Polyurethane aqueous dispersion and water-based coating material

Abstract

Provided is a polyurethane aqueous dispersion with which it is possible to improve the blocking resistance and adhesion of a coating film with respect to a resin. A polyurethane aqueous dispersion according to an embodiment is obtained by dispersing a polyurethane resin (A) that contains an aromatic polyester polyol as a constituent component in an aqueous dispersion medium, the polyurethane aqueous dispersion containing an oxazoline-group-containing water-soluble polymer (B). The polyurethane resin (A) has a carboxy group, and the acid value of the polyurethane resin (A) is 5-25 mg KOH / g. The polyurethane aqueous dispersion contains 120-300 mol of oxazoline groups in the oxazoline-group-containing water-soluble polymer (B) per 100 mol of carboxy groups in the polyurethane resin (A).

Description

Polyurethane water-based dispersion and water-based paint

[0001] An embodiment of the present invention relates to a polyurethane aqueous dispersion and a water-based paint containing the same.

[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 the use of an easy-adhesion composition containing a water-dispersible polyurethane resin and an epoxy compound to form an easy-adhesion layer for laminating another functional film on an optical film made of a (meth)acrylic resin.

[0003] International Publication No. 2022 / 239648

[0004] 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.

[0005] Patent Document 1 discloses an aqueous polyurethane dispersion containing a water-dispersible polyurethane resin having a carboxy group and an oxazoline compound. However, the aqueous polyurethane dispersion containing the oxazoline compound disclosed in Patent Document 1 is a comparative example that exhibits poor initial adhesion, and does not achieve both adhesion of the coating film to the resin and blocking resistance.

[0006] 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.

[0007] The present invention includes the following embodiments: [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 also containing an oxazoline group-containing water-soluble polymer (B), the polyurethane resin (A) having a carboxy group, an acid value of the polyurethane resin (A) being 5 to 25 mgKOH / g, and the oxazoline group-containing water-soluble polymer (B) containing 120 to 300 moles of oxazoline groups per 100 moles of carboxy groups in the polyurethane resin (A).

[0008] [2] The polyurethane aqueous dispersion according to [1], wherein the polyurethane resin (A) further comprises a polyalkylene glycol as a constituent. [3] The polyurethane aqueous 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 polyurethane aqueous dispersion according to any one of [1] to [3], wherein the polyurethane resin (A) further comprises an aromatic ring-containing polyisocyanate as a constituent. [5] The polyurethane aqueous dispersion according to any one of [1] to [4], wherein the oxazoline group-containing water-soluble polymer (B) comprises an oxazoline group-containing water-soluble acrylic polymer. [6] An aqueous paint comprising the polyurethane aqueous dispersion according to any one of [1] to [5]. [7] The aqueous paint according to [6], wherein the aqueous paint is used as a primer.

[0009] According to an embodiment of the present invention, the adhesion and blocking resistance of the coating film to the resin can be improved.

[0010] The polyurethane aqueous dispersion according to this embodiment (hereinafter sometimes simply referred to as aqueous dispersion) contains a polyurethane resin (A), an oxazoline group-containing water-soluble polymer (B), and an aqueous dispersion medium (C).

[0011] [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 used as a raw material (monomer) for synthesizing the polyurethane resin (A), and the polyurethane resin (A) has a structure derived from this.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] The molecular weight of the aromatic polyester polyol is not particularly limited, and may be, for example, 500 to 5,000 in number average molecular weight (Mn), 800 to 4,000, or 1,000 to 3,000.

[0016] In this specification, the number average molecular weight (Mn) and weight average molecular weight (Mw) are values ​​measured by GPC (gel permeation chromatography) and calculated using a calibration curve of standard polystyrene. Specifically, 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%.

[0017] 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 %.

[0018] In this specification, when the polyol contains a carboxyl group-containing polyol described below, the amount of each component constituting the polyol is calculated based on 100% by mass of the polyol, with the carboxyl group being in the acid form. Similarly, the amount of the carboxyl group-containing polyol is calculated based on the carboxyl group being in the acid form.

[0019] In this embodiment, the polyurethane resin (A) has a carboxy group, which can react with the oxazoline group-containing water-soluble polymer (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.

[0020] Examples of salts of carboxylate groups 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 carboxy group is likely to be converted to an acid form by evaporation during heat drying of the aqueous dispersion, thereby improving reactivity with the oxazoline group-containing water-soluble polymer (B), and thereby enhancing the effect of improving adhesion of the coating film to the resin.

