JPH11263926A - Epoxy powder coating composition for coating of outer surface of cast iron pipe and outer surface-coated cast iron pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an epoxy powder coating composition for coating of the outer surface of a cast iron pipe capable of preventing any exfoliations and swells in the damaged or defective sections of the coating and excellent in safety to human and the environment, and to provide the outer surface-coated cast iron pipes. SOLUTION: This composition comprises (A) a bisphenol A type epoxy resin having a melting point of 75 to 128 deg.C and epoxy equivalent of 600 to 2,200 g/eq, (B) a setting agent of a composition of the formula ((m) is an integer of 1 to 4) having a mean phenolic hydroxyl equivalent of 200 to 800 g/eq, (C) at least one of imidazole-based and imidazoline-based setting-accelerators, and (D) a burnt plaster.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an epoxy powder coating composition for coating an outer surface of a cast iron tube and an outer surface coated cast iron tube.

[0002]

2. Description of the Related Art Cast iron pipes have been widely used as piping materials for water and sewage, industrial water, agricultural water, gas and the like. Cast iron pipes, depending on the shape, straight pipe, deformed pipe,
It is classified as a joint part such as a pressing wheel. In this specification,
These joints are collectively called cast iron tubes.

[0003] The outer surface of a cast iron pipe is usually coated with a normal temperature solvent-based anticorrosive paint such as an epoxy-based, acrylic-based, or polyester-based paint. In recent years, room temperature dry solvent type has been used for the purpose of effective utilization of residual heat when baking the inner surface of cast iron pipes, shortening the drying and curing time of the coating film, streamlining the coating process such as reducing the curing place, and improving the coating work environment. In addition to anticorrosive paints, epoxy powder paints have also been used.

When the outer surface of a cast iron tube is coated, it is difficult to apply a uniform coating on the protrusions and ends, and generally, the coating film thickness is insufficient, and defects such as pinholes occur. Cheap. If such a defect exists, water enters from that location, and the corrosion resistance becomes insufficient. Also, the outer surface of the cast iron tube
During transportation and burial, it is susceptible to impacts, and such impacts can easily cause damage. For this reason, in the coating applied to the coating of the outer surface of the cast iron pipe, improvement of the corrosion resistance of a defective portion or a damaged portion of the coating film has been a problem.

[0005] Defects and damaged portions of the coating film on the outer surface of the cast iron pipe cause rust on the surface of the cast iron pipe due to the action of electrolytes such as sea salt particles contained in the atmosphere or rainwater and electrolytes present near the buried area. Occurs. At this time, a part of the surface of the cast iron tube such as a defective portion or a damaged portion of the coating film becomes a minute anode, and a cathode site is formed near the defective portion or the damaged portion.

At the formed cathode portion, hydroxide ions are generated, and the action of the hydroxide ions reduces the adhesion between the cast iron surface and the coating film, thereby causing peeling and blistering of the coating film. . In the present specification, such peeling or blistering is referred to as “cathode peeling” or “cathode blister”. These phenomena are magnified, and the water-soluble electrolyte easily penetrates into the peeling portion and blister portion, resulting in a problem that the peeling portion and blister portion are further enlarged.

In order to suppress the peeling of the coating film and the occurrence of blisters, it has heretofore been considered to add a rust preventive pigment such as strontium chromate to the paint. However, a rust preventive pigment such as strontium chromate has been considered. However, it could not be used because it might adversely affect the human body and the environment.

Japanese Patent Application Laid-Open No. 6-228466 discloses a paint that uses a solid superacid carrying sulfuric acid or a metal oxide to consume hydroxide ions generated at the cathode site, thereby preventing blistering. ing. However, with this technique, it is difficult to handle the solid superacid during production, and it is disadvantageous in terms of cost. In addition, since sulfuric acid is carried, there is a possibility that the paint may deteriorate.

Therefore, in coating the outer surface of the cast iron tube, it is excellent in safety and can be manufactured at a low cost, and the performance required as a coating film on the outer surface of the cast iron tube such as corrosion resistance, impact resistance and flexibility. There is a demand for the development of a paint capable of forming a coating film having the following.

