JP2005290532A - Chemical treatment of Ni-plated steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a chemically treated film excellent in paint adhesion, corrosion resistance and weldability on a Ni-plated steel sheet.
SOLUTION: On a steel plate plated with 300 to 2000 mg / m ² of Ni, a bath temperature containing H ₂ SO ₄ of 1/50 to 1/300 by mass ratio with CrO ₃ and CrO ₃ is less than 45 ° C. Subsequent to cathodic electrolysis of 30 A / dm ² or more in the treatment bath, immersion treatment is performed in a treatment bath containing CrO _{3 and} having a bath temperature of 50 ° C. or more, and the amount of chromium metal deposition is 30 to 200 mg / m ² . corrosion resistance of chromium coating weight is characterized in that it is a 1-15 mg / m ^2, coating adherence, chemical treatment method superior Ni-plated steel sheet weldability. It is desirable that the concentration of CrO ₃ in the cathode electrolytic treatment bath is 100 to 250 g / l, and the concentration of CrO ₃ in the immersion bath is 10 to 200 g / l.
[Selection figure] None

Description

  The present invention relates to a method for forming a chemically treated coating having excellent paint adhesion, corrosion resistance and weldability on a Ni-plated steel sheet.

  Conventionally, nickel-plated steel sheets have been widely used as materials for various metal containers such as cans and dry batteries. However, the usage of coating the inside and outside of the can to ensure corrosion resistance is increasing. In this case, the quality of the coating film adhesion is an important factor affecting the corrosion resistance. Hydrating oxidation with metallic chromium (hereinafter referred to as Me-Cr) by cathodic electrolysis in a chromic anhydride-based treatment bath containing sulfuric acid, fluorine compounds and the like as a method for improving the coating film adhesion of nickel-plated steel sheet A method of forming a film made of chromium (hereinafter referred to as Ox-Cr) or a method of performing high-temperature cleaning after the above treatment {Japanese Patent Laid-Open No. 57-35697 (Patent Document 1), or {Japanese Patent Laid-Open No. 57-35698 ( Patent Document 2) etc. are known. However, simply performing the cathodic electrolysis treatment in a chromic anhydride bath has the following problems. That is, when the amount of Me-Cr necessary for improving paint adhesion is generated, the amount of Ox-Cr generated at the same time tends to be excessively increased, the seam weldability is impaired, and the amount of Ox-Cr generated is reduced. Appearance unevenness easily occurs due to non-uniformity.

JP 57-35697 A Japanese Patent Laid-Open No. 57-35698

  Accordingly, as a result of intensive studies, the inventors have found that the coverage of Me—Cr and Ox—Cr is so good that the cathode electrolytic treatment bath temperature in the chromic anhydride bath described in the claims is lowered, and Ox— Although the amount of Cr increases, the all-type Ox-Cr in the upper layer of the Ox-Cr coating produced at this time has a high solubility due to the large amount of eutectoid of sulfate ions, so that it is immersed in a high-temperature chromic anhydride bath after electrolysis. It was clarified that the Ox-Cr remaining at this time was a film having a high degree of oxonation and excellent adhesion.

  That is, the present invention improves solderability and weldability by improving the coverage of Me-Cr by electrolysis due to high current density in a predetermined bath composition and low temperature bath and reducing Ox-Cr efficiently by immersion treatment in a high temperature bath. The object of the present invention is to provide a chemical treatment method for a nickel-plated steel sheet that improves the uniformity of appearance, improves the productivity in a continuous production line, and also has a remarkable effect on paint adhesion.

The gist of the present invention is as follows.
(1) Treatment with a bath temperature of less than 45 ° C. containing H ₂ SO ₄ of 1/50 to 1/300 by mass ratio of CrO ₃ and CrO ₃ on a steel plate subjected to 300 to 2000 mg / m ² of Ni plating. Subsequent to cathodic electrolysis of 30 A / dm ² or more in the bath, immersion treatment is performed in a treatment bath containing CrO _{3 and} having a bath temperature of 50 ° C. or more, and the amount of metal chromium deposited is 30 to 200 mg / m ² . A chemical treatment method for a Ni—Cr plated steel sheet excellent in corrosion resistance, paint adhesion, and weldability, wherein the adhesion amount is 1 to 15 mg / m ² .

(2) The concentration of CrO ₃ in the cathodic electrolytic treatment bath is 100 to 250 g / l. The Ni—Cr plated steel sheet having excellent corrosion resistance, paint adhesion, and weldability as described in (1) above Chemical processing method.
(3) Ni—Cr excellent in corrosion resistance, paint adhesion and weldability according to (1) to (2) above, wherein the concentration of CrO ₃ in the immersion bath is 10 to 200 g / l. It is in the chemical treatment method of plated steel sheets.

