Polyurethane water-based dispersion and water-based paint

Abstract

Improves the adhesion and UV resistance of coating films to resins. [Solution] The polyurethane aqueous dispersion according to the embodiment is prepared by dispersing a polyurethane resin (A) containing a polyester polyol as a constituent in an aqueous dispersion medium, and contains a carbodiimide group-containing compound (B) and a compound (C) having a group represented by the following general formula (1). The polyurethane resin (A) has a carboxy group, and the acid value of the polyurethane resin (A) is 5 to 25 mgKOH / g. In formula (1), R 1 and R 2 each independently represents a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, and * represents a bond. [Formula 1] JPEG0007629139000010.jpg23156

Description

[Technical field]

[0001] An embodiment of the present invention relates to a polyurethane water-based dispersion and a water-based coating material containing the same. [Background technology]

[0002] Aqueous polyurethane dispersions obtained by dispersing a polyurethane resin in an aqueous dispersion medium are widely used in paints, inks, adhesives, etc. For example, Patent Documents 1 and 2 disclose blending a crosslinking agent having a functional group that reacts with an acidic group and / or a hydroxyl group with an aqueous ink containing an aqueous polyester-based urethane resin, and list as the crosslinking agent hydrazide compounds, carbodiimide compounds, oxazoline compounds, epoxy compounds, isocyanate compounds, and aziridine compounds. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2023-146694 A [Patent Document 2] JP 2021-147428 A Summary of the Invention [Problem to be solved by the invention]

[0004] When the polyurethane aqueous dispersion is used as a coating material to be applied to the surface of a resin such as polyester resin, the coating film is required to have good adhesion (adhesion) to the resin to be coated. When the polyurethane aqueous dispersion is used as a primer, the coating film is required to have adhesion to the resin substrate as well as adhesion to the topcoat layer applied via the primer. Thus, the polyurethane aqueous dispersion is required to have adhesion to the resin.

[0005] According to the present inventor's research, it was found that the adhesion of the coating film to the resin can be improved by setting the acid value of the polyurethane resin to a low level and blending a carbodiimide group-containing compound. However, when the coating film is irradiated with ultraviolet (UV) rays and then coated with a topcoat layer to form a three-layer structure, for example, when the coating film is used as a primer, it was found that the coating film has poor adhesion, i.e., poor UV-resistant adhesion.

[0006] In addition, the above Patent Documents 1 and 2 specifically disclose that a carbodiimide compound or a hydrazide compound is blended with a polyurethane resin having a relatively high acid value, but do not disclose the use of a carbodiimide compound and a hydrazide compound in combination with a polyester-based urethane resin having a relatively low acid value, or that this improves UV-resistant adhesion.

[0007] An object of the present invention is to provide an aqueous polyurethane dispersion capable of improving the adhesion and UV-resistant adhesion of a coating film to a resin, and an aqueous coating material using the same. [Means for solving the problem]

[0008] The present invention includes the embodiments set forth below. [1] A polyurethane aqueous dispersion in which a polyurethane resin (A) containing a polyester polyol as a constituent component is dispersed in an aqueous dispersion medium, The polyurethane aqueous dispersion contains a carbodiimide group-containing compound (B) and a compound (C) having a group represented by the following general formula (1), [ka] In general formula (1), R 1 and R 2 each independently represents a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, * represents a bond, The polyurethane resin (A) has a carboxy group, and the acid value of the polyurethane resin (A) is 5 to 25 mgKOH / g. Polyurethane water-based dispersion.

[0009] [2] The aqueous polyurethane dispersion according to [1], wherein the compound (C) has two groups represented by the general formula (1) in one molecule. [3] R in the general formula (1) 1 and R 2 The aqueous polyurethane dispersion according to [1] or [2], wherein at least one of the following represents a hydrocarbon group having 1 to 3 carbon atoms: [4] The aqueous polyurethane dispersion according to any one of [1] to [3], wherein the polyester polyol contains an aromatic polyester polyol. [5] The aqueous polyurethane dispersion according to any one of [1] to [4], wherein the carbodiimide group-containing compound (B) contains 100 to 350 moles of carbodiimide groups per 100 moles of carboxy groups in the polyurethane resin (A). [6] The polyurethane aqueous dispersion according to any one of [1] to [5], wherein the content of the compound (C) is 0.1 to 20 parts by mass per 100 parts by mass of the polyurethane resin (A). [7] An aqueous paint comprising the aqueous polyurethane dispersion according to any one of [1] to [6]. [8] The water-based paint according to [7], which is used as a primer. Effect of the Invention

[0010] According to an embodiment of the present invention, the adhesion and UV resistance of a coating film to a resin can be improved. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The polyurethane aqueous dispersion according to this embodiment (hereinafter, simply referred to as an aqueous dispersion) contains a polyurethane resin (A), a carbodiimide group-containing compound (B), a compound (C) having a group represented by general formula (1), and an aqueous dispersion medium (D).

[0012] [Polyurethane resin (A)] The polyurethane resin (A) is obtained by reacting a polyol with a polyisocyanate, and is a polymer having a urethane bond in the molecule. In this embodiment, a polyurethane resin (A) containing a polyester polyol as a constituent component is used. This can improve adhesion to a polyester resin substrate. In this specification, "containing as a constituent component" means that the polyurethane resin (A) is used as a raw material (monomer) for synthesizing the polyurethane resin (A), and the polyurethane resin (A) has a structure derived from the polyester polyol.

[0013] The polyester polyol is a polyol having a plurality of ester bonds (-COO-) in the molecule, and is preferably one obtained by a condensation reaction between a polyvalent carboxylic acid and a polyvalent hydroxyl group-containing compound.

[0014] As the polyvalent carboxylic acid, dicarboxylic acids are preferable, and examples thereof include aromatic dicarboxylic acids such as phthalic acid, terephthalic acid, isophthalic acid, and naphthalenedicarboxylic acid, and aliphatic dicarboxylic acids such as adipic acid, succinic acid, sebacic acid, azelaic acid, maleic acid, and fumaric acid. Any of these may be used alone or in combination of two or more.

