Aqueous dispersion of polyurethane resin and aqueous coating material

Abstract

The storage stability and the heat resistance of a coating film are improved while the viscosity is reduced. An aqueous polyurethane resin dispersion according to an embodiment is obtained by reacting a polyol (A), a polyisocyanate (B), and a chain extender (C). The polyol (A) includes an aromatic polyester polyol (A1) and an aliphatic diol (A2) having a hydrocarbon group in a side chain. The chain extender (C) contains a compound (C1) having three primary amino groups and / or secondary amino groups and not having a hydroxyl group, and a compound (C2) having one or more hydroxyl groups and two or more primary amino groups and / or secondary amino groups. The acid value is 11.0 to 23.0 mgKOH / g, and the hydroxyl value is 8.0 to 23.0 mgKOH / g.

Description

Technical Field

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

[0002] Aqueous dispersions of polyurethane resins are widely used in coatings, inks, adhesives, coating agents, and the like. For example, Patent Document 1 discloses an emulsion composition of a polyurethane resin neutralized with a neutralizer as an aqueous polyurethane emulsion composition having good adhesion to various substrate films, wherein the polyurethane resin is obtained by reacting a polyester polyol, a carboxyl-containing acrylic polyol, a carboxyl-containing polyol, an organic diisocyanate, a chain extender, and a molecular weight regulator. In Patent Document 1, as the polyester polyol, a polyester polyol obtained by reacting an aromatic dicarboxylic acid, an aliphatic dicarboxylic acid, and a diol containing a side chain alkyl group is used, and as a chain extender, a diamine and a triamine are used.

[0003] Patent Document 2 discloses the use of a polyurethane having a hydroxyl group as an aqueous polyurethane resin to be formulated together with a water-soluble acrylic resin in an aqueous coating composition, wherein the polyurethane having a hydroxyl group is obtained by reacting a polyol having a number average molecular weight of 500 to 5000, a low molecular weight alcohol having at least two hydroxyl groups, a compound having at least one primary or secondary amino group, a polyisocyanate compound, and a compound having a carboxyl group and active hydrogen.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2007-119772

[0007] Patent Document 2: Japanese Patent Application Publication No. 2005-89613 Summary of the invention

[0008] In the aqueous dispersion of polyurethane resin, in view of workability, etc., if the solid content is the same, it is preferred that the viscosity is low, and storage stability is also required. In addition, heat resistance is sometimes required for the coating film formed by the aqueous dispersion depending on the application. However, the conventional aqueous dispersion of polyurethane resin may not necessarily meet the requirements of low viscosity, storage stability and heat resistance.

[0009] An object of an embodiment of the present invention is to provide an aqueous dispersion of a polyurethane resin that can achieve low viscosity and improve storage stability and heat resistance.

[0010] The present invention includes the following embodiments.

[0011] [1] An aqueous dispersion of a polyurethane resin obtained by reacting a polyol (A), a polyisocyanate (B) and a chain extender (C),

[0012] The polyol (A) comprises an aromatic polyester polyol (A1) and an aliphatic diol (A2) having a hydrocarbon group in a side chain.

[0013] The chain extender (C) comprises a compound (C1) having three primary and / or secondary amino groups and no hydroxyl group, and a compound (C2) having one or more hydroxyl groups and two or more primary and / or secondary amino groups.

[0014] The acid value is 11.0 to 23.0 mgKOH / g, and the hydroxyl value is 8.0 to 23.0 mgKOH / g.

[0015] [2] The aqueous dispersion of the polyurethane resin according to [1], wherein the mass ratio (C1) / (C2) of the compound (C1) to the compound (C2) is 0.3 to 1.4.

[0016] [3] The aqueous dispersion of the polyurethane resin according to [1] or [2], wherein the aliphatic diol (A2) has 3 to 10 carbon atoms.

[0017] [4] The aqueous dispersion of the polyurethane resin according to any one of [1] to [3], wherein the polyisocyanate (B) contains an alicyclic polyisocyanate.

[0018] [5] The aqueous dispersion of the polyurethane resin according to any one of [1] to [4], wherein the amount of the aromatic polyester polyol (A1) is 70 to 90% by mass relative to 100% by mass of the polyol (A).

[0019] [6] The aqueous dispersion of the polyurethane resin according to any one of [1] to [5], wherein the polyol (A) further contains a carboxyl group-containing polyol (A3).

[0020] [7] The aqueous dispersion of the polyurethane resin according to any one of [1] to [6], wherein the polyol (A) further contains a trivalent alcohol (A4) having a molecular weight of 350 or less.

[0021] [8] A water-based coating material comprising an aqueous dispersion of the polyurethane resin according to any one of [1] to [7].

