JPH10231324A - Resin for powder coating and powder coating using the same resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject resin for powder coating, etc., having uniform coated film face, capable of thinly applying and having performance protecting a metal (substrate) from rust and solvent and impact resistance of coated film face. SOLUTION: This resin comprises >=30mol% recurring unit represented by the formula (R<1> is H or a 1-2C alkyl; R<2> is H or a 1-3C alkyl). Furthermore, the resin has 0.1-3dl/g intrinsic viscosity at 30 deg.C in meta-cresol and has each <=30ml∼20μm/m<2> .day.atm oxygen transmittance at 20 deg.C and 62% and 100% relative humidities and has <=30g.30μm/m<2> .day oxygen transmittance at 40 deg.C and 90% relative humidity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to gas barrier properties, adhesiveness, and the like that can be coated on metals, ceramics, glass, and the like.
The present invention relates to a powder coating resin having excellent solvent resistance and a powder coating containing the same.

[0002]

2. Description of the Related Art Conventionally, as a resin for powder coating, polyethylene, polyamide, epoxy resin, ethylene-vinyl alcohol copolymer (EVOH) and the like have been mainly used to protect metals (base materials) from rust and solvents. In recent years, powder coating has attracted attention because of the complexity of the base material, the use of solvent-based paints due to environmental issues, and the expectation of increased production speed and reduced costs. I have. However, these resins have poor adhesion to metals and the like, or have insufficient gas barrier properties (especially oxygen gas barrier properties) and solvent resistance, so the coatings have to be thickened more than necessary. There are drawbacks such as poor economic efficiency.

On the other hand, polymers having repeating units of allyl alcohols represented by polyallyl alcohol and polymethallyl alcohol have been known for a long time, and are disclosed in US Pat. Nos. 2,455,722 and 246,710.
Nos. 3,858,897, 3,666,740 (JP-B-47-40308), 4,125,694 and British Patent No. 854207 are known. These prior arts describe applications such as coatings and paints (US Pat. No. 32858).
No. 97, 4125694), but there is no description of a specific use of the powder coating. Also,
There is no description at all regarding that such a polymer has a very good gas barrier property, and there is no description regarding its use in applications requiring high gas barrier properties.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a coating film having a uniform and thin coating surface, and yet capable of protecting a metal (substrate) from rust and a solvent, and having an excellent resistance to the coating film surface. An object of the present invention is to provide a powder coating resin having an impact property and a powder coating containing the resin as a main component.

[0005]

The above object can be attained by providing a resin for powder coating containing at least 30 mol% of a repeating structural unit represented by the following formula (1) or a powder coating containing the same. Is done.

[0006]

Embedded image

(Wherein, R ¹ is a hydrogen atom or a group having 1 to 1 carbon atoms)
R ² represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. )

At this time, the oxygen permeation amount at 20 ° C. and 65% relative humidity is 30 ml · 20 μm / m ² · day · a
tm or less, and the oxygen permeation amount at 20 ° C. and a relative humidity of 100% is 30 ml · 20 μm / m ² · day · a
tm or less, or 40 ° C, 90% relative humidity
Is preferably 30 g · 30 μm / m ² · day or less. 30 ° C in metacresol
Is preferably 0.1 to 3 dL / g. Further, it is preferable that R ¹ in the formula (1) is CH ₃ or that R ² is H or CH ₃ , and R ¹ in the formula (1) is CH ₃ and R ² is H Is most preferred.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The resin for powder coating according to the present invention contains at least 30 mol% of a repeating structural unit represented by the following formula (1).

[0010]

Embedded image

(Wherein, R ¹ represents a hydrogen atom or an alkyl group having 1 to 2 carbon atoms, and R ² represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, respectively)

R ¹ represents a substituent selected from a hydrogen atom, a methyl group, and an ethyl group, and among these, a methyl group is most preferable from the viewpoint of gas barrier properties. R ² represents a substituent selected from a hydrogen atom, a methyl group, an ethyl group, a propyl group, and an isopropyl group, and among these, a hydrogen atom or a methyl group is optimal from the viewpoint of gas barrier properties.

