Title of invention: Surface-treated steel sheet Technical field [0001] 　The present invention relates to a surface-treated steel sheet having excellent corrosion resistance. Background technology [0002] 　Various galvanized steel sheets with excellent corrosion resistance used for home appliances, building materials, automobiles, etc. are known. For example, a galvanized steel sheet in which a zinc-plated layer is formed on a steel sheet by hot-dip galvanizing or the like is known. When the galvanized layer is provided on the steel sheet in this way, even if the galvanized steel sheet is damaged and the steel sheet is exposed, zinc, which is more corrosive than the iron constituting the steel sheet, corrodes first to form a protective film, and The protective film can prevent corrosion of the steel sheet. Therefore, galvanized steel sheets are developed in various applications that require corrosion resistance. [0003] 　However, the surface of various plated steel sheets such as galvanized steel sheets may deteriorate depending on the surrounding environment. For example, there is a problem that the plating layer is oxidized by an electrolyte such as salt contained in the atmosphere, oxygen and moisture existing in a high temperature and high humidity environment to generate white rust. Since the formation of white rust may impair the appearance uniformity, galvanized steel sheets are required to have higher corrosion resistance. [0004] 　As a technique for further improving the corrosion resistance of galvanized steel sheets, Zn-based alloy-plated steel sheets subjected to Zn—Al—Mg-based alloy plating or the like are known. [0005] 　However, even in such a Zn-based alloy-plated steel sheet, further improvement in corrosion resistance is required, and in particular, excellent corrosion resistance is ensured by preventing corrosion factors such as oxygen from reaching the alloy-plated layer. Such technology is required. Further, even when such an alloy-plated steel sheet is processed, it is required that excellent corrosion resistance can be maintained. [0006] 　In Patent Document 1, a galvanized steel sheet having excellent corrosion resistance, which includes a steel sheet, a Zn—Al—Mg based alloy plating layer formed on the surface of the steel sheet, and an aluminum-containing film formed on the alloy plating layer, is described. It is disclosed. [0007] 　Further, in Patent Document 2, a surface-treated metal plate having at least one coating layer on a metal plate or the like, wherein the coating layer formed on the outermost surface is an organic resin having an anionic functional group, Li, etc. A surface-treated metal plate containing at least one cationic metal element selected from the above and characterized in that the cationic metal element is concentrated in a region close to the outer surface of the coating layer is disclosed. It is taught that such a surface-treated steel sheet can improve alkali resistance and solvent resistance without lowering corrosion resistance. [0008] 　Further, Patent Document 3 discloses a base treatment composition for a coated steel sheet containing a specific organosilicon compound, a hexafluorometallic acid, a urethane resin having a specific cationic group, a vanadium compound, and an aqueous medium. It is taught that by using such a composition, a base treatment layer having corrosion resistance under the eaves can be formed on the steel sheet. [0009] 　Patent Documents 4 to 6 disclose coated steel sheets having, for example, a resin film containing a vanadium-based rust preventive pigment on a zinc-based plated steel sheet. Prior art literature Patent documents [0010] Patent Document 1: International Publication No. 2015/075792 Patent Document 2: Japanese Patent Application Laid-Open No. 2009-248460 Patent Document 3: Japanese Patent Application Laid-Open No. 2014-214315 Patent Document 4: Japanese Patent Application Laid-Open No. 2005-015834 Patent Document 5: Japanese Patent Application Laid-Open No. 2013-194145 Japanese Patent Document 6: Japanese Patent Application Laid-Open No. 2001-0031181 Outline of the invention Problems to be solved by the invention [0011] 　In the galvanized steel sheet described in Patent Document 1, a Zn—Al—Mg—Si alloy plating layer is provided on the steel sheet, and the corrosion resistance of the galvanized steel sheet is mainly ensured by this alloy plating layer. Further, Patent Document 1 teaches that a rust inhibitor can be further added to the film on the alloy plating layer, but the concentration distribution of the rust inhibitor in the film and the control method thereof are not always sufficient. Not considered. Therefore, the galvanized steel sheet described in Patent Document 1 still has room for improvement in improving corrosion resistance. [0012] 　Further, the invention described in Patent Document 2 relates mainly to a surface-treated metal plate having a coating film having improved alkali resistance and solvent resistance without lowering corrosion resistance. The degree of concentration of the cationic metal element in the coating film layer has not always been sufficiently examined. Therefore, even in the surface-treated metal plate described in Patent Document 2, the improvement in corrosion resistance is still improved. There is room. [0013] 　Further, in the composition described in Patent Document 3, a vanadium compound is used in order to improve corrosion resistance, but the concentration distribution of the vanadium compound in the base treatment layer obtained by using this composition is not necessarily the same. Not enough study has been done and there is still room for improvement in improving corrosion resistance. Similarly, in the inventions described in Patent Documents 4 to 6, the concentration distribution of rust preventive pigments such as vanadium compounds in the film has not always been sufficiently examined, and there is still room for improvement in the improvement of corrosion resistance. [0014] 　Therefore, in view of the above problems, an object of the present invention is to provide a surface-treated steel sheet having excellent corrosion resistance in a Zn-based alloy-plated steel sheet. Means to solve problems [0015] 　In order to obtain a surface-treated steel sheet having excellent corrosion resistance, the present inventors include a rust preventive in the coating film formed on the Zn-based alloy plating layer, and the Zn-based alloy plating layer and the coating film. It is important that the concentration of the rust inhibitor in the coating film at a position 10 nm away from the interface with the coating film is 1.5 times or more and 5.0 times or less the average concentration of the rust inhibitor in the coating film. I found it. That is, according to the present invention, in the region near the interface between the coating film and the Zn-based alloy plating layer, the rust preventive agent is present in a thicker region than in other regions. Therefore, the concentrated region of the rust preventive can prevent corrosion factors such as oxygen from passing through the coating film and corroding the Zn-based alloy plating layer. That is, the concentrated region of the rust preventive can serve as a barrier region for the underlying Zn-based alloy plating layer in the coating film. Further, such a barrier region can sufficiently play a role even after the surface-treated steel sheet according to the present invention is processed. Therefore, the surface-treated steel sheet according to the present invention having such a coating film can provide extremely excellent corrosion resistance. [0016] 　The present invention has been made based on the above findings, and the gist thereof is as follows. 　(1) 　steel sheet, having a coating comprising at least Zn alloy plating layer formed on one side, and a binder resin which formed rust agent to the Zn alloy plating layer of the steel sheet, 　the Zn-based The chemical composition of the alloy plating layer is, in mass%, 　Al: 0.01 to 60%, 　Mg: 0.001 to 10%, and 　Si: 0 to 2%, and the 　Zn-based alloy plating layer and the coating film. The concentration of the rust preventive agent in the coating film at a position 10 nm away from the interface with the coating film is 1.5 to 5.0 times the average concentration of the rust preventive agent in the coating film. , Surface treated steel plate. 　(2) 　The surface-treated steel sheet according to (1), wherein the rust preventive agent contains at least one of P, V and Mg. 　(3) 　The surface-treated steel sheet according to (1) or (2), wherein the average concentration of the rust inhibitor in the coating film is 3 to 15% by mass. 　(4) 　The surface according to any one of (1) to (3), wherein the coating film further contains a bright pigment, and the bright pigment contains at least one of aluminum and an oxide. Treated steel sheet. 　