KR102425853B1 - surface treatment steel plate - Google Patents

Abstract

The present invention has a steel sheet, a Zn-based alloy plating layer formed on at least one side of the steel sheet, and a coating film comprising a rust preventive agent and a binder resin formed on the Zn-based alloy plating layer, wherein the Zn-based alloy plating layer and the coating film are separated by 10 nm from the interface. It relates to a surface-treated steel sheet, wherein the concentration of the rust preventive agent in the coating film is 1.5 to 5.0 times the average concentration of the rust inhibitor in the coating film.

Description

surface treatment steel plate

The present invention relates to a surface-treated steel sheet excellent in corrosion resistance.

Various plated steel sheets with excellent corrosion resistance used for home appliances, building materials, automobiles, and the like are known. For example, a galvanized steel sheet in which a zinc plating 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, for example, even when the galvanized steel sheet is damaged and the steel sheet is exposed, zinc, which is more susceptible to corrosion than iron constituting the steel sheet, is corroded first to form a protective film, and the protective film corrosion of the steel sheet can be prevented. Accordingly, the galvanized steel sheet is being developed for various uses requiring corrosion resistance.

However, the surface of various galvanized steel sheets, such as a galvanized steel sheet, may deteriorate by the surrounding environment. For example, there is a problem that the plating layer is oxidized by electrolytes such as salt contained in the air, oxygen and moisture present in a high-temperature and high-humidity environment, thereby generating white rust. Since generation|generation of white rust may impair external appearance uniformity, higher corrosion resistance is calculated|required of a galvanized steel sheet.

As a technique for further improving the corrosion resistance of a galvanized steel sheet, a Zn-based alloy-coated steel sheet subjected to Zn-Al-Mg-based alloy plating or the like is known.

However, also in such a Zn-based alloy plated steel sheet, an additional improvement of corrosion resistance is required, and in particular, a technique for ensuring excellent corrosion resistance by preventing corrosion factors such as oxygen from reaching the alloy plating layer is required. And also when processing is given to such an alloy plated steel sheet, it is calculated|required that the outstanding corrosion resistance can be maintained.

Patent Document 1 discloses a galvanized steel sheet excellent in corrosion resistance, comprising a steel sheet, a Zn-Al-Mg-based alloy plating layer formed on the surface of the steel sheet, and a film containing aluminum formed on the alloy plating layer.

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, and at least one cationic property selected from Li and the like. A surface-treated metal sheet containing a metal element and having a cationic metal element concentrated in a region close to the outer surface of the coating layer is disclosed, and such a surface-treated steel sheet does not reduce corrosion resistance and has alkali resistance , it is taught that solvent resistance can be improved.

Further, Patent Document 3 discloses a base treatment composition for a coated steel sheet comprising a specific organosilicon compound, hexafluoro metal acid, a urethane resin having a specific cationic group, a vanadium compound, and an aqueous medium, such a composition It is taught that it is possible to form a base treatment layer having corrosion resistance under the eaves on a steel sheet by using

Patent Documents 4 to 6 disclose a coated steel sheet having a resin film containing, for example, a vanadium-based rust preventive pigment on a zinc-based plated steel sheet.

International Publication No. 2015/075792 Japanese Patent Laid-Open No. 2009-248460 Japanese Patent Laid-Open No. 2014-214315 Japanese Patent Laid-Open No. 2005-015834 Japanese Patent Laid-Open No. 2013-194145 Japanese Patent Laid-Open No. 2001-003181

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 secured by this alloy plating layer. Moreover, although the fact that a rust preventive agent can be further added to the film on an alloy plating layer is taught in patent document 1, about the density|concentration distribution of the rust prevention agent in a film, and its control method, sufficient examination is not necessarily made|formed. Therefore, in the galvanized steel sheet described in Patent Document 1, there is still room for improvement with respect to the improvement of corrosion resistance.

Moreover, invention described in patent document 2 relates to the surface-treated metal plate which has a coating film which mainly improved alkali resistance and solvent resistance, without reducing corrosion resistance. And sufficient examination is not necessarily made about the concentration degree of the cationic metal element in a coating film layer, Therefore, also in the surface-treated metal plate of patent document 2, there is still room for improvement with respect to the improvement of corrosion resistance.

In addition, in the composition described in Patent Document 3, although a vanadium compound is used in order to improve corrosion resistance, sufficient examination is not necessarily made about the concentration distribution of the vanadium compound in the base treatment layer obtained using this composition. There is still room for improvement. Similarly, in the invention described in Patent Documents 4 to 6, sufficient examination has not always been made about the concentration distribution of the rust preventive pigment such as a vanadium compound in the film, and there is still room for improvement in the improvement of the corrosion resistance.

Then, in view of the said problem, this invention WHEREIN: An object of this invention is to provide the surface-treated steel plate excellent in corrosion resistance.

In order to obtain a surface-treated steel sheet having excellent corrosion resistance, the present inventors include a rust preventive agent in the coating film formed on the Zn-based alloy plating layer, and furthermore, contain a rust preventive agent in the coating film at a position 10 nm away from the interface between the Zn-based alloy plating layer and the coating film. It was discovered that it is important to make a density|concentration into 1.5 times or more and 5.0 times or less of the average concentration of the rust preventive agent in a coating film. That is, according to the present invention, in the coating film, in the region near the interface between the coating film and the Zn-based alloy plating layer, the rust preventive agent is concentrated and present compared to the other regions. Therefore, it can suppress that corrosion factors, such as oxygen, pass through a coating film and corrode a Zn-type alloy plating layer by the concentration area|region of this rust preventive agent. That is, the concentrated region of this rust preventive agent can serve as a barrier region for the underlying Zn-based alloy plating layer in the coating film. In addition, such a barrier region can fully fulfill its role even after processing the surface-treated steel sheet according to the present invention. Accordingly, the surface-treated steel sheet according to the present invention having such a coating film can provide extremely excellent corrosion resistance.

This invention is made|formed based on the said knowledge, The main point is as follows.

(One)

A steel sheet, a Zn-based alloy plating layer formed on at least one side of the steel sheet, and a coating film comprising a rust preventive agent and a binder resin formed on the Zn-based alloy plating layer,

The chemical composition of the Zn-based alloy plating layer is in mass%,

Al: 0.01 to 60%,

Mg: 0.001 to 10%, and

Si: 0 to 2%,

A surface-treated steel sheet, characterized in that the concentration of the rust preventive agent 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 to 5.0 times the average concentration of the rust inhibitor in the coating film.

(2)

The said rust preventive agent contains at least 1 sort(s) of P, V, and Mg, The surface-treated steel sheet as described in said (1) characterized by the above-mentioned.

(3)

The surface-treated steel sheet according to (1) or (2), wherein the average concentration of the rust preventive agent in the coating film is 3 to 15% by mass.

(4)

The surface-treated steel sheet 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.

(5)

The surface-treated steel sheet according to (4) above, 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.

According to the present invention, the rust preventive agent is included in the coating film formed on the Zn-based alloy plating layer, and the concentration of the rust inhibitor at a position 10 nm away from the interface between the Zn-based alloy plating layer and the coating film is 1.5 times the average concentration of the rust inhibitor in the coating film or more and 5.0 times or less. That is, it is in a coating film, and in the area|region near the interface of a coating film and a Zn-type alloy plating layer, a rust preventive agent is concentrated compared with other parts, and exists. Therefore, the concentrated region of the rust preventive agent fulfills the role of 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 excellent in corrosion resistance can be provided. Further, according to the present invention, even when the surface-treated steel sheet according to the present invention is processed, it becomes possible to maintain excellent corrosion resistance.

