JP2009254939A - Painting method of galvanized steel structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the painting method of galvanized steel structure enabling formation of multilayered coating films with extremely excellent adhesiveness with a base and corrosion resistance, even in a case of a film thickness of the multilayered coating films of 200 μm or less. <P>SOLUTION: In the painting method of a galvanized steel structure, primary paint (I) containing (A) epoxy resin having two or more epoxy groups in one molecule, (B) modified resin, (C) amine-based resin, (D) phosphoric acid-based rust-preventive pigment, and (E) constitution pigment, are applied to the galvanized steel structure to have a cured film thickness of 80-150 μm; and at least one kind of finishing paint (II) selected among fluororesin-based paint, acrylic silicone resin-base paint, and polyurethane resin-based paint is applied to have a cured thickness of 15-60 μm. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for coating galvanized steel structures such as power transmission towers and communication towers.

  Steel structures such as power transmission towers are exposed to wind and rain and are prone to rust, so the surface of the steel material is subjected to anticorrosion treatment such as galvanization.

  On the surface of a steel material that has been subjected to galvanizing treatment such as hot dip galvanizing treatment, a δ1 layer and a ζ layer, which are alloy layers of iron and zinc, are usually formed sequentially from the side closer to the iron base, and the zinc layer is formed thereon. It has a structure of a plating film in which an η layer is formed. Steel structures that have been galvanized are conventionally said to be maintenance-free, and are used without painting, or when identification of aviation signs, etc. is required, or when harmony with the surrounding environment is required Colored and painted, etc. are used.

  However, in recent years, the consumption of the η layer of the zinc layer has become faster than expected due to the influence of acid rain, etc., the η layer disappears, and the ζ layer, which is an alloy layer of iron and zinc, is exposed. In reality, there are many steel structures such as power transmission towers in which the δ1 layer, which is the alloy layer in contact with the iron substrate, is exposed. In the steel structure in which the ζ layer or the δ1 layer is exposed, red rust is gradually generated. Such red rust not only has a poor appearance, but also causes a decrease in the strength of the steel structure, and thus requires anticorrosion coating.

  Patent Document 1 proposes a method of subjecting such a rusted steel structure to anticorrosion coating by subjecting the surface of the steel structure to keren treatment, followed by undercoating, topcoating, and the like. Patent Document 2 proposes a coating method using a one-pack type epoxy resin paint containing an epoxy resin, a flake pigment, a ketimine compound, etc. as an undercoat paint. According to these coating methods, it is possible to form a coating film with excellent adhesion and corrosion resistance on the surface of a steel structure that has been galvanized, but the η layer of the zinc layer in the galvanized film is consumed. As a result, in the portions where the ζ layer and the δ1 layer of the alloy layer are exposed, the adhesion is insufficient, and it is difficult to ensure long-term corrosion resistance.

On the other hand, in Patent Document 3, an undercoat paint in which the shrinkage stress of the formed coating film is controlled is applied with a specific film thickness, and an overcoat paint containing a scaly pigment is applied thereon with a specific film thickness. There has been proposed a coating method capable of forming a coating film having adhesion and anticorrosion properties even on the substrate surface where the δ1 layer is exposed. However, it is easy to increase the cost for the thick film specification as described above, and the top coating material has a high viscosity and a thick film. Therefore, the coating cost tends to be high, and the unevenness of the coating film surface is large and the cosmetic property is lacking. There was a case. Therefore, it was considered to reduce the film thickness to solve these problems, but when the film thickness of the multilayer coating film was about 200 μm or less, it was difficult to ensure long-term adhesion in an outdoor environment.
JP 2000-140746 A JP 2001-198521 A WO2007 / 23934 Brochure

The object of the present invention is extremely excellent in adhesion and corrosion resistance to the substrate even when the film thickness of the multilayer coating film is 200 μm or less for steel structures such as power transmission towers that have been galvanized. An object of the present invention is to provide a method for coating a steel structure capable of forming a multilayer coating film excellent in the above.

The present invention provides the following coating method.
1. (A) epoxy resin having two or more epoxy groups in one molecule, (B) modified resin, (C) amine curing agent, (D) phosphoric acid rust prevention A pigment and (E) an extender, the content of the modified resin (B) is 10 to 150 parts by weight with respect to 100 parts by weight of the solid content of the resin (A), and the amine curing agent (C) Is a ratio in which the active hydrogen equivalent in the amine curing agent (C) is 0.4 to 1.2 equivalents relative to 1 equivalent of the epoxy group in the epoxy resin (A), and The content of the phosphoric acid-based anticorrosive pigment (D) is 10 to 150 parts by weight with respect to 100 parts by weight of the total solid content of the resin (A), the resin (B) and the curing agent (C), and is formed. Undercoat paint (I) having a pigment volume concentration of 35 to 60% in the coating film is 80 to 150 in terms of cured film thickness. Then, at least one top coating (II) selected from a fluororesin-based paint, an acrylic silicon resin-based paint and a polyurethane resin-based paint is applied so as to have a cured film thickness of 15 to 60 μm. A galvanized steel structure, characterized in that it is a coating method, and the adhesion after 3000 hours of immersion in hot water at 60 ° C. of the multilayer coating film by the paints (I) and (II) is 2.5 MPa or more. Painting method,
2. The pigment used in the undercoat paint (I) consists of a rust preventive pigment (D), an extender pigment (E), and a colored pigment (F), and in the total amount of the extender pigment (E), aluminum silicate, magnesium silicate, aluminum silicate 50% by weight or more of at least one selected from potassium and silica is used, the pigment volume concentration in the formed coating film is in the range of 40 to 50%, and the content of the modified resin (B) The coating method according to 1, wherein the amount is 30 to 100 parts by weight with respect to 100 parts by weight of the solid content of the resin (A),
3. The mixing ratio of the amine curing agent (C) in the undercoat paint (I) is such that the active hydrogen equivalent in the amine curing agent (C) is 0.4 to 1 equivalent to 1 equivalent of the epoxy group in the epoxy resin (A). The coating method according to 1 or 2, which is a ratio of 0.8 equivalents,
4). The mixing ratio of the amine curing agent (C) in the undercoat paint (I) is such that the active hydrogen equivalent in the amine curing agent (C) is 0.5 to 1 equivalent to 1 equivalent of the epoxy group in the epoxy resin (A). Item 3. The extender pigment (E) contains 70% by weight or more of at least one selected from aluminum silicate-based, magnesium silicate-based, aluminum potassium silicate-based, and silica-based at a ratio of 0.7 equivalent. Painting method,
5. The amine-based curing agent (C) in the undercoat paint (I) is a mixture of aminosilane and polyamine compound ketimine compound in a molar ratio of 2: 1 to 20: 1. Item 1 or 2, wherein the blending ratio is such that the active hydrogen equivalent in the amine-based curing agent (C) is 0.7 to 1.0 equivalent with respect to 1 equivalent of the epoxy group in the epoxy resin (A). Painting method,
6). The coating method according to claim 5, wherein the active hydrogen equivalent of the ketiminate is 60 to 150, and the active hydrogen equivalent of aminosilane is 60 to 120.
7). The undercoat paint (I) is a two-component paint comprising a main agent containing components other than the amine curing agent (C) and a curing agent containing the amine curing agent (C), and the main agent contains a glycidyl group. The coating method according to any one of 1 to 6, wherein a silane coupling agent is blended and aminosilane is blended in the curing agent.
8). The coating method according to any one of 1 to 7, wherein the top coating material (II) is a coating material in which the swelling area ratio after 1000 hours of salt spraying of the single coating film is 5% or less,
9. The coating according to any one of 1 to 8, wherein the surface of the steel structure subjected to the galvanizing treatment is an exposed surface of the ζ layer and / or an exposed surface of the δ1 layer, which is an alloy layer of iron and zinc. Method.

