WO2025027919A1 - Al-zn-si-mg hot-dipped steel sheet, surface-treated steel sheet, and coated steel sheet - Google Patents

Al-zn-si-mg hot-dipped steel sheet, surface-treated steel sheet, and coated steel sheet Download PDF

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Publication number
WO2025027919A1
WO2025027919A1 PCT/JP2024/008325 JP2024008325W WO2025027919A1 WO 2025027919 A1 WO2025027919 A1 WO 2025027919A1 JP 2024008325 W JP2024008325 W JP 2024008325W WO 2025027919 A1 WO2025027919 A1 WO 2025027919A1
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Prior art keywords
steel sheet
mass
plating film
compounds
coating
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PCT/JP2024/008325
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French (fr)
Japanese (ja)
Inventor
昌浩 吉田
章一郎 平
純久 岩野
洋平 佐藤
史嵩 菅野
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Ｊｆｅスチール株式会社
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Publication of WO2025027919A1 publication Critical patent/WO2025027919A1/en

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C18/00—Alloys based on zinc
    • C22C18/04—Alloys based on zinc with aluminium as the next major constituent
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C21/00—Alloys based on aluminium
    • C22C21/10—Alloys based on aluminium with zinc as the next major constituent
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/06—Zinc or cadmium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/12—Aluminium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D

