TW201839170A - Surface treatment agent for galvanized steel sheets - Google Patents

Abstract

Provided is a surface treatment agent for galvanized steel sheets, the surface treatment agent having excellent film formability and being capable of providing a coating film having excellent corrosion resistance, chemical resistance, and weather resistance. The surface treatment agent for galvanized steel sheets contains a zirconium compound (A), a chelating agent (B) having at least one hydroxyl group in one molecule, and an organic resin (C) having a carboxyl group (c1), wherein the content of the zirconium compound (A) in the surface treatment agent for galvanized steel sheets is in the range of 200-1000 mass ppm, the molar ratio of elemental zirconium (Zr) derived from the zirconium compound (A) to the chelating agent (B), i.e., (Zr)/(B), is in the range of 4-100, the acid value of the organic resin (C) is in the range of 10-30 mgKOH/g, and the molar ratio of the carboxyl group (c1) to the chelating agent (B), i.e., (c1)/(B), is in the range of 30-1000.

Description

Surface treatment agent for zinc-based plated steel sheet

The invention relates to a surface treatment agent for a zinc-based plated steel sheet.

Conventionally, as a steel sheet excellent in corrosion resistance, a zinc-based plated steel sheet obtained by performing zinc plating, zinc alloy plating, or the like has been used. Such a zinc-based plated steel sheet is oxidized due to contact between the plated layer and air, and white rust is generated. Therefore, it is necessary to prevent the oxidation by increasing the corrosion resistance by performing a surface treatment. In addition, for example, when used outdoors as a building material, weather resistance and chemical resistance of the surface treatment layer are required depending on the application. As such a surface treatment agent, a chromium-based surface treatment agent such as a chromate treatment or a chromium phosphate treatment has been previously applied.

However, since chromium is toxic, from the viewpoint of reducing the environmental load and the cost required for drainage treatment, a chromium-free technology that does not include chromium is being studied. Specifically, the following surface treatment agents are mentioned, which disperse an aqueous resin or the like in water to form an aqueous emulsion, apply coating to the object by roller coating, etc., and fuse them by drying and drying. A coating film can be formed on a zinc-based plated steel sheet.

For example, Patent Document 1 describes a chromium-free surface-treated steel sheet containing, in a specific ratio, one or two or more resins, colloidal silica, a zirconium compound, and triazole / tetrazole, The resin is selected from the group consisting of an acrylic resin, a polyester resin, and an amine ester resin, and has a glass transition temperature of -10 ° C or higher.

Further, Patent Document 2 describes a chromium-free and fluorine-free aqueous metal surface treatment composition in which a certain amount of an organic phosphoric acid compound is added to an aqueous organic resin dispersion liquid containing an anionic amine ester resin (CII). , Colloidal silicon dioxide, vanadium compounds, zirconium carbonate compounds, silane coupling agents and polyolefin waxes.

In addition, Patent Document 3 describes a surface treatment agent for a metal plate that does not contain chromium, and includes a water-based resin having a carboxyl group and an amido bond, one or two or more metal compounds, and a silicon compound. The metal compound is selected from the group consisting of aluminum (Al), magnesium (Mg), calcium (Ca), zinc (Zn), nickel (Ni), cobalt (Co), iron (Fe), zirconium (Zr), and titanium (Ti ), Metal compounds of vanadium (V), tungsten (W), manganese (Mn) and cerium (Ce). [Prior Art Literature] (Patent Literature)

Patent Document 1: Japanese Patent Application Publication No. 2013-237874 Patent Document 2: Japanese Patent Application Publication No. 2014-055319 Patent Document 3: Japanese Patent Application Publication No. 2003-201579

However, these prior chromium-free treatment agents, especially when drying and drying at low temperature and for a short time, may cause insufficient film corrosion resistance due to insufficient film-forming properties, and when applied to In various applications such as chemical resistance, weather resistance, and paint adhesion, performance may be insufficient.

[Problems to be Solved by the Invention] In view of the foregoing, an object of the present invention is to provide a surface treatment agent for a zinc-based plated steel sheet. The surface treatment agent for a zinc-based plated steel sheet is excellent in film-forming properties, and Excellent corrosion resistance, chemical resistance, weather resistance, and paint adhesion. [Technical means to solve the problem]

The present invention relates to a surface treatment agent for a zinc-based plated steel sheet, which comprises a zirconium compound (A), a chelating agent (B) having one or more hydroxyl groups in one molecule, and an organic resin having a carboxyl group (c1). (C); wherein the content of the zirconium compound (A) in the surface treatment agent for zinc-based plated steel sheet is in the range of 200 to 10,000 ppm by mass in terms of zirconium element, and is derived from the zirconium compound (A) The molar ratio of the zirconium element (Zr) to the chelating agent (B) is in the range of (Zr) / (B) = 4 to 100, and the acid value of the organic resin (C) is 10 to 30 mg KOH / g. The molar ratio of the carboxyl group (c1) to the chelating agent (B) is within the range of (c1) / (B) = 30 to 1000.

The organic resin (C) preferably has a hydroxyl group (c2), a hydroxyl value of the organic resin (C) is in a range of 10 to 30 mg KOH / g, and the hydroxyl group (c2) and the chelating agent ( The molar ratio of B) is in the range of (c2) / (B) = 30 to 1000.

The organic resin (C) is preferably at least one selected from the group consisting of an acrylic resin, an amine ester resin, a polyolefin resin, and a vinyl resin.

Moreover, it is preferable that the vanadium compound (D) is contained, and its content is in the range of 20 to 300 ppm by mass in terms of vanadium element.

The titanium compound (E) is preferably contained in a range of 50 to 1,000 mass ppm in terms of titanium element.

The silane coupling agent (F) is preferably contained in an amount of 0.5 to 5% by mass based on the solid content of the organic resin (C).

In addition, it is preferable that silicon oxide (G) is contained, and its content is in the range of 2.0 to 4.0% by mass in terms of silicon dioxide. [Effect of the invention]

According to the present invention, it is possible to provide a surface treatment agent for a zinc-based plated steel sheet which is excellent in film-forming properties and has excellent corrosion resistance, chemical resistance, weather resistance, and coating adhesion.

Hereinafter, embodiments of the present invention will be described. The present invention is not limited to the following embodiments.

