JP2001040280A - Coating composition for weather-resistant steel, and formation of stable rust by using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a coating capable of forming a stable rust on the surface of a weather-resistant steel, and further to provide a method for forming the stable rust by using the coating composition. SOLUTION: This coating composition for a weather-resistant steel contains a chelate-modified epoxy resin as a part thereof. One or more kinds of copper oxide, chromium nitrate and chromium phosphate, in an amount of 1-60 wt.% as the total based on the total coating composition are preferably added as additives for promoting the formation of the stable rust. The coating composition forms a coated membrane on the new surface, the surface having unstable rust formed thereon, or the surface after removing the unstable rust, of a weather-resistant steel. At the time, the thickness of the dried membrane is preferably 5-100 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating composition used for anticorrosion surface treatment of weather-resistant steel used for bridges, steel towers, buildings, marine structures, etc., and more particularly to a coating composition capable of forming stable rust. The present invention relates to a composition and a method for forming stable rust on the surface of a weather-resistant steel material.

[0002]

2. Description of the Related Art Steel materials used for bridges, steel towers, buildings, marine structures, etc., as they are, not only cause red rust, yellow-brown floating rust, flow rust due to corrosion, but also impair the landscape.
Since the strength of the structure is reduced due to the decrease in wall thickness due to corrosion, some anticorrosion measures are required. Conventionally, as a method of preventing corrosion of these structures, a painting method is generally used, and a heavy-duty anticorrosive coating with improved long-term durability is known, but the coating cost is high and the service life is limited. In addition, there is a problem that maintenance cost is high since regular repainting is necessary.

On the other hand, by adding a small amount of elements such as P, Cu, Cr and Ni to steel materials, dense rust (stable rust) having protection against corrosion is formed in the air in several years. A weather-resistant steel is known as a steel material having a very low corrosion rate. Since weather-resistant steel is a so-called maintenance-free steel that has a permanent anticorrosive effect without being painted after stable rust is formed, its use in structures such as bridges and steel towers has been increasing in recent years.

However, in places where stable rust is unlikely to be formed, for example, at the end of a girder of a bridge or under a flange, or in a sea salt particle flying environment or a snowmelt salt scattering area on a coast, unstable rust is generated, so that the appearance is unstable. Not preferred. Further, floating rust such as red rust and yellow rust and flowing rust may be generated to cause pollution of the surrounding environment, and there is a problem that the usable area is limited.

[0005] Regarding these problems, for a newly-built structure, for example, Japanese Patent Publication No. 56-33991 discloses a method in which a resin layer containing a stable rust component is formed in a lower layer, and the upper layer has weather resistance and corrosion resistance. A surface treatment method by two-layer coating provided with a resin layer having excellent properties and the like is disclosed. In addition, Japanese Unexamined Patent Publication No.
JP-A-226198 discloses that a structure is covered with an organic resin paint containing at least one of chromium sulfate and copper sulfate in a total amount of 1 to 65% by mass.

[0006]

However, there is no effective means for an area where unstable rust is formed on an existing structure using weather-resistant steel. There is a problem that stable rust is not formed after painting on a portion where rust is formed.

Accordingly, the present invention provides a coating composition capable of forming stable rust when applied to the surface of a weather-resistant steel material on which unstable rust has been formed or the surface of a weather-resistant steel material from which the unstable rust has been removed. The purpose is to do. Another object of the present invention is to provide a method for forming stable rust on the surface of a weather-resistant steel material on which unstable rust has been formed or on the surface of a weather-resistant steel material on which the unstable rust has been removed.

[0008]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have developed a method for stabilizing a surface of a weather-resistant steel having unstable rust and a surface of a weather-resistant steel from which unstable rust has been removed. Investigation was conducted to find a coating composition capable of forming rust properly, and as a result, a coating composition containing a chelate-modified epoxy resin as a part thereof was applied to the above-mentioned weather-resistant steel material surface. The stable rust can be properly formed under the coating film, and the formation of stable rust is more effective by adding at least one of copper oxide, chromium nitrate, and chromium phosphate to the coating composition. Was found to be promoted.

