JPH0544095A - Chromate treatment for galvanized steel sheet - Google Patents

Abstract

PURPOSE:To grant excellent corrosion resistance, finger-print resistance, coating adhesion, and appearance of a surface to a galvanized steel sheet thereby. CONSTITUTION:A chromating liquid containing Cr<6+> and Cr<3+> at which total Cr is 5-70g/l and Cr<6+>/total Cr in wt. ratio is >=0.8, Ni<2+> at which Ni<2+>/total Cr in wt. ratio is 0.05-0.8, 1-60g/l silica, 10-100g/l SO4<2-> and 0.1-10g/l aq. acryl system resin, of which pH value is 1-5 and temp. is 30-70 deg.C is used, and a cathodic electrolysis processing is applied to a galvanized steel sheet with 0.5-40C/dm<2> amt. of electricity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chromate treatment method for zinc-based plated steel sheet, which can impart excellent corrosion resistance, paint adhesion, fingerprint resistance and surface appearance to zinc or zinc alloy plated steel sheet. Is.

[0002]

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

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 dipped in the chromate treatment solution to form a zinc-based plating film and a chromate. Reaction treatment solution, reacting chromate treatment consisting of forming a chromate film on the surface of the zinc-based plating film, applying the chromate treatment liquid on the surface of the zinc-based plating film, Coating type chromate treatment consisting of drying without washing with water,
There is also an electrolytic chromate treatment which comprises forming a chromate film on the surface of a zinc-based plating film by electrolysis.

The reactive chromate treatment has the following problems. That is, in general, the chromate treatment liquid easily reacts with the metal. Therefore, the metal ions eluted in the chromate treatment liquid are contained in the chromate film, and have a significant adverse effect on the quality of the chromate film. In the reactive chromate treatment, the surface of the zinc-based plating film of the zinc-based plated steel sheet to which the chromate treatment is applied is particularly susceptible to the influence. Therefore, the amount and quality of the chromate film formed on the zinc-based plating film may vary depending on the plating conditions before the chromate treatment, the pretreatment conditions such as pickling and alkali washing, and the fluctuations in the operating conditions such as the line speed. The quality of the chromate film tends to be unstable due to large changes. Further, it cannot be applied to a zinc-based plating film having poor reactivity with a chromate treatment liquid.

The coating type chromate treatment has the following problems. That is, in the case of the coating type chromate treatment, by adjusting the components of the chromate treatment liquid, the influence of the reaction between the chromate treatment liquid and the zinc-based plating film can be suppressed to some extent and the chromate film can be controlled. However, in order to control the amount of the chromate coating film, it is necessary to change the concentration of the chromate treatment liquid and to properly set the coating conditions by the coater, so it is extremely difficult to quickly respond to the operating conditions. Furthermore, since the wettability differs depending on the surface properties of the chromate treatment liquid and the zinc-based plating film, defects such as cissing and coating unevenness are likely to occur on the chromate film.

On the other hand, in the electrolytic chromate treatment, cathodic electrolysis is performed in an aqueous solution containing Cr ⁶⁺ as a main component with a zinc-based plated steel sheet as a cathode to form a chromate film on the surface of the zinc-based plated film. Consists of forming. Therefore, according to the electrolytic chromate treatment, the amount of the chromate coating adhered is not affected by the type of zinc-based plated steel sheet or the surface texture of the zinc-based plated coating, and the amount of chromate coating depends on the current density and the amount of electricity during cathodic electrolytic treatment. Further, there are advantages that the quality can be controlled easily and stably, and uneven adhesion is less likely to occur.

Recently, the requirements for corrosion resistance and coating adhesion have become much higher for zinc-based plated steel sheets that have been subjected to such electrolytic chromate treatment. Furthermore, for cost reduction of products, since zinc-based plated steel sheets are often used without coating, excellent anti-fingerprint properties against zinc-plated steel sheets subjected to electrolytic chromate treatment, Also, an excellent surface appearance having a uniform color tone is strongly demanded.

As a method for producing a zinc-based plated steel sheet which is excellent in corrosion resistance, paint adhesion and fingerprint resistance, JP-A-2-8879
Publication No. 9 discloses a method consisting of the following. Contains 5 to 75 g / l of Cr ⁶⁺ , Ni ²⁺ with Ni / Cr weight ratio of 0.05 to 0.8, and silica of 10 to 150 g / l based on galvanized steel sheet and, _{^{further, SO 4 2-, Cl -,}} NO 3, F - by performing cathodic electrolysis treatment in the chromating solution containing 80 g / l at least one of 0.05 to among, on the zinc-based plating film Forming a chromate film on (hereinafter,
Prior art).

