KR102428620B1 - surface treatment steel plate - Google Patents

Abstract

The present invention relates to a steel sheet, a Zn-based alloy plating layer formed on at least one side of the steel sheet, and a coating film of an average thickness T ₁ formed on the Zn-based alloy plating layer and containing a color pigment, a rust preventive pigment, and a binder resin, and a color pigment in the coating film The average concentration of is 5 to 15% in mass %, the average concentration C _A1 of the color pigment present in the region of width T ₂ from the surface of the coating film to the thickness direction of the coating film, and the interface on the Zn-based alloy plating layer side of the coating film The ratio C _A1 /C _A2 of the average concentration C _A2 of the color pigment present in the region of width T ₂ in the thickness direction of the coating film is 0.2 to 0.9, T ₂ (μm) = 0.1×T ₁ (μm) + 1.1 μm It relates to a surface-treated steel sheet, characterized in that.

Description

surface treatment steel plate

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

Coated 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 deteriorate with the surrounding environment. For example, a plating layer is oxidized by electrolytes, such as salt contained in air|atmosphere, oxygen, and water|moisture content which exist in a high-temperature and high-humidity environment, and produces|generates white rust. Since the appearance uniformity of a plated steel sheet is impaired when white rust is produced|generated, the corrosion resistance which suppresses generation|occurrence|production of a white rust is generally calculated|required of a plated steel sheet.

In particular, when a plated steel sheet is used outdoors, such as for a building material or an outdoor household appliance, it is more susceptible to the influence of the surrounding environment and is liable to deteriorate over time, so that high corrosion resistance is required.

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

In a Zn-based alloy plated steel sheet, both short-term corrosion resistance and long-term corrosion resistance are calculated|required. "Short-term corrosion resistance" means, for example, that the plated steel sheet is not corroded during the period (about 1 year) until the contractor delivers the plated steel sheet to the client. It means to make as long as possible the period until the thickness decreases by corrosion and the required strength is not obtained.

As a separate characteristic required for the Zn-based alloy plated steel sheet, there is blackening resistance. Black discoloration means that a plating layer oxidizes and discolors black. Black discoloration especially occurs notably in a Zn-Al-based alloy-coated steel sheet or a Zn-Al-Mg-based alloy-coated steel sheet to which Al or Mg is added during zinc plating. It is undesirable in use for discoloration of a plated steel sheet to be visually recognized from an external appearance by such blackening of a plating layer. Accordingly, in a Zn-based alloy-coated steel sheet such as a Zn-Al-Mg-based alloy-coated steel sheet, excellent blackening resistance is required while having corrosion resistance.

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

Further, Patent Document 2 discloses a chromate-free coated metal plate having, on at least one side of the metal plate, a coating film containing an organic resin as a film forming component and a flake-shaped aluminum pigment whose surface has been inactivated, such a metal plate. It is taught that silver has excellent corrosion resistance and blackening resistance.

In Patent Document 3, a plated steel sheet having a steel sheet and a plating layer disposed on the surface of the steel sheet, and a chemical conversion coating film disposed on the surface of the plating layer, the chemical conversion coating film is a fluororesin, a base resin, a metal flake, and a chemical conversion treatment component A chemical conversion-treated steel sheet containing

International Publication No. 2015/075792 International Publication No. 2013/065354 Japanese Patent Laid-Open No. 2016-121390

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 decreases in thickness due to deterioration of the resin. have. Then, with the protruding pigment as a starting point, a path through which corrosion factors such as oxygen can pass through the inside of the film is formed. Corrosion may proceed. Therefore, it leaves room for improvement in corrosion resistance. Moreover, in patent document 1, examination is not necessarily fully made about the density|concentration distribution in the film of an aluminum pigment, but still room for improvement with respect to blackening resistance.

Moreover, in patent documents 2 and 3, sufficient examination is not necessarily made about control of the density|concentration distribution of pigments, such as flake-shaped aluminum, but still room for improvement with respect to 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.

In order to obtain a surface-treated steel sheet having such high corrosion resistance and excellent blackening resistance, the present inventors set the average concentration of color pigments such as aluminum pigments in the coating film formed on the Zn-based alloy plating layer to 5 to 15% by mass. I have learned that it is important to be in control. With such 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, so that the color pigment does not show blackening of the Zn-based alloy plating layer, thereby changing the appearance can be suppressed, and excellent blackening resistance can be obtained.

The present inventors also found that it is important to concentrate the color pigment toward the Zn-based alloy plating layer side in the coating film. By concentrating the color pigment on the Zn-based alloy plating layer side as described above, 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. In addition, by concentrating the color pigment toward the Zn-based alloy plating layer side, it becomes possible to arrange the color pigment in a narrow area in the coating film and at a distance closer to each other. Therefore, a color pigment can be distributed at high density in a coating film, a more extensive Zn-type alloy plating layer can be made invisible effectively, As a result, blackening resistance improves.

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

(One)

A steel sheet, a Zn-based alloy plating layer formed on at least one side of the steel sheet, and a coating film of an average thickness T ₁ formed on the Zn-based alloy plating layer and comprising a color pigment, a rust preventive pigment, and a binder resin,

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

Al: 0.01 to 60%,

Mg: 0.001 to 10%, and

Si: 0 to 2%,

The average concentration of the colored pigment in the coating film is 5 to 15% by mass,

The average concentration C _A1 of the color pigment existing in the region of the width T ₂ from the surface of the coating film in the thickness direction of the coating film, and the region of the width T ₂ in the thickness direction of the coating film from the interface on the side of the Zn-based alloy plating layer of the coating film the ratio C _A1 /C _A2 of the average concentration C _A2 of the colored pigment present in is 0.2 to 0.9,

T ₂ (㎛) = 0.1 × T ₁ (㎛) + 1.1㎛, characterized in that the surface-treated steel sheet.

(2)

The average concentration of the rust preventive pigment in the coating film is 3 to 12% by mass,

The average concentration C _B1 of the rust preventive pigment existing in a region having a width T ₂ from the surface of the coating film in the thickness direction of the coating film, and a region having a width T ₂ from the interface on the side of the Zn-based alloy plating layer of the coating film in the thickness direction of the coating film The ratio C _B1 /C _B2 of the average concentration C _B2 of the rust preventive pigment present in is 1.3 to 4.0,

T ₂ (㎛) = 0.1 × T ₁ (㎛) + 1.1㎛,

The surface-treated steel sheet according to (1) above, wherein the rust-preventing pigment contains one or more of Si, Mo, W and Ba.

