Surface-coated metal member, aqueous anticorrosive surface treatment composition for use therein, and method for producing same

Abstract

To provide a method for producing a surface-coated metal member having stably excellent corrosion resistance.SOLUTION: A method for producing surface-coated metal member has a chemical conversion step of subjecting a plating film provided on the surface of a metal member to chemical conversion to form a chemical conversion film, and a surface treatment step of coating the chemical conversion film with an aqueous anticorrosive surface treatment composition comprising a silane coupling agent, aqueous colloidal silica, a water-dispersible resin, and solvent comprising water, and drying it, to form a silicon film.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a surface-coated metal member, an aqueous rust-preventive surface treatment composition used therefor, and a method for producing the same. [Background technology]

[0002] Various developments have been made so far in aqueous surface treatment agents for treating the surfaces of metal components. For example, the technology described in Patent Document 1 is known as a technology of this type. Patent Document 1 describes a metal surface treatment method using an aqueous metal surface treatment agent containing an epoxy group-containing silane coupling agent and colloidal silica (Claim 1, paragraph 0012, etc.). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-237880 Summary of the Invention [Problem to be solved by the invention]

[0004] However, as a result of investigations by the present inventors, it has been found that the metal surface treatment method described in Patent Document 1 has room for improvement in terms of stable and excellent corrosion resistance. [Means for solving the problem]

[0005] The plating solution in the plating bath has variation in composition due to variations between lots and the influence of impurities that arise from repeated use, reuse, etc. It is presumed that impurities arise from contamination during the work process and the elution of iron from the plating tank or the object to be plated.

[0006] As a result of the inventor's investigations, it was found that variations in the composition of the plating solution can significantly affect the time it takes for white rust to appear in a continuous salt spray test (SST test). In other words, even if an aqueous anti-corrosion surface treatment is applied to the plating film of a metal component, variations in the underlying plating film can cause variations in the time it takes for white rust to appear in the SST test, which can lead to variations in corrosion resistance.

[0007] Based on this knowledge, the inventors conducted extensive research and found that the formation of a chemical conversion coating on a plating film suppresses variations in corrosion resistance. As a result of further investigation, they discovered that the formation of a silicon film made of a predetermined aqueous rust-preventive surface treatment composition on a plating film or a chemical conversion coating can improve corrosion resistance while suppressing variations in corrosion resistance, and thus completed the present invention.

[0008] According to the present invention, a chemical conversion treatment step of forming a chemical conversion coating on the plating film provided on the surface of the metal member by performing a chemical conversion treatment; a surface treatment step of applying an aqueous rust-preventive surface treatment composition containing a silane coupling agent, aqueous colloidal silica, a water-dispersible resin, and a solvent containing water to the chemical conversion coating, and drying the composition to form a silicon coating; The present invention provides a method for producing a surface-coated metal component, comprising:

[0009] Further, according to the present invention, An aqueous rust-preventive surface treatment composition used to form a silicon film on a metal member having a plating film, a chemical conversion film, and a silicon film on the surface of the metal member, the aqueous rust-preventive surface treatment composition comprising: a silane coupling agent; aqueous colloidal silica; a water-dispersible resin; a solvent comprising water, An aqueous anticorrosive surface treatment composition is provided.

[0010] Further, according to the present invention, a metal member having a plating film on its surface; a chemical conversion coating formed on the surface of the plating film; a silicon coating formed on the surface of the chemical conversion coating and comprising an aqueous rust-preventive surface treatment composition containing a silane coupling agent, aqueous colloidal silica, and a water-dispersible resin; A surface-coated metal component is provided. [Effects of the Invention]

[0011] According to the present invention, there are provided a surface-coated metal member having stable and excellent corrosion resistance, which eliminates differences in corrosion resistance due to variations in the type of zinc plating bath or treatment, an aqueous rust-preventive surface treatment composition used therefor, and a method for producing the same. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is a cross-sectional view schematically illustrating an example of the configuration of a surface-coated metal member in the structure according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all drawings, similar components are designated by similar reference numerals, and their description will be omitted where appropriate. The drawings are schematic diagrams and do not correspond to the actual dimensional proportions.

[0014] The method for manufacturing the surface-coated metal member of this embodiment will be outlined below.

[0015] The method for producing a surface-coated metal member includes a chemical conversion treatment step and a surface treatment step. The chemical conversion treatment step includes a step of forming a chemical conversion coating by performing a chemical conversion treatment on the plating film provided on the surface of the metal member. The surface treatment step includes applying an aqueous anticorrosive surface treatment composition onto the resulting chemical conversion coating and drying the composition to form a silicon coating. This aqueous anticorrosive surface treatment composition (hereinafter sometimes simply referred to as the "composition") contains a silane coupling agent, aqueous colloidal silica, a water-dispersible resin, and a solvent containing water.

[0016] According to the findings of the present inventors, by forming a chemical conversion coating on the plating film of a metal member, it is possible to suppress variations in corrosion resistance, and further by forming a silicon film made of a predetermined aqueous rust-preventive surface treatment composition on the chemical conversion coating, it is possible to improve corrosion resistance while suppressing variations in corrosion resistance. Therefore, the manufacturing method of this embodiment makes it possible to realize a surface-coated metal member having stable and excellent corrosion resistance.

