JP3065189B2 - Coating method to improve coating durability of 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 coating steel used for bridges, buildings, and the like. The present invention relates to a method of coating a steel material which is to be formed after forming a coating having an effect of improving coating durability.

[0002]

2. Description of the Related Art In general, steel materials used for bridges, buildings, and the like are used after being painted to secure corrosion resistance and landscape. Normally, steel material is processed into members,
It is cleaned and then painted (undercoat, middle coat, top coat). This coating, especially in terms of corrosion resistance, blistering of the coating,
The importance of the coating durability such as peeling is an important point, and painting durability has been improved in terms of coating technology such as changing and improving the coating resin or the contained rust preventive pigment. . That is, for example, there are various types of topcoat paints such as long-oil phthalic resin, silicone alkyd resin, chlorinated rubber, polyurethane resin, and fluororesin.

On the other hand, weather-resistant steel, which is known as a steel that protects rust with rust, is generally used bare, in order to make use of its unique rust color. In general, rust stabilization treatment is performed to prevent contamination due to flowing rust until stable rust occurs (for example, Japanese Patent Publication No. 56-33991).

[0004]

The above-mentioned painted bridges, buildings, etc. are, for example, in the case of a bridge, for example, the paint durability, which is currently the standard, is about 4 years on the coast and about 8 in the mountains. It is the year, and after this, the paint is repainted. However, even in mountainous areas, in recent years, the spraying of chlorides to prevent roads from freezing has increased the corrosiveness of the atmospheric environment, and the coating durability has been increasingly degraded. On the other hand, there is a general shortage of painters due to the fact that the paint work is not always in a clean environment, and there is a major social and economic problem that it is becoming difficult to change the paint.

[0005] An object of the present invention is to provide a method of coating a steel material capable of significantly extending the coating durability of the steel material and improving the coating durability of the steel material capable of solving the above-mentioned problems at once. .

[0006]

The gist of the present invention for solving the above-mentioned problems is that the steel contains Cu 0.2 to 0.7.
%, And the surface of the steel material is Fe ₂ O ₃ + F
_{e 3 O 4 1~50%, 0.01~5} % phosphoric acid, P
b, Ni, Cu, P, Zn, Cr or other simple substance or one or more compounds of 0.01 to 10%, butyral resin alone or butyral resin and 3 to 30% of resin compatible with butyral resin This is a coating method for improving the coating durability of a steel material, which comprises applying a mixed treatment liquid comprising a residual solvent and a coating additive to form an undercoat coating, and then applying coating. Hereinafter, the present invention will be described in more detail.

[0007]

The present inventors have conducted intensive studies on the durability of a coating film on a steel material, that is, the coating durability, on the type of steel material and the coating undercoat, and found that the coating durability is greatly affected by these. Was. In other words, the coating durability is affected by the slight corrosion that occurs at the interface between the steel and the coating film, except that the coating film itself is deteriorated by ultraviolet rays, etc. Was found to be greatly affected by the corrosion of steel.

[0008] More specifically, the corrosion of the steel at the interface between the steel and the coating is caused by the moisture transmitted through the coating,
Caused by corrosive ions such as oxygen and chloride ions, a part of the steel material surface elutes as a fine anode, forming fine blisters, and then peeling occurs in the surrounding cathode region to form a full-fledged coating blister. It is known that coating durability deteriorates. Therefore, it is considered that if this anode reaction can be suppressed, the coating durability will be improved.

[0009] The present inventors have found that in steels, Cu 0.2 to 0.
7% by weight, and the surface of the steel material is Fe ₂ O ₃ +
_{Fe 3 O 4 1~50%, 0.01~5} % phosphoric acid, P
b, Ni, Cu, P, Zn, Cr or other simple substance or one or more compounds of 0.01 to 10%, butyral resin alone or butyral resin and 3 to 30% of resin compatible with butyral resin When a base coat is formed by applying a mixed treatment solution consisting of a solvent and a paint additive, an extremely thin film (considered to be a complex phosphate) is formed on the lowermost layer of the coat, that is, on the surface of the weathering steel. It was found that it was formed, and furthermore, by peeling off the resin layer and performing electrochemical measurement, it was found that the weather-resistant steel on which this extremely thin film had been formed had large anodic polarization and suppressed the anodic reaction. Therefore, in this case, the generation of minute anodes under the coating film is suppressed, and the occurrence of minute blisters does not occur.

Furthermore, even if minute blisters occur, the cathodic current is consumed in the reduction of iron oxide contained in the undercoat film in contact with the steel sheet in the peripheral cathode region. The movement of the OH ions, which are the cause of the generation, to the interface is suppressed, and the cathode blister is hardly generated.