<Surface treatment agent for zinc-based plated steel sheets> The surface treatment agent for zinc-based plated steel sheets in this embodiment includes a zirconium compound (A), a chelating agent (B), and an organic resin (C). The surface treatment agent for a zinc-based plated steel sheet in the present embodiment preferably contains a vanadium compound (D), a titanium compound (E), a silane coupling agent (F), silicon oxide (G), or other components (H ). Compared with the conventional surface treatment agent for zinc-based plated steel sheets, the surface treatment agent for zinc-based plated steel sheets of this embodiment is superior in film-forming properties, and has corrosion resistance, chemical resistance, weather resistance, and It is excellent in coating adhesion, and is characterized by the advantage that it can be used suitably as a temporary antirust agent of a zinc-based plated steel sheet.

<Zirconium Compound (A)> The zirconium compound (A) in this embodiment is a compound containing a zirconium element (Zr), and the zirconium compound (A) is based on the mass of the surface treatment agent for a zinc-based plated steel sheet, In terms of zirconium element, the content in the surface treatment agent for zinc-based plated steel sheets is in the range of 200 to 10,000 ppm by mass. Thereby, the zirconium compound (A) can have a function which improves the corrosion resistance of a coating film. More preferably, the content of the zirconium compound (A) in the surface treatment agent for zinc-based plated steel plates is in the range of 335 to 7,500 mass ppm in terms of zirconium element; more preferably, the content is 2000 to 3500 mass Within the ppm range. If the content of the zirconium compound (A) is less than 200 mass ppm, corrosion resistance cannot be sufficiently provided, and if it exceeds 10,000 mass ppm, the flexibility of the film becomes insufficient, and the processing of the coating film becomes dense. Doubts about deterioration of suitability.

The type of the zirconium compound (A) in this embodiment is not particularly limited, and for example, zirconium carbonate, ammonium zirconium carbonate, zirconium borate, zirconium succinate, zirconium sulfate, zirconium nitrate, zirconyl nitrate, fluorinated Zirconium, fluorozirconic acid, ammonium fluorozirconate, ammonium oxyzirconate carbonate, zirconium hydroxide, potassium fluorozirconate, sodium fluorozirconate, dibutyl zirconium dilaurate, dibutyl zirconium dioctoate, zirconium naphthenate , Zirconium octoate, Acetylacetone Zirconium, Zirconium Acetylacetonate, Zirconium Butoxide 1-Butanol Solution, zirconium n-propoxide, and the like. In addition, these zirconium compounds (A) may be used individually by 1 type, and may use 2 or more types together.

<Chelating Agent (B)> The chelating agent (B) in the present embodiment may have one or more molecules per molecule from the viewpoint of the storage stability of the surface treatment agent and the corrosion resistance of the zinc-based plated steel sheet. Hydroxyl. Thereby, since the chelating agent (B) can stabilize and disperse the zirconium compound (A) in the surface treatment agent, a surface treatment agent excellent in storage stability can be obtained. In addition, since aggregation of the zirconium compound (A) can be suppressed, a coating film excellent in corrosion resistance can be formed.

The type of the chelating agent (B) is not particularly limited as long as it has one or more hydroxyl groups in one molecule. For example, 1-hydroxyethane-1,1-diphosphate (1-hydroxyethane 1, 1-diphosphonic acid (HEDP), triethanolamine (TEA), citric acid, gluconic acid, or salts thereof (aluminum citrate, sodium gluconate, etc.). In addition, these chelating agents (B) may be used individually by 1 type, or may use 2 or more types together.

<Organic resin (C)> The organic resin (C) in this embodiment has a carboxyl group (c1). The acid value of the organic resin (C) is in the range of 10 to 30 mg KOH / g. If the acid value is less than 10 mg KOH / g, there will be fewer carboxyl groups that contribute to the stabilization of the resin, and the stability of the surface treatment agent will be reduced. Therefore, it will not only promote thickening or gelation, but also make The adhesion of the film performance to the metal substrate is low. In addition, if the acid value exceeds 30 mg KOH / g, since the carboxyl group also functioning as a hydrophilic group will be excessively present in the film, the surface after the film is formed will be hydrophilic, which results in corrosion resistance, alkali resistance, Boiling water resistance, water resistance, and the like are reduced.

In this embodiment, the organic resin (C) has a hydroxyl group (c2). The hydroxyl value of the organic resin (C) is in the range of 10 to 30 mg KOH / g. If the hydroxyl valence is less than 10 mg KOH / g, it cannot sufficiently function as an adhesive functional group with the top coat coating material, and thus coating adhesion is reduced. If the valence of the hydroxyl group exceeds 30 mg KOH / g, since the hydroxyl group also functioning as a hydrophilic group will be excessively present in the film, the surface after the film formation will be hydrophilic, resulting in corrosion resistance, alkali resistance, Boiling water resistance, water resistance, and the like are reduced.

The organic resin (C) is not particularly limited as long as it has a carboxyl group (c1). For example, it is preferably selected from acrylic resin (CI), amine ester resin (CII), polyolefin resin (CIII), and vinyl. At least one or more of the group consisting of resin (CIV). The organic resin (C) is selected from the group consisting of these resins, and the metal surface treatment composition has good film-forming properties, and can form a coating film excellent in blocking properties, uniformity, and low-temperature drying properties. In addition, the metal surface treatment composition can form a continuous film in the form of a thin film. These resins are also necessary components for ensuring adhesion to a metal surface. Hereinafter, each of the following cases will be described in detail. As the organic resin (C), an acrylic resin (CI), an amine ester resin (CII), a polyolefin resin (CIII), and a vinyl resin (CIV) are each used; Resin (CI) and amine ester resin (CII).

<Acrylic Resin (CI)> When acrylic resin (CI) is used as the organic resin (C), it is preferable that acrylic resin (CI) has either or both of acrylic acid and methacrylic acid as the main component. The resulting copolymer does not have an aromatic structure in the structure. Since acrylic resin (CI) does not have an aromatic structure in the structure, it is possible to form a chemically stable coating film. For example, since deterioration of the coating film due to absorption of ultraviolet light can be suppressed, a coating film excellent in weather resistance can be formed.

Examples of the copolymer of acrylic resin (CI) include derivatives such as methyl acrylate, ethyl acrylate, methyl methacrylate, and ethyl methacrylate, and copolymers with other acrylic monomers. Since it does not have an aromatic structure in the structure, it does not include, for example, an acrylic-styrene copolymer that is generally used.

