WO2020121431A1 - Covered steel plate - Google Patents

Abstract

This covered steel plate according to one embodiment of the present invention comprises a steel plate, an inorganic coating containing Zn as well as V or Zr, and a coating film with a film thickness in excess of 5 but at most 20 μm, containing a binder resin, an inorganic pigment A with a particle size of 10 to 500 nm, and an inorganic pigment B with a particle size of 1,000 to 10,000 nm. At least one of the inorganic pigment A and the inorganic pigment B contains P. Relative to 100 parts by volume of the coating film, the total amount of the inorganic pigment A and the inorganic pigment B in the coating film is 5 to 50 parts by volume, and the ratio of the parts by volume (A) for the inorganic pigment A over the parts by volume (B) for the inorganic pigment B is such that 0.5 ≤ (A)/(B) ≤ 2.0. In a cross section orthogonal to the rolling direction of the coating film, when t represents the film thickness of the coating film, the number of inorganic pigment A particles is 60 to 100,000, and the number of inorganic pigment B particles is 2 to 50, as observed in a region of t μm in the plate thickness direction by 20 μm in a direction parallel to the plate width direction.

Description

Coated steel sheet

The present invention relates to a coated steel sheet used for automobiles, home appliances, building materials, civil engineering, machinery, furniture, containers, etc.

∙ As exterior materials for home appliances, building materials, automobiles, etc., coated products that have been processed into the desired shape and then painted, or precoated metal sheets with a coating on the steel sheet surface are used.

Generally, pre-coated steel sheets are coated with multiple coatings with different functions on the surface of the steel sheet, so it is required to have excellent adhesion to the coatings. In many cases, the precoated steel sheet is coated with a coating film composed of two layers, a primer layer having corrosion resistance and a top layer having designability, solvent resistance and the like. For example, Patent Document 1 discloses a coated steel sheet having a coating film containing a plurality of anticorrosion pigments on Zn plating.

In recent years, from the viewpoint of manufacturability and economic efficiency, studies have been conducted on colored steel sheets that have excellent workability and can be manufactured at low cost. For example, Patent Document 2 discloses a chromate-free black coated metal plate having a thickness of 2 to 10 μm and having a resin-based black coating film formed thereon.

Japanese Patent Laid-Open No. 2008-291160 International Publication No. 2010/137726 International Publication No. 2012/133671

Patent Document 1 discloses a coated galvanized steel sheet in which a cured coating film is formed on a galvanized steel sheet that has been subjected to chemical conversion treatment. In Patent Document 1, it is premised that a coating film is further formed on the coating film containing a plurality of anticorrosion pigments. In Patent Document 1, it is difficult to obtain the effect of improving the corrosion resistance with only one layer of the coating film containing a plurality of anticorrosion pigments, and a large amount of Zn is eluted from the coating film, which may result in poor corrosion resistance.

The chromate-free black painted metal plate described in Patent Document 2 has a metal portion because the metal plate is scratched when the coating film is scratched during the process until it is processed into a product shape or during processing. When exposed, scratches may be noticeable on the surface of the metal plate.

The inventors of the present invention solve the above problems by forming a hard inorganic film containing Zn and V or Zr on a steel sheet by cathodic electrolysis and further applying a single coating film thereon. planned. That is, by forming a hard inorganic film on a steel sheet, scratches are less likely to reach the steel sheet, and the coated steel sheet having excellent corrosion resistance due to V or Zr is manufactured at low cost to solve the above-mentioned problems. ..

Patent Document 3 discloses a surface-treated steel sheet having a plating layer containing Zn and V.

However, the inventors of the present invention generate a gas containing water when the plating layer described in Patent Document 3 and the inorganic film containing Zn and V or Zr formed by cathodic electrolysis treatment are heated. I found out that. Furthermore, when the present inventors further apply a coating material on the plating layer described in Patent Document 3 or the inorganic film and heat it to form a coating film, the plating layer or the inorganic film is used to form a gas. It was found that the gas penetrates the coating film and the design of the steel sheet on which the coating film is formed deteriorates. It is considered that the gas generated from the plating layer or the inorganic film is caused by water adsorbed on the surface of the plating layer or the inorganic film. In order to obtain a coated steel sheet having excellent design properties, scratch resistance, and solvent resistance, it is necessary to form a coating film that has undergone a curing reaction (polymerization reaction, condensation reaction, etc.) or to increase the film thickness of the coating film. is necessary. However, the present inventors noticeably generate a defect that a gas generated from a lower layer of the coating film penetrates the coating film when forming a cured coating film or when increasing the film thickness of the coating film. I found out that.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a coated steel sheet having excellent designability, flaw resistance, solvent resistance, corrosion resistance, workability, and adhesion.

In order to solve the above problems, the present inventors have studied a coating film to be applied on an inorganic film. When the coating film is subjected to a curing reaction to improve the solvent resistance of the coating film, the gas permeability of the coating film may decrease. Therefore, the present inventors have studied a method of maintaining a solvent resistance and a corrosion resistance of a coating film and not causing a defect in the coating film even when a gas is generated from an inorganic film as a lower layer of the coating film during heating. As a result, in the coating film, at least two kinds of inorganic pigments having a predetermined average particle diameter and different average particle diameters are contained in the coating film in a predetermined content, a predetermined ratio and a predetermined number. It was found that gas permeation through the interface between the binder resin and the inorganic pigment improves the gas permeability of the coating film and improves the design of the coated steel sheet. On the other hand, the present inventors have found that when the gas permeability of the coating film is improved, the permeability of the corrosion factor at the interface between the binder resin and the inorganic pigment in the coating film is also improved, and the corrosion resistance of the coated steel sheet is poor. ..

As a result of further diligent studies by the present inventors, it was found that by including an inorganic pigment containing P in the coating film, the corrosion resistance can be improved even in the coating film having high gas permeability. It is considered that this is due to the following mechanism. When the coating film is water-cooled immediately after curing, a part of the water vapor contained in the gas generated from the lower inorganic film of the coating film is cooled to become water. The P in the inorganic pigment is eluted into this water, and the eluted P penetrates into the inorganic film together with the water, whereby the pH of the inorganic film is lowered. As the pH of the inorganic film decreases, V or Zr in the inorganic film is ionized. By combining P with ionized V or Zr, a protective film made of a phosphorus compound is formed at the interface between the inorganic film and the coating film. By forming a protective film at the interface between the inorganic film and the coating film, elution of Zn and Fe in the inorganic film into the coating film can be suppressed, so that the corrosion resistance of the coated steel sheet is improved.

The present invention was made based on the above findings, and the gist thereof is as follows.

(1) A coated steel sheet according to one aspect of the present invention includes a steel sheet,
An inorganic film formed on at least one surface of the steel sheet and containing Zn and V or Zr;
A binder resin, which is formed on the inorganic film and has a film thickness of more than 5 to 20 μm, and a particle diameter of 10 to 500 nm, and an inorganic pigment B having a particle diameter of 1000 to 10000 nm. Coating film,
A coated steel sheet having
At least one of the inorganic pigment A and the inorganic pigment B contains P,
The total amount of the inorganic pigment A and the inorganic pigment B in the coating film is 5 to 50 parts by volume with respect to 100 parts by volume of the coating film. The ratio of (A) to the volume part (B) of the inorganic pigment B is 0.5≦(A)/(B)≦2.0,
The inorganic pigment is observed in a region of 20 μm in the direction parallel to the plate width direction and t μm in the plate thickness direction in a section perpendicular to the rolling direction of the coating film, where t is the film thickness of the coating film. The number of A is 60 to 100,000, and the number of the inorganic pigment B is 2 to 50.
(2) In the coated steel sheet according to (1) above, the inorganic pigment A or the inorganic pigment B containing P in the coating film may further contain Mg.
(3) In the coated steel sheet according to (1) or (2), the binder resin may include a polyester resin and a melamine resin.
(4) In the coated steel sheet according to (3), the melamine resin may be a butylated melamine resin.
(5) In the coated steel sheet according to any one of (1) to (4) above, the binder resin may include an epoxy resin.
(6) In the coated steel sheet according to any one of (1) to (5) above, V/Zn, which is a mass ratio of V to Zn in the inorganic coating, or Zr to V. Zr/Zn, which is the mass ratio with respect to, may be 0.05 to 0.50 in terms of metal.