[0021] In this embodiment, the acid value of the polyurethane resin (A) is 5 to 25 mgKOH / g. An acid value of 5 mgKOH / g or more makes it easier to emulsify the polyurethane resin (A) in an aqueous dispersion medium. An acid value of 25 mgKOH / g or less can improve the adhesion of a coating film to the resin. 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.

[0022] 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).

[0023] 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.

[0024] 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.

[0025] The amount of the carboxyl group-containing polyol in the polyol is not particularly limited, and may be, for example, 0.5 to 15% by mass, 1 to 10% by mass, or 2 to 7% by mass relative to 100% by mass of the polyol.

[0026] 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.

[0027] Examples of polyalkylene glycols include polyethylene glycol, polytrimethylene glycol, polypropylene glycol, polytetramethylene glycol, polybutylene glycol, and copolymers of 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.

[0028] 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.

[0029] 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.

[0030] 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 of two or more.

[0031] The amount of polyol constituting the polyurethane resin (A) (i.e., the amount of the structure derived from the 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).

[0032] Examples of polyisocyanates used to synthesize the polyurethane resin (A) include aromatic polyisocyanates, araliphatic polyisocyanates, aliphatic polyisocyanates, and alicyclic polyisocyanates.

[0033] 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.

[0034] Examples of the aromatic aliphatic polyisocyanate 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.

[0035] Examples of aliphatic polyisocyanates include tetramethylene diisocyanate, dodecamethylene diisocyanate, hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, and modified products thereof such as isocyanurates, adducts, biurets, allophenates, and carbodiimides.

[0036] 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.

[0037] These polyisocyanates may be used alone or in combination of two or more.

[0038] 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.

[0039] The amount of polyisocyanate constituting the polyurethane resin (A) (i.e., the amount of polyisocyanate-derived structures) 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).

[0040] In one embodiment, the polyurethane resin (A) may be any of 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 chain-extending the urethane prepolymer with a chain extender; (A2) a hydroxyl group-containing anionic polyurethane resin obtained by reacting a polyol containing an aromatic polyester polyol and a carboxyl group-containing polyol with a polyisocyanate.

[0041] [Oxazoline Group-Containing Water-Soluble Polymer (B)] The oxazoline group-containing water-soluble polymer (B) is a polymer containing multiple oxazoline groups in the molecule, and forms a crosslinked structure (amide ester bond) by reacting with a carboxy group of the polyurethane resin (A).

[0042] The oxazoline group is a five-membered heterocyclic group containing an oxygen atom and a nitrogen atom, represented by the following formula, and may have a substituent as long as it can react with a carboxy group to form an amide ester bond.

[0043] As the oxazoline group-containing water-soluble polymer (B), it is preferable to use an oxazoline group-containing water-soluble acrylic polymer whose polymer main chain is an acrylic polymer. The amount of the oxazoline group-containing water-soluble acrylic polymer in 100% by mass of the oxazoline group-containing water-soluble polymer (B) is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 100% by mass. Here, the acrylic polymer refers to a polymer containing an acrylic monomer such as (meth)acrylic acid, a (meth)acrylic acid ester, or acrylonitrile as a main raw material.

[0044] The oxazoline equivalent of the oxazoline group-containing water-soluble polymer (B) is not particularly limited and may be, for example, 100 to 300, or 150 to 250. Here, the oxazoline equivalent represents the chemical formula weight per mole of oxazoline groups.

[0045] The weight average molecular weight (Mw) of the oxazoline group-containing water-soluble polymer (B) is not particularly limited, and may be, for example, 10,000 to 200,000, 15,000 to 100,000, or 20,000 to 80,000.

[0046] Examples of the oxazoline group-containing water-soluble polymer (B) include commercially available products such as "Epocross WS-300," "Epocross WS-500," and "Epocross WS-700" manufactured by Nippon Shokubai Co., Ltd., and these can be used.

[0047] [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.

[0048] 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.

[0049] [Polyurethane Aqueous 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 an oxazoline group-containing water-soluble polymer (B). By blending the oxazoline group-containing water-soluble polymer (B) in the aqueous dispersion of the polyurethane resin (A), the adhesion of the coating film to the resin can be improved.

[0050] In this embodiment, the amount of the oxazoline group-containing water-soluble polymer (B) in the aqueous dispersion is set as follows: That is, the aqueous dispersion contains 120 to 300 moles of oxazoline groups of the oxazoline group-containing water-soluble polymer (B) per 100 moles of carboxy groups of the polyurethane resin (A).

