Aqueous coating composition

Abstract

To provide an aqueous coating composition that is capable of realizing a coating film having excellent weather resistant, and has excellent normal temperature curability, and a method for producing silicone acrylic resin emulsion used for an aqueous coating composition that is capable of realizing a coating film having excellent external appearance and weather resistance, and has excellent storage stability and normal temperature curability.SOLUTION: An aqueous coating composition contains main agent (I) and curing agent (II), where the main agent (I) contains coating film forming resin (A), the curing agent (II) contains polyisocyanate compound (B), the coating film forming resin (A) contains core-shell type silicone acrylic resin emulsion (A1), a core part of the core-shell type silicone acrylic resin emulsion (A1) contains units derived from silicone oligomer (a1), hydrolyzable silane compound (a2) and radically polymerizable monomer (a3), and a shell part of the core-shell type silicone acrylic resin emulsion (A1) contains units derived from radically polymerizable monomer (a4) and chain transfer agent (a7). In the core part, the total of proportions of the units derived from the silicone oligomer (a1) and the hydrolyzable silane compound (a2) is 15 mass% or more and 60 mass% or less in the total 100 mass% of the units derived from silicone oligomer (a1), hydrolyzable silane compound (a2), radically polymerizable monomer (a3) and radically polymerizable monomer (a4).SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to water-based coating compositions. [Background technology]

[0002] In recent years, awareness of reducing environmental load has increased, and there is a demand for replacing with environmentally friendly products. In the coating field, for example, there is a demand for reducing the amount of organic solvent used, and such a demand can be met by using an aqueous coating composition using water as a solvent. In addition, in the automotive field, etc., a method is used in which a bake-curable coating composition is applied to a coating object, and the coating film is formed by heating at a high temperature and curing.

[0003] Industrial machinery and construction machinery are generally large and can withstand heavy loads, and are characterized by having thicker constituent substrates (steel plates) than automobile bodies, etc. When such industrial machinery and construction machinery are used as substrates, there is a problem that the substrates have a large heat capacity and heat is not sufficiently transferred to the substrates in the heating furnace. Therefore, when coating such substrates, a room temperature film-forming coating composition is selected, which does not require a high-temperature heating process and can form a coating film at room temperature.

[0004] As a room temperature film-forming coating composition, for example, an isocyanate-cured two-component curing coating composition is known. As an isocyanate-cured two-component curing coating composition, Patent Document 1 describes a clear coating composition containing a coating film-forming resin and an organic / inorganic hybrid polymer dispersion, and describes that the organic / inorganic hybrid polymer dispersion has an aromatic group-containing portion, and that the organic / inorganic hybrid polymer dispersion is a dispersion of a polymer of a mixture containing a radical polymerizable hydrolyzable silane compound.

[0005] Patent Document 2 describes a silicone resin-containing emulsion paint containing a silicone resin-containing emulsion and an isocyanate group-containing compound as a curable resin component. The silicone resin-containing emulsion contains 30 to 100 mol% of a structural unit represented by R-SiZ3 (where R is a substituted or unsubstituted monovalent hydrocarbon group, and Z is an OH group, a hydrolyzable group, or a siloxane residue), and among these, 30 to 80 mol% of a structural unit containing one silanol group represented by R-Si(OH)Z’2 (where Z’ is a siloxane residue), and the number average molecular weight is 500 or more, etc. are described.

[0006] Patent Document 3 describes a crosslinkable aqueous coating composition comprising an aqueous resin composition containing a composite copolymer having a hydroxyl value of 5 to 200 mgKOH / g obtained by copolymerizing an ethylenically unsaturated monomer having a hydroxyl group and another ethylenically unsaturated monomer in the presence of a hydrolyzable silane, a polyisocyanate compound having two or more isocyanate groups in one molecule, and a curing agent composition containing a hydrolyzable silane and / or its condensate. The equivalent ratio of the isocyanate group in the polyisocyanate compound to the hydroxyl group in the composite copolymer is 0.05 to 5.0, and a crosslinkable aqueous coating composition containing 0.5 to 50 parts by mass of the hydrolyzable silane and / or its condensate with respect to a total of 100 parts by mass of the solid content of the composite copolymer and the polyisocyanate compound is described.

[0007] In recent years, further performance improvement has been demanded for such paint compositions. In particular, excellent weather resistance and durability, such as being able to maintain the appearance for a long time even in a harsh environment such as outdoors, are being demanded. As means for achieving excellent weather resistance and durability, for example, using a silicone acrylic resin emulsion, etc. have been proposed. A silicone acrylic resin emulsion can be prepared, for example, by subjecting an acrylic resin emulsion to silicone modification using a modifier having a silicone structure during the preparation of the acrylic resin emulsion.

[0008] As a method for producing such a silicone acrylic resin emulsion, Patent Document 4 describes emulsion polymerization of an ethylenically unsaturated monomer mixture containing an ethylenically unsaturated monomer having a carboxyl group, an ethylenically unsaturated monomer having an aldo or keto group, and a chain transfer agent.

[0009] Patent Document 5 describes a method of emulsion polymerization of a mixture containing a (meth)acrylic acid ester monomer and / or an aromatic unsaturated monomer, an ethylenically unsaturated carboxylic acid monomer, a crosslinkable vinyl monomer, a chain transfer agent, and a silane compound to obtain an emulsion, and then, in the presence of the emulsion, emulsion polymerization of a mixture containing a (meth)acrylic acid ester monomer and / or an aromatic unsaturated monomer, an ethylenically unsaturated carboxylic acid monomer, a chain transfer agent, and a silane compound.

[0010] Patent Document 6 describes a method in which a mixture of a silicone oligomer, a hydrolyzable silane compound, and a radically polymerizable unsaturated monomer, an emulsifier, and an aqueous medium are mixed to prepare a pre-reaction emulsion mixture, and the pre-reaction emulsifier mixture and a polymerization initiator are mixed in the aqueous medium to carry out emulsion polymerization. Furthermore, after the emulsion polymerization, a base component is added under conditions of 50° C. or higher to adjust the pH of the emulsion polymer to 8 to 10. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] JP 2020-105370 A [Patent Document 2] JP 2000-281971 A [Patent Document 3] JP 2008-106163 A [Patent Document 4] JP 2010-215874 A [Patent Document 5] JP 2003-192981 A [Patent Document 6] JP 2017-165802 A Summary of the Invention [Problem to be solved by the invention]

[0012] Here, industrial machinery, construction machinery, and the like are often used in physically harsh environments, and therefore the coating film that protects the surface may be required to have excellent weather resistance as well as excellent corrosion resistance. However, when using conventional aqueous coating compositions, it has been difficult to fully meet these requirements.

[0013] The present disclosure has been made in view of the above circumstances, and aims to provide an aqueous coating composition capable of realizing a coating film having good weather resistance and good room temperature curing properties. The present disclosure also aims to provide a method for producing a silicone acrylic resin emulsion used in an aqueous coating composition capable of realizing a coating film having good appearance and weather resistance, and good storage stability and room temperature curing properties. [Means for solving the problem]

[0014] The present disclosure includes the following. [1] Contains a base agent (I) and a curing agent (II), The main component (I) contains a coating film-forming resin (A), The curing agent (II) contains a polyisocyanate compound (B), The coating film-forming resin (A) comprises a core-shell type silicone acrylic resin emulsion (A1), The core portion of the core-shell type silicone acrylic resin emulsion (A1) contains units derived from a silicone oligomer (a1), a hydrolyzable silane compound (a2), and a radical polymerizable monomer (a3), the shell portion of the core-shell type silicone acrylic resin emulsion (A1) contains units derived from a radical polymerizable monomer (a4) and a chain transfer agent (a7), the core portion has a total proportion of units derived from the silicone oligomer (a1) and the hydrolyzable silane compound (a2) of 15 mass% or more and 60 mass% or less, based on a total of 100 mass% of units derived from the silicone oligomer (a1), the hydrolyzable silane compound (a2), the radical polymerizable monomer (a3), and the radical polymerizable monomer (a4). [2] The aqueous coating composition according to [1], wherein in the core-shell type silicone acrylic resin emulsion (A1), the hydroxyl value of the shell portion is 20 mgKOH / g or more and 250 mgKOH / g or less. [3] The aqueous coating composition according to [1] or [2], wherein in the core-shell type silicone acrylic resin emulsion (A1), the proportion of the core part is 20% by mass or more and 75% by mass or less in 100% by mass of the total amount of the core-shell type silicone acrylic resin. [4] The aqueous coating composition according to any one of [1] to [3], wherein the content of the chain transfer agent (a7) contained in the shell portion of the core-shell type silicone acrylic resin emulsion (A1) is 0.5 parts by mass or more and 10 parts by mass or less, relative to 100 parts by mass of the total amount of the shell portions of the core-shell type silicone acrylic resin emulsion (A1). [5] The aqueous coating composition according to any one of [1] to [4], wherein the average particle size of the core-shell type silicone acrylic resin emulsion (A1) is 70 nm or more and 300 nm or less. [6] The aqueous coating composition according to any one of [1] to [5], wherein the polyisocyanate compound (B) comprises one or more compounds selected from the group consisting of aliphatic polyisocyanates and alicyclic polyisocyanates. [7] adjusting the pH of the aqueous medium to 10 or more; preparing a first emulsion mixture using the aqueous medium, a silicone oligomer (a1), a hydrolyzable silane compound (a2), a radical polymerizable monomer (a3), and an emulsifier (a5); preparing a second emulsion mixture using the aqueous medium, a radical polymerizable monomer (a4), a chain transfer agent (a7), and an emulsifier (5); a step of mixing the first emulsified mixture and a polymerization initiator (a6) in the aqueous medium and emulsion-polymerizing the mixture to obtain a core portion; a step of mixing the reaction liquid containing the core portion, the second emulsion mixture, and a polymerization initiator, and emulsion-polymerizing the mixture to form a shell portion on the surface of the core portion, thereby preparing a core-shell type silicone acrylic resin; and and adjusting the pH of the reaction liquid containing the core-shell type silicone acrylic resin to 8 to 10 to obtain a core-shell type silicone acrylic resin emulsion. A method for producing a core-shell type silicone acrylic resin emulsion used in the aqueous coating composition according to any one of [1] to [6]. Effect of the Invention

[0015] The aqueous coating composition of the present disclosure can realize a coating film with good weather resistance and good room temperature curing properties. In addition, the aqueous coating composition containing the silicone acrylic resin emulsion produced by the production method of the present disclosure has good storage stability and room temperature curing properties, and can provide a coating film with excellent appearance and weather resistance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The aqueous coating composition of the present disclosure comprises a base agent (I) and a curing agent (II), The main component (I) contains a coating film-forming resin (A), The curing agent (II) contains a polyisocyanate compound (B), The coating film-forming resin (A) comprises a core-shell type silicone acrylic resin emulsion (A1), The core portion of the core-shell type silicone acrylic resin emulsion (A1) contains units derived from a silicone oligomer (a1), a hydrolyzable silane compound (a2), and a radical polymerizable monomer (a3), The shell part of the core-shell type silicone acrylic resin emulsion (A1) contains units derived from the radically polymerizable monomer (a4) and a chain transfer agent (a7). In the core part, the proportion of the units derived from the silicone oligomer (a1) and the hydrolyzable silane compound (a2) is 15% by mass or more and 60% by mass or less in the total 100% by mass of the units derived from the silicone oligomer (a1), the hydrolyzable silane compound (a2), the radically polymerizable monomer (a3), and the radically polymerizable monomer (a4).

