JP2015175002A - Electric anticorrosion apparatus for outer surface of steel building structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric anticorrosion apparatus for outer surfaces of steel building structures which is usable in electric anticorrosion of outer surfaces of steel building structures exposed to the atmosphere and is provided with a conductive coating film excellent in water and weather resistances.SOLUTION: An electric anticorrosion apparatus includes one or more anticorrosion coating films 2 and 3 applied to the outer surface of a steel building structure 1 exposed to the atmosphere, a conductive coating film applied to the outermost layer or interlayer of anticorrosion coating films and a power source flowing a DC current with the steel building structure as the cathode and the conductive coating film as the anode, and the conductive coating film is an ion conductive coating film 4 containing, as a composition, a graft polymer including a fluororesin ionomer as the trunk and sulfonate groups in side chains.

Description

  The present invention relates to an anticorrosion device for an outer surface of a steel building, and specifically, steel having an outer surface exposed to the air such as a steel tank, a bridge, a steel frame, a piping facility, a power device, a crane, and the like. The present invention relates to anticorrosion technology for the outer surface of buildings.

  In general, corrosion prevention of an outer surface of a steel structure exposed to the air is performed by applying a plurality of layers of anticorrosion coating films exclusively on the outer surface. However, for example, it is known that when the relative humidity is 60% or more, moisture in the air is condensed on the surface of the anticorrosion coating film to form a water film. Usually, since a coating film has innumerable pores such as pinholes, rainwater or condensed condensed water enters the pores and corrodes the steel material under the coating film. In particular, when sea salt is contained in the water entering the pores, the corrosion of the steel material is accelerated. In addition, when the anticorrosion coating film is deteriorated with the influence of ultraviolet rays or the like, the anticorrosion performance is impaired, so that there is a problem that the anticorrosion coating film is repaired or repainted earlier.

  In view of this, proposals have been made to apply cathodic protection to the outer surface of steel buildings exposed in the air (Patent Documents 1 to 3). According to these, a conductive coating film is formed on one layer of a plurality of anticorrosion coating films, the conductive coating film is used as an anode, a steel building is used as a cathode, and a direct current is passed between them to steel. The building is protected from corrosion. In other words, even if rainwater or dew condensation water enters the pores of the anticorrosion coating film, the anticorrosion current flows through the water in the pores through the conductive coating film as a current path and flows into the steel building. The potential of the object can be maintained in an inert region of steel corrosion. Thereby, the electric corrosion protection of the steel building outer surface exposed to the air can be performed.

  In Patent Document 3, a hydrophilic coating film having high wettability is formed on the outer surface of a steel building exposed to the air, and a water film formed on the surface of the hydrophilic coating film is used as an anode. It has been proposed to use a building as a cathode and to prevent corrosion of the steel building by passing a direct current between them. That is, a water film is formed on the surface of the hydrophilic coating film by rainwater or condensed water in the air, and the anticorrosive current is applied to the steel building through the water in the pores of the anticorrosion coating film using the water film as a current path. It can be flowed to prevent corrosion.

JP-A-9-268388 JP 11-314309 A JP-A-10-121274

  By the way, in Patent Documents 1 to 3, a resin for forming a coating film is blended with an electronic conductor such as carbon or metal to form a conductive coating film, or water-soluble or water having hydrophilicity such as a sulfone group. A hydrophilic coating film is formed of a binder resin obtained by modifying a dispersible acrylic or epoxy resin.

  However, a conductive coating film in which an electronic conductor such as carbon or metal is blended with a coating resin as described in Patent Documents 1 to 3, or a hydrophilic coating film in Patent Document 3 is an outside of a steel building exposed to the air. There is a problem that sufficient consideration has not been given to water resistance and weather resistance (particularly, UV resistance) required for the surface.

  For example, a conductive coating film containing an electron conductor is simply a physical bond between the electron conductor and the coating resin, so that the water resistance and weather resistance of the coating film deteriorate when exposed to wind and rain or ultraviolet rays. There is a problem that it is easy to do. Further, since hydrophilicity and water resistance are generally contradictory properties, there is a problem that the hydrophilic coating film deteriorates rapidly when exposed to wind and rain or ultraviolet rays. Therefore, the conductive coating film in which the electron conductor is blended or the hydrophilic coating film of Patent Document 3 has a problem that when it deteriorates with the passage of the use period, it peels off and cannot withstand long-term use. In addition, if the water film formed on the outer surface of the hydrophilic coating film is uneven, there is a problem that the entire surface cannot be protected.

