JPH06143488A - Coating application for enhancing coating durability of steel material - Google Patents

Abstract

PURPOSE:To provide a steel material capable of greatly enhancing the coating durability of a coated steel material used in a bridge or a building. CONSTITUTION:A steel material containing 0.2-0.7% of Cu is used, and a mixed treatment soln. containing 1-50% of Fe2O3 + Fe3O4, 0.01-5% of phosphoric acid, 0.01-10% of one or more kind of Pb, Ni Cu, P, Zn, Cr or a compd. thereof as main components and containing the remainder of a solvent and coating additives is applied to the surface of the steel material to form a coating substrate treatment film. As a result, the coating durability is greatly enhanced and a repainting period is greatly extended and the maintenance cost can be reduced and the sale of weather-resistant steel is promoted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating method for steel materials used for bridges, constructions, etc. More specifically, weather-resistant steel is used as a coating steel material, and the surface of the weather-resistant steel is treated as the first step of coating. The present invention relates to a steel material coating method in which a coating film having an effect of enhancing coating durability is formed and then post-coated.

[0002]

2. Description of the Related Art Steel materials used for bridges, buildings, etc. are generally coated and used for ensuring corrosion resistance and landscape. After steel is usually processed into parts,
It is blasted and then painted (primer, middle coat, topcoat). This coating, especially from the viewpoint of corrosion resistance, swelling of the coating film,
The important point is the degree of coating durability such as peeling, and it has been attempted to improve the coating durability in terms of coating technology, such as changing or improving the coating resin or the contained rust preventive pigment. . That is, for example, there are various topcoat paints such as long-oil phthalic acid resin, silicon alkyd resin, chlorinated rubber, polyurethane resin, and fluororesin.

On the other hand, weather-resistant steel, which is known as a steel that protects against rust by rust, is generally used naked because it takes advantage of its unique rust color. In general, rust stabilization treatment is performed to prevent stains due to flow rust until stable rust (for example, Japanese Patent Publication No. 56-33991).

[0004]

In the above-mentioned painted bridges, buildings, etc., for example, if the bridges are taken as an example, the current standard paint durability is about 4 years on the coast and about 8 years in the mountains. It is said to be the year, and after this, the paint is being repainted. However, even in the mountainous areas, chloride spraying has been recently used to prevent road freezing, which has increased the atmospheric environmental corrosiveness and has further deteriorated the coating durability. On the other hand, a shortage of painters due to the fact that the painting work is not always in a clean environment has become common, and it has become a major social and economic problem that painting repainting is becoming difficult.

An object of the present invention is to provide a coating method for a steel material which can greatly extend the coating durability of the steel material and can solve the above-mentioned problems all at once. .

[0006]

SUMMARY OF THE INVENTION The gist of the present invention for solving such a problem is that Cu in steel is 0.2 to 0.7.
% Of Fe ₂ O ₃ + F on the surface of the steel material
e ₃ O ₄ 1 to 50%, phosphoric acid 0.01 to 5%, P
b, Ni, Cu, P, Zn, Cr, etc., one or more simple substance or compound, 0.01 to 10%, butyral resin alone or 3 to 30% butyral resin and resin compatible with butyral resin The coating method is to improve the coating durability of a steel material, which comprises coating a coating base film by coating a mixed treatment liquid consisting of a residual solvent and a coating additive, and then coating. Hereinafter, the present invention will be described in more detail.

[0007]

The present inventors have conducted intensive studies on the durability of the coating film on the steel material, that is, the coating durability, and the type of the steel material and the coating base coating, and as a result, found that the coating durability is greatly affected by these. It was That is, the coating durability depends on trace corrosion occurring at the interface between the steel and the coating film, except that the coating film itself deteriorates due to ultraviolet rays, etc. It was found to be greatly affected by the corrosion of.

More specifically, first, the corrosion of the steel material at the interface between the steel material and the coating film is caused by the water content passing through the coating film,
It is caused by corrosive ions such as oxygen and chloride ions, and a part of the steel surface elutes as a minute anode and elutes, forming minute blisters, and then peeling off in the cathode area around it causing full-scale coating blisters. It is known that the coating durability will deteriorate. Therefore, it is considered that the coating durability is improved if the anode reaction can be suppressed.

The present inventors have found that Cu 0.2 to 0.
Using weathering steel containing 7%, Fe ₂ O ₃ + on the surface of the steel material
Fe ₃ O ₄ 1-50%, phosphoric acid 0.01-5%, P
b, Ni, Cu, P, Zn, Cr, etc., one or more simple substance or compound, 0.01 to 10%, butyral resin alone or 3 to 30% butyral resin and resin compatible with butyral resin When a coating base film is formed by applying a mixed treatment liquid consisting of the balance solvent and paint additive, an ultra-thin film (think of complex phosphate) is formed on the bottom layer of this film, that is, the surface of weather resistant steel. It was found that they were formed, and by further peeling off the resin layer and performing an electrochemical measurement, it was found that the weather resistant steel on which this ultrathin film was formed had a large anodic polarization and suppressed the anodic reaction. Therefore, in this case, since the generation of the minute anode under the coating film is suppressed, the generation of minute swelling does not occur.

Further, even if minute blisters occur, the cathode current is consumed for the reduction of the iron oxide contained in the coating undercoating which is in contact with the steel sheet in the peripheral cathode region. The movement of OH ions, which causes the generation, to the interface is suppressed, and the cathode swelling is also less likely to occur.

