Surface treated steel sheet for organic resin coating and method of producing same, and organic resin coated steel sheet and method of producing same

Abstract

Disclosed is a method of producing a surface-treated steel sheet for organic resin coating comprising: applying, to a surface of a zinc or zinc alloy coated or plated steel sheet, a surface-treatment solution containing a resin compound having a specific bisphenol skeleton, a cationic urethane resin emulsion, a silane coupling agent having a specific reactive functional group, an organic titanium chelate compound, a tetravalent vanadium compound, a molybdate compound, a fluorine compound, and water in a specific ratio and with a pH of 4 to 5 to form a surface-treatment layer such that a coating weight of the surface-treatment layer per surface after drying of the surface-treatment solution is 0.005 g / m2 to 1.8 g / m2.

Description

Surface-treated steel sheet for organic resin coating and manufacturing method thereof, and organic resin-coated steel sheet and manufacturing method thereof

[0001] The present invention relates to a surface-treated steel sheet for organic resin coating and a manufacturing method thereof, and an organic resin-coated steel sheet and a manufacturing method thereof.

[0002] Zinc-based plated steel sheets are widely used in fields such as automobiles, home appliances, and building materials. Conventionally, surface-treated steel sheets have been widely used in which the surface of a zinc-based plated steel sheet is subjected to a chromate treatment using a treatment solution containing chromic acid, dichromic acid, or a salt thereof as a main component, in order to improve corrosion resistance. However, in light of recent global environmental concerns, there has been an increasing demand for zinc-based plated steel sheets that have been subjected to a chromate-free surface treatment (hereinafter referred to as "chromate-free treated steel sheets"), and various chromate-free treated steel sheets have been developed and put into practical use.

[0003] Considering that chromate-free treated steel sheets are used in a variety of applications, including automobiles, home appliances, and building materials, they are required to have excellent resistance to blackening and storage stability of surface treatment solutions in addition to corrosion resistance.

[0004] Patent Document 1 discloses a method for producing a zinc-based coated steel sheet by applying a surface treatment solution containing a resin compound having a specific bisphenol skeleton, a cationic urethane resin emulsion, a silane coupling agent having a specific reactive functional group, an organic titanium chelate compound, a tetravalent vanadium compound, a molybdenum acid compound, a fluorine compound, and water in specific ratios and having a pH of 4 to 5, and then drying the solution to produce a coating weight of 0.2 to 1.8 g / m per side. ２ The document describes a method for producing a surface-treated steel sheet, which is characterized by forming a surface treatment film such that:

[0005] JP 2012-67369 A

[0006] The method for producing a surface-treated steel sheet described in Patent Document 1 is preferable in that it can produce a surface-treated steel sheet with excellent corrosion resistance and blackening resistance, and also has excellent storage stability of the surface treatment solution. However, Patent Document 1 did not consider (i) the corrosion resistance when an organic resin film with a thickness of 60 μm or more or an organic resin film with small elongation is formed on the surface-treated steel sheet, or (ii) the adhesion between the organic resin film and the surface treatment film and the plating layer when the organic resin film is formed on the surface-treated steel sheet and then subjected to severe processing. The main purpose of forming an organic resin film on a surface-treated steel sheet is to impart design and durability, and ensuring a film thickness is effective. The appropriate film thickness depends on the type of organic resin film and the environment in which it is used, but is often 60 μm or more. The inventors' investigations revealed that the method for producing a surface-treated steel sheet described in Patent Document 1 leaves room for improvement in terms of (i) and (ii) above.

[0007] In view of the above problems, the present invention has an object to provide a method for producing a surface-treated steel sheet for organic resin coating, which does not contain chromium compounds in the surface treatment film, and which, in addition to blackening resistance, can produce a surface-treated steel sheet that has (i) excellent corrosion resistance when an organic resin film with a thickness of 60 μm or more or an organic resin film with small elongation is formed on the surface-treated steel sheet, and (ii) excellent adhesion between the organic resin film and the surface treatment film and between the surface treatment film and a plating layer when the organic resin film is formed on the surface-treated steel sheet and then subjected to severe processing, and which also has excellent storage stability of the surface treatment solution.

[0008] As a result of intensive research, the present inventors have found that: (A) using a surface treatment liquid containing a resin compound having a specific bisphenol skeleton, a cationic urethane resin emulsion, a silane coupling agent having a specific reactive functional group, an organic titanium chelate compound, a tetravalent vanadium compound, a molybdic acid compound, a fluorine compound, and water in specific ratios and having a pH of 4 to 5, wherein the content of the fluorine compound in the specific ratios is intentionally set to be particularly high; and (B) applying the surface treatment liquid to the surface of a zinc-based plated steel sheet and drying it to form a surface treatment film, wherein the coating weight per side is 0.005 to 0.18 g / m. ２It has been found that the above-mentioned properties (i) and (ii) can be improved by combining the above and solving the above problems.