According to the present invention, a multi-layer formed by coating a specific undercoat paint with a specific film thickness on a galvanized steel structure, and applying a specific overcoat paint with a specific film thickness thereon. 60 ° C of coating film
By ensuring that the adhesion after 3000 hours of immersion in hot water exceeds a specific value, even if the film thickness of the multilayer coating is 200 μm or less, adhesion to the substrate is ensured over a long period even in harsh outdoor environments In addition, it is possible to form a multilayer coating film having excellent anticorrosion properties, finish properties, and coating workability.

  In particular, according to the inventions according to claims 3 and 4, it is considered that a coating film having a low crosslinking density and a high anticorrosion durability is formed. In the multilayer coating film formed by overlapping, it is considered that the adhesion after 3000 hours of 60 ° C. hot water immersion was able to ensure a specific value or more. Further, according to the inventions according to claims 5 and 6, it is considered that the coating film has a low crosslinking density and is formed with a high anticorrosion durability film having excellent flexibility and water resistance. In the multilayer coating film formed by recoating with the top coating (II), it is considered that the adhesion after 3000 hours of immersion in hot water at 60 ° C. could ensure a specific value or more.

Undercoat paint (I)
The undercoat paint (I) used in the method of the present invention is an epoxy resin (A) having two or more epoxy groups in one molecule, a modified resin (B), an amine curing agent (C), and a phosphoric acid anticorrosive pigment. (D) and extender pigment (E) are contained.

  The epoxy resin (A) is an epoxy resin having 2 or more, preferably 2 to 5, epoxy groups in one molecule. The epoxy resin (A) preferably has a number average molecular weight of about 350 to 3,000, more preferably about 400 to 1,500. Furthermore, the epoxy equivalent is preferably about 80 to 1,000, more preferably about 150 to 700.

  As an example of the said epoxy resin (A), the epoxy resin obtained by making polyhydric alcohol, a polyhydric phenol, etc. react with excess epichlorohydrin or alkylene oxide can be mentioned. Examples of the polyhydric alcohol include ethylene glycol, polyethylene glycol, propylene glycol, neopentyl glycol, butylene glycol, hexanediol, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, diglycerol, sorbitol and the like. Examples of the polyhydric phenol include 2,2-bis (4-hydroxyphenyl) propane [bisphenol A], halogenated bisphenol A, 4,4-dihydroxyphenylmethane [bisphenol F], and tris (4-hydroxyphenyl). ) Propane, resorcin, tetrahydroxyphenyl ethane, novolac polyhydric phenol, cresol polyhydric phenol, and the like.

  Examples of other epoxy resins include 1,2,3-tris (2,3-epoxypropoxy) propane, phthalic acid diglycidyl ester, hexahydrophthalic acid glycidyl ester, tetrahydrophthalic acid glycidyl ester, and dimer acid glycidyl ester. , Tetraglycidylaminodiphenylmethane, 3,4-epoxy-6-methylcyclohexylmethyl carboxylate, triglycidyl isocyanurate, 3,4-epoxycyclohexylmethyl carboxylate, polypropylene glycol glycidyl ether and the like.

  The modified resin (B) is blended from the viewpoint of the flexibility and water resistance improvement of the formed coating film, and 10 to 150 parts by weight with respect to 100 parts by weight of the solid content of the epoxy resin (A). Preferably, 30 to 100 parts by weight is blended from the viewpoint of curability and anticorrosion.

Specific examples of the modified resin (B) include C4 to C12 petroleum resins or mixtures thereof, ketone resins, polybutadiene resins, chroman resins, xylene resins, toluene resins, terpene resins, and phenol resins. Styrene resin, indene resin and the like. Furthermore, a urethane-modified epoxy resin can also be used as the modified resin (B). The modified resin (B) is effective whether it is liquid or solid, but is preferably liquid in order to keep the solid content of the paint high.

  The said amine type hardening | curing agent (C) is a hardening | curing agent of the said epoxy resin (A), and a conventionally well-known thing can be especially used without a restriction | limiting. Examples of the amine curing agent include polyamine compounds.

  The polyamine compound may be aliphatic, alicyclic, or aromatic. The polyamine compound needs to have a primary amino group and / or a secondary amino group that undergoes a curing reaction with an epoxy resin, but is generally about 2,000 or less, preferably about 30 to 1,000. It is advantageous to have an active hydrogen equivalent weight within the range. The polyamine compound generally has a number average molecular weight of about 5,000 or less, preferably in the range of about 80 to 3,000.

  Examples of the polyamine compound include aliphatic polyamines such as ethylenediamine, propylenediamine, butylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, and pentaethylenehexamine; aromatic polyamines such as metaxylenediamine, diaminodiphenylmethane, and phenylenediamine. Alicyclic polyamines such as isophorone diamine, cyclohexylpropyl diamine and norbornene diamine; modified polyamines such as epoxy adducts of these polyamines; polyamides having at least one primary amino group at the molecular end, etc. Can be mentioned. Furthermore, ketimine compounds of these polyamine compounds can be used. The ketimine compound is obtained by blocking the polyamine compound with a carbonyl compound. Examples of the carbonyl compound include ketones such as acetone, methyl ethyl ketone, methyl isopropyl ketone, methyl isobutyl ketone, diisobutyl ketone and cyclohexanone; acetaldehyde, benzaldehyde and the like. Examples include aldehydes.

