JP2023064339A - Resin composition for powder coating, powder coating, and article having coated film of the coating - Google Patents

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

In recent years, regulations on organic solvents have become stricter due to problems such as air pollution, and environment-friendly paints have attracted attention. Among them, powder coatings are attracting attention from the viewpoint of environmental protection as solvent-free coatings. In particular, acrylic powder coatings are excellent in coating performance such as weather resistance and stain resistance. It is attracting attention for use in automobile parts, metal exteriors, and home appliances. However, powder coatings have the disadvantage that the smoothness of coating films is inferior to that of solvent-based coatings.

On the other hand, epoxy group-containing acrylic resins obtained by copolymerizing (meth)acrylic acid alkyl esters, epoxy group-containing acrylic monomers, and other copolymerizable vinyl monomers can react with epoxy groups. A powder coating containing a curing agent having a functional group has been proposed (see, for example, Patent Document 1). However, although the cured coating film obtained from this powder coating has improved smoothness, there is a problem that the thread rust resistance is insufficient.

JP-A-2002-69368

The problem to be solved by the present invention is to provide a resin composition for powder coating, a powder coating, and a coating film of the coating that can obtain a cured coating film having excellent curability, smoothness, and thread rust resistance. It is to provide goods.

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

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

The resin composition for powder coating of the present invention is excellent in curability, appearance, and thread rust resistance, and can form a cured coating film. can be done.

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

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

The acrylic monomer (a1) is an acrylic monomer having an epoxy group, such as glycidyl (meth) acrylate, methyl glycidyl (meth) acrylate, (meth) allyl glycidyl ether, (meth) allyl methyl glycidyl ether , 3,4-epoxycyclohexylmethyl (meth)acrylate and the like. Among these, glycidyl (meth)acrylate is preferred. These acrylic monomers (a1) can be used alone or in combination of two or more.

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, and "(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.

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

The other unsaturated monomer (a4) is an unsaturated monomer other than the acrylic monomer (a1), (meth)acrylamide, and styrene, such as (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 ) 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 ) acrylate, cetyl (meth) acrylate, stearyl (meth) acrylate, behenyl (meth) acrylate, cyclohexyl (meth) acrylate, 4-tert-butylcyclohexyl (meth) acrylate, isobornyl (meth) acrylate, dicyclopentanyl (meth) acrylate ) 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-hydroxy Propyl (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)acrylates having terminal hydroxyl groups; ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, tri ethylene 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, hydroxy pivalic acid ester neo Bifunctional monomers such as pentyl glycol di (meth) acrylate, bisphenol A-di (meth) acrylate, bisphenol A-EO-modified di (meth) acrylate, isocyanuric acid EO-modified diacrylate; Methylolpropane tri(meth)acrylate, trimethylolpropane EO-modified tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetraacrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol penta(meth)acrylate Among them, alkyl (meth)acrylates are preferred, and the number of carbon atoms is from 1 to Alkyl (meth)acrylates with 4 alkyl groups are more preferred. These unsaturated monomers (a4) can be used alone or in combination of two or more.

The amount of the acrylic monomer (a1) used is 20 to 60% by mass in the monomer component that is the raw material of the acrylic resin (A), and the balance between curability and thread rust resistance is further improved. Therefore, it is preferably 25 to 50% by mass, more preferably 25 to 40% by mass.

The amount of the (meth)acrylamide (a2) used is 0.1 to 30% by mass in the monomer component that is the raw material of the acrylic resin (A). 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, because it is more improved.

The amount of the styrene (a3) used is 10 to 50% by mass in the monomer component that is the raw material of the acrylic resin (A). , preferably 15 to 45% by mass, more preferably 15 to 40% by mass.

The amount of the unsaturated monomer (a4) used is 20 to 70 mass in the monomer components that are the raw materials of the acrylic resin (A), since the balance between curability and thread rust resistance is further improved. % is preferred.

Further, the glass transition temperature of the acrylic resin (A) is preferably 20 to 120° C., since the coating film has improved thread rust resistance. More preferably, it is 40 to 100°C.

In the present invention, the glass transition temperature is
FOX formula: 1/Tg=W1/Tg1+W2/Tg2+...
(Tg: glass transition temperature to be obtained, W1: weight fraction of component 1, Tg1: glass transition temperature of homopolymer of component 1)
It is obtained by calculation according to For the value of the glass transition temperature of the homopolymer of each component, the value described in "Adhesive Technology Handbook" published by Nikkan Kogyo Shimbun or "Polymer Handbook" published by Wiley-Interscience is adopted. The Tg of the homopolymer of methacrylamide is assumed to be 77°C. Hereinafter, the calculated glass transition temperature may be abbreviated as “design Tg”.

