JPH09170085A - Galvanized steel sheet excellent in corrosion resistance and lubricity and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a galvanized steel sheet having superior corrosion resistance comparable to that obtained by chromate treatment and also having high-degree lubricating property and its production. SOLUTION: This galvanized steel sheet has a lubricating layer, containing two kinds of mercaptide compounds as respective reaction products of undermentioned two kinds of thiol compounds and a plating film of the galvanized steel sheet and a lubricant, on the surface of the galvanized steel sheet: (a) an alkylthiol compound having a thiol group at an end or both ends of a >=8C straight chain alkyl group; (b) trithiocyanuric acid.

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 having excellent corrosion resistance and lubricity and a method for producing the same.

[0002]

2. Description of the Related Art Zinc-based plated steel sheets have hitherto been produced by electroplating or hot dip plating, and are widely used because the corrosion of the base metal can be greatly suppressed by the sacrificial corrosion resistance of the zinc-based plating film. However, zinc-based plated steel sheet produces white zinc rust during its corrosion process,
The appearance quality is greatly reduced. Therefore, in order to suppress the white rust, a chromate treatment mainly containing chromic acid, dichromic acid or salts thereof is performed. This chromate treatment is an economical treatment method that has excellent corrosion resistance and can be performed relatively easily, but it uses hexavalent chromium, and it requires a large amount of equipment for managing the chromate treatment plant and treating wastewater. There is a problem that costs are required.

Further, since the chromate-treated zinc-plated steel sheet has poor lubricity, it is based on animal and vegetable oils, mineral oils or synthetic oils as a rust-preventing lubricating oil at the time of press working, and lubricated by adding an extreme pressure additive or the like thereto. The agent is generally used, but in that case, dechromization treatment of the degreasing liquid containing chromium is indispensable in the degreasing step after processing.

Further, in recent years, there has been a demand for higher press formability for press working materials, and it has become difficult for conventional rust preventive lubricating oils to sufficiently meet such demands. is there.

From the above, many methods have been proposed for preventing white rust on zinc-plated steel sheets without using chromate treatment. For example, there is the following method. (1) A method of coating a polymetal oxide such as molybdenum or tungsten (JP-A-57-5875, etc.) (2) A method of using a treatment liquid containing phytic acid as a main component (JP-B-48-43406) (3) Method using tannic acid (Japanese Patent Publication No. 51-2902)
No.)

However, in the above method (1), the stable region against corrosion of polymetal oxides such as molybdenum and tungsten is narrower than that of chromium, and it is impossible to obtain corrosion resistance comparable to that of a chromate film. In addition, the methods (2) and (3) have considerably poorer corrosion resistance than the chromate coating, and there are problems that the plating surface is colored and the appearance is poor due to the treatment, and the cost of the treatment liquid is high. A possible method of preventing white rust on zinc-based plated steel sheet has not yet been developed.

[0007]

In order to solve the above problems, the present invention has excellent corrosion resistance comparable to that of a chromate-treated zinc-plated steel sheet, and zinc having a high degree of lubricating property. An object is to provide a system-plated steel sheet and a method for manufacturing the same.

[0008]

The invention according to claim 1 contains a mercaptide compound, which is a reaction product of the following two thiol compounds and a galvanized coating, and a lubricant on the surface of a galvanized steel sheet. It is a galvanized steel sheet having excellent corrosion resistance and lubricity, which is characterized by having a lubricating layer. (A) An alkylthiol compound having a thiol group at the terminal or both ends of a linear alkyl group having 8 or more carbon atoms. (B) Trithiocyanuric acid.

In the invention according to claim 2, the following two kinds of thiol compounds are present on the surface of the zinc-plated steel sheet in a molar ratio of alkylthiol compound / (alkylthiol compound + trithiocyanuric acid) of 0.2 to 0.8. The method for producing a zinc-based plated steel sheet excellent in corrosion resistance and lubricity is characterized by applying a lubricant after applying the solution containing in 1. (A) An alkylthiol compound having a thiol group at the terminal or both ends of a linear alkyl group having 8 or more carbon atoms. (B) Trithiocyanuric acid.

