Water-based polyurethane dispersions and water-based paints

Abstract

To improve the adhesion of the coating film to the resin and the resistance of the coating films to blocking each other. [Solution] The polyurethane aqueous dispersion according to the embodiment comprises a polyurethane resin (A) containing a polyester polyol as a constituent component dispersed in an aqueous dispersion medium, and includes a carbodiimide group-containing compound (B) and a salt (C) of an acid and an alkali metal. The polyurethane resin (A) has carboxyl groups, and the salt (C) is at least one selected from the group consisting of bicarbonates, carbonates, monocarboxylates, dicarboxylates, tricarboxylates, and phosphates, and the salt (C) exists in an ionized state in the aqueous dispersion medium.

Description

Technical Field

[0001] Embodiments of the present invention relate to a polyurethane aqueous dispersion and an aqueous paint containing the same.

Background Art

[0002] A polyurethane aqueous dispersion obtained by dispersing a polyurethane resin in an aqueous dispersion medium is widely used in paints, inks, adhesives, etc. For example, Patent Documents 1 and 2 disclose that a crosslinking agent having a functional group that reacts with an acidic group and / or a hydroxyl group is blended into an aqueous ink containing an aqueous polyester-based urethane resin, and examples of the crosslinking agent include hydrazide compounds, carbodiimide compounds, oxazoline compounds, epoxy compounds, isocyanate compounds, and aziridine compounds.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] When a polyurethane aqueous dispersion is used as a primer, for example, it is desired that the coating film has excellent adhesion to the topcoat layer applied through the resin substrate and the primer. Further, when the coating film is stored in a rolled state, for example, it is desired that the coating film has excellent blocking resistance.

[0005] Embodiments of the present invention aim to provide a polyurethane aqueous dispersion capable of improving the adhesion of the coating film to the resin and the blocking resistance between the coating films, and an aqueous paint using the same.

Means for Solving the Problems

[0006] The present invention includes embodiments shown below. [1] A polyurethane aqueous dispersion comprising a polyurethane resin (A) containing a polyester polyol as a constituent component, dispersed in an aqueous dispersion medium, The polyurethane aqueous dispersion comprises a carbodiimide group-containing compound (B) and a salt of an acid and an alkali metal (C). The polyurethane resin (A) has a carboxyl group, The salt (C) is at least one selected from the group consisting of bicarbonates, carbonates, monocarboxylates, dicarboxylates, tricarboxylates, and phosphates. The salt (C) exists in an ionized state in the aqueous dispersion medium. Aqueous polyurethane dispersion. [2] The polyurethane aqueous dispersion according to [1], wherein the molar ratio (alkali metal / carboxyl group) of alkali metal contained in the salt (C) to the carboxyl groups of the polyurethane resin (A) is 0.1 to 1.5. [3] The polyurethane aqueous dispersion according to [1] or [2], wherein the polyester polyol comprises an aromatic polyester polyol. [4] A water-based paint comprising a polyurethane aqueous dispersion as described in any one of items [1] to [3]. [5] The water-based paint described in [4] used as a primer. [Effects of the Invention]

[0007] According to embodiments of the present invention, the adhesion of the coating film to the resin and the resistance of the coating films to blocking each other can be improved. [Modes for carrying out the invention]

[0008] The polyurethane aqueous dispersion according to this embodiment (hereinafter sometimes simply referred to as "aqueous dispersion") comprises a polyurethane resin (A), a carbodiimide group-containing compound (B), a salt of an acid and an alkali metal (C), and an aqueous dispersion medium (D).

[0009] [Polyurethane resin (A)] Polyurethane resin (A) is obtained by reacting a polyol with a polyisocyanate and is a polymer having a urethane bond in its molecule. In this embodiment, polyurethane resin (A) containing polyester polyol as a constituent component is used. This improves adhesion to the polyester resin substrate. In this specification, "containing as a constituent component" means using it as a raw material (monomer) for synthesizing polyurethane resin (A), and having a structure derived from it in polyurethane resin (A).

[0010] Polyester polyols are polyols having multiple ester bonds (-COO-) within the molecule, and are preferably obtained by a condensation reaction between a polyvalent carboxylic acid and a polyvalent hydroxyl group-containing compound.

[0011] As the polycarboxylic acid, dicarboxylic acids are preferred, and examples 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 one of these may be used, or two or more may be used in combination.

[0012] Preferred polyvalent hydroxyl group-containing compounds are diols, such as aliphatic diols like 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; bisphenols like bisphenol A and bisphenol F; and aromatic diols such as their alkylene oxide adducts. Any one of these may be used, or two or more may be used in combination.

[0013] In one embodiment, the polyester polyol preferably includes an aromatic polyester polyol. By using an aromatic polyester polyol, the adhesion of the coating film to the resin and the blocking resistance between coating films can be improved. The aromatic polyester polyol is a polyester polyol having an aromatic ring in its molecule, and it is sufficient if at least one of the polycarboxylic acid and the polyhydroxy group-containing compound contains an aromatic ring. The amount of aromatic polyester polyol relative to 100% by mass of polyester polyol is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass.

