Powder coating

Abstract

To provide a powder coating that can suppress a solid phase reaction during the storage period after the production of the powder coating, and also excels in the finished appearance and coating performance of the resultant coating layer.SOLUTION: A powder coating contains an acid group-containing polyester resin (A), a glycidyl group-containing acryl resin (B), and a polycarbodiimide compound (C). Particularly, the content of the polycarbodiimide compound (C) is 1.5-6.0 mass% relative to the total solid content of the acid group-containing polyester resin (A) and the glycidyl group-containing acrylic resin (B).SELECTED DRAWING: None

Description

Technical Field

[0007]

[0001] The present invention relates to a powder coating containing an acid group-containing polyester resin, a glycidyl group-containing acrylic resin, and a polycarbodiimide compound, which can particularly suppress the solid-phase reaction during the storage period after the production of the powder coating, and has excellent finish appearance and coating film performance.

Background Art

[0002] There is a powder coating as an environmentally friendly coating that does not contain VOCs (volatile organic compounds) such as organic solvents.

[0003] From the perspective of reducing environmental impact, powder coatings that cure at relatively low temperatures are in demand. One such type is the acid / epoxy curing system. For example, as a combination of a binder resin and a curing agent, an acid group-containing polyester resin and a glycidyl group-containing acrylic resin are known.

[0004] For example, Patent Document 1 discloses a thermosetting polyester powder coating characterized by containing (A) a carboxyl group-containing amorphous polyester resin, (B) a crystalline polyester resin containing a carboxyl group and / or a hydroxy group, and (C) an epoxy group-containing acrylic powder crosslinking agent as essential components.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the thermosetting polyester powder coatings such as those in Patent Document 1, the suppression of the solid-phase reaction during the storage period after the production of the powder coating is insufficient, and problems may occur where the coating film performance deteriorates, such as poor gloss and reduced adhesion of the coating film.

[0007] The present invention aims to provide a powder coating that can suppress solid-phase reactions during storage after production and that also exhibits excellent finished appearance and coating performance. [Means for solving the problem]

[0008] The inventors, in order to solve the above problems, conducted development and found that by using an acid / epoxy curing powder coating containing an acid group-containing polyester resin and a glycidyl group-containing acrylic resin, and further containing a carbodiimide compound, the above problems can be solved, and thus the present invention was completed.

[0009] According to the present invention, Item 1. A powder coating characterized by containing an acid group-containing polyester resin (A), a glycidyl group-containing acrylic resin (B), and a polycarbodiimide compound (C). Item 2. The powder coating described in Item 1 above, wherein the content of the polycarbodiimide compound (C) is in the range of 1.5 to 6.0% by mass relative to the total solid content of the acid group-containing polyester resin (A) and the glycidyl group-containing acrylic resin (B). Item 3. A painted article having a coating film of the powder coating described in Item 1 or 2 above is provided. [Effects of the Invention]

[0010] According to the powder coating of the present invention, solid-phase reactions during storage after the production of the powder coating can be suppressed, and a powder coating with excellent finish appearance and coating performance can be provided. [Modes for carrying out the invention]

[0011] The powder coating of the present invention will be described in more detail below.

[0012] The powder coating of the present invention is characterized by containing an acid group-containing polyester resin (A), a glycidyl group-containing acrylic resin (B), and a polycarbodiimide compound (C).

[0013] <Acid group-containing polyester resin (A)> Acid group-containing polyester resin (A) is a polyester resin having acid groups, and can be obtained, for example, by condensation polymerization using an acid component mainly composed of a polybasic acid and an alcohol component mainly composed of a polyhydric alcohol as raw materials by a conventional method. In particular, it is a polyester resin containing acid groups as terminal functional groups.

[0014] A carboxyl group is preferred as the acid group.

[0015] Examples of the polybasic acid components mentioned above include aromatic dicarboxylic acids such as terephthalic acid, dimethyl terephthalate, isophthalic acid, dimethyl isophthalate, phthalic acid, hexahydrophthalic acid, tetrahydrophthalic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid and their anhydrides, trivalent or higher aromatic polycarboxylic acids such as trimellitic acid and their anhydrides, saturated aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid and their anhydrides.

