KR102756617B1 - HOT-DIP Al-Zn-Si-Mg-Sr COATED STEEL SHEET, SURFACE-TREATED STEEL SHEET, AND PRE-PAINTED STEEL SHEET - Google Patents

Abstract

The purpose of the present invention is to provide a hot-dip Al-Zn-Si-Mg-Sr plated steel sheet having stable, excellent corrosion resistance and good surface appearance. In order to achieve the above purpose, the present invention provides a hot-dip Al-Zn-Si-Mg-Sr plated steel sheet having a plating film, wherein the plating film has a composition containing Al: 45 to 65 mass%, Si: 1.0 to 4.0 mass%, Mg: 1.0 to 10.0 mass%, and Sr: 0.01 to 1.0 mass%, with the remainder being Zn and unavoidable impurities, and wherein the diffraction intensity of Si and Mg ₂ Si in the plating film by X-ray diffraction method satisfies the following relationship (1).
Si(111)/Mg ₂ Si(111)≤0.8... (1)

Description

HOT-DIP Al-Zn-Si-Mg-Sr COATED STEEL SHEET, SURFACE-TREATED STEEL SHEET, AND PRE-PAINTED STEEL SHEET

The present invention relates to a hot-dip Al-Zn-Si-Mg-Sr system plated steel sheet, a surface-treated steel sheet, and a painted steel sheet having stable and excellent corrosion resistance.

It is known that hot-dip Al-Zn-based galvanized steel sheets, represented by 55% Al-Zn-based steel sheets, exhibit high corrosion resistance even among hot-dip galvanized steel sheets because they have both the sacrificial protection property of Zn and the high corrosion resistance of Al. Therefore, hot-dip Al-Zn-based galvanized steel sheets are mainly used in the field of building materials such as roofs and walls that are exposed to the outdoors for long periods of time, and in the field of civil engineering and construction such as guardrails, wiring piping, and soundproofing walls, due to their excellent corrosion resistance. In particular, in harsher usage environments such as acid rain caused by air pollution, the dispersion of snow melting agents to prevent roads from freezing in snowy areas, and development of coastal areas, the demand for materials with excellent corrosion resistance or maintenance-free materials has been increasing in recent years.

The plating film of a hot-dip Al-Zn-plated steel sheet is composed of a portion (α-Al phase) in which Al containing Zn supersaturated is solidified in a dendrite shape, and a Zn-Al eutectic structure existing in the gaps between the dendrites (interdendrite), and has a structure in which the α-Al phase is laminated in multiple layers in the direction of the film thickness of the plating film. Because of this characteristic film structure, the corrosion progression path from the surface becomes complicated, making it difficult for corrosion to progress easily, and it is also known that a hot-dip Al-Zn-plated steel sheet can realize superior corrosion resistance compared to a hot-dip galvanized steel sheet having the same plating film thickness.

Attempts are being made to further extend the life of these hot-dip Al-Zn-based galvanized steel sheets, and hot-dip Al-Zn-Si-Mg-Sr galvanized steel sheets with added Mg are being commercialized.

As such a molten Al-Zn-Si-Mg-Sr plated steel sheet, for example, Patent Document 1 discloses a molten Al-Zn-Si-Mg-Sr plated steel sheet including an Al-Zn-Si alloy containing Mg in the plating film, wherein the Al-Zn-Si alloy is an alloy containing 45 to 60 wt% of elemental aluminum, 37 to 46 wt% of elemental zinc, and 1.2 to 2.3 wt% of Si, and wherein the concentration of Mg is 1 to 5 wt%.

In addition, Patent Document 2 discloses a hot-dip Al-Zn-Si-Mg-Sr plated steel sheet for the purpose of improving corrosion resistance by containing at least one of 2 to 10% Mg and 0.01 to 10% Ca in the plating film, and enhancing the protective effect after the base steel sheet is exposed.

In addition, Patent Document 3 discloses a hot-dip Al-Zn-Si-Mg-Sr plated steel sheet which forms a coating layer containing, in mass%, Mg: 1 to 15%, Si: 2 to 15%, Zn: 11 to 25%, with the remainder being Al and unavoidable impurities, and which improves the corrosion resistance of a flat plate and cross section by making the size of intermetallic compounds such as Mg ₂ Si phase or MgZn ₂ phase present in the plating film 10 µm or less.

The aforementioned hot-dip Al-Zn-based galvanized steel sheet has a beautiful appearance with a spangle pattern of white metallic luster, and is therefore often used without being painted, and the demand for its appearance is actually strong. Therefore, technologies for improving the appearance of hot-dip Al-Zn-based galvanized steel sheets are also being developed.

For example, Patent Document 4 discloses a hot-dip Al-Zn-Si-Mg-Sr plated steel sheet that suppresses wrinkle-shaped irregularities by containing 0.01 to 10% of Sr in the plating film.

In addition, Patent Document 5 discloses a hot-dip Al-Zn-Si-Mg-Sr plated steel sheet that suppresses speckled defects by containing 500 to 3,000 ppm of Sr in the plating film.

For example, Patent Document 4 discloses a hot-dip Al-Zn-Si-Mg plated steel sheet that suppresses wrinkle-shaped irregularities by containing 0.01 to 10% of Sr in the plating film.

In addition, Patent Document 5 discloses a hot-dip Al-Zn-Si-Mg plated steel sheet that suppresses spot defects by containing 500 to 3,000 ppm of Sr in the plating film.

In addition, Patent Document 6 discloses a hot-dip Al-Zn-Si-Mg plated steel sheet that achieves both surface appearance and corrosion resistance by containing 0.001 to 1.0% of Sr in the plating film.

In addition, Patent Document 7 discloses a hot-dip Al-Zn-Si-Mg plated steel sheet that achieves both surface appearance and corrosion resistance of the flat portion and the processed portion by containing 0.001 to 1.0% of Sr in the plating film.

In addition, Patent Document 8 also discloses a hot-dip Al-Zn-Si-Mg plated steel sheet that achieves both surface appearance and corrosion resistance by containing 0.01 to 0.2% Sr in the plating film.

In addition, Patent Document 9 discloses a hot-dip Al-Zn-Si-Mg plated steel sheet having improved corrosion resistance by controlling the concentrations of Si and Mg in the plating film at a specific ratio.

In addition, for the aforementioned hot-dip Al-Zn-based galvanized steel sheet, there was a problem that white rust occurred due to corrosion of the galvanized film when used in a severe corrosive environment. Since this white rust causes a deterioration in the appearance of the steel sheet, galvanized steel sheets that aim to improve white rust resistance are being developed.

For example, Patent Document 10 discloses a hot-dip Al-Zn-Si-Mg plated steel sheet in which the mass ratio of Mg in the Si-Mg phase to the total amount of Mg in the plating layer is optimized for the purpose of improving the rust resistance of the processed portion.

In addition, Patent Document 11 discloses a technology for improving blackening resistance and white rust resistance by forming a chemical film containing a urethane resin on the plating film of a molten Al-Zn-Si-Mg plated steel sheet.

In addition, a painted steel sheet having a chemical conversion film, a primer film, a top coating layer, etc. formed on the surface of a hot-dip Al-Zn-based plated steel sheet is subjected to various processing such as 90-degree bending or 180-degree bending by press forming, roll forming, or embossing forming, and long-term durability of the coating film is also required. In order to meet these requirements, a painted steel sheet is known in which a hot-dip Al-Zn-based plated steel sheet forms a chemical conversion film containing chromate, the primer coating also contains a chromate-based rust-preventive pigment, and on top of that, a top coating film having excellent weather resistance such as a thermosetting polyester-based resin film or a fluorine-based resin film is formed.

However, recently, the use of chromate, an environmentally hazardous substance, has become a problem for these painted steel plates, and there is a strong demand for the development of painted steel plates that can improve corrosion resistance and surface appearance even if they are chromate-free.

As a technology responding to these demands, for example, Patent Document 12 discloses a surface-treated hot-dip galvanized steel material, which comprises plating an aluminum-zinc alloy plating layer (α) containing Al, Zn, Si, and Mg, and further attempting to adjust the content of these elements, on the surface of a steel material, and further forming a film (β) as an upper layer thereof, which comprises at least one compound (A) selected from a titanium compound and a zirconium compound as a layer forming component, so that the mass ratio of the Si-Mg phase in the aluminum-zinc alloy plating layer (α) with respect to the total amount of Mg in the plating layer is adjusted to 3% or more.

Japanese Patent No. 5020228 Japanese Patent No. 5000039 Japanese Patent Publication No. 2002-12959 Japanese Patent No. 3983932 Japanese Patent Publication No. 2011-514934 International Publication No. 2020/179147 International Publication No. 2020/179148 Japanese Patent Publication No. 2020-143370 International Publication No. 2016/140370 Japanese Patent No. 5751093 Japanese Patent Publication No. 2019-155872 Japanese Patent Publication No. 2005-169765

However, the technology of including Mg in the plating film, as disclosed in Patent Documents 1 to 3, is not limited to automatically improving corrosion resistance.

In the hot-dip Al-Zn-Si-Mg-Sr plated steel sheets disclosed in Patent Documents 1 to 3, corrosion resistance is improved simply by including Mg in the plating components, but the characteristics of the metal phase and intermetallic compound phase constituting the plating film are not taken into consideration, and therefore it is not possible to uniformly state the superiority or inferiority of corrosion resistance. Therefore, even when a hot-dip Al-Zn-Si-Mg-Sr plated steel sheet is manufactured using the same plating bath composition, there is a problem in that there is variation in corrosion resistance when a corrosion acceleration test is performed, and it is not necessarily superior to an Al-Zn plated steel sheet to which Mg is not added.

Likewise, in terms of improving the appearance of the plating, simply adding Sr to the plating film does not necessarily eliminate wrinkle-shaped defects, and even with the hot-dip Al-Zn-Si-Mg-Sr plated steel sheets disclosed in Patent Documents 4 to 8, there were cases where both corrosion resistance and appearance could not be achieved.

In addition, it is known that when plating is performed on a steel plate in a molten Al-Zn-Si bath to which Mg is added, in addition to the α-Al phase, a Mg ₂ Si phase, a MgZn ₂ phase, and a Si phase are precipitated in the plating film. However, little has been known about the effect of the precipitation amount or existence ratio of each phase on corrosion resistance.

In the molten Al-Zn-Si-Mg plated steel sheet disclosed in Patent Document 9, the concentrations of Si and Mg are controlled at a specific ratio to eliminate precipitation of the Si phase in the plating film, thereby attempting to improve corrosion resistance. However, it is not necessarily possible to suppress the Si phase, and even in cases where the formation of the Si phase in the plating film can be suppressed, there are cases where excellent corrosion resistance is not obtained, making it technically incomplete.

In addition, with regard to white rust resistance, sufficient improvement could not be attempted for any technology. For the hot-dip Al-Zn-Si-Mg plated steel sheet of Patent Document 10, improvement in white rust resistance in the processed section and the flat plate section after heating is described, but white rust resistance in the unheated flat plate section is not considered, and therefore stable white rust resistance was still a challenge. In addition, for the hot-dip Al-Zn-Si-Mg plated steel sheet of Patent Document 11, it is not limited to obtaining stable and excellent corrosion resistance or white rust resistance, and therefore further improvement has been desired.

In addition, for the painted steel plate, as described above, long-term durability of the coating film is required in a state where various processing such as 90-degree bending or 180-degree bending is performed by press forming, roll forming, embossing forming, etc., but in the technology of Patent Document 12, it could not be said that the corrosion resistance or surface appearance after processing was necessarily stably obtained.

The corrosion resistance of a painted steel sheet is, of course, affected by the corrosion resistance of the underlying plating steel sheet, and in terms of surface appearance, since the height difference of the irregularities of the wrinkle-shaped defects can reach several tens of micrometers, even if the surface is smoothed by the coating film, the irregularities are not completely eliminated, and it is thought that improvement in the appearance as a painted steel sheet cannot be expected. In addition, since the coating film becomes thinner at the convex portion, there is also a concern that the corrosion resistance may be reduced locally. Therefore, in order to obtain a painted steel sheet with excellent corrosion resistance and surface appearance, it is important to improve the corrosion resistance and surface appearance of the underlying plating steel sheet.

In consideration of these circumstances, the present invention aims to provide a hot-dip Al-Zn-Si-Mg-Sr plated steel sheet having stable and excellent corrosion resistance and good surface appearance.

In addition, the present invention aims to provide a surface-treated steel sheet having stable and excellent corrosion resistance and white rust resistance.

In addition, the present invention aims to provide a painted steel sheet having excellent corrosion resistance and machined part corrosion resistance.

The present inventors, as a result of studies conducted to solve the above-described problems, have found that, with respect to the Mg ₂ Si phase, the MgZn ₂ phase, and the Si phase formed in the plating film of a molten Al-Zn-Si-Mg-Sr system plating steel sheet, the amount of precipitation increases and decreases depending on the balance of each component in the plating film and the formation conditions of the plating film, the presence ratio thereof changes, and depending on the balance of the composition, there are cases where a certain phase is not precipitated. In addition, they have found that the corrosion resistance of a molten Al-Zn-Si-Mg-Sr system plating steel sheet changes depending on the presence ratio of these phases, and in particular, the corrosion resistance stably improves when the Si phase is less than the Mg ₂ Si phase.

However, it is known that it is very difficult to determine the difference in phases for these Mg ₂ Si phases and Si phases even when observing secondary electron images or reflected electron images of the surface or cross-section of the plating film using general techniques, such as a scanning electron microscope. Although it is possible to obtain microscopic information by observing using a transmission electron microscope as a technique for more detailed analysis, it has not been possible to determine the presence ratio of the Mg ₂ Si phase and Si phase, which affect macroscopic information such as corrosion resistance and appearance.

