JP2002129353A - Surface treated steel material with weather resistance and treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface treated steel material, on which weather resistant, stable rust is formed at an early stage without deteriorating an appearance. SOLUTION: The surface treated steel material with weather resistance comprises an organic resin coating of which the dry film thickness is 5-50 μm including chromic sulphate of 0.1-15 mass% as a lower layer, and an organic resin coating of which the dry film thickness is 5-30 μm including carbon powder of 0.1-10 mass% instead of chromic sulphate as an upper layer. This method comprises coating the lower and upper layers which include the above respective component, so as to make the each dry film thickness as the above respective predetermined thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a rust layer (hereinafter referred to as "weather-resistant stable rust" or simply "stable rust") having an action of protecting steel from corrosion in an atmospheric corrosion environment without impairing the appearance. The present invention relates to a surface-treated steel material which is formed early and has excellent weather resistance and landscape properties, and a method for treating the same.

[0002]

2. Description of the Related Art Generally, the corrosion resistance of steel 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. Rust that protects against corrosion (hereinafter referred to as “weather-resistant rust”) is formed on the steel surface in a few years outdoors, and requires anti-corrosion treatment such as painting. And so-called maintenance-free steel. However, since it takes several years before weather-resistant rust is formed, floating rust such as red rust and yellow rust and flowing rust occur during the period, not only giving an unfavorable appearance, but also causing contamination of the surrounding environment. The problem remains. Regarding this problem, a method of forming a phosphate film on the surface of a steel material has been proposed, for example, as described in JP-A-1-142008. However, the content of the treatment is complicated, such as the necessity of performing an appropriate pretreatment before forming the phosphate film, and when welding of steel materials is necessary, it is not easy to apply treatment to the welded part. However, there is also a problem in application to building structures. Japanese Patent Application Laid-Open No. 6-226198 discloses a method in which an organic resin paint containing 1 to 65% by mass of chromium sulfate or copper sulfate is coated on the surface of a steel material to generate stable rust at an early stage. However, although this method has a great effect of preventing flow rust, a green or white reaction by-product (iron sulfate) precipitates on the surface of the coating material depending on the use environment or use, and the landscape of the steel sheet is impaired. This problem is particularly noticeable in an environment with severe condensation such as inside a bridge girder. Further, in a relatively mild atmospheric corrosion environment such as a rural area, the generation of stable rust was sometimes delayed.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a so-called rust-forming steel material such as a low-alloy steel such as a weather-resistant steel or an ordinary steel, on which a stable and stable rust is formed earlier. In the forming process, generation of flowing rust, coloring by a reaction by-product such as iron sulfate, etc., a weather-resistant surface-treated steel material formed without deteriorating viewability, and a surface for obtaining the surface-treated steel material It is to provide a processing method.

[0004]

The inventors of the present invention have analyzed the rust generated by an atmospheric exposure test for more than 20 years and found that the weather-resistant stable rust was α- (Fe, Cr) OOH (hereinafter, referred to as “chrome gate”). Site)). Therefore, in order to suppress the generation of floating rust and flowing rust by generating weatherable stable rust at an early stage, the point is how to promote the generation of dense chromium goethite. Note that the refined α
-(Fe, Cr) OOH is a so-called X-ray amorphous substance which does not give a diffraction peak in X-ray diffraction, but according to Mossbauer spectroscopy, a weather-resistant stable rust (chrome goethite) is clearly formed. You can see that it is. Therefore,
As a result of repeated studies to promote the formation of chromium goethite, an organic resin paint containing an appropriate amount of chromium sulfate was applied to the steel surface or the rust layer formed on the steel surface, and then carbon powder was applied on top. By applying a surface treatment to apply an organic resin paint containing a small amount of rust, the steel surface can be weather-resistant and stable without causing the occurrence of flowing rust and without deteriorating the landscape due to reaction by-products such as iron sulfate. Was found to be able to be formed early. The present invention has been made based on the above findings, and the gist of the present invention is as follows (1)
And (2) the surface treatment method. (1) The lower layer has an organic resin coating film having a dry film thickness of 5 to 50 μm and containing 0.1 to 15 mass% of chromium sulfate,
A weather-resistant surface-treated steel material having an upper layer having a dry film thickness of 5 to 30 µm, containing no chromium sulfate, and having an organic resin coating film containing 0.1 to 10 mass% of carbon powder. (2) An organic resin paint containing 0.1 to 15% by mass of chromium sulfate with respect to the solid content of the paint is applied to the surface of the steel material so that the dry film thickness becomes 5 to 50 μm. A surface treatment method comprising applying an organic resin paint containing 0.1 to 10 mass% of carbon powder to the paint solid content so as to have a dry film thickness of 5 to 30 μm. The `` steel material '' is not particularly limited to steel types,
It may be ordinary steel or low alloy steel such as weathering steel. What is necessary is just the steel material which produces what is called rust. The “dry film thickness” is the film thickness after drying after the application of the organic resin paint and the volatilization of the organic solvent added during the preparation of the paint. The “paint solids” refers to a resin as a binder,
A coating additive such as chromium sulfate or carbon powder to be added to the resin and a pigment to be added to the resin.The organic solvent such as an organic solvent is volatilized by natural drying after coating to form an organic resin coating film formed on the steel material surface. Does not include those that do not remain.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a weather-resistant surface-treated steel material and a surface treatment method of the present invention will be described in detail. If the rust structure is dense, the surface of the steel material is easily physically shielded from the atmospheric corrosion environment, and the elution of iron ions, which is a fundamental cause of floating rust and flow rust, is reduced. However, if there is a defect such as a crack or a pore in the rust, it becomes a supply path for water or oxygen, and the corrosion prevention performance of the rust decreases. Therefore, it is necessary to form a dense and defect-free continuous rust layer on the steel surface. As described above, the weather-resistant surface-treated steel material of the present invention is a steel material having a two-layer organic resin coating film on the surface of a base steel.