  From the viewpoint of adhesion to the galvanized surface, aminosilane can be used in combination with the ketimine product of the polyamine compound. Examples of aminosilane include γ- (2-aminoethyl) aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N- (β-aminoethyl) -γ-aminopropyltrimethoxysilane, and N- (β-amino). Ethyl) -γ-aminopropylmethyldimethoxysilane and the like. When aminosilane is used in combination with the ketimine product of the polyamine compound, it is preferable that these are used in a molar ratio of 2: 1 to 20: 1, preferably 4: 1 to 7: 1. Desirable in terms.

  The mixing ratio of the amine-based curing agent (C) is such that the active hydrogen equivalent in the amine-based curing agent (C) is 0.4 to 1.2 equivalents relative to 1 equivalent of the epoxy group in the epoxy resin (A). It is desirable from the viewpoint of the physical properties, curability, and anticorrosive properties of the coating film to be used in such a ratio that it is about 0.4, preferably about 0.4 to 1.0 equivalent.

  As the rust preventive pigment (D), conventionally known ones can be used without particular limitation, such as phosphoric acid rust preventive pigments, phosphorous acid rust preventive pigments, polyphosphoric acid rust preventive pigments, phosphomolybdic acid rust preventive pigments, Is mentioned. Specific examples of these include, for example, zinc phosphate, phosphorous zinc silicate, aluminum zinc phosphate, calcium zinc phosphate, calcium phosphate, aluminum pyrophosphate, calcium pyrophosphate, aluminum trihydrogen phosphate, aluminum metaphosphate, calcium metaphosphate, phosphorus Examples thereof include, but are not limited to, zinc molybdate and aluminum phosphomolybdate. Of these, aluminum dihydrogen phosphate and aluminum phosphomolybdate are particularly preferred from the viewpoint of the corrosion resistance of the formed coating film.

  As the extender pigment (E), conventionally known pigments can be used without particular limitation. For example, aluminum silicates represented by clay, kaolin and the like, magnesium silicates represented by talc and the like, and aluminum silicates represented by mica and the like. Particularly preferred are potassium-based and silica-based materials such as silica powder and quartz powder, but are not limited thereto. In particular, from the viewpoint of the durability of the formed coating film, at least one selected from aluminum silicate-based, magnesium silicate-based, aluminum potassium silicate-based and silica-based in the total amount of extender pigment (E) is 50% by weight or more, preferably 70% by weight. % Content is preferable.

  In addition to the rust preventive pigment and extender pigment, a conventionally known color pigment (F) can be blended in the undercoat paint (I) as necessary.

  As the color pigment (F), conventionally known pigments can be used without particular limitation, and examples thereof include titanium white, bengara, carbon black, and phthalocyanine blue.

  In the present invention, from the viewpoint of relaxation of internal stress, the pigment volume concentration in the coating film formed from the undercoat paint (I) is 35 to 60%, preferably 40 to 50% from the viewpoint of the stability of the paint properties. It is desirable. Here, the “pigment volume concentration” is a volume ratio of the pigment content in the total solid content of the total resin content and the total pigment content in the paint. In this specification, the specific gravity of the pigment which is the basis for calculating the volume of the pigment is according to “Paint Raw Material Handbook 6th Edition” (Japan Paint Manufacturers Association), and the specific gravity of the resin solids is Approximate to 1.

  Among the above descriptions, the pigment type is appropriately selected, the pigment volume concentration is set, and the combined use of the modified resin, and the active hydrogen equivalent is particularly about 0.4 to 0.8 equivalent, more preferably about 1 equivalent of epoxy group. Undercoat film (I) obtained by the present invention has a lower crosslink density than conventional films and has high anticorrosion durability due to a synergistic effect with 0.5 to 0.7. It is thought that it forms. In this way, in a multi-layer coating film formed by recoating with the top coating (II), the adhesion after 3000 hours of 60 ° C. hot water immersion is 2.5 MPa or more, and further 3.5 MPa or more is obtained. Further, it is considered that the rust and blister width from the crosscut portion after 5000 hours of spraying with salt water could be within 5 mm.

  In addition, the setting of the pigment volume concentration and the combined use of the modified resin, in particular, ketimine compound and aminosilane are used in a specific ratio as an amine curing agent, and the active hydrogen equivalent is 0.7 to 1.0 with respect to 1 equivalent of epoxy group. Due to the synergistic effect with the equivalent amount, it is considered that a coating film having a low cross-linking density and a high anticorrosion durability excellent in flexibility and water resistance is formed. In this way, in a multi-layer coating film formed by recoating with the top coating (II), the adhesion after 3000 hours of 60 ° C. hot water immersion is 2.5 MPa or more, and further 3.5 MPa or more is obtained. Further, it is considered that the rust and blister width from the crosscut portion after 5000 hours of spraying with salt water could be within 5 mm.

  In the undercoat paint (I), a silane coupling agent can be blended as necessary from the viewpoint of improving adhesion and pigment dispersibility. Examples of the silane coupling agent include glycidyl group-containing silane coupling agents such as γ-glycidoxypropyltrimethoxysilane and γ-glycidoxypropylmethyldimethoxysilane, excluding the above-mentioned aminosilane; γ-mercaptopropyltrimethoxysilane And mercapto group-containing silane coupling agents. The content thereof is suitably within the range of 0.5 to 20 parts by weight, preferably 1 to 15 parts by weight with respect to 100 parts by weight of the resin solid content in the paint. Of these, when a glycidyl group-containing silane coupling agent is used as the main agent, it is desirable to blend the aforementioned aminosilane into the curing agent from the viewpoint of improving the stability of the paint. In this case, the amount of aminosilane is 0.5 to 20 parts by weight, preferably 1 to 15 parts by weight, based on 100 parts by weight of the resin solid content in the paint.

  Moreover, various additives, such as a thickener, a plasticizer, a filler, a sagging stop agent, a pigment dispersant, can be further mix | blended with primer coating (I) as needed.

  The undercoat paint (I) is usually an organic solvent-type paint, and its solid content is preferably about 40 to 80% by weight. As an organic solvent, the thing at the time of resin component manufacture may be sufficient, and you may add suitably for the purpose of solid content adjustment. Examples of the organic solvent include aromatic hydrocarbon solvents such as toluene, xylene and aromatic naphtha; n-hexane, n-heptane, n-octane, n-decane, n-dodecane, cyclopentane, cyclohexane, mineral spirits Aliphatic hydrocarbon solvents such as acetone; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone; ester solvents such as ethyl acetate, n-butyl acetate, isobutyl acetate; ethyl alcohol, propyl alcohol, butyl alcohol, etc. Alcohol solvents such as ethylene glycol, diethylene glycol, propylene glycol, and hexylene glycol; glycol solvents such as methyl ether, ethyl ether, propyl ether, and butyl ether. Known solvent ether type solvents and the like can be used.

