Chemical conversion treatment agent for zinc-plated steel sheet, chemically treated zinc-plated steel sheet, and method for producing same

Abstract

To provide a chemical conversion treatment agent for a galvanized steel sheet capable of forming a chromate-free film excellent in corrosion resistance, conductivity and dew condensation whitening resistance.SOLUTION: Silicon, at least one metal selected from the group consisting of zirconium and titanium, phosphorus, vanadium, carbon, and free fluoride ions, wherein a mass ratio of a total of zirconium and titanium to silicon [(Zr + Ti) / (Si)] is 0.1 to 0.2, A mass ratio of phosphorus to silicon [(P) / (Si)] is 0.15 to 0.31, a mass ratio of vanadium to silicon [(V) / (Si)] is 0.1 to 0.3, a mass ratio of carbon atom to silicon [(C) / (Si)] is 3.0 to 5.0, a mass ratio of vanadium to a total of zirconium and titanium [(V) / (Zr + Ti)] is 1.0 to 2.8, and a concentration of free fluoride ions is 200 to 1000mg / L.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a chemical conversion treatment agent for zinc-based plated steel sheets, a chemically treated zinc-based plated steel sheet using the same, and a method for producing the same. [Background technology]

[0002] Various types of plated steel sheets with excellent corrosion resistance are known and are used for home appliances, building materials, automobiles, and the like. For example, zinc-based plated steel sheets are known, in which a zinc-containing plating layer is formed on a steel sheet by hot-dip galvanizing or the like. In zinc-based plated steel sheets, even if the steel sheet is damaged and exposed, the zinc, which corrodes more easily than the iron constituting the steel sheet, corrodes first and forms a protective film, which can prevent corrosion of the steel sheet. Therefore, zinc-based plated steel sheets are used in a variety of applications requiring corrosion resistance.

[0003] However, the surfaces of various plated steel sheets, such as zinc-based plated steel sheets, can deteriorate depending on the surrounding environment. For example, in the case of zinc-based plated steel sheets, there is a problem that the plating layer oxidizes due to electrolytes such as salt contained in the atmosphere, or oxygen and moisture present in a high-temperature, high-humidity environment, resulting in the formation of white rust. Since the formation of white rust may impair the uniformity of the appearance, zinc-based plated steel sheets are required to have higher corrosion resistance.

[0004] Patent Document 1 describes a coating composition containing an organosilicon compound as a film-forming component, and containing at least one metal compound selected from the group consisting of titanium compounds and zirconium compounds, a phosphoric acid compound, and a fluorine compound as inhibitor components, and the ratio of cyclic siloxane bonds to linear siloxane bonds in the organosilicon compound is determined by the FT-IR reflectance spectrum of 1090 to 1100 cm, which indicates cyclic siloxane bonds. -1 The absorbance W1 and the linear siloxane bond at 1030-1040 cm -1 The document discloses a chemically treated metal material having on its surface a composite coating in which the ratio W1 / W2 of absorbance W1 to absorbance W2 is 1.0 to 2.0.

[0005] Patent Document 2 discloses a chemical conversion treatment composition for zinc-based plated steel sheets, which is a solution containing a silane compound, a molybdenum compound, a vanadium compound, a nickel compound, and a copper compound, in which the copper and nickel in the solution are Cu: 0.05 to 0.5 wt % and Ni: 0.5 to 3.0 wt %, respectively, with a weight ratio of Cu to Ni of 0.1:1.0 to 3.0.

[0006] However, in recent years, as the quality requirements for these anticorrosive coatings have become more stringent, there has been a demand for further improvements in corrosion resistance without a significant increase in cost.

[0007] Patent Document 3 discloses a chemically treated steel sheet having a coating that contains acrylic resin, zirconium, vanadium, phosphorus, and cobalt, and in a region in a cross section of the coating from the surface to 1 / 5 of the film thickness, the area ratio of the acrylic resin is 80 to 100 area %, and in a region consisting of a region from the film thickness center to 1 / 10 of the film thickness toward the surface and a region from the film thickness center to 1 / 10 of the film thickness toward the plating layer, the area ratio of the acrylic resin is 5 to 50 area %. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2012 / 147860 [Patent Document 2] International Publication No. 2014 / 104428 [Patent Document 3] International Publication No. 2017 / 155028 Summary of the Invention [Problem to be solved by the invention]

[0009] The technology of Patent Document 3 is known to exhibit excellent corrosion resistance, but because it must contain an organic resin, even if it is excellent in corrosion resistance and coating film adhesion, it has the problem of being poor in electrical conductivity and resistance to black residue during coating.

