Water-based polyurethane dispersions and water-based paints

Abstract

To improve the adhesion and UV resistance of the coating film to the resin. [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 compound (C) having a group represented by the following general formula (1). The polyurethane resin (A) has a carboxyl group, and the acid value of the polyurethane resin (A) is 5 to 25 mgKOH / g. In formula (1), R 1 and R 2 Each of the symbols independently represents a hydrogen atom or a hydrocarbon group with 1 to 3 carbon atoms, and * represents a bonding bond. [Case 1] JPEG2026055846000010.jpg23156

Description

[Technical Field]

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

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

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-146694 [Patent Document 2] Japanese Patent Publication No. 2021-147428 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] When a polyurethane aqueous dispersion is used as a coating applied to the surface of a resin, such as polyester resin, the coating film must have good adhesion to the resin being coated. Furthermore, when used as a primer, the coating film must have adhesion not only to the resin substrate but also to the topcoat layer applied via the primer. Thus, in the case of polyurethane aqueous dispersions, good adhesion of the coating film to the resin is required.

[0005] According to the inventors' research, the adhesion of the coating film to the resin was found to be improved by setting a lower acid value for the polyurethane resin and incorporating a carbodiimide group-containing compound. However, it was found that when used, for example, as a primer, the coating film is irradiated with ultraviolet (UV) light, and then a topcoat layer is applied to form a three-layer structure, resulting in poor adhesion of the coating film, i.e., poor UV resistance to adhesion.

[0006] Furthermore, the aforementioned Patent Documents 1 and 2 specifically describe the blending of a carbodiimide compound or a hydrazide compound with a polyurethane resin having a relatively high acid value. They do not disclose the combined use of a carbodiimide compound and a hydrazide compound with a polyester-based urethane resin having a relatively low acid value, nor do they disclose that this improves UV-resistant adhesion.

[0007] The embodiments of the present invention aim to provide a polyurethane aqueous dispersion that can improve the adhesion and UV resistance of a coating film to a resin, and an aqueous coating using the same. [Means for solving the problem]

[0008] 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 compound (C) having a group represented by the following general formula (1). [ka] In general formula (1), R 1 and R 2 Each of the symbols independently represents a hydrogen atom or a hydrocarbon group with 1 to 3 carbon atoms, and * represents a bond. The polyurethane resin (A) has a carboxyl group, and the acid value of the polyurethane resin (A) is 5 to 25 mgKOH / g. Aqueous polyurethane dispersion.

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

[0010] According to the embodiment of the present invention, the adhesion of the coating film to the resin and the adhesion resistance to UV can be improved. [Embodiments for Carrying Out the Invention]

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

[0012] [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).

[0013] 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.

[0014] 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.

[0015] Preferred polyvalent hydroxyl group-containing compounds are diols, such as aliphatic diols including 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 such as 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.

[0016] Aromatic polyester polyols are preferred as the polyester polyol. That is, in a preferred embodiment, the polyester polyol includes an aromatic polyester polyol. By using an aromatic polyester polyol, the water-resistant adhesion of the coating film to the resin can be improved. An 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, more preferably 90% by mass or more, and even more preferably 100% by mass.

[0017] The molecular weight of the polyester polyol is not particularly limited; for example, the number-average molecular weight (Mn) may be 500 to 5000, 800 to 4000, or 1000 to 3000.

[0018] 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.

[0019] The amount of polyester polyol in the polyol constituting the polyurethane resin (A) is not particularly limited, but for example, it is preferably 60 to 99% 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, based on 100% by mass of the polyol.

[0020] In this specification, when calculating the amount of each component constituting a polyol, 100% by mass of the polyol used as the standard is calculated with the carboxyl group in the acid form if the polyol contains a carboxyl group-containing polyol as described later. Similarly, the amount of the carboxyl group-containing polyol is also calculated with the carboxyl group in the acid form.

