JPH1095929A - Powder coating for coating inner surface of cast iron pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject coating material remarkably excellent in a pinhole-preventing property and in the heat resistance of coating films by using bis(diglycidyloxynaphthyl) alkane as an epoxy resin for the powder coating. SOLUTION: This powder coating contains (A) bis(diglycidyloxynaphthyl) alkane and (B) a curing agent as essential components. Bis(2,7-diglycidyloxy-1- naphthyl)methane is preferable as the raw material of the component A. The epoxy resin is preferably obtained by reacting 2,7-dihydroxynaphthalene with formaldehyde and subsequently reacting the obtained bis(2,7-dihydroxy-1- naphthyl)methane of raw material phenolic compound with epichlorohydrin. The component B is preferably dicyandiamide or a phenol novolak resin. The further formulating (C) a bisphenol type epoxy resin is preferable, because the heat resistance of the powder coating is remarkably improved. Therein, the component A is preferably compounded in an amount of 20-80wt.% based on the total amount of the components A and C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder coating for cast iron pipe coating having a high glass transition point of a coating film at the time of curing and having an excellent pinhole prevention property.

[0002]

2. Description of the Related Art Heretofore, as an inner coating material for cast iron pipes used for water pipes or sewer pipes,
Powder coatings are widely used due to hygienic problems or superiority in the coating process.

[0003] Epoxy resins have heretofore been widely used as a coating resin for coating the inner surface of cast iron pipes. However, their epoxy resins have high melt viscosities. Due to poor properties, there is a problem that air is hardly evacuated from the inside or the surface of the object to be coated and pinholes are easily generated, and the film thickness after curing tends to be non-uniform.

In order to improve this point, for example, Japanese Patent Laid-Open No.
JP-A-370162 discloses the use of crystalline tetrabromobisphenol A-type epoxy resin as a resin for powder coating for coating the inner surface of cast iron pipes, increasing the fluidity of the resin and crushing micropores inside the cast iron pipe to generate pinholes. There is disclosed a technique for preventing such a situation.

[0005]

However, the above-mentioned Japanese Patent Application Laid-Open No.
Although the powder coating described in -370162 has high fluidity and a certain pinhole preventing effect,
There is a problem that the resin cannot be closed up to the deepest part of the micropores present on the inner surface of the cast iron pipe with the resin, the gas ejection from the inner surface of the workpiece is not suppressed under high temperature conditions, and pinholes are also easily generated. In addition, there has been a problem that bromine is easily desorbed and the physical properties of the coating such as heat resistance of the coating are reduced.

SUMMARY OF THE INVENTION An object of the present invention is to provide a powder coating for coating the inner surface of a cast iron pipe, which is remarkably excellent in preventing pinholes and remarkably excellent in heat resistance of a coating film.

[0007]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, when an epoxy resin having a specific structure is used as an epoxy resin for powder coating, the pinhole prevention property is reduced. Have been found to provide a coating layer on the inner surface of a cast iron pipe with remarkably excellent coating film properties, and have completed the present invention.

[0008] That is, the present invention relates to a powder coating for inner surface coating of cast iron pipes, which comprises a bis (diglycidyloxynaphthyl) alkane (A) and a curing agent (B) as essential components.

The bis (diglycidyloxynaphthyl) alkane (A) used in the present invention is a dimer of a naphthalene skeleton in which a naphthalene skeleton having a glycidyloxy group is bonded via a hydrocarbon group.

The bis (diglycidyloxynaphthyl)
In order to obtain the alkane (A), for example, a method of reacting epihalohydrin with a phenol resin obtained by reacting dihydroxynaphthalene with an aldehyde may be mentioned.

When the desired epoxy resin is obtained by this method, if the number of nuclei in the naphthalene skeleton is 3 or more, the dinuclear is purified and separated to obtain the desired product. Can be produced,
When 7-dihydroxynaphthalene is used, a binuclear phenol can be obtained in a pure product without polynuclear formation to a trinuclear or higher nucleus, and the target can be very easily obtained simply by reacting it with epihalohydrin. An epoxy resin can be obtained.

In order to produce a raw material phenol using the above-mentioned 2,7-dihydroxynaphthalene, specifically,
2,7-dihydroxynaphthalene and an aldehyde,
If necessary, a method of reacting in the presence of a catalyst may be mentioned.

