JP5934495B2 - Manufacturing method of heavy anti-corrosion coated steel - Google Patents

Description

  The present invention relates to a method for improving adhesion durability without performing chromate treatment after blast treatment in a pre-coating base treatment of heavy anticorrosion coated steel material that requires long-term durability.

  When long-term corrosion resistance is required for large steel materials such as offshore structures and line pipes, rust removal is performed by blasting as the ground treatment in factory coating, but when chromate treatment is performed, the effect of chromic acid is significant. For blasting, only the control of roughness and visual rust removal degree has been performed. However, due to the recent increase in awareness of environmental problems, a method that does not perform chromate treatment is required. However, conventional blast treatment is not sufficient when chromate treatment is not performed due to the low reactivity of the steel surface. There was a problem that adhesion could not be secured.

  As a method for ensuring adhesiveness in the blasting process, a method for improving the adhesiveness by removing dust by performing high-pressure water washing after blasting has been proposed as disclosed in Patent Document 1. Further, as disclosed in Patent Document 2, a method of cleaning with an atmospheric gas and water higher than the dew point has been proposed, but all of them are premised on high reactivity of chromate treatment, and are not effective methods without chromate treatment. It was.

As a chemical conversion treatment without using chromate, in Patent Document 3, a treatment liquid in which silica fine particles are added to a metal phosphate compound represented by magnesium, aluminum, and calcium as a base treatment is used in a metal compound of 0.3 to 5 g / m ^2. There has been proposed a method in which a coating layer is formed by coating and drying under conditions such that the amount of adhesion of the resin primer layer is increased, and then a resin primer layer and an anticorrosion coating layer having a thickness of 0.3 mm or more are sequentially laminated.

Japanese Patent No. 3244804 JP 2001-277423 A Japanese Patent No. 4416167

  When heavy-duty corrosion protection is applied to large steel materials such as steel sheet piles, steel pipe piles, steel pipe sheet piles, and steel pipes used in offshore structures and pipelines, It is an object of the present invention to provide a method for producing a heavy anticorrosion-coated steel material having excellent anticorrosion performance without using such a complex treatment agent.

  For large steel structures, dry blasting is generally used as a base treatment before painting. However, the surface condition after blasting varies greatly without chromate treatment, and the wetting required for adhesion to the coating film. I could not always secure sex.

Therefore, the present inventors have studied a method for improving the performance of blasting, which is a pretreatment of steel materials, as means for solving the above-described problems. As a result, after blasting to ensure the roughness that contributes to physical adhesion, the wet tension of the steel surface is 38 mN / m or more by washing and drying with alkaline electrolyzed water containing no cations. It was found that the anticorrosion property after formation of heavy anticorrosion can be enhanced. Furthermore, it is possible to ensure higher corrosion resistance by combining a chemical conversion treatment including an acidic silica solution.

The gist of the present invention together with preferred embodiments thereof is as follows.
The steel material from which surface rust has been removed by impeller or air blasting is washed and dried with alkaline electrolyzed water that does not contain cations to form a highly reactive steel material surface, and then a chemical conversion treatment that includes an acidic silica solution is performed. Further, a heavy anticorrosion coating layer having a thickness of several mm, typically epoxy, polyolefin or polyurethane resin, is formed on the surface.

  According to the production method of the present invention, the treatment can be performed by a simple combination of coating and drying, and without using chromic acid for the base treatment of the steel material, excellent water resistance adhesion and peeling resistance of the coating film. It is possible to provide a heavy anticorrosion coated steel material having As a result, large structures such as steel pipe sheet piles, steel pipe piles, and steel pipes can also be provided without requiring special environmental measures.

  Hereinafter, the present invention will be described in detail.

  The heavy anticorrosion coated steel material according to the present invention is, for example, as shown in the cross-sectional view of FIG. 2. A heavy anticorrosion coated steel material in which a primer layer 3 and an adhesive and a polyolefin layer or a polyurethane layer 4 are laminated thereon.

  Similarly, FIG. 2 shows a cross-sectional view when the chemical conversion treatment is not performed.

