JPH07166103A - Resin composition for thermosetting powder coating - Google Patents

Abstract

PURPOSE:To obtain a resin composition containing a copolymer from a vinylic monomer having a specific chemical structure at side chains in a vinyl resin, excellent in coating film and capable of simultaneously attaining smoothness, curing properties, weather resistance and storage stability. CONSTITUTION:This composition contains a vinyl-based copolymer composed of (A) 5-50wt.% of a recurring unit derived from a vinyl-based monomer of formula I [R<1> is H or methyl; R<2> is polycyclic aliphatic hydrocarbon; (n) is 0-41, (B) 5-35wt.% of a recurring unit derived from a vinyl-based monomer having a curable functional group in a chemical structure and (C) 15-90wt.% of a recurring unit derived from the other non-reactive vinyl-based monomer. The composition has 40-120 deg.C glass transition temperature and 2000-50000 weight- average molecular weight.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel resin composition for thermosetting powder coatings, which can simultaneously achieve excellent smoothness and coating performance such as weather resistance. When blended, it can be suitably used as a thermosetting powder coating material on the surface of various metals, plastic moldings or building materials.

[0002]

2. Description of the Related Art Powder coatings, which do not contain any organic solvent in their coating composition, have recently been in worldwide demand as coatings that can comply with the strict regulations of organic solvent emission in each country. ing. Above all, vinyl (acrylic) resin-based powder coatings have excellent weather resistance compared to other powder coatings, that is, polyester resin-based powder coatings and epoxy-based powder coatings. It is used in home appliances and other applications that require high weather resistance. On the other hand, vinyl (acrylic) resin-based powder coatings have the drawback that the melt viscosity in the film-forming process is higher than other resin-based powder coatings, and as a result, only coatings with poor smoothness can be obtained. Was there. In order to overcome this drawback, a method of reducing the melt viscosity by copolymerizing styrene with another vinyl-based monomer has been conventionally used, but it is an advantage of vinyl (acrylic) resin by using styrene. Weather resistance is sacrificed.

Various studies have already been made on the problem of compatibility between the smoothness and weather resistance of the coating film. For example, a method in which styrene and cyclohexyl methacrylate are used in combination (JP-A-50-124934) or a method in which styrene and tert-butyl (meth) acrylate are used in combination (JP-A-52-38541 and JP-A-4-359971). ), Etc., but all of them are merely methods in which styrene is used in combination with other acrylic monomers, and vinyl resins for powder coatings that do not contain styrene in the resin component that can achieve smoothness and weather resistance at the same time ( No acrylic) resin composition has been found.

[0004]

SUMMARY OF THE INVENTION The present invention is directed to various metals,
A vinyl-based copolymer with good storage stability that shows good smoothness on the surface of plastic moldings and building materials, and easily forms a coating film with excellent weather resistance, water resistance, solvent resistance, and acid resistance. An object of the present invention is to provide a resin composition for thermosetting powder coating material containing a united resin.

[0005]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found that a vinyl-based monomer having a specific chemical structure in its side chain is copolymerized in a vinyl resin. As a result, it has been found that the melt viscosity and photochemical stability of the conventional vinyl resin can be improved and good smoothness and coating performance such as weather resistance can be achieved at the same time, and the present invention has been completed.

That is, the present invention comprises (A) 5 to 50% by weight of a repeating unit derived from a vinyl monomer represented by the following general formula (1):

[0007]

[Chemical 2]

(In the formula, R ¹ is a hydrogen atom or a methyl group, R ² is a polycyclic aliphatic hydrocarbon group, and n is 0-4.
Indicates an integer. ) (B) The repeating unit derived from a vinyl-based monomer having a curable functional group in the chemical structure is 5
To 35% by weight and (C) 15 to 90% by weight of repeating units derived from other non-reactive vinyl monomers, the glass transition temperature is in the range of 40 to 120 ° C., and the weight average molecular weight is 2000 to The present invention provides a resin composition for a thermosetting powder coating material, which contains a vinyl copolymer resin in the range of 50,000. Hereinafter, the present invention will be described in detail.