Therefore, the inventors of the present invention have conducted additional and detailed studies and, as a result, have found that, by using the intensity ratio of specific diffraction peaks for the Mg ₂ Si phase and the Si phase, the phase existence ratio can be quantitatively determined, focusing on the X-ray diffraction method, and that, if the Mg ₂ Si phase and the Si phase in the plating film satisfy a specific existence ratio, excellent corrosion resistance can be stably realized.

In addition, the inventors of the present invention have also recognized that by controlling the proportions of the _Mg2Si phase, Si phase, etc. in a molten Al-Zn-Si-Mg-Sr system plated steel sheet and then controlling the Sr concentration in the bath, the occurrence of wrinkle-shaped irregularities can be reliably suppressed, thereby obtaining a plated steel sheet having excellent surface appearance.

In addition, the inventors of the present invention also investigated a chemistry film formed on the plating film, and discovered that by composing the chemistry film with a specific resin and a specific metal compound, the affinity of the chemistry film with the plating film, the rust prevention effect, etc. are increased, and the stable improvement in white rust resistance is enhanced.

In addition, the inventors of the present invention also investigated a chemical film and a primer film formed on the plating film, and found that by composing the chemical film with a specific resin and a specific inorganic compound, and composing the primer film with a specific polyester resin and an inorganic compound, the barrier properties and adhesion of the film can be increased, and excellent corrosion resistance after processing can be realized even in a chromate-free state.

The present invention has been made based on the above knowledge, and its gist is as follows.

1. A hot-dip Al-Zn-Si-Mg-Sr plated steel sheet having a plating film,

The above plating film has a composition containing Al: 45 to 65 mass%, Si: 1.0 to 4.0 mass%, Mg: 1.0 to 10.0 mass%, and Sr: 0.01 to 1.0 mass%, with the remainder being Zn and inevitable impurities.

A hot-dip Al-Zn-Si-Mg-Sr plated steel sheet, characterized in that the diffraction intensities of Si and Mg ₂ Si in the plating film, as determined by X-ray diffraction, satisfy the following relationship (1).

Si(111)/Mg ₂ Si(111)≤0.8... (1)

Si(111): Diffraction intensity of the (111) plane of Si (plane spacing d = 0.3135 nm),

Mg ₂ Si(111): Diffraction intensity of the (111) plane of Mg ₂ Si (plane spacing d = 0.3668 nm)

2. A hot-dipped Al-Zn-Si-Mg-Sr plated steel sheet as described in 1 above, characterized in that the diffraction intensity of Si in the plating film as determined by X-ray diffraction satisfies the following relationship (2).

Si(111)＝0…(2)

Si(111): Diffraction intensity of the (111) plane of Si (plane spacing d = 0.3135 nm)

3. A hot-dip Al-Zn-Si-Mg-Sr plated steel sheet as described in 1 or 2 above, characterized in that the Al content in the plating film is 50 to 60 mass%.

4. A hot-dip Al-Zn-Si-Mg-Sr plated steel sheet according to any one of 1 to 3 above, characterized in that the content of Si in the plating film is 1.0 to 3.0 mass%.

5. A hot-dip Al-Zn-Si-Mg-Sr plated steel sheet according to any one of 1 to 4 above, characterized in that the content of Mg in the plating film is 1.0 to 5.0 mass%.

6. A surface-treated steel sheet having a plating film described in any one of 1 to 5 above and a chemical film formed on the plating film,

A surface-treated steel sheet, characterized in that the above-mentioned Martian coating contains at least one resin selected from epoxy resin, urethane resin, acrylic resin, acrylic silicone resin, alkyd resin, polyester resin, polyalkylene resin, amino resin and fluororesin, and at least one metal compound selected from P compound, Si compound, Co compound, Ni compound, Zn compound, Al compound, Mg compound, V compound, Mo compound, Zr compound, Ti compound and Ca compound.

7. A coated steel sheet having a coating film formed directly or by interposing a chemical film on the plating film described in any one of 1 to 5 above,

The above-mentioned Martian film contains a total of 30 to 50 mass% of (a): anionic polyurethane resin having an ester bond and (b): an epoxy resin having a bisphenol skeleton, and contains a resin component in which the content ratio ((a):(b)) of (a) and (b) is in the range of 3:97 to 60:40 by mass, and an inorganic compound including 2 to 10 mass% of a vanadium compound, 40 to 60 mass% of a zirconium compound, and 0.5 to 5 mass% of a fluorine compound.

A painted steel sheet, characterized in that the coating film has at least a primer coating film, and the primer coating film contains a polyester resin having a urethane bond and an inorganic compound including a vanadium compound, a phosphoric acid compound, and magnesium oxide.

According to the present invention, it is possible to provide a hot-dip Al-Zn-Si-Mg-Sr plated steel sheet having stable and excellent corrosion resistance and good surface appearance.

In addition, according to the present invention, a surface-treated steel sheet having excellent corrosion resistance and white rust resistance can be provided.

In addition, according to the present invention, a painted steel sheet having excellent corrosion resistance and machined part corrosion resistance can be provided.

Figure 1 is a diagram explaining the flow of the combined cycle test (JASO-CCT) of the Japanese automobile standard.

(Form for carrying out the invention)

(Hot-dip Al-Zn-Si-Mg-Sr coated steel sheet)

The molten Al-Zn-Si-Mg-Sr plated steel sheet of the present invention has a plated film on the surface of the steel sheet. And, the plated film has a composition containing Al: 45 to 65 mass%, Si: 1.0 to 4.0 mass%, Mg: 1.0 to 10.0 mass%, and Sr: 0.01 to 1.0 mass%, with the remainder being Zn and inevitable impurities.

The Al content in the above-mentioned plating film is 45 to 65 mass%, and preferably 50 to 60 mass%, from the balance of corrosion resistance and operability. This is because, when the Al content in the above-mentioned plating film is at least 45 mass%, Al dendrite solidification occurs, and a plating film structure mainly composed of an α-Al phase dendrite solidification structure can be obtained. Since the dendrite solidification structure takes on a structure in which it is laminated in the film thickness direction of the plating film, the corrosion progression path becomes complicated, and the corrosion resistance of the plating film itself improves. In addition, the more α-Al phase dendrite parts are laminated, the more complicated the corrosion progression path becomes, and it becomes difficult for corrosion to easily reach the steel plate, so that the corrosion resistance improves, and therefore, the Al content is preferably 50 mass% or more. On the other hand, if the Al content in the plating film exceeds 65 mass%, most of the Zn changes into a structure dissolved in α-Al, and the dissolution reaction of the α-Al phase cannot be suppressed, so that the corrosion resistance of the Al-Zn-Si-Mg-Sr system plating deteriorates. Therefore, the Al content in the plating film must be 65 mass% or less, and preferably 60 mass% or less.

The Si in the above plating film is mainly added to suppress the growth of an Fe-Al and/or Fe-Al-Si interface alloy layer formed at the interface with the underlying steel sheet, so as not to deteriorate the adhesion between the plating film and the steel sheet. In fact, when the steel sheet is immersed in an Al-Zn plating bath containing Si, Fe on the surface of the steel sheet and Al or Si in the bath undergo an alloying reaction, so that an Fe-Al and/or Fe-Al-Si intermetallic compound layer is formed at the underlying steel sheet/plating film interface. However, since the Fe-Al-Si alloy has a slower growth rate than the Fe-Al alloy, the higher the proportion of the Fe-Al-Si alloy, the more the growth of the entire interface alloy layer is suppressed. Therefore, the Si content in the above plating film needs to be 1.0 mass% or more. On the other hand, if the Si content in the plating film exceeds 4.0 mass%, not only will the growth inhibition effect of the interface alloy layer described above be saturated, but corrosion will also be promoted due to the presence of an excessive Si phase in the plating film. Therefore, the Si content is set to 4.0 mass% or less. In addition, from the viewpoint of suppressing the presence of an excessive Si phase, the Si content in the plating film is preferably set to 3.0 mass% or less. Furthermore, from the viewpoint of easily satisfying the relationship of (1) described later in terms of the relationship with the Mg content described later, it is preferable that the Si content be 1.0 to 3.0 mass%.

The above plating film contains 1.0 to 10.0 mass% of Mg. By containing Mg in the above plating film, the above-mentioned Si can exist in the form of an intermetallic compound of Mg ₂ Si phase, thereby suppressing the promotion of corrosion.

In addition, when Mg is contained in the plating film, an MgZn ₂ phase, which is an intermetallic compound, is also formed in the plating film, so that the effect of further improving corrosion resistance is obtained. When the Mg content in the plating film is less than 1.0 mass%, Mg is used for solid solution in the main phase, α-Al phase, rather than for the formation of the intermetallic compound (Mg ₂ Si, MgZn ₂ ), so that sufficient corrosion resistance cannot be secured. On the other hand, when the Mg content in the plating film increases, not only the effect of improving corrosion resistance is saturated, but also the workability deteriorates due to the weakening of the α-Al phase, so the content is set to 10.0 mass% or less. In addition, the Mg content in the plating film is preferably set to 5.0 mass% or less from the viewpoint of suppressing dross generation during plating formation and facilitating plating bath management. In addition, in terms of the relationship with the content of Si, from the viewpoint of easily satisfying the relational expression (1) described below, it is preferable to set the content of Mg to 3.0 mass% or more, and considering compatibility with dross suppression, it is more preferable to set the content of Mg to 3.0 to 5.0 mass%.

And, in the molten Al-Zn-Si-Mg-Sr system plated steel sheet of the present invention, the diffraction intensity of Si and Mg ₂ Si in the plating film by X-ray diffraction method is required to satisfy the following relationship (1).

Si(111)/Mg ₂ Si(111)≤0.8... (1)

Si(111): Diffraction intensity of the (111) plane of Si (interface spacing d=0.3135 nm), Mg ₂ Si(111): Diffraction intensity of the (111) plane of Mg ₂ Si (interface spacing d=0.3668 nm)

As described above, in the present invention, it is important to control the presence ratio of the Mg ₂ Si phase and the Si phase generated in the plating film by containing Mg or Si to a specific ratio. The influence of these on corrosion resistance is currently being investigated, and many unknown points remain, but the following mechanism is presumed.

When a molten Al-Zn-Si-Mg-Sr plated steel sheet is exposed to a corrosive environment, the intermetallic compound described above is preferentially dissolved over the α-Al phase, and as a result, the vicinity of the formed corrosion product becomes an environment rich in Mg. It is presumed that in such a Mg-rich environment, the formed corrosion product is difficult to decompose, and as a result, the protective effect of the plating film is enhanced. In addition, since this effect of improving the protective effect of the plating film is more clearly expressed when the Si in the plating film exists as the Mg ₂ Si phase rather than the Si phase, it is thought that it is effective to lower the existence ratio of the Si phase with respect to the Mg ₂ Si phase.

The existence ratio of Mg ₂ Si and Si in the above-mentioned plating film requires that the relationship (1): Si(111)/Mg ₂ Si(111)≤0.8 is satisfied using the diffraction peak intensity obtained by the X-ray diffraction method. However, if the existence ratio of Mg ₂ Si and Si in the above-mentioned plating film does not satisfy the relationship (1), that is, when Si(111)/Mg ₂ Si(111)>0.8, since the Si phase present in the plating film increases, the above-mentioned Mg-rich environment cannot be obtained in the vicinity of the corrosion product, and it becomes difficult to obtain the effect of improving the protective action of the plating film. From the same viewpoint, the existence ratio of Si to Mg ₂ Si (Si(111)/Mg ₂ Si(111)) is preferably 0.5 or less, more preferably 0.3 or less, and particularly preferably 0.2 or less.

In addition, regarding the existence ratio of Mg ₂ Si and Si in the plating film, even if the composition of the plating film satisfies the range of the present invention (containing Al: 45 to 65 mass%, Si: 1.0 to 4.0 mass%, Mg: 1.0 to 10.0 mass%, and Sr: 0.01 to 1.0 mass%, and the remainder being Zn and unavoidable impurities), if the existence ratio of Mg ₂ Si and Si does not satisfy relationship (1), the effect of improving the protective action of the plating film according to the present invention cannot be sufficiently obtained.

Here, in the above relationship (1), Si(111) is the diffraction intensity of the (111) plane of Si (interface spacing d=0.3135 nm), and Mg ₂ Si(111) is the diffraction intensity of the (111) plane of Mg ₂ Si (interface spacing d=0.3668 nm).

As a method for measuring Si(111) and Mg ₂ Si(111) by the above X-ray diffraction, a part of the above plating film is mechanically scraped off, and X-ray diffraction is performed in a powdered state (powder X-ray diffraction measurement method) so that the results can be calculated. As for the measurement of the diffraction intensity, the diffraction peak intensity of Si corresponding to the interplanar spacing d=0.3135 nm and the diffraction peak intensity of Mg ₂ Si corresponding to the interplanar spacing d=0.3668 nm are measured, and the ratio of these is calculated so that Si(111)/Mg ₂ Si(111) can be obtained.

In addition, when performing powder X-ray diffraction measurement, the amount of plating film required (the amount of plating film scraped off) is preferably 0.1 g or more, and preferably 0.3 g or more, from the viewpoint of accurately measuring Si(111) and _Mg2Si (111). In addition, when the plating film is scraped off, there are cases where components of the steel plate other than the plating film are included in the powder, but these intermetallic compound phases are included only in the plating film and do not affect the peak intensity described above. In addition, the reason why X-ray diffraction is performed using the plating film as a powder is that when X-ray diffraction is performed on a plating film formed on a plated steel plate, it is difficult to correctly calculate the phase ratio due to the influence of the plane orientation of the plating film solidification structure.