[0009] The present invention was completed based on these findings, and its gist is as follows: [1] A surface treatment solution containing (A) a resin compound having a bisphenol skeleton represented by the following general formula (I): (B) a cationic urethane resin emulsion having at least one cationic functional group selected from primary to tertiary amino groups and quaternary ammonium salt groups: (C) a silane coupling agent having at least one reactive functional group selected from an active hydrogen-containing amino group, an epoxy group, a mercapto group, and a methacryloxy group: (D) an organic titanium chelate compound: (E) a tetravalent vanadium compound: (F) a molybdic acid compound: (G) a fluorine compound: (G) water: (H) in a range satisfying the following conditions (1) to (6), and having a pH of 4 to 5, is applied to the surface of a zinc-based plated steel sheet and dried to obtain a coating weight of 0.005 to 0.18 g / m per side. ２ (1) The solid content mass of the resin compound (A) (A Ｓ ), the solid content mass of the cationic urethane resin emulsion (B) (B Ｓ ), and the solid content mass of the silane coupling agent (C) (C Ｓ ) the solid content mass (B) of the cationic urethane resin emulsion (B) relative to the total Ｓ ) ratio [(B Ｓ ) / {(A Ｓ ) + (B Ｓ ) + (C Ｓ )}] is 0.10 to 0.30 (2) The solid content mass (A Ｓ ), the solid content mass of the cationic urethane resin emulsion (B) (B Ｓ ), and the solid content mass of the silane coupling agent (C) (C Ｓ ) the solid content mass (C Ｓ ) ratio [(CＳ ) / {(A Ｓ ) + (B Ｓ ) + (C Ｓ (3) The titanium-equivalent mass (D) of the organic titanium chelate compound (D) is 0.60 to 0.85. Ｔｉ ) the solid content mass (C Ｓ ) ratio {(C Ｓ ) / (D Ｔｉ (4) The titanium-equivalent mass (D) of the organic titanium chelate compound (D) is 50 to 70. Ｔｉ ) the vanadium-equivalent mass (E) of the tetravalent vanadium compound (E) relative to Ｖ ) ratio {(E Ｖ ) / (D Ｔｉ )} is 0.30 to 0.50 (5) The solid content mass (A Ｓ ), the solid content mass of the cationic urethane resin emulsion (B) (B Ｓ ), and the solid content mass of the silane coupling agent (C) (C Ｓ ) the molybdenum-equivalent mass (F) of the molybdic acid compound (F) relative to the total Ｍｏ ) ratio [(F Ｍｏ ) / {(A Ｓ ) + (B Ｓ ) + (C Ｓ )}] is 0.003 to 0.030 (6) The solid content mass (A Ｓ ), the solid content mass of the cationic urethane resin emulsion (B) (B Ｓ ), and the solid content mass of the silane coupling agent (C) (C Ｓ ) the fluorine equivalent mass (G Ｆ ) ratio [(G Ｆ ) / {(A Ｓ ) + (B Ｓ ) + (C Ｓ )}] is 0.101 to 0.200 In formula (I), Y bonded to a benzene ring １ and Y ２are each independently a hydrogen atom or a Z group represented by the following general formula (II) or (III), the average number of Z groups substituted per benzene ring is 0.2 to 1.0, and n represents an integer of 2 to 50. In formulas (II) and (III), R １ , R ２ , R ３ , R ４ and R ５ are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or a hydroxyalkyl group having 1 to 10 carbon atoms, and A － represents a hydroxide ion or an acid ion.

[0010] [2] The method for producing a surface-treated steel sheet to be coated with an organic resin according to the above [1], wherein the drying of the surface treatment liquid is carried out under conditions in which the maximum sheet temperature is 50 to 180°C.

[0011] [3] A surface-treated steel sheet for organic resin coating, produced by the method for producing a surface-treated steel sheet for organic resin coating according to [1] or [2] above.

[0012] [4] A method for producing an organic resin-coated steel sheet, comprising: the method for producing a surface-treated steel sheet for organic resin coating according to the above [1] or [2]; and a step of forming an organic resin film on the surface treatment film of the surface-treated steel sheet for organic resin coating.

[0013] [5] The method for producing an organic resin-coated steel sheet according to the above [4], wherein the organic resin coating is formed by laminating an organic resin film on the surface treatment coating.

[0014] [6] The method for producing an organic resin-coated steel sheet according to the above [5], wherein the organic resin film has a thickness of 60 μm or more.

[0015] [7] The method for producing an organic resin-coated steel sheet according to [5] or [6] above, wherein the organic resin film is one or more films selected from a polyvinyl chloride film, a polyolefin-based film, a polyester-based film, and a fluororesin-based film.

[0016] [8] An organic resin-coated steel sheet manufactured by the method for manufacturing an organic resin-coated steel sheet according to any one of [4] to [7] above.

[0017] The method for producing a surface-treated steel sheet for organic resin coating of the present invention does not contain chromium compounds in the surface treatment film, and in addition to blackening resistance, it is possible to produce a surface-treated steel sheet that has excellent (i) corrosion resistance when an organic resin film with a thickness of 60 μm or more or an organic resin film with small elongation is formed on the surface-treated steel sheet, and (ii) adhesion between the organic resin film and the surface treatment film and adhesion between the surface treatment film and the plating layer when the organic resin film is formed on the surface-treated steel sheet and then subjected to severe processing, and further the storage stability of the surface treatment solution is excellent.

[0018] [Zinc-Based Coated Steel Sheet] The zinc-based coated steel sheet used in the present invention may be an electrolytic zinc-plated steel sheet based on a cold-rolled steel sheet, a hot-dip zinc-plated steel sheet, a Zn-Al-plated steel sheet, a Zn-Al-Mg-plated steel sheet, a Zn-Mg-plated steel sheet, a Zn-Fe-plated steel sheet, or a Zn-Ni-plated steel sheet. The plating method may be either electroplating or hot-dip plating. Furthermore, for the purpose of improving the blackening resistance of the zinc-based coated steel sheet, the zinc-based coated steel sheet may be one in which trace amounts of Ni or Co are added to the plating, or in which these metals are precipitated on the surface of the zinc-based coated steel sheet using an acidic or alkaline aqueous solution containing Ni, Co, or Fe. The coating weight of the zinc-based coated steel sheet is 5 g / m per side from the viewpoint of ensuring corrosion resistance. ２ It is desirable that this is the case.

[0019] [Surface Treatment Liquid] The surface treatment liquid used in the present invention contains a resin compound (A) having a specific bisphenol skeleton, a cationic urethane resin emulsion (B), a silane coupling agent (C) having a specific reactive functional group, an organic titanium chelate compound (D), a tetravalent vanadium compound (E), a molybdic acid compound (F), a fluorine compound (G), and water.

[0020] <Resin Compound (A)> The resin compound (A) contained in the surface treatment liquid has a bisphenol skeleton represented by the following general formula (I). In formula (I), Y bonded to a benzene ring １and Y ２ are each independently a hydrogen atom or a Z group represented by the following general formula (II) or (III), the average number of Z groups substituted per benzene ring is 0.2 to 1.0, and n represents an integer of 2 to 50.

[0021] Here, the average value of the number of Z groups substituted is a value obtained by dividing the total number of Z groups introduced by the total number of benzene rings (i.e., 2n). １ and Y ２ When a Z group is selected as at least one of the groups, the resin compound (A) has at least one cationic functional group selected from a secondary amino group, a tertiary amino group, and a quaternary ammonium base, thereby enabling it to dissolve more stably in the surface treatment solution. If the average number of Z group substitutions is less than 0.2, the stability of the surface treatment solution decreases. If it exceeds 1.0, the corrosion resistance shown in (i) above and the adhesion shown in (ii) above (particularly adhesion after a boiling water test) deteriorate. Furthermore, in the present invention, the average degree of polymerization n is set to 2 to 50. If n is less than 2, the corrosion resistance shown in (i) above becomes insufficient. On the other hand, if n exceeds 50, the stability of the resin compound (A) in the surface treatment solution decreases due to reduced water solubility and increased viscosity, resulting in insufficient storage stability. Preferably, n is 2 to 10.