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

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) are used as raw materials, Although it can be carried out by a known polymerization method, a solution radical polymerization method is preferred because it is the simplest.

The solution radical polymerization method is a method of dissolving each monomer as a raw material in a solvent and performing a polymerization reaction 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; alcohols such as methanol, ethanol, isopropanol, n-butanol, isobutanol and sec-butanol. Ether-based solvents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, and diethylene glycol dimethyl ether; Esters such as methyl acetate, ethyl acetate, n-butyl acetate, isobutyl acetate, and amyl acetate System solvent; ketone system solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and the like. These solvents can be used alone or in combination of two or more.

Examples of the polymerization initiator include ketone peroxide compounds such as cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide and methylcyclohexanone peroxide; 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-ditert-amylperoxycyclohexyl)propane, 2,2-bis(4,4-ditert-hexylperoxycyclohexyl)propane, 2 , 2-bis(4,4-di-tert-octylperoxycyclohexyl)propane, 2,2-bis(4,4-dicumylperoxycyclohexyl)propane and other peroxyketal compounds; cumene hydroperoxide, 2, Hydroperoxides such as 5-dimethylhexane-2,5-dihydroperoxide; 1,3-bis(tert-butylperoxy-m-isopropyl)benzene, 2,5-dimethyl-2,5-di( dialkyl peroxide compounds such as tert-butylperoxy)hexane, diisopropylbenzene peroxide, and tert-butylcumyl peroxide; diacyl compounds such as decanoyl peroxide, lauroyl peroxide, benzoyl peroxide, and 2,4-dichlorobenzoyl peroxide Peroxide compounds; peroxycarbonate compounds such as bis(tert-butylcyclohexyl) peroxydicarbonate; tert-butylperoxy-2-ethylhexanoate, tert-butylperoxybenzoate, 2,5-dimethyl-2, Organic peroxides such as peroxyester compounds such as 5-di(benzoylperoxy)hexane, 2,2'-azobisisobutyronitrile, 1,1'-azobis(cyclohexane-1-carbonitrile), etc. and an azo compound of.

The resin composition for powder coating of the present invention contains the above-mentioned acrylic resin (A), and since the physical properties of the coating film are further improved, a curing agent (B ) is preferably contained.

The curing agent (B) is a curing agent having a functional group capable of reacting with an epoxy group. Polyvalent carboxylic acid compounds such as brassylic acid, tetradecanedicarboxylic acid, pentadecanedicarboxylic acid, hexadecanedicarboxylic acid, heptadecanedicarboxylic acid, octadecanedicarboxylic acid, eicosanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, butanetricarboxylic acid, etc. Examples include anhydrides of carboxylic acids and polyhydric phenol compounds. Among these, aliphatic polyvalent carboxylic acid compounds and their anhydrides are preferable, and dodecanedicarboxylic acid is more preferable, since a high-strength coating film can be obtained. These curing agents (B) can be used alone or in combination of two or more.

The amount of the acrylic resin (A) and the curing agent (B) in the resin composition for powder coating of the present invention is, since a high-strength coating film is obtained, the amount of the acrylic resin (A) The equivalent ratio (A/B) between the number of equivalents of the epoxy group and the number of equivalents of the functional group capable of reacting with the epoxy group in the curing agent (B) is preferably 0.5 to 1.5, and 0.8. ~1.2 is more preferred.

The resin composition for powder coating of the present invention may contain organic or inorganic pigments, leveling agents, flow control agents, light stabilizers, ultraviolet absorbers, oxidation Various known and commonly used additives such as inhibitors can be added. A catalyst may also be added for the purpose of accelerating the curing reaction during baking.

In order to improve the thread rust resistance of the coating film, the resin composition for powder coating of the present invention contains silica and water such as alkoxysilane and silane coupling agent within a range that does not impair the effects of the present invention. It can further include a decomposable silane compound. These compounds can be used alone or in combination of two or more.

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

The amount of the silane coupling agent is preferably 0.01 to 3% by mass, more preferably 0.01 to 1% by mass, in the resin composition for powder coatings, since a coating film having excellent thread rust resistance can be obtained. % is more preferred.

As a method for preparing the powder coating material of the present invention, various known and commonly used methods can be used. , various additives such as surface conditioners, and the like, which are then melt-kneaded, finely pulverized, and classified.

The powder coating of the present invention can be applied to exteriors, home appliances, automobiles, motorcycles, protective fences, etc., but it has weather resistance, impact resistance, chipping resistance, water resistance, and thread rust resistance. It is suitable for coating on metal members such as aluminum wheel alloy members because a coating film with excellent appearance can be obtained.

