Coating composition and cured coating film

Abstract

The present invention provides a coating composition that yields a cured coating film with excellent pot life, substrate adhesion, water resistance, solvent resistance, and chemical resistance, without the use of isocyanate-based curing agents. [Solution] A coating composition is used that contains an acrylic polymer (A), an aqueous medium (B), an acrylate compound (C), and a strong base catalyst (D), wherein the acrylic polymer (A) contains 5 to 50% by mass of a β-diketone group-containing monomer (a1), 5 to 30% by mass of a polyoxyethylene chain-containing monomer (a2), and 40 to 90% by mass of a monomer (a3) ​​other than monomers (a1) and (a2), which does not contain any of the functional groups hydroxyl, nitrile, and amide, and has a homopolymer glass transition temperature of 60°C or higher.

Description

Technical Field

[0004] ,

[0001] The present invention relates to a coating composition and a cured coating film.

Background Art

[0002] For coating compositions used in automobiles, household electrical appliances, building materials, etc., various performances such as chemical resistance, scratch resistance, and substrate adhesion are required. As a curing type that satisfies these required performances, an NCO-OH curing system that reacts an isocyanate group (NCO) and a hydroxyl group (OH) is generally widely used (see Patent Document 1).

[0003] This NCO-OH curing system has high versatility, but has problems with the influence of moisture in the air and the pot life after blending with an isocyanate curing agent. In addition, regulations have been made on the toxicity of free isocyanate in the curing agent, mainly in Europe and the United States.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The problem to be solved by the present invention is to provide a coating composition that can obtain a cured coating film excellent in pot life, substrate adhesion, water resistance, solvent resistance, and chemical resistance without using an isocyanate-based curing agent.

Means for Solving the Problems

[0006] The inventors of the present invention conducted extensive research to solve the above problems and, as a result, discovered that the above problems can be solved by using a coating composition containing a specific acrylic polymer (A), an aqueous medium (B), an acrylate compound (C), and a strong base catalyst (D), thus completing the present invention.

[0007] In other words, the present invention relates to a coating composition comprising an acrylic polymer (A), an aqueous medium (B), an acrylate compound (C), and a strong base catalyst (D), wherein the acrylate compound (C) comprises a compound having two or more (meth)acryloyl groups in one molecule, and the acrylic polymer (A) comprises 5 to 50% by mass of a β-diketone group-containing monomer (a1), 5 to 30% by mass of a polyoxyethylene chain-containing monomer (a2), and 40 to 90% by mass of a monomer (a3) ​​other than monomers (a1) and (a2), which does not contain any of the functional groups of hydroxyl, nitrile, and amide groups, and whose homopolymer glass transition temperature is 60°C or higher. [Effects of the Invention]

[0008] The coating composition of the present invention exhibits excellent adhesion to substrates, water resistance, solvent resistance, and chemical resistance of the resulting coating film, making it suitable for use in various industrial water-based coatings, including those for vehicles, building exteriors, bridges, industrial machinery, gas tanks, construction machinery, ships, plastics, and woodworking. [Modes for carrying out the invention]

[0009] The coating composition of the present invention is a coating composition comprising an acrylic polymer (A), an aqueous medium (B), an acrylate compound (C), and a strong base catalyst (D), wherein the acrylate compound (C) comprises a compound having two or more (meth)acryloyl groups in one molecule, and the monomer components constituting the acrylic polymer (A) include 5 to 50% by mass of a β-diketone group-containing monomer (a1), 5 to 30% by mass of a polyoxyethylene chain-containing monomer (a2), and 40 to 90% by mass of a monomer (a3) ​​other than monomers (a1) and (a2), which does not contain any of the functional groups hydroxyl, nitrile, and amide, and whose homopolymer glass transition temperature is 60°C or higher.

[0010] By using a specific monomer in a specific proportion in the acrylic polymer (A), a cured coating film with excellent substrate adhesion, water resistance, solvent resistance, and chemical resistance can be obtained.

[0011] The β-diketone group-containing monomer (a1) is present in an amount of 5 to 50% by mass of the total monomer components, but is preferably 10 to 40% by mass, as this improves the balance between substrate adhesion and coating film properties such as water resistance, solvent resistance, and chemical resistance.

