Polyurethane aqueous dispersion and water-based coating material

Abstract

To provide a polyurethane aqueous dispersion capable of improving adhesion of a coating film to a resin and blocking resistance.SOLUTION: The polyurethane aqueous dispersion according to an embodiment is obtained by dispersing a polyurethane resin (A) containing an aromatic polyester polyol as a constituent in an aqueous dispersion medium and contains a carbodiimide group-containing compound (B). The polyurethane resin (A) has carboxy groups and has an acid value of 5-25 mg KOH / g. The polyurethane aqueous dispersion contains 120-300 moles of carbodiimide groups of the carbodiimide group-containing compound (B) based on 100 moles of carboxy groups of the polyurethane resin (A).SELECTED DRAWING: None

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a polyurethane aqueous dispersion and a water-based paint 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 Document 1 discloses an aqueous polyurethane resin composition in which a urethane prepolymer, the constituent components of which are polyester glycol, an organic diisocyanate, and a chain extender having a free carboxy group, is crosslinked with water, and further discloses a primer composition containing the composition and a carbodiimide compound.

[0003] Patent Document 2 discloses that a carbodiimide compound is blended as an aqueous crosslinking agent together with a polyurethane resin in an aqueous ink layer that constitutes a laminated film. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-302526 [Patent Document 2] Patent Publication No. 2021-066031 Summary of the Invention [Problem to be solved by the invention]

[0005] When a polyurethane aqueous dispersion is used as a coating material to be applied to the surface of a resin such as a polyester resin, the coating film must have good adhesion to the resin substrate. Furthermore, when used as a primer, the coating film must have good adhesion to the resin substrate as well as to a topcoat layer applied via the primer. Thus, polyurethane aqueous dispersions are required to have good adhesion to the resin. It is also preferable that polyurethane aqueous dispersions have low tack, i.e., blocking resistance, when applied to a substrate to form a coating film. Here, blocking resistance refers to the ability of the coating films to easily adhere to each other and peel off when substrates on which the coating films are formed are stacked.

[0006] As described above, it has been known to incorporate a carbodiimide compound into an aqueous polyurethane dispersion. However, for example, the composition described in Patent Document 1 contains a small amount of carbodiimide compound, and is not necessarily satisfactory in terms of adhesion to resins.

[0007] An object of an embodiment of the present invention is to provide a polyurethane aqueous dispersion that can improve the adhesion and blocking resistance of a coating film to a resin, and an aqueous paint using the same. [Means for solving the problem]

[0008] The present invention includes the embodiments shown below. [1] A polyurethane aqueous dispersion in which a polyurethane resin (A) containing an aromatic polyester polyol as a constituent component is dispersed in an aqueous dispersion medium, The polyurethane aqueous dispersion contains a carbodiimide group-containing compound (B), the polyurethane resin (A) has a carboxy group and has an acid value of 5 to 25 mgKOH / g; the carbodiimide group-containing compound (B) contains 120 to 300 moles of carbodiimide groups relative to 100 moles of carboxy groups in the polyurethane resin (A); Polyurethane water-based dispersion.

[0009] [2] The polyurethane aqueous dispersion according to [1], wherein the polyurethane resin (A) further contains polyalkylene glycol as a constituent component. [3] The aqueous polyurethane dispersion according to [2], wherein the amount of the polyalkylene glycol is 5 to 15 parts by mass per 100 parts by mass of the polyurethane resin (A). [4] The aqueous polyurethane dispersion according to any one of [1] to [3], wherein the polyurethane resin (A) further contains an aromatic ring-containing polyisocyanate as a constituent component. [5] An aqueous paint comprising the polyurethane aqueous dispersion according to any one of [1] to [4]. [6] The water-based paint according to [5], which is used as a primer. [Effects of the Invention]

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

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

[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, the polyurethane resin (A) contains an aromatic polyester polyol as a constituent component. This can enhance the effect of improving adhesion to polyester resin substrates. In this specification, "containing as a constituent component" means that the polyurethane resin (A) is synthesized using the aromatic polyester polyol as a raw material (monomer), and the polyurethane resin (A) has a structure derived from the aromatic polyester polyol.

