JP7723852B1 - Polyurethane water-based dispersion and water-based paint - Google Patents

Abstract

[Problem] To improve the adhesion and UV-resistant adhesion of a coating film to a resin. [Solution] An aqueous polyurethane dispersion according to an embodiment comprises a polyurethane resin (A) containing a polyester polyol as a constituent dispersed in an aqueous dispersion medium, a carbodiimide group-containing compound (B), and a compound (C) having two groups represented by the following general formula (1) per molecule. The polyurethane resin (A) has a carboxy group. In formula (1), R1 represents a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, R2 represents a hydrocarbon group having 1 to 3 carbon atoms, and * represents a bond. [Chemical 1] JPEG0007723852000015.jpg23135 [Selected Figure] None

Description

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

Aqueous polyurethane dispersions, which are made by dispersing polyurethane resins in an aqueous dispersion medium, are widely used in paints, inks, adhesives, and more. For example, Patent Documents 1 and 2 disclose blending a crosslinking agent having a functional group that reacts with acidic groups and/or hydroxyl groups into an aqueous ink containing an aqueous polyester-based urethane resin, listing hydrazide compounds, carbodiimide compounds, oxazoline compounds, epoxy compounds, isocyanate compounds, and aziridine compounds as examples of such crosslinking agents.

Japanese Patent Application Laid-Open No. 2023-146694 Japanese Patent Application Laid-Open No. 2021-147428

When a polyurethane aqueous dispersion is used as a coating to be applied to the surface of a resin such as polyester resin, the coating film must have good adhesion (bonding) to the resin substrate. Furthermore, when used as a primer, for example, the coating film must have good adhesion to the resin substrate as well as to the topcoat layer that is applied via the primer. Thus, polyurethane aqueous dispersions require good adhesion to the resin.

The inventors' research has revealed that the adhesion of a coating film to a resin can be improved by incorporating a carbodiimide group-containing compound. However, when used as a primer, for example, and the coating film is irradiated with ultraviolet (UV) rays, and then a topcoat layer is applied to form a three-layer structure, the coating film's adhesion, i.e., its UV-resistant adhesion, is found to be poor.

In the above-mentioned Patent Documents 1 and 2, specifically, a carbodiimide compound or a hydrazide compound is blended with a polyurethane resin, and adipic acid dihydrazide is used as the hydrazide compound. However, Patent Documents 1 and 2 do not disclose the use of a specific hydrazide group-containing compound in combination with a carbodiimide compound, or the improvement in UV-resistant adhesion that results from this.

An embodiment of the present invention aims to provide a polyurethane aqueous dispersion that can improve the adhesion and UV resistance of a coating film to resin, and an aqueous paint using the same.

The present invention includes the embodiments shown below.
[1] A polyurethane aqueous dispersion in which a polyurethane resin (A) containing a polyester polyol as a constituent component is dispersed in an aqueous dispersion medium,
The polyurethane resin (A) has a carboxy group,
The polyurethane aqueous dispersion contains a carbodiimide group-containing compound (B) and a compound (C) having two groups represented by the following general formula (1) in one molecule:
In general formula (1), R ¹ represents a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, R ² represents a hydrocarbon group having 1 to 3 carbon atoms, and * represents a bond.
Polyurethane water-based dispersion.

[2] The compound (C) includes a compound represented by the following general formula (3):
In general formula (3), R ¹ represents a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, R ² represents a hydrocarbon group having 1 to 3 carbon atoms, and m represents an integer of 1 to 12. The polyurethane aqueous dispersion according to [1].
[3] The polyurethane aqueous dispersion according to [1] or [2], wherein the polyester polyol contains an aromatic polyester polyol.
[4] The polyurethane aqueous dispersion according to any one of [1] to [3], wherein the carbodiimide group-containing compound (B) contains 100 to 350 moles of carbodiimide groups per 100 moles of carboxy groups in the polyurethane resin (A).
[5] The polyurethane aqueous dispersion according to any one of [1] to [4], wherein the content of the compound (C) is 0.1 to 20 parts by mass per 100 parts by mass of the polyurethane resin (A).
[6] An aqueous coating material comprising the polyurethane aqueous dispersion according to any one of [1] to [5].
[7] The water-based paint according to [6], which is used as a primer.

According to an embodiment of the present invention, the adhesion and UV resistance of the coating film to the resin can be improved.