[0010]

SUMMARY OF THE INVENTION In view of the above, the present invention does not cause peeling or blistering at a damaged or defective portion of a coating film, is excellent in safety to the human body and the environment, and is suitable for a cast iron pipe. Epoxy powder coating composition for outer coating of cast iron pipe, which has good adhesion, can be easily manufactured at low cost and can be baked at low temperature, and has excellent corrosion resistance, impact resistance and flexibility An object of the present invention is to provide an externally coated cast iron pipe whose outer surface is coated with an excellent coating film.

[0011]

According to the present invention, the softening point is 75%.
~ 128 ° C, epoxy equivalent is 600 ~ 2200g
/ Eq bisphenol A type epoxy resin (A),
The following general formula (1);

[0012]

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A curing agent (B) having an average phenolic hydroxyl group equivalent of 200 to 800 g / eq, and an imidazole-based curing compound, wherein m is an integer of 1 to 4; An epoxy powder coating composition for exterior coating of cast iron pipes, comprising at least one curing accelerator (C) among an accelerator and an imidazoline-based curing accelerator, and calcined gypsum (D), wherein the curing agent (B )), The amount of the phenolic hydroxyl group is determined by the above-mentioned bisphenol A type epoxy resin (A).
Is 0.5 to 1.2 equivalents with respect to 1 equivalent of the epoxy, and the compounding amount of the curing accelerator (C) is 0.1 to 15.2 equivalents with respect to the compounding amount of the curing agent (B). 0% by weight, and the amount of the calcined gypsum (D) is 2 to 50% by weight based on the epoxy powder coating composition for coating the outer surface of a cast iron pipe. It is an epoxy powder coating composition for coating the outer surface of a tube. Further, the present invention is an externally coated cast iron pipe coated using the epoxy powder coating composition for externally coating a cast iron pipe of the present invention. Hereinafter, the present invention will be described in detail.

The epoxy powder coating composition for coating the outer surface of a cast iron pipe of the present invention has a softening point of 75 to 128 ° C. and an epoxy equivalent of 600 to 2200 g / eq. Formula (1);

[0015]

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A curing agent (B) having a mean phenolic hydroxyl group equivalent of 200 to 800 g / eq, wherein the m is an integer of 1 to 4; It comprises at least one of a curing accelerator and an imidazoline curing accelerator (C), and calcined gypsum (D).

The bisphenol A type epoxy resin (A) has a softening point of 75 to 128 ° C. If the temperature is lower than 75 ° C., the powder coatings are liable to be fused to each other during storage of the powder coating. If the temperature exceeds 128 ° C., the melt viscosity increases, and the coating is baked at a low temperature or using the residual heat. Since the finish of formation is reduced, the content is limited to the above range.
Preferably, it is 90 to 110 ° C.

The bisphenol A type epoxy resin (A) has an epoxy equivalent of 600 to 2200 g / eq. When it is less than 600 g / eq, generally the molecular weight becomes small and the softening temperature becomes too low, and 2200 g / eq
If it exceeds, the molecular weight is generally increased and the softening temperature is too high, so that it is limited to the above range. Preferably, it is 650 to 1100 g / eq.

The bisphenol A type epoxy resin (A) is not particularly limited as long as it has a softening point of 75 to 128 ° C. and an epoxy equivalent of 600 to 2200 g / eq. , 2
-Bis (4-hydroxyphenyl) propane] and an epihalohydrin such as epichlorohydrin to produce a low-molecular-weight epoxy resin, and then to add-polymerize bisphenol A to adjust to a desired molecular weight.
Those obtained by the step method can be exemplified.

As the bisphenol A type epoxy resin (A), a commercially available one can be used. Specifically, for example, Epotote YD-014
(Epoxy equivalent: 900 to 1000 g / eq, softening point: 91
〜１０102 ° C., manufactured by Toto Kasei Co., Ltd.), Epototo YD-017
(Epoxy equivalent 1750-2100 g / eq, softening point 1
17-127 ° C, manufactured by Toto Kasei Co., Ltd.), Epototo YD-9
04 (epoxy equivalent: 900-1000 g / eq, softening point: 96-107 ° C, manufactured by Toto Kasei Co., Ltd.), Epototo YD-9
07 (epoxy equivalent 1300-1700 g / eq, softening point 117-127 ° C, manufactured by Toto Kasei Co., Ltd.), Epicoat 10
03F (epoxy equivalent: 700-800 g / eq, softening point: about 96 ° C, manufactured by Yuka Shell Epoxy), Epicoat 10
04F (epoxy equivalent: 875-975 g / eq, softening point: about 103 ° C., manufactured by Yuka Shell Epoxy), Epicoat 1
005F (epoxy equivalent: 950-1050 g / eq, softening point: about 107 ° C., manufactured by Yuka Shell Epoxy), Araldite XAC5007 (epoxy equivalent: 600-700 g /
eq, softening point of about 90 ° C, manufactured by Nippon Ciba Geigy), Araldite GT7004 (epoxy equivalent 730-830 g)
/ Eq, softening point about 100 ° C, manufactured by Nippon Ciba Geigy)
Araldite GT7097 (epoxy equivalent 1650-2
000 g / eq, a softening point of about 120 ° C., manufactured by Ciba-Geigy Japan). These may be used alone or in combination of two or more. Among them, Epicoat 1003F, Epicoat 1005F, and the like are preferable from the viewpoint of the finish (leveling property) in low-temperature baking.