The aldehyde used here is not particularly restricted but includes, for example, formaldehyde, acetaldehyde, propylaldehyde, butyraldehyde, benzaldehyde, p-hydroxybenzaldehyde, bromobenzaldehyde and the like. Among these, formaldehyde is particularly preferred from the viewpoint of excellent heat resistance of the coating film when used as a paint finally obtained.

The catalyst to be used is not particularly limited. Examples of the basic catalyst include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, lithium hydroxide and calcium hydroxide, and alkaline earth metal hydroxides. Or alkali metal carbonates such as sodium carbonate and potassium carbonate. As the acidic catalyst, sulfuric acid,
Mineral acids such as hydrochloric acid, nitric acid, hydrobromic acid and perchloric acid, sulfonic acids such as paratoluenesulfonic acid and benzenesulfonic acid, and carboxylic acids such as oxalic acid, succinic acid, malonic acid, monochloroacetic acid and dichloroacetic acid are used. Is done. The amount of these catalysts to be used is usually 0.01 to 0.1 mol per 1 mol of hydroxynaphthalene. Although a larger amount may be used, a large amount of acid or alkali and an extra time are required in the neutralization step.

In conducting the reaction, 2,7-dihydroxynaphthalene may be used alone, but other phenols and naphthols may be used in combination.

The reaction is described in more detail. For example, in an aqueous dispersion system, in the presence of a basic catalyst or an acidic catalyst, aldehydes are added in an amount of 0.5 to 1 mol per 2,7-dihydroxynaphthalene.
1.0 mol, preferably 0.5-0.55 mol,
At a temperature of 30-100 ° C, preferably 60-80 ° C,
After stirring for 0.5 to 3 hours and then neutralizing, the product is separated by filtration, washed with water, washed and dried to obtain the target compound.

In this way, bis (2,7-dihydroxy-1-naphthyl) alkane, which is a raw phenolic resin, is obtained. The phenolic resin has, for example, the following structure. Formula (I)

[0018]

Embedded image

Wherein R 1 and R 2 are a hydrogen atom, a lower alkyl group, a phenyl group, a hydroxyphenyl group, and a halogen-substituted phenyl group, respectively. ]

Next, the above bis (2,7-dihydroxy-
The desired bis (2,7-diglycidyloxy-1-naphthyl) alkane is obtained by reacting 1-naphthyl) alkane with epihalohydrin.

The reaction is not particularly limited, and a method generally used for obtaining an epoxidized product from ordinary phenol and epihalohydrin can be applied.

For example, epihalohydrin is used in an amount of 1.5 to 20 mol, preferably 3.0 to 20 mol per 1 mol of the hydroxyl group of the above bis (2,7-dihydroxy-1-naphthyl) alkane.
10.0-mol, 20-120 ° C in the presence of a base,
Preferably, it can be easily produced by performing an epoxidation reaction at 50 to 80 ° C for 2 to 7 hours.

The base used in the epoxidation is not particularly restricted but includes, for example, potassium hydroxide, sodium hydroxide, barium hydroxide, magnesium oxide, sodium carbonate, potassium carbonate and the like. Potassium oxide and sodium hydroxide are preferred.

As the epihalohydrin, epichlorohydrin, epibromohydrin, β-methylepichlorohydrin and the like are used, and epichlorohydrin is preferred from the viewpoint of industrial availability.

The molecular weight, epoxy equivalent and melt viscosity of the obtained epoxy resin are controlled by adjusting the excess ratio of the number of moles of epihalohydrin to the number of moles of hydroxyl groups of the above bis (2,7-dihydroxy-1-naphthyl) alkane. can do. Decreasing the molar excess of epihalohydrin will increase the molecular weight of the epoxy resin, while increasing it will decrease the molecular weight. The molecular weight is not particularly limited, but is preferably in the range of 400 to 1000 from the viewpoint of fluidity.

The bis (2,7-diglycidyloxy-1-naphthyl) alkane thus obtained includes, for example, compounds having a structure represented by the following formula (II). Formula (II)

[0027]

Embedded image

Wherein R 1 and R 2 are a hydrogen atom, a lower alkyl group, a phenyl group, a hydroxyphenyl group, and a halogen-substituted phenyl group, respectively. ]

Among the epoxy resins represented by the above formula (II), bis (2,7-diglycidyloxy-1-naphthyl) methane is particularly preferred from the viewpoint of excellent coating film strength and heat resistance.