In the invention according to claim 3, the following two kinds of thiol compounds are present on the surface of a zinc-based plated steel sheet in a molar ratio of alkylthiol compound / (alkylthiol compound + trithiocyanuric acid) of 0.2 to 0.8. The method for producing a zinc-based plated steel sheet excellent in corrosion resistance and lubricity is characterized by applying the lubricant contained in 1. (A) An alkylthiol compound having a thiol group at the terminal or both ends of a linear alkyl group having 8 or more carbon atoms. (B) Trithiocyanuric acid.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The feature of the present invention is that the surface of a zinc-based plated steel sheet contains an alkylthiol compound and two kinds of mercaptide compounds which are reaction products of trithiocyanuric acid and a galvanized coating, and is excellent in corrosion resistance and lubricity. It is to provide a coating.

Examples of the zinc-based plated steel sheet to which the present invention is applied include hot-dip galvanized steel sheet, electrogalvanized steel sheet, alloyed hot-dip galvanized steel sheet, Zn-Al alloy-plated steel sheet,
Examples include various plated steel sheets such as Al-Zn alloy plated steel sheet.

Each of the materials described above may be, for example, alkali-degreased before forming the lubricating layer.

Although the reason why the galvanized steel sheet of the present invention exhibits excellent corrosion resistance is not always clear, trithiocyanuric acid (2,4,6-trimercapto-s-tri) is used.
It is considered that azine) mainly acts. The structural formula of trithiocyanuric acid is shown in Chemical formula 1.

[0015]

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That is, in the mercaptide compound produced by the reaction between trithiocyanuric acid and the zinc plating film, one or two thiol groups among the three thiol groups of trithiocyanuric acid are zinc or zinc oxides on the surface of the plating film. While reacting with a substance to form a network in the plane direction, the remaining thiol groups crosslink with other thiol groups and accumulate in the direction perpendicular to the steel plate surface.

As a result, it is considered that a three-dimensional dense network of thiol groups is formed on the surface of the plating film, and extremely high corrosion resistance can be obtained.

Further, in the mercaptide compound produced by the reaction between the alkyl thiol compound and the zinc plating film, it is considered that the alkyl group, which is a hydrophobic group, makes the surface of the galvanized steel sheet hydrophobic and plays an auxiliary role of improving the corrosion resistance. To be

Further, although the reason why the galvanized steel sheet of the present invention exhibits excellent lubricity is not always clear, two kinds of reaction products of an alkylthiol compound, both thiol compounds of trithiocyanuric acid, and a galvanized coating are used. Since the mercaptide compound lowers the surface energy of the steel sheet surface, it is considered that extremely high lubricity can be obtained. In particular, the alkyl thiol compound acts to improve the lubricity, and the larger the molecular chain length, the better the lubricity. As the alkyl thiol compound, an alkyl thiol compound having a thiol group at the terminal or both ends of a linear alkyl group having 8 or more carbon atoms is preferable.

Of these, examples of the alkyl thiol compound having a thiol group at the end of the alkyl group include, for example, 1-
Octadecanethiol, 1-hexadecanethiol, 1
Alkyl thiols such as -dodecane thiol and 1-octa thiol can be mentioned, and as an alkyl thiol compound having thiol groups at both ends of an alkyl group, n-decane diol [C ₁₀ H ₂₀ (SH) ₂ ] Can be mentioned.

These thiol compounds have a particularly excellent lubricity-improving effect, and do not cause abnormal appearance due to so-called oil burn.