[0014] The molecular weight of the polyester polyol is not particularly limited; for example, the number-average molecular weight (Mn) may be 500-5000, 600-4000, 800-3000, or 1000-2000.

[0015] In this specification, the number-average molecular weight (Mn) is measured by GPC (gel permeation chromatography) and calculated using a calibration curve with 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 volume: 50 μL, Sample concentration: 0.2% by mass.

[0016] The amount of polyester polyol in the polyol constituting the polyurethane resin (A) is not particularly limited, but is preferably 60 to 99% by mass, more preferably 70 to 98% by mass, even more preferably 75 to 95% by mass, and especially preferably 80 to 90% by mass, based on 100% by mass of the polyol.

[0017] In this specification, regarding the amounts of the respective components constituting the polyol, the 100% by mass of the polyol as the reference is calculated with the carboxy groups in the acid form when the polyol contains the carboxy group-containing polyol described later. Similarly, regarding the amount of the carboxy group-containing polyol, the carboxy groups are calculated in the acid form.

[0018] In the present embodiment, the polyurethane resin (A) has carboxy groups, and thereby, when the aqueous dispersion is heat-dried, it can react with the carbodiimide group-containing compound (B) to form a crosslinked structure. In this specification, the carboxy groups are a concept including not only the acid form (-COOH) but also the salt form, that is, carboxylate groups (-COOX, where X is a cation forming a salt with the carboxylic acid), and the acid form and the salt form may coexist, unless otherwise specified.

[0019] The salts of the carboxylate groups include, for example, 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), quaternary ammonium salts, and the like. Among these, salts of volatile bases such as ammonium salts and amine salts are preferable. Being a volatile base, it can be vaporized during the heat-drying of the aqueous dispersion, making the carboxy groups likely to be in the acid form, improving the reactivity with the carbodiimide group-containing compound (B), and enhancing the effect of improving the adhesion of the coating film to the resin. [[ID=II]]

[0020] The acid value of the polyurethane resin (A) is not particularly limited, and for example, it may be 5 to 50 mgKOH / g, may be 10 to 45 mgKOH / g, may be 10 to 30 mgKOH / g, or may be 10 to 20 mgKOH / g.

[0021] In this specification, the acid value can be determined from the amount (mg) of KOH required to neutralize the carboxy groups contained in 1 g of the polyurethane resin (A) in accordance with JIS K0070-1992. When the polyurethane resin (A) is a salt of a volatile base, the volatile base vaporizes during the measurement of the mass of the polyurethane resin (A). Therefore, the acid value is a value calculated based on the mass of the acid-type polyurethane resin, which is the non-volatile content. Thus, the mass of the polyurethane resin (A) in this specification is the mass as the non-volatile content.

[0022] In order to introduce carboxy groups into the polyurethane resin (A), it is preferable to use a carboxy group-containing polyol together with a polyester polyol in the polyol used for synthesizing the polyurethane resin (A). That is, the polyurethane resin (A) preferably contains a carboxy group-containing polyol as a constituent component.

[0023] Examples of the carboxy group-containing polyol include carboxylic acid-containing compounds such as dimethylolpropionic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolvaleric acid, dihydroxymaleic acid, 2,6-dihydroxybenzoic acid, tartaric acid, and their derivatives and their salts. Any one of these may be used, or two or more of them may be used in combination.

[0024] The amount of the carboxy group-containing polyol in the polyol is not particularly limited. For example, it may be 0.5 to 20% by mass, 1 to 15% by mass, 1 to 10% by mass, or 2 to 6% by mass based on 100% by mass of the polyol.

[0025] Polyalkylene glycol may be used as the polyol used to synthesize the polyurethane resin (A). That is, it is preferable that the polyurethane resin (A) further contains polyalkylene glycol as a constituent component. By including polyalkylene glycol, for example, when a polyurethane aqueous dispersion is used as a primer, and the resin constituting the topcoat layer contains polyalkylene glycol as a constituent component, the adhesion to the topcoat layer can be improved.

[0026] 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; for example, the number average molecular weight (Mn) may be 500 to 5000, 800 to 4000, or 1000 to 3000.

[0027] The amount of polyalkylene glycol in the polyurethane resin (A) (i.e., the amount of structure derived from polyalkylene glycol) is preferably 0 to 20 parts by mass, more preferably 3 to 15 parts by mass, and even more preferably 5 to 10 parts by mass, per 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, 0 to 20% by mass, 3 to 15% by mass, or 5 to 10% by mass, per 100% by mass of the polyol.

