Matte powder coating composition and coating film forming method

Abstract

To provide a matte powder coating composition having excellent coating film smoothness and gloss stability, as well as superior storage stability.SOLUTION: A matte powder coating composition comprises a carboxyl group-containing polyester resin (A), a β-hydroxyalkyl amide compound (B), and a phyllosilicate (C) and has a melt flow value of 30 mm or more, wherein the composition has a gloss value of 60 or less at an incident angle of 60° in a coating film obtained therefrom. The acid value of the carboxyl group-containing polyester resin (A) is 10-200 mgKOH / g.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a matte powder coating composition which provides a coating film with excellent smoothness and gloss stability, and also has excellent storage stability, and to a coating film forming method. [Background technology]

[0002] Powder coatings have attracted attention as low-pollution coatings because they do not release organic solvents into the atmosphere during application. In particular, polyester resin-based powder coatings, which use a combination of polyester resin and a crosslinker, are known as coatings that are applied to metal products such as steel furniture, electrical appliances, and automobile parts. In addition, a matte coating may be required to impart a high-quality texture to these metal products.

[0003] One known method for adjusting the gloss of polyester resin-based powder paints is to add a matting agent such as silica, but this has the problem of reducing the smoothness of the coating film and degrading the finished appearance.

[0004] Patent Document 1 describes a polyester resin composition for powder coatings, which comprises an ungelled polyester having an acid value of 70 mgKOH / g or more, an ungelled polyester having an acid value of 10 to 50 mgKOH / g, and a hydroxyl alkylamide-based curing agent.

[0005] The method of using two or more polyester resins with different acid values ​​in combination has a matte effect, but has the problems of reducing the smoothness of the coating film and poor storage stability of the powder coating.

[0006] Patent Document 2 describes a matte powder coating composition that contains a curable resin, a curing agent, and polyolefin waxes, the polyolefin waxes including polyolefin wax A having a melting point of 141 to 180°C and polyolefin wax B having a melting point of 90 to 140°C.

[0007] The matte technique using polyolefin wax has the problem that the gloss of the matte coating film is not stable depending on the baking conditions. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 10-007944 [Patent Document 2] Japanese Patent Publication No. 2020-090663 Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a matte powder coating composition which provides excellent coating film smoothness and gloss stability, and also has excellent storage stability. [Means for solving the problem]

[0010] As a result of intensive research conducted by the inventors to solve the above problems, they discovered that by applying a phyllosilicate (C) to a powder coating composition containing a carboxyl group-containing polyester resin (A) and a β-hydroxyalkylamide compound (B), it is possible to obtain a matte powder coating composition that has excellent storage stability and that provides smooth coating film and a stable matte appearance regardless of baking conditions, and thus completed the present invention.

[0011] That is, the present invention relates to the following.

[0012] 1. A matte powder coating composition comprising a carboxyl group-containing polyester resin (A), a β-hydroxyalkylamide compound (B), and a phyllosilicate (C), the powder coating composition having a melt flow value of 30 mm or more, and the gloss of the resulting coating film at an incident angle of 60° being 60 or less.

[0013] 2. A matte powder coating composition according to item 1, wherein the carboxyl group-containing polyester resin (A) has an acid value of 10 to 200 mgKOH / g.

[0014] 3. A matte powder coating composition according to item 1 or 2, containing 0.5 to 5 parts by mass of phyllosilicate (C) per 100 parts by mass of the total solid content of the carboxyl group-containing polyester resin (A) and the β-hydroxyalkylamide compound (B).

[0015] 4. A method for forming a coating film, which comprises applying the matte powder coating composition according to item 1 or 2 above to a substrate.

[0016] 5. A method for producing a powder coating composition, which comprises dry-mixing a phyllosilicate (C) with a powder coating composition containing a carboxyl group-containing polyester resin (A) and a β-hydroxyalkylamide compound (B). [Effects of the Invention]

[0017] The matte powder coating composition of the present invention is obtained by mixing a carboxyl group-containing polyester resin (A) and a β-hydroxyalkylamide compound (B) with a phyllosilicate (C), and has excellent storage stability, excellent coating film smoothness, and can form a stable matte appearance coating film regardless of the baking conditions. BEST MODE FOR CARRYING OUT THE INVENTION

[0018] The matte powder coating composition of the present invention is a matte powder coating composition containing a carboxyl group-containing polyester resin (A), a β-hydroxyalkylamide compound (B) and a phyllosilicate (C).