[0013] The aromatic polyester polyol is a polyester polyol having an aromatic ring in the molecule. The polyester polyol is obtained by a condensation reaction between a polycarboxylic acid and a polyhydroxy group-containing compound, and it is sufficient that at least one of the polycarboxylic acid and the polyhydroxy group-containing compound contains an aromatic ring.

[0014] The polycarboxylic acid is preferably a dicarboxylic acid, 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 molecular weight of the aromatic polyester polyol is not particularly limited, and the number average molecular weight (Mn) may be 500 to 5,000, 800 to 4,000, or 1,000 to 3,000, for example.

[0017] 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. Specifically, the GPC conditions are as follows: columns: "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 volume: 50 μL; sample concentration: 0.2% by mass.

[0018] The amount of aromatic polyester polyol in the polyol constituting the polyurethane resin (A) is not particularly limited, but is, for example, 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 %.

[0019] In this specification, when the amount of each component constituting the polyol is based on 100% by mass of the polyol, if the polyol contains a carboxyl group-containing polyol described below, the carboxyl group is calculated as being in the acid form. Similarly, the amount of the carboxyl group-containing polyol is calculated as being in the acid form.

[0020] 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 during heat drying of the aqueous dispersion. 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.

[0021] Examples of salts of carboxylic acid bases 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. When the base is a volatile base, the carboxyl group is easily converted to an acid form by evaporation during heat drying of the aqueous dispersion, which improves reactivity with the carbodiimide group-containing compound (B) and can enhance the effect of improving the adhesion of the coating film to the resin.

[0022] 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 a 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 even more preferably 10 to 15 mgKOH / g.

[0023] In this specification, the acid value can be determined in accordance with JIS K0070-1992 from the amount (mg) of KOH required to neutralize the carboxyl groups contained in 1 g of polyurethane resin (A).

[0024] In order to introduce a carboxy group into the polyurethane resin (A), it is preferable to use a carboxy group-containing polyol together with an aromatic 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.

[0025] Examples of carboxyl group-containing polyols 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.

[0026] 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 %, or 2 to 7 mass % relative to 100 mass % of the polyol.

[0027] The polyol used to synthesize the polyurethane resin (A) may further include a polyalkylene glycol. That is, the polyurethane resin (A) preferably further includes a polyalkylene glycol as a constituent. By including a polyalkylene glycol, for example, when the polyurethane aqueous dispersion is used as a primer and the resin constituting the topcoat layer includes a polyalkylene glycol as a constituent, adhesion to the topcoat layer can be improved.

[0028] 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 the number average molecular weight (Mn) may be, for example, 500 to 5,000, 800 to 4,000, or 1,000 to 3,000.

[0029] 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.

[0030] The polyol used to synthesize the polyurethane resin (A) may be a polyol having three or more functional groups. Preferred examples of polyols 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% by mass, 0.2 to 3% by mass, or 0.3 to 1% by mass relative to 100% by mass of the polyol.

[0031] The polyol used to synthesize the polyurethane resin (A) may be a polyol other than those mentioned above. Examples of such other polyols include polymer polyols such as aliphatic polyester polyols, polycarbonate polyols, polyether polyols other than polyalkylene glycols, and polybutadiene polyols. Examples of other polyols that may be used 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.

[0032] The amount of polyol constituting the polyurethane resin (A) (i.e., the amount of polyol-derived structure) 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).

[0033] Examples of polyisocyanates used to synthesize the polyurethane resin (A) include aromatic polyisocyanates, araliphatic polyisocyanates, aliphatic polyisocyanates, and alicyclic polyisocyanates.

[0034] 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.

[0035] 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 products thereof such as isocyanurates, adducts, biurets, allophenates, and carbodiimides.

[0036] 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.

[0037] 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(isocyanatomethyl)cyclohexane, and modified products thereof such as isocyanurates, adducts, biurets, allophenates, and carbodiimides.

[0038] These polyisocyanates may be used alone or in combination of two or more.

[0039] 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 an aromatic aliphatic polyisocyanate, because it has an excellent effect of improving blocking resistance. The amount of the aromatic ring-containing polyisocyanate relative to 100% by mass of 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.

[0040] The amount of polyisocyanate constituting the polyurethane resin (A) (i.e., the amount of polyisocyanate-derived structure) 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).

