Powder coating composition

Abstract

To provide a powder coating composition that can form a coating film that exhibits high dielectric breakdown strength even in thin films, while also possessing high edge coverage and excellent smoothness. [Solution] A powder coating composition comprising a polyester resin (A) containing acidic groups at its terminals and having an acid value of 10 to 100 mg KOH / g, an epoxy resin (B), and a metal oxyhydroxide (C) containing at least one metal selected from the group consisting of aluminum, manganese, iron, nickel, cobalt, and vanadium.

Description

Technical Field

[0001] The present invention relates to a powder coating composition.

Background Art

[0002] In fields such as electrical equipment and electronic equipment, electrical insulating materials are widely used. Electrical insulating materials generally have a base material such as a conductor and an insulating film. The insulating film is formed by an electrical insulating paint composition containing an organic resin such as a synthetic resin or a natural resin.

[0003] Powder coating compositions do not contain organic solvents, are easy to recover, and have a low environmental impact. Therefore, powder coating compositions are widely used for coating household appliances, automotive parts, steel furniture, etc., and are also used for the above electrical insulation applications.

[0004] For example, Patent Document 1 discloses an epoxy resin powder coating for forming a cured product, which contains the following (A), (B), (C), and (D). (A) A bisphenol A type epoxy resin having an epoxy equivalent of 450 to 630 g / eq, (B) a novolak type epoxy resin, (C) a filler having an average particle size D50 of 5 to 12 μm, (D) a curing agent. When the total amount of the epoxy resin is 100 parts by mass, 65 to 85 parts by mass of the above (C) is contained.

[0005] Patent Document 2 discloses an epoxy resin powder coating for forming a cured product, which contains (A): a bisphenol type epoxy resin having an epoxy equivalent of 670 to 1200 g / eq, (B): a rubber-modified epoxy resin, (C): a bisphenol type phenol resin curing agent, (D): a curing accelerator. (D) contains the following (D1) an imidazole derivative and (D2) an addition reaction product of an imidazole compound and an epoxy resin. (D1) is composed of a fine pulverized product of a composition in which the mass ratio of (D2) to 1 is 0.5 or more and 5.0 or less, and has a melting point of an epoxy resin powder coating of 60 to 90 °C.

Prior Art Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2024-146159 [Patent Document 2] Japanese Patent Publication No. 2019-172814 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] With the recent improvements in the performance of electrical and electronic components, coatings obtained from powder coating compositions require higher insulation performance. Furthermore, with the increasing complexity of the shapes of electrical and electronic components, coatings that are smooth and have excellent edge coverage are required. Even when using the powder coating compositions described in Patent Documents 1 and 2, it is difficult to obtain a coating that is thin (e.g., 50-200 μm) and possesses both high edge coverage and excellent smoothness.

[0008] "Edge coverage" refers to the ability to ensure a coating thickness equivalent to or sufficient to that of flat surfaces on edges such as corners, bends, and protrusions of the object to be coated (mountain-shaped corners and burrs on the substrate).

[0009] The present invention aims to solve the aforementioned conventional problems and to provide a powder coating composition that can form a coating film that exhibits high dielectric breakdown strength even in thin films, while also possessing high edge coverage and excellent smoothness. [Means for solving the problem]

[0010] To solve the aforementioned problems, the present invention provides the following embodiments. [1] A polyester resin (A) containing an acid group at the terminal end and having an acid value of 10-100 mgKOH / g, Epoxy resin (B) and, A powder coating composition comprising a metal oxyhydroxide (C) containing at least one metal selected from the group consisting of aluminum, manganese, iron, nickel, cobalt, and vanadium. [2] The powder coating composition according to [1] above, wherein the ratio of the mass content of the polyester resin (A) to the epoxy resin (B) (A:B) is 85:15 to 15:85. [3] The powder coating composition according to [1] or [2] above, wherein the volume concentration of the metal oxyhydroxide (C) is 2.5 to 15.0 volume% with respect to the total volume of the polyester resin (A), the epoxy resin (B), and the metal oxyhydroxide (C). [4] The polyester resin (A) is any of the powder coating compositions [1] to [3] above, wherein the polyester resin (A) has a hydroxyl value of 10 mg KOH / g or less, a weight-average molecular weight of 4,000 to 100,000, and a glass transition temperature of 40 to 90°C. [5] The epoxy resin (B) is a powder coating composition according to any of the above [1] to [4], wherein the epoxy equivalent is 200 to 2,000 g / eq and the softening point is 70 to 120°C. [6] The metal oxyhydroxide (C) is any of the powder coating compositions [1] to [5] above, having an aspect ratio of 2 or more. [7] The epoxy resin (B) is at least one selected from the group consisting of novolac-type epoxy resin, biphenyl-type epoxy resin, naphthalene-type epoxy resin, biphenyl aralkyl-type epoxy resin, and dicyclopentadiene-type epoxy resin, in any of the powder coating compositions [1] to [6] above. [8] A powder coating composition according to any of the above [1] to [7], wherein the dielectric breakdown strength of the cured coating film with a thickness of 50 to 200 μm formed by the powder coating composition is 50 kV / mm or more. [Effects of the Invention]

[0011] According to the present invention, there is provided a powder coating composition that exhibits high dielectric breakdown strength even in a thin film and can form a coating film having high edge coverage and excellent smoothness.

Mode for Carrying Out the Invention

[0012] [Powder Coating Composition] The powder coating composition of the present disclosure contains a polyester resin (A) having an acid group at its terminal and an acid value of 10 to 100 mgKOH / g, an epoxy resin (B), and a metal oxyhydroxide (C) containing at least one metal selected from the group consisting of aluminum, manganese, iron, nickel, cobalt, and vanadium.

