JP2012057379A - Coating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating method which can prevent deterioration at a region of a bolt joint part in a steel frame member having the bolt joint part, with enhanced water resistance, durability, and heat resistance.SOLUTION: A coating method comprises the steps of applying a synthetic resin which enhances heat resistance and durability and a resin composition containing a phosphorous compound which exhibits effects such as dehydration and cooling, incombustible gas generation, and carbonization acceleration, to a region of a bolt joint part in a steel frame member having the bolt joint part to form a coating film (X)8, and then laminating an elastic coating material (Y)9 thereon which prevents dew condensation water from penetrating the bolt joint part and inhibits cracking and peeling of the coating resulting from movement of the bolt joint part.

Description

The present invention relates to a novel coating method.

  2. Description of the Related Art Conventionally, there are structures using steel members in which bolt joints are employed as structures such as columns and beams of buildings and civil engineering buildings. Bolt joints usually consist of bolts, nuts, and optionally washers. In such a structure, the bolt joint portion may be inferior in heat resistance, and there is a problem that the mechanical strength is reduced when exposed to high temperatures such as in a fire.

On the other hand, Patent Document 1 describes a method of locally covering a protruding portion of each bolt / nut (and washer) with a heat shield in a bolt joint region including a plurality of bolt joints. ing. According to the method of Patent Document 1, the thermally shielded part can be partially shielded from thermal radiation, and the decrease in the high-temperature strength of the entire steel structure due to the bolt joint can be compensated.

Japanese Patent No. 3954882

However, since the shape of the bolt joint region is complicated, water tends to accumulate between the bolts, and in some cases, condensation may occur. As a result, the bolt joint region is prone to rust and may deteriorate. When exposed to high temperatures such as in a fire, the mechanical strength may be significantly reduced.
As in Patent Document 1, in a method in which the bolt joint is partially covered with a heat shield, the bolts are likely to deteriorate between the bolts, and the heat resistance may be insufficient.

  This invention is made in view of such a point, and aims at preventing deterioration of a bolt junction part area | region and improving water resistance, durability, and heat resistance in the steel frame member which has a bolt junction part. Is.

As a result of intensive studies to achieve the above object, the present inventor has conceived a specific coating method for the bolt joint region and completed the present invention.

That is, the coating method of the present invention has the following characteristics.
1. A method for coating a steel member having a bolt joint, wherein a resin composition containing a synthetic resin and a phosphorus compound is applied to a bolt joint region to form a coating (X), and then the coating A step of laminating an elastic covering material (Y) on (X). The resin composition containing the synthetic resin and the phosphorus compound is a polymer of a monomer group including, as a synthetic resin, an alkyl group (meth) acrylic acid alkyl ester having 4 or more carbon atoms and an aromatic monomer. 1. A synthetic resin having an average molecular weight of 50,000 or more is included. Coating method described in

  The present invention is a method for coating a steel member having a bolt joint part, which prevents deterioration of the bolt joint part region and exhibits excellent water resistance, durability, and heat resistance.

It is an example of the steel frame member which has a bolt junction part. It is an example of the coating method of this invention.

The present invention relates to a method for coating a steel member having a bolt joint,
A step of applying a resin composition containing a synthetic resin and a phosphorus compound to the bolt joint region to form a coating (X), and then an elastic coating (Y) on the coating (X) A step of laminating.
In the present invention, bolts, nuts, and if necessary, washers are collectively referred to as “bolts”. A bolt joint part is a part (FIG. 1 (A) -2) to which a steel frame member is fixed with a set of bolts. The bolt joint region is a region including a plurality of bolt joints and the periphery thereof, and is a region (FIG. 1 (A) -3) including a portion in which a bolt protrudes from an object to be joined to the outer surface side. As shown in FIG. 1, usually various joining members (splice plate, split tee, end plate, flange plate, etc.) are used in the bolt joint region (FIG. 1 (B) -6). In the present invention, it is desirable to target at least a region including such a joining member as the bolt joint region.

  As a steel member having a bolt joint, for example, steel members such as columns and beams, columns and columns, beams and beams, etc. in steel structures are joined using bolts (bolt joint, high strength bolt joint, etc.) The thing which was done is mentioned.

