Metal-based coating agent, surface-treated metal, and surface treatment method

Abstract

The present invention provides a metal-based coating agent that imparts excellent corrosion resistance and adhesion to a substrate even when the substrate is at a high temperature. A metal-based coating agent in which the total of zinc particles (A) and Al particles (B), i.e., (A) + (B), is 10 to 51 mass% relative to the total mass of the metal-based coating agent, the mass ratio of zinc particles (A) relative to Al particles (B), i.e., (A) / (B), is 0.9 to 9.0, the ratio of a silane coupling agent (C) relative to (A) + (B), i.e., (C) / ((A) + (B)), is 10 to 50 mass%, the volume expansion ratio of a solvent (D) from a liquid to a gas is 500 times or less, the ratio of the solvent (D) relative to the total of the solvent (D) and water (E), i.e., (D) / ((D) + (E)), is 20 to 80 mass%, and the total content of water-based resins selected from the group consisting of water-soluble resins, water-based resin emulsions, cellulose-based resins, and polysaccharides is 0.15 mass% or less relative to the total mass.

Description

Technical Field

[0001] This invention relates to metal-based coating agents, surface-treated metals, and surface-treated methods. Background Technology

[0002] Previously, metal-based coatings containing zinc or other metal powders as rust-preventive pigments that sacrifice corrosion protection are known. From the viewpoint of reducing environmental impact, water-based metal-based coatings are preferred as metal-based coatings (for example, see Patent Document 1).

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2005-041987 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] The technology disclosed in Patent Document 1 improves the adhesion between the formed film and the substrate by including an aqueous resin emulsion as a binder in the metal-based coating agent. However, since the metal-based coating agent contains resin components, there is a problem that the anti-corrosion effect cannot be fully achieved at the expense of resin. In addition, when the substrate is at a high temperature during manufacturing, there is a problem that the resin may sinter, scorch, and produce a burnt color on the substrate.

[0008] The present invention was made in view of the above-mentioned problems, and its object is to provide a metal-based coating agent that can impart excellent corrosion resistance and adhesion to the substrate even when the substrate is at a high temperature during coating, and can suppress the scorching of the film during high-temperature sintering.

[0009] Methods for solving problems

[0010] (1) This invention relates to a metal-based coating agent comprising zinc particles (A), Al particles (B) being at least one of aluminum particles and aluminum compound particles, a silane coupling agent (C), a solvent (D), and water (E). The total mass of the zinc particles (A) and the Al particles (B), i.e., (A) + (B), relative to the total mass of the metal-based coating agent is 10 to 51% by mass, and the mass ratio of the zinc particles (A) to the Al particles (B), i.e., (A) / (B), is 0.9 to 9.0. The silane coupling agent... (C) The ratio of (A) + (B) above, i.e., (C) / ((A) + (B)) is 10 to 50% by mass; the volume expansion rate of the solvent (D) from liquid to gas is less than 500 times; the ratio of the solvent (D) above to the total of the solvent (D) above and the water (E) above, i.e., (D) / ((D) + (E)) is 20 to 80% by mass; and the total content of the waterborne resin selected from the group consisting of water-soluble resin, waterborne resin emulsion, cellulose resin and polysaccharide is less than 0.15% by mass relative to the total mass.

[0011] (2) The metal-based coating agent according to (1), wherein the zinc particles (A) are spherical and have an average particle size of 1 to 15 μm.

[0012] (3) The metal-based coating agent according to (1) or (2), wherein the Al particles (B) comprise aluminum particles and aluminum compound particles.

[0013] (4) The metal-based coating agent according to any one of (1) to (3), wherein the silane coupling agent (C) is a silane coupling agent having an epoxy group.

[0014] (5) The metal-based coating agent according to any one of (1) to (4), wherein the solvent (D) is at least one of dipropylene glycol, N-methylpyrrolidone, ethylene glycol mono-n-butyl ether, and isopropanol.

[0015] (6) A surface-treated metal, wherein a film is formed on the surface of a metal substrate, which is the object to be coated, by any one of (1) to (5), wherein the zinc content in the film is 4 g / m2 or more in terms of zinc atoms.

[0016] (7) A surface treatment method comprising a coating step of applying a metal-based coating agent as described in any one of (1) to (5) to the surface of a workpiece and a sintering step.

