JP3511440B2 - Powder coating for cast iron pipe - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention belongs to the technical field of producing and using powder coating materials for cast iron pipes.

[0002]

2. Description of the Related Art Powder coatings have no solvent-containing pollution-free property, and because they can be completely cured by thick coating and heat curing, they are reasonably easy to mechanize and automate. It is widely used for painting various pipes, home appliances, metal furniture, etc. from the standpoints of high efficiency and high paint recovery rate.
Above all, epoxy powder coatings have excellent corrosion resistance, water resistance, solvent resistance, chemical resistance, mechanical properties, insulation properties, etc., so they are widely used especially in fields requiring corrosion resistance, hygiene, insulation properties, etc. Has been.

On the other hand, in the ductile cast iron pipe on the side of the object to be coated, shrinkage cavities easily occur on the inner surface of the cast iron pipe during casting,
In addition, since a hydraulic test is incorporated in the manufacturing process, water remains inside the shrinkage cavity and on the tube surface. When this cast iron pipe is heated for powder coating, the shrinkage cavities of the object to be coated and the water remaining on the pipe surface are vaporized to break through the heated and melted paint layer after coating and cure as it is. In this case, a pinhole is generated as a result.
This is because the epoxy resin has a high melt viscosity and the powder coating material has poor flowability during heating and melting.

In order to solve these problems, the flowability can be improved by raising the coating temperature or the heat curing temperature to lower the melt viscosity of the epoxy resin, or by using an epoxy resin having a lower melting point. I'm sick.

However, if the curing temperature is increased in order to improve the flowability, more heat energy is required and the coating cost becomes higher. Further, when the curing temperature is high, the curing time of the resin composition is shortened, it becomes difficult to control the coating curing step, and when the curing time is too short,
As a result, it becomes a paint with poor flowability. on the other hand,
The method using an epoxy resin having a lower melting point improves the flowability, but tends to cause blocking, which is a major problem in paint management.

Therefore, as a method of improving the flowability without relying on these methods, a method using a crystalline epoxy resin is known.

However, when the crystalline epoxy resin is used, the effect of improving the flowability is not sufficient, the generation of pinholes cannot be suppressed when the coating of the cast iron pipe is cured, and the appearance of the coated surface is inferior. It becomes a thing. Further, the obtained coating film also has poor corrosion resistance. When the amount of the crystalline epoxy resin used is remarkably increased, the flowability is improved accordingly, but the corrosion resistance such as water resistance and salt water resistance is remarkably lowered, and the coating film appearance is also deteriorated.

Further, in Japanese Patent Publication No. 62-35434, an epoxy resin powder having good flowability is treated with special surface-treated calcium carbonate having a specific average particle diameter, and an epoxy resin powder having good flowability is provided with average particles. It is described that by dry-blending a long-chain aliphatic polyamide having a diameter, an epoxy resin powder composition having no blocking in a normal state, a low melt viscosity and a high flowability can be obtained.

In this case, however, the useful application is for impregnating coils, laminated plates, decorative plates, etc. When used in cast iron pipes, sufficient flowability cannot be obtained, and pinhole prevention is still impossible. In addition, it is not possible to use for this application because there are problems such as not being able to obtain a coating film which is tough and has excellent adhesiveness and poor corrosion resistance.

Further, in any of the above powder coatings, a general-purpose curing agent such as adipic acid dihydrazide is used as a curing agent. In the end, however, when such a curing agent is used, As a powder coating material for cast iron pipes, one having good flowability cannot be obtained.

[0011]

SUMMARY OF THE INVENTION The present invention solves the problems described above, and has the advantages (adhesion,
(Blocking resistance, coating appearance, corrosion resistance), without unnecessarily raising the curing temperature, low melt viscosity, good flowability, excellent pinhole prevention, uniform coating it has been made for the purpose that may excellent epoxy powder paint to sell, and an epoxy resin (a) and aryl imidazoline compound and (B), epoxy resin (a) and aryl imidazoline system of
Compounding ratio with compound (B) is an epoxy resin on an equivalent basis.
(A) / aryl imidazoline compound (B) = 1.0
/0.10 to 1.0 / 0.80 and epoxy
As the resin (A), it is combined with the non-crystalline epoxy resin (a1).
Amorphous epoxy resin is used in combination with the crystalline epoxy resin (a2).
Compounding of resin (a1) and crystalline epoxy resin (a2)
The ratio is the weight-based non-crystalline epoxy resin (a1) / binding
Crystalline epoxy resin (a2) = 80/20 to 99/1 , a powder coating for cast iron pipes (claim 1), and an aryl imidazoline compound (B) having the general formula ( I):

