JP3141489B2 - Chromate treatment method for galvanized steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a galvanized steel sheet capable of imparting a uniform color tone with high corrosion resistance, paint adhesion and high whiteness to a galvanized steel sheet or a zinc-based alloy-coated steel sheet. And a chromating method.

[0002]

2. Description of the Related Art A galvanized steel sheet or a zinc-based alloy-plated steel sheet (hereinafter, referred to as a "zinc-based plating film") having a zinc-plated film or a zinc-based alloy-plated film formed on at least one surface thereof. Zinc-plated steel sheet "
) Is widely used in steel sheets for automobiles, steel sheets for household appliances, steel sheets for building materials and the like.

In recent years, the automobile industry has been aggressively reducing the weight of automobile bodies in order to save energy. For this reason, automobile manufacturers have requested thinner and thinner rust-preventive measures. There is a demand for the development of galvanized steel sheets having excellent paint adhesion and corrosion resistance. In the home electric appliance industry, in order to reduce the cost of products, home electric appliances steel sheets are often used without painting. For this reason, home electric appliance manufacturers provide uniform bare corrosion resistance and high whiteness uniformity. There is a demand for the development of a galvanized steel sheet having a beautiful appearance with various colors. In addition, the construction material industry has demanded the development of galvanized steel sheets having excellent paint adhesion and corrosion resistance as a measure against rust in order to increase the long-term durability of building materials.

[0004] As a zinc-based plated steel sheet satisfying the above requirements, a chromate-treated zinc-based plated steel sheet in which a chromate treatment is applied to a zinc-based plated steel sheet and a chromate film is formed on the zinc-based plated film is known. I have.

[0005] The chromate treatment method includes spraying a chromate treatment solution on a zinc-based plated steel plate or immersing the zinc-based plated steel plate in the chromate-treated solution to form a zinc-based plated film and a chromate treatment. A reactive chromate treatment comprising forming a chromate film on the surface of a zinc-based plating film by reacting with a chromate treatment solution, and applying a chromate treatment solution on the surface of the zinc-based plating film; Coating-type chromate treatment consisting of drying without washing with water,
Further, there is an electrolytic chromate treatment comprising forming a chromate film on the surface of a zinc-based plating film by electrolysis.

[0006] The reaction type chromate treatment has the following problems. That is, generally, 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. The reactive chromate treatment is particularly susceptible to the influence of the zinc-based coating film surface of the zinc-based plated steel sheet subjected to the chromate treatment. Therefore, before the chromate treatment, the amount and quality of the chromate film formed on the zinc-based plating film may be reduced due to fluctuations in plating conditions, pretreatment conditions such as pickling and alkali cleaning, and operating conditions such as line speed. It changes greatly and the quality of the chromate film tends to be unstable. Further, it cannot be applied to a zinc-based plating film having poor reactivity with a chromate treatment solution.

[0007] The coating type chromate treatment has the following problems. That is, in the case of the coating type chromate treatment, by controlling 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 film, it is necessary to change the concentration of the chromate treatment solution or to appropriately set the application conditions by the coater, so that 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 solution and the zinc-based plating film, defects such as repelling and uneven coating are likely to occur in the chromate film.

On the other hand, in the electrolytic chromate treatment, a ^chromate film is formed on the surface of a zinc-based plating film by performing cathodic electrolysis using a zinc-based plated steel sheet as a cathode in an aqueous solution containing Cr ⁶⁺ as a main component. It consists of forming. Therefore, according to the electrolytic chromate treatment, the amount of the chromate film does not depend on the type of the zinc-based plated steel sheet or the surface properties of the zinc-based plating film, and the amount of the chromate film depends on the current density and the amount of electricity during the cathodic electrolytic treatment. In addition, there are advantages that the quality can be easily and stably controlled, and that uneven adhesion is less likely to occur.

[0009] Therefore, researches on a method of forming a chromate film on the surface of a zinc-based plated film by such electrolytic chromate treatment and thereby improving the corrosion resistance and paint adhesion of the zinc-based plated steel sheet have been conducted. For example, Japanese Patent Publication No. 24880/1990 discloses a method comprising: It contains Cr ⁶⁺ and Cr ³⁺ , silica and / or silicate, and NO ₃ ⁻ and the ratio of Cr ³⁺ / Cr ⁶⁺ is in the range of ^1/50 to 1/3. Using the adjusted chromate treatment solution, a cathodic electrolysis treatment is applied to the zinc-based plated steel sheet (hereinafter referred to as prior art 1).

