Powder coating resin composition, powder coating, and article having a coating film of the coating

Abstract

To provide a resin composition for a powder coating, and a powder coating which enable the formation of a cured coated film excellent in curability, smoothness and filiform corrosion resistance, and an article having a coated film of the coating.SOLUTION: A resin composition for a powder coating contains an acrylic resin (A) containing an acrylic monomer (a1) having an epoxy group, (meth)acrylamide (a2), styrene (a3) and other unsaturated monomer (a4) as essential raw materials, wherein the acrylic monomer (a1) in a monomer component that is a raw material of the acrylic resin (A) is 20-60 mass%, the (meth)acrylamide is 0.1-30 mass%, and the styrene is 10-50 mass%.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a resin composition for powder coatings, a powder coating, and an article having a coating film of the coating.

Background Art

[0002] In recent years, due to problems such as air pollution, regulations on organic solvents have become stricter, and environmentally friendly coatings have attracted attention. Among them, powder coatings, as solvent-free coatings, have been in the spotlight from the perspective of environmental protection. In particular, acrylic powder coatings are excellent in coating film properties such as weather resistance and stain resistance, and thus have been attracting attention for applications in automotive parts such as aluminum wheels, metal exteriors, and household appliances. However, compared with solvent-based coatings, powder coatings have the drawback that the smoothness of the coating film is inferior.

[0003] In contrast, a powder coating comprising an epoxy group-containing acrylic resin obtained by copolymerizing an alkyl (meth)acrylate, an acrylic monomer containing an epoxy group, and other copolymerizable vinyl monomers, and a curing agent having a functional group capable of reacting with the epoxy group has been proposed (see, for example, Patent Document 1). However, although the smoothness of the cured coating film obtained from this powder coating is improved, there is a problem that the rust resistance is insufficient.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The problem to be solved by the present invention is to provide a resin composition for powder coatings, a powder coating, and an article having a coating film of the coating, which can obtain a cured coating film excellent in curability, smoothness, and rust resistance.

Means for Solving the Problems

[0006] As a result of intensive research to solve the above problems, the inventors of the present invention have found that a cured coating film obtained from a resin composition for powder coatings containing an acrylic resin having an acrylic monomer having an epoxy group, (meth)acrylamide, styrene, and other unsaturated monomers as essential raw materials is excellent in curability, smoothness, and rust resistance to yarn, and completed the invention.

[0007] That is, the present invention relates to a resin composition for powder coatings containing an acrylic resin (A) having an acrylic monomer (a1) having an epoxy group, (meth)acrylamide (a2), styrene (a3), and other unsaturated monomers (a4) as essential raw materials, wherein the acrylic monomer (a1) in the monomer component as a raw material of the acrylic resin (A) is 20 to 60% by mass, (meth)acrylamide is 0.1 to 30% by mass, and styrene is 10 to 50% by mass. The present invention relates to a resin composition for powder coatings, a powder coating, and an article coated with the coating.

Effect of the Invention

[0008] Since the resin composition for powder coatings of the present invention is excellent in curability, appearance, and rust resistance to yarn and can form a cured coating film, it can be suitably used as a coating for coating articles such as aluminum wheels.

Mode for Carrying Out the Invention

[0009] The resin composition for powder coatings of the present invention is a resin composition for powder coatings containing an acrylic resin (A) having an acrylic monomer (a1) having an epoxy group, (meth)acrylamide (a2), styrene (a3), and other unsaturated monomers (a4) as essential raw materials, wherein the acrylic monomer (a1) in the monomer component as a raw material of the acrylic resin (A) is 20 to 60% by mass, (meth)acrylamide is 0.1 to 30% by mass, and styrene is 10 to 50% by mass.

[0010] First, the acrylic resin (A) will be described. The acrylic resin (A) has an epoxy group and is obtained by copolymerizing the acrylic monomer (a1), (meth)acrylamide (a2), styrene (a3), and other unsaturated monomers (a4).