[0017] The method for producing the surface-coated metal member will be described in detail below.

[0018] The method for producing a surface-coated metal member may include a plating step.

[0019] The plating process includes forming a plating film on at least a portion of the surface of the metal member.

[0020] The metal material constituting the metal member can be appropriately selected depending on the application, and examples thereof include zinc, iron, copper, aluminum, tin, alloys containing these metals, plated steel with these metals, or vapor-deposited products, etc. These may be used alone or in combination of two or more. An example of a metal member may be made of steel, but may also be made of non-steel material. For a fee It may be configured.

[0021] The plating film is formed on the surface of the metal member using a known plating process. For example, the metal member may be immersed in a molten zinc bath to form a hot-dip galvanized film on the surface.

[0022] The plating film may be a metal layer containing one or more metal species, and may contain at least zinc or chromium. In one preferred embodiment, the plating film may be a zinc-containing plating film (galvanized film). It is preferable to use a hot-dip galvanized film as the zinc plating film.

[0023] Examples of metal members with a plating film include JIS H 8641: hot-dip galvanized, JIS H 8610: electrogalvanized, JIS H 8625: chromate film (containing trivalent Cr), JIS G 3313: electrogalvanized steel sheet, and JIS G 3302: hot-dip galvanized steel sheet.

[0024] The method for producing a surface-coated metal member includes a chemical conversion treatment step.

[0025] As the chemical conversion treatment, known treatment methods can be used, and examples thereof include phosphate treatment containing zinc, manganese, iron, calcium, etc.; zirconium-based treatment containing zirconium, titanium, hafnium, etc.; chromium salt treatment (chromate treatment) containing zinc, aluminum, copper, etc.; fermite treatment (black oxide treatment); chemical conversion treatment containing cerium, vanadium, tungsten, etc. Among these, from the viewpoint of reducing the environmental load, non-chromium-based chemical conversion treatments such as phosphate treatment and zirconium-based treatment can be used. For the phosphate treatment, a treatment solution containing zinc phosphate can be used. For the zirconium-based treatment, a treatment solution containing zirconium can be used.

[0026] In the chemical conversion treatment step, a chemical conversion film such as a zinc phosphate film or a zirconium film can be formed on at least a portion of the plating film.

[0027] Furthermore, phosphate treatment and zirconium-based treatment can suppress variations in corrosion resistance compared to cerium (Ce)-based chemical conversion treatment and chromate treatment.

[0028] Furthermore, phosphate treatment and zirconium-based treatment are superior in aesthetics and scratch resistance compared to fermite treatment. Among these, zirconium-based treatments, compared to phosphate treatments, allow the color of the underlying plating film to be visually observed through the zirconium chemical conversion coating, resulting in a more aesthetically pleasing appearance. Furthermore, zirconium-based treatments can prevent discoloration of the plating film, making them suitable for a variety of applications.

[0029] The method for producing a surface-coated metal member includes a surface treatment step.

[0030] In the surface treatment step, for example, an aqueous rust-preventive surface treatment composition is applied to at least a portion of the chemical conversion coating, followed by drying treatment to form a silicon coating. The drying treatment may be carried out at room temperature of 20 to 25° C., or may be carried out by heating to an appropriate temperature, for example, at 80 to 200° C. for 5 to 240 minutes. Alternatively, a metal member having a plating film and a chemical conversion coating may be immersed in the aqueous rust-preventive surface treatment composition, followed by drying.

[0031] Here, each component of the aqueous rust-preventive surface treatment composition will be described in detail.

[0032] The aqueous anticorrosive surface treatment composition contains at least a silane coupling agent, aqueous colloidal silica, a water-dispersible resin, and a solvent containing water.

[0033] The aqueous rust-preventive surface treatment composition can be used to form a silicon film on a chemical conversion film of a metal member having a plating film, a chemical conversion film, and a silicon film on the surface thereof.

[0034] Although the detailed mechanism is unclear, it is thought that the metal atoms contained in the metal layer and the silicon (Si) elements derived from the silane coupling agent in the silicon film form a bridge structure via oxygen atoms, resulting in a silicon film with silica appropriately positioned within this bridge structure, thereby improving the corrosion resistance of the structure. Furthermore, by using a water-dispersible resin, the resin is prevented from dissolving due to H-groups and OH-groups that remain due to incomplete reaction in the silicon film during film formation, or due to water, which is thought to improve corrosion resistance.

[0035] <Silane coupling agent> The aqueous anticorrosive surface treatment composition contains a silane coupling agent. The use of a silane coupling agent can stabilize a composition containing a water-dispersible resin or aqueous colloidal silica as an aqueous solution. Furthermore, the silane coupling agent can improve the affinity between the aqueous colloidal silica and the water-dispersible resin, thereby forming a stable aqueous solution (composition). As the silane coupling agent, a water-soluble silane coupling agent that can be dissolved in water is used.