The curing agent (B) used in the present invention includes curing agents usually used in epoxy resin powder coatings, such as dicyandiamide, adipic dihydrazide, imidazolines, and phenol novolak resins. However, dicyandiamide and phenol novolak resins are preferred from the viewpoint of pinhole resistance.

The powder coating for cast iron pipes of the present invention comprises the above (A)
Although the component and the component (B) are essential components, the use of a bisphenol-type epoxy resin (C) is preferred in that the impact resistance of the paint is significantly improved.

Examples of the bisphenol type epoxy resin (C) include bisphenol A type epoxy resin, bisphenol F type epoxy resin, tetrabromobisphenol A epoxy resin, phenol novolak type epoxy resin, cresol novolak type epoxy resin, and alicyclic type epoxy resin. Resins, polyhydric alcohol type epoxy resins, glycidyl ester type epoxy resins, copolymer resins of these epoxy resins, and partially modified epoxy resins of these epoxy resins. Specifically, EPICL
ON 1050 (manufactured by Dainippon Ink and Chemicals, Inc.), E
PICLON 1055 (same as above), EPICLON 205
5 (same), EPICLON 3050 (same), EPIC
LON 4050 (same as above), EPICLON 4055
(Same as above), EPICLON 7050 (Same as above), EPICL
ON 9055 (same as above), EPICLON 9155
(Ibid.) And the like. In particular, a bisphenol A or bisphenol F epoxy resin composed of bisphenol A or bisphenol F and epichlorohydrin is desirable from the viewpoint of adhesion, corrosion resistance, flexibility, and coating film hardness. Although the molecular weight and epoxy equivalent of the above-mentioned bisphenol-type epoxy resin (C) are not particularly limited, they are usually number average molecular weight of 1500 to 3000, and especially 1800 to 2500 from the viewpoint of excellent impact resistance. preferable.

In the present invention, the mixing ratio of the components (A) and (B) or the mixing ratio of each of the components (A) to (C) is not particularly limited. When used, the mixing ratio of the bis (diglycidyloxynaphthyl) alkane (A) is 20 to 80 with respect to the total amount of the component (A) and the component (C), since the effect of the combined use of the components becomes remarkable. The range which becomes wt% is preferable. The curing agent (B) is an active hydrogen / epoxy group = 0.3 in an equivalent ratio of active hydrogen in the curing agent (B) to epoxy groups in the paint.
The range which becomes -1.0 is preferable.

In the present invention, the coating film strength can be made extremely good by further blending an extender and / or a coloring agent (D) as required. Examples of such an extender and / or colorant (D) include titanium oxide, talc, calcium carbonate, barium carbonate, silica,
Examples include mica, alumina, carbon black, phthalocyanine green, and phthalocyanine blue.

These extenders and / or colorants (D)
Although there is no particular limitation on the amount of
It is preferably from 0 to 60% by weight, particularly preferably from 40 to 50% by weight, from the viewpoint of excellent pinhole prevention properties and facilitating the production of paint.

If necessary, additives such as a thixotropic agent and a flow control agent may be added to improve the surface condition of the coating film.

The epoxy resin composition for powder coating of the present invention comprises the epoxy resin (A), a curing agent (B) capable of curing the epoxy resin, an epoxy resin (C), an extender pigment to be blended if necessary. After mixing the coloring material (D) and, if necessary, various additives with a Henschel mixer or the like, the mixture is melt-kneaded with a heated extruder, cooled and then pulverized and classified.

The melting and kneading temperature is not particularly limited as long as it is higher than the melting point of the component (A).
Is preferred from the viewpoint of production stability.

The powder coating for inner surface coating of a cast iron pipe of the present invention obtained by pulverization and classification usually has a particle diameter of 30 in number average particle diameter.
１４０140 μm, but especially 35
It is preferably from 70 to 70 μm.

The cast iron tube to be coated with the powder coating of the present invention is not particularly limited in its shape, material, dimensions, etc., and can be applied to any material. And ductile cast iron pipes manufactured by the method. In particular, shrinkage cavities often occur in cast iron pipes made by a die casting method having a high cooling rate during casting, and the effect of the present invention is remarkable.