(5) 　The surface-treated steel sheet according to (4), wherein the oxide is alumina, silica, mica, zirconia, titania, glass, or zinc oxide. 　(6) 　The surface-treated steel sheet according to (4) or (5), wherein the bright pigment further contains at least one of Rh, Cr, Ti, Ag, and Cu. 　(7) 　The surface-treated steel sheet according to any one of (4) to (6), wherein the average concentration of the bright pigment in the coating film is 5 to 15% by mass. .. Effect of the invention [0017] 　According to the present invention, a rust preventive is contained in the coating film formed on the Zn-based alloy plating layer, and the rust preventive is located at a position 10 nm away from the interface between the Zn-based alloy plating layer and the coating film. The concentration of is 1.5 times or more and 5.0 times or less the average concentration of the rust preventive in the coating film. That is, in the region near the interface between the coating film and the Zn-based alloy plating layer in the coating film, the rust preventive agent is present in a thicker region than the other portions. Therefore, the concentrated region of the rust inhibitor serves as a barrier region for the Zn-based alloy plating layer against corrosion factors such as oxygen, and as a result, a surface-treated steel sheet having excellent corrosion resistance can be provided. Further, according to the present invention, it is possible to maintain excellent corrosion resistance even when the surface-treated steel sheet according to the present invention is processed. [0018] 　Further, according to the present invention, a bright pigment may be contained in the coating film on the Zn-based alloy plating layer. In such a case, the metallic appearance of the bright pigment improves the brightness of the surface-treated steel sheet according to the present invention, and it is possible to provide a surface-treated steel sheet having excellent design. Further, when the bright pigment is contained in the coating film, even if the Zn-based alloy plating layer turns black (hereinafter referred to as blackening) due to, for example, oxidation of zinc in the Zn-based alloy plating layer, it is contained in the coating film. The blackening can be made invisible by the bright pigment, that is, a change in the appearance of the coating film can be suppressed, and a surface-treated steel sheet having excellent design can be provided. [0019] 　Further, according to the present invention, since an acidic paint having a pH of 3.0 to 5.0 is used when forming the coating film, the oxide film on the surface of the Zn-based alloy plating layer is appropriately removed, and the Zn-based alloy plating is performed. By chemically bonding the layer and the coating film, it is possible to have excellent adhesion during processing. Further, according to the present invention, by adjusting the pH of the paint to the above pH, it is possible to prepare a paint in which the rust preventive is stably dissolved, and the paint has excellent storage stability as compared with the alkaline paint. Is possible. Mode for carrying out the invention [0020] 　[Surface-treated steel sheet] 　The surface-treated steel sheet of the present invention is coated with a steel sheet, a Zn-based alloy plating layer formed on at least one side of the steel sheet, and a rust preventive and a binder resin formed on the Zn-based alloy plating layer. The Zn-based alloy plating layer having a film has a chemical composition of Al: 0.01 to 60%, Mg: 0.001 to 10%, and Si: 0 to 2% in mass%, and is Zn-based. The concentration of the rust preventive agent in the coating film at a position 10 nm away from the interface between the alloy plating layer and the coating film is 1.5 to 5.0 times the average concentration of the rust preventive agent in the coating film. It is a feature. Hereinafter, the constituent requirements of the surface-treated steel sheet according to the present invention will be described. [0021] 　 　The steel plate (plated original plate) in the present invention is not particularly limited, and a general steel plate such as a hot-rolled steel plate or a cold-rolled steel plate can be used. The steel type is not particularly limited, and for example, Al killed steel, ultra-low carbon steel containing Ti, Nb, etc., and high-strength steel containing elements such as P, Si, Mn, etc. can be used. is there. The thickness of the steel plate in the present invention is not particularly limited, but may be, for example, 0.25 to 3.5 mm. [0022] 　 　The Zn-based alloy plating layer in the present invention is formed on a steel sheet. The Zn-based alloy plating layer may be formed on one side of the steel sheet or on both sides. The Zn-based alloy plating layer may be a Zn—Al—Mg alloy plating layer containing at least Al and Mg, or may be a Zn—Al—Mg—Si alloy plating layer containing Si. Each of these contents (concentration) is mass%, Al: 0.01 to 60%, Mg: 0.001 to 10%, Si: 0 to 2%, and the balance is Zn and impurities. Hereinafter, when the chemical composition of the Zn-based alloy plating layer is simply described as "%", it means "mass%". [0023] 　If the Al content of the Zn-based alloy plating layer is less than 0.01%, the effect of improving the corrosion resistance of the plated steel sheet due to the inclusion of Al is not sufficiently exhibited, and if it exceeds 60%, the effect of improving the corrosion resistance is saturated. Therefore, the Al content may be 0.01% or more, for example, 0.1% or more, 0.5% or more, 1% or more, 3% or more or 5% or more, and 60% or less, for example. , 55% or less, 50% or less, 40% or less, or 30% or less. The Al content is preferably 1 to 60%, more preferably 5 to 60%. [0024] 　If the Mg content of the Zn-based alloy plating layer is less than 0.001%, the effect of improving the corrosion resistance of the plated steel sheet due to the inclusion of Mg may not be sufficiently exhibited. On the other hand, if it exceeds 10%, Mg cannot be completely dissolved in the plating bath and floats as an oxide (generally called dross), and when galvanized in this plating bath, the oxide adheres to the plating surface layer and causes poor appearance, or , There is a risk that unplated parts (generally called non-plating) will occur. Therefore, the Mg content may be 0.001% or more, for example, 0.01% or more, 0.1% or more, 0.5% or more, 1% or more or 2% or more, and 10% or less. For example, it may be 8% or less, 6% or less, 5% or less, or 4% or less. The Mg content is preferably 1 to 5%, more preferably 1 to 4%. [0025] 　The lower limit of the Si content of the Zn-based alloy plating layer may be 0%, but it may be 0.001% to 2% in order to further improve the corrosion resistance of the Zn-based alloy plating layer. The Si content may be, for example, 0.005% or more, 0.01% or more, 0.05% or more, 0.1% or more or 0.5% or more, and 1.8% or less. It may be 1.5% or less or 1.2% or less. The Si content is preferably 0.1 to 2%, more preferably 0.5 to 1.5%. [0026] 　The Zn-based alloy plating layer in the present invention can be formed by a known plating method such as hot-dip galvanizing or thin-film deposition plating. For example, the thickness of the Zn-based alloy plating layer may be 1 to 30 μm. [0027] 　 　The coating film in the present invention is formed on a Zn-based alloy plating layer. The coating film contains a rust preventive and a binder resin. In order to improve the brightness of the surface-treated steel sheet, it is preferable that the coating film further contains a bright pigment. In the coating film of the surface-treated steel sheet according to the present invention, the rust inhibitor exists as a fine compound (for example, P compound or V compound). In order to allow the rust inhibitor to exist as a fine compound in the coating film and to form a concentrated region of the rust preventive in the interface region between the coating film and the Zn-based alloy plating layer as described above. As the coating film for forming the coating film in the present invention, it is effective to use, for example, an acidic coating film having a pH of 3.0 to 5.0. Since the rust preventive is micro-dispersed in the coating film, the fine rust preventive and the binder resin forming the coating film are clearly distinguished and specified in the coating film by a normal analysis method. It is difficult to do so, and it is observed that the rust inhibitor and the binder resin are distributed in the same region in the coating film. Therefore, in the present invention, "containing a rust preventive agent" in the coating film means that the coating film contains elements such as P, V, and Mg that exhibit the rust preventive function constituting the fine compound. Means. Therefore, the "concentration" of the rust preventive agent described later means, for example, the total concentration (content) of the