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 luminance of the surface-treated steel sheet according to the present invention is improved by the metallic appearance of the bright pigment, and a surface-treated steel sheet excellent in design can be provided. In addition, when a bright pigment is contained in the coating film, for example, even if the Zn-based alloy plating layer is discolored black (hereinafter referred to as 'blackening') due to the oxidation of zinc of the Zn-based alloy plating layer, the bright pigment contained in the coating film The blackening can be made invisible, that is, the change in the appearance of a coating film can be suppressed, and the surface-treated steel plate excellent in designability can be provided.

In addition, according to the present invention, since an acidic paint having a pH of 3.0 to 5.0 is used to form 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 layer and the coating film are chemically bonded. , it becomes possible to have excellent adhesion during processing. Further, according to the present invention, by adjusting the paint to the above pH, a paint in a state in which the rust preventive agent is stably dissolved can be produced, and it becomes possible to have excellent storage stability compared to an alkaline paint.

[Surface treated steel plate]

The surface-treated steel sheet of the present invention has a steel sheet, a Zn-based alloy plating layer formed on at least one side of the steel sheet, and a coating film containing a rust preventive agent and a binder resin formed on the Zn-based alloy plating layer, wherein the chemical composition of the Zn-based alloy plating layer is the mass %, Al: 0.01 to 60%, Mg: 0.001 to 10%, and Si: 0 to 2%, the concentration of the rust preventive agent 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 It is characterized in that it is 1.5 to 5.0 times the average concentration of the rust inhibitor. Hereinafter, the structural requirements of the surface-treated steel sheet according to the present invention will be described.

<Steel plate>

It does not specifically limit as a steel plate (plating original plate) in this invention, Common steel plates, such as a hot-rolled steel plate and a cold-rolled steel plate, can be used. The grade of steel is not particularly limited, and for example, it is possible to use Al killed steel, ultra-low carbon steel containing Ti, Nb, and the like, and high-tensile steel containing elements such as P, Si, and Mn. Although the plate|board thickness of the steel plate in this invention is not specifically limited, For example, what is necessary is just 0.25-3.5 mm.

<Zn-based alloy plating layer>

The Zn-based alloy plating layer in the present invention is formed on the steel sheet. This Zn-based alloy plating layer may be formed on one side of the steel sheet, or it may be formed 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 a Zn-Al-Mg-Si alloy plating layer containing Si. Each of these contents (concentration) is, in mass%, Al: 0.01 to 60%, Mg: 0.001 to 10%, and Si: 0 to 2%, with the balance being Zn and impurities. Hereinafter, when simply describing the chemical composition of the Zn-based alloy plating layer as "%", "mass %" is meant.

When 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 by containing Al is not sufficiently exhibited, and when 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 may be sufficient. A preferable Al content is 1 to 60 %, More preferably, it is 5 to 60 %.

When 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 by containing 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'). , or, there is a possibility that a portion that is not plated (generally called 'no plating') may 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 8% or less, 6% or more. Below, 5 % or less, or 4 % or less may be sufficient. Mg content becomes like this. Preferably it is 1 to 5 %, More preferably, it is 1-4 %.

The lower limit of the Si content of the Zn-based alloy plating layer may be 0%, but in order to further improve the corrosion resistance of the Zn-based alloy plating layer, it is good also as 0.001% to 2%. 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 may be 1.8% or less, 1.5% or less, or 1.2% or less. Si content becomes like this. Preferably it is 0.1 to 2 %, More preferably, it is 0.5 to 1.5 %.

The Zn-based alloy plating layer in the present invention can be formed by a known plating method such as hot-dip plating or vapor deposition plating. For example, the thickness of the Zn-based alloy plating layer should just be 1-30 micrometers.

<Paint>

The coating film in this invention is formed on the Zn-type alloy plating layer. A rust preventive agent and binder resin are contained in a coating film. In order to improve the brightness|luminance of a surface-treated steel plate, Preferably, what is necessary is just to further contain a bright pigment in a coating film. In the coating film in the surface-treated steel sheet which concerns on this invention, a rust preventive agent exists as a fine compound (for example, P compound or V compound). In this way, the rust inhibitor is present as a fine compound in the coating film, and as described above, in order to form a concentration region of the rust inhibitor in the interface region between the coating film and the Zn-based alloy plating layer, in the coating material for forming the coating film in the present invention, For example, it is effective to use an acid paint having a pH of 3.0 to 5.0. In addition, since the rust preventive agent is extremely dispersed in the coating film, in a normal analysis method, it is difficult to clearly distinguish and specify a fine rust preventive agent and a binder resin forming the coating film in the coating film, and in the coating film, the rust preventive agent and It is observed that the binder resin is distributed in the same area. Therefore, in the present invention, "including a rust preventive agent" in the coating film means that an element exhibiting a rust prevention function constituting the fine compound, for example, an element of P, V, Mg, is included in the coating film. . Therefore, the "concentration" of the rust preventive agent mentioned later means the sum total of the density|concentration (content) of elements P, V, and Mg, for example, Let the unit be mass %.

Thus, by making the coating material for forming the coating film in this invention acidic of pH3.0-5.0, for example, it becomes possible for the component of a rust preventive agent to exist in the melt|dissolved state in a coating material. That is, the component of the rust inhibitor according to the present invention is not contained in the paint as a compound state (that is, a solid component), but is contained in the paint as an ion state (i.e., a dissolved component). Therefore, when such a coating material is applied to the surface of the Zn-based alloy plating layer and cured, it becomes possible to make the rust inhibitor substantially uniformly present as a fine compound in the formed coating film.

In addition, 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 near the surface of the Zn-based alloy plating layer, The component of the rust preventive agent in an ionic state reacts with the component in the Zn-based alloy plating layer. As a result, after curing the coating material, 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 in which such a reaction product exists in the coating film, as a rust preventive agent, not only the fine compound which exists substantially uniformly in the coating film but also the reaction product formed as described above exist, so that the rust preventive agent (for example, P, V , Mg) is concentrated compared to other regions, and as a result, this thickened region acts as a barrier region for preventing the intrusion of corrosion factors in the coating film. Therefore, the surface-treated steel sheet according to the present invention produced using an acid paint having a pH of 3.0 to 5.0 has a concentration region of the rust inhibitor near the interface between the Zn-based alloy plating layer and the coating film, and can provide very high corrosion resistance.

The average thickness of the coating film is not particularly limited, and may be, for example, 3 to 15 µm. By having the average thickness of the coating film in such a range, the coating film serves as a barrier for sufficiently suppressing corrosion of the underlying Zn-based alloy plating layer, thereby providing sufficient corrosion resistance to the surface-treated steel sheet according to the present invention. In addition, if the average thickness of the coating film is in the above-mentioned range, even if processing is applied to the surface-treated steel sheet according to the present invention having such a coating film, cracks or the like do not occur in the coating film, and it is possible to provide a coating film excellent in workability.