[0022] According to the embodiment of the present invention, the viscosity of the aqueous dispersion of the polyurethane resin can be reduced, and the storage stability and heat resistance can be improved. DETAILED DESCRIPTION

[0023] The aqueous dispersion of the polyurethane resin of the present embodiment (hereinafter, sometimes simply referred to as an aqueous dispersion) is an aqueous dispersion obtained by reacting a polyol (A), a polyisocyanate (B), and a chain extender (C).

[0024] [Polyol (A)]

[0025] In this embodiment, aromatic polyester polyol (A1) and aliphatic diol (A2) having a hydrocarbon group in a side chain are used as polyol (A). By using aromatic polyester polyol (A1), the storage stability of the aqueous dispersion can be improved, and the strength of the coating film can be improved compared to the case of using aliphatic polyester polyol. By using aliphatic diol (A2) having a hydrocarbon group in a side chain, the viscosity of the aqueous dispersion can be reduced, and the storage stability can be improved.

[0026] (Aromatic polyester polyol (A1))

[0027] As the aromatic polyester polyol (A1), an aromatic polyester polyol obtained by esterification reaction of a polycarboxylic acid including an aromatic polycarboxylic acid and a polyol can be used.

[0028] As aromatic polycarboxylic acids, for example, phthalic acid, isophthalic acid, terephthalic acid, 1,4-naphthalene dicarboxylic acid, 2,3-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, biphenyl dicarboxylic acid, trimellitic acid, pyromellitic acid and their anhydrides or ester derivatives can be cited. Any one of these can be used, or two or more can be used in combination. If the polycarboxylic acid constituting the aromatic polyester polyol (A1) includes an aromatic polycarboxylic acid, for example, aliphatic polycarboxylic acids such as adipic acid, glutaric acid, succinic acid and their anhydrides can be used in combination. The amount of the aromatic polycarboxylic acid relative to 100 parts by mass of the polycarboxylic acid is preferably 50 parts by mass or more, more preferably 55 parts by mass or more, further preferably 60 parts by mass or more, and can be 65 to 90 parts by mass.

[0029] Examples of the polyols to be reacted with the polycarboxylic acid include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, dipropylene glycol, tripropylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 2,3-butylene glycol, 1,5-pentanediol, 1,5-hexanediol, 1,6-hexanediol, 2,5-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, and 1,13-hexanediol. aliphatic polyols such as 1,4-cyclohexanedimethanol and hydrogenated bisphenol A; and bisphenol-type polyols such as bisphenol A, bisphenol A alkylene oxide adducts, bisphenol S, and bisphenol S alkylene oxide adducts. Any one of these may be used, or two or more of them may be used in combination.

[0030] The number average molecular weight (Mn) of the aromatic polyester polyol (A1) is not particularly limited, and may be, for example, 500 to 3,000, 800 to 2,500, or 1,000 to 2,000.

[0031] In this specification, the number average molecular weight (Mn) is a value calculated by measuring by GPC (gel permeation chromatography) and using a calibration curve based on standard polystyrene. Specifically, as the conditions of GPC, the conditions of chromatographic 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, injection volume: 50 μL, sample concentration: 0.2 mass % can be used for measurement.

[0032] (Aliphatic diol (A2) having a hydrocarbon group in a side chain)

[0033] In the aliphatic diol (A2) having a hydrocarbon group in the side chain, the side chain refers to a hydrocarbon group branching from a carbon chain connecting two hydroxyl groups as the main chain. The hydrocarbon group of the side chain may be saturated or unsaturated, and is preferably an alkyl group. The aliphatic diol (A2) may be saturated or unsaturated, and is preferably a saturated aliphatic diol (A2). The number of side chains branching from the main chain is not particularly limited, and may be, for example, 1 to 3, or 1 to 2. The number of carbon atoms in the side chain is not particularly limited, and may be, for example, the total of the side chains may be 1 to 8, or 1 to 6.

[0034] Specific examples of the aliphatic diol (A2) include 1,2-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 2,3-butylene glycol, 1,5-hexanediol, 2,5-hexanediol, 2-methyl-1,3-propylene glycol, 2,2-dimethyl-1,3-propylene glycol (also known as neopentyl glycol), 2-ethyl-1,3-propylene glycol, 2-butyl-2-ethyl-1,3-propylene glycol, 2,4-dimethyl-2-ethylhexyl-1,3-propylene glycol, 2-methyl-2-ethyl-1, 3-propylene glycol, 2-ethyl-2-isobutyl-1,3-propylene glycol, 2-methyl-1,4-butanediol, 2,2-dimethyl-1,4-butanediol, 2,3-dimethyl-1,4-butanediol, 2-methyl-1,5-pentanediol, 3-methyl-1,5-pentanediol, 2,3-dimethyl-1,5-pentanediol, 3,3-dimethyl-1,5-pentanediol, 2-ethyl-1,3-hexanediol, 2,2,4-trimethyl-1,6-hexanediol, 2-methyl-1,8-octanediol. Any one of these may be used, or two or more of them may be used in combination.

