TW202225425A - Hot dipped Al-Zn-Si-Mg-Sr coated steel sheet, surface-treated steel sheet, and coated steel sheet - Google Patents

Abstract

The purpose of the present invention is to provide a hot dipped Al-Zn-Si-Mg-Sr coated steel sheet which stably exhibits excellent corrosion resistance, while having good surface appearance. In order to achieve the above-described purpose, the present invention provides a hot dipped Al-Zn-Si-Mg-Sr coated steel sheet which has a coating film and is characterized in that: the coating film has a composition that contains from 45% by mass to 65% by mass of Al, from 1.0% by mass to 4.0% by mass of Si, from 1.0% by mass to 10.0% by mass of Mg and from 0.01% by mass to 1.0% by mass of Sr, with the balance being made up of Zn and unavoidable impurities; and the diffraction intensities of Si and Mg2Si in the coating film as determined by an X-ray diffraction method satisfy the relational expression (1) below. (1): Si (111)/Mg2Si (111) ≤ 0.8.

Description

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

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

Molten Al-Zn-based plated steel sheets represented by 55% Al-Zn-based steel sheets are known to exhibit high corrosion resistance in hot dip galvanized steel sheets because they can have both sacrificial corrosion resistance of Zn and 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 and walls exposed to the outdoors for a long time, and in the field of civil engineering such as guardrails, wiring pipes, and sound insulation walls. In particular, the demand for materials with excellent corrosion resistance in harsher operating environments, such as acid rain caused by air pollution, or the distribution of snow-melting agents for road antifreeze in snow-covered areas, and development in coastal areas, or for materials that do not require maintenance has increased in recent years. , the demand for molten Al-Zn plated steel sheets has increased.

The characteristic of the coating film of the molten Al-Zn-based plated steel sheet is that the supersaturated Al containing Zn solidifies into a dendritic part (α-Al phase) and the Zn-Al existing in the inter-dendrite. Constituted by the crystal structure, the α-Al phase is laminated in the thickness direction of the plated film. Therefore, the characteristic film structure complicates the path of corrosion from the surface, so that corrosion does not progress easily. It is also known that molten Al-Zn-based plated steel sheets can achieve molten zinc plating with the same thickness as the plated film. The steel plate has more excellent corrosion resistance.

With regard to such a molten Al-Zn-based plated steel sheet, an attempt has been made to further prolong the life, and a molten Al-Zn-Si-Mg-Sr-based plated steel sheet to which Mg has been added has been put into practical use. As such a molten Al-Zn-Si-Mg-Sr-based plated steel sheet, for example, Patent Document 1 discloses a molten Al-Zn-Si-Mg-Sr-based plated steel sheet in which a plated film contains a Al-Zn-Si alloy of Mg, 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, the concentration of Mg 1 to 5% by weight. In addition, Patent Document 2 discloses a molten Al-Zn-Si-Mg-Sr-based plated steel sheet, the purpose of which is that the plated film contains 2 to 10% of Mg and 0.01 to 10% of Ca. As described above, the corrosion resistance is improved, and the protective effect after the base steel sheet is exposed is improved. Furthermore, Patent Document 3 discloses a molten Al-Zn-Si-Mg-Sr-based plated steel sheet which, in mass %, contains Mg: 1 to 15%, Si: 2 to 15%, and Zn: 11 to 11% by mass. 25%, and the rest of the coating layer is composed of Al and unavoidable impurities. By making the size of the Mg ₂ Si phase or the intermetallic compound equal to MgZn ₂ in the plated film to be 10 μm or less, the flat plate and the end face are realized. Improved corrosion resistance.

The above-mentioned molten Al-Zn-based plated steel sheet has a beautiful appearance with white metallic luster and bright crystal pattern, so it is mostly used without coating, and the actual situation is that the requirements for its appearance are still strong. 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-Sr-based plated steel sheet in which wrinkle-like irregularity defects 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-Sr-based plated steel sheet in which plaque defects are suppressed by containing 500 to 3000 ppm of Sr in the plated film. Revealing techniques for trying to see improvements. For example, Patent Document 4 discloses a molten Al-Zn-Si-Mg-based plated steel sheet in which wrinkle-like irregularity defects are suppressed by containing 0.01 to 10% of Sr in the plated film. Furthermore, 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-based plated steel sheet which has surface appearance and corrosion resistance of flat and processed parts by containing 0.001 to 1.0% of Sr in the plated film. Furthermore, 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. Furthermore, Patent Document 9 discloses a molten Al-Zn-Si-Mg-based plated steel sheet having improved corrosion resistance by controlling the Si and Mg concentrations in the plated film at a specific ratio.

In addition, regarding the above-mentioned molten Al-Zn-based plated steel sheet, when used in a severe corrosive environment, there is a problem that white rust occurs along with corrosion of the plated film. Since this white rust causes a reduction in the appearance of the steel sheet, development of a plated steel sheet for improving the white rust resistance has been carried out. 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 a plated steel sheet. In addition, Patent Document 11 discloses that the blackening resistance and the white rust resistance are improved by forming a chemical conversion coating containing a urethane resin on the coating coating of the molten Al-Zn-Si-Mg-based plated steel sheet. technology.

In addition, the coated steel sheet with the chemical conversion film, the primer coating film, the top coating film, etc. formed on the surface of the molten Al-Zn-based coated steel sheet is required to be subjected to pressure forming, roll forming, or embossing forming as described above. Various processing such as 90-degree bending or 180-degree bending requires long-term coating durability. In order to meet these requirements, it is known that a chemical conversion film containing chromate is formed on a molten Al-Zn-based plated steel sheet, and a chromate-based rust preventive pigment is also contained in the primer coating film, and a thermosetting coating is formed thereon. Coated steel sheet for top coating film with excellent weather resistance such as polyester-based resin coating film or fluorine-based resin coating film. However, with these recently painted steel sheets, the use of chromates, which are environmentally harmful substances, is regarded as a problem, and development of painted steel sheets that can improve corrosion resistance or surface appearance even without chromate is strongly desired. As a technique for responding to these demands, for example, Patent Document 12 discloses a surface treatment hot-dip plated steel material in which Al, Zn, Si, and Mg are plated on the surface of the steel material and aluminum and zinc whose contents are adjusted for these elements are plated. Alloy plating layer (α), and as an upper layer, a film (β) containing at least one compound (A) selected from titanium compounds and zirconium compounds as a film-forming component, and an aluminum-zinc alloy plating layer (α) The mass ratio of the Si-Mg phase to the total amount of Mg in the plating layer is adjusted to be 3% or more. [Prior Art Literature] [Patent Literature]

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 Patent 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 Application Laid-Open No. 2019-155872 Patent Document 12: Japanese Patent Laid-Open No. 2005-169765

[The problem to be solved by the invention]

However, as disclosed in Patent Documents 1 to 3, the technique of adding Mg to the plated film does not necessarily improve corrosion resistance remarkably. The molten Al-Zn-Si-Mg-Sr-based plated steel sheets disclosed in Patent Documents 1 to 3 achieve an improvement in corrosion resistance only by including Mg in the plated components. The characteristics of the inter-compound phase are not considered, and the corrosion resistance cannot be discussed in a general way. Therefore, even when the molten Al-Zn-Si-Mg-Sr-based plated steel sheet is produced using the same plating bath composition, the corrosion resistance is different when the corrosion promotion test is carried out. Compared with the Al-Zn-based plating without Mg addition Steel plates are not necessarily dominant, but there are problems. Similarly, in improving the appearance of plating, the addition of Sr to the plating film may not necessarily be interpreted as eliminating the wrinkle-like unevenness defect. The molten Al-Zn-Si-Mg-Sr-based plated steel sheets disclosed in Patent Documents 4 to 8 , and there are cases where both corrosion resistance and appearance cannot be achieved.

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, Mg ₂ Si phase, MgZn ₂ phase, and Si phase are also precipitated in the plated film. . However, the effect of the precipitation amount or the existence ratio of each phase on the corrosion resistance is not known. The molten Al-Zn-Si-Mg-based plated steel sheet disclosed in Patent Document 9 achieves improvement in corrosion resistance by controlling the concentration of Si and Mg at a specific ratio so that no Si phase is precipitated in the plated film. It is said that the Si phase is inevitably suppressed, and even when the formation of the Si phase in the plated film can be suppressed, there are cases where excellent corrosion resistance cannot be obtained, etc., which is technically incomplete.

In addition, with regard to white rust resistance, sufficient improvement cannot be achieved by any technology. Regarding the molten Al-Zn-Si-Mg-based plated steel sheet of Patent Document 10, although it is described that the white rust resistance of the processed part and the heated flat part is improved, the white rust resistance of the unheated flat part is not Considering that, achieving stable white rust resistance is still a problem. In addition, 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, but also further improvement is desired.

In addition, as mentioned above, the coated steel sheet is required to have long-term coating film durability in a state where various processes such as 90-degree bending or 180-degree bending are performed by press forming, roll forming, embossing, etc., but The technique of Patent Document 12 does not necessarily and stably obtain the corrosion resistance and surface appearance after processing. It goes without saying that the corrosion resistance of the coated steel sheet affects the corrosion resistance of the base coated steel sheet. Regarding the surface appearance, the unevenness of the wrinkle defects reaches several tens of μm, so even if the surface is smoothed by the coating film Even if it is changed, the unevenness cannot be completely eliminated, and it is considered that it cannot be expected to improve the appearance as a coated steel sheet. In addition, since the coating film becomes thinner in the convex portion, there is also a concern that the local corrosion resistance is lowered. Therefore, in order to obtain a coated steel sheet having excellent corrosion resistance and surface appearance, it is important to improve the corrosion resistance and surface appearance of the underlying coated steel sheet.

In view of the above-mentioned circumstances, an object of the present invention is to provide a molten Al-Zn-Si-Mg-Sr-based plated steel sheet which is stable and has excellent corrosion resistance and good surface appearance. And the objective of this invention is to provide the surface-treated steel sheet which is stable and has excellent corrosion resistance and white rust resistance. Furthermore, the objective of this invention is to provide the painted steel sheet which is stable and has excellent corrosion resistance and corrosion resistance of a processed part. [means to solve the problem]

As a result of intensive research to solve the above problems, the present inventors have found that the Mg ₂ Si phase, the MgZn ₂ phase and the Si phase formed in the plated film of the molten Al-Zn-Si-Mg-Sr-based plated steel sheet, Depending on the balance of the components in the plated film or the formation conditions of the plated film, the amount of precipitation is increased or decreased to make the ratio change. Depending on the balance of the composition, a certain phase may not be precipitated. Furthermore, it was found that the corrosion resistance of molten Al-Zn-Si-Mg-Sr-based plated steel sheet varies with the existence ratio of these phases, and the corrosion resistance is stabilized especially when the Si phase is less than the Mg ₂ Si phase. improve. However, it is known that these Mg ₂ Si phases and Si phases are not observed even if a secondary electron image or a reflected electron image, etc. is performed on the plated film from the surface or cross-section using a general method such as a scanning electron microscope. It is very difficult to tell the difference between the phases. As a method for more detailed analysis, microscopic information can be obtained by observation using a transmission electron microscope, but the existence ratio of Mg ₂ Si and Si phases, which influence macroscopic information on corrosion resistance and appearance, cannot be grasped. Therefore, as a result of further active research by the present inventors, it was found that by focusing on the X-ray diffraction method, the existence ratio of the phase can be quantified by using the intensity ratio of the specific diffraction peaks of the Mg ₂ Si phase and the Si phase. In addition, When the Mg ₂ Si phase and the Si phase in the plated film satisfy a specific existence ratio, stable and excellent corrosion resistance can be realized. Furthermore, the present inventors have also found that by controlling the Sr concentration in the bath after controlling the presence ratio of the Mg ₂ Si phase and Si in the molten Al-Zn-Si-Mg-Sr-based plated steel sheet, the concentration of Sr in the bath can be reliably suppressed. The occurrence of wrinkle-like irregularity 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 forming the chemical conversion film with a specific resin and a specific metal compound And anti-rust effect, etc., and improve the stability of white rust resistance.