[0013] A powder coating composition (hereinafter sometimes simply referred to as a powder coating) can generally easily form a thick coating film as compared with solvent-based and water-based paints. On the other hand, it is difficult to form a sufficiently thick coating film on an edge portion (also referred to as an end portion, a corner portion, or a ridge line) using a powder coating.

[0014] When the viscosity (melt viscosity) of the powder coating during heating is high, the edge coverage can be improved. However, the smoothness of the coating film tends to decrease. The unevenness of the coating film deteriorates the appearance and insulation properties.

[0015] The powder coating composition of the present disclosure contains a polyester resin (A) containing an acid group, an epoxy resin (B), and a metal oxyhydroxide (C). The oxyhydroxide (C) of metal M is represented by M-OOH, and O 2- and OH - are bonded to the metal M ion. The hydroxyl group (-OH) of the metal oxyhydroxide (C) can form a coordination bond and / or a hydrogen bond with other metal oxyhydroxides or the acid group of the polyester resin (A). Therefore, it is assumed that the smoothness and the edge coverage can be made compatible by the interaction based on the hydrogen bond or the like between the metal oxyhydroxide (C) and the polyester resin (A).

[0016] The average particle size of the powder coating composition can be selected within a desirable range according to, for example, the coating method and the like. For example, in the case of electrostatic coating, the average particle size of the powder coating composition of the present disclosure is preferably 25 μm or more and 50 μm or less, more preferably 25 μm or more and 45 μm or less, and still more preferably 25 μm or more and 35 μm or less. By having such an average particle size in the case of electrostatic coating, the formed coating film can have excellent smoothness.

[0017] In this specification, the glass transition temperature is a value measured by a differential scanning calorimeter, and can be measured, for example, by a differential scanning calorimeter DSC-6100 (manufactured by Seiko Instruments Inc.) or the like.

[0018] In this specification, the softening point can be measured, for example, using an apparatus such as a heat flow evaluation apparatus (manufactured by Shimadzu Corporation, Flow Tester CFT-500T).

[0019] In this specification, the weight average molecular weight is a polystyrene equivalent value measured by gel permeation chromatography (GPC).

[0020] In this specification, both the hydroxyl value and the acid value indicate values in terms of solid content and are values measured by a method conforming to JIS K 0070.

[0021] The average particle size means the volume average particle size (D50). The volume average particle size (D50) can be measured, for example, using a particle size measuring apparatus such as a laser diffraction / scattering type particle size distribution measuring apparatus (manufactured by Microtrac Bell, Microtrac).

[0022] The epoxy equivalent represents the solid content epoxy equivalent and can be measured by a method conforming to JIS K 7236.

[0023] Polyester resin (A) Polyester resin (A) contains acidic groups at its ends. As described above, these acidic groups interact with metal oxyhydroxides (C) to develop viscosity. Furthermore, since the acidic groups react with epoxy groups, polyester resin (A) functions as a curing agent for epoxy resin (B). Examples of acidic groups include carboxyl groups and sulfonic acid groups. The acidic group may be a carboxyl group.

[0024] The polyester resin (A) has an acid value of 10 to 100 mgKOH / g. When the acid value is 10 mgKOH / g or higher, high curability and good mechanical properties are obtained. When the acid value is 100 mgKOH / g or lower, the edge coverage of the resulting coating film is improved. The acid value may be 15 mgKOH / g or higher, or 20 mgKOH / g or higher. The acid value may be 85 mgKOH / g or lower, 80 mgKOH / g or lower, or 70 mgKOH / g or lower. The acid value may be 15 to 85 mgKOH / g, 15 to 80 mgKOH / g, or 20 to 70 mgKOH / g.

[0025] The polyester resin (A) may have a hydroxyl value of 10 mg KOH / g or less. When the acid value is 10 mg KOH / g or less, the edge covering properties of the resulting coating film can be further improved. The hydroxyl value may be 5 mg KOH / g or less.

[0026] The polyester resin (A) may have a weight-average molecular weight of 4,000 to 100,000. If the weight-average molecular weight is 4,000 or more, the performance and physical properties of the resulting coating film may be improved. If the weight-average molecular weight is 100,000 or less, the smoothness of the resulting coating film may be further improved. The weight-average molecular weight may be 5,000 or more. The weight-average molecular weight may be 65,000 or less, or 50,000 or less. The weight-average molecular weight may be 5,000 to 65,000, or 5,000 to 50,000.

[0027] The polyester resin (A) may have a glass transition temperature (Tg) of 40 to 90°C. If the Tg is 40°C or higher, the blocking resistance (performance to prevent powder particles from sticking together during storage) may be improved, and if the Tg is 90°C or lower, the smoothness of the resulting coating film may be further improved. The Tg may be 50°C or higher, or 55°C or higher. The Tg may be 70°C or lower. The Tg may be 50 to 90°C, 50 to 70°C, or 55 to 70°C.

[0028] The polyester resin (A) may have a hydroxyl value of 10 mgKOH / g or less, a weight-average molecular weight of 4,000 to 100,000, and a Tg of 40 to 90°C.

[0029] Polyester resin (A) can be obtained by condensation polymerization using an acid component mainly composed of a polyhydric carboxylic acid and an alcohol component mainly composed of a polyhydric alcohol as raw materials, by a conventional method. By selecting each component, its content, and the conditions for condensation polymerization, polyester resin (A) having the above-mentioned characteristic values ​​can be obtained.

[0030] The aforementioned acidic components are not limited and include, for example, terephthalic acid, isophthalic acid, phthalic acid, trimellitic acid, pyromellitic acid and their anhydrides, aromatic dicarboxylic acids such as 2,6-naphthalenedicarboxylic acid and 2,7-naphthalenedicarboxylic acid and their anhydrides; saturated aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebatic acid, dodecanedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid and their anhydrides; lactones such as γ-butyrolactone and ε-caprolactone; hydroxycarboxylic acids corresponding to the aforementioned lactones; and aromatic oxymonocarboxylic acids such as p-oxyethoxybenzoic acid. These may be used individually or in combination of two or more.