  The steel material used in the present invention is a steel material that needs to be blasted mainly in a large size such as a steel pipe, a steel pipe pile, a steel sheet pile, or a steel pipe sheet pile. The steel material type is not particularly limited, and any steel type such as weather resistant steel or high tensile steel can be applied.

  Blasting is necessary to remove the scale and contaminants on the surface of the steel material and add roughness to the surface to increase adhesion. Sand, steel grid, steel shot, alumina, etc. are used as the abrasive for blasting. However, since sand and alumina are easily crushed, steel grids or shot grains that can be recycled are generally used.

  As a blasting method, the abrasive grains are accelerated by either the impeller or air method to collide with the steel surface to remove surface rust.

  Next, the steel material surface is washed with alkaline electrolyzed water. Alkaline electrolyzed water is alkaline electrolyzed water that is purified by electrolyzing water to increase the amount of hydroxide ions in the water, and has an alkaline pH. In the aqueous solution, there is no cation paired with a hydroxide ion, so it is not alkaline. For this reason, unlike the case where chemicals such as sodium hydroxide are used, it is difficult for a component that easily dissolves in water to remain.

  The alkaline electrolyzed water in the present invention has a pH of 10 or more and 12 or less. If the pH is less than 10, the surface modification effect cannot be obtained sufficiently. Moreover, when pH exceeds 12, the adhesive force after immersion will fall.

  Alkaline electrolyzed water may be produced by any method. For example, if the electrolyzed water purifying apparatus disclosed in Japanese Patent No. 3922439 is used, there is no mixing of electrolytes such as sodium chloride and potassium carbonate, which may affect the corrosion resistance. Not preferred.

By washing the blast surface with the alkaline electrolyzed water of the present invention, the adhesion of the steel material surface is improved. This also appears in a change in wet tension on the steel surface. The wetting tension, which is an index of surface adhesion, can be easily measured using a wet tension test mixture (WAKO Pharmaceutical). The steel surface after blasting has a wettability of 36 mN / m , whereas it improves to 38 mN / m after the alkaline electrolyzed water treatment.

  If a chemical conversion treatment is used in combination after the alkaline electrolyzed water cleaning treatment, the corrosion resistance of the chemical conversion treatment is further improved. In that case, the chemical conversion treatment is performed after the treated alkaline electrolyzed water is sufficiently dried. If the drying is insufficient, hydroxide ions are mixed into the chemical conversion treatment, and the reactivity is hindered.

  A solution containing primary silica particles having a diameter of 5 to 50 nm is used for the phosphoric acid acid conversion treatment not containing chromic acid and having a pH of 3 or less used in the present invention. For example, an acid solution containing vapor phase silica typified by Nippon Aerosil or liquid phase silica typified by Nissan Chemical is used. The acid component having a pH of 3 or less is preferably one containing a hydrofluoric acid, nitric acid, or phosphoric acid component, and is used alone or in combination.

  Further, as other components, a metal such as calcium, magnesium, aluminum, titanium, vanadium, manganese, cobalt, nickel, copper, zinc, zirconium, and molybdenum, and a metal salt of the above acid may be added.

A heavy anticorrosive coating is applied to the steel sheet after the base treatment (blast treatment + alkaline electrolytic water treatment + phosphoric acid acidification treatment) . The heavy anticorrosion coating in the present invention is an existing coating having a thickness of several millimeters mainly made of polyolefin or polyurethane, but the anticorrosion performance can be improved even when applied to heavy anticorrosion coating mainly made of epoxy. However, a primer containing epoxy or urethane as a component is always provided as the first layer on the surface of the steel material after the base treatment.

  In polyolefin heavy corrosion protection, an epoxy primer is used and the polyolefin is coated via an adhesive. The main components of polyolefin include conventionally known polyolefins used for steel pipe coating such as low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, polypropylene, and ethylene-propylene block or random copolymer. A resin containing a known polyolefin copolymer such as a polymer, a polyamide-propylene block, or a random copolymer can be used. As an additive component, carbon black and an antioxidant are added as heat resistance and weather resistance countermeasures. As other components, a filler reinforcing agent, an ultraviolet absorber, a hindered amine-based weathering agent, and the like may be added.