[0019] The matte powder coating composition of the present invention (hereinafter sometimes referred to as "the coating") will be described in detail below.

[0020] <Carboxy group-containing polyester resin (A)> The carboxyl group-containing polyester resin (A) used in the matte powder coating composition of the present invention can be prepared by subjecting a polybasic acid and a polyhydric alcohol to an esterification reaction.

[0021] The polybasic acid may be a polybasic acid having two or more carboxy groups in one molecule. Examples of the polybasic acid include phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, 4,4-diphenyldicarboxylic acid, diphenylmethane-4,4'-dicarboxylic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, HET acid, maleic acid, fumaric acid, itaconic acid, cyclohexane-1,3-dicarboxylic acid, cyclohexane-1,4-dicarboxylic acid, hexahydrophthalic acid, hexahydroisophthalic acid, hexahydroterephthalic acid, hexahydrotrimellitic acid, methylhexahydrophthalic acid, trimellitic acid, pyromellitic acid, trimesic acid, methylcyclohexene tricarboxylic acid, tetrachlorohexene tricarboxylic acid, and lower alkyl esters of these acids, as well as anhydrides thereof.

[0022] These polybasic acid components can be used alone or in combination of two or more.

[0023] In addition to the above polybasic acids, monobasic acids such as benzoic acid, crotonic acid, and pt-butylbenzoic acid can also be used as the acid component, if necessary.

[0024] As the polyhydric alcohol, a polyhydric alcohol having two or more hydroxyl groups in one molecule can be used, and examples thereof include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, 1,3-butanediol, 2,3-butanediol, 1,2-butanediol, 3-methyl-1,2-butanediol, 1,2-pentanediol, 1,5-pentanediol, 1,4-pentanediol, 2,4-pentanediol, 3-methyl-4,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,6-hexanediol, 1,5-hexanediol, 1,4-hexanediol, 2,5-hexanediol, neopentanediol, and the like. Examples of suitable hydroxypropyl ethers include glycols such as pentyl glycol and hydroxypivalic acid neopentyl glycol ester, polylactone diols obtained by adding lactones such as ε-caprolactone to these glycols, polyester diols such as bis(hydroxyethyl) terephthalate, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, tricyclodecane dimethanol, hydrogenated bisphenol A, hydrogenated bisphenol F, spiroglycol, dihydroxymethyltricyclodecane, glycerin, trimethylolpropane, trimethylolethane, diglycerin, triglycerin, 1,2,6-hexanetriol, pentaerythritol, dipentaerythritol, sorbitol, and mannitol.

[0025] These alcohol components can be used alone or in combination of two or more.

[0026] The esterification or transesterification reaction between the acid component and the alcohol component can be carried out by a method known per se, for example, by polycondensing the acid component and the alcohol component at a temperature of 100 to 250°C.

[0027] In the present invention, a polyester resin having hydroxyl groups may be obtained from the acid component and the alcohol component, and then the hydroxyl groups of the obtained polyester resin may be reacted with a polybasic acid such as maleic acid, maleic anhydride, phthalic anhydride, trimellitic anhydride, hexahydrophthalic anhydride, or tetrahydrophthalic anhydride to introduce carboxyl groups into the resin, thereby forming a carboxyl group-containing polyester resin.

[0028] The glass transition temperature of the carboxyl group-containing polyester resin (A) is preferably in the range of 20°C to 80°C, particularly 30°C to 70°C, from the viewpoint of storage stability and coating film smoothness in the powder coating.

[0029] The number average molecular weight of the carboxyl group-containing polyester resin (A) is preferably in the range of 400 to 20,000, particularly 1,000 to 10,000, from the viewpoint of coating film performance and coating film smoothness.