[0017] Invention Effects

[0018] According to the present invention, a metal-based coating agent can be provided that imparts excellent corrosion resistance and adhesion to the substrate even when the substrate is at a high temperature during coating, and can suppress scorching of the film during high-temperature sintering. Detailed Implementation

[0019] Hereinafter, embodiments of the present invention will be described. The present invention is not limited to the embodiments described below.

[0020] <Metallic Coating Agents>

[0021] The metal-based coating agent of this embodiment imparts excellent corrosion resistance to the substrate by forming a film on the surface of a substrate such as iron. The metal-based coating agent of this embodiment is a water-based coating agent, comprising zinc particles (A), Al particles (B) which are at least one of aluminum particles and aluminum compound particles, a silane coupling agent (C), a solvent (D), and water (E).

[0022] (Zinc particles (A))

[0023] Zinc particles (A) are a component of the anti-rust pigment. Compared to the substrate being coated, they have a high tendency to ionize, thus oxidizing before the substrate and exerting a sacrificial corrosion protection effect. Zinc particles (A) are particles containing zinc. In this specification, zinc particles (A) refer to metallic particles that mainly contain elemental zinc, zinc alloys with zinc as the main component, or zinc oxide (i.e., the total amount of elemental zinc, the aforementioned zinc alloys, and zinc oxide is 50% by mass or more). The shape of the zinc particles (A) is preferably spherical. By having spherical zinc particles, they easily become denser in the film formed by the metal-based coating agent, resulting in excellent sacrificial corrosion protection. From the above perspective, the concept of spherical zinc particles includes not only spheres but also ellipsoidal particles that deform spheres. The average aspect ratio (average aspect ratio / average thickness) of the spherical zinc particles is preferably 2 or less.

[0024] The average particle size of the zinc particles (A) is preferably 1 μm to 15 μm. When the average particle size of the zinc particles (A) is less than 1 μm, the workability and liquid stability during the preparation of the metal-based coating agent decrease. In addition, the adhesion and corrosion resistance of the formed film decrease. When the average particle size of the zinc particles (A) exceeds 15 μm, the surface area per unit mass of the zinc particles (A) decreases, and therefore a good sacrificial corrosion protection effect is not obtained. From the above point of view, the average particle size of the zinc particles (A) is more preferably 3 μm to 5 μm. It should be noted that the above average particle size refers to the average particle size on a volume basis, which can be measured using a particle size distribution measuring device based on laser diffraction-scattering method. As zinc particles (A), commercially available products can be used, specifically, zinc powder series manufactured by Nippon Paint Anti-corrosion Coating Co., Ltd., etc.

[0025] (Al particles (B))

[0026] Al particles (B) are at least one of aluminum particles and aluminum compound particles. Al particles are a rust-preventive pigment component; by including Al particles (B) in a metal-based coating agent, the same sacrificial corrosion protection effect as zinc particles (A) can be obtained. Furthermore, it is believed that coating the substrate with an oxide film formed by aluminum or aluminum compounds can inhibit the leaching of iron or other substances contained in the substrate or zinc from the film. The sacrificial corrosion protection effect of zinc particles (A) complements the aforementioned coating effect, thereby imparting superior corrosion resistance to the substrate. Additionally, it can impart excellent aesthetics to the substrate. The aluminum constituting the aluminum particles is not particularly limited; it can be elemental aluminum or an aluminum alloy. It should be noted that Al particles (B) in this specification refer to alloy, metal, or aluminum compound particles that mainly contain the aforementioned aluminum or aluminum compounds (i.e., the total amount of the aforementioned aluminum or aluminum compounds is 50% by mass or more). The aluminum compound constituting the aluminum compound particles is not particularly limited; examples include aluminum dihydrogen tripolyphosphate, zinc aluminum polyphosphate hydrate, and condensed aluminum phosphate. As an aluminum compound, by using the aforementioned aluminum phosphate compound containing a phosphate compound in its structure, the phosphate compound forms a passive film with the iron contained in the substrate or the zinc contained in the film, thereby imparting further excellent corrosion resistance to the substrate. Al particles (B) can be commercially available in powder or paste form.