[0035] The aliphatic diol (A2) has preferably 3 to 10 carbon atoms, more preferably 4 to 10 carbon atoms, further preferably 5 to 10 carbon atoms, particularly preferably 6 to 9 carbon atoms.

[0036] (Carboxyl group-containing polyol (A3))

[0037] The polyol (A) preferably contains a carboxyl-containing polyol (A3) together with the aromatic polyester polyol (A1) and the aliphatic diol (A2). By containing the carboxyl-containing polyol (A3), the polyurethane resin can have an acid value. It should be noted that as a means for providing an acid value, for example, a polyol having other anionic hydrophilic groups such as a sulfonic acid-containing polyol can be used, but the carboxyl-containing polyol (A3) is more preferably used.

[0038] The carboxyl group-containing polyol (A3) is a polyol having a carboxyl group in the molecule, and examples thereof include carboxylic acid-containing compounds such as dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, 2,2-dimethylolvaleric acid, dihydroxymaleic acid (dioxymaleic acid), 2,6-dihydroxybenzoic acid (2,6-dioxybenzoic acid), 3,4-diaminobenzoic acid, and derivatives of these compounds and salts of these compounds. Any one of these may be used, or two or more of them may be used in combination.

[0039] Here, the carboxyl group is a concept that includes not only the acid type (-COOH) but also the salt type, that is, the carboxylate group (-COOX. X: a cation that forms a salt with a carboxylic acid), and the acid type and the salt type can exist in a mixture. The carboxyl group becomes a salt by neutralization, so that the final polyurethane resin can be water-dispersible. Therefore, in the aqueous dispersion of the polyurethane resin, the carboxyl group exists as a salt type. On the other hand, in the state of the coating obtained by drying the aqueous dispersion, it exists as a salt type when a non-volatile base is used as a neutralizer, and exists as an acid type when a volatile base is used. The type of salt type varies depending on the type of neutralizer described later, and can be an alkali metal salt such as a sodium salt, a tertiary amine salt such as a triethylamine salt, or an ammonium salt.

[0040] (Triol (A4) with a molecular weight of 350 or less)

[0041] The polyol (A) preferably contains a triol (A4) having a molecular weight of 350 or less together with the aromatic polyester polyol (A1) and the aliphatic diol (A2). By containing the low molecular weight triol (A4), the heat resistance of the coating film can be improved. The polyol (A) more preferably contains an aromatic polyester polyol (A1), an aliphatic diol (A2), a carboxyl group-containing polyol (A3) and the triol (A4).

[0042] As triols (A4) having a molecular weight of 350 or less, for example, trimethylolpropane, glycerol, trimethylolethane, butanetriol, pentanetriol, hexanetriol, and triols (e.g., polycaprolactone triol) obtained by ring-opening addition of lactones and / or epoxy compounds using these triols as initiators, etc. can be cited. Any one of these can be used, or two or more can be used in combination. The molecular weight of the triol (A4) is preferably 92 to 200, more preferably 100 to 150. It should be noted that in the case of the above-mentioned lactone and / or epoxy compound addition type triol, the molecular weight of the triol (A4) is the number average molecular weight (Mn).

[0043] (Amount of each component in polyol (A))

[0044] The amount of the aromatic polyester polyol (A1) is not particularly limited, but is preferably 70 to 90% by mass, more preferably 80 to 90% by mass, relative to 100% by mass of the polyol (A). When the amount of the aromatic polyester polyol (A1) is 70% by mass or more, the effects of improving storage stability and coating film strength can be improved.

[0045] The amount of the aliphatic diol (A2) having a hydrocarbon group in a side chain is not particularly limited, but is preferably 1 to 15% by mass, more preferably 2 to 10% by mass, based on 100% by mass of the polyol (A).

[0046] The amount of the carboxyl group-containing polyol (A3) is not particularly limited, and may be 20% by mass or less, 2 to 15% by mass, or 3 to 12% by mass relative to 100% by mass of the polyol (A).

[0047] The amount of the triol (A4) having a molecular weight of 350 or less is not particularly limited, and may be 10% by mass or less, 0.1 to 5% by mass, or 1 to 3% by mass relative to 100% by mass of the polyol (A).