According to the above aspect of the present invention, it is possible to provide a coated steel sheet that is excellent in designability, flaw resistance, solvent resistance, corrosion resistance, workability, and adhesion.

It is sectional drawing of the coated steel plate which concerns on one Embodiment of this invention. It is a figure which shows an example of the relationship between the particle size and number of the inorganic pigment contained in the coating film of the coated steel plate which concerns on the same embodiment.

A preferred embodiment of the present invention will be described in detail below.

FIG. 1 is a diagram showing a coated steel sheet 10 according to the present embodiment. The coated steel sheet 10 according to the present embodiment contains an inorganic coating 5 formed by cathodic electrolysis on at least one surface of the steel sheet 4, and a binder resin 3 and two or more kinds of inorganic pigments having different particle sizes thereon. Coating film 6 formed by applying a coating material, heating and drying. Note that, in FIG. 1, the coating film 6 is illustrated in an enlarged manner in the plate thickness direction of the coated steel plate 10.
The coated steel sheet 10 according to the present embodiment has the inorganic coating 5 on at least one surface of the steel sheet 4 and the coating 6 on the inorganic coating 5, so that workability, adhesion, designability, and scratch resistance are provided. Excellent in resistance, solvent resistance and corrosion resistance. In addition, in the present embodiment, excellent workability means that a coating film in a practically processed portion is difficult to be visually recognized as a defect such as a crack, and excellent adhesion means that a coating film is practically used from a steel sheet. It means that it is difficult to peel off, excellent design means that there are few defects visually recognized on the surface of the coating film, and excellent scratch resistance means that scratches are difficult to be visually recognized when scratched. It means that the solvent resistance is excellent, and the mark is hard to be visually recognized when the coating film is rubbed with the solvent, and the excellent corrosion resistance means that the corrosion during the use in the practical environment. This means less generation of product.

(Steel plate 4)
The steel plate 4 according to the present embodiment is not particularly limited, and includes, for example, an extremely low C type (ferrite-based structure), an Al-k type, a two-phase structure type (for example, a structure containing martensite in ferrite, ferrite Any type of steel plate may be used, such as a structure containing bainite therein, a work-induced transformation type (structure containing retained austenite in ferrite), and a fine crystal type (structure mainly containing ferrite).

(Inorganic film 5)
The coated steel sheet 10 according to the present embodiment has an inorganic coating 5 containing Zn and V or Zr, which is formed by cathodic electrolysis on at least one surface of the steel sheet 4. Zn in the inorganic coating 5 exists in the form of at least one of Zn metal, oxide, and hydroxide. V or Zr in the inorganic coating 5 exists in the form of at least one of oxides and hydroxides of V or Zr. When the inorganic coating 5 contains Zn, the corrosion resistance of the coated steel sheet 10 is secured, and when the inorganic coating 5 contains V or Zr, dissolution of Zn in the inorganic coating 5 into the coating film 6 is suppressed, Moreover, the hardness of the coated steel sheet 10 is improved. Therefore, the coated steel sheet 10 is excellent in corrosion resistance and scratch resistance.
In addition, in this embodiment, when the inorganic film 5 contains Zn and V or Zr, when the component analysis of the inorganic film 5 is carried out, at least 1 g/m ^{2 of} Zn and V or Zr are contained in the inorganic film 5. It means that it is contained at least 0.1 g/m ² .

V/Zn, which is the mass ratio of Zn and V in the inorganic coating 5, or Zr/Zn, which is the mass ratio of Zn and Zr in the inorganic coating 5, is 0.05 to 0.50 in terms of metal. preferable. The metal conversion value of V/Zn can be obtained by dividing the content of V in the inorganic coating 5 by the content of Zn in the inorganic coating 5. Further, the Zr/Zn conversion value of metal can be obtained by dividing the content of Zr in the inorganic coating 5 by the content of Zn in the inorganic coating 5.
By setting V/Zn or Zr/Zn in the inorganic coating 5 to 0.05 or more, the corrosion resistance and flaw resistance of the coated steel sheet 10 can be further improved. By setting V/Zn or Zr/Zn in the inorganic coating 5 to 0.50 or less, the adhesion between the inorganic coating 5 and the steel sheet 4 can be further improved.

The components other than Zn and V or Zr in the inorganic film 5 are not particularly limited. The inorganic film 5 may contain Fe, Ni, or the like in an amount of less than 5%.

The component of the inorganic film 5 is cut out from any position on the coated steel sheet, and the surface coating film is removed by rubbing with a film release agent, followed by ICP (Inductively Coupled Plasma) emission spectroscopy and fluorescent X-ray spectroscopy. It can be analyzed by a known method such as an analytical method. When the components of the inorganic film 5 are analyzed by ICP emission spectroscopic analysis, it is advisable to dissolve them in a solution prepared by adding an inhibitor to hydrochloric acid or the like so that the steel sheet does not dissolve.

(Coating film 6)
The coated steel sheet 10 according to the present embodiment has, on the inorganic coating 5, an inorganic pigment A (inorganic pigment 1) having a particle diameter of 10 to 500 nm and an inorganic pigment B (inorganic pigment 2) having a particle diameter of 1000 to 10000 nm. ) And a coating film 6 containing at least two kinds thereof. The coating film 6 contains the inorganic pigment A (inorganic pigment 1) and the inorganic pigment B (inorganic pigment 2) in a predetermined content, a predetermined ratio, and a predetermined number. As a result, when a coating material is applied on the inorganic film 5 and heated to form the coating film 6, the gas generated from the inorganic film 5 causes the binder resin 3 of the coating film 6 and the inorganic pigment A (inorganic pigment 1) and / Or because it easily penetrates the interface with the inorganic pigment B (inorganic pigment 2), the coated steel sheet 10 can have a good appearance.

At least one of the inorganic pigment A (inorganic pigment 1) and the inorganic pigment B (inorganic pigment 2) in the coating film 6 contains P. Therefore, when elemental mapping analysis is performed on the cross section of the coating film 6 according to the present embodiment by EDX (energy dispersive fluorescent X-ray analysis method), the inorganic pigment A (inorganic pigment 1) or the inorganic pigment B (inorganic pigment 2) is detected. P is detected in either one. P in the coating film 6 according to the present embodiment exists in the form of a phosphorus compound. When the coating film 6 is water-cooled immediately after curing, a part of the water vapor contained in the gas generated from the lower inorganic coating film 5 of the coating film 6 is cooled to become water. P in the inorganic pigment containing P is eluted into this water, and the eluted P penetrates into the inorganic film 5 together with the water, whereby the pH of the inorganic film 5 is lowered. As the pH of the inorganic coating 5 decreases, V or Zr in the inorganic coating 5 is ionized. By combining P with ionized V or Zr, a protective film made of a phosphorus compound is formed at the interface between the inorganic film 5 and the film 6. By forming the protective film at the interface between the inorganic film 5 and the film 6, dissolution of Zn in the inorganic film 5 and Fe in the steel plate 4 due to a corrosion factor is suppressed. It is considered that the coated steel sheet 10 can obtain excellent corrosion resistance by the above mechanism.