[0028] Polyols with three or more functional groups may be used as the polyol used to synthesize polyurethane resin (A). Examples of polyols with three or more functional groups include low molecular weight polyhydric alcohols (preferably trihydric alcohols) such as trimethylolpropane, glycerin, and pentaerythritol. The amount of such polyols with three or more functional groups is not particularly limited and may be 0.1 to 5% by mass, 0.2 to 3% by mass, or 0.3 to 1% by mass, based on 100% by mass of the polyol.

[0029] The polyol used to synthesize polyurethane resin (A) may include polyols other than those mentioned above. Examples of such other polyols include polymer polyols such as polycarbonate polyols, polyether polyols other than polyalkylene glycols, and polybutadiene polyols. Other polyols may also 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. Any one of these other polyols may be used, or two or more may be used in combination.

[0030] The amount of polyol constituting the polyurethane resin (A) (i.e., the amount of polyol-derived structure) is not particularly limited. For example, it may be 70 to 90 parts by mass, 73 to 85 parts by mass, or 75 to 80 parts by mass per 100 parts by mass of polyurethane resin (A).

[0031] Examples of polyisocyanates used to synthesize polyurethane resin (A) include aromatic polyisocyanates, aliphatic polyisocyanates, and alicyclic polyisocyanates.

[0032] Examples of aromatic polyisocyanates include diphenylmethane diisocyanate (MDI), polymeric MDI, tolylene diisocyanate (TDI), naphthalene diisocyanate, xylylene diisocyanate (XDI), ω,ω'-diisocyanate-1,4-diethylbenzene, 1,3- or 1,4-bis(1-isocyanate-1-methylethyl)benzene, and modified forms thereof such as isocyanurates, adducts, burettes, allophenates, and carbodiimides.

[0033] Examples of aliphatic polyisocyanates include tetramethylene diisocyanate, dodecamethylene diisocyanate, hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, and modified forms thereof such as isocyanurates, adducts, biuret compounds, allophenates, and carbodiimides.

[0034] 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(isocyanate-methyl)cyclohexane, and modified forms thereof such as isocyanurates, adducts, biuret compounds, allophenates, and carbodiimides.

[0035] These polyisocyanates may be used individually or in combination of two or more.

[0036] The polyisocyanate is not particularly limited, but it is preferable to use an aromatic polyisocyanate, and more preferably xylylene diisocyanate (XDI). The amount of aromatic polyisocyanate (more preferably xylylene diisocyanate (XDI)) 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.

[0037] The amount of polyisocyanate constituting the polyurethane resin (A) (i.e., the amount of polyisocyanate-derived structure) is not particularly limited, and may be 10 to 30 parts by mass or 15 to 25 parts by mass per 100 parts by mass of polyurethane resin (A).

[0038] In one embodiment, the polyurethane resin (A) can be any of the following (A1) and (A2). (A1) An anionic polyurethane resin obtained by reacting a polyol containing a polyester polyol and a carboxyl group-containing polyol with a polyisocyanate to synthesize an isocyanate group-containing urethane prepolymer, and then extending the chains of the urethane prepolymer with a chain extender. (A2) A hydroxyl group-containing anionic polyurethane resin obtained by reacting a polyol containing a polyester polyol and a carboxyl group-containing polyol with a polyisocyanate.

[0039] [Carbodiimide group-containing compound (B)] The carbodiimide group-containing compound (B) is a compound that contains a carbodiimide group (-N=C=N-) in its molecule and reacts with the carboxyl group of the polyurethane resin (A).

[0040] Examples of carbodiimide group-containing compounds (B) include carbodiimide group-containing compounds used as aqueous crosslinking agents. Preferably, these are polycarbodiimides, which are polymers having carbodiimide groups in their molecules, and more preferably, aqueous polycarbodiimides obtained by introducing a hydrophilic segment into a polycarbodiimide having multiple carbodiimide groups in its molecule. Examples of such aqueous polycarbodiimides include the water-soluble types "Carbodilite V-02", "Carbodilite V-02-L2", "Carbodilite SV-02", "Carbodilite V-04", and "Carbodilite V-10", and the emulsion / dispersion types "Carbodilite E-02" and "Carbodilite E-05" (all manufactured by Nisshinbo Chemical Co., Ltd.).

[0041] The NCN equivalent of a carbodiimide group-containing compound is not particularly limited and may be, for example, 300-600, 350-500, or 350-450. Here, NCN equivalent represents the chemical formula weight per mole of carbodiimide group.

[0042] [Salt (C)] In this embodiment, salt (C) is at least one selected from the group consisting of bicarbonates, carbonates, monocarboxylates, dicarboxylates, tricarboxylates, and phosphates. Among these, salt (C) is preferably at least one selected from the group consisting of bicarbonates, carbonates, and monocarboxylates. In this embodiment, salt (C) exists in an ionized state in an aqueous dispersion medium (D).