[0016] Furthermore, as acidic components, lactones such as γ-butyrolactone and ε-caprolactone, and aromatic oxymonocarboxylic acids such as p-oxyethoxybenzoic acid can also be used. Of the above, terephthalic acid, isophthalic acid, etc., can be suitably used. One or more of the above acid components can be used.

[0017] Examples of the alcohol components mentioned above 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, 1,6-hexanediol, 2,3-pentanediol, 1,4-hexanediol, 1,5-hexanediol, 2,5-hexanediol, 3-methyl-1,5-pentanediol, and neopentyl Examples include linear or branched aliphatic glycols such as glycols, 1,2-dodecanediol, 1,2-octadecanediol, diethylene glycol, triethylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, bisphenol A alkylene oxide adducts, and bisphenol S alkylene oxide adducts, as well as trivalent or higher polyhydric alcohols such as trimethylolethane, trimethylolpropane, glycerin, and pentaerythritol.

[0018] Of the above, ethylene glycol, neopentyl glycol, etc., can be suitably used. One or more of the above alcohol components can be used.

[0019] The acid value of the polyester resin (A) is preferably in the range of 10 to 50 mgKOH / g, and particularly 15 to 45 mgKOH / g, from the viewpoint of curability and finished appearance.

[0020] The weight-average molecular weight of the polyester resin (A) is preferably in the range of 5,000 to 15,000, and particularly 6,500 to 13,500, from the viewpoint of finished appearance, processability, and impact resistance.

[0021] In this specification, the weight-average molecular weight and the number-average molecular weight are values obtained by converting the retention time (retention volume) measured using gel permeation chromatography (GPC) into the molecular weight of polystyrene based on the retention time (retention volume) of standard polystyrene with a known molecular weight measured under the same conditions. Four columns, namely, "TSKgel G-4000H×L", "TSKgel G-3000H×L", "TSKgel G-2500H×L", and "TSKgel G-2000H×L" (all are product names manufactured by Tosoh Corporation), were used. The measurement was carried out under the conditions of mobile phase: tetrahydrofuran, measurement temperature: 40°C, flow rate: 1 ml / min, and detector: RI.

[0022] From the viewpoints of the finished appearance, processability, and impact resistance, the glass transition temperature of the polyester resin (A) is preferably within the range of 40 to 80°C, particularly 50 to 70°C. The glass transition temperature can be measured using a differential scanning calorimeter (DSC) in accordance with JIS K 7121.

[0023] Also, from the viewpoints of the finished appearance and blocking resistance, the softening temperature of the polyester resin (A) is preferably within the range of 80 to 130°C, particularly 90 to 120°C. In the present invention, the softening point is a value measured by the ball and tube method.

[0024] <Glycidyl group-containing acrylic resin (B)> The glycidyl group-containing acrylic resin (B) is a vinyl copolymer having a glycidyl group at the terminal or side chain of the molecule.

[0025] The acrylic resin (B) can be obtained by copolymerizing at least one polymerizable monomer having a glycidyl group with other vinyl monomers copolymerizable therewith.

[0026] Examples of the polymerizable monomer having a glycidyl group include glycidyl (meth)acrylate, β-methyl glycidyl (meth)acrylate, etc. These can be used alone or in combination of two or more.

[0027] Other vinyl monomers copolymerizable with the polymerizable monomer having a glycidyl group include those having at least one unsaturated bond, such as a vinyl group, in their molecule, and include derivatives of acrylic acid and methacrylic acid.

