JP2001295064A - Galvanized steel sheet having excellent corrosion resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a galvanized steel sheet which may be easily manufacturing, may be manufactured without using chromic acid, fluoride and organic solvent and has the excellent corrosion resistance of zinc case plating films. SOLUTION: The zinc corrosion protective films are formed on the galvanized steel sheet. The zinc corrosion protective films are composed of inorganic films consisting essentially of phosphate ions, ammonium ions and condensed phosphate ions. The zinc corrosion protective films may also be formed of the composite films having the inorganic films consisting essentially of the phosphate ions, the ammonium ions and/or the condensed phosphate ion and organic coating material films formed on these inorganic films. The zinc corrosion protective film may also be formed of the organic coating material films containing zinc corrosion protective components containing the phosphate ions, the ammonium ions and/or the condensed phosphate ion as the essential components in an organic coating material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a galvanized steel sheet capable of suppressing blackening and white rust of a zinc-based plating film.

[0002]

2. Description of the Related Art A zinc-based plated steel sheet in which a zinc-based plating film containing zinc as a main component is coated on the surface of a base steel sheet has excellent corrosion resistance due to the cathodic corrosion protection effect of zinc.
Also, since it can be produced at low cost, it has been widely used in automobiles, building materials, and home appliances.

[0003] By applying zinc-based plating to the base steel sheet in this way, corrosion of the steel sheet can be prevented, but on the other hand, the zinc-based plating film itself is corroded, causing blackening or white corrosion products ( It is known that white rust occurs.
For this reason, in order to suppress blackening and white rust of the zinc-based plated film, various surface treatments are performed on the zinc-based plated steel sheet.

As this kind of surface treatment, there is a chromate treatment. According to this treatment, an excellent anticorrosion effect can be obtained by a relatively simple and economical treatment. Also, in the phosphate treatment, a rinsing treatment with chromic acid is performed after the phosphate treatment for the purpose of imparting corrosion resistance of the zinc-based plating film.

However, since the chromate treatment uses a harmful chromate, there is a concern that it may adversely affect the human body, and it is essential to remove chromium eluted in the degreasing solution of the chromate-treated steel sheet. It is strongly desired not to use a chromate treatment because of the problems of equipment and cost. In addition, the phosphating treatment combined with chromic acid rinsing involves the problem of chromium treatment, the reaction accelerator in the phosphating agent, the drainage treatment of metal ions, and the sludge treatment by elution of metal ions from the metal to be treated. There is a problem.

Therefore, in recent years, various methods for improving the corrosion resistance of a zinc-based plating film without using toxic chromic acid have been proposed as follows. (1) A method of forming an organic resin film or an organic composite silicate film on an organic polymer chelating agent film on the surface of a galvanized steel sheet (JP-A-11-158646). (2) A method of treating the surface of a metallic material with an acidic surface treating agent containing the components described in the following A to D on the surface of a galvanized steel sheet (JP-A-11-106945). A: a cation component comprising a metal ion selected from the group consisting of manganese, cobalt, zinc, magnesium, nickel, iron, titanium, aluminum and zirconium B: at least one of fluoroacid, phosphoric acid, and acetic acid C: silane coupling Component D: Water-soluble polymer component having 2 to 50 polymerized units (3) A zinc-based plated steel sheet has a Si-O bond, an Al-O bond, an OH group, and a Si-R (R: alkyl group) bond A film having no Al, (Al + (Al + Si)) in a molar ratio in the range of 0.025 to 0.75, and Mg, Co, N
i. A method for forming a chemical conversion treatment layer containing one or more elements selected from i in a molar ratio to Al in the range of 0.01 to 1.0 in terms of mole ratio (JP-A-10-180)
No. 49).

[0007]

Although the problem of toxicity can be avoided by using a treatment method that does not use chromic acid, the above-mentioned various methods also have the following problems. In the above method (1), the production of the polymer chelating agent is complicated, resulting in high cost. Since the method (2) substantially contains a fluoride, it is difficult to handle the treatment liquid and treat the waste liquid. Further, in the method (3), since a treatment liquid with an organic solvent is used, equipment for preventing evaporation of the solvent and explosion-proof equipment is required.

