TWI789061B - Molten Al-Zn-Si-Mg system plated steel sheet, surface treated steel sheet and coated steel sheet - Google Patents

Abstract

The object of the present invention is to provide a molten Al-Zn-Si-Mg plated steel sheet which is stable and has excellent corrosion resistance. In order to achieve the above object, the present invention is a molten Al-Zn-Si-Mg plated steel sheet provided with a plated film, characterized in that the plated film has the following composition: Al: 45 to 65% by mass, Si: 1.0 ~4.0% by mass and Mg: 1.0~10.0% by mass, and the rest is composed of Zn and unavoidable impurities. The diffraction intensity of Si and Mg ₂ Si in the aforementioned plating film by X-ray diffraction method satisfies the following relationship (1), Si(111)/Mg ₂ Si(111)≦0.8...(1).

Description

Molten Al-Zn-Si-Mg system plated steel sheet, surface treated steel sheet and coated steel sheet

The present invention relates to molten Al-Zn-Si-Mg plated steel sheets, surface-treated steel sheets, and coated steel sheets that are stable and have excellent corrosion resistance.

Hot-dip Al-Zn-based plated steel sheets represented by 55% Al-Zn-based steel sheets are known to exhibit high corrosion resistance among hot-dip galvanized steel sheets because they can combine the sacrificial corrosion resistance of Zn and the high corrosion resistance of Al. Therefore, due to its excellent corrosion resistance, molten Al-Zn plated steel sheet is mainly used in the field of building materials such as roofs or walls exposed to the outdoors for a long time, and civil engineering fields such as guardrails, wiring and piping, and sound insulation walls. In particular, there is an increasing demand for materials with excellent corrosion resistance or maintenance-free materials in harsher environments such as acid rain caused by air pollution, or snow-melting agents for road antifreeze in snow-covered areas, and development in coastal areas. , The demand for molten Al-Zn-based plated steel sheets has increased.

The coating film of the molten Al-Zn-based plated steel sheet is characterized by a part (α-Al phase) in which supersaturated Al containing Zn solidifies into dendrites (α-Al phase) and Zn-Al existing in the dendrite gap (inter-dendrite). Composed of crystal structure, the α-Al phase is laminated in multiple layers in the thickness direction of the plating film. Because of this characteristic film structure, the path of corrosion from the surface becomes complicated, so the corrosion becomes difficult to proceed. It is also known that molten Al-Zn-based plated steel sheet can achieve molten zinc plating with the same thickness as the plated film. Steel plate has better corrosion resistance.

For such a molten Al-Zn-based plated steel sheet, attempts have been made to further increase the life, and molten Al-Zn-Si-Mg-based plated steel sheets to which Mg has been added have been put into practical use. As such a molten Al-Zn-Si-Mg-based plated steel sheet, for example, Patent Document 1 discloses a molten Al-Zn-Si-Mg-based plated steel sheet containing Mg-containing Al- Zn-Si alloy, the Al-Zn-Si alloy is an alloy containing 45-60% by weight of elemental aluminum, 37-46% by weight of elemental zinc and 1.2-2.3% by weight of Si, and the concentration of the Mg is 1-5 weight%. And, in patent document 2, disclose a kind of molten Al-Zn-Si-Mg system plated steel sheet, its purpose is by containing at least one kind of Mg of 2～10% and Ca of 0.01～10% in the plated film. Realize the improvement of corrosion resistance, and improve the protective effect of the exposed base steel plate. Furthermore, Patent Document 3 discloses a molten Al-Zn-Si-Mg-based plated steel sheet containing Mg: 1 to 15%, Si: 2 to 15%, and Zn: 11 to 25% in mass%. , the rest of the coating layer is made of Al and unavoidable impurities, and the corrosion resistance of the flat plate and the end surface is realized by making the size of the Mg ₂ Si phase or the intermetallic compound equal to MgZn ₂ existing in the plating film to be 10 μm or less. improvement.

The above-mentioned molten Al-Zn-based plated steel sheet has a beautiful appearance with white metallic luster and sparkling pattern, so it is mostly used in the state of unpainted, but the actual situation is still strong in its appearance. Therefore, techniques for improving the appearance of molten Al-Zn-based plated steel sheets have also been developed. For example, Patent Document 4 discloses a molten Al-Zn-Si-Mg-based plated steel sheet in which wrinkle-like irregularities are suppressed by containing 0.01 to 10% of Sr in the plated film. In addition, Patent Document 5 also discloses a molten Al-Zn-Si-Mg-based plated steel sheet in which plaque defects are suppressed by containing 500 to 3000 ppm of Sr in the plated film. In addition, Patent Document 6 discloses a molten Al-Zn-Si-Mg-based plated steel sheet having both surface appearance and corrosion resistance by containing 0.001 to 1.0% of Sr in the plated film. In addition, Patent Document 7 discloses a molten Al-Zn-Si-Mg plated steel sheet having both surface appearance and corrosion resistance of flat and processed portions by containing 0.001 to 1.0% of Sr in the plating film. In addition, Patent Document 8 also discloses a molten Al-Zn-Si-Mg-based plated steel sheet having both surface appearance and corrosion resistance by containing 0.01 to 0.2% of Sr in the plated film. In addition, Patent Document 9 discloses a molten Al-Zn-Si-Mg-based plated steel sheet in which corrosion resistance is improved by controlling Si and Mg concentrations in a plated film at a specific ratio.

In addition, when the above-mentioned molten Al-Zn-based plated steel sheet is used in a severely corrosive environment, there is a problem that white rust occurs due to corrosion of the plated film. Since this white rust causes deterioration of the appearance of the steel sheet, the development of a plated steel sheet for improving the white rust resistance has been pursued. For example, Patent Document 10 discloses molten Al-Zn-Si-Mg having an appropriate mass ratio of Mg in the Si-Mg phase to the total amount of Mg in the plating layer for the purpose of improving the white rust resistance of the processed part. It is plated steel plate. Also, Patent Document 11 discloses that blackening resistance and white rust resistance are improved by forming a chemical conversion film containing a urethane resin on a plated film of a molten Al-Zn-Si-Mg plated steel sheet. technology.

Also, coated steel sheets with chemical conversion coatings, primer coatings, top coatings, etc. formed on the surface of molten Al-Zn-based plated steel sheets are required to be formed by press forming, roll forming, or embossing. Various processing such as 90-degree bending or 180-degree bending requires long-term coating film durability. In order to meet these requirements, it is known that molten Al-Zn-based plated steel sheets form a chemical conversion film containing chromate, and the primer film also contains chromate-based antirust pigments, forming a thermally hardened coating on it. Coated steel sheet with a top-coated film that has excellent weather resistance such as polyester-based resin coating or fluorine-based resin coating. However, for these recently painted steel sheets, the use of chromates, which are substances of concern to the environment, has been regarded as a problem, and the development of painted steel sheets that can improve corrosion resistance or surface appearance even without chromates has been strongly desired. As a technology to meet these requirements, for example, Patent Document 12 discloses surface treatment of hot-dip galvanized steel materials, which is to plate aluminum and zinc containing Al, Zn, Si, and Mg on the surface of steel materials and adjust the content of these elements. Alloy plating layer (α), and as the upper layer, a film (β) containing at least one compound (A) selected from titanium compounds and zirconium compounds as a film-forming component is formed, aluminum-zinc alloy plating layer (α) The mass ratio of the Si-Mg phase relative to the total amount of Mg in the plating layer is adjusted to be more than 3%. [Prior Art Literature] [Patent Document]

Patent Document 1: Japanese Patent No. 5020228 Patent Document 2: Japanese Patent No. 5000039 Patent Document 3: Japanese Patent Laid-Open No. 2002-12959 Patent Document 4: Japanese Patent No. 3983932 Patent Document 5: Japanese PCT Publication No. 2011-514934 Patent Document 6: International Publication No. 2020/179147 Patent Document 7: International Publication No. 2020/179148 Patent Document 8: Japanese Patent Laid-Open No. 2020-143370 Patent Document 9: International Publication No. 2016/140370 Patent Document 10: Japanese Patent No. 5751093 Patent Document 11: Japanese Patent Laid-Open No. 2019-155872 Patent Document 12: Japanese Patent Laid-Open No. 2005-169765

[Problem to be solved by the invention]

However, as disclosed in Patent Documents 1 to 3, the technology of including Mg in the plating film does not necessarily improve the corrosion resistance significantly. In the molten Al-Zn-Si-Mg plated steel sheets disclosed in Patent Documents 1 to 3, the corrosion resistance is improved only by including Mg in the plating composition, but the metal phase and intermetallic compound forming the plating film The phase characteristics are not considered, and it is impossible to discuss the advantages and disadvantages of corrosion resistance in general. Therefore, even when the molten Al-Zn-Si-Mg-based plated steel sheet is manufactured using the same plating bath composition, there is a difference in corrosion resistance if the corrosion acceleration test is carried out. Compared with the Al-Zn-based plated steel sheet without Mg added Not necessarily an advantage, but a problem. Similarly, in improving the appearance of plating, only adding Sr to the plating film may not necessarily explain that wrinkle-shaped unevenness defects can be eliminated. The molten Al-Zn-Si-Mg-based plated steel sheets disclosed in Patent Documents 4 to 8 are also There are cases where corrosion resistance and appearance cannot be achieved at the same time. In addition, since Mg is an element that is easily oxidized, the Mg contained in the plating bath generates oxides (scum) near the bath surface, or in the plating bath or in the plating bath over time during hot-dip plating. Iron-containing FeAl-based compounds (bottom dross) are partially present at the bottom, and these slags adhere to the surface of the plating film, causing convex defects, and may damage the surface appearance of the plating film.

Also, when a steel sheet is plated with a bath in which Mg is added to a molten Al-Zn-Si bath, it is known that in addition to the α-Al phase, the _Mg2Si phase, _MgZn2 phase, and Si phase are also precipitated in the plated film. . However, the influence of the precipitation amount or the existence ratio of each phase on the corrosion resistance is not yet clear. In the molten Al-Zn-Si-Mg plated steel sheet disclosed in Patent Document 9, by controlling the concentration of Si and Mg at a specific ratio, the Si phase is not precipitated in the plated film, and the corrosion resistance is improved. It is technically incomplete to say that the Si phase must be suppressed, and even when the formation of the Si phase in the plating film can be suppressed, excellent corrosion resistance may not be obtained.

Also, with regard to white rust resistance, any technique cannot achieve sufficient improvement. Regarding the molten Al-Zn-Si-Mg plated steel sheet of Patent Document 10, although it is described that the white rust resistance of the processed portion and the heated flat plate portion is improved, there is no improvement in the white rust resistance of the unheated flat plate portion. Considering that, achieving stable white rust resistance is still a problem. Furthermore, regarding the molten Al-Zn-Si-Mg-based plated steel sheet of Patent Document 11, not only stable and excellent corrosion resistance and white rust resistance are desired, but also further improvement is desired.

In addition, for coated steel sheets, as mentioned above, long-term coating film durability is required in the state of performing various processing such as 90-degree bending or 180-degree bending by press forming, roll forming, embossing, etc., but The technique of Patent Document 12 cannot necessarily and stably obtain corrosion resistance and surface appearance after processing. The corrosion resistance of the coated steel sheet will of course affect the corrosion resistance of the plated steel sheet used as the base. As for the surface appearance, the unevenness of the wrinkle defect can reach tens of μm, so even if the surface is smoothed by the coating film It is also impossible to completely eliminate the unevenness, and it is considered that the appearance of the coated steel sheet cannot be expected to be improved. In addition, since the coating film becomes thinner at the convex portion, there is also a possibility that the local corrosion resistance may be lowered. Therefore, in order to obtain a coated steel sheet excellent in corrosion resistance and surface appearance, it is important to improve the corrosion resistance and surface appearance of the base plated steel sheet.

In view of the above circumstances, an object of the present invention is to provide a molten Al-Zn-Si-Mg plated steel sheet which is stable and has excellent corrosion resistance. Furthermore, the object of the present invention is to provide a surface-treated steel sheet which is stable and has excellent corrosion resistance and white rust resistance. Furthermore, an object of the present invention is to provide a stable coated steel sheet having excellent corrosion resistance and corrosion resistance of processed parts. [Means to solve the problem]

As a result of active research by the present inventors to solve the above-mentioned problems, it was found that the _Mg2Si phase, _MgZn2 phase, and Si phase formed in the plated film of the molten Al-Zn-Si-Mg-based plated steel sheet are The balance of each component in the coating film or the formation conditions of the plating film increase or decrease the amount of precipitation, so that the ratio of existence changes. Depending on the balance of the composition, there may be cases where a certain phase does not precipitate. And it was found that the corrosion resistance of the molten Al-Zn-Si-Mg system plated steel sheet changes with the existence ratio of these phases, especially when the MgZn ₂ phase is more than the Mg ₂ Si phase or Si phase, the corrosion resistance is improved. Sexuality has been steadily improved. However, regarding these Mg ₂ Si phases and Si phases, it is known that even if a general method, such as a scanning electron microscope, is used to observe a secondary electron image or a reflection electron image of a plating film from the surface or cross section, it is known that It is very difficult to discern the difference between the phases. As a method that can analyze in more detail, observation using a transmission electron microscope can obtain microscopic information, but it is impossible to grasp the existence ratio of Mg ₂ Si and Si phases that affect the macroscopic information of corrosion resistance and appearance. Therefore, as a result of further intensive studies by the present inventors, it has been found that by focusing on the X-ray diffraction method, the ratio of the intensity of the specific diffraction peaks of the _Mg2Si phase and the Si phase can be used to quantitatively specify the abundance ratio of the phases. In addition, If the Mg ₂ Si phase and the Si phase in the plating film satisfy a specific ratio, in addition to achieving stable and excellent corrosion resistance, the occurrence of slag can be suppressed and a good surface appearance can also be ensured. Furthermore, the inventors of the present invention also found that wrinkling can be reliably suppressed by controlling the Sr concentration in the bath after controlling the ratio of the Mg ₂ Si phase and Si phase in the molten Al-Zn-Si-Mg system plated steel sheet. Occurrence of concavo-convex defects can obtain a plated steel sheet with excellent surface appearance.

