JP2001279414A - HOT DIP Zn-Al ALLOY COATED BLACK COLOR STEEL SHEET - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low cost black color steel sheet having a good uniform appearance and allowing a high grade designing. SOLUTION: A hot dip Zn-Al alloy coated black color steel sheet has the surface with good appearance having 25-45 L value of lightness index and further, -4 to 10 (a) value of saturation index by coating of the black color film composed essentially of metallic Ni, Zn-oxide, Al-oxide, Si-oxide and, if necessary, Mg-oxide on the surface of the hot dip Zn-Al alloy. A hot dip Zn-Al alloy coated steel sheet plated with the alloy composed of 3-60 mass % Al and, if necessary, 1-5 mass % Mg and the residuce substantially Zn is suitable for practical use. The black color film can be formed with a method for dipping into e.g. a chemical treating solution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blackened hot-dip Zn-Al-based alloy-plated steel sheet having excellent design and used for building materials, home appliances, automobiles and the like.

[0002]

2. Description of the Related Art In the fields of building materials, home appliances, automobiles, and the like, there is an increasing need for steel plates having a black appearance from the viewpoint of design and the like. As a means for blackening the surface of the steel sheet, there is a method of applying a black paint. However, in the above fields, steel plates plated with Zn, Zn-Al, Zn-Ni, etc. are often used from the viewpoint of corrosion resistance, and these plated surfaces are white or gray-white. For this reason, in order to obtain a black appearance with high designability by painting, it is usually 20 μm to hide the base color.
A coating thickness of m or more is required, and coating costs increase.

[0003] As another blackening means, Japanese Patent Laid-Open No.
Japanese Patent Application Publication No. -11792 discloses a method of applying black chromium plating to the surface of a steel sheet. Japanese Patent Application Laid-Open No. 3-122290 discloses a method of performing chemical treatment in JP-A-2-282485, a method of subjecting a Zn or Zn alloy-plated steel sheet to a chemical conversion treatment or an electrolytic treatment, followed by a coating chromate treatment and a polymer coating treatment. A method of forming a chemical conversion-treated black film, a coating type chromate film, and a resin film containing a black pigment on a Zn-based plated steel sheet is disclosed in JP-A-8-2.
No. 18158 discloses a method of treating a hot-dip Zn or Zn alloy-plated steel sheet with a solution obtained by adding a special metal ion to a zinc phosphate treating solution.

[0004]

However, according to the investigations by the inventors, it is difficult to stably obtain a highly uniform black film by short-time processing, and It was found that the appearance was likely to be uneven.

Further, the method disclosed in Japanese Patent Application Laid-Open No. 58-11792 has a problem of wastewater treatment since chromium is used.
The method of 77482 discloses that the addition of a blackening element such as Ni or Co during plating is indispensable, so that applicable plating types are limited.
The method disclosed in Japanese Patent Application Laid-Open No. 2-282485 requires capital investment for electrolytic treatment, and the process is complicated, so that the cost tends to be high. Was not always easy.

Therefore, there is still room for study on the technology for blackening steel sheets. An object of the present invention is to improve the above-mentioned various problems of the prior art, and to provide a low-cost, highly-designed black steel sheet having a highly uniform black appearance.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted various studies to develop a high-design black steel sheet as described above, and as a result, have found that the surface of a hot-dip Zn-Al-based alloy plating layer has Ni, Zn, Al, It was found that a film with a highly uniform black appearance can be obtained when a black film containing Si or further Mg was formed. As a result of further study, among the above elements, Ni was present in the film as metal Ni, and Zn, Al, Si, and Mg were all present in the film as oxides. Has been found to be very important in producing a solid black appearance with high designability. The present invention has been completed based on such findings.

That is, the invention of claim 1 is characterized in that molten Zn—Al
Blackened molten Zn having a surface appearance with a lightness index L value: 25 to 45 by forming a black film mainly composed of metallic Ni, Zn oxide, Al oxide and Si oxide on the surface of the base alloy plating layer -Al
It is a base alloy plated steel sheet. Here, the hot-dip Zn-Al-based alloy plating refers to hot-dip plating in which Zn and Al are at least 50% by mass in total as the main components of the plating metal. The lightness index L value is an L value measured by a color difference meter.

