Aqueous surface treatment agent, method of surface treatment and surface-treated galvanized steel sheet

Abstract

The present invention provides an aqueous surface treatment agent, a method of surface treatment and a surface-treated galvanized steel sheet. The aqueous surface treatment agent includes organosilicon compound (A) generated from an aminosilane coupling agent (A1), an epoxysilane coupling agent (A2) and an acidic solution (A3), along with a cationic polyurethane resin (B), thereby improving the cross-linking reactivity and storage stability of the aqueous surface treatment agent. Moreover, a coating film formed on a galvanized steel sheet through the method of surface treatment has great solvent resistance and corrosion resistance.

Description

[Technical Field]

[0001] This invention relates to an aqueous surface treatment agent, and more particularly to an aqueous surface treatment agent comprising an organosilicon compound generated by an acidic solution and an aminosilane coupling agent, a surface treatment method, and a surface-treated galvanized steel sheet. [Previous Technology]

[0002] Water-based surface treatment agents can be applied to metal products such as steel, aluminum alloys, or stainless steel to form a uniform and dense protective film on the surface, preventing oxidation, cracking, or corrosion due to long-term use or environmental changes. Therefore, they are widely used in automotive parts, electrical products, and building materials. However, coatings applied to galvanized steel sheets often suffer from poor solvent resistance and corrosion resistance. As a result, when solvents are used to wipe away dirt, oil stains, or marker marks on the coating surface during processing, the coating may peel off or develop color differences (whitening), which in turn affects the corrosion resistance and appearance quality of the product.

[0003] Conventional water-based surface treatment agents improve the solvent resistance of coatings by adding resins with benzene ring structures or using a variety of organic resins as the main components of the coating. However, coatings made from resins containing benzene ring structures are prone to yellowing at high temperatures, making them unsuitable for household appliances with high appearance quality requirements. On the other hand, using large quantities of high-cost organic resins is not cost-effective.

[0004] In view of this, there is an urgent need to provide a new water-based surface treatment agent, surface treatment method and surface-treated galvanized steel sheet to improve the solvent resistance and corrosion resistance of conventional coatings. [Summary of the Invention]

[0005] One aspect of the present invention provides an aqueous surface treatment agent, which is an organosilicone compound generated by an aminosilane coupling agent and an acidic solution having a specific molecular weight and acid dissociation constant, thereby improving the crosslinking reactivity and storage stability of the aqueous surface treatment agent.

[0006] Another aspect of the present invention provides a surface treatment method, which uses the above-mentioned water-based surface treatment agent to form a coating film with good solvent resistance and corrosion resistance on a galvanized steel plate.

[0007] Another aspect of the present invention provides a surface-treated galvanized steel sheet, which is obtained by the above-described surface treatment method.

[0008] According to one aspect of the present invention, an aqueous surface treatment agent is provided, comprising an organosilicone compound (A), wherein the organosilicone compound (A) is obtained by reacting an aminosilane coupling agent (A1), an epoxysilane coupling agent (A2), and an acidic solution (A3), wherein the molecular weight of the acidic solution (A3) is less than 300, and the acidic solution (A3) can dissociate to release at least one hydrogen ion, and the at least one acid dissociation constant (pKa) of the acidic solution (A3) is less than 3; and a cationic polyurethane resin (B).

[0009] According to one embodiment of the present invention, the molar ratio ((a3) / (A1)) of the hydrogen ions (a3) ​​dissociated from the above-mentioned acidic solution (A3) to the aminosilane coupling agent (A1) is 0.9 to 1.1, and the pH value of the aqueous surface treatment agent is 3 to 6.

[0010] According to one embodiment of the present invention, the molar ratio ((A2) / (A1)) of the above-mentioned epoxy silane coupling agent (A2) to amino silane coupling agent (A1) is 2 to 2.5.

[0011] According to one embodiment of the present invention, the total solid content of the above-mentioned water-based surface treatment agent is 100 wt%, and the organosilicone compound (A) is 40 wt% to 65 wt%.

[0012] According to one embodiment of the present invention, the mass ratio ((A) / (B)) of the above-mentioned organosilicone compound (A) to cationic polyurethane resin (B) is 1 to 4.3.

[0013] According to one embodiment of the present invention, the above-mentioned aqueous surface treatment agent further comprises at least one metal compound (C), the metal compound (C) comprising titanium, vanadium, zirconium or a combination thereof, and based on the total solid content of the aqueous surface treatment agent being 100 wt%, the metal compound (C) being 5 wt% to 10 wt%.

