Powder coating material and coating film

Abstract

Provided is a powder coating material capable of providing a coating film in which cracking and / or peeling during deformation is reduced. This powder coating material contains certain amounts of polymer particles and a thermosetting resin, wherein the polymer particles include: an elastic body containing (meth)acrylate-based rubber; an intermediate part containing certain amounts of a crosslinkable unit and a graft unit; and a grafting part having a certain constituent unit.

Description

Powder Coatings and Coatings

[0001] The present invention relates to powder coatings and coatings.

[0002] BACKGROUND ART Powder coatings have been known in the past, in which a powder coating material is directly applied to metal or the like, heated, dried, and solidified to form a coating film.

[0003] Generally, thermosetting resins are used in powder coatings. However, thermosetting resins have the problem of insufficient impact resistance, which is a characteristic of thermosetting resins. To improve the impact resistance of thermosetting resins, a method of adding elastomers to thermosetting resins is widely used.

[0004] The elastomer may be a polymer particle. Various polymer particles having a core-shell structure have been developed (for example, Patent Document 1).

[0005] Japanese Patent Application Laid-Open No. 2000-001633

[0006] However, the above-mentioned conventional techniques are not sufficient from the viewpoint of preventing cracking and / or peeling when the coating film is deformed, and there is room for further improvement.

[0007] One embodiment of the present invention has been made in consideration of the above-mentioned problems, and its object is to provide a novel powder coating material that can provide a coating film with reduced cracking and / or peeling during deformation of the coating film.

[0008] The present inventors have conducted extensive research to solve the above problems and have completed the present invention.

[0009] That is, a powder coating according to one embodiment of the present invention contains a thermosetting resin (A) and polymer particles (B), the polymer particles (B) having an elastomer, an intermediate portion, and a graft portion, the elastomer containing a (meth)acrylate rubber, the intermediate portion containing, as structural units, crosslinkable units and graftable units in a total amount of 16.0 parts by mass or more per 100 parts by mass of the intermediate portion, the graft portion containing, as structural units, one or more structural units selected from the group consisting of aromatic vinyl units, vinyl cyan units, and (meth)acrylate units, and the content of the polymer particles (B) is 0.1 parts by mass or more and 50.0 parts by mass or less per 100 parts by mass of the thermosetting resin (A).

[0010] According to one embodiment of the present invention, it is possible to provide a powder coating material that can provide a coating film with reduced cracking and / or peeling when the coating film is deformed.

[0011] An embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the respective configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments or examples obtained by combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic and patent literature described in this specification is incorporated herein by reference.

[0012] Unless otherwise specified in this specification, the structural unit is X １ A structural unit derived from a monomer, and X ２ Structural units derived from monomers, ... and X ｎ and a copolymer containing a structural unit derived from a monomer (n is an integer of 2 or more) is referred to as "X １ / X ２ / ・・・ / X ｎ Also referred to as "copolymer". X １ / X ２ / ・・・ / X ｎUnless otherwise specified, the polymerization mode of the copolymer is not particularly limited, and the copolymer may be a random copolymer, an alternating copolymer, a block copolymer, or a graft copolymer.

[0013] In this specification, the term "X unit" contained in a polymer, copolymer, or resin refers to a "structural unit derived from an X monomer." For example, the term "(meth)acrylate unit" refers to a "structural unit derived from a (meth)acrylate monomer."

[0014] [1. Powder Coating] A powder coating according to one embodiment of the present invention comprises a thermosetting resin (A) and polymer particles (B), the polymer particles (B) having an elastomer, an intermediate portion, and a graft portion, the elastomer containing a (meth)acrylate rubber, the intermediate portion containing, as structural units, crosslinkable units and graftable units in a total amount of 16.0 parts by mass or more per 100 parts by mass of the intermediate portion, the graft portion containing, as structural units, one or more structural units selected from the group consisting of aromatic vinyl units, vinyl cyan units, and (meth)acrylate units, and the content of the polymer particles (B) is 0.1 part by mass or more and 50.0 parts by mass or less per 100 parts by mass of the thermosetting resin (A).

[0015] In this specification, "a powder coating according to one embodiment of the present invention" may also be referred to as "the present powder coating."

[0016] The present powder coating has the above-mentioned constitution, and therefore has the advantage of being able to provide a coating film that is less susceptible to cracking and / or peeling when the coating film is deformed.

[0017] In this specification, whether a powder coating can provide a coating film with reduced cracking and / or peeling during deformation is determined by evaluating the cupping resistance of a test piece (coated plate) obtained using the powder coating. The method for evaluating the cupping resistance of a test piece (coated plate) obtained using a powder coating will be described in detail in the Examples below. In this specification, if the following condition is met, it can be considered that a powder coating can provide a coating film with reduced cracking and / or peeling during deformation: Condition: As a result of evaluating the cupping resistance of a test piece (coated plate) obtained using a powder coating, the extrusion height (mm) just before cracking occurs in the coating is 3 mm or more. In a cupping resistance test on a test piece (coated plate) obtained using a powder coating, the higher the extrusion height just before cracking occurs in the coating, the more preferable. When the cupping resistance of a test piece (coated plate) obtained using the powder coating is evaluated by the method described in the Examples below, the extrusion height (mm) just before cracks appear in the coating film is preferably 3 mm or more, more preferably 4 mm or more, and particularly preferably 5 mm or more.

[0018] In a preferred embodiment of the present invention, the powder coating has the above-mentioned configuration, and in particular, the polymer particles (B) contain intermediate portions, which has the advantage of providing good dispersibility of the polymer particles (B) in the powder coating and in the coating film. As a result, in a preferred embodiment of the present invention, the powder coating also has the advantage of being able to provide a coating film with good aesthetic appearance. The method for evaluating the aesthetic appearance of the coating film will be described in detail in the Examples below. Note that good dispersibility of the polymer particles (B) in the coating film also contributes to reducing cracking and / or peeling during the above-mentioned coating film deformation.

[0019] <1-1. Thermosetting Resin (A)> The thermosetting resin (A) is not particularly limited, and any thermosetting resin commonly used in the field of powder coatings can be used as appropriate. From the viewpoint of thermosetting properties, the thermosetting resin (A) preferably contains at least one resin selected from the group consisting of epoxy resins, thermosetting (meth)acrylic resins, and thermosetting polyester resins. As the thermosetting resin (A), only one of the above-mentioned thermosetting resins may be used, or two or more may be used in combination. For example, an epoxy resin and a thermosetting polyester resin may be used in combination. The thermosetting resin (A) can function as a matrix resin in the powder coating and the coating film. The thermosetting resin (A) is sometimes referred to as a "binder resin."

[0020] (Epoxy Resin) The epoxy resin is not particularly limited as long as it has at least one epoxy group in the molecule.

[0021] Specific examples of epoxy resins include bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol AD ​​type epoxy resins, bisphenol S type epoxy resins, glycidyl ester type epoxy resins, glycidylamine type epoxy resins, novolac type epoxy resins, glycidyl ether type epoxy resins of bisphenol A propylene oxide adducts, hydrogenated bisphenol A (or F) type epoxy resins, fluorinated epoxy resins, rubber-modified epoxy resins containing polybutadiene or NBR, flame-retardant epoxy resins such as glycidyl ether of tetrabromobisphenol A, p-oxybenzoic acid glycidyl ether ester type epoxy resins, m-aminophenol type epoxy resins, diaminodiphenylmethane-based epoxy resins, urethane-modified epoxy resins having a urethane bond, various alicyclic epoxy resins, glycidyl ethers of polyhydric alcohols, hydantoin type epoxy resins, epoxidized products of unsaturated polymers such as petroleum resins, and amino-containing glycidyl ether resins. Examples of the polyhydric alcohol include N,N-diglycidylaniline, N,N-diglycidyl-o-toluidine, triglycidyl isocyanurate, polyalkylene glycol diglycidyl ether, and glycerin. Examples of the epoxy resin include epoxy compounds obtained by subjecting the above-mentioned epoxy resins to an addition reaction with bisphenol A (or F), polybasic acids, or the like. The epoxy resin is not limited to these, and commonly used epoxy resins can be used. These epoxy resins may be used alone or in combination of two or more.

[0022] Among the above-mentioned epoxy resins, those having at least two epoxy groups per molecule are preferred because they have high reactivity during curing of the powder coating and the resulting coating film is likely to form a three-dimensional network. Furthermore, among epoxy resins having at least two epoxy groups per molecule, those containing bisphenol-type epoxy resin as the main component are preferred because of their excellent economical efficiency and ease of availability.

[0023] (Thermosetting (meth)acrylic resin) The thermosetting (meth)acrylic resin is a (meth)acrylic resin having a thermosetting reactive group. "(Meth)acrylic" means "methacrylic and / or acrylic". For example, "(meth)acrylic resin" means "methacrylic resin and / or acrylic resin". "(Meth)acrylic resin" means "resin containing at least a (meth)acrylic unit". "Thermosetting reactive group" means "functional group that exhibits a curing reaction upon heating" and can also be said to be "functional group that cures upon heating". "(Meth)acrylic" means "methacrylic and / or acrylic". The (meth)acrylic unit includes a (meth)acrylate unit. It is preferable that the thermosetting (meth)acrylic resin contains the largest (molar amount) of (meth)acrylic units in total among all constituent units.

[0024] To introduce a thermosetting reactive group into a (meth)acrylic resin, it is preferable to use a vinyl monomer having a thermosetting reactive group. In other words, it is preferable that the thermosetting (meth)acrylic resin contains a structural unit derived from a vinyl monomer having a thermosetting reactive group. The vinyl monomer having a thermosetting reactive group may be a (meth)acrylic monomer (a monomer having a (meth)acryloyl group), or may be a vinyl monomer other than a (meth)acrylic monomer. "(Meth)acryloyl" refers to "methacryloyl and / or acryloyl." For example, "(meth)acryloyl group" refers to "methacryloyl group and / or acryloyl group." A thermosetting (meth)acrylic resin can be obtained by (i) polymerizing a monomer mixture containing a (meth)acrylic monomer not having a thermosetting reactive group and a vinyl monomer other than the (meth)acrylic monomer having a thermosetting reactive group, (ii) polymerizing a monomer mixture containing a (meth)acrylic monomer having a thermosetting reactive group and a vinyl monomer other than the (meth)acrylic monomer not having a thermosetting reactive group, (iii) polymerizing a monomer mixture containing a (meth)acrylic monomer having a thermosetting reactive group and a vinyl monomer other than the (meth)acrylic monomer having a thermosetting reactive group, (iv) polymerizing a monomer mixture containing a (meth)acrylic monomer having a thermosetting reactive group and a (meth)acrylic monomer not having a thermosetting reactive group, or (v) polymerizing a monomer mixture consisting of a (meth)acrylic monomer having a thermosetting reactive group.

[0025] Examples of the thermosetting reactive group of the thermosetting (meth)acrylic resin include an epoxy group, a carboxyl group, a hydroxyl group, an amide group, an amino group, an acid anhydride group, and a (blocked) isocyanate group. Among these, the thermosetting reactive group of the thermosetting (meth)acrylic resin is preferably at least one selected from the group consisting of an epoxy group, a carboxyl group, and a hydroxyl group, because the thermosetting (meth)acrylic resin is easy to produce. From the viewpoint of excellent storage stability of the powder coating and excellent appearance of the coating film, it is more preferable that the thermosetting (meth)acrylic resin contains at least an epoxy group as the thermosetting reactive group.

[0026] Examples of vinyl monomers having an epoxy group as a thermosetting reactive group include various chain epoxy group-containing monomers (e.g., glycidyl (meth)acrylate, β-methylglycidyl (meth)acrylate, glycidyl vinyl ether, allyl glycidyl ether, etc.); various (2-oxo-1,3-oxolane) group-containing vinyl monomers (e.g., (2-oxo-1,3-oxolane)methyl (meth)acrylate, etc.); and various alicyclic epoxy group-containing vinyl monomers (e.g., 3,4-epoxycyclohexyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, 3,4-epoxycyclohexylethyl (meth)acrylate, etc.).

[0027] Examples of vinyl monomers having a carboxyl group as a thermosetting reactive group include various carboxyl group-containing monomers (e.g., (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, etc.); monoesters of various α,β-unsaturated dicarboxylic acids with monohydric alcohols having from 1 to 18 carbon atoms (e.g., monomethyl fumarate, monoethyl fumarate, monobutyl fumarate, monoisobutyl fumarate, mono-tert-butyl fumarate, monohexyl fumarate, monooctyl fumarate, mono-2-ethyl fumarate); monohexyl maleate, monomethyl maleate, monoethyl maleate, monobutyl maleate, monoisobutyl maleate, mono-tert-butyl maleate, monohexyl maleate, monooctyl maleate, mono-2-ethylhexyl maleate, etc.); monoalkyl itaconate esters (for example, monomethyl itaconate, monoethyl itaconate, monobutyl itaconate, monoisobutyl itaconate, monohexyl itaconate, monooctyl itaconate, mono-2-ethylhexyl itaconate, etc.);

[0028] Examples of vinyl monomers having a hydroxyl group as a thermosetting reactive group include various hydroxyl group-containing (meth)acrylates (e.g., 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, etc.); addition reaction products of the above-mentioned various hydroxyl group-containing (meth)acrylates with ε-caprolactone; various hydroxyl group-containing vinyl ethers (e.g., 2-hydroxyethyl vinyl ether, 3-hydroxypropyl vinyl ether, 2-hydroxypropyl vinyl ether, 4-hydroxybutyl vinyl ether, 3-hydroxybutyl vinyl ether, vinyl ether, 2-hydroxy-2-methylpropyl vinyl ether, 5-hydroxypentyl vinyl ether, 6-hydroxyhexyl vinyl ether, etc.); addition reaction products of the above-mentioned various hydroxyl group-containing vinyl ethers with ε-caprolactone; various hydroxyl group-containing allyl ethers (for example, 2-hydroxyethyl(meth)allyl ether, 3-hydroxypropyl(meth)allyl ether, 2-hydroxypropyl(meth)allyl ether, 4-hydroxybutyl(meth)allyl ether, 3-hydroxybutyl(meth)allyl ether, 2-hydroxy-2-methylpropyl(meth)allyl ether, 5-hydroxypentyl(meth)allyl ether, 6-hydroxyhexyl(meth)allyl ether, etc.); addition reaction products of the above-mentioned various hydroxyl group-containing allyl ethers with ε-caprolactone;

[0029] The thermosetting (meth)acrylic resin may contain, in addition to the (meth)acrylic units, structural units derived from vinyl monomers other than (meth)acrylic monomers that do not have a thermosetting reactive group.

[0030] Examples of vinyl monomers other than (meth)acrylic monomers that do not have a thermosetting reactive group include various α-olefins (e.g., ethylene, propylene, butene-1, etc.); various halogenated olefins excluding fluoroolefins (e.g., vinyl chloride, vinylidene chloride, etc.); various aromatic vinyl monomers (e.g., styrene, α-methylstyrene, vinyltoluene, etc.); diesters of various unsaturated dicarboxylic acids and monohydric alcohols having from 1 to 18 carbon atoms (e.g., dimethyl fumarate, diethyl fumarate, etc.); ethyl, dibutyl fumarate, dioctyl fumarate, dimethyl maleate, diethyl maleate, dibutyl maleate, dioctyl maleate, dimethyl itaconate, diethyl itaconate, dibutyl itaconate, dioctyl itaconate, etc.); various acid anhydride group-containing monomers (for example, maleic anhydride, itaconic anhydride, citraconic anhydride, (meth)acrylic anhydride, tetrahydrophthalic anhydride, etc.); various phosphate group-containing monomers (for example, diethyl-2-(meth)acryloyloxyethyl phosphate phosphate, dibutyl-2-(meth)acryloyloxybutyl phosphate, dioctyl-2-(meth)acryloyloxyethyl phosphate, diphenyl-2-(meth)acryloyloxyethyl phosphate, etc.); various hydrolyzable silyl group-containing monomers (for example, γ-(meth)acryloyloxypropyltrimethoxysilane, γ-(meth)acryloyloxypropyltriethoxysilane, γ-(meth)acryloyloxypropylmethyldimethoxysilane, etc.); various aliphatic vinyl carboxylates (for example, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl caproate, vinyl caprylate, vinyl caprate, vinyl laurate, branched aliphatic vinyl carboxylates having from 9 to 11 carbon atoms, vinyl stearate, etc.); various vinyl esters of carboxylic acids having a cyclic structure (for example, vinyl cyclohexanecarboxylate, vinyl methylcyclohexanecarboxylate, vinyl benzoate, vinyl p-tert-butylbenzoate, etc.); and the like.

[0031] When a thermosetting (meth)acrylic resin contains a constituent unit derived from a vinyl monomer other than a (meth)acrylic monomer as a constituent unit derived from a vinyl monomer having a thermosetting reactive group, the thermosetting (meth)acrylic resin further contains a constituent unit derived from a (meth)acrylic monomer that does not have a thermosetting reactive group.

[0032] Examples of the (meth)acrylic monomer not having a thermosetting reactive group include (meth)acrylic acid alkyl esters (e.g., methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, neopentyl (meth)acrylate, n-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, (meth)acrylate, isooctyl (meth)acrylate, 2-ethyloctyl (meth)acrylate, dodecyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, stearyl (meth)acrylate, etc.); various hydroxy group-containing (meth)acrylic acid alkyl esters (for example, 2-hydroxyethyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxyethyl (meth)acrylate, etc.); various (meth)acrylic acid alkoxy esters (for example, (meth)acrylate methoxy, (meth)acrylate ethoxy, (meth)acrylate 2-methoxyethyl, etc.); various (meth)acrylic acid halide alkyl esters (e.g., (meth)acrylate chloroethyl, (meth)acrylate trifluoroethyl, etc.); various (meth)acrylic acid aryl esters (e.g., (meth)acrylate benzyl, (meth)acrylate phenyl, (meth)acrylate phenoxyethyl, etc.); various alkyl carbitol (meth)acrylates (e.g., ethyl carbitol (meth)acrylate, etc.); other various ( (meth)acrylic acid esters (for example, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, etc.); various amino group-containing amide-based unsaturated monomers (for example, N-dimethylaminoethyl (meth)acrylamide, N-diethylaminoethyl (meth)acrylamide, N-dimethylaminopropyl (meth)acrylamide, N-diethylaminopropyl (meth)acrylamide, etc.);Examples include various dialkylaminoalkyl (meth)acrylates (e.g., dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, etc.); various amino group-containing monomers (e.g., tert-butylaminoethyl (meth)acrylate, tert-butylaminopropyl (meth)acrylate, aziridinylethyl (meth)acrylate, pyrrolidinylethyl (meth)acrylate, piperidinylethyl (meth)acrylate, etc.); and the like.

[0033] The number average molecular weight of the thermosetting (meth)acrylic resin is not particularly limited, but is preferably from 1,000 to 20,000, and more preferably from 1,500 to 15,000. When the number average molecular weight of the thermosetting (meth)acrylic resin is within the above range, there is an advantage that the smoothness and mechanical properties of the coating film are easily improved.

[0034] The number average molecular weight of the thermosetting (meth)acrylic resin is measured by gel permeation chromatography (GPC). The weight average molecular weight and number average molecular weight are calculated from the measurement results using a molecular weight calibration curve prepared with monodisperse polystyrene standard samples. Molecular weight measurement by GPC is performed using a solution obtained by dissolving the thermosetting (meth)acrylic resin in THF as a sample, for example, under the following conditions: Measurement apparatus: Tosoh GPC HLC-8420GPC; Column: Tosoh TSKgel Super HZ column; Mobile phase: THF solvent.