The lower organic resin coating film (hereinafter, the organic resin coating film is also simply referred to as “coating film”) contains 0.1 to 15 mass% of chromium sulfate. Chromium sulfate dissociates into chromium ions and sulfate ions when water permeates into the coating film, and reaches the interface between the coating film and the base steel. Sulfate ions and moisture corrode steel and produce iron ions. In addition, goethite (α-FeOOH) is preferentially generated as a corrosion product due to the presence of sulfate ions. On the other hand, the chromium ions change the generated goethite to chromium goethite, which is a main component of weatherable stable rust. Also, sulfate ions not only accelerate the production of iron ions at the beginning,
It is thought to be involved in the refinement and densification of stable rust.
In order to obtain this effect under an atmospheric corrosion environment, it is necessary that the lower coating film contains chromium sulfate of 0.1 mass% or more. Thus, when the surface-treated steel material of the present invention is placed in an atmospheric corrosive environment, weather-resistant stable rust is generated at an early stage, and the rust is extremely dense and chloride ions (Cl ⁻ ) existing in the atmospheric corrosive environment are formed. ¹ ) It has an excellent effect of suppressing the permeation of corrosive anions such as ¹ ). In addition, the reason why the content of chromium sulfate in the lower coating film is limited to 15 mass% or less is that if the content is more than this, the initial corrosion of the base steel is too large, and as a result, the weathering stability The protective effect of the steel in the severe atmospheric corrosion environment cannot be guaranteed, and iron sulfate generated by the reaction between the sulfate ion and the base steel precipitates on the surface of the steel material, which significantly impairs the appearance. is there. The type of organic resin (base resin) contained in the lower coating film is not particularly limited, and epoxy resin, urethane resin, vinyl resin, polyester resin, acrylic resin, alkyd resin, phthalic resin, etc. are used. can do. In addition to chromium sulfate, the lower layer coating film includes coloring pigments such as red iron oxide, titanium dioxide, carbon black, and phthalocyanine blue; extender pigments such as talc, silica, mica, barium sulfate, and calcium carbonate; chromium oxide; zinc chromate; Conventional additives such as anticorrosive pigments such as lead chromate and basic lead sulfate, and other thixotropic agents, dispersants, and antioxidants may be contained. The film thickness (dry film thickness) of the lower layer coating film is set to 5 to 50 μm. If it is less than 5 μm, the ability to form stable rust is inferior, and if it exceeds 50 μm, the effect is saturated, and it is economically disadvantageous. This is because the generation of stable rust may be delayed in a less severe countryside or the like. As the resin in the upper layer coating film, a resin mainly composed of the same resin as the resin in the lower layer coating film is preferably used. If different types of resins are used, the interlayer adhesion between the lower coating film and the upper coating film decreases, and the upper coating film peels off, which is not appropriate. The purpose of providing the upper coating film is to suppress the formation of reaction by-products (iron sulfate) caused by chromium sulfate contained in the lower coating film and to prevent precipitation outside the coating film. Prevention of chromium sulfate escape. If there is no upper layer coating, chromium sulfate elutes, so it is necessary to include excess chromium sulfate in the lower layer coating in order to generate stable rust, but if the upper layer coating exists, Since the elution of chromium sulfate is suppressed, stable rust can be generated with a small amount of chromium sulfate. Furthermore, due to the presence of the upper layer coating film, the generated iron sulfate does not precipitate on the surface, but can be taken in at the interface between the base metal and the coating film or inside the coating film, and the formation of rust is promoted. Combines with chromium sulfate in the coating film to form stable rust.

