JP2001288586A - Heavy corrosion protection-coated steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide heavy corrosion protection-coated steel excellent in cathode peeling resistance at a high temperature of 100 deg.C and also high in reliability. SOLUTION: The surface of steel subjected to substrate treatment is coated with galvanizing 2, a chromate treated layer 3 containing dry type silica fine particles is formed thereon, and after that, a resin primer layer 4 and a corrosion protection coated layer 5 having a thickness of >=0.3 mm are successively laminated and applied thereon. Since defective parts in which iron is exposed to the surface of the steel are eliminated by galvanizing, its cathode peeling resistance at high temperature can be suppressed, so that corrosion protection coating high in reliability is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heavy duty anticorrosion coated steel material which is subjected to cathodic protection such as a countermeasure for flaws at the time of construction of a line pipe. About.

[0002]

2. Description of the Related Art When a long-term anticorrosion property is required for a line pipe or the like, a heavy anticorrosion coated steel pipe coated with a polyolefin resin is used. Since pipes are often used buried, cathodic protection is also used to suppress corrosion of steel at flaws, assuming that penetration flaws may occur during transportation and construction work on synthetic resin-coated steel pipes. However, since cathodic protection causes cathodic peeling to reduce the coating adhesive strength around the flaw, cathodic peeling resistance is important for heavy corrosion-resistant coated steel pipes used for line pipes. On the other hand, in the prior art, the chromate treatment and the resin primer treatment are applied to the base treatment of the heavy-duty anticorrosion coating, thereby greatly improving the cathode peeling resistance. The chromate treatment agent used for the undercoat treatment has a large effect of suppressing cathode peeling, and phosphoric acid chromate having improved high-temperature cathode peeling properties as shown in Japanese Patent No. 1696992,
As shown in Japanese Patent No. 1985806, there is a method in which a silane coupling agent is added to improve the performance.

On the other hand, as a technique for preventing corrosion of steel materials, there is a method of applying zinc plating having a sacrificial anticorrosion action to steel materials. However, since the galvanized layer itself is vulnerable to chemical changes such as oxidation and dissolution in water, there is a technique for improving the corrosion resistance by performing a chromate treatment on the surface. An example in which this zinc plating is used as a base treatment for a heavy corrosion protection coating is disclosed in
There is a polyethylene-coated corrosion-resistant galvanized steel material disclosed in JP-A-160549.

[0004]

Since cathodic peeling resistance is important, various improvements have been made in heavy corrosion resistant coated steel materials. In particular, in recent years, demands for use in a high-temperature environment represented by polypropylene have been increasing, and a heavy-duty corrosion-resistant coated steel material excellent in peeling resistance at a high temperature of 100 ° C. has been demanded. On the other hand, the chromate treatment agent represented by Japanese Patent No. 1991880 has a limit in the achievable high-temperature performance. Further, in the method of adding a silane coupling agent, which is the third component as typified by Japanese Patent No. 1696992, a problem is likely to occur in the stability of the processing solution.

[0005] Under such circumstances, there is a demand for a base treatment having excellent cathode peeling resistance in each temperature range up to a high temperature. Chromate treatment used for heavy duty anticorrosion coating has a defect that the coating itself is severely dried and shrinks because it is a film of several μm, cracks and adhesion of steel material tend to decrease, which lowers the cathode peeling performance. . On the other hand, a method of lowering the drying temperature of the chromate film on the steel material can be considered, but in this case, the secondary adhesion after immersion is reduced due to an increase in the elution property of the film. Accordingly, there is a demand for an undercoating film having excellent cathodic peeling resistance by a stable treatment. Here, a method of changing the metal surface state by plating the steel surface can be considered. Among the plating, zinc plating is particularly widely used for general corrosion prevention, and is used in combination with a surface chromate treatment for preventing white rust. However, mere plating or base treatment combining plating with chromate treatment does not provide sufficient performance with respect to adhesion and cathode peeling resistance required for heavy corrosion protection coating.