[0031] The alcohol component is not limited. Examples of the alcohol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 2,3-pentanediol, 1,4-hexanediol, 1,5-hexanediol, 1,6-hexanediol, 2,5-hexanediol, and 3-methyl-1,5-pentanediol. Examples include linear or branched glycols such as 1,12-dodecanediol, 1,8-octadecanediol, diethylene glycol, triethylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, alkylene oxide adducts of bisphenol A, alkylene oxide adducts of bisphenol S, and neopentyl glycol; and polyhydric alcohols of trivalent or higher valency such as trimethylolpropane, glycerin, and pentaerythritol. These may be used individually or in combination of two or more.

[0032] In one embodiment, the alcohol component may include at least one selected from the group consisting of ethylene glycol, neopentyl glycol, and 1,6-hexanediol.

[0033] A commercially available polyester resin (A) may be used. Examples of commercially available products include the CRYLCOAT1540-0 series from Daicel Ornex Corporation, and the FineDic M-8800 series and M-8900 series (carboxyl group-containing polyester resins) from DIC Corporation.

[0034] Polyester resin (A) may be used alone or in combination of two or more types. When two or more types are used in combination, the aforementioned characteristic value is calculated based on the characteristic value of each polyester resin (A) and its solid content mass ratio.

[0035] The content of polyester resin (A) is, for example, 5.0 to 55.0% by mass of the powder coating. Being within this range allows for both edge coverage and smoothness of the resulting coating film. The content may be 8.0% by mass or more, or 10.0% by mass or more. The content may be 50.0% by mass or less. The content may be 8.0 to 55.0% by mass, or 10.0 to 50.0% by mass.

[0036] Epoxy resin (B) The epoxy resin (B) may have an average of one or more epoxy groups per molecule, and moreover, an average of 1.1 or more epoxy groups.

[0037] The epoxy resin (B) is not particularly limited. Examples of epoxy resin (B) include bisphenol-type epoxy resins (type A, type B, type F, etc.); novolac-type phenolic resins such as phenol novolac-type epoxy resins and cresol novolac-type epoxy resins; reaction products of phenol novolac or o-cresol novolac with bisphenol-type epoxy resins (type A, type B, type F, etc.) and epichlorohydrin; and reaction products of phenol novolac or o-cresol novolac with bisphenol-type epoxy resins (type A, type B, type F, etc.). These may be used individually or in combination of two or more. Epoxy resin (B) may be a modified form of the epoxy resin described above.

[0038] Examples of novolac-type epoxy resins include phenol novolac type, cresol novolac type, and bisphenol A novolac type.

[0039] Examples of biphenyl-type, naphthalene-type, biphenylaralkyl-type, and dicyclopentadiene-type resins include those in which one or more glycidyl ether groups are substituted at any position of biphenyl, naphthalene, biphenylaralkyl, or dicyclopentadiene.

[0040] The epoxy resin (B) may be at least one selected from the group consisting of novolac-type epoxy resin, biphenyl-type epoxy resin, naphthalene-type epoxy resin, biphenyl aralkyl-type epoxy resin, and dicyclopentadiene-type epoxy resin. This improves the heat resistance of the resulting coating film. The epoxy resin (B) may be a biphenyl aralkyl-type epoxy resin.

[0041] The epoxy resin (B) may have an epoxy equivalent of 200 to 2,000 g / eq. If the epoxy equivalent is 200 g / eq or more, the storage stability of the coating may be improved. If the epoxy equivalent is 2,000 g / eq or less, the smoothness of the resulting coating may be improved. The epoxy equivalent may be 250 g / eq or more. The epoxy equivalent may be 1,700 g / eq or less. The epoxy equivalent may be 250 to 1,700 g / eq or less.

[0042] The epoxy resin (B) may have a softening point of 70 to 120°C. If the softening point is 70°C or higher, blocking resistance may be improved, and if the softening point is 120°C or lower, the smoothness of the resulting coating film may be further improved. The softening point may be 85°C or higher. The softening point may be 115°C or lower. The softening point may be 85 to 115°C.

[0043] The epoxy resin (B) may have an epoxy equivalent of 200 to 2,000 g / eq and a softening point of 70 to 120°C.

[0044] Commercial epoxy resin (B) can also be used. Examples of commercially available epoxy resin (B) include Epotote YD-128, Epotote YD-014, Epotote YD-019, Epotote YDPN-639, Epotote YDCN-701, Epotote YDCN-701, ST-4000D, ST-6100 (Nippon Steel Chemical & Material Co.), EHPA-3150 (Daicel Corporation), Araldite CY179 (Ha Examples include Huntsman (manufactured by Huntsman), Denacol EX-711 (manufactured by Nagase ChemteX), Epiclon N-680, Epiclon N-695, Epiclon HP-4032, Epiclon HP-7200H (all manufactured by DIC), Araldite PT810, Araldite PT910 (manufactured by Huntsman), TEPIC (manufactured by Nissan Chemical Corporation), and NC-3000H (manufactured by Nippon Kayaku Co., Ltd.).

[0045] The content of epoxy resin (B) is, for example, 5.0 to 55.0% by mass of the powder coating. Being within this range allows for both edge coverage and smoothness of the resulting coating film. The content may be 8.0% by mass or more, or 10.0% by mass or more. The content may be 50.0% by mass or less. The content may be 8.0 to 55.0% by mass, or 10.0 to 50.0% by mass.