As described above, in the surface-treated steel material of the present invention,
The upper layer coating and the lower layer coating complement each other,
Acting synergistically, it is possible to form weatherable stable rust on the base steel surface at an early stage. In the surface-treated steel material of the present invention, the upper coating film contains 0.1 to 10 mass% of carbon powder. This carbon powder acts as a catalyst,
It has the effect of promoting the oxidation of divalent iron ions eluted from the base steel due to corrosion to trivalent iron ions by oxygen in the air. For this reason, precipitation of divalent iron ions as iron sulfate on the surface of the coating film is suppressed, and the surface of the coating material does not exhibit white or green, and the landscape of the steel material surface is maintained. In addition, oxidation of divalent iron ions to trivalent iron ions is promoted, and as a result, generation of weather-resistant stable rust is promoted.
When the content of the carbon powder is less than 0.1 mass%, the above-mentioned effect of promoting the oxidation of iron ions is not remarkably recognized, and when the content exceeds 10 mass%, the corrosion of the base steel is remarkably accelerated. , The formation of stable rust may be hindered. Therefore, the content of the carbon powder is 0.1 to 1
0 mass%. The carbon powder may be contained in the lower coating film, but in that case, the content is preferably 10 mass% or less. Examples of the carbon powder include activated carbon and carbon black. As in the case of the above-mentioned lower layer coating, the upper layer coating includes red iron oxide, titanium dioxide,
Color pigments such as carbon black and phthalocyanine blue; extender pigments such as talc, silica, mica, barium sulfate, and calcium carbonate; rust preventive pigments such as chromium oxide, zinc chromate, lead chromate, and basic lead sulfate; and other thixotropic agents ,
Additives such as dispersants and antioxidants may be included.
However, chromium sulfate is not included. When chromium sulfate is contained in the upper layer coating film, iron dissolved from the base steel precipitates as iron sulfate on the outer surface of the coating film, and not only the landscape is easily impaired, but also the generation of stable rust may be suppressed. . The thickness (dry film thickness) of the upper coating film is 5 to 30 μm. Film thickness 5μm
If less than 30, the effect of promoting iron ion oxidation is small, and iron sulfate may precipitate to impair the viewability. On the other hand, if it exceeds 30 μm, permeation of moisture from the surface of the coating film to the base steel is excessively suppressed. The formation of stable rust may be significantly delayed. The surface treatment method of the present invention is a surface treatment method for obtaining the weather-resistant surface-treated steel material of the present invention, as described above,
0.1 ~ 15mass% of paint solids on steel surface
Organic paint containing chromium sulfate (hereinafter simply referred to as "paint")
) To form a lower coating film, and further apply a paint containing 0.1 to 10% by mass of carbon powder thereon to form an upper coating film. The paint used for forming the lower coating film (undercoat paint) and the paint used for forming the upper coating film (overcoat paint) are both suitable amounts of an organic solvent (hereinafter simply referred to as "solvent") at the time of use. The viscosity is adjusted with water to a level suitable for painting. The solvent or moisture evaporates by natural drying after coating, and in particular, a part of the moisture contained in the undercoat paint is considered to contribute to the formation reaction of weather-resistant stable rust. Both the undercoat and the topcoat may contain the above-mentioned coloring pigment, extender pigment, rust-preventive pigment, and other conventional additives. Further, the undercoat paint may contain a compound of iron, copper, and nickel, or phosphoric acid or an aqueous solution thereof, which is more preferable. Iron ions, copper ions, nickel ions or phosphoric acid have the effect of promoting the formation of chromium goethite when they coexist with chromium ions. However, when a compound of iron, copper, and nickel is added as a sulfuric acid compound, it is preferable that the total amount of the compound with chromium sulfate be 15 mass% or less. When the total amount exceeds 15%, the initial corrosion due to sulfate ions is excessively accelerated, and as a result, the formation of stable rust may be inhibited, or iron sulfate may precipitate on the surface of the coating film to impair the appearance. Because. For the application of these undercoats and topcoats, conventional methods such as air spray, airless spray or brushing can be used in the same manner as ordinary coating, so that they can be applied anywhere, and relatively It is economical because it can be coated with a thin film. Furthermore, since on-site painting is possible, it is possible to deal with painting after processing such as cutting and welding of steel material on site, and painting of steel material with rust generated on the surface. In order to apply the paint to a predetermined dry film thickness, a relationship between the thickness of the coating film at the time of application (coating film thickness) and the film thickness after drying is obtained in advance, and based on the relationship, The thickness of the coating at the time of application may be determined. The thus obtained surface-treated steel sheet of the present invention can form weather-resistant and stable rust on the surface of steel material at an early stage under an atmospheric corrosion environment, and can secure excellent weather resistance. In addition, there is no occurrence of floating rust such as red rust or yellow rust or flowing rust in the process of forming stable rust, or deterioration of the landscape due to coloring by reaction by-products. No precipitation of iron sulfate, which is likely to occur in places with severe condensation, such as inside a bridge girder, is observed. Also, even if some external force acts on the above-mentioned weather-resistant stable rust and cracks or peeling occurs, if chromium sulfate remains in the coating film of the healthy part, the chromium sulfate is supplied to the damaged part and again. We can expect self-repair performance to produce stable rust with weather resistance.

[0008]

EXAMPLE An exposure test was conducted on a sample produced by the surface treatment method of the present invention, and then the corrosion loss, the state of chromium goethite formation and the appearance were examined. In addition, the generation of by-products (iron sulfate) in the dew condensation environment was investigated using a box-shaped test material. Table 1 shows the chemical compositions of the test steels (1) and (2) used. In addition, the base resins A and B used for the paint
Table 2 shows the compositions of C and C. In Table 2, base resins B and C using a curing agent were of a two-pack type, and a resin (base resin + additive) and a curing agent were mixed and used immediately before coating.