In addition, the present inventors also examined the chemical conversion film formed on the above-mentioned plating film, and found that the affinity between the chemical conversion film and the plating film can be improved by making the chemical conversion film consist of a specific resin and a specific metal compound. And anti-rust effect, etc., and improve the stability of white rust resistance.

Furthermore, the inventors of the present invention have also examined the chemical conversion film and primer coating film formed on the above-mentioned plating film, and found that by making the chemical conversion film consist of a specific resin and a specific inorganic compound, and the primer coating film is composed of Composed of specific polyester resin and inorganic compound, it can improve the barrier property and adhesion of the coating film, and even if it is chromate-free, it can achieve excellent corrosion resistance after processing.

The present invention was completed based on the above findings, and its gist is as follows. 1. A molten Al-Zn-Si-Mg-based plated steel sheet, which is a molten Al-Zn-Si-Mg-based plated steel sheet provided with a plated film, wherein the plated film has the following composition: containing Al : 45~65% by mass, Si: 1.0~4.0% by mass and Mg: 1.0~10.0% by mass, and the _rest is composed of Zn and unavoidable impurities. The diffraction intensity of the diffraction method satisfies the following relationship (1), Si(111)/Mg ₂ Si(111)≦0.8...(1) Si(111): Si (111) plane (plane distance d=0.3135nm) The diffraction intensity of Mg ₂ Si (111): the diffraction intensity of the (111) plane (plane spacing d=0.3668nm) of Mg ₂ Si.

2. The molten Al-Zn-Si-Mg plated steel sheet as described in 1 above, wherein the diffraction intensity of Si in the above-mentioned plated film by the X-ray diffraction method satisfies the following relationship (2), Si(111)=0...(2), Si(111): Diffraction intensity of Si (111) plane (plane spacing d=0.3135nm),

3. The molten Al-Zn-Si-Mg-based plated steel sheet as described in 1 or 2 above, wherein the plated film further contains Sr: 0.01 to 1.0% by mass.

4. The molten Al-Zn-Si-Mg-based plated steel sheet according to any one of 1 to 3 above, wherein the Al content in the plated film is 50 to 60% by mass.

5. The molten Al-Zn-Si-Mg-based plated steel sheet according to any one of 1 to 4 above, wherein the Si content in the plated film is 1.0 to 3.0% by mass.

6. The molten Al-Zn-Si-Mg-based plated steel sheet according to any one of 1 to 5 above, wherein the Mg content in the plated film is 1.0 to 5.0% by mass.

7. A surface-treated steel sheet, which is a surface-treated steel sheet provided with a plated film as described in any one of 1 to 6 above and a chemical conversion film formed on the plated film, characterized in that The aforementioned chemical conversion film contains at least one resin selected from the group consisting of 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 compounds, Si compounds, Co compounds, Ni compounds, Zn compounds, Al compounds, Mg compounds, V compounds, Mo compounds, Zr compounds, Ti compounds and Ca compounds.

8. A coated steel plate, which is a coated steel plate that forms a coating film directly or through a chemical conversion film on the plated film according to any one of the aforementioned 1 to 6, and is characterized in that The aforementioned chemical conversion film contains: a resin component containing a total of 30 to 50% by mass of (a): anionic polyurethane resin having an ester bond and (b): an epoxy resin having a bisphenol skeleton, and The content ratio of (a) and (b) ((a):(b)) is in the range of 3:97 to 60:40 by mass ratio; and an inorganic compound including 2 to 10% by mass of a vanadium compound, 40~60% by mass of zirconium compound and 0.5~5% by mass of fluorine compound, The aforementioned 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. [Invention effect]

According to the present invention, a molten Al-Zn-Si-Mg-based plated steel sheet that is stable and excellent in corrosion resistance can be provided. Furthermore, according to the present invention, a stable surface-treated steel sheet having excellent corrosion resistance and white rust resistance can be provided. Furthermore, according to the present invention, a stable coated steel sheet having excellent corrosion resistance and corrosion resistance of processed parts can be provided.

(Molten Al-Zn-Si-Mg system plated steel sheet)

The molten Al-Zn-Si-Mg plated steel sheet of the present invention has a plated film on the surface of the steel sheet. And this plating film has a composition which contains Al: 45-65 mass %, Si: 1.0-4.0 mass %, Mg: 1.0-10.0 mass %, and the balance consists of Zn and unavoidable impurities.

The Al content in the aforementioned plating film is 45-65% by mass, preferably 50-60% by mass, based on the balance between the corrosion resistance and the work surface. The reason is that if the Al content in the above-mentioned plating film is at least 45% by mass, dendritic solidification of Al occurs, and a plating film structure mainly composed of a dendritic solidified structure of the α-Al phase can be obtained. By adopting a structure in which the dendritic solidified structure is laminated in the film thickness direction of the plating film, the path of corrosion progression becomes complicated, and the corrosion resistance of the plating film itself is improved. And the more dendritic parts of the α-Al phase are laminated, the more complicated the corrosion path will be, and the less likely the corrosion will reach the base steel plate. Therefore, in order to improve the corrosion resistance, the preferred Al content is set to 50% by mass or more. On the other hand, when the Al content in the above-mentioned plating film exceeds 65% by mass, Zn is almost changed to a solid solution structure in α-Al, and the dissolution reaction of the α-Al phase cannot be suppressed, making Al-Zn-Si-Mg The corrosion resistance of plating is reduced. Therefore, the Al content in the aforementioned plating film must be 65% by mass or less, preferably 60% by mass or less.

The main purpose of adding Si in the above-mentioned plating film is to inhibit the growth of the Fe-Al-based and/or Fe-Al-Si-based interface alloy layer formed at the interface with the base steel plate, so as not to make the plating film and the steel plate adhere sexual deterioration. In fact, if the steel sheet is immersed in an Al-Zn-based coating bath containing Si, the Fe on the surface of the steel sheet will undergo an alloying reaction with Al or Si in the bath, and an Fe-Al-based and /or Fe-Al-Si intermetallic compound layer. At this time, the growth rate of Fe-Al-Si alloy is slower than that of Fe-Al alloy, so the higher the ratio of Fe-Al-Si alloy, the more it can inhibit The overall growth of the interfacial alloy layer. Therefore, the Si content in the plating film needs to be 1.0% by mass or more. On the other hand, when the Si content in the above-mentioned plating film exceeds 4.0% by mass, not only the growth inhibitory effect of the aforementioned interface alloy layer is saturated, but also corrosion is promoted due to the presence of an excessive Si phase in the plating film, so the Si content is set to 4.0% by mass. %the following. In addition, the Si content in the above-mentioned plating film is preferably 3.0% or less from the viewpoint of suppressing the existence of an excess Si phase. In addition, the relationship with the Mg content described later is from the viewpoint that the relational expression (1) described later can be easily satisfied, and the Si content is preferably 1.0 to 3.0% by mass.

The plating film contains 1.0 to 10.0% of Mg. By containing Mg in the above-mentioned plating film, the above-mentioned Si can exist in the form of an intermetallic compound of the Mg ₂ Si phase, and the promotion of corrosion can be suppressed. Furthermore, when Mg is contained in the above-mentioned plating film, the MgZn ₂ phase of an intermetallic compound is also formed in the plating film, and the effect of further improving the corrosion resistance can be obtained. When the Mg content in the above-mentioned plating film is less than 1.0% by mass, Mg is mainly used for the solid solution of the α-Al phase of the main phase due to the formation of the above-mentioned intermetallic compound ( _Mg2Si , _MgZn2 ), so it cannot Ensure sufficient corrosion resistance. On the other hand, when the content of Mg in the above-mentioned plating film is increased, not only the effect of improving the corrosion resistance is saturated, but also the workability is reduced due to the weakening of the α-Al phase, so the content is made 10.0% or less. In addition, the Mg content in the above-mentioned plating film is preferably 5.0% by mass or less from the viewpoint of suppressing generation of slag during plating formation and facilitating plating bath management. In addition, the relationship with the above-mentioned Si content is based on the viewpoint that the relational expression (1) described later is easily satisfied. It is preferable that the above-mentioned Mg content is set to 3.0% by mass. In consideration of compatibility with slag suppression, the above-mentioned Mg content is more preferably The content is 3.0 to 5.0% by mass.

Furthermore, in the molten Al-Zn-Si-Mg-based plated steel sheet of the present invention, the diffraction intensity of Si and _Mg2Si in the above-mentioned plated film by the X-ray diffraction method satisfies the following relationship (1), Si( 111)/Mg ₂ Si(111)≦0.8...(1) Si(111): Diffraction intensity of (111) plane of Si (plane spacing d=0.3135nm), Mg ₂ Si(111): Mg ₂ Si Diffraction intensity of (111) plane (plane spacing d=0.3668nm).

As described above, it is important in the present invention to control the abundance ratio of the Mg ₂ Si phase and the Si phase generated in the plating film to a specific ratio by containing Mg or Si. These effects on corrosion resistance are still being investigated and there are still many things that are not understood, but the following mechanism is speculated.

When the molten Al-Zn-Si-Mg plated steel sheet is exposed to a corrosive environment, the above-mentioned intermetallic compound dissolves preferentially over the α-Al phase, and the vicinity of the formed corrosion product becomes a Mg-rich environment. It is presumed that in such an environment rich in Mg, the formed corrosion products are not easily decomposed, and as a result, the protective effect of the plating film is enhanced. Moreover, the effect of improving the protective effect of the plating film is more reliably exhibited when Si does not exist as the Si phase in the plating film but as the Mg ₂ Si phase, so it is considered that the ratio of the Si phase to the Mg ₂ Si phase is reduced. is valid.

It is important to use the diffraction peak intensity obtained by X-ray diffraction method to satisfy the relationship (1): Si(111)/Mg ₂ Si(111) for the ratio of Mg ₂ Si and Si in the aforementioned plating film. ≦0.8, but the 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, due to the presence of Si in the above-mentioned plating film Relatively large, so the above-mentioned Mg-rich environment cannot be obtained near the corrosion products, and it is difficult to obtain the above-mentioned protective effect of the plating film. From the same viewpoint, the abundance 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, particularly preferably 0.2 or less. Also, regarding the ratio of Mg ₂ Si and Si in the aforementioned plating film, it is assumed that the composition of the plating film satisfies the scope of the present invention (containing Al: 45-65% by mass, Si: 1.0-4.0% by mass, and Mg: 1.0-4.0% by mass). 10.0% by mass, and the remainder is made of Zn and unavoidable impurities), when the ratio of Mg _Si and Si does not satisfy the relationship (1), it is impossible to fully obtain the improvement of the protective effect of the plating film caused by the present invention Effect.

Here, in the aforementioned relationship (1), Si(111) is the diffraction intensity of the (111) plane of Si (interplanar spacing d=0.3135nm), and Mg ₂ Si(111) is the (111) plane of Mg ₂ Si ( Diffraction intensity of plane spacing d=0.3668nm). As a method of measuring Si(111) and Mg ₂ Si(111) by the aforementioned X-ray diffraction, a part of the aforementioned coating film can be mechanically peeled off, and X-ray diffraction (powder X-ray diffraction) can be performed in a powder state. measurement method) and calculated. Regarding the measurement of the diffraction intensity, the diffraction peak intensity corresponding to Si with a plane spacing d=0.3135nm is measured, and the diffraction peak intensity corresponding to _Mg2Si with a plane spacing d=0.3668nm is measured. By calculating these ratios, it is possible to obtain Si(111)/Mg ₂ Si(111). In addition, the amount of the plating film (the amount of peeling the plating film) necessary for powder X-ray diffraction measurement should only be 0.1 g from the viewpoint of accurately measuring Si(111) and _Mg2Si (111). More than enough, preferably 0.3 g or more. In addition, when the above-mentioned plating film is cut out, steel plate components other than the plating film may be included in the powder, and these intermetallic compound phases are only contained in the plating film and do not affect the above-mentioned peak strength. In addition, the reason for performing X-ray diffraction by making the above-mentioned plated film into powder is that when X-ray diffraction is performed on the plated film formed on the plated steel plate, it is affected by the plane orientation of the solidified structure of the plated film, and It is difficult to calculate the correct phase ratio.