[0035] (Thermosetting polyester resin) The thermosetting polyester resin is, for example, a polycondensate obtained by polycondensing at least a polybasic acid and a polyhydric alcohol. The introduction of a thermosetting reactive group into the thermosetting polyester resin is carried out by adjusting the amount of the polybasic acid and the polyhydric alcohol used. By this adjustment, a thermosetting polyester resin having at least one of a carboxyl group and a hydroxyl group as the thermosetting reactive group can be obtained.

[0036] Examples of polybasic acids include terephthalic acid, isophthalic acid, phthalic acid, methyl terephthalic acid, trimellitic acid, pyromellitic acid, and anhydrides of these acids; succinic acid, adipic acid, azelaic acid, sebacic acid, and anhydrides of these acids; maleic acid, itaconic acid, and anhydrides of these acids; fumaric acid, tetrahydrophthalic acid, methyltetrahydrophthalic acid, hexahydrophthalic acid, methylhexahydrophthalic acid, and anhydrides of these acids; cyclohexanedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and the like.

[0037] Examples of polyhydric alcohols include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, triethylene glycol, bis-hydroxyethyl terephthalate, cyclohexanedimethanol, octanediol, diethylpropanediol, butylethylpropanediol, 2-methyl-1,3-propanediol, 2,2,4-trimethylpentanediol, hydrogenated bisphenol A, an ethylene oxide adduct of hydrogenated bisphenol A, a propylene oxide adduct of hydrogenated bisphenol A, trimethylolethane, trimethylolpropane, glycerin, pentaerythritol, trishydroxyethyl isocyanurate, and hydroxypivalyl hydroxypivalate.

[0038] The thermosetting polyester resin may be obtained by polycondensation of a monomer other than the polybasic acid and the polyhydric alcohol.

[0039] Examples of other monomers include compounds having both a carboxyl group and a hydroxyl group in one molecule (e.g., dimethanolpropionic acid, hydroxypivalate, etc.), monoepoxy compounds (e.g., glycidyl esters of branched aliphatic carboxylic acids such as "Cardura E10 (manufactured by Shell)"), various monohydric alcohols (e.g., methanol, propanol, butanol, benzyl alcohol, etc.), various monobasic acids (e.g., benzoic acid, p-tert-butylbenzoic acid, etc.), various fatty acids (e.g., castor oil fatty acid, coconut oil fatty acid, soybean oil fatty acid, etc.), and the like.

[0040] The structure of the thermosetting polyester resin may be a branched structure or a linear structure.

[0041] The thermosetting polyester resin preferably has a total acid value and hydroxyl value of 10 mgKOH / g or more and 250 mgKOH / g or less. When the total acid value and hydroxyl value is within the above range, the smoothness and mechanical properties of the coating film are easily improved. The acid value and hydroxyl value of the thermosetting polyester resin are measured in accordance with JIS K-0070-1992.

[0042] The thermosetting polyester resin preferably has a number average molecular weight of 1,000 or more and 100,000 or less. When the number average molecular weight is within the above range, the smoothness and mechanical properties of the coating film are improved, and the storage stability of the powder coating material is also likely to be improved. The number average molecular weight of the thermosetting polyester resin is measured in the same manner as that of the thermosetting (meth)acrylic resin.

[0043] The thermosetting resins may be used alone or in combination of two or more.

[0044] From the viewpoint of the properties as a powder coating, the thermoplastic resin (A) is preferably a solid at room temperature (for example, 25° C.).

[0045] <1-2. Polymer particles (B)> The polymer particles (B) have an elastomer and a graft portion graft-bonded to the elastomer. By including the polymer particles (B), the present powder coating has the advantage of being able to provide a coating film that is less susceptible to cracking and / or peeling during deformation of the coating film. The reason for this is unclear, but it is presumed that the polymer particles (B) reduce the stress in the coating film after deformation caused by deformation of the coating film. However, one embodiment of the present invention is in no way limited to this presumption.

[0046] (Elastomer) ((Meth)acrylate-based Rubber) The elastomer can also be referred to as an elastic portion or rubber particles. The elastomer contains a (meth)acrylate-based rubber. In this specification, "(meth)acrylate" refers to "acrylate and / or methacrylate." For example, "(meth)acrylate-based rubber" refers to "acrylate-based rubber and / or methacrylate-based rubber." When the elastomer contains a (meth)acrylate-based rubber, the resulting powder coating has the advantage of being able to provide a coating film with reduced cracking and / or peeling during deformation. Furthermore, many types of (meth)acrylate monomers with different alkyl group carbon chains are known and are easily available. Therefore, a wide range of polymer designs for elastomers are possible by combining a variety of monomers.

[0047] The (meth)acrylate rubber is an elastomer containing a (meth)acrylate unit as a structural unit. In other words, the elastomer contains a (meth)acrylate unit as a structural unit. The (meth)acrylate rubber may further contain, in addition to the (meth)acrylate unit as a structural unit, a structural unit derived from a vinyl monomer other than the (meth)acrylate monomer that is copolymerizable with the (meth)acrylate monomer. In this specification, the "vinyl monomer other than the (meth)acrylate monomer that is copolymerizable with the (meth)acrylate monomer" may also be referred to as "vinyl monomer A," and the "structural unit derived from the vinyl monomer A" may also be referred to as "vinyl unit A." In other words, the elastomer may contain the vinyl unit A as a structural unit.

[0048] The (meth)acrylate rubber preferably contains the (meth)acrylate unit in the largest amount (by mole) of all structural units, and the elastomer preferably contains the (meth)acrylate unit in the largest amount (by mole) of all structural units.

[0049] The (meth)acrylate rubber may contain 50% by mass or more and 100% by mass or less of (meth)acrylate units and 0% by mass or more and 50% by mass or less of vinyl-based units A, based on 100% by mass of structural units.

[0050] The (meth)acrylate rubber may contain, as structural units, diene units and / or organosilyloxy units in an amount less than the amount of structural units derived from (meth)acrylate monomers.

[0051] Examples of (meth)acrylate monomers from which (meth)acrylate units are derived include: (a) alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, dodecyl (meth)acrylate, stearyl (meth)acrylate, and behenyl (meth)acrylate; (b) aromatic ring-containing (meth)acrylates such as phenoxyethyl (meth)acrylate and benzyl (meth)acrylate; (c) 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and the like; Examples of suitable (meth)acrylate monomers include hydroxyalkyl (meth)acrylates such as ethyl (meth)acrylate; (d) glycidyl (meth)acrylates such as glycidyl (meth)acrylate and glycidyl alkyl (meth)acrylate; (e) alkoxyalkyl (meth)acrylates; (f) allyl alkyl (meth)acrylates such as allyl (meth)acrylate and allyl alkyl (meth)acrylate; and (g) polyfunctional (meth)acrylates such as monoethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, and tetraethylene glycol di(meth)acrylate. These (meth)acrylate monomers may be used alone or in combination of two or more. Among these (meth)acrylate monomers, ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate are preferred, with butyl (meth)acrylate being more preferred.

[0052] Examples of the vinyl monomer A include: (a) diene monomers such as 1,3-butadiene, isoprene (2-methyl-1,3-butadiene), and 2-chloro-1,3-butadiene; (b) vinyl arenes such as styrene, α-methylstyrene, monochlorostyrene, and dichlorostyrene; (c) vinyl carboxylic acids such as acrylic acid and methacrylic acid; (d) vinyl cyanides such as acrylonitrile and methacrylonitrile; (e) vinyl halides such as vinyl chloride, vinyl bromide, and chloroprene; (f) vinyl acetate; (g) alkenes such as ethylene, propylene, butylene, and isobutylene; and (h) polyfunctional monomers such as diallyl phthalate, triallyl cyanurate, triallyl isocyanurate, and divinylbenzene. The above-mentioned vinyl monomer A may be used alone or in combination of two or more. Among the above-mentioned vinyl monomers A, styrene is particularly preferred.

[0053] The (meth)acrylate rubber preferably contains (a) one or more structural units selected from the group consisting of ethyl (meth)acrylate units, butyl (meth)acrylate units, and 2-ethylhexyl (meth)acrylate units, and may be composed solely of one or more structural units selected from this group, more preferably (b) butyl (meth)acrylate units, and may be composed solely of butyl (meth)acrylate units, or even more preferably (c) butyl acrylate units, and may be composed solely of butyl acrylate units. This configuration has the advantage that the resulting powder coating can provide a coating film with even less cracking and / or peeling during coating film deformation.

[0054] The (meth)acrylate rubber preferably contains, per 100 parts by mass of the (meth)acrylate rubber, more preferably more than 50 parts by mass and not more than 100 parts by mass, more preferably 60 parts by mass or more and not more than 100 parts by mass, even more preferably 70 parts by mass or more and not more than 100 parts by mass, even more preferably 80 parts by mass or more and not more than 100 parts by mass, and particularly preferably 90 parts by mass or more and not more than 100 parts by mass, of one or more structural units selected from the group consisting of ethyl (meth)acrylate units, butyl (meth)acrylate units, and 2-ethylhexyl (meth)acrylate units. This configuration has the advantage that the resulting powder coating can provide a coating film that is particularly prone to reduced cracking and / or peeling during coating film deformation.

[0055] The elastomer preferably contains (a) one or more structural units selected from the group consisting of ethyl (meth)acrylate units, butyl (meth)acrylate units, and 2-ethylhexyl (meth)acrylate units, and may be composed solely of one or more structural units selected from this group, more preferably (b) butyl (meth)acrylate units, and may be composed solely of butyl (meth)acrylate units, or even more preferably (c) butyl acrylate units, and may be composed solely of butyl acrylate units. This configuration has the advantage that the resulting powder coating can provide a coating film with even less cracking and / or peeling during coating film deformation.

[0056] The elastomer preferably contains, per 100 parts by mass of the elastomer, more preferably more than 50 parts by mass and not more than 100 parts by mass, more preferably 60 parts by mass or more and not more than 100 parts by mass, even more preferably 70 parts by mass or more and not more than 100 parts by mass, even more preferably 80 parts by mass or more and not more than 100 parts by mass, and particularly preferably 90 parts by mass or more and not more than 100 parts by mass, of one or more structural units selected from the group consisting of ethyl (meth)acrylate units, butyl (meth)acrylate units, and 2-ethylhexyl (meth)acrylate units. This configuration has the advantage that the resulting powder coating can provide a coating film that is particularly prone to reduced cracking and / or peeling during coating film deformation.

[0057] The (meth)acrylate rubber is preferably one or more selected from the group consisting of ethyl (meth)acrylate rubber, butyl (meth)acrylate rubber, and 2-ethylhexyl (meth)acrylate rubber, with butyl (meth)acrylate rubber being more preferred. According to this configuration, the elastomer has a low glass transition temperature (Tg). As a result, (a) the powder coating can provide a coating film with reduced cracking and / or peeling during coating film deformation, (b) a coating film with excellent toughness can be provided, and / or (c) the viscosity of the powder coating can be reduced. The term "ethyl (meth)acrylate rubber" refers to an elastomer having the highest molar amount of ethyl (meth)acrylate units among all structural units contained in the elastomer. The term "butyl (meth)acrylate rubber" refers to an elastomer having the highest molar amount of butyl (meth)acrylate units among all structural units contained in the elastomer. The 2-ethylhexyl (meth)acrylate rubber is intended to mean an elastomer in which the molar amount of 2-ethylhexyl (meth)acrylate units is the largest among all the constituent units contained in the elastomer.

[0058] The elastomer may contain, in addition to the (meth)acrylate rubber, a rubber (elastomer) other than the (meth)acrylate rubber, such as natural rubber, diene rubber, or organosiloxane rubber.

[0059] The elastomer preferably contains 50 to 100 parts by mass of (meth)acrylate rubber per 100 parts by mass of the elastomer, preferably 60 to 100 parts by mass, more preferably 70 to 100 parts by mass, more preferably 80 to 100 parts by mass, even more preferably 90 to 100 parts by mass, and particularly preferably 95 to 100 parts by mass. The elastomer most preferably contains 100 parts by mass of (meth)acrylate rubber per 100 parts by mass of the elastomer. In other words, the elastomer is most preferably composed solely of (meth)acrylate rubber. When the content of (meth)acrylate rubber in the elastomer is within the above-mentioned range, the resulting powder coating has the advantage of being able to provide a coating film with reduced cracking and / or peeling during coating film deformation.

[0060] The (meth)acrylate rubber preferably contains, per 100 parts by mass of the (meth)acrylate rubber, a total of 50 parts by mass or more and 100 parts by mass or less, preferably 60 parts by mass or more and 100 parts by mass or less, more preferably 70 parts by mass or more and 100 parts by mass or less, more preferably 80 parts by mass or more and 100 parts by mass or less, even more preferably 90 parts by mass or more and 100 parts by mass or less, and particularly preferably 95 parts by mass or more and 100 parts by mass or less. The (meth)acrylate rubber most preferably contains a total of 100 parts by mass of one or more rubbers selected from the group consisting of ethyl (meth)acrylate rubber, butyl (meth)acrylate rubber, and 2-ethylhexyl (meth)acrylate rubber, per 100 parts by mass of the (meth)acrylate rubber. In other words, the (meth)acrylate rubber most preferably consists of only one or more rubbers selected from the group consisting of ethyl (meth)acrylate rubber, butyl (meth)acrylate rubber, and 2-ethylhexyl (meth)acrylate rubber. When the total content of one or more rubbers selected from the above group in the (meth)acrylate rubber is within the above-mentioned range, the resulting powder coating has the advantage of being able to provide a coating film with even less cracking and / or peeling during coating film deformation.

[0061] The elastomer preferably contains, per 100 parts by mass of the elastomer, a total of 50 to 100 parts by mass of one or more (meth)acrylate rubbers selected from the group consisting of ethyl (meth)acrylate rubber, butyl (meth)acrylate rubber, and 2-ethylhexyl (meth)acrylate rubber, preferably 60 to 100 parts by mass, preferably 70 to 100 parts by mass, preferably 80 to 100 parts by mass, more preferably 90 to 100 parts by mass, and particularly preferably 95 to 100 parts by mass. The elastomer most preferably contains, per 100 parts by mass of the elastomer, a total of 100 parts by mass of one or more rubbers selected from the group consisting of ethyl (meth)acrylate rubber, butyl (meth)acrylate rubber, and 2-ethylhexyl (meth)acrylate rubber. In other words, it is most preferable that the elastomer is composed solely of one or more (meth)acrylate rubbers selected from the group consisting of ethyl (meth)acrylate rubber, butyl (meth)acrylate rubber, and 2-ethylhexyl (meth)acrylate rubber. When the total content of one or more rubbers selected from the above group in the elastomer is within the above range, the obtained powder coating has the advantage of being able to provide a coating film with even less cracking and / or peeling during coating film deformation.

[0062] It is preferable to use a crosslinkable monomer and / or a graftable monomer in the elastomer formation (polymerization) process. When a crosslinkable monomer and / or a graftable monomer is used in the elastomer formation (polymerization) process, a crosslinked structure can be introduced into the elastomer, which has the advantage that the elastomer can maintain its particulate form in powder coatings and coating films. When a crosslinkable monomer and / or a graftable monomer is used in the elastomer formation (polymerization) process, it also has the advantage that the dispersibility of the polymer particles (B) in powder coatings and coating films can be improved. A polymer obtained by using a crosslinkable monomer in the formation (polymerization) process may have a crosslinkable unit. A polymer obtained by using a graftable monomer in the formation (polymerization) process may have a graftable unit. In other words, it is preferable that the elastomer contains a crosslinkable unit and / or a graftable unit as a constituent unit.

[0063] Examples of crosslinkable monomers include monomers having at least two or more of the same type of polymerizable group in the molecule. Examples of crosslinkable monomers include alkane polyol polyacrylates or alkane polyol polymethacrylates such as ethylene glycol diacrylate, ethylene glycol dimethacrylate, butylene glycol diacrylate (e.g., 1,4-butylene glycol diacrylate), butylene glycol dimethacrylate, hexanediol diacrylate, hexanediol dimethacrylate, oligoethylene glycol diacrylate, oligoethylene glycol dimethacrylate, trimethylolpropane diacrylate, trimethylolpropane triacrylate, and trimethylolpropane trimethacrylate. Examples of crosslinkable monomers include divinylbenzene and triallyl cyanurate. Of these, butylene glycol diacrylate, hexanediol diacrylate, divinylbenzene, and triallyl cyanurate are particularly preferred.

[0064] The graftable monomer may be a monomer having at least two or more polymerizable groups with different reactivities in the molecule. Examples of the graftable monomer include unsaturated carboxylic acid allyl esters such as allyl acrylate, allyl methacrylate, diallyl maleate, diallyl fumarate, and diallyl itaconate. Of these, allyl methacrylate is particularly preferred.

[0065] The above-mentioned crosslinkable monomers and graftable monomers may be used singly or in combination of two or more.

[0066] When the elastomer contains a crosslinkable unit, the crosslinkable unit in the elastomer preferably contains one or more types selected from the group consisting of butylene glycol diacrylate units, hexanediol diacrylate units, divinylbenzene units, and triallyl cyanurate units, and may be composed of only one or more types selected from this group.

[0067] When the elastomer contains graftable units, the graftable units in the elastomer preferably contain allyl methacrylate units, and may be composed solely of allyl methacrylate units.

[0068] The elastomer may contain no crosslinkable units but may contain graftable units. The elastomer may contain no crosslinkable units but may contain allyl methacrylate units as graftable units. The elastomer may contain no crosslinkable units but may contain only allyl methacrylate units as graftable units.

[0069] The total content of the crosslinkable unit and the graftable unit in the elastomer can be regarded as the total amount of the crosslinkable monomer and the graftable monomer used in the formation (polymerization) process of the elastomer. When the elastomer contains a crosslinkable unit and / or a graftable unit, the elastomer preferably contains more than 0 parts by mass but not more than 1.2 parts by mass of the crosslinkable unit and the graftable unit in total, per 100 parts by mass of the elastomer, more preferably more than 0 parts by mass but not more than 1.0 parts by mass, more preferably more than 0 parts by mass but not more than 0.8 parts by mass, more preferably more than 0 parts by mass but not more than 0.6 parts by mass, even more preferably more than 0 parts by mass but not more than 0.4 parts by mass, and particularly preferably more than 0 parts by mass but not more than 0.2 parts by mass. This configuration has the advantage that the resulting powder coating can provide a coating film with even less cracking and / or peeling during coating film deformation.

[0070] The volume average particle diameter of the elastomer is preferably 30 nm or more and 50,000 nm or less, more preferably 50 nm or more and 10,000 nm or less, more preferably 80 nm or more and 5,000 nm or less, more preferably 100 nm or more and 2,500 nm or less, more preferably 100 nm or more and 2,000 nm or less, more preferably 100 nm or more and 1,500 nm or less, more preferably 100 nm or more and 1,000 nm or less, even more preferably 100 nm or more and 750 nm or less, and particularly preferably 100 nm or more and 500 nm or less. When the volume average particle diameter of the elastomer is 30 nm or more, an elastomer having a desired volume average particle diameter can be stably obtained. When the volume average particle diameter of the elastomer is 100 nm or more, the dispersibility of the polymer particles (B) during the preparation of the powder coating is particularly excellent, resulting in the advantage of excellent dispersibility of the polymer particles (B) in the powder coating and coating film. When the volume average particle diameter of the elastomer is 50,000 nm or less, the heat resistance and impact resistance of the resulting coating film are good. The volume average particle diameter of the elastomer can be measured using a dynamic light scattering particle size distribution analyzer or the like, using an aqueous latex containing the elastomer as a sample. The method for measuring the volume average particle diameter of the elastomer will be described in detail in the Examples below.