[0017] The aqueous coating composition of the present disclosure can realize a coating film excellent in weather resistance and has good room temperature curability. Although the present disclosure should not be construed as being limited to a specific theory, the reason why the aqueous coating composition of the present disclosure can exhibit such effects is considered as follows.

[0018] That is, in the aqueous coating composition of the present disclosure, a polyisocyanate compound is used as a curing agent, and a core-shell type silicone acrylic resin emulsion is used as a film-forming resin. And since the core part of the emulsion is produced using a predetermined amount of a silicone oligomer and a hydrolyzable silane compound, the resulting emulsion will contain a large amount of inorganic components. Therefore, it is considered that such an aqueous coating composition can realize a coating film excellent in weather resistance and can have good room temperature curability.

[0019] Main component (I) (A) Film-forming resin: The aqueous main agent (I) contains a film-forming resin (A).

[0020] And the film-forming resin (A) contains a core-shell type silicone acrylic resin emulsion (A). In the present disclosure, the silicone acrylic resin can typically be an emulsion of a resin containing a silicon atom and units derived from a (meth)acrylic monomer. In the present disclosure, the unit derived from a monomer means the divalent group when the monomer becomes a divalent group by polymerization.

[0021] (Core-shell type silicone acrylic resin emulsion (A1)) The core-shell type silicone acrylic resin emulsion (A1) may be an emulsion of a silicone acrylic resin having a core part and a shell part disposed on the core part.

[0022] (Core part) The core part of the silicone acrylic resin emulsion (A1) contains units derived from a silicone oligomer (a1), a hydrolyzable silane compound (a2), and a radically polymerizable monomer (a3).

[0023] (a1) Silicone oligomer: In the present disclosure, the silicone oligomer (a1) may typically be a condensate of a hydrolyzable silane represented by the following formula (a), and may be linear or branched. SiR 1 n R 2 4-n (a) [In formula (a), R 1 each occurrence independently represents one or more selected from a hydrogen atom, a C 1-16 aliphatic hydrocarbon group, a C 5-10 aryl group, a C 5-6 cycloalkyl group, a vinyl group, a phenyl group, an epoxy group, an amino group, a mercapto group, and a C 4-10 (meth)acryloxyalkyl group, R 2 each occurrence independently represents one or more selected from a C 1-8 alkoxy group, an acetoxy group, a hydroxyl group, an epoxy group, and a halogen atom, provided that at least one R2 is a C 1-8 alkoxy group, and n is an integer from 0 to 3.]

[0024] When n is 2 or 3, each R 1 may be the same or different. When n is 0 or 1, each R2 may be the same or different from each other.

[0025] Examples of the silicone oligomer (a1), which is a condensate of the hydrolyzable silane, include oligomers represented by the following formulas (1), (2), or (3).

[0026]

Chemical formula

[0027]

Chemical formula

[0028]

Chemical formula

[0029] In formulas (1) to (3), R 1 and R 2 have the same meanings as described above. However, in each of formulas (1) to (3), at least one R 2 is a C 1-8 alkoxy group, and m represents an integer from 1 to 999.

[0030] In formulas (a), (1) to (3), R 1 is, in each occurrence, independently preferably one or more selected from a hydrogen atom, a C 1-16 aliphatic hydrocarbon group, a C 5-6 cycloalkyl group, a phenyl group, and a C 4-10 (meth)acryloxyalkyl group. R 2 is, in each occurrence, independently preferably one or more selected from a C 1-8 alkoxy group, an acetoxy group, and a hydroxyl group. However, at least one R 2 is a C 1-8 alkoxy group.

[0031] Preferably, m is from 2 to 50, more preferably from 2 to 20. When the value of m is within such a range, there are advantages such as improved dispersibility in an aqueous solvent.

[0032] The amount of the alkoxy group in the silicone oligomer (a1) is preferably 2 to 50% by mass, more preferably 2 to 30% by mass. When the amount of the alkoxy group is within such a range, a silicone acrylate resin emulsion containing a relatively large amount of a silicone structure can be produced, and the weather resistance of the resulting coating film can be improved.

[0033] As the silicone oligomer (a1), commercially available products may be used. Examples of such commercially available products include methyl methoxy group-based oligomers such as KC-89, KR-500, X-40-9225, X-40-9246, and X-40-9250; phenyl methoxy group-based oligomers such as KR-217; methyl / phenyl methoxy-based oligomers such as KR-9218, KR-213, KR-510, X-40-9227, X-40-9247, and KR-401N (all manufactured by Shin-Etsu Chemical Co., Ltd.); methyl methoxy group-based oligomers such as MSE-100 (manufactured by Wacker Silicone Corporation), and the like. As the silicone oligomer, only one kind may be used, or two or more kinds may be used in combination.

[0034] As the silicone oligomer (a1), a hydrolysis condensate of a compound represented by the formula (a) may be used. The alcohol that may be generated during the hydrolysis condensation of the compound represented by the formula (a) may be removed after the production of the core-shell type silicone acrylate resin emulsion (A1).

[0035] In the core part, the proportion of the unit derived from the silicone oligomer (a1) is preferably 1% by mass or more and 50% by mass or less, more preferably 5% by mass or more and 30% by mass or less, still more preferably 5% by mass or more and 15% by mass or less in the total 100% by mass of the units derived from the silicone oligomer (a1), the hydrolyzable silane compound (a2), and the radically polymerizable monomer (a3). When the proportion of the unit derived from the silicone oligomer (a1) is within such a range, the weather resistance of the resulting coating film can be improved.

[0036] (a2) Hydrolyzable silane compound The hydrolyzable silane compound (a2) can typically be a compound having a silicon atom and a hydrolyzable group bonded to the silicon atom. By including the hydrolyzable silane compound (a2), the crosslinking density of the obtained core-shell type silicone acrylic resin emulsion (A1) can be increased.

[0037] The hydrolyzable silane compound (a2) preferably contains at least one silane compound represented by the following formula (b). SiR 1 n R 3 4-n (b) [In formula (b), R 1 represents, in each occurrence, independently of one another, one or more selected from a hydrogen atom, a C 1-16 aliphatic hydrocarbon group, a C 5-10 aryl group, a C 5-6 cycloalkyl group, a vinyl group, a phenyl group, an epoxy group, an amino group, a mercapto group, and a C 4-10 (meth)acryloyloxyalkyl group, R 3 represents, in each occurrence, independently of one another, one or more selected from a C 1-8 alkoxy group and a hydroxyl group, n is an integer from 0 to 3. ]

[0038] When n is 2 or 3, each R 1may be the same or different. When n is 0 or 1, each R 3 may be the same or different.

[0039] In formula (b), R 1 is, in each occurrence, independently preferably one or more selected from C 1-6 aliphatic hydrocarbon groups, vinyl groups, phenyl groups and C 4-10 (meth)acryloxyalkyl groups, more preferably one or more selected from methyl groups, phenyl groups, vinyl groups and γ-(meth)acryloxypropyl groups. R 3 is, in each occurrence, independently preferably one or more selected from methoxy groups, ethoxy groups, propoxy groups, butoxy groups, methoxyethoxy groups and hydroxyl groups.

[0040] Specific examples of the silane compound where n = 1 in formula (b) include methyltrimethoxysilane, phenyltrimethoxysilane, methyltriethoxysilane, phenyltriethoxysilane, isobutyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, γ-acryloxypropyltrimethoxysilane, γ-acryloxypropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane and the like.

[0041] Specific examples of the silane compound where n = 2 in formula (b) include dimethyldimethoxysilane, diphenyldimethoxysilane, dimethyldiethoxysilane, diphenyldiethoxysilane, methylphenyldimethoxysilane, methylphenyldiethoxysilane, γ-methacryloxypropylmethyldimethoxysilane and the like.

[0042] Specific examples of the silane compound where n = 0 in formula (b) include tetramethoxysilane, tetraethoxysilane and the like.

[0043] As the hydrolyzable silane compound (a2), a cyclic silane compound may be used. Examples of the cyclic silane compound include octamethylcyclotetrasiloxane, octaphenylcyclosiloxane, hexamethylcyclotrisiloxane, decamethylcyclopentasiloxane, tetramethyltetravinylcyclotetrasiloxane, and the like.

[0044] Only one kind of the hydrolyzable silane compound (a2) may be used, or two or more kinds may be used in combination. For example, by mainly using a silane compound with n = 1, the crosslinking density can be increased, and water resistance and the like can be enhanced. Further, for example, by combining and using a silane compound with n = 1, a silane compound with n = 2, and / or the cyclic silane compound, the crosslinking density can be adjusted, and flexibility can be imparted to the resulting coating film.

