JPH10251864A - Production of galvanized steel sheet excellent in white rust resistance, paint adhesion and alkali-resistant degreasability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the method for producing a galvanized steel sheet having a safe and pollution-free chemically converted film in the production stage and in use and excellent in white rust resistance, paint adhesion and alkali- resistant degreasability. SOLUTION: A soln. contg. a silicic ester and the inorg. salt of aluminum in 0.001 to 0.75 molar ratio of Al to (Al+Si) and contg. 0.01 to 1.0mol of a silane coupling agent per mol of the silicic ester is applied on a galvanized steel sheet at 10 to 1000mg/m<2> , expressed in terms of Al and Si, and then heated and dried.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a galvanized steel sheet having a surface capable of suppressing the generation of white rust on the surface of a zinc-based plating.

[0002]

2. Description of the Related Art Galvanized steel sheets have been widely used because they are conventionally produced by electroplating or hot-dip galvanizing, and the corrosion resistance of ground iron can be largely suppressed by the sacrificial corrosion resistance of the plating film.

[0003] However, zinc-plated steel sheets generate white zinc rust during the corrosion process, and thus the appearance quality is greatly reduced.

Therefore, post-treatment for suppressing the white rust is widely performed. A typical method of this post-treatment is a chromate treatment mainly using chromic acid, dichromic acid or salts thereof.

[0005] This chromate treatment is an economical treatment method which has excellent corrosion resistance and can be performed relatively easily.

However, the chromate treatment uses hexavalent chromium, which is a pollution-controlling substance. In the treatment process, chromate salts have an adverse effect on the human body, and it is difficult to dispose of chromium sludge after wastewater treatment. In addition, there are various problems such as the possibility that hexavalent chromium may be eluted from the product after the chromate treatment. Accordingly, the use control standards for chromic acids have become stricter, and at the same time, problems such as management of a chromate treatment plant, wastewater treatment, and secondary contamination by chromate-treated products have been progressing. At each plant, the wastewater system is closed and chromium ions are prevented from being discharged to the outside as much as possible, and pollution measures are taken, but these require enormous equipment and costs. In addition, when an alkaline degreasing solution is used in the degreasing step of the rust-preventive oil and the press oil of the chromate-treated steel sheet, chromium in particular is considerably eluted.

[0007] In view of the above, a number of pollution-free treatment techniques that do not rely on chromate treatment to prevent the generation of white rust on zinc-based plated steel sheets have been proposed. For example, there is a method in which a thin film is formed by a method such as immersion, coating, or electrolytic treatment using an inorganic compound, an organic compound, an organic polymer material, or a solution in which these are combined.

Specifically, (1) a method using a polymetal oxide such as molybdenum and tungsten (for example, JP-A-57-5875); (2) a method using tannic acid (for example, JP-A-51-5875) −
(3) A pollution-free chromate treatment method that does not contain hexavalent chromium and is composed of trivalent chromium (for example, JP-A-61-587) is known.

However, in the method (1), molybdenum,
The stable area against corrosion of oxides of polymetals such as tungsten is narrower than that of chromium, and it is impossible to obtain the same corrosion resistance as chromate.

In the method (2), if sufficient corrosion resistance is to be obtained, coloring by tannic acid occurs.

Furthermore, the method (3) does not fundamentally meet the need for chromium-free because soluble chromium is used.

Therefore, the inventors of the present invention have a corrosion resistance equal to or higher than that of chromium without containing chromium at all,
In addition, as a result of intensive studies to develop a film having no coloring problem, a method of applying and drying a liquid containing a silicate ester and an inorganic salt of aluminum was developed (Japanese Patent Laid-Open No. Hei 8-2320).
No. 76). This film was harmful as an inorganic film as a substitute for chromate, since white rust resistance equal to or higher than that of chromate was obtained.

[0013]

However, there have been problems such as poor white rust resistance in a salt spray environment and after alkaline degreasing, and insufficient paint adhesion.

The present invention has been made in view of such circumstances, and has a chemical treatment film that is safe and non-polluting in the manufacturing process and further in the use process, and is resistant to white rust, paint adhesion, and alkali. An object of the present invention is to provide a method for producing a zinc-based plated steel sheet having excellent degreasing properties.

[0015]

Means for Solving the Problems The present invention has the following arrangement to solve the above-mentioned problems.