[0071] The glass transition temperature of the elastomer is preferably below 0°C, more preferably -10°C or lower, more preferably -20°C or lower, more preferably -30°C or lower, even more preferably -40°C or lower, and particularly preferably -50°C or lower. When the glass transition temperature of the elastomer is within the above-mentioned range, polymer particles (B) having an elastomer with a low Tg can be obtained. As a result, the obtained powder coating can provide a coating film with excellent toughness, which has the advantage of providing a coating film with reduced cracking and / or peeling during deformation of the coating film. The lower limit of the glass transition temperature of the elastomer is not particularly limited, and is, for example, -150°C. In this specification, "glass transition temperature" may also be referred to as "Tg".

[0072] In this specification, the Tg of the elastomer is either (a) a value determined by viscoelasticity measurement using a flat plate made of the elastomer, (b) a value determined by viscoelasticity measurement using a flat plate made of polymer particles (B), or (c) a value calculated by the FOX formula based on the constituent units other than the crosslinkable units and the graftable units among the constituent units constituting the elastomer.

[0073] A method for determining the Tg of an elastomer by viscoelasticity measurement using a flat plate made of the elastomer will be described. Viscoelasticity measurement (shear method, measurement frequency: 1 Hz) is performed using a flat plate made of the elastomer (thickness: 1 mm), a graph of loss tangent (tan δ) is obtained, and the peak temperature value in the obtained graph is used as the Tg of the elastomer. A flat plate made of the elastomer can be obtained, for example, by the following method using an aqueous latex of the elastomer. First, the elastomer in the aqueous latex of the elastomer is coagulated by any method (e.g., salting out, freeze-thawing, shearing) to obtain a coagulated product of the elastomer. The obtained coagulated product is dried to obtain a powder or granular product of the elastomer. Alternatively, the aqueous latex of the elastomer is spray-dried to obtain a powder or granular product of the elastomer. Next, the powder or granular product of the elastomer is pressed under conditions that result in a flat plate as uniform as possible, thereby obtaining a flat plate with a thickness of 1 mm.

[0074] A method for determining the Tg of an elastomer by viscoelasticity measurement using a flat plate made of polymer particles (B) will be described. Viscoelasticity measurement (shear method, measurement frequency: 1 Hz) is performed using a flat plate (thickness: 1 mm) made of polymer particles (B) to obtain a graph of loss tangent (tan δ). The Tg of the elastomer is determined from the peak in the obtained tan δ graph. Here, when the compositions of the elastomer, intermediate portion, and graft portion contained in the polymer particles (B) are all the same, the tan δ graph obtained by viscoelasticity measurement using the flat plate made of the polymer particles (B) may have one clear peak. In this case, the peak temperature can be used as the Tg of the elastomer. On the other hand, when the compositions of the elastomer, intermediate portion, and graft portion contained in the polymer particles (B) are different from each other, the tan δ graph obtained by viscoelasticity measurement using the flat plate made of the polymer particles (B) may have multiple peaks or an abnormally shaped peak. Examples of peaks with abnormal shapes include (i) a peak with a single peak (shoulder peak), (ii) a peak with a split peak, (iii) a broad peak, and (iv) a peak with a tailing or leading edge. When the compositions of the elastomer, intermediate portion, and graft portion contained in the polymer particles (B) are different from one another, the glass transition temperature of the elastomer can be determined by combining the data from the tan δ graph with other analytical data such as composition analysis. A flat plate made of polymer particles (B) can be obtained, for example, by the following method using an aqueous latex of polymer particles (B). First, the polymer particles (B) in the aqueous latex of polymer particles (B) are coagulated by any method (e.g., salting out, freeze-thawing, shearing) to obtain a coagulated product of polymer particles (B). The obtained coagulated product is dried to obtain a powder of polymer particles (B). Alternatively, the aqueous latex of polymer particles (B) is spray-dried to obtain a powder of polymer particles (B). Next, the powder of polymer particles (B) is pressed under conditions that allow a flat plate to be obtained that is as uniform as possible, thereby obtaining a flat plate having a thickness of 1 mm.

[0075] The Tg of the elastomer can be calculated based on the structural units contained in the elastomer, i.e., the monomers used in the production (polymerization) of the elastomer, using the FOX formula (Formula 1) shown below: 1 / Tg=w １ / Tg １ +w ２ / Tg ２ +...+w ｎ / Tg ｎ (Formula 1): In the FOX formula for calculating the Tg of an elastic body, Tg １ , Tg ２ , ..., Tg ｎ represent the Tg (K) of the homopolymer of the monomer from which the structural units 1, 2, ..., n constituting the elastomer are derived, and w １ , w ２ ,...,w ｎ and represent the mass fractions of the structural units 1, 2, ..., n that constitute the elastomer, respectively. The Tg of the homopolymer can be, for example, the numerical values ​​described in "Polymer Handbook Fourth Edition" (edited by J. Brandup et al., Jphn Wiley & Sons, Inc.).

[0076] However, when calculating the Tg of an elastomer using the FOX formula, the crosslinking units and grafting units are not taken into consideration. That is, the Tg of the elastomer is calculated using the mass fraction of the structural units constituting the elastomer other than the crosslinking units and grafting units, and the Tg of the homopolymer of the monomer from which the structural units are derived. Therefore, when calculating the Tg of an elastomer using the FOX formula, the "glass transition temperature of the elastomer" can also be said to be the "glass transition temperature of the structure of the elastomer excluding the crosslinking units and grafting units."

[0077] When the total content of the crosslinkable unit and the graftable unit in 100 parts by mass of the elastomer is 1.2 parts by mass or less, it can be said that the influence of the crosslinkable unit and the graftable unit on the Tg of the elastomer is very small.Therefore, when the total content of the crosslinkable unit and the graftable unit in 100 parts by mass of the elastomer is 1.2 parts by mass or less, the Tg of the elastomer determined by viscoelasticity measurement using a flat plate made of the elastomer and the Tg of the elastomer determined by viscoelasticity measurement using a flat plate made of polymer particles (B) can be considered to be the same as the Tg of the elastomer calculated by the FOX formula based on the structural units other than the crosslinkable unit and the graftable unit among the structural units constituting the elastomer.

[0078] The Tg of the elastomer can be determined by the composition of the structural units contained in the elastomer, etc. In other words, the Tg of the resulting elastomer can be adjusted by changing the composition of the monomers used when producing (polymerizing) the elastomer.

[0079] The polymer particles (B) preferably contain 40% by mass or more and 97% by mass or less of the elastomer, more preferably 60% by mass or more and 95% by mass or less, and even more preferably 70% by mass or more and 93% by mass or less, based on 100% by mass of the polymer particles (B). When the polymer particles (B) contain (a) 40% by mass or more of the elastomer, based on 100% by mass of the polymer particles (B), the powder coating has the advantage of being able to provide a coating film excellent in toughness and impact resistance, and when (b) 97% by mass or less, the polymer particles (B) do not easily aggregate (are unlikely to aggregate), so the powder coating does not become highly viscous, and as a result, the powder coating has the advantage of being easy to handle.

[0080] (Intermediate portion) The intermediate portion of the polymer particles (B) can contribute to improving the dispersibility of the polymer particles (B) when preparing a powder coating, and as a result, can contribute to improving the dispersibility of the polymer particles (B) in the powder coating and coating film. In other words, by having the intermediate portion, the polymer particles (B) have excellent dispersibility when preparing a powder coating, and as a result, excellent dispersibility in the powder coating and coating film. When the dispersibility of the polymer particles (B) in the coating film is good, it has the advantages of (i) reducing cracking and / or peeling of the coating film during deformation, and (ii) having a good appearance beauty of the coating film.

[0081] As described below, the intermediate section can be formed (polymerized) in the presence of the elastic body after the elastic body has been formed (polymerized) and before the graft section has been formed (polymerized). At least a portion of the intermediate section preferably covers at least a portion of the elastic body. At least a portion of the intermediate section may be covered by at least a portion of the graft section. At least a portion of the intermediate section may be embedded inside the elastic body.

[0082] The structural units constituting the intermediate portion, in other words, the structural units contained in the intermediate portion, are not particularly limited. The intermediate portion preferably contains, as a structural unit, one or more structural units selected from the group consisting of aromatic vinyl units, vinyl cyan units, and (meth)acrylate units. This structure has the advantage that the dispersibility of the polymer particles (B) is excellent when preparing the powder coating, and as a result, the dispersibility of the polymer particles (B) is excellent in the powder coating and the coating film.

[0083] The intermediate portion preferably contains aromatic vinyl units, vinyl cyan units, and (meth)acrylate units in a total amount of 0% by mass or more and 84% by mass or less, more preferably 0% by mass or more and 80% by mass or less, even more preferably 0% by mass or more and 75% by mass or less, and particularly preferably 0% by mass or more and 70% by mass or less, relative to 100% by mass of all structural units of the intermediate portion. This configuration has the advantage of providing better dispersibility of the polymer particles (B) during powder coating production, resulting in better dispersibility of the polymer particles (B) in the powder coating and coating film.

[0084] The intermediate portion more preferably contains, as a structural unit, one or more selected from the group consisting of methyl (meth)acrylate units, styrene units, butyl (meth)acrylate units, and acrylonitrile units, and particularly preferably contains (ii) one or more selected from the group consisting of methyl methacrylate units and styrene units. This configuration has the advantage of providing better dispersibility of the polymer particles (B) during powder coating production, and as a result, better dispersibility of the polymer particles (B) in the powder coating and coating film.

[0085] The intermediate portion preferably contains one or more structural units selected from the group consisting of methyl (meth)acrylate units, styrene units, butyl (meth)acrylate units, and acrylonitrile units in a total amount of 0% by mass or more and 84% by mass or less, more preferably 0% by mass or more and 80% by mass or less, even more preferably 0% by mass or more and 75% by mass or less, and particularly preferably 0% by mass or more and 70% by mass or less, relative to 100% by mass of all structural units in the intermediate portion. This configuration has the advantage of providing even better dispersibility of the polymer particles (B) during powder coating production, and as a result, even better dispersibility of the polymer particles (B) in the powder coating and coating film.

[0086] In the process of forming (polymerizing) the intermediate portion, a crosslinkable monomer and / or a graftable monomer is used. Therefore, the intermediate portion contains a crosslinkable unit and / or a graftable unit. The inclusion of the crosslinkable unit and / or the graftable unit in the intermediate portion provides the advantage of improved dispersibility of the polymer particles (B) during the preparation of the powder coating, resulting in improved dispersibility of the polymer particles (B) in the powder coating and the coating film.

[0087] Specific examples of the crosslinkable monomer and the graftable monomer are the same as those described in the section ((meth)acrylate rubber) of (Elastomer) above, and therefore, the description therein is incorporated by reference and the description thereof will be omitted here.

[0088] The crosslinkable unit in the intermediate portion preferably contains one or more units selected from the group consisting of butylene glycol diacrylate units, hexanediol diacrylate units, divinylbenzene units, and triallyl cyanurate units, and may be composed of only one or more units selected from this group.

[0089] The graftable units in the intermediate portion preferably contain allyl methacrylate units, and may be composed solely of allyl methacrylate units.

[0090] The intermediate portion may contain no crosslinkable units but contain graftable units. The intermediate portion may contain no crosslinkable units but contain allyl methacrylate units as graftable units. The intermediate portion may contain no crosslinkable units but contain only allyl methacrylate units as graftable units.

[0091] The total content of the crosslinkable units and graftable units in the intermediate portion can be considered to be the total amount of the crosslinkable monomers and graftable monomers used in the formation (polymerization) process of the intermediate portion. The intermediate portion preferably contains 16.0 parts by mass or more of the crosslinkable units and graftable units in total, per 100 parts by mass of the intermediate portion, more preferably 20.0 parts by mass or more, even more preferably 25.0 parts by mass or more, and particularly preferably 30.0 parts by mass or more. This configuration has the advantage of providing better dispersibility of the polymer particles (B) during powder coating production, resulting in better dispersibility of the polymer particles (B) in the powder coating and coating film. The upper limit of the total content of the crosslinkable units and graftable units in the intermediate portion is not particularly limited, but is, for example, 100 parts by mass or 80 parts by mass. That is, the intermediate portion may be composed solely of crosslinkable units and / or graftable units.

[0092] The glass transition temperature (Tg) of the intermediate portion is preferably 0°C or higher, more preferably 10°C or higher, more preferably 20°C or higher, more preferably 30°C or higher, more preferably 40°C or higher, more preferably 50°C or higher, more preferably 60°C or higher, more preferably 70°C or higher, more preferably 80°C or higher, even more preferably 90°C or higher, and particularly preferably 100°C or higher. When the Tg of the intermediate portion is within the above-mentioned range, there is an advantage that the dispersibility of the polymer particles (B) in the powder coating and coating film is even better. The upper limit of the Tg of the intermediate portion is not particularly limited, and is, for example, 150°C.

[0093] In this specification, the Tg of the intermediate portion is either (a) a value determined by viscoelasticity measurement using a flat plate made of polymer particles (B), or (b) a value calculated by the FOX equation based on the constituent units other than the crosslinkable units and the graftable units among the constituent units constituting the intermediate portion.

[0094] A method for determining the Tg of the intermediate portion by viscoelasticity measurement using a flat plate made of polymer particles (B) will be described. Viscoelasticity measurement (shear method, measurement frequency: 1 Hz) is performed using a flat plate (thickness: 1 mm) made of polymer particles (B) to obtain a loss tangent (tan δ) graph. The Tg of the intermediate portion is determined from the peak in the obtained tan δ graph. As described above, if the obtained tan δ graph has one clean peak, the peak temperature can be used as the Tg of the intermediate portion. On the other hand, if the obtained tan δ graph has multiple peaks or a peak with an abnormal shape, the glass transition temperature of the intermediate portion can be determined by combining the data from the tan δ graph with other analytical data such as composition analysis.

[0095] The Tg of the intermediate portion can be calculated by the above-mentioned FOX formula (Formula 1) based on the structural units contained in the intermediate portion, i.e., the monomers used in the production (polymerization) of the intermediate portion. １ , Tg ２ , ..., Tg ｎrepresent the Tg (K) of the homopolymer of the monomer from which the structural units 1, 2, ..., n constituting the intermediate portion are derived, and w １ , w ２ ,...,w ｎ respectively represent the mass fractions of the structural units 1, 2, . . . , n that constitute the intermediate portion.

[0096] However, when calculating the Tg of the intermediate portion using the FOX formula, the crosslinking units and grafting units are not taken into consideration. That is, the Tg of the intermediate portion is calculated using the mass fraction of the structural units constituting the intermediate portion other than the crosslinking units and grafting units, and the Tg of the homopolymer of the monomer from which the structural units are derived. Therefore, when calculating the Tg of the intermediate portion using the FOX formula, the "glass transition temperature of the intermediate portion" can also be said to be the "glass transition temperature of the intermediate portion excluding the crosslinking units and grafting units."

[0097] The polymer particles (B) preferably contain the intermediate portion in an amount of 0.5% by mass or more and 5.0% by mass or less, more preferably 1.0% by mass or more and 4.0% by mass or less, even more preferably 2.0% by mass or more and 4.0% by mass or less, and particularly preferably 2.5% by mass or more and 4.0% by mass or less, based on 100% by mass of the polymer particles (B). When the polymer particles (B) contain (a) 0.5% by mass or more of the intermediate portion based on 100% by mass of the polymer particles (B), the dispersibility of the polymer particles (B) during the preparation of the powder coating is superior, resulting in superior dispersibility of the polymer particles (B) in the powder coating and the coating film. When the polymer particles (B) contain (b) 5.0% by mass or less, the obtained powder coating has the advantage of being able to provide a coating film with further reduced cracking and / or peeling during coating film deformation.

[0098] (Graft portion) In this specification, the term "graft portion" refers to a polymer grafted to the elastomer and / or intermediate portion. The graft portion can be obtained by forming (polymerizing) the elastomer, then forming (polymerizing) the intermediate portion in the presence of the elastomer, and then further forming (polymerizing) the graft portion in the presence of a polymer containing the elastomer and the intermediate portion. The graft portion may be grafted only to the elastomer, only to the intermediate portion, or both to the elastomer and the intermediate portion. It is preferable that at least a portion of the graft portion covers at least a portion of the elastomer and / or at least a portion of the intermediate portion. It is also possible that at least a portion of the graft portion penetrates into the elastomer and / or the intermediate portion. It is preferable that at least a portion of the graft portion is present at the outermost portion of the polymer particle (B).

[0099] The graft moiety contains one or more structural units selected from the group consisting of aromatic vinyl units, vinyl cyan units, and (meth)acrylate units. Because of this structure, the graft moiety can fulfill various roles. Examples of the "various roles" include (a) improving the compatibility between the resin components (e.g., thermoplastic resin (A)) in the powder coating and the polymer particles (B), (b) improving the dispersibility of the polymer particles (B) in the powder coating and the coating film, and (c) enabling the polymer particles (B) to be dispersed in the form of primary particles in the powder coating and the coating film.

[0100] Specific examples of aromatic vinyl monomers from which the aromatic vinyl units are derived include styrene, α-methylstyrene, p-methylstyrene, and divinylbenzene.

[0101] Specific examples of vinylcyanide monomers from which vinylcyanide units are derived include acrylonitrile and methacrylonitrile.

[0102] Specific examples of the (meth)acrylate monomer from which the (meth)acrylate unit is derived are the same as those described in the section ((meth)acrylate-based rubber) of (Elastomer) above, and therefore, the description therein is incorporated by reference and will not be described here.

[0103] The graft portion may contain, as a structural unit, only one type of structural unit derived from one type of monomer selected from the group consisting of the above-mentioned aromatic vinyl monomer, vinyl cyan monomer, and (meth)acrylate monomer, or may contain two or more types of structural units derived from two or more types of monomers in any combination.

[0104] The graft portion preferably contains aromatic vinyl units, vinyl cyan units, and (meth)acrylate units in a total amount of 10% by mass or more and 95% by mass or less, more preferably 30% by mass or more and 92% by mass or less, even more preferably 50% by mass or more and 90% by mass or less, particularly preferably 60% by mass or more and 87% by mass or less, and most preferably 70% by mass or more and 85% by mass or less, based on 100% by mass of all structural units of the graft portion. According to this configuration, the resulting powder coating can provide a coating film with reduced cracking and / or peeling during deformation of the coating film. To particularly exhibit the above-mentioned advantages, the graft portion may contain, as structural units, one or more selected from the group consisting of aromatic vinyl units, vinyl cyan units, and (meth)acrylate units in a total amount of 100% by mass or less, based on 100% by mass of all structural units of the graft portion. In other words, the graft portion may be composed of only one or more structural units selected from the group consisting of aromatic vinyl units, vinylcyan units, and (meth)acrylate units.

[0105] The graft moiety more preferably contains, as a structural unit, one or more selected from the group consisting of methyl (meth)acrylate units, butyl (meth)acrylate units, styrene units, acrylonitrile units, and 2-ethylhexyl (meth)acrylate units, and particularly preferably contains (ii) one or more selected from the group consisting of methyl (meth)acrylate units and butyl (meth)acrylate units. This configuration has the advantage of providing better dispersibility of the polymer particles (B) during powder coating production, resulting in better dispersibility of the polymer particles (B) in the powder coating and coating film.