[0009] The invention of claim 2 is based on the invention of claim 1, and in particular, the molten Zn—Al-based alloy plating layer uses an alloy plating bath containing Al: 3 to 60% by mass and the balance substantially consisting of Zn. And that the black film is a chemically treated film formed by chemically treating the plating layer. Here, "the remainder of the alloy plating bath is substantially Zn
“Consisting of” means that, in addition to Zn, a small amount (generally 2% by mass or less) of additional elements and unavoidable impurities may be contained. The chemical treatment means a treatment in which a metal material (plated steel sheet) is immersed in an aqueous solution containing a chemical substance or an ionic species to form a film on the surface of the material (plated layer surface).

[0010] The invention of claim 3 is to form a black coating mainly composed of metal Ni, Zn oxide, Al oxide, Si oxide and Mg oxide on the surface of the molten Zn-Al based alloy plating layer. This is a blackened hot-dip Zn-Al-based alloy plated steel sheet having a surface appearance with a lightness index L value: 25 to 45 and a saturation index a value: -4 to 10. This means that, in the invention of claim 1, Mg oxide is further added as a component of the black film, and the saturation index a value is defined. Here, the saturation index a value is an a value measured by a color difference meter.

The invention according to claim 4 is the invention according to claim 3, wherein the plating layer of the molten Zn—Al-based alloy has an Al content of 3 to 60% by mass,
Mg: formed by using an alloy plating bath containing 1 to 5% by mass and the balance substantially consisting of Zn, and the black film is a chemically treated film formed by chemically treating the plating layer. Is specified.

A fifth aspect of the present invention is the invention according to the first to fourth aspects, wherein a chromate film of 5 to 70 mg / m ² is formed on the black film. The invention of claim 6 is
In the invention according to claim 5, a clear coating film having a thickness of 1 to 10 μm is further formed on the chromate film.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present invention examined various degrees of blackening of a blackened hot-dip Zn-Al-based alloy-plated steel sheet used for building materials, home appliances, automobiles, and the like, which were suitable for these uses. It has been found that by setting the L value in the range of 25 to 45, a surface appearance having a high design property can be obtained. And such surface appearance has the above-mentioned surface structure, that is, “the hot-dip Zn—Al-based plating layer” + “the metal Ni formed on the surface layer,
It has been confirmed that this can be achieved by forming a surface structure on a steel sheet, which is a black film mainly composed of Zn oxide, Al oxide, Si oxide, or even Mg oxide. In particular,
When the black film has a structure containing Mg oxide, the lightness index L
In addition to the value being 25 to 45, the saturation index a value is -4 to 10
, A surface appearance close to an achromatic color with a more stable feeling can be obtained.

In order to obtain such a black appearance, metal
Ni, Zn oxide, Al oxide, Si oxide, or even Mg
It is necessary to form a film mainly composed of an oxide. Each of the above oxides is substantially transparent when used alone, but when metallic Ni is mixed in the film together with these oxides, a black appearance having a high design property is obtained. Although the reason is not always clear at this time, it is thought that metallic Ni particles are present in a finely dispersed state in the film composed of the above substances, and this may cause irregular reflection of light. Inferred.

As a method of providing such a black film, there are an electroplating method, a chemical plating method, a chemical treatment method and the like, and the same effect can be expected by any of the treatment methods. Among them, according to the chemical treatment method in which the plated steel sheet is immersed in an aqueous solution containing Ni and silicofluoride, a black film can be continuously formed at low cost, which is useful for producing the blackened steel sheet of the present invention. This is the preferred method.