[0009]

The prior art has the following problems. That is, according to the method of the prior art, in order to exert excellent fingerprint resistance, it is necessary to increase the amount of electricity during the cathodic electrolysis treatment in the chromate treatment liquid to form a thick chromate film. As a result, the color of the formed chromate film is emphasized and discolored, and further, unevenness in color tone is likely to occur due to changes in the surface properties of the chromate film and operating conditions, and the surface appearance is deteriorated.

Therefore, an object of the present invention is to solve the above-mentioned problems and to impart a zinc-based plated steel sheet with excellent corrosion resistance, paint adhesion, fingerprint resistance, and a surface appearance having a uniform color tone. It is to provide a method for chromate treatment of a zinc-based plated steel sheet that can be performed.

[0011]

[Means for Solving the Problems] The inventors of the present invention have conducted extensive studies to solve the above problems. As a result, a chromate treatment liquid containing a predetermined amount of Cr ⁶⁺ + Cr ³⁺ , Ni ²⁺ , silica, SO ₄ ²⁻ and an aqueous acrylic resin and having a predetermined pH value and temperature is used, By applying a cathodic electrolysis treatment to a zinc-based plated steel sheet with a predetermined amount of electricity and forming a chromate film on the zinc-based plated film, the zinc-based plated steel sheet has excellent corrosion resistance, paint adhesion, and fingerprint resistance. It was found that a surface appearance having a uniform color tone can be provided.

The present invention has been made based on the above-mentioned findings, and the present invention is a zinc or zinc alloy plated steel sheet having a zinc plated coating or a zinc alloy plated coating formed on at least one surface thereof. On the other hand, by performing cathodic electrolytic treatment in the chromate treatment liquid,
In the chromate treatment method of a zinc-based plated steel sheet, which comprises forming a chromate coat on the zinc or zinc alloy plated coat, as the chromate treatment liquid,
The total Cr amount is 5 to 70 g / l, and the Cr ⁶⁺ / total Cr weight ratio is 0.8.
The weight ratio of the above amount of Cr ⁶⁺ and Cr ³⁺ to Ni ²⁺ / total Cr is 0.05.
Ni ^{2+ in} an amount of ~ 0.8, silica in an amount of 1-60 g / l, 10 ~
It contains SO ₄ ^{2- in} an amount of 100 g / l and an aqueous acrylic resin in an amount of 0.1 to 10 g / l, and has a pH value of 1 to 5 and a temperature of 30 to 70 ° C. Using processing solution, 0.5 to 40C /
It is characterized in that the zinc or zinc alloy plated steel sheet is subjected to cathodic electrolysis treatment according to the quantity of electricity of dm ² .

[0013]

Next, the reason why the component composition of the chromate treating liquid is limited as described above in the present invention will be explained. (1) Cr ⁶⁺ and Cr ³⁺ : As Cr ⁶⁺ , chromic anhydride,
Also, one or a mixture of two or more of chromic acid, an alkali metal salt of dichromic acid and an ammonium salt is used. Cr ³⁺ is produced by the reduction reaction of Cr ⁶⁺ in the treatment liquid during the cathodic electrolysis treatment. Alternatively, Cr ⁶⁺ may be previously reduced to Cr ³⁺ with alcohol, tannic acid or the like.
^{The 3+} compound may be directly added to the treatment liquid. Cr ⁶⁺ and Cr
The total amount with ³⁺ or total Cr amount should be limited within the range of 5 to 70 g / l. If the total chromium content is less than 5 g / l, the formation efficiency of the chromate film is poor. On the other hand, the total amount of chromium is 70 g /
Even if it exceeds l, not only is it uneconomical because the coating properties cannot be further improved, but also the work environment is contaminated by the chromate treatment liquid that adheres to the steel strip and is taken out of the chromate treatment tank. Occurs. Cr ³⁺ is
It does not have a particular effect on the quality of the chromate coating, but rather has the advantage of increasing the efficiency of film formation. However, the Cr ³⁺ / total Cr weight ratio exceeds 0.2, that is, Cr ⁶⁺ / total Cr
If the weight ratio of is less than 0.8, the fingerprint resistance decreases. Therefore, the Cr ⁶⁺ / total Cr weight ratio should be greater than 0.8.