[0051] As described above, by setting the acid value of the polyurethane resin (A) relatively low and the number of moles of oxazoline groups in excess of the number of moles of carboxyl groups (specifically, a molar ratio of 1.2 or more), oxazoline groups remain in the cured coating film. These remaining oxazoline groups can improve the adhesion of the coating film to the resin, particularly to the topcoat layer. It is believed that the remaining oxazoline groups contribute to adhesion to the acrylate resin contained in the topcoat layer, but this is not a limitation. Furthermore, by having 300 moles or less of oxazoline groups, blocking resistance can be improved. The amount of oxazoline 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.

[0052] 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.

[0053] 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.

[0054] 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 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 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). Note that the oxazoline group-containing water-soluble polymer (B) is water-soluble and therefore is usually contained in a state where it is dissolved in the aqueous dispersion medium, but this is not limited thereto.

[0055] [Method of Manufacturing Aqueous Dispersion] The method of manufacturing the aqueous polyurethane dispersion according to this embodiment is not particularly limited. In one embodiment, the aqueous dispersion containing the anionic polyurethane resin (A1) may be manufactured by the following steps (a1) to (a5). Step (a1): A step of synthesizing an isocyanate group-containing urethane prepolymer by reacting a polyol containing an aromatic polyester polyol and a carboxy group-containing polyol with a polyisocyanate. Step (a2): A step of neutralizing the carboxy 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. Step (a4): A step of chain-extending the isocyanate group-containing urethane prepolymer with a chain extender. Step (a5): A step of mixing an oxazoline group-containing water-soluble polymer (B) with the aqueous dispersion containing the anionic polyurethane resin after chain extension.

[0056] 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).

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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 acid dihydrazide).

[0061] The neutralization in step (a2), the dispersion in step (a3), and the chain extension in step (a4) may be carried out in this order, or two or more steps may be carried out simultaneously. For example, when ammonia water is used to neutralize the carboxyl group, dispersion in an aqueous dispersion medium may be carried out simultaneously with neutralization, and chain extension with water may then be carried out. Note that when the reaction between the polyol and the polyisocyanate is carried out in an organic solvent in step (a1), the organic solvent may be removed after dispersion in an aqueous dispersion medium in step (a4).

[0062] In one embodiment, the aqueous dispersion containing the anionic polyurethane resin of (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 anionic groups in the hydroxy group-containing polyurethane resin. Step (b3): ​​A step of dispersing the hydroxy group-containing polyurethane resin in an aqueous dispersion medium. Step (b4): A step of mixing an oxazoline group-containing water-soluble polymer (B) with the aqueous dispersion containing the hydroxy group-containing polyurethane resin.

[0063] 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).

[0064] 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 is performed in an organic solvent in step (b1), the organic solvent may be removed after dispersion in an aqueous dispersion medium in step (b3).

[0065] [Water-based paint] The water-based paint according to this embodiment contains the above-mentioned polyurethane aqueous dispersion, and therefore contains an aqueous dispersion medium (C), a polyurethane resin (A) dispersed in the aqueous dispersion medium, and an oxazoline group-containing water-soluble polymer (B). The water-based paint can be applied to various substrates such as resin substrates and metal substrates. However, since the water-based dispersion has excellent adhesion of the coating film to the resin as described above, it is preferably used as a water-based paint for application to substrates whose surfaces are made of resin. More preferably, it is a water-based paint for application to polyester resin substrates such as PET film. Here, the substrate may be a film or a plate-shaped substrate, and the shape, such as thickness, is not particularly limited.

[0066] 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 such primer applications.

[0067] 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.

[0068] 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.

[0069] The contents of the polyurethane resin (A) and the oxazoline group-containing water-soluble polymer (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.

[0070] 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.

[0071] The present invention will be explained in more detail below based on examples and comparative examples, but the present invention is not limited thereto.

[0072] Details of each component used in the examples are as follows:

[0073] [Polyol] Aromatic polyester polyol 1: Functionality 2, number average molecular weight 1000, solids content 70% by mass, diluent MEK. The synthesis method is as follows. 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.) were charged into a reaction vessel equipped with a stirrer, thermometer, reflux condenser, dropping tank, and nitrogen gas inlet tube, and the temperature was raised to 250 ° C. while stirring under a nitrogen stream. The reaction was carried out until the acid value was 5 mg KOH / g or less (distilled water 2.92 parts by mass), cooled to 70 ° C., and then 41.61 parts by mass of methyl ethyl ketone was added to obtain aromatic polyester polyol 1.