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

[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 a polyester polyol as a constituent component. This can improve adhesion to polyester resin substrates. In this specification, "containing a polyester polyol as a constituent component" means that the polyester polyol is used as a raw material (monomer) for synthesizing the polyurethane resin (A), and the polyurethane resin (A) has a structure derived from the polyester polyol.

Polyester polyols are polyols that contain multiple ester bonds (-COO-) within the molecule, and are preferably obtained by the condensation reaction of a polycarboxylic acid and a compound containing a polyhydroxy group.

Dicarboxylic acids are preferred as polycarboxylic acids, 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. These may be used alone or in combination of two or more.

Diols are preferred as polyvalent hydroxy group-containing compounds, and examples 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 their alkylene oxide adducts. These may be used alone or in combination of two or more.

Aromatic polyester polyols are preferred as polyester polyols. That is, in a preferred embodiment, the polyester polyol includes an aromatic polyester polyol. The use of an aromatic polyester polyol can improve the water-resistant adhesion of the coating film to the resin. The aromatic polyester polyol is a polyester polyol having an aromatic ring in the molecule, and it is sufficient that at least one of the polycarboxylic acid and the polyvalent hydroxy 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, more preferably 90% by mass or more, and even more preferably 100% by mass.

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

In this specification, the number average molecular weight (Mn) is a value measured by gel permeation chromatography (GPC) and calculated using a calibration curve based on standard polystyrene. Specifically, the GPC conditions are as follows: Column: Tosoh Corporation's "TSKgel G4000HXL + TSKgel G3000HXL + TSKgel G2000HXL + TSKgel G1000HXL + TSKgel G1000HXL," 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.

The amount of polyester polyol in the polyol that constitutes polyurethane resin (A) is not particularly limited, but is preferably 60 to 99% by mass, more preferably 70 to 97% by mass, more preferably 75 to 95% by mass, and even more preferably 80 to 90% by mass, relative to 100% by mass of polyol.

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

In this embodiment, the polyurethane resin (A) has a carboxy group, which can react with the carbodiimide group-containing compound (B) to form a crosslinked structure when the aqueous dispersion is dried by heating. In this specification, unless otherwise specified, the term "carboxy group" refers not only to the acid type (-COOH) but also to the salt type, i.e., carboxylate salt 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.

Examples of salts of carboxylic acid bases include alkali metal salts such as sodium salts and potassium salts, alkaline earth metal salts such as magnesium salts and calcium salts, ammonium salts, amine salts (primary amine salts, secondary amine salts, tertiary amine salts), and quaternary ammonium salts. Among these, salts of volatile bases such as ammonium salts and amine salts are preferred. Volatile bases tend to convert the carboxyl group to the acid form when vaporized during heating and drying of the aqueous dispersion, improving reactivity with the carbodiimide group-containing compound (B) and enhancing the effect of improving the adhesion of the coating film to the resin.

In this embodiment, the acid value of the polyurethane resin (A) is not particularly limited and may be, for example, 5 to 45 mgKOH/g, 5 to 25 mgKOH/g, 7 to 20 mgKOH/g, or 10 to 15 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 45 mgKOH/g or less can enhance the effect of improving the adhesion of the coating film to the resin.

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). If polyurethane resin (A) is a salt of a volatile base, the volatile base evaporates when the mass of polyurethane resin (A) is measured, and therefore the acid value is a value calculated based on the mass of the acid-form polyurethane resin, which is the non-volatile content. Thus, the mass of polyurethane resin (A) in this specification refers to the mass of the non-volatile content.

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

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 their derivatives and salts. Any of these may be used alone, or two or more may be used in combination.

The amount of 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, 2 to 8% by mass, or 3 to 6% by mass relative to 100% by mass of the polyol.

The polyol used to synthesize polyurethane resin (A) may further include polyalkylene glycol. That is, polyurethane resin (A) preferably further includes polyalkylene glycol as a constituent. For example, when the polyurethane aqueous dispersion is used as a primer and the resin that constitutes the topcoat layer includes polyalkylene glycol as a constituent, the inclusion of polyalkylene glycol can improve adhesion to the topcoat layer.

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

The amount of polyalkylene glycol in 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, per 100 parts by mass of 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, per 100% by mass of polyol.

The polyol used to synthesize polyurethane resin (A) may further include a polyol with three or more functional groups. Preferred 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 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 polyol.

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 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.

The amount of polyol constituting polyurethane resin (A) (i.e., the amount of polyol-derived structures) 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 polyurethane resin (A).

