JPH09157862A - Chromate treated galvanized steel sheet and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To impart excellent corrosion resistance, fingerpring resistance, coating suitability and appearance to a galvanized steel sheet. SOLUTION: In a chromate treated galvanized steel sheet in which a chromate film is formed on a zinc or zinc alloy plating layer, the chromate film is essentially consisting of the oxides or hydroxides of Cr and Al, colloidal silica and a phosphoric acid radical. The coating weight of the oxides or hydroxides of Cr is regulated to the range of 3 to 100mg/m<2> expressed in terms of Cr, the coating weight of the oxides or hydroxides of Al is regulated to the range of 0.2 to 10 by the weight ratio of Al/Cr expressed in terms of metal, the coating weight of colloidal silica is regulated to the range of 0.2 to 10 by the weight ratio of Si/Cr expressed in terms of metal, and the coating weight of a phosphoric acid radical is regulated to the range of 1 to 2 by P/Al, i.e., the molar ratio of P to Al.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chromate-treated zinc-plated steel sheet or a chromate-treated zinc alloy-plated steel sheet excellent in corrosion resistance, fingerprint resistance, paintability and white appearance and a method for producing the same.

[0002]

2. Description of the Related Art A zinc-plated steel sheet or a zinc alloy-plated steel sheet (hereinafter referred to as "zinc-based steel sheet") having a zinc-plated layer or a zinc alloy-plated layer (hereinafter referred to as "zinc-based plated layer") formed on at least one surface thereof. (Hereinafter referred to as "plated steel sheet"), chromate treatment is performed in order to improve its corrosion resistance and fingerprint resistance, and a chromate film is formed on the zinc-based plating film.

In the chromate treatment method, a zinc-based plated steel sheet is sprayed with a chromate treatment solution, or a zinc-based plated steel sheet is immersed in the chromate treatment solution to form a zinc-based plated layer and a chromate. Reaction treatment solution, reacting chromate treatment consisting of forming a chromate coating on the surface of the zinc-based plating layer, applying the chromate treatment liquid on the surface of the zinc-based plating coating, There are a coating type chrome treatment, which comprises drying without washing with water, and an electrolytic chrome treatment, which comprises forming a chrome coating film on the surface of the zinc-based plating layer by electrolysis.

In the reaction type chromate treatment and the coating type chromate treatment, adhesion unevenness occurs in the width direction of the steel sheet to deteriorate the appearance, and due to changes in operating conditions such as the line speed, the amount of the chromate film adhered is changed. There is a problem that it becomes difficult to control.

On the other hand, in the electrolytic chromate treatment, in an aqueous solution containing Cr ⁶⁺ as a main component and anions such as SO ₄ ²⁻ and F ⁻ added thereto, a cathodic electrolytic treatment is performed using a zinc-based plated steel sheet as a cathode. By applying, a chromate film is formed on the surface of the zinc-based plating layer. Therefore, according to the electrolytic chromate treatment, the amount of the chromate film deposited does not depend on the type of the zinc-based plated steel sheet, and the amount of chromate film deposited can be easily adjusted by the current density and the amount of electricity during the cathodic electrolytic treatment. Moreover, there are advantages such that stable control can be performed and uneven adhesion is less likely to occur.

In recent years, the demand for corrosion resistance of the zinc-based plated steel sheet subjected to such electrolytic chromate treatment has been further increased, and the chromate coating formed by the conventional chromate treatment satisfies such demand for corrosion resistance. I can't. Further, since fingerprints attached to the surface of the plated steel sheet greatly influence the commercial value of the final product, there is an increasing demand for fingerprint resistance of the zinc-based plated steel sheet.

As a means for improving the corrosion resistance of a chromate-treated zinc-based plated steel sheet, for example, in Japanese Patent Publication No. Sho 61-54880, a solution containing a cation-based colloidal silica in a solution containing 30 coulomb / A method of forming a chromate coating containing Cr and Si on the surface of a zinc-based plating layer by subjecting it to cathodic electrolysis with an electric quantity of dm ² or more (hereinafter referred to as Prior Art 1) is disclosed.