[0022] In formulas (II) and (III), R １ , R ２ , R ３ , R ４ and R ５ are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or a hydroxyalkyl group having 1 to 10 carbon atoms. If the alkyl group or hydroxyalkyl group has more than 10 carbon atoms, the resin compound (A) cannot be sufficiently water-soluble, and becomes unstable in the surface treatment solution. １ , R ２ , R ３ , R ４ and R ５ Specific examples of A include methyl, ethyl, propyl, butyl, hydroxyethyl, 2-hydroxypropyl, and hydroxyisobutyl. －represents a hydroxide ion or an acid ion. Specific examples of the acid ion include an acetate ion, a phosphate ion, and a formate ion.

[0023] The resin compound (A) represented by general formula (I) is a bisphenol-formalin condensate, and its synthesis method is not limited. For example, it can be obtained by reacting bisphenol A with formalin and an amine in the presence of an alkali catalyst.

[0024] <Cationic Urethane Resin Emulsion (B)> The cationic urethane resin emulsion (B) contained in the surface treatment liquid is not particularly limited in terms of the polyol and isocyanate components constituting the monomer components, or the polymerization method, as long as it has at least one cationic functional group selected from primary to tertiary amino groups and quaternary ammonium salt groups. Examples of the cationic functional group include an amino group, a methylamino group, an ethylamino group, a dimethylamino group, a diethylamino group, a trimethylamino group, and a triethylamino group, but is not particularly limited as long as it is a primary to tertiary amino group or a quaternary ammonium salt group.

[0025] <Silane Coupling Agent (C)> The silane coupling agent (C) contained in the surface treatment liquid is not particularly limited as long as it has at least one reactive functional group selected from an active hydrogen-containing amino group, an epoxy group, a mercapto group, and a methacryloxy group. Trialkoxysilanes having three alkoxy groups are particularly preferred. Specific examples that can be used include N-(2-aminoethyl)3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, and 3-mercaptopropyltrimethoxysilane.

[0026] <Organic Titanium Chelate Compound (D)> The organic titanium chelate compound (D) contained in the surface treatment solution is not particularly limited, but examples thereof include titanium acetylacetonate, titanium octylene glycolate, titanium tetraacetylacetonate, and titanium ethylacetoacetate. Inorganic salts such as titanium nitrate, titanium sulfate, titanium acetate, titanium phosphate, and titanium carbonate are not preferred because they do not exhibit the effect of improving corrosion resistance shown in (i) above. When the organic titanium chelate compound (D) is dissolved in water for use, titanium is dissolved as a chelate complex, so it is preferable not to add highly polar water-soluble solvents or peroxides that would affect this complex.

[0027] <Tetravalent Vanadium Compound (E)> The tetravalent vanadium compound (E) contained in the surface treatment solution is not particularly limited, but examples thereof include vanadyl sulfate, vanadyl dichloride, vanadyl phosphate, vanadyl oxalate, vanadyl acetylacetonate, etc. From the viewpoint of obtaining a higher effect of improving corrosion resistance, the tetravalent vanadium compound (E) is preferably VO ２＋ Vanadium compounds that generate (vanadyl) ions are preferred. Pentavalent vanadium compounds (e.g., ammonium metavanadate) are too water-soluble and therefore highly elutable from the coating, resulting in insufficient adhesion (particularly after a boiling water test) as described in (ii) above, and are therefore not used in the present invention.

[0028] <Molybdic Acid Compound (F)> The molybdic acid compound (F) contained in the surface treatment liquid is not particularly limited, and examples thereof include molybdic acid, ammonium molybdate, sodium molybdate, potassium molybdate, magnesium molybdate, zinc molybdate, etc., and also include phosphomolybdic acid, ammonium phosphomolybdate, sodium phosphomolybdate, etc. In the present invention, it is preferable to use one or more compounds selected from these.

[0029] <Fluorine Compound (G)> The fluorine compound (G) contained in the surface treatment liquid is not particularly limited, and examples thereof include acids and salts thereof such as hydrofluoric acid, hydrofluorosilicic acid, fluoroboric acid, hydrofluoric titanic acid, acidic ammonium fluoride, sodium fluoride, and hydrofluorozirconic acid. In the present invention, it is preferable to use one or more compounds selected from these.

[0030] [(B Ｓ ) / {(A Ｓ ) + (B Ｓ ) + (C Ｓ )}]: 0.10 to 0.30 In the surface treatment liquid, the solid content mass of the resin compound (A) (A Ｓ ), the solid content mass of the cationic urethane resin emulsion (B) (B Ｓ ), and the solid content mass of the silane coupling agent (C) (C Ｓ ) the solid content mass of the cationic urethane resin emulsion (B) relative to the total mass (B Ｓ ) ratio [(B Ｓ ) / {(A Ｓ ) + (B Ｓ ) + (C Ｓ )}] must be 0.10 to 0.30. If the mass ratio is less than 0.10, the proportion of urethane resin is too low, and the surface treatment film tends to be hard. As a result, when the surface-treated steel sheet is processed after forming an organic resin film on its upper layer, the surface treatment film is destroyed, and peeling occurs from that point between the surface treatment film and the organic resin film formed thereon. In other words, the adhesion (particularly after a boiling water test) shown in (ii) above deteriorates. Therefore, the mass ratio is set to 0.10 or more, preferably 0.12 or more. On the other hand, if the mass ratio exceeds 0.30, the adhesion (particularly after a boiling water test) shown in (ii) above deteriorates. Therefore, the mass ratio is set to 0.30 or less, preferably 0.28 or less.