The acrylic resin (CI) preferably has a core / shell structure, which has a multi-layer structure rather than a generally uniform structure. This is because by using an acrylic resin (CI) having a structurally stiff core portion and a structurally soft shell portion, it becomes easy to take into account properties such as film formability and corrosion resistance of a coating film. A method for producing a core / shell acrylic resin (CI), for example, polymerizable unsaturated monomers that all contain a carboxyl group or polymerizable unsaturated monomers that hardly contain a carboxyl group are subjected to emulsion polymerization, and then a large amount of The acrylic resin (CI) with a core / shell structure can be obtained by carrying out emulsion polymerization of the polymerizable unsaturated monomer component of the polymerizable unsaturated monomer containing a carboxyl group. The bond between the core and the shell can be made, for example, of a polymerizable unsaturated bond derived from allyl acrylate, allyl methacrylate, and the like remaining on the surface of the core to contain a polymerizable unsaturated monomer containing a carboxyl group. The polymerizable unsaturated monomer component is polymerized.

The glass transition temperature (Tg) of the acrylic resin (CI) is 10 ° C to 100 ° C. When the Tg is less than 10 ° C, the formed coating film has insufficient barrier properties against water and chemicals, so a coating film having excellent corrosion resistance and chemical resistance cannot be obtained. On the other hand, when When Tg exceeds 100 ° C., the resin cannot be sufficiently welded at the time of forming the coating film, and thus the film forming properties are deteriorated.

When an amine ester resin (CII) is used as the organic resin (C), the amine ester resin (CII) is preferably a saturated aliphatic amine ester resin obtained by a chemical reaction of a cyclic aliphatic polyol compound and an isocyanate. . The urethane resin (CII) can form a coating film with high corrosion resistance, and can form a coating film that is chemically stable because it does not contain multiple bonds. For example, since degradation of the coating film due to absorption of ultraviolet light can be suppressed, a coating film excellent in weather resistance can be formed.

The cyclic aliphatic polyhydric alcohol compound is not particularly limited, and one polyhydric alcohol or two or more polyhydric alcohols in general can be used. Specific examples of the cyclic aliphatic polyol compound include 1,2-cyclohexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,2-bis (hydroxy Methyl) cyclohexane, hydrogenated bisphenol A, and the like.

The isocyanate compound is not particularly limited as long as it is an isocyanate compound such as a double bond, a triple bond, and an aromatic ring that is not included in the resin skeleton of the amine ester resin (CII) produced. Diisocyanate, other polyisocyanate, Isocyanate. As the diisocyanate, one type of diisocyanate generally used or a mixture of two or more types can be used. Specific examples of the diisocyanate include alicyclic rings such as isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, trans-1,4-cyclohexyl diisocyanate, and norbornene diisocyanate. Diisocyanate of formula; or 1,6-hexyl diisocyanate, 2,2,4-trimethylhexyl diisocyanate, 2,4,4-trimethylhexyl diisocyanate, 2,6-diisocyanate Aliphatic diisocyanates such as methyl hexanoate. The other polyisocyanate is preferably a polyisocyanate having three or more isocyanate groups in one molecule. Examples include the above-mentioned trifunctional isocyanates such as the trimeric isocyanate trimer, diurea trimer, and trimethylolpropane addition compound of the above-mentioned diisocyanates. Modified products such as amine modification, trimer isocyanate modification, and diurea modification are used.

The glass transition temperature (hereinafter referred to as "Tg") of the amine ester resin (CII) is preferably 90 ° C or higher. This is because when the Tg is less than 90 ° C, the formed coating film has insufficient barrier properties against water and chemicals, so a coating film having excellent corrosion resistance and chemical resistance cannot be obtained.

<Olefin Resin (CIII)> As the olefin resin of the organic resin (C), for example, the following water dispersion acrylic resin is used, which is a mixture of ethylene-acrylic acid, methacrylic acid, and maleic anhydride with unsaturated A carboxylic acid copolymer resin (for example, an ethylene-acrylic acid copolymer) is obtained by neutralizing an alkali metal hydroxide such as sodium hydroxide and potassium hydroxide, ammonia, or an organic amine, and dispersing it in water. When the ethylene-acrylic copolymer resin is used, the ethylene content is preferably in a range of 70 to 90% by mass and the content of acrylic acid is in a range of 10 to 30% by mass.

<Ethylene resin (CIV)> When vinyl resin (CIV) is used as the organic resin (C), PVA such as polyvinyl alcohol (PVA), modified PVA such as carboxyl modified PVA, etc. can be used; Cellulose derivatives such as ethyl cellulose and carboxymethyl cellulose; copolymers of α-olefins and unsaturated carboxylic acids such as copolymers of isobutylene and maleic anhydride; or water-soluble substances of derivatives thereof. Moreover, it is suitable to use 1 type or 2 or more types of these vinyl resin (CIV).

<Acrylic resin (CI) and amine ester resin (CII)> When the acrylic resin (CI) and the amine ester resin (CII) are used in combination, the solid content mass ratio of the acrylic resin (CI) and the amine ester resin (CII) is preferred. It is in the range of (CI) / (CII) = 5/95 to 50/50. If the solid content mass ratio of the acrylic resin (CI) and the amine ester resin (CII) is less than 5/95, the weather resistance of the coating film may not be sufficiently obtained in some cases. On the other hand, if the solid content mass ratio of the acrylic resin (CI) and the amine ester resin (CII) exceeds 50/50, the resin's cohesive force will be insufficient and the resin will not be fully welded when the coating film is formed. In some cases, sufficient film-forming properties cannot be obtained.

The difference in the Tg of the resins used in combination (for example, the difference in the Tg of the amine ester resin (CII) and the Tg of the acrylic resin (CI)) is preferably in the range of 40 ° C to 120 ° C. Furthermore, when the acrylic resin (CI) has a core / shell structure, the difference between the Tg of the core portion in the core / shell structure and the Tg of the amine ester resin (CII) is more preferably in the range of 0 ° C to 100 ° C. In addition, the difference between the Tg of the shell portion of the core / shell structure and the Tg of the amine ester resin (CII) is 40 ° C or higher and 120 ° C or lower. If the differences in Tg are outside the above ranges, sufficient film-forming properties may not be obtained, and the corrosion resistance and chemical resistance of the coating film may be poor.