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

Examples of aromatic polyisocyanates include diphenylmethane diisocyanate (MDI), polymeric MDI, tolylene diisocyanate (TDI), naphthalene diisocyanate, and modified versions of these, such as isocyanurates, adducts, biurets, allophenates, and carbodiimides.

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

Aliphatic polyisocyanates include, for example, tetramethylene diisocyanate, dodecamethylene diisocyanate, hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, and modified versions of these compounds, such as isocyanurates, adducts, biurets, allophenates, and carbodiimides.

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 versions of these, such as isocyanurates, adducts, biurets, allophenates, and carbodiimides.

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

Among the polyisocyanates listed above, it is preferable to use aromatic ring-containing polyisocyanates such as aromatic polyisocyanates and araliphatic polyisocyanates, and it is more preferable to use araliphatic polyisocyanates. The amount of 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 even 100% by mass.

The amount of polyisocyanate constituting 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 polyurethane resin (A).

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

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

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

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

[Compound (C)]
Compound (C) is a compound having two groups (hereinafter referred to as hydrazide groups) represented by the following general formula (1) in the molecule, and hereinafter referred to as hydrazide group-containing compound (C). Here, the hydrazide group also encompasses within its concept the atomic group constituting the semicarbazide group formed by bonding -NH- to the bond in formula (1).

In formula (1), ^R1 represents a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, ^R2 represents a hydrocarbon group having 1 to 3 carbon atoms, and * represents a bond. ^R1 is preferably a hydrocarbon group having 1 to 3 carbon atoms because this provides better UV adhesion resistance. Two ^R1s in the same molecule may be the same or different, and two ^R2s in the same molecule may be the same or different.

The hydrocarbon group having 1 to 3 carbon atoms is a monovalent hydrocarbon group that may be saturated or unsaturated, and may be straight-chain or branched, and is preferably an alkyl group, i.e., a methyl group, an ethyl group, or a propyl group, and more preferably a methyl group.

The hydrazide group-containing compound (C) includes compounds represented by the following general formula (2).

In formula (2), ^R1 and ^R2 are the same as ^R1 and ^R2 in formula (1), respectively. ^R3 represents a divalent organic group having 1 to 12 carbon atoms, preferably 2 to 10 carbon atoms, and more preferably 3 to 8 carbon atoms.

In one embodiment, the hydrazide group-containing compound (C) preferably includes a compound having two semicarbazide groups in one molecule, specifically a disemicarbazide compound (C1) represented by the following general formula (3): In this case, the amount of the disemicarbazide compound (C1) in 100% by mass of the hydrazide group-containing compound (C) is not particularly limited, but is preferably 50% by mass or more, more preferably 70% by mass or more, and may be 100% by mass.

In formula (3), ^R1 and ^R2 are the same as ^R1 and ^R2 in formula (1), respectively. m represents an integer of 1 to 12, preferably an integer of 2 to 10, and more preferably an integer of 3 to 8.

A specific example of a preferred hydrazide group-containing compound (C) is 1,6-hexamethylenebis(N,N-dimethylsemicarbazide).

[Aqueous dispersion medium (D)]
The aqueous dispersion medium (D) 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 (D) is preferably water, and an organic solvent may be contained, but preferably in a small amount. In one embodiment, the aqueous dispersion medium (D) preferably contains 70% by mass or more of water, more preferably 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 (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.

As the hydrophilic organic solvent, various organic solvents that dissolve in water can be used, including, for example, 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.

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

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

By setting the number of moles of carbodiimide groups to an amount equal to or greater than the number of moles of carboxy groups, carbodiimide groups are more likely to remain in the cured coating film. These remaining carbodiimide groups can enhance the coating film's adhesion to resins, particularly to the topcoat layer. It is believed that the remaining carbodiimide groups contribute to adhesion to the acrylate resin contained in the topcoat layer, but this is not limited to this. Furthermore, by setting the number of carbodiimide groups to 350 moles or less, the coating film's adhesion to resin substrates, particularly UV-resistant adhesion, can be enhanced. The amount of carbodiimide groups per 100 moles of carboxy groups is more preferably 120 to 320 moles, more preferably 180 to 300 moles, and even more preferably 220 to 280 moles.

To enhance its effects, the content of the hydrazide group-containing compound (C) in the polyurethane aqueous dispersion is preferably 0.1 to 20 parts by mass per 100 parts by mass of the polyurethane resin (A). The content of the hydrazide group-containing compound (C) is more preferably 0.3 to 18 parts by mass, more preferably 1 to 15 parts by mass, and even more preferably 2 to 10 parts by mass.