[0043] The acids that make up salt (C) are carbonic acid, monocarboxylic acids having one carboxyl group in the molecule (e.g., acetic acid, benzoic acid, etc.), dicarboxylic acids having two carboxyl groups in the molecule (e.g., succinic acid, terephthalic acid, etc.), tricarboxylic acids having three carboxyl groups in the molecule (e.g., 3-butene-1,2,3-tricarboxylic acid, 1,3,5-benzenetricarboxylic acid, etc.), and phosphoric acid. Examples of alkali metals in salt (C) include sodium, potassium, and lithium. That is, examples of salt (C) include sodium salts, potassium salts, and lithium salts.

[0044] Specific examples of salt (C) include sodium salts such as sodium bicarbonate, sodium carbonate, sodium monocarboxylates such as sodium acetate and sodium benzoate, sodium dicarboxylates such as sodium succinate and sodium terephthalate, sodium tricarboxylates such as sodium 3-butene-1,2,3-tricarboxylate and sodium 1,3,5-benzenetricarboxylate, and sodium phosphate; potassium salts such as potassium bicarbonate, potassium carbonate, potassium monocarboxylates such as potassium acetate and potassium benzoate, potassium dicarboxylates such as potassium succinate and potassium terephthalate, potassium tricarboxylates such as potassium 3-butene-1,2,3-tricarboxylate and potassium 1,3,5-benzenetricarboxylate, and potassium phosphate; lithium salts such as lithium bicarbonate, lithium carbonate, lithium monocarboxylates such as lithium acetate and lithium benzoate, lithium dicarboxylates such as lithium succinate and lithium terephthalate, lithium tricarboxylates such as lithium 3-butene-1,2,3-tricarboxylate and lithium 1,3,5-benzenetricarboxylate, and lithium phosphate. Any one of these may be used, or two or more may be used in combination. Among these, sodium salts and / or potassium salts are preferred as salt (C), and sodium salts are more preferred.

[0045] [Aqueous dispersion medium (D)] The aqueous dispersion medium (D) is a dispersion medium containing water, and includes water or a mixed medium of water and a hydrophilic organic solvent. From the viewpoint of dispersion stability of the aqueous dispersion, the aqueous dispersion medium (D) is preferably water, and although an organic solvent may be included, it is preferable that it be in small amounts. In one embodiment, the aqueous dispersion medium (D) 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 even contain 100% by mass of water. That is, in the aqueous dispersion medium (D), the mass ratio of water / hydrophilic organic solvent is preferably 70 / 30 to 100 / 0, more preferably 80 / 20 to 100 / 0, and even more preferably 90 / 10 to 100 / 0.

[0046] As hydrophilic organic solvents, various organic solvents that dissolve in water can be used, such as lower monohydric alcohols like methanol, ethanol, and propanol; polyhydric alcohols like ethylene glycol and glycerin; and aprotic polar solvents like N-methylpyrrolidone, dimethyl sulfoxide, dimethylformamide, and acetonitrile.

[0047] [Polyurethane aqueous dispersion] The polyurethane aqueous dispersion is an aqueous dispersion in which polyurethane resin (A) is dispersed in an aqueous dispersion medium (D), and contains a carbodiimide group-containing compound (B) and a salt (C). By incorporating the carbodiimide group-containing compound (B) and the salt (C) into the aqueous dispersion of polyurethane resin (A) in this way, the adhesion of the coating film to the resin and the blocking resistance between coating films can be improved. Here, the salt (C) exists in an ionized state in the aqueous dispersion medium (D). That is, the salt (C) exists in the polyurethane aqueous dispersion in a dissolved state in the aqueous dispersion medium (D).

[0048] The content of the carbodiimide group-containing compound (B) in the polyurethane aqueous dispersion is not particularly limited. For example, the aqueous dispersion may contain 50 to 350 moles, 60 to 300 moles, 80 to 280 moles, 100 to 250 moles, or 150 to 250 moles of carbodiimide groups of the carbodiimide group-containing compound (B) per 100 moles of carboxyl groups of the polyurethane resin (A).

[0049] The content of salt (C) in the polyurethane aqueous dispersion is not particularly limited, and may be, for example, 0.1 to 10 parts by mass, 0.5 to 4 parts by mass, or 1 to 2 parts by mass per 100 parts by mass of polyurethane resin (A).

[0050] The content of polyurethane resin (A) in the aqueous polyurethane dispersion is not particularly limited and may be, for example, 5 to 50% by mass, 10 to 40% by mass, or 15 to 35% by mass, relative to the total mass of the aqueous dispersion.

[0051] In one embodiment, the molar ratio (alkali metal / carboxyl group) of alkali metal contained in the salt (C) to the carboxyl groups of polyurethane resin (A) is preferably 0.1 to 1.5, and more preferably 0.3 to 1.

[0052] The particle size of the polyurethane resin (A) in the polyurethane aqueous dispersion is not particularly limited, and for example, the average particle diameter may be 0.001 to 0.5 μm. Here, the average particle diameter is the 50% cumulative particle diameter (d50) measured using the "NANOTRAC WAVE II-EX150" manufactured by Microtrac Bell Co., Ltd.