  The problem to be solved by the present invention is to provide an anti-corrosion device that can be used for the anti-corrosion of the outer surface of a steel structure exposed in the air and has a conductive coating film excellent in water resistance and weather resistance. There is.

  In order to solve the above-mentioned problems, an electro-corrosion protection device for an outer surface of a steel building according to the present invention comprises at least one anti-corrosion coating film applied to the outer surface of the steel building exposed to the air, and the anti-corrosion coating film. A conductive coating film applied between the outermost layer or the interlayer and a power source for passing a direct current using the steel structure as a cathode and the conductive coating film as an anode, and the conductive coating film is mainly composed of a fluororesin ionomer. And an ion conductive coating film containing a graft polymer having a sulfonic acid group in the side chain as a composition.

That is, the fluororesin ionomer has a high C—F bond energy and forms a dense and stable molecular chain. Therefore, it has high crystallinity, excellent water resistance and weather resistance, is highly stable against electrochemical reaction, and is excellent in adhesion to the underlying anticorrosion coating film. In addition, hydrogen ions H ^{+ of} the sulfonic acid group (—SO ₃ H) are liberated and exhibit ionic conductivity. Furthermore, since the sulfonic acid group exhibits excellent hydrophilicity, when it is applied to the outermost layer, a stable water film can be formed and acts as a current path together with the ion conductive coating film. From these things, according to the ion conductive coating film of the present invention, it is possible to form a conductive coating film having excellent anticorrosion on the outer surface of a steel building, and to perform stable anticorrosion over a long period of time. it can. As a result, it is possible to prolong the repair and repaint cycle of the anticorrosion coating film.

  In addition, the ion conductive coating film of the present invention has 100 parts by weight of a photocatalyst mainly composed of a transition metal oxide in 100 parts by weight of a graft polymer composition having a fluororesin ionomer as a main backbone and a sulfonic acid group in the side chain. Can be added within the range not exceeding. According to this, since the hydrophilicity of the ion conductive coating film can be remarkably improved by the photocatalyst, the surface resistance of the ion conductive coating film can be further reduced. As a result, as will be described later, from one anode electrode made of a metal material embedded in the ion conductive coating film, the range of the anticorrosion current that can be evenly flown can be expanded, and the steel construction with a large outer surface area The number of anode electrodes provided on the object can be reduced, or the distance between the anode electrodes can be increased.

  Here, the anode electrode is formed of, for example, a metal material such as aluminum, platinum, or copper, and is attached to the surface of the anticorrosion coating film below the ion conductive coating film with an insulating adhesive, and the ion conductive coating. At least a part of the film is embedded in the film, and can be provided exposed on the outermost surface of the anticorrosion coating film including the ion conductive coating film. According to this, since at least a part of the anode electrode formed of a metal material is embedded in the ion conductive coating film, the electrical connection area between the anode electrode and the ion conductive coating film can be increased. It is possible to flow the anticorrosion current stably. The outer surface of the anode electrode can be covered with a finish coating film.

  ADVANTAGE OF THE INVENTION According to this invention, providing the anticorrosion apparatus provided with the ion conductive coating film excellent in the weather resistance which can be used for the anticorrosion of the outer surface of the steel building which has the outer surface exposed to the air. it can.

It is a block diagram of one Embodiment of the anti-corrosion apparatus of the steel building outer surface of this invention. It is a diagram explaining the result of the comparative test implemented by applying one embodiment of the present invention.

  Hereinafter, the present invention will be described based on embodiments.

  The electro-corrosion protection device for the outer surface of a steel building according to the present invention will be described based on an embodiment in which it is applied to the electro-corrosion protection of the outer surface of a steel tank that stores fluid such as liquid or gas. However, the cathodic protection device for the outer surface of the steel building of the present invention is not limited to the outer surface of the steel tank, and is exposed to the air such as steel bridges, steel frames, piping facilities, electric power equipment, cranes, etc. The present invention can be applied to the anticorrosion of the outer surface of a steel structure having an outer surface.

  FIG. 1 shows a cross section of a part of a side wall 1 of a steel tank and a system configuration of an anticorrosion power source. As shown in the figure, an undercoat anticorrosion coating film 2, an overcoat anticorrosion coating film 3, and an ion conductive coating film 4 are sequentially stacked on the outer surface 1a of the side wall 1 of the steel tank. The anticorrosion coating film 2 is formed by applying a well-known epoxy anticorrosion paint, for example. The anticorrosion coating film 3 is formed by applying a well-known water-repellent paint, for example.