In Japanese Patent Publication No. 30475/1992, a metallic Cr coating is formed on a zinc-based plating layer, an oxide coating mainly composed of Cr ³⁺ is formed on the metallic Cr coating, and , A zinc-based plated steel sheet on which a chromate film consisting of an oxide and a hydrated oxide film containing silica and alumina and an appropriate amount of Cr ⁶⁺ mainly containing Cr ³⁺ is formed on the oxide film (hereinafter referred to as prior art 2) is disclosed.

Furthermore, Japanese Patent Publication No. 2-14436 discloses Cr ^6+.
Containing PO ₄ ³⁻ and one or two kinds of fluorine compounds, and one or two kinds of silica and silicate,
Furthermore, using a chromate treatment solution containing at least one of Zn, Ni, Co, Al, Mg, Sn, Mn, and Pb ions, the zinc-based plated steel sheet is subjected to cathodic electrolysis treatment to form a zinc-based plating layer. A method (hereinafter referred to as Prior Art 3) of forming a chromate film on the upper surface and then immediately performing an anodic electrolytic treatment is disclosed.

[0010]

The above-mentioned prior art has the following problems. That is, according to Prior Art 1,
Although the effect of improving the corrosion resistance is recognized to some extent by the inclusion of silica, no satisfactory improvement in the coatability is recognized.

According to the prior art 2, although the silica sol and the alumina sol are contained, the corrosion resistance is improved. However, in order to improve the corrosion resistance, it is necessary to increase the amount of Cr deposited. Is likely to occur,
Further, the chromate coating also has a poor surface appearance such as a decrease in whiteness.

According to the prior art 3, since the coating amount is much larger than that of the chromate coating produced only by cathodic electrolysis, the corrosion resistance is good, but the uneven coating makes the appearance non-uniform and the coatability is good. Is not improved at all. Furthermore, since anodic electrolysis is performed in addition to cathodic electrolysis, equipment for that is required, which is uneconomical.

Therefore, an object of the present invention is to solve the above-mentioned problems and to provide a chromate-treated zinc-based electroplated steel sheet having a stable chromate coating which is excellent in corrosion resistance, fingerprint resistance, paintability and appearance, and this It is an object of the present invention to provide a method capable of industrially stably producing such a chromate-treated zinc-based electroplated steel sheet.

[0014]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems. The present inventors, in addition to colloidal silica which is effective in improving the corrosion resistance and fingerprint resistance of the chromate coating, focus on the fact that the oxide or hydroxide of Al is effective in improving the corrosion resistance, and conduct research. It was As a result, Al ³⁺ and PO ₄
^{In the} presence of ^3- , Al ³⁺ and PO ₄ ³⁻ form complex ions, and when Al ³⁺ forms an oxide or hydroxide and precipitates, phosphoric acid It was found that the phosphoric acid group, which is an anionic oxide, was effectively introduced into the oxide layer by co-depositing while partially coordinating the groups.

Furthermore, the phosphoric acid group coordinated to Al introduced into the chromate coating strengthens the network between oxides such as Cr oxide and silica to enhance the corrosion resistance of the coating.
It has been found that by increasing the corrosion resistance of the coating, it is possible to reduce the amount of the chromate coating attached and to maintain the appearance uniformity.

Based on the above, an appropriate amount of Al oxide or hydroxide partially coordinating a phosphoric acid group and colloidal silica is arranged on the hydrated oxide film of Cr, and Cr and Al are added.
If a complex oxide film that strengthens the network between the oxide and the silica is formed on the surface of the zinc-based plating film,
It was found that a chromate-treated steel sheet excellent in corrosion resistance, fingerprint resistance, paintability and appearance can be obtained.

The present invention has been made on the basis of the above-mentioned findings, and a chromate-treated zinc-based plated steel sheet of the present invention is a steel sheet and zinc or a zinc alloy formed on at least one surface of the steel sheet. In a chromate-treated zinc-based plated steel sheet comprising a gold plating layer and a chromate coating formed on the zinc or zinc alloy plating layer, the chromate coating is an oxide or hydroxide of Cr and Al, colloidal silica and phosphorus. An acid group is the main component, and the amount of the Cr oxide or hydroxide attached is
It is within the range of 3 to 100 mg / m ^{2 in} terms of Cr, and the adhered amount of the oxide or hydroxide of Al is the weight ratio Al / Cr in terms of metal.
In the range of 0.2 to 10, the amount of the colloidal silica deposited is in the range of 0.2 to 10 in terms of metal weight ratio Si / Cr, and the amount of the phosphate group deposited is P. and
It is characterized in that the molar ratio P / Al of Al is within the range of 1 to 2.

