TW202003918A - Surface-treated steel plate - Google Patents

Abstract

The present invention pertains to a surface-treated steel plate characterized by: having a steel plate, a Zn alloy plating layer formed on at least one surface of the steel plate, and a coating film that is formed upon the Zn alloy plating layer, has an average thickness T1, and includes a colored pigment, an antirust pigment, and a binder resin; the average concentration of the colored pigment in the coating film being 5%-15% by mass; having a ratio CA1/CA2 of 0.2-0.9 between the average concentration CA1 of the colored pigment present in an area at a width T2 from the surface of the coating film in the thickness direction of the coating film and the average concentration CA2 of the colored pigment present in an area at a width T2 from the interface of the coating film on the Zn alloy plating layer side, in the coating film thickness direction; and T2 ([mu]m) = 0.1 * T1 ([mu]m) + 1.1 [mu]m.

Description

Surface treated steel plate

The present invention relates to a surface-treated steel sheet having high corrosion resistance and excellent blackening resistance.

Background of the invention Galvanized steel sheets such as galvanized steel sheets with excellent corrosion resistance and black resistance are widely used in home appliances, building materials, automobiles and other applications.

The surface of various plated steel sheets such as galvanized steel sheets may deteriorate due to the surrounding environment. For example, electrolytes such as salts contained in the atmosphere or oxygen and moisture present in a high-temperature and humid environment can cause the coating to oxidize and generate white rust. If white rust is formed, the appearance uniformity of the plated steel sheet will be impaired, so the plated steel sheet generally requires corrosion resistance that can suppress the generation of white rust.

In particular, when a plated steel plate is used outdoors for building materials or outdoor home appliances, it is more susceptible to deterioration due to the influence of the surrounding environment over time, so high corrosion resistance is required.

As a technique for further improving the corrosion resistance of galvanized steel sheets, there is known a steel sheet that has been subjected to Zn-based alloy plating such as Zn-Al-Mg-based alloy plating.

What is required for the Zn-based alloy plated steel sheet is both short-term corrosion resistance and long-term corrosion resistance. "Short-term corrosion resistance" means, for example, that it will not corrode until the builder submits the plated steel sheet to the orderer (about 1 year), and "long-term corrosion resistance" means, for example, increase as much as possible until the construction materials and other products. Corrosion and thinning to lose the required strength.

Another characteristic required for Zn-based alloy plated steel sheets is resistance to blackening. Blackening refers to the oxidation of the plating layer and blackening. Blackening occurs particularly remarkably on Zn-Al-based alloy plated steel sheets or Zn-Al-Mg-based alloy plated steel sheets to which Al or Mg is added during zinc plating. Due to the blackening of the above plating layer, the discoloration of the plated steel sheet is seen from the appearance, so it is not ideal for use. Therefore, Zn-based alloy plated steel sheets such as Zn-Al-Mg-based alloy plated steel sheets are expected to have corrosion resistance and excellent blackening resistance.

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

In addition, Patent Document 2 discloses a chromate-free coated metal plate having a coating film using organic resin as a film-forming component on at least one side of the metal plate, and the coating film includes a thin sheet whose surface has been inactivated Aluminum pigment, and shows that the metal plate has good corrosion resistance and black resistance.

In addition, Patent Document 3 discloses a chemical conversion steel sheet having: a plated steel sheet having a steel sheet and a plating layer arranged on the surface of the steel sheet; and a chemical conversion treatment film arranged on the surface of the plating layer; and the chemical conversion treatment film contains fluorine resin, Base resin, metal flakes, and chemical conversion treatment components, and it is shown that if the steel sheet is used, corrosion resistance and blackening resistance can be improved.

Prior technical literature Patent Literature Patent Literature 1: International Publication No. 2015/075792 Patent Literature 2: International Publication No. 2013/065354 Patent Document 3: Japanese Patent Laid-Open No. 2016-121390

Summary of the invention Problems to be solved by invention However, in the Zn-Al-Mg-based alloy plated steel sheet described in Patent Document 1, some aluminum pigments in the film may protrude from the film surface after production or when the film surface becomes thin due to resin degradation. In this way, the protruding pigment will be used as a starting point to form a channel that allows corrosion factors such as oxygen to pass through the film. As a result, the corrosion factor will enter the plating layer of the substrate through the channel, which may promote corrosion of the plating layer. Therefore, there is room for improvement in corrosion resistance. Moreover, in Patent Document 1, the concentration distribution of the aluminum pigment in the coating film has not been fully reviewed, and there is still room for improvement in blackening resistance.

In addition, in Patent Documents 2 and 3, the concentration distribution of pigments such as flake-shaped aluminum has not been sufficiently reviewed, and there is still room for improvement in blackening resistance.

In view of the above problems, an object of the present invention is to provide a surface-treated steel sheet with high corrosion resistance and excellent blackening resistance for a Zn-based alloy plated steel sheet.

Means to solve the problem The inventors found that it is important to control the average concentration of coloring pigments such as aluminum pigments in the coating film formed on the Zn-based alloy plating layer in order to obtain the surface-treated steel sheet having high corrosion resistance and excellent blackening resistance. 5 to 15% in terms of mass%. With the above control, when viewed from a direction perpendicular to the surface of the coating film, the coloring pigment sufficiently covers the Zn-based alloy plating layer, so the coloring pigment can prevent blackening of the Zn-based alloy plating layer from being seen, thereby suppressing the appearance Changes in the above to obtain excellent blackening resistance.

The inventors also found that it is important to concentrate the coloring pigment on the Zn-based alloy plating layer in the coating film. Concentrating the coloring pigment on the Zn-based alloy plating layer as described above can suppress the coloring pigment from protruding from the surface of the coating film, thereby suppressing the formation of channels of corrosion factors and ensuring corrosion resistance. In addition, by concentrating the coloring pigment on the Zn-based alloy plating layer side, the coloring pigment can be arranged in a narrow area in the coating film and at a close distance to each other. Therefore, the color pigments can be distributed in the coating film with high density, and the Zn-based alloy plating layer in a wider range can be effectively not seen, and as a result, the blackening resistance can be improved.

The present invention is based on the above findings, and its gist is as follows. (1) A surface-treated steel sheet characterized by having a steel sheet, a Zn-based alloy plating layer formed on at least one side of the steel sheet, and a coating film having an average thickness T ₁ formed on the Zn-based alloy plating layer, and the coating The film contains coloring pigments, anti-rust pigments and binder resin; the chemical composition of the aforementioned Zn-based alloy plating layer in mass% is: Al: 0.01~60%, Mg: 0.001~10% and Si: 0~2%; the average concentration in the film of the coloring pigment in mass%, 5 to 15%, and the ratio C _A1 average concentration C _A2 of the coloring pigment average concentration C _A1 and the colored pigments / C _A2 0.2 to 0.9, an average The concentration _CA1 is the average concentration of the coloring pigment existing in the width T ₂ region in the thickness direction of the coating film from the surface of the coating film, and the average concentration _CA2 is from the interface of the coating film on the side of the Zn-based alloy plating layer The average concentration of the coloring pigment existing in the area of the width T ₂ in the thickness direction of the coating film, and T ₂ (μm)=0.1×T ₁ (μm)+1.1 μm. (2) The surface-treated steel sheet according to (1), wherein the average concentration of the anti-rust pigment in the coating film is 3 to 12% in mass %, and the average concentration of the anti-rust pigment C _B1 and the anti-rust The ratio of the average concentration of the pigment C _B2 C _B1 /C _B2 is 1.3 to 4.0, the average concentration C _B1 is the average concentration of the rust-preventive pigment existing in the region of the width T ₂ in the thickness direction of the coating film from the surface of the coating film, The average concentration C _B2 is the average concentration of the rust-preventive pigment existing in the width T ₂ region in the thickness direction of the coating film from the interface of the Zn-based alloy plating side of the coating film, and T ₂ (μm)=0.1× T ₁ (μm) + 1.1 μm, and the anti-corrosive pigment includes one or more of Si, Mo, W, and Ba. (3) The surface-treated steel sheet according to (1) or (2), wherein the coloring pigment has a long axis X _{1 of} 5-30 μm, a short axis X ₂ of 1-30 μm, and a thickness X _{3 of} 0.0025 μm or more, and When the average particle diameter = (X ₁ +X ₂ )/2 and the average aspect ratio = (X ₁ +X ₂ )/2X ₃ , the average particle diameter of the coloring pigment is 7-30 μm, and the average aspect ratio is 20 or more. (4) The surface-treated steel sheet according to any one of (1) to (3), wherein the average thickness T ₁ of the coating film is 3 to 15 μm. (5) The surface-treated steel sheet according to any one of (1) to (4), wherein the thickness of the coloring pigment is 0.5T ₁ or less.

