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

Abstract

An aqueous multicomponent coating composition comprising: a first liquid containing a hydroxyl group-containing acrylic resin (A) and a polyurethane resin (B); and a second liquid containing a polyisocyanate compound (C), wherein the polyisocyanate compound (C) contains: a polyisocyanate compound (C1) not containing a hydrophilic group having a number average molecular weight of 150 or more and 2500 or less; and a polyisocyanate compound (C2) containing a nonionic hydrophilic group.

Description

Technical Field

[0001] This invention relates to a method for manufacturing water-based multi-component coating compositions and coated articles. Background Technology

[0002] In recent years, environmental considerations have become increasingly important in technological fields such as automobiles. Therefore, methods for reducing heating temperatures or shortening heating times during coating processes have been developed with energy conservation as a goal. For example, Patent Document 1 discloses a water-based multi-component coating composition comprising: a base agent (I) containing a hydroxyl-containing acrylic resin; and a curing agent (II) containing a polyisocyanate compound with anionic hydrophilic groups and / or a polyisocyanate compound with nonionic hydrophilic groups. In Patent Document 1, the coating film is dried at a low temperature of 60°C.

[0003] Existing technical documents Patent documents Patent document 1: Japanese Patent Application Publication No. 2021-130812. Summary of the Invention

[0004] The problem that the invention aims to solve According to Patent Document 1, the above-mentioned waterborne multi-component coating composition exhibits excellent drying properties, workability (pot life, manual stirring, etc.), storage properties, weather resistance, and finishability such as gloss. However, it is difficult to obtain a coating film with excellent crack resistance, water resistance, and appearance in the above-mentioned waterborne multi-component coating composition.

[0005] The present invention was made in view of the above circumstances, and its object is to provide: a water-based multi-component coating composition that can be cured at low temperature and forms a coating film with excellent crack resistance, water resistance and appearance; and a method for manufacturing a coated article using the water-based multi-component coating composition.

[0006] Methods for solving problems To address the aforementioned issues, the present invention provides the following solution.

[0007] [1] A water-based multi-component coating composition comprising: A first liquid containing hydroxyl-containing acrylic resin (A) and polyurethane resin (B); and The second liquid contains a polyisocyanate compound (C). The polyisocyanate compound (C) comprises: Polyisocyanate compounds (C1) without hydrophilic groups and having a number average molecular weight of 150 or higher and 2500 or lower; and Polyisocyanate compounds containing nonionic hydrophilic groups (C2).

[0008] [2] The water-based multi-component coating composition described in [1] above, wherein the hydroxyl value of the polyurethane resin (B) is less than 30 mg KOH / g.

[0009] [3] The waterborne multi-component coating composition described in [1] or [2] above, wherein the content of the polyurethane resin (B) is 10 parts by mass or more and 100 parts by mass or less relative to 100 parts by mass of the solid component of the hydroxyl-containing acrylic resin (A).

[0010] [4] The waterborne multi-component coating composition described in any one of [1] to [3] above, wherein the acid value of the hydroxyl-containing acrylic resin (A) is 5 mg KOH / g or more and 70 mg KOH / g or less.

[0011] [5] The waterborne multi-component coating composition described in any one of [1] to [4] above, wherein the hydrophilic polyisocyanate compound (C1) comprises at least one selected from the following: aliphatic diisocyanate, aliphatic triisocyanate, alicyclic diisocyanate, alicyclic triisocyanate, aromatic diisocyanate, aromatic triisocyanate and derivatives thereof.

[0012] [6] The waterborne multi-component coating composition described in any one of [1] to [5] above, wherein the mass ratio (WC2 / WC1) of the content of the polyisocyanate compound (C2) containing nonionic hydrophilic groups to the content of the polyisocyanate compound (C1) without hydrophilic groups is 0.1 or more and 4 or less.

[0013] [7] The waterborne multi-component coating composition described in any one of [1] to [6] above, further comprising a coloring pigment (D), The content of the coloring pigment (D) is 1 part by mass or more and 150 parts by mass or less, relative to the total solid content of 100 parts by mass of the hydroxyl-containing acrylic resin (A), the polyurethane resin (B) and the polyisocyanate compound (C).

[0014] [8] The waterborne multi-component coating composition described in any one of [1] to [7] above, wherein the polyisocyanate compound (C2) containing nonionic hydrophilic groups has three or more isocyanate groups.

[0015] [9] The waterborne multi-component coating composition described in any one of [1] to [8] above, wherein the polyisocyanate compound (C2) containing nonionic hydrophilic groups further has urea-formate groups.

[0016]

[10] The waterborne multi-component coating composition described in any one of [1] to [9] above, wherein, The polyurethane resin (B) is obtained by chain extension of a polyisocyanate compound (b1) and a polyol (b2), namely a urethane prepolymer containing terminal NCO groups, using a polyamine compound (b3). The polyisocyanate compound (b1) comprises: Aromatic polyisocyanates; and It is selected from at least one of aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic aliphatic polyisocyanates.

[0017]

[11] A method for manufacturing a coated article, comprising the following steps: Apply the water-based multi-component coating composition described in any one of [1] to

[10] above onto the object to form an uncured first coating film; A second water-based coating composition is applied to the uncured first coating film to form an uncured second coating film; A transparent coating composition is applied to the uncured second coating film to form an uncured transparent coating film; and The uncured first coating, the uncured second coating, and the uncured transparent coating are heated and cured at a temperature above 70°C and below 100°C.

[0018]

[12] The method for manufacturing a coated article described in

[11] above, wherein the coated article comprises a metal part and a resin part.

[0019] Invention Effects According to the present invention, there is provided: a water-based multi-component coating composition that can be cured at low temperatures and forms a coating film with excellent crack resistance, water resistance and appearance; and a method for manufacturing a coated article using the water-based multi-component coating composition. Detailed Implementation

[0020] [Coating Composition] The waterborne multi-component coating composition disclosed herein comprises: a first liquid containing a hydroxyl-containing acrylic resin (A) and a polyurethane resin (B); and a second liquid containing a polyisocyanate compound (C). The polyisocyanate compound (C) comprises: a polyisocyanate compound (C1) without hydrophilic groups having a number average molecular weight of 150 or more and 2500 or less; and a polyisocyanate compound (C2) containing nonionic hydrophilic groups.

[0021] The waterborne multi-component coating compositions disclosed herein (hereinafter, sometimes simply referred to as waterborne coating compositions) comprise polyurethane resins. It is generally believed that polyurethane resins improve crack resistance. However, it has been determined that if a polyisocyanate compound containing anionic hydrophilic groups is used as a curing agent, even when blended with polyurethane resin, a sufficient improvement in crack resistance cannot be obtained. The reason for this is not yet determined, but it is believed to be because the reactant of hydroxyl-containing acrylic resin and polyisocyanate compound containing anionic hydrophilic groups has high hardness, making it difficult to sufficiently reduce the elastic modulus of the resulting coating film even when blended with polyurethane resin.

[0022] In this disclosure, a polyisocyanate compound (C1) without hydrophilic groups and a polyisocyanate compound (C2) containing nonionic hydrophilic groups are used as curing agents. This achieves improved crack resistance based on the blended polyurethane resin, while also enhancing water resistance and appearance.

[0023] Polyisocyanate compounds (C2) containing nonionic hydrophilic groups are typically obtained by modifying polyisocyanate compounds with hydrophilic polyols and / or hydrophilic polyethers. These modified portions (nonionic hydroxyl groups), also known as so-called soft segments, impart flexibility to the coating film. Furthermore, the soft segments exhibit high compatibility with polyurethane resins, allowing for partial dissolution of the polyurethane resin in waterborne coating compositions. Therefore, it is believed that the flexibility of the coating film is further improved, and its resistance to chipping is further enhanced.