[0031] [(C Ｓ ) / {(A Ｓ ) + (B Ｓ ) + (C Ｓ )}]: 0.60 to 0.85 In the surface treatment liquid, the solid content mass (A Ｓ), the solid content mass of the cationic urethane resin emulsion (B) (B Ｓ ), and the solid content mass of the silane coupling agent (C) (C Ｓ ) the solid content mass (C Ｓ ) ratio [(C Ｓ ) / {(A Ｓ ) + (B Ｓ ) + (C Ｓ )}] must be 0.60 to 0.85. If the mass ratio is less than 0.60, the adhesion (particularly adhesion after a boiling water test) shown in (ii) above will be poor. Therefore, the mass ratio is set to 0.60 or more, preferably 0.65 or more. On the other hand, if the mass ratio exceeds 0.85, the storage stability of the surface treatment solution will decrease. Therefore, the mass ratio is set to 0.85 or less, preferably 0.80 or less.

[0032] {(C Ｓ ) / (D Ｔｉ )}: 50 to 70 In the surface treatment liquid, the titanium-equivalent mass (D Ｔｉ ) the solid content mass (C Ｓ ) ratio {(C Ｓ ) / (D Ｔｉ )} must be 50 to 70. If the mass ratio is less than 50, the corrosion resistance shown in (i) above and the adhesion shown in (ii) above (particularly the adhesion after a boiling water test) will deteriorate. Therefore, the mass ratio is set to 50 or more, preferably 55 or more. On the other hand, if the mass ratio exceeds 70, the elution of the surface treatment film will increase, and the adhesion shown in (ii) above (particularly the adhesion after a boiling water test) will deteriorate. Therefore, the mass ratio is set to 70 or less, preferably 65 or less.

[0033] In the present invention, when calculating various mass ratios, the solid mass of the silane coupling agent (C) Ｓ ) is an alkoxysilane (R—Si(—OR １ ) ３ ) is hydrolyzed to form silanol (R-Si(-OH) ３This is because when the silane coupling agent is dissolved in water, most of it is hydrolyzed, and the alcohol generated by the hydrolysis volatilizes when the surface treatment liquid is applied and dried to form a surface treatment film, and does not act as an active ingredient.

[0034] {(E Ｖ ) / (D Ｔｉ In the surface treatment liquid, the titanium-equivalent mass (D Ｔｉ ) to the vanadium-equivalent mass (E) of the tetravalent vanadium compound (E) Ｖ ) ratio {(E Ｖ ) / (D Ｔｉ )} must be 0.30 to 0.50. If the mass ratio is less than 0.30, the corrosion resistance shown in (i) above deteriorates. Therefore, the mass ratio is set to 0.30 or more, preferably 0.35 or more. On the other hand, if the mass ratio exceeds 0.50, the adhesion shown in (ii) above (particularly adhesion after a boiling water test) deteriorates. Therefore, the mass ratio is set to 0.50 or less, preferably 0.48 or less.

[0035] [(F Ｍｏ ) / {(A Ｓ ) + (B Ｓ ) + (C Ｓ In the surface treatment liquid, the solid content mass (A Ｓ ), the solid content mass of the cationic urethane resin emulsion (B) (B Ｓ ), and the solid content mass of the silane coupling agent (C) (C Ｓ ) the molybdenum-equivalent mass (F) of the molybdic acid compound (F) relative to the total Ｍｏ ) ratio [(F Ｍｏ ) / {(A Ｓ ) + (B Ｓ ) + (C Ｓ )}] must be 0.003 to 0.030. If the mass ratio is less than 0.003, the blackening resistance deteriorates. Therefore, the mass ratio is set to 0.003 or more, and preferably 0.006 or more. On the other hand, if the mass ratio exceeds 0.030, the storage stability of the surface treatment solution deteriorates. Therefore, the mass ratio is set to 0.030 or less.

[0036] [(G Ｆ ) / {(A Ｓ ) + (B Ｓ ) + (C Ｓ )}]: 0.101 to 0.200 In the surface treatment liquid, the solid content mass of the resin compound (A) (A Ｓ ), the solid content mass of the cationic urethane resin emulsion (B) (B Ｓ ), and the solid content mass of the silane coupling agent (C) (C Ｓ ) the fluorine equivalent mass (G) of the fluorine compound (G) relative to the total Ｆ ) ratio [(G Ｆ ) / {(A Ｓ ) + (B Ｓ ) + (C Ｓ )}] must be 0.101 to 0.200. If the mass ratio is less than 0.101, the adhesion (particularly adhesion after a boiling water test) shown in (ii) above will be poor. Therefore, the mass ratio is set to 0.101 or more, preferably 0.105 or more. On the other hand, if the mass ratio exceeds 0.200, the soluble components of the surface treatment film will increase, deteriorating the corrosion resistance (particularly adhesion after a boiling water test) shown in (i) above and the adhesion (particularly adhesion after a boiling water test) shown in (ii) above. Therefore, the mass ratio is set to 0.200 or less.

[0037] pH: 4 to 5 The pH of the surface treatment solution is 4 to 5. If the pH is less than 4, zinc will be eluted from the plating layer of the zinc-based plated steel sheet to a large extent, resulting in a deterioration in the corrosion resistance described in (i) above. On the other hand, if the pH exceeds 5, the surface treatment solution will not be able to achieve storage stability.

[0038] Here, preferred acidic agents used to adjust the pH to 4 to 5 include phosphoric acid (orthophosphoric acid), acetic acid, formic acid, hydrofluoric acid, and fluorides. Acetic acid and formic acid are weak acids, making them suitable for pH adjustment. Furthermore, they are highly volatile and volatilize when the surface treatment solution dries, leaving little residue in the surface treatment film. Therefore, even if they are added in excess, performance degradation is minimal, making them preferred. On the other hand, preferred alkaline agents used to adjust the pH to 4 to 5 when the pH is too low, such as ammonia water or amines with a boiling point of 100°C or less, are ammonia water and amines with a boiling point of 100°C or less.

[0039] <Water> The water contained in the surface treatment solution is preferably one that has little effect on the resin compound (A), cationic urethane resin emulsion (B), silane coupling agent (C), and organic titanium chelate compound (D), as well as on the acid or alkaline component used to adjust the pH. Impurities such as Na and Cl contained in water can reduce corrosion resistance or paintability if they remain in the coating. Therefore, it is preferable to use water with few impurities, and for example, its electrical conductivity is preferably less than 100 μS / cm. It is more preferably 50 μS / cm or less, and even more preferably 10 μS / cm or less.

[0040] <Solid Content Concentration> The solid content concentration of the surface treatment liquid is preferably 0.05 to 5 mass % as the solid content concentration when dried at 110° C. for 2 hours. This is because, when the solid content concentration is in the range of 0.05 to 5 mass %, it becomes easy to ensure the deposition amount of the surface treatment film described below, and the stability of the surface treatment liquid can also be ensured.

