JPH11350156A - Surface treated steel material with excellent weather resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface treated steel material with an excellent weather resistance, causing no aesthetic harm and no environmental pollution, and ensuring formation of a uniform and stable stabilizing rust layer. SOLUTION: A steel material is covered with a monolayered coating comprising α-FeOOH and a resin on the surface. α-FeOOH contains V and/or W. Besides one or two or more kinds selected from Cr, Cu, P and Ni are incorporated in α-FeOOH. Optionally the coating is covered with a resinous coating on the surface. α-FeOOH sol is preferable as a starting material for α-FeOOH.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a surface-treated steel material having excellent weather resistance.

[0002]

2. Description of the Related Art Generally, corrosion resistance in the atmosphere can be improved by adding elements such as P, Cu, Cr, and Ni to steel. These low alloy steels are called weatherable steels,
It is a so-called maintenance-free steel that forms rust (hereinafter referred to as stable rust) having anti-corrosion properties in a few years outdoors, and after the formation of the stable rust, no corrosion-resistant treatment such as painting is required.

However, since it takes several years before stable rust is formed, floating rust such as red rust and yellow rust and flowing rust occur during the period until the stable rust is formed. The problem remains that it also becomes pollution.
As a means for solving this problem, for example, Japanese Patent Application Laid-Open No. 1-142088 discloses a steel material prepared by using an acidic aqueous solution containing a certain amount of Fe ions and one or more of P, Cu, Cr and Mn ions in advance. Surface treatment methods for weathering steel have been proposed in which a coating is formed by treatment and then a phosphate coating is formed.
However, in this method, the pretreatment prior to the formation of the phosphate film is complicated, and it is difficult to apply this pretreatment to a welded portion, so that it is difficult to apply the method to a building structure.

[0004] On the other hand, coating has been conventionally performed directly or after forming a phosphate film on the surface of weather-resistant steel. However, the coating slows down the formation of stable rust, There is a problem that the metal is deteriorated to significantly impair the appearance.
Japanese Patent Application Laid-Open No. Hei 6-93467 discloses that the steel surface is made of Cr, Cu,
Α-F containing one or two or more of P and Ni
A steel material covered with eOOH and having excellent weather resistance is disclosed. One method of forming a rust layer for obtaining the steel material is to add Cr (III) ions and / or Cu ( II) an aqueous solution containing a certain amount of ion or aqueous solution and Fe, P, by applying a mixed solution of an aqueous solution containing a certain amount of one or more of Ni ions, formed rust layer OH ^- supplying The method of making the environment more than pH7, or one is to add Cr (III) ion and / or
Alternatively, a certain amount of α-FeOOH powder is mixed with an aqueous solution containing a certain amount of Cu (II) ion or an aqueous solution containing a certain amount of one or more of Fe, P, and Ni ions. A method for applying such a solution is disclosed.

However, in this steel material, there is a problem that a stable rust layer is formed non-uniformly, corrosion resistance is insufficient, and appearance defects are caused by flowing rust and spot rust. JP-A-6-322549 discloses a surface-treated steel material in which a lower layer is coated with an α-FeOOH film and an upper layer is coated with an organic resin film, as a steel material which can be freely colored and has long-term weather resistance. Examples of the method for forming the lower α-FeOOH film include: (a) sandblasting → Cr, Cu treatment → alkali treatment → water washing → drying;
And (b) 20 years of outdoor exposure in an industrial area → wire brush keren → water washing → hot air drying.

However, in this steel material, at least one of the adhesion between the ground iron and the α-FeOOH coating and / or the adhesion between the α-FeOOH coating and the organic resin coating is unstable. In some cases, partial peeling or lifting of the coating film occurred.

[0007]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, the present invention provides a surface-treated steel material which is capable of forming a stable rust layer uniformly and stably without aesthetic impairment or environmental pollution and has excellent weather resistance. The purpose is to provide.

[0008]

Means for Solving the Problems The present inventors have made intensive studies and experiments in order to achieve the above object, and found that V and / or
Alternatively, by adding a resin to an α-FeOOH solution to which W is added and applying the resin to the surface of a steel material, almost uniform α
-FeOOH layer can be formed, which leads to the finding that weather resistance and coating film adhesion are dramatically improved. Based on this finding, the present inventors have further studied and completed the present invention.

The present invention is a surface-treated steel material whose surface is covered with a single-layer coating film composed of α-FeOOH and a resin, and which has V and / or W contained in α-FeOOH and has excellent weather resistance. In the present invention, α-FeOOH preferably further contains one or more selected from Cr, Cu, P, and Ni. It is preferable that the total content of V and / or W in α-FeOOH is 0.10 wt% or more. The total content of one or more selected from Cr, Cu, P and Ni in α-FeOOH is 0.10
It is preferably at least wt%.

