JP3216383B2 - Manufacturing method of electrolytic chromate treated steel sheet with excellent surface appearance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an electrolytic chromate-treated steel sheet having an excellent surface appearance.

[0002]

2. Description of the Related Art Electrolytic chromate-treated steel sheets (hereinafter referred to as TFS) have excellent paintability and corrosion resistance, and are inexpensive compared to tinplate. It is used as a material for general cans. T
FS is widely used as a two-piece can by drawing and an adhesive can material in which seams are adhered by an organic resin, special cement, or the like, depending on the classification of the can-making method.

[0003] Recently, a TFS which can be welded without polishing has been developed. In the production of TFS, the steel plate is moved at a high speed in accordance with the advancement of the manufacturing technology for improving the productivity. Wound by conductor roll and sink roll, inverted by sink roll,
The steel sheet is run vertically in an electrolytic solution containing Cr ions, an anode electrode is provided in parallel with the steel sheet, and the steel sheet is subjected to a cathodic electrolytic treatment with the anode electrode at a current density of about ²⁰ to 100 A / dm ² . Due to this repetition for each vertical plating tank, it is necessary to perform the cathodic electrolytic treatment on the steel sheet a plurality of times.

In this case, in order to perform the cathodic electrolysis treatment by arranging a plurality of plating tanks as described above, the running steel sheet must be provided in one plating tank with the lower end of the anode electrode on the side where the steel sheet descends, The section in which the steel sheet moves to the lower end of the anode electrode on the ascending side of the steel sheet via the sink roll is an electroless section. In addition, the traveling steel sheet is between the plating tanks, the moving section of the steel sheet from the electrolytic solution of one plating tank to the electrolytic solution of the next plating tank is an electroless section, and the steel sheet is as described above. Electroless time occurs when traveling in the electroless section. During this electroless time, the formed uppermost chromium hydrated oxide layer is non-uniformly dissolved, and a metal chromium layer of granular projections is inevitably formed. There is a problem in that the granular appearance of the metal chromium layer impairs the surface appearance of TFS.

Various studies have been made on this problem since ancient times. As an example, when performing chrome plating using a plurality of plating tanks, after each plating tank, the surface of the plating layer of the running steel plate is washed with 0.1% or more sulfuric acid, and plating discontinuity is caused. (Japanese Patent Publication No. 36-15155) discloses a method for producing a chrome-plated steel sheet having a bluish and glossy color in a next plating tank by subjecting the surface coating of a steel sheet plating layer to a treatment for removing the surface film.

Alternatively, the steel sheet is subjected to chromium plating, and after completion of the plating, the steel sheet is brought into contact with an aqueous solution of chromic anhydride, nitric acid, sulfuric acid, hydrochloric acid or the like for 0.1 to 1 second to remove an inhomogeneous soluble portion of the metal chromium surface. A production method for removing and leaving a homogeneous chromium oxide has been disclosed (JP-A-52-356).
No. 19).

[0007]

With respect to TFS, the demand for TFS having an excellent surface appearance by users has been further increased with the expansion of the applications described above. Here, a design utilizing the metallic color tone of the TFS substrate is preferred, and it is said that such a color tone has a great influence not only on the composition of the paint and the ink but also on the surface color tone of the TFS. Therefore, there is a problem that the above-described cleaning method alone is not sufficient for producing TFS having excellent surface appearance by a user.

In the above-mentioned method, a sulfuric acid washing step is required for each chromium plating, or a dissolving step is required after chromium plating, which complicates the manufacturing method and increases equipment and production costs.

In both methods, the chromium plating film plated in the previous step may be dissolved in the washing step of sulfuric acid or the like depending on the concentration of sulfuric acid or the like and the washing conditions such as bath temperature. Is difficult to do.

On the other hand, various studies have been made on the cause of impairing the surface appearance of TFS, and the following is known. Due to the absorption of short wavelength in the visible light wavelength region with the increase in the thickness of the chromium hydrated oxide layer, and due to the absorption of short wavelength in the visible light wavelength region due to the physical shape of the granular protrusions of the metal chromium layer .