After the paint is applied on the inorganic film 5, the solvent contained in the paint volatilizes from the surface of the coating film 6, so that the coating film 6 is cured from the surface. Therefore, in order for the gas in the inorganic coating 5 to pass through the coating film 6, the binder resin 3 and the inorganic pigment A (inorganic pigment 1) and/or the inorganic pigment B (inorganic pigment B from the inorganic coating 5 to the surface of the coating film 6 are used. It is important to ensure the path of the interface with the pigment 2). Whatever pigment is used, the path is formed by adding many pigments to the coating film 6 so that almost all the pigments come into contact with each other.

The inventors diligently studied a method for optimally forming a route. As a result, the present inventors have found that the inorganic coating 5 contains the inorganic pigment A (inorganic pigment 1) having a particle diameter of 10 to 500 nm and the inorganic pigment B (inorganic pigment 2) having a particle diameter of 1000 to 10000 nm. Then, the total amount of the volume part (A) of the inorganic pigment A (inorganic pigment 1) and the volume part (B) of the inorganic pigment B (inorganic pigment 2) of the coating film 6 is 5 with respect to 100 parts by volume of the coating film. ˜50 parts by volume, and the ratio of the volume part (A) of the inorganic pigment A (inorganic pigment 1) to the volume part (B) of the inorganic pigment B (inorganic pigment 2) is 0.5≦(A). /(B)≦2.0, and a region of 20 μm in the direction parallel to the plate width direction and t μm in the plate thickness direction in a cross section perpendicular to the rolling direction, where t is the film thickness of the coating film 6. When the number of the inorganic pigment A (inorganic pigment 1) is 60 to 100,000 and the number of the inorganic pigment B (inorganic pigment 2) is 2 to 50, which are observed in (region of 20 μm×tμm), the route is changed. We have found that it can be formed optimally. The details of the mechanism by which the gas can optimally form the path are unknown, but the present inventors presume as follows. The maximum particle size of the inorganic pigment A (inorganic pigment 1) in this embodiment is equal to or smaller than the radius of the minimum particle size of the inorganic pigment B (inorganic pigment 2). Therefore, the gap between the adjacent inorganic pigments B (inorganic pigment 2) having a relatively large particle diameter and the inorganic pigment B (inorganic pigment 2) is likely to be filled with the inorganic pigment A (inorganic pigment 1). Therefore, not only the interface between the inorganic pigment B (inorganic pigment 2) and the binder resin 3, but also the inorganic pigment A (inorganic pigment 1) and the binder resin 3 located between the adjacent inorganic pigments B (inorganic pigment 2). The interface with and also acts as a gas path. Further, not only the contact points between the inorganic pigments B (inorganic pigment 2) but also the contact points between the inorganic pigment B (inorganic pigment 2) and the inorganic pigment A (inorganic pigment 1) are routes. Thereby, the path from the inorganic coating 5 to the surface of the coating 6 is optimally formed. Therefore, the gas generated from the inorganic film 5 is likely to escape from the surface of the coating film 6, and the coating film 6 is less likely to have defects.

When the coating film 6 contains only the inorganic pigment A (inorganic pigment 1), compared to the case where the inorganic pigment B (inorganic pigment 2) and the inorganic pigment A (inorganic pigment 1) are mixed in the coating film 6, gas The area of the interface between the pigment and the binder resin 3 which becomes the route of (2) becomes too large. Therefore, the gas permeability at the interface between the binder resin 3 in the coating film 6 and the inorganic pigment A (inorganic pigment 1) becomes too large, and the corrosion resistance of the coated steel sheet 10 deteriorates. On the other hand, when the coating film 6 contains only the inorganic pigment B (inorganic pigment 2), compared with the case where the inorganic pigment B (inorganic pigment 2) and the inorganic pigment A (inorganic pigment 1) are mixed in the coating film 6. The area of the interface between the pigment and the binder resin 3, which serves as a gas path, is reduced. Further, the number of contacts between the inorganic pigments B (inorganic pigment 2) is also the number of contacts between the inorganic pigments B (inorganic pigment 2) and the inorganic pigment A (inorganic pigment 1) mixed in the coating film 6. Less than contacts. For this reason, the gas permeability of the coating film 6 becomes insufficient, and the design of the coated steel sheet 10 deteriorates.

In general, inorganic pigments have a small particle size, so they tend to agglomerate during the process of dispersion in paint. Therefore, it is difficult to disperse the inorganic pigment having a small particle diameter in the coating film 6 while maintaining the primary particle diameter of each inorganic pigment. Inorganic pigments having a small particle size (inorganic pigments having a particle size of 100 nm or less) are aggregated, and the aggregated inorganic pigments are present in the coating film 6 in the form of secondary particles having a particle size larger than the primary particle size. There are cases. The particle size of the secondary particles (particles in which the inorganic pigment is aggregated) is hereinafter referred to as “secondary particle size”. The particle diameters of the inorganic pigment A (inorganic pigment 1) and the inorganic pigment B (inorganic pigment 2) in the coating film 6 in the present embodiment include not only the primary particle diameter but also the secondary particle diameter. That is, the inorganic pigment A (inorganic pigment 1) having a particle diameter of 10 to 500 nm indicates an inorganic pigment having a primary particle diameter and a secondary particle diameter of 10 to 500 nm, which are present in the coating film 6. The inorganic pigment B (inorganic pigment 2) having a particle size of 1000 to 10000 nm is an inorganic pigment present in the coating film 6 having a primary particle size and a secondary particle size of 1000 to 10000 nm.

The total amount of the volume part (A) of the inorganic pigment A (inorganic pigment 1) and the volume part (B) of the inorganic pigment B (inorganic pigment 2) of the coating film 6 is 5 parts with respect to 100 parts by volume of the coating film 6. ˜50 parts by volume. When the total amount of the inorganic pigment A (inorganic pigment 1) and the inorganic pigment B (inorganic pigment 2) in the coating film 6 is less than 5 parts by volume, the area of the interface between the pigment and the binder resin 3 that serves as a path for gas is Since it becomes smaller, the gas permeability of the coating film 6 becomes insufficient, and the design of the coated steel sheet 10 deteriorates. On the other hand, when the total amount of the inorganic pigment A (inorganic pigment 1) and the inorganic pigment B (inorganic pigment 2) in the coating film 6 exceeds 50 parts by volume, the area of the interface between the pigment and the binder resin 3 becomes too large. Therefore, the gas permeability of the coating film 6 becomes too high, and the corrosion resistance of the inorganic coating film 5 and the coated steel sheet 10 deteriorates. Furthermore, since the total amount of the inorganic pigment A (inorganic pigment 1) and the inorganic pigment B (inorganic pigment 2) increases, the amount of the binder resin 3 becomes too small, and the durability of the coating film 6 decreases. From the viewpoint of processability, the total amount of the inorganic pigment A (inorganic pigment 1) volume part and the inorganic pigment B (inorganic pigment 2) volume part of the coating film 6 is 10 parts with respect to 100 parts by volume of the coating film 6. It is preferably from 30 to 30 parts by volume.