Furthermore, the present inventors also examined the chemical conversion film and the 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, the primer coating film is composed of It is composed of a specific polyester resin and an inorganic compound, which can improve the barrier properties and adhesion of the coating film, and can achieve excellent corrosion resistance after processing even if it is chromate-free.

The present invention has been completed based on the above findings, and the gist is as follows. 1. A fused Al-Zn-Si-Mg-Sr system plated steel sheet, which is a fused Al-Zn-Si-Mg-Sr system plated steel sheet with a plated film, characterized in that the aforementioned plated film has the following Composition: Contains Al: 45 to 65 mass %, Si: 1.0 to 4.0 mass %, Mg: 1.0 to 10.0 mass %, and Sr: 0.01 to 1.0 mass %, and the rest is composed of Zn and inevitable impurities. The above-mentioned plating The diffraction intensity of Si and Mg ₂ Si in the film by X-ray diffraction satisfies the following relationship (1), Si(111)/Mg ₂ Si(111)≦0.8…(1) Si(111): Si(111) Diffraction intensity of the (111) plane (interplane spacing d=0.3135 nm), Mg ₂ Si (111): diffraction intensity of the (111) plane (interplane spacing d=0.3668 nm) of Mg ₂ Si.

2. The molten Al-Zn-Si-Mg-Sr system plated steel sheet of the aforementioned 1, wherein the Si in the aforementioned coating film satisfies the following relation (2) by the diffraction intensity of the X-ray diffraction method, Si(111)=0…(2), Si(111): Diffraction intensity of the (111) plane of Si (plane spacing d=0.3135 nm).

3. The molten Al-Zn-Si-Mg-Sr-based plated steel sheet according to 1 or 2 above, wherein the Al content in the plated film is 50 to 60% by mass.

4. The molten Al-Zn-Si-Mg-Sr-based plated steel sheet according to any one of 1 to 3 above, wherein the Si content in the plated film is 1.0 to 3.0 mass %.

5. The molten Al-Zn-Si-Mg-Sr-based plated steel sheet according to any one of 1 to 4 above, wherein the Mg content in the plated film is 1.0 to 5.0 mass %.

6. A surface-treated steel sheet, which is provided with the surface-treated steel sheet of the plated film as any one of the aforementioned 1 to 5 and the chemical conversion film formed on the plated film, characterized by the following: 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. At least one metal compound selected from the group consisting of P compound, Si compound, Co compound, Ni compound, Zn compound, Al compound, Mg compound, V compound, Mo compound, Zr compound, Ti compound and Ca compound.

7. A coated steel sheet, it is on the coating film as any one of the aforementioned 1 to 5, the coated steel sheet that forms a coating film directly or via a chemical conversion film, is characterized in that The chemical conversion film contains: a resin component containing in total 30 to 50% by mass of (a): an anionic polyurethane resin having an ester bond and (b): an epoxy resin having a bisphenol skeleton, and The content ratio ((a):(b)) of the (a) and the (b) is in the range of 3:97 to 60:40 by mass ratio; and an inorganic compound comprising 2 to 10 mass % of a vanadium compound, 40 to 60 mass % of zirconium compounds and 0.5 to 5 mass % of fluorine compounds, 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 containing a vanadium compound, a phosphoric acid compound, and magnesium oxide. [Inventive effect]

According to the present invention, a stable molten Al-Zn-Si-Mg-Sr-based plated steel sheet having excellent corrosion resistance and good surface appearance 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, it is possible to provide a coated steel sheet which is stable and has excellent corrosion resistance and corrosion resistance of processed parts.

(Fused Al-Zn-Si-Mg-Sr-based plated steel sheet)

The molten Al-Zn-Si-Mg-Sr-based plated steel sheet of the present invention is provided with a plated film on the surface of the steel sheet. In addition, the plated film has the following composition: Al: 45 to 65 mass %, Si: 1.0 to 4.0 mass %, Mg: 1.0 to 10.0 mass %, and Sr: 0.01 to 1.0 mass %, and the rest is composed of Zn and unavoidable made of impurities.

The Al content in the plating film is 45 to 65 mass %, preferably 50 to 60 mass %, based on the balance between the corrosion resistance and the work surface. The reason for this is that when the Al content in the plating film is at least 45% by mass, dendritic coagulation of Al occurs, and a plating film structure mainly composed of a dendritic coagulation structure of the α-Al phase can be obtained. By adopting the structure in which the dendritic solidified structure is laminated in the thickness direction of the plating film, the corrosion progression path becomes complicated, and the corrosion resistance of the plating film itself is improved. In addition, the more dendritic parts of the α-Al phase are stacked, the more complicated the corrosion path and the less likely the corrosion reaches the base steel plate. Therefore, in order to improve corrosion resistance, the content of Al is preferably 50 mass % or more. On the other hand, when the Al content in the plated film exceeds 65% by mass, Zn is almost changed into a solid-dissolved structure in α-Al, the dissolution reaction of the α-Al phase cannot be suppressed, and the Al-Zn-Si-Mg - Corrosion resistance of Sr-based plating decreases. Therefore, the Al content in the plating film must be 65 mass % or less, preferably 60 mass % or less.

The main purpose of adding Si in the above-mentioned coating film is to suppress the growth of the Fe-Al-based and/or Fe-Al-Si-based interface alloy layer formed at the interface with the base steel sheet, and prevent the coating film from adhering to the steel sheet. Sexual deterioration. In fact, when a steel sheet is immersed in an Al-Zn-based plating bath containing Si, Fe on the surface of the steel sheet undergoes an alloying reaction with Al or Si in the bath, and Fe-Al-based and / or Fe-Al-Si based intermetallic compound layer, at this time, the Fe-Al-Si based alloy has a slower growth rate than the Fe-Al based alloy, so the higher the ratio of the Fe-Al-Si based alloy, the more inhibited Growth of the entire interface alloy layer. Therefore, the Si content in the plating film needs to be 1.0 mass % or more. On the other hand, when the Si content in the plated film exceeds 4.0 mass %, not only the effect of suppressing the growth of the interface alloy layer is saturated, but also the presence of an excessive Si phase in the plated film promotes corrosion, so the Si content was set to 4.0 %the following. In addition, the Si content in the plated film is preferably 3.0% or less from the viewpoint of suppressing the presence of an excess Si phase. In addition, the content of Si is preferably 1.0 to 3.0 mass % from the viewpoint of easily satisfying the relational expression (1) described later in relation to the Mg content described later.

The said plating film contains 1.0 to 10.0% of Mg. Since Mg is contained in the said plating film, the said Si can exist in the form of the intermetallic _compound of Mg2Si phase, and the promotion of corrosion can be suppressed. Moreover, when Mg is contained in the said plating film, the MgZn ₂ phase of an intermetallic compound is also formed in a plating film, and the effect of further improving corrosion resistance can be acquired. When the Mg content in the plated film is less than 1.0% by mass, Mg is mainly used for the solid solution of the α-Al phase as the main phase due to the formation of the intermetallic compounds (Mg ₂ Si, MgZn ₂ ), so it cannot be used. Ensure adequate corrosion resistance. On the other hand, when the content of Mg in the plated film increases, the effect of improving the corrosion resistance is saturated, and 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 plating film is preferably 5.0 mass % or less from the viewpoint of suppressing the generation of dross at the time of plating formation and facilitating the management of the plating bath. In addition, from the viewpoint of easily satisfying the relational expression (1) described below, the content of Mg is preferably 3.0% by mass in relation to the Si content, and the content of Mg is more preferably 3.0% by mass in consideration of the compatibility with slag suppression. Content is 3.0-5.0 mass %.

Furthermore, in the molten Al-Zn-Si-Mg-Sr-based plated steel sheet of the present invention, the diffraction intensities of Si and Mg ₂ Si in the plated film by X-ray diffraction need to satisfy the following relation (1) . Si(111)/Mg ₂ Si(111)≦0.8…(1) Si(111): Diffraction intensity of the (111) plane of Si (plane spacing d=0.3135nm), Mg ₂ Si(111): Mg ₂ Diffraction intensity of Si (111) plane (plane spacing d=0.3668 nm).

As described above, it is important in the present invention to control the existence ratio of the Mg ₂ Si phase and the Si phase generated in the plating film to a specific ratio by containing Mg and Si. These effects on corrosion resistance are still under investigation and there are still many unknowns, but the following mechanisms are presumed.

When the molten Al-Zn-Si-Mg-Sr-based plated steel sheet is exposed to a corrosive environment, the 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 corrosion products formed are not easily decomposed, and as a result, the protective effect of the plating film is improved. In addition, the effect of improving the protective effect of the plating film is more reliably exhibited when Si does not exist in the Si phase but in the Mg ₂ Si phase in the plating film, 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 the X-ray diffraction method to satisfy the relation (1): Si(111)/Mg2Si ₍ 111) for the ratio of Mg ₂ Si to Si in the plated film. ≤ 0.8, but the ratio of Mg ₂ Si and Si in the plated film does not satisfy the relation (1), that is, when Si(111)/Mg ₂ Si(111)>0.8, the presence of Si in the plated film As a result, the Mg-rich environment cannot be obtained near the corrosion product, and it is difficult to obtain the protective effect of the plating film. From the same viewpoint, the presence ratio of Si to Mg ₂ Si (Si(111)/Mg ₂ Si(111)) is preferably 0.5 or less, more preferably 0.3 or less, and particularly preferably 0.2 or less. In addition, regarding the ratio of Mg ₂ Si to Si in the plated film, it is assumed that the composition of the plated film satisfies the range of the present invention (Al: 45 to 65 mass %, Si: 1.0 to 4.0 mass %, Mg: 1.0 to 1.0 mass %) 10.0 mass % and Sr: 0.01 to 1.0 mass %, and the rest is composed of Zn and inevitable impurities), when the ratio of Mg ₂ Si and Si does not satisfy the relation (1), the present invention cannot be sufficiently obtained. The protective effect of the coating film enhances the effect.

