JPH0243847Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a metal weld structure, and more particularly to a weld structure in which the weld is covered with a coating layer made of a fluorine-based polymer.

[Conventional technology]

Conventionally, galvanized iron plates, copper plates, stainless steel plates, etc. have been used as roofing materials, and these are used by welding together multiple pieces of a certain size.

Since the galvanized iron plates are galvanized, there is no need to paint them for a certain period of time after installation.

Furthermore, since copper plates are protected by an oxide film formed on their surfaces, they are often used as is without any coating.

Stainless steel is broadly classified into martensitic, ferrite, and austenitic types depending on its type. When the surface of stainless steel is corroded by coming into contact with moisture or liquid media, a thin but strong and dense oxide film forms on the surface. Since it protects the steel and prevents further corrosion, it is generally considered to have excellent corrosion resistance. Because of this, in the 1980s,
As mentioned in Publication No. 15466, stainless steel sheets have recently come into widespread use as roofing materials, and because of their excellent corrosion resistance, they do not need to be painted.

[Problem that the invention attempts to solve]

However, the oxide film that protects copper plates and stainless steel is strong against oxidizing acids such as nitric acid, but weak against non-oxidizing acids. Preventive measures need to be taken.

In addition, in a welded part of metal, the metal structure changes due to the influence of welding heat, resulting in embrittlement and deterioration of corrosion resistance. Looking at stainless steel as an example, austenitic Cr-Ni stainless steel,
When welding using a welding metal (welding rod), the third
As shown in the figure, a region b, which is coarse-grained but heated above the solution heat treatment temperature, is formed adjacent to the weld metal a, and a region b of 480 to 680
A portion c is formed which is heated to a temperature of 0.degree. C. and undergoes grain boundary precipitation of carbides to some extent. When this grain boundary precipitated portion c is used in a corrosive atmosphere, intergranular corrosion occurs, causing so-called weld decay. Therefore, it is necessary to protect such grain boundary precipitated portions c from a corrosive atmosphere.

In addition, when welding is performed using a welding rod, the weld metal is made up of materials with different chemical compositions and microstructures, so its corrosion resistance is lower than that of the base metal, and selective corrosion often occurs in the welded area. .

Furthermore, since stainless steel is expensive, the use of high-grade austenitic Cr-Ni steel is often limited and cheaper stainless steel is substituted for other parts, and when welding such dissimilar metals, the weld metal is Its chemical components are diluted for wood,
This may cause problems in corrosion resistance.

The present invention was devised in view of these points, and its technical problem is to provide a metal welded portion with excellent corrosion resistance.

[Means for solving problems]

That is, the gist of the present invention is that, as shown in FIGS. 1 and 2, a welded part 1 of a metal 3 is covered with a coating layer 2 whose main component is a specific fluorine-based polymer. A specific fluorinated polymer is a copolymer consisting essentially of (a) a fluoroolefin, (b) a vinyl ether, and (c) an organosilicon compound having an olefinic unsaturated bond and a hydrolyzable group. It is a combination, at least a part of which is crosslinked.

[Effect]

Since the metal weld is covered with a coating layer mainly composed of a fluorine-based polymer which is inherently durable, it is protected from various external destructive factors.

Here, the welded area to be covered with the fluoropolymer refers to the welded heat affected zone which is at least affected by welding heat. The structure of this weld differs depending on the welding method, and there are cases in which stainless steels are directly welded together, and structures in which stainless steels are joined together using a welding rod with the intervening welding rod.

The metal to be welded can be any type of metal. Examples include galvanized iron plates, copper plates, and stainless steel plates. There are martensitic, ferritic, and austenitic stainless steels.
In particular, it is effective to cover austenitic stainless steel, which is prone to intergranular corrosion due to grain boundary precipitation in the weld heat affected zone, with a coating layer containing the fluoropolymer as a main component according to the present invention.

Further, the metals to be welded may be dissimilar metals such as martensitic stainless steel on one side and austenitic stainless steel on the other.

When using a welding rod for welding, the material of the welding rod is preferably one whose chemical composition is as close as possible to the metal base material to be welded. This is because if different chemical components are used, the chemical components will migrate from the metal base material to the weld metal, or from the weld metal to the metal base material, and the corrosion resistance will deteriorate in areas where the chemical components are diluted. However, in this invention, the welded part is covered with a coating layer mainly composed of fluorine-based polymer, so
It is not necessarily necessary to be particular about the material of the welding rod.