[0011] The acrylic monomer (a1) is an acrylic monomer having an epoxy group, and examples thereof include glycidyl (meth)acrylate, methyl glycidyl (meth)acrylate, (meth)allyl glycidyl ether, (meth)allyl methyl glycidyl ether, 3,4-epoxycyclohexylmethyl (meth)acrylate, etc. Among these, glycidyl (meth)acrylate is preferred. These acrylic monomers (a1) can be used alone or in combination of two or more.

[0012] In the present invention, "(meth)acrylic acid" refers to one or both of methacrylic acid and acrylic acid, "(meth)acrylate" refers to one or both of methacrylate and acrylate, "(meth)acrylamide" refers to one or both of methacrylamide and acrylamide, and "(meth)acryloyl group" refers to one or both of methacryloyl group and acryloyl group.

[0013] The (meth)acrylamide (a2) can be used alone or in combination of two or more.

[0014] The other unsaturated monomer (a4) is an unsaturated monomer other than the acrylic monomer (a1), (meth)acrylamide, and styrene. For example, (meth)acrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, behenyl (meth)acrylate, cyclohexyl (meth)acrylate, 4-tert-butylcyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, benzyl (meth)acrylate, (meth)acrylonitrile, N,N-dimethylaminoethyl (meth)acrylate, 3-(meth)acryloyloxypropyltrimethoxysilane, 3-(meth)acryloyloxypropyltriethoxysilane, 3-(meth)acryloyloxypropylmethyldimethoxysilane, styrene, α-methylstyrene, p-methylstyrene, p-methoxystyrene, 2-methoxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxy-n-butyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxy-n-butyl (meth)acrylate, 3-hydroxy-n-butyl (meth)acrylate, 1,4-cyclohexanedimethanol mono(meth)acrylate, glycerin mono(meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-(meth)acryloyloxyethyl-2-hydroxyethyl phthalate, monofunctional monomers such as lactone-modified (meth)acrylate having a hydroxyl group at the terminal;Ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, hydroxypivalic acid ester neopentyl glycol di(meth)acrylate, bisphenol A-di(meth)acrylate, bisphenol A-EO modified di(meth)acrylate, isocyanuric acid EO modified diacrylate and other difunctional monomers; isocyanuric acid EO modified triacrylate, trimethylolpropane tri(meth)acrylate, trimethylolpropane EO modified tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetraacrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol penta(meth)acrylate and other trifunctional or higher functional monomers. Among these, alkyl (meth)acrylate is preferred because the curability and rust resistance of the coating film are further improved, and alkyl (meth)acrylate having an alkyl group with 1 to 4 carbon atoms is more preferred. These unsaturated monomers (a4) can be used alone or in combination of two or more.;

[0015] The usage amount of the acrylic monomer (a1) is 20 to 60% by mass in the monomer component which is the raw material of the acrylic resin (A). However, since the balance between curability and rust resistance is further improved, 25 to 50% by mass is preferred, and 25 to 40% by mass is more preferred.

[0016] The amount of the (meth)acrylamide (a2) used is 0.1 to 30% by mass in the monomer components which are the raw materials of the acrylic resin (A). However, since the balance between curability and resistance to rusting of the yarn is further improved, 0.1 to 20% by mass is preferable, 0.2 to 15% by mass is more preferable, and 0.5 to 5% by mass is even more preferable.

[0017] The amount of the styrene (a3) used is 10 to 50% by mass in the monomer components which are the raw materials of the acrylic resin (A). However, since the balance between curability and resistance to rusting of the yarn is further improved, 15 to 45% by mass is preferable, and 15 to 40% by mass is more preferable.

[0018] The amount of the unsaturated monomer (a4) used is preferably 20 to 70% by mass in the monomer components which are the raw materials of the acrylic resin (A) since the balance between curability and resistance to rusting of the yarn is further improved.

[0019] In addition, the glass transition temperature of the acrylic resin (A) is preferably 20 to 120°C since the resistance to rusting of the yarn of the coating film is improved. More preferably, 40 to 100°C is preferable.