In addition, in the molten Al-Zn-Si-Mg-Sr system plated steel sheet of the present invention, in order to more stably improve corrosion resistance, it is preferable that the diffraction intensity of Si in the plating film by X-ray diffraction method satisfies the following relationship (2).

Si(111)＝0…(2)

Si(111): Diffraction intensity of the (111) plane of Si (plane spacing d = 0.3135 nm)

In general, in the dissolution reaction of Al alloys into aqueous solutions, it is known that the Si phase promotes the dissolution of the surrounding α-Al phase by existing as a cathode site. Therefore, reducing the Si phase is also effective from the viewpoint of suppressing the dissolution of the α-Al phase, and among these, forming a film in which no Si phase exists, as in relationship (2) (making the diffraction peak intensity of the Si (111) zero) is the best for stabilizing corrosion resistance.

Additionally, the method for measuring the diffraction peak intensity of the (111) plane of Si by X-ray diffraction is as described above.

Here, there is no particular limitation on the method for satisfying the above-mentioned relationship (1) or relationship (2). For example, in order to satisfy the relationship (1) or relationship (2), the existence ratio of Mg ₂ Si and Si (diffraction intensity of Mg ₂ Si (111) and Si (111)) can be controlled by adjusting the balance of the content of Si, the content of Mg, and the content of Al in the plating film. In addition, the balance of the content of Si, the content of Mg, and the content of Al in the plating film does not necessarily satisfy the relationship (1) or relationship (2) by setting it to a constant content ratio. For example, it is necessary to change the content ratio of Mg and Al depending on the content of Si (mass%).

In addition, in addition to adjusting the balance of the Si content, Mg content, and Al content in the plating film, the diffraction intensity of Mg ₂ Si (111) and Si (111) can be controlled to satisfy relationship (1) or relationship (2) by adjusting the conditions at the time of forming the plating film (e.g., cooling conditions after plating).

In addition, in the molten Al-Zn-Si-Mg-Sr steel sheet of the present invention, the plating film contains 0.01 to 1.0 mass% of Sr. Since the plating film contains Sr, the occurrence of surface defects such as wrinkle-shaped uneven defects can be more reliably suppressed, thereby realizing good surface appearance.

In addition, the above wrinkle-shaped defect is a wrinkle-shaped uneven defect formed on the surface of the plating film, and is observed as a white line on the surface of the plating film. Such a wrinkle-shaped defect is likely to occur when a large amount of Mg is added to the plating film. Therefore, in the above hot-dip galvanized steel sheet, by containing Sr in the plating film, Sr is preferentially oxidized over Mg in the surface layer of the plating film, and by suppressing the oxidation reaction of Mg, it becomes possible to suppress the occurrence of the wrinkle-shaped defect.

The above-mentioned plating film contains 0.01 to 1.0 mass% of Sr. However, when the Sr content in the above-mentioned plating film is less than 0.01 mass%, the appearance improvement effect is not obtained, and when the Sr content in the above-mentioned plating film exceeds 1.0 mass%, Sr is excessively incorporated into the interface alloy layer, which adversely affects plating adhesion, etc. From the same viewpoint, the Sr content in the above-mentioned plating film is preferably 0.05 to 0.5 mass%, and more preferably 0.1 to 0.4 mass%.

And, in the molten Al-Zn-Si-Mg-Sr steel sheet of the present invention, the existence ratio of Si and Mg ₂ Si in the above-described plating film satisfies relationship (1), and further, the plating film contains 0.01 to 1.0 mass% of Sr. Accordingly, the effect of improving the surface appearance by Sr described above can be more enjoyed. Although the cause for this is not clear, it is presumed that when the Si in the above-described plating film increases, it is difficult to suppress oxidation of the plating surface layer in the first place, which affects the effect of improving the appearance when Sr is added.

In addition, the molten Al-Zn-Si-Mg-Sr plated steel sheet of the present invention contains Zn and inevitable impurities.

Among these, the inevitable impurities contain Fe. This Fe is inevitably included in the plating film as a result of being eluted from the steel plate or the device in the bath into the plating bath and being supplied by diffusion from the underlying steel plate during the formation of the interface alloy layer. The Fe content in the plating film is usually about 0.3 to 2.0 mass%. Other inevitable impurities include Cr, Ni, Cu, and the like. The total content of the inevitable impurities is not particularly limited, but since there is a possibility that various properties of the plated steel plate may be affected if contained excessively, it is preferable that the total content is 5.0 mass% or less.

In addition, the plating film preferably additionally contains one or more kinds selected from Cr, Mn, V, Mo, Ti, Ca, Ni, Co, Sb and B, in a total of 0.01 to 10 mass%, since it can have the effect of improving the stability of corrosion products and delaying the progress of corrosion, similar to the above-mentioned Mg. The reason why the total content of the above-mentioned components is set to 0.01 to 10 mass% is that a sufficient corrosion delaying effect can be obtained and the effect will not be saturated.

In addition, the coating weight of the plating film is preferably 45 to 120 g/m2 per side from the viewpoint of satisfying various characteristics. When the coating weight of the plating film is 45 g/m2 or more, sufficient corrosion resistance is obtained even for applications requiring long-term corrosion resistance such as building materials, and further, when the coating weight of the plating film is 120 g/m2 or less, excellent corrosion resistance can be realized while suppressing the occurrence of plating cracks, etc. during processing. From the same viewpoint, the coating weight of the plating film is more preferably 45 to 100 g/m2.

The amount of adhesion of the above-mentioned plating film can be derived, for example, by dissolving and peeling off a specific area of the plating film with a mixture of hydrochloric acid and hexamethylenetetramine as shown in JIS H 0401: 2013, and calculating it from the weight difference of the steel sheet before and after peeling. To obtain the amount of adhesion of the plating per side by this method, the plating surface of the non-target side is sealed with tape so as not to be exposed, and then the amount can be obtained by performing the above-mentioned dissolution.

In addition, the composition of the plating film can be confirmed by, for example, immersing the plating film in hydrochloric acid or the like to dissolve it, and analyzing the solution using ICP emission spectrometry or atomic absorption spectrometry. This method is merely an example, and any method that can accurately quantify the composition of the plating film may be used, and there are no particular limitations.

In addition, the plating film of the molten Al-Zn-Si-Mg-Sr system plated steel sheet obtained by the present invention becomes almost identical to the composition of the plating bath as a whole. Therefore, the composition of the plating film can be controlled with high precision by controlling the composition of the plating bath.

In addition, there is no particular limitation on the base steel sheet constituting the molten Al-Zn-Si-Mg-Sr-based plated steel sheet of the present invention, and cold-rolled steel sheets, hot-rolled steel sheets, etc. can be appropriately used depending on the required performance or specifications.

In addition, there is no particular limitation on the method for obtaining the above-mentioned steel plate. For example, in the case of the above-mentioned hot-rolled steel plate, a steel plate that has undergone a hot rolling process and an acid washing process can be used, and in the case of the above-mentioned cold-rolled steel plate, a cold rolling process can be additionally added to manufacture it. In addition, in order to obtain the properties of the steel plate, it is also possible to perform a recrystallization annealing process, etc. before the hot-dip plating process.

In addition, there is no particular limitation on the method for manufacturing the molten Al-Zn-Si-Mg-Sr-based plated steel sheet of the present invention. For example, the base steel sheet can be manufactured by washing, heating, and immersing in a plating bath using a continuous hot-dip plating facility. In the heating process of the steel sheet, recrystallization annealing, etc. are performed to control the structure of the base steel sheet itself, and in order to prevent oxidation of the steel sheet and reduce a trace oxide film existing on the surface, heating in a reducing atmosphere such as a nitrogen-hydrogen atmosphere is effective.

In addition, with respect to the plating bath used when manufacturing the molten Al-Zn-Si-Mg-Sr plated steel sheet of the present invention, as described above, since the composition of the plating film as a whole is almost equivalent to the composition of the plating bath, it is possible to use a composition containing Al: 45 to 65 mass%, Si: 1.0 to 4.0 mass%, Mg: 1.0 to 10.0 mass%, and Sr: 0.01 to 1.0 mass%, with the remainder being Zn, Fe, and unavoidable impurities.

In addition, the bath temperature of the plating bath is not particularly limited, but is preferably within the temperature range of (melting point + 20°C) to 650°C.

The reason why the lower limit of the bath temperature is set to the melting point + 20°C is that, in order to perform a hot-dip plating process, it is necessary to set the bath temperature to the solidification point or higher, and by setting it to the melting point + 20°C, solidification due to a local decrease in the bath temperature of the plating bath is prevented. On the other hand, the reason why the upper limit of the bath temperature is set to 650°C is that, if it exceeds 650°C, rapid cooling of the plating film becomes difficult, and there is a concern that the interface alloy layer formed between the plating film and the steel sheet may become thicker.

In addition, there is no particular limitation on the temperature of the steel sheet entering the plating bath (entering sheet temperature), but from the viewpoint of securing plating characteristics and preventing changes in the bath temperature in the continuous hot-dip plating operation, it is preferable to control the temperature of the plating bath within ±20°C.

In addition, the immersion time of the steel plate in the plating bath is 0.5 seconds or longer. This is because if it is less than 0.5 seconds, there is a concern that a sufficient plating film may not be formed on the surface of the steel plate. There is no particular limitation on the upper limit of the immersion time, but if the immersion time is prolonged, there is a concern that the interface alloy layer formed between the plating film and the steel plate may become thicker, so it is preferable to set it to 8 seconds or less.

In addition, in the cooling process after plating, it is preferable to cool the plate temperature from 520°C to 500°C over a period of 3 seconds or more. The precipitation initiation temperatures of the single Si phase and Mg ₂ Si in the plating film are 500 to 490°C for the single Si phase and 520 to 500°C for Mg ₂ Si. Therefore, by increasing the residence time in the temperature range of 520 to 500°C in which only the Mg ₂ Si precipitates, the precipitation of Mg ₂ Si is promoted and the precipitation of the single Si phase is suppressed, making it easy to satisfy the relationship (1) above.

In addition, the molten Al-Zn-Si-Mg-Sr system plated steel sheet can form a film directly on the plating film or by interposing an intermediate layer, depending on the required performance.

In addition, there is no particular limitation on the method for forming the coating film, and it can be appropriately selected according to the required performance. For example, a forming method such as roll coater coating, curtain flow coating, or spray coating can be mentioned. After coating with a paint containing an organic resin, it is possible to form the coating film by heating and drying by means such as hot air drying, infrared heating, or induction heating.

In addition, there is no particular limitation on the intermediate layer as long as it is a layer formed between the plating film of the molten galvanized steel sheet and the coating film.

(Surface treated steel plate)

The surface-treated steel sheet of the present invention has a plating film on the surface of the steel sheet and a chemical conversion film formed on the plating film.

Among these, the composition of the plating film is the same as the plating film of the molten Al-Zn-Si-Mg-Sr system plating steel sheet of the present invention described above.

The surface-treated steel plate of the present invention has a chemical film formed on the above-described plating film.

In addition, the above-mentioned Mars film is preferably formed on at least one side of the surface-treated steel sheet, and may be formed on both sides of the surface-treated steel sheet depending on the intended use or required performance.

And, in the surface-treated steel sheet of the present invention, the chemical composition film is characterized by containing at least one resin selected from among an epoxy resin, a urethane resin, an acrylic resin, an acrylsilicon resin, an alkyd resin, a polyester resin, a polyalkylene resin, an amino resin, and a fluororesin, and at least one metal compound selected from among a P compound, a Si compound, a Co compound, a Ni compound, a Zn compound, an Al compound, a Mg compound, a V compound, a Mo compound, a Zr compound, a Ti compound, and a Ca compound.

By forming the aforementioned ignition film on the plating film, the affinity with the plating film is increased, and in addition to making it possible to uniformly form the ignition film on the plating film, the rust prevention effect or barrier effect of the ignition film can be increased. As a result, stable corrosion resistance and white rust resistance of the surface-treated steel sheet of the present invention can be realized.

Here, with respect to the resin constituting the chemical film, from the viewpoint of improving corrosion resistance, at least one selected from among epoxy resins, urethane resins, acrylic resins, acrylic silicone resins, alkyd resins, polyester resins, polyalkylene resins, amino resins, and fluororesins is used. From the same viewpoint, it is preferable that the resin contains at least one of a urethane resin and an acrylic resin. In addition, the resin constituting the chemical film also includes an addition polymer of the above-mentioned resins.

For the above epoxy resin, for example, glycidyl etherified epoxy resins such as bisphenol A type, bisphenol F type, and novolac type, glycidyl etherified epoxy resins obtained by adding propylene oxide, ethylene oxide, or polyalkylene glycol to bisphenol A type epoxy resin, aliphatic epoxy resins, alicyclic epoxy resins, and polyether epoxy resins can be used.

For the above urethane resin, for example, oil-modified polyurethane resin, alkyd-based polyurethane resin, polyester-based polyurethane resin, polyether-based polyurethane resin, polycarbonate-based polyurethane resin, etc. can be used.

As for the above acrylic resin, examples thereof include polyacrylic acid and copolymers thereof, polyacrylic acid esters and copolymers thereof, polymethacrylic acid and copolymers thereof, polymethacrylic acid esters and copolymers thereof, urethane-acrylic acid copolymers (or urethane-modified acrylic resins), styrene-acrylic acid copolymers, etc., and additionally, those resins modified with other alkyd resins, epoxy resins, phenol resins, etc. can be used.

As the above-mentioned acrylic silicone resin, examples thereof include those in which a curing agent is added to a resin having a hydrolyzable alkoxysilyl group at the side chain or terminal of an acrylic copolymer as a main subject. In addition, when an acrylic silicone resin is used, excellent weather resistance can be expected in addition to corrosion resistance.