[0013] The content of the above structural units in the resin must be 30 mol% or more, and more preferably in the range of 45 to 100 mol%. More preferably, it is 70 to 100 mol%, and the range of 80 to 100 mol% is optimal. If the content of the structural unit is below the above range, the gas barrier properties will be poor. Further, two or more kinds of the above structural units having different R1 and / or R2 may be contained. In this case, the content of the structural unit in the resin is the total thereof.

The copolymerization components other than the above structural units include:
There is no particular limitation as long as the performance is not adversely affected.
Specific examples of the copolymer component include ethylene, propylene,
Olefins such as 1-butene, isobutene, 1-pentene, 1-hexene, 1-octene, diene monomers such as butadiene and isoprene, and aromatic-substituted vinyl monomers such as styrene and α-methylstyrene. Monomers, methyl acrylate, ethyl acrylate, butyl acrylate, acrylic monomers such as methyl methacrylate, methyl vinyl ether, ethyl vinyl ether, vinyl ether monomers such as butyl vinyl ether, vinyl chloride,
Vinyl halide monomers such as vinyl fluoride, vinylidene chloride, vinylidene halide monomers such as vinylidene fluoride, acrylonitrile, acrylonitrile monomers such as methacrylonitrile, maleimide, N-methylmaleimide, And maleic acid derivative monomers such as dimethyl maleate.

When a copolymer component is contained, the copolymerization method may be either random copolymerization or alternating copolymerization, but when the copolymer component is large (the copolymer component is about 30%).
Mol% or more) preferably has high alternating copolymerizability from the viewpoint of gas barrier properties. When the alternating copolymerizability is high, the content of the structural unit represented by the formula (1) is 45 to 60 mol%.
Is preferable.

The intrinsic viscosity of the resin for powder coating of the present invention is as follows: a value measured in meta-cresol at 30 ° C.
The range of 0.1 to 3 dl / g is preferable, and 0.2 to 2 dl.
/ G is more preferable, and 0.3 dl / g to 1.5 d
A range of 1 / g is most preferred. If the intrinsic viscosity is too small, cracking or cracking may occur due to bending or impact. If the intrinsic viscosity is too high, there may be a problem that a coating having a uniform thickness cannot be obtained.

The method for producing the resin for powder coating of the present invention is not particularly limited, and various methods can be employed, including the methods described in the prior art.
The main methods include the following production methods. First production method: produced by polymerizing a monomer represented by the following formula (2) and then reducing it.

[0018]

Embedded image

(In the formula, R ¹ represents a hydrogen atom, a methyl group or an ethyl group, X represents an alkoxyl group, a hydroxyl group, a halogen atom, a hydrogen atom, a methyl group, an ethyl group, a propyl group, or an isopropyl group.)

Specific examples of the above monomers include acrylic acid derivatives such as acrylic acid, methacrylic acid, and 2-ethylacrylic acid; methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, and 2-ethyl acrylate. Acrylic ester derivatives such as methyl acrylate; acrolein derivatives such as acrolein, methacrolein and 2-ethylacrolein; methyl vinyl ketone, ethyl vinyl ketone, isopropenyl methyl ketone, isopropenyl ethyl ketone, isopropenyl propyl ketone, isopropenyl isopropyl And vinyl ketone derivatives such as ketones.

The above monomers can be polymerized by known polymerization methods such as radical polymerization and anion polymerization. Examples of the radical polymerization initiator include 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4′-dimethylvaleronitrile), and 2,2′-azobis (4-methoxy-
Azo-based initiators such as 2,4'-dimethylvaleronitrile); and peroxide-based initiators such as isobutyl peroxide, di-n-propylperoxydicarbonate, and t-butylperoxypivalate. The polymerization temperature at this time is not particularly limited, and the polymerization is usually performed in a temperature range from room temperature to about 100 ° C.

The conditions for the anionic polymerization are as follows: Basic alkali metal or alkaline earth metal derivatives such as butyllithium, lithium aluminum hydride, methylmagnesium bromide, ethylmagnesium chloride and triphenylmethylcalcium chloride are used as initiators. The polymerization is carried out at room temperature to about -100 ° C using an aprotic solvent such as tetrahydrofuran, dimethoxyethane, diethyl ether or the like as a solvent.