As the coating method of the powder coating material of the present invention, various known and commonly used methods such as an electrostatic powder coating method can be used. In addition, the method for forming a cured coating film after coating the powder coating of the present invention can be appropriately selected according to the type and purpose of the base material, but it is excellent in thread rust resistance, water resistance and weather resistance. It is preferable to bake in the temperature range of 120 to 250° C. for 5 to 30 minutes so that a coating film can be obtained. Moreover, the coating film thickness is preferably in the range of 50 to 200 μm.

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 are measured by the following methods.

[Method for measuring epoxy equivalent]
Measured by the hydrochloride-pyridine method. 25 ml of a hydrochloric acid-pyridine solution was added to the resin, dissolved by heating at 130° C. for 1 hour, and then titrated with a 0.1N-potassium hydroxide alcohol solution using phenolphthalein as an indicator. The epoxy equivalent was calculated by the amount of 0.1N-potassium hydroxide alcohol solution consumed.

[Method for measuring number average molecular weight]
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" (7.8mm I.D. x 30cm) x 1 "TSKgel G4000" (7.8mm I.D. x 30cm) x 1 "TSKgel G3000" (7.8mm I.D. x 30cm) x 1 Book "TSKgel G2000" (7.8 mm I.D. x 30 cm) x 1 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.

(monodispersed 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

(Synthesis Example 1: Synthesis of acrylic resin (A-1))
A reaction vessel equipped with a stirrer, a thermometer, a condenser and a nitrogen gas inlet was charged with 67 parts by mass of xylene and heated to 135° C. under a nitrogen atmosphere. 25 parts by mass of styrene (hereinafter abbreviated as "St"), 49 parts by mass of methyl methacrylate (hereinafter abbreviated as "MMA"), and 25 parts by mass of glycidyl methacrylate (hereinafter abbreviated as "GMA") are added thereto. A mixture of parts by mass, acrylamide (hereinafter abbreviated as "AM") 1 part by mass and 6 parts by mass of t-butylperoxy 2-ethylhexanoate was added dropwise over 6 hours. The polymerization reaction was carried out by maintaining the temperature for 6 hours, after which the solvent was removed under a reduced pressure of 20 mmHg at 160°C to give a solid acrylic resin (number average molecular weight 3,000, glass transition temperature 84°C, epoxy equivalent 569 g/eq A-1) was obtained.

(Synthesis Example 2: Synthesis of acrylic resin (A-2))
In the same manner as in Synthesis Example 1, except that the composition of the monomers 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, a number average molecular weight of 3,000 and glass A solid acrylic resin (A-2) having a transition temperature of 91° C. and an epoxy equivalent of 569 g/eq was obtained.

(Synthesis Example 3: Synthesis of acrylic resin (A-3))
The same procedure as in Synthesis Example 1 was performed except that the composition of the monomers 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"). Thus, 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.

(Synthesis Example 4: Synthesis of acrylic resin (A-4))
In the same manner as in Synthesis Example 1, except that the composition of the monomers 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, a number average molecular weight of 3,000 and glass A solid acrylic resin (A-4) having a transition temperature of 88° C. and an epoxy equivalent of 569 g/eq was obtained.

(Synthesis Example 5: Synthesis of acrylic resin (A-5))
In the same manner as in Synthesis Example 1, except that the composition of the monomers 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, a number average molecular weight of 3,000 and glass A solid acrylic resin (A-5) having a transition temperature of 72° C. and an epoxy equivalent of 284 g/eq was obtained.

(Synthesis Example 6: Synthesis of acrylic resin (RA-1))
In the same manner as in Synthesis Example 1, except that the composition of the monomers was changed to 25 parts by mass of St, 47 parts by mass of MMA, and 28 parts by mass of GMA, a number average molecular weight of 3,000, a glass transition temperature of 85°C, A solid acrylic resin (RA-1) having an epoxy equivalent of 508 g/eq was obtained.

(Synthesis Example 7: Synthesis of acrylic resin (RA-2))
In the same manner as in Synthesis Example 1, except that the composition of the monomers 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, a number average molecular weight of 3,350 and glass A solid acrylic resin (RA-2) having a transition temperature of 97° C. and an epoxy equivalent of 1,422 g/eq was obtained.

(Synthesis Example 8: Synthesis of acrylic resin (RA-3))
In the same manner as in Synthesis Example 1 except that the composition of the monomers 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, a number average molecular weight of 3,400 and glass A solid acrylic resin (RA-3) having a transition temperature of 87° C. and an epoxy equivalent of 508 g/eq was obtained.