[0012]

[Chemical 2]

(Wherein R¹~ R^FiveIs H or 1 to 9 carbon atoms
A compound represented by
The powder coating composition according to claim 1 (claim 2), Amorphous epoxy resin
(A1) has a melting point of 80 to 120 ° C. according to the ring and ball method and 1
Viscosity at 60 ℃ is less than 100 poise, and 200 ℃
The viscosity at 20 is less than 20 poise.1Powder coating described
Fee (ClaimThree), In the non-crystalline epoxy resin (a1)
Polystyrene-equivalent weight average molecular weight (Mw) and number average
The ratio (Mw / Mn) with the molecular weight (Mn) is 2.0 to 3.5.
Claims that are1OrThreePowder coating described (claimFour) Non
Crystalline epoxy resin (a1) is bisphenol type epoxy
Claims that are resin1,ThreeOrFourPowder coating described (contract
Requirement5),andBisphenol type epoxy resin
The xyquivalent is 670 to 1500 g / eq.5Description
Powder coating (Claims6)Concerned.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION As the epoxy resin (A) used in the present invention, a non-crystalline epoxy resin (a1) and a crystalline epoxy resin (a2) are used in order to further improve the flowability and the pinhole prevention property. Is preferably used in combination.

Here, the non-crystalline epoxy resin (a1) is a resin whose absolute value of the difference between the melting point Tm by the ring and ball method and the glass transition point Tg by the differential scanning calorimetry is larger than 10 ° C., that is, | Tm-Tg |> 10 (° C) is referred to as an epoxy resin, while crystalline epoxy resin (a2) is the absolute value of the difference between the melting point Tm by the ring and ball method and the glass transition point Tg by the differential scanning calorimetry. Is 10 ° C
The following are the epoxy resins that satisfy the condition of | Tm-Tg | ≦ 10 (° C.).

Examples of the non-crystalline epoxy resin (a1) include epoxy resins generally used as an epoxy resin for powder coatings. Specifically, bisphenol A type epoxy resin, bisphenol F type epoxy resin, tetrabromobisphenol A type epoxy resin or other bisphenol type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin or other novolac type epoxy resin, fat Examples thereof include a cyclic epoxy resin, a polyhydric alcohol ether epoxy resin, a glycidyl ester epoxy resin, a cocondensation of the epoxy resin, a copolymer resin, and a partially modified resin of these epoxy resins. Among these, the bisphenol type epoxy resin is preferable from the viewpoints of adhesion, corrosion resistance, flexibility, and good appearance of the coating film.

The melting point of the non-crystalline epoxy resin (a1) according to the ring and ball method is preferably 80 to 120 ° C., more preferably 90 to 110 ° C. from the viewpoint of blocking resistance and easiness of coating.

The melting point measured by the ring and ball method is, for example, "ASP-M2", an automatic softening point apparatus for ring and ball method manufactured by Akemine Co.
It is the melting point when measured using the "mold".

The non-crystalline epoxy resin (a1) has a viscosity of 100 poise or less when measured under conditions of 160 ° C. and a shear rate of 50 / sec, more preferably 50 poise or less and 3 poise or more, and 200 ° C. At this time, the viscosity is preferably 20 poises or less, more preferably 10 poises or less and 0.7 poises or more. When the viscosity at 160 ° C. is 100 poises or less or the viscosity at 200 ° C. is 20 poises or less, the appearance of the cured coating film is excellent because the flowability is good, and the powder coating is easily formed. . Also, 16
Viscosity at 0 ° C. is 100 poise or less, viscosity at 200 ° C. is 20 poise or less, and melting point is 80 to 1
When the condition of 20 ° C. is satisfied, the flowability and blocking resistance are excellent, and the powder coating material can be easily formed.

In the case of an epoxy resin for powder coating for cast iron pipes, which is usually used as a main raw material, the viscosity at 160 ° C. does not become less than 3 poises or the viscosity at 200 ° C. does not become less than 0.7 poises. .