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 thus the corrosion resistance of the surface-treated steel sheet according to the present invention may become insufficient. On the other hand, when 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 small, and it takes time to cure, and there is a possibility that it is disadvantageous in terms of cost. In addition, when the coating film is too thick, there is a fear that cracks may occur in the coating film when bending or the like is applied to the steel sheet having the coating film, and the workability of the surface-treated steel sheet according to the present invention may be reduced. 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 a coating film becomes like this. Preferably they are 3 micrometers or more and 12 micrometers or less, More preferably, they are 5 micrometers or more and 10 micrometers or less.

The "average thickness" of the coating film which concerns on this invention can be determined by arbitrary methods well-known to those skilled in the art. For example, by observing the cross section of a steel sheet having a coating film, the shortest distance from five arbitrary positions 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, in the direction perpendicular to the interface). distance) and averaging their measurements.

(binder resin)

Although it will not specifically limit if binder resin used as a coating-film component of this invention is resin usable in an acidic solvent, For example, a polyester resin, a urethane resin, or an acrylic resin may be sufficient. The curing agent for the binder resin is not particularly limited as long as it can be used in an acidic solvent and can cure the binder resin. For example, a melamine resin, an isocyanate resin, or an epoxy resin can be used. Preferably, the binder resin in this invention is a polyester resin, and a hardening|curing agent is a melamine resin. Moreover, it is preferable that polyester resin has glass transition temperature Tg of -20-70 degreeC, and average molecular weight of 3000-30000. When binder resin is a urethane resin, the thing of 0-50 degreeC and number average molecular weights of Tg of 5000-25000 is preferable. When binder resin is an acrylic resin, as for Tg, 0-50 degreeC, as for the number average molecular weight, the thing of 3000-25000 is preferable.

(rust inhibitor)

In order to improve the corrosion resistance of the surface-treated steel sheet according to the present invention, a rust inhibitor (typically P and/or V) is included in the coating film. As described above, the rust preventive agent in the present invention exists as a fine compound substantially uniformly in the coating film. , V element, and Mg element. As such, the rust inhibitor present as a fine compound in the coating film is soluble in water, so when the coating film is exposed to, for example, a wet environment, the rust inhibitor in the coating film is dissolved in water and the components of the rust inhibitor are eluted, and corrosion of the Zn-based alloy plating layer is prevented. It can exhibit a rust-preventing function. In addition, as described above, in the concentrated region near the interface between the Zn-based alloy plating layer and the coating film, a reaction product of the components of the rust inhibitor (eg, P, V, etc.) and the components in the Zn-based alloy plating layer is formed, and this reaction The region where the product is present acts as a barrier region for corrosion factors. Therefore, the surface-treated steel sheet according to the present invention has excellent corrosion resistance because the rust preventive agent is present as a fine compound in the coating film, and has a concentration region of the rust preventive agent in the interface region between the Zn-based alloy plating layer and the coating film.

As a compound that can be added to a paint for forming a coating film containing the rust preventive agent according to the present invention (hereinafter referred to as 'corrosive agent source'), any compound that can be dissolved in an acidic paint can be used. The rust preventive agent dissolved in such an acidic paint is sometimes called a cation inhibitor.

As a rust preventive agent in this invention, a P (phosphorus) compound, a V (vanadium) compound, and an Mg (magnesium) compound are mentioned, for example. Preferably, P and V are contained in the coating film in this invention individually or in combination. More preferably, P alone or a combination of P and V is contained in the coating film.

When P is contained as a rust preventive agent in a coating film, corrosion resistance of a process part can be improved especially. Processed part corrosion resistance means corrosion resistance in the processed part at the time of giving a process (for example, bending process) to the steel plate which has a coating film. The reason why the corrosion resistance of the processed part is improved by the inclusion of P in the coating film is the effect of P reacting with the surface of the Zn-based alloy plating layer to form a phosphate layer to passivate the processed part, and P itself forms a poorly soluble coating film and is a corrosion factor It is thought that it is because it has the effect of exhibiting the barrier property with respect to and P supplements the metal ion eluted from the underlying metal plate, forms a sparingly soluble compound with the metal ion, and has the effect of exhibiting barrier property. Although it does not specifically limit as a rust preventive agent source containing P in this invention, For example, Phosphoric acids, such as orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, triphosphate, phosphoric acid, ammonium salts, such as triammonium phosphate and diammonium hydrogenphosphate; Metal salts with Na, Mg, Al, K, Ca, Mn, Ni, Zn, Fe, etc., aminotri(methylenephosphonic acid), 1-hydroxyethylidene-1,1-diphosphonic acid, ethylenediaminetetra(methylene phosphonic acids and salts thereof, such as phosphonic acid) and diethylenetriaminepenta (methylenephosphonic acid), and organic phosphoric acids such as phytic acid and salts thereof. These rust preventive agents can be added individually or in combination in the coating material for forming the coating film in this invention.

Moreover, when V is contained as a rust preventive agent in a coating film, especially cross-section corrosion resistance can be improved. Cross-section corrosion resistance means the corrosion resistance in the cross-section at the time of giving a process (for example, cutting process) to the steel plate which has a coating film, for example. The reason that the corrosion resistance of the cross-section is improved by the inclusion of V in the coating film is that, in the cross-section, V eluted from the coating film and Zn or Al eluted from the Zn-based alloy plating layer react to form a corrosion product, and a Zn-based alloy It is because progress of corrosion can be suppressed by passivating the surface layer of a plating layer. As a rust preventive agent containing V in the present invention, vanadium pentoxide, metavanadic acid HVO ₃ , ammonium metavanadate, vanadium oxytrichloride VOCl ₃ , vanadium trioxide V2O ₃ , vanadium dioxide, vanadium oxysulfate VOSO ₄ , vanadium oxyacetyl acetonate 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 agents can be added individually or in combination in the coating material for forming the coating film in this invention.

As a rust preventive agent containing Mg in this invention, magnesium nitrate Mg( _NO3 ) ₂ , magnesium sulfate MgSO4, magnesium acetate Mg ₍ CH3COO) _{2 ,} etc. are mentioned. These rust preventive agents can be added individually or in combination in the coating material for forming the coating film in this invention. Mg may improve the corrosion resistance of the cross-section, as in V above. The reason why the cross-section corrosion resistance is improved is also considered to be the same as that of V.

The average concentration of the rust preventive agent in the coating film may be 3 to 15% by mass. In addition, as mentioned above, the "average concentration of a rust preventive agent" is based on the sum total of the concentrations (mass %) of the elements of P, V, and Mg in a coating film, for example. When the average concentration of the rust preventive agent in the coating film in this range is in the coating film, it becomes possible to provide sufficient corrosion resistance to the surface-treated steel sheet according to the present invention, since sufficient rust preventive agent is present in the entire coating film. In addition, even if the rust preventive agent is concentrated in the vicinity of the interface between the coating film and the Zn-based alloy plating layer as described above, the concentration of the rust preventive agent in other regions is not insufficient, so that the entire coating film, that is, the surface-treated steel sheet according to the present invention, has sufficient corrosion resistance. can provide

If the average concentration of the rust preventive agent in the coating film is less than 3% by mass, the concentration of the rust preventive agent in the entire coating film is insufficient, the improvement of corrosion resistance by the effect of the rust inhibitor is limited, and there is a possibility that sufficient corrosion resistance cannot be obtained. . On the other hand, when the average concentration of the rust preventive agent in the coating film is more than 15%, the effect of improving the corrosion resistance by the addition of the rust preventive agent is saturated, which is not preferable in terms of cost. The average concentration of the rust preventive agent 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% or more and 15% or less, More preferably, they are 10 % or more and 15 % or less.