Further, the welding method is not particularly limited, and various welding means such as coated arc welding, inert gas arc welding, and submerged arc welding may be used.

Incidentally, the fluoropolymer used in the present invention is a random copolymer consisting of at least the above-mentioned three types of monomer component units a, b, and c, but a small amount of other copolymers may be used as long as the purpose of the present invention is not impaired. Polymerizable monomer components such as α-olefins, cycloolefins, unsaturated carboxylic acids, etc. may be copolymerized.

Fluoroolefin a, which is a monomer component constituting the fluoropolymer, contains at least one
Perhaloolefins having fluorine atoms, preferably all hydrogen atoms of the olefin are substituted with fluorine atoms and other halogen atoms, and perfluoroolefins are particularly preferred. Furthermore, from the viewpoint of polymerizability and properties of the produced polymer, fluoroolefins having 2 or 3 carbon atoms, particularly perfluoroolefins, are preferred.

Examples of such fluoroolefins are _CF2 = _CF2 , CHF= _CF2 , _CH2 = _CF2 , _CH2 =
CHF, CClF= _CF2 , CHCl= _CF2 , _CCl2 = _CF2 ,
CClF=CClF, CHF= _CCl2 , _CH2 =CClF, _CCl2
= Fluoroethylene type such as CClF, CF ₃ CF = CF ₂ ,
CF ₃ CF=CHF, CF ₃ CH=CF ₂ , CF ₃ CF=CH ₂ ,
CF ₃ CF=CHF, CHF ₂ CF=CHF, CF ₃ CH=
CH ₂ , CH ₃ CF=CF ₂ , CH ₃ CH=CF ₂ , CH ₃ CF=
CH ₂ , CF ₂ ClCF=CF ₂ , CF ₃ CCl=CF ₂ , CF ₃ CF
= CFCl, CF ₂ ClCCl = CF ₂ , CF ₂ ClCF = CFCl,
CFCl ₂ CF=CF ₂ , CF ₃ CCl=CClF, CF ₃ CCl=
CCl ₂ , CClF ₂ CF=CCl ₂ , CCl ₃ CF=CF ₂ ,
CF ₂ ClCCl=CCl ₂ , CFCl ₂ CCl=CCl ₂ , CF ₃ CF=
CHCl, CClF ₂ CF=CHCl, CF ₃ CCl=CHCl,
CHF ₂ CCl=CCl ₂ , CF ₂ ClCH=CCl ₂ , CF ₂ ClCCl
=CHCl, CCl ₃ CF=CHCl, CF ₂₁ CF=CF ₂ ,
CF ₂ BrCH=CF ₂ , CF ₃ CBr=CHBr, CF ₂ ClCBr
＝CH ₂ C ₂ BrCF＝CCl ₂ , CF ₃ CBr＝CH ₂ , CF ₂ CH
= CHBr, CF ₂ BrCH = CHF, CF ₂ BrCF = fluoropropene such as CF ₂ , CF ₃ CF ₂ CF = CF ₂ ,
CF ₃ CF=CFCF ₃ , CF ₃ CH=CFCF ₃ , CF ₂ =
CFCF ₂ CHF ₂ , CF ₃ CF ₂ CF=CH ₂ , CF ₃ CH=
CHCF ₃ , CF ₂ = CFCF ₂ CH ₃ , CF ₂ = CFCH ₂ CH ₃
CF ₃ CH ₂ CH=CH ₂ , CF ₃ CH=CHCH ₃ , CF ₂ =
CHCH ₂ CH ₃ , CH ₃ CF ₂ CH=CH ₂ , CFH ₂ CH=
CHCFH ₂ , CH ₃ CF ₂ CH=CH ₃ , CH ₂ =
CFCH ₂ CH ₃ , CF ₃ (CF ₂ ) ₂ CF=CF ₂ , CF ₃
Examples include fluoroolefin systems having 4 or more carbon atoms, such as (CF ₂ ) ₃ CF=CF ₂ .