The present invention provides a heavy-duty corrosion-resistant coated steel material, which is excellent in cathodic peeling resistance, by combining zinc plating with a specific chromate treatment, primer treatment, and a corrosion-resistant coating layer. Is what you do.

[0007]

A feature of the present invention is that zinc plating is applied to the surface of a steel material which has been subjected to a base treatment at a rate of 10 to 1000 g / m 2.
^{(2) After being} subjected to surface treatment with a chromate treating agent containing dry fine-particle silica and partially reduced chromic acid, an epoxy resin primer layer, a heavy corrosion protection coated steel material coated with a corrosion protection resin layer having a thickness of 0.3 mm or more. .

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As a means for solving the above-mentioned problems, the present inventors formed a galvanized layer 2 on the surface of a steel material 1 as shown in the sectional view of FIG. A coating chromate treatment 3 containing fumed silica is performed thereon, and thereafter, a resin primer layer 4 and an anticorrosion resin coating layer 5 having a thickness of 0.3 mm or more are sequentially laminated and used. In this case, as the anticorrosion resin layer, a modified polyolefin alone, a two-layer coating of a modified polyolefin adhesive layer and a polyolefin, or a polyurethane resin coating is desirable. By the above-described laminated coating, a heavy corrosion-resistant coated steel material having a plating base excellent in cathodic peeling resistance is obtained.

Hereinafter, the present invention will be described in detail.
The steel material used in the present invention is ordinary steel, or C, Si,
Steel with controlled Mn, nitrogen and oxygen, and Cu, N
It is a high alloy steel to which elements such as i, Cr, Mo, Nb, Ti, Al, Mg, V, and Ca are added. Typical varieties are steel pipes to which heavy corrosion protection coating is applied, and steel pipe piles, steel pipe sheet piles, steel sheet piles, H-section steel, wire rods and the like used in marine structures and the like. In order to remove scale, contaminants, and the like on the surface of these steel materials, any one of base treatments such as alkali degreasing, pickling, sand blasting, grid blasting, and shot blasting is always performed.

Next, the plating used in the present invention will be described. The plating may be performed by any of electroplating and hot-dip plating. As a plating component, one mainly composed of zinc was used, and Al, Mg, Fe, Co, N
Metals such as i and Mn may be added. The plating thickness is preferably in the range of 10 to 1000 g / m ² .

After the above-mentioned plating treatment, a coating chromate treatment is performed, followed by drying and baking. In the coating type chromate treatment, the amount of adhesion is adjusted to 50 to 800 mg / m ^{2 in} terms of chromium. As the components of the treatment liquid, an aqueous solution in which chromic anhydride (CrO ₃ ) is dissolved in distilled water is partially reduced with an organic reducing agent, and hexavalent chromium ions and trivalent chromium ions are mixed, and silica is mixed. What is necessary is just to mix system type fine particles. As the silica-based fine particles, those obtained by secondary aggregation of primary particles having a diameter of 5 to 50 nm synthesized by a dry method are used.
For example, AEROSIL 13 manufactured by Nippon Aerosil Co., Ltd.
0, AEROSIL 200, AEROSIL 200
V, AEROSIL 200CF, AEROSIL 2
00FAD, AEROSIL 300, AEROSIL
300CF, AEROSIL 380, AEROSI
L OX50, AEROSIL TT600, AERO
Silica fine particles such as SIL MOX. The addition amount of the silica fine particles is 0.5 to 4.
Add in the range of 0. Further, the reduction ratio from hexavalent to trivalent chromium is desirably in the range of 20 to 70% based on all chromium. Further, if necessary, phosphoric acid or the like may be added in the range of 0.1 to 2 with respect to all chromium. If the stability of the solution does not matter, a silane coupling agent, an emulsion resin or the like may be added.