[0012] Examples of the monomer (a1) include 2-acetoacetoxyethyl (meth)acrylate, 2-acetoacetoxypropyl (meth)acrylate, and acetoacetoxybutyl (meth)acrylate, but among these, 2-acetoacetoxyethyl methacrylate (AAEM) is preferred. These monomers can be used individually or in combination of two or more.

[0013] The polyoxyethylene chain-containing monomer (a2) is present in an amount of 5 to 30% by mass of the total monomer components, but is preferably 8 to 20% by mass, as this improves the balance between water dispersibility and coating film properties such as water resistance, solvent resistance, and chemical resistance.

[0014] Examples of the polyoxyethylene chain-containing monomer (a2) include alkoxy polyethylene glycol (meth)acrylates such as methoxy polyethylene glycol (meth)acrylate, ethoxy polyethylene glycol (meth)acrylate, and butoxy polyethylene glycol (meth)acrylate, phenoxy polyethylene glycol (meth)acrylate, methoxy polyethylene glycol-polypropylene glycol (meth)acrylate, methoxy polyethylene glycol-polybutylene glycol (meth)acrylate, polyethylene glycol (meth)acrylate, and polyethylene glycol-polybutylene glycol (meth)acrylate. Among these, methoxy polyethylene glycol (meth)acrylate is preferred because it improves the dispersibility of the acrylic polymer (A) in the aqueous medium (D), and methoxy polyethylene glycol (meth)acrylate with a molecular weight of 400 to 1,500 is more preferred. These monomers can be used individually or in combination of two or more.

[0015] The monomer (a3) ​​is a monomer other than monomer (a1) and monomer (a2), and does not contain any of the functional groups hydroxyl, nitrile, and amide, and has a homopolymer glass transition temperature of 60°C or higher.

[0016] In this invention, the glass transition temperatures of the homopolymers of each component were determined using the values ​​listed in Polymer Handbook (4th Edition) by J. Brandrup, E. H. Mimmergut, and E. A. Grulke (Wiley Interscience, 2003) and the measured values ​​obtained by differential scanning calorimetry (DSC) after synthesis of the homopolymers.

[0017] The monomer (a3) ​​is present in an amount of 40 to 90% by mass of the total monomer components, but is preferably 45 to 85% by mass, as this improves the balance between the water dispersibility, solvent resistance, chemical resistance, and other coating film properties of the acrylic polymer (A).

[0018] Examples of the monomer (a3) ​​include styrene, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, isobonyl acrylate, and the like. These may be used individually or in combination of two or more.

[0019] The monomer components constituting the acrylic polymer (A) may further include alkyl (meth)acrylate (a4) having an alkyl group having 2 to 10 carbon atoms and having a homopolymer glass transition temperature of less than 60°C (hereinafter sometimes referred to as "monomer (a4)"). In particular, from the viewpoint of the polarity of the polymer after polymerization and solubility in solvents, alkyl (meth)acrylate having an alkyl group having 2 to 4 carbon atoms and having a homopolymer glass transition temperature of less than 60°C may be included.

[0020] Examples of the monomer (a4) include ethyl acrylate, propyl (meth)acrylate, isopropyl acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, etc., among which butyl (meth)acrylate is more preferred from the viewpoint of the polarity of the polymer after polymerization and its solubility in solvents. These may be used alone or in combination of two or more.

[0021] The monomer (a4) is preferably present in an amount of 20% by mass or less of the total monomer components.

[0022] The monomer components constituting the acrylic polymer (A) may, if necessary, include, as other monomer components (hereinafter sometimes referred to as "monomer (a5)") other than those described above, polymerizable monomers such as hydroxyl group-containing monomers, amide group-containing monomers, amino group-containing monomers, and epoxy group-containing monomers.

[0023] The monomer (a5) is preferably 5% by mass or less in all the monomer components.

[0024] The weight average molecular weight of the acrylic polymer (A) is preferably from 3,000 to 200,000, more preferably from 5,000 to 100,000, since the water dispersibility, curability, and coating film physical properties are further improved.

[0025] The average molecular weight of the present invention is a value in terms of polystyrene based on gel permeation chromatography (hereinafter abbreviated as "GPC") measurement.

[0026] As the method for producing the acrylic polymer (A), various methods can be used. For example, a method of polymerizing an unsaturated monomer raw material in an organic solvent using a polymerization initiator can be mentioned.