[Ratio of Zirconium Compound (A) / Chelating Agent (B) / Organic Resin (C)] The zirconium compound (A) -derived zirconium element ( The molar ratio (mol ÷ mol) of Zr) to the chelating agent (B) is preferably in the range of (Zr) / (B) = 4 to 100. The molar ratio of the carboxyl group (c1) of the organic resin (C) contained in the surface treatment agent for a zinc-based plated steel sheet in this embodiment to the chelating agent (B) is preferably (c1) / (B) = In the range of 30 to 1,000. The molar ratio of the hydroxyl group (c2) of the organic resin (C) contained in the surface treatment agent for a zinc-based plated steel sheet in this embodiment to the chelating agent (B) is preferably (c2) / (B) = In the range of 30 to 1,000.

If these ratios are outside the above range, sufficient film-forming properties may not be obtained, and the corrosion resistance, chemical resistance, weather resistance, and coating adhesion of the coating film may be poor. For example, if the zirconium compound (A) is excessive with respect to the chelating agent (B), the stability of the zirconium compound (A) will be reduced, and the stability of the treatment agent will not be obtained. As a chelating agent (B) having a specific structure, The coating adhesion exhibited by the effect of) cannot be fully exhibited. Conversely, if the chelating agent (B) is excessive, the chelating agent that contributes to the stabilization of the zirconium compound (A) becomes excessive, the chelating effect becomes saturated, and the film becomes a film that easily absorbs water. Structure, water resistance is reduced, and corrosion resistance, alkali resistance, and boiling water resistance cannot be fully exhibited.

<Vanadium Compound (D)> By further containing the vanadium compound (D) in the surface treatment agent for the zinc-based plated steel sheet in this embodiment, a coating film having improved corrosion resistance can be formed.

The type of the vanadium compound (D) used in this embodiment is not particularly limited. For example, vanadium acid and its salts, vanadium oxide, vanadium trichloride, vanadium oxytrichloride, and acetoacetic acid are preferably used. Vanadium, vanadyl acetate, vanadium sulfate, vanadium sulfate, vanadium nitrate, vanadium phosphate, vanadium acetate, vanadium dihydrogen phosphate, vanadium alkoxide, vanadium oxyalkoxide, etc. Among these, a compound having an oxidation number of 5 of vanadium is preferably used, and specifically, metavanadic acid and its salt, vanadium oxide, vanadium oxytrichloride, vanadium alkoxide, vanadium oxyalkoxide .

In this embodiment, it is preferable that the surface treatment agent for zinc-based plated steel sheets contains a vanadium compound (D), and the content of the surface treatment agent for zinc-based plated steel sheets is 20 to 60 in terms of vanadium. 300 mass ppm. The surface treatment agent can improve the corrosion resistance when the content of the vanadium compound (D) is in the range of 20 to 300 mass ppm.

<Titanium Compound (E)> By further containing the titanium compound (E) as the surface treatment agent for the zinc-based plated steel sheet in this embodiment, the performance of the coating film can be further improved.

The type of the titanium compound (E) used in this embodiment is not particularly limited, and examples thereof include titanium oxide (IV) (titanium dioxide), titanium nitrate, zirconyl acetate zirconium sulfate (III), titanium sulfate, and titanium fluoride (III), titanium (IV) fluoride, hexafluorotitanate (H ₂ TiF ₆ ), ammonium hexafluorotitanate, tetraisopropyl titanate, tetra-n-butyl titanate, tetraoctyl titanate, acetamidine Titanium acetone, titanium octyl glycolate, titanium lactate, titanium ethyl lactate, titanium triethanolamine, titanium tetraisopropoxide, titanium tetra-n-butoxide, tetra-2-ethyltitanium oxide, diisopropoxybis (Ethylacetone) titanium, titanium tetraacetamidine acetone, titanium dioctyl bis (octyl glycolate), titanium diisopropoxy (ethylacetone) titanium, diisopropoxy bis (triethanolamine) ) Titanium, titanium laurate, titanium aluminum lactate, titanium diisopropoxide, diacetone, titanium acetoacetone and the like. These can be acid anhydrides or hydrates. These compounds may be used alone or in combination of two or more.

In this embodiment, it is preferable that the surface treatment agent for zinc-based plated steel sheets contains a titanium compound (E), and the content thereof is 50 to 50% in terms of titanium based on the mass of the surface treatment agent for zinc-based plated steel sheets. Within the range of 1000 mass ppm. If the content of the titanium compound (E) is less than 50 mass ppm, the amount of titanium contained in the film is insufficient, and it is difficult to form a blocking film generated by the bonding of Ti-O-Ti. Alkalinity and corrosion resistance are reduced. If the content of the titanium compound (E) exceeds 1,000 mass ppm, the corrosion resistance is still fully exhibited, but the stability of the treatment liquid is reduced.

<Silane coupling agent (F)> The silane coupling agent (F) in the present embodiment can function as a cross-linking agent for the organic resin (C), and can represent the relationship between the zinc-based plated steel sheet and the coating film. The adhesive effect has the function of improving the adhesion of the coating film and improving the corrosion resistance.

The type of the silane coupling agent (F) used in this embodiment is not particularly limited, and for example, vinyl methoxysilane, vinyltrimethoxysilane, vinylethoxysilane, and vinyltrisiloxane are preferably used. Ethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-methacryloxypropyl Trimethoxysilane, 3-mercaptopropyltrimethoxysilane, N- (1,3-dimethylbutylene) -3- (triethoxysilyl) -1-propylamine, N, N'-bis [3- (Trimethoxysilyl) propyl] ethylenediamine, N- (β-aminoethyl) -γ-aminopropylmethyldimethoxysilane, N- (β-aminoethyl) -γ-aminopropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-epoxy Propoxypropyltriethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, γ- Methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-mercaptopropane Trimethoxy Silane, γ- mercaptopropyl triethoxy Silane, N- [2- (vinylbenzyl amino) ethyl] -3-aminopropyl trimethoxy Silane like.

In addition, these silane coupling agents (F) may be used individually by 1 type, or may use 2 or more types together, and may use the hydrolysis condensation product of these silane coupling agents, or the mixture of a silane coupling agent and its hydrolysis condensation product.

In this embodiment, it is preferable that the surface treatment agent for zinc-based plated steel sheets contains a silane coupling agent (F), and its content is in the range of 0.5 to 5 mass% based on the solid content of the organic resin particles (C). Inside. As the surface treatment agent, when the content of the silane coupling agent (F) is in the range of 0.5 to 5% by mass, sufficient film-forming properties can be obtained, and a coating film excellent in corrosion resistance and chemical resistance can be formed.