[0009]

[Table 1]

[0010]

[Table 2]

The size of the base material test piece before surface treatment is 150 m
m × 70 mm × 3.2 mm (thickness).
Rust was removed until it reached 5. Table 3 and Table 4 (continuation of Table 3)
Shows the conditions for preparing the samples used in the exposure test.

[0012]

[Table 3]

[0013]

[Table 4]

An appropriate amount of a solvent is added to the resin having the composition shown in Tables 3 and 4 to adjust the viscosity to 0.2 to 1 N · s / m ² (2
(1000-1000 centipoise, measured using a B-type viscometer), and applied to both surfaces of a base material test piece by air spray to obtain a sample. The sample was exposed horizontally to the countryside in Hyogo Prefecture for one and two years. After the exposure test, the coating film and rust remaining on the surface were removed, the mass of the base material test piece was measured, and the weight loss from corrosion was determined from the difference from the previously measured mass before coating. In Tables 3 and 4, the average corrosion weight loss on one side, which is half the corrosion weight loss, is shown in terms of the corrosion depth. Regarding the formation state of chromium goethite, the cross section of the rust was subjected to structural analysis with a deflection microscope and Raman spectroscopy, and if a weather-resistant stable rust consisting of goethite was formed at the interface between the coating film and the base steel. It was evaluated as good (indicated by a mark) and bad (indicated by a cross) if not formed. Regarding the appearance of the coating film surface, check for the precipitation of iron sulfate, floating or peeling off of the upper coating film, and if they are hardly observed, they are good (indicated by a circle). When it was found, it was evaluated as defective (indicated by x). In addition, in the investigation of the by-product (iron sulfate) generation status using the box-shaped test material, the length of 300 by 300 mm was used to simulate severe dew condensation inside the bridge girder.
A box-shaped container having a size of 300 mm x 300 mm x 50 mm in height is used as a test material, and the bottom of the box is filled with ion-exchanged water so as to have a film thickness of 1 mm. And leave for one day (while the water in the box evaporates)
A test was performed in which the process was one cycle and the process was repeated 50 cycles. When no iron sulfate was generated in the box-shaped test material, it was evaluated as good (indicated by a circle), and when iron sulfate was generated, it was evaluated as poor (indicated with a cross). The investigation results are shown in Tables 3 and 4. From these results, in Examples 1 to 9 of the present invention (see Table 3), the samples after the exposure test did not show flow rust or fouling due to iron sulfate. Within one year of the exposure period), the formation of weather-resistant stable rust was observed. In addition, the formation of iron sulfate was not observed in the examination using the box-shaped test material. On the other hand, in Comparative Examples 10 to 17 (see Table 4), when the upper layer coating film did not contain carbon powder (Comparative Example 10), when the content of carbon powder was out of the specified range (Comparative Example 17), the lower layer coating When the base resin of the film and the upper layer coating film are different (Comparative Example 11), when the film thickness is out of the specified range (Comparative Examples 12 and 14), and when the content of chromium sulfate is out of the specified range (Comparative Example 15, 16)
In some cases, peeling of the upper coating film and precipitation of iron sulfate were observed, and the formation of weather-resistant stable rust was sometimes insufficient. Also,
Investigation with a box-shaped test material showed formation of iron sulfate (all except Comparative Example 13). In Comparative Example 13, although the corrosion weight loss was small and no precipitation of iron sulfate was observed in the examination with the box-shaped test material, the formation of weather-resistant stable rust was insufficient because the film thickness was too large.

[0015]

According to the weather-resistant surface-treated steel sheet of the present invention, stable weather-resistant rust is formed on the surface of the steel material at an early stage under an atmospheric corrosion environment. At that time, the landscape is maintained without floating rust such as red rust and yellow rust and flowing rust. In addition, no precipitation of iron sulfate, which is likely to occur in places with severe condensation such as inside a bridge girder, is observed. This surface-treated steel sheet is suitable as a steel material for civil engineering and building structures because it does not require maintenance for corrosion protection of the steel material and does not impair the landscape of the steel sheet. This surface-treated steel sheet can be easily and economically obtained by the processing method of the present invention.

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[Procedure amendment]

[Submission date] October 23, 2000 (2000.10.
23)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction contents]

[Document Name] Statement

Patent application title: Weather-resistant surface-treated steel material and treatment method

[Claims]

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a rust layer (hereinafter referred to as "weather-resistant stable rust" or simply "stable rust") having an action of protecting steel from corrosion in an atmospheric corrosion environment without impairing the appearance. The present invention relates to a surface-treated steel material which is formed early and has excellent weather resistance and landscape properties, and a method for treating the same.

[0002]

2. Description of the Related Art Generally, the corrosion resistance of steel 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. Rust that protects against corrosion (hereinafter referred to as “weather-resistant rust”) is formed on the steel surface in a few years outdoors, and requires anti-corrosion treatment such as painting. And so-called maintenance-free steel.

However, since it takes several years to form weather-resistant rust, floating rust such as red rust and yellow rust and flowing rust are generated during the period, and not only an undesired appearance is exhibited, but also the surrounding environment is reduced. The problem remains that it can also be a source of pollution.