[0027] Examples of the aforementioned organic solvents include aromatic hydrocarbon compounds such as toluene and xylene; alicyclic hydrocarbon compounds such as cyclohexane, methylcyclohexane, and ethylcyclohexane; ketone compounds such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ester compounds such as ethyl acetate, n-butyl acetate, isobutyl acetate, and propylene glycol monomethyl ether acetate; alcohol compounds such as n-butanol, isopropyl alcohol, and cyclohexanol; glycol compounds such as ethylene glycol monobutyl ether, propylene glycol monomethyl ether, and diethylene glycol dimethyl ether; and aliphatic hydrocarbon compounds such as heptane, hexane, octane, and mineral turpentine. Among these, it is preferable to use a water-miscible organic solvent because it can be used directly as the aqueous medium (B). These organic solvents can be used individually or in combination of two or more.

[0028] Examples of polymerization initiators include ketone peroxide compounds such as cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, and methylcyclohexanone peroxide; 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(tert-butylperoxy)cyclohexane, n-butyl-4,4-bis(tert-butylperoxy)valerate, and 2,2-bis(4,4-ditert-butylperoxycyclohexyl)propane. Peroxyketal compounds such as 2,2-bis(4,4-ditert-amylperoxycyclohexyl)propane, 2,2-bis(4,4-ditert-hexylperoxycyclohexyl)propane, 2,2-bis(4,4-ditert-octylperoxycyclohexyl)propane, and 2,2-bis(4,4-dicumylperoxycyclohexyl)propane; hydroperoxide compounds such as cumene hydroperoxide and 2,5-dimethylhexane-2,5-dihydroperoxide; and 1,3-bis(tert Dialkyl peroxide compounds such as butylperoxy-m-isopropyl)benzene, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, diisopropylbenzene peroxide, tert-butylcumyl peroxide, and ditert-butyl peroxide; diacyl peroxide compounds such as decanoyl peroxide, lauroyl peroxide, benzoyl peroxide, and 2,4-dichlorobenzoyl peroxide; and bis(tert-butylcyclohexyl)peroxydicarbon Examples include peroxycarbonate compounds such as nates; organic peroxides such as peroxyester compounds such as tert-butylperoxy-2-ethylhexanoate, tert-amylperoxy-2-ethylhexanoate, tert-butylperoxybenzoate, and 2,5-dimethyl-2,5-di(benzoylperoxy)hexane; and azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methyl)butyronitrile, and 1,1'-azobis(cyclohexane-1-carbonitride). These polymerization initiators can be used individually or in combination of two or more.

[0029] Examples of the aqueous medium (B) include water, hydrophilic organic solvents, and mixtures thereof. The hydrophilic organic solvent is preferably a water-miscible organic solvent that mixes with water without separation, and among these, an organic solvent with a solubility in water (the number of grams of organic solvent that dissolve in 100 g of water) of 3 g or more at 25°C is preferred. Examples of these water-miscible organic solvents include alcohol-based solvents such as methanol, ethanol, propanol, butanol, 1,3-butylene glycol-3-monomethyl ether (general name: 3-methoxybutanol), and 3-methyl-3-methoxybutanol (product name: Solfit, manufactured by Kuraray Co., Ltd.); ketone-based solvents such as acetone and methyl ethyl ketone; and glycol ether-based solvents such as ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, ethylene glycol diethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol monoethyl ether, diethylene glycol diethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol dimethyl ether, propylene glycol monomethyl ether, propylene glycol dimethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, and dipropylene glycol dimethyl ether. These aqueous media (B) can be used individually or in combination of two or more types.

[0030] In the present invention, the acrylic polymer (A) is preferably dispersed in an aqueous medium from the viewpoint of workability. Methods for dispersing the acrylic polymer (A) in an aqueous medium include, for example, adding water to the acrylic polymer (A) or adding the acrylic polymer (A) to water. The acrylic polymer (A) can also be neutralized with an amine compound or the like before being dispersed in water.

[0031] The acrylate compound (C) is different from the acrylic polymer (A) and plays a role as a crosslinking agent (crosslinkable monomer), which is important for obtaining a cured coating film using the coating composition. The acrylate compound (C) contains a compound having two or more (meth)acryloyl groups in one molecule (polyfunctional acrylate compound), but may also contain a monofunctional acrylate compound. From the viewpoint of improving water resistance, chemical resistance, and solvent resistance, the polyfunctional acrylate compound in the acrylate compound (C) is preferably 50% by mass or more, and more preferably 70% by mass or more.