The present inventors have made various studies based on the above findings, and as a result, have arrived at the present invention.

An object of the present invention is to provide a method capable of easily producing an electrolytic chromated steel sheet having an excellent surface appearance without requiring a complicated washing step.

[0013]

The above object is achieved as follows. The present invention winds a steel sheet by a conductor roll and a sink roll, runs vertically in an electrolytic solution containing Cr ions, has an anode electrode in parallel with the steel sheet, and has a cathode between the anode electrode and the steel sheet. Electrolytic treatment, metal chromium in the lower layer, in the method of manufacturing an electrolytic chromate-treated steel plate composed of chromium hydrated oxide in the upper layer, the lower end of the anode electrode on the descending side of the steel plate, the anode electrode on the ascending side of the steel plate At the lower end, a non-conductive member is connected to form an electroless portion of the dummy electrode, and the length of the electroless portion is set to be at least 1/3 of the length of the electrolytic portion of the anode electrode.
Cathode electrolytic treatment is applied to the steel sheet at a current density of dm ² or more, and a lower layer of metallic chromium having a granular projection density of 20 / μm ² or less,
A method for producing an electrolytic chromate-treated steel sheet having an excellent surface appearance characterized by forming an upper layer of hydrated chromium oxide of 3 to 25 mg / m ^{2 in} terms of chromium.

[0014]

According to the present invention, a lower layer of metallic chromium having a granular projection density of not more than 20 particles / μm ² and a chromium equivalent of 3 to 25 mg / m ^{2 are provided.}
It is necessary to form an upper layer of the chromium hydrated oxide. As a method effective for evaluating the metal surface appearance, particularly the surface appearance of TFS, a known K value (Japanese Patent Application Laid-Open No. 03-193)
No. 897) to evaluate the appearance of TFS.

The K value (% / 1000 nm) is a wavelength of 480 n.
This is a numerical value obtained by determining the reflectance-wavelength gradient at intervals of 10 nm between m and 700 nm, and correcting the average value to a reflectance difference per 1000 nm.

FIG. 1 shows the surface appearance (K) of the TFS according to the present invention.
FIG. 6 is a graph showing the relationship between the chromium oxide hydrate and the amount of chromium hydrate oxide.

One cause of impairing the surface appearance of TFS, namely, absorption of short wavelengths in the visible light wavelength region accompanying an increase in the thickness of the hydrated chromium oxide layer, is as follows.
25 mg / m ² or less in terms of chromium, preferably 15 mg / m ²
This can be solved by forming a chromium hydrate oxide of m ² or less, and the surface appearance of TFS can be improved. On the other hand, if it is less than 3 mg / m ² , characteristics such as paint adhesion required of TFS cannot be satisfied.

FIG. 2 shows the surface appearance (K) of the TFS according to the present invention.
FIG. 4 is a graph showing the relationship between the density of the metallic chromium particles and the density (particles / μm ² ).

The other factor that impairs the surface appearance of TFS, namely, due to the absorption of short wavelengths in the visible light wavelength region due to the physical shape of the granular projections of the metal chromium layer, is that the density of the granular projections is 20 / μm ^{2 and} preferably 5 / μm ² or less by forming metallic chromium.
Surface appearance can be improved.

In the present invention, a plurality of plating tanks are arranged, and the electroless section of the steel sheet is defined by the lower end of the anode electrode on the lower side of the steel sheet and the lower end of the anode electrode on the upper side of the steel sheet via the sink roll. The steel plate is subjected to cathodic electrolysis in a plating tank having the same.

Then, metal chromium,
In order to manufacture an electrolytic chromate-treated steel sheet having a chromium hydrated oxide as an upper layer, the following is necessary.

FIG. 3 is an explanatory view showing a relationship between an anode electrode connected to a dummy electrode of the present invention and a leakage current, and FIG. 3A is a view showing an anode electrode connected to a dummy electrode of an electroless portion of the present invention. (B) is a diagram showing a normal anode electrode. FIG.
As shown in (a), the length of the electroless portion of the dummy electrode is set to 1/3 of the length of the electrolytic portion of the anode electrode.