The ratio of the volume part (A) of the inorganic pigment A (inorganic pigment 1) and the volume part (B) of the inorganic pigment B (inorganic pigment 2) of the coating film 6 is 0.5≦(A)/(B)≦ It is 2.0. When the ratio of the volume part (A) of the inorganic pigment A (inorganic pigment 1) and the volume part (B) of the inorganic pigment B (inorganic pigment 2) of the coating film 6 is less than 0.5 or more than 2.0, Since the gas permeability of the coating film 6 deteriorates, the design of the coated steel sheet 10 deteriorates. The ratio of the volume part (A) of the inorganic pigment A (inorganic pigment 1) and the volume part (B) of the inorganic pigment B (inorganic pigment 2) of the coating film 6 is 0.7≦(A)/(B)≦ 1.7 is preferred.

The film thickness of the coating film 6 is more than 5 to 20 μm (more than 5 μm, 20 μm or less). When the thickness of the coating film 6 is 5 μm or less, when the coating film 6 has a flaw, the ratio of the depth of the flaw to the thickness of the coating film 6 tends to be large. For this reason, the flaws are apt to stand out, and the flaw resistance of the coated steel sheet 10 deteriorates. When the film thickness of the coating film 6 is more than 20 μm, the coating film 6 becomes thicker, the gas permeability is lowered, and the design of the coated steel sheet 10 is deteriorated. The film thickness of the coating film 6 is preferably more than 7 μm or 16 μm or less.

The number of the inorganic pigment A (inorganic pigment 1) and the inorganic pigment B (inorganic pigment 2) in the coating film 6 is the cross section perpendicular to the rolling direction and the plate width direction when the thickness of the coating film 6 is t. The number of inorganic pigments A (inorganic pigment 1) is 60 to 100,000 and the number of inorganic pigments B (inorganic pigment 2) is 20 μm in the parallel direction and tμm in the plate thickness direction (region of 20 μm×tμm). 2 to 50. By setting the number of each of the inorganic pigment A (inorganic pigment 1) and the inorganic pigment B (inorganic pigment 2) in the above area in the coating film 6 within the above range, the pigment serving as a gas path and the binder resin 3 It is possible to secure a sufficient amount of the binder resin 3 while securing the area of the interface. For this reason, the gas permeability and durability of the coating film 6 can be maintained, and as a result, the design and corrosion resistance of the coated steel sheet 10 can be improved.

The coating film 6 may include an inorganic pigment C having a particle size (greater than 500 nm and less than 1000 nm) other than the inorganic pigment A (inorganic pigment 1) and the inorganic pigment B (inorganic pigment 2). However, the number of inorganic pigments having a particle size of more than 500 nm and less than 1000 nm contained in the coating film 6 is in the above-described 20 μm×tμm region (20 μm in the direction parallel to the plate width direction, and film thickness tμm in the plate thickness direction). In the area), 10 or less are preferable. When the number of the inorganic pigments C having a particle size of more than 500 nm and less than 1000 nm in the coating film 6 is 10 or less in the above region (region of 20 μm×tμm), the inorganic pigment B and other inorganic pigments C are The number of contacting portions does not increase too much, the inorganic pigment B is pushed by the inorganic pigment C, and the inorganic pigments B (inorganic pigment 2) easily contact each other. Therefore, the gas permeability of the coating film 6 can be further improved, and the designability of the coated steel sheet 10 can be further improved.
Further, even if the coating film 6 contains an inorganic pigment having a particle size of “less than 10 nm” or “more than 10000 nm”, the number of particles of “less than 10 nm” is 30 or less, and the particle size of “more than 10000 nm” is 4 or less. If the number is less than or equal to the number, the characteristics of the coated steel sheet according to this embodiment are not affected.

The particle size of the inorganic pigment in the coating film 6 of the coated steel sheet 10 is obtained by the following method. First, a thin film sample is prepared by the microtome method so that the cross section of the coated steel sheet 10 perpendicular to the rolling direction can be observed. Using a 200 kV field emission transmission electron microscope (FE-TEM) in a region of 20 μm×t of the obtained thin film sample (region in which the thickness is 20 μm in the direction parallel to the plate width direction and the film thickness tμm in the plate thickness direction). Observe at least 5 areas at a magnification of 100,000. The equivalent circle diameters of all the inorganic pigments in the observation region are calculated using the following formula 1, and the equivalent circle diameters are taken as the particle diameters of the respective inorganic pigments.

Equivalent circle diameter=2√(S/π) Equation 1
However, S is the area of the inorganic pigment, and π is the circular constant.

In the above observation region, an inorganic pigment having a particle diameter of 10 to 500 nm is referred to as an inorganic pigment A (inorganic pigment 1), an inorganic pigment having a particle diameter of more than 500 nm and less than 1000 nm is referred to as an inorganic pigment C, and a particle diameter of 1000 to 10000 nm. Let some inorganic pigment be the inorganic pigment B (inorganic pigment 2). Furthermore, the numbers of the inorganic pigment A (inorganic pigment 1), the inorganic pigment C, and the inorganic pigment B (inorganic pigment 2) observed in the above observation area are obtained, and the number of the pigments in the plurality of observation areas (5 areas) is calculated. By calculating the average, the numbers of the inorganic pigment A (inorganic pigment 1), the inorganic pigment C, and the inorganic pigment B (inorganic pigment 2) are obtained.
Further, P element mapping analysis is performed on the above observation region by EDX to determine whether the inorganic pigment A (inorganic pigment 1) and/or the inorganic pigment B (inorganic pigment 2) is an inorganic pigment containing P (phosphorus compound). To do. In addition, it is determined whether or not the inorganic pigment A and/or the inorganic pigment B containing P (phosphorus compound) contains Mg by Mg element mapping analysis.

In the coated steel sheet 10 according to the present embodiment, when the particle size of the inorganic pigment in the coating film 6 is measured by the method described above, the inorganic pigment A (inorganic pigment 1) having a particle size within the range of 10 to 500 nm, At least two kinds of the inorganic pigment B (inorganic pigment 2) having a particle diameter in the range of 1,000 to 10,000 nm are included. The relationship between the particle diameter and the number of inorganic pigments in the coating film 6 of the coated steel sheet 10 according to this embodiment is as shown in FIG.

The contents of the inorganic pigment A (inorganic pigment 1) and the inorganic pigment B (inorganic pigment 2) in the coating film 6 are calculated by observing the coating film cross section of the coating film 6. Hereinafter, an example of the calculation method will be described.
Using a 200 kV field emission transmission electron microscope (FE-TEM), at least a cross section of the coating film 6 (a portion of the coating film 6 in the steel plate cut in the direction perpendicular to the rolling direction) at a magnification of 100,000 was used. Observe the field of view. The total area of the coating film 6 observed in the entire visual field is obtained. Next, the average value and the average particle size of the number of each of the inorganic pigment A (inorganic pigment 1) and the inorganic pigment B (inorganic pigment 2) in each visual field are determined. From the average value and the average particle size of the number of each of the inorganic pigment A (inorganic pigment 1) and the inorganic pigment B (inorganic pigment 2), all of the inorganic pigment A (inorganic pigment 1) and the inorganic pigment B (inorganic pigment 2) are obtained. The total area of view is obtained. From the total area of the coating film 6 and the total area of the inorganic pigment A (inorganic pigment 1) and the inorganic pigment B (inorganic pigment 2) in all fields of view, the inorganic pigment A (inorganic pigment 1) and the inorganic material for the coating film 6 The area ratio of each of the pigments B (inorganic pigment 2) (area of coating film 6: area of inorganic pigment A (inorganic pigment 1), area of coating film 6: area of inorganic pigment B (inorganic pigment 2)) is obtained. Since the volume ratio can be calculated by multiplying the area ratio by the power of 3/2, the area ratio of the inorganic pigment A (inorganic pigment 1) and the inorganic pigment B (inorganic pigment 2) to the area of the coating film 6 is 3 respectively. /2, the volume ratio of the inorganic pigment A (inorganic pigment 1) and the inorganic pigment B (inorganic pigment 2) to the coating film 6 (volume of coating film 6: volume of inorganic pigment A (inorganic pigment 1), The volume of the coating film 6: the volume of the inorganic pigment B (inorganic pigment 2) is obtained. From these volume ratios, the volume part of the inorganic pigment A (inorganic pigment 1) and the volume part of the inorganic pigment B (inorganic pigment 2) with respect to 100 volume parts of the coating film 6 are calculated. By calculating these total values, the total amount of the volume part of the inorganic pigment A (inorganic pigment 1) and the volume part of the inorganic pigment B (inorganic pigment 2) to 100 volume parts of the coating film 6 is obtained. Further, based on 100 parts by volume of the obtained coating film 6 and 100 parts by volume of the inorganic pigment A (inorganic pigment 1) and the inorganic pigment B (inorganic pigment 2), the inorganic pigment A (inorganic pigment 1) by volume is obtained. The ratio ((A)/(B)) of (A) and the volume part (B) of the inorganic pigment B (inorganic pigment 2) is obtained.