[0027] The total amount of zinc particles (A) and Al particles (B) as rust-inhibiting pigment components, i.e., (A) + (B), contains 10 to 51% by mass relative to the total mass of the metal-based coating agent. Therefore, the film formed by the metal-based coating agent imparts excellent corrosion resistance to the substrate. When (A) + (B) is less than 10% by mass, the sacrificial corrosion protection effect provided by the rust-inhibiting pigment components is insufficient. Furthermore, when (A) + (B) exceeds 51% by mass, a uniform film cannot be formed, resulting in reduced corrosion resistance due to decreased adhesion, and the film does not achieve sufficient corrosion resistance. From the above perspective, (A) + (B) is preferably 25 to 45% by mass, more preferably 30 to 40% by mass.

[0028] The mass ratio of zinc particles (A) to Al particles (B), i.e., (A) / (B), is 0.9 to 9.0. When (A) / (B) is less than 0.9, the metal-based coating agent may separate, leading to decreased liquid stability, reduced workability, and decreased corrosion resistance of the formed film. When (A) / (B) exceeds 9.0, especially in humid environments, zinc is more likely to dissolve from the film, causing zinc fracture (lead breakage), thereby reducing the corrosion resistance of the film. From the above perspective, (A) / (B) is preferably 2.0 to 7.5, and more preferably 2.5 to 6.5.

[0029] (Silane coupling agent (C))

[0030] The silane coupling agent (C) functions as a crosslinking agent between the substrate and the rust-preventive pigment component, or between the rust-preventive pigment component and itself, thereby improving the adhesion between the film formed by the metal-based coating agent and the substrate. In addition to the above-mentioned effects, the silane coupling agent (C) also has the effect of stabilizing the zinc particles (A) contained in the metal-based coating agent. In conventional metal-based coating agents, acidic components such as boric acid and molybdic acid are sometimes contained to stabilize the zinc particles. However, the metal coating agent of this embodiment can stabilize the zinc particles (A) through the silane coupling agent (C), thus enabling the metal-based coating agent to be formed without containing acidic components such as boric acid and molybdic acid. The type of silane coupling agent (C) is not particularly limited, and examples include vinylmethoxysilane, vinyltrimethoxysilane, vinylethoxysilane, vinyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-epoxypropoxypropyltrimethoxysilane, 3-epoxypropoxypropyltriethoxysilane, 3-methacryloyloxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, N-(1,3-dimethylbutylene)-3-(triethoxysilyl)-1-propylamine, N,N'-bis[3-(trimethoxysilyl)propyl]ethylenediamine, N-( β-aminoethyl)-γ-aminopropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-epoxypropoxypropyltrimethoxysilane, γ-epoxypropoxypropyltriethoxysilane, γ-epoxypropoxypropylmethyldimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, γ-methacryloyloxypropyltriethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, N-[2-(vinylbenzylamino)ethyl]-3-aminopropyltrimethoxysilane, etc. In addition, as a silane coupling agent (C), besides the above, organosilicon compounds having reactive functional groups such as alkoxysilyl and epoxy, acryloyl groups can also be used. From the perspective of excellent liquid stability, silane coupling agents containing epoxy groups are preferred.

[0031] As the silane coupling agent (C), oligomeric silane coupling agents can also be used. Oligomeric silane coupling agents are relatively low-molecular-weight polymers, for example, composed of 2 to 20 polymers, possessing both organic functional groups and alkoxysilyl groups. The aforementioned oligomeric silane coupling agents can be manufactured by known methods and are also available as commercially available products. Examples of commercially available products include "KR-516" and "KR-517" (both trade names, manufactured by Shin-Etsu Chemical Co., Ltd.). It should be noted that the concept of "resin" in this specification does not include the aforementioned silane coupling agent (C). The aforementioned silane coupling agent (C) can be used alone or in combination.

[0032] The content of silane coupling agent (C) is 10 to 50% by mass relative to the total of zinc particles (A) and Al particles (B) as rust-preventive pigment components, i.e., (A) + (B). When the content of silane coupling agent (C) is less than 10% by mass, sufficient adhesion between the formed film and the substrate cannot be obtained. When the content exceeds 50% by mass, the silane coupling agent (C) hinders the sacrificial corrosion protection effect brought about by the rust-preventive pigment components, and therefore sufficient corrosion resistance of the formed film cannot be obtained. From the above viewpoint, the content of silane coupling agent (C) is preferably 15 to 40% by mass, more preferably 18 to 30% by mass.

