JP2019172804A - Epoxy resin powder coating - Google Patents

Abstract

To provide an epoxy resin powder coating capable of providing good coating appearance with uniform coated film thickness even in a coating method by depositing the same on an inner surface of a hollow body pre-heated under reduced pressure, without heating and temperature rising, and suitable for a tube inner surface or the like.SOLUTION: There is provided an epoxy resin powder coating used in a coating method including aspirating and depositing the powder coating to an inner surface of a hollow article to be coated which is heated in a specific pre-heating temperature in a range of 150 to 280°C, and curing as it is to form a cured coated film, containing an epoxy resin (A), a curing agent (B), and a pigment (C), and having D10 in particle size distribution of 5 μm or more and D90 of 200 μm, bulk density of 0.4 to 0.8 g/cm, and gel time at the pre-heating temperature of 20 to 60 sec.SELECTED DRAWING: None

Description

  The present invention relates to an epoxy resin powder coating suitable for pipe inner surfaces. More specifically, the present invention relates to a powder coating suitable for the inner surface of a pipe, which is excellent in storage stability and coolability, and can obtain a coating film having excellent coating appearance, corrosion resistance and mechanical strength.

  Gas, water, oil, cable protection pipes, etc., which are currently buried as industrial and living facilities, have anti-corrosion treatment on the inner surfaces of the pipes. Epoxy resin powder paint is used because of its height.

  As a coating method of the epoxy resin powder coating on the buried pipe, a rotary spraying method, an electrostatic coating method, a fluid immersion method, or a thermal spraying method is used. A rotary spraying method is generally used for straight pipes, and an electrostatic coating method and a fluid immersion method are generally used for deformed pipes and valves. In the electrostatic coating method, a ductile cast iron deformed pipe, which is the object to be coated, is preheated to 150 to 250 ° C., and is installed or suspended on a coating table, and then the airborne powder coating is sprayed onto the inner surface of the coating film. A layer is formed, and a cured coating film is obtained by post-heating at the same temperature for about 10 to 20 minutes or by cooling without post-heating.

  The deformed pipes are used for connecting and branching straight pipes having different diameters, and thus have various shapes and sizes. Curved pipes and cut-off pipes are difficult to paint by rotating the rollers because of the structure, and the inside of the deformed pipe that is the object to be coated is hung on the inner surface. For painting, spray using a manual painting gun, and recently, spray painting by a robot is also performed.

  On the other hand, in the conventional rotary spray coating method and spray coating method using a coating gun, not all powder particles discharged at the time of coating are applied to the object to be coated and a coating film is not formed. The surplus at the time of painting is collected and only a part is used for repainting, most of which is discarded. In addition, what is released outside the system after staying in the work environment cannot be ignored.

  In recent years, from the viewpoint of such work efficiency and work environment and energy cost reduction, a coating method for improving the yield of powder paint is also being performed.

  In Patent Documents 1 to 3, as a powder coating method and a powder coating apparatus, a method and an apparatus for applying a powder coating under vacuum and reduced pressure are proposed, but an inner surface of a pipe using an epoxy resin powder coating is proposed. No specific proposal has been made for a powder coating material that has been applied to the surface and satisfies the appearance and physical properties of the coating film.

  In this field, industrially, there is a problem that there is no powder coating material that ensures a smooth film thickness and satisfies storage stability by passing through a preheating atmosphere on the inner surface of the tube.

JP 7-328494 A Japanese Patent Laid-Open No. 2003-33699 JP-A-10-337515

  The present invention can be applied to the inner surface of a hollow body preheated under reduced pressure, and can obtain a good coating appearance with a uniform coating thickness even in a coating method without heating and heating thereafter. In addition, the present invention provides an epoxy resin powder coating suitable for use on the inner surface of a pipe and the like that can obtain basic coating film properties such as anticorrosion, mechanical properties, and hygiene.

  The present inventors have found that a powder coating material having a specific gel time, a specific particle size distribution, and a bulk density can solve the above problems, and has reached the present invention.