(2) Ni ²⁺ : Nickel sulfate is used as Ni ²⁺ . Such Ni ²⁺ can be added by being dissolved in the chromate treatment liquid in the form of carbonate, chloride, nitrate or the like. Ni ²⁺ has the effect of improving corrosion resistance and paint adhesion. The amount of Ni ²⁺ should be limited within the range of 0.05 to 0.8 in a weight ratio of Ni ²⁺ / total Cr. In is less than 0.05 amount Ni ²⁺ / total Cr weight ratio of Ni ^2+, above effect can not be obtained, while the amount of Ni ²⁺ is in a weight ratio of Ni ²⁺ / total Cr 0.8
When it exceeds, the chromate coating tends to have uneven color tone.

(3) Silica Silica has a function of improving corrosion resistance and coating adhesion. The amount of silica should be limited to the range of 1 to 60 g / l. If the amount of silica is less than 1 g / l, the above effects cannot be obtained, while if the amount of silica exceeds 60 g / l,
On the contrary, the paint adhesion deteriorates.

(4) SO ₄ ²⁻ : Conventionally, when a small amount of SO ₄ ²⁻ is contained in a chromate treatment liquid, a non-uniform coating film is formed by the cathodic electrolytic treatment, which may deteriorate the corrosion resistance and other properties. It is said that the coating film is likely to be blackened.
However, according to the study of the present inventors, SO ₄ ^2-
By containing a large amount within the range of ~ 100 g / l, the stability of the chromate treatment liquid is dramatically improved without impairing quality characteristics such as corrosion resistance and paint adhesion, and a uniform surface color tone is obtained. It has been found that a chromate film having can be formed. Therefore, in the present invention, SO ₄ ²⁻ is contained in the chromate treatment liquid within the range of 10 to 100 g / l. The amount of SO ₄ ²⁻ should be limited to the range of 10 to 100 g / l, as mentioned above. The amount of SO ₄ ^2-
If it is less than 10 g / l, the above-mentioned effects cannot be obtained, while on the other hand, SO ₄
^{Even if} the amount of ^2- exceeds 100 g / l, no further effect is obtained and it is uneconomic. The more preferable content of SO ₄ ²⁻ is 20 to 100 g / l.

(5) Aqueous acrylic resin: As the aqueous acrylic resin, polyacrylic acid obtained by polymerizing or copolymerizing acrylic acid, methacrylic acid or acrylamide,
Polymethacrylic acid, polyacrylamide, and their derivatives, or polyacrylic acid, polymethacrylic acid, polyacrylamide, and their derivatives,
An emulsion dispersed in water with a surfactant, a surface charge adjusting agent, a dispersant or the like can be used.

On the water-based acrylic resin, the corrosion resistance, fingerprint resistance and paint adhesion are remarkably improved, and a chromate film having a uniform color tone and a beautiful surface appearance is formed by electrolytic treatment with a relatively low amount of electricity. There is an action that can. Furthermore, the water-based acrylic resin has the function of preventing the blackening and discoloration of the zinc-plated steel sheet on which the chromate film is formed at high temperature and high humidity, that is, improving the blackening resistance and improving the press moldability. is there. The amount of waterborne acrylic resin should be limited to the range of 0.1 to 10 g / l. The viscous substance adheres to the chromate film and deteriorates the appearance of the film. If the amount of the water-based acrylic resin is less than 0.1 g / l, the above effects cannot be obtained, while if the amount exceeds 10 g / l, the reactivity with the cation in the chromate treatment liquid becomes high, and The treatment liquid becomes severely deteriorated and becomes unstable.

(6) Cl ⁻ , F ⁻ , BF ₄ ⁻ , SiF ₆ ²⁻ and NO
₃ ^- at least one ^{of: Cl -, F -, BF} 4 -, Si
F ₆ ²⁻ and NO ₃ ⁻ have the function of uniformly dissolving the surface of the plating film and forming a uniform chromate film. In particular, it effectively acts on a plating film having a thick oxide film formed by a hot dipping method or the like, or a plating film containing a large amount of alloying elements and having non-uniform active points. Therefore, in the present invention, if necessary, Cl ⁻ , F ⁻ , BF
₄ ^-, SiF ₆ ^2- and NO ₃ ^- at least one of,
It is contained in the chromate treatment liquid. Cl ^-, F ^-, B
The amount of at least one of F ₄ ⁻ , SiF ₆ ²⁻ and NO ₃ ⁻ should be limited to the range of 0.01 to 0.1 gram ion / l. If the amount of at least one of Cl ⁻ , F ⁻ , BF ₄ ⁻ , SiF ₆ ²⁻ and NO ₃ ⁻ is less than 0.01 gram ion / l, the above effect cannot be obtained. On the other hand, if it exceeds 0.1 gram ion / l, the plating surface is excessively dissolved, resulting in deterioration of corrosion resistance.