Furthermore, in the molten Al-Zn-Si-Mg plated steel sheet of the present invention, from the viewpoint of improving the corrosion resistance more stably, the diffraction intensity of Si in the above-mentioned plated film by the X-ray diffraction method preferably satisfies The following relation (2). Si(111)=0...(2) Si(111): Diffraction intensity of Si (111) plane (plane spacing d=0.3135nm). Generally, in the dissolution reaction of Al alloys in aqueous solution, it is known that the Si phase exists as the cathode site and promotes the dissolution of the surrounding α-Al phase. Therefore, it is also effective to reduce the Si phase to suppress the dissolution of the α-Al phase. Among them, the relationship (2) Generally, there is no film of Si phase (the diffraction peak intensity of Si (111) mentioned above is zero) in order to stabilize the corrosion resistance, it is the best. In addition, the method of measuring the diffraction peak intensity of the Si(111) surface by X-ray diffraction is as described above.

Here, there is no particular limitation on the method of satisfying the above-mentioned relationship (1) and relationship (2). For example, in order to satisfy relationship (1) and relationship (2), by adjusting the balance of Si content, Mg content and Al content in the aforementioned plating film, the ratio of Mg ₂ Si and Si can be controlled (Mg ₂ Si(111) and the diffraction intensity of Si(111)). Also, if the balance of the Si content, Mg content, and Al content in the above-mentioned plating film must be set at a certain content ratio, it is not interpreted as satisfying the relationship (1) and the relationship (2). For example, it must be based on the Si content (mass % ) to change the content ratio of Mg and Al. In addition, in addition to adjusting the balance of the Si content, Mg content, and Al content in the aforementioned plating film, by adjusting the conditions when the plating film is formed (such as cooling conditions after plating), the relationship (1) and the relationship (2) The diffraction intensity of Mg ₂ Si(111) and Si(111) can also be controlled.

Moreover, the molten Al-Zn-Si-Mg system plated steel sheet of this invention contains Zn and unavoidable impurities. However, the aforementioned unavoidable impurities contain Fe. This Fe is unavoidably contained in the plating bath due to the steel plate or in-bath machine elution, and is unavoidably contained in the above-mentioned plating film as a result of being supplied by diffusion from the base steel plate when the interface alloy layer is formed. The content of Fe in the plating film is usually about 0.3 to 2.0% by mass. Examples of other unavoidable impurities include Cr, Ni, Cu, and the like. The total content of the aforementioned unavoidable impurities is not particularly limited, but when contained in excess, various properties of the plated steel sheet may be affected, so the total content is preferably 5.0% by mass or less.

Also, in the molten Al-Zn-Si-Mg steel sheet of the present invention, it is preferable that the plating film contains 0.01 to 1.0% by mass of Sr. When the above-mentioned plating film contains Sr, the occurrence of surface defects such as wrinkle-shaped unevenness defects can be more reliably suppressed, and a good surface appearance can be realized. In addition, the wrinkle defect is a defect of wrinkle-like unevenness formed on the surface of the plating film, and white streaks are observed on the surface of the plating film. Such wrinkle-like defects tend to occur when a large amount of Mg is added to the above-mentioned plating film. Therefore, in the above-mentioned hot-coated steel sheet, since Sr is contained in the above-mentioned plating film, Sr in the surface layer of the above-mentioned plating film is oxidized more preferentially than Mg, and by suppressing the oxidation reaction of Mg, the occurrence of the wrinkle defect can be suppressed. occur.

Furthermore, in the molten Al-Zn-Si-Mg steel sheet of the present invention, it is preferable that the abundance ratio of Si and _Mg2Si in the above-mentioned plating film satisfies the relationship (1), and the above-mentioned plating film contains 0.01 to 1.0% by mass of Sr . Thereby, the surface appearance improvement effect by said Sr can be enjoyed more. Although the reason is not clear, it is presumed that if there is more Si in the plating film, the oxidation of the plating surface layer is not easily suppressed after all, and the addition of Sr affects the effect of improving the appearance. Also, when the Sr content in the above-mentioned plating film is less than 0.01% by mass, it is difficult to obtain the effect of suppressing the occurrence of the above-mentioned wrinkle defects, and if the Sr content in the above-mentioned plating film exceeds 1.0% by mass, then Sr is excessively incorporated into the interface alloy layer, and there is The influence on plating adhesion and the like is greater than the effect of improving the appearance, so the Sr content in the above-mentioned plating film is preferably 0.01 to 1.0% by mass.

In addition, the above-mentioned plating film, from the viewpoint of improving the stability of the corrosion product and exhibiting the effect of delaying the progress of corrosion, like the above-mentioned Mg, preferably further contains a total of 0.01 to 10% by mass selected from Cr, Mn, V , Mo, Ti, Ca, Ni, Co, Sb and B, or one or more of them. The reason why the total content of the above components is 0.01 to 10% by mass is that a sufficient corrosion retarding effect can be obtained and the effect will not be saturated.

In addition, the adhesion amount of the aforementioned plating film is preferably 45 to 120 g/m ² per one side from the viewpoint of satisfying various characteristics. When the adhesion amount of the above-mentioned plating film is 45g/m2 ^or more, sufficient corrosion resistance can be obtained for applications requiring long-term corrosion resistance such as building materials, and when the adhesion amount of the above-mentioned plating film is 120g/ ^m2 or less, it can be It suppresses the occurrence of plating cracks during processing and achieves excellent corrosion resistance at the same time. Based on the same viewpoint, the adhesion amount of the aforementioned plating film is more preferably 45-100 g/m ² .

Regarding the adhesion amount of the above-mentioned plating film, for example, as shown in JIS H 0401: 2013, a mixture of hydrochloric acid and hexamethylenetetramine is used to dissolve and peel off a specific area of the plating film, and the difference in weight of the steel plate before and after peeling derived from the calculated method. In this method, the plating adhesion amount per one side can be obtained by performing the above-mentioned dissolution after sealing with tape so that the plating surface of the non-target surface is not exposed.

Furthermore, the component composition of the above-mentioned plating film can be dissolved by immersing the plating film in hydrochloric acid, etc., for example, and confirming the solution by ICP emission spectroscopic analysis or atomic absorption analysis. After all, this method is only an example, and any method may be used without any particular limitation as long as the composition of the plating film can be accurately quantified.

Moreover, the composition of the coating film of the molten Al-Zn-Si-Mg system plated steel sheet obtained by this invention is substantially the same as that of a coating bath as a whole. Therefore, by controlling the composition of the plating bath, the composition of the above-mentioned plating film can be controlled with high precision.

Also, the base steel sheet constituting the molten Al-Zn-Si-Mg-based plated steel sheet of the present invention is not particularly limited, and a cold-rolled steel sheet or a hot-rolled steel sheet can be appropriately used depending on the required performance and specifications.

In addition, there is no particular limitation regarding the method of obtaining the aforementioned base steel sheet. For example, in the case of the above-mentioned hot-rolled steel sheet, one that has undergone a hot-rolling step and a pickling step can be used, and in the case of the above-mentioned cold-rolled steel sheet, it can be manufactured by further applying a cold-rolling step. Furthermore, a recrystallization annealing step or the like may be performed before the hot-dip plating step in order to obtain the properties of the steel sheet.

Moreover, the method of manufacturing the molten Al-Zn-Si-Mg system plated steel sheet of this invention is not specifically limited. For example, it can be manufactured by washing, heating, and immersing the aforementioned base steel sheet in a continuous hot-dip coating facility. In the heating step of the steel sheet, recrystallization annealing and the like are performed for the purpose of controlling the structure of the base steel sheet itself, and heating in a reducing environment such as a nitrogen-hydrogen environment is performed in order to prevent oxidation of the steel sheet and reduce a small amount of oxide film existing on the surface. efficient.

And, regarding the coating bath used when manufacturing the molten Al-Zn-Si-Mg system plated steel sheet of the present invention, as mentioned above, since the composition of the above-mentioned coating film is generally equal to the composition of the coating bath, it can be Use a composition that contains Al: 45-65% by mass, Si: 1.0-4.0% by mass, Mg: 1.0-10.0% by mass, and the rest is composed of Zn, Fe and unavoidable impurities.

In addition, the bath temperature of the aforementioned plating bath is not particularly limited, and is preferably within a temperature range of (melting point+20°C) to 650°C. The reason why the lower limit of the above-mentioned bath temperature is the melting point + 20°C is that in order to perform the hot-dip plating process, the above-mentioned bath temperature must be above the freezing point, and the reason for setting the lower limit of the melting point + 20°C is to prevent the local bath temperature of the above-mentioned plating bath from falling. To solidify. On the other hand, the reason why the upper limit of the bath temperature is set at 650°C is that if it exceeds 650°C, it is difficult to rapidly cool the plating film, and the interface alloy layer formed between the plating film and the steel sheet may become thick.

Also, the temperature of the base steel sheet immersed in the coating bath (immersion plate temperature) is not particularly limited, but from the viewpoint of ensuring the coating characteristics in the aforementioned continuous hot-dip coating operation and preventing changes in the bath temperature, it is preferably controlled within a range relative to the aforementioned temperature. The temperature of the plating bath is within ±20°C.

In addition, the immersion time of the steel sheet in the above-mentioned coating bath is 0.5 second or more. If it is less than 0.5 second, there is a possibility that a sufficient plating film cannot be formed on the surface of the aforementioned base steel sheet. The upper limit of the immersion time is not particularly limited, but if the immersion time is longer, the interface alloy layer formed between the plating film and the steel sheet may become thicker, so it is preferably within 8 seconds.

Furthermore, in the cooling process after plating, it is preferable to cool the board temperature from 520° C. to 500° C. for more than 3 seconds. The precipitation start temperature of the single Si phase and Mg ₂ Si in the aforementioned plating film is 500~490°C for the single Si phase and 520~500°C for Mg ₂ Si. Therefore, by increasing the residence time in the temperature range of 520~500°C where only Mg ₂ Si is precipitated, the precipitation of Mg ₂ Si is promoted and the precipitation of Si phase alone is suppressed, so it is easy to satisfy the relationship of (1) above .

In addition, the molten Al-Zn-Si-Mg plated steel sheet can form a coating film on the above-mentioned plated film, directly or via an intermediate layer, depending on the required performance.

In addition, there is no particular limitation on the method of forming the aforementioned coating film, and it can be appropriately selected according to the required performance. Examples include forming methods such as roll coating, curtain coating, and spray coating. After coating the paint containing organic resin, it can be heated and dried by means of hot air drying, infrared heating, induction heating, etc. to form a coating film.

Also, the intermediate layer is not particularly limited as long as it is a layer formed between the plated film of the hot-dip coated steel sheet and the aforementioned coating film.

(Surface treated steel plate) The surface-treated steel sheet of the present invention includes a plating film on the surface of the steel sheet and a chemical conversion film formed on the plating film. Here, the constitution of the above-mentioned plated film is the same as that of the above-mentioned plated film of the molten Al-Zn-Si-Mg system plated steel sheet of the present invention.

In the surface-treated steel sheet of the present invention, a chemical conversion film is formed on the aforementioned film. In addition, the aforementioned chemical conversion film may be formed on at least one surface of the surface-treated steel sheet, and may be formed on both surfaces of the surface-treated steel sheet depending on the application or required performance.

Furthermore, in the surface-treated steel sheet of the present invention, the aforementioned chemical conversion film is characterized by containing a compound selected from epoxy resins, urethane resins, acrylic resins, acrylic silicone resins, alkyd resins, polyester resins, and polyalkylene resins. , at least one of amino resins and fluororesins, and selected from P compounds, Si compounds, Co compounds, Ni compounds, Zn compounds, Al compounds, Mg compounds, V compounds, Mo compounds, Zr compounds, Ti compounds and Ca compounds at least one metal compound in the compound. By forming the above-mentioned chemical conversion film on the plating film, in addition to improving the affinity with the plating film and uniformly forming the chemical conversion film on the above-mentioned plating film, the anti-rust effect and barrier of the chemical conversion film can also be improved. Effect. As a result, stable corrosion resistance and white rust resistance of the surface-treated steel sheet of the present invention can be realized.

Here, the resin constituting the aforementioned chemical conversion film is selected from the group consisting of epoxy resin, urethane resin, acrylic resin, acrylic silicone resin, alkyd resin, polyester resin, polyester resin, etc. from the viewpoint of improving corrosion resistance. At least one of alkane resin, amino resin and fluororesin. From the same point of view, the aforementioned resin preferably contains at least one of urethane resin and acrylic resin. Moreover, the resin which comprises the said chemical conversion film also includes the addition polymer of the said resin.

As for the above-mentioned epoxy resin, for example, those who have glycidyl etherified epoxy resins such as bisphenol A type, bisphenol F type, and novolac type, and those who have added propylene oxide to bisphenol A type epoxy resins, cycloheximide, etc. Glycidyl etherification of ethylene oxide or polyalkylene glycol, aliphatic epoxy resin, alicyclic epoxy resin, polyether epoxy resin, etc.

As the aforementioned urethane resin, for example, oil-modified polyurethane resin, alkyd-based polyurethane resin, polyester-based polyurethane resin, polyether-based polyurethane resin, polyether-based polyurethane resin, etc., can be used. Urethane resins, polycarbonate-based polyurethane resins, etc.

Regarding the aforementioned acrylic resin, for example, polyacrylic acid and its copolymer, polyacrylate and its copolymer, polymethacrylic acid and its copolymer, polymethacrylate and its copolymer, urethane-acrylic acid copolymer (or urethane-modified acrylic resin), styrene-acrylic acid copolymer, etc., and those modified by other alkyd resins, epoxy resins, phenolic resins, etc. can be used.