[0032] The aforementioned polyfunctional acrylate compounds include di(meth)acrylate compounds such as ethylene glycol diacrylate, propylene glycol diacrylate, butanediol diacrylate, pentanediol diacrylate, hexanediol diacrylate, heptanediol diacrylate, octanediol diacrylate, nonanediol diacrylate, decanediol diacrylate, glycerin-1,2-diacrylate, glycerin-1,3-diacrylate, pentaerythritol diacrylate, 2-hydroxy-3-acryloyloxypropyl methacrylate, tricyclodecanedimethanol diacrylate, dipropylene glycol diacrylate, and tripropylene glycol diacrylate; glycerin triacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, and dipentaerythritol triacrylate. Examples include tri(meth)acrylate compounds such as acrylate, ethoxylated isocyanuric acid triacrylate, ethoxylated glycerin triacrylate, ethoxylated trimethylolpropane triacrylate, and trimethylolpropane trimethacrylate, as well as tetrafunctional or more (meth)acrylate compounds such as pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, ditrimethylolpropane tetraacrylate, ethoxylated pentaerythritol tetraacrylate, and trispentaerythritol octaacrylate. Among these, tricyclodecanedimethanol diacrylate, trimethylolpropane triacrylate, dipentaerythritol pentaacrylate, and dipentaerythritol hexaacrylate are more preferred from the viewpoint of achieving both substrate adhesion, water resistance, chemical resistance, and solvent resistance. These may be used individually or in combination of two or more.

[0033] Examples of the monofunctional acrylate compounds include mono(meth)acrylate compounds such as methyl acrylate, lauryl acrylate, stearyl acrylate, isostearyl acrylate, tetrahydrofurfuryl acrylate, methoxyethyl acrylate, methoxypolyethylene glycol acrylate, 2-methyl-2-ethyl-1,3-dioxolan-4-yl acrylate, [{cyclohexanespiro-2-(1,3-dioxolan-4-yl)}methyl acrylate], and {(3-ethyloxetane-3-yl)methyl acrylate}.

[0034] The coating composition of the present invention may optionally further contain other curing agents (crosslinking agents) in addition to the acrylate compound (C). The crosslinking agent is not particularly limited, but examples include epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, metal chelate crosslinking agents, and carbodiimide crosslinking agents. The crosslinking agent can be used as appropriate depending on the type of functional group contained in the acrylic polymer (A) used. It is preferable not to use isocyanate crosslinking agents because they have problems such as shortening the pot life of the coating composition. These may be used individually or in combination of two or more.

[0035] The amount of acrylate compound (C) used can be selected from a range of 0.5 to 2.0 for the molar ratio of the active proton CH in the β-diketone group-containing monomer (a1) constituting the acrylic polymer (A) to the unsaturated double bond C=C in the acrylate compound (C). From the viewpoint of balancing substrate adhesion, chemical resistance, and solvent resistance, it is preferable to select a range of 0.8 to 1.2.

[0036] Examples of the strong base catalyst (D) include 1,8-diazabicyclo[5.4.0]undeca-7-ene (DBU), a salt consisting of DBU and an acid compound, 1,5-diazabicyclo[4.3.0]nonene-5-diazabicyclononene (DBN), 1,4-diazabicyclo[2.2.2]octane (DABCO), dimethylaminopyridine, sodium hydroxide, potassium hydroxide, triethylamine, etc., but DBU and sodium hydroxide are preferred from the viewpoint of balancing chemical resistance and solvent resistance. These may be used alone or in combination of two or more. In addition to the strong base catalyst (D), the coating composition of the present invention may also contain other base catalysts such as quaternary ammonium compounds.

[0037] The amount of the strong base catalyst (D) used can be selected from 0.1 to 7 parts by mass per 100 parts by mass of the total amount of monomer components constituting the acrylic polymer (A), with 0.2 to 2.5 parts by mass being preferred, from the viewpoint of balancing curability and coating film properties.

