JP2002097559A - Black steel sheet and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a black steel sheet capable of giving a refined design, with a black appearance of high uniformity, with high corrosion resistance and low in a cost. SOLUTION: The black steel sheet with a lightness figure L 45 or less comprises a black film consisting of 30-55 mass% Zn, 3-12 mass% Al, 1-8 mass% Mg, 3-20 mass% O, and substantially Co as the balance, on a surface of a plated layer of a molten Zn-Al-Mg alloy plated steel-sheet of which the plated layer component consists of 4-22 mass% Al, 1-4 mass% Mg, 0-0.1 mass% Ti, 0-0.045 mass% B, and substantially Zn as the balance. The method for manufacturing the steel sheet includes dipping the molten Zn-Al-Mg alloy plated steel- sheet in a solution which contains 3-50 g/L Co ion, 3-50 g/L organic acid, and 10-80 g/L ammonium sulfate, is adjusted to pH of 8 or more by acquous ammonia, and is adjusted to a liquid temperature of 65-90 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blackened steel sheet excellent in design and corrosion resistance suitable for use in building materials, home appliances, automobiles, etc., wherein the surface of a coating layer of a molten Zn-Al-Mg alloy-plated steel sheet is provided. And a method for producing the same.

[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 chrome plating to the surface of a steel sheet, and Japanese Patent Application Laid-Open No. 62-77482 discloses a method of applying a steel sheet coated with a Zn-based alloy containing Ni, Co, etc. to an acidic aqueous solution containing phosphate ions. 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.

An object of the present invention is to provide a low-cost high-design black steel sheet which solves the above-mentioned various problems of the prior art, exhibits a uniform and stable black appearance, and is excellent in corrosion resistance.

[0007]

Means for Solving the Problems As a result of various studies, the inventors have found that Co, Zn, and Co are deposited on the surface of a molten Zn—Al—Mg alloy plating layer.
By forming a chemically treated film having a specific composition of Al, Mg, and O, it was revealed that a black appearance having a high uniformity and a solid color tone was obtained, and at the same time, high corrosion resistance was exhibited. In addition, steel sheets with such chemically treated coatings
It has been found that stable production can be achieved by chemically treating the surface of the plating layer of a Zn-Al-Mg alloy-plated steel sheet with a basic buffer solution containing a specific concentration of Co ions and containing an organic acid. The present invention has been completed based on such findings.

That is, the invention of claim 1 is characterized in that the molten Zn—Al
-30% to 55% by mass of Zn, 3% to 12% by mass of Al, 1% to 8% by mass of Mg, 3% to 20% by mass of O, and the balance substantially Co A blackened steel sheet having a lightness index L value of 45 or less in which a blackened film made of here,
"Substantially" means that the blackened film may contain unavoidable impurities. The lightness index L value is an L value measured by a color difference meter.

According to a second aspect of the present invention, there is provided the steel sheet according to the first aspect, wherein the molten Zn—Al—Mg-based alloy plating includes Al: 4 to 22% by mass, Mg: 1 to 4% by mass, and Ti: 0 to 0.1% by mass. %, B: 0 to 0.045
It is specified that the composition has a composition of mass%, and the balance substantially consists of Zn. Here, the lower limit of 0% for Ti and B means that the element is not contained in the plating layer. "Substantially" means that the plating layer contains a small amount (generally
(2% by mass or less) and additional elements and unavoidable impurities.

The invention according to claim 3 is that the surface of the plating layer of the hot-dip Zn-Al-Mg alloy plated steel sheet contains Co ions: 3 to 50 g / L (liter), organic acids: 3 to 50 g / L, and It contains a pH buffer consisting of sulfate, the pH is adjusted to 8 or more, and the liquid temperature is 6
This is a method for producing a blackened steel sheet in which a blackened film having a lightness index L value of 45 or less is formed on the surface of a plating layer by chemical treatment with an aqueous solution (chemical treatment liquid) adjusted to 5 to 90 ° C. . Here, the chemical treatment is a treatment in which a chemical treatment solution is brought into contact with the surface of the material to be treated (the surface of the plating layer) to deposit a film on the surface. As a typical form of the “contact”, there is a method of immersing a material to be treated in a chemical treatment liquid. The pH buffer is not particularly limited as long as it produces a pH buffering action in the solution.