Examples of the aforementioned acrylic silicone resin include, for example, those in which a curing agent is added to a resin having a hydrolyzable alkoxysilyl group on a side chain or terminal of an acrylic copolymer as a main component. Furthermore, when acrylic silicone resin is used, in addition to corrosion resistance, excellent weather resistance can also be expected.

Regarding the aforementioned alkyd resins, for example, oil-modified alkyd resins, rosin-modified alkyd resins, phenol-modified alkyd resins, styrenated alkyd resins, silicon-modified alkyd resins, acrylic-modified alkyd resins, etc. resin, oil-free alkyd resin, high molecular weight oil-free alkyd resin, etc.

The aforementioned polyester resin is a polycondensate synthesized by dehydrating and condensing a polycarboxylic acid and a polyhydric alcohol to form an ester bond. As the polycarboxylic acid, for example, terephthalic acid, 2,6-naphthalene dicarboxylic acid, etc. are used, Examples of the polyhydric alcohol include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol and the like. Specifically, examples of the aforementioned polyester include polyethylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, and the like. Also, those polyester resins modified with acrylic acid can also be used.

The aforementioned polyalkylene resins include, for example, ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers, ethylene-based copolymers such as carboxyl-modified polyolefin resins, ethylene-unsaturated carboxylic acid copolymers, ethylene-based ionomers, etc. In addition, those modified with other alkyd resins, epoxy resins, phenol resins, etc. can be used.

The aforementioned amino resins are thermosetting resins produced by the reaction of amine or amide compounds with aldehydes, such as melamine resins, guanamine resins, thiourea resins, etc., based on corrosion resistance, weather resistance, adhesion, etc. From this point of view, it is preferable to use melamine resin. The melamine resin is not particularly limited, and examples thereof include butylated melamine resins, methylated melamine resins, and aqueous melamine resins.

The aforementioned fluororesins include fluoroolefin-based polymers, or fluoroolefins and alkyl vinyl ethers, cycloalkyl vinyl ethers, carboxylic acid-modified vinyl esters, hydroxyalkyl allyl ethers, tetrafluoropropyl vinyl ethers, etc. of copolymers. When these fluororesins are used, not only corrosion resistance but also excellent weather resistance and excellent water repellency can be expected.

Furthermore, in order to improve corrosion resistance and workability, it is particularly preferable to use a hardener. As the curing agent, urea resin (butylated urea resin, etc.), melamine resin (butylated melamine resin, butyl etherified melamine resin, etc.), butylated urea-melamine resin, benzoguanamine resin, etc. can be suitably used. Amino resins, blocked isocyanates, oxazoline compounds, phenolic resins, etc.

In addition, as the metal compound constituting the aforementioned chemical conversion film, a compound selected from P compounds, Si compounds, Co compounds, Ni compounds, Zn compounds, Al compounds, Mg compounds, V compounds, Mo compounds, Zr compounds, Ti compounds, and Ca compounds can be used. at least one of the compounds. Based on the same viewpoint, the aforementioned metal compound preferably contains at least one of P compound, Si compound and V compound.

Here, by containing the P compound in the chemical conversion film, corrosion resistance and sweat resistance can be improved. The aforementioned 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 aforementioned inorganic phosphoric acid, organic phosphoric acid, and salts thereof, any compound can be used without particular limitation. For example, as the aforementioned inorganic phosphoric acid, preferably used are phosphoric acid, dihydrogen phosphate, hydrogen phosphate, phosphate, pyrophosphoric acid, pyrophosphate, tripolyphosphoric acid, tripolyphosphate, phosphorous acid, phosphite, hypophosphorous acid. , one or more of hypophosphite. Also, as the organic phosphoric acid, phosphonic acid (phosphonic acid compound) is preferably used. In addition, as the aforementioned phosphonic acid, one selected from the group consisting of nitrogen trimethylene phosphonic acid, phosphonobutane tricarboxylic acid, methyl diphosphonic acid, methylene phosphonic acid and ethylene diphosphonic acid is preferably used. above. In addition, when the aforementioned P compound is a salt, the salt is preferably a salt of Group 1 to Group 13 elements in the periodic table, more preferably a metal salt, preferably one or more selected from alkali metal salts and alkaline earth metal salts .

When the chemical conversion treatment solution containing the above-mentioned P compound is coated on the molten Al-Zn-Si-Mg plated steel sheet, the surface of the plated film is etched by the action of the P compound, and the above-mentioned plating on the chemical conversion film On the film side, a concentrated layer of Al, Zn, Si, and Mg containing constituent elements of the plating film is formed. By forming the above-mentioned concentrated layer, the chemical conversion film and the surface of the plated film are bonded firmly, and the adhesion of the chemical conversion film is improved. The concentration of the P compound in the aforementioned chemical conversion treatment solution is not particularly limited, and may be set at 0.25% by mass to 5% by mass. When the concentration of the above-mentioned P compound is less than 0.25% by mass, not only the etching effect is insufficient, the adhesion with the plating interface is reduced, and the corrosion resistance of the flat part is reduced, but also the plating on the defect part, the cut end face, and the processing, etc. The corrosion resistance and sweat resistance of the damaged part of the coating film may also be reduced. From the same viewpoint, the concentration of the P compound is preferably at least 0.35% by mass, more preferably at least 0.50% by mass. On the other hand, when the concentration of the above-mentioned P compound exceeds 5% by mass, not only the service life of the chemical conversion treatment solution is shortened, but also the appearance of the film is likely to be uneven when the film is formed, and the amount of P eluted from the chemical conversion film increases, and it also has blackening resistance. risk of reduction. From the same viewpoint, the concentration of the P compound is preferably 3.5% by mass or less, more preferably 2.5% by mass or less. Regarding the content of the P compound in the aforementioned chemical conversion film, for example, a chemical conversion treatment solution having a P compound concentration of 0.25 mass % to 5 mass % can be applied and dried to allow P to adhere to the dried chemical conversion film. The amount is 5~100mg/m ² .

The Si compound is a component that forms the skeleton of the chemical conversion film together with the resin, improves the affinity with the plating film, and uniformly forms the chemical conversion film. The aforementioned Si compound is a compound containing Si, and is preferably at least one selected from silicon oxide, trialkoxysilane, tetraalkylsilane, and silane coupling agents, for example.

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

As the aforementioned trialkoxysilane, any one can be used without particular limitation. Preferably used, for example, with the general formula: R ₁ Si(OR ₂ ) ₃ (wherein, R ₁ is hydrogen or an alkyl group with 1 to 5 carbons, and R ₂ is the same or different alkyl groups with 1 to 5 carbons) Represented trialkoxysilane. Examples of such trialkoxysilanes include trimethoxysilane, triethoxysilane, methyltriethoxysilane and the like.

Any one can be used without particular limitation as said tetraalkoxysilane. For example, tetraalkoxysilanes represented by the general formula: Si(OR) ₄ (wherein, R is the same or different alkyl groups with 1 to 5 carbon atoms) are preferably used. As such tetraalkoxysilane, tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane etc. are mentioned, for example.

As the aforementioned silane coupling agent, any one can be used without particular limitation. Examples include γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-amino Propyltrimethoxysilane, γ-aminopropylmethyldiethoxysilane, γ-aminopropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methoxysilane Acryloxypropyltriethoxysilane, γ-mercaptopropylmethyldimethoxysilane and γ-mercaptopropyltrimethoxysilane, vinyltriethoxysilane, γ-isocyanatopropyltrimethoxysilane Ethoxysilane, etc.

Also, by containing the aforementioned Si compound in the chemical conversion coating, the Si compound is dehydrated and condensed to form an amorphous chemical conversion coating having a siloxane bond with a high barrier effect of shielding corrosion factors. Also, by combining with the above resin, a chemical conversion film with higher barrier properties is formed. In addition, in a corrosive environment, a dense and stable corrosion product is formed at the defective part or the damaged part of the plating film caused by processing, and the combined effect with the above plating film also has the effect of inhibiting the corrosion of the base steel sheet. From the viewpoint of the high effect of forming stable corrosion products, it is preferable to use at least one of colloidal silicon oxide and dry silicon oxide as the Si compound.

The Si compound concentration in the chemical conversion treatment solution for forming the chemical conversion film is 0.2% by mass to 9.5% by mass. If the concentration of the Si compound in the aforementioned chemical conversion treatment liquid is 0.2% by mass or more, the barrier effect due to the siloxane bond can be obtained. The corrosion resistance and sweat resistance of the damaged part are improved. And, if the concentration of the aforementioned Si compound is 9.5% by mass or less, the life of the chemical conversion treatment liquid can be extended. The concentration of Si compound is set at 0.2 mass % to 9.5 mass % of the chemical conversion treatment solution. By coating and drying, the Si adhesion amount in the dried chemical conversion film can be 2 to 95 mg/m ² .

Blackening resistance can be improved by containing the said Co compound and the said Ni compound in the said chemical conversion film. This is considered to be because Co and Ni have the effect of slowing down the elution of water-soluble components from the film under a corrosive environment. Furthermore, the aforementioned Co and the aforementioned Ni are elements that are more difficult to oxidize than Al, Zn, Si, and Mg. Therefore, by concentrating (forming a concentrated layer) at least one of the Co compound and the Ni compound at the interface between the chemical conversion film and the plating film, the concentrated layer can be used as a result of blocking corrosion. Improve black degeneration resistance.

By using the chemical conversion treatment liquid containing the aforementioned Co compound, Co can be contained in the aforementioned chemical conversion film and incorporated into the aforementioned concentrated layer. As the aforementioned Co compound, cobalt salts are preferably used. As the cobalt salt, it is more preferable to use one or two or more selected from cobalt sulfate, cobalt carbonate, and cobalt chloride. Also, by using the chemical conversion treatment solution containing the Ni compound, Ni can be contained in the chemical conversion film and can be included in the concentrated layer. As the aforementioned Ni compound, a nickel salt is preferably used. As the above-mentioned nickel salt, it is more preferable to use one or two or more kinds selected from nickel sulfate, nickel carbonate, and nickel chloride.

The concentration of the Co compound and/or the Ni compound in the aforementioned chemical conversion treatment liquid is not particularly limited, but the total may be 0.25% by mass to 5% by mass. When the concentration of the above-mentioned Co compound and/or Ni compound is less than 0.25% by mass, the interface concentration layer becomes inhomogeneous, and not only the corrosion resistance of the flat part decreases, but also defects caused by defects, cut end faces, processing, etc. There is a possibility that the corrosion resistance of the damaged portion of the plating film may decrease. From the same viewpoint, it is preferably at least 0.5% by mass, more preferably at least 0.75% by mass. On the other hand, when the concentration of the above-mentioned Co compound and/or Ni compound exceeds 5% by mass, the appearance when forming a film tends to be uneven, and there is a possibility that the corrosion resistance may decrease. From the same viewpoint, it is preferably at most 4.0 mass %, more preferably at most 3.0 mass %. The chemical conversion treatment solution with a total concentration of the aforementioned Co compound and/or Ni compound of 0.25% by mass to 5% by mass can be coated and dried so that the total adhesion amount of Co and Ni in the dried chemical conversion film can be 5% ~100 mg/m ² .

Regarding the aforementioned Al compound, the aforementioned Zn compound, and the aforementioned Mg compound, by being contained in the chemical conversion treatment liquid, a concentrated compound containing at least one selected from Al, Zn, and Mg can be formed on the plating film side of the aforementioned chemical conversion film. layers. The formed concentrated layer can improve the corrosion resistance. Also, the aforementioned Al compound, the aforementioned Zn compound, and the aforementioned Mg compound are not particularly limited if they are compounds containing Al, Zn, and Mg, but are preferably inorganic compounds, and are preferably salts, chlorides, oxides, or hydroxides. .

As the aforementioned Al compound, for example, one or more selected from the group consisting of aluminum sulfate, aluminum carbonate, aluminum chloride, aluminum oxide, and aluminum hydroxide is exemplified. As the aforementioned Zn compound, for example, one or more kinds selected from zinc sulfate, zinc carbonate, zinc chloride, zinc oxide, and zinc hydroxide are exemplified. As the aforementioned Mg compound, for example, one or more kinds selected from magnesium sulfate, magnesium carbonate, magnesium chloride, magnesium oxide, and magnesium hydroxide are exemplified.

The total concentration of the Al compound, the Zn compound and/or the Mg compound in the chemical conversion treatment solution for forming the aforementioned chemical conversion film is preferably 0.25% by mass to 5% by mass. When the said total concentration is 0.25 mass % or more, the said concentrated layer can be formed more efficiently, and as a result, corrosion resistance can further be improved. On the other hand, if the above-mentioned total concentration is 5% by mass or less, the appearance of the chemical conversion film will be more uniform, and the corrosion resistance of the damaged part of the plated film caused by flat parts, defect parts, processing, etc. will be further improved.

By containing the aforementioned V compound in the aforementioned chemical conversion film, V can be moderately eluted in a corrosive environment, and combined with zinc ions, etc., which are also eluted in a plating component, to form a dense protective film. With the formed protective film, not only the flat part of the steel plate, but also the corrosion resistance of the defect part, the damaged part of the plating film caused by processing, etc., and the corrosion from the cut end surface to the flat part can be further improved.

The aforementioned V compound is a compound containing V, for example, one or more selected from sodium metavanadate, vanadium sulfate, and vanadium acetylpyruvate.