[0106] The graft portion preferably contains one or more structural units selected from the group consisting of methyl (meth)acrylate units, butyl (meth)acrylate units, styrene units, acrylonitrile units, and 2-ethylhexyl (meth)acrylate units in a total amount of 50% by mass or more and 100% by mass or less, more preferably 60% by mass or more and 100% by mass or less, even more preferably 70% by mass or more and 100% by mass or less, particularly preferably 80% by mass or more and 100% by mass or less, and most preferably 90% by mass or more and 100% by mass or less. This configuration has the advantage of providing even better dispersibility of the polymer particles (B) during powder coating production, resulting in even better dispersibility of the polymer particles (B) in the powder coating and coating film. To particularly exhibit the above-mentioned advantages, the graft portion may contain, as structural units, one or more structural units selected from the group consisting of methyl (meth)acrylate units, butyl (meth)acrylate units, styrene units, acrylonitrile units, and 2-ethylhexyl (meth)acrylate units in a total amount of 100 mass% relative to 100 mass% of all structural units in the graft portion. In other words, the graft portion may be composed of only one or more structural units selected from the group consisting of methyl (meth)acrylate units, butyl (meth)acrylate units, styrene units, acrylonitrile units, and 2-ethylhexyl (meth)acrylate units.

[0107] It is preferable that crosslinking monomers and grafting monomers are substantially not used in the grafting (polymerization) process. In this specification, "substantially not using crosslinking monomers and grafting monomers in the grafting (polymerization) process" means that the total content (amount used) of the crosslinking monomers and grafting monomers is 0.25 parts by mass or less per 100 parts by mass of the monomer mixture used in the grafting (polymerization) process. When crosslinking monomers and grafting monomers are substantially not used in the grafting (polymerization) process, the resulting powder coating has the advantage of being able to provide a coating film with even less cracking and / or peeling during coating film deformation. When crosslinking monomers and grafting monomers are substantially not used in the grafting (polymerization) process, the resulting graft is substantially free of crosslinking units and grafting units. It is preferable that the graft is substantially free of crosslinking units and grafting units as constituent units. In this specification, the phrase "the graft portion is substantially free of crosslinkable units and graftable units" means that the total content of the crosslinkable units and graftable units in the graft portion is 0.25 parts by mass or less per 100 parts by mass of the graft portion. When no crosslinkable monomer or graftable monomer is used in the process of forming (polymerizing) the graft portion, the total amount of the crosslinkable monomer and graftable monomer used is 0 parts by mass, and the total content of the crosslinkable units and graftable units in the graft portion of the obtained polymer particles (B) is 0 parts by mass. In this specification, the phrase "the graft portion is substantially free of crosslinkable units and graftable units" can also be interpreted as "(i) the graft portion is free of crosslinkable units and graftable units, or (ii) the graft portion contains crosslinkable units and / or graftable units, and the total content of the crosslinkable units and graftable units per 100 parts by mass of the graft portion is more than 0 parts by mass and 0.25 parts by mass or less."

[0108] Specific examples of the crosslinkable monomer and the graftable monomer are the same as those described in the section ((meth)acrylate rubber) of (Elastomer) above, and therefore, the description therein is incorporated by reference and the description thereof will be omitted here.

[0109] The glass transition temperature (Tg) of the graft moiety is preferably 0°C or higher, more preferably 10°C or higher, more preferably 20°C or higher, more preferably 30°C or higher, more preferably 40°C or higher, more preferably 50°C or higher, more preferably 60°C or higher, more preferably 70°C or higher, more preferably 80°C or higher, even more preferably 90°C or higher, and particularly preferably 100°C or higher. When the Tg of the graft moiety is within the above-mentioned range, there is an advantage that the dispersibility of the polymer particles (B) in the powder coating and coating film is better. The upper limit of the Tg of the graft moiety is not particularly limited, and is, for example, 150°C.

[0110] In this specification, the Tg of the graft portion is either (a) a value determined by viscoelasticity measurement using a flat plate made of polymer particles (B), or (b) a value calculated by the FOX equation based on the constituent units other than the crosslinkable unit and the graftable unit among the constituent units constituting the graft portion.

[0111] A method for determining the Tg of the graft portion by viscoelasticity measurement using a flat plate made of polymer particles (B) will be described. Viscoelasticity measurement (shear method, measurement frequency: 1 Hz) is performed using a flat plate (thickness: 1 mm) made of polymer particles (B) to obtain a graph of loss tangent (tan δ). The Tg of the graft portion is determined from the peak in the obtained tan δ graph. As described above, if the obtained tan δ graph has one clean peak, the peak temperature can be used as the Tg of the intermediate portion. On the other hand, if the obtained tan δ graph has multiple peaks or a peak with an abnormal shape, the glass transition temperature of the graft portion can be determined by combining the data from the tan δ graph with other analytical data such as composition analysis.

[0112] The Tg of the graft portion can be calculated by the above-mentioned FOX formula (Formula 1) based on the structural units contained in the graft portion, i.e., the monomers used in the production (polymerization) of the graft portion. In the FOX formula for calculating the Tg of the graft portion, Tg １ , Tg ２ , ..., Tgｎ represent the Tg (K) of the homopolymer of the monomer from which the structural units 1, 2, ..., n constituting the graft portion are derived, and w １ , w ２ ,...,w ｎ respectively represent the mass fractions of the structural units 1, 2, . . . , n that constitute the graft portion.

[0113] However, when calculating the Tg of the graft portion using the FOX formula, the crosslinking unit and the grafted unit are not taken into consideration. That is, the Tg of the graft portion is calculated using the mass fraction of the constituent units constituting the graft portion other than the crosslinking unit and the grafted unit, and the Tg of the homopolymer of the monomer from which the constituent units are derived. Therefore, when calculating the Tg of the graft portion using the FOX formula, the "glass transition temperature of the graft portion" can also be said to be the "glass transition temperature of the configuration of the graft portion excluding the crosslinking unit and the grafted unit."

[0114] When the graft portion does not substantially contain a crosslinkable unit or a graftable unit, the influence of the crosslinkable unit and the graftable unit on the Tg of the graft portion is so small that it can be ignored. Therefore, when the graft portion does not substantially contain a crosslinkable unit or a graftable unit, the Tg of the graft portion determined by viscoelasticity measurement using a flat plate made of polymer particles (B) can be considered to be the same as the Tg of the graft portion calculated by the FOX formula based on the constituent units other than the crosslinkable unit and the graftable unit among the constituent units constituting the graft portion.

[0115] The polymer particles (B) preferably contain graft moieties in an amount of 5.0 mass% or more and 60.0 mass% or less, more preferably 7.5 mass% or more and 40.0 mass% or less, even more preferably 10.00 mass% or more and 30.0 mass% or less, and particularly preferably 12.5 mass% or more and 20.0 mass% or less, based on 100 mass% of the polymer particles (B). When the polymer particles (B) contain (a) 5.0 mass% or more of graft moieties based on 100 mass% of the polymer particles (B), the dispersibility of the polymer particles (B) during powder coating preparation is superior, resulting in superior dispersibility of the polymer particles (B) in the powder coating and coating film. When the polymer particles (B) contain (b) 60.0 mass% or less, the resulting powder coating can provide a coating film with further reduced cracking and / or peeling during coating film deformation.

[0116] In this specification, a "reactive monomer having one or more reactive functional groups X selected from the group consisting of an oxetane group, a hydroxyl group, an epoxy group, an amino group, an imide group, a carboxylic acid group, a carboxylic anhydride group, a cyclic ester group, a cyclic amide group, a benzoxazine group, and a cyanate ester group" is also referred to as a "reactive monomer X." In this specification, a "structural unit derived from a reactive monomer X" is also referred to as a "structural unit X."

[0117] It is preferable that reactive monomer X is not substantially used in the production process of polymer particles (B). In this specification, "reactive monomer X is not substantially used in the production process of polymer particles (B)" means that the total content (amount used) of reactive monomer X is 0.25 parts by mass or less per 100 parts by mass of the total amount of the monomer mixture used in the production process of polymer particles (B). When reactive monomer X is not substantially used in the production process of polymer particles (B), the resulting powder coating has the advantage of being able to provide a coating film with even less cracking and / or peeling during coating film deformation. When reactive monomer X is not substantially used in the production process of polymer particles (B), the resulting polymer particles (B) are substantially free of structural units X derived from reactive monomer X. It is preferable that polymer particles (B) are substantially free of structural units X derived from reactive monomer X. In this specification, the phrase "polymer particles (B) are substantially free of structural units X derived from reactive monomer X" means that the total content of structural units X derived from reactive monomer X in polymer particles (B) is 0.25 parts by mass or less per 100 parts by mass of polymer particles (B). When reactive monomer X is not used in the production process of polymer particles (B), the total amount of reactive monomer X used is 0 parts by mass, and the total content of structural units X derived from reactive monomer X in the obtained polymer particles (B) is 0 parts by mass.

[0118] Specific examples of reactive monomers having an oxetane group include (vinyloxyalkyl)alkyloxetane, (meth)acryloyloxyalkyloxetane, and [(meth)acryloyloxyalkyl]alkyloxetane.

[0119] Specific examples of reactive monomers having a hydroxyl group include: (a) hydroxy linear alkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate (particularly preferably, hydroxy linear C1-6 alkyl (meth)acrylates); (b) caprolactone-modified hydroxy (meth)acrylates; (c) hydroxy branched alkyl (meth)acrylates such as α-(hydroxymethyl)methyl acrylate and α-(hydroxymethyl)ethyl acrylate; and (d) hydroxyl group-containing (meth)acrylates such as mono(meth)acrylates of polyester diols (particularly preferably, saturated polyester diols) obtained from divalent carboxylic acids (such as phthalic acid) and dihydric alcohols (such as propylene glycol). Note that "linear C1-6 alkyl" refers to linear alkyls having 1 to 6 carbon atoms.

[0120] Specific examples of the reactive monomer having an epoxy group include glycidyl group-containing vinyl monomers such as glycidyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate glycidyl ether, and allyl glycidyl ether. Among these, as the reactive monomer having an epoxy group, from the viewpoint of reactivity, glycidyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate glycidyl ether are preferred, glycidyl methacrylate and 4-hydroxybutyl acrylate glycidyl ether are more preferred, and glycidyl methacrylate is even more preferred.

[0121] Specific examples of reactive monomers having an amino group include N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate, N,N-diethylaminopropyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylamide, N,N-diethylaminoethyl (meth)acrylamide, N,N-dimethylaminopropyl (meth)acrylamide, N,N-diethylaminopropyl (meth)acrylamide, 2-vinylpyridine, 4-vinylpyridine, and those obtained by reacting these with H ＋ X － and compounds having a structure obtained by neutralizing the compound with an acid represented by the formula:

[0122] Specific examples of the reactive monomer having an imide group include maleimide, phenylmaleimide, N-methylmaleimide, N-ethylmaleimide, N-propylmaleimide, N-isopropylmaleimide, N-butylmaleimide, N-isobutylmaleimide, N-t-butylmaleimide, N-cyclohexylmaleimide, N-chlorophenylmaleimide, N-methylphenylmaleimide, N-bromophenylmaleimide, N-naphthylmaleimide, N-laurylmaleimide, N-hydroxyphenylmaleimide, N-methoxyphenylmaleimide, N-carboxyphenylmaleimide, N-nitrophenylmaleimide, and N-benzylmaleimide.

[0123] Specific examples of reactive monomers having a carboxylic acid group include monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, and dicarboxylic acids such as maleic acid, fumaric acid, and itaconic acid. As the monomer having a carboxylic acid group, monocarboxylic acids are preferably used from the viewpoint of reactivity.

[0124] A specific example of a reactive monomer having a carboxylic acid anhydride group is maleic anhydride.

[0125] In the polymer particles (B), the elastomer, the intermediate portion, and the graft portion may have a layer structure. For example, one embodiment of the present invention is one in which the elastomer is present as the innermost layer, the intermediate portion is present as an intermediate layer, and the graft portion is present as the outermost layer.

[0126] (Volume average particle diameter (Mv) of polymer particles (B)) Since a powder coating having the desired viscosity and high stability can be obtained, the volume average particle diameter (Mv) of the polymer particles (B) is preferably 30 nm or more and 50,000 nm or less, more preferably 50 nm or more and 10,000 nm or less, more preferably 80 nm or more and 5,000 nm or less, more preferably 100 nm or more and 2,500 nm or less, more preferably 100 nm or more and 2,000 nm or less, more preferably 100 nm or more and 1,500 nm or less, more preferably 100 nm or more and 1,000 nm or less, even more preferably 100 nm or more and 750 nm or less, and particularly preferably 100 nm or more and 500 nm or less. When the volume average particle diameter (Mv) of the polymer particles (B) is within the above range, there is also the advantage that the dispersibility of the polymer particles (B) in the powder coating is improved. In this specification, the term "volume average particle diameter (Mv) of polymer particles (B)" refers to the volume average particle diameter of primary particles of polymer particles (B), unless otherwise specified. The volume average particle diameter of polymer particles (B) can be measured using a dynamic light scattering particle size distribution analyzer or the like, using an aqueous latex containing polymer particles (B) as a sample. The volume average particle diameter of polymer particles (B) will be described in detail in the Examples below. The volume average particle diameter of polymer particles (B) can also be measured by cutting a coating film of a powder coating, photographing the cut surface using an electron microscope or the like, and using the obtained photographed data (photographed image).

[0127] (Method for producing polymer particles (B)) Polymer particles (B) can be produced by sequentially carrying out the following steps (A1) to (A3): (A1) polymerizing an elastomer; (A2) polymerizing an intermediate portion in the presence of the obtained elastomer; and (A3) polymerizing a graft portion in the presence of the obtained elastomer and a polymer having an intermediate portion. The polymerization of the graft portion in (A3) is graft polymerization. An example of a method for producing polymer particles (B) (polymerization method) will be described below.

[0128] The polymer particles (B) can be produced by known methods, such as emulsion polymerization, suspension polymerization, and microsuspension polymerization. Specifically, the polymerization of the elastomer, the polymerization of the intermediate portion, and the polymerization of the graft portion (graft polymerization) in the polymer particles (B) can each be carried out by known methods (such as emulsion polymerization, suspension polymerization, and microsuspension polymerization). Among these, emulsion polymerization is particularly preferred as a method for producing the polymer particles (B). The emulsion polymerization method has the advantages of (a) easy compositional design of the polymer particles (B) and (b) easy industrial production of the polymer particles (B). When the polymer particles (B) are obtained by emulsion polymerization, a latex (e.g., aqueous latex) containing the polymer particles (B) can be obtained.

[0129] When emulsion polymerization is employed as the method for producing the polymer particles (B), a known emulsifier (dispersant) can be used for producing the polymer particles (B).

[0130] Examples of emulsifiers include anionic emulsifiers, nonionic emulsifiers, polyvinyl alcohol, alkyl-substituted cellulose, polyvinylpyrrolidone, and polyacrylic acid derivatives. Examples of anionic emulsifiers include sulfur-based emulsifiers, phosphorus-based emulsifiers, sarcosinic acid-based emulsifiers, and carboxylic acid-based emulsifiers. Examples of sulfur-based emulsifiers include sodium dodecylbenzenesulfonate (abbreviated as SDBS). Examples of phosphorus-based emulsifiers include sodium polyoxyethylene lauryl ether phosphate.

[0131] When emulsion polymerization is used as the method for producing the polymer particles (B), a thermally decomposable initiator can be used to produce the polymer particles (B). Examples of the thermally decomposable initiator include known initiators such as (a) 2,2'-azobisisobutyronitrile and (b) peroxides such as organic peroxides and inorganic peroxides. Examples of the organic peroxides include t-butylperoxyisopropyl carbonate, paramenthane hydroperoxide, cumene hydroperoxide, dicumyl peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, and t-hexyl peroxide. Examples of the inorganic peroxides include hydrogen peroxide, potassium persulfate, and ammonium persulfate.

[0132] A redox initiator can also be used to produce the polymer particles (B). The redox initiator is an initiator that combines (a) a peroxide, such as an organic peroxide or an inorganic peroxide, with (b) a transition metal salt, such as iron (II) sulfate, and / or a reducing agent, such as sodium formaldehyde sulfoxylate or glucose. If necessary, a chelating agent, such as disodium ethylenediaminetetraacetate, and if necessary, a phosphorus-containing compound, such as sodium pyrophosphate, may also be used in combination with the transition metal salt and / or reducing agent.

[0133] When a redox initiator is used, polymerization can be carried out even at a low temperature where the peroxide does not substantially decompose thermally, and the polymerization temperature can be set over a wide range. Therefore, it is preferable to use a redox initiator. Among redox initiators, redox initiators using organic peroxides such as cumene hydroperoxide, dicumyl peroxide, paramenthane hydroperoxide, and t-butyl hydroperoxide as the peroxide are preferred. The amount of the initiator used, and when a redox initiator is used, the amounts of the reducing agent, transition metal salt, chelating agent, etc. used can be within known ranges.

[0134] A chain transfer agent may be used in the production of the polymer particles (B). When a chain transfer agent is used, the molecular weight and / or degree of crosslinking of the resulting elastomer, intermediate portion or graft portion can be easily adjusted.

[0135] In addition to the above-mentioned components, a surfactant may be used in the production of the polymer particles (B). The type and amount of the surfactant used are within known ranges.

[0136] In the production of the polymer particles (B), conditions within known numerical ranges can be appropriately applied as the polymerization conditions such as polymerization temperature, pressure, and deoxidation.

[0137] (Content of polymer particles (B)) The content of polymer particles (B) in the present powder coating is not particularly limited. The content of polymer particles (B) in the present powder coating is 0.1 mass% or more and 50.0 mass% or less, preferably 0.1 mass% or more and 30.0 mass% or less, more preferably 0.3 mass% or more and 20.0 mass% or less, even more preferably 0.5 mass% or more and 10.0 mass% or less, and particularly preferably 0.8 mass% or more and 5.0 mass% or less, based on 100 mass% of the powder coating. When the content of polymer particles (B) in the powder coating is (a) 0.1 mass% or more, based on 100 mass% of the powder coating, the powder coating has the advantage of being able to provide a coating film that is reduced in cracking and / or peeling during coating film deformation, and when (b) 50.0 mass% or less, the obtained powder coating has the advantage of being excellent in surface properties.

[0138] 1-3. Pigment (C) In one embodiment of the present invention, the powder coating may or may not contain a pigment (C). In this specification, "pigment (C)" may be referred to as "component (C)".

[0139] The pigment (C) is not particularly limited, but examples thereof include (a) extender pigments with extremely low hiding power, (b) colored pigments (colored pigments), and (c) glitter pigments, which are pigments that impart sparkling properties to a coating film when dispersed in the coating film.

[0140] The extender pigment is not particularly limited, but suitable examples include baryta powder, barium sulfate, barium carbonate, calcium carbonate, gypsum, clay, silica, white carbon, diatomaceous earth, talc, magnesium carbonate, hydrous magnesium silicate, alumina white, gloss white, and mica powder.

[0141] The color pigment is not particularly limited, and known inorganic pigments and known organic pigments can be used. Specific examples of color pigments include white pigments such as titanium dioxide (titanium white), zinc white, white lead, basic lead sulfate, lead sulfate, lithopone, zinc sulfide, and antimony white; black pigments such as carbon black, acetylene black, lamp black, graphite, iron black (black iron oxide), and aniline black; yellow pigments such as naphthol yellow S, Hansa yellow, Pigment yellow L, benzidine yellow, permanent yellow, and iron pyrite (yellow iron oxide); orange pigments such as chrome orange, chrome vermilion, and permanent orange; brown pigments such as iron oxide and umber; red pigments such as red iron oxide, red lead, permanent red, quinacridone red pigments, and diketopyrrolopyrrole red pigments; purple pigments such as cobalt purple, fast violet, and methyl violet lake; blue pigments such as ultramarine, iron blue, cobalt blue, phthalocyanine blue, and indigo; and green pigments such as chrome green, pigment green B, and phthalocyanine green. The color pigments are not limited to these.