[0010] Furthermore, one of the important required properties for the surface appearance quality of chemically treated steel sheets used without painting is condensation whitening resistance. Condensation whitening is a problem that occurs when condensation occurs on coils or cut sheet piles of chemically treated steel sheets due to high humidity and a sudden drop in temperature, allowing water to seep in from the edges, causing the areas in contact with the water to turn white, and the whitened areas are deemed to be white rust and are discarded. None of Patent Documents 1 to 3 discusses condensation whitening resistance.

[0011] An object of the present invention is to provide a chemical conversion treatment agent for zinc-based plated steel sheets that can form a chromate-free coating that is excellent in corrosion resistance, electrical conductivity, and resistance to condensation whitening, a chemically treated zinc-based plated steel sheet using the same, and a method for producing the same. [Means for solving the problem]

[0012] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by a chemical conversion treatment agent containing silicon, either one or both of zirconium and titanium, phosphorus, vanadium, carbon, and free fluoride ions, with the mass ratio of each element and the concentration of the free fluoride ions being within specific ranges, and have thus completed the present invention.

[0013] The present invention has the following aspects. [1] Silicon (Si) and At least one metal selected from the group consisting of zirconium (Zr) and titanium (Ti); Rin (P) and Vanadium (V) and Carbon (C) and free fluoride ions, and A chemical conversion treatment agent for zinc-based plated steel sheets, comprising: the mass ratio of the sum of zirconium and titanium to silicon [(Zr+Ti) / (Si)] is 0.1 to 0.2; the mass ratio of phosphorus to silicon [(P) / (Si)] is 0.15 to 0.31; the mass ratio of vanadium to silicon [(V) / (Si)] is 0.1 to 0.3; the mass ratio of carbon to silicon [(C) / (Si)] is 3.0 to 5.0; the mass ratio of vanadium to the total of zirconium and titanium [(V) / (Zr+Ti)] is 1.0 to 2.8; The concentration of free fluoride ions is 200 to 1000 mg / L. Chemical conversion treatment agent for zinc-based coated steel sheets. [2] Further containing cobalt (Co), The chemical conversion treatment agent for zinc-based plated steel sheets according to [1] above, wherein the mass ratio of cobalt to silicon [(Co) / (Si)] is 0.02 to 0.2. [3] A zinc-based plated steel sheet having a plating layer containing zinc on at least one surface; a coating formed from the chemical conversion treatment agent for zinc-based plated steel sheet according to [1] or [2] above, provided on and in contact with the plating layer; A chemically treated zinc-based coated steel sheet. [4] The mass per unit area of ​​the coating is 0.05 to 2.0 g / m 2 The chemically treated zinc-based plated steel sheet according to [3] above, [5] A method for producing a chemically treated zinc-plated steel sheet, comprising contacting the surface of a zinc-containing plating layer of a zinc-plated steel sheet having the zinc-containing plating layer on at least one surface with the chemical conversion treatment agent for zinc-plated steel sheet according to [1] or [2] above, and drying the resulting temperature at a temperature higher than 50°C and lower than 250°C to form a coating. [6] The mass per unit area of ​​the coating is 0.05 to 2.0 g / m 2 The method for producing a chemically treated zinc-plated steel sheet according to [5] above, [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a chemical conversion treatment agent for zinc-based plated steel sheets that can form a chromate-free coating that is excellent in corrosion resistance, electrical conductivity, and resistance to condensation whitening, a chemically treated zinc-based plated steel sheet using the same, and a method for producing the same. DETAILED DESCRIPTION OF THE INVENTION

[0015] In this specification, the use of "to" to indicate a range of values ​​means that the values ​​before and after it are included as the lower and upper limits.

[0016] (Chemical conversion treatment agent for zinc-based coated steel sheets) The chemical conversion treatment agent for zinc-based plated steel sheet of the present invention (hereinafter also referred to simply as "chemical conversion treatment agent") contains silicon (Si), at least one metal selected from the group consisting of zirconium (Zr) and titanium (Ti) (hereinafter also referred to as "metal M"), phosphorus (P), vanadium (V), carbon (C), and free fluoride ions.