[0041] In one embodiment, examples of the polyurethane resin (A) include the following (A1) and (A2). (A1) An anionic polyurethane resin obtained by reacting a polyol containing an aromatic 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 hydroxy group-containing anionic polyurethane resin obtained by reacting a polyol containing an aromatic polyester polyol and a carboxy group-containing polyol with a polyisocyanate.

[0042] [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).

[0043] The carbodiimide group-containing compound (B) may be a carbodiimide group-containing compound used as an aqueous crosslinking agent. It is preferably a polycarbodiimide, which is a polymer having a carbodiimide group in the molecule, and more preferably an aqueous polycarbodiimide in which a hydrophilic segment has been introduced into a polycarbodiimide having multiple 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 Inc.).

[0044] The NCN equivalent of the carbodiimide group-containing compound is not particularly limited, and may be, for example, 300 to 600, or 350 to 500. Here, the NCN equivalent represents the chemical formula weight per mole of carbodiimide group.

[0045] [Aqueous dispersion medium (C)] The aqueous dispersion medium is a dispersion medium containing water, and examples thereof include 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 is preferably water, and an organic solvent may be contained, but preferably in a small amount. In one embodiment, the aqueous dispersion medium preferably contains 70% by mass or more of water, more preferably 80% by mass or more of water, more preferably 90% by mass or more of water, and may be 100% by mass of water. That is, in the aqueous dispersion medium, the mass ratio of water / hydrophilic organic solvent is preferably 70 / 30 to 100 / 0, more preferably 80 / 20 to 100 / 0, and even more preferably 90 / 10 to 100 / 0.

[0046] As the hydrophilic organic solvent, various organic solvents that are soluble 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.

[0047] [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 (C), and contains a carbodiimide group-containing compound (B). By blending the carbodiimide group-containing compound (B) into the aqueous dispersion of the polyurethane resin (A), the adhesion of the coating film to the resin can be improved.

[0048] In this embodiment, the amount of the carbodiimide group-containing compound (B) in the aqueous dispersion is set as follows: That is, the aqueous dispersion contains 120 to 300 moles of carbodiimide groups of the carbodiimide group-containing compound (B) per 100 moles of carboxy groups of the polyurethane resin (A).

[0049] As described above, by setting the acid value of the polyurethane resin (A) relatively low and the number of moles of carbodiimide groups in excess of the number of moles of carboxyl groups (specifically, a molar ratio of 1.2 or more), carbodiimide groups remain in the cured coating film. These remaining carbodiimide groups can improve the adhesion of the coating film to the resin, particularly to the topcoat layer. It is believed that the remaining carbodiimide groups contribute to adhesion to the acrylate resin contained in the topcoat layer, but this is not a limitation. Furthermore, by keeping the number of carbodiimide groups to 300 moles or less, blocking resistance can be improved. The amount of carbodiimide groups per 100 moles of carboxyl groups is more preferably 130 to 280 moles, more preferably 150 to 250 moles, and even more preferably 180 to 220 moles.

[0050] The content of 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.

[0051] 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 a "Microtrac UPA-UZ152" manufactured by Nikkiso Co., Ltd.

[0052] The polyurethane aqueous dispersion may contain other components as long as the effects of the polyurethane aqueous dispersion are not impaired. The other components may be contained in the resin particles as a dispersoid, or may be contained in a state where they are separately dispersed or dissolved in the aqueous dispersion medium. For example, in the polyurethane aqueous dispersion, the resin particles as a dispersoid may be composed only of 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 (C). The carbodiimide group-containing compound (B) may be contained in the resin particles, or in the case of the above-mentioned aqueous polycarbodiimide, it may be contained in a state where it is separately dispersed or dissolved in the aqueous dispersion medium.

[0053] [Method for producing 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 containing an aromatic 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 an isocyanate group-containing urethane prepolymer in an aqueous dispersion medium. Step (a4): A step of extending the chain of the isocyanate group-containing urethane prepolymer with a chain extender. Step (a5): A step of mixing a carbodiimide group-containing compound (B) with an aqueous dispersion containing the chain-extended anionic polyurethane resin.

[0054] 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 hydroxy groups contained in the polyol, for example, so that the equivalent ratio of hydroxy groups to isocyanate groups (NCO / OH) is 1.05 to 1.70 (more preferably 1.10 to 1.60).