elements of P, V, and Mg, and the unit thereof is mass%. [0028] 　By making the paint for forming the coating film in the present invention acidic, for example, at pH 3.0 to 5.0, the components of the rust preventive can be present in the paint in a dissolved state. .. That is, the component of the rust inhibitor according to the present invention is not contained in the coating material as a compound state (that is, a solid component), but is contained in the coating material as an ionic state (that is, a dissolving component). Therefore, when such a paint is applied to the surface of the Zn-based alloy plating layer and cured, the rust preventive can be substantially uniformly present as a fine compound in the formed coating film. [0029] 　Further, when an acidic paint having a pH of 3.0 to 5.0 is applied to the surface of the Zn-based alloy plating layer, the acidic paint removes the oxide film on the surface of the Zn-based alloy plating layer, and the Zn-based alloy plating layer is used. In the vicinity of the surface of the surface, the component of the rust preventive in the ion state reacts with the component in the Zn-based alloy plating layer. As a result, after the coating material is cured, a region in which the reaction product is concentrated can be formed in the vicinity of the interface between the Zn-based alloy plating layer and the coating film. Therefore, in the region where such a reaction product is present in the coating film, not only the fine compound present substantially uniformly in the coating film but also the reaction product formed as described above is used as a rust preventive. As a result, the rust preventive (for example, P, V, Mg) is concentrated as compared with other regions, and as a result, this concentrated region serves as a barrier region for preventing the invasion of corrosive factors in the coating film. It works. Therefore, the surface-treated steel sheet according to the present invention produced by using an acidic paint having a pH of 3.0 to 5.0 has a rust preventive concentrated region near the interface between the Zn-based alloy plating layer and the coating film. However, it can provide extremely high corrosion resistance. [0030] 　The average thickness of the coating film is not particularly limited, but can be, for example, 3 to 15 μm. With an average thickness of the coating film in such a range, the coating film serves as a barrier that sufficiently suppresses corrosion of the underlying Zn-based alloy plating layer, which is sufficient for the surface-treated steel sheet according to the present invention. Corrosion resistance can be provided. Further, if the average thickness of the coating film is within the above range, even if the surface-treated steel sheet according to the present invention having such a coating film is processed, the coating film is not cracked and the workability is excellent. It is possible to provide a coating film. [0031] 　If the average thickness of the coating film is less than 3 μm, the thickness may be insufficient to sufficiently suppress the progress of corrosion of the underlying Zn-based alloy plating layer, and therefore the surface treatment according to the present invention. Corrosion resistance of the steel sheet may be insufficient. On the other hand, if the average thickness of the coating film is more than 15 μm, the effect of increasing the corrosion resistance by increasing the thickness of the coating film is reduced, and it takes time to cure, which may be disadvantageous in terms of cost. is there. Further, if the coating film is too thick, the coating film may be cracked when the steel sheet having the coating film is bent or the like, and the workability of the surface-treated steel sheet according to the present invention may be deteriorated. The average thickness of the coating film may be, for example, 3 μm or more, 4 μm or more, or 5 μm or more, and may be 12 μm or less or 10 μm or less. Therefore, the average thickness of the coating film is preferably 3 μm or more and 12 μm or less, and more preferably 5 μm or more and 10 μm or less. [0032] 　The "average thickness" of the coating film according to the present invention can be determined by any method known to those skilled in the art. For example, the cross section of a steel sheet having a coating film is observed, and the shortest distance from any position on the interface between the Zn-based alloy plating layer and the coating film to the surface of each coating film is measured (that is,). It can be determined by measuring the distance perpendicular to the interface) and averaging those measurements. [0033] 　(Binder resin) 　The binder resin used as a component of the coating film of the present invention is not particularly limited as long as it can be used in an acidic solvent, and is, for example, a polyester resin, a urethane resin, or an acrylic resin. Good. The binder resin curing agent is not particularly limited as long as it can be used in an acidic solvent and can cure the above binder resin, and for example, a melamine resin, an isocyanate resin, or an epoxy resin can be used. Can be used. Preferably, the binder resin in the present invention is a polyester resin, and the curing agent is a melamine resin. Further, the polyester resin preferably has a glass transition temperature Tg of −20 to 70 ° C. and an average molecular weight of 3000 to 30,000. When the binder resin is a urethane resin, the Tg is preferably 0 to 50 ° C., and the number average molecular weight is preferably 5000 to 25000. When the binder resin is an acrylic resin, the Tg is preferably 0 to 50 ° C., and the number average molecular weight is preferably 3000 to 25000. [0034] 　(Rust preventive agent) In 　order to improve the corrosion resistance of the surface-treated steel sheet according to the present invention, a rust preventive agent (typically P and / or V) is contained in the coating film. As described above, the rust inhibitor in the present invention exists as a fine compound substantially uniformly in the coating film, but in the present invention, the "rust inhibitor" is a rust inhibitor constituting the rust inhibitor. It means an element that exerts a function, for example, a P element, a V element, and an Mg element. Since the rust inhibitor present as a fine compound in the coating film is soluble in water, the rust inhibitor in the coating film dissolves in water when the coating film is exposed to, for example, a wet environment. As a result, the components of the rust preventive agent are eluted, and the rust preventive function of suppressing the corrosion of the Zn-based alloy plating layer can be exhibited. Further, as described above, in the concentrated region near the interface between the Zn-based alloy plating layer and the coating film, the reaction generation of the rust preventive component (for example, P, V, etc.) and the component in the Zn-based alloy plating layer is generated. The product is formed, and the region where this reaction product exists acts as a barrier region of the corrosion factor. Therefore, in the surface-treated steel sheet according to the present invention, the rust preventive is present as a fine compound in the coating film, and the rust preventive is concentrated in the interface region between the Zn-based alloy plating layer and the coating film. Therefore, it has excellent corrosion resistance. [0035] 　As the compound that can be added to the coating film for forming the coating film containing the rust inhibitor according to the present invention (hereinafter, referred to as the rust inhibitor source), any compound that can be dissolved in the acidic coating material. Can be used. The rust inhibitor dissolved in such an acidic paint may be referred to as a cation inhibitor. [0036] 　Examples of the rust preventive agent source in the present invention include P (phosphorus) compound, V (vanadium) compound, and Mg (magnesium) compound. Preferably, P and V are contained alone or in combination in the coating film in the present invention. More preferably, the coating film contains P alone or a combination of P and V. [0037] 　When P is contained as a rust preventive in the coating film, the corrosion resistance of the processed portion can be particularly improved. Corrosion resistance of the processed portion means the corrosion resistance of the processed portion when the steel sheet having the coating film is processed (for example, bending). The reason why the corrosion resistance of the processed portion is improved by containing P in the coating film in this way is that P reacts with the surface of the Zn-based alloy plating layer to form a phosphate layer and passivate the processed portion. The effect, the effect that P itself forms a sparingly soluble coating film and exerts a barrier property against corrosion factors, and the effect