Regarding this problem, see, for example,
As described in Japanese Patent No. 42008, a method of forming a phosphate film on a steel material surface has been proposed. But,
The content of the treatment is complicated, such as the necessity of performing an appropriate pre-treatment before forming a phosphate film, and when welding of steel materials is necessary, it is not easy to apply treatment to the welded part.
There are also problems with application to building structures.

Further, Japanese Patent Application Laid-Open No. Hei 6-226198 discloses a method of forming a stable rust at an early stage by coating an organic resin paint containing 1 to 65% by mass of chromium sulfate or copper sulfate on a steel material surface. . However, although this method has a great effect of preventing flow rust, a green or white reaction by-product (iron sulfate) precipitates on the surface of the coating material depending on the use environment or use, and the landscape of the steel sheet is impaired. This problem is particularly noticeable in an environment with severe condensation such as inside a bridge girder. Further, in a relatively mild atmospheric corrosion environment such as a rural area, the generation of stable rust was sometimes delayed.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a so-called rust-forming steel material such as a low-alloy steel such as a weather-resistant steel or an ordinary steel, on which a stable and stable rust is formed earlier. In the forming process, generation of flowing rust, coloring by a reaction by-product such as iron sulfate, etc., a weather-resistant surface-treated steel material formed without deteriorating viewability, and a surface for obtaining the surface-treated steel material It is to provide a processing method.

[0007]

The inventors of the present invention have analyzed the rust generated by an atmospheric exposure test for more than 20 years and found that the weather-resistant stable rust was α- (Fe, Cr) OOH (hereinafter, referred to as “chrome gate”). Site)). Therefore, in order to suppress the generation of floating rust and flowing rust by generating weatherable stable rust at an early stage, the point is how to promote the generation of dense chromium goethite. Note that the refined α
-(Fe, Cr) OOH is a so-called X-ray amorphous substance which does not give a diffraction peak in X-ray diffraction, but according to Mossbauer spectroscopy, a weather-resistant stable rust (chrome goethite) is clearly formed. You can see that it is.

Therefore, as a result of repeated studies to promote the formation of chromium goethite, an organic resin paint containing an appropriate amount of chromium sulfate was applied to the surface of the steel material or a rust layer formed on the surface of the steel material. By applying a surface treatment to apply an organic resin paint containing an appropriate amount of carbon powder to the surface of the steel without the occurrence of flow rust and without the deterioration of the landscape due to reaction by-products such as iron sulfate. It was found that stable rust of weather resistance can be formed early.

The present invention has been made based on the above findings, and the gist of the present invention lies in the following (1) a weather-resistant surface-treated steel material and (2) a surface treatment method. (1) The lower layer has a dry film thickness of 5 to 50 μm and chromium sulfate of 0.1 to
A weather-resistant surface having an organic resin coating containing 15 mass%, an upper layer having a dry film thickness of 5 to 30 μm, not containing chromium sulfate, and having an organic resin coating containing 0.1 to 10 mass% of carbon powder. Treated steel. (2) An organic resin paint containing 0.1 to 15% by mass of chromium sulfate with respect to the solid content of the paint is applied to the surface of the steel material so that the dry film thickness becomes 5 to 50 μm. A surface treatment method comprising applying an organic resin paint containing 0.1 to 10 mass% of carbon powder to the paint solid content so as to have a dry film thickness of 5 to 30 μm.

The "steel material" is not particularly limited in steel type, and may be ordinary steel or low alloy steel such as weathering steel. What is necessary is just the steel material which produces what is called rust.

The “dry film thickness” is the film thickness after drying after the application of the organic resin paint and the volatilization of the organic solvent added during the preparation of the paint. In addition, “paint solids” refers to a resin as a binder, chromium sulfate or carbon powder to be added to the resin, and a paint additive such as a pigment to be added to the resin. Does not remain in the organic resin coating film formed on the surface of the steel material by volatilization.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a weather-resistant surface-treated steel material and a surface treatment method of the present invention will be described in detail.

If the structure of the rust is dense, the surface of the steel material is physically easily shielded from the atmospheric corrosion environment, and the elution of iron ions, which is a fundamental cause of floating rust and flowing rust, is reduced.
However, if there is a defect such as a crack or a pore in the rust, it becomes a supply path for water or oxygen, and the corrosion prevention performance of the rust decreases. Therefore, it is necessary to form a dense and defect-free continuous rust layer on the steel surface.

As described above, the weather-resistant surface-treated steel material of the present invention is a steel material having a two-layer organic resin coating film on the surface of a base steel.

The lower organic resin coating film (hereinafter, the organic resin coating film is also simply referred to as “coating film”) contains 0.1 to 15 mass% of chromium sulfate. Chromium sulfate dissociates into chromium ions and sulfate ions when water permeates into the coating film, and reaches the interface between the coating film and the base steel. Sulfate ions and moisture corrode steel and produce iron ions. In addition, goethite (α-FeOOH) is preferentially generated as a corrosion product due to the presence of sulfate ions. On the other hand, the chromium ions change the generated goethite to chromium goethite, which is a main component of weatherable stable rust. Also, sulfate ions not only accelerate the production of iron ions at the beginning,
It is thought to be involved in the refinement and densification of stable rust.