Examples of the above alkyd resin include rheological alkyd resin, rosin-modified alkyd resin, phenol-modified alkyd resin, styrenated alkyd resin, silicone-modified alkyd resin, acrylic-modified alkyd resin, oil-free alkyd resin, and high molecular weight oil-free alkyd resin.

As for the above polyester resin, it is a polycondensate synthesized by dehydrating and condensing a polycarboxylic acid and a polyalcohol to form an ester bond. As the polycarboxylic acid, examples of the polycarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and as the polyalcohol, examples of the polyalcohol include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol, and the like. Specifically, the polyester includes polyethylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, and the like. In addition, these polyester resins that have been modified with acrylics can also be used.

As for the above polyalkylene resin, examples thereof include ethylene copolymers such as ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers, carboxyl-modified polyolefin resins, ethylene-unsaturated carboxylic acid copolymers, ethylene ionomers, etc., and further, those obtained by modifying these resins with other alkyd resins, epoxy resins, phenol resins, etc. can be used.

As for the above amino resin, it is a thermosetting resin produced by the reaction of an amine or amide compound with an aldehyde, and examples thereof include melamine resin, guanamine resin, thiourea resin, etc., but from the viewpoints of corrosion resistance, weather resistance, adhesion, etc., it is preferable to use a melamine resin. As the melamine resin, there is no particular limitation, but examples thereof include butylated melamine resin, methylated melamine resin, and aqueous melamine resin.

As for the above fluororesin, examples thereof include fluoroolefin polymers, copolymers of fluoroolefins and alkyl vinyl ethers, cycloalkyl vinyl ethers, carbonic acid-modified vinyl esters, hydroxyalkyl allyl ethers, tetrafluoropropyl vinyl ethers, etc. When these fluororesins are used, not only corrosion resistance but also excellent weather resistance and excellent hydrophobicity can be expected.

In addition, for the purpose of improving corrosion resistance or processability, it is particularly preferable to use a hardener. As the hardener, an amino resin such as a urea resin (butylated urea resin, etc.), a melamine resin (butylated melamine resin, butyl etherified melamine resin, etc.), a butylated urea/melamine resin, a benzoguanamine resin, a blocked isocyanate, an oxazoline compound, a phenol resin, etc. can be appropriately used.

In addition, for the metal compound constituting the above-mentioned Martian film, at least one selected from among a P compound, a Si compound, a Co compound, a Ni compound, a Zn compound, an Al compound, a Mg compound, a V compound, a Mo compound, a Zr compound, a Ti compound, and a Ca compound is used. From the same viewpoint, it is preferable that the metal compound contains at least one of a P compound, a Si compound, and a V compound.

Here, the P compound can improve corrosion resistance or perspiration resistance by being included in the Martian film. The P compound is a compound containing P, and may contain, for example, one or two or more selected from inorganic phosphoric acid, organic phosphoric acid, and salts thereof.

As the inorganic phosphoric acid, organic phosphoric acid and salts thereof, any compound can be used without particular limitation. For example, as the inorganic phosphoric acid, it is preferable to use at least one selected from phosphoric acid, a primary phosphate, a secondary phosphate, a tertiary phosphate, pyrophosphate, a pyrophosphate salt, a tripolyphosphoric acid, a tripolyphosphate, phosphorous acid, a phosphite salt, a hypophosphorous acid and a hypophosphorous salt. In addition, as the organic phosphoric acid, it is preferable to use phosphonic acid (a phosphonic acid compound). In addition, as the phosphonic acid, it is preferable to use at least one selected from nitrilotrismethylenephosphonic acid, phosphonobutanetricarboxylic acid, methyldiphosphonic acid, methylenephosphonic acid and ethylidenediphosphonic acid.

In addition, when the above P compound is a salt, the salt is preferably a salt of an element of Groups 1 to 13 in the periodic table, more preferably a metal salt, and preferably at least one selected from an alkali metal salt and an alkaline earth metal salt.

When the chemical treatment solution containing the above P compound is applied to a molten Al-Zn-Si-Mg plated steel sheet, the surface of the plating film is etched by the action of the P compound, and an enriched layer in which Al, Zn, Si, and Mg, which are constituent elements of the plating film, are incorporated is formed on the plating film side of the chemical treatment film. By forming the enriched layer, the bonding between the chemical treatment film and the surface of the plating film is strengthened, and the adhesion of the chemical treatment film is improved.

The concentration of the P compound in the above-mentioned chemical treatment solution is not particularly limited, but can be 0.25 mass% to 5 mass%. If the concentration of the P compound is less than 0.25 mass%, the etching effect is insufficient, the adhesion with the plating interface decreases, and not only the corrosion resistance of the flat surface decreases, but also the corrosion resistance and cold resistance of damaged parts of the plating or film resulting from defective parts, cut sections, processing, etc. may decrease. From the same viewpoint, the concentration of the P compound is preferably 0.35 mass% or more, more preferably 0.50 mass% or more. On the other hand, if the concentration of the P compound exceeds 5 mass%, not only the life of the chemical treatment solution becomes short, but also the appearance when the film is formed tends to become uneven, and furthermore, the amount of P eluted from the chemical treatment film increases, and there is also a concern that the blackening resistance may decrease. From the same viewpoint, the concentration of the P compound is preferably 3.5 mass% or less, more preferably 2.5 mass% or less. Regarding the content of the P compound in the above-mentioned chemical compound film, for example, by applying and drying a chemical treatment solution having a concentration of the P compound of 0.25 mass% to 5 mass%, the adhesion amount of P in the chemical compound film after drying can be 5 to 100 mg/m2.

The above Si compound is a component that forms a skeleton for forming a chemical film together with the resin, and increases affinity with the plating film, thereby enabling the chemical film to be formed uniformly. The above Si compound is a compound containing Si, and for example, it is preferable to contain at least one selected from silica, trialkoxysilane, tetraalkoxysilane, and a silane coupling agent.

As the silica, any one can be used without particular limitation. As the silica, for example, at least one of wet silica and dry silica can be used. As the colloidal silica, which is one type of the wet silica, for example, Snowtex O, C, N, S, 20, OS, OXS, NS manufactured by Nissan Chemical Industries, Ltd. can be suitably used. In addition, as the dry silica, for example, AEROSIL 50, 130, 200, 300, 380 manufactured by Nippon Aerosil Co., Ltd. can be suitably used.

As the above trialkoxysilane, any one can be used without particular limitation. For example, it is preferable to use a trialkoxysilane represented by the general formula: R ₁ Si(OR ₂ ) ₃ (wherein R ₁ is hydrogen or an alkyl group having 1 to 5 carbon atoms, and R ₂ is the same or different alkyl groups having 1 to 5 carbon atoms). Examples of such trialkoxysilane include trimethoxysilane, triethoxysilane, and methyltriethoxysilane.

As the above tetraalkoxysilane, any one can be used without particular limitation. For example, it is preferable to use a tetraalkoxysilane represented by the general formula: Si(OR) ₄ (wherein R is an alkyl group having 1 to 5 carbon atoms, which is the same or different). Examples of such tetraalkoxysilane include tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane.

Any silane coupling agent can be used without particular limitation. For example, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropylmethyldiethoxysilane, γ-aminopropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-mercaptopropylmethyldimethoxysilane, γ-mercaptopropyltrimethoxysilane, vinyltriethoxysilane, γ-isocyanatepropyltriethoxysilane, etc. can be mentioned.

In addition, by including the Si compound in the chemical conversion film, the Si compound dehydrates and condenses to form an amorphous chemical conversion film having a siloxane bond with a high barrier effect that shields corrosion factors. In addition, by combining with the resin described above, a chemical conversion film with a higher barrier property is formed. In addition, in a corrosive environment, a dense and stable corrosion product is formed in a damaged portion of the plating or film resulting from a defective portion or processing, and there is also an effect of suppressing corrosion of the underlying steel sheet due to the combined effect with the plating film. From the viewpoint of a high effect of forming a stable corrosion product, it is preferable to use at least one of colloidal silica and dry silica as the Si compound.

The concentration of the Si compound in the chemical treatment solution for forming the above-mentioned chemical film is 0.2 mass% to 9.5 mass%. When the concentration of the Si compound in the chemical treatment solution is 0.2 mass% or more, a barrier effect by a siloxane bond can be obtained, and as a result, in addition to the corrosion resistance of a flat surface, the corrosion resistance in damaged parts due to defective parts, cut parts, and processing, and cold resistance are improved. Furthermore, when the concentration of the Si compound is 9.5 mass% or less, the service life of the chemical treatment solution can be extended. By applying and drying a chemical treatment solution having a Si compound concentration of 0.2 mass% to 9.5 mass%, the Si adhesion amount in the chemical treatment film after drying can be 2 to 95 mg/m2.

The above Co compound and the above Ni compound can improve the blackening resistance by being included in the chemical conversion film. This is thought to be because Co and Ni have the effect of delaying the elution of water-soluble components from the film in a corrosive environment. In addition, the Co and the above Ni are elements that are less likely to be oxidized than Al, Zn, Si, Mg, etc. Therefore, by concentrating at least one of the Co compound and the Ni compound at the interface between the chemical conversion film and the plating film (forming a concentrated layer), the concentrated layer acts as a barrier against corrosion, and as a result, the blackening resistance can be improved.

By using the Martian treatment solution including the above Co compound, Co can be contained in the Martian film and incorporated into the concentrated layer. As the Co compound, it is preferable to use a cobalt salt. As the cobalt salt, it is more preferable to use one or two or more selected from cobalt sulfate, cobalt carbonate, and cobalt chloride.

In addition, by using the Martian treatment solution containing the Ni compound, Ni can be contained in the Martian film and incorporated into the concentrated layer. As the Ni compound, it is preferable to use a nickel salt. As the nickel salt, it is more preferable to use one or two or more selected from nickel sulfate, nickel carbonate, and nickel chloride.

The concentration of the Co compound and/or the Ni compound in the above-mentioned Martian treatment solution is not particularly limited, but can be 0.25 mass% to 5 mass% in total. If the concentration of the Co compound and/or the Ni compound is less than 0.25 mass%, the interface concentration layer becomes uneven, which reduces not only the corrosion resistance of the flat surface, but also the corrosion resistance of the plating or film damaged portion due to defective portions, cut cross-sections, processing, etc. may be reduced. From the same viewpoint, it is preferably 0.5 mass% or more, more preferably 0.75 mass% or more. On the other hand, if the concentration of the Co compound and/or the Ni compound exceeds 5 mass%, the appearance when the film is formed tends to become uneven, which may reduce the corrosion resistance. From the same viewpoint, it is preferably 4.0 mass% or less, more preferably 3.0 mass% or less. By applying and drying a chemical treatment solution having a total concentration of the Co compound and/or the Ni compound of 0.25 mass% to 5 mass%, the total adhesion amount of Co and Ni in the chemical film after drying can be set to 5 to 100 mg/m2.

For the above Al compound, the above Zn compound and the above Mg compound, by containing them in the Martian treatment solution, a concentrated layer containing at least one of Al, Zn and Mg can be formed on the plating film side of the Martian film. The formed concentrated layer can improve corrosion resistance.

In addition, the Al compound, the Zn compound and the Mg compound are not particularly limited as long as they are compounds containing Al, Zn and Mg, respectively, but are preferably inorganic compounds and are preferably salts, chlorides, oxides or hydroxides.

As the above Al compound, for example, one or more selected from aluminum sulfate, aluminum carbonate, aluminum chloride, aluminum oxide, and aluminum hydroxide can be mentioned.

As the above Zn compound, for example, one or more selected from zinc sulfate, zinc carbonate, zinc chloride, zinc oxide, and zinc hydroxide can be mentioned.

As the above Mg compound, for example, one or more selected from magnesium sulfate, magnesium carbonate, magnesium chloride, magnesium oxide, and magnesium hydroxide can be mentioned.

The concentration of the Al compound, the Zn compound and/or the Mg compound in the chemical treatment solution for forming the above-mentioned chemical film is preferably 0.25 mass% to 5 mass% in total. When the above-mentioned total concentration is 0.25 mass% or more, the above-mentioned concentrated layer can be formed more effectively, and as a result, the corrosion resistance can be further improved. On the other hand, when the above-mentioned total concentration is 5 mass% or less, the appearance of the chemical film becomes more uniform, and the corrosion resistance of the plating or film damaged by flat portions, defective portions, processing, etc. is further improved.

The above V compound, by being included in the above Mars film, appropriately dissolves V in a corrosive environment and combines with zinc ions of the plating component that dissolve in the same environment to form a dense protective film. By the formed protective film, corrosion resistance can be further enhanced not only for the flat surface of the steel plate, but also for defective parts, damaged parts of the plating film caused by processing, and corrosion that progresses from a cut section to the flat surface.

As for the above V compound, it is a compound containing V, and examples thereof include at least one selected from sodium metavanadate, vanadyl sulfate, and vanadium acetylacetonate.

The V compound in the chemical treatment solution for forming the above-mentioned chemical film is preferably 0.05 mass% to 4 mass%. When the concentration of the V compound is 0.05 mass% or more, it is easy to form a protective film by dissolving in a corrosive environment, thereby improving the corrosion resistance of a defective portion, a cut section, or a damaged portion of the plating film caused by processing. On the other hand, when the concentration of the V compound exceeds 4 mass%, the appearance when the chemical film is formed is easy to become uneven, and the blackening resistance also decreases.

The above Mo compound can improve the blackening resistance of the surface-treated steel sheet by being included in the above Mars film. The above Mo compound is a compound containing Mo, and can be obtained by adding one or both of molybdic acid and a molybdic acid salt to the Mars treatment solution.