(3)

The color pigment has a major diameter X ₁ of 5 to 30 μm, a minor diameter X ₂ of 1 to 30 μm, and a thickness X ₃ of 0.0025 μm or more, and an average particle diameter = (X ₁ +X ₂ )/2, and (1) or (2) above, characterized in that, when average aspect ratio = (X ₁ +X ₂ )/2X ₃ , the color pigment has an average particle diameter of 7 to 30 µm and an average aspect ratio of 20 or more The surface-treated steel sheet described in.

(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 color pigment has a thickness of 0.5T ₁ or less.

According to the present invention, the average concentration of the colored pigment in the coating film is 5 to 15% by mass, and in the coating film, the colored pigment is concentrated toward the Zn-based alloy plating layer side, so that the colored pigment protrudes from the coating film and corrodes. To provide a surface-treated steel sheet having high corrosion resistance and excellent blackening resistance because it suppresses the formation of a printing path and the colored pigment makes the Zn-based alloy plating layer invisible when viewed from a direction perpendicular to the surface of the coating film can In particular, the surface-treated steel sheet according to the present invention can provide high corrosion resistance and blackening resistance even when the thickness of the coating film is reduced because the color pigment in the coating film is concentrated toward the Zn-based alloy plating layer side.

[Surface-treated steel plate]

The surface-treated steel sheet according to the present invention is formed on a steel sheet, a Zn-based alloy plating layer formed on at least one side of the steel sheet, and a Zn-based alloy plating layer, and has a coating film having an average thickness T ₁ comprising a color pigment, a rust preventive pigment, and a binder resin. , the chemical composition of the Zn-based alloy plating layer is, in mass%, Al: 0.01 to 60%, Mg: 0.001 to 10%, and Si: 0 to 2%, the average concentration of the colored pigment in the coating film is, in mass%, 5 to 15%, the average concentration C _A1 of the color pigment existing in the region of width T ₂ from the surface of the coating film in the thickness direction of the coating film, and the width T ₂ from the interface on the side of the Zn-based alloy plating layer of the coating film in the thickness direction of the coating film It is characterized in that the ratio C _A1 /C _A2 of the average concentration C _A2 of the colored pigment present in the region of is 0.2 to 0.9, and T ₂ (μm)=0.1×T ₁ (μm)+1.1 μm. Hereinafter, the structural requirements of the surface-treated steel sheet according to the present invention will be described.

<Steel plate>

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

<Zn-based alloy plating layer>

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

When the Al content of the Zn-based alloy plating layer is less than 0.01%, the effect of improving the corrosion resistance of the plated steel sheet by containing Al is not sufficiently exhibited, and when it exceeds 60%, the effect of improving the corrosion resistance is saturated. Therefore, the Al content may be 0.01% or more, for example, 0.1% or more, 0.5% or more, 1% or more, 3% or more, or 5% or more, and 60% or less, for example 55% or less, 50%. or less, 40% or less, or 30% or less may be sufficient. A preferable Al content is 1 to 60 %, More preferably, it is 5 to 60 %.

When the Mg content of the Zn-based alloy plating layer is less than 0.001%, the effect of improving the corrosion resistance of the plated steel sheet by containing Mg may not be sufficiently exhibited. On the other hand, if it exceeds 10%, Mg is not completely dissolved in the plating bath, and it floats as an oxide (generally called 'dross'). , or there is a possibility that a portion that is not plated (generally called 'no plating') may occur. Therefore, the Mg content may be 0.001% or more, for example, 0.01% or more, 0.1% or more, 0.5% or more, 1% or more, or 2% or more, and 10% or less, for example 8% or more, 6% or less. , 5% or less or 4% or less may be sufficient. Mg content becomes like this. Preferably it is 1 to 5 %, More preferably, it is 1-4 %.

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

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

<Paint>

The coating film in this invention is formed on the Zn-type alloy plating layer. In a coating film, a rust preventive pigment and binder resin are included other than a color pigment. Although the average thickness T1 _of a coating film may be any value as long as sufficient corrosion resistance and blackening resistance are ensured, it is preferable that they are 3 micrometers or more and 15 micrometers or less, for example. When the average thickness T ₁ of the coating film is less than 3 μm, the possibility that a part of the colored pigment protrudes from the coating film and the corrosion factor reaches the alloy plating layer is increased, and there is a fear that sufficient corrosion resistance cannot be ensured. Moreover, in order to ensure the effect of making a Zn-type alloy plating layer invisible by the coloring pigment in a coating film, thickness becomes inadequate, and there exists a possibility that blackening resistance may deteriorate. In addition, 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, as for average thickness T1 _of a coating film, it is more preferable that they are 3 micrometers or more and 12 micrometers or less. In addition, in this specification, "blackening resistance" does not mean that the blackening of the underlying Zn-based alloy plating layer of the coating film is suppressed, and even if blackening occurs in the Zn-based alloy plating layer, blackening is externally caused by the colored pigment in the coating film. It means that no change in appearance occurs in the surface-treated steel sheet by making it invisible.

As used herein, “average thickness T ₁ ” refers to a cross section of a steel sheet having a coating film observed under a microscope, from five arbitrary positions on the interface on the Zn-based alloy plating layer side of the coating film to the surface of the coating film, respectively. It is defined as a value obtained by measuring the shortest distance of , and averaging their measured values. In addition, when a substance (for example, aggregate) whose particle diameter is larger than the film thickness is contained in a coating film, the said distance is measured at the position where the substance does not exist. This is because, due to the presence of such a substance, when the coating film is observed from the cross-sectional direction, the distance may be measured to be larger than the actual coating film thickness. Further, another layer such as a chemical conversion treatment layer may exist between the Zn-based alloy plating layer and the coating film. If such a separate layer is present, its thickness is not included in the average thickness T ₁ .

(color pigment)

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

The average concentration (average content) of the colored pigment in the coating film is 5 to 15% by mass. By setting the average concentration of the color pigment within the above range, and by concentrating the color pigment near the interface with the Zn-based alloy plating layer, the direction perpendicular to the surface of the coating film, even if the film thickness is relatively thin compared to the coating film of a general coated steel sheet. In the case of observation from , it is possible to secure an amount that the color pigment sufficiently covers and hides the Zn-based alloy plating layer. Moreover, it can fully suppress that a color pigment protrudes from the surface of a coating film. Accordingly, while maintaining high corrosion resistance, the color pigment prevents blackening of the Zn-based alloy plating layer, thereby suppressing the change in appearance and obtaining excellent blackening resistance. When the average concentration of the colored pigment in the coating film is less than 5%, the density of the colored pigment in the coating film for preventing blackening of the Zn-based alloy plating layer from being seen is insufficient, and the blackening resistance decreases. On the other hand, if the average concentration of the color pigment in the coating film is more than 15%, a large amount of the color pigment is present in the coating film, and when the thickness of the coating film is reduced, a part of the color pigment is more likely to protrude from the surface of the coating film at a relatively early stage, and corrosion resistance This is likely to worsen. Moreover, there exists a possibility that adhesiveness may also fall. 6 % or more, 7 % or more may be sufficient as the average density|concentration of the color pigment in a coating film, and 12 % or less or 10 % or less may be sufficient as it. The average density|concentration of the color pigment in a coating film becomes like this. Preferably it is 5 to 12 %, More preferably, it is 5 to 10 %.