The present invention has been made based on such findings, and is a coating composition for weathering steel having the following features and a method for forming stable rust using the same. [1] A coating composition for weather-resistant steel, comprising a chelate-modified epoxy resin. [2] The coating composition according to the above [1], wherein at least one selected from copper oxide, chromium nitrate and chromium phosphate is contained in a total of 1 to 60% by weight based on the whole coating composition. A paint composition for weather-resistant steel. [3] A stable rust is formed on the surface of the weathering steel by applying the coating composition of the above [1] or [2] to the weathering steel to form a coating film having a dry film thickness of 5 to 100 μm. Forming a stable rust. [4] The method for forming stable rust according to the above [3], wherein a coating composition is applied to an unstable rust surface or a surface from which the unstable rust has been removed of the weatherable steel material.

In the present invention, unstable rust means rust that has no protective effect against atmospheric corrosion and generates floating rust such as red rust and yellow rust. Means dense rust that has a protective action against corrosion.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below together with the reasons for limiting the same.

The coating composition for a weather-resistant steel material of the present invention contains a chelate-modified epoxy resin in a part thereof.

Here, the chelate-modified epoxy resin refers to an epoxy resin having a chelate-forming group in the basic skeleton of the resin. As the chelate-forming group, those having an acid group having a salt-forming ability such as a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, or a hydroxyl group, or an amine group or an atomic group having a coordination ability such as a carbonyl group are preferable. It is. In addition, particularly suitable ones are
Adhesive phenolic, phosphoric, and carboxylic acids.

The preferred ratio of the chelate-modified epoxy resin to the whole coating composition is from 8% by weight to 20% by weight. If the proportion of the chelate-modified epoxy resin is less than 8% by weight with respect to the whole coating composition, the effect of fixing rust is not sufficient when applied to a weather-resistant steel surface. But the effect remains the same.

Further, the coating composition for weathering steel of the present invention may contain one or more of copper oxide, chromium nitrate and chromium phosphate as additives for promoting the formation of stable rust. It is preferable to contain 1 to 60% by weight in total.

When the total content of at least one of copper oxide, chromium nitrate, and chromium phosphate in the coating composition is less than 1% by weight, stable rust is formed when applied to a weather-resistant steel surface. On the other hand, when the content exceeds 60% by weight, rust formation is excessively promoted, and there is a possibility that stable rust may not be obtained. Further, the coating film itself becomes brittle and the coating film is not formed stably.

The total content of at least one of copper oxide, chromium nitrate and chromium phosphate is more preferably 2% by weight or more and 20% by weight or less.

The coating composition according to the present invention may further contain additives. As an additive, a rust preventive pigment, an extender pigment, an antioxidant, a stable rust forming aid, and the like can be added.

The rust-preventive pigment is not particularly limited, but iron hydroxide, copper sulfate, nickel sulfate, lead chromate, zinc chromate, iron oxide, red iron oxide and the like are suitable. The extender pigment is not particularly limited, but talc, Silica and the like are preferred.

The antioxidant is not particularly limited, but tannin compounds and zinc phosphate are preferred. The auxiliary agent for forming stable rust is not particularly limited, but nickel oxide and manganese oxide are preferred.

The total amount of the additives as described above is preferably 3% by weight or more and 16% by weight or less based on the whole coating composition.

The coating composition of the present invention can be prepared by dissolving the above-mentioned components in a solvent. As the solvent, aromatic hydrocarbons, alcohols, esters, and ketones are preferable from the viewpoint of coating properties and compatibility, and the amount of the solvent is 20% by weight based on the whole coating composition.
It is about 80% by weight or more.

The coating composition of the present invention is applied to a new surface of a weather-resistant steel material, a surface on which unstable rust has been formed, or a surface from which unstable rust has been removed by brushing or the like to form a coating film. . The film thickness at this time is preferably 5 μm or more and 100 μm or less as a dry film thickness.