That is, the present invention is a cured coating film in which a powder coating material is sucked and applied under reduced pressure to a hollow inner surface heated to a constant preheating temperature in the range of 150 to 280 ° C. and cured. A powder coating used in a coating method for forming a powder, wherein the powder coating contains an epoxy resin (A), a curing agent (B), and a pigment (C), and D10 in the particle size distribution of the powder coating is 5 μm or more. And D90 is 200 μm or less, the bulk density is 0.4 to 0.8 g / cm ³ , and the gel time at the preheating temperature is 20 to 60 seconds.

The epoxy resin (A) is an epoxidized product of bisphenols with epichlorohydrin and has an epoxy equivalent of 700 to 3000 g / eq. An epoxy resin having a softening point of 70 to 130 ° C. is preferred.
Examples of the bisphenols include tetramethyl bisphenol F, bisphenol F, tetramethyl bisphenol A, and bisphenol A.

  As said hardening | curing agent (B), an imidazoline derivative and / or an imidazole derivative are mentioned preferably.

  Preferred examples of the pigment (C) include at least one selected from iron oxide, yellow iron oxide, silica powder, quartz-based powder, titanium oxide, calcium carbonate, barium sulfate, and carbon black.

Examples of the object to be coated include a straight pipe and a deformed pipe.
Moreover, this invention is a straight pipe or a deformed pipe painted with said epoxy resin powder coating material.

Furthermore, in the present invention, a hollow article to be preheated to a constant temperature within a range of 150 to 280 ° C. is placed on a gantry, and the inside of the article to be coated is sucked in from the paint supply tank under reduced pressure. A coating method in which a cured coating film can be formed as it is by being applied to the inner surface of a coating, wherein the epoxy resin powder coating is used as the powder coating.
Moreover, this invention is a straight pipe or a deformed pipe painted by said coating method.

  The epoxy resin powder coating of the present invention provides a coating film having no pinholes, sagging, etc. on the inner surface of the hollow article in a coating method under reduced pressure, and also having a coating film with excellent corrosion resistance and mechanical strength. Can do. Furthermore, basic coating film properties such as anticorrosion, mechanical properties and hygiene can be obtained.

The present invention will be specifically described below.
The epoxy resin powder coating of the present invention contains an epoxy resin (A), a curing agent (B), and a pigment (C) as essential components.

  The particle size distribution of the epoxy resin powder coating is such that D10 is 5 μm or more and D90 is 200 μm or less, preferably D10 is 10 μm or more, D90 is 150 μm or less, more preferably D10 is 20 μm or more, and D90 is D90. The range is 130 μm or less. If D10 is small in the particle size distribution, it is easy to harden before the extra portion passes through the pipe and is collected during painting, and if it adheres to the inner surface, the coating tends to become rough, and if D90 is too large, the paint storage tank before painting The convection in the water tends to be non-uniform and may cause unstable discharge. Here, D10 is a weight passing percentage, and 10 wt% passes through the opening.

The bulk density of the epoxy resin powder coating is in the range of 0.4 to 0.8 g / cm ^3, preferably in the range from 0.45~0.75g / cm ^3, more preferably 0.5 to 0 The range is 0.7 g / cm ³ . Although the bulk density depends on the specific gravity of the material used, if the bulk density is too small, more particles will float during the flow before coating, and the film will be coated when a preheated object is installed, resulting in film thickness uniformity. If the bulk density is too high, it may become unstable when convection is performed in the paint storage tank before painting.

  The gel time at the preheating temperature of the coating object of the epoxy resin powder coating is in the range of 20 seconds to 80 seconds, preferably in the range of 30 seconds to 70 seconds, and more preferably in the range of 40 seconds to 60 seconds. . If the gel time is early, the coating will melt and become smooth before the coating melts and becomes smooth, and the coating may appear uneven or rough. The film thickness may be uneven and the film thickness may be non-uniform, and sufficient physical properties of the coating film may not be exhibited unless post-heating is performed. When the gel time with respect to the preheating temperature is from 20 seconds to 80 seconds, a coating film having good coating film appearance and excellent basic physical properties such as mechanical properties and anticorrosion properties can be obtained even without heating after coating.

