JP3416874B2 - Surface treatment method for highly designed steel - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for surface treatment of a highly-designed steel material, and particularly to a rust layer (hereinafter referred to as “weather resistance "Stable rust"), which relates to a surface treatment method for a highly-designed steel material that can be formed early without contaminating the surface appearance.

[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 weather resistant steels, but in order to form rust that protects against corrosion in a few years outdoors (hereinafter referred to as "weather resistant rust"), corrosion resistant treatment work such as painting It is so-called maintenance-free steel that does not require.

However, since it takes several years until the weather-resistant rust is formed, floating rust such as red rust and yellow rust or flow rust is generated during the period until then, which is not only visually unfavorable. The problem remains that it also causes pollution of the surrounding environment. Especially in an environment where sea salt particles fly in, not only this tendency is remarkable, but also weather resistant rust is not formed.

Regarding this problem, for example, Japanese Patent Laid-Open No. 1-1
Japanese Patent No. 42088 proposes a surface treatment method for forming a phosphate film.

However, the process of processing is complicated because it is necessary to carry out an appropriate pretreatment before forming the phosphate coating, and when welding of steel materials is required, it is a work to treat the welded portion. It is difficult from the standpoint of property, and it is difficult to apply it to building structures in terms of cost.

Further, this method cannot be said to form stable weather-resistant rust in the severe atmospheric corrosive environment where the salt content comes in.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to apply a coating to the surface or rust layer of a low-alloy steel such as weather-resistant steel or a so-called rust-producing steel material such as ordinary steel, so that the appearance can be improved at an early stage. It is an object of the present invention to provide a surface treatment method for a highly designable steel material which forms stable weather-resistant rust on the surface of the steel material without damaging it.

[0009]

As a result of analyzing stable rust generated by a long-term exposure test for 20 years or more in order to achieve the above-mentioned problems, weather-resistant stable rust was found to be α- (Fe, Cr) O.
To clarify that it is composed of a fine aggregate of fine crystals made of OH (hereinafter referred to as "chroma goethite"), and to generate weather-resistant stable rust early to suppress the formation of floating rust and flow rust. It was found that the key point is how to promote the formation of dense chrome goethite.

As a concrete method for solving the above-mentioned problems, the inventors of the present invention coated the surface of the steel material or the rust layer of the steel material with a treating agent composed of chromium sulfate and a butyral resin,
A method for early formation of weather resistant stable rust without the occurrence of flow rust and the like was found and disclosed in WO-9832895. Furthermore, the present invention was developed by developing a treatment method for preventing aesthetic appearance at the initial stage and environmental pollution by Cr ions.

The gist of the present invention is as follows (1) and (2)
Is.

(1) An organic resin paint containing 1 to 15% by mass of chromium sulfate is applied on a steel material in a dry film thickness of 5 to 150 μm and dried, and then a liquid having a water content of 50% by mass or more is used to A method for surface treatment of a highly-designed steel material, which comprises performing cleaning treatment more than once.

(2) The organic resin coating material contains 10 to 40% by mass of an organic resin composed of butyral resin or a mixture of butyral resin and a resin compatible with butyral resin. Surface treatment method for high design steel.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.

(1) Effect of chromium sulfate If the structure of rust is dense, it is easy to physically block the atmospheric corrosive environment, so that the elution of iron ions, which is the fundamental cause of floating rust and flow rust, is reduced and stable. Form rust. However,
If there are cracks or pores in the rust, it becomes a supply path for water and oxygen,
Rust stability is reduced. Therefore, it is necessary to form a dense and continuous stable rust layer.

Chromium sulfate becomes chromium ions and sulfate ions when water penetrates into the coating film, and reaches the coating film / steel interface. Sulfate ions and water corrode steel and produce iron ions. Chromium ions have the effect of converting these iron ions into goethite substituted with chromium, which is the main component of weathering stable rust. Further, it is considered that the sulfate ions not only accelerate the initial generation of iron ions but also contribute to the generation, miniaturization and densification of the stable rust layer, gersite.

In order to obtain this effect even in a severe atmospheric corrosive environment where salt is scattered, it is necessary to add 1 to 15% by mass of chromium sulfate to the solid content in the organic resin coating material. By adding 1 mass% or more, when the steel material after coating and drying is placed in an atmospheric corrosive environment, weather resistant stable rust can be generated early. Further, the upper limit is limited to 15% by mass because the soluble content in the coating material increases, so that the coating film disintegrates faster and is exposed to a corrosion factor before forming sufficient weather-resistant stable rust. This is because the weather resistance cannot be guaranteed in a severe corrosive environment. The mass ratio of chromium sulfate to the solid content as used herein means the ratio to the coating solid content excluding volatile components such as solvents.

(2) Effect of Resin The resin used as a binder in the coating composition is a butyral resin alone or a mixture of a butyral resin and a resin compatible with the butyral resin (eg, melamine resin or phenol resin). It can be illustrated. If the amount of resin in the treatment agent is less than 10% by mass, it is difficult to obtain a uniform coating film,
In addition, the strength and adhesiveness of the formed coating film also decrease, so
0 mass% or more is preferable. On the other hand, when the amount of the resin exceeds 40% by mass, the amount of water permeating into the coating film decreases and the formation of weather resistant stable rust is significantly delayed. In addition, butyral resin is a very suitable component for this treatment agent because it is extremely flexible and follows the change of the steel surface accompanying the formation of the rust layer without difficulty.

