JP2001115274A - Surface-treated steel sheet with excellent workability and weather resistance - Google Patents

Abstract

(57) [Summary] [Issues] Stable rust is formed early in the coastal area as well as in the rural areas, and there is no generation of flowing rust and elution of environmental pollutants in the course of the formation. Good adhesion,
Provide a surface-treated steel sheet having excellent workability and weather resistance. SOLUTION: The steel sheet has an iron phosphate coating on its surface, and contains a first component composed of nickel sulfate at 1 wt% or more based on the resin solid content as an upper layer, or further contains a phosphate-based inorganic compound and a Cu-based inorganic compound. A surface-treated steel sheet having a butyral resin coating film having a thickness of 10 to 50 μm containing one or two kinds of second components selected from the above.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-treated steel sheet having excellent workability and weather resistance, which is preferably applied to a steel material for a building mainly used outdoors. In the present invention, the workability means the adhesion (secondary adhesion) of the coating film after processing.

[0002]

2. Description of the Related Art A steel material made of a weather-resistant steel made by adding a small amount of Cu, P, Cr, etc. to a steel is stable against atmospheric corrosion when used naked in an outdoor environment with a small amount of flying salt particles. A dense rust layer (referred to as stable rust) is formed, and this rust layer has the characteristic of keeping the corrosion rate of steel for a long period of time, so it is widely used for bridges and steel towers, and its life is extended. Has contributed.

However, in conventional weathering steel, it takes 5 to 10 years for the stable rust to be formed, and the flowing rust generated during that time significantly impairs the steel material surface and the surrounding scenery. Therefore, there has been a demand for a technical means for forming stable rust at an early stage on the surface of the weatherable steel and for suppressing the generation of flowing rust during the formation of the stable rust. As such means,
The inventions described in JP-B-58-39915 and JP-A-6-226198 are known.

[0004] The invention described in Japanese Patent Publication No. 58-39915 discloses a method of depositing a 1 mg / cm ² or less Fe, Zn, Mn-based phosphate coating on weathering steel, and further adding Fe ₂ O ₃ + Fe ₃ O thereon. ₄ 3-20%, phosphoric acid 0.1-3%, at least one of Fe, Zn, Mn-based phosphates 0.1
0.1 to 5%, one or more of Ni and Cu based inorganic compounds 0.1 to 5%, one or more of chromate, zinc chromate, lead chromate 0.5 to 10
% Butyral resin having a thickness of 5 to 100 μm. The invention described in JP-A-6-226198 is to coat a steel coating containing 1 to 65% by weight of at least one of chromium sulfate and copper sulfate on a steel material surface directly or via a rust layer.

[0005]

Both of the above two prior arts have a corresponding effect in preventing the occurrence of flow rust during the formation of stable rust in weathering steel, but are described in Japanese Patent Publication No. 58-39915. In the invention, there is a problem that the chromium-based compound in the coating film is eluted by getting wet with rainwater, and contaminates the surrounding environment. Also, in the invention described in JP-A-6-226198, a thick plate used for a bridge or a steel tower is applied, and no consideration is given to coating film adhesion after processing. It is difficult to apply to building materials with many bent parts.

[0006] In view of the problems of the prior art, the present invention provides:
Stable rust is formed early in the coastal area as well as in the countryside, there is no generation of flowing rust or elution of environmental pollutants during the formation, good coating adhesion after processing, good workability and weather resistance. An object of the present invention is to provide a surface-treated steel sheet having excellent properties.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, by applying a paint containing a specific resin composition to the surface of a steel sheet, it has excellent workability and corrosion resistance. The present inventors have found that a surface-treated steel sheet excellent in weather resistance that prevents the generation of flowing rust and forms stable rust at an early stage even in a coastal area where the environment is severe can be obtained, and has accomplished the present invention.

That is, the gist of the present invention resides in a surface-treated steel sheet having excellent workability and weather resistance described below. (1) A steel plate having an iron phosphate coating on the surface thereof, and a first component composed of nickel sulfate as an upper layer is 1% based on the resin solid content
A surface-treated steel sheet having excellent workability and weather resistance, characterized by having a butyral resin coating film containing 10 wt.