The steel sheet 1 running between the electrolysis part 2a of the anode electrode 2 applies a leakage current 4 generated by the cathodic electrolysis treatment to the steel sheet 1 in the electroless part 3a of the dummy electrode 3 and the subsequent electroless section.
Of the chromium hydrated oxide layer in the electroless section by effectively collecting the chromium hydrated oxide layer in the electroless section and maintaining a uniform chromium hydrated oxide layer. This makes it possible to manufacture a TFS having a plate-like metal chromium layer.
5 is a sink roll. Here, so that as described above the length L ₂ of the electroless portion 3a, it becomes 1/3 of the length L ₁ of the electrolytic unit.

As shown in FIG. 3B, this is the case of a normal anode electrode 2, and there is no leakage current 4 generated by performing cathodic electrolysis on the steel sheet 1 running between the electrolytic portions 2 a of the anode electrode 2. The chromium hydrated oxide layer cannot be dispersed and collected in the steel sheet 1 in the electrolysis section, and the chromium hydrated oxide layer is dissolved in the electroless section, so that an uneven chromium hydrated oxide layer is formed. In a place where the chromium hydrated oxide layer is thin, the deposition rate of metallic chromium increases, and the amount of metallic chromium increases at that location, resulting in granulation.

FIG. 4 is a diagram showing a leakage current density distribution in the electrolyte in a section where the running steel sheet of FIGS. 3A and 3B rises from the position where the running steel sheet is inverted by the sink roll to the lower end of the anode electrode. (A) is a diagram showing the relationship between the distance from the lower end of the anode electrode and the leakage current density, and (b) is a diagram showing the position where the leakage current density of (a) is measured.

Here, the position where the lowermost end of the sink roll 5 contacts the running steel sheet is X = 0 cm, and the running distance of the steel sheet from there to the lower end of the electrolytic part of the anode electrode is X = 25 cm.
Assuming that the distance is 0 cm, the leakage current density applied to the steel sheet running at a position in the section is determined.

In FIG. 4 (a), the length of the electroless portion 3a of the dummy electrode 3 of the present invention is set to 1/3 of the length of the electrolysis portion 2a of the anode electrode 2 for connection. In the case of a current density of 30 A / dm ^2, the mark is indicated by ●, and the current density is 50 A / dm ^2.
The case of ² is indicated by a triangle. In the case of the current density of 30 A / dm ² by the anode electrode by comparison, the mark “○” indicates that the current density was 50 A / dm ^2.
The case of dm ² is indicated by a triangle.

As is clear from FIG. 4A, when the anode electrode to which the dummy electrode of the present invention is connected is used, the leakage current density applied to the running steel sheet 1 is 50 A / d.
In the case of m ² , even at the position of X = 100 cm, 10 A / dm
I'm holding ² .

However, when the current density is 30 A / dm ² , the leakage current density is 10 A / d at the position of X = 200 cm.
m ² , and 5 A / dm ² at the position of X = 100 cm. On the other hand, when the comparative anode electrode was used, the leakage current density applied to the running steel sheet 1 was 50 A
/ Dm ² , 2-3 at the position of X = 200 cm.
A / dm ² .

From the above, according to the present invention, an electrolytic chromate for forming a lower layer of metallic chromium having a granular projection density of 20 / μm ² or less and an upper layer of chromium hydrate oxide of 3 to 25 mg / m ^{2 in} terms of chromium. In order to manufacture treated steel sheets,
A minimum current density of 50 A / dm ² is required,
The length of the electroless part of the dummy electrode is one of the length of the electrolytic part of the anode.
It has been found that a minimum length of / 3 is required.

Thus, the leakage current generated in the cathodic electrolysis treatment of the steel sheet in the electrolytic part of the anode electrode can be effectively collected in the electroless part of the dummy electrode and the steel sheet running in the subsequent electroless section. Thereby, dissolution of the chromium hydrate oxide on the surface of the steel sheet plating layer is suppressed, and appearance defects caused thereby are prevented.