(1) The silicate ester and the inorganic salt of aluminum are mixed in a molar ratio of Al / (Al + Si) of 0.01 to 0.01.
0.75, and a silane coupling agent in an amount of 0.01 to the number of moles of the silicate ester.
The total amount of the solution in terms of Al and the amount in terms of Si is 5 to 1000 mg / m ² of the solution containing the solution in the range of 1 to 1.0 times on the zinc-plated steel sheet. A method for producing a galvanized steel sheet having excellent white rust resistance, paint adhesion, and alkali resistance, characterized by being applied to a substrate and then dried by heating.

(2) The solution may further contain at least one of colloidal silica and fumed silica in a range of 0.01 to 2.0 times the number of moles of the silicate ester. The method for producing a galvanized steel sheet according to the above (1), which is characterized in that:

(3) The method for producing a galvanized steel sheet according to the above (1) or (2), wherein at least one of aluminum nitrate and aluminum chloride is used as the inorganic salt of aluminum.

(4) The method for producing a galvanized steel sheet according to any one of the above (1) to (3), wherein the temperature of the heating and drying is 300 ° C. or less.

The reason that the film obtained by applying a solution of a mixture of a silicate ester and an inorganic salt of aluminum developed by the present inventors has excellent corrosion resistance is not necessarily clear, but the use of a silicate ester is not clear. In the hydrolysis / condensation process, a siloxane bond is formed, and the siloxane bond is formed into a thin film, and the ability to suppress white rust is obtained. Further, the addition of aluminum improves the uniformity and denseness of the film, thereby improving the corrosion resistance. It is thought to be.

In the present invention, by further adding a silane coupling agent to a solution containing a silicate ester and an aluminum inorganic salt, it is possible to improve paint adhesion and further improve white rust resistance such as alkali degreasing. found.

[0022] Cl as a mechanism that can impart such a plurality of effects, Si, by introducing an organic component in the inorganic coating consisting of Al, can form a denser network, a corrosion factor ^- And the like, for example, γ-glycidoxypropyltrimethoxysilane, etc.

Embedded image The functional group represented by can provide more excellent paint adhesion by reacting with the topcoat paint. Generally, the bond of the -Si-O-Si bond in the inorganic substance is easily broken in a strong alkaline environment, It is conceivable that a Si-based inorganic / organic film having high alkali resistance can be formed by introducing a strong organic component into the environment or by introducing a functional group as described above.

[0023]

DETAILED DESCRIPTION OF THE INVENTION As the silicate ester, Si
(OC _n H _{2n + 1)} may be used a compound represented by structure _4. The alkyl group forming the ester preferably has about 1 to 4 carbon atoms, and examples thereof include methyl silicate, ethyl silicate and n-butyl silicate. From the viewpoint of cost, it is desirable to use relatively inexpensive ethyl silicate, but the present invention is not limited to this.

As the inorganic salt of aluminum, various ones such as aluminum nitrate, aluminum chloride and aluminum sulfate can be used. Among them, aluminum nitrate or aluminum chloride is preferable.

The mixing ratio of the inorganic salt of aluminum of the silicate ester is from 0.01 to 0.01 by the molar ratio of Al / (Al + Si).
About 0.75, preferably about 0.1 to 0.5 is appropriate. When the molar ratio is lower than 0.01 and 0.75
This is because, when it is higher than the above range, the corrosion resistance is greatly reduced as compared with the case within the above range, and it is confirmed that the ability to suppress white rust is insufficient. Here, Al / (Al +
The mechanism by which the corrosion resistance is changed by Si) is not clear at present, but it is considered that it depends on the film structure of the obtained Al-Si-based film.

As the silane coupling agent, for example,
Vinyltrimethoxysilane, vinyltriethoxysilane, γ-chloropropyltrimethoxysilane, γ-chloropropylmethyldichlorosilane, γ-chloropropylmethyldimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyl Methyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ
-Mercaptopropyltrimethoxysilane, N- (β-
(Aminoethyl) -γ-aminopropyltrimethoxysilane, N- (β-aminoethyl) -γ-aminopropylmethyldimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, and the like can be used.

The addition amount of these silane coupling agents is about 0.01 to 1.0 times, preferably about 0.05 to 0.5 times, the number of moles of the silicate ester.
If the addition amount is less than 0.01 times the number of moles of the silicate ester, the effect of improving paint adhesion and white rust resistance after alkali degreasing is insufficient. On the other hand, when the ratio is more than 1.0, there is a problem that the stability of the processing solution is poor.

