Chromium-free surface passivation film solution for galvanized sheet as well as preparation method and coating method of chromium-free surface passivation film solution

Abstract

The invention relates to a chromium-free surface passivation film solution for a galvanized sheet as well as a preparation method and a coating method of the chromium-free surface passivation film solution, and belongs to the technical field of passivators. The preparation method of the chromium-free surface passivation film solution for the galvanized sheet comprises the following steps: dissolving vinyltrimethoxysilane in a mixed solution of ethanol and deionized water, and adjusting the pH value of the solution to 2-6 by using 1mol / L acetic acid; and then stearic acid and silver nitrite are added into the prepared vinyl trimethoxy silane solution, stirring is conducted for 20 min at the temperature of 60 DEG C, and the chromium-free surface passivation film solution of the galvanized sheet is obtained. The environment-friendly chromate-free passivating agent is adopted, chromate-free treatment of the hot-dip galvanized surface is achieved, and the excellent performance of a hot-dip galvanized material is kept. The preparation method has the characteristics of simplicity, environmental protection, high efficiency and economy, is suitable for various application fields, such as buildings, automobiles, aerospace and the like, and has important application values and economic benefits.

Description

Technical Field

[0001] The invention relates to the technical field of passivators, and in particular to a chromium-free surface passivation film solution for a galvanized sheet and a preparation method and a coating method thereof. Background Art

[0002] Hot-dip galvanizing is one of the most effective means to delay environmental corrosion of steel materials. It is a commonly used surface protection method. It involves immersing the cleaned and activated steel products in molten zinc liquid. Through the reaction and diffusion between iron and zinc, a zinc alloy coating with good adhesion is plated on the surface of the steel products. Hot-dip galvanizing is widely used in the fields of anti-corrosion and durability of metal materials.

[0003] The traditional hot-dip galvanizing process usually includes the steps of surface preparation, zinc coating formation and passivation treatment. In the passivation treatment, a passivating agent containing chromate is often used to form a chromium compound layer with corrosion resistance and passivation properties. However, the use of chromate passivating agents faces problems such as environmental pollution and safety, because chromium in certain forms is potentially harmful to both the human body and the environment. In order to solve these problems, researchers began to look for alternative chromium-free passivating agents. At present, some methods of chromium-free passivating agents have been proposed, such as titanates, zinc salts and organic complexes. However, there are some limitations when using these passivating agents, such as complex passivation process, unstable passivation effect or high cost. Therefore, it is necessary to develop a simple, environmentally friendly, efficient and economical method for preparing a chromium-free surface passivation film for hot-dip galvanizing. Summary of the invention

[0004] In view of the problems of environmental pollution and safety of existing chromate passivators, the present invention provides a chromium-free surface passivation film solution for galvanized sheet and a preparation method and coating method thereof to solve the above problems. The present invention adopts an environmentally friendly chromium-free passivator to achieve chromium-free treatment of the hot-dip galvanized surface and maintain the excellent performance of the hot-dip galvanized material. The preparation method is simple, environmentally friendly, efficient and economical, and is suitable for various application fields, such as construction, automobiles, aerospace, etc., and has important application value and economic benefits.

[0005] The technical solution of the present invention is as follows: In a first aspect, the present invention provides a method for preparing a chromium-free surface passivation film solution for a galvanized sheet, comprising the following steps: Vinyl trimethoxysilane was dissolved in a mixture of ethanol and deionized water. To ensure that the vinyl trimethoxysilane solution was fully hydrolyzed, it was stirred at 25°C for 48 hours before use. The pH value of the solution was adjusted to 2-6 with 1 mol / L acetic acid. Then, stearic acid and silver nitrite were added to the prepared vinyl trimethoxysilane solution and stirred at 60°C for 20 minutes to obtain a chromium-free surface passivation film solution for galvanized sheet.

[0006] Furthermore, in the vinyltrimethoxysilane solution, the content of vinyltrimethoxysilane accounts for 2% to 7% of the total volume.

[0007] Furthermore, the chromium-free surface passivation film solution of the galvanized sheet also includes cerium nitrate, and the concentration of the cerium nitrate is 0-0.01 mol / L.

[0008] Furthermore, in the chromium-free surface passivation film solution of the galvanized sheet, the concentrations of stearic acid and silver nitrite are 0.03~0.06 mol / L and 0.01~0.04 mol / L, respectively.

[0009] Furthermore, the pH value of the chromium-free surface passivation film solution of the galvanized sheet is 3~6.

[0010] In a second aspect, a chromium-free surface passivation film solution for a galvanized sheet is prepared using the above-mentioned preparation method.

[0011] In a third aspect, the present invention provides a method for coating a passivation film on a galvanized sheet surface, which is as follows: (1) Treatment of galvanized sheet: Grind the galvanized sheet on 80-mesh sandpaper, clean it with clean water, and then grind it with 120-mesh sandpaper until the surface is smooth. The hot-dip galvanized substrate is immersed in 1 mol / L sodium hydroxide solution under ultrasonic conditions for 1 min to hydroxylate the surface.