[0048] Here, regarding the amount of each component constituting the polyol (A), for 100% by mass of the polyol (A) serving as the reference, when the polyol (A) contains an anionic hydrophilic group such as the carboxyl-containing polyol (A3), the anionic hydrophilic group is calculated as an acid type. The amount of the carboxyl-containing polyol (A3) is also calculated as an acid type.

[0049] [Polyisocyanate (B)]

[0050] As the polyisocyanate (B) reacting with the polyol (A), aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic polyisocyanates can be mentioned. Among them, alicyclic polyisocyanates are preferably used from the aspects of suppressing the coloring of the polyurethane resin and improving the coating film strength compared with the case of using aliphatic polyisocyanates.

[0051] Examples of the alicyclic polyisocyanate 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, etc. Any one of these may be used, or two or more of them may be used in combination.

[0052] The amount of the polyisocyanate (B), preferably the alicyclic polyisocyanate, is not particularly limited, and may be, for example, 10 to 60 parts by mass, 20 to 55 parts by mass, or 30 to 50 parts by mass relative to 100 parts by mass of the total amount of the polyol (A) and the polyisocyanate (B).

[0053] [Chain Extender (C)]

[0054] In this embodiment, as the chain extender (C), a compound (C1) having three primary and / or secondary amino groups and no hydroxyl group and a compound (C2) having one or more hydroxyl groups and two or more primary and / or secondary amino groups are used. By using the above two chain extenders in combination, the storage stability of the aqueous dispersion can be improved, and the heat resistance of the coating film can be improved.

[0055] Compound (C1) is a compound having three primary and / or secondary amino groups in one molecule and having no hydroxyl group. Both the primary amino group (-NH2) and the secondary amino group (-NHR) are amino groups having active hydrogen that reacts with an isocyanate group, and compound (C1) is a trifunctional amine having three primary and secondary amino groups in total. The number of carbon atoms in compound (C1) is not particularly limited, but is preferably 3 to 15.

[0056] As a specific example of compound (C1), as a compound having two primary amino groups and one secondary amino group in one molecule, for example, diethylenetriamine, iminodipropylamine, bis(6-aminohexyl)amine and other iminodialkylamines can be mentioned. In addition, as a compound having one primary amino group and two secondary amino groups in one molecule, for example, aminoalkylpiperazines such as 2-aminomethylpiperazine can be mentioned. Any one of these can be used, or two or more can be used in combination.

[0057] Compound (C2) is a compound having one or more hydroxyl groups and two or more primary and / or secondary amino groups in one molecule. That is, compound (C2) has either or both of a primary and secondary amino group with active hydrogen and has a total of two or more, and has one or more hydroxyl groups at the same time. Among hydroxyl groups and amino groups, amino groups are more reactive to isocyanate groups. If the isocyanate group and the amino group are equivalent during the reaction, the hydroxyl group hardly reacts. Therefore, the hydroxyl group of compound (C2) remains without reacting, which gives the polyurethane resin a hydroxyl value. As compound (C2), a compound having one hydroxyl group and two primary and / or secondary amino groups is preferred. The number of carbon atoms in compound (C2) is not particularly limited, but is preferably 3 to 10.

[0058] Specific examples of compound (C2) include N-(2-hydroxyethyl)ethylenediamine (also known as N-(2-aminoethyl)ethanolamine), N-(2-hydroxypropyl)ethylenediamine (also known as N-(2-aminoethyl)propanolamine), N-(3-hydroxypropyl)ethylenediamine, and N-(2-hydroxyethyl)-1,3-propylenediamine (also known as 3-(2-hydroxyethylamino)propylamine). As a compound having one hydroxyl group and two primary amino groups in one molecule, for example, diamino alcohols such as 1,3-diamino-2-propanol can be mentioned. Any one of these can be used, or two or more can be used in combination.

[0059] As the ratio of compound (C1) to compound (C2), the mass ratio (C1) / (C2) of the amount of compound (C1) relative to the amount of compound (C2) is preferably 0.3 to 1.4. This can improve the low viscosity and storage stability of the aqueous dispersion and the heat resistance of the coating film. The mass ratio (C1) / (C2) is preferably 0.4 to 1.0, and more preferably 0.5 to 0.9.

[0060] The amount of the chain extender (C) (more preferably the total amount of the compound (C1) and the compound (C2)) is not particularly limited, and for example, it can be 0.5 to 15 parts by mass, 1 to 10 parts by mass, or 2 to 8 parts by mass relative to 100 parts by mass of the total amount of the polyol (A) and the polyisocyanate (B).

[0061] [Aqueous dispersion of polyurethane resin]

[0062] The aqueous dispersion of the polyurethane resin is obtained by reacting a polyol (A), a polyisocyanate (B) and a chain extender (C) and dispersing the polyurethane resin in water. More specifically, the aqueous dispersion of the polyurethane resin is obtained by reacting a urethane prepolymer obtained by reacting a polyol (A) and a polyisocyanate (B) with a chain extender (C).