Definitions

  • the present invention relates to hot-dip Al-Zn-Si-Mg plated steel sheets, surface-treated steel sheets, and painted steel sheets that have excellent surface appearance.
  • Hot-dip Al-Zn-plated steel sheets typified by 55% Al-Zn, are known to exhibit high corrosion resistance among various plated steel sheets because they combine the sacrificial corrosion protection of Zn with the high corrosion resistance of Al, as shown in, for example, Patent Document 1.
  • hot-dip Al-Zn-plated steel sheets are used mainly in the field of building materials such as roofs and walls that are exposed outdoors for long periods of time, and in the field of civil engineering and construction such as guardrails, wiring and piping, and soundproof walls, due to their excellent corrosion resistance.
  • the coating of hot-dip Al-Zn-plated steel sheets is composed of areas where Al containing supersaturated Zn has solidified into dendrites ( ⁇ -Al phase) and a Zn-Al eutectic structure that exists in the gaps between dendrites (interdendrites), and is characterized by a structure in which the ⁇ -Al phase is layered in the thickness direction of the coating.
  • This characteristic coating structure makes the corrosion progression path from the surface complex, making it difficult for corrosion to progress easily, and it is also known that hot-dip Al-Zn-plated steel sheets can achieve superior corrosion resistance compared to hot-dip galvanized steel sheets with the same coating thickness.
  • Patent Document 1 discloses a hot-dip Al-Zn-Si-Mg-plated steel sheet that contains an Al-Zn-Si alloy containing Mg in a plating film, the Al-Zn-Si alloy being an alloy containing 45 to 60 wt % of elemental aluminum, 37 to 46 wt % of elemental zinc, and 1.2 to 2.3 wt % of Si, and the concentration of the Mg is 1 to 5 wt %.
  • Patent Document 2 discloses a hot-dip Al-Zn-Si-Mg plated steel sheet in which the plating film contains one or more of 2 to 10 mass % Mg and 0.01 to 10 mass % Ca, thereby improving corrosion resistance and enhancing protective action after the base steel sheet is exposed.
  • Patent Document 3 discloses a hot-dip Al-Zn-Si-Mg plated steel sheet which forms a coating layer containing, by mass%, 1 to 15% Mg, 2 to 15 % Si, 11 to 25% Zn, with the remainder being Al and unavoidable impurities, and which aims to improve the corrosion resistance of the flat sheet and end faces by restricting the size of intermetallic compounds such as Mg2Si phase and MgZn2 phase present in the plating film to 10 ⁇ m or less.
  • Mg is an element that oxidizes more easily than other plating constituent elements, so during the cooling and solidification process of the plating film, Mg reacts with oxygen in the outermost layer that comes into contact with the air to produce Mg-based oxides. As a result, the Mg concentration in the vicinity of the outermost layer decreases, and to compensate for this, Mg gradually diffuses from the inside of the plating film to the outermost layer.
  • Patent Documents 4 and 5 disclose a technology that includes Sr in the plating film to suppress oxidation of Mg on the plating surface and prevent wrinkle defects. These technologies utilize the phenomenon that Sr is oxidized preferentially over Mg on the unsolidified plating surface layer that comes out of the plating bath.
  • Patent Documents 6 and 7 disclose surface-treated steel sheets in which a chemical conversion coating containing a urethane resin is formed on a coating film of a hot-dip Al-Zn-Si-Mg-plated steel sheet, thereby improving the white rust resistance.
  • the above-mentioned hot-dip Al-Zn-Si-Mg-plated steel sheet may be used as a painted steel sheet having a chemical conversion coating or a primer coating formed on the surface and various other coating films formed thereon.
  • Such coated steel sheets are subjected to various processes, including bending at 90 degrees or 180 degrees by press forming, roll forming, or embossing, and are required to have coating film durability over a long period of time after use.
  • Patent Documents 4 and 5 have a problem that, during the production of a hot-dip Al-Zn-Si-Mg-plated steel sheet having Sr added to the plating film, the surface of the plating bath containing Sr is easily oxidized, and the generated oxide-based dross adheres to the plating film to cause new dross defects, which deteriorate the surface appearance.
  • Patent Documents 6 and 7 can improve white rust resistance, even in the case of a surface-treated steel sheet, the surface is affected by the underlying hot-dip Al-Zn-Si-Mg-plated steel sheet, and deterioration in surface appearance due to the occurrence of wrinkle-like defects is still desired to be improved.
  • the surface appearance of a coated steel sheet is naturally affected by the surface shape of the plated steel sheet that serves as the base, and since the height difference of the unevenness caused by the occurrence of the above-mentioned wrinkle-like defects and dross defects reaches several tens of ⁇ m, even if the surface is smoothed by a coating film, the unevenness is not completely eliminated, and improvement of the surface appearance of the coated steel sheet remains an issue.
  • the coating film formed on the convex parts of the plating film has a thin film thickness, there is a concern that the corrosion resistance may be locally reduced, and therefore it has been desired to improve the surface appearance of the plated steel sheet that serves as the base, particularly the surface shape.
  • an object of the present invention is to provide a hot-dip Al-Zn-Si-Mg coated steel sheet which is free from other defects such as dross defects, suppresses the occurrence of wrinkle-like defects, and has an excellent surface appearance.
  • Another object of the present invention is to provide a surface-treated steel sheet having excellent surface appearance and white rust resistance, and a coated steel sheet having excellent surface appearance and excellent corrosion resistance.
  • the hot-dip Al-Zn-Si-Mg plated steel sheet according to 1 above characterized in that the plating film has a Mn content of 0.1 to 0.3 mass %. 3.
  • a surface-treated steel sheet comprising the plating film according to any one of 1 to 4 above and a chemical conversion film formed on the plating film
  • the chemical conversion coating film is a surface-treated steel sheet characterized in that it contains at least one resin selected from the group consisting of epoxy resins, urethane resins, acrylic resins, acrylic silicone resins, alkyd resins, polyester resins, polyalkylene resins, amino resins, and fluororesins, and at least one metal compound selected from the group consisting of P compounds, Si compounds, Co compounds, Ni compounds, Zn compounds, Al compounds, Mg compounds, V compounds, Mo compounds, Zr compounds, Ti compounds, and Ca compounds. 6.
  • the present invention it is possible to provide a hot-dip Al-Zn-Si-Mg-plated steel sheet which is free from other defects such as dross defects, suppresses the occurrence of wrinkle-like defects, and has an excellent surface appearance. Furthermore, according to the present invention, it is possible to provide a surface-treated steel sheet having an excellent surface appearance and white rust resistance, and a coated steel sheet having an excellent surface appearance and excellent corrosion resistance.
  • the hot-dip Al-Zn-Si-Mg plated steel sheet of the present invention has a plating film on the surface of the steel sheet.
  • the plating film has a composition containing 45 to 65 mass % Al, 1.0 to 3.0 mass % Si, 1.0 to 10.0 mass % Mg, and 0.01 to 0.5 mass % Mn, with the remainder being Zn and unavoidable impurities.
  • the Al content in the plating film is 45 to 65 mass %, and preferably 50 to 60 mass %, in view of the balance between corrosion resistance and operability. This is because, if the Al content in the plating film is at least 45% by mass, dendritic solidification of Al occurs, and a plating film structure mainly composed of a dendritic solidification structure of the ⁇ -Al phase can be obtained.
  • the dendritic solidification structure is laminated in the thickness direction of the plating film, which complicates the corrosion progression path and improves the corrosion resistance of the plating film itself.
  • the Al content in the plating film exceeds 65% by mass, most of the Zn changes to a structure in which it is solid-dissolved in ⁇ -Al, and the dissolution reaction of the ⁇ -Al phase cannot be suppressed, which may deteriorate the corrosion resistance of the hot-dip Al-Zn-Si-Mg-plated steel sheet.
  • the Al content in the plating film must be 65% by mass or less, and is preferably 60% by mass or less.
  • the Si in the plating film is added mainly for the purpose of suppressing the growth of an Fe-Al and/or Fe-Al-Si interfacial alloy layer formed at the interface with the base steel sheet and preventing deterioration of the adhesion between the plating film and the steel sheet.
  • an alloying reaction occurs between the Fe on the steel sheet surface and the Al and Si in the bath, and an Fe-Al and/or Fe-Al-Si intermetallic compound layer is formed at the interface between the base steel sheet and the plating film.
  • the Si content in the plating film must be 1.0 mass% or more.
  • the Si content in the plating film exceeds 4.0 mass%, not only will the aforementioned effect of inhibiting the growth of the interface alloy layer saturate, but the presence of excess Si phase in the plating film will also promote corrosion, so the Si content in the plating film is set to 4.0 mass% or less.
  • the Si content in the plating film is preferably set to 3.0 mass% or less.
  • the plating film contains 1.0 to 10.0 mass % of Mg.
  • Mg in the plating film, the above-mentioned Si can be present in the form of an intermetallic compound of Mg2Si phase, and the promotion of corrosion can be suppressed.
  • the plating film contains Mg, the intermetallic compound MgZn2 phase is also formed in the plating film, which further improves the corrosion resistance. If the Mg content in the plating film is less than 1.0 mass%, Mg is used to dissolve in the ⁇ -Al phase, which is the main phase, rather than to form the intermetallic compounds ( Mg2Si , MgZn2 ), and sufficient corrosion resistance cannot be ensured.
  • the Mg content in the plating film is high, the effect of improving the corrosion resistance is saturated, and the ⁇ -Al phase becomes weaker, which reduces the workability, so the content is set to 10.0 mass% or less.
  • the Mg content in the plating film is preferably 5.0 mass % or less from the viewpoints of suppressing the generation of dross during plating formation, facilitating plating bath management, and further improving the surface appearance.
  • the plating film contains 0.01 to 0.5 mass% of Mn.
  • the plating film contains 0.01 mass% or more of Mn, a needle-shaped and/or chunky Mn-Fe-based interfacial alloy layer is formed between the plating film and the base steel, and the alloy layer has an anchor effect that suppresses the movement of the plating solution film while the plating is completely solidified, thereby suppressing the occurrence of wrinkle-like defects caused by Mg-based oxides formed on the surface of the plating film.
  • the Mn content in the plating film exceeds 0.5 mass%, the melting point of the plating bath rises, and plating treatment must be performed at a high bath temperature, which causes abnormal growth of the interfacial alloy layer formed between the plating film and the base steel, deteriorating workability, increasing the amount of dross generated, and deteriorating the plating appearance, particularly the surface shape.
  • the Mn content in the plating film is 0.5 mass% or less, the amount of dross generated in the plating bath is the same as when no Mn is added, so the occurrence of dross defects can be suppressed and a stable excellent surface appearance can be obtained. For this reason, the Mn content in the plating film is set to 0.01 to 0.5 mass %. From the same viewpoint, the Mn content in the plating film is preferably 0.1 to 0.3 mass %.
  • the ratio of the Mn content to the Mg content is 0.02 or more (Mn/Mg ⁇ 0.02) by mass ratio with respect to the Mg content of the plating film. From the same viewpoint, it is more preferable that the ratio of the Mn content to the Mg content (Mn/Mg) is 0.03 or more (Mn/Mg ⁇ 0.03).
  • the plating film contains Zn and unavoidable impurities in addition to the above-mentioned Al, Si, Mg, and Mn.
  • the inevitable impurities include Fe.
  • This Fe is inevitably contained in the plating film as a result of dissolution of the steel sheet or bath-immersed equipment into the plating bath, and as a result of being supplied by diffusion from the base steel sheet during the formation of the interface alloy layer.
  • the Fe content in the plating film is usually about 0.3 to 2.0 mass%.
  • Other inevitable impurities include Ni, Cu, etc.
  • the total content of the unavoidable impurities is not particularly limited, but if contained in excess, various properties of the plated steel sheet may be adversely affected, so the total content is preferably 5.0 mass % or less.
  • the hot-dip Al-Zn-Si-Mg plated steel sheet of the present invention is characterized in that the difference in height of the coating surface per mm length is 10 ⁇ m or less in an area excluding 50 mm from both ends of the steel sheet surface.
  • the difference in height of the steel sheet surface i.e., the plating film surface
  • the wrinkle defect is a defect in which the surface of the plating film has a wrinkled uneven shape due to Mg-based oxides, and appears as a white streak pattern on the surface of the plating film. Therefore, suppressing the wrinkle defect means that the streak pattern is not visible.
  • the streak pattern is not visible, and an excellent surface appearance can be obtained. From the same viewpoint, it is preferable that the height difference within a 1 mm long range on the steel sheet surface is within 5 ⁇ m.
  • the steel sheet surface means the outermost surface of the steel sheet, and in the case of a hot-dip Al-Zn-Si-Mg-plated steel sheet, means the surface of the plating film.
  • the height difference on the surface of the steel sheet refers to the difference in height between the highest point and the lowest point on the steel sheet (on the plating film) when the height is taken in the direction perpendicular to the surface of the base steel sheet (in the direction of the plating film thickness).
  • the height difference within a range of 1 mm in length on the steel sheet surface can be obtained, for example, by using a laser microscope to measure the height differences within a range of 1 mm at any 100 points on the hot-dip Al-Zn-Si-Mg-plated steel sheet on which a plating film has been formed, and calculating the average of the measured values.
  • the reason for controlling the height difference of the steel plate surface in the range excluding 50 mm from both ends of the steel plate surface is that it is generally difficult to control the amount of coating at both ends of hot-dip galvanized steel plate compared to the center of the plate, and the cooling rate is also different, making wrinkle-like defects more likely to occur.
  • both ends of the plate are often trimmed before use, so there is little problem with the surface appearance.
  • the method for controlling the height difference of the steel sheet surface per 1 mm of the plating film length to 10 ⁇ m or less is not particularly limited, other than the Mn content in the plating film described above (0.01 to 0.5 mass%).
  • the height difference of the film surface can be reduced by adjusting the content ratio of Mg and Mn in the plating film, or by carrying out other surface treatments to reduce the height difference.
  • an alloy layer containing Mn is preferably formed at the interface between the plating film and the base steel.
  • the alloy layer is formed by an alloying reaction between Mn and Al, Fe, Si, etc. in the bath, and is mainly an Fe-Al-Mn or Fe-Al-Si-Mn intermetallic compound, and has an uneven shape in the plating surface direction, which can improve the adhesion between the plating film and the base steel sheet by an anchor effect.
  • the anchor effect of the Mn-containing alloy layer appears at the time when the plating film solidifies, and the Mn-based interfacial alloy layer acts to minimize the movement of the plating solution film, so that it is also possible to suppress the occurrence of wrinkle-like defects.
  • the intermetallic compounds dissolve preferentially over the ⁇ -Al phase, resulting in a Mg-rich environment in the vicinity of the formed corrosion products. It is presumed that in such a Mg-rich environment, the formed corrosion products are less likely to decompose, and as a result, the protective effect of the plating film is enhanced. In addition, the protective effect of the plating film is more reliably expressed when the Si in the plating film exists as the Mg 2 Si phase rather than the Si phase, so it is considered effective to reduce the ratio of the Si phase to the Mg 2 Si phase.
  • the amount of the plating film required for carrying out the powder X-ray diffraction measurement is 0.1 g or more, preferably 0.3 g or more, from the viewpoint of accurately measuring Si(111) and Mg2Si (111).
  • steel sheet components other than the plating film may be contained in the powder, but these intermetallic compound phases are contained only in the plating film and do not affect the above-mentioned peak intensity.
  • the plating film is powdered and X-ray diffraction is carried out because, when X-ray diffraction is carried out on the plating film formed on the plated steel sheet, it is difficult to calculate the correct phase ratio due to the influence of the plane orientation of the plating film solidification structure.
  • reducing the amount of Si phase is also effective in terms of suppressing the dissolution of the ⁇ -Al phase.
  • a coating without a Si phase as shown in relationship (2) (making the diffraction peak intensity of the Si (111) zero) is the most excellent in terms of stabilizing corrosion resistance.
  • the method for measuring the diffraction peak intensity of the Si (111) plane by X-ray diffraction is as described above.
  • the method for satisfying the above-mentioned relationship (1) or (2) is not particularly limited.
  • the abundance ratio of Mg 2 Si and Si (diffraction intensity of Mg 2 Si (111) and Si (111)) can be controlled by adjusting the balance of the Si content, Mg content, and Al content in the plating film.
  • the balance of the Si content, Mg content, and Al content in the plating film does not necessarily satisfy the relationship (1) or (2) by setting them to a constant content ratio, and it is necessary to change the content ratio of Mg and Al depending on the Si content (mass%), for example.
  • the diffraction intensities of Mg 2 Si (111) and Si (111) can be controlled so as to satisfy relationship (1) or relationship (2) by adjusting the conditions during plating film formation (e.g., cooling conditions after plating).
  • the coating weight of the plating film is preferably 45 to 120 g/ m2 per side from the viewpoint of satisfying various characteristics.
  • the coating weight of the plating film is 45 g/ m2 or more, sufficient corrosion resistance is obtained for applications requiring long-term corrosion resistance, such as building materials, and when the coating weight of the plating film is 120 g/m2 or less , excellent corrosion resistance can be achieved while suppressing the occurrence of plating cracks during processing.
  • the coating weight of the plating film is more preferably 45 to 100 g/ m2 .
  • the coating weight of the plating film can be derived, for example, by a method in which a specific area of the plating film is dissolved and peeled off with a mixed solution of hydrochloric acid and hexamethylenetetramine as specified in JIS H 0401: 2013, and the coating weight is calculated from the difference in the weight of the steel sheet before and after peeling. To determine the coating weight per side using this method, the plating surface of the non-target side is sealed with tape so as not to be exposed, and then the above-mentioned dissolution is carried out.
  • the base steel sheet constituting the hot-dip Al-Zn-Si-Mg-plated steel sheet of the present invention is not particularly limited, and a cold-rolled steel sheet, a hot-rolled steel sheet, or the like can be used as appropriate depending on the required performance and specifications.
  • the method for obtaining the base steel sheet is not particularly limited.
  • the hot-rolled steel sheet one that has been subjected to a hot rolling process and a pickling process can be used, and in the case of the cold-rolled steel sheet, it can be manufactured by further adding a cold rolling process.
  • the method for producing the hot-dip Al-Zn-Si-Mg-plated steel sheet of the present invention is not particularly limited.
  • it can be produced by cleaning, heating, and immersing the base steel sheet in a plating bath in a continuous hot-dip plating facility.
  • recrystallization annealing is performed to control the structure of the base steel sheet itself, and heating in a reducing atmosphere such as a nitrogen-hydrogen atmosphere is effective in preventing oxidation of the steel sheet and reducing the small amount of oxide film present on the surface.
  • the composition of the plating film as a whole is substantially the same as the composition of the plating bath, so that a plating bath containing 45-65 mass% Al, 1.0-3.0 mass% Si, 1.0-10.0 mass% Mg, and 0.1-0.5 mass% Mn, with the remainder consisting of Zn, Fe, and unavoidable impurities, can be used.
  • the temperature of the plating bath is not particularly limited, but is preferably in the 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 needs to be equal to or higher than the solidification point in order to perform hot-dip plating, and by setting the temperature to the melting point + 20° C., solidification due to a local drop in the bath temperature of the plating bath is prevented.
  • the reason why the upper limit of the bath temperature is set to 650° C. is that if the bath temperature exceeds 650° C., rapid cooling of the plating film becomes difficult, and there is a risk that the interfacial alloy layer formed between the plating film and the steel sheet becomes thick.
  • the temperature of the base steel sheet immersed in the coating bath is not particularly limited, but from the viewpoint of ensuring coating characteristics in continuous hot-dip coating operations and preventing changes in bath temperature, it is preferable to control it to within ⁇ 20°C of the coating bath temperature.
