JP2001115270A - Protective rust generation promoting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a protective rust generation promoting method by which weather resistant protective rust is formed on the surface of steel at an early stage, and the generation of floating rust and flowing rust can be prevented. SOLUTION: The surface of steel is coated with an aqueous solution containing one or more kinds among sodium sulfate, iron sulfate and chromium sulfate to a thickness of 0.1 to 1 mm under the conditions that the total concentration is controlled to >=0.001 mol/L in the case iron sulfate is contained, and to >=0.01 mol/L in the case iron sulfate is not contained, is subjected to pretreatment of executing holding for >=0.1 hr without drying the surface after the coating and is thereafter coated with a resin coating material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a rust layer having a protective effect on steel in an atmospheric corrosion environment (hereinafter referred to as "weather-resistant protective rust" or "protective rust") at an early stage on the surface of the steel. The present invention relates to a protective rust generation accelerating treatment method.

[0002]

2. Description of the Related Art Generally, phosphorus (P), copper (Cu),
By containing elements such as chromium (Cr) and nickel (Ni), the corrosion resistance of the steel in the air can be improved. These low-alloy steels are called weather-resistant steels, which are so-called maintenance-free steels in which a weather-resistant protective rust is formed on the surface in a few years outdoors, and no corrosion-resistant treatment such as painting is required thereafter.

However, since it takes several years for the weather-resistant protective rust to be formed, floating rust such as red rust and yellow rust and flowing rust occur during the period, which is not only unfavorable in appearance, but also However, there is a problem that it causes pollution to the environment. In particular, in an environment where sea salt particles fly, not only this tendency is remarkable, but also there is a problem that weather-resistant protective rust is not formed.

[0004] In order to solve this problem, for example, a surface treatment method for forming a phosphate film on the surface of a steel material has been proposed (Japanese Patent Application Laid-Open No. 1-142088). But,
This method requires a complicated pretreatment before forming a phosphate film.
In addition, there is a question about the effect of the phosphate film on accelerating the formation of weather-resistant protective rust.

Further, Japanese Patent Application Laid-Open No. 6-226198 discloses that
Organic resin containing a predetermined amount of chromium sulfate on the surface of steel
Alternatively, a method is disclosed in which a rust layer is formed on the surface of a steel material and the rust layer is coated on the surface to form a weather-resistant protective rust at an early stage. However, the rate of protective rust formation varies greatly because it depends on the atmospheric environment.
Even after more than a year, protective rust may not form.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of such a situation, and has as its object to provide a so-called rust-forming steel material, such as low-alloy steel such as weathering steel and ordinary steel. An object of the present invention is to provide a protective rust generation promoting treatment method capable of forming a rust layer having a protective action at an early stage without being affected by the atmospheric environment and preventing the occurrence of floating rust and flow rust.

[0007]

The gist of the present invention resides in the following protective rust generation promoting treatment method.

[0008] An aqueous solution containing at least one of sodium sulfate, iron sulfate and chromium sulfate is applied to the surface of steel material at a total concentration of 0.001 mol / l when iron sulfate is contained.
As described above, when iron sulfate is not contained, under the condition of 0.01 mol / l or more, application is performed so that the thickness is 0.1 to 1 mm.
A method for accelerating the formation of protective rust, comprising: holding a surface after application for 0.1 hour or more without drying, and then applying a resin coating thereon.

The term "thickness of the aqueous solution" as used herein refers to the thickness of the aqueous solution containing at least one of sodium sulfate, iron sulfate, and chromium sulfate applied to the surface of a steel material, converted into the unit surface area (that is, the thickness). , Aqueous solution amount / area).

When the aqueous solution contains two or more of sodium sulfate, iron sulfate and chromium sulfate, the “total concentration” refers to a concentration obtained by adding the respective concentrations of sodium sulfate, iron sulfate and chromium sulfate. If it contains only one of iron and chromium sulfate, it refers to the concentration of that one.