Here, in the aforementioned relation (1), Si(111) is the diffraction intensity of the (111) plane of Si (interplane spacing d=0.3135 nm), and Mg ₂ Si(111) is the (111) plane of Mg ₂ Si ( Diffraction intensity of plane spacing d=0.3668nm). As a method for measuring Si(111) and Mg ₂ Si(111) by the aforementioned X-ray diffraction, a part of the aforementioned plated film can be machined off, and X-ray diffraction can be performed in a powder state (powder X-ray diffraction) measurement method). Regarding the measurement of diffraction intensity, the diffraction peak intensity of Si corresponding to the interplanar spacing d=0.3135 nm and the diffraction peak intensity of Mg ₂ Si corresponding to the interplanar spacing d=0.3668 nm are measured, and by calculating these ratios, it is possible to obtain Si(111)/Mg2Si ₍ 111). In addition, the amount of the plated film (the amount of shaved off the plated film) necessary to perform the powder X-ray diffraction measurement should be 0.1 g from the viewpoint of accurately measuring Si(111) and Mg ₂ Si(111). The above may be sufficient, and 0.3 g or more is preferred. In addition, when the plated film is cut out, steel sheet components other than the plated film may be included in the powder, and these intermetallic compound phases are only contained in the plated film and do not affect the peak strength. In addition, the reason why the above-mentioned plated film is powdered and subjected to X-ray diffraction is that when X-ray diffraction is performed on the plated film formed on the plated steel sheet, the surface orientation of the solidified structure of the plated film is affected, and It is difficult to calculate the correct ratio.

Furthermore, in the molten Al-Zn-Si-Mg-Sr-based plated steel sheet of the present invention, from the viewpoint of improving corrosion resistance more stably, the diffraction intensity of Si in the plated film by the X-ray diffraction method is higher than that of the steel sheet. It is best to satisfy the following relation (2). Si(111)=0…(2) Si(111): Diffraction intensity of the (111) plane of Si (plane spacing d=0.3135 nm). Generally, in the dissolution reaction of Al alloy in aqueous solution, it is known that the Si phase exists as a 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. (2) Generally, there is no film of Si phase (the above-mentioned Si(111) has zero diffraction peak intensity) in order to stabilize the corrosion resistance. In addition, the measurement method of the diffraction peak intensity of the Si (111) plane by X-ray diffraction is as described above.

Here, there is no particular limitation on the method for satisfying the above-mentioned relationship (1) and relationship (2). For example, in order to satisfy the relationship (1) and the relationship (2), by adjusting the balance of the Si content, the Mg content, and the Al content in the plated film, the presence ratio of Mg ₂ Si and Si can be controlled (Mg ₂ Si (111) and the diffraction intensity of Si(111)). In addition, if the balance of Si content, Mg content and Al content in the above-mentioned plated film must be set to a certain content ratio, it is not interpreted as satisfying the relationship (1) and relationship (2), for example, it must be based on the Si content (mass %) ) to change the content ratio of Mg and Al. Furthermore, in addition to adjusting the balance of Si content, Mg content and Al content in the plated film, the conditions during the formation of the plated film (for example, cooling conditions after plating) are adjusted so as to satisfy the relationship (1) and the relationship (2), the diffraction intensity of Mg ₂ Si(111) and Si(111) can also be controlled.

Moreover, in the molten Al-Zn-Si-Mg-Sr-based plated steel sheet of the present invention, the plated film contains 0.01 to 1.0 mass % of Sr. By containing Sr in the said plating film, generation|occurrence|production of surface defects, such as a wrinkle-shaped uneven|corrugated defect, can be suppressed more reliably, and favorable surface appearance can be achieved. In addition, the said wrinkle-like defect is the defect of the wrinkle-shaped unevenness|corrugation formed on the said plating film surface, and white streaks were observed on the said plating film surface. Such wrinkle defects are likely to occur when a large amount of Mg is added to the above-mentioned plated film. Therefore, in the hot-dip plated steel sheet, by containing Sr in the plated film, Sr in the surface layer of the plated 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.

The plating film contains 0.01 to 1.0 mass % of Sr. When the Sr content in the plating film is less than 0.01 mass %, the appearance improvement effect cannot be obtained. When the Sr content in the plating film exceeds 1.0 mass %, the Sr Excessive incorporation into the interface alloy layer adversely affects plating adhesion and the like. From the same viewpoint, the content of Sr in the plated film is preferably 0.05 to 0.5 mass %, more preferably 0.1 to 0.4 mass %. Furthermore, in the molten Al-Zn-Si-Mg-Sr-based plated steel sheet of the present invention, the presence ratio of Si and Mg ₂ Si in the above-mentioned plated film satisfies the relation (1), and the plated film contains 0.01 to 0.01 to 1.0 mass % of Sr. Thereby, the surface appearance improvement effect by the said Sr can be enjoyed more. The reason for this is not clear, but it is presumed that if the amount of Si in the plated film is large, oxidation of the plated surface layer is not easily suppressed after all, and the addition of Sr affects the effect of improving the appearance.

Furthermore, the molten Al-Zn-Si-Mg-Sr-based plated steel sheet of the present invention contains Zn and unavoidable impurities. Among them, the aforementioned inevitable impurities contain Fe. This Fe is unavoidably contained in the plating bath due to dissolution of the steel sheet or equipment in the bath, and is unavoidably contained in the plated film as a result of diffusion and supply from the base steel sheet when the interface alloy layer is formed. The Fe content in the plated film is usually about 0.3 to 2.0 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 excessively contained, it may affect various properties of the plated steel sheet, so the total content is preferably 5.0 mass % or less.

In addition, the above-mentioned plating film preferably further contains 0.01 to 10 mass % in total of 0.01 to 10 mass % selected from the group consisting of Cr, Mn, and V, from the viewpoint of enhancing the stability of corrosion products and exhibiting the effect of delaying corrosion as in the case of the above-mentioned Mg. , one or more of Mo, Ti, Ca, Ni, Co, Sb and B. The reason why the total content of the above components is set to 0.01 to 10% by mass is that a sufficient corrosion retardation effect can be obtained, and the effect is not saturated.

Moreover, it is preferable that the adhesion amount of the said plating film is 45-120 g/m< ² > per single side from a viewpoint of satisfying various characteristics. When the adhesion amount of the plating film is 45 g/m ² or more, sufficient corrosion resistance can be obtained for applications that require long-term corrosion resistance such as building materials, and when the adhesion amount of the plating film is 120 g/m ² or less, it can be It is possible to achieve excellent corrosion resistance while suppressing the occurrence of plating cracks during processing. From the same viewpoint, the adhesion amount of the aforementioned plating film is more preferably 45 to 100 g/m ² .

Regarding the adhesion amount of the above-mentioned plating film, for example, as shown in JIS H 0401:2013, the plating film of a specific area can be peeled off by dissolving the mixed solution of hydrochloric acid and hexamethylenetetramine, and the difference in weight of the steel sheet before and after peeling derived from the calculated method. The plating adhesion amount per single surface can be determined by this method, and can be determined by sealing with a tape so that the plating surface of the non-target surface is not exposed, and then performing the aforementioned dissolution.

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

In addition, the composition of the whole plated film of the molten Al-Zn-Si-Mg-Sr-based plated steel sheet obtained by the present invention is substantially the same as that of the plating bath. Therefore, by controlling the composition of the plating bath, the above-mentioned control of the composition of the plating film can be performed accurately.

Further, the base steel sheet constituting the molten Al-Zn-Si-Mg-Sr-based plated steel sheet of the present invention is not particularly limited, and cold-rolled steel sheets or hot-rolled steel sheets can be appropriately used according to required properties and specifications.

In addition, there is no particular limitation on the method of obtaining the aforementioned base steel sheet. For example, in the case of the above-mentioned hot-rolled steel sheet, a hot-rolling step and a pickling step can be used, and in the case of the aforementioned cold-rolled steel sheet, a cold-rolling step can be further applied and produced. Further, in order to obtain the characteristics of the steel sheet, a recrystallization annealing step or the like may be carried out before the molten plating step.

In addition, the method for producing the molten Al-Zn-Si-Mg-Sr-based plated steel sheet of the present invention is not particularly limited. For example, it can be manufactured by washing, heating, and immersing the said base steel sheet in a plating bath by a continuous hot-dip coating facility. In the heating step of the steel sheet, recrystallization annealing is performed for the purpose of controlling the structure of the base steel sheet itself, and the heating in a reducing environment such as a nitrogen-hydrogen environment is performed in order to prevent the steel sheet from being oxidized and reduce the trace oxide film existing on the surface. efficient.

In addition, as for the coating bath used in the production of the molten Al-Zn-Si-Mg-Sr-based plated steel sheet of the present invention, as described above, since the composition of the above-mentioned coating film is substantially equal to the composition of the coating bath as a whole, Therefore, it is possible to use a compound containing Al: 45 to 65 mass %, Si: 1.0 to 4.0 mass %, Mg: 1.0 to 10.0 mass %, and Sr: 0.01 to 1.0 mass %, and the rest is composed of Zn, Fe and inevitable impurities. constituents.

In addition, the bath temperature of the aforementioned plating bath is not particularly limited, but is preferably within a temperature range of (melting point+20°C) to 650°C. The reason why the lower limit of the bath temperature is set to the melting point + 20°C is that the bath temperature must be above the freezing point in order to perform the fusion plating process, and the reason why the lower limit of the bath temperature is set to the melting point + 20°C is to prevent the local bath temperature of the plating bath from being lowered. Caused by solidification. On the other hand, the reason why the upper limit of the bath temperature is set to 650°C is that if it exceeds 650°C, the plated film becomes difficult to rapidly cool, and the interface alloy layer formed between the plated film and the steel sheet may become thick.

In addition, the temperature of the base steel sheet immersed in the plating bath (immersion temperature) is not particularly limited, but is preferably controlled to be lower than the aforementioned temperature from the viewpoint of ensuring the plating properties during the continuous hot-dip coating operation and preventing the bath temperature from changing. The temperature of the plating bath is within ±20˚C.

In addition, the immersion time of the steel sheet in the above-mentioned plating bath is 0.5 seconds 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 base steel sheet. The upper limit of the immersion time is not particularly limited, but when the immersion time is long, the interface alloy layer formed between the plated film and the steel sheet may become thick, so it is preferably within 8 seconds.

Furthermore, in the cooling process after plating, it is preferable to cool the board temperature from 520 degreeC to 500 degreeC over 3 seconds or more. The precipitation start temperature of the simple Si phase and Mg ₂ Si in the above-mentioned plating film is 500 to 490° C. for the simple Si phase, and 520 to 500° C. for Mg ₂ Si. Therefore, by increasing the residence time in the temperature range of 520 to 500°C for the precipitation of Mg ₂ Si, the precipitation of Mg ₂ Si is accelerated and the precipitation of the single Si phase is suppressed, so that the relationship (1) above is easily satisfied. .

In addition, the molten Al-Zn-Si-Mg-Sr-based plated steel sheet can form a coating film directly or via an intermediate layer on the plated film according to the required properties.

In addition, the method for forming the aforementioned coating film is not particularly limited, and can be appropriately selected according to the required performance. Examples include forming methods such as roll coating, curtain coating, and spray coating. After applying the paint containing the organic resin, it can be heated and dried by means of hot air drying, infrared heating, induction heating, etc. to form a coating film.

Moreover, about the said intermediate layer, if it is a layer formed between the plating film of a hot-dip plated steel sheet, and the said coating film, it will not specifically limit.

(Surface treated steel sheet) The surface-treated steel sheet of the present invention is provided with a plated film on the surface of the steel sheet and a chemical conversion film formed on the plated film. However, the structure of the said plated film is the same as that of the plated film of the molten Al-Zn-Si-Mg-Sr-based 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 above-mentioned plating film. In addition, the chemical conversion film may be formed on at least one side of the surface-treated steel sheet, and may be formed on both sides of the surface-treated steel sheet according to the application or required performance.