As the inorganic pigment containing no P, which can be used for the coating film 6 of the coated steel sheet 10 according to the present embodiment, it is possible to use a powder paint which is insoluble in water or oil, which is generally used as a paint. it can. Examples thereof include carbon black, iron oxide, titanium oxide, silica, aluminum, alumina, kaolin, calcium carbonate, barium sulfate, vanadate pigments, molybdate pigments and the like. When a compound that dissolves in water or oil is used as the inorganic pigment of the coating film 6, the corrosion resistance of the coated steel sheet 10 may be significantly reduced. As the inorganic pigment used for the coating film 6 of the coated steel sheet 10 according to this embodiment, carbon black, titanium oxide, silica and aluminum are preferable.

As described above, the inorganic pigment A or the inorganic pigment B in the coating film 6 contains P (phosphorus compound). P contained in the inorganic pigment in the coating film 6 is appropriately eluted into water in the gas generated from the inorganic coating film 5, penetrates into the inorganic coating film 5, and is an inorganic component (V or Zr) in the inorganic coating film 5. By combining with, a protective film made of a phosphorus compound is formed at the interface between the inorganic film 5 and the coating film 6. Examples of the inorganic pigment containing P in the coating film 6 include phosphate pigments and phosphomolybdate pigments. In particular, an inorganic pigment produced by baking a phosphoric acid compound and an organic acid is suitable as an inorganic pigment containing P in the coating film 6 because the P component is easily eluted. In addition, as the inorganic pigment containing P in the coating film 6, condensed aluminum phosphate, a pigment obtained by modifying a phosphate pigment with an alkaline earth metal ion, and the like can be given. Examples of alkaline earth metal ions include Ca ions and Mg ions.

It is preferable that the inorganic pigment containing P in the coating film 6 is aluminum tripolyphosphate, zinc molybdenum orthophosphate, zinc polyphosphate, or the like because the corrosion resistance of the coated steel sheet 10 can be further improved.

When the P-containing inorganic pigment in the coating film 6 further contains Mg, a protective coating is more likely to be formed at the interface between the inorganic coating 5 and the coating film 6, and the corrosion resistance of the coated steel sheet 10 is further improved. You can Examples of the inorganic pigment containing P and Mg include magnesium phosphate, magnesium diphosphate, and magnesium tripolyphosphate treated with magnesium.

The coating film 6 of the coated steel sheet 10 according to the present embodiment contains one kind or two or more kinds of the binder resin 3. The binder resin 3 has a hydroxyl group, a carboxylic acid group, an amino group or an epoxy group as a functional group at the terminal of the resin. The binder resin 3 in the coating film 6 is not particularly limited, but examples thereof include acrylic resin, urethane resin, polyester resin, epoxy resin, and melamine resin. In order to cause the binder resin 3 to undergo a curing reaction, a binder resin in which functional groups generally known as functional groups to be cured are combined may be used, and examples thereof include a hydroxyl group and an amino group, a carboxylic acid group and an amino group, and the like. A combination of a hydroxyl group and an epoxy group may be used.

Since the binder resin 3 contains a polyester resin and a melamine resin, it becomes a cured coating film, so that the solvent resistance of the coating film 6 can be further improved. In addition, the polyester resin is suitable because it improves the adhesion and workability between the inorganic coating 5 and the coating 6.

The polyester resin that can be used for the coating film 6 according to this embodiment can be formed by a polymerization reaction of a polyvalent carboxylic acid and a polyhydric alcohol. The polyester resin that can be used for the coating film 6 according to the present embodiment may be modified.

The polyvalent carboxylic acid component is not particularly limited, and examples thereof include terephthalic acid, isophthalic acid, orthophthalic acid, 2,6-naphthalenedicarboxylic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, dodecanedicarboxylic acid, Azelaic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, dimer acid, trimellitic anhydride, pyromellitic anhydride and the like can be mentioned. As the polyvalent carboxylic acid component, one kind or two kinds or more of these can be optionally used.

The polyhydric alcohol is not particularly limited, but for example, ethylene glycol, diethylene glycol, 1,3-propanediol, 1,2-propanediol, triethylene glycol, 2-methyl-1,3-propanediol, 2, 2-dimethyl-1,3-propanediol, 2-butyl-2-ethyl 1,3-propanediol, 1,4-butanediol, 2-methyl-1,4-butanediol, 2-methyl-3-methyl -1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1 , 2-cyclohexanedimethanol, hydrogenated bisphenol-A, dimer diol, trimethylolethane, trimethylolpropane, glycerin, pentaerythritol and the like. As said polyhydric alcohol, 1 type(s) or 2 or more types can be arbitrarily used among these.

The melamine resin is not particularly limited, but examples thereof include methylated melamine and butylated melamine. Examples of commercially available melamine resin, Orunekkusu Co., Ltd. of melamine resin "Cymel ^TM", can be used, such as "My coat ^TM", DIC Co., Ltd. melamine resin "Super BECKAMIN ^TM".

When a butylated melamine resin is used as the melamine resin, the gas easily passes therethrough, so that the design of the coated steel sheet 10 can be further improved. Therefore, in the coated steel sheet 10 according to the present embodiment, the binder resin 3 of the coating film 6 preferably contains a polyester resin and a butylated melamine resin.
Butylated melamine resin is excellent in self-condensation. In self-condensation, since the reaction proceeds after the temperature of the coating film 6 becomes higher, the time until the reaction (self-condensation) of the methylated melamine starts (the time until the binder resin 3 hardens) becomes longer. .. By increasing the time until the binder resin 3 hardens, the gas generated from the inorganic film 5 can escape from the surface of the coating film 6 for a longer time, and more gas permeates, so that the design of the coated steel sheet 10 is improved. Sex is improved. Since the butylated melamine resin is insoluble in water, it is preferable to use a solvent-based paint rather than an aqueous paint.

In the coated steel sheet 10 according to the present embodiment, the binder resin 3 of the coating film 6 preferably contains an epoxy resin. Epoxy resins reduce the melt viscosity of the resin. Therefore, the gas permeability of the coating film 6 can be further improved in the time period until the coating film 6 is cured after the solvent is dried, and the design of the coated steel sheet 10 can be further improved.

The weight ratio of the polyester resin and the melamine resin in the binder resin 3 represented by [Pes]/[Me] is preferably 1≦[Pes]/[Me]≦10. In addition, [Pes] indicates the weight of the polyester resin in the binder resin 3, and [Me] indicates the weight of the melamine resin in the binder resin 3. When the weight ratio of the polyester resin and the melamine resin in the binder resin 3 is within the above range, the gas permeability of the coating film 6 can be further improved, and the designability of the coated steel sheet 10 can be further improved. ..