Next, the epoxy resin (A) will be described.
The epoxy equivalent (g / eq.) Of the epoxy resin (A) is preferably in the range of 700 to 3000, more preferably in the range of 900 to 2500, and still more preferably in the range of 1000 to 2000. If the epoxy equivalent is small, the storage stability in the case of a powder coating is deteriorated, and when it is stored for a long period of time, it may be blocked and cannot be used as a coating. When the epoxy equivalent is large, the melt viscosity becomes high, and in the case of a powder coating, even if the gel time is adjusted, the fluidity is poor and the appearance may be defective such as irregularities. When the epoxy equivalent is in the range of 700 to 3000, when a powder coating is used, a powder coating having no problem in storage stability is obtained, the coating film appearance is good, and the basic physical properties such as mechanical properties and anticorrosion properties are also obtained. A good coating film is obtained.

  The softening point of an epoxy resin (A) becomes like this. Preferably it is the range of 70-130 degreeC, More preferably, it is the range of 90-120 degreeC, More preferably, it is the range of 100-115 degreeC. If the softening point is low, the blocking property of the powder coating may be deteriorated. If the softening point is high, the gel time may be increased when the powder coating is used, and the fluidity of the coating may be deteriorated. However, the fluidity is poor and the smoothness of the coating film surface may be impaired. When the softening point is in the range of 70 to 130 ° C., when a powder coating is used, a powder coating having no blocking property is obtained, the coating film appearance is good, and the basic physical properties such as mechanical properties and anticorrosion properties are also obtained. A good coating film is obtained.

  The epoxy resin (A) used in the present invention is not particularly limited as long as it is solid, but is preferably a bisphenol-type epoxy resin and may have a substituent. As the substituent, an alkyl group, a phenyl group or an α-methylbenzyl group is preferable, and a methyl group or an α-methylbenzyl group is more preferable. The number of substituents is preferably 1 or 2 with respect to the phenol ring. Specific examples of the epoxy resin (A) include bisphenol F-type epoxy resins, tetramethylbisphenol F-type epoxy resins, bisphenol A-type epoxy resins, and tetramethylbisphenol A-type epoxy resins. Among these, bisphenol F type epoxy resin is preferable.

Bisphenol-type epoxy resins are usually added by direct polymerization epoxy resin obtained by condensation polymerization reaction of bisphenols and epichlorohydrin, liquid bisphenol-type epoxy resin obtained by condensation reaction of bisphenols and a large excess of epichlorohydrin, and bisphenols. There is an indirect epoxy resin obtained by polymerization.
The epoxy resin (A) used in the present invention may be either a direct method epoxy resin or an indirect method epoxy resin, but a direct method epoxy resin is preferred. The direct process epoxy resin has a narrower molecular weight distribution than the indirect process epoxy resin, and a powder coating having a low melt viscosity is obtained before curing.

  Some bisphenols, such as commercially available bisphenol F, contain a polynuclear body having three or more phenol rings in addition to a binuclear body having two phenol rings. Therefore, the binuclear purity of bisphenols is preferably 70 area% or more, more preferably 90 area% or more, as measured by gel permeation chromatography. In particular, in the production of an indirect epoxy resin, it is preferable to use high-purity bisphenols of 95 area% or more.

Next, the curing agent (B) will be described.
As the curing agent (B) used in the present invention, an imidazoline derivative, an imidazole derivative or a mixture thereof is preferable. Examples of the imidazoline derivative include methyl imidazoline and 2-phenylimidazoline. Examples of the imidazole derivatives include methyl imidazole, dodecyl imidazole, phenyl imidazole, quaternary salts such as 1-dodecyl-2-methyl-3-benzylimidazolium chloride, isocyanuric acid adducts of 2-methyl imidazole, Examples include triazine ring-containing materials such as 2,4-diamino-6- (2′-methylimidazolyl- (1 ′))-ethyl-s-triazine.
Among these, 2-phenylimidazoline is used as an imidazoline derivative, and 2,4-diamino-6- (2′-methylimidazolyl- (1 ′))-ethyl-s-triazine or 2-imidazole is used as an imidazole derivative. Phenylimidazole is particularly preferred. If these hardeners are used as powder coatings, the specific gel time can be easily adjusted within the range where the effect can be obtained, so the appearance of the coating film is good, and the basic physical properties such as mechanical properties and anticorrosion properties are also obtained. A good coating film is obtained.
In addition, the use of organic acid hydrazide, modified aromatic amine adducts, trimellitic acid and acid anhydrides mainly composed of ethylene glycol is not prohibited as long as the characteristics are not impaired.

