Aqueous multi-component coating composition and method for producing coated article

Abstract

An aqueous multi-component coating composition including: a first liquid including a hydroxyl group-containing acrylic resin (A), a polyurethane resin (B), and a copolymer (C) having a first segment (c1) that is derived from a nitrogen-containing polymerizable unsaturated monomer having at least one of a tertiary amino group and a nitrogen-containing heterocyclic group, and a second segment (c2) that is derived from a polymerizable unsaturated monomer having a polyoxyalkylene chain; and a second liquid including a polyisocyanate compound (D).

Description

Water-based multi-component coating composition and method for producing coated articles

[0001] The present invention relates to an aqueous multi-component coating composition and a method for producing a coated article.

[0002] In recent years, consideration for the natural environment has been required in technical fields such as automobiles. Therefore, methods have been developed to lower the heating temperature or shorten the heating time during painting in order to save energy. For example, Patent Document 1 discloses an aqueous multi-component coating composition containing a main component (I) containing a hydroxyl group-containing acrylic resin and a curing agent (II) containing an anionic hydrophilic group-containing polyisocyanate compound and / or a nonionic hydrophilic group-containing polyisocyanate compound.

[0003] Japanese Patent Application Laid-Open No. 2021-130812

[0004] An object of the present invention is to provide an aqueous multi-component coating composition which can be cured at low temperatures, yet gives a coating film with excellent chipping resistance, and in addition has excellent resolubility of the thin film formed from the base resin.

[0005] To solve the above problems, the present invention provides the following aspects. [1] An aqueous multi-component coating composition comprising a first liquid containing a hydroxyl-containing acrylic resin (A), a polyurethane resin (B), and a copolymer (C) having a first segment (c1) derived from a nitrogen-containing polymerizable unsaturated monomer having at least one of a tertiary amino group and a nitrogen-containing heterocyclic group, and a second segment (c2) derived from a polymerizable unsaturated monomer having a polyoxyalkylene chain, and a second liquid containing a polyisocyanate compound (D). [2] The aqueous multi-component coating composition according to [1] above, wherein the hydroxyl-containing acrylic resin (A) has an acid value of 5 mg KOH / g or more and 70 mg KOH / g or less. [3] The aqueous multi-component coating composition according to [1] or [2] above, wherein the copolymer (C) has an acid value of less than 5 mg KOH / g. [4] The aqueous multi-component coating composition according to any one of [1] to [3] above, wherein the polyurethane resin (B) has a hydroxyl value of 30 mg KOH / g or less. [5] The aqueous multi-component coating composition according to any one of the above [1] to [4], wherein the polyurethane resin (B) is obtained by chain extension of a urethane prepolymer having terminal NCO groups, which is a reaction product of a polyisocyanate compound (b1) and a polyol (b2), with a polyamine compound (b3), and the polyol (b2) comprises a polyether polyol. [6] The aqueous multi-component coating composition according to any one of the above [1] to [5], wherein the nitrogen-containing polymerizable unsaturated monomer comprises an N,N-dialkylaminoalkyl (meth)acrylate. [7] The aqueous multi-component coating composition according to any one of the above [1] to [5], wherein the polymerizable unsaturated monomer having a polyoxyalkylene chain is a polymerizable unsaturated monomer having the following general formula: CH ２ = C(R １ )C(=O)O(C ｎ H ２ｎ O) ｍ -R ２ (In the formula, R １ represents a hydrogen atom or a methyl group, R ２ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, m is an integer of 4 to 60, n is 2 or 3, and m oxyalkylene units (C ｎ H ２ｎThe aqueous multi-component coating composition according to any one of the above [1] to [6], wherein the copolymer (C) has an amine value of 3 mgKOH / g or more and 100 mgKOH / g or less, and a hydroxyl value of 20 mgKOH / g or more and 180 mgKOH / g or less. [8] The aqueous multi-component coating composition according to any one of the above [1] to [7], wherein the copolymer (C) has an amine value of 3 mgKOH / g or more and 100 mgKOH / g or less, and a hydroxyl value of 20 mgKOH / g or more and 180 mgKOH / g or less. [9] The aqueous multi-component coating composition according to any one of [1] to [8] above, wherein the copolymer (C) further comprises a third segment (c3) derived from a polymerizable unsaturated monomer other than the nitrogen-containing polymerizable unsaturated monomer and the polymerizable unsaturated monomer having a polyoxyalkylene chain, wherein in the copolymer (C), the mass proportion of the first segment (c1) is 5% by mass or more and 30% by mass or less, the mass proportion of the second segment (c2) is 20% by mass or more and 80% by mass or less, and the mass proportion of the third segment (c3) is 10% by mass or more and 60% by mass or less.

[10] The aqueous multi-component coating composition according to [9] above, wherein the third segment (c3) comprises a segment (c31) derived from a hydroxyl group-containing polymerizable saturated monomer, wherein the mass proportion of the segment (c31) in the copolymer (C) is 10% by mass or more and 30% by mass or less.

[11] The aqueous multi-component coating composition according to any one of [1] to

[10] above, wherein the content of the copolymer (C) is 20 parts by mass or more and 300 parts by mass or less per 100 parts by mass of the solid content of the polyurethane resin (B).

[12] The aqueous multi-component coating composition according to any one of [1] to

[11] above, wherein the polyisocyanate compound (D) comprises at least one selected from the group consisting of aliphatic diisocyanates, aliphatic triisocyanates, alicyclic diisocyanates, alicyclic triisocyanates, aromatic diisocyanates, aromatic triisocyanates, and derivatives thereof.

[13] The aqueous multi-component coating composition according to any one of the above [1] to

[12] , further comprising a coloring pigment (E), wherein the content of the coloring pigment (E) is 1 part by mass or more and 150 parts by mass or less per 100 parts by mass of the total solid content of the hydroxyl group-containing acrylic resin (A), the polyurethane resin (B), the copolymer (C), and the polyisocyanate compound (D).

[14] A method for producing a coated article, comprising the steps of applying an aqueous multi-component coating composition according to any one of [1] to

[13] above onto a substrate to form an uncured first coating film, applying a second aqueous coating composition onto said uncured first coating film to form an uncured second coating film, applying a clear coating composition onto said uncured second coating film to form an uncured clear coating film, and heating said uncured first coating film, said uncured second coating film and said uncured clear coating film at a temperature of 70°C or higher and 100°C or lower to cure them.

[15] A method for producing a coated article according to

[14] above, wherein said substrate includes a metal part and a resin part.

[0006] The aqueous multi-component coating composition of the present invention can be cured at low temperatures, yet gives a coating film that is excellent in chipping resistance, and in addition, the thin film formed from the base resin has excellent resolubility.

[0007] In multi-component paint compositions, the base agent and curing agent are stored in separate tanks. A thin film of solidified base agent adheres to the inner wall of the base agent storage tank. This thin film can peel off and become mixed into the base agent. If the thin film does not redissolve in the base agent, it can cause small bumps (protrusions) to appear on the paint film. Thin films formed from base agents containing polyurethane resins are difficult to redissolve. The base agent of a multi-component paint composition also forms a thin film that is difficult to redissolve.

[0008] A copolymer (C) having a first segment (c1) derived from a polymerizable unsaturated monomer having a tertiary amino group and a second segment (c2) derived from a polymerizable unsaturated monomer having a polyoxyalkylene chain can redissolve a thin film formed from a base material containing a polyurethane resin in the base material or in water. If the thin film is redissolved in the base material, the generation of particles is suppressed. If the thin film is redissolved in water, it is removed by washing with water, and the generation of particles is also suppressed. "The thin film redissolves" means that the thin film exists as a liquid in the base material, not as a solid.

[0009] Although the reason why copolymer (C) makes the thin film redissolvable is unclear, it is thought that the tertiary amino groups of copolymer (C) interact with the acid groups of the polyurethane resin, and the hydrophilic polyoxyalkylene chains have affinity for water or the base resin, making the solidified polyurethane resin soluble in water or the base resin, resulting in the thin film being redissolvable.

[0010] The aqueous multi-component coating composition according to the present disclosure is a multi-component type, which allows for low-temperature curing. In addition, the base resin contains a polyurethane resin, which improves chipping resistance. The present disclosure improves the resolubility of the thin film formed from the base resin in the aqueous multi-component coating composition, thereby improving the appearance of the coating film.

[0011] Hereinafter, the weight average molecular weight and number average molecular weight are measured using a polystyrene standard by GPC (gel permeation chromatography) method.

[0012] The glass transition temperature (Tg) may be calculated from the types and amounts of raw material monomers, or may be measured by a differential scanning calorimeter (DSC).

[0013] The hydroxyl value (OHV) and acid value (AV) are determined based on the solid content mass. The hydroxyl value and acid value can be measured by a known method described in JIS K 0070:1992. The hydroxyl value and acid value may be calculated from the blending amount of unsaturated monomers in the raw material monomers of the resin (e.g., hydroxyl group-containing acrylic resin (A)).

[0014] The amine value can be determined in accordance with ASTM D2073 by the following method: (1) Accurately weigh out 500 mg of the object to be tested into a 200 ml Erlenmeyer flask. (2) Add approximately 50 ml of glacial acetic acid and dissolve uniformly. (3) Add 5 to 6 drops of indicator (methyl violet solution) and stir until uniform. (4) Titrate with 0.1 N perchloric acid acetic acid solution, and the endpoint is the point at which the color turns bright green. (The above steps (3) and (4) can also be replaced with potentiometric titration.)

[0015] The average particle size is the 50% average particle size (D50) in the volume-based particle size distribution measured using a laser diffraction / scattering particle size distribution measuring device.

[0016] (Meth)acrylic acid includes both methacrylic acid and acrylic acid, and (meth)acrylate includes both methacrylate and acrylate.