As used herein, the "average concentration of the colored pigment in the coating film" is measured using a glow discharge optical emission spectrometry (GD-OES). Specifically, when the type of the color pigment, ie, the specific compound of the color pigment, is known, the coating film is sputtered from the surface toward the plating layer, and the concentration profile in the depth direction of the main elements constituting the color pigment is set to 1.0 µm. measure every Then, the average value of the measured concentration of the main element is calculated|required, the measured density|concentration is converted based on the molecular weight of the compound of a known color pigment, and the average density|concentration of the color pigment in a coating film is calculated|required. When the type of the color pigment, that is, the specific compound of the color pigment, is unclear, a Field Emission-Electron Prove Micro Analyzer (Field Emission-Electron Prove Micro Analyzer: What is necessary is just to measure the "average density|concentration of the color pigment in a coating film" as mentioned above after specifying the kind of a colored pigment by elemental analysis using FE-EPMA).

The color pigment in the coating film is concentrated toward the Zn-based alloy plating layer side. The index of the color pigment concentration is the average concentration C _A1 of the color pigment existing in the region of width T ₂ from the surface of the coating film in the thickness direction of the coating film, and the width in the thickness direction of the coating film from the interface on the Zn-based alloy plating layer side of the coating film The average concentration of the colored pigment present in the region of T ₂ is determined by the ratio C _A1 /C _A2 of C _A2 . 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 formula: T ₂ (μm)=0.1×T ₁ (μm)+1.1 μm. That is, according to the value of the average thickness T ₁ of a coating film, the width T ₂ of the measurement area|region of the average density|concentration C _A1 and C _A2 of a color pigment is 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 formula based on the T ₁ , Then, the average concentrations C _A1 and C _A2 of the color pigment are measured within the width T ₂ . Also, even when the region determining C _A1 and the region determining C _A2 overlap (that is, when T ₂ >0.5T ₁ ), C _A1 and C _A2 are measured as described above, and the ratio C _A1 / C _A2 can be determined. _In addition, when T2>T1 becomes (for example, when T1 ₌ 1.2 micrometer), such _a surface-treated steel plate 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. When this ratio C _A1 /C _A2 is less than 0.2, the rust preventive pigment is relatively concentrated excessively on the surface side of the coating film, and when the thickness of the coating film is reduced, the layer with a low concentration of the rust preventive pigment is exposed in a relatively short time, and a sufficient long-term no corrosion resistance On the other hand, when the ratio C _A1 /C _A2 is more than 0.9, the thickening effect of the colored pigment cannot be obtained, a part of the colored pigment protrudes from the coating film, and the corrosion resistance becomes insufficient. Moreover, since the density|concentration of the color pigment in a coating film runs short when a coating film thickness decreases, a Zn-type alloy plating layer cannot be made invisible effectively, but blackening resistance becomes inadequate. The C _A1 /C _A2 ratio may be, for example, 0.3 or more or 0.4 or more, or 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 the color pigment existing in the region of width T ₂ from the surface of the coating film in the thickness direction of the coating film" and "Exist in the region of width T ₂ from the interface on the Zn-based alloy plating layer side of the coating film in the thickness direction of the coating film The average concentration C _A2 of the colored pigment to be used is measured using GD-OES similarly to the measurement of the “average concentration of the colored pigment in the coating film”. Specifically, sputtering is carried out from the surface direction of the coating film to the depth direction of the Zn-based alloy plating layer, and the concentration distribution in the depth direction of the coating film for the main elements constituting the color pigment is measured in the range of width T ₂ every 0.1 μm. . Then, the average value of the measured concentration of the main element is calculated|required, the measured density|concentration is converted based on the molecular weight of the compound of a known color pigment, and the average density|concentration of the color pigment in a coating film is calculated|required. In addition, the sputtering time can be converted into the coating film thickness information by measuring the relationship between the sputtering time and the coating film depth in advance. C _A1 and C _A2 can be calculated|required by measuring the density|concentration distribution of the film thickness direction of the element which comprises a color pigment.

By concentrating the color pigment in the coating film toward the Zn-based alloy plating layer in the coating film so that the value of the ratio C _A1 /C _A2 in the coating film is 0.2 or more and 0.9 or less, the color pigment concentration on the surface side of the coating film is relatively low. Thereby, it can suppress that a part of a color pigment protrudes from the surface of a coating film after manufacture or when the surface of a coating film reduces in thickness. Therefore, since it is possible to suppress the generation of a pass-through path of the corrosion factor, high corrosion resistance can be ensured. Moreover, when the density|concentration of the color pigment on the surface side of a coating film decreases, when the surface of a coating film thickness decreases, drop-off|omission of a colored pigment is suppressed and blackening resistance is maintained over a long period of time. Therefore, under the condition that the average concentration of the color pigment in the coating film is constant, the surface-treated steel sheet according to the present invention can effectively make the Zn-based alloy plating layer invisible from the outside, compared to the case where the color pigment is uniformly distributed in the coating film, Accordingly, the blackening resistance is remarkably improved. In addition to this, as another advantage that the colored pigment is distributed in a narrow area, when a pigment having an orientation having a high average aspect ratio (eg, scaly shape, flat shape, etc.) is used, the direction of the colored pigment is determined by the direction of the coating film. It can be aligned parallel or substantially parallel to the surface, and can effectively make the plating layer invisible, thereby improving blackening resistance.

The color pigment according to the present invention may have any shape as long as sufficient corrosion resistance and blackening resistance are ensured. The shape of the color pigment is, for example, but not limited to, spherical shape, oval shape, needle shape, flat shape, thin plate shape, and scale. A phase, a spindle shape, etc. are mentioned. In order that the color pigment in this invention makes a Zn-type alloy plating layer invisible more effectively and acquires the outstanding blackening resistance, it is preferable that it is flaky.