<Coating (X)>
In the present invention, as the step (I), a resin composition (hereinafter, also referred to as “resin composition”) containing a synthetic resin and a phosphorus compound as essential components is applied to the bolt joint region, and the bolt joint portion. A coating (X) is formed so as to cover the entire region (FIG. 2). Thereby, when exposed to high temperatures, such as at the time of a fire, heat resistance is exhibited and the deterioration prevention property of a bolt junction part area | region, durability, and heat resistance can be improved.

  The resin composition of the present invention contains (a) a synthetic resin (hereinafter also referred to as “component (a)”) and (b) a phosphorus compound (hereinafter also referred to as “component (b)”) as essential components. .

(A) Synthetic resin As the component (a), a known synthetic resin can be used. Examples thereof include organic binders such as acrylic resin, vinyl acetate resin, polyester resin, phenol resin, petroleum resin, vinyl chloride resin, epoxy resin, urethane resin, alkyd resin, propylene rubber, chloroprene rubber, butyl rubber, and isobutylene rubber. These can be used alone or in combination of two or more.

In the present invention, a synthetic resin having a weight average molecular weight of 50,000 or more, which is a polymer of a monomer group including (meth) acrylic acid alkyl ester having an alkyl group having 4 or more carbon atoms and an aromatic monomer. a-1) (hereinafter referred to as “component (a-1)”) is preferably used. In this invention, heat resistance and durability can be improved by using such a component (a-1). The mechanism of action is not clear, but it is presumed that the following points contributed in general.
-By using a synthetic resin having the above specific composition and specific weight average molecular weight, the dispersibility of the powder component such as a phosphorus compound is enhanced and the powder component is covered with the resin. Appropriate hydrophobicity is imparted to the powder component, and resistance to water from the outside is increased. These synergistic effects improve durability.
The synthetic resin has a specific weight average molecular weight, and the conjugated unsaturated ring structure by the aromatic monomer acts effectively, so that a porous carbonized layer is formed during heating, and heat resistance is improved.

The component (a-1) is obtained by polymerizing a (meth) acrylic acid alkyl ester having 4 or more carbon atoms in an alkyl group and a monomer group containing an aromatic monomer. As the polymerization method, a known method can be employed.
Examples of the (meth) acrylic acid alkyl ester having 4 or more carbon atoms in the alkyl group include n-butyl (meth) acrylate, isobutyl (meth) acrylate, sec-butyl (meth) acrylate, and tert-butyl (meth). Acrylate, n-amyl (meth) acrylate, isoamyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, Examples include octadecyl (meth) acrylate, cyclohexyl (meth) acrylate, phenyl (meth) acrylate, and benzyl (meth) acrylate. Among these, an alkyl group having 4 to 8 carbon atoms is particularly suitable. In the present invention, the acrylic acid alkyl ester and the methacrylic acid alkyl ester are collectively referred to as (meth) acrylic acid alkyl ester.

Examples of the aromatic monomer include styrene, 2-methylstyrene, vinyltoluene, t-butylstyrene, chlorostyrene, vinylanisole, vinylnaphthalene, divinylbenzene, and the like.
The weight ratio of the (meth) acrylic acid alkyl ester to the aromatic monomer in the monomer group is preferably 80:20 to 20:80, more preferably 70:30 to 30:70. If the ratio of both is in such a range, it is suitable at the point of the effect expression of this invention.

  (A-1) The monomer group in a component can also mix monomer components other than the above. As the component (a-1), in particular, a polymer of a monomer group including a carboxyl group-containing monomer in addition to the above monomer is preferable. In this case, the acid value of the component (a-1) is preferably 0.5 to 15 mgKOH / g, more preferably 1 to 10 mgKOH / g. In the present invention, by using such a component (a-1), durability can be enhanced while maintaining heat resistance. It is presumed that the effect of improving the dispersibility of the powder component contributes to this effect.

Examples of the carboxyl group-containing monomer include acrylic acid, methacrylic acid, crotonic acid, maleic acid or a monoalkyl ester thereof, itaconic acid or a monoalkyl ester thereof, fumaric acid or a monoalkyl ester thereof. Among these, at least one selected from acrylic acid and methacrylic acid is particularly preferable.
The acid value of the synthetic resin is a value represented by the number of mg of potassium hydroxide equimolar to the acid group contained in 1 g of the solid content.