[0028] Examples of vinyl monomers include carboxyl group-containing monomers such as (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, or fumaric acid; Mono- or diesters of polyvalent carboxyl group-containing monomers such as itaconic acid, maleic acid, or fumaric acid with monoalkyl alcohols having 1 to 18 carbon atoms; Ethylene-based unsaturated carboxylate alkyl monomers such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; Cycloalkyl group-containing polymerizable monomers such as cyclopentyl (meth)acrylate and cyclohexyl (meth)acrylate; Hydroxypropyl (meth)acrylates such as 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, and polypropylene glycol mono(meth)acrylate; The above hydroxyl group-containing (meth)acrylate, such as the main component of the addition reaction between 2-hydroxyethyl (meth)acrylate and ε-caprolactone, and the main component of the addition reaction between ε-caprolactone (the main component constituting the addition product); Hydroxyl group-containing vinyl ethers such as 2-hydroxyethyl vinyl ether, 3-hydroxypropyl vinyl ether, 2-hydroxypropyl vinyl ether, 4-hydroxybutyl vinyl ether, 3-hydroxybutyl vinyl ether, 2-hydroxy-2-methylpropyl vinyl ether, 5-hydroxypentyl vinyl ether, and 6-hydroxyhexyl vinyl ether; The addition reaction product of the above hydroxyl group-containing vinyl ether and ε-caprolactone; Hydroxylate-containing allyl ethers such as 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, and 6-hydroxyhexyl (meth)allyl ether; Addition reaction product of the above hydroxyl group-containing allyl ether and ε-caprolactone; Amyloid-containing ethylene-based unsaturated carboxylic acid monomers such as acrylamide, methacrylamide, N-methylolacrylamide, methoxybutylacrylamide, and diacetoneacrylamide; Amino group-containing amide-based unsaturated monomers such as N-dimethylaminoethyl(meth)acrylamide, N-diethylaminoethyl(meth)acrylamide, N-dimethylaminopropyl(meth)acrylamide, or N-diethylaminopropyl(meth)acrylamide; Dialkylaminoalkyl(meth)acrylates such as dimethylaminoethyl(meth)acrylate and diethylaminoethyl(meth)acrylate; Other amino group-containing monomers such as tert-butylaminoethyl (meth)acrylate, tert-butylaminopropyl (meth)acrylate, aziridinylethyl (meth)acrylate, pyrrolidinylethyl (meth)acrylate, or piperidinylethyl (meth)acrylate; α-olefins such as ethylene, propylene, and butene-1; halogenated olefins (haloolefins) excluding fluoroolefins, such as vinyl chloride and vinylidene chloride; aromatic vinyl monomers such as styrene, α-methylstyrene, and vinyltoluene; Hydrolyzable silyl group-containing monomers such as γ-(meth)acryloyloxypropyltrimethoxysilane, γ-(meth)acryloyloxypropyltriethoxysilane, and γ-(meth)acryloyloxypropylmethyldimethoxysilane; Vinyl cyanide monomers such as (meth)acrylonitrile and α-chloroacrylonitrile; Aliphatic carboxylates such as vinyl acetate, vinyl propionate, vinyl butyrate, iso(iso-)vinyl butyrate, vinyl caproate, vinyl caprylate, vinyl caprate, vinyl laurate, C9 branched aliphatic carboxylates, C10 branched aliphatic carboxylates, C11 branched aliphatic carboxylates, and vinyl stearate; Examples include vinyl esters of cyclic carboxylic acids such as vinyl cyclohexanecarboxylate, vinyl methylcyclohexanecarboxylate, vinyl benzoate, and p-tert-butylbenzoic acid.

[0029] These can be used individually or in combination of two or more. In this specification, "(meth)acrylate" means acrylate or methacrylate, and "(meth)acrylic acid" means acrylic acid or methacrylic acid. Also, "(meth)acryloyl" means acryloyl or methacryloyl, and "(meth)acrylamide" means acrylamide or methacrylamide.

[0030] The epoxy equivalent of acrylic resin (B) is preferably 150 to 500 g / eq, and more preferably 200 to 450 g / eq or less, from the viewpoint of curability, adhesion, and finished appearance. The epoxy equivalent can be measured by a method in accordance with JIS K 7236.

[0031] From the viewpoint of finished appearance, impact resistance, and processability during film formation, it is preferable that the acrylic resin (B) has a glass transition temperature within the range of 45°C to 80°C, particularly 50°C to 75°C, and even more particularly 55°C to 70°C.

[0032] In this specification, the glass transition temperature Tg of acrylic resin is the value calculated by the following formula.

[0033] 1 / Tg(K)=W1 / T1+W2 / T2+...Wn / Tn Tg(°C) = Tg(K) - 273 In the formula, W1, W2, ...Wn are the mass fractions of each monomer, and T1, T2, ...Tn are the glass transition temperatures Tg(K) of the homopolymers of each monomer.