When the dry thickness of the coating composition is less than 5 μm, the effect of preventing chloride ions from permeating and preventing rusting is inferior. On the other hand, when the thickness exceeds 100 μm, the protective effect on the underlying steel material becomes excessive and water and oxygen And the formation of stable rust takes time. The film thickness is 10 μm or more and 30 μm or more.
It is more preferred that:

The formation mechanism of stable rust in the present invention is explained as follows. When the coating composition of the present invention is applied to the surface of the steel material on which the unstable rust is formed to form a coating film, first, the resin component in the coating film penetrates into the unstable rust portion, and the dense and unstable Immobilize rust. The resin component has an action of selectively blocking the influence of the environment on the steel surface, and prevents the permeation of chlorine ions that are harmful to the formation of dense rust.
Further, the resin component allows an appropriate amount of water and oxygen necessary for formation of stable rust to permeate the steel surface.

Further, since the coating composition of the present invention contains a chelate-modified epoxy resin, the unstable rust remaining on the surface of the steel material is solidified by the chelate reaction, and the rust is strongly bonded to the iron base material to significantly enhance the fixing effect. .

In the above-described chelate reaction, the chelate ligand in the chelate-modified epoxy resin catches iron ions in the unstable rust layer in the skeleton, and further, red rust (FeOOH)
Is reduced to black rust (Fe ₃ O ₄ ) to stabilize the rust. In addition, as described above, the chelate-modified epoxy resin has excellent permeability to the rust layer, fixes the rust layer, and improves the adhesion of the rust layer to the steel base.

When at least one of copper oxide, chromium nitrate, and chromium phosphate is contained in the coating composition of the present invention, the copper oxide acts as an oxidizing agent and transmits a suitable amount of water to the steel surface. Moderately promotes corrosion. Chromium nitrate and chromium phosphate moderately permeate water and, when they reach the steel surface as nitrate ions and phosphate ions, moderately promote iron corrosion. On the other hand, the chromium is taken into the newly formed rust and makes the rust dense. As a result, stable rust is formed on the existing structure using the weather-resistant steel.

Further, when a coating composition of the present invention is applied to a new surface of a weather-resistant steel material to form a coating film, the resin component in the coating film selects the influence of the environment on the steel surface as described above. It has a function of blocking the flow of ions, and prevents the penetration of chloride ions that are harmful to the formation of dense rust. Further, the resin component allows an appropriate amount of water and oxygen necessary for the formation of stable rust to permeate the steel surface and promotes the formation of stable rust. In addition, when the coating composition of the present invention contains at least one of copper oxide, chromium nitrate, and chromium phosphate, the copper oxide acts as an oxidizing agent and causes appropriate water permeation and moderate corrosion of the steel surface. To promote. Chromium nitrate and chromium phosphate moderately permeate water and, when they reach the steel surface as nitrate ions and phosphate ions, moderately promote iron corrosion. On the other hand, the chromium is taken into the newly formed rust and makes the rust dense. As a result, even when used on a new surface of a weather-resistant steel material, dense and stable rust is formed under a coating film formed by applying the coating composition of the present invention.

By these actions, a dense and stable rust is formed under the coating film formed by applying the coating composition of the present invention, and this coating film weathers and disappears over time, and A stable rust formed below appears.

[0031]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

In the present embodiment, as a chelate-modified epoxy resin having three types of chelate structures of a direct phenol type, a phosphoric acid type and a carboxylic acid type, Adeka Resin EP-49- manufactured by Asahi Denka Kogyo KK is used. 55C (product name)
It was used.

Table 1 shows the component compositions of the coating compositions 1 to 10 of the present invention. The color tone of each composition was the same as that of stable rust.

[0034]

[Table 1]

On the other hand, as a test steel material, a weather resistant steel (150 mm × 70 mm × 6 mm) on which unstable rust was formed was prepared, and only the floating rust on the rust surface was removed to form an unstable rust. Surface (rust surface), surface with steel surface exposed by wire brushing on rust surface (polishing surface), and surface with blast treatment on new surface of weather resistant steel material (new surface) An underlayer treated surface was formed.