[0055] 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.

[0056] In the above step (a2), examples of the base used to neutralize 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.

[0057] 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 to the aqueous dispersion medium while stirring it with a homogenizer, a homomixer, or the like, and (ii) a method in which the aqueous dispersion medium is added to the urethane prepolymer or a solution thereof while stirring it with a homogenizer, a homomixer, or the like.

[0058] In the above step (a4), the chain extender is not particularly limited, and examples thereof include water, and also polyvalent amine compounds such as aliphatic polyamine compounds (e.g., ethylenediamine, trimethylenediamine, propylenediamine, diethylenetriamine, triethylenetetramine), aromatic polyamine compounds (e.g., metaxylenediamine, tolylenediamine, diaminodiphenylmethane), alicyclic polyamine compounds (e.g., piperazine, isophoronediamine), and polyhydrazide compounds (e.g., hydrazine, adipic dihydrazide).

[0059] 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, dispersion in an aqueous dispersion medium may be performed simultaneously with neutralization, and chain extension may be further performed with water. Note that 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).

[0060] 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 synthesizing a hydroxy group-containing polyurethane resin by reacting a polyol containing an aromatic polyester polyol and a carboxy group-containing polyol with a polyisocyanate. Step (b2): A step of neutralizing the anionic groups of the hydroxy group-containing polyurethane resin. Step (b3): ​​A step of dispersing a hydroxy group-containing polyurethane resin in an aqueous dispersion medium. Step (b4): A step of mixing a carbodiimide group-containing compound (B) with an aqueous dispersion containing a hydroxy group-containing polyurethane resin.

[0061] 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).

[0062] The neutralization in step (b2) and the dispersion in step (b3) may be performed in this order, or may be performed simultaneously. For example, when ammonia water is used to neutralize the carboxyl group, dispersion in an aqueous dispersion medium may be performed simultaneously with neutralization. Note that when the reaction between the polyol and the polyisocyanate in step (b1) is performed in an organic solvent, the organic solvent may be removed after dispersion in an aqueous dispersion medium in step (b3).

[0063] [Water-based paint] The aqueous coating material according to this embodiment contains the aqueous polyurethane dispersion, and therefore contains an aqueous dispersion medium (C), a polyurethane resin (A) dispersed in the aqueous dispersion medium, and a carbodiimide group-containing compound (B). The aqueous coating material can be applied to various substrates, such as resin substrates and metal substrates. However, since the aqueous dispersion exhibits excellent adhesion of the coating film to the resin, it is preferably used as an aqueous coating material for application to substrates whose surfaces are made of resin. More preferably, the aqueous coating material is for application to polyester resin substrates, such as PET films. The substrate may be a film or a plate-like substrate, and the shape, such as thickness, is not particularly limited.

[0064] In one embodiment, the aqueous coating material may be a primer coating material used as a primer. For example, the aqueous coating material according to this embodiment may be applied to a resin substrate such as a polyester resin substrate to form a coating film, and then an ultraviolet-curable resin (UV-curable resin) is applied as a topcoat layer on the coating film to form a UV-curable resin layer. One example of the use of such a laminate is an optical film. The coating material made of the aqueous coating material according to this embodiment has excellent adhesion to resin substrates such as polyester resins, and also has excellent adhesion to UV-curable resins. Therefore, it is suitable for use as such a primer.

[0065] The ultraviolet curable 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 curable resin containing polyalkylene glycol as a constituent may be used.

[0066] The aqueous coating material may or may not contain other aqueous resins generally used as film-forming components in aqueous coating materials in combination with the polyurethane resin (A). Examples of other aqueous resins include water-soluble or water-dispersible acrylic resins, water-soluble or water-dispersible polyester resins, water-soluble or water-dispersible alkyd resins, and water-soluble or water-dispersible cellulose resins.

[0067] The contents of the polyurethane resin (A) and the carbodiimide group-containing compound (B) in the aqueous coating material are not particularly limited, and may be, for example, 20 to 100 mass% or 50 to 100 mass% in total relative to 100 mass% of the total resin solid content in the aqueous coating material.