Furthermore, the weight average molecular weight (Mw) of the amorphous epoxy resin (a1) is 400 in terms of polystyrene.
It is preferably 0 to 8000, and more preferably 4500 to 7000. When the weight average molecular weight (Mw) is 4000 or more, blocking resistance and impact resistance are good, and when it is 8,000 or less, melt viscosity is low, flowability and pinhole prevention are good.

The number average molecular weight (Mn) of the non-crystalline epoxy resin (a1) is 1600 in terms of polystyrene.
It is preferably 2500, more preferably 1800 to 2300. When the number average molecular weight (Mn) is 1600 or more,
It has good blocking resistance and impact resistance.
When it is 00 or less, the melt viscosity is low, and the flowability and the pinhole prevention property are good.

Further, the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), that is, Mw / Mn is 2.
It is preferably 0 to 3.5, and more preferably 2.2 to 2.7. When Mw / Mn is within the above range, the melt viscosity is low and the flowability is improved.

The epoxy equivalent of the bisphenol type epoxy resin which can be preferably used is the blocking resistance,
The epoxy equivalent is preferably 670 to 1500 g / eq from the viewpoints of impact resistance, easiness of conversion to powder coating, pinhole prevention, and the like. That is, the epoxy equivalent is 670 g /
If it is eq or more, blocking resistance and impact resistance will be good, while if it is 1500 g / eq or less, the melting point will be low and powder coating will be easy, and the melt viscosity will be low. Flowability and pinhole prevention are improved.
From the viewpoint of excellent performance balance, the epoxy equivalent is 740 to 1200 g / eq, the shock resistance is 790 to 1000 g / eq, and the shock resistance and flexibility and adhesion are 810 to 900 g / eq. It is preferably eq.

In order to adjust the epoxy equivalent to the preferable range, two or more kinds of the non-crystalline epoxy resin (a1) may be used in combination.

Specific examples of the bisphenol type epoxy resin are, for example, EPICLON1050 and EPICL.
ON 2055, EPIC LON 3050, EPIC
LON 4050, EPIC LON 4055, EPI
CLON 7050 (above, Dainippon Ink and Chemicals, Inc.) etc. are mentioned.

Of the above-mentioned specific examples of the bisphenol type epoxy resin, the epoxy equivalent of the main one, the viscosity at 160 ° C. and 200 ° C., Mw /
Table 1 collectively shows Mn, Tm, Tg, and | Tm-Tg |.

The epoxy equivalent is JIS K723.
Value measured in accordance with 6-1995, 160 ° C. and 2
Viscosity at 00 ° C is a precision rotational viscometer (RV
20 type), Mw / Mn are measured by Tosoh Corp. HLC-8020 as a stationary phase column TS.
It is a value measured by mounting K gel and using tetrahydrofuran as a mobile phase solvent.

[0029]

[Table 1]

Next, in the present invention, when the crystalline epoxy resin (a2) is used as described above, a low melt viscosity,
A composition having advantages such as high flowability and uniform coating film can be obtained. Specific preferred examples of the crystalline epoxy resin (a2) include, for example, triglycidyl isocyanurate (Nissan Chemical Co., Ltd., trade name TEPIC G),
4,4'-bis (2,3-epoxypropoxy) -3,
3 ′, 5,5′-tetramethylbiphenyl (Yukaka Shell Epoxy Co., Ltd., trade name Epicoat YX-4000),
2,6-bis (2,3-epoxypropoxy) naphthalene, bis (1,2-epoxypropoxy-naphthyl) methane, 2,2-bis [3,5-dibromo-4- (1,2)
-Epoxypropoxy) phenyl] propane and the like. Table 2 collectively shows epoxy equivalents, viscosities at 150 ° C., Tm, Tg, and | Tm-Tg | of those listed as preferable specific examples of the crystalline epoxy resin (a2).

[0031]

[Table 2]

The non-crystalline epoxy resin (a1) and the crystalline epoxy resin (a2) are used in proportions by weight based on the non-crystalline epoxy resin (a1) / the crystalline epoxy resin (a).
2) = 80/20 to 99/1, and further 85/15 to 9
6/4 is preferred. When the ratio of the non-crystalline epoxy resin (a1) / the crystalline epoxy resin (a2) used is within the above range, the use of the crystalline epoxy resin (a2) has the effect of improving the flowability and the pinhole prevention property. It will be remarkable.