[0020] In the present invention, the glass transition temperature is FOX's formula: 1 / Tg = W1 / Tg1 + W2 / Tg2 + ··· (Tg: glass transition temperature to be determined, W1: weight fraction of component 1, Tg1: glass transition temperature of the homopolymer of component 1) and is obtained by calculation according to this. The values of the glass transition temperatures of the homopolymers of the respective components shall adopt the values described in the "Adhesion Technology Handbook" of Nikkan Kogyo Shimbun, Ltd. or the "Polymer Handbook" of Wiley-Interscience. Note that the Tg of the homopolymer of methacrylamide is 77°C. Hereinafter, the glass transition temperature obtained by this calculation may be abbreviated as "designed Tg".

[0021] Furthermore, since the number average molecular weight of the acrylic resin (A) is excellent in melt fluidity and resistance to yarn rust, it is preferably from 1,000 to 10,000, more preferably from 2,000 to 8,000. Here, the number average molecular weight is a value converted to polystyrene based on gel permeation chromatography (hereinafter abbreviated as "GPC") measurement.

[0022] As a method for obtaining the acrylic resin (A), the acrylic monomer (a1), the (meth)acrylamide (a2), the styrene (a3), and the unsaturated monomer (a4) can be used as raw materials and carried out by a known polymerization method. However, the solution radical polymerization method is preferred because it is the simplest.

[0023] The above solution radical polymerization method is a method in which each monomer as a raw material is dissolved in a solvent and a polymerization reaction is carried out in the presence of a polymerization initiator. Solvents that can be used at this time include, for example, hydrocarbon solvents such as toluene, xylene, cyclohexane, n-hexane, and octane; alcohol solvents such as methanol, ethanol, isopropanol, n-butanol, isobutanol, and sec-butanol; ether solvents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, and diethylene glycol dimethyl ether; ester solvents such as methyl acetate, ethyl acetate, n-butyl acetate, isobutyl acetate, and amyl acetate; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. These solvents can be used alone or in combination of two or more.

[0024] Examples of the polymerization initiator include ketone peroxide compounds such as cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, and methylcyclohexanone peroxide; peroxyketal compounds such as 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(tert-butylperoxy)cyclohexane, n-butyl-4,4-bis(tert-butylperoxy)valerate, 2,2-bis(4,4-di-tert-butylperoxycyclohexyl)propane, 2,2-bis(4,4-di-tert-amylperoxycyclohexyl)propane, 2,2-bis(4,4-di-tert-hexylperoxycyclohexyl)propane, 2,2-bis(4,4-di-tert-octylperoxycyclohexyl)propane, and 2,2-bis(4,4-dicumylperoxycyclohexyl)propane; hydroperoxides such as cumene hydroperoxide and 2,5-dimethylhexane-2,5-dihydroperoxide; dialkyl peroxide compounds such as 1,3-bis(tert-butylperoxy-m-isopropyl)benzene, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, diisopropylbenzene peroxide, and tert-butylcumyl peroxide; diacyl peroxide compounds such as decanoyl peroxide, lauroyl peroxide, benzoyl peroxide, and 2,4-dichlorobenzoyl peroxide; peroxycarbonate compounds such as bis(tert-butylcyclohexyl) peroxydicarbonate; peroxyester compounds such as tert-butylperoxy-2-ethylhexanoate, tert-butylperoxybenzoate, and 2,5-dimethyl-2,5-di(benzoylperoxy)hexane; and azo compounds such as 2,2'-azobisisobutyronitrile and 1,1'-azobis(cyclohexane-1-carbonitrile).

[0025] The resin composition for powder coatings of the present invention contains the acrylic resin (A), and preferably contains a curing agent (B) having a functional group capable of reacting with an epoxy group in order to further improve the physical properties of the coating film.

[0026] The hardener (B) is a hardener having a functional group capable of reacting with an epoxy group, and examples thereof include polycarboxylic acid compounds such as suberic acid, azelaic acid, 2,4-diethylglutaric acid, sebacic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid, brassilic acid, tetradecanedicarboxylic acid, pentadecanedicarboxylic acid, hexadecanedicarboxylic acid, heptadecanedicarboxylic acid, octadecanedicarboxylic acid, eicosanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, and butanetricarboxylic acid, anhydrides of these polycarboxylic acids, and polyhydric phenol compounds. Among these, aliphatic polycarboxylic acid compounds and their anhydrides are preferable, and dodecanedicarboxylic acid is more preferable because a high-strength coating film can be obtained. Further, these hardeners (B) can be used alone or in combination of two or more.