According to the method of forming a black film by using a chemical treatment method, a steel sheet containing a hot-dip coating layer of a composition containing Al: 3 to 60% by mass and a balance substantially consisting of Zn as a material to be treated. (Hereinafter, it may be referred to as “hot-dip Zn-3 to 60% by mass Al alloy-plated steel sheet”) or Al: 3 to 60
Steel sheet having a hot-dip coating layer having a composition of 1% to 5% by weight, Mg: 1 to 5% by weight, and the balance being substantially Zn.
-3 to 60 mass% Al-1 to 5 mass% Mg alloy-plated steel sheet "). In particular, when the latter is applied, in addition to a lightness index L value of 25 to 45, a color index a value of −4 to 10, which exhibits a particularly excellent black appearance, is obtained. In the case of the chemical treatment method,
The composition of the black film can be controlled by changing the processing solution concentration, bath pH, and processing time.

FIGS. 1 to 4 show the results of ESCA analysis of a black film formed by immersing a hot-dip Zn-5 mass% Al alloy plated steel sheet in an aqueous solution containing Ni and Si compounds and chemically treating it. 2 shows a measurement example after 10 minutes of Ar sputtering. This sample has a good black appearance with an L value of 38. In FIG. 1, peaks are seen at the positions of 870 eV and 852 eV. These are, respectively, metallic Ni
They correspond to the peaks of the 2p _1/2 and 2p _3/2 orbitals. On the other hand, FIGS. 2, 3 and 4 show ZnO, Al ₂ O ₃ and SiO _{2 respectively.}
Peak is seen. In other words, in the obtained black film,
It can be seen that Ni exists in the form of metallic Ni, and Zn, Al, and Si exist in the form of oxide.

In order to protect the black film and further improve the corrosion resistance, it is desirable to form a chromate film on the black film. Further, in order to prevent surface flaws at the time of molding at the consumer, it is desirable to further form a clear coating film on the chromate film.

If the amount of the attached chromate film is less than 5 mg / m ^{2, the} effect of improving the corrosion resistance cannot be expected. The chromate film improves the adhesion of the clear film but, 5 mg / m ²
If less than that, the effect is not sufficiently exhibited. On the other hand, if the amount of the attached chromate film exceeds 70 mg / m ² , a yellow tint due to chromate is generated, which is not preferable. Therefore, when a chromate film is formed, it is desirable that the amount of coating be in the range of 5 to 70 mg / m ² .

The clear coating film can be formed by a generally known clear coating, but if the thickness of the clear coating film is less than 1 μm, the effect of protecting the undercoat film is not sufficiently exhibited. On the other hand, even if the thickness of the clear coating film exceeds 10 μm, the protective effect of the undercoat film is saturated, which is uneconomical. Therefore, in applications where emphasis is placed on prevention of flaws during processing, it is preferable to further form a clear coating film with a thickness of 1 to 10 μm on the chromate coating film.

[0021] The hot-dip Zn-Al-based coated steel sheet to be used in the present invention is a hot-dip coated steel sheet containing at least 50% by mass in total of Zn and Al in a plating layer. 3 to 60% by mass Al alloy plated steel sheet "and" Hot Zn-3 to 60% by mass Al-1 to 5% by mass Mg alloy plated steel sheet "are preferably used. Among them, those having a Zn-Al binary alloy plating layer are basically used, and typical ones are a hot-dip Zn-5 mass% Al alloy-plated steel sheet, a hot-dip Zn-5
5 mass% Al alloy plated steel sheet and the like. Basically has a Zn-Al-Mg ternary alloy plating layer, and a typical example is a hot-dip Zn-6% by mass Al-3% by mass Mg alloy plated steel plate. In these, there is no problem even if they contain about 2% by mass or less of additional elements and unavoidable impurities. In this case, for example, Si, La,
Ce, Cu, Ti, B, Ni and the like can be mentioned. Inevitable impurities include Pb, Sn, Fe and the like. In the plated steel sheet targeted in the present invention, there is no particular limitation on the steel type and the coating weight of the plated original sheet.

