JP3073448B2 - Corrosion protection of steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing corrosion of steel in a steel structure existing in the air such as a bridge, a plant, a building steel frame, etc., and more particularly, to an external power supply system capable of effectively protecting steel from corrosion for a long period of time. The present invention relates to an anticorrosion method for a steel material using an electrolytic anticorrosion method.

[0002]

2. Description of the Related Art Conventionally, as an anticorrosion method for a marine steel structure or a steel structure in soil, an external power supply system or a galvanic anode system has been widely used. On the other hand, steel structures in the atmospheric environment do not come into contact with water like marine steel structures and steel structures in soil, which makes it difficult to secure a route for anticorrosion current. No anticorrosion method was used at all. Therefore, for a steel structure existing in the atmosphere, an anticorrosion method by applying an anticorrosion paint is mainly used. However, the method of anticorrosion by applying anticorrosion paint is poor in coating or when the steel surface is rough, coating defects such as pinholes are likely to occur, and mechanical damage is likely to occur. There was a problem that corrosion occurred from the defective portion. For this reason, a heavy-duty anticorrosion coating system in which an anticorrosion paint is applied about 4 to 6 times is also used. However, in such a method of performing recoating a plurality of times, the number of coatings and the number of steps are increased, and there is a problem in the coating process.

[0003]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in view of such problems of the prior art.
An object of the present invention is to provide an anticorrosion method capable of protecting steel present in the atmosphere from corrosion for a long time, even for unpainted steel or for coated steel having coating film defects such as pinholes. I do.

[0004]

The present inventors have conducted intensive studies to solve the above-mentioned problems. As a result, corrosion progresses when water is present such as during rainfall or dew condensation. The research was conducted on the assumption that corrosion could be prevented if the route was secured. As a result, a knowledge was obtained that a steel coating could be protected by providing a conductive coating or a hydrophilic coating on the surface of a painted or unpainted steel and applying an anticorrosion current by an electrolytic protection method using an external power supply. Based on this finding, the present invention has been completed. That is, according to the present invention, the surface resistance of a steel material existing in the atmosphere or the surface of a painted steel material is 10 ^7.
Ω / cm ² or less conductive film or contact angle to water is 70
An object of the present invention is to provide a method for preventing corrosion of steel, characterized in that a hydrophilic coating having a degree of not more than a degree or a coating which simultaneously satisfies both characteristics is formed, and an anticorrosion current is applied by an external anticorrosion method.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. In the present invention, the conductive coating film is formed on a painted or unpainted steel material surface so that an anticorrosion current flows from an external power supply. From this viewpoint, the surface resistance of the conductive coating film is 10 ⁷ Ω / cm ² or less, preferably 10 ⁵ Ω / cm ² or less.
/ Cm ² or less. Examples of the paint for forming the conductive coating film include, for example, conductive binder resins such as polyaniline, polypyrrole, polythiophene, poly-p-phenylenevinylene, and polyacetylene, and powders such as carbon black, brass, aluminum, zinc oxide, and graphite. And a flake-like or fibrous conductive filler to impart conductivity within the above-mentioned surface resistance range.

[0006] The hydrophilic coating film used in the present invention, like the conductive coating film, is used to allow an anticorrosion current to flow by an external power supply, and is formed on a painted or unpainted steel material surface. Therefore, the hydrophilic coating film has a water contact angle of 7
It must be 0 ° or less, preferably 40 ° or less. Water-soluble or water-dispersible acrylics having a hydroxyl group, a carboxyl group, an amino group, a carbonyl group, a hydrophilic group such as a sulfone group, epoxy-based, polyester-based, and alkyd-based paints for forming a hydrophilic coating film. , Urethane,
Phenol-based, polyether-based, polyamide-based, polyvinyl alcohol-based or modified binder resins thereof (a melamine resin or a crosslinking agent such as a polyisocyanate compound may be used in some cases), a surfactant, or the like. A paint which is blended to impart hydrophilicity in the above-mentioned contact angle range to water may be used.