Further, the method for producing a chromate-treated zinc-based plated steel sheet according to the present invention uses a chromate treatment liquid of 5 to 5.
Cr ^{6+ in} an amount of 75 g / l, Al ^{3+ in} an amount of 1-20 g / l, 2-10
Colloidal silica in an amount of 0 g / l and 3.5-200 g /
Characterized by subjecting zinc or zinc alloy-plated steel sheet to cathodic electrolysis using a chromate treatment solution containing an amount of PO ₄ ^3- and a pH value in the range of 1.5 to 4.0 Is.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the reason why the component composition of the chromate film is limited as described above in the present invention will be explained.

(1) Cr oxide or hydroxide: The amount of Cr oxide or hydroxide constituting the oxide layer should be limited to the range of 3 to 100 mg / m ^{2 in} terms of Cr. is there. When the amount of Cr oxide or hydroxide is less than 3 mg / m ^{2 in} terms of Cr,
Corrosion resistance cannot be improved, while when the amount of Cr oxide or hydroxide exceeds 100 mg / m ^{2 in} terms of Cr,
Paintability deteriorates.

(2) Al oxides or hydroxides: Al oxides or hydroxides not only impart excellent corrosion resistance to the coating, but also eutectoid with phosphate groups to strengthen the oxide network, Further, it has the effect of improving the whiteness of the chromate film and improving the appearance. The adhered amount of Al oxide or hydroxide constituting the oxide layer is the weight ratio Al in terms of metal.
/ Cr should be limited to the range of 0.2-10. If the weight ratio of Al to Cr is less than 0.2, the corrosion resistance cannot be improved. On the other hand, when the weight ratio of Al to Cr exceeds 10, the relative amount of the oxide or hydroxide of Cr in forming the oxide network becomes insufficient and the corrosion resistance deteriorates.

(3) Colloidal silica: The adhered amount of colloidal silica forming the oxide layer is the weight ratio Si / metal equivalent.
Cr should be limited to the range of 0.2-10. If the weight ratio of Si to Cr is less than 0.2, the corrosion resistance and fingerprint resistance cannot be improved. On the other hand, if the weight ratio of Si to Cr exceeds 10, it is necessary to form an oxide network.
The relative amount of Cr oxide is insufficient, corrosion resistance deteriorates,
The colloidal silica particles are easily peeled off from the chromate film, and the paintability deteriorates.

(4) Phosphoric acid group: The phosphoric acid group has the function of eutectoid with the oxide of Al, binds with other oxides in the coating, strengthens the network between oxides, and improves corrosion resistance. Have When the eutectoid behavior of the phosphate group and the Al oxide was examined, it was found that P was co-deposited at a ratio of 1 to 2 per 1 Al atom as shown in FIG. Therefore, the attached amount of the phosphate groups constituting the oxide layer is 1 to the molar ratio P / Al in terms of P.
It should be limited to the range of 2.

Next, the reason why the component composition of the chromate treatment liquid in the present invention is limited as described above will be explained.

(1) Cr ⁶⁺ : The content of Cr ⁶⁺ is 5 to 75 g / l.
Should be limited within the range. If the content of Cr ⁶⁺ is less than 5 g / l, the chromate film cannot be formed uniformly and stably over a long period of time. On the other hand, the content of Cr ⁶⁺ is 75 g /
If it exceeds l, zinc on the plating surface will be easily eluted,
The concentration balance in the chromate treatment liquid is lost, and the corrosion resistance and paintability cannot be stably improved. As such Cr ⁶⁺ , one or more of chromic anhydride, ammonium dichromate, and alkali metal dichromate can be optionally used.