  (A-1) The weight average molecular weight of a component is 50,000 or more normally, Preferably it is 50,000-200,000, More preferably, it is 60,000-100,000. When the weight average molecular weight of the component (A) is within such a range, suitable effects can be obtained in both heat resistance and durability. If the weight average molecular weight is too small, the durability tends to be insufficient. On the other hand, when the weight average molecular weight is too large, the heat resistance tends to be insufficient, and the durability may be disadvantageous. In addition, a weight average molecular weight is the value which measured using gel permeation chromatography and was computed by polystyrene conversion.

(B) The phosphorus compound (b) component exhibits at least one effect such as dehydration cooling effect, non-combustible gas generation effect, carbonization promotion effect, etc. at the time of temperature rise, formation of porous carbonized layer, heat resistance It is an essential ingredient for demonstrating. Examples of the component (b) include tricresyl phosphate, diphenyl cresyl phosphate, diphenyl octyl phosphate, tri (β-chloroethyl) phosphate, tributyl phosphate, tri (dichloropropyl) phosphate, triphenyl phosphate. , Tri (dibromopropyl) phosphate, chlorophosphonate, bromophosphonate, diethyl-N, N-bis (2-hydroxyethyl) aminomethylphosphate, di (polyoxyethylene) hydroxymethylphosphate, three Examples thereof include phosphorus compounds such as phosphorus chloride, phosphorus pentachloride, ammonium phosphate, and ammonium polyphosphate. Of these, ammonium polyphosphate is particularly preferred in the present invention. As these phosphorus compounds, uncoated products can be used, but coated products can also be used.

  The component (b) is usually contained in an amount of 150 to 1000 parts by weight, preferably 200 to 800 parts by weight, more preferably 250 to 600 parts by weight with respect to 100 parts by weight of the component (a). In the present invention, even when the component (b) is contained at a relatively high ratio, sufficient durability can be ensured. When the amount of the component (b) is too small, the heat resistance is insufficient. When there is too much (b) component, it will become difficult to ensure practical durability.

  In the present invention, in addition to the component (b), the polyhydric alcohol compound (c) (hereinafter also referred to as “(c) component”), the nitrogen-containing compound (d) (hereinafter also referred to as “(d) component”). It is preferable to include one or more powder components selected from fillers (e) (hereinafter also referred to as “component (e)”). By including such a component, it becomes possible to form a porous carbonized layer that is more suitable as a heat-resistant material. In the present invention, in particular, the powder component preferably includes a phosphorus compound (b), a polyhydric alcohol compound (c), and a nitrogen-containing compound (d), and more preferably includes a filler (e) in addition to these. preferable.

  Examples of the polyhydric alcohol (c) include pentaerythritol, dipentaerythritol, tripentaerythritol, neopentaerythritol, trimethylolpropane, sorbitol, inositol, mannitol, glucose fructose, starch, cellulose and the like. The mixing ratio of the component (c) is preferably 5 to 600 parts by weight, more preferably 10 to 400 parts by weight with respect to 100 parts by weight of the synthetic resin (a).

  Examples of the nitrogen-containing compound (d) include melamine and derivatives thereof, dicyandiamide and derivatives thereof, azobistetrazole and derivatives thereof, azodicarbonamide, urea and thiourea. The mixing ratio of the component (d) is preferably 5 to 600 parts by weight, more preferably 10 to 400 parts by weight with respect to 100 parts by weight of the synthetic resin (d).

  Examples of the filler (e) include silicates such as talc; carbonates such as calcium carbonate and sodium carbonate; metal oxides such as aluminum oxide, titanium dioxide and zinc oxide; clay, clay, shirasu, mica, silica and the like Natural minerals and the like. Of these, metal oxides are particularly preferred. The mixing ratio of the component (e) is preferably 5 to 600 parts by weight, more preferably 10 to 400 parts by weight with respect to 100 parts by weight of the synthetic resin (a).

As the powder component, in addition to the above components, an expandable material such as expandable graphite and unexpanded vermiculite, a color pigment, a flame retardant, and the like can be mixed. Moreover, various additives etc. can also be mix | blended with the resin composition of this invention as components other than the above. Examples of such additives include thickeners, leveling agents, wetting agents, plasticizers, lubricants, antiseptics, antifungal agents, anti-algae agents, antibacterial agents, dispersants, antifoaming agents, cross-linking agents, and UV absorbing agents. Agents, antioxidants, fibers, catalysts and the like.
The resin composition of this invention can be manufactured by mixing the above components uniformly by a conventional method. At the time of mixing, a solvent can be mixed or heated as necessary.