[0032]

Embodiments of the present invention will be described below in detail. Example 1
4 and Comparative Examples 1 to 6. FIG. 3 is a view showing a path structure of an electrolytic chromate treatment apparatus for a real machine test used in the present invention. Reference numeral 6 denotes a conductor roll, and reference numeral 7 denotes a plating tank of an electrolytic chromate treatment device.

In FIG. 3, the number of cathodic electrolysis passes is four, which is indicated by reference numerals # 1 to # 4. Chrome plating solution is 175
g / l CrO ₃ , 1 g / l SO ₄ ^-2 , 3 g / l F
^-Used .

Further, the moving speed of the steel sheet was set to 200 m / min, and in all the samples of the comparative example and the example, the amount of chromium metal was adjusted to 100 mg / m ² .
In the case of 50 and 100 A / dm ² , anode electrodes were used in which the lengths of the electrolytic portions were 1.3 m, 0.8 m, and 0.4 m, respectively. Further, the amount of chromium hydrated oxide was adjusted to 15 mg / m ² with respect to all the samples of Comparative Examples and Examples.

(Comparative Example 1) L at positions # 1 to # 4 in FIG.
An anode electrode of an electrolytic part having a length of ₁ = 1.3 m was arranged, and chromium plating was performed at a cathode current density of 30 A / dm ² . (Comparative Example 2) # 1 to # 4 in the position of FIG. 3 L ₁ = 0.8 m
The anode electrode of the electrolytic part having a length of
Chrome plating was performed at A / dm ² .

(Comparative Example 3) L at positions # 1 to # 4 in FIG.
₁ = L ₂ = 0.3 on the anode electrode of the electrolytic part with a length of 1.3 m
Connect the dummy electrode of the electroless part with a length of m to the lower end,
(L ₂ / L ₁ ) < _１ ／
Chrome plating was performed at 0 A / dm ² . (Comparative Example 4) # 1 to # 4 in the position of FIG. 3 L ₁ = 1.3 m
The dummy electrodes of the electroless portion of the length of L ₂ = 0.40 m to the anode electrode of the electrolysis part length to connect the bottom of, (L ₂ / L ₁₎
<In the third place, it was subjected to chrome plating the cathode current density of 30A / dm ^2.

(Comparative Example 5) L is set at the positions # 1 to # 4 in FIG.
₁ = L ₂ = 0.2 to the anode electrode of the electrolysis part of the length of 0.8m
The dummy electrode of the electroless section having a length of m is connected to the lower end, and (L
₂ / L ₁ ) <1/3 and the cathode current density is 50 A
/ Dm ² was plated with chromium. (Comparative Example 6) in # 1 to # 4 in the position of FIG. 3 L ₁ = 0.8 m
A dummy electrode of an electroless part having a length of L ₂ = 0.2 m is connected below to an anode electrode of an electrolytic part having a length of (L ₂ / L ₁ ) <1 /
3 or less, and chromium plating was performed at a cathode current density of 50 A / dm ² .

(Embodiment 1) L at positions # 1 to # 4 in FIG.
₁ = L ₂ = 0.40 on the anode electrode of the electrolytic part with a length of 0.8 m
Connect the dummy electrode of the electroless part with a length of m to the lower end,
(L ₂ / L ₁ )> _１ ／, and the cathode current density 5
Chrome plating was performed at 0 A / dm ² . (Example 2) connecting the dummy electrode of the electroless part length of L ₂ = 0.40 m at the lower end to the # 1 to # anode of the electrolytic unit of length of 0.4m at the position of 4 in Figure 3 And (L ₂ / L ₁ )> 1
/ 3, and plated with chromium at a cathode current density of 100 A / dm ² .