The present invention has been made in view of the above problems, and provides a galvanized steel sheet which is easy to produce and can be produced without using chromic acid, fluoride and organic solvent and which has excellent corrosion resistance of a zinc-based plating film. The purpose is to provide.

[0009]

Means for Solving the Problems The present inventors have conducted intensive studies on a method for suppressing rust formation on a zinc-based plating film, and found that condensed phosphate ions, phosphate ions and ammonium ions are present on the surface of a zinc-based plated steel sheet. Under such conditions, it has been found that the black change and the generation of white rust of the zinc-based plating film can be effectively suppressed, and the present invention has been completed.

That is, the galvanized steel sheet of the present invention comprises:
A zinc corrosion protection film is formed on a zinc-based plated steel sheet, and the zinc corrosion protection film is composed of an inorganic film containing phosphate ions, ammonium ions and condensed phosphate ions as essential components.

[0011] Further, the zinc anticorrosion coating is, as described in claim 2, an inorganic coating containing phosphate ions and ammonium ions and / or condensed phosphate ions as an essential component, and an inorganic coating on the inorganic coating. And an organic coating film formed on the substrate.

Further, as described in claim 3, the zinc anticorrosion film contains a zinc anticorrosion component containing a phosphate ion and an ammonium ion and / or a condensed phosphate ion as an essential component in an organic paint. It can be an organic paint film.

Phosphate ions contained in the zinc anticorrosion coating are 0.01 g / m ² or more, and ammonium ions are 0.0
It is preferable that the concentration is 1 g / m ² or more and the condensed phosphate ion is 0.04 g / m ² or more. In the present invention, each ion that is an essential component includes not only a case where the ion is present in an ionized state but also a case where the ion exists as a solid-state salt bonded to a counter ion.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The black change and white rust of a zinc-based plating film of a zinc-based plated steel sheet are caused by a substance formed as a result of corrosion of zinc. That is, zinc is oxidized to generate Zn ions as shown in the following formula, and the Zn ions are further changed to hydroxides, oxides, carbonates, chlorides, etc., thereby causing black change or white rust. . Therefore, if this is immobilized as a compound at the stage of Zn ions, black change and white rust can be prevented. Zn → Zn ²⁺ + 2e ⁻

The condensed phosphate ion, which is an essential component of the zinc anticorrosion coating according to the present invention, forms a chelate as shown in the following formula (1), and the phosphate ion and ammonium ion, which are the essential components, are as follows: As shown in equation (2), Z
Immobilizes n ions and forms a dense film. For this reason,
In a corrosive atmosphere in the presence of moisture in which Zn ions are generated, the above-mentioned condensed phosphate ions, or a zinc anticorrosive film capable of supplying phosphate ions and ammonium ions, is formed on a zinc-based plated steel sheet to form Zn ions. Does not change to the hydroxides, oxides, carbonates and chlorides, and blackening and generation of white rust can be suppressed.

[0016]

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As an embodiment of the zinc anticorrosion coating, an inorganic coating containing the above-mentioned condensed phosphate ion, phosphate ion and ammonium ion as essential components can be used. Further, a composite film in which an organic paint film is coated on the inorganic film may be used. Furthermore, a water-soluble or water-dispersible organic paint containing the essential component ions may form an organic paint film containing a zinc anticorrosive component. In the case of a composite film or an organic paint film containing a zinc anticorrosive component, the organic paint film is expected to block corrosion components such as moisture, so that condensed phosphate ions alone or two types of phosphate ions and ammonium ions are used. Can be used alone. In the present invention, the condensed phosphate ion, phosphate ion and ammonium ion may be present in a corrosive atmosphere in the presence of moisture in which Zn can exist as an ion. It may be present as a salt in a state.

Examples of the salt containing the condensed phosphate ion include:
Polyphosphate, metaphosphate, and ultraphosphate can be used alone or in combination. On the other hand, the phosphate ions and the salts containing ammonium ions include:
Salts containing each ion alone can be used in combination, but salts capable of producing them simultaneously,
For example, ammonium hydrogen phosphate can be used alone, which is preferable.