[0074] Aromatic polyester polyol 2: Functionality 2, number average molecular weight 2000, solids content 70% by mass, diluent MEK. The synthesis method is as follows. 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.) were charged into a reaction vessel equipped with a stirrer, thermometer, reflux condenser, dropping tank, and nitrogen gas inlet tube, 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.

[0075] Aromatic polyester polyol 3: Functionality 2, number average molecular weight 1000, solids content 70% by mass, diluent MEK. The synthesis method was as follows: 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 into a reaction vessel equipped with a stirrer, thermometer, reflux condenser, dropping tank, and nitrogen gas inlet tube, and the mixture was heated to 250°C while 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), cooled to 70°C, and then 36.96 parts by mass of methyl ethyl ketone was added to obtain aromatic polyester polyol 3.

[0076] Aliphatic polyester polyol: Functional group number 2, number average molecular weight 1000, solids content 100% by mass. The synthesis method was as follows: 53.1 parts by mass of adipic acid and 46.9 parts by mass of neopentyl glycol were charged into a reaction vessel equipped with a stirrer, thermometer, reflux condenser, dropping tank, and nitrogen gas inlet tube, and the temperature was raised to 250°C while stirring under a nitrogen stream. The reaction was continued until the acid value was 5 mgKOH / g or less (distilled water 13.08 parts by mass), yielding an aliphatic polyester polyol.

[0077] Dimethylolpropionic acid: 2,2-bis(hydroxymethyl)propionic acid, functional group number 2 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, "PEG 1000" manufactured by Daiichi Kogyo Seiyaku

[0078] [Polyisocyanate] XDI: xylylene diisocyanate (functional group: 2) TDI: tolylene diisocyanate (functional group: 2) HDI: hexamethylene diisocyanate (functional group: 2)

[0079] [Oxazoline group-containing water-soluble polymer] WS-700: oxazoline group-containing water-soluble acrylic polymer, manufactured by Nippon Shokubai Co., Ltd., "Epocross WS-700", solid content 25% by mass, oxazoline equivalent 220, weight average molecular weight 40,000 WS-500: oxazoline group-containing water-soluble acrylic polymer, manufactured by Nippon Shokubai Co., Ltd., "Epocross WS-500", solid content 39% by mass, oxazoline equivalent 220, weight average molecular weight 70,000

[0080] The polyurethane aqueous dispersions were evaluated as follows.

[0081] [Adhesion 1 and 2] Using an aqueous polyurethane dispersion as a primer coating, 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.

[0082] A polyethylene terephthalate (PET) film ("Lumirror T-60" manufactured by Toray Industries, Inc.) was used as a substrate, and the surface of the substrate was degreased with isopropyl alcohol. Next, the following formulation of an aqueous polyurethane dispersion was applied to the substrate using a bar coater to a dry film thickness of 1 μm, and the coating was dried at 180° C. for 1 minute, yielding a test piece X on which a polyurethane resin coating film had been formed.

[0083] - Formulation of aqueous polyurethane dispersion: A formulation was prepared by adding water to the aqueous polyurethane 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.

[0084] 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 coated with the UV-curable resin formulation with 600 mJ / cm ２ The test piece Y was irradiated with ultraviolet light of 1000 kJ / cm to obtain a test piece Y. A 1 mm cross-cut test was carried out in accordance with JIS K5400-8.5:1990 using the test piece Y as a sample, 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)

[0085] Details of the UV-curable resin formulation are as follows. UV-curable resin formulation with adhesion 1: 100 parts by mass of the epoxy acrylate obtained in the synthesis example below was added with 3 parts by mass of a photopolymerization initiator ("Irgacure 184" manufactured by Ciba Specialty Chemicals). 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 were charged into a flask and reacted at 100 to 105°C until the acid value reached 5 mgKOH / g or less. 55 parts by mass of a diluent monomer ("New Frontier OPPE" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was added to obtain an epoxy acrylate.

[0086] UV-curable resin formulation with adhesion 2: 100 parts by weight of the urethane acrylate obtained in the synthesis example below was mixed with 3 parts by weight of a photopolymerization initiator ("Irgacure 184" manufactured by Ciba Specialty Chemicals). 20 parts by weight of TDI was placed in a flask, and 60 parts by weight of PEG 1000 was added while stirring. The mixture was heated to 80°C and reacted until the free isocyanate content reached 5.8% by weight. Next, 0.05 parts by weight of hydroquinone monomethyl ether was added as a polymerization inhibitor, and then 20 parts by weight 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 weight, producing a urethane acrylate.