[0024] Furthermore, the water resistance of the resulting coating film is improved due to the use of a hydrophilic-free polyisocyanate compound (C1) in a portion of the curing agent. Additionally, the viscosity increase of the water-based coating composition is suppressed by using the hydrophilic-free polyisocyanate compound (C1), resulting in improved coating smoothness. The hydrophilic-free polyisocyanate compound (C1) can be dispersed in the water-based coating composition by a polyisocyanate compound (C2) containing nonionic hydrophilic groups. Therefore, the localized reaction between the hydrophilic-free polyisocyanate compound (C1) and the hydroxyl-containing acrylic resin (A) is suppressed, and the number of particles (bumps) is reduced. This is considered to improve the appearance of the coating film.

[0025] The waterborne coating composition is a multi-component type comprising a first liquid and a second liquid. The waterborne coating composition may further comprise a third liquid containing other components. The waterborne coating composition is prepared using methods commonly employed by those skilled in the art. The waterborne coating composition can be prepared by mixing the first liquid, the second liquid, and the third liquid. Examples of mixing methods include kneading and mixing using a kneader or rollers, and dispersing and mixing using a sand mill or disperser.

[0026] The water-based coating composition contains water as a solvent. In the water-based coating composition, the proportion of water in the solvent can be 50% by mass or more, 70% by mass or more, or 100% by mass.

[0027] Waterborne coating compositions can be cured at low temperatures. For example, waterborne coating compositions can be cured at temperatures above 70°C and below 100°C. The curing temperature can be above 75°C or above 80°C. The curing temperature can be below 95°C or below 90°C.

[0028] (First Liquid) The first liquid contains: hydroxyl-containing acrylic resin (A) and polyurethane resin (B).

[0029] (A) Hydroxyl-containing acrylic resin Hydroxyl-containing acrylic resin (A) is the resin that forms the base of the coating (coating-forming component). Hydroxyl-containing acrylic resin (A) reacts with a polyisocyanate compound (C) to form a cross-linked structure. A coating with sufficient hardness is obtained using hydroxyl-containing acrylic resin (A). The hardness of the coating can be evaluated by its tensile strength.

[0030] Hydroxyl-containing acrylic resin (A) has multiple acryloyl groups and one or more (typically two or more) hydroxyl groups within one molecule.

[0031] The hydroxyl-containing acrylic resin (A) has a hydroxyl value (OHV) of, for example, 20 mg KOH / g or higher and 180 mg KOH / g or lower. If the hydroxyl value of the hydroxyl-containing acrylic resin (A) is 20 mg KOH / g or higher, the tensile strength of the coating film is easily improved. If the hydroxyl value of the hydroxyl-containing acrylic resin (A) is 180 mg KOH / g or lower, the hydrophilicity of the coating film is inhibited, and the water resistance is easily improved. The hydroxyl value of the hydroxyl-containing acrylic resin (A) can be 30 mg KOH / g or higher, or 50 mg KOH / g or higher. The hydroxyl value of the hydroxyl-containing acrylic resin (A) can be 150 mg KOH / g or lower, or 140 mg KOH / g or lower.

[0032] Hydroxyl value and acid value are determined based on the mass of the solid components. Hydroxyl value and acid value can be determined by known methods described in JIS K 0070:1992. Hydroxyl value and acid value can be calculated based on the amount of unsaturated monomers blended in the raw material monomers of the resin (e.g., hydroxyl-containing acrylic resin (A)).

[0033] The glass transition temperature (Tg) of the hydroxyl-containing acrylic resin (A) is, for example, 15°C or higher and 100°C or lower. If the Tg of the hydroxyl-containing acrylic resin (A) is 15°C or higher, the tensile strength and hardness of the resulting coating film are easily improved. If the Tg of the hydroxyl-containing acrylic resin (A) is 100°C or lower, the drying speed of the waterborne coating composition is easily improved. The Tg of the hydroxyl-containing acrylic resin (A) can be 18°C ​​or higher, or 20°C or higher. The Tg of the hydroxyl-containing acrylic resin (A) can be 90°C or lower, 80°C or lower, or 70°C or lower.

[0034] Tg can be calculated based on the type and amount of monomers used in the resin. Tg can also be measured using differential scanning calorimetry (DSC).

[0035] From the perspective of hardness, the hydroxyl value of hydroxyl-containing acrylic resin (A) is above 20 mg KOH / g and below 180 mg KOH / g, and the Tg can be above 15℃ and below 100℃.

[0036] The acid value (AV) of the hydroxyl-containing acrylic resin (A) can be above 0 mg KOH / g and below 70 mg KOH / g, or above 5 mg KOH / g and below 70 mg KOH / g. This easily improves the hardness of the resulting coating. The acid value of the hydroxyl-containing acrylic resin (A) can be above 8 mg KOH / g or above 10 mg KOH / g. The acid value of the hydroxyl-containing acrylic resin (A) can be below 60 mg KOH / g, below 50 mg KOH / g, or below 40 mg KOH / g.

[0037] The solid component acid value and solid component hydroxyl value of hydroxyl-containing acrylic resin (A) can be calculated based on the solid component acid value and solid component hydroxyl value of the monomer mixture used.

[0038] The solubility parameter (SP) of the hydroxyl-containing acrylic resin (A) can be 8.5 or higher and 12 or lower. This makes the hydroxyl-containing acrylic resin (A) readily compatible in water-based coating compositions, further suppressing particle formation. The SP value of the hydroxyl-containing acrylic resin (A) can be 9.0 or higher, or 9.5 or higher. The SP value of the hydroxyl-containing acrylic resin (A) can be 11.5 or lower, or 11.0 or lower.

[0039] SP value is one of the measures of a compound's solubility. The larger the SP value, the higher the polarity of the compound; the smaller the SP value, the lower the polarity of the compound.

[0040] The SP value of hydroxyl-containing acrylic resin (A) can be considered as a weighted average obtained by taking into account the SP values ​​of multiple raw material monomers and the mass ratio of these solid components. In cases where hydroxyl-containing acrylic resin (A) comprises multiple acrylic resins, the weighted average of all acrylic resins obtained by further considering the mass ratio of the solid components of each acrylic resin can be regarded as the SP value of hydroxyl-containing acrylic resin (A).

[0041] [Method for determining solubility parameter (SP)] The SP value of the monomer was actually determined, for example, by the following method. [Reference: SUH, CLARKE, JPSA-1, 5, 1671~1681 (1967)].

[0042] As a sample, 0.5 g of monomer was weighed into a 100 ml beaker and dissolved in 10 ml of acetone. Using a 50 ml pipette, the unsuitable solvent was added dropwise to the sample at a measurement temperature of 20°C, with the point of turbidity being the volume added. Deionized water was used as a high-SP unsuitable solvent, and n-hexane was used as a low-SP unsuitable solvent; the turbidity point of each was measured. The SP value δ of the monomer was calculated using the following formula.

[0043] [Mathematical Expression 1] Vi: Molecular volume of solvent i (ml / mol) φi: Volume fraction of solvent i at the cloud point δi: SP value of solvent i ml: Low SP poor solvent mixture mh: High SP poor solvent mixture [Mathematical Expression 2] [Mathematical Expression 3] Hydroxyl-containing acrylic resin (A) can be manufactured by polymerizing a hydroxyl-containing α,β-ene unsaturated monomer with other α,β-ene unsaturated monomers using a known method. Hydroxyl-containing acrylic resin (A) can be manufactured, for example, by solution polymerization. Commercially available hydroxyl-containing acrylic resins can be used.