[0030] From the viewpoint of coating film performance and coating film smoothness, the acid value of the carboxyl group-containing polyester resin (A) is preferably in the range of 10 to 200 mgKOH / g, particularly 20 to 70 mgKOH / g, and more particularly 25 to 50 mgKOH / g.

[0031] The softening point of the carboxyl group-containing polyester resin (A) is preferably in the range of 60 to 150°C, particularly 70 to 110°C, from the viewpoint of coating film performance and coating film smoothness.

[0032] The glass transition temperature can be determined, for example, by DSC (differential scanning calorimetry).

[0033] <β-Hydroxyalkylamide Compound (B)> The matte powder coating composition of the present invention contains a β-hydroxyalkylamide compound as a crosslinking agent for the carboxyl group-containing polyester resin (A). As the β-hydroxyalkylamide compound, those having two or more functional groups per molecule are preferred from the viewpoints of low-temperature curing ability and coating film smoothness. For example, a β-hydroxyalkylamide represented by the following formula can be used: (Here, n is an integer of 1 or more. From the viewpoints of low-temperature curing ability and coating film smoothness, n is preferably in the range of 3 to 8, more preferably in the range of 4 to 6.)

[0034] [ka]

[0035] Commercially available compounds of the formula above include "PRIMID XL-552" (manufactured by EMS-PRIMD, n=4 in the formula above) and "INOMID AH-001" (manufactured by INOPOL, n=4 in the formula above).

[0036] The blending ratio of the carboxy group-containing polyester resin (A) and the β-hydroxyalkylamide compound (B) is arbitrary, but from the viewpoint of coating film curability, it is preferable that the equivalent ratio of carboxy groups to hydroxyalkylamide groups is in the range of 1 / 0.7 to 0.7 / 1, particularly 1 / 0.9 to 0.9 / 1.

[0037] <Phyllosilicate (C)> The matte powder coating composition of the present invention contains a phyllosilicate (C) from the viewpoints of forming a low-gloss coating film and improving coating film smoothness.

[0038] Phyllosilicates are a subgroup of silicate minerals. Phyllosilicates are sheet silicate materials (layered silicates) formed by parallel sheets of silicate tetrahedra with a SiO2O5 or 2:5 ratio. The tetrahedral layers alternate with octahedral layers. In the octahedral layers, cations are surrounded by hydroxide ions and / or oxygen in octahedral coordination. The actual layers themselves are usually negatively charged, and the charge is partially offset by additional cations in the interstices of each layer. These additional cations should be distinguished from the cations in the octahedral layers. Many phyllosilicates can be well swelled and / or dispersed in water. This process is called exfoliation (or equivalently, delamination).

[0039] Phyllosilicates usually have a thin, flat, scaly shape.

[0040] Examples of phyllosilicates include montmorillonite, bentonite, kaolinite, hectorite, fluorohectorite, saponite, beidellite, nontronite, stevensite, vermiculite, fluorovermiculite, halloysite, volkonskoite, suconite, magadiite, sauconite, stibensite, stipulgites, attapulgite, illite, kenyaite, smectite, allevardite, muscovite, palygorskite, sepiolite, sillinite, grumantite, revdite, zeolite, fuller's earth, natural or synthetic talc, and mica.

[0041] As the phyllosilicate (C), natural or synthetic talc and mica can be suitably used from the viewpoint of matte effect and coating film smoothness. As the phyllosilicate (C), modified products can also be used.

[0042] As the modified phyllosilicates, organically modified products can be used in particular, that is, products obtained by known methods in which a structure containing an organic group (hydrocarbon group) such as an alkyl group is bonded to the crystals.

[0043] The phyllosilicates (C) can be used alone or in combination of two or more.

[0044] In the present coating material, the average particle size of the phyllosilicate (C) is preferably within the range of 0.5 to 100 μm, particularly 0.5 to 50 μm, and even more particularly 0.5 to 30 μm, from the viewpoint of the appearance and smoothness of the coating film.

[0045] In this specification, the average particle size is a value obtained by centrifugal sedimentation particle size measurement, for example, using a centrifugal sedimentation particle size distribution analyzer BI-DCP (manufactured by Brookhaven Instruments).