(7) Additive: In order to improve the stability of operation, the following additives may be added to the chromate treatment liquid. PH buffers such as borates, phosphates and phthalates to suppress pH fluctuations at the treated interface during electrolysis and to form stable chromate coatings, ammonium, alkali metal sulfates and A chelate compound of amines and carboxylic acids that fixes the metal ions in the chromate treatment solution and prevents the formation of sludge by fixing electrical conduction aids such as halides.

(8) Others: In the chromate treatment liquid,
Ions such as Zn, Fe, Al, Mn, Co, Mo, Pb, Sn, Cu, and Ag, which are eluted from the zinc-plated steel sheet or electrode to be chromated, may inevitably be mixed in. There is no problem if the total amount of contamination is 0.1 gram ion / l or less. In addition, as cations, alkali metal ions such as Na and K contained in SO ₄ ² -supplied salt or additives such as electric conduction auxiliary agents and pH buffers, and alkaline earth metal ions such as Mg and Ca or Although it may contain ammonium ions, these do not adversely affect the effects of the present invention, and thus are not particularly limited.

(9) pH value of chromate treatment liquid: The pH value of the chromate treatment liquid should be limited within the range of 1 to 5. When the pH value of the chromate treatment liquid is less than 1, the efficiency of depositing the chromate film decreases. Furthermore, at pH values below 1,
After the electrolytic treatment, the chromate treatment liquid adhering to the surface of the chromate coating partially redissolves the chromate coating, resulting in deterioration of corrosion resistance and paint adhesion, and the appearance of the chromate coating tends to be uneven. Become.
On the other hand, when the pH value of the chromate treatment liquid exceeds 5, the stability of the chromate treatment liquid is lowered and a precipitate is likely to be generated in the treatment liquid. The pH value can be adjusted by adding sulfuric acid, alkali metal hydroxide or the like to the chromate treatment liquid.

(10) Temperature of chromate treatment liquid: The temperature of the chromate treatment liquid should be limited within the range of 30 to 70 ° C. When the temperature of the chromate treatment liquid is lower than 30 ° C., undissolved substances are likely to be generated in the treatment liquid, and the electric conductivity is lowered. On the other hand, when the temperature of the chromate treatment liquid exceeds 70 ° C., the treatment liquid adhered to the surface of the chromate coating immediately dries after the electrolytic treatment, resulting in a problem that the appearance of the chromate coating remarkably deteriorates due to contact with a roll or the like. Occurs.

(11) Electricity of Cathodic Electrolysis The amount of chromate film adhered can be controlled by changing the current density and the treatment time, that is, the amount of electricity during cathodic electrolysis for chromate treatment. The amount of electricity is 0.5
To 40 C / dm ² should be limited. Electricity is 0.
If it is less than 5 C / dm ² , the chromate film is not uniformly formed, and desired quality characteristics cannot be obtained. On the other hand, the amount of electricity is 40C /
When it exceeds dm ² , the chromate film is formed excessively thick, resulting in a decrease in whiteness and deterioration in appearance. The current density for cathodic electrolysis is preferably in the range of 0.2 to 40 A / dm ² . The current density is less than 0.2 A / dm ² or 40A / dm ² greater, problems arise which lead to a decrease in precipitation efficiency of the chromate film.

The zinc-based plated steel sheet to be chromated according to the present invention includes electroplating, hot dipping,
Various zinc-based plated steel sheets with a plated coating formed by vapor deposition plating, ion plating, etc., for example, Zn
Galvanized steel sheet, Zn-Ni-based, Zn-Fe-based, Zn-Mn-based, Zn-Al-based, etc. zinc alloy-plated steel sheet or zinc composite-plated steel sheet, or the above, Zn, Zn-Ni, Zn-Fe, Zn- It is possible to use a so-called dispersed galvanized steel sheet in which a metal oxide, a polymer, or an insoluble salt such as barium chromate is dispersed in a zinc-based plating film such as Mn or Zn-Al.

The chromate-treated zinc-based plated steel sheet on which the chromate film has been formed by the method of the present invention is used as a non-painted steel sheet or a steel sheet for coating base in the state of being washed and dried. However, if necessary, the steel sheet may be subjected to a commonly used chromate sealing treatment or a post-treatment with an organic composite treatment liquid. Next, the present invention will be described in more detail with reference to Examples and comparison with Comparative Examples.

