JP6658988B1 - Surface treated steel sheet - Google Patents

Abstract

The present invention provides a steel sheet, a Zn-based alloy plating layer formed on at least one surface of the steel sheet, and a coating having an average thickness T1 formed on the Zn-based alloy plating layer and containing a color pigment, an anticorrosive pigment, and a binder resin. The average concentration of the color pigment in the coating film is 5 to 15% by mass, and the average of the color pigments existing in the width T2 region in the thickness direction of the coating film from the surface of the coating film. The ratio CA1 / CA2 of the concentration CA1 and the average concentration CA2 of the color pigment present in the region of the width T2 in the thickness direction of the coating film from the interface of the coating film on the Zn-based alloy plating layer side is 0.2 to 0.9. And T2 (μm) = 0.1 × T1 (μm) +1.1 μm.

Description

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

  BACKGROUND ART Galvanized steel sheets such as galvanized steel sheets having excellent corrosion resistance and blackening resistance are widely used for home appliances, building materials, automobiles, and the like.

  The surface of various galvanized steel sheets such as a galvanized steel sheet may be deteriorated depending on the surrounding environment. For example, the plating layer is oxidized by an electrolyte such as salt contained in the air, or oxygen and moisture existing in a high-temperature and high-humidity environment, and white rust is generated. The generation of white rust impairs the uniformity of the appearance of the plated steel sheet. Therefore, the plated steel sheet is generally required to have corrosion resistance that suppresses the generation of white rust.

  In particular, when a plated steel sheet is used outdoors, such as for construction materials and outdoor home appliances, high corrosion resistance is required because it is more susceptible to the influence of the surrounding environment and easily deteriorates with age.

  As a technique for further improving the corrosion resistance of a galvanized steel sheet, a steel sheet plated with a Zn-based alloy such as a Zn-Al-Mg-based alloy is known.

  Zn-based alloy plated steel sheets are required to have both short-term corrosion resistance and long-term corrosion resistance. "Short-term corrosion resistance" means, for example, that the installer does not corrode during the period (about one year) before handing over the plated steel sheet to the orderer. "Long-term corrosion resistance" means, for example, that products such as building materials are not used. This means that the period until the required strength is not obtained by reducing the thickness by corrosion is as long as possible.

  Another property required for the Zn-based alloy plated steel sheet is blackening resistance. Black discoloration means that the plating layer is oxidized and discolored black. Blackening is particularly noticeable in Zn-Al-based alloy-plated steel sheets and Zn-Al-Mg-based alloy-plated steel sheets in which Al or Mg is added during galvanization. It is not preferable in use that the discoloration of the plated steel sheet is visually recognized from the appearance due to such blackening of the plating layer. Therefore, a Zn-based alloy-plated steel sheet such as a Zn-Al-Mg-based alloy-plated steel sheet is required to have excellent blackening resistance while having corrosion resistance.

  Patent Literature 1 has excellent blackening resistance and corrosion resistance including 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. A galvanized steel sheet is disclosed.

  Patent Document 2 discloses a chromate-free coated metal plate having a coating containing at least one surface of a metal plate using an organic resin as a film-forming component and having a surface inactivated and containing a flake-shaped aluminum pigment. It is taught that such a metal plate is excellent in corrosion resistance and blackening resistance.

  Further, in Patent Document 3, a steel sheet and a plated steel sheet having a plating layer disposed on the surface of the steel sheet, and a chemical conversion treatment film disposed on the surface of the plating layer, the chemical conversion treatment film is a fluororesin, a substrate A chemical conversion treated steel sheet containing a resin, metal flakes, and a chemical conversion treatment component is disclosed, and it is taught that the use of such a steel sheet can improve corrosion resistance and blackening resistance.

International Publication No. 2015/075792 WO 2013/065354 JP-A-2006-121390

  However, in the Zn-Al-Mg-based alloy-plated steel sheet described in Patent Document 1, a part of the aluminum pigment in the film protrudes from the surface of the film after production or when the surface of the film is reduced in thickness due to deterioration of the resin. May be. Then, starting from the protruding pigment, a path through which a corrosion factor such as oxygen can pass through the film is formed. As a result, the corrosion factor penetrates into the underlying plating layer through the path, and the plating layer Corrosion may progress. Therefore, there is room for improvement in corrosion resistance. Further, in Patent Document 1, the concentration distribution of the aluminum pigment in the film is not always sufficiently studied, and there is still room for improvement in blackening resistance.

  Further, in Patent Documents 2 and 3, control of the concentration distribution of a flake-like pigment such as aluminum is not always sufficiently studied, 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 having high corrosion resistance and excellent blackening resistance in a Zn-based alloy-plated steel sheet.

  The present inventors, in order to obtain a surface-treated steel sheet having such high corrosion resistance and excellent blackening resistance, a coloring pigment such as an aluminum pigment in a coating film formed on a Zn-based alloy plating layer. It has been found that it is important to control the average concentration to 5 to 15% by mass%. With such a control, the color pigment sufficiently covers and hides the Zn-based alloy plating layer when observed from a direction perpendicular to the surface of the coating film. Thereby, a change in appearance can be suppressed, and excellent blackening resistance can be obtained.

  The present inventors have also found that it is important to concentrate the coloring pigment on the Zn-based alloy plating layer side in the coating film. By concentrating the color pigment on the Zn-based alloy plating layer side in this way, it is possible to suppress the color pigment from protruding from the surface of the coating film, thereby suppressing the formation of a path of a corrosion factor and ensuring corrosion resistance. can do. Further, 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 closer distance to each other. Therefore, the coloring pigment can be distributed in the coating film at a high density, and the Zn-based alloy plating layer in a wider range can be effectively made invisible, and as a result, blackening resistance is improved.

The present invention has been made based on the above findings, and the gist thereof is as follows.
(1)
Steel, Zn-based alloy plating layer formed on at least one surface on the steel plate, and is formed on the Zn-based alloy plating layer, the average thickness T ₁ of the coating film containing a coloring pigment and a rust-preventive pigment and a binder resin Has,
The chemical composition of the Zn-based alloy plating layer is represented by mass%,
Al: 0.01 to 60%,
Mg: 0.001 to 10%, and Si: 0 to 2%,
The average concentration of the coloring pigment in the coating film is 5% to 15% by mass,
The average concentration C _{A1 of the} coloring pigment present in a region of width T ₂ in the thickness direction of the coating film from the surface of the coating film, and the thickness of the coating film from the interface of the coating film on the Zn-based alloy plating layer side. A ratio C _A1 / C _A2 of 0.2 to 0.9 with respect to the average concentration C _A2 of the color pigment present in the direction of width T _{2 in} the direction,
A surface-treated steel sheet, wherein T ₂ (μm) = 0.1 × T ₁ (μm) +1.1 μm.
(2)
The average concentration of the rust preventive pigment in the coating film is 3 to 12% by mass%,
The thickness of the from the surface of the coating film and the average concentration C _B1 of the rust-preventive pigment present in the thickness direction of the width T ₂ areas of the coating, the coating film coating the surface of said Zn alloy plating layer side A ratio C _B1 / C _B2 with respect to the average concentration C _B2 of the rust-preventive pigment present in the region of width T ₂ in the width direction is 1.3 to 4.0,
T ₂ (μm) = 0.1 × T ₁ (μm) +1.1 μm,
The surface-treated steel sheet according to (1), wherein the rust preventive pigment contains one or more of Si, Mo, W, and Ba.
(3)
The color pigment has a major axis X _{1 of} 5 to 30 μm, a minor axis X ₂ of ₁ to 30 μm, and a thickness X _{3 of} 0.0025 μm or more, and the average particle size is (X ₁ + X _2). ) / 2 and the average aspect ratio = (X ₁ + X ₂ ) / 2X ₃ , the average particle diameter of the color pigment is 7 to 30 μm, and the average aspect ratio is 20 or more. , (1) or (2).
(4)
The average coating film thickness T ₁ is characterized in that it is a 3 to 15 [mu] m, (1) a surface treated steel sheet according to any one of - (3).
(5)
The thickness of the colored pigment is 0.5 T ₁ or less, (1) a surface treated steel sheet according to any one of to (4).