The reasons for limiting the scope of the claims of the present invention invented based on such a principle will be described below.

First, the steel material is made a weather-resistant steel containing 0.2 to 0.7% of Cu, because the above-mentioned effect of suppressing the anode reaction of the ultra-thin film on the steel surface is due to the inclusion of Cu and Cr in the steel. This is because it is remarkable when there is. This is C in the ultrathin film
It is considered that u and Cr are taken in, but Cu
If it is less than 0.2%, this effect does not occur, and if it exceeds 0.7%, it is effective, but 0.2-
It was set to 0.7%.

Phosphoric acid and Pb, Ni, Cu, P, Z
The reason for adding one or more of simple substances or compounds such as n and Cr is that phosphoric acid reacts with these simple substances or compounds and Cu in steel to form an extremely thin film of complex phosphate. Yes, in this case the content of phosphoric acid is 0.0
The content of 1 to 5% is because if it is 0.01% or less, there is no effect on the formation of an ultrathin film, and if it exceeds 5%, the coating becomes sticky and cannot be formed by drying at room temperature. Furthermore, Pb, N
The content of a simple substance or a compound such as i, Cu, P, Zn, and Cr is set to 0.01 to 10% because it is difficult to form an ultrathin film at 0.01% or less and stable treatment is performed at more than 10%. This is because it hinders the application of the liquid and makes it easier to peel off the treated film.

Fe ₂ O ₃ + Fe ₃ O ₄ is added in order to consume and suppress the cathode current by its own reduction when the minute anode swells and the cathode is formed in the periphery as described above. However, the content is set to 1 to 50% because if it is less than 1%, the distribution in the coating is small, the chance of contact with the steel surface is small, and it is not possible to receive a sufficient cathode current. 50%
If it exceeds, the effect is great, but the coating becomes brittle and easily scratched, which is not suitable for practical use.

Further, the resins for curing the undercoat are limited to butyral resin alone or resins compatible with butyral resin and butyral resin, because these resins easily mix with other processing liquid components, and In performing the treatment of the present invention on weather-resistant steel, spray coating and brush coating can be easily performed, short drying time,
Furthermore, the reason is that the adhesion to the coating film applied on this treated film is good, and the addition amount is set to 3 to 30%. If the addition amount is less than 3%, the coating is fragile and easily scratched. This is because if it exceeds 30%, the viscosity of the treatment liquid increases, workability deteriorates, and it takes time to dry the coating.

In order to maintain the stability of the treatment liquid, ordinary paint additives such as a pigment dispersant that suppresses sedimentation and separation of solids, which are usually added in small amounts to the paint, are added to the treatment liquid. With regard to the above, it is possible to appropriately select and use one that is suitable for the blending of the treatment liquid, if necessary.

Next, the coating applied on the undercoat,
This is not particularly limited, and may be applied with a normal coating suitable for applications such as bridges and construction.For example, in the case of bridge applications, long-lasting phthalic acid resin, silicone alkyd resin, chlorinated rubber type, polyurethane resin, fluorine is used as the top coat paint. Resin or the like can be used. In addition, undercoating such as zinc-rich primer and cyanamide lead rust preventive paint is applied in normal painting, but this undercoating can be omitted in the present invention.

[0018]

EXAMPLES The present invention will be specifically described below based on examples. Test pieces of weather resistant steel and ordinary steel shown in Table 1 (plate thickness 6
mm, size 300 × 300 mm), after completely removing the scale by shot blasting, the treatment shown in Table 2 was performed.

The treatment was carried out by first applying an undercoat forming liquid by spraying to a film thickness of about 15 μm, naturally drying for 3 hours, and then applying a coating film. A normal coating material as a comparative material was subjected to undercoating, intermediate coating and topcoating after shot blasting.

Scratches reaching the surface of the steel material were put into these test pieces with a cutter knife, and an atmospheric exposure test was conducted for 3 years in a semi-industrial zone (Sagamihara City, Kanagawa Prefecture) to determine the coating durability.

As shown in Table 3, the weather-resistant steels according to the present invention coated with a coating undercoat did not cause rust at all, nor did the coating bulge. Rust and swelling were observed in some of the steel materials treated in the same manner, and many rust and swelling occurred in the comparatively coated steel materials.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

[Table 3]

[0025]

As is apparent from the above examples, the coating method of the present invention, when applied to bridges, constructions, etc., is used every several years when the conventional coating method is used in order to significantly improve the coating durability. Since it does not require repainting, the maintenance cost can be significantly reduced, and it has an extremely high industrial value effect that is very useful for retaining social capital in the social trend of lack of labor for painting.

Claims (1)

[Claims] 1. A weather resistant steel containing 0.2 to 0.7% of Cu is used, and Fe ₂ O ₃ + Fe ₃ O _{4 is} formed on the surface of the steel material.
1 to 50%, phosphoric acid 0.01 to 5%, Pb, Ni, C
u, P, Zn, Cr, etc., one or more kinds of 0.01 or more, 0.01 to 10%, butyral resin alone or 3 to 30% butyral resin and a resin compatible with butyral resin as a main component, and the balance solvent A coating method for improving the coating durability of a steel material, which comprises applying a coating undercoating film by applying a mixed treatment liquid comprising a paint additive and a coating additive, and then applying the coating.