[0068] The aqueous paint may also contain various additives that are generally used in aqueous paints, provided that the effects of the aqueous paint are not impaired. Examples of such additives include pigments, ultraviolet absorbers, light stabilizers, surface conditioners, inorganic fillers, organic fillers, dispersing aids, preservatives, rust inhibitors, antioxidants, silane coupling agents, antifoaming agents, viscosity modifiers, antistatic agents, crosslinking agents, and organic solvents. [Example]

[0069] The present invention will be explained in more detail below based on examples and comparative examples, but the present invention is not limited thereto.

[0070] Details of each component used in the examples are as follows:

[0071] [Polyol] Aromatic polyester polyol 1: 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, thermometer, reflux condenser, dropping tank, and 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 with stirring under a nitrogen stream. The reaction was continued until the acid value reached 5 mgKOH / g or less (2.92 parts by mass of distilled water), and the mixture was cooled to 70°C. 41.61 parts by mass of methyl ethyl ketone was added to obtain aromatic polyester polyol 1.

[0072] Aromatic polyester polyol 2: Functional group number 2, number average molecular weight 2000, solid content 70% by mass, dilution solvent MEK. The synthesis method is as follows: A reaction vessel equipped with a stirrer, thermometer, reflux condenser, dropping tank, and 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 with stirring under a nitrogen stream. The reaction was continued until the acid value reached 5 mgKOH / g or less (3.58 parts by mass of distilled water), and the mixture was cooled to 70°C. 41.32 parts by mass of methyl ethyl ketone was added to obtain aromatic polyester polyol 2.

[0073] Aromatic polyester polyol 3: 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, thermometer, reflux condenser, dropping tank, and nitrogen gas inlet tube was charged with 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, and the mixture was heated to 250° C. with stirring under a nitrogen stream. The reaction was continued until the acid value reached 5 mgKOH / g or less (13.76 parts by mass of distilled water), and the mixture was cooled to 70° C. After that, 36.96 parts by mass of methyl ethyl ketone was added to obtain aromatic polyester polyol 3.

[0074] Aliphatic polyester polyol: Functional group number 2, number average molecular weight 1000, solid content 100% by mass. 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 reached 5 mgKOH / g or less (13.08 parts by mass of distilled water), yielding an aliphatic polyester polyol.

[0075] Dimethylolpropionic acid: 2,2-bis(hydroxymethyl)propionic acid, 2 functional groups 2,2-Dimethylolbutyric acid: 2,2-bis(hydroxymethyl)butyric acid, functional group 2 Trimethylolpropane: Functional group number 3 PEG1000: Polyethylene glycol, functional group 2, number average molecular weight 1000, Daiichi Kogyo Seiyaku "PEG 1000"

[0076] [Polyisocyanate] XDI: Xylylene diisocyanate (functional group number 2) TDI: Tolylene diisocyanate (functional groups: 2) HDI: Hexamethylene diisocyanate (functional group 2)

[0077] [Carbodiimide group-containing compounds] Water-soluble polycarbodiimide 1: "Carbodilite SV-02" manufactured by Nisshinbo Chemical Co., Ltd., solid content 40% by mass, NCN equivalent 430 Water-soluble polycarbodiimide 2: "Carbodilite V-02-L2" manufactured by Nisshinbo Chemical Co., Ltd., solid content 40% by mass, NCN equivalent 385

[0078] The polyurethane aqueous dispersions were evaluated as follows.

[0079] [Adhesion 1 and 2] The polyurethane aqueous dispersion was used as a primer coating, and the adhesion of the coating film to resin (particularly the adhesion between the primer layer and the UV-cured resin layer) was evaluated using the following method in a triple-layered configuration of PET film / primer layer / UV-cured resin layer.

[0080] 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 polyurethane aqueous dispersion formulation was applied to the substrate with a bar coater to a dry film thickness of 1 μm, and the coating was dried at 180°C for 1 minute to obtain a test piece X on which a polyurethane resin coating film was formed.

[0081] Polyurethane water-based dispersion formulation: A formulation was prepared by adding water to the polyurethane aqueous dispersion of each Example or Comparative Example so that the solid content was 10% by mass, and then adding 0.1% by mass of a wetting agent ("Neocol SW-C" manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) relative to 100% by mass of the aqueous dispersion.