[0017] The solid content is also referred to as the non-volatile content. Specifically, the solid content of a target object is all components excluding the solvent from the target object. The solid content concentration is determined by dividing the total mass of the solid content excluding the solvent from the target object by the total mass of the target object. The solid content concentration can also be calculated from the residue when the target object is heated at 140°C in accordance with JIS K 5601-1-2 Heat Residue Measurement Method.

[0018] [Aqueous Multi-Component Coating Composition] The aqueous multi-component coating composition according to the present disclosure (hereinafter sometimes simply referred to as the aqueous coating composition) comprises a first component (base) containing a hydroxyl group-containing acrylic resin (A), a polyurethane resin (B), and a copolymer (C), and a second component (curing agent) containing a polyisocyanate compound (D). The copolymer (C) has a first segment (c1) derived from a polymerizable unsaturated monomer having a tertiary amino group and a second segment (c2) derived from a polymerizable unsaturated monomer having a polyoxyalkylene chain.

[0019] The aqueous coating composition is a multi-component type containing a first liquid and a second liquid. The aqueous coating composition may further contain a third liquid containing other components. The aqueous coating composition is prepared using a method commonly used by those skilled in the art. The aqueous coating composition can be prepared by mixing the first liquid, the second liquid, and the third liquid. Examples of mixing methods include a kneading and mixing method using a kneader or roll, and a dispersion and mixing method using a sand grind mill or disperser.

[0020] The aqueous coating composition contains water as a solvent. In the aqueous coating composition, the proportion of water in the solvent may be 50% by mass or more, 70% by mass or more, or 100% by mass.

[0021] The aqueous coating composition can be cured at low temperatures. For example, the aqueous coating composition can be cured at a temperature of 70°C or higher and 100°C or lower. The curing temperature may be 75°C or higher, or 80°C or higher. The curing temperature may be 95°C or lower, or 90°C or lower.

[0022] (First Liquid) The first liquid contains a hydroxyl group-containing acrylic resin (A), a polyurethane resin (B), and a copolymer (C).

[0023] The resin is water-based. Aqueous resins are generally broadly classified into water-soluble and water-dispersed types. Water-dispersed types are further classified into dispersion types (generally referred to as colloidal dispersion types) and emulsion types. Water-soluble aqueous resins are typically obtained by dissolving a resin synthesized in an organic solvent in water with a neutralizer. Colloidal dispersion-type aqueous resins are typically obtained by semi-dissolving a resin synthesized in an organic solvent in water with a neutralizer. Emulsion-type aqueous resins are typically produced by emulsion polymerization or by mechanically forced emulsification.

[0024] (A) Hydroxyl-containing acrylic resin The hydroxyl-containing acrylic resin (A) is the base resin (film-forming component) of the coating film. The hydroxyl-containing acrylic resin (A) reacts with the polyisocyanate compound (D) to form a crosslinked structure. The hydroxyl-containing acrylic resin (A) provides a coating film with sufficient hardness. The hardness of the coating film can be evaluated by its breaking strength.

[0025] The hydroxyl group-containing acrylic resin (A) has a plurality of acryloyl groups and one or more (typically, two or more) hydroxyl groups in one molecule.

[0026] The hydroxyl value (OHV) of the hydroxyl-containing acrylic resin (A) is, for example, 20 mgKOH / g or more and 180 mgKOH / g or less. When the hydroxyl value of the hydroxyl-containing acrylic resin (A) is 20 mgKOH / g or more, the breaking strength of the coating film is likely to be high. When the hydroxyl value of the hydroxyl-containing acrylic resin (A) is 180 mgKOH / g or less, hydrophilization of the coating film is suppressed, and water resistance is likely to be improved. The hydroxyl value of the hydroxyl-containing acrylic resin (A) may be 30 mgKOH / g or more, or may be 50 mgKOH / g or more. The hydroxyl value of the hydroxyl-containing acrylic resin (A) may be 150 mgKOH / g or less, or may be 140 mgKOH / g or less.

[0027] The glass transition temperature (Tg) of the hydroxyl-containing acrylic resin (A) is, for example, 15°C or higher and 100°C or lower. When the Tg of the hydroxyl-containing acrylic resin (A) is 15°C or higher, the breaking strength and hardness of the resulting coating film are likely to be improved. When the Tg of the hydroxyl-containing acrylic resin (A) is 100°C or lower, the quick-drying properties of the aqueous coating composition are likely to be improved. The Tg of the hydroxyl-containing acrylic resin (A) may be 18°C ​​or higher, or 20°C or higher. The Tg of the hydroxyl-containing acrylic resin (A) may be 90°C or lower, 80°C or lower, or 70°C or lower.

[0028] From the viewpoint of hardness, the hydroxyl group-containing acrylic resin (A) may have a hydroxyl value of 20 mgKOH / g or more and 180 mgKOH / g or less and a Tg of 15°C or more and 100°C or less.

[0029] The hydroxyl group-containing acrylic resin (A) may have an acid value (AV) of 5 mgKOH / g or more and 70 mgKOH / g or less. This makes it easier to improve the hardness of the resulting coating film. The acid value of the hydroxyl group-containing acrylic resin (A) may be 8 mgKOH / g or more, or 10 mgKOH / g or more. The acid value of the hydroxyl group-containing acrylic resin (A) may be 60 mgKOH / g or less, 50 mgKOH / g or less, or 40 mgKOH / g or less.

[0030] The hydroxyl-containing acrylic resin (A) may have a solubility parameter (SP) of 8.5 or more and 12 or less. This makes the hydroxyl-containing acrylic resin (A) more compatible with the aqueous coating composition, and the occurrence of lumps can be further suppressed. The SP value of the hydroxyl-containing acrylic resin (A) may be 9.0 or more, or 9.5 or more. The SP value of the hydroxyl-containing acrylic resin (A) may be 11.5 or less, or 11.0 or less.

[0031] The SP value is a measure of the solubility of a compound. A larger SP value indicates a higher polarity of the compound, and a smaller SP value indicates a lower polarity of the compound.

[0032] The SP value of the hydroxyl-containing acrylic resin (A) can be regarded as a weighted average value obtained from the SP values ​​of a plurality of raw material monomers, taking into account their solid content mass ratios. When the hydroxyl-containing acrylic resin (A) contains a plurality of acrylic resins, the weighted average value of all acrylic resins obtained by further taking into account the solid content mass ratios of each acrylic resin can be regarded as the SP value of the hydroxyl-containing acrylic resin (A).

[0033] [Method for Measuring Solubility Parameter (SP)] The SP value of a monomer is measured, for example, by the following method [Reference: SUH, CLARKE, J. P. S. A-1, 5, 1671-1681 (1967)].

[0034] The sample used is 0.5 g of monomer weighed into a 100 ml beaker and dissolved in 10 ml of acetone. A poor solvent is added dropwise to this sample using a 50 ml burette at a measurement temperature of 20°C, and the point at which turbidity occurs is recorded as the amount added. As the poor solvent, ion-exchanged water is used as a high SP poor solvent, and n-hexane is used as a low SP poor solvent, and the clouding point of each is measured. The SP value δ of the monomer is given by the following calculation formula:

[0035] Vi: Molar volume of solvent i (ml / mol) φi: Volume fraction of solvent i at the clouding point δi: SP value of solvent i ml: Low SP poor solvent mixture mh: High SP poor solvent mixture

[0036]

[0037]

[0038] The hydroxyl group-containing acrylic resin (A) can be produced by polymerizing a hydroxyl group-containing α,β-ethylenically unsaturated monomer with another α,β-ethylenically unsaturated monomer by a known method. The hydroxyl group-containing acrylic resin (A) is produced, for example, by solution polymerization. Commercially available hydroxyl group-containing acrylic resins may also be used.

[0039] The hydroxyl group-containing acrylic resin may be contained as an emulsion, a dispersion, or in a state of being dissolved in a solvent. For example, an acrylic resin dispersion can be prepared by solution polymerizing the above-mentioned α,β-ethylenically unsaturated monomer and dispersing the polymer using a basic compound. A water-soluble acrylic resin can be prepared by solution polymerizing the above-mentioned α,β-ethylenically unsaturated monomer and solubilizing the polymer using a basic compound.

[0040] The emulsion of the hydroxyl group-containing acrylic resin can be prepared, for example, by emulsion polymerization of α,β-ethylenically unsaturated monomers. Examples of the α,β-ethylenically unsaturated monomers include (meth)acrylic acid esters, α,β-ethylenically unsaturated monomers having an acid group, and α,β-ethylenically unsaturated monomers having a hydroxyl group. The monomers can be used alone or in combination of two or more.

[0041] Examples of (meth)acrylic acid esters include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, phenyl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, dicyclopentadienyl (meth)acrylate, and dihydrodicyclopentadienyl (meth)acrylate. (Meth)acrylic acid esters refer to acrylic acid esters and methacrylic acid esters.

[0042] Examples of α,β-ethylenically unsaturated monomers having an acid group include acrylic acid, methacrylic acid, crotonic acid, 2-acryloyloxyethyl phthalic acid, 2-acryloyloxyethyl succinic acid, ω-carboxy-polycaprolactone mono(meth)acrylate, isocrotonic acid, α-hydro-ω-((1-oxo-2-propenyl)oxy)poly(oxy(1-oxo-1,6-hexanediyl)), maleic acid, fumaric acid, itaconic acid, 3-vinylsalicylic acid, 3-vinylacetylsalicylic acid, 2-acrylamido-2-methylpropanesulfonic acid, p-hydroxystyrene, and 2,4-dihydroxy-4′-vinylbenzophenone.

[0043] Examples of the α,β-ethylenically unsaturated monomer having a hydroxyl group include hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, allyl alcohol, methallyl alcohol, and adducts of these with ε-caprolactone.