[0014] According to one embodiment of the present invention, the above-mentioned aqueous surface treatment agent further comprises olefin wax (D), and based on the total solid content of the aqueous surface treatment agent being 100 wt%, the olefin wax (D) is 4 wt% to 6 wt%.

[0015] According to one embodiment of the present invention, the above-mentioned aqueous surface treatment agent further comprises a phosphorus-containing compound (E), and the total solid content of the aqueous surface treatment agent is 100 wt%, and the phosphorus-containing compound (E) is 6 wt% to 10 wt%.

[0016] According to another aspect of the present invention, a surface treatment method is provided. The method includes first coating the above-mentioned aqueous surface treatment agent onto the surface of a galvanized steel sheet. Next, a drying step is performed on the aqueous surface treatment agent to obtain a dried coating film formed on the galvanized steel sheet.

[0017] According to another aspect of the present invention, a surface-treated galvanized steel sheet is provided, which is obtained by the above-described surface treatment method. The film weight of the aforementioned surface-treated galvanized steel sheet is 0.2 g / m² to 1.5 g / m².

[0018] As described above, the water-based surface treatment agent of the present invention generates an organosilicon compound by reacting an aminosilane coupling agent with an acidic solution having a specific molecular weight and acid dissociation constant, thereby improving the crosslinking reactivity and storage stability of the water-based surface treatment agent. The surface treatment method of the present invention utilizes the water-based surface treatment agent to form a coating film with good solvent resistance and corrosion resistance on a galvanized steel sheet, thereby obtaining a surface-treated galvanized steel sheet.

Implementation Method

[0019] The manufacture and use of embodiments of the present invention will be discussed in detail below. However, it will be understood that the embodiments provide many applicable inventive concepts that can be implemented in a wide variety of specific situations. The specific embodiments discussed are for illustrative purposes only and are not intended to limit the scope of the invention.

[0020] Unless otherwise specified, the numerical ranges mentioned in this invention (such as 10% to 11% of A) include upper and lower limits (i.e., 10% ≤ A ≤ 11%). If the numerical range does not define a lower limit (such as B below 0.2%, or B less than 0.2%), it means that the lower limit may be 0 (i.e., 0% ≤ B ≤ 0.2%). The terms "around," "about," "approximately," or "substantially" as used in this invention generally mean within 20%, 10%, or 5% of the stated value or range. These terms are used to explain and understand this invention, and not to limit it.

[0021] It should be noted that the term "total solids content" as used herein refers to all solid substances contained in the water-based surface treatment agent.

[0022] As described above, the present invention provides an aqueous surface treatment agent that enhances the crosslinking reactivity and storage stability of the aqueous surface treatment agent by generating an organosilicon compound from an aminosilane coupling agent and an acidic solution having a specific molecular weight and acid dissociation constant. The surface treatment method of the present invention utilizes the aqueous surface treatment agent to form a coating film with good solvent resistance and corrosion resistance on a galvanized steel sheet, thereby obtaining a surface-treated galvanized steel sheet.

[0023] The aqueous surface treatment agent of the present invention comprises an organosilicone compound (A) and a cationic polyurethane resin (B). In some embodiments, the organosilicone compound (A) is obtained by reacting an aminosilane coupling agent (A1), an epoxysilane coupling agent (A2), and an acidic solution (A3). Generally, the organosilicone compound (A) comprises a plurality of functional groups (a) and reactive functional groups (b) as shown in formula (I); -SiR1R2R3 (I).

[0024] In formula (I), R1, R2 and R3 each independently represent alkyl, silicaloxy or hydroxyl groups.

[0025] The reactive functional group (b) is selected from at least one of amino, aminonitric acid, aminophosphoric acid, epoxy, and hydroxyl groups. Specifically, the siloxane group (-Si-OR) of the aminosilane coupling agent (A1) and the epoxysilane coupling agent (A2) can first be hydrolyzed to generate silanol (-Si-OH), and then a uniform and dense three-dimensional cross-linked structure of siloxane bonds (-Si-O-Si-) is formed through a condensation reaction. Furthermore, the amino alcohol cross-linked network formed by the ring-opening addition reaction of the epoxy group of the epoxysilane coupling agent and the amino group of the aminosilane coupling agent can further enhance the cross-linking density and mechanical strength of the coating film. In this embodiment, the aminosilane coupling agent (A1) may be, for example, 3-aminopropyltriethoxysilane (AMEO), and the epoxysilane coupling agent (A2) may be, for example, 3-glycidyloxypropyltrimethoxysilane (GLYMO).