Japanese Patent Publication No. 1-14436 discloses a method comprising: Cr ⁶⁺ , PO ₄ ^3- , and fluorine compound 1
Species or two, silica and / or silicate, Z
n, Ni, Co, Al, Mg, Sn, Pb, at least one of Mn ions
Using a chromate treatment liquid containing a seed, a zinc-based plated steel sheet, an aluminum alloy plated steel sheet, a lead or lead alloy plated steel sheet is subjected to a cathodic electrolytic treatment to form a chromate film on the plated film, Immediately an anodic electrolytic treatment (hereinafter referred to as prior art 2).

JP-A-2-145797 discloses a method comprising the following. CrO ₃ , SiO ₂ and H ₂ ZrF ₆ as main components,
Further, in a chromate treatment solution containing H ₂ SO ₄ and F ⁻ , a cathodic electrolytic treatment is performed on the zinc-based plated steel sheet to form a chromate film on the surface of the zinc-based plated film (hereinafter referred to as prior art 3). ).

[0012]

The methods of the prior arts 1 and 2 have the following problems. That is, although a certain degree of improvement in corrosion resistance or paint adhesion is recognized as compared with the prior art, it is still insufficient to improve both. That is, when consideration is given to improvement in paint adhesion, desired corrosion resistance cannot be obtained. On the other hand, when the amount of the chromate film is increased to improve the corrosion resistance, the chromate film is unevenly colored and its appearance is deteriorated. As described above, depending on the prior arts 1 and 2, it is difficult to form a chromate film having excellent corrosion resistance, paint adhesion, and appearance.

[0013] In particular, the methods of the prior art 1, when a zinc-plated steel sheet was continuously chromate treatment, NO ₃ which is contained in the chromate processing solution ^- by elution of the plated metal is promoted, eluted The metal ions thus accumulated are accumulated in the chromate treatment liquid. As a result, the silica and / or silicate in the chromate treatment liquid gels and precipitates in the liquid, and the precipitate adheres to the surface of the chromate film. When the zinc-based plated steel sheet is continuously chromated by the method of Prior Art 2, the chromate film formed by the cathodic electrolysis is partially dissolved or peeled off during the anodic electrolysis to form sludge. Sludge is contained in or adheres to the surface of the chromate coating. As described above, depending on the prior arts 1 and 2, the precipitate in the chromate treatment solution is contained in the chromate film or adheres to the surface of the chromate film, so that the color tone of the formed chromate film is uneven. And its appearance is significantly deteriorated.

In the case of the method of Prior Art 3, a chromate film having a high whiteness can be obtained by the H ₂ ZrF ₆ contained in the chromate treatment solution, but the stability of the chromate treatment solution is low. It is difficult to obtain a stable and uniform color appearance due to the poor quality.

[0015] Accordingly, an object of the present invention is to solve the above-mentioned problems, and to provide a galvanized steel sheet with excellent corrosion resistance and paint adhesion, and a uniform white appearance with high whiteness. An object of the present invention is to provide a method for chromate treatment of a galvanized steel sheet.

[0016]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems. As a result, predetermined amounts of Cr ⁶⁺ + Cr ³⁺ , Mg ²⁺ , Ni ²⁺ , SO ₄ ^2- , and Al ₂ O ₃ ,
It contains at least one member of the group of Sb ₂ O _5, SiO ₂ , SnO _2, TiO _{2, and} ZrO ₂ , and Cr ³⁺ / total Cr content and Ni ²⁺ / Mg ²⁺ are within predetermined ranges Using a chromate treatment solution having a predetermined pH value and temperature and subjecting a zinc-based plated steel sheet to cathodic electrolysis with a predetermined amount of electricity to form a chromate film on the zinc-based plating film, a zinc-based plating film is formed. It has been found that a plated steel sheet can be imparted with excellent corrosion resistance and paint adhesion, and a uniform appearance with high whiteness and uniform color tone.

The present invention has been made on the basis of the above-mentioned findings, and the present invention relates to a method of treating a zinc-based plated steel sheet having at least one surface with a zinc-based plating film formed thereon in a chromate treatment solution. By performing a cathodic electrolytic treatment in, comprising forming a chromate film on the zinc-based plating film, in a method for chromate treatment of a zinc-based plated steel sheet, as the chromate treatment solution,
Cr ⁶⁺ + Cr ³⁺ (total chromium content): 5 to 70 g / l, Mg ²⁺ : 1 to 40 g / l, Ni ²⁺ : 0.5 to 20 g / l, SO ₄ ²⁻ : 10 to 100 g / l, and , Al ₂ O
₃ , Sb ₂ O _5, SiO ₂ , SnO _2, TiO _2, and At least one oxide sol of ZrO ₂ : containing 1 to 60 g / l as a solid content, and a Cr ³⁺ / total Cr content weight ratio: 0.5 or less, Ni ²⁺ / Mg ²⁺ weight ratio: PH of 1 between 0.05 and 2
-5, using a processing solution at a temperature of 30-70 ° C.,
The present invention is characterized in that a cathodic electrolytic treatment is performed on the zinc or zinc alloy-plated steel sheet with an amount of electricity of 4040 C / dm ² .