[0027] As the blending amounts of the acrylic resin (A) and the hardener (B) in the resin composition for powder coatings of the present invention, since a high-strength coating film can be obtained, the equivalent ratio (A / B) of the number of equivalents of epoxy groups in the acrylic resin (A) to the number of equivalents of functional groups capable of reacting with epoxy groups in the hardener (B) is preferably 0.5 to 1.5, and more preferably 0.8 to 1.2.

[0028] In the resin composition for powder coatings of the present invention, various known and commonly used additives such as organic or inorganic pigments, leveling agents, flow regulators, light stabilizers, ultraviolet absorbers, and antioxidants can be added within a range not impairing the effects of the present invention. Further, a catalyst can also be added for the purpose of accelerating the curing reaction during baking.

[0029] In the resin composition for powder coatings of the present invention, in order to improve the thread rust resistance of the coating film, it can further contain hydrolyzable silane compounds such as silica, alkoxysilane, and silane coupling agent within a range not impairing the effects of the present invention. These compounds can be used alone or in combination of two or more.

[0030] Examples of suitable silane coupling agents include glycidylalkoxysilanes and aminoalkoxysilanes. Among these, glycidyltrialkoxysilane is preferred because a coating film with excellent thread rust resistance can be obtained, and glycidyltrimethoxysilane is more preferred.

[0031] As the blending amount of the silane coupling agent, since a coating film with excellent thread rust resistance can be obtained, in the resin composition for powder coatings, 0.01 to 3% by mass is preferred, and 0.01 to 1% by mass is more preferred.

[0032] As a method for preparing the powder coating of the present invention, various known and commonly used methods can be used. For example, the acrylic resin (A), the curing agent (B), and, if necessary, various additives such as pigments and surface modifiers are mixed, and then after melt-kneading them, so-called mechanical pulverization methods such as fine pulverization and classification can be used.

[0033] The powder coating of the present invention can be applied to exteriors, household appliances, automotive products, two-wheeler products, guard fences, etc. However, since a high-appearance coating film excellent in weather resistance, impact resistance, chipping resistance, water resistance, thread rust resistance, etc. can be obtained, it is suitable for coating metal members such as aluminum wheel alloy members.

[0034] As the coating method of the powder coating of the present invention, various known and commonly used methods such as electrostatic powder coating methods can be mentioned. Further, as a method for obtaining a cured coating film after applying the powder coating of the present invention, it can be appropriately selected according to the type of the substrate and the purpose. However, since a coating film excellent in thread rust resistance, water resistance and weather resistance can be obtained, it is preferable to bake in the temperature range of 120 to 250°C for 5 to 30 minutes. Also, the coating film thickness is preferably in the range of 50 to 200 μm.

Examples

[0035] The present invention will be described in more detail below with specific examples. The epoxy equivalent and number average molecular weight of the acrylic resin were measured by the following methods.

[0036] [Method for Measuring Epoxy Equivalent] It was measured by the hydrochloric acid-pyridine method. 25 ml of hydrochloric acid-pyridine solution was added to the resin, and after heating and dissolving at 130 °C for 1 hour, it was titrated with 0.1 N potassium hydroxide alcohol solution using phenolphthalein as an indicator. The epoxy equivalent was calculated based on the amount of 0.1 N potassium hydroxide alcohol solution consumed.