(2) The surface-treated steel sheet according to (1), wherein the coating further contains a second component comprising one or two selected from a phosphoric acid-based inorganic compound and a Cu-based inorganic compound.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the reasons for limiting the requirements of the surface-treated steel sheet according to the gist (1) of the present invention will be described. In the present invention,
It is necessary to have an iron phosphate coating on the steel sheet surface. The iron phosphate coating is formed by iron phosphate treatment, which is one of the chemical conversion treatments, and is dense and has excellent adhesion, so the initial adhesion of the butyral resin coating film as the upper layer and the adhesion after processing are remarkable. improves. The amount of iron phosphate coating was 0.3
If it is less than mg / m ² , the effect of improving adhesion is small, and if it is more than 2 mg / m ² , delamination may occur within the iron phosphate coating, so that 0.3 to ² mg / m ² is preferred.

The coating film as the upper layer of the iron phosphate coating film is limited to a butyral resin coating film. That is, the base resin of the paint used for forming the coating film must be a butyral resin.
Generally, there are epoxy resins, acrylic resins, and urethane resins as base resins for paints applied to steel materials, but these have low water absorption of several percent, so that stable rust is formed under the coating film. The required water cannot be supplied in a short time. Only when a butyral resin having high hydrophilicity and high water absorption (several tens%) is employed, water necessary for forming stable rust under the coating film can be supplied in a short time.

The butyral resin referred to in the present invention is not only a basic type having a chemical structural characteristic consisting of a butyral group, a hydroxyl group and an acetyl group, but also a product obtained by reacting and crosslinking the basic type with an isocyanate-based curing agent. Modified molding, such as one in which the mold is mixed with a phenolic resin to reduce the hydroxyl group concentration, is also included. The modified molding is suitable for reducing the water absorption of the entire system to an appropriate value when used in an extremely high humidity and severely corrosive environment.

If the film thickness of the butyral resin coating is less than 10 μm, flowing rust is generated, and if it is more than 50 μm, the supply of water and oxygen necessary for the formation of stable rust is insufficient and the formation of stable rust becomes slow. Limited to 50 μm. Furthermore, the butyral resin coating is made of a first nickel sulfate for stabilizing rust.
Must be contained.

When the butyral resin film containing nickel sulfate is wetted by rainfall or condensation, the butyral resin absorbs water, and the nickel sulfate in the resin is ionized to form Ni ²⁺ and SO ₄ ^2- . SO ₄ ^2- contributes to the early formation of stable rust by dissolving ground iron and supplying iron ions to the steel surface.
On the other hand, Ni ²⁺ acts on the corrosion reaction product at the interface between the steel material and the surface treatment layer (iron phosphate layer + coating layer) and transforms it into α-FeOOH, the main component of stable rust. Promote. Ni
²⁺ further reduces the crystal grains of α-FeOOH by being partially incorporated into the generated α-FeOOH, and forms a dense rust layer having a high barrier effect. In order to prevent the flow rust of weathering steel and to form a stable rust layer on the surface early,
The rapid supply of iron ions by SO ₄ ^2- and the formation of stable rust by Ni ²⁺ must be performed simultaneously. Therefore, even if a nickel-based compound other than nickel sulfate is used,
Early rust stabilization of weathering steel is difficult.

In order to exhibit the above effects, the first component must be contained in the butyral resin coating in an amount of 1 wt% or more based on the solid content of the resin. Hereinafter, the percentage by weight of the components other than the resin in the resin paint with respect to the resin solid content is referred to as the amount of resin. The amount of the first component relative to the resin was 1 wt.
However, if the content is less than 5% by weight, the effect is relatively small, and if it exceeds 20% by weight, the effect is not only saturated but also the cost is increased. Therefore, 5 to 20% by weight is preferable.

Next, the reasons for limiting the requirements of the surface-treated steel sheet according to the gist (2) of the present invention will be described. (2) The surface-treated steel sheet according to (1), in which the coating film further stabilizes rust.
One or two selected from phosphoric acid-based inorganic compounds and Cu-based inorganic compounds as a substance exhibiting a synergistic effect with the components of
It contains a second component consisting of a seed. Each of the second components can exhibit a sufficient effect only when coexisting with the first component in the butyral resin coating film.

The phosphoric acid-based inorganic compound is caused by water absorption of the resin.
Phosphate ion is Cu²⁺, Fe ²⁺Such as metal ions
Combines to form a complex, chemically stable phosphate coating
Therefore, it is effective to protect the generated stable rust layer.
This effect is small when the amount of resin is less than 1 wt% and it is small and exceeds 20 wt%.
Is saturated, the amount of phosphate-based inorganic compound to resin is 1
~ 20 wt% is preferred. Specific composition of inorganic phosphate compounds
As, for example, H_ThreePO_Four, AlPO_Four, Zn_Three(PO_Four)_TwoEtc. are good
It can be adopted well.