[0018]

Next, the reason why the composition of the chromate treatment liquid is limited as described above in the present invention will be described. (1) Cr ⁶⁺ and Cr ³⁺ : Cr ⁶⁺ includes chromic anhydride,
Also, one or a mixture of two or more of chromic acid, magnesium salt of dichromic acid, alkali metal salt and ammonium salt is used. Cr ³⁺ is generated by a reduction reaction of Cr ⁶⁺ in the treatment liquid during cathodic electrolysis. In addition, Cr
³⁺ is converted to Cr ⁶⁺ by alcohols or tannic acid in advance.
It may be contained in the treatment liquid by reducing the Cr ^3+, or may be added directly to the treatment solution of a compound of cr ^3+. The total amount of Cr ⁶⁺ and Cr ^{3+, that} is, the total amount of Cr is 5 to 70 g /
It should be limited to within l. 5g / l total chromium
If it is less than 1, the efficiency of forming a chromate film is poor. On the other hand, if the total chromium content exceeds 70 g / l, the coating properties cannot be further improved, which is not only uneconomical, but also the chromate treatment liquid attached to the steel strip and taken out of the chromate treatment tank. This causes a problem that the working environment is polluted. Cr ³⁺ has no special effect on the quality of the chromate film, but rather has the advantage of increasing the film formation efficiency. However, the amount of Cr ³⁺ / total Cr is 0.5% by weight.
If it exceeds, the stability of the chromate treatment liquid will decrease. Therefore, the amount of Cr ³⁺ / total Cr should be 0.5 or less by weight.

(2) Mg ²⁺ : As Mg ²⁺ , magnesium sulfate is used. Such Mg ²⁺ is used for adjusting the ion concentration in the chromate treatment solution, for example, oxides, hydroxides,
It can be added by dissolving it in a processing solution in the form of a carbonate, chloride or the like. Mg ²⁺ has an effect of uniformly depositing a chromate film and forming an appearance having high whiteness. The amount of Mg ²⁺ should be limited to the range from 1 to 40 g / l. When the amount of Mg ²⁺ is less than 1 g / l, the above-mentioned effects cannot be obtained. On the other hand, when the amount of Mg ²⁺ exceeds 40 g / l, the adhesion to the paint decreases. A more preferred content of Mg ²⁺ is 5 to 20 g /
l.

(3) Ni ²⁺ : Nickel sulfate is used as Ni ²⁺ . Such Ni ²⁺ can be added in the form of carbonate, chloride, nitrate or the like dissolved in a chromate treatment solution. Ni ²⁺ has an effect of improving corrosion resistance and paint adhesion. The amount of Ni ²⁺ should be limited within the range of 0.5 to 20 g / l. If the amount of Ni ²⁺ is less than 0.5 g / l, the above-mentioned effects cannot be obtained, while the amount of Ni ²⁺ is 20 g / l
If the ratio exceeds the above range, the appearance of the chromate film tends to be unevenly discolored, and the corrosion resistance of the chromate film deteriorates. Ni ²⁺ / Mg ²⁺ should be limited to a range of 0.05 to 2 by weight. If the weight ratio of Ni ²⁺ / Mg ²⁺ is less than 0.05, the corrosion resistance after painting is reduced. On the other hand, Ni ²⁺ / Mg
^{When 2+} exceeds 2 by weight, the whiteness of the appearance is reduced.

(4) SO ₄ ²⁻ : Conventionally, if a small amount of SO ₄ ²⁻ is contained in the chromate treatment solution, a non-uniform film is formed by the cathodic electrolytic treatment, and the deterioration of corrosion resistance and other properties is deteriorated. It was said that the film was easily blackened.
However, according to the study of the present inventors, SO ₄ ^2-
By adding a large amount in the range of ~ 100 g / l, the stability of the chromate treatment solution is dramatically improved without impairing quality characteristics such as corrosion resistance and paint adhesion, and a uniform appearance color tone is obtained. It was found that a chromate film having the same could be formed. Accordingly, in the present invention, in the chromate treatment solution it is intended to contain SO ₄ ^2-a in the range of 10 to 100 g / l. The amount of SO ₄ ^2- should be limited to the range from 10 to 100 g / l, as described above. The amount of SO ₄ ^2-
Is less than 10 g / l, not to obtain the effect described above, while, SO ₄
^{Even if} the amount of ^2- exceeds 100 g / l, no further effect is obtained and it is uneconomical. The more preferable content of SO ₄ ^2- is 20 to 100 g / l.

