JP2002053975A - METHOD FOR DEPOSITING CHROMIUM-FREE CORROSION RESISTANT FILM ON Sn-Zn ALLOY PLATING - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method in which a chemical conversion treatment that does not use chromium exerting influence on the human body and environment is applied on an Sn-Zn alloy plating to deposit a film having corrosion resistance equal to the corrosion resistance obtained by the conventional chromate method. SOLUTION: This method in which a chromate-free film is deposited on an Sn-Zn alloy plating film, includes a stage that a substrate having a Sn-Zn alloy plating film containing 5 to 95 mass% Zn is brought into contact with an aqueous solution containing (1) the slat or oxysalt of at least one kind of metal selected from the groups consisting of Ti, V, Mn, Zr, Mo, W and Si and (2) inorganic acid ions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a chromium-free corrosion-resistant film on a Sn-Zn alloy plating film and an aqueous solution for forming a chromium-free film used therefor.

2. Description of the Related Art In recent years, various alloy platings of zinc and dissimilar metals have been studied for the purpose of improving the corrosion resistance of zinc plating, and have been put to practical use. Among them, Sn—Zn alloy plating has been widely used as industrial plating used for automobile parts, electronic parts, etc. because of its excellent corrosion resistance, salt water resistance, secondary workability, and solderability. This Sn-Z
The n-alloy plating alone does not have sufficient corrosion resistance, and post-plating chromic acid treatment, a so-called chromate treatment, is widely used in the industry. However, in recent years, it has been pointed out that hexavalent chromium has a bad effect on the human body and the environment, and the movement to regulate the use of hexavalent chromium has become active.

[0002]

SUMMARY OF THE INVENTION The present invention relates to a Sn--Zn
An object of the present invention is to provide a method capable of performing a chemical conversion treatment on chromium alloy that does not use chromium, which affects the human body and the environment, and forming a film having corrosion resistance equivalent to that of a conventional chromate. Another object of the present invention is to provide an aqueous solution for forming a chromium-free film used in this method.

SUMMARY OF THE INVENTION The present invention relates to a method for forming a Sn film on a substrate.
The present invention has been made based on the finding that the above problem can be efficiently solved by performing a chemical conversion treatment using a treatment liquid having a specific composition after depositing the Zn alloy plating. That is,
The present invention relates to an S-containing substrate containing 5-95% by mass of Zn.
A substrate having an n-Zn alloy plating film was prepared by (1) Ti,
(2) a salt or oxyacid salt of at least one metal selected from the group consisting of V, Mn, Zr, Mo, W and Si;
A method for forming a chromium-free film on a Sn—Zn alloy plating film, characterized by contacting with an aqueous solution containing an inorganic acid ion. The present invention also provides (1) T
a salt or oxyacid salt of at least one metal selected from the group consisting of i, V, Mn, Zr, Mo, W and Si;
(2) An aqueous solution for forming a chromium-free film on a Sn—Zn alloy plating film, characterized by containing an inorganic acid ion.

[0003]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The substrate used in the present invention includes:
Various metals such as iron, nickel and copper, and their alloys,
Alternatively, various shapes such as a plate-like material of a metal or alloy such as aluminum subjected to a zinc substitution treatment, a rectangular parallelepiped, a cylinder, a cylinder, and a sphere may be used. In the present invention, first, Sn-Z containing 5 to 95% by mass (hereinafter abbreviated as%), preferably 5 to 80% Zn, is formed on a substrate by a conventional method.
Deposit n alloy plating. It is preferable to form a Sn—Zn alloy plating film containing Zn in this range because high corrosion resistance can be imparted to the final product. To deposit the Sn—Zn alloy plating on the substrate, specifically, it is preferable to carry out the method described in JP-A-51-75632. The thickness of the Sn—Zn alloy plating deposited on the substrate can be arbitrarily set, but is preferably 1 μm or more, and more preferably 5 to 20 μm.