The aryl imidazoline compound (B) used in the present invention is used as a curing agent for an epoxy resin and has the general formula (I):

[0034]

[Chemical 3]

A compound represented by the formula (wherein R ^{1 to} R ⁵ represent a hydrogen atom or an alkyl group having 1 to 9 carbon atoms) is preferable from the viewpoint of the appearance of the cured coating film and the pinhole prevention property. Particularly, when the compound represented by the general formula (I) is phenylimidazoline (R ^{1 to} R ⁵ are hydrogen atoms), flowability, pinhole prevention property, corrosion resistance and the like are preferable.

Specific examples of the compound represented by the general formula (I) include phenylimidazoline (appearance: flake, color number: yellowish white, melting point: 99-10, manufactured by Huls).
1 ° C). The compounds represented by general formula (I) may be used alone or in combination of two or more. Depending on the case, polycarboxylic acid hydrazides (such as adipic acid dihydrazide, sebacic acid dihydrazide,
Dodecanedioic acid dihydrazide, isophthalic acid dihydrazide, carbon dihydrazide, etc.), imidazoles (for example, imidazole, 2-methylimidazole, 2-ethylimidazole, 2-isopropylimidazole, 2
-Heptadecyl imidazole, 2-phenyl imidazole, etc.) and the like, which are generally used for epoxy powder coatings, may be used in combination. In this case, the amount of the other curing agent used relative to 100 parts of the compound represented by the general formula (I) is 1000 to 5 parts, and further 500 to 5 parts.
The part is preferable from the viewpoint of flowability and pinhole property.

The mixing ratio of the epoxy resin (A) and the aryl imidazoline compound (B) used in the present invention is
Epoxy resin (A) / aryl imidazolyl compound (B) = 1.0 / 0.10 to 1.0 / 0.80 on an equivalent basis.
Is preferable, and 1.0 / 0.20 to 1.0 / 0.5 is more preferable.
0 is more preferable. When the compounding ratio is 1.0 / 0.10 or less, the curing is accelerated, the melt viscosity is low, and the flowability, the pinhole prevention property and the anticorrosion property are improved. Also,
When it is 1.0 / 0.80 or more, the curing is accelerated, the molecular weight can be made higher, and the anticorrosion property is remarkably improved.

In the powder coating material of the present invention, if necessary, an extender pigment or a coloring material such as titanium oxide, talc, calcium carbonate, barium carbonate, silica, mica, alumina, carbon black, phthalocyanine green, phthalocyanine blue and the like. It can be blended.

Production of a powder coating material using the above-mentioned materials can be carried out by a usual method. That is, the epoxy resin (A) (including the crystalline epoxy resin (a2) used as one component of the epoxy resin (A) if necessary), the curing agent aryl imidazoline compound (B), the extender pigment or the coloring. Material, other additives, etc. are roughly crushed and mixed, this mixture is thoroughly crushed using a Henschel mixer, mixed and then melt-kneaded using a heated extruder, and after cooling it is crushed and classified. Done by. The particle size after classification is not particularly limited, but usually 60 to 140 μm is preferable.

In a preferred embodiment of the present invention, for example, the epoxy resin (A) has an epoxy equivalent of 79.
0 to 1000 g / eq of bisphenol type epoxy resin (a1) and 4,4'-bis (2,3-epoxypropoxy) -3,3 ', 5,5'-tetramethylbiphenyl (a2) are used in combination, and , A powder coating using phenylimidazoline as the aryl imidazoline compound (B). In this case, the impact resistance is particularly excellent among the effects of the present invention.

[0041]

EXAMPLES The powder coating material of the present invention will be described in more detail based on the following examples and comparative examples, but the present invention is not limited to these examples.

Examples 1 to 4 and Comparative Examples 1 to 5 and a to b , the components shown in Tables 3 and 4 were coarsely crushed, and then Tables 3 and 4 were used.
The ingredients were blended in the proportions described in, and were sufficiently pulverized and mixed using a Henschel mixer. After that, the mixture was melt-kneaded using an extruder heated to 110 ° C., extruded, cooled and then pulverized and classified to obtain a powder coating material having a particle diameter of 80 to 120 μm. At this time, the productivity of the paint and the blocking resistance of the obtained paint were examined by the following methods.