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

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.

The polyurethane aqueous dispersion may contain other components as long as the effects of the polyurethane aqueous dispersion are not impaired. These other components may be contained in the resin particles as dispersoid, or may be contained separately dispersed or dissolved in the aqueous dispersion medium (D). For example, in the polyurethane aqueous dispersion, the resin particles as dispersoid may be composed solely of polyurethane resin (A), or may contain other components in addition to the polyurethane resin (A). The polyurethane aqueous dispersion may also contain a surfactant for dispersing the polyurethane resin (A) in the aqueous dispersion medium (D). The carbodiimide group-containing compound (B) and the hydrazide group-containing compound (C) may be contained in the resin particles, but if they are hydrophilic or water-soluble, they may be contained separately dispersed or dissolved in the aqueous dispersion medium (D).

[Method of producing aqueous dispersion]
The method for producing 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 produced by the following steps (a1) to (a5).
Step (a1): A step of reacting a polyol including a polyester polyol and a carboxyl group-containing polyol with a polyisocyanate to synthesize an isocyanate group-containing urethane prepolymer.
Step (a2): A step of neutralizing the 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 (D).
Step (a4): A step of extending the chain of the isocyanate group-containing urethane prepolymer with a chain extender.
Step (a5): A step of mixing a carbodiimide group-containing compound (B) and a hydrazide group-containing compound (C) with an aqueous dispersion containing the chain-extended anionic polyurethane resin.

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).

In addition, 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 that does not have an active hydrogen group, such as methyl ethyl ketone or acetone.

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

In 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, 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, homomixer, or the like.

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

Neutralization in step (a2), dispersion in step (a3), and chain elongation in step (a4) may be performed in this order, or two or more steps may be performed simultaneously. For example, when ammonia water is used to neutralize the carboxyl groups, dispersion in an aqueous dispersion medium may be performed simultaneously with neutralization, and chain elongation using water may then be performed. If the reaction between polyol and 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 (a3). When a compound that does not react with isocyanate groups is used as the hydrazide group-containing compound (C), the compound may be added at any stage of steps (a1) to (a4).

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

In the above step (b1), the polyol is used so that the hydroxy groups are in stoichiometric excess over 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).

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 groups, dispersion in an aqueous dispersion medium may be performed simultaneously with neutralization. Note that 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 dispersion in an aqueous dispersion medium in step (b3).

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

In one embodiment, the water-based paint may be a primer paint used as a primer. For example, the water-based paint according to this embodiment may be applied to a resin substrate such as a polyester resin substrate to form a coating film, and 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, resulting in a laminate used as a primer layer. One example of an application of such a laminate is an optical film. A coating film made from the water-based paint according to this embodiment has excellent adhesion to resin substrates such as polyester resins, and also has excellent adhesion to UV-curable resins. Therefore, it is suitable for use as such a primer.

In one embodiment, the primer may be used in the following application: A primer is applied to both sides (side A and side B) of a resin substrate such as a PET film and dried to form a primer layer. Next, a UV-curable resin is applied to side A and irradiated with UV light to form a UV-curable resin layer. After that, a UV-curable resin is applied to side B and irradiated with UV light to form a UV-curable resin layer. In such applications, if UV irradiation on side A causes the primer in the primer layer on side B to deteriorate, even if a UV-curable resin is subsequently applied to side B and cured, the adhesion of the UV-curable resin layer to the primer layer may be poor. The water-based paint of this embodiment suppresses deterioration due to UV irradiation and has excellent UV-resistant adhesion, thereby improving the adhesion of the coating film on both sides A and B even in such applications.

The UV-curable resin that constitutes 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-curable resin containing polyalkylene glycol as a constituent may also be used.

The aqueous paint may or may not contain other aqueous resins commonly used as film-forming components in aqueous paints 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.

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

Water-based paints can also contain various additives commonly used in water-based paints, as long as the additives do not impair their effectiveness. Examples of such additives include wetting agents, pigments, UV absorbers, light stabilizers, surface conditioners, inorganic fillers, organic fillers, dispersing aids, preservatives, rust inhibitors, antioxidants, silane coupling agents, defoamers, viscosity modifiers, antistatic agents, crosslinking agents, and organic solvents.

The present invention will be explained in more detail below based on examples and comparative examples, but the present invention is not limited to these.