[0034] The glass transition temperatures of each monomer homopolymer are based on the values ​​in POLYMER HANDBOOK Fourth Edition, edited by J. Brandrup, Eh Immergut, and E.A. Grulke (1999). For monomers not listed in this literature, the glass transition temperature of the monomer homopolymer was synthesized to have a weight-average molecular weight of approximately 50,000, and the glass transition temperature was measured by differential scanning thermal analysis.

[0035] The weight-average molecular weight of the acrylic resin (B) is preferably in the range of 3500 to 6500, particularly 4000 to 6000, from the viewpoint of compatibility with the polyester resin (A) and surface smoothness during film formation.

[0036] If the acrylic resin (B) has a hydroxyl value, it is preferable that the hydroxyl value be in the range of 0 to 30 mg KOH / g, particularly 0 to 20 mg KOH / g, from the viewpoint of curability and water resistance.

[0037] The method for synthesizing the glycidyl group-containing acrylic resin (B) is not particularly limited, as long as it involves copolymerizing the monomer having at least one glycidyl group with other vinyl monomers that can copolymerize with them. For example, it can be carried out by various known methods, and for example, a method in which the above-mentioned various monomers are subjected to a radical polymerization reaction in solution, followed by desolventization, to obtain the desired polymer is preferred in that the molecular weight can be easily adjusted.

[0038] In the final manufactured powder coating, the ratio of polyester resin (A) to acrylic resin (B) is preferably such that, from the viewpoint of curability, processability, and impact resistance, the epoxy equivalent of acrylic resin (B) is within the range of 0.70 to 1.50 equivalents, particularly 0.75 to 1.40 equivalents, and even more particularly 0.80 to 1.30 equivalents, per equivalent of carboxyl groups of polyester resin (A).

[0039] <Polycarbodiimide compound (C)> Polycarbodiimide compounds (C) are compounds having an -N=C=N- group in their molecule and can be produced, for example, by the decarboxylation condensation reaction of diisocyanates in the presence of a carbodiimide catalyst. Examples of carbodiimide catalysts include tin, magnesium oxide, potassium ions, 18-crown-6, 3-methyl-1-phenyl-2-phosphorene oxide, and combinations thereof. These can be used individually or in combination of two or more.

[0040] Examples of diisocyanates include polyfunctional isocyanate compounds such as 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, isophorone diisocyanate, methylcyclohexyl diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, tetramethylxylylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, hexamethylene diisocyanate, norbornene diisocyanate, 2,4,6-triisopropylphenyl diisocyanate, 1,12-diisocyanate dodecane, 2,4,-bis-(8-isocyanate octyl)-1,3-dioctylcyclobutane, and n-pentane-1,4-diisocyanate.

[0041] More specifically, carbodiimide compounds can be produced, for example, by decarbonization condensation of one or more of the above-mentioned compounds to produce carbodiimide, and then encapsulating the remaining isocyanate groups at the terminals with hydrophilic groups or the like.

[0042] Examples of hydrophilic groups to be encapsulated include alkyl sulfonate residues, quaternary salts of dialkylamino alcohol residues, and polyoxyalkylene residues with occluded alkoxy group ends.

[0043] From the viewpoint of processability, impact resistance, and finished appearance, the polycarbodiimide compound (C) preferably has a carbodiimide equivalent of 150 to 450 g / eq, particularly in the range of 200 to 400 g / eq.

[0044] A commercially available polycarbodiimide compound (C) can be used. Specifically, for example, "Stabaxol I (carbodiimide equivalent 360g / eq)", "StabaxoP (carbodiimide equivalent 295g / eq)", "Stabaxol P100 (carbodiimide equivalent 285g / eq)", "Stabaxol Examples include "1LF (carbodiimide equivalent 390g / eq)" (product name, manufactured by Rhein Chemie Japan Co., Ltd.), "Carbodilite LA-1 (carbodiimide equivalent 245g / eq)", "Carbodilite HMV-15CA (carbodiimide equivalent 260g / eq)", "Carbodilite HMV-5CA-LC (carbodiimide equivalent 310g / eq)", "Carbodilite V-04 (carbodiimide equivalent 335g / eq)", "Carbodilite V-02-L2 (carbodiimide equivalent 385g / eq)", and "Carbodilite E-05 (carbodiimide equivalent 310g / eq)" (product names, manufactured by Nisshinbo Chemical Co., Ltd.).