<Silicon Oxide (G)> When the surface treatment agent for zinc-based plated steel sheets in this embodiment further contains silicon oxide (G), the performance of the coating film can be further improved.

The shape of the silicon oxide (G) used in the present invention is not particularly limited, and it is preferably a granular silicon oxide, more preferably a silicon oxide having a number of primary particles having an average particle diameter of 5 to 50 nm, and further preferably 5 ~ 20nm. Such silica (G) can be appropriately selected and used from colloidal silica and fumed silica. Specific examples of silicon oxide (G) include SNOWTEX N and SNOWTEX C (manufactured by Nissan Chemical Industries); ADELITE AT-20N and AT-20A (manufactured by ADEKA); and Cataloid S-20L, Cataloid SA ( Niwa Catalyst Co., Ltd.) and so on. These silicon oxides (G) may be used alone or in combination of two or more kinds. The number-average particle diameter of the primary particles of silicon oxide (G) can be determined by observation with an electron microscope. In this embodiment, it is preferable that the surface treatment agent for a zinc-based plated steel sheet contains silicon oxide (G), and its content is in the range of 2.0 to 4.0% by mass in terms of silicon dioxide. As long as the content of silicon oxide (G) is less than 2.0% by mass, sufficient coating film properties cannot be obtained, and in particular, corrosion resistance and substrate adhesion cannot be obtained. Moreover, from the viewpoint of adjusting the balance with the content of other components to make the effect of the present invention good, the content of silicon oxide (G) is 4.0% by mass or less.

<Other components (H)> The surface treatment agent of the present embodiment may further contain other components within a range that does not impede the above functions depending on the function to be added. For example, tannic acid or a salt thereof, phytic acid or a salt thereof; and other water-based resins, such as epoxy resins, ethylene acrylic acid copolymers, polyester resins, polyolefin resins, alkyd resins, and polymers Carbonate resin and the like. These water-based resins may be used alone, or two or more of them may be used in combination, and copolymerization may be used. In addition, in order to improve the film forming property and form a more uniform and smooth coating film, an organic solvent may be used. In addition, a leveling agent, a wettability enhancer, and an antifoaming agent can be used.

<Zinc-based plated steel sheet> The zinc-based plated steel sheet using the surface treatment agent in this embodiment as a temporary rust inhibitor is widely used as a steel sheet having high corrosion resistance. The zinc plating and zinc alloy plating are collectively referred to herein as "zinc-based plating." The zinc-based plated steel sheet to which the surface treatment agent of this embodiment can be used is not particularly limited, and examples thereof include zinc or zinc-based alloy plating such as zinc-based electrolytic plating, fusion plating, and vapor-deposited steel sheets. Steel plates, etc., which are zinc plated steel plates, zinc-nickel plated steel plates, zinc-iron plated steel plates, zinc-chrome plated steel plates, zinc-aluminum plated steel plates, zinc-titanium plated steel plates, zinc-magnesium plated Steel plates, zinc-manganese plated steel plates, etc. Among them, zinc-55wt% aluminum alloy plated steel plate (Galvalume steel plate (registered trademark)) has high corrosion resistance and can be preferably used.

The method for producing the surface treatment agent in this embodiment is not particularly limited. For example, the zirconium compound (A) and the chelating agent (B) can be mixed and stirred in advance to stabilize the zirconium compound (A), and then The zirconium compound (A) and the chelating agent (B) were poured into the organic resin (C) while being stirred, and then diluted and prepared.

The method for applying the surface treatment agent to the zinc-based plated steel sheet in this embodiment is not particularly limited, and for example, the surface treatment agent may be applied to the zinc-based plated steel sheet, and after the application, heating may be performed. Let's dry the coating. Alternatively, a method may be adopted in which the zinc-based plated steel sheet is heated in advance, and the surface treatment agent is then applied to be dried with residual heat.

The method for applying the surface treatment agent is not particularly limited, and can be applied by roll coating, shower coating, spraying, dipping, brush coating, or the like. In addition, it is preferable to use a coating method by roll coating in a common roll coating production line. The surface treatment agent in this embodiment has a film-forming property even when a roll coating is considered. Excellent. The heating and drying conditions of the surface treatment agent described above preferably have a maximum material temperature (hereinafter referred to as PMT) of 20 to 250 ° C, and more preferably 50 to 220 ° C. The heating temperature is 50 ° C or higher. Since the evaporation rate of water is fast and sufficient film-forming properties can be ensured, corrosion resistance and alkali resistance can be improved. On the other hand, if the PMT exceeds 250 ° C., the components in the formed coating film may be decomposed due to the high temperature, and thus the adhesion and corrosion resistance may be poor. In addition, even if the PMT is dried by evaporating water under a low temperature condition of about 20 ° C, a film having sufficiently excellent performance can be formed. The coating amount of the surface treatment agent is preferably such that the film thickness of the coating film is about 0.5 to 3.0 μm. If the film thickness is thinner than the above range, the corrosion resistance will be insufficient. On the other hand, if the film thickness is too thick, the workability and adhesiveness are reduced, and it is not economical.

As described above, the surface treatment agent for a zinc-based plated steel sheet in the present embodiment includes a zirconium compound (A), a chelating agent (B) having one or more hydroxyl groups in one molecule, and a chelating agent having a carboxyl group (c1). Organic resin (C); wherein the content of the zirconium compound (A) in terms of zirconium element in the surface treatment agent for zinc-based plated steel sheets is in the range of 200 to 10,000 ppm by mass; derived from the zirconium compound (A) The molar ratio of the zirconium element (Zr) to the chelating agent (B) is in the range of (Zr) / (B) = 4 to 100, and the acid value of the organic resin (C) is in the range of 10 to 30 mg KOH / g The molar ratio of the carboxyl group (c1) to the chelating agent (B) is in a range of (c1) / (B) = 30 to 1000. Thereby, the metal surface treatment composition is excellent in film-forming property, and a coating film excellent in chemical resistance, weather resistance, and paintability can be formed on a zinc-based plated steel sheet.