[0036] The silane coupling agent may be, for example, a silane coupling agent represented by the general formula: (R 1 ) m Si(OR 2 ) 4―m (In the above general formula, R 1 is a functional group having 1 to 20 carbon atoms, R 2 is a lower alkyl group. m is an integer of 0 to 3.) or a compound obtained by hydrolyzing and condensation polymerizing the alkoxysilane. The silane coupling agent may be partially hydrolyzed in the composition.

[0037] Specific examples of silane coupling agents represented by the above general formula include Si(OCH3)4, Si(OC2H5)4, CH3Si(OCH3)3, CH3Si(OC2H5)3, C2H5Si(OCH3)3, C2H5Si(OC2H5)3, CH2(O)CHCHO(CH2)3Si(OCH3)3, CH2=C(CH3)COO(CH2)3Si(OCH3)3, CH2=CHCOO(CH2)3Si(OCH3)3, H2N(CH2)3Si(OCH3)3, HS(CH2)3Si(OCH3)3, OCN(CH2)3Si(OC2H5)3, etc.

[0038] In addition, in the above chemical formula, R 1Examples of functional groups therein include vinyl, 3-glycidoxypropyl, 3-glycidoxypropylmethyl, 2-(3,4-epoxycyclohexyl)ethyl, p-styryl, 3-methacryloxypropyl, 3-methacryloxypropylmethyl, 3-acryloxypropyl, 3-aminopropyl, N-2-(aminoethyl)-3-aminopropyl, N-2-(aminoethyl)-3-aminopropylmethyl, N-phenyl-3-aminopropyl, N-(vinylbenzyl)-2-aminoethyl-3-aminopropyl, 3-ureidopropyl, 3-mercaptopropyl, and 3-isocyanatopropyl.

[0039] In the above chemical formula, specific examples of the lower alkyl group include linear or branched alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, sec-butyl, n-pentyl, 1-ethylpropyl, isopentyl, and neopentyl.

[0040] The water-soluble silane coupling agent may include, for example, a silane coupling agent having an epoxy group as a functional group (epoxysilane) or a silane coupling agent having an amino group as a functional group (aminosilane). Among these, it is more preferable to use epoxysilane from the viewpoint of corrosion resistance.

[0041] Examples of the epoxy silane include glycidyl or epoxy group-containing trialkoxysilane compounds such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, and 2-(3,4-epoxycyclohexylethyl)trimethoxysilane.

[0042] The content of the silane coupling agent is, for example, 0.5 to 12 mass%, preferably 1 to 11 mass%, and more preferably 3 to 10 mass%, converted into solid content based on the entire aqueous rust-preventive surface treatment composition.

[0043] In this specification, unless otherwise specified, the symbol "to" indicates that the upper and lower limits are included. The solid content refers to the remainder after removing volatile components such as water, alcohol solvents, etc. This solid content may be the residue remaining after the reaction of each component of the aqueous rust-preventive surface treatment composition after heat treatment.

[0044] <Aqueous colloidal silica> The aqueous anticorrosive surface treatment composition contains aqueous colloidal silica.

[0045] The water-soluble colloidal silica is dispersed in a water solvent or a mixed solvent containing water, and contains inorganic particles made of SiO2. The average particle size of the inorganic particles may be, for example, 1 to 200 nm.

[0046] The aqueous anticorrosive surface treatment composition may contain inorganic colloidal particles other than aqueous colloidal silica, which are composed of inorganic oxides such as Al2O3, TiO2, ZrO2, Fe2O3, etc. The inorganic colloidal particles are composed of inorganic particles dispersed in water.

[0047] The use of aqueous colloidal silica can further improve the strength of the film obtained from the aqueous rust-preventive surface treatment composition, and also improve the dispersibility in the composition, thereby forming a silicon film in which the silica particles are uniformly dispersed throughout the film.

[0048] The stable pH range of the aqueous colloidal silica is on the acidic, neutral, or alkaline side. Among these, aqueous colloidal silica that is stable at an acidic pH can be used from the viewpoint of solution stability of the composition.

[0049] The inorganic particles have an average particle size of, for example, 1 to 200 nm, preferably 3 to 100 nm. By using nano-sized inorganic particles, aggregation and sedimentation can be suppressed when an aqueous mixed solvent of water and alcohol is used, allowing the preparation of a composition with excellent liquid stability. Furthermore, the rust prevention performance of products surface-treated with the composition can be improved.

[0050] By using inorganic colloidal particles such as aqueous colloidal silica, a stronger coating structure can be achieved. Although the detailed mechanism is unclear, it is thought that inorganic particles such as silica are appropriately arranged in the spaces within the coating, which increases the density of the coating, such as the silicon coating, and improves corrosion resistance.

[0051] The content of the aqueous colloidal silica in the aqueous rust-preventive surface treatment composition is, for example, 0.5% by mass to 12% by mass, preferably 0.6% by mass to 10% by mass, and more preferably 0.8% by mass to 8% by mass, calculated as solid content. By setting the content at or above the lower limit, it is possible to impart appropriate strength to the coating. By setting the content at or below the upper limit, it is possible to achieve a balanced physical property of the coating.