When the binder resin 3 contains a polyester resin and a melamine resin, it is more preferable that the coating film 6 further contains at least one of amine-neutralized dodecylbenzenesulfonic acid and amine-neutralized paratoluenesulfonic acid. When one or more of these are contained in the coating film 6, the crosslinking reaction between the polyester and melamine contained in the binder resin 3 is suppressed and the self-condensation reaction of melamine is promoted, so that the gas permeability of the coating film 6 is further improved. However, the design of the coated steel sheet 10 is further improved.

The type and weight of the binder resin component in the coating film 6 can be analyzed by using an FT-IR (Fourier transform infrared spectrophotometer) or an NMR apparatus (nuclear magnetic resonance apparatus).

Next, a method of manufacturing the coated steel sheet 10 according to the present embodiment will be described. The coated steel sheet 10 according to the present embodiment is manufactured by forming an inorganic coating 5 on at least one surface of the steel sheet 4 by cathodic electrolysis and applying a coating material on the inorganic coating 5 to form a coating film 6. It

For the cathodic electrolysis treatment, a solution containing Zn ions and V ions or Zr ions can be used. The solution containing Zn ions and V ions or Zr ions can be prepared by a known method. For example, it can be prepared by dissolving Zn sulfate and vanadyl oxide or zirconyl nitrate in sulfuric acid. ..

It is desirable that the pH of the solution for cathodic electrolysis be 1.0 to 4.0. If the pH of the solution for cathodic electrolysis is lower than 1.0, V ions or Zr ions may not be incorporated into the inorganic film 5. If the pH of the solution for cathodic electrolysis is higher than 4.0, V ions or Zr ions may precipitate in the solution as oxides, and V ions or Zr ions may not be incorporated into the inorganic coating 5.

It is desirable that the mass ratio of V ions or Zr ions in the solution for cathodic electrolysis treatment to Zn ions (V ions/Zn ions, or Zr ions/Zn ions) is 0.2 to 0.9. When V ion/Zn ion or Zr ion/Zn ion in the solution for cathodic electrolysis is less than 0.2 or more than 0.9, V ion or Zr ion is not taken into the inorganic film 5. There is.

The content of ions in the solution for cathodic electrolysis can be analyzed by a known method such as ICP (Inductively Coupled Plasma) emission spectroscopy or fluorescent X-ray spectroscopy. Further, the content of ions in the solution for cathodic electrolysis is determined by measuring the amount of components dissolved in the solution for cathodic electrolysis (amounts of Zn sulfate, vanadyl oxide, zirconyl nitrate, etc.) as V ions (g/L), Zn. It can also be obtained by converting into ions (g/L) and Zr ions (g/L).

As a coating method of the coating material for forming the coating film 6, there are known methods such as a bar coater method, a roll coating method, a Ringer roll coating method, an air spray method, an airless spray method and a dipping method.

The method for drying the paint for forming the coating film 6 is not particularly limited, and examples thereof include a method of using hot air, induction heating, near infrared rays, open flame, or the like, alone or in combination.

The following is a detailed description of examples of the present invention. The conditions in the examples are merely examples adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to these example conditions. The present invention can employ various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

1. Steel plate As the steel plate, a SPCD steel plate described in JIS G 3141:2011, having a plate thickness of 0.8 mm and being a general cold-rolled steel plate for drawing was used.

2. Inorganic film A solution containing Zn ions and V ions and a solution containing Zn ions and Zr ions were prepared. The solution was prepared by dissolving Zn sulfate and vanadyl oxide or zirconyl nitrate in sulfuric acid. The components of the inorganic film were adjusted by adjusting the amounts of the components dissolved in the solution. The pH of the solution was adjusted by the amount of sulfuric acid and the amount of Na hydroxide. The prepared solution is shown in Table 1. The mass (g/L) of each ion in Table 1 was obtained by converting the amount of components (Zn sulfate, vanadyl oxide, zirconyl nitrate) dissolved in the solution into the amount of each ion.
Using the solutions in Table 1, an inorganic coating was formed on both sides of the steel sheet by cathodic electrolysis treatment. Each component in the formed inorganic film was identified and confirmed by ICP emission spectroscopy. Table 2 shows the components of the inorganic coating formed on both sides of the steel sheet.

3. Coating film Using the Solvesso 150 as a solvent, the binder resin shown in Table 3, the inorganic pigments shown in Table 4-1 and, if necessary, the additives shown in Table 4-2 are mixed and stirred to obtain a coating material. Was produced. The prepared coating materials are shown in Table 5-1 and Table 5-2.
Table 4-1 lists the secondary particle diameters of the inorganic pigments, but these values are estimated values. When the coating material prepared by mixing the inorganic pigments shown in Table 4-1 was formed as a coating film on the inorganic film, the particle diameters of the inorganic pigments in the coating film were the primary particle diameter of Table 4-1 and 2 It is not always the value of the secondary particle size.
In Tables 5-1 and 5-2, [Pes]/[Me] represents the weight ratio of the polyester resin and the melamine resin in the binder resin, and [Pes]+[Me] represents the binder resin. Shows the total weight of the polyester resin and the melamine resin.

The coating materials shown in Table 5-1 and Table 5-2 were applied on the above inorganic film with a bar coater in an amount of 10 μm, and then heated in a hot air oven so that the ultimate plate temperature reached 230° C. in 30 seconds. Then, it was immersed in water and cooled to form a coating film. A coated steel sheet was obtained by the above method.

Regarding the coating film of the obtained coated steel sheet, the components of the inorganic coating film and the coating film were analyzed by the following methods. The obtained results are shown in Table 6-1 and Table 6-2.

(Inorganic film)
The components of the inorganic film were analyzed by the following methods. A sample was cut out from an arbitrary position on the coated steel sheet, and the coating film on the surface was removed by a coating film peeling agent. The components of the inorganic film were analyzed by performing ICP (Inductively Coupled Plasma) emission spectroscopy on the inorganic film exposed on the surface. In the ICP emission spectroscopic analysis method, the solution was measured by dissolving it in a solution of an inhibitor added to hydrochloric acid so as not to dissolve the steel sheet. When the inorganic coating contained 1 g/m ² or more of Zn, it was described as “Yes” in Tables 6-1 and 6-2, and when Zn was less than 1 g/m ² , it was described as “No”. Further, when the inorganic coating contains 0.1 g/m ² or more of V or Zr, it is described as “Yes” in Table 6-1 and Table 6-2, and V or Zr is less than 0.1 g/m ^2. In the case of, it described as "No."

(Inorganic pigment in coating film)
A thin film sample was prepared by the microtome method so that the cross section of the coated steel sheet 10 perpendicular to the rolling direction can be observed. In a 20 μm×tμm region (20 μm in the direction parallel to the plate width direction and film thickness tμm in the plate thickness direction of the steel sheet) of the coating film portion of the obtained thin film sample, a 200 kV field emission transmission electron microscope (FE- 5 regions were observed using TEM) at a magnification of 100,000. Using the following formula 1, the equivalent circle diameters of all the inorganic pigments in the observation visual field were calculated, and this equivalent circle diameter was defined as the particle diameter of each inorganic pigment.
Number of inorganic pigment A having a particle size in the range of 10 to 500 nm, inorganic pigment having a particle size of more than 500 nm and less than 1000 nm, and inorganic pigment B having a particle size in the range of 1000 to 10000 nm in the observation region And the average number of particles in a plurality of observation regions was calculated to obtain the numbers of the inorganic pigment A, the inorganic pigments having a particle size of more than 500 nm and less than 1000 nm, and the inorganic pigment B.
Elemental mapping analysis was performed on the above observation region by EDX to determine whether the inorganic pigment A or the inorganic pigment B is an inorganic pigment containing P (phosphorus compound). In addition, it was determined by element mapping analysis whether the inorganic pigment A or the inorganic pigment B containing P (phosphorus compound) contains Mg.