  According to the present invention, the average concentration of the coloring pigment in the coating film is 5 to 15% by mass, and the coloring pigment is concentrated on the Zn-based alloy plating layer side in the coating film. In order to suppress the formation of a path of the corrosion factor by protruding the coloring pigment from the coating film, and to make the Zn-based alloy plating layer not sufficiently visible when observed from a direction perpendicular to the surface of the coating film. A surface-treated steel sheet having high corrosion resistance and excellent blackening resistance can be provided. In particular, the surface-treated steel sheet according to the present invention has high corrosion resistance and resistance even when the thickness of the coating film is reduced because the coloring pigment in the coating film is concentrated on the Zn-based alloy plating layer side. Blackening can be provided.

[Surface treated steel sheet]
The surface-treated steel sheet according to the present invention is a steel sheet, a Zn-based alloy plating layer formed on at least one surface of the steel sheet, and an average containing a coloring pigment, a rust-preventive pigment, and a binder resin formed on the Zn-based alloy plating layer. It has a coating film of thickness T ₁ , and 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% , and the average density of the colored pigment in the coating film, by mass%, 5 to 15%, the average concentration of the coloring pigment present from the surface of the coating film in a thickness direction of the width T ₂ areas of the coating a C _A1, the ratio C _A1 / C _A2 between the average concentration C _A2 of coloring pigment present from the interface of Zn alloy plating layer side of the coated film in a thickness direction of the width T ₂ areas of the coating and 0.2 ０．９0.9, and T ₂ (μm) = 0.1 × T ₁ (μm) +1.1 μm. Hereinafter, constituent components of the surface-treated steel sheet according to the present invention will be described.

<Steel plate>
The steel sheet (plated steel sheet) in the present invention is not particularly limited, and a general steel sheet such as a hot-rolled steel sheet or a cold-rolled steel sheet can be used. The type of steel is also not particularly limited, and for example, Al-killed steel, ultra-low carbon steel containing Ti, Nb, and the like, and high-strength steel containing elements such as P, Si, Mn, and the like can be used. is there. The thickness of the steel sheet in the present invention is not particularly limited, but may be, for example, 0.25 to 3.5 mm.

<Zn-based alloy plating layer>
The Zn-based alloy plating layer in the present invention is formed on a steel plate. The Zn-based alloy plating layer may be formed on one side of the steel sheet or on both sides. The Zn-based alloy plating layer may be a Zn-Al-Mg alloy plating layer containing at least Al and Mg, or may be a Zn-Al-Mg-Si alloy plating layer containing Si. The contents (concentrations) of these are, 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 the chemical composition of the Zn-based alloy plating layer is simply described as “%”, it means “% by mass”.

  If the Al content of the Zn-based alloy plating layer is less than 0.01%, the effect of improving the corrosion resistance of the plated steel sheet due to the inclusion of Al is not sufficiently exhibited, and if it exceeds 60%, the effect of improving the corrosion resistance is saturated. Therefore, the Al content may be 0.01% or more, for example, 0.1% or more, 0.5% or more, 1% or more, 3% or more, or 5% or more, and 60% or less, for example, , 55% or less, 50% or less, 40% or less, or 30% or less. The 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 due to the inclusion of Mg may not be sufficiently exhibited. On the other hand, if it exceeds 10%, Mg is not completely dissolved in the plating bath and floats as an oxide (generally called dross). When zinc plating is performed in this plating bath, the oxide adheres to the surface layer of the plating to cause poor appearance, There is a possibility that a portion that is not plated (generally called non-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, it may be 8% or less, 6% or less, 5% or less, or 4% or less. The Mg content is preferably 1 to 5%, more preferably 1 to 4%.

  The lower limit of the Si content of the Zn-based alloy plating layer may be 0%, but it may be 0.001% to 2% in order to further improve the corrosion resistance of the Zn-based alloy plating layer. The Si content may be, for example, 0.005% or more, 0.01% or more, 0.05% or more, 0.1% or more, or 0.5% or more, or 1.8% or less. It may be 1.5% or less or 1.2% or less. The Si content is preferably 0.1 to 2%, more preferably 0.5 to 1.5%.

  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 may be 1 to 30 μm.

<Coating>
The coating film in the present invention is formed on a Zn-based alloy plating layer. The coating film contains a rust preventive pigment and a binder resin in addition to the color pigment. The average thickness T ₁ of the coating film may be any value as long as sufficient corrosion resistance and blackening resistance are ensured, and for example, is preferably 3 μm or more and 15 μm or less. When the average thickness T ₁ of the coating film is less than 3 μm, the possibility that a part of the coloring pigment protrudes from the coating film and the corrosion factor reaches the alloy plating layer increases, and there is a possibility that sufficient corrosion resistance may not be secured. . Furthermore, the thickness is insufficient to ensure the effect of making the Zn-based alloy plating layer invisible by the coloring pigment in the coating film, and blackening resistance may be deteriorated. When the average thickness T ₁ of the coating film is more than 15 μm, the effect of improving the corrosion resistance and blackening resistance by increasing the average thickness of the coating film is 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 the present specification, “blackening resistance” does not mean that blackening of a Zn-based alloy plating layer underlying a coating film is not suppressed, and even if blackening occurs in the Zn-based alloy plating layer. This means that blackening is not seen from the outside due to the coloring pigment in the coating film, so that the appearance of the surface-treated steel sheet is not changed.

As used herein, “average thickness T ₁ ” refers to any of five locations on the interface of the coating film on the Zn-based alloy plating layer side, which is obtained by observing the cross section of the steel sheet having the coating film with a microscope. Is measured as the shortest distance from the position to the surface of the coating film, respectively, and is defined as a value obtained by averaging those measured values. When a substance having a larger particle size than the film thickness (eg, aggregate) is contained in the coating film, the distance is measured at a position where the substance does not exist. This is because the presence of such a substance may cause the distance to be measured to be larger than the actual thickness of the coating when the coating is observed from the cross-sectional direction. Further, another layer such as a chemical conversion treatment layer may be present between the Zn-based alloy plating layer and the coating film. If such another layer is present, the thickness of the layer is not included in the average thickness T _1.

(Color pigment)
As the coloring pigment in the present invention, for example, a general coloring pigment such as titanium oxide, zinc oxide, iron oxide, aluminum oxide, barium sulfate, aluminum, or carbon black can be used. Preferably, the color pigment is aluminum. However, aluminum reacts with water and elutes. Therefore, when a water-based paint is used as a paint for forming a coating film as in the present invention, it is necessary to coat aluminum with an oxide or a resin.