Invention effect According to the present invention, it is possible to provide a surface-treated steel sheet in which the average concentration of coloring pigments in the coating film is 5 to 15% in mass %, and the coloring pigments in the coating film are concentrated on the side of the Zn-based alloy plating layer, so coloring can be suppressed The pigment protrudes from the coating film to form a channel for corrosion factors, and when viewed from a direction perpendicular to the surface of the coating film, the coloring pigment can sufficiently prevent the Zn-based alloy plating layer from being seen, so it has high corrosion resistance and good black resistance. In particular, the surface-treated steel sheet of the present invention is characterized in that the color pigment in the coating film is concentrated on the side of the Zn-based alloy plating layer, so even if the thickness of the coating film is thinned, high corrosion resistance and blackening resistance can still be provided.

[Mode for implementing the invention] [Surface-treated steel sheet] The surface-treated steel sheet of the present invention is characterized by having: a steel sheet, a Zn-based alloy plating layer formed on at least one side of the steel sheet, and an average thickness T ₁ formed on the Zn-based alloy plating layer Coating film, and the coating film contains color pigments, rust-preventive pigments and binder resin; the chemical composition of the Zn-based alloy plating layer in mass% is: Al: 0.01~60%, Mg: 0.001~10% and Si:0 ~2%; the average concentration of color pigments in the coating film is 5~15% in mass %, and the ratio of the average concentration of color pigments C _A1 and the average concentration of color pigments C _A2 C _A1 /C _A2 is 0.2~0.9 , The average concentration _CA1 is the average concentration of the coloring pigment existing in the region of the width T ₂ in the thickness direction of the coating film from the surface of the coating film, and the average concentration _CA2 is from the interface of the Zn-based alloy coating side of the coating film The average concentration of the coloring pigment existing in the region of the width T ₂ in the thickness direction of the coating film, and T ₂ (μm)=0.1×T ₁ (μm)+1.1 μm. The following describes the structural requirements of the surface-treated steel sheet of the present invention.

>Steel plate> The steel sheet (original plated sheet) of the present invention is not particularly limited, and general steel sheets such as hot-rolled steel sheets and cold-rolled steel sheets can be used. The type of steel is not particularly limited. For example, Al deoxidized steel, very low-carbon steel containing Ti, Nb, etc., and high-tensile steel containing P, Si, Mn, etc. in these can be used. The thickness of the steel plate of the present invention is not particularly limited, and it may be, for example, 0.25 to 3.5 mm.

>Zn alloy coating> The Zn-based alloy plating layer of the present invention is formed on a steel plate. The Zn-based alloy plating layer may be formed on one side of the steel plate 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, and may be a Zn-Al-Mg-Si alloy plating layer further containing Si. The various contents (concentrations) in terms of mass% are Al: 0.01-60%, Mg: 0.001-10%, and Si: 0-2%, and the remainder is Zn and impurities. In the following, when the chemical composition of the Zn-based alloy plating is only referred to as "%", it means "mass %".

If the Al content of the Zn-based alloy coating is less than 0.01%, the effect of improving the corrosion resistance of the plated steel sheet containing Al cannot be fully exerted, and if it is more than 60%, the effect of improving the corrosion resistance will be saturated. Therefore, the Al content is 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 preferred Al content is 1 to 60%, more preferably 5 to 60%.

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 containing Mg may not be fully exhibited. On the other hand, if it exceeds 10%, Mg will not be completely dissolved in the plating bath and will be suspended in the state of oxide (generally called scum). When zinc plating is performed in this plating bath, the oxide will adhere The appearance of the plating surface layer may cause a poor appearance, or there may be parts that are not plated (generally referred to as unplated). Therefore, the Mg content is 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 less, 5 % Or less or 4% or less. The Mg content should be 1 to 5%, more preferably 1 to 4%.

The lower limit of the Si content of the Zn-based alloy coating can be 0%, but in order to improve the corrosion resistance of the Zn-based alloy coating, it should be set to 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. The Si content is preferably 0.1 to 2%, and more preferably 0.5 to 1.5%.

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

>Coating film> The coating film of the present invention is formed on a Zn-based alloy plating layer. In addition to coloring pigments, the coating film also contains anti-rust pigments and binder resin. The average thickness T _{1 of the} coating film may be any value as long as sufficient corrosion resistance and blackening resistance can be secured, and for example, it is preferably 3 μm or more and 15 μm or less. If the average thickness T _{1 of the} coating film is less than 3 μm, part of the coloring pigment may protrude from the coating film and increase the possibility that the corrosion factor reaches the alloy plating layer, and there is a possibility that sufficient corrosion resistance may not be ensured. Moreover, the effect of ensuring that the Zn-based alloy plating layer is not seen by the color pigments in the coating film is insufficient, and there is a possibility of poor black resistance. In addition, if the average thickness T _{1 of the} coating film is greater than 15 μm, the effect of increasing the average thickness of the coating film to improve corrosion resistance and blackening resistance will be saturated. The average thickness T _{1 of the} coating film may be, for example, 4 μm or more, 5 μm or more, or 6 μm or more, and may be 12 μm or less or 10 μm or less. Therefore, the average thickness T _{1 of the} coating film is more preferably 3 μm or more and 12 μm or less. In addition, "blackening resistance" in this specification does not mean suppressing the blackening of the Zn-based alloy coating on the base of the coating film, but even if the Zn-based alloy coating is blackened, the color pigment in the coating film is used to No blackening is visible on the outside, so that the surface-treated steel sheet does not change in appearance.

As used in this specification, "average thickness T ₁ "is defined as a section of a steel plate with a coating film observed under a microscope, and measured from any five locations on the interface of the coating film on the Zn-based alloy coating side to the coating film surface After the shortest distance, the measured values are averaged. In addition, when the coating film contains a substance with a larger particle size than the film thickness (for example, an aggregate), the above distance is measured at a position where the substance does not exist. This is because when the coating film is viewed from the cross-sectional direction, when the substance is present, the above distance may be measured to be greater than the actual coating film thickness. In addition, another layer such as a chemical conversion treatment layer may exist between the Zn-based alloy plating layer and the coating film. When the other layer is present, the thickness of the other layer is not included in the average thickness T ₁ .

(Coloring pigment) For the coloring pigment of the present invention, general coloring pigments such as titanium oxide, zinc oxide, iron oxide, aluminum oxide, barium sulfate, aluminum, or carbon black can be used. The coloring pigment is preferably aluminum. But aluminum will react with water to dissolve. Therefore, when using water-based paint as the paint for forming a coating film as in the present invention, it is necessary to coat aluminum with oxide or resin.