[0053] The polyurethane aqueous dispersion may contain other components as long as its effectiveness is not impaired. These other components may be contained in the resin particles as the dispersed phase, or they may be contained separately in the aqueous dispersion medium (D) in a dispersed or dissolved state. For example, in the polyurethane aqueous dispersion, the resin particles as the dispersed phase may consist only of polyurethane resin (A), or they may consist of polyurethane resin (A) along with other components. The polyurethane aqueous dispersion may also contain a surfactant for dispersing the polyurethane resin (A) in the aqueous dispersion medium (D). The carbodiimide group-containing compound (B) may be contained in the resin particles, but if it is hydrophilic or water-soluble, it may be contained separately in the aqueous dispersion medium (D) in a dispersed or dissolved state.

[0054] [Method for producing aqueous dispersions] 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 described in (A1) above may be produced by the following steps (a1) to (a5). Step (a1): A step of synthesizing an isocyanate group-containing urethane prepolymer by reacting a polyol containing polyester polyol and carboxyl group-containing polyol with a polyisocyanate. Step (a2): A step to neutralize 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 (D). Step (a4): A step of extending the chains of an isocyanate group-containing urethane prepolymer with a chain extender. Step (a5): A step of mixing a carbodiimide group-containing compound (B) and a salt (C) into an aqueous dispersion containing the anionic polyurethane resin after chain elongation.

[0055] In step (a1) described above, the polyisocyanate may be used such that the isocyanate groups are stoichiometrically in excess of the hydroxyl groups contained in the polyol, for example, the equivalent ratio of hydroxyl groups to isocyanate groups (NCO / OH) is 1.05 to 1.70 (more preferably 1.10 to 1.60).

[0056] Furthermore, in step (a1), the reaction between the polyol and the polyisocyanate may be carried out without an organic solvent, or in an organic solvent that does not have active hydrogen groups, such as methyl ethyl ketone or acetone.

[0057] In step (a2) above, examples of bases used to neutralize the carboxyl 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.

[0058] In step (a3) ​​described above, the method for dispersing the urethane prepolymer in an aqueous dispersion medium is not particularly limited. Examples include (i) adding the urethane prepolymer or a solution thereof while stirring the aqueous dispersion medium with a homogenizer or homomixer, and (ii) adding the aqueous dispersion medium while stirring the urethane prepolymer or a solution thereof with a homogenizer or homomixer.

[0059] In step (a4) described above, the chain extender is not particularly limited and can be water, or polyhydric amine compounds such as aliphatic polyamine compounds (e.g., ethylenediamine, trimethylenediamine, propylenediamine, diethylenetriamine, triethylenetetramine), aromatic polyamine compounds (e.g., metaxylenediamine, tolylenediamine, diaminodiphenylmethane), or alicyclic polyamine compounds (e.g., piperazine, isophoronediamine).

[0060] The neutralization in step (a2), the dispersion in step (a3), and the chain extension in step (a4) may be carried out in this order, but two or more steps may be carried out simultaneously. For example, if aqueous ammonia is used to neutralize the carboxyl group, the dispersion in an aqueous dispersion medium may be carried out simultaneously with the neutralization, and then the chain extension with water may be carried out. If the reaction between the polyol and polyisocyanate in step (a1) is carried out in an organic solvent, the organic solvent may be removed after the dispersion in an aqueous dispersion medium in step (a4).

[0061] In one embodiment, the aqueous dispersion containing the anionic polyurethane resin described in (A2) above may be produced by the following steps (b1) to (b4). Step (b1): A step of synthesizing a hydroxyl group-containing polyurethane resin by reacting a polyol containing polyester polyol and carboxyl group-containing polyol with a polyisocyanate. Step (b2): A step to neutralize the anionic groups of the hydroxyl group-containing polyurethane resin. Step (b3): ​​A step of dispersing a hydroxyl group-containing polyurethane resin in an aqueous dispersion medium (D). Step (b4): A step of mixing a carbodiimide group-containing compound (B) and a salt (C) into an aqueous dispersion containing a hydroxyl group-containing polyurethane resin.

[0062] In step (b1) described above, the polyol is used such that the amount of hydroxyl groups is stoichiometrically in excess of the amount of isocyanate groups contained in the polyisocyanate, for example, the equivalent ratio of hydroxyl groups to isocyanate groups (NCO / OH) is 0.70 to 0.95 (more preferably 0.75 to 0.90).

[0063] The neutralization in step (b2) and the dispersion in step (b3) may be carried out in this order, or they may be carried out simultaneously. For example, if aqueous ammonia is used to neutralize the carboxyl group, the dispersion in an aqueous dispersion medium may be carried out simultaneously with the neutralization. Furthermore, if the reaction between the polyol and polyisocyanate in step (b1) is carried out in an organic solvent, the organic solvent may be removed after the dispersion in the aqueous dispersion medium in step (b3).