[0045] The hydrolyzable silane compound (a2) has one of the R 1 preferably contains a radical-polymerizable silane compound in which is a vinyl group or a C 4-10 (meth)acryloxyalkyl group. Examples of the radical-polymerizable silane compound include γ-(meth)acryloxypropyltrimethoxysilane, γ-(meth)acryloxypropyltriethoxysilane, γ-(meth)acryloxypropylmethyldimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyldimethoxymethylsilane, vinylmethoxydimethylsilane, vinyltris(β-methoxyethoxy)silane, and the like. Only one kind of these radical-polymerizable silane compounds may be used, or two or more kinds may be used in combination. Among the above compounds, one or more selected from the group consisting of γ-(meth)acryloxypropyltrimethoxysilane, γ-(meth)acryloxypropylmethyldimethoxysilane, γ-(meth)acryloxypropyltriethoxysilane, vinyltrimethoxysilane, and vinyltriethoxysilane are preferred.

[0046] The radical polymerizable silane compound can preferably be 0.1 to 3 parts by mass, more preferably 0.2 to 2 parts by mass, based on 100 parts by mass of the total of the silicone oligomer (a1), the hydrolyzable silane compound (a2), and the radical polymerizable unsaturated monomer (a3). By using the radical polymerizable silane compound, the film-forming property, blocking resistance, and water resistance of the resulting coating film can be improved.

[0047] In addition to the compound represented by the formula (b) and the cyclic silane compound, the hydrolyzable silane compound (a2) may contain other hydrolyzable silane compounds. Examples of the hydrolyzable silane compound include chlorosilanes such as methylchlorosilane, methyldichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, phenyltrichlorosilane, diphenylchlorosilane, vinylchlorosilane, γ-acryloxypropyltrichlorosilane, γ-methacryloxypropyltrichlorosilane, γ-acryloxypropyldichloromethylsilane, γ-methacryloxypropyldichloromethylsilane, and the like.

[0048] In the core part, the proportion of the unit derived from the hydrolyzable silane compound (a2) can preferably be 50% by mass or more and 90% by mass or less, more preferably 60% by mass or more and 80% by mass or less, in 100% by mass of the total of the units derived from the silicone oligomer (a1), the hydrolyzable silane compound (a2), and the radical polymerizable monomer (a3). When the proportion of the unit derived from the hydrolyzable silane compound (a2) is within such a range, the weather resistance of the resulting coating film can be improved.

[0049] The total proportion of units derived from the silicone oligomer (a1) and the hydrolyzable silane compound (a2) is preferably 15% by mass or more and 60% by mass or less, more preferably 20% by mass or more and 50% by mass or less, still more preferably 30% by mass or more and 45% by mass or less in 100% by mass of the total of units derived from the silicone oligomer (a1), the hydrolyzable silane compound (a2), the radically polymerizable monomer (a3), and the radically polymerizable monomer (a4). By the total proportion of units derived from the silicone oligomer (a1) and the hydrolyzable silane compound (a2) being within such a range, a silicone acrylate resin emulsion containing a relatively large amount of a silicone structure can be produced, and the appearance and weather resistance of the resulting coating film can be improved.

[0050] (a3) Radically polymerizable monomer The radically polymerizable monomer (a3) typically represents a monomer having at least one radically polymerizable bond such as a vinyl group in the molecule, and may include (meth)acrylic acid, derivatives thereof, and aromatic monomers. However, in the present disclosure, the radically polymerizable silane compound is classified as the hydrolyzable silane compound (a2), rather than the radically polymerizable monomer (a3) or (a4).

[0051] The radical polymerizable monomer (a3) is not particularly limited. For example, unsaturated carboxylic acid monomers such as (meth)acrylic acid, maleic acid, and itaconic acid; aliphatic (meth)acrylate monomers such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; alicyclic (meth)acrylate monomers such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, hydroxymethylcyclohexyl (meth)acrylate, cyclooctyl (meth)acrylate, cyclodecyl (meth)acrylate, and cyclododecyl (meth)acrylate; monoester monomers of unsaturated dicarboxylic acids such as ethyl maleate, butyl maleate, ethyl itaconate, and butyl itaconate; hydroxyl group-containing monomers such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and the reaction product of 2-hydroxyethyl (meth)acrylate and ε-caprolactone; amino group-containing monomers such as aminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, and butylaminoethyl (meth)acrylate; other amide group-containing monomers such as aminoethyl (meth)acrylamide, dimethylaminomethyl (meth)acrylamide, methylaminopropyl (meth)acrylamide, (meth)acrylamide, N-methylol (meth)acrylamide, methoxybutyl (meth)acrylamide, and diacetone (meth)acrylamide; epoxy group-containing monomers such as glycidyl (meth)acrylate; vinyl cyanide monomers such as (meth)acrylonitrile and α-chloroacrylonitrile; saturated aliphatic carboxylic acid vinyl ester monomers such as vinyl acetate and vinyl propionate; aromatic monomers such as styrene, α-methylstyrene, and vinyltoluene, etc. can be mentioned.

[0052] These may be used alone or in combination of two or more. In the present disclosure, (meth)acrylic acid means acrylic acid or methacrylic acid.

[0053] As the radical polymerizable monomer (a3), one or more selected from the group consisting of (meth) acrylic acid, methyl (meth) acrylate, butyl (meth) acrylate, cyclohexyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate are preferred.

[0054] The radical polymerizable monomer (a3) more preferably contains an alicyclic (meth) acrylic acid ester monomer. Thereby, excellent weather resistance, discoloration resistance, hydrolysis resistance, crack resistance, water resistance, gloss, and gloss retention can be imparted. Furthermore, by reaction with other components, excellent film-forming properties and blocking resistance can also be imparted.

[0055] In the core part, the proportion of the unit derived from the radical polymerizable monomer (a3) is preferably 1% by mass or more and 50% by mass or less, more preferably 10% by mass or more and 30% by mass or less, in 100% by mass in total of the units derived from the silicone oligomer (a1), the hydrolyzable silane compound (a2), and the radical polymerizable monomer (a3). When the proportion of the unit derived from the radical polymerizable monomer (a3) is within such a range, good production stability can be obtained.

[0056] In the core part, the total proportion of the units derived from the silicone oligomer (a1), the hydrolyzable silane compound (a2), and the radical polymerizable monomer (a3) can be preferably 80% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, still more preferably 95% by mass or more and 100% by mass or less in 100% by mass of the core part of the core-shell type silicone acrylic resin emulsion (A1).

[0057] In one aspect, the hydroxyl value of the core part is preferably 0 mgKOH / g, and in another aspect, it is preferably 1 mgKOH / g or more and 200 mgKOH / g or less.

[0058] In one aspect, the acid value of the core part is preferably 0 mgKOH / g, and in another aspect, it is preferably 1 mgKOH / g or more and 150 mgKOH / g or less.

[0059] In the present disclosure, both the hydroxyl value and the acid value indicate values on a solid content basis and are values measured by a method conforming to JIS K 0070.

[0060] The proportion of the core part can be 10% by mass or more and 85% by mass or less, more preferably 15% by mass or more and 80% by mass or less, still more preferably 18% by mass or more and 76% by mass or less in 100% by mass of the total amount of the core-shell type silicone acrylic resin in the core-shell type silicone acrylic resin emulsion (A1). When the proportion of the core part is within such a range, the appearance and weather resistance of the obtained coating film can be improved.

[0061] (Shell part) The shell part is disposed on the core part. It is preferable that the shell part covers all or part of the surface of the core part.

[0062] The hydroxyl value of the shell part is preferably 20 mgKOH / g or more and 250 mgKOH / g or less, more preferably 20 mgKOH / g or more and 200 mgKOH / g or less, still more preferably 20 mgKOH / g or more and 150 mgKOH / g or less. When the hydroxyl value of the shell part is within such a range, the appearance of the obtained coating film can be improved.

[0063] In the present disclosure, both the hydroxyl value and the acid value indicate values on a solid content basis and are values measured by a method conforming to JIS K 0070.

[0064] The glass transition temperature of the shell part is preferably 0°C or more and 80°C or less, more preferably 20°C or more and 60°C or less. When the glass transition temperature of the shell part is within such a range, the durability of the coating film obtained using the aqueous coating composition of the present disclosure can be improved.

[0065] In the present disclosure, the glass transition temperature (Tg) of the silicone acrylic resin emulsion can be calculated as the reciprocal of the sum of the respective quotients obtained by dividing the mass fraction of each monomer constituting the silicone acrylic resin emulsion by the Tg (expressed in K: Kelvin) value of the homopolymer (homopolymer) derived from each monomer.

[0066] More specifically, in the present disclosure, the glass transition temperature (Tg) of the fine particles can be calculated by Fox's equation (T.G. Fox; Bull. Am. Phys. Soc., 1(3), 123(1956)).

[0067] Specifically, when the resin (polymer) is a polymer of a plurality of monomers 1, 2,..., N, it can be calculated by the following general formula. 1 / Tg = w1 / Tg1 + w2 / Tg2 + ··· + w n / Tg n Let Tg represented by the above be the Tg of the resin (polymer). Tg1: Glass transition temperature (K) of the homopolymer of monomer 1, w1: Mass fraction of monomer 1 Tg2: Glass transition temperature (K) of the homopolymer of monomer 2, w2: Mass fraction of monomer 2 Tg n : Glass transition temperature (K) of the homopolymer of monomer N, w n : Mass fraction of monomer N (w1 + w2 + ··· + w n = 1)

[0068] The shell part typically contains units derived from the radically polymerizable monomer (a4).

[0069] (a4) Radically polymerizable monomer The radically polymerizable monomer (a4) typically represents a monomer having at least one radically polymerizable bond such as a vinyl group in the molecule, and may include (meth)acrylic acid, derivatives thereof, and aromatic monomers.

[0070] As the radical polymerizable monomer (a4), any of the compounds exemplified as the radical polymerizable monomer (a3) can be used. As the radical polymerizable monomer (a4), only one kind may be used, or two or more kinds may be used in combination.