[0044] Other α,β-ethylenically unsaturated monomers may be used in combination. Examples of the other α,β-ethylenically unsaturated monomers include polymerizable amide compounds, polymerizable aromatic compounds, polymerizable nitriles, polymerizable alkylene oxide compounds, polyfunctional vinyl compounds, polymerizable amine compounds, α-olefins, dienes, polymerizable carbonyl compounds, polymerizable alkoxysilyl compounds, and other polymerizable compounds.

[0045] The emulsion polymerization method is not particularly limited. For example, an emulsifier is dissolved in an aqueous medium containing water or, if necessary, an organic solvent such as an alcohol or an ether (e.g., dipropylene glycol methyl ether, propylene glycol methyl ether, etc.), and an α,β-ethylenically unsaturated monomer and a polymerization initiator are added dropwise with heating and stirring. The α,β-ethylenically unsaturated monomer may be previously emulsified with an emulsifier.

[0046] Polymerization initiators and emulsifiers commonly used by those skilled in the art can be used. If necessary, a chain transfer agent such as a mercaptan (e.g., lauryl mercaptan) or α-methylstyrene dimer may be used to adjust the molecular weight. The reaction temperature, reaction time, and the like can be appropriately selected within ranges commonly used by those skilled in the art. The resulting acrylic resin emulsion is neutralized with a base, if necessary.

[0047] (B) Polyurethane Resin The polyurethane resin (B) is also a coating film-forming component. The polyurethane resin (B) increases the elasticity of the coating film and improves chipping resistance. The elasticity of the coating film can be evaluated not only by chipping resistance but also by the elastic modulus and elongation at break.

[0048] The polyurethane resin (B) may have a hydroxyl value of 30 mgKOH / g or less. This inhibits the reaction between the polyisocyanate compound (D) and the polyurethane resin (B), facilitating the reaction between the polyisocyanate compound (D) and the hydroxyl-containing acrylic resin (A). The reaction between the polyisocyanate compound (D) and the hydroxyl-containing acrylic resin (A) increases the hardness of the resulting coating film. That is, a hydroxyl value of 30 mgKOH / g or less makes it easier to ensure the hardness of the resulting coating film. The hydroxyl value of the polyurethane resin (B) may be 20 mgKOH / g or less, 10 mgKOH / g or less, or 0 mgKOH / g.

[0049] The polyurethane resin (B) may have an acid value of 5 mgKOH / g or more and 70 mgKOH / g or less. This makes it easier to improve the hardness of the resulting coating film and ensure the water resistance of the resulting coating film. The acid value of the polyurethane resin (B) may be 8 mgKOH / g or more, or 10 mgKOH / g or more. The acid value of the polyurethane resin (B) may be 60 mgKOH / g or less, 50 mgKOH / g or less, or 40 mgKOH / g or less.

[0050] The content of polyurethane resin (B) may be 10 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the solid content of hydroxyl group-containing acrylic resin (A). This provides a good balance between the hardness and elasticity of the resulting coating film, making it easier to obtain a coating film that has moderate hardness and excellent chipping resistance. The content of polyurethane resin (B) may be 15 parts by mass or more, or 20 parts by mass or more. The content of polyurethane resin (B) may be 160 parts by mass or less, or 120 parts by mass or less.

[0051] In the first liquid, the polyurethane resin (B) may be dissolved. That is, the polyurethane resin (B) may be a water-soluble polyurethane resin. In the first liquid, the polyurethane resin (B) may be in the form of a dispersion.

[0052] The average particle size of the polyurethane resin dispersion may be 10 nm or more and 1000 nm or less. This makes it easier to control the viscosity of the aqueous coating composition within an appropriate range and improves dispersion stability. The average particle size may be 20 nm or more, 40 nm or more, or 80 nm or more. The average particle size may be 700 nm or less, 400 nm or less, or 200 nm or less.

[0053] The water-soluble polyurethane resin and polyurethane resin dispersion can be obtained, for example, by a method of forcibly emulsifying a polyurethane resin using a surfactant or a method of neutralizing a urethane resin with a base or acid. The polyurethane resin is not particularly limited and can be obtained, for example, by the method disclosed in JP-A-2021-75680.

[0054] The polyurethane resin (B) can be obtained, for example, by chain-extending a urethane prepolymer containing terminal NCO groups, which is a reaction product of a polyisocyanate compound (b1) and a polyol (b2), with a polyamine compound (b3). This polyurethane resin (B) has the advantage of being able to have a high molecular weight.

[0055] (b1) Polyisocyanate Compound The polyisocyanate compound (b1) has two or more isocyanate groups in the molecule. In this specification, the term "isocyanate group" refers to an unblocked free isocyanate group.

[0056] Examples of the polyisocyanate compound (b1) include aromatic polyisocyanates, aliphatic polyisocyanates, alicyclic polyisocyanates, and araliphatic polyisocyanates. Among these, the polyisocyanate compound (b1) may contain at least one selected from the group consisting of aromatic polyisocyanates, aliphatic polyisocyanates, alicyclic polyisocyanates, araliphatic polyisocyanates, and derivatives thereof (e.g., hydrogenated products, polymers). This tends to increase the flexibility of the resulting polyurethane resin (B).

[0057] The aromatic polyisocyanate has two or more isocyanate groups bonded to carbon atoms constituting an aromatic ring. Examples of aromatic polyisocyanates include aromatic diisocyanates such as m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 2,4'- or 4,4'-diphenylmethane diisocyanate (MDI), or mixtures thereof, 2,4- or 2,6-tolylene diisocyanate, or mixtures thereof, 4,4'-toluidine diisocyanate, and 4,4'-diphenylether diisocyanate; aromatic triisocyanates such as triphenylmethane-4,4',4''-triisocyanate, 1,3,5-triisocyanatobenzene, and 2,4,6-triisocyanatotoluene; and aromatic tetraisocyanates such as 4,4'-diphenylmethane-2,2',5,5'-tetraisocyanate. These may be used alone or in combination of two or more.

[0058] Aliphatic polyisocyanates do not have an aromatic ring and have two or more isocyanate groups bonded to carbon atoms constituting a linear or branched aliphatic hydrocarbon group. Examples of aliphatic polyisocyanates include ethylene diisocyanate, trimethylene diisocyanate, 1,2-propylene diisocyanate, butylene diisocyanate (tetramethylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate), 1,5-pentamethylene diisocyanate (PDI), 1,6-hexamethylene diisocyanate (HDI), 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, and the like. aliphatic diisocyanates such as lysine ester triisocyanate, 1,4,8-triisocyanatooctane, 1,6,11-triisocyanatoundecane, 1,8-diisocyanato-4-isocyanatomethyloctane, 1,3,6-triisocyanatohexane, and 2,5,7-trimethyl-1,8-diisocyanato-5-isocyanatomethyloctane. These may be used alone or in combination of two or more.

[0059] Alicyclic polyisocyanates do not have an aromatic ring, but have two or more isocyanate groups bonded to carbon atoms constituting a cyclic aliphatic hydrocarbon group. Examples of alicyclic polyisocyanates include 1,3-cyclopentene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (common name: isophorone diisocyanate, IPDI), methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane (common name: hydrogenated xylylene diisocyanate), or mixtures thereof, and alicyclic diisocyanates such as norbornane diisocyanate; 1,3,5-triisocyanatocyclohexane, 1,3,5-trimethylisocyanatocyclohexane, 2-(3-isocyanatopropyl)-2,5-di(isocyanatomethyl)-bicyclo[2.2 . 1]heptane, 2-(3-isocyanatopropyl)-2,6-di(isocyanatomethyl)-bicyclo[2.2.1]heptane, 3-(3-isocyanatopropyl)-2,5-di(isocyanatomethyl)-bicyclo[2.2.1]heptane, 5-(2-isocyanatoethyl)-2-isocyanatomethyl-3-(3-isocyanatopropyl)-bicyclo[2.2.1]heptane, 6-(2-isocyanatoethyl)-2- Examples of such alicyclic triisocyanates include isocyanatomethyl-3-(3-isocyanatopropyl)-bicyclo[2.2.1]heptane, 5-(2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo[2.2.1]heptane, and 6-(2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo[2.2.1]heptane. These may be used alone or in combination of two or more.

[0060] Aromatic aliphatic polyisocyanates have an aromatic ring and two or more isocyanate groups bonded to carbon atoms constituting an aliphatic hydrocarbon group. Examples of araliphatic polyisocyanates include araliphatic diisocyanates such as 1,3- or 1,4-xylylene diisocyanate, or mixtures thereof, ω,ω'-diisocyanato-1,4-diethylbenzene, 1,3- or 1,4-bis(1-isocyanato-1-methylethyl)benzene (common name: tetramethylxylylene diisocyanate), or mixtures thereof; and araliphatic triisocyanates such as 1,3,5-triisocyanatomethylbenzene. These may be used alone or in combination of two or more.

[0061] Examples of the multimer of the polyisocyanate compound (b1) include dimer, trimer, biuret, allophanate, uretdione, uretoimine, isocyanurate, oxadiazinetrione, polymethylene polyphenyl polyisocyanate (crude MDI, polymeric MDI), and crude TDI.

[0062] (b2) Polyol The polyol (b2) has two or more hydroxyl groups in the molecule. Examples of polyol compounds include polyhydric alcohols such as ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, trimethylolpropane, and glycerin; polyether polyols such as polyethylene glycol, polypropylene glycol, and polytetramethylene ether glycol; polyols having a carboxy group such as 2,2-dimethylolpropionic acid and 2,2-dimethylolbutanoic acid; polyester polyols obtained from dicarboxylic acids such as adipic acid, sebacic acid, itaconic acid, maleic anhydride, phthalic acid, and isophthalic acid and glycols such as ethylene glycol, triethylene glycol, propylene glycol, butylene glycol, tripropylene glycol, and neopentyl glycol; polycaprolactone polyols; polybutadiene polyols; polycarbonate polyols; and polythioether polyols. These may be used alone or in combination of two or more. The polyol (b2) may comprise a polyether polyol.