The method of coating the cast iron pipe is not particularly limited, and examples thereof include a rotary spraying method and an electrostatic coating method. When these coatings are performed, the temperature of the object to be coated is 200 to 230 ° C.
It is preferable to perform the process in the range of 0 to 600 μm because the effects of the present invention are remarkable.

Hereinafter, the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited only to these Examples.

[0043]

【Example】

Examples 1 to 3 and Comparative Examples 1 to 4 The components shown in Table 1 were roughly pulverized, then blended in the proportions shown in Table 1, and sufficiently pulverized and mixed using a Henschel mixer. Thereafter, the mixture was melt-kneaded using an extruder heated to 110 ° C., extruded, cooled, pulverized, and classified to obtain a powder coating having a particle size of 80 to 120 μm.

The obtained powder coating was cured at 170 ° C. for 3 minutes, and Tg was measured. Then, the above powder coating was applied to the end of the ductile cast iron pipe heated to 200 ° C. using an electrostatic coating apparatus to a thickness of 200 μm, and touch-up coated. Immediately after coating, Dainippon Paint Co., Ltd. Resin powder paint V-PET # 16
Thickness of 500μm using a rotary spray coating device for 00 gray
And the occurrence of pinholes was visually inspected.

Next, an impact resistance test was performed for 150 mm × 70 mm.
The powder coating of each example and the comparative example was touch-up coated to a thickness of 200 μm on a steel sheet of × 2.0 mm, and JIS K
Tested according to 8.3.2 (DuPont impact test) of 5400-1990. The results are shown in Table 1.

[0046]

[Table 1] * 1 Bis (diglycidyloxynaphthyl) methane manufactured by Dainippon Ink and Chemicals, Inc. * 2 Bisphenol A type solid epoxy resin manufactured by Dainippon Ink and Chemicals, Inc. * 3 Cresol novolac type manufactured by Dainippon Ink and Chemicals, Inc. Solid epoxy resin * 4 Tetrabromobisphenol A type epoxy resin manufactured by Dainippon Ink & Chemicals, Inc. * 5 Dimethyl diphenyl type epoxy resin manufactured by Yuka Shell Epoxy * 6 Phenol novolak manufactured by Dainippon Ink & Chemicals, Inc. resin

[0047]

According to the present invention, it is an object of the present invention to provide a powder coating material for coating the inner surface of a cast iron pipe, which is extremely excellent in preventing pinholes and extremely excellent in heat resistance of a coating film.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Makoto Kitagawa 1-12-19 Kitahorie, Nishi-ku, Osaka-shi, Osaka Inside Kurimoto Ironworks Co., Ltd. (72) Inventor Yoshisada Michiura 1 Kitahorie, Nishi-ku, Osaka-shi, Osaka No. 12-19, Kurimoto Iron Works Co., Ltd. (72) Inventor Takaaki Exit 1-12-12, Kitahorie, Nishi-ku, Osaka-shi, Osaka Prefecture Inside Kurimoto Iron Works Co., Ltd. (72) Kazuhito Hanano, Nishi-ku, Osaka-shi, Osaka 1-12-19 Kitahorie, Kurimoto Iron Works Co., Ltd.

Claims (5)

[Claims] 1. A powder coating for coating the inner surface of a cast iron pipe, comprising bis (diglycidyloxynaphthyl) alkane (A) and a curing agent (B) as essential components. 2. The powder for coating the inner surface of a cast iron pipe according to claim 1, comprising bis (diglycidyloxynaphthyl) alkane (A), a curing agent (B), and a bisphenol-type epoxy resin (C) as essential components. paint. 3. The inner coating of a cast iron pipe according to claim 2, wherein the mixing ratio of the bis (diglycidyloxynaphthyl) alkane (A) is 20 to 80% by weight based on the total of (A) and (C). For powder coating. 4. The powder paint for coating the inner surface of a cast iron pipe according to claim 1, further comprising an extender pigment and / or a colorant. 5. The number average particle diameter is 30 to 140 μm.
The powder coating material for coating the inner surface of a cast iron pipe according to any one of claims 1 to 4, wherein