  The Ni-plated steel sheet chemically treated according to the present invention can obtain excellent seam weldability, paint adhesion and corrosion resistance.

Hereinafter, the present invention will be described in more detail.
Ni plating is necessary to improve the corrosion resistance and seam weldability, and the amount of adhesion that can sufficiently cover the surface of the steel sheet is 300 mg / m ² , and the amount of adhesion of 300 mg / m ² or more is necessary to ensure sufficient corrosion resistance. is necessary. As the amount of deposited Ni increases, the corrosion resistance and seam weldability also improve. However, if it exceeds 2000 mg / m ² , the effect is saturated and uneconomical, so the upper limit is set to 2000 mg / m ² . After Ni plating, a film made of Me-Cr and Ox-Cr is formed by cathodic electrolysis in a low-temperature chromic anhydride-based bath according to claim and immersion treatment in a high-temperature chromic anhydride-based bath. Adhesion amounts of 30 to 200 mg / m ² and 1 to 15 mg / m ² (both per side) are necessary.

If the amount of Me—Cr deposited is less than 30 mg / m ² , Ni cannot be completely covered, so a local battery is formed with Ni and Me—Cr, and the corrosion resistance deteriorates. Moreover, although corrosion resistance improves with the increase in the amount of Me-Cr attached, if 200 mg / m ² is exceeded, the effect is saturated and uneconomical, so the upper limit is set to 200 mg / m ² . Further, when the Ox-Cr adhesion amount is less than 1 mg / m ² , the paint adhesion deteriorates, and when it exceeds 15 mg / m ² , the surface resistance value increases, and the seam weldability deteriorates. Therefore, the lower limit of the Ox—Cr adhesion amount is 1 mg / m ² and the upper limit is 15 mg / m ² .

A particularly important point of the present invention is to lower the temperature of the cathode electrolyzed in a chromic acid bath at 30 A / dm ² or more and to perform an immersion treatment in the high temperature bath. The uniform coverage of Me—Cr is improved by lowering the temperature of the cathode electrolytic treatment bath. Ox-Cr has a two-layer structure of an all-type compound in the upper layer and an oxo-type compound in the lower layer, and the precipitation amount of all-type and oxo-type Ox-Cr increases with the low temperature of the electrolytic treatment bath. At this time, it was clarified that the amount of sulfate ions co-deposited in the upper all-type Ox-Cr increased, and the solubility of the all-type Ox-Cr increased in the next immersion treatment step. Therefore, the bath temperature of the electrolytic treatment bath needs to be less than 45 ° C. The lower limit of the electrolytic treatment bath temperature is not particularly provided, but if it is too low, a powerful cooler needs to be installed, which is uneconomical.

Furthermore, in order to form a uniform Me—Cr film on the Ni plating, electrolysis of 30 A / dm ² or more is required. In addition, it is desirable that the concentration of CrO ₃ contained in the electrolytic treatment bath is 100 g / l or more. If it is too high, the generation of Ox—Cr becomes non-uniform, resulting in a decrease in paint / film adhesion. It is desirable to set l as the upper limit.

The addition of sulfuric acid to the treatment bath is indispensable for the production of Me—Cr, and it is necessary to make the mass ratio to chromic anhydride (hereinafter referred to as sulfuric acid concentration ratio) 1/300 to 1/50. If the sulfuric acid concentration ratio is too high or too low, the Me—Cr electrodeposition efficiency is remarkably reduced, so the lower limit of the sulfuric acid concentration ratio is 1/300 and the upper limit is 1/50.
In addition, the said treatment bath may contain fluorine compounds, such as sodium silicofluoride, sodium borofluoride, and ammonium fluoride other than a sulfuric acid, as a Me-Cr precipitation adjuvant. Further, if the purchase amount of trivalent chromium ions in the treatment bath is 0.1 to 5 g / l, it does not adversely affect the homogenization of the chromate film, so it may be mixed.

  Following the cathodic electrolysis under the above treatment conditions, the purpose is to reduce the amount of all-type Ox-Cr produced excessively by this cathodic electrolysis and to improve the adhesion of the coating film by forming Ox-Cr having a high degree of oxoation. The obtained chromic anhydride aqueous solution immersion treatment is performed. The dissolution capacity of all-type Ox-Cr increases with an increase in bath temperature, and a bath temperature of 50 ° C. or higher is necessary for efficient dissolution. The upper limit of the bath temperature is not particularly defined, but if the temperature is too high, the recovery of the bath fume becomes large and uneconomical, so it is desirable to set the upper limit at 80 ° C.