Further, by adding silica in combination with the silane coupling agent, a more excellent white rust resistance after alkali degreasing can be exhibited due to a synergistic effect of the both.

Although silica alone is effective in improving white rust resistance, the bond between the silane coupling agent and the silica and the bond between the silica and the silicate or Al salt due to the coexistence with the silane coupling agent. By bonding the silane coupling agent and the silicate or Al salt, a denser and stronger film is formed, and the number of defects in the film is reduced, thereby significantly improving the white rust resistance after alkali degreasing.

The silica may be either colloidal silica or fumed silica. As the colloidal silica, an organosilica sol MA in which a dispersion medium is an organic solvent is used.
-ST-M, IPA-ST, EG-ST, EG-
ST-ZL, NPC-ST, DMAC-ST, D
MAC-ST-ZL, XBA-ST, MIBK-S
T (manufactured by Nissan Chemical Industries, Ltd.), OSCAL 1132, 1232, 1332, 1432, 1532, 1632,
1722 (manufactured by Catalyst Chemical Industry Co., Ltd.) and the like, but aqueous silica sol such as Snowtex O,
N, 20, 30, 40, C, S, etc. may be added in small amounts.

As the fumed silica, silica whose surface is hydrophobized, for example, AEROSIL R972,
R812, R811, R974, R282, R805
(Manufactured by Nissan Chemical Industries, Ltd.), silica that remains hydrophilic, AEROSIL 130, 200, 200 V, 2
00CF, 300CF, and 300CF (the same) may be used.

The amount of the silica added is about 0.01 to 2.0 times, preferably about 0.025 to 1.0 times, the mole number of the silicate ester. If it is less than 0.025, the effect of improving black spot rust resistance and white rust resistance after alkali degreasing is small. On the other hand, if it is more than 1.0, paint adhesion is undesirably reduced.

The organic solvent used in the above solution is not particularly limited. For example, methanol, ethanol, butanol, propanol, methylcellosolve, ethylcellosolve, ethylcellosolve, butylcellosolve, ethylene glycol, diglycol A solvent capable of dissolving a silicate ester or an aluminum salt such as formaldehyde methoxyethanol can be used, and a non-polar solvent such as 1,4 dioxane is used in combination with a polar solvent such as an alcohol. be able to. Water can also be used in combination with alcohol and the like.

The amount of the solvent used is determined as necessary according to the amount of the film adhered after drying by heating.

The coating amount of the solution is about 5-1000 mg / m ² , preferably 50-1000 mg / m ² , in terms of the total amount of the coating in Al and the coating in Si.
About 1000 mg / m ² , particularly preferably 100 to 10
It is set to be about 00 ms / m ² .

The method for applying the solution is not particularly limited, and examples thereof include a method using a roll coater, a method of dipping in a treatment liquid, and a method of spraying.

After applying the solution as described above, it is heated and dried to form a film.
It affects the corrosion resistance of the Al-Si based coating. The heating temperature is 300 ° C. or less at the plate temperature, preferably about 60 to 200 ° C.,
Particularly preferably, about 70 to 150 ° C. is appropriate. Even if this temperature is 300 ° C. or higher, the ability to inhibit white rust is sufficiently high. However, when the heating temperature is increased to a temperature higher than this temperature, the corrosion resistance tends to decrease. Therefore, the heating temperature is preferably 300 ° C. or lower. The decrease in corrosion resistance when the heating temperature is increased in this way is presumed to be due to an increase in the number of pinholes caused by the rapid evaporation of the organic solvent and an increase in the film peeling area in the processed part due to the hardening of the film. You. In any case, since the treatment of the present invention is a chemical conversion treatment on zinc-based plating, the upper limit of the treatment temperature is defined by the temperature at which the thermal diffusion of the zinc plating and the steel sheet as the substrate occurs rapidly, and is about 350 ° C. Is considered to be the upper limit.

Examples of the zinc-based steel sheet of the present invention include a galvanized steel sheet by electroplating, a zinc-nickel alloy-coated steel sheet, a galvanized steel sheet by hot-dip plating, an alloyed galvanized steel sheet, and an aluminum-zinc-coated steel sheet. Examples include, but are not limited to:

[0039]

EXAMPLES Various zinc-plated steel sheets each having a thickness of 0.7 mm shown in Table 1 were used.