The repeating unit (A) contained in the vinyl copolymer resin used as the resin component of the resin composition for thermosetting powder coating material of the present invention is represented by the general formula (1). It is a repeating unit derived by polymerizing a monomer. R ² in the general formula (1) is a polycyclic aliphatic hydrocarbon group, and is an alkyl group, an alkenyl group, an aryl group, an aralkyl group, an alkoxyl group, an acyl group, a hydroxyl group, an amino group, a nitrile group, a carboxyl group, Those in which various substituents such as a halogen atom are substituted are also included. R ² is preferably a polycyclic aliphatic hydrocarbon group having 7 to 30 carbon atoms, and particularly preferably 7 to 7 carbon atoms.
15 are polycyclic aliphatic hydrocarbon groups. Specific examples of suitable polycyclic aliphatic hydrocarbon groups include the following.

Bicyclo [2.2.1] heptyl

[Chemical 3]

6-Methylbicyclo [2.2.1] heptyl

[Chemical 4]

5,6-Dimethylbicyclo [2.2.1]
Heptyl

[Chemical 5]

1-Methylbicyclo [2.2.1] heptyl

[Chemical 6]

6-ethylbicyclo [2.2.1] heptyl

[Chemical 7]

1,7,7-trimethylbicyclo [2.
2.1] Heptyl

[Chemical 8]

Bicyclo [4.4.0] decyl

[Chemical 9]

Tricyclo [3.3.1.1 ^3,7 ] decyl

[Chemical 10]

Tricyclo [4.3.0.1 ^2,5 ] decyl

[Chemical 11]

Tricyclo [4.4.0.1 ^2,5 ] undecyl

[Chemical 12]

Tetracyclo [4.4.0.1 ^2,5 . 1
^7,10 ] dodecyl

[Chemical 13]

Pentacyclo [6.6.1.1 ^3,6 . 1
^10,13 . 0 ^2,7 . 0 ^9,14 ] Hexadecyl

[Chemical 14]

Pentacyclo [6.5.1.1 ^3,6 .
0 ^2,7 . 0 ^9,13 ] Pentadecyl

[Chemical 15]

Hexacyclo [6.6.1.1 ^3,6 . 1
^10,13 . 0 ^2,7 . 0 ^9,14 ] Heptadecyl

[Chemical 16]

Further, various polycyclic aliphatic hydrocarbon groups such as an alkyl group, an alkenyl group, an aryl group, an aralkyl group, an alkoxyl group, an acyl group, a hydroxyl group, an amino group, a nitrile group, a carboxyl group and a halogen atom can be used. The thing etc. which the substituent substituted were mentioned.

Typical examples of these vinyl monomers include, for example, tetracyclo [4.4.0.
1 ^2,5 . 1 ^7,10 ] dodecyl acrylate, tricyclo [4.4.0.1 ^2,5 ] undecyl acrylate, bicyclo [4.4.0] decyl acrylate, 1,7,7-
Trimethylbicyclo [2.2.1] heptyl acrylate, bicyclo [2.2.1] heptyl acrylate, tricyclo [3.3.1.1 ^3,7 ] decylmethyl acrylate, tetracyclo [4.4.0.1 ^{2] , 5} . 1 ^7,10] dodecyl methacrylate, tricyclo [4.4.0.1
^2,5 ] undecyl methacrylate, bicyclo [4.4.
0] decyl methacrylate, 1,7,7-trimethylbicyclo [2.2.1] heptyl methacrylate, tricyclo [3.3.1.1 ^3,7 ] decyl methacrylate, tricyclo [3.3.1.1 ^{3, 7} ] Decylmethyl methacrylate and the like. These vinyl-based monomers may be used alone or in combination of two or more.

The repeating unit (B) of the vinyl-based copolymer resin used as the resin component of the resin composition for thermosetting powder coating material of the present invention is a vinyl-based resin having a curable functional group in its chemical structure. It is a repeating unit derived by polymerizing a monomer. A vinyl-based monomer having a curable functional group in its chemical structure is a compound having a vinyl group and a curable functional group in its chemical structure, such as acrylic acid, methacrylic acid, maleic anhydride, or itaconic anhydride. Compounds having both vinyl group and carboxyl group such as monoalkyl ester, or 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 4-hydroxy Compounds having both a vinyl group and a hydroxyl group, such as butyl methacrylate and ε-caprolactone adducts thereof, or compounds having a vinyl group and a glycidyl group in its structure, such as glycidyl acrylate and β-methylglycidyl Acrylate, glycidyl methacrylate, β-methylglycidyl methacrylate and other acrylic acid or methacrylic acid glycidyl esters, allyl alcohol glycidyl ethers or methyl glycidyl ethers, methallyl alcote glycidyl ethers or methyl glycidyl ethers, N- Glycidyl acrylic acid amide,
Glycidyl vinyl sulfonate or the like, or a compound having a vinyl group and a β-hydroxyalkylamide group in its structure, for example, N- (2-hydroxyethyl) acrylamide, N- (2-hydroxyethyl) methacrylamide and the like can be mentioned. . These vinyl-based monomers having a curable functional group in their chemical structure can be used alone or in combination of two or more.