Equivalent circle diameter=2√(S/π) Equation 1
However, S is the area of the inorganic pigment, and π is the circular constant.

When the coating film contains the inorganic pigment A having a particle size in the range of 10 to 500 nm and the number of the inorganic pigment A in the coating film is 60 to 100,000, Table 6-1 and Table 6- In the column of the inorganic pigment A of 2, "Yes" was described, and when the coating film did not contain the inorganic pigment A, it was described as "No". When the number of the inorganic pigments A in the coating film is less than 60, "less than" is described in the column of the inorganic pigment A in Table 6-1 and Table 6-2, and the inorganic pigments in the coating film are indicated. When the number density of A was more than 100,000, it was described as "extra".

When the coating film contains the inorganic pigment B having a particle diameter in the range of 1000 to 10000 nm, and the number of the inorganic pigment B in the coating film is 2 to 50, Table 6-1 and Table 6- In the column of No. 2 inorganic pigment B, “Yes” was described, and when the coating film did not contain the inorganic pigment B, it was described as “No”. When the number of the inorganic pigments B in the coating film is less than 2, it is described as “less than” in the column of the inorganic pigment B in Table 6-1 and Table 6-2, and the inorganic pigments in the coating film are indicated. When the number of B was more than 50, it was described as "super."

When the number of inorganic pigments (inorganic pigment C) having a particle size of more than 500 nm and less than 1000 nm in the coating film is 10 or less, the values of “more than 500 nm and less than 1000 nm” in Table 6-1 and Table 6-2 are shown. When the number of the inorganic pigments (inorganic pigment C) having a particle size of more than 500 nm and less than 1000 nm in the coating film is more than 10 when "Yes" is described in the column of "10 particles", "No" is displayed. ".

When at least one of the inorganic pigment A and the inorganic pigment B in the coating film is an inorganic pigment containing P (phosphorus compound), “Yes” is indicated in the “P content” column in Tables 6-1 and 6-2. If the inorganic pigment A and the inorganic pigment B in the coating film were inorganic pigments containing no P (phosphorus compound), they were described as “No”.
When the inorganic pigment A or the inorganic pigment B in the coating film contains P (phosphorus compound) and the inorganic pigment A or the inorganic pigment B containing P further contains Mg, the results shown in Table 6-1 and Table 6-2 In the column of “P*Mg”, “Yes” is described, and when the inorganic pigment A or inorganic pigment B containing P does not contain Mg, “No” is described.

The volume part of the inorganic pigment A and the volume part of the inorganic pigment B with respect to 100 volume parts of the coating film were obtained by the following method.
Five-view observation of the cross section of the coating film (the coating film 6 part of the steel plate cut in the direction perpendicular to the rolling direction) at a magnification of 100,000 times using a 200 kV field emission transmission electron microscope (FE-TEM) did. The total area of the coating film observed in all visual fields was determined. Next, the average value and the average particle size of the number of each of the inorganic pigment A and the inorganic pigment B in each visual field were obtained. From the average value of the number of each of the inorganic pigment A and the inorganic pigment B and the average particle diameter, the total area of the inorganic pigment A and the inorganic pigment B in the entire visual field was obtained. From the total area of the coating film and the total area of the inorganic pigment A and the inorganic pigment B in the entire field of view, the area ratio of each of the inorganic pigment A and the inorganic pigment B to the area of the coating film (coating area: inorganic pigment A Area, coating film area: inorganic pigment B area). The volume ratio of each of the inorganic pigment A and the inorganic pigment B to the coating film (volume of the coating film: volume of the inorganic pigment A is calculated by multiplying the area ratio of each of the inorganic pigment A and the inorganic pigment B to the area of the coating film by 3/2. , Volume of coating film: volume of inorganic pigment B). From these volume ratios, the volume part of the inorganic pigment A and the volume part of the inorganic pigment B with respect to 100 volume parts of the coating film were calculated. By calculating the total of these, the total ((A)+(B)) of the volume of the inorganic pigment A and the volume of the inorganic pigment B with respect to 100 parts by volume of the coating film was obtained. Further, from the volume part of the inorganic pigment A and the volume part of the inorganic pigment B relative to 100 parts by volume of the obtained coating film, the ratio of the volume part (A) of the inorganic pigment A and the volume part (B) of the inorganic pigment B ( (A)/(B)) was obtained.
The total ((A)+(B)) of the volume part of the inorganic pigment A and the volume part of the inorganic pigment B relative to 100 volume parts of the obtained coating film, and the volume part (A) of the inorganic pigment A and the inorganic pigment B. Tables 6-1 and 6-2 show the ratio ((A)/(B)) to the volume part (B).

(Binder resin in coating film)
The kinds of components of the binder resin in the coating film were analyzed using an NMR apparatus (nuclear magnetic resonance apparatus).
In the case where the weight ratio [Pes]/[Me] of the polyester resin and the melamine resin in the binder resin was 1 to 10, in the case of “1≦Pes/Me≦10” in Table 6-1 and Table 6-2. “Yes” is described in the column, and “No” is described when [Pes]/[Me] is less than 1 or more than 10.
If the binder resin contains a butylated melamine resin, enter “Yes” in the “BuMe-containing” column in Table 6-1 and Table 6-2, and “No” if the butylated melamine resin is not included. I wrote.
When the binder resin contained an epoxy resin, “Yes” was described in the “Ep-containing” column in Tables 6-1 and 6-2, and when the epoxy resin was not contained, “No” was described.

The following tests 1 to 6 were conducted on the coated steel sheets in Table 6-1 and Table 6-2. Out of the tests 1 to 6, when the evaluation in all the tests was 3 or more, the coated steel sheet according to the present invention was judged to be acceptable as the coated steel sheet having the desired characteristics. If at least one of the tests 1 to 6 was evaluated to be 2 or less, the coated steel sheet according to the present invention was determined to be unacceptable as a coated steel sheet having no desired characteristics. The tests 1 to 6 will be described in detail below.

Test 1. Solvent resistance As for the solvent resistance of the coated steel sheet, a test piece of a predetermined size was sampled from the coated steel sheet of Table 6-1 and Table 6-2, the test piece was placed on a rubbing tester, and then impregnated with ethanol. The state of the coating film after the absorbent cotton was rubbed 10 times with a load of 49.03 kPa (0.5 kgf/cm ² ) was evaluated according to the following evaluation criteria.
5: No mark is left on the rubbing surface.
4: An extremely slight mark is left on the rubbing surface (a level at which the rubbing mark can be discriminated by focusing on the eyes).
3: A slight mark is left on the rubbing surface (a level at which rubbing marks can be discerned when the eyes are closed).
2: A clear mark is attached to the rubbing surface (a level where the rubbing mark can be instantly identified).
1: The coating film is completely dissolved on the rubbed surface, and the inorganic coating film is exposed.

Test 2. Scratch resistance As for the scratch resistance of the coated steel sheet, a test piece of a predetermined size was sampled from the coated steel sheet of Table 6-1 and Table 6-2, and the test piece was placed on a rubbing tester and then the rubbing tester was tested. A cylindrical eraser manufactured by Ugawa Rubber Co., Ltd. was attached to the tip of the sliding jig, and the state of the coating film and the inorganic film after rubbing 100 times with a load of 16 N was evaluated according to the following evaluation criteria.
5: No exposed steel plate.
4: The exposed width of the steel sheet is less than 1 mm.
3: The exposed width of the steel sheet is 1 mm or more and less than 2 mm.
2: The exposed width of the steel sheet is 2 mm or more and less than 3 mm.
1: The exposed width of the steel plate is 3 mm or more.