Among these, as mentioned above, fluoroethylene and fluoropropene are preferred, particularly tetrafluoroethylene (CF ₂ = CF ₂ ), hexafluoropropene (CF ₂ = CFCF ₃ ), and chlorotrifluoroethylene (ClFC = CF _{2 ).} ) is preferred;
Furthermore, from the viewpoint of safety and ease of handling, hexafluoropropene and chlorotrifluoroethylene are preferred.

Furthermore, in the present invention, it goes without saying that fluoroolefins may be used alone or in combination.

Vinyl ether b includes a vinyl group, an alkyl (including cycloalkyl) group, an aryl group,
It is a compound in which aralkyl groups, etc. are bonded to ether, and among them, alkyl vinyl ether,
Particularly suitable are alkyl vinyl ethers bonded to alkyl groups having 8 or less carbon atoms, preferably 2 to 4 carbon atoms. Furthermore, alkyl vinyl ethers in which the alkyl group is in the form of a chain are most preferred.

Examples of such vinyl ethers include ethyl vinyl ether, propyl vinyl ether, isopropyl ether, butyl vinyl ether, tert-
Chain alkyl vinyl ethers such as butyl vinyl ether, pentyl vinyl ether, hexyl vinyl ether, isohexyl vinyl ether, octyl vinyl ether, 4-methyl-1-pentyl vinyl ether, cycloalkyl vinyl ethers such as cyclopentyl vinyl ether, cyclohexyl vinyl ether, phenyl vinyl ether, o- , m-,p-chlorophenyl vinyl ether, aryl vinyl ethers, benzyl vinyl alkyl vinyl ether, phenethyl vinyl ether, and other aralkyl vinyl ethers.

Among these, chain alkyl vinyl ethers and cycloalkyl vinyl ethers are particularly preferred, and ethyl vinyl ether, propyl vinyl ether, and butyl vinyl ether are more preferred.

Furthermore, in the present invention, it goes without saying that the vinyl ether may be used alone or in combination.

The organosilicon compound c may be one having an olefinic unsaturated bond and a hydrolyzable group in the molecule, and specifically, those shown in the following general formulas (1) to (3) are exemplified. Can be done.

R ¹ R ² SiY ¹ Y ² (1) R ¹ XSiY ¹ Y ² (2) R ¹ SiY ^{1 Y} 2 Y ³ (3) (In the formula, R ¹ and R ² have olefinic unsaturated bonds and , hydrogen and optionally oxygen, each of which is the same or different; X is an organic group having no olefinic unsaturated bond; Y ¹ , Y ² , Y ³ are each the same or different hydrolyzable ) More specific examples of R ¹ and R ² include vinylallyl, butenyl, cyclohexenyl,
Cyclopentadienyl is preferred, and terminal olefinically unsaturated groups are particularly preferred. Other preferred examples include _CH2 =C(CH3)COO( _CH2 ) _3- , _CH2 =C( _CH3 )COO( _CH2 )3-, which has an ester bond of an unsaturated acid at the other end, CH2=CH-O-( _CH2 ) _3- C ( _CH3 )
COO( _CH2 ) ₂ -O-( _CH2 ) _3- , Examples include groups such as. Among these, vinyl groups are most suitable. Specific examples of X include monovalent hydrocarbon groups such as methyl, ethyl, propyl, tetradecyl, octadecyl,
Groups include phenyl, benzyl, tolyl, etc., and these groups may also be halogen-substituted hydrocarbon groups.

Specific examples of Y ¹ , Y ² and Y ³ include alkoxy groups such as methoxy, ethoxy, butoxy and methoxyethoxy, alkoxyalkoxy groups, acyloxy groups such as formyloxy, acetoxy and propionoxy, oximes such as -
ON=C( _CH3 ) ₂ , _-ON = _CHCH2C2H5 and _-
ON=C( _{C6H5 ) 2} , or substituted amino and arylamino groups such as _{-NHCH3 , -NHC2H5}
and -NH (C ₆ H ₅ ), and any other hydrolyzable organic groups.

Preferably used organosilicon compounds have general formula (3)
It is a compound represented by, especially the groups Y ¹ , Y ² , Y ³
Organosilicon compounds having the same values are suitable. Among these, R ¹ is a vinyloxyalkyl group (CH ₂ =CH-
O-( _CH2 )n-) or a vinyl group, and Y1 ^~
It is preferable that Y ³ is an alkoxy group or an alkoxyalkoxy group, such as vinyloxypropyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(methoxyethoxy)silane, and the like.
However, vinylmethyldiethoxysilane, vinylphenyldimethoxysilane, etc. can be used as well.

