WO2013051268A1

WO2013051268A1 - Production method for zinc-electroplated steel sheet

Info

Publication number: WO2013051268A1
Application number: PCT/JP2012/006372
Authority: WO
Inventors: 妹川　透; 土本　和明; 松崎　晃
Original assignee: Ｊｆｅスチール株式会社
Priority date: 2011-10-04
Filing date: 2012-10-04
Publication date: 2013-04-11
Also published as: KR20160113312A; TWI461575B; TW201315843A; KR20140064995A; CN103842558B; CN103842558A; JP2013079422A

Abstract

Provided is a production method for a zinc-electroplated steel sheet that has a high degree of whiteness and that limits decreases in electrical current efficiency. A zinc-electroplating process is carried out in a zinc-electroplating bath containing less than 0.01 mass ppm total of one or more organic compounds having a 2-benzothiazolylthio group. Next, a zinc-electroplating process is carried out in a zinc-electroplating bath containing a total of 0.01-3 mass ppm of one or more organic compounds having a 2-benzothiazolylthio group so that the amount of deposited zinc constitutes 1-50% of the entire plating layer.

Description

Method for producing electrogalvanized steel sheet

The present invention relates to a method for producing a high whiteness electrogalvanized steel sheet.

Electro-galvanized steel sheets are used in a wide range of applications such as home appliances, automobiles, and building materials. Among them, in recent years, the demand for various types of chemically treated electrogalvanized steel sheets used for home appliances that are used without coating is increasing, which is an important application field. In this application, since it is used without coating, it is required to have an excellent surface appearance. As a condition of excellent surface appearance, in addition to no surface defects such as unevenness, whiteness is high. And since the external appearance after various chemical conversion treatments is greatly influenced by the external appearance of the galvanization before chemical conversion treatment, it is calculated | required to obtain a galvanized steel plate with high whiteness.

Patent Document 1 is cited as a technique for improving whiteness by optimizing electrogalvanizing conditions. Patent Document 1 discloses a method for producing a galvanized steel sheet in which an organic compound having a 2-benzothiazolylthio group is added to a plating bath, and the steel sheet is subjected to cathodic electrolytic treatment.

JP 2007-297646

However, in Patent Document 1, the current efficiency slightly decreases by adding an organic compound having a 2-benzothiazolylthio group to the electroplating bath. Therefore, the amount of electricity for obtaining a predetermined plating amount increases, the power cost increases, and as a result, the manufacturing cost of the electrogalvanized steel sheet increases.

In view of such circumstances, an object of the present invention is to provide a method for producing an electrogalvanized steel sheet that suppresses a decrease in current efficiency and has high whiteness.

The inventors of the present invention have made extensive studies to obtain a galvanized steel sheet having high whiteness. The steel sheet is subjected to cathode electrolytic treatment in an electrogalvanizing bath containing a total of 0.01 to 3 mass ppm of one or more organic compounds having a 2-benzothiazolylthio group without deteriorating the corrosion resistance. The inventors found that an electrogalvanized steel sheet having high whiteness can be obtained without causing glossing, and filed an application as Patent Document 1. However, as described above, the current efficiency decreases, and as a result, the manufacturing cost of the electrogalvanized steel sheet increases.

Therefore, further research was conducted to obtain an electrogalvanized steel sheet with high whiteness while suppressing a decrease in current efficiency. As a result, when electrogalvanizing treatment is performed in an electrogalvanizing bath containing an organic compound having a 2-benzothiazolylthio group, one or more organic compounds having a 2-benzothiazolylthio group It has been found that the current efficiency does not decrease if the total content is less than 0.01 mass ppm.

Based on the above findings, a) electrogalvanizing treatment in an electrogalvanizing bath with one or more organic compounds having a 2-benzothiazolylthio group totaling less than 0.01 mass% ppm; ) Combining electrogalvanizing treatment with an electrogalvanizing bath containing one or more organic compounds with 2-benzothiazolylthio group in a total of 0.01 to 3 massmass ppm suppresses the decrease in current efficiency. It was considered effective in producing an electrogalvanized steel sheet having high whiteness. In order to minimize the decrease in current efficiency, it is necessary to increase the amount of plating attached by the electrogalvanizing treatment in the above a) and relatively reduce the amount of plating attached in the electrogalvanizing treatment of the above a). It is valid. Therefore, in any order, the amount of plating adhesion in the electrogalvanizing treatment of a) above is 90% of the total plating layer, and the amount of plating adhesion in the electrogalvanizing treatment of b) is 10% of the entire plating layer. It was investigated whether the production of electrogalvanized steel sheet is most effective in terms of suppressing the decrease in current efficiency and having high whiteness.