[0045] In the powder coating of the present invention, the ratio of polyester resin (A) to polycarbodiimide compound (C) is preferably such that, from the viewpoint of processability and impact resistance, the amount of carbodiimide equivalent of polycarbodiimide compound (C) is in the range of 0.10 to 0.30 equivalents, particularly 0.15 to 0.25 equivalents, per 1 equivalent of carboxyl group of polyester resin (A).

[0046] The content of the polycarbodiimide compound (C) is preferably in the range of 1.5 to 6.0% by mass, particularly 2.0 to 5.5% by mass, and even more particularly 2.5 to 5.0% by mass, relative to the total solid content of the acid group-containing polyester resin (A) and the glycidyl group-containing acrylic resin (B), from the viewpoint of suppressing solid-phase reactions and the finished appearance of the resulting coating film.

[0047] The powder coating of the present invention may also, as needed, contain various known additives such as organic or inorganic pigments, catalysts, surface modifiers, plasticizers, ultraviolet absorbers, light stabilizers, antioxidants, anti-wrinkle agents, and pigment dispersants; cellulose derivatives such as nitrocellulose and cellulose acetate butyrate; and resins and curing agents other than polyester resins (A) and acrylic resins (B), such as chlorinated polyethylene, chlorinated polypropylene, petroleum resins, epoxy resins, and chlorinated rubber. Resins may also be added.

[0048] Examples of pigments include rust-preventive pigments such as zinc phosphate and aluminum phosphate; extender pigments such as barium sulfate, calcium carbonate, clay, talc, silica, and mica; and coloring pigments such as titanium dioxide, red iron oxide, yellow iron oxide, carbon black, phthalocyanine blue, phthalocyanine green, and quinacridone-based red pigments.

[0049] If a pigment is included, its content is preferably in the range of 10 to 120% by mass, particularly 20 to 100% by mass, relative to the total solid content of the polyester resin (A) and acrylic resin (B), from the viewpoint of finished appearance and blocking resistance.

[0050] Examples of catalysts include imidazole compounds, imidazoline compounds and metal salt complexes thereof, tertiary phosphine compounds, quaternary phosphonium salt compounds, and quaternary ammonium salt compounds.

[0051] If a catalyst is included, its content is preferably in the range of 0 to 2.0% by mass, particularly 0 to 1.0% by mass, relative to the total solid content of the polyester resin (A) and acrylic resin (B), from the viewpoint of curability and finished appearance.

[0052] The above-mentioned pigments and additives may be used individually or in combination of two or more types.

[0053] As described above, the powder coating of the present invention can be manufactured using known methods, which involve mixing each essential component with pigments and other additives as needed, then melting and kneading the resulting mixture, followed by a fine grinding step, and then classification as needed.

[0054] The volume-average particle size of the powder coating of the present invention is preferably in the range of 30 to 45 μm, and more preferably in the range of 30 to 40 μm.

[0055] If the average volume particle size is less than 30 μm, the coating efficiency may be poor, and if it exceeds 45 μm, the finished appearance and coating performance of the resulting powder coating may be reduced.

[0056] In this specification, unless otherwise specified, the average particle diameter refers to the volume-average particle diameter (D50). The volume-average particle diameter (D50) can be measured using a particle size analyzer, such as a laser diffraction / scattering particle size distribution analyzer (Microtrac, manufactured by Nikkiso Co., Ltd.). Specifically, it refers to the value measured using the "Microtrac MT3000II" (manufactured by Nikkiso Co., Ltd.) as the measuring device.

[0057] The powder coating of the present invention contains a polycarbodiimide compound (C) in addition to an acid group-containing polyester resin (A) and a glycidyl group-containing acrylic resin (B). Therefore, during coating production, the polycarbodiimide compound (C) and the low molecular weight components of the acid group-containing polyester resin (A) react preferentially, and the decrease in the highly reactive low molecular weight components of the acid group-containing polyester resin during storage suppresses solid-phase reactions during storage.