  The undercoat paint (I) is usually a two-component paint comprising a main agent containing a component other than the amine curing agent (C) and a curing agent containing the amine curing agent (C). And a curing agent are mixed and used. The pot life after mixing is usually about 1 to 8 hours at 20 ° C.

Top coating (II)
The top coating (II) in the method of the present invention is at least one selected from a fluororesin-based paint, an acrylic silicon resin-based paint, and a polyurethane resin-based paint.

The fluororesin-based paint is a paint containing a fluororesin as a main film-forming component, and a paint containing a fluororesin (i), a color pigment (ii) and an isocyanate-based curing agent (iii) can be preferably used.

  As the fluororesin (i), fluoroolefin-based fluororesins such as fluoroolefin-vinyl ethers and fluoroolefin-vinyl esters, and further vinylidene fluoride-based fluororesins are suitable for the weather resistance of coating films, coating workability, etc. It can be preferably used from the point.

  As the fluoroolefin, for example, a fluoroolefin having 2 to 3 carbon atoms such as tetrafluoroethylene, chlorotrifluoroethylene, trifluoroethylene, hexafluoropropylene, and pentafluoropropylene can be suitably used. As the vinyl ether, for example, alkyl vinyl ethers such as ethyl vinyl ether, butyl vinyl ether, cyclohexyl vinyl ether, fluoroalkyl vinyl ether, and perfluoro (alkyl vinyl ether) are preferable. As vinyl ester, for example, vinyl butyrate, vinyl acetate, fatty acid vinyl ester having a branched alkyl group, vinyl pivalate, vinyl carboxylate and the like are preferable. In addition, at least one simple substance selected from alkyl allyl ether, alkyl allyl ester, alkyl isopropenyl ether, carboxylic acid isopropenyl ester, alkyl methallyl ether, carboxylic acid methallyl ester, α-olefin, acrylic acid ester, methacrylic acid ester and the like. The monomer may be further copolymerized with the fluoroolefin.

  In the fluororesin (i), the copolymerization ratio of fluoroolefin is 30 to 70 mol%, preferably 40 to 60 mol%, and the hydroxyl value is in the range of 30 to 60 mgKOH / g. It is desirable in terms of sex.

As the color pigment (ii), conventionally known pigments can be used without particular limitation, and examples thereof include titanium dioxide, carbon black, zinc oxide, bengara, benzidine yellow, phthalocyanine blue, phthalocyanine green, and carbazole violet. These can be used alone or in combination. Conventionally known luster pigments, extender pigments, and the like can be appropriately used in combination with the color pigments as necessary.
The isocyanate curing agent (iii) can be used without particular limitation as long as it contains a compound containing two or more isocyanate groups in one molecule, such as tetramethylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, etc. Aliphatic diisocyanates; cycloaliphatic diisocyanates such as 4,4'-methylenebis (cyclohexyl isocyanate) and isophorone diisocyanate; xylylene diisocyanate, tolylene diisocyanate, polytolylene polyisocyanate, diphenylmethane diisocyanate, polymethylene polyphenylene diisocyanate, polyphenylmethane Aromatic diisocyanates such as diisocyanate and naphthalene diisocyanate are listed. Other than these, isocyanurate-modified products of the above polyisocyanates, urethane polymers (for example, reaction products of polyols and excess polyisocyanates having an isocyanate group at the molecular terminal), similar to burettes, etc. A compound is mentioned, These can be used 1 type or in mixture of 2 or more types.

The blending ratio of the isocyanate curing agent (iii) is preferably about 0.1 to 1.5 equivalents of the isocyanate group of the isocyanate curing agent (iii) with respect to 1 equivalent of the hydroxyl group in the fluororesin (i). Is preferably used at a ratio of about 0.7 to 1.3 equivalents from the viewpoint of the curability and weather resistance of the coating film. Acrylic silicone resin-based paints consist mainly of acrylic silicone resin, which is a copolymer of a polymerizable monomer having a hydrolyzable silyl group and other polymerizable monomers, and further hydrolyzes organotin compounds, etc. The coating composition is obtained by blending a catalyst for the dehydration condensation reaction of a functional silyl group, and can further contain the above-mentioned color pigment (ii) and isocyanate curing agent (iii).

As the polyurethane resin-based paint, a polyurethane lacquer-based resin is used, and a one-component polyurethane resin paint that obtains a dry coating film by evaporating the solvent, or a polyol such as an acrylic polyol or a polyester polyol as the main agent, and the curing agent described above. In particular, from the viewpoint of the weather resistance of the formed coating film, there may be mentioned two-component polyurethane resin paints that use a polyisocyanate like A two-component polyurethane resin paint can be suitably used.

  For the top coating (II) as described above, if necessary, a curing catalyst, a thickener, an ultraviolet absorber, a light stabilizer, a leveling agent, a sagging agent, a pigment dispersant, a dehydrating agent, and an antifoaming agent. Various additives such as can be blended.

  The top coating (II) is usually an organic solvent-type coating, and the solid content is preferably about 40 to 80% by weight. As an organic solvent, the thing at the time of resin component manufacture may be sufficient, and you may add suitably for the purpose of solid content adjustment. As such an organic solvent, among those listed in the description of the undercoat paint (I), alcohol solvents, glycol solvents, and glycol ether solvents can be appropriately selected and used.

In the present invention, it is possible to select, as a top coating material (II), a coating material having an area ratio of blister generation after 1000 hours of salt spray of the single coating film of 5% or less, preferably 3% or less in combination with the undercoat. When painted, it is suitable from the viewpoint of improving the rust prevention property as a multilayer coating film.

Here, the salt spray of the single coating is JIS K5600-7-1 using a test plate obtained by directly decoating the surface of the pickled steel plate and then applying a top coating to a dry film thickness of 60 μm: The 1999 medium-resistance salt spray test is conducted for 1,000 hours.
Painting process The coating method of the present invention is to coat the surface of steel structures such as power transmission towers, communication towers, bridge piers, guardrails, etc., which have been subjected to galvanizing treatment such as hot dip galvanizing treatment, with an undercoating paint (I). Then, the top coat (II) is applied thereon.

  Steel structures such as power transmission towers that have been subjected to galvanizing treatment may be unpainted or may have an old paint film by painting such as an aerial sign color. In addition, the surface of the steel structure has a surface where the η layer, which is a zinc layer, remains, the surface where the η layer disappears, the surface where the ζ layer, which is an alloy layer of iron and zinc, is exposed, and further, the η layer and the ζ layer disappear. Any of the surfaces on which the δ1 layer is exposed may be used.

