JPH1129886A - Electric corrosion protection device of coated metallic body in atmospheric environment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric corrosion protection device for a coated metallic body in an atmospheric environment, in which the degradation of a coating film due to the generation of gaseous chlorine from an electrode of the electric corrosion protection device is hardly caused, a corrosion protective current is made to reach over the broad range of a coated structure by the ion conduction of a moisture adhered to a hydrophilic layer, and further, drying around the electrode is prevented by a water retentive layer around the electrode and the corrosion protection of the coated steel structure in the atmospheric environment is achieved over a long period. SOLUTION: A durable electrode 2, in which the generation of oxygen is dominant in the case of electrolyzing an electrolytic soln. contg. chloride ions, is mounted arbitrary area of the surface of the coated metallic body 1 in the atmospheric environment by being electrically isolated from the metallic body 1. An arbitrary range of a surface of the coated metallic body 1 around the durable electrode 2 is covered with the hydrophilic layer 5. Simultaneously the water retentive layer 4 in contact with the hydrophilic layer 5 is mounted around the durable electrode 2. The durable electrode 2 is connected to a positive electrode of a DC power unit 8 and the coated metallic body 1 is connected to a negative electrode of the DC power unit 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anticorrosion device for a painted metal body in an atmospheric environment, such as an iron bridge, a tank, a chimney, a pipe, an automobile, and other metal structures, the surface of which is painted.

[0002]

2. Description of the Related Art Conventionally, railway bridges, tanks, chimneys, pipes,
Atmospheric portions of painted metal bodies such as automobiles and other metal structures are subjected to anticorrosion treatment by appropriate painting. However, in general, paints deteriorate over time due to so-called "tanning" caused by sunlight, collision of foreign matter, or penetration of rainwater into the paint film and its expansion. And salt will penetrate and cause corrosion. For this reason, coating repair work has been performed regularly in the past, but there is a danger in repairing the coating of painted metal on high-rise structures such as bridge girders, tanks, and chimneys. Costly.

[0003] The undercarriage of an automobile is also damaged due to frequent collisions of rocks, mud, etc., which splash when the paint film is running.
In addition, they are exposed to a severely corrosive environment in which salt deposited on the road adheres to the metal substrate to avoid slippage due to snow and ice. On the other hand, as a method of electrochemically protecting a metal body, there is a cathode protection method (hereinafter, referred to as "electrolytic protection") in which the potential of the metal body is shifted in a negative (negative side) direction to make it an inactive region. In order to apply this cathodic protection to the above coated metal body, an electrolyte such as seawater or fresh water must be maintained between the anode and the cathode.

In order to maintain this electrolyte even in an atmospheric environment, Japanese Patent Application Laid-Open No. 53-40652 discloses a method of manufacturing a metal body of a car having an electrically insulating coating in a portion where the coating is wetted with an electrolyte. In a cathode protection system for automobiles, the anode is electrically connected to the body, the anode is attached to the DC power supply, and the metal body is electrically connected to the anode. , Formed of synthetic material, having a high extensibility tendency and being hydrophilic,
It is assumed that the electrolyte is spread and maintained on the coating.
In this cathodic protection, an expanded mesh of platinum and a platinum group metal is disclosed as an anode.

On the other hand, in Japanese Patent Application Laid-Open Publication No. 63-500312, in order to protect a metal part which is not placed on the ground, for example, a metal part of a vehicle over a wide area, a linear shape electrically connected to an electrolyte. Or a lamellar electrode (this electrode is in particular a material that does not have ionic conductivity at the interface to the electrolyte, such as graphite or a graphitized carrier material, for example,
It is finished from graphitized rubber, is not degraded by current, such as the so-called "sacrificial electrode", well known, and is, for example, finished metallically and is surrounded by such a non-ionically conductive material. ) Is mounted adjacently over a wide range of the metal surface to be protected, and a cathodic protection device is shown. Graphitized rubber or the like is used as the material of the electrode.

The interposition of electrolytes is based on the premise that they are guaranteed.

[0007]

[0007] However, in the electrolyte, the anodic reaction in electrolysis in an electrolytic solution containing _{^{chlorine, 2C1 - → C1 2 + 2e}} - (1) H 2 O → 1 / 2O 2 ^{+ 2H + + 2e - (2} ) 2 single there, but including the platinum and platinum group metals described above, what is used as an insoluble anode for cathodic protection from conventional reactions as shown in Table 1 (1) Is dominant.