[0052] The content of the aqueous colloidal silica is, in terms of solid content, for example, 10 to 300 parts by mass, preferably 15 to 200 parts by mass, and more preferably 20 to 150 parts by mass relative to 100 parts by mass of the silane coupling agent.

[0053] <Water dispersible resin> The aqueous rust-preventive surface treatment composition contains a water-dispersible resin.

[0054] The water-dispersible resin is composed of a resin that disperses in water. The resin constituting the water-dispersible resin may be appropriately selected from resins that can be dispersed in water, and examples thereof include polyacrylic acid resins, silicone resins, phenolic resins, epoxy resins, polyurethane resins, polyester resins, polyvinyl butyral resins, phenolic resins, and modified products thereof. These may be used alone or in combination of two or more. Among these, polyacrylic resins and silicone resins may be used from the viewpoint of corrosion resistance and durability of the coating.

[0055] The use of water-dispersible resins can further improve the corrosion resistance of coatings compared to water-soluble resins. Although the detailed mechanism is unclear, it is thought that this is because the resin can be prevented from dissolving in water components.

[0056] The content of the water-dispersible resin in the aqueous rust-preventive surface treatment composition, calculated as solid content, is, for example, 1% by mass to 12% by mass, preferably 1.5% by mass to 11% by mass, and more preferably 2% by mass to 10% by mass. By setting the content at or above the lower limit, the heat resistance and corrosion resistance of the coating can be improved. By setting the content at or below the upper limit, the physical properties of the coating can be balanced.

[0057] <Solvent> The aqueous rust-preventive surface treatment composition includes a water-containing solvent, which may be an aqueous solvent containing only water, or an aqueous mixed solvent containing water and a hydrophilic solvent other than water.

[0058] Examples of the water include city water, distilled water, and ion-exchanged water.

[0059] The hydrophilic solvent may be a polar organic solvent such as alcohol. From the viewpoint of solution stability, the aqueous mixed solvent may be composed of a mixed solvent of water and alcohol. The content of water in the aqueous mixed solvent can be determined in consideration of the chemical properties and blending amounts of each component in the aqueous rust-preventive surface treatment composition.

[0060] Examples of the alcohol that can be used include low-boiling alcohols with a boiling point of less than 100° C., such as methanol, ethanol, n-propyl alcohol, and isopropyl alcohol, and high-boiling alcohols with a boiling point of 100° C. or higher, such as isobutanol, methyl cellosolve, ethyl cellosolve, propylene glycol monomethyl ether (PGME), butyl cellosolve, ethylene glycol monotertiary butyl ether (ETB), and diformaldehyde methoxyethanol. These may be used alone or in combination of two or more.

[0061] Among these, one or more alcohols selected from the group consisting of methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, s-butyl alcohol, and t-butyl alcohol can be included because of their high availability and high solubility in each component. Furthermore, the use of low-boiling-point alcohols such as methyl alcohol (boiling point: 64.7°C), ethyl alcohol (boiling point: 78.37°C), and isopropyl alcohol (boiling point: 82.4°C) enables the formation of a coating film in a lower temperature or drier environment.

[0062] In this embodiment, the use of alcohol improves the solubility of each component and improves the storage stability of the resulting aqueous rust-preventive surface treatment composition. Although the reason is unclear, the use of a mixed solvent containing water and alcohol can improve the rust-preventive performance of the coating formed on the surface of a metal member having a zinc surface. Furthermore, alcohol can suppress foaming of the aqueous rust-preventive surface treatment composition, thereby preventing bubbles from entering the coating and causing the siliceous coating to become non-uniform.

[0063] The content of the alcohol in the aqueous rust-preventive surface treatment composition is, for example, 0.1% by mass to 15% by mass, preferably 0.2% by mass to 12% by mass, and more preferably 0.3% by mass to 10% by mass. By adjusting the content within the above range, the long-term storage stability of the composition can be improved. Furthermore, by adjusting the content to the above upper limit or less, the adhesion can be improved.

[0064] The content of the alcohol is, for example, 0.1% by mass to 18% by mass, preferably 0.2% by mass to 15% by mass, and more preferably 0.3% by mass to 14% by mass, relative to 100% by mass of the total content of the water and alcohol. By keeping the content within this range, the long-term storage stability of the aqueous rust-preventive surface treatment composition can be improved.

[0065] The content of the alcohol is, for example, 1 to 300 parts by mass, preferably 2 to 200 parts by mass, and more preferably 3 to 170 parts by mass, relative to 100 parts by mass of the total content of the silane coupling agent and the water-dispersible resin. By setting the content at or above the lower limit, a composition in which the silane coupling agent is stably dissolved can be realized. By setting the content at or below the upper limit, the dispersibility of the water-dispersible resin can be improved. By setting the content within the above range, the long-term storage stability of the composition can be improved.