  • the immersion time of the base steel sheet in the plating bath is 0.5 seconds or more. This is because if it is less than 0.5 seconds, there is a risk that a sufficient plating film may not be formed on the surface of the base steel sheet.
  • There is no particular upper limit to the immersion time but since a longer immersion time may cause a thicker interface alloy layer to form between the plating film and the steel sheet, it is preferable to set the immersion time to 8 seconds or less.
  • a coating film can be formed directly or via an intermediate layer on the plated film, depending on the required performance.
  • the method for forming the coating film is not particularly limited and can be appropriately selected depending on the required performance.
  • the coating film can be formed by a method such as roll coater coating, curtain flow coating, spray coating, etc. After coating the coating material containing an organic resin, the coating film can be formed by heating and drying the coating film by means of hot air drying, infrared heating, induction heating, etc.
  • the intermediate layer is not particularly limited as long as it is a layer formed between the plating film of the hot-dip plated steel sheet and the coating film.
  • the surface-treated steel sheet of the present invention comprises a plating film on the surface of the steel sheet, and a chemical conversion film formed on the plating film.
  • the composition of the plating film is the same as that of the plating film of the hot-dip Al-Zn-Si-Mg plated steel sheet of the present invention described above.
  • Other configurations of the plating film are also the same as those of the plating film of the hot-dip Al-Zn-Si-Mg-plated steel sheet of the present invention described above.
  • the chemical conversion coating is characterized by containing at least one resin selected from epoxy resins, urethane resins, acrylic resins, acrylic silicone resins, alkyd resins, polyester resins, polyalkylene resins, amino resins, and fluororesins, and at least one metal compound selected from P compounds, Si compounds, Co compounds, Ni compounds, Zn compounds, Al compounds, Mg compounds, V compounds, Mo compounds, Zr compounds, Ti compounds, and Ca compounds.
  • At least one resin selected from epoxy resin, urethane resin, acrylic resin, acrylic silicone resin, alkyd resin, polyester resin, polyalkylene resin, amino resin, and fluororesin is used as the resin constituting the conversion coating.
  • the resin contains at least one of urethane resin and acrylic resin.
  • the resin constituting the conversion coating also includes addition polymers of the above-mentioned resins.
  • epoxy resin for example, glycidyl etherified epoxy resins such as bisphenol A type, bisphenol F type, and novolac type, glycidyl etherified bisphenol A type epoxy resins with propylene oxide, ethylene oxide, or polyalkylene glycol added thereto, aliphatic epoxy resins, alicyclic epoxy resins, polyether-based epoxy resins, etc. can be used.
  • glycidyl etherified epoxy resins such as bisphenol A type, bisphenol F type, and novolac type
  • glycidyl etherified bisphenol A type epoxy resins with propylene oxide, ethylene oxide, or polyalkylene glycol added thereto aliphatic epoxy resins, alicyclic epoxy resins, polyether-based epoxy resins, etc.
  • urethane resin for example, oil-modified polyurethane resin, alkyd-based polyurethane resin, polyester-based polyurethane resin, polyether-based polyurethane resin, polycarbonate-based polyurethane resin, etc. can be used.
  • the acrylic resins include, for example, polyacrylic acid and its copolymers, polyacrylic acid esters and its copolymers, polymethacrylic acid and its copolymers, polymethacrylic acid esters and its copolymers, urethane-acrylic acid copolymers (or urethane-modified acrylic resins), styrene-acrylic acid copolymers, etc. Furthermore, these resins modified with other alkyd resins, epoxy resins, phenolic resins, etc. can also be used.
  • the acrylic silicone resin may be, for example, a resin having hydrolyzable alkoxysilyl groups on the side chains or ends of an acrylic copolymer as the base resin to which a curing agent has been added. Furthermore, when an acrylic silicone resin is used, excellent weather resistance can be expected in addition to corrosion resistance.
  • alkyd resin examples include oil-modified alkyd resin, rosin-modified alkyd resin, phenol-modified alkyd resin, styrenic alkyd resin, silicon-modified alkyd resin, acrylic-modified alkyd resin, oil-free alkyd resin, and high molecular weight oil-free alkyd resin.
  • the polyester resin is a polycondensate synthesized by dehydrating and condensing a polycarboxylic acid and a polyalcohol to form an ester bond.
  • the polycarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid
  • examples of the polyalcohol include ethylene glycol, 1,3-propanediol, 1,4-butanediol, and 1,4-cyclohexanedimethanol.
  • Specific examples of the polyester include polyethylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, and polybutylene naphthalate. Acrylic-modified versions of these polyester resins can also be used.
  • the polyalkylene resin may, for example, be an ethylene-based copolymer such as an ethylene-acrylic acid copolymer, an ethylene-methacrylic acid copolymer, or a carboxyl-modified polyolefin resin, an ethylene-unsaturated carboxylic acid copolymer, or an ethylene-based ionomer.
  • these resins may be modified with other alkyd resins, epoxy resins, phenolic resins, or the like.
  • the amino resin is a thermosetting resin produced by the reaction of an amine or amide compound with an aldehyde, and examples thereof include melamine resin, guanamine resin, and thiourea resin. From the viewpoints of corrosion resistance, weather resistance, and adhesion, it is preferable to use melamine resin.
  • the melamine resin is not particularly limited, but examples thereof include butylated melamine resin, methylated melamine resin, and aqueous melamine resin.
  • the fluororesins mentioned above include fluoroolefin polymers and copolymers of fluoroolefins with alkyl vinyl ethers, cycloalkyl vinyl ethers, carboxylic acid-modified vinyl esters, hydroxyalkyl allyl ethers, tetrafluoropropyl vinyl ethers, etc.
  • fluororesins When these fluororesins are used, not only corrosion resistance but also excellent weather resistance and hydrophobicity can be expected.
  • a hardener for the resin that constitutes the chemical conversion coating, in order to improve corrosion resistance and workability.
  • urea resin butylated urea resin, etc.
  • melamine resin butylated melamine resin, butyl etherified melamine resin, etc.
  • butylated urea-melamine resin amino resin such as benzoguanamine resin, blocked isocyanate, oxazoline compound, phenol resin, etc.
  • the metal compound constituting the chemical conversion coating at least one selected from P compounds, Si compounds, Co compounds, Ni compounds, Zn compounds, Al compounds, Mg compounds, V compounds, Mo compounds, Zr compounds, Ti compounds and Ca compounds is used. From the same viewpoint, it is preferable that the metal compound contains at least one of P compounds, Si compounds and V compounds.
  • the P compound is contained in the chemical conversion coating, thereby improving corrosion resistance and sweat resistance.
  • the P compound is a compound containing P, and may contain, for example, one or more selected from inorganic phosphoric acid, organic phosphoric acid, and salts thereof.
  • the inorganic phosphoric acid, organic phosphoric acid, and salts thereof are not particularly limited and any compound can be used.
  • the inorganic phosphoric acid is preferably one or more selected from phosphoric acid, primary phosphate, secondary phosphate, tertiary phosphate, pyrophosphoric acid, pyrophosphate, tripolyphosphoric acid, tripolyphosphate, phosphorous acid, phosphite, hypophosphorous acid, and hypophosphite.
  • the organic phosphoric acid is preferably phosphonic acid (phosphonic acid compound).
  • the phosphonic acid is preferably one or more selected from nitrilotrismethylenephosphonic acid, phosphonobutanetricarboxylic acid, methyldiphosphonic acid, methylenephosphonic acid, and ethylidenediphosphonic acid.
  • the salt is preferably a salt of an element of Groups 1 to 13 in the periodic table, more preferably a metal salt, and is preferably one or more selected from an alkali metal salt and an alkaline earth metal salt.
  • the chemical conversion treatment solution containing the above-mentioned P compound When the chemical conversion treatment solution containing the above-mentioned P compound is applied to a plated steel sheet, the surface of the plated film is etched by the action of the P compound, and a concentrated layer containing Al, Zn, Si, and Mg, which are the constituent elements of the plated film, is formed on the plated film side of the chemical conversion film.
  • the formation of the concentrated layer strengthens the bond between the chemical conversion film and the plated film surface, improving the adhesion of the chemical conversion film.
  • the concentration of the P compound in the chemical conversion treatment solution is not particularly limited, but can be 0.25% by mass to 5% by mass.
  • the concentration of the P compound is less than 0.25% by mass, the etching effect is insufficient, the adhesion to the plating interface is reduced, and not only the corrosion resistance of the flat surface is reduced, but also the corrosion resistance and sweat resistance of defective parts, cut end faces, and damaged parts of the plating and film caused by processing may be reduced.
  • the concentration of the P compound is preferably 0.35% by mass or more, more preferably 0.50% by mass or more.
  • the concentration of the 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 when formed is likely to be non-uniform, and the amount of P eluted from the chemical conversion film may increase, which may reduce the resistance to blackening.
  • the concentration of the P compound is preferably 3.5% by mass or less, more preferably 2.5% by mass or less.
  • the content of the P compound in the chemical conversion coating for example, by applying a chemical conversion treatment solution with a P compound concentration of 0.25% by mass to 5% by mass and drying it, the amount of P attached in the chemical conversion coating after drying can be set to 5 to 100 mg/ m2 .
  • the Si compound is a component that becomes the framework that forms the chemical conversion film together with the resin, and it enhances the affinity with the plating film, and can form a uniform chemical conversion film.
  • the Si compound is a compound that contains Si, and preferably contains one or more selected from, for example, silica, trialkoxysilane, tetraalkoxysilane, and a silane coupling agent.
  • the silica is not particularly limited and any type can be used.
  • at least one of wet silica and dry silica can be used.
  • colloidal silica which is a type of wet silica, for example, Snowtex O, C, N, S, 20, OS, OXS, NS, etc. manufactured by Nissan Chemical Co., Ltd. can be suitably used.
  • dry silica for example, AEROSIL 50, 130, 200, 300, 380, etc. manufactured by Nippon Aerosil Co., Ltd. can be suitably used.
  • the trialkoxysilane is not particularly limited and any trialkoxysilane can be used.
  • a trialkoxysilane represented by the general formula: R 1 Si(OR 2 ) 3 (wherein R 1 is hydrogen or an alkyl group having 1 to 5 carbon atoms, and R 2 is the same or different alkyl group having 1 to 5 carbon atoms).
  • R 1 is hydrogen or an alkyl group having 1 to 5 carbon atoms
  • R 2 is the same or different alkyl group having 1 to 5 carbon atoms.
  • Examples of such trialkoxysilane include trimethoxysilane, triethoxysilane, and methyltriethoxysilane.
  • the tetraalkoxysilane is not particularly limited and any tetraalkoxysilane can be used.
  • R is the same or different alkyl group having 1 to 5 carbon atoms.
  • Examples of such tetraalkoxysilane include tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane.
  • the silane coupling agent is not particularly limited and any one can be used. Examples include ⁇ -glycidoxypropyltrimethoxysilane, ⁇ -glycidoxypropylmethyldiethoxysilane, ⁇ -glycidoxypropyltriethoxysilane, ⁇ -aminopropyltrimethoxysilane, ⁇ -aminopropylmethyldiethoxysilane, ⁇ -aminopropyltriethoxysilane, ⁇ -methacryloxypropyltrimethoxysilane, ⁇ -methacryloxypropyltriethoxysilane, ⁇ -mercaptopropylmethyldimethoxysilane, ⁇ -mercaptopropyltrimethoxysilane, vinyltriethoxysilane, ⁇ -isocyanatopropyltriethoxysilane, etc.
  • the Si compound undergoes dehydration condensation to form an amorphous chemical conversion film having siloxane bonds that have a high barrier effect of blocking corrosion factors.
  • a chemical conversion film with higher barrier properties is formed.
  • dense and stable corrosion products are formed in defective parts and damaged parts of the plating or film caused by processing, etc., and the combined effect with the plating film also has the effect of suppressing corrosion of the underlying steel sheet. From the viewpoint of a high effect of forming stable corrosion products, it is preferable to use at least one of colloidal silica and dry silica as the Si compound.
  • the concentration of the Si compound in the chemical 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% by mass or more, a barrier effect due to siloxane bonds can be obtained, and as a result, in addition to the corrosion resistance of the flat surface, the corrosion resistance of defective parts, cut parts, and damaged parts caused by processing, etc., and sweat resistance are improved. Furthermore, if the concentration of the Si compound is 9.5% by mass or less, the life of the chemical conversion treatment liquid can be extended. By applying and drying a chemical conversion treatment liquid with a concentration of Si compound of 0.2% by mass to 9.5% by mass, the Si adhesion amount in the chemical conversion film after drying can be set to 2 to 95 mg/ m2 .
  • the Co compounds and Ni compounds contained in the chemical conversion coating can improve resistance to blackening. This is believed to be because Co and Ni have the effect of delaying the elution of water-soluble components from the coating in a corrosive environment. Furthermore, the Co and Ni are elements that are less susceptible to oxidation than Al, Zn, Si, Mg, etc. Therefore, by concentrating at least one of the Co compounds and the Ni compounds (forming a concentrated layer) at the interface between the chemical conversion coating and the plating coating, the concentrated layer acts as a barrier against corrosion, improving resistance to blackening.
  • Co By using a chemical conversion treatment solution containing the Co compound, Co can be contained in the chemical conversion coating and incorporated into the concentrated layer.
  • a cobalt salt is preferably used.
  • the cobalt salt one or more selected from cobalt sulfate, cobalt carbonate, and cobalt chloride are more preferably used.
  • a chemical conversion treatment solution containing the Ni compound Ni can be contained in the chemical conversion coating and incorporated into the concentrated layer.
  • a nickel salt is preferably used.
  • the nickel salt it is more preferable to use one or more selected from nickel sulfate, nickel carbonate, and nickel chloride.
  • the concentration of the Co compound and/or Ni compound in the chemical conversion treatment liquid is not particularly limited, but can be 0.25% by mass to 5% by mass in total. If the concentration of the Co compound and/or Ni compound is less than 0.25% by mass, the interface thickening layer becomes nonuniform, and not only the corrosion resistance of the flat portion decreases, but also the corrosion resistance of the defective portion, the cut end surface portion, the plating or the film damaged portion due to processing, etc. may decrease. From the same viewpoint, it is preferably 0.5% by mass or more, more preferably 0.75% by mass or more. On the other hand, if the concentration of the Co compound and/or Ni compound exceeds 5% by mass, the appearance when the film is formed tends to be nonuniform, and the corrosion resistance may decrease.
  • the total adhesion amount of Co and Ni in the chemical conversion film after drying can be 5 to 100 mg/m 2 .
  • the Al compound, the Zn compound, and the Mg compound are contained in the chemical conversion treatment solution, so that a concentrated layer containing at least one of Al, Zn, and Mg can be formed on the plating film side of the chemical conversion film.
  • the formed concentrated layer can improve corrosion resistance.
  • the Al compound, the Zn compound, and the Mg compound are not particularly limited as long as they are compounds containing Al, Zn, and Mg, respectively, but are preferably inorganic compounds, and are preferably salts, chlorides, oxides, or hydroxides.
  • the Al compound may be, for example, one or more selected from aluminum sulfate, aluminum carbonate, aluminum chloride, aluminum oxide, and aluminum hydroxide.
  • the Zn compound may be, for example, one or more selected from zinc sulfate, zinc carbonate, zinc chloride, zinc oxide, and zinc hydroxide.
  • the Mg compound may be, for example, one or more selected from magnesium sulfate, magnesium carbonate, magnesium chloride, magnesium oxide, and magnesium hydroxide.
  • the concentration of the Al compounds, Zn compounds and/or Mg compounds in the chemical conversion treatment solution for forming the chemical conversion coating is preferably 0.25% to 5% by mass in total. If the total concentration is 0.25% by mass or more, the concentrated layer can be formed more effectively, and as a result, corrosion resistance can be further improved. On the other hand, if the total concentration is 5% by mass or less, the appearance of the chemical conversion coating becomes more uniform, and the corrosion resistance of flat areas, defective areas, and damaged areas of the plating or coating caused by processing, etc. is further improved.
  • the V compound contained in the chemical conversion film allows the V to dissolve appropriately in a corrosive environment and bind with zinc ions and other plating components that also dissolve in a corrosive environment to form a dense protective film.
  • the protective film formed can further increase corrosion resistance not only to the flat surface of the steel sheet, but also to defects, damaged areas of the plating film caused by processing, and corrosion that progresses from the cut end surface to the flat surface.
  • the V compound is a compound containing V, and examples thereof include one or more selected from sodium metavanadate, vanadyl sulfate, and vanadium acetylacetonate.
  • the V compound in the chemical conversion treatment solution for forming the chemical conversion film is preferably 0.05% to 4% by mass. If the concentration of the V compound is 0.05% by mass or more, it will be easier to dissolve in a corrosive environment and form a protective film, improving the corrosion resistance of defects, cut end surfaces, and damaged areas of the plating film caused by processing. On the other hand, if the concentration of the V compound exceeds 4% by mass, the appearance of the formed chemical conversion film is likely to be non-uniform, and resistance to blackening will also decrease.
  • the Mo compound when contained in the chemical conversion coating, can enhance the blackening resistance of the surface-treated steel sheet.
  • the Mo compound is a compound containing Mo, and can be obtained by adding one or both of molybdic acid and a molybdate to the chemical conversion treatment solution.
  • the molybdate may be, for example, one or more selected from sodium molybdate, potassium molybdate, magnesium molybdate, and zinc molybdate.
  • the concentration of the Mo compound in the chemical conversion treatment solution for forming the chemical conversion coating is preferably 0.01% to 3% by mass. If the concentration of the Mo compound is 0.01% by mass or more, the generation of oxygen-deficient zinc oxide is further suppressed, and blackening resistance can be further improved. On the other hand, if the concentration of the Mo compound is 3% by mass or less, the life of the chemical conversion treatment solution is further extended and corrosion resistance can be further improved.
  • the Zr compound and the Ti compound contained in the chemical conversion coating prevent the chemical conversion coating from becoming porous and make the coating denser. As a result, corrosion factors are less likely to penetrate the chemical conversion coating, and corrosion resistance can be improved.
  • the Zr compound is a compound containing Zr, and for example, one or more selected from zirconyl acetate, zirconyl sulfate, potassium zirconyl carbonate, sodium zirconyl carbonate, and ammonium zirconyl carbonate can be used.
  • organic titanium chelate compounds are preferred because they densify the film when the chemical conversion treatment liquid is dried to form the film, resulting in better corrosion resistance.
  • the Ti compound is a compound containing Ti, and can be, for example, one or more selected from titanium sulfate, titanium chloride, titanium hydroxide, titanium acetylacetonate, titanium octylene glycolate, and titanium ethyl acetoacetate.
  • the concentration of Zr compounds and/or Ti compounds in the chemical conversion treatment solution for forming the chemical conversion film is preferably 0.2% to 20% by mass in total. If the total concentration of the Zr compounds and/or Ti compounds is 0.2% by mass or more, the effect of inhibiting the permeation of corrosion factors is enhanced, and the corrosion resistance of not only flat surface parts but also defective parts, cut end faces, and parts of the plating film damaged by processing can be further improved. On the other hand, if the total concentration of the Zr compounds and/or Ti compounds is 20% by mass or less, the life of the chemical conversion treatment solution can be further extended.
  • the Ca compound when contained in the chemical conversion coating, can exert the effect of reducing the corrosion rate.
  • the Ca compound is a compound containing Ca, and examples of the Ca compound include Ca oxide, Ca nitrate, Ca sulfate, and intermetallic compounds containing Ca. More specifically, examples of the Ca compound include CaO, CaCO3 , Ca( OH ) 2 , Ca (NO3)2.4H2O , and CaSO4.2H2O .
  • the content of the Ca compound in the chemical conversion coating is not particularly limited.