As a method for reducing the obtained polymer, a method using a metal hydride such as lithium aluminum hydride, sodium borohydride, lithium borohydride, diborane or the like as a reducing agent, ruthenium-based, rhodium-based, nickel-based , Palladium-based and platinum-based transition metal catalysts. The reduction reaction solvent is appropriately selected in consideration of the solubility of the polymer and the reactivity with the reducing agent. Examples include tetrahydrofuran,
N-methylmorpholine, dimethylacetamide, dimethylformamide, dimethylsulfoxide, dimethoxyethane, methanol, ethanol, propanol and the like. The reduction reaction temperature is usually selected from the range of room temperature to 200 ° C, and the range of 50 ° C to 150 ° C is preferable.

Second production method: produced by polymerization of an allyl alcohol having a structure represented by the following formula (3).

[0025]

Embedded image

(Wherein R ¹ is a hydrogen atom or a group having 1 to 1 carbon atoms)
R ² represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. )

The method of polymerizing the second allyl alcohol is not particularly limited, but for example, US Pat.
897, 3666740 (JP-B 47-4030)
8) and British Patent 854207.

Third production method: It is obtained by chemically converting a halogen atom into a hydroxyl group after polymerization of an allyl halide derivative having a structure represented by the following formula (4).

[0029]

Embedded image

(Wherein, R ¹ is a hydrogen atom or a group having 1 to 1 carbon atoms)
2 represents an alkyl group, R ² represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and X represents a halogen atom. )

The third production method is described, for example, in US Pat. No. 4,125,694.

The oxygen permeability of the resin for powder coating of the present invention at 20 ° C. and a relative humidity of 65% is 30 ml · 20 μm / m ² · day · a measured as a film alone.
tm or less, and more preferably 20 m
l · 20 μm / m ² · day · at or less, more preferably 10 ml · 20 μm / m ² · day · at
m, optimally 5 ml · 20 μm / m ² · da
y · atm or less. 30ml ・ 20μm / m ²・ d
When it is larger than ay.atm, it cannot withstand use as a powder coating requiring high gas barrier performance.

The oxygen permeability of the resin for powder coating of the present invention at 20 ° C. and 100% relative humidity is 30 ml · 20 μm / m ² · day ·
atm or less, more preferably 20 atm or less.
ml · 20 μm / m ² · day · atm or less, more preferably 10 ml · 20 μm / m ² · day · a
tm or less, optimally 5 ml · 20 μm / m ² · d
ay · atm or less. 30ml ・ 20μm / m ²・
When it is larger than day · atm, it may not be able to be used as a powder coating used under high humidity.

Further, the resin for powder coating of the present invention has a temperature of 40 ° C.
The moisture permeability at a relative humidity of 90% is preferably 30 g · 30 μm / m ² · day or less, more preferably 20 g · 30 μm, as a value measured as a single film.
/ M ² · day or less, more preferably 10 g · day
30 μm / m ² · day or less. 30g ・ 30μm
When it is larger than / m ² · day, a problem may occur in the rust prevention effect of the powder coating.

The powder coating of the present invention is a coating comprising a powder containing the resin for powder coating. Other thermoplastic resins and additives may be blended as long as the object of the present invention is not hindered.

Examples of thermoplastic resins that can be blended include polyolefins such as polyethylene, polypropylene, polybutene and polymethylpentene; polyesters such as polyethylene terephthalate and polybutylene terephthalate; polycaprolactam (6-nylon); Examples include polyamides such as lactam (12-nylon) and polyhexamethylene adipamide (6,6-nylon), polystyrene, polyvinyl chloride, polycarbonate, polymethyl methacrylate, and polyurethane. Those obtained by modifying a part of these resins with a carboxylic acid such as maleic anhydride or a compound having an epoxy group can be mentioned as preferable ones from the viewpoint of the adhesion of the paint. The amount of the resin to be blended is usually in the range of 50% by weight or less. The method of blending these thermoplastic resins is not particularly limited, and they may be melt-mixed and then pulverized, or powders may be mixed together.

Further, pigment powder or various inorganic fine powders may be added. Examples of these powders include various organic and inorganic pigments, metals such as silicon, aluminum, iron, zinc, magnesium, and sodium and oxides, hydroxides, chlorides, and mixtures and alloys thereof. There is no particular limitation. The particle size is 1
It is preferred that the particles having a particle size of 0 μ or less account for 80% by weight or more of the total weight,
More preferably, 1 μ or less is 80% or more.