  The blending amount of the curing agent (B) is preferably in the range of 0.1 to 10 parts by mass and more preferably in the range of 1 to 6 parts by mass with respect to 100 parts by mass of the epoxy resin (A). When the blending amount is small, the gel time in the case of a powder coating becomes slow, and there is a fear that the coating film is insufficiently cured. When the blending amount is large, the gel time in the case of a powder coating becomes fast, the resulting coating film may cause appearance defects such as wrinkles and roughness, and storage stability may be deteriorated. When the blending amount of the curing agent (B) is in the range of 0.1 to 10 parts by mass, the gel time in the case of a powder coating is in an appropriate range, and a powder coating having no problem in storage stability is obtained. And a coating film with good basic physical properties such as mechanical properties and anticorrosion properties can be obtained. In order to adjust the gel time of the powder coating material and the melt viscosity at the time of curing, two or more kinds of curing agents can be mixed and used.

Next, the pigment (C) will be described.
As the pigment (C), a color pigment, an extender pigment, a bright pigment, a rust preventive pigment and the like generally used in powder coatings can be used. These pigments may be used alone, or two or more of the same pigments may be used in combination, or different pigments may be used in combination.

  Examples of the color pigment include inorganic pigments such as titanium oxide, yellow iron oxide, titanium yellow, Bengala, lithopone, and antimony oxide, Hansa Yellow 5G, Permanent Yellow FGL, Cyanine Blue, Phthalocyanine Blue, Indanthrene Blue RS And organic pigments such as Permanent Red F5RK, Brilliant First Scarlet G, Cyanine Green, Carbazole, Quinacridone Red, and Carbon Black.

  Examples of extender pigments include inorganic pigments such as barium sulfate, barium carbonate, calcium carbonate, clay, silica powder, quartz powder, diatomaceous earth, zinc oxide, talc, basic magnesium carbonate, and alumina, and porous internal structures. And plastic pigments typified by resin beads having a hollow structure or a crosslinked type.

  As bright pigments, for example, aluminum powder, nickel powder, stainless steel powder, copper powder, bronze powder, gold powder, silver powder, mica, graphite, glass flake, metal-coated glass powder, metal-coated mica powder, metal coating Plastic powder, thinned plastic powder, and flaky iron oxide.

  Examples of rust preventive pigments include condensed calcium phosphate, aluminum phosphate, condensed aluminum phosphate, zinc phosphate, aluminum phosphite, zinc phosphite, calcium phosphite, zinc molybdate, calcium molybdate, and manganese molybdate. Can be mentioned.

  Of these pigments, iron oxide, yellow iron oxide, silica powder, quartz powder, titanium oxide, calcium carbonate, barium sulfate and carbon black are preferable, and quartz powder, titanium oxide and carbon black are more preferable. Moreover, 1-50 micrometers is preferable and, as for the average particle diameter of a pigment, 5-50 micrometers is more preferable.

  The blending amount of the pigment (C) is preferably in the range of 10 to 100 parts by mass, more preferably in the range of 20 to 80 parts by mass, and in the range of 30 to 70 parts by mass with respect to 100 parts by mass of the epoxy resin (A). More preferred is a range of 40-60 parts by mass. If the blending amount is small, the melt viscosity in the curing process is low, the melt viscosity in the curing process is low, and there is a possibility that the effect of controlling the generation of pinholes may not be obtained. The basic physical properties such as mechanical properties and corrosion resistance of the film may be deteriorated. If the blending amount is large, the fluidity of the paint is poor, and a smooth coating film may not be obtained. Further, it may be difficult to prevent coating film appearance defects such as pinholes. When the blending amount of the pigment is in the range of 10 to 100 parts by mass, a flat coating film appearance is good, and a coating film having good basic physical properties such as mechanical properties and corrosion resistance can be obtained. Moreover, in order to adjust the bulk density of a powder coating material, 2 or more types of pigments can be mixed and used.