  • the conversion coating may contain various known components commonly used in the coating field, if necessary. Examples include various surface conditioners such as leveling agents and defoamers, various additives such as dispersants, anti-settling agents, UV absorbers, light stabilizers, silane coupling agents, and titanate coupling agents, various pigments such as color pigments, extender pigments, and lustrous materials, curing catalysts, organic solvents, and lubricants.
  • various surface conditioners such as leveling agents and defoamers
  • various additives such as dispersants, anti-settling agents, UV absorbers, light stabilizers, silane coupling agents, and titanate coupling agents
  • various pigments such as color pigments, extender pigments, and lustrous materials
  • curing catalysts organic solvents, and lubricants.
  • the chemical conversion coating does not contain harmful components such as hexavalent chromium, trivalent chromium, and fluorine. This is because the chemical conversion treatment liquid used to form the chemical conversion coating does not contain these harmful components, making it safer and less impactful on the environment.
  • the coating weight of the chemical conversion coating is not particularly limited.
  • the coating weight of the chemical conversion coating is preferably 0.1 to 3.0 g/ m2 , and more preferably 0.5 to 2.5 g/ m2 .
  • the coating weight of the chemical conversion coating may be determined by a method appropriately selected from existing techniques, such as a method of subjecting the coating to fluorescent X-ray analysis to measure the amount of an element present in the coating whose content is known in advance.
  • the method for forming the chemical conversion coating is not particularly limited, and can be appropriately selected depending on the required performance, manufacturing equipment, etc.
  • the chemical conversion coating can be formed by continuously applying a chemical conversion treatment liquid onto the plating film using a roll coater or the like, and then drying at a peak metal temperature (PMT) of about 60 to 200°C using hot air or induction heating.
  • PMT peak metal temperature
  • known methods such as airless spray, electrostatic spray, and curtain flow coater can be appropriately used to apply the chemical conversion treatment liquid.
  • the chemical conversion coating can be either a single-layer film or a multi-layer film as long as it contains the resin and the metal compound, and is not particularly limited.
  • the surface-treated steel sheet of the present invention has a height difference of 10 ⁇ m or less per mm length in a range excluding 50 mm from both ends of the steel sheet surface (chemical conversion coating surface), similar to the surface of the hot-dip Al-Zn-Si-Mg-plated steel sheet of the present invention described above.
  • the height difference of the surface of the chemical conversion coating is 10 ⁇ m or less, there are no wrinkle-like defects and an excellent surface appearance can be obtained.
  • the wrinkle defects are defects in which the surface of the chemical conversion coating is wrinkled and uneven due to Mg-based oxides, and appear as white streaks on the surface of the chemical conversion coating. Therefore, suppressing the wrinkle defects means that the streaks are not visible.
  • the height difference within a 1 mm long range of the steel sheet surface i.e., the chemical conversion coating surface
  • the streaks are not visible, and an excellent surface appearance can be obtained.
  • it is preferable that the height difference within a 1 mm long range of the steel sheet surface is within 5 ⁇ m.
  • the steel sheet surface means the outermost surface of the steel sheet, and in the case of a surface-treated steel sheet, means the surface of the chemical conversion coating.
  • the height difference on the surface of the steel sheet refers to the difference in height between the highest point and the lowest point on the steel sheet (on the chemical conversion coating) when the height is taken in the direction perpendicular to the surface of the base steel sheet (in the direction of the plating thickness).
  • the method of obtaining the height difference within a 1 mm long range of the chemical conversion coating surface can be similar to that of the plating coating surface described above, in which the height difference within a 1 mm range at any 100 points on the surface-treated steel sheet is measured using a laser microscope and the average of the measured values is calculated.
  • the reason for controlling the height difference on the surface of the steel plate in the area excluding 50 mm from both ends of the steel plate is that it is generally difficult to control the amount of coating at both ends of a hot-dip galvanized steel plate compared to the center of the plate, and the cooling rate is also different, making wrinkle-like defects more likely to occur.
  • both ends of the plate are often trimmed before use, so the surface appearance is of little concern.
  • the method of controlling the height difference of the coating surface to 10 ⁇ m or less per 1 mm of length of the steel plate surface, it is important to suppress the height difference of the plating film surface as described above, and the height difference of the coating surface can be suppressed by adjusting the content ratio of Mg and Mn in the plating film or by carrying out other surface treatments to suppress the height difference.
  • the surface-treated steel sheet of the present invention can have a paint film formed on the chemical conversion coating.
  • the method for producing a surface-treated steel sheet of the present invention is a method for producing a surface-treated steel sheet comprising a plating film and a chemical conversion film formed on the plating film.
  • the chemical conversion coating contains at least one resin selected from the group consisting of epoxy resins, urethane resins, acrylic resins, acrylic silicone resins, alkyd resins, polyester resins, polyalkylene resins, amino resins, and fluororesins, and at least one metal compound selected from the group consisting of P compounds, Si compounds, Co compounds, Ni compounds, Zn compounds, Al compounds, Mg compounds, V compounds, Mo compounds, Zr compounds, Ti compounds, and Ca compounds,
  • the formation of the plating film includes a hot-dip galvanizing process in which a base steel sheet is immersed in a plating bath having a composition containing 45 to 65 mass% Al, 1.0 to 4.0 mass% Si, and 1.0 to 10.0 mass% Mg, with the balance being Zn and unavoidable impurities.
  • the conditions for the hot-dip galvanizing process are the same as those described for the hot-dip Al-Zn-Si-Mg-plated steel sheet of the present invention.
  • the coated steel sheet of the present invention is a coated steel sheet in which a coating film is formed on a plating film directly or via a chemical conversion film.
  • the composition of the plating film is the same as that of the plating film of the above-mentioned hot-dip Al-Zn-Si-Mg plated steel sheet of the present invention.
  • Other configurations of the plating film are also the same as those of the plating film of the hot-dip Al-Zn-Si-Mg-plated steel sheet of the present invention described above.
  • a chemical conversion film can be formed on the plating film.
  • the chemical conversion coating may be formed on at least one side of the coated steel sheet, and may also be formed on both sides of the coated steel sheet depending on the application and required performance.
  • Chemical conversion coating In the coated steel sheet of the present invention, the chemical conversion coating is characterized in that it contains a resin component containing 30 to 50 mass% in total of (a): an anionic polyurethane resin having an ester bond and (b): an epoxy resin having a bisphenol skeleton, the content ratio of (a) to (b) ((a):(b)) being in the range of 3:97 to 60:40 in terms of mass ratio, and inorganic compounds including 2 to 10 mass% of a vanadium compound, 40 to 60 mass% of a zirconium compound, and 0.5 to 5 mass% of a fluorine compound.
  • a resin component containing 30 to 50 mass% in total of (a): an anionic polyurethane resin having an ester bond and (b): an epoxy resin having a bisphenol skeleton, the content ratio of (a) to (b) ((a):(b)) being in the range of 3:97 to 60:40 in terms of mass ratio, and inorganic compounds including 2 to
  • the resin components constituting the chemical conversion coating include (a): an anionic polyurethane resin having an ester bond and (b): an epoxy resin having a bisphenol skeleton.
  • the (a) anionic polyurethane resin having an ester bond there can be mentioned a resin obtained by copolymerizing a reaction product of a polyester polyol with a diisocyanate or polyisocyanate having two or more isocyanate groups with a dimethylol alkyl acid.
  • a chemical conversion treatment liquid can be obtained by dispersing the resin in a liquid such as water by a known method.
  • polyester polyol examples include polyesters obtained by a dehydration condensation reaction between a glycol component and an acid component such as an ester-forming derivative of a hydroxyl carboxylic acid, polyesters obtained by a ring-opening polymerization reaction of a cyclic ester compound such as ⁇ -caprolactone, and copolymer polyesters thereof.
  • polyisocyanate examples include aromatic polyisocyanates, aliphatic polyisocyanates, alicyclic polyisocyanates, etc.
  • aromatic polyisocyanate examples include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, m-xylylene diisocyanate, diphenylmethane diisocyanate, 2,4-diphenylmethane diisocyanate, 2,2-diphenylmethane diisocyanate, triphenylmethane triisocyanate, polymethylene polyphenyl polyisocyanate, naphthalene diisocyanate, and derivatives thereof (for example, prepolymers obtained by reaction with polyols, modified polyisocyanates such as carbodiimide compounds of diphenylmethane diisocyanate, etc.).
  • dimethylol alkyl acid When synthesizing urethane by reacting the polyester polyol with the diisocyanate or polyisocyanate, for example, dimethylol alkyl acid can be copolymerized and self-emulsified to be water-soluble (dispersed in water) to obtain the anionic polyurethane resin having the ester bond (a).
  • examples of the dimethylol alkyl acid include dimethylol alkyl acids having 2 to 6 carbon atoms, and more specifically, dimethylol ethanoic acid, dimethylol propanoic acid, dimethylol butanoic acid, dimethylol heptanoic acid, and dimethylol hexanoic acid.
  • the resin components act as binders for the chemical conversion coating, and the (a) anionic polyurethane resin having ester bonds that constitutes the binder is flexible and therefore has the effect of making the chemical conversion coating less likely to be destroyed (peeled off) when processed, and the (b) epoxy resin having a bisphenol skeleton has the effect of improving adhesion to the underlying zinc-based plated steel sheet and the overlying primer coating.
  • the resin components are contained in the chemical conversion coating in a total amount of 30 to 50% by mass. If the content of the resin components is less than 30% by mass, the binder effect of the chemical conversion coating is reduced, and if it exceeds 50% by mass, the functions of the inorganic components described below, such as the inhibitor action, are reduced. From the same viewpoint, the content of the resin components in the chemical conversion coating is preferably 35 to 45% by mass.
  • the resin component requires that the content ratio ((a):(b)) of the anionic polyurethane resin having an ester bond (a) and the epoxy resin having a bisphenol skeleton (b) is in the range of 3:97 to 60:40 by mass. If the (a):(b) ratio is outside the above range, the flexibility and adhesion of the chemical conversion coating will decrease, and sufficient corrosion resistance will not be obtained. From the same viewpoint, the (a):(b) ratio is preferably 10:90 to 55:45.
  • the resin component may contain resins (other resin components) other than the above-mentioned (a) anionic polyurethane resin having an ester bond and (b) epoxy resin having a bisphenol skeleton, depending on the required performance.
  • the other resin components are not particularly limited, and may be, for example, at least one selected from acrylic resins, acrylic silicone resins, alkyd resins, polyester resins, polyalkylene resins, amino resins, and fluororesins, or a combination of two or more selected therefrom.
  • 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 75% by mass or more, in order to more reliably prevent a decrease in flexibility and obtain adhesion as a conversion coating.
  • the chemical conversion coating contains, as inorganic compounds, 2 to 10 mass % of a vanadium compound, 40 to 60 mass % of a zirconium compound, and 0.5 to 5 mass % of a fluorine compound. By including these compounds, the corrosion resistance of the chemical conversion coating can be improved.
  • the vanadium compound is added to the chemical conversion solution and acts as a rust inhibitor.
  • the vanadium compound is contained in the chemical conversion coating, so that the vanadium compound is appropriately dissolved in a corrosive environment and combines with zinc ions of the plating components that are also dissolved in a corrosive environment to form a dense protective coating.
  • the formed protective coating can further increase the corrosion resistance not only of the flat surface of the steel sheet, but also of defects, damaged parts of the plating film caused by processing, corrosion that progresses from the cut end surface to the flat surface, and the like.
  • vanadium compound examples include vanadium pentoxide, metavanadic acid, ammonium metavanadate, vanadium oxytrichloride, vanadium trioxide, vanadium dioxide, magnesium vanadate, vanadyl acetylacetonate, vanadium acetylacetonate, etc.
  • vanadium pentoxide metavanadic acid
  • ammonium metavanadate vanadium oxytrichloride
  • vanadium trioxide vanadium dioxide
  • magnesium vanadate vanadyl acetylacetonate
  • vanadium acetylacetonate etc.
  • the content of the vanadium compound in the chemical conversion coating is 2 to 10% by mass. If the content of the vanadium compound in the chemical conversion coating is less than 2% by mass, the inhibitor effect is insufficient, resulting in a decrease in corrosion resistance, while if the content of the vanadium compound exceeds 10% by mass, the moisture resistance of the chemical conversion coating decreases.
  • the zirconium compound is contained in the chemical conversion coating, and is expected to improve the strength and corrosion resistance of the chemical conversion coating through its reaction with the plating metal and its coexistence with a resin component. Furthermore, the zirconium compound itself contributes to the formation of a dense chemical conversion coating, and because of its excellent covering properties, a barrier effect can be expected. Examples of the zirconium compound include neutral salts of zirconium sulfate, zirconium carbonate, zirconium nitrate, zirconium lactate, zirconium acetate, zirconium chloride, and the like.
  • the content of the zirconium compound in the chemical conversion coating is 40-60% by mass. If the content of the zirconium compound in the chemical conversion coating is less than 40% by mass, the strength and corrosion resistance of the chemical conversion coating will decrease, and if the content of the zirconium compound exceeds 60% by mass, the chemical conversion coating will become brittle, causing damage or peeling of the chemical conversion coating when subjected to severe processing.
  • the fluorine compound is contained in the chemical conversion coating and acts as an adhesive agent for the plating coating, thereby making it possible to improve the corrosion resistance of the chemical conversion coating.
  • fluorine compound for example, fluoride salts such as ammonium salts, sodium salts, potassium salts, or fluorine compounds such as ferrous fluoride, ferric fluoride, etc.
  • fluoride salts such as ammonium fluoride, sodium fluoride, and potassium fluoride.
  • the content of the fluorine compound in the chemical conversion coating is 0.5 to 5% by mass. If the content of the fluorine compound in the chemical conversion coating is less than 0.5% by mass, sufficient adhesion cannot be obtained at the processed area, and if the content of the fluorine compound exceeds 5% by mass, the moisture resistance of the chemical conversion coating decreases.
  • the coating weight of the chemical conversion coating is not particularly limited. For example, from the viewpoint of improving the adhesion of the chemical conversion coating while more reliably ensuring corrosion resistance, it is preferable to set the coating weight of the chemical conversion coating to 0.025 to 0.5 g/m2. By setting the coating weight of the chemical conversion coating to 0.025 g/ m2 or more, corrosion resistance can be more reliably ensured, and by setting the coating weight of the chemical conversion coating to 0.5 g/ m2 or less , peeling of the chemical conversion coating can be suppressed.
  • the coating weight of the chemical conversion coating may be determined by a method appropriately selected from existing techniques, such as a method of subjecting the coating to fluorescent X-ray analysis to measure the amount of an element present in the coating whose content is known in advance.
  • the method for forming the chemical conversion coating is not particularly limited, and can be appropriately selected depending on the required performance, manufacturing equipment, etc.
  • the chemical conversion coating can be formed by continuously applying a chemical conversion treatment liquid onto the plating film using a roll coater or the like, and then drying at a peak metal temperature (PMT) of about 60 to 200°C using hot air or induction heating.
  • PMT peak metal temperature
  • known methods such as airless spray, electrostatic spray, and curtain flow coater can be appropriately used to apply the chemical conversion treatment liquid.
  • the chemical conversion coating can be either a single-layer film or a multi-layer film as long as it contains the resin and the metal compound, and is not particularly limited.
  • the coated steel sheet of the present invention has a coating film formed directly or via a chemical conversion film on the plating film, and the coating film has at least a primer coating film.
  • the primer coating film contains a polyester resin having a urethane bond, and an inorganic compound including a vanadium compound, a phosphate compound, and magnesium oxide.
  • the primer coating film contains the polyester resin having a urethane bond and the inorganic compound, and therefore the adhesion of the coating film can be increased and the corrosion resistance can be improved.
  • the primer coating contains a polyester resin having a urethane bond as a main component.
  • the polyester resin having a urethane bond is flexible and strong, so that the primer coating is less likely to crack when processed, and has a high affinity with the chemical conversion coating containing a urethane resin, so that the primer coating can particularly contribute to improving the corrosion resistance of the processed part.
  • the term "main component” used herein means the component that is contained in the greatest amount among all the components in the primer coating film.
  • polyester resin having urethane bonds known resins can be used, such as resins obtained by reacting polyester polyol with diisocyanate or polyisocyanate having two or more isocyanate groups.
  • resins obtained by reacting the polyester polyol with the diisocyanate or polyisocyanate in a state of excess hydroxyl groups (urethane-modified polyester resin) with blocked polyisocyanate can also be used.
  • the polyester polyol can be obtained by a known method utilizing a dehydration condensation reaction between a polyhydric alcohol component and a polybasic acid component.
  • the polyhydric alcohol include glycols and trihydric or higher polyhydric alcohols.
  • the glycols include ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, neopentyl glycol, hexylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2-butyl-2-ethyl-1,3-propanediol, methylpropanediol, cyclohexanedimethanol, and 3,3-diethyl-1,5-pentanediol.
  • trihydric or higher polyhydric alcohols examples include glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, and dipentaerythritol. These polyhydric alcohols can be used alone or in combination of two or more.
  • a polyvalent carboxylic acid is usually used, but a monovalent fatty acid or the like can be used in combination as necessary.
  • polybasic acid examples include phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, 4-methylhexahydrophthalic acid, bicyclo[2,2,1]heptane-2,3-dicarboxylic acid, trimellitic acid, adipic acid, sebacic acid, succinic acid, azelaic acid, fumaric acid, maleic acid, itaconic acid, pyromellitic acid, dimer acid, and the like, and acid anhydrides thereof, as well as 1,4-cyclohexanedicarboxylic acid, isophthalic acid, tetrahydroisophthalic acid, hexahydroisophthalic acid, hexahydroterephthalic acid, and the like. These polybasic acids can be used alone or in combination of two or more.
  • 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, and even more preferably 10 to 80 mgKOH/g.
  • 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 even more preferably 800 to 10,000, from the viewpoints of solvent resistance, processability, and the like.
  • the content of the polyester resin having urethane bonds in the primer coating is preferably 40 to 88% by mass. If the content of the polyester resin having urethane bonds is less than 40% by mass, the binder function of the primer coating may be reduced, while if the content of the polyester resin having urethane bonds exceeds 88% by mass, the functions of the inorganic substances described below, such as the inhibitor effect, may be reduced.
  • Vanadium compounds which are one of the inorganic compounds, act as inhibitors.
  • the vanadium compounds include vanadium pentoxide, metavanadic acid, ammonium metavanadate, vanadium oxytrichloride, vanadium trioxide, vanadium dioxide, magnesium vanadate, vanadyl acetylacetonate, vanadium acetylacetonate, etc.
  • the vanadium compound added to the primer coating may be the same or different from the vanadium compound added to the chemical conversion coating.