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

First, the reason why the steel material is weather-resistant steel containing 0.2 to 0.7% of Cu is that the extremely thin film on the steel surface suppresses the anodic reaction because the steel contains Cu and Cr. This is because it is remarkable when there is. This is because C
It is considered that u and Cr are taken in.
If it is less than 0.2%, this effect is not obtained. If it exceeds 0.7%, although the effect is obtained, the rolling performance of steel is impaired.
0.7%.

Phosphoric acid and Pb, Ni, Cu, P, Z
The reason for adding at least one element or compound such as n or Cr is that phosphoric acid reacts with these element or compound and Cu in steel to form an extremely thin film composed of a complex phosphate. In this case, the phosphoric acid content is set to 0.0
The reason for setting the content to 1 to 5% is that if the content is 0.01% or less, there is no effect on the formation of an extremely thin film, and if it exceeds 5%, the coating becomes sticky and cannot be formed by drying at room temperature. Furthermore, Pb, N
The reason why the content of a single substance or a compound such as i, Cu, P, Zn, and Cr is set to 0.01 to 10% is that an extremely thin film is hardly formed when the content is 0.01% or less, and a stable treatment is performed when the content exceeds 10%. This is because it hinders the application of the liquid, and the treated film is easily peeled off.

Fe ₂ O ₃ + Fe ₃ O ₄ is added in order to consume and suppress the cathode current by its own reduction when a minute anode blister occurs and a cathode is formed in the periphery as described above. However, the content is set to 1 to 50%. When the content is less than 1%, the distribution in the coating is small and the chance of contact with the steel surface is reduced, so that the cathode current cannot be sufficiently received. 50%
If the ratio exceeds 1, the effect is large, but the coating becomes brittle and easily scratched, which is not practically suitable.

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

In order to maintain the stability of the treatment liquid, a usual paint additive, such as a pigment dispersant which suppresses sedimentation and separation of solids, is added to the treatment liquid in a small amount. As for the method, a material suitable for the composition of the processing solution may be appropriately selected and used as needed.

Next, the coating applied on the base coat,
This is not particularly limited, and a normal coating suitable for bridge or architectural applications may be applied.For example, for bridge applications, long-lasting phthalic acid resin, silicone alkyd resin, chlorinated rubber, polyurethane resin, fluorine resin, etc. Resin or the like can be used. In the usual coating, an undercoat such as a zinc-rich primer or a cyanamide lead rust preventive paint is applied, but in the present invention, this undercoat can be omitted.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments. Test pieces of weathering steel and ordinary steel shown in Table 1 (thickness 6
(mm, size 300 × 300 mm) was completely removed from the scale by shot blasting, and then subjected to the processing shown in Table 2.

In the treatment, first, a coating solution for forming an undercoat film was applied by spraying so as to have a film thickness of about 15 μm, dried naturally for 3 hours, and then applied. An ordinary coating material as a comparative material was subjected to undercoating, intermediate coating, and topcoating after shot blasting.

The test pieces were scratched with a cutter knife to the surface of the steel material, and subjected to an atmospheric exposure test in a semi-industrial zone (Sagamihara City, Kanagawa Prefecture) for three years to determine the coating durability.

The results are shown in Table 3. As shown in Table 3, the weather-resistant steel according to the present invention coated with the undercoat film after coating formed no rust and no blistering of the coating film. When the same treatment was applied to the steel material, rust and swelling were observed in part, and the rust and swelling occurred in the case of the normal coating as a comparative material.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

[Table 3]

[0025]

As is clear from the above examples, when the coating method of the present invention is applied to a bridge, a building, or the like, in order to greatly improve the coating durability, the coating method of the present invention is applied every several years. Since repainting is not required, not only can maintenance costs be significantly reduced, but it also has an extremely high industrial value, which greatly contributes to the maintenance of social capital in the context of a shortage of paint labor.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-B 53-22530 (JP, B2) JP-B 58-39915 (JP, B2) (58) Fields surveyed (Int. Cl. ⁷ , DB name) B32B 15/08 B05D 7/14 C23F 11/00

Claims (1)

(57) [Claims] 1. A weather-resistant steel containing 0.2 to 0.7% of Cu in steel, and the surface of the steel material is Fe ₂ O ₃ + Fe ₃ O _4.
1-50%, phosphoric acid 0.01-5%, Pb, Ni, C
0.01 to 10% of at least one element or compound of u, P, Zn, Cr and the like, butyral resin alone or 3 to 30% of butyral resin and a resin having compatibility with butyral resin as a main component; A coating method for improving the coating durability of a steel material, comprising forming a base coating film by applying a mixed treatment liquid comprising a coating additive and a coating additive, and then applying a coating.