Since the content of the mercaptide compound in the lubricating layer (the amount of reaction of thiol with respect to the surface of the galvanized steel sheet) is very small, it is difficult to quantitatively measure it. For example, an X-ray electron spectrometer The presence or absence of the mercaptide compound can be confirmed by investigating the states of C, S, O and Zn by using an analysis means such as (XPS). If the content can be confirmed by such means, it is desirable. The effect of improving corrosion resistance and lubricity can be obtained.

The present invention does not prevent the presence of unreacted thiol compound on the surface of the galvanized steel sheet,
Even if such an unreacted thiol compound is present, desired corrosion resistance and lubricity can be obtained as long as the mercaptide compound is produced.

There are no particular restrictions on the type or composition of the lubricant constituting the lubricating layer. Therefore, in the case of lubricating oils, those consisting only of base oils (animal and vegetable oils, mineral oils, synthetic oils, etc.), those with additives for the purpose of improving lubricity added to the base oils, and those for the purpose of improving corrosion resistance to the base oils Any type and composition of lubricant can be used, such as a rust additive added or a base oil added with two or more types of additives for the purpose of improving lubricity and corrosion resistance. Also in this case, a good effect of improving lubricity can be obtained.
However, since the degreasing property of the steel sheet of the present invention mainly depends on the lubricating oil itself, it is preferable to use a lubricant having a good degreasing property.

Other than this, so-called solid lubricants such as fluorine-based wax, polyolefin-based wax,
A difluidized molybdenum or the like can be used.

Since the thiol compound forming the mercaptide compound has a property of being easily oxidized, it is preferable to prevent the oxidant component from being contained in the lubricating oil as much as possible. In some cases, it is desirable to add an antioxidant. .

As a method for forming the above-mentioned coating, a method in which a thiol compound dissolved and diluted with ether, alcohol, water or the like is applied to the surface of the galvanized coating and then a lubricant is applied is generally used. Alternatively, a coating can be formed by mixing a thiol compound with a lubricant and applying this to the surface of the galvanized coating.

The intended coating can be obtained by such a method as well. Even when the thiol compound is mixed in a lubricant and applied to a steel sheet or a plated steel sheet, the thiol compound selectively forms on the surface of the galvanized coating. It is considered that this is because of adsorption and reaction.

It is also possible to use both of the above methods in combination, that is, to apply a solution containing a thiol compound and then apply a lubricant containing a thiol compound.

The mixing ratio of the above-mentioned alkyl thiol compound and trithiocyanuric acid in the solution or lubricant containing the thiol compound is not particularly limited.
When the mixing ratio of (alkyl thiol + trithiocyanuric acid) is less than 0.2 in terms of molar ratio, the effect of improving lubricity is reduced, and when it is more than 0.8, the effect of improving corrosion resistance is reduced, resulting in a balance between the two. Therefore, the mixing ratio is preferably 0.2 to 0.8.

The amount of the thiol compound attached when applied to the surface of the galvanized coating is not particularly limited,
Even if it is excessively adhered, the effect of improving the lubricity is limited, and if it is excessively adhered, abnormal appearance such as so-called oil stain may occur, which is not preferable.

Generally, the acidity of a thiol compound is affected by the size of the alkyl group, and the larger the alkyl group, the smaller the acidity. The thiol compound tends to have a lower acidity in the order of primary>secondary> tertiary.
If the acidity is excessively high, the action of etching the surface of the galvanized coating becomes large, which is not preferable. Therefore,
In consideration of the above, it is preferable to select the structure of the thiol compound according to the material.

[0033]

[Examples] Alloyed hot-dip galvanized steel sheet (plating amount 20 g / m ^{2 on} one side) was used as a raw material steel sheet, and a test material having the following lubricating layer formed on the surface was manufactured to obtain lubricity (friction coefficient). And the corrosion resistance was measured and evaluated. The results are shown in Tables 1, 2 and 3.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

[Table 3]

Example 1 A galvanized steel sheet was immersed in a solution prepared by mixing 1-octadecanethiol and trithiocyanuric acid in a mixed solvent of ethanol and water (4: 1) in a composition shown in Table 1, and then commercially available. The test material was prepared by applying the rust-preventive lubricating oil of.