  • vanadate ions which are gradually dissolved by moisture entering from the outside, react with ions on the surface of the zinc-based plated steel sheet to form a passive film with good adhesion, protecting the exposed metal parts and exerting a rust-preventing effect.
  • the content of the vanadium compound in the primer coating is not particularly limited, but is preferably 4 to 20 mass% from the viewpoint of achieving both corrosion resistance and moisture resistance. If the content of the vanadium compound is less than 4 mass%, the inhibitor effect may decrease, leading to a decrease in corrosion resistance, and if the content of the vanadium compound is more than 20 mass%, the moisture resistance of the primer coating may decrease.
  • the content of the phosphate compound in the primer coating is not particularly limited, but is preferably 4 to 20% by mass from the viewpoint of achieving both corrosion resistance and moisture resistance. If the content of the phosphate compound is less than 4% by mass, the inhibitor effect may decrease, leading to a decrease in corrosion resistance, and if the content of the phosphate compound is more than 20% by mass, the moisture resistance of the primer coating may decrease.
  • Magnesium oxide one of the inorganic compounds, produces products containing Mg during initial corrosion, and as a poorly soluble magnesium salt, it has the effect of stabilizing the material and improving corrosion resistance.
  • the content of the magnesium oxide in the primer coating is not particularly limited, but is preferably 4 to 20% by mass from the viewpoint of achieving both corrosion resistance and corrosion resistance of the processed part. If the content of the magnesium oxide is less than 4% by mass, the above effect may decrease, leading to a decrease in corrosion resistance, and if the content of the magnesium oxide is more than 20% by mass, the flexibility of the primer coating may decrease, leading to a decrease in the corrosion resistance of the processed part.
  • the primer coating film may also contain components other than the above-mentioned polyester resin having a urethane bond and inorganic compound.
  • a crosslinking agent used in forming a primer coating film can be mentioned.
  • the crosslinking agent reacts with the polyester resin having the urethane bond to form a crosslinked coating film, and examples thereof include oxazoline compounds, epoxy compounds, melamine compounds, isocyanate compounds, carbodiimide compounds, silane coupling compounds, etc., and it is also possible to use two or more types of crosslinking agents in combination. Among them, from the viewpoint of corrosion resistance of the processed part of the obtained coated steel plate, blocked polyisocyanate compounds and the like can be preferably used.
  • blocked polyisocyanate examples include those in which the isocyanate group of a polyisocyanate compound is blocked with, for example, alcohols such as butanol, oximes such as methyl ethyl ketoxime, lactams such as ⁇ -caprolactams, diketones such as acetoacetic acid diester, imidazoles such as imidazole and 2-ethylimidazole, or phenols such as m-cresol.
  • alcohols such as butanol
  • oximes such as methyl ethyl ketoxime
  • lactams such as ⁇ -caprolactams
  • diketones such as acetoacetic acid diester
  • imidazoles such as imidazole and 2-ethylimidazole
  • phenols such as m-cresol.
  • the primer coating film may contain various known components commonly used in the paint industry, if necessary. Specific examples include various surface conditioners such as leveling agents and defoamers, various additives such as dispersants, anti-settling agents, UV absorbers, light stabilizers, silane coupling agents, and titanate coupling agents, various pigments such as color pigments and extender pigments, luster materials, curing catalysts, and organic solvents.
  • various surface conditioners such as leveling agents and defoamers
  • various additives such as dispersants, anti-settling agents, UV absorbers, light stabilizers, silane coupling agents, and titanate coupling agents
  • various pigments such as color pigments and extender pigments, luster materials, curing catalysts, and organic solvents.
  • the thickness of the primer coating is preferably 1.5 ⁇ m or more. By making the thickness of the primer coating 1.5 ⁇ m or more, it is possible to more reliably obtain the effect of improving corrosion resistance and the effect of improving adhesion with the chemical conversion coating and the topcoat coating formed on the primer coating.
  • the method for forming the primer coating is not particularly limited.
  • the coating composition constituting the primer coating can be preferably applied by a method such as roll coater coating or curtain flow coating.
  • the primer coating can be obtained by baking using a heating means such as hot air heating, infrared heating, or induction heating. The baking process is usually performed at a maximum plate temperature of about 180 to 270°C for about 30 seconds to 3 minutes in this temperature range.
  • a top coating film is further formed on the primer coating film.
  • the topcoat coating film can impart beauty to the coated steel sheet, such as color, gloss, and surface condition, and can also improve various performance properties, such as processability, weather resistance, chemical resistance, stain resistance, water resistance, and corrosion resistance.
  • the configuration of the topcoat coating is not particularly limited, and the material, thickness, etc. can be appropriately selected depending on the required performance.
  • the topcoat film can be formed using a polyester resin paint, a silicon polyester resin paint, a polyurethane resin paint, an acrylic resin paint, a fluororesin paint, or the like.
  • the topcoat coating film may contain appropriate amounts of titanium oxide, red iron oxide, mica, carbon black or other various coloring pigments; metallic pigments such as aluminum powder and mica; extender pigments consisting of carbonates, sulfates, etc.; various fine particles such as silica fine particles, nylon resin beads, acrylic resin beads, etc.; curing catalysts such as p-toluenesulfonic acid and dibutyltin dilaurate; wax; and other additives.
  • the thickness of the topcoat film is 5 to 30 ⁇ m. If the thickness of the topcoat film is 5 ⁇ m or more, it is possible to more reliably stabilize the color appearance, and if the thickness of the topcoat film is 30 ⁇ m or less, it is possible to more reliably prevent a decrease in workability (the occurrence of cracks in the topcoat film).
  • the method of applying the coating composition to form the topcoat film is not particularly limited.
  • the coating composition can be applied by a method such as roll coater coating or curtain flow coating.
  • the topcoat film can be formed by baking using a heating means such as hot air heating, infrared heating or induction heating.
  • the baking process is usually performed at a maximum plate temperature of about 180 to 270°C for about 30 seconds to 3 minutes in this temperature range.
  • the coated steel sheet of the present invention is characterized in that, like the surface of the hot-dip Al-Zn-Si-Mg-plated steel sheet of the present invention described above, the height difference of the steel sheet surface (coating surface) per mm length is 10 ⁇ m or less in an area excluding 50 mm from both ends of the steel sheet.
  • the height difference of the coating film surface is 10 ⁇ m or less, there are no wrinkle-like defects and an excellent surface appearance can be obtained.
  • the wrinkle defects are defects in which the surface of the coating film is wrinkled and uneven due to Mg-based oxides, and appear as white streaks on the surface of the coating film. Therefore, suppressing the wrinkle defects means that the streaks are not visible.
  • the height difference within a 1 mm long range of the steel sheet surface i.e., the coating film surface
  • the streaks are not visible, and an excellent surface appearance can be obtained.
  • it is preferable that the height difference within a 1 mm long range of the steel sheet surface is within 5 ⁇ m.
  • the steel sheet surface means the outermost surface of the steel sheet, and in the case of a coated steel sheet, means the surface of the coating film.
  • the height difference on the steel sheet surface refers to the difference in height between the highest point and the lowest point on the steel sheet (on the coating film) when the height is taken in the direction perpendicular to the surface of the base steel sheet (in the direction of the coating film thickness).
  • the method of obtaining the height difference within a 1 mm long range of the coating surface can be similar to that of the plating film surface described above, in which the height difference within a 1 mm range at any 100 points on the coated steel sheet is measured using a laser microscope and the average of the measured values is calculated.
  • the reason for controlling the height difference on the surface of the steel plate in the area excluding 50 mm from both ends of the steel plate is that it is generally difficult to control the amount of coating at both ends of a hot-dip galvanized steel plate compared to the center of the plate, and the cooling rate is also different, making wrinkle-like defects more likely to occur.
  • both ends of the plate are often trimmed before use, so the surface appearance is of little concern.
  • the method of controlling the height difference of the coating surface to 10 ⁇ m or less per 1 mm of length of the steel plate surface, it is important to suppress the height difference of the plating film surface as described above, and the height difference of the film surface can be suppressed by adjusting the Mg and Mn content ratio in the plating film or by carrying out other surface treatments to suppress the height difference.
  • the method for producing a coated steel sheet of the present invention is a method for producing a coated steel sheet in which a coating film is formed directly or via a chemical conversion coating on a plating film.
  • the chemical conversion coating comprises a resin component containing 30 to 50 mass% in total of (a): an anionic polyurethane resin having an ester bond and (b): an epoxy resin having a bisphenol skeleton, the content ratio of (a) to (b) ((a):(b)) being in the range of 3:97 to 60:40 in terms of mass ratio, and an inorganic compound including 2 to 10 mass% of a vanadium compound, 40 to 60 mass% of a zirconium compound, and 0.5 to 5 mass% of a fluorine compound;
  • the coating film has at least a primer coating film, and the primer coating film contains a polyester resin having a urethane bond, and an inorganic compound containing a vanadium compound, a phosphoric acid compound, and magnesium oxide,
  • the coating film
  • the conditions for the hot-dip galvanizing process are the same as those described for the hot-dip Al-Zn-Si-Mg-plated steel sheet of the present invention.
  • Example 1 Samples 1 to 28
  • a cold-rolled steel sheet having a thickness of 0.8 mm produced by a conventional method was used as a base steel sheet, and degreasing treatment, annealing treatment and plating treatment were performed in a continuous hot-dip plating equipment to produce samples 1 to 28 of hot-dip Al-Zn-Si-Mg-plated steel sheets under the conditions shown in Table 1.
  • composition of the coating bath used in the production of the hot-dip Al-Zn-Si-Mg-plated steel sheets was varied in the ranges of Al: 45-65 mass%, Si: 1.5-2.5 mass%, Mg: 1.0-4.5 mass%, Mn: 0.00-1.0 mass%, Sr: 0.00-1.0 mass%, B: 0.00-0.05 mass%, Ca: 0.00-1.0 mass%, Cr: 0.00-0.2 mass%, Ti: 0.00-0.2 mass%, and V: 0.00-0.2 mass%, so as to obtain the composition of the coating film of each sample shown in Table 1.
  • the bath temperature of the coating bath was 590°C for Al: 45-55 mass%, and 630°C for Al: 65 mass%, and was controlled so that the temperature of the substrate steel sheet entering the coating was the same as the coating bath temperature. Furthermore, the plating process was carried out under conditions where the sheet temperature was cooled to a temperature range of 520 to 500°C in 3 seconds.
  • the plating film weight was controlled to be 85 ⁇ 5 g/m 2 per side for Samples 1-23 and Samples 27-28, and 50-125 g/m 2 per side for Samples 24-26.
  • the stripper solution was then filtered, and the filtrate and solid content were analyzed. Specifically, the filtrate was analyzed by ICP atomic emission spectroscopy to quantify the components other than insoluble Si.
  • the solids were dried and incinerated in a 650°C heating furnace, and then melted by adding sodium carbonate and sodium tetraborate.
  • the molten material was dissolved in hydrochloric acid, and the solution was analyzed by ICP emission spectroscopy to quantify the insoluble silicon.
  • the silicon concentration in the plating film was calculated by adding the soluble silicon concentration obtained by filtrate analysis to the insoluble silicon concentration obtained by solid content analysis.
  • the composition of the plating film obtained as a result of the calculation is shown in Table 1.
  • the intensity (cps) obtained by subtracting the base intensity from each peak intensity was used as the diffraction intensity.
  • the corrosion loss of all three samples was 45g/m2 or less .
  • the corrosion loss of all three samples is 90g/ m2 or less.
  • the corrosion loss of one or more samples is more than 90g/ m2.
  • Table 1 show that the samples of the present invention have superior surface appearance compared to the samples of the comparative examples.
  • Example 2 Samples 1 to 34
  • composition of the coating bath used in the production of the hot-dip Al-Zn-Si-Mg-plated steel sheets was varied in the ranges of Al: 45-65 mass%, Si: 1.5-2.5 mass%, Mg: 1.0-4.5 mass%, Mn: 0.00-1.0 mass%, Sr: 0.00-0.00-1.0 mass%, B: 0.00-0.05 mass%, Ca: 0.00-1.0 mass%, Cr: 0.00-0.2 mass%, Ti: 0.00-0.2 mass%, and V: 0.00-0.2 mass%, so as to obtain the composition of the coating film of each sample shown in Table 3.
  • the bath temperature of the coating bath was 590°C for Al: 45-55 mass%, and 630°C for Al: 65 mass%, and was controlled so that the temperature of the substrate steel sheet entering the coating was the same as the coating bath temperature. Furthermore, the plating process was carried out under conditions where the sheet temperature was cooled to a temperature range of 520 to 500°C in 3 seconds.
  • the plating film weight was controlled to be 85 ⁇ 5 g/m 2 per side for Samples 1-29 and Samples 33-34, and 50-125 g/m 2 per side for Samples 30-32.
  • each component (resin, metal compound) contained in the surface treatment solutions are as follows: (resin) Urethane resin: Superflex 130, Superflex 126 (Dai-ichi Kogyo Seiyaku Co., Ltd.) Acrylic resin: Boncoat EC-740EF (DIC Corporation) (Metal Compounds) P compound: Aluminum dihydrogen tripolyphosphate Si compound: Silica V compound: Sodium metavanadate Mo compound: Molybdic acid Zr compound: potassium zirconyl carbonate The compositions of the prepared chemical conversion treatment solutions A to F and the adhesion weights of the formed chemical conversion coatings are shown in Table 1. The concentration of each component in Table 1 of this specification is the concentration (mass%) of the solid content.
  • the filtrate was analyzed by ICP atomic emission spectroscopy to quantify the components other than insoluble Si.
  • the solids were dried and incinerated in a 650°C heating furnace, and then melted by adding sodium carbonate and sodium tetraborate.
  • the molten material was dissolved in hydrochloric acid, and the solution was analyzed by ICP emission spectroscopy to quantify the insoluble silicon.
  • the silicon concentration in the plating film was calculated by adding the soluble silicon concentration obtained by filtrate analysis to the insoluble silicon concentration obtained by solid content analysis.
  • the composition of the plating film obtained as a result of the calculation is shown in Table 3.
  • the measurement results are shown in Table 3.
  • the corrosion weight loss of each sample was measured using the methods specified in JIS Z 2383 and ISO 8407, and evaluated according to the following criteria.
  • ⁇ The corrosion loss of all three samples is 30 g/m2 or less .
  • ⁇ The corrosion loss of all three samples is 70 g/m2 or less.
  • ⁇ The corrosion loss of one or more samples is more than 70 g/ m2.
  • Example 3 Samples 1 to 37
  • a cold-rolled steel sheet having a thickness of 0.8 mm which was produced by a conventional method, was used as a base steel sheet, and was subjected to degreasing treatment, annealing treatment and plating treatment in a continuous hot-dip plating facility to produce samples 1 to 37 of hot-dip Al-Zn-Si-Mg-plated steel sheets having the conditions shown in Table 5.
  • composition of the coating bath used in the production of hot-dip Al-Zn-Si-Mg-plated steel sheets was varied in the ranges of Al: 45-65 mass%, Si: 1.5-2.5 mass%, Mg: 1.0-4.5 mass%, Mn: 0.00-1.0 mass%, Sr: 0.00-1.0 mass%, B: 0.00-0.05 mass%, Ca: 0.00-1.0 mass%, Cr: 0.00-0.2 mass%, Ti: 0.00-0.2 mass%, and V: 0.00-0.2 mass%, so as to obtain the composition of the coating film of each sample shown in Table 5.
  • the bath temperature of the coating bath was 590° C. in the case of Al: 45-55 mass%, and 630° C.
  • the plating process was carried out under conditions where the sheet temperature was cooled to a temperature range of 520 to 500°C in 3 seconds.
  • the plating film weight was controlled to be 85 ⁇ 5 g/m 2 per side for Samples 1-32 and Samples 36-37, and 50-125 g/m 2 per side for Samples 33-35.
  • the chemical conversion coating film of each sample of the prepared hot-dip galvanized steel sheet was coated with the chemical conversion coating solution shown in Table 4 using a bar coater, and then dried in a hot air drying furnace (ultimate sheet temperature: 90°C) to form a chemical conversion coating film with a coating weight of 0.1 g/ m2 .
  • the chemical conversion treatment solution used was prepared by dissolving each component in water as a solvent, and had a pH of 8 to 10.
  • each component (resin component, inorganic compound) contained in the chemical conversion treatment solution are as follows:
  • Resin B an acrylic resin ("Boncoat EC-740EF” manufactured by DIC Corporation).
  • Vanadium compounds organic vanadium compounds chelated with acetylacetone Zirconium compounds: ammonium zirconium carbonate Fluorine compounds: ammonium fluoride
  • a primer paint was applied onto the chemical conversion coating film formed as described above using a bar coater, and baked under conditions of a steel plate temperature of 230°C and a baking time of 35 seconds, thereby forming a primer coating film having the component composition shown in Table 4.
  • a topcoat paint composition was applied onto the primer coating film formed as described above using a bar coater, and baked under conditions of a steel plate temperature of 230°C to 260°C and a baking time of 40 seconds, thereby forming a topcoat coating film having the resin conditions and film thickness shown in Table 4, and each sample coated steel plate was produced.
  • the primer coating was obtained by mixing the components and then stirring for about 1 hour in a ball mill. The following resin components and inorganic compounds were used to form the primer coating film.
  • Resin ⁇ A urethane-modified polyester resin (obtained by reacting 455 parts by mass of polyester resin and 45 parts by mass of isophorone diisocyanate, having a resin acid value of 3, a number average molecular weight of 5,600, and a hydroxyl value of 36) cured with a blocked isocyanate was used.
  • the polyester resin to be urethane-modified was prepared under the following conditions: 320 parts by mass of isophthalic acid, 200 parts by mass of adipic acid, 60 parts by mass of trimethylolpropane, and 420 parts by mass of cyclohexanedimethanenol were charged into a flask equipped with a stirrer, a distillation column, a water separator, a cooling tube, and a thermometer, and the mixture was heated and stirred, and the temperature was raised from 160°C to 230°C at a constant rate over 4 hours while distilling off the generated condensed water outside the system.
  • Resin ⁇ urethane-cured polyester resin ("Evaclad 4900” manufactured by Kansai Paint Co., Ltd.) (Inorganic Compounds) Vanadium compound: magnesium vanadate Phosphate compound: calcium phosphate Magnesium oxide compound: magnesium oxide Furthermore, for the resins used in the topcoat coatings shown in Table 4, the following paints were used.
  • Resin I Melamine-cured polyester paint (BASF Japan Ltd. "Precolor HD0030HR")
  • Resin II An organosol-based baking-type fluororesin-based paint having a mass ratio of polyvinylidene fluoride and acrylic resin of 80:20 (BASF Japan Ltd. "Precolor No. 8800HR”)
  • the stripper solution was then filtered, and the filtrate and solid content were analyzed. Specifically, the filtrate was analyzed by ICP atomic emission spectrometry to quantify the components other than insoluble Si.
  • the solids were dried and incinerated in a 650°C heating furnace, and then melted by adding sodium carbonate and sodium tetraborate.
  • the molten material was dissolved in hydrochloric acid, and the solution was analyzed by ICP emission spectroscopy to quantify the insoluble silicon.
  • the silicon concentration in the plating film was calculated by adding the soluble silicon concentration obtained by filtrate analysis to the insoluble silicon concentration obtained by solid content analysis.
  • the composition of the plating film obtained as a result of the calculation is shown in Table 5.
  • the intensity (cps) obtained by subtracting the base intensity from each peak intensity was used as the diffraction intensity.
  • the number of cycles at which red rust was confirmed on the sheared edge of one side that was not sealed with tape was evaluated according to the following criteria. ⁇ : Number of cycles in which red rust occurs on three samples is ⁇ 600 cycles ⁇ : Number of cycles in which red rust occurs on three samples is ⁇ 400 cycles ⁇ : Number of cycles in which red rust occurs on one or more samples is ⁇ 400 cycles
  • the present invention it is possible to provide a hot-dip Al-Zn-Si-Mg-plated steel sheet which is free from other defects such as dross defects, suppresses the occurrence of wrinkle-like defects, and has an excellent surface appearance. Furthermore, according to the present invention, it is possible to provide a surface-treated steel sheet having an excellent surface appearance and white rust resistance, and a coated steel sheet having an excellent surface appearance and excellent corrosion resistance.