When used in this specification, "the average concentration of the rust preventive agent in a coating film" is determined by the following method. First, a cross section of a steel sheet having a coating film is observed with a TEM, and a straight line is drawn from a randomly selected position on the surface of the coating film toward the Zn-based alloy plating layer in a direction perpendicular to the surface of the coating film (thickness direction). 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 in 10 regions of the coating film except for the region closest to the Zn-based alloy plating layer among those regions, that is, the sum of the concentrations of elements of P, V, and Mg, for example, is measured, and the measured values are determined by averaging. 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.

In the present invention, the concentration of the rust preventive agent 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 and 5.0 times or less of the average concentration of the rust inhibitor in the coating film. That is, in the coating film, the rust preventive agent is concentrated in the area|region near the interface of a coating film and a Zn-type alloy plating layer. In this way, if the rust inhibitor is concentrated in the region near the interface between the coating film and the Zn-based alloy plating layer compared to other parts, the concentrated region of the rust inhibitor can act as a barrier region for the Zn-based alloy plating layer against corrosion factors such as oxygen. becomes Therefore, it is possible to minimize corrosion of the corrosion factor into the Zn-based alloy plating layer, and the surface-treated steel sheet can have very excellent corrosion resistance. Moreover, it becomes possible to fully maintain corrosion resistance even after giving a process to a surface-treated steel plate by the concentration area|region of the rust preventive agent as mentioned above.

If this value is less than 1.5 times, the effect as a barrier region for suppressing corrosion of the Zn-based alloy plating layer through passing of a corrosion factor in the vicinity of the interface between the coating film and the Zn-based alloy plating layer is weakened, and the corrosion factor is Zn It may reach a system alloy plating layer, and a coating film may not be able to provide sufficient corrosion resistance. On the other hand, when this value is more than 5.0 times, since the degree of thickening in the thickening region of the rust preventive agent is too high, the coating film may cohesively fail in the thickened region of the rust preventive agent when the surface-treated steel sheet is processed. When it does so, processing adhesiveness falls, as a result, it becomes impossible to maintain corrosion resistance in a processed part, and there exists a possibility that corrosion resistance may become inadequate. 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 may be 1.7 times or more, 2.0 times or more, or 2.2 times or more, and 4.8 times or less, 4.5 times the average concentration of the rust inhibitor in the coating film. Times or less, 4.2 times or less, 4.0 times or less, or 3.5 times or less may be sufficient, Preferably they are 2.0 times or more and 4.5 times or less, More preferably, they are 2.0 times or more and 4.0 times or less, More preferably, they are 2.5 times or more and 4.0 times or less.

"The concentration of the rust preventive agent 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, the concentration ( That is, for example, it is determined by measuring the total concentration of the elements of P, V, and Mg) and averaging those measured values.

As described above, in order for the acid paint of pH 3.0 to 5.0 to remove the oxide film on the surface of the Zn-based alloy plating layer, the component (eg P) of the rust preventive agent contained in the coating film of the present invention, and the Zn-based A component (eg, Zn) contained in the alloy plating layer reacts in the vicinity of the interface between the coating film and the Zn-based alloy plating layer to form a reaction product (eg, a reaction product containing Zn and P) in the region near the interface. do. In the region where the reaction product exists, both the component of the rust preventive agent uniformly dispersed in the coating film and the component of the rust preventive agent constituting the reaction product exist in the same manner as in other regions. Therefore, in the surface-treated steel sheet according to the present invention, the rust inhibitor (for example, P) is concentrated in the region near the interface between the coating film and the Zn-based alloy plating layer during the coating film, compared to other regions.

The region in which such a reaction product exists can be measured using an elemental analysis method known to those skilled in the art. Specifically, for example, when P is contained as a rust preventive agent, elemental analysis is performed from the surface of the coating film toward the Zn-based alloy plating layer in a direction perpendicular to the surface of the coating film, that is, in the thickness direction. The region in which P as a component of the rust preventive agent is concentrated in the vicinity of the interface can be measured. In addition, by analyzing the concentration region of P measured in this way by a method of measuring the bonding energy between atoms known to those skilled in the art, the reaction product of P of the rust inhibitor and Zn or Al of the Zn-based alloy plating layer can be measured. have.

(bright pigment)

In the surface-treated steel sheet according to the present invention, in addition to the above-mentioned rust preventive agent, in order to improve designability, it is preferable that a bright pigment is contained in the coating film. As used herein, "bright pigment" means a pigment reflected by light on the surface. In addition, as a bright pigment, it is not melt|dissolved in the acidic paint for producing a coating film, but what is contained in a coating film as it is added to a coating material is used. Therefore, in the present invention, in the coating film, "including a bright pigment" means to include a metal element, oxide or alloy, etc. described below in the coating film, and in the coating film, the bright pigment and the coating film It is possible to clearly distinguish and specify the binder resin to be formed. Therefore, the "concentration" of the bright pigment mentioned later means the total concentration as a metal single-piece|unit, an oxide, an alloy, etc. which are demonstrated below.

As a reason for improving design, products using Zn-based alloy-coated steel sheets for building materials or outdoor home appliances are generally used in places where users can see them, so such Zn-based alloy-coated steel sheets are good Because it is desirable to have a visual quality (appearance). In particular, in the case of a design in which the bright pigment is close to the Zn-based alloy plating layer, the unevenness of the coating film thickness is hardly conspicuous, or the flaw is difficult to be conspicuous. Therefore, the coating film thickness can be made thin, and it is economically preferable.

Therefore, by using the bright pigment as described above in the coating film, the luminance of the surface-treated steel sheet can be improved by its metallic appearance (for example, silver color), and a surface-treated steel sheet having excellent appearance and high designability It becomes possible to provide In addition, when the bright pigment has the same or similar color tone to the Zn-based alloy plating layer, when the coating film is damaged, it may be difficult to notice the change in appearance due to scratches, and thus scratch resistance can be improved, so that in the long term The excellent appearance of the surface-treated steel sheet according to the present invention can be maintained.

And, when the bright pigment is contained in the coating film, when the surface-treated steel sheet in the present invention is observed in a direction perpendicular to the surface of the coating film, the underlying Zn-based alloy plating layer can be made invisible by the bright pigment. In this way, for example, Zn contained in the Zn-based alloy plating layer is oxidized under the influence of oxygen in the air to form Zn oxide lacking oxygen, and even when the Zn-based alloy plating layer is blackened, the blackening is brightened. It becomes possible to make it invisible by a pigment, and it becomes possible to maintain the designability of the surface-treated steel plate which concerns on this invention.

The bright pigment in the present invention is not particularly limited as long as it can be used in the acid paint of pH 3.0 to 5.0 used in the present invention, that is, it does not dissolve in this pH range. For example, aluminum or oxide can be used. have. Although it does not limit as an example of an oxide, For example, alumina, silica, mica, zirconia, titania, glass, zinc oxide, etc. are mentioned. 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 individually or in combination in a coating film.

