Metallic coating agent, surface-treated metal, and surface treatment method

Abstract

To provide a metal-based coating agent capable of imparting preferable corrosion resistance and appearance to a metal substrate.SOLUTION: A metal-based coating agent containing zinc particles (A), aluminum particles (B), an antirust pigment (C), a silane coupling agent (D), and a nonionic surfactant (E), wherein (E) / ((A)+(B)+(C)) that is a ratio of the nonionic surfactant (E) relative to a total of zinc particles (A), aluminum particles (B), and an antirust pigment (C) is 25 to 90 mass%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a metal coating agent, a surface-treated metal, and a surface treatment method. [Background technology]

[0002] Metallic coating agents containing zinc or other metal powders as anti-rust pigments, which exhibit sacrificial corrosion protection, have been known. While organic solvents have traditionally been used as metallic coating agents, in recent years, water-based metallic coating agents have become more widely used, as they are preferred from the standpoint of reducing environmental impact (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-041987 Summary of the Invention [Problem to be solved by the invention]

[0004] The water-based metal anticorrosive paint disclosed in Patent Document 1 is said to exhibit excellent anticorrosion performance and film strength even when the film is thin by using a water-based resin emulsion and a water-soluble silane coupling agent as a binder. However, the dispersibility and paintability of the pigment components are still insufficient, so there is still room for improvement in the corrosion resistance and appearance of the metal substrate on which the film is formed.

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to provide a metal coating agent that can impart desirable corrosion resistance and appearance to a metal substrate. [Means for solving the problem]

[0006] (1) The present invention relates to a metal-based coating agent comprising zinc particles (A), aluminum particles (B), an anti-rust pigment (C), a silane coupling agent (D), and a nonionic surfactant (E), wherein the ratio of the nonionic surfactant (E) to the total of the zinc particles (A), the aluminum particles (B), and the anti-rust pigment (C), (E) / ((A)+(B)+(C)), is 25 to 90 mass%.

[0007] (2) The metal coating agent according to (1), wherein the zinc particles (A) are flaky.

[0008] (3) The metal coating agent according to (1) or (2), further comprising a water-soluble organic solvent (F) and water (G).

[0009] (4) A surface-treated metal obtained by forming a film on the surface of a metal substrate using the metal-based coating agent according to any one of (1) to (3).

[0010] (5) A surface treatment method comprising a coating step of coating the surface of an object with the metal coating agent according to any one of (1) to (3) above, and a baking step. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a metal coating agent that can impart desirable corrosion resistance and appearance to a metal substrate. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the description of the following embodiments.

[0013] <Metallic coating agent> The metal coating agent according to this embodiment can provide preferable corrosion resistance to a metal substrate by forming a film on the surface of the metal substrate, such as iron, which is the substrate to be coated. The metal coating agent according to this embodiment contains zinc particles (A), aluminum particles (B), a rust-preventive pigment (C), a silane coupling agent (D), and a nonionic surfactant (E). It is also preferable that the metal coating agent further contains a water-soluble organic solvent (F) and water (G).

[0014] (Zinc particles (A)) Zinc particles (A) are an anti-corrosion pigment component that exhibit a high ionization tendency relative to the metal substrate to be coated, oxidizing before the metal substrate and thereby exhibiting a sacrificial corrosion protection effect. Zinc particles (A) are particles containing zinc. In this specification, zinc particles (A) refer to metal particles containing zinc alone, a zinc alloy containing zinc as a main component, or zinc oxide (i.e., the total amount of zinc alone, the zinc alloy, and zinc oxide is 50% by mass or more). The zinc particles (A) are preferably flaky in shape. The flaky shape of the zinc particles allows for the formation of a highly corrosion-resistant coating on the surface of the metal substrate, even when a metal-based coating agent is applied to the substrate by a method such as dip spin coating. The flaky zinc particles preferably have an average aspect ratio (average ratio of major axis / thickness) of 20 or more, more preferably 40 or more. The average aspect ratio can be calculated by measuring the major axis and thickness of 10 randomly selected zinc particles using SEM observation.