The Cu-based inorganic compound has an effect of densifying the generated rust and improving the barrier property of the rust layer, and is effective in improving the weather resistance and corrosion resistance of the steel material. This effect is small when the amount of resin relative to the resin is less than 5% by weight and is saturated when the amount exceeds 20% by weight. Therefore, the amount of resin relative to the Cu-based inorganic compound is preferably 5 to 20% by weight. As a specific composition of the Cu-based inorganic compound, for example, Cu
₃ (PO ₄ ) ₂ etc. can be preferably employed.

These second components exhibit a sufficient effect only in the coexistence with the first component, and have little effect alone. By the way, the main purpose of the present invention is to improve the adhesion of the coating by the iron phosphate coating under the coating, and to form the stable rust early by the butyral resin coating containing the first component or the second component. Since the prevention of flow rust has been achieved, as long as the function of the first component or the second component is not hindered, a third component other than these, for example, in order to achieve harmony with the surrounding environment. Or a coloring pigment such as iron oxide or carbon black, or an ultraviolet absorber or an anti-settling agent. But,
If the total amount of the first to third components with respect to the resin exceeds 150 wt%, the first to third components come into direct contact with each other in the resin and penetrate from the surface of the coating film to the steel surface. Since holes are easily formed and it is difficult to prevent flow rust, 150 wt.
% Is preferable.

In the present invention, the steel type of the steel sheet used as the base of the surface treatment layer is not particularly limited. In the present invention, even if the steel type is, for example, ordinary steel, the first component in the coating film acts on the rust layer formed below the surface treatment layer to transform it into stable rust.
Nevertheless, when the present invention is applied to steel materials used outdoors in coastal areas where the amount of flying salt particles is high and the corrosive environment is severe, if the steel type is ordinary steel, the period until the formation of stable rust is completed. It is preferable to use weathering steel, Ni-added steel, or the like as the steel type because the length of the steel becomes longer.

Thus, in the structural steel material for outdoor use composed of the surface-treated steel sheet according to (1), stable rust is formed early under the surface-treated layer, flow rust during the formation period is significantly reduced, and The corrosion rate can be suppressed from the stage, that is, the service life of the steel material can be extended, and the surface treatment layer has excellent workability. Further, since the surface treatment layer does not contain any environmental pollution sources such as Cr, there is no concern about environmental pollution. Also,
(2) In the structural steel material for outdoor use composed of the surface-treated steel sheet described in (2), the formation of stable rust is further accelerated.

Next, a method for producing the surface-treated steel sheet of the present invention will be described. In general, when chemical conversion or painting is performed on the steel surface, it is important to first remove oil, dirt, scale, etc. by a base treatment and keep the steel surface clean.
This is the same in the present invention. In the present invention, since a steel plate (particularly a thin steel plate) is subjected to surface treatment, on the premise of performing coil coating, the base treatment method is preferably alkali degreasing. Note that the steel type of the steel sheet may be selected according to the product use in consideration of the above points.

The steel sheet after the base treatment is subjected to an iron phosphate treatment. The iron phosphate treatment may be carried out according to a conventional method, but it is preferable that the operation target of the amount of the iron phosphate coating adhered is within the above-mentioned suitable range of 0.3 to ² mg / m ² . The steel sheet after the iron phosphate treatment is coated. The coating may be carried out by a conventional method, but the coating used is, of course, a butyral resin coating containing the first or further second component. The amount of the first and second components to be added to the butyral resin paint may be appropriately set in consideration of the above-described preferable range of the amount of resin. The coating amount is the film thickness (dry film thickness)
Is set within the management target range.

When the butyral resin film is exposed outdoors for a long period of time, the film thickness gradually decreases due to photodegradation. However, the life time of the coating film is sufficient if it is not shorter than the required period for forming stable rust. Further, in the surface-treated steel sheet of the present invention, the required period for forming stable rust is as short as a little less than one year, so that the decrease in film thickness during that period is negligible. Therefore, the film thickness limit range 10 to 10 of the present invention as a control target range of the coating film thickness
50 μm can be adopted as it is.

The coated steel sheet is dried (baked). Drying is preferably carried out so that the temperature of the steel sheet reaches 60 to 140 ° C. from the viewpoint of sufficiently evaporating the organic solvent in the resin and preventing the resin from being thermally degraded.

[0026]

[Example] 150 × 15 from steel material having the chemical composition shown in Table 1.
A strip of steel having a composition shown in Table 2 was cut out from a strip of 0 × 0.7 (mm) and subjected to alkali degreasing or further iron phosphate treatment (iron phosphate coating adhesion amount 1 mg / m ² ). Was coated on one side using a bar coater so that the dry film thickness became a predetermined value, and baked under the condition of a steel sheet reaching sheet temperature of 140 ° C., and then a coating film adhesion evaluation test and an exposure test were performed.