  A part of the anode electrode 5 is embedded in the ion conductive coating film 4. In the present embodiment, the anode electrode 5 is formed of a flat metal material, and is provided by being bonded to the outer surface of the anticorrosion coating film 3 with an adhesive material 6 having electrical insulating properties. The anode electrode 5 is connected to the anode side of the DC power supply 10 via an electric wire (or cable) 7. Further, the cathode side of the DC power supply 10 is electrically connected to the side wall 1 of the steel tank via an electric wire (or cable) 8.

Next, the configuration of the ion conductive coating film 4 will be described in detail. The ion conductive coating film 4 of the present embodiment generates a paint containing Nafion (registered trademark of DuPont) having a molecular structure represented by the following chemical formula 1 as a composition, and is formed on the outer surface of the anticorrosion coating film 3. It is provided by application or the like. Specifically, the ion conductive coating film 4 is composed of a graft polymer having a main component of a tetrafluoroethylene monomer which is one kind of fluororesin ionomer and having a sulfonic acid group (—SO ₃ H) in the side chain. As a coating film. In Formula 1, m and n are both arbitrary integers. Rf is any one of a perfluorinated alkyl chain, an alkyl ether chain, an alkyl ester chain, and a cycloalkyl chain. As an example belonging to a perfluorinated alkyl chain, a perfluoro group having a molecular structure represented by the following chemical formula 2 can be given.

Since the ion conductive coating film 4 containing Nafion (registered trademark of DuPont) as a composition has the following characteristics, it is suitable as a conductive coating film used for the electric protection of the outer surface of the steel structure.
(1) A tetrafluoroethylene monomer, which is a kind of fluororesin ionomer, has a large binding energy of C—F bond and forms a dense and stable molecular chain. Therefore, it has high crystallinity, is excellent in water resistance and weather resistance, and is highly stable against electrochemical reaction (Plastics and Functional Polymer Material Dictionary: Published by Industry Research Association Dictionary Publishing Center, 2004, No. 306) Page).
(2) The sulfonic acid group (—SO ₃ H) liberates hydrogen ions H ⁺ , and Nafion (registered trademark of DuPont), which is a composition of the ion conductive coating film 4 of this embodiment, is used as a solid electrolyte. It has ionic conductivity.
(3) The sulfonic acid group (—SO ₃ H) has excellent hydrophilicity (Patent Document 3).
From these things, according to the ion conductive coating film 4 of this embodiment, forming the conductive coating film which is excellent in the electrocorrosion prevention of the steel building outer surface and excellent in the adhesion with the base anticorrosion coating film. In addition, since water resistance, weather resistance, and conductivity are stable, stable anticorrosion can be performed over a long period of time.

  With reference to FIG. 1, an explanation will be given of the anticorrosion action in the anticorrosion device of the outer surface 1 a of the side wall 1 of the steel tank using the ion conductive coating film 4 of the present embodiment configured as described above. In addition, although this embodiment demonstrates the side wall 1 as an example, it cannot be overemphasized that this invention can be applied not only to a side wall but to the top plate of steel tanks. In general, since a coating film has numerous pores such as pinholes, rainwater or condensed condensed water enters the pores and corrodes the steel material under the coating film. In particular, when sea salt is contained in the water in the pores, the steel material is further corroded. For example, as schematically shown in FIG. 1, pores 9 communicating between the undercoat anticorrosion coating film 2, the topcoat anticorrosion coating film 3, and the ion conductive coating film 4 are formed on the outer surface of the side wall 1 of the steel tank. It is assumed that 1a has been reached. Note that the pores 9 are actually innumerable, but only one is shown in the figure for the sake of simplicity. When water such as rain water or condensed water enters the pores 9 and reaches the outer surface 1a, the iron in the side wall 1 is ionized and eluted in the water in the pores 9 and corrosion proceeds.