[0066] The pH of the aqueous anticorrosive surface treatment composition can be appropriately selected depending on the components contained therein, and when a phosphate-based anticorrosive agent is contained, it may be on the acidic side, for example, 4.0 to 6.9, while when no phosphate-based anticorrosive agent is contained, it may be on the alkaline side. The alkaline aqueous anticorrosive surface treatment composition does not need to contain a water-soluble transition metal compound.

[0067] The alkaline aqueous rust-preventive surface treatment composition has a pH of, for example, 7.0 to 13.0, preferably 7.2 to 12.0.

[0068] In this embodiment, the pH can be measured using a pH meter at a liquid temperature of the aqueous rust-preventive surface treatment composition of 25° C.±1° C. The liquid temperature is usually 25° C., but variations of about +1° C. or −1° C. are acceptable.

[0069] <Water-soluble transition metal compounds> The aqueous anticorrosive surface treatment composition may or may not contain a water-soluble transition metal compound. The water-soluble transition metal compound includes a water-soluble titanium compound or a water-soluble zirconium compound. The water-soluble transition metal compound is capable of dissolving in water.

[0070] The water-soluble titanium compound may include one or more selected from the group consisting of inorganic titanium compounds, peroxotitanates, amine-based water-soluble titanates, and chelate-based titanates (water-soluble titanium chelating agents). Specific examples of the water-soluble titanium compound include inorganic titanium compounds such as titanium trichloride, titanium tetrachloride, titanium sulfate, and titanium oxychloride, inorganic or chelate-based peroxotitanates, amine-based water-soluble titanates obtained by reacting titanium alkoxide with water in the presence of amines, and chelate-based titanates (water-soluble titanium chelating agents) such as oxycarboxylic acid chelate titanium in which oxycarboxylic acids such as lactic acid, malic acid, citric acid, tartaric acid, gluconic acid, and glycol are coordinated, and alkanolamine chelate titanium in which alkanols such as monoethanolamine, diethanolamine, and triethanolamine are coordinated. The water-soluble zirconium compound may have a structure similar to that of the water-soluble titanium compound, and may include, for example, one or more compounds selected from the group consisting of inorganic zirconium compounds, peroxozirconates, amine-based water-soluble zirconates, and chelate-based zirconates.

[0071] The titanium chelating agent can be, for example, an organic compound represented by the general formula: Ti(X)4 and its oligomers. In the general formula, X is selected from a hydroxyl group, a lower alkoxy group, and a chelating substituent, and the four Xs may be the same or different.

[0072] Examples of the lower alkoxy group include alkoxy groups having 6 or less, preferably 4 or less, carbon atoms, such as methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, and tert-butoxy. The chelating substituent is, for example, a group derived from an organic compound capable of forming a chelating group, such as β-diketones such as acetylacetone, alkylcarbonylcarboxylic acids and their esters such as acetoacetic acid, and alkanolamines such as triethanolamine. Specific examples of the chelating substituent include lactate, ammonium lactate, triethanolamine, acetylacetonate, acetoacetate, and ethylacetoacetate.

[0073] The water-soluble transition metal compound is present in the entire aqueous rust-preventive surface treatment composition in an amount of, for example, 0.1 to 7 mass %, preferably 0.2 to 5 mass %, and more preferably 0.3 to 3 mass %, calculated as solid content.

[0074] <Phosphate-based rust inhibitor> The aqueous anticorrosive surface treatment composition may or may not contain a phosphoric acid-based anticorrosive agent.

[0075] As the phosphoric acid-based rust inhibitor, at least one of a highly condensed phosphate and a polyvalent phosphate ester may be used.

[0076] The highly condensed phosphate may be a salt of a highly condensed product obtained by dehydration condensation of four or more phosphoric acids. The degree of condensation of phosphoric acid in the highly condensed phosphate (the number of structural units derived from phosphoric acid in the molecule) is, for example, 4 or more, preferably 5 or more, and more preferably 6 or more. This can improve corrosion resistance. On the other hand, the upper limit of the degree of condensation is not particularly limited, but may be, for example, 50 or less, 40 or less, or 30 or less.

[0077] The highly condensed phosphate may have, for example, a linear structure, a cyclic structure, or a network structure in which linear structures and cyclic structures are mutually bonded. Among these, the highly condensed phosphate preferably has a cyclic structure or a network structure.

[0078] The polyphosphate ester is a compound having multiple phosphate ester residues. The phosphate ester residues have a monophosphate structure or a diphosphate structure. The alcohol moiety forming the phosphate ester residue may be a primary alcohol, a secondary alcohol, or a tertiary alcohol. A specific example of the polyphosphate ester is phytic acid.

[0079] The content of either the highly condensed phosphate or the polyphosphate ester, or the total content of these, is, for example, 0.1% by mass to 1.0% by mass, preferably 0.15% by mass to 0.9% by mass, and more preferably 0.3% by mass to 0.75% by mass, calculated as solid content in the entire aqueous rust-preventive surface treatment composition. By setting it to be equal to or greater than the lower limit, corrosion resistance can be improved. By setting it to be equal to or less than the upper limit, the physical properties of the coating can be balanced. (Other ingredients) The aqueous rust-preventive surface treatment composition may contain other additives in addition to the above components. As other additives, various additives typically contained in primer materials can be used, such as pH adjusters, lubricants, preservatives, fillers, colorants, surfactants, antifoaming agents, leveling agents, and antibacterial agents. These may be used alone or in combination of two or more. The amount of additive added can be appropriately determined depending on the application.