Furthermore, in the surface-treated steel sheet of the present invention, the chemical conversion film is characterized by containing epoxy resin, urethane resin, acrylic resin, acrylic silicone resin, alkyd resin, polyester resin, polyalkylene resin , at least one resin selected from the group consisting of P compound, Si compound, Co compound, Ni compound, Zn compound, Al compound, Mg compound, V compound, Mo compound, Zr compound, Ti compound and Ca At least one metal compound in the compound. By forming the above-mentioned chemical conversion film on the plated film, in addition to improving the affinity with the plated film, the chemical conversion film can be uniformly formed on the above-mentioned plated film, and the rust prevention 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 achieved.

Here, from the viewpoint of improving the corrosion resistance, the resin constituting the chemical conversion film is selected from epoxy resins, urethane resins, acrylic resins, acrylic silicone resins, alkyd resins, polyester resins, and polyester resins. At least one of alkylene resin, amine resin and fluororesin. From the same viewpoint, the aforementioned resin preferably contains at least one of a urethane resin and an acrylic resin. Moreover, the resin which comprises the said chemical conversion film also contains the addition polymer of the said resin.

As the above-mentioned epoxy resins, for example, glycidyl-etherified epoxy resins of bisphenol A type, bisphenol F type, and novolac type, epoxy resins of p-bisphenol A type added with propylene oxide, cyclic epoxy resins, etc. can be used. Ethylene oxide or polyalkylene glycol and glycidyl etherified, aliphatic epoxy resin, alicyclic epoxy resin, polyether epoxy resin, and the like.

Regarding the aforementioned urethane resin, for example, oil-modified polyurethane resin, alkyd-based polyurethane resin, polyester-based polyurethane resin, and polyether-based polyamine can be used. Urethane resin, polycarbonate-based polyurethane resin, 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 are exemplified. (or urethane-modified acrylic resin), styrene-acrylic copolymer, etc., and these resins modified by other alkyd resins, epoxy resins, phenol resins, etc. can be used.

As the aforementioned acrylic silicone resin, for example, a curing agent is added to a resin having a hydrolyzable alkoxysilyl group in a side chain or a terminal of an acrylic copolymer serving as a main agent. Furthermore, in the case of using acrylic silicone resin, in addition to corrosion resistance, excellent weather resistance can be expected.

The aforementioned alkyd resins include, for example, oil-modified alkyd resins, rosin-modified alkyd resins, phenol-modified alkyd resins, styrenated alkyd resins, silicon-modified alkyd resins, and acrylic-modified alkyd resins. 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 polyvalent carboxylic acid and a polyhydric alcohol to form an ester bond. As the polyvalent carboxylic acid, for example, terephthalic acid, 2,6-naphthalenedicarboxylic acid, etc. As a polyhydric alcohol, ethylene glycol, 1, 3- propanediol, 1, 4- butanediol, 1, 4- cyclohexane dimethanol, etc. are mentioned, for example. Specifically, the aforementioned polyester is exemplified by polyethylene terephthalate, polypropylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, and the like. And these polyester resins modified by 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, and ethylene-based ionomers. In addition, those resins modified with other alkyd resins, epoxy resins, phenol resins, etc. can be used.

The aforementioned amine-based 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 a viewpoint, it is preferable to use a melamine resin. Although it does not specifically limit as a melamine resin, For example, a butylated melamine resin, a methylated melamine resin, an aqueous melamine resin, etc. are mentioned.

The aforementioned fluororesins include fluoroolefin-based polymers, fluoroolefins and alkyl vinyl ethers, cycloalkyl vinyl ethers, carboxylic acid-modified vinyl esters, hydroxyalkyl allyl ethers, tetrafluoropropyl vinyl ethers, and the like. the copolymer. When these fluororesins are used, not only corrosion resistance, but also excellent weather resistance and excellent hydrophobicity 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 resins (butylated urea resins, etc.), melamine resins (butylated melamine resins, butylated melamine resins, etc.), butylated urea/melamine resins, benzoguanamine resins, and the like can be appropriately used Amine-based resins, blocked isocyanates, oxazoline compounds, phenolic resins, etc.

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

Here, since the P compound is contained 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, those selected from phosphoric acid, dihydrogen phosphate, hydrogen phosphate, phosphate, pyrophosphoric acid, pyrophosphate, tripolyphosphoric acid, tripolyphosphate, phosphorous acid, phosphite, and hypophosphorous acid are preferably used. , one or more of hypophosphite. In addition, as the aforementioned 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. Also, when the aforementioned P compound is a salt, the salt is preferably a salt of an element of Group 1 to Group 13 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 above-mentioned chemical conversion treatment solution containing the P compound is used to coat 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 of the chemical conversion film is carried out. 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 bond between the chemical conversion film and the surface of the plating film becomes firm, and the adhesion of the chemical conversion film is improved. The concentration of the P compound in the chemical conversion treatment liquid is not particularly limited, and can be set to 0.25% by mass to 5% by mass. When the concentration of the above-mentioned P compound is less than 0.25 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. Corrosion resistance and perspiration resistance of the damaged part of the coating film may also decrease. From the same viewpoint, the concentration of the P compound is preferably 0.35 mass % or more, more preferably 0.50 mass % or more. On the other hand, when the concentration of the aforementioned P compound exceeds 5% by mass, not only the life of the chemical conversion treatment solution is shortened, but also the appearance of the film is likely to be uneven, and the amount of P eluted from the chemical conversion film increases, and there is also resistance to blackening. reduce the risk. From the same viewpoint, the concentration of the P compound is preferably 3.5 mass % or less, more preferably 2.5 mass % or less. Regarding the content of the P compound in the chemical conversion film, for example, a chemical conversion treatment solution having a concentration of the P compound of 0.25 mass % to 5 mass % can be applied and dried to allow P to adhere to the chemical conversion film after drying. 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 can uniformly form the chemical conversion film. The aforementioned Si compound is a compound containing Si, and is preferably one or more selected from, for example, silicon oxide, trialkoxysilane, tetraalkylsilane, and a silane coupling agent.

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 silicon oxide, which is one of the aforementioned wet silicon oxides, for example, SNOWTEX O, C, N, S, 20, OS, OXS, NS, etc., manufactured by Nissan Chemical Co., Ltd., can be suitably used. In addition, as the aforementioned dry silica, for example, AEROSIL 50, 130, 200, 300, 380, etc., manufactured by Japan Aerosil Co., Ltd., can be suitably used.

As the aforementioned trialkoxysilane, any one can be used without particular limitation. It is preferable to use, for example, the general formula: R ₁ Si(OR ₂ ) ₃ (in the formula, R ₁ is hydrogen or an alkyl group with 1 to 5 carbon atoms, and R ₂ is an alkyl group with the same or different carbon numbers of 1 to 5) Represented trialkoxysilane. As these trialkoxysilanes, trimethoxysilane, triethoxysilane, methyltriethoxysilane, etc. are mentioned, for example.

As the aforementioned tetraalkoxysilane, any one can be used without particular limitation. Preferably, for example, a tetraalkoxysilane represented by the general formula: Si(OR) ₄ (wherein R is the same or different alkyl group having 1 to 5 carbon atoms) is used. As these tetraalkoxysilanes, for example, tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, etc. are mentioned.

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

Furthermore, by containing the Si compound in the chemical conversion film, the Si compound is dehydrated and condensed to form an amorphous chemical conversion film having siloxane bonds with a high blocking effect of shielding corrosion factors. Furthermore, by combining with the above-mentioned resin, a chemical conversion film having higher barrier properties is formed. In addition, in a corrosive environment, dense and stable corrosion products are formed in defective parts or damaged parts of the plating film caused by processing, etc., and the composite effect of the plating film also has the effect of suppressing the corrosion of the base steel plate. From the viewpoint that the effect of forming a stable corrosion product is high, as the Si compound, at least one of colloidal silica and dry silica is preferably used.

The concentration of the Si compound in the chemical conversion treatment liquid 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 chemical conversion treatment liquid is 0.2 mass % or more, the barrier effect due to the siloxane bond can be obtained. As a result, in addition to the corrosion resistance of the flat part, the defect part, the cut part and Corrosion resistance and sweat resistance of damaged parts are improved. In addition, if the concentration of the Si compound is 9.5 mass % or less, the life of the chemical conversion treatment liquid can be extended. By coating and drying a chemical conversion treatment liquid having a concentration of Si compound of 0.2 to 9.5 mass %, the Si adhesion amount in the chemical conversion film after drying can be 2 to 95 mg/m ² .

Since the Co compound and the Ni compound are contained in the chemical conversion coating, the blackening resistance can be improved. This is considered to be because Co and Ni have the effect of slowing elution of water-soluble components from the film in a corrosive environment. In addition, the aforementioned Co and the aforementioned Ni are elements that are more difficult to oxidize than Al, Zn, Si, and Mg. Therefore, by concentrating at least one of the Co compound and the Ni compound at the interface between the chemical conversion coating and the plating coating (forming a concentrated layer), the concentrated layer can be used as a corrosion barrier. Improves resistance to blackening.

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

The concentration of the Co compound and/or the Ni compound in the chemical conversion treatment liquid is not particularly limited, but may be 0.25% by mass to 5% by mass in total. When the concentration of the Co compound and/or Ni compound is less than 0.25 mass %, the interface concentration layer becomes non-uniform, and not only the corrosion resistance of the flat part is reduced, but also the defect part, the cut end surface part, the processing and the like. There is a possibility that the corrosion resistance of the damaged portion of the plated film may decrease. From the same viewpoint, it is preferably 0.5 mass % or more, more preferably 0.75 mass % or more. On the other hand, when the concentration of the Co compound and/or the Ni compound exceeds 5 mass %, the appearance at the time of film formation tends to be non-uniform, and the corrosion resistance may be lowered. From the same viewpoint, it is preferably 4.0 mass % or less, more preferably 3.0 mass % or less. By coating and drying the chemical conversion treatment liquid with the total concentration of the Co compound and/or the Ni compound being 0.25% by mass to 5% by mass, the total adhesion amount of Co and Ni in the chemical conversion coating after drying can be made to be 5%. ~100mg/m ² .

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

As the aforementioned Al compound, for example, at least one 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, at least one selected from the group consisting of zinc sulfate, zinc carbonate, zinc chloride, zinc oxide, and zinc hydroxide is exemplified. As the aforementioned Mg compound, for example, at least one selected from the group consisting of magnesium sulfate, magnesium carbonate, magnesium chloride, magnesium oxide, and magnesium hydroxide is exemplified.

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

Since the chemical conversion film contains the V compound, V can be eluted moderately in a corrosive environment, and combined with zinc ions, which are also eluted in a corrosive environment, as a plating component, a dense protective film is formed. By forming the protective film, the corrosion resistance of not only the flat part of the steel sheet but also the defect part, the damaged part of the plating film caused by processing, etc., and the corrosion from the cut end face to the flat part can be further improved, etc.

The aforementioned V compound is a compound containing V, for example, one or more selected from the group consisting of sodium metavanadate, vanadium sulfate, and vanadium acetylacetonate.