[0015] The average particle size of the zinc particles (A) is preferably 1 μm to 30 μm. If the average particle size of the zinc particles (A) is less than 1 μm, the workability and liquid stability during preparation of the metal coating agent will decrease. In addition, the corrosion resistance of the formed film will decrease. If the average particle size of the zinc particles (A) exceeds 30 μm, the coatability by dip spin coating will decrease. From the above viewpoints, the average particle size of the zinc particles (A) is more preferably 5 μm to 20 μm. Commercially available zinc particles (A) can be used.

[0016] The average particle size of zinc particles (A) in this specification means the average particle size on a volume basis, which can be measured with a particle size distribution measuring device using a laser diffraction / scattering method. The same applies to aluminum particles (B).

[0017] (Aluminum particles (B)) The aluminum particles (B) are a rust-preventive pigment component, and when the aluminum particles (B) are contained in a metal-based coating agent, a sacrificial anticorrosion effect similar to that of the zinc particles (A) can be obtained. Furthermore, it is believed that the oxide film formed by the aluminum coats the metal substrate, thereby suppressing the elution of iron and other components contained in the metal substrate and zinc in the coating. The sacrificial anticorrosion effect of the zinc particles (A) combined with the coating effect can impart more favorable corrosion resistance to the metal substrate. Furthermore, it can impart a favorable aesthetic appearance to the metal substrate. In this specification, the aluminum particles (B) refer to alloy particles or metal particles primarily containing aluminum (i.e., the total amount of aluminum is 50% by mass or more). Commercially available aluminum particles (B) can be used.

[0018] The average particle size of the aluminum particles (B) is preferably 1 μm to 15 μm. If the average particle size exceeds 15 μm, the coating properties by dip spin coating will be reduced.

[0019] (Anti-rust pigment (C)) The anti-rust pigment (C) is an anti-rust pigment component other than the zinc particles (A) and the aluminum particles (B). Specifically, it refers to aluminum compound particles, magnesium metal particles, magnesium compound particles, known silica-based anti-rust pigments, etc. The anti-rust pigment (C) preferably contains aluminum compound particles. When the aluminum compound particles are incorporated into the metal-based coating agent, a coating effect is obtained by forming an oxide film, similar to the aluminum particles (B). The aluminum compound constituting the aluminum compound particles is not particularly limited, and examples include aluminum dihydrogen tripolyphosphate, zinc aluminum polyphosphate hydrate, and condensed aluminum phosphate. By using the aluminum phosphate-based compound containing a phosphate compound in its structure as the aluminum compound, the phosphate compound and the iron contained in the metal substrate or the zinc contained in the coating form a passive film, thereby imparting even better corrosion resistance to the metal substrate. Commercially available products can be used as the anti-rust pigment (C). The anti-rust pigment (C) may be used alone or in combination.

[0020] (Silane coupling agent (D)) The silane coupling agent (D) functions as a crosslinker between the metal substrate and the anti-rust pigment component, or between the anti-rust pigment components themselves, improving adhesion between the film formed by the metal coating agent and the metal substrate. In addition to the above, the silane coupling agent (D) also has the effect of stabilizing the zinc particles (A) contained in the metal coating agent. Conventional metal coating agents may contain acidic components such as boric acid and molybdic acid to stabilize the zinc particles. However, the metal coating agent of this embodiment can be constructed without containing acidic components such as boric acid and molybdic acid, because the zinc particles (A) can be stabilized by the silane coupling agent (D). The type of silane coupling agent (D) is not particularly limited, and examples thereof include vinyl methoxysilane, vinyl trimethoxysilane, vinyl ethoxysilane, vinyl triethoxysilane, 3-aminopropyl trimethoxysilane, 3-aminopropyl triethoxysilane, 3-glycidoxypropyl trimethoxysilane, 3-glycidoxypropyl triethoxysilane, 3-methacryloxypropyl trimethoxysilane, 3-mercaptopropyl trimethoxysilane, N-(1,3-dimethylbutylidene)-3-(triethoxysilyl)-1-propanamine, N,N'-bis[3-(trimethoxysilyl)propyl]ethylenediamine, N-(β-aminoethyl) Examples of the silane coupling agent (D) include γ-aminopropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, N-[2-(vinylbenzylamino)ethyl]-3-aminopropyltrimethoxysilane, etc. In addition to the above, the silane coupling agent (D) may also be a silicone compound having both an alkoxysilyl group and a reactive functional group such as an epoxy group or an acrylic group.Among these, it is preferable to use a silane coupling agent containing an epoxy group because it has favorable liquid stability.