The content ratio of monomer components (a) to (c) in the fluorine-based polymer is based on the total number of moles of (a) to (c).
(a): 30-70 mol%, (b): 20-60 mol%, (c): 1-
80 mol% ((a)+(b)+(c)=100), preferably
(a): 40-60 mol%, (b): 20-50 mol%, (c): 1-
It is in the range of 25 mol%.

Here, (a) is 30 to 70 mol%, which means 30 mol%
If it is less than 1 mol%, the durability will be poor, and if it is more than 70 mol%, the adhesion to metal will be poor. This is because it is difficult to form a film, and stability deteriorates when the amount exceeds 80 mol%.

The fluoropolymers used in this invention are those listed in (a) to (c) above.
It is produced by copolymerizing each of the monomers in the presence of a well-known radical initiator (or by heating in its absence). Here, each component (a) to (c) is important, for example, component (a) and (c)
Copolymerization does not occur when the components alone are used, but when component (b) is added, components (a), (b), and (c) are copolymerized.

Various known radical initiators can be used for copolymerization. Specifically, organic peroxides, organic peresters such as benzoyl peroxide, dichlorobenzoyl peroxide,
Dicumyl peroxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di(peroxybenzoate) hexyne-3,1,4-bis(tert-butylperoxyisopropyl)benzene, lauroyl peroxide, tert-butyl Peracetate, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3,2,
5-dimethyl-2,5-di(tert-butylperoxy)hexane, tert-butyl perbenzoate, tert-butyl perphenylacetate, tert
-butyl perisoptylate, tert-butylber-sec-octoate, tert-butyl perpivalate, cumyl perpivalate, tert-butyl perdiethyl acetate, etc., and other azo compounds such as azobis-isobutylnitrile, dimethyl azoisobutyrate. and so on. Among these, dicumyl peroxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3,2,5-dimethyl-2,5-di(tert- Dialkyl peroxides such as butylperoxy)hexane and 1,4-bis(tert-butylperoxyisopropyl)benzene are preferred.

The copolymerization takes place in a reaction medium consisting of an organic solvent. The solvents used here include aromatic hydrocarbons such as benzene, toluene, and xylene, aliphatic hydrocarbons such as n-hexane, cyclohexane, and n-heptane, and chlorobenzene, bromobenzene, iodobenzene, and o-bromotoluene. Examples include halogenated aromatic hydrocarbons, halogenated aliphatic hydrocarbons such as tetrachloromethane, 1,1,1-trichloroethane, tetrachloroethylene, and 1-chlorobutane.

Copolymerization is carried out by adding the radical initiator in the above solvent in a molar ratio of 10 ² to 2×10 ³ based on the total number of moles of monomers. Also, the polymerization temperature is -30 to 200
℃, preferably 20~100℃, polymerization pressure 0~100℃
Kg/cm ² ·G, preferably 0 to 50 kg/cm ² ·G.

The molecular weight of the fluoropolymer thus obtained was determined by gel permeation chromatography (GPC) using tetrahydrofuran as a solvent and monodisperse polystyrene of known molecular weight as a standard substance. It is desirable that the number average molecular weight (Mn) is usually 3,000 to 200,000, preferably 5,000 to 100,000. If the molecular weight is less than 300, it is generally difficult to form a coating layer, and if it exceeds 200,000, solvent solubility is often poor. By adopting the above composition ratio and the molecular weight described here, it becomes solvent-compatible, and after being cured by the method described below, it has excellent solvent resistance, chemical resistance, heat resistance, weather resistance, and even mechanical resistance. It has excellent physical properties. Another property of fluorine-based polymers is that they are amorphous or have low crystallinity, and many are amorphous. In general, the degree of crystallinity measured by X-rays is 0%, and in many cases no melting point can be observed using a differential scanning calorimeter (DSC). Therefore, transparency is good.

The glass transition temperature (Tg) is usually -60 to +20°C, often -40 to +5 when measured by DSC at a heating rate of 10°C/min after cooling the sample to -120°C.
in the range of ℃.