[0046] The ratio of the mass content of polyester resin (A) to epoxy resin (B) (A:B) may be 85:15 to 15:85. This allows for both edge coverage and smoothness to be achieved. The ratio of the mass content of polyester resin (A):B) may be 80:20 to 20:80.

[0047] Metal oxyhydroxide (C) Metal oxyhydroxides (C) are represented as M-OOH (where M is a metal). M is at least one selected from the group consisting of aluminum, manganese, iron, nickel, cobalt, and vanadium. M may be aluminum or iron.

[0048] The volume concentration of the metal oxyhydroxide (C) is, for example, 2.5 to 15.0 volume percent relative to the total volume of the polyester resin (A), epoxy resin (B), and metal oxyhydroxide (C). When the volume concentration of the metal oxyhydroxide (C) is 2.5 volume percent or higher, the edge coverage of the resulting coating film is improved. When the volume concentration of the metal oxyhydroxide (C) is 15.0 volume percent or lower, the smoothness of the resulting coating film and the dielectric breakdown strength can be maintained.

[0049] The volume concentration of the metal oxyhydroxide (C) may be 3.0% by volume or more. The volume concentration of the metal oxyhydroxide (C) may be 11.0% by volume or less. The volume concentration of the metal oxyhydroxide (C) may be between 3.0 and 15.0% by volume, or between 3.0 and 11.0% by volume.

[0050] The metal oxyhydroxide (C) is in powder form. The shape of the metal oxyhydroxide (C) is not particularly limited. For example, the shape of the metal oxyhydroxide (C) may be needle-shaped, flake-shaped, plate-shaped, or cube-shaped.

[0051] The aspect ratio of the metal oxyhydroxide (C) is not limited. The aspect ratio of the metal oxyhydroxide (C) may be 2 or greater. Being within the aforementioned range improves the edge coverage of the resulting coating film.

[0052] If the metal oxyhydroxide (C) is in the form of a long columnar (fibrous) structure, the aspect ratio can be calculated as (average length of the longest side of the metal oxyhydroxide (C)) / (average length of the shortest side of the metal oxyhydroxide (C)). If the metal oxyhydroxide (C) is in the form of flakes, plates, or cubes, the aspect ratio can be calculated as (average length of the longest side of the metal oxyhydroxide (C)) / (average thickness of the metal oxyhydroxide (C)).

[0053] In this specification, the average length of the longest side and the average length of the shortest side (or average thickness) of a metal oxyhydroxide (C) are determined by taking images of the material with a microscope (scanning electron microscope (SEM), transmission electron microscope (TEM), optical microscope, etc.), measuring the lengths of 10 arbitrarily selected longest and shortest sides (or thicknesses) using image analysis software, and then taking the arithmetic mean of each.

[0054] The aspect ratio of the metal oxyhydroxide (C) may be 10 or more, 20 or more, 30 or more, or 40 or more. The aspect ratio of the metal oxyhydroxide (C) may be 100 or less, or 70 or less. The aspect ratio of the metal oxyhydroxide (C) may be between 10 and 100, 20 and 100, 30 and 100, 40 and 100, or 40 and 70.

[0055] curing catalyst The powder coating compositions of this disclosure may include a curing catalyst. The curing catalyst can be appropriately selected depending on the purpose. Examples of curing catalysts include at least one curing catalyst selected from imidazole compounds, imidazoline compounds and metal salt complexes thereof, tertiary phosphine compounds, quaternary phosphonium salt compounds, and quaternary ammonium salt compounds.

[0056] Examples of imidazole compounds include alkylimidazoles such as 2-ethyl-4-methylimidazole, 1-methylimidazole, 1,2-dimethylimidazole, 2-methylimidazole, 2-ethylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, and 2-isopropylimidazole; carbamyl alkyl-substituted imidazoles such as 1-(2-carbamylethyl)imidazole; and sheapropylimidazoles such as 1-cyanoethyl-2-methylimidazole. Examples include noalkyl-substituted imidazoles, aromatic-substituted imidazoles such as 2-phenylimidazole, 2-phenyl-4-methylimidazole, and 1-benzyl-2-methylimidazole, alkenyl-substituted imidazoles such as 1-vinyl-2-methylimidazole, allyl-substituted imidazoles such as 1-allyl-2-ethyl-4-methylimidazole, and polyimidazoles, but alkylimidazoles and aromatic-substituted imidazoles are preferred.

[0057] Commercially available imidazole compounds may be used. Examples of commercially available products include the Curesol series (manufactured by Shikoku Chemicals Co., Ltd.), such as 2MZ-H (2-methylimidazole), C11Z (2-undecylimidazole), C17Z (2-heptadecylimidazole), 1,2DMZ (1,2-dimethylimidazole), 2E4MZ (2-ethyl-4-methylimidazole), 2P4MZ (2-phenyl-4-methylimidazole), 1B2MZ (1-benzyl-2-methylimidazole), and 1B2PZ (1-benzyl-2-phenylimidazole).

[0058] Examples of imidazoline compounds include 2-phenylimidazole, 2-methylimidazole, 2-undecylimidazole, and 2-heptadecylimidazole. Commercial products may also be used. An example of a commercial product is Curesol 2PZL-T (manufactured by Shikoku Chemicals Co., Ltd.; 2-phenylimidazole).

[0059] Examples of metal salt complexes include those obtained by compounding the imidazole compounds or imidazoline compounds with a metal salt. The metal salts are not particularly limited, but examples include those consisting of metals such as copper, nickel, cobalt, calcium, zinc, zirconium, silver, chromium, manganese, tin, iron, titanium, antimony, and aluminum, and salts such as chloride, bromide, fluoride, sulfate, nitrate, acetate, malate, stearate, benzoate, and methacrylate.