<Elastic covering material (Y)>
In the present invention, as the step (II), the elastic coating material (Y) is laminated on the coating (X) coated in the step (I). Thereby, even when water accumulates in the bolt joint region or condensation occurs, it is possible to prevent water from entering the coating (X) and to accompany the movement of the bolt joint portion (and the bolt joint region). It is possible to suppress cracking, peeling, etc. of the coating, and to maintain the effect of the present invention for a long time.

Any elastic coating material (Y) may be used as long as it prevents water from entering from the outside and does not impair the effect of the coating (X). In particular, in the present invention, an elastic coating material containing a resin component and a pigment is used. It is preferable. As such an elastic coating material, those that form a film having an elongation at 20 ° C. of 50 to 800%, preferably 120 to 500%, and a water permeability of 0.5 ml / 24 h or less are preferable. . In such a range, it is possible to follow the displacement of the bolt joint (and the bolt joint region) and sufficiently prevent the occurrence of cracks on the surface of the elastic coating material. Furthermore, water can be reliably prevented from entering from the outside.
The elongation in the present invention is JIS A 6909 7.29 “Elongation test” “Elongation test at 20 ° C.”, and the water permeability is JIS A.
A 6909 7.12 This is a value measured according to “Water permeability test method B”.

Examples of the elastic covering material include a waterproof coating material as defined in JIS A6021 architectural waterproofing coating material, and a waterproof multi-layer coating material E and a waterproof multi-layer coating among JIS A6909 architectural finishing coating materials. The coating material prescribed | regulated to material RE, waterproof type multilayer coating material RS, etc. is mentioned. For example, JIS
Examples of the waterproof coating material for A6021 include an acrylic rubber-based, chloroprene rubber-based, and urethane rubber-based waterproof coating material. Moreover, as waterproof type multi-layer coating material E of JIS A6909 building finish coating material, waterproofing of synthetic resin emulsion-type multi-layer coating material using a single or mixture of synthetic resin emulsions such as acrylic and vinyl acetate as a binder. As a waterproof type multi-layer coating material RS, a waterproof type of a synthetic resin solution-type multi-layer coating material using a single or mixture of reaction-curing solvent-based resins such as epoxy and urethane as a binder, Examples of the waterproof multi-layer coating material RE include a waterproof type of a reactive curable synthetic resin emulsion-based multi-layer coating material having a reactive curable synthetic resin emulsion such as an epoxy-based binder as a binder.

The elastic coating material forms a film having a pigment volume concentration (hereinafter referred to as “PVC”) of preferably 20 to 70%, more preferably 30 to 65%, and still more preferably 35 to 60%. is there. When PVC is in such a range, the followability, heat resistance, and durability are excellent, and the effects of the present invention can be sufficiently exhibited.
Further, the elastic coating material preferably has a viscosity of 3 to 120 Pa · s, more preferably 5 to 100 Pa · s, and a thixotropic index (TI value) of preferably 2 to 7, more preferably 3 to 6. . In such a case, excellent workability can be exhibited and a film can be efficiently formed in a complicated shape such as the edge portion of the bolt in the bolt joint region or between the bolts.

In addition, the viscosity said here is a measured value when using a BH type viscometer as a measuring device, setting the rotation speed to 20 rpm, and measuring temperature to 23 ° C. (guide value of the rotation). The TI value is a value obtained from the following formula (Formula 1) using a BH viscometer.
TI value = η1 / η2
(Formula 1)
However, η1: viscosity at 2 rpm (Pa · s: guide value for the second rotation), η2: viscosity at 20 rpm (Pa · s: guide value for the fourth rotation)

<Coating method>
The method for coating a steel structure having a bolt joint according to the present invention includes at least the following two steps. According to this method, excellent water resistance, durability, and heat resistance can be exhibited at the bolt joint.
(I) The process of apply | coating the resin composition containing a synthetic resin and a phosphorus compound with respect to a bolt junction part area | region, and forming a film (X),
(II) Next, the step of laminating the elastic coating material (Y) on the coating (X)

  In this invention, unless the effect of this invention is inhibited, a rust preventive primer can also be applied with respect to a bolt junction area | region before the said (I) process. A well-known thing can be used as a rust preventive primer.