Test 3. Corrosion resistance Corrosion resistance of the coated steel sheet was measured in accordance with JIS Z 2371:2000 after collecting test pieces of a predetermined size from the coated steel sheets in Tables 6-1 and 6-2 and masking the end faces of the test pieces. A salt spray test (SST) was performed for 48 hours, the rust generation state on the coating film surface was observed, and evaluated according to the following evaluation criteria.
5: No rust was generated.
4: Rust generation area is less than 1% of the entire surface of the test piece.
3: Rust generation area is 1% or more and less than 3% of the entire surface of the test piece.
2: Rust generation area is 3% or more and less than 5% of the entire surface of the test piece.
1: Rust generation area is 5% or more of the entire surface of the test piece.

Test 4. Appearance (design)
The designability of the coated steel sheet was evaluated by taking 50×50 mm test pieces from the coated steel sheets shown in Tables 6-1 and 6-2, and measuring the number of sides (pinholes generated by foaming) in the test pieces.
5: There are 0 pinholes.
4: The number of pinholes is 1 or more and less than 5.
3: There are 5 or more pinholes and less than 10 pinholes.
2: The number of pinholes is 10 or more and less than 20.
1: 20 or more pinholes.

Test 5. Workability Test pieces obtained by cutting the coated steel sheets shown in Tables 6-1 and 6-2 to have a width of 5 cm and a predetermined length were subjected to JIS G 3312:2013 in an atmosphere of 20°C. A 2T bending test was performed. Specifically, two coated plates taken from the same steel plate as the test piece were sandwiched inside, and 180 degrees intimate bending was performed with the surface coated with the coating as the outside. The designability of the coated steel sheet was evaluated by observing the state of the coating film after the test and using the following evaluation criteria.
5: The coating film has no defects such as cracks and has a uniform colored appearance. No discoloration is observed.
4: A slight amount of cracking is observed in the coating film, and therefore a slight color fading is observed, but the color appearance is almost uniform (the test piece after the test and another test piece before the test were arranged side by side for some reason). Understandable level).
3: A slight crack is observed in the coating film, and therefore a slight color fading is observed, but the color appearance is almost uniform. (It can be seen that the test piece after the test and another test plate before the test are arranged side by side. level).
2: Cracks are observed in the coating film, and discoloration is observed (a level that can be seen only by looking at the test piece after the test).
1: Cracks were observed in the coating film, and color fading was remarkable (level that can be seen only by the test piece after the test).

Test 6. Adhesion The adhesion of the coated steel sheet (adhesion between the coating film and the inorganic film) was evaluated by the tape peeling test (used tape: Nichiban Cellotape (registered trademark)) after the workability evaluation of Test 5. The occurrence of film peeling was observed and evaluated according to the following evaluation criteria.
5: No peeling.
4: The peeled coating film was more than 0% and less than 5% of the area where the tape was attached.
3: The peeled coating film was 5% or more and less than 20% of the area where the tape was attached.
2: The peeled coating film is 20% or more and less than 50% of the area where the tape is attached.
1: The peeled coating film is 50% or more and less than 70% of the area of the tape.

The evaluation results of tests 1 to 6 are shown in Table 7-1 and Table 7-2.

As can be seen from Table 7-1, Examples 1 to 56 of the present invention were all excellent in solvent resistance, scratch resistance, corrosion resistance, appearance (designability), workability, and adhesion.

In Comparative Examples 1 to 5, since the inorganic coating did not contain V or Zr, the scratch resistance and the corrosion resistance were poor.
In Comparative Example 6, since the coating film did not contain the inorganic pigment A and the inorganic pigment B, the corrosion resistance and the designability were poor.
In Comparative Example 7, since the inorganic pigment A and the inorganic pigment B in the coating film did not contain P, the corrosion resistance was poor.
In Comparative Examples 8 and 11, since the coating film did not contain the inorganic pigment A, the corrosion resistance and the designability were poor.
In Comparative Example 9, since the coating film did not contain the inorganic pigment B, the designability was poor.
In Comparative Examples 10, 17, 20 and 21, the coating film did not contain either the inorganic pigment A or the inorganic pigment B, and the inorganic pigment A or the inorganic pigment B did not contain P, so that the corrosion resistance and the designability were good. inferior.
In Comparative Example 12, the number of the inorganic pigments A and B contained in the coating film was small, and (A)/(B) was small, so that the designability was poor.
In Comparative Example 13, the number of the inorganic pigment A and the inorganic pigment B contained in the coating film was large, and (A)+(B) was more than 50 parts by volume, so that the corrosion resistance and the designability were poor.
In Comparative Example 14, the number of the inorganic pigments B contained in the coating film is small and (A)/(B) is small, and in Comparative Example 15, the number of the inorganic pigments A contained in the coating film is large, and (A). Since /(B) was large and P was not included, the designability was poor.
In Comparative Example 16, since the coating film did not contain the inorganic pigment B, the corrosion resistance and the designability were poor.
In Comparative Example 18, the coating film did not contain the inorganic pigment B, so the corrosion resistance and the designability were poor.
In Comparative Example 19, (A)+(B) was more than 50 parts by volume and (A)/(B) was small, so that the workability and the adhesion were poor.
In Comparative Example 22, the film thickness of the coating film was 5 μm, and thus the scratch resistance was poor.
In Comparative Example 23, the coating film thickness was more than 20 μm, so the designability was poor.

1 Inorganic pigment A
2 Inorganic pigment B
3 Binder resin 4 Steel plate 5 Inorganic film 6 Coating film 10 Coated steel plate

Claims (6)

1. Steel plate,
   An inorganic film formed on at least one surface of the steel sheet and containing Zn and V or Zr;
   A binder resin, which is formed on the inorganic film and has a film thickness of more than 5 to 20 μm, and a particle diameter of 10 to 500 nm, and an inorganic pigment B having a particle diameter of 1000 to 10000 nm. Coating film,
   A coated steel sheet having
   At least one of the inorganic pigment A and the inorganic pigment B contains P,
   The total amount of the inorganic pigment A and the inorganic pigment B in the coating film is 5 to 50 parts by volume with respect to 100 parts by volume of the coating film. The ratio of (A) to the volume part (B) of the inorganic pigment B is 0.5≦(A)/(B)≦2.0,
   The inorganic pigment is observed in a region of 20 μm in the direction parallel to the plate width direction and t μm in the plate thickness direction in a section perpendicular to the rolling direction of the coating film, where t is the film thickness of the coating film. A coated steel sheet, wherein the number of A is 60 to 100,000 and the number of the inorganic pigment B is 2 to 50.
2. The coated steel sheet according to claim 1, wherein the inorganic pigment A or the inorganic pigment B containing P in the coating film further contains Mg.
3. The coated steel sheet according to claim 1 or 2, wherein the binder resin contains a polyester resin and a melamine resin.
4. The coated steel sheet according to claim 3, wherein the melamine resin is a butylated melamine resin.
5. The coated steel sheet according to any one of claims 1 to 4, wherein the binder resin contains an epoxy resin.
6. V/Zn, which is the mass ratio of V and Zn, or Zr/Zn, which is the mass ratio of Zr and V, in the inorganic coating is 0.05 to 0.50 in terms of metal. The coated steel sheet according to any one of claims 1 to 5, wherein

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