  In the present invention, when rust is generated in the coating site, a ground treatment such as blast treatment, power tool treatment, hand cleansing with a wire brush or the like can be appropriately performed. When there is a deteriorated old paint film, it is preferable to remove the old paint film by the same base treatment. In addition, when there is an old coating film that has not deteriorated, it is preferable to perform a roughening treatment instead of the base treatment.

  As a method for applying the undercoat paint (I) or the topcoat paint (II), a general coating method such as brush coating, roller coating or spray coating can be used. The coating amount of the undercoat paint (I) is about 80 to 150 μm, preferably about 90 to 120 μm in terms of the cured film thickness, and the top coat (II) is about 15 to 60 μm in thickness of the cured film, preferably 25. The amount is in the range of about 50 μm. Outside these ranges, problems such as a decrease in corrosion resistance, a decrease in adhesion, or a decrease in coating workability may occur, which is not preferable.

  After the undercoat paint (I) is applied, it is usually preferable to apply the topcoat paint (II) after drying and curing at room temperature for about 16 hours to 7 days.

  In the present invention, the adhesive force after 3000 hours of 60 ° C. hot water immersion of the multi-layer coating film by the undercoat paint (I) and the top coat paint (II) is 2.5 MPa or more, preferably 3.5 MPa or more. This is essential from the viewpoint of ensuring long-term adhesion in outdoor environments. If the adhesive strength of the multilayer coating film after immersing in hot water at 60 ° C. is less than 2.5 MPa, it is difficult to ensure long-term adhesion in an outdoor environment, which is not desirable.

  Here, the 60 ° C. hot water immersion of the multi-layer coating film is performed according to JIS K 5600-6-1: 1999 General test method for paints-Part 6: Chemical properties of the coating film-Section 1: Liquid resistance (general method) 7) In Method 1 (immersion method), pure water is used as a test solution and the test temperature is set to 60 ± 2 ° C., and the adhesion of the multilayer coating film is JIS K 5600-5-7: 1999 General test method for paints -Part 5: Mechanical properties of the coating film-Section 7: Measured by adhesion (pull-off method). In addition, the pure water liquid to be immersed is replaced with a new pure water liquid every 500 hours.

Hereinafter, the present invention will be described in more detail with reference to examples. “Part” and “%” indicate “part by weight” and “% by weight” unless otherwise specified.
(1) Manufacture of base coat base agent Production Example 1 Manufacture of base agent X-1
In a 2 liter container, 200 parts of bisphenol A type epoxy resin liquid (Note 1), 100 parts of modified resin B1 (Note 2), 2 parts of silane coupling agent (Note 3), 2 parts of dispersant (Note 4), magnesium silicate 250 parts, aluminum dihydrogen phosphate 100 parts, titanium dioxide 200 parts, anti-sagging agent (Note 6) 40 parts, antifoaming agent (Note 7) 1 part, xylene 55 parts, propylene glycol monomethyl ether 50 parts, The mixture was mixed with an agitator, and dispersed with a sand mill until the dispersion degree specified in JIS K 5600-2-5 was 50 μm or less to obtain an undercoat paint base X-1.

  The degree of dispersion was measured using a grind gauge. The same applies to the following production examples.

Production Example 2 Production of main agent X-2
In a 2 liter container, 200 parts of bisphenol A epoxy resin liquid (Note 1), 70 parts of modified resin B2 (Note 5), 2 parts of silane coupling agent (Note 3), 2 parts of dispersant (Note 4), aluminum silicate 250 parts potassium, 100 parts aluminum phosphomolybdate, 200 parts titanium dioxide, 40 parts anti-sagging agent (Note 6), 1 part antifoaming agent (Note 7), 85 parts xylene, 50 parts propylene glycol monomethyl ether The mixture was mixed with an agitator and dispersed with a sand mill until the dispersion degree specified in JIS K 5600-2-5 was 50 μm or less to obtain a main coating X-2 of an undercoat paint.

Production Example 3 Production of main agent X-3
In a 2 liter container, 200 parts of bisphenol A type epoxy resin liquid (Note 1) 25 parts of modified resin B1 (Note 2), 2 parts of silane coupling agent (Note 3), 2 parts of dispersant (Note 4), 250 parts of magnesium silicate Parts, 100 parts of aluminum phosphomolybdate, 200 parts of titanium dioxide, 40 parts of sagging agent (Note 6),
Add 1 part of antifoaming agent (Note 7), 105 parts of xylene and 75 parts of propylene glycol monomethyl ether in order, mix with an agitator, and reduce to 50 μm or less with a dispersity specified in JIS K 5600-2-5 using a sand mill. To obtain a main agent X-3 of an undercoat paint.

Production Example 4 Production of main agent X-4
In a 2 liter container, 200 parts of bisphenol A type epoxy resin liquid (Note 1), 160 parts of modified resin B2 (Note 5), 2 parts of silane coupling agent (Note 3), 2 parts of dispersant (Note 4), magnesium silicate 190 parts, 100 parts aluminum dihydrogen triphosphate, 200 parts titanium dioxide, 40 parts anti-sagging agent (Note 6), 1 part antifoaming agent (Note 7), 55 parts xylene, 50 parts propylene glycol monomethyl ether, The mixture was mixed with an agitator and dispersed with a sand mill until the dispersion degree specified in JIS K 5600-2-5 was 50 μm or less to obtain a base coating X-4 for an undercoat.

Production Example 5 Production of main agent X-5
In a 2 liter container, 200 parts of bisphenol A type epoxy resin liquid (Note 1), 100 parts of modified resin B1 (Note 2), 2 parts of silane coupling agent (Note 3), 2 parts of dispersant (Note 4), barium sulfate 355 parts, 100 parts of aluminum dihydrogen triphosphate, 200 parts of titanium dioxide, 40 parts of anti-sagging agent (Note 6), 1 part of antifoaming agent (Note 7) are sequentially added, mixed with an agitator, and JIS K 5600 in a sand mill Dispersion was performed until the dispersion degree specified in -2-5 was 50 μm or less, to obtain a main agent X-5 of an undercoat paint.