In the said (I) process, a resin composition is uniformly apply | coated with respect to a bolt junction part area | region, and a film (X) is formed. The thickness of the coating (X) may be appropriately set according to the application site and the like, but is preferably about 0.2 to 10 mm, more preferably about 0.5 to 6 mm.
By forming the coating (X), excellent heat resistance can be exhibited when exposed to high temperatures such as in a fire.

In the above (I), when applying the resin composition, for example, a method using means such as spray, roller, trowel, brush coating, etc. can be employed. Moreover, what is necessary is just to perform normally at normal temperature, when drying a resin composition.

In (II) above, as a method of laminating the elastic coating material (Y) on the coating (X), for example, at least the elastic coating material may be applied to the coating (X). The thickness of the elastic coating material may be set as appropriate according to the application site and the like, but the dry film thickness is preferably about 0.3 to 2 mm, more preferably about 0.5 to 1.5 mm.

Moreover, an intermediate coating layer can be provided as needed. When such an intermediate coating layer is used, the elastic coating material is laminated after laminating the intermediate coating material on the coating (X). Such an intermediate coating material is not particularly limited as long as it does not impair the effect of the coating (X). For example, an acrylic, urethane, epoxy, chlorinated polyolefin-based intermediate coating material, or an aqueous intermediate coating material. Etc. can be used. What is necessary is just to set the thickness of an intermediate coating layer suitably.

Furthermore, if the elastic coating material (Y) is within a range that does not significantly impair the effects of the present invention, it is desirable to provide a finishing layer on the elastic coating material for the purpose of improving surface protection, designability, and the like. Such a finishing material is not particularly limited as long as it can be in close contact with the elastic covering material.
K 5654 “Acrylic resin enamel”, JIS K 5656 “Polyurethane resin paint for construction”, JIS K 5658 “Fluorine resin paint for construction”, JIS K 5660 “Glossy synthetic resin emulsion paint, JIS”
K 5663 “Synthetic Resin Emulsion Paint”, JIS K 5667 “Multicolored Paint”, JIS K 5668 “Synthetic Resin Emulsion” and the like are preferable. What is necessary is just to set the thickness of a finishing material suitably.

  As mentioned above, when applying each coating material of an intermediate coating material, an elastic coating material, and a finishing material, the method using the means similar to the coating method of the said resin composition is employable. Moreover, what is necessary is just to perform normally at normal temperature, when drying each coating material.

  Examples are given below to clarify the features of the present invention.

<Resin composition>
The following were used as raw materials.
Synthetic resin 1: acrylic styrene resin (Ac: St = 17: 83, weight average molecular weight 68000, acid value 3 mgKOH / g)
Synthetic resin 2: acrylic styrene resin (Ac: St = 33: 67, weight average molecular weight 76000, acid value 3 mgKOH / g)
Synthetic resin 3: acrylic styrene resin (Ac: St = 44: 56, weight average molecular weight 74000, acid value 3 mgKOH / g)
Synthetic resin 4: acrylic styrene resin (Ac: St = 60: 40, weight average molecular weight 79000, acid value 3 mgKOH / g)
Synthetic resin 5: acrylic styrene resin (Ac: St = 82: 18, weight average molecular weight 66000, acid value 3 mgKOH / g)
Synthetic resin 6: acrylic styrene resin (Ac: St = 44: 56, weight average molecular weight 95000, acid value 3 mgKOH / g)
Synthetic resin 7: acrylic styrene resin (Ac: St = 44: 56, weight average molecular weight 72000, acid value 7 mgKOH / g)
Synthetic resin 8: acrylic styrene resin (Ac: St = 44: 56, weight average molecular weight 71000, acid value 1 mgKOH / g)
Synthetic resin 9: acrylic styrene resin (Ac: St = 44: 56, weight average molecular weight 69000, acid value 20 mgKOH / g)
Synthetic resin 10: acrylic styrene resin (Ac: St = 44: 56, weight average molecular weight 70000, acid value 0 mgKOH / g)
Synthetic resin 11: acrylic styrene resin (Ac: St = 44: 56, weight average molecular weight 28000, acid value 3 mgKOH / g)
Synthetic resin 12: acrylic resin (Ac: St = 100: 0, weight average molecular weight 67000, acid value 3 mgKOH / g)
Phosphorus compound: ammonium polyphosphate Polyhydric alcohol: dipentaerythritol Nitrogen compound: melamine Filler: titanium oxide In addition, Ac in the synthetic resins 1 to 12 represents (meth) acrylic acid alkyl ester, and St represents styrene. In the synthetic resins 1 to 11, isobutyl methacrylate and 2-ethylhexyl acrylate are included as Ac. The synthetic resin 12 contains methyl methacrylate, isobutyl methacrylate and 2-ethylhexyl acrylate as Ac. Each synthetic resin other than the synthetic resin 10 is copolymerized with methacrylic acid.