[0142] The luster pigment is not particularly limited, but examples thereof include metallic pigments that shine metallically and pearlescent pigments that shine pearlescently. Metallic pigments are preferred as luster pigments. Examples of metallic pigments include aluminum pigments for paints (e.g., aluminum particles, aluminum foil, vapor-deposited aluminum, aluminum oxide, and aluminum oxide coated with at least one of titanium oxide and iron oxide), copper, zinc, brass, nickel, glass flakes, and glass flakes coated with at least one of titanium oxide and iron oxide. Examples of pearlescent pigments include mica powder and mica powder coated with at least one of titanium oxide and iron oxide.

[0143] Furthermore, as the pigment (C), pigments described in "Dictionary of Pigments" edited by Seijiro Ito (published in 2000), "Industrial Organic Pigments" by W. Herbst and K. Hunger, and JP-A Nos. 2002-12607, 2002-188025, 2003-26978, and 2003-342503 can also be used.

[0144] When the present powder coating contains pigment (C), the content of pigment (C) in the powder coating is not particularly limited, but is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, more preferably 1.0% by mass or more, more preferably 5.0% by mass or more, even more preferably 10.0% by mass or more, and particularly preferably 15.0% by mass or more, based on 100% by mass of the powder coating. This configuration has the advantage that the coating film obtained by curing the powder coating has excellent color development. The upper limit of the content of pigment (C) in the powder coating is not particularly limited, but is, for example, 50% by mass or less, based on 100% by mass of the powder coating.

[0145] The present powder coating may not contain pigment (C). When the present powder coating does not contain pigment (C), the powder coating can provide a colorless and transparent coating film or a slightly opaque and transparent coating film.

[0146] <1-4. Curing agent (D)> In one embodiment of the present invention, the powder coating may or may not contain a curing agent (D). In this specification, the "curing agent (D)" may be referred to as the "component (D)".

[0147] The curing agent (D) used in one embodiment of the present invention is not particularly limited, but suitable examples include curing agents that can accelerate the curing of thermosetting resins by heat.

[0148] The curing agent (D) may be appropriately selected depending on the thermosetting resin (A) contained in the powder coating or depending on the type of thermosetting reactive group of the thermosetting resin (A).

[0149] When the thermosetting reactive group of the thermosetting resin (A) is an epoxy group, examples of the curing agent (D) include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, eicosane diacid, maleic acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, trimellitic acid, pyromellitic acid, tetrahydrophthalic acid, hexahydrophthalic acid, cyclohexene-1,2-dicarboxylic acid, trimellitic acid, and pyromellitic acid; anhydrides of these acids; urethane-modified products of these acids; etc. Among these, aliphatic dibasic acids are preferred as the curing agent (D) because they provide excellent coating film properties and storage stability, and dodecanedioic acid is particularly preferred because they provide even more excellent coating film properties.

[0150] When the thermosetting reactive group of the thermosetting resin (A) is a carboxyl group, examples of the curing agent (D) include various epoxy resins (for example, polyglycidyl ether of bisphenol A, etc.); various epoxy group-containing acrylic resins (for example, glycidyl group-containing acrylic resins, etc.); polyglycidyl ethers of various polyhydric alcohols (for example, 1,6-hexanediol, trimethylolpropane, trimethylolethane, etc.); polyglycidyl esters of various polycarboxylic acids (for example, phthalic acid, terephthalic acid, isophthalic acid, hexahydrophthalic acid, methylhexahydrophthalic acid, trimellitic acid, pyromellitic acid, etc.); various alicyclic epoxy group-containing compounds (for example, bis(3,4-epoxycyclohexyl)methyl adipate, etc.); hydroxyamides (for example, triglycidyl isocyanurate, β-hydroxyalkylamide, etc.); and the like.

[0151] When the thermosetting reactive group of the thermosetting resin (A) is a hydroxyl group, examples of the curing agent (D) include polyblock isocyanate and aminoplast. Examples of polyblock polyisocyanates include organic diisocyanates such as various aliphatic diisocyanates (e.g., hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, etc.), various cyclic aliphatic diisocyanates (e.g., xylylene diisocyanate, isophorone diisocyanate, etc.), and various aromatic diisocyanates (e.g., tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, etc.); adducts of these organic diisocyanates with polyhydric alcohols, low-molecular-weight polyester resins (e.g., polyester polyols), water, etc.; polymers of these organic diisocyanates (polymers also containing isocyanurate-type polyisocyanate compounds); polyisocyanate compounds such as isocyanate-biuret compounds blocked with known and commonly used blocking agents; and self-blocked polyisocyanate compounds having uretdione bonds as structural units.

[0152] The curing agent (D) may be used alone or in combination of two or more.

[0153] <1-5. Resin (E)> The present powder coating preferably further contains a resin (E). The resin (E) is preferably contained in the powder of the polymer particles (B) described below. In other words, the powder of the polymer particles (B) preferably contains the resin (E). This configuration has the surprising advantage that the polymer particles (B) have excellent dispersibility in the powder coating.

[0154] Resin (E) may be, for example, a thermosetting resin, a thermoplastic resin, or any combination of a thermosetting resin and a thermoplastic resin.

[0155] (1-5-1. Thermosetting Resin) The thermosetting resin in resin (E) is not particularly limited, but preferably contains at least one selected from the group consisting of epoxy resins, thermosetting (meth)acrylic resins, thermosetting polyester resins, phenolic resins, polyol resins, and amino-formaldehyde resins. Examples of the thermosetting resin in resin (E) include resins containing polymers obtained by polymerizing aromatic polyester raw materials. Resin (E) may contain only one type of thermosetting resin, or two or more types may be used in combination.

[0156] (Epoxy Resin) Specific examples of the epoxy resin are the same as those described in the (Epoxy Resin) section of the section <1-1. Thermosetting Resin (A)> above, and therefore, the description therein is incorporated by reference and will not be described here.

[0157] (Thermosetting (meth)acrylic resin) Specific examples of the thermosetting (meth)acrylic resin are the same as those described in the section (Thermosetting (meth)acrylic resin) in the section <1-1. Thermosetting resin (A)> above, and therefore, the description therein is incorporated by reference and will not be described here.

[0158] (Thermosetting polyester resin) Specific examples of the thermosetting polyester resin are the same as those described in the section (Thermosetting polyester resin) in the section <1-1. Thermosetting resin (A)> above, and therefore the description therein is incorporated by reference and will not be repeated here.

[0159] (Phenol Resin) The phenol resin is not particularly limited as long as it is a compound obtained by reacting a phenol with an aldehyde. The phenol is not particularly limited, but examples thereof include phenol, orthocresol, meta-cresol, para-cresol, xylenol, para-tertiary butylphenol, para-octylphenol, paraphenylphenol, bisphenol A, bisphenol F, and resorcinol. Particularly preferred phenols include phenol and cresol.

[0160] The aldehydes are not particularly limited, but examples thereof include formaldehyde, acetaldehyde, butylaldehyde, acrolein, and mixtures thereof. As the aldehydes, the above-mentioned substances that are sources of aldehydes or solutions of these aldehydes can also be used. As the aldehydes, formaldehyde is preferred because the operation when reacting phenols with aldehydes is easy.

[0161] When reacting phenols with aldehydes, the molar ratio (F / R) of the phenols (P) to the aldehydes (R) (hereinafter also referred to as the reaction molar ratio) is not particularly limited. When an acid catalyst is used in the reaction, the reaction molar ratio (F / R) is preferably 0.4 to 1.0, more preferably 0.5 to 0.8. When an alkali catalyst is used in the reaction, the reaction molar ratio (F / R) is preferably 0.4 to 4.0, more preferably 0.8 to 2.5. When the reaction molar ratio is equal to or greater than the lower limit, the yield does not become too low, and there is no risk of the molecular weight of the resulting phenolic resin becoming small. On the other hand, when the reaction molar ratio is equal to or less than the upper limit, the molecular weight of the phenolic resin does not become too large, and the softening point does not become too high, so sufficient fluidity can be obtained when heated. Furthermore, when the reaction molar ratio is equal to or less than the upper limit, molecular weight control is easy, and there is no risk of gelation or partial gelation occurring due to the reaction conditions.

[0162] (Polyol Resin) A polyol resin is a compound having two or more active hydrogens at its terminals, and is a polyol having two or more functionalities and a molecular weight of about 50 to 20,000. Examples of polyol resins include aliphatic alcohols, aromatic alcohols, polyether polyols, polyester polyols, polyolefin polyols, and acrylic polyols.

[0163] The aliphatic alcohol may be either a dihydric alcohol or a trihydric or higher alcohol (such as a trihydric alcohol or a tetrahydric alcohol). Examples of dihydric alcohols include (a) alkylene glycols (particularly alkylene glycols having about 1 to 6 carbon atoms) such as ethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, and neopentyl glycol, and (b) dehydration condensates of two or more molecules (e.g., about 2 to 6 molecules) of such alkylene glycol compounds (diethylene glycol, dipropylene glycol, tripropylene glycol, etc.). Examples of trihydric alcohols include glycerin, trimethylolpropane, trimethylolethane, and 1,2,6-hexanetriol (particularly trihydric alcohols having about 3 to 10 carbon atoms). Examples of tetrahydric alcohols include pentaerythritol and diglycerin. Further examples include sugars such as monosaccharides, oligosaccharides, and polysaccharides.

[0164] Examples of aromatic alcohols include bisphenols such as bisphenol A and bisphenol F; biphenyls such as dihydroxybiphenyl; polyhydric phenols such as hydroquinone and phenol formaldehyde condensates; and naphthalenediol.

[0165] Examples of polyether polyols include (a) random copolymers or block copolymers obtained by ring-opening polymerization of ethylene oxide, propylene oxide, butylene oxide, styrene oxide, or the like in the presence of one or more active hydrogen-containing initiators, and (b) mixtures of these copolymers. Examples of active hydrogen-containing initiators used in the ring-opening polymerization of polyether polyols include diols such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, and bisphenol A; triols such as trimethylolethane, trimethylolpropane, and glycerin; saccharides such as monosaccharides, oligosaccharides, and polysaccharides; sorbitol; and amines such as ammonia, ethylenediamine, urea, monomethyldiethanolamine, and monoethyldiethanolamine.

[0166] Examples of polyester-type polyols include polymers obtained by polycondensing a polybasic acid and / or anhydride of a polybasic acid with a polyhydric alcohol in the presence of an esterification catalyst at a temperature ranging from 150 to 270°C. Examples of the polybasic acid include maleic acid, fumaric acid, adipic acid, sebacic acid, phthalic acid, dodecanedioic acid, isophthalic acid, and azelaic acid. Examples of the polyhydric alcohol include ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, dipropylene glycol, neopentyl glycol, and 3-methyl-1,5-pentanediol. Examples of polyester-type polyols include (a) ring-opening polymers of ε-caprolactone, valerolactone, and the like, and (b) active hydrogen compounds having two or more active hydrogen atoms, such as polycarbonate diol and castor oil.

[0167] Examples of polyolefin polyols include polybutadiene polyols, polyisoprene polyols, and hydrogenated products thereof.

[0168] Examples of acrylic polyols include (a) copolymers of hydroxyl group-containing monomers such as hydroxyethyl (meth)acrylate, hydroxybutyl (meth)acrylate, and vinylphenol with (b) general-purpose monomers such as n-butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate, and mixtures of such copolymers.

[0169] Among these polyol resins, polyether polyols are preferred because they provide powder coatings with low viscosity and excellent workability, and the powder coatings can provide coating films with an excellent balance between hardness and toughness.Furthermore, among these polyol resins, polyester polyols are preferred because the powder coatings can provide coating films with excellent adhesive properties.

[0170] (Amino-formaldehyde resin) The amino-formaldehyde resin is not particularly limited as long as it is a compound obtained by reacting an amino compound with an aldehyde in the presence of an alkaline catalyst. Examples of the amino compound include melamine; 6-substituted guanamines such as guanamine, acetoguanamine, and benzoguanamine; amine-substituted triazine compounds such as CTU guanamine (3,9-bis[2-(3,5-diamino-2,4,6-triazaphenyl)ethyl]-2,4,8,10-tetraoxaspiro[5,5]undecane) and CMTU guanamine (3,9-bis[(3,5-diamino-2,4,6-triazaphenyl)methyl]-2,4,8,10-tetraoxaspiro[5,5]undecane); and ureas such as urea, thiourea, and ethylene urea. Examples of the amino compound that can be used include (a) substituted melamine compounds in which hydrogen atoms on the amino groups of melamine are substituted with alkyl groups, alkenyl groups, and / or phenyl groups (as described in U.S. Pat. No. 5,998,573 (corresponding Japanese Patent Publication No. JP-A-9-143238)), and (b) substituted melamine compounds in which hydrogen atoms on the amino groups of melamine are substituted with hydroxyalkyl groups, hydroxyalkyloxyalkyl groups, and / or aminoalkyl groups (as described in U.S. Pat. No. 5,322,915 (corresponding Japanese Patent Publication No. JP-A-5-202157)). Among the above-mentioned compounds, polyfunctional amino compounds such as melamine, guanamine, acetoguanamine, and benzoguanamine are preferred, as they are industrially produced and inexpensive, with melamine being particularly preferred. The above-mentioned amino compounds may be used alone or in combination of two or more. In addition to these amino compounds, (a) phenols such as phenol, cresol, alkylphenol, resorcinol, hydroquinone, and pyrogallol, and (b) aniline may also be used.

[0171] Examples of the aldehydes include formaldehyde, paraformaldehyde, acetaldehyde, benzaldehyde, and furfural. Formaldehyde and paraformaldehyde are preferred as the aldehydes because they are inexpensive and have good reactivity with the amino compounds listed above. In producing the amino-formaldehyde resin, the aldehydes are preferably used in an amount of 1.1 to 6.0 moles, and particularly preferably 1.2 to 4.0 moles, per mole of the amino compound, per available aldehyde group.

[0172] (Aromatic polyester raw material) Examples of aromatic polyester raw materials include radical polymerizable monomers such as aromatic vinyl compounds, (meth)acrylic acid derivatives, vinyl cyanide compounds, and maleimide compounds, dimethyl terephthalate, and alkylene glycol. In this specification, (meth)acrylic acid means acrylic acid and / or methacrylic acid.

[0173] The thermosetting resin in resin (E) is a compound obtained by bonding an ethylenically unsaturated monomer to a compound having a reactive group (e.g., an epoxy group, an oxetane group, a hydroxyl group, an amino group, an imide group, a carboxylic acid group, a carboxylic anhydride group, a cyclic ester, a cyclic amide, a benzoxazine group, a cyanate ester group, etc.) by a method other than radical polymerization, and also includes a compound having at least one ethylenically unsaturated bond in the molecule. In this specification, a "compound obtained by bonding an ethylenically unsaturated monomer to a compound having a reactive group by a method other than radical polymerization" is sometimes referred to as a "reactive group-ethylenically unsaturated bond-containing monomer." The thermosetting resin in resin (E) also includes a reactive group-ethylenically unsaturated bond-containing monomer.

[0174] The compound having a reactive group also includes thermosetting resins such as the above-mentioned epoxy resins, phenol resins, polyol resins, amino-formaldehyde resins, and resins containing polymers obtained by polymerizing aromatic polyester raw materials. The reactive group-ethylenically unsaturated bond-containing monomer may be a compound obtained by bonding an ethylenically unsaturated monomer to one or more selected from the group consisting of epoxy resins, phenol resins, polyol resins, amino-formaldehyde resins, and polymers obtained by polymerizing aromatic polyester raw materials by a method other than radical polymerization.

[0175] Examples of the reactive group-ethylenically unsaturated bond-containing monomer include unsaturated polyester resins, vinyl ester resins, epoxy acrylates, etc. These may be used alone or in combination of two or more.

[0176] (1-5-2. Thermoplastic Resin) Examples of the thermoplastic resin in the resin (E) include thermoplastic (meth)acrylic resins, vinyl copolymers, polycarbonates, polyamides, thermoplastic polyesters, polyphenylene ethers, polyurethanes, polyvinyl acetates, etc. These may be used alone or in combination of two or more.

[0177] The thermoplastic (meth)acrylic resin is a (meth)acrylic resin that does not have a thermosetting reactive group. The thermoplastic (meth)acrylic resin contains at least a (meth)acrylic unit that does not have a thermosetting reactive group. The (meth)acrylic unit that does not have a thermosetting reactive group contained in the thermoplastic (meth)acrylic resin preferably has 1 to 20 carbon atoms in the portion other than the (meth)acryloyl group. The thermoplastic (meth)acrylic resin may be a homopolymer of a (meth)acrylic monomer that does not have a thermosetting reactive group. The thermoplastic (meth)acrylic resin may be a copolymer (hereinafter also referred to as a thermoplastic (meth)acrylic copolymer) of (a) a (meth)acrylic monomer that does not have a thermosetting reactive group and (b) (b-1) a monomer such as an unsaturated fatty acid, an acrylamide monomer, a maleimide monomer, or vinyl acetate that does not have a thermosetting reactive group, or (b-2) a vinyl copolymer that does not have a thermosetting reactive group. The thermoplastic (meth)acrylic resin preferably contains the largest amount (by mole) of (meth)acrylic units that do not have a thermosetting reactive group in total among all the constituent units.

[0178] Specific examples of the (meth)acrylic monomer having no thermosetting reactive group are the same as those described in the section (thermosetting (meth)acrylic resin) in the section <1-1. Thermosetting resin (A)> above, and therefore, the description therein is incorporated by reference and will not be described here.

[0179] In the thermoplastic acrylic copolymer, "structural units derived from (meth)acrylic monomers that do not have a thermosetting reactive group" are referred to as "structural units (a)." In the thermoplastic acrylic copolymer, "structural units derived from monomers such as unsaturated fatty acids, acrylamide monomers, maleimide monomers, and vinyl acetate that do not have a thermosetting reactive group, and structural units derived from vinyl copolymers that do not have a thermosetting reactive group" are referred to as "structural units (b)." In the thermoplastic acrylic copolymer, it is preferable that, out of a total of 100% by mass of the structural units (a) and (b), the structural units (a) account for 50% to 100% by mass, and the structural units (b) account for 0% to 50% by mass.

[0180] The thermoplastic (meth)acrylic resin preferably contains 50% by mass or more of structural units derived from butyl acrylate (BA), more preferably 60% by mass or more, even more preferably 70% by mass or more, particularly preferably 80% by mass or more, and most preferably 90% by mass or more.

[0181] The vinyl copolymer is obtained by copolymerizing a mixture of vinyl monomers containing at least one selected from the group consisting of an aromatic vinyl monomer, a cyanide vinyl monomer, and an unsaturated carboxylic acid alkyl ester monomer. The vinyl monomer mixture may further contain another monomer (hereinafter also referred to as "monomer C") copolymerizable with the above-mentioned monomer.

[0182] Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, t-butylstyrene, and vinyltoluene. These vinyl monomers may be used alone or in combination of two or more. Among these, aromatic vinyl monomers are preferred, and styrene is more preferred, from the viewpoint of easily increasing the refractive index.

[0183] The unsaturated carboxylic acid alkyl ester monomer is not particularly limited. For example, an ester of an alcohol having 1 to 6 carbon atoms with acrylic acid or methacrylic acid is preferred. The ester of an alcohol having 1 to 6 carbon atoms with acrylic acid or methacrylic acid may further have a substituent such as a hydroxyl group or a halogen group.

[0184] Examples of esters of C1 to C6 alcohols with acrylic acid or methacrylic acid include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, n-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, chloromethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2,3,4,5,6-pentahydroxyhexyl (meth)acrylate, 2,3,4,5-tetrahydroxypentyl (meth)acrylate, etc. These may be used alone or in combination of two or more.