[0021] As the silane coupling agent (D), an oligomeric silane coupling agent may be used. An oligomeric silane coupling agent is a relatively low molecular weight polymer having both an organic functional group and an alkoxysilyl group, for example, consisting of a dimer to 20-mer. The oligomeric silane coupling agent may be produced by a known method or may be obtained as a commercially available product. Examples of commercially available products include "MP200" (trade name: manufactured by Momentive Corporation), "KR-516", and "KR-517" (all of which are trade names manufactured by Shin-Etsu Chemical Co., Ltd.). The silane coupling agent (D) may be used alone or in combination.

[0022] The total mass of the zinc particles (A), aluminum particles (B), and anti-rust pigment (C) ((A) + (B) + (C)) is preferably 20 to 50 mass % of the total mass of the metal coating agent. This allows the anti-rust pigment components to fully exert their sacrificial anti-corrosion effect, and the film formed by the metal coating agent can impart desirable corrosion resistance and adhesion to the metal substrate to be coated.

[0023] The mass ratio ((A) / ((A)+(B)+(C))) of the zinc particles (A) to the total mass ((A)+(B)+(C)) of the zinc particles (A), aluminum particles (B), and anti-rust pigment (C) is preferably 50 to 80 mass %. This allows the metal coating agent to have good liquid stability, and the film formed by the metal coating agent can impart good corrosion resistance to the metal substrate to be coated.

[0024] The mass ratio of the silane coupling agent (D) ((D) / ((A)+(B)+(C))) to the total mass of the zinc particles (A), aluminum particles (B), and anti-rust pigment (C) ((A)+(B)+(C)) is preferably 40 to 70 mass %. This allows the silane coupling agent (D) to not inhibit the sacrificial anti-corrosion effect of the anti-rust pigment components, and allows the film formed by the metal coating agent to impart desirable corrosion resistance and adhesion to the metal substrate to be coated.

[0025] (Nonionic surfactant (E)) The inclusion of the nonionic surfactant (E) in the metal coating agent can improve the dispersibility of the anti-rust pigment components, zinc particles (A), aluminum particles (B), and anti-rust pigment (C), thereby forming a uniform coating on the surface of the metal substrate to be coated. This can improve the appearance and corrosion resistance of the metal substrate with the coating formed on its surface. The nonionic surfactant (E) is not particularly limited, and known nonionic surfactants can be used. Examples include polyoxyalkylene ethers, polyoxyalkylene glycol fatty acid esters, polyalkylene glycol fatty acid esters, and polyoxyalkylene alkyl ethers. Commercially available products can be used as the nonionic surfactant (E). The nonionic surfactants (E) may be used alone or in combination.

[0026] The ratio of the nonionic surfactant (E) to the total of the zinc particles (A), aluminum particles (B), and anti-rust pigment (C), that is, (E) / ((A)+(B)+(C)), is 25 to 90 mass%. If this ratio is less than 25 mass%, a uniform coating cannot be formed on the surface of the metal substrate, and the metal substrate will not have a desirable appearance or corrosion resistance. If this ratio exceeds 90 mass%, the metal substrate will not have desirable corrosion resistance. From the above viewpoints, (E) / ((A)+(B)+(C)) is preferably 40 to 70 mass%.