When used in this specification, "average particle diameter" and "average aspect-ratio" with respect to the colored pigment which concern on this invention are calculated|required by the following method. First, any one colored pigment is elementally mapped from the surface to FE-EPMA, and the long diameter X ₁ and the short diameter X ₂ of the colored pigment are determined. Here, the long diameter X ₁ means the length of the largest line segment traversing the colored pigment within the outline of the image of the colored pigment specified by element mapping, and the short diameter X ₂ is traversing the colored pigment means the length of a line segment perpendicular to the long diameter X ₁ . Then, elemental mapping is performed from the cross-sectional direction to FE-EPMA, and a value of thickness X ₃ (generally, a dimension in a direction perpendicular to the measurement planes of the above-described major and minor diameters) is measured. Next, from these measured values, the particle size = [(X ₁ +X ₂ )/2] of the colored pigment and the aspect ratio = [(X ₁ +X ₂ )/2X ₃ ] are calculated. And the particle diameter and aspect-ratio are calculated|required with respect to arbitrary 10 or more colored pigments using the same method, each is averaged, and "average particle diameter" and "average aspect-ratio" of a colored pigment are calculated|required.

The long diameter X ₁ , the short diameter X ₂ and the thickness X ₃ of the colored pigment according to the present invention may be any value as long as they can be present in the coating film. For example, the long diameter X ₁ is 5 μm or more and 30 μm or less, and the short diameter X ₂ is preferably 1 µm or more and 30 µm or less, and thickness X ₃ is preferably 0.0025 µm or more. It becomes possible to make a Zn-type alloy plating layer invisible effectively, suppressing that a color pigment protrudes from a coating film by having a long diameter, a short diameter, and thickness of such a range. Moreover, it is preferable that the average particle diameters of the colored pigment which concern on this invention are 7 micrometers or more and 30 micrometers or less, for example, and it is preferable that average aspect-ratios are 20 or more. By having an average particle diameter of such a range, a Zn-based alloy plating layer can be effectively made invisible, suppressing that a color pigment protrudes from the surface of a coating film. Moreover, when a color pigment has a high aspect-ratio, it becomes possible to make a Zn-type alloy plating layer invisible by a color pigment in a wide range, and blackening resistance can be improved more. When the average particle diameter of a colored pigment is less than 7 micrometers, a Zn-type alloy plating layer cannot fully be made invisible, but blackening resistance may become inadequate. On the other hand, when the average particle diameter of the color pigment exceeds 30 µm, the possibility that the color pigment protrudes from the coating film is increased, and there is a possibility that sufficient corrosion resistance cannot be ensured. Further, if the average aspect ratio is less than 20, the Zn-based alloy plating layer cannot be sufficiently made invisible, and there is a possibility that the blackening resistance becomes insufficient. As for the average particle diameter of the colored pigment which concerns on this invention, it is more preferable that they are 10 micrometers or more and 25 micrometers or less. Moreover, it is more preferable that it is 25 or more, and, as for average aspect-ratio, it is still more preferable that it is 30 or more. Although the upper limit of an average aspect-ratio is not limited, For example, what is necessary is just 100. Moreover, in order to make the Zn-based alloy plating layer invisible more effectively by using a color pigment, it is advantageous that the values of the long diameter X ₁ and the short diameter 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 still more preferably 1.0 or more and 2.0 or less.

Since the color pigment which concerns on this invention is contained in a coating film, thickness X3 of a color pigment becomes smaller than _average thickness T1 _of a coating film. Moreover, when a color pigment protrudes from a coating film, since there exists a possibility that the penetration path of a corrosion factor may be formed and corrosion resistance may deteriorate, the thickness X ₃ of a color pigment is smaller with respect to the average thickness T ₁ of a coating film. For example, thickness X3 of a coloring pigment becomes like this. Preferably it is _0.5T1 or _less , More preferably, it is 0.4T1 or _less .

(Anti-rust pigment)

As a rust preventive pigment used in the coating film in this invention, 1 type, or 2 or more types of Si, Mo, W and Ba can be contained. Preferably, one or two or more of Si, Mo and Ba are included. Although it does not limit as these specific compounds, For example, Silica (made by Grace, MSK-8D), calcium-modified silica (made by W.R. Grace, SHIELDEXC303), barium borate (reagent manufactured by Showa Chemicals), barium metaborate, for example. (Reagent manufactured by Showa Chemicals), zinc molybdate (reagent manufactured by Wako Pure Chemical Industries, Ltd.), calcium molybdate (reagent manufactured by Wako Pure Chemical Industries, Ltd.), sodium tungstate (reagent manufactured by Kanto Chemical Company), calcium tungstate ( Kanto Chemical Co., Ltd. reagent), tungsten oxide (Kanto Chemical Co., Ltd. reagent), etc. are mentioned. Preferably, the antirust pigment is silica. Also, the anti-rust pigment may be porous. By setting it as porous, a specific surface area is large, and since apparent specific gravity becomes low, it becomes easier to concentrate on the surface side of a coating film. For example, as the rust preventive pigment, a rust preventive pigment (eg 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 can be used. . Although the upper limit of the specific surface area of a rust preventive pigment is not specifically limited, For example, what is necessary is just 500 m<2>/g. In addition, in this specification, "apparent specific gravity" means the density at the time of making the volume of the rust preventive pigment itself and internal voids, and "the volume of the rust preventive pigment itself" and "the volume of internal voids" are included.

The average concentration of the rust preventive pigment in the coating film may be 3 to 12% by mass. By setting it as such a range, a coating film can fully act as a film|membrane which prevents corrosion of a Zn-type 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 distribution of the concentration of the rust preventive pigment in the coating film, the concentration of the rust preventive pigment in the entire coating film is insufficient, and sufficient corrosion resistance 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 rust preventive pigment becomes small, which may be disadvantageous in terms of cost. Moreover, adhesiveness may also fall. 4 % or more, 5 % or more, or 6 % or more may be sufficient as the average density|concentration of the rust preventive pigment in a coating film, and 11 % or less or 10 % or less may be sufficient as it. 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 density|concentration of the rust preventive pigment in a coating film" is calculated|required using the method similar to the "average density|concentration of the color pigment in a coating film" mentioned above.

The rust preventive pigment in the coating film is concentrated toward the surface side of the coating film. The index of the concentration of the rust preventive pigment is the average concentration C _B1 of the rust preventive pigment existing in the region of width T ₂ from the surface of the coating film in the thickness direction of the coating film, and the width in the thickness direction of the coating film from the interface on the Zn-based alloy plating layer side of the coating film It is determined by the ratio C _B1 /C _B2 of the average concentration C _B2 of the rust preventive pigment present in the region of T ₂ . As described above, it is determined that 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 ratio C _A1 /C _A2 to the above-mentioned colored pigment is 0.2 or more and 0.9 or less, the concentration on the surface layer side of the rust preventive pigment In order to more reliably acquire the effect of , it is preferable in it being 1.3 or more and 4.0 or less. When this ratio C _B1 /C _B2 becomes less than 1.3, the thickening effect of the rust preventive pigment that long-term planar part corrosion resistance improves may not fully be acquired. On the other hand, when the ratio C _B1 /C _B2 is more than 4.0, the rust preventive pigment is excessively concentrated toward the surface side of the coating film, and when the thickness of the coating film decreases with the passage of time, the surface lacking the rust preventive pigment is exposed in a relatively short time, and a 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 for C _A1 and C _A2 described above.