In the present invention, it is preferable that the surface of the coating film is covered with a resin film. In the present invention, the raw material of α-FeOOH is preferably an α-FeOOH sol.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION If rust is chemically stable in an atmospheric corrosive environment, an electrochemical reaction accompanying phase transformation and dissolution of rust is suppressed. Furthermore, if chemically stable rust is physically dense, structural defects such as cracks and voids are unlikely to be generated, and it is necessary to prevent intrusion of corrosive substances such as oxygen and water in the atmosphere and chlorine ions. As a result, it becomes easier to block the atmospheric corrosion environment, which is a fundamental cause such as floating rust and flow rust
Fe ion outflow can be reduced.

The surface-treated steel material of the present invention (the steel material of the present invention)
Its surface is covered with a coating (known as an artificial rust layer) consisting of resin and α-FeOOH, the final compound that is stable in a normal atmospheric corrosion environment. The structure is filled with a resin, and the structure provides good weather resistance, excellent adhesion to steel base iron, and excellent adhesion to the upper layer coating when applied to the upper layer. In addition, since V and / or W is contained in α-FeOOH, V and W are eutectoid in α-FeOOH rust, and further excellent weather resistance is exhibited.

Regarding the effect of the addition of V and / or W, V or W takes a form in which Fe of α-FeOOH is partially replaced, or α-FeOOH is simply mixed with V-based ions and W-based ions. V-type ions and W
A stable compound is generated by the system ion, and the compound is α
Dispersed in -FeOOH, it is inferred that the more stable to changes in the rust layer of the natural environment, for example, corrosion factors such as Cl ions and SO ₄ ions by V-based ion or W-based ion An effect of suppressing corrosion on the steel surface due to a shielding (transmission suppression) effect or the like is considered.

Regarding the contents of V and W in α-FeOOH,
If the content is less than 0.10 wt%, the effect of improving the weather resistance is small. Therefore, it is preferable to add 0.10 wt% or more in the case of single addition and 0.10 wt% or more in the case of composite addition. The upper limit is preferably about 15% by weight or less from the viewpoint of the balance between the effect and the cost. Α-FeO containing V and / or W
When one or more of the second additive elements (Cr, Cu, P, Ni) are contained in OH in a total amount of 0.10 wt% or more, the effect of improving weather resistance is further increased. It is considered that these second additive elements have an action of eutectoidizing rust to further densify rust and promote a structural shielding effect. Note that the content of the second additive element is preferably set to about 15 wt% or less from the viewpoint of the balance between the effect and the cost.

When the weight ratio of α-FeOOH of the artificial rust layer is less than 0.10, the effect of improving the weather resistance is reduced. On the other hand, when the ratio is more than 95, the resin is insufficient and the effect of improving the adhesion is reduced. The weight ratio of α-FeOOH of the rust layer is desirably 0.10 to 95. The type of resin contained in the artificial rust layer is not particularly limited, and urethane resin, epoxy resin, vinyl resin, polyester resin, acrylic resin, butyral resin, alkyd resin, silicone resin, fluorine resin, etc.
A species or a combination of two or more species can be applied. From the viewpoints of adhesion and α-FeOOH uniform dispersion, butyral resin, acrylic resin, silicone resin, and epoxy resin are preferred.

The thickness of the artificial rust layer (refers to the dry thickness).
The same applies hereinafter) is less than 1.0 μm, there is a high possibility that partial uncovering will occur, and there is a concern that the weather resistance may differ depending on the location.
It is desirable that it is not less than μm. In consideration of unevenness due to surface irregularities, the thickness is more preferably 3 μm or more. On the other hand, as the artificial rust layer is thicker, the effect of suppressing flow rust increases as the film thickness increases. However, the film thickness is preferably about 50 μm, more preferably about 30 μm or less in view of cost.

To form an artificial rust layer, the raw material α-F
eOOH powder, more preferably α-FeOOH sol (colloidal α-F
eOOH) together with V and / or W, or V and / or W + a second additive element to water or an organic solvent to form a solution. Coating and film formation. The reason that the sol is preferable is based on the experimental fact that the sol is more effective in improving the weather resistance than the powder. One reason for this is that the sol is more evenly dispersed in the solution and evenly dispersed in the artificial rust layer after film formation.
Another reason is that the sol itself is fine and the artificial rust layer after film formation becomes dense.

The α-FeOOH as a raw material may be pure α-FeOOH, but may be β-FeOOH, γ-FeOOH, Fe ₂ O ₃ , FeO, Fe ₃ O ₄
Iron compounds such as may be contained as impurities. However, the content of impurities is desirably less than 30 wt% in total. When the content of impurities is 30 wt% or more, the effect of improving weather resistance is weakened. Preferably, the surface of the artificial rust layer is covered with a resin film (upper film). Thereby, the artificial rust layer is protected by the upper layer film, and the generation of flowing rust is further suppressed. In the present invention, since the resin is contained in the artificial rust layer,
Adhesion with the upper layer film is stronger than before. In addition, a pigment can be added to the resin constituting the upper layer film, and the resin can be freely colored to obtain a steel material having a color tone according to the surrounding scenery.