that P captures the metal ions eluted from the underlying metal plate to form a sparingly soluble compound together with the metal ions, and the barrier It is considered that this is because it has an effect of exerting sex. The source of the rust preventive agent containing P in the present invention is not particularly limited, and for example, phosphoric acids such as orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, and tetraphosphoric acid, triammonium phosphate, and dihydrogen phosphate Ammonium salts such as ammonium, metal salts with Na, Mg, Al, K, Ca, Mn, Ni, Zn, Fe, etc., aminotri (methylenephosphonic acid), 1-hydroxyethylidene-1,1-diphosphonic acid, ethylenediaminetetra Examples thereof include phosphonic acids such as (methylenephosphonic acid) and diethylenetriaminepenta (methylenephosphonic acid) and salts thereof, organic phosphoric acids such as phytic acid and salts thereof. These rust preventive sources can be added alone or in combination in the coating film for forming the coating film in the present invention. [0038] 　Further, when V is contained as a rust preventive in the coating film, the corrosion resistance of the end face portion can be particularly improved. The end face portion corrosion resistance means, for example, the corrosion resistance at the end face portion when a steel sheet having a coating film is processed (for example, cut processing). The reason why the corrosion resistance of the end face is improved by containing V in the coating film in this way is that V eluted from the coating film reacts with Zn and Al eluted from the Zn-based alloy plating layer to generate corrosion. This is because the progress of corrosion can be suppressed by forming an object and passivating the surface layer of the Zn-based alloy plating layer. Examples of the V-containing rust preventive source in the present invention include vanadium pentoxide, HVO 3 metavanadate , ammonium metavanadium, vanadium oxytrichloride VOCl 3 , vanadium trioxide V 2 O 3 , vanadium dioxide, and vanadium oxysulfate VOSO 4. , Vanadium oxyacetylacetonate VO (OC (= CH 2 ) CH 2 COCH 3 ) 3 , Vanadium acetylacetonate V (OC (= CH 2 ) CH 2 COCH 3 ) 3, Vanadium trichloride VCl 3 and the like. These rust preventive sources can be added alone or in combination in the coating film for forming the coating film in the present invention. [0039] 　Examples of the source of the rust preventive agent containing Mg in the present invention include magnesium nitrate Mg (NO 3 ) 2 , magnesium sulfate sulfonyl 4 , magnesium acetate Mg (CH 3 COO) 2, and the like. These rust preventive sources can be added alone or in combination in the coating film for forming the coating film in the present invention. Similar to V, Mg can improve the corrosion resistance of the end face portion. The reason why the corrosion resistance of the end face is improved is considered to be the same as that of V. [0040] 　The average concentration of the rust inhibitor in the coating film can be 3 to 15% by mass. As described above, the "average concentration of the rust inhibitor" is based on the total concentration (mass%) of the elements of, for example, P, V, and Mg in the coating film. With the average concentration of the rust inhibitor in the coating film in such a range, a sufficient rust inhibitor is present in the entire coating film, so that the surface-treated steel sheet according to the present invention can be provided with sufficient corrosion resistance. It will be possible. Further, even if the rust inhibitor is concentrated near the interface between the coating film and the Zn-based alloy plating layer as described above, the concentration of the rust inhibitor is not insufficient in other regions, and the entire coating film, that is, the present invention Sufficient corrosion resistance can be provided in the surface-treated steel sheet according to the above. [0041] 　If the average concentration of the rust inhibitor in the coating film is less than 3% by mass%, the concentration of the rust inhibitor in the entire coating film is insufficient, and the improvement of corrosion resistance due to the effect of the rust inhibitor is limited. Therefore, there is a risk that sufficient corrosion resistance cannot be obtained. On the other hand, if the average concentration of the rust preventive in the coating film is more than 15%, the effect of improving the corrosion resistance by adding the rust preventive is saturated, which is not preferable in terms of cost. The average concentration of the rust inhibitor in the coating film may be 5% or more, 7% or more, or 10% or more in mass%, and therefore preferably 5% or more and 15% or less, more preferably 7%. It is 15% or more, more preferably 10% or more and 15% or less. [0042] 　As used herein, the "average concentration of rust inhibitor in the coating" is determined by the following method. First, the cross section of the steel sheet having the coating film is observed by TEM, and from a position randomly selected on the surface of the coating film, the zinc-based alloy plating layer is directed in the direction perpendicular to the surface of the coating film (thickness direction). Draw a straight line. Next, the thickness of the coating film is divided into 11 equal parts on the straight line and divided into 11 regions. Then, the concentration of the rust inhibitor, that is, the total concentration of the elements of P, V, and Mg, for example, is measured in 10 regions in the coating film excluding the region closest to the Zn-based alloy plating layer from the region. Then, those measured values ​​are averaged and determined. The measurement of the concentration of the rust inhibitor at each position is obtained by elemental analysis using an energy dispersive X-ray spectrometer (EDS) attached to SEM or TEM. [0043] 　In the present invention, the concentration of the rust inhibitor in the coating film at a position 10 nm away from the interface between the Zn-based alloy plating layer and the coating film is 1.5 times or more the average concentration of the rust inhibitor in the coating film. It is 0.0 times or less. That is, the rust preventive is concentrated in the region near the interface between the coating film and the Zn-based alloy plating layer in the coating film. In this way, when the rust inhibitor is thickened in the region near the interface between the coating film and the Zn-based alloy plating layer as compared with other parts, the concentrated region of the rust inhibitor is Zn against corrosion factors such as oxygen. It can act as a barrier region for the system alloy plating layer. Therefore, it is possible to minimize the erosion of the corrosion factor in the Zn-based alloy plating layer, and the surface-treated steel sheet can have extremely excellent corrosion resistance. Further, the above-mentioned concentrated region of the rust preventive makes it possible to sufficiently maintain the corrosion resistance even after the surface-treated steel sheet is processed. [0044] 　If this value is less than 1.5 times, the corrosion factor passes through and corrodes the Zn-based alloy plating layer in the vicinity of the interface between the coating film and the Zn-based alloy plating layer side. The effect as a barrier region to suppress may be weakened, the corrosion factor may reach the Zn-based alloy plating layer, and the coating film may not be able to provide sufficient corrosion resistance. On the other hand, if this value is more than 5.0 times, the degree of thickening in the rust preventive concentrated region is too high, so that when the surface-treated steel sheet is processed, the coating film is applied in the rust preventive concentrated region. May coagulate and break. Then, the processing adhesion is lowered, and as a result, the corrosion resistance at the processed portion cannot be maintained, and the corrosion resistance may be insufficient. The concentration of the rust inhibitor in the coating film at a position 10 nm away from the interface between the Zn-based alloy plating layer and the coating film is 1.7 times or more and 2.0 times or more the average concentration of the rust inhibitor in the coating film. , Or 2.2 times or more, and may be 4.8 times or less, 4.5 times or less, 4.2 times or less, 4.0 times or less, or 3.5 times or less, preferably. It is 2.0 times or more and 4.5 times or less, more preferably 2.0 times or more and 4.0 times or less, and further preferably 2.5 times or more and 4.0 times or less. [0045] 　The "concentration of the rust inhibitor in the coating film at a position 10 nm away from the interface between the Zn-based alloy plating layer and the coating film" is determined from the cross section of the steel sheet having the coating film using TEM-EDS. Specifically, from the TEM image of the observed cross section, five positions 10 nm