JP2000080499A - Chemical treatment of nickel plated steel sheet - Google Patents

Abstract

[Problem] To provide a chromate coating excellent in weldability, adhesion to paints and films, and corrosion resistance on nickel-based plated steel sheets by low-temperature electrolytic treatment and high-temperature low-current density electrolytic treatment in a CrO ₃ -based bath. Form. SOLUTION: The nickel-based plated steel sheet has at least Cr.
Cathodic electrolysis is performed in a treatment bath containing H ₂ SO ₄ at a weight ratio of O ₃ and CrO ₃ of 1/50 to 1/300 and a bath temperature of less than 45 ° C., followed by a bath temperature containing at least CrO ₃ of 50%.
A method for chemically treating a nickel-based plated steel sheet, comprising performing cathodic electrolysis at 1 to 20 A / dm ² in a treatment bath at a temperature of at least 100 ° C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Nickel-plated steel sheets are widely used as materials for various metal containers such as cans and dry batteries, but the use of coating inside and outside of cans to ensure corrosion resistance is increasing. . In this case, the quality of the coating film adhesion is an important factor that determines the corrosion resistance. As a method for improving the adhesion of the coating film of a nickel-plated steel sheet, cathodic electrolysis is performed in a chromic anhydride-based treatment bath containing sulfuric acid, a fluorine compound or the like as an auxiliary agent to hydrate with chromium metal (hereinafter, Me-Cr) A method of forming a coating made of chromium oxide (hereinafter referred to as Ox-Cr) and a method of high-temperature washing after the above treatment (JP-A-57-35697, JP-A-57-3)
No. 5698) is known, but there is the following problem simply by performing the cathodic electrolytic treatment in a chromic anhydride-based bath.

That is, when the amount of Me-Cr necessary for improving the paint adhesion is generated, the Ox generated at the same time is generated.
-The amount of Cr tends to be too large, which impairs the seam weldability and tends to cause unevenness in appearance due to the uneven amount of Ox-Cr generated. For tin-plated steel sheets, a treatment method in which cathodic electrolysis is performed in a chromic anhydride-based bath is used to improve paint adhesion.However, nickel and tin have different hydrogen overvoltages, so hydrogen generation is a necessary condition. Me-
In the precipitation of Cr and Ox-Cr, the optimum processing conditions also differ.

[0004]

The inventors of the present invention have conducted a sincere study and found that the lower the temperature of the cathodic electrolysis bath in the preceding chromic anhydride-based bath, the better the Me-Cr coatability. In addition, as the temperature of the cathodic electrolysis treatment in the latter chromic anhydride-based bath is increased and the electrolysis is performed at a lower current density, the uniform coverage of the Ox-Cr film is improved.
Ox-Cr film with excellent paint / film adhesion due to the small amount of eutectoid of sulfate ion in the film of No.3 can be formed. Even if the line speed changes, a certain amount of Ox-Cr We found that we could secure quantity.

That is, the present invention improves Me-Cr coating properties by cathodic electrolysis in a pre-chromic anhydride-based low-temperature bath and further dissolves Ox-Cr generated by cathodic electrolysis in a post-chromic anhydride-based high-temperature bath. While ensuring the amount of Ox-Cr by low current density cathodic electrolysis, this aims to improve solderability, weldability, appearance uniformity, productivity in a continuous production line, and improve paint adhesion. Another object of the present invention is to provide a method for chemically treating a nickel-based plated steel sheet having a remarkable effect.

[0006]

The gist of the present invention is as follows. (1) At least 1/50 to 1/300 H ₂ SO in weight ratio of CrO ₃ and CrO ₃ to a nickel-based plated steel sheet
Perform cathodic electrolysis in a processing bath having a bath temperature of less than 45 ° C. containing ₄ ,
Subsequently, a cathodic electrolysis is carried out at 1 to 20 A / dm ² in a treatment bath containing at least CrO ₃ at a bath temperature of 50 ° C. or more. (2) When the concentration of CrO ₃ in the cathodic electrolytic treatment bath is 10
The chemical treatment method for a nickel-based plated steel sheet according to the above (1), wherein the amount is from 200 to 200 g / l.

(3) The chemical treatment method for a nickel-based plated steel sheet according to (1) or (2), wherein the concentration of CrO ₃ in the immersion treatment bath is 10 to 200 g / l. (4) The concentration of CrO ₃ in the cathodic electrolysis bath is 10
The above (1), which is で あ 50 g / l;
The chemical treatment method for a nickel-based plated steel sheet according to (3). (5) The concentration of CrO ₃ in the immersion treatment bath is 10 to 5
0 g / l, (1), (2),
(4) The method for chemically treating a nickel-based plated steel sheet according to (4).