(5) Al ₂ O ₃ , Sb ₂ O _5, SiO ₂ , SnO _2, TiO _2, and At least one oxide sol of ZrO ₂ : Al ₂ O
Most of the oxide sols of ₃ , Sb ₂ O _5, SiO ₂ , SnO _2, TiO _2, and ZrO ₂ are converted into colloids by adjusting the surface charge and counter ion of the hydroxide or each oxide, and the processing solution Stably dispersed in. Such an oxide sol has an effect of improving corrosion resistance and paint adhesion. The amount of oxide sol should be limited to a range of 1 to 60 g / l solids. When the amount of the oxide sol is less than 1 g / l, the above-mentioned effects cannot be obtained. On the other hand, when the amount of the oxide sol exceeds 60 g / l, the oxide particles are easily separated from the chromate film, and the paint adhesion Deteriorates. The smaller the particle size of the oxide sol, the more excellent the corrosion resistance is imparted to the chromate film, and the larger the particle size, the more the chromate film tends to have excellent paint adhesion. Therefore, it is effective to use a mixture of an oxide sol having a large particle diameter and an oxide sol having a small particle diameter. However,
An oxide sol having a too large particle diameter deteriorates the dispersion stability in the processing solution. Therefore, it is preferable to use an oxide sol having a particle diameter of 50 nm or less.

[0023] ^{(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 ^- in the surface of the plating film was uniformly dissolved, has an effect of forming a homogeneous chromate film. In particular, it effectively works on a plating film having a thick oxide film formed by a hot-dip plating 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 solution. 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 ions / l. _{^{Cl -, F -, BF 4}} -, SiF 6 2- and NO ₃ ^-
The amount of at least one is 0.01 gram ion / l
If it is less than the above, the above-described effects cannot be obtained. On the other hand, if it exceeds 0.1 g ion / l, the plating surface is excessively dissolved, resulting in deterioration of corrosion resistance.

(7) Additives: In order to improve the stability of operation, the following additives may be added to the chromate treatment solution. PH buffers such as borates, phosphates and phthalates, ammonium and alkali metal sulfates to suppress pH fluctuations at the interface to be treated during electrolytic treatment and form a stable chromate film Electric conduction aids such as halides, and chelate compounds of amines and carboxylic acids for fixing metal ions in the chromate treatment solution and preventing sludge formation.

(8) Others: In the chromate treatment solution,
There are cases where ions such as Zn, Fe, Al, Mn, Co, Mo, Pb, Sn, Cu and Ag, which are eluted from the galvanized steel sheet or electrode to be chromated, are inevitably mixed,
There is no problem if the total amount is 0.1 g ion / l or less. In addition, as a cation, it is contained in additives such as SO ₄ ^2- supply salt or electric conduction aid and pH buffer
It may contain an alkali metal ion such as Na or K, or an ammonium ion, but these do not adversely affect the effects of the present invention and are not particularly limited.

(9) pH value of chromate treatment solution: The pH value of the chromate treatment solution should be limited to the range of 1 to 5. If the pH value of the chromate treatment liquid is less than 1, the chromate film deposition efficiency is reduced. Further, if the pH value is less than 1,
After the electrolytic treatment, the chromate treatment liquid adhering to the surface of the chromate film partially redissolves the chromate film, resulting in deterioration of corrosion resistance and paint adhesion, and the appearance of the chromate film 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 reduced, and a precipitate is easily 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 solution.

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

(11) Electricity of cathodic electrolysis The amount of chromate film deposited can be controlled by changing the current density and the treatment time during cathodic electrolysis for chromate treatment, ie, the amount of electricity. Electricity is 0.5
Should be limited to the range of from 40 C / dm ² . Electricity is 0.
If it is less than 5 C / dm ² , a uniform chromate film is not formed, and desired quality characteristics cannot be obtained. On the other hand, electricity amount is 40C /
Beyond dm ^2, the chromate film is excessively thick, the appearance is deteriorated inviting a decrease in whiteness. The current density of the 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 galvanized steel sheet subjected to the chromate treatment of the present invention includes electroplating, hot-dip galvanizing, and the like.
Various zinc-based plated steel sheets on which a plating film is formed by vapor deposition plating, ion plating, etc., for example, Zn
Plated steel sheet, Zn-Ni, Zn-Fe, Zn-Mn, Zn-Al
Steel, Zn-Cr based zinc alloy plated steel sheet or zinc composite plated steel sheet, or above, Zn, Zn-Ni, Zn-Fe, Zn-Mn
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 Zn-Al, Zn-Cr or the like can be used.