[0004] In the present invention, Sn on the substrate in this way
-After depositing Zn alloy plating, for example, washed with water,
(1) a salt or oxyacid salt of at least one metal selected from the group consisting of Ti, V, Mn, Zr, Mo, W and Si; and (2) inorganic acid ions, for example, hydrochloric acid, sulfuric acid, nitric acid,
Contact with an aqueous solution containing one or more of phosphoric acid and salts thereof, for example, immersion treatment using this aqueous solution. Here, (1) As a salt or oxyacid salt of at least one metal selected from the group consisting of Ti, V, Mn, Zr, Mo, W and Si, with respect to Ti, titanium chloride, titanium sulfate, etc. , Manganese chloride, manganese sulfate, permanganate, etc. for Zr, zirconate, etc. for Zr, molybdate, etc. for Mo, tungstate, etc. for W, silicate for Si, etc. Colloidal silica (colloidal silicon oxide) and the like. For various metal concentrations, 0.
It is preferably from 001 to 5 mol / l, more preferably from 0.005 to 0.5 mol / l. When the component (1) is used in this concentration range in the present invention, a stable chemical conversion film can be continuously formed, and excellent corrosion resistance can be obtained. or,
The inorganic acid ion concentration in the aqueous solution is preferably 0.5 to 100 g / liter, more preferably 1 to 50 g / liter. In the present invention, the treatment liquid may further contain an organic acid. It is preferable to include an organic acid because a more uniform and strong chromium-free film is generated. Examples of usable organic acids include, for example, formic acid, acetic acid,
1 to 1 carbon atoms such as propionic acid, butyric acid, valeric acid and benzoic acid
10 monocarboxylic acids, oxalic acid, malonic acid, maleic acid, succinic acid, adipic acid, glutaric acid, dicarboxylic acids having 2 to 10 carbon atoms such as phthalic acid, lactic acid, glycolic acid,
Oxymonocarboxylic acids having 3 to 10 carbon atoms, such as glyceric acid, gluconic acid, β-oxybutyric acid, and salicylic acid, are particularly preferred because of their high effects.

In addition to the above organic acids, oxypolycarboxylic acids such as citric acid, tartaric acid and malic acid, and polycarboxylic acids such as tricarballylic acid are also effective. Here, as the organic acid, the above-mentioned acids or salts thereof (eg, sodium,
One or two or more kinds of salts such as potassium and ammonium) can be used, and the organic acid or a salt thereof is preferably contained in a total amount of 1 to 100 g / l, more preferably 5 to 80 g / l. It is preferable that the pH of the chemical conversion treatment liquid is 0.5 to 7.0. In order to adjust the pH to this range, the above-mentioned inorganic acid and / or organic acid may be used, or an alkali agent such as alkali hydroxide or aqueous ammonia may be used. The remainder of the essential components in the chemical conversion treatment solution used in the present invention is water, and amines such as methylamine, ethylenediamine, diethylenetriamine and the like can be added.

[0006] As a treatment method for forming a chromium-free coating of the Sn-Zn alloy plating according to the present invention, it is general to immerse the alloy plating in the above aqueous solution. For example, 10 to 50
It is preferable to soak at a liquid temperature of 5 ° C. for 5 to 600 seconds, more preferably for 15 to 120 seconds, for example, to form a chromium-free film having a thickness of 0.01 to 3 μm, preferably 0.05 to 1 μm. In addition, in zinc plating, in order to increase the luster of the chromate film, the object to be treated is usually immersed in a dilute nitric acid solution before the chromate treatment. However, in the present invention, such a pretreatment may not be used. Conditions and processing operations other than those described above can be performed according to a conventional chromate treatment method.