In order to obtain this effect in an atmospheric corrosion environment, it is necessary that the lower coating film contains chromium sulfate of 0.1 mass% or more. Thus, when the surface-treated steel material of the present invention is placed in an atmospheric corrosive environment, weather-resistant stable rust is generated at an early stage, and the rust is extremely dense and chloride ions (Cl ⁻ ) existing in the atmospheric corrosive environment are formed. ¹ ) It has an excellent effect of suppressing the permeation of corrosive anions such as ¹ ). In addition, the content of chromium sulfate in the lower coating film is set to 1
The reason for limiting the content to 5 mass% or less is that if the content exceeds this, corrosion of the base steel at the initial stage is too large, and as a result, the protection of weather resistant and stable rust is reduced, and the corrosion prevention in severe atmospheric corrosion environment is performed. This is because the effect cannot be guaranteed, and iron sulfate generated by the reaction between the sulfate ions and the base material steel precipitates on the surface of the steel material, and the appearance is significantly impaired.

The type of organic resin (referred to as a base resin) contained in the lower coating film is not particularly limited, and may be epoxy resin, urethane resin, vinyl resin, polyester resin, acrylic resin, alkyd resin, phthalic acid resin. Etc. can be used.

In addition to chromium sulfate, color pigments such as red iron oxide, titanium dioxide, carbon black and phthalocyanine blue; extender pigments such as talc, silica, mica, barium sulfate and calcium carbonate; chromium oxide; Rust preventive pigments such as zinc oxide, lead chromate, and basic lead sulfate,
In addition, conventional additives such as a thixotropic agent, a dispersant, and an antioxidant may be contained.

The thickness (dry film thickness) of the lower coating film is 5 to 50 μm.
When it is less than 5 μm, the ability to generate stable rust is inferior,
If the thickness exceeds 50 μm, the effect is saturated, which is economically disadvantageous, and the generation of stable rust may be delayed in a rural area where the atmospheric corrosion environment is not so severe.

As the resin in the upper coating film, it is preferable to use a resin mainly composed of the same resin as the resin in the lower coating film. If different types of resins are used, the interlayer adhesion between the lower coating film and the upper coating film decreases, and the upper coating film peels off, which is not appropriate.

The purpose of providing the upper layer coating film is to suppress the formation of reaction by-products (iron sulfate) caused by chromium sulfate contained in the lower layer coating film and to prevent precipitation outside the coating film. It prevents the escape of chromium sulfate in the coating film. If there is no upper layer coating, chromium sulfate elutes, so it is necessary to include excess chromium sulfate in the lower layer coating in order to generate stable rust, but if the upper layer coating exists, Since the elution of chromium sulfate is suppressed, stable rust can be generated with a small amount of chromium sulfate. Furthermore, due to the presence of the upper layer coating film, the generated iron sulfate does not precipitate on the surface, but can be taken in at the interface between the base metal and the coating film or inside the coating film, and the formation of rust is promoted. Combines with chromium sulfate in the coating film to form stable rust.

Thus, in the surface-treated steel material of the present invention,
The upper layer coating and the lower layer coating complement each other,
Acting synergistically, it is possible to form weatherable stable rust on the base steel surface at an early stage.

In the surface-treated steel material of the present invention, the upper coating film contains 0.1 to 10% by mass of carbon powder.
This carbon powder acts as a catalyst and has the effect of promoting the oxidation of divalent iron ions eluted from the base steel by corrosion to trivalent iron ions by oxygen in the air. For this reason, precipitation of divalent iron ions as iron sulfate on the surface of the coating film is suppressed, and the surface of the coating material does not exhibit white or green, and the landscape of the steel material surface is maintained. In addition, oxidation of divalent iron ions to trivalent iron ions is promoted,
The formation of weather resistant stable rust is promoted.

When the content of the carbon powder is less than 0.1 mass%, the above-mentioned effect of promoting the oxidation of iron ions is not remarkably recognized, and when the content exceeds 10 mass%, corrosion of the base steel is reduced. It may be significantly accelerated and the formation of stable rust may be hindered. Therefore, the content of carbon powder is
0.1 to 10 mass%. Although the carbon powder may be contained in the lower layer coating film, the content in that case is 1%.
It is preferred to be 0 mass% or less.

Activated carbon and carbon black are examples of the carbon powder.

As in the case of the lower layer coating film, the upper layer coating film includes coloring pigments such as red iron oxide, titanium dioxide, carbon black and phthalocyanine blue; extender pigments such as talc, silica, mica, barium sulfate and calcium carbonate; Rust-preventing pigments such as chromium oxide, zinc chromate, lead chromate, and basic lead sulfate, and other additives such as thixotropic agents, dispersants, and antioxidants may be contained. However, chromium sulfate is not included. When chromium sulfate is contained in the upper layer coating film, iron dissolved from the base steel precipitates as iron sulfate on the outer surface of the coating film, and not only the landscape is easily impaired, but also the generation of stable rust may be suppressed. .