[0058] As a result, it is presumed that an acid / epoxy curing type powder coating with excellent finished appearance and superior coating film performance such as adhesion can be obtained.

[0059] The powder coatings of the present invention are not particularly limited in their application, but can be applied to metal materials or metal products such as steel, zinc, aluminum, copper, and tin; these metal materials that have undergone surface treatment; these metal materials with primers and intermediate coatings applied as needed to create a base coating film; roof tiles; glass; inorganic building materials, etc.

[0060] Specifically, this includes automobile bodies or automobile parts, motorcycles or motorcycle parts, building materials such as gates or fences, building materials for interior and exterior use such as aluminum sashes, and various ferrous or non-ferrous metal materials or products such as aluminum foil.

[0061] The powder coating of the present invention can be applied to the surface of an object to be coated to a desired film thickness (usually about 30 to 200 μm, preferably about 40 to 100 μm) by conventional methods such as electrostatic spraying or fluidized bed immersion, and then baked and dried (usually at an object temperature of about 160 to 210°C for about 30 to 60 minutes).

[0062] Furthermore, it is also possible to paint a preheated object using the conventional method described above. [Examples]

[0063] The present invention will be described more specifically below with reference to examples and comparative examples. However, the present invention is not limited to these examples. Note that "parts" and "%" are all based on mass.

[0064] Example 1 45.6 parts of carboxyl group-containing polyester resin (neopentyl glycol / terephthalic acid / isophthalic acid = 38.8 / 5.7 / 55.5 mass ratio, hydroxyl value 10 mg KOH / g, acid value 15 mg KOH / g, weight-average molecular weight 9000, glass transition temperature 60°C), 6.40 parts of glycidyl group-containing acrylic resin (glycidyl methacrylate / methyl methacrylate / styrene / n-butyl methacrylate = 20 / 60 / 10 / 10 mass ratio, epoxy equivalent 350 g / eq, weight-average molecular weight 6000, glass transition temperature 62°C), 1.34 parts of LA-1 (polycarbodiimide compound manufactured by Nisshinbo Chemical Co., Ltd., carbodiimide equivalent 245 g / eq), JR605 47 parts of titanium dioxide (manufactured by Teika Co., Ltd.) and 0.1 parts of C17Z (imidazole-based epoxy resin curing accelerator manufactured by Shikoku Chemicals Co., Ltd.) were mixed, melt-kneaded in an extruder, cooled, finely pulverized in an atomizer, and filtered through a 150 mesh to obtain powder coating No. 1 (volume average particle size 33 μm).

[0065] Example 2 Powder coating No. 2 was obtained in the same manner as in Example 1, except that the polycarbodiimide compound used in Example 1 was replaced with 1.42 parts of HMV-15CA (a polycarbodiimide compound manufactured by Nisshinbo Chemical Co., Ltd., with a carbodiimide equivalent of 260 g / eq).

[0066] Example 3 Powder coating No. 3 was obtained in the same manner as in Example 1, except that the polycarbodiimide compound used in Example 1 was replaced with 1.68 parts of HMV-5CA-LC (polycarbodiimide compound manufactured by Nisshinbo Chemical Co., Ltd., carbodiimide equivalent 310 g / eq).

[0067] Example 4 Powder coating No. 4 was obtained in the same manner as in Example 1, except that the polycarbodiimide compound used in Example 1 was replaced with 1.97 parts of Stabaxol I (a polycarbodiimide compound manufactured by Rhein Chemie Co., Ltd., with a carbodiimide equivalent of 360 g / eq).

[0068] Example 5 Powder coating No. 5 was obtained in the same manner as in Example 1, except that the polycarbodiimide compound used in Example 1 was replaced with 1.61 parts of Stabaxol P (a polycarbodiimide compound manufactured by Rhein Chemie Co., Ltd., with a carbodiimide equivalent of 295 g / eq).