[0017] In the chemical conversion treatment agent, the mass ratio of the sum of zirconium and titanium to silicon [(Zr+Ti) / (Si)] is 0.1 to 0.2, preferably 0.12 to 0.18. When the mass ratio (Zr+Ti) / (Si) is 0.1 or more, the effect of metal M is fully exerted, improving the oxide film removal effect on the plating layer surface and the reactivity between the silicon source and the plating layer surface of the zinc-based plated steel sheet. The resulting film has improved adhesion and barrier effect, resulting in excellent corrosion resistance and condensation whitening resistance. On the other hand, when the mass ratio is 0.2 or less, excessive formation of a reaction film by metal M on the plating layer surface of the zinc-based plated steel sheet can be suppressed, resulting in excellent electrical conductivity.

[0018] The mass ratio of phosphorus to silicon [(P) / (Si)] is 0.15 to 0.31, preferably 0.18 to 0.28. When the mass ratio [(P) / (Si)] is 0.15 or more, the inhibitor effect of phosphorus is fully exerted. On the other hand, when the mass ratio is 0.31 or less, the water-solubilization of the coating can be suppressed.

[0019] The mass ratio of vanadium to silicon [(V) / (Si)] is 0.1 to 0.3, preferably 0.14 to 0.20. When the mass ratio [(V) / (Si)] is 0.1 or more, the inhibitor effect of vanadium is fully exhibited. On the other hand, when the mass ratio is 0.3 or less, the solution stability of the chemical conversion treatment agent is improved.

[0020] The mass ratio of carbon to silicon [(C) / (Si)] is 3.0 to 5.0, preferably 3.3 to 4.7. In chemical conversion treatment agents, carbon typically constitutes an organic substance. When the mass ratio [(C) / (Si)] is 2.0 or more, the adhesion and barrier effect of the formed coating are improved, and excellent corrosion resistance and whitening resistance are exhibited. On the other hand, when it is 5.0 or less, excellent conductivity is achieved.

[0021] The mass ratio of vanadium to the sum of zirconium and titanium [(V) / (Zr+Ti)] is 1.0 to 2.8, preferably 1.1 to 2.6. When the mass ratio [(V) / (Ti+Zr)] is 1.0 or more, the vanadium inhibitor effect is fully exhibited. On the other hand, when it is 4.0 or less, excellent liquid stability and condensation whitening resistance are achieved.

[0022] The concentration of free fluoride ions in the chemical conversion treatment agent is 200 to 1000 mg / L, preferably 400 to 700 mg / L. When the concentration of free fluoride ions is 200 mg / L or higher, the solution stability of the chemical conversion treatment agent is improved, and the effect of adding free fluoride ions is fully exerted, resulting in excellent corrosion resistance. On the other hand, when the concentration of free fluoride ions is 1000 mg / L or lower, excessive etching of the plating layer, increased incorporation of plating components into the film, and elution of excess fluoride ions from the film can be suppressed, resulting in excellent condensation whitening resistance and a dense film with excellent corrosion resistance.

[0023] The chemical conversion treatment agent preferably further contains cobalt (Co), which can inhibit oxygen-deficient corrosion. When the chemical conversion treatment agent contains cobalt, the mass ratio of cobalt to silicon [(Co) / (Si)] is preferably 0.02 to 0.2, and more preferably 0.05 to 0.17. When the mass ratio [(Co) / (Si)] is 0.02 or more, the effect of adding cobalt is fully exhibited. On the other hand, when the mass ratio is 0.2 or less, corrosion resistance is more excellent.

[0024] The silicon, zirconium, titanium, vanadium, and cobalt in the chemical conversion treatment agent can be quantified by an ICP atomic emission spectrometer to determine their mass ratios. More specifically, a sample diluted to an arbitrary ratio is pretreated by adding nitric acid, perchloric acid, and hydrofluoric acid, and heating it at 1000 W for 25 minutes in a microwave decomposition device, and then quantified by an ICP atomic emission spectrometer.

[0025] The carbon content in the chemical conversion treatment agent can be determined by a total organic carbon meter to determine the mass ratio. More specifically, a sample diluted to an arbitrary ratio can be quantified by oxidative decomposition at 700°C using the total organic carbon meter.

[0026] The concentration of free fluoride ions in the chemical conversion treatment agent was measured at a pH of 4.0 and a liquid temperature of 30°C. The concentration of free fluoride ions can be measured using a portable ion-pH meter such as the IM-32P (manufactured by DKK-TOA Corporation).