According to a fourth aspect of the present invention, the surface of the coating layer of the hot-dip Zn—Al—Mg alloy-coated steel sheet is formed such that Co ions: 3 to 50 g / L, organic acids: 3 to 50 g / L, and ammonium sulfate: 10 to 80 g / L. L, pH is adjusted to 8 or more with ammonia water, and chemically treated with an aqueous solution whose solution temperature is adjusted to 65 to 90 ° C., and the plating layer surface has an appearance with a lightness index L value of 45 or less. This is a method for producing a blackened steel sheet that forms an oxide film.

A fifth aspect of the present invention is the method according to the third or fourth aspect, wherein the organic acid is ascorbic acid. The invention of claim 6 stipulates that a method of immersing a molten Zn—Al—Mg-based alloy-plated steel sheet in an aqueous solution is adopted as a chemical treatment method.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a hot-dip Zn-Al-Mg alloy plated steel sheet is used as a material to be subjected to a blackening treatment. Hot-dip Zn-Al-Mg-based alloy-plated steel sheets have been promoted for practical use in various applications recently because of their good corrosion resistance.
The inventors of the present invention have studied various methods of performing a blackening treatment based on the plated steel sheet, and as a result, those having a chemical treatment with a specific treatment solution containing Co ions can have a solid black appearance. It was found that it was possible.

The hot-dip Zn—Al—Mg alloy plated steel sheet used in the present invention is composed of Al: 4 to 22% by mass, Mg: 1 to 4% by mass, and Ti: 0%.
It is preferable to have a plating layer containing 0.1 to 0.1% by mass, B: 0 to 0.045% by mass, and the balance being substantially composed of Zn. Further, there is no problem even if the plating layer contains Fe, Si, La, Ce, Cu, Be, Sr, etc. in a total of 2% by mass or less in addition to the above elements. The plating weight is not particularly limited.

By chemically treating the surface of the plating layer with a specific treatment solution containing Co ions, a blackened film having a black appearance with a lightness index L value of 45 or less by a color difference meter can be formed. When the L value exceeds 45, the appearance becomes whitish, which is not preferable as a blackened steel sheet used for building materials, home appliances, automobiles and the like.

According to the present invention, as the blackened film, Zn:
30 to 55% by mass, Al: 3 to 12% by mass, Mg: 1 to 8% by mass,
O: Defines a composition consisting of 3 to 20% by mass and the balance substantially consisting of Co. When the composition of the blackening film is in this range, a black appearance having an L value of 45 or less can be obtained stably, and the adhesion of the blackening film is sufficiently ensured. Zn in blackened film
If the amount is out of the above-mentioned appropriate range, an L value of 45 or less may not be obtained stably, and the adhesion may decrease. Al content, Mg
If the amount is less than the appropriate range, processing unevenness occurs, and if it exceeds the appropriate range, the adhesion is reduced. If the O content is less than the appropriate range, the L value of 45 or less cannot be obtained stably. If the O content exceeds the appropriate range, the adhesiveness is reduced.

[0017] The preferred blackening film as described above is prepared by melting
The plating layer surface of the Zn-Al-Mg-based alloy-coated steel sheet contains Co ions: 3 to 50 g / L, organic acids: 3 to 50 g / L, and contains a pH buffer consisting of sulfate, and has a pH of 8 or more. It can be formed by performing a chemical treatment with an aqueous solution (chemical treatment liquid) adjusted to. As the chemical treatment method, basically any method can be adopted as long as the chemical treatment liquid sufficiently contacts the agent to be treated, and specific examples include a dipping treatment method and a spray treatment method. In consideration of the continuous processability of the steel strip and the stability of the black appearance, the immersion treatment method is relatively advantageous.

If the Co ion concentration in the chemical treatment liquid is less than 3 g / L, it is difficult to obtain a black appearance having an L value of 45 or less, and if it exceeds 50 g / L, the adhesion of the blackened film may be reduced. Co ions can be added to the aqueous solution in the form of sulfates, nitrates, chlorides, and the like, but addition of sulfates is preferable in consideration of corrosion of a chemical treatment apparatus. Specifically, it can be added, for example, as cobalt sulfate.

Organic acids have an excellent effect on the formation of a blackened film. That is, the organic acid prevents precipitation of metal ions, particularly zinc eluted in a wide pH range, and Zn
-Improve the etching power for the Al-Mg alloy plating layer and shorten the processing time. Such organic acids include those having COOH groups, CHO groups, and C =
Those having an O group can be used, and those having a reducing property are particularly preferable. Specific examples include ascorbic acid, citric acid, oxalic acid, tartaric acid, and the like. If the concentration of the organic acid in the chemical treatment liquid is less than 3 g / L, the treatment time cannot be reduced. On the other hand, if it exceeds 50 g / L, the effect is saturated and uneconomical.