Next, the resin primer used will be described. A thermosetting resin is used as a primer used in the heavy-corrosion-coated steel material of the present invention, and a resin obtained by adding a curing agent and an inorganic pigment to an epoxy resin, a polyurethane resin, or a polyester resin is used as a main component. As a polyurethane resin, a moisture-curable one-pack type using a prepolymer,
Alternatively, a two-liquid curing type using a reaction between an isocyanate and a polyol is typical. In particular, an epoxy resin is preferably used for the primer to meet the requirement of high heat resistance. Generally, bisphenol A type and bisphenol F type resins are used singly or as a mixture as the main component. If high-temperature properties are required, a polyfunctional phenol novolak or a halogenated resin is used in combination with the above-mentioned bisphenol A type or bisphenol F type resin. When a two-part curing type amine-based curing agent or an imidazole compound which is a latent curing agent and a dicyandiamide or phenol-based curing agent is used in combination as the curing agent, adhesion and corrosion resistance are excellent. The inorganic pigment to be added is 3 to 30 vol% based on the total volume.
When added in the range, the shrinkage strain is reduced, and the adhesion characteristics are greatly improved. For inorganic pigments, pigments such as silica, titanium oxide, wollastonite, mica, talc, kaolin, chromium oxide, zinc borate, zinc borate, zinc phosphate,
Alternatively, a metal powder such as zinc or Al, a ceramic powder, or the like, or an anticorrosive pigment such as strontium chromate is used as appropriate. These pigments may be subjected to a silane coupling treatment on the surface in order to improve the wettability with the resin.

Using the above thermosetting resin primer,
By combining with the above-described chromate treatment, it is possible to provide a base treatment for a heavy corrosion-resistant coated steel material having excellent performance in peel resistance. When the resin primer is supplied as a liquid, a method such as roll or brush coating, ironing, air spray coating, or the like is used. When supplied in the form of powder, a method such as electrostatic powder coating is used, and
Paint in the range of m. When the film thickness is smaller than 10 μm, many pinholes are generated. On the other hand, although the upper limit of the film thickness varies depending on the type of the resin, in the case of a thick film coating exceeding 500 μm, characteristics such as impact resistance at a low temperature tend to be deteriorated.

After the above base treatment, a heavy duty anticorrosion coating is applied.
As the resin to be coated, any resin such as vinyl chloride, polyester, acrylic, epoxy, and fluorine-based resin may be used as long as it has excellent durability and barrier properties against water and oxygen, but a polyolefin resin and a polyurethane resin are preferable. In particular, polyolefin resins are excellent in corrosion resistance such as resistance to cathodic peeling and in price. Polyolefin resin is low-density polyethylene, medium-density polyethylene,
Conventionally known polyolefins such as high-density polyethylene, linear low-density polyethylene and polypropylene, and resins containing known polyolefin copolymers such as ethylene-propylene block or random copolymer, polyamide-propylene block or random copolymer It is. As other components, carbon black or other coloring pigments, a filler, an antioxidant, an ultraviolet absorber, a hindered amine-based weathering agent and the like are added in any combination as heat resistance and weathering resistance measures. When a polyolefin resin is used for coating, an adhesive obtained by modifying a polyolefin is used for a lower layer portion that comes into contact with the primer of the base. This adhesive is
Polyethylene, polypropylene, known polyolefins such as nylon, and known polyolefin copolymer resins, maleic acid, acrylic acid, unsaturated carboxylic acids such as methacrylic acid or those modified with acid anhydrides, or It is a conventionally known modified polyolefin such as one obtained by appropriately diluting a modified product with a polyolefin resin. A method in which a thin modified polyolefin adhesive layer having a thickness of 50 to 700 μm is used in combination with a polyolefin resin layer having a thickness of 0.3 to 5 mm is preferable from the viewpoint of price and performance balance. However, the polyolefin coating layer is omitted and the modified polyolefin resin layer has a thickness of 0. It may be coated as 3 mm or more and used as an anticorrosion layer. As the polyolefin coating method, for example, an extrusion coating method in which a resin melted by heating with a die is directly coated on a steel material is used. Alternatively, there is a method in which a preformed polyolefin sheet is attached to a heated steel material, or a method in which pulverized polyolefin is powder-coated and melted to form a film. According to these methods, a polyolefin anticorrosion coating layer having a thickness of 0.3 mm or more is formed.