Further, by performing an overcoating treatment on the chromium-free film of the present invention, the corrosion resistance can be further improved, and this is a very effective means for imparting more corrosion resistance. For example, first, the above-mentioned chromate-free conversion coating treatment is performed on the Sn-Zn alloy plating, washed with water, immersed in an overcoat treatment liquid, and dried. Further, after the chromate-free chemical conversion coating treatment and drying, it can be newly immersed in an overcoat treatment solution and dried. Here, the overcoat means not only inorganic films such as silicates and phosphates, but also polyethylene, polyvinyl chloride, polystyrene,
Polypropylene, methacrylic resin, polycarbonate,
Polyamide, polyacetal, fluororesin, urea resin,
Organic films such as phenolic resins, unsaturated polyester resins, polyurethanes, alkyd resins, epoxy resins, and melamine resins are also effective. As an overcoat treatment solution for applying such an overcoat, for example, Dipcoat W manufactured by Dipsol Corporation can be used. The thickness of the overcoat film can be arbitrarily set, but is preferably 0.1 to 20 μm.

[0008]

According to the present invention, a chromium-free chemical conversion film can be formed directly on Sn-Zn alloy plating. The plated material obtained by this method has the excellent corrosion resistance of the chromium-free chemical conversion film in addition to the corrosion resistance of the Sn—Zn alloy plating itself. Therefore, Sn-Z
The film obtained by direct chromium-free conversion treatment on the n-alloy plating has the same corrosion resistance, salt water resistance and heat resistance as the conventional hexavalent chromate, and can be bent due to the spreadability of the Sn-Zn alloy plating. Is expected to be widely used in various fields in the future. Next, the present invention will be described with reference to examples and comparative examples.

[0009]

EXAMPLE 1 A steel sheet coated with a Sn—Zn alloy having a different Zn content to a thickness of 8 μm was immersed in a chemical conversion treatment solution shown in Table 1 (bath temperature: 25 ° C.—treatment time: 30 seconds).

[Table 1] Table 1 In the table, Ti, V, Mn, Mo and Si are each Ti
Cl ₃ , NH ₄ VO ₃ , KMnO ₄ , (NH ₄ ) ₆ M ₀₇ O _24.
4H ₂ O, added as Na ₂ SiO ₃ . Also, Cl ^- and SO ₄ ^{2-respectively} TiCl _3, HCl, NaCl, H
₂ SO ₄ and Na ₂ SO ₄ were added. The balance is water.

Example 2 Example 1 After the No. 3 Ti chemical conversion coating treatment, an overcoat treatment was performed. Table 2 shows the overcoat treatment conditions.

[Table 2] Table 2

Comparative Example 1 As a comparative example, a steel sheet plated with 8 μm Sn—Zn alloy was subjected to hexavalent chromate treatment. The hexavalent chromate used was SZ-248S (50 ml / l) manufactured by Dipsol Corporation. Sn-Z obtained in Examples 1 and 2 and Comparative Example
Appearance of n alloy plating and salt spray test (JIS-Z-2
371) The results are summarized in Table 3. As shown in Table 3, even in the case of the coatings of Examples 1 No. 1 to 14, Comparative Example N
As compared with the conventional chromate films of Nos. o1 to o3, the same corrosion resistance was obtained. Further, the film overcoated in Example 2 had better corrosion resistance results than the conventional chromate.

[0012]

[Table 3] Table 3 Salt spray test results (JIS-Z-2371)

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Claims (5)

[Claims] 1. A substrate having a Sn—Zn alloy plating film containing 5 to 95% by mass of Zn on a substrate is prepared by using (1) T
a salt or oxyacid salt of at least one metal selected from the group consisting of i, V, Mn, Zr, Mo, W and Si;
(2) A method of forming a chromium-free film on a Sn—Zn alloy plating film, which is brought into contact with an aqueous solution containing inorganic acid ions. 2. The component (1) is composed of Ti, V, Mn, Zr, M
The method according to claim 1, which is a salt or an oxyacid salt of o, W. 3. The method according to claim 1, wherein the aqueous solution further contains an organic acid. 4. The method according to claim 1, wherein the obtained chromium-free film is further overcoated. 5. It contains (1) a salt or oxyacid salt of at least one metal selected from the group consisting of Ti, V, Mn, Zr, Mo, W and Si, (2) and an inorganic acid ion. An aqueous solution for forming a chromium-free film on a Sn-Zn alloy plating film.