[0064] [Water-based paint] An aqueous coating according to one embodiment contains the above-mentioned aqueous polyurethane dispersion, and therefore comprises an aqueous dispersion medium (D), a polyurethane resin (A) dispersed in the aqueous dispersion medium, a carbodiimide group-containing compound (B), and a salt (C). The aqueous coating can be applied to various substrates such as resin substrates and metal substrates, but as described above, the aqueous dispersion has excellent adhesion of the coating film to the resin, so it is preferably used as an aqueous coating for application to substrates whose surface is made of resin. More preferably, it is an aqueous coating for application to polyester resin substrates such as PET (polyethylene terephthalate) film, PBT (polybutylene terephthalate) film, and PEN (polyethylene naphthalate) film. Here, the substrate may be a film or a plate-shaped substrate, and its shape, such as thickness, is not particularly limited.

[0065] In one embodiment, the water-based paint may be a primer paint used as a primer. For example, it may be used as a primer layer in a laminate formed by applying the water-based paint according to this embodiment to a resin substrate such as a polyester resin substrate to form a coating film, and then applying an ultraviolet-curing resin (UV-curing resin) as a topcoat layer on the coating film to form a UV-curing resin layer. An example of the application of such a laminate is an optical film. The coating film made of the water-based paint according to this embodiment has excellent adhesion to resin substrates such as polyester resin, as well as excellent adhesion to ultraviolet-curing resins. Therefore, it is suitable for use as such a primer.

[0066] The UV-curing resin constituting the topcoat layer is not particularly limited, and examples include acrylate resins such as epoxy acrylate, urethane acrylate, and polyester acrylate. In one embodiment, a UV-curing resin containing polyalkylene glycol as a component may be used.

[0067] Water-based paints may or may not use other water-based resins, which are generally used as film-forming components in water-based paints, together with the polyurethane resin (A) described above. Examples of other water-based resins include water-soluble or water-dispersible acrylic resins, water-soluble or water-dispersible polyester resins, water-soluble or water-dispersible alkyd resins, water-soluble or water-dispersible cellulose resins, and the like.

[0068] The content of polyurethane resin (A), carbodiimide group-containing compound (B), and salt (C) in the water-based paint is not particularly limited. For example, the total of these three components may be 20-100% by mass, 50-100% by mass, or 70-100% by mass, relative to 100% by mass of the total resin solids contained in the water-based paint. The solids concentration of the water-based paint is also not particularly limited. For example, it may be 5-50% by mass or 6-30% by mass.

[0069] Water-based paints may also contain various additives commonly used in water-based paints, provided that their effectiveness is not impaired. Examples of such additives include wetting agents, pigments, UV absorbers, light stabilizers, surface modifiers, inorganic fillers, organic fillers, dispersion aids, preservatives, rust inhibitors, antioxidants, silane coupling agents, defoamers, viscosity modifiers, antistatic agents, crosslinking agents, and organic solvents. [Examples]

[0070] The present invention will be described in more detail below based on examples and comparative examples, but it is not limited thereto.

[0071] Details of each component used in the examples are as follows.

[0072] [Polyol] Aromatic polyester polyol 1: 2 functional groups, number average molecular weight 1000, solids content 70% by mass, diluent MEK. The synthesis method is as follows. In a reaction vessel equipped with a stirrer, thermometer, reflux condenser, dropping tank, and nitrogen gas inlet tube, 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, 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 (2.92 parts by mass of distilled water was added), and after cooling to 70°C, 41.32 parts by mass of methyl ethyl ketone was added to obtain aromatic polyester polyol 1.

[0073] Aromatic polyester polyol 2: 2 functional groups, number average molecular weight 2000, solids content 70% by mass, diluent MEK. The synthesis method is as follows. In a reaction vessel equipped with a stirrer, thermometer, reflux condenser, dropping tank, and nitrogen gas inlet tube, 40.9 parts by mass of isophthalic acid, 19.89 parts by mass of adipic acid, 25.14 parts by mass of neopentyl glycol, and 14.07 parts by mass of ethylene glycol were charged, and the mixture was heated to 250°C while stirring under a nitrogen atmosphere. The reaction was continued until the acid value was 5 mg KOH / g or less (13.76 parts by mass of water was removed), and after cooling to 70°C, 36.96 parts by mass of methyl ethyl ketone was added to obtain aromatic polyester polyol 2.

[0074] • PTMG1000: Polytetramethylene ether glycol, 2 functional groups, molecular weight 1000, manufactured by Mitsubishi Chemical Corporation.

[0075] Trimethylolpropane: 3 functional groups • 2,2-Dimethylolpropionic acid: 2 functional groups • PEG1000: Polyethylene glycol, 2 functional groups, number average molecular weight 1000, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.