As the bright pigment in the present invention, a metal capable of providing a high luminance in addition to the above-mentioned aluminum or oxide can be further added to the coating film. Examples of such metals are not particularly limited as long as they are metals with high luminance and can be used in acidic paints. For example, Rh (rhodium), Cr (chromium), Ti (titanium), Ag (silver), and Cu A single metal, such as (copper), alloys, such as Zn-Cu (brass), etc. are mentioned. These metals can be used individually or in combination in a coating film. By including a metal capable of providing such high luminance in the coating film, it becomes possible to further enhance the metallic appearance of the coating film, and thus the luminance of the surface-treated steel sheet according to the present invention can be further improved. Designability can be further improved.

Although the average particle diameter of the bright pigment in this invention is not specifically limited, For example, it may be the range of 1 micrometer or more and 30 micrometers or less. When the average particle diameter of a bright pigment is the range of 1 micrometer or more and 30 micrometers or less, the nonuniformity of a luminance does not generate|occur|produce and it becomes possible to provide sufficient designability, maintaining corrosion resistance. If the average particle diameter of the bright pigment is less than 1 μm, it becomes difficult to uniformly disperse it in the coating material for forming the coating film in the present invention, and unevenness occurs in the color tone of the formed coating film, and sufficient designability cannot be ensured. have. On the other hand, if the average particle diameter of the bright pigment is more than 30 μm, the bright pigment protrudes from the surface of the coating film, there is a fear that corrosion factors may enter from the protruding portion, and there is a risk of deterioration of corrosion resistance. Moreover, when such a protruding part exists, it becomes difficult to have a uniform external appearance, and there exists a possibility that designability may become inadequate. The average particle diameter 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. It is 20 micrometers or less, More preferably, it is 3 micrometers or more and 15 micrometers or less.

When used herein, the "average particle diameter" for 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 from a direction perpendicular to the surface of the coating film by a Field Emission-Electron Prove Micro Analyzer (FE-EPMA). The area of the measurement range on the mapping shall be 20 mm x 20 mm or more. From the obtained mapping image, the outline of the bright pigment existing within the measurement range is specified, and the area S of the sum enclosed by the outline is calculated|required. In addition, the number N of bright pigments present within the measurement range is obtained. Then, assuming that the obtained area S is composed of N number of bright pigments having a circular cross section having a diameter (particle diameter) D, the average particle diameter of the bright pigment is [D=2×(S/(πN)) ^0.5 ] is obtained from the expression of

Although the thing of any shape can be used for the shape of the bright pigment in this invention, For example, a spherical shape, an ellipse, needle shape, a flat shape, a thin plate shape, a scale shape, etc. may be sufficient. Preferably, the shape of the bright pigment may be scale-like. If the shape of the bright pigment in the present invention is flaky, the bright pigment can effectively make the underlying Zn-based alloy plating layer invisible, that is, effectively suppress the change in appearance of the product due to blackening of the Zn-based alloy plating layer. This makes it possible to provide a surface-treated steel sheet having very excellent designability.

The average concentration of the bright pigment in the coating film may be, for example, 5% to 15% by mass. By the average concentration of the bright pigment in the coating film within this range, it becomes possible to provide a uniform metallic appearance to the surface-treated steel sheet according to the present invention without impairing the workability of the coating film, and the surface-treated steel sheet excellent in designability can provide When the average concentration of the bright pigment in the coating film is less than 5%, the bright pigment in the coating film is insufficient to provide a sufficient metallic appearance, the luminance becomes insufficient, and sufficient designability may not be provided. On the other hand, since the improvement of the brightness|luminance by addition of a bright pigment is saturated that the average density|concentration of the bright pigment in a coating film is more than 15 %, it is unpreferable in terms of cost. In addition, by the presence of a large number of bright pigments in the coating film, the proportion of the binder resin constituting the coating film is relatively reduced, and there is a possibility that the workability may decrease, such as cracks in the coating film when processed. Preferably, the average density|concentration of the bright pigment in a coating film is 5 % or more and 12 % or less, More preferably, they are 6 % or more and 10 % or less.

When used in this specification, "average concentration of the bright pigment in a coating film" can be calculated|required by a well-known method. For example, it can be measured using a glow discharge optical emission spectrometry (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, and the main element constituting the bright pigment is the concentration in the depth direction. Profiles are measured every 1.0 μm. Then, the average value of the measured concentration of the main element is calculated|required, the measured density|concentration is converted based on the compound molecular weight of a known color pigment, and the average density|concentration of the bright pigment in a coating film is calculated|required. Further, the coating film is mechanically or chemically peeled off, and the total mass of the coating film is measured. Thereafter, 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 fluorescence X-ray analysis can be used. When the type of the bright pigment, that is, the specific compound of the bright pigment is unclear, by analyzing the elements constituting the bright pigment by FE-EPMA for the cross section of the coating film (the surface perpendicular to the surface of the coating film), the type of bright pigment After specifying , "the average concentration of the bright pigment in the coating film" can be measured as described above. In the case of brass as a bright pigment alloy, the sum of Cu and Zn content (concentration) is taken as the average concentration of the bright pigment in the coating film.

In the coating film in this invention, pigments, aggregates, etc. other than the rust preventive agent and bright pigment in this invention can be added as needed. In addition, waxes such as polyethylene wax 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 may be added to the coating film. By adding these, the intensity|strength of a coating film can be raised, or since a desired color can also be provided to a coating film, it is more preferable. What is necessary is just to determine these addition amounts suitably so that it may not be disadvantageous in the coating film in this invention.

In particular, in order to impart a desired color to the coating film in the present invention, and hence the surface-treated steel sheet according to the present invention, a dye may be used as a colorant. A dye may be used independently and may be used combining some dye. Moreover, you may use dye together with a coloring pigment. Although it does not specifically limit as a kind of dye which can be used in the coating film in this invention, A well-known dye can be used, For example, phthalocyanine blue, phthalocyanine green, methyl orange, methyl violet, or alizarin can be used. .

[Method for producing surface-treated steel sheet]

A method for manufacturing a surface-treated steel sheet according to the present invention will be described below. The surface-treated steel sheet according to the present invention can be produced by, for example, applying an acidic paint of pH 3.0 to 5.0 containing at least a rust preventive agent and a binder resin on a Zn-based alloy plating layer formed on the steel sheet, and curing the paint by heating. .

<Formation of Zn-Based Alloy Plating Layer>

As a steel plate, what has arbitrary plate|board thickness and chemical composition can be used. For example, a cold-rolled steel sheet having a thickness of 0.25 to 3.5 mm can be used. In addition, the Zn-based alloy plating layer may be formed to a thickness of 5 to 30 μm using, for example, a Zn-Al-Mg hot-dip plating bath or a Zn-Al-Mg-Si hot-dip bath at 400 to 550°C.

<Preparation of paint>

The paint can be obtained, for example, by mixing a binder resin dispersed in a solvent and a curing agent, and then dispersing a predetermined amount of a rust preventive agent and optionally a bright pigment in the mixture. The mixing order may be different. Although it does not specifically limit as binder resin, A polyester resin, a urethane resin, an acrylic resin, etc. can be used, A melamine resin etc. can be used as a hardening|curing agent. In addition, as a solvent, an acidic thing is used, and as a rust preventive agent, what melt|dissolves in the acidic solvent, for example, a P compound, a V compound, an Mg compound, or 2 or more types thereof can be used. In addition, as a bright pigment, it can select suitably from the pigment which does not melt|dissolve in an acidic solvent. The ratio of the binder resin and the curing agent may be appropriately determined, but may be, for example, in the range of 1:1 to 9:1.