By distributing the rust preventive pigment in the coating film in the coating film so that the value of the ratio C _B1 /C _B2 is 1.3 or more and 4.0 or less, that is, by concentrating the rust preventive pigment toward the surface side of the coating film, the corrosion resistance of the surface of the coating film is sufficiently improved, and the flat part Long-term corrosion resistance is further improved.

The average particle diameter of the rust preventive pigment can be appropriately selected according to the average thickness T ₁ of the coating film or the like, but may be 0.2 to 10 µm. It is preferable that it is 0.4-8 micrometers, and, as for the average particle diameter of a rust preventive pigment, it is more preferable that it is 0.5-6 micrometers.

The average particle diameter of a rust preventive pigment can be determined by the method similar to the average particle diameter of the above-mentioned colored pigment. That is, elemental mapping by FE-EPMA is performed for 10 or more rust preventive pigments from the surface and cross-sectional direction of the coating film, and the long diameter Y ₁ , the short diameter Y ₂ and the thickness Y ₃ of the rust preventive pigment are obtained, and rust prevention is obtained from their values. The average particle diameter of a pigment can be calculated|required.

Moreover, from an adhesive viewpoint, it is preferable that thickness Y3 of a rust preventive pigment is somewhat smaller than _average thickness T1 _of a coating film similarly to a colored pigment, For example, thickness Y3 of _a rust preventive pigment, Preferably _0.5T1 or less, more preferably 0.4T ₁ or less, still more preferably 0.3T ₁ or less, and most preferably 0.1T ₁ or less.

(binder resin)

The binder resin used as a component of the coating film in this invention should just be 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 this invention is a polyester resin. Moreover, as a polyester resin used by this invention, what has glass transition temperature Tg of -20-70 degreeC, and the number average molecular weight of 3000-30000 is preferable. When binder resin is a urethane resin, it is preferable that Tg is 0-50 degreeC, and a number average molecular weight is 5000-25000. When binder resin is an acrylic resin, it is preferable that 0-50 degreeC and number average molecular weights of Tg are 3000-25000. In addition, in this invention, an aqueous solvent is used for the solvent with respect to binder resin.

In the coating film in the present invention, if necessary, waxes 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, or alizarin A dye or the like may be added. By adding these, the intensity|strength of a coating film becomes high, or since a desired color can also be provided to a coating film, it is more preferable. What is necessary is just to determine these addition amounts suitably so that it may not become disadvantageous in the coating film in this invention.

In particular, in order to impart a desired color to the coating film in the present invention, and hence the surface-treated steel sheet according to the present invention, a dye may be used as a colorant. A dye may be used independently and may be used combining some dye. Although there is no limitation in particular as a kind of dye which can be used in the coating film in this invention, A well-known dye can be used, For example, phthalocyanine blue, phthalocyanine green, methyl orange, methyl violet, or alizarin can be used. .

[Method for producing surface-treated steel sheet]

An example of a method for manufacturing a surface-treated steel sheet according to the present invention will be described below. The surface-treated steel sheet according to the present invention is, for example, on a Zn-based alloy plating layer formed on the steel sheet, a color pigment and a rust preventive pigment are added, and an imino group-type melamine resin is added as a curing agent for a binder resin. It can be produced by curing the paint by heating with a heat pattern of

<Formation of Zn-Based Alloy Plating Layer>

As a steel plate, what has arbitrary plate|board thickness and chemical composition can be used. For example, a cold-rolled steel sheet having a thickness of 0.25 to 3.5 mm can be used. The Zn-based alloy plating layer may be formed, for example, by hot-dip plating by Zn-Al-Mg alloy plating on a steel sheet to a thickness of 1 to 30 µm. Hot-dip plating can be performed, for example with a 400-550 degreeC hot-dip plating bath to which various metals were added. 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. Moreover, in addition to the above chemical composition, Si: 0.001 to 2% by mass %, and a Zn-Al-Mg-Si alloy plating layer can also be formed.

<Preparation of paint>

The paint is prepared 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, and then , by dispersing predetermined amounts of a color pigment and a rust preventive pigment in a mixture thereof. In addition, as a 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 toward the surface side of the coating film, and the color pigment in the coating film is concentrated toward the Zn-based alloy plating layer side. The present inventors found that the formation of such a concentration distribution of the rust preventive pigment and the color pigment becomes possible by utilizing the phenomenon that, under certain conditions, the iminogi type melamine resin is thickened on the surface layer of the coating film when it is cured. That is, the thickening of the rust preventive pigment on the surface side of the coating film is performed by selecting a rust preventive pigment (for example, porous silica) having a small apparent specific gravity compared to the colored pigment, that is, a large specific surface area, so that the imino group type melamine resin of the coating film is This becomes possible by moving the antirust pigment to the surface layer together with the melamine resin when it is concentrated on the surface layer. Regarding the mechanism of this thickening, not only the effect of the apparent specific gravity difference between the colored pigment and the rust preventive pigment, but also the imino group type melamine resin and the rust preventive pigment have chemical affinity, and they interact with each other, so that the imino group type melamine resin It is also considered that the rust preventive pigment is concentrated toward the surface side of the coating film along with the concentration on the surface layer of the coating film.

In addition, as in the present invention, when a water-based paint is used as a paint for forming a coating film, the present inventors found that the thickening of the imino group-type melamine resin on the surface layer is more remarkable than when a solvent system is used. This is thought to be because, when the coating material is cured and a coating film is formed, an imino group type melamine resin that is not crosslinked with polyester or the like exists more in the water-based coating material than in the solvent-based coating material. To put it another way, in the case of a water-based paint, since the polyester resin is dispersed in an emulsion state, the crosslinking reaction between the reactive functional group (OH group) inside the emulsion particle and the imino-type melamine resin is inhibited, It is thought that this is because the imino group type melamine resin increases. Thereby, the self-condensation reaction of imino group type melamine occurs more easily than crosslinking reaction, and it is thought that the thickening with respect to the surface layer of imino group type melamine resin was remarkable. In addition, the large concentrating effect of the imino-type melamine resin in the water-based paint has low compatibility with water and melamine, and the surface free energy of the imino-type melamine resin is small compared to water, so that the imino-type melamine resin is It is also thought that it is because it becomes easy to float on the surface layer. Therefore, in this invention, in order to accelerate|stimulate the thickening with respect to the surface layer of an imino group type melamine resin, it is effective to use an aqueous solvent as a solvent.