[0080] Examples of the preservative include isothiazolinone compounds.

[0081] As an example of an aqueous rust-preventive surface treatment composition (aqueous rust-preventive treatment agent), all of the components contained in the composition may be composed of water-soluble or water-dispersible components, i.e., the aqueous rust-preventive surface treatment composition may be composed of an aqueous solution containing only water-soluble or water-dispersible components.

[0082] In the technical field of aqueous rust prevention treatment agents, the content of chromium components in aqueous rust prevention treatment agents is limited from the viewpoint of environmental considerations, but some aqueous rust prevention treatment agents contain trivalent chromium or hexavalent chromium.

[0083] In contrast, the aqueous rust-preventive surface treatment composition of the present embodiment is substantially free of chromium components such as hexavalent chromium and trivalent chromium, and can therefore be used as a chromium-free rust-preventive treatment agent, thereby realizing an aqueous rust-preventive surface treatment composition with reduced environmental impact.

[0084] In order to further improve the rust prevention properties, it is possible to include a necessary amount of trivalent chromium. However, for example, the amount of trivalent chromium is preferably limited to 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less, based on the total amount of the aqueous rust prevention surface treatment composition. It is particularly preferable that the amount of trivalent chromium is substantially zero. In this specification, the amounts of hexavalent chromium and trivalent chromium refer to the content of chromium salts having these specific valence numbers.

[0085] The aqueous rust-preventive surface treatment composition can be obtained by mixing the components. The order in which the components are mixed is not limited, and they can be mixed in any order.

[0086] By the above manufacturing method, a surface-coated metal member can be obtained.

[0087] FIG. 1 is a cross-sectional view showing an example of the configuration of a surface-coated metal member 100. As shown in FIG.

[0088] The surface-coated metal member 100 includes a substrate 10, a plating film 20, a chemical conversion film 30, and a silicon film 40. As an example, the substrate 10 (metal member) has a plating film 20 on its surface, the chemical conversion film 30 is formed on the surface of the plating film 20 , and the silicon film 40 is formed on the surface of the chemical conversion film 30 . These may be the same as those exemplified in the method for producing the surface-coated metal member described above. For example, the silicon coating 40 is made of an aqueous rust-preventive surface treatment composition containing a silane coupling agent, aqueous colloidal silica, and a water-dispersible resin.

[0089] The chemical conversion coating 30 may contain one or more metals contained in the treatment solution used for the chemical conversion treatment. For example, the chemical conversion coating 30 may contain one or more elements selected from the group consisting of zinc and zirconium.

[0090] The silicon coating 40 in the surface-coated metal member 100 may be used as the outermost top coat layer.

[0091] The surface-coated metal member 100 may be provided with films other than these depending on the purpose, and may have a single layer or multiple layers of each of the plating film 20, the chemical conversion film 30, and the silicon film 40.

[0092] The surface-coated metal component 100 can provide excellent rust prevention properties to metal components, and can therefore be used in a wide range of applications, including automotive parts that are exposed to high temperature and humidity conditions, as well as building components and electronic components.

[0093] Examples of surface-coated metal components 100 include steel structures such as various civil engineering structures, buildings, port facilities, plants, ships, marine structures, bridges, tanks, industrial water systems, power facilities, and communication facilities, as well as steel components used therein.