  In the epoxy resin powder paint of the present invention, as long as the object of the present invention is not impaired, as general paint additives, plasticizers, curing accelerators, crosslinking accelerators, ultraviolet absorbers, light stabilizers, sagging inhibitors, You may mix | blend antioxidant, a surface regulator, a flowability regulator, an antifoamer, etc. as needed. Examples of antioxidants include phenolic antioxidants such as pentaerythritol tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], dilauryl-3,3′-thiodipropionate, and the like. And sulfur-based antioxidants such as 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide. Examples of the flow conditioner and the surface conditioner include acrylic polymers.

The epoxy resin powder coating of the present invention is applied to the inner surface of a hollow article, preferably the inner surface of a tube. In this case, it is used in the Probak method, the suction method, or the like. That is, a predetermined pipe is preheated to a constant temperature within a range of 150 to 280 ° C., preferably 170 to 250 ° C., more preferably 180 to 230 ° C., then placed on a gantry, the inside of the pipe is decompressed, The powder paint is sucked into the pipe from a paint supply tank such as a paint fluid tank, and is applied to the inner surface of the pipe. And it is suitable for the coating method which forms a cured coating film as it is at the preheating temperature.
The powder paint that has not been applied is returned to the paint supply tank and recycled. In this coating method, the force with which the powder coating adheres to the surface of the object to be coated is due to the adhesive force of the molten layer formed on the surface of the object to be coated. It is important to manage the curing rate (gel time) at the preheating temperature as well as the particle size distribution and bulk density. If it is the epoxy resin powder coating of the present invention, it has basic coating film properties such as uniformity of thickness and anticorrosion, and can obtain a good cured coating film without occurrence of pinholes, and can be recycled. Use is also possible.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example, this invention is not limited to these Examples. In the examples, “parts” and “%” are based on mass unless otherwise specified. The unit of epoxy equivalent is g / eq. It is.

Evaluation of an epoxy resin is based on the following method.
(1) Epoxy equivalent: Measured according to JIS K7236.
(2) Softening point: Measured according to JIS K7234.

The evaluation methods of the powder coatings obtained in the examples and comparative examples are shown below.
(1) Gel time: 0.1 g of the powder coating material was placed on a hot plate heated to 200 ° C., and the mixture was melted with a round bar made of a fluororesin and measured for gelation.
(2) Particle size distribution D10, D90: Measured by a wet laser diffraction method using a particle size distribution meter.
(3) Bulk density: A powder tester is used to put a paint from a funnel into a 100 cm ³ container with constant vibration. The paint overflowing on the top of the container is scraped, and the weight of each container is measured to determine the bulk density (g / cm ³ ). Was calculated.
(4) Blocking property: The state of the paint after storing the powder paint at 40 ° C. for 2 weeks was indicated by the following judgment.
Without blocking: ○, With blocking: ×

The evaluation method of coating film properties is shown below.
(1) The flexibility test was conducted according to the standards of JIS Z 5528 and 5.4.4, and the Ericksen test was performed according to JIS Z 2247 to determine the flexibility.
3 mm or more: ○, less than 3 mm: ×

(2) The impact resistance test was a DuPont impact test according to JIS K 5400, 8.3.2 according to the standards of JIS Z 5528, 54.3. The shooting mold had a radius of 1/4 inch and dropped a 500 g weight from a height of 50 cm.
No cracking or peeling: ○, cracking or peeling: ×

(3) Coating film appearance test Abnormality of coating film appearance was evaluated by visual inspection of the inner surface of the coating tube.
No abnormality: Yes, Abnormal: ×
When there was an abnormality, it was written as follows according to the type of abnormality.
Salad: × 1
Concavity and convexity: × 2
Wrinkles: × 3

(4) MEK rubbing test A MEK rubbing test (1 kg load / 10 reciprocation) was performed as a confirmation of curability and judged according to the following criteria.
No coating adhesion: ○, Coating adhesion: ×