In addition, as the molybdic acid salt, for example, at least one selected from sodium molybdate, potassium molybdate, magnesium molybdate, and zinc molybdate can be mentioned.

The concentration of the Mo compound in the chemical treatment solution for forming the above-mentioned chemical film is preferably 0.01 mass% to 3 mass%. When the concentration of the Mo compound is 0.01 mass% or more, the formation of oxygen-deficient zinc oxide is further suppressed, and blackening resistance can be further improved. On the other hand, when the concentration of the Mo compound is 3 mass% or less, the service life of the chemical treatment solution is further extended, and corrosion resistance can be further improved.

The above Zr compound and the above Ti compound, by being included in the igneous film, can prevent the igneous film from becoming porous, thereby densifying the film. As a result, it becomes difficult for corrosion factors to penetrate the igneous film, thereby enhancing corrosion resistance.

For the above Zr compound, it is a compound containing Zr, and for example, one or more selected from zirconyl acetate, zirconyl sulfate, potassium zirconyl carbonate, sodium zirconyl carbonate, and ammonium zirconyl carbonate can be used. Among these, an organic titanium chelate compound is suitable because when the ignition treatment liquid is dried to form a film, the film becomes denser, thereby obtaining better corrosion resistance.

For the above Ti compound, it is a compound containing Ti, and for example, at least one selected from titanium sulfate, titanium chloride, titanium hydroxide, titanium acetylacetonate, titanium octylene glycolate, and titanium ethylacetoacetate can be used.

The concentration of the Zr compound and/or the Ti compound in the chemical treatment solution for forming the above-mentioned chemical film is preferably 0.2 mass% to 20 mass% in total. When the total concentration of the Zr compound and/or the Ti compound is 0.2 mass% or more, the effect of inhibiting the penetration of corrosion factors is enhanced, so that not only the corrosion resistance of a flat surface but also the corrosion resistance of a defective portion, a cut cross-section, and a portion of the plating film damaged by processing can be further improved. On the other hand, when the total concentration of the Zr compound and/or the Ti compound is 20 mass% or less, the service life of the chemical treatment solution can be further extended.

The above Ca compound, by being included in the Martian film, can exhibit an effect of reducing the corrosion rate.

As for the above Ca compound, it is a compound containing Ca, and examples thereof include Ca oxide, Ca nitrate, Ca sulfate, Ca intermetallic compound containing Ca, etc. More specifically, as the Ca compound, CaO, CaCO ₃ , Ca(OH) ₂ , Ca(NO ₃ ) ₂ ·4H ₂ O, CaSO ₄ ·2H ₂ O, etc. can be mentioned. The content of the Ca compound in the above-mentioned chemical film is not particularly limited.

In addition, the above-mentioned Martian coating may contain various known components commonly used in the paint field, if necessary. For example, various surface conditioners such as leveling agents and anti-foaming agents, dispersants, anti-settling agents, ultraviolet absorbers, light stabilizers, silane coupling agents, titanate coupling agents, various additives such as color pigments, extender pigments, and light brighteners, various pigments such as curing catalysts, organic solvents, lubricants, etc.

In addition, in the surface-treated steel sheet of the present invention, it is preferable that the chemical conversion film does not contain harmful components such as hexavalent chromium, trivalent chromium, and fluorine. This is because the chemical conversion treatment solution for forming the chemical conversion film does not contain these harmful components, and thus the safety is high and the burden on the environment is reduced.

In addition, the adhesion amount of the chemical film is not particularly limited. For example, from the viewpoint of ensuring corrosion resistance more reliably and preventing peeling of the chemical film, the adhesion amount of the chemical film is preferably 0.1 to 3.0 g/m2, and more preferably 0.5 to 2.5 g/m2. By setting the adhesion amount of the chemical film to 0.1 g/m2 or more, corrosion resistance can be secured more reliably, and by setting the adhesion amount of the chemical film to 3.0 g/m2 or less, cracking or peeling of the chemical film can be prevented.

The above-mentioned amount of the Martian film adhesion can be obtained by a method appropriately selected from existing methods, such as a method of measuring the amount of elements whose content in the film is known in advance by performing a fluorescence X-ray analysis of the film.

In addition, the method for forming the above-mentioned chemical film is not particularly limited, and can be appropriately selected according to the required performance, manufacturing equipment, etc. For example, the chemical treatment solution is continuously applied onto the above-mentioned plating film by a roll coater or the like, and then dried at a peak metal temperature (PMT) of about 60 to 200°C using hot air, induction heating, or the like, thereby forming the film. In addition to a roll coater, a known method such as airless spray, electrostatic spray, or curtain flow coater can be appropriately employed for applying the chemical treatment solution. In addition, the chemical treatment film may be either a single-layer film or a double-layer film, as long as it contains the above-mentioned resin and the above-mentioned metal compound, and is not particularly limited.

In addition, the surface-treated steel plate of the present invention can form a coating film on the Mars film, if necessary.

(painted steel plate)

The painted steel sheet of the present invention is a painted steel sheet in which a coating film is formed directly on a plating film or by interposing a chemical film.

Among these, the composition of the plating film is the same as the plating film of the molten Al-Zn-Si-Mg-Sr system plating steel sheet of the present invention described above.

The painted steel plate of the present invention can form a Mars film on the plating film.

In addition, the above-mentioned Martian film is preferably formed on at least one side of the painted steel plate, and may be formed on both sides of the painted steel plate depending on the intended use or required performance.

And, in the painted steel plate of the present invention, the chemical composition is characterized in that the chemical composition contains a resin component containing (a): an anionic polyurethane resin having an ester bond and (b): an epoxy resin having a bisphenol skeleton, in a total amount of 30 to 50 mass%, and the content ratio ((a):(b)) of (a) and (b) is in a range of 3:97 to 60:40 in mass ratio, and an inorganic compound containing 2 to 10 mass% of a vanadium compound, 40 to 60 mass% of a zirconium compound, and 0.5 to 5 mass% of a fluorine compound.

By forming the aforementioned Mars film on the plating film, the strength and adhesion of the Mars film can be increased, while also improving corrosion resistance.

Here, the resin component constituting the above-mentioned Martian film contains (a): anionic polyurethane resin having an ester bond and (b): epoxy resin having a bisphenol skeleton.

As for the anionic polyurethane resin having the above (a) ester bond, examples thereof include a resin obtained by copolymerizing a dimethylol alkyl acid with a reaction product of a polyester polyol and a diisocyanate or polyisocyanate having two or more isocyanate groups. In addition, a chemical treatment solution can be obtained by dispersing the resin in a liquid such as water by a known method.

As the polyester polyol, examples thereof include polyesters obtained by a dehydration condensation reaction from a glycol component and an acid component such as an ester-forming derivative of hydroxylcarboxylic acid, polyesters obtained by a ring-opening polymerization reaction of a cyclic ester compound such as ε-caprolactone, and copolymerized polyesters thereof.

Examples of the above polyisocyanates include aromatic polyisocyanates, aliphatic polyisocyanates, and alicyclic polyisocyanates. Examples of the above aromatic polyisocyanates include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, m-xylene diisocyanate, diphenylmethane diisocyanate, 2,4-diphenylmethane diisocyanate, 2,2-diphenylmethane diisocyanate, triphenylmethane triisocyanate, polymethylene polyphenyl polyisocyanate, naphthalene diisocyanate, and derivatives thereof (for example, prepolymers obtained by reaction with polyols, modified polyisocyanates such as carbodiamide compounds of diphenylmethane diisocyanate, etc.).

In addition, when synthesizing urethane by reacting the polyester polyol with the diisocyanate or polyisocyanate, for example, by copolymerizing dimethylol alkyl acid and self-emulsifying it to obtain a water-soluble (water-dispersed) anionic polyurethane resin having the (a) ester bond can be obtained. In this case, examples of the dimethylol alkyl acid include dimethylol alkyl acids having 2 to 6 carbon atoms, and more specifically, dimethylol ethane ester acid, dimethylol propanoic acid, dimethylol butanoic acid, dimethylol heptanoic acid, and dimethylol hexanoic acid.

In addition, for the epoxy resin having a bisphenol skeleton (b), a known epoxy resin can be used. For example, bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol AD type epoxy resin, bisphenol S type epoxy resin, etc. can be mentioned. These epoxy resins can be obtained by reacting a bisphenol compound such as bisphenol A, bisphenol F, bisphenol AD, bisphenol S, etc. with epichlorohydrin in the presence of an alkaline catalyst. Among these, those containing a bisphenol A type epoxy resin or a bisphenol F type epoxy resin are preferable, and those containing a bisphenol A type epoxy resin are more preferable. The epoxy resin having a bisphenol skeleton (b) can be dispersed in a liquid such as water by a known method to obtain a chemical treatment solution.

The above resin component acts as a binder of the above-mentioned ignition film, but the anionic polyurethane resin having (a) ester bonds constituting the binder can have the effect of making it difficult for the ignition film to be destroyed (peeled) when processed because it is flexible, and the (b) epoxy resin having a bisphenol skeleton can have the effect of improving the adhesion between the zinc-plated steel sheet as the base and the primer coating as the upper layer.

The above resin component is contained in the total amount of 30 to 50 mass% in the above chemical film. When the content of the above resin component is less than 30 mass%, the binder effect of the chemical film is reduced, and when it exceeds 50 mass%, the function of the inorganic component shown below, for example, the inhibitor action, is reduced. From the same viewpoint, the content of the above resin component in the above chemical film is preferably 35 to 45 mass%.

In addition, the resin component requires that the content ratio ((a):(b)) of the anionic polyurethane resin having the (a) ester bond and the epoxy resin having the (b) bisphenol skeleton be in the range of 3:97 to 60:40 in mass ratio. If the (a):(b) is outside the range, sufficient corrosion resistance is not obtained due to a decrease in flexibility or a decrease in adhesion as a chemistry treatment film. From the same viewpoint, the (a):(b) is preferably 10:90 to 55:45.

In addition, for the resin component, depending on the required performance, a resin other than (a) anionic polyurethane resin having an ester bond and (b) epoxy resin having a bisphenol skeleton (other resin component) may be included. There is no particular limitation on the other resin component, and for example, at least one or two or more selected from among acrylic resins, acrylic silicone resins, alkyd resins, polyester resins, polyalkylene resins, amino resins, and fluororesins may be used in combination.

When the above resin component contains other resins, the total content of the (a) anionic polyurethane resin having an ester bond and the (b) epoxy resin having a bisphenol skeleton is preferably 50 mass% or more, and more preferably 75 mass% or more. This is to more reliably obtain the flexibility reduction and adhesion as a chemical treatment film.

In addition, the above-mentioned Martian film contains, as inorganic compounds, 2 to 10 mass% of a vanadium compound, 40 to 60 mass% of a zirconium compound, and 0.5 to 5 mass% of a fluorine compound.

By including these compounds, the corrosion resistance of the Martian film can be improved.

The above vanadium compound acts as a rust inhibitor when added to the chemical treatment solution. When the vanadium compound is included in the chemical film, the vanadium compound is appropriately eluted in a corrosive environment and combines with zinc ions of the plating component that are also eluted in the corrosive environment, thereby forming a dense protective film. By the formed protective film, the corrosion resistance can be further enhanced not only against the flat surface of the steel plate, but also against defective portions, damaged portions of the plating film caused by processing, and corrosion that progresses from a cut section to the flat surface.

Examples of the vanadium compound include vanadium pentoxide, metavanadic acid, ammonium metavanadate, vanadium oxytrichloride, vanadium trioxide, vanadium dioxide, magnesium vanadate, vanadyl acetylacetonate, vanadium acetylacetonate, and the like. In particular, among these, it is preferable to use a tetravalent vanadium compound or a tetravalent vanadium compound obtained by reduction or oxidation.

In addition, the content of the vanadium compound in the chemical treatment film is 2 to 10 mass%. If the content of the vanadium compound in the chemical treatment film is less than 2 mass%, the inhibitor effect is not sufficient, resulting in a decrease in corrosion resistance, and if the content of the vanadium compound exceeds 10 mass%, the moisture resistance of the chemical treatment film is reduced.

Zirconium compounds are contained in the above-mentioned ignition film, and through reaction with the plating metal or coexistence with the resin component, it is expected that the strength and corrosion resistance of the ignition treatment film will be improved. Furthermore, since the zirconium compound itself contributes to the formation of a dense ignition treatment film, a barrier effect can be expected from the point of view of its rich covering properties.

Examples of the zirconium compounds include neutralized salts such as zirconium sulfate, zirconium carbonate, zirconium nitrate, zirconium lactate, zirconium acetate, and zirconium chloride.

In addition, the content of the zirconium compound in the above-mentioned chemical treatment film is 40 to 60 mass%. If the content of the zirconium compound in the above-mentioned chemical treatment film is less than 40 mass%, the strength and corrosion resistance of the chemical treatment film are reduced, and if the content of the zirconium compound exceeds 60 mass%, the chemical treatment film becomes brittle, and when subjected to harsh processing, the chemical treatment film is destroyed or peeled off.

The above fluorine compound is contained in the ignition film and acts as an adhesion-improving agent with the plating film. As a result, it becomes possible to increase the corrosion resistance of the ignition film.

As the above fluorine compound, for example, fluoride salts such as ammonium salt, sodium salt, potassium salt, or fluoride compounds such as ferrous fluoride or ferric fluoride can be used. Among these, it is preferable to use fluoride salts such as ammonium fluoride, sodium fluoride, and potassium fluoride.

In addition, the content of the fluorine compound in the above-mentioned chemical treatment film is 0.5 to 5 mass%. If the content of the fluorine compound in the above-mentioned chemical treatment film is less than 0.5 mass%, sufficient adhesion in the processed area is not obtained, and if the content of the fluorine compound exceeds 5 mass%, the moisture resistance of the chemical treatment film deteriorates.