[0033] The content of silane coupling agent (C) is preferably 15 to 45% by mass, more preferably 20 to 35% by mass, relative to the content of zinc particles (A) as a rust-preventive pigment component. Thus, zinc particles (A) can be stabilized in the metal coating agent using silane coupling agent (C).

[0034] (solvent(D))

[0035] Solvent (D), together with water (E), functions as a solvent to dissolve or disperse the various components of the zinc-based coating material. The presence of solvent (D) in the metal-based coating agent contributes to liquid stability. Furthermore, it improves the film-forming properties of the film formed by the metal-based coating agent, resulting in a more uniform and smooth film. Additionally, it suppresses the repulsion between the metal-based coating agent and the substrate due to the Leidenfrost phenomenon when the substrate is at a high temperature during coating. Solvent (D) is a water-soluble organic compound with a volume expansion rate of less than 500 times from liquid to gas. This reduces the volume expansion during the vaporization of water, thus mitigating the effects of the Leidenfrost phenomenon.

[0036] The volume expansion rate described above is calculated using the ideal gas law (PV = nRT). For 1g of liquid solvent (D), the volume V1 (P = 1 atm) of the gaseous solvent (D) at its boiling point is determined, and this volume is used as the ratio (V1 / V2) of the liquid solvent (D) to V1. It should be noted that V2 is calculated from the density of the solvent (D) at 20°C. There are no particular limitations on the solvent (D) as long as the above conditions are met; examples include dipropylene glycol (volume expansion rate 316 times), N-methylpyrrolidone (volume expansion rate 406 times), ethylene glycol monobutyl ether (volume expansion rate 192 times), and isopropanol (volume expansion rate 382 times). Dipropylene glycol is preferred as the solvent (D). These can be used alone or in combination. When multiple solvents are used as solvent (D), solvent (D) is preferably a combination of solvents (D) containing dipropylene glycol. That is, the solvent (D) is preferably one or more solvents that contain at least dipropylene glycol.

[0037] The ratio of solvent (D) to the total amount of solvent (D) and water (E), i.e., (D) / ((D)+(E)), is 20-80% by mass. When (D) / ((D)+(E)) is less than 20% by mass, the effect of reducing the Leidenfrost phenomenon cannot be fully obtained, and the coatability is reduced. When (D) / ((D)+(E)) exceeds 80% by mass, solvent residue will remain in the film, reducing adhesion and corrosion resistance. From the above point of view, (D) / ((D)+(E)) is preferably 30-70% by mass, and more preferably 40-65% by mass.

[0038] (Other ingredients)

[0039] Metallic coating agents can contain components other than those mentioned above, depending on the need. For example, as a rust-inhibiting pigment component, it may contain metals such as magnesium other than zinc and aluminum. Additionally, it may contain silica-based rust-inhibiting pigments, etc., as known rust-inhibiting pigments. Furthermore, known paint additives such as extender pigments, coloring pigments, and dyes may be added as needed. It should be noted that the metallic coating agent of this embodiment has excellent liquid stability, therefore it may or may not contain acidic components such as boric acid and molybdic acid.

[0040] Metallic coating agents may contain solvents other than solvent (D) as needed. However, the amount of solvents other than solvent (D) included shall be limited to a level that does not impair the effects of the present invention.

[0041] Furthermore, the metal-based coating agent of this embodiment preferably does not contain resin substantially. It should be noted that "substantially does not contain resin" means that, in this specification, the total content of aqueous resins selected from the group consisting of water-soluble resins, aqueous resin emulsions, cellulose resins, and polysaccharides is 0.15% by mass or less relative to the total mass. The total content of the aforementioned aqueous resins is preferably 0.10% by mass or less, more preferably 0.05% by mass or less.

[0042] It should be noted that the aforementioned cellulose-based resins refer to resins containing cellulose, such as alkyl-containing cellulose, hydroxyl-containing cellulose, carboxyl-containing cellulose, and their derivatives. Specific examples of the aforementioned cellulose-based resins include inorganic acid esters such as hydroxyethyl cellulose, methylcellulose, methyl hydroxypropyl cellulose, ethyl hydroxyethyl cellulose, methyl ethyl cellulose, cellulose acetate, cellulose nitrate, and cellulose phosphate, as well as cellulose ether esters such as acetylated hydroxypropyl cellulose. The aforementioned polysaccharides refer to polysaccharides other than the aforementioned cellulose-based resins and their derivatives.