[0037] [Method for Measuring Number-Average Molecular Weight] It was measured by GPC. Measuring device: High-speed GPC device ("HLC-8220GPC" manufactured by Tosoh Corporation) Column: The following columns manufactured by Tosoh Corporation were connected in series and used. "TSKgel G5000" (7.8 mm I.D. × 30 cm) × 1 piece "TSKgel G4000" (7.8 mm I.D. × 30 cm) × 1 piece "TSKgel G3000" (7.8 mm I.D. × 30 cm) × 1 piece "TSKgel G2000" (7.8 mm I.D. × 30 cm) × 1 piece Detector: RI (Differential Refractometer) Column temperature: 40 °C Eluent: Tetrahydrofuran (THF) Flow rate: 1.0 mL / min Injection volume: 100 μL (tetrahydrofuran solution with a sample concentration of 4 mg / mL) Standard sample: A calibration curve was created using the following monodisperse polystyrene.

[0038] (Monodisperse Polystyrene) "TSKgel Standard Polystyrene A-500" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene A-1000" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene A-2500" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene A-5000" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-1" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-2" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-4" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-20" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-40" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-80" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-128" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-288" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-550" manufactured by Tosoh Corporation

[0039] (Synthesis Example 1: Synthesis of Acrylic Resin (A-1)) 67 parts by mass of xylene was charged into a reaction vessel equipped with a stirrer, a thermometer, a condenser, and a nitrogen gas inlet, and the temperature was raised to 135°C under a nitrogen atmosphere. Then, a mixture consisting of 25 parts by mass of styrene (hereinafter abbreviated as "St"), 49 parts by mass of methyl methacrylate (hereinafter abbreviated as "MMA"), 25 parts by mass of glycidyl methacrylate (hereinafter abbreviated as "GMA"), 1 part by mass of acrylamide (hereinafter abbreviated as "AM"), and 6 parts by mass of t-butyl peroxy 2-ethylhexanoate was added dropwise over 6 hours. After the addition was completed, the mixture was held at the same temperature for 6 hours to carry out a polymerization reaction. Then, the solvent was removed under a reduced pressure of 20 mmHg at 160°C to obtain a solid acrylic resin (A-1) having a number average molecular weight of 3,000, a glass transition temperature of 84°C, and an epoxy equivalent of 569 g / eq.

[0040] (Synthesis Example 2: Synthesis of Acrylic Resin (A-2)) ​The monomer composition was changed to 25 parts by mass of St, 40 parts by mass of MMA, 25 parts by mass of GMA, and 10 parts by mass of AM, and the operation was carried out in the same manner as in Synthesis Example 1, whereby a solid acrylic resin (A-2) having a number average molecular weight of 3,000, a glass transition temperature of 91 ° C, and an epoxy equivalent of 569 g / eq was obtained.

[0041] (Synthesis Example 3: Synthesis of Acrylic Resin (A-3)) The monomer composition was changed to 25 parts by mass of St, 40 parts by mass of MMA, 25 parts by mass of GMA, and 10 parts by mass of methacrylamide (hereinafter abbreviated as "MAM"), and the operation was carried out in the same manner as in Synthesis Example 1, whereby a solid acrylic resin (A-3) having a number average molecular weight of 3,000, a glass transition temperature of 84 ° C, and an epoxy equivalent of 569 g / eq was obtained.

[0042] (Synthesis Example 4: Synthesis of Acrylic Resin (A-4)) The monomer composition was changed to 10 parts by mass of St, 64 parts by mass of MMA, 25 parts by mass of GMA, and 1 part by mass of AM, and the operation was carried out in the same manner as in Synthesis Example 1, whereby a solid acrylic resin (A-4) having a number average molecular weight of 3,000, a glass transition temperature of 88 ° C, and an epoxy equivalent of 569 g / eq was obtained

[0043] (Synthesis Example 5: Synthesis of Acrylic Resin (A-5)) The monomer composition was changed to 20 parts by mass of St, 29 parts by mass of MMA, 50 parts by mass of GMA, and 1 part by mass of AM, and the operation was carried out in the same manner as in Synthesis Example 1, whereby a solid acrylic resin (A-5) having a number average molecular weight of 3,000, a glass transition temperature of 72 ° C, and an epoxy equivalent of 284 g / eq was obtained.