(Resin composition 1)
100 parts by weight of synthetic resin 1, 400 parts by weight of a phosphorus compound, 75 parts by weight of a polyhydric alcohol, 75 parts by weight of a nitrogen-containing compound and 90 parts by weight of a filler are mixed, and xylene is added so that each component is uniform. The resin composition 1 was obtained by stirring.

(Resin compositions 2 to 12)
Resin compositions 2 to 12 were obtained in the same manner as the resin composition 1 except that synthetic resins 2 to 12 were used instead of the synthetic resin 1.

<Elastic covering material>
(Elastic coating 1)
JIS A 6909 waterproof multilayer coating material E Main material (PVC 42%, viscosity 45 Pa · s, TI value 3.6, elongation rate 320%, water permeability less than 0.1 ml / 24h)
(Elastic covering material 2)
JIS A 6909 waterproof multi-layer coating material E Main material (PVC 58%, viscosity 40Pa · s, TI value 3.4, elongation 210%, water permeability less than 0.1ml / 24h)

(Test Example 1)
As a steel structure having bolt joints, a base material in which bolts were attached to steel plates (150 mm × 300 mm × 1.6 mm) at intervals of 50 mm was used. The height from the steel plate to the bolt head is 20 mm.
The resin composition 1 was applied to the bolt joint region with a spray and a brush so that the dry film thickness was about 1 mm, and dried for 7 days at a temperature of 20 ° C. and a relative humidity of 65%.
Next, the elastic coating material 1 was applied so as to have a dry film thickness of about 0.5 mm, and dried for 7 days at a temperature of 20 ° C. and a relative humidity of 65%. The test body was evaluated as follows. The results are shown in Table 1.

・ Evaluation 1 (rust prevention test)

The test specimen was subjected to a salt spray resistance test for 120 hours by the method described in JIS K 5400: 1990 9.1. Evaluation is as follows.
A: No swelling or peeling of the coating film was found, and no rust was found.
B: Almost no occurrence of rust was found.
C: A part of rust was observed.
D: Swelling / peeling of the coating film was observed and generation of rust was observed.

・ Evaluation 2 (heating test)
A heater at 600 ° C. was installed on the resin composition coating surface side of the test body 1 and the state of the coating (expandability, denseness) after heating for 15 minutes was observed. Evaluation is as follows.
(Expandable)
A: The thickness after heating is 20 times or more B: The thickness after heating is less than 10 to 20 times C: The thickness after heating is less than 10 times (dense)
A: The inside of the porous carbonized layer is dense B: Cavities are observed in a part of the inside of the porous carbonized layer C: Many cavities are observed in the inside of the porous carbonized layer

(Test Examples 2 to 14)
Next, using the resin composition and the elastic coating material shown in Table 1, a test body was prepared in the same manner as in Test Example 1, and the same evaluation as in Test Example 1 was performed on the obtained test body. The results are shown in Table 1.

DESCRIPTION OF SYMBOLS 1 ... Steel-frame member which has a bolt junction part 2 ... Bolt junction part 3 ... Bolt junction part area | region 4 ... Bolt 5 ... Nut 6 ... Splice plate 7 ... Beam 8 ... Coating (X)
9 ... Elastic covering material (Y)

Claims (2)

A method for coating a steel member having a bolt joint,
Applying a resin composition containing a synthetic resin and a phosphorus compound to the bolt joint region to form a film (X);
Next, a step of laminating the elastic coating material (Y) on the coating film (X),
A coating method comprising: A resin composition containing the synthetic resin and the phosphorus compound,
As a synthetic resin,
It is a polymer of a monomer group containing an alkyl group (meth) acrylic acid alkyl ester having an alkyl group having 4 or more carbon atoms and an aromatic monomer, and includes a synthetic resin having a polymerization average molecular weight of 50,000 or more. The coating method according to claim 1

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