[0043] There are no particular limitations on the preparation method of the above-mentioned metal-based coating agent. For example, a known method of combining and mixing the above-mentioned components can be used.

[0044] <Surface-treated metals>

[0045] Using the metal-based coating agent of this embodiment, a film is formed on the surface of a metal substrate, which is the object to be coated, thereby generating a surface-treated metal. The metal substrate is not particularly limited; for example, an ferrous substrate can be used. The ferrous substrate is also not particularly limited; examples include cold-rolled steel sheet, mild steel sheet, and high-tensile steel sheet.

[0046] In this embodiment, the zinc content in the surface-treated metal formed is preferably 4 g / m² or more, calculated in terms of zinc atoms. This imparts excellent corrosion resistance to the metal substrate to which the coating is applied. More preferably, the zinc content is 7 g / m² or more.

[0047] <Surface Treatment Methods>

[0048] The surface treatment method for treating metal substrates using the metal-based coating agent of this embodiment includes a coating process and a sintering process.

[0049] (Painting process)

[0050] The coating process involves applying the metallic coating agent of this embodiment to the surface of the aforementioned metal substrate. There are no particular limitations on the coating method; known methods can be used, such as air spraying, airless spraying, electrostatic spraying, brush coating, bar coating, roller coating, and curtain coating. In the coating process, the metallic coating agent can be applied while the substrate is heated to 250°C to 450°C. The metallic coating agent of this embodiment reduces the effects of the Leidenfrost phenomenon, thus enabling excellent coating even at high temperatures of 250°C to 450°C.

[0051] (Sintering process)

[0052] The sintering process involves heating the metal substrate after applying a metal-based coating agent through the coating process to form a film. The sintering temperature (the highest temperature of the metal substrate to which the coating is applied) can be set, for example, from 250°C to 450°C. While conventional metal-based coating agents typically have sintering temperatures below 250°C, the metal-based coating agent of this embodiment can form a film with excellent corrosion resistance even when the coated object is at a high temperature. Examples of such high-temperature coated objects include, for example, steel sheets that have undergone hot-dip galvanizing or other plating treatments on other surfaces. The sintering time can be set, for example, from 8 seconds to 300 seconds.

[0053] Example

[0054] The present invention will now be described in more detail based on embodiments. However, the present invention is not limited to the embodiments described below.

[0055] (Example 1)

[0056] As shown in Table 1, ZN-A (shown below) was used as zinc particles (A), AL-A (shown below) was used as aluminum particles (B)-1, ALX-A (shown below) was used as aluminum compound particles (B)-2, SI-A (shown below) was used as a silane coupling agent (C), and SA (shown below) was used as a solvent (D). The components were mixed to prepare the metal-based coating agent of Example 1. The proportions are shown in Table 1. It should be noted that the proportions of each component shown in Tables 1 and 2 refer to parts by mass.

[0057] (Examples 2-37, Comparative Examples 1-10)

[0058] The metal-based coating agents of the above examples and comparative examples were prepared in the same manner as in Example 1, with the proportions of each component shown in Tables 1 and 2. The types of each component represented by symbols in Tables 1 and 2 are shown below.

[0059] (Zinc particles (A))

[0060] ZN-A: Micro-sized zinc powder LS-4 (average particle size 4.0μm, manufactured by Nippon Paint & Anti-corrosion Coating Co., Ltd.)

[0061] ZN-B: Micro-sized zinc powder LS-5 (average particle size 5.0μm, manufactured by Nippon Paint & Anti-corrosion Coating Co., Ltd.)

[0062] ZN-C: Zinc powder F-500 (average particle size 7.0 μm, manufactured by Honjo Chemical Co., Ltd.)

[0063] ZN-D: Micro-sized zinc powder LS-10 (average particle size 10.0μm, manufactured by Nippon Paint & Anti-corrosion Coating Co., Ltd.)

[0064] ZN-E: Zinc powder F-2000 (average particle size 4.0 μm, manufactured by Honjo Chemical Co., Ltd.)

[0065] ZN-F: Micro-particle zinc powder MCS (average particle size 8.0μm, manufactured by Nippon Paint & Anti-corrosion Coating Co., Ltd.)