[0063] (b3) Polyamine Compound The polyamine compound (b3) has two or more amino groups in the molecule and functions as a chain extender.

[0064] Examples of the polyamine compound (b3) include ethylenediamine, tetramethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, piperazine, hydrazine, tolylenediamine, xylylenediamine, and isophoronediamine. These may be used alone or in combination of two or more.

[0065] (b4) Other Components In preparing the polyurethane resin (B), other components (b4) may be used as necessary. Representative examples include monoisocyanate compounds. Examples of monoisocyanate compounds include methyl isocyanate, ethyl isocyanate, propyl isocyanate, butyl isocyanate, lauryl isocyanate, cyclohexyl isocyanate, phenyl isocyanate, and tolylene isocyanate. These compounds may be used alone or in combination of two or more.

[0066] <Preparation Method> The polyurethane resin (B) can be obtained, for example, by reacting a polyisocyanate compound (b1) with a portion of a polyol (b2) to obtain a urethane prepolymer having terminal NCO groups, and then reacting this prepolymer with a polyamine compound (b3) and the remainder of the polyol (b2). The other component (b4) may be added at any stage.

[0067] The reaction temperature may be 40°C or higher and 140°C or lower, or 60°C or higher and 120°C or lower. A tin-based catalyst such as dibutyltin laurate or tin octoate, or an amine-based catalyst such as triethylenediamine, which are used in ordinary urethanization reactions, may also be used. The reaction may be carried out in an organic solvent inert to isocyanates (e.g., acetone, toluene, ethyl acetate, dimethylformamide, methyl ethyl ketone), and an organic solvent may be added during or after the reaction.

[0068] The polyisocyanate compound (b1) and the polyol (b2) are each used in an amount such that the ratio of isocyanate groups to hydroxyl groups (NCO / OH) is, for example, 1.03 to 1.99.

[0069] (C) Copolymer The copolymer (C) improves the resolubility of the thin film containing the polyurethane resin (B).

[0070] In the first liquid, the copolymer (C) may be dissolved. That is, the copolymer (C) may be water-soluble. In the first liquid, the copolymer (C) may be in the form of a dispersion. The copolymer (C) may be water-soluble.

[0071] The content of copolymer (C) may be 20 parts by mass or more and 300 parts by mass or less per 100 parts by mass of the solid content of polyurethane resin (B). This can further improve resolubility. The content of copolymer (C) may be 23 parts by mass or more, or may be 25 parts by mass or more. The content of copolymer (C) may be 200 parts by mass or less, or may be 100 parts by mass or less.

[0072] The weight average molecular weight of copolymer (C) may be 10,000 or more and 40,000 or less. The weight average molecular weight of copolymer (C) may be 15,000 or more, or 20,000 or more. The weight average molecular weight of copolymer (C) may be 38,000 or less, or 35,000 or less.

[0073] The acid value of the copolymer (C) may be less than 5 mgKOH / g, may be 2 mgKOH / g or less, or may be 0 mgKOH / g.

[0074] The hydroxyl value of the copolymer (C) may be 20 mgKOH / g or more and 180 mgKOH / g or less. This tends to increase the breaking strength of the coating film and tends to inhibit the coating film from becoming hydrophilic. The hydroxyl value of the copolymer (C) may be 30 mgKOH / g or more, or 50 mgKOH / g or more. The hydroxyl value of the copolymer (C) may be 150 mgKOH / g or less, or 140 mgKOH / g or less.

[0075] The amine value of the copolymer (C) may be 3 mgKOH / g or more and 100 mgKOH / g or less. This can improve the surface smoothness of the coating film. The amine value of the copolymer (C) may be 20 mgKOH / g or more, or 30 mgKOH / g or more. The amine value of the copolymer (C) may be 90 mgKOH / g or less, or 80 mgKOH / g or less.

[0076] The copolymer (C) has a first segment (c1) derived from a nitrogen-containing polymerizable unsaturated monomer (hereinafter, sometimes referred to as a "nitrogen-containing monomer") having a tertiary amino group and / or a nitrogen-containing heterocyclic group (hereinafter, sometimes referred to as a "nitrogen-containing group"), and a second segment (c2) derived from a polymerizable unsaturated monomer having a polyoxyalkylene chain (hereinafter, sometimes referred to as a "hydrophilic monomer").

[0077] In the copolymer (C), the nitrogen-containing group and the polyoxyalkylene chain may both be arranged as side chains or may constitute part of the main chain. The nitrogen-containing group and the polyoxyalkylene chain may both be arranged as side chains, and the main chain of the copolymer (C) may be constituted by carbon-carbon bonds. The nitrogen-containing polymerizable unsaturated monomer may have a tertiary amino group.

[0078] The copolymer (C) may have an amine value of 3 mgKOH / g or more and 100 mgKOH / g or less and a hydroxyl value of 20 mgKOH / g or more and 180 mgKOH / g or less. This can further improve the surface smoothness of the coating film. The copolymer (C) may have a first segment (c1) derived from a nitrogen-containing monomer having a tertiary amino group.

[0079] First Segment (c1) The first segment (c1) has at least one nitrogen-containing group. The nitrogen-containing group generates a cation in an aqueous solvent and can adsorb to the acid group of the polyurethane resin (B).

[0080] Examples of tertiary amino group-containing monomers include N,N-dialkylaminoalkyl (meth)acrylates such as N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate, N,N-di-t-butylaminoethyl (meth)acrylate, and N,N-dimethylaminobutyl (meth)acrylate; and N,N-dialkylaminoalkyl (meth)acrylamides such as N,N-dimethylaminoethyl (meth)acrylamide, N,N-diethylaminoethyl (meth)acrylamide, and N,N-dimethylaminopropyl (meth)acrylamide. These may be used alone or in combination of two or more.

[0081] Among these, N,N-dialkylaminoalkyl(meth)acrylate may be used, and N,N-dimethylaminoethyl(meth)acrylate and N,N-diethylaminoethyl(meth)acrylate may be used.

[0082] Examples of the nitrogen-containing heterocyclic group include a pyridine ring group, a quinoline ring group, a thiazole ring group, an oxazole ring group, a benzothiazole ring group, an imidazole ring group, a pyrazole ring group, an imidazoline ring group, a pyrimidine ring group, a pyrazine ring group, a triazole ring group, and a tetrazole ring group.

[0083] Examples of polymerizable unsaturated monomers (vinyl monomers) having a pyridine ring include 2-vinylpyridine and 4-vinylpyridine. Examples of polymerizable unsaturated monomers having a thiazole ring include 2-vinylthiazole and 4-methyl-5-vinylthiazole. Examples of polymerizable unsaturated monomers having an oxazole ring include 2-phenyl-5-vinyloxazole. Examples of polymerizable unsaturated monomers having a benzothiazole ring include 2-vinylbenzothiazole, 2-[2-(1-naphthyl)vinyl]benzothiazole, and 2-[2-(dimethylamino)vinyl]benzothiazole. Examples of polymerizable unsaturated monomers having an imidazole ring include 1-vinylimidazole, 2-methyl-1-vinylimidazole, 2-vinylimidazole, 4-vinylimidazole, 2-phenyl-1-vinylimidazole, 1-vinylcarbazole, and 2-(1H-imidazol-1-yl)ethyl (meth)acrylate. Examples of polymerizable unsaturated monomers having a pyrazole ring include 1-vinylpyrazole and 3-vinylpyrazole. Examples of polymerizable unsaturated monomers having an imidazoline ring include 1-vinyl-2-imidazoline, 1-vinyl-2-methylimidazoline, 2-vinyl-2-imidazoline, and 2-(1H-imidazolin-1-yl)ethyl (meth)acrylate. Examples of polymerizable unsaturated monomers having a pyrimidine ring include 5-vinylpyrimidine and 2,4-dichloro-6-vinylpyrimidine. Examples of polymerizable unsaturated monomers having a pyrazine ring include 2-vinylpyrazine, 2,5-dimethyl-3-vinylpyrazine, and 2-methyl-5-vinylpyrazine. Examples of vinyl monomers having a triazole ring include 2,4-diamino-6-vinyltriazine. Examples of polymerizable unsaturated monomers having a tetrazole ring include 1-vinyl-1H-tetrazole, 2-vinyl-2H-tetrazole, 5-vinyl-1H-tetrazole, and 1-methyl-5-vinyl-1H-tetrazole. These may be used alone or in combination of two or more.

[0084] Among these, at least one of a vinyl monomer having a pyridine ring group and a vinyl monomer having an imidazole ring group may be used.

[0085] In particular, the nitrogen-containing monomer may be an N,N-dialkylaminoalkyl(meth)acrylate, which further improves the dispersibility of the pigment. A preferred N,N-dialkylaminoalkyl(meth)acrylate is represented by the following general formula:

[0086] In the formula, A represents hydrogen or a methyl group, and B １ and B ２ each independently represents a linear or branched hydrocarbon group having 1 to 4 carbon atoms, and n is an integer of 1 to 3. In the formula, A may be a methyl group, B １ and B ２ may be a hydrocarbon group having 1 or 2 carbon atoms, and n may be 1 or 2.

[0087] Second Segment (c2) The second segment (c2) has at least one polyoxyalkylene chain, which increases the hydrophilicity of the copolymer (C) and promotes re-dissolution.

[0088] Examples of the polyoxyalkylene chain include a polyoxyethylene chain, a polyoxypropylene chain, a polyoxyethylene block, and a chain containing a polyoxypropylene block. The proportion of polyoxyethylene chains in all polyoxyalkylene chains may be 65% by mass or more, 70% by mass or more, 75% by mass or more, or 80% by mass or more. In one embodiment, the polyoxyalkylene chain is composed of polyoxyethylene.