[0021] In this embodiment, the polyurethane resin (A) has a carboxyl group, which allows it to react with the carbodiimide group-containing compound (B) to form a crosslinked structure during the heat drying of the aqueous dispersion. In this specification, unless otherwise specified, the carboxyl group is a concept that includes not only the acidic form (-COOH) but also the saltic form, i.e., a carboxylic acid base (-COOX, where X is a cation that forms a salt with a carboxylic acid), and acidic and saltic forms may be present together.

[0022] Examples of carboxylic acid base salts include alkali metal salts such as sodium salts and potassium salts, alkaline earth metal salts such as magnesium salts and calcium salts, ammonium salts, amine salts (primary amine salts, secondary amine salts, tertiary amine salts), and quaternary ammonium salts. Among these, salts of volatile bases such as ammonium salts and amine salts are preferred. When a volatile base is used, it vaporizes during heating and drying of the aqueous dispersion, causing the carboxyl group to easily become acidic, which improves the reactivity with the carbodiimide group-containing compound (B) and enhances the adhesion of the coating film to the resin.

[0023] In this embodiment, the acid value of the polyurethane resin (A) is 5 to 25 mgKOH / g. An acid value of 5 mgKOH / g or higher facilitates emulsification of the polyurethane resin (A) in an aqueous dispersion medium. An acid value of 25 mgKOH / g or lower improves the adhesion of the coating film to the resin. The acid value of the polyurethane resin (A) is more preferably 7 to 20 mgKOH / g, and even more preferably 10 to 15 mgKOH / g.

[0024] In this specification, the acid value can be determined from the amount of KOH (mg) required to neutralize the carboxyl groups contained in 1 g of polyurethane resin (A), in accordance with JIS K0070-1992. Note that if polyurethane resin (A) is a salt of a volatile base, the volatile base vaporizes when measuring the mass of polyurethane resin (A), so the acid value is calculated based on the mass of the non-volatile acidic polyurethane resin. Thus, the mass of polyurethane resin (A) in this specification refers to the mass of the non-volatile content.

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

[0026] 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 one of these may be used, or two or more may be used in combination.

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

[0028] 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.

[0029] Examples of polyalkylene glycols include polyethylene glycol, polytrimethylene glycol, polypropylene glycol, polytetramethylene glycol, polybutylene glycol, and copolymers using two or more of these constituent monomers. The molecular weight of the polyalkylene glycol is not particularly limited; for example, the number average molecular weight (Mn) may be 500 to 5000, 800 to 4000, or 1000 to 3000.

[0030] The amount of polyalkylene glycol in the polyurethane resin (A) (i.e., the amount of structure 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 the polyurethane resin (A). The amount of polyalkylene glycol in the polyol is not particularly limited and may be, for example, 3 to 25% by mass, 5 to 20% by mass, or 10 to 15% by mass, per 100% by mass of the polyol.

[0031] 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.

[0032] 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.

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

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

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

[0036] Examples of aromatic aliphatic polyisocyanates include 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, biuret compounds, allophenates, and carbodiimides.

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

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

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

[0040] As the polyisocyanate, it is preferable to use aromatic ring-containing polyisocyanates such as aromatic polyisocyanates and aromatic aliphatic polyisocyanates, and more preferably aromatic aliphatic 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 100% by mass.

[0041] 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).

[0042] 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.

[0043] [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).

[0044] 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.).

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

[0046] [Compound (C)] Compound (C) is a compound containing a group represented by the following general formula (1) in the molecule, that is, a hydrazide group. Therefore, hereinafter, it is referred to as a hydrazide group-containing compound (C). Here, the hydrazide group also includes an atomic group constituting a semicarbazide group in which -NH- is bonded to the bond in formula (1) in its concept. [Chemical formula]

[0047] In formula (1), R 1 and R 2 each independently represents a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, and * represents a bond. Since the UV-resistant adhesion is more excellent, at least one of R 1 and R 2 is preferably a hydrocarbon group having 1 to 3 carbon atoms, and more preferably both R 1 and R 2 are hydrocarbon groups having 1 to 3 carbon atoms.