[0066] ZN-G: Two types of zinc oxide (average particle size 0.6 μm, manufactured by Sakai Chemical Co., Ltd.)

[0067] (Aluminum particles (B)-1)

[0068] AL-A: WM-2025 (Aluminum particles, manufactured by Toyo Aluminum Co., Ltd.)

[0069] AL-B: WL-Z465 (aluminum particles, manufactured by Toyo Aluminum Co., Ltd.)

[0070] AL-C: 6320NS (aluminum particles, manufactured by Toyo Aluminum Co., Ltd.)

[0071] AL-D: EMR-D7670 (aluminum particles, manufactured by Toyo Aluminum Co., Ltd.)

[0072] (Aluminum compound particles (B)-2)

[0073] ALX-A: Heucophos (registered trademark) ZAPP (zinc aluminum polyphosphate hydrate, manufactured by Heubach Japan Co., Ltd.)

[0074] ALX-B: K-WHITE#82 (Condensed aluminum phosphate, manufactured by Tayca Co., Ltd.)

[0075] ALX-C: K-WHITE G105 (Condensed Aluminum Phosphate, manufactured by Tayca Corporation)

[0076] ALX-D: NP-1102 (Aluminum phosphite, manufactured by Toho Pigment Industry Co., Ltd.)

[0077] ALX-E: NP-1162 (Aluminum phosphite, manufactured by Toho Pigment Industry Co., Ltd.)

[0078] (Silane coupling agent (C))

[0079] SI-A: KBM-403 (3-Epoxypropoxypropyltrimethoxysilane, manufactured by Shin-Etsu Chemical Industry Co., Ltd.)

[0080] SI-B: KBE-403 (3-Epoxypropoxypropyltriethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.)

[0081] SI-C: KR-516 (an epoxy-containing organosilanicotin oligomer, manufactured by Shin-Etsu Chemical Co., Ltd.)

[0082] SI-D: KBM-603 (N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, manufactured by Shin-Etsu Chemical Industry Co., Ltd.)

[0083] SI-E: KBM-903 (3-Aminopropyltrimethoxysilane, manufactured by Shin-Etsu Chemical Industry Co., Ltd.)

[0084] (solvent(D))

[0085] SA: Dipropylene glycol (manufactured by AGC Corporation, with a volume expansion rate of 316 times).

[0086] SB: N-methylpyrrolidone (manufactured by Mitsubishi Chemical Corporation, with a volume expansion rate of 406 times).

[0087] SC: Butyl cellosolve (ethylene glycol mono-n-butyl ether, manufactured by KH Neochem Co., Ltd., with a volume expansion rate of 192 times)

[0088] SD: Isopropanol (manufactured by Showa Chemical Industry Co., Ltd., with a volume expansion rate of 382 times)

[0089] SE: Ethylene glycol (manufactured by Mitsubishi Chemical Corporation, with a volume expansion rate of 694 times).

[0090] (resin)

[0091] CELLOGEN BSH-6 (a cellulose resin manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.)

[0092] Using the metal-based coating agents of the above embodiments and comparative examples, cold-rolled steel sheets were coated using a bar coater. The temperature of the substrate used as the coating material was room temperature. Then, test plates of the surface-treated metals of the embodiments and comparative examples were prepared by sintering at the sintering temperatures shown in Tables 3 and 4 for 60 seconds. It should be noted that the Zn content of the film in Tables 3 and 4 is a value expressed as the zinc content converted from zinc atoms in the film, expressed as the mass per unit area, i.e., g / m2. In Example 24, the substrate temperature was set to 350°C, and coating was performed using an airless sprayer.

[0093] [Table 1]

[0094]

[0095] [Table 2]

[0096]

[0097] [Evaluation of shrinkage hole (hajiki)]

[0098] The metal-based coatings obtained through the above-described embodiments and comparative examples were used to evaluate pinholes. The evaluation was conducted as follows: The metal-based coatings of the embodiments and comparative examples were applied to cold-rolled steel sheets heated to 350°C using airless spraying, with the zinc content in the film calculated as 8 g / m² (calculated as zinc atoms). The presence or absence of pinholes was visually observed (a state where, due to the Leidenfrost phenomenon, droplets of the applied metal-based coating only intermittently contact the substrate surface without being fully coated). Evaluation was based on the following criteria, with 2 being considered acceptable. The results are shown in Tables 3 and 4.