The 11 kinds of powder coatings thus obtained were spray-painted on the surface of the test piece heated to 180 to 210 ° C. while leaving the oxide scale on the substrate by surface treatment only by brushing and then allowed to cool. To form a coating film having a thickness of 300 ± 50 μm. About the obtained sample, the appearance of the cured coating film,
The pinhole prevention property, impact resistance, Erichsen test, salt spray test and water resistance were evaluated by the following methods.

The results are shown in Tables 3 and 4.

[0045] Incidentally, the epoxy resin used in Example 4 (a
1) (EPICLON 3050 and EPICLON 4
050) and the epoxy equivalent of 869 g / eq,
The active hydrogen equivalent of phenylimidazoline is 146 g / e.
q, adipic acid dihydrazide is 44 g / eq, and 2-methyl-2-imidazoline is 84 g / eq.

Further, the EPICL of the curing agent in Tables 3 and 4
ON B-605IM is a urea-based curing agent manufactured by Dainippon Ink and Chemicals, Inc.

(Productivity of coating material) At the time of forming a powder coating material, a predetermined composition was melt-kneaded (residence time 40 seconds) using an extruder (Plasticorder PL2000 type manufactured by Gravender Co.) heated to 110 ° C. Then, it was judged whether or not the melt-kneaded product was uniform.

◯: The melt-kneaded product obtained through the extruder is visually free of any spots, and the surface is smooth.

X: The melt-kneaded product obtained through the extruder has some visually noticeable spots on the melt-kneaded product, or the surface is not smooth.

(Blocking resistance) 20 g of the powder coating material was placed in a glass bottle (inner diameter: 4 cm), applied with a load of 25 g / cm ² , stored at 35 ° C. for 1 week, then taken out from the glass bottle, and the shape at this time was judged. .

◯: Return to the fine powder state before weighting and storing.

X: No return to the fine powder state before weighted storage.

(Appearance of cured coating film) 150 mm as base material
A gray cast iron piece with a casting defect of x70 mm x 15.0 mm was used.

The appearance of the sample was visually observed, and when the surface was smooth and shiny, it was evaluated as good, and when the surface was not shiny and uneven, it was evaluated as uneven.

(Pinhole preventive property) 150 m as a base material
Four murine cast iron pieces with m × 70 mm × 15.0 mm and casting defects were used per one of the examples or comparative examples.

The sample was measured with a holiday detector to 200
The coating film surface was scanned while applying a voltage of 0 V, and the average number of pinholes present in one sample was examined.

(Impact resistance) 150 mm × 70 as a base material
A mm × 2.0 mm steel plate was used.

JIS K 5400-1990 8.3
-Tested according to 2 (DuPont type impact test).

(Erichsen test) 90 mm × as a base material
A 90 mm × 1.2 mm steel plate was used.

It was evaluated by the A method of JIS Z 2247.

(Salt spray test) 150 mm × as a base material
A 70 mm × 2.0 mm steel plate was used.

A scratch reaching the base material was placed on the surface of the coating film, and a 3% NaCl aqueous solution was continuously sprayed at 35 ° C. for 3000 hours to examine the state of the coating film and the width of creep peeling by inserting a knife into the scratch.

(Water resistance) 150 mm × 70 m as a base material
A steel plate of m × 2.0 mm was used.

After immersing the sample in water for 1 year, the state of the coating film was examined.

[0065]

[Table 3]

[0066]

[Table 4]

Comparative Examples 6 to 7 Brominated bisphenol A type epoxy resin (XD809400, manufactured by Dow Chemical Co.) tetrahydrophthalic anhydride and 2-undecylimidazole in the amounts shown in Table 5 were melt mixed and extruded. It was then crushed.

The obtained pulverized product, organic acid surface-treated calcium carbonate (manufactured by Shiraishi Kogyo Co., Ltd., Shiragure CCR, average particle size 8)
0 mμ) and long-chain aliphatic polyamide (manufactured by Glycochemical Co., Ltd., Acrowax C, average particle size 50 mμ or less)
Was dry-blended in the ratio shown in Table 5 to obtain a mixture having a 150 mesh pass, and evaluated in the same manner as in Examples 1 to 4 . The results are shown in Table 5.