[0026] In the above embodiments, the hydrogen ions in the acidic solution (A3) can react with the amino group of the aminosilane coupling agent (A1) through an ionization reaction to form an ammonium salt, and further control the condensation reaction orientation between silane monomers through its steric effect to generate an organosilicon compound (A) with a specific structure, so that the water-based surface treatment agent has better crosslinking reactivity and storage stability, thereby improving the solvent resistance of the coating film.

[0027] In some embodiments, the molecular weight of the acidic solution (A3) is less than 300. If the molecular weight of the acidic solution (A3) is greater than or equal to 300, it will affect the diffusion rate and dispersion uniformity of the molecular acid in the treatment agent, resulting in a decrease in the degree of ionization reaction and making it impossible to effectively control the orientation of the polycondensation reaction between silane monomers.

[0028] In some embodiments, the acidic solution (A3) can dissociate to release at least one hydrogen ion, and the acid dissociation constant (pKa) of at least one acid in the acidic solution (A3) is less than 3. If the acid dissociation constant (pKa) of all hydrogen atoms in the acidic solution (A3) is greater than or equal to 3, the hydrogen ions in the acidic solution (A3) are not easily dissociated or the concentration of hydrogen ions generated by dissociation is too low, making it difficult to combine with aminosilane monomers and effectively control the reaction orientation between silane monomers, and also making it impossible to form organosilicon compounds with specific structures. In this embodiment, the acidic solution (A3) may be, for example, nitric acid or 1-hydroxyethane 1,1-diphosphonic acid (HEDP).

[0029] In some embodiments, in an aqueous surface treatment agent with a pH of about 3 to about 6, the molar ratio ((a3) / (A1)) of the hydrogen ions (a3) ​​dissociated from the acidic solution (A3) to the aminosilane coupling agent (A1) is about 0.9 to about 1.1. When the molar ratio of the hydrogen ions (a3) ​​dissociated from the acidic solution (A3) in the treatment agent with a pH of about 3 to about 6 to the aminosilane coupling agent (A1) is within the aforementioned range, the reaction orientation between silane monomers can be appropriately controlled, and excessive hydrogen ions can be avoided from affecting the crosslinking reactivity of the aqueous surface treatment agent.

[0030] In some embodiments, the molar ratio ((A2) / (A1)) of the epoxy silane coupling agent (A2) to the amino silane coupling agent (A1) is about 2 to about 2.5. Controlling the molar ratio of the epoxy silane coupling agent (A2) to the amino silane coupling agent (A1) within the aforementioned range can appropriately enhance the crosslinking properties, flexibility, and adhesion to metallic materials of the coating film.

[0031] In some embodiments, the total solids content of the aqueous surface treatment agent is 100 wt%, and the organosilicone compound (A) is about 40 wt% to about 65 wt%. When the content of the organosilicone compound is within the aforementioned range, the coating film can have better solvent resistance.

[0032] In the above embodiments, the cationic polyurethane resin (B) may include, but is not limited to, polymers containing aliphatic isocyanates and aliphatic polyols as polymerization units. Its cationic groups can condense with the aminosilane coupling agent (A1) in the organosilicon compound to form a more stable crosslinking structure, which is beneficial to improve the crosslinking density of the water-based surface treatment agent and improve the corrosion resistance and wear resistance of the coating film.

[0033] In some embodiments, the mass ratio of organosilicon compound (A) to cationic polyurethane resin (B) ((A) / (B)) is about 1 to about 4.3. Controlling the mass ratio of organosilicon compound (A) to cationic polyurethane resin (B) within the aforementioned range can improve the solvent resistance of the coating film and also prevent yellowing under high temperature conditions.

[0034] In some embodiments, the aqueous surface treatment agent may selectively include at least one metal compound (C), wherein the metal compound (C) comprises titanium, vanadium, zirconium, or a combination thereof. In this embodiment, the metal compound (C) may be, for example, a metal corrosion-resistant salt of fluorotitanic acid (H2TiF6) or vanadium acetone oxyacetate (VO(acac)2). In some embodiments, based on a total solid content of 100 wt% for the aqueous surface treatment agent, the metal compound (C) comprises about 5 wt% to about 10 wt%. By adding a metal compound within the aforementioned content range, a stable oxide layer can be formed on the coating surface, giving it better corrosion resistance.