The V compound in the chemical conversion treatment liquid for forming the chemical conversion film is preferably 0.05% by mass to 4% by mass. When the concentration of the V compound is 0.05 mass % or more, it is easily eluted in a corrosive environment to form a protective film, and the corrosion resistance of defective parts, cut end surface parts, and damaged parts of the plating film caused by processing is improved. On the other hand, when the concentration of the aforementioned V compound exceeds 4 mass %, the appearance of the chemical conversion film is liable to be nonuniform, and the blackening resistance also decreases.

Since the Mo compound is contained in the chemical conversion coating, 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, 1 or more types chosen from sodium molybdate, potassium molybdate, magnesium molybdate, and zinc molybdate are illustrated.

The concentration of the Mo compound in the chemical conversion treatment liquid for forming the chemical conversion film is preferably 0.01% by mass to 3% by mass. When the concentration of the Mo compound is 0.01 mass % or more, the generation of oxygen-deficient zinc oxide can be further suppressed, and the blackening resistance can be further improved. On the other hand, when the concentration of the aforementioned Mo compound is 3 mass % or less, in addition to further prolonging the life of the chemical conversion treatment liquid, 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, it is difficult for corrosion factors to pass through the chemical conversion film, and the corrosion resistance can be improved.

As the aforementioned Zr compound, a compound containing Zr, 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 organotitanium chelate compound is preferable because it densifies the film when the chemical conversion treatment liquid is dried to form a film, and can obtain more excellent corrosion resistance.

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 octylate, and titanium ethylacetonate can be used.

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

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

The aforementioned Ca compound is a compound containing Ca, and examples thereof include oxides of Ca, nitrates of Ca, sulfates of Ca, intermetallic compounds containing Ca, and the like. More specifically, as the aforementioned Ca compound, CaO, CaCO ₃ , Ca(OH) ₂ , Ca(NO ₃ ) ₂ ·4H ₂ O, CaSO ₄ ·2H ₂ O, and the like are exemplified. The content of the aforementioned Ca compound in the aforementioned chemical conversion coating is not particularly limited.

Moreover, the said chemical conversion film may contain conventional various components normally used in the coating field as needed. Examples include various additives such as leveling agents, antifoaming agents, etc., dispersing agents, anti-settling agents, ultraviolet absorbers, light stabilizers, silane coupling agents, titanate coupling agents, etc., coloring pigments, body Various pigments such as pigments and bright materials, hardening catalysts, organic solvents, lubricants, etc.

In addition, it is preferable that the surface-treated steel sheet of the present invention does not contain harmful components such as hexavalent chromium, trivalent chromium, and fluorine in the chemical conversion coating. Since the chemical conversion treatment liquid used to form the chemical conversion film does not contain such harmful components, it has high safety and less environmental impact.

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

In addition, the above-mentioned method for forming the chemical conversion film is not particularly limited, and can be appropriately selected according to required properties, manufacturing equipment, and the like. For example, the chemical conversion treatment solution can be continuously applied on the above-mentioned plated film by a roll coater, etc., and then, hot air or induction heating can be used to reach the plate temperature (peak metal temperature (Peak metal temperature) at about 60~200°C Metal Temperature): PMT) is formed by drying. In addition to the roll coater, known methods such as airless spray, electrostatic spray, and curtain coater can be suitably used for the application of the chemical conversion treatment liquid. Moreover, as long as the said chemical conversion film contains the said resin and the said metal compound, it can be either a single-layer film or a multilayer film, and it does not specifically limit.

Moreover, in the surface-treated steel sheet of the present invention, if necessary, a coating film may be formed on the chemical conversion film.

(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 via a chemical conversion film on the coating film. However, the structure of the said plated film is the same as that of the plated film of the molten Al-Zn-Si-Mg-Sr-based plated steel sheet of the present invention.

In the coated steel sheet of the present invention, a chemical conversion coating can be formed on the aforementioned coating coating. In addition, the 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 according to the application and required performance.

Further, the coated steel sheet of the present invention is characterized in that the chemical conversion film contains: a resin component containing in total 30 to 50% by mass of (a): an anionic polyurethane resin having an ester bond and (b) : epoxy resin with bisphenol skeleton, and the content ratio ((a):(b)) of (a) and (b) is in the range of 3:97~60:40 by mass ratio; and inorganic compounds, 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, about the resin component which comprises the said chemical conversion film, (a): the anionic polyurethane resin which has an ester bond and (b): the epoxy resin which has a bisphenol skeleton.

Regarding the above-mentioned (a) anionic polyurethane resin having an ester bond, for example, a reaction product of polyester polyol and diisocyanate or polyisocyanate having two or more isocyanate groups, copolymerized dimethylolalkanoic acid The obtained resin. In addition, a chemical conversion treatment liquid can be obtained by dispersing in a liquid such as water by a conventional method.

Examples of the polyester polyols include polyesters obtained by dehydration condensation reactions of acid components such as derivatives of diol components and esters of hydroxycarboxylic acids, and cyclic ester compounds such as ε-caprolactone. Polyesters obtained by cyclopolymerization and their copolyesters. 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, and 2,4-diphenylmethane diisocyanate are exemplified. , 2,2-diphenylmethane diisocyanate, triphenylmethane triisocyanate, polymethylene polyphenyl polyisocyanate, naphthalene diisocyanate and their derivatives (such as prepolymers obtained by reacting with polyols) such as modified polyisocyanates such as carbodiimide compounds of diphenylmethane diisocyanate, etc.), etc.

In addition, when the polyester polyol and the diisocyanate or polyisocyanate are reacted to form a urethane, the aforementioned ( a) Anionic polyurethane resin having an ester bond. In this case, examples of the dimethylolalkanoic acid include, for example, dimethylolalkanoic acid having 2 to 6 carbon atoms, and more specific examples include dimethylolacetic acid, dimethylolpropionic acid, and dimethylolbutylene. acid, dimethylol heptanoic acid and dimethylolhexanoic acid.

Moreover, about the said (b) epoxy resin which has a bisphenol skeleton, a conventional epoxy resin can be used. For example, bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol AD type epoxy resin, bisphenol S type epoxy resin, etc. 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, the component [A] preferably contains a bisphenol A type epoxy resin or a bisphenol F type epoxy resin, and more preferably contains a bisphenol A type epoxy resin. The (b) epoxy resin having a bisphenol skeleton can be dispersed in a liquid such as water by a conventional method to obtain a chemical conversion treatment liquid.

The resin component acts as an adhesive for the chemical conversion film, and the (a) anionic polyurethane resin having an ester bond constituting the adhesive is flexible, so it can be used during processing. The chemical conversion film is not easily destroyed (peeled), and the epoxy resin (b) with a bisphenol skeleton can improve the adhesion to the zinc-based coated steel sheet of the base and the primer coating film of the upper layer. The said resin component is contained in the said chemical conversion film in a total of 30-50 mass %. When the content of the resin component is less than 30% by mass, the adhesive effect of the chemical conversion film is reduced, and when it exceeds 50% by mass, the functions such as the inhibitory effect of the inorganic components shown below are reduced. From the same viewpoint, the content of the resin component in the chemical conversion film is preferably 35 to 45% by mass.

Furthermore, the resin component must be the content ratio ((a):(b)) of the above-mentioned (a) anionic polyurethane resin having an ester bond and the above-mentioned (b) epoxy resin having a bisphenol skeleton. The mass ratio is in the range of 3:97~60:40. If the above-mentioned (a): (b) are outside the above-mentioned ranges, sufficient corrosion resistance cannot be obtained due to a decrease in flexibility or adhesion as a chemically treated film. From the same viewpoint, the above-mentioned (a):(b) is preferably 10:90 to 55:45.

In addition, the resin component may contain resins other than the above-mentioned (a) anionic polyurethane resin having an ester bond and (b) epoxy resin having a bisphenol skeleton (other resins) depending on the performance required. Element). The aforementioned other resin components are not particularly limited, and for example, at least one selected from the group consisting of acrylic resins, acrylic silicone resins, alkyd resins, polyester resins, polyalkylene resins, amino resins, and fluororesins can be used, or two or more of them can be used in combination. . When the resin component contains other resins, the total content of the (a) anionic polyurethane resin having an ester bond and the (b) epoxy resin having a bisphenol skeleton is preferably 50% by mass or more, and more Preferably it is 75 mass % or more. This is because the reduction in flexibility or the adhesiveness of the chemical conversion treatment film can be obtained more reliably.

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 is added to the chemical conversion treatment liquid and functions as a rust inhibitor (inhibitor). Since the chemical conversion coating contains the vanadium compound, the vanadium compound can be moderately eluted in a corrosive environment, and combined with the zinc ions of the plating component which is also eluted in the corrosive environment, a dense protective coating is formed. By forming the protective film, the corrosion resistance of not only the flat portion of the steel sheet, but also the defect portion, the damaged portion of the plating film caused by processing, and the corrosion from the cut end face to the flat portion can be further improved. Regarding the aforementioned vanadium compound, for example, vanadium pentoxide, metavanadic acid, ammonium metavanadate, vanadium oxytrichloride, vanadium trioxide, vanadium dioxide, magnesium vanadate, vanadium acetoacetate pyruvate, Vanadium Acetyl Pyruvate, etc. In particular, among these, it is desirable to use a tetravalent vanadium compound or a tetravalent vanadium compound obtained by reduction or oxidation.

In addition, the content of the vanadium compound in the chemical conversion treatment film is 2 to 10 mass %. When the content of the vanadium compound in the chemical conversion treatment film is less than 2 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 caused. Moisture resistance is reduced.

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

In addition, the content of the zirconium compound in the chemical conversion treatment film is 40 to 60 mass %. The reason for this is that when the content of the zirconium compound in the chemical conversion treatment film is less than 40 mass %, the strength or corrosion resistance of the chemical conversion treatment film is reduced, and when the content of the zirconium compound exceeds 60 mass %, the chemical conversion treatment film becomes brittle. , When subjected to strict processing, the chemical conversion treatment film will be damaged or peeled off.

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

In addition, the content of the fluorine compound in the chemical conversion treatment film is 0.5 to 5 mass %. The reason for this is that when the content of the fluorine compound in the chemical conversion treatment film is less than 0.5 mass %, the adhesion of the processed part cannot be sufficiently obtained, and when the content of the fluorine compound exceeds 5 mass %, the moisture resistance of the chemical conversion treatment film decreases. the reason.

In addition, the adhesion amount of the chemical conversion film is not particularly limited. For example, the adhesion amount of the chemical conversion film is preferably 0.025 to 0.5 g/m ² from the viewpoint of improving the adhesion of the chemical conversion film while securing the corrosion resistance more reliably. When the adhesion amount of the chemical conversion film is 0.025 g/m ² or more, the corrosion resistance can be more reliably ensured, and the peeling of the chemical conversion film can be suppressed by the adhesion amount of the chemical conversion film being 0.5 g/m ² or less. The adhesion amount of the chemical conversion coating can be obtained by a method appropriately selected from existing methods such as a method of analyzing the coating by fluorescent X-rays to measure the amount of an element whose content is known in the coating in advance.