[0060] Examples of tertiary phosphine compounds include triphenylphosphine and tritlylphosphine.

[0061] Examples of quaternary phosphonium salt compounds include benzyltriphenylphosphonium chloride, butyltriphenylphosphonium bromide, ethyltriphenylphosphonium iodide, and ethyltriphenylphosphonium bromide.

[0062] Examples of quaternary ammonium salt compounds include tetraethylammonium chloride, tetraethylammonium bromide, and benzyltrimethylammonium bromide.

[0063] The curing catalyst may be at least one of the imidazole compounds and imidazoline compounds. This allows the powder coating to cure at a lower temperature.

[0064] The content of the curing catalyst may be 0.0 to 10.0 parts by mass per 100.0 parts by mass of the resin solids. By having the curing catalyst content within the above range, the curing speed of the powder coating composition can be controlled, and various workpieces, coating equipment, or drying equipment can be used. The above content of the curing catalyst may be 0.1 parts by mass or more. The above content of the curing catalyst may be 8.0 parts by mass or less, or 5.0 parts by mass or less. The above content of the curing catalyst may be 0.0 to 10.0 parts by mass, 0.1 to 8.0 parts by mass, or 0.1 to 5.0 parts by mass.

[0065] Other ingredients The powder coating compositions of this disclosure may include coloring pigments as colorants and inorganic fillers.

[0066] (Coloring pigments) Examples of coloring pigments include inorganic pigments and organic pigments.

[0067] Examples of chromatic inorganic pigments include red iron oxide, chromium titanium yellow, and iron oxide. Examples of achromatic inorganic pigments include titanium dioxide and carbon black.

[0068] Examples of chromatic organic pigments include azo, perylene, condensed azo, nitro, nitroso, phthalocyanine, anthraquinone, quinacridone, and dioxane pigments. Specific examples of azo pigments include lake red, fast yellow, disazo yellow, and permanent red. Specific examples of nitro pigments include naphthol yellow. Specific examples of nitroso pigments include pigment green B and naphthol green. Specific examples of phthalocyanine pigments include phthalocyanine blue and phthalocyanine green. Specific examples of anthraquinone pigments include induthlene blue and diantraquinonyl red. Specific examples of quinacridone pigments include quinacridone red and quinacridone violet. Specific examples of dioxane pigments include carbazole dioxazine violet.

[0069] The content of the coloring pigment is, for example, 0.05 to 60.0 parts by mass per 100.0 parts by mass of the resin solids. The content of the inorganic pigment is, for example, 0.05 to 60.0 parts by mass per 100.0 parts by mass of the resin solids. The content of the organic pigment is, for example, 0.05 to 20.0 parts by mass per 100.0 parts by mass of the resin solids.

[0070] (Inorganic fillers) Inorganic fillers can improve chemical resistance by contributing to the blocking of corrosive factors. Examples of inorganic fillers include extender pigments such as alumina, silica, precipitated barium sulfate, calcium carbonate, clay, talc, and mica; and rust-preventive pigments such as zinc phosphate and aluminum phosphate.

[0071] The amount of inorganic filler is, for example, 5.0 to 60.0 parts by mass per 100.0 parts by mass of the resin solids. The content may be 50.0 parts by mass or less, or 35.0 parts by mass or less. The content may be 5.0 to 50.0 parts by mass, or 5.0 to 35.0 parts by mass.

[0072] The powder coating composition may contain known additives such as surface modifiers, UV absorbers, antioxidants, and anti-wrinkle agents.

[0073] Dielectric breakdown strength The initial dielectric breakdown strength of a cured coating film with a thickness of 50 to 200 μm formed by the powder coating composition of this disclosure may be 50 kV / mm or higher. Such a cured coating film is suitable for electrical insulation applications.

[0074] The dielectric breakdown strength can be measured in accordance with JIS C 2161:2010 (Test Methods for Electrical Insulating Powder Coatings 8.9), Method 8.9.4 b) Short-Time Method. For example, a digital withstand voltage tester 8504 (manufactured by Tsuruga Electric Co., Ltd.) can be used as a measuring instrument.

[0075] The initial dielectric breakdown strength of the cured coating may be 60 kV / mm or higher.

[0076] Manufacturing method The powder coating compositions of this disclosure can be manufactured by known methods. For example, the powder coating compositions of this disclosure can be manufactured by the following methods. First, prepare each of the aforementioned raw materials and pre-mix them using a super mixer, Henschel mixer, or similar device.

[0077] Next, the mixture is melt-kneaded using a kneader, extruder, or other mixing machine. The melt-kneading is performed at a temperature at which at least a portion of the raw materials are melted and the whole mixture is kneaded. The temperature during melt-kneading is generally between 80°C and 130°C, and in some embodiments, it is between 80°C and 120°C.

[0078] The resulting molten material is cooled and solidified using cooling rolls, a cooling conveyor, etc. Subsequently, it is ground to the desired particle size through coarse grinding and fine grinding processes. Grinding can be carried out by physical grinding (coarse grinding, fine grinding), for example, using grinding equipment such as a hammer mill or a jet impact mill.

[0079] Finally, classification is performed as desired. For classification, for example, air classifiers, vibrating sieves, and ultrasonic sieves are used. This removes large and small particles and adjusts the particle size distribution.

[0080] [Coating film formation method] The method for forming a coating film includes applying the powder coating composition of this disclosure onto an object to be coated and heating to form a cured coating film. The heating is performed, for example, at a temperature in which the object to be coated reaches 140°C to 200°C.

[0081] Object to be coated The material to be coated is not particularly limited. Examples of materials to be coated include iron plates, steel plates, aluminum plates, ceramic plates, copper plates, etc., and materials made by surface treatment thereof. The material to be coated may be a component made by processing the aforementioned metal plates into a complex shape.