(2) Al ³⁺ : The content of Al ³⁺ should be limited to the range of 1 to 20 g / l. When the content of Al ³⁺ is less than 1 g / l or more than 20 g / l, the amount of Al oxide in the chromate film can be within the range of 0.2 to 10 in terms of metal weight ratio Al / Cr. Therefore, the corrosion resistance cannot be improved.
Such Al ³⁺ includes Al (H ₂ PO ₄ ) _3, Al (0H) _3, Al
_{One or two of 2} (SO ₄ ) _3, AlCl ₃ and Al (NO ₃ ) ₃
Any number of species can be used.

(3) Colloidal silica: The content of colloidal silica should be limited to the range of 2 to 100 g / l. Colloidal silica content less than 2g / l or 100
If it exceeds g / l, the amount of silica in the chromate film cannot be kept within the range of 0.2 to 10 in terms of metal weight ratio Si / Cr, achieving improvement in corrosion resistance, fingerprint resistance and paintability. Can not do it.

[0028] ₍₄₎ PO 4 ^3-: PO in the chromate treatment liquid ₄ ³
Should be limited to the range of 3.5-200 g / l. PO ₄ the content of ³ is less than 3.5 g / l, the deposition amount of phosphate group in the oxide, 1-2 in a molar ratio P / Al of P in terms
However, as a result of insufficient strengthening of the network of the complex oxide layer, the effect of improving corrosion resistance cannot be obtained. On the other hand, even if the content of PO ₄ ^3- exceeds 200 g / l,
It is uneconomical because the content of phosphate groups in the chromate film cannot be increased. Moreover, the content of PO ₄ ^3- is
If it exceeds 200 g / l, the surface of the chromate film may become uneven due to the etching action after the cathodic electrolysis and before the chromate film is washed with water, which may deteriorate the appearance. PO like this
₄ ³ _{The, H 3 PO 4, Al (} H 2 PO 4) 3, alkali metal salts of phosphoric acid, can be used one or more of the ammonium phosphate.

[0029] ^{_{(5) SO 4 2-, NO}} 3-, Cl -, F -: SO 4 2-,
An anion consisting of at least one of NO ^{3 −} , Cl ⁻ , F ⁻ dissolves the weak part of the chromate film, and
It acts as an etching agent for growing the film. Therefore, if necessary, it is added to the chromate treatment liquid. The content of the anion affects the quality of the chromate film, and if it is too small or too large, the corrosion resistance, fingerprint resistance, paintability and white appearance cannot be improved. The preferred content of the anion is
The total amount is within the range of 0.1 to 100 g / l.

The pH value of the chromate treatment liquid should be limited to the range of 1.5 to 4.0. If the pH value of the chromate treatment solution is
If it is less than 1.5, zinc on the plating surface is eluted, the concentration balance of Cr ⁶⁺ in the chromate treatment liquid is disturbed, and the deposition efficiency of silica is lowered, so that the corrosion resistance and fingerprint resistance cannot be improved. On the other hand, the pH of the chromate treatment liquid
If the value exceeds 4.0, precipitates will be generated in the chromate treatment solution and stable treatment cannot be performed. A more preferable pH value for stable treatment is in the range of 1.8 to 2.5.

Examples of the zinc-plated steel sheet to be chromated according to the present invention include electrogalvanized steel sheet, Zn-Fe,
An electrogalvanized steel sheet such as Zn-Ni, a hot-dip galvanized steel sheet, or a hot zinc alloy-plated steel sheet can be used.

[0032]

Next, the present invention will be described in more detail with reference to Examples and Comparative Examples. By a known method, for the electrogalvanized steel sheet on which a galvanized coating of an amount of 20 g / m ² is formed, by the method of the present invention, the following No.
Cathodic electrolysis was performed under the electrolysis conditions of 1 to 6 to form a chromate film on the galvanized film. Then, this is washed with water and then dried, and the steel sheets of the present invention No. 1 to 6 shown in Table 1 are obtained.
Was prepared.