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

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

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

[0051] In one embodiment, the hydrazide group-containing compound (C) has two groups represented by formula (1) in one molecule, and R in formula (1) 1 and R 2 It is preferable that the compound (C1) contains at least one of which is a hydrocarbon group having 1 to 3 carbon atoms. In that case, the amount of 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.

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

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

[0054] Specific examples of hydrazide group-containing compounds (C) include 1,6-hexamethylenebis(N,N-dimethyl semicarbazide), adipic acid dihydrazide, sebacate acid dihydrazide, and dodecanedihydrazide. Any one of these may be used, or two or more may be used in combination.

[0055] [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.

[0056] 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.

[0057] [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 hydrazide group-containing compound (C). By incorporating the carbodiimide group-containing compound (B) into the aqueous dispersion of polyurethane resin (A) in this way, the adhesion of the coating film to the resin can be improved. Furthermore, by incorporating the hydrazide group-containing compound (C), UV resistance and adhesion can be improved.

[0058] 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 of the carbodiimide group-containing compound (B) per 100 moles of carboxyl groups of the polyurethane resin (A).

[0059] As described above, by making the acid value of the polyurethane resin (A) relatively low and setting the number of moles of carbodiimide groups to be equal to or greater than the number of moles of carboxyl groups, carbodiimide groups tend to remain in the cured coating film. These remaining carbodiimide groups can enhance the effect of improving the adhesion of the coating film to the resin, and in particular, the effect of improving adhesion to the topcoat layer. It is thought that the remaining carbodiimide groups contribute to the adhesion with the acrylate resin contained in the topcoat layer, but this is not limited to this. Furthermore, by having 350 moles or less of carbodiimide groups, the effect of improving the adhesion of the coating film to the resin substrate, in particular UV-resistant adhesion, can be enhanced. The amount of carbodiimide groups per 100 moles of carboxyl groups is more preferably 120 to 320 moles, more preferably 180 to 300 moles, and even more preferably 220 to 280 moles.

[0060] From the viewpoint of enhancing its effect, 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 polyurethane resin (A). More preferably, the content of the hydrazide group-containing compound (C) is 0.3 to 18 parts by mass, more preferably 1 to 15 parts by mass, and even more preferably 2 to 10 parts by mass.

[0061] The content of 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.

[0062] 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 "Microtrac UPA-UZ152" manufactured by Nikkiso Co., Ltd.

[0063] 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) 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 in the aqueous dispersion medium (D) in a dispersed or dissolved state.

[0064] [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 hydrazide group-containing compound (C) into an aqueous dispersion containing the anionic polyurethane resin after chain elongation.

[0065] 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).

[0066] 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.

[0067] In step (a2) described 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.

[0068] 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.

[0069] 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).

[0070] 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, when 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 the polyisocyanate in step (a1) is carried out in an organic solvent, the organic solvent may be removed after dispersion in an aqueous dispersion medium in step (a4). If a compound that does not react with the isocyanate group is used as the hydrazide group-containing compound (C), the compound may be added at any of the steps (a1) to (a4).

[0071] 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 hydrazide group-containing compound (C) into an aqueous dispersion containing a hydroxyl group-containing polyurethane resin.

[0072] 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).

[0073] 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).

[0074] [Water-based paint] The aqueous coating according to this 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 hydrazide group-containing compound (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.

[0075] 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.

[0076] In one embodiment, the primer may be used in the following applications: 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 UV irradiation is performed to form a UV-curable resin layer. Subsequently, a UV-curable resin is applied to side B, and UV irradiation is performed to form a UV-curable resin layer. In such applications, if UV irradiation of side A causes the primer in the primer layer on side B to deteriorate, even if 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. With the water-based paint according to this embodiment, deterioration due to UV irradiation is suppressed and UV adhesion is excellent, so even in such applications, the adhesion of the coating film can be improved on both sides A and B.