[0041] <Other Components> The surface treatment solution may contain an antifoaming agent or a wettability enhancer as needed. The type of antifoaming agent is not particularly limited, and examples include silicone-based and fatty acid-based emulsions. The wettability enhancer reduces the surface tension of the surface treatment solution, improving wettability to zinc-plated steel sheets and improving appearance uniformity. Examples of wettability enhancers include, but are not limited to, water-soluble solvents such as ethanol, t-butanol, and butyl cellosolve. Wettability enhancers containing acetylene are also suitable because they also have a defoaming effect. Nitrates such as nickel nitrate and ammonium nitrate may be added to the surface treatment solution to further improve blackening resistance. In the surface treatment solution, the solid content of these antifoaming agents, wettability enhancers, and other components, including nitrates, is limited to 7% by mass or less.

[0042] [Method for producing surface-treated steel sheet for organic resin coating] The method for producing a surface-treated steel sheet for organic resin coating of the present invention comprises applying the above-mentioned surface treatment solution to the surface of a zinc-based plated steel sheet, drying the surface, and depositing a coating weight of 0.005 to 0.18 g / m per side. ２This makes it possible to produce a surface-treated steel sheet for organic resin coating that does not contain chromium compounds and that has excellent corrosion resistance as shown in (i) above and excellent adhesion as shown in (ii) above, in addition to blackening resistance.

[0043] The surface treatment solution may be applied to the surface of a zinc-based plated steel sheet by any of coating, dipping, and spraying methods. The application method may be any of a roll coater (three-roll system, two-roll system, etc.), squeeze coater, die coater, and bar coater. After application of the surface treatment solution, the amount of application may be adjusted, and the appearance and film thickness may be made uniform by an air knife method or a roll squeezing method.

[0044] Maximum sheet temperature: 50 to 180°C. After application of the surface treatment solution, heating and drying are typically performed without rinsing. Heating and drying methods that can be used include dryers, hot air ovens, high-frequency induction heating furnaces, and infrared ovens. When the surface treatment solution comes into contact with the surface of a zinc-based plated steel sheet, the plating components react with the reactive fluorine compound (G) in the surface treatment solution on the surface of the zinc-based plated layer, forming a reaction layer between the plating components and fluorides, etc., and the surface treatment solution dries, forming a surface treatment film. The inventors speculate that this results in improved adhesion between the plated layer and the surface treatment film. If the amount of (G) is too large, fluorine compounds that are not consumed in the reaction at the interface between the plated layer and the surface treatment film remain in the surface treatment film, resulting in insufficient film formation and reduced corrosion resistance of the organic resin film when formed and reduced adhesion between the organic resin film and the surface treatment film after a boiling water test. However, the inventors speculate that by allowing a suitable amount of reactive components not consumed in the reaction at the interface between the plating layer and the surface treatment solution to remain in the surface treatment film as soluble components, it becomes possible to form a mixed layer at the interface between the organic resin film and the surface treatment film, thereby improving the adhesion between the organic resin film and the surface treatment film. Furthermore, since the surface treatment film contains a water-soluble solvent derived from the wettability improver and surfactants derived from the resin compound (A) and the cationic urethane resin emulsion (B), it is thought that even if the treatment solution used to form the organic resin film is solvent-based, trace amounts of reactive components will be mixed into the organic resin. To achieve the above effect, the maximum sheet temperature is preferably 50°C or higher. If the temperature is lower than 50°C, excessive reactive components will remain in the surface treatment film, resulting in insufficient film formation of the surface treatment film. When the organic resin film is processed after its formation, the surface treatment film will be destroyed, and peeling between the surface treatment film and the organic resin film formed thereon will easily occur from this point. A temperature of 70°C or higher is preferred. On the other hand, if the temperature exceeds 180°C, the amount of reactive components remaining in the surface treatment film will be reduced, and an interfacial mixed layer with the organic resin film formed thereon will not be formed, resulting in a decrease in the effect of improving adhesion at the interface between the surface treatment film and the organic resin film. Therefore, the maximum sheet temperature is preferably 180°C or less, more preferably 140°C or less, and even more preferably 110°C or less.Furthermore, it is desirable that the holding time at the maximum sheet temperature be less than 15 seconds.

[0045] Amount of surface treatment film applied per side: 0.005 to 0.18 g / m ２ In the present invention, the amount of the surface treatment film applied per side is 0.005 to 0.18 g / m ２ The amount of adhesion must be 0.005 g / m ２ If the coating weight is less than 0.005 g / m, the corrosion resistance shown in (i) above and the adhesion (particularly the adhesion after the boiling water test) shown in (ii) above will deteriorate. ２ or more, preferably 0.010 g / m ２ On the other hand, the adhesion amount is 0.18 g / m or more. ２ If the coating weight exceeds 0.18 g / m, the surface treatment film will be destroyed when processing is performed after the organic resin film is formed, and peeling of the surface treatment film and the organic resin film formed thereon will occur starting from that point. In other words, the adhesion (particularly the adhesion after the boiling water test) shown in (ii) above will deteriorate. Therefore, a coating weight of 0.18 g / m ２ Preferably, it is 0.14 g / m or less. ２ The following applies.

[0046] The above surface treatment film may be applied to one side or both sides of the zinc-based plated steel sheet.

[0047] [Actions of the Present Invention] It is assumed that the components of the surface treatment solution used in the present invention have the following actions, but the present invention is not limited by these assumptions.

[0048] The surface treatment liquid used in the present invention is mainly composed of a resin compound (A), a cationic urethane resin emulsion (B), and a silane coupling agent (C), and these main components form the skeleton of the surface treatment film.

[0049] The resin compound (A) has a bisphenol as a phenol skeleton, and therefore is less soluble in polar solvents (imparting solvent resistance) and improves the corrosion resistance shown in (i) above.

[0050] However, the resin compound (A) tends to harden the surface treatment film. As a result, when the organic resin film is processed after it is formed, the surface treatment film is destroyed, and peeling of the surface treatment film and the organic resin film formed thereon occurs from the destroyed portion. Therefore, in the present invention, the hardness of the phenolic resin can be reduced by adding the cationic urethane resin emulsion (B), thereby preventing the surface treatment film from being destroyed by processing.