[0027] One embodiment of the chemical conversion treatment agent comprises an aqueous medium containing a silicon source, a metal M source, a phosphorus source, a vanadium source, and a free fluoride ion source, with at least a portion of each source also serving as a carbon source. The chemical conversion treatment agent of this embodiment preferably further contains a cobalt source. In the chemical conversion treatment agent of this embodiment, it is preferable that at least a portion of the silicon source also serves as a carbon source. At least a part of the supply source of each element may also serve as a supply source of the other element.

[0028] The silicon source is not particularly limited, but examples thereof include silane coupling agents such as 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, etc. Only one silicon source may be used, or two or more silicon sources may be used.

[0029] The source of metal M is not particularly limited, but examples thereof include zirconium hydrofluoric acid and titanium hydrofluoric acid. Only one source of metal M may be used, or two or more sources may be used.

[0030] The phosphorus source is not particularly limited, but may be, for example, phosphoric acid. Only one phosphorus source may be used, or two or more phosphorus sources may be used.

[0031] Examples of vanadium sources include, but are not limited to, vanadium pentoxide (VO), metavanadate (HVO), ammonium metavanadate, sodium metavanadate, vanadium oxytrichloride (VOCl), vanadium trioxide (VO), vanadium dioxide (VO), vanadium oxysulfate (VOSO), vanadium oxyacetylacetonate (VO(OC(=CH)CHCOCH)), vanadium acetylacetonate (V(OC(=CH)CHCOCH)), vanadium trichloride (VCl), and phosphovanadomolybdic acid. Pentavalent vanadium compounds can also be used that have been reduced to tetravalent or divalent vanadium with an organic compound containing at least one functional group selected from the group consisting of hydroxyl, carbonyl, carboxyl, primary to tertiary amino, amide, phosphate, and phosphonate. One or more vanadium sources may be used.

[0032] The source of free fluoride ions is not particularly limited as long as it can provide free fluoride ions when mixed with an aqueous medium, and examples thereof include hydrofluoric acid, hydrofluorosilicic acid, hydrofluoroboric acid, ammonium fluoride, magnesium fluoride, aluminum fluoride, sodium fluoride, potassium fluoride, and zinc fluoride. Only one type of source of free fluoride ions may be used, or two or more types may be used.

[0033] The source of cobalt is not particularly limited, but examples include cobalt sulfate, cobalt nitrate, and cobalt carbonate.

[0034] Examples of aqueous media include water, and mixtures of water and water-soluble organic solvents. The water-soluble organic solvent is mixed with water, for example, to improve the coatability of the chemical conversion treatment agent. Examples of the water-soluble organic solvent include alcohols such as ethanol, isopropyl alcohol, t-butyl alcohol, and propylene glycol; cellosolves such as ethylene glycol monobutyl ether and ethylene glycol monoethyl ether; esters such as ethyl acetate and butyl acetate; and ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone. Only one water-soluble organic solvent may be used, or two or more may be used. The content of the water-soluble organic solvent in the aqueous medium is not particularly limited, but is, for example, 0 to 10% by mass relative to the total mass of the aqueous medium.

[0035] The chemical conversion treatment agent may contain additives such as a leveling agent, a metal stabilizer, an etching inhibitor, and a pH adjuster, as long as the effects of the present invention are not impaired. Examples of the leveling agent include nonionic or cationic surfactants such as polyethylene oxide adducts, polypropylene oxide adducts, and acetylene glycol compounds. Examples of metal stabilizers include chelating compounds such as ethylenediaminetetraacetic acid (EDTA) and diethylenetriamine-N,N,N',N'',N''-pentaacetic acid (DTPA). Examples of etching inhibitors include amine compounds such as ethylenediamine, triethylenepentamine, guanidine, and pyrimidine. In particular, compounds having two or more amino groups in one molecule are preferred because they are also effective as metal stabilizers. Examples of pH adjusters include organic acids such as acetic acid and lactic acid, inorganic acids such as hydrofluoric acid, ammonium salts, and amines. These additives may be used alone or in combination of two or more.

[0036] The contents of the sources of silicon, metal M, phosphorus, vanadium, and cobalt in the chemical conversion treatment agent are set according to the mass ratio of each element. The content of the source of free fluoride ions is set according to the concentration of free fluoride ions, which can be adjusted not only by the content of the source of free fluoride ions but also by the pH of the chemical conversion treatment agent. The content of the aqueous medium is set according to the solids concentration of the chemical conversion treatment agent.