The experimental conditions are as follows. In addition, the measuring method and evaluation of current efficiency and whiteness are the same as those in Examples described later.
Electroplating conditions: Relative flow velocity 1.5m / s, current density: 100A / dm ²
Electro-galvanizing treatment conditions of a) above Plating bath: Acidic bath of sulfuric acid (pH 2.0, temperature 50 ° C) with 1.5 mol / l of Zn ²⁺ ions that does not contain organic compounds with 2-benzothiazolylthio group
Electro-galvanizing treatment conditions in (a) above: Plating bath: Zn ²⁺ ion 1.5 mol / l sulfuric acid acid bath (pH 2.0, temperature 50 ° C) containing 0.5 mass ppm of sodium salt of 2-mercaptobenzothiazole
The experimental results obtained above are shown in Table 1.

From Table 1, after carrying out the electrogalvanizing treatment under the condition A, that is, the above a), the method of carrying out the electrogalvanizing treatment in the above a) suppresses the decrease in current efficiency, It was proved effective from the viewpoint of obtaining a high galvanized steel sheet.

The present invention has been made based on the above findings, and the gist thereof is as follows.
[1] One or more organic compounds with 2-benzothiazolylthio group are subjected to electrogalvanizing treatment in an electrogalvanizing bath with a total of less than 0.01 mass ppm, and then 2-benzothiazolylthio Electrogalvanizing is performed in an electrogalvanizing bath containing a total of 0.01 to 3 mass ppm of one or more organic compounds having a group, so that the amount deposited is 1 to 50% of the total plating layer. A method for producing an electrogalvanized steel sheet.
[2] The method for producing an electrogalvanized steel sheet according to [1], wherein the organic compound having a 2-benzothiazolylthio group is 2-mercaptobenzothiazole or a salt of 2-mercaptobenzothiazole.

According to the present invention, by appropriately controlling the concentration of an organic compound having a 2-benzothiazolylthio group, it is possible to produce an electrogalvanized steel sheet having high whiteness without greatly reducing current efficiency. .
And as a result, the chemical conversion treatment electrogalvanized steel plate excellent in the surface external appearance will be obtained.

The electrogalvanized steel sheet that is the subject of the present invention is a steel sheet obtained by electrogalvanizing using an acidic bath. From the balance of performance (corrosion resistance, workability, whiteness, etc.) and operation, the preferable range of the zinc content in the plating film is 98 mass% or more.

In the present invention, in the electrogalvanizing treatment, the electrogalvanizing treatment is performed in an electrogalvanizing bath in which one or more organic compounds having a 2-benzothiazolylthio group are less than 0.01 mass% ppm. After performing the test, the amount of adhesion in an electrogalvanizing bath containing one or more organic compounds with 2-benzothiazolylthio group in a total of 0.01 to 3 mass ppm is 1 to 50% of the total plating layer. Electrogalvanization treatment is performed so as to be. That is, the electrogalvanizing process is performed in two steps. First, in the first step, one or more organic compounds having a 2-benzothiazolylthio group are electrogalvanized by electrolytic treatment using a steel plate as a cathode in an electrogalvanizing bath with a total of less than 0.01 mass ppm. Processing is performed (hereinafter abbreviated as the first step). In the second step, the coating amount is 1 to 50% of the total plating layer in an electrogalvanizing bath containing one or more organic compounds having 2-benzothiazolylthio group in a total of 0.01 to 3 mass ppm. Then, electrogalvanizing treatment is performed by electrolytic treatment using the steel plate as a cathode (hereinafter abbreviated as the second step). By the above, the electrogalvanized steel plate which suppresses the fall of current efficiency and has high whiteness will be obtained.