The average concentration (average content) of the coloring pigment in the coating film is 5 to 15% in mass%. By setting the average concentration of the coloring pigment to the above range and concentrating the coloring pigment near the interface with the Zn-based alloy plating layer, even if the film thickness is thinner than the coating film of the general coated steel sheet, it can be ensured from The amount of the coloring pigment can fully cover the Zn-based alloy plating layer when viewed perpendicular to the surface of the coating film. It can sufficiently suppress the color pigments from protruding from the surface of the coating film. Therefore, the high corrosion resistance can be maintained, and the color pigment can prevent the blackening of the Zn-based alloy plating layer from being seen, whereby the change in appearance can be suppressed and excellent blackening resistance can be obtained. If the average concentration of the coloring pigment in the coating film is less than 5%, the density of the coloring pigment used in the coating film to prevent the blackening of the Zn-based alloy plating layer from being seen will be insufficient, and the blackening resistance will be reduced. On the other hand, if the average concentration of the coloring pigments in the coating film is greater than 15%, coloring pigments will be present in the coating film in large amounts. When the coating film becomes thinner, some of the coloring pigments will be removed from the surface of the coating film at an earlier stage. The possibility of protruding becomes higher, and there is a risk of deterioration of corrosion resistance. Furthermore, there is a possibility that the adhesion may be lowered. The average concentration of the coloring pigment in the coating film may be 6% or more, 7% or more, and may be 12% or less or 10% or less. The average concentration of the coloring pigment in the coating film should be 5-12%, more preferably 5-10%.

In the case of use in this specification, "the average concentration of the coloring pigment in the coating film" is measured with a glow discharge luminescence surface analysis device (Glow Discharge Optical Emission Spectrometry: GD-OES). Specifically, when the type of the color pigment, that is, the specific compound of the color pigment can be confirmed, the coating film is sputtered from the surface toward the plating layer, and the main elements constituting the color pigment are measured in the depth direction per 1.0 μm Concentration curve. After that, the average value of the measured concentration of the main element is calculated, and the concentration measured from the molecular weight of the compound of the known color pigment is converted, and the average concentration of the color pigment in the coating film is obtained. When the type of coloring pigment is unknown, that is, the specific compound of the coloring pigment is unknown, the field emission type electron probe micro analyzer (Field Emission-Analyzer) is used for the coloring pigment from the cross section of the coating film (the surface perpendicular to the surface of the coating film). Electron Prove Micro Analyzer: FE-EPMA) to perform elemental analysis to determine the type of coloring pigment and then determine the "average concentration of coloring pigment in the coating film" as described above.

The color pigments in the coating film are concentrated on the side of the Zn-based alloy plating layer. Concentrated indicators based coloring pigment is the average concentration C _A1 and C _A2 average concentration ratio C _A1 / C _A2 decision, the average concentration C _A1-based coating from the surface is present in the width of a region T ₂ in the thickness direction of the film the average concentration of the coloring pigment, the average concentration C _A2 based coating film from the interface between the Zn-based alloy plating layer is present in the starting side of the average concentration of the coloring pigment area width T ₂ in the film thickness direction. The ratio C _A1 /C _A2 of the surface-treated steel sheet of the present invention is 0.2 or more and 0.9 or less. Here, the width T ₂ is determined by the following formula: T ₂ (μm)=0.1×T ₁ (μm)+1.1 μm. That is, the width T ₂ of the measurement area of the average concentration of color pigments C _A1 and C _A2 is determined according to the value of the average thickness T ₁ of the coating film. More specifically described, as viewed from above to determine the average cross-sectional thickness of the coating film T _1, T and then the inside width of the T _{2. 1} determined from the formula C _A1 and C _A2 of the measured width of the region T _2, based on Measure the average concentration of color pigments C _A1 and C _A2 . Further, even if the area used to determine the C _A1 and C _A2 is used to determine when the area of overlap (i.e., T _2> 0.5T _1), it can still be determined as described above C _A1 and C _A2, determines the ratio C _A1 / C _A2 . In addition, when T ₂ >T ₁ (for example, when T ₁ =1.2 μm), the surface-treated steel sheet is not included in the scope of the present invention.

The ratio C _A1 /C _A2 of the surface-treated steel sheet of the present invention is 0.2 or more and 0.9 or less. If the ratio C _A1 /C _{A2 is} less than 0.2, the anticorrosive pigment will be relatively concentrated on the surface of the coating film, and when the coating film becomes thinner, the layer with a lower concentration of anticorrosive pigment will be exposed in a shorter time. Unable to obtain sufficient long-term corrosion resistance. On the other hand, if the ratio C _A1 /C _{A2 is} greater than 0.9, the effect of thickening the coloring pigment cannot be obtained, and part of the coloring pigment protrudes from the coating film, making the corrosion resistance insufficient. Moreover, when the coating film becomes thinner, the concentration of the coloring pigment in the coating film will be insufficient, and the Zn-based alloy plating layer cannot be effectively prevented from being seen, so that the blackening resistance is insufficient. The C _A1 /C _A2 ratio may be, for example, 0.3 or more or 0.4 or more, and may be 0.8 or less or 0.7 or less. The C _A1 /C _A2 ratio is preferably 0.3 or more and 0.8 or less, and the C _A1 /C _A2 ratio is more preferably 0.4 or more and 0.7 or less.

"Average concentration of color pigment C _A1 in the region of width T ₂ in the thickness direction of the coating film from the surface of the coating film" and "In the thickness direction of the coating film from the interface of the Zn-based alloy plating side of the coating film The average concentration of coloring pigments in the area of width T ₂ C _A2 ”is measured using GD-OES in the same manner as the measurement of the “average concentration of coloring pigments in the coating film”. Specifically, it is sputtered from the surface direction of the coating film to the depth direction of the Zn-based alloy coating layer, and the concentration of the coating film in the depth direction of the main elements constituting the coloring pigment is measured within a range of width T ₂ per 0.1 μm distributed. After that, the average value of the measured concentration of the main element is calculated, and the concentration measured from the molecular weight of the compound of the known color pigment is converted, and the average concentration of the color pigment in the coating film is obtained. In addition, by measuring the relationship between the sputtering time and the coating film depth in advance, the sputtering time can be converted into coating film thickness information. By measuring the concentration distribution of the elements constituting the color pigment in the film thickness direction, _CA1 and _CA2 can be obtained.

The color pigment in the coating film is concentrated on the Zn-based alloy plating side of the coating film so that the value of the above ratio C _A1 /C _A2 in the coating film becomes 0.2 or more and 0.9 or less, whereby the surface of the coating film can be relatively reduced Coloring pigment concentration. Thereby, after production or when the surface of the coating film becomes thin, it is possible to suppress a part of the color pigments from protruding from the surface of the coating film. Therefore, the passage channel of the corrosion factor can be suppressed, so high corrosion resistance can be ensured. Moreover, by reducing the concentration of the coloring pigment on the surface side of the coating film, when the surface of the coating film becomes thin, the color pigment can be suppressed from falling off, and the black resistance can be maintained for a long time. Therefore, when the average concentration of the coloring pigment in the coating film is a fixed condition, the surface-treated steel sheet of the present invention is more effective in making the Zn-based alloy plating layer invisible from the outside compared to the case where the coloring pigment is evenly distributed in the coating film. Can significantly improve the resistance to black denaturation. In addition, in terms of another advantage of color pigments being distributed in narrow areas, when using pigments with high average aspect ratio (such as scales, flats, etc.), the direction of the color pigments can be adjusted to relative The surface of the coating film is parallel or substantially parallel, which can more effectively prevent the plating layer from being seen, so that the black resistance can be improved.

The coloring pigment of the present invention may have any shape as long as sufficient corrosion resistance and blackening resistance can be ensured, and the shape of the coloring pigment is not limited but can be exemplified by spherical, elliptical, needle-shaped, flat, thin-plate, scale Shape, spindle shape, etc. The coloring pigment of the present invention is preferably scaly in order to prevent the Zn-based alloy plating layer from being seen more effectively to obtain excellent blackening resistance.