[0037] The solid content of the chemical conversion treatment agent is not particularly limited, but is, for example, 1.0 to 20.0 mass %. The solid content of the chemical conversion treatment agent is the total of all components of the chemical conversion treatment agent excluding the aqueous medium. The pH of the chemical conversion treatment agent is preferably 3.0 to 5.0, more preferably 3.5 to 4.5. When the pH is equal to or higher than the lower limit of the above range, excessive etching of the plating layer can be suppressed, resulting in better corrosion resistance. On the other hand, when the pH is equal to or lower than the upper limit of the above range, the solution stability is better.

[0038] The chemical conversion treatment agent can be prepared, for example, by mixing an aqueous medium, a silicon source, a metal M source, a phosphorus source, a vanadium source, and a free fluoride ion source. At this time, a cobalt source, additives, etc. may also be mixed, if necessary.

[0039] (chemically treated zinc-plated steel sheet) The chemically treated zinc-based plated steel sheet of the present invention comprises a zinc-based plated steel sheet and a coating formed from the chemical conversion treatment agent of the present invention.

[0040] A zinc-based plated steel sheet has a plating layer containing zinc on at least one surface of the steel sheet. The metal material constituting the plating layer of the zinc-based plated steel sheet is not particularly limited as long as it contains zinc, and may be zinc or an alloy containing zinc and other elements such as aluminum, magnesium, silicon, etc. in any ratio. Examples of zinc-based plated steel sheets include, but are not limited to, zinc-plated steel sheets (Zn-plated steel sheets), zinc-aluminum-plated steel sheets (Zn-Al-plated steel sheets), zinc-aluminum-magnesium-plated steel sheets (Zn-Al-Mg-plated steel sheets), and zinc-aluminum-magnesium-silicon-plated steel sheets (Zn-Al-Mg-Si-plated steel sheets). The mass per unit area of ​​the plating layer is not particularly limited, but for example, it is 50 to 800 g / m on both sides. 2 is. The thickness (sheet thickness) of the zinc-based plated steel sheet is not particularly limited, but is, for example, 0.2 to 9.0 mm.

[0041] The coating is provided on and in contact with the plating layer of the zinc-based plated steel sheet. When the zinc-based plated steel sheet has plating layers on both surfaces, the coating may be provided on one surface or on both surfaces of the zinc-based plated steel sheet. The method for forming the coating will be described in detail later.

[0042] In a coating formed from the chemical conversion treatment agent of the present invention, the mass ratio of the sum of zirconium and titanium to silicon [(Zr + Ti) / (Si)] is usually the same as the mass ratio of the sum of zirconium and titanium to silicon [(Zr + Ti) / (Si)] in the chemical conversion treatment agent. The same is true for the mass ratio of phosphorus to silicon [(P) / (Si)], the mass ratio of vanadium to silicon [(V) / (Si)], and the mass ratio of vanadium to the sum of zirconium and titanium [(V) / (Zr + Ti)]. Depending on the carbon source, the mass ratio of carbon to silicon [(C) / (Si)] in the coating may be lower than that in the chemical conversion treatment agent.

[0043] The mass per unit area of ​​the coating is 0.05 to 2.0 g / m 2 It is preferable that the density is 0.2 to 1.0 g / m 2 More preferably, it is 0.3 to 0.6 g / m 2 It is most preferable that the mass per unit area of ​​the coating is 0.05 g / m 2When the coating thickness is 2.0 g / m or more, the surface of the plating layer can be coated with a sufficient thickness, and corrosion resistance is superior. 2 When the thickness is less than 100 μm, the resistance to condensation whitening is more excellent.

[0044] (Method of manufacturing chemically treated zinc-based coated steel sheet) The chemically treated zinc-based plated steel sheet of the present invention can be produced, for example, by a method in which the chemical conversion treatment agent of the present invention is brought into contact with the surface of the plating layer of a zinc-based plated steel sheet and dried to form a coating.

[0045] The zinc-based plated steel sheet may be a commercially available one, or may be one produced by a known method. Before contacting the surface of the zinc-based plated steel sheet with the chemical conversion treatment agent, the surface may be subjected to treatments such as alkaline or acid degreasing, water washing, solvent degreasing, and electrolytic degreasing.