[0035] In some embodiments, the aqueous surface treatment agent may selectively include an olefinic wax (D), and based on a total solid content of 100 wt% for the aqueous surface treatment agent, the olefinic wax (D) is approximately 4 wt% to approximately 6 wt%. In this embodiment, the olefinic wax (D) may be, for example, PE wax. By adding an olefinic wax (D) within the aforementioned range, the lubricity of the aqueous surface treatment agent can be increased to prevent wrinkling or breakage during the processing.

[0036] In some embodiments, the aqueous surface treatment agent may selectively include a phosphorus-containing compound (E). This phosphorus-containing compound (E) can act as a "chelating agent" to form chelates with metal ions, preventing the metal ions from binding with each other or forming precipitates with other anions, thereby improving the stability and dispersibility of the metal ions in water. In some specific examples, the phosphorus-containing compound (E) may contain at least one of inorganic ammonium phosphate or organic phosphoric acid. In this embodiment, the phosphorus-containing compound (E) may be, for example, HEDP. In some embodiments, based on a total solids content of 100 wt% for the aqueous surface treatment agent, the phosphorus-containing compound (E) is about 6 wt% to about 10 wt%. Adding a phosphorus-containing compound (E) within the aforementioned range is beneficial for improving the dispersibility of metal ions in water.

[0037] The present invention also provides a surface treatment method. This method involves first coating the surface of a galvanized steel sheet with the aforementioned water-based surface treatment agent. Next, a drying step is performed on the water-based surface treatment agent to obtain a dried coating film on the galvanized steel sheet. In some embodiments, the temperature of the aforementioned drying step can be, for example, from about 60°C to about 90°C. Utilizing this temperature range can effectively remove moisture from the water-based surface treatment agent and increase its cross-linking reaction degree, thereby improving the chemical resistance of the coating film. Furthermore, it can maintain the density of the cured coating film, enhancing its wear resistance and corrosion resistance. In addition, low-temperature drying can reduce process carbon emissions, achieving energy saving and carbon reduction effects.

[0038] The present invention also provides a surface-treated galvanized steel sheet, which is prepared using the above-mentioned water-based surface treatment agent and surface treatment method. In this embodiment, the film weight of the surface-treated galvanized steel sheet is about 0.2 g / m2 to about 1.5 g / m2, which is beneficial for the coating to have better corrosion resistance and yellowing resistance.

[0039] As described above, by utilizing the steric hindrance effect formed when the amino group of the amino silane coupling agent combines with hydrogen ions in a specific acidic solution, the reaction orientation between the silane monomers of the organosilicon compound is controlled, thereby improving the crosslinking reactivity and storage stability of the water-based surface treatment agent. Next, a coating with good solvent resistance and corrosion resistance is formed on the galvanized steel sheet using the water-based surface treatment agent and surface treatment method to obtain a surface-treated galvanized steel sheet.

[0040] The following examples illustrate the application of the present invention, but they are not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention. Example E1

[0041] The solid component of the water-based surface treatment agent of Example E1 includes 50 wt% of an organosilicon compound (A), 30 wt% of a cationic polyurethane resin (B), a metal compound (C) containing 5 wt% of H2TiF6 and 2 wt% of VO(acac)2, 6 wt% of PE wax (olefin wax (D)) and 7 wt% of HEDP (phosphorus-containing compound (E)), and the mass ratio of organosilicon compound (A) to cationic polyurethane resin (B) ((A) / (B)) is 1.7. The organosilicone compound (A) in Example E1 is the organosilicone compound numbered S1, as shown in Table 1. The aminosilane coupling agent (A1) used is 3-aminopropyltriethoxysilane, the epoxysilane coupling agent (A2) is 3-glycidylpropyltrimethoxysilane, and the acidic solution (A3) is nitric acid. The molar ratio ((A2) / (A1)) of the epoxysilane coupling agent (A2) to the aminosilane coupling agent (A1) is 2, and the molar ratio ((a3) / (A1)) of the hydrogen ions (a3) ​​dissociated from the acidic solution (A3) to the aminosilane coupling agent (A1) is 1.1.