It is important that the pH of the coating material used in order to obtain the coating film in this invention is 3.0 or more and 5.0 or less. By setting the pH of the paint within this range, not only can the rust preventive agent be dissolved in the paint, but when such a paint is applied to the Zn-based alloy plating layer, the oxide film on the surface of the Zn-based alloy plating layer is appropriately removed can do. Then, in the vicinity of the surface of the Zn-based alloy plating layer, the component of the ionic rust preventive agent and the component in the Zn-based alloy plating layer react, as a result, after curing the coating material, in the vicinity of the interface between the Zn-based alloy plating layer and the coating film, the reaction It becomes possible to form regions in which the product is concentrated. When the pH of the coating material is less than 3.0, the degree of thickening in the thickening region of the rust preventive agent becomes too high, and when the surface-treated steel sheet is processed, the coating film may cohesively fail in the concentrated region of the rust preventive agent. When it does so, processing adhesiveness falls, as a result, it becomes impossible to maintain corrosion resistance in a processed part, and there exists a possibility that corrosion resistance may become inadequate. In addition, there is a possibility that Zn is eluted in the paint, thereby reducing the storage stability of the paint. On the other hand, if the pH of the coating material is more than 5.0, the oxide film on the surface of the Zn-based alloy plating layer cannot be sufficiently removed, and there is a possibility that the rust inhibitor may not be sufficiently concentrated in the region near the interface between the coating film and the Zn-based alloy plating layer. In addition, when the pH is alkaline, that is, more than 7.0, the paint is solidified (gelled) at the time of preparation of the paint, and storage stability as a paint is insufficient, resulting in a problem in use. 3.2 or more or 3.5 or more may be sufficient as the pH of a coating material, and 4.8 or less or 4.5 or less may be sufficient as it. The pH of the paint is preferably 3.2 to 4.8, more preferably 3.5 to 4.5. In addition, the pH cannot be measured after the coating material is cured to form a coating film.

The pH of a coating material may change with the manufacturing lot, such as a solvent of a raw material. For this reason, it is necessary to adjust the pH using an acid or aqueous alkali solution. More specifically, the pH after the combination of the paint is measured, and depending on the target pH, when lowering the pH value, nitric acid, hydrochloric acid or sulfuric acid can be used, and when raising the pH value, an aqueous sodium hydroxide solution, etc. can be used. have. It is preferable to dilute and use these acid or alkali aqueous solution before using for pH adjustment.

<Formation of coating film>

Next, the obtained coating material is applied so that the coating film has a predetermined thickness on the Zn-based alloy plating layer, and is baked and cured. The coating method of a coating material is not specifically limited, It can perform by arbitrary coating methods well-known to those skilled in the art, for example, what is necessary is just to carry out with a roll coater etc. Baking can be carried out under any heating conditions under which the paint is cured, for example, heated to a steel sheet temperature of 180 to 230°C at a heating rate of 5 to 70°C/sec.

As described above, in the surface-treated steel sheet according to the present invention, the rust inhibitor containing P, V or Mg exists as a fine compound in the coating film. In order to achieve such a structure, in the method for manufacturing a surface-treated steel sheet according to the present invention, a rust preventive agent (for example, P compound, V compound or Mg compound) is added to an acidic solvent in order to make the rust preventive agent exist in the paint in an ionic state. By dissolving it, the coating material for forming the coating film in this invention is prepared. The present inventors discovered the fact that using such a manufacturing method is advantageous in the following points.

For example, unlike the present invention, when the rust preventive pigment is included as a solid component (for example, powder) in the coating film, in order to uniformly distribute the rust preventive pigment in the formed coating film, rust prevention in the coating material for forming the coating film It is considered that it will become necessary to uniformly disperse the pigment. In addition, in such a production method, if a large amount of the rust preventive pigment is added to the paint, it becomes difficult to uniformly disperse the rust preventive pigment in the paint, and furthermore, the ratio of the resin as the main component of the formed paint film is lowered, and there is a risk that the paint film may become brittle. , it is considered that there is an upper limit to the amount of the rust preventive pigment added to the coating film. In addition, such a paint has a problem that, after preparing the paint by dispersing the rust preventive pigment, the dispersion state deteriorates while the paint is stored until use, and as a result, a coating film in which the rust preventive pigment is uniformly distributed cannot be obtained. .

Also, unlike the present invention, for example, when an alkaline paint for a coating film is prepared using a compound soluble in an alkaline solvent as a rust preventive agent, if the amount of the compound is increased, the rust preventive agent is sufficiently It does not dissolve, and solid matter may be generated in the paint. Moreover, the paint may harden (gelatinize) during storage of the paint, and there is a problem of storage stability of the paint in storage of the paint. Moreover, even if an alkaline coating material is apply|coated on a Zn-type alloy plating layer, it is thought that the oxide film on a Zn-type alloy plating layer cannot fully be removed.

On the other hand, in the present invention, an acidic paint and a compound soluble in the paint are used as a rust preventive agent, and the compound is dissolved in the acidic paint. Therefore, with respect to uniformly dispersing the component of the rust preventive agent in the coating material, there is no restriction as in the case of using a powder rust preventive pigment. Therefore, in such a manufacturing method, compared with the coating material containing rust preventive pigments, such as powder, in a state in which the rust preventive agent is uniformly disperse|distributed, many rust preventive agents can be added in a coating material. In addition, the acidic paint having a pH of 3.0 to 5.0 for forming the coating film according to the present invention is less difficult to harden than the alkaline paint, even when a large amount of a rust preventive agent is added to the paint, and the storage stability of the paint is excellent. . As described above, the coating material for forming a coating film in the present invention can add many rust preventive agents while having storage stability of the coating material, and as a result, it is possible to form a coating film containing a high concentration of rust preventive agent in the coating film becomes Therefore, by forming a coating film using such a coating material, it becomes possible to form the surface-treated steel plate which has very excellent corrosion resistance.

In addition, as described above, the present inventors have found that when such an acidic paint having a pH of 3.0 to 5.0 is applied on the Zn-based alloy plating layer, the oxide film formed on the surface of the Zn-based alloy plating layer is removed by the paint, and the rust preventive agent The component of Zn and the component in the Zn-based alloy plating layer react, and as a result, in the region near the interface between the coating film and the Zn-based alloy plating layer, the reaction product of the rust inhibitor and the metal in the Zn-based alloy plating layer (for example, the reaction of P and Zn) product) was found to be formed. The removal of this oxide film originates in that the paint used by this invention apply|coated on the Zn-type alloy plating layer is acidic. Then, the active metal under the oxide film of the Zn-based alloy plating layer is exposed by the removal of the oxide film, and the active metal reacts with a component of the rust preventive agent in the coating film to form the reaction product. In the region where the reaction product thus generated exists, the rust inhibitor is more concentrated than in the other regions. Therefore, this thickened region acts as a barrier region for preventing corrosion factors from penetrating into the Zn-based alloy plating layer, thereby making it possible for the surface-treated steel sheet according to the present invention to have very high corrosion resistance.