When used in this specification, the "average particle diameter" and "average aspect ratio" of the color pigment of the present invention can be obtained by the following method. First, any one color pigment is element-distributed with FE-EPMA from the surface, and the long axis X ₁ and the short axis X _{2 of} the color pigment are obtained. Here, the long axis X ₁ refers to the length of the largest line segment of the color pigment in the horizontal direction of the color pigment image specified by the element distribution, and the short axis X ₂ refers to the long axis X _{1 of the} medium horizontal color pigment The length of the vertical line segment. Next, element distribution is performed with FE-EPMA from the cross-sectional direction, and the value of the thickness X ₃ (generally, the dimension in the direction perpendicular to the measurement plane of the above-mentioned long and short diameters) is measured. Then, from these measured values, the particle diameter of the coloring pigment = [(X ₁ +X ₂ )/2] and the aspect ratio = [(X ₁ +X ₂ )/2X ₃ ]. And use the same method to determine the particle size and aspect ratio of any 10 or more color pigments, and then average these to obtain the "average particle size" and "average aspect ratio" of the coloring pigment.

The long axis X ₁ , the short axis X ₂ and the thickness X ₃ of the coloring pigment of the present invention may have any values as long as they exist in the coating film, and for example, the long axis X ₁ is preferably 5 μm or more and 30 μm or less, and the short axis X ₂ is 1 μm or more and 30 μm or less, and the thickness X ₃ is 0.0025 μm or more. By having a long diameter, a short diameter, and a thickness in the above range, the color pigment can be suppressed from protruding from the coating film, and the Zn-based alloy plating layer can be effectively prevented from being seen. In addition, the average particle diameter of the coloring pigment of the present invention is preferably 7 μm or more and 30 μm or less, and the average aspect ratio is preferably 20 or more. By having an average particle diameter in the above range, the color pigment can be suppressed from protruding from the coating film, and the Zn-based alloy plating layer can be effectively prevented from being seen. In addition, because the coloring pigment has a high aspect ratio, the coloring pigment can be used to prevent a wide range of Zn-based alloy plating from being seen, and the blackening resistance can be further improved. When the average particle diameter of the coloring pigment is less than 7 μm, the Zn-based alloy plating layer cannot be sufficiently seen, and the blackening resistance may be insufficient. On the other hand, if the average particle diameter of the color pigment is greater than 30 μm, the possibility that the color pigment will protrude from the coating film increases, and there is a possibility that sufficient corrosion resistance cannot be ensured. In addition, when the average aspect ratio is less than 20, the Zn-based alloy plating layer cannot be sufficiently seen, and the blackening resistance may be insufficient. The average particle diameter of the coloring pigment of the present invention is more preferably 10 μm or more and 25 μm or less. Also, the average aspect ratio is more preferably 25 or more, and more preferably 30 or more. The upper limit of the average aspect ratio is not limited, and may be 100, for example. In addition, in order to use a coloring pigment to more effectively prevent the Zn-based alloy plating layer from being seen, it is advantageous that the value of the major axis X ₁ and the minor axis X ₂ are close, that is, the ratio X ₁ /X _{2 is} close to 1.0. In the present invention, for example, the ratio X ₁ /X _{2 is} preferably 1.0 or more and 3.0 or less, more preferably 1.0 or more and 2.5 or less, and may more preferably be 1.0 or more and 2.0 or less.

The coloring pigment of the present invention is contained in the coating film, so the thickness X _{3 of the} coloring pigment becomes smaller than the average thickness T _{1 of the} coating film. In addition, if the color pigment protrudes from the coating film, an intrusion path of the corrosion factor may be formed and the corrosion resistance may be deteriorated. Therefore, it is advantageous that the thickness X _{3 of the} color pigment is smaller than the average thickness T _{1 of the} coating film. For example, the thickness X _{3 of the} color pigment is preferably 0.5T ₁ or less, and more preferably 0.4T ₁ or less.

(Anti-rust pigment) The anti-rust pigment used in the coating film of the present invention may contain one or more of Si, Mo, W, and Ba. It is preferable to include one or more of Si, Mo and Ba. Such specific compounds are not limited, and examples thereof include silicon oxide (manufactured by Grace Corporation, MSK-8D), calcium-modified silicon oxide (manufactured by WR Grace Corporation, SHIELDEXC303), barium borate (prototype manufactured by Showa Chemical Co., Ltd.), barium metaborate (Test reagent manufactured by Showa Chemical Co., Ltd.), zinc molybdate (produced by Wako Pure Chemical Industries), calcium molybdate (produced by Wako Pure Chemical Industries), sodium tungstate (produced by Kanto Chemical Co., Ltd.), tungsten Calcium acid (prototype manufactured by Kanto Chemical Company), tungsten oxide (prototype manufactured by Kanto Chemical Company), etc. The anti-rust pigment is preferably silicon oxide. Furthermore, the anti-rust pigment may be porous. Making it porous can increase the specific surface area and lower the specific gravity, and it can be easily concentrated on the surface side of the coating film. For example, an anti-corrosive pigment (such as silicon oxide) having a specific surface area of 20 m ² /g or more, for example, 50 m ² /g or more, 100 m ² /g or more, or 200 m ² /g or more can be used. The upper limit of the specific surface area of the rust preventive pigment is not particularly limited, and it may be, for example, 500 m ² /g. In addition, the "apparent specific gravity" in this specification refers to the density when the anticorrosive pigment itself and the internal void are volume, and includes "volume of the anticorrosive pigment itself" and "volume of internal void".

The average concentration of the anti-rust pigment in the coating film can be 3 to 12% in mass%. By setting it as the said range, a coating film can fully function as a film which prevents corrosion of a Zn-based alloy plating layer, and can provide high corrosion resistance. If the average concentration of the rust-preventive pigment in the coating film is less than 3%, regardless of the concentration distribution of the rust-preventive pigment in the coating film, the concentration of the rust-preventive pigment in the entire coating film will be insufficient, and sufficient corrosion resistance may not be obtained Situation. On the other hand, if the average concentration of the rust-preventive pigment in the coating film is greater than 12%, the effect of increasing the rust-preventive pigment to improve the corrosion resistance will be reduced, which is not conducive to cost. Also, there are cases where the adhesion is reduced. The average concentration of the anti-rust pigment in the coating film may be 4% or more, 5% or more, or 6% or more, and may be 11% or less or 10% or less. The average concentration of the anti-rust pigment in the coating film is preferably 5-12% or less, more preferably 5-10% or less.

Here, the "average concentration of rust-preventive pigment in the coating film" can be obtained by the same method as the above-mentioned "average concentration of coloring pigment in the coating film".

The anti-rust pigment in the coating film is concentrated on the surface side of the coating film. The concentration index of the anti-rust pigment is determined by the ratio C _B1 /C _{B2 of the} average concentration C _B1 to the average concentration C _B2 , and the average concentration C _B1 is present in the area of the width T ₂ in the thickness direction of the coating film from the surface of the coating film The average concentration of the anti-corrosive pigment, the average concentration C _B2 is the average concentration of the anti-corrosive pigment existing in the area of the width T ₂ in the thickness direction of the coating film from the interface of the Zn-based alloy plating side of the coating film. As described above, it is determined by T ₂ (μm)=0.1×T ₁ (μm)+1.1 μm. When the ratio of the above-mentioned coloring pigments C _A1 /C _A2 is 0.2 or more and 0.9 or less, the ratio C _B1 /C _B2 of the surface-treated steel sheet of the present invention is 1.2 or more and 5.0 or less, and in order to more surely obtain the anti-rust pigment on the surface layer side The effect of concentration is preferably 1.3 or more and 4.0 or less. If the ratio C _B1 /C _{B2 is} less than 1.3, there may be a case where the concentration effect of the rust-preventive pigment that enhances the corrosion resistance of the long-term planar portion cannot be sufficiently obtained. On the other hand, if the ratio C _B1 /C _{B2 is} greater than 4.0, the anticorrosive pigment will be excessively concentrated on the surface of the coating film, and when the coating film becomes thinner with time, the insufficient anticorrosive pigment will be exposed in a shorter time The surface may not be able to obtain sufficient long-term corrosion resistance. The ratio C _B1 /C _B2 may be 1.5 or more, 1.8 or more, or 2.0 or more, and may be 3.8 or less, 3.5 or less, or 3.2 or less. The ratio C _B1 /C _{B2 is} preferably 1.5 or more and 3.5 or less, and the ratio C _B1 /C _B2 is preferably 1.8 or more and 3.2 or less.