[0042] Next, the aqueous surface treatment agent of Example E1 was coated onto the surface of the galvanized steel sheet. Then, a drying step was performed at a temperature of 60°C to 90°C to obtain a dried coating film on the galvanized steel sheet. Subsequently, the solvent resistance, corrosion resistance, yellowing resistance, lubricity, and conductivity of the coating film obtained with the aqueous surface treatment agent of Example E1 were evaluated, and the evaluation results are shown in Table 4 below. Examples E2 to E4 and Comparative Examples C1 to C7

[0043] Examples E2 to E4 and Comparative Examples C1 to C7 used the same surface treatment method as Example E1, which will not be repeated here. The formulation of the aqueous surface treatment agent and the evaluation results of the obtained coating are shown in Tables 1 to 4 below.

[0044] Table 1

[0045] Table 2

[0046] Table 3

[0047] Table 4 Evaluation Methods for Solvent Resistance

[0048] Fix the coating test piece on a friction testing machine. Rub the surface of the test piece 50 times with a cotton gauze ball soaked in ethanol at a load of 1.0 kg / cm². Visually observe the changes in surface appearance. Evaluate the solvent resistance of the coating using the following criteria: ◎: No trace left after wiping; ○: Very few traces left after wiping; △: Slight traces left after wiping; ╳: Noticeably whitened after wiping, the coating dissolves. Corrosion Resistance

[0049] After alkaline washing (immersion in 2% alkaline degreasing agent CLN364S at 65°C for 2 minutes), the flat areas or Erichsen 7 mm extruded areas of the coating test pieces were subjected to a 120-hour or 72-hour salt spray test (SST, according to JIS Z2371 test method) and the area of ​​white rust formation was observed. The corrosion resistance of the coating was evaluated using the following criteria: ◎: The area of ​​white rust formation is less than 1% of the total area; ○: The area of ​​white rust formation is more than 1% and less than 5% of the total area; △: The area of ​​white rust formation is more than 5% and less than 15% of the total area; ╳: The area of ​​white rust formation is more than 15% of the total area. Yellowing resistance

[0050] After baking the coating test pieces at 220℃ for 15 minutes, the color difference ΔE before and after baking was compared using a colorimeter. The yellowing resistance of the coating was evaluated using the following criteria: ◎: ΔE≦2; ○: 2<ΔE≦3; △: 3<ΔE≦4; ╳: ΔE>4. Lubricity

[0051] The coating sample was fixed on a tribometer (Heidon 14S), and a friction test was conducted under the following conditions: the sliding element was a stainless steel ball with a diameter of 10 mm, the load was 200 gf, the sliding speed of the ball was 150 mm / min, the test temperature was 25℃, and the dynamic friction coefficient Fk < 0.2 was evaluated as qualified (○). Conductivity

[0052] Using a Loresta EP MCP-T360 / T610 resistance meter and an ASP probe, the conductivity was measured. Five points were measured at different locations on the same sample. A resistance <10⁻³ Ω was considered conductive, and thus marked as passed. The following criteria were used to evaluate the conductivity of the coating: ◎: Pass at 5 points; ○: Pass at 3 or more points; △: Pass at 2 or more points; ╳: Pass at ≤1 point.

[0053] According to Tables 1 to 4 above, since the content of organosilicon compound (A) in the water-based surface treatment agent of Comparative Example C1 is greater than 65 wt%, the coating film is prone to yellowing under high temperature environment, resulting in a decrease in the corrosion resistance of the coating film. Secondly, compared with Comparative Examples C2, C3 and C4, the coating films of Examples E1, E3 and E4 have better solvent resistance and corrosion resistance, indicating that when the molar ratio of the hydrogen ions (a3) ​​dissociated in the acidic solution (A3) to the aminosilane coupling agent (A1) is within an appropriate range, the reaction orientation between silane monomers can be effectively controlled, so that the coating film has better chemical resistance and long-term corrosion resistance.