[0046] In this paint, the content of phyllosilicate (C) is preferably within the range of 0.5 to 5 parts by mass, particularly 1 to 5 parts by mass, per 100 parts by mass of the total solid content of the carboxyl group-containing polyester resin (A) and the β-hydroxyalkylamide compound (B), from the viewpoints of matte effect and coating film smoothness.

[0047] If the content of the phyllosilicate (C) is less than 0.5 parts by mass, the matting effect may be insufficient, and if it exceeds 5 parts by mass, the smoothness of the coating film may decrease.

[0048] From the viewpoint of the matting effect, the phyllosilicate (C) is preferably added by dry mixing.

[0049] In the present invention, dry mixing refers to so-called dry blending, which means a method of mixing two or more powders in a dry state without using a liquid dispersion medium. Dry mixing can be carried out at room temperature, but from the viewpoint of the appearance of the coating film, it is preferable to carry out the dry mixing at a temperature of 50°C or less.

[0050] In addition, in the above-mentioned dry mixing, from the viewpoint of coating film smoothness, it is preferable to carry out the mixing so that the melt flow value of the powder coating composition containing the carboxyl group-containing polyester resin (A), the β-hydroxyalkylamide compound (B) and the phyllosilicate (C) is 30 mm or more, preferably 40 mm or more, and particularly preferably 45 mm or more.

[0051] In the present invention, the melt flow value was measured in accordance with the specified measurement conditions in accordance with the powder coatings - Section 2: Inclined melt flow test method of the Japanese Industrial Standard "JIS K 5600-9-2," except that the heating temperature of the circulation oven was 160°C, the heating holding time of the circulation oven was 10 minutes, and the angle of the metal plate was 45° to the horizontal plane.

[0052] 1.4 g of the powder coating composition was applied at a rate of 20 kg / mm ​​to form a cylindrical shape with a diameter of 12.5 mm and a height of approximately 6.5 mm. 2 The value is obtained by applying a pressure of 1000 kJ / cm2 to a molded pellet, heating it to 160°C for 10 minutes on a metal plate held at an angle of 45° to the horizontal, and measuring the length from the tip of the sample pellet to the tip of the melted and flowed pellet to the nearest 0.5 mm.

[0053] <Pigment (D)> The paint of the present invention may further contain coloring pigments, extender pigments, and anti-rust pigments as required. Note that in the present invention, the phyllosilicate (C) is excluded from the pigment (D).

[0054] As the color pigment, one or a combination of two or more conventionally known pigments for inks and paints can be used. Specific examples of the color pigment include metal oxide pigments such as titanium oxide and iron oxide, composite metal oxide pigments such as titanium yellow, carbon black, azo pigments, quinacridone pigments, diketopyrrolopyrrole pigments, perylene pigments, perinone pigments, benzimidazolone pigments, isoindoline pigments, isoindolinone pigments, metal chelate azo pigments, phthalocyanine pigments, indanthrone pigments, dioxane pigments, and indigo pigments.

[0055] From the viewpoint of the coloring power and finished appearance of the resulting coating film, the blending amount of the color pigment is preferably within a range of 1 to 150 parts by mass, more preferably within a range of 3 to 100 parts by mass, per 100 parts by mass of the total solid content of the carboxyl group-containing polyester resin (A) and the β-hydroxyalkylamide compound (B).

[0056] As the extender pigment, one or a combination of two or more pigments conventionally known for use in inks and paints can be used. Specific examples of extender pigments include calcium carbonate, barium sulfate, magnesium carbonate, calcium sulfate (gypsum), diatomaceous earth, clay (kaolin), and silica.

[0057] The extender pigment preferably has an average particle size of 0.01 to 30 μm, more preferably 0.5 to 10 μm. If the average particle size is larger than 30 μm, the appearance may be poor when the pigment is formed into a thin film, and if it is smaller than 0.1 μm, melt dispersion may be difficult. The maximum particle size is preferably 200 μm or less, more preferably 50 μm or less.