As a melamine resin, methylated melamine resin and a butylated melamine resin other than the imino group type melamine resin used by this invention are generally known. However, when a methylated melamine resin is added as a curing agent in the water-based paint, the thickening phenomenon of the anti-rust pigment on the surface layer during baking does not occur significantly, and when a butylated melamine resin is used as a curing agent in the water-based paint The present inventors found that the paint solidified when mixed with an aqueous solvent, and thus could not be used as a paint. Therefore, in order to obtain a coating film as in the present invention, it is very 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 properties of the imino-type melamine resin in such a water-based paint, when the rust preventive pigment is concentrated on the surface side of the coating film in the coating film, relatively heavy colored pigments such as aluminum in the coating film are difficult to be distributed on the surface side of the coating film, and relatively Zn It is concentrated toward the alloy plating layer side. In other words, when the rust preventive pigment is concentrated toward the surface side of the coating film, the color pigment is pressed so as to be fixed to the Zn-based alloy plating layer side in the coating film. In this way, a surface-treated steel sheet having a ratio C _B1/ C _B2 of the rust preventive pigment in the coating film of 1.2 or more and 5.0 or less, preferably 1.3 or more and 4.0 or less is obtained, and the ratio C _A1 /C _A2 of the color pigment in the coating film is 0.2 The surface-treated steel sheet according to the present invention of 0.9 or more is obtained. In addition, in order to thicken the rust preventive pigment and the color pigment to the surface layer side and the Zn-based alloy plating layer side, respectively, due to the properties of the imino group type melamine resin in the water-based paint, it is effective to select the particle size and specific gravity of the rust preventive pigment. In order to obtain the concentration distribution of the rust preventive pigment and the colored pigment according to the present invention, it is effective to set the average particle diameter of the rust preventive pigment to 0.2 to 10 µm and to set the specific surface area to 20 m 2 /g or more.

Moreover, in order to thicken a melamine resin in the surface layer of a coating film as needed when it can use together with a color pigment and a rust preventive pigment, an acidic catalyst can be added in a coating material. Although not limited as an acidic catalyst, A weakly acidic catalyst (Catalyst 296-9/Allex Japan company make), a strong acidic catalyst (Catalyst 600/Allnex Japan company make), or an amine block strong acid catalyst (Catalyst 602/Allnex Japan) Japan Corporation) can be used. An acidic catalyst is added 0.1-1.0 mass % in a coating material, for example.

<Formation of coating film>

Next, the obtained coating material may be applied to a predetermined thickness on the Zn-based alloy plating layer by, for example, a roll coater or the like, and baked and cured in a predetermined heat pattern. Baking is heated at a heating rate of 5 to 70° C./sec so that the final steel sheet temperature is 180 to 230° C. Specifically, in the process of heating to the steel sheet temperature, the steel sheet temperature is maintained for 1 to 5 seconds, preferably 1 to 3 seconds, at a temperature between 70 to 150° C., preferably 100 to 150° C. it is important That is, after the paint is applied on the Zn-based alloy plating layer, the plated steel sheet at room temperature (for example, 20° C.) is once heated to 70 to 150° C. (first heating step), and then maintained at that temperature for 1 to 5 seconds. (Temperature maintenance process) Furthermore, the coating film in this invention is obtained by heating at 180-230 degreeC (2nd heating process). Such a heat pattern can be realized with two heating furnaces. Specifically, with respect to the sheet-feeding direction of the Zn-based alloy plated steel sheet to which the paint is applied, a heating furnace A and a heating furnace B are sequentially provided, and between the heating furnace A and the heating furnace B, a temperature holding region in which no heat treatment is performed is formed. you have to prepare Therefore, the temperature of the plated steel sheet coated with the paint in the heating furnace A is raised to a temperature between 70 and 150° C., and the temperature is maintained for 1 to 5 seconds in the temperature holding region at that temperature, and then in the heating furnace B between 180 and 230° C. By raising the temperature to a temperature, the paint can be cured. In addition, as mentioned above, the said heat pattern may be performed continuously, and may be performed in a batch type.

By carrying out a temperature holding process at the above holding temperature and holding time, an antirust pigment can be efficiently concentrated to a surface layer with surface layer thickening of an imino group type melamine resin. When the above holding time 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 thus the concentration of the colored pigment may not be efficiently obtained. In particular, when the holding temperature exceeds 150 ° C., the binder resin and the curing agent react, the viscosity of the paint increases, and the rust preventive material becomes difficult to move to the surface layer, so that the desired surface layer thickening of the rust preventive pigment may not be obtained.

The concentration ratio of the rust preventive pigment according to the present invention (the concentration ratio of the colored pigment) is based on the melamine thickening as described above, and can be controlled by the melamine resin species and the melamine resin concentration to be used. In addition, it can adjust also with the heat pattern at the time of coating film hardening, the average particle diameter, specific gravity, etc. of a rust preventive pigment. 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 mixed so that the binder resin:curing agent ratio is in the range of 100:10 to 100:30, and a colored pigment is used. And a rust preventive pigment is added to prepare a paint. And, as described above, after applying such a coating material on the Zn-based alloy plating layer, it is heated to 70 to 150° C. Heat as much as possible. By doing in this way, it becomes possible to generate effectively the thickening with respect to the surface layer side of a rust preventive pigment, and the thickening with respect to the Zn-type alloy plating layer side of the accompanying color pigment. And it is effective that the average particle diameter of the rust preventive pigment added to a paint shall be 0.2-10 micrometers, and make a specific surface area be 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 existing in the region of width T ₂ from the surface of the coating film in the thickness direction of the coating film, and the surface of the coating film present in the region of width T ₂ in the thickness direction of the coating film from the interface on the Zn-based alloy plating layer side A surface-treated steel sheet having a ratio C _A1 /C _A2 of 0.2 or more and 0.9 or less and T ₂ (μm) = 0.1×T ₁ (μm) + 1.1 μm of the average concentration C _A2 of the colored pigment to be used can be manufactured.

Example

With respect to the surface-treated steel sheet according to the present invention, some examples will be described below in more detail. However, it is not intended that the scope of the invention as set forth in the claims be limited by the specific examples set forth below.