Hereinafter, the present invention will be described in more detail. In the present invention, the nickel-based plated steel sheet includes not only a nickel-plated steel sheet, but also a Fe-Ni plated steel sheet or a plated steel sheet that has been subjected to Ni plating and further subjected to a heat diffusion treatment. Also, the method of the present invention can be applied. After nickel-based plating, M is subjected to cathodic electrolytic treatment in a low-temperature chromic anhydride-based bath and immersion treatment in a high-temperature chromic anhydride-based bath according to the claims.
A coating composed of e-Cr and Ox-Cr is formed, and the coating amount is 0.5 to ²⁰ mg / m ² and 0.5 to ²⁰ mg / m ^2, respectively.
15 mg / m ² (both per side) is desirable.

Particularly important points of the present invention are cathodic electrolysis in a low-temperature chromic acid-based bath and low-current density cathodic electrolysis in a high-temperature chromic acid-based bath. The uniform coverage of Me-Cr is improved by lowering the temperature of the pre-cathode electrolysis bath. Therefore, the bath temperature of the treatment bath needs to be lower than 45 ° C.
The lower limit of the treatment bath temperature is not particularly set, but if it is too low, a powerful cooler must be installed, which is uneconomical. Therefore, it is preferable to set the lower limit to 10 ° C. In addition, when a Me-Cr film having a low adhesion amount as described above is generated, short-time treatment at a high current density is effective for uniformity of the film.
It is desirable to perform high current density processing of 0 A / dm ² or more. If the current density is too high, a decrease in electrodeposition efficiency due to an increase in hydrogen generation is observed, so it is desirable to perform electrolysis at 150 A / dm ² or less.

Furthermore, in order to form a low adhesion amount of uniform Me-Cr coating in such a high current density electrolysis, it is desirable to CrO ₃ concentration above 10 g / l contained in a treatment bath, If it is too high, the adhesion of the paint / film will decrease, so the upper limit is preferably 200 g / l, more preferably 50 g / l or less. The addition of sulfuric acid to the former-stage cathode electrolytic bath is indispensable for the generation of Me-Cr, and it is necessary to make the weight ratio to chromic anhydride (hereinafter referred to as sulfuric acid concentration ratio) from 1/300 to 1/50. If the sulfuric acid concentration ratio is too high or too low, the Me-Cr electrodeposition efficiency drops significantly, so the lower limit of the sulfuric acid concentration ratio is 1/300 and the upper limit is 1/50. The treatment bath may contain a fluorine compound such as sodium silicofluoride, sodium borofluoride, or ammonium fluoride as a Me-Cr deposition aid in addition to sulfuric acid. If the amount of trivalent chromate ion mixed in the treatment bath is 0.1 to 5 g / l, it may be mixed because it is effective in making the chromate film uniform.

[0011] The pre-cathode electrolysis under the above processing conditions
Then, in a high temperature chromic anhydride bath, low current density electrolysis was performed.
Ox-Cr amount is generated more. At this time, the low current
Before performing the density electrolysis, set the immersion time in the post-stage electrolysis bath.
You can secure it. 1A / dm^Two If less than Ox-C
r is not generated and 20 A / dm^Two Exceeds Me-Cr
Because of preferential generation, the lower limit of the current density is 1 A / dm
^Two , Upper limit is 20A / dm ^Two Becomes High paint and film
A bath temperature of 50 ° C or higher is required to ensure adhesion.
You. The upper limit of the bath temperature is not specified, but it should be too high
Recovery of fumes from the bath was enormous and uneconomical
Therefore, the upper limit is desirably 80 ° C. In addition, anhydrous
Ox-Cr precipitates when the concentration of humic acid is too low or too high
The lower limit is 10 g / l and the upper limit is 200 g / l
It is desirable. Preferably, it is 50 g / l or less.
In addition, the above-mentioned treatment bath is not limited to chromic anhydride but trivalent chromic acid.
Ion, sulfuric acid, sodium fluorosilicate, sodium borofluoride
Contains fluorine compounds such as lithium and ammonium fluoride
It does not matter.

Hereinafter, embodiments of the present invention will be described.