Further, the repeating unit of (C) is a repeating unit derived by polymerizing a non-reactive vinyl monomer other than the vinyl monomer for deriving the repeating units of (A) and (B). is there. Other non-reactive vinyl monomers include, for example, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, stearyl methacrylate, phenyl methacrylate. , Benzyl methacrylate, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-
Butyl acrylate, isobutyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, stearyl acrylate,
Phenyl acrylate, methacrylic acid or acrylic acid esters having no reactive functional group such as benzyl acrylate, or styrene, α-methylstyrene, vinyltoluene, fumaric acid dialkyl ester, itaconic acid dialkyl ester, acrylonitrile, methacrylonitrile, Examples thereof include ethylenically unsaturated monomers such as vinyl acetate, vinyl propionate, and vinyl chloride.
These other non-reactive vinyl monomers can be used alone or in combination of two or more.

The vinyl copolymer resin used in the present invention contains 5 to 50% by weight, preferably 10 to 30% by weight of repeating units derived from (A) the vinyl monomer represented by the general formula (1). % By weight, and (B) 5 to 35% by weight, preferably 10 to 30% by weight of a repeating unit derived from a vinyl-based monomer having a curable functional group in its chemical structure, and (C) other non-reactive vinyl. 15-90% by weight, preferably 40-90% by weight of the repeating unit derived from the system monomer.
It consists of 80% by weight. When the content of the repeating unit (A) is less than 5% by weight, the effect is not sufficient, and when it exceeds 50% by weight, the coating film becomes too brittle and the coating film performance deteriorates. When the content of the repeating unit (B) is less than 5% by weight, curability is insufficient, and when it exceeds 35% by weight, the degree of curing proceeds excessively, resulting in poor coating performance. In addition, the vinyl copolymer resin may have other repeating units other than the above within the range not impairing the object of the present invention.

The glass transition temperature of the vinyl copolymer resin used in the present invention needs to be in the range of 40 to 120 ° C, preferably 50 to 100 ° C. When the glass transition temperature of this resin is less than 40 ° C., the stability as a resin for powder coating material is extremely poor, and blocking occurs and the powder cannot exist stably. On the other hand, when the glass transition temperature of this resin exceeds 120 ° C., the melt viscosity is too high and the leveling property at the time of curing is poor, and a uniform and smooth coating film cannot be obtained.

Further, the weight average molecular weight of the vinyl copolymer resin used in the present invention must be in the range of 2000 to 50,000, preferably 5000 to 2
The range is 0000. The weight average molecular weight of this resin is 2
If it is less than 000, the physical properties of the coating film are insufficient and the coating film performance such as coating film strength or solvent resistance is deteriorated. On the other hand, when the weight average molecular weight of this resin exceeds 50,000, the melt viscosity is too high and the leveling property at the time of curing is poor, and a uniform and smooth coating film cannot be obtained.

The vinyl-based copolymer resin used in the resin composition for thermosetting powder coating material of the present invention is a vinyl-based copolymer resin having the general formula (1) and a vinyl-based copolymer having a curable functional group in its chemical structure. It can be obtained by copolymerizing a monomer and other non-reactive vinyl monomers. The polymerization method for synthesizing the vinyl-based copolymer resin used in the resin composition for the thermosetting powder coating material of the present invention is not limited at all, and a commonly used solution polymerization method, melt polymerization method, Emulsion polymerization method, suspension polymerization method, dispersion polymerization method, radiation polymerization method and the like are applicable. Further, even if a chain transfer agent such as mercaptans is used as a method for controlling the molecular weight of the vinyl-based copolymer resin, there is no effect.