Production Example 6 Production of main agent X-6
In a 2 liter container, 130 parts of bisphenol A type epoxy resin liquid (Note 8), 140 parts of modified resin B3 (Note 9), 5 parts of silane coupling agent (Note 3), 2 parts of dispersant (Note 4), 170 parts of talc Parts, 80 parts of barium sulfate, 100 parts of aluminum dihydrogen triphosphate, 150 parts of titanium dioxide, 5 parts of anti-sagging agent (Note 10), 1 part of antifoaming agent (Note 7), 65 parts of xylene, 45 parts of methyl ethyl ketone, propylene glycol 110 parts of monomethyl ether were sequentially charged, mixed with an agitator, and dispersed with a sand mill until the dispersion degree specified in JIS K 5600-2-5 was 50 μm or less, thereby obtaining a base coating X-6.

Production Example 7 Production of main agent X-7
In a 2 liter container, 130 parts of bisphenol A type epoxy resin liquid (Note 8), 140 parts of modified resin B4 (Note 11), 5 parts of silane coupling agent (Note 3), 2 parts of dispersant (Note 4), 170 parts of talc Parts, 80 parts of barium sulfate, 100 parts of aluminum dihydrogen triphosphate, 150 parts of titanium dioxide, 5 parts of anti-sagging agent (Note 10), 1 part of antifoaming agent (Note 7), 65 parts of xylene, 45 parts of methyl ethyl ketone, propylene glycol 110 parts of monomethyl ether were sequentially charged, mixed with an agitator, and dispersed with a sand mill until the dispersity specified in JIS K 5600-2-5 was 50 μm or less to obtain a main coating X-7 of an undercoat paint.

Production Example 8 Production of main agent X-8
In a 2-liter container, 186 parts of bisphenol A type epoxy resin liquid (Note 1), 140 parts of modified resin B3 (Note 9), 5 parts of silane coupling agent (Note 3), 2 parts of dispersant (Note 4), 170 parts of talc Parts, 80 parts barium sulfate, 100 parts aluminum dihydrogen triphosphate, 150 parts titanium dioxide, 5 parts anti-sagging agent (Note 10), 1 part antifoaming agent (Note 7), 45 parts xylene, 30 parts methyl ethyl ketone, propylene glycol 75 parts of monomethyl ether were sequentially charged, mixed with an agitator, and dispersed with a sand mill until the dispersion degree specified in JIS K5600-2-5 was 50 μm or less to obtain a main agent X-8 of an undercoat paint.

Production Example 9 Production of main agent Y-1
In a 2 liter container, 330 parts of bisphenol A epoxy resin liquid (Note 1), 2 parts of silane coupling agent (Note 3), 2 parts of dispersant (Note 4), 250 parts of magnesium silicate, 100 parts of aluminum dihydrogen phosphate , 200 parts of titanium dioxide, 40 parts of anti-sagging agent (Note 6), 1 part of antifoaming agent (Note 7), 35 parts of xylene and 40 parts of propylene glycol monomethyl ether are mixed in order, mixed with an agitator, and JIS K The main dispersion Y-1 of the undercoat paint was obtained by dispersing the dispersion at 5600-2-5 at a specified dispersity until it became 50 μm or less.

Production Example 10 Production of main agent Y-2
In a 2 liter container, 200 parts of bisphenol A type epoxy resin liquid (Note 1), 180 parts of modified resin B1 (Note 2), 2 parts of silane coupling agent (Note 3), 2 parts of dispersant (Note 4), magnesium silicate 250 parts, aluminum dihydrogen phosphate 100 parts, titanium dioxide 200 parts, anti-sagging agent (Note 6) 40 parts, antifoaming agent (Note 7) 1 part, xylene 15 parts, propylene glycol monomethyl ether 10 parts, The mixture was mixed with an agitator and dispersed with a sand mill until the dispersion degree specified in JIS K 5600-2-5 was 50 μm or less to obtain a base Y-2 for an undercoat paint.

Production Example 11 Production of main agent Y-3
In a 2 liter container, 200 parts of bisphenol A type epoxy resin liquid (Note 1), 100 parts of modified resin B1 (Note 2), 2 parts of silane coupling agent (Note 3), 2 parts of dispersant (Note 4), magnesium silicate 350 parts, 200 parts of titanium dioxide, 40 parts of anti-sagging agent (Note 6), 1 part of antifoaming agent (Note 7), 55 parts of xylene, 50 parts of propylene glycol monomethyl ether are mixed in order and mixed in an agitator Dispersion was carried out at a dispersion degree specified in JIS K 5600-2-5 until it became 50 μm or less to obtain a main agent Y-3 for an undercoat paint.

Production Example 12 Production of main agent Y-4
In a 2-liter container, 130 parts of bisphenol A type epoxy resin liquid (Note 8), 140 parts of modified resin B3 (Note 9), 5 parts of silane coupling agent (Note 3), 2 parts of dispersant (Note 4), talc 230 Parts, 120 parts of barium sulfate, 150 parts of titanium dioxide, 5 parts of anti-sagging agent (Note 10), 1 part of antifoaming agent (Note 7), 65 parts of xylene, 45 parts of methyl ethyl ketone, 110 parts of propylene glycol monomethyl ether, The mixture was mixed with an agitator and dispersed with a sand mill until the dispersion degree specified in JIS K 5600-2-5 was 50 μm or less to obtain a base coating Y-4.

Production Example 13 Production of main agent Y-5
In a 2 liter container, 130 parts of bisphenol A type epoxy resin liquid (Note 8), 140 parts of modified resin B3 (Note 9), 5 parts of silane coupling agent (Note 3), 2 parts of dispersant (Note 4), 170 parts of talc Parts, 80 parts of barium sulfate, 100 parts of calcium chloride, 150 parts of titanium dioxide, 5 parts of anti-sagging agent (Note 10), 1 part of antifoaming agent (Note 7), 65 parts of xylene, 45 parts of methyl ethyl ketone, 110 parts of propylene glycol monomethyl ether The parts are sequentially charged, mixed with an agitator, and JIS K 5600-2-5 in a sand mill.
To a base dispersion Y-5 of the undercoat paint.

Production Example 14 Production of main agent Y-6
In a 2 liter container, 130 parts of bisphenol A type epoxy resin liquid (Note 8), 30 parts of modified resin B3 (Note 9), 5 parts of silane coupling agent (Note 3), 2 parts of dispersant (Note 4), 130 parts of talc Parts, 70 parts of barium sulfate, 80 parts of aluminum dihydrogen triphosphate, 120 parts of titanium dioxide, anti-sagging agent (
* 10) 5 parts, 1 part of antifoaming agent (Note 7), 69 parts of xylene, 46 parts of methyl ethyl ketone, 116 parts of propylene glycol monomethyl ether are mixed in order, mixed with an agitator, and JIS K 5600-2-5 The main dispersion Y-6 of the undercoat paint was obtained by dispersing until the prescribed dispersity was 50 μm or less.