[0089] The molecular weight of the polyoxyalkylene chain is, for example, 200 or more and 5,000 or less. From the viewpoint of dispersion stability, the molecular weight of the polyoxyalkylene chain may be 300 or more, 400 or more, 800 or more, or 1,000 or more. The molecular weight of the polyoxyalkylene chain may be 3,500 or less, or 2,500 or less. In particular, when the molecular weight of the polyoxyalkylene chain is 800 or more, long-term dispersion stability is likely to be obtained.

[0090] The second segment (c2) is derived from a hydrophilic monomer having a polyoxyalkylene chain and a polymerizable unsaturated group in one molecule.

[0091] The hydrophilic monomer may be, for example, a monomer represented by the following general formula: ２ = C(R １ )C(=O)O(C ｎ H ２ｎ O) ｍ -R ２ (In the formula, R １ represents a hydrogen atom or a methyl group, R ２ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, m is an integer of 4 to 60, n is 2 or 3, and m oxyalkylene units (C ｎ H ２ｎ O) may be the same or different from each other. m may be an integer of 5 to 100.

[0092] Examples of hydrophilic monomers include acrylates having a polyoxyethylene chain, such as tetraethylene glycol (meth)acrylate, methoxytetraethylene glycol (meth)acrylate, ethoxytetraethylene glycol (meth)acrylate, n-butoxytetraethylene glycol (meth)acrylate, polyethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, and ethoxypolyethylene glycol (meth)acrylate; and acrylates having a polyoxypropylene chain, such as tetrapropylene glycol (meth)acrylate, methoxytetrapropylene glycol (meth)acrylate, ethoxytetrapropylene glycol (meth)acrylate, n-butoxytetrapropylene glycol (meth)acrylate, and polypropylene glycol (meth)acrylate. These may be used alone or in combination of two or more.

[0093] Third Segment (c3) The copolymer (C) may further have a third segment (c3) derived from a polymerizable unsaturated monomer other than the nitrogen-containing monomer and the hydrophilic monomer. The other polymerizable unsaturated monomer (hereinafter sometimes referred to as "other raw material monomer") has a polymerizable unsaturated group in one molecule, but does not have a polyoxyalkylene chain or a nitrogen-containing group. The third segment (c3) derived from the other raw material monomer can impart various functions to the copolymer (C).

[0094] The other raw material monomers preferably do not have acid groups such as carboxyl groups, phosphate groups, sulfonic acid groups, and phenol groups, because interactions between acid groups and nitrogen-containing groups can generate intermolecular forces in the copolymer (C), resulting in an excessively high viscosity of the aqueous coating composition.

[0095] The other raw material monomers may have a hydroxyl group and a polymerizable unsaturated group in one molecule. The hydroxyl group can chemically react with the curing agent blended in the aqueous coating composition, thereby improving the water resistance of the resulting coating film.

[0096] Examples of hydroxyl group-containing polymerizable unsaturated monomers (hereinafter sometimes referred to as "hydroxyl group-containing monomers") include monoesters of (meth)acrylic acid with dihydric alcohols having 2 to 8 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; ε-caprolactone-modified monoesters of (meth)acrylic acid with dihydric alcohols having 2 to 8 carbon atoms; and allyl alcohol. These may be used alone or in combination of two or more.

[0097] Examples of raw material monomers other than the hydroxyl group-containing monomer include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, and tert-butyl (meth)acrylate; vinyl aromatic compounds such as styrene, α-methylstyrene, and vinyl toluene; (meth)acrylonitrile, (meth)acrylamide, and vinyl acetate. These may be used alone or in combination of two or more.

[0098] The mass proportion of the first segment (c1) may be 5% by mass or more and 30% by mass or less, the mass proportion of the second segment (c2) may be 20% by mass or more and 80% by mass or less, and the mass proportion of the third segment (c3) may be 10% by mass or more and 60% by mass or less.

[0099] When the mass proportion of the first segment (c1) is 5% by mass or more, the adsorption performance to the polyurethane resin (B) is improved. When the mass proportion of the first segment (c1) is 30% by mass or less, the hydrophilicity of the copolymer (C) is prevented from becoming excessively high, and a decrease in the water resistance of the coating film is prevented. The mass proportion of the first segment (c1) may be 7% by mass or more, 10% by mass or more, or 12% by mass or more. The mass proportion of the first segment (c1) may be 27% by mass or less, 25% by mass or less, or 22% by mass or less.

[0100] When the mass proportion of the second segment (c2) is 20% by mass or more, the water dispersibility of the polyurethane resin having the copolymer (C) adsorbed thereon is improved. When the mass proportion of the second segment (c2) is 80% by mass or less, the hydrophilicity of the copolymer (C) is prevented from becoming excessively high, and a decrease in the water resistance of the coating film is prevented. The mass proportion of the second segment (c2) may be 30% by mass or more, 35% by mass or more, or 40% by mass or more. The mass proportion of the second segment (c2) may be 75% by mass or less, 70% by mass or less, or 65% by mass or less.

[0101] The mass proportion of the third segment (c3) may be, for example, 10% by mass or more and 60% by mass or less. The mass proportion of the third segment (c3) may be 15% by mass or more, or 20% by mass or more. The mass proportion of the third segment (c3) may be 55% by mass or less, or 50% by mass or less.

[0102] The mass proportion of the hydroxyl group-containing segment (c31) may be 10% by mass or more and 30% by mass or less. When the mass proportion of the hydroxyl group-containing segment (c31) is within this range, improvement in coating film properties can be expected. The mass proportion of the hydroxyl group-containing segment (c31) may be 12% by mass or more, or 15% by mass or more. The mass proportion of the hydroxyl group-containing segment (c31) may be 25% by mass or less, or 20% by mass or less.

[0103] The content of the first segment (c1) relative to all structural units can be calculated by dividing the charged mass of the nitrogen-containing polymerizable unsaturated monomer used in synthesizing the copolymer (C) by the total charged mass of all raw material monomers. Similarly, the content of all structural units of the other segments can be calculated by dividing the charged mass of the monomers forming the segments used in synthesizing the copolymer (C) by the total charged mass of all raw material monomers.

[0104] <Other Hydroxyl Group-Containing Components> The first liquid may further contain, as a hydroxyl group-containing component other than the hydroxyl group-containing acrylic resin (A), at least one selected from the group consisting of, for example, polyester polyol resins, polycarbonate polyol resins, polyether polyol resins, and polycaprolactone polyol resins.

[0105] The solid content of hydroxyl group-containing components other than the hydroxyl group-containing acrylic resin (A) relative to 100% by mass of the total solid content of the hydroxyl group-containing components is, for example, 20% by mass or less, or may be 15% by mass or less, or may be 10% by mass or less.

[0106] <Solvent> The first liquid contains water as a solvent. The first liquid may further contain a water-soluble or water-miscible organic solvent, as necessary.

[0107] <Preparation Method> The first liquid can be prepared by mixing the above components by a method known to those skilled in the art. Examples of the mixing method include the same methods as those used to prepare the aqueous coating composition.

[0108] (Second Liquid) The second liquid contains a polyisocyanate compound (D).

[0109] (D) Polyisocyanate Compound The polyisocyanate compound (D) is a curing agent. The polyisocyanate compound (D) reacts with the hydroxyl group-containing resin (typically the hydroxyl group-containing acrylic resin (A)) to form a crosslinked structure, thereby curing the aqueous coating composition. The polyisocyanate compound (D) improves the chipping resistance of the coating film.

[0110] The polyisocyanate compound (D) has two or more isocyanate groups in the molecule. When the polyisocyanate compound (D) has unblocked free isocyanate groups, low-temperature curing becomes possible.

[0111] The polyisocyanate compound (D) includes, for example, at least one selected from the group consisting of aliphatic diisocyanates, aliphatic triisocyanates, alicyclic diisocyanates, alicyclic triisocyanates, aromatic diisocyanates, aromatic triisocyanates, and derivatives thereof. Specific examples of these diisocyanates and triisocyanates include the same compounds as those exemplified as the polyisocyanate compound (b1).

[0112] The number average molecular weight of the polyisocyanate compound (D) may be 150 or more and 2500 or less. This may provide flexibility to the coating film and further improve chipping resistance. The number average molecular weight of the polyisocyanate compound (D) may be 250 or more, 360 or more, or 400 or more. The number average molecular weight of the polyisocyanate compound (D) may be 2000 or less, 1800 or less, or 1600 or less.

[0113] The polyisocyanate compound (D) may contain a hydrophilic group. The hydrophilic group is roughly classified into anionic and nonionic. The anionic hydrophilic group is derived from, for example, carboxylic acid, sulfonic acid, phosphoric acid, silicic acid, sulfate ester, phosphate ester, or a metal salt or organic salt thereof. The nonionic hydrophilic group is derived from a hydrophilic compound. Examples of the hydrophilic compound include hydrophilic polyols and hydrophilic polyethers.

[0114] The polyisocyanate compound (D) may have an allophanate group (—NH—CO—N—CO(═O)—). This improves compatibility with the polyurethane resin (B). As a result, the polyurethane resin (B) can be more easily mixed uniformly in the aqueous coating composition, further improving chipping resistance.

[0115] The equivalent ratio (NCO / OH) of all isocyanate groups contained in the polyisocyanate compound (D) to all hydroxyl groups contained in the hydroxyl group-containing component is, for example, 0.7 or more and 2.0 or less. The equivalent ratio (NCO / OH) may be 0.8 or more. The equivalent ratio (NCO / OH) may be 1.8 or less.

[0116] <<Other Curing Agents>> The aqueous coating composition may contain a curing agent other than the polyisocyanate compound (D). Examples of other curing agents include amino resins, epoxy compounds, aziridine compounds, carbodiimide compounds, and oxazoline compounds. These may be used alone or in combination of two or more. The content of the other curing agent is appropriately determined depending on the hydroxyl group-containing resin.