[0051] While cationic urethane resin emulsion (B) has the above-mentioned effects, it exhibits poor adhesion between the organic resin film and the surface treatment film, and between the surface treatment film and the plating layer. Therefore, to address the insufficient adhesion between the organic resin film and the surface treatment film and the plating layer after the organic resin film is formed, a silane coupling agent (C) is added. The terminal alkoxy groups of the silane coupling agent (C) hydrolyze to generate active silanol groups (Si—OH), which bond with the surface of the zinc-plated steel sheet and contribute to improving the adhesion between the surface treatment film and the plating layer after the organic resin film is formed. Furthermore, the silane coupling agent contains organic functional groups, which also contribute to improving adhesion to the organic resin film. Furthermore, a portion of the silane coupling agent (C) undergoes dehydration condensation to generate siloxane bonds (Si—O—Si), which subsequently polymerize (polysiloxane formation: -Si—O—Si—O—Si—). This results in an extremely stable structure, improving the corrosion resistance shown in (i) above and the adhesion (particularly the adhesion after a boiling water test) shown in (ii) above.

[0052] Therefore, by using the main components of the surface treatment solution, namely the resin compound (A), the cationic urethane resin emulsion (B), and the silane coupling agent (C), in appropriate proportions, it is believed that a variety of performance characteristics can be obtained in a well-balanced manner. However, when the adhesion weight of the surface treatment film is low, as in the present invention, the above main components alone cannot ensure corrosion resistance after organic resin coating. Therefore, the surface treatment solution used in the present invention contains, in addition to the above main components, an organic titanium chelate compound (D) as an essential component. It is presumed that the organic titanium chelate compound (D) acts as a catalyst to promote polysiloxane formation when the surface treatment solution is dried to form the surface treatment film. This ensures corrosion resistance after organic resin coating, even when the adhesion weight of the surface treatment film is low.

[0053] To achieve the above-mentioned effect, as mentioned above, a predetermined amount of the organic titanium chelate compound (D) is required, which is determined depending on the amount of the silane coupling agent (C). If the amount of (D) is small, the desired effect cannot be obtained. If the amount of (D) is excessive, the polysiloxane content increases too much, resulting in a hard and brittle surface treatment film. When the organic resin film is formed and then processed, the surface treatment film is destroyed, and peeling occurs from that point between the surface treatment film and the organic resin film formed thereon. In other words, the adhesion (especially adhesion after a boiling water test) shown in (ii) above is deteriorated. Furthermore, although polysiloxanization by the organic titanium chelate compound (D) is ideally promoted during the formation of the surface treatment film, polysiloxanization is also promoted during storage of the surface treatment solution. Therefore, if the content of (D) is excessive, storage stability (suppression of thickening and gelation) is reduced, and the quality after storage is no longer the same as before storage.

[0054] The surface treatment solution of the present invention also contains a tetravalent vanadium compound (E) as an essential component. In the present invention, the tetravalent vanadium compound (E) is presumed to act as a corrosion inhibitor, such as passivating zinc during plating. In particular, vanadyl ions having one oxygen atom [VO ２＋

[0003] is unlikely to elute even in a humid environment and remains in the surface treatment film, exerting its inhibitor effect, and is therefore presumed to prevent deterioration of corrosion resistance in areas where scratches are present on the surface treatment film or the plating surface itself. The inventors presume that this effect is achieved by a synergistic effect with Ti, which also exists as a cation, provided that the film skeleton having cationic functional groups is appropriate.

[0055] Furthermore, the surface treatment solution used in the present invention also contains a molybdic acid compound (F) as an essential component. Zinc-based plated steel sheets, regardless of whether they are electroplated or hot-dip plated steel sheets, are prone to blackening, a phenomenon in which the plating surface darkens in a corrosive environment. In particular, when Mg or Al is added to hot-dip galvanized steel sheets to improve corrosion resistance or adhesion between the plating layer and the substrate steel sheet, these elements concentrate at the interface between the plating layer and the substrate steel sheet or at the surface of the plating layer, promoting blackening and resulting in a darker appearance than pure galvanized steel sheets. The cause of blackening in zinc-based plated steel sheets is still unclear, but it is believed that zinc oxide formed on the outermost surface of the plating layer loses oxygen and transforms into oxygen-deficient zinc oxide, or that oxygen-deficient zinc oxide forms on the plating surface due to insufficient oxygen supply during the zinc corrosion (oxidation) process, resulting in the black appearance.

[0056] In the present invention, excellent resistance to blackening can be obtained by incorporating a molybdic acid compound (F) into the surface treatment film. Molybdenum is a transition metal and bonds with oxygen to form molybdenum oxide (MoO ２ , MoO ３ ) and molybdic acid (MoO ４ ２－ In the present invention, molybdic acid (MoO ４ ２－ ) turns into molybdenum oxide (MoO) under high temperature and humidity or corrosive environment. ２ , MoO ３ ) is thought to supply an appropriate amount of oxygen to the surface of the zinc-coated layer, making it difficult for oxygen-deficient zinc oxide to form. The inventors speculate that this mechanism is what improves blackening resistance.

[0057] It is important that the surface treatment solution used in the present invention also contains a fluorine compound (G) as an essential component. The inventors speculate that the addition of the fluorine compound (G) results in the formation of a reaction layer between the plating components and fluorides on the surface of the zinc-based plating layer when the surface treatment solution comes into contact with the surface of a zinc-based plated steel sheet, thereby improving the adhesion between the plating layer and the surface treatment film. If the amount of (G) is small, the reaction layer will not be uniformly formed on the plating surface, and when an organic resin film is formed, the surface treatment film will peel off at the interface between the plating layer and the surface treatment film. On the other hand, if the amount of (G) is large, the fluorine compound that is not consumed in the reaction at the interface between the plating layer and the surface treatment film will remain in the surface treatment film, resulting in reduced corrosion resistance when the organic resin film is formed and reduced adhesion between the organic resin film and the surface treatment film after a boiling water test. However, by reducing the amount of adhesion of the surface treatment film and further lowering the drying temperature (or shortening the drying time), it is possible to form a thin and uniform reaction layer on the surface of the plating layer and leave an appropriate amount of unreacted fluorine compound in the surface treatment film. As a result, it is possible to ensure the corrosion resistance shown in (i) above and the adhesion (particularly the adhesion after the boiling water test) shown in (ii) above. － Hydrofluoric acid and its salts, ammonium fluoride, and sodium fluoride, which readily generate ions, are particularly preferred because they are effective in improving the adhesion between the surface treatment film and the plating layer and tend to leave a moderate amount of soluble components in the film.