[0027]

【Example】

Example 1 For an electrogalvanized steel sheet having a galvanized coating of 20 g / m ² formed on its surface by electroplating, the composition and pH within the scope of the present invention shown in Tables 1 and 2 are shown. A chromate film was formed on the galvanized film by using a chromate treatment solution having a value and a temperature and subjecting it to cathodic electrolysis under the following electrolysis conditions within the scope of the present invention. Then, this was washed with water and dried to prepare Samples Nos. 1 to 23 of the present invention shown in Tables 1 and 2. Current density: 5 A / dm ² Processing time: 2 seconds Electric quantity: 10 C / dm ²

[0028]

[Table 1]

[0029]

[Table 2]

For comparison, the electrogalvanized steel sheet was prepared by using a chromate treatment liquid whose component composition, pH value and temperature shown in Tables 1 and 2 together are outside the scope of the present invention. Cathodic electrolysis was performed under the same conditions as above to form a chromate film on the galvanized film, and comparative sample Nos. 1 to 17 shown in Tables 1 and 2 were prepared.

Example 2 An electrogalvanized steel sheet having a galvanized film of 20 g / m ² formed on its surface by electroplating has the following composition within the scope of the present invention. Using a chromate treatment liquid, cathodic electrolysis treatment was performed under the electrolysis treatment conditions within the scope of the present invention shown in Table 3 to form a chromate coating film on the galvanized coating film. Next, this was washed with water and dried to prepare Samples Nos. 24 to 33 of the present invention shown in Table 3. Total Cr: 10g / l (Cr ⁶⁺ / Total Cr: ＞ 0.9) Ni ²⁺ : 3g / l (Ni ²⁺ / Total Cr 0.3) SO ₄ ^2- : 40g / l Silica: 10g / l Polyacrylic acid: 0.3 g / l

For comparison, the electrogalvanized steel sheet was subjected to cathodic electrolysis treatment using a chromate treatment solution having the same composition as the above and under electrolysis conditions outside the scope of the present invention shown in Table 3 together. , A chromate film was formed on the galvanized film, and the comparative specimen No. 18 to
23 was prepared.

[0033]

[Table 3]

Example 3 Hot-dip zinc having a Zn-Al alloy plating film containing 55 wt.% Al and 1.6 wt.% Si in an amount of 75 g / m ² formed on its surface by the hot dipping method. For alloy-plated steel sheet, using a chromate treatment solution having the following component composition, pH value and temperature within the scope of the present invention, and subjecting it to cathodic electrolysis under the electrolysis conditions within the scope of the present invention, Zn A chrome coating was formed on the Al alloy plating coating. Then, this was washed with water and then dried to obtain a sample No. 3 of the present invention.
4,35 were prepared. For comparison, for the hot-dip zinc alloy-plated steel sheet, a chromate treatment liquid having a composition outside the scope of the present invention shown below was used.
o. 24 was prepared.

Sample No. 34 of the present invention Chromate treatment liquid Total Cr: 20 g / l (Cr ⁶⁺
/ Total ^{Cr 0.97) Ni 2+: 10g /} l (Ni 2+ / total ^{_{Cr 0.5) SO 4 2-: 50g}} / l Silica: 10 g / l of polyacrylic ^{acid: 0.6 g / l F -:} 0.02 click Bu Ramuion / l pH value: 2.8 Temperature: 45 ° C Cathodic electrolysis conditions Current density: 10 A / dm ² Treatment time: 1 second Electricity: 10 C / dm ²

Sample No. 35 of the present invention Chromate treatment liquid Total Cr: 20 g / l (Cr
⁶⁺ / Total Cr 0.85) Ni ²⁺ : 10g / l (Ni ²⁺ / Total Cr 0.5) SO ₄ ^2- : 50g / l Silica: 10g / l Polymethacrylic acid: 1g / l SiF ₆ ^2- : 0.06 Club ion / l NO ₃ ^-: 0.04 click Bu Ramuion / l pH value: 2.8 temperature: 45 ° C. cathodic electrolysis conditions current density: 10 A / dm ² treatment time: 1 second electrical quantity: 10 C / dm ²