apart from the surface of the coating film in the direction perpendicular to the interface between the Zn-based alloy plating layer and the coating film randomly selected. The concentration of the rust preventive agent (that is, for example, the total concentration of the elements of P, V, and Mg) is measured by TEM-EDS, and the measured values ​​are averaged to determine. [0046] 　As described above, since the acidic coating material having a pH of 3.0 to 5.0 removes the oxide film on the surface of the Zn-based alloy plating layer, the component of the rust preventive agent (for example, P) contained in the coating film in the present invention. And the component (for example, Zn) contained in the Zn-based alloy plating layer reacts near the interface between the coating film and the Zn-based alloy plating layer, and the reaction product (for example, Zn and P) is formed in the region near the interface. The reaction product containing) is formed. In the region where the reaction product exists, both the rust preventive component uniformly dispersed in the coating film and the rust preventive component constituting the reaction product are present as in the other regions. doing. Therefore, in the surface-treated steel sheet according to the present invention, the rust preventive (for example, P) is thickened in the region near the interface between the coating film and the Zn-based alloy plating layer in the coating film as compared with other regions. Exists. [0047] 　Regions in which such reaction products are present can be measured using elemental analysis methods known to those of skill in the art. Specifically, for example, when P is contained as a rust preventive, element analysis is performed in the direction perpendicular to the surface of the coating film from the surface of the coating film toward the Zn-based alloy plating layer, that is, in the thickness direction. It is possible to measure the region where P as a component of the rust preventive is concentrated near the interface between the coating film and the Zn-based alloy plating layer. Further, by analyzing the concentrated region of P measured in this way by a method of measuring the binding energy between atoms known to those skilled in the art, P of the rust preventive component and the component of the Zn-based alloy plating layer are analyzed. The reaction product with Zn and Al can be measured. [0048] 　(Glowing Pigment) In the 　surface-treated steel sheet according to the present invention, in addition to the above-mentioned rust preventive, it is preferable that a bright pigment is contained in the coating film in order to improve the design. As used herein, "bright pigment" means a pigment that reflects light on its surface. As the bright pigment, a pigment that does not dissolve in the acidic paint for producing the coating film and is contained in the coating film as it is added to the coating film is used. Therefore, in the present invention, "containing a bright pigment" in the coating film means that the coating film contains a metal simple substance, an oxide, an alloy, or the like described below, and the bright pigment in the coating film. And the binder resin that forms the coating film can be clearly distinguished and specified. Therefore, the "concentration" of the bright pigment described later means the total concentration of the metal simple substance, oxide, alloy, etc. described below. [0049] 　The reason for improving the design is that products using Zn-based alloy-plated steel sheets for building materials and outdoor home appliances are generally used in places that are visible to users, etc. This is because the system alloy galvanized steel sheet preferably has good visual quality (appearance). In particular, when the bright pigment has a design close to that of the Zn-based alloy plating layer, unevenness in the coating thickness may be inconspicuous or flaws may be inconspicuous. Therefore, the coating thickness can be reduced, which is economically preferable. [0050] 　Therefore, by using the above-mentioned bright pigment in the coating film, the brightness of the surface-treated steel sheet can be improved by its metallic appearance (for example, silver color), and the surface having excellent appearance and high designability can be improved. It becomes possible to provide a treated steel sheet. Further, when the bright pigment has the same or similar color tone as the Zn-based alloy plating layer, when the coating film is damaged, the change in appearance due to the scratch can be made less noticeable, and therefore the scratch resistance can be improved. Therefore, the excellent appearance of the surface-treated steel sheet according to the present invention can be maintained for a long period of time. [0051] 　Then, since the bright pigment is contained in the coating film, when the surface-treated steel sheet of the present invention is observed from a direction perpendicular to the surface of the coating film, the underlying Zn-based alloy plating layer is made invisible by the bright pigment. be able to. In this way, for example, when Zn contained in the Zn-based alloy plating layer is oxidized by the influence of oxygen in the air to form an oxygen-deficient Zn oxide, and the Zn-based alloy plating layer turns black. Even so, the blackening can be made invisible by the bright pigment, and the design of the surface-treated steel plate according to the present invention can be maintained. [0052] 　The bright pigment in the present invention is not particularly limited as long as it can be used in an acidic paint having a pH of 3.0 to 5.0 used in the present invention, that is, it does not dissolve in this pH range, but for example, aluminum or oxide. Can be used. Examples of oxides include, but are not limited to, alumina, silica, mica, zirconia, titania, glass, zinc oxide and the like. These pigments are coated with a metal oxide such as silica and have a metallic appearance (also referred to as a metallic appearance). These can be used alone or in combination in the coating. [0053] 　As the bright pigment in the present invention, in addition to the above-mentioned aluminum or oxide, a metal capable of providing high brightness can be further added to the coating film. Examples of such metals are not particularly limited as long as they are metals having high brightness and can be used in acidic paints, but for example, Rh (rosium), Cr (chromium), Ti (titanium), and the like. Examples thereof include simple metals such as Ag (silver) and Cu (copper), and alloys such as Zn—Cu (brass). These metals can be used alone or in combination in the coating. By including a metal capable of providing such high brightness in the coating film, it is possible to further enhance the metallic appearance of the coating film, and therefore the brightness of the surface-treated steel sheet according to the present invention can be further improved. The design of the product can be further improved. [0054] 　The average particle size of the bright pigment in the present invention is not particularly limited, but can be, for example, in the range of 1 μm or more and 30 μm or less. When the average particle size of the bright pigment is in the range of 1 μm or more and 30 μm or less, it is possible to provide sufficient designability while maintaining corrosion resistance without causing uneven brightness. If the average particle size of the bright pigment is less than 1 μm, it becomes difficult to disperse it uniformly in the coating film for forming the coating film in the present invention, and the color tone of the formed coating film becomes uneven, resulting in a sufficient design. It may not be possible to guarantee sex. On the other hand, if the average particle size of the bright pigment is more than 30 μm, the bright pigment may protrude from the surface of the coating film, and a corrosion factor may invade from the protruding portion, which may deteriorate the corrosion resistance. Further, the presence of such a protruding portion makes it difficult to have a uniform appearance, which may result in insufficient design. The average particle size of the bright pigment may be 2 μm or more or 3 μm or more, and may be 25 μm or more, 20 μm or less or 15 μm or less, preferably 3 μm or more and 25 μm or less, more preferably 3 μm or more and 20 μm or less, and further. It is preferably 3 μm or more and 15 μm or less. [0055] 　As used herein, the "average particle size" of the bright pigment according to the present invention can be determined, for example, by the following method. A mapping image of the elements constituting the bright pigment is obtained by a field emission electron probe microanalyzer (FE-EPMA) from a direction perpendicular to the surface of the coating film. The area of ​​the measurement range of the mapping image shall be 20 mm × 20 mm or