Synthesis example 1
A separable flask equipped with a stirrer, a nitrogen inlet tube, a side temperature resistor, a dropping device, and a cooling condenser was charged with 110.6 parts of a 49% aqueous sodium hydroxide solution and 399 parts of water, and the system moisture was replaced with nitrogen while stirring. Next, 200 parts of bisphenol F (manufactured by Nippon Steel & Sumikin Chemical Co., Ltd., binuclear purity 97 area%) was added, and the system temperature was controlled at 50 ° C. to dissolve with stirring. Next, 110.5 parts of epichlorohydrin was charged from the dropping funnel. After the addition, the system temperature was controlled at 92 ° C. and the reaction was carried out for 2 hours. After completion of the reaction, 330 parts of methyl isobutyl ketone was added, and the mixture was stirred for 15 minutes and allowed to stand to remove the lower layer water. Next, the mixture was neutralized with phosphoric acid and washed with water, the aqueous layer was removed, and after filtration, methyl isobutyl ketone was distilled off to obtain an epoxy resin (A-1). The epoxy equivalent was 1350 and the softening point was 92 ° C.

Synthesis example 2
Except for using 250 parts of epichlorohydrin, the same apparatus and operation as in Synthesis Example 1 were performed to obtain an epoxy resin (A-2). The epoxy equivalent was 900, and the softening point was 84 ° C.

Synthesis example 3
Except for using 102 parts of epichlorohydrin, the same apparatus and operation as in Synthesis Example 1 were performed to obtain an epoxy resin (A-3). The epoxy equivalent was 2500, and the softening point was 119 ° C.

Synthesis example 4
In a separable flask equipped with a stirrer, nitrogen introduction tube, side temperature resistor, dropping device and cooling condenser, 500 parts of YDF-8170 (manufactured by Nippon Steel & Sumikin Chemical Co., Ltd., liquid bisphenol F type epoxy resin, epoxy equivalent 159) After 126 parts of bisphenol F was charged and dissolved at 120 ° C., 0.12 part of triphenylphosphonium bromide was added and reacted at 160 ° C. for 2 hours. Thereafter, 150 parts of bisphenol F was charged and dissolved at 130 ° C., 0.15 part of triphenylphosphonium bromide was added, and the reaction was terminated by heating at 180 ° C. for 5 hours to obtain an epoxy resin (A-4). The epoxy equivalent was 2500 and the softening point was 118 ° C.

  The abbreviations used in Examples and Comparative Examples are as follows.

[Epoxy resin (A)]
Epoxy resins (A-1) to epoxy resins (A-4) obtained in Synthesis Examples 1 to 4

[Curing agent (B)]
2PZL: 2-phenylimidazoline, manufactured by Shikoku Kasei Kogyo Co., Ltd., Curesol 2PZL
2MZ-A: 2,4-diamino-6- (2'-methylimidazolyl- (1 '))-ethyl-s-triazine, manufactured by Shikoku Chemicals Co., Ltd., Curesol 2MZ-A
2PZ: 2-Phenylimidazole, Shikoku Kasei Kogyo Co., Ltd., Curesol 2PZ

[Pigment (C)]
Silica stone powder: average particle size 50μm,
Titanium oxide: Color pigment, manufactured by Teika Co., Ltd., JR-301
Carbon black: coloring pigment, manufactured by Mitsubishi Chemical Corporation, MA-100

[Others]
Modaflow: Acrylic polymer, manufactured by Nippon Monsanto Co., Ltd., Modaflow III

Example 1
100 parts of epoxy resin (A-1) as epoxy resin (A), 2.0 parts of 2PZL, 0.2 parts of 2MZ-A and 0.5 parts of 2PZ as curing agent (B), 50 parts of silica powder as pigment (C) and oxidation 12 parts of titanium, 0.3 part of carbon black, and 0.4 part of Modaflow as other additives were mixed. The mixture is dry blended using a Henschel mixer (Mitsui Miike Chemical Co., Ltd., type 10B), then melt kneaded at 100 ° C. using an extruder (Ikekai Tekko Co., Ltd., PCM-30), and cooled roll Was used to flake to a thickness of 3 to 5 mm, cooled to room temperature, finely pulverized and classified to obtain a powder coating material. The paint properties are shown in Table 1.

  A 1.2 mm × 70 mm × 150 mm SPCC-SB steel plate was preheated in a hot air circulating oven at 200 ° C. for 30 minutes. After preheating, it was taken out and hung vertically, installed in a painting booth, and painted with a painting gun so that the film thickness was 200 to 300 μm, and it was painted once and half a halfway. After coating, it was allowed to cool to room temperature at room temperature to obtain a test plate for flexibility test. The evaluation results are shown in Table 1.