[0027] (Water-soluble organic solvent (F)) The water-soluble organic solvent (F), when contained in the metal coating agent according to this embodiment, has the function of improving the pot life of the metal coating agent. When the metal coating agent according to this embodiment is an aqueous metal coating agent containing water (G), the zinc particles (A) in the metal coating agent react with the water (G) to generate fine hydrogen gas bubbles. This hydrogen gas bubbles cause the metal coating agent containing the nonionic surfactant (E) to thicken, reducing its pot life. However, when the water-soluble organic solvent (F) is contained in the metal coating agent, the generated hydrogen gas bubbles are more easily released outside the system, improving the pot life of the metal coating agent.

[0028] The water-soluble organic solvent (F) is not particularly limited, but examples thereof include alcohols such as methanol, ethanol, and isopropyl alcohol, ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate, glycols such as propylene glycol, dipropylene glycol, and tripropylene glycol, and ethers such as diethylene glycol diethyl ether and dipropylene glycol monomethyl ether. The water-soluble organic solvent (F) is preferably an alcohol, glycol, or ether. The water-soluble organic solvent (F) may be used alone or in combination.

[0029] The ratio of the water-soluble organic solvent (F) to the total of the water-soluble organic solvent (F) and water (G), that is, (F) / ((F)+(G)), is preferably 20 to 90 mass %, more preferably 20 to 45 mass %.

[0030] The ratio of the nonionic surfactant (E) to the total of the nonionic surfactant (E) and the water-soluble organic solvent (F), (E) / ((E)+(F)), is preferably 40 to 100 mass%, more preferably 50 to 100 mass%.

[0031] (Other ingredients) The metal-based coating agent may contain other components as needed. For example, it may contain a vanadium compound, a boron compound, a molybdenum compound, or the like as an inhibitor. The component contained as an inhibitor is preferably a vanadium compound.

[0032] In addition to the above, known paint additives such as extender pigments, coloring pigments, dyes, etc. may be added to the metal coating agent as needed. Note that the metal coating agent according to this embodiment does not necessarily need to contain an acidic component such as boric acid or molybdic acid, but may contain such an acidic component in order to improve the liquid stability.

[0033] Furthermore, since the metal-based coating agent according to this embodiment can suppress scorching of the coating during high-temperature baking, it is preferable that it contains substantially no resin. In this specification, "substantially no resin" means that the content of any aqueous resin selected from the group consisting of water-soluble resins, aqueous resin emulsions, cellulose-based resins, and polysaccharides is 0.15% by mass or less relative to the total mass of the metal-based coating agent. The content of the aqueous resin is preferably 0.10% by mass or less, and more preferably 0.05% by mass or less. The cellulose-based resin refers to a resin containing cellulose, such as alkyl group-containing cellulose, hydroxy group-containing cellulose, carboxy group-containing cellulose, and derivatives thereof. Specific examples of the cellulose-based resin include inorganic acid esters such as hydroxyethyl cellulose, methyl cellulose, methylhydroxypropyl cellulose, ethylhydroxyethyl cellulose, methylethyl cellulose, cellulose acetate, cellulose nitrate, and cellulose phosphate, and cellulose ether esters such as acetylated hydroxypropyl cellulose. The polysaccharide refers to polysaccharides other than the cellulose-based resins and their derivatives.

[0034] The method for preparing the metal coating agent is not particularly limited, and for example, a known method of blending and mixing the above-mentioned components can be used.

[0035] The metal coating agent may be a one-component metal coating agent or a two-component metal coating agent. From the viewpoint of liquid stability, a two-component metal coating agent is preferable. When a two-component metal coating agent is used, for example, a solution containing at least water and a solution containing at least the zinc particles (A), aluminum particles (B), rust-preventive pigment (C), silane coupling agent (D), and nonionic surfactant (E), and optionally a water-soluble organic solvent (F), are separately prepared and mixed before coating, thereby preparing the metal coating agent.