The C _B1 and C _B2 can be obtained in the same manner as the C _A1 and C _A2 described above.

By thickening the anti-corrosive pigment on the surface of the coating film, even if the anti-corrosive pigment in the coating film is distributed in the coating film, the value of the above ratio C _B1 /C _B2 becomes 1.3 or more and 4.0 or less, which can be sufficiently improved The corrosion resistance of the surface of the coating film can fully improve the long-term corrosion resistance of the planar portion.

The average particle diameter of the anti-rust pigment can be appropriately selected according to the average thickness T _{1 of the} coating film, etc., and can be 0.2 to 10 μm. The average particle size of the anti-rust pigment is preferably 0.4 to 8 μm, and more preferably 0.5 to 6 μm.

The average particle size of the rust-preventive pigment can be determined in the same way as the average particle size of the color pigment. That is, FE-EPMA can be used for element distribution from the surface and cross-sectional direction of the coating film for 10 or more anti-rust pigments to obtain the long axis Y ₁ , the short axis Y ₂ and the thickness Y _{3 of} the anti-rust pigment, and from these values The average particle size of the anti-rust pigment is determined.

In addition, from the viewpoint of adhesion, the thickness Y _{3 of the} rust preventive pigment is preferably smaller than the average thickness T _{1 of the} coating film to a certain extent, for example, the thickness Y _{3 of the} rust preventive pigment is preferably 0.5 T ₁ or less, and It is preferably 0.4T ₁ or less, more preferably 0.3T ₁ or less, and most preferably 0.1T ₁ or less.

(Binder resin) The binder resin used as the coating film component of the present invention may be a polyester resin, urethane resin or acrylic resin. In the present invention, it is important to use an imine-type melamine resin as the hardener of these resins. The binder resin of the present invention is preferably a polyester resin. In addition, the polyester resin used in the present invention is preferably one having a glass transition temperature Tg of -20 to 70°C and a number average molecular weight of 3000 to 30,000. When the binder resin is urethane resin, the Tg is preferably 0 to 50°C and the number average molecular weight is 5000 to 25000. When the binder resin is an acrylic resin, a Tg of 0 to 50°C and a number average molecular weight of 3000 to 25000 are preferred. In the present invention, the solvent used for the binder resin is an aqueous solvent.

In the coating film of the present invention, wax such as polyethylene wax or PTFE wax, resin beads such as acrylic resin beads or urethane resin beads, and phthalocyanine blue, phthalocyanine green, Dyes such as methyl orange, methyl violet or alizarin. By adding these, the strength of the coating film can be improved and the desired color can be given to the coating film, so it is better. These addition amounts can be appropriately determined as long as they do not adversely affect the coating film of the present invention.

In particular, in order to impart a desired color to the coating film of the present invention, and further to impart a desired color to the surface-treated steel sheet of the present invention, a dye can be used as a colorant. The dye can be used alone or in combination with multiple dyes. The type of dye that can be used in the coating film of the present invention is not particularly limited, and known dyes can be used, and for example, phthalocyanine blue, phthalocyanine green, methyl orange, methyl violet, or alizarin can be used.

[Manufacturing method of surface-treated steel sheet] An example of the method for manufacturing the surface-treated steel sheet of the present invention will be described below. The surface-treated steel sheet of the present invention can be manufactured, for example, by coating an aqueous coating on a Zn-based alloy plating layer formed on the steel sheet and heating the coating using a predetermined heat curve to harden the coating, the aqueous coating is added with coloring pigments and anti-rust pigments, and The imine-based melamine resin is used as the hardener of the binder resin.

>Formation of Zn alloy coating> The steel plate can be any one having any plate thickness and chemical composition. For example, cold-rolled steel plates with a thickness of 0.25 to 3.5 mm can be used. The Zn-based alloy plating layer can be formed by galvanizing a Zn-Al-Mg alloy plating with a thickness of 1 to 30 μm on a steel plate, for example. The molten plating can be performed, for example, in a 400 to 550°C molten plating bath to which various metals are added. The content of Al and Mg in terms of mass% is Al: 0.01-60%, Mg: 0.001-10%, and the remainder is typically Zn and impurities. In addition to the above chemical composition, Si may be contained in a mass% of 0.001 to 2% to form a Zn-Al-Mg-Si alloy plating layer.

>Modulation coating> The coating can be prepared by: dispersing a binder resin such as polyester resin (for example, molecular weight: 16000, Tg: 10°C) and imine-based melamine resin in a solid content mass ratio of 100: 10~ 100:30 mixed, and then a predetermined amount of color pigments and anti-rust pigments are dispersed in the mixture to prepare. In addition, as the solvent system, an aqueous solvent (for example, water) is used.

As described above, in the surface-treated steel sheet of the present invention, the rust-preventive pigment in the coating film is concentrated on the surface side of the coating film, and the coloring pigment in the coating film is concentrated on the side of the Zn-based alloy plating layer. Regarding the formation of the concentration distribution of the rust-preventive pigment and the color pigment, the present inventors found that it can be achieved by utilizing the phenomenon that the imine-type melamine resin is concentrated on the surface layer of the coating film when it is cured under specific conditions. That is, the concentration of the rust-preventive pigment on the surface of the coating film is determined by selecting an rust-preventive pigment (such as porous silica) having a smaller specific gravity than the colored pigment, that is, a larger specific surface area. The melamine resin moves to the surface layer together with the melamine resin when the surface layer of the coating film is concentrated to achieve. We believe that the mechanism of this concentration is not only the effect of the difference in apparent specific gravity of the coloring pigment and the anti-rust pigment, but also the chemical affinity between the imine-based melamine resin and the anti-rust pigment and the mutual interaction of these, thereby The anti-rust pigment can be concentrated on the surface of the coating film while the amine-based melamine resin is concentrated on the surface layer.

Furthermore, the present inventors found that when the aqueous coating is used as a coating for forming a coating film like the present invention, the concentration of the imine-type melamine resin on the surface layer is more obvious than when using a solvent system. We believe that it is due to the fact that imide-type melamine resins that are not cross-linked with polyester and the like when the coating film is hardened to form a coating film will be present in a large amount in water-based coatings compared to solvent-based coatings. In other words, in the case of water-based coatings, polyester resins and the like are dispersed in an emulsion state, and we believe that this will hinder the crosslinking reaction between the reactive functional group (OH group) inside the emulsion particles and the imine-based melamine resin, This causes the remaining imine-based melamine resin to increase. Therefore, it is easier to cause the self-condensation reaction of the amine-based melamine than the cross-linking reaction, so that the amine-based melamine resin is more concentrated in the surface layer. In addition, we believe that the concentration effect of the amine-based melamine resin in water-based coatings is also large because the compatibility of water and melamine is low, and the surface free energy of the amine-based melamine resin is smaller than that of water. Type melamine resin easily floats on the surface. Therefore, in the present invention, in order to promote the concentration of the imine-type melamine resin on the surface layer, it is effective to use an aqueous solvent as the solvent.

Melamine resins In addition to the imino-type melamine resins used in the present invention, methylated melamine resins and butylated melamine resins are also known. However, the present inventors found that when methylated melamine resin is added as a hardener in water-based paint, the phenomenon of thickening of the rust-preventive pigment on the surface layer does not significantly occur during baking, and the use of butyl in water-based paint When the melamine-based resin is used as a hardener, the paint will solidify after being mixed with an aqueous solvent and cannot be used as a paint. Therefore, in order to obtain a coating film like the present invention, it is extremely effective to use an aqueous-based solvent, a binder resin, and an imide-type melamine resin as a hardener of the binder resin in combination.