more. From the obtained mapping image, the contour of the bright pigment existing in the measurement range is specified, and the total area S surrounded by the contour is obtained. In addition, the number N of bright pigments existing in the measurement range is determined. Then, assuming that the obtained area S is composed of N circular bright pigments having a circular cross section having a diameter (particle size) D, the average particle size of the bright pigments is set to [D = 2 × (S /). (ΠN)) 0.5 ]. [0056] 　The shape of the bright pigment in the present invention may be any shape, and may be, for example, spherical, elliptical, needle-shaped, flat-shaped, thin plate-shaped, scaly-shaped, or the like. Preferably, the shape of the bright pigment can be scaly. When the shape of the bright pigment in the present invention is scaly, the bright pigment can effectively obscure the underlying Zn-based alloy plating layer, that is, effectively blacken the Zn-based alloy plating layer of the product. It is possible to suppress changes in appearance and provide a surface-treated steel sheet having extremely excellent design. [0057] 　The average concentration of the bright pigment in the coating film can be, for example, 5 to 15% by mass. By setting the average concentration of the bright pigment in the coating film in such a range, it is possible to provide a uniform metallic appearance to the surface-treated steel sheet according to the present invention without impairing the processability of the coating film. It is possible to provide a surface-treated steel sheet having excellent designability. If the average concentration of the bright pigment in the coating film is less than 5%, the bright pigment in the coating film is insufficient, a sufficient metallic appearance cannot be provided, the brightness is insufficient, and sufficient designability can be provided. It may disappear. On the other hand, if the average concentration of the bright pigment in the coating film is more than 15%, the improvement in brightness due to the addition of the bright pigment is saturated, which is not preferable in terms of cost. In addition, since a large amount of bright pigment is present in the coating film, the proportion of the binder resin constituting the coating film is relatively reduced, and the coating film may be cracked during processing to reduce workability. .. Preferably, the average concentration of the bright pigment in the coating film is 5% or more and 12% or less, more preferably 6% or more and 10% or less. [0058] 　When used in the present specification, the "average concentration of the bright pigment in the coating film" can be determined by a known method. For example, it can be measured using a glow discharge emission surface analyzer (Glow Discharge Optical Operation Spectrometery: GD-OES). Specifically, when the type of the bright pigment, that is, the specific compound of the bright pigment is known, the coating film is first sputtered from the surface toward the Zn-based alloy plating layer to form the bright pigment. For the element, the concentration profile in the depth direction is measured every 1.0 μm. Then, the average value of the measured concentrations of the main elements is obtained, the measured concentration is converted based on the molecular weight of the compound of the known coloring pigment, and the average concentration of the bright pigment in the coating film is obtained. In addition, the coating film is mechanically or chemically peeled off, and the total mass of the coating film is measured. Then, the concentration of the bright pigment contained in the peeled coating film is measured by analysis. As a method for analyzing the concentration of the bright pigment in the peeled coating film, for example, inductively coupled plasma (ICP) or fluorescent X-ray analysis can be used. When the type of the bright pigment, that is, the specific compound of the bright pigment is unknown, the elements constituting the bright pigment are analyzed by FE-EPMA with respect to the cross section of the coating film (the surface perpendicular to the surface of the coating film). After specifying the type of the bright pigment, the "average concentration of the bright pigment in the coating film" can be measured as described above. When the bright pigment is brass, which is an alloy, the total content (concentration) of Cu and Zn is taken as the average concentration of the bright pigment in the coating film. [0059] 　If necessary, a pigment or aggregate other than the rust preventive and the bright pigment of the present invention can be added to the coating film of the present invention. In addition, waxes such as polyethylene wack or PTFE wax, resin beads such as acrylic resin beads or urethane resin beads, and dyes such as phthalocyanine blue, phthalocyanine green, methyl orange, methyl violet, or alizarin are applied to the coating film. Can be added. It is more preferable to add these because the strength of the coating film can be increased and a desired color can be imparted to the coating film. The amount of these additions may be appropriately determined so as not to be disadvantageous to the coating film in the present invention. [0060] 　In particular, dyes can be used as colorants to impart the desired color to the coating film in the present invention, and thus the surface-treated steel sheet according to the present invention. The dyes may be used alone or in combination of a plurality of dyes. Further, the dye may be used in combination with the coloring pigment. The type of dye that can be used in the coating film in the present invention is not particularly limited, but known dyes can be used, and for example, phthalocyanine blue, phthalocyanine green, methyl orange, methyl violet, or alizarin are used. be able to. [0061] 　[Method for manufacturing surface-treated steel sheet] 　The method for manufacturing a surface-treated steel sheet according to the present invention will be described below. In the surface-treated steel sheet according to the present invention, for example, an acidic paint having a pH of 3.0 to 5.0 containing at least a rust preventive and a binder resin is applied onto a Zn-based alloy plating layer formed on the steel sheet. It can be produced by heating and curing the paint. [0062] 　 As the 　steel sheet, a steel sheet having an arbitrary plate thickness and chemical composition can be used. For example, a cold-rolled steel sheet having a plate thickness of 0.25 to 3.5 mm can be used. Further, the Zn-based alloy plating layer can be formed with a thickness of 5 to 30 μm using, for example, a Zn—Al—Mg hot-dip galvanizing bath or a Zn-Al-Mg-Si hot-dip galvanizing bath at 400 to 550 ° C. .. [0063] 　 For example, the paint is prepared by mixing a binder resin dispersed in a solvent and a curing agent, and then dispersing a predetermined amount of a rust preventive agent source and optionally a bright pigment in the mixture. It can be obtained by letting it. The order of mixing may be different. The binder resin is not particularly limited, but a polyester resin, a urethane resin, an acrylic resin, or the like can be used, and a melamine resin or the like can be used as the curing agent. Further, an acidic solvent can be used, and as the rust preventive source, a solvent that dissolves in the acidic solvent, for example, a P compound, a V compound, an Mg compound, or two or more of them can be used. On the other hand, the bright pigment can be appropriately selected from pigments that do not dissolve in an acidic solvent. The ratio of the binder resin to the curing agent can be appropriately determined, and can be, for example, in the range of 1: 1 to 9: 1. [0064] 　It is important that the pH of the paint used to obtain the coating film in the present invention is 3.0 or more and 5.0 or less. By setting the pH of the paint in such a range, not only can the rust preventive source be dissolved in the paint, but also when such a paint is applied to the Zn-based alloy plating layer, the Zn-based alloy plating layer is used. The oxide film on the surface of the surface can be appropriately removed. Then, near the surface of the Zn-based alloy plating layer, the component of the rust preventive in the ion state reacts with the component in the Zn-based alloy plating layer, and as a result, after the paint is cured, the Zn-based alloy plating layer is used. It is possible to form a region in which the reaction product is concentrated near the interface between the coating film and the coating film. If the pH of the paint is less than 3.0, the degree of thickening in the rust preventive concentrated region becomes too high, and when the surface-treated steel sheet is processed, the coating film coagulates and breaks in the rust preventive concentrated region. May be done. Then, the processing adhesion