[0044] Examples of hydroxyl-containing α,β-ene unsaturated monomers include: hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, allyl alcohol, methyl allyl alcohol, and their adducts with ε-caprolactone.

[0045] (Meth)acrylic acid contains both methacrylic acid and acrylic acid.

[0046] Examples of α,β-ene unsaturated monomers other than those mentioned above include: carboxylic acids or their dicarboxylic acid monoesters such as acrylic acid, methacrylic acid, ethylacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid; styrene such as styrene and α-methylstyrene; acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, allyl acrylate, and lauryl acrylate; methacrylates such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, allyl methacrylate, and lauryl methacrylate; polymerizable amide compounds such as acrylamide and methacrylamide; polymerizable aromatic compounds, polymerizable nitriles, polymerizable epoxide alkane compounds, polyfunctional vinyl compounds, polymerizable amine compounds, α-olefins, dienes, polymerizable carbonyl compounds, polymerizable alkoxysilyl compounds, and other polymerizable compounds.

[0047] (B) Polyurethane resin Polyurethane resin (B) is also a film-forming component. Polyurethane resin (B) improves the elasticity and crack resistance of the coating film. Besides crack resistance, the elasticity of the coating film can also be evaluated by its elastic modulus and elongation at break.

[0048] The hydroxyl value of polyurethane resin (B) can be below 40 mg KOH / g or below 30 mg KOH / g. This inhibits the reaction between polyisocyanate compound (C) and polyurethane resin (B), facilitating the reaction between polyisocyanate compound (C) and hydroxyl-containing acrylic resin (A). The reaction between polyisocyanate compound (C) and hydroxyl-containing acrylic resin (A) increases the hardness of the resulting coating. That is, by keeping the hydroxyl value below 30 mg KOH / g, the hardness of the resulting coating is easily ensured. The hydroxyl value of polyurethane resin (B) can be below 20 mg KOH / g, below 10 mg KOH / g, or even 0 mg KOH / g.

[0049] The content of polyurethane resin (B) can be 10 parts by mass or more and 100 parts by mass or less, relative to 100 parts by mass of the solid component of hydroxyl-containing acrylic resin (A). This results in a coating film with a good balance between hardness and elasticity, achieving moderate hardness while easily obtaining a coating film with excellent crack resistance. The aforementioned content of polyurethane resin (B) can be 15 parts by mass or more, or 20 parts by mass or more. The aforementioned content of polyurethane resin (B) can be 80 parts by mass or less, or 70 parts by mass or less.

[0050] The above-mentioned content of polyurethane resin (B) with a hydroxyl value of 30 mg KOH / g or less may be 30 parts by weight or more and 100 parts by weight or less. The above-mentioned content of polyurethane resin (B) with a hydroxyl value of 30 mg KOH / g or less may be 40 parts by weight or more, or 45 parts by weight or more.

[0051] Solid components are also called non-volatile components. Specifically, the solid component of a water-based coating composition refers to all components remaining after removing the solvent from the composition. The solid component concentration is determined by dividing the total mass of the solid components remaining after removing the solvent from the object by the total mass of the object.

[0052] In the first liquid, polyurethane resin (B) is soluble. That is, polyurethane resin (B) can be a water-soluble polyurethane resin. In the first liquid, polyurethane resin (B) can be in the form of a dispersion.

[0053] Water-soluble polyurethane resins and polyurethane resin dispersions are obtained, for example, by using a surfactant to forcibly emulsify the polyurethane resin, or by neutralizing the polyurethane resin with an alkali or acid.

[0054] Polyurethane resin (B) is obtained, for example, by chain extension of a polyisocyanate compound (b1) and a polyol (b2), namely a urethane prepolymer containing terminal NCO groups, using a polyamine compound (b3). An advantage of this polyurethane resin (B) is that it can have a high molecular weight.

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

[0056] Examples of polyisocyanate compounds (b1) include aromatic polyisocyanates, aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic aliphatic polyisocyanates. These may include aromatic polyisocyanates, and at least one selected from aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic aliphatic polyisocyanates. This readily improves the flexibility of the resulting polyurethane resin (B).

[0057] Aromatic polyisocyanates have two or more isocyanate groups bonded to the carbon atoms constituting the aromatic ring. Examples of aromatic polyisocyanates include: m-phenylene diisocyanate, terephthalene diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 2,4'- or 4,4'-diphenylmethane diisocyanate or mixtures thereof, 2,4- or 2,6-toluene diisocyanate or mixtures thereof, 4,4'-toluidine diisocyanate, 4,4'-diphenyl ether diisocyanate, etc.; triphenylmethane-4,4',4''-triisocyanate, 1,3,5-triisocyanate-benzene, 2,4,6-triisocyanate-toluene, etc.; and 4,4'-diphenylmethane-2,2',5,5'-tetraisocyanate, etc. They can be used individually or in combination of two or more.

[0058] Aliphatic polyisocyanates lack an aromatic ring and have two or more isocyanate groups bonded to the carbon atoms constituting the straight-chain or branched aliphatic hydrocarbon groups. Examples of aliphatic polyisocyanates include: ethylene diisocyanate, trimethylene diisocyanate, 1,2-propylidene diisocyanate, butylidene diisocyanate (tetramethylene diisocyanate, 1,2-butylidene diisocyanate, 2,3-butylidene diisocyanate, 1,3-butylidene diisocyanate), 1,5-pentamethylene diisocyanate (PDI), 1,6-hexamethylene diisocyanate (HDI), and 2,4,4- or 2,2,4-trimethylhexamethylene. Aliphatic diisocyanates include heptamethylene diisocyanate, octamethylene diisocyanate, and dodecamethylene diisocyanate; aliphatic triisocyanates include lysine ester triisocyanate, 1,4,8-triisocyanate octane, 1,6,11-triisocyanate undecane, 1,8-diisocyanate-4-isocyanate methyl octane, 1,3,6-triisocyanate hexane, and 2,5,7-trimethyl-1,8-diisocyanate-5-isocyanate methyl octane. They can be used alone or in combination of two or more.

[0059] Alicyclic polyisocyanates lack an aromatic ring and have two or more isocyanate groups bonded to the carbon atoms constituting the cyclic aliphatic hydrocarbon group. Examples of alicyclic polyisocyanates include: 1,3-cyclopentene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanate-methyl-3,5,5-trimethylcyclohexyl isocyanate (common name: isophorone diisocyanate), methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 1,3- or 1,4-bis(cyclohexane diisocyanate). (isocyanate-methyl)cyclohexane (common name: hydrogenated phenylenedimethyl diisocyanate) or mixtures thereof, norbornene diisocyanate and other alicyclic diisocyanates; 1,3,5-triisocyanate-cyclohexane, 1,3,5-trimethylisocyanate-cyclohexane, 2-(3-isocyanate-propyl)-2,5-bis(isocyanate-methyl)-bicyclo[2.2.1]heptane, 2-(3-isocyanate-methyl)cyclohexane, etc. 3-(3-isocyanopropyl)-2,5-di(isocyanomethyl)-bicyclo[2.2.1]heptane, 5-(2-isocyanoethyl)-2-isocyanomethyl-3-(3-isocyanopropyl)-bicyclo[2.2.1]heptane, 6-(2-isocyanoethyl)-2-isocyanomethyl Alicyclic triisocyanates include methyl-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. They can 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 the carbon atoms constituting the aliphatic hydrocarbon group. Examples of aromatic aliphatic polyisocyanates include: 1,3- or 1,4-phenylenedimethylene diisocyanate or mixtures thereof, ω,ω'-diisocyanate-1,4-diethylbenzene, 1,3- or 1,4-bis(1-isocyanate-1-methylethyl)benzene (common name: tetramethylphenylenedimethylene diisocyanate) or mixtures thereof, and other aromatic aliphatic diisocyanates; 1,3,5-triisocyanate-methylbenzene, and other aromatic aliphatic triisocyanates. They can be used alone or in combination of two or more.