Details of the present invention will be described below.
In the first step, the total amount of one or more organic compounds having a 2-benzothiazolylthio group shown below in the plating bath is less than 0.01 mass ppm.
In the first step, when an organic compound having a 2-benzothiazolylthio group is contained in an amount of 0.01 mass ppm or more, the current efficiency is lowered. Also, if the zinc adhesion amount in the first step exceeds 50% with respect to the entire plating layer, the ratio of the zinc adhesion amount in the second step with low current efficiency will not be too high, leading to a decrease in current efficiency. Absent. Furthermore, if the zinc adhesion amount in the first step is less than 99% with respect to the entire plating layer, the ratio of the zinc adhesion amount in the second step is not too low, and sufficient whiteness can be obtained. Therefore, in the first step, it is preferable to perform the electrogalvanizing treatment so that the zinc adhesion amount is more than 50% and less than 99% of the entire plating layer.

In the second step, the plating bath contains a total of 0.01 to 3 mass ppm of one or more organic compounds having the 2-benzothiazolylthio group shown above.
In the second step, when the organic compound having a 2-benzothiazolylthio group is less than 0.01 mass ppm or exceeds 3 mass ppm, sufficient whiteness cannot be obtained.
Further, if the zinc adhesion amount in the second step is less than 1% with respect to the entire plating layer, sufficient whiteness cannot be obtained. When the zinc adhesion amount exceeds 50% with respect to the entire plating layer, the ratio of the zinc adhesion amount in the second step with low current efficiency is too high, which causes a decrease in current efficiency. Therefore, in the second step, the electrogalvanizing treatment is performed so that the zinc adhesion amount is 1 to 50% of the entire plating layer.

As the organic compound having a 2-benzothiazolylthio group, it is preferable to use the following 2-mercaptobenzothiazole or a salt of 2-mercaptobenzothiazole. The whiteness can be increased more effectively. Examples of the salt of 2-mercaptobenzothiazole include Na salt, K salt, Zn salt and Cu salt.

The electrogalvanizing treatment is not particularly limited except that the organic compound is contained in the concentration range in the electroplating bath and the above-described two-stage treatment is performed. For example, as the electroplating bath, a sulfuric acid acidic bath, a hydrochloric acid acidic bath, or a mixture of both can be applied. The zinc content in the electrogalvanizing bath is preferably 1.0 mol / L or more as ZnSO ₄ . If it is 1.0 mol / L or more, sufficiently high whiteness can be obtained. In addition to Zn ions, the electroplating bath may contain additives or impurities as conductivity aids such as sodium sulfate and potassium sulfate, metal ions such as Fe, Ni, Pb, Sn, and Co. . The electroplating bath conditions are not particularly limited. For example, the bath temperature may be 30 to 70 ° C., the pH may be 0.5 to 4.5, and the relative flow rate may be 0 to 4.0 m / sec. The electrolytic current density is not particularly limited, but may be, for example, 10 to 150 A / dm ² . The amount of electrogalvanized adhesion is not particularly limited, but is usually about 5 to 40 g / m ² per side in total for the first step and the second step.

Further, in the production of an electrogalvanized steel sheet, as a treatment prior to performing the electrogalvanizing treatment, degreasing treatment and water washing for cleaning the steel plate surface, and further pickling for activating the steel plate surface are preferred. Treatment and water washing are performed, and following these pretreatments, an electrogalvanizing treatment is performed.
The degreasing treatment and the water washing method are not particularly limited. Conventional methods can be used.
In the pickling treatment, various acids such as sulfuric acid, hydrochloric acid, nitric acid, and mixtures thereof can be used. Of these, sulfuric acid, hydrochloric acid, or a mixture thereof is desirable. The concentration of the acid is not particularly specified, but it is preferably about 1 to 20 mass% in consideration of the ability to remove the oxide film and the prevention of rough skin by peracid washing. The pickling treatment liquid may contain an antifoaming agent, a pickling accelerator, a pickling inhibitor, and the like.