[0022]

EXAMPLES The following four types of plated steel sheets, A: electric Zn-coated steel sheet, B: alloyed hot-dip Zn-coated steel sheet, C: hot-dip Zn-5 mass% Al alloy-coated steel sheet, D: hot-dip Zn-6 mass% Al The −3 mass% Mg alloy-plated steel sheet was immersed in a chemical treatment solution containing Ni and a silicate to form a chemically treated film. The chemical treatment solution used was an aqueous solution consisting of Nippon Paint Co., Ltd., trade name "NP Conditioner 500 Building Bath Agent" and aqueous ammonia. The chemical treatment conditions were bath temperature 70 ° C, pH 5.0, and immersion time 10 seconds. And After immersion, it was washed with water and immediately dried with hot air. The morphology of the obtained film was investigated using ESCA. The lightness of the film surface was measured with a color difference meter, and the L value was 25.
Those falling within the range of ~ 45 were evaluated as ○, and the others were evaluated as ×. Table 1 shows the results.

[0023]

[Table 1]

The plating type A containing no Al in the plating layer,
In the steel sheet B, the L value was higher than 45, and exhibited a whitish appearance which was not suitable for a blackened steel sheet. On the other hand, the steel sheets of the plating types C and D containing Al in the plating layer exhibited a good black appearance in which the L value was in the range of 25 to 45. In addition, looking at the existing forms of the elements constituting the film, Ni was present as metallic Ni, and Zn was present as oxide. However, C and D, which exhibited good black appearance,
This was different from the others in that Al oxide was present. This indicates that it is important to use a steel sheet containing Al in the plating layer in the present invention.

[0025]

According to the present invention, it has become possible to provide a low-cost black steel plate having a highly uniform black appearance. Its color tone is deeper than black paint, and it has a high design. Further, the present invention is relatively easy to put into practice at an operation site where a hot-dip galvanized steel sheet or its coated steel sheet is manufactured. Therefore, the present invention contributes to the spread of blackened hot-dip coated steel sheets.

[Brief description of the drawings]

FIG. 1 is a graph showing the results of ESCA measurement showing that metallic Ni is present in a black film according to the present invention formed by chemically treating a hot-dip Zn-5 mass% Al alloy-plated steel sheet.

FIG. 2 is a graph showing the results of ESCA measurement showing that ZnO is present in the same black film as in FIG. 1;

FIG. 3 is a graph showing the results of ESCA measurement showing that Al ₂ O ₃ is present in the same black film as in FIG. 1;

FIG. 4 is a graph showing the results of ESCA measurement showing that SiO ₂ is present in the same black film as in FIG. 1;

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 4K026 AA02 AA13 AA22 BA08 BA12 BB01 CA16 CA28 DA03 4K027 AA02 AA05 AA22 AB05 AB15 AB26 AB44 AB48 AC32 AC82

Claims (6)

[Claims] 1. A black film mainly composed of metallic Ni, Zn oxide, Al oxide and Si oxide is formed on the surface of a hot-dip Zn—Al-based alloy plating layer to obtain a lightness index L value of 25 to 45. A blackened hot-dip Zn-Al-based alloy plated steel sheet with a surface appearance of. 2. The hot-dip Zn—Al-based alloy plating layer is formed by using an alloy plating bath containing Al: 3 to 60% by mass and the balance substantially consisting of Zn. The blackened hot-dip Zn-Al-based alloy-plated steel sheet according to claim 1, wherein the steel sheet is a chemically treated film formed by chemically treating. 3. A lightness index L value by forming a black film mainly composed of metallic Ni, Zn oxide, Al oxide, Si oxide and Mg oxide on the surface of the hot-dip Zn-Al-based alloy plating layer. ： 25〜4
5, and a blackened hot-dip Zn-Al-based alloy-plated steel sheet having a surface appearance with a saturation index a value of -4 to 10. 4. The hot-dip Zn—Al-based alloy plating layer is formed by using an alloy plating bath containing Al: 3 to 60% by mass, Mg: 1 to 5% by mass, and the balance being substantially Zn. The blackened hot-dip Zn-Al-based alloy-plated steel sheet according to claim 3, wherein the black film is a chemically-treated film formed by chemically treating the plating layer. 5. The blackened molten Zn—Al according to claim 1, wherein a 5-70 mg / m ² chromate film is formed on the black film.
Base alloy plated steel sheet. 6. A thickness of 1 to 10 on the chromate film.
The blackened hot-dip Zn-Al-based alloy-plated steel sheet according to claim 5, wherein a clear coating film having a thickness of μm is formed.