[0082] Painting method A typical method for applying powder coating compositions is electrostatic powder coating.

[0083] Before applying the powder coating composition, the object to be coated may be primed. The primed coating film is formed using known primers such as electrodeposition coatings or primers.

[0084] The heating temperature can be set appropriately depending on the type and amount of curing agent. The heating temperature may be 140 to 200°C from the viewpoint of preventing the generation of bubbles on or inside the coating film. The heating temperature may be 150°C or higher, or 160°C or higher. The heating temperature may be 190°C or lower, or 180°C or lower. The heating temperature may be 150 to 190°C, 150 to 180°C, or 160 to 180°C.

[0085] The heating temperature can be set appropriately depending on the desired heating time. For example, the heating time can range from 10 to 40 minutes.

[0086] [coating film] The powder coating composition disclosed herein forms a coating film on an object to be coated. The coating film exhibits high dielectric breakdown strength and combines high edge coverage with excellent smoothness. In addition, the coating film has excellent properties such as resistance to falling weights.

[0087] According to the powder coating composition of this disclosure, even a thin film can be obtained that is smooth and has excellent edge coverage. The film thickness may be 50 to 150 μm, from the viewpoint of preventing unevenness and transparency of the coating film, and preventing the generation of bubbles on or inside the coating film. The film thickness may be 60 μm or more.

[0088] The powder coating compositions of this disclosure are preferably used in electrical products, office equipment, automobile bodies, exterior panels and parts, etc. [Examples]

[0089] The present invention will be further described by the following examples, but the present invention is not limited thereto. In the examples, "parts" and "%" are based on mass unless otherwise specified.

[0090] Details of the polyester resin (A), epoxy resin (B), metal oxyhydroxide (C), and other materials used are shown below.

[0091] [Polyester resin (A-1)] Product name: "CRYLCOAT1540-0", manufactured by Daicel Ornex Co., Ltd.

[0092] (Manufacturing example A-2) [Preparation of polyester resin (A-2)] In a reaction vessel equipped with a reflux condenser, agitator, thermometer, condenser, and nitrogen gas inlet, 62 parts by mass of terephthalic acid, 38 parts by mass of neopentyl glycol, and 0.1 parts by mass of di-n-butyltin oxide as a catalyst were charged and mixed. The mixture was then gradually heated to 240°C in a nitrogen stream, and the esterification reaction was carried out while distilling off the water produced, thereby obtaining polyester resin (A-2) (solid content concentration: 100% by mass).

[0093] (Manufacturing example A-3)~(Manufacturing example A-6) [Preparation of polyester resins (A-3) to (A-6)] Polyester resins (A-3) to (A-6) were prepared in the same manner as in (Production Example A-2), except that the types and amounts of each component were as shown in Table 1. The composition and various properties of polyester resin (A) are shown in Tables 1 and 2.

[0094] [Table 1]

[0095] [Table 2]

[0096] [Epoxy resin (B-1)] Product name: "Epotote YD-014", manufactured by Nippon Steel Chemical & Material Co., Ltd. [Epoxy resin (B-2)] Product name: "NC3000H", manufactured by Nippon Kayaku Co., Ltd. [Epoxy resin (B-3)] Product name: "Epotote YD-904H", manufactured by Nippon Steel Chemical & Material Co., Ltd.

[0097] (Manufacturing example B-4) [Preparation of epoxy resin (B-4)] In a reaction vessel equipped with a reflux condenser, agitator, thermometer, condenser, and nitrogen gas inlet, 66 parts by mass of EPPMOK R140N (Mitsui Chemicals, bisphenol A type epoxy resin), 34 parts by mass of bisphenol A (Nippon Steel Chemical & Material Co., Ltd.), and 0.02 parts by mass of tetra-n-butylammonium bromide (Fuji Pure Chemical Industries, Ltd.) as a catalyst were charged, mixed, and reacted under a nitrogen atmosphere while being heated and maintained at 150°C until the epoxy equivalent reached 2,000 g / eq, thereby obtaining epoxy resin (B-4).

[0098] (Manufacturing example B-5) [Preparation of epoxy resin (B-5)] Epoxy resin (B-5) was obtained in the same manner as in (Production Example B-4), except that the proportions of each material were 94 parts by mass of EPPMOK R140N and 6 parts by mass of bisphenol A. Table 3 shows the various characteristic values ​​of epoxy resin (B).

[0099] [Table 3]

[0100] (Manufacturing example C-1) [Preparation of metal oxyhydroxides (C-1)] 750 g of aluminum nitrate nonahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., reagent grade) was dissolved in 1,000 ml of deionized water. While stirring, 180 g of sodium hydroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., reagent grade) dissolved in 1,000 ml of deionized water was gradually added dropwise to prepare a slurry. Next, the slurry was packed into an autoclave and aged at a heating temperature of 120°C for 24 hours. After completion, it was reheated in an oven at 180°C for 30 minutes and then cooled to room temperature. After that, it was heated again in an oven at 140°C for 4 days. After cooling, the obtained product was washed with water, filtered, and dried to obtain metal oxyhydroxide (C-1).

[0101] (Manufacturing example C-2) [Preparation of metal oxyhydroxides (C-2)] A slurry was prepared by adding 78g of aluminum hydroxide particles (manufactured by Nippon Light Metal Co., Ltd., BF013), 2.8g of sodium hydroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., reagent grade), and 78g of deionized water, and stirring. The slurry was packed into an autoclave and aged at a heating temperature of 300°C for 2 hours. After cooling, the obtained product was washed with water, filtered, and dried to obtain metal oxyhydroxide (C-2).

