 100°C or lower.

[0103] 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.

[0104] Example 1 (Production of Blocked Polyisocyanate Composition) A four-necked flask equipped with a stirrer, a thermometer, a heating device, a nitrogen seal tube, and a cooling tube was charged with 362 g of Coronate 2793 (manufactured by Tosoh Corporation, hexamethylene diisocyanate trimer, NCO content 14.3% by mass, trade name, "C2793" in Table 1), 40 g of MPEG-1000 (manufactured by Nippon Nyukazai Co., Ltd., polyethylene glycol monomethyl ether, number average molecular weight = 1000, trade name), and 231 g of diethyl diglycol (manufactured by Nippon Nyukazai Co., Ltd., diethylene glycol diethyl ether, trade name, "DEDG" in Table 1), and the atmosphere in the flask was replaced with nitrogen. The mixture was heated to 80°C with stirring and reacted at the same temperature for 4 hours to obtain an isocyanate group-terminated precursor having an alkoxypolyethylene oxide group as the hydrophilic group. Subsequently, 120 g of methyl ethyl ketoxime (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., "MEKO" in Table 1) was added so that the temperature did not exceed 80°C, and the mixture was reacted at 70°C for 2 hours. In the infrared absorption spectrum (IR measurement), the peak of the NCO group (2270 cm －１ When the solids concentration (around 100%) disappeared, the mixture was cooled to room temperature, and 143 g of trimethyl-n-octylammonium monomethyl carbonate solution (manufactured by Tosoh Corporation, solids concentration 55% by mass, “TMOA-MC” in Table 1) and 104 g of 2-ethyl-1-octanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., log Pow: 2.7, “A-1” in Table 1) were added and stirred for 30 minutes to obtain a composition containing a blocked polyisocyanate (blocked polyisocyanate composition (BI-1)).

[0105] Example 2 A blocked polyisocyanate composition (BI-2) was obtained in the same manner as in Example 1, except that 2-octanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., log Pow: 2.7, “A-2” in Table 1) was used instead of 2-ethyl-1-octanol.

[0106] Example 3 A blocked polyisocyanate composition (BI-3) was obtained in the same manner as in Example 1, except that octanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., log Pow: 3.0, “A-3” in Table 1) was used instead of 2-ethyl-1-octanol.

[0107] Example 4 A blocked polyisocyanate composition (BI-4) was obtained in the same manner as in Example 1, except that 2-butyl-1-octanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., log Pow: 5.5, “A-4” in Table 1) was used instead of 2-ethyl-1-octanol.

[0108] Example 5 A blocked polyisocyanate composition (BI-5) was obtained in the same manner as in Example 1, except that tridecanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., log Pow: 5.6, “A-5” in Table 1) was used instead of 2-ethyl-1-octanol.

[0109] Example 6 A blocked polyisocyanate composition (BI-6) was obtained in the same manner as in Example 1, except that 7-ethyl-2-methyl-4-undecanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., log Pow: 5.8, “A-6” in Table 1) was used instead of 2-ethyl-1-octanol.

[0110] Example 7 A blocked polyisocyanate composition (BI-7) was obtained in the same manner as in Example 1, except that diisopropyl malonate (manufactured by Tokyo Chemical Industry Co., Ltd., “DIPM” in Table 1) was used instead of methyl ethyl ketoxime and the blending amounts of the materials were changed to the amounts shown in Table 1.

[0111] Example 8 A blocked polyisocyanate composition (BI-8) was obtained in the same manner as in Example 7, except that tridecanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., log Pow: 5.6, “A-5” in Table 1) was used instead of 2-ethyl-1-octanol.

[0112] Example 9 A blocked polyisocyanate composition (BI-9) was obtained in the same manner as in Example 1, except that diethyl malonate (manufactured by Tokyo Chemical Industry Co., Ltd., "DEM" in Table 1) was used instead of methyl ethyl ketoxime and the blending amounts of the materials were changed to those shown in Table 1.

[0113] Example 10 A blocked polyisocyanate composition (BI-10) was obtained in the same manner as in Example 9, except that tridecanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., log Pow: 5.6, “A-5” in Table 1) was used instead of 2-ethyl-1-octanol.

[0114] Example 11 A blocked polyisocyanate composition (BI-11) was obtained in the same manner as in Example 1, except that 3,5-dimethylpyrazole (manufactured by Tokyo Chemical Industry Co., Ltd., “DMP” in Table 1) was used instead of methyl ethyl ketoxime and the blending amounts of the materials were changed to the amounts shown in Table 1.

[0115] Example 12 A blocked polyisocyanate composition (BI-12) was obtained in the same manner as in Example 11, except that tridecanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., log Pow: 5.6, “A-5” in Table 1) was used instead of 2-ethyl-1-octanol.

[0116] Comparative Example 1 A blocked polyisocyanate composition (BI-13) was obtained in the same manner as in Example 1, except that the blending amounts of the materials (emulsification aid (c) and solvent) were changed to the amounts shown in Table 1.

[0117] Comparative Example 2 A blocked polyisocyanate composition (BI-14) was obtained in the same manner as in Example 1, except that butanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., log Pow: 0.9, “A-7” in Table 2) was used instead of 2-ethyl-1-octanol.

[0118] Comparative Example 3 A blocked polyisocyanate composition (BI-15) was obtained in the same manner as in Example 1, except that hexanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., log Pow: 1.9, "A-8" in Table 2) was used instead of 2-ethyl-1-octanol.

[0119] Comparative Example 4 A blocked polyisocyanate composition (BI-16) was obtained in the same manner as in Example 1, except that oleyl alcohol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., log Pow: 7.6, "A-9" in Table 2) was used instead of 2-ethyl-1-octanol.