No. 1 Chromate treatment liquid: Cr ⁶⁺ : 13.0 g / l (using Cr 0 ₃ ), Al ³⁺ : 1.7 g / l (using Al (H ₂ PO ₄ ) ₃ ), SiO ₂ : 10.0 g / l (using Snowtex O), PO ₄ ^3- : 18.0 g / l (using Al (H ₂ PO ₄ ) ₃ ), SO ₄ ^2- : 11.2 g / l (using Na ₂ SO ₄ ), PH value: 2.0. Cathodic electrolysis conditions: current density: 10 A / dm ² , treatment time: 1.0 second.

No. 2 Chromate treatment liquid: Cr ⁶⁺ : 19.5 g / l (using Cr 0 ₃ ), Al ³⁺ : 3.4 g / l (using Al (H ₂ PO ₄ ) ₃ ), SiO ₂ : 20.0 g / l (using Snowtex O), PO ₄ ^3- : 36.0 g / l (using Al (H ₂ PO ₄ ) ₃ ), SO ₄ ^2- : 11.2 g / l (using Na ₂ SO ₄ ), PH value: 2.3. Cathodic electrolysis conditions: current density: 10 A / dm ² , treatment time: 1.0 second.

No. 3 chromate treatment liquid: Cr ⁶⁺ : 13.0 g / l (using Na ₂ Cr ₂ O ₇・ 2H ₂ O), Al ³⁺ : 8.5 g / l (Al ₂ (SO ₄ ) ₂・18H ₂ O), SiO ₂ : 10.0 g / l (Snowtex O is used), PO ₄ ^3- : 40.0 g / l (H ₃ PO ₄ is used), SO ₄ ^2- : 45.3 g / l (Using Al ₂ (SO ₄ ) ₂ · 18H ₂ O), pH value: 2.3. Cathodic electrolysis conditions: current density: 10 A / dm ² , treatment time: 2.0 seconds.

No. 4 Chromate treatment liquid: Cr ⁶⁺ : 70.0 g / l (using CrO ₃ ), Al ³⁺ : 8.5 g / l (using Al (H ₂ PO ₄ ) ₃ ), SiO ₂ : 20.0 g / l (using Snowtex O), PO ₄ ^3- : 90.0 g / l (using Al (H ₂ PO ₄ ) ₃ ), SO ₄ ^2- : 22.4 g / l (using Na ₂ SO ₄₎ ), PH value: 1.8. Cathodic electrolysis conditions: current density: 10 A / dm ² , treatment time: 1.0 second.

No. 5 Chromate treatment liquid: Cr ⁶⁺ : 70.0 g / l (using CrO ₃ ), Al ³⁺ : 18.0 g / l (using Al (H ₂ PO ₄ ) ₃ ), SiO ₂ : 30.0 g / l (using Snowtex So O), PO ₄ ^3- : 190.5 g / l (using Al (H ₂ PO ₄ ) ₃ ), SO ₄ ^2- : 22.4 g / l (using Na ₂ SO ₄ ), NO ^3- : 14.5 g / l (using HNO ₃ ), pH value: 1.8. Cathodic electrolysis conditions: current density: 20 A / dm ² , treatment time: 1.5 seconds.

No. 6 Chromate treatment liquid: Cr ⁶⁺ : 7.0 g / l (using Na ₂ Cr ₂ O ₇ · 2H ₂ O), Al ³⁺ : 1.7 g / l (Al (H ₂ PO ₄ ) ₃ the _{use), SiO 2: 5.0 g /} l ( using Snowtex over ^{_{O), PO 4 3-: 18.0}} g / l (Al (H 2 PO 4) using _3), pH value: 2.0. Cathodic electrolysis conditions: current density: 2.5 A / dm ² , treatment time: 2.0 seconds.

For comparison, the above-mentioned electrogalvanized steel sheet was subjected to the following No. 1 by a method outside the scope of the present invention.
Cathodic electrolysis treatment was performed under the electrolytic conditions of ~ 6, and the comparative steel plate No.
1-6 were prepared.

No. 1 Chromate treatment solution: Cr ⁶⁺ : 13.0 g / l (using Cr 0 ₃ ), SiO ₂ : 10.0 g / l (using Snowtex O), PO ₄ ^3- : 20.0 g / l (using _{H 3 PO 4), SO 4} 2-: 11.2 ( using _{Na 2 SO 4) g / l} , pH value: 2.0. Cathodic electrolysis conditions: current density: 10 A / dm ² , treatment time: 1.0 second.