[0038] The coating composition of the present invention may optionally contain other additives. Examples of such other additives include silane coupling agents, lubricants, fillers, thixotropic agents, tackifiers, waxes, heat stabilizers, light stabilizers, fluorescent whitening agents, foaming agents, pH adjusters, leveling agents, gelation inhibitors, dispersion stabilizers, antioxidants, radical scavengers, heat resistance modifiers, inorganic fillers, organic fillers, plasticizers, reinforcing agents, antibacterial agents, antifungal agents, rust inhibitors, thermoplastic resins, thermosetting resins, pigments, dyes, conductivity modifiers, antistatic agents, moisture permeability enhancers, water repellents, oil repellents, hollow foams, water-containing compounds, flame retardants, water absorbents, moisture absorbents, deodorants, foam stabilizers, defoamers, antifungal agents, preservatives, antialgal agents, pigment dispersants, blocking inhibitors, and hydrolysis inhibitors. The amounts of these additives are not particularly limited and can be selected as appropriate.

[0039] The coating composition of the present invention has thermal latent properties, and the reaction proceeds rapidly upon heating, resulting in a long pot life for the composition, excellent storage stability and handling properties, and the resulting cured coating film has excellent substrate adhesion, water resistance, chemical resistance, and solvent resistance, making it very useful.

[0040] The method for preparing the coating composition is not particularly limited and can be done by known methods. For example, it can be prepared by uniformly mixing each component, such as the acrylic polymer (A). More specifically, a method can be used to prepare the coating composition by blending the acrylate compound (C) and the strong base catalyst (D) into an aqueous dispersion of the acrylic polymer (A).

[0041] The cured product of the present invention is a cured coating (film) obtained by the crosslinking reaction of the coating composition, and is a useful cured product with excellent substrate adhesion, water resistance, chemical resistance, and solvent resistance.

[0042] The cured product (coating) can be formed by applying and drying the coating composition on the surface of a substrate or the like. Methods for forming the cured product (coating) include, for example, uniformly applying the coating composition to the substrate surface using a roller, spray, applicator, bar coater, brush, or other known method, and then curing it at room temperature or under heating. If the coating composition contains an organic solvent, it is preferable to heat-dry it after application using a heating roller, hot air, or hot plate.

[0043] Furthermore, when the curing is performed, for example, to form a coating film (film) cured by a crosslinking reaction of the coating composition, it is preferable from the viewpoint of curability to heat at, for example, 40 to 120°C, and more preferably 60 to 90°C. Other curing methods include, for example, heating under pressure (e.g., 1 to 5 MPa) (e.g., 50 to 120°C) or radical polymerization by light irradiation. In such cases, the known crosslinking agents (thermosetting agents and photocuring agents) mentioned above can be used in combination.

[0044] The coating composition of the present invention yields a cured product (coating) with excellent substrate adhesion, chemical resistance, and solvent resistance, making it suitable for use in fields requiring high durability and safety, such as automotive interior and exteriors, home appliances, building materials, and film coatings. [Examples]

[0045] The present invention will be described in more detail below with reference to specific examples. The average molecular weight was measured under the GPC measurement conditions described below.

[0046] [GPC measurement conditions] Measurement device: High-speed GPC device (HLC-8220GPC manufactured by Tosoh Corporation) Columns: The following columns manufactured by Tosoh Corporation were used, connected in series. "TSKgel G5000" (7.8mm I.D. x 30cm) x 1 "TSKgel G4000" (7.8mm I.D. x 30cm) x 1 "TSKgel G3000" (7.8mm I.D. x 30cm) x 1 "TSKgel G2000" (7.8mmI.D. x 30cm) x 1 Detector: RI (Differential Refractometer) Column temperature: 40℃ Eluent: Tetrahydrofuran (THF) Flow rate: 1.0mL / min Injection volume: 100 μL (tetrahydrofuran solution with a sample concentration of 4 mg / mL) Standard samples: Calibration curves were prepared using the following monodisperse polystyrene.