The test material according to the present invention is No. 1 to No. 3
No. is the test material according to the comparative example. 4, no. 5

(Example 2) The same rust preventive lubricant as that used in Example 1: 1 liter of 1-octadecanethiol and trithiocyanuric acid were mixed in the composition shown in Table 1 to form a rust preventive lubricant galvanized steel sheet. To prepare a test material.

The test material according to the present invention is No. 6-No. 8
No. is the test material according to the comparative example. 9, No. It is 10.

(Conventional Example 3) Example 1 was applied to a galvanized steel sheet.
Specimen No. just coated with the same rust preventive lubricant as used in 11 was produced.

The lubricity is obtained by sandwiching the sample material between the tools made of SKD11 (contact area between the tool and the sample material is 10 m ² ).
The pulling load P when a flat pulling test was performed at a pressing load W of 100 kgf was measured, and this was used to determine the friction coefficient (= P /
(W × 2)) and evaluated as lubricity.

As for the corrosion resistance, assuming a degreasing step after pressing, a commercially available degreasing agent (FC-L4480, manufactured by Nippon Parkerizing Co., Ltd.) was used to perform degreasing by immersing at a concentration of 18 g / l for 2 minutes at 40 ° C. After rinsing, washing with water and drying,
A salt spray test (JIS-Z-2371) was performed, and the test time during which the white rust generation area ratio was suppressed to less than 10% was measured.

According to Tables 1 and 2, the test material No. which is an example of the present invention. 1-3, sample material No. Nos. 6 to 8 have good corrosion resistance and lubricity. Also, 1-octadecanethiol /
Specimen N which is a comparative example in which the molar ratio of the mixing ratio of (1-octadecanethiol + trithiocyanuric acid) is less than 0.2
o. 4, no. Sample No. 9 has a high friction coefficient and is inferior in lubricity as compared with the examples of the present invention. The molar ratio of the above mixing ratio is 0.
Sample material Nos. 5, no. 10 is
Corrosion resistance is remarkably inferior to the examples of the present invention.

Further, in the conventional example shown in Table 3, the test material 11
However, both the lubricity and the corrosion resistance are remarkably inferior to the above-mentioned examples of the present invention.

[0046]

As described above, according to the present invention, it is possible to produce a zinc-based plated steel sheet having both excellent corrosion resistance and lubricity without performing chromate treatment.

Claims (3)

[Claims] 1. A lubricating layer containing a mercaptide compound, which is a reaction product of the following two kinds of thiol compounds and a plating film of a galvanized steel sheet, and a lubricant on the surface of the galvanized steel sheet. Zinc-based plated steel sheet with excellent corrosion resistance and lubricity. (A) An alkylthiol compound having a thiol group at the terminal or both ends of a linear alkyl group having 8 or more carbon atoms. (B) Trithiocyanuric acid. 2. A solution containing, on the surface of a zinc-based plated steel sheet, the following two kinds of thiol compounds in a molar ratio of alkylthiol compound / (alkylthiol compound + trithiocyanuric acid) of 0.2 to 0.8. A method for producing a zinc-based plated steel sheet having excellent corrosion resistance and lubricity, which comprises applying a lubricant after the application. (A) An alkylthiol compound having a thiol group at the terminal or both ends of a linear alkyl group having 8 or more carbon atoms. (B) Trithiocyanuric acid. 3. A lubricant containing the following two thiol compounds on the surface of a zinc-based plated steel sheet in a molar ratio of alkylthiol compound / (alkylthiol compound + trithiocyanuric acid) of 0.2 to 0.8. A method for producing a zinc-based plated steel sheet having excellent corrosion resistance and lubricity, which comprises applying (A) An alkylthiol compound having a thiol group at the terminal or both ends of a linear alkyl group having 8 or more carbon atoms. (B) Trithiocyanuric acid.