  A 2.0 mm × 70 mm × 150 mm SPCC-SB steel plate was preheated in a hot air circulating oven at 200 ° C. for 30 minutes. After preheating, it was taken out and hung vertically, installed in a painting booth, and painted up and down half a half with a coating gun so that the film thickness was 300 μm. After coating, it was allowed to cool to room temperature at room temperature to obtain test plates for impact resistance test and MEK rubbing test. The evaluation results are shown in Table 1.

  A steel tube of 50 mmφ × 100 mmL was preheated for 30 minutes in a 200 ° C. hot air circulating oven. Take out after preheating, connect a heat resistant hose to both ends of the preheated steel pipe, install an aspirator on one side and reduce the pressure in the system, then insert the tip of the other hose into the paint supply tank and install it between the steel pipe and the supply layer The ball valve was opened for 1 second to allow the paint to pass through the steel pipe, and the paint was applied to the inner surface of the steel pipe to form a coating film as it was, and allowed to cool to room temperature to obtain a test tube for coating film appearance test. At this time, the reduced pressure was adjusted so that the powder coating material could be discharged at 2 g / 10 seconds. The thickness of the coating film was about 300 μm, and a uniform coating film was formed. The evaluation results are shown in Table 1.

Examples 2-8
A powder paint, a test plate and a test tube were obtained in the same manner using the same apparatus as in Example 1 using the blending amount (parts) of the formulation shown in Table 1. The same test as in Example 1 was performed and the results are shown in Table 1.

Comparative Examples 1-5
A powder paint, a test plate, and a test tube were obtained in the same manner using the same apparatus as in Example 1 using the blending amount (parts) of the formulation in Table 2. The same test as in Example 1 was performed and the results are shown in Table 2.

Claims (9)

A coating method in which a powder coating is sucked and applied under reduced pressure to a hollow inner surface heated to a constant preheating temperature in the range of 150 to 280 ° C., and then cured to form a cured coating film. A powder coating used, wherein the powder coating includes an epoxy resin (A), a curing agent (B), and a pigment (C), and D10 in the particle size distribution of the powder coating is 5 μm or more and D90 is 200 μm or less. An epoxy resin powder coating material having a bulk density of 0.4 to 0.8 g / cm ³ and a gel time of 20 to 60 seconds at the preheating temperature.   The epoxy resin (A) is an epoxidized product of bisphenols with epichlorohydrin, and the epoxy equivalent is 700 to 3000 g / eq. The epoxy resin powder paint according to claim 1, wherein the softening point is 70 to 130 ° C.   The epoxy resin powder coating material according to claim 2, wherein the bisphenol is at least one selected from tetramethylbisphenol F, bisphenol F, tetramethylbisphenol A and bisphenol A.   The epoxy resin powder coating material according to any one of claims 1 to 3, wherein the curing agent (B) is an imidazoline derivative and / or an imidazole derivative.   The pigment (C) is at least one selected from iron oxide, yellow iron oxide, silica powder, quartz powder, titanium oxide, calcium carbonate, barium sulfate, and carbon black. The epoxy resin powder coating described.   The epoxy resin powder coating material according to any one of claims 1 to 5, wherein the article to be coated is a straight pipe or a modified pipe.   A straight pipe or a deformed pipe coated with the epoxy resin powder paint according to any one of claims 1 to 6. A hollow object to be preheated to a constant temperature in the range of 150 to 280 ° C. is placed on a stand, and the inside of the object to be coated is sucked in from the paint supply tank under reduced pressure and applied to the inner surface of the object to be coated. It is a coating method in which a cured coating film can be formed as it is, and includes the epoxy resin (A), the curing agent (B) and the pigment (C) as the powder coating, and the particle size distribution of the powder coating Use an epoxy resin powder coating in which D10 is 5 μm or more and D90 is 200 μm or less, the bulk density is 0.4 to 0.8 g / cm ³ , and the gel time at the preheating temperature is 20 to 60 seconds. A painting method characterized by A straight pipe or a deformed pipe painted by the coating method according to claim 8.