[0047] (Monodisperse polystyrene) TSKgel Standard Polystyrene A-500, manufactured by Tosoh Corporation. TSKgel Standard Polystyrene A-1000, manufactured by Tosoh Corporation. TSKgel Standard Polystyrene A-2500, manufactured by Tosoh Corporation. TSKgel Standard Polystyrene A-5000, manufactured by Tosoh Corporation. TSKgel Standard Polystyrene F-1, manufactured by Tosoh Corporation. TSKgel Standard Polystyrene F-2, manufactured by Tosoh Corporation. TSKgel Standard Polystyrene F-4, manufactured by Tosoh Corporation. TSKgel Standard Polystyrene F-10, manufactured by Tosoh Corporation. TSKgel Standard Polystyrene F-20, manufactured by Tosoh Corporation. TSKgel Standard Polystyrene F-40, manufactured by Tosoh Corporation. TSKgel Standard Polystyrene F-80, manufactured by Tosoh Corporation. TSKgel Standard Polystyrene F-128, manufactured by Tosoh Corporation. TSKgel Standard Polystyrene F-288, manufactured by Tosoh Corporation. TSKgel Standard Polystyrene F-550, manufactured by Tosoh Corporation.

[0048] (Manufacturing Example 1: Production of an aqueous dispersion of acrylic polymer (A-1)) In a flask equipped with a condenser, thermometer, dropping funnel, and stirrer, 192.3 parts by mass of propylene glycol monobutyl ether was added, and the internal temperature was raised to 120°C. Then, a mixture of 44.9 parts by mass of 2-acetoacetoxyethyl methacrylate, 89.8 parts by mass of styrene, 179.5 parts by mass of methyl methacrylate, 67.3 parts by mass of butyl methacrylate, 67.3 parts by mass of methoxypolyethylene glycol methacrylate ("NK Ester M-230G" manufactured by Shin-Nakamura Chemical Industry Co., Ltd., 23 moles of ethylene oxide, number average molecular weight (Mn) 1,200), and 2.7 parts by mass of t-butyl peroxy-2-ethylhexanoate ("Perbutyl O" manufactured by NOF Corporation) was added dropwise over 5 hours. After that, the mixture was allowed to react for 10 hours while maintaining the internal temperature at 120°C. Next, after raising the internal temperature to 80°C, water was added in an amount that resulted in a non-volatile content of 45% by mass, to obtain an aqueous dispersion of acrylic polymer (A-1). The weight-average molecular weight (Mw) of this acrylic polymer (A-1) was 35,000.

[0049] (Manufacturing Examples 2-6: Production of aqueous dispersions of acrylic polymers (A-2)-(A-6)) Aqueous dispersions of acrylic polymers (A-2) to (A-6) were obtained in the same manner as in Production Example 1, except that the monomers and polymerization initiators used were changed as shown in Table 1 or 2.

[0050] (Manufacturing Example 7: Production of an aqueous dispersion of acrylic polymer (A-7)) In a flask equipped with a condenser, thermometer, dropping funnel, and stirrer, 192.1 parts by mass of propylene glycol monobutyl ether was added, and the internal temperature was raised to 120°C. Then, a mixture of 67.2 parts by mass of 2-acetoacetoxyethyl methacrylate, 89.6 parts by mass of styrene, 134.4 parts by mass of methyl methacrylate, 89.6 parts by mass of tert-butyl methacrylate, 42.6 parts by mass of butyl acrylate, 22.4 parts by mass of NK ester M-230G, 2.2 parts by mass of methacrylic acid, and 1.8 parts by mass of perbutyl O was added dropwise over 5 hours. After that, the reaction was allowed to proceed for 10 hours while maintaining the internal temperature at 120°C. Then, after lowering the internal temperature to 80°C, 2.3 parts by mass of dimethylethanolamine and an amount of water to which the non-volatile content was 45% by mass were added to obtain an aqueous dispersion of acrylic polymer (A-7). The weight-average molecular weight (Mw) of this acrylic polymer (A-1) was 51,000.

[0051] (Manufacturing Examples 8-9: Production of aqueous dispersions of acrylic polymers (RA-1)-(RA-2)) Aqueous dispersions of acrylic polymers (RA-1) to (RA-2) were obtained in the same manner as in Production Example 1, except that the monomers and polymerization initiators used were changed as shown in Table 2.

[0052] (Manufacturing Example 10: Production of an aqueous dispersion of acrylic polymer (RA-3)) Aqueous dispersions of acrylic polymers (RA-1) to (RA-2) were obtained in the same manner as in Production Example 7, except that the monomers, polymerization initiators, and neutralizing agents used were changed as shown in Table 2.

[0053] The compositions of the acrylic polymers (A-1) to (A-7) and (RA-1) to (RA-3) obtained above are shown in Table 1 or 2.