The thickness (dry film thickness) of the upper coating film is 5 to 30 μm.
m. When the film thickness is less than 5 μm, the effect of promoting iron ion oxidation is small, and iron sulfate may precipitate to impair the landscape. On the other hand, when the film thickness exceeds 30 μm, the permeation of moisture from the surface of the coating film to the base metal steel may be reduced. It is excessively suppressed, and the generation of stable rust may be significantly delayed.

The surface treatment method of the present invention is a surface treatment method for obtaining the above-mentioned weather-resistant surface-treated steel material of the present invention.
An organic resin paint containing 5 mass% chromium sulfate (hereinafter also simply referred to as “paint”) is applied to form a lower coating film, and a paint containing 0.1 to 10 mass% carbon powder is further applied thereon. This is a method of forming an upper layer coating film.

The paint used for forming the lower coating film (undercoat paint) and the paint used for forming the upper coating film (overcoat paint) are both used in an appropriate amount of an organic solvent (hereinafter, referred to as “coating paint”).
The viscosity is adjusted to a value suitable for the coating operation by water or water. The solvent or moisture evaporates by natural drying after coating, and in particular, a part of the moisture contained in the undercoat paint is considered to contribute to the formation reaction of weather-resistant stable rust.

In any of the undercoat paint and the topcoat paint, the above-mentioned coloring pigment, extender pigment, rust-preventive pigment, etc.
Conventional additives may be included.

Further, the undercoat paint may contain a compound of iron, copper, and nickel, or phosphoric acid or an aqueous solution thereof, which is more preferable. Iron ions, copper ions, nickel ions or phosphoric acid have the effect of promoting the formation of chromium goethite when they coexist with chromium ions. However, when a compound of iron, copper, and nickel is added as a sulfuric acid compound, it is preferable that the total amount of the compound with chromium sulfate be 15 mass% or less.
When the total amount exceeds 15%, the initial corrosion due to sulfate ions is excessively accelerated, and as a result, the formation of stable rust may be inhibited, or iron sulfate may precipitate on the surface of the coating film to impair the appearance. Because.

For the application of these undercoat paints and top coat paints, it is possible to use a conventional method such as air spray, airless spray or brush coating as in the case of ordinary coating, so that it can be applied to any place. It is also economical because relatively thin film coating is sufficient. Moreover,
Since on-site painting is possible, it can be used for painting after cutting and welding of steel materials on site, and for painting steel materials with rust on the surface. In order to apply the paint to a predetermined dry film thickness, a relationship between the thickness of the coating film at the time of application (coating film thickness) and the film thickness after drying is obtained in advance, and based on the relationship, The thickness of the coating at the time of application may be determined.

The thus obtained surface-treated steel sheet of the present invention can form a weather-resistant stable rust on the surface of a steel material at an early stage under an atmospheric corrosion environment, and can secure excellent weather resistance. In addition, there is no occurrence of floating rust such as red rust or yellow rust or flowing rust in the process of forming stable rust, and no deterioration in landscape due to coloring by reaction by-products. No precipitation of iron sulfate, which is likely to occur in places with severe condensation, such as inside a bridge girder, is observed.

Further, even if any external force acts on the above-mentioned weather-resistant stable rust to cause cracking or peeling, if chromium sulfate remains in the coating film of the healthy part, the chromium sulfate is supplied to the damaged part. Thus, self-repair performance, in which weather-resistant stable rust is generated again, can be expected.

[0035]

EXAMPLE An exposure test was conducted on a sample produced by the surface treatment method of the present invention, and then the corrosion loss, the state of chromium goethite formation and the appearance were examined. In addition, the generation of by-products (iron sulfate) in the dew condensation environment was investigated using a box-shaped test material.

Table 1 shows the chemical compositions of the test steels (1) and (2) used. Table 2 shows the compositions of the base resins A, B and C used in the paint. In Table 2, base resins B and C using a curing agent were of a two-pack type, and a resin (base resin + additive) and a curing agent were mixed and used immediately before coating.

[0037]

[Table 1]

[0038]

[Table 2]

The size of the base material test piece before surface treatment is 150 m
m × 70 mm × 3.2 mm (thickness).
Rust was removed until it reached 5.

Tables 3 and 4 (continuation of Table 3) show the conditions for preparing the samples used in the exposure test.

[0041]

[Table 3]

[0042]

[Table 4]

An appropriate amount of a solvent was added to the resins having the formulations shown in Tables 3 and 4 to adjust the viscosity to 0.2 to 1 N · s / m ² (2
(1000-1000 centipoise, measured using a B-type viscometer), and applied to both surfaces of a base material test piece by air spray to obtain a sample. The sample was exposed horizontally to the countryside in Hyogo Prefecture for one and two years.

After the exposure test, the coating film and rust remaining on the surface were removed, the mass of the base material test piece was measured, and the weight loss from corrosion was determined from the difference from the previously measured mass before coating.
In Tables 3 and 4, the average corrosion weight loss on one side, which is half the corrosion weight loss, is shown in terms of the corrosion depth.