[0012] (2) Coating of surface passivation film: The galvanized sheet is immersed in a chromium-free surface passivation film solution of the galvanized sheet at room temperature, then taken out, washed with ethanol and dried in air to obtain a hot-dip galvanized chromium-free surface passivation film.

[0013] Furthermore, in step (2), the galvanized sheet is immersed in the chromium-free surface passivation film solution of the galvanized sheet for 300 to 900 seconds.

[0014] The beneficial effects of the present invention are: The present invention adopts vinyl trimethoxysilane as a chromium-free passivating agent, which has a significant improvement in corrosion resistance compared with traditional passivating agents containing chromates. Chromate passivating agents may pollute the environment during use and have potential hazards. The chromium-free passivating agent of the present invention solves the environmental and safety problems of chromate passivating agents and realizes a more environmentally friendly hot-dip galvanizing surface treatment. In addition, the present invention provides a simplified preparation method, including the steps of dissolving silane, adjusting the pH value, adding stearic acid and an aqueous solution containing silver nitrite and hexahydrated cerium (III) nitrate. Compared with some complex preparation processes, the steps of the present method are simple and easy to implement. This not only improves production efficiency, but also reduces preparation costs. The preparation method adopts an environmentally friendly chromium-free passivating agent, which solves the pollution and safety problems of the chromate passivating agent used in the traditional hot-dip galvanizing process. At the same time, the method provides efficient surface passivation treatment while maintaining the excellent performance of the hot-dip galvanizing material. DETAILED DESCRIPTION

[0015] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0016] Example 1 A method for coating a passivation film on a galvanized sheet surface, as follows: (1) Preparation of chromium-free surface passivation film solution for galvanized sheet: Dissolve 1L of vinyltrimethoxysilane in a mixture of 18L of ethanol and 1L of deionized water and stir at 25°C for 48 hours. Adjust the pH value of the solution to 4 with 1mol / L acetic acid. Add 228g of stearic acid, 92g of silver nitrite and 26.5g of cerium (III) nitrate hexahydrate to the above solution and stir magnetically at 60°C for 20min.

[0017] (2) Treatment of galvanized sheet: Grind the galvanized sheet on 80-grit sandpaper, clean it with clean water, and then grind it with 120-grit sandpaper until the surface is smooth. The hot-dip galvanized substrate is immersed in 1 mol / L sodium hydroxide solution under ultrasonic conditions for 1 minute to hydroxylate the surface.

[0018] (3) Preparation of surface passivation film: The sample was immersed in the chromium-free surface passivation film solution of galvanized sheet at room temperature for 600 seconds, then slowly taken out, washed with ethanol and dried in air.

[0019] Example 2 A method for coating a passivation film on a galvanized sheet surface, as follows: (1) Preparation of chromium-free surface passivation film solution for galvanized sheet: Dissolve 1L of vinyl trimethoxysilane in a mixture of 18L of ethanol and 1L of deionized water, and stir at 25°C for 48 hours. Adjust the pH value of the solution to 4 with 1mol / L acetic acid. Add 228g of stearic acid and 92g of silver nitrite to the above solution, and stir magnetically at 60°C for 20min.

[0020] (2) Treatment of galvanized sheet: Grind the galvanized sheet on 80-grit sandpaper, clean it with clean water, and then grind it with 120-grit sandpaper until the surface is smooth. The hot-dip galvanized substrate is immersed in 1 mol / L sodium hydroxide solution under ultrasonic conditions for 1 minute to hydroxylate the surface.

[0021] (3) Preparation of surface passivation film: The sample was immersed in the chromium-free surface passivation film solution of galvanized sheet at room temperature for 600 seconds, then slowly taken out, washed with ethanol and dried in air.

[0022] Example 3 A method for coating a passivation film on a galvanized sheet surface, as follows: (1) Preparation of chromium-free surface passivation film solution for galvanized sheet: Dissolve 1L of vinyltrimethoxysilane in a mixture of 18L of ethanol and 1L of deionized water and stir at 25°C for 48 hours. Adjust the pH value of the solution to 4 with 1mol / L acetic acid. Add 284.5g of stearic acid, 61.5g of silver nitrite and 24.6g of cerium (III) nitrate hexahydrate to the above solution and stir magnetically at 60°C for 20min.

[0023] (2) Treatment of galvanized sheet: Grind the galvanized sheet on 80-grit sandpaper, clean it with clean water, and then grind it with 120-grit sandpaper until the surface is smooth. The hot-dip galvanized substrate is immersed in 1 mol / L sodium hydroxide solution under ultrasonic conditions for 1 minute to hydroxylate the surface.

[0024] (3) Preparation of surface passivation film: The sample was immersed in the chromium-free surface passivation film solution of galvanized sheet at room temperature for 400 seconds, then slowly taken out, washed with ethanol and dried in air.