Specimen for comparison No. 24 Chromate treatment liquid Total Cr: 20 g / l (Cr
⁶⁺ / total Cr 0.85) Ni ²⁺ : 10g / l (Ni ²⁺ / total Cr 0.5) SO ₄ ^2- : 50g / l Silica: 10g / l Polymethacrylic acid: 1g / l SiF ₆ ^2- : 0.08 club ion / l NO ₃ ^-: 0.05 click Bu Ramuion / l pH value: 2.8 temperature: 45 ° C. cathodic electrolysis conditions current density: 10 A / dm ² treatment time: 1 second electrical quantity: 10 C / dm ²

Example 4 For an electrogalvanized steel sheet on which a Zn-Mn alloy plated coating containing 60 wt.% Mn in an amount of 30 g / m ² was formed on the surface by electroplating, On the Zn-Mn alloy plating film, a chromate treatment solution having a component composition, a pH value and a temperature within the range of the present invention shown in is used, and a cathodic electrolysis treatment is performed under electrolytic conditions within the range of the present invention. A chromate film was formed on the film. Next, this was washed with water and dried to prepare Samples Nos. 36 and 37 of the present invention.
For comparison, a comparative specimen No. 25 was prepared by using a chromate treatment liquid having the following composition outside the scope of the present invention for the electrogalvanized steel sheet.

Sample No. 36 of the present invention Chromate treatment liquid Total Cr: 10 g / l (Cr
⁶⁺ / Total Cr 0.91) Ni ²⁺ : 4g / l (Ni ²⁺ / Total Cr 0.4) SO ₄ ^2- : 30g / l Silica: 15g / l Acrylic resin emulsion: 8g / l pH value: 4.6 Temperature: 40 ℃ Cathodic electrolysis conditions Current density: 8 A / dm ² Treatment time: 1.2 seconds Electric quantity: 9.6 C / dm ²

Sample No. 37 of the present invention Chromate treatment liquid Total Cr: 15 g / l (Cr ⁶⁺
/ Total ^{Cr 0.87) Ni 2+: 6g /} l (Ni 2+ / total ^{_{Cr 0.4) SO 4 2-: 10g}} / l Silica: 15 g / l of polyacrylic ^{_{acid: 1.2 g / l BF 4 -}} : 0.1 click Bu Ramuion / l pH value: 3.0 Temperature: 40 ° C Cathodic electrolysis conditions Current density: 8 A / dm ² Treatment time: 1.2 seconds Electric quantity: 9.6 C / dm ²

Specimen for comparison No. 25 Chromate treatment liquid Total Cr: 15g / l (Cr ⁶⁺
/ Total ^{Cr 0.87) Ni 2+: 6g /} l (Ni 2+ / total ^{_{Cr 0.4) SO 4 2-: 10g}} / l Silica: 15 g / l of polyacrylic ^{_{acid: 1.2 g / l BF 4 -}} : 0.12 click Bu Ramuion / l pH value: 3.0 Temperature: 40 ° C Cathodic electrolysis conditions Current density: 8 A / dm ² Treatment time: 1.2 seconds Electric quantity: 9.6 C / dm ²

Example 5 For an electrogalvanized steel sheet on which a Zn-Ni alloy plated coating containing 12 wt.% Ni in an amount of 30 g / m ² was formed on the surface by electroplating, On the Zn-Mn alloy plating film, a chromate treatment solution having a component composition, a pH value and a temperature within the range of the present invention shown in is used, and a cathodic electrolysis treatment is performed under electrolytic conditions within the range of the present invention. A chromate film was formed on the film. Next, this was washed with water and then dried to prepare Samples Nos. 38 and 39 of the present invention.
For comparison, Comparative Specimen Nos. 26 and 27 were prepared by using a chromate treatment liquid having the following composition outside the scope of the present invention for the electrogalvanized steel sheet.

Sample No. 38 of the present invention Chromate treatment liquid Total Cr: 10 g / l (Cr ⁶⁺
/ Total Cr 0.98) Ni ²⁺ : 4g / l (Ni ²⁺ / Total Cr 0.4) SO ₄ ^2- : 40g / l Silica: 10g / l Polyacrylic acid: 0.2g / l pH value: 2.8 Temperature: 40 ° C Cathodic electrolysis conditions Current density: 10 A / dm ² Treatment time: 0.5 seconds Electric quantity: 5 C / dm ²

Sample No. 39 of the present invention Chromate treatment liquid Total Cr: 15 g / l (
Cr ⁶⁺ / total ^{Cr 0.98) Ni 2+: 3g /} l (Ni 2+ / total ^{_{Cr 0.2) SO 4 2-: 20g}} / l Silica: 15 g / l ^{polyacrylamide: 1.5 g / l Cl -:} 0.01 click Bu Ramuion / l pH value: 2.4 Temperature: 45 ° C Cathodic electrolysis conditions Current density: 10 A / dm ² Treatment time: 0.5 seconds Electricity: 5 C / dm ²