<Preparation of sample of surface-treated steel sheet>

(Formation of Zn-based alloy plating layer)

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

(Preparation of paint)

A polyester resin (molecular weight: 16,000; glass transition point: 10°C) as a binder resin in water was dispersed as an emulsion, and the pH was adjusted to be 8.0 to 9.0. An imino group type melamine resin was mixed therein. The ratio of the concentration of the polyester resin and the imino-type melamine resin was 100:20. Next, in the mixture thereof, 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), and a rust preventive pigment Two Si compounds with an average particle diameter of 3 μm (Silica A: specific surface area 320 m/g, Silica B: specific surface area 180 m/g), two Ba compounds (barium borate A: specific surface area 40 m/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) was added to prepare a paint. The addition amount of a color pigment and a rust preventive pigment was suitably adjusted so that the desired density|concentration may be obtained in a coating film, when it measured using GD-OES so that it may mention later. Table 1 shows the types of rust preventive pigments added (Si-A is silica A, Si-B is silica B, Ba-A is barium borate A, Ba-B is barium borate B, Mo is calcium molybdate and W represents tungsten oxide). In addition, sample No. 32 is an example to which a rust preventive pigment is not added, and Sample No. 35 is an example in which a methylated melamine resin is used instead of the imino group type melamine resin. In addition, although not described in Table 1, paints using butylated melamine resins instead of imino group type melamine resins were also prepared, but coating films could not be formed because the paints were solidified during production. In Table 1, the thing using the imino group type melamine resin was shown as "imino group type", and the thing using the methylation melamine resin was shown as "methylation".

(Formation of coating film)

The coating material prepared as described above was coated with a roll coater on the Zn-based alloy plating layer so that the average thickness T ₁ of the coating film to be formed was 5 µm, and cured by baking. Baking was performed under the conditions (achievement temperature A, heating time A, heating rate A, holding time, reaching temperature B, heating time B, heating rate B) as described in Table 1. 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. After heating up at the heating rate A to the temperature A and holding|maintaining the predetermined holding time at the attained temperature A, it heated up at the heating rate B from the heating furnace B to the attained temperature B. The sample ratio C _A1 /C _A2 and/or ratio C _B1 /C _B2 of the surface-treated steel sheet was adjusted by changing the combination of the heating rate during baking and the attained temperature and holding time of the steel sheet.

From the obtained coating film, the average density|concentration of the color pigment in a coating film; average concentration of rust preventive pigment in the coating film; Ratio C _A1 /C _A2 for colored pigments; and the ratio C _B1 /C _B2 to the rust preventive pigment was determined by elemental analysis using GD-OES. The values determined in this way are shown in Table 1.

<Evaluation of sample of surface-treated steel sheet>

A sample of the surface-treated steel sheet was prepared as described above, and for each sample having the plating chemical composition, the concentration and concentration distribution of the color pigment and the rust preventive pigment, and the type of the rust preventive pigment as shown in Table 1, the corrosion resistance and resistance are as follows. The evaluation test of blackening was done.

(Evaluation test of corrosion resistance)

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

Evaluation of corrosion resistance was performed by observing the surface (planar part) of the sample 960 hours after the salt spray test with an optical microscope, and determining the rust generation|occurrence|production area rate Z. Specifically, first, the surface of the sample was read with a scanner. Then, the area|region in which rust has generate|occur|produced was selected using image editing software, and the rust generation|occurrence|production area rate was calculated|required. This procedure was performed with respect to five samples, the rust generation|occurrence|production area rate was averaged, and "rust generation area rate Z" was determined. Thus, based on the "rust generation area rate Z" determined for each sample, the rating of each sample was determined in eight steps as follows. A rating of 3 or more was made into the passing point of corrosion resistance.

Rating 8: Z=0%

Rating 7: 0%<Z≤5%

Rating 6: 5%<Z≤10%

Rating 5: 10%<Z≤20%

Rating 4: 20%<Z≤30%

Rating 3: 30%<Z≤40%

Rating 2: 40%<Z≤50%

Rating 1: 50%<Z

(Evaluation test of blackening resistance)

About each sample, as an evaluation test of blackening resistance, the sunshine carbon arc type weather resistance test (SWOM) (based on JIS D0205) was done. The test sprayed water for 12 minutes during the arc lamp injection time for 60 minutes, and performed this for a total of 500 hours. Each sample had a width of 50 mm and a length of 50 mm.

The evaluation of blackening resistance was determined by measuring the "tone change ΔL ^* " of the sample surface before and after performing the weathering test (brightness L of the sample after the test - the lightness L of the sample before the test). ΔL ^* was determined by color tone measurement (JIS Z8729) based on the CIE color system (L*a*b* color system) using a spectrophotometer (Suga Steel Co., Ltd.: SC-T45). According to the measured ΔL ^* , the rating was determined in 8 steps as follows. A rating of 3 or more was made into the 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. About 1-40, the evaluation test of corrosion resistance and blackening resistance was done as mentioned above, and each rating was determined. The obtained results are shown in Table 1.

Sample No. in Table 1. 1 to 8 are examples when the ratio C _A1 /C _A2 of the color pigment is changed. Sample No. In 2-7, since the ratio was in the range of 0.2-0.9 of the range according to this invention, it had sufficient corrosion resistance and blackening resistance.

On the other hand, sample No. In 1, since the ratio C _A1 /C _A2 was less than 0.2, the rust preventive pigment was relatively concentrated excessively on the surface side of the coating film, and a region lacking the rust preventive pigment appeared in a relatively short time, and the corrosion resistance became insufficient. Sample No. In 8, since the ratio C _A1 /C _A2 was greater than 0.9, the colored pigment was dispersed approximately uniformly in the coating film, and many colored pigments were present on the surface side of the coating film. It could not be sufficiently suppressed, and the corrosion resistance became insufficient. In addition, sample No. In 8, since the density|concentration of the color pigment in a coating film was insufficient when the surface of a coating film thickness decreased, the Zn-based alloy plating layer of the underlying layer could not be made completely invisible, and blackening resistance became inadequate.

Sample No. in Table 1. 4 and 9 to 12 are examples when the type of the rust preventive pigment is changed while keeping the ratio C _A1 /C _A2 constant. Sample No. All of 4 and 9 to 12 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 more excellent corrosion resistance. Also, No. 13 is No. It is an example in which the ratio C _A1 /C _A2 and ratio C _B1 /C _B2 were changed using the same rust preventive agent Si-B as in 12, and had sufficient corrosion resistance and blackening resistance.

Sample No. in Table 1. 3 and 14 to 16, or Sample No. 6 and 17 to 19 are examples when the ratio C _A1 /C _A2 to the color pigment is constant and the ratio C _B1 /C _B2 to the rust preventive pigment is changed. All samples had sufficient corrosion resistance and blackening resistance. In addition, when the ratio C _B1 /C _B2 to the rust preventive pigment was 1.3 or more and 4.0 or less, the corrosion resistance was further excellent.

Sample No. in Table 1. 20-25 is an example at the time of changing the average density|concentration of the color pigment in a coating film. Sample No. In 21-24, since the average density|concentration of a colored pigment was the range of 5 mass % or more and 15 mass % or less of the range which concerns on this invention, it had sufficient blackening resistance and corrosion resistance.