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

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

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

Aromatic polyester polyol 3: number of functional groups: 2, number average molecular weight: 1000, solid content: 70% by mass, diluent: MEK.
A reaction vessel equipped with a stirrer, thermometer, reflux condenser, dropping tank, and nitrogen gas inlet tube was charged with 40.9 parts by mass of isophthalic acid, 19.89 parts by mass of adipic acid, 25.14 parts by mass of neopentyl glycol, and 14.07 parts by mass of ethylene glycol, and the mixture was heated to 250° C. with stirring under a nitrogen stream. The reaction was continued until the acid value reached 5 mg KOH/g or less (13.76 parts by mass of distilled water), and the mixture was cooled to 70° C., followed by the addition of 36.96 parts by mass of methyl ethyl ketone, to obtain aromatic polyester polyol 3.

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

Dimethylolpropionic acid: 2,2-bis(hydroxymethyl)propionic acid, functional group number 2
2,2-dimethylol butyric 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 Dai-ichi Kogyo Seiyaku Co., Ltd.

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

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

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

[Additives]
(Hydrazide group-containing compound)
HN-130: 1,6-hexamethylenebis(N,N-dimethylsemicarbazide), "HN-130" manufactured by Mitsubishi Gas Chemical Company, Ltd.
(Other additives)
・Sodium sulfite

The evaluation method for polyurethane aqueous dispersions is as follows:

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

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

- Polyurethane aqueous dispersion formulation:
A formulation was prepared by adding water to the polyurethane aqueous dispersion of each Example or Comparative Example so that the solid content was 10% by mass, and then adding 0.2% 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.

The following 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. Next, the surface coated with the UV-curable resin formulation was irradiated with ultraviolet light at 600 mJ/ ^cm2 using a high-pressure mercury lamp to obtain test piece Y. Using test piece Y as a sample, a 1 mm cross-cut test was carried out in accordance with JIS K5400-8.5:1990, and the initial adhesion between the PET film, primer layer, and UV-curable resin layer was calculated using the following formula. The test was carried out twice (n=1 and n=2), and the average value was calculated.
Initial adhesion (%) = 100 - (number of peeled squares)

UV-curable resin formulation: New Frontier BPE-4 (Dai-ichi Kogyo Seiyaku Co., Ltd.) / New Frontier PHE (Dai-ichi Kogyo Seiyaku Co., Ltd.) / Omnirad 184 (IGM Resins B.V.) = 32.7/64.3/3 (mass ratio)

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

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

[Example 1]
Into a four-neck flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen gas inlet tube, 92.5 parts by mass (64.8 parts by mass as solids) of aromatic polyester polyol 1, 3.0 parts by mass of dimethylolpropionic acid, 0.5 parts by mass of trimethylolpropane, 9.8 parts by mass of PEG 1000, and 100 parts by mass of methyl ethyl ketone were added and thoroughly mixed and dissolved. Next, 21.9 parts by mass of XDI was added as 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 content of free isocyanate groups relative to the solids content in the resulting urethane prepolymer solution was 1.2% by mass. The resulting urethane prepolymer solution was cooled to 60°C, and while stirring using a homogenizer, a solution of 3.5 parts by mass of 25% ammonia water and 350 parts by mass of water was gradually added to emulsify and disperse the 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, and water was added to adjust the solids content, yielding an aqueous dispersion with a solids content of 25% by mass. To the resulting aqueous dispersion, 62.5 parts by mass (25.0 parts by mass as solids) of water-soluble polycarbodiimide 1 and 5 parts by mass of HN-130 were added and stirred to obtain the polyurethane aqueous dispersion of Example 1. In the resulting polyurethane aqueous dispersion, the acid value of the polyurethane resin was 12.5 mgKOH/g. Furthermore, the amount of carbodiimide groups per 100 moles of carboxy groups in the polyurethane resin was 260 moles.

[Examples 2 to 17 and Comparative Examples 1 to 3]
The types and amounts (parts by mass) of the polyol, polyisocyanate, neutralizing agent, crosslinking agent, and additives were changed as shown in Tables 1 to 4 below, and the rest was the same as in Example 1, to obtain aqueous polyurethane dispersions of Examples 2 to 17 and Comparative Examples 1 to 3.

The polyurethane aqueous dispersions of Examples 1 to 17 and Comparative Examples 1 to 3 were evaluated for initial adhesion, UV-resistant adhesion, and water-resistant adhesion. The results are shown in Tables 1 to 4.