Production Example 15 Production of main agent Y-7
In a 2 liter container, 210 parts of bisphenol A type epoxy resin liquid (Note 8), 240 parts of modified resin B3 (Note 9), 5 parts of silane coupling agent (Note 3), 2 parts of dispersant (Note 4), talc 130 Parts, 70 parts barium sulfate, 100 parts aluminum dihydrogen triphosphate, 120 parts titanium dioxide, 5 parts anti-sagging agent (Note 10), 1 part antifoaming agent (Note 7), 36 parts xylene, 24 parts methyl ethyl ketone, propylene glycol 60 parts of monomethyl ether were sequentially added, mixed with an agitator, and dispersed with a sand mill until the dispersion degree specified in JIS K5600-2-5 was 50 μm or less to obtain a base material Y-7 for an undercoat paint.

Production Example 16 Production of main agent Y-8
In a 2 liter container, 90 parts of bisphenol A type epoxy resin liquid (Note 8), modified resin B3 (Note 9)
) 350 parts, silane coupling agent (Note 3) 5 parts, dispersant (Note 4) 2 parts, talc 160 parts, barium sulfate 80 parts, aluminum trihydrogen phosphate 100 parts, titanium dioxide 150 parts, anti-sagging agent ( Note 10) 5 parts, 1 part of antifoaming agent (Note 7), 51 parts of xylene, 34 parts of methyl ethyl ketone, and 85 parts of propylene glycol monomethyl ether are sequentially added, mixed with an agitator, and stipulated in JIS K5600-2-5 using a sand mill. The main component Y-8 of the undercoat paint was obtained by dispersing until the dispersion degree became 50 μm or less.
(2) Production of undercoat paint curing agent Production Example 17 Production of curing agent C1
In a 2 liter container, 400 parts of a modified polyamine resin liquid (Note 12), 200 parts of xylene, 200 parts of isobutyl alcohol and 200 parts of propylene glycol monomethyl ether were charged and mixed with an agitator to obtain a curing agent C1.

Production Example 18 Production of curing agent C2
In a 2 liter container, 600 parts of a modified polyamidoamine resin liquid (Note 13), 200 parts of xylene, 100 parts of isobutyl alcohol and 100 parts of propylene glycol monomethyl ether were charged and mixed with an agitator to obtain a curing agent C2.

Production Example 19 Production of curing agent C3
In a 2 liter container, 600 parts of modified polyamidoamine resin (Note 13), 50 parts of aminosilane (Note 15), 150 parts of xylene, 100 parts of isobutyl alcohol and 100 parts of propylene glycol monomethyl ether are mixed and hardened by an agitator. C3 was obtained.

Production Example 20 Production of curing agent C4
A 2 liter container is charged with 390 parts of polyamine ketiminate (Note 14), 60 parts of aminosilane (Note 15), 160 parts of xylene, 120 parts of methyl ethyl ketone, and 270 parts of propylene glycol monomethyl ether, and mixed with an agitator to add curing agent C4. Obtained.

Production Example 21 Production of curing agent C5
A 2 liter container is charged with 180 parts of polyamine ketiminate (Note 14), 30 parts of aminosilane (Note 15), 234 parts of xylene, 156 parts of methyl ethyl ketone, and 400 parts of propylene glycol monomethyl ether, and mixed with an agitator to add curing agent C5. Obtained.

Production Example 22 Production of curing agent C6
In a 2 liter container, 120 parts of polyamine ketiminate (Note 14), 60 parts of aminosilane (Note 15), 246 parts of xylene, 164 parts of methyl ethyl ketone and 410 parts of propylene glycol monomethyl ether are mixed with an agitator to add curing agent C6. Obtained.

Production Example 23 Production of curing agent C7
In a 2 liter container, charge 620 parts of polyamine ketiminate (Note 14), 80 parts of aminosilane (Note 15), 90 parts of xylene, 60 parts of methyl ethyl ketone, 150 parts of propylene glycol monomethyl ether and mix with an agitator to add curing agent C7. Obtained.

Production Example 24 Production of curing agent C8
A 2 liter container is charged with 250 parts of polyamine ketiminate (Note 14), 50 parts of aminosilane (Note 15), 210 parts of xylene, 140 parts of methyl ethyl ketone, and 350 parts of propylene glycol monomethyl ether, and mixed with an agitator to add curing agent C8. Obtained.

Production Example 25 Production of curing agent C9
A 2 liter container was charged with 450 parts of polyamine ketiminate (14), 160 parts of xylene, 120 parts of methyl ethyl ketone, and 270 parts of propylene glycol monomethyl ether, and mixed with an agitator to obtain a curing agent C9.
(Note 1) Bisphenol A resin solution: Trade name “JER1001X75”, Japan Epoxy Resin (
Co., Ltd., solid content 75%, number average molecular weight of the epoxy resin about 900, epoxy equivalent 475 (median)
(Note 2) Modified resin B1: Phenol-modified aromatic hydrocarbon resin
(Note 3) Silane coupling agent: γ-glycidoxypropyltrimethoxysilane
(Note 4) Dispersant: Trade name “Lecithin DX”, manufactured by Nisshin Oil Co., Ltd.
(Note 5) Modified resin B2: Phenol-modified terpene resin
(Note 6) Anti-sagging agent: Trade name “DISPARON 6900-20X”, manufactured by Enomoto Kasei Co., Ltd.
(Note 7) Antifoaming agent: Trade name “DISPARON 1950”, manufactured by Enomoto Kasei Co., Ltd.
(Note 8) Bisphenol A type epoxy resin liquid: solid content 100%, number average molecular weight of the epoxy resin about 400, epoxy equivalent 190 (median value)
(Note 9) Modified resin B3: Urethane-modified epoxy resin liquid (diisocyanate reaction product of amine-added epoxy resin), solid content 40%
(Note 10) Sagging stop agent: Trade name “Tallen 7200-20”, manufactured by Kyoeisha Chemical Co., Ltd., solid content 20%, amide wax thixotropic agent
(Note 11) Modified resin B4: aromatic petroleum resin (C8-C10 aromatic hydrocarbon fraction polymer), solid content 40%
(Note 12) Modified polyamine resin liquid: solid content 100%, active hydrogen equivalent 110
(Note 13) Modified polyamidoamine resin solution: solid content 80%, active hydrogen equivalent 170
(Note 14) Ketimine product of polyamine: solid content 100%, ketiminate product of modified alicyclic polyamine compound, active hydrogen equivalent 83
(Note 15) Aminosilane: solid content 100%, γ- (2-aminoethyl) aminopropyltrimethoxysilane, active hydrogen equivalent 74
(3) Manufacture of test plate By exposing a commercially available hot-dip galvanized steel sheet (3.2 mm x 70 mm x 150 mm) in the beach area, it is consumed until the surface of the ζ layer, which is an alloy layer of iron and zinc, is exposed. The surface was polished with sandpaper (# 240) to obtain a test plate (i).
Separately, the above hot-dip galvanized steel sheet was subjected to grid blasting until it became a base-adjusted grade of ISO Sa1.0 to obtain a test plate (ii). The surface of the test plate (ii) was judged to be an η layer.
(4) Top coat type Top coat P Fluororesin paint: Trade name “Shintofuron # 100 for bridges”, Shinto Paint Co., Ltd. top coat Q Acrylic silicone resin paint: Trade name “Ceraborn top coat”, Shinto paint ( Topcoat paint R manufactured by Co., Ltd. Polyurethane resin paint: Trade name “NY POLIN K topcoat”, Topcoat paint S manufactured by Shinto Paint Co., Ltd. About 3% bulge generation area rate after 1000 hours of salt spray on the coating
Top coat T Acrylic silicone resin paint: Trade name “Silico Tect AC top coat white”, manufactured by Kansai Paint Co., Ltd.
Top coat U Polyurethane resin paint: Trade name “Seratet U top coat white”, manufactured by Kansai Paint Co., Ltd.
Topcoat V Alkyd resin paint: Trade name “SD Marine Topcoat White for Bridges”, manufactured by Kansai Paint Co., Ltd.