[0185] Examples of vinyl cyanide monomers include acrylonitrile, methacrylonitrile, ethacrylonitrile, etc. These may be used alone or in combination of two or more.

[0186] Monomer C is a vinyl monomer other than the aromatic vinyl monomers, unsaturated carboxylic acid alkyl ester monomers, and vinyl cyanide monomers, and is not particularly limited as long as it does not impair the effects of the present invention. Specific examples of monomer C include unsaturated fatty acids, acrylamide monomers, maleimide monomers, vinyl acetate, and (meth)acrylic acid ester monomers. These may be used alone or in combination of two or more.

[0187] The unsaturated fatty acid may be selected from, for example, itaconic acid, maleic acid, fumaric acid, butenoic acid, acrylic acid, methacrylic acid, and the like.

[0188] The acrylamide monomer may be selected from, for example, acrylamide, methacrylamide, N-methylacrylamide, and the like.

[0189] The maleimide monomer may be selected from, for example, N-methylmaleimide, N-ethylmaleimide, N-isopropylmaleimide, N-butylmaleimide, N-hexylmaleimide, N-octylmaleimide, N-dodecylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, and the like.

[0190] The method for producing the vinyl copolymer is not particularly limited, but examples thereof include emulsion polymerization, suspension polymerization, bulk polymerization, and solution polymerization.

[0191] In the method for producing a vinyl copolymer, a polymerization initiator may be used as needed. The polymerization initiator may be, for example, one or more appropriately selected from the group consisting of peroxides, azo compounds, potassium persulfate, etc. The amount of the polymerization initiator to be added is not particularly limited.

[0192] Examples of peroxides include benzoyl peroxide, cumene hydroperoxide, dicumyl peroxide, diisopropylbenzene hydroperoxide, t-butyl hydroperoxide, t-butyl peroxyacetate, t-butyl peroxybenzoate, t-butyl isopropyl carbonate, di-t-butyl peroxide, t-butyl peroctate, 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, and t-butylperoxy-2-ethylhexanoate. Of these, cumene hydroperoxide, 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, and 1,1-bis(t-butylperoxy)cyclohexane are particularly preferred.

[0193] Examples of azo compounds include azobisisobutyronitrile, azobis(2,4-dimethylvaleronitrile), 2-phenylazo-2,4-dimethyl-4-methoxyvaleronitrile, 2-cyano-2-propylazoformamide, 1,1'-azobiscyclohexane-1-carbonitrile, azobis(4-methoxy-2,4-dimethylvaleronitrile), dimethyl 2,2'-azobisisobutyrate, 1-t-butylazo-2-cyanobutane, and 2-t-butylazo-2-cyano-4-methoxy-4-methylpentane. Of these, 1,1'-azobiscyclohexane-1-carbonitrile is particularly preferred.

[0194] Specific examples of vinyl copolymers include polyvinyl chloride, chlorinated polyvinyl chloride, polystyrene, styrene-acrylonitrile copolymer, styrene-acrylonitrile-N-phenylmaleimide copolymer, α-methylstyrene-acrylonitrile copolymer, polymethyl methacrylate, methyl methacrylate-styrene copolymer, etc. These may be used alone or in combination of two or more.

[0195] Examples of thermoplastic polyesters include polyethylene terephthalate and polybutylene terephthalate.

[0196] The resin (E) may be the same resin as the thermosetting resin (A) (a resin having the same composition), or may be a resin different from the thermosetting resin (A). In the powder coating, it is preferable that the thermosetting resin (A) and the resin (E) are not phase-separated. The resin (E) is preferably a resin that is compatible with the thermosetting resin (A).

[0197] When the resin (E) is the same as the thermosetting resin (A) described below, there is an advantage that the resin (E) does not affect the various physical properties of the powder coating material or coating film containing the obtained powder particles.

[0198] As an example, consider the case where resin (E) is the same type of resin as thermosetting resin (A). In this case, it is impossible to distinguish between thermosetting resin (A) and resin (E) in powder paint. Therefore, from the outside, the powder paint appears to contain (a) thermosetting resin (A) but not resin (E), or (b) resin (E) but not thermosetting resin (A). Next, consider the case where resin (E) is a different type of resin from thermosetting resin (A). In this case, it is possible to distinguish between thermosetting resin (A) and resin (E) in powder paint. In this case, the powder paint may contain thermosetting resin (A) and resin (E) as a resin other than thermosetting resin (A).

[0199] (1-5-3. Others) In this specification, fats and oils and fatty acid esters are also included in resin (E). Resin (E) preferably contains fats and oils, and more preferably consists of fats and oils. Examples of fats and oils that can be suitably used as resin (E) include epoxidized fats and oils such as epoxidized soybean oil and epoxidized linseed oil. These resins may be used alone or in combination of two or more. Resin (E) preferably contains epoxidized soybean oil, and more preferably consists of epoxidized soybean oil. Commercially available epoxidized soybean oils can also be used, and examples include Adekaiser O-130P manufactured by ADEKA Corporation. Examples of fatty acid esters that can be suitably used as resin (E) include epoxidized fatty acid esters such as epoxidized fatty acid butyl, epoxidized fatty acid 2-ethylhexyl, epoxidized fatty acid octyl ester, and epoxidized fatty acid alkyl ester.

[0200] Epoxidized fats and oils and epoxidized fatty acid esters are sometimes referred to as epoxy plasticizers. That is, in this specification, epoxy plasticizers are also included in resin (E). Examples of epoxy plasticizers other than epoxidized fats and oils and epoxidized fatty acid esters include diepoxystearyl epoxyhexahydrophthalate and di-2-ethylhexyl epoxyhexahydrophthalate.

[0201] The above-mentioned thermosetting resins, thermoplastic resins, mixtures of thermosetting and thermoplastic resins, oils and fats, and fatty acid esters can each be used in combination with an antioxidant. In this specification, the antioxidant is considered to be part of resin (E) only when used in combination with each of the above-mentioned substances. When the antioxidant is used alone, it is not considered to be resin (E). The case where the antioxidant is used alone instead of resin (E) will be described. Because the antioxidant is a component that does not contribute to crosslinking, the physical properties of the coating film obtained by curing the powder coating tend to be inferior. For example, the Tg of the coating film may decrease or the impact resistance may be poor.

[0202] The antioxidant is not particularly limited and examples thereof include (a) primary antioxidants such as phenol-based antioxidants, amine-based antioxidants, lactone-based antioxidants, and hydroxylamine-based antioxidants, and (b) secondary antioxidants such as sulfur-based antioxidants and phosphorus-based antioxidants.

[0203] The phenol-based antioxidant may be a hindered phenol-based antioxidant. Examples of the hindered phenol-based antioxidant include compounds having a hindered phenol structure or a mono-hindered phenol structure in the molecule. Commercially available phenol-based antioxidants may also be used, such as Irganox 245 manufactured by BASF Japan Ltd.

[0204] The amine-based antioxidant is not particularly limited, and a wide variety of conventionally known amine-based antioxidants can be used. Specific examples of the amine-ketone compounds include 2,2,4-trimethyl-1,2-dihydroquinoline polymers, 6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline, and reaction products of diphenylamine and acetone.

[0205] The amine antioxidants also include aromatic amine compounds, such as naphthylamine antioxidants, diphenylamine antioxidants, and p-phenylenediamine antioxidants.

[0206] The lactone-based antioxidant, the hydroxylamine-based antioxidant, and the sulfur-based antioxidant are not particularly limited, and a wide variety of conventionally known antioxidants can be used.

[0207] The phosphorus-based antioxidant is not particularly limited, and a wide variety of conventionally known antioxidants can be used. Phosphoric acid and phosphate esters containing active hydrogen can adversely affect the storage stability of powder coatings and the heat resistance of coating films provided by the powder coatings. Therefore, preferred phosphorus-based antioxidants are alkyl phosphites, aryl phosphites, alkylaryl phosphite compounds, and the like, which do not contain phosphoric acid or phosphate esters in their molecules.

[0208] Other conventionally known substances may also be used as the antioxidant, including various substances described in "Antioxidant Handbook" published by Taiseisha (first edition published on October 25, 1976) and "Polymer Additives Handbook" published by CMC Publishing (edited by Toru Haruna, first edition published on November 7, 2010).

[0209] Resin (E) is preferably one or more selected from the group consisting of thermosetting resins, mixtures of thermosetting resins and antioxidants, thermoplastic resins, mixtures of thermoplastic resins and antioxidants, oils and fats, mixtures of oils and antioxidants, fatty acid esters, mixtures of fatty acid esters and antioxidants, epoxy plasticizers, and mixtures of epoxy plasticizers and antioxidants, more preferably one or more selected from the group consisting of epoxy resins, acrylic polymers, mixtures of epoxy resins and antioxidants, mixtures of acrylic polymers and antioxidants, epoxy plasticizers, and mixtures of epoxy plasticizers and antioxidants, still more preferably one or more selected from the group consisting of mixtures of epoxy resins and antioxidants, mixtures of acrylic polymers and antioxidants, and mixtures of epoxy plasticizers and antioxidants, and particularly preferably a mixture of epoxy plasticizers and antioxidants. According to this configuration, (a) the powder coating has the advantages of being able to provide a coating film with excellent heat resistance and improving the dispersibility of polymer particles (B) in the powder coating.

[0210] (1-5-4. Physical Properties of Resin (E)) Resin (E) is preferably a liquid, semi-solid, or solid having a viscosity of 100 mPa·s to 1,000,000 mPa·s at 25° C. Note that "resin (E) has a viscosity of 100 mPa·s to 1,000,000 mPa·s at 25° C." means "resin (E) at 25° C. has a viscosity of 100 mPa·s to 1,000,000 mPa·s."

[0211] When resin (E) is a liquid, the viscosity of resin (E) at 25°C is preferably 750,000 mPa·s or less, more preferably 700,000 mPa·s or less, more preferably 500,000 mPa·s or less, more preferably 350,000 mPa·s or less, more preferably 300,000 mPa·s or less, more preferably 250,000 mPa·s or less, more preferably 100,000 mPa·s or less, more preferably 75,000 mPa·s or less, more preferably 50,000 mPa·s or less, more preferably 30,000 mPa·s or less, more preferably 25,000 mPa·s or less, even more preferably 20,000 mPa·s or less, and particularly preferably 15,000 mPa·s or less. According to the above-mentioned configuration, the resin (E) has an advantage of being excellent in fluidity.

[0212] When the resin (E) is a liquid, the viscosity of the resin (E) at 25°C is more preferably 100 mPa·s or more, more preferably 200 mPa·s or more, more preferably 300 mPa·s or more, more preferably 400 mPa·s or more, more preferably 500 mPa·s or more, even more preferably 750 mPa·s or more, even more preferably 1000 mPa·s or more, and particularly preferably 1500 mPa·s or more. According to this configuration, the resin (E) does not impregnate the polymer particles (B). Therefore, the resin (E) can prevent the polymer particles (B) from fusing together.

[0213] When resin (E) is a liquid, the viscosity of resin (E) at 25°C is more preferably 100 mPa·s to 750,000 mPa·s, more preferably 100 mPa·s to 700,000 mPa·s, more preferably 100 mPa·s to 350,000 mPa·s, more preferably 100 mPa·s to 300,000 mPa·s, more preferably 100 mPa·s to 50,000 mPa·s, even more preferably 100 mPa·s to 30,000 mPa·s, and particularly preferably 100 mPa·s to 15,000 mPa·s.

[0214] When resin (E) is semi-solid at 25° C., resin (E) can also be said to be semi-liquid at 25° C., and resin (E) can also be said to have a viscosity of greater than 1,000,000 mPa s at 25° C. When resin (E) is semi-solid or solid at 25° C., the resulting composition has the advantage of being less sticky and easier to handle.

[0215] The viscosity of the resin (E) can be measured using a viscometer. The method for measuring the viscosity of the resin (E) will be described in detail in the following examples.

[0216] Resin (E) is preferably a resin having an endothermic peak of 25°C or less in a differential scanning calorimetry (DSC) thermogram, more preferably a resin having an endothermic peak of 0°C or less.

[0217] <1-6. Additives> The powder coating may contain other optional components (additives) in addition to the components described above, as necessary. Examples of other optional components (additives) include various additives used in powder coatings. Specific examples of other optional components (additives) include defoamers, antifoaming agents, leveling agents, silicone compounds, waxes, surface conditioners (silicone oil, acrylic oligomers, etc.), antifoaming (popping) agents (e.g., benzoin, benzoin derivatives, etc.), curing accelerators (amine compounds, imidazole compounds, cationic polymerization catalysts, etc.), plasticizers, charge control agents, antioxidants, ultraviolet absorbers, light stabilizers, pigment dispersants, magnetic powders, flame retardants, flow imparting agents, flow control agents, and flow extenders.

[0218] <1-7. Method for producing powder coating> The powder coating can be produced by mixing the above-mentioned components. For example, the powder coating can be produced by mixing a powder containing the polymer particles (B) and optionally the resin (E) with the components other than the polymer particles (B) (or commercially available products containing the components) (for example, the thermosetting resin (A)).

[0219] A method for producing a powder coating according to one embodiment of the present invention may be configured as follows: A method for producing a powder coating, comprising the steps of preparing a powder containing polymer particles (B), and mixing the powder with a thermosetting resin (A) to prepare a powder coating, wherein the polymer particles (B) have an elastomer, an intermediate portion, and a graft portion, the elastomer comprises a (meth)acrylate rubber, the intermediate portion includes, as structural units, crosslinkable units and graftable units in a total amount of 16.0 parts by mass or more per 100 parts by mass of the intermediate portion, and the graft portion includes, as structural units, one or more structural units selected from the group consisting of aromatic vinyl units, vinyl cyan units, and (meth)acrylate units, and the content of the polymer particles (B) in the powder coating is 0.1 part by mass or more and 50.0 parts by mass or less per 100 parts by mass of the thermosetting resin (A).

[0220] In the method for producing a powder coating according to one embodiment of the present invention, the powder or granules may further contain a resin (E). That is, a method for producing a powder coating according to one embodiment of the present invention may be configured as follows: A method for producing a powder coating, comprising the steps of preparing a powder containing polymer particles (B) and a resin (E), and mixing the powder with a thermosetting resin (A) to prepare a powder coating, wherein the polymer particles (B) have an elastomer, an intermediate portion, and a graft portion, wherein the elastomer contains a (meth)acrylate rubber, wherein the intermediate portion contains, as structural units, crosslinkable units and graftable units in a total amount of 16.0 parts by mass or more per 100 parts by mass of the intermediate portion, and the graft portion contains, as structural units, one or more structural units selected from the group consisting of aromatic vinyl units, vinyl cyan units, and (meth)acrylate units, and wherein the content of the polymer particles (B) in the powder coating is 0.1 part by mass or more and 50.0 parts by mass or less per 100 parts by mass of the thermosetting resin (A).

[0221] (Powder) A powder containing polymer particles (B) can be obtained by drying an aggregate of polymer particles (B). Therefore, "powder containing polymer particles (B)" can also be called "secondary particles of polymer particles (B)". It is preferable that the powder containing polymer particles (B) further contains a resin (E). A powder containing polymer particles (B) and a resin (E) can be obtained by drying an aggregate containing polymer particles (B) and a resin (E).

[0222] As used herein, the term "granular material" refers to both powder and granules, and refers to an aggregate of powder, granules, etc. Furthermore, when specifically distinguishing between the two, "powder" refers to a material having a volume average particle diameter of 0.01 mm or more and 0.1 mm or less, and "granules" refers to a material having a volume average particle diameter of more than 0.1 mm and 10 mm or less. That is, the volume average particle diameter of a granular material is, for example, 0.01 mm or more and 10 mm or less. However, the granular material may contain coarse particles of 10 mm or more. The "volume average particle diameter" of a granular material in the range of less than 10 μm can be measured using a dynamic light scattering (DLS) particle size distribution analyzer Nanotrac Wave II-EX150 (manufactured by Microtrack Bell Co., Ltd.). The "volume average particle diameter" of a granular material in the range of 10 μm or more can be measured using a laser diffraction particle size distribution analyzer Microtrac MT3000II (manufactured by Microtrack Bell Co., Ltd.). The volume average particle diameter of the secondary particles of the powder or granules, i.e., the polymer particles (B), is preferably greater than 10 μm (0.01 mm). This configuration has the advantage that the polymer particles (B) have better dispersibility during the preparation of the powder coating, and as a result, the polymer particles (B) have better dispersibility in the powder coating and the coating film.

[0223] (Method for producing powder or granule (step of preparing powder or granule)) In one embodiment of the present invention, the method for producing powder or granule containing polymer particles (B) (step of preparing powder or granule) is not particularly limited. The method for producing powder or granule containing polymer particles (B) may include an aggregation step of preparing aggregates containing polymer particles (B) and a drying step of drying the aggregates.

[0224] In a preferred embodiment of the present invention, the powder or granule contains polymer particles (B) and resin (E). In a preferred embodiment of the present invention, a method for producing a powder or granule containing polymer particles (B) and resin (E) (a step of preparing a powder or granule) may include an aggregation step of preparing aggregates containing polymer particles (B) and resin (E), and a drying step of drying the aggregates.

[0225] (Aggregation Step) The aggregation step is not particularly limited as long as it can ultimately obtain aggregates containing polymer particles (B). In the aggregation step, it is preferable to ultimately obtain aggregates containing polymer particles (B) and resin (E). In the aggregation step, for example, an aqueous latex containing polymer particles (B) obtained by emulsion polymerization and optionally resin (E) is used. The method for aggregating the polymer particles (B) or the polymer particles (B) and resin (E) using the aqueous latex containing polymer particles (B) and optionally resin (E) is not particularly limited. Examples of such methods include known methods such as a method using a coagulant, a method using a solvent, and a method of spraying an aqueous latex. Here, the "mixture containing aggregates containing polymer particles (B) and optionally resin (E) and an aqueous solvent" obtained by aggregating the polymer particles (B) and optionally resin (E) in the aqueous latex is also referred to as a slurry.

[0226] Examples of methods for obtaining an aqueous latex containing the polymer particles (B) and the resin (E) include (i) a method of adding the resin (E) to a reaction solution during the polymerization process of the polymer particles (B), (ii) a method of adding the resin (E) to an aqueous latex of the polymer particles (B), and (iii) a method of polymerizing the resin (E) in the aqueous latex of the polymer particles (B).

[0227] The aggregation step preferably employs a method using a coagulant. The coagulant is not particularly limited as long as it has the property of aggregating (also referred to as coagulation or solidification) the polymer particles (B) in the aqueous latex by contacting the aqueous latex containing the polymer particles (B) and, optionally, the resin (E). Examples of the coagulant include an aqueous solution of an inorganic salt (e.g., calcium chloride), an aqueous solution of an inorganic acid, an aqueous solution of an organic salt, an aqueous solution of an organic acid, and a polymer coagulant.

[0228] The polymer particles (B) can be aggregated by contacting an aqueous latex containing the polymer particles (B) with a coagulant or a solution of the coagulant (e.g., an aqueous solution). For example, by mixing an aqueous latex containing the polymer particles (B) with an aqueous solution of the coagulant, the polymer particles (B) can be aggregated in the resulting mixture. As a result, aggregates containing the polymer particles (B) can be obtained. Furthermore, by contacting an aqueous latex containing the polymer particles (B) and the resin (E) with a coagulant or a solution of the coagulant (e.g., an aqueous solution), (i) both the polymer particles (B) and the resin (E) can be aggregated, or (ii) the polymer particles (B) can be aggregated while incorporating the resin (E). For example, by mixing an aqueous latex containing the polymer particles (B) and the resin (E) with an aqueous solution of the coagulant, (i) both the polymer particles (B) and the resin (E) can be aggregated in the resulting mixture, or (ii) the polymer particles (B) can be aggregated while incorporating the resin (E). As a result, an aggregate containing the polymer particles (B) and the resin (E) can be obtained.