Regarding the state of formation of chromium goethite,
Structural analysis of the cross section of the rust with a deflection microscope and Raman spectroscopy. If weather resistant stable rust consisting of goethite, which is continuous at the interface between the coating film and the base metal steel, is formed (marked by ○), formation If not, it was evaluated as defective (indicated by x).

With respect to the appearance of the coating film surface, the presence or absence of precipitation of iron sulfate, floating or peeling of the upper coating film, and the like were examined. If they were hardly observed, they were good (indicated by ○). Was evaluated as defective (indicated by x).

In the investigation of the by-product (iron sulfate) generation state using the box-shaped test material, in order to simulate a severe dew condensation environment such as the inside of a bridge girder, the height is 300 mm × 300 mm × width.
A box-shaped container having a height of 50 mm is used as a test material, and ion-exchanged water is placed at the bottom of the box so as to have a film thickness of 1 mm, and the container is left for 1 day in a thermo-hygrostat at a temperature of 25 ° C. and a relative humidity of 60%. (The water in the box evaporates during this period) was set as one cycle, and a test in which this was repeated 50 cycles was performed. Good if no iron sulfate was found in the box-shaped test material (marked with ○), poor if iron sulfate was found (marked with ×)
Was evaluated.

The results of the examination are shown in Tables 3 and 4.
From these results, in Examples 1 to 9 of the present invention (see Table 3), the samples after the exposure test did not show flow rust or fouling due to iron sulfate. Within one year of the exposure period), the formation of weather-resistant stable rust was observed. In addition, the formation of iron sulfate was not observed in the examination using the box-shaped test material.

On the other hand, in Comparative Examples 10 to 17 (see Table 4), when the upper layer coating film did not contain carbon powder (Comparative Example 10), and when the content of carbon powder was outside the specified range (Comparative Example 17). In the case where the lower layer coating film and the upper layer coating film have different base resins (Comparative Example 11), when the film thickness is out of the specified range (Comparative Example 1)
2, 14) and when the content of chromium sulfate is out of the specified range (Comparative Examples 15 and 16), peeling of the upper layer coating film and precipitation of iron sulfate are observed, and furthermore, formation of weather-resistant stable rust is insufficient. In some cases. In addition, formation of iron sulfate was observed in the examination with the box-shaped test material (all except Comparative Example 13). In Comparative Example 13, although the corrosion weight loss was small and no precipitation of iron sulfate was observed in the examination with the box-shaped test material, the formation of weather-resistant stable rust was insufficient because the film thickness was too large.

[0050]

According to the weather-resistant surface-treated steel sheet of the present invention, stable weather-resistant rust is formed on the surface of the steel material at an early stage under an atmospheric corrosion environment. At that time, the landscape is maintained without floating rust such as red rust and yellow rust and flowing rust. In addition, no precipitation of iron sulfate, which is likely to occur in places with severe condensation such as inside a bridge girder, is observed. This surface-treated steel sheet is suitable as a steel material for civil engineering and building structures because it does not require maintenance for corrosion protection of the steel material and does not impair the landscape of the steel sheet.

This surface-treated steel sheet can be easily and economically obtained by the processing method of the present invention.

Continued on the front page (72) Inventor Takayuki Uemura 4-5-33 Kitahama, Chuo-ku, Osaka-shi, Osaka Inside Sumitomo Metal Industries, Ltd. (72) Inventor Hideaki Sachi 4-5-33 Kitahama, Chuo-ku, Osaka-shi, Osaka Within Sumitomo Metal Industries, Ltd. (72) Inventor Norifumi Doi 4-53, Kitahama, Chuo-ku, Osaka City, Osaka Prefecture Inside Sumitomo Metal Industries, Ltd. (72) Inventor Seishi Kawanishi 6-10, Minamitsukaguchicho, Amagasaki City, Hyogo Prefecture 73 Shinto Paint Co., Ltd. (72) Inventor Masafumi Ueda 6-10-7 Minamitsukaguchi-cho, Amagasaki-shi, Hyogo F-term in Shinto Paint Co., Ltd. AK01A AK01B AK53B BA02 BA03 BA07 BA10A BA10B BA10C BA13 BA16 CC00 DE01B DE01H GB90 JB02 JL09 YY00A 4K026 AA02 AA22 BA01 BA12 BB08 CA18 CA39 DA02

Claims (2)

[Claims] 1. A lower layer having an organic resin coating film having a dry film thickness of 5 to 50 μm and containing 0.1 to 15 mass% of chromium sulfate, and an upper layer having a dry film thickness of 5 to 30 μm and a chromium sulfate film. A weather-resistant surface-treated steel material characterized by having an organic resin coating film containing 0.1 to 10 mass% of carbon powder, excluding carbon. 2. An organic resin paint containing 0.1 to 15 mass% of chromium sulfate with respect to the solid content of the paint is applied to the surface of the steel material so that the dry film thickness becomes 5 to 50 μm, and further applied thereon. A surface treatment method comprising applying an organic resin paint containing no chromium sulfate and containing 0.1 to 10 mass% of carbon powder based on the solid content of the paint so that a dry film thickness is 5 to 30 μm.