[0061] The polyisocyanate compound (b1) can be a derivative of the aforementioned polyisocyanates. Examples of polyisocyanate derivatives include: dimers, trimers, biuret, urethane, urea diketone, urea ketimide, isocyanurate, diazine trione, polymethylene polyphenyl polyisocyanate (crude MDI, polymeric MDI), and crude TDI.

[0062] (b2) Polyols Polyols (b2) have two or more hydroxyl groups in their molecules. Examples of polyol compounds include: ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, trimethylolpropane, glycerol, etc.; polyether polyols such as polyethylene glycol, polypropylene glycol, and polytetramethylene ether glycol; polyester polyols obtained from dicarboxylic acids such as adipic acid, sebacic acid, itaconic acid, maleic anhydride, phthalic acid, and isophthalic acid with diols such as ethylene glycol, triethylene glycol, propylene glycol, butanediol, tripropylene glycol, and neopentyl glycol; polycaprolactone polyols; polybutadiene polyols; polycarbonate polyols; and polysulfide polyols. They can be used alone or in combination of two or more.

[0063] (b3) Polyamine compounds Polyamine compound (b3) has two or more amino groups in its molecule. Polyamine compound (b3) functions as a chain extender. Examples of polyamine compounds (b3) include: ethylenediamine, tetramethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, piperazine, hydrazine, toluenediamine, phenylenediamine, and isophoronediamine. They can be used alone or in combination of two or more.

[0064] (b4) Other ingredients In the formulation of polyurethane resin (B), other components (b4) may be used as needed. 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 toluene isocyanate. They may be used alone or in combination of two or more.

[0065] <Modulation Method> Polyurethane resin (B) is obtained, for example, by reacting a polyisocyanate compound (b1) with a portion of a polyol (b2) to obtain a urethane prepolymer containing terminal NCO groups, followed by reacting a polyamine compound (b3) and the remaining polyol (b2) with the prepolymer. Other components (b4) may be added at any stage.

[0066] The reaction temperature can be above 40°C and below 140°C, or above 60°C and below 120°C. Catalysts commonly used in urethane esterification reactions, such as dibutyltin dilaurate, tin octoate, or amine-based catalysts like triethylenediamine, can be used. The reaction can be carried out in an organic solvent inert to isocyanates (e.g., acetone, toluene, ethyl acetate, dimethylformamide, methyl ethyl ketone), or the organic solvent can be added during or after the reaction.

[0067] The polyisocyanate compound (b1) and the polyol (b2) are used in amounts, for example, of 1.03 to 1.4, with an isocyanate group to hydroxyl group ratio (NCO / OH).

[0068] Other hydroxyl-containing ingredients The first liquid may further include at least one selected from polyester polyol resin, polycarbonate polyol resin, polyether polyol resin, and polycaprolactone polyol resin as other hydroxyl-containing components.

[0069] In the total solids of 100% by mass of hydroxyl-containing components, the proportion of solids of hydroxyl-containing components other than hydroxyl-containing acrylic resin (A) is, for example, 20% by mass or less, 15% by mass or less, or 10% by mass or less.

[0070] Solvent The first liquid contains water as a solvent. The first liquid may further contain water-soluble or water-miscible organic solvents, if necessary.

[0071] Modulation Methods The first liquid can be prepared by mixing the above-mentioned components using methods known to those skilled in the art. Examples of such mixing methods include those used for preparing water-based coating compositions.

[0072] (Second liquid) The second liquid contains a polyisocyanate compound (C).

[0073] (C) Polyisocyanate compounds Polyisocyanate compound (C) is a curing agent that reacts with hydroxyl-containing resin (representatively hydroxyl-containing acrylic resin (A)) to form a cross-linked structure, thereby curing the waterborne coating composition.

[0074] The polyisocyanate compound (C) includes: a polyisocyanate compound (C1) without hydrophilic groups with a number average molecular weight of 150 or more and 2500 or less; and a polyisocyanate compound (C2) containing nonionic hydrophilic groups. By using the above two polyisocyanate compounds together with polyurethane resin, a coating film with excellent crack resistance, water resistance and appearance is obtained.

[0075] The use of polyisocyanate compounds containing anionic hydrophilic groups is not excluded. However, from the viewpoint of crack resistance, it is desirable to use a small amount. For example, in the total solids of polyisocyanate compounds contained in 100% by mass of the second liquid, the amount of polyisocyanate compounds containing anionic hydrophilic groups may be less than 20% by mass, less than 10% by mass, or even 0% by mass.

[0076] (C1) Polyisocyanate compounds without hydrophilic groups Polyisocyanate compounds (C1) without hydrophilic groups have two or more isocyanate groups in their molecules, but lack hydrophilic groups. Therefore, the resulting coating film exhibits improved water resistance. Furthermore, polyisocyanate compounds (C1) without hydrophilic groups can achieve low-temperature curing due to their uncapped free isocyanate groups.

[0077] Hydrophilic groups are broadly classified into anionic and nonionic groups. Anionic hydrophilic groups are derived from carboxylic acids, sulfonic acids, phosphoric acids, silicic acids, sulfate esters, phosphate esters, and their metal or organic salts. Polyisocyanate compounds (Cl) that do not contain hydrophilic groups do not have hydrophilic groups derived from these compounds. Polyisocyanate compounds (Cl) that do not contain hydrophilic groups also do not have nonionic hydrophilic groups. Nonionic hydrophilic groups are discussed later.

[0078] The polyisocyanate compound (C1) that does not contain a hydrophilic group includes, for example, at least one selected from aliphatic diisocyanates, aliphatic triisocyanates, alicyclic diisocyanates, alicyclic triisocyanates, aromatic diisocyanates, aromatic triisocyanates and their derivatives. As specific examples of these diisocyanates and triisocyanates, compounds identical to those exemplified as polyisocyanate compound (b1) can be given.

[0079] The number average molecular weight of the polyisocyanate compound (C1) without hydrophilic groups is 150 or higher and 2500 or lower. This allows for a flexible coating film, further improving its resistance to chipping. The number average molecular weight of the polyisocyanate compound (C1) without hydrophilic groups can be 250 or higher, 360 or higher, or 400 or higher. The number average molecular weight of the polyisocyanate compound (C1) without hydrophilic groups can be 2000 or lower, 1800 or lower, or 1600 or lower.

[0080] (C2) Polyisocyanate compounds containing nonionic hydrophilic groups The polyisocyanate compound (C2) containing nonionic hydrophilic groups has two or more isocyanate groups in its molecule. Because the polyisocyanate compound (C2) also has unclosed free isocyanate groups, low-temperature curing is possible. Furthermore, by incorporating nonionic hydrophilic groups into the polyisocyanate compound (C2), the resulting coating film becomes more flexible and exhibits improved resistance to chipping. Moreover, the polyisocyanate compound (C2) disperses the non-hydrophilic polyisocyanate compound (C1) in the waterborne coating composition, inhibiting localized reactions between the non-hydrophilic polyisocyanate compound (C1) and the hydroxyl-containing acrylic resin (A). This results in an improved appearance of the resulting coating film. The appearance of the coating film can be evaluated by the presence or absence of particles and its smoothness.

[0081] The nonionic hydrophilic group is derived from a hydrophilic compound. That is, a polyisocyanate compound (C2) containing a nonionic hydrophilic group can be obtained, for example, by modifying a polyisocyanate compound (b1) with a hydrophilic compound.