The curing agent (B) used in the present invention is a component used as a curing agent for the bisphenol A type epoxy resin (A), and is a compound represented by the following general formula (1).

[0022]

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In the formula, m represents an integer of 1 to 4. The above m
Is less than 1, when bisphenol A is used as a raw material, it cannot exist, as described in detail below. When m exceeds 4, the reaction proceeds too much during the synthesis, and the synthesis proceeds. Since it becomes difficult, it is limited to the above range.

The compound represented by the general formula (1) is not particularly limited, and examples thereof include compounds obtained by reacting bisphenol A type epoxy resin with bisphenol A.

The curing agent (B) has a phenolic hydroxyl equivalent of 200 to 800 g / eq. 200g / eq
If it is less than 1, the softening point of the coating material is lowered, and the powder coating material is liable to be blocked during storage.
If it exceeds eq, the reactivity will decrease and low-temperature curing will be difficult, so it will be limited to the above range.

As the curing agent (B), a commercially available one may be used. Specifically, for example, TH-
4100 (phenolic hydroxyl group equivalent of about 725 g / eq,
Softening point about 110 ° C, manufactured by Toto Kasei Co., Ltd.), EpiCure 171
(Phenolic hydroxyl equivalent: 200 to 286 g / eq, softening point: about 80 ° C., manufactured by Yuka Shell Co.), Epicure 170
(Phenolic hydroxyl equivalent: 286 to 400 g / eq, softening point: about 90 ° C., manufactured by Yuka Shell Co., Ltd.). These may be used alone or in combination of two or more. Above all, Epicure 170 is preferable in terms of storage stability and finish (leveling property).

In the present invention, the curing agent (B) includes:
Unreacted bisphenol A may be contained within the range of the phenolic hydroxyl group equivalent of 200 to 800 g / eq. The content of the bisphenol A is at most 30% by weight based on the total of the curing agent (B) and the bisphenol A.

The amount of the phenolic hydroxyl group of the curing agent (B) is 0.5 to 1.2 equivalents to 1 equivalent of the epoxy of the bisphenol A type epoxy resin (A).
If the amount is less than 0.5 equivalent, a sufficient cured product cannot be obtained, and mechanical strength such as impact resistance becomes poor. If the amount exceeds 1.2 equivalents, an unreacted curing agent remains in the coating film. , The curability becomes poor, so that it is limited to the above range. Preferably, 0.
5 to 1.0 equivalent.

In the present invention, the above bisphenol A
As a curing agent for the epoxy resin (A), the curing agent (B) and dicyandiamide may be used in combination for the purpose of improving adhesion to a cast iron pipe and improving corrosion resistance.

The curing accelerator (C) used in the present invention comprises:
At least one of an imidazole-based curing accelerator and an imidazoline-based curing accelerator. In the present invention, the curing accelerator (C) is used to improve low-temperature baking properties. The imidazole-based curing accelerator and the imidazoline-based curing accelerator are compounds represented by the following general formulas (2) and (3), respectively.

[0031]

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In the formula, R ¹ is a hydrogen atom, having 1 to 17 carbon atoms.
Represents an alkyl group or a phenyl group. R ² represents a hydrogen atom or a methyl group.

The alkyl group having 1 to 17 carbon atoms is not particularly limited, and examples thereof include a methyl group, an ethyl group, an n-propyl group and an i-propyl group.