is lowered, and as a result, the corrosion resistance at the processed portion cannot be maintained, and the corrosion resistance may be insufficient. Further, Zn may elute in the paint and the storage stability of the paint may decrease. On the other hand, if the pH of the coating material exceeds 5.0, the oxide film on the surface of the Zn-based alloy plating layer cannot be sufficiently removed, and a rust preventive agent is applied to the region near the interface between the coating film and the Zn-based alloy plating layer. May not be sufficiently thickened. Further, when the pH becomes alkaline, that is, more than 7.0, the paint solidifies (gels) when the paint is prepared, lacks storage stability as a paint, and causes a problem in use. The pH of the paint may be 3.2 or higher or 3.5 or higher, and may be 4.8 or lower or 4.5 or lower. The pH of the paint is preferably 3.2 to 4.8, more preferably 3.5 to 4.5. The pH cannot be measured after the paint is cured to form a coating film. [0065] 　The pH of the paint may change depending on the production lot such as the solvent of the raw material. Therefore, it is necessary to adjust the pH using an acid or alkaline aqueous solution. More specifically, the pH after preparation of the paint is measured, and nitric acid, hydrochloric acid or sulfuric acid may be used to lower the pH value according to the target pH, and an aqueous sodium hydroxide solution to raise the pH value. Etc. can be used. It is preferable that these acid or alkaline aqueous solutions are diluted before use for pH adjustment. [0066] 　 　Next, the obtained coating film is applied onto the Zn-based alloy plating layer so that the coating film has a predetermined thickness, and is baked and cured. The method of applying the paint is not particularly limited, and any coating method known to those skilled in the art can be used, and for example, a roll coater may be used. The baking can be performed under any heating condition in which the paint is cured. For example, the baking is performed at a heating rate of 5 to 70 ° C./sec so as to reach a steel sheet temperature of 180 to 230 ° C. [0067] 　As described above, in the surface-treated steel sheet according to the present invention, the rust inhibitor containing, for example, P, V or Mg is present as a fine compound in the coating film. In order to obtain such a structure, in the method for producing a surface-treated steel sheet according to the present invention, in order to allow the rust inhibitor to exist in the paint in the ionic state, a rust inhibitor source (for example, P compound, for example, P compound, etc., is used in an acidic solvent. A coating material for forming the coating film in the present invention is prepared by dissolving (V compound or Mg compound). The present inventors have found that the use of such a production method is advantageous in the following points. [0068] 　For example, unlike the present invention, when the rust preventive pigment is contained as a solid component (for example, powder) in the coating film, the coating film is used to uniformly distribute the rust preventive pigment in the formed coating film. It is considered necessary to uniformly disperse the rust preventive pigment in the paint for forming the rust preventive pigment. Moreover, in such a manufacturing method, if a large amount of rust preventive pigment is added to the paint, it becomes difficult to uniformly disperse the rust preventive pigment in the paint, and further, the resin as the main component of the formed coating film There is a risk that the proportion of the rust preventive pigment may decrease and the coating film may become brittle, and it is considered that there is an upper limit to the amount of the rust preventive pigment added to the coating film. Further, in such a paint, the dispersed state deteriorates while the paint is stored until use after the paint is prepared by dispersing the rust preventive pigment, and as a result, the rust preventive pigment is uniformly distributed. There are problems such as not being able to obtain a film. [0069] 　Further, for example, unlike the present invention, when an alkaline coating material for a coating film is prepared by using a compound that dissolves in an alkaline solvent as a rust preventive source, the amount of the compound added is increased. In some cases, the rust preventive source is not sufficiently dissolved and solid matter is generated in the paint. In addition, the paint may harden (gel) during storage of the paint, and there is a problem of storage stability of the paint when storing the paint. Further, it is considered that even if an alkaline paint is applied on the Zn-based alloy plating layer, the oxide film on the Zn-based alloy plating layer cannot be sufficiently removed. [0070] 　On the other hand, in the present invention, an acidic paint and a compound that dissolves in the paint as a source of a rust preventive agent are used, and the compound is dissolved in the acidic paint. Therefore, there is no restriction on uniformly dispersing the components of the rust preventive agent in the paint as in the case of using the powder rust preventive pigment. Therefore, in such a manufacturing method, more rust preventives can be added to the paint in a state where the rust preventives are uniformly dispersed as compared with the paint containing the rust preventive pigment such as powder. Further, the acidic paint having a pH of 3.0 to 5.0 for forming a coating film in the present invention is a paint that is less likely to harden than an alkaline paint even when a large amount of a rust inhibitor source is added to the paint. Has excellent storage stability. As described above, in the coating film for forming the coating film in the present invention, many sources of rust preventive agents can be added while maintaining the storage stability of the coating film, and as a result, a high concentration is contained in the coating film. It is possible to form a coating film containing a rust preventive. Therefore, by forming a coating film using such a paint, it is possible to form a surface-treated steel sheet having extremely excellent corrosion resistance. [0071] 　Further, as described above, when such an acidic paint having a pH of 3.0 to 5.0 is applied onto the Zn-based alloy plating layer, the present inventors have formed it on the surface of the Zn-based alloy plating layer. The oxide film is removed by the paint, and the components of the rust preventive agent react with the components in the Zn-based alloy plating layer, resulting in the rust preventive agent in the region near the interface between the coating film and the Zn-based alloy plating layer. It has been found that a reaction product with a metal (for example, a reaction product between P and Zn) is formed in the Zn-based alloy plating layer. This removal of the oxide film is due to the fact that the paint used in the present invention applied on the Zn-based alloy plating layer is acidic. Then, by removing the oxide film, the active metal under the oxide film of the Zn-based alloy plating layer is exposed, and the active metal reacts with the component of the rust inhibitor in the coating film to form the above reaction product. To. In the region where the reaction product thus produced exists, the rust preventive is concentrated as compared with the other regions. Therefore, since this concentrated region acts as a barrier region for preventing the corrosion factor from invading the Zn-based alloy plating layer, the surface-treated steel sheet according to the present invention can have extremely high corrosion resistance. [0072] 　The concentration of the rust inhibitor in the surface-treated steel sheet according to the present invention, that is, at a position 10 nm away from the interface between the Zn-based alloy plating layer and the coating film, is 1 of the average concentration of the rust inhibitor in the coating film. For surface-treated steel sheets that are 5 times or more and 5.0 times or less, an acidic paint with a pH of 3.0 to 5.0 is used, and various parameters during manufacturing, such as the type of rust inhibitor in the paint, are used. Manufacture by appropriately adjusting the amount of rust inhibitor added, the temperature of the paint, the heating temperature and heating time when curing the paint, the ratio of the binder resin to the hardener, the pretreatment to the alloy plating layer, etc. Can be done. That is, by using an acidic paint having a pH of 3.0 to 5.0 containing a predetermined amount of a rust preventive component and optionally a bright pigment, and appropriately adjusting such parameters, the coating material can be prevented. It is possible to adjust the degree of concentration of the rust inhibitor, and therefore, it is possible to manufacture the surface-treated steel