Further, various additives may be blended as required. Examples of such additives include antioxidants, plasticizers, heat stabilizers, ultraviolet absorbers, antistatic agents, lubricants, coloring agents or other high molecular compounds, which are used in the present invention. Blending can be performed within a range in which the effect is not inhibited. Specific examples of the additives include the following.

Antioxidants: 2,5-di-t-butylhydroquinone, 2,6-di-t-butyl-p-cresol, 4,4'-thiobis- (6-t-butylphenol), 2,2 '-Methylene-bis- (4-methyl-6-
t-butylphenol), octadecyl-3- (3 ′,
5'-di-t-butyl-4'-hydroxyphenyl) propionate, 4,4'-thiobis- (6-t-butylphenol) and the like.

UV absorber: ethylene-2-cyano-
3,3′-diphenyl acrylate, 2- (2′-hydroxy-5′-methylphenyl) benzotriazole,
2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3'-t-butyl-5 '-Methylphenyl) 5-
Chlorobenzotriazole, 2-hydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone and the like.

Plasticizer: dimethyl phthalate, diethyl phthalate, dioctyl phthalate, wax, liquid paraffin, phosphate ester and the like. Antistatic agents: pentaerythritol monostearate, sorbitan monopalmitate, sulfated polyolefins,
Polyethylene oxide, carbowax, etc. Lubricants: ethylene bis stearamide, butyl stearate and the like.

The powder coating material of the present invention contains a resin containing a monomer having a hydroxyl group as a repeating unit as a main component as described above. Such a hydrophilic resin containing a hydroxyl group, as represented by ethylene-vinyl alcohol resin and polyvinyl alcohol resin, shows good resistance to various hydrophobic solvents, but the resin of the present invention has the same effect. Provides resistance. Further, the resin of the present invention does not have a functional group capable of being decomposed, for example, hydrolyzed, by an acid or an alkali in its molecular structure, and has good acid resistance and alkali resistance.

As described above, the coating film made of the powder coating material of the present invention has good resistance to various hydrophobic solvents generally used widely as solvents for coating materials, or to acids and alkalis. Is shown. In addition, since it has good oxygen barrier properties and excellent rust prevention properties, it is possible to provide powder coatings that can be used in various environments.

Further, as a result of using a resin having barrier properties and hydrophilicity, various odor components (flavors) and odor components (order), particularly components composed of hydrophobic low molecular weight substances are blocked and not adsorbed. But it is effective.
This feature is effective in that the quality of the content can be maintained when the powder coating of the present invention is used for the interior coat of a container containing such a flavor or order.

The particle size of the resin powder of the powder coating of the present invention is:
20 to 100 mesh (JIS-K8801), that is, a material that passes through a 20 mesh sieve and contains 80% by weight or more of a material that does not pass through a 100 mesh sieve, and preferably contains 80% by weight or more of 30 to 100 mesh. It is a thing. If a large amount of powder having a large particle diameter that does not pass through a 20-mesh sieve is used in a large amount, the nozzle may be blocked or the smoothness of the coating film may be deteriorated. On the other hand, if a large amount of powder having a small particle diameter that passes through a 100-mesh sieve is used, dangers such as fire and explosion are likely to occur.

Examples of the powder coating in the present invention include coating methods such as a fluid immersion method, an electrostatic method, a thermal spraying method and a rotational molding method. The thermal spraying method is a method in which powder resin is sprayed from a nozzle to a base material together with a flame and fused, and only one thin layer is formed by one thermal spraying, and the unevenness is large. Is done. The electrostatic method means that a charged powder is sprayed on a substrate having a polarity opposite to that of the powder with an air gun or the like, and a powder having a predetermined thickness is applied to the substrate, and then heated in a heating furnace at 200 to 400 ° C. And then heat until the powder is completely melted and finished to a smooth surface, then cooled.

In the fluid immersion method, a substrate (metal, glass, pottery, etc.) heated to 200 to 400 ° C. is immersed for 1 to 30 seconds in a bath in which powder is fluidized with a gas fluid such as air. ,
It is a method of cooling by standing or heating and cooling again until the powder that has melted and adhered to the substrate is completely melted and finished to a smooth surface. The rotational molding method refers to a method in which a rotating container-shaped base material is heated to 200 to 400 ° C. from the outside with a gas burner or the like, and powder resin is sprayed into the inside of the container to perform melt coating.