The imidazole-based curing accelerator is not particularly limited, and a commercially available one may be used.
Specifically, for example, 2MZ (2-methylimidazole, manufactured by Shikoku Chemicals), 2PZ (2-phenylimidazole, manufactured by Shikoku Chemicals), C ₁₁ Z (2-undecylimidazole, manufactured by Shikoku Chemicals) ), C ₁₇ Z (2-heptadecyl imidazole, manufactured by Shikoku Chemicals) and the like. These may be used alone or in combination of two or more. Among them, 2MZ is preferable from the viewpoint of the curing acceleration function.

The imidazoline curing accelerator is not particularly limited, and commercially available ones may be used.
Specifically, for example, 2MZL (2-methylimidazoline, manufactured by Shikoku Kasei Kogyo), 2E · 4MZL (2-ethyl-4-methylimidazoline, manufactured by Shikoku Kasei Kogyo) and the like can be mentioned. These may be used alone,
More than one species may be used in combination.

The curing accelerator (C) is blended in an amount of 0.1 to 15.0% by weight based on the blending amount of the curing agent (B). If the amount is less than 0.1% by weight, curing is not promoted. If the amount exceeds 15.0% by weight, the reactivity becomes too high, blocking tends to occur, and storage stability becomes poor. Is limited to Preferably, it is 0.5 to 10.0% by weight.

The gypsum (D) used in the present invention is:
Is intended to be used as a pigment component, of the hydrates of calcium sulfate (CaSO _4), the chemical formula CaSO ₄ · 1
/ 2H ₂ O. By using the calcined gypsum, it is possible to prevent cathode peeling and cathode blistering caused by the hydroxide ions. Such an effect is found only in the calcined gypsum among the above-mentioned calcium sulfate hydrates.

The calcined gypsum (D) is blended in an amount of 2 to 50% by weight based on the epoxy powder coating composition for coating the outer surface of a cast iron pipe. If it is less than 2% by weight, the performance of preventing peeling and blistering of the obtained coating film is not sufficient,
If it exceeds 50% by weight, the melt viscosity will be high, and the formation of a continuous coating film will tend to be difficult, and the finish will be poor. Preferably, it is 5 to 30% by weight.

The epoxy powder coating composition for coating the outer surface of a cast iron pipe of the present invention further comprises calcium carbonate, barium sulfate,
An inorganic filler such as an extender such as silica may be blended. The amount of the inorganic filler to be added is preferably 50% by weight or less based on the epoxy powder coating composition for coating the outer surface of a cast iron pipe as the total amount with the calcined gypsum (D) from the viewpoint of finishability.

The epoxy powder coating composition for coating the outer surface of a cast iron pipe of the present invention further comprises various calcined coloring pigments such as carbon black, titanium white, red iron oxide, etc .; a flow regulator at the time of melting; A thermoplastic resin such as a resin may be blended.

The epoxy powder coating composition for coating the outer surface of a cast iron pipe according to the present invention may optionally contain a bisphenol A type epoxy resin (A), a curing agent (B) and a curing agent in order to improve the low-temperature curability. The precursor reaction may be performed in the presence of the accelerator (C).

In the precursor reaction, the powder coating composition is preliminarily reacted within a range that can be converted into a powder state, and the powder coating composition which is difficult to react during the film forming process and easily remains is formed. This is performed in order to keep unreacted functional groups in the resin as small as possible and to enable low-temperature baking. In other words, the reactivity of the functional group involved in the reaction is increased to maximize the performance of the cured coating film.

The epoxy powder coating composition for coating the outer surface of a cast iron pipe according to the present invention, when subjected to the above-mentioned precursor reaction, is subjected to ISO 813
It is preferable that the gel time of the paint when heated at 200 ° C. by the method of 0-6 is adjusted to 10 to 40 seconds. If the time is less than 10 seconds, the reaction proceeds too much and the melt viscosity increases,
Adhesion to the cast iron pipe and appearance of the coating film become poor, and if it exceeds 40 seconds, the expected low-temperature curability becomes insufficient.

The epoxy powder coating composition for coating the outer surface of a cast iron pipe of the present invention is applied to coating the outer surface of a cast iron pipe. The coating method is not particularly limited. For example, it is used as a normal powder coating method such as electrostatic powder coating, negative charging electrostatic coating (corona), friction charging electrostatic coating (tribo), and fluid immersion coating. And the like. The coating is preferably performed so that the dry film thickness is 60 to 200 μm.

