JP2000160363A - Surface treated steel excellent in weather resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a stable rust layer on steel without deteriorating its beautiful appearance and without causing environmental contamination by coating the surface of steel with a soln. composed of amorphous rust added with Cr or amorphous rust moreover incorporated with Ni, P and Cu and a resin. SOLUTION: The surface of steel is coated with a soln. composed of amorphous rust contg. Cr and a resin to form a coating film of a uniform single layer (artificial rust layer), by which its weather resistance and adhesion for a coating material are improved. It is preferable that the content of Cr in the amorphous rust is >=0.10%, and, the amorphous rust is incorporated with one or >= two kinds selected from Ni, P and Cu by >=0.10% in total. In the amorphous rust, the one having >=50 wt.% amorphous components is desirable. In this steel, Cr is precipitated into the amorphous rust, by which excellent weather resistance can be exhibited. The form in which Cr is substituted with a part of Fe in the amorphous rust is produced, and when corrosive factors infiltrate, a stable compd. is formed by the Cr ions, and this compd. is dispersed into the amorphous rust, which is made as a stable one.

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 In general, 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 weather-resistant steels, but form rust (hereinafter, referred to as stable rust) that protects against corrosion in a few years outdoors. This is a so-called maintenance-free steel that does not require a corrosion-resistant treatment such as painting after the stable rust is formed.

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 subsequently a phosphated coating is formed. However, this method is complicated in that it requires an appropriate pre-treatment before forming a phosphating film, and when a steel material needs to be welded, the treatment is applied to the welded portion. Is not easy to apply and it is difficult to apply it to building structures.

[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 this 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. In addition, Japanese Patent Application Laid-Open No. 6-322549 discloses that a steel material that can be freely colored and has long-term weather resistance includes an α-FeOOH film as a lower layer,
A surface-treated steel material in which an upper layer is coated with an organic resin film is disclosed, and as an example of a method for forming a lower layer α-FeOOH film, (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 film and / or the adhesion between the α-FeOOH film and the organic resin film 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 deteriorating the aesthetic appearance and without causing environmental pollution. The purpose is to provide.

[0008]

Means for Solving the Problems The inventors of the present invention have made intensive studies and experiments in order to achieve the above object, and as a result, have found that a solution consisting of amorphous rust and a resin to which Cr is added is applied to the steel surface. Thereby, it is possible to form a substantially uniform coating film (referred to as an artificial rust layer) over the entire surface, which leads to the finding that weather resistance and coating film adhesion are improved. The present invention has been completed by study.

The present invention is a surface-treated steel material whose surface is covered with a single-layer coating film composed of an amorphous rust and a resin, and which has excellent weatherability and contains Cr in the amorphous rust. In the present invention, it is preferable that one or more selected from Ni, P, and Cu are contained in the amorphous rust. The content of Cr in the amorphous rust is preferably 0.10 wt% or more.

Also, one kind selected from Ni, P, Cu or
The total content of two or more types of amorphous rust is 0.10wt% or more.
Preferably, there is. Further, in the present invention, the surface of the coating film
Preferably, the surface is covered with a resin film. In the present invention
The term “amorphous rust” refers to iron rust (Fe, O, H).
Compound of iron oxide or hydroxide
Compound) which contains at least 20% of an amorphous component.
U. The amorphous component in iron rust is the crystalline component in iron rust.
Was identified and quantified by X-ray diffraction and the difference from the total amount of iron rust was determined.
It can be quantified by subtraction. Amorphous rust
Among them, less than 80 wt% α-FeOOH, β-FeOOH, γ-FeOOH,
Fe _TwoO_Three, FeO, Fe_ThreeO_Four In addition to crystalline components such as
It may contain impurities that are mixed in. In addition,
Iron rust contains active ingredients other than Fe, O and H (Mo, Ni, C
r, P, V, Cu, W)
You may.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION If chemically stable rust is physically dense, structural defects such as cracks and voids are unlikely to occur, and corrosive substances such as oxygen and water in the air and chlorine ions enter. Can be prevented, and as a result, it becomes easier to shut off the atmospheric corrosion environment, which is a basic cause of floating rust and flow rust.
Fe ion outflow can be reduced. Furthermore, if the rust is chemically stable in an atmospheric corrosion environment, the electrochemical reaction accompanying the phase transformation and dissolution of the rust is suppressed.

The surface-treated steel material of the present invention (the steel material of the present invention)
When the surface has a structure in which the resin fills the gaps between iron rusts containing amorphous components, this structure provides good weather resistance, has excellent adhesion to steel base iron, and when the upper layer is painted Has excellent adhesion to the upper layer coating film. However, crystalline components in iron rust (α-FeOOH, β-FeOOH, γ
-FeOOH, Fe ₂ O ₃ , FeO ₂ , Fe ₃ O _4, etc.) when the total is 80 wt% or more, the effect of improving the weather resistance is weakened. It should be noted that the content ratio of α-FeOOH in the crystalline component is preferably 50% by weight or more. This is because when iron rust in the artificial rust layer contains crystalline components of 80 wt% or less, the more stable α-FeOOH, the final compound that is stable in an atmospheric corrosion environment, the higher the stability of the artificial rust layer Because it is possible.

From the viewpoint of further improving the weather resistance, among the amorphous rust (iron rust having an amorphous component of 20 wt% or more), those having an amorphous component of 50 wt% or more are more preferable. Then, in the steel material of the present invention in which Cr is contained in the amorphous rust, Cr is eutectoid in the amorphous rust, and further excellent weather resistance is exhibited. Cr
Regarding the effect of the addition, Cr is partially replaced by Fe in the amorphous rust, or
Cr-based ions are mixed, and when the corrosion factor penetrates, a stable compound is generated by the Cr ions and the compound is dispersed in the amorphous rust, and the rust layer is more stable against changes in the natural environment. For example, it is conceivable that a corrosion inhibitory effect on the steel surface due to a shielding (permeation suppression) effect of a corrosion factor such as Cl ion or SO ₄ ion by Cr-based ions is considered.