Specimen for comparison No. 26 Chromate treatment solution Total Cr: 15g / l (Cr ⁶⁺ / Total
Cr 0.98) ^{_{silica: 15g / l NO 3 -:}} 0.02 click Bu Ramuion / l pH value: 3.5 Temperature: 45 ° C. cathodic electrolysis conditions Current density: 10 A / dm ² Treatment time: 0.5 sec quantity of electricity: 5 C / dm ²

Specimen for comparison No. 27 Chromate treatment solution Total Cr: 10g / l (Cr ⁶⁺ / Total
^{Cr 0.96) Ni 2+: 3g /} l (Ni 2+ / total Cr 0.3) F ^-: 0.005 click Bu Ramuion / l Cl ^-: 0.01 click Bu Ramuion / l pH value: 2.8 Temperature: 45 ° C. cathodic electrolysis conditions Current density: 10 A / dm ² Processing time: 0.5 seconds Electricity: 5 C / dm ²

The test described below was conducted on each of the specimens thus prepared. (1) Appearance The appearance of the specimen, in particular its surface color uniformity, was visually evaluated. (2) Fingerprint resistance The surface of the sample was touched with a fingertip and the state of fingerprint attachment was visually evaluated. (3) 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 120 hours, and the result was shown by%. (4) Paint Adhesion Test A commercially available alkyd melamine-based paint was applied on the surface of the specimen to a thickness of about 30 μm to form a coating film. Next, 100 checker-like notches were formed in the coating film immediately after coating at intervals of 1 mm, and then extruded by 7 mm with an Erichsen tester, and then an adhesive tape was applied and peeled off on the surface of the extruded portion. As a result, the peeled area is 50% of the 100 grid-shaped notches.
The number of coating films below was evaluated as the coating residual rate (%).

The test results of each of the above-mentioned specimens are shown in Tables 4-6.
Shown in.

[0049]

[Table 4]

[0050]

[Table 5]

[0051]

[Table 6]

As is clear from Tables 4 to 6, Comparative Sample No. 1 in which the total amount of Cr in the chromate treatment solution is outside the range of the present invention and is small, results in a decrease in the formation efficiency of the chromate film, resulting in an appearance. Was poor, and the corrosion resistance and paint adhesion became unstable. Comparative sample No. 2, which had a Cr ⁶⁺ / total Cr ratio outside the range of the present invention and was small, had poor appearance and fingerprint resistance, and also had poor corrosion resistance and paint adhesion. Comparative sample No. 3 in which the amount of Ni ²⁺ / total Cr in the chromate treatment solution was less than the range of the present invention was poor in fingerprint resistance, and conversely, a large amount of the comparative sample exceeded the range of the present invention. Specimen No.
No. 4 had a poor appearance, and all had poor corrosion resistance and paint adhesion.

Comparative sample No. 5, in which the amount of silica in the chromate treatment solution was out of the range of the present invention, was fingerprint resistance,
The corrosion resistance and paint adhesion were poor. Comparative sample No. 6 in which the amount of SO ₄ ²⁻ in the chromate treatment liquid was less than the range of the present invention, the treatment liquid deteriorated with time, and the appearance, fingerprint resistance, corrosion resistance and paint adhesion were poor. It was stable. Comparative specimen N containing no Ni ²⁺ in the chromate treatment solution N
o.7 and Comparative Specimen No. 8 containing no silica all had poor fingerprint resistance, corrosion resistance and paint adhesion.

The amount of the acrylic resin in the chromate treatment solution was outside the range of the present invention and was small. Comparative sample No. 9, 1
Sample Nos. 1, 13 and 15 had poor corrosion resistance and paint adhesion, and Comparative Sample No. 13 had poor fingerprint resistance, and Comparative Sample No. 15 had poor appearance and fingerprint resistance. It was
Comparative sample Nos. 10, 12 and 14 in which the amount of the acrylic resin in the chromate treatment liquid is larger than the range of the present invention, the treatment liquid deteriorates with time and its viscosity increases, and the appearance, Corrosion resistance and paint adhesion are unstable, similarly the comparative sample No. 16 in which the amount of acrylic resin exceeds the range of the present invention, the treatment liquid deteriorates with time, the appearance is poor, Fingerprint resistance, corrosion resistance and paint adhesion were unstable.