[0027]

[Table 1]

[0028]

[Table 2]

In the coating film adhesion evaluation test, the initial adhesion and the secondary adhesion after processing were examined. The initial adhesion was evaluated by making a cut into the painted surface to reach a 1-mm square grid-like steel surface with a cutter, and then peeling off Cellotape (registered trademark), and evaluating the remaining area ratio of the coating film. Secondary adhesion was measured using a 1/2 inch diameter punch on a steel plate with the same cut as described above.
After performing a Dupont test to drop a 0 g weight from a height of 50 cm and applying an impact from the unpainted surface, perform cellophane tape peeling, evaluate with the remaining area ratio of the coating film, and paint on the steel plate without cutting A 3T bending test was performed with the surface facing outward, and the presence or absence of peeling or cracking of the coating film in the bent portion was visually evaluated.

In the exposure test, a place about 10 m away from the coast (coastal zone) and a place 13 km away from the coast (countryside)
Then, the steel sheet was held for one year with its painted surface facing upward and inclined 30 degrees with respect to the ground. During this retention period,
The presence or absence of flowing rust was visually evaluated over time. In addition, a sample of the steel sheet is collected every month, the cross section is observed with a polarizing microscope, and the exposure period required for stable rust observed as a quenching layer to cover 80% or more of the interface between the steel sheet and the rust layer is measured. I asked.

The results of the coating film adhesion evaluation test and the exposure test were
Table 3 shows the adopted surface treatment conditions, that is, the types of steel materials, the presence or absence of chemical conversion treatment (iron phosphate treatment), the types of paints, and the combinations of coating thicknesses (dry film thicknesses). In Table 3,
In the bending test column, 欄 means no peeling or cracking, × means one or both of peeling and cracking, and ○ in the flowing rust column means no flowing rust, and × means flowing rust. During the exposure, the coating thickness was almost constant.

[0032]

[Table 3]

Steel plate satisfying the gist (1) of the present invention (Example)
Has excellent coating adhesion at initial and after processing,
There was no run-off rust in any of the coastal areas, and the stable rust formation period was as short as 6 months or less. In particular, the steel sheet satisfying the gist (2) of the present invention among the examples (Examples 2 to 2)
5) is even shorter than 6 months for unfulfilled ones
A stable rust formed in a month.

On the other hand, a steel sheet having a coating film thickness deviating from the range of the present invention (Comparative Example 1) failed to form stable rust even after one year, and flow rust occurred during that time. Further, the steel sheet (Comparative Example 2) in which the coating film thickness deviated from the range of the present invention above did not generate flow rust, but could not form stable rust even after one year. Moreover, the steel plate which lacked the first component in the coating film (Comparative Examples 3 to 6)
In one year, stable rust could not be formed in one year, and flowing rust occurred during that time. The steel sheet lacking an iron phosphate film between the steel sheet and the coating film (Comparative Example 7) was comparable to the example in terms of flow rust suppression and stable rust early formation. Was significantly inferior.

[0035]

The surface-treated steel sheet of the present invention forms stable rust at an early stage not only in a rural area but also in a coastal area, and there is no generation of flowing rust and elution of environmental pollutants in the course of the formation. It is excellent in the adhesion of the coating film afterwards, and by applying this to building construction steel materials for outdoor use that requires bending, it is possible to achieve environmental purification, landscape beautification, and long life of buildings at the same time. It works.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) E04B 1/64 E04B 1/64 Z 4K044 E04C 2/08 E04C 2/08 B F-term (reference) 2E001 DH25 EA05 FA30 GA51 HB02 KA01 2E162 CB02 EA18 4D075 CA32 DB02 EB11 EC01 4F100 AA01C AA04B AA07C AB03A AK23C BA03 BA07 BA10A BA10C BA13 EJ68B JA20C JK06 JL01 JL09 YY00C 4K026 AA02 BB02 BA03 BA03 BA03 BA03 BA03 BA03 BA03

Claims (2)

[Claims] 1. A steel sheet having an iron phosphate coating on its surface and a 10 to 50 μm thick butyral resin coating containing 1 wt% or more of the first component made of nickel sulfate with respect to the resin solid content as an upper layer. A surface-treated steel sheet having excellent workability and weather resistance, characterized by being formed by: 2. The coating film further comprises a phosphoric acid inorganic compound,
The surface-treated steel sheet according to claim 1, further comprising a second component selected from one or two selected from Cu-based inorganic compounds.