In addition, the adhesion amount of the chemical film is not particularly limited. For example, from the viewpoint of ensuring corrosion resistance more reliably and improving the adhesion of the chemical film, it is preferable to set the adhesion amount of the chemical film to 0.025 to 0.5 g/m2. By setting the adhesion amount of the chemical film to 0.025 g/m2 or more, corrosion resistance can be ensured more reliably, and by setting the adhesion amount of the chemical film to 0.5 g/m2 or less, peeling of the chemical film can be suppressed.

The above-mentioned amount of the Martian film adhesion can be obtained by a method appropriately selected from existing methods, such as a method of measuring the amount of elements whose content in the film is known in advance by performing a fluorescence X-ray analysis of the film.

In addition, the method for forming the above-mentioned chemical film is not particularly limited, and can be appropriately selected according to the required performance, manufacturing equipment, etc. For example, the chemical treatment solution is continuously applied onto the above-mentioned plating film by a roll coater or the like, and then dried at a peak metal temperature (PMT) of about 60 to 200°C using hot air, induction heating, or the like, thereby forming the film. In addition to a roll coater, a known method such as airless spray, electrostatic spray, or curtain flow coater can be appropriately employed for applying the chemical treatment solution. In addition, the chemical treatment film may be either a single-layer film or a multi-layer film, as long as it contains the above-mentioned resin and the above-mentioned metal compound, and is not particularly limited.

As described above, the coated steel plate of the present invention has a coating film formed directly or through a chemical film on the plating film, and the coating film has at least a primer coating film.

And, the present invention comprises a primer coating film containing a polyester resin having a urethane bond and an inorganic compound including a vanadium compound, a phosphoric acid compound and magnesium oxide.

The above primer coating film can improve corrosion resistance while increasing the adhesion of the coating film by containing the polyester resin having the urethane bond and the inorganic compound.

The above primer coating contains, as a main component, a polyester resin having a urethane bond. Since the polyester resin having the urethane bond has both flexibility and strength, it is possible to obtain effects such as making it difficult for cracks to occur in the primer coating when processed, and since it has high affinity with a chemical treatment film containing a urethane resin, it can particularly contribute to improving the corrosion resistance of the processed portion.

Additionally, the “main ingredient” mentioned here means the ingredient with the largest content among each ingredient in the primer film.

As the polyester resin having the above urethane bond, a known resin can be used, such as a resin obtained by reaction of a polyester polyol and a diisocyanate or polyisocyanate having two or more isocyanate groups. In addition, a resin obtained by reacting the polyester polyol with the diisocyanate or polyisocyanate in an excess of hydroxyl groups (urethane-modified polyester resin) and curing it with a blocked polyisocyanate can also be used.

In addition, the polyester polyol can be obtained by a known method utilizing a dehydration condensation reaction of a polyhydric alcohol component and a polybasic acid component.

As the above polyhydric alcohol, glycol and trihydric or higher polyhydric alcohols can be mentioned. The glycol can be mentioned, for example, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, neopentyl glycol, hexylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2-butyl-2-ethyl-1,3-propanediol, methylpropanediol, cyclohexanedimethanol, 3,3-diethyl-1,5-pentanediol, etc. In addition, the above trihydric or higher polyhydric alcohol can be mentioned, for example, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, dipentaerythritol, etc. These polyhydric alcohols can be used alone or in combination of two or more.

The above polybasic acid is usually a polycarboxylic acid, but a monovalent fatty acid, etc. can be used in combination as needed. Examples of the polycarboxylic acid include phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, 4-methylhexahydrophthalic acid, bicyclo[2,2,1]heptane-2,3-dicarboxylic acid, trimellitic acid, adipic acid, sebacic acid, succinic acid, azelaic acid, fumaric acid, maleic acid, itaconic acid, pyromellitic acid, dimer acid, and the like, as well as acid anhydrides thereof, and 1,4-cyclohexanedicarboxylic acid, isophthalic acid, tetrahydroisophthalic acid, hexahydroisophthalic acid, hexahydroterephthalic acid, etc. These polybasic acids can be used alone or in combination of two or more.

Examples of the polyisocyanate include aliphatic diisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and dimer acid diisocyanate; aromatic diisocyanates such as xylylene diisocyanate (XDI), metaxylylene diisocyanate, tolylene diisocyanate (TDI), and 4,4-diphenylmethane diisocyanate (MDI); and cyclic aliphatic diisocyanates such as isophorone diisocyanate, hydrogenated XDI, hydrogenated TDI, and hydrogenated MDI; and adducts, biurets, and isocyanurates thereof. These polyisocyanates may be used alone or in combination of two or more.

In addition, the hydroxyl value of the polyester resin having the urethane bond is not particularly limited, but from the viewpoints of content resistance, processability, etc., it is preferably 5 to 120 mgKOH/g, more preferably 7 to 100 mgKOH/g, and even more preferably 10 to 80 mgKOH/g.

In addition, the number average molecular weight of the polyester resin having the urethane bond is preferably 500 to 15,000, more preferably 700 to 12,000, and even more preferably 800 to 10,000, from the viewpoints of content resistance, processability, etc.

In the above primer coating, the content of the polyester resin having the urethane bond is preferably 40 to 88 mass%. If the content of the polyester resin having the urethane bond is less than 40 mass%, there is a concern that the binder function as the primer coating may be reduced, and on the other hand, if the content of the polyester resin having the urethane bond exceeds 88 mass%, there is a concern that the function by the inorganic substance shown below, for example, the inhibitor action, may be reduced.

Among the above inorganic compounds, the vanadium compound acts as an inhibitor. Examples of the vanadium compound include vanadium pentoxide, metavanadic acid, ammonium metavanadate, vanadium oxytrichloride, vanadium trioxide, vanadium dioxide, magnesium vanadate, vanadyl acetylacetonate, and vanadium acetylacetonate. In particular, among these, it is preferable to use a tetravalent vanadium compound or a tetravalent vanadium compound obtained by reduction or oxidation.

The vanadium compound added to the above primer coating may be the same or different from the vanadium compound added to the above chemical treatment film. It is thought that the vanadic acid compound forms a passive film with good adhesion by reacting with vanadic acid ions that are slowly dissolved by moisture that penetrates from the outside and ions on the surface of the zinc-plated steel sheet, thereby protecting the exposed metal portion and exhibiting a rust-preventive effect.

The content of the vanadium compound in the above primer coating is not particularly limited, but is preferably 4 to 20 mass% from the viewpoint of achieving both corrosion resistance and moisture resistance. If the content of the vanadium compound is less than 4 mass%, there is a concern that the inhibitor effect may decrease, resulting in a decrease in corrosion resistance, and if the content of the vanadium compound exceeds 20 mass%, there is a concern that the moisture resistance of the primer coating may decrease.

Regarding the phosphoric acid compound, which is one of the above inorganic compounds, it also acts as an inhibitor. As the phosphoric acid compound, for example, phosphoric acid, ammonium salt of phosphoric acid, alkali metal salt of phosphoric acid, alkaline earth metal salt of phosphoric acid, etc. can be used. In particular, alkali metal salt of phosphoric acid, such as calcium phosphate, can be suitably used.

The content of the phosphoric acid compound in the above primer coating is not particularly limited, but is preferably 4 to 20 mass% from the viewpoint of achieving both corrosion resistance and moisture resistance. If the content of the phosphoric acid compound is less than 4 mass%, there is a concern that the inhibitor effect may decrease, resulting in a decrease in corrosion resistance, and if the content of the phosphoric acid compound exceeds 20 mass%, there is a concern that the moisture resistance of the primer coating may decrease.

Magnesium oxide, one of the above inorganic compounds, produces a product containing Mg by initial corrosion and, as a sparingly soluble magnesium salt, promotes stabilization and has the effect of improving corrosion resistance.

The content of the magnesium oxide in the above primer coating is not particularly limited, but is preferably 4 to 20 mass% from the viewpoint of achieving both corrosion resistance and corrosion resistance of the processed portion. If the content of the magnesium oxide is less than 4 mass%, there is a concern that the effect may be reduced, resulting in a reduction in corrosion resistance, and if the content of the magnesium oxide exceeds 20 mass%, the flexibility of the primer coating may be reduced, thereby reducing the corrosion resistance of the processed portion.

In addition, the primer coating may contain components other than the polyester resin and inorganic compound having the above-described urethane bond.

For example, a crosslinking agent used when forming a primer film can be mentioned. The crosslinking agent forms a crosslinking film by reacting with a polyester resin having the urethane bond, and examples thereof include oxazoline compounds, epoxy compounds, melamine compounds, isocyanate compounds, carbodiimide compounds, silane coupling compounds, etc., and it is also possible to use two or more types of crosslinking agents in combination. Among these, from the viewpoint of the corrosion resistance of the processed portion of the resulting coated steel sheet, a blocked polyisocyanate compound or the like can be preferably used. Examples of the blocked polyisocyanate include those in which the isocyanate group of a polyisocyanate compound is blocked with, for example, alcohols such as butanol, oximes such as methyl ethyl ketoxime, lactams such as ε-caprolactam, diketones such as acetoacetic acid diester, imidazoles such as imidazole and 2-ethylimidazole, or phenols such as m-cresol.

In addition, the primer coating may contain various known components commonly used in the paint field, if necessary. Specifically, examples thereof include various surface conditioners such as leveling agents and anti-foaming agents, dispersants, anti-settling agents, ultraviolet absorbers, light stabilizers, silane coupling agents, titanate coupling agents, various additives such as color pigments and extender pigments, light brighteners, curing catalysts, organic solvents, etc.

The thickness of the above primer coating is preferably 1.5 ㎛ or more. By setting the thickness of the above primer coating to 1.5 ㎛ or more, the effect of improving corrosion resistance and the effect of improving adhesion with the overcoat coating formed on the chemical treatment film or primer coating can be more reliably obtained.

There is no particular limitation on the method for forming the above primer film. In addition, as for the coating method of the paint composition constituting the above primer film, the paint composition can preferably be applied by a method such as roll coater coating, curtain flow coating, etc. After coating the paint composition, the primer film can be obtained by baking by a heating means such as hot air heating, infrared heating, or induction heating. The baking treatment can usually be performed at a maximum plate temperature of about 180 to 270°C and for about 30 seconds to 3 minutes in this temperature range.

In addition, with respect to the coating film constituting the painted steel plate of the present invention, it is preferable that an additional overcoat film is formed on the primer coating film.

The above-mentioned overcoat film can, in addition to providing the painted steel plate with aesthetics such as color, gloss, and surface condition, improve various performances such as workability, weather resistance, chemical resistance, contamination resistance, water resistance, and corrosion resistance.

There is no particular limitation on the composition of the above overcoat, and materials and thickness, etc. can be appropriately selected according to the required performance.

For example, the above-mentioned overcoat film can be formed using a polyester resin-based paint, a silicone polyester resin-based paint, a polyurethane resin-based paint, an acrylic resin-based paint, a fluorine resin-based paint, or the like.

In addition, the above-mentioned overcoat film may contain an appropriate amount of various coloring pigments such as titanium oxide, bengala, mica, carbon black or other pigments; metallic pigments such as aluminum powder or mica; body pigments composed of carbonates or sulfates; various fine particles such as silica particles, nylon resin beads, and acrylic resin beads; curing catalysts such as p-toluenesulfonic acid and dibutyl tin dilaurate; waxes; and other additives.

In addition, the thickness of the overcoat film is preferably 5 to 30 µm from the viewpoint of achieving both appearance and workability. When the thickness of the overcoat film is 5 µm or more, it becomes possible to more reliably stabilize the color tone appearance, and when the thickness of the overcoat film is 30 µm or less, it becomes possible to more reliably suppress deterioration of workability (occurrence of cracks in the overcoat film).

The coating method of the paint composition for forming the above-mentioned overcoat film is not particularly limited. For example, the paint composition can be applied by a method such as roll coater coating or curtain flow coating. After coating the paint composition, it can be baked by a heating means such as hot air heating, infrared heating, or induction heating to form the overcoat film. The baking treatment can usually be performed at a maximum plate temperature of about 180 to 270°C and for about 30 seconds to 3 minutes in this temperature range.

Example

<Example 1: Samples 1 to 44>

Using a cold rolled steel sheet with a thickness of 0.8 mm manufactured by a conventional method as the base steel sheet, annealing and plating were performed using a hot-dip galvanizing simulator manufactured by Lesca Co., Ltd., to produce samples 1 to 44 of hot-dip galvanized steel sheets having the conditions shown in Table 1.

In addition, regarding the composition of the plating bath used in the manufacture of the hot-dip galvanized steel sheet, the composition of the plating bath was varied in the range of Al: 30 to 75 mass%, Si: 0.5 to 4.5 mass%, Mg: 0 to 10 mass%, and Sr: 0.00 to 0.15 mass% so as to obtain the composition of the plating film of each sample shown in Table 1. In addition, the bath temperature of the plating bath was set to 590°C when Al: 30 to 60 mass%, and 630°C when Al: exceeded 60 mass%, and the plating penetration plate temperature of the base steel sheet was controlled to be the same temperature as the plating bath temperature. In addition, the plating treatment was performed under the condition of cooling to a temperature range of 520 to 500°C in 3 seconds.

In addition, the adhesion amount of the plating film was controlled to be 85±5 g/m2 per side for samples 1 to 41, and 51 to 125 g/m2 per side for samples 42 to 44.

(evaluation)

For each sample of the molten galvanized steel sheet obtained as described above, the following evaluation was performed. The evaluation results are shown in Table 1.