Due to the properties of the imino-type melamine resin in the water-based paint, when the anti-rust pigment in the coating film is concentrated on the surface side of the coating film, the heavier color pigments like aluminum in the coating film are not easily distributed in the coating On the film surface side, it is relatively concentrated on the Zn-based alloy plating layer side. In other words, by concentrating the anti-rust pigment on the surface of the coating film, it is possible to suppress the color pigment from staying on the Zn-based alloy plating layer side of the coating film. In this way, it is possible to obtain a surface-treated steel sheet in which the ratio of anti-rust pigments in the coating film is C _B1 /C _B2 is 1.2 or more and 5.0 or less, preferably 1.3 or more and 4.0 or less, and the color pigments in the coating film can be prepared The surface-treated steel sheet of the present invention having a ratio _CA1 / _CA2 of 0.2 or more and 0.9 or less. In addition, the particle size and specific gravity of the rust-preventive pigment are effective for thickening the rust-preventive pigment and the color pigment on the surface layer side and the Zn-based alloy plating layer, respectively, based on the properties of the imino melamine resin in the water-based paint. In order to obtain the concentration distribution of the rust preventive pigment and coloring pigment of the present invention, it is effective to set the average particle size of the rust preventive pigment to 0.2 to 10 μm and the specific surface area to 20 m ² /g or more.

In addition, when a coloring pigment and a rust preventive pigment can be used in combination, an acid catalyst may be added to the coating in order to thicken the melamine resin on the surface layer of the coating film as necessary. The acid catalyst is not limited, and a weak acid catalyst (Catalyst 296-9/manufactured by ALLNEX JAPAN), a strong acid catalyst (Catalyst 600/manufactured by ALLNEX JAPAN), or an amine-terminated strong acid catalyst (Catalyst 602) can be used / Manufactured by ALLNEX JAPAN). The acid catalyst can be added to the paint, for example, 0.1 to 1.0% by mass.

>Forming a coating film> Then, the prepared paint is applied to the Zn-based alloy plating layer with a roll coater or the like so as to have a predetermined thickness, and is baked by a predetermined heat curve to harden it. Baking is carried out at a heating rate of 5~70℃/sec to a steel plate temperature of 180~230℃. Specifically, in the process of heating to the temperature of the steel plate, it is important to maintain the temperature of the steel plate for 1 to 5 seconds at a temperature between 70 to 150°C and preferably 100 to 150°C and preferably 1 to 3 seconds. That is, after coating the coating on the Zn-based alloy plating layer, the plated steel plate at room temperature (for example, 20°C) is temporarily heated to 70 to 150°C (the first heating step), and maintained at this temperature for 1 After ~5 seconds (temperature maintaining step), it is heated again to 180~230°C (second heating step), thereby producing the coating film of the present invention. The thermal curve can be achieved by two heating furnaces. Specifically, the heating furnace A and the heating furnace B are provided in order with respect to the passing direction of the Zn-based alloy plated steel plate to which the coating is applied, and the temperature between the heating furnace A and the heating furnace B without heating treatment is set Just keep the area. Therefore, the temperature of the plated steel plate coated with the paint can be raised to a temperature between 70 and 150°C in the heating furnace A, and then maintained in the temperature maintenance area at this temperature for 1 to 5 seconds, in the heating furnace B The temperature is raised to a temperature between 180 and 230°C to harden the paint. In addition, the aforementioned thermal curve may be performed in a continuous manner or in a batch manner as described above.

By performing the temperature maintenance step at the maintenance temperature and the maintenance time as described above, the rust-proof pigment can be efficiently concentrated on the surface layer as the imine-type melamine resin is concentrated on the surface layer. When the maintenance time as described above is not set, and/or the temperature in the first heating step is too high, the concentration of the rust-preventive pigment of the present invention cannot be obtained efficiently, and the coloring pigment cannot be obtained efficiently The concentration of the situation. Especially when the maintenance temperature is higher than 150°C, the binder resin will react with the hardener to increase the viscosity of the coating, making it difficult for the anti-rust material to move to the surface layer, so that the desired surface layer concentration of the anti-rust pigment cannot be obtained.

The concentration ratio (concentration ratio of coloring pigments) of the rust-preventive pigment of the present invention is obtained by melamine concentration as described above, and can be controlled by the type of melamine resin used and the concentration of melamine resin. In addition, it can be adjusted by the thermal curve when the coating film is hardened, the average particle size and specific gravity of the anti-rust pigment. Specifically, the binder resin of the water-based solvent, polyester resin, etc. and the hardener of the imine-based melamine resin are mixed and mixed into a binder resin: hardener ratio of 100:10~100:30. , Add coloring pigment and anti-rust pigment to prepare paint. Then, as described above, after the coating is applied on the Zn-based alloy plating layer, it is temporarily heated to 70 to 150°C and maintained at the heated temperature for 1 to 5 seconds, and then heated to 180 to 230°C. Steel plate temperature. By performing the above procedure, the concentration of the rust-preventive pigment on the surface layer side and the concentration of the coloring pigment accompanying it on the Zn-based alloy plating layer side can be effectively produced. In addition, it is effective to set the average particle diameter of the anti-rust pigment to be added to the paint to 0.2 to 10 μm, and to set the specific surface area to 20 m ² /g or more.

By using the manufacturing method as described above, the surface-treated steel sheet of the present invention can be manufactured. That is, the following surface-treated steel sheet can be manufactured: the average concentration of the coloring pigment C _A1 existing in the region of the width T ₂ in the thickness direction of the coating film from the surface of the coating film, and the interface from the Zn-based alloy plating side of the coating film present in the film thickness direction than the width C _A1 T C _A2 of the average concentration of coloring pigment of area ₂ / C _A2 0.2 or more and 0.9 or less, and _{T 2 (μm) = 0.1 ×} T 1 (μm) +1.1 μm. Examples

The following examples illustrate the surface-treated steel sheet of the present invention in detail. However, it is not intended to limit the scope of the invention described in the scope of patent application by the specific examples described below.

>Sample for surface treatment steel plate> (Formation of Zn-based alloy coating) Immerse a cold-rolled steel sheet with a thickness of 1 mm in a molten plating bath of approximately 450° C. with a chemical composition of Al: about 11%, Mg: about 3%, and Zn: about 86% for 3 to 5 seconds, and cold-rolled steel sheet A Zn-11%Al-3%Mg alloy plating layer with a thickness of about 10 μm is formed thereon. Then, the composition of the dissolution plating bath was changed, and a Zn-1%Al-1%Mg alloy plating layer and a Zn-40%Al-8%Mg alloy plating layer with a thickness of about 10 μm were formed on the cold-rolled steel sheet by the same procedure. Or immersing a cold-rolled steel plate with a thickness of 1 mm in a molten plating bath of about 450° C. with a chemical composition of Al: about 11%, Mg: about 3%, Si: about 1%, and Zn: about 85%. In seconds, a Zn-11%Al-3%Mg-1%Si alloy coating with a thickness of about 10 μm is formed on the cold-rolled steel sheet. Then, the composition of the dissolution plating bath was changed, and the Zn-11%Al-3%Mg-0.4%Si alloy plating layer and Zn-11%Al-3%Mg- were formed on the cold-rolled steel sheet by the same procedure. 1.5%Si alloy coating.