The V compound in the chemical conversion treatment solution used to form the aforementioned chemical conversion film is preferably 0.05% by mass to 4% by mass. If the concentration of the above-mentioned V compound is 0.05% by mass or more, it will be easily eluted to form a protective film in a corrosive environment, and the corrosion resistance of the damaged part of the plating film caused by defective parts, cut end faces, and processing will be improved. On the other hand, when the concentration of the above-mentioned compound V exceeds 4% by mass, the appearance of the chemical conversion film is likely to be non-uniform, and the blackening resistance is also reduced.

By containing the aforementioned Mo compound in the aforementioned chemical conversion film, the blackening resistance of the surface-treated steel sheet can be improved. The aforementioned Mo compound is a compound containing Mo, and can be obtained by adding one or both of molybdic acid and molybdate to the chemical conversion treatment liquid. Moreover, as said molybdate, for example, one or more types selected from sodium molybdate, potassium molybdate, magnesium molybdate, and zinc molybdate are exemplified.

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

By containing the Zr compound and the Ti compound in the chemical conversion film, the chemical conversion film can be prevented from becoming porous, and the film can be densified. Therefore, corrosion factors are less likely to pass through the aforementioned chemical conversion film, and corrosion resistance can be improved.

As the aforementioned Zr compound is a Zr-containing compound, for example, one or more selected from the group consisting of zirconium acetate, zirconium sulfate, potassium zirconium carbonate, sodium zirconium carbonate, and ammonium zirconium carbonate can be used. Among them, the organic titanium chelate compound is preferable because it can make the film denser and obtain more excellent corrosion resistance when the chemical conversion treatment solution is dried to form the film.

As the aforementioned Ti compound is a compound containing Ti, for example, one or more selected from the group consisting of titanium sulfate, titanium chloride, titanium hydroxide, titanium acetylacetonate, titanium octane glycolate, and titanium ethyl acetylacetonate can be used.

The total concentration of the Zr compound and/or the Ti compound in the chemical conversion treatment solution for forming the aforementioned chemical conversion film is preferably 0.2% by mass to 20% by mass. If the total concentration of the above-mentioned Zr compound and/or Ti compound is 0.2% by mass or more, the effect of inhibiting the penetration of corrosion factors will be improved, and not only the corrosion resistance of the flat part will be improved, but also the defect part, the cut end part, and the plating film caused by processing The corrosion resistance of the damaged part is further improved. On the other hand, if the total concentration of the aforementioned Zr compound and/or Ti compound is 20% by mass or less, the lifetime of the aforementioned chemical conversion treatment liquid can be further extended.

By containing the aforementioned Ca compound in the aforementioned chemical conversion film, an effect of reducing the corrosion rate can be exhibited.

The aforementioned Ca compound is a compound containing Ca, for example, Ca oxide, Ca nitrate, Ca sulfate, Ca-containing intermetallic compound, and the like. More specifically, examples of the Ca compound include CaO, CaCO ₃ , Ca(OH) ₂ , Ca(NO ₃ ) ₂ ·4H ₂ O, CaSO ₄ ·2H ₂ O and the like. The aforementioned Ca compound content of the aforementioned chemical conversion film is not particularly limited.

In addition, the aforementioned chemical conversion film may contain various conventional components commonly used in the field of paints, if necessary. Examples include various surface regulators such as leveling agents and defoamers, various additives such as dispersants, anti-settling agents, ultraviolet absorbers, light stabilizers, silane coupling agents, titanate coupling agents, coloring pigments, and body Various pigments for pigments and bright materials, hardening catalysts, organic solvents, lubricants, etc.

Furthermore, in the surface-treated steel sheet of the present invention, it is preferable that the aforementioned chemical conversion film does not contain harmful components such as hexavalent chromium, trivalent chromium, and fluorine. The chemical conversion treatment liquid used to form the aforementioned chemical conversion film does not contain such harmful components, so it is highly safe and has a small environmental load.

Also, the adhesion amount of the aforementioned chemical conversion film is not particularly limited. For example, from the viewpoint of ensuring more reliable corrosion resistance and preventing peeling of the chemical conversion film, the adhesion amount of the chemical conversion film is preferably 0.1-3.0 g/m ² , more preferably 0.5-2.5 g/m ² . By setting the adhesion amount of the chemical conversion film to 0.1 g/m ² or more, the corrosion resistance can be ensured more reliably, and by keeping the adhesion amount of the chemical conversion film to 3.0 g/m ² or less, cracking and peel off. The aforementioned chemical conversion film adhesion amount can be determined based on a method appropriately selected from known methods such as a method of analyzing the film by fluorescent X-rays and measuring in advance the amount of an element whose content is known in the film.

In addition, the aforementioned method for forming the chemical conversion film is not particularly limited, and may be appropriately selected according to required performance or manufacturing equipment. For example, the chemical conversion treatment liquid can be continuously coated on the above-mentioned plating film by a roll coater, and then hot air or induction heating can be used to reach the plate temperature (peak metal temperature (Peak Metal Temperature) of about 60-200°C Metal Temperature): PMT) is formed by drying. For the application of the above-mentioned chemical conversion treatment liquid, known methods such as airless spray, electrostatic spray, curtain coater, etc. can also be suitably used in addition to the roll coater. In addition, if the aforementioned chemical conversion film contains the aforementioned resin and the aforementioned metal compound, it may be either a single-layer film or a multi-layer film, and is not particularly limited.

In addition, in the surface-treated steel sheet of the present invention, a coating film may be formed on the aforementioned chemical conversion film as needed.

(coated steel sheet) The coated steel sheet of the present invention is a coated steel sheet in which a coating film is formed directly or through a chemical conversion film on a plating film. Here, the constitution of the above-mentioned plated film is the same as that of the above-mentioned plated film of the molten Al-Zn-Si-Mg system plated steel sheet of the present invention.

The coated steel sheet of the present invention can form a chemical conversion film on the aforementioned plated film. In addition, the aforementioned chemical conversion film may be formed on at least one side of the coated steel sheet, and may be formed on both sides of the coated steel sheet depending on the application and required performance.

Furthermore, the coated steel sheet of the present invention is characterized in that the chemical conversion film contains: a resin component containing (a): an anionic polyurethane resin having an ester bond and (b) in a total of 30 to 50% by mass. : Epoxy resin with bisphenol skeleton, and the content ratio of (a) to (b) ((a):(b)) is in the range of 3:97~60:40 by mass ratio; and inorganic compound, It contains 2-10 mass % of vanadium compound, 40-60 mass % of zirconium compound and 0.5-5 mass % of fluorine compound. By forming the above-mentioned chemical conversion film on the plating film, the strength and adhesion of the chemical conversion film can be improved, and the corrosion resistance can also be improved.

Here, the resin component which comprises the said chemical conversion film contains (a): the anionic polyurethane resin which has an ester bond, and (b): the epoxy resin which has a bisphenol skeleton.

Regarding the aforementioned (a) anionic polyurethane resin having an ester bond, for example, the reaction product of polyester polyol and diisocyanate or polyisocyanate having two or more isocyanate groups, copolymerized dimethylol alkanoic acid The resulting resin. And, by dispersing in a liquid such as water by a known method, a chemical conversion treatment liquid can be obtained.

Examples of the aforementioned polyester polyols include polyesters obtained by dehydration and condensation reactions of acid components such as ester-forming derivatives of diol components and hydroxycarboxylic acids, and compounds of cyclic ester compounds such as ε-caprolactone and the like. Polyesters obtained by ring polymerization and their co-polymerized polyesters. As said polyisocyanate, aromatic polyisocyanate, aliphatic polyisocyanate, alicyclic polyisocyanate etc. are mentioned, for example. As the aforementioned aromatic polyisocyanate, for example, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, m-xylene diisocyanate, diphenylmethane diisocyanate, 2,4-diphenylmethane diisocyanate , 2,2-diphenylmethane diisocyanate, triphenylmethane triisocyanate, polymethylene polyphenyl polyisocyanate, naphthalene diisocyanate and their derivatives (such as prepolymers obtained by reacting with polyols Classes, modified polyisocyanates such as carbodiimide compounds of diphenylmethane diisocyanate, etc.), etc.

In addition, when the above-mentioned polyester polyol is reacted with the above-mentioned diisocyanate or polyisocyanate to form a urethane, the above-mentioned ( a) Anionic polyurethane resin having an ester bond. In this case, examples of the dimethylol alkanoic acid include, for example, dimethylol alkanoic acid having 2 to 6 carbon atoms, more specifically dimethylol acetic acid, dimethylol propionic acid, dimethylol butane acid, dimethylol heptanoic acid and dimethylol hexanoic acid, etc.

Also, as the epoxy resin having a bisphenol skeleton in (b) above, known epoxy resins 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. are mentioned. These epoxy resins can be obtained by reacting bisphenol compounds such as bisphenol A, bisphenol F, bisphenol AD, and bisphenol S with epichlorohydrin in the presence of an alkali catalyst. Among them, component [A] preferably contains bisphenol A type epoxy resin or bisphenol F type epoxy resin, more preferably contains bisphenol A type epoxy resin. The (b) epoxy resin having a bisphenol skeleton can be dispersed in a liquid such as water by a known method to obtain a chemical conversion treatment liquid.

The aforementioned resin component functions as a binder for the aforementioned chemical conversion film, and the aforementioned (a) anionic polyurethane resin having an ester bond that constitutes the binder can be used when processed due to its flexibility. The effect of the chemical conversion film being difficult to break (peel off), and the aforementioned (b) epoxy resin with a bisphenol skeleton can exert the effect of improving the adhesion with the zinc-based coated steel sheet on the base and the primer coating film on the upper layer. The aforementioned resin components are contained in a total of 30 to 50% by mass in the aforementioned chemical conversion film. When the content of the above-mentioned resin component is less than 30% by mass, the adhesive effect of the chemical conversion film decreases, and when it exceeds 50% by mass, the functions due to the inorganic components shown below, such as the inhibitor effect, decrease. Based on the same viewpoint, the content of the aforementioned resin component in the aforementioned chemical conversion film is preferably 35-45% by mass.

Furthermore, the aforementioned resin component must be the content ratio of the aforementioned (a) anionic polyurethane resin having an ester bond to the aforementioned (b) epoxy resin having a bisphenol skeleton ((a):(b)) In terms of mass ratio, it is in the range of 3:97~60:40. If the above-mentioned (a): (b) is outside the above-mentioned range, the flexibility as the chemically treated coating will decrease or the adhesion will decrease, and sufficient corrosion resistance will not be obtained. Based on the same point of view, the ratio of (a):(b) above is preferably 10:90~55:45.

In addition, the aforementioned resin components may contain resins other than the aforementioned (a) anionic polyurethane resin having an ester bond and (b) epoxy resin having a bisphenol skeleton (other resins) depending on the required performance. Element). There are no particular limitations on the aforementioned other resin components, and at least one or a combination of two or more selected from acrylic resins, acrylic silicone resins, alkyd resins, polyester resins, polyalkylene resins, amino resins, and fluororesins can be used . When the aforementioned resin component contains other resins, the total content of the aforementioned (a) anionic polyurethane resin having an ester bond and the aforementioned (b) epoxy resin having a bisphenol skeleton is preferably at least 50% by mass, and more preferably Preferably at least 75% by mass. This is because the reduction in flexibility and adhesion as a chemical conversion treatment film can be more reliably obtained.

Moreover, the said chemical conversion film contains 2-10 mass % of vanadium compounds, 40-60 mass % of zirconium compounds, and 0.5-5 mass % of fluorine compounds as inorganic compounds. By including these compounds, the corrosion resistance of the chemical conversion coating can be improved.

The aforementioned vanadium compound functions as a rust preventive agent (inhibitor) when added to the chemical conversion treatment liquid. Due to the above-mentioned vanadium compound contained in the chemical conversion film, the vanadium compound can be moderately leached out in a corrosive environment, and combined with zinc ions, etc., which are also eluted in a corrosive environment, to form a dense protective film. The formed protective film can further improve the corrosion resistance not only to the flat part of the steel sheet, but also to defect parts, damaged parts of the plating film caused by processing, corrosion from the cut end surface to the flat part, and the like. Regarding the aforementioned vanadium compound, examples include vanadium pentoxide, metavanadic acid, ammonium metavanadate, oxyvanadium trichloride, vanadium trioxide, vanadium dioxide, magnesium vanadate, vanadyl acetylpyruvate, Vanadium acetylpyruvate, etc. In particular, among these, it is desirable to use a tetravalent vanadium compound or a tetravalent vanadium compound obtained by reduction or oxidation.

Also, the content of the vanadium compound in the aforementioned chemical conversion treatment film is 2 to 10% by mass. When the content of the vanadium compound in the chemical conversion treatment film is less than 2% by mass, the corrosion resistance is reduced due to insufficient inhibitor effect. On the other hand, when the content of the vanadium compound exceeds 10 mass%, the chemical conversion treatment film is damaged Reduced moisture resistance.

Containing zirconium compound in the chemical conversion film mentioned above can be expected to improve the strength and corrosion resistance of the chemical conversion film by reacting with the plating metal and coexisting with the resin component, and the zirconium compound itself contributes to the formation of dense chemical conversion treatment The film is rich in coating properties, so a barrier effect can be expected. Examples of the aforementioned zirconium compound include neutralization salts such as zirconium sulfate, zirconium carbonate, zirconium nitrate, zirconium lactate, zirconium acetate, and zirconium chloride.