[0015] The polyvalent hydroxy group-containing compound is preferably a diol, and examples thereof include aliphatic diols such as ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, and 1,6-hexanediol, and aromatic diols such as bisphenols such as bisphenol A and bisphenol F, and alkylene oxide adducts thereof. Any of these may be used alone or in combination of two or more.

[0016] The polyester polyol is preferably an aromatic polyester polyol. That is, in a preferred embodiment, the polyester polyol includes an aromatic polyester polyol. By using an aromatic polyester polyol, the water-resistant adhesion of the coating film to the resin can be improved. The aromatic polyester polyol is a polyester polyol having an aromatic ring in the molecule, and it is sufficient that at least one of the polyvalent carboxylic acid and the polyvalent hydroxyl group-containing compound contains an aromatic ring. The amount of the aromatic polyester polyol relative to 100% by mass of the polyester polyol is preferably 50% by mass or more, more preferably 70% by mass or more, more preferably 90% by mass or more, and even more preferably 100% by mass.

[0017] The molecular weight of the polyester polyol is not particularly limited, and may be, for example, a number average molecular weight (Mn) of 500-5,000, 800-4,000, or 1,000-3,000.

[0018] In this specification, the number average molecular weight (Mn) is a value measured by GPC (gel permeation chromatography) and calculated using a calibration curve of standard polystyrene. In detail, the GPC conditions are as follows: column: "TSKgel G4000HXL+TSKgel G3000HXL+TSKgel G2000HXL+TSKgel G1000HXL+TSKgel G1000HXL" manufactured by Tosoh Corporation, mobile phase: THF (tetrahydrofuran), mobile phase flow rate: 1.0 mL / min, column temperature: 40°C, sample injection amount: 50 μL, sample concentration: 0.2 mass%.

[0019] The amount of polyester polyol in the polyol constituting the polyurethane resin (A) is not particularly limited, but for example, it is preferably 60 to 99 mass% relative to 100 mass% of the polyol, more preferably 70 to 97 mass%, more preferably 75 to 95 mass%, and even more preferably 80 to 90 mass%.

[0020] In this specification, when the amount of each component constituting the polyol is based on 100% by mass of the polyol, the carboxyl group is calculated as an acid type when the polyol contains a carboxyl group-containing polyol described later. The amount of the carboxyl group-containing polyol is also calculated as an acid type.

[0021] In this embodiment, the polyurethane resin (A) has a carboxy group, which can react with the carbodiimide group-containing compound (B) to form a crosslinked structure when the aqueous dispersion is dried by heating. In this specification, unless otherwise specified, the carboxy group is a concept that includes not only the acid type (-COOH) but also the salt type, i.e., the carboxyl group (-COOX, where X is a cation that forms a salt with a carboxylic acid), and the acid type and the salt type may be mixed.

[0022] Examples of the salt of the carboxylate group include alkali metal salts such as sodium salts and potassium salts, alkaline earth metal salts such as magnesium salts and calcium salts, ammonium salts, amine salts (primary amine salts, secondary amine salts, tertiary amine salts), and quaternary ammonium salts. Among these, salts of volatile bases such as ammonium salts and amine salts are preferred. If the base is a volatile base, the carboxyl group is easily converted to an acid form by vaporization during heating and drying of the aqueous dispersion, and the reactivity with the carbodiimide group-containing compound (B) can be improved, thereby enhancing the effect of improving the adhesion of the coating film to the resin.

[0023] In this embodiment, the polyurethane resin (A) has an acid value of 5 to 25 mgKOH / g. When the acid value is 5 mgKOH / g or more, the polyurethane resin (A) can be easily emulsified in an aqueous dispersion medium. When the acid value is 25 mgKOH / g or less, the adhesion of the coating film to the resin can be improved. The acid value of the polyurethane resin (A) is more preferably 7 to 20 mgKOH / g, and further preferably 10 to 15 mgKOH / g.

[0024] In this specification, the acid value can be calculated based on the amount of KOH (mg) required to neutralize the carboxyl group contained in 1 g of polyurethane resin (A) according to JIS K0070-1992. When polyurethane resin (A) is a salt of a volatile base, the volatile base vaporizes when the mass of polyurethane resin (A) is measured, so the acid value is a value calculated based on the mass of the acid type polyurethane resin, which is a non-volatile content. Thus, the mass of polyurethane resin (A) in this specification is the mass of the non-volatile content.

[0025] In order to introduce a carboxy group into the polyurethane resin (A), it is preferable to use a carboxy group-containing polyol together with a polyester polyol as the polyol used to synthesize the polyurethane resin (A). That is, it is preferable that the polyurethane resin (A) contains a carboxy group-containing polyol as a constituent component.

[0026] Examples of the carboxyl group-containing polyol include carboxylic acid-containing compounds such as dimethylolpropionic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolvaleric acid, dihydroxymaleic acid, 2,6-dihydroxybenzoic acid, and tartaric acid, as well as derivatives and salts thereof. Any of these may be used alone or in combination of two or more.

[0027] The amount of the carboxyl group-containing polyol in the polyol is not particularly limited, and may be, for example, 0.5 to 15 mass %, 1 to 10 mass %, 2 to 8 mass %, or 3 to 6 mass % relative to 100 mass % of the polyol.

[0028] The polyol used to synthesize the polyurethane resin (A) may further include polyalkylene glycol. That is, the polyurethane resin (A) preferably further includes polyalkylene glycol as a constituent. By including polyalkylene glycol, for example, when the polyurethane aqueous dispersion is used as a primer and the resin constituting the topcoat layer includes polyalkylene glycol as a constituent, the adhesion to the topcoat layer can be improved.

[0029] Examples of polyalkylene glycols include polyethylene glycol, polytrimethylene glycol, polypropylene glycol, polytetramethylene glycol, polybutylene glycol, and copolymers using two or more of these constituent monomers. The molecular weight of the polyalkylene glycol is not particularly limited, and may be, for example, a number average molecular weight (Mn) of 500 to 5,000, 800 to 4,000, or 1,000 to 3,000.