[0014] Regarding the Cr content in the amorphous rust, if the total content is less than 0.10 wt%, the effect of improving the weather resistance is small, so it is preferable to contain Cr in an amount of 0.10 wt% or more. The upper limit is preferably about 15 wt% from the viewpoint of the balance between the effect and the cost. In addition, one or more of the second elements (Ni, P, Cu) are contained in the amorphous rust containing Cr in a total amount of 0.2%.
When the content is 10% by weight or more, the effect of improving weather resistance is further increased. It is considered that the addition of these second elements has an effect of eutectoidizing the rust to further densify the rust and promote a structural shielding effect. Note that the content of the second element is preferably set to about 15 wt% or less in consideration of the effect and the cost.

In the artificial rust layer, if the weight ratio of the amorphous rust to the resin is less than 10% by weight, the effect of improving the weather resistance is reduced. On the other hand, if it exceeds 95% by weight, the resin is insufficient to improve the adhesion. The weight ratio of the amorphous rust to the resin is desirably 10 to 95% by weight because the effect is reduced. The type of resin contained in the artificial rust layer is not particularly limited, and one or two types of urethane resin, epoxy resin, vinyl resin, polyester resin, acrylic resin, butyral resin, alkyd resin, silicone resin, fluorine resin, and the like can be used.
A combination of more than one species can be applied. In addition, from the viewpoint of adhesion and uniform dispersion of amorphous rust, 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, the thicker the artificial rust layer, the greater the flow rust prevention effect. However, the thickness is preferably about 50 μm, more preferably about 30 μm or less in view of cost.

In order to form an artificial rust layer, amorphous rust as a raw material is added to water or an organic solvent together with a compound of Cr or a compound of Cr and a second element to form a solution, and a resin is mixed with the solution. It is preferable to apply and form a film on the surface of the steel material by brushing, spraying, coater or the like. 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, a pigment can be added to the resin forming 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, acrylic resin, fluororesin, butyral resin, and silicone resin are preferable in terms of being hardly discolored by ultraviolet rays or the like.

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 pigments such as zinc phosphate, zinc molybdate, calcium molybdate, and aluminum phosphomolybdate can be used. In addition, conventional additives such as a thixotropic agent, a dispersant, and an antioxidant can 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.

[0021]

[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) At a dose of 0.2 mg / dm ² / day), an atmospheric exposure test was conducted for 150 days. The content of the amorphous component in iron rust as a raw material was determined by α-FeOOH, which was measured from the total amount of iron rust by X-ray internal quantitative analysis (using ZnO as a standard substance),
It was determined by subtracting each amount of β-FeOOH, γ-FeOOH, and Fe ₃ O ₄ .

The weather resistance was examined by observing the state of rust occurrence (flow rust occurrence and appearance change due to the occurrence of red rust, etc.), and measuring corrosion loss and maximum sheet thickness loss. In addition, for the adhesion of the coating film, the test piece after the coating film formation is 50 mm × 20 mm
After the shearing, the non-inspection surface was ground to obtain a 2 mm thick sample. This sample was subjected to a 45-degree torsion and untwisting test at both ends with a vice and pliers, and then a cellophane tape was applied to the inspection surface (non-ground surface). A peel test was performed 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 within the scope of the present invention, the occurrence of flowing rust is small,
The amount of maximum sheet thickness reduction is small, the coating film adhesion is good, and the overall evaluation is 4 or more.
The overall evaluation reached 5 in Example 4 with the highest content of 10.00 wt%, and Examples 6 and 7 in which a multilayer coating film consisting of an artificial rust layer and an upper film was used.

On the other hand, Comparative Example 1 contained Cr in the amorphous rust.
In Comparative Example 2, an artificial rust layer was formed by chemical change instead of coating, and in Comparative Example 3, the amorphous component in iron rust was 20%.
Less than wt% did not correspond to amorphous rust, and Comparative Example 4 was coated only with resin. Since all of them were outside the scope of the present invention, the overall evaluation was 3 or less.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

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, so there is less paint film peeling due to touch-up, which is likely to occur during painting work during construction, and good weather resistance can be secured uniformly throughout the steel material It has an excellent effect.

Continued on the front page (72) Inventor Tsurino, 1-chome, Kawasaki-dori Mizushima, Kurashiki-shi, Okayama Pref. (No address) F-term in Kawasaki Steel Corporation Mizushima Works (Reference) 4K044 AA02 AB02 BA12 BA21 BB01 BB03 BB11 BB16 BB17 BC02 CA04 CA07 CA16 CA53 CA62

Claims (5)

[Claims] 1. A surface-treated steel material whose surface is covered with a single-layer coating film composed of an amorphous rust and a resin, and which has excellent weather resistance and contains Cr in the amorphous rust. 2. The steel according to claim 1, wherein the amorphous rust contains one or more selected from Ni, P, and Cu. 3. The steel material according to claim 1, wherein the surface is covered with a single-layer coating film composed of an amorphous rust and a resin, and the amorphous rust contains 0.10 wt% or more of Cr. 4. The steel material according to claim 2, wherein one or more selected from Ni, P, and Cu are contained in the amorphous rust in a total amount of 0.10 wt% or more. 5. The steel material according to claim 1, wherein the surface of the coating film is covered with a resin film.