[0058] The finer the particles of the extender pigments, the stronger their surface activity and the more likely they are to form agglomerates, so they may be surface-treated to prevent agglomeration and increase their affinity with the vehicle-forming components. Examples of surface treatments include treatments with fatty acids and their salts, resin acids, other organic carboxylic acids and their salts, and surfactants, either alone or in combination; treatments with titanate and silane coupling agents; and surface treatments with inorganic acids, alkalis, silica, alumina, and zinc compounds.

[0059] The average particle size of the extender pigment is preferably within the range of 0.01 to 10 μm in terms of the smoothness and gloss of the coating film.

[0060] The content of the extender pigment is not particularly limited, but from the viewpoint of the smoothness of the resulting coating film, it is preferably 5 to 40 parts by mass, and more preferably 10 to 25 parts by mass, per 100 parts by mass of the total solid content of the carboxyl group-containing polyester resin (A) and the β-hydroxyalkylamide compound (B).

[0061] As the anti-rust pigment, conventionally known pigments for use in paints can be used, such as aluminum phosphomolybdate, aluminum tripolyphosphate, and zinc oxide (zinc white). Aluminum dihydrogen tripolyphosphate can be used, particularly from the viewpoint of anti-rust power and storage stability of the paint. Furthermore, pigments whose surfaces have been treated with compounds of zinc, calcium, sodium, manganese, tin, titanium, etc. may also be used.

[0062] In the present invention, when an anti-rust pigment is used, the amount of the anti-rust pigment to be added is preferably 1 to 20 parts by mass, more preferably 3 to 10 parts by mass, per 100 parts by mass of the total solid content of the carboxyl group-containing polyester resin (A) and the β-hydroxyalkylamide compound (B), from the viewpoint of the anti-rust properties and smoothness of the coating film.

[0063] In addition to the above components, the present coating material may contain, as necessary, luster pigments, flowability modifiers, antiblocking agents, ultraviolet absorbers, ultraviolet stabilizers, surface conditioners, anti-foaming agents, charge control agents, curing accelerators, epoxy resins, and the like, which are commonly used in powder coating materials.

[0064] The matte powder coating composition of the present invention can be produced by known methods, for example, by melt-mixing the above-mentioned carboxyl group-containing polyester resin (A), β-hydroxyalkylamide compound (B), phyllosilicate (C), and optional components, followed by cooling and pulverization.

[0065] Specifically, the above components are mixed and dispersed, then melt-mixed using an extrusion kneader, single-screw or twin-screw extruder, or the like, usually at about 80 to 150°C, pelletized, and cooled, and then finely pulverized using an impact pulverizer, airflow pulverizer, or the like, and classified to produce the product.

[0066] Regarding the addition and mixing of the phyllosilicate (C), the dry mixing method described in the phyllosilicate (C) and attached attachment is preferred, specifically, a method of dry mixing the phyllosilicate (C) with a powder coating containing a carboxyl group-containing polyester resin (A) and a β-hydroxyalkylamide compound (B).

[0067] The average particle size of the matte powder coating composition of the present invention is preferably adjusted to a volume average particle size within the range of 10 μm to 80 μm from the viewpoint of powder fluidity and the finished appearance and smoothness of the coating film obtained by application, and more preferably within the range of 20 μm to 45 μm.

[0068] The coating thickness of the matte powder coating composition of the present invention may be appropriately set as needed, but is preferably within the range of 30 to 100 μm, particularly 40 to 80 μm, as a dry coating thickness.

[0069] The matte powder coating composition of the present invention can be cured by heat drying at 140 to 200°C for 10 to 40 minutes, particularly at 140 to 160°C for 10 to 20 minutes.

[0070] When a coating film formed from the matte powder coating composition of the present invention is cured at 160°C for 20 minutes to form a coating film with a thickness of 60 μm, the coating film preferably has a gloss of 60 or less at an incident angle of 60°. A gloss of 60 or less can be said to provide a low-gloss appearance at a level that is acceptable for practical use.

[0071] In other words, the powder coating composition of the present invention is preferably a powder coating composition that, when cured at 160°C for 20 minutes to form a coating film with a thickness of 60 μm, has a gloss of 60 or less at an incident angle of 60°.