The above cast iron tube is generally 75 to 2600 m
mφ, the thickness is as thick as 10 mm or more, and the heat capacity is large. Therefore, it is important from the viewpoint of energy saving to lower the temperature at the time of baking. The epoxy powder coating composition for coating the outer surface of a cast iron pipe of the present invention has, for example, a baking temperature of 160.
When set to ° C., curing can be performed in a short time of 2 to 4 minutes, which is very preferable from the viewpoint of energy saving. When the inner surface of the cast iron pipe is coated using an epoxy resin powder coating or the like, the outer coating film may be hardened by the residual heat at the time of forming the inner coating film. In this case, the object temperature 14
It is preferable that a coating film is formed at 0 to 180 ° C.

The above-mentioned cast iron pipe may have been subjected to a pre-coating treatment such as a shot blast treatment. If necessary, post-baking may be performed. The post-baking conditions are
The temperature is preferably about 5 to 20 minutes at a temperature of 150 to 200 ° C.

When the epoxy powder coating composition for outer surface coating of a cast iron pipe of the present invention has been subjected to a precursor reaction, it is preferable to form a coating film, for example, as follows. 20
After coating the inner surface of the cast iron tube preheated to about 0 ° C., after the coating is completed, if necessary,
The outer surface of the cast iron pipe heated to 60 ° C. is coated with the epoxy powder coating composition for coating the outer surface of a cast iron pipe of the present invention, which has undergone a precursor reaction, and a coating film is formed at an object temperature of 140 to 160 ° C.

An externally coated cast iron pipe in which the outer surface of the cast iron pipe is coated with the epoxy powder coating composition for coating the outer surface of a cast iron pipe of the present invention in this way is also one of the present invention. This exterior painted cast iron pipe has the performance required as a coating film on the outer surface of the cast iron pipe,
For example, it has a coating film having corrosion resistance, impact resistance, flexibility, and the like on its outer surface, and is suitable as a piping material for water and sewage, industrial water, agricultural water, gas, and the like.

The epoxy powder coating composition for coating the outer surface of a cast iron pipe according to the present invention uses a bisphenol A type epoxy resin (A) having a softening point of 75 to 128 ° C. and an epoxy equivalent of 600 to 2200 g / eq. Therefore, the adhesiveness, flexibility and chemical resistance are very good, the powder coatings are hardly fused to each other during storage.
A good coating film can be formed at a low temperature of 180 ° C. Further, since the curing agent (B) is used, flexibility can be further imparted to the cured coating film.

Further, the epoxy powder coating composition for coating an outer surface of a cast iron pipe according to the present invention is characterized in that calcined gypsum (D) is 2 to 50% by weight based on the epoxy powder coating composition for an outer coating of a cast iron pipe.
Therefore, in a cast iron pipe coated with the epoxy powder coating composition for coating an outer surface of a cast iron pipe of the present invention, peeling of the coating film from a damaged or defective portion of the coating film or blistering occurs. Does not occur. This is because hydroxide ions, which reduce the adhesion between the cast iron pipe and the coating film, are generated from the cathode site formed near the damaged or defective portion such as a scratch or a pinhole in the coating film. Baked gypsum (D)
However, it is considered that this has a function of capturing this hydroxide ion.

[0051]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1 Production of Epoxy Powder Coating Epicoat 1005F (Epoxy equivalent 950-1050)
g / eq, softening point of about 107 ° C., 100 parts by weight of Yuka Shell Epoxy Co., Ltd .; Epicure 170 (phenolic hydroxyl equivalent 286 to 400 g / eq, softening point of about 90 ° C., of Yuka Shell Co.) 34 parts by weight; 0.7 parts by weight of 2MZ (2-methylimidazole, manufactured by Shikoku Chemicals), 20.0 parts by weight of calcined gypsum PH-200 (manufactured by Marubishi Gypsum), Mitsubishi Carbon MA100 (carbon black, manufactured by Mitsubishi Chemical Corporation)
2.0 parts by weight, Acronal 4F (surface conditioner, BAS
0.6 parts by weight (made by F company) were made into a granular uniform mixture using a super mixer (manufactured by Kawada Seisakusho), and then a casing temperature of 95 ° C. was obtained using a coneder (manufactured by Swissbus).
The shaft rotation speed was adjusted so that the passage time was 45 seconds at a shaft temperature of 35 ° C., and the precursor reaction was performed simultaneously with the melt mixing. After cooling, the mixture was pulverized using an ACM pulverizer (manufactured by Hosokawa Micron Corporation) so as to have an average particle size of 35 μm to prepare an epoxy powder coating material (1).