  In this respect, according to the present embodiment, the anode voltage 5 of the DC power supply device 10 is applied to the anode electrode 5 embedded in the ion conductive coating film 4 via the electric wire 7, and is made of steel constituting one cathode. A cathode voltage of a DC power supply device 10 is applied to the side wall 1 of the tank via an electric wire 8. In this state, when water such as rain water or dew condensation water enters the pores 9 and reaches the outer surface 1a, the water generally has conductivity, so that the DC power supply 10 to the anode 5 and the ion conductive coating film 4 A current path from the water in the pore 9 to the side wall 1 of the steel tank is formed, and a direct current flows. When the potential of the side wall 1 of the steel tank is lowered to a well-known inactive region of steel corrosion by this direct current, iron of the side wall 1 is suppressed or prevented from being ionized and eluted into the water in the pores 9. Corrosion of steel is prevented. The direct current voltage of the direct current power supply device 10 is adjusted so that the current flowing at this time flows the anticorrosion current required to maintain the potential of the side wall 1 in the inactive region of the steel corrosion.

  Thus, according to this embodiment, even if water such as rain water or dew condensation water enters the pores 9 of the anticorrosion coating films 2 and 3, the ion conductive coating film 4 is used as a current path in the pores. Since the anticorrosion current flows to the side wall 1 of the steel tank through the water, and the potential of the side wall 1 can be maintained in the inactive region of the steel corrosion, the outer surface of the steel building that is a steel tank exposed to the air The anticorrosion can be performed.

With reference to FIG. 2 and Table 1, the result of the comparative test performed by applying this embodiment will be described. In the comparative test, a rectangular flat plate formed in the same way is used as a test piece, as shown in Table 1, as shown in Comparative Examples 1 and 2 and Test Piece No. 3 shown in Test Piece Nos. 1 and 2, Different coating films were formed. Moreover, in each test piece No. 1-3, an anode electrode is stuck to one end part of the longitudinal direction of a flat plate with an insulating adhesive, and the coating film on the other end part is scratched to artificially provide a defective part. Formed. In addition, each test piece No. 1 to 3 was sprayed with salt water (2 hours, 35 ° C., 5% NaCl) → dried (4 hours, 60 ° C., 20-30% RH) → wet (2 hours, 50 ° C.,> 95). The combined cycle consisting of>% RH was repeated. Note that RH is relative humidity. In the cycle process, with respect to the test pieces No. 1 to No. 3, a direct current was passed through the anode electrode, the painted portion and the defective portion of each test piece, and the respective direct currents were measured and recorded. The test results are shown in the graph of FIG. In FIG. 2, the horizontal axis represents time and the vertical axis represents current mA. Moreover, the DC voltage applied between the anode and the coating part of each test piece or the cathode of a defective part is 12V.

In FIG. 2, the comparative example 1 of test piece No. 1 is carrying the electric current by making the water film formed in the coating film surface into an electric current path. In Comparative Example 2 of test piece No. 2, since the water-repellent coating film was formed, water was repelled and a water film as a current path was not formed, so that the necessary current value was not satisfied. On the other hand, in the embodiment of test piece No. 3, since the ion conductive coating film was formed, an anticorrosion current of about 0.8 mA or more flows through the artificial defect portion and about 0.2 mA flows through the coating portion. In this comparative test, since the coating portion has few coating defects such as pores, the anticorrosion current is small. Incidentally, according to the calculation, the anticorrosive current density required for the defective portion was 64 mA / m ² , and the anticorrosive current density of the coated portion with few defects was 1.9 mA / m ² . According to this comparative test, it can be seen that by using the ion conductive coating film of the present embodiment, it is possible to effectively perform the anticorrosion of the outer surface of the steel building exposed to the air.

  In addition, the electric current value of the comparative test mentioned above has a meaning mainly as a relative value of each test piece, and is further applied according to the size of the defect in the artificial defect portion and the number of pores in the coating portion. As is well known, it varies depending on the DC voltage.

As described above, according to the ion conductive coating film 4 containing Nafion (registered trademark of DuPont) of the present embodiment as a composition, the outer surface of the steel building exposed to the air is effectively subjected to the electric protection. be able to. However, the sulfonic acid group (—SO ₃ H) is strongly acidic. Therefore, it is desirable to react with an alkali metal hydroxide (for example, NaOH, LiOH, KOH, etc.) and replace with, for example, —SO ₃ Na as shown in the following formula.
-SO ₃ H + NaOH → -SO ₃ Na + H ₂ O
Thus, it is possible to alter the sulfonic acid group exhibiting a strong acidic (-SO 3 _H) in a neutral or weakly alkaline. In the ion conductor, Na ⁺ is added to the original H ⁺ .