[0077] 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.

[0078] 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.

[0079] The content of polyurethane resin (A), carbodiimide group-containing compound (B), and hydrazide group-containing compound (C) in the water-based paint is not particularly limited. For example, the total content 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 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.

[0080] 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]

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

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

[0083] [Polyol] Aromatic polyester polyol 1: 2 functional groups, number average molecular weight 1000, solids content 70% by mass, diluting solvent 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, 16.2 parts by mass of succinic anhydride and 83.8 parts by mass of bisphenol A ethylene oxide adduct ("Newpol BPE-20NK" manufactured by Sanyo Chemical Industries, Ltd.) were charged, 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 (2.92 parts by mass of distilled water was added), and after cooling to 70°C, 41.61 parts by mass of methyl ethyl ketone was added to obtain aromatic polyester polyol 1.

[0084] 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, 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 continued until the acid value was 5 mg KOH / g or less (3.58 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 2.

[0085] Aromatic polyester polyol 3: 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, 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 removed by distillation), and after cooling to 70°C, 36.96 parts by mass of methyl ethyl ketone was added to obtain aromatic polyester polyol 3.

[0086] Aliphatic polyester polyol: 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, 53.1 parts by mass of adipic acid and 46.9 parts by mass of neopentyl glycol were charged, and the mixture was heated to 250°C while stirring under a nitrogen stream. The reaction was continued until the acid value was 5 mg KOH / g or less (13.08 parts by mass of water removed by distillation), and after cooling to 70°C, 37.25 parts by mass of methyl ethyl ketone was added to obtain an aliphatic polyester polyol.

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

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

[0089] [Neutralizing agent] • Ammonia water: 25% by mass aqueous solution Triethylamine

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

[0091] [Additives] (hydrazide group-containing compound) • HN-130: 1,6-Hexamethylenebis(N,N-dimethyl semicarbazide), manufactured by Nippon Finechem Co., Ltd. "HN-130" • ADH: Dihydrazide adipic acid, manufactured by Nippon Finechem Co., Ltd. ("ADH") (Other additives) Sodium sulfite

[0092] The evaluation method for polyurethane aqueous dispersions is as follows:

[0093] [Initial 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.

[0094] A polyethylene terephthalate (PET) film (Toray Industries, Inc.'s "Lumirror T-60") was used as a substrate, and 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 1 μm, and dried at 180°C for 1 minute to obtain a test piece X with a polyurethane resin coating.

[0095] • 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 0.2% by mass of a wetting agent (NeoCall SW-C, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) per 100% by mass of the aqueous dispersion.

[0096] The following UV-curing resin formulation was applied to the coating of test specimen X using a bar coater to a thickness of 12 μm. Then, 600 mJ / cm² of UV-curing resin formulation was applied to the coated surface using a high-pressure mercury lamp. 2 Test specimen Y was obtained by irradiating it with ultraviolet light. Using test specimen Y as a sample, a 1 mm grid test was performed 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 performed twice (n=1 and n=2), and the average value was calculated. Initial adhesion (%) = 100 - (number of squares that peeled off)

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

[0098] [UV-resistant adhesion] On the surface of the coating of the above test specimen X, a high-pressure mercury lamp was used to apply 600 mJ / cm² of pressure. 2 After irradiation with ultraviolet light, the UV-curing resin formulation was applied to the coating film using a bar coater to a thickness of 12 μm. Next, 600 mJ / cm² of UV-curing resin formulation light was applied to the coated surface using a high-pressure mercury lamp. 2 Test specimen Z was obtained by irradiating it with ultraviolet light. Using test specimen Z as a sample, a 1 mm grid test was performed 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 performed twice (n=1 and n=2), and the average value was calculated. UV resistance (%) = 100 - (number of peeled squares)