[0069]

[Table 5]

Comparative Examples 8 to 9 Bisphenol A type epoxy resin (manufactured by Yuka Shell Epoxy Co., Ltd., Epicoat 1002), trisglycidyl isocyanurate, and ethylene glycol bistrimellitate were melt mixed in an extruder with the amounts shown in Table 6. It was then extruded and then crushed.

The obtained pulverized product, resin acid surface-treated calcium carbonate (manufactured by Shiraishi Kogyo Co., Ltd., Shiro Ginka TDD, average particle size 400 mμ) and long-chain aliphatic polyamide (manufactured by Glycochemical Co., Ltd., Acrowax C), The average particle size was 50 mμ or less) was dry-blended in the ratio shown in Table 6 to obtain a mixture having a 150 mesh pass, and evaluated in the same manner as in Examples 1 to 4 . The results are shown in Table 6.

[0072]

[Table 6]

[0073]

When the powder coating material of the present invention is used, the melt viscosity is low and the flowability is high without impairing the adhesion, blocking resistance, coating film appearance and corrosion resistance, and further without raising the curing temperature. Thus, it is possible to obtain a cast iron pipe having a uniform coating film without pinholes.

─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Mayoshi Kitagawa 1-12-19 Kitahori, Nishi-ku, Osaka City Kurimoto Iron Works Co., Ltd. (72) Inventor Masahiko Saito 1-12-19 Kitahori, Nishi-ku, Osaka Stock Company Kurimoto Works (72) Inventor Yoshisada Michiura 1-12-19 Kitahori, Nishi-ku, Osaka City Stock Company Kurimoto Works (72) Inventor Ryusuke Exit 12-12 Kitahori, Nishi-ku, Osaka City Shares Kurimoto Iron Works Co., Ltd. (72) Inventor Kazuhito Hanano 1-12-19 Kitahorie, Nishi-ku, Osaka City Kurimoto Iron Works Co., Ltd. (72) Inventor Norio Kobayashi 1-22-7 Hanamigawa-ku, Chiba City (72) Inventor Kazuyuki Onodera 1805-1 Kamishizu, Sakura City, Chiba Ic-713 (72) Inventor Toshihiko Adachi Meiji Co., Ltd., 1-27-6 Taishibashi, Asahi-ku, Osaka (56) Reference Japanese Patent Laid-Open No. 7- 2242 34 (JP, A) JP 8-1151429 (JP, A) JP 8-176470 (JP, A) JP 7-196952 (JP, A) JP 4-370162 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) C09D 163/00 C09D 5/03 C08G 59/40 C08G 59/50

Claims (6)

(57) [Claims] 1. An epoxy resin (A) containing an epoxy resin (A) and an arylimidazoline compound (B).
The mixing ratio with the aryl imidazoline compound (B) is
Epoxy resin (A) / aryl imidazoline on an equivalent basis
System compound (B) = 1.0 / 0.10 to 1.0 / 0.80
And the epoxy resin (A) is a non-crystalline resin.
The epoxy resin (a1) and the crystalline epoxy resin (a2)
Used in combination, the non-crystalline epoxy resin (a1) and crystalline epoxy
The blending ratio with the resin (a2) is non-crystalline based on the weight.
Poxy resin (a1) / Crystalline epoxy resin (a2) = 8
0 / 20-99 / 1 der Rukoto cast iron pipe for powder coating according to claim. 2. An aryl imidazoline compound (B)
Is represented by the general formula (I): The powder coating composition according to claim 1, which is a compound represented by the formula: wherein R ^{1 to} R ⁵ represent a hydrogen atom or an alkyl group having 1 to 9 carbon atoms. 3. The amorphous epoxy resin (a1) has a melting point of 80 to 120 ° C. according to the ring and ball method, a viscosity at 160 ° C. of 100 poises or less, and a viscosity at 200 ° C. of 20 poises or less. The powder coating material according to claim 1 . 4. The ratio (Mw / Mn) of the polystyrene-equivalent weight average molecular weight (Mw) to the number average molecular weight (Mn) in the amorphous epoxy resin (a1) is 2.0 to 3.5. The powder coating composition according to 1 or 3 . 5. The non-crystalline epoxy resin (a1) according to claim 1 is bisphenol type epoxy resin, 3 or 4, wherein the powder coating. 6. The method of claim 5, wherein the powder coating bisphenol epoxy resin is an epoxy equivalent of 670~1500g / eq.