[0040]

[Table 1]

In the chemical conversion treatment solution, ethyl silicate (tetraethoxysilane) as a silicate ester, aluminum chloride or aluminum nitrate as an aluminum inorganic salt, a silane coupling agent shown in Table 2 and a silica as a silica coupling agent are listed in Table 2. The solutions described in Tables 4 to 6 were prepared by using each of those described in No. 3 and using ethyl cellosolve as a solvent.

[0042]

[Table 2]

[0043]

[Table 3]

The surface of each plated steel sheet was degreased with an alkali, and the above-mentioned chemical conversion treatment solution was applied by a roll coater so as to have the adhesion amount shown in Tables 4 to 6. Next, each steel sheet was prepared according to Tables 4-6.
It was dried in a hot air drying furnace under the conditions shown in (1).

Tables 4 to 6 show the results obtained by measuring the white rust resistance, white rust resistance after alkali degreasing, and paint adhesion of each of the chemical conversion-treated steel sheets thus obtained.

[0046]

[Table 4]

[0047]

[Table 5]

[0048]

[Table 6]

The evaluation of each quality performance was performed by the following method.

(1) White rust resistance For each sample, salt spray test (JIS-Z-23)
71) and evaluated by the area ratio of white rust after a predetermined time.
The silica-free film (No. 1-41) was evaluated for white rust resistance after 48 hours, and the silica-containing film (N
o.42-126), since no significant difference appears in 48 hours due to the rust preventive effect of silica, the
Evaluated 2 hours later.

The determination method is as follows. ◎: White rust area ratio less than 5% ○: White rust area ratio 5% or more and less than 25% △: White rust area ratio 25% or more and less than 50% ×: White rust area ratio 50% or more and 100% or less

(2) White rust resistance after alkali degreasing Each sample was subjected to alkali degreasing (“CLN364S” manufactured by Nippon Parkerizing Co., Ltd.), and then subjected to a salt spray test (JIS-Z-2371). The evaluation was based on the white rust area ratio. In addition, a film containing no silica (No. 1)
-41) was evaluated in terms of white rust resistance after 48 hours, and for the film containing silica (No. 42-126), no significant difference appeared in 48 hours due to the rust-preventive effect of silica. Later evaluated.

The criteria are as follows. ◎: White rust area ratio less than 5% ○: White rust area ratio 5% or more and less than 25% △: White rust area ratio 25% or more and less than 50% ×: White rust area ratio 50% or more and 100% or less

(3) Adhesiveness of paint For each sample, a melamine-based baked paint (28
(0 ° C., 60 seconds), immersed in boiling water for 2 hours, cut immediately (10 × 10), and peeled off with cellophane tape. The criteria are as follows.

◎: No peeling ：: Peeling area rate less than 5% Δ: Peeling area rate 5% or more, less than 20% ×: Peeling area rate 20% or more

[0056]

As described above, according to the present invention, a zinc-based plating solution containing a certain range of a silicate ester and an inorganic salt of aluminum and further containing a silane coupling agent in a certain range. By applying it on a steel sheet that has been subjected to heat drying after heating, it is not only excellent in white rust resistance but also excellent in white spray rust under salt spray environment and after alkaline degreasing, and also has good paint adhesion A galvanized steel sheet can be obtained, and the chemical conversion coating thus formed has an industrially significant effect that it is industrially safe and has no pollution.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Masaru Sagiyama 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd.

Claims (4)

[Claims] 1. The method according to claim 1, wherein the silicate ester and the inorganic salt of aluminum are present in a molar ratio of Al / (Al + Si) of 0.01 to 0.7.
5. A zinc-plated steel sheet containing a solution containing a silane coupling agent in a range of 0.01 times to 1.0 times the number of moles of the silicate ester. The coating is performed so that the total amount of the adhesion in terms of Al and the adhesion in terms of Si is applied to a total amount of 5 to 1000 mg / m ² , and then heated and dried. Manufacturing method of galvanized steel sheet with excellent alkali resistance 2. The solution according to claim 1, further comprising at least one of colloidal silica and fumed silica in a range of 0.01 to 2.0 times the number of moles of the silicate ester. The method for producing a galvanized steel sheet according to claim 1. 3. The method according to claim 1, wherein at least one of aluminum nitrate and aluminum hydrochloride is used as the inorganic salt of aluminum. 4. The method for producing a galvanized steel sheet according to claim 1, wherein the heating and drying temperature is set to 300 ° C. or less.