[0015]

EXAMPLES AND COMPARATIVE EXAMPLES As a chromate treatment agent 1 for coating, a silica sol of a wet method (manufactured by Nissan Chemical Co., Ltd.) was used as a chromate treatment agent corresponding to JP-A-2-160549.
A chromate treating agent which partially reduced chromium to which Snowtex O) was added was prepared. Other chromating agents include chromic acid solution and dry silica (Aerosil 200:
Nippon Aerosil Co., Ltd.), a phosphoric acid component, and partial reduction using dextrin as a reducing agent.
8 chromate treatment agents were prepared.

[0016] Heavy corrosion protection coated steel material 200A, length 5.
Using a 5 m steel pipe, a polypropylene coated steel pipe shown in Table 2 was produced. If the surface of the steel pipe is first blasted with a grid and then hot-dip galvanized, alkali degrease-pickling is performed, immersed and dried in a flux bath, and then zinc (97% or more) -Al (1%). In a hot-dip galvanizing bath. The steel pipe was pulled up from the plating bath while performing air blowing, and a hot-dip galvanized steel pipe was manufactured. After applying the above-mentioned chromate treatment agent to the hot-dip galvanized steel pipe, the steel material was heated to 200 ° C. in a heating furnace. Thereafter, a powdered primer obtained by half-reacting an epoxy resin (including a bisphenol A type main ingredient, 20% of a phenol novolak resin, an imidazole curing accelerator, a phenolic curing agent, and a silica-based inorganic pigment) is used. Average film thickness of 50
Electrostatic powder coating was performed to a thickness of μm. Thereafter, using a two-layer T-die, a lower layer of 0.1 mm of a modified polyolefin adhesive layer and an upper layer of 2 mm of a polypropylene resin layer were extrusion-coated in a spiral manner by rotary conveyance, and the steel pipe was cooled with water.
Levels 1 to 17, 19 (Chromate components are disclosed in
No. 0549), 20 (with no primer, the coating structure of JP-A-2-160549), and 22 (without chromate) polypropylene-coated heavy duty corrosion-resistant steel pipes were produced.

Further, as an example of the case where electrogalvanizing is used, a steel pipe having a length of 5.5 m and a length of 200 A is first blasted with a grid, then subjected to alkali degreasing and pickling, and then subjected to a zinc sulfate bath. Electroplating in the room, 10 g / m
^The current and the energizing time that became ² were adjusted. After washing the surface of the steel pipe with water and drying with hot air, applying and drying a chromate treatment agent, heating the steel pipe to 200 ° C., and using an epoxy resin powder primer to obtain an electrostatic powder having an average thickness of 50 μm. Body painting was performed. Then, using a two-layer T-die, a 0.1 mm modified polyolefin adhesive layer was formed on the lower layer, and a 2 mm
After spirally extruding and coating the polypropylene resin layer of Example 1 in a spiral shape by rotating and conveying, the steel pipe was cooled with water to produce a polypropylene-coated heavy corrosion-resistant steel pipe of Level 18 of the present invention.