[0082] Examples of hydrophilic compounds include hydrophilic polyols and hydrophilic polyethers. Examples of hydrophilic polyols include ethylene glycol, glycerol, trimethylolpropane, pentaerythritol, and sorbitol.

[0083] Examples of hydrophilic polyethers include: polyalkylene glycols (-(OC)). n H 2n ) a -). The number of carbon atoms n in the alkyl group is, for example, 2 or more and 4 or less, or 2 or more and 3 or less. The number of repeating units a is, for example, 2 or more and 12 or less. The number of repeating units a can be 3 or more. The number of repeating units a can be 8 or less.

[0084] Hydrophilic polyethers can be polyethylene glycol or polypropylene glycol. One hydroxyl group of a polyalkylene glycol can be alkoxylated with alkyl groups such as methyl, ethyl, propyl, or butyl.

[0085] Modification based on hydrophilic compounds is carried out in such a way that two or more isocyanate groups remain in one molecule. Polyisocyanate compounds (C2) containing nonionic hydrophilic groups can have three or more isocyanate groups. This increases reactivity and further facilitates low-temperature curing. Polyisocyanate compounds (C2) containing nonionic hydrophilic groups and having three or more isocyanate groups are obtained, for example, by modifying the triisocyanate or tetraisocyanate compounds exemplified above with a hydrophilic compound (typically, a polyalkylene glycol).

[0086] The polyisocyanate compound (C2) containing nonionic hydrophilic groups can further have urea-formate groups (-NH-CO-N-CO(=O)-). This improves its compatibility with polyurethane resin (B). Consequently, polyurethane resin (B) is easily and uniformly mixed in waterborne coating compositions, further improving its resistance to chipping.

[0087] The mass ratio (WC2 / WC1) of the polyisocyanate compound (C2) containing nonionic hydrophilic groups to the polyisocyanate compound (C1) without hydrophilic groups can be 0.1 or higher and 4 or lower. This makes it easier to achieve improvements in both crack resistance and appearance, as well as water resistance.

[0088] The mass ratio (WC2 / WC1) can be 0.2 or higher, 0.3 or higher, 0.5 or higher, or 0.7 or higher. The mass ratio (WC2 / WC1) can be less than 3, less than 2, less than 1.5, or less than 1.0.

[0089] The equivalent ratio (NCO / OH) of all isocyanate groups in the polyisocyanate compound (C) to all hydroxyl groups in the hydroxyl-containing component is, for example, 0.7 or more and 2.0 or less. The aforementioned equivalent ratio (NCO / OH) may be 0.8 or more. The aforementioned equivalent ratio (NCO / OH) may be 1.8 or less, or 1.5 or less.

[0090] Other curing agents Waterborne coating compositions may contain curing agents other than polyisocyanate compounds (C). Examples of other curing agents include, for instance, amino resins, epoxy compounds, aziridine compounds, carbodiimide compounds, and α-azoline compounds. These may be used alone or in combination of two or more. The content of other curing agents is appropriately determined based on the hydroxyl-containing resin.

[0091] Solvent The second liquid may contain a solvent that does not have hydroxyl groups. Examples of such solvents include: glycol ether-based organic solvents; acetate-based organic solvents; ketone-based organic solvents; and ester-based organic solvents. They may be used alone or in combination of two or more.

[0092] Modulation Methods The second liquid can be prepared by mixing the above-mentioned components using methods known to those skilled in the art. As a mixing method, the same method as that used for preparing the first liquid can be cited.

[0093] (D) Coloring pigments Waterborne coating compositions may contain coloring pigments (D). Coloring pigments (D) improve the opacity of the resulting coating film. Waterborne coating compositions containing coloring pigments (D) are particularly suitable for the formation of intermediate coating films (the first coating film described later). Coloring pigments (D) may be added to any of the first, second, and third liquids. Coloring pigments (D) may also be added after being dispersed into a paste using a pigment dispersant.

[0094] For example, relative to the total solid content of 100 parts by weight of hydroxyl-containing acrylic resin (A), polyurethane resin (B), and polyisocyanate compound (C), the content of coloring pigment (D) is 1 part by weight or more and 150 parts by weight or less. Therefore, when the water-based coating composition is used to form an intermediate coating film, sufficient hiding power can be exhibited. The aforementioned content of coloring pigment (D) can be 5 parts by weight or more, 10 parts by weight or more, 20 parts by weight or more, or 40 parts by weight or more. The aforementioned content of coloring pigment (D) can be 130 parts by weight or less, or 110 parts by weight or less.

[0095] Coloring pigments (D) can be inorganic or organic. Coloring pigments (D) can be colored or achromatic.

[0096] Examples of organic pigments include: azo chelate pigments, insoluble azo pigments, condensed azo pigments, diketopyrrolopyrrole pigments, phthalocyanine pigments, indigo pigments, perylene ketone pigments, perylene pigments, dialkyl pigments, quinacridone pigments, isoindolinone pigments, and metal complex pigments. Examples of inorganic pigments include: chrome yellow, iron oxide yellow, iron oxide red, carbon black, and titanium dioxide. They can be used alone or in combination of two or more.

[0097] (Other pigments) In water-based coating compositions, pigments other than coloring pigment (D) may be included, either in place of coloring pigment (D) or together with coloring pigment (D). Examples of other pigments include extender pigments and rust-preventing pigments. Examples of extender pigments include calcium carbonate, barium sulfate, clay, and talc.

[0098] (Other ingredients) Waterborne coating compositions may contain additives commonly used in the coatings industry. These additives may be added to any of the first, second, and third liquids. Examples of additives include, for instance, UV absorbers, hindered amine light stabilizers, antioxidants, crosslinking resin particles, leveling agents, defoamers, curing accelerators, and viscosity modifiers.

[0099] [Painted Items] A coated article is obtained using the water-based coating composition disclosed herein. The coated article, for example, comprises: a substrate; and a multilayer coating having a first coating film, a second coating film, and a clear coating film sequentially stacked. The first coating film is formed from the water-based coating composition disclosed herein. Therefore, the coated article exhibits excellent chipping resistance, water resistance, and appearance.

[0100] (Object to be painted) Materials that can be coated include, for example, metal, resin, and glass. More specifically, examples of objects that can be coated include: car bodies and parts used in cars, trucks, motorcycles, buses, etc., such as spoilers, bumpers, rearview mirror covers, grilles, and door handles.

[0101] Examples of metals include iron, copper, aluminum, tin, zinc, or their alloys (e.g., steel). Representative examples of metal coatings include cold-rolled steel sheets, hot-rolled steel sheets, stainless steel, electro-galvanized steel sheets, hot-dip galvanized steel sheets, galvanized-aluminum alloy steel sheets, galvanized-iron alloy steel sheets, galvanized-magnesium alloy steel sheets, galvanized-aluminum-magnesium alloy steel sheets, aluminized steel sheets, aluminized-silicon alloy steel sheets, tin-plated steel sheets, etc.

[0102] Metallic substrates can also undergo surface treatment. Examples of surface treatments include phosphate treatment, chromate treatment, zirconium formation treatment, and composite oxide treatment. After surface treatment, metallic substrates can be further coated with electrodeposited coatings. Electrodeposited coatings can be cationic or anionic.

[0103] Examples of resins include: polyethylene resin, EVA resin, polyolefin resins (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, fluoropolymer resin, melamine resin, polyurethane resin, epoxy resin, and polyphenylene oxide (PPO). Resin-coated substrates can also be degreased.