The present inventors have analyzed the weather-resistant protective rust formed on the surface of steel exposed to the atmosphere for more than 20 years by means of X-ray diffraction and the like. They have been found to be constituted by a dense set of fine crystals composed of α-FeOOH (goethite). Therefore, in order to suppress the occurrence of floating rust and flow rust by generating weather-resistant protective rust on the surface of the steel material at an early stage, the point is how to promote the generation of dense goethite.

Therefore, as a result of further study on the method of promoting the formation of goethite, a thin aqueous solution containing at least one of sodium sulfate, iron sulfate and chromium sulfate was applied to the surface of the steel material and dried for a certain period of time. After applying a pre-treatment to hold, by applying a resin paint,
It has been found that it is possible to form a weather-resistant protective rust early without causing flow rust or the like on the surface of the steel material.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The protective rust generation promoting treatment method (the method of the present invention) of the present invention will be described in detail below.

According to the method of the present invention, as described above, an aqueous solution containing at least one of sodium sulfate, iron sulfate and chromium sulfate is applied to the surface of a steel material at a concentration of 0.001 mol when the total concentration thereof is iron sulfate. / L or more, and when not containing iron sulfate, the thickness is 0.1 mol / l or more under the condition of 0.01 mol / l or more.
This is a protective rust formation accelerating treatment method in which a pretreatment is performed so that the surface is kept dry for 0.1 hour or more without drying, and then a resin paint is applied.

In order to suppress corrosion of the steel material by forming rust on the surface of the steel material, in particular, the structure of the rust,
Denseness and adhesion to the steel surface are important. If the rust satisfies these conditions, the rust has few cracks and pores as a supply path of water and oxygen, and the elution of iron ions from the base iron can be reduced.

[0016] Such rust is usually not formed unless the steel is exposed to an atmospheric corrosive environment for several to several decades. However, taking the case of using an aqueous solution of sodium sulfate as an example, the concentration of 0.01 mol
/ L or more aqueous sodium sulfate solution with a thickness of 0.1 to 1 m
When it is applied to have a thickness of m, the formation of a weather-resistant protective rust made of α-FeOOH (goethite) can be promoted.

The concentration of the aqueous sodium sulfate solution is 0.01 m
If the amount is less than ol / l, the generated rust is mainly γ-FeOOH. The upper limit of the concentration of the aqueous sodium sulfate solution is not limited. For example, a saturated aqueous solution may be used.

As a method for applying the aqueous solution of sodium sulfate to the surface of the steel material, a method used in ordinary coating, such as spray coating or brush coating, can be employed as in the case of applying a resin coating described later.

The thickness of the aqueous solution of sodium sulfate applied to the steel surface is 0.1 to 1 mm. 0.1m thick
If it is less than m not dissolve sufficiently proceed in the base steel, less the amount of rust, whereas exceeding 1 mm, in rust Fe ₂ O
Increased amounts of ₃ and γ-FeOOH adversely affect the subsequent formation and growth of protective rust (goethite).

In order to form the protective rust, the aqueous solution of sodium sulfate applied to the surface of the steel material is held for at least 0.1 hour under the condition that it does not dry. The “non-drying condition” refers to a condition in which a state of moisture or moisture is maintained during the holding time. When dried, the dissolution of the base iron does not progress and rust does not form. For example, it is desirable to keep in an atmosphere with a relative humidity of 90% or more. If the holding time is less than 0.1 hour, it is difficult to obtain a sufficient amount of rust. The holding time may be about 24 hours, but even if the holding time is longer than that, moisture is consumed for the generation of rust, and the rate of rust generation thereafter decreases.

The temperature for holding can be set freely between 6 ° C. and 90 ° C. If the temperature is lower than 6 ° C., the grain size of the rust formed is sufficiently small, but the generation rate is small. Protective protection with functions Less likely to rust.