The above four methods may be applied once or twice or more, respectively, and may be multi-layered by changing the brand of the powder resin or multi-layered by changing the method. Further, an anchor coat agent (adhesiveness imparting agent) may be applied to the substrate in advance in order to improve the adhesion to the substrate.

In the present invention, as a substrate to be subjected to powder coating, a metal (a steel plate, an iron plate, a wire mesh, etc.) is a typical example. For example, the inner and outer surfaces of a metal tank, the surface of a pump impeller, The surface ranges from simple to complex, such as the inner and outer surfaces of metal pipes and the surface of wire mesh such as fences. Further, examples of the substrate include pottery, ceramic, glass, and plastic.

[0050]

The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the invention thereto. In the following examples, unless otherwise specified, the ratio means the weight ratio, and “%” means “% by weight”. The measuring method and the evaluation method are as follows.

(1) Intrinsic viscosity The m-cresol solution was measured at 30 ° C. using an Ostwald viscometer. (2) Oxygen permeability MODERN CONTROLS INC. It measured according to the method of JISK7126 (isobaric method) under the conditions of 20 ° C., 65% RH and 20 ° C., 100% RH using an oxygen permeability measuring apparatus MOCONOX-TRAN 2/20. The oxygen permeability in the present invention refers to a value obtained by converting oxygen permeability measured at an arbitrary film thickness into oxygen permeability at a film thickness of 20 μm. (3) Moisture Permeability: Measured under the conditions of 40 ° C. and 90% RH according to the description of JIS Z0208, and calculated the value obtained by converting the film thickness to 30 μm.

EXAMPLE 1 Lithium aluminum hydride 25 was placed in a reaction vessel equipped with a cooler.
After charging 0 parts by weight, replacing with nitrogen and adding 3000 parts of N-methylmorpholine, the mixture was heated to 130 ° C. and refluxed. 600 parts by weight of polymethyl methacrylate and N
-A solution consisting of 6000 parts of methylmorpholine is added,
After the addition was completed, the mixture was refluxed for 4 hours. Thereafter, 1000 parts by weight of ethyl acetate was added dropwise to deactivate the unreacted hydride, and 5000 parts by weight of a 50% aqueous phosphoric acid solution was further added dropwise. After cooling, the mixture was separated into a supernatant and a solid by centrifugation. The obtained supernatant was added to distilled water to precipitate a polymer (No. 1). In addition, the obtained solid content is 1000
After adding 0 parts of ethanol and heating and dissolving at 60 ° C. for 1 hour, the solution was filtered through a glass filter. The obtained filtrate was concentrated by an evaporator, and then added to distilled water to precipitate a polymer (No. 2). The polymers obtained by the precipitation (Nos. 1 and 2) were combined, sufficiently washed by boiling with distilled water at 100 ° C., and dried under vacuum to obtain 380 parts by weight of polymethallyl alcohol.

30 of the resulting polymethallyl alcohol
° C, intrinsic viscosity in m-cresol 0.77 dl / g
Met. The vacuum-dried polymethallyl alcohol was measured by a scanning differential thermal analyzer (DSC) at a heating rate of 10 ° C./min after being melted and quenched in a nitrogen stream, and the glass transition temperature was 75 ° C. And no crystal melting peak was present.

The obtained resin was melt-extruded at 220 ° C. into pellets by a Labo Plastomill manufactured by Toyo Seiki equipped with a twin screw extruder having a screw diameter of 20 mm. Using the obtained pellets, a single-screw extruder having a screw diameter of 20 mm,
And a thickness of 20 mm by forming a single layer film at a die temperature of 220 ° C. using a laboratory plastomill manufactured by Toyo Seiki equipped with a coat hanger die having a width of 300 mm and a lip gap of 0.3 mm.
μ of polymethallyl alcohol film was obtained. The resulting film was colorless and transparent, and had a good appearance. Table 1
At 20 ° C., 65% RH and 20 ° C.
C., oxygen permeability measured at 100% RH and 40.degree.
The measurement result of the moisture permeability measured at 90% RH is shown.

Comparative Example 1 In Example 1, the raw material resin was changed to LDPE (“Milason 67” manufactured by Mitsui Petrochemical, MI = 22 g / 10 min).
A film was prepared and evaluated in the same manner as in Example 1. Table 1 shows the results.