[Example] A material α obtained by subjecting a steel sheet subjected to cold rolling, annealing and temper rolling to degreasing and pickling and then nickel plating at 600 g / m ² per side, and 300 mg as Ni after degreasing and pickling. / M ² Fe-Ni plated material β was subjected to chemical treatment under various conditions, and the effects on appearance uniformity, seam weldability, coating film adhesion, and corrosion resistance were examined.

Each of the processing materials (A) to (A)
Each item of (D) was performed, and the performance was evaluated. (A) Uniformity of appearance It was visually evaluated as follows. 〇: No color tone unevenness ×: Color tone unevenness

(B) Seam weldability Under the conditions of a lap margin of 0.5 mm, a pressing force of 45 kgf, and a welding wire speed of 100 m / min, the current is changed and welding is performed. Judgment was made comprehensively from the width of the appropriate current range consisting of the maximum current value at which welding defects at which the welding defects start to stand out were evaluated in three stages (段 階: very wide, Δ: no problem in practical use, ×: narrow).

(C) Adhesion of paint The epoxyphenol-based paint is applied at 55 mg / dm ² on the surface corresponding to the inner surface of the can of the test piece, and the clear lacquer is applied at 40 mg / dm ² on the surface corresponding to the outer surface of the can. ,
Drying and curing were performed under a baking condition of 15 seconds up to 290 ° C. Subsequently, scratches were made on each surface at intervals of 1 mm to prepare 100 grids, the tape was peeled off promptly, the peeling state was observed, and three stages (、 ３: no peeling,
Δ: 1 to 4 pieces peeled, ×: 5 or more pieces peeled) to evaluate paint adhesion.

(D) UCC (Undercutting Corrosion) Evaluation Test In order to evaluate the corrosion resistance of the surface of the test piece corresponding to the inner surface of the can,
A PET (polyethylene terephthalate) film having a thickness of 15 μm was laminated on a surface corresponding to the inner surface of the can.
After that, make a cross cut until the steel reaches 1.5%
It was immersed in a test solution composed of a citric acid-1.5% salt mixture at 55 ° C. for 4 days in the open to the atmosphere. After the test is completed, the scratch part and the flat part are immediately peeled off with a tape, and the corrosion state near the scratch part, the pitting state of the scratch part, and the film peeling state of the flat part are evaluated in three stages. Not observed, Δ: slight peeling but no corrosion was observed, x: peeling was observed in most parts and severe corrosion was observed). As shown in Table 1, it was revealed that the nickel-plated steel sheet chemically treated according to the present invention had excellent seam weldability, paint adhesion, and corrosion resistance.

[0017]

[Table 1]

[0018]

As described above, the nickel-plated steel sheet chemically treated according to the present invention has extremely excellent seam weldability, paint adhesion and corrosion resistance.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Kazunari Hasegawa 1-1, Hibata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka New Nippon Steel Corporation Yawata Works (72) Inventor Hirokazu Yokoya Tobata, Kitakyushu-shi, Fukuoka No. 1-1, Hibata-cho, Ward New Nippon Steel Corporation Yawata Works F-term (reference) 4K024 AA02 AB01 AB02 BA03 BB21 CA01 CA04 CA06 GA04 GA12 GA14

Claims (5)

[Claims] 1. A nickel-based plated steel sheet having at least Cr
Cathodic electrolysis is performed in a treatment bath containing H ₂ SO ₄ at a weight ratio of O ₃ and CrO ₃ of 1/50 to 1/300 and a bath temperature of less than 45 ° C., followed by a bath temperature containing at least CrO ₃ of 50%.
A method for chemically treating a nickel-based plated steel sheet, comprising performing cathodic electrolysis at 1 to 20 A / dm ² in a treatment bath at a temperature of at least 100 ° C. 2. The method according to claim 1, wherein the concentration of CrO ₃ in the cathodic electrolysis bath is 10 to 200 g / l. 3. The immersion treatment bath according to claim 1, wherein the concentration of CrO ₃ is 10 to 200 g / l.
3. The method for chemically treating a nickel-based plated steel sheet according to item 2. 4. The chemical treatment method for a nickel-based plated steel sheet according to claim 1, wherein the concentration of CrO ₃ in the cathodic electrolytic treatment bath is 10 to 50 g / l. 5. The method according to claim 1, wherein the concentration of CrO ₃ in the immersion treatment bath is 10 to 50 g / l.
The method for chemically treating a nickel-based plated steel sheet according to any one of claims 2 and 4.