[0036] <Surface-treated metal> The metal-based coating agent according to this embodiment forms a coating on the surface of a metal substrate, which is the object to be coated, thereby producing a surface-treated metal. The material of the metal substrate is not particularly limited, but examples thereof include iron-based substrates. Examples of the iron-based substrate include, but are not particularly limited to, cold-rolled steel sheets, hot-rolled steel sheets, mild steel sheets, and high-tensile steel sheets. Furthermore, the metal substrate is preferably a small part having a complex shape, such as a screw, bolt, nut, washer, spring, or other small part. This is because the metal-based coating agent according to this embodiment can be preferably applied to dip spin coating, which is used to paint the small part. Furthermore, since the metal-based coating agent according to this embodiment can significantly improve the corrosion resistance of the metal substrate, the small part can be preferably applied to applications requiring corrosion resistance, such as for fastening components in a vehicle.

[0037] The coating formed on the surface-treated metal according to this embodiment has a zinc content of 4 g / m in terms of zinc atoms. 2 This makes it possible to impart desirable corrosion resistance to the metal substrate to be coated. The zinc content is preferably 7 g / m or more. 2 More preferably, it is equal to or greater than this.

[0038] <Surface treatment method> The surface treatment method for treating a metal substrate with the metal-based coating agent according to this embodiment includes a coating step and a baking step.

[0039] (painting process) The coating process is a process of coating the surface of the metal substrate with the metal-based coating agent according to this embodiment. The coating method is not particularly limited and can be any known method, such as dip spin coating, air spraying, airless spraying, electrostatic spraying, brush coating, bar coating, roll coating, curtain flow coating, etc. When the metal substrate is a screw, bolt, nut, washer, spring, or other small part, dip spin coating is preferred. Dip spin coating can be performed using a known dip spin coating device. The dip spin coating device is a device in which a basket containing the object to be coated is immersed in a metal-based coating agent placed in a coating tank at the bottom of the device, and then lifted out of the coating and rotated at high speed to centrifuge and remove excess coating adhering to the surface of the object to be coated.

[0040] (Baking process) The baking process is a process in which, after the metal coating agent has been applied to the surface of the metal substrate in the painting process, the substrate is heated to form a film. The baking temperature (maximum temperature of the metal substrate to be coated) can be, for example, 250°C to 450°C. The baking time can be, for example, 10 to 30 minutes.

[0041] When the metal substrate is a small part such as a screw, bolt, nut, washer, spring, or the like, it is preferable to repeat the painting and baking steps twice, thereby completely covering the surface of the metal substrate with a coating and forming a coating having the desired thickness on the surface of the metal substrate. [Example]

[0042] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0043] Example 1 As shown in Table 1, ZN-1 shown below was used as zinc particles (A), Al-1 shown below was used as aluminum particles (B), PG-1 shown below was used as anti-rust pigment (C), SI-1 shown below was used as silane coupling agent (D), and SF-1 shown below was used as nonionic surfactant (E). The metal coating agent of Example 1 was prepared by mixing each component. The blending amounts are as shown in Table 1. The blending amounts of each component shown in Tables 1 to 3 refer to parts by mass.

[0044] (Examples 2 to 44, Comparative Examples 1 to 18) The blending amounts of each component are shown in Tables 1 to 3, and the metal coating agents of the above Examples and Comparative Examples were prepared in the same manner as in Example 1. The types of each component indicated by symbols in Tables 1 to 3 are as follows:

[0045] (Zinc particles (A)) ZN-1: STANDART Zinc flake GTT (scale-shaped zinc particles, aspect ratio 40, average particle size 11-20 μm, manufactured by ECKART GmbH) ZN-2:MF-ZF (scale-shaped zinc particles, aspect ratio 40-50, average particle size 11-20 μm, manufactured by Metal Face) ZN-3: ZN-S-D8 (flake zinc particles, aspect ratio 20, average particle diameter 10 μm, manufactured by Fukuda Metal Foil and Powder Co., Ltd.) ZN-4: LS-4 (spherical zinc particles, aspect ratio 1-2, average particle diameter 4 μm, manufactured by Nippon Paint Anticorrosion Coatings Co., Ltd.)