The resin composition for thermosetting powder coating material of the present invention has a functional group capable of reacting with the curable functional group of the repeating unit (B) contained in the vinyl-based copolymer resin in the molecule.
A desired thermosetting powder coating material is put into practical use by blending a hardener that is solid at room temperature. In this case, examples of the curing agent include dibasic acid compounds such as sebacic acid, azelaic acid and dodecadioic acid or phthalic anhydride as a curing agent for epoxy-functional vinyl resin.
Hexahydrophthalic anhydride, acid anhydride compounds such as maleic anhydride, and diglycidyl isophthalate, diglycidyl terephthalate, triglycidyl isocyanurate, glycidyl acrylate, glycidyl methacrylate or 3,4-epoxy as a curing agent for carboxylic acid functional vinyl resins. Polyepoxy compounds such as cyclohexylmethyl acrylate and 3,4-epoxycyclohexylmethylmethacrylate monomers or copolymers, or N, N'-di (β-hydroxyethyl) as a β-hydroxyalkylamide functional curing agent Adipic acid diamide, N, N, N ', N'-tetra (β-hydroxyethyl) adipic acid diamide, N, N, N', N'-
Poly (β-hydroxyalkylamide) compounds such as tetra (β-hydroxyethyl) sebacic acid diamide, isophorone diisocyanate and ε of isophorone diisocyanate as a curing agent for hydroxyl functional vinyl resin.
-Caprolactam block, isophorone diisocyanate dimer and the like.

The vinyl-type copolymer resin in the resin composition for thermosetting powder coating material of the present invention is used as a main resin component, and its compounding ratio is not particularly limited and may be appropriately selected. It may be selected, but it is usually in the range of 5 to 100% by weight in the resin component, preferably 20.
It may be in the range of ˜100 wt%. Further, the mixing ratio of the curing agent is not particularly limited and may be appropriately selected, but the molar ratio of the reactive group of the curing agent to the functional group of the resin component is usually in the range of 0.5 to 1.5. , Preferably within the range of 0.8 to 1.2.

The thermosetting powder coating resin composition of the present invention contains various resins such as epoxy, acrylic, polyester, polyamide, etc., which are added in addition to ordinary powder coatings, phthalocyanine-based and indanthrone-based resins. , Flavanthlon-based, quinacridone-based organic pigments and titanium dioxide,
Inorganic pigments such as iron oxide, chromium oxide and carbon black, coloring aids or UV absorbers, light stabilizers, antistatic agents, anti-armpit agents, antiblocking agents, antioxidants,
If necessary, one or more additives for paints such as a plasticizer, a flow control agent, and a curing catalyst can be added, and they are put to practical use as a powder paint. Appropriate amounts of these components may be selected according to the required characteristics. Further, these components may be added when mixing the vinyl copolymer resin and the curing agent, or may be mixed in advance with the vinyl copolymer resin or the curing agent before mixing the both. Good.

In producing the powder coating material, a so-called dry method using a melt-kneader such as a heating roll, an extruder or a kneader can be applied. Regarding the coating method of the powder coating material, the coating object is coated by a well-known coating method such as an electrostatic coating method or a fluidized dipping method, and usually 140 to 2
By baking at a temperature of 00 ° C. for 5 minutes to 2 hours, a sufficiently cured coating film can be obtained. The thickness of the coating film may be appropriately selected as necessary and is usually 20 to 20.
The range may be 0 μm, preferably 40 to 100 μm.
The range is m.

[0036]

EXAMPLES Next, the present invention will be described more specifically by way of examples. The present invention is not limited to these examples. In the examples, the coating film performance test was performed by the following method. (1) Coating smoothness The center line average roughness of the powder coating cured coating surface was measured using a surface roughness meter Surfcom manufactured by Toyo Seimitsu Co., Ltd. (2) Adhesiveness JIS K5400 8.5.2. It was measured by. (3) Solvent resistance The cured coating film was rubbed with a flannel dipped in xylene 100 times, and the change in the coating film state was evaluated according to the following criteria. ◯: No change in coating film. Δ: Whitening of coating film. X: Coating film dissolution.