[0044] (Synthesis Example 6: Synthesis of Acrylic Resin (RA-1)) The monomer composition was changed to 25 parts by mass of St, 47 parts by mass of MMA, and 28 parts by mass of GMA, and the operation was carried out in the same manner as in Synthesis Example 1, whereby a solid acrylic resin (RA-1) having a number average molecular weight of 3,000, a glass transition temperature of 85 ° C, and an epoxy equivalent of 508 g / eq was obtained.

[0045] (Synthesis Example 7: Synthesis of Acrylic Resin (RA-2)) The monomer composition was changed to 25 parts by mass of St, 64 parts by mass of MMA, 10 parts by mass of GMA, and 1 part by mass of AM, and the same operations as in Synthesis Example 1 were carried out to obtain a solid acrylic resin (RA-2) having a number average molecular weight of 3,350, a glass transition temperature of 97 °C, and an epoxy equivalent of 1,422 g / eq.

[0046] (Synthesis Example 8: Synthesis of acrylic resin (RA-3)) The monomer composition was changed to 5 parts by mass of St, 66 parts by mass of MMA, 28 parts by mass of GMA, and 1 part by mass of AM, and the same operations as in Synthesis Example 1 were carried out to obtain a solid acrylic resin (RA-3) having a number average molecular weight of 3,400, a glass transition temperature of 87 °C, and an epoxy equivalent of 508 g / eq.

[0047] (Synthesis Example 9: Synthesis of acrylic resin (RA-4)) The monomer composition was changed to 5 parts by mass of St, 35 parts by mass of MMA, 40 parts by mass of n-butyl methacrylate (hereinafter abbreviated as "nBMA"), 15 parts by mass of GMA, and 5 parts by mass of MAM, and the same operations as in Synthesis Example 1 were carried out to obtain a solid acrylic resin (RA-4) having a number average molecular weight of 3,000, a glass transition temperature of 56 °C, and an epoxy equivalent of 948 g / eq.

[0048] The monomer compositions and property values of the acrylic resins (A-1) to (A-5) and (RA-1) to (RA-4) synthesized in Synthesis Examples 1 to 5 above are shown in Tables 1 and 2.

[0049] [Table 1]

[0050] [Table 2]

[0051] (Example 1: Production and evaluation of powder coating (1)) 85 parts by mass of the acrylic resin (A-1) obtained in Synthesis Example 1, 15 parts by mass of dodecanedicarboxylic acid (hereinafter abbreviated as "DDDA"), 0.5 parts by mass of benzoin, and 0.3 parts by mass of a leveling agent ("Resiflow LF" manufactured by ESTRON) were blended, and the resin composition was melt-kneaded using a twin-screw kneader ("APV Kneader MP-2015 type" manufactured by Tubaco Yokohama Sales Co., Ltd.), then finely pulverized, and further classified with a 200-mesh wire net to obtain a powder coating (1).

[0052] [Preparation of Cured Coating Film for Evaluation] The powder coating obtained above was electrostatically powder-coated onto an untreated aluminum plate (A-1050P) (7 cm × 15 cm) so that the film thickness after baking was 80 to 120 μm, and then baked at 170°C for 20 minutes to prepare a cured coating film for evaluation.

[0053] [Evaluation of Curing Property] 0.5 g of the powder coating obtained above was dropped onto a hot plate heated to 160°C, and the time until the tack disappeared (gel time) was measured. Based on the gel time, the curability was determined as follows. 〇: Gel time is less than 160 seconds △: Gel time is 160 seconds or more and less than 200 seconds ×: Gel time is 200 seconds or more

[0054] [Smoothness Test] The smoothness of the powder coating film was judged using a standard plate for visual judgment of the smoothness of the powder coating film by PCI (Powder Coating Institute). There are 10 standard plates numbered from 1 to 10, and the smoothness becomes better as the number increases. It was visually judged which standard plate the smoothness of the prepared powder coating film corresponded to. Based on the judged results, the smoothness was determined as follows. 〇: Smoothness is 8 or more △: Smoothness is 6 to 7 ×: Smoothness is 5 or less