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Abstract

The purpose of the present invention is to provide an Al-Zn-Si-Mg hot-dipped steel sheet in which there are no other defects such as dross defects, in which the occurrence of wrinkle-shaped defects is suppressed, and the outer surface of which has an excellent appearance.　In order to achieve this purpose, the present invention is an Al-Zn-Si-Mg hot-dipped steel sheet comprising a plating film, said Al-Zn-Si-Mg hot-dipped steel sheet being characterized in that: the plating film has a composition comprising 45-65 mass% Al, 1.0-3.0 mass% Si, 1.0-10.0 mass% Mg, and 0.01-0.5 mass% Mn, with the remainder being Zn and unavoidable impurities; and in a range excluding 50 mm from both ends of the steel sheet, the height difference of the surface of the steel sheet per 1 mm of length is not more than 10 μm.

Description

溶融Ａｌ－Ｚｎ－Ｓｉ－Ｍｇ系めっき鋼板、表面処理鋼板及び塗装鋼板Hot-dip Al-Zn-Si-Mg plated steel sheets, surface-treated steel sheets and painted steel sheets

　本発明は、優れた表面外観を有する溶融Al-Zn-Si-Mg系めっき鋼板、表面処理鋼板及び塗装鋼板に関するものである。 The present invention relates to hot-dip Al-Zn-Si-Mg plated steel sheets, surface-treated steel sheets, and painted steel sheets that have excellent surface appearance.

　55％Al-Zn系に代表される溶融Al-Zn系めっき鋼板は、例えば特許文献１に示すように、Znの犠牲防食性とAlの高い耐食性とが両立できているため、種々のめっき鋼板の中でも高い耐食性を示すことが知られている。そのため、溶融Al-Znめっき鋼板は、その優れた耐食性から、長期間屋外に曝される屋根や壁等の建材分野、ガードレール、配線配管、防音壁等の土木建築分野を中心に使用されている。
　特に、大気汚染による酸性雨や、積雪地帯での道路凍結防止用融雪剤の散布、海岸地域開発のような、より厳しい使用環境下での耐食性に優れる材料や、メンテナンスフリー材料への要求が高まっていることから、近年、溶融Al-Zn系めっき鋼板の需要はより増加している。 Hot-dip Al-Zn-plated steel sheets, typified by 55% Al-Zn, are known to exhibit high corrosion resistance among various plated steel sheets because they combine the sacrificial corrosion protection of Zn with the high corrosion resistance of Al, as shown in, for example, Patent Document 1. For this reason, hot-dip Al-Zn-plated steel sheets are used mainly in the field of building materials such as roofs and walls that are exposed outdoors for long periods of time, and in the field of civil engineering and construction such as guardrails, wiring and piping, and soundproof walls, due to their excellent corrosion resistance.
In particular, the demand for hot-dip Al-Zn coated steel sheets has been increasing in recent years due to the growing demand for materials with excellent corrosion resistance and maintenance-free materials in more severe environments, such as acid rain caused by air pollution, the spraying of de-icing agents to prevent roads from freezing in snowy areas, and coastal area development.

　溶融Al-Zn系めっき鋼板のめっき皮膜は、Znを過飽和に含有したAlがデンドライト状に凝固した部分（α-Al相）と、デンドライト間隙（インターデンドライト）に存在するZn-Al共晶組織から構成され、α-Al相がめっき皮膜の膜厚方向に複数積層した構造を有することが特徴である。このような特徴的な皮膜構造により、表面からの腐食進行経路が複雑になるため、腐食が容易に進行しにくくなり、溶融Al-Zn系めっき鋼板はめっき皮膜厚が同一の溶融亜鉛めっき鋼板に比べ優れた耐食性を実現できることも知られている。 The coating of hot-dip Al-Zn-plated steel sheets is composed of areas where Al containing supersaturated Zn has solidified into dendrites (α-Al phase) and a Zn-Al eutectic structure that exists in the gaps between dendrites (interdendrites), and is characterized by a structure in which the α-Al phase is layered in the thickness direction of the coating. This characteristic coating structure makes the corrosion progression path from the surface complex, making it difficult for corrosion to progress easily, and it is also known that hot-dip Al-Zn-plated steel sheets can achieve superior corrosion resistance compared to hot-dip galvanized steel sheets with the same coating thickness.

　そして、溶融Al-Zn系めっき鋼板に対して、さらに長寿命化を図ろうとする試みがなされており、Mgを添加した溶融Al-Zn-Si-Mg系めっき鋼板が知られている。
　このような溶融Al-Zn-Si-Mg系めっき鋼板としては、例えば特許文献１に、めっき皮膜中にMgを含むAl-Zn-Si合金を含み、該Al-Zn-Si合金が、45～60重量％の元素アルミニウム、37～46重量％の元素亜鉛及び1.2～2.3重量％のSiを含有する合金であり、該Mgの濃度が1～5重量％である、溶融Al-Zn-Si-Mg系めっき鋼板が開示されている。
　また、特許文献２には、めっき皮膜中に2～10質量%のMg、0.01～10質量%のCaの1種以上を含有させることで耐食性の向上を図るとともに、下地鋼板が露出した後の保護作用を高めることを目的とした溶融Al-Zn-Si-Mg系めっき鋼板が開示されている。
　さらに、特許文献３には、質量％で、Mg：1～15質量％、Si：2～15質量％、Zn：11～25質量％を含有し、残部がAl及び不可避的不純物からなる被覆層を形成し、めっき皮膜中に存在するMg2Si相やMgZn2相などの金属間化合物の大きさを10μm以下とすることで、平板及び端面の耐食性の改善を図った溶融Al-Zn-Si-Mg系めっき鋼板が開示されている。 Attempts have been made to further extend the life of hot-dip Al-Zn-plated steel sheets, and hot-dip Al-Zn-Si-Mg-plated steel sheets to which Mg has been added are known.
As such a hot-dip Al-Zn-Si-Mg-plated steel sheet, for example, Patent Document 1 discloses a hot-dip Al-Zn-Si-Mg-plated steel sheet that contains an Al-Zn-Si alloy containing Mg in a plating film, the Al-Zn-Si alloy being an alloy containing 45 to 60 wt % of elemental aluminum, 37 to 46 wt % of elemental zinc, and 1.2 to 2.3 wt % of Si, and the concentration of the Mg is 1 to 5 wt %.
Furthermore, Patent Document 2 discloses a hot-dip Al-Zn-Si-Mg plated steel sheet in which the plating film contains one or more of 2 to 10 mass % Mg and 0.01 to 10 mass % Ca, thereby improving corrosion resistance and enhancing protective action after the base steel sheet is exposed.
Furthermore, Patent Document 3 discloses a hot-dip Al-Zn-Si-Mg plated steel sheet which forms a coating layer containing, by mass%, 1 to 15% Mg, 2 to 15 % Si, 11 to 25% Zn, with the remainder being Al and unavoidable impurities, and which aims to improve the corrosion resistance of the flat sheet and end faces by restricting the size of intermetallic compounds such as Mg2Si phase and MgZn2 phase present in the plating film to 10 μm or less.

　しかしながら、溶融Al-Zn-Si-Mg系めっき鋼板は、後述するしわ状の凹凸欠陥の発生により、表面外観が著しく低下するという問題があった。溶融Al-Zn-Si浴にMgを添加して鋼板にめっきを施すと、Mgは他のめっき構成元素に比較して酸化し易い元素であるため、めっき皮膜の冷却凝固過程では、大気と接する最表層部でMgと酸素が反応してMg系酸化物が生成する。これに伴い最表層近傍のMg濃度が低下し、それを補うべく逐次的にめっき皮膜内部から最表層にMgが拡散する結果、めっき皮膜が内部まで完全に凝固するよりも前に、最表層にMg系酸化物が厚く層状に形成し、凝固前で流動しやすいめっき皮膜内部とMg系酸化物層との間で流動性の差異が生じ、めっき皮膜内部の流動にMg系酸化物層が追随できずに、製造される溶融Al-Zn-Si-Mg系めっき鋼板のめっき表面にはしわ状の凹凸欠陥（：しわ状欠陥）が発生することとなる。
　そのため、溶融Al-Zn-Si-Mg系めっき鋼板のしわ状欠陥を改善するような技術の開発が望まれていた。 However, hot-dip Al-Zn-Si-Mg-plated steel sheets have a problem in that the surface appearance is significantly deteriorated due to the occurrence of wrinkle-like irregular defects, which will be described later. When Mg is added to a molten Al-Zn-Si bath and a steel sheet is plated, Mg is an element that oxidizes more easily than other plating constituent elements, so during the cooling and solidification process of the plating film, Mg reacts with oxygen in the outermost layer that comes into contact with the air to produce Mg-based oxides. As a result, the Mg concentration in the vicinity of the outermost layer decreases, and to compensate for this, Mg gradually diffuses from the inside of the plating film to the outermost layer. As a result, a thick layer of Mg-based oxide is formed in the outermost layer before the plating film completely solidifies to the inside, and a difference in fluidity occurs between the inside of the plating film, which is prone to flow before solidification, and the Mg-based oxide layer. As a result, the Mg-based oxide layer cannot keep up with the flow inside the plating film, and wrinkle-like uneven defects (wrinkle-like defects) occur on the plating surface of the hot-dip Al-Zn-Si-Mg-plated steel sheet that is produced.
Therefore, there has been a demand for the development of a technology to improve wrinkle defects in hot-dip Al-Zn-Si-Mg coated steel sheets.