  The average concentration (average content) of the coloring pigment in the coating film is 5 to 15% by mass%. By keeping the average concentration of the color pigment in such a range and concentrating the color pigment in the vicinity of the interface with the Zn-based alloy plating layer, even with a relatively thin film thickness as compared with a coating film of a general coated steel sheet. Even if there is, when observed from a direction perpendicular to the surface of the coating film, the amount of the colored pigment that sufficiently covers and covers the Zn-based alloy plating layer can be secured. Further, it is possible to sufficiently suppress the color pigment from protruding from the surface of the coating film. Therefore, while maintaining high corrosion resistance, the coloring pigment makes the blackening of the Zn-based alloy plating layer invisible, whereby a 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 in the coating film for making the blackening of the Zn-based alloy plating layer invisible becomes insufficient, and the blackening resistance decreases. On the other hand, if the average concentration of the coloring pigment in the coating film is more than 15%, a large amount of the coloring pigment is present in the coating film, and when the coating film is reduced in thickness, a part of the coloring pigment is removed at a relatively early stage. The possibility of protruding from the surface of the coating film increases, and the corrosion resistance may deteriorate. Further, the adhesion may be reduced. The average concentration of the color 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 is preferably 5 to 12%, more preferably 5 to 10%.

  As used herein, the "average concentration of the color pigment in the coating film" is measured using a glow discharge optical emission spectrometry (GD-OES). Specifically, when the type of the coloring pigment, that is, the specific compound of the coloring pigment, is known, the coating film is sputtered from the surface toward the plating layer, and the main elements constituting the coloring pigment are deepened. The density profile in the vertical direction is measured every 1.0 μm. Thereafter, the average value of the measured concentrations of the main elements is determined, and the measured concentration is converted based on the molecular weight of the compound of the known coloring pigment, thereby determining the average concentration of the coloring pigment in the coating film. When the type of the color pigment, that is, the specific compound of the color pigment is unknown, the field emission electron probe microanalyzer (Field Emission-Electron Probe) is used for the color pigment from the cross section of the coating film (the surface perpendicular to the surface of the coating film). After specifying the type of the color pigment by elemental analysis using a Micro Analyzer (FE-EPMA), the “average concentration of the color pigment in the coating film” may be measured as described above.

The coloring pigment in the coating film is concentrated on the Zn-based alloy plating layer side. The index of the concentration of the coloring pigment is calculated from the average concentration C _A1 of the coloring 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 interface of the coating film on the Zn-based alloy plating layer side. The ratio is determined by the ratio C _A1 / C _A2 with respect to the average concentration C _A2 of the coloring pigment present in the region of the width T ₂ in the thickness direction of the coating film. The ratio C _A1 / C _A2 of the surface-treated steel sheet according to the present invention is 0.2 or more and 0.9 or less. Here, the width T ₂ is determined by the following equation: T ₂ (μm) = 0.1 × T ₁ (μm) +1.1 μm. That is, according to the mean value of the thickness T ₁ of the coating film, the width T ₂ of the measuring region of the average concentration C _A1 and C _A2 of the coloring pigment are determined. More specifically, as described above, the average thickness T ₁ of the coating film is determined from the cross-sectional observation of the coating film, and the width T ₂ of the measurement area of C _A1 and C _A2 is determined from the above equation based on the T _1. Is determined, and the average concentration C _A1 and C _A2 of the color pigment are measured within the width T ₂ . Incidentally, an area for determining the C _A1, even if a an area for determining the C _A2 overlap (i.e., when it is T _2> 0.5T _1), the C _A1 and C _A2, as described above Measurement and the ratio C _A1 / C _A2 can be determined. When T ₂ > T ₁ (for example, when T ₁ = 1.2 μm), such a 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 according to 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 rust-preventive pigment is relatively concentrated too much on the surface side of the coating film, and the rust-preventive pigment is produced in a relatively short time when the coating film is reduced in thickness. Is exposed, and sufficient long-term corrosion resistance cannot be obtained. On the other hand, if the ratio C _A1 / C _A2 exceeds 0.9, the effect of thickening the coloring pigment cannot be obtained, and a part of the coloring pigment protrudes from the coating film, resulting in insufficient corrosion resistance. Further, when the thickness of the coating film is reduced, the concentration of the coloring pigment in the coating film is insufficient, so that the Zn-based alloy plating layer cannot be effectively made invisible and the blackening resistance becomes insufficient. The C _A1 / C _A2 ratio may be, for example, 0.3 or more or 0.4 or more, and 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 more preferably the C _A1 / C _A2 ratio is 0.4 or more and 0.7 or less.

"Average concentration C _{A1 of} color pigment present in a 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 coating film on the Zn-based alloy plating layer side. The “average concentration C _A2 of the color pigment present in the region of the width T ₂ ” is measured using GD-OES in the same manner as the measurement of “average concentration of the color pigment in the coating film”. Specifically, sputtering is performed in the depth direction of the Zn-based alloy plating layer from the surface direction of the coating film, and the concentration distribution in the depth direction of the coating film for each of the main elements constituting the color pigment is changed by 0.1 μm. measured in the range of T _2. Thereafter, the average value of the measured concentrations of the main elements is determined, and the measured concentration is converted based on the molecular weight of the compound of the known coloring pigment, thereby determining the average concentration of the coloring pigment in the coating film. By measuring the relationship between the sputtering time and the coating film depth in advance, the sputtering time can be converted to coating film thickness information. By measuring the concentration distribution of the elements constituting the color pigment in the film thickness direction, C _A1 and C _A2 can be obtained.

The color pigment in the coating film is concentrated on the Zn-based alloy plating layer side in the coating film so that the value of the ratio C _A1 / C _A2 becomes 0.2 to 0.9 in the coating film. In addition, the concentration of the coloring pigment on the surface side of the coating film becomes relatively low. Thereby, after manufacturing or when the surface of the coating film is reduced in thickness, it is possible to suppress a portion of the coloring pigment from protruding from the surface of the coating film. Therefore, the generation of the passage of the corrosion factor can be suppressed, so that high corrosion resistance can be secured. Further, since the concentration of the coloring pigment on the surface side of the coating film is reduced, when the surface of the coating film is reduced in thickness, the coloring pigment is prevented from falling off, and blackening resistance is maintained for a long time. Therefore, under the condition that the average concentration of the coloring pigment in the coating film is constant, the surface-treated steel sheet according to the present invention has a Zn-based alloy plating layer in comparison with the case where the coloring pigment is uniformly distributed in the coating film. It can be effectively invisible from the outside, so that blackening resistance is significantly improved. In addition to this, another advantage of distributing the coloring pigment in a narrow region is that when a pigment having an orientation having a high average aspect ratio (for example, flaky or flat) is used, The direction can be aligned parallel or substantially parallel to the surface of the coating film, and the plating layer can be more effectively made invisible to improve blackening resistance.

  The colored pigment according to the present invention can be in any shape as long as sufficient corrosion resistance and blackening resistance are ensured.Examples of the shape of the colored pigment include, but are not limited to, spherical, elliptical, acicular, Examples of the shape include a flat shape, a thin plate shape, a scale shape, and a spindle shape. The color pigment in the present invention is preferably in the form of a scale to make the Zn-based alloy plating layer more invisible and to obtain excellent blackening resistance.

As used herein, the “average particle size” and “average aspect ratio” of the color pigment according to the present invention are determined by the following method. First, an arbitrary color pigment is elementally mapped from the surface by FE-EPMA, and the major axis X ₁ and minor axis X ₂ of the color pigment are determined. Here, the major axis X ₁ means the length of the largest line segment that traverses the color pigment within the outline of the color pigment image specified by the element mapping, and the minor axis X ₂ refers to the color pigment. It means the length of the perpendicular line to the major axis X ₁ across the. Next, the elemental mapping by FE-EPMA from the sectional direction, (typically dimension of perpendicular to the measurement plane above the major axis to the minor axis) thickness X ₃ for measuring the value of. Next, from these measured values, the particle size of the color pigment = [(X ₁ + X ₂ ) / 2] and the aspect ratio = [(X ₁ + X ₂ ) / 2X ₃ ] are obtained. Then, the particle size and the aspect ratio of any 10 or more coloring pigments are determined by using the same method, and the “average particle size” and “average aspect ratio” of the coloring pigment are determined by averaging them.