[0054] [Table 1]

[0055] [Table 2]

[0056] In Table 2, "NK Ester AM-130G" is methoxypolyethylene glycol acrylate (ethylene oxide 13 moles, number average molecular weight (Mn) 700) manufactured by Shin Nakamura Chemical Industry Co., Ltd.

[0057] (Example 1: Preparation and evaluation of coating composition (1)) 50 parts by mass of the aqueous dispersion of the acrylic polymer (A-1) obtained above was combined with 2.07 parts by mass of trimethylolpropane triacrylate (TMPTA) as the acrylate compound (C), and then 0.06 parts by mass of DBU and 0.02 parts by mass of sodium hydroxide were added as the strong base catalyst (D). Using water as the solvent, the viscosity was adjusted to approximately 12 seconds using an NK-2 Iwata viscosity cup (manufactured by Anest Iwata Corporation) to obtain coating composition (1).

[0058] (Examples 2-7: Preparation and evaluation of coating compositions (2)-(7)) Coating compositions (2) to (7) were obtained in the same manner as in Example 1, except that the acrylic polymer (A-1), acrylate compound (C), and strong base catalyst (D) used in Example 1 were changed as shown in Table 3 or 4.

[0059] (Comparative Examples 1-3: Preparation and Evaluation of Coating Compositions (R1)-(R3)) Coating compositions (R1) to (R3) were obtained in the same manner as in Example 1, except that the acrylic polymer (A-1), acrylate compound (C), and strong base catalyst (D) used in Example 1 were changed as shown in Table 4.

[0060] [Pot Life Rating] The coating composition (1) obtained above was stored at 23°C, and its viscosity was measured over time using an NK-2 Iwata viscosity cup (manufactured by Anest Iwata Corporation). (Evaluation Criteria) A: If, after 24 hours, it is still fluid and its viscosity is less than twice the initial viscosity. B: After 24 hours, it is fluid, but the viscosity is more than twice the initial viscosity. C: No liquidity for more than 10 hours and within the last 24 hours. D: No liquidity for more than 0 hours and within the next 10 hours.

[0061] [Preparation of coating film for evaluation] The coating composition (1) obtained above was spray-painted onto a substrate (ABS: acrylonitrile-butadiene-styrene copolymer). After setting for 15 minutes, it was dried at 80°C for 1 hour, and then left to stand at room temperature (approximately 23°C) for about 7 days to form a coating film (film thickness: 20-30 μm (after drying)) on the substrate.

[0062] [Evaluation of substrate adhesion] The evaluation coating film (ABS substrate) obtained as described above was subjected to a grid test (1 mm, 100 squares, 4 directions) in accordance with JIS K 5600-5-6, and the substrate adhesion was visually confirmed. (Evaluation Criteria) 5B: No missing parts 4B: Damage is within 5% 3B: Missing area exceeds 5% but is within 15%. 2B: Missing area exceeds 15% but is within 35%. 1B: Missing area exceeds 35% but is within 65%. 0B: Missing area exceeds 65%

[0063] [Evaluation of water resistance] The evaluation coating film (ABS substrate) obtained above was immersed in 40°C hot water (tap water) for 240 hours, and a grid test (1 mm, 100 squares, 4 directions) was performed in accordance with JIS K 5600-5-6, and the substrate adhesion was evaluated visually. (Evaluation Criteria) 5B: No missing parts 4B: Damage is within 5% 3B: Missing area exceeds 5% but is within 15%. 2B: Missing area exceeds 15% but is within 35%. 1B: Missing area exceeds 35% but is within 65%. 0B: Missing portion exceeds 65.

[0064] [Evaluation of solvent resistance] (Ethanol resistance test) A rubbing test was conducted by pressing a felt pad (manufactured by Valqua Corporation, 10mm wide x 10mm high x 40mm deep) soaked in ethanol (reagent grade 1, 95% or higher) against the evaluation coating film (ABS substrate) obtained above, and applying a load of 1kg while back-and-forth up to 500 times. The condition of the coating film after rubbing was observed visually and evaluated according to the following criteria based on the number of times it took for the ABS substrate to become visible. (Evaluation Criteria) A: Over 500 times B: More than 350 times, but less than 500 times C: More than 150 times, but less than or equal to 350 times D: 150 times or less