　なお、特許文献４及び特許文献５には、めっき皮膜中にSrを含有させることで、めっき表層におけるMgの酸化を抑え、しわ状欠陥の発生の抑制を図る技術が開示されている。これらの技術は、めっき浴から出た未凝固のめっき層表層においてSrがMgよりも優先的に酸化される現象を利用したものである。 Patent Documents 4 and 5 disclose a technology that includes Sr in the plating film to suppress oxidation of Mg on the plating surface and prevent wrinkle defects. These technologies utilize the phenomenon that Sr is oxidized preferentially over Mg on the unsolidified plating surface layer that comes out of the plating bath.

　また、上述した溶融Al-Zn-Si-Mg系めっき鋼板については、厳しい腐食環境で使用された場合、めっき皮膜の腐食に伴う白錆が発生するという問題もあった。この白錆は、鋼板の外観性低下を招くため、耐白錆性の改善を図っためっき鋼板の開発が行われている。
　そのため、特許文献６及び特許文献７には、溶融Al-Zn-Si-Mg系めっき鋼板のめっき皮膜上にウレタン樹脂を含有する化成皮膜を形成することで、耐白錆性の改善を図った表面処理鋼板が開示されている。
　しかしながら、特許文献６及び特許文献７のような表面処理鋼板の場合も、下地となる溶融Al-Zn-Si-Mg系めっき鋼板の影響を受けることから、上述したしわ状欠陥の発生に起因した表面外観の低下は、依然として改善を図る必要があった。 Furthermore, the above-mentioned hot-dip Al-Zn-Si-Mg-plated steel sheets have a problem in that, when used in a severely corrosive environment, the plating film corrodes and white rust occurs. Since this white rust deteriorates the appearance of the steel sheet, plated steel sheets with improved white rust resistance are being developed.
Therefore, Patent Documents 6 and 7 disclose surface-treated steel sheets in which a chemical conversion coating containing a urethane resin is formed on a coating film of a hot-dip Al-Zn-Si-Mg-plated steel sheet, thereby improving the white rust resistance.
However, even in the case of surface-treated steel sheets as disclosed in Patent Documents 6 and 7, the steel sheets are affected by the underlying hot-dip Al-Zn-Si-Mg-plated steel sheet, and therefore there remains a need to improve the deterioration of surface appearance caused by the occurrence of the above-mentioned wrinkle defects.

　さらに、上述した溶融Al-Zn-Si-Mg系めっき鋼板については、表面上に、化成処理皮膜や、プライマー塗膜を形成し、その上に様々な塗膜を形成した塗装鋼板として使用されることがある。
　このような塗装鋼板は、プレス成形やロール成形、あるいはエンボス成形によって90度曲げ、あるいは180度曲げなどを含む様々な加工を施され、かつ使用後の長期の塗膜耐久性能が要求されおり、これらの要求に応えるべく、溶融Al-Zn系めっき鋼板にクロメートを含有する化成処理を施し、プライマー塗膜中にクロメート系防錆顔料を含有させ、その上に上塗り塗膜として、熱硬化型のポリエステル系樹脂塗膜やより耐候性の高い要求に対してはフッ素系樹脂塗膜を形成した塗装亜鉛系めっき鋼板が適用されているのが一般的であった。
　ただし、昨今このような塗装鋼板について、環境負荷物質であるクロメートを使用することが問題視されており、クロメートを含まないクロメートフリーの塗装鋼板が強く望まれており、例えば特許文献８に開示されているようなクロメートフリーの塗装鋼板が提案されている。 Furthermore, the above-mentioned hot-dip Al-Zn-Si-Mg-plated steel sheet may be used as a painted steel sheet having a chemical conversion coating or a primer coating formed on the surface and various other coating films formed thereon.
Such coated steel sheets are subjected to various processes, including bending at 90 degrees or 180 degrees by press forming, roll forming, or embossing, and are required to have coating film durability over a long period of time after use. To meet these requirements, it has been common to apply a coated zinc-based coated steel sheet in which a chromate-containing chemical conversion treatment is applied to a hot-dip Al-Zn-plated steel sheet, a chromate-based rust-preventive pigment is contained in a primer coating, and a thermosetting polyester-based resin coating or, for those requiring higher weather resistance, a fluororesin coating is formed as a top coating on top of that.
However, in recent years, the use of chromate, an environmentally hazardous substance, in such coated steel sheets has come to be viewed as problematic, and there is a strong demand for chromate-free coated steel sheets that do not contain chromate. For example, a chromate-free coated steel sheet as disclosed in Patent Document 8 has been proposed.

特許５０２０２２８号公報Patent No. 5020228 特許５００００３９号公報Patent No. 5000039 特開２００２－１２９５９号公報JP 2002-12959 A 特開２０００－３２８２１４号公報JP 2000-328214 A 国際公開第２０２０／１７９１４７号International Publication No. 2020/179147 特開２０１９－１５５８７２号公報JP 2019-155872 A 特開２０２１－１８１２１４号公報JP 2021-181214 A 特開２００５－１６９７６５号公報JP 2005-169765 A

　しかしながら、いずれの文献に開示された技術についても、他の物性を低下させることなく、上述したしわ状欠陥の発生を抑制することは難しかった。
　特許文献４及び特許文献５に開示された技術では、めっき皮膜中にSrを添加した溶融Al-Zn-Si-Mg系めっき鋼板の製造時、Srを添加しためっき浴の表面が酸化し易くなり、生成される酸化物系のドロスがめっき皮膜に付着したドロス欠陥が新たに発生し、表面外観の悪化を招くという問題があった。 However, in any of the techniques disclosed in the documents, it is difficult to suppress the occurrence of the wrinkle defects described above without deteriorating other physical properties.
The techniques disclosed in Patent Documents 4 and 5 have a problem that, during the production of a hot-dip Al-Zn-Si-Mg-plated steel sheet having Sr added to the plating film, the surface of the plating bath containing Sr is easily oxidized, and the generated oxide-based dross adheres to the plating film to cause new dross defects, which deteriorate the surface appearance.

　また、特許文献６及び特許文献７の技術では、耐白錆性の改善を図ることはできるものの、表面処理鋼板の場合でもまた、下地となる溶融Al-Zn-Si-Mg系めっき鋼板の影響を受け、しわ状欠陥の発生による表面外観の低下は依然として改善が望まれていた。
　さらに、特許文献８の技術についても、塗装鋼板の表面外観、特に鮮写性は、下地とするめっき鋼板の表面形状に影響されることはいうまでもなく、上述したしわ状欠陥やドロス欠陥の発生に伴う凹凸の高低差は数十μmにも及ぶため、塗膜により表面が平滑化しても、凹凸の完全解消には至らず、塗装鋼板としての表面外観の改善が依然として課題であった。加えて、めっき皮膜の凸部の上に形成された塗膜は、その膜厚が薄くなるため、局部的に耐食性が低下する懸念もあることから、下地であるめっき鋼板の表面外観、特に表面形状を改善することが望まれていた。 In addition, although the techniques of Patent Documents 6 and 7 can improve white rust resistance, even in the case of a surface-treated steel sheet, the surface is affected by the underlying hot-dip Al-Zn-Si-Mg-plated steel sheet, and deterioration in surface appearance due to the occurrence of wrinkle-like defects is still desired to be improved.
Furthermore, with regard to the technology of Patent Document 8, the surface appearance of a coated steel sheet, particularly its image clarity, is naturally affected by the surface shape of the plated steel sheet that serves as the base, and since the height difference of the unevenness caused by the occurrence of the above-mentioned wrinkle-like defects and dross defects reaches several tens of μm, even if the surface is smoothed by a coating film, the unevenness is not completely eliminated, and improvement of the surface appearance of the coated steel sheet remains an issue. In addition, since the coating film formed on the convex parts of the plating film has a thin film thickness, there is a concern that the corrosion resistance may be locally reduced, and therefore it has been desired to improve the surface appearance of the plated steel sheet that serves as the base, particularly the surface shape.

　本発明は、かかる事情に鑑み、ドロス欠陥等の他の欠陥がなく、しわ状欠陥の発生が抑制され、優れた表面外観を有する溶融Al-Zn-Si-Mg系めっき鋼板を提供することを目的とする。
　また、本発明は、優れた表面外観及び耐白錆性を有する表面処理鋼板、並びに、優れた表面外観及び耐食性に優れた塗装鋼板を提供することを目的とする。 In view of the above circumstances, an object of the present invention is to provide a hot-dip Al-Zn-Si-Mg coated steel sheet which is free from other defects such as dross defects, suppresses the occurrence of wrinkle-like defects, and has an excellent surface appearance.
Another object of the present invention is to provide a surface-treated steel sheet having excellent surface appearance and white rust resistance, and a coated steel sheet having excellent surface appearance and excellent corrosion resistance.

　本発明者らは、上記の課題を解決すべく検討を行った結果、溶融Al-Zn-Si-Mg系めっき鋼板のめっき皮膜中にMnを添加することで、ドロス欠陥等を引き起こすことなく、しわ状欠陥を抑制できることに着目し、Mnの添加量を調整し、鋼板表面（めっき皮膜表面）の高低差を小さく抑えることによって、しわ状欠陥の発生を抑制できることを見出した。 As a result of investigations aimed at solving the above problems, the inventors noticed that wrinkle defects can be suppressed without causing dross defects by adding Mn to the plating film of hot-dip Al-Zn-Si-Mg-plated steel sheets, and discovered that wrinkle defects can be suppressed by adjusting the amount of Mn added and minimizing the height difference on the steel sheet surface (plating film surface).

　本発明は、以上の知見に基づきなされたものであり、その要旨は以下の通りである。
１．めっき皮膜を備える溶融Al-Zn-Si-Mg系めっき鋼板であって、
　前記めっき皮膜は、Al：45～65質量％、Si：1.0～3.0質量％、Mg：1.0～10.0質量％及びMn：0.01～0.5質量％を含有し、残部がZn及び不可避的不純物からなる組成を有し、
　鋼板の両端から50mmを除いた範囲において、長さ1mmあたりの鋼板表面の高低差が10μm以下であることを特徴とする、溶融Al-Zn-Si-Mg系めっき鋼板。
２．前記めっき皮膜中のMnの含有量が0.1～0.3質量％であることを特徴とする、上記１に記載の溶融Al-Zn-Si-Mg系めっき鋼板。
３．前記めっき皮膜と下地鋼板との界面にMnを含有した合金層を備えることを特徴とする、上記１又は２に記載の溶融Al-Zn-Si-Mg系めっき鋼板。
４．前記めっき皮膜が、さらに、B、Ca、Ti、V、Cr、Sr、Mo、In、Sn、Sb、Ce、及びBiのうちから選択される一種又は二種以上を合計で0.01～3.0質量％含有することを特徴とする上記１～３のいずれかに記載の溶融Al-Zn-Si-Mg系めっき鋼板。
５．上記１～４のいずれかに記載のめっき皮膜と、該めっき皮膜上に形成された化成皮膜と、を備える表面処理鋼板であって、
　前記化成皮膜は、エポキシ樹脂、ウレタン樹脂、アクリル樹脂、アクリルシリコン樹脂、アルキド樹脂、ポリエステル樹脂、ポリアルキレン樹脂、アミノ樹脂及びフッ素樹脂のうちから選択される少なくとも一種の樹脂と、P化合物、Si化合物、Co化合物、Ni化合物、Zn化合物、Al化合物、Mg化合物、V化合物、Mo化合物、Zr化合物、Ti化合物及びCa化合物のうちから選択される少なくとも一種の金属化合物と、を含有することを特徴とする、表面処理鋼板。
６．上記１～４のいずれかに記載のめっき皮膜上に、直接又は化成皮膜を介して、塗膜が形成された塗装鋼板であって、
　前記化成皮膜は、（ａ）：エステル結合を有するアニオン性ポリウレタン樹脂及び（ｂ）：ビスフェノール骨格を有するエポキシ樹脂を合計で30～50質量％含有し、該（ａ）と該（ｂ）の含有比率（（ａ）：（ｂ））が、質量比で3：97 ～60：40の範囲である樹脂成分と、2～10質量％のバナジウム化合物、40～60質量％のジルコニウム化合物及び0.5～5質量％のフッ素化合物を含む無機化合物と、を含有し、
　前記塗膜は、プライマー塗膜を少なくとも有し、該プライマー塗膜が、ウレタン結合を有するポリエステル樹脂と、バナジウム化合物、リン酸化合物及び酸化マグネシウムを含む無機化合物と、を含有することを特徴とする、塗装鋼板。  The present invention has been made based on the above findings, and the gist of the present invention is as follows.
1. A hot-dip Al-Zn-Si-Mg-based plated steel sheet having a plating film,
The plating film has a composition containing 45 to 65 mass% Al, 1.0 to 3.0 mass% Si, 1.0 to 10.0 mass% Mg, and 0.01 to 0.5 mass% Mn, with the remainder being Zn and unavoidable impurities;
A hot-dip Al-Zn-Si-Mg plated steel sheet, characterized in that the height difference of the steel sheet surface per mm of length is 10 μm or less in an area excluding 50 mm from both ends of the steel sheet.
2. The hot-dip Al-Zn-Si-Mg plated steel sheet according to 1 above, characterized in that the plating film has a Mn content of 0.1 to 0.3 mass %.
3. The hot-dip Al-Zn-Si-Mg plated steel sheet according to 1 or 2 above, characterized in that an alloy layer containing Mn is provided at the interface between the plated film and a base steel sheet.
4. The hot-dip Al-Zn-Si-Mg plated steel sheet according to any one of 1 to 3 above, wherein the plating film further contains 0.01 to 3.0 mass% in total of one or more elements selected from B, Ca, Ti, V, Cr, Sr, Mo, In, Sn, Sb, Ce, and Bi.
5. A surface-treated steel sheet comprising the plating film according to any one of 1 to 4 above and a chemical conversion film formed on the plating film,
The chemical conversion coating film is a surface-treated steel sheet characterized in that it contains at least one resin selected from the group consisting of epoxy resins, urethane resins, acrylic resins, acrylic silicone resins, alkyd resins, polyester resins, polyalkylene resins, amino resins, and fluororesins, and at least one metal compound selected from the group consisting of P compounds, Si compounds, Co compounds, Ni compounds, Zn compounds, Al compounds, Mg compounds, V compounds, Mo compounds, Zr compounds, Ti compounds, and Ca compounds.
6. A coated steel sheet having a coating film formed directly or via a chemical conversion coating on the plating film according to any one of 1 to 4 above,
The chemical conversion coating contains a resin component that contains 30 to 50 mass% in total of (a): an anionic polyurethane resin having an ester bond and (b): an epoxy resin having a bisphenol skeleton, the content ratio of (a) to (b) ((a):(b)) being in the range of 3:97 to 60:40 in terms of mass ratio, and an inorganic compound that contains 2 to 10 mass% of a vanadium compound, 40 to 60 mass% of a zirconium compound, and 0.5 to 5 mass% of a fluorine compound;
The coating film has at least a primer coating film, and the primer coating film contains a polyester resin having a urethane bond, and an inorganic compound including a vanadium compound, a phosphate compound, and magnesium oxide.