[0072] The gloss of the coating film can typically be measured using a gloss meter at a predetermined incident angle. The lower the gloss, the lower the appearance of the coating film.

[0073] The substrate for the object to be coated is not particularly limited, but examples include alloyed zinc-plated materials, cast iron materials, hot-dip galvanized materials, magnesium alloy materials, aluminum die-cast materials, various metal plates or processed products obtained by surface treatment of these metals such as degreasing or chemical conversion treatment, and plastic plates or processed products that have been treated to be conductive by coating with a conductive primer or the like.

[0074] The matte powder coating composition of the present invention can be applied to a substrate by known methods such as electrostatic coating, fluidized bed immersion, spraying, in-mold coating, etc., but it is preferable to employ an electrostatic powder coating method using a powder coating gun. Examples of electrostatic powder coating methods include a method in which a metal substrate is grounded, and then the powder coating composition is sprayed using a powder coating device such as a corona-charged coating gun, a friction-charged coating gun, or an electrostatic field cloud fluidized bed immersion coating device manufactured by Mesac.

[0075] When using the above-mentioned corona charging type coating gun, the charging voltage applied to the matte powder coating composition by corona discharge treatment is preferably set to -50 to -100 KV, more preferably -60 to -90 KV from the viewpoints of coating efficiency and finished appearance. On the other hand, when using a triboelectric charging type coating gun, it is preferable to perform triboelectric charging treatment so that the internally generated current value of the powder coating composition is 1.0 to 8.0 μA from the viewpoints of coating efficiency and finished appearance.

[0076] The preferred discharge rate of each of the above coating guns is 50 to 400 g / min, and the preferred discharge pressure is 4.9 × 10 to 4.9 × 10 Pa. The distance from the tip of the coating gun to the substrate to be coated is preferably 10 to 50 cm, and coating within these ranges allows the particles of the matte powder coating composition to be electrostatically attached to the conductive substrate to be coated with good coating efficiency, thereby forming a powder coating layer. [Example]

[0077] Next, the present invention will be described more specifically with reference to examples and comparative examples, in which "parts" and "%" mean "parts by mass" and "% by mass", respectively.

[0078] Example 1 95 parts of Uralac P785 (trade name, polyester resin, manufactured by Covestro, acid value 36 mg KOH / g), 5 parts of PRIMID XL-552 (trade name, β-hydroxyalkylamide compound, manufactured by M-Chemie), 0.5 parts of benzoin, 1 part of Resiflow P67 (trade name, surface conditioner, manufactured by Estro Chemical), TITANIX 50 parts of JR-605 (trade name, white titanium oxide, manufactured by Teika Corporation) were mixed together with 50 parts of R-70A (trade name, calcium carbonate, manufactured by Maruo Calcium Corporation) and charged into a high-speed mixer (trade name, manufactured by Fukae Kogyo Co., Ltd., capacity 2 liters), and the mixture was stirred for 1 minute at an agitator speed of 500 rpm and a chopper speed of 4000 rpm to mix uniformly. The mixture was then melt-kneaded at a temperature of 120°C using an extrusion kneader (trade name, Buss Kneader PR46, manufactured by Buss Co., Ltd.), cooled, and then finely pulverized using a hammer-type impact crusher. After classification using a 150-mesh wire screen, a powder coating composition with an average particle size of 40 μm was obtained.

[0079] 100 parts of the powder coating composition obtained above and 1 part of BYK-3938P (trade name, modified ferrosilicate, manufactured by BYK-Chemie) were mixed, and the mixture was placed in a high-speed mixer (trade name, manufactured by Fukae Kogyo Co., Ltd., capacity 2 liters) and stirred for 1 minute at an agitator speed of 500 rpm and a chopper speed of 4000 rpm to mix uniformly, thereby producing matte powder coating composition 1 having an average particle size of 40 μm.

[0080] Examples 2 to 9 and Comparative Examples 1 to 3 Preparation of Matte Powder Coating Compositions 2 to 12 Using the formulations shown in Table 1, matte powder coating compositions 2 to 17 were obtained in the same manner as in Example 1.

[0081] Matte powder coating compositions 10 to 12 are comparative examples.