No. 2 Chromate treatment liquid: Cr ⁶⁺ : 3.0 g / l (using Na ₂ Cr ₂ O ₇ · 2H ₂ O), Al ³⁺ : 1.7 g / l (Al (H ₂ PO ₄ ) ₃ , SiO ₂ : 10.0 g / l (using Snowtex O), PO ₄ ^3- : 18.0 g / l (using Al (H ₂ PO ₄ ) ₃ ), SO ₄ ^2- : 11.2 g / l (using Na ₂ SO ₄ ), pH value: 2.0. Cathodic electrolysis conditions: current density: 10 A / dm ² , treatment time: 1.0 second.

No. 3 chromate treatment liquid: Cr ⁶⁺ : 13.0 g / l (using CrO ₃ ), Al ³⁺ : 5.4 g / l (using Al ₂ (SO ₄ ) ₂ · 18H ₂ O), SiO ₂ : 10.0 g / l (Snowtex O is used), PO ₄ ^3- : 3.0 g / l (H ₃ PO ₄ is used), SO ₄ ^2- : 28.8 g / l (Al ₂ (SO ₄ ) ₂・ Using 18H ₂ O), pH value: 2.0. Cathodic electrolysis conditions: current density: 10 A / dm ² , treatment time: 1.0 second.

No. 4 Chromate treatment liquid: Cr ⁶⁺ : 13.0 g / l (using CrO ₃ ), Al ³⁺ : 1.7 g / l (using Al (H ₂ PO ₄ ) ₃ ), PO ₄ ^3- : 18.0 g / l (Al ( H 2 PO 4) using ^{_{3), SO 4 2-: 11.2}} ( using _{Na 2 SO 4) g / l} , pH value: 2.0. Cathodic electrolysis conditions: current density: 10 A / dm ² , treatment time: 1.0 second.

No. 5 Chromate treatment liquid: Cr ⁶⁺ : 6.5 g / l (using CrO ₃ ), Al ³⁺ : 25.0 g / l (using Al (H ₂ PO ₄ ) ₃ ), SiO ₂ : 20.0 g / l (using Snowtex O), PO ₄ ^3- : 264.0 g / l (using Al (H ₂ PO ₄ ) ₃ ), SO ₄ ^2- : 11.2 g / l (using Na ₂ SO ₄ ), PH value: 2.3. Cathodic electrolysis conditions: current density: 10 A / dm ² , treatment time: 1.0 second.

No. 6 Chromate treatment liquid: Cr ⁶⁺ : 6.5 g / l (using CrO ₃ ), Al ³⁺ : 18.0 g / l (using Al (H ₂ PO ₄ ) ₃ ), SiO ₂ : 120.0 g / l (Snowtex O is used), PO ₄ ^3- : 190.0g / l (Al (H ₂ PO ₄ ) ₃ is used), SO ₄ ^2- : 11.2 g / l (Na ₂ SO ₄ is used) ), PH value: 2.3. Cathodic electrolysis conditions: current density: 20 A / dm ² , treatment time: 1.0 second.

For each of the specimens thus prepared,
The tests described below were performed. (1) Corrosion resistance test The salt spray test specified in JIS-Z-2371 was applied to the test piece, the white rust generation area was measured after 168 hours, and the result was shown by%. Further, the generation state of black spot rust on the surface after 168 hours was visually inspected and evaluated by the following. ⊚: Black spots did not occur, ◯: Black spot rust was slightly found, Δ: Black spot rust was found on one side, ×: White rust covered and indistinguishable.

(2) Fingerprint resistance test The surface of the test piece was touched with a sweaty hand, and the state of the attached fingerprint was visually observed and evaluated by the following. ⊚: Very good, ◯: Good, Δ: Bad, ×: Very bad.

(3) Paintability test A commercially available alkyd melamine-based white paint was applied on the surface of the test piece to a thickness of about 30 μm to form a coating film. Next, 100 cross-cut notches were formed at intervals of 1 mm in the coating film immediately after coating, and extruded 7 mm with an Erichsen tester. Then, an adhesive tape was stuck on the surface of the extruded portion and peeled off.
Evaluation was made by the peeling state of the coating at that time.