The major axis X ₁ , minor axis X ₂ and thickness X ₃ of the color pigment according to the present invention can be any value as long as they can be present in the coating film. For example, the major axis X ₁ is 5 μm or more and 30 μm or less. It is preferable that the short diameter 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 the major axis, the minor axis, and the thickness in such a range, the Zn-based alloy plating layer can be effectively made invisible while suppressing the color pigment from protruding from the coating film. The average particle size of the coloring pigment according to the present invention is preferably, for example, 7 μm or more and 30 μm or less, and the average aspect ratio is preferably 20 or more. By having the average particle diameter in such a range, the Zn-based alloy plating layer can be effectively made invisible while suppressing the color pigment from protruding from the surface of the coating film. In addition, since the color pigment has a high aspect ratio, the wide range of the Zn-based alloy plating layer can be made invisible by the color pigment, and the blackening resistance can be further increased. When the average particle size of the color pigment is less than 7 μm, the Zn-based alloy plating layer cannot be sufficiently made invisible, and the blackening resistance may be insufficient. On the other hand, when the average particle size of the color pigment exceeds 30 μm, the possibility that the color pigment protrudes from the coating film increases, and there is a possibility that sufficient corrosion resistance may not be secured. On the other hand, if the average aspect ratio is less than 20, the Zn-based alloy plating layer cannot be sufficiently invisible, and blackening resistance may be insufficient. The average particle size of the color pigment according to the present invention is more preferably 10 μm or more and 25 μm or less. Further, the average aspect ratio is more preferably 25 or more, and further preferably 30 or more. The upper limit of the average aspect ratio is not limited, but may be, for example, 100. Furthermore, in order to obscure more effectively Zn alloy plating layer with a colored pigment, the value of the major axis X ₁ and the minor axis X ₂ are close, ie, the ratio X ₁ / X ₂ is close to 1.0 Is more advantageous. 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 still more preferably 1.0 or more and 2.0 or less. There can be.

Since the coloring pigment according to the present invention is contained in the coating film, the thickness X ₃ of the coloring pigment is smaller than the average thickness T ₁ of the coating film. Further, when the coloring pigment protrudes from the coating film, a corrosive factor intrusion path may be formed and the corrosion resistance may be deteriorated. Therefore, the thickness X ₃ of the coloring pigment is smaller than the average thickness T ₁ of the coating film. Is more advantageous. For example, the thickness X ₃ of the color pigment is preferably not 0.5 T ₁ or less, more preferably 0.4 T ₁ or less.

(Rust prevention pigment)
The rust preventive pigment used in the coating film of the present invention may include one or more of Si, Mo, W and Ba. Preferably, it contains one or more of Si, Mo and Ba. Specific examples of these compounds include, but are not limited to, silica (manufactured by Grace, MSK-8D), calcium-modified silica (manufactured by WR Grace, SHIELDEXC303), barium borate (reagent manufactured by Showa Chemical Co., Ltd.) ), Barium metaborate (reagent from Showa Chemical Co., Ltd.), zinc molybdate (reagent from Wako Pure Chemical Industries, Ltd.), calcium molybdate (reagent from Wako Pure Chemical Industries, Ltd.), sodium tungstate (reagent from Kanto Chemical Co., Ltd.), Examples include calcium tungstate (a reagent manufactured by Kanto Chemical Co., Ltd.) and tungsten oxide (a reagent manufactured by Kanto Chemical Co., Ltd.). Preferably, the rust preventive pigment is silica. Further, the rust preventive pigment can be porous. By making it porous, the specific surface area is large and the apparent specific gravity is low, so that it becomes easier to concentrate on the surface side of the coating film. For example, as the rust preventive pigment, a rust preventive pigment (for example, silica) 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 may be used. it can. The upper limit of the specific surface area of the rust preventive pigment is not particularly limited, but may be, for example, 500 m ² / g. In this specification, the "apparent specific gravity" is the density when the rust-preventive pigment itself and the internal voids are defined as volumes, and includes the "volume of the rust-proof pigment itself" and the "volume of the internal voids" It is.

  The average concentration of the rust preventive pigment in the coating film can be 3 to 12% by mass. By setting the content in such a range, the coating film sufficiently functions as a film for preventing corrosion of the Zn-based alloy plating layer, and high corrosion resistance can be provided. If the average concentration of the rust-preventive pigment in the coating film is less than 3%, the concentration of the rust-preventive pigment in the entire coating film is insufficient, irrespective of the distribution of the concentration of the rust-preventive pigment in the coating film, and the corrosion resistance is sufficient. May not be obtained. On the other hand, when the average concentration of the rust-preventive pigment in the coating film is more than 12%, the effect of improving the corrosion resistance by increasing the amount of the rust-preventive pigment is reduced, which may be disadvantageous in cost. Further, the adhesion may be reduced. The average concentration of the rust preventive 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 rust preventive pigment in the coating film is preferably 5 to 12% or less, more preferably 5 to 10% or less.

  Here, the “average concentration of the rust-preventive pigment in the coating film” is determined using the same method as the above-mentioned “average concentration of the coloring pigment in the coating film”.

The rust preventive pigment in the coating film is concentrated on the surface side of the coating film. Indication of enrichment of anticorrosive pigments from the surface of the coating film and the average concentration C _B1 anticorrosive pigment present in the thickness direction of the width T ₂ areas of the coating, the Zn alloy coated layer side of the coating It is determined by the ratio C _B1 / C _B2 with respect to the average concentration C _B2 of the rust preventive pigment existing in the region of width T ₂ in the thickness direction of the coating film from the interface. As described above, T ₂ (μm) = 0.1 × T ₁ (μm) +1.1 μm. The ratio C _B1 / C _B2 of the surface-treated steel sheet according to the present invention is 1.2 or more and 5.0 or less when the above-mentioned ratio C _A1 / C _{A2 of} the color pigment is 0.2 or more and 0.9 or less. In order to more reliably obtain the effect of concentrating the rust-preventive pigment on the surface layer side, it is preferable that the ratio be 1.3 or more and 4.0 or less. If the ratio C _B1 / C _B2 is less than 1.3, the effect of thickening the rust-preventive pigment, that is, improvement in long-term flat portion corrosion resistance, may not be obtained. On the other hand, when the ratio C _B1 / C _B2 exceeds 4.0, the rust-preventive pigment is excessively concentrated on the surface side of the coating film, and the rust-preventive pigment is reduced in a relatively short time when the coating film loses its thickness over time. The surface where the pigment is insufficient may be exposed, and sufficient long-term corrosion resistance may not be obtained. 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 more preferably the ratio C _B1 / C _B2 is 1.8 or more and 3.2 or less.

C _B1 and C _B2 are obtained in the same manner as C _A1 and C _A2 described above.

The rust-preventive pigment in the coating film is distributed in the coating film such that the value of the ratio C _B1 / C _B2 is 1.3 or more and 4.0 or less, that is, the rust-preventive pigment is distributed on the surface side of the coating film. By thickening, the corrosion resistance of the surface of the coating film is sufficiently improved, and the long-term corrosion resistance in the flat portion is further improved.