(4) Accelerated weather resistance A clear-cured coating film cracking test time was measured with a dew panel light control weather meter (manufactured by Suga Test Instruments Co., Ltd.). (5) Storage stability The powder coating material was stored at 30 ° C. for 30 days, and changes in the coating material state were evaluated according to the following criteria. ◯: No change. Δ: Paint aggregation. X: Paint blocking.

Resin Production Examples 1 to 5 In a reaction vessel equipped with a thermometer, a stirrer, a reflux condenser and a nitrogen inlet tube, ethyl acetate was added in an amount shown in Tables 1 and 2, and nitrogen gas was added to the reaction vessel. Replace air and heat to reflux with stirring. Each of the monomer mixtures shown in Tables 1 and 2 was added thereto dropwise over 2 hours, and the mixture was kept under reflux for 30 minutes, and then added to Tables 1 and 2.
The additional catalyst component shown in Table 1 was added, and the remaining monmer was polymerized at reflux for 2 hours to complete the polymerization.
And vinyl-based copolymer resins 1 to 5 having the resin compositions and the characteristic values shown in Table 2 were obtained. Next, ethyl acetate, which is a synthesis solvent, was distilled off under reduced pressure to solidify the mixture, which was pulverized and then dried under reduced pressure to remove the residual solvent to obtain a vinyl resin for powder coating. In addition, Table 3 shows the values obtained by measuring the melt viscosity characteristics of each powdered resin at each temperature with a melt viscometer (measuring device name: Liquid Liquid MR300, manufactured by Rheology Co., Ltd.).

Resin Production Comparative Example 1.2 In the same manner as in Resin Production Examples 1 to 5, the solvents shown in Table 2 were used.
A monomer was added for polymerization, solidification, pulverization and drying under reduced pressure, and residual solvent was removed to produce an acrylic resin for powder coating. In addition, in Table 1 and Table 2, tetracyclododecyl acrylate is tetracyclo [4.4.0.
1 ^2,5 . 1 ^7,10 ] dodecyl acrylate,
Isobornyl acrylate is 1,7,7-trimethylbicyclo [2.2.1] heptyl acrylate.

Example 1 Production of Powder Coating Composition To 1000 parts by weight of the resin obtained in Resin Production Example 1 was added 198 parts by weight of triglycidyl isocyanurate as a curing agent,
10 parts by weight of TINUVIN 900 (trade name: manufactured by Ciba Geigy) as an ultraviolet absorber, and SANOL LS as a light stabilizer
10 parts by weight of 440 (trade name: manufactured by Sankyosha), 5 parts by weight of Resmix RL-4 (trade name: manufactured by Mitsui Toatsu Chemical Co., Inc.) as a leveling agent, and 5 parts by weight of benzoin as a pinhole inhibitor, Mix well with a Henschel mixer. Next, the same mixture was melt-kneaded in a heating kneader at 80 ° C. for 2 passes, pulverized with a sample mill, and finally 150
The powder was obtained by classification with a sieve of mesh. Method for preparing coating film performance test plate Bellcoat No. 1 as a metallic base coat for cationic electrodeposition / intermediate coating plate 6000BCG2 (trade name: manufactured by NOF CORPORATION) was applied for about 15 μm and then flashed at 140 ° C. for 5 minutes. Next, the above-prepared powder coating material is applied to about 80 μm using an electrostatic spray coating machine for powder coating material, and 1
A coating film performance test plate was obtained by baking at 60 ° C. for 30 minutes to cure. The obtained cured film had a center line surface roughness of about 1 μm measured by a surface roughness meter (measuring device name: Surfcom, manufactured by Toyo Seimitsu Co., Ltd.), and showed excellent smoothness. In addition, it showed sufficient curability in an adhesion test by a goose eye test and a solvent resistance test by xylene rubbing. On the other hand, in the due panel type accelerated weather resistance test (manufactured by Suga Test Instruments Co., Ltd.), no change was observed in the coating film even after a test time of 1000 hours, and excellent weather resistance was exhibited. Furthermore, 30 of the powder coating
It showed excellent storage stability as a powder coating without blocking even after storage at 1 ° C for 1 month.