(1) Composition of plating film (adhesion amount, composition, X-ray diffraction intensity)

For each sample after plating, a 100 mmφ was punched out, the non-measurement surface was sealed with tape, and the plating was dissolved and peeled off with a mixture of hydrochloric acid and hexamethylenetetramine as specified in JIS H 0401: 2013, and the adhesion amount of the plating film was calculated from the mass difference between the sample before and after peeling. The adhesion amounts of the obtained plating films as a result of the calculation are shown in Table 1.

Thereafter, the stripping solution was filtered, and the filtrate and solid content were analyzed respectively. Specifically, the filtrate was analyzed by ICP emission spectrometry to quantify components other than insoluble Si.

In addition, the solid content was dried and ash in a 650℃ furnace, and then melted by adding sodium carbonate and sodium tetraborate. In addition, the melt was dissolved with hydrochloric acid, and the solution was subjected to ICP emission spectroscopic analysis to quantify the insoluble Si. The Si concentration in the plating film is the insoluble Si concentration obtained by solid content analysis added to the available Si concentration obtained by filtrate analysis. The composition of the obtained plating film as a result of the calculation is shown in Table 1.

In addition, for each sample, after shearing to a size of 100 mm × 100 mm, the plating film on the evaluation symmetry plane was mechanically scraped off until a steel plate appeared, the obtained powder was well mixed, 0.3 g was taken out, and a qualitative analysis of the powder was performed using an X-ray diffraction device ("SmartLab" manufactured by Rigaku Corporation) under the following conditions: used X-ray: Cu-Kα (wavelength = 1.54178 Å), removal of Kβ line: Ni filter, tube voltage: 40 kV, tube current: 30 mA, scanning speed: 4°/min, sampling interval: 0.020°, divergence slit: 2/3°, solar slit: 5°, and detector: high-speed 1D detector (D/teX Ultra). The intensity obtained by subtracting the base intensity from each peak intensity was defined as each diffraction intensity (cps), and the diffraction intensity of the (111) plane of Mg ₂ Si (interface spacing d = 0.3668 nm) and the diffraction intensity of the (111) plane of Si (interface spacing d = 0.3135 nm) were measured. The measurement results are shown in Table 1.

(2) Corrosion resistance evaluation

For each sample of the obtained hot-dip galvanized steel sheet, after shearing to a size of 120 mm x 120 mm, a range of 10 mm from each edge of the surface to be evaluated and a cross-section of the sample and a non-target surface of the evaluation were sealed with tape, and the surface to be evaluated was exposed to a size of 100 mm x 100 mm, and these were used as evaluation samples. In addition, three identical evaluation samples were produced.

For the three evaluation samples manufactured as described above, a corrosion acceleration test was performed on all of them using the cycle shown in Fig. 1. The corrosion acceleration test was performed starting from wetting and up to 300 cycles, and the corrosion loss of each sample was measured by the method described in JIS Z 2383 and ISO8407, and evaluated according to the following criteria. The evaluation results are shown in Table 1.

◎: The corrosion loss of all three samples was less than 45 g/㎡

○: The corrosion loss of all three samples is less than 70 g/㎡

×: Corrosion loss of one or more samples exceeds 70 g/㎡

(3) Surface appearance

For each sample of the obtained hot-dip galvanized steel sheet, the surface of the plating film was observed visually.

And, the observation results were evaluated according to the following criteria. The evaluation results are shown in Table 1.

◎: No wrinkle shape defects were observed at all.

○: Wrinkle-shaped defects were observed only within a range of 50 mm from the edge.

×: Wrinkle-shaped defects were observed outside the range of 50 mm from the edge.

(4) Processability

For each sample of the obtained hot-dip galvanized steel plate, after shearing to a size of 70 mm x 150 mm, 8 plates of the same thickness were inserted inside and a 180° bending process (8T bending) was performed. After bending, Sellotape (registered trademark) was strongly adhered to the outer surface of the bent portion and then peeled off. The surface condition of the plating film on the outer surface of the bent portion and the presence or absence of adhesion (peeling) of the plating film on the surface of the tape used were visually observed, and the workability was evaluated according to the following criteria. The evaluation results are shown in Table 1.

○: No cracks or peeling are observed in the plating film.

△: There are cracks in the plating film, but no peeling is observed.

×: Cracks and peeling are both observed in the plating film.

(5) Bath stability

When manufacturing each sample of the hot-dip galvanized steel sheet, the condition of the bath surface of the plating bath was visually checked and compared with the bath surface of the plating bath used when manufacturing the hot-dip Al-Zn type plating steel sheet (bath surface without Mg-containing oxide). The evaluation was performed based on the following criteria, and the evaluation results are shown in Table 1.

○: Same as molten Al-Zn plating bath (55 mass% Al, balance Zn, 1.6 mass% bath)

△: More white oxides compared to molten Al-Zn plating bath (55 mass% Al, balance Zn, 1.6 mass% bath)

×: Formation of black oxide is observed during the plating bath.

From the results in Table 1, it can be seen that each sample of the present invention is excellent in a well-balanced manner in corrosion resistance, surface appearance, processability, and bath stability compared to each sample of the comparative example.

<Example 2: Samples 1 to 112>

(1) Using a cold rolled steel sheet with a thickness of 0.8 mm manufactured by a commercial method as the base steel sheet, annealing and plating were performed using a hot-dip plating simulator manufactured by Lesca Co., Ltd., to produce a sample of a hot-dip galvanized steel sheet with the plating film conditions shown in Tables 3 and 4.

In addition, regarding the composition of the plating bath used in the manufacture of the hot-dip galvanized steel sheet, the composition of the plating bath was varied in the range of Al: 30 to 75 mass%, Si: 0.5 to 4.5 mass%, Mg: 0 to 10 mass%, and Sr: 0.00 to 0.15 mass% so as to obtain the composition of the plating film of each sample shown in Table 2. In addition, the bath temperature of the plating bath was set to 590°C when Al: 30 to 60 mass%, and 630°C when Al: exceeded 60 mass%, and the plating penetration plate temperature of the base steel sheet was controlled to be the same temperature as the plating bath temperature. In addition, the plating treatment was performed under the condition of cooling to a temperature range of 520 to 500°C in 3 seconds.

In addition, the adhesion amount of the plating film was controlled to be 85±5 g/m2 per side for samples 1 to 82 and 95 to 112, and to be 51 to 125 g/m2 per side for samples 83 to 94.

(2) Thereafter, a chemical treatment solution was applied onto the plating film of each sample of the manufactured hot-dip galvanized steel sheet using a bar coater, and dried in a hot-air furnace (heating rate: 60°C/s, PMT: 120°C) to form a chemical treatment film, thereby manufacturing each sample of the surface-treated steel sheet shown in Tables 3 and 4.

In addition, the Mars treatment solution was prepared as surface treatment solutions A to F by dissolving each component in water as a solvent. The types of each component (resin, metal compound) contained in the surface treatment solution are as follows.

(profit)

Urethane resin: Super Flex 130, Super Flex 126 (Daiichi Kogyo Seiyaku Co., Ltd.)

Acrylic Resin: Boncoat EC-740 EF (DIC Corporation)

(metal compound)

P Compound: Aluminum dihydrogen tripolyphosphate

Si compound: silica

V Compound: Sodium metavanadate

Mo compound: molybdic acid

Zr compound: potassium zirconyl carbonate

The compositions of the prepared Mars treatment solutions A to F and the adhesion amounts of the formed Mars film are shown in Table 2. In addition, the concentration of each component in Table 2 of this specification is the concentration of solid content (mass%).

(evaluation)

For each sample of the molten galvanized steel sheet and surface-treated steel sheet obtained as described above, the following evaluation was performed. The evaluation results are shown in Tables 3 and 4.

(1) Composition of plating film (adhesion amount, composition, X-ray diffraction intensity)

For each sample of the hot-dip galvanized steel sheet, 100 mmφ was punched out, the non-measurement surface was sealed with tape, and the plating was dissolved and peeled off with a mixture of hydrochloric acid and hexamethylenetetramine as specified in JIS H 0401: 2013, and the adhesion amount of the plating film was calculated from the mass difference between the sample before and after peeling. The adhesion amounts of the obtained plating films as a result of the calculation are shown in Tables 3 and 4.

Thereafter, the stripping solution was filtered, and the filtrate and solid content were analyzed, respectively. Specifically, the filtrate was analyzed by ICP emission spectrometry to quantify components other than insoluble Si.

In addition, the solid content was dried and oxidized in a 650℃ furnace, and then dissolved by adding sodium carbonate and sodium tetraborate. In addition, the melt was dissolved with hydrochloric acid, and the solution was subjected to ICP emission spectroscopic analysis to quantify the insoluble Si. The Si concentration in the plating film is the concentration of insoluble Si obtained by solid content analysis added to the concentration of soluble Si obtained by filtrate analysis. The compositions of the obtained plating films as a result of the calculation are shown in Tables 3 and 4.

In addition, for each sample, after shearing to a size of 100 mm × 100 mm, the plating film on the evaluation symmetry plane was mechanically scraped off until a steel plate appeared, the obtained powder was well mixed, 0.3 g was taken out, and a qualitative analysis of the powder was performed using an X-ray diffraction device ("SmartLab" manufactured by Rigaku Corporation) under the following conditions: used X-ray: Cu-Kα (wavelength = 1.54178 Å), removal of Kβ line: Ni filter, tube voltage: 40 kV, tube current: 30 mA, scanning speed: 4°/min, sampling interval: 0.020°, divergence slit: 2/3°, solar slit: 5°, and detector: high-speed 1D detector (D/teX Ultra). The intensity obtained by subtracting the base intensity from each peak intensity was defined as each diffraction intensity (cps), and the diffraction intensity of the (111) plane of Mg ₂ Si (interface spacing d = 0.3668 nm) and the diffraction intensity of the (111) plane of Si (interface spacing d = 0.3135 nm) were measured. The measurement results are shown in Tables 3 and 4.

(2) Corrosion resistance evaluation

For each sample of the hot-dip galvanized steel sheet and the surface-treated steel sheet, a sample for evaluation was used in which, after shearing to a size of 120 mm x 120 mm, a range of 10 mm from each edge of the surface to be evaluated and a cross-section of the sample and a non-target surface were sealed with tape, and the surface to be evaluated was exposed to a size of 100 mm x 100 mm. In addition, three identical samples for evaluation were produced.

For the three evaluation samples manufactured as described above, a corrosion acceleration test was performed on all of them using the cycle shown in Fig. 1. The corrosion acceleration test was started from wetting and was performed for 300 cycles. The corrosion loss of each sample was measured by the method described in JIS Z 2383 and ISO8407, and evaluated according to the following criteria. The evaluation results are shown in Tables 3 and 4.

◎: The corrosion loss of all three samples is less than 30 g/㎡

○: The corrosion loss of all three samples is less than 50 g/㎡

×: Corrosion loss of one or more samples exceeds 50 g/㎡

(3) My white and clear skin

For each sample of the hot-dip galvanized steel sheet and the surface-treated steel sheet, a sample was used for evaluation in which, after shearing to a size of 120 mm x 120 mm, a range of 10 mm from each edge of the surface to be evaluated and the cross-section of the sample and the non-target surface of the evaluation were sealed with tape, and the surface to be evaluated was exposed to a size of 100 mm x 100 mm.

Using the above evaluation sample, the salt spray test described in JIS Z 2371 was performed for 90 hours and evaluated according to the following criteria. The evaluation results are shown in Tables 3 and 4.

◎: No white collar on the reputation section

○: Area of white rust occurring in the reputation area is less than 10%

×: Area of white spots on the reputation surface of 10% or more

(4) Surface appearance

For each sample of the hot-dip galvanized steel sheet, the surface of the plating film was observed visually.

And, the observation results were evaluated according to the following criteria. The evaluation results are shown in Tables 3 and 4.

◎: No wrinkle shape defects were observed at all.

○: Wrinkle-shaped defects were observed only within a range of 50 mm from the edge.

×: Wrinkle-shaped defects were observed outside the range of 50 mm from the edge.

(5) Processability

For each sample of the hot-dip galvanized steel plate, after shearing to a size of 70 mm x 150 mm, 8 plates of the same thickness as the copper plate were inserted inside and a 180° bending process (8T bending) was performed. After bending, Cellotape (registered trademark) was strongly adhered to the outer surface of the bent portion and then peeled off. The surface condition of the plating film on the outer surface of the bent portion and the presence or absence of adhesion (peeling) of the plating film on the surface of the tape used were visually observed, and the workability was evaluated according to the following criteria. The evaluation results are shown in Tables 3 and 4.

○: No cracks or peeling are observed in the plating film.

△: There are cracks in the plating film, but no peeling is observed.

×: Cracks and peeling are both observed in the plating film.

(6) Bath stability

During hot-dip plating, the state of the bath surface of the plating bath was visually confirmed and compared with the bath surface of the plating bath used when manufacturing a hot-dip Al-Zn type plating steel sheet (bath surface without Mg-containing oxide). The evaluation was performed based on the following criteria, and the evaluation results are shown in Tables 3 and 4.

○: Identical to molten Al-Zn plating bath (55 mass% Al, balance Zn, 1.6 mass% bath)

△: More white oxides compared to the molten Al-Zn plating bath (55 mass% Al, balance Zn, 1.6 mass% bath)

×: Formation of black oxide is observed during the plating bath.

From the results in Tables 3 and 4, it can be seen that each sample of the present invention is excellent in a well-balanced manner in corrosion resistance, white rust resistance, surface appearance, processability, and bath stability compared to each sample of the comparative example.

In addition, from the results in Table 4, it can be seen that each sample subjected to Mars treatments A to D exhibited excellent whitening resistance.