The hydrophilic coating is preferably roughened in order to improve the water retaining property of the coating film surface. In order to roughen the surface, acrylic resin, epoxy resin, polystyrene resin, acrylonitrile Organic particles made of resin, polyamide resin, polyester resin, cellulose resin, and the like,
It is desirable to mix inorganic particles composed of silica, alumina, calcium carbonate, kaolin and the like. Next, the method for preventing corrosion of steel according to the present invention will be described. FIG. 1 is a side sectional view of a steel material subjected to a typical anticorrosion treatment of the present invention, and the anticorrosion method of the present invention will be described with reference to FIG. Steel material 1
After the surface is subjected to ordinary pretreatment as necessary, a primer, an anticorrosive paint or the like is applied to form an anticorrosive coating film 2 having a thickness of usually 100 to 300 μm. The anticorrosion coating 2 is not an essential component in the present invention, and need not be used. Further, the anticorrosion coating film 2 may be an old coating film that has already been painted.

A paint for forming the above-mentioned conductive coating or a paint for forming the hydrophilic coating is applied to the surface of the coated or unpainted steel material to form the conductive or hydrophilic coating 3. The thickness (after drying) of the coating film 3 is not particularly limited, but is usually 5 to 50 μm for a painted steel material, and is usually 50 to 50 μm for an unpainted steel material in order to protect the steel material. 2
00 μm is appropriate. Next, the anode plate 4 is laminated on the conductive or hydrophilic coating film 3 thus formed. In the present invention, the conductive or hydrophilic coating 3
A material that is insulative when not wet with water or that exhibits electrical conductivity when wet with water may be interposed between the anode and the anode plate 4. The fixing method of the anode plate 4 is, for example, a conventional method using bolts or the like. The anode plate 4 is required to have long-term durability, so that it is hardly melted even when exposed to wind and rain in the air, and is a conductive material for the purpose of flowing electricity. Specifically, platinum, graphite, cast iron , Aluminum alloy and the like are suitable.

The anode plate 4 and the steel plate 1 thus formed are connected via a power source 5 with a lead wire 6 such as a copper wire whose surface is insulated and coated. The anticorrosion current flows between the anode plate 4 and the steel material 1 by applying a DC voltage from a power supply to prevent corrosion of the steel material 1. The DC voltage is 5-20
V, preferably 10 to 15 V is suitable. If the DC voltage is lower than the above range, a sufficient anticorrosion current does not easily flow, and the anticorrosion effect is reduced. Conversely, if the DC voltage is higher, the anode plate tends to be consumed. According to the method of the present invention, the anode plate 4, the conductive or hydrophilic coating and (if coated, the coating itself is conductive when the coating itself is conductive, and the coating itself When it is insulative, an anticorrosion current flows between the steel materials (via pinholes or damaged portions of the coating) to prevent corrosion.

[0010]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples. Example 1 An epoxy resin paint was applied to a 1 × 50 × 1000 (mm) polished mild steel sheet so as to have a thickness (after drying) of 100 μm.
20% N- of polyaniline resin (trade name VERSICON, manufactured by Allied-Signal Co.)
A methylpyrrolidone solution was applied to a thickness of 5 μm (after drying) to form a conductive coating having a surface resistance value shown in Table 1 below. The back and side surfaces were sealed with an epoxy resin, and the room temperature was maintained at room temperature for 7 days. And dried. Then, at the edge of the surface,
An aluminum anode plate having a size of × 50 × 50 (mm) was attached. Further, a coating defect reaching the substrate was formed at a position 800 mm away therefrom with a drill having a diameter of 1 mm. Finally, the anode plate and the mild steel plate were connected by a lead wire via a power source as shown in FIG. 1, a voltage of 10 V was applied, and the plate was exposed outdoors for 6 months.

Table 1 shows the potential and appearance at the corners of the coating defect after exposure.
As shown in FIG. Example 2 1000 g of isopropyl alcohol was placed in a 2 liter three-necked fluffco equipped with a stirrer, heated to 70 ° C., and 5 g of azobisisobutyronitrile was added. Then, 175 g of acrylic acid and 175 g of 2-hydroxyethyl methacrylate were added. 75
g, methyl methacrylate 200 g and styrene 50 g
Is dropped over 3 hours, and further,
The polymerization was continued for 3 hours to obtain an acrylic resin solution. Ammonia was added to the mixture so that the pH of the acrylic resin solution became 7.5, and 1000 g of water was added dropwise little by little. The heating residue was 19% by weight, and the hydroxyl value per resin solid content was 65 mg KOH.
/ G, a water-soluble acrylic resin composition (A) having an acid value of 273 mgKOH / g.