[0019] The phosphate ion concentration of ammonium ion (coating amount) is, ZnNH ₄ by the reaction of equation (2)
In order to form a PO ₄ film and to expect an effective anticorrosion effect, each is preferably 0.01 g / m ² or more. However, even if each of them exceeds 10 g / m ² , the corrosion resistance is saturated.
/ m ² or less. On the other hand, the concentration of the condensed phosphate ions is desirably 0.04 to 16 g / m ² . At 0.04 g / m ² or less, the effect is too small.
Even if the content exceeds g / m ^{2, the} effect of improving corrosion resistance is saturated.

The water-soluble and water-dispersible organic resin paint for preparing the above-mentioned organic paint film containing condensed phosphate ions or ammonium ions and phosphate ions includes acrylic, polyolefin, urethane and epoxy resins. And a synthetic resin paint such as a polyester resin can be used.

As the components of the zinc anticorrosion coating, in addition to the condensed phosphate ion or essential components of ammonium ion and phosphate ion, if necessary, an anticorrosion additive such as molybdate or tannic acid may be used. Ultramarine,
Inorganic pigments such as carbon black and titanium oxide, and organic pigments such as azo pigments, phthalocyanine pigments, and anthraquinone pigments can be added.

The amount of each ion contained in the zinc anticorrosion coating is determined by dissolving the coating in an aqueous solution having a pH of 4 to 8,
Ammonium ion and phosphate ion (including orthophosphate ion and condensed phosphate ion) were separated and quantified by ion exchange chromatography, and the total amount of phosphorus was quantified by ICP-MS and determined by ion exchange chromatography. The amount of condensed phosphate ions can be confirmed by subtracting the amount corresponding to orthophosphate ions. In the case of an organic paint film containing a zinc anticorrosive component, the organic paint film can be finely crushed, and the soluble component can be extracted with an aqueous solution having a pH of 4 to 8 and measured by the above method.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not construed as being limited to such examples.

[0024]

EXAMPLE As a test material, a hot-dip galvanized steel sheet having a coating weight of 60 g / m ² and a thickness of 0.6 mm (abbreviated as GI) was used.
And an electrogalvanized steel sheet (abbreviated as EG) having a coating weight of 20 g / m ² and a sheet thickness of 0.6 mm were prepared.

Example Group 1 A zinc anticorrosion coating composed of an inorganic coating was formed on the GI or EG galvanized steel sheet. As shown in Table 1, the zinc anticorrosion film was coated on a galvanized steel sheet degreased with a weak alkali with an aqueous solution obtained by mixing a predetermined amount of sodium ultraphosphate, sodium hexametaphosphate, and ammonium dihydrogen phosphate with a bar coater. Formed by drying at ° C.
In Table 1 (the same applies to Tables 2 and 3 described later), the coating amount as ions as essential components is also described.

The coating amount of each component in the zinc anticorrosion coating was measured by the following method. After dissolving the film in 0.0001 M hydrochloric acid, by ion exchange chromatography,
Ammonium ions were quantified using methanesulfonic acid as eluent, then pH was adjusted with acetic acid-potassium acetate.
Orthophosphate ions were eluted with a 0.25 M potassium chloride solution adjusted to 5.0, and condensed phosphate ions were eluted and quantified with a 1 M potassium chloride solution at pH 5. Then, the total P was quantified by ICP-MS, and the amount corresponding to orthophosphate ion determined by ion exchange chromatography was subtracted to confirm the amount of condensed phosphate ion.

With respect to the obtained sample, JIS-Z-23
The salt spray test specified in No. 71 was carried out, and the area ratio of black change and white rust after 48 hours had elapsed was examined.
The white rust resistance was evaluated on a 5-point scale. AA has an incidence of blackening and white rust of less than 5%, A has an incidence of 5% or more and less than 25%, B has an occurrence rate of 25% or more and less than 50%, C has an occurrence rate of 50% or more and less than 80%, D
Is 80% or more. Table 1 also shows the results of the corrosion resistance evaluation.

From Table 1, it can be seen that the sample Nos.
Indicates that the galvanized film has excellent corrosion resistance.
On the other hand, in Samples Nos. 11 and 12 according to Comparative Examples, since no condensed phosphate ions were contained,
However, since no phosphate ion and ammonium ion are contained, the corrosion resistance is deteriorated.