Further, if the chromic anhydride concentration is less than 10 g / l, the ability to dissolve all-type Ox-Cr is remarkably reduced. Therefore, a concentration higher than this is desirable, and if it is higher than 200 g / l, the etching action is too strong and oxo Since the type Ox-Cr is also dissolved, it may lead to a decrease in paint adhesion and corrosion resistance. Therefore, it is desirable to set the upper limit of the chromic anhydride concentration to 200 g / l. Preferably it is 50 g / l or less.
In addition to the anhydrous chromic acid, the treatment bath may contain a trivalent chromate ion, a fluorine compound such as sulfuric acid, sodium silicofluoride, sodium borofluoride, and ammonium fluoride.

Examples of the present invention will be described below.
Steel sheets that have been cold-rolled, annealed, and temper-rolled are subjected to chemical treatment on the Ni-plated material after degreasing, pickling, and effects on appearance uniformity, seam weldability, coating film adhesion, and corrosion resistance I investigated.
About each processing material, it implemented about each item of (A)-(D) shown below, and evaluated the performance.
(A) Appearance uniformity Visually evaluated as follows.
○: Color tone unevenness ×: Color tone unevenness

(B) Seam weldability Welding such as dust and the minimum current value at which sufficient welding strength can be obtained by changing the current under the conditions of lap allowance of 0.5 mm, pressure of 45 kgf, and welding wire speed of 100 m / min. Judging comprehensively from the width of the appropriate current range consisting of the maximum current value at which defects begin to be noticeable, the evaluation was made in three stages (（: very wide, ○: no practical problem, ×: narrow).

(C) Paint adhesion The surface of the test piece corresponding to the inner surface of the can was coated with 55 mg / dm ² of epoxyphenol-based paint, and the surface corresponding to the outer surface of the can was coated with 40 mg / dm ² of clear lacquer. Until it was dried and cured under a baking condition of 15 sec. Subsequently, scratches are placed on each surface at intervals of 1 mm, 100 grids are produced, the tape is peeled off quickly, and the peeled state is observed in three stages (◎: no peeling, ○: 1-4 pieces) The paint adhesion was evaluated by peeling, x: peeling 5 or more.

(D) UCC (Under Cutting Corrosion) Evaluation Test In order to evaluate the corrosion resistance of the surface corresponding to the inner surface of the can of the test piece, a PET (polyethylene terephthalate) film having a thickness of 15 μm was laminated on the surface corresponding to the inner surface of the can. After that, a cross cut was put in until it reached the ground iron, and it was immersed in a test solution composed of a 1.5% citric acid-1.5% sodium chloride mixture at 55 ° C. for 4 days under open air. Immediately after the test, the scratch part and the flat part are peeled off with tape, and the corrosion situation near the scratch part, the pitting situation of the scratch part, and the film peeling situation of the flat part are classified into three stages (◎: no peeling and corrosion) Not recognized, ○: There was slight peeling but no corrosion was observed, and X: Most peeled and severe corrosion was observed).
As shown in Table 1, it was revealed that the Ni-plated steel sheet chemically treated according to the present invention has excellent seam weldability, paint adhesion, and corrosion resistance.

特許出願人 新日本製鐡株式会社
代理人 弁理士 椎 名 彊 他１

Patent applicant: Nippon Steel Corporation
Attorney Attorney Shiina and others 1

Claims (3)

In a treatment bath having a bath temperature of less than 45 ° C. containing H ₂ SO ₄ of 1/50 to 1/300 by mass ratio of CrO ₃ and CrO ₃ on a steel plate plated with 300 to 2000 mg / m ² of Ni. Subsequent to cathodic electrolysis of 30 A / dm ² or more, immersion treatment is performed in a treatment bath containing CrO _{3 and} having a bath temperature of 50 ° C. or more, and the metal chromium adhesion amount is 30 to 200 mg / m ² , and the oxide chromium adhesion amount is chemical treatment of the Ni-plated steel sheet corrosion resistance, paint adhesion, excellent weldability, which is a 1-15 mg / m ^2. The chemical treatment method for a Ni-plated steel sheet excellent in corrosion resistance, paint adhesion, and weldability according to claim 1, wherein the concentration of CrO ₃ in the cathode electrolytic treatment bath is 100 to 250 g / l. The chemical treatment method for a Ni-plated steel sheet excellent in corrosion resistance, paint adhesion, and weldability according to claim 1, wherein the concentration of CrO ₃ in the immersion treatment bath is 10 to 200 g / l.