Examples 2 to 8, Comparative Examples 1 to 4 Epoxy powder
Production of body paint According to the composition shown in Table 1, in the same manner as in Example 1, epoxy powder paints (2) to (8) and comparative epoxy powder paints (1) to (4) were prepared.

Example 9 Production of Epoxy Powder Coating According to the composition shown in Table 1, each component was made into a granular uniform mixture using a super mixer and extruded using a co-kneader in the same manner as in Example 1. Further, the molten mixture is kept at 50 ° C. for 20 hours to obtain an ISO 81
After aging so that the gel time of the coating when heated at 200 ° C. by the method of 30-6 is 15 seconds, the average particle size is 35 μm.
m to obtain an epoxy powder coating (9).

[0055]

[Table 1]

In Table 1, Epicoat 1003F is a bisphenol A type epoxy resin (epoxy equivalent of 700 to 80).
0g / eq, softening point of about 96 ° C, manufactured by Yuka Shell Epoxy Co., Ltd.), and Epotote YD-907 is a bisphenol A type epoxy resin (epoxy equivalent of 1300 to 1700).
g / eq, softening point 117-127 ° C, manufactured by Toto Kasei Co., Ltd., and TH-4100 is a phenolic curing agent (phenolic hydroxyl equivalent 725 g / eq, softening point about 110 ° C,
And C ₁₁ Z is a curing accelerator (2-undecylimidazole, manufactured by Shikoku Chemicals Co., Ltd.).

[0057] Examples 11 to 17, Comparative Examples 5 to 8 epoxy
According to the formulations composition shown in preparation Table 2 shea powder coating, in the same manner as in Example 1, an epoxy powder coating (11) to (17) were prepared to compare epoxy powder coating (5) - (8) . The dicyandiamide used was manufactured by Nippon Carbide Industry Co., Ltd.

Example 18 Production of Epoxy Powder Coating According to the composition shown in Table 2, an epoxy powder coating (18) was prepared in the same manner as in Example 9.

[0059]

[Table 2]

Coating of cast iron members using the epoxy powder coatings (1) to (18) and comparative epoxy powder coatings (1) to (8) obtained in Examples 1 to 18 and Comparative Examples 1 to 8. Was done. Production of Painted Cast Iron Member A shot blast treatment was applied to a ductile cast iron member (70 × 150 × 20 mm) to obtain SSPC-SP5 (white metal). This processing plate is baked in a baking oven and the plate temperature is 1
The epoxy powder coatings (1) to (18) and the comparative epoxy powder coatings (1) to (8) obtained in Example 1 were immediately heated to 70 ° C. and immediately applied to the ductile cast iron member taken out of the baking furnace. ) Was subjected to electrostatic spray coating so that each coating film thickness was 100 μm, and left at room temperature of 25 ° C. to form a cured coating film. The coating was started when the temperature of the ductile cast iron member was 160 ° C, and the temperature at the end of the coating was 155 ° C. The following evaluation was performed about the obtained painted cast iron member. In addition, about a bending resistance and a water quality test, a test piece was separately prepared and evaluated.

[0061] By visually coated surface finish of paint ductile cast iron, and evaluated according to the following criteria. The results are shown in Tables 3 and 4. ◎: Smoothness with little unevenness 平滑: Smoothness with unevenness か な り: Slight unevenness and poor smoothness ×: Extremely uneven and extremely poor smoothness

A single straight scratch (length 10 cm) was made on the corrosion-resistant painted ductile cast iron member until it reached the substrate, and the material was subjected to JIS K5
According to the salt spray test of 400 9.1, the maximum value of the cathode peeling width after 500 hours was evaluated according to the following criteria. The results are shown in Tables 3 and 4. ：: less than 3 mm on one side from the cut wound ○: 3 mm or more and less than 5 mm on one side from the cut wound Δ: 5 mm or more and less than 10 mm on one side from the cut wound ×: 10 mm or more on one side from the cut wound