After the electrogalvanizing treatment, if necessary, chromate treatment or chromate-free treatment (coating type, reaction type, electrolytic type) is performed for the purpose of further improving various performances such as corrosion resistance, scratch resistance, and workability. Furthermore, a resin coating process etc. can also be implemented on it. The type of the chemical conversion coating is not particularly limited, and a known method can be used.
In addition, it cannot be overemphasized that the effect of this invention is acquired also about the steel plate which performed these processes. In particular, the appearance of the chemical conversion treated steel sheet subjected to these treatments greatly depends on the appearance after electrogalvanizing (before chemical conversion treatment) when used without coating. Therefore, when using the steel plate after such a chemical conversion treatment without coating, it has high whiteness by using the electrogalvanized steel plate produced by the method of the present invention.

Moreover, the electrogalvanized steel sheet of the present invention can form a chemical conversion film, and further, a single layer or a multilayer film containing an organic resin, depending on the application. Examples of the coating film include a polyester resin coating film, an epoxy resin coating film, an acrylic resin coating film, a urethane resin coating film, and a fluorine resin coating film. Further, for example, an epoxy-modified polyester resin coating film in which a part of the resin is modified with another resin can be applied. Furthermore, a hardening | curing agent, a hardening catalyst, a pigment, other additives, etc. can be added to the said resin as needed.

Although the coating method for forming the coating film is not particularly defined, examples of the coating method include roll coater coating, curtain flow coating, and spray coating. After coating a paint containing an organic resin, the coating film can be formed by heating and drying by means of hot air drying, infrared heating, induction heating or the like.
However, the manufacturing method of the said surface treatment steel plate is an example, and is not limited to this.

Next, the present invention will be described in more detail with reference to examples.
A cold rolled steel sheet with a thickness of 0.7 mm manufactured by a conventional method is degreased with alkali, washed with water, then pickled, washed with water, and then in the following conditions and in Tables 2 and 3 Electrogalvanization was performed using the steel sheet as the cathode at the types and concentrations of the organic compounds shown. In addition, about some things, the metal-plating process was implemented without adding an organic compound in an electroplating bath. The amount of zinc plating deposited on one side was determined by dissolving zinc plating with dilute hydrochloric acid, measuring the zinc concentration in the solution with an ICP (Inductively Coupled Plasma) mass spectrometer, and converting it to the amount deposited.
Electrolytic conditions Organic substance content, current density: plating bath shown in Table 2: Acidic acid bath containing Zn ²⁺ ions 1.5 mol / l Bath temperature: 50 ° C
pH: 2.0
Relative flow velocity: 1.5m / s
Electrode (Anode): Iridium Oxide Electrode The electrogalvanized steel sheet obtained above was measured and evaluated for brightness (L value) as whiteness evaluation based on the following measurement method and evaluation criteria. In addition, the current efficiency was obtained and evaluated. The obtained results are also shown in Table 2.

Whiteness: Lightness (L value)
Using a spectral color difference meter (SD5000 manufactured by Nippon Denshoku Industries Co., Ltd.), the whiteness was measured by SCE (removing regular reflection light) and evaluated as follows.
<As plated>
◎: L value 85 or more ○: L value 82 or more and less than 85 ×: L value 82 or less Current efficiency From the theoretical value obtained from the value of galvanized adhesion amount and the amount of electricity energized during plating, the current efficiency according to the following formula Asked.
Current efficiency (%) = (Amount of zinc plating obtained by measurement) / (Theoretical adhesion amount) x 100

From Table 2, it can be seen that the electrogalvanized steel sheet having a high L value, that is, a high whiteness, is obtained efficiently in the present invention example.
On the other hand, in the comparative example, the L value is low or the current efficiency is low.

The electrogalvanized steel sheet of the present invention has an excellent surface appearance and can be used without any problem without being painted. Therefore, it can be used in a wide range of applications such as home appliances, automobiles, and building materials.

Claims

One or more organic compounds with 2-benzothiazolylthio group have 2-benzothiazolylthio group after electrogalvanizing treatment in electrogalvanizing bath with a total of less than 0.01 massmasppm Electrogalvanizing is performed in an electrogalvanizing bath containing one or more organic compounds in a total of 0.01 to 3 mass ppm, so that the amount of zinc deposited is 1 to 50% of the total plating layer. A method for producing an electrogalvanized steel sheet.
2. The method for producing an electrogalvanized steel sheet according to claim 1, wherein the organic compound having a 2-benzothiazolylthio group is 2-mercaptobenzothiazole or a salt of 2-mercaptobenzothiazole.