The pH of the chemical treatment solution is preferably an alkalinity of 8 or more. If the pH is less than 8, the reaction rate is sharply reduced, and blackening treatment in a short time, particularly in a continuous line, becomes difficult. As the pH adjuster, various acids, aqueous ammonia, hydroxides, carbonates and the like can be used, and among them, the use of aqueous ammonia is preferable because the processing speed is improved.

In the present invention, a pH buffer is added to
Keep alkalinity of 8 or more. The pH buffer is used in combination with the pH adjuster used, Co-containing substances, organic acids, etc.
A substance having a pH buffering action may be used. Also, the amount of addition may be a content that exhibits a pH buffering action in the solution and does not cause precipitation, and may be in accordance with a general method of using a pH buffer. The pH buffering agent can be added in the form of sulfate, phosphate, borate, etc. However, when added with phosphate or borate, precipitation tends to occur on the alkali side with metal ions. Ammonium sulfate, sodium sulfate, etc.).

When the pH is adjusted with aqueous ammonia,
Use ammonium sulfate as a pH buffer and adjust its concentration.
It is desirable to set it to 10 to 80 g / L. If the ammonium sulfate concentration is less than 10 g / L, the pH buffering action is insufficient, and
It also affects the deposition rate of the chemically treated film, and blackening in a short time is not possible. On the other hand, if it exceeds 80 g / L, a precipitate is likely to be formed from the viewpoint of solubility, which is not preferable.

The temperature of the chemical treatment liquid is the degree of blackening (L value)
Affect. At a low temperature of less than 65 ° C., it is difficult to stably obtain a black appearance having an L value of 45 or less.
It is desirable that the temperature be equal to or higher than C. However, if the temperature is too high, processing unevenness is likely to occur.

[0024]

[Example 1] [Example 1] Hot-dip Zn-Al-Mg alloy coated steel sheet (sheet thickness 0.8 mm, plating layer composition; Al: 4 to 22% by mass, Mg:
1 to 4% by mass, Ti: 0 to 0.1% by mass, B: 0 to 0.045% by mass,
The remainder substantially in the range of Zn) was immersed in a chemical treatment solution containing Co ions to form a chemical treatment film on the plating layer surface. As the chemical treatment solution, an aqueous solution was used in which cobalt sulfate was added as a Co ion source, ascorbic acid was added as an organic acid, ammonia water was added as a pH adjuster, and ammonium sulfate was added as a pH buffer. By changing the concentration of additives in the chemical treatment solution, bath pH, bath temperature and immersion time, chemically treated films of various compositions were obtained.

With respect to the obtained samples, the composition of the chemically treated film, the lightness index L value, the adhesion of the chemically treated film, and the appearance were examined. The composition of the chemically treated film was measured by ESCA. The lightness index L value is measured using a color difference meter (Minolta Camera Co., Ltd.)
And CR-300), and those having an L value of 45 or less were evaluated as ○, and those exceeding 45 were evaluated as ×. The adhesion of the chemically treated film was evaluated by 180 ° contact bending of the sample, and a peeling test was performed on the bent part using a cellophane tape. △, those with marked transcription
Was evaluated. The appearance was evaluated by visually observing the surface of the sample after the chemical treatment. Table 1 shows the results.

[0026]

[Table 1]

In any of the invention examples in which the composition of the chemically treated film is within the range specified in the present invention, the lightness index L value is 45%.
A “blackened film” having the following black appearance was formed, and it was confirmed that the adhesion and the appearance were good.

Example 2 Hot-dip Zn-Al-Mg alloy coated steel sheet (sheet thickness 0.8 mm, plating layer composition: Al: 6% by mass, Mg: 3)
% Of Ti, 0.05% by mass of Ti, 0.02% by mass of B, and substantially the remainder of Zn) are immersed in a chemical treatment solution containing Co ions, and the component concentration, pH, and solution temperature of the chemical treatment solution, and The relationship between the stability, the lightness index L value of the steel sheet after the chemical treatment, the adhesion of the chemically treated film, and the appearance was investigated. As in the case of Example 1, the chemical treatment solution was an aqueous solution in which cobalt sulfate was added as a Co ion source, ascorbic acid was added as an organic acid, ammonia water was added as a pH adjuster, and ammonium sulfate was added as a pH buffer. Was used. Immersion time in chemical treatment solution is
It was 8 seconds, and immediately after immersion, it was washed with water and dried.