Examples 2 to 5 Resins obtained in Production Examples 2 to 5 were blended in the same amounts as in Example 1 with the additives shown in Table 5 in predetermined amounts, melt-kneaded, pulverized and classified to obtain powder. Got body paint. Then, each powder coating material was applied in the same manner as in Example 1 and baked at the curing temperature shown in Table 7 for 30 minutes to be cured to obtain a coating film performance test plate. Next, when the coating film performance was evaluated in the same manner as in Example 1, all showed the same excellent smoothness, curability, weather resistance and storage stability as in Example 1.

Comparative Examples 1 and 2 Resin Production The resins obtained in Comparative Examples 1 and 2 were blended with the additives shown in Table 6 in the same amounts as in Example 1 and melt-kneaded, pulverized and classified. A powder coating was obtained. Next, each powder coating material was applied in the same manner as in Example 1 and baked at the curing temperature shown in Table 8 for 30 minutes to obtain a coating film performance test plate. Next, the coating properties were evaluated using the same items as in Example 1. As a result, in Comparative Example 1, the curability and weather resistance were excellent, but the smoothness was inferior, and in Comparative Example 2, the smoothness and curability were excellent, but the weather resistance was inferior.

[0043]

[Table 1]

[0044]

[Table 2]

In Tables 1 and 2, the subscripts mean the following. * 1: Resin solid content measured value (140 ° C, 30 minutes) * 2: Resin acid value measured value (potassium hydroxide / ethanol solution) * 3: GPC measured value (polystyrene conversion) * 4: Measured resin Tg by DSC ( JIS K 712
1) In Table 1 and Table 2, the unit of the numerical value indicating the blending amount of the synthetic solvent, the monomer mixture and the additional catalyst is part by weight.

[0046]

[Table 3]

[0047]

[Table 4]

[0048]

[Table 5]

[0049]

[Table 6]

In Tables 5 and 6, the subscripts mean the following. * 1: Blocked isocyanate curing agent (manufactured by Huls) * 2: UV absorber (manufactured by Ciba Geigy) * 3: Light stabilizer (manufactured by Sankyo) * 4: Leveling agent (manufactured by Mitsui Toatsu Kagaku) In Tables 5 and 6, the unit of the numerical value indicating the blending amount of the resin, the curing agent and the additive is part by weight.

[0051]

[Table 7]

[0052]

[Table 8]

From the coating film performance test results shown in Tables 7 and 8, Examples 1 to 5 according to the present invention can simultaneously achieve excellent smoothness, curability, weather resistance and storage stability. Particularly regarding the improvement of smoothness, the melt viscosity behavior shown in Table 3 can be reduced by the effect of copolymerizing a vinyl-based monomer having a polycyclic aliphatic hydrocarbon group contained in the vinyl-based copolymer resin. I think it was because we achieved it. Also,
Regarding the weather resistance, it is considered that the vinyl-based copolymer resin does not contain styrene. On the other hand, in Comparative Example 1, since styrene is contained in the vinyl-based copolymer resin, the smoothness and curability are excellent, but the weather resistance is poor. Further, in Comparative Example 2, since the vinyl-based copolymer resin is not copolymerized with the vinyl-based monomer having a polycyclic aliphatic hydrocarbon group,
The curability and weather resistance are excellent, but the smoothness is poor. Thus, since the resin composition for thermosetting powder coating material of the present invention can achieve excellent smoothness, curability, weather resistance and storage stability at the same time, various metals, plastics or building material surfaces It can be suitably used as a powder coating material.

[0054]

The resin composition for thermosetting powder coating material of the present invention can simultaneously achieve excellent smoothness, curability, weather resistance and storage stability of the coating film. Therefore, the resin composition for thermosetting powder coating material of the present invention is extremely useful in practice.

Claims (1)

[Claims] 1. (A) 5 to 50% by weight of a repeating unit derived from a vinyl-based monomer represented by the following general formula (1): (In the formula, R ¹ is a hydrogen atom or a methyl group, R ² is a polycyclic aliphatic hydrocarbon group, and n is an integer of 0 to 4.) (B) A curable functional group in the chemical structure The repeating unit derived from a vinyl-based monomer having a group is 5 to 35% by weight and the repeating unit derived from (C) another non-reactive vinyl-based monomer is 15 to 90% by weight, and has a glass transition temperature of 40. The resin composition for thermosetting powder coatings is characterized by containing a vinyl-based copolymer resin having a weight average molecular weight of 2,000 to 50,000.