[0025] Test Case The galvanized sheets with the surface coated with the passivation film prepared in Examples 1 to 3 were compared with the galvanized sheets passivated by chromate. The test method was as follows: the galvanized sheets were sealed with tape, with 1 cm exposed. 2 The flat and smooth coating surface is used as the test area, and the electrochemical workstation uses the three-electrode method for testing. In the test, the reference electrode is a saturated calomel electrode (SCE), the working electrode is a galvanized plate, the auxiliary electrode is a platinum sheet, and the mass fraction of 3.5% NaCl solution is used as the corrosion medium. After data collection, the data is processed using the fitting processing function of the computer software to calculate the corrosion potential (E corr) and self-corrosion current density (I corr ), the test results are shown in Table 1.

[0026] Table 1 - Test results

[0027] It can be seen from the experimental results in Table 1 that the self-corrosion current densities of Example 1 and Example 3 are 2.109×10 -8 and 6.778×10 -8 A / cm 2 , which is 4 orders of magnitude lower than that of a blank galvanized sheet. In the present invention, the surface of the galvanized sheet is coated with a chromium-free surface passivation film solution to form a passivation film, which provides a physical barrier for the galvanized sheet. In addition, the zinc film on the surface of the original galvanized sheet also provides chemical protection for the galvanized sheet, thereby effectively preventing the corrosion of the substrate by oxygen, water and other corrosive media, thereby significantly improving the anti-corrosion performance.

[0028] For the sample of Example 2, no cerium salt was added to modify the chromium-free surface passivation film solution of the galvanized sheet. Compared with Example 1 and Example 3, the corrosion current density increased by 1 order of magnitude, indicating that the chromium-free surface passivation film of the present invention can be modified after adding cerium salt. At the same time, the passivation film prepared by the present invention does not contain chromate that is harmful to the human body, and the corrosion resistance is significantly better than that of the galvanized sheet passivated with chromium salt.

[0029] Comparing the passivation film obtained in the embodiment of the present invention with the unpassivated galvanized steel sheet, it can be clearly found that the corrosion potential of the bare substrate of the sample treated with the cerium-modified silane solution is significantly improved, and the self-corrosion current density is reduced by 4 orders of magnitude.

[0030] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and such modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily conceive of changes or substitutions within the technical scope disclosed by the present invention, and such changes or substitutions shall be within the scope of protection of the present invention.

Claims

1. A method for preparing a chromium-free surface passivation film solution for a galvanized sheet, characterized in that: The following steps are involved: Vinyltrimethoxysilane was dissolved in a mixture of ethanol and deionized water, and the pH value of the solution was adjusted to 2-6 with 1 mol / L acetic acid; then, stearic acid and silver nitrite were added to the prepared vinyltrimethoxysilane solution, and stirred at 60°C for 20 minutes to obtain a chromium-free surface passivation film solution for the galvanized sheet.

2. The method for preparing a chromium-free surface passivation film solution for a galvanized sheet as claimed in claim 1, wherein: In the vinyltrimethoxysilane solution, the content of vinyltrimethoxysilane accounts for 2% to 7% of the total volume.

3. The method for preparing a chromium-free surface passivation film solution for a galvanized sheet as claimed in claim 1, wherein: The chromium-free surface passivation film solution of the galvanized sheet also includes cerium nitrate, and the concentration of cerium nitrate is 0-0.01 mol / L.

4. The method for preparing a chromium-free surface passivation film solution for a galvanized sheet as claimed in claim 1, wherein: In the chromium-free surface passivation film solution of galvanized sheet, the concentration of stearic acid is 0.03~0.06mol / L.

5. The method for preparing a chromium-free surface passivation film solution for a galvanized sheet as claimed in claim 1, wherein: The concentration of silver nitrite in the chromium-free surface passivation film solution of galvanized sheet is 0.01~0.04mol / L.

6. The method for preparing a chromium-free surface passivation film solution for a galvanized sheet as claimed in claim 1, wherein: The pH value of the chromium-free surface passivation film solution of galvanized sheet is 3~6.

7. A chromium-free surface passivation film solution for a galvanized sheet prepared using the preparation method as claimed in claim 1.

8. A method for coating a passivation film on a galvanized sheet surface, characterized in that: The details are as follows: (1) Treatment of galvanized sheet: Grind the galvanized sheet on 80-mesh sandpaper, clean it with clean water, and then grind it with 120-mesh sandpaper until the hot-dip galvanized surface is smooth. Then immerse it in 1 mol / L sodium hydroxide solution under ultrasonic conditions for 1 min to hydroxylate the surface. (2) Coating of surface passivation film: The galvanized sheet is immersed in the chromium-free surface passivation film solution of the galvanized sheet as claimed in claim 7 at room temperature, then taken out, washed with ethanol and dried in air to obtain a hot-dip galvanized chromium-free surface passivation film.

9. The method for coating a passivation film on a galvanized sheet surface as claimed in claim 8, characterized in that: In step (2), the galvanized sheet is immersed in the chromium-free surface passivation film solution of the galvanized sheet for 300 to 900 seconds.

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