Also, the content of the zirconium compound in the aforementioned chemical conversion treatment film is 40 to 60% by mass. The reason is that when the content of the zirconium compound in the chemical conversion treatment film is less than 40% by mass, the strength or corrosion resistance of the chemical conversion treatment film will decrease, and if the content of the aforementioned zirconium compound exceeds 60 mass%, the chemical conversion treatment film will be brittle. , When subjected to strict processing, the chemical conversion treatment film is damaged or peeled off.

The aforementioned fluorine compound is contained in the aforementioned chemical conversion coating, and functions as an adhesion imparting agent to the plating coating. As a result, the corrosion resistance of the chemical conversion film can be improved. As the aforementioned fluorine compound, for example, fluoride salts such as ammonium salt, sodium salt, and potassium salt, or fluorine compounds such as ferrous fluoride and ferric fluoride, can be used. Among these, ammonium fluoride, or fluoride salts such as sodium fluoride and potassium fluoride are preferably used.

Also, the content of fluorine compounds in the chemical conversion treatment film is 0.5-5% by mass. The reason is that when the content of the fluorine compound in the chemical conversion treatment film is less than 0.5% by mass, the adhesion of the processed part cannot be obtained sufficiently, and when the content of the above-mentioned fluorine compound exceeds 5 mass%, the moisture resistance of the chemical conversion treatment film decreases. The reason.

Moreover, the adhesion amount of the said chemical conversion film is not specifically limited. For example, from the viewpoint of ensuring more reliable corrosion resistance and improving the adhesion of the chemical conversion film, the adhesion amount of the chemical conversion film is preferably 0.025-0.5 g/m ² . When the adhesion amount of the chemical conversion film is 0.025 g/m ² or more, the corrosion resistance can be ensured more reliably, and when the adhesion amount of the chemical conversion film is 0.5 g/m ² or less, peeling of the chemical conversion film can be suppressed. The above-mentioned adhesion amount of the chemical conversion film can be determined by a method appropriately selected from existing methods, such as a method of analyzing the film by fluorescent X-rays and measuring in advance the amount of an element whose content is known in the film.

Also, the method for forming the aforementioned chemical conversion film is not particularly limited, and may be appropriately selected according to required performance, manufacturing equipment, and the like. For example, on the above-mentioned plating film, a chemical conversion treatment solution is continuously applied by a roll coater, and then, using hot air or induction heating, etc., at a plate temperature (peak metal temperature: PMT) of about 60 to 200°C formed by drying. For the application of the aforementioned chemical conversion treatment liquid, known methods such as windless spray, electrostatic spray, curtain coater, etc. can also be suitably used in addition to the roll coater. In addition, the aforementioned chemical conversion film may be any of a single-layer film or a multi-layer film as long as it contains the aforementioned resin and the aforementioned metal compound, and is not particularly limited.

In the coated steel sheet of the present invention, as described above, a coating film is formed on the plating film directly or through a chemical conversion film, and the coating film has at least a primer coating film.

Furthermore, in the present invention, the primer coating film contains a polyester resin having a urethane bond, and an inorganic compound containing a vanadium compound, a phosphoric acid compound, and magnesium oxide. The aforementioned primer coating film contains the aforementioned polyester resin having a urethane bond and the aforementioned inorganic compound, so that the adhesion of the coating film can be improved and the corrosion resistance can be improved.

The aforementioned primer coating film contains a polyester resin having a urethane bond as a main component. The above-mentioned polyester resin with urethane bonds has both flexibility and strength, so when it is processed, it can obtain the effect that the primer coating film is not easy to crack, etc., due to the chemical conversion with the urethane-containing resin The affinity of the treatment film is high, so it is especially helpful to improve the corrosion resistance of the processed part. In addition, the "main component" here refers to the component with the largest content among the components in the primer coating film.

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

In addition, the aforementioned polyester polyol can be obtained by a known method utilizing a dehydration condensation reaction of a polyol component and a polybasic acid component. As said polyhydric alcohol, a diol and a polyvalent alcohol more than trivalent are mentioned. The aforementioned diols are exemplified by, for example, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, neopentyl glycol, hexanediol, 1,3 -Butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2-butyl-2-ethyl-1,3-propanediol, methylpropanediol, cyclo Hexanedimethanol, 3,3-diethyl-1,5-pentanediol, etc. In addition, examples of the above-mentioned trivalent or higher polyhydric alcohol include glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, dipentaerythritol, and the like. These polyols may be used alone or in combination of two or more. As the above-mentioned polybasic acid, common polybasic carboxylic acids are used, but unit fatty acids and the like may be used in combination as needed. As the aforementioned polycarboxylic acid, for example, 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, glutaric acid, fumaric acid, maleic acid, itaconic acid, pyromellitic acid, dimer acid, etc., and the Anhydrides such as 1,4-cyclohexanedicarboxylic acid, isophthalic acid, tetrahydroisophthalic acid, hexahydroisophthalic acid, hexahydroterephthalic acid, etc. These polybasic acids may be used alone or in combination of two or more.

Regarding the aforementioned polyisocyanate, for example, aliphatic diisocyanate such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, dimer acid diisocyanate, xylene diisocyanate (XDI), m-xylene diisocyanate, etc. Isocyanate, aromatic diisocyanate such as toluene diisocyanate (TDI), 4,4-diphenylmethane diisocyanate (MDI), and further cyclic isophorone diisocyanate, hydrogenated XDI, hydrogenated TDI, hydrogenated MDI, etc. Aliphatic diisocyanates and their adducts, urets, isocyanurates, etc. These polyisocyanates may be used alone or in combination of two or more.

Also, the hydroxyl value of the aforementioned polyester resin having a urethane bond is not particularly limited, but is preferably 5-120 mgKOH/g, more preferably 7-100 mgKOH/g, from the viewpoint of solvent resistance, processability, etc. And more preferably 10~80mgKOH/g. Furthermore, the number average molecular weight of the aforementioned polyester resin having a urethane bond is preferably from 500 to 15,000, more preferably from 700 to 12,000, and more preferably from 800 to 12,000, from the viewpoint of solvent resistance and processability. 10,000.

In the primer coating film, the content of the polyester resin having a urethane bond is preferably 40 to 88% by mass. When the content of the above-mentioned polyester resin having a urethane bond is less than 40% by mass, the function as a binder for the primer coating film may be reduced. On the other hand, the above-mentioned polyester resin having a urethane bond When the content exceeds 88% by mass, there is a possibility that the functions of the inorganic substances shown below, such as inhibitory effects, may decrease.

The vanadium compound, which is one of the aforementioned inorganic compounds, acts as an inhibitor. Examples of the aforementioned vanadium compound include, for example, vanadium pentoxide, metavanadic acid, ammonium metavanadate, oxyvanadium trichloride, vanadium trioxide, vanadium dioxide, magnesium vanadate, vanadyl acetylacetonate, Vanadium acetylpyruvate, etc. Among these, a tetravalent vanadium compound or a tetravalent vanadium compound obtained by reduction or oxidation is particularly preferably used. The vanadium compound added to the primer coating film may be the same or different from the vanadium compound added to the chemical conversion treatment film. The vanadic acid compound is considered to be due to the reaction of the vanadic acid ions slowly dissolved by the moisture intruding from the outside and the ions on the surface of the zinc-based plated steel sheet to form a passive film with good adhesion, which protects the exposed metal parts and presents an anti-rust effect.

The content of the vanadium compound in the primer coating film is not particularly limited, but is preferably 4 to 20% by mass from the viewpoint of both corrosion resistance and moisture resistance. When the content of the above-mentioned vanadium compound is less than 4% by mass, the effect of the inhibitor may decrease, resulting in a decrease in corrosion resistance. When the content of the above-mentioned vanadium compound exceeds 20% by mass, the moisture resistance of the primer film may decrease.

A phosphoric acid compound, which is one of the aforementioned inorganic compounds, also functions as an inhibitor. As said phosphoric acid compound, phosphoric acid, the ammonium salt of phosphoric acid, the alkali metal salt of phosphoric acid, the alkaline earth metal salt of phosphoric acid, etc. can be used, for example. In particular, alkali metal salts of phosphoric acid such as calcium phosphate can be preferably used.

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

Magnesium oxide, one of the aforementioned inorganic compounds, has the effect of stabilizing a product containing Mg as a poorly soluble magnesium salt by initial corrosion, and improving corrosion resistance.

The content of the magnesium oxide in the primer coating film is not particularly limited, but is preferably 4 to 20% by mass from the viewpoint of achieving both corrosion resistance and corrosion resistance of processed parts. When the content of the aforementioned magnesium oxide is less than 4% by mass, there is a possibility that the above-mentioned effect is reduced, resulting in a decrease in corrosion resistance. There is a risk that the corrosion resistance of the part will be reduced.

In addition, the aforementioned primer coating film may contain components other than the above-mentioned polyester resin having a urethane bond and an inorganic compound. For example, the crosslinking agent used when forming a primer coating film is mentioned. The aforementioned crosslinking agent is one that reacts with the aforementioned polyester resin having a urethane bond to form a crosslinked coating film, such as oxazoline compounds, epoxy compounds, melamine compounds, isocyanate compounds, and carbodiimides It is also possible to use two or more crosslinking agents in combination, such as a series compound, a silane coupling compound, etc. Among them, it is preferable to use a blocked polyisocyanate compound or the like from the viewpoint of the corrosion resistance of the processed portion of the coated steel sheet to be obtained. As the blocked polyisocyanate, for example, the isocyanate group of the polyisocyanate compound is passed through alcohols such as butanol, oximes such as methyl ethyl ketone oxime, and lactams such as ε-caprolactam. Diketones such as diketones such as acetoacetate diesters, imidazoles such as imidazoles and 2-ethylimidazoles, or phenols such as m-cresol, etc. are blocked.

In addition, the said primer coating film may contain the well-known various components normally used in the field of a coating material as needed. Specific examples include various additives such as leveling agents, defoaming agents, various surface regulators, dispersants, anti-settling agents, ultraviolet absorbers, light stabilizers, silane coupling agents, titanate coupling agents, etc., coloring pigments, Various pigments such as extender pigments, bright materials, hardening catalysts, organic solvents, etc.

The thickness of the primer coating film is preferably 1.5 μm or more. The reason is that the effect of improving the corrosion resistance and the effect of improving the adhesion of the top coating film formed on the chemical conversion treatment film or the primer coating film can be more reliably obtained by the thickness of the aforementioned primer coating film being 1.5 μm or more. The reason.

There is no particular limitation on the method of forming the aforementioned undercoat film. Furthermore, as for the coating method of the coating composition constituting the aforementioned primer coating film, it is preferable to apply the coating composition by methods such as roll coater coating and curtain coater coating. After the aforementioned coating composition is applied, it is baked by means of heating such as hot air heating, infrared heating, induction heating, etc., to obtain a primer coating film. In the aforementioned baking process, the maximum plate temperature is usually set at about 180-270° C., and it can be carried out in this temperature range for about 30 seconds to 3 minutes.

Also, with regard to the coating film constituting the coated steel sheet of the present invention, it is preferable to form a top coating film on the aforementioned primer coating film. The above-mentioned top coating film can not only impart color, gloss, and surface appearance to the coated steel sheet, but also improve various properties such as workability, weather resistance, chemical resistance, stain resistance, water resistance, and corrosion resistance.

There is no particular limitation on the composition of the above-mentioned top coating film, and the material, thickness, etc. can be appropriately selected according to the required performance. For example, the above-mentioned top coating 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 fluororesin-based paint, or the like. Furthermore, the above-mentioned top coating film may contain an appropriate amount of titanium oxide, iron oxide red, mica, carbon black or other various coloring pigments; metal pigments such as aluminum powder or mica; extender pigments made of carbonates or sulfates, etc.; Various microparticles such as silicon microparticles, nylon resin beads, acrylic resin beads, etc.; hardening catalysts such as p-toluenesulfonic acid, dibutyltin dilaurate, etc.; wax; other additives.

In addition, from the viewpoint of both appearance and workability, the thickness of the top coating film is preferably 5 to 30 μm. When the thickness of the top coating film is 5 μm or more, the color tone and appearance can be more reliably stabilized, and when the thickness of the top coating film is 30 μm or less, the decrease in workability (cracking of the top coating film) can be more reliably suppressed.

The coating method of the coating composition for forming the aforementioned top coating film is not particularly limited. The aforementioned coating composition can be applied by methods such as roll coater coating and curtain coating. After the aforementioned coating composition is applied, it is baked by means of heating such as hot air heating, infrared heating, induction heating, etc., to form a top coating film. In the aforementioned baking process, the maximum attained plate temperature is generally set at about 180 to 270° C., and it is performed within this temperature range for about 30 seconds to 3 minutes. [Example]

<Example 1: Samples 1 to 44> Using a cold-rolled steel sheet with a thickness of 0.8mm manufactured by a common method as a base steel sheet, annealing treatment and plating treatment were performed in a hot-dip plating simulator manufactured by RHESCA Co., Ltd. Samples 1 to 44 of hot-dip coated steel sheets under the conditions shown in Table 1 were produced. Also, regarding the composition of the coating bath used in the production of the hot-dip-coated steel sheet, the composition of the coating bath was Al: 30 to 75% by mass, Si: 0.5 to 4.5% by mass, Mg: 0 to 10% by mass, and Sr: 0.00 to 0.15% by mass are variously changed. In addition, the bath temperature of the plating bath is 590°C when Al: 30-60% by mass, and 630°C when Al: exceeds 60% by mass, and the temperature of the dipped plate of the base steel plate is controlled to be the same as the temperature of the plating bath. temperature. In addition, the plating process was performed under the condition that the plate temperature was cooled to within a temperature range of 520° C. to 500° C. within 3 seconds. In addition, the adhesion amount of the plating film was controlled to be 85±5g/m ² per side for samples 1~41, and 51~125g/m ² per side for samples 42~44.