[0063] The acid value of the polyurethane resin is 11.0 to 23.0 mgKOH / g. When the acid value is 11.0 mgKOH / g or more, the emulsification and dispersibility in water can be improved, and the storage stability of the aqueous dispersion can be improved. When the acid value is 23.0 mgKOH / g or less, the viscosity of the aqueous dispersion can be reduced, and the storage stability can be improved. The acid value of the polyurethane resin is more preferably 13.0 to 20.0 mgKOH / g. The acid value of the polyurethane resin can be adjusted, for example, according to the type and amount of the carboxyl-containing polyol (A3).

[0064] In this specification, the acid value can be determined according to JIS K0070-1992 from the amount (mg) of KOH required to neutralize free carboxyl groups contained in 1 g of the solid content of the aqueous dispersion of the polyurethane resin (ie, the polyurethane resin).

[0065] The hydroxyl value of the polyurethane resin is 8.0 to 23.0 mgKOH / g. When the hydroxyl value is 8.0 mgKOH / g or more, the affinity for water can be improved, and the storage stability of the aqueous dispersion can be improved. When the hydroxyl value is 23.0 mgKOH / g or less, the viscosity of the aqueous dispersion can be reduced, the storage stability can be improved, and the heat resistance of the coating can be improved. The hydroxyl value of the polyurethane resin is more preferably 10.0 to 18.0 mgKOH / g. The hydroxyl value of the polyurethane resin can be adjusted, for example, according to the type and amount of compound (C2).

[0066] In this specification, the hydroxyl value is measured according to the A method of JIS K1557-1:2007.

[0067] The number average molecular weight (Mn) of the polyurethane resin is not particularly limited, and may be, for example, 10,000 or more, or 50,000 or more. The average particle size of the aqueous dispersion of the polyurethane resin is not particularly limited, and may be, for example, 0.005 to 0.5 μm. Here, the average particle size is the 50% cumulative particle size (d50) measured using "Microtrac UPA-UZ152" manufactured by Nikkiso Co., Ltd.

[0068] The method for producing the aqueous dispersion of the polyurethane resin is not particularly limited, and examples thereof include the following method: a polyol (A) and a polyisocyanate (B) are reacted to obtain a urethane prepolymer, the urethane prepolymer is neutralized with a neutralizing agent, the urethane prepolymer is emulsified and dispersed in water, and then the urethane prepolymer is reacted with a chain extender (C).

[0069] In detail, polyol (A) and polyisocyanate (B) are reacted in the absence of solvent or in an organic solvent having no active hydrogen group to synthesize an isocyanate-terminated urethane prepolymer. At this time, the polyisocyanate (B) is used in a stoichiometric excess of the amount of isocyanate groups compared to the amount of active hydrogen groups contained in the polyol (A), for example, in a manner where the equivalent ratio of isocyanate groups to active hydrogen groups is 1:0.85 to 0.99. After the synthesis of the above-mentioned urethane prepolymer, anionic hydrophilic groups such as carboxyl groups are neutralized with a neutralizer, and then emulsified and dispersed in water. Then, a chain extender (C) is added in an equivalent amount less than the residual isocyanate groups (for example, the equivalent ratio of isocyanate groups to the active hydrogen groups of the chain extender (C) is 1:0.50 to 0.95), so that the isocyanate groups in the emulsified micelles undergo surface polymerization reaction with the chain extender (C) to generate urea bonds. As a result, the crosslinking density in the emulsified micelles is increased, and a three-dimensional crosslinking structure is formed. Then, the used solvent is removed as necessary, thereby obtaining an aqueous dispersion of the polyurethane resin.

[0070] Examples of the neutralizing agent include non-volatile bases such as sodium hydroxide and potassium hydroxide; tertiary amines such as trimethylamine, triethylamine, dimethylethanolamine, methyldiethanolamine, triethanolamine; and volatile bases such as ammonia. Neutralization can be performed before, during, or after the amination reaction.

[0071] As an organic solvent arbitrarily used in the synthesis of the urethane prepolymer, there can be mentioned an organic solvent which is inert to isocyanate groups and can dissolve the generated urethane prepolymer. Alkane, methyl ethyl ketone, acetone, dimethylformamide, tetrahydrofuran, N-methyl-2-pyrrolidone, toluene, propylene glycol monomethyl ether acetate, etc.

[0072] The aqueous dispersion of polyurethane resin contains water and polyurethane resin dispersed in water, but may contain other components as long as the effect is not impaired. The concentration of polyurethane resin in the aqueous dispersion is not particularly limited, and may be, for example, 10 to 50% by mass, 20 to 45% by mass, or 30 to 40% by mass.