sheet according to the present invention. [0073] 　Furthermore, the oxide film of the Zn-based alloy plating layer is removed, and the active metal of the Zn-based alloy plating layer reacts with the components in the paint, so that strong chemicals are formed between the Zn-based alloy plating layer and the coating film. Therefore, it is possible to obtain a surface-treated steel sheet having excellent adhesion between the Zn-based alloy plating layer and the coating film. More specifically, although not bound by a particular theory, the components of the rust inhibitor in the paint react to form hydroxides, and the functional groups of the hydroxide react with the resin to be irreversible. As a result, the adhesion between the Zn-based alloy plating layer and the coating film is improved by providing a proper and chemical bond. Such adhesion cannot be achieved, for example, when a neutral or alkaline paint is used to form the coating film, and therefore an acidic paint having a pH of 3.0 to 5.0 is used to form the coating film. When this is done, the adhesion is improved as compared with the case where a neutral or alkaline paint is used. [0074] 　By using the manufacturing method as described above, the surface-treated steel sheet according to the present invention can be manufactured. That is, it has a steel plate, a Zn-based alloy plating layer formed on at least one surface of the steel plate, and a coating film containing a rust preventive and a binder resin formed on the Zn-based alloy plating layer, and the Zn-based alloy plating layer. Manufactures surface-treated steel sheets in which the concentration of the rust inhibitor in the coating at a position 10 nm away from the interface with the coating is 1.5 times or more and 5.0 times or less the average concentration of the rust inhibitor in the coating. can do. Example [0075] 　In this example, the average concentration and concentration distribution of the rust preventive in the coating film, the average concentration of the bright pigment, the types of the rust preventive and the bright pigment, the type of the binder resin, and the chemical composition of the Zn-based alloy plating layer are varied. The surface-treated steel sheets produced by the modification were evaluated for their corrosion resistance, brightness, work adhesion and storage stability. The surface-treated steel sheet according to the present invention will be described in more detail below with some examples. However, it is not intended that the particular examples described below limit the scope of the invention described in the claims. [0076] 　 　(Formation of Zn-based alloy plating layer) 　A cold-rolled steel sheet with a thickness of 1 mm has a chemical composition of Al: about 11%, Mg: about 3%, and Zn: about 86%. It was immersed in a hot-dip plating bath at 450 ° C. for 3 to 5 seconds to form a Zn-11% Al-3% Mg alloy plating layer having a thickness of about 10 μm on a cold-rolled steel sheet. Further, the composition of the hot-dip plating bath was changed, and the Zn-1% Al-1% Mg alloy plating layer and the Zn-40% Al-8% Mg alloy plating having a thickness of about 10 μm were plated on the cold-rolled steel sheet by the same procedure. A layer was formed. Alternatively, a cold-rolled steel sheet having a thickness of 1 mm is placed in a hot-dip galvanizing bath having a chemical composition of Al: about 11%, Mg: about 3%, Si: about 1%, and Zn: about 85% at about 450 ° C. 3 to 5 After immersion for seconds, a Zn-11% Al-3% Mg-1% Si alloy plating layer having a thickness of about 10 μm was formed on the cold-rolled steel sheet. Further, the composition of the hot-dip plating bath was changed, and the Zn-11% Al-3% Mg-0.4% Si alloy plating layer and the Zn-11% Al having a thickness of about 10 μm were placed on the cold-rolled steel sheet by the same procedure. A -3% Mg-1.5% Si alloy plating layer was formed. [0077] 　(Preparation of paint) A 　polyester resin (molecular weight: 16,000; glass transition point: 10 ° C.) and a polyurethane resin (molecular weight: 10000; glass transition point: 20 ° C.) are dispersed as an emulsion in an acidic solvent as a binder resin. Sample No. The paints used in 3 to 21 and 25 to 36 were adjusted to have a pH of 3.0 to 5.0 using nitric acid or sodium hydroxide. An imino-based melamine resin was mixed therein. The concentration ratio of the polyester resin and the melamine resin was 100:20. Then, a rust preventive source and a bright pigment were added to the mixture to prepare a paint. In addition, sample No. For the paints used in 1, 2 and 24, the pH was adjusted to exceed 5.0, and the sample No. The paints used in 22 and 23 were adjusted so that the pH was less than 3.0. Table 1 shows the pH of the paint used in each sample. And No. No bright pigment was added to 25. Orthophosphoric acid, vanadium pentoxide, and magnesium sulfate were used as the sources of the rust preventive for the sample containing P, V, and Mg as the rust preventive, respectively. As the bright pigment, those shown in Table 1 were used. [0078] 　The amount of the rust inhibitor added to the coating film was the average concentration of the rust inhibitor in the desired coating film (3%, 5) when measured using TEM-EDS based on the cross section of the obtained coating film. %, 10%, 13% or 15%) was appropriately adjusted. Further, the concentration of the bright pigment was appropriately adjusted so that the average concentration would be 10% or 5% when measured using GD-OES. [0079] 　(Formation of coating film) 　The coating film prepared as described above was applied onto a Zn-based alloy plating layer so that the average thickness of the formed coating film was 5 μm, and cured by baking. The baking was carried out at a heating rate of about 20 ° C./sec and a steel sheet temperature of about 200 ° C. until the paint was completely cured. [0080] 　The ratio of the concentration of the rust inhibitor in the coating film to the average concentration of the rust inhibitor in the coating film at a position 10 nm away from the interface between the Zn-based alloy plating layer and the coating film should be changed as appropriate for the pH of the coating film. So I adjusted it. [0081] 　From the obtained coating film, elemental analysis using TEM-EDS was performed to obtain an average concentration (mass%) of the rust inhibitor in the coating film; and from the interface between the Zn-based alloy plating layer and the coating film with respect to the average concentration. The ratio of the concentration of the rust inhibitor in the coating film at a position separated by 10 nm was determined. The values ​​determined in this way are shown in Table 1. Table 1 shows the types of rust preventives and bright pigments contained in the coating film. When two types of rust preventives are contained in the coating film, the total of the average concentrations of the two rust preventives corresponds to the average concentrations shown in the table, and each rust preventive is contained in the coating film. Exists in quantity. The same applies to bright pigments. [0082] 　 Prepare surface-treated steel sheet samples as 　described above , and evaluate the corrosion resistance, brightness, processing adhesion, and storage stability of each sample as shown in Table 1 as follows. Was done. [0083] 　(Evaluation test of corrosion resistance) For 　each sample, a 0.6 mm test material for testing was obtained by processing (7 mm extrusion) according to the Eriksen test (JIS Z2247: 2006), which is a simulation of actual use, and the test material was obtained. A salt spray test (based on the JASO M609-91 method) was performed on the material as an evaluation test of corrosion resistance. This salt spray test involves (1) salt spray for 2 hours (5% NaCl, 35 ° C); (2) drying for 4 hours (60 ° C); and (3) wetting for 2 hours (50 ° C, humidity of 95% or more). A total of 120 cycles (total of 960 hours) were carried out as one cycle. In order to prevent corrosion from the end face, the end face of each sample was sealed with tape and tested. [0084] 　The corrosion resistance was evaluated by observing the surface (planar portion) of the sample after 960 hours of the salt spray test with an optical microscope and determining the rust generation area ratio Z. Specifically, first, the surface of the sample was read by a scanner. After that, the area where rust was generated was selected using image editing software, and the rust area ratio was calculated. This procedure was performed on five samples, and "rust-generated area ratio Z" was determined as the average of the rust-generated area ratio. Based on the "rust generation area ratio Z" determined for each sample in this way, the score of each sample was determined in eight stages as follows. A score of 4 or higher was used as a passing score for corrosion resistance. 　Score 8: Z = 0% 　Score 7.0%