[0030] The amount of polyalkylene glycol in the polyurethane resin (A) (i.e., the amount of structures derived from polyalkylene glycol) is preferably 5 to 15 parts by mass, more preferably 7 to 13 parts by mass, and even more preferably 8 to 10 parts by mass, relative to 100 parts by mass of the polyurethane resin (A). The amount of polyalkylene glycol in the polyol is not particularly limited, and may be, for example, 3 to 25% by mass, 5 to 20% by mass, or 10 to 15% by mass, relative to 100% by mass of the polyol.

[0031] The polyol used to synthesize the polyurethane resin (A) may be a polyol having three or more functional groups. Preferred examples of the polyol having three or more functional groups include low molecular weight polyhydric alcohols (preferably trihydric alcohols) such as trimethylolpropane, glycerin, and pentaerythritol. The amount of such tri- or higher functional polyols is not particularly limited, and may be, for example, 0.1 to 5 mass%, 0.2 to 3 mass%, or 0.3 to 1 mass% relative to 100 mass% of the polyol.

[0032] The polyol used to synthesize the polyurethane resin (A) may include polyols other than those mentioned above. Examples of such other polyols include polymer polyols such as polycarbonate polyols, polyether polyols other than polyalkylene glycols, and polybutadiene polyols. Examples of other polyols include low molecular weight diols such as ethylene glycol, propylene glycol, propanediol, butanediol, pentanediol, 3-methyl-1,5-pentanediol, hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, bisphenol A, bisphenol F, bisphenol S, and hydrogenated bisphenol A. These other polyols may be used alone or in combination of two or more.

[0033] The amount of polyol constituting the polyurethane resin (A) (i.e., the amount of structures derived from polyol) is not particularly limited, and may be, for example, 70 to 90 parts by mass or 75 to 85 parts by mass per 100 parts by mass of the polyurethane resin (A).

[0034] Examples of the polyisocyanate used to synthesize the polyurethane resin (A) include aromatic polyisocyanates, araliphatic polyisocyanates, aliphatic polyisocyanates, and alicyclic polyisocyanates.

[0035] Examples of aromatic polyisocyanates include diphenylmethane diisocyanate (MDI), polymeric MDI, tolylene diisocyanate (TDI), naphthalene diisocyanate, and modified products thereof such as isocyanurates, adducts, biurets, allophenates, and carbodiimides.

[0036] Examples of aromatic aliphatic polyisocyanates include xylylene diisocyanate (XDI), ω,ω'-diisocyanato-1,4-diethylbenzene, 1,3- or 1,4-bis(1-isocyanato-1-methylethyl)benzene, and modified forms thereof such as isocyanurates, adducts, biurets, allophenates, and carbodiimides.

[0037] Examples of aliphatic polyisocyanates include tetramethylene diisocyanate, dodecamethylene diisocyanate, hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, and modified versions thereof, such as isocyanurates, adducts, biurets, allophenates, and carbodiimides.

[0038] Examples of alicyclic polyisocyanates include isophorone diisocyanate (IPDI), dicyclohexylmethane 4,4'-diisocyanate (hydrogenated MDI), hydrogenated xylylene diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexylene diisocyanate, 1,3-bis(isocyanatemethyl)cyclohexane, and modified products thereof such as isocyanurates, adducts, biurets, allophenates, and carbodiimides.

[0039] These polyisocyanates may be used alone or in combination of two or more.

[0040] As the polyisocyanate, among the above, it is preferable to use an aromatic ring-containing polyisocyanate such as an aromatic polyisocyanate or an aromatic aliphatic polyisocyanate, and more preferably to use an aromatic aliphatic polyisocyanate. The amount of the aromatic ring-containing polyisocyanate relative to 100% by mass of the polyisocyanate is not particularly limited, and may be, for example, 50% by mass or more, 70% by mass or more, 90% by mass or more, or 100% by mass.

[0041] The amount of polyisocyanate constituting the polyurethane resin (A) (i.e., the amount of structures derived from polyisocyanate) is not particularly limited, and may be, for example, 10 to 30 parts by mass or 15 to 25 parts by mass per 100 parts by mass of the polyurethane resin (A).

[0042] In one embodiment, the polyurethane resin (A) includes the following (A1) and (A2). (A1) An anionic polyurethane resin obtained by reacting a polyol containing a polyester polyol and a carboxyl group-containing polyol with a polyisocyanate to synthesize an isocyanate group-containing urethane prepolymer, and then extending the chain of the urethane prepolymer with a chain extender. (A2) A hydroxyl group-containing anionic polyurethane resin obtained by reacting a polyol including a polyester polyol and a carboxyl group-containing polyol with a polyisocyanate.

[0043] [Carbodiimide group-containing compound (B)] The carbodiimide group-containing compound (B) is a compound that contains a carbodiimide group (-N=C=N-) in the molecule, and reacts with the carboxy group of the polyurethane resin (A).

[0044] The carbodiimide group-containing compound (B) may be a carbodiimide group-containing compound used as an aqueous crosslinking agent. Preferably, it is a polycarbodiimide, which is a polymer having a carbodiimide group in the molecule, and more preferably, it is an aqueous polycarbodiimide in which a hydrophilic segment is introduced into a polycarbodiimide having a plurality of carbodiimide groups in the molecule. Examples of such aqueous polycarbodiimides include water-soluble types such as "Carbodilite V-02", "Carbodilite V-02-L2", "Carbodilite SV-02", "Carbodilite V-04", and "Carbodilite V-10", and emulsion / dispersion types such as "Carbodilite E-02" and "Carbodilite E-05" (all manufactured by Nisshinbo Chemical Co., Ltd.).

[0045] The NCN equivalent of the carbodiimide group-containing compound is not particularly limited, and may be, for example, from 300 to 600, or from 350 to 500. Here, the NCN equivalent represents the chemical formula weight per 1 mole of the carbodiimide group.

[0046] [Compound (C)] Compound (C) is a compound containing a group represented by the following general formula (1) in the molecule, i.e., a hydrazide group, and is therefore referred to as hydrazide group-containing compound (C) below. Here, the concept of the hydrazide group includes the atomic group constituting the semicarbazide group in which -NH- is bonded to the bond in formula (1). [ka]

[0047] In formula (1), R 1 and R 2 each independently represents a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, and * represents a bond. R 1 and R 2 At least one of R is preferably a hydrocarbon group having 1 to 3 carbon atoms, and more preferably R 1 and R 2 Both of these are hydrocarbon groups having 1 to 3 carbon atoms.