[0104] Because the waterborne coating compositions disclosed herein can cure at low temperatures, they are suitable for coating resins. The coatings obtained from the waterborne coating compositions disclosed herein exhibit excellent resistance to chipping, making them suitable for coating metals. The substrate may comprise both a metal portion (a portion formed of metal) and a resin portion (a portion formed of resin). The metal portion may be a steel plate.

[0105] (First coating) The first coating film is formed from the aqueous coating composition disclosed herein. The cured film thickness (dry film thickness) of the first coating film is, for example, 5 μm or more and 80 μm or less. The dried film thickness of the first coating film may be 7 μm or more. The dried film thickness of the first coating film may be 50 μm or less.

[0106] The thickness of the coating can be measured using an electromagnetic thickness gauge (e.g., the SDM-miniR manufactured by SANKO). The coating thickness is the average of the coating thickness at any 5 points.

[0107] (Second coating) The second coating film is formed from the second coating composition. The second coating composition is described below. The second coating film can be a single layer or a laminated film of two or more layers. The dried film thickness of each layer of the second coating film is, for example, 5 μm or more and 35 μm or less. The dried film thickness of each layer of the second coating film can be 7 μm or more. The dried film thickness of each layer of the second coating film can be 30 μm or less.

[0108] (Transparent coating) The transparent coating film is formed from a transparent coating composition. The transparent coating composition is described below. The dried film thickness of the transparent coating film is, for example, 10 μm or more and 80 μm or less. The dried film thickness of the transparent coating film may be 20 μm or more. The dried film thickness of the transparent coating film may be 60 μm or less.

[0109] [Manufacturing Method for Painted Items] The aforementioned coated article can be manufactured, for example, by a method comprising the following steps: applying the aforementioned water-based coating composition to a substrate to form an uncured first coating film; applying a second water-based 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 can be 70°C or higher and 100°C or lower. According to the water-based coating composition disclosed herein, even at such low temperatures, a coating film with excellent crack resistance, water resistance, and appearance is formed.

[0110] (I) The process of forming an uncured first coating film The aqueous coating composition disclosed herein is applied to a substrate to form an uncured first coating film. The adhesion of the second coating film to the substrate is improved by the first coating film. Furthermore, the first coating film makes the coating surface more uniform, making it easier to suppress unevenness in the second coating film. As described above, the substrate may comprise both a metallic portion and a resin portion.

[0111] Examples of coating methods include roller coating, air spray coating, airless spray coating, and rotary atomization coating. These methods can also be combined with electrostatic coating. From the viewpoint of coating efficiency, rotary atomization electrostatic coating is preferred. In rotary atomization electrostatic coating, rotary atomization electrostatic coating machines commonly referred to as "Micro·Micro Bell (μμBell)," "Micro Bell (μBell)," or "Metallic Bell (MetaBell)" can be used, for example.

[0112] Pre-drying (also known as preheating) can be performed after applying the water-based coating composition and before applying the second coating composition. This suppresses sudden boiling of the solvent contained in the water-based coating composition during the curing process, and easily inhibits foaming. Moreover, pre-drying prevents the uncured first coating film from mixing with the second coating composition, making it difficult to form a mixed layer. Therefore, the smoothness of the resulting coated article can be further improved.

[0113] As a pre-drying process, examples include: placing the product at a temperature of 20°C or higher and 25°C or lower for 5 to 15 minutes; or heating it at a temperature of 50°C or higher and 80°C or lower for 30 to 10 minutes.

[0114] (II) The process of forming an uncured second coating film A second coating composition is applied over an uncured first coating film to form an uncured second coating film. Two or more 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 can be set between the nth application of the second coating composition and the (n+1)th application of the second coating composition.

[0115] As a coating method, for example, the same method as that used for coating water-based paint compositions can be cited. After applying the second paint composition, pre-drying can be performed in the same manner as described above.

[0116] (Second coating composition) The second coating composition can be water-based or solvent-based. The second coating composition can be water-based. For example, a water-based second coating composition may include: an acrylic resin emulsion, a water-soluble acrylic resin, a curing agent (typically melamine resin), and a polyether polyol resin. The second coating composition may further include the aforementioned pigments, gloss pigments, and various additives.

[0117] (III) The process of forming an uncured transparent coating film A transparent coating composition is applied over an uncured second coating to form an uncured transparent coating.

[0118] There are no particular limitations on the coating method. For example, a method similar to that used for water-based coating compositions can be cited. From the viewpoint of coating efficiency, rotary atomizing electrostatic coating is preferred. After applying the clear coating composition, pre-drying can also be performed in the same manner as described above.

[0119] (Transparent coating composition) Transparent coating compositions can be solvent-based, water-based, or powder-based. From the perspective of transparency or acid resistance, solvent-based transparent coating compositions may contain acrylic resins and / or polyester resins as film-forming resins, and amino resins and / or isocyanates as curing agents. Solvent-based transparent coating compositions may also contain acrylic resins and / or polyester resins having carboxylic acid and / or epoxy groups. Without compromising transparency, transparent coating compositions may contain the various pigments and additives described above.

[0120] (IV) Curing process The uncured coatings are then cured. Each coating can be cured by heating. In this method, the first coating, the second coating, and the clear coating are cured in one step.

[0121] The heating temperature is, for example, above 70°C and below 100°C. The heating temperature can be above 75°C or above 80°C. The heating temperature can be below 95°C or below 90°C. Heating time refers to the time it takes for the target temperature to be reached within the heating device and for the object to be coated to remain at the target temperature, excluding the time before reaching the target temperature. Examples of heating devices include drying ovens that utilize heating sources such as hot air, electricity, gas, or infrared radiation.

[0122] The heating time can be set appropriately according to the heating temperature. When the heating temperature is above 70℃ and below 100℃, the heating time can be, for example, more than 10 minutes and less than 60 minutes, or more than 15 minutes and less than 45 minutes. Example

[0123] The invention is illustrated in more detail by means of the following examples, but is not limited thereto. In the examples, unless otherwise stated, “parts” and “%” are based on the mass of the solid components.

[0124] Acid value and hydroxyl value are calculated based on the blending amounts of the unsaturated monomers used, as well as the acid value and hydroxyl value of these solid components.

[0125] [Manufacturing Example 1-1] Manufacturing of Hydroxyl Acrylic Resin (A-1) 127 parts of deionized water were added to the reaction vessel, and the mixture was heated to 80°C under a nitrogen atmosphere with stirring. Then, a monomer emulsion consisting of 1.9 parts acrylic acid (AA), 30.2 parts 2-hydroxyethyl methacrylate (HEMA), 8.1 parts butyl acrylate (nBA), 47.9 parts n-butyl methacrylate (nBMA), 10.9 parts styrene (ST), 1.0 part allyl methacrylate (AMA), 4.0 parts ADEKA REASOAP SR-10 (polyoxyethylene-1-alkoxymethyl-2-(2-propenyloxy)ethyl ether sulfate ammonium salt, manufactured by ADEKA Corporation) and 80 parts deionized water, along with an initiator solution consisting of 0.3 parts ammonium persulfate and 10 parts deionized water, was added dropwise to the reaction vessel in parallel over 2 hours. After the addition was complete, the mixture was allowed to mature at the same temperature for 2 hours. Next, the mixture was cooled to 40°C, filtered through a 400-mesh filter, and then 20 parts of deionized water and 0.32 parts of dimethylaminoethanol were added to adjust the pH. The non-volatile components, Tg, Sp, hydroxyl value, and acid value of the resulting acrylic emulsion (A-1) are shown in Table 1 below.

[0126] [Manufacturing Examples 1-2 to 15] Manufacturing of Hydroxyl Acrylic Resins (A-2) to (A-15) In Manufacturing Example 1-1, except that the monomer composition and blending amount of each copolymer component were set as shown in Table 1 below, the operation was carried out in the same manner as in Manufacturing Example 1, and acrylic resin emulsions (A-2) to (A-15) were obtained.