Although the organic resin coating material is liquefied and applied, it may contain other necessary organic solvent.

In the coating material of the present invention, in addition to chromium sulfate, coloring pigments such as iron oxide, titanium dioxide, carbon black and phthalocyanine blue, and 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 sulfate, and other additives such as thickeners, dispersants and reaction accelerators.

In use, the coating material of the present invention is adjusted with an organic solvent to a viscosity suitable for coating work, and the solvent evaporates by natural drying after coating.

Further, an oxygen acid such as phosphoric acid or molybdic acid or an aqueous solution thereof may be added. Rather, the addition of oxygen acid is adsorbed on the resulting chromium-substituted geesite layer,
The ion permeability of a stable rust layer, chloride ion (Cl ^-)
It is suitable because it suppresses the permeation of corrosive anions such as Hg and selectively permeates the cations, and thus has the effect of improving the chloride corrosion resistance of the stable rust layer. If the coating film described here has a film thickness of 5 to 150 μm after it is dried and solidified, the balance of supply of chromium ions and iron ions will be optimum at the stage of producing weathering stable rust.

The coating material described above can be applied by an air spray method, an airless spray method, a brush coating method, or the like, as in the ordinary coating method, and therefore, the coating can be applied anywhere.

Further, since the effect can be obtained even by one coating operation, it is excellent in economical efficiency. Furthermore, since it can be painted on-site, it can be used for repairing steel materials with rust on the surface after cutting or welding, etc.

Since the corrosion rate of the steel material becomes extremely low after the formation of weather resistant stable rust, it is possible to apply a colored paint to the upper layer, and a colored coating film is applied to a bare steel material having a surface such as blast. The life extension effect of the colored coating film can be expected compared with the case of coating.

The steel material to which the present coating composition is applied is not particularly limited to a steel type, and may be a common steel or a low-alloy steel having weather resistance or the like, which produces so-called rust. It doesn't matter.

Even if some external force acts on the protective rust layer generated in this way to generate cracks or peel off, if chromium sulfate remains in the coating film of the sound part, the damaged part is sound. Since there is chromium sulphate supplied from the part, it can be expected to have the self-repairing ability to generate weather resistant stable rust again.

(3) Effect of Washing Treatment Although weather resistance can be obtained by forming the resin layer containing chromium sulfate as described above, two problems can be considered in the early stage before sufficient formation of chromium goethite. One is that trivalent Cr ions in chromium sulfate are eluted,
The other is an aesthetic problem until chromium goethite is formed, that is, the reaction between chromium sulfate and the underlying iron produces a green or white reaction by-product (mainly iron sulfate), which is The problem is that it deposits on the surface of the coating film and spoils the appearance. The following processing methods have been developed to solve these problems.

After the above coating material is applied and dried, a washing treatment is further performed once or more with a liquid having a water content of 50% or more. By this processing, the following effects can be obtained.

(1) Moisture in the liquid promotes the reaction between chromium sulfate and base iron, and chromium goethite is produced early.

(2) Excessive sulfate ions and Cr ions are washed away, so that the production of reaction by-products (iron sulfate) can be suppressed and the outflow of Cr ions into the environment can be prevented.

In this treatment, there are a method of directly applying a liquid to the coated steel material and a method of physically rubbing the surface by soaking it in a mop or the like. It is desirable that the cleaning be performed as soon as possible after coating and drying. Preferably after drying 1
Within a year, more preferably within a day. The content of water may be 100%, but if it is 50% or more, the effect is sufficient, and if it is less than 50%, the economical efficiency of the liquid occurs, so the content is limited to 50% or more.

The liquid may be tap water, or a mixed liquid of water and methanol for the purpose of degreasing. This washing treatment may be performed once or may be repeated twice or more.

It should be noted that 1 to 15 mass% of chromium sulfate is added to the steel material.
After coating the containing organic resin coating material with a dry film thickness of 5 to 50 μm, a series of steps of performing the cleaning treatment once or more with a liquid having a water content of 50% or more may be repeated a plurality of times.

[0035]

EXAMPLES The processing method and effects of the present invention will be described by way of examples. The chemical composition of the test steel used is shown in Table 1, and the treatment method before coating the steel material is shown in Table 2. The size of the test piece is 150 × 7
It was set to 0 × 3.2 mm. Table 3 shows the composition of the coating treatment agent used in the test, the sample preparation conditions, and the test results. Table 4 shows the cleaning conditions (cleaning liquid, cleaning method) after the coating treatment, and Table 5 shows the test results.