[0071] As the radical polymerizable monomer (a4), one or more selected from the group consisting of (meth) acrylic acid, methyl (meth) acrylate, butyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate are preferable.

[0072] In the shell part, the proportion of the unit derived from the radical polymerizable monomer (a4) can be preferably 70% by mass or more and 100% by mass or less, more preferably 80% by mass or more and 100% by mass or less in 100% by mass of the shell part of the core-shell type silicone acrylic resin emulsion (A1).

[0073] The average particle diameter of the core-shell type silicone acrylic resin in the core-shell type silicone acrylic resin emulsion (A1) is preferably 70 to 300 nm, more preferably 100 to 250 nm, and still more preferably 120 to 200 nm. When the average particle diameter is in such a range, it is easy to control the viscosity of the obtained aqueous coating composition, the coating workability is good, the storage stability of the core-shell type silicone acrylic resin emulsion and further the aqueous coating composition is good, and the water resistance of the obtained coating film can be good.

[0074] The average particle diameter in this specification is the average particle diameter determined by the dynamic light scattering method, and specifically, it can be measured using an electrophoretic light scattering photometer ELSZ series (manufactured by Otsuka Electronics Co., Ltd.) or the like.

[0075] The core-shell type silicone acrylic resin emulsion (A1) may contain one or more selected from an emulsifier (a5), a polymerization initiator (a6), and a chain transfer agent (a7), and may contain an aqueous medium.

[0076] (a5) Emulsifier In the present disclosure, the core-shell type silicone acrylic resin emulsion (A1) may contain an emulsifier (a5) in addition to the components (a1) to (a4). The emulsifier (a5) is not particularly limited, and commonly used emulsifiers can be used, for example, non-reactive emulsifiers having no polymerizable unsaturated bond such as a vinyl group in the molecule, and / or reactive emulsifiers having a polymerizable unsaturated bond such as a vinyl group in the molecule.

[0077] Specific examples of the emulsifier (a5) include, for example, sodium dodecylbenzenesulfonate, sodium lauryl sulfate, ammonium lauryl sulfate, sodium diphenyl ether sulfonate, polyoxyethylene alkyl ester, etc., and commercially available products such as Aqualon HS-10 and other Aqualon HS series (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.); Aqualon RN series (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.); Eleminol JS-2 (manufactured by Sanyo Chemical Industries, Ltd.); Latemul S-120, S-180A, PD-104 and other Latemul series, Emulgen 109P and other Emulgen series (manufactured by Kao Corporation); Newcol 706, 707SN and other Newcol series (manufactured by Nippon Emulsion Co., Ltd.); Antox MS-2N (2-sodium sulfoethyl methacrylate) and other Antox series (manufactured by Nippon Emulsion Co., Ltd.); Adeka Resin Soap NE-10 (α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-hydroxypolyoxyethylene) and other Adeka Resin Soap series (manufactured by ADEKA Corporation); etc. These may be used alone or in combination of two or more.

[0078] The amount of the solid content of the emulsifier (a5) is preferably 0.5 parts by mass or more and 20 parts by mass or less, more preferably 2 parts by mass or more and 15 parts by mass or less, based on 100 parts by mass of the total amount of the core-shell type silicone acrylic resin emulsion (A1). By the amount of the emulsifier being in such a range, a silicone acrylic resin emulsion containing a relatively large amount of silicone structure can be produced, and the water resistance of the obtained coating film can be improved.

[0079] (a6) Polymerization initiator As the polymerization initiator (a6), a known initiator usually used in the emulsion polymerization of acrylic resins can be used. Specifically, as a water-soluble free radical polymerization initiator, for example, persulfates such as potassium persulfate, sodium persulfate, ammonium persulfate, etc. can be used in the form of an aqueous solution. In addition, a so-called redox initiator in which an oxidizing agent such as potassium persulfate, sodium persulfate, ammonium persulfate, hydrogen peroxide, etc. is combined with a reducing agent such as sodium bisulfite, sodium thiosulfate, Rongalit, ascorbic acid, etc. can be used in the form of an aqueous solution.

[0080] In combination with the polymerization initiator (a6), a reducing agent such as sodium sulfite, ferrous chloride, ascorbate, Rongalit, etc. may be used in combination. By using a reducing agent in combination, the emulsion polymerization rate can be adjusted, and the emulsion polymerization can also be carried out at a lower temperature.

[0081] The polymerization initiator (a6) is preferably 0.02 to 1 part by mass, more preferably 0.05 to 0.5 part by mass, and still more preferably 0.1 to 0.3 part by mass with respect to 100 parts by mass of the total amount of the silicone oligomer (a1), hydrolyzable silane compound (a2), radically polymerizable monomer (a3), and radically polymerizable monomer (a4).

[0082] (a7) Chain transfer agent The chain transfer agent (a7) can typically have an action of combining with the radical at the growing end during radical polymerization to generate a new radical. As a result, the polymerization reaction tends to proceed uniformly, and the molecular weight of the obtained silicone acrylic resin emulsion can be reduced. Furthermore, it is considered that the amount of low molecular compounds and oligomers that can be contained in the obtained silicone acrylic resin emulsion can be reduced.

[0083] Specific examples of the chain transfer agent (a7) include alkyl mercaptans such as dodecyl mercaptan, n-butyl mercaptan, t-butyl mercaptan, and octyl mercaptan; 2-ethylhexyl thioglycolate, 2-methyl-5-t-butyl thiophenol, carbon tetrabromide, α-methylstyrene dimer, and the like.

[0084] The chain transfer agent (a7) is preferably 0.5 part by mass or more and 12 parts by mass or less, more preferably 1.0 part by mass or more and 5.0 part by mass or less, based on 100 parts by mass of the total amount of the radically polymerizable monomer (a4). When the amount of the chain transfer agent (a7) is within such a range, the appearance and weather resistance of the resulting coating film are improved.

[0085] The core-shell type silicone acrylic resin emulsion may further contain a basic component. Examples of the basic component include amines such as ammonia, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethanolamine, diethanolamine, triethanolamine, and dimethylaminoethanol; and alkali metal hydroxides such as potassium hydroxide and sodium hydroxide. The pH range adjusted by adding the basic component is more preferably pH 9 to 10. As the basic component, ammonia, triethylamine, and diethylamine are more preferably used. These basic components may be used in the form of an aqueous solution.

[0086] In the present disclosure, the aqueous medium means a medium containing water, and the aqueous medium may contain a hydrophilic organic solvent. Examples of the hydrophilic organic solvent include glycol solvents such as ethylene glycol; alcohol solvents such as methanol, ethanol, and isopropyl alcohol; ketone solvents such as acetone; and N-methyl-2-pyrrolidone. In the aqueous medium, the water content can be preferably 90% by mass or more and 100% by mass or less, more preferably 95% by mass or more and 100% by mass or less.

[0087] (Method for producing core-shell type silicone acrylic resin emulsion) The method for producing the core-shell type silicone acrylic resin emulsion of the present disclosure comprises: a step of adjusting the pH of the aqueous medium to 10 or more; a step of preparing a first emulsified mixture using the aqueous medium, a silicone oligomer (a1), a hydrolyzable silane compound (a2), a radically polymerizable monomer (a3), and an emulsifier (a5); a step of preparing a second emulsified mixture using the aqueous medium, a radically polymerizable monomer (a4), a chain transfer agent (a7), and an emulsifier (5); a step of mixing and emulsion-polymerizing the first emulsified mixture and a polymerization initiator (a6) in the aqueous medium to obtain a core part; a step of mixing and emulsion-polymerizing the reaction solution containing the core part, the second emulsified mixture, and a polymerization initiator (a6) to form a shell part on the surface of the core part, thereby preparing a core-shell type silicone acrylic resin; and a step of adjusting the pH of the reaction solution containing the core-shell type silicone acrylic resin to 8 to 10 to obtain a core-shell type silicone acrylic resin emulsion.

[0088] By using the silicone acrylic resin emulsion obtained by the production method, it is possible to realize a coating film having good appearance and weather resistance, and to provide an aqueous coating composition having good storage stability and room temperature curability. Although the present disclosure should not be construed as being limited to a specific theory, the reason why the production method of the present disclosure can achieve such effects is considered as follows.

[0089] That is, as a means for enhancing the weather resistance of the resulting coating film, increasing the proportion of the silicone structure contained in the silicone acrylate resin emulsion used can be mentioned. In order to increase the proportion of the silicone structure, typically, it is necessary to increase the amount of silicone modification with a modifier having a silicone structure (for example, alkoxysilane, polyalkoxysiloxane, a monomer containing an alkoxysilyl group, etc.). However, for example, polyalkoxysiloxane by-produces alcohol due to hydrolysis in an aqueous medium and the progress of the condensation reaction. The by-produced alcohol reduces the stability of the resin emulsion, so it has been difficult to increase the amount of silicone modification in the emulsion polymerization method generally performed in the preparation of the resin emulsion. Furthermore, when a modifier having a silicone structure is used, the radical polymerization reaction may not proceed uniformly, and low molecules or oligomers may be generated, which may affect the appearance of the resulting coating film. In the production method of the present disclosure, since a silicone oligomer (a1), a hydrolyzable silane compound (a2), and a radically polymerizable monomer (a3) are used for the core part, and a chain transfer agent (a7) is used in the formation of the shell part, it is considered that a coating film having good appearance and weather resistance can be realized, and an aqueous paint composition having good storage stability and room temperature curability can be provided.

[0090] Hereinafter, the aqueous medium, the base component, the silicone oligomer (a1), the hydrolyzable silane compound (a2), the radically polymerizable monomer (a3), the radically polymerizable monomer (a4), the emulsifier (a5), the polymerization initiator (a6), and the chain transfer agent (a7) are each synonymous with those described above.

[0091] (i) A step of adjusting the pH of the aqueous medium to 10 or more (first pH adjustment step) Prepare an aqueous medium and adjust the pH of the aqueous medium to 10 or more. The pH of the aqueous medium can typically be adjusted by mixing the aqueous medium and the base component. As the base component, it is more preferable to use ammonia, triethylamine, diethylamine, dimethylaminoethanol, etc. as the base component. Further, these base components may be used in the form of an aqueous solution.