[0094] Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various other configurations may be adopted. Furthermore, the present invention is not limited to the above-described embodiments, and modifications and improvements within the scope of achieving the object of the present invention are included in the present invention. Below, examples of reference forms are added. 1. A chemical conversion treatment process in which a chemical conversion coating is formed on a plating film provided on the surface of a metal member by performing a chemical conversion treatment; a surface treatment step of applying an aqueous rust-preventive surface treatment composition containing a silane coupling agent, aqueous colloidal silica, a water-dispersible resin, and a solvent containing water to the chemical conversion coating, and drying the composition to form a silicon coating; The method for producing a surface-coated metal member includes the steps of: 2. A method for producing a surface-coated metal member according to 1., A method for producing a surface-coated metal member, wherein the chemical conversion treatment is selected from phosphate treatment or zirconium-based treatment. 3. A method for producing a surface-coated metal member according to 1. or 2., A method for producing a surface-coated metal member, wherein the water-dispersible resin comprises one or more selected from the group consisting of polyacrylic resin, silicone resin, phenolic resin, epoxy resin, polyurethane resin, polyester resin, polyvinyl butyral resin, phenolic resin, and modified products thereof. 4. A method for producing a surface-coated metal member according to any one of 1. to 3., The method for producing a surface-coated metal member, wherein the solvent contains an alcohol. 5. A method for producing a surface-coated metal member according to 4., The method for producing a surface-coated metal member, wherein the content of the alcohol in the aqueous rust-preventive surface treatment composition is 0.1 mass % or more and 15 mass % or less. 6. A method for producing a surface-coated metal member according to any one of 1. to 5., A method for producing a surface-coated metal member, wherein the aqueous rust-preventive surface treatment composition contains at least one of a highly condensed phosphate and a polyvalent phosphate ester as a phosphorus-based rust inhibitor. 7. A method for producing a surface-coated metal member according to any one of 1. to 6., A method for producing a surface-coated metal member, wherein the aqueous rust-preventive surface treatment composition contains a water-soluble transition metal compound. 8. A method for producing a surface-coated metal member according to any one of 1. to 7., The method for producing a surface-coated metal member, wherein the aqueous rust-preventive surface treatment composition is substantially free of chromium components. 9. A method for producing a surface-coated metal member according to any one of 1. to 8., A method for producing a surface-coated metal member, wherein the plating film contains zinc or chromium. 10. An aqueous rust-preventive surface treatment composition for use in forming a silicon film on a chemical conversion film of a metal member having a plating film, a chemical conversion film, and a silicon film on the surface thereof, the aqueous rust-preventive surface treatment composition comprising: a silane coupling agent; aqueous colloidal silica; a water-dispersible resin; a solvent comprising water, Aqueous anti-rust surface treatment composition. 11. A metal member having a plating film on its surface; a chemical conversion coating formed on the surface of the plating film; a silicon coating formed on the surface of the chemical conversion coating and comprising an aqueous rust-preventive surface treatment composition containing a silane coupling agent, aqueous colloidal silica, and a water-dispersible resin; A surface-coated metal member. 12. The surface-coated metal member according to 11, A surface-coated metal member, wherein the chemical conversion coating contains one or more elements selected from the group consisting of zinc element and zirconium element. [Example]

[0095] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the descriptions of these examples.

[0096] The information for each component shown in Table 1 is as follows: (Silane coupling agent) Epoxy silane 1: 3-glycidoxypropyltriethoxysilane (Wacker Asahi Kasei Silicone Co., Ltd., GF-82, solid content: 67% by mass) (Water dispersible resin) Polyacrylic acid resin 1: Water-dispersible acrylic resin (Stahl Polymers, solid content: 60% by mass) Silicone resin 1: Water-dispersible silicone resin (manufactured by Wacker Asahi Kasei Silicone Co., Ltd., solid content: 60% by mass) (Water-soluble transition metal compound) Titanium chelating agent 1: titanium lactate ammonium salt (manufactured by Matsumoto Fine Chemical Co., Ltd., TC-300, solid content: 20% by mass) (inorganic colloidal particles) Aqueous colloidal silica 1: (Nissan Chemical Industries, Ltd., Snowtex ST-O, acidic sol, particle size: 20 nm, solid content: 40% by mass) (Phosphorus-based rust inhibitor) Highly condensed phosphate 1: Ultra sodium phosphate (Kanto Chemical Co., Ltd., network structure of linear and cyclic phosphates interconnected, solid content: 100% by mass) Polyphosphate ester 1: Phytic acid (Fuso Chemical Co., Ltd., solid content: 100% by mass) (preservatives) Isothiazolinone compound 1: isothiazolinone compound (manufactured by San-ai Oil Co., Ltd., IT-25XA, solid content: 100% by mass) (solvent) Water 1: Ion-exchanged water Alcohol 1: Isopropyl alcohol (manufactured by Taishin Chemical Co., Ltd.)

[0097] Steel plate (manufactured by Standard Test Piece)

[0098] (plating bath) Hot-dip galvanizing bath A (Fe ion concentration in the bath: 2 ppm) Hot-dip galvanizing bath B (Fe ion concentration in the plating bath: 20 ppm) Hot-dip galvanizing bath C (Fe ion concentration in the plating bath: 10 ppm)

[0099] [Table 1]

[0100] In Table 1, the contents of the non-solvent components (silane coupling agent, water-dispersible resin, water-soluble transition metal compound, inorganic colloid particles, phosphorus-based rust inhibitor, and preservative) represent the amounts used.

[0101] <Preparation of aqueous anticorrosive surface treatment composition> Each component was weighed according to the blending ratio (mass %) of the raw material components shown in Table 1, and mixed using a stirrer to obtain aqueous solutions (samples 1 to 4) for each example and comparative example.

[0102] [Table 2]

[0103] <Production of surface-coated metal members> (plating process) In accordance with JIS H8641, the surface of the above steel sheet was degreased, washed with an acidic solution, flux-treated, and immersed in any of the above hot-dip galvanizing baths A to C to form a plating film, and then cooled to prepare a steel sheet (test piece) with a plating film.

[0104] (chemical conversion treatment) The plating film of the obtained test piece was either not subjected to chemical conversion treatment or subjected to zinc phosphate treatment or zirconium treatment, as shown in Table 2, to form a chemical conversion coating on the plating film. (Surface treatment) The chemically treated test pieces were immersed in one of Samples 1 to 4 (aqueous anti-rust surface treatment compositions) in Table 2, and Samples 1 to 3 were heat-treated at 120°C for 15 minutes, and Sample 4 was heat-treated at 200°C for 120 minutes, to form a silicon film approximately 1 μm thick on the surface of the chemical conversion coating. On the other hand, samples 1 to 4 (aqueous rust-preventive surface treatment compositions) in Table 2 were used to form silicon films on the plating films of test pieces that had not been subjected to chemical conversion treatment in the same manner.