[0076] [Polyisocyanate] • XDI: Xylylene diisocyanate, 2 functional groups • TDI: Tolylene diisocyanate, 2 functional groups • HDI: Hexamethylene diisocyanate, 2 functional groups

[0077] [Neutralizing agent] • Ammonia water: 25% by mass aqueous solution Triethylamine

[0078] [Crosslinking agent] (Carbodiimide group-containing compound) • Water-soluble polycarbodiimide 1: "Carbodilite V-02-L2" manufactured by Nisshinbo Chemical Co., Ltd., solids content 40% by mass (solvent: water), NCN equivalent 385 • Water-soluble polycarbodiimide 2: "Carbodilite SV-02" manufactured by Nisshinbo Chemical Co., Ltd., solids content 40% by mass (solvent: water), NCN equivalent 430 (Oxazoline group-containing compound) • Oxazoline compound: "Epocross WS-700" manufactured by Nippon Shokubai Co., Ltd., solids content 25% by mass (solvent: water), oxazoline equivalent 220 (comparative example)

[0079] [Additives] (salt) Sodium bicarbonate Sodium carbonate Sodium acetate Sodium benzoate • Potassium acetate • Sodium polyacrylate (Aron T-50, manufactured by Toagosei Co., Ltd.) (Comparative example) • Sodium chloride (comparative example)

[0080] The evaluation method for polyurethane aqueous dispersions is as follows:

[0081] [Adhesion] Using a polyurethane aqueous dispersion as a primer coating, the adhesion of the coating film to the resin (particularly the adhesion between the primer layer and the UV-curing resin layer) was evaluated using the following method in a three-layer configuration consisting of a PET film, primer layer, and UV-curing resin layer.

[0082] Using polyethylene terephthalate (PET) film (Toray Industries, Inc.'s "Lumirror T-60") as a substrate, the substrate surface was degreased with isopropyl alcohol. Next, the following polyurethane aqueous dispersion formulation was applied using a bar coater to a dry film thickness of 150 nm, and dried at 180°C for 1 minute to obtain test piece X with a polyurethane resin coating. Subsequently, the following UV-curing resin formulation was applied to the PET film (Toray Industries, Inc.'s "Lumirror T-60") to a film thickness of 10 μm to obtain test piece Y. The side of test piece X with the primer layer and the side of test piece Y coated with UV-curing resin were bonded together using a hand roller. Then, 600 mJ / cm² of high-pressure mercury lamp was used to expose the PET film surface on test piece X to UV radiation. 2The specimen was irradiated with ultraviolet light. After curing the UV-curing resin, the PET film on the Y side of the specimen was peeled off to prepare an evaluation specimen (PET film / primer layer / UV-curing resin layer). Using the prepared evaluation specimen, a 1 mm grid test was performed in accordance with JIS K5400-8.5:1990, and the adhesion between the PET film, primer layer, and UV-curing resin layer was calculated using the following formula. Adhesion (%) = 100 - (Number of squares that peeled off)

[0083] • Formulation solution of polyurethane aqueous dispersion: A formulation solution was prepared by adding water to the polyurethane aqueous dispersion of each example or comparative example to obtain an aqueous dispersion with a solid content of 10% by mass, and then adding 0.1% by mass of a wetting agent (NeoCall SW-C, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) per 100% by mass of the aqueous dispersion.

[0084] • UV-curing resin formulation: "New Frontier GX-8821L-M9" (epoxy acrylate) manufactured by Daiichi Kogyo Seiyaku Co., Ltd. / "A-BPE-20" (ethoxylated bisphenol A diacrylate) manufactured by Shin Nakamura Chemical Industry Co., Ltd. / "Omnirad TPO-H" manufactured by IGM Resins BV = 60 / 40 / 1 (mass ratio)

[0085] [Blocking resistance] Two PET films (Toray Industries, Inc.'s "Lumirror T-60") (3 x 5 cm) were coated with the above polyurethane aqueous dispersion formulation using a bar coater to a dry film thickness of 1 μm. The films were dried at 180°C for 1 minute to obtain test specimens with polyurethane resin coatings. The two test specimens were stacked with the coated sides facing inward, a 1000 g weight was placed on top, and the specimens were left standing for 20 hours under conditions of 40°C and 95% humidity. After cooling to room temperature, the peeled surfaces of the two test specimens were observed and evaluated when they were peeled apart by hand. "A" was evaluated as the films peeling apart without blocking, "B" as the films blocking only at the edges, and "C" as the films blocking across the entire surface. A rating of "B" or higher is preferred for blocking resistance. Here, blocking refers to one film peeling off and adhering to the other film.