[0048] The hydrocarbon group having 1 to 3 carbon atoms may be saturated or unsaturated, and may be linear or branched, and is preferably an alkyl group, that is, a methyl group, an ethyl group, or a propyl group, and more preferably a methyl group.

[0049] The hydrazide group-containing compound (C) is preferably a compound having two groups represented by formula (1) in one molecule. In that case, two R 1 may be the same or different, and two R 2 may be the same or different. For example, a compound represented by the following general formula (2) is an example of the hydrazide group-containing compound (C). [ka]

[0050] In formula (2), R 1 and R 2 is R in formula (1). 1 and R 2 Similarly, each independently represents a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, and R 1 and R 2 may be the same or different. 3 represents a divalent organic group having 1 to 12 carbon atoms, preferably 2 to 10 carbon atoms, and more preferably 3 to 8 carbon atoms.

[0051] In one embodiment, the hydrazide group-containing compound (C) has two groups represented by formula (1) in one molecule, and R 1 and R 2 It is preferable that the compound (C1) contains at least one of the hydrazide group-containing compounds (C) in a total amount of 100% by mass of the hydrazide group-containing compound (C), and the amount of the compound (C1) is not particularly limited, but is preferably 50% by mass or more, more preferably 70% by mass or more, and may be 100% by mass.

[0052] In one embodiment, the hydrazide group-containing compound (C) preferably contains a compound having two semicarbazide groups in one molecule, specifically, a disemicarbazide compound (C2) represented by the following general formula (3). In this case, the amount of the disemicarbazide compound (C2) in 100% by mass of the hydrazide group-containing compound (C) is not particularly limited, but is preferably 50% by mass or more, more preferably 70% by mass or more, and may be 100% by mass. [ka]

[0053] In formula (3), R 1 and R 2 is R in formula (1). 1 and R 2 Similarly, each independently represents a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, and R1 and R 2 may be the same or different. 1 and R 2 At least one of R is preferably a hydrocarbon group having 1 to 3 carbon atoms, and more preferably R 1 and R 2 Both of these are hydrocarbon groups having a carbon number of 1 to 3. m represents an integer of 1 to 12, preferably an integer of 2 to 10, and more preferably an integer of 3 to 8.

[0054] Specific examples of the hydrazide group-containing compound (C) include 1,6-hexamethylenebis(N,N-dimethylsemicarbazide), adipic acid dihydrazide, sebacic acid dihydrazide, dodecanediohydrazide, etc. These may be used alone or in combination of two or more.

[0055] [Aqueous dispersion medium (D)] The aqueous dispersion medium (D) is a dispersion medium containing water, and may be water or a mixed medium of water and a hydrophilic organic solvent. From the viewpoint of dispersion stability of the aqueous dispersion, the aqueous dispersion medium (D) is preferably water, and an organic solvent may be contained, but preferably in a small amount. In one embodiment, the aqueous dispersion medium (D) preferably contains 70% by mass or more of water, more preferably contains 80% by mass or more of water, more preferably contains 90% by mass or more of water, and may be 100% by mass of water. That is, in the aqueous dispersion medium (D), the mass ratio of water / hydrophilic organic solvent is preferably 70 / 30 to 100 / 0, more preferably 80 / 20 to 100 / 0, and further preferably 90 / 10 to 100 / 0.

[0056] As the hydrophilic organic solvent, various organic solvents that dissolve in water can be used, and examples thereof include lower monohydric alcohols such as methanol, ethanol, and propanol, polyhydric alcohols such as ethylene glycol and glycerin, and aprotic polar solvents such as N-methylpyrrolidone, dimethyl sulfoxide, dimethylformamide, and acetonitrile.

[0057] [Polyurethane water-based dispersion] The polyurethane aqueous dispersion is an aqueous dispersion in which a polyurethane resin (A) is dispersed in an aqueous dispersion medium (D), and contains a carbodiimide group-containing compound (B) and a hydrazide group-containing compound (C). By blending the carbodiimide group-containing compound (B) in the aqueous dispersion of the polyurethane resin (A), the adhesion of the coating film to the resin can be improved. In addition, by blending the hydrazide group-containing compound (C), the UV adhesion can be improved.

[0058] The content of the carbodiimide group-containing compound (B) in the polyurethane aqueous dispersion is preferably set as follows: The aqueous dispersion preferably contains 100 to 350 moles of carbodiimide groups of the carbodiimide group-containing compound (B) per 100 moles of carboxy groups of the polyurethane resin (A).

[0059] As described above, by setting the acid value of the polyurethane resin (A) relatively small and the number of moles of the carbodiimide group to be equal to or greater than the number of moles of the carboxyl group, the carbodiimide group is likely to remain in the coating film after curing. The remaining carbodiimide group can enhance the effect of improving the adhesion of the coating film to the resin, particularly the effect of improving the adhesion to the topcoat layer. It is considered that the remaining carbodiimide group contributes to the adhesion to the acrylate resin contained in the topcoat layer, but this is not limited thereto. In addition, by having the carbodiimide group of 350 moles or less, the effect of improving the adhesion of the coating film to the resin substrate, particularly the UV-resistant adhesion, can be enhanced. The amount of the carbodiimide group per 100 moles of the carboxyl group is more preferably 120 to 320 moles, more preferably 180 to 300 moles, and even more preferably 220 to 280 moles.

[0060] In order to enhance the effect, the content of the hydrazide group-containing compound (C) in the polyurethane aqueous dispersion is preferably 0.1 to 20 parts by mass relative to 100 parts by mass of the polyurethane resin (A). The content of the hydrazide group-containing compound (C) is more preferably 0.3 to 18 parts by mass, more preferably 1 to 15 parts by mass, and even more preferably 2 to 10 parts by mass.

[0061] The content of the polyurethane resin (A) in the polyurethane aqueous dispersion is not particularly limited and may be, for example, 5 to 50 mass %, 7 to 40 mass %, 10 to 30 mass %, or 15 to 25 mass % relative to the total mass of the aqueous dispersion.