In addition to the aqueous sodium sulfate solution, iron sulfate,
The same effect is obtained by applying an aqueous solution of chromium sulfate. Therefore, an aqueous solution containing iron sulfate and / or chromium sulfate, or an aqueous solution further containing sodium sulfate in those aqueous solutions may be used as the coating liquid. At that time, when iron sulfate is contained, the total concentration is 0.001 mol /
When iron sulfate is not contained, the total concentration is adjusted to 0.01 mol / l or more. Total concentration is less than 0.001 mol / l (when iron sulfate is included) or less than 0.01 mol / l (when iron sulfate is not included)
In this case, the generated rust is mainly γ-FeOOH. The upper limit of the concentration of the aqueous solution containing iron sulfate and / or chromium sulfate or the aqueous solution further containing sodium sulfate is not limited, and one or two or more of these dissolved components are saturated. Aqueous solution may be used.

After applying an aqueous solution containing at least one of sodium sulfate, iron sulfate and chromium sulfate as described above, by holding the solution for a certain period of time under non-drying conditions, protective rust is formed on the steel material surface. As a result, water is consumed in the formation of rust. However, in the case where the applied aqueous solution of sodium sulfate or the like is thick and the holding time is short, for example, it is preferable to dry in a dry atmosphere at a relative humidity of 40% before applying the resin paint in the next step. desirable.

After the pretreatment is performed on the surface of the steel material, a resin paint is applied. Applying the resin paint protects the goethite formed on the steel surface by the pretreatment,
This is to prevent the occurrence of flow rust from the ground iron.

The organic resin used in the resin coating is not particularly limited as long as it can be used as an organic solvent-based coating or an aqueous coating. For example, epoxy resin, urethane resin, vinyl resin, polyester resin, acrylic resin , Alkyd resin, phthalic acid resin and the like can be used. In the paint, along with the resin, coloring pigments such as red iron oxide, titanium dioxide, carbon black, phthalocyanine blue, extenders such as talc, silica, mica, barium sulfate, calcium carbonate, chromium oxide, zinc chromate, lead chromate, Rust-preventing pigments such as basic lead sulfate, and other conventional additives such as thixotropic agents, dispersants, and antioxidants may be contained.

Further, the paint may contain sodium sulfate, iron sulfate, and chromium sulfate used for the pretreatment, either alone or as a mixture of two or more of them. Generation is accelerated. In that case, the content is preferably up to 15% by mass based on the solid content of the paint. If the content exceeds 15% by mass, the effect of suppressing the corrosive anion permeation of the protective rust tends to decrease, and the anticorrosive effect may be reduced in a severe corrosive environment.

When applying a resin coating to the steel surface after the pretreatment, the above-mentioned resin, various additives, sodium sulfate and the like are dissolved in an appropriate amount of an organic solvent or water to be suitable for coating work. Adjust to viscosity. As the organic solvent, a thinner or the like used in ordinary coating may be appropriately used.

As a method for applying the resin paint, a method used in ordinary coating such as air spray coating, airless spray coating, or brush coating can be employed. Therefore, it is possible to perform construction anywhere, and
It is economical because the effect can be obtained by a single painting operation. Furthermore, since on-site painting is possible, the present invention can be applied even after processing such as cutting and welding of steel at a construction site, and can be applied to steel having rust on the surface as it is.

When a resin coating is applied to the surface of the steel material after the pretreatment, the organic solvent or moisture in the coating evaporates by natural drying to form a coating layer (coating film) on the steel material surface. When water is used as the solvent, a part of the water is considered to contribute to the protective rust generation reaction.

The thickness of the coating film is preferably in the range of 5 to 150 μm after the resin coating has been dried and solidified.
If the thickness of the coating film is within this range, protective rust is likely to be formed on the surface of the steel material, and when chromium sulfate is contained in the organic resin, chromium ions are formed during the protective rust generation stage. The supply balance of iron ions is optimized.

The steel material is not limited to the weather-resistant steel, but may be any other steel that generates so-called "rust" such as other low alloy steels and ordinary steels.

According to the method of the present invention, a weather-resistant protective rust is formed on the surface of a so-called rust-forming steel material such as a low-alloy steel such as a weather-resistant steel or ordinary steel at an early stage without being affected by the atmospheric environment. In addition, occurrence of floating rust and flow rust can be prevented.