In addition, the method for forming the chemical conversion film is not particularly limited, and can be appropriately selected according to required properties, manufacturing equipment, and the like. For example, a chemical conversion treatment liquid is continuously applied on the above-mentioned plated film by a roll coater, etc., and then, hot air or induction heating is used to reach the plate temperature (peak metal temperature: PMT) at about 60 to 200°C. formed by drying. In addition to the roll coater, known methods such as airless spray, electrostatic spray, and curtain coater can be suitably used for the application of the chemical conversion treatment liquid. In addition, as long as the said chemical conversion film contains the said resin and the said metal compound, it may be either a single-layer film or a multilayer film, and it will not specifically limit.

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

Moreover, in this invention, the said primer coating film contains the polyester resin which has a urethane bond, and the inorganic compound containing a vanadium compound, a phosphoric acid compound, and magnesium oxide. By containing the polyester resin having a urethane bond and the inorganic compound in the primer coating film, the adhesion of the coating film can be improved and the corrosion resistance can be improved.

The aforementioned primer coating film contains, as a main component, a polyester resin having a urethane bond. The above-mentioned polyester resin with urethane bond has both flexibility and strength, so the effect of cracking of the primer coating film is not easy to occur during processing, due to chemical conversion with the urethane resin containing The affinity of the treated film is high, so it is particularly helpful to improve the corrosion resistance of the processed part. In addition, the term "main component" here refers to the component with the largest content among the components in the primer coating film.

As the polyester resin having the aforementioned urethane bond, conventional resins such as those obtained by reacting a polyester polyol with a diisocyanate or polyisocyanate having two or more isocyanate groups can be used. In addition, the resin (urethane-modified polyester resin) in which the above-mentioned polyester polyol and the above-mentioned diisocyanate or the above-mentioned polyisocyanate are reacted in a state in which the hydroxyl group is excessive can also be used as a resin after curing with a blocked polyisocyanate.

Moreover, the said polyester polyol can be obtained by the conventional method using the dehydration condensation reaction of a polyol component and a polybasic acid component. As said polyol, a diol and a trivalent or higher polyol are exemplified. The aforementioned glycols are exemplified by, for example, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, neopentyl glycol, hexylene glycol, 1,3 -Butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2-butyl-2-ethyl-1,3-propanediol, methylpropanediol, cyclo Hexanedimethanol, 3,3-diethyl-1,5-pentanediol, etc. In addition, the polyhydric alcohol of the said trivalent or more, for example, glycerol, trimethylolethane, trimethylolpropane, pentaerythritol, dipentaerythritol, etc. are mentioned. These polyols may be used alone or in combination of two or more. As the above-mentioned polybasic acid, a general polyvalent carboxylic acid is used, but if necessary, a unit fatty acid or the like may be used in combination. As the aforementioned polyvalent carboxylic 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 and other acid anhydrides, as well 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 polyisocyanates, there are exemplified aliphatic diisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, dimer acid diisocyanate, etc., and xylene diisocyanate (XDI), m-xylene diisocyanate, etc. Aromatic diisocyanates such as isocyanates, toluene diisocyanate (TDI), 4,4-diphenylmethane diisocyanate (MDI), etc., and further cyclic diisocyanates such as 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.

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

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

The vanadium compound which is one of the aforementioned inorganic compounds acts as an inhibitor. Examples of the aforementioned vanadium compound include vanadium pentoxide, metavanadic acid, ammonium metavanadate, vanadium oxytrichloride, vanadium trioxide, vanadium dioxide, magnesium vanadate, vanadium acetoacetate pyruvate, Vanadium Acetyl Pyruvate, 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 aforementioned primer coating film may be of the same kind or different from the vanadium compound added to the aforementioned chemical conversion treatment film. The vanadate compound is thought to be caused by the reaction of vanadate ions gradually eluted by moisture intruding from the outside and ions on the surface of the zinc-based plated steel sheet to form a passivation film with good adhesion, which protects the exposed metal parts and exhibits a rust prevention effect.

The content of the vanadium compound in the primer coating film is not particularly limited, but from the viewpoint of having both corrosion resistance and moisture resistance, it is preferably 4 to 20% by mass. If the content of the vanadium compound is less than 4% by mass, the inhibitor effect may be reduced, and the corrosion resistance may be lowered, and if the content of the vanadium compound exceeds 20% by mass, the moisture resistance of the primer coating film may be lowered.

The phosphoric acid compound, which is one of the aforementioned inorganic compounds, also acts as an inhibitor. As the aforementioned phosphoric acid compound, for example, phosphoric acid, an ammonium salt of phosphoric acid, an alkali metal salt of phosphoric acid, an alkaline earth metal salt of phosphoric acid, and the like can be used. 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 from the viewpoint of having both corrosion resistance and moisture resistance, it is preferably 4 to 20% by mass. If the content of the phosphoric acid compound is less than 4 mass %, the inhibitor effect may be reduced, resulting in a reduction in corrosion resistance, and if the content of the phosphoric acid compound exceeds 20 mass %, the moisture resistance of the primer coating film may be lowered.

Magnesium oxide, one of the aforementioned inorganic compounds, has the effect of generating a product containing Mg as a poorly soluble magnesium salt by initial corrosion, thereby achieving stabilization 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 mass % from the viewpoint of having both corrosion resistance and corrosion resistance of the processed part. When the content of the magnesium oxide is less than 4% by mass, the above-mentioned effect may be reduced and the corrosion resistance may be lowered, and when the content of the magnesium oxide exceeds 20% by mass, the flexibility of the primer coating film may be reduced, and the processing may be deteriorated. There is a risk that the corrosion resistance of the part will decrease.

Moreover, the said primer coating film may contain components other than the polyester resin which has a urethane bond mentioned above, and an inorganic compound. An example is a crosslinking agent used when forming a primer coating film. The aforementioned cross-linking agent reacts with the aforementioned polyester resin having a urethane bond to form a cross-linked coating film, such as oxazoline compounds, epoxy compounds, melamine compounds, isocyanate-based compounds, carbodiimide It is also possible to use two or more types of crosslinking agents in combination, such as a series compound, a silane coupling compound, or the like. Among them, a blocked polyisocyanate compound or the like can be preferably used from the viewpoint of the corrosion resistance of the processed part of the obtained coated steel sheet. As the blocked polyisocyanate, for example, the isocyanate group of the polyisocyanate compound is exemplified by alcohols such as butanol, oximes such as methyl ethyl ketoxime, and lactamides such as ε-caprolactam. Those that are end-capped with diketones such as acetoacetate diesters, imidazoles such as imidazole, 2-ethylimidazole, or phenols such as m-cresol.

In addition, the above-mentioned primer coating film may contain various known components generally used in the coating field as needed. Specific examples include various surface conditioners such as leveling agents and antifoaming agents, dispersants, anti-settling agents, ultraviolet absorbers, light stabilizers, various additives such as silane coupling agents, titanate coupling agents, coloring pigments, Various pigments such as extenders, bright materials, hardening catalysts, organic solvents, etc.

The thickness of the aforementioned primer coating film is preferably 1.5 μm or more. The reason for this is that when the thickness of the above-mentioned primer coating film is 1.5 μm or more, the effect of improving the corrosion resistance and the adhesion improvement effect of the top coating film formed on the chemical conversion treatment film or the primer coating film can be more reliably obtained. the reason.

There is no particular limitation on the method of forming the aforementioned primer coating film. In addition, as for the coating method of the coating composition constituting the above-mentioned primer coating film, the coating composition can be preferably coated by methods such as roll coater coating and curtain coater coating. After the coating composition is coated, it is baked by heating means such as hot air heating, infrared heating, induction heating, etc., to obtain a primer coating film. The above-mentioned baking process is usually set to a maximum board temperature of about 180 to 270° C., and can be performed in this temperature range for about 30 seconds to 3 minutes.

Moreover, about the coating film which comprises the coated steel sheet of this invention, it is preferable to form a top coating film further on the said primer coating film. In addition to imparting color, gloss, and surface appearance to the coated steel sheet, the top coat film can 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 coat film, and the material, thickness, etc. can be appropriately selected according to the required performance. For example, the above-mentioned top coat 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, red iron oxide, mica, carbon black or other various coloring pigments; metallic pigments such as aluminum powder or mica; extender pigments made of carbonate or sulfate; Various fine particles of silicon particles, nylon resin beads, acrylic resin beads, etc.; hardening catalysts such as p-toluenesulfonic acid, dibutyltin dilaurate, etc.; wax; other additives.

Moreover, it is preferable that the thickness of the said top coating film is 5-30 micrometers from the viewpoint of having both appearance and workability. When the thickness of the top coating film is 5 μm or more, the appearance of the color tone can be more reliably stabilized, and when the thickness of the top coating film is 30 μm or less, the decrease in workability (the occurrence of cracks in the top coating film) can be more reliably suppressed.

The coating method of the coating composition for forming the aforementioned topcoat coating film is not particularly limited. The aforementioned coating composition can be applied by methods such as roll coater coating, curtain coating, and the like. After the coating composition is applied, it is baked by heating means such as hot air heating, infrared heating, and induction heating to form a top coating film. The above-mentioned baking process is usually carried out for about 30 seconds to 3 minutes within the temperature range of about 180 to 270° C. at the highest attainable board temperature. [Example]

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

(Evaluation) The following evaluations were performed about each sample of the hot-dip plated steel sheet obtained as described above. The evaluation results are shown in Table 1.

(1) Composition of the plated film (adhesion amount, composition, X-ray diffraction intensity) Each sample after plating was punched out to 100 mmφ, and the non-measuring surface was sealed with a tape, and then mixed with hydrochloric acid as shown in JIS H 0401:2013. The mixed solution of hexamethylenetetramine was dissolved in peeling plating, and the quality of the samples before and after peeling was poor, and the adhesion amount of the plating film was calculated. Table 1 shows the calculation results and the adhesion amount of the obtained plated film. Then, the peeling liquid was filtered, and the filtrate and the solid content were analyzed respectively. Specifically, components other than insoluble Si were quantified by analyzing the filtrate by ICP emission spectroscopy. In addition, after the solid content was dried and ashed in a heating furnace at 650° C., sodium carbonate and sodium tetraborate were added and dissolved. Furthermore, the melt was dissolved with hydrochloric acid, and the dissolved solution was analyzed by ICP emission spectroscopy to quantify insoluble Si. The Si concentration in the plated film is obtained by adding the soluble Si concentration obtained by the filtrate analysis and the insoluble Si concentration obtained by the solid content analysis. The calculation result and the composition of the obtained plated film are shown in Table 1. Furthermore, after cutting each sample into a size of 100 mm×100 mm, the plated film of the evaluation symmetry plane was mechanically cut until the base steel plate was exposed, the obtained powder was thoroughly mixed, 0.3 g was taken out, and an X-ray diffraction apparatus (RIGAKU Co., Ltd.) was used. "SmartLab" manufactured by Co., Ltd.), using X-ray: Cu-Kα (wavelength=1.54178Å), removal of kβ-ray: Ni filter, tube voltage: 40kV, tube current: 30mA, scanning speed: 4˚/min, sampling The above powders were qualitatively analyzed under the conditions of interval: 0.020°, divergence slit: 2/3°, Soller slit: 5°, detector: high-speed one-dimensional detector (D/teX Ultra). The intensity obtained by subtracting the base intensity from each peak intensity was used as each diffraction intensity (cps), and the diffraction intensity of the (111) plane (interplane spacing d=0.3668 nm) of Mg ₂ Si and the (111) plane (plane) of Si were measured. Diffraction intensity of interval d=0.3135nm). The measurement results are shown in Table 1.