[0082] In the table, U-Picacoat GV-350 and CERAFLOUR-970 are as follows. (Note 1) U-Pica Coat GV-350: Product name, polyester resin, acid value 29 mg KOH / g, manufactured by Japan U-Pica Co., Ltd. (Note 2) CERAFLOUR-970: Product name, micronized polypropylene wax, manufactured by BYK Creating test panels Each of the obtained matte powder coating compositions 1 to 12 was electrostatically powder coated onto a substrate (0.8 mm thick SPCC steel plate zinc phosphate treated with Palbond #3118, manufactured by Nippon Parkerizing Co., Ltd.) using an electrostatic coater PG-1 (trade name, manufactured by Asahi Sunac Corporation) so that the cured film thickness was 60 μm, and the substrate was heated and dried under conditions of maintaining the substrate temperature at 160 ° C for 20 minutes and at 180 ° C for 20 minutes, obtaining two levels of test panels for each of the matte powder coating compositions 1 to 12. The evaluation results of the coating performance tests described below for the obtained test panels are also shown in Table 1.

[0083] Coating performance tests and evaluation criteria Finished appearance: The finished appearance of the coating film was visually evaluated according to the following criteria. ⊚: There is no yuzu peel, uneven gloss, repelling, bumps or dents, and the paint surface is in good condition. ○: Some yuzu peel, uneven gloss, repelling, bumps, or dents are observed, but there is no problem in practical use. △: Yuzu peel, uneven gloss, repelling, bumps, or dents are observed. ×: Any of the following is observed: citron peel, uneven gloss, repelling, bumps, or dents, and the degree is significant.

[0084] 60-degree specular gloss: The degree of gloss of the test plate was measured by measuring the reflectance at an incident angle of 60 degrees in accordance with JIS K 5600-4-7 (1999) 60-degree specular gloss, and expressed as a percentage with the gloss of the standard specular gloss surface taken as 100.

[0085] Coating curability: The substrate temperature was maintained at 160°C for 20 minutes, and the coating on the test plate was then cured, and the curability was evaluated by the following test.

[0086] The test plate was rubbed 10 times with a gauze soaked in acetone under a load of 500 g, and the state of the coating film was evaluated based on the following criteria. ◯: There is no exposure of the substrate, no transfer to the gauze, and no change in the gloss of the coating film, and the coating surface condition is good. ×: Any of the following is observed: exposure of the substrate, transfer to the gauze, or change in gloss of the coating film.

[0087] Storage stability of paint: The storage stability of the paint was evaluated according to the following criteria.

[0088] Each coating composition was placed in a 100 mL glass container and stored in a sealed container at 35° C. for 30 days. The condition thereafter was evaluated according to the following criteria. Good: No change from before storage. △: There is some aggregation, but it can be pulverized and used as a paint.

[0089] [Table 1]

[0090] [Table 2] [Industrial Applicability]

[0091] The matte powder coating composition of the present invention can provide a matte powder coating composition which has excellent coating film smoothness and gloss stability, and also has excellent storage stability.

Claims

1. A matte powder coating composition comprising a carboxyl group-containing polyester resin (A), a β-hydroxyalkylamide compound (B), and a phyllosilicate (C), the powder coating composition having a melt flow value of 30 mm or more, and the gloss of the resulting coating film at an incident angle of 60° of 60 or less.

2. 2. The matte powder coating composition according to claim 1, wherein the carboxyl group-containing polyester resin (A) has an acid value of 10 to 200 mgKOH / g.

3. 3. The matte powder coating composition according to claim 1, wherein the phyllosilicate (C) is contained in an amount of 0.5 to 5 parts by mass per 100 parts by mass of the total solid content of the carboxyl group-containing polyester resin (A) and the β-hydroxyalkylamide compound (B).

4. A method for forming a coating film, which comprises applying the matte powder coating composition according to claim 1 or 2 to a substrate.

5. A method for producing a powder coating composition, comprising dry-mixing a phyllosilicate (C) with a powder coating composition containing a carboxyl group-containing polyester resin (A) and a β-hydroxyalkylamide compound (B).

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