The average particle size of anticorrosive pigment can be appropriately selected depending on the average thickness T _1, etc. of the coating film, it can be 0.2 to 10 [mu] m. The average particle size of the rust preventive pigment is preferably 0.4 to 8 μm, more preferably 0.5 to 6 μm.

The average particle size of the rust-preventive pigment can be determined in the same manner as the above-described average particle size of the color pigment. That is, for 10 or more rust-preventive pigments, element mapping by FE-EPMA is performed from the surface and cross-sectional direction of the coating film, and the major axis Y ₁ , the minor axis Y ₂ and the thickness Y ₃ of the rust-preventive pigment are obtained. The average particle size of the rust preventive pigment can be determined from the value.

From the viewpoint of adhesion, the thickness Y ₃ of the anticorrosive pigment is preferably somewhat smaller than the average thickness T ₁ of the coated film in the same manner as color pigments, for example, the thickness Y ₃ of the rust-preventive pigment , preferably at 0.5 T ₁ or less, more preferably 0.4 T ₁ or less, even more preferably at 0.3 T ₁ or less, most preferably 0.1 T ₁ or less.

(Binder resin)
The binder resin used as a component of the coating film in the present invention is preferably a polyester resin, a urethane resin, or an acrylic resin. In the present invention, it is important to use an imino group type melamine resin as a curing agent for these resins. Preferably, the binder resin in the present invention is a polyester resin. The polyester resin used in the present invention preferably has a glass transition temperature Tg of -20 to 70 ° C and a number average molecular weight of 3,000 to 30,000. When the binder resin is a urethane resin, Tg is preferably from 0 to 50 ° C and the number average molecular weight is preferably from 5,000 to 25,000. When the binder resin is an acrylic resin, the Tg is preferably from 0 to 50 ° C. and the number average molecular weight is preferably from 3,000 to 25,000. In the present invention, an aqueous solvent is used as a solvent for the binder resin.

  In the coating film of the present invention, if necessary, wax such as polyethylene wax or PTFE wax, resin beads such as acrylic resin beads or urethane resin beads, and phthalocyanine blue, phthalocyanine green, methyl orange, methyl violet, Alternatively, a dye such as alizarin can be added. The addition of these is more preferable because the strength of the coating film is increased and a desired color can be imparted to the coating film. These addition amounts may be appropriately determined so as not to be disadvantageous for the coating film in the present invention.

  In particular, dyes can be used as colorants in order to impart the desired color to the coatings according to the invention, and thus to the surface-treated steel sheet according to the invention. The dye may be used alone, or a plurality of dyes may be used in combination. The type of the dye that can be used in the coating film of the present invention is not particularly limited, and a known dye can be used.For example, phthalocyanine blue, phthalocyanine green, methyl orange, methyl violet, or alizarin is used. be able to.

[Production method of surface-treated steel sheet]
An example of the method for producing a surface-treated steel sheet according to the present invention will be described below. The surface-treated steel sheet according to the present invention is, for example, an aqueous solution obtained by adding a coloring pigment and a rust-preventive pigment on a Zn-based alloy plating layer formed on the steel sheet, and adding an imino-based melamine resin as a curing agent for the binder resin. It can be manufactured by applying a coating material and heating it according to a predetermined heat pattern to cure the coating material.

<Formation of Zn-based alloy plating layer>
As the steel sheet, a steel sheet having an arbitrary 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. The Zn-based alloy plating layer can be formed by, for example, hot-dip Zn-Al-Mg alloy plating on a steel plate to a thickness of 1 to 30 μm. Hot-dip plating can be performed, for example, in a hot-dip plating bath at 400 to 550 ° C. to which various metals are added. The Al and Mg contents are, in mass%, Al: 0.01 to 60%, Mg: 0.001 to 10%, and the balance is typically Zn and impurities. Further, in addition to the chemical composition as described above, a Zn-Al-Mg-Si alloy plating layer containing 0.001 to 2% by mass of Si can be formed.

<Preparation of paint>
The coating material is obtained by mixing a binder resin such as a polyester resin (for example, molecular weight: 16000, Tg: 10 ° C.) dispersed in a solvent and an imino group type melamine resin at a solid content mass ratio of 100: 10 to 100: 30, Next, the mixture can be obtained by dispersing a predetermined amount of a coloring pigment and a rust preventive pigment in the mixture. As the solvent, an aqueous solvent (for example, water) is used.

  As described above, in the surface-treated steel sheet according to 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 Zn-based alloy plating layer side. The formation of such a concentration distribution of the rust-preventive pigment and the coloring pigment can be achieved by utilizing a phenomenon that the imino group-type melamine resin is concentrated on the surface layer of the coating film when the resin is cured under specific conditions. The present inventors have found. That is, the concentration of the rust-preventive pigment on the surface side of the coating film is reduced by selecting an rust-preventive pigment (for example, porous silica) having a smaller apparent specific gravity than the color pigment, that is, a large specific surface area. When the base melamine resin concentrates on the surface layer of the coating film, the rust-preventive pigment moves to the surface layer together with the melamine resin. Regarding the mechanism of this thickening, not only the effect of the apparent specific gravity difference between the coloring pigment and the rust-preventive pigment, but also the chemical affinity between the imino-based melamine resin and the rust-preventive pigment, It is considered that the rust preventive pigment concentrates on the surface side of the coating film together with the concentration of the imino group type melamine resin on the surface layer by acting.

  Further, as in the present invention, when an aqueous coating is used as a coating for forming a coating film, the concentration of the imino group type melamine resin on the surface layer is more remarkable than when a solvent is used. The present inventors have found. This is considered to be because the imino group type melamine resin, which did not crosslink with polyester or the like when the coating was cured to form a coating film, was present more in the aqueous coating than in the solvent-based coating. In other words, in the case of a water-based paint, the crosslinking reaction between the reactive functional group (OH group) inside the emulsion particle and the imino group type melamine resin is caused by the dispersion of the polyester resin and the like in the emulsion state. This is considered to be due to inhibition and an increase in excess imino group type melamine resin. Thereby, it is considered that the self-condensation reaction of the imino group-type melamine easily occurs rather than the crosslinking reaction, and the concentration of the imino group-type melamine resin on the surface layer is remarkable. Furthermore, the effect of concentrating the imino-based melamine resin in water-based paints is large because the compatibility between water and melamine is low and the surface free energy of the imino-based melamine resin is smaller than that of water. It can be considered that this is because the melamine resin easily floats on the surface layer. Therefore, in the present invention, it is effective to use an aqueous solvent as a solvent in order to promote the concentration of the imino group type melamine resin in the surface layer.

  As the melamine resin, a methylated melamine resin and a butylated melamine resin are generally known in addition to the imino group type melamine resin used in the present invention. However, when a methylated melamine resin is added as a hardening agent in the water-based paint, the phenomenon of concentration of the rust-preventive pigment on the surface layer during baking does not significantly occur, and butylation as a hardening agent in the water-based paint. The present inventors have found that when a melamine resin is used, the coating solidifies when mixed with an aqueous solvent and cannot be used as a coating. Therefore, in order to obtain a coating film as in the present invention, it is extremely effective to use a combination of an aqueous solvent, a binder resin, and an imino group type melamine resin as a curing agent for the binder resin.