[0092] In the first pH adjustment step, the method of adding and mixing the basic component can be carried out by a technique commonly used by those skilled in the art. As the mixing method, for example, a method of stirring at 10 to 45 °C for 1 to 30 minutes can be mentioned.

[0093] The pH of the aqueous medium after pH adjustment is preferably 10 or more. When the pH of the aqueous medium is within such a range, the production stability and storage stability of the core-shell type silicone acrylic resin emulsion can be good.

[0094] (ii) A step of preparing a first pre-reaction emulsified mixture (first pre-reaction emulsified mixture preparation step) Using the aqueous medium, the silicone oligomer (a1), the hydrolyzable silane compound (a2), the radically polymerizable monomer (a3), and the emulsifier (a5), a first emulsified mixture is prepared. The first emulsified mixture may form the core part of the obtained core-shell type silicone acrylic resin emulsion, may form the shell part, and preferably can form the core part.

[0095] In the preparation of the first pre-reaction emulsified mixture, an emulsifier (a5) and an aqueous medium may be added to and mixed with a mixture of the silicone oligomer (a1), the hydrolyzable silane compound (a2), and the radically polymerizable unsaturated monomer (a3) to prepare the first emulsified mixture, or an aqueous medium containing the emulsifier (a5) may be prepared in advance, and this aqueous medium may be mixed with a mixture of the silicone oligomer (a1), the hydrolyzable silane compound (a2), and the radically polymerizable unsaturated monomer (a3). Further, the means and conditions for mixing the above components are not particularly limited, and the mixing means and conditions commonly used by those skilled in the art can be used. Specific examples of the mixing means include, for example, mixing means using a stirrer such as a homomixer or a homodisper. The mixing conditions can be appropriately selected according to the mixing means and the production scale. Specific examples of the mixing conditions include, for example, conditions of adding the above components and mixing at 10 to 45 °C for 1 to 120 minutes.

[0096] The average particle size of the first pre-reaction emulsion mixture is preferably 200 to 2,000 nm, more preferably 200 to 1,000 nm. When the average particle size is within such a range, the production stability and storage stability of the core-shell type silicone acrylic resin emulsion are good, and the water resistance of the resulting coating film can be good.

[0097] (iii) A step of preparing a second pre-reaction emulsified mixture (a step of preparing a second pre-reaction emulsified mixture) A second emulsion mixture is prepared using an aqueous medium, a radically polymerizable monomer (a4), a chain transfer agent (a7), and an emulsifier (a5). Since the second emulsion mixture contains the chain transfer agent (a7), when forming the shell part, the polymerization reaction tends to proceed uniformly, and it is considered that the amount of low molecular compounds and oligomers that can be contained in the resulting silicone acrylic resin emulsion can be reduced. As a result, the storage stability and room temperature curability of the resulting aqueous coating composition are good, and the appearance and weather resistance of the resulting coating film can be good.

[0098] The second pre-reaction emulsion mixture may form the shell part of the core-shell type silicone acrylic resin emulsion (A1), or may form the core part, and preferably can form the shell part.

[0099] In the preparation of the second pre-reaction emulsion mixture, the chain transfer agent (a7), the emulsifier (5), and the aqueous medium may be added to and mixed with the mixture of the radically polymerizable monomer (a4) to prepare the second emulsion mixture, or an aqueous medium containing the chain transfer agent (a7) and the emulsifier (a5) may be prepared in advance, and this aqueous medium may be mixed with the mixture of the radically polymerizable monomer (a4). Further, the means and mixing conditions for mixing the above components are not particularly limited, and may be the same conditions as in the step of preparing the first emulsion mixture.

[0100] The average particle size of the second pre-reaction emulsion mixture is preferably 200 to 2,000 nm, more preferably 200 to 1,000 nm. When the average particle size is within such a range, the production stability and storage stability of the core-shell type silicone acrylic resin emulsion are good, and the water resistance of the resulting coating film can be good.

[0101] (iv) Emulsion polymerization step of the first pre-reaction emulsion mixture (first emulsion polymerization step) Next, the first pre-reaction emulsified mixture and the polymerization initiator (a6) are mixed and emulsion-polymerized in the aqueous medium. Thereby, a core part or a shell part can be formed, and preferably a core part can be formed.

[0102] The emulsion polymerization step can be carried out, for example, by dropping the first pre-reaction emulsified mixture and the polymerization initiator (a6) into the aqueous medium respectively. The time required for dropping the first pre-reaction emulsified mixture and the polymerization initiator (a6) can be arbitrarily selected depending on the reaction scale, reaction vessel, etc., and can be selected, for example, in the range of 30 minutes to 6 hours. The emulsion polymerization step can be carried out, for example, at a polymerization temperature of 50 to 85°C. The polymerization temperature is more preferably 60 to 80°C. The emulsion polymerization step may be carried out under normal pressure conditions, or may be carried out under high pressure conditions according to physical properties such as the vapor pressure of the monomer. When the polymerization temperature is in such a range, the reaction proceeds sufficiently and the influence of the by-produced alcohol can be minimized.

[0103] (v) Emulsion polymerization step of the second pre-reaction emulsion mixture (second emulsion polymerization step) Next, the reaction solution obtained by emulsion polymerization of the first pre-reaction emulsified mixture, the second pre-reaction emulsified mixture, and the polymerization initiator (a6) are mixed and emulsion-polymerized. Thereby, on the surface of the polymer of the first pre-reaction emulsified mixture, the polymerization of the second pre-reaction emulsified mixture proceeds to form a shell part, or the second pre-reaction emulsified mixture penetrates into the polymer of the first pre-reaction emulsified mixture and polymerizes to form a core part.

[0104] The emulsion polymerization step can be carried out, for example, by dropping the second pre-reaction emulsified mixture and the polymerization initiator (a6) into the reaction solution containing the core part respectively. The time required for dropping the emulsified mixture 2 for the shell part and the polymerization initiator (a6) can be arbitrarily selected depending on the reaction scale, reaction vessel, etc., and can be selected, for example, in the range of 30 minutes to 6 hours. The emulsion polymerization step may be carried out under the same conditions as the step of obtaining the core part.

[0105] (vi) A step of adjusting the pH of the reaction solution to 8 to 10 (second pH adjustment step) Next, the pH of the reaction solution containing the core-shell type silicone acrylic resin is adjusted to 8 to 10 to obtain a core-shell type silicone acrylic resin emulsion. The pH of the reaction solution can typically be adjusted by mixing the reaction solution and a base component. By adjusting the pH, the hydrolysis of the hydrolyzable group and the dehydration-condensation reaction of the silanol group generated thereby are promoted, and the storage stability of the obtained core-shell type silicone acrylic resin emulsion and the storage stability of the aqueous paint composition can be improved.

[0106] The timing for adjusting the pH of the reaction solution is preferably within 10 minutes to 3 hours after the emulsion polymerization step for forming the shell part. By adjusting the pH at such timing, gelation of the emulsion polymer can be suppressed and productivity can also be maintained. In the disclosure, "the emulsion polymerization step is completed" means the time point when the dropping of the emulsion mixture 1 for the shell part and the polymerization initiator (a6) is completed in the emulsion polymerization step for forming the shell part.

[0107] The pH of the reaction solution after pH adjustment is 8 to 10. When the pH is within such a range, the production stability and storage stability of the core-shell type silicone acrylic resin emulsion are good, and the water resistance of the obtained coating film can be good.

[0108] The step of adjusting the pH can preferably be carried out under temperature conditions of 50°C or higher, more preferably under temperature conditions of 60 to 85°C, and still more preferably under temperature conditions of 70 to 85°C. Thereby, thickening and gelation of the emulsion polymer can be suppressed.

[0109] After adjusting the pH of the reaction solution to 8 - 10, it is preferable to maintain the temperature at 60°C or higher. By doing so, the hydrolysis of the hydrolyzable group and the dehydration - condensation of the silanol group can proceed sufficiently, and the storage stability of the obtained core - shell type silicone - acrylic resin emulsion, and further the storage stability of the aqueous paint composition can be improved. The temperature at which the reaction solution is maintained after pH adjustment can preferably be 70 - 85°C, more preferably 75 - 85°C. The time for maintaining the temperature can be appropriately selected according to the maintained temperature and the reaction scale, and can be selected, for example, in the range of 2 - 12 hours, preferably 3 - 10 hours, and more preferably 4 - 8 hours.

[0110] After adjusting the pH of the reaction solution to 8 - 10, if necessary, at least a part of the alcohol may be removed by means such as reaction system release or reduced pressure. Examples of the alcohol to be removed include the alcohol by - produced by the hydrolysis - condensation reaction. By removing at least a part of the by - produced alcohol, a silicone - acrylic resin emulsion excellent in storage stability can be prepared. For example, when removing at least a part of the alcohol by reduced pressure means, an aqueous medium may be added as necessary before reducing the pressure.

[0111] Hardener (II) (B) Cross - linking agent (polyisocyanate compound): The aqueous paint composition contains an aqueous main agent (I) and a water - dispersible curing agent (II). And the water - dispersible curing agent (II) contains a polyisocyanate compound (B).

[0112] The polyisocyanate compound (B) is preferably a polyisocyanate compound having water - dispersibility and can be dispersed without separation when added to an aqueous medium. The polyisocyanate compound (B) may be modified with a hydrophilic compound having a hydrophilic group as necessary. The hydrophilic group may be an ionic hydrophilic group or a non - ionic hydrophilic group.

[0113] It is preferable to use a water-dispersible curing agent as the curing agent (B). The water-dispersible curing agent preferably contains a polyisocyanate aqueous dispersion.

[0114] The polyisocyanate aqueous dispersion is a polyisocyanate compound having water-dispersibility, and refers to a polyisocyanate compound that can be dispersed without separation when added to an aqueous medium. The polyisocyanate aqueous dispersion may be modified with a hydrophilic compound having a hydrophilic group as necessary. The hydrophilic group may be an ionic hydrophilic group or a nonionic hydrophilic group.