[0069] Example 6 Powder coating No. 6 was obtained in the same manner as in Example 1, except that the polycarbodiimide compound used in Example 1 was replaced with 1.56 parts of Stabaxol P100 (a polycarbodiimide compound manufactured by Rhein Chemie Co., Ltd., with a carbodiimide equivalent of 285 g / eq).

[0070] Comparative Example 1 Powder coating No. 7 was obtained in the same manner as in Example 1, except that the polycarbodiimide compound was not included and the amount of acrylic resin was 8.23 ​​parts.

[0071] Furthermore, the volume-average particle size of powder coatings No. 1 to 7 was 33 μm for all of them.

[0072] The following performance tests and evaluations were performed on each of the powder coatings No. 1 to 7 obtained in Examples 1 to 6 and Comparative Example 1.

[0073] The test panels were prepared by electrostatically coating cold-rolled steel sheets with each powder coating No. 1 to 7 using an electrostatic coating machine PG-1 (manufactured by Asahi Sanac Co., Ltd., product name) to achieve a dry film thickness of 70 μm, and then curing at 180°C for 30 minutes.

[0074] Table 1 shows the formulation composition and performance test results for each powder coating No. 1 to 7.

[0075] The equivalent amounts of each ingredient in the table are as follows:

[0076] Equivalent weight (acrylic resin): The epoxy equivalent weight of glycidyl group-containing acrylic resin relative to 1 equivalent weight of carboxyl group-containing polyester resin in powder coatings. Equivalent weight (polycarbodiimide compound): Carbodiimide equivalent of a polycarbodiimide compound relative to 1 equivalent of carboxyl groups in a carboxyl group-containing polyester resin in a powder coating. Equivalent weight (total); sum of equivalent weight (acrylic resin) and equivalent weight (polycarbodiimide compound)

[0077] [Table 1]

[0078] Weight drop resistance (impact resistance test): In accordance with JIS K 5600-5-3 (1999), an impact was applied to the coated surface of the test plate at -30°C under the conditions of a weight of 500g, a tip diameter of 1 / 2 inch, and a height of 50cm. Then, cellophane adhesive tape was attached to the impacted area, and the degree of peeling of the coating film when the tape was instantly removed was evaluated according to the following criteria.

[0079] ○: No peeling is observed on the painted surface. △: Slight peeling is observed on the painted surface. ×: Significant peeling is observed on the painted surface. Cupping resistance (Erichsen test): Measured at -30°C in accordance with JIS K 5600-5-2 (1999). The extrusion distance (mm) until cracking or peeling occurred in the test plate was measured.

[0080] ○: Extrusion distance of 5mm or more △: Extrusion distance of 2mm or more and less than 5mm ×: Extrusion distance less than 2mm Storage stability of the coatings: Each powder coating was stored in a sealed container at 35°C for one month. Subsequently, test plates with a film thickness of 70 μm were prepared using the powder coating according to the above test plate preparation conditions, and the finished appearance was evaluated according to the following criteria.

[0081] ○: There is almost no change compared to the painted board made with powder coating before storage. △: Slightly less smooth compared to a painted board made with powder coating before storage. ×: The smoothness is significantly worse compared to the coated board made with the powder coating before storage, or it does not flow at all. [Industrial applicability]

[0082] This method enables the control of solid-phase reactions during storage after powder coating production, resulting in a powder coating with excellent finish appearance and coating performance.

Claims

1. It contains an acid group-containing polyester resin (A), a glycidyl group-containing acrylic resin (B), and a polycarbodiimide compound (C), A powder coating characterized in that the amount of carbodiimide equivalents of the polycarbodiimide compound (C) is 0.10 to 0.30 equivalents per equivalent of carboxyl groups of the polyester resin (A).

2. The powder coating according to claim 1, wherein the content of the polycarbodiimide compound (C) is in the range of 1.5 to 6.0% by mass with respect to the total amount of solids of the acid group-containing polyester resin (A) and the glycidyl group-containing acrylic resin (B).

3. The powder coating according to Claim 1, wherein the epoxy equivalent of acrylic resin (B) is 0.70 to 1.50 equivalents per equivalent of carboxyl groups of polyester resin (A).

4. A painted article having a coating film of the powder coating described in claim 1 or 2.

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