The organic resin (C) has a hydroxyl group (c2), the hydroxyl value of the organic resin (C) is in a range of 10 to 30 mg KOH / g, and the molar ratio of the hydroxyl group (c2) to the chelating agent (B) is ( c2) / (B) = The range is 30-1000. Since the zirconium compound (A) can be stabilized by a hydroxyl-containing organic resin, a chelating agent, and the like, the chelating agent (B) can exhibit coating adhesion and further use an organic resin having a hydroxyl group ( C) Coating adhesion can be further improved. Further, by using the organic resin (C) having a hydroxyl group, it is possible to improve the compatibility with the chelating agent, the organic resin, and the surface coating film. The effect of the organic resin (C) having a hydroxyl group as described above can be fully exhibited as long as the molar ratio of the hydroxyl group (c2) to the chelating agent (B) is in the range of (c2) / (B) = 30 to 1000. Thereby, the metal surface treatment composition can form a coating film excellent in coating adhesion especially.

The organic resin (C) is at least one or more selected from the group consisting of an acrylic resin, an amine ester resin, a polyolefin resin, and a vinyl-based resin. Thereby, the metal surface treatment composition is excellent in film-forming property, and in particular, a coating film having excellent blocking properties, uniformity, and low-temperature drying properties can be formed. Moreover, a continuous film can be formed in the form of a thin film.

The surface treatment agent for zinc-based plated steel sheets contains a vanadium compound (D), and its content is within a range of 20 to 300 ppm by mass in terms of vanadium element. The surface treatment agent for a zinc-based plated steel sheet contains a titanium compound (E), and its content is within a range of 50 to 1,000 mass ppm in terms of titanium element conversion. The surface treatment agent for a zinc-based plated steel sheet contains a silane coupling agent (F), and its content is within a range of 0.5 to 5% by mass based on the solid content of the organic resin (C). The surface treatment agent for zinc-based plated steel sheets contains silicon oxide (G), and its content is in the range of 2.0 to 4.0% by mass in terms of silicon dioxide. Thereby, the metal surface treatment composition can form a coating film excellent in corrosion resistance in particular. [Example]

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

<Production Examples and Coating Examples of Surface Treatment Agents> [Examples 1 to 26] The zirconium compound (A) and the chelating agent (B) were mixed and stirred in advance, and the zirconium compound (A) was first stabilized. While stirring the zirconium compound (A) and the chelating agent (B), the zirconium compound (A) and the chelating agent (B) were poured into an organic resin (C), and diluted and prepared to obtain a surface treatment agent described in Table 1. Regarding the resin (C), a single resin was used for Examples 1 to 20. On the other hand, for Examples 21 to 26, a plurality of resins were used, which were mixed in a combination and ratio of the types shown in Table 1.

[Table 1]

Each material in Table 1 is the following. [Zirconium compound (A)] A1: Zircosol AC-7 A2: Zirconium nitrate A3: Ammonium zirconium fluoride

[Chelating agent (B)] B1: HEDP B2: TEA B3: ammonium citrate B4: sodium gluconate

[Organic resin (C)] C1: An acrylic resin having an acid value of 20 mg KOH / g and a hydroxyl value of 20 mg KOH / g. C2: An acrylic resin having an acid value of 10 mg KOH / g and a hydroxyl value of 20 mg KOH / g. C3: An acrylic resin having an acid value of 30 mg KOH / g and a hydroxyl value of 20 mg KOH / g. C4: An acrylic resin having an acid value of 20 mg KOH / g and having no hydroxyl group (c2). C5: An acrylic resin having an acid value of 20 mg KOH / g and a hydroxyl value of 30 mg KOH / g. C6: An acrylic resin having an acid value of 20 mg KOH / g and a hydroxyl value of 10 mg KOH / g. C7: An acrylic resin having an acid value of 10 mg KOH / g and a hydroxyl value of 5 mg KOH / g. C8: An amine ester resin having an acid value of 20 mg KOH / g and having no hydroxyl group (c2). C9: An olefin resin having an acid value of 25 mg KOH / g and having no hydroxyl group (c2). C10: A vinyl acetate resin having an acid value of 20 mg KOH / g and having no hydroxyl group (c2).

[Examples 27 to 54] The zirconium compound (A) and the chelating agent (B) were previously mixed and stirred to stabilize the zirconium compound (A). The organic resin (C) was stirred. For Examples 27 to 31, 47 to 50, 53 and 54, a vanadium compound (D) was added to the organic resin (C) and stirred. For Examples 32 to 36 and 48 to 50, a titanium compound (E) was further added and stirred. For Examples 38 to 41, 49, and 50, a silane coupling agent (F) was further added and stirred. For Examples 42 to 46 and 50 to 52, silicon oxide (G) was further added and stirred. The zirconium compound (A) and the chelating agent (B) were further added to the organic resin (C), stirred, diluted, and prepared to obtain the surface treatment agents described in Table 2.

[Table 2]

Each of the materials appearing for the first time in Table 2 is the following. [Vanadium compound (D)] D1: ammonium metavanadate (manufactured by Shin Hing Chemical Industry Co., Ltd.). D2: Sodium metavanadate (manufactured by Xinxing Chemical Industry Co., Ltd.). D3: vanadyl sulfate (manufactured by Xinxing Chemical Industry Co., Ltd.). D4: Acetylacetone vanadylacetate (manufactured by Xinxing Chemical Industry Co., Ltd.).

[Titanium compound (E)] E1: ammonium fluoride titanate (manufactured by Morita Chemical Industry Co., Ltd.). E2: TC400 (product model, manufactured by Matsumoto Precision Chemical Co., Ltd.). E3: T-50 (product model, manufactured by Soda Co., Ltd.).

[Silane coupling agent (F)] F1: 3-glycidoxypropyltrimethoxysilane (made by Shin-Etsu Chemical Industry Co., Ltd.). F2: 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane (manufactured by Shin Hing Chemical Industry Co., Ltd.). F3: N-2- (aminoethyl) -3-aminopropyltrimethylsilane (manufactured by Shin Hing Chemical Industry Co., Ltd.). F4: 3-aminopropyltrimethylsilane (manufactured by Shin Hing Chemical Industry Co., Ltd.).

[Silicon oxide (G)] G1: ST-N (product model, manufactured by Nissan Chemical Co., Ltd.). G2: AT-20A (product model, manufactured by ADEKA Corporation). G3: ST-C (product model, manufactured by Nissan Chemical Co., Ltd.).