The chromated zinc-coated steel sheet having a chromate film formed thereon by the method of the present invention is used as an unpainted steel sheet or a steel sheet for undercoating in a state of being washed and dried. However, if necessary, the steel sheet may be subjected to a chromate sealing treatment or a post-treatment with an organic composite treatment solution, which is generally performed. Next, the present invention will be described in more detail with reference to examples and comparative examples.

[0031]

【Example】

Example 1 A zinc electroplated steel sheet having a surface coated with a galvanized coating in an amount of 20 g / m ² by an electroplating method was subjected to the composition shown in Tables 1 and 2 within the scope of the present invention and the pH. Using a chromate treatment solution having a value and a temperature, a cathodic electrolysis treatment was performed under the following electrolysis conditions within the scope of the present invention to form a chromate film on the galvanized film. Next, this was washed with water and then dried to prepare inventive specimens Nos. 1 to 23 shown in Tables 1 and 2. Current density: 10 A / dm ² Processing time: 1.0 second Electricity: 10 C / dm ²

[0032]

[Table 1]

[0033]

[Table 2]

For comparison, the above zinc electroplated steel sheet was treated with a chromate treatment solution having any one of the component composition, pH value and temperature shown in Tables 1 and 2 out of the range of the present invention. Under the same conditions as above, a cathodic electrolytic treatment was performed to form a chromate film on the galvanized film, and Comparative Sample Nos. 1 to 14 shown in Tables 1 and 2 were prepared.

Example 2 A zinc electroplated steel sheet having a surface coated with a galvanized film in an amount of 20 g / m ² by an electroplating method has the following component composition within the scope of the present invention. Using a chromate treatment solution, cathodic electrolysis was performed under electrolysis conditions within the range of the present invention shown in Table 3 to form a chromate film on the zinc plating film. Next, this was washed with water and then dried to prepare inventive samples Nos. 24 to 33 shown in Table 3. Cr ⁶⁺ + Cr ³⁺ : 10 g / l (Cr ³⁺ / Total Cr: <0.05) Mg ²⁺ : 10 g / l Ni ²⁺ : 3 g / l SO ₄ ^2- : 40 g / l SiO ₂ : 10g / l as solid content

For comparison, the above zinc electroplated steel sheet was subjected to cathodic electrolysis under electrolysis conditions outside the range of the present invention shown in Table 3 using a chromate treatment solution having the same composition as above. , A chromate film was formed on the galvanized film, and Comparative Sample Nos. 15 to
20 were prepared.

[0037]

[Table 3]

Example 3 A Zn-Al alloy plating film having an amount of 75 g / m ² containing 55% by weight of Al and 1.6% by weight of Si was formed on its surface by a hot-dip plating method. For the aluminum alloy hot-dip coated steel sheet, the component composition within the scope of the present invention shown below,
A chromate treatment solution having a pH value and a temperature was used, and a cathodic electrolysis treatment was performed under electrolysis conditions within the range of the present invention to form a chromate film on the Zn-Al alloy plating film. Next, this was washed with water and dried to prepare a test sample No. 34 of the present invention. For comparison, a sample No. 21 for comparison was prepared on the above zinc-aluminum alloy hot-dip coated steel sheet using a chromate treatment solution having a component composition out of the scope of the present invention shown below.

Specimen No. 34 of the present invention Chromate treatment solution Total Cr: 20 g / l (Cr ³⁺ / Total Cr
<0.05) Mg ²⁺ : 12 g / l Ni ²⁺ : 5 g / l SO ₄ ²⁻ : 50 g / l SiO ₂ : 15 g / l as solid content SiF ₆ ²⁻ : 0.03 gram ion / l pH value: 2.2 Temperature: 45 ° C Cathodic electrolysis conditions Current density: 8 A / dm ² Processing time: 1.5 seconds Electricity: 12 C / dm ²

Specimen No. 21 for comparison Chromate treatment solution Total Cr: 20 g / l (Cr ³⁺ / Total Cr
<0.05) Mg ²⁺ : 12 g / l Ni ²⁺ : 5 g / l SO ₄ ²⁻ : 40 g / l SiO ₂ : 15 g / l as solid content SiF ₆ ²⁻ : 0.12 gram ion / l pH value: 2.2 Temperature: 45 ° C Cathodic electrolysis conditions Current density: 8 A / dm ² Processing time: 1.5 seconds Electricity: 12 C / dm ²

Example 4 A zinc-iron alloy hot-dip coated steel sheet having a Zn-Fe alloy plating film of 11 g / m ² containing 11 wt.% Fe formed on its surface by a hot-dip plating method. Using a chromate treatment solution having a component composition, pH value and temperature within the scope of the present invention shown below, and performing a cathodic electrolytic treatment under electrolysis conditions within the scope of the present invention, a Zn-Fe alloy plating film A chromate film was formed on the substrate. Next, this was washed with water and dried to prepare Specimen No. 35 of the present invention. For comparison, a comparative specimen No. 22 was prepared for the zinc-iron alloy hot-dip coated steel sheet by using a chromate treatment solution having a component composition out of the scope of the present invention shown below.