The surface-treated steel sheet according to the present invention, that is, the surface-treated steel sheet in which the concentration of the rust preventive agent 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 and 5.0 times or less of the average concentration of the rust inhibitor in the coating film, An acidic paint having a pH of 3.0 to 5.0 is used, and further, various parameters during manufacture, such as the type of rust preventive agent in the paint, the amount of the rust preventive agent added, the temperature of the paint, the heating temperature and heating time when curing the paint, the binder resin It can be manufactured by appropriately adjusting the ratio of the curing agent to the pretreatment for the alloy plating layer. In other words, it is possible to adjust the degree of thickening of the rust preventive agent in the coating film by using an acidic paint having a pH of 3.0 to 5.0 containing a predetermined amount of a component of the rust inhibitor and optionally a bright pigment, and by appropriately adjusting such parameters. Thus, it becomes possible to manufacture the surface-treated steel sheet according to the present invention.

In addition, 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 coating material, thereby generating a strong chemical bond between the Zn-based alloy plating layer and the coating film. It becomes possible to obtain the surface-treated steel sheet which has the adhesiveness excellent in it. More specifically, without being bound by a particular theory, the components of the rust preventive agent in the paint react to form a hydroxide, and the functional group of the hydroxide reacts with the resin to cause an irreversible and chemical bond, resulting in a Zn-based alloy plating layer Adhesiveness is improved between a film and a coating film. Such adhesion cannot be achieved, for example, when a neutral or alkaline paint is used to form a coating film. Adhesiveness is improved compared with the case where a paint is used.

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 sheet, a Zn-based alloy plating layer formed on at least one side of the steel sheet, and a coating film containing a rust preventive agent and a binder resin formed on the Zn-based alloy plating layer, and is 10 nm away from the interface between the Zn-based alloy plating layer and the coating film. A surface-treated steel sheet in which the concentration of the rust preventive agent is 1.5 times or more and 5.0 times or less of the average concentration of the rust preventive agent in the coating film can be produced.

Example

In this example, the average concentration and concentration distribution of the rust preventive agent in the coating film, the average concentration of the bright pigment, the type of the rust inhibitor and the bright pigment, the type of the binder resin, and the chemical composition of the Zn-based alloy plating layer are variously changed. In contrast, their corrosion resistance, brightness, processing adhesion, and storage stability were evaluated. In addition, with respect to the surface-treated steel sheet according to the present invention, some examples will be described below in more detail. However, it is not intended that the scope of the invention as set forth in the claims be limited by the specific examples set forth below.

<Preparation of sample of surface-treated steel sheet>

(Formation of Zn-based alloy plating layer)

A cold-rolled steel sheet having a thickness of 1 mm is immersed in a hot-dip plating bath at about 450° C. having a chemical composition of Al: about 11%, Mg: about 3%, and Zn: about 86% for 3 to 5 seconds, and about 10 on the cold-rolled steel sheet. A Zn-11% Al-3% Mg alloy plating layer having a thickness of μm was formed. Further, the composition of the molten plating bath was changed, and a Zn-1% Al-1% Mg alloy plating layer and a Zn-40% Al-8% Mg alloy plating layer having a thickness of about 10 μm were formed on the cold-rolled steel sheet in the same procedure. Alternatively, a cold-rolled steel sheet having a thickness of 1 mm is placed in a hot-dip plating bath at about 450° C. of chemical composition Al: about 11%, Mg: about 3%, Si: about 1%, and Zn: about 85% for 3 to 5 seconds. After immersion, 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 molten plating bath is changed, and the Zn-11% Al-3% Mg-0.4% Si alloy plating layer and Zn-11% Al-3% Mg-1.5 having a thickness of about 10 µm on the cold-rolled steel sheet in the same procedure. % Si alloy plating layer was formed.

(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) as binder resins were dispersed as emulsions in an acidic solvent, and sample No. For the paints used in 3-21 and 25-36, pH was adjusted so that it might become 3.0-5.0 using nitric acid or sodium hydroxide. Among them, imino group type melamine resin was mixed. The ratio of the concentration of the polyester resin and the melamine resin was 100:20. Then, the paint was prepared by adding a rust preventive agent and a bright pigment to the mixture. In addition, sample No. For the paints used in 1, 2, and 24, the pH was adjusted to be more than 5.0, and sample No. For the paints used in 22 and 23, pH was adjusted so that it might become less than 3.0. Table 1 shows the pH of the paint used in each sample. And, No. For 25, no bright pigment was added. Orthophosphoric acid, vanadium pentoxide, and magnesium sulfate were used as rust inhibitors for samples containing P, V and Mg as rust inhibitors, respectively. As a bright pigment, the thing of Table 1 was used.

The amount of the rust preventive agent added into the coating material is the average concentration of the rust inhibitor in the desired coating film (3%, 5%, 10%, 13% or 15%) when measured using TEM-EDS based on the obtained cross section of the coating film. was appropriately adjusted to obtain . In addition, the density|concentration of a bright pigment was adjusted suitably so that it might become 10 % or 5 % of average density|concentration when measured by GD-OES.

(Formation of coating film)

The coating material prepared as mentioned above was apply|coated on the Zn-type alloy plating layer so that the average thickness of the coating film to be formed might be set to 5 micrometers, and it was hardened by baking. Baking was performed at a heating rate of about 20°C/sec and a steel plate temperature of about 200°C until the paint was completely cured.

The ratio of the concentration of the rust preventive agent in the coating film at a position 10 nm away from the interface between the Zn-based alloy plating layer and the coating film to the average concentration of the rust inhibitor in the coating film was adjusted by appropriately changing the pH of the coating material.

Average concentration (mass %) of the rust preventive agent in a coating film by elemental analysis using TEM-EDS from the obtained coating film; And the ratio of the concentration of the rust preventive agent in the coating film at a position 10 nm away from the interface between the Zn-based alloy plating layer and the coating film to the average concentration thereof was determined. The values determined in this way are shown in Table 1. In addition, Table 1 shows the types of rust inhibitors and bright pigments contained in the coating film. In addition, when two types of rust preventive agents are contained in a coating film, the sum total of the average concentrations of two rust preventive agents respond|corresponds to the average density|concentration described in a table|surface, and each rust preventive agent exists in an equal amount in a coating film. The same is true for bright pigments.

<Evaluation of sample of surface-treated steel sheet>

As described above, samples of the surface-treated steel sheet were prepared, and as shown in Table 1, evaluation tests of corrosion resistance, brightness, work adhesion and storage stability were performed on each sample as follows.

(Evaluation test of corrosion resistance)

For each sample, a test material of 0.6 mm for testing is 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 is subjected to an evaluation test of corrosion resistance A salt spray test (based on the JASO M609-91 method) was performed as This salt spray test was conducted for (1) salt spray 2 hours (5% NaCl, 35°C); (2) drying 4 hours (60° C.); and (3) a total of 120 cycles (960 hours in total) were carried out by making one cycle of 2 hours wet (50°C, humidity 95% or more). In order to prevent corrosion from the end face, the end face of each sample was tested by sealing it with a tape.

Evaluation of corrosion resistance was performed by observing the surface (planar part) of the sample 960 hours after the salt spray test with an optical microscope, and determining the rust generation|occurrence|production area rate Z. Specifically, first, the surface of the sample was read with a scanner. Thereafter, an area in which rust was generated was selected using image editing software, and the rate of area in which rust was generated was obtained. This procedure was performed with respect to five samples, and "rust generation|occurrence|production area rate Z" was determined as an average of rust generation|occurrence|production area rate. Thus, based on the "rust occurrence area rate Z" determined for each sample, the rating of each sample was determined in eight steps as follows. A rating of 4 or more was made into the passing point of corrosion resistance.