(Embodiment 3) L at positions # 1 and # 2 in FIG.
₁ = Place an anode electrode of the electrolytic part with a length of 0.8 m, # 3,
In the position of # 4, L ₁ = 0.8 m in length,
₂ = 0.40 m length of the electroless part dummy electrode is connected to the lower end, (L ₂ / L ₁ )> _１ ／, and chromium plating is applied at a cathode current density of 50 A / dm ^2. did. (Example 4) # 2 in FIG. 3, L ₁ to the position of # 4 = 0.8 m
The anode electrode of the electrolytic part having a length is arranged, and the anode electrode of the electrolytic part having a length of L ₁ = 0.8 m and L ₂ = 0.4 at positions # 1 and # 3.
Connect the dummy electrode of the electroless part with a length of 0 m to the lower end,
(L ₂ / L ₁ )> _１ ／, and the cathode current density 5
Chrome plating was performed at 0 A / dm ² .

FIG. 4 is a transmission electron micrograph showing the metal structure of the electrolytic chromate-treated steel sheets of Comparative Examples 1 to 4 and Examples 1 to 4. In the photographs, in Comparative Examples 1 to 4, granular protrusions (black spots in a transmission electron micrograph) of the metal chromium layer were observed. Although not shown in the photograph, similar results were obtained for Comparative Examples 5 and 6.

On the other hand, in Examples 1 to 4, no protrusion of the metal chromium layer was observed, and only the complete metal chromium layer was observed. Table 1 shows the results of evaluating the surface appearance of the experimental samples of Examples 1 to 4 and Comparative Examples 1 to 6.

[0042]

[Table 1] In Table 1, Comparative Examples 1 to 3 having granular projections of metallic chromium
The sample of No. 6 was inferior in surface appearance, and the samples of Examples 1 to 4 having plate-like metal chromium were confirmed to be excellent in surface appearance.

According to the present invention, as shown in the embodiment,
This makes it possible to manufacture TFS having an excellent surface appearance without having a complicated electrolytic chromate treatment step. As a result, it is possible to reduce equipment cost and manufacturing energy, and furthermore, to manufacture stable and high-yield TFS.

[0044]

As described above, according to the present invention, T is excellent in surface appearance without complicated electrolytic chromate treatment step.
FS can be easily manufactured.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the chromium hydrated oxide amount and the K value.

FIG. 2 is a diagram showing the relationship between the density of metallic chromium granular protrusions and the K value.

FIG. 3 is an explanatory diagram showing a relationship between an anode electrode used in the present invention and a leakage current.

FIG. 4 is a diagram illustrating a leakage current density distribution in an electrolytic solution in a section in which a running steel sheet according to the present invention rises from a position where it is inverted by a sink roll to a lower end of an anode electrode.

FIG. 5 is a view showing a path structure of an electrolytic chromate treatment apparatus for a real machine test used in the present invention.

FIG. 6 is a transmission electron micrograph showing a metal structure of an electrolytic chromate-treated steel sheet according to the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel plate 2 Anode electrode 2a Electrolytic part of anode electrode 3 Dummy electrode 3a Electroless part of dummy electrode electrode 4 Leakage current 5 Sink roll 6 Conductor roll 7 Plating tank

Continuation of the front page (72) Inventor Shinsuke Watanabe 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (56) References JP-A-59-100291 (JP, A) JP-B-46-19522 ( JP, B1) JP-B-43-6367 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) C25D 11/38

Claims (1)

(57) [Claims] 1. A steel sheet is wound by a conductor roll and a sink roll, vertically run in an electrolytic solution containing Cr ions, and provided with an anode electrode in parallel with the steel sheet. Cathodic electrolytic treatment, the lower layer of chromium metal, the upper layer of the method for producing an electrolytic chromate-treated steel sheet comprising chromium hydrated oxide, the lower end of the anode electrode on the descending side of the steel sheet, the anode on the ascending side of the steel sheet A non-conductive member is connected to the lower end of the electrode to form an electroless portion of the dummy electrode, and the length of the electroless portion is set to be at least 1/3 of the length of the electrolytic portion of the anode electrode. / Dm ² is subjected to cathodic electrolytic treatment at a current density of at least
A method for producing an electrolytic chromate-treated steel sheet having an excellent surface appearance, characterized by forming a lower layer of metallic chromium of 0 / μm ² or less and an upper layer of hydrated chromium oxide of 3 to 25 mg / m ^{2 in} terms of chromium. .