[0008]

[Table 1]

Therefore, in the above-mentioned prior art, when an anticorrosive current is applied by an expanded mesh electrode of platinum or a platinum group metal, a large amount of chlorine gas is generated from the electrode, while a paint or rubber lining which is an electrically insulating coating is used. Is generally deteriorated by chlorine gas generated from the electrode due to low chlorine resistance.As a result, a large amount of anticorrosion current flows to the metal in the vicinity of the electrode, and the supply of anticorrosion current to a distant place is hindered. There is a problem that the anticorrosion effect is significantly reduced, and in the latter prior art, when a corrosion prevention current is applied, the rubber forming the electrode is deteriorated by the chlorine gas generated by the graphitized rubber electrode itself, so that the electrode is used as an electrode. There is a problem of impairing the function of.

In addition, when an anticorrosion current is applied, water generally moves in a direction away from the anode by electrophoresis, so that a thin electrolyte film is interposed in the atmosphere of a vehicle or the like to perform the anticorrosion. In such a case, there is a problem that the periphery of the electrode is easily dried, the electric resistance is increased, and the anticorrosion current is largely reduced, so that the anticorrosion effect is significantly reduced. The present invention has been made in view of the circumstances described above, and its object is to achieve the elimination of the deterioration of the coating film, the application of the anticorrosion current to a wide range, and the maintenance of the electrolyte for a long period of time. An object of the present invention is to provide an apparatus for preventing corrosion of a coated metal body in an atmospheric environment.

[0011]

In order to achieve the above object, the present invention provides an apparatus for preventing corrosion of a coated metal body in an atmospheric environment.
At any part of the surface of the coated metal body in the air environment, a durable electrode in which oxygen generation is dominant when the electrolytic solution containing chlorine ions is electrolyzed and electrically insulated from the metal body is mounted. An arbitrary area on the surface of the coated metal body around the non-conductive electrode is covered with a hydrophilic layer, and a water retention layer in contact with the non-conductive layer is attached around the non-conductive electrode, and the non-conductive electrode is used as a positive electrode of a DC power supply. And the coated metal body is connected to a negative electrode of the DC power supply.

As a durable electrode in which oxygen generation is dominant,
For example, it is preferable to use an oxygen-selective anode having an amorphous manganese dioxide or delta manganese dioxide topcoat disclosed in Japanese Patent Application Laid-Open No. 54-155197, depending on the size and shape of the metal body to be protected. It is preferable to select and use the most suitable one from various shapes such as a mesh shape, a strip shape, a line shape, and a sheet shape.

Various known materials can be applied as a hydrophilic layer covering the metal body surface around the durable electrode in order to distribute the current generated from the durable electrode over a wide range. Considering the properties and economy, it is preferable to use a hydrophilic paint containing many hydroxyl groups, carboxyl groups and the like. A paint having a hygroscopic property such as a vinyl acetate resin can also be used.

As the water-retaining layer, a known water-absorbing material such as a sponge can be used in addition to the hydrophilic plastic porous material, but the above-mentioned hydrophilic paint used as the hydrophilic layer may be used. Further, although a commercial AC power supply is usually used as a power supply of the external power supply type anticorrosion device, a loaded storage battery can be used as a power supply to protect the undercarriage of an automobile. Further, in the case of protecting a steel bridge or the like in a mountainous area where a commercial power supply cannot be easily drawn, it is preferable to use a solar cell as a power supply. Furthermore, since it is most necessary to prevent corrosion of metallic bodies in the atmosphere during rainfall when the solar cell does not work, it is necessary to charge the storage battery from the solar cell when the weather is fine and to use the storage battery as a power supply during rainfall. Is preferred.

[0015]

By using an electrode having a high oxygen generation efficiency, there is almost no chlorine gas generated from the durable electrode due to the electrolytic reaction, so that the coating of the metal body around the electrode deteriorates and a large amount of No current flows. Also,
By providing a hydrophilic layer on the metal body surface around the electrode,
Since the continuity of water adhering to the surface during rainfall can be secured in a wide range, cathodic protection of a large area can be achieved.

Further, since a water retention layer is provided around the electrode,
Even if water moves away from the electrode by electrophoresis, water is constantly supplied, so that the electric resistance does not increase and the anticorrosion current does not decrease.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments will be described with reference to the drawings. FIG. 1 shows the apparatus of the present invention. That is, on one end of an epoxy resin-coated steel sheet 1, a metal oxide-coated electrode based on titanium was electrolyzed in an acidic chloride solution containing manganous chloride to provide a catalyst layer of amorphous manganese dioxide. A manganese dioxide electrode 2 was attached using an epoxy adhesive 3.