[0062] The particle size of the polyurethane resin (A) in the polyurethane aqueous dispersion is not particularly limited, and may be, for example, an average particle size of 0.001 to 0.5 μm. Here, the average particle size is the 50% cumulative particle size (d50) measured using "Microtrac UPA-UZ152" manufactured by Nikkiso Co., Ltd.

[0063] The polyurethane aqueous dispersion may contain other components as long as the effect is not impaired. The other components may be contained in the resin particles as dispersoid, or may be contained in a state where they are separately dispersed or dissolved in the aqueous dispersion medium (D). For example, in the polyurethane aqueous dispersion, the resin particles as the dispersoid may be composed of only the polyurethane resin (A), or may be composed of the polyurethane resin (A) and other components. The polyurethane aqueous dispersion may also contain a surfactant for dispersing the polyurethane resin (A) in the aqueous dispersion medium (D). The carbodiimide group-containing compound (B) and the hydrazide group-containing compound (C) may be contained in the resin particles, but when they are hydrophilic or water-soluble, they may be contained in a state where they are separately dispersed or dissolved in the aqueous dispersion medium (D).

[0064] [Method of manufacturing aqueous dispersion] The method for producing the polyurethane aqueous dispersion according to this embodiment is not particularly limited. In one embodiment, the aqueous dispersion containing the anionic polyurethane resin (A1) may be produced by the following steps (a1) to (a5). Step (a1): A step of reacting a polyol including a polyester polyol and a carboxyl group-containing polyol with a polyisocyanate to synthesize an isocyanate group-containing urethane prepolymer. Step (a2): A step of neutralizing the carboxyl groups of the isocyanate group-containing urethane prepolymer. Step (a3): A step of dispersing the isocyanate group-containing urethane prepolymer in an aqueous dispersion medium (D). Step (a4): A step of chain-extending the isocyanate group-containing urethane prepolymer with a chain extender. Step (a5): A step of mixing a carbodiimide group-containing compound (B) and a hydrazide group-containing compound (C) with an aqueous dispersion containing the chain-extended anionic polyurethane resin.

[0065] In the above step (a1), the polyisocyanate may be used so that the amount of isocyanate groups is stoichiometrically in excess of the amount of hydroxyl groups contained in the polyol, for example, such that the equivalent ratio of hydroxyl groups to isocyanate groups (NCO / OH) is 1.05 to 1.70 (more preferably 1.10 to 1.60).

[0066] In step (a1), the reaction between the polyol and the polyisocyanate may be carried out without an organic solvent, or may be carried out in an organic solvent having no active hydrogen group, such as methyl ethyl ketone or acetone.

[0067] In the above step (a2), examples of the base for neutralizing the carboxy group include non-volatile bases such as sodium hydroxide and potassium hydroxide, tertiary amines such as trimethylamine, triethylamine, dimethylethanolamine, methyldiethanolamine and triethanolamine, and volatile bases such as ammonia.

[0068] In the above step (a3), the method for dispersing the urethane prepolymer in the aqueous dispersion medium is not particularly limited, and examples include (i) a method in which the urethane prepolymer or a solution thereof is added while the aqueous dispersion medium is stirred with a homogenizer, homomixer, or the like, and (ii) a method in which the aqueous dispersion medium is added while the urethane prepolymer or a solution thereof is stirred with a homogenizer, homomixer, or the like.

[0069] In the above step (a4), the chain extender is not particularly limited and examples thereof include water and polyvalent amine compounds such as aliphatic polyamine compounds (e.g., ethylenediamine, trimethylenediamine, propylenediamine, diethylenetriamine, triethylenetetramine), aromatic polyamine compounds (e.g., metaxylenediamine, tolylenediamine, diaminodiphenylmethane), and alicyclic polyamine compounds (e.g., piperazine, isophoronediamine).

[0070] The neutralization in step (a2), the dispersion in step (a3), and the chain extension in step (a4) may be performed in this order, or two or more steps may be performed simultaneously. For example, when ammonia water is used to neutralize the carboxyl group, the neutralization may be performed simultaneously with dispersion in an aqueous dispersion medium, and chain extension may be further performed with water. When the reaction between the polyol and the polyisocyanate is performed in an organic solvent in step (a1), the organic solvent may be removed after dispersion in an aqueous dispersion medium in step (a4). When a compound that does not react with an isocyanate group is used as the hydrazide group-containing compound (C), the compound may be added at any stage of steps (a1) to (a4).

[0071] In one embodiment, the aqueous dispersion containing the anionic polyurethane resin (A2) may be produced by the following steps (b1) to (b4). Step (b1): A step of reacting a polyol including a polyester polyol and a carboxyl group-containing polyol with a polyisocyanate to synthesize a hydroxyl group-containing polyurethane resin. Step (b2): A step of neutralizing the anionic groups of the hydroxy group-containing polyurethane resin. Step (b3): ​​A step of dispersing the hydroxy group-containing polyurethane resin in an aqueous dispersion medium (D). Step (b4): A step of mixing a carbodiimide group-containing compound (B) and a hydrazide group-containing compound (C) with an aqueous dispersion containing a hydroxy group-containing polyurethane resin.

[0072] In the above step (b1), the polyol is used so that the amount of hydroxy groups is stoichiometrically in excess of the amount of isocyanate groups contained in the polyisocyanate, for example, so that the equivalent ratio of hydroxy groups to isocyanate groups (NCO / OH) is 0.70 to 0.95 (more preferably 0.75 to 0.90).

[0073] The neutralization in step (b2) and the dispersion in step (b3) may be carried out in this order, or may be carried out simultaneously. For example, when ammonia water is used to neutralize the carboxyl group, the neutralization and dispersion in the aqueous dispersion medium may be carried out simultaneously. When the reaction between the polyol and the polyisocyanate is carried out in an organic solvent in step (b1), the organic solvent may be removed after dispersion in the aqueous dispersion medium in step (b3).