[0065] [Evaluation of chemical resistance] (Acid resistance test) The evaluation coating (ABS substrate) obtained above was placed horizontally, and 0.2 mL of 5% sulfuric acid aqueous solution was dropped onto it using a polydropper. The droplet on the coating surface was covered with a glass cup and sealed. After being left at 23°C for 24 hours, the coating test piece was washed with water, air dried, and the gloss loss, blistering, cracking, wrinkling, softening, and discoloration of the coating surface were observed visually, and the chemical resistance was evaluated according to the following criteria. A: No change in the coating. B: The paint film has changed very slightly. C: The paint film has changed slightly. D: The paint film has changed very clearly. E: The paint film has changed significantly. (Alkali resistance test) The evaluation coating (ABS substrate) obtained above was placed horizontally, and 0.2 mL of 5% sodium hydroxide aqueous solution was dropped onto it using a polydropper. The droplet on the coated surface was covered with a glass cup and sealed. After being left at 23°C for 24 hours, the coated test piece was washed with water, air dried, and the gloss loss, blistering, cracking, wrinkling, softening, and discoloration of the coated surface were observed visually, and the chemical resistance was evaluated according to the following criteria. A: No change in the coating. B: The paint film has changed or deteriorated very slightly. C: The paint film has changed slightly. D: The paint film has changed very clearly. E: The paint film has changed significantly.

[0066] The compositions and evaluation results of the coating compositions (1) to (7) and (R1) to (R3) obtained above are shown in Tables 3 and 4.

[0067] [Table 3]

[0068] [Table 4]

[0069] The abbreviations in Tables 3 and 4 are explained below. DPHA: Dipentaerythritol pentaacrylate / dipentaerythritol hexaacrylate (product name: Aronics M-402), manufactured by Toagosei Co., Ltd. TMPTA: Trimethylolpropane triacrylate (product name: Miramar M300), manufactured by MIWON Corporation. A-DCP: Manufactured by Shin-Nakamura Chemical Co., Ltd., Tricyclodecanedimethanol diacrylate (product name: NK ester A-DCP) U-CAT 18X: Manufactured by Sunapro Co., Ltd., triethylmethylammonium 2-ethylhexanoate (product name: U-CAT 18X) TOYOCAT TRX: Manufactured by Tosoh Corporation, a quaternary ammonium salt (product name: TOYOCAT TRX)

[0070] The coating compositions of Examples 1 to 7 exhibited excellent pot life, and the resulting coating films were confirmed to have excellent substrate adhesion, water resistance, solvent resistance, and chemical resistance.

[0071] Comparative Example 1 is an example in which the amount of monomer (a3) ​​with a homopolymer glass transition temperature of 60°C or higher in the total monomer components is less than the lower limit of 40% by mass of the present invention. It was confirmed that the solvent resistance and chemical resistance were insufficient.

[0072] Comparative Example 2 is an example in which the amount of polyoxyethylene chain-containing monomer (a2) in the total monomer components is greater than the upper limit of 30% by mass of the present invention, but it was confirmed that the solvent resistance and chemical resistance were insufficient.

[0073] Comparative Example 3 is an example in which the monomer component does not contain polyoxyethylene chain-containing monomer (a2), but it was confirmed that the substrate adhesion, water resistance, solvent resistance, and chemical resistance were insufficient.

Claims

1. A coating composition comprising an acrylic polymer (A), an aqueous medium (B), an acrylate compound (C), and a strong base catalyst (D), The acrylate compound (C) contains a compound having two or more (meth)acryloyl groups in one molecule. As monomer components constituting the acrylic polymer (A), 5 to 50% by mass of a β-diketone group-containing monomer (a1), Polyoxyethylene chain-containing monomer (a2) in an amount of 5 to 30% by mass, A coating composition containing 40 to 90% by mass of monomer (a3), which is other than monomer (a1) and monomer (a2), and does not contain any of the functional groups hydroxyl, nitrile, and amide, and whose homopolymer glass transition temperature is 60°C or higher.

2. The coating composition according to claim 1, wherein the weight-average molecular weight of the acrylic polymer (A) is 5,000 to 100,000.

3. The coating composition according to claim 1, wherein the strong base catalyst (D) is 1,8-diazabicyclo[5.4.0]undeca-7-ene and / or sodium hydroxide.

4. A cured coating film of the coating composition according to any one of claims 1 to 3.

Images