On both sides of the electrode 2, a hydrophilic plastic porous functional material (trade name: Sunfine A) is used as the water retention layer 4.
Q, made by Asahi Kasei Kogyo Co., Ltd.) over a width of 50 mm, and apply a hydrophilic paint 5 (thermosetting water-soluble acrylic resin paint) to the remaining surface of the steel sheet 1, and then separate from the electrode 2 by about 70 cm. A hole having a diameter of about 2 mm was made in the coating film as a simulated defect 6 in the test piece to obtain a test specimen.

In order to prevent a rapid drying of a water film, which will be described later, due to the influence of wind or the like, the above-mentioned test specimen is placed in a box 7 having an open top, and is placed horizontally. To form a water film, provide a corrosive environment, and then air dry. The formation of the water film and the natural drying were repeated once a day for one month. The electrode 2 is connected to the positive electrode of the DC power supply 8,
The coated steel plate 1 is connected to the negative electrode, and a voltage of 5 V is applied continuously for one month to change the anticorrosion current, the anticorrosion state of the defective portion, the state of the water film, the change of the water content of the water retaining layer 4, and the coating film around the electrode. The state of deterioration was observed.

As Comparative Example 1, the same corrosion environment and the same anti-corrosion voltage as those of the example were applied to the structure of the example except for the water retaining layer 4, and comparative observation was performed. As Comparative Example 2, an electrode in which platinum was plated on a titanium substrate was used as the electrode 2, and the same corrosion environment and corrosion protection voltage as those of the example were applied without providing the water-retaining layer 4 and the hydrophilic paint 6, and compared with the example. Observations were made.

As a conventional example, the same corrosion environment as in the example was given to the epoxy resin-coated steel sheet 1 without any cathodic protection device, and comparative observation with the example and the comparative example was performed.
The test results are as follows. (1) Reduction of anticorrosion current.

FIG. 2 shows an example of the tendency of reduction of the anticorrosion current between the embodiment and comparative examples 1 and 2 during the natural drying after the formation of the water film. In the example, the reduction of the anticorrosion current was relatively slow, whereas in the comparative example, the reduction of the anticorrosion current was large. In particular, in the comparative example 2, the anticorrosion current almost disappeared almost 60 minutes after the start of energization. . (2) Formation of a water film on the coating film.

Immediately after the seawater spraying, a uniform water film was formed on the entire surface of the hydrophilic paint 6 of the example and the comparative example 1.
There were several places where there was no water film on the painted surface, and the continuity of the water film was impaired. Further, after about one hour from the operation of the DC power supply device, the periphery of the electrodes of Comparative Examples 1 and 2 was considerably dry, but the water retaining layer 4 of the example contained sufficient moisture. (3) Corrosion state of simulated defect.

One month after the start of the test, rust bumps were formed on the simulated defective portion of the conventional example, and traces of erosion were observed on the metal substrate after the removal, but the simulated defective portion of the example was slightly affected. Severe corrosion was observed, and no erosion of the metal substrate was observed, indicating a sufficient anticorrosion effect. In addition, traces of red rust and erosion of the metal base were observed in the simulated defective portions of Comparative Examples 1 and 2, though not as much as in the conventional example. (4) Deterioration of the coating film around the electrode.

No deterioration was observed in the coating films around the electrodes of Example and Comparative Example 1 even after one month from the start of the test.
In the coating film around the electrode of Comparative Example 2, discoloration which was considered to be caused by generation of chlorine gas was observed.

[0026]

As described above, since the present invention is constituted, there is almost no deterioration of the coating film due to the generation of chlorine gas from the electrode of the cathodic protection device, and the ionic conduction of moisture adhering to the hydrophilic layer allows the coating structure to be formed. An industrially superior effect that the anticorrosion current can reach a wide range and the water retention layer around the electrodes prevents drying around the electrodes, thus achieving long-term corrosion protection of painted steel structures in the atmosphere. To play.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a test apparatus according to the present invention.

FIG. 2 is a graph showing the change over time of the anticorrosion current of the present invention and a comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Painted steel plate 2 Electrode 3 Epoxy adhesive 4 Water retention layer 5 Hydrophilic paint 6 Simulated defect 7 Box 8 DC power supply

Claims (1)

[Claims] 1. A durable electrode in which oxygen generation is dominant when an electrolytic solution containing chlorine ions is electrolyzed on an arbitrary portion of a surface of a coated metal body in an atmospheric environment, and electrically insulated from the metal body. Attach, cover an arbitrary area of the surface of the coated metal body around the durable electrode with a hydrophilic layer, and attach a water retention layer in contact with the hydrophilic layer around the durable electrode, and apply a DC voltage to the durable electrode. An apparatus for preventing corrosion of a coated metal body in an atmospheric environment, wherein the coated metal body is connected to a positive electrode of a power supply unit and the negative electrode of the DC power supply unit.