[0086] [Example 1] In a four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen gas inlet tube, 99.4 parts by mass (69.58 parts by mass as solids) of aromatic polyester polyol 1, 0.5 parts by mass of trimethylolpropane, 3 parts by mass of 2,2-dimethylolpropionic acid, 5 parts by mass of PEG1000, and 100 parts by mass of methyl ethyl ketone were added and thoroughly mixed and dissolved. Next, 21.92 parts by mass of XDI as polyisocyanate was added, and the mixture was reacted at 70-75°C for 300 minutes to obtain a methyl ethyl ketone solution of isocyanate group-containing urethane prepolymer. In the obtained urethane prepolymer solution, the content of free isocyanate groups relative to the solids was 1.2% by mass. The obtained urethane prepolymer solution was cooled to 60°C, and while stirring with a homogenizer, an emulsified dispersion was carried out by gradually adding a solution of 3.46 parts by mass of 25% by mass of aqueous ammonia and 300 parts by mass of water. Subsequently, the emulsion was stirred at 40°C for 1 hour to complete the chain extension reaction with water. Methyl ethyl ketone was removed by distillation under heating and reduced pressure, and water was further added to adjust the solid content to obtain an aqueous dispersion with a solid content of 30% by mass. To the obtained aqueous dispersion, 43.06 parts by mass (17.22 parts by mass as solid content) of water-soluble polycarbodiimide 1 and 1.13 parts by mass of sodium bicarbonate were added 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 mg KOH / g. In addition, the molar ratio of alkali metals contained in salt (C) to carboxyl groups of polyurethane resin (A) (alkali metal / carboxyl group) was 0.6.

[0087] [Examples 2-20 and Comparative Examples 1-6] The types and amounts (parts by mass) of polyols, polyisocyanates, neutralizing agents, crosslinking agents, and additives were changed as shown in Tables 1 to 5 below, and the rest of the procedure was the same as in Example 1 to obtain the polyurethane aqueous dispersions of Examples 2 to 20 and Comparative Examples 1 to 6.

[0088] The adhesion and blocking resistance of the polyurethane aqueous dispersions of Examples 1-20 and Comparative Examples 1-6 were evaluated. The results are shown in Tables 1-5.

[0089] In Tables 1-5, the amount of polyester polyol represents the amount of solids, which are the active ingredient. In Tables 1-5, the amount of carbodiimide group-containing compound represents the amount of each component, including the solvent, with the number in parentheses representing the amount of solids, which are the active ingredient. "Solids of polyurethane resin" is the solids concentration (mass%) of the polyurethane resin in the aqueous dispersion before the addition of crosslinking agents and additives. "Alkali metal / carboxyl group" is the molar ratio of alkali metal contained in salt (C) to carboxyl groups of polyurethane resin (A). "(Carbodiimide group*100) / carboxyl group [mol]" is the amount (moles) of carbodiimide groups in carbodiimide group-containing compound (B) relative to 100 moles of carboxyl groups in polyurethane resin (A).

[0090] [Table 1]

[0091] [Table 2]

[0092] [Table 3]

[0093] [Table 4]

[0094] [Table 5]

[0095] The results are shown in Tables 1 to 5. Comparative Example 1 was an example in which polytetramethylene ether glycol was used as the polyol component and did not contain polyester polyol as a constituent component, and it exhibited poor adhesion and blocking resistance. Comparative Example 2 was an example in which sodium polyacrylate was added as an additive, and although it had excellent blocking resistance, it exhibited poor adhesion. Comparative Example 3 was an example in which no salt was added as an additive, and although it had excellent blocking resistance, it exhibited poor adhesion. Comparative Example 4 was an example in which an oxazoline compound was added as a crosslinking agent, and although it had excellent blocking resistance, it exhibited poor adhesion. Comparative Example 5 was an example in which no crosslinking agent was added, and it exhibited poor adhesion and blocking resistance. Comparative Example 6 was an example in which sodium chloride was added as an additive, and although it had excellent blocking resistance, it exhibited poor adhesion.

[0096] In contrast, Examples 1 to 20 exhibited excellent adhesion and blocking resistance.

[0097] Furthermore, the various numerical ranges described in this specification can be any combination of their upper and lower limits, and all such combinations are described herein as preferred numerical ranges. Also, the description of a numerical range as "X~Y" means X or greater and Y or less.

[0098] Although several embodiments of the present invention have been described above, these embodiments are presented as examples only 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, and modifications are included in the scope and spirit of the invention, as well as in the claims and their equivalents.

Claims

1. A polyurethane aqueous dispersion comprising a polyurethane resin (A) containing a polyester polyol as a constituent component, dispersed in an aqueous dispersion medium, The polyurethane aqueous dispersion comprises a carbodiimide group-containing compound (B) and a salt of an acid and an alkali metal (C). The polyurethane resin (A) has a carboxyl group, The salt (C) is at least one selected from the group consisting of bicarbonates, monocarboxylates, dicarboxylates, tricarboxylates, and phosphates. The salt (C) exists in an ionized state in the aqueous dispersion medium, The molar ratio (alkali metal / carboxyl group) of alkali metal contained in the salt (C) to the carboxyl groups of the polyurethane resin (A) is 0.1 to 1.

5. Aqueous polyurethane dispersion.

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

3. A water-based paint comprising the polyurethane aqueous dispersion described in claim 1 or 2.

4. The aqueous paint according to claim 3, used as a primer.

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