A carboxyl cap may be introduced into the molecular chain of the fluorine-based polymer used in the present invention in order to further improve the affinity with organic pigments and the like. One example is a method of graft polymerizing unsaturated carboxylic acids and their derivatives. Examples of unsaturated carboxylic acids used for this purpose include acrylic acid, methacrylic acid, α-ethyl acrylic acid, maleic acid, Fumaric acid, itaconic acid, citraconic acid, tetrahydrophthalic acid, methyltetrahydrophthalic acid, endocys-bicyclo[2,2,1]
Hept-5-ene-2,3-dicarboxylic acid (nadic acid), methyl-endocys-bicyclo[2,
2,1] Unsaturated carboxylic acids such as hept-5-ene-2,3-dicarboxylic acid (methylnadic acid), halides, amides, imides, acid anhydrides, esters of the unsaturated carboxylic acids, i.e. maleyl chloride, maleimide, Examples include maleic anhydride, citraconic anhydride, monomethyl maleate, and dimethyl maleate.

The above-mentioned fluorine-based polymers are soluble in organic solvents at room temperature, such as aromatic hydrocarbons such as benzene, toluene, and xylene, acetone, ketones such as methyl ethyl ketone,
It dissolves in ethers such as dimethyl ether, diethylether, and dipropyl ether, alcohols such as methanol and ethanol, and halogenated hydrocarbons such as tokuchloroethane, dichloroethane, and chlorobenzene.

Therefore, using a solution of a fluoropolymer in an organic solvent, the fluoropolymer is applied to the surface of the metal weld by a method such as spraying, brushing, or roll coating, and then dried. As a result, the welded part structure of the present invention is obtained.

By the way, since the fluorine-based polymer has a hydrolyzable organic group derived from the organosilicon compound C, when exposed to moisture, a cross-linking reaction occurs between the molecular chains of the polymer and the polymer is cured. Therefore,
Naturally, crosslinking can also occur due to atmospheric moisture. Although it is clear that crosslinking will proceed even if the fluoropolymer is used alone, it is preferable to add a silanol condensation catalyst so that the fluoropolymer film applied to the welded area is rapidly cured.

In this case, a silanol condensation catalyst is added in advance to an organic solvent solution in which a fluoropolymer is dissolved.
When this is applied to a welded area, the organic solvent evaporates and a curing reaction occurs at the same time as it comes into contact with moisture in the air, causing the coating layer to harden.

Known silal catalysts can be used, such as carboxylic acid metal salts such as dibutyltin dilaurate, stannous acetate, stannous octoate, lead naphthenate, iron 2-ethylhexanoate, cobalt naphthenate, and organic bases. Examples include acids such as ethylamine, hexylamine, dibutylamine, piperidine, mineral acids and organic fatty acids. Suitable catalysts are alkyltin salts of carboxylic acids, such as dibutyltin dilaurate, dibutyltin dioctoate, diptyltin diacetate.

The cross-linking reaction progresses well at room temperature (0 to 40℃), but if the weld is applied while the temperature is still high,
A coating layer may be formed at a high temperature to promote the crosslinking reaction. The thickness of the coating layer is usually about 25 μm to 2 mm, and preferably about 50 to 500 μm. In order to improve the adhesion or adhesion of the fluoropolymer to the surface of the weld, it is preferable that the surface of the weld is subjected to a surface treatment such as coating with a primer or degreasing. As the primer, Unistol-Q (manufactured by Mitsui Petrochemical Industries, Ltd.) and the like are suitable. Further, other suitable primers include titanium-based primers such as titanium tetrabutoxide (for example, Orgatics TA-25 manufactured by Matsumoto Pharmaceutical Co., Ltd.) and silane-based primers such as Tosprime A manufactured by Toshiba Silicone Corporation.

The coating layer made of fluorine-based polymer after curing (after being left for 14 days after application) conforms to JIS K 5400 (1979).
Pencil hardness according to 6.16 is usually 3H to 2B, often H to
It is in the B range, and the bending resistance according to JIS K (1979) 6.16 usually passes 3 mmφ, and most pass 2 mmφ.

In addition, when applying a fluorine-based polymer to the welded area, pigments and dyes may be added.
Furthermore, various additives that are usually blended into synthetic resins may be blended as necessary.

〔Example〕

The contents of the present invention will be explained below using preferred examples, but unless otherwise specified, the present invention is not limited to these examples, and any embodiments may be made without detracting from the purpose of the present invention. be.