[0099] [Water-resistant adhesion] The above test specimen X was immersed in 100°C hot water for 48 hours. After cooling to room temperature, the test specimen X was removed, and its condition was checked by rubbing the surface with a finger while wet. It was then evaluated according to the following criteria. A: No peeling (good water-resistant adhesion) B: Peeling present (poor water-resistant adhesion)

[0100] [Example 1] In a four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen gas inlet tube, 1 part by mass of aromatic polyester polyol (64.8 parts by mass as solids), 3.0 parts by mass of dimethylolpropionic acid, 0.5 parts by mass of trimethylolpropane, 9.8 parts by mass of PEG1000, and 100 parts by mass of methyl ethyl ketone were added and thoroughly mixed and dissolved. Next, 21.9 parts by mass of XDI 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 3.5 parts by mass of 25% by mass of aqueous ammonia and 350 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 added to adjust the solid content to obtain an aqueous dispersion with a solid content of 25% by mass. To the obtained aqueous dispersion, 62.5 parts by mass (25.0 parts by mass as solid content) of water-soluble polycarbodiimide 1 and 5 parts by mass of HN-130 were added and stirred to obtain the polyurethane aqueous dispersion of Example 1. In the obtained polyurethane aqueous dispersion, the acid value of the polyurethane resin was 12.5 mgKOH / g. Also, the amount of carbodiimide groups per 100 moles of carboxyl groups in the polyurethane resin was 260 moles.

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

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

[0103] In Tables 1-4, the amount of polyester polyol represents the amount of solids, which are the active ingredient, and the number in parentheses represents the amount including the solvent. In Tables 1-4, the amount of carbodiimide group-containing compound represents the amount of each component including the solvent, and the number in parentheses represents 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. "(Carbodiimide group*100) / carboxyl group [mol]" is the amount (moles) of carbodiimide groups in the carbodiimide group-containing compound per 100 moles of carboxyl groups in the polyurethane resin.

[0104] [Table 1]

[0105] [Table 2]

[0106] [Table 3]

[0107] [Table 4]

[0108] The results are shown in Tables 1-4. 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 resistance. In Comparative Example 2, sodium sulfite was added as an additive, and despite the inclusion of the carbodiimide group-containing compound (B), the initial adhesion was poor.

[0109] In Comparative Example 3, the acid value of the polyurethane resin was too high, resulting in poor initial adhesion despite the addition of sufficient carbodiimide group-containing compound (B). In Comparative Example 4, an attempt was made to prepare the polyurethane resin so that its acid value was lower than the set value at 4.2 mg KOH / g. However, the amount of carboxyl group-containing polyol was too small, and the urethane prepolymer could not be emulsified.

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

[0111] In contrast, Examples 1 to 18 showed excellent initial adhesion as well as excellent UV resistance. Comparing Example 1 with Example 7, HN-130 showed superior UV resistance compared to ADH as the hydrazide group-containing compound (C). Comparing Example 1 with Examples 12 and 13, aromatic ring-containing polyisocyanates showed superior initial adhesion and UV resistance compared to aliphatic polyisocyanates. Comparing Example 1 with Example 15, ammonia tended to show better initial adhesion than tertiary amine (triethylamine) as a neutralizing agent. Comparing Example 1 with Examples 8, 9 and 18, aromatic polyester polyols showed superior water resistance compared to aliphatic polyester polyols.

[0112] Furthermore, the various numerical ranges described in the 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.

[0113] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the 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 compound (C) having a group represented by the following general formula (1). 【Chemistry 1】 In general formula (1), R １ and R ２ Each of these independently represents a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, and * represents a bonding bond. The polyurethane resin (A) has a carboxyl group, and the acid value of the polyurethane resin (A) is 5 to 25 mg KOH / g. Aqueous polyurethane dispersion.

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

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

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

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

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

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

8. A water-based paint according to claim 7, used as a primer.

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