[0102] (Manufacturing example C-3) [Preparation of Metal Oxyhydroxides (C-3)] Except for changing the amount of sodium hydroxide particles added to 1.2 g, metal oxyhydroxide (C-3) was obtained in the same manner as in (Production Example C-2).

[0103] (Manufacturing example C-4) [Preparation of Metal Oxyhydroxide (C-4)] Except for changing the amount of sodium hydroxide particles added to 0.4 g, metal oxyhydroxide (C-4) was obtained in the same manner as in (Production Example C-2).

[0104] (Manufacturing example C-5) [Preparation of Metal Oxyhydroxide (C-5)] A slurry was prepared by stirring 400g of aluminum hydroxide particles (manufactured by Nippon Light Metal Co., Ltd., BE043) and 600g of deionized water. The slurry was packed into an autoclave and aged at a heating temperature of 200°C for 2 hours. After cooling, the obtained product was washed with water, filtered, and dried to obtain metal oxyhydroxide (C-5).

[0105] • [Metal oxyhydroxide (C-6)] Product name: "TAROX HY100", manufactured by Titanium Industry Co., Ltd. Table 4 shows the characteristic values ​​of metal oxyhydroxides (C).

[0106] [Table 4]

[0107] others (Hardening agent 1) PRIMID XL-552 (manufactured by Ms. Chemie, β-hydroxyalkylamide) (Hardening agent 2) JER Cure 170 (manufactured by Mitsubishi Chemical Corporation, bisphenol A type phenolic resin) (Curing catalyst) Cureazole C-17Z (manufactured by Shikoku Chemicals Co., Ltd., imidazole-based catalyst) (Surface modifier) ​​KF-54 (manufactured by Sanyu Industrial Co., Ltd., silicone-based surface modifier) (Extender pigment 1) Super 2000 (manufactured by Maruo Calcium Co., Ltd., calcium carbonate), aspect ratio: 1 (Extender Pigment 2) Wollastonite (manufactured by Maruto Co., Ltd., wollastonite), Aspect Ratio: 8 (Coloring pigment) SUNBLACK X15 (manufactured by Asahi Carbon Co., Ltd., carbon black) (Flow-improving agent) AEROXIDE Alu C (manufactured by Nippon Aerosil Co., Ltd., aluminum oxide)

[0108] [Example 1] A mixture was obtained by mixing 20.0 parts by mass of polyester resin (A-1), 80.0 parts by mass of epoxy resin (B-1), 18.0 parts by mass of metal oxyhydroxide (C-1), 5.0 parts by mass of curing catalyst, 35.0 parts by mass of extender pigment 1, 1.7 parts by mass of coloring pigment, and 2.0 parts by mass of surface modifier using a super mixer (manufactured by Nippon Spindle Co., Ltd.) for 3 minutes.

[0109] Next, the mixture was melt-kneaded at 100°C using a kneader (manufactured by Buss). The resulting mixture was extruded, cooled, and then 0.5 parts by mass of a fluidity imparter was added and coarsely ground. Subsequently, the coarsely ground material was further ground using a cryptron. The resulting pulverized material was classified using a turboclassifier (manufactured by Nisshin Engineering Co., Ltd.) to obtain a powder coating composition with an average particle size of 35 μm.

[0110] [Examples 2-18, Comparative Examples 1-6] A powder coating composition was prepared in the same manner as in Example 1, except that the types and amounts of each component were changed as shown in Tables 5 to 7 below.

[0111] [evaluation] (1)Smoothness First, a test panel was fabricated. A solvent-degreased aluminum sheet was used as the substrate. The powder coating composition prepared above was applied using an electrostatic coating machine for powder coatings (product name "OPTI Handgun", manufactured by Graco) under the following conditions: discharge rate: 120 g / min, set voltage: 60 kV, set current: 40 μA, free ion removal enabled, and gun distance: 15 cm, to a film thickness of 50 μm. After that, the test plate was heated at 180 °C for 20 minutes to obtain the test plate.

[0112] The test panels were visually inspected and evaluated according to the following criteria. A score of 3 or higher was considered a pass. 5: The entire surface is uniform and smooth, without any bumps or irregularities. 4: It is smooth, although there are slight bumps and irregularities. 3: It is slightly uneven but smooth. 2: It has fine bumps and irregularities. 1: Granular irregularities can be visually confirmed.

[0113] (2) Edge coverage First, we prepared the test specimens. A 10 x 10 x 10 mm aluminum square bar was prepared as the workpiece. The powder coating composition was applied to this bar using the aforementioned electrostatic coating machine for powder coatings, so that the film thickness on the flat surface was 100 μm. Next, the bar was heated at 180°C for 20 minutes to obtain a test specimen.

[0114] The aforementioned test specimen was cut so that its cross-section was visible, and the film thickness of the flat portion and the edge portion were measured. The edge portion film thickness is the film thickness perpendicular to the apex of the edge. The flat portion film thickness is the film thickness of the flat portions (right edge and left edge) located 10 mm to the left and right of the apex of the edge. The film thickness was measured by image observation using a digital microscope VHX-6000 (manufactured by Keyence Corporation). The film thickness was measured at three locations each for the edge portion and the flat portion (right edge and left edge), and the arithmetic mean was taken as the average film thickness.

[0115] Next, the edge coverage ratio was calculated as follows. A higher edge coverage ratio means that the film thickness of the coating formed on the edges is closer to the film thickness on the flat surfaces, indicating superior edge coverage. Edge coverage rate (%) = 100 × Average film thickness at the edge (μm) / Average film thickness at the flat surface (μm)

[0116] Edge coverage was evaluated according to the following criteria. A score of 3 or higher was considered a passing grade. 5: Greater than 70%. 4: Greater than 60% and less than or equal to 70%. 3: Greater than 50% and less than or equal to 60%. 2: Greater than 30% and less than or equal to 50%. 1:30% or less

[0117] (3) Dielectric breakdown strength First, test specimens were prepared using the same method as for (2) edge coverage evaluation. The dielectric breakdown strength of the test specimens was evaluated using the short-time method with a digital withstand voltage tester 8504 (manufactured by Tsuruga Electric Co., Ltd.), in accordance with JIS C 2161:2010 (Test method for powder coatings for electrical insulation, 8.9).