  In urethane heavy anti-corrosion, after forming a primer layer mainly composed of epoxy or urethane, urethane is applied. The polyurethane resin is a two-component mixed coating of a main agent composed of a mixture of a polyol, a filled inorganic pigment and a color pigment, and a curing agent composed of an isocyanate compound. Polyols such as polyester polyols, polybutadiene polyols, and polypropylene glycols, acrylic polyols, castor oil derivatives, and other hydroxyl-containing compounds are used as the polyols. As the isocyanate, a commercially available isocyanate such as methylene diphenyl diisocyanate is used. As the filled inorganic pigment, a commercially available inorganic pigment such as silica, titanium oxide, kaolin clay or the like is used, and when carbon black is used as the colored pigment, good weather resistance can be imparted.

  When an epoxy is applied alone to a thick film, there is a problem in weather resistance, so that a top coat containing a modified component such as acrylic, silicon, and fluorine having good weather resistance is used for outdoor use.

Comparative Example 1 and Examples 1 and 2 in the case where a chemical conversion treatment with an acidic silica solution having a pH of 3 or less and containing no chromic acid in polyurethane is described below with reference to Table 1 .

[Comparative Example 1 ]
A pH that does not contain chromic acid after blasting the surface with an impeller-type blasting apparatus using a steel grid TGC70 manufactured by IKK SHOT Co., Ltd. on a 100 × 150 mm steel sheet cut out from a 10H-shaped steel sheet pile = A chemical conversion solution (pH = 2.2) containing phosphoric acid 2%, magnesium 1% and calcium 1%, and aerosil silica # 200 2% as an acidic silica solution of 3 or less is applied in an amount of silica of 400 mg / m ^2. And dried. Thereafter, Permguard 331 primer manufactured by Daiichi Kogyo Seiyaku was spray-coated so that the dry film thickness was 30 μm, and after 24 hours, PermGuard 137 was spray-coated so that the dry film thickness was 2 mm. About 2 weeks after coating, it was subjected to a post-curing test at room temperature to produce a heavy-duty anticorrosive steel material of Comparative Example 1 .

[Example 1 ]
In the same manufacturing process as Comparative Example 1, between the blast treatment and the chemical conversion treatment, a step of immersing in a solution adjusted to pH 12 with alkaline electrolyzed water not containing a cation for 10 seconds and then drying by air blow was added. Thus, the heavy anticorrosive steel material of Example 1 was manufactured.
[Example 2 ]
In the same manufacturing process as in Example 1 , the primer resin was changed from urethane to epoxy resin, and the heavy anticorrosive steel material of Example 2 was manufactured.

Comparative Examples 2 to 3 when no treatment, chromate treatment, or chemical conversion treatment was performed with polyethylene, Next, Example 3 using a combination of electrolytic water cleaning and chemical conversion treatment with an acidic silica solution having a pH of 3 or less will be described with reference to Table 2 .

[Comparative Example 2 ]
A process corresponding to Patent Document 1 was performed. That is, the outer surface rust of the 200A steel pipe is derusted by blasting the surface with an impeller type blasting apparatus using a steel grid TGC100 made by IKK Shot Co., Ltd. It was washed with 6 MPa high-pressure water satisfying 1 MPa or more, and dried by air blow after 3 minutes. The chromate treatment was a hexavalent chromium partial reduction type with phosphoric acid added. The chromium adhesion amount was 400 mg / m ² . Then, the steel pipe was heated to 180 ° C. by electromagnetic induction heating, the epoxy primer was coated with 50 μm, and the adhesive (made by Mitsui Chemicals) and polyethylene resin (made by Nippon Polyethylene) melted using a T-die on the surface. A heavy anticorrosion coated steel pipe of Comparative Example 2 corresponding to Patent Document 1 was produced by coating each with 150 μm and 2 mm.