Due to the nature of the imino-based melamine resin in such an aqueous paint, when the rust-preventive pigment is concentrated on the surface side of the paint film, a relatively heavy colored pigment such as aluminum in the paint film is coated. Are hardly distributed on the surface side, and relatively concentrated on the Zn-based alloy plating layer side. In other words, as the rust-preventive pigment concentrates on the surface side of the coating film, the coloring pigment is pressed down so as to remain on the Zn-based alloy plating layer side in the coating film. In this way, a surface-treated steel sheet having a rust-preventive pigment ratio C _B1 / C _B2 of 1.2 to 5.0, preferably 1.3 to 4.0 in the coating film is obtained. The surface-treated steel sheet according to the present invention, in which the ratio C _A1 / C _A2 of the coloring pigment in the coating film is 0.2 or more and 0.9 or less, is obtained. Further, in order to concentrate the rust-preventive pigment and the color pigment on the surface layer side and the Zn-based alloy plating layer side, respectively, depending on the properties of the imino group type melamine resin in the water-based paint, the particle size and specific gravity of the rust-preventive pigment must be selected. Is valid. In order to obtain the concentration distribution of the rust preventive pigment and the coloring pigment according to 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.

  When it can be used in combination with the coloring pigment and the rust-preventive pigment, an acidic catalyst can be added to the paint, if necessary, in order to concentrate the melamine resin in the surface layer of the coating film. Examples of the acidic catalyst include, but are not limited to, a weak acidic catalyst (Catalyst 296-9 / Ornex Japan), a strong acidic catalyst (Catalyst 600 / Ornex Japan), or an amine block strong acidic catalyst (Catalyst). 602 / Ornex Japan). The acidic catalyst is added, for example, in the coating material in an amount of 0.1 to 1.0% by mass.

<Formation of coating film>
Next, the obtained paint can be applied on the Zn-based alloy plating layer to a predetermined thickness, for example, by a roll coater or the like, and can be baked and cured in a predetermined heat pattern. In the baking, the steel sheet is heated at a heating rate of 5 to 70 ° C./sec to finally reach a steel sheet temperature of 180 to 230 ° C. Specifically, in the process of heating to the steel sheet temperature, the steel sheet temperature may be maintained at 70 to 150 ° C., preferably 100 to 150 ° C., for 1 to 5 seconds, preferably 1 to 3 seconds. is important. That is, after the coating material is applied on the Zn-based alloy plating layer, the coated steel sheet at room temperature (for example, 20 ° C.) is once heated to 70 to 150 ° C. (first heating step) and held at that temperature for 1 to 5 seconds. (Temperature holding step) and further heating to 180 to 230 ° C. (second heating step), the coating film of the present invention is obtained. Such a heat pattern can be realized with two heating furnaces. Specifically, the heating furnace A and the heating furnace B are installed in order with respect to the passing direction of the Zn-based alloy plated steel sheet to which the paint is applied, and the heating treatment is performed between the heating furnace A and the heating furnace B. It is preferable to provide a temperature holding region where the temperature is not kept. Therefore, the temperature of the coated steel sheet coated with the paint in the heating furnace A is raised to a temperature of 70 to 150 ° C., and the temperature is maintained in the temperature holding region at the temperature for 1 to 5 seconds. The temperature can be raised to an intermediate temperature to cure the paint. The heat pattern may be performed continuously as described above, or may be performed batchwise.

  By performing the temperature holding step at the holding temperature and the holding time as described above, the rust preventive pigment can be efficiently concentrated on the surface layer as the surface layer of the imino group type melamine resin is concentrated. When the holding time as described above is not provided and / or when the temperature in the first heating step is too high, the concentration of the rust preventive pigment according to the present invention, and hence the concentration of the color pigment, can be efficiently obtained. May not be possible. In particular, when the holding temperature exceeds 150 ° C., the binder resin and the curing agent react with each other, the viscosity of the coating material increases, and the rust preventive material hardly moves to the surface layer. May not be obtained.

The concentration ratio of the rust-preventive pigment according to the present invention (the concentration ratio of the color pigment) is based on the melamine concentration as described above, and can be controlled by the melamine resin used and the melamine resin concentration. In addition, it can be adjusted by the heat pattern at the time of curing the coating film, the average particle diameter and specific gravity of the rust preventive pigment, and the like. Specifically, an aqueous solvent, a binder resin such as a polyester resin, and a curing agent that is an imino group-type melamine resin are used, and the ratio of the binder resin to the curing agent is in the range of 100: 10 to 100: 30. And a coloring pigment and a rust-preventive pigment are added to prepare a paint. And as mentioned above, after apply | coating such a coating material on a Zn-based alloy plating layer, it heats once to 70-150 degreeC, after hold | maintained at the heated temperature for 1 to 5 seconds, further, 180-230 degreeC Heat to steel sheet temperature. By doing so, it is possible to effectively cause the rust-preventive pigment to concentrate on the surface layer side and, accordingly, the color pigment to concentrate on the Zn-based alloy plating layer side. It is effective that the average particle size of the rust preventive pigment to be added to the paint is 0.2 to 10 μm and the specific surface area is 20 m ² / g or more.

By using the manufacturing method as described above, the surface-treated steel sheet according to the present invention can be manufactured. That is, the average concentration C _A1 of the color pigment present 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 thickness direction of the coating film from the interface of the coating film on the Zn-based alloy plating layer side. The ratio C _A1 / C _A2 to the average concentration C _A2 of the coloring pigment present in the region of the width T ₂ is 0.2 or more and 0.9 or less, and T ₂ (μm) = 0.1 × T ₁ (μm) A surface-treated steel sheet having a size of +1.1 μm can be manufactured.

  The surface-treated steel sheet according to the present invention will be described in more detail below with some examples. However, the specific examples described below are not intended to limit the scope of the claimed invention.

<Preparation of surface-treated steel sheet sample>
(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 having a chemical composition of about 11% Al, about 3% Mg, and about 86% Zn at about 450 ° C. for about 3 to 5 seconds. Then, a Zn-11% Al-3% Mg alloy plating layer having a thickness of about 10 μm was formed. Further, the composition of the hot-dip 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. A layer was formed. Alternatively, a cold-rolled steel sheet having a thickness of 1 mm is placed in a hot-dip plating bath having a chemical composition of about 11% Al, about 3% Mg, about 1% Si and about 85% Zn at about 450 ° C. After immersion for 2 seconds, a Zn-11% Al-3% Mg-1% Si alloy plating layer having a thickness of about 10 μm was formed on the cold-rolled steel sheet. Further, the composition of the hot-dip plating bath was changed, and a Zn-11% Al-3% Mg-0.4% Si alloy plating layer having a thickness of about 10 μm and a Zn-11% Al A -3% Mg-1.5% Si alloy plating layer was formed.