[Comparative Examples 1 to 16] In Comparative Example 1, a zirconium compound (A) was added to the organic resin (C), stirred, and diluted and prepared to obtain the surface treatment agents described in Table 3. In Comparative Examples 2, 3, 5 to 7, and 9 to 12, the zirconium compound (A) and the chelating agent (B) were previously mixed and stirred to stabilize the zirconium compound (A). A zirconium compound (A) and a chelating agent (B) were added to the organic resin (C), stirred, diluted, and prepared to obtain the surface treatment agent described in Table 3. Regarding Comparative Examples 4 and 13 to 16, a chelating agent (B) was added to the organic resin (C), stirred, diluted, and prepared to obtain the surface treatment agents described in Table 3. With respect to Comparative Example 8, the zirconium compound (A) and the chelating agent (B) were stirred, diluted, and prepared to obtain a surface treatment agent described in Table 3.

[table 3]

The first materials in Table 3 are the following

[Chelator (B)] B5: EDTA (ethylenediaminetetraacetic acid) In addition, the B5 (EDTA) does not have one or more hydroxyl groups in one molecule.

[Organic resin (C)] C11: An acrylic resin having an acid value of 5 mg KOH / g and a hydroxyl value of 20 mg KOH / g. C12: An acrylic resin having an acid value of 40 mg KOH / g and a hydroxyl value of 20 mg KOH / g.

<Storage stability> The surface-treating agents for the zinc-based plated steel sheets of each of the Examples and Comparative Examples were allowed to stand in a constant-temperature bath at 40 ° C, and the storage time for the longest time to 3 months was evaluated based on the following criteria. Liquid state. The results are shown in Table 4. 1: In the treating agent held at 40 ° C for 3 months, no precipitate, thickening, etc. were generated. 2: In the treatment agent held at 40 ° C for one month, no precipitate, thickening, etc. occurred. 3: In the treatment agent maintained at 40 ° C for one week, precipitates, thickening, and the like were generated. 4: Gelation occurred in the treatment agent during one week of holding at 40 ° C. As shown in Table 4, it was confirmed that the surface treatment agents of all the examples satisfies a higher storage stability than the evaluation criteria (1 or 2) higher than the evaluation 2.

Using the surface treatment agents described in Tables 1 to 3, a test plate for each test evaluation was prepared by the following method. Using a commercially available alkaline degreasing agent ("SURF CLEANER 53S" manufactured by Nitto Co., Ltd.), each of the steel materials described in Tables 1 to 3 was spray-treated at 60 ° C for 2 minutes to degrease, washed with water, and After drying, the surface treatment agents of Examples and Comparative Examples were applied with a bar coater so that the film thickness after drying became 1 to 2 μm. After that, the material was dried so that the material reached a maximum temperature of 80 ° C. to obtain a test plate. The steel materials described in Tables 1 to 3 are as follows. GL: molten 55% aluminum / zinc plated steel sheet (Galvalume steel sheet (registered trademark)). GI: molten zinc-plated steel sheet. EG: electrolytic zinc plated steel sheet. GF: molten 5% aluminum / zinc alloy plated steel sheet. ZL: electrolytic zinc-10% nickel alloy plated steel plate

<Corrosion resistance of the flat portion> The end portion and the back surface of the test plate were sealed with an adhesive tape to perform a salt spray test SST (Japanese Industrial Standard JIS-Z-2371). The occurrence of white rust after 240 hours was observed and evaluated based on the following criteria. The results are shown in Table 4. 1: No white rust was generated. 2: The area where white rust is generated is less than 10%. 3: The area where white rust is generated is 10% or more and less than 30%. 4: The area where white rust is generated is 30% or more. As shown in Table 4, it was confirmed that the test plate of all the examples satisfies the high level of the corrosion resistance of the flat portion such that it satisfies the higher evaluation criterion (1 or 2) than the evaluation 2.

<Corrosion resistance after alkaline degreasing> While agitating a 2% aqueous solution (pH 12.5) of an alkaline degreasing agent (SURF CLEANER 155, manufactured by Nippon Paint Co., Ltd.) at 60 ° C for 2 minutes, The end portion and the back surface of the test plate were sealed with an adhesive tape to perform a salt spray test SST (Japanese Industrial Standard JIS-Z-2371). The occurrence of white rust after 96 hours was observed and evaluated based on the following criteria. The results are shown in Table 4. 1: No white rust was generated. 2: The area where white rust is generated is less than 10%. 3: The area where white rust is generated is 10% or more and less than 30%. 4: The area where white rust is generated is 30% or more. As shown in Table 4, it was confirmed that the corrosion resistance after degreasing as high as the evaluation criterion (1 or 2) higher than the evaluation 2 was satisfied for the test plates of all the examples.

<Corrosion resistance of the processing section> The test plate was subjected to 7 mm indentation in an Erichsen tester, and then the end and the back of the test plate were sealed with tape to perform a salt spray test SST (Japanese Industrial Standard) JIS-Z-2371). The occurrence of white rust after 120 hours was observed and evaluated based on the following criteria. The results are shown in Table 4. 1: No white rust was generated. 2: The area where white rust is generated is less than 10%. 3: The area where white rust is generated is 10% or more and less than 30%. 4: The area where white rust is generated is 30% or more. As shown in Table 4, with respect to the test plates of all the examples, it was confirmed that the processed portion has higher corrosion resistance than the evaluation criteria (1 or 2) higher than Evaluation 2.

<Alkali resistance> The end and back of the test plate were sealed with tape, and after immersion in a 20% NaOH solution at room temperature for 2 minutes, the appearance discoloration area and the change in color difference before and after the test were observed, and evaluated according to the following criteria . The results are shown in Table 4. 1: No discoloration (ΔE (color difference) <2.0). 2: The discoloration area is less than 25% ((ΔE <2.0). 3: The discoloration area is more than 25% and less than 50% (2.0 ≦ ΔE <3.0). 4: The entire surface is discolored (ΔE ≧ 3.0). See Table 4 As shown, for all the test plates of the examples, it was confirmed that the alkali resistance was as high as the evaluation criteria (1 or 2) higher than that of Evaluation 2.

<Substrate Adhesion> After the test plate was subjected to 8 mm indentation in an Allison indentation tester, a cellophane tape (manufactured by NICHIBAN) was affixed to the indentation portion to perform forced peeling. The test plate was immersed in methyl violet staining solution, and the state of the film was observed and evaluated according to the following criteria. The results are shown in Table 4. 1: There is almost no peeling. 2: The peeling area is less than 10%. 3: The peeling area is 10% or more and less than 25%. 4: The peeling area is 25% or more. As shown in Table 4, with respect to the test plates of all the examples, it was confirmed that the substrate adherence was as high as the evaluation criteria (1 or 2) higher than that of Evaluation 2.