[0115] The polyisocyanate compound contained in the polyisocyanate compound is not particularly limited as long as it does not deviate from the scope of the present disclosure. For example, aromatic diisocyanates such as tolylene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), and metaxylylene diisocyanate (MXDI); aliphatic diisocyanates such as hexamethylene diisocyanate (HDI); alicyclic polyisocyanates such as isophorone diisocyanate (IPDI); and their multimers such as biuret type, nurate type, and trimethylolpropane (TMP) adduct type can be mentioned. A mixture of two or more of these polyisocyanates may also be used.

[0116] Preferably, the polyisocyanate compound is an aliphatic diisocyanate and / or an alicyclic polyisocyanate, and more preferably, hexamethylene diisocyanate (HDI) and / or isophorone diisocyanate (IPDI). Such a polyisocyanate compound has lower reactivity than aromatic isocyanate compounds and can suppress side reactions with aqueous media such as water.

[0117] Within the scope not departing from the present disclosure, the polyisocyanate chain may be modified as desired, and further, a crosslinking reaction may occur due to the isocyanate groups contained in the polyisocyanate. Since the polyisocyanate compound, which is a multimer, has a functionality of 3 or more, at least one of the plurality of isocyanate groups may be modified, and a crosslinking reaction may occur due to at least two isocyanate groups.

[0118] Commercially available products may be used as the polyisocyanate. Examples of commercially available products include Bayhydur 304, Bayhydur XP-2655, Bayhydur 401-70 (manufactured by Sumitomo Covestro Urethane Co., Ltd.), Barnock DNW-5000, Barnock DNW-6000 (manufactured by DIC Corporation), Duranate WR80-70P, Duranate WB40-100, Duranate WT20-100, Duranate WL70-100 (manufactured by Asahi Kasei Corporation), and the like.

[0119] The content of the polyisocyanate compound (B) in the aqueous coating composition is preferably an amount such that the equivalent ratio (NCO / OH) of the isocyanate groups possessed by the polyisocyanate compound (B) to the hydroxyl groups possessed by the film-forming resin (A) is within the range of 0.5 to 3.0, and more preferably within the range of 1.0 to 2.0. When the equivalent ratio (NCO / OH) is within such a range, there is an advantage that the curing reactivity of the aqueous coating composition can be ensured within a good range. It should be noted that all of the above equivalent ratios are based on solid content conversion.

[0120] The aqueous main agent (I) and the water-dispersible curing agent (II) may contain the aqueous medium.

[0121] Other components, etc. In addition to the above components, the aqueous coating composition may optionally contain other components according to the purpose and application. Examples of other components include pigments such as coloring pigments, extender pigments, and rust preventive pigments, resin particles, resin emulsions other than those described above, resin components, dispersants, curing catalysts, viscosity modifiers, film-forming aids, and additives commonly used in coating compositions (e.g., ultraviolet absorbers, light stabilizers, antioxidants, defoamers, surface modifiers, pinhole preventives, rust preventives, etc.). These components can be added to the main agent (I) and / or the curing agent (II) in a manner that does not impair the various physical properties of the coating composition of the present disclosure.

[0122] (Organic solvent) As the organic solvent, those commonly used in aqueous coatings can be used. For example, linear, branched, or cyclic aliphatic alcohols having 5 to 10 carbon atoms, alcohols containing an aromatic group; general formula HO-(CH2CHXO) n -R1 (R1; a linear or branched alkyl group having 1 to 10 carbon atoms, X; hydrogen or a methyl group, n is an integer of n≦5) represented by (poly)ethylene glycol or (poly)propylene glycol monoethers; general formula R2COO-(CH2CHXO) n -R3 (R2, R3: a linear or branched alkyl group having 1 to 10 carbon atoms, X: hydrogen or a methyl group, n is an integer of n≦5) represented by (poly)ethylene glycol ether esters or (poly)propylene glycol ether esters; aromatic organic solvents such as toluene, xylene, and S-100 (manufactured by ENEOS); diester compounds such as mono- or diisobutyrates of 2,2,4-trimethyl-1,3-pentanediol and diisobutyl adipate; fatty acid esters such as 2-hydroxypropyl oleate; 3-methoxybutanol, 3-methoxybutanol acetate, 3-methyl-3-methoxybutanol, and 3-methyl-3-methoxybutanol acetate, etc.

[0123] Specific examples of the monoethers include glycol solvents such as propylene glycol, butanediol, pentanediol, diethylene glycol, dipropylene glycol, and triethylene glycol; and glycol ether solvents such as diethylene glycol dibutyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, and propylene glycol monomethyl ether acetate.

[0124] These may be used individually or in combination of two or more.

[0125] (Method for preparing aqueous coating composition, method for forming coating film) The aqueous coating composition can be prepared by mixing the above components by methods known to those skilled in the art. A method for producing a two-component curable aqueous coating composition, which includes a step of preparing the main agent (I) using the core-shell type silicone acrylic resin emulsion and a step of preparing the curing agent (II) using the polyisocyanate compound (B), is also included in the scope of the present disclosure.

[0126] As the method for preparing the coating composition, methods commonly used by those skilled in the art can be used. For example, methods commonly used by those skilled in the art, such as kneading and mixing means using a kneader or a roll, or dispersing and mixing means using a sand grinder mill or a disper, can be used.

[0127] Regarding the timing of mixing the aqueous main agent (I) and the water-dispersible curing agent (II) in the aqueous coating composition, the aqueous main agent (I) and the water-dispersible curing agent (II) may be mixed before use and applied by a normal coating method. Alternatively, each liquid may be fed to the gun by a two-component mixing gun and mixed at the gun tip for application.

[0128] By applying the aqueous coating material to an object to be coated and curing it, a coating film can be formed on the object to be coated. Examples of the object to be coated include metal substrates, plastic substrates, and composite substrates thereof, as well as wood, glass, cloth, concrete, ceramic materials, and the like. Examples of the metal substrate include metals such as iron, steel, copper, aluminum, tin, zinc, and alloys containing these metals. The metal substrate may be plated with zinc, copper, chromium, or the like, or may be subjected to surface treatment using a surface treatment agent such as chromic acid, zinc phosphate, or a zirconium salt. Examples of the plastic substrate include polypropylene resin, polycarbonate resin, urethane resin, polyester resin, polystyrene resin, ABS resin, vinyl chloride resin, polyamide resin, and the like. These plastic substrates may be subjected to primer coating.

[0129] The object to be coated may be a molded article including the substrate. Examples of the molded article include various molded articles such as automobile bodies, various vehicle bodies, and parts for household electrical appliances. And the aqueous coating composition can be particularly preferably used, for example, when the object to be coated is a metal substrate or the like that has a large heat capacity or is large in size and heat is not sufficiently transferred to the object to be coated in a heating furnace. Specific examples of such an object to be coated include construction machinery (e.g., bulldozers, scrapers, hydraulic excavators, excavators, transport machinery (trucks, trailers, etc.), cranes and handling machinery, foundation construction machinery (diesel hammers, hydraulic hammers, etc.), tunnel construction machinery (boring machines, etc.), road rollers, etc.); industrial machinery such as weak current and heavy electrical equipment, agricultural machinery, steel furniture, machine tools, and large vehicles, which are called general industrial use; and objects to be coated that have a large heat capacity or are large in size and are difficult to increase in temperature even when heated (e.g., railway vehicles, ship hulls, buildings, and structures, etc.).

[0130] Workpieces such as industrial machines, construction machines, railway vehicles, ship hulls, buildings or structures as described above are generally large-sized and can withstand strong loads. Therefore, compared with automobile bodies etc., the constituent base material (steel plate) has a greater thickness and a larger heat capacity. For this reason, there is a problem that heat is not sufficiently transferred to such workpieces in a heating furnace. One of the features of the aqueous coating composition is that it can be cured at a low temperature. The aqueous coating composition has an advantage that it can be suitably used even for coating workpieces with a large heat capacity or large-sized workpieces for which high-temperature heat curing treatment after coating is difficult.

[0131] The method of coating the aqueous coating composition is not particularly limited, and examples thereof include commonly used coating methods such as dipping, brushing, roller, roll coater, air spray, airless spray, curtain flow coater, roller curtain coater, die coater, etc. In the spray coating, a two-component mixing gun may be used as necessary. These can be appropriately selected according to the workpiece.

[0132] Coating of the aqueous coating composition is carried out so that the dry film thickness after film formation is 20 to 200 μm, preferably 30 to 100 μm. The curing temperature of the aqueous coating composition can preferably be 20°C to 150°C, more preferably 40°C to 100°C. The curing time can be appropriately selected according to the curing temperature and can be, for example, between 10 minutes and 7 days.

[0133] The aqueous coating composition of the present disclosure can achieve a coating film with good weather resistance and has good room-temperature curability. Further, an aqueous coating composition containing a silicone acrylic resin emulsion produced by the production method of the present disclosure has good storage stability and room-temperature curability, and can provide a coating film excellent in appearance and weather resistance. Therefore, the production method of the aqueous coating composition and the silicone acrylic resin emulsion of the present disclosure is preferably used for construction machinery (for example, bulldozers, scrapers, hydraulic excavators, excavators, transportation machinery (trucks, trailers, etc.), cranes and cargo handling machinery, foundation construction machinery (diesel hammers, hydraulic hammers, etc.), tunnel construction machinery (boring machines, etc.), road rollers, etc.); industrial machinery such as weak and heavy electrical equipment, agricultural machinery, steel furniture, machine tools, and large vehicles, which are called general industrial use; and workpieces with a large heat capacity or large size and difficult to increase in temperature even when heated (for example, railway vehicles, ship hulls, buildings, and structures, etc.).

Examples

[0134] The present disclosure will be described more specifically by the following examples, but the present disclosure is not limited thereto.