[0058] [Organic Resin-Coated Steel Sheet and Manufacturing Method Thereof] The organic resin-coated steel sheet of the present invention has an organic resin film formed on the surface treatment film of the surface-treated steel sheet described above. Any method for forming this organic resin film can be used, including, for example, applying and drying a coating composition or laminating an organic resin film. Suitable coating compositions include acrylic resins, epoxy resins, urethane resins, phenolic resins, polyester resins, and mixtures thereof. Preferred organic resin films are one or more films selected from polyvinyl chloride films, polyolefin films, polyester films, and fluororesin films, or laminated films comprising two or more of these films. The thickness of the organic resin film is preferably 60 μm or more, more preferably 100 μm or more. While there is no particular upper limit, the thickness is preferably 600 μm or less.

[0059] The organic resin-coated steel sheet of the present invention is also excellent in the corrosion resistance shown in (i) above and the adhesion (particularly the adhesion after a boiling water test) shown in (ii) above.

[0060] The organic resin film may contain various additives such as non-chromium based rust preventative additives, solid lubricants, and color pigments.

[0061] The components of the surface treatment solution used were the resin compound (A) shown in Table 1 (Table 1a and Table 1b), the urethane resin emulsion (B) shown in Table 2, the silane coupling agent (C) shown in Table 3, the titanium compound (D) shown in Table 4, the vanadium compound (E) shown in Table 5, the molybdenum acid compound (F) shown in Table 6, and the fluorine compound (G) shown in Table 7. In addition, various zinc-based plated steel sheets shown in Table 8 were prepared.

[0062] The components listed in Tables 1 to 7 were mixed in the proportions shown in Tables 9-1 and 9-2, the pH was adjusted with acetic acid or ammonia to the value shown in Table 9-2, and deionized water was added so that the solids concentration after drying at 110°C for 2 hours would be the value shown in Table 10, to prepare surface treatment solutions of various levels. Note that ion-exchanged water with an electrical conductivity of 10 μS / cm was used as the deionized water. Note that the mass ratios (X1) to (X6) listed in Table 9-2 respectively represent the mass ratios (1) to (6) defined in claim 1.

[0063] Surface-treated steel sheets of each level were produced by applying each level of surface treatment solution to one side of a zinc-based plated steel sheet of the type shown in Table 10 using a roll coater, and then heating and drying, without rinsing with water, so that the peak temperature (PMT) reached the value shown in Table 10. The adhesion weight of the surface treatment film per side was adjusted to the value shown in Table 10 depending on the application conditions (roll compression force, rotation speed, etc.) and the solids concentration of the surface treatment solution. The adhesion weight of the surface treatment film was determined by quantifying the amount of Si in the silane coupling agent (C) blended in the surface treatment film using an X-ray fluorescence analyzer and converting from this Si amount.

[0064] Furthermore, the organic resin films or paints shown in Table 11 were prepared. In Table 11, R1 is a polyvinyl chloride film with a high elongation and a thickness of 200 μm, R2 is a polyester film with a low elongation and a thickness of 100 μm, and R3 is a polyolefin film with a low elongation and a thickness of 100 μm. For each level, an adhesive was applied to the surface treatment film to a dry thickness of 3 μm to form an adhesive layer, which was then heated and dried (maximum plate temperature reached: 80°C). Subsequently, organic resin films of the types shown in Table 10 were thermocompressed onto the adhesive layer at 210°C to adhere each film (organic resin film), thereby producing organic resin-coated steel sheets. Furthermore, R4 is a polyolefin-based paint composition, which was applied to the surface treatment film and then dried at 150°C for 30 minutes to produce organic resin-coated steel sheets.

[0065] Samples taken from the surface-treated steel sheets of each level were evaluated for blackening resistance as shown in (1) below. Furthermore, samples taken from the organic resin-coated steel sheets of each level were evaluated for corrosion resistance and adhesion as shown in (2) to (6) below. Furthermore, the surface treatment solutions of each level were evaluated for storage stability as shown in (7) below. The results are shown in Table 12.

[0066] (1) Resistance to Blackening Each sample was left for 24 hours in a thermo-hygrostat controlled at an atmosphere of 50°C temperature and 95% relative humidity, and the change in lightness (L value) (ΔL = L value after test - L value before test) was calculated. The evaluation criteria were as follows. The L value was measured using an SR2000 manufactured by Nippon Denshoku Industries Co., Ltd. in SCE mode (specular reflection removed). ◎: -6≦ΔL ○: -10≦ΔL<-6 △: -14≦ΔL<-10 ×: ΔL<-14

[0067] (2) Corrosion Resistance of Organic Resin-Coated Steel Sheet A cross-cut was made on the surface of a 50 mm x 100 mm sample, and a salt spray test was carried out for 1000 hours in accordance with the provisions of JIS-Z-2371-2000. The corrosion width on one side from the cross-cut was measured. The evaluation criteria are as follows: ◎: The average corrosion width from the cut is less than 5 mm. ○: The average corrosion width from the cut is 5 mm or more but less than 10 mm. △: The average corrosion width from the cut is 10 mm or more but less than 15 mm. ×: The average corrosion width from the cut is 15 mm or more.