[0118] Specifically, it is as follows: Only the painted portion of the test specimen was immersed in a glycerin solution, and electrodes were attached to the glycerin solution and the unpainted portion of the specimen. Lead wires were connected to these electrodes to form a test circuit. A voltage was applied to the formed circuit, and the breakdown voltage (kV / 100μm) at which the painted portion of the test specimen broke down was measured. The voltage was increased at a constant rate from 0 to an average of 10-20 seconds before dielectric breakdown of the test specimen occurred. The same test was repeated 8 times, changing the measurement location, and the average value was defined as the dielectric breakdown strength.

[0119] Dielectric breakdown strength was evaluated according to the following criteria. A score of 3 or higher was considered acceptable. 5: 80kV / mm or higher. 4: Between 70kV / mm and less than 80kV / mm. 3: Between 50kV / mm and less than 70kV / mm. 2: The voltage is between 30kV / mm and less than 50kV / mm. 1: Less than 30kV / mm.

[0120] [Table 5]

[0121] [Table 6]

[0122] [Table 7]

[0123] (4) Heat resistance The heat resistance of the test specimens from Examples 1, 17, and 18 was evaluated. First, test specimens were prepared using the same method as for the smoothness evaluation. During this process, the mass of the aluminum sheet before painting and the test specimen after painting (the mass of the test specimen before the test) were measured. Next, a heat resistance test was performed on the test specimen using a Perfect Jet Oven (manufactured by espec) at 240°C for 500 hours, and the mass of the test specimen was measured after the test.

[0124] Next, the mass retention rate of the coating film was calculated according to the following formula. Mass retention rate of the coating film (%) = 100 × Mass of the coating film after testing / Mass of the coating film before testing

[0125] The mass of the coating film before or after the test was calculated according to the following formula. Mass of the coating before testing = Mass of the test piece after painting - Mass of the aluminum plate before painting Mass of the coating after testing = Mass of the test specimen after testing - Mass of the aluminum plate before painting

[0126] The heat resistance of the coating film was evaluated using the following criteria based on mass retention rate. A higher mass retention rate indicates superior heat resistance. A score of 3 or higher was considered acceptable. 5. The mass retention rate of the coating film is between 80% and 100%. 4. The mass retention rate of the coating film is 60% or more but less than 80%. 3. The mass retention rate of the coating film is 40% or more but less than 60%. 2: The mass retention rate of the coating film is 20% or more but less than 40%. 1: The mass retention rate of the coating film is 0% or more and less than 20%.

[0127] Regarding heat resistance, Example 1 received a score of 3, while Examples 17 and 18 both received a score of 4.

[0128] The coating compositions of Examples 1 to 18 yielded coating films with excellent smoothness, edge coverage, and dielectric breakdown strength. Examples 17 and 18 also yielded coating films with excellent heat resistance in addition to the above.

[0129] Comparative Examples 1-3 and 6 were examples that did not contain metal oxyhydroxide (C), and the resulting coatings were inferior in at least one of the following: smoothness, edge coverage, and dielectric breakdown strength. Comparative Example 4 is an example that does not contain polyester resin (A), and the resulting coating film was inferior in edge coverage and dielectric breakdown strength. Comparative Example 5 is an example that does not contain epoxy resin (B), and the resulting coating film was inferior in edge coverage and dielectric breakdown strength. [Industrial applicability]

[0130] The powder coating composition of the present invention can form a coating film that exhibits high dielectric breakdown strength even in thin films, while also possessing high edge coverage and excellent smoothness.

Claims

1. A polyester resin (A) containing an acid group at the terminal end and having an acid value of 10 to 100 mg KOH / g, Epoxy resin (B) and A powder coating composition comprising a metal oxyhydroxide (C) containing at least one metal selected from the group consisting of aluminum, manganese, iron, nickel, cobalt, and vanadium.

2. The powder coating composition according to claim 1, wherein the ratio of the mass content of the polyester resin (A) to the epoxy resin (B) (A:B) is 85:15 to 15:

85.

3. The powder coating composition according to claim 1 or 2, wherein the volume concentration of the metal oxyhydroxide (C) is 2.5 to 15.0% by volume with respect to the total volume of the polyester resin (A), the epoxy resin (B), and the metal oxyhydroxide (C).

4. The powder coating composition according to claim 1 or 2, wherein the polyester resin (A) has a hydroxyl value of 10 mg KOH / g or less, a weight-average molecular weight of 4,000 to 100,000, and a glass transition temperature of 40 to 90°C.

5. The powder coating composition according to claim 1 or 2, wherein the epoxy resin (B) has an epoxy equivalent of 200 to 2,000 g / eq and a softening point of 70 to 120°C.

6. The powder coating composition according to claim 1 or 2, wherein the metal oxyhydroxide (C) has an aspect ratio of 2 or more.

7. The powder coating composition according to claim 1 or 2, wherein the epoxy resin (B) is at least one selected from the group consisting of novolac-type epoxy resin, biphenyl-type epoxy resin, naphthalene-type epoxy resin, biphenylaralkyl-type epoxy resin, and dicyclopentadiene-type epoxy resin.

8. The powder coating composition according to claim 1 or 2, wherein the dielectric breakdown strength of a cured coating film with a thickness of 50 to 200 μm formed by the powder coating composition is 50 kV / mm or more.

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