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

Sample No. in Table 1. 26-31 is an example at the time of changing the average density|concentration of the rust preventive pigment in a coating film. All samples had sufficient corrosion resistance and blackening resistance. In particular, when the average concentration of the rust preventive pigment in the coating film is in the range of 3 mass % or more and 12 mass % or less, the effect of improving the corrosion resistance by the rust preventive pigment becomes remarkable, and an appropriate amount of the rust preventive pigment moves to the surface layer, and the color pigment Since the orientation was excellent, it had more excellent corrosion resistance and blackening resistance.

Sample No. in Table 1. Since 32 did not contain a rust preventive pigment in a coating film, corrosion resistance and blackening resistance became inadequate. Sample No. In No. 33, the specific surface area of the rust preventive pigment is small, that is, the specific gravity is high, and even if an imino group type melamine resin is used as a curing agent, the concentration distribution of the color pigment and the rust preventive pigment could not be controlled, so the corrosion resistance and blackening resistance became insufficient. Sample No. 34, the holding temperature is high, the desired concentration distribution of the color pigment and the rust preventive pigment cannot be obtained, and the rust preventive pigment is relatively concentrated excessively on the surface side of the coating film, and a region lacking the rust preventive pigment appears in a relatively short time, corrosion resistance This became insufficient. Sample No. No. 35 used a methylated melamine resin for the curing agent, and the thickening phenomenon did not occur remarkably and the concentration distribution of the color pigment and the rust preventive pigment could not be controlled, so the corrosion resistance and blackening resistance became insufficient.

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

As described above, the surface-treated steel sheet according to the present invention in which the average concentration of the color pigment in the coating film is 5% by mass or more and 15% by mass or less, and the color pigment is concentrated toward the Zn-based alloy plating layer side in the coating film, has high corrosion resistance. and had a surface-treated steel sheet excellent in blackening resistance.

Next, sample No. in Table 1. 4, the average particle diameter and average aspect-ratio of the color pigment contained in the coating film, and the average thickness T ₁ of the coating film were changed on the basis of the sample No. of the surface-treated steel sheet. 41 to 58 were produced, and their corrosion resistance and blackening resistance were evaluated. In addition, sample No. For 41-58, the manufacturing conditions were changed suitably, and Sample No. of Table 1 was used. A ratio C _A1 /C _A2 :0.5 and a ratio C _B1 /C _B2 :2.5 similar to 4 were obtained. As a color pigment, resin-coated aluminum was used similarly to the sample in Table 1. As the rust preventive pigment, silica A having an average particle diameter of 3 µm was used. As mentioned above, the determination of the rating of corrosion resistance and blackening resistance is sample No. It carried out similarly to 1-40.

Long diameter X ₁ , short diameter X ₂ and thickness X ₃ of the used colored pigment, the average particle diameter and average aspect ratio of the colored pigment obtained therefrom, the average thickness T ₁ of the obtained coating film, the corrosion resistance score, and the blackening resistance score is shown in Table 2. X ₁ to X ₃ were determined by irradiating 15 colored pigments in the coating film using FE-EPMA, and the average particle diameter and average aspect ratio of the colored pigments were determined from their values. Average thickness T ₁ of the coating film was determined from cross-sectional observation by SEM.

According to Table 2, sample No. In 41-58, any sample had sufficient corrosion resistance and blackening resistance. In particular, when the average particle diameter of the color pigment is 7 µm or more and 30 µm or less, and the average aspect ratio is 20 or more, it is possible to prevent a part of the color pigment from protruding from the coating film and more effectively prevent the color pigment from showing Zn-based alloy plating. Therefore, it had more excellent corrosion resistance and blackening resistance. In particular, when the average thickness T ₁ of the coating film is 3 µm or more, it has a sufficient thickness to make the Zn-based alloy plating layer invisible while suppressing the color pigment from protruding from the coating film, 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 the thickness of such a coating film is preferable from the viewpoint of cost.

According to the present invention, it is possible to provide a surface-treated steel sheet having high corrosion resistance and excellent blackening resistance. Thereby, as a steel plate used for a building material or a household appliance, it becomes possible to guarantee short-term corrosion resistance and long-term corrosion resistance, and furthermore, it becomes possible to prevent the appearance change of a steel plate from occurring over a long period of time. Therefore, it can be said that the present invention is an invention of very high industrial value.

Claims (5)

A steel sheet, a Zn-based alloy plating layer formed on at least one side of the steel sheet, and a coating film of an average thickness T ₁ formed on the Zn-based alloy plating layer and comprising a color pigment, a rust preventive pigment, and a binder resin,
The chemical composition of the Zn-based alloy plating layer is in mass%,
Al: 0.01 to 60%,
Mg: 0.001 to 10%,
Si: 0 to 2%, and
Zn and impurities as the balance,
The average concentration of the colored pigment in the coating film is 5 to 15% by mass, and the average concentration C _A1 of the colored pigment present in the region of the width T ₂ from the surface of the coating film to the thickness direction of the coating film, The ratio C _A1 /C _A2 of the average concentration C _A2 of the color pigment present in the region of width T ₂ in the thickness direction of the coating film from the interface between the coating film and the Zn-based alloy plating layer is 0.2 to 0.9,
The color pigment includes titanium oxide, zinc oxide, iron oxide, aluminum oxide, barium sulfate, aluminum or carbon black,
The rust preventive pigment includes silica, calcium-modified silica, barium borate, barium metaborate, zinc molybdate, calcium molybdate, sodium tungstate, calcium tungstate or tungsten oxide,
The binder resin includes a polyester resin, a urethane resin, or an acrylic resin,
The average thickness T ₁ of the coating film is 3 μm to 15 μm,
T ₂ (㎛) = 0.1 × T ₁ (㎛) + 1.1㎛, characterized in that the surface-treated steel sheet. According to claim 1,
The average concentration of the rust preventive pigment in the coating film is 3 to 12% by mass,
The average concentration C _B1 of the rust preventive pigment existing in the region of width T ₂ from the surface of the coating film in the thickness direction of the coating film, and the width T ₂ from the interface between the coating film and the Zn-based alloy plating layer in the thickness direction of the coating film the ratio C _B1 /C _B2 of the average concentration C _B2 of the rust-preventing pigment present is 1.3 to 4.0,
T ₂ (㎛) = 0.1 × T ₁ (㎛) + 1.1㎛, characterized in that the surface-treated steel sheet. 3. The method of claim 1 or 2,
The color pigment has a long diameter X ₁ of 5 to 30 μm, a short diameter X ₂ of 1 to 30 μm, and a thickness X ₃ of 0.0025 μm or more and 0.5T ₁ or less, and average particle diameter = (X ₁ +X ₂ ) /2, and average aspect ratio = (X ₁ +X ₂ )/2X ₃ , the color pigment has an average particle diameter of 7 to 30 µm, and an average aspect ratio of 20 or more and 100 or less. Surface treatment, characterized in that grater. delete delete