[0068] (3) Adhesion 1 of organic resin coated steel sheet A cutter knife was used to make a 5 mm square grid (well-shaped) in the center of the sample surface during the Erichsen processing described below, reaching all the way to the zinc-based plated steel sheet, and the sample was extended to 6 mm using an Erichsen tester, after which the peeled area of ​​the organic resin film within the 5 mm grid was measured. ◎: No peeling ○: Peeled area less than 3% △: Peeled area 3% or more but less than 10% ×: Peeled area 10% or more

[0069] (4) Adhesion of organic resin-coated steel sheet after boiling water test 1 Each sample was immersed in boiling water for 2 hours and then pulled out. After that, the peeled area of ​​each sample was measured in the same manner as in (3) above. ◎: No peeling ○: Peeled area less than 3% △: Peeled area 3% or more but less than 10% ×: Peeled area 10% or more

[0070] (5) Adhesion 2 of organic resin coated steel sheet A cutter knife was used to make a 5 mm square grid (well-shaped) in the center of the sample surface during the Erichsen processing described below, reaching all the way to the zinc-based plated steel sheet, and the sample was extended to 8 mm using an Erichsen tester, after which the peeled area of ​​the organic resin film within the 5 mm grid was measured. ◎: No peeling ○: Peeled area less than 3% △: Peeled area 3% or more but less than 10% ×: Peeled area 10% or more

[0071] (6) Adhesion after organic resin coating after boiling water test 2 Each sample was immersed in boiling water for 2 hours and then pulled out. After that, the peeled area of ​​each sample was measured in the same manner as in (5) above. ◎: No peeling ○: Peeled area less than 3% △: Peeled area 3% or more but less than 10% ×: Peeled area 10% or more

[0072] (7) Storage stability After storing each level of surface treatment solution in a thermostatic chamber at 40°C for 30 days, the appearance of each surface treatment solution was visually inspected and evaluated. The evaluation criteria are as follows: ◎: No change ○: A very small amount of precipitation was observed △: A small amount of precipitation was observed or the viscosity increased slightly ×: A large amount of precipitation was observed or the solution became gelled

[0073]

[0074]

[0075]

[0076]

[0077]

[0078]

[0079]

[0080]

[0081]

[0082]

[0083]

[0084]

[0085]

[0086]

[0087] As shown in Table 12, all of the examples of the present invention have excellent blackening resistance, corrosion resistance and adhesion after being coated with an organic resin, and storage stability.

[0088] The zinc-based plated steel sheet with a surface treatment film produced by the production method of the present invention can be widely used in the fields of automobiles, home appliances, building materials, etc.

Claims

1. A resin compound (A) having a bisphenol skeleton represented by the following general formula (I), a cationic urethane resin emulsion (B) having at least one cationic functional group selected from primary to tertiary amino groups and quaternary ammonium base, a silane coupling agent (C) having at least one reactive functional group selected from an active hydrogen-containing amino group, an epoxy group, a mercapto group, and a methacryloxy group, an organic titanium chelate compound (D), a tetravalent vanadium compound (E), a molybdic acid compound (F), a fluorine compound (G), and water (H) are contained within a range satisfying the following conditions (1) to (6), and a surface treatment liquid having a pH of 4 to 5 is applied to the surface of a zinc-based plated steel sheet and dried, so that the adhesion amount per side is 0.005 to 0.18 g / m ２ to form a surface treatment film, which is a manufacturing method of a surface-treated steel sheet for organic resin coating. Note (1) The ratio of the solid content mass (B Ｓ of the cationic urethane resin emulsion (B) to the total of the solid content mass (A Ｓ of the resin compound (A), the solid content mass (B Ｓ of the cationic urethane resin emulsion (B), and the solid content mass (C Ｓ of the silane coupling agent (C) [(B Ｓ ) / {(A Ｓ ) + (B Ｓ ) + (C Ｓ )}] is 0.10 to 0.

30. (2) The ratio of the solid content mass (C Ｓ of the silane coupling agent (C) to the total of the solid content mass (A Ｓ of the resin compound (A), the solid content mass (B Ｓ of the cationic urethane resin emulsion (B), and the solid content mass (C Ｓ of the silane coupling agent (C) [(C Ｓ ) / {(A Ｓ ) + (B Ｓ ) + (C Ｓ )}] is 0.60 to 0.

85. (3) The titanium-converted mass (D ＴｉThe solid content mass (C) of the silane coupling agent (C) with respect to Ｓ ), the ratio {(C Ｓ ) / (D Ｔｉ )} is 50 to 70 (4) The vanadium conversion mass (E) of the tetravalent vanadium compound (E) with respect to the titanium conversion mass (D) of the organic titanium chelate compound (D Ｔｉ ), the ratio {(E Ｖ ) / (D Ｖ )} is 0.30 to 0.50 (5) The solid content mass (A) of the resin compound (A), the solid content mass (B) of the cationic urethane resin emulsion (B Ｔｉ ), and the solid content mass (C) of the silane coupling agent (C Ｓ ), the ratio [(F Ｓ ) / {(A Ｓ )+(B Ｍｏ )+(C Ｍｏ )}] of the molybdenum conversion mass (F) of the molybdate compound (F) with respect to the total is 0.003 to 0.030 (6) The solid content mass (A) of the resin compound (A), the solid content mass (B) of the cationic urethane resin emulsion (B Ｓ ), and the solid content mass (C) of the silane coupling agent (C Ｓ ), the ratio [(G Ｓ ) / {(A Ｓ )+(B Ｓ )+(C Ｓ )}] of the fluorine conversion mass (G) of the fluorine compound (G) with respect to the total is 0.101 to 0.200 Ｆ ) is 0.101 to 0.200 Ｆ ) / {(A Ｓ )+(B Ｓ )+(C Ｓ )}] In formulas (II) and (III), R １ , R ２ , R ３ , R ４ and R ５ are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or a hydroxyalkyl group having 1 to 10 carbon atoms, and A － represents a hydroxide ion or an acid ion.

2. The method for manufacturing a surface-treated steel sheet for organic resin coating according to claim 1, wherein drying of the surface treatment liquid is performed under the condition that the maximum temperature of the plate reaches 50 to 180°C.

3. The surface-treated steel sheet for organic resin coating produced by the method for producing a surface-treated steel sheet for organic resin coating according to claim 1 or 2.

4. A method for producing an organic resin-coated steel sheet, comprising: the method for producing a surface-treated steel sheet for organic resin coating according to claim 1 or 2; and a step of forming an organic resin film on the surface treatment film of the surface-treated steel sheet for organic resin coating.

5. The method for producing an organic resin-coated steel sheet according to claim 4, wherein the organic resin film is formed by laminating an organic resin film on the surface treatment film.

6. The method for producing an organic resin-coated steel sheet according to claim 5, wherein the organic resin film has a thickness of 60 μm or more.

7. The method for producing an organic resin-coated steel sheet according to claim 5 or 6, wherein the organic resin film is one or more films selected from a polyvinyl chloride film, a polyolefin-based film, a polyester-based film, and a fluororesin-based film.

8. The organic resin-coated steel sheet produced by the method for producing an organic resin-coated steel sheet according to any one of claims 4 to 7.