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

The results are shown in Tables 1 to 4. In Comparative Example 1, the inclusion of the carbodiimide group-containing compound (B) resulted in excellent initial adhesion, but the absence of the hydrazide group-containing compound (C) resulted in poor UV-resistant adhesion. In Comparative Example 2, sodium sulfite was added as an additive, and despite the inclusion of the carbodiimide group-containing compound (B), initial adhesion was poor. In Comparative Example 3, epoxy compound 1 was added as a crosslinking agent instead of the carbodiimide group-containing compound (B), resulting in poor initial adhesion.

In contrast, Examples 1 to 17 exhibited excellent initial adhesion and UV-resistant adhesion. A comparison of Examples 1, 11, and 12 revealed that, as a polyisocyanate, an aromatic ring-containing polyisocyanate exhibited better initial adhesion and UV-resistant adhesion than an aliphatic polyisocyanate. A comparison of Examples 1 and 14 revealed that, as a neutralizing agent, ammonia tended to provide better initial adhesion than a tertiary amine (triethylamine). A comparison of Examples 1, 7, 8, and 17 revealed that aromatic polyester polyol exhibited better water-resistant adhesion than aliphatic polyester polyol.

The various numerical ranges described in this specification can each be combined with any upper and lower limit, and all such combinations are considered to be preferred numerical ranges and are described in this specification. Furthermore, a numerical range described as "X to Y" means greater than or equal to X and less than or equal to Y.

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 (7)

A polyurethane aqueous dispersion obtained by dispersing a polyurethane resin (A) containing a polyester polyol as a constituent component in an aqueous dispersion medium,
The polyurethane resin (A) has a carboxy group,
The polyurethane aqueous dispersion contains a carbodiimide group-containing compound (B) and a compound (C) represented by the following general formula (2) :
In general formula (2) , R ¹ represents a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, R ² represents a hydrocarbon group having 1 to 3 carbon atoms, and R ³ represents a divalent organic group having 1 to 12 carbon atoms .
Polyurethane water-based dispersion. A polyurethane aqueous dispersion obtained by dispersing a polyurethane resin (A) containing a polyester polyol as a constituent component in an aqueous dispersion medium,
The polyurethane resin (A) has a carboxy group,
The polyurethane aqueous dispersion contains a carbodiimide group-containing compound (B) and a compound (C) having two groups represented by the following general formula (1) in one molecule:
In general formula (1), R ¹ represents a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, R ² represents a hydrocarbon group having 1 to 3 carbon atoms, * represents a bond,
The compound (C) includes a compound represented by the following general formula (3):
In general formula (3), R ¹ represents a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, R ² represents a hydrocarbon group having 1 to 3 carbon atoms, and m represents an integer of 1 to 12.
Polyurethane water-based dispersion. The polyurethane aqueous dispersion according to claim 1, wherein the polyester polyol comprises an aromatic polyester polyol. A polyurethane aqueous dispersion obtained by dispersing a polyurethane resin (A) containing a polyester polyol as a constituent component in an aqueous dispersion medium,
The polyurethane resin (A) has a carboxy group,
The polyurethane aqueous dispersion contains a carbodiimide group-containing compound (B) and a compound (C) having two groups represented by the following general formula (1) in one molecule:
In general formula (1), R ¹ represents a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, R ² represents a hydrocarbon group having 1 to 3 carbon atoms, * represents a bond,
The polyurethane aqueous dispersion contains 100 to 350 moles of carbodiimide groups in the carbodiimide group - containing compound (B) per 100 moles of carboxy groups in the polyurethane resin (A). A polyurethane aqueous dispersion obtained by dispersing a polyurethane resin (A) containing a polyester polyol as a constituent component in an aqueous dispersion medium,
The polyurethane resin (A) has a carboxy group,
The polyurethane aqueous dispersion contains a carbodiimide group-containing compound (B) and a compound (C) having two groups represented by the following general formula (1) in one molecule:
In general formula (1), R ¹ represents a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, R ² represents a hydrocarbon group having 1 to 3 carbon atoms, * represents a bond,
The polyurethane aqueous dispersion contains the compound (C) in an amount of 0.1 to 20 parts by mass per 100 parts by mass of the polyurethane resin (A). An aqueous paint comprising the polyurethane aqueous dispersion described in any one of claims 1 to 5. The water-based paint according to claim 6, which is used as a primer.