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

[Table 3]

[0039]

[Table 4]

[0040]

[Table 5]

The viscosity (measured by a B-type viscometer) was adjusted to 20 by adding an appropriate amount of a solvent to the composition of the resin, pigment and additive shown in Table 3.
A paint having 0 to 1000 CPS was prepared and applied by air spray. After coating and drying, cleaning treatment was performed under various conditions. This sample test piece is 10
It was installed horizontally on the coastal area of Naoetsu City, Niigata Prefecture, at a position of 0 m, and the raw powder of artificial seawater was sprinkled on the upper surface of the test piece every day so as to be 1 mg / dm ^2, and exposed for 1 year.

After removing the residual coating film and rust, the mass was measured, and the corrosion weight loss was measured by subtracting from the previously measured steel material amount before coating. The corrosion weight loss thickness (μm) converted from the density of the steel material was determined. The test results in Table 3 include:
The average corrosion weight loss on one side, which is half the measured corrosion weight loss, is shown. For the sample of pretreatment (Y) shown in Test No. 4, the average corrosion weight loss of the uncoated sample was calculated,
The average value of the amount of rust generated by the initial exposure was calculated, and this was subtracted as a blank value.

Further, with respect to the exposed sample, the cross section of the formed rust was subjected to structural analysis by Raman spectroscopy and elemental analysis in rust was performed to confirm the presence or absence of the chrome goethite layer. According to the generation state of the chrome goethite layer, it was evaluated as “◯” if it was continuously generated so as to cover the entire surface, “Δ” for discontinuous generation, and “x” for no generation.

The cross-cut adhesiveness is JIS K5400-
The evaluation was made at 8.5.1 (clearance interval 2 mm), and the result was displayed as [10 (good) to 0 (bad)].

As a result, in Invention Examples 1 to 6 in Table 3, generation of flow rust was not recognized, corrosion weight loss was small, and weathering stable rust (chroma goethite) was formed on the surface of the underlying steel. Was found to exist. In particular, in the case where the binder resin is a mixture of butyral resin (A) and phenol resin (B) compatible with butyral resin as in Inventive Example 3, a steel material in which rust is generated in the base as in Inventive Example 4 ( It was confirmed that the effect is exhibited even when the undercoating Y) shown in Table 2 is used or when the ordinary steel is coated as in Inventive Example 5.

On the other hand, Comparative Example 7 did not contain chromium sulfate, so the formation of weather-resistant stable rust was insufficient, and the corrosion weight loss was large, and Comparative Example 8 had an excessive amount of chromium sulfate, and therefore the coating film adhered. It lacks in suitability as a surface-treated steel material with high design properties such as poor appearance and poor appearance.

Further, as shown in Inventive Example 9, except that the binder resin is a butyral resin or a mixture of a butyral resin and a resin compatible with the butyral resin, the corrosion weight loss is slightly large, but it is suitable as a paint. Met. As shown in Inventive Example 10, when the binder resin amount was a little small, the corrosion weight loss was a little large, and as shown in Inventive Example 11, when the binder resin amount was a little large, the generation of the chrome gate site layer was discontinuous. However, all were suitable as paints.

The influence of changing the cleaning treatment conditions after coating (shown in Table 5) is that the liquid having a water content of 50% or more is discharged (water amount: 100 liter / m ² ) or mop ( In the invention examples (2) to (7) in which the amount of water: 1 liter / m ² ) was performed once or more, the reaction by-products were less than those in the comparative example (1), and the aesthetic appearance was good. The Cr concentration was also low.

The amount of Cr ions eluted was determined by placing a pan under the sample, collecting rainwater flowing down through the sample during rainy weather, and measuring the Cr concentration in the rainwater.

[0050]

EFFECTS OF THE INVENTION According to the surface treatment method of the present invention, the weather resistance of the steel material surface is maintained without impairing the initial appearance and without causing floating rust such as red rust or yellow rust or flow rust even in a severe atmospheric corrosive environment. The stable rust layer can be formed early. It can be said to be a very useful treatment method because it exerts its effect even in an environment where sea salt particles fly near the coast, which is a particularly severe corrosive environment. Further, excess chromium ions can be recovered and by-products such as sulfate ions can be reduced to further improve the design.

When the method of the present invention is applied to a steel material for civil engineering or a building structure, it is possible to form weatherproof stable rust at an early stage without causing floating rust or flow rust such as red rust or yellow rust. Maintenance related to anticorrosion of steel is not required, and it is expected to make a great contribution to the industry.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI C23C 22/07 C23C 22/07 22/30 22/30 C23F 11/00 C23F 11/00 Z (56) References JP-A-8 -325506 (JP, A) JP-A-10-204650 (JP, A) JP-A-6-220653 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C23C 22/00- 22/86 B05D 3/10 B05D 5/00 B05D 7/14 C23F 11/00

Claims (2)

(57) [Claims] 1. An organic resin paint containing 1 to 15% by mass of chromium sulfate is applied to a steel material in a dry film thickness of 5 to 150 μm and dried, and then a liquid having a water content of 50% by mass or more is used.
A method for surface treatment of a highly-designed steel material, which comprises performing cleaning treatment more than once. 2. The high design steel material according to claim 1, wherein the organic resin coating material contains 10 to 40% by mass of an organic resin composed of butyral resin or a mixture of butyral resin and a resin compatible with butyral resin. Surface treatment method.