(Synthesis Example 9: Synthesis of acrylic resin (RA-4))
The composition of the monomers 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. By operating in the same manner as in Synthesis Example 1, 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 was obtained.

Tables 1 and 2 show 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. .

(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 a leveling agent ("Reiflow" manufactured by ESTRON) LF") 0.3 parts by mass of the resin composition is melt-kneaded using a twin-screw kneader ("APV Kneader MP-2015" manufactured by Tsubako Yokohama Sales Co., Ltd.), and then pulverized. Furthermore, it was classified with a wire mesh of 200 mesh to obtain a powder coating material (1).

[Preparation of cured coating film for evaluation]
The powder coating obtained above was electrostatically powder coated on an untreated aluminum plate (A-1050P) (7 cm x 15 cm) so that the film thickness after baking was 80 to 120 μm, and then heated at 170 ° C. for 20 minutes. Baking was performed for a minute to prepare a cured coating film for evaluation.

[Curability evaluation]
0.5 g of the powder coating obtained above was dropped onto a hot plate heated to 160° C., and the time until tack disappeared (gel time) was measured. Based on the gel time, curability was determined as follows.
○: 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

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

[Evaluation of yarn rust resistance]
Two 13 cm linear scratches were made on the cured coating film for evaluation obtained above with a cutter knife so as to reach the base material of the base material, and the following tests were performed using a CASS tester. 10 L of salt water (2.6 g of copper (II) chloride hydrate, 10 cc of glacial acetic acid, 500 g of common salt) under the conditions of a temperature of 50° C., a spray amount of 1.2 to 1.8 cc/h, and a spray pressure of 0.1 MPa. A total of 5 cycles were conducted, with test 1 of spraying for 6 hours and test 2 of leaving for 96 hours at a temperature of 60° C. and a humidity of 85%. After completion of the CASS test, rust threads generated from scratches on the coated plate were visually observed, and the rust thread resistance was evaluated based on the length of the longest growing rust threads. Based on the length of the longest growing rust thread, the rust thread resistance of the coating film was determined as follows.
○: The longest length of thread rust is 2.0 mm or less △: The longest length of thread rust exceeds 2.0 mm and is 3.0 mm or less ×: The longest length of thread rust exceeds 3.0 mm

(Examples 2 to 5: Production and evaluation of powder coatings (2) to (5))
Powder coatings (2) to (5) were prepared in the same manner as in Example 1 except that the acrylic resin (A-1) and DDDA blended in Example 1 were changed to the compositions shown in Table 3. It was prepared and evaluated for various physical properties.

(Comparative Examples 1 to 4: Production and evaluation of powder coatings (R1) to (R4))
Powder coatings (R1) to (R4) were prepared in the same manner as in Example 1 except that the acrylic resin (A-1) and DDDA blended in Example 1 were changed as shown in Table 4. It was prepared and evaluated for various physical properties.

Tables 3 and 4 show the composition and evaluation results of the powder coatings (1) to (5) obtained in Examples 1 to 5 and the powder coatings (R1) to (R4) obtained in Comparative Examples 1 to 4. shown.

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

On the other hand, Comparative Example 1 was an example in which the (meth)acrylamide (a2) was not used as the raw material of the acrylic resin (A), but it was confirmed that the string rust resistance was insufficient.

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

Comparative Example 3 is an example in which the amount of styrene in the monomer component, which is the raw material of the acrylic resin (A), is less than 10% by mass, which is the lower limit of the present invention, but it was confirmed that the curability was insufficient. rice field.

Comparative Example 4 is an example in which the acrylic monomer (a1) and styrene in the monomer component, which is the raw material of the acrylic resin (A), are less than the lower limits of the present invention, but the curability is insufficient. was confirmed.

Claims (5)

An acrylic resin (A) comprising, as essential raw materials, an acrylic monomer (a1) having an epoxy group, (meth)acrylamide (a2), styrene (a3), and another unsaturated monomer (a4) The resin composition for powder coating containing, wherein the acrylic monomer (a1) in the monomer component which is the raw material of the acrylic resin (A) is 20 to 60% by mass, and (meth)acrylamide is 0.1 to 30% by mass, and styrene is 10 to 50% by mass. 2. The resin composition for powder coating according to claim 1, further comprising a curing agent (B) having a functional group capable of reacting with an epoxy group. 3. The resin composition for powder coating according to claim 2, wherein the curing agent (B) is an aliphatic polycarboxylic acid and/or its anhydride. A powder coating obtained from the resin composition for powder coating according to any one of claims 1 to 3. An article having a coating film of the powder coating according to claim 4.