(evaluate) The following evaluation was performed about each sample of the hot-dip-coated steel sheet obtained as mentioned above. The evaluation results are shown in Table 1.

(1) Composition of the plating film (adhesion amount, composition, X-ray diffraction intensity) For each sample after plating, stamp out 100mmφ, seal the non-measurement surface with tape, and use hydrochloric acid and The mixed solution of hexamethylenetetramine dissolves and strips the plating, and the adhesion amount of the plating film is calculated from the poor quality of the sample before and after stripping. Table 1 shows the calculation results and the deposition amount of the obtained plating film. Then, the stripping solution was filtered, and the filtrate and solid content were analyzed respectively. Specifically, the filtrate was analyzed by ICP emission spectroscopy to quantify components other than insoluble Si. And, after the solid content was dried and ashed in a heating furnace at 650°C, sodium carbonate and sodium tetraborate were added to dissolve it. Furthermore, the melt was dissolved with hydrochloric acid, and the dissolved liquid was analyzed by ICP emission spectroscopy to quantify insoluble Si. The Si concentration in the plating film is the sum of the soluble Si concentration obtained by the filtrate analysis and the insoluble Si concentration obtained by the solid content analysis. Table 1 shows the calculation results and the composition of the obtained plating film. Furthermore, after each sample was cut into a size of 100mm×100mm, the plated film on the evaluation symmetry plane was mechanically cut until the base steel plate was exposed, and after the obtained powder was fully mixed, 0.3g was taken out and used an X-ray diffraction device (RIGAKU Co., Ltd. Co., Ltd. "SmartLab"), X-rays used: Cu-Kα (wavelength = 1.54178Å), removal of kβ rays: Ni filter, tube voltage: 40kV, tube current: 30mA, scanning speed: 4˚/min, sampling Interval: 0.020˚, Divergent slit: 2/3˚, Parallel slit (Soller slit): 5˚, Detector: High-speed one-dimensional detector (D/teX Ultra) for qualitative analysis of the above powder. The intensity obtained by subtracting the base intensity from each peak intensity is taken as each diffraction intensity (cps), and the diffraction intensity of the (111) plane (plane spacing d=0.3668nm) of Mg ₂ Si and the (111) plane (plane) of Si are measured. Interval d = 0.3135nm) diffraction intensity. The measurement results are shown in Table 1.

(2) Corrosion resistance evaluation For each sample of the obtained hot-dip-coated steel sheet, cut it into a size of 120mm×120mm, and tape the edge of each edge of the surface to be evaluated at a distance of 10mm, and the end surface of the sample and the surface not to be evaluated. It was sealed and used as an evaluation sample in a state where the surface to be evaluated was exposed in a size of 100 mm×100 mm. In addition, three samples of the same sample were produced for this evaluation. For the three samples for evaluation produced as described above, the corrosion acceleration test was implemented in the cycle shown in FIG. 1 . The corrosion acceleration test starts from wetting, and after 300 cycles, the corrosion loss of each sample is measured by the method described in JIS Z 2383 and ISO8407, and the evaluation is based on the following criteria. The evaluation results are shown in Table 1. ◎: Corrosion loss of 3 samples is less than 45g/m ² ○: Corrosion loss of 3 samples is less than 70g/m ² ×: Corrosion loss of more than 1 sample exceeds 70g/m ²

(3) Surface appearance About each sample of the obtained hot-plated steel sheet, the plating film surface was observed visually. Next, the observation results were evaluated according to the following criteria. The evaluation results are shown in Table 1. ◎: Wrinkle defects were not observed at all ○: Wrinkle defects are only observed within 50mm from the edge ×: Wrinkle defects observed outside the range of 50mm from the edge

(4) Processability Each sample of the obtained hot-coated steel sheet was cut to a size of 70mm x 150mm, and eight sheets of the same thickness were sandwiched inside and subjected to 180° bending (8T bending). After bending, stick SELLOTAPE (registered trademark) glass tape on the outer surface of the bent part strongly and peel it off. Visually observe the surface state of the plating film on the outer surface of the bent portion and the presence or absence of plating film adhesion (peeling) on the surface of the tape, and evaluate the processability according to the following criteria. The evaluation results are shown in Table 1. ○: No cracking or peeling was observed on the plating film △: Cracks were observed in the plating film, but no peeling was observed ×: Cracks and peeling were observed on the plating film at the same time

(5) Bath stability When producing each sample of the hot-dip-coated steel sheet, the state of the coating bath surface was confirmed visually, and the bath surface of the coating bath used in the production of the molten Al-Zn-based plated steel sheet (bath surface without Mg oxide) )Compare. The evaluation was performed based on the following criteria, and the evaluation results are shown in Table 1. ○: About the same as molten Al-Zn-based plating bath (55 mass% Al-remainder Zn-1.6 mass% bath) △: Compared with the molten Al-Zn-based plating bath (55 mass% Al-the balance Zn-1.6 mass% bath), there are more white oxides ×: Black oxide formation was observed in the plating bath

From the results in Table 1, it can be seen that the samples of the examples of the present invention have a good balance in terms of corrosion resistance, surface appearance, processability and bath stability compared with the samples of the comparative examples.

<Example 2: Samples 1 to 112> (1) Using a cold-rolled steel sheet with a thickness of 0.8mm produced by a common method as a base steel sheet, annealing treatment and plating treatment were performed with a hot-dip plating simulator manufactured by RHESCA Co., Ltd. , Prepare hot-dip coated steel sheet samples with the coating film conditions shown in Tables 3 and 4. Also, regarding the composition of the coating bath used in the manufacture of hot-dip-coated steel sheets, the composition of the coating bath was Al: 30 to 75% by mass, Si: 0.5% so that the coating film composition of each sample shown in Table 2 ~4.5% by mass, Mg: 0 to 10% by mass, and Sr: 0.00 to 0.15% by mass are varied in various ways. In addition, the bath temperature of the plating bath is set at 590°C when Al: 30-60% by mass, and at 630°C when Al: more than 60% by mass, and the temperature of the plated immersion plate of the base steel plate is controlled to match the temperature of the plating bath same. In addition, the plating process was performed under the condition that the plate temperature was cooled to within a temperature range of 520 to 500° C. within 3 seconds. In addition, the adhesion amount of the plating film is controlled to be 85±5g/m ² per side for samples 1~82 and 95~112, and 51~125g/m ² for each side of samples 83~94. . (2) Subsequently, on the coating film of each sample of the prepared hot-dip steel plate, the chemical conversion treatment solution was coated with a bar coater, and dried in a hot air furnace (heating rate: 60°C/s, PMT: 120 °C) to form a chemical conversion film, and each sample of the surface-treated steel sheet shown in Tables 3 and 4 was produced. In addition, the chemical conversion treatment liquid system prepared surface treatment liquids A to F in which each component was dissolved in water as a solvent. The types of components (resin, metal compound) contained in the surface treatment liquid are as follows. (Resin) Urethane resin: SUPERFLEX 130, SUPERFLEX 126 (Daiichi Kogyo Pharmaceutical Co., Ltd.) Acrylic resin: BONCOAT EC-740EF (DIC Co., Ltd.) (Metal compound) P compound: Aluminum dihydrogen tripolyphosphate Si compound: Silicon oxide V compound: Sodium metavanadate Mo compound: Molybdate Zr compound: Potassium zirconium carbonate Table 2 shows the composition of the prepared chemical conversion treatment solutions A~F and the adhesion amount of the formed chemical conversion film. In addition, the concentration of each component in Table 2 of this specification is a solid content concentration (mass %).

(evaluate) The following evaluations were performed on each sample of the hot-dip-coated steel sheet and the surface-treated steel sheet obtained as described above. The evaluation results are shown in Table 3 and Table 4.

(1) Composition of the plating film (adhesion amount, composition, X-ray diffraction intensity) For each sample of the hot-dip plated steel sheet, punch 100mmφ, seal the non-measurement surface with tape, and use hydrochloric acid as shown in JIS H 0401:2013 The mixed solution with hexamethylenetetramine dissolves and strips the plating, and the adhesion amount of the plating film is calculated from the poor quality of the sample before and after stripping. Tables 3 and 4 show the calculation results and the deposition amount of the obtained plating film. Then, the stripping solution was filtered, and the filtrate and solid content were analyzed respectively. Specifically, the filtrate was analyzed by ICP emission spectroscopy to quantify components other than insoluble Si. And, after the solid content was dried and ashed in a heating furnace at 650°C, sodium carbonate and sodium tetraborate were added to dissolve it. Furthermore, the melt was dissolved with hydrochloric acid, and the dissolved liquid was analyzed by ICP emission spectroscopy to quantify insoluble Si. The Si concentration in the plating film is the sum of the soluble Si concentration obtained by the filtrate analysis and the insoluble Si concentration obtained by the solid content analysis. Tables 3 and 4 show the calculation results and the composition of the obtained plating film. Furthermore, after each sample was cut into a size of 100mm×100mm, the plated film on the evaluation symmetry plane was mechanically cut until the base steel plate was exposed, and after the obtained powder was fully mixed, 0.3g was taken out and used an X-ray diffraction device (RIGAKU Co., Ltd. Co., Ltd. "SmartLab"), X-rays used: Cu-Kα (wavelength = 1.54178Å), removal of kβ rays: Ni filter, tube voltage: 40kV, tube current: 30mA, scanning speed: 4˚/min, sampling Interval: 0.020°, Divergent slit: 2/3°, Parallel slit: 5°, Detector: High-speed one-dimensional detector (D/teX Ultra) for qualitative analysis of the above powder. The intensity obtained by subtracting the base intensity from each peak intensity is taken as each diffraction intensity (cps), and the diffraction intensity of the (111) plane (plane spacing d=0.3668nm) of Mg ₂ Si and the (111) plane (plane) of Si are measured. Interval d = 0.3135nm) diffraction intensity. The measurement results are shown in Tables 3 and 4.

(2) Corrosion resistance evaluation For each sample of the hot-dip coated steel sheet and the surface-treated steel sheet, after cutting it into a size of 120mm×120mm, separate the range of 10mm from each edge of the evaluation object surface and the end surface of the sample and the non-evaluation surface It was sealed with tape and the surface to be evaluated was exposed in a size of 100mm×100mm, and used as an evaluation sample. In addition, three samples of the same sample were produced for this evaluation. For the three samples for evaluation produced as described above, the corrosion acceleration test was implemented in the cycle shown in FIG. 1 . The corrosion acceleration test starts from wetting, and after 300 cycles, the corrosion loss of each sample is measured by the method described in JIS Z 2383 and ISO8407, and the evaluation is based on the following criteria. The evaluation results are shown in Tables 3 and 4. ◎: Corrosion loss of 3 samples is less than 30g/m ² ○: Corrosion loss of 3 samples is less than 50g/m ² ×: Corrosion loss of more than 1 sample exceeds 50g/m ²

(3) White rust resistance For each sample of hot-dip-coated steel sheet and surface-treated steel sheet, after cutting it into a size of 120mm×120mm, seal the range of 10mm from each edge of the evaluation object surface and the end surface of the sample and the non-evaluation object surface with tape, and seal the evaluation The state where the object surface was exposed in a size of 100mm×100mm was used as a sample for evaluation. Using the above-mentioned samples for evaluation, the salt spray test described in JIS Z 2371 was implemented for 90 hours, and the following criteria were used for evaluation. The evaluation results are shown in Tables 3 and 4. ◎: No white rust on flat plate ○: The occurrence area of white rust on the flat plate is less than 10% ×: More than 10% of the area of white rust on the flat plate

(4) Surface appearance For each sample of the hot-dip-coated steel sheet, the surface of the plating film was observed visually. Next, the observation results were evaluated according to the following criteria. The evaluation results are shown in Tables 3 and 4. ◎: Wrinkle-like defects were not observed at all ○: Wrinkle defects are only observed within 50mm from the edge ×: Wrinkle defects observed outside the range of 50mm from the edge

(5) Processability For each sample of the hot-dip galvanized steel sheet, after cutting it to a size of 70mm×150mm, sandwich 8 sheets of the same thickness inside and perform 180˚ bending (8T bending). After bending, apply SELLOTAPE (registered trademark) glass tape strongly to the outer surface of the bent part and peel it off. Visually observe the surface state of the plating film on the outer surface of the bent portion and the presence or absence of plating film adhesion (peeling) on the surface of the tape, and evaluate the processability according to the following criteria. The evaluation results are shown in Tables 3 and 4. ○: No cracking or peeling was observed on the plating film △: Cracks were observed in the plating film, but no peeling was observed ×: Cracks and peeling were observed on the plating film at the same time

(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 in the production of molten Al-Zn-based plated steel sheet (bath surface without Mg oxide). The evaluation was performed based on the following criteria, and the evaluation results are shown in Tables 3 and 4. ○: About the same as molten Al-Zn-based plating bath (55 mass% Al-remainder Zn-1.6 mass% bath) △: Compared with the molten Al-Zn-based plating bath (55 mass% Al-the balance Zn-1.6 mass% bath), there are more white oxides ×: Black oxide formation was observed in the plating bath

From the results in Tables 3 and 4, it can be seen that the samples of the examples of the present invention are well-balanced in corrosion resistance, white rust resistance, surface appearance, processability and bath stability compared with the samples of the comparative examples. Also, as can be seen from the results in Table 4, the white rust resistance of the samples subjected to chemical conversion treatments A to D showed particularly excellent results.