[0099] 2: No pinholes in the metallic coating agent can be visually observed.

[0100] 1. Visually observe pinholes in the metallic coating agent.

[0101] [Fitness Assessment]

[0102] Adhesion was evaluated using test plates of surface-treated metals obtained through the above embodiments and comparative examples. The evaluation was conducted using a tape peel test according to JIS K 56005-6. Evaluation was performed based on the following criteria, with a score of 2 or higher considered acceptable. The results are shown in Tables 3 and 4.

[0103] 3: No peeling

[0104] 2: No peeling from the interface between the substrate and the film.

[0105] 1: There is peeling from the interface between the substrate and the film.

[0106] [Corrosion Resistance Evaluation]

[0107] Using test plates of surface-treated metals obtained through the above embodiments and comparative examples, a composite cycle test (CCT) as specified in JIS H 8502 was performed for 30 cycles. The results were then evaluated according to the following criteria, with a score of 3 or higher considered acceptable. The results are shown in Tables 3 and 4.

[0108] 4: No red rust was observed after 30 cycles of CCT.

[0109] 3: When red rust appears, the number of CCT cycles should be more than 15 but less than 30.

[0110] 2: When red rust appears, it takes more than 9 cycles of CCT but less than 15 cycles of CCT.

[0111] 1: Less than 9 CCT cycles are needed for red rust to form.

[0112] [Scorching properties]

[0113] The scorching properties were evaluated using the following method. Cold-rolled steel sheets at room temperature were used as the coating material. The metal-based coating agents of each example and comparative example were applied using a bar coater (No. 28), and sintered at 350°C for 60 seconds. The condition of the coating at this time was evaluated visually based on the following criteria. Evaluation 2 was considered acceptable. The results are shown in Tables 3 and 4.

[0114] 2: No burning

[0115] 1: There is some burning.

[0116] [Table 3]

[0117]

[0118] [Table 4]

[0119]

[0120] The results in Tables 3 and 4 confirm that, compared to the metal-based coatings of the comparative examples, the metal-based coatings of the various embodiments do not exhibit pinholes even at high sintering temperatures, resulting in excellent coatability and providing excellent adhesion and corrosion resistance to the metal substrate. Furthermore, it was confirmed that the metal-based coatings of the various embodiments can suppress film scorching during high-temperature sintering.

Claims

1. A metal-based coating agent comprising at least one of zinc particles (A), aluminum particles, and aluminum compound particles (Al particles, B), a silane coupling agent (C), a solvent (D), and water (E). The total mass of the zinc particles (A) and the Al particles (B), i.e., (A) + (B), is 10-51% by mass relative to the total mass of the metal-based coating agent. The mass ratio of zinc particles (A) to Al particles (B), i.e., (A) / (B), is 0.9 to 9.

0. The ratio of the silane coupling agent (C) to (A)+(B), i.e., (C) / ((A)+(B)), is 10-50% by mass. The solvent (D) expands less than 500 times in volume from liquid to gas. The ratio of solvent (D) to the total of solvent (D) and water (E), i.e., (D) / ((D)+(E)), is 20-80% by mass. The content of water-based resins selected from the group consisting of water-soluble resins, water-based resin emulsions, cellulose-based resins, and polysaccharides is less than 0.05% by mass relative to the total mass. The zinc particles (A) are spherical with an average particle size of 1–15 μm.

2. The metal-based coating agent according to claim 1, wherein, The Al particles (B) comprise aluminum particles and aluminum compound particles.

3. The metal-based coating agent according to claim 1 or 2, wherein, The silane coupling agent (C) is a silane coupling agent with an epoxy group.

4. The metal-based coating agent according to claim 1 or 2, wherein, The solvent (D) is at least one of dipropylene glycol, N-methylpyrrolidone, ethylene glycol monobutyl ether, and isopropanol.

5. A surface-treated metal, wherein a film is formed on the surface of a metal substrate as the object to be coated using the metal-based coating agent according to any one of claims 1 to 4, wherein the zinc content in the film, calculated in terms of zinc atoms, is 4 g / m³. 2 above.

6. A surface treatment method comprising a coating step of applying a metal-based coating agent according to any one of claims 1 to 4 to the surface of an object to be coated, and a sintering step.

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