Specimen No. 35 of the present invention Chromate treatment solution Total Cr: 15 g / l (Cr ³⁺ / Total Cr
<0.05) Mg ²⁺ : 4 g / l Ni ²⁺ : 6 g / l SO ₄ ^2- : 30 g / l SiO ₂ : 15 g / l as solid content pH value: 3.0 Temperature: 40 ° C Cathodic electrolysis conditions Current density ： 10 A / dm ² Processing time ： 0.8 seconds Electricity ： 8 C / dm ²

Specimen No. 22 for comparison Chromate treatment solution Total Cr: 15 g / l (Cr ³⁺ / Total Cr
<0.05) Mg ²⁺ : 4 g / l SO ₄ ^2- : 12 g / l SiO ₂ : 15 g / l as solid content pH value: 3.0 Temperature: 40 ° C Cathodic electrolysis condition Current density: 10 A / dm ² Processing time ： 0.8 seconds Electricity ： 8 C / dm ²

Example 5 A zinc-nickel alloy electroplated steel sheet having a Zn-Ni alloy plating film of 30 g / m ² containing 12 wt.% Ni formed on its surface by electroplating was used. Using a chromate treatment solution having a component composition, pH value and temperature within the scope of the present invention shown below, and performing cathodic electrolysis under electrolysis conditions within the scope of the present invention, a Zn-Ni alloy plating film A chromate film was formed on the substrate. Next, this was washed with water and dried to prepare Test Sample Nos. 36 and 37 of the present invention. For comparison, for the zinc-nickel alloy electroplated steel sheet, a chromate treatment solution having a component composition out of the scope of the present invention shown below was used, and a comparative specimen was used.
Nos. 23 and 24 were prepared.

Specimen No. 36 of the present invention Chromate treatment solution Total Cr: 10 g / l (Cr ³⁺ / Total Cr)
<0.05) Mg ²⁺ : 11 g / l Ni ²⁺ : 3 g / l SO ₄ ^2- : 40 g / l SiO ₂ : 10 g / l as solid pH value: 3.3 Temperature: 40 ° C Cathodic electrolysis conditions Current density : 8 A / dm ² Processing time: 1.0 second Electricity: 8 C / dm ²

Specimen No. 37 of the present invention Chromate treatment solution Total Cr: 15 g / l (Cr ³⁺ / Total Cr
^{0.12) Mg 2+: 15 g /} l Ni 2+: 4 g / l SO 4 2-: 50 g / l SiO 2: 10g / l Cl as solids ^- 0.01 click Bu Ramuion / l pH value: 3.5 Temperature: Cathodic electrolysis conditions at 45 ° C Current density: 8 A / dm ² Processing time: 1.0 second Electricity: 8 C / dm ²

Specimen No. 23 for comparison Chromate treatment solution Total Cr: 15 g / l (Cr ³⁺ / Total Cr
^{0.12) Mg 2+: 0.6 g /} l Ni 2+: 4 g / l SO 4 2-: 8 g / l SiO 2: 10g / l Cl as solids ^- 0.01 click Bu Ramuion / l pH value: 3.5 Temperature: Cathodic electrolysis conditions at 45 ° C Current density: 8 A / dm ² Processing time: 1.0 second Electricity: 8 C / dm ²

Specimen No. 24 for comparison Chromate treatment solution
All Cr: 20 g / l (Cr 3+ / total ^{Cr 0.12) Mg 2+: 15 g} / l Ni 2+: 4 g / l SO 4 2-: 3 g / l Cl -: 0.01 click Bu Ramuion / l pH Value: 3.0 Temperature: 45 ° C Cathodic electrolysis conditions Current density: 8 A / dm ² Processing time: 1.0 second Electricity: 8 C / dm ²

Example 6 By the electroplating method, 11 wt.
. wt% of Cr and zinc Zn-Ni-Cr composite plating film in an amount of 30 g / m ² containing formed a - nickel - to chrome composite electroplated steel sheet, components within the scope of the present invention shown below A chromate treatment solution having a composition, a pH value and a temperature is used, and a cathodic electrolysis treatment is performed under electrolysis conditions within the scope of the present invention to form a chromate treatment solution on the Zn-Ni-Cr composite plating film.
A coating was formed. Next, this was washed with water and then dried to prepare test samples Nos. 38 and 39 of the present invention. For comparison, a specimen No. 25 for comparison was prepared for the zinc-nickel-chromium composite electroplated steel sheet by using a chromate treatment solution having a component composition out of the scope of the present invention shown below.