(2) Corrosion resistance evaluation For each sample of the obtained hot-dip plated steel sheet, after shearing to a size of 120 mm×120 mm, a range of 10 mm from each edge of the evaluation object surface and the end surface of the sample and the evaluation non-object surface were tapered. It was sealed, and the state which exposed the evaluation object surface in the dimension of 100 mm x 100 mm was used as the sample for evaluation. In addition, three samples for this evaluation were produced by the same person. For the three samples for evaluation prepared as described above, the corrosion promotion test was performed in the cycle shown in FIG. 1 . The corrosion promotion test was performed from the wet start to 300 cycles, and the corrosion loss of each sample was measured by the method described in JIS Z 2383 and ISO8407, and evaluated by the following criteria. The evaluation results are shown in Table 1. ◎: Corrosion loss of ³ samples is below 45g/m2 ○: Corrosion loss of ³ samples is below 70g/m2 ×: Corrosion loss of 1 or more samples exceeds 70g/ ^m2

(3) Surface appearance For each sample of the obtained hot-dip plated steel sheet, the surface of the plated film was visually observed. Next, the observation results were evaluated according to the following criteria. The evaluation results are shown in Table 1. ⊚: No wrinkle defect was observed at all ○: Wrinkle defects are observed only within 50 mm from the edge ×: Wrinkle-like defects were observed outside the range of 50 mm from the edge

(4) Processability Each sample of the obtained hot-dip plated steel sheet was cut to a size of 70 mm×150 mm, and then 8 sheets of the same thickness were sandwiched inside and subjected to 180° bending (8T bending). After bending, SELLOTAPE (registered trademark) glass tape is strongly attached to the outer surface of the curved part and then peeled off. The surface state of the plated film on the outer surface of the curved portion and the presence or absence of the plated film attached (peeled) on the surface of the tape used were visually observed, and the workability was evaluated according to the following criteria. The evaluation results are shown in Table 1. ○: No cracks and peeling were observed on the plated film △: There are cracks in the plated film, but no peeling is observed ×: Both cracks and peeling were observed on the plated film

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

As can be seen from the results in Table 1, each of the samples of the present invention exhibited a good balance in corrosion resistance, surface appearance, workability, and bath stability compared with each of the samples of the comparative example.

<Example 2: Samples 1 to 112> (1) A cold-rolled steel sheet with a thickness of 0.8 mm produced by a conventional method was used as a base steel sheet, and annealing treatment and plating treatment were carried out with a hot-dip coating simulator made by RHESCA (stock). , the hot-dip plated steel sheet samples of the plating film conditions shown in Tables 3 and 4 were produced. In addition, regarding the composition of the coating bath used for the production of the hot-dip plated steel sheet, the composition of the coating bath was set to Al: 30 to 75 mass %, Si: 0.5 so that the composition of the coating film of each sample shown in Table 2 would be obtained. Various changes are made in the range of ~4.5 mass %, Mg: 0 to 10 mass %, and Sr: 0.00 to 0.15 mass %. In addition, the bath temperature of the plating bath was set to 590°C when Al: 30 to 60 mass %, and 630° C. when Al: exceeded 60 mass %, and the plating immersion plate temperature of the base steel sheet was controlled to be the same as the plating bath temperature. same. In addition, the plating process was performed on the conditions that the board temperature was cooled in the temperature range of 520-500 degreeC in 3 seconds. In addition, the adhesion amount of the plated film is controlled to be 85±5g/m ² per single side in samples 1~82 and 95~112, and 51~125g/m ² per single side in samples 83~94 . (2) Subsequently, on the plated film of each sample of the produced hot-dip plated steel sheet, a chemical conversion treatment solution was applied with a bar coater, and dried with a hot-air furnace (heating rate: 60°C/s, PMT: 120°C). °C) to form a chemical conversion film, and each sample of the surface-treated steel sheets shown in Tables 3 and 4 was produced. In addition, the chemical conversion treatment liquid system prepares surface treatment liquids A to F in which each component is dissolved in water as a solvent. The types of each component (resin, metal compound) contained in the surface treatment liquid are as follows. (Resin) Urethane resin: SUPERFLEX 130, SUPERFLEX 126 (Daiichi Kogyo 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: zirconium potassium carbonate In addition, the concentration of each component in Table 2 of this specification is a solid content concentration (mass %).

(Evaluation) The following evaluations were performed about each sample of the hot-dip plated steel sheet and the surface-treated steel sheet obtained as described above. The evaluation results are shown in Tables 3 and 4.

(1) Composition of plated film (adhesion amount, composition, X-ray diffraction intensity) Each sample of the hot-dip plated steel sheet was punched out to 100 mmφ, and the non-measuring surface was sealed with tape, and then treated with hydrochloric acid specified in JIS H 0401:2013. The peeling plating was dissolved in a mixed solution with hexamethylenetetramine, and the quality of the samples before and after peeling was poor, and the adhesion amount of the plating film was calculated. The calculation result and the adhesion amount of the obtained plating film are shown in Tables 3 and 4. Then, the peeling liquid was filtered, and the filtrate and the solid content were analyzed respectively. Specifically, components other than insoluble Si were quantified by analyzing the filtrate by ICP emission spectroscopy. In addition, after the solid content was dried and ashed in a heating furnace at 650° C., sodium carbonate and sodium tetraborate were added and dissolved. Furthermore, the melt was dissolved with hydrochloric acid, and the dissolved solution was analyzed by ICP emission spectroscopy to quantify insoluble Si. The Si concentration in the plated film is obtained by adding the soluble Si concentration obtained by the filtrate analysis and the insoluble Si concentration obtained by the solid content analysis. The calculation result and the composition of the obtained plated film are shown in Tables 3 and 4. Furthermore, after cutting each sample into a size of 100 mm×100 mm, the plated film of the evaluation symmetry plane was mechanically cut until the base steel plate was exposed, the obtained powder was thoroughly mixed, 0.3 g was taken out, and an X-ray diffraction apparatus (RIGAKU Co., Ltd.) was used. "SmartLab" manufactured by Co., Ltd.), using X-ray: Cu-Kα (wavelength=1.54178Å), removal of kβ-ray: Ni filter, tube voltage: 40kV, tube current: 30mA, scanning speed: 4˚/min, sampling Spacing: 0.020°, divergent slit: 2/3°, parallel slit: 5°, detector: high-speed one-dimensional detector (D/teX Ultra), the above powders were qualitatively analyzed. The intensity obtained by subtracting the base intensity from each peak intensity was used as each diffraction intensity (cps), and the diffraction intensity of the (111) plane (interplane spacing d=0.3668 nm) of Mg ₂ Si and the (111) plane (plane) of Si were measured. Diffraction intensity of interval d=0.3135nm). The measurement results are shown in Tables 3 and 4.

(2) Corrosion resistance evaluation For each sample of the hot-dip plated steel sheet and the surface-treated steel sheet, after shearing to a size of 120 mm × 120 mm, the range of 10 mm from each edge of the evaluation object surface and the end surface of the sample and the evaluation non-object surface were separated. It sealed with a tape, and the state which exposed the evaluation object surface in the dimension of 100 mm x 100 mm was used as the sample for evaluation. In addition, three samples for this evaluation were produced by the same person. For the three samples for evaluation prepared as described above, the corrosion promotion test was performed in the cycle shown in FIG. 1 . The corrosion promotion test was performed from the wet start to 300 cycles, and the corrosion loss of each sample was measured by the method described in JIS Z 2383 and ISO8407, and evaluated by the following criteria. The evaluation results are shown in Tables 3 and 4. ◎: Corrosion loss of ³ samples is below 30g/m2 ○: Corrosion loss of ³ samples is below 50g/m2 ×: Corrosion loss of more than 1 sample exceeds 50g/ ^m2

(3) White rust resistance Each sample of the hot-dip plated steel sheet and the surface-treated steel sheet was cut to a size of 120 mm × 120 mm, and the range of 10 mm from each edge of the evaluation object surface and the end surface of the sample and the evaluation non-object surface were sealed with tape. A state in which the object surface was exposed with a size of 100 mm×100 mm 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 evaluated by the following criteria. The evaluation results are shown in Tables 3 and 4. ◎: No white rust on the flat part ○: The area where white rust occurs on the flat plate is less than 10% ×: 10% or more of the white rust occurrence area of the flat plate

(4) Surface appearance For each sample of the hot-dip plated steel sheet, the surface of the plated film was visually observed. Next, the observation results were evaluated according to the following criteria. The evaluation results are shown in Tables 3 and 4. ⊚: No wrinkle defect was observed at all ○: Wrinkle defects are observed only within 50 mm from the edge ×: Wrinkle-like defects were observed outside the range of 50 mm from the edge

(5) Processability Each sample of the hot-dip plated steel sheet was cut to a size of 70 mm×150 mm, and then 8 sheets of the same thickness were sandwiched inside and subjected to 180° bending (8T bending). After bending, SELLOTAPE (registered trademark) glass tape is strongly attached to the outer surface of the curved part and then peeled off. The surface state of the plated film on the outer surface of the curved portion and the presence or absence of the plated film attached (peeled) on the surface of the tape used were visually observed, and the workability was evaluated according to the following criteria. The evaluation results are shown in Tables 3 and 4. ○: No cracks and peeling were observed on the plated film △: There are cracks in the plated film, but no peeling is observed ×: Both cracks and peeling were observed on the plated film

(6) Bath stability At the time of hot-dip plating, the state of the bath surface of the coating bath was visually checked and compared with the bath surface of the coating bath used in the production of molten Al-Zn-based plated steel sheets (the 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 the molten Al-Zn-based plating bath (55 mass % Al-the remainder Zn-1.6 mass % bath) △: There are more white oxides than the molten Al-Zn-based plating bath (55 mass % Al-the remainder Zn-1.6 mass % bath) ×: Black oxide formation was observed in the plating bath

As can be seen from the results in Tables 3 and 4, each of the samples of the present invention has a good balance of corrosion resistance, white rust resistance, surface appearance, workability, and bath stability compared with the samples of the comparative example. In addition, as can be seen from the results in Table 4, the white rust resistance of each of the samples subjected to chemical conversion treatments A to D showed particularly excellent results.

<Example 3: Samples 1 to 44> (1) A cold-rolled steel sheet with a thickness of 0.8 mm produced by a conventional method was used as a base steel sheet, and annealing treatment and plating treatment were carried out with a hot-dip coating simulator made by RHESCA (stock). , the hot-dip plated steel sheet samples of the plating film conditions shown in Table 6 were produced. In addition, regarding the composition of the coating bath used for the production of the hot-dip plated steel sheet, the composition of the coating bath was set to Al: 30 to 75 mass %, Si: 0.5 so that the composition of the coating film of each sample shown in Table 6 would be obtained. Various changes are made in the range of ~4.5 mass %, Mg: 0 to 10 mass %, and Sr: 0.00 to 0.15 mass %. In addition, the bath temperature of the plating bath was set to 590°C when Al: 30 to 60 mass %, and 630° C. when Al: exceeded 60 mass %, and the plating immersion plate temperature of the base steel sheet was controlled to be the same as the plating bath temperature. same. In addition, the plating process was performed on the conditions that the board temperature was cooled in the temperature range of 520-500 degreeC in 3 seconds. In addition, the adhesion amount of the plating film was controlled to be 85±5 g/m ² per single side in samples 1 to 41, and 42 to 125 g/m ² per single side in samples 42 to 44.