[0127] [Manufacturing Example 2-1] Manufacturing of Polyurethane Resin (B-1) A prepolymer with isocyanate terminals was synthesized in methyl ethyl ketone (MEK) using 100 parts polybutylene adipate diol, 2 parts trimethylolpropane, 5 parts dimethylolpropionic acid, and 40 parts isophorone diisocyanate. The reaction temperature was 85°C. Next, a mixed solvent of 3.6 parts triethylamine and 350 parts water was added to emulsify the prepolymer. Then, 21.5 parts of a 5% aqueous solution of ethylenediamine was added, and the mixture was stirred at the same temperature for 80 minutes. Following this, the mixture was heated under reduced pressure to distill off the MEK. This yielded a milky white polyurethane resin (B-1) with a hydroxyl value of 0 mg KOH / g.

[0128] [Manufacturing Example 2-2] Manufacturing of Polyurethane Resin (B-3) A polyurethane resin with hydroxyl terminals was synthesized in methyl ethyl ketone (MEK) solvent using 100 parts of polytetramethylene ether glycol (number-average molecular weight 250), 13 parts of dimethylolpropionic acid, and 45 parts of isophorone diisocyanate. The reaction temperature was 85°C. Then, a mixed solvent of 8.0 parts of triethylamine and 350 parts of water was added for emulsification. Next, the mixture was heated under reduced pressure to distill off the MEK. This yielded a milky white polyurethane resin (B-3) with a hydroxyl value of 37 mg KOH / g.

[0129] Superflex-460S (manufactured by Daiichi Kogyo Co., Ltd., with a hydroxyl value of 0 mg KOH / g) was used as the polyurethane resin (B-2).

[0130] Details of the polyisocyanate compound (C) used are described below.

[0131] [Polyisocyanate compounds without hydrophilic groups (C1)] (1) Desmodur N3300: Manufactured by Sumika Covestro Urethane Co., Ltd., hydrophilic-free, HDI trimer type, number average molecular weight 550 (2) Desmodur N3800: Manufactured by Sumika Covestro Urethane Co., Ltd., hydrophilic-free, HDI trimer type, number average molecular weight 900 (3) Desmodur N3400: Manufactured by Sumika Covestro Urethane Co., Ltd., contains no hydrophilic groups, HDI dimer type, number average molecular weight 350.

[0132] [Polyisocyanate compounds containing nonionic hydrophilic groups (C2)] (1) Bayhydur 304: Manufactured by SumikaCovestro Urethane Co., Ltd., a hydrophilic polyether-modified HDI trimer containing urea-formaldehyde groups. (2) Bayhydur 3100: Manufactured by Sumika Covestro Urethane Co., Ltd., a hydrophilic polyether-modified HDI trimer, free of urea-formaldehyde groups. [Polyisocyanate compounds containing anionic hydrophilic groups (C3)] Bayhydur XP2655: Manufactured by Sumika Covestro Urethane Co., Ltd., a hexamethylene diisocyanate containing sulfonic acid groups.

[0133] [Preparation of Pigment Dispersion Paste] 19.2 parts Tipaque CR-97 (manufactured by Ishihara Sangyo Co., Ltd., titanium dioxide), 4.8 parts MA-100 (manufactured by Mitsubishi Carbon Co., Ltd., carbon black) and 16 parts barium sulfate B-34 (manufactured by Sakai Chemical Co., Ltd., barium sulfate) were placed in a 1L stainless steel container and mixed and dispersed at room temperature for 45 minutes using a paint conditioner to obtain a pigment dispersion paste (the solid content of the pigment was 70%).

[0134] [Example 1] (1) Preparation of the first liquid Add 50 parts of the above pigment dispersion paste, 30 parts of hydroxyl-containing acrylic resin (A-1), 20 parts of polyurethane resin (B-1), and an appropriate amount of water to a 1L metal container in sequence, and stir thoroughly with a disperser to obtain the first liquid.

[0135] (2) Preparation of the second liquid In another metal container, 12 parts of a polyisocyanate compound (C1) without hydrophilic groups (Desmodur N3300), 10 parts of a polyisocyanate compound (C2) with nonionic hydrophilic groups (Bayhydur 304), and an appropriate amount of solvent (dipropylene glycol dimethyl ether and / or ethylene glycol monobutyl acetate) were mixed and stirred thoroughly with a disperser to obtain a second liquid.

[0136] (3) Preparation of water-based coating composition The first liquid and the second liquid were mixed to obtain an aqueous coating composition.

[0137] [Examples 2-24 and Comparative Examples 1-4] Except for changing the types and amounts of the blended components and the mass of the solid components during coating as described in Tables 2-4, a water-based coating composition was prepared using the same steps as in Example 1.

[0138] [evaluate] The following evaluation was conducted using the water-based coating compositions prepared in the above examples and comparative examples. Test panels having a first coating film formed from the water-based coating compositions were used in the evaluation. The evaluation results are shown in Tables 2-4. In this invention, excellent performance in all aspects is crucial; a product is considered unqualified if any aspect is evaluated as "D".

[0139] (Fabrication of steel plate test panels) The pearled steel plate was washed by a common method and treated with zinc phosphate. Thereafter, using a cationic electrodeposition coating (manufactured by Nippon Paint Co., Ltd., Power Top U-100), the steel plate was electrodeposition coated and heated at 170 °C for 20 minutes. Thus, an electrodeposition coating film with a dry film thickness of 15 μm was formed.

[0140] Next, using a rotary atomization type electrostatic coater, an aqueous coating composition was electrostatically coated on the electrodeposition coating film. After leaving it for 5 minutes, it was heated at 85 °C for 20 minutes. Thus, a steel plate test piece having a cured first coating film (dry film thickness 15 μm) was obtained.

[0141] (Production of resin test piece) The polypropylene plate was degreased to obtain a resin test piece. Next, the same operation as above was carried out to obtain a resin test piece having a cured first coating film (dry film thickness 15 μm).

[0142] (1) Chipping resistance The steel plate test piece was set on the specimen holder of a flying stone tester (manufactured by Suga Test Instruments Co., Ltd., Gravero tester KSS-1). At -30 °C, from a position 30 cm away from the test piece, using compressed air at 0.5 MPa, 100 g of No. 6 grit gravel was made to collide with the test piece at an angle of 45 degrees. Thereafter, the obtained test piece was washed with water and dried, and a cloth-based tape (manufactured by NICHIBAN Co., Ltd.) was pasted on the coating surface. Then, the above tape was peeled off, and the maximum diameters at multiple positions of the exposed part of the steel plate were measured and averaged. The obtained average diameter (average exposed diameter) was evaluated according to the following criteria. In the following evaluation, a C evaluation or above is considered qualified.

[0143] (Evaluation criteria) A: The average exposed diameter is less than 0.5 mm B: The average exposed diameter is 0.5 mm or more and less than 1.0 mm C: The average exposed diameter is 1.0 mm or more and less than 2.0 mm D: The average exposed diameter is 2.0 mm or more and less than 2.5 mm E: The average exposed diameter is 2.5 mm or more.

[0144] (2) Water resistance The steel plate test piece was immersed in warm water at 40 °C for 10 days. Thereafter, it was taken out of the water and dried at room temperature for 1 hour. The appearance of the dried coating film was visually observed and evaluated according to the following criteria. In the following evaluation, a C evaluation or above is considered qualified.