[0082] A UV-curable resin formulation was applied to the coating film of test piece X using 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 test piece Y was irradiated with ultraviolet light of 1000 kJ / min to obtain a test piece Y. Using test piece Y as a sample, a 1 mm cross-cut test was carried out in accordance with JIS K5400-8.5:1990, and the adhesion between the PET film, the primer layer, and the UV-cured resin layer was calculated using the following formula. Adhesion (%) = 100 - (number of peeled squares)

[0083] The details of the UV curable resin formulation are as follows: UV-curable resin formulation with adhesion 1: To 100 parts by mass of the epoxy acrylate obtained in the synthesis example below, 3 parts by mass of a photopolymerization initiator (Irgacure 184 manufactured by Ciba Specialty Chemicals) was added. A flask was charged with 39 parts by mass of bisphenol A-type epoxy resin ("YD-901" manufactured by Nippon Steel Chemical & Material Co., Ltd.), 6 parts by mass of acrylic acid, 0.05 parts by mass of hydroquinone monomethyl ether as a polymerization inhibitor, and 0.35 parts by mass of tetrabutylammonium bromide, and the mixture was reacted at 100 to 105°C until the acid value reached 5 mgKOH / g or less. 55 parts by mass of diluent monomer ("New Frontier OPPE" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was added to obtain an epoxy acrylate.

[0084] UV-curable resin formulation with adhesion 2: To 100 parts by mass of the urethane acrylate obtained in the synthesis example below, 3 parts by mass of a photopolymerization initiator (Irgacure 184 manufactured by Ciba Specialty Chemicals) was added. 20 parts by mass of TDI was placed in a flask, and 60 parts by mass of PEG1000 was added while stirring, and the mixture was heated to 80°C and reacted until the free isocyanate content reached 5.8% by mass. Next, 0.05 parts by mass of hydroquinone monomethyl ether was added as a polymerization inhibitor, and then 20 parts by mass of 2-hydroxyethyl acrylate was added. The reaction was continued at 70 to 80°C until the residual isocyanate concentration reached less than 0.1% by mass, producing a urethane acrylate.

[0085] [Blocking resistance] The blocking resistance of the polyurethane aqueous dispersion was evaluated using the following method. Two test pieces X (3 x 5 cm) from the above adhesion evaluation were stacked with the coated surface facing inward, and a weight (1000 g) was placed on top of each other. The test pieces were then left to stand for 20 hours at a temperature of 40°C and a humidity of 95%. After 20 hours, the test pieces were cooled to room temperature, and the two test pieces X were peeled apart by hand and their appearances were observed. Test pieces that showed no zipping or change in appearance upon peeling were rated "A" (good); test pieces that showed zipping but no change in appearance upon peeling were rated "B" (good); and test pieces in which one coating film peeled off and remained adhered to the other were rated "C" (poor).

[0086] [Example 1] A four-neck flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet tube was charged with 92.51 parts by weight of aromatic polyester polyol 1, 3.0 parts by weight of dimethylolpropionic acid, 0.5 parts by weight of trimethylolpropane, 9.82 parts by weight of PEG 1000, and 100 parts by weight of methyl ethyl ketone, and thoroughly mixed and dissolved. Next, 21.92 parts by weight of XDI (polyisocyanate) was added, and the mixture was allowed to react at 70-75°C for 300 minutes to obtain a methyl ethyl ketone solution of an isocyanate group-containing urethane prepolymer. The resulting urethane prepolymer solution had a free isocyanate group content of 1.2% by weight relative to the solids content. The resulting urethane prepolymer solution was cooled to 60°C and emulsified while stirring with a homogenizer by gradually adding a solution of 3.46 parts by weight of 25% aqueous ammonia and 350 parts by weight of water. The emulsion was then stirred at 40°C for 1 hour to complete the chain extension reaction with water. The mixture was heated under reduced pressure to remove methyl ethyl ketone, yielding an aqueous dispersion of polyurethane resin with a solids content of 25% by mass. 48.09 parts by mass of water-soluble polycarbodiimide 1 was added to the resulting aqueous dispersion and stirred to obtain the polyurethane aqueous dispersion of Example 1. In the resulting polyurethane aqueous dispersion, the acid value of the polyurethane resin was 12.5 mg KOH / g. Furthermore, the amount of carbodiimide groups per 100 moles of carboxy groups in the polyurethane resin was 200 moles.