[0229] Before mixing the aqueous latex containing the polymer particles (B) and optionally the resin (E) with the aqueous coagulant solution, the aqueous latex containing the polymer particles (B) and optionally the resin (E) may be preheated, the aqueous coagulant solution may be preheated, or both the aqueous latex containing the polymer particles (B) and optionally the resin (E) and the aqueous coagulant solution may be preheated. The mixed liquid obtained by mixing the aqueous latex containing the polymer particles (B) and optionally the resin (E) with the aqueous coagulant solution may also be heated.

[0230] The agglomeration step may further include a recovery step of recovering the resulting agglomerates, i.e., agglomerates containing the polymer particles (B) and optionally the resin (E), from the slurry.

[0231] The recovery step is not particularly limited as long as it can separate the aqueous solvent of the slurry from the aggregates, and any known method can be used. Examples of the recovery step include a method of filtering the slurry and a method of centrifugal dehydration of the slurry.

[0232] (Drying Step) The drying step is a step of drying the aggregates containing the polymer particles (B) and optionally the resin (E) obtained in the above-described aggregation step. The method for drying the aggregates is not particularly limited, and known methods can be used. For example, the aggregates can be dried by leaving them in a dryer set at a certain temperature (drying temperature).

[0233] The ambient temperature during the drying step (i.e., drying temperature) is not particularly limited. Since the resulting powder can provide a powder coating material having superior dispersibility to the polymer particles (B), the drying temperature is preferably 40° C. or higher and 100° C. or lower, more preferably 40° C. or higher and 80° C. or lower, and even more preferably 40° C. or higher and 60° C. or lower.

[0234] The time for the drying step is not particularly limited and can be appropriately set depending on the drying temperature, the degree of drying of the aggregate, etc. The drying time may be, for example, 1 minute or more and 24 hours or less, 1 minute or more and 12 hours or less, or 1 minute or more and 6 hours or less.

[0235] A washing step of washing the aggregates obtained in the aggregation step may be further included between the aggregation step and the drying step. When a recovery step is performed, the washing step can be performed between the recovery step and the drying step. By washing the aggregates, powder or granules with a low content of impurities and the like can be obtained. In the washing step, it is more preferable to wash the aggregates with water, and even more preferable to wash them with ion-exchanged water or pure water.

[0236] The case where the powder further contains a resin (E) in addition to the polymer particles (B) will be described. In this case, it is preferable that the polymer particles (B) account for 50% by mass or more and 99% by mass or less, and the resin (E) account for 1% by mass or more and 50% by mass or less, based on a total of 100% by mass of the polymer particles (B) and the resin (E). The amount of resin (E) in the powder can be appropriately set within the above-mentioned numerical range depending on the type of resin (E) and the physical properties of the resin (E) (solid, semi-solid, liquid, viscosity, etc.). When the resin (E) is liquid at 25°C and the content of the resin (E) in the powder is within the above-mentioned range, there is an advantage that the fluidity (smoothness) of the powder is not deteriorated.

[0237] When the powder further contains a resin (E) in addition to the polymer particles (B), the respective amounts of the polymer particles (B) and the resin (E) in the powder will be explained from the viewpoint of excellent blocking resistance. In the powder, the total amount of the polymer particles (B) and the resin (E) is 100% by mass, and more preferably the polymer particles (B) is 55% by mass or more and 99% by mass or less, and the resin (E) is 1% by mass or more and 45% by mass or less, more preferably the polymer particles (B) is 60% by mass or more and 99% by mass or less, and the resin (E) is 1% by mass or more and 40% by mass or less, more preferably the polymer particles (B) is 65% by mass or more and 99% by mass or less, and the resin (E) is 1% by mass or more and 35% by mass or less, more preferably the polymer particles (B) is 70% by mass or more and 99% by mass or less, and the resin (E) is 1% by mass or more and 30% by mass or less, and the polymer particles (B) is 75% by mass or more. It is more preferable that the polymer particles (B) are 80% by mass or more and 99% by mass or less and the resin (E) is 1% by mass or more and 25% by mass or less, it is more preferable that the polymer particles (B) are 80% by mass or more and 99% by mass or less and the resin (E) is 1% by mass or more and 20% by mass or less, it is even more preferable that the polymer particles (B) are 85% by mass or more and 99% by mass or less and the resin (E) is 1% by mass or more and 15% by mass or less, it is even more preferable that the polymer particles (B) are 90% by mass or more and 99% by mass or less and the resin (E) is 1% by mass or more and 10% by mass or less, it is particularly preferable that the polymer particles (B) are 95% by mass or more and 99% by mass or less and the resin (E) is 1% by mass or more and 5% by mass or less.

[0238] When the powder further contains a resin (E) in addition to the polymer particles (B), the respective amounts of the polymer particles (B) and the resin (E) in the powder will be explained from the viewpoint of improving the dispersibility of the polymer particles (B) in the powder coating. In the powder, the total of the polymer particles (B) and the resin (E) is 100% by mass, and it is preferable that the polymer particles (B) are 50% by mass or more and 97% by mass or less, and the resin (E) is 3% by mass or more and 50% by mass or less, more preferably that the polymer particles (B) are 50% by mass or more and 95% by mass or less, and the resin (E) is 5% by mass or more and 50% by mass or less, more preferably that the polymer particles (B) are 50% by mass or more and 92% by mass or less, and the resin (E) is 8% by mass or more and 50% by mass or less, more preferably that the polymer particles (B) are 50% by mass or more and 90% by mass or less, and the resin (E) is 10% by mass or more and 50% by mass or less, and it is more preferable ...8% by mass or less. It is more preferred that the polymer particles (B) are 50% by mass or more and 85% by mass or less and the resin (E) is 15% by mass or more and 50% by mass or less, it is even more preferred that the polymer particles (B) are 50% by mass or more and 82% by mass or less and the resin (E) is 18% by mass or more and 50% by mass or less, it is even more preferred that the polymer particles (B) are 50% by mass or more and 80% by mass or less and the resin (E) is 20% by mass or more and 50% by mass or less, it is particularly preferred that the polymer particles (B) are 60% by mass or more and 80% by mass or less and the resin (E) is 20% by mass or more and 40% by mass or less.

[0239] As described above, when (i) a thermosetting resin, a thermoplastic resin, a mixture of a thermosetting resin and a thermoplastic resin, a fat or oil, or a fatty acid ester is mixed with (ii) an antioxidant, the antioxidant is considered to be part of resin (E). Therefore, for example, when a mixture of a fat or oil (e.g., epoxidized soybean oil) and an antioxidant (e.g., Irganox 245) is used, the content of the mixture is the content of resin (E).

[0240] (Step of Preparing Powder Coating) In the step of preparing a powder coating, the specific method for mixing the powder containing polymer particles (B) and optionally resin (E), the thermosetting resin (A), and optionally other components other than the thermosetting resin (A), polymer particles (B), and resin (E) is not particularly limited, and known methods can be appropriately adopted. Mixing the powder containing polymer particles (B) and optionally resin (E), the thermosetting resin (A), and optionally other components other than the thermosetting resin (A), polymer particles (B), and resin (E) is, for example, dry mixing. Various mixers such as a Henschel mixer, a Banbury mixer, a high-speed mixer, or a Nauta mixer can be used in this dry mixing. The mixture thus obtained containing at least the thermosetting resin (A) and polymer particles (B) (or the mixture containing the thermosetting resin (A), polymer particles (B), and optionally resin (E)) may be used as a powder coating.

[0241] In the production of a powder coating, the mixture containing the thermosetting resin (A), polymer particles (B), and optionally the resin (E) obtained by the above-mentioned method may be further melt-kneaded (B1), cooled (B2), and pulverized (B3). The pulverized product containing the thermosetting resin (A), polymer particles (B), and optionally the resin (E) obtained by the above-mentioned method may be used as a powder coating.

[0242] In the above (B1), a heating roller, a heating kneader, an extruder, or the like can be used as the device for melt-kneading the mixture.

[0243] The melt-kneading temperature of (B1) is not particularly limited and is, for example, a temperature equal to or higher than the softening point of the thermosetting resin (A). The melt-kneading temperature of (B1) is, for example, 50°C or higher and 140°C or lower, preferably 50°C or higher and 130°C or lower, more preferably 60°C or higher and 110°C or lower, and even more preferably 80°C or higher and 130°C or lower.

[0244] In (B2), for example, the melt-kneaded product obtained in (B1) is cooled to 50° C. or less. Any method can be used to cool the melt-kneaded product, and examples of the method include leaving it at room temperature, using a cooling roll, or using a cooling conveyor.

[0245] In (B3), the pulverizer used to pulverize the cooled product obtained in (B2) is not particularly limited. The pulverizer may be a mechanical pulverizer or an airflow pulverizer. For example, an impact pulverizer such as a hammer mill or a pin mill can be used. Furthermore, the pulverization of the cooled product in (B3) may be carried out, for example, in two steps: coarse pulverization and fine pulverization.

[0246] The pulverized product containing the thermosetting resin (A), the polymer particles (B), and optionally the resin (E) obtained by steps (B1) to (B3) may be further classified to obtain a desired particle size. The classifier is not particularly limited, and a sieve (vibrating sieve), an air current classifier, or the like may be used.

[0247] The weight average particle size of the powder coating is not particularly limited, but is preferably 10 μm or more and 100 μm or less, and more preferably 20 μm or more and 80 μm or less.

[0248] With regard to the method for producing a powder coating material according to one embodiment of the present invention, the above descriptions (e.g., the descriptions in the sections <1-1. Thermosetting resin (A)> to <1-5. Resin (E)>) are used as appropriate for aspects (matters) other than those detailed in the section <1-6. Method for producing powder coating material> (e.g., aspects related to the thermosetting resin (A) and the polymer particles (B)).

[0249] <1-8. Uses> The powder coating material according to one embodiment of the present invention can be used to paint any substance (substrate). The powder coating material according to one embodiment of the present invention can be particularly suitably used to paint the metal exteriors of various devices, automobile parts, and automobile bodies.

[0250] [2. Coating Film] The coating film according to one embodiment of the present invention is preferably obtained by curing the powder coating described in [1. Powder Coating]. According to this configuration, the coating film has the advantage of being less susceptible to cracking and / or peeling during deformation.

[0251] The substrate to which the powder coating is applied is not particularly limited, and examples thereof include metals such as iron, zinc, tin, stainless steel, copper, and aluminum, and inorganic materials such as glass. The substrate is preferably one having thermal resistance, and metals are particularly preferred. The substrate may be subjected to a surface treatment such as plast treatment, iron phosphate, or zinc phosphate before application of the powder coating. The substrate may be subjected to a primer coating and / or an intermediate coating before application of the powder coating.

[0252] The method for applying the powder coating to the substrate is not particularly limited, and examples thereof include common coating methods such as electrostatic coating, electrostatic powder spraying, fluidized bed dipping, and electrostatic fluidized bed dipping.

[0253] The thickness of the applied powder coating is not particularly limited, but may be, for example, 15 μm or more and 1 mm or less, or 30 μm or more and 300 μm or less.

[0254] By heating the powder coating applied to the substrate, the powder coating can be cured to obtain a coating film.

[0255] The curing temperature is not particularly limited, but is preferably equal to or higher than the melting point of the thermosetting resin (A). Examples of the curing temperature include 100°C or higher and 280°C or lower, 130°C or higher and 250°C or lower, or 120°C or higher and 250°C or lower.

[0256] The curing time is not particularly limited, and may be, for example, 5 minutes or more and 60 minutes or less.

[0257] An embodiment of the present invention may include the following configuration.

[0258] [1] A powder coating comprising a thermosetting resin (A) and polymer particles (B), the polymer particles (B) having an elastomer, an intermediate portion, and a graft portion, the elastomer containing a (meth)acrylate rubber, the intermediate portion containing, as structural units, crosslinkable units and graftable units in a total amount of 16.0 parts by mass or more per 100 parts by mass of the intermediate portion, the graft portion containing, as structural units, one or more structural units selected from the group consisting of aromatic vinyl units, vinyl cyan units, and (meth)acrylate units, and the content of the polymer particles (B) is 0.1 part by mass or more and 50.0 parts by mass or less per 100 parts by mass of the thermosetting resin (A).

[0259] [2] The powder coating according to [1], wherein the polymer particles (B) are substantially free of structural units X derived from a reactive monomer X having one or more reactive functional groups X selected from the group consisting of an oxetane group, a hydroxyl group, an epoxy group, an amino group, an imide group, a carboxylic acid group, a carboxylic anhydride group, a cyclic ester group, a cyclic amide group, a benzoxazine group, and a cyanate ester group.

[0260] [3] The powder coating material according to [1] or [2], wherein the volume average particle diameter of the elastic body is 100 nm or more.

[0261] [4] The powder coating material according to any one of [1] to [3], wherein the elastomer contains a crosslinkable unit and / or a graftable unit as a constituent unit, and the elastomer contains the crosslinkable unit and the graftable unit in a total amount of more than 0 parts by mass and not more than 1.2 parts by mass per 100 parts by mass of the elastomer.

[0262] [5] The powder coating material according to any one of [1] to [4], wherein the graft portion does not substantially contain a crosslinkable unit or a graftable unit as a constituent unit.

[0263] [6] The powder coating material according to any one of [1] to [5], wherein the glass transition temperature of the elastic body is less than 0°C.

[0264] [7] The powder coating material according to any one of [1] to [6], wherein the glass transition temperature of the intermediate portion is 0°C or higher.

[0265] [8] The powder coating material according to any one of [1] to [7], wherein the polymer particles (B) contain the intermediate portion in an amount of 0.5 mass% or more and 5.0 mass% or less based on 100 mass% of the polymer particles (B).

[0266] [9] The powder coating material according to any one of [1] to [8], wherein the glass transition temperature of the graft portion is 0°C or higher.

[0267]

[10] The powder coating material according to any one of [1] to [9], wherein the intermediate portion is composed only of crosslinkable units and / or graftable units.

[0268]

[11] The powder coating material according to any one of [1] to

[10] , further comprising a resin (E).

[0269]

[12] A coating film obtained by curing the powder coating material according to any one of [1] to

[11] .

[0270]

[13] A method for producing a powder coating, comprising the steps of preparing a powder containing polymer particles (B) and mixing the powder with a thermosetting resin (A) to prepare a powder coating, wherein the polymer particles (B) have an elastomer, an intermediate portion, and a graft portion, the elastomer contains a (meth)acrylate rubber, the intermediate portion contains, as structural units, crosslinkable units and graftable units in a total amount of 16.0 parts by mass or more per 100 parts by mass of the intermediate portion, and the graft portion contains, as structural units, one or more structural units selected from the group consisting of aromatic vinyl units, vinyl cyan units, and (meth)acrylate units, and the content of the polymer particles (B) in the powder coating is 0.1 part by mass or more and 50.0 parts by mass or less per 100 parts by mass of the thermosetting resin (A).

[0271]

[14] The method for producing a powder coating material according to

[13] , wherein the powder or granule further contains a resin (E).

[0272]

[15] The method for producing a powder coating according to

[14] , wherein the step of preparing the powder or granule comprises an aggregating step of preparing aggregates containing the polymer particles (B) and the resin (E), and a drying step of drying the aggregates, wherein the resin (E) is a liquid, semi-solid, or solid having a viscosity of 100 mPa·s to 1,000,000 mPa·s at 25°C, and wherein, in the powder or granule, the polymer particles (B) account for 50% by mass or more and 99% by mass or less, and the resin (E) accounts for 1% by mass or more and 50% by mass or less, based on a total of 100% by mass of the polymer particles (B) and the resin (E).

[0273] Hereinafter, one embodiment of the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these. One embodiment of the present invention can be practiced with appropriate modifications within the scope of the above-mentioned or below-mentioned gist, and all such modifications are included in the technical scope of the present invention.

[0274] [Measurement and Evaluation Methods] (Volume Average Particle Diameter of Elastomer and Polymer Particles (B)) The volume average particle diameter (Mv) of the elastomer and polymer particles (B) dispersed in the aqueous latex was measured using a Nanotrac Wave II-EX150 (manufactured by Microtrackbell Co., Ltd.). Aqueous latex of the elastomer and polymer particles (B) diluted with deionized water was used as the measurement sample. The measurement was performed by inputting the refractive index of water and each polymer particle, adjusting the sample concentration so that the measurement time was 120 seconds, and the loading index was within the range of 1 or more and 10 or less.

[0275] (Method of Measuring (Calculating) Glass Transition Temperature) The glass transition temperatures of the elastic body, intermediate portion and graft portion were calculated by the above-mentioned FOX formula.

[0276] The Tg of the homopolymers is as follows: methyl methacrylate (MMA): 105°C, styrene (St): 80°C, butyl acrylate (BA): -54°C, ethyl acrylate (EA): -22°C, hydroxyethyl methacrylate: 55°C.

[0277] (Method for Evaluating Cupping Resistance) Test pieces (coated panels) obtained using the powder coatings obtained in the Examples and Comparative Examples were evaluated for flexibility (cupping resistance) in accordance with JIS K 5600-5-2 (cupping resistance test). Specifically, the test pieces were extruded from the backside of the coated surface using a cupping tester with a 20 mm diameter punch, while varying (gradually increasing) the extrusion height. The extrusion height (mm) just before cracks appeared in the coating film was evaluated as flexibility (cupping resistance). The results are shown in Table 1.

[0278] (Method for Evaluating Appearance Beauty) The appearance beauty of test pieces (coated panels) obtained using the powder coatings obtained in the Examples and Comparative Examples was evaluated. Specifically, a randomly selected 10 cm x 10 cm area on the coated surface (coating film) of the test piece was visually observed, and the number of bumps (protrusions and raised areas) present within the area was counted. The results obtained were evaluated for appearance beauty of the coating film based on the following evaluation criteria. The results are shown in Table 1. S (Very Excellent): Zero bumps present within the area (in other words, no bumps present within the area) A (Excellent): One to two bumps present within the area B (Good): Three to five bumps present within the area C (Poor): Six or more bumps present within the area

[0279] 1. Formation of Elastic Body (Production Example 1-1: Preparation of Aqueous Latex (R-1)) 182 parts by mass of deionized water, 0.006 parts by mass of EDTA, 0.0015 parts by mass of ferrous sulfate heptahydrate, 0.2 parts by mass of SFS, and 0.02 parts by mass of sodium dodecylbenzenesulfonate (SDBS) were charged into a glass reactor. The glass reactor was equipped with a thermometer, a stirrer, a reflux condenser, a nitrogen inlet, and a monomer and emulsifier addition device. The charged raw materials were stirred at 50°C while the gas in the glass reactor was replaced with nitrogen (i.e., in a nitrogen stream). Next, a mixture of 82.2 parts by mass of butyl acrylate (BA), 0.42 parts by mass of allyl methacrylate (ALMA), and 0.021 parts by mass of t-butyl hydroperoxide was continuously added dropwise to the glass reactor over 175 minutes. After the addition of the mixture was completed, the mixture in the glass reactor was stirred for an additional 0.5 hour to complete the polymerization. By the above operations, an aqueous latex (R-1) of an elastic material was obtained. The volume average particle diameter of the obtained elastic material was measured by the method described above and found to be 302 nm. The glass transition temperature of the obtained elastic material was measured by the method described above and found to be -54°C.