The kind of the resin forming the upper layer film is not particularly limited, but one or two kinds of urethane resin, epoxy resin, vinyl resin, polyester resin, acrylic resin, butyral resin, alkyd resin, silicon resin, fluorine resin and the like are used. A combination of the above may be used to form a single layer or multiple layers. In addition, in terms of being difficult to discolor due to ultraviolet light, etc.,
Acrylic resin, fluorine resin, butyral resin, and silicone resin are preferred.

Examples of the pigment include coloring pigments such as red iron oxide, titanium dioxide, carbon black, titanium yellow, phthalocyanine green, and phthalocyanine blue.
Extender pigments such as talc, mica, barium sulfate, calcium carbonate, rust preventive pigments such as zinc chromate and chromium oxide,
Pollution-free rust preventive pigments such as zinc phosphate, zinc molybdate, calcium molybdate, and aluminum phosphomolybdate can be used. In addition, thixotropic agents, dispersants,
Conventional additives such as antioxidants can also be added.

The thickness of the upper layer film (upper layer thickness) is 3 μm.
If it is less than 3, the flow rust generation suppressing effect is weak and the color effect is also weak. Therefore, when an upper layer film is provided, it is preferable that the film thickness is 3 μm or more. In consideration of unevenness due to surface irregularities of the base (artificial rust layer), more preferable is 5 μm.
m or more. The effect is larger as the thickness of the upper layer is larger, but it is 50 μm in consideration of the effect and the cost.
The thickness is preferably about 20 μm or less, more preferably about 20 μm or less.

[0022]

[Example] 150 mm from each steel material having the chemical composition shown in Table 1
× 70mm × 3mm test pieces were collected and
After the surface was cleaned by shot blasting and the residual oil was removed with alcohol, surface treatment was performed under various conditions shown in Table 2 as examples and comparative examples of the present invention to form various coating films, and the coastal zone (flying salt) An air exposure test was conducted for 150 days at an amount of 0.2 mg / dm ² / day), and the weather resistance was investigated by observing the rust occurrence (the appearance of flowing rust and appearance change due to the occurrence of red rust, etc.) and measuring the corrosion weight loss. Regarding the adhesion of the coating film, the test piece after forming the coating film was sheared to 50 mm x 20 mm, and the non-inspection surface side was ground to obtain a 2 mm thick sample. After the torsion and untwisting tests were performed, a peeling test using a cellophane tape was performed on the investigation surface (non-ground surface) to investigate.

The results are arranged according to the evaluation criteria described in the note column of Table 2 and are shown in the same table. From Table 2, it can be seen that, in Examples having the requirements of the present invention, there is no occurrence of flow rust, little loss of corrosion, good adhesion to the coating film, and the overall evaluation is 4 or more. In Comparative Examples 1 to 6 lacking any one, the overall evaluation was 3 or less.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

As described above, according to the present invention, a steel material which can maintain sufficient weather resistance for an extremely long time in an atmospheric corrosive environment is realized. By applying this steel material to a building structure, maintenance can be omitted or the number of maintenance times can be reduced. Not only can this be reduced, but this steel material has excellent paint film adhesion, eliminating paint film peeling due to touch-up, which tends to occur during painting work during construction, and ensuring good weather resistance uniformity over the entire steel material. It has excellent effects.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasuyoshi Yamane 1-chome, Kawasaki-dori, Mizushima, Kurashiki-shi, Okayama Pref. Chome (without address) Mizushima Works, Kawasaki Steel Corporation (72) Inventor Nobuyuki Morito 1-chome, Mizushima, Kawasaki-dori, Kurashiki City, Okayama Prefecture (without address) Inside Mizushima Works, Kawasaki Steel Corporation

Claims (6)

[Claims] 1. A surface-treated steel material whose surface is covered with a single-layer coating film composed of α-FeOOH and a resin, wherein α-FeOOH contains V and / or W and has excellent weather resistance. 2. The steel material according to claim 1, wherein the α-FeOOH contains one or more selected from Cr, Cu, P, and Ni. 3. The method according to claim 1, wherein the surface is covered with a single-layer coating film consisting of α-FeOOH and a resin, and α-FeOOH contains 0.10 wt% or more of V and / or W in total. Steel. 4. The steel according to claim 2, wherein α-FeOOH contains at least 0.10 wt% of one or more selected from Cr, Cu, P, and Ni. 5. The steel material according to claim 1, wherein the surface of the coating film is covered with a resin film. 6. The steel material according to claim 1, wherein the raw material of α-FeOOH is α-FeOOH sol.