The lightness index L, adhesion and appearance of the chemically treated film were evaluated according to the same criteria as in Example 1. The stability of the bath was evaluated by visually observing the presence or absence of the formation of a precipitate. Table 2 shows the results.

[0030]

[Table 2]

The component concentration of the liquid is in the range of Co ion: 3 to 50 g / L, organic acid (ascorbic acid): 3 to 50 g / L, sulfate (ammonium sulfate): 10 to 80 g / L, and the pH is 8 or more. The invention examples of Nos. 1 to 10 in which the chemical treatment was performed using the chemical treatment liquid whose solution temperature was adjusted to 65 ° C. or higher, the brightness index L value was 45 or less, and there was no processing unevenness. An excellent black appearance was exhibited, the adhesion of the blackened film was good, and excellent bath stability with no precipitation was exhibited. In the invention example of No. 18, the sulfate concentration was higher than 80 g / L, and a precipitate was formed in the solution.
A blackened film with good adhesion was obtained at 45 or less.

In Comparative Examples Nos. 11 and 12, since the pH was less than 8, a black appearance having a lightness index L value of 45 or less could not be obtained in a short time of immersion time of 8 seconds. No. 13 and No. 14 have a liquid temperature of 6
Since the temperature was lower than 5 ° C., a black appearance having a lightness index L value of 45 or less could not be obtained. The comparative example of No. 15 has an organic acid concentration of 50 g / L
Therefore, a blackened film having high adhesion could not be formed. In Comparative Example No. 16, since the organic acid concentration was as low as less than 3 g / L, a blackened film having a lightness index L value of 45 or less could not be formed. In Comparative Example No. 17, the sulfate concentration was too low to function as a pH buffer, and as a result, a blackened film having a lightness index L value of 45 or less could not be formed. No.19
In Comparative Example No., since the Co ion concentration was as low as less than 3 g / L, a black appearance having a lightness index L value of 45 or less could not be obtained. No.20
In Comparative Example No., since the Co ion concentration was higher than 50 g / L, a blackened film having high adhesion could not be formed.

[0033]

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. In addition, this blackened steel sheet is molten Zn-
Since it is based on an Al-Mg alloy plated steel sheet, it has excellent corrosion resistance. Further, the present invention, hot-dip galvanized steel sheet, or at an operation site that manufactures the coated steel sheet,
It is relatively easy to implement.

Claims (6)

[Claims] 1. The coating layer surface of a hot-dip Zn—Al—Mg alloy plated steel sheet has Zn: 30 to 55% by mass, Al: 3 to 12% by mass,
g: 1 to 8% by mass, O: 3 to 20% by mass, the balance being a blackened steel sheet having a lightness index L value of 45 or less in which a blackened film substantially made of Co is formed. 2. A hot-dip Zn—Al—Mg based alloy plating comprising: Al: 4
-22% by mass, Mg: 1-4% by mass, Ti: 0-0.1% by mass, B:
The blackened steel sheet according to claim 1, wherein the composition has a composition of 0 to 0.045% by mass and the balance substantially consisting of Zn. 3. The plating layer surface of a hot-dip Zn—Al—Mg-based alloy plated steel sheet is coated with a pH buffer containing 3 to 50 g / L of Co ions and 3 to 50 g / L of an organic acid and comprising a sulfate. Chemical treatment with an aqueous solution having a pH adjusted to 8 or more and a liquid temperature adjusted to 65 to 90 ° C. to form a blackened film having a lightness index L value of 45 or less on the surface of the plating layer. , Manufacturing method of blackened steel sheet. 4. The plating layer surface of a hot-dip Zn—Al—Mg alloy plated steel sheet is coated with Co ions: 3 to 50 g / L, organic acids: 3 to 50 g / L,
Ammonium sulfate: contains 10 to 80 g / L, is chemically treated with an aqueous solution whose pH is adjusted to 8 or more with aqueous ammonia and whose solution temperature is adjusted to 65 to 90 ° C., and the lightness index L value is 45 on the surface of the plating layer. A method for producing a blackened steel sheet, which forms a blackened film having the following appearance. 5. The method according to claim 3, wherein the organic acid is ascorbic acid. 6. The method according to claim 3, wherein the chemical treatment is performed by immersing a hot-dip Zn—Al—Mg-based alloy-plated steel sheet in an aqueous solution.