(Preparation of paint)
A polyester resin (molecular weight: 16,000; glass transition point: 10 ° C.) as a binder resin was dispersed in water as an emulsion, and the pH was adjusted to 8.0 to 9.0. An imino group type melamine resin was mixed therein. The concentration ratio between the polyester resin and the imino group type melamine resin was 100: 20. Next, in the mixture, as a color pigment, resin-coated aluminum having an average particle diameter of 10 μm and an average aspect ratio of 25 (long diameter X ₁ : 12 μm, short diameter X ₂ : 8 μm, thickness X ₃ : 0.40 μm); As rust pigments, two Si compounds having an average particle size of 3 μm (silica A: specific surface area 320 m ² / g, silica B: specific surface area 180 m ² / g), and two Ba compounds (barium borate A: specific surface area 40 m ² / g) , Barium borate B: specific surface area 4.2 m ² / g), Mo compound (calcium molybdate: specific surface area 80 m ² / g) or W compound (tungsten oxide: specific surface area 40 m ² / g). To prepare a paint. As will be described later, the amounts of the coloring pigment and the rust-preventive pigment were appropriately adjusted so that a desired concentration could be obtained in the coating film when measured using GD-OES. The types of rust preventive pigments added are shown in Table 1 (Si-A is silica A, Si-B is silica B, Ba-A is barium borate A, Ba-B is barium borate B, Mo is molybdic acid. Calcium and W indicate tungsten oxide). In addition, the sample No. Sample No. 32 is an example in which no rust preventive pigment was added. 35 is an example using a methylated melamine resin instead of the imino group type melamine resin. Although not shown in Table 1, a coating using a butylated melamine resin instead of the imino group type melamine resin was also prepared, but a coating film could not be formed because the coating was solidified during the preparation. In Table 1, those using an imino group type melamine resin are indicated as "imino group type", and those using a methylated melamine resin are indicated as "methylated".

(Formation of coating film)
The coating material prepared as described above was applied on a Zn-based alloy plating layer by a roll coater so that the average thickness T ₁ of the formed coating film was 5 μm, and was cured by baking. The baking was performed under the conditions described in Table 1 (attained temperature A, heating time A, heating rate A, holding time, reached 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 was formed was maintained at 20 ° C., and after applying the paint to the plated steel sheet, as shown in Table 1. In the heating furnace A, the temperature was raised to the ultimate temperature A at the heating rate A, and after the temperature was held at the ultimate temperature A for a predetermined holding time, the temperature was raised to the ultimate temperature B in the heating furnace B at the heating rate B. The ratio C _A1 / C _A2 and / or the ratio C _B1 / C _B2 of the sample of the surface-treated steel sheet was adjusted by changing the combination of the heating rate during baking, the attained temperature of the steel sheet, and the holding time.

From the obtained coating film, the average concentration of the coloring pigment in the coating film; the average concentration of the rust preventing pigment in the coating film; the ratio C _A1 / C _A2 for the coloring pigment; and the ratio C _B1 / C for the rust preventing pigment _B2 was determined by elemental analysis using GD-OES. The values thus determined are shown in Table 1.

<Evaluation of surface treated steel sheet samples>
A sample of the surface-treated steel sheet was prepared as described above, and the plating chemical composition, the concentration and concentration distribution of the coloring pigment and the rust-preventive pigment as shown in Table 1, and the type of the rust-preventive pigment were as follows. Were evaluated for corrosion resistance and blackening resistance.

(Corrosion resistance evaluation test)
Each sample was subjected to a salt spray test (based on JASO M609-91 method) as an evaluation test of corrosion resistance. The salt spray test included (1) salt spray 2 hours (5% NaCl, 35 ° C.); (2) dry 4 hours (60 ° C.); and (3) wet 2 hours (50 ° C., humidity 95% or more). One cycle was performed for a total of 120 cycles (a total of 960 hours). In order to prevent corrosion from the end face, the end face of each sample was sealed with a tape and tested. Each sample had a width of 50 mm and a length of 100 mm.

The corrosion resistance was evaluated by observing the surface (plane portion) of the sample after 960 hours of the salt spray test with an optical microscope and determining the rust generation area ratio Z. Specifically, first, the surface of the sample was read by a scanner. Then, the area where rust was generated was selected using image editing software, and the rust generation area ratio was determined. This procedure was performed on five samples, and the rust generation area ratio was averaged to determine “rust generation area ratio Z”. Based on the "rust generation area ratio Z" determined for each sample in this way, the rating of each sample was determined in eight steps as follows. A score of 3 or higher was regarded as a 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 for blackening resistance)
For each sample, a sunshine carbon arc lamp type weather resistance test (SWOM) (based on JIS D0205) was performed as an evaluation test of blackening resistance. The test sprayed water for 12 minutes during the 60 minute arc lamp spray time, which was performed for a total of 500 hours. Each sample had a width of 50 mm and a length of 50 mm.

The evaluation of the blackening resistance was determined by measuring the “color tone change ΔL ^* ” (the lightness L of the sample after the test−the lightness L of the sample before the test) on the surface of the sample before and after performing the weather resistance test. ΔL ^* was determined by a color tone measurement (JIS Z8729) based on the CIE color system (L * a * b * color system) using a spectrophotometer (Suga Test Instruments Co., Ltd .: SC-T45). . According to the measured ΔL ^* , the score was determined in eight steps as follows. A score of 3 or more was regarded as a pass of blackening 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 ^*

  Sample No. of surface-treated steel sheet Evaluation tests for corrosion resistance and blackening resistance were performed on 1 to 40 as described above, and the respective scores were determined. Table 1 shows the obtained results.

In Table 1, the sample No. Nos. 1 to 8 are examples in which the ratio C _A1 / C _A2 of the color pigment is changed. Sample No. In the case of 2 to 7, the ratio was in the range of 0.2 to 0.9 in the range according to the present invention, so that the samples had sufficient corrosion resistance and blackening resistance.

On the other hand, sample No. In the case of 1, since the ratio C _A1 / C _A2 was less than 0.2, the rust-preventive pigment was relatively concentrated too much on the surface side of the coating film, and a region where the rust-preventive pigment was insufficient in a relatively short time was obtained. Appearance, corrosion resistance became insufficient. Sample No. In _No. 8, since the ratio C _A1 / C _A2 was more than 0.9, the coloring pigment was substantially uniformly dispersed in the coating film, and many coloring pigments were present on the surface side of the coating film, so that the corrosion factor could pass through. The formation of the path could not be sufficiently suppressed, and the corrosion resistance was insufficient. Further, the sample No. In No. 8, when the surface of the coating film was reduced in thickness, the concentration of the coloring pigment in the coating film was insufficient, so that the underlying Zn-based alloy plating layer could not be sufficiently invisible, and the blackening resistance was insufficient. became.

In Table 1, the sample No. Nos. 4 and 9 to 12 are examples in which the type of rust preventive pigment was changed while the ratio C _A1 / C _A2 was kept constant. Sample No. Nos. 4 and 9 to 12 all had excellent corrosion resistance and blackening resistance. In particular, when the rust preventive pigment contained Si-A, Si-B, Ba-A or Mo, it had better corrosion resistance. In addition, No. No. 13 is No. This is an example in which the same rust preventive agent Si-B as in No. 12 was used and the ratio C _A1 / C _A2 and the ratio C _B1 / C _B2 were changed, and had sufficient corrosion resistance and blackening resistance.

In Table 1, the sample No. 3 and 14 to 16, or sample No. Nos. 6 and 17 to 19 are examples in which the ratio C _B1 / C _B2 of the rust preventive pigment was changed while the ratio C _A1 / C _A2 of the coloring pigment was constant. All samples had sufficient corrosion resistance and blackening resistance. Further, when the ratio C _B1 / C _{B2 of} the rust preventive pigment was 1.3 or more and 4.0 or less, the corrosion resistance was further excellent.

  In Table 1, the sample No. Nos. 20 to 25 are examples in which the average concentration of the coloring pigment in the coating film is changed. Sample No. In Nos. 21 to 24, since the average concentration of the coloring pigment was in the range of 5% by mass or more and 15% by mass or less in the range according to the present invention, sufficient blackening resistance and corrosion resistance were obtained.