[0117] <<Solvent>> The second liquid may contain a solvent that does not have a hydroxyl group. Examples of such solvents include glycol ether-based organic solvents, acetate-based organic solvents, ketone-based organic solvents, and ester-based organic solvents. These may be used alone or in combination of two or more.

[0118] <Preparation Method> The second liquid can be prepared by mixing the above components by a method known to those skilled in the art. Examples of the mixing method include the same method as used to prepare the first liquid.

[0119] (E) Color Pigment The aqueous coating composition may contain a color pigment (E). The color pigment (E) enhances the hiding power of the resulting coating film. An aqueous coating composition containing the color pigment (E) is particularly suitable for forming an intermediate coating film (the first coating film described below). The color pigment (E) may be added to any of the first, second, and third liquids. The color pigment (E) may be dispersed with a pigment dispersant to form a paste, and then added.

[0120] The content of the color pigment (E) is, for example, 1 part by mass or more and 150 parts by mass or less per 100 parts by mass of the total solids content of the hydroxyl group-containing acrylic resin (A), polyurethane resin (B), copolymer (C), and polyisocyanate compound (D). This makes it difficult for chipping resistance to be impaired. Furthermore, when the aqueous coating composition is used to form an intermediate coating film, sufficient hiding power can be exhibited. The content of the color pigment (E) may be 5 parts by mass or more, 10 parts by mass or more, 20 parts by mass or more, or 40 parts by mass or more. The content of the color pigment (E) may be 130 parts by mass or less, or 110 parts by mass or less.

[0121] The color pigment (E) may be an inorganic substance or an organic substance. The color pigment (E) may be a chromatic color or an achromatic color.

[0122] Examples of organic color pigments include azo chelate pigments, insoluble azo pigments, condensed azo pigments, diketopyrrolopyrrole pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxane pigments, quinacridone pigments, isoindolinone pigments, and metal complex pigments. Examples of inorganic color pigments include yellow lead, yellow iron oxide, red iron oxide, carbon black, and titanium dioxide. These may be used alone or in combination of two or more.

[0123] (Other Pigments) The aqueous coating composition may contain a pigment other than the color pigment (E) instead of or in addition to the color pigment (E). Examples of other pigments include extender pigments and anti-rust pigments. Examples of extender pigments include calcium carbonate, barium sulfate, clay, and talc.

[0124] (Other Components) The aqueous coating composition may contain additives commonly used in the coating field. The additives may be added to any of the first, second, and third liquids. Examples of additives include ultraviolet absorbers, hindered amine light stabilizers, antioxidants, crosslinked resin particles, leveling agents, antifoaming agents, curing accelerators, and viscosity adjusters.

[0125] [Coated Article] A coated article can be obtained using the aqueous coating composition according to the present disclosure. The coated article comprises, for example, a substrate and a multilayer coating film in which a first coating film, a second coating film, and a clear coating film are laminated in this order. The first coating film is formed using the aqueous coating composition according to the present disclosure. Therefore, the coated article has excellent chipping resistance, water resistance, and appearance.

[0126] (Substrate) Examples of the substrate material include metal, resin, and glass. Specific examples of the substrate include automobile bodies and automobile body parts such as passenger cars, trucks, motorcycles, and buses, and automobile parts such as spoilers, bumpers, mirror covers, grilles, and door knobs.

[0127] Examples of metals include iron, copper, aluminum, tin, zinc, and alloys thereof (e.g., steel). Representative examples of metal substrates include steel sheets such as cold-rolled steel sheets, hot-rolled steel sheets, stainless steel, electrogalvanized steel sheets, hot-dip galvanized steel sheets, zinc-aluminum alloy-plated steel sheets, zinc-iron alloy-plated steel sheets, zinc-magnesium alloy-plated steel sheets, zinc-aluminum-magnesium alloy-plated steel sheets, aluminum-plated steel sheets, aluminum-silicon alloy-plated steel sheets, and tin-plated steel sheets.

[0128] The metal substrate may be surface-treated. Examples of surface treatments include phosphate treatment, chromate treatment, zirconium conversion treatment, and composite oxide treatment. After the surface treatment, the metal substrate may be further coated with an electrodeposition paint. The electrodeposition paint may be either a cationic type or an anionic type.

[0129] Examples of resins include polyethylene resin, EVA resin, polyolefin resin (polyethylene resin, polypropylene resin, etc.), vinyl chloride resin, styrene resin, polyester resin (including PET resin, PBT resin, etc.), polycarbonate resin, acrylic resin, acrylonitrile butadiene styrene (ABS) resin, acrylonitrile styrene (AS) resin, polyamide resin, acetal resin, phenolic resin, fluororesin, melamine resin, urethane resin, epoxy resin, and polyphenylene oxide (PPO). Resin substrates may be degreased.

[0130] The aqueous coating composition according to the present disclosure can be cured at low temperatures, making it suitable for application to resins. The coating film obtained by the aqueous coating composition according to the present disclosure has excellent chipping resistance, making it suitable for application to metals. The substrate may include both a metal portion (a portion formed by metal) and a resin portion (a portion formed by resin). The metal portion may be a steel plate.

[0131] (First coating film) The first coating film is formed from the aqueous coating composition according to the present disclosure. The film thickness (dry film thickness) of the first coating film after curing is, for example, 5 μm or more and 80 μm or less. The dry film thickness of the first coating film may be 7 μm or more. The dry film thickness of the first coating film may be 50 μm or less.

[0132] The thickness of the coating film can be measured using an electromagnetic film thickness meter (for example, SDM-miniR manufactured by SANKO Co., Ltd.) The thickness of the coating film is the average value of the thickness of the coating film at any five points.

[0133] (Second Coating Film) The second coating film is formed from a second coating composition. The second coating composition will be described later. The second coating film may be a single layer, or may be a laminated coating film of two or more layers. The dry film thickness per layer of the second coating film is, for example, 5 μm or more and 35 μm or less. The dry film thickness per layer of the second coating film may be 7 μm or more. The dry film thickness per layer of the second coating film may be 30 μm or less.

[0134] (Clear Coating Film) The clear coating film is formed from a clear coating composition. The clear coating composition will be described later. The dry film thickness of the clear coating film is, for example, 10 μm or more and 80 μm or less. The dry film thickness of the clear coating film may be 20 μm or more. The dry film thickness of the clear coating film may be 60 μm or less.

[0135] [Method for manufacturing coated articles] The coated articles are manufactured by a method comprising, for example, the steps of applying the aqueous coating composition to a substrate to form an uncured first coating film, applying a second aqueous coating composition to the uncured first coating film to form an uncured second coating film, applying a clear coating composition to the uncured second coating film to form an uncured clear coating film, and heating and curing the uncured first coating film, the uncured second coating film, and the uncured clear coating film. The heating temperature may be 70°C or higher and 100°C or lower. The aqueous coating composition according to the present disclosure forms a coating film with excellent chipping resistance, water resistance, and appearance, even at such low temperatures.

[0136] (I) Step of forming an uncured first coating film: The aqueous coating composition according to the present disclosure is applied to a substrate to form an uncured first coating film. The first coating film improves adhesion between the second coating film and the substrate. The first coating film also makes the painted surface uniform, making it easier to suppress unevenness in the second coating film. As described above, the substrate may include both metal and resin parts.

[0137] Examples of coating methods include roll coating, air spray coating, airless spray coating, and rotary atomization coating. These methods may be combined with electrostatic coating. Among these, rotary atomization electrostatic coating is preferred from the viewpoint of coating efficiency. For rotary atomization electrostatic coating, for example, rotary atomization electrostatic coating machines commonly known as "micro-microbell (μμbell)," "microbell (μbell)," and "metallicbell (metabell)" may be used.

[0138] After applying the aqueous coating composition, pre-drying (also called preheating) may be performed before applying the second coating composition. This prevents the solvent contained in the aqueous coating composition from bumping during the curing process, making it easier to prevent popping. Furthermore, pre-drying prevents the uncured first coating film and the second coating composition from mixing, making it difficult for a mixed layer to form. This can further improve the smoothness of the resulting coated article.

[0139] Examples of pre-drying include a method of leaving the film at a temperature of 20°C to 25°C for 5 to 15 minutes, and a method of heating the film at a temperature of 50°C to 80°C for 30 seconds to 10 minutes.

[0140] (II) Step of forming an uncured second coating film A second coating composition is applied onto the uncured first coating film to form an uncured second coating film. Two or more layers of uncured second coating films can be formed by applying the same or different second coating compositions two or more times. An interval of several minutes may be provided between the nth application of the second coating composition and the (n+1)th application of the second coating composition.

[0141] The coating method may be, for example, the same method as the coating method for the aqueous coating composition. After the second coating composition has been applied, preliminary drying may be carried out in the same manner as above.

[0142] (Second Coating Composition) The second coating composition may be aqueous or solvent-based. The second coating composition may be aqueous. The aqueous second coating composition contains, for example, an acrylic resin emulsion, a water-soluble acrylic resin, a curing agent (typically, a melamine resin), and a polyether polyol resin. The second coating composition may further contain the various pigments, luster pigments, and various additives described above.

[0143] (III) Step of forming an uncured clear coating film The clear coating composition is applied onto the uncured second coating film to form an uncured clear coating film.

[0144] The coating method is not particularly limited. For example, the coating method may be the same as the coating method for the aqueous coating composition. Among them, rotary atomization electrostatic coating is preferred from the viewpoint of coating efficiency. After applying the clear coating composition, preliminary drying may be performed in the same manner as above.

[0145] (Clear Coating Composition) The clear coating composition may be solvent-based, water-based, or powder-type. From the viewpoints of transparency or acid etching resistance, the solvent-based clear coating composition may contain an acrylic resin and / or polyester resin as a film-forming resin, and an amino resin and / or isocyanate as a curing agent. The solvent-based clear coating composition may also contain an acrylic resin and / or polyester resin having a carboxylic acid and / or an epoxy group. The clear coating composition may contain the various pigments and additives described above, as long as the transparency is not impaired.