(Preparation of paint) Polyester resin (molecular weight: 16,000; glass transition point: 10°C) as binder resin is dispersed in water into an emulsion state, and the pH is adjusted to 8.0 to 9.0. And mixed with imine-based melamine resin. The concentration ratio of polyester resin to imine-based melamine resin is 100:20. Then, to this mixture, resin-coated aluminum having an average particle diameter of 10 μm and an average aspect ratio of 25 (long axis X ₁ : 12 μm, short axis X ₂ : 8 μm, thickness X ₃ : 0.40 μm) was added to the mixture. And two kinds of Si compounds (silica A: specific surface area 320 m ² /g, silicon oxide B: specific surface area 180 m ² /g) and two kinds of Ba compounds (barium borate A: specific surface area) with an average particle size of 3 μm as anti-rust pigments 40m ² /g, barium borate B: specific surface area 4.2m ² /g), and either Mo compound (calcium molybdate: specific surface area 80m ² /g) or W compound (tungsten oxide: specific surface area 40m ² /g) , While preparing paint. The amount of coloring pigments and anti-rust pigments to be added will be described later. After measurement using GD-OES, it is appropriately adjusted to obtain the desired concentration in the coating film. The types of anti-rust pigments added are shown in Table 1 (Si-A represents silicon oxide A, Si-B represents silicon oxide B, Ba-A represents barium borate A, Ba-B represents barium borate B, and Mo represents molybdic acid Calcium and W represent tungsten oxide). Sample No. 32 is an example in which no anti-rust pigment is added, and Sample No. 35 is an example in which a methylated melamine resin is used instead of an imino melamine resin. In addition, although not described in Table 1, we have also prepared a paint using a butylated melamine resin instead of an imino-type melamine resin, but the paint was cured during the preparation and the coating film could not be formed. In Table 1, those using an imino-type melamine resin are expressed as "imino-type", and those using a methylated melamine resin are expressed as "methylation".

(Formation of coating film) The coating material prepared above is applied onto a Zn-based alloy plating layer using a roll coater or the like so that the average thickness T ₁ of the formed coating film becomes 5 μm, and baked to harden it. The baking is performed under the conditions described in Table 1 (arrival temperature A, heating time A, heating rate A, maintenance time, reaching temperature B, heating time B, heating rate B). Specifically, first, the temperature at the start of baking of the plated steel sheet on which the Zn-based alloy plating layer is formed is maintained at 20° C., and the plated steel sheet is coated with the coating material, as described in Table 1, in the heating furnace A The temperature is increased to the temperature A at the heating rate A, and after the temperature A is maintained for the predetermined maintenance time, the temperature is increased to the temperature B at the heating rate B in the heating furnace B. The combination of the heating rate at the time of baking, the reaching temperature of the steel plate and the holding time was changed, and the ratio of the sample of the surface-treated steel plate C _A1 /C _A2 and/or the ratio C _B1 / C _{B2 was} adjusted.

The average concentration of the coloring pigments in the coating film from the prepared coating film; the average concentration of the anti-rust pigments in the coating film; the ratio of coloring pigments C _A1 /C _A2 ; and the ratio of anti-rust pigments C _B1 /C _B2 is determined by element analysis using GD-OES. The values determined according to the above are shown in Table 1.

>Evaluation of samples of surface-treated steel sheets> After the samples of the surface-treated steel sheet are made as described above, the corrosion resistance of each sample having the plating chemical composition shown in Table 1, the concentration and concentration distribution of the coloring pigment and the anti-rust pigment, and the type of the anti-rust pigment is as follows And evaluation test of resistance to blackening.

(Evaluation test of corrosion resistance) A salt water spray test (according to JASO M609-91 method) was performed on each sample as an evaluation test for corrosion resistance. The salt water spray test is based on (1) salt water spray for 2 hours (5% NaCl, 35°C); (2) dry for 4 hours (60°C); and (3) wet for 2 hours (50°C, humidity above 95%) as 1 cycle, 120 cycles in total (960 hours in total). In order to prevent corrosion from the end face, the end face of each sample was sealed with tape and tested. The width of each sample is set to 50 mm, and the length is set to 100 mm.

The corrosion resistance was evaluated by observing the surface (planar part) of the sample after the salt water spray test for 960 hours using an optical microscope to confirm the area ratio Z where rust was generated. Specifically, first, the surface of the sample is read with a scanner. Then, use the image editing software to select the area where the rust is generated, and find the area ratio of the rust. This procedure was performed on five samples, and the rust-generating area ratio was averaged to determine the "rust-generating area ratio Z". And according to the "area of rust generation area Z" determined by the above method for each sample, the score of each sample is determined in 8 stages in the following manner. Take a score of 3 or higher as the acceptable score for 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 black resistance) A sunlight carbon arc lamp type weather resistance test (SWOM) (in accordance with JIS D0205) was performed on each sample as an evaluation test for blackening resistance. The test consists of spraying water for 12 minutes in a 60-minute arc lamp spraying time and carrying out a total of 500 hours. The width of each sample is set to 50 mm, and the length is set to 50 mm.

The evaluation of blackening resistance is determined by measuring the "color change ΔL ^* " of the surface of the sample before and after the weather resistance test (lightness L of the sample after the test-lightness L of the sample before the test). ΔL ^* is determined by using a spectrophotometer (Suga Test Machine Co., Ltd.: SC-T45) and color tone measurement (JIS Z8729) using a CIE color system (L*a*b* color system). According to the measured ΔL ^* , the score is determined in 8 stages in the following manner. A rating of 3 or higher was evaluated as passing black resistance. Rating 8: ΔL ^* ≦1 Rating 7: 1>ΔL ^* ≦2 Rating 6: 2>ΔL ^* ≦3 Rating 5: 3>ΔL ^* ≦4 Rating 4: 4>ΔL ^* ≦5 Rating 3: 5>ΔL ^* ≦6 Rating 2: 6>ΔL ^* ≦7 Rating 1: 7>ΔL ^*

For the sample Nos. 1 to 40 of the surface-treated steel sheet, the evaluation test of corrosion resistance and blackening resistance was carried out as described above, and the respective scores were determined. The obtained results are shown in Table 1.

[Table 1]

Sample Nos. 1 to 8 in Table 1 are examples where the ratio of coloring pigments C _A1 /C _A2 was changed. Sample Nos. 2 to 7 have a ratio of 0.2 to 0.9 in the range of the present invention, and therefore have sufficient corrosion resistance and blackening resistance.

On the other hand, the ratio No. 1 of sample No. 1 is C _A1 /C _{A2 is} less than 0.2, so the anti-rust pigment will be relatively concentrated on the surface of the coating film, and the areas where the anti-rust pigment is insufficient will be exposed in a short time. Therefore, the corrosion resistance is insufficient. The ratio of sample No. 8, C _A1 /C _A2 , is greater than 0.9, so the color pigments are slightly uniformly dispersed in the coating film, and a large number of color pigments exist on the surface of the coating film, so the formation of channels through which corrosion factors can pass cannot be sufficiently suppressed. Therefore, the corrosion resistance is insufficient. Furthermore, in sample No. 8, the concentration of the coloring pigment in the coating film is insufficient when the surface of the coating film becomes thin, so that the Zn-based alloy plating layer on the base cannot be sufficiently seen, and the blackening resistance is insufficient.

Sample Nos. 4 and 9 to 12 in Table 1 are examples where the ratio C _A1 /C _{A2 is} fixed and the type of the anti-rust pigment is changed. Samples No. 4 and 9 to 12 have excellent corrosion resistance and blackening resistance. Especially when the anti-rust pigment contains Si-A, Si-B, Ba-A or Mo, it has more excellent corrosion resistance. In addition, No. 13 is an example in which the same rust inhibitor Si-B as No. 12 is used, and the ratio C _A1 /C _A2 and the ratio C _B1 /C _B2 are changed, and it has sufficient corrosion resistance and blackening resistance.

Sample Nos. 3 and 14 to 16 or Sample Nos. 6 and 17 to 19 in Table 1 changed the ratio of coloring pigments C _A1 /C _A2 under fixed conditions regarding the ratio of anti-rust pigments C _B1 /C _B2 Example. Any sample has sufficient corrosion resistance and blackening resistance. In addition, the ratio of anti-corrosion pigments C _B1 /C _B2 is 1.3 or more and 4.0 or less, and has more excellent corrosion resistance.

Sample Nos. 20 to 25 in Table 1 are examples where the average concentration of the coloring pigment in the coating film is changed. The average concentration of the coloring pigments of Sample Nos. 21 to 24 is in the range of 5 mass% or more and 15 mass% or less in the range of the present invention, so they have sufficient blackening resistance and corrosion resistance.