[0046] There are no particular limitations on the method for contacting the chemical conversion treatment agent, and examples thereof include a method in which the chemical conversion treatment agent is applied. The drying temperature of the chemical conversion treatment agent is preferably higher than 50°C and lower than 250°C, more preferably 70°C to 150°C, and most preferably 100°C to 140°C. If the temperature is higher than 50°C, the aqueous medium can be sufficiently volatilized. On the other hand, if the temperature is lower than 250°C, thermal decomposition of organic matter in the chemical conversion treatment agent can be suppressed.

[0047] The chemically treated zinc-based plated steel sheet of the present invention has a coating formed from the chemical conversion treatment agent of the present invention, and therefore exhibits excellent corrosion resistance, electrical conductivity, and resistance to condensation whitening. The reasons for this are presumed to be as follows, but the present invention is not bound by such presumption. The coating formed by the chemical conversion treatment agent of the present invention is primarily composed of silicon compounds. It is believed that corrosion resistance is due to the fact that when some of the silicon compounds are concentrated by drying or other means, the silicon compounds react with each other to form a continuous coating, and that the -Si-OH groups generated by hydrolysis of some of the silicon compounds form Si-O-M' bonds (M': metal element on the surface of the plating layer) with the surface of the plating layer, thereby providing a significant barrier effect. Furthermore, the ability to form a dense coating allows for the coating to be thin, and electrical conductivity is also improved.

[0048] On the other hand, a coating using the chemical conversion treatment agent of the present invention is formed based on silicon, and in its structure, the silicon-organic chain is arranged in a regular pattern, and because the organic chain is relatively short, silicon-containing portions and organic portions, i.e., inorganic and organic materials, are arranged in a regular and dense pattern in extremely small regions within the coating, and it is presumed that this makes it possible to form a novel coating that combines the properties normally possessed by inorganic coatings (heat resistance, electrical conductivity, and resistance to black scum during processing, etc.) with the properties normally possessed by organic coatings (fingerprint resistance, paintability, etc.). Furthermore, analysis has confirmed that approximately 80% of the silicon in the silicon-containing portion of the coating forms siloxane bonds.

[0049] By including in this base film a metal M that forms a dense film due to the increase in pH in the immediate vicinity of the surface of the metal being treated caused by the etching reaction, corrosion resistance is further improved. Free fluoride ions act as the starting point for the etching reaction and contribute to the chemical equilibrium of metal M as shown in the following formula (1). Therefore, by keeping the concentration of free fluoride ions within an appropriate range, the etching reaction and the formation of a dense film are balanced, and the amount of fluoride ions eluted from the film after hardening is limited, resulting in excellent corrosion resistance and resistance to condensation whitening. MF6 2- +2H2O ⇔ MO2+6F - +4H + (1) (wherein M represents Ti or Zr) In addition, it is believed that the inclusion of phosphorus as an elution inhibitor and vanadium, which imparts corrosion resistance through an oxidation-reduction reaction, will result in excellent corrosion resistance and resistance to condensation whitening. [Example]

[0050] The present invention will be specifically explained below with reference to examples and comparative examples of the present invention, but the present invention is not limited to these examples.

[0051] [Plated steel sheet] The following commercially available plated steel sheets were prepared. Galvanized steel sheet A: A hot-dip galvanized steel sheet having a hot-dip galvanized layer on both sides, sheet thickness = 0.8 mm, coating weight per side = 60 g / m 2 Coated steel sheet B: Hot-dip zinc-aluminum coated steel sheet with hot-dip zinc-55% aluminum coating layers on both sides, sheet thickness = 0.8 mm, coating weight per side = 60 g / m 2 Coated steel sheet D: Hot-dip zinc-aluminum-magnesium coated steel sheet with hot-dip zinc-6% aluminum-3% magnesium coating layers on both sides, sheet thickness = 0.8 mm, coating weight per side = 60 g / m 2 Coated steel sheet E: Hot-dip zinc-aluminum-magnesium-silicon coated steel sheet with hot-dip zinc-11% aluminum-3% magnesium-0.2% silicon coating layers on both sides, sheet thickness = 0.8 mm, coating weight per side = 60 g / m 2 Coated steel sheet F: Hot-dip zinc-aluminum-magnesium coated steel sheet with hot-dip zinc-19% aluminum-6% magnesium coating layers on both sides, sheet thickness = 1.6 mm, coating weight per side = 60 g / m 2

[0052] [Pretreatment of plated steel sheets] A silicate-based alkaline degreasing agent, Fine Cleaner 4336 (registered trademark: manufactured by Nippon Parkerizing Co., Ltd.), was prepared as an aqueous solution at a concentration of 20 g / L at 60°C, and this aqueous solution was sprayed onto both sides of the plated steel sheet for 2 minutes, followed by rinsing with pure water for 30 seconds and drying. This pretreated plated steel sheet was used to prepare a chemically treated plated steel sheet.