<Boiling water resistance> The end portion and the back surface of the test plate were sealed with an adhesive tape, and after immersion in boiling water for 1 hour, the appearance discoloration area and the change in color difference before and after the test were observed, and evaluated according to the following criteria. The results are shown in Table 4. 1: No discoloration on the entire surface (ΔE <1.0). 2: The discoloration area is less than 25% ((ΔE <1.0). 3: The discoloration area is more than 25% and less than 50% (1.0 ≦ ΔE <3.0). 4: The entire surface is discolored (ΔE ≧ 3.0). See Table 4 As shown, for all the test plates of the examples, it was confirmed that a higher boiling water resistance than that of Evaluation 2 (1 or 2) was satisfied.

<Coating adhesion> A melamine coating (Orgaeco White, manufactured by Japan Coatings Co., Ltd.) was applied to the surface of the test plate with a bar coater so that the dry film thickness became 20 μm, and the temperature was 130 ° C. Bake for 15 minutes to make a coated sheet. Next, the coated film board was immersed in boiling water for 30 minutes, and then left for 24 hours. Then, the test plate was dented at 7 mm in an Allison indentation tester, and a celluloid tape (manufactured by NICHIBAN) was attached to the indented portion. The state of the coating film after forced peeling was evaluated based on the following evaluation criteria. The results are shown in Table 4. 1: There is almost no peeling. 2: The peeling area is less than 10%. 3: The peeling area is 10% or more and less than 25%. 4: The peeling area is 25% or more. As shown in Table 4, with respect to the test plates of all the examples, it was confirmed that the coating adhesion satisfies a higher evaluation criterion (1 or 2) than that of Evaluation 2.

<Water resistance> Water drops were dropped on the treated steel sheet coated with the surface treatment agent and dried, and the water droplets were removed after 15 minutes. After that, the water drop marks on the treated steel sheet surface and the change in color difference before and after the test were visually observed. Benchmark. The results are shown in Table 4. 1: Traces of water droplets were not recognized at all and ΔE <1.0. 2: Some traces of water droplets can be confirmed, but ΔE <1.0. 3: Some traces of water droplets can be confirmed and ΔE> 1.0. 4: Traces of water droplets can be clearly recognized and ΔE> 3.0. As shown in Table 4, it was confirmed that for the test plates of all the examples, a higher water resistance than the evaluation criteria (1 or 2) higher than the evaluation 2 was satisfied.

[Table 4]

Although the amount of the zirconium compound (A) in the surface treatment agent in Examples 1 to 3 is different in the range of 200 to 10,000 ppm by mass, as long as it is within this range, it can be confirmed that any All evaluations met the higher evaluation criteria.

In the surface treatment agents of Examples 4 to 6, the molar ratio (Zr) / (B) of the zirconium element (Zr) and the chelating agent (B) in the surface treatment agent differed in a range of 4 to 100. Yes, but as long as it is within this range, it can be confirmed that any evaluation meets a higher evaluation standard.

In the surface treatment agents of Examples 7 to 9, the molar ratios (c1) / (B) of the carboxyl group (c1) and the chelating agent (B) in the surface treatment agent are different within a range of 30 to 1,000. , But as long as it is within this range, it can be confirmed that any evaluation satisfies a higher evaluation standard.

Moreover, although the surface treatment agents of Examples 10 to 26 have different acid values in the range of 10 to 30 mg KOH / g of the organic resin (C), any evaluation can be confirmed as long as the acid value is within the range. All meet high evaluation standards.

The surface treatment agents of Examples 27 to 54 include at least one of a certain amount of a vanadium compound (D), a titanium compound (E), a silane coupling agent (F), and a silicon oxide (G). For these surface treatment agents, it can be confirmed that any evaluation satisfies a higher evaluation standard.

In addition, although the details are omitted, it can be confirmed that the test plates of each example satisfy a higher evaluation standard than the test plates of the comparative example. Judging from the above results, it is shown that the surface treatment agent for zinc-based plated steel sheets in the present embodiment is obtained by adjusting the content, ratio, and organic resin of the zirconium compound (A), the chelating agent (B), and the organic resin (C). (C) The acid value and the like can not only improve the storage stability, but also improve the surface coating adhesion and boiling water resistance (black discoloration resistance).

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Claims (7)

A surface treatment agent for a zinc-based plated steel sheet, comprising: a zirconium compound (A); a chelating agent (B) having one or more hydroxyl groups in one molecule; and an organic resin (C) having a carboxyl group (c1); The content of the zirconium compound (A) in terms of zirconium element in the surface treatment agent for zinc-based plated steel sheets is in the range of 200 to 10,000 ppm by mass, and the zirconium element ( The molar ratio of Zr) to the chelating agent (B) is in the range of (Zr) / (B) = 4 to 100, the acid value of the organic resin (C) is in the range of 10 to 30 mg KOH / g, and The molar ratio of the carboxyl group (c1) to the chelating agent (B) is in a range of (c1) / (B) = 30 to 1000. The surface treatment agent for a zinc-based plated steel sheet according to claim 1, wherein the organic resin (C) has a hydroxyl group (c2), and the hydroxyl value of the organic resin (C) is in a range of 10 to 30 mg KOH / g The molar ratio of the hydroxyl group (c2) to the chelating agent (B) is in a range of (c2) / (B) = 30 to 1,000. The surface treatment agent for a zinc-based plated steel sheet according to claim 1 or 2, wherein the organic resin (C) is selected from the group consisting of an acrylic resin, an amine ester resin, a polyolefin resin, and a vinyl resin. At least 1 kind. The surface treatment agent for a zinc-based plated steel sheet according to any one of claims 1 to 3, which contains a vanadium compound (D), and its content is within a range of 20 to 300 ppm by mass in terms of vanadium element conversion. The surface treatment agent for a zinc-based plated steel sheet according to any one of claims 1 to 4, which contains a titanium compound (E), and its content is within a range of 50 to 1000 mass ppm in terms of titanium element conversion. The surface treatment agent for a zinc-based plated steel sheet according to any one of claims 1 to 5, which contains a silane coupling agent (F), and the content of the silane coupling agent (F) is 0.5 to 0.5% of the solid content of the organic resin (C). Within 5 mass%. The surface treatment agent for zinc-based plated steel sheets according to any one of claims 1 to 6, which contains silicon oxide (G), and its content is in the range of 2.0 to 4.0% by mass in terms of silicon dioxide.