<Example 1> 80 g of benzene, 25.2 g of butyl vinyl ether (BVE), 7.1 g of trimethoxy vinyl silane (TMVS), and 1 g of dilauroyl peroxide were placed in a stainless steel autoclave with an internal volume of 300 c.c. and equipped with a stirrer, followed by acetone and dry ice. Solidification and degassing are performed to remove oxygen from the system. Thereafter, 45 g of hexafluoropropene (HFP) is introduced into the autoclave and the temperature is raised. When the temperature inside the autoclave reached 65°C, the pressure was 8.1 Kg/cm ² . The reaction continued for 8 hours with stirring until the pressure reached 4.6
When the temperature reached Kg/cm ² , the autoclave was cooled with water to stop the reaction. After cooling, unreacted monomers were expelled, the autoclave was opened, and the reaction solution was taken out. After concentration, the mixture was washed with a benzene-methanol mixed solvent, concentrated again, and dried. Polymer yield is 60
It was hot at g.

The number average molecular weight of the obtained polymer by GPC was 1.0×10 ⁴ and the glass transition point was -14°C.

The compositional analysis of this copolymer was performed using elemental analysis and NMR.
HFP/BVE/TMVS=
The molar ratio was 48/40/12.

A solution was prepared in which 5 kg of the polymer thus obtained and 0.25 kg of tetramethylorthosilicate were dissolved in 3.3 kg of xylene, and 7.9 g of dibutyltin diurarate (DBTDL) was added thereto.

On the other hand, as shown in Fig. 1, a pair of stainless steel plates 3 with their ends erected are welded by inert gas arc welding using argon gas, and after applying an epoxy primer to this welded part, the above-mentioned foot A toluene solution of a base polymer was applied and air-dried at room temperature to form a weld structure having a coating layer (thickness: 55 μm) made of a fluoropolymer on the surface.

The gloss retention rate of this coating layer was measured based on JIS-K-5400. As a result, the gloss retention rate after 3600 hours was 96%, showing excellent performance.

<Example 2> In the same manner as in Example 1, n-butyl vinyl ether (BVE), ethyl vinyl ether (EVE), trimethoxyvinylsilane (TMVS), chlorotrifluoroethylene (CTFE), and dilauroyl peroxide (DLPO) were used. Polymer B was obtained by polymerization.

The GPC equivalent number average molecular weight of this polymer B is 0.85×
10 ⁴ and the glass transition point was -8°C.

In addition, the composition of polymer B is CTFE/
EVE/BVE/TMVS=48/38/7/7.

A solution was prepared by dissolving 5 kg of Polymer B in 2.25 kg of toluene and adding 0.25 kg of tetolmethyl orthosilicate (Methyl Silicate 39, manufactured by Colcoat Co., Ltd.) and 8 g of dibutyltin dilaurate.

Apply this to the welded area in the same manner as in Example 1,
A coating layer (20 μm thick) was formed.

The gloss retention rate of this coating layer was measured in the same manner as in Example 1. As a result, the gloss retention rate after 3600 hours was 96%, showing excellent performance.

[Effects of the invention] According to the invention, since the welded part is covered with a coating layer mainly composed of a fluorine-based polymer, it is possible to weld metals with excellent durability such as corrosion resistance, chemical resistance, and water resistance. The partial structure is obtained.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing an example of the weld structure according to the present invention, Fig. 2 is a sectional view showing another example of the weld structure, and Fig. 3 is a sectional view showing the structure of the weld heat affected zone of austenitic stainless steel. FIG. 1... Welded part, 2... Covering layer.

Claims (1)

[Claims for Utility Model Registration] (1) A metal welded part made of (a) a fluoroolefin, (b) a vinyl ether, (c) an organosilicon compound having an olefinic unsaturated bond and a hydrolyzable group; A coating layer of a fluorine-containing polymer, characterized in that the coating layer is a copolymer consisting essentially of a fluorine-containing polymer and is covered with a coating layer whose main component is a fluorine-containing polymer which is at least partially crosslinked. Metal welded structure with. (2) A metal welded structure having a coating layer of a fluoropolymer according to claim 1, wherein the crosslinking of the fluoropolymer is carried out in the presence of a silanol catalyst. .