<Example 3: Samples 1 to 44>

(1) Using a cold rolled steel sheet with a thickness of 0.8 mm manufactured by a commercial method as the base steel sheet, annealing and plating were performed using a hot-dip plating simulator manufactured by Lesca Co., Ltd., to produce a sample of a hot-dip galvanized steel sheet with the plating film conditions shown in Table 6.

In addition, regarding the composition of the plating bath used in the manufacture of the hot-dip galvanized steel sheet, the composition of the plating bath was varied in the range of Al: 30 to 75 mass%, Si: 0.5 to 4.5 mass%, Mg: 0 to 10 mass%, and Sr: 0.00 to 0.15 mass% so as to obtain the composition of the plating film of each sample shown in Table 6. In addition, the bath temperature of the plating bath was set to 590°C when Al: 30 to 60 mass%, and 630°C when Al: exceeded 60 mass%, and the plating penetration plate temperature of the base steel sheet was controlled to be the same temperature as the plating bath temperature. In addition, the plating treatment was performed under the condition of cooling to a temperature range of 520 to 500°C in 3 seconds.

In addition, the adhesion amount of the plating film was controlled to be 85±5 g/m2 per side for samples 1 to 41, and 42 to 125 g/m2 per side for samples 42 to 44.

(2) Thereafter, the chemical treatment solution shown in Table 5 was applied onto the plating film of each sample of the manufactured hot-dip galvanized steel plate using a bar coater, and dried in a hot air drying oven (reaching plate temperature: 90°C), thereby forming a chemical treatment film having an adhesion amount of 0.1 g/㎡.

In addition, the chemical treatment solution used was a chemical treatment solution having a pH of 8 to 10 prepared by dissolving each component in water as a solvent. The types of each component (resin component, inorganic compound) contained in the chemical treatment solution are as follows.

(resin component)

Resin A: (a) an anionic polyurethane resin having an ester bond ("Super Flex 210" manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) and (b) an epoxy resin having a bisphenol skeleton ("Yuka Resin RE-1050" manufactured by Yoshimura Yukagaku Co., Ltd.), mixed in a mass ratio of (a):(b) = 50:50.

Resin B: Acrylic resin (DIC Co., Ltd. manufactured “Bon Coat EC-740 EF”)

(inorganic compounds)

Vanadium compounds: Organic vanadium compounds chelated with acetylacetone

Zirconium compounds: ammonium zirconium carbonate

Fluorine compounds: ammonium fluoride

(3) Then, a primer paint was applied onto the Mars film formed as described above with a bar coater, and baking was performed under the conditions of a steel plate reaching temperature of 230°C and a baking time of 35 seconds, thereby forming a primer film having a composition shown in Table 5. Thereafter, a topcoat paint composition was applied onto the primer film formed as described above with a bar coater, and baking was performed under the conditions of a steel plate reaching temperature of 230°C to 260°C and a baking time of 40 seconds, thereby forming a topcoat film having the resin conditions and film thickness shown in Table 5, thereby producing a painted steel sheet of each sample.

In addition, for the primer coating, each component was mixed and then stirred with a ball mill for about 1 hour to obtain the composition. The resin components and inorganic compounds constituting the primer coating were as follows.

(resin component)

Resin α: A urethane-modified polyester resin (obtained by reacting 455 parts by mass of polyester resin and 45 parts by mass of isophorone diisocyanate, and having an acid value of 3, a number average molecular weight of 5,600, and a hydroxyl value of 36) cured with blocked isocyanate was used.

In addition, for the polyester resin modified with urethane, it was produced under the following conditions. In a flask equipped with a stirrer, a rectifying column, a water separator, a condenser, and a thermometer, 320 parts by mass of isophthalic acid, 200 parts by mass of adipic acid, 60 parts by mass of trimethylolpropane, and 420 parts by mass of cyclohexanedimethanol are charged, heated and stirred, and while distilling the generated condensation water out of the system, the temperature is increased at a constant rate from 160°C to 230°C over 4 hours, and after the temperature reaches 230°C, 20 parts by mass of xylene is gradually added, and the condensation reaction is continued while maintaining the temperature at 230°C, and when the acid value becomes 5 or less, the reaction is terminated, and after cooling to 100°C, 120 parts by mass of Solvexo 100 (trade name, high boiling point aromatic hydrocarbon solvent manufactured by ExxonMobil) and 100 parts by mass of butyl cellosolve are added, A polyester resin solution was obtained.

Resin β: Urethane-cured polyester resin ("Everclad 4900" manufactured by Kansai Paint Co., Ltd.)

(inorganic compounds)

Vanadium compounds: Magnesium vanadate

Phosphoric acid compound: calcium phosphate

Magnesium oxide compounds: Magnesium oxide

Also, regarding the resin used in the overcoat, the following paints were used.

Resin Ⅰ: Melamine-cured polyester paint (BASF Japan Co., Ltd., “Free Color HD0030HR”)

Resin II: Organosol-based fluororesin paint with a mass ratio of 80:20 polyvinylidene fluoride and acrylic resin ("Free Color No. 8800HR" manufactured by BASF Japan Co., Ltd.)

(evaluation)

For each sample of the painted steel plate obtained as described above, the following evaluation was performed. The evaluation results are shown in Table 6.

(1) Composition of plating film (adhesion amount, composition, X-ray diffraction intensity)

For each sample of the hot-dip galvanized steel sheet, 100 mmφ was punched out, the non-measurement surface was sealed with tape, and the plating was dissolved and peeled off with a mixture of hydrochloric acid and hexamethylenetetramine as specified in JIS H 0401: 2013, and the adhesion amount of the plating film was calculated from the mass difference between the sample before and after peeling. The adhesion amounts of the obtained plating films as a result of the calculation are shown in Table 6.

Thereafter, the stripping solution was filtered, and the filtrate and solid content were analyzed respectively. Specifically, the filtrate was analyzed by ICP emission spectrometry to quantify components other than insoluble Si.

In addition, the solid content was dried and oxidized in a 650℃ furnace, and then dissolved by adding sodium carbonate and sodium tetraborate. In addition, the melt was dissolved with hydrochloric acid, and the solution was subjected to ICP emission spectroscopic analysis to quantify the insoluble Si. The Si concentration in the plating film is the insoluble Si concentration obtained by solid content analysis added to the available Si concentration obtained by filtrate analysis. The composition of the obtained plating film as a result of the calculation is shown in Table 6.

In addition, for each sample, after shearing to a size of 100 mm × 100 mm, the plating film on the evaluation symmetry plane was mechanically scraped off until a steel plate appeared, the obtained powder was well mixed, 0.3 g was taken out, and a qualitative analysis of the powder was performed using an X-ray diffraction device ("SmartLab" manufactured by Rigaku Corporation) under the following conditions: used X-ray: Cu-Kα (wavelength = 1.54178 Å), removal of Kβ line: Ni filter, tube voltage: 40 kV, tube current: 30 mA, scanning speed: 4°/min, sampling interval: 0.020°, divergence slit: 2/3°, solar slit: 5°, and detector: high-speed 1D detector (D/teX Ultra). The intensity obtained by subtracting the base intensity from each peak intensity was defined as each diffraction intensity (cps), and the diffraction intensity of the (111) plane of Mg ₂ Si (interface spacing d = 0.3668 nm) and the diffraction intensity of the (111) plane of Si (interface spacing d = 0.3135 nm) were measured. The measurement results are shown in Table 6.

(2) Corrosion resistance evaluation

For each sample of the painted steel plate, after shearing to a size of 120 mm x 120 mm, a range of 10 mm from the edges of three randomly selected sides of the surface to be evaluated and the cross-sections of the same three sides of the sample and the non-target surface were sealed with tape, and the surface to be evaluated was exposed to a size of 100 mm x 100 mm, and this was used as an evaluation sample. In addition, three identical evaluation samples were produced.

For the three evaluation samples manufactured as described above, a corrosion acceleration test was performed on all of them using the cycle shown in Fig. 1. The corrosion acceleration test was started from wetting, and samples were taken out every 20 cycles, washed with water, dried, and then visually observed to check for the occurrence of rust on one side of the shear section that was not sealed with tape.

And, the number of cycles when red-blue was confirmed was evaluated according to the following criteria. The evaluation results are shown in Table 6.

◎: Number of red-and-blue occurrence cycles of 3 samples≥600 cycles

○: 600 cycles > Number of red and blue occurrence cycles of 3 samples ≥ 500 cycles

×: At least 1 sample's red-blue occurrence cycle number < 500 cycles

(3) Appearance after painting

For each sample of painted steel plate, the surface was observed visually.

And, the observation results were evaluated according to the following criteria. The evaluation results are shown in Table 6.

◎: No wrinkle shape defects were observed at all.

○: Wrinkle-shaped defects were observed only within a range of 50 mm from the edge.

×: Wrinkle-shaped defects were observed outside the range of 50 mm from the edge.

(4) Processability after painting

For each sample of the painted steel plate, after shearing to a size of 70 mm x 150 mm, 8 plates of the same thickness as the copper plate were inserted inside and 180° bending processing (8T bending) was performed. After bending, Cellotape (registered trademark) was strongly adhered to the outer surface of the bent portion and then peeled off. The surface condition of the coating on the outer surface of the bent portion and the presence or absence of adhesion (peeling) of the coating on the surface of the tape used were visually observed, and the workability was evaluated according to the following criteria. The evaluation results are shown in Table 6.

○: No cracks or peeling are observed in the plating film.

△: There are cracks in the plating film, but no peeling is observed.

×: Cracks and peeling are both observed in the plating film.

(5) Bath stability

During hot-dip plating, the state of the bath surface of the plating bath was visually confirmed and compared with the bath surface of the plating bath used when manufacturing a hot-dip Al-Zn type plating steel sheet (bath surface without Mg-containing oxide). The evaluation was performed based on the following criteria, and the evaluation results are shown in Table 6.

○: Identical to molten Al-Zn plating bath (55 mass% Al, balance Zn, 1.6 mass% bath)

△: More white oxides compared to the molten Al-Zn plating bath (55 mass% Al, balance Zn, 1.6 mass% bath)

×: Formation of black oxide is observed during the plating bath.

From the results in Table 6, it can be seen that each sample of the present invention is excellent in a well-balanced manner in corrosion resistance, appearance after painting, workability after painting, and bath stability compared to each sample of the comparative example.

(Industrial applicability)

According to the present invention, it is possible to provide a hot-dip Al-Zn-Si-Mg-Sr plated steel sheet having stable excellent corrosion resistance and good surface appearance.

In addition, according to the present invention, a surface-treated steel sheet having excellent corrosion resistance and white rust resistance can be provided.

In addition, according to the present invention, a painted steel sheet having excellent corrosion resistance and machined part corrosion resistance can be provided.

Claims (7)

A hot-dip Al-Zn-Si-Mg-Sr plated steel sheet having a plating film,
The above plating film has a composition containing Al: 45 to 65 mass%, Si: 1.0 to 4.0 mass%, Mg: 1.0 to 10.0 mass%, and Sr: 0.01 to 1.0 mass%, with the remainder being Zn and inevitable impurities.
A hot-dip Al-Zn-Si-Mg-Sr plated steel sheet, characterized in that the diffraction intensity measured by X-ray diffraction method of Si and Mg ₂ Si in the plating film, which is mechanically scraped off until a part of the plating film appears and turned into powder, satisfies the following relationship (1).
Si(111)/Mg ₂ Si(111)≤0.8... (1)
Si(111): Diffraction intensity of the (111) plane of Si (plane spacing d = 0.3135 nm),
Mg ₂ Si(111): Diffraction intensity of the (111) plane of Mg ₂ Si (plane spacing d = 0.3668 nm) In the first paragraph,
A hot-dip Al-Zn-Si-Mg-Sr plated steel sheet, characterized in that the diffraction intensity of the Si in the plating film, as determined by X-ray diffraction, satisfies the following relationship (2).
Si(111)＝0…(2) In paragraph 1 or 2,
A hot-dip Al-Zn-Si-Mg-Sr plated steel sheet, characterized in that the Al content in the plating film is 50 to 60 mass%. In paragraph 1 or 2,
A hot-dip Al-Zn-Si-Mg-Sr plated steel sheet, characterized in that the Si content in the plating film is 1.0 to 3.0 mass%. In paragraph 1 or 2,
A hot-dip Al-Zn-Si-Mg-Sr plated steel sheet, characterized in that the content of Mg in the plating film is 1.0 to 5.0 mass%. A surface-treated steel sheet having a plating film as described in claim 1 or claim 2 and a chemical conversion film formed on the plating film,
A surface-treated steel sheet, characterized in that the above-mentioned Martian coating contains at least one resin selected from epoxy resin, urethane resin, acrylic resin, acrylic silicone resin, alkyd resin, polyester resin, polyalkylene resin, amino resin and fluororesin, and at least one metal compound selected from P compound, Si compound, Co compound, Ni compound, Zn compound, Al compound, Mg compound, V compound, Mo compound, Zr compound, Ti compound and Ca compound. A coated steel sheet having a coating formed directly or by intervening a plating film on the plating film described in claim 1 or claim 2,
The above-mentioned Martian film contains a total of 30 to 50 mass% of (a): anionic polyurethane resin having an ester bond and (b): an epoxy resin having a bisphenol skeleton, and contains a resin component in which the content ratio ((a):(b)) of (a) and (b) is in the range of 3:97 to 60:40 by mass, and an inorganic compound including 2 to 10 mass% of a vanadium compound, 40 to 60 mass% of a zirconium compound, and 0.5 to 5 mass% of a fluorine compound.
A painted steel sheet, characterized in that the coating film has at least a primer coating film, and the primer coating film contains a polyester resin having a urethane bond and an inorganic compound including a vanadium compound, a phosphoric acid compound, and magnesium oxide.