[0146] (IV) Curing step: Each uncured coating film is cured. Each coating film can be cured by heating. In this embodiment, the first coating film, the second coating film, and the clear coating film are cured at the same time.

[0147] The heating temperature is, for example, 70°C or higher and 100°C or lower. The heating temperature may be 75°C or higher, or 80°C or higher. The heating temperature may be 95°C or lower, or 90°C or lower. The heating time means the time it takes for the interior of the heating device to reach the target temperature and for the substrate to be maintained at the target temperature, and does not take into account the time it takes to reach the target temperature. Examples of heating devices include drying ovens that use heat sources such as hot air, electricity, gas, and infrared rays.

[0148] The heating time may be appropriately set depending on the heating temperature. When the heating temperature is 70° C. or higher and 100° C. or lower, the heating time is, for example, 10 minutes or longer and 60 minutes or shorter, and may be 15 minutes or longer and 45 minutes or shorter.

[0149] The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. In the examples, "parts" and "%" are based on the mass of the solid content unless otherwise specified.

[0150] The acid value and hydroxyl value were calculated based on the blend amount of each unsaturated monomer used and the solid content acid value and solid content hydroxyl value of these unsaturated monomers.

[0151] [Production Example 1-1] Production of Hydroxyl Group-Containing Acrylic Resin (A-1) 127 parts of deionized water was added to a reaction vessel, and the temperature was raised to 80°C while mixing and stirring in a nitrogen stream. Next, a monomer emulsion consisting of 1.9 parts of acrylic acid (AA), 30.2 parts of 2-hydroxyethyl methacrylate (HEMA), 8.1 parts of butyl acrylate (nBA), 47.9 parts of n-butyl methacrylate (nBMA), 10.9 parts of styrene (ST), 1.0 parts of allyl methacrylate (AMA), 4.0 parts of ADEKA REASOAP SR-10 (polyoxyethylene-1-alkoxymethyl-2-(2-propenyloxy)ethyl ether sulfate ester ammonium salt, manufactured by ADEKA Corporation), and 80 parts of deionized water, and an initiator solution consisting of 0.3 parts of ammonium persulfate and 10 parts of deionized water were added dropwise to the reaction vessel in parallel over a period of 2 hours. After completion of the dropwise addition, the mixture was aged at the same temperature for 2 hours. The mixture was then cooled to 40°C and filtered through a 400-mesh filter. The pH was then adjusted by adding 20 parts of deionized water and 0.32 parts of dimethylaminoethanol. The non-volatile content, Tg, Sp, hydroxyl value, and acid value of the resulting acrylic emulsion (A-1) are shown in Table 1 below.

[0152] [Production Examples 1-2 to 1-15] Production of Hydroxyl Group-Containing Acrylic Resins (A-2) to (A-15) Acrylic resin emulsions (A-2) to (A-15) were obtained in the same manner as in Production Example 1-1, except that the monomer compositions and blending amounts of each copolymerization component were changed as shown in Table 1 below.

[0153]

[0154] Production Example 2-1 Production of Polyurethane Resin (B-1) A simple pressurized reaction apparatus equipped with a stirrer and a heater was charged with 36.1 parts by weight of polyisocyanate compound (b1-1), 100.0 parts by weight of polyol (b2-1), 1.6 parts by weight of polyol (b2-7), 4.6 parts by weight of polyol (b2-10), 70.0 parts by weight of organic solvent (THF, tetrahydrofuran), and 0.06 parts by weight of catalyst (Neostan U-600, bismuth tris(2-ethylhexanoate, manufactured by Nitto Kasei Co., Ltd.)), and the mixture was stirred at 85°C for 10 hours to carry out a urethanization reaction, thereby producing a THF solution of a urethane prepolymer.

[0155] A simple pressure reactor equipped with a stirrer and a heating reactor was charged with a THF solution of the obtained urethane prepolymer, and 3.5 parts by weight of a neutralizer (triethylamine) was added while stirring at 50°C. After homogenization at 60 rpm for 30 minutes, the temperature was maintained at 50°C, and 220 parts by weight of ion-exchanged water was gradually added while stirring at 500 rpm to emulsify. Next, 5.2 parts by weight of a 10% water dilution of polyamine compound (b3-1) was added, and the THF was distilled off under reduced pressure at 65°C over 12 hours to obtain a dispersion of polyurethane resin (B-1).

[0156] [Production Examples 2-2 to 2-15] Production of polyurethane resins (B-2) to (B-15) Dispersions of polyurethane resins (B-2) to (B-15) were obtained in the same manner as in Production Example 2-1, except that the types and amounts of raw materials were changed as shown in Table 2 below.

[0157] Details of the raw materials used for polyurethane resin (B) are as follows: Polyisocyanate compounds (b1) (b1-1) IPDI (b1-2) HDI (b1-3) Hydrogenated MDI (b1-4) PDI (1,5-pentamethylene diisocyanate)

[0158] Polyol (b2) (b2-1) Kuraray Polyol P-2010, Mn=2,000, poly(3-methyl-1,5 pentanediol, adipic acid polycondensate, manufactured by Kuraray Co., Ltd. (b2-2) Kuraray Polyol P-2011, Mn=2,000, poly(3-methyl-1,5 pentanediol, adipic acid, terephthalic acid polycondensate, manufactured by Kuraray Co., Ltd. (b2-3) Kuraray Polyol P-2012, Mn=2,000, poly(3-methyl-1,5 pentanediol, adipic acid, isophthalic acid polycondensate, manufactured by Kuraray Co., Ltd. (b2-4) Kuraray Polyol P-2020, Mn=2,000, poly(3-methyl-1,5 pentanediol, terephthalic acid polycondensate, manufactured by Kuraray Co., Ltd. (b2-5) Ethanacole UH-200, Mn=2,000, polyhexamethylene carbonate diol, manufactured by Ube Industries, Ltd. (b2-6) PTMG2000, Mn=2,000, poly(oxytetramethylene) glycol, manufactured by Mitsubishi Chemical Corporation, polyether polyol (b2-7) 1,4-butanediol (b2-8) neopentyl glycol (b2-9) trimethylolpropane (b2-10) 2,2-dimethylolpropionic acid (b2-11) 2,2-dimethylolbutanoic acid

[0159] Polyamine compounds (b3): ​​(b3-1) ethylenediamine (b3-2) diethylenetriamine

[0160]

[0161] [Polyurethane Resin (B-16)] As polyurethane resin (B-16), U-coat D-338 (product name, manufactured by Sanyo Chemical Industries, Ltd., hydroxyl value 37 mgKOH / g) was prepared.

[0162] [Production Example 3-1] Production of Copolymer (C-1) A reaction vessel equipped with a stirrer, temperature controller, condenser, and dropping device was charged with 78 parts of dipropylene glycol monomethyl ether, and the mixture was heated to 120 °C with stirring and refluxed. Next, a solution of 15 parts of 2-(dimethylamino)ethyl methacrylate, 60 parts of a monomer having a polyoxyalkylene structure (product name: PME-1000, manufactured by NOF Corporation, methoxypolyethylene glycol methacrylate), 19 parts of 2-hydroxyethyl methacrylate, and 6 parts of butyl acrylate, 0.5 parts of Kayaester O (manufactured by NOF Corporation), and 76 parts of dipropylene glycol monomethyl ether was added dropwise over 3 hours and allowed to react. As a post-shot, a polymerization initiator solution prepared by dissolving 0.3 parts of Kayaester O (manufactured by NOF Corporation) in 11 parts of dipropylene glycol monomethyl ether was added dropwise over 0.5 hours, and the mixture was allowed to polymerize with continued stirring for 0.5 hours to obtain Copolymer (C-1). Subsequently, the solvent was distilled off by vacuum distillation at 90°C, and then 100 parts of ion-exchanged water was added to 1000 parts of copolymer (C-1) and stirred to obtain an aqueous solution of copolymer (C-1) (solid content: 50% by mass). The obtained copolymer (C-1) had a hydroxyl value of 82 mgKOH / g and a weight-average molecular weight of 30,000.

[0163] [Production Examples 1-2 to 1-14] Production of Copolymers (C-2) to (C-12), (c-1), and (c-2) Copolymers (C-2) to (C-12), (c-1), and (c-2) were produced in the same manner as in Production Example 1-1, except that the monomers shown in the table below were used in the amounts shown in Table 1.

[0164]

[0165] [Preparation of Pigment Dispersion Paste] 19.2 parts of Typec CR-97 (titanium dioxide, manufactured by Ishihara Sangyo Kaisha), 4.8 parts of MA-100 (carbon black, manufactured by Mitsubishi Carbon Corporation), and 16 parts of barium sulfate B-34 (barium sulfate, manufactured by Sakai Chemical Industry Co., Ltd.) were placed in a 1 L stainless steel container and mixed and dispersed at room temperature for 45 minutes using a paint conditioner to obtain a pigment dispersion paste (pigment solids content: 70%).

[0166] Example 1 (1) Preparation of First Liquid To a 1 L metal container, 98 parts of the pigment dispersion paste, 30 parts of the hydroxyl group-containing acrylic resin (A-1), 25 parts of the polyurethane resin (B-1), 10 parts of the copolymer (C-1), and an appropriate amount of water were sequentially added, and the mixture was thoroughly stirred with a disper to obtain a first liquid.

[0167] (2) Preparation of Second Liquid Into another metal container, 35 parts of a polyisocyanate compound (D) (Bayhydur 304, manufactured by Sumika Covestro Urethane Co., Ltd., hydrophilic polyether-modified HDI trimer, containing allophanate groups) and an appropriate amount of a solvent (1-methoxypropyl 2-acetate) were mixed and thoroughly stirred with a disper to obtain a second liquid.

[0168] (3) Preparation of aqueous coating composition The first liquid and the second liquid were mixed within 60 minutes after preparation to obtain an aqueous coating composition.