[0055] [Evaluation of Resistance to Thread Rust] Two 13-cm straight scratches reaching the substrate of the cured coating film for evaluation obtained above were made with a cutter knife, and the following tests were conducted using a CASS tester. Test 1: Spraying salt water (prepared by dissolving 2.6 g of copper(II) chloride hydrate, 10 cc of glacial acetic acid, and 500 g of salt in 10 L of ion-exchanged water) for 6 hours under the conditions of a temperature of 50°C, a spraying liquid volume of 1.2 - 1.8 cc / h, and a spraying pressure of 0.1 MPa; Test 2: Leaving it standing for 96 hours under the conditions of a temperature of 60°C and a humidity of 85%. One cycle consisted of these two tests, and a total of 5 cycles were carried out. After the CASS test, the thread rust generated from the scratches on the painted plate was visually confirmed, and the thread rust resistance was evaluated based on the length of the longest grown thread rust. Based on the length of the longest grown thread rust, the thread rust resistance of the coating film was determined as follows. 〇: The longest length of the thread rust is 2.0 mm or less △: The longest length of the thread rust exceeds 2.0 mm and is 3.0 mm or less ×: The longest length of the thread rust exceeds 3.0 mm

[0056] (Examples 2 - 5: Production and Evaluation of Powder Coatings (2) - (5)) Powder coatings (2) - (5) were prepared and various physical properties were evaluated by operating in the same manner as in Example 1, except that the acrylic resin (A-1) and DDDA compounded in Example 1 were changed to the compositions shown in Table 3.

[0057] (Comparative Examples 1 - 4: Production and Evaluation of Powder Coatings (R1) - (R4)) Powder coatings (R1) - (R4) were prepared and various physical properties were evaluated by operating in the same manner as in Example 1, except that the acrylic resin (A-1) and DDDA compounded in Example 1 were changed as shown in Table 4.

[0058] The compounding compositions and evaluation results of the powder coatings (1) - (5) obtained in Examples 1 - 5 and the powder coatings (R1) - (R4) obtained in Comparative Examples 1 - 4 are shown in Tables 3 and 4.

[0059]

Table 3

[0060]

Table 4

[0061] It was confirmed that the cured coating films obtained from the resin compositions for powder coatings of the present invention in Examples 1 to 5 are excellent in curability, smoothness, and rust resistance to yarns.

[0062] On the other hand, Comparative Example 1 is an example in which (meth)acrylamide (a2) was not used as a raw material for the acrylic resin (A), and it was confirmed that the rust resistance to yarns is insufficient.

[0063] Comparative Example 2 is an example in which the acrylic monomer (a1) in the monomer component that is a raw material for the acrylic resin (A) is less than 20% by mass, which is the lower limit of the present invention, and it was confirmed that the smoothness is insufficient.

[0064] Comparative Example 3 is an example in which styrene in the monomer component that is a raw material for the acrylic resin (A) is less than 10% by mass, which is the lower limit of the present invention, and it was confirmed that the curability is insufficient.

[0065] Comparative Example 4 is an example in which the acrylic monomer (a1) and styrene in the monomer component that is a raw material for the acrylic resin (A) are less than the lower limit of the present invention, and it was confirmed that the curability is insufficient.

Claims

1. A resin composition for powder coatings containing an acrylic resin (A) having an acrylic monomer (a1) having an epoxy group, (meth)acrylamide (a2), styrene (a3), and other unsaturated monomers (a4) as essential raw materials, wherein the acrylic monomer (a1) in the monomer components that are the raw materials of the acrylic resin (A) is 20 to 60% by mass, (meth)acrylamide is 0.1 to 30% by mass, and styrene is 10 to 50% by mass. A resin composition for powder coatings characterized by the above.

2. The resin composition for powder coatings according to Claim 1, further containing a curing agent (B) having a functional group capable of reacting with an epoxy group.

3. The resin composition for powder coatings according to Claim 2, wherein the curing agent (B) is an aliphatic polyvalent carboxylic acid and / or its anhydride.

4. A powder coating obtained from the resin composition for powder coatings according to any one of Claims 1 to 3.

5. An article having a coating film of the powder coating according to Claim 4.

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