Examples 1-17 and Comparative Examples 1-14
The base agent and the curing agent produced as described above were mixed at a mixing ratio (parts) shown in Table 1 to prepare each undercoat paint. The obtained undercoat and topcoat were applied to the test plate (i) or (ii) in the combinations shown in Table 1. The coating interval between the undercoat paint and the topcoat paint was 24 hours, and after the finish of the topcoat paint, it was dried and cured at 23 ° C. for 30 days to form a multilayer coating film. The cured film thickness of each example and comparative example is as shown in Table 1.

  About each coating board obtained by the Example and the comparative example, it used for the hot water immersion test and the salt spray test. The test method is as follows.

(Test method)
(* 1) Hot water immersion test-Adhesive force: Adhesive force after 3000 hours of 60 ° C hot water immersion (MPa)
-Destruction location: Destruction location after adhesion test after 3000 hours of hot water immersion at 60 ° C. When the destruction location is “within the undercoat film”, the adhesion between the substrate and the undercoat film and the adhesion between the undercoat film and the topcoat film are maintained, indicating that the undercoat film layer has been cohesively broken.
(* 2) Salt spray test ・ Appearance of general part: Appearance of coating film after 5000 hours of salt spray test ・ Swelling width: Swelling and rust width (mm) from crosscut after 5000 hours of salt spray test
The “-” display means that the entire cut surface is swollen.

Claims (9)

(A) epoxy resin having two or more epoxy groups in one molecule, (B) modified resin, (C) amine curing agent, (D) phosphoric acid rust prevention A pigment and (E) an extender, the content of the modified resin (B) is 10 to 150 parts by weight with respect to 100 parts by weight of the solid content of the resin (A), and the amine curing agent (C) Is a ratio in which the active hydrogen equivalent in the amine curing agent (C) is 0.4 to 1.2 equivalents relative to 1 equivalent of the epoxy group in the epoxy resin (A), and The content of the phosphoric acid-based anticorrosive pigment (D) is 10 to 150 parts by weight with respect to 100 parts by weight of the total solid content of the resin (A), the resin (B) and the curing agent (C), and is formed. Undercoat paint (I) having a pigment volume concentration of 35 to 60% in the coating film is 80 to 150 in terms of cured film thickness. Then, at least one top coating (II) selected from a fluororesin-based paint, an acrylic silicon resin-based paint and a polyurethane resin-based paint is applied so as to have a cured film thickness of 15 to 60 μm. A galvanized steel structure, characterized in that it is a coating method, and the adhesion after 3000 hours of immersion in hot water at 60 ° C. of the multilayer coating film by the paints (I) and (II) is 2.5 MPa or more. Painting method. The pigment used in the undercoat paint (I) consists of a rust preventive pigment (D), an extender pigment (E), and a colored pigment (F), and in the total amount of the extender pigment (E), aluminum silicate, magnesium silicate, aluminum silicate 50% by weight or more of at least one selected from potassium and silica is used, the pigment volume concentration in the formed coating film is in the range of 40 to 50%, and the content of the modified resin (B) The coating method according to claim 1, wherein the amount is 30 to 100 parts by weight with respect to 100 parts by weight of the solid content of the resin (A). The mixing ratio of the amine curing agent (C) in the undercoat paint (I) is such that the active hydrogen equivalent in the amine curing agent (C) is 0.4 to 1 equivalent to 1 equivalent of the epoxy group in the epoxy resin (A). The coating method according to claim 1 or 2, wherein the ratio is 0.8 equivalent. The mixing ratio of the amine curing agent (C) in the undercoat paint (I) is such that the active hydrogen equivalent in the amine curing agent (C) is 0.5 to 1 equivalent to 1 equivalent of the epoxy group in the epoxy resin (A). The extender pigment (E) contains 70 wt% or more of at least one selected from aluminum silicate, magnesium silicate, aluminum silicate, and silica in a total amount of 0.7 equivalent. The painting method described. The amine-based curing agent (C) in the undercoat paint (I) is a mixture of aminosilane and polyamine compound ketimine compound in a molar ratio of 2: 1 to 20: 1. The blending ratio is such that the active hydrogen equivalent in the amine curing agent (C) is 0.7 to 1.0 equivalent with respect to 1 equivalent of the epoxy group in the epoxy resin (A). The painting method described. The coating method according to claim 5, wherein the active hydrogen equivalent of the ketiminate is 60 to 150, and the active hydrogen equivalent of aminosilane is 60 to 120. The undercoat paint (I) is a two-component paint comprising a main agent containing components other than the amine curing agent (C) and a curing agent containing the amine curing agent (C), and the main agent contains a glycidyl group. The coating method according to any one of claims 1 to 6, wherein a silane coupling agent is blended and aminosilane is blended in a curing agent. The coating method according to any one of claims 1 to 7, wherein the top coating material (II) is a coating material having a bulge generation area ratio after 1000 hours of salt water spraying of the single coating film of 5% or less. The surface of the steel structure subjected to the galvanizing treatment is an exposed surface of the ζ layer and / or an exposed surface of the δ1 layer, which is an alloy layer of iron and zinc. Painting method.