[0169] (4) Preparation of Coated Articles A matte steel plate was washed and zinc phosphate treated in a conventional manner. The steel plate was then electrodeposited using a cationic electrodeposition paint (Power Top U-100, manufactured by Nippon Paint Co., Ltd.) and heated at 170°C for 20 minutes. This resulted in the formation of an electrodeposited coating film with a dry thickness of 15 µm.

[0170] Next, the aqueous coating composition was electrostatically coated onto the electrodeposition coating film using a rotary atomizer electrostatic coater. After leaving it for 5 minutes, an aqueous base coating composition (manufactured by Nippon Paint Automotive Coatings Co., Ltd., trade name: Aqueous Base AR-3020-1 (gray metallic)) was applied using a rotary atomizer electrostatic coater to a dry film thickness of 12 μm under conditions of room temperature 23 ° C and humidity 68%. After setting for 4 minutes, the coating was preheated at 80 ° C for 5 minutes. Next, a clear coating (manufactured by Nippon Paint Automotive Coatings Co., Ltd., trade name: Polyurexcel O-1200, a two-component acrylic urethane organic solvent-based clear coating containing a polyisocyanate compound) was applied using a rotary atomizer electrostatic coater to a dry film thickness of 35 μm. Finally, the coating was heated at 85 ° C for 20 minutes to obtain a coated article having a multi-layer coating film.

[0171] Examples 2 to 48 and Comparative Examples 1 to 7 Aqueous coating compositions were prepared and coated articles were produced in the same manner as in Example 1, except that the types and amounts of the ingredients and the mass of solids at the time of coating were changed as shown in Tables 4 to 7. In Comparative Example 7, a melamine resin (product name: Cymel 325, manufactured by Mitsui Cytec Co., Ltd., methylated melamine resin, solids content 80%) was blended into the second liquid as a curing agent.

[0172] [Evaluation] The aqueous coating compositions and coated articles were evaluated as follows. The evaluation results are shown in Tables 4 to 7.

[0173] (1) Resolubility 3 g of the first liquid was placed in a 300 ml plastic cup and allowed to stand in an open state for 24 hours. Then, 100 g of the first liquid having the same composition was added to the plastic cup and stirred for 3 minutes at a rotation speed of 1500 rpm using a disperser. The mixture was then filtered through a 200 mesh filter. The residue was washed with water. The resulting residue was dried for at least 3 days to thoroughly remove moisture, and then evaluated according to the following criteria. A rating of C or higher was considered acceptable.

[0174] (Evaluation criteria) A: Residue amount 0.05 g or less B: Residue amount more than 0.05 g but not more than 0.10 g C: Residue amount more than 0.10 g but not more than 0.50 g D: Residue amount more than 0.50 g but not more than 1.00 g E: Residue amount more than 1.00 g

[0175] (2) Chipping Resistance The coated article was placed on the specimen holder of a stone chipping tester (Grabero Tester KSS-1, manufactured by Suga Testing Instruments Co., Ltd.), and 100 g of crushed stone with a particle size of No. 6 was collided with the multi-layer coating film at a 45-degree angle from a distance of 30 cm from the test plate using 0.5 MPa compressed air at -30°C. The coated article was then washed with water and dried, and cloth adhesive tape (manufactured by Nichiban Co., Ltd.) was applied to the coated surface. The tape was then peeled off, and the maximum diameters of multiple locations where the steel plate was exposed were measured and averaged. The obtained average diameter (average exposed diameter) was evaluated according to the following criteria. A rating of C or higher was considered a pass.

[0176] (Evaluation criteria) A: Average exposed diameter less than 0.5 mm B: Average exposed diameter 0.5 mm or more and less than 1.0 mm C: Average exposed diameter 1.0 mm or more and less than 2.0 mm D: Average exposed diameter 2.0 mm or more and less than 2.5 mm E: Average exposed diameter 2.5 mm or more

[0177] (3) Water Resistance: The coated article was immersed in warm water at 40°C for 10 days. After that, it was removed from the water and dried at room temperature for 1 hour. The appearance of the coating film after drying was visually observed and evaluated according to the following criteria. A rating of C or higher was considered to be acceptable.

[0178] (Evaluation criteria) A: No abnormalities B: At least one of the following abnormalities is slightly observed: fading of the gloss, cracks, and blisters (blisters) C: At least one of the following abnormalities is partially observed: fading of the gloss, cracks, and blisters (blisters) D: At least one of the following abnormalities is significantly observed partially or over the entire surface of the coating film

[0179] (4) Surface Smoothness The appearance of the coating film on the coated article was visually observed and the surface smoothness was evaluated according to the following criteria. A rating of C or higher was considered to be acceptable.

[0180] (Evaluation criteria) A: Very good B: Good C: Slightly poor D: Poor E: Obvious irregularities observed

[0181]

[0182]

[0183]

[0184]

[0185] The aqueous coating composition of the present invention can be cured at low temperatures, yet provides a coating film with excellent chipping resistance, and also has excellent resolubility of the thin film formed from the base resin, making it particularly suitable for use on substrates containing both metal and resin parts.

[0186] This application claims priority based on Japanese Patent Application No. 2023-218564, filed on December 25, 2023, the entire contents of which are incorporated herein by reference.

Claims

1. A water-based multi-component coating composition comprising a first liquid containing a hydroxyl group-containing acrylic resin (A), a polyurethane resin (B), and a copolymer (C) having a first segment (c1) derived from a nitrogen-containing polymerizable unsaturated monomer having at least one of a tertiary amino group and a nitrogen-containing heterocyclic group and a second segment (c2) derived from a polymerizable unsaturated monomer having a polyoxyalkylene chain, and a second liquid containing a polyisocyanate compound (D).

2. The water-based multi-component coating composition according to claim 1, wherein the hydroxyl group-containing acrylic resin (A) has an acid value of 5 mgKOH / g or more and 70 mgKOH / g or less.

3. The water-based multi-component coating composition according to claim 1 or 2, wherein the copolymer (C) has an acid value of less than 5 mgKOH / g.

4. The water-based multi-component coating composition according to any one of claims 1 to 3, wherein the polyurethane resin (B) has a hydroxyl value of 30 mgKOH / g or less.

5. The water-based multi-component coating composition according to any one of claims 1 to 4, wherein the polyurethane resin (B) is obtained by chain-extending a terminal NCO group-containing urethane prepolymer, which is a reaction product of a polyisocyanate compound (b1) and a polyol (b2), with a polyamine compound (b3), and the polyol (b2) contains a polyether polyol.

6. The water-based multi-component coating composition according to any one of claims 1 to 5, wherein the nitrogen-containing polymerizable unsaturated monomer contains N,N-dialkylaminoalkyl (meth)acrylate.

7. The polymerizable unsaturated monomer having a polyoxyalkylene chain is represented by the following general formula: CH ２ =C(R １ )C(=O)O(C ｎ H ２ｎ O) ｍ -R ２ (In the formula, R １ represents a hydrogen atom or a methyl group, R ２ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, m is an integer of 4 to 60, n is 2 or 3, and the m oxyalkylene units (C ｎ H ２ｎ O) may be the same or different from each other.) The aqueous multi-liquid type coating composition according to any one of claims 1 to 6.

8. The water-based multi-component coating composition according to any one of claims 1 to 7, wherein the copolymer (C) has an amine value of 3 mgKOH / g or more and 100 mgKOH / g or less and a hydroxyl value of 20 mgKOH / g or more and 180 mgKOH / g or less.

9. The water-based multi-component coating composition according to any one of claims 1 to 8, wherein the copolymer (C) further has a third segment (c3) derived from a polymerizable unsaturated monomer other than the nitrogen-containing polymerizable unsaturated monomer and the polymerizable unsaturated monomer having a polyoxyalkylene chain, and in the copolymer (C), the mass ratio of the first segment (c1) is 5% by mass or more and 30% by mass or less, the mass ratio of the second segment (c2) is 20% by mass or more and 80% by mass or less, and the mass ratio of the third segment (c3) is 10% by mass or more and 60% by mass or less.

10. The third segment (c3) contains a segment (c31) derived from a hydroxyl group-containing polymerizable saturated monomer, and the mass ratio of the segment (c31) in the copolymer (C) is 10% by mass or more and 30% by mass or less. The aqueous multi-component paint composition according to claim 9.

11. The content of the copolymer (C) is 20 parts by mass or more and 300 parts by mass or less with respect to 100 parts by mass of the solid content of the polyurethane resin (B). The aqueous multi-component paint composition according to any one of claims 1 to 10.

12. The polyisocyanate compound (D) contains at least one selected from the group consisting of aliphatic diisocyanates, aliphatic triisocyanates, alicyclic diisocyanates, alicyclic triisocyanates, aromatic diisocyanates, aromatic triisocyanates, and derivatives thereof. The aqueous multi-component paint composition according to any one of claims 1 to 11.

13. Further comprising a coloring pigment (E), and the content of the coloring pigment (E) is 1 part by mass or more and 150 parts by mass or less with respect to 100 parts by mass of the total solid content of the hydroxyl group-containing acrylic resin (A), the polyurethane resin (B), the copolymer (C), and the polyisocyanate compound (D). The aqueous multi-component paint composition according to any one of claims 1 to 12.

14. A method for manufacturing a painted article, comprising: a step of applying the aqueous multi-component paint composition according to any one of claims 1 to 13 onto an object to be painted to form an uncured first paint film; a step of applying a second aqueous paint composition onto the uncured first paint film to form an uncured second paint film; a step of applying a clear paint composition onto the uncured second paint film to form an uncured clear paint film; and a step of heating and curing the uncured first paint film, the uncured second paint film, and the uncured clear paint film at 70°C or higher and 100°C or lower.

15. The object to be painted includes a metal part and a resin part. The method for manufacturing a painted article according to claim 14.

Images