[0073] [Water-based paint]

[0074] The water-based coating of the present embodiment is a water-based coating comprising an aqueous dispersion of the above-mentioned polyurethane resin, and therefore comprises water and the polyurethane resin dispersed in water. In the water-based coating, other water-based resins generally used as film-forming components of the water-based coating can be used together with the above-mentioned polyurethane resin. As other water-based resins, 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, etc. can be cited.

[0075] The content of the polyurethane resin in the water-based paint is not particularly limited, and may be 20 to 100% by mass, or 50 to 100% by mass, relative to 100% by mass of the total resin solid content contained in the water-based paint.

[0076] In addition, various additives generally used in water-based paints may be added to the water-based paint as long as the effect is not impaired. Examples of such additives include pigments, ultraviolet absorbers, light stabilizers, surface conditioners, inorganic fillers, organic fillers, dispersing aids, preservatives, rust inhibitors, antioxidants, silane coupling agents, defoamers, viscosity modifiers, antistatic agents, crosslinking agents, organic solvents, and the like.

[0077] Example

[0078] Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples, but the present invention is not limited thereto.

[0079] The details of each component used in the examples are as follows.

[0080] [(A1) Ingredient]

[0081] Aromatic polyester polyols (1):

[0082] Into a reaction vessel equipped with a stirrer, a thermometer, a reflux cooling tube, a dropping tank and a nitrogen inlet tube, 47.74 parts by mass of terephthalic acid, 12.45 parts by mass of adipic acid, 33.26 parts by mass of neopentyl glycol and 6.55 parts by mass of ethylene glycol were placed, and the temperature was raised to 250° C. under a nitrogen stream while stirring. The reaction was continued until the acid value became 5 mgKOH / g or less, and then the pressure was gradually reduced, and a deglycolization reaction was carried out at 1 mmHg for 5 hours to obtain an aromatic polyester polyol (1) having a number average molecular weight of 1780.

[0083] Aromatic polyester polyols (2):

[0084] Into a reaction vessel equipped with a stirrer, a thermometer, a reflux cooling tube, a dropping tank and a nitrogen inlet tube, 32.81 parts by mass of isophthalic acid, 23.60 parts by mass of adipic acid, 38.02 parts by mass of 1,6-hexanediol and 5.57 parts by mass of ethylene glycol were placed, and the temperature was raised to 250° C. while stirring under a nitrogen stream. The reaction was continued until the acid value became 5 mgKOH / g or less, and then the pressure was gradually reduced, and a deglycolization reaction was carried out at 1 mmHg for 5 hours to obtain an aromatic polyester polyol (2) having a number average molecular weight of 1780.

[0085] Aromatic polyester polyols (3):

[0086] Into a reaction vessel equipped with a stirrer, a thermometer, a reflux cooling tube, a dropping tank and a nitrogen inlet tube, 18.01 parts by mass of terephthalic acid, 18.01 parts by mass of isophthalic acid, 23.40 parts by mass of adipic acid, 34.48 parts by mass of neopentyl glycol and 6.09 parts by mass of ethylene glycol were placed, and the temperature was raised to 250° C. while stirring under a nitrogen stream. The reaction was continued until the acid value became 5 mgKOH / g or less, and then the pressure was gradually reduced, and a deglycolization reaction was carried out at 1 mmHg for 5 hours to obtain an aromatic polyester polyol (3) having a number average molecular weight of 1780.

[0087] Aliphatic polyester polyols (4):

[0088] A reaction vessel equipped with a stirrer, a thermometer, a reflux cooling tube, a dropping tank and a nitrogen inlet tube was charged with 55.20 parts by mass of adipic acid and 44.80 parts by mass of 3-methyl-1,5-pentanediol, and heated to 250° C. under a nitrogen stream while stirring. The reaction was continued until the acid value became 5 mgKOH / g or less, and then the pressure was gradually reduced, and a deglycolization reaction was carried out at 1 mmHg for 5 hours to obtain an aliphatic polyester polyol (4) having a number average molecular weight of 1780.

[0089] [(A2) ingredient]

[0090] ·MPD: 3-methyl-1,5-pentanediol manufactured by Kuraray Co., Ltd.

[0091] BEPG: 2-Butyl-2-ethyl-1,3-propanediol manufactured by KH Neochem Co., Ltd.