[0087] [Examples 2 to 13 and Comparative Examples 1 to 5] The types and amounts (parts by mass) of polyol, polyisocyanate, neutralizing agent, and carbodiimide group-containing compound were changed as shown in Tables 1 to 3 below, and other polyurethane aqueous dispersions were obtained in the same manner as in Example 1. However, in Comparative Example 3, emulsification and dispersion could not be achieved, and therefore, the carbodiimide group-containing compound was not added, and no polyurethane aqueous dispersion was obtained.

[0088] The polyurethane aqueous dispersions of Examples 1 to 13 and Comparative Examples 1 to 5 (excluding Comparative Example 3) were evaluated for adhesion 1 and 2 and blocking resistance. The results are shown in Tables 1 to 3.

[0089] In Tables 1 to 3, the amount of aromatic polyester polyol is the amount of solid content, which is the active ingredient, and the value in parentheses is the amount including the solvent. 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 solid content, which is the active ingredient. The "solid content of polyurethane resin" is the solid content (% by mass) of polyurethane resin in the aqueous dispersion before adding the carbodiimide group-containing compound.

[0090] [Table 1]

[0091] [Table 2]

[0092] [Table 3]

[0093] The results are shown in Tables 1 to 3. In Comparative Example 1, the polyol did not contain an aromatic polyester polyol, so blocking resistance was poor. In Comparative Example 2, the acid value of the polyurethane resin was too high, so adhesion was poor despite the addition of an excess amount of a carbodiimide group-containing compound. In Comparative Example 3, 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, but the amount of carboxy group-containing polyol was too small to emulsify the urethane prepolymer.

[0094] In Comparative Example 4, the amount of carbodiimide groups was too large relative to the amount of carboxy groups, resulting in poor blocking resistance. Conversely, in Comparative Example 5, the amount of carbodiimide groups was too small relative to the amount of carboxy groups, resulting in poor adhesion.

[0095] In contrast, Examples 1 to 13 exhibited excellent adhesion and blocking resistance. Comparing Examples 1, 5, and 6, it was found that aromatic ring-containing polyisocyanates tended to provide better blocking resistance than aliphatic polyisocyanates. Comparing Examples 1 and 12, it was found that the inclusion of polyalkylene glycol as a polyol tended to improve adhesion 2, particularly to a UV-cured resin layer containing urethane acrylate. Comparing Examples 1 and 13, it was found that ammonia, as a neutralizing agent, tended to provide better adhesion than tertiary amine (triethylamine).

[0096] The various numerical ranges described in this specification can be arbitrarily combined with their upper and lower limits, and all such combinations are considered to be preferred numerical ranges described in this specification. Furthermore, a numerical range described as "X to Y" means from X to Y.

[0097] 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 spirit of the invention. These embodiments and their omissions, substitutions, modifications, etc. are included within the scope and spirit of the invention, as well as within the scope of the invention described in the claims and their equivalents.

Claims

1. A polyurethane aqueous dispersion obtained by dispersing a polyurethane resin (A) containing an aromatic polyester polyol as a constituent component in an aqueous dispersion medium, The polyurethane aqueous dispersion contains a carbodiimide group-containing compound (B), the polyurethane resin (A) has a carboxy group, and the acid value of the polyurethane resin (A) is 5 to 25 mgKOH / g; the carbodiimide group-containing compound (B) contains 120 to 300 moles of carbodiimide groups per 100 moles of carboxy groups in the polyurethane resin (A); Polyurethane water-based dispersion.

2. The polyurethane aqueous dispersion according to claim 1 , wherein the polyurethane resin (A) further contains a polyalkylene glycol as a constituent component.

3. 3. The polyurethane aqueous dispersion according to claim 2, wherein the amount of the polyalkylene glycol is 5 to 15 parts by mass per 100 parts by mass of the polyurethane resin (A).

4. The polyurethane aqueous dispersion according to claim 1 , wherein the polyurethane resin (A) further contains an aromatic ring-containing polyisocyanate as a constituent component.

5. An aqueous paint comprising the polyurethane aqueous dispersion according to any one of claims 1 to 4.

6. The water-based paint according to claim 5, which is used as a primer.

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