[0056]

[Table 1]

Example 2 The resin pellets obtained in Example 1 were applied to a low-temperature pulverizer (using liquid nitrogen) and passed through a 20-mesh wire mesh.
The powder remaining on the 100 mesh wire net was obtained. The obtained powder was put into a thermal spraying facility, degreased with a solvent and washed 150 ×
It was sprayed on a 250 × 2 mm steel plate and allowed to cool in the air.
The average thickness of the resin coated on the steel plate is 55 microns, and the average thickness is 400 microns.
The smoothness was good. Both were evaluated for corrosivity in seawater at 50 ° C for one month. As a result, both corrosion,
No rust was observed. Further, the thin steel sheet having an average thickness of 55 μm of the resin was cooled to 40 ° C. below zero, a 1 kg hard ball was dropped from a height of 2 m, and the impact resistance was evaluated. Further, the corrosiveness was evaluated in sea water at 50 ° C. for one month, but no corrosion or rust was observed.

Comparative Example 2 A test was conducted in the same manner as in Example 2 except that the resin used in Example 2 was changed to LDPE ("Milason 67" manufactured by Mitsui Petrochemicals, MI = 22 g / 10 min). As a result, the average thickness of the resin coated on the steel plate was 50 microns,
Both products having a normal thickness of 430 μm and both had good gloss and smoothness. Both of them were evaluated for corrosiveness in seawater at 50 ° C. for one month. As a result, a 430 micron thick product was good, but a 50 micron thin product was corroded and rusted. The steel sheet having a thickness of 430 microns was cooled to 40 ° C. below 0 ° C., and a 1 kg hard sphere was dropped from a height of 2 m to evaluate the impact resistance. There is slight cloudiness, and 50
Evaluation of the corrosiveness in seawater at 1 ° C. for one month revealed local corrosion, rust, and lifting (peeling), mainly in the cloudy areas.

Example 3 The resin powder obtained in Example 2 was placed in a fluidized bed apparatus (stainless steel: diameter = 200 mm, height = 300 mm, air was uniformly blown through a sintered metal wire mesh from near the bottom). The powder was charged to make the powder flow uniformly, degreased and washed with a solvent, and a 150 × 250 × 2 mm steel sheet heated to 300 ° C. was immersed for about 3 seconds. After taking out, to further improve the smoothness of the painted surface,
After being left in a 300 ° C. electric heating furnace for 10 minutes, it was allowed to cool in the air. The glossiness of the steel sheet was good, and the same corrosion and impact resistance evaluations as in Example 2 were performed.

[0060]

EFFECT OF THE INVENTION The coating film surface is uniform and can be coated thinly, yet has the ability to protect metals (base materials) from rust and solvents,
In addition, it is possible to provide a resin composition for powder coating imparting impact resistance to a coating film surface and a powder coating containing the same as a main component.

Claims (9)

[Claims] 1. A resin for powder coating containing at least 30 mol% of a repeating structural unit represented by the following formula (1). Embedded image (In the formula, R ¹ represents a hydrogen atom or an alkyl group having 1 to 2 carbon atoms, and R ² represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.) 2. The resin for powder coating according to claim 1, which has an intrinsic viscosity in meta-cresol at 30 ° C. of 0.1 to 3 dL / g. 3. The resin for powder coating according to claim 1, wherein the oxygen permeability at 20 ° C. and a relative humidity of 65% is 30 ml · 20 μm / m ² · day · atm or less. 4. The resin for powder coating according to claim 1, wherein the oxygen permeability at 20 ° C. and a relative humidity of 100% is 30 ml · 20 μm / m ² · day · atm or less. 5. The water vapor permeability at 40 ° C. and 90% relative humidity is 30 g · 30 μm / m ² · day or less.
5. The resin for powder coating according to any one of items 1 to 4. 6. The method of claim 1, wherein R ¹ in formula (1) is CH _3.
6. The resin for powder coating according to any one of items 1 to 5. 7. The resin for powder coating according to claim 1, wherein R ² in the formula (1) is H or CH ₃ . 8. The resin for powder coating according to claim ¹ , wherein R ¹ in the formula (1) is CH ₃ and R ² is H. 9. A powder coating comprising the resin for powder coating according to claim 1.