Rating 8: Z=0%

Rating 7: 0%<Z≤5%

Rating 6: 5%<Z≤10%

Rating 5: 10%<Z≤20%

Rating 4: 20%<Z≤30%

Rating 3: 30%<Z≤40%

Rating 2: 40%<Z≤50%

Rating 1: 50%<Z

(Evaluation test of luminance)

For each sample, 10 randomly selected testers visually observed the surface of the sample, and evaluated the "luminance level" on a scale of 1 to 5 as follows.

1 point|piece: A metallic appearance was not confirmed at all or a metallic appearance was confirmed slightly.

2 points|pieces: Although a metal external appearance is confirmed, it observes from the front, and an external appearance nonuniformity is confirmed easily.

3 points|pieces: Although a metal external appearance is confirmed, it observes from the front, and some external appearance unevenness is confirmed.

4 points|pieces: Although the metal external appearance is confirmed in the whole, it observes obliquely, and some external appearance nonuniformity is observed.

5 points|pieces: A metallic appearance is confirmed in the whole

Regarding the luminance, the rating of each sample was determined in eight steps as follows according to the total points of the "luminance levels" of the 10 testers. A rating of 4 or more was made into the passing point of luminance.

Rating 8: 40<total score

Rating 7: 35<total score ≤40

Rating 6: 30<total score ≤35

Rating 5: 25<total score ≤30

Rating 4: 20<total score ≤25

Rating 3: 15<total score ≤20

Rating 2: 10<total score≤15

Rating 1: Total score=10

(Evaluation test of processing adhesion)

As described above, 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 for actual use. About the test material, after making a 24 mm width cellophane adhesive tape (Nichi Reflective Cellophane tape: registered trademark) close to the coating film, it was sharply torn off at an angle of 45 degrees. From the peeled coating film area, peeling area ratio Z' was calculated|required, and the following reference|standard evaluated.

Rating 5: 0% (no peeling) <Z'≤5%

Rating 4: 5%<Z'≤10%

Rating 3: 10%<Z'≤30%

Rating 2: 30%<Z'≤50%

Rating 1: 50%<Z'

(Evaluation test of storage stability)

100 g of the paint prepared at the pH shown in Table 1 was maintained at 25°C, and a Zn-11% Al-3% Mg alloy plated steel sheet was immersed. The paint was visually observed after immersion for 60 minutes, and the storage stability score of each sample was determined as follows according to the state of the paint before immersion (when preparing the paint) and after immersion. A rating of 3 or more was made into the passing point of storage stability.

Rating 5: No change is seen in the paint before and after steel plate immersion

Rating 4: Any of discoloration or viscosity increase is seen in the paint before and after immersion of the steel sheet

Rating 3: Both discoloration and viscosity increase are seen in the paint before and after steel plate immersion

Rating 2: After immersion of the steel plate, the paint is solidified (gelation)

Rating 1: Solidification (gelation) before immersion (when preparing paint)

For the sample of the surface-treated steel sheet, the evaluation test of corrosion resistance, brightness|luminance, work adhesiveness, and storage stability was done as mentioned above, and each rating was determined. The obtained results are shown in Table 1.

Sample No. In 1 and 2, the pH of the coating material was high and the ratio of the concentration of the rust preventive agent at a position 10 nm away from the interface between the Zn-based alloy plating layer and the coating film to the average concentration of the rust inhibitor in the coating film was less than 1.5, so the concentration of the rust inhibitor was insufficient. As a result, the thickened region did not sufficiently function as a barrier layer for protecting the Zn-based alloy plating layer, resulting in insufficient corrosion resistance. In addition, sample No. In 22 and 23, the pH of the coating material was low, and the ratio of the concentration of the rust preventive agent at a position 10 nm away from the interface between the Zn-based alloy plating layer and the coating film to the average concentration of the rust preventive agent in the coating film was more than 5.0, so the corrosion resistance was insufficient. When this was processed in order to obtain a test material, a coating film cohesively fractured in the concentration area|region of a rust preventive agent, processing adhesiveness fell, as a result, it is thought that it is because the corrosion resistance in a processed part deteriorated. Sample No. At 24, the pH of the coating material was alkaline, and the coating material was solidified at the time of coating material production, and a coating film could not be formed, so it was not possible to evaluate corrosion resistance, luminance, and processing adhesion.

On the other hand, sample No. 3 to 21, No. In 25-36, since the ratio of the concentration of the rust preventive agent at a position 10 nm away from the interface between the Zn-based alloy plating layer and the coating film to the average concentration of the rust inhibitor in the coating film was 1.5 or more and 5.0 or less, it had excellent corrosion resistance. In particular, the sample containing either or both of P and V as a rust preventive agent had more excellent corrosion resistance.

And, sample No. In any sample except 25, since the bright pigment was contained in the coating film, it had sufficient brightness|luminance. Moreover, in the sample in which _a bright pigment contains either or both of aluminum (Al) and an oxide (SiO2, alumina, mica), it was more excellent in luminance. In particular, in addition to Al or SiO ₂ , the sample further containing metal Rh, Ti, or Ag having high luminance in the coating film had very high luminance.

Sample No. 14 to 17 and No. 35 is the sample which changed the average concentration of the rust preventive agent in a coating film. All samples had sufficient corrosion resistance.

Advantageous Effects of Invention According to the present invention, a surface-treated steel sheet having high corrosion resistance can be provided because it has an antirust concentration region near the interface between the Zn-based alloy plating layer and the coating film. Thereby, it becomes possible to provide sufficient corrosion resistance and designability as a steel plate used for building materials and household electrical appliances, Therefore, this invention can be said to be invention with very high industrial value.

Claims (7)

A steel sheet, a Zn-based alloy plating layer formed on at least one side of the steel sheet, and a coating film comprising a rust preventive agent and a binder resin formed on the Zn-based alloy plating layer,
The chemical composition of the Zn-based alloy plating layer is in mass%,
Al: 0.01 to 60%,
Mg: 0.001 to 10%, and
Si: 0 to 2%,
The rust inhibitor is composed of at least one of P, V and Mg,
The average concentration of the total of P, V and Mg in the coating film is 3 to 15% by mass,
The concentration of the rust preventive agent 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 to 5.0 times the average concentration of the rust inhibitor in the coating film,
The surface-treated steel sheet, characterized in that the average thickness of the coating film is 3 to 15 μm. The method of claim 1,
A surface-treated steel sheet, wherein an average concentration of the total of P, V and Mg in the coating film is 5 to 15% in mass%. 3. The method of claim 1 or 2,
The coating film further includes a bright pigment, and the bright pigment includes at least one of aluminum and an oxide, a surface-treated steel sheet. 4. The method of claim 3,
The surface-treated steel sheet, wherein the oxide is alumina, silica, mica, zirconia, titania, glass, or zinc oxide. 4. The method of claim 3,
The surface-treated steel sheet, characterized in that the bright pigment further contains at least one of Rh, Cr, Ti, Ag, and Cu. 4. The method of claim 3,
The average concentration of the bright pigment in the coating film is 5 to 15% in mass %, A surface-treated steel sheet. 3. The method of claim 1 or 2,
The surface-treated steel sheet, characterized in that the binder resin is a polyester resin.