[0135] (Production Example A1-1) Preparation of Silicone Acrylic Resin Emulsion (A1-1) (Preparation Step of Pre-Emulsion Mixture Before the First Reaction) As the silicone oligomer (a1), 15.1 parts by mass of KR-500, as the hydrolyzable silane compound (a2), 35.3 parts by mass of dimethyldimethoxysilane, 26.6 parts by mass of methyltrimethoxysilane, 62.9 parts by mass of phenyltrimethoxysilane, and 1.6 parts by mass of γ-methacryloxypropyltrimethoxysilane, as the radically polymerizable unsaturated monomer (a3), 9.2 parts by mass of methyl methacrylate, 0.5 parts by mass of cyclohexyl methacrylate, 16.0 parts by mass of butyl acrylate, and 10.6 parts by mass of butyl methacrylate were stirred and mixed, and then 32.9 parts by mass of Latemul PD-104 and 101.9 parts by mass of water were added as the emulsifier (a5). Using a homomixer, it was stirred at room temperature for 15 minutes to obtain 312.6 parts by mass of a pre-emulsion mixture before the first reaction.

[0136] (First pH Adjustment Step) Into a reaction vessel equipped with a stirrer, a reflux condenser, a dropping tank, and a thermometer, 127.1 parts by mass of water and 3.7 parts by mass of Latemul PD-104 as an emulsifier (a5) were placed, and 0.5 part by mass of 25% by mass aqueous ammonia was added to adjust the pH to 11.0.

[0137] (First Emulsion Polymerization Step) After raising the temperature of the reaction vessel containing the pH-adjusted water obtained in the first pH adjustment step to 80°C, 312.6 parts by mass of the above first pre-reaction emulsion mixture and 4.1 parts by mass of a 12% by mass aqueous solution of ammonium persulfate were simultaneously added dropwise from separate dropping layers over 80 minutes. After the addition was completed, the temperature in the reaction vessel was maintained at 80°C for 1 hour to obtain a first emulsion polymer.

[0138] (Second Pre-Reaction Emulsion Mixture Preparation Step) In a separate container, 92.3 parts by mass of methyl methacrylate, 27.9 parts by mass of butyl acrylate, 106.8 parts by mass of butyl methacrylate, 4.1 parts by mass of acrylic acid, 62.7 parts by mass of 2-hydroxyethyl methacrylate, and 2.9 parts by mass of dodecyl mercaptan as a chain transfer agent (a7) were stirred and mixed, and then 44 parts by mass of Latemul PD-104 as an emulsifier and 177.8 parts by mass of water were added, and the mixture was stirred at room temperature for 15 minutes using a homomixer to obtain 518.5 parts by mass of a second pre-reaction emulsion mixture.

[0139] To the container containing the first emulsion polymer obtained previously, 518.5 parts by mass of the second pre-reaction emulsion mixture and 24.5 parts by mass of a 2.5% by mass aqueous solution of ammonium persulfate as a reaction initiator were simultaneously added dropwise from separate dropping funnels over 70 minutes. After the addition was completed, the temperature in the reaction vessel was maintained at 80°C for 1 hour.

[0140] (Second pH Adjustment Step) Next, 8.9 parts by mass of 25% by mass aqueous ammonia was added to adjust the pH of the reaction system to 9.9, then the temperature was raised to 80°C, and the reaction was allowed to proceed over 2 hours. Furthermore, the obtained aqueous emulsion solution was cooled to 40°C, and under reduced pressure conditions, the by-produced methanol was distilled off together with water to obtain 1,000 parts by mass of a silicone acrylic resin emulsion (A1-1) (solid content concentration: 49.4% by mass, average particle diameter: 123 nm).

[0141] Production Examples (A1-2) to (A1-7) and (a1-8) to (a1-16) Silicone acrylic resin emulsions (A1-2) to (A1-7) and (a1-8) to (a1-16) were produced in the same manner as in Production Example (A1-1), except that the types and amounts of the components used were changed as described in Table 1.

[0142] Manufacturing example (a1-16) Preparation of silicone acrylic resin emulsion (a1-16) (Pre-reaction Emulsion Mixture Preparation Step) As the silicone oligomer (a1), 15.1 parts by mass of KR-500, as the hydrolyzable silane compound (a2), 35.3 parts by mass of dimethyldimethoxysilane, 26.6 parts by mass of methyltrimethoxysilane, 62.9 parts by mass of phenyltrimethoxysilane, 1.6 parts by mass of γ-methacryloxypropyltrimethoxysilane, as the radically polymerizable unsaturated monomer (a3), 103.9 parts by mass of methyl methacrylate, 31.4 parts by mass of butyl acrylate and 119.8 parts by mass of butyl methacrylate, 70.4 parts by mass of 2-hydroxyethyl methacrylate; were stirred and mixed, and then 76.9 parts by mass of Latemul PD-104 as the emulsifier (a5) and 279.7 parts by mass of water were added, and the mixture was stirred at room temperature for 15 minutes using a homomixer to obtain 823.6 parts by mass of a pre-reaction emulsion mixture.

[0143] (First pH Adjustment Step) 127.1 parts by mass of water and 3.7 parts by mass of Latemul PD-104 as the emulsifier (a5) were placed in a reaction vessel equipped with a stirrer, a reflux condenser, a dropping funnel and a thermometer, and 0.5 part by mass of 25% by mass aqueous ammonia was added to adjust the pH to 11.0.

[0144] After raising the temperature of the reaction vessel containing the pH-adjusted water obtained in the first pH adjustment step to 80°C, 823.6 parts by mass of the pre-emulsion mixture before the reaction and 31.6 parts by mass of a 3.5% by mass aqueous solution of ammonium persulfate were simultaneously added dropwise from separate dropping layers over 80 minutes. After the dropping was completed, the temperature in the reaction vessel was maintained at 80°C for 1 hour to obtain a silicone acrylic resin emulsion (a1-16).

[0145]

Table 1

[0146] Preparation of pigment dispersion paste for water-based paint composition In a dispersion vessel, 23.4 parts by mass of ion-exchanged water, 0.5 part by mass of BYK-420 as a viscosity modifier, 5.6 parts by mass of BYK-2015 as a dispersant, 2.0 parts by mass of Surfynol104 as an antifoaming agent, and 70.0 parts by mass of TI-PURE R-960 as a pigment were premixed using a disper. Then, using an SG mill (dispersion medium: glass beads), dispersion treatment was performed at 1,500 rpm until the coarse particles of the pigment became 25 μm or less to obtain a pigment dispersion paste for an aqueous coating composition.

[0147] Preparation of Water-Based Coating Composition <Aqueous main agent (I-1)> 54.8 parts by mass of the silicone acrylic resin emulsion (A1-1) prepared in Production Example 1, 25.0 parts by mass of the pigment dispersion paste for the aqueous coating composition, 0.7 part by mass of S-100 as a film-forming aid, 0.5 part by mass of TEGO Twin4100 as a surface conditioner, and 1.0 part by mass of Surfynol104 as an antifoaming agent were mixed by a disper and stirred to obtain an aqueous main agent 1.

[0148] <Aqueous curing agent (II-1)> Duranate WR80-70P was used as the polyisocyanate compound (B1-1) and the aqueous curing agent (II-1).

[0149] (Examples 2 to 10, Comparative Examples 1 to 9) A paint composition was prepared in the same manner as in Example 1, except that the types and amounts of the respective components were the same as those described in Tables 2 and 3. The composition and various characteristic values are shown in Tables 2 and 3. Note that the compounding amounts in the tables indicate the amounts as they are (amounts including both solid components and liquid components). Silicone oligomer (a1 ) KR-500: Methylmethoxysilicone oligomer, manufactured by Shin-Etsu Chemical Co., Ltd., alkoxy group content: 28% by mass KR-9218: Methylphenylmethoxysilicone oligomer, manufactured by Shin-Etsu Chemical Co., Ltd., alkoxy group content: 15% by mass Hydrolyzable silane compound (a2) γ-Methacryloxypropyltrimethoxysilane Methyltrimethoxysilane Dimethyldimethoxysilane Phenyltrimethoxysilane Radical polymerizable monomers (a3) ​​and (a4) Methyl methacrylate Cyclohexyl methacrylate Butyl methacrylate Butyl acrylate Ethylhexyl acrylate Isobutyl methacrylate Acrylic acid 2-Hydroxyethyl methacrylate Emulsifier (A5) Latemul PD-104: Anionic surfactant (ammonium polyoxyalkylene alkenyl ether sulfate), manufactured by Kao Corporation; active ingredient concentration: 20% by mass Reaction initiator (a6) Ammonium persulfate: manufactured by Kishida Chemical Co., Ltd.; active ingredient concentration: 100% by mass Chain transfer agent (a7) Dodecyl mercaptan: manufactured by Arkema; active ingredient concentration: 100% by mass 2-Ethylhexyl thioglycolate: manufactured by Wako Pure Chemical Industries, Ltd.; active ingredient concentration: 100% by mass Polyisocyanate compound (B) (B-1) Duranate WR80-70P: Water-dispersible hexamethylene diisocyanate, manufactured by Asahi Kasei Corporation; NCO content: 9.2 mass%, solid content concentration: 70 mass% (B-2) Barnock DNW-5500: Water-dispersible polyisocyanate, manufactured by DIC Corporation; NCO concentration: 13.0 - 14.0 mass%, solid content concentration: 80 mass% Organic solvents Organic solvent 1: S-100: Aromatic organic solvent, manufactured by ENEOS Corporation Organic solvent 2: Diethylene glycol monobutyl ether (DBDG): Glycol ether-based solvent, manufactured by Nippon Emulsion Co., Ltd. others · Viscosity modifier: BYK-420, manufactured by BYK-Chemie Japan Co., Ltd.; Active ingredient concentration: 52 mass% · Dispersant: BYK-2015, manufactured by BYK-Chemie Japan Co., Ltd.; Active ingredient concentration: 40 mass% · Defoamer: Surfynol 104, manufactured by Nisshin Chemical Industry Co., Ltd.; Active ingredient concentration: 100 mass% · Surface conditioner: TEGO Twin 4100, manufactured by Evonik Corporation; Active ingredient concentration: 100 mass% · Pigment: TI-PURE R-960 (titanium oxide), manufactured by DuPont Corporation; Active ingredient concentration: 100 mass%

[0150] Test plate manufacturing After degreasing a cold-rolled steel sheet of JIS G 3141 (SPCC-SD) with a thickness of 0.8 mm and a size of 70 × 150 mm using a solvent, as a solvent-based primer paint, a paint composition containing Uni-Epox 30 Primer NC (manufactured by Nippon Paint Industrial Coatings Co., Ltd.) as the main agent and Uni-Epox 30 Primer Hardener (manufactured by Nippon Paint Industrial Coatings Co., Ltd.) as the curing agent was mixed using a disperser and applied using a spray gun so that the dry film thickness was 30 - 50 μm, and dried at 23°C for 1 day.