Impact Resistant Coating A DuPont type impact test [1/2 inch (impact portion) × 500 g (load) × 50 cm (height)] was performed on the painted surface of the ductile cast iron member at 20 ° C. The state of the coating film was evaluated according to the following criteria. ：: Damage of the coating film only at the impacted part △: Damaged coating at the impacted part and floating of the coating on the part except the impacted part ×: Damaged coating at the impacted part and peeling of the coating around the impacted part

Gauze containing curable methyl ethyl ketone was lightly applied to the coating film of the painted ductile cast iron member, and the state of the coating film after reciprocating 10 times was evaluated according to the following criteria. The results are shown in Tables 3 and 4. ：: No abnormality ：: There is a slight trace on the coating film, but there is no loss of gloss. 溶解: No dissolution of the coating film is observed, but the gloss disappears. ×: The coating film is dissolved.

A test piece was prepared by polishing a flex-resistant tin plate (150 × 50 × 0.3 mm) using # 180 paper. Epoxy powder coatings (1) to (18) and comparative epoxy powder coatings (1) to (8) were applied to the test pieces so as to have a film thickness of about 100 μm, respectively. Baked. The bending resistance test was performed according to JIS K 5400 8.1.
(Bending resistance), and the diameter of the mandrel of the bending tester is 1
The measurement was performed at 0 mm and evaluated according to the following criteria. The results are shown in Tables 3 and 4. ：: No cracking or peeling was observed in the coating film ×: Cracking or peeling occurred in the coating film

Water quality test Double-sided frosted glass (200 × 70 × 2 m
m) was used as a test piece. Epoxy powder coating on test piece (1)
To (18) and comparative epoxy powder coatings (1) to (8) were applied on both sides and ends in a size of 120 × 70 mm on each side, and baked in a drying oven at an ambient temperature of 180 ° C. for 15 minutes. The test was performed according to the method of JWWA K-139, and evaluated according to the following criteria. The results are shown in Tables 3 and 4. ○: All items passed ×: Some items failed

[0067]

[Table 3]

[0068]

[Table 4]

[0069]

The epoxy powder coating composition for coating the outer surface of a cast iron pipe according to the present invention has the above-mentioned constitution, is extremely excellent in corrosion resistance, has excellent adhesion to a cast iron pipe, and has excellent finish. Therefore, it is very suitable for coating the outer surface of a cast iron tube. Moreover, since the outer surface coated cast iron pipe of the present invention is coated using the epoxy powder coating composition for outer surface coating of the cast iron tube of the present invention, a coating film having excellent corrosion resistance, impact resistance, flexibility, etc. Can be formed on the outer surface of a cast iron pipe, and an externally coated cast iron pipe that does not cause peeling or blistering at a damaged portion or a defective portion of a coating film can be provided.

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification code FI C09D 163/00 C09D 163/00 F16L 58/04 F16L 58/04 // C08G 59/62 C08G 59/62 59/68 59/68 (72) Inventor Masahiko Saito 1-12-19 Kitahorie, Nishi-ku, Osaka City Inside Kurimoto Iron Works, Ltd. (72) Inventor Norio Nakamura 19-17 Ikedanakacho, Neyagawa-shi, Osaka Inside Nippon Paint Co., Ltd.

Claims (2)

[Claims] 1. A bisphenol A type epoxy resin (A) having a softening point of 75 to 128 ° C. and an epoxy equivalent of 600 to 2200 g / eq, represented by the following general formula (1): (Wherein, m represents an integer of 1 to 4), wherein the average phenolic hydroxyl equivalent is 200 to 8;
A hardening agent (B) of at least 00 g / eq, at least one of an imidazole-based hardening accelerator and an imidazoline-based hardening accelerator (C), and an epoxy for coating the outer surface of a cast iron pipe comprising calcined gypsum (D) A powder coating composition, wherein the amount of the phenolic hydroxyl group in the curing agent (B) is the same as the amount of the epoxy 1 in the bisphenol A type epoxy resin (A).
The equivalent amount is 0.5 to 1.2 equivalents, and the compounding amount of the curing accelerator (C) is 0.1 to 15.0% by weight based on the compounding amount of the curing agent (B). And the compounding amount of the calcined gypsum (D) is 2 to 50% by weight based on the epoxy powder coating composition for coating the outer surface of a cast iron pipe. Epoxy powder coating composition for exterior coating of cast iron pipes. 2. An externally coated cast iron pipe coated with the epoxy powder coating composition for external coating of a cast iron pipe according to claim 1.