Specimen No. 38 of the present invention Chromate treatment solution Total Cr: 12 g / l (Cr ³⁺ / Total Cr
<0.18) Mg ²⁺ : 12 g / l Ni ²⁺ : 5 g / l SO ₄ ^2- : 40 g / l SiO ₂ : 10 g / l as solid content pH value: 3.3 Temperature: 40 ° C Cathodic electrolysis conditions Current density ： 10 A / dm ² Processing time ： 1.5 seconds Electricity ： 15 C / dm ²

Specimen No. 39 of the present invention Chromate treatment solution Total Cr: 12 g / l (Cr ³⁺ / Total Cr
0.15) Mg ²⁺ : 10 g / l Ni ²⁺ : 3 g / l SO ₄ ^2- : 30 g / l SiO ₂ : 15 g / l as solid matter NO ^3- : 0.02 gram ion / l pH value: 3.0 Temperature ： 40 ℃ Cathodic electrolysis condition Current density ： 12 A / dm ² Processing time ： 1.5 sec Electric quantity ： 18 C / dm ²

Specimen No. 25 for comparison Chromate treatment solution Total Cr: 12 g / l (Cr ³⁺ / Total Cr
0.18) Mg ²⁺ : 12 g / l Ni ²⁺ : 5 g / l SO ₄ ^2- : 40 g / l pH value: 3.3 Temperature: 40 ° C Cathodic electrolysis condition Current density: 10 A / dm ² Processing time: 1.5 Second electricity quantity: 15 C / dm ²

The test described below was performed on each specimen thus prepared. (1) Corrosion resistance test The test specimen was subjected to a salt spray test specified in JIS-Z-2371, and the area of white rust occurrence after 72 hours was measured. The result was indicated by%. (2) Paint Adhesion Test A commercially available alkyd melamine-based paint was applied on the surface of the test specimen by 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. As a result, of the 100 grid-shaped notches, the peeled area was 50
The number of coating films of less than% was evaluated as a coating film remaining ratio (%). (3) Appearance The appearance of the specimen was visually evaluated.

Tables 4 to 6 show the test results of each specimen described above.
Shown in

[0055]

[Table 4]

[0056]

[Table 5]

[0057]

[Table 6]

As is clear from Tables 4 to 6, Comparative Sample No. 1 in which the total amount of Cr in the chromate-treated solution was out of the range of the present invention was small, and as a result, the formation efficiency of the chromate film was lowered and the color tone was lowered. Became uneven, and the corrosion resistance and paint adhesion became unstable. Comparative sample No. 2 having a Cr ³⁺ / total Cr ratio larger than the range of the present invention turned gray as a result of an increase in sludge in the chromate treatment solution, and
Corrosion resistance and paint adhesion became unstable. Specimen No. for comparison containing no Ni ²⁺ in the chromate treatment solution
No. 3 and a comparative specimen containing no Mg ²⁺
No. 4 had poor corrosion resistance and paint adhesion, and Comparative Sample No. 4 turned yellow.

Comparative Sample No. 5 in which the amount of Ni ²⁺ in the chromate-treated solution was out of the range of the present invention, and Comparative Sample No. 5 in which the amount of Mg ²⁺ was out of the range of the present invention. 6 is
In each case, the corrosion resistance and paint adhesion were poor, and Comparative Sample No. 6 turned yellow. Comparative specimens Nos. 7 and 8 having a high Ni ²⁺ / Mg ²⁺ ratio beyond the scope of the present invention, and comparative specimens having a low Ni ²⁺ / Mg ²⁺ ratio outside the scope of the present invention No. 9 was inferior in corrosion resistance and paint adhesion, and Comparative Sample Nos. 7 and 8 turned yellow or brown. In Comparative Specimen No. 10 in which the amount of SO ₄ ^2- in the chromate treatment liquid was out of the range of the present invention, the treatment liquid deteriorated with time, and the appearance, corrosion resistance and paint adhesion were unstable. .