[0280] (Production Example 1-2: Preparation of Aqueous Latex (R-2)) 182 parts by mass of deionized water, 0.006 parts by mass of EDTA, 0.0015 parts by mass of ferrous sulfate heptahydrate, 0.2 parts by mass of SFS, and 0.02 parts by mass of SDBS were charged into a glass reactor. The glass reactor was equipped with a thermometer, a stirrer, a reflux condenser, a nitrogen inlet, and a monomer and emulsifier addition device. The charged raw materials were stirred at 50°C while the gas in the glass reactor was replaced with nitrogen (i.e., in a nitrogen stream). Next, a mixture of 82.2 parts by mass of butyl acrylate (BA), 1.75 parts by mass of 1,4-butylene glycol diacrylate, 3.5 parts by mass of allyl methacrylate (ALMA), and 0.021 parts by mass of t-butyl hydroperoxide was continuously added dropwise to the glass reactor over 175 minutes. After the addition of the mixture was completed, the mixture in the glass reactor was stirred for an additional 0.5 hour to complete the polymerization. By the above operations, an aqueous latex of an elastomer (R-2) was obtained. The volume average particle diameter of the obtained elastomer was measured by the method described above and found to be 307 nm. The glass transition temperature of the obtained elastomer was measured by the method described above and found to be -54°C.

[0281] <2. Formation of Intermediate Portion> (Production Example 2-1: Preparation of Aqueous Latex (M-1)) Following the formation of the elastomer in Production Example 1-1, the following operation was carried out using the glass reactor (containing 82.62 parts of aqueous latex (R-1)) used after the production of aqueous latex (R-1). A mixture of 2.3 parts by mass of methyl methacrylate (MMA), 0.5 parts by mass of allyl methacrylate (ALMA), and 0.4 parts by mass of t-butyl hydroperoxide was continuously added dropwise to the glass reactor over a period of 15 minutes. After the addition of the mixture was completed, the mixture in the glass reactor was stirred for an additional 0.5 hours to complete the polymerization. Through the above operation, an aqueous latex (M-1) of polymer particles having an elastomer and intermediate portions was obtained. In the production of the intermediate portions of the polymer particles of aqueous latex (M-1), MMA and ALMA were used as the grafting monomer. Therefore, the Tg of the intermediate part of the polymer particle of the aqueous latex (M-1), in other words, the glass transition temperature of the structure excluding the crosslinkable unit and the graftable unit, is 105°C, which is the same as the Tg value of the MMA homopolymer, according to the above-mentioned FOX equation.

[0282] (Production Example 2-2: Preparation of Aqueous Latex (M-2)) Following the formation of the elastomer in Production Example 1-1, the following operation was carried out using the glass reactor (containing 82.62 parts of aqueous latex (R-1)) used after the production of aqueous latex (R-1). A mixture of 2.3 parts by mass of styrene (St), 0.5 parts by mass of allyl methacrylate (ALMA), and 0.4 parts by mass of t-butyl hydroperoxide was continuously added dropwise to the glass reactor over a period of 15 minutes. After the addition of the mixture was completed, stirring of the mixture in the glass reactor was continued for an additional 0.5 hour to complete the polymerization. By the above operation, an aqueous latex (M-2) of polymer particles having an elastomer and a middle portion was obtained.

[0283] (Production Example 2-3: Preparation of Aqueous Latex (M-3)) Following the formation of the elastomer in Production Example 1-1, the following operation was carried out using the glass reactor (containing 82.62 parts of aqueous latex (R-1)) used after the production of aqueous latex (R-1). A mixture of 1.8 parts by mass of styrene (St), 1.0 part by mass of allyl methacrylate (ALMA), and 0.4 parts by mass of t-butyl hydroperoxide was continuously added dropwise to the glass reactor over a period of 15 minutes. After the addition of the mixture was completed, stirring of the mixture in the glass reactor was continued for an additional 0.5 hour to complete the polymerization. By the above operation, an aqueous latex (M-3) of polymer particles having an elastomer and a middle portion was obtained.

[0284] (Production Example 2-4: Preparation of Aqueous Latex (M-4)) Following the formation of the elastomer in Production Example 1-1, the following operation was carried out using the glass reactor (containing 82.62 parts of aqueous latex (R-1)) used after the production of aqueous latex (R-1). A mixture of 1.3 parts by mass of styrene (St), 1.5 parts by mass of allyl methacrylate (ALMA), and 0.4 parts by mass of t-butyl hydroperoxide was continuously added dropwise to the glass reactor over a period of 15 minutes. After the addition of the mixture was completed, stirring of the mixture in the glass reactor was continued for an additional 0.5 hour to complete the polymerization. By the above operation, an aqueous latex (M-4) of polymer particles having an elastomer and a middle portion was obtained.

[0285] (Production Example 2-5: Preparation of Aqueous Latex (M-5)) Following the formation of the elastomer in Production Example 1-1, the following operation was carried out using the glass reactor (containing 82.62 parts of aqueous latex (R-1)) used after the production of aqueous latex (R-1). A mixture of 0.8 parts by mass of styrene (St), 2.0 parts by mass of allyl methacrylate (ALMA), and 0.4 parts by mass of t-butyl hydroperoxide was continuously added dropwise to the glass reactor over a period of 15 minutes. After the addition of the mixture was completed, stirring of the mixture in the glass reactor was continued for an additional 0.5 hour to complete the polymerization. By the above operation, an aqueous latex (M-5) of polymer particles having an elastomer and a middle portion was obtained.

[0286] In the production of the intermediate part of the polymer particles of the aqueous latexes (M-2) to (M-5), St and ALMA were used as the grafting monomer. Therefore, the Tg of the intermediate part of the polymer particles of the aqueous latexes (M-2) to (M-5), in other words, the glass transition temperature of the structure excluding the crosslinking unit and the grafting unit, is 80°C, which is the same as the Tg value of the homopolymer of St, according to the above-mentioned FOX equation.

[0287] (Production Example 2-6: Preparation of Aqueous Latex (M-6)) Following the formation of the elastomer in Production Example 1-1, the following operation was carried out using the glass reactor (containing 82.62 parts of aqueous latex (R-1)) used after producing the aqueous latex (R-1). A mixture of 2.0 parts by mass of allyl methacrylate (ALMA) and 0.4 parts by mass of t-butyl hydroperoxide was continuously added dropwise to the glass reactor over a period of 15 minutes. After the addition of the mixture was completed, stirring of the mixture in the glass reactor was continued for an additional 0.5 hour to complete the polymerization. By the above operation, an aqueous latex (M-6) of polymer particles having an elastomer and a middle portion was obtained.

[0288] 3. Preparation of Polymer Particles (Formation of Graft Portion) (Production Example 3-1: Preparation of Aqueous Latex (L-1) of Polymer Particles) Following the formation of the intermediate portion in Production Example 2-1, the following operation was carried out using the glass reactor (containing 85.7 parts of aqueous latex (M-1)) used after the production of aqueous latex (M-1). A mixture of 13.5 parts by mass of methyl methacrylate (MMA), 1.5 parts by mass of butyl acrylate (BA), and 0.01 parts by mass of t-butyl hydroperoxide was continuously added dropwise to the glass reactor over a period of 60 minutes. After the addition of the mixture was completed, stirring of the mixture in the glass reactor was continued for an additional 0.5 hour to complete the polymerization. Through the above operations, an aqueous latex (L-1) of polymer particles having an elastomer, an intermediate portion, and a graft portion was obtained. No reactive monomer X was used in the production process of the obtained polymer particles. Therefore, the obtained polymer particles do not contain the structural unit X and can be said to be polymer particles (B) in one embodiment of the present invention.

[0289] (Production Examples 3-2 to 3-6: Preparation of Aqueous Latexes (L-2) to (L-6) of Polymer Particles) Aqueous latexes (L-2) to (L-6) of polymer particles having an elastomer, an intermediate portion, and a graft portion were obtained by the same method (operation) as in Production Example 3-1, except for the following points: The glass reactors used to produce the aqueous latexes (M-2) to (M-6) were used instead of the glass reactor used to produce the aqueous latex (M-1).

[0290] In the process of producing the aqueous latexes (L-1) to (L-6) (specifically, the process of forming the graft portion), no crosslinkable monomer or graftable monomer is used. Therefore, the graft portion of the polymer particles contained in the obtained aqueous latexes (L-1) to (L-6) does not contain a crosslinkable unit or a graftable unit.

[0291] In the production process of the aqueous latexes (L-1) to (L-6), the reactive monomer X is not used. Therefore, the polymer particles contained in the obtained aqueous latexes (L-1) to (L-6) do not contain the structural unit X, and can be said to be polymer particles (B) in one embodiment of the present invention.

[0292] The Tg of the graft portion of the polymer particles (B) of the aqueous latexes (L-1) to (L-6), in other words, the glass transition temperature of the structure excluding the crosslinkable unit and the graftable unit, is 79.4°C according to the above-mentioned FOX equation.

[0293] (Production Example 3-7: Preparation of Aqueous Latex (L-7) of Polymer Particles) Following the formation of the elastomer in Production Example 1-2, the following operation was carried out using the glass reactor (containing 85.7 parts of aqueous latex (R-2)) used after the production of aqueous latex (R-2). A mixture of 14.6 parts by mass of methyl methacrylate (MMA), 1.78 parts by mass of ethyl acrylate (EA), 0.18 parts by mass of 1,4-butylene glycol diacrylate, 1.2 parts by mass of hydroxyethyl methacrylate, and 0.01 parts by mass of t-butyl hydroperoxide was continuously added dropwise to the glass reactor over a period of 60 minutes. After the addition of the mixture was completed, stirring of the mixture in the glass reactor was continued for an additional 0.5 hour to complete the polymerization. Through the above operation, an aqueous latex (L-7) of polymer particles having an elastomer and a graft moiety was obtained. In the production process of the obtained polymer particles, specifically in the process of forming the graft portion, hydroxyethyl methacrylate was used as the reactive monomer X. The obtained polymer particles contained 1.5 parts by mass of hydroxyethyl methacrylate units as the structural unit X per 100 parts by mass of the polymer particles.

[0294] The Tg of the graft portion of the polymer particles (B) of the aqueous latex (L-7), in other words, the glass transition temperature of the structure excluding the crosslinkable unit and the graftable unit, is 83.1°C according to the above-mentioned FOX equation.

[0295] The volume average particle diameter of the polymer particles contained in each of the aqueous polymer particle latexes (L-1) to (L-7) was measured by the method described above. The results are shown in Table 1.

[0296] <3. Preparation of Granular Material> (Preparation of Granular Material (P-1)) 4 parts by mass of calcium chloride was dissolved in 600 parts by mass of ion-exchanged water adjusted to 50°C. Next, 280 parts by mass of aqueous latex (L-1) corresponding to 100 parts by mass of polymer particles (B) was added to the 600 parts by mass of the ion-exchanged water to obtain a slurry containing a coagulated product of polymer particles (B). Next, the slurry was centrifuged to obtain a wet powder of the coagulated product. Furthermore, using the obtained wet powder, a total of two cycles were repeated: an operation of adding the wet powder to 500 parts by mass of ion-exchanged water; and an operation of centrifuging the obtained mixture to obtain a wet powder. Finally, the wet powder was dried in a dryer at 50°C for 48 hours to obtain a powder (P-1).

[0297] (Preparation of Powder and Granules (P-2) to (P-7)) Powder and granules (P-2) to (P-7) were obtained in the same manner as in the above section (Preparation of Powder and Granule (P-1)), except that the aqueous latexes (L-2) to (L-7) were used instead of the aqueous latex (L-1).

[0298] (Preparation of powder (P-8)) (i) water, (ii) 50 parts by mass of epoxidized soybean oil (manufactured by ADEKA Corporation, Adeka Cizer O-130P) as resin (E) and 50 parts by mass of triethylene glycol bis [3- (-t-butyl-4-hydroxy-5-methylphenyl) propionate] (Irganox 245, manufactured by BASF Japan Co., Ltd.) as antioxidant, and (iii) SDBS as emulsifier, by mixing together using a homogenizer, an aqueous emulsion (S-1) (a mixture of resin (E) (epoxidized soybean oil and Irganox 245) content of 50%) was prepared in which the resin (E) was emulsified. 4 parts by mass of calcium chloride was dissolved, and 600 parts by mass of ion-exchanged water adjusted to 50 ° C. was prepared. Next, 280 parts by mass of aqueous latex (L-1), which corresponds to 100 parts by mass of polymer particles (B), and 22.2 parts by mass of the aqueous emulsion (S-1) (corresponding to 11.1 parts by mass of resin (E) (a mixture of epoxidized soybean oil and Irganox 245)) were mixed. Subsequently, the resulting mixture was poured into 600 parts by mass of the ion-exchanged water to obtain a slurry containing a coagulum containing polymer particles (B) and resin (E). Next, the slurry was centrifuged to obtain a wet powder, which was the coagulum. Furthermore, using the obtained wet powder, a total of two cycles were repeated: an operation of pouring the wet powder into 500 parts by mass of ion-exchanged water; and an operation of centrifuging the resulting mixture to obtain a wet powder. Finally, the wet powder was dried in a dryer at 50 ° C. for 48 hours to obtain a powder (P-8) containing polymer particles (B) and resin (E). In the powder (P-8), the polymer particles (B) accounted for 90 mass% and the resin (E) accounted for 10 mass% of the total of the polymer particles (B) and the resin (E), which was 100 mass%.

[0299] (Preparation of Powder (P-9)) Powder (P-9) was obtained in the same manner as described in the section (Preparation of Powder (P-8)) above, except that the aqueous latex (L-1) was replaced with the aqueous latex (L-2). In the powder (P-9), the polymer particles (B) accounted for 90 mass% and the resin (E) accounted for 10 mass% of the total of the polymer particles (B) and the resin (E).

[0300] 4. Preparation of Powder Coatings In the following examples and comparative examples, a polyester resin having a hydroxyl group as a thermosetting reactive group (hydroxyl group-containing polyester resin, GV-500 manufactured by U-Pica Corporation) was used as the thermosetting resin (A), a blocked isocyanate (VESTAGON B-1530 manufactured by EVONIK Corporation) was used as the curing agent (D), and titanium oxide (CR-95 manufactured by Ishihara Sangyo Kaisha) was used as the pigment (D).

[0301] (Example 1: Preparation of powder coating material (C-1)) 66 parts by mass of thermosetting resin (A), 1 part by mass of powder (P-1), 12 parts by mass of curing agent (D), 20 parts by mass of pigment (D), 0.5 parts by mass of defoaming agent, and 0.5 parts by mass of leveling agent were mixed. Next, the obtained mixture was melt-kneaded using an extruder, cooled, and then finely pulverized. Subsequently, the obtained finely pulverized product was sieved through a sieve with 150 μm openings to obtain powder coating material (C-1).

[0302] (Examples 2 to 6: Preparation of Powder Coatings (C-2) to (C-6)) Powder coatings (C-2) to (P-6) were obtained in the same manner as in Example 1, except that powder (P-1) was replaced with powder (P-2) to (P-6), respectively.

[0303] (Examples 7 to 8: Preparation of Powder Coatings (C-8) to (C-9)) Powder coatings (C-8) to (P-9) were obtained in the same manner as in Example 1, except that powder (P-8) to (P-9) were used instead of powder (P-1).

[0304] Comparative Example 1: Preparation of powder coating material (C-7) A powder coating material (C-7) was obtained in the same manner as in Example 1, except that the powder (P-7) was used instead of the powder (P-1).

[0305] 5. Application of Powder Coating and Production of Coating Film The powder coatings obtained in each Example and Comparative Example were applied (painted) to a zinc phosphate conversion-treated steel plate (0.7 × 70 × 150 mm) to a film thickness of 60 μm. The steel plate was then heated at a substrate temperature of 190°C for 30 minutes to bake and harden the powder coating onto the steel plate, forming a coating film, thereby producing a test specimen (coated plate). The resulting test specimens were evaluated for cupping resistance and appearance aesthetics using the methods described above. The results are shown in Table 1.

[0306] According to one embodiment of the present invention, a powder coating can be provided that can provide a coating film with reduced cracking and / or peeling during deformation, and therefore, one embodiment of the present invention can be particularly suitably used in the fields of painting metal exteriors, automobile parts, and automobile bodies.

Claims

1. A powder coating comprising a thermosetting resin (A) and polymer particles (B), wherein the polymer particles (B) have an elastomer, an intermediate portion, and a graft portion, the elastomer comprises a (meth)acrylate rubber, the intermediate portion comprises, as structural units, crosslinkable units and graftable units in a total amount of 16.0 parts by mass or more per 100 parts by mass of the intermediate portion, the graft portion comprises, as structural units, one or more structural units selected from the group consisting of aromatic vinyl units, vinyl cyan units, and (meth)acrylate units, and the content of the polymer particles (B) is 0.1 part by mass or more and 50.0 parts by mass or less per 100 parts by mass of the thermosetting resin (A).

2. The powder coating according to claim 1, wherein the polymer particles (B) are substantially free of structural units X derived from a reactive monomer X having one or more reactive functional groups X selected from the group consisting of oxetane groups, hydroxyl groups, epoxy groups, amino groups, imide groups, carboxylic acid groups, carboxylic anhydride groups, cyclic ester groups, cyclic amide groups, benzoxazine groups, and cyanate ester groups.

3. The powder coating according to claim 1, wherein the volume average particle size of the elastic body is 100 nm or more.

4. The powder coating material according to claim 1, wherein the elastomer contains crosslinkable units and / or graftable units as constituent units, and the elastomer contains a total of more than 0 parts by mass and not more than 1.2 parts by mass of the crosslinkable units and graftable units per 100 parts by mass of the elastomer.

5. The powder coating material according to claim 1, wherein the graft portion is substantially free of crosslinkable units and graftable units as constituent units.

6. The powder coating material according to claim 1, wherein the glass transition temperature of the elastomer is less than 0°C.

7. The powder coating material according to claim 1, wherein the glass transition temperature of the intermediate portion is 0°C or higher.

8. The powder coating material according to claim 1, wherein the polymer particles (B) contain the intermediate portion in an amount of 0.5 mass % or more and 5.0 mass % or less based on 100 mass % of the polymer particles (B).

9. The powder coating material according to claim 1, wherein the glass transition temperature of the grafted portion is 0°C or higher.

10. The powder coating material according to claim 1, wherein the intermediate portion is composed solely of crosslinkable units and / or graftable units.

11. The powder coating composition according to claim 1, further comprising a resin (E).

12. A coating film obtained by curing the powder coating material according to any one of claims 1 to 11.

13. A method for producing a powder coating, comprising the steps of preparing a powder containing polymer particles (B); and mixing the powder with a thermosetting resin (A) to prepare a powder coating, wherein the polymer particles (B) have an elastomer, an intermediate portion, and a graft portion, the elastomer contains a (meth)acrylate rubber, the intermediate portion contains, as structural units, crosslinkable units and graftable units in a total amount of 16.0 parts by mass or more per 100 parts by mass of the intermediate portion, and the graft portion contains, as structural units, one or more structural units selected from the group consisting of aromatic vinyl units, vinyl cyan units, and (meth)acrylate units, and the content of the polymer particles (B) in the powder coating is 0.1 part by mass or more and 50.0 parts by mass or less per 100 parts by mass of the thermosetting resin (A).

14. The method for producing a powder coating according to claim 13, wherein the powder further contains a resin (E).

15. A method for producing a powder coating according to claim 14, wherein the step of preparing the powder or granule comprises: an aggregating step of preparing aggregates containing the polymer particles (B) and the resin (E); and a drying step of drying the aggregates, wherein the resin (E) is a liquid, semi-solid, or solid having a viscosity of 100 mPa·s to 1,000,000 mPa·s at 25°C, and wherein in the powder or granule, the polymer particles (B) account for 50 mass% or more and 99 mass% or less, and the resin (E) accounts for 1 mass% or more and 50 mass% or less, of a total of 100 mass% of the polymer particles (B) and the resin (E).

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