An epoxy resin paint is applied to a polished mild steel sheet of 1 × 50 × 1000 (mm) to a thickness of 100 μm after drying, and dried for 24 hours. (A) and fine fumed silica (Aerosil 200, trade name, manufactured by Nippon Aerosil Co., Ltd.) were applied to a thickness of 5 μm (after drying), and the contact angle to water shown in Table 1 below was obtained. Was formed, the back and side surfaces were sealed with an epoxy resin, and dried at room temperature for 7 days. Next, an aluminum anode plate was attached in the same manner as in Example 1, and further a coating defect was formed, and the anode plate and the mild steel plate were connected by a lead wire via a power source as shown in FIG. Finally, it was exposed outdoors for 6 months with a voltage of 10 V applied. The potential and appearance of the coating defect after the exposure were as shown in Table 1. Comparative Example 1 In the same manner as in Example 1, an epoxy resin paint was applied to a polished mild steel sheet so as to have a thickness (after drying) of 200 μm and dried at room temperature for 7 days. The film was exposed outdoors for a while, and the potential and appearance of the coating defect after the exposure were examined.
The results are shown in Table 1 below.

[0013]

[Table 1] Table 1 Potential of coating defect of conductive coating of hydrophilic coating Coating after 6 months Contact angle (degree) Surface resistance value (after 6 months / 70% RH) Appearance of defect ( ^{Ω / cm 2) [mV /} Ag · AgCl] example 1 105 10 ⁵ -820 No abnormality example 2 32 10 ¹² -950 None abnormality Comparative example 1 86 10 ¹⁴ -120 significantly obvious from rust table 1 As described above, Examples 1 and 2, which are the cathodic protection method of the present invention, had an excellent anticorrosion effect. On the other hand, in Comparative Example 1, which is a conventional anticorrosion method using only painting, rust was generated in a short time.

[0014]

According to the method of the present invention, corrosion can be effectively prevented even for steel materials existing in the atmosphere by an external power supply type of electrolytic protection method. It is possible to prevent rust from being generated from the spot without applying the number of coatings or man-hours, and even if a coating film defect occurs.

[Brief description of the drawings]

FIG. 1 is a side cross-sectional view of a steel material subjected to a typical cathodic protection treatment according to the method of the present invention.

[Explanation of Signs] 1 ... steel material 2 ... anticorrosion coating film 3 ... conductive or hydrophilic coating film 4 ... anode plate 5 ... power supply 6 ... lead line

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C23F 11 / 00,13 / 00 E04B 1/64 E01D 9/00

Claims (4)

(57) [Claims] 1. A conductive film having a surface resistance of 10 ⁷ Ω / cm ² or less is formed on a steel material surface which is present in the air and is not always in contact with water. , Poorly soluble,
A method for preventing corrosion of a steel material, comprising laminating an anode plate made of a conductive material, using a steel material as a cathode, applying a DC voltage between the anode plate and the steel material, and flowing an anticorrosion current. 2. A coated steel material which is present in the atmosphere and is not always in contact with water has a surface resistance of 10 ⁷ Ω.
/ Cm ² or less, an anode plate made of a poorly soluble and conductive material is laminated on the conductive coating film, and a direct current is applied between the anode plate and the steel material using the steel material as a cathode. An anticorrosion method for steel, characterized in that an anticorrosion current is applied by applying a voltage. 3. A water-based hydrophilic coating film having a contact angle of 70 ° or less is formed on a surface of a steel material which is present in the atmosphere and is not in constant contact with water or a coated steel material. An anticorrosion method for a steel material, wherein an anticorrosion current is applied by an anticorrosion method. 4. An anode plate made of a poorly soluble and conductive material is laminated on the hydrophilic coating film, and a steel material is used as a cathode.
4. The method according to claim 3, wherein a direct current voltage is applied between the anode plate and the steel to flow an anticorrosion current.