[0053] [Preparation of Chemical Conversion Treatment Agent] A chemical conversion treatment agent was obtained by adding the sources of each element and the source of free fluoride ions to water, stirring, and adjusting the pH with ammonia or acetic acid as necessary so that the mass ratio of each element and the free fluoride ion concentration would be the values ​​shown in Tables 1 to 4. The amount of water was such that the solids concentration of the chemical conversion treatment agent would be 10.0 mass%. Phosphoric acid was used as the phosphorus source. The sources of elements other than phosphorus are shown in Tables 1 to 4. The symbols in the tables have the following meanings. <Silicon supply source (Si supply source)> G1: 3-aminopropyltrimethoxysilane G2: 3-aminopropyltriethoxysilane G3: 3-glycidoxypropyltrimethoxysilane G4: 3-glycidoxypropyltriethoxysilane <Source of Metal M (Source of Metal M)> H1: Titanium Hydrofluoric Acid H2: Zirconium hydrofluoric acid <Vanadium supply source (V supply source)> J1: Vanadium oxysulfate J2: Vanadium oxyacetylacetonate J3: Vanadium acetylacetonate <Source of free fluoride ions> K1: Hydrofluoric acid K2: Hydrofluoric acid K3: Sodium fluoride <Source of cobalt> L1: Cobalt sulfate L2: Cobalt nitrate L3: Cobalt carbonate

[0054] [Preparation of chemically treated plated steel sheet] The chemical conversion treatment agent prepared above was applied to one side of a plated steel sheet (pretreated) shown in Tables 1 to 4 by bar coating at room temperature of 25°C so that the mass after drying (film mass) would be the value shown in Tables 1 to 4. The plated steel sheet was then dried in a hot air drying furnace until the temperature of the plated steel sheet, as confirmed by a temperature indicator (manufactured by NOF Corp., product name "Thermo Label (registered trademark)") attached to the plated steel sheet, reached the temperature shown in Tables 1 to 4, thereby obtaining a chemical conversion treated plated steel sheet in which a film was formed on the plating layer of the plated steel sheet.

[0055] 〔evaluation〕 The obtained chemical conversion coated steel sheets were used as test pieces and were subjected to the following evaluations. The results are shown in Tables 5 to 8.

[0056] 1.SST flat surface test A 70mm x 150mm rectangular test piece (flat plate) with its edges sealed with tape was subjected to a salt spray test (SST) according to JIS Z 2371 for 240 hours, and the occurrence of white rust was observed and evaluated according to the following criteria. <Evaluation criteria> ◎ = Rust occurs on less than 3% of the total area ○ = Rust occurs on 3% to less than 10% of the total area △ = Rust occurs on 10% to less than 30% of the total area × = Rust occurs on 30% or more of the total area

[0057] 2.SST processed part test The center of a 70mm x 150mm rectangular test piece (flat plate) with the edges sealed with tape was subjected to an Erichsen test (7mm push-out), and then a salt spray test (SST) according to JIS Z 2371 was carried out for 120 hours, and the occurrence of white rust in the extruded part was observed and evaluated according to the following criteria. <Evaluation criteria> ◎ = Rust occurs on less than 10% of the total area ○ = Rust occurs on 10% to less than 20% of the total area △ = Rust occurs on 20% to less than 30% of the total area × = Rust occurs on 30% or more of the total area

[0058] 3.Conductivity test The interlaminar resistance of the test piece was measured using an interlaminar resistance measuring device. <Evaluation criteria> ◎ = Interlayer resistance is less than 1.0Ω ○ = Interlayer resistance is 1.0Ω or more and less than 2.0Ω △ = Interlayer resistance is 2.0Ω or more and less than 3.0Ω × = Interlayer resistance less than 3.0Ω