Comparative sample No. 18, in which the pH value of the chromate treatment solution was out of the range of the present invention, the dissolution of the plating film occurred and the efficiency of formation of the chromate film was lowered, resulting in poor appearance and fingerprint resistance. Both were poor, and the corrosion resistance and paint adhesion were also poor. The comparative test sample No. 19 having a pH value outside the range of the present invention has a large amount of sludge in the treatment liquid over time, and the formation efficiency of the chromate film is reduced, and the appearance, fingerprint resistance, corrosion resistance and The paint adhesion was both unstable. Comparative sample No. 20, in which the temperature of the chromate treatment liquid was outside the range of the present invention and was low, was inferior in fingerprint resistance as a result of a decrease in the coating formation efficiency and the electric conductivity of the treatment liquid. Comparative sample No. 21 in which the temperature of the chromate treatment solution is outside the range of the present invention and is high, results in dryness after the chromate treatment, resulting in poor appearance and fingerprint resistance, and corrosion resistance and paint adhesion. Was unstable.

Comparative sample No. 22 whose amount of electricity during cathodic electrolysis was outside the range of the present invention was low in chromate film formation efficiency, poor fingerprint resistance, and corrosion resistance and corrosion resistance. The paint adhesion was poor. The amount of electricity during the cathodic electrolysis treatment is many outside the scope of the present invention Comparative specimen No. 23
Had an excessively large amount of chromate coating and had a poor appearance.

SiF ₆ ²⁻ and NO ₃ ^{− in} chromate treatment liquid
Is larger than the range of the present invention in the comparative specimen No. 24, and BF ₄ ⁻ is larger than the scope of the present invention in the comparative specimen N
As for o.25, as a result of the dissolution of the plated coating, both the appearance and fingerprint resistance were poor, and the corrosion resistance and paint adhesion were also unstable. Chromate treatment solution does not contain Ni ²⁺ , SO ₄ ²⁻ and water ^- based acrylic resin Conventional Cr-SiO ₂ −
NO ₃ ^- based specimen N for comparison using the chromate treating solution of
In o.26, the fingerprint resistance was poor, and the corrosion resistance and paint adhesion were unstable. And silica, SO ₄ ^2-
And conventional Cr containing no water-based acrylic resin
-Ni-F ^-- Cl ^- system test solution for comparison N
In o.27, the treatment liquid deteriorated with time, the appearance and fingerprint resistance were poor, and the corrosion resistance and paint adhesion were unstable.

On the other hand, the sample Nos. 1 to 39 of the present invention are
The appearance, fingerprint resistance, corrosion resistance and paint adhesion were all excellent.

[0059]

As described above, according to the present invention,
The zinc-plated steel sheet can be provided with an industrially useful effect that can impart a surface appearance having excellent corrosion resistance, paint adhesion, fingerprint resistance, and uniform color tone.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Masaaki Yamashita 1-2, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Toyofumi Watanabe 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Date Inside the steel pipe company

Claims (2)

[Claims] 1. A zinc or zinc alloy-plated steel sheet having a zinc-plated coating or a zinc alloy-plated coating formed on at least one surface thereof is subjected to cathodic electrolysis treatment in a chromate treatment solution to obtain the zinc or A chromate treatment method for a zinc-based plated steel sheet, which comprises forming a chromate coat on a zinc alloy plated coat, wherein the chromate treatment liquid has a total Cr amount of 5 to 70 g / l, and Cr ⁶⁺ / and Cr ⁶⁺ Oyo Cr ³⁺ weight ratio of 0.8 or more in the amount of total Cr, Ni ²⁺ / total Cr weight ratio of the amount of 0.05 to 0.8 Ni ²⁺
And silica in an amount of 1 to 60 g / l and SO _{4 in} an amount of 10 to 100 g / l.
^2- and 0.1 to 10 g / l of an aqueous acrylic resin, and a treatment solution having a pH value of 1 to 5 and a temperature of 30 to 70 ° C. A method for chromate treatment of a zinc-based plated steel sheet, which comprises subjecting the zinc- or zinc alloy-plated steel sheet to a cathodic electrolysis treatment with an electric quantity of dm ² . 2. The chromate treatment liquid is Cl ⁻ , F ⁻ ,
The method according to claim 1, further comprising 0.01 to 0.1 gram ion / l of at least one of BF ₄ ⁻ , SiF ₆ ²⁻ and NO ₃ ⁻ .