Comparative Sample No. 11, in which the amount of oxide sol in the chromate treatment solution was small outside the range of the present invention, was poor in corrosion resistance and paint adhesion. Comparative specimens Nos. 12 and 13 in which the amount of oxide sol is large beyond the scope of the present invention are:
Due to the peeling of the oxide from the chromate film, the corrosion resistance and paint adhesion were unstable, and the appearance color tone was also uneven. Comparative Sample No. 14 in which the oxide sol was not contained in the chromate treatment solution had poor corrosion resistance and paint adhesion.

In Comparative Sample No. 15 in which the pH value of the chromate treatment solution was outside the range of the present invention and the plating film was dissolved, the formation efficiency of the chromate film was reduced, and as a result, the color turned gray and the corrosion resistance was reduced. And the paint adhesion was unstable. Comparative specimen No. 1 whose pH value is more than the range of the present invention
In No. 6, the sludge increased in the treatment liquid over time, the formation efficiency of the chromate film decreased, and the corrosion resistance and paint adhesion were unstable.

In Comparative Sample No. 17 in which the temperature of the chromate treatment solution was lower than the range of the present invention, the formation efficiency of the chromate film and the electrical conductivity of the chromate treatment solution were lowered. Specimen No. 18 for comparison, in which the temperature of the chromate treatment solution was higher than the range of the present invention, was changed to brown as a result of drying after chromate treatment, and the corrosion resistance and paint adhesion were unstable. . The amount of electricity and the current density during the cathodic electrolysis treatment are small for comparison purposes outside the scope of the present invention.
In No. 19, the formation efficiency of the chromate film was reduced, the corrosion resistance and paint adhesion were poor, and the color was changed to pale yellow. The amount of electricity during the cathodic electrolysis treatment is larger than the range of the present invention, and the comparative sample No. 20 has an excessive amount of chromate film,
Poor corrosion resistance and paint adhesion and discolored to yellow.

[0063] SiF ₆ ^2-is Specimen No.21 comparative often beyond the scope of the present invention in the chromating solution, the result of dissolution of the plated film occurs, discolored to gray, and, corrosion resistance and paint adhesion Sex was unstable. Ni ^{2+ in} chromate treatment solution
In Comparative Sample No. 22 containing no, the corrosion resistance and paint adhesion were poor. Comparative Sample No. 23, in which the amount of Mg ^{2+ and the} amount of SO ₄ ²⁻ in the chromate treatment solution were small outside the range of the present invention, turned brown and had poor corrosion resistance and paint adhesion. In Comparative Specimen No. 24, the amount of SO ₄ ^2- in the chromate treatment solution was out of the range of the present invention, the treatment solution deteriorated with time, the color tone was unevenly changed to yellow, and
Corrosion resistance and paint adhesion were unstable. Specimen for comparison containing no oxide sol in chromate treatment liquid
No. 25 was poor in corrosion resistance and paint adhesion.

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

[0065]

As described above, according to the present invention,
Excellent corrosion resistance and paint adhesion to galvanized steel sheet,
In addition, an industrially useful effect capable of imparting a uniform white appearance with a high degree of whiteness is provided.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Toyofumi Watanabe 1-2-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan stock (56) References JP-A-62-164895 (JP, A) JP-A-62- 278297 (JP, A) JP-A-63-143292 (JP, A) JP-A-5-44093 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C25D 11/38

Claims (2)

(57) [Claims] 1. A galvanized steel sheet having a galvanized film or a zinc-based alloy plated film formed on at least one surface thereof is subjected to a cathodic electrolytic treatment in a chromate treatment solution, whereby the galvanized film is formed. Alternatively, in a method for chromate treatment of a zinc-based plated steel sheet, comprising forming a chromate film on a zinc-based alloy plating film, wherein the chromate treatment solution is Cr ⁶⁺ + Cr ³⁺ (total chromium amount): 5 to 70 g / ^{l, Mg 2+: 1~ 40g /} l, Ni 2+: 0.5 ~ 20g / l, SO 4 2-: 10~100g / l, _{and, Al 2 O 3, Sb 2} O 5, SiO 2, SnO 2 _, TiO _2, and At least one oxide sol of ZrO ₂ : 1 to 60 g / l as solid content, and Cr ³⁺ / total Cr content: 0.5 or less, Ni ²⁺ / Mg ²⁺ weight ratio: A cathodic electrolytic treatment is applied to the galvanized steel sheet using a treating solution having a pH value of 1 to 5 and a temperature of 30 to 70 ° C. and an electric quantity of 0.5 to 40 C / dm ^2. Chromate treatment method for galvanized steel sheet. Wherein said chromate treatment solution, Cl ^-, F ^-,
At least one of BF ₄ ⁻ , SiF ₆ ²⁻ and NO ₃ ⁻ , further containing 0.01 to 0.1 gram ions / l;
The method of claim 1.