  In addition, the ion conductive coating film of the present invention has 100 parts by weight of a photocatalyst mainly composed of a transition metal oxide in 100 parts by weight of a graft polymer composition having a fluororesin ionomer as a main backbone and a sulfonic acid group in the side chain. Can be added within the range not exceeding. According to this, since the hydrophilicity of the ion conductive coating film can be remarkably improved by the photocatalyst, the surface resistance of the ion conductive coating film can be further reduced. As a result, as will be described later, the area of the outer surface of the anticorrosive current that can be flowed uniformly can be expanded from one anode electrode made of a metal material embedded in the ion conductive coating film, and the area of the outer surface can be increased. The number of anode electrodes provided in a wide steel structure can be reduced.

  The anode electrode is made of a metal material such as aluminum, and is attached to the surface of the anticorrosion coating film below the ion conductive coating film with an insulating adhesive, and at least a part of the ion conductive coating film is formed. It can be embedded and exposed on the surface of the outermost layer of the anticorrosion coating film including the ion conductive coating film. According to this, since at least a part of the anode electrode formed of a metal material is embedded in the ion conductive coating film, the electrical connection area between the anode electrode and the ion conductive coating film can be increased. It is possible to flow the anticorrosion current stably. The outer surface of the anode electrode can be covered with a finish coating film. Needless to say, when all of the anode electrode is embedded in the coating film, the terminal to which the electric wire is connected protrudes from the coating film.

Moreover, in said embodiment, although tetrafluoroethylene was employ | adopted as a fluororesin ionomer of this invention, this invention is not limited to this. For example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF) represented by Chemical Formula 3, polytrifluoroethylene chloride (PCTFE) represented by Chemical Formula 4, polyvinyl fluoride (PFE) represented by Chemical Formula 5, A copolymer of one or two or more monomers selected from the group of polyhexafluoropropylene (HFEP) represented by Formula 6 can be used. These copolymers, like the tetrafluoroethylene monomer, have a C—F bond with a large binding energy, so they form dense and stable molecular chains, have high crystallinity, and are excellent in water resistance and weather resistance. It is highly stable against the electrochemical reaction associated with anticorrosion, and has excellent adhesion to the underlying anticorrosion coating film.

  As mentioned above, although this invention was demonstrated based on one Embodiment, this invention is not limited to these, It is possible to implement in the form deform | transformed or changed in the range of the main point of this invention. It will be obvious to those skilled in the art, and it is obvious that such modifications or alterations belong to the scope of the claims of the present application.

DESCRIPTION OF SYMBOLS 1 Side wall 2 Anticorrosion coating film 3 Anticorrosion coating film 4 Ion conductive coating film 5 Anode electrode 7, 8 Electric wire 10 DC power supply device 10a DC power supply 10b Ammeter 10c Voltmeter

Claims (5)

At least one anticorrosion coating film applied to the outer surface of the steel building exposed in the air, an electroconductive coating film applied between the outermost layer or the interlayer of the anticorrosion coating film, and the steel building as a cathode With a conductive paint film as an anode and a DC power supply
The electrically conductive coating film is an ion-conductive coating film containing a graft polymer having a fluoropolymer ionomer as a main backbone and a sulfonic acid group in the side chain as a composition, and an anticorrosion device for an outer surface of a steel structure, . The said anti-corrosion apparatus of the steel building outer surface of Claim 1 whose said fluororesin ionomer is Nafion (registered trademark of DuPont) represented by the following chemical formula.

Here, Rf in Formula 1 is any one of a perfluorinated alkyl chain, an alkyl ether chain, an alkyl ester chain, and a cycloalkyl chain.
  The fluororesin ionomer is composed of one or more monomers selected from the group consisting of polytetrafluoroethylene, poly (vinylidene fluoride), poly (trifluorofluoroethylene) polyvinyl fluoride, poly (hexafluoropropylene), and poly (vinylidene fluoride). It is a copolymer, The cathodic protection apparatus of the steel building outer surface of Claim 1 or 2 characterized by the above-mentioned.   The ion-conductive coating film is formed by adding to 100 parts by weight of the composition within a range not exceeding 100 parts by weight of a photocatalyst containing a transition metal oxide as a component. The anti-corrosion apparatus of the steel building outer surface of any one of Claims 1.   An anode electrode formed of a metal material and attached to the surface of the anticorrosion coating film under the ion conductive coating film with an insulating adhesive, and the anode electrode is at least one piece of the ion conductive coating film; 2. The apparatus for catalyzing an outer surface of a steel structure according to claim 1, wherein a portion is embedded and exposed on the outer surface of the outermost layer of the anticorrosion coating film including the ion conductive coating film. .

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