[0046] (Aluminum particles (B)) Al-1: WL-Z465 (aluminum particles, average particle diameter 10 μm, manufactured by Toyo Aluminum Co., Ltd.) Al-2: WL-6360 (aluminum particles, average particle diameter 10 μm, manufactured by Toyo Aluminum Co., Ltd.) Al-3: STAPA IL Hydrolan 9160 (aluminum particles, average particle size 10 μm, manufactured by ECKART GmbH) Al-4: WM-2025 (aluminum particles, average particle diameter 30 μm, manufactured by Toyo Aluminum Co., Ltd.)

[0047] (Anti-rust pigment (C)) PG-1: K-WHITE #105 (condensed aluminum phosphate, manufactured by Teika Corporation) PG-2: Heucophos (registered trademark) ZAPP (zinc aluminum polyphosphate hydrate, manufactured by Heubach Japan Co., Ltd.) PG-3: LF Bousei MZP-500 (magnesium phosphate and zinc phosphite, manufactured by Kikuchi Color Co., Ltd.) PG-4: K-WHITE #82 (condensed aluminum phosphate, manufactured by Teika Corporation) PG-5: Heucophos (registered trademark) CAPP (zinc aluminum tripolyphosphate hydrate, manufactured by Heubach Japan Co., Ltd.) PG-6: K-WHITE Ca650 (condensed aluminum phosphate, manufactured by Teika Corporation) PG-7: K-WHITE ZF150W (condensed aluminum phosphate, manufactured by Teika Corporation)

[0048] (Silane coupling agent (D)) SI-1: KBM-403 (3-glycidoxypropyltrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.) SI-2:MP200 (epoxy silane (oligomer), manufactured by Momentive Performance Materials Japan, LLC)

[0049] (Surfactant (E)) SF-1: XL-80 (nonionic surfactant / EO 8 mol, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) SF-2: XL-100 (nonionic surfactant / EO 10 mol, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) SF-3: Catiogen D2 (cationic surfactant, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) SF-4: Neogen AS-20 (anionic surfactant, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.)

[0050] (Water-soluble organic solvent (F)) SV-1: Dipropylene glycol (AGC) SV-2: Isopropyl alcohol (Shoei Chemical Industry Co., Ltd.)

[0051] <Bar coater painting> Using the metal-based coating agents of Examples 1 to 24 and Comparative Examples 1 to 9, cold-rolled steel sheets were used as substrates and coated with a bar coater. After that, the sheets were baked at 350°C for 15 minutes to prepare evaluation samples of the surface-treated metals of each Example and Comparative Example. The coating amounts (g / m2) in Tables 4 and 5 were 2 ) is the change in weight (g) before and after painting / surface area of ​​the cold-rolled steel sheet (m 2 The grit size of the bar coater was determined based on the target film amount shown in Tables 4 and 5.

[0052] <Dip spin coating> Using the metal coating agents of Examples 25 to 44 and Comparative Examples 10 to 18, iron bolts were used as the substrates for coating, and coating was performed using a dip spin coating device. Then, the bolts were baked at 350°C for 15 minutes, and the coating and baking process was repeated twice to prepare evaluation samples of the surface-treated metals of each Example and Comparative Example. The coating amounts (g / m2) in Tables 4 and 5 were calculated based on the coating weights of the respective Examples and Comparative Examples. 2 ) is the change in weight (g) before and after painting / bolt surface area (m 2 The rotation speed (rpm) of the dip spin coating device was determined based on the target film amount shown in Tables 4 and 5.