(2) Subsequently, the chemical conversion treatment solution shown in Table 5 was applied on the plated film of each sample of the produced molten plated steel sheet with a bar coater, and dried with a hot air drying furnace (at plate temperature: 90 ℃) to form a chemical conversion treatment film with an adhesion amount of 0.1 g/m ² . In addition, as the chemical conversion treatment liquid used, the chemical conversion treatment liquid of pH 8-10 prepared by dissolving each component in water as a solvent was used. The types of each component (resin component, inorganic compound) 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 Co., Ltd.) and (b) an epoxy resin having a bisphenol skeleton ( "YUKA RESIN RE-1050" manufactured by Yoshimura Oil Chemical Co., Ltd.) mixed with a mass ratio of (a): (b) = 50:50 Resin B: Acrylic resin ("BONCOAT EC-740EF" manufactured by DIC Corporation) (Inorganic compound) Vanadium compound: Organovanadium compound chelated with acetylacetone Zirconium compound: Ammonium zirconium carbonate Fluorine compound: Ammonium fluoride

(3) Next, on the chemical conversion film formed as described above, a primer coating was applied with a bar coater, and the steel plate reached a temperature of 230°C and was baked for a baking time of 35 seconds. A primer coating film showing the composition of the composition. Subsequently, on the primer coating film formed as described above, the top coating coating composition was coated with a bar coater, and the steel plate was baked under the conditions of a reaching temperature of 230° C. to 260° C. and a baking time of 40 seconds to form The top-coat coating film having the resin conditions and film thickness shown in Table 5 was produced as the coated steel sheet of each sample. In addition, the primer is obtained by mixing each component and stirring it 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: A 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) which is hardened with blocked isocyanate. In addition, the urethane-modified polyester resin was produced under the following conditions. 320 parts by mass of isophthalic acid, 200 parts by mass of adipic acid, 60 parts by mass of trimethylolpropane, 420 parts by mass of cyclohexane were fed into a flask equipped with a stirrer, a distillation column, a water separator, a cooling pipe and a thermometer Dimethanol was heated and stirred, while distilling the generated condensation water to the outside of the system, the temperature was raised from 160°C to 230°C at a constant speed for 4 hours. After reaching a temperature of 230°C, 20 parts by mass of xylene was slowly added to the temperature The condensation reaction was continued at 230°C, the reaction was terminated when the acid value was 5 or less, and after cooling to 100°C, 120 mass of SOLVESSO 100 (manufactured by EXXON MOBILE, trade name, high-boiling aromatic hydrocarbon solvent) was added. parts and 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 In addition, the following coating materials were used for the resin system used for the top coating film. Resin I: Melamine-cured polyester paint ("PRECOLOR HD0030HR" manufactured by BASF JAPAN Co., Ltd.) Resin II: Polyvinylidene fluoride and acrylic resin in a mass ratio of 80:20 Organosol sintering type fluororesin-based paint ("PRECOLOR No. 8800HR" manufactured by BASF JAPAN Co., Ltd.)

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

(1) Composition of plated film (adhesion amount, composition, X-ray diffraction intensity) Each sample of the hot-dip plated steel sheet was punched out to 100 mmφ, and the non-measuring surface was sealed with tape, and then treated with hydrochloric acid specified in JIS H 0401:2013. The peeling plating was dissolved in a mixed solution with hexamethylenetetramine, and the quality of the samples before and after peeling was poor, and the adhesion amount of the plating film was calculated. Table 6 shows the calculation results and the adhesion amount of the obtained plated film. Then, the peeling liquid was filtered, and the filtrate and the solid content were analyzed respectively. Specifically, components other than insoluble Si were quantified by analyzing the filtrate by ICP emission spectroscopy. In addition, after the solid content was dried and ashed in a heating furnace at 650° C., sodium carbonate and sodium tetraborate were added and dissolved. Furthermore, the melt was dissolved with hydrochloric acid, and the dissolved solution was analyzed by ICP emission spectroscopy to quantify insoluble Si. The Si concentration in the plated film is obtained by adding the soluble Si concentration obtained by the filtrate analysis and the insoluble Si concentration obtained by the solid content analysis. The calculation result and the composition of the obtained plated film are shown in Table 6. Furthermore, after cutting each sample into a size of 100 mm×100 mm, the plated film of the evaluation symmetry plane was mechanically cut until the base steel plate was exposed, the obtained powder was thoroughly mixed, 0.3 g was taken out, and an X-ray diffraction apparatus (RIGAKU Co., Ltd.) was used. "SmartLab" manufactured by Co., Ltd.), using X-ray: Cu-Kα (wavelength=1.54178Å), removal of kβ-ray: Ni filter, tube voltage: 40kV, tube current: 30mA, scanning speed: 4˚/min, sampling Spacing: 0.020°, divergent slit: 2/3°, parallel slit: 5°, detector: high-speed one-dimensional detector (D/teX Ultra), the above powders were qualitatively analyzed. The intensity obtained by subtracting the base intensity from each peak intensity was used as each diffraction intensity (cps), and the diffraction intensity of the (111) plane (interplane spacing d=0.3668 nm) of Mg ₂ Si and the (111) plane (plane) of Si were measured. Diffraction intensity of interval d=0.3135nm). The measurement results are shown in Table 6.

(2) Evaluation of corrosion resistance Each sample of the coated steel plate was cut to a size of 120mm×120mm, and the edge of the three sides arbitrarily selected from the evaluation object surface with a distance of 10mm and the same three edge surfaces of the sample and the non-evaluation object surface were sealed with tape. The state in which the evaluation object surface was exposed with the size of 100 mm x 100 mm was used as a sample for evaluation. In addition, three samples for this evaluation were produced by the same person. For the three samples for evaluation prepared as described above, the corrosion promotion test was performed in the cycle shown in FIG. 1 . In the corrosion promotion test, the samples were taken out every 20 cycles, washed with water and dried, and the occurrence of red rust on the sheared end face of one side not sealed with the tape was confirmed by visual observation. Next, the number of cycles at the time of red rust was confirmed, and the evaluation was performed according to the following criteria. The evaluation results are shown in Table 6. ◎: The number of cycles in which red rust occurs on 3 samples≧600 cycles ○: 600 cycles > The number of cycles where red rust occurs on 3 samples ≧ 500 cycles ×: The number of cycles of occurrence of red rust in at least one sample is less than 500 cycles

(3) Appearance after painting For each sample of the coated steel sheet, the surface was visually observed. Next, the observation results were evaluated according to the following criteria. The evaluation results are shown in Table 6. ⊚: No wrinkle defect was observed at all ○: Wrinkle defects are observed only within 50 mm from the edge ×: Wrinkle-like defects were observed outside the range of 50 mm from the edge

(4) Processability after painting For each sample of the coated steel sheet, after shearing to a size of 70mm×150mm, 8 sheets of the same sheet thickness were sandwiched inside and subjected to 180° bending (8T bending). After bending, SELLOTAPE (registered trademark) glass tape is strongly attached to the outer surface of the curved part and then peeled off. The state of the coating film surface on the outer surface of the curved portion and the presence or absence of coating film adhesion (peeling) on the surface using the tape were visually observed, and the workability was evaluated according to the following criteria. The evaluation results are shown in Table 6. ○: No cracks and peeling were observed on the plated film △: There are cracks in the plated film, but no peeling is observed ×: Both cracks and peeling were observed on the plated film

(5) Bath stability At the time of hot-dip plating, the state of the bath surface of the coating bath was visually checked and compared with the bath surface of the coating bath used in the production of molten Al-Zn-based plated steel sheets (the bath surface without Mg oxide). The evaluation was performed based on the following criteria, and Table 6 shows the evaluation results. ○: About the same as the molten Al-Zn-based plating bath (55 mass % Al-the remainder Zn-1.6 mass % bath) △: There are more white oxides than the molten Al-Zn-based plating bath (55 mass % Al-the remainder Zn-1.6 mass % bath) ×: Black oxide formation was observed in the plating bath

As can be seen from the results in Table 6, each of the samples of the present invention is well balanced in terms of corrosion resistance, appearance after coating, workability after coating, and bath stability compared with the samples of the comparative example. [Industrial Availability]

According to the present invention, a stable molten Al-Zn-Si-Mg-Sr-based plated steel sheet having excellent corrosion resistance and good surface appearance can be provided. In addition, 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, it is possible to provide a coated steel sheet which is stable and has excellent corrosion resistance and corrosion resistance of processed parts.

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

Claims (7)

A fused Al-Zn-Si-Mg-Sr plated steel sheet, which is a fused Al-Zn-Si-Mg-Sr plated steel sheet with a plated film, characterized in that the plated film has the following composition: Contains Al: 45 to 65 mass %, Si: 1.0 to 4.0 mass %, Mg: 1.0 to 10.0 mass %, and Sr: 0.01 to 1.0 mass %, and the rest is composed of Zn and inevitable impurities. The diffraction intensities of Si and Mg ₂ Si by X-ray diffraction satisfy the following relation (1), Si(111)/Mg ₂ Si(111)≦0.8…(1) Si(111):(111 of Si) ) plane (interplane spacing d=0.3135nm) diffraction intensity, Mg ₂ Si (111): Mg ₂ Si (111) plane (plane spacing d=0.3668nm) diffraction intensity. The molten Al-Zn-Si-Mg-Sr-based plated steel sheet according to claim 1, wherein the diffraction intensity of the Si in the plated film by X-ray diffraction satisfies the following relation (2), Si(111)=0...(2). The molten Al-Zn-Si-Mg-Sr-based plated steel sheet according to claim 1 or 2, wherein the Al content in the plated film is 50 to 60 mass %. The molten Al-Zn-Si-Mg-Sr-based plated steel sheet according to any one of claims 1 to 3, wherein the Si content in the pre-plated film is 1.0 to 3.0 mass %. The molten Al-Zn-Si-Mg-Sr-based plated steel sheet according to any one of claims 1 to 4, wherein the Mg content in the plated film is 1.0 to 5.0 mass %. A surface-treated steel sheet, which is a surface-treated steel sheet provided with a plated film as claimed in any one of claims 1 to 5 and a chemical conversion film formed on the plated film, characterized by: 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. At least one metal compound selected from the group consisting of P compound, Si compound, Co compound, Ni compound, Zn compound, Al compound, Mg compound, V compound, Mo compound, Zr compound, Ti compound and Ca compound. A coated steel sheet, which is formed on the coated film as claimed in any one of claims 1 to 5, directly or via a chemical conversion film to form a coated steel sheet, characterized by: The chemical conversion film contains: a resin component containing in total 30 to 50% by mass of (a): an anionic polyurethane resin having an ester bond and (b): an epoxy resin having a bisphenol skeleton, and The content ratio ((a):(b)) of the (a) and the (b) is in the range of 3:97 to 60:40 by mass ratio; and an inorganic compound comprising 2 to 10 mass % of a vanadium compound, 40 to 60 mass % of zirconium compounds and 0.5 to 5 mass % of fluorine compounds, 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 containing a vanadium compound, a phosphoric acid compound, and magnesium oxide.

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