[0059] 4.Condensation and whitening resistance A drop of ion-exchanged water was dropped onto the surface of the test piece, and another test piece was placed on top of the dropped surface with the coatings facing each other, sandwiching the water between the two test pieces. Next, these test pieces were wrapped in food wrap film (manufactured by Asahi Kasei Corporation, product name "Saran Wrap (registered trademark)"), clipped at the four corners, and stored in a dryer at 50 ° C for 72 hours. Thereafter, the two test pieces were removed, and the presence or absence of whitening and gloss reduction in the area where the water droplet was dropped was visually observed, and evaluated according to the following criteria. <Evaluation criteria> ◎ = No change ○ = No whitening by visual inspection, gloss reduction × = Visual whitening and loss of gloss

[0060] [Table 1]

[0061] [Table 2]

[0062] [Table 3]

[0063] [Table 4]

[0064] [Table 5]

[0065] [Table 6]

[0066] [Table 7]

[0067] [Table 8]

[0068] Examples 1 to 66 were excellent in corrosion resistance, electrical conductivity, and resistance to condensation whitening. On the other hand, Comparative Example 1, in which (Zr+Ti) / Si was less than 0.1, was poor in corrosion resistance. Comparative Example 2, in which (Zr+Ti) / Si was greater than 0.2, was poor in electrical conductivity and resistance to condensation whitening. Comparative Example 3, in which P / Si was less than 0.15, was poor in corrosion resistance. Comparative Example 4, in which P / Si was greater than 0.31, was poor in resistance to condensation whitening. Comparative Example 5, in which V / Si was less than 0.1 and V / (Zr+Ti) was less than 1.0, was poor in corrosion resistance. Comparative Example 6, in which V / Si was greater than 0.3, was poor in resistance to condensation whitening. Comparative Example 7, in which V / (Zr+Ti) was greater than 2.8, was poor in resistance to condensation whitening. Comparative Example 8, in which C / Si was less than 3.0, was poor in corrosion resistance and condensation whitening resistance. Comparative Example 9, in which C / Si was greater than 5.0, was poor in electrical conductivity. Comparative Examples 10, 12, 14, 16, and 18, in which the concentration of free fluoride ions was less than 200 mg / L, were inferior in corrosion resistance. Comparative Examples 11, 13, 15, 17, and 19, in which the concentration of free fluoride ions exceeded 1000 mg / L, were poor in corrosion resistance and resistance to condensation whitening.

Claims

1. Silicon (Si), At least one metal selected from the group consisting of zirconium (Zr) and titanium (Ti); Rin (P) and Vanadium (V), Carbon (C), free fluoride ions, and A chemical conversion treatment agent for zinc-based plated steel sheets, comprising: a mass ratio of the sum of zirconium and titanium to silicon [(Zr+Ti) / (Si)] of 0.1 to 0.2; a mass ratio of phosphorus to silicon [(P) / (Si)] of 0.15 to 0.31; the mass ratio of vanadium to silicon [(V) / (Si)] is 0.1 to 0.3; the mass ratio of carbon to silicon [(C) / (Si)] is 3.0 to 5.0; the mass ratio of vanadium to the total of zirconium and titanium [(V) / (Zr+Ti)] is 1.0 to 2.8; The concentration of free fluoride ions is 200 to 1000 mg / L. Chemical conversion treatment agent for zinc-based coated steel sheets.

2. Further containing cobalt (Co), 2. The chemical conversion treatment agent for zinc-based plated steel sheet according to claim 1, wherein the mass ratio of cobalt to silicon [(Co) / (Si)] is 0.02 to 0.

2.

3. a zinc-based plated steel sheet having a plating layer containing zinc on at least one surface; a coating formed from the chemical conversion treatment agent for zinc-based plated steel sheet according to claim 1 or 2, which is provided on and in contact with the plating layer; A chemically treated zinc-based coated steel sheet.

4. The mass per unit area of ​​the coating is 0.05 to 2.0 g / m ２ The chemically treated zinc-based plated steel sheet according to claim 3, wherein

5. A method for producing a chemically treated zinc-based plated steel sheet, comprising contacting the surface of a zinc-based plated steel sheet having a zinc-containing plated layer on at least one surface thereof with the chemical conversion treatment agent for zinc-based plated steel sheet according to claim 1 or 2, and drying the resulting steel sheet at an ultimate temperature higher than 50°C and lower than 250°C to form a coating.

6. The mass per unit area of ​​the coating is 0.05 to 2.0 g / m ２ The method for producing a chemically treated zinc-based plated steel sheet according to claim 5, wherein

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