Each of the coating compositions was applied with a brush coating on the base treated surface of each of the test steel materials at the film thicknesses shown in Tables 2 and 3 to prepare test pieces of Examples 1 to 36.

Further, as Comparative Examples 1 to 3, commercially available oil-based rust preventive paints were applied to the above three types of base treated surfaces.

Examples 1 to 36 obtained as described above
The test pieces of Comparative Examples 1 to 3 were exposed at an exposure test site for 6 months. This exposure test site is about 200m from the coastline
It is located in a remote place, and is in an environment suitable for generating unstable rust because sea salt particles fly from the sea side.

FIG. 1 shows a method of exposing the test piece.
The lower surface side of the test piece 2 installed at an angle of about 45 ° with respect to the ground 4 in order to make the painted test surface 3 of the test piece 2 difficult to be dried by the sunlight 1 and easily generate unstable rust. It was made to become.

After exposing the test piece for 6 months, the amount of floating rust was measured by a tape peeling test. In this tape peeling test, a 50 mm × 50 mm adhesive tape was used, and the total amount of floating rust peeled off when the test was repeated three times on the same portion of the test piece was measured.

Further, the number of defects in the rust layer was counted based on the number of coloring points by performing a ferroxyl test, and the formation of stable rust was evaluated.

The results of the floating rust evaluation and the ferroxyl test are shown together in Tables 2 and 3 together with the conditions of each Example and Comparative Example.

[0043]

[Table 2]

[0044]

[Table 3]

As shown in Tables 2 and 3, the test pieces coated with the coating composition of the present invention (Examples 1 to 36) were exposed to a severe corrosive environment in which sea salt particles near the shore were flying. Regardless, the amount of floating rust is less than 0.03 g and the number of defects is less than 150 / dm ^{2 in} most cases even in the ferroxyl test. Therefore, it can be seen that stable rust was formed on the weather-resistant steel surface on which unstable rust was formed, on the steel surface on which unstable rust was removed, and on the new steel surface of the weather-resistant steel material.

On the other hand, in Comparative Examples 1 to 3 coated with a commercially available rust preventive paint, the amount of floating rust was as large as 0.03 g or more.
The number of defects in the ferroxyl test evaluation is also 200 / d
m ² or more and stable rust understood that not formed.

[0047]

As described above, according to the present invention, the surface of weather-resistant steel on which unstable rust is formed, the surface of weather-resistant steel from which the unstable rust has been removed, and the new surface of weather-resistant steel are coated. A coating composition capable of forming stable rust when provided. Further, according to the present invention, there is provided a method for forming stable rust on the surface of a weather-resistant steel material on which unstable rust has been formed, the surface of the weather-resistant steel material from which the unstable rust has been removed, and the new surface of the weather-resistant steel material. Further, according to the present invention, it is possible to form stable rust on existing steel structures such as bridges and steel towers on which unstable rust has been formed, and its industrial value is great.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a method of exposing a test piece.

[Explanation of symbols]

 1 Sunlight 2 Specimen 3 Painted surface 4 Ground

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Claims (4)

[Claims] 1. A weatherable steel coating composition comprising a chelate-modified epoxy resin. 2. The coating composition according to claim 1, wherein the coating composition contains at least one selected from copper oxide, chromium nitrate, and chromium phosphate in a total amount of 1 to 60% by weight. A coating composition for weathering steel. 3. The weather-resistant steel material according to claim 1 or claim 2.
The coating composition according to the above is applied and the dry film thickness is 5 to 100 μm.
Forming a stable rust on the surface of the weather-resistant steel material by forming the coating film of (1). 4. The method for forming stable rust according to claim 3, wherein a coating composition is applied to an unstable rust surface or a surface from which the unstable rust has been removed of the weatherable steel material.