[0151] Next, on the surface of the primer coating film on this cold-rolled steel sheet, as a surfacer (intermediate coating) paint, a paint composition containing naxBES Non-Sampura Surf HS (manufactured by Nippon Paint Industrial Coatings Co., Ltd.) as the main agent and naxBES Non-Sampura Surf Hardener HS (manufactured by Nippon Paint Industrial Coatings Co., Ltd.) as the curing agent was mixed using a disperser, and then coated using a spray gun so that the dry film thickness would be 40 to 50 μm, and dried at 23°C for 1 day.

[0152] Next, the aqueous main agent (I) and the water-dispersible curing agent (II) obtained as described above were mixed using a disperser according to the formulation in Table 1 below, and then coated on the surface of the surfacer coating film using a spray gun so that the dry film thickness would be 30 to 50 μm, and dried at 80°C for 30 minutes to obtain a test panel.

[0153] 1) Storage stability of the silicone acrylic resin emulsion (A1) Evaluation of the storage stability of the silicone acrylic resin emulsion (A1) obtained above (measurement of the residue amount in 200-mesh filtration after standing at room temperature for 3 months or at 40°C for 1 month) After the filtration, the silicone acrylic resin emulsion that had been standing at room temperature for 3 months or at 40°C for 1 month was filtered through a 200-mesh filter, and the amount of the filtration residue and the average particle diameter were measured. In this test, those with no new residue generation due to the formation of aggregates and no change in the average particle diameter after standing were considered to pass.

[0154] 2) Appearance of the coating film The 60° gloss of the coating films obtained in the examples and comparative examples was measured using a specular gloss meter (gloss meter VG7000 (manufactured by Nippon Denshoku Industries Co., Ltd.)) in accordance with JIS K 5600-4-7 (specular gloss) to evaluate the appearance of the coating films. The evaluation criteria are as follows. 5: Gloss is 85 or more 4: Gloss is 80 or more and less than 85 3: Gloss is 75 or more and less than 80 2: Gloss is 70 or more and less than 75 1: Gloss is less than 70

[0155] 3) Weather resistance According to the xenon lamp method described in JIS K 5600-7-7, an accelerated weather resistance test was carried out using a super xenon weather meter SX2-75 (manufactured by Suga Test Instruments Co., Ltd.). The 60° gloss of the coating film after 1,250 hours of the test was measured with a multi-angle gloss meter GS-4K (manufactured by Suga Test Instruments Co., Ltd.), and evaluated by the change rate (gloss retention rate) with respect to the 60° gloss before the test. The evaluation criteria are as follows. 5: Gloss retention rate is 75% or more 4: Gloss retention rate is 65% or more and less than 75% 3: Gloss retention rate is 55% or more and less than 65% 2: Gloss retention rate is 45% or more and less than 55% 1: Gloss retention rate is less than 45%

[0156]

Table 2

[0157]

Table 3

[0158] Examples 1 to 10 are examples of the present invention, and the obtained aqueous coating composition had good storage stability and was able to obtain a coating film excellent in appearance and weather resistance. Comparative Example 1 is an example in which the total proportion of units derived from the silicone oligomer (a1) and the hydrolyzable silane compound (a2) in the core part of the core-shell type silicone acrylic resin emulsion (A1) is less than 15% by mass in the total 100% by mass of the units derived from the silicone oligomer (a1), the hydrolyzable silane compound (a2), the radically polymerizable monomer (a3), and the radically polymerizable monomer (a4), and the weather resistance of the obtained coating film was inferior. In Comparative Example 2, in the core part of the core-shell type silicone resin emulsion (A1), the total proportion of units derived from the silicone oligomer (a1) and the hydrolyzable silane compound (a2) exceeded 60% by mass in the total 100% by mass of the units derived from the silicone oligomer (a1), the hydrolyzable silane compound (a2), the radically polymerizable monomer (a3), and the radically polymerizable monomer (a4). The storage stability of the obtained emulsion, the appearance of the coating film, and the weather resistance were poor. Comparative Example 3 is an example in which the core part of the core-shell type silicone acrylate resin emulsion (A1) does not contain the silicone oligomer (a1), and the weather resistance of the obtained coating film was poor. Comparative Example 4 is an example in which the core part of the core-shell type silicone acrylate resin emulsion (A1) does not contain the hydrolyzable silane compound (a2), and the weather resistance of the obtained coating film was poor. Comparative Example 5 is an example in which the core part of the core-shell type silicone acrylate resin emulsion (A1) does not contain the radically polymerizable monomer (a3), and an emulsion could not be prepared. Comparative Example 6 is an example in which the shell part of the core-shell type silicone acrylate resin emulsion (A1) does not contain the chain transfer agent (a7), and the appearance of the obtained coating film was poor. Comparative Example 7 is an example in which the core part of the core-shell type silicone acrylate resin emulsion (A1) does not contain the silicone oligomer (a1) and the hydrolyzable silane compound (a2), and the weather resistance of the obtained coating film was poor. Comparative Example 8 is an example in which the core part of the core-shell type silicone acrylate resin emulsion (A1) contains the radically polymerizable monomer (a3) and the shell part does not contain the radically polymerizable monomer (a4), and an emulsion could not be prepared. Comparative Example 9 is an example including a silicone resin emulsion having no core-shell structure (single-layer type), and the storage stability of the obtained emulsion and the weather resistance of the coating film were poor.

Industrial Applicability

[0159] The aqueous coating composition of the present disclosure can achieve a coating film with good weather resistance and has good room temperature curability. Further, the aqueous coating composition containing the silicone acrylic resin emulsion produced by the production method of the present disclosure has good storage stability and room temperature curability, and can provide a coating film excellent in appearance and weather resistance. Therefore, the aqueous coating composition of the present disclosure and the production method of the silicone acrylic resin emulsion are preferably used for construction machinery (e.g., bulldozers, scrapers, hydraulic excavators, excavators, transport machinery (trucks, trailers, etc.), cranes and handling machinery, foundation construction machinery (diesel hammers, hydraulic hammers, etc.), tunnel construction machinery (boring machines, etc.), road rollers, etc.); industrial machinery such as weak and heavy electrical equipment, agricultural machinery, steel furniture, machine tools and large vehicles, which are called general industrial use; and objects to be coated that have a large heat capacity or are large in size and are difficult to increase in temperature even when heated (e.g., railway vehicles, ship hulls, buildings and structures, etc.).

Claims

1. comprising a main agent (I) and a curing agent (II), wherein the main agent (I) contains a film-forming resin (A), the curing agent (II) contains a polyisocyanate compound (B), the film-forming resin (A) contains a core-shell type silicone acrylic resin emulsion (A1), the core part of the core-shell type silicone acrylic resin emulsion (A1) contains units derived from a silicone oligomer (a1), a hydrolyzable silane compound (a2), and a radically polymerizable monomer (a3), the shell part of the core-shell type silicone acrylic resin emulsion (A1) contains units derived from a radically polymerizable monomer (a4) and a chain transfer agent (a7), in the core part, the total proportion of the units derived from the silicone oligomer (a1) and the hydrolyzable silane compound (a2) is 15% by mass or more and 60% by mass or less in the total 100% by mass of the units derived from the silicone oligomer (a1), the hydrolyzable silane compound (a2), the radically polymerizable monomer (a3), and the radically polymerizable monomer (a4), an aqueous paint composition.

2. In the core-shell type silicone acrylic resin emulsion (A1), the hydroxyl value of the shell part is 20 mgKOH / g or more and 250 mgKOH / g or less, the aqueous paint composition according to Claim 1.

3. In the core-shell type silicone acrylic resin emulsion (A1), the proportion of the core part is 20% by mass or more and 75% by mass or less in the total 100% by mass of the core-shell type silicone acrylic resin, the aqueous paint composition according to Claim 1.

4. The content of the chain transfer agent (a7) contained in the shell part of the core-shell type silicone acrylic resin emulsion (A1) is 0.5 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the total amount of the shell part of the core-shell type silicone acrylic resin emulsion (A1), the aqueous paint composition according to Claim 1.

5. The average particle diameter of the core-shell type silicone acrylic resin emulsion (A1) is 70 nm or more and 300 nm or less, the aqueous paint composition according to Claim 1.

6. The polyisocyanate compound (B) contains one or more selected from aliphatic polyisocyanates and alicyclic polyisocyanates, the aqueous paint composition according to Claim 1.

7. a step of adjusting the pH of the aqueous medium to 10 or more A step of preparing a first emulsified mixture using the aqueous medium, the silicone oligomer (a1), the hydrolyzable silane compound (a2), the radically polymerizable monomer (a3), and the emulsifier (a5); A step of preparing a second emulsified mixture using the aqueous medium, the radically polymerizable monomer (a4), the chain transfer agent (a7), and the emulsifier (5); A step of mixing and emulsion-polymerizing the first emulsified mixture and the polymerization initiator (a6) in the aqueous medium to obtain a core part; A step of mixing and emulsion-polymerizing the reaction solution containing the core part, the second emulsified mixture, and the polymerization initiator to form a shell part on the surface of the core part, and preparing a core-shell type silicone acrylic resin; and Adjusting the pH of the reaction solution containing the core-shell type silicone acrylic resin to 8 to 10; A step of obtaining a core-shell type silicone acrylic resin emulsion, including: A method for producing a core-shell type silicone acrylic resin emulsion used in the aqueous paint composition according to any one of claims 1 to 6.

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