[0074] [Water-based paint] The aqueous paint according to this embodiment contains the above-mentioned polyurethane aqueous dispersion, and therefore contains an aqueous dispersion medium (D), a polyurethane resin (A) dispersed in the aqueous dispersion medium, a carbodiimide group-containing compound (B), and a hydrazide group-containing compound (C). The aqueous paint can be applied to various substrates such as resin substrates and metal substrates, but since the aqueous dispersion has excellent adhesion of the coating film to the resin as described above, it is preferably used as an aqueous paint for application to substrates whose surfaces are made of resin. More preferably, it is an aqueous paint for application to polyester resin substrates such as PET (polyethylene terephthalate) film, PBT (polybutylene terephthalate) film, and PEN (polyethylene naphthalate) film. Here, the substrate may be a film or a plate-shaped substrate, and the shape such as thickness is not particularly limited.

[0075] In one embodiment, the water-based paint may be a primer paint used as a primer. For example, the water-based paint according to this embodiment may be applied to a resin substrate such as a polyester resin substrate to form a coating film, and an ultraviolet-curable resin (UV-curable resin) is applied as a topcoat layer on the coating film to form a UV-curable resin layer, to form a laminate. An example of the use of the laminate is an optical film. The coating film made of the water-based paint according to this embodiment has excellent adhesion to a resin substrate such as a polyester resin, and also has excellent adhesion to an ultraviolet-curable resin. Therefore, it is suitable for such a primer.

[0076] In one embodiment, the primer may be used in the following applications. A primer is applied to both sides (A and B) of a resin substrate such as a PET film, and dried to form a primer layer. Next, a UV-curable resin is applied to the A-side side, and UV-irradiated to form a UV-curable resin layer. After that, a UV-curable resin is applied to the B-side side, and UV-irradiated to form a UV-curable resin layer. In such applications, if the primer is altered in the primer layer on the B-side side by irradiating the A-side side with UV, the adhesion of the UV-curable resin layer to the primer layer may be poor even if a UV-curable resin is subsequently applied to the B-side side and cured. The water-based paint according to this embodiment is suppressed from deterioration due to UV irradiation and has excellent UV-resistant adhesion, so that the adhesion of the coating film can be improved on both sides A and B even in such applications.

[0077] The ultraviolet curing resin constituting the topcoat layer is not particularly limited, and examples thereof include acrylate resins such as epoxy acrylate, urethane acrylate, polyester acrylate, etc. In one embodiment, an ultraviolet curing resin containing polyalkylene glycol as a constituent may be used.

[0078] In the water-based paint, other water-based resins generally used as film-forming components of water-based paints may or may not be used in combination with the polyurethane resin (A). Examples of other water-based resins include water-soluble or water-dispersible acrylic resins, water-soluble or water-dispersible polyester resins, water-soluble or water-dispersible alkyd resins, water-soluble or water-dispersible cellulose resins, etc.

[0079] The contents of the polyurethane resin (A), the carbodiimide group-containing compound (B), and the hydrazide group-containing compound (C) in the aqueous coating material are not particularly limited, and may be, for example, 20 to 100 mass% of the total resin solid content in the aqueous coating material, 50 to 100 mass%, or 70 to 100 mass% of the total of these three components. The solid content concentration of the aqueous coating material is also not particularly limited, and may be, for example, 5 to 50 mass%, or 6 to 30 mass%.

[0080] The water-based paint may also contain various additives that are generally used in water-based paints, provided that the additives do not impair the effects of the paint. Examples of such additives include wetting agents, pigments, ultraviolet absorbers, light stabilizers, surface conditioners, inorganic fillers, organic fillers, dispersing aids, preservatives, rust inhibitors, antioxidants, silane coupling agents, defoamers, viscosity adjusters, antistatic agents, crosslinking agents, organic solvents, etc. EXAMPLES

[0081] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited thereto.

[0082] Details of each component used in the examples are as follows.

[0083] [Polyol] Aromatic polyester polyol 1: Functional group number 2, number average molecular weight 1000, solid content 70 mass%, dilution solvent MEK. The synthesis method is as follows. A reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping tank, and a nitrogen gas inlet tube was charged with 16.2 parts by mass of succinic anhydride and 83.8 parts by mass of bisphenol A ethylene oxide adduct ("Newpol BPE-20NK" manufactured by Sanyo Chemical Industries, Ltd.), and the temperature was raised to 250° C. while stirring under a nitrogen stream. The reaction was continued until the acid value was 5 mg KOH / g or less (distilled water 2.92 parts by mass), and the mixture was cooled to 70° C., and then 41.61 parts by mass of methyl ethyl ketone was added to obtain aromatic polyester polyol 1.

[0084] Aromatic polyester polyol 2: Functional group number 2, number average molecular weight 2000, solid content 70 mass%, dilution solvent MEK. The synthesis method is as follows. A reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping tank, and a nitrogen gas inlet tube was charged with 19.9 parts by mass of succinic anhydride and 80.1 parts by mass of bisphenol A ethylene oxide adduct ("Newpol BPE-20NK" manufactured by Sanyo Chemical Industries, Ltd.), and the temperature was raised to 250° C. while stirring under a nitrogen stream. The reaction was continued until the acid value was 5 mg KOH / g or less (distilled water 3.58 parts by mass), and the mixture was cooled to 70° C., and then 41.32 parts by mass of methyl ethyl ketone was added to obtain aromatic polyester polyol 2.

[0085] Aromatic polyester polyol 3: Functional group number 2, number average molecular weight 1000, solid content 70 mass%, dilution solvent MEK. The synthesis method is as follows. In a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping tank, and a nitrogen gas inlet tube, 40.9 parts by mass of isophthalic acid, 19.89 parts by mass of adipic acid, 25.14 parts by mass of neopentyl glycol, and 14.07 parts by mass of ethylene glycol were charged, and the mixture was heated to 250° C. with stirring under a nitrogen stream. The reaction was continued until the acid value was 5 mgKOH / g or less (13.76 parts by mass of distilled water), and the mixture was cooled to 70° C., and then 36.96 parts by mass of methyl ethyl ketone was added to obtain aromatic polyester polyol 3.

[0086] Aliphatic polyester polyol: Functional group number 2, number average molecular weight 1000, solid content 70% by mass, dilution solvent MEK. The synthesis method is as follows. A reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping tank, and a nitrogen gas inlet tube was charged with 53.1 parts by mass of adipic acid and 46.9 parts by mass of neopentyl glycol, and the mixture was heated to 250° C. with stirring under a nitrogen stream. The reaction was continued until the acid value was 5 mgKOH / g or less (13.08 parts by mass of distilled water), and the mixture was cooled to 70° C., after which 37.25 parts by mass of methyl ethyl ketone was added to obtain an aliphatic polyester polyol.