[0105] In Table 2, examples are those in which chemical conversion treatment was performed and samples 2 to 4 were used as the aqueous rust-preventive surface treatment composition, while comparative examples are those in which no chemical conversion treatment was performed or sample 1 was used as the aqueous rust-preventive surface treatment composition.

[0106] Using each of the obtained test pieces, the following evaluation items were evaluated.

[0107] <Continuous salt spray test: SST test> The test pieces of each example and comparative example shown in Table 2 were subjected to a salt spray test (SST, test temperature: 35°C) in accordance with JIS Z2371, and the test time (h) until white rust appeared was measured. The results are shown in Table 2.

[0108] The test pieces in Table 2 that were not subjected to chemical conversion treatment (comparative examples) showed that the time it took for white rust to develop varied depending on the type of plating bath, resulting in variations in corrosion resistance depending on the state of the plating film. On the other hand, the test piece of Sample 1 (comparison example) with chemical conversion treatment (zinc phosphate treatment) in Table 2 showed a small variation in the time to white rust formation between plating baths A to C, but the absolute value of the time to white rust formation was smaller than the reference value, indicating insufficient corrosion resistance.

[0109] In contrast, the test pieces (embodiments) of Samples 2 to 4 in Table 2, which were chemically treated (zinc phosphate treatment / zirconium treatment), showed little variation in the time to white rust development between plating baths A to C, and the absolute value of the time to white rust development was greater than the reference value, demonstrating stable and excellent corrosion resistance. Furthermore, the test pieces of Samples 3 and 4 (Examples) in Table 2 that had undergone chemical conversion treatment (zirconium treatment) showed that the color of the plating film on the steel sheet could be visually observed through the zirconium chemical conversion coating, and had a good appearance equivalent to the gloss of the plating, while the zinc phosphate treatment gave an appearance with an excellent matte appearance. [Explanation of symbols]

[0110] 10 Base material 20 Plating film 30 Chemical conversion coating 40 Silicon film 100 Surface coated metal parts

Claims

1. a chemical conversion treatment step of forming a chemical conversion coating on the plating film provided on the surface of the metal member by performing a chemical conversion treatment; a surface treatment step of applying an aqueous rust-preventive surface treatment composition containing a silane coupling agent, aqueous colloidal silica, a water-dispersible resin, and a solvent containing water to the chemical conversion coating, and drying the composition to form a silicon coating; and the chemical conversion treatment is selected from a phosphate treatment or a zirconium-based treatment; the solvent comprises an alcohol; the aqueous rust-preventive surface treatment composition contains a water-soluble transition metal compound, and the water-soluble transition metal compound contains a water-soluble titanium compound or a water-soluble zirconium compound; A method for manufacturing a surface-coated metal member.

2. 2. A method for producing a surface-coated metal member according to claim 1, comprising: A method for producing a surface-coated metal member, wherein the water-dispersible resin comprises one or more selected from the group consisting of polyacrylic resin, silicone resin, phenolic resin, epoxy resin, polyurethane resin, polyester resin, polyvinyl butyral resin, phenolic resin, and modified products thereof.

3. 3. A method for producing a surface-coated metal member according to claim 1 or 2, A method for producing a surface-coated metal member, wherein the content of the alcohol in the aqueous rust-preventive surface treatment composition is 0.1 mass % or more and 15 mass % or less.

4. A method for producing a surface-coated metal member according to any one of claims 1 to 3, A method for producing a surface-coated metal member, wherein the aqueous rust-preventive surface treatment composition contains at least one of a highly condensed phosphate and a polyvalent phosphate ester as a phosphorus-based rust inhibitor.

5. A method for producing a surface-coated metal member according to any one of claims 1 to 4, The method for producing a surface-coated metal member, wherein the aqueous rust-preventive surface treatment composition is substantially free of chromium components.

6. A method for producing a surface-coated metal member according to any one of claims 1 to 5, A method for producing a surface-coated metal member, wherein the plating film contains zinc or chromium.

7. An aqueous rust-preventive surface treatment composition used to form a silicon film on a metal member having a plating film, a chemical conversion film, and a silicon film on the surface of the metal member, the aqueous rust-preventive surface treatment composition comprising: a silane coupling agent; aqueous colloidal silica; a water-dispersible resin; a solvent comprising water, the chemical conversion coating is formed by applying a chemical conversion treatment selected from a phosphate treatment or a zirconium-based treatment, the solvent comprises an alcohol; the aqueous rust-preventive surface treatment composition contains a water-soluble transition metal compound, and the water-soluble transition metal compound contains a water-soluble titanium compound or a water-soluble zirconium compound; Aqueous anti-rust surface treatment composition.

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