[0087] [Blocking Resistance] The blocking resistance of the polyurethane aqueous dispersion was evaluated by the following method. Two test pieces X (3 × 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).

[0088] Example 1: 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 were added to a four-neck flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet tube, and thoroughly mixed and dissolved. Next, 21.92 parts by weight of XDI was added as a polyisocyanate, and the mixture was allowed to react at 70 to 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 while stirring with a homogenizer, a solution of 3.46 parts by weight of 25% ammonia water and 350 parts by weight of water was gradually added to emulsify and disperse the mixture. The emulsion was then stirred at 40°C for 1 hour to complete the chain extension reaction with water. Methyl ethyl ketone was distilled off under reduced pressure while heating to obtain an aqueous dispersion of polyurethane resin with a solids content of 25% by mass. 39.36 parts by mass of WS-700 was added to the obtained aqueous dispersion and stirred to obtain the polyurethane aqueous dispersion of Example 1. In the obtained polyurethane aqueous dispersion, the acid value of the polyurethane resin was 12.5 mgKOH / g. Furthermore, the amount of oxazoline groups per 100 moles of carboxy groups in the polyurethane resin was 200 moles.

[0089] Examples 2 to 13 and Comparative Examples 1 to 5 The types and charged amounts (parts by mass) of the polyol, polyisocyanate, neutralizing agent, and oxazoline group-containing water-soluble polymer were changed as shown in Tables 1 to 3 below, and the rest was the same as in Example 1 to obtain aqueous polyurethane dispersions of Examples 2 to 13 and Comparative Examples 1 to 5. However, in Comparative Example 3, emulsification and dispersion could not be achieved, and therefore the oxazoline group-containing water-soluble polymer was not added, and no aqueous polyurethane dispersion was obtained.

[0090] 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.

[0091] In Tables 1 to 3, the amount of aromatic polyester polyol is the amount of solids, which is the active ingredient, and the value in parentheses is the amount including the solvent. The amount of oxazoline group-containing water-soluble polymer is the amount of each component including the solvent, and the value in parentheses is the amount of solids, which is the active ingredient. The "solids content of polyurethane resin" is the solids content (% by mass) of the polyurethane resin in the aqueous dispersion before the addition of the oxazoline group-containing water-soluble polymer.

[0092]

[0093]

[0094]

[0095] 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 the oxazoline group-containing water-soluble polymer. In Comparative Example 3, an attempt was made to prepare a polyurethane resin with an acid value of 4.2 mg KOH / g, which is lower than the set value, but the amount of carboxy group-containing polyol was too small to emulsify the urethane prepolymer.

[0096] In Comparative Example 4, the amount of oxazoline groups was too large relative to the amount of carboxy groups, resulting in poor blocking resistance. Conversely, in Comparative Example 5, the amount of oxazoline groups was too small relative to the amount of carboxy groups, resulting in poor adhesion.

[0097] In contrast, Examples 1 to 13 exhibited excellent adhesion and blocking resistance. A comparison between Examples 1, 5, and 6 revealed that aromatic ring-containing polyisocyanates tended to provide better blocking resistance than aliphatic polyisocyanates. A comparison between Examples 1 and 12 revealed that the inclusion of polyalkylene glycol as a polyol tended to improve adhesion 2, particularly to a UV-cured resin layer containing urethane acrylate. A comparison between Examples 1 and 13 revealed that ammonia, as a neutralizing agent, tended to provide better adhesion than tertiary amine (triethylamine).

[0098] The various numerical ranges described in this specification can be arbitrarily combined with their respective upper and lower limit values, 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.

[0099] 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 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 also containing an oxazoline group-containing water-soluble polymer (B), the polyurethane resin (A) having a carboxy group, the acid value of the polyurethane resin (A) being 5 to 25 mgKOH / g, and the oxazoline group-containing water-soluble polymer (B) containing 120 to 300 moles of oxazoline groups per 100 moles of carboxy groups in the polyurethane resin (A).

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

3. The aqueous polyurethane 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. The polyurethane aqueous dispersion according to claim 1, wherein the oxazoline group-containing water-soluble polymer (B) comprises an oxazoline group-containing water-soluble acrylic polymer.

6. A water-based paint comprising the polyurethane aqueous dispersion according to any one of claims 1 to 5.

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

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