[0145] (Evaluation Criteria) A: No abnormality B: At least one abnormality such as loss of gloss, crack, and blistering (bubbling) is slightly observed C: At least one abnormality such as loss of gloss, crack, and blistering (bubbling) is locally observed D: At least one abnormality such as loss of gloss, crack, and blistering (bubbling) is significantly observed locally or on the entire surface of the coating film

[0146] (3) Surface Smoothness The appearance of the coating film on the steel plate test panel was visually observed, and the smoothness was evaluated according to the following criteria. In the following evaluation, a C evaluation or above is considered qualified

[0147] A: Excellent B: Good C: Somewhat poor D: Poor E: Obvious unevenness is observed

[0148] (4) Surface Particles The appearance of the coating film on the steel plate test panel was visually observed, and the evaluation was carried out according to the following criteria. In the following evaluation, a C evaluation or above is considered qualified

[0149] A: No abnormality B: A very small number of fine particles are observed C: Particles are locally observed D: Solids are observed on the entire surface of the coating film

[0150] (5) Elastic Modulus of Coating Film Samples with a width of 10 mm × a length of 50 mm were cut from the resin test panel, and the thickness was measured. The samples were installed on an Autograph AG-IS manufactured by Shimadzu Corporation and stretched at a speed of 50 mm / minute at 25°C. The elastic modulus (also known as Young's modulus) was measured based on the stress when the coating film elongated by 0.5 mm, the width, and the thickness of the coating film. The samples were changed and measured 3 times, and the average value was taken as the elastic modulus of the coating film. In the following evaluation, a C evaluation or above is considered qualified

[0151] (Evaluation Criteria) A: Less than 700 N / mm 2 B: 700 N / mm 2 or more and less than 1000 N / mm 2 C: 1000 N / mm 2 or more and less than 1200 N / mm 2 D: 1200 N / mm2 Above and less than 1500 N / mm 2 E: 1500 N / mm 2 Above.

[0152] (6) Film strength The operation was carried out in the same manner as in (5) above. The film was stretched until it broke, and the stress at break was divided by the cross-sectional area at break to measure the film strength. The samples were changed and measured 3 times, and the average value was taken as the film strength. In the following evaluation, a C evaluation or above was considered qualified.

[0153] (Evaluation criteria) A: 25 N / mm 2 Above B: 22 N / mm 2 Above and less than 25 N / mm 2 C: 18 N / mm 2 Above and less than 22 N / mm 2 D: 15 N / mm 2 Above and less than 18 N / mm 2 E: Less than 15 N / mm 2 .

[0154] (7) Film elongation The operation was carried out in the same manner as in (5) above. The film was stretched until it broke, and the elongation at break of the film was measured. The samples were changed and measured 3 times, and the average value was taken as the film elongation. In the following evaluation, a C evaluation or above was considered qualified.

[0155] (Evaluation criteria) A: 35% or above B: 30% or above and less than 35% C: 20% or above and less than 30% D: 15% or above and less than 20% E: Less than 15%.

[0156] [Table 2] [Table 3] [Table 4] Although the aqueous coating compositions of the examples were cured under low-temperature conditions, films with excellent chipping resistance, water resistance and appearance could still be formed.

[0157] Comparative Example 1 is an aqueous coating composition that does not contain a polyisocyanate compound (C2) containing nonionic hydrophilic groups. In this example, the crack resistance is poor, and defects such as surface particles appear. In addition, poor elastic modulus and elongation of the coating film were confirmed.

[0158] Comparative Example 2 is a waterborne coating composition that does not contain a polyisocyanate compound (C1) without hydrophilic groups. In this example, poor water resistance and surface smoothness were observed.

[0159] Comparative Example 3 is a waterborne coating composition that does not contain polyurethane resin (B). In this example, poor chipping resistance, as well as poor film elastic modulus and film elongation, were confirmed.

[0160] Comparative Example 4 is an aqueous multi-component coating composition that uses a polyisocyanate compound containing anionic hydrophilic groups instead of a polyisocyanate compound containing nonionic hydrophilic groups (C2). In this example, poor chipping resistance and defects such as surface particles were observed. Furthermore, poor elastic modulus and elongation of the coating film were confirmed.

[0161] Industrial applicability The coating composition according to the invention can form a coating film with excellent crack resistance, water resistance, and appearance while curing at low temperatures. Therefore, it is particularly suitable for coatings comprising both metal and resin components.

[0162] This application claims priority based on Japanese Patent Application No. 2023-218559 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 hydroxyl-containing acrylic resin (A) and polyurethane resin (B); and The second liquid contains a polyisocyanate compound (C). in, The polyisocyanate compound (C) comprises: Polyisocyanate compounds (C1) without hydrophilic groups and having a number average molecular weight of 150 or higher and 2500 or lower; and Polyisocyanate compounds containing nonionic hydrophilic groups (C2).

2. The water-based multi-component coating composition according to claim 1, wherein, The hydroxyl value of the polyurethane resin (B) is below 30 mg KOH / g.

3. The water-based multi-component coating composition according to claim 1 or 2, wherein, The content of the polyurethane resin (B) is 10 parts by mass or more and 100 parts by mass or less, relative to 100 parts by mass of the solid component of the hydroxyl-containing acrylic resin (A).

4. The water-based multi-component coating composition according to any one of claims 1 to 3, wherein, The acid value of the hydroxyl-containing acrylic resin (A) is above 5 mg KOH / g and below 70 mg KOH / g.

5. The water-based multi-component coating composition according to any one of claims 1 to 4, wherein, The hydrophilic-free polyisocyanate compound (C1) comprises at least one selected from the following: aliphatic diisocyanate, aliphatic triisocyanate, alicyclic diisocyanate, alicyclic triisocyanate, aromatic diisocyanate, aromatic triisocyanate and derivatives thereof.

6. The water-based multi-component coating composition according to any one of claims 1 to 5, wherein, The mass ratio (WC2 / WC1) of the polyisocyanate compound (C2) containing nonionic hydrophilic groups to the polyisocyanate compound (C1) without hydrophilic groups is 0.1 or more and 4 or less.

7. The water-based multi-component coating composition according to any one of claims 1 to 6, further comprising a coloring pigment (D), in, The content of the coloring pigment (D) is more than 1 part by mass and less than 150 parts by mass relative to the total solid content of 100 parts by mass of the hydroxyl-containing acrylic resin (A), the polyurethane resin (B) and the polyisocyanate compound (C).

8. The water-based multi-component coating composition according to any one of claims 1 to 7, wherein, The polyisocyanate compound (C2) containing nonionic hydrophilic groups has more than three isocyanate groups.

9. The water-based multi-component coating composition according to any one of claims 1 to 8, wherein, The polyisocyanate compound (C2) containing a nonionic hydrophilic group further has a urea-formate group.

10. The water-based multi-component coating composition according to any one of claims 1 to 9, wherein, The polyurethane resin (B) is obtained by chain extension of a polyisocyanate compound (b1) and a polyol (b2), namely a urethane prepolymer containing terminal NCO groups, using a polyamine compound (b3). The polyisocyanate compound (b1) comprises: Aromatic polyisocyanates; as well as It is selected from at least one of aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic aliphatic polyisocyanates.

11. A method for manufacturing a coated article, comprising the following steps: Applying the water-based multi-component coating composition according to any one of claims 1 to 10 to a substrate to form an uncured first coating film; A second water-based coating composition is applied to the uncured first coating film to form an uncured second coating film; A transparent coating composition is applied to the uncured second coating film to form an uncured transparent coating film; and The uncured first coating, the uncured second coating, and the uncured transparent coating are heated and cured at a temperature above 70°C and below 100°C.

12. The method for manufacturing a coated article according to claim 11, wherein, The coating material comprises a metal portion and a resin portion.

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