[0092] [(A3) ingredient]

[0093] ·Dimethylolpropionic acid

[0094] 2,2-Dihydroxymethylbutyric acid

[0095] [(A4) ingredient]

[0096] ·Trimethylolpropane (molecular weight: 134.17)

[0097] ·Polycaprolactone triol: "PLACCEL 303" manufactured by Daicel Co., Ltd. (Mn: 300)

[0098] [(B) ingredient]

[0099] ·Hydrogenated MDI: Dicyclohexylmethane 4,4'-diisocyanate

[0100] IPDI: Isophorone diisocyanate

[0101] [(C1) ingredient]

[0102] ·Diethylenetriamine

[0103] [(C2) ingredient]

[0104] Amino alcohol (1): "Amino alcohol EA" manufactured by Nippon Emulsifier Co., Ltd., N-(2-hydroxyethyl)ethylenediamine

[0105] Amino alcohol (2): "Amino alcohol PA" manufactured by Nippon Emulsifier Co., Ltd., N-(2-hydroxypropyl)ethylenediamine

[0106] <Synthesis of aqueous dispersion of polyurethane resin>

[0107] [Example 1]

[0108] In a four-necked flask equipped with a stirrer, a reflux cooling tube, a thermometer and a nitrogen blowing tube, 52.24 parts by mass of aromatic polyester polyol (1), 0.75 parts by mass of trimethylolpropane, 2.64 parts by mass of MPD, 4.32 parts by mass of dimethylolpropionic acid and 30 parts by mass of methyl ethyl ketone were added and stirred thoroughly to dissolve. Then, 40.05 parts by mass of hydrogenated MDI was added and reacted at 75° C. until the content of free isocyanate groups became 5.46% by mass relative to the solid content, thereby obtaining a methyl ethyl ketone solution of a urethane prepolymer. The prepolymer solution was cooled to 45° C., neutralized by adding 1.96 parts by mass of triethylamine, and then 163 parts by mass of distilled water was added while stirring with a homogenizer to emulsify and disperse it. Then, an aqueous solution prepared by diluting 2.09 parts by mass of diethylenetriamine and 2.81 parts by mass of amino alcohol (1) with 49 parts by mass of water was added, and a chain extension reaction was carried out at 20° C. for 1 hour. Methyl ethyl ketone was distilled off under heating and reduced pressure to obtain an aqueous dispersion of a polyurethane resin having a solid content of 38% by mass. The obtained polyurethane resin had an acid value of 17.2 mgKOH / g and a hydroxyl value of 14.4 mgKOH / g.

[0109] [Examples 2 to 16 and Comparative Examples 1 to 8]

[0110] Except that the types and charging amounts of each raw material were changed as shown in the following Tables 1 to 3, the synthesis was carried out in the same manner as in Example 1 to obtain aqueous dispersions of each polyurethane resin. Regarding the mixing ratios in Tables 1 to 3, "(A1) / (A) [mass %]" is the ratio of the amount of aromatic polyester polyol (A1) relative to 100 mass % of polyol (A). "(A2) / (A) [mass %]" is the ratio of the amount of aliphatic diol (A2) relative to 100 mass % of polyol (A). "(C1) / (C2)" is the mass ratio of compound (C1) to compound (C2).

[0111] <Evaluation of aqueous dispersion of polyurethane resin>

[0112] The viscosity, storage stability, heat resistance and tensile strength of each polyurethane resin aqueous dispersion were measured and evaluated in the following manner.

[0113] [Viscosity]

[0114] The viscosity of the aqueous dispersion of the polyurethane resin immediately after synthesis is measured at 20° C. at a solid content of 38% by mass using a single cylindrical rotational viscometer (JIS Z-8803:2011). The viscosity is preferably 500 mPa·s or less.

[0115] [Storage stability]

[0116] A water dispersion of a polyurethane resin having a solid content of 38% by mass was stored at 35°C for 12 months, and the viscosity was measured before and after storage, and the storage stability was evaluated by the change in viscosity. The viscosity measurement method is as described above. In the evaluation, a water dispersion whose viscosity change before and after storage was less than 50 mPa·s was evaluated as having excellent storage stability and was recorded as "◎", a water dispersion whose viscosity change was 50 mPa·s or more and less than 200 mPa·s was recorded as "○", and a water dispersion whose viscosity change was 200 mPa·s or more or gelled after storage was evaluated as having poor storage stability and was recorded as "×".