On the other hand, in sample No. 20, the average concentration of the coloring pigments in the coating film is less than 5 mass%, so the density of the coloring pigments in the entire coating film is insufficient, so that the Zn-based alloy plating layer on the substrate cannot be sufficiently seen. Inadequate resistance to black denaturation. In sample No. 25, since the average concentration of the coloring pigment in the coating film is greater than 15% by mass, even if it is the ratio C _A1 /C _A2 within the scope of the invention of the present invention, the coloring pigment still protrudes from the surface of the coating film and cannot be sufficiently suppressed The formation of channels through which corrosion factors can pass, resulting in insufficient corrosion resistance.

Sample Nos. 26 to 31 of Table 1 are examples of the case where the average concentration of the anti-rust pigment in the coating film is changed. Any sample has sufficient corrosion resistance and blackening resistance. In particular, when the average concentration of the anti-rust pigment in the coating film is within the range of 3% by mass or more and 12% by mass or less, the effect of the anti-rust pigment to improve the corrosion resistance is remarkable, and the appropriate amount of anti-rust pigment will move To the surface layer, the color pigments have good orientation, so they have more excellent corrosion resistance and blackening resistance.

Sample No. 32 in Table 1 does not contain anti-rust pigments, so the corrosion resistance and blackening resistance are insufficient. In sample No. 33, the specific surface area of the anti-rust pigment is small, that is, the specific gravity is high, and even if the imine-based melamine resin is used as the hardener, the concentration distribution of the color pigment and the anti-rust pigment cannot be controlled, so the corrosion resistance and black resistance Insufficient transgender. The maintenance temperature of Sample No. 34 is high and the desired concentration distribution of coloring pigments and anti-rust pigments cannot be obtained, and the anti-rust pigments are relatively concentrated on the surface of the coating film, and the areas where the anti-rust pigments are insufficient are in a short time The inside is exposed, so that the corrosion resistance is insufficient. Sample No. 35 is based on the use of methylated melamine resin as the hardener. The concentration phenomenon does not occur significantly and the concentration distribution of the coloring pigment and the anti-rust pigment cannot be controlled, so the corrosion resistance and blackening resistance are insufficient.

Sample Nos. 36 to 40 of Table 1 are examples of the case where only the chemical composition of the Zn-based alloy plating layer is changed from Sample No. 4, and it has sufficient black resistance and corrosion resistance.

As described above, the average concentration of the coloring pigment in the coating film is 5% by mass or more and 15% by mass or less, and the surface-treated steel sheet of the present invention in which the coloring pigment in the coating film is concentrated on the Zn-based alloy plating layer has high corrosion resistance Surface-treated steel sheet with good resistance and good blackening resistance.

Then, based on the sample No. 4 in Table 1, the average particle diameter and the average aspect ratio of the coloring pigment contained in the coating film and the average thickness T _{1 of} the coating film were changed to produce a sample No. of the surface-treated steel sheet. 41~58, and evaluate the corrosion resistance and blackening resistance. In addition, the manufacturing conditions were appropriately changed for the sample Nos. 41 to 58 to obtain the same ratio C _A1 /C _A2 :0.5 and sample ratio No.4 as shown in Table 1 :C _B1 /C _B2 :2.5. As the coloring pigment, resin-coated aluminum was used in the same manner as the sample in Table 1. The anti-rust pigment uses silica A with an average particle size of 3 μm. The scores of the corrosion resistance and the blackening resistance are determined in the same manner as the sample Nos. 1 to 40 as described above.

The long diameter X ₁ , the short diameter X ₂ and the thickness X ₃ of the color pigments to be used, the average particle diameter and average aspect ratio of the color pigments obtained from these, the average thickness T _{1 of the} resulting coating film and the corrosion resistance score The scores for resistance to blackening are shown in Table 2. X ₁ ~ X ₃ are determined by using FE-EPMA to investigate 15 color pigments in the coating film, and the average particle size and average aspect ratio of the color pigments are determined from these values. The average thickness T ₁ of the coating film is determined by SEM observation of the cross section.

[Table 2]

According to Table 2, any of the samples Nos. 41 to 58 have sufficient corrosion resistance and blackening resistance. In particular, if the average particle diameter of the coloring pigment is 7 μm or more and 30 μm or less, and the average aspect ratio is 20 or more, part of the coloring pigment can be suppressed from protruding from the coating film, and the coloring pigment can more effectively prevent the Zn-based alloy from being plated Seen, it has more excellent corrosion resistance and blackening resistance. In particular, when the average thickness T ₁ of the coating film is 3 μm or more, the coloring pigment can be suppressed from protruding from the coating film, and the thickness of the Zn-based alloy plating layer is not sufficiently seen, so it has more excellent corrosion resistance and blackening resistance. In addition, in order to obtain excellent corrosion resistance and blackening resistance, it is sufficient if the thickness of the coating film is 15 μm or less, and from the viewpoint of cost, the thickness is preferably the thickness of the coating film.

Industrial availability According to the present invention, a surface-treated steel sheet having high corrosion resistance and excellent blackening resistance can be provided. As a result, the steel plate used as a building material or a product for home appliances can ensure short-term corrosion resistance and long-term corrosion resistance, and can prevent the appearance of the steel plate from changing for a long time. Therefore, the present invention can be said to be an extremely valuable industrial invention.

Claims (5)

A surface-treated steel sheet characterized by having a steel sheet, a Zn-based alloy plating layer formed on at least one side of the steel sheet, and a coating film having an average thickness T ₁ formed on the Zn-based alloy plating layer, and the coating film includes coloring Pigments, anti-rust pigments and binder resin; the chemical composition of the aforementioned Zn-based alloy coating in mass% is: Al: 0.01~60%, Mg: 0.001~10% and Si: 0~2%; the average concentration of the coloring pigments in mass%, 5 to 15%, and the ratio C _A1 average concentration C _A2 of the coloring pigment average concentration C _A1 and the colored pigments / C _A2 0.2 to 0.9, the average concentration C _A1 The average concentration of the coloring pigment existing in the region of the width T ₂ in the thickness direction of the coating film from the surface of the coating film, and the average concentration CA ₂ is from the interface of the Zn alloy plating layer side of the coating film in the coating film The average concentration of the coloring pigment existing in the region of the width T ₂ in the thickness direction, and T ₂ (μm)=0.1×T ₁ (μm)+1.1 μm. The surface-treated steel sheet according to claim 1, wherein the average concentration of the anticorrosive pigment in the coating film is 3 to 12% in mass %, and the average concentration of the anticorrosive pigment C _B1 and the average concentration of the anticorrosive pigment The ratio of C _B2 C _B1 /C _B2 is 1.3 to 4.0, and the average concentration C _B1 is the average concentration of the rust-preventive pigment existing in the region of width T ₂ in the thickness direction of the coating film from the surface of the coating film, and the average concentration C _B2 is the average concentration of the rust-preventive pigment existing in the area of the width T ₂ in the thickness direction of the coating film from the interface of the Zn-based alloy plating side of the coating film, and T ₂ (μm)=0.1×T ₁ (μm ) +1.1 μm, and the anti-corrosive pigment contains one or more of Si, Mo, W and Ba. The surface-treated steel sheet according to claim 1 or 2, wherein the aforementioned coloring pigment has a long axis X ₁ of 5 to 30 μm, a short axis X _{2 of} 1 to 30 μm, and a thickness X _{3 of} 0.0025 μm or more, and the average particle size = ( When X ₁ +X ₂ )/2 and the average aspect ratio=(X ₁ +X ₂ )/2X ₃ , the average particle diameter of the coloring pigment is 7 to 30 μm, and the average aspect ratio is 20 or more. The surface-treated steel sheet according to any one of claims 1 to 3, wherein the average thickness T ₁ of the aforementioned coating film is 3 to 15 μm. The surface-treated steel sheet according to any one of claims 1 to 4, wherein the thickness of the aforementioned color pigment is 0.5T ₁ or less.