(4) Appearance test The appearance uniformity and whiteness of the test piece were visually observed and evaluated by the following. ⊚: Very good, ◯: Good, Δ: Bad, ×: Very bad.

Table 1 shows the composition of the chromate film of each of the steel sheet of the present invention and the comparative steel sheet and the test results.

[0051]

[Table 1]

As is clear from Table 1, Comparative Steel Sheet No. 1 in which the chromate film did not contain an oxide of Al had poor corrosion resistance and poor whiteness in appearance. Comparative steel sheet in which the amount of Cr in the chromate film is less than the range of the present invention
No. 2 had poor corrosion resistance. Comparative steel sheet No. 3 in which the amount of phosphoric acid groups in the chromate coating is small outside the range of the present invention
Caused insufficient black spot rust due to insufficient strengthening of the network between oxides.

Comparative Steel Sheet No. 4, in which silica was not contained in the chromate coating, had poor corrosion resistance and fingerprint resistance. Cr comparison the weight ratio of Al is often beyond the scope of the present invention to the steel sheet in the chromate film No. 5, to PO ₄ ^3- amount of corrosion resistance is poor and the treatment solution was often out of the scope of the present invention The coating surface was uneven and the appearance was poor. The comparative steel sheet No. 6 in which the amount of colloidal silica exceeded the range of the present invention was poor in coatability.

On the other hand, the steel sheets Nos. 1 to 6 of the present invention were all excellent in corrosion resistance, fingerprint resistance, paintability and appearance.

[0055]

As described above, according to the present invention,
A chromate-treated zinc-based electroplated steel sheet having a stable chromate coating, which is excellent in corrosion resistance, fingerprint resistance, paintability, and appearance, can be industrially produced in a stable manner, which brings industrially useful effects. .

[Brief description of the drawings]

FIG. 1 is a diagram showing a co-deposition state of an Al oxide and a phosphoric acid group.

Front Page Continuation (72) Inventor Kotaro Okamoto 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Tube Co., Ltd. (72) Inventor Yoshiharu Sugimoto 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Stocks In the company

Claims (3)

[Claims] 1. A chromate-treated zinc-based system comprising a steel sheet, a zinc or zinc alloy plating layer formed on at least one surface of the steel sheet, and a chromate coating formed on the zinc or zinc alloy plating layer. In the plated steel sheet, the chromate coating contains Cr and Al oxides or hydroxides, colloidal silica, and a phosphate group as main components, and the amount of the Cr oxides or hydroxides attached is , 3 in Cr conversion
To 100 mg / m ² , and the amount of the oxide or hydroxide of Al deposited is in the range of 0.2 to 10 in terms of metal weight ratio Al / Cr, and the deposition of the colloidal silica. The amount is the metal equivalent weight ratio Si
/ Cr in the range of 0.2 to 10, and the amount of the phosphate groups attached is a molar ratio of P and Al P / Al
The chromate-treated zinc-based plated steel sheet is characterized by being in the range of 1 to 2. 2. A zinc membrane on at least one surface thereof.
Zinc or zinc alloy plated layer,
Odor in chromate treatment solution for zinc alloy plated steel sheet
The above-mentioned zinc or zinc
Forming a chromate film on the alloy plating layer
In the method for producing chromate-treated zinc-based plated steel sheet
As the chromate treatment liquid, an amount of Cr of 5 to 75 g / l was used.
⁶⁺And an amount of 1-20 g / l of Al ³⁺And a quantity of 2-100 g / l
Loydal silica and PO in amounts of 3.5-200 g / l_Four ^3-Including
A processing solution having a pH value within the range of 1.5 to 4.0
To the zinc or zinc alloy plated steel sheet
Zinc-based plated steel sheet characterized by being subjected to electrodeposition treatment
Chromate treatment method. 3. The chromate treatment liquid further comprises S
_{^{0 4 2-, NO 3 -,}} Cl - and F ^- at least one of
The method according to claim 2, wherein the seeds are contained in a total amount of 0.1 to 100 g / l.