As a comparative example, a heavy corrosion protection coated steel material in which zinc plating was omitted, and a case in which chromate treatment was not performed, a 200 A, 5.5 m long steel pipe surface was subjected to grid blast treatment, and coated with chromate. In the case of performing the treatment, the powder was roll-coated so as to have a chromium adhesion amount of 500 mg / m ² and dried, and then electrostatic powder coating was performed using a powder primer so that the average film thickness became 50 μm.
Thereafter, the steel pipe was heated to 200 ° C., and a 0.1 mm modified polyolefin adhesive layer was formed as a lower layer and a 2 mm polypropylene resin layer was formed as an upper layer by extrusion using a two-layer T-die. After cooling with water, a heavy duty anticorrosion steel pipe coated with polypropylene of Comparative Example 21 was produced. Further, a polypropylene-coated steel pipe of Comparative Example 23 which was not subjected to a chromate treatment by the same process was prepared.

The coated steel pipe thus produced was cut into a 150 × 80 mm piece of steel, a coating penetrating flaw reaching the steel surface of 8 mmφ was formed at the center of the coating surface, and a cylindrical plastic cell was erected on the coating, and 3% inside the coating. Brine was charged. The voltage was adjusted to -1.5 V with respect to the standard saturated calomel electrode potential on the scratched steel part, and the cathode peel test was performed in ovens at 60 ° C and 100 ° C.
Performed on days 0 and 60.

As is clear from the results of the cathodic peeling test in Table 2, as shown in the levels 1, 6, 7, and 16, the performance of the chromate component is degraded if it is out of the proper range, but the proper range of the present invention. Levels 2 to 5, 8 to 15, 1
The heavy corrosion protection coating materials Nos. 7 to 18 are described in JP-A-2-160549, chromate treatment (level 19), chromate treatment and coating configuration (level 20), and a conventional patent No. 1696.
Coating chromate treatment equivalent to No. 992 (level 21),
Alternatively, it can be seen that the performance is much better than that of the untreated (levels 22 and 23).

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

According to the heavy corrosion protection coated steel material of the present invention, the occurrence of peeling from a flaw portion in the case of electrolytic protection is prevented by using the plating base treatment of the present invention for the heavy corrosion protection coating. A high peeling suppression effect which cannot be obtained by the mold chromate treatment can be obtained. As a result, excellent cathodic peeling resistance, which has not been obtained until now, can be obtained even in a high-temperature region, so that it is possible to provide a more reliable heavy corrosion-resistant coated steel material.

[Brief description of the drawings]

FIG. 1 shows an example of a cross-sectional view of a coating configuration of a heavy-corrosion-coated steel material of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Steel material 2 Galvanization 3 Coating type chromate treatment layer containing fine silica particles 4 Primer resin layer 5 Corrosion prevention coating layer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B05D 7/24 302 B05D 7/24 302U 302G B32B 15/08 B32B 15/08 G 103 103Z 27/38 27 / 38 C23C 22/30 C23C 22/30 C23F 15/00 C23F 15/00 (72) Inventor Shintaro Yamanaka 20-1 Shintomi, Futtsu-shi, Chiba F-term in the Technology Development Division of Nippon Steel Corporation 4D075 AE03 BB74X CA33 DB05 EA02 EA06 EB13 EB33 4F100 AA20B AA22B AB03A AB18A AK01D AK03G AK07 AK53C AL06G BA04 BA05 BA07 BA10A BA10D CB00 DA11 DE01B EH23 EH46 EH71A EJ65C EJ69B AA12 JA02A02A JB02A20A CA41 EB08 4K044 AA02 AB02 AB03 BA10 BA15 BA21 BB05 BC02 BC05 CA11 CA16 CA18 CA53 4K062 AA01 BA0 1 BA10 BC07 BC12 BC15 EA04 FA04 FA12 GA01 GA10

Claims (1)

[Claims] Claims: 1. A steel material surface which has been subjected to a base treatment is subjected to zinc plating at a rate of 10 to 1000 g / m ² , and a surface treatment is carried out with a chromate treatment agent containing dry particulate silica and partially reduced chromic acid, followed by an epoxy resin primer. A heavy corrosion-resistant coated steel material, characterized by being coated with a corrosion-resistant resin layer having a thickness of 0.3 mm or more.