[0054] Furthermore, the acid dissociation constant (pKa) of the acidic solution (acetic acid) in Comparative Examples C5 and C6 is greater than 3. Therefore, the hydrogen ions in the acidic solution are not easily dissociated or the concentration of hydrogen ions generated by dissociation is too low, resulting in a lower degree of ionization reaction with the aminosilane coupling agent. This affects the cross-linking reaction between organosilicon compounds, leading to gelation of the coating film and making it impossible to continue testing for solvent resistance, corrosion resistance, and other properties. Although the coating film of Comparative Example C7 did not exhibit gelation, it still could not effectively exert the steric barrier effect and control the reaction orientation between silane monomers because the acid dissociation constant (pKa) of its acidic solution (acetic acid) was greater than 3. Consequently, the solvent resistance and corrosion resistance of the coating film were poor.

[0055] As can be seen from the above embodiments, the water-based surface treatment agent provided by the present invention can generate organosilicon compounds by reacting an aminosilane coupling agent with an acidic solution having a specific molecular weight and acid dissociation constant, thereby improving the crosslinking reactivity and storage stability of the water-based surface treatment agent. Furthermore, by using the water-based surface treatment agent to perform surface treatment on galvanized steel sheets, a coating film with good solvent resistance and corrosion resistance can be formed to obtain surface-treated galvanized steel sheets.

[0056] Although the present invention has been disclosed above by way of embodiments, it is not intended to limit the present invention. Anyone with ordinary knowledge in the technical field to which the present invention pertains may make various modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims. [Simplified Explanation of the Diagram]

[0057] (None) [Biomaterial Storage]

[0059] Domestic storage information (please note in order of storage institution, date, and number): None. International storage information (please note in order of storage country, institution, date, and number): None.

Claims

1. An aqueous surface treatment agent, comprising: An organosilicone compound (A), wherein the organosilicone compound (A) is obtained by reacting an aminosilane coupling agent (A1), an epoxysilane coupling agent (A2), and an acidic solution (A3), wherein the acidic solution (A3) has a molecular weight of less than 300, and the acidic solution (A3) can dissociate to release at least one hydrogen ion, and the acidic solution (A3) has at least one acid dissociation constant (pKa) of less than 3; and a cationic polyurethane resin (B), wherein the cationic polyurethane resin (B) comprises a polymer of an aliphatic isocyanate and an aliphatic polyol.

2. The aqueous surface treatment agent as claimed in claim 1, wherein the molar ratio ((a3) / (A1)) of the hydrogen ions (a3) ​​dissociated from the acidic solution (A3) to one of the aminosilane coupling agents (A1) is 0.9 to 1.1, and the pH value of the aqueous surface treatment agent is 3 to 6.

3. The aqueous surface treatment agent as claimed in claim 1, wherein the molar ratio ((A2) / (A1)) of one of the epoxy silane coupling agent (A2) and the amino silane coupling agent (A1) is 2 to 2.

5.

4. The aqueous surface treatment agent as claimed in claim 1, wherein the total solid content of the aqueous surface treatment agent is 100 wt%, and the organosilicone compound (A) is 40 wt% to 65 wt%.

5. The aqueous surface treatment agent as claimed in claim 1, wherein the mass ratio ((A) / (B)) of the organosilicone compound (A) to the cationic polyurethane resin (B) is 1 to 4.

3.

6. The aqueous surface treatment agent as claimed in claim 1, wherein the aqueous surface treatment agent further comprises at least one metal compound (C), the metal compound (C) comprising titanium, vanadium, zirconium or a combination thereof, and the metal compound (C) comprises 5 wt% to 10 wt% based on the total solid content of the aqueous surface treatment agent being 100 wt%.

7. The aqueous surface treatment agent as claimed in claim 1, wherein the aqueous surface treatment agent further comprises an olefinic wax (D), and the olefinic wax (D) is 4 wt% to 6 wt% based on the total solid content of the aqueous surface treatment agent being 100 wt%.

8. The aqueous surface treatment agent as claimed in claim 1, wherein the aqueous surface treatment agent further comprises a phosphorus-containing compound (E), and the phosphorus-containing compound (E) is 6 wt% to 10 wt% based on the total solid content of the aqueous surface treatment agent being 100 wt%.

9. A surface treatment method comprising: coating a surface of a galvanized steel sheet with an aqueous surface treatment agent according to any one of claims 1 to 8; and performing a drying step on the aqueous surface treatment agent to obtain a dried coating film, wherein the dried coating film is formed on the galvanized steel sheet.

10. A surface-treated galvanized steel sheet, which is obtained by the surface treatment method described in claim 9, wherein the film weight of the surface-treated galvanized steel sheet is from 0.2 g / m2 to 1.5 g / m2.