[Comparative Example 3 ]
A steel grid TGC100 manufactured by IKK Shot Co., Ltd. was used on the outer surface of the 200A steel pipe, and the surface was derusted with an impeller blasting apparatus. Thereafter, a chemical conversion treatment solution containing 2% phosphoric acid, 1% magnesium and 1% calcium, 1% nitric acid and 2% Aerosil silica # 200 (pH = 2) as an acidic silica solution containing no chromic acid and having a pH of 3 or less. ) Was applied at a silica adhesion amount of 600 mg / m ² and dried. Then, the steel pipe was heated to 180 ° C. by electromagnetic induction heating, the epoxy primer was coated with 50 μm, and the adhesive (made by Mitsui Chemicals) and polyethylene resin (made by Nippon Polyethylene) melted using a T-die on the surface. A heavy anticorrosion coated steel pipe of Comparative Example 3 was produced when the chemical conversion treatment was performed without coating the alkaline electrolyzed water cleaning treatment of the present invention after coating with 150 μm and 2 mm, respectively.

[Example 3 ]
In the same process as Comparative Example 1 , as an alkaline electrolyzed water treatment not containing cations, a liquid adjusted to pH 11 was sprayed and washed on the surface of the steel pipe after blasting at a water pressure of 6 MPa, and then wiped with an air nozzle. A heavy anticorrosion-coated steel pipe of Example 3 was produced by adding a drying treatment.

The manufactured coated steel sheets of Comparative Example 1 and Examples 1 and 2 were each cut from 1 cm to 8 × 13 cm. Similarly, the coated steel pipes of Comparative Examples 2 to 3 and Example 3 were cut into 8 × 13 cm pieces. An immersion test was performed without performing seal coating on the cut surface, and after the test, peeling from the cut end was measured. The test was conducted for 60 days for polyurethane coating and 120 days for polyethylene coating. As immersion conditions, 3% saline solution heated to 50 ° C. was used, and air bubbling was performed from the lower part of the immersion trough in an environment in which corrosion was promoted. In addition, when corrosion-free steel is added to the test environment of this time, corrosion occurs at a rate of 1.2 mm / year, and a corrosion rate corresponding to one year of underwater corrosion can be obtained in one month.

When performing chemical conversion treatment with a polyurethane coating, by comparison of Example 1 and Comparative Example 1, Example 1 was subjected to proper alkaline electrolytic water treatment after blasting treatment peeling is greatly reduced. Further, when the epoxy is used as the primer instead of the urethane primer as in Example 2 , peeling can be further suppressed.

When performing chemical conversion treatment with polyethylene coating was added electrolyzed alkaline water in Comparative Example 3 with respect to the chemical conversion treatment of chromate used and Comparative Example 3 Comparative Example 2 The peeling in Example 3 is much smaller.

  From the above results, it can be seen that the polyolefin-coated steel material and polyurethane-coated steel material produced by the present invention in which electrolytic water washing is performed after blasting can provide excellent peeling resistance.

An example of the coating | coated structure sectional drawing of the heavy-duty-proof coating steel material by manufacture of this invention is shown.

DESCRIPTION OF SYMBOLS 1 Steel material which performed the blast and alkaline electrolyzed water washing process on the surface 2 Acidic silica containing chemical conversion coating layer of pH = 3 or less which does not contain chromic acid 3 Urethane or epoxy primer layer 4 Polyolefin which has adhesive layer, or polyurethane anticorrosive layer

Claims (1)

After blasting with a polishing material, the surface is washed with alkaline electrolyzed water adjusted to pH = 10 or more and 12 or less without containing cations, and dried to obtain a surface wetting tension of 38 mN / m or more. An acidic silica solution containing no chromic acid and having a pH of 3 or less is applied and dried on the surface of the steel material that has been further improved, and further, a polyolefin anticorrosive coating layer having an epoxy resin as a main component and an adhesive layer, or urethane Or the manufacturing method of the heavy anti-corrosion coating | coated steel material characterized by laminating | stacking the primer layer which has an epoxy resin as a main component, and a polyurethane anti-corrosion coating layer.