[0120] Comparative Example 5 A blocked polyisocyanate composition (BI-17) was obtained in the same manner as in Example 1, except that octodecanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., log Pow: 8.0, "A-10" in Table 2) was used instead of 2-ethyl-1-octanol.

[0121] Comparative Example 6 A blocked polyisocyanate composition (BI-18) was obtained in the same manner as in Example 7, except that the blending amounts of the materials (emulsification aid (c) and solvent) were changed to the amounts shown in Table 1.

[0122] Comparative Example 7 A blocked polyisocyanate composition (BI-19) was obtained in the same manner as in Example 7, except that butanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., log Pow: 0.9, "A-7" in Table 2) was used instead of 2-ethyl-1-octanol.

[0123] Comparative Example 8 A blocked polyisocyanate composition (BI-20) was obtained in the same manner as in Example 7, except that octodecanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., log Pow: 8.0, "A-10" in Table 2) was used instead of 2-ethyl-1-octanol.

[0124]

[0125]

[0126] The hydrophilic group content in Tables 1 and 2 is the content of hydrophilic groups (alkoxypolyethylene oxide groups) in the isocyanate group-terminated precursor, and is equal to the content of alkoxypolyethylene oxide groups, based on the total amount of isocyanate compounds, in the isocyanate composition obtained by dissociating the blocking agent from the blocked polyisocyanate in the blocked polyisocyanate composition.

[0127] The effective NCO content in Tables 1 and 2 is the content of effective isocyanate groups in the blocked polyisocyanate composition, and was determined by adding an excess amount of secondary amine relative to the isocyanate groups to the blocked polyisocyanate composition, heating the composition at a temperature equal to or higher than the dissociation temperature of the oxime-based blocking agent (e.g., 160°C) for a time period sufficient for the blocking agent to dissociate (e.g., 1 hour), and allowing the free isocyanate groups to react with the secondary amine, followed by back-titrating the unreacted secondary amine with hydrochloric acid.

[0128] The amount of emulsifying aid in Tables 1 and 2 is the content of the emulsifying aid relative to 100 parts by mass of the blocked polyisocyanate.

[0129] <Evaluation> (Preparation of Aqueous Coating Compositions) The blocked polyisocyanate compositions of Examples 1 to 12 and Comparative Examples 1 to 8 were used to prepare aqueous coating compositions of Examples 1 to 12 and Comparative Examples 1 to 8, respectively. Specifically, the aqueous coating compositions were prepared by mixing the main agent, Burnock WE-306 (manufactured by DIC Corporation, acrylic emulsion, solids concentration 45% by mass, hydroxyl value 45 mgKOH / g, trade name), the curing agent, the blocked polyisocyanate composition, and water, and stirring the mixture at high speed for 2 minutes at 2000 rpm using a homomixer. The amounts (units: g) of the main agent (Burnoc WE-306), curing agent (blocked polyisocyanate composition), and water used were as shown in Tables 3 and 4. The blend amount of the main agent shown in Tables 3 and 4 is the total mass including the solvent.

[0130] (Low-temperature curing evaluation) [Gel fraction measurement] The aqueous coating 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 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 Tables 3 and 4. Gel fraction (unit: mass %) = mass of coating film after immersion (mass of undissolved portion) / mass of coating film before immersion × 100

[0131] When the gel fraction measured above was 60% by mass or more, the composition was evaluated as having excellent low-temperature curing properties.

[0132] (Evaluation of storage stability) The aqueous coating composition was allowed to stand at 40°C, and the dispersion state before and after standing was visually observed to evaluate storage stability. The storage stability was evaluated based on the number of days after standing that the composition remained liquid and no precipitation occurred.

[0133]

[0134]

Claims

1. A blocked polyisocyanate composition comprising a blocked polyisocyanate, a blocking agent dissociation catalyst, and an emulsification aid, wherein the blocked polyisocyanate has a hydrophilic group, the blocking agent dissociation catalyst contains a quaternary ammonium salt, and the emulsification aid contains an alcohol having an octanol / water partition coefficient of 2.5 to 7.

0.

2. The blocked polyisocyanate composition according to claim 1, wherein the blocked polyisocyanate has at least one group selected from the group consisting of an isocyanate group blocked with an oxime compound and an isocyanate group blocked with an active methylene compound.

3. The blocked polyisocyanate composition according to claim 1, 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.

4. The blocked polyisocyanate composition according to claim 1, wherein the hydrophilic group comprises a group derived from a nonionic hydrophilic compound having a number average molecular weight of 600 to 2,000.

5. The blocked polyisocyanate composition according to claim 1, wherein the content of the hydrophilic group is 5 to 30 parts by mass per 100 parts by mass of the blocked polyisocyanate.

6. The blocked polyisocyanate composition according to claim 1, wherein the quaternary ammonium salt contains a cationic group 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, or an aryl group having 6 to 16 carbon atoms; R ２ ~R ４ each independently represents an alkyl group having 1 to 8 carbon atoms.

7. The blocked polyisocyanate composition of claim 1, wherein the alcohol comprises a monohydric alcohol.

8. A coating composition comprising a base agent and a curing agent, the coating composition comprising the blocked polyisocyanate composition according to any one of claims 1 to 7.

9. A curing agent for aqueous paints, comprising the blocked polyisocyanate composition according to any one of claims 1 to 7.

10. An aqueous coating composition comprising a compound having two or more isocyanate-reactive groups, a blocked polyisocyanate, a blocking agent dissociation catalyst, an emulsification aid, and water, wherein the blocked polyisocyanate has a hydrophilic group, the blocking agent dissociation catalyst contains a quaternary ammonium salt, and the emulsification aid contains an alcohol having an octanol / water partition coefficient of 2.5 to 7.

0.

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

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