[0087] Dimethylolpropionic acid: 2,2-bis(hydroxymethyl)propionic acid, with 2 functional groups 2,2-Dimethylolbutyric acid: 2,2-bis(hydroxymethyl)butyric acid, functional group number 2 Trimethylolpropane: Functional group number 3 PEG1000: Polyethylene glycol, functional group number 2, number average molecular weight 1000, Daiichi Kogyo Seiyaku Co., Ltd. "PEG 1000"

[0088] [Polyisocyanate] XDI: Xylylene diisocyanate (functional group: 2) · TDI: Tolylene diisocyanate (functional group: 2) HDI: Hexamethylene diisocyanate (functional group: 2)

[0089] [Neutralizer] Ammonia water: 25% by weight aqueous solution Triethylamine

[0090] [Crosslinking agent] (Carbodiimide group-containing compound) Water-soluble polycarbodiimide 1: "Carbodilite SV-02" manufactured by Nisshinbo Chemical Co., Ltd., solid content 40% by mass (solvent: water), NCN equivalent 430 Water-soluble polycarbodiimide 2: "Carbodilite V-02-L2" manufactured by Nisshinbo Chemical Co., Ltd., solid content 40% by mass (solvent: water), NCN equivalent 385 (Epoxy group-containing compound) Epoxy compound 1: "Denacol EX-614B" manufactured by Nagase ChemteX Corporation, solid content 100% by mass, epoxy equivalent 173

[0091] [Additives] (hydrazide group-containing compound) HN-130: 1,6-hexamethylenebis(N,N-dimethylsemicarbazide), "HN-130" manufactured by Japan Finechem Co., Ltd. ADH: Adipic dihydrazide, manufactured by Japan Finechem Co., Ltd. (Other additives) Sodium sulfite

[0092] The polyurethane aqueous dispersions were evaluated as follows.

[0093] [Initial adhesion] The polyurethane aqueous dispersion was used as a primer paint, and the adhesion of the coating film to resin (particularly the adhesion between the primer layer and the UV-cured resin layer) was evaluated by the following method in a triple-layered state of PET film / primer layer / UV-cured resin layer.

[0094] A polyethylene terephthalate (PET) film ("Lumirror T-60" manufactured by Toray Industries, Inc.) was used as the substrate, and the substrate surface was degreased with isopropyl alcohol. Next, the following formulation of polyurethane aqueous dispersion was applied to the substrate with a bar coater to a dry film thickness of 1 μm, and then dried at 180° C. for 1 minute to obtain a test piece X on which a polyurethane resin coating film was formed.

[0095] Polyurethane water-based dispersion formulation: A formulation was prepared by adding water to an aqueous polyurethane dispersion of each Example or Comparative Example so that the solid content was 10 mass %. Then, 0.2 mass % of a wetting agent ("Neocol SW-C" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was added relative to the aqueous dispersion (100 mass %).

[0096] The following UV-curable resin formulation was applied to the coating film of test piece X with a bar coater to a film thickness of 12 μm. Then, a high-pressure mercury lamp was used to irradiate the surface with the UV-curable resin formulation with 600 mJ / cm. 2 The specimen Y was irradiated with ultraviolet light of 1000 nm to obtain a test piece Y. A 1 mm cross-cut test in accordance with JIS K5400-8.5:1990 was carried out using the test piece Y as a sample, and the initial adhesion between the PET film, the primer layer, and the UV-cured resin layer was calculated using the following formula. The test was carried out twice (n=1 and n=2), and the average value was calculated. Initial adhesion (%) = 100 - (number of peeled squares)

[0097] UV curable resin formulation: New Frontier BPE-4 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) / New Frontier PHE (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) / Omnirad 184 (manufactured by IGM Resins BV) = 32.7 / 64.3 / 3 (mass ratio)

[0098] [UV resistance] The surface of the coating of the above test piece X was exposed to 600 mJ / cm using a high-pressure mercury lamp. 2 After irradiating the coating with ultraviolet light of 600 mJ / cm2, the above-mentioned UV-curable resin formulation was applied to the coating film with a bar coater to a film thickness of 12 μm. Next, a high-pressure mercury lamp was used to irradiate the surface coated with the UV-curable resin formulation with 600 mJ / cm2. 2 The specimen was irradiated with ultraviolet light of 1000 nm to obtain a test piece Z. A 1 mm cross-cut test in accordance with JIS K5400-8.5:1990 was carried out using the test piece Z as a sample, and the UV resistance adhesion between the PET film, the primer layer, and the UV-cured resin layer was calculated using the following formula. The test was carried out twice (n=1 and n=2), and the average value was calculated. UV adhesion resistance (%) = 100 - (number of peeled squares)

[0099] [Water-resistant adhesion] The above test piece X was immersed in hot water at 100° C. for 48 hours. After that, it was cooled to room temperature, and the test piece X was taken out and the condition of the surface when rubbed with a finger in a wet state was confirmed and evaluated according to the following criteria. A: No peeling (good water-resistant adhesion) B: Peeling occurred (poor water-resistant adhesion)

[0100] [Example 1] In a four-neck flask equipped with a stirrer, a reflux condenser, a thermometer and a nitrogen gas inlet tube, 92.5 parts by mass (64.8 parts by mass as solids) of aromatic polyester polyol 1, 3.0 parts by mass of dimethylolpropionic acid, 0.5 parts by mass of trimethylolpropane, 9.8 parts by mass of PEG1000, and 100 parts by mass of methyl ethyl ketone were added and thoroughly mixed and dissolved. Next, 21.9 parts by mass of XDI was added as polyisocyanate, and reacted at 70 to 75 ° C for 300 minutes to obtain a methyl ethyl ketone solution of an isocyanate group-containing urethane prepolymer. In the obtained urethane prepolymer solution, the content of free isocyanate groups relative to the solids was 1.2% by mass. The obtained urethane prepolymer solution was cooled to 60 ° C, and while stirring with a homogenizer, a solution of 3.5 parts by mass of 25% ammonia water and 350 parts by mass of water was gradually added to emulsify and disperse. The emulsion was then stirred at 40°C for 1 hour to complete the chain extension reaction with water. Methyl ethyl ketone was removed by distillation under reduced pressure while heating, and water was added to adjust the solid content to obtain an aqueous dispersion with a solid content of 25% by mass. 62.5 parts by mass (25.0 parts by mass as solid content) of water-soluble polycarbodiimide 1 and 5 parts by mass of HN-130 were added to the obtained aqueous dispersion and stirred to obtain an aqueous polyurethane dispersion of Example 1. In the obtained aqueous polyurethane dispersion, the acid value of the polyurethane resin was 12.5 mgKOH / g. In addition, the amount of carbodiimide groups per 100 moles of carboxy groups in the polyurethane resin was 260 moles.