[0033]

EXAMPLES Steel materials (test steel materials) having the chemical compositions shown in Table 1 were used.
A test piece (size: 150 m) which has been subjected to a pretreatment of applying an aqueous solution of sodium sulfate or the like, and further subjected to a protective rust generation accelerating treatment of applying a resin-based paint shown in Table 2 thereon
m × 70 mm × thickness 3.2 mm).

In the pretreatment, aqueous solutions of various concentrations of sodium sulfate, iron sulfate or chromium sulfate were applied to the surface of the test steel material by changing the thickness by spray coating, and the relative humidity was 95%.
And then dried for 24 hours in an atmosphere with a relative humidity of 40%. Also,
To apply the paint, add a predetermined amount of additives (chromium sulfate and sodium sulfate) to each resin system, or add an organic solvent (thinner) without adding additives, and add a viscosity (B-type viscometer). (Measurement) was set to 0.2 to 1 Newton second per square meter (N · s / m ² ), and the coating was performed by air spray coating.
In addition, two-component type resin systems B and C using a curing agent
Then, the main agent (base resin + additive) and the curing agent were mixed immediately before coating.

[0035]

[Table 1]

[0036]

[Table 2]

Tables 3 to 5 show the conditions for preparing the test pieces.
The reference numerals in the column of “test steel material” correspond to the reference numerals of the steel types shown in Table 1. "Thickness" in the column of "pretreatment" is a thickness obtained by dividing the amount of an aqueous solution of sodium sulfate or the like applied by spray coating by the surface area of the test piece. “Resin-based” of “paint”
The symbols in the column correspond to the symbols of the resin system shown in Table 2, and "thickness" is the thickness after the paint has dried and solidified.

[0038]

[Table 3]

[0039]

[Table 4]

[0040]

[Table 5]

The test piece prepared as described above was placed horizontally in a factory area and exposed for two months, and the occurrence of flow rust was examined over time. In addition, the specimen after the exposure was checked for the presence of protective rust (goethite) by cross-sectional observation with a polarizing microscope (the part where the protective rust was generated was extinguished), and the protective rust against the total rust amount was analyzed by image analysis. The proportion of the amount (protective rust ratio) was determined in percentage. Further, the coating film and rust on the surface of the test piece were removed, the weight was measured, and the weight loss was determined by subtracting the weight from the test piece before the protective rust formation promoting treatment, which was obtained in advance.

The results are shown in Tables 3 to 5. In the table, a circle in the column of “flow rust” indicates that no flow rust was generated, and a triangle indicates that generation of flow rust was recognized.

In Test Nos. 1 to 32 (Examples of the present invention) in Tables 3 and 4, no occurrence of flow rust was observed, the corrosion weight loss (not shown) was small, and the surface of the base test steel material was protected. It was observed that rust was continuously formed.
When the protective rust ratio exceeds 45%, it can be said that the protective rust is generated almost continuously over the entire surface of the steel material.

On the other hand, in Test Nos. 33 to 42 (Comparative Example) in Table 5, the pretreatment was out of the conditions specified by the method of the present invention, and therefore, the protective rust ratio was low and generation of flow rust was recognized. In some cases, it was not possible to form protective rust early.

[0045]

According to the protective rust generation promoting treatment method of the present invention, the surface of a so-called rust-forming steel material such as low alloy steel such as weathering steel or ordinary steel can be formed without being affected by the atmospheric environment. Early weathering protection rust can be formed to prevent the occurrence of floating rust and flow rust, thereby minimizing maintenance related to corrosion protection of steel materials.

Claims (1)

[Claims] 1. An aqueous solution containing at least one of sodium sulfate, iron sulfate and chromium sulfate on the surface of a steel material, and 0.001 mol / l when the total concentration thereof is iron sulfate.
As described above, when iron sulfate is not contained, under the condition of 0.01 mol / l or more, application is performed so that the thickness is 0.1 to 1 mm.
A method for accelerating the formation of protective rust, comprising: holding a surface after application for 0.1 hour or more without drying, and then applying a resin coating thereon.