<Example 3: Samples 1 to 44> (1) Using a cold-rolled steel sheet with a thickness of 0.8mm manufactured by a common method as a base steel sheet, annealing treatment and plating treatment were performed with a hot-dip plating simulator manufactured by RHESCA Co., Ltd. , The hot-dip-coated steel sheet samples of the coating film conditions shown in Table 6 were prepared. Also, regarding the composition of the coating bath used in the manufacture of hot-dip-coated steel sheets, the composition of the coating bath was Al: 30 to 75% by mass, Si: 0.5 ~4.5% by mass, Mg: 0 to 10% by mass, and Sr: 0.00 to 0.15% by mass are varied in various ways. In addition, the bath temperature of the plating bath is set at 590°C when Al: 30-60% by mass, and at 630°C when Al: more than 60% by mass, and the temperature of the plated immersion plate of the base steel plate is controlled to match the temperature of the plating bath same. In addition, the plating process was performed under the condition that the plate temperature was cooled to within a temperature range of 520° C. to 500° C. within 3 seconds. In addition, the adhesion amount of the plating film is controlled at 85±5g/m ² per side for samples 1~41, and 42~125 g/m ² per side for samples 42~44.

(2) Subsequently, the chemical conversion treatment solution shown in Table 5 was coated with a bar coater on the coating film of each sample of the prepared hot-air-dried steel sheet, and dried in a hot-air drying oven (attained plate temperature: 90 ℃), forming a chemical conversion treatment film with an adhesion amount of 0.1g/m ² . In addition, the chemical conversion treatment solution used is a chemical conversion treatment solution having a pH of 8 to 10 prepared by dissolving each component in water as a solvent. The types of components (resin components, inorganic compounds) contained in the chemical conversion treatment liquid are as follows. (Resin component) Resin A: (a) an anionic polyurethane resin having an ester bond ("SUPERFLEX 210" manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.) and (b) an epoxy resin having a bisphenol skeleton ( Yoshimura Oleochemical Co., Ltd. "YUKA RESIN RE-1050") is mixed with a mass ratio (a):(b)=50:50 resin B: acrylic resin (DIC Co., Ltd. "BONCOAT EC-740EF") (Inorganic compound) Vanadium compound: Organic vanadium compound chelated with acetylacetone Zirconium compound: Ammonium zirconium carbonate Fluorine compound: Ammonium fluoride

(3) Then, on the chemical conversion film formed as above, apply a primer with a bar coater, and bake the steel plate at a temperature of 230°C and a baking time of 35 seconds to form Indicates the composition of the primer coating film. Subsequently, on the primer coating film formed as above, apply the top coating composition with a bar coater, and bake the steel plate under the conditions of reaching the temperature of 230 ° C ~ 260 ° C and the baking time of 40 seconds to form The top coating film having the resin conditions and film thicknesses shown in Table 5 was used to prepare coated steel sheets for each sample. Also, the primer was obtained by mixing the components and then stirring them with a ball mill for about 1 hour. The following resin components and inorganic compounds constituting the primer coating film were used. (resin component) Resin α: Urethane-modified polyester resin (obtained by reacting 455 parts by mass of polyester resin and 45 parts by mass of isophorone diisocyanate, resin acid value 3, number average molecular weight 5,600, The hydroxyl value is 36) to be hardened with blocked isocyanate. Also, the urethane-modified polyester resin was produced under the following conditions. Feed 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 cyclohexane into a flask equipped with a mixer, a distillation tower, a water separator, a cooling pipe, and a thermometer Dimethanol, heating and stirring, while distilling the generated condensation water out of the system, at a certain speed for 4 hours from 160 ° C to 230 ° C, after reaching the temperature of 230 ° C, slowly add 20 parts by mass of xylene, with the temperature Continue the condensation reaction at 230°C, terminate the reaction when the acid value is 5 or less, cool to 100°C, add 120 wt. parts, 100 parts by mass of butyl cellosolve to obtain a polyester resin solution. Resin β: Urethane cured polyester resin ("EVERCLAD 4900" manufactured by Kansai Paint Co., Ltd.) (inorganic compound) Vanadium compound: magnesium vanadate Phosphate Compound: Calcium Phosphate Magnesium Oxide Compound: Magnesium Oxide And the following paints are used for the resin used for the top coating film. Resin I: Melamine hardened polyester paint ("Precolor HD0030HR" manufactured by BASF JAPAN Co., Ltd.) Resin II: Polyvinylidene fluoride and acrylic resin with a mass ratio of 80:20 organosol firing type fluororesin coating (BASF JAPAN Co., Ltd. "PRECOLOR No. 8800HR")

(evaluate) The following evaluations were performed on each sample of the coated steel sheet obtained as described above. The evaluation results are shown in Table 6.

(1) Composition of the plating film (adhesion amount, composition, X-ray diffraction intensity) For each sample of the hot-dip plated steel sheet, punch 100mmφ, seal the non-measurement surface with tape, and use hydrochloric acid as shown in JIS H 0401:2013 The mixed solution with hexamethylenetetramine dissolves and strips the plating, and the adhesion amount of the plating film is calculated from the poor quality of the sample before and after stripping. Table 6 shows the calculation results and the deposition amount of the obtained plating film. Then, the stripping solution was filtered, and the filtrate and solid content were analyzed respectively. Specifically, the filtrate was analyzed by ICP emission spectroscopy to quantify components other than insoluble Si. And, after the solid content was dried and ashed in a heating furnace at 650°C, sodium carbonate and sodium tetraborate were added to dissolve it. Furthermore, the melt was dissolved with hydrochloric acid, and the dissolved liquid was analyzed by ICP emission spectroscopy to quantify insoluble Si. The Si concentration in the plating film is the sum of the soluble Si concentration obtained by the filtrate analysis and the insoluble Si concentration obtained by the solid content analysis. Table 6 shows the calculation results and the composition of the obtained plating film. Furthermore, after each sample was cut into a size of 100mm×100mm, the plated film on the evaluation symmetry plane was mechanically cut until the base steel plate was exposed, and after the obtained powder was fully mixed, 0.3g was taken out and used an X-ray diffraction device (RIGAKU Co., Ltd. Co., Ltd. "SmartLab"), X-rays used: Cu-Kα (wavelength = 1.54178Å), removal of kβ rays: Ni filter, tube voltage: 40kV, tube current: 30mA, scanning speed: 4˚/min, sampling Interval: 0.020°, Divergent slit: 2/3°, Parallel slit: 5°, Detector: High-speed one-dimensional detector (D/teX Ultra) for qualitative analysis of the above powder. The intensity obtained by subtracting the base intensity from each peak intensity is taken as each diffraction intensity (cps), and the diffraction intensity of the (111) plane (plane spacing d=0.3668nm) of Mg ₂ Si and the (111) plane (plane) of Si are measured. Interval d = 0.3135nm) diffraction intensity. The measurement results are shown in Table 6.

(2) Evaluation of corrosion resistance For each sample of the coated steel plate, after cutting it into a size of 120mm×120mm, seal the range of 10mm distance from the edge of the three sides arbitrarily selected from the evaluation object surface and the end surface of the same three sides of the sample and the non-evaluation surface with tape. The state where the surface to be evaluated was exposed in a size of 100 mm×100 mm was used as a sample for evaluation. In addition, three samples of the same sample were produced for this evaluation. For the three samples for evaluation produced as described above, the corrosion acceleration test was implemented in the cycle shown in FIG. 1 . The corrosion promotion test starts from wetness, takes out samples every 20 cycles, washes and dries, and then visually observes to confirm the occurrence of red rust on the cut end surface of one side that is not sealed by tape. Next, the number of cycles when red rust was confirmed was evaluated based on the following criteria. The evaluation results are shown in Table 6. ◎: 3 samples with red rust cycle number ≧ 600 cycles ○: 600 cycles > 3 samples with red rust ≧ 500 cycles ×: The number of red rust occurrence cycles of at least 1 sample <500 cycles

(3) Appearance after painting For each sample of the coated steel sheet, the surface was observed visually. Next, the observation results were evaluated according to the following criteria. The evaluation results are shown in Table 6. ◎: Wrinkle-like defects were not observed at all ○: Wrinkle defects are only observed within 50mm from the edge ×: Wrinkle defects observed outside the range of 50mm from the edge

(4) Machinability after painting For each sample of the coated steel plate, after cutting it to a size of 70mm×150mm, insert 8 plates of the same plate thickness inside and perform 180˚ bending (8T bending). After bending, stick SELLOTAPE (registered trademark) glass tape on the outer surface of the bent part strongly and peel it off. Visually observe the surface state of the coating film on the outer surface of the curved part and the presence or absence of coating film adhesion (peeling) on the surface using the tape, and evaluate the processability according to the following criteria. The evaluation results are shown in Table 6. ○: No cracking or peeling was observed on the plating film △: Cracks were observed in the plating film, but no peeling was observed ×: Cracks and peeling were observed on the plating film at the same time

(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 in the production of molten Al-Zn-based plated steel sheet (bath surface without Mg oxide). The evaluation was performed based on the following criteria, and the evaluation results are shown in Table 6. ○: About the same as molten Al-Zn-based plating bath (55 mass% Al-remainder Zn-1.6 mass% bath) △: Compared with the molten Al-Zn-based plating bath (55 mass% Al-the balance Zn-1.6 mass% bath), there are more white oxides ×: Black oxide formation was observed in the plating bath

From the results in Table 6, it can be seen that the samples of the examples of the present invention are well-balanced in corrosion resistance, appearance after painting, workability after painting, and bath stability compared with the samples of the comparative examples. [Industrial availability]

According to the present invention, it is possible to provide a molten Al-Zn-Si-Mg plated steel sheet which is stable and has excellent corrosion resistance. Also, according to the present invention, a stable surface-treated steel sheet having excellent corrosion resistance and white rust resistance can be provided. Furthermore, according to the present invention, a stable coated steel sheet having excellent corrosion resistance and processed portion corrosion resistance can be provided.

[FIG. 1] It is a figure for explaining the flow of the combined cycle test (JASO-CCT) of Japanese automobile standard.

Claims (8)

A molten Al-Zn-Si-Mg plated steel sheet, which is a molten Al-Zn-Si-Mg plated steel sheet provided with a plated film, characterized in that the plated film has the following composition: containing Al: 45 ~65% by mass, Si: 1.0~4.0% by mass and Mg: 1.0~10.0% by mass, and the rest is composed of Zn and unavoidable impurities. Si and Mg ₂ Si in the aforementioned plating film are detected by X-ray diffraction The diffraction intensity of the method satisfies the following relationship (1), Si(111)/Mg ₂ Si(111)≦0.8...(1) Si(111): (111) plane of Si (plane spacing d=0.3135nm) The diffraction intensity of Mg ₂ Si (111): the diffraction intensity of the (111) plane (plane spacing d=0.3668nm) of Mg ₂ Si. Such as the molten Al-Zn-Si-Mg plated steel sheet of claim 1, wherein the diffraction intensity of the aforementioned Si in the aforementioned plated film satisfies the following relationship (2) by the X-ray diffraction method, Si(111)= 0...(2). The molten Al-Zn-Si-Mg plated steel sheet according to claim 1 or 2, wherein the plated film further contains Sr: 0.01 to 1.0% by mass. The molten Al-Zn-Si-Mg plated steel sheet according to claim 1 or 2, wherein the Al content in the above-mentioned plated film is 50 to 60% by mass. The molten Al-Zn-Si-Mg plated steel sheet according to claim 1 or 2, wherein the Si content in the above-mentioned plated film is 1.0 to 3.0% by mass. The molten Al-Zn-Si-Mg plated steel sheet according to claim 1 or 2, wherein the Mg content in the above-mentioned plated film is 1.0 to 5.0% by mass. A surface-treated steel sheet, which is a surface-treated steel sheet provided with a plated film according to any one of Claims 1 to 6 and a chemical conversion film formed on the plated film, wherein the chemical conversion film contains Oxygen resins, urethane resins, acrylic resins, acrylic silicone resins, alkyd resins, polyester resins, polyalkylene resins, amino resins, and fluororesins, and at least one resin selected from P compounds and Si compounds , Co compound, Ni compound, Zn compound, Al compound, Mg compound, V compound, Mo compound, Zr compound, Ti compound and Ca compound at least one metal compound. A coated steel plate, which is a coated steel plate that forms a coating film directly or through a chemical conversion film on the plated film according to any one of claims 1 to 6, characterized in that the chemical conversion film contains: a resin component, It contains a total of 30~50% by mass of (a): anionic polyurethane resin with ester bond and (b): epoxy resin with bisphenol skeleton, and the (a) and (b) The content ratio ((a):(b)) is in the range of 3:97~60:40 by mass ratio; and inorganic compounds, which include 2~10% by mass of vanadium compounds, 40~60% by mass of zirconium compounds and 0.5~5% by mass of fluorine compound, the above-mentioned 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 .

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