[0053] [Table 1]

[0054] [Table 2]

[0055] [Table 3]

[0056] [Corrosion resistance rating: CCT] Using the evaluation samples of the surface-treated metals obtained in Examples 1 to 24 and Comparative Examples 1 to 9, a combined cycle test (CCT) according to JIS H 8502 was carried out. The number of cycles until the appearance of red rust was observed was counted and evaluated according to the following criteria. A score of 2 or more was considered to be acceptable. The results are shown in Tables 4 and 5. 4: 250 cycles or more 3: 150 or more cycles, less than 250 cycles 2: 50 or more cycles, less than 150 cycles Less than 1:50 cycles

[0057] [Corrosion resistance evaluation: SST] A salt spray test (SST) was carried out using the evaluation samples of the surface-treated metals of Examples 25 to 44 and Comparative Examples 10 to 18 obtained as described above. The test time until the occurrence of red rust was observed was confirmed and the sample was evaluated according to the following criteria. A score of 2 or higher was considered to be acceptable. The results are shown in Tables 4 and 5. 4: Over 1,500 hours 3: Over 1000 hours and less than 1500 hours 2: Over 500 hours and under 1000 hours Less than 1:500 hours

[0058] [Appearance evaluation] Using evaluation samples of the surface-treated metals of each Example and Comparative Example, the uniformity and hiding power of the surface-treated metal film after painting and baking were visually observed and evaluated according to the following criteria. A score of 2 or higher was considered acceptable. The results are shown in Tables 4 and 5. 4: Excellent uniformity and hiding power 3: Excellent uniformity and hiding power 2: Uniformity and hiding power 1: Pigment clumping, uneven coating, etc., poor hiding power

[0059] [Pot life evaluation] Pot life evaluation was performed using the metal coating agents of Examples 20 to 22 and Comparative Example 9 obtained as described above. Specifically, a metal coating agent was prepared by mixing water with a solution previously prepared by mixing components other than water. The viscosity of the solution, when the temperature was brought to 20°C immediately after preparation, was measured using a cup viscometer (NK-2 cup, manufactured by Anest Iwata Corporation) as the time until the metal coating agent in the cup had completely dropped, and this was taken as the initial viscosity. After preparation, the metal coating agent was left to stand at 20°C, and the viscosity of the metal coating agent was measured in the same manner every time a certain number of days had passed since preparation of the solution. The number of days during which the change in viscosity (time) from the initial viscosity was within 30 seconds was determined over the course of the days since preparation of the solution, and evaluation was performed according to the following criteria. A score of 3 was considered acceptable. The results are shown in Tables 4 and 5. 3: 14 days or more 2: 7 days or more but less than 14 days 1: Less than 7 days

[0060] [Table 4]

[0061] [Table 5]

[0062] The results in Tables 4 and 5 confirm that the metal coating agents according to each example can impart preferable corrosion resistance and appearance to metal substrates compared to the metal coating agents according to the comparative examples.

Claims

1. A metal coating agent comprising zinc particles (A), aluminum particles (B), a rust-preventive pigment (C), a silane coupling agent (D), and a nonionic surfactant (E), The metal-based coating agent, wherein the ratio of the nonionic surfactant (E) to the total of the zinc particles (A), the aluminum particles (B), and the rust-preventive pigment (C), (E) / ((A)+(B)+(C)), is 25 to 90 mass%.

2. The metal-based coating agent according to claim 1 , wherein the zinc particles (A) are flaky.

3. The metal coating agent according to claim 1 or 2, further comprising a water-soluble organic solvent (F) and water (G).

4. A surface-treated metal obtained by forming a film on the surface of a metal substrate using the metal-based coating agent according to any one of claims 1 to 3.

5. A surface treatment method comprising a coating step of coating the metal-based coating agent according to any one of claims 1 to 3 onto the surface of an object to be coated, and a baking step.

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