[0029]

[Table 1]

[Example group 2] In the same manner as in Example group 1,
After forming a zinc anticorrosion film shown in Table 2 on a galvanized steel sheet (EG), a water-soluble and water-dispersible organic resin paint shown in the same table was applied thereon with a bar coater and baked at 150 ° C. An organic paint film was formed. The application amount of the components in the zinc anticorrosion film was measured in the same manner as in Example Group 1 after dissolving and removing the organic paint film with an organic solvent.

The samples thus obtained were subjected to a salt spray test in the same manner as in Example Group 1, and the resistance to blackening and white rust were evaluated on a five-point scale. The results are also shown in Table 2. From the table,
In each of the examples, excellent corrosion resistance to the galvanized film was obtained. In particular, when an organic paint film is formed, sample No.
22 and 24 show that excellent corrosion resistance can be obtained even by adding ultraphosphate ions alone or by adding only two types of ammonium ions and phosphate ions.

[0032]

[Table 2]

Example Group 3 As shown in Table 3 below, an aqueous solution in which predetermined amounts of sodium ultraphosphate and ammonium dihydrogen phosphate were mixed with a water-soluble or water-dispersible organic synthetic resin paint was applied to a bar coater using a bar coater. It was applied to a system-plated steel plate (EG) and baked at 150 ° C. to form an organic paint film containing a zinc anticorrosive component on the surface of the test material. The application amount of the zinc anticorrosion component in the film was measured in the same manner as in Example Group 1 after finely crushing the film and extracting a soluble component with 0.0001 M hydrochloric acid.

The obtained sample was subjected to a salt spray test in the same manner as in Example Group 1, and the resistance to blackening and white rust was evaluated on a five-point scale. The results are shown in Table 3. From the table,
In each of the examples, excellent corrosion resistance to the galvanized film was obtained. In particular, when an organic coating film containing a zinc anticorrosive component is formed, good corrosion resistance can be obtained by adding ultraphosphate ions alone or by adding only two types of ammonium ions and phosphate ions from Nos. 35 and 36. I understand.

[0035]

[Table 3]

[0036]

According to the present invention, a zinc anticorrosion film containing phosphate ions for fixing zinc ions as an essential component is formed on a zinc-based plated steel sheet. Excellent white rust resistance. Moreover, in forming the zinc anticorrosion film, no complicated operation is required, and chromic acid, fluoride, and organic solvent are not used, so that there is no generation of harmful substances, and the operation can be performed with simple equipment. Excellent productivity.

Continued on the front page F term (reference) 4K026 AA02 AA07 AA12 AA13 AA22 BA03 BA12 BB08 BB10 CA16 CA23 CA25 CA36 CA39 DA15 EB08 4K044 AA02 AB02 BA10 BA17 BB03 BC02 CA11 CA16 CA18 CA53

Claims (4)

[Claims] 1. A zinc-based anticorrosion coating is formed on a zinc-based plated steel sheet, and said zinc anticorrosion coating is excellent in corrosion resistance constituted by an inorganic coating containing a phosphate ion, an ammonium ion and a condensed phosphate ion as essential components. Galvanized steel sheet. 2. A zinc anticorrosion coating is formed on a zinc-based plated steel sheet. The zinc anticorrosion coating includes an inorganic coating containing phosphate ions and ammonium ions and / or condensed phosphate ions as essential components, A galvanized steel sheet with excellent corrosion resistance composed of a composite film comprising an organic paint film formed on the film. 3. A zinc corrosion protection film is formed on a galvanized steel sheet, and the zinc corrosion protection film contains a phosphate ion and an ammonium ion and / or a condensed phosphate ion as an essential component in an organic paint. A galvanized steel sheet with excellent corrosion resistance composed of an organic paint film containing components. 4. The zinc ion anticorrosion film contains 0.01 g / m ² or more of phosphate ions and 0.1% of ammonium ions.
01G / m ² or more, superior galvanized steel sheet corrosion resistance according to any one of claims 1 to 3 condensed phosphate ions is 0.04 g / m ² or more.