[0117] [Heat resistance]

[0118] An aqueous dispersion of a polyurethane resin is applied to a rod coated with Teflon (registered trademark) so that the dry film thickness is 300 μm, and then dried at 40°C for 15 hours, then dried at 80°C for 6 hours, and further dried at 120°C for 30 minutes to obtain a film composed of a polyurethane resin. The obtained film was subjected to a heat resistance test at 180°C × 1 hour. The film before and after the heat resistance test was subjected to a dynamic viscoelasticity measurement in a tensile mode (measurement mode: temperature-dependent measurement), and the storage modulus E' at 50°C was determined. The heating rate for the dynamic viscoelasticity measurement is 3°C per minute, the frequency is 10 Hz, the initial strain is 0.02%, and the dynamic strain is 0.02%. According to the ratio of the storage modulus E' before and after the heat resistance test (log 10 E' / log before test 10 The film having the ratio of 0.95 or more was marked as having excellent heat resistance, the film having the ratio of 0.93 or more and less than 0.95 was marked as “○”, and the film having the ratio of less than 0.93 was marked as having poor heat resistance.

[0119] [tensile strength]

[0120] The tensile strength (tensile strength) of the film produced in the same manner as in the above evaluation of heat resistance was measured using a tensile tester in accordance with JIS A6021: 2011. The tensile strength is preferably 25 MPa or more.

[0121] [Table 1]

[0122] [Table 2]

[0123] [Table 3]

[0124]

[0125] The results are shown in Tables 1 to 3. In Comparative Example 1, in which the aliphatic diol (A2) was not used, the viscosity of the aqueous dispersion was high and the storage stability was poor. In Comparative Example 2, in which the compound (C1) was not used as a chain extender, the viscosity of the aqueous dispersion was high and the storage stability and heat resistance of the film were poor. In Comparative Example 3, in which the compound (C2) was not used as a chain extender, the heat resistance of the film was poor.

[0126] Comparative Examples 4 to 7 are examples of using aromatic polyester polyol (A1) and aliphatic diol (A2) as polyols, and using compound (C1) and compound (C2) as chain extenders. However, in Comparative Example 4, the acid value is higher than the prescribed range, so the viscosity of the aqueous dispersion is high and the storage stability is poor. In Comparative Example 5, the acid value is lower than the prescribed range, and the storage stability of the aqueous dispersion is poor. In Comparative Example 6, the hydroxyl value is higher than the prescribed range, so the viscosity of the aqueous dispersion is high, and the storage stability and heat resistance of the film are poor. In Comparative Example 7, the hydroxyl value is lower than the prescribed range, and the storage stability of the aqueous dispersion is poor.

[0127] On the other hand, in Comparative Example 8, in which an aliphatic polyester polyol was used instead of the aromatic polyester polyol (A1), the storage stability of the aqueous dispersion was poor, and the tensile strength of the film was low.

[0128] In contrast, in Examples 1 to 16, the polyurethane resin aqueous dispersions had low viscosities and good storage stability, and films formed from the aqueous dispersions had good heat resistance and high tensile strength.

[0129] It should be noted that the various numerical ranges described in the specification can be arbitrarily combined with their upper and lower limits, and all of their combinations are described in this specification as preferred numerical ranges. In addition, the description of the numerical range "X to Y" means more than X and less than Y.

[0130] Several embodiments of the present invention have been described above. These embodiments are provided 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 changes can be made without departing from the scope of the gist of the invention. These embodiments and their omissions, substitutions, and changes are included in the scope and gist of the invention, and are also included in the invention described in the claims and their equivalents.

Claims

1. A polyurethane resin aqueous dispersion obtained by reacting a polyol A, a polyisocyanate B and a chain extender C, The polyol A comprises an aromatic polyester polyol A1 and an aliphatic diol A2 having a hydrocarbon group in a side chain. The chain extender C comprises a compound C1 having three primary and / or secondary amino groups and no hydroxyl group, and a compound C2 having one or more hydroxyl groups and two or more primary and / or secondary amino groups. The acid value is 11.0 to 23.0 mgKOH / g, and the hydroxyl value is 8.0 to 23.0 mgKOH / g.

2. The aqueous dispersion of the polyurethane resin according to claim 1, wherein The mass ratio C1 / C2 of the compound C1 to the compound C2 is 0.3 to 1.

4.

3. The aqueous dispersion of the polyurethane resin according to claim 1, wherein The aliphatic diol A2 has 3 to 10 carbon atoms.

4. The aqueous dispersion of the polyurethane resin according to claim 1, wherein The polyisocyanate B contains an alicyclic polyisocyanate.

5. The aqueous dispersion of polyurethane resin according to claim 1, wherein The amount of the aromatic polyester polyol A1 is 70 to 90% by mass based on 100% by mass of the polyol A.

6. The aqueous dispersion of the polyurethane resin according to claim 1, wherein The polyol A further comprises a carboxyl group-containing polyol A3.

7. The aqueous dispersion of polyurethane resin according to claim 1, wherein The polyol A further comprises a triol A4 having a molecular weight of 350 or less.

8. A water-based paint comprising the aqueous dispersion of the polyurethane resin according to any one of claims 1 to 7.

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