On the other hand, sample No. In No. 20, since the average concentration of the coloring pigment in the coating film was less than 5% by mass, the density of the coloring pigment in the entire coating film was insufficient, and the underlying Zn-based alloy plating layer could not be sufficiently seen. And the blackening resistance was insufficient. Sample No. In No. 25, since the average concentration of the coloring pigment in the coating film was more than 15% by mass, the coloring pigment protruded from the surface of the coating film and corroded even at a ratio C _A1 / C _A2 within the range according to the present invention. The formation of the path through which the factor can pass could not be sufficiently suppressed, and the corrosion resistance became insufficient.

  In Table 1, the sample No. 26 to 31 are examples in the case where the average concentration of the rust preventive pigment in the coating film was changed. All samples had sufficient corrosion resistance and blackening resistance. In particular, when the average concentration of the rust-inhibiting pigment in the coating film is in the range of 3% by mass or more and 12% by mass or less, the effect of improving the corrosion resistance by the rust-inhibiting pigment becomes remarkable. , And the orientation of the coloring pigment was excellent, so that it had better corrosion resistance and blackening resistance.

  In Table 1, the sample No. No. 32 did not contain a rust-preventive pigment in the coating film, so that the corrosion resistance and blackening resistance were insufficient. Sample No. No. 33 has a small specific surface area of the rust preventive pigment, that is, a high specific gravity, and the concentration distribution of the color pigment and the rust preventive pigment could not be controlled even when the imino group type melamine resin was used as a curing agent. Became inadequate. Sample No. In No. 34, the holding temperature was high, the desired concentration distribution of the coloring pigment and the rust-preventive pigment could not be obtained, and the rust-preventive pigment was relatively concentrated too much on the surface side of the coating film. An area where the pigment was insufficient appeared, and the corrosion resistance became insufficient. Sample No. No. 35 uses a methylated melamine resin as a curing agent, and the concentration phenomenon does not occur significantly, and the concentration distribution of the coloring pigment and the rust-preventive pigment cannot be controlled, so that the corrosion resistance and the blackening resistance are insufficient. It became.

  In Table 1, the sample No. Sample Nos. 36 to 40 are sample Nos. This is an example in which only the chemical composition of the Zn-based alloy plating layer was changed from No. 4 and had sufficient blackening resistance and corrosion resistance.

  As described above, according to the present invention, 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 coloring pigment is concentrated on the Zn-based alloy plating layer side in the coating film. The surface-treated steel sheet had a surface-treated steel sheet having high corrosion resistance and excellent blackening resistance.

Next, the sample Nos. 4 as a reference, the average particle diameter and average aspect ratio of color pigment to be contained in the coating film, and a sample of the surface treated steel sheet by changing the average thickness T ₁ of the coating film No. 41 to 58 were prepared, and their corrosion resistance and blackening resistance were evaluated. The sample No. Regarding Samples Nos. 41 to 58, the production conditions were appropriately changed to obtain Sample Nos. The same ratio C _A1 / C _A2 : 0.5 and ratio C _B1 / C _B2 : 2.5 were obtained. As the coloring pigment, resin-coated aluminum was used in the same manner as the samples in Table 1. Silica A having an average particle size of 3 μm was used as a rust preventive pigment. As described above, the determination of the scores of the corrosion resistance and the blackening resistance was made according to Sample No. Performed similarly to 1-40.

The major axis X ₁ , minor axis X ₂ and thickness X ₃ of the used color pigment, the average particle size and average aspect ratio of the color pigment obtained therefrom, the average thickness T ₁ of the obtained coating film, Table 2 shows the evaluation of corrosion resistance and the evaluation of blackening resistance. X ₁ to X ₃ uses the FE-EPMA, was determined by examining the 15 colored pigment in the coating film was determined average particle diameter and average aspect ratio of colored pigment from those values. The average thickness T ₁ of the coating film was determined from cross-sectional observation by SEM.

According to Table 2, the sample No. In samples 41 to 58, all samples had sufficient corrosion resistance and blackening resistance. In particular, when the average particle size of the color pigment is 7 μm or more and 30 μm or less, and the average aspect ratio is 20 or more, the color pigment is more effectively colored while suppressing projection of part of the color pigment from the coating film. Since the pigment could make the Zn-based alloy plating invisible, it had better 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 has a thickness sufficient to make the Zn-based alloy plating layer invisible while suppressing the color pigment from protruding from the coating film. Therefore, it had better corrosion resistance and blackening resistance. Further, in order to obtain excellent corrosion resistance and blackening resistance, it is sufficient that the thickness of the coating film is 15 μm or less, and such a coating film thickness is preferable from the viewpoint of cost.

  According to the present invention, a surface-treated steel sheet having high corrosion resistance and excellent blackening resistance can be provided. As a result, it is possible to secure short-term corrosion resistance and long-term corrosion resistance as a steel sheet used for building materials and products for home appliances, and to prevent the appearance of the steel sheet from changing over a long period of time. Therefore, the present invention is an invention having extremely high industrial value.

Claims (5)

Steel, Zn-based alloy plating layer formed on at least one surface on the steel plate, and is formed on the Zn-based alloy plating layer, the average thickness T ₁ of the coating film containing a coloring pigment and a rust-preventive pigment and a binder resin Has,
The chemical composition of the Zn-based alloy plating layer is represented by mass%,
Al: 0.01 to 60%,
Mg: 0.001 to 10%, and Si: 0 to 2%,
The average concentration of the coloring pigment in the coating film, by mass%, 5 to 15%, the average of the coloring pigment present in the coating surface from the coating film in the thickness direction in a width T ₂ area of film and concentration C _A1, the ratio of the Zn-based alloy plating layer side of the interface of the coating and the average concentration C _A2 of the coloring pigment present in the region having a width T ₂ in the thickness direction of the coating film C _A1 / C _A2 Is 0.2 to 0.9,
The coloring pigment is titanium oxide, zinc oxide, iron oxide, aluminum oxide, barium sulfate, aluminum, or carbon black,
_{T 2 (μm) = 0.1 ×} ( excluding T _2> If T ₁ to become) T ₁ (μm) + 1.1μm is characterized in that, the surface treated steel sheet. The average concentration of the rust preventive pigment in the coating film is 3 to 12% by mass%,
The thickness of the from the surface of the coating film and the average concentration C _B1 of the rust-preventive pigment present in the thickness direction of the width T ₂ areas of the coating, the coating film coating the surface of said Zn alloy plating layer side A ratio C _B1 / C _B2 with respect to the average concentration C _B2 of the rust-preventive pigment present in the region of width T ₂ in the width direction is 1.3 to 4.0,
The rust preventive pigment is silica, calcium-modified silica, barium borate, barium metaborate, zinc molybdate, calcium molybdate, sodium tungstate, calcium tungstate, or tungsten oxide,
_{T 2 (μm) = 0.1 ×} ( unless a _{T 2> T 1) T 1} (μm) + 1.1μm Ru der be characterized, surface treated steel sheet according to claim 1. The color pigment has a major axis X _{1 of} 5 to 30 μm, a minor axis X ₂ of ₁ to 30 μm, and a thickness X _{3 of} 0.0025 μm or more, and the average particle size is (X ₁ + X _2). ) / 2 and the average aspect ratio = (X ₁ + X ₂ ) / 2X ₃ , the average particle size of the color pigment is 7 to 30 μm, and the average aspect ratio is 20 or more. The surface-treated steel sheet according to claim 1. The surface treated steel sheet according to any one of claims 1 to 3, wherein the coating has an average thickness T1 of ₃ to 15 m. The thickness of the colored pigment is 0.5 T ₁ or less, surface-treated steel sheet according to any one of claims 1 to 4.