[0101] [Examples 2 to 18 and Comparative Examples 1 to 5] The types and amounts (parts by mass) of polyol, polyisocyanate, neutralizing agent, crosslinking agent, and additives were changed as shown in Tables 1 to 4 below, and the rest was the same as in Example 1 to obtain polyurethane aqueous dispersions of Examples 2 to 18 and Comparative Examples 1 to 5. However, in Comparative Example 4, emulsification and dispersion could not be achieved, and therefore the crosslinking agent and additives were not added, and no polyurethane aqueous dispersion was obtained.

[0102] The polyurethane aqueous dispersions of Examples 1 to 18 and Comparative Examples 1 to 5 (excluding Comparative Example 4) were evaluated for initial adhesion, UV-resistant adhesion, and water-resistant adhesion. The results are shown in Tables 1 to 4.

[0103] In Tables 1 to 4, the amount of polyester polyol is the amount of solids, which is the active ingredient, and the value in parentheses is the amount including the solvent. In Tables 1 to 4, the amount of carbodiimide group-containing compound is the amount of each component including the solvent, and the value in parentheses is the amount of solids, which is the active ingredient. "Solid content of polyurethane resin" is the solid content concentration (mass%) of polyurethane resin in the aqueous dispersion before adding crosslinking agent and additives. "(Carbodiimide group * 100) / carboxy group [mol]" is the amount (mol) of carbodiimide groups of the carbodiimide group-containing compound per 100 moles of carboxy groups of the polyurethane resin.

[0104] [Table 1]

[0105] [Table 2]

[0106] [Table 3]

[0107] [Table 4]

[0108] The results are shown in Tables 1 to 4. In Comparative Example 1, the incorporation of the carbodiimide group-containing compound (B) resulted in excellent initial adhesion, but the absence of the hydrazide group-containing compound (C) resulted in poor UV-resistant adhesion. In Comparative Example 2, sodium sulfite was incorporated as an additive, and the incorporation of the carbodiimide group-containing compound (B) did not result in poor initial adhesion.

[0109] In Comparative Example 3, the acid value of the polyurethane resin was too high, and therefore the initial adhesion was poor, even though a sufficient amount of the carbodiimide group-containing compound (B) was added. In Comparative Example 4, an attempt was made to prepare a polyurethane resin with an acid value of 4.2 mgKOH / g, which is lower than the set value, and the amount of the carboxyl group-containing polyol was too small to emulsify the urethane prepolymer.

[0110] In Comparative Example 5, the epoxy compound 1 was used as the crosslinking agent instead of the carbodiimide group-containing compound (B), and the initial adhesion was poor.

[0111] In contrast, in Examples 1 to 18, the initial adhesion was excellent and the UV resistance was excellent. Comparing Example 1 with Example 7, as the hydrazide group-containing compound (C), HN-130 was more excellent in UV resistance than ADH. Comparing Example 1 with Example 12 with Example 13, as the polyisocyanate, aromatic ring-containing polyisocyanate was more excellent in initial adhesion and UV resistance than aliphatic polyisocyanate. Comparing Example 1 with Example 15, as the neutralizing agent, ammonia tended to have better initial adhesion than tertiary amine (triethylamine). Comparing Example 1 with Example 8 with Example 9 with Example 18, aromatic polyester polyol was more excellent in water-resistant adhesion than aliphatic polyester polyol.

[0112] In addition, the various numerical ranges described in the specification can be arbitrarily combined with their upper and lower limits, and all such combinations are considered to be preferred numerical ranges described in the specification. In addition, a numerical range described as "X to Y" means from X to Y.

[0113] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments and their omissions, substitutions, modifications, etc. are included in the scope and gist of the invention as well as the invention and its equivalents described in the claims.

Claims

1. A polyurethane aqueous dispersion in which a polyurethane resin (A) containing a polyester polyol as a constituent component is dispersed in an aqueous dispersion medium, The polyurethane aqueous dispersion contains a carbodiimide group-containing compound (B) and a compound (C) having a group represented by the following general formula (1), 【Chemistry 1】 In general formula (1), R １ and R ２ each independently represents a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, * represents a bond, The polyurethane resin (A) has a carboxy group, and the acid value of the polyurethane resin (A) is 5 to 25 mgKOH / g. Polyurethane water-based dispersion.

2. The polyurethane aqueous dispersion according to claim 1 , wherein the compound (C) has two groups represented by the general formula (1) in one molecule.

3. R in the general formula (1) １ and R ２ The polyurethane aqueous dispersion according to claim 1, wherein at least one of the following represents a hydrocarbon group having 1 to 3 carbon atoms:

4. The polyurethane aqueous dispersion according to claim 1 , wherein the polyester polyol comprises an aromatic polyester polyol.

5. 2. The polyurethane aqueous dispersion according to claim 1, wherein the carbodiimide group-containing compound (B) contains 100 to 350 moles of carbodiimide groups per 100 moles of carboxy groups in the polyurethane resin (A).

6. 2. The polyurethane aqueous dispersion according to claim 1, wherein the content of the compound (C) is 0.1 to 20 parts by mass based on 100 parts by mass of the polyurethane resin (A).

7. An aqueous coating material comprising the polyurethane aqueous dispersion according to any one of claims 1 to 6.

8. The water-based paint according to claim 7, which is used as a primer.

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