　本発明によれば、ドロス欠陥等の他の欠陥がなく、しわ状欠陥の発生が抑制され、優れた表面外観を有する溶融Al-Zn-Si-Mg系めっき鋼板を提供することが可能となる。
　また、本発明によれば、優れた表面外観及び耐白錆性を有する表面処理鋼板、並びに、優れた表面外観及び耐食性に優れた塗装鋼板を提供することが可能となる。 According to the present invention, it is possible to provide a hot-dip Al-Zn-Si-Mg-plated steel sheet which is free from other defects such as dross defects, suppresses the occurrence of wrinkle-like defects, and has an excellent surface appearance.
Furthermore, according to the present invention, it is possible to provide a surface-treated steel sheet having an excellent surface appearance and white rust resistance, and a coated steel sheet having an excellent surface appearance and excellent corrosion resistance.

＜溶融Al-Zn-Si-Mg系めっき鋼板＞
　本発明の溶融Al-Zn-Si-Mg系めっき鋼板は、鋼板表面にめっき皮膜を備える。
　前記めっき皮膜は、Al：45～65質量％、Si：1.0～3.0質量％、Mg：1.0～10.0質量％及びMn：0.01～0.5質量％を含有し、残部がZn及び不可避的不純物からなる組成を有する。 <Hot-dip Al-Zn-Si-Mg coated steel sheet>
The hot-dip Al-Zn-Si-Mg plated steel sheet of the present invention has a plating film on the surface of the steel sheet.
The plating film has a composition containing 45 to 65 mass % Al, 1.0 to 3.0 mass % Si, 1.0 to 10.0 mass % Mg, and 0.01 to 0.5 mass % Mn, with the remainder being Zn and unavoidable impurities.

　前記めっき皮膜中のAl含有量は、耐食性と操業面のバランスから、45～65質量％であり、好ましくは50～60質量％である。
　これは、前記めっき皮膜中のAl含有量が少なくとも45質量％あれば、Alのデンドライト凝固が生じ、α-Al相のデンドライト凝固組織を主体にするめっき皮膜構造を得ることができるためである。該デンドライト凝固組織がめっき皮膜の膜厚方向に積層する構造を取ることで、腐食進行経路が複雑になり、めっき皮膜自体の耐食性が向上する。また、このα-Al相のデンドライト部分が、多く積層するほど、腐食進行経路が複雑になり、腐食が容易に下地鋼板に到達しにくくなるため、耐食性が向上するため、Alの含有量を50質量％以上とすることが好ましい。一方、前記めっき皮膜中のAl含有量が65質量％を超えると、Znの殆どがα-Al中に固溶した組織に変化し、α-Al相の溶解反応が抑制できず、溶融Al-Zn-Si-Mg系めっき鋼板の耐食性が劣化するおそれがある。このため、前記めっき皮膜中のAl含有量は65質量％以下であることを要し、好ましくは60質量％以下である。 The Al content in the plating film is 45 to 65 mass %, and preferably 50 to 60 mass %, in view of the balance between corrosion resistance and operability.
This is because, if the Al content in the plating film is at least 45% by mass, dendritic solidification of Al occurs, and a plating film structure mainly composed of a dendritic solidification structure of the α-Al phase can be obtained. The dendritic solidification structure is laminated in the thickness direction of the plating film, which complicates the corrosion progression path and improves the corrosion resistance of the plating film itself. In addition, the more the α-Al phase dendrite parts are laminated, the more complex the corrosion progression path becomes, and the more difficult it is for corrosion to reach the base steel sheet, so that the corrosion resistance is improved, and therefore the Al content is preferably 50% by mass or more. On the other hand, if the Al content in the plating film exceeds 65% by mass, most of the Zn changes to a structure in which it is solid-dissolved in α-Al, and the dissolution reaction of the α-Al phase cannot be suppressed, which may deteriorate the corrosion resistance of the hot-dip Al-Zn-Si-Mg-plated steel sheet. For this reason, the Al content in the plating film must be 65% by mass or less, and is preferably 60% by mass or less.

　前記めっき皮膜中のSiは、主に下地鋼板との界面に生成するFe-Al系及び／又はFe-Al-Si系の界面合金層の成長を抑制し、めっき皮膜と鋼板の密着性を劣化させない目的で添加される。実際に、Siを含有したAl-Zn系めっき浴に鋼板を浸漬させると、鋼板表面のFeと浴中のAlやSiが合金化反応し、Fe-Al系及び／又はFe-Al-Si系の金属間化合物層が下地鋼板／めっき皮膜界面に生成するが、このときFe-Al-Si系合金はFe-Al系合金よりも成長速度が遅いので、Fe-Al-Si系合金の比率が高いほど、界面合金層全体の成長が抑制される。
　そのため、前記めっき皮膜中のSi含有量は、1.0質量％以上とすることを要する。一方、前記めっき皮膜中のSi含有量が4.0質量％を超えると、前述した界面合金層の成長抑制効果が飽和するだけでなく、めっき皮膜中に過剰なSi相が存在することで腐食が促進されるため、前記めっき皮膜中のSi含有量は、4.0質量％以下とする。加えて、前記めっき皮膜中のSiの含有量は、過剰なSi相の存在抑制の観点から、好ましくは3.0質量％以下とする。 The Si in the plating film is added mainly for the purpose of suppressing the growth of an Fe-Al and/or Fe-Al-Si interfacial alloy layer formed at the interface with the base steel sheet and preventing deterioration of the adhesion between the plating film and the steel sheet. In fact, when a steel sheet is immersed in an Al-Zn plating bath containing Si, an alloying reaction occurs between the Fe on the steel sheet surface and the Al and Si in the bath, and an Fe-Al and/or Fe-Al-Si intermetallic compound layer is formed at the interface between the base steel sheet and the plating film. At this time, the growth rate of the Fe-Al-Si alloy is slower than that of the Fe-Al alloy, so that the higher the ratio of the Fe-Al-Si alloy, the more the growth of the entire interfacial alloy layer is suppressed.
Therefore, the Si content in the plating film must be 1.0 mass% or more. On the other hand, if the Si content in the plating film exceeds 4.0 mass%, not only will the aforementioned effect of inhibiting the growth of the interface alloy layer saturate, but the presence of excess Si phase in the plating film will also promote corrosion, so the Si content in the plating film is set to 4.0 mass% or less. In addition, from the viewpoint of inhibiting the presence of excess Si phase, the Si content in the plating film is preferably set to 3.0 mass% or less.

　前記めっき皮膜は、Mgを1.0～10.0質量％含有する。前記めっき皮膜中にMgを含有することで、上述したSiをMg2Si相の金属間化合物の形で存在させることができ、腐食の促進を抑制することができる。
　また、前記めっき皮膜中にMgを含有すると、めっき皮膜中に金属間化合物であるMgZn2相も形成され、より耐食性を向上させる効果が得られる。前記めっき皮膜中のMg含有量が1.0質量％未満の場合、前記金属間化合物（Mg2Si、MgZn2）の生成よりも、主要相であるα-Al相への固溶にMgが使用されるため、十分な耐食性が確保できない。一方、前記めっき皮膜中のMg含有量が多くなると、耐食性の向上効果が飽和することに加え、α-Al相の脆弱化に伴い加工性が低下するため、含有量は10.0質量％以下とする。
　さらに、前記めっき皮膜中のMg含有量は、めっき形成時のドロス発生を抑制し、めっき浴管理を容易にする観点及び表面外観をより向上させる観点から、5.0質量％以下とすることが好ましい。 The plating film contains 1.0 to 10.0 mass % of Mg. By including Mg in the plating film, the above-mentioned Si can be present in the form of an intermetallic compound of Mg2Si phase, and the promotion of corrosion can be suppressed.
Furthermore, when the plating film contains Mg, the intermetallic compound MgZn2 phase is also formed in the plating film, which further improves the corrosion resistance. If the Mg content in the plating film is less than 1.0 mass%, Mg is used to dissolve in the α-Al phase, which is the main phase, rather than to form the intermetallic compounds ( Mg2Si , MgZn2 ), and sufficient corrosion resistance cannot be ensured. On the other hand, if the Mg content in the plating film is high, the effect of improving the corrosion resistance is saturated, and the α-Al phase becomes weaker, which reduces the workability, so the content is set to 10.0 mass% or less.
Furthermore, the Mg content in the plating film is preferably 5.0 mass % or less from the viewpoints of suppressing the generation of dross during plating formation, facilitating plating bath management, and further improving the surface appearance.

　また、本発明の溶融Al-Zn-Si-Mg系鋼板では、前記めっき皮膜が、0.01～0.5質量％のMnを含有する。前記めっき皮膜が0.01質量％以上のMnを含有することで、めっき皮膜と地鉄間に針状及び／又は塊状のMn-Fe系の界面合金層が形成し、該合金層がアンカー効果によって、めっきが完全に凝固する間のめっき液膜の移動を抑制するため、めっき皮膜の表面に形成したMg系酸化物に起因したしわ状欠陥の発生を抑制できる。
　一方、前記めっき皮膜中のMn含有量が0.5質量％を超えると、めっき浴の融点が上がり、高浴温でのめっき処理が強いられるため、めっき皮膜と地鉄間に形成する界面合金層が異常成長し、加工性が劣化する他、ドロスの生成量が増加し、めっき外観、特に表面形状が劣化する。なお、前記めっき皮膜中のMn含有量が0.5質量％以下であれば、めっき浴のドロス生成量はMnが無添加の場合と同等となるため、ドロス欠陥の発生も抑制でき、安定的に優れた表面外観を得ることができる。
　そのため、前記めっき皮膜中のMn含有量は0.01～0.5質量％とする。同様の観点から、前記めっき皮膜中のMn含有量は、0.1～0.3質量％であることが好ましい。 In the hot-dip Al-Zn-Si-Mg steel sheet of the present invention, the plating film contains 0.01 to 0.5 mass% of Mn. When the plating film contains 0.01 mass% or more of Mn, a needle-shaped and/or chunky Mn-Fe-based interfacial alloy layer is formed between the plating film and the base steel, and the alloy layer has an anchor effect that suppresses the movement of the plating solution film while the plating is completely solidified, thereby suppressing the occurrence of wrinkle-like defects caused by Mg-based oxides formed on the surface of the plating film.
On the other hand, if the Mn content in the plating film exceeds 0.5 mass%, the melting point of the plating bath rises, and plating treatment must be performed at a high bath temperature, which causes abnormal growth of the interfacial alloy layer formed between the plating film and the base steel, deteriorating workability, increasing the amount of dross generated, and deteriorating the plating appearance, particularly the surface shape. If the Mn content in the plating film is 0.5 mass% or less, the amount of dross generated in the plating bath is the same as when no Mn is added, so the occurrence of dross defects can be suppressed and a stable excellent surface appearance can be obtained.
For this reason, the Mn content in the plating film is set to 0.01 to 0.5 mass %. From the same viewpoint, the Mn content in the plating film is preferably 0.1 to 0.3 mass %.

　ここで、前記めっき皮膜中のMg及びMnの含有量は、耐食性の向上効果、しわ状欠陥の抑制効果及びドロス欠陥の抑制効果のバランスの観点から、Mg含有量に対するMn含有量の比率（Mn／Mg）は、質量比で、0.02以上（Mn／Mg≧0.02）であることが好ましい。同様の観点から、Mg含有量に対するMn含有量の比率（Mn／Mg）は、0.03以上（Mn／Mg≧0.03）であることがより好ましい。 Here, from the viewpoint of a balance between the effects of improving corrosion resistance, suppressing wrinkle defects, and suppressing dross defects, it is preferable that the ratio of the Mn content to the Mg content (Mn/Mg) is 0.02 or more (Mn/Mg≧0.02) by mass ratio with respect to the Mg content of the plating film. From the same viewpoint, it is more preferable that the ratio of the Mn content to the Mg content (Mn/Mg) is 0.03 or more (Mn/Mg≧0.03).

　また、前記めっき皮膜は、上述したAl、Si、 Mg及びMnの他に、Zn及び不可避的不純物を含有する。
　このうち、前記不可避的不純物については、Feを含有する。このFeは、鋼板や浴中機器がめっき浴中に溶出することで不可避的に含まれるものと界面合金層の形成時に下地鋼板からの拡散によって供給される結果、前記めっき皮膜中に不可避的に含まれることとなる。前記めっき皮膜中のFe含有量は、通常0.3～2.0質量％程度である。その他の不可避的不純物としては、Ni、Cu等が挙げられる。
　前記不可避的不純物の総含有量については、特に限定はされないが、過剰に含有した場合、めっき鋼板の各種特性に影響を及ぼす可能性があるため、合計で5.0質量％以下であることが好ましい。 The plating film contains Zn and unavoidable impurities in addition to the above-mentioned Al, Si, Mg, and Mn.
Among these, the inevitable impurities include Fe. This Fe is inevitably contained in the plating film as a result of dissolution of the steel sheet or bath-immersed equipment into the plating bath, and as a result of being supplied by diffusion from the base steel sheet during the formation of the interface alloy layer. The Fe content in the plating film is usually about 0.3 to 2.0 mass%. Other inevitable impurities include Ni, Cu, etc.
The total content of the unavoidable impurities is not particularly limited, but if contained in excess, various properties of the plated steel sheet may be adversely affected, so the total content is preferably 5.0 mass % or less.

　また、前記めっき皮膜は、必要に応じて、B、Ca、Ti、V、Cr、Sr、Mo、In、Sn、Sb、Ce及びBiのうちから選択される一種又は二種以上を、合計で0.1～3質量％さらに含有することが好ましい。これらの元素は、めっき皮膜が腐食する際に腐食生成物の安定性を向上させて腐食の進行を遅延させる効果や、めっき表面のスパングルサイズを安定化させて表面外観を良好にする効果を得ることができる。 Furthermore, the plating film preferably further contains, as necessary, one or more elements selected from B, Ca, Ti, V, Cr, Sr, Mo, In, Sn, Sb, Ce and Bi in a total amount of 0.1 to 3 mass %. These elements can improve the stability of the corrosion products when the plating film corrodes, slowing the progress of corrosion, and can stabilize the spangle size on the plating surface, improving the surface appearance.

　なお、前記めっき皮膜の成分組成は、例えば、めっき皮膜を塩酸等に浸漬して溶解させ、その溶液をICP発光分光分析や原子吸光分析等で確認することができる。この方法はあくまでも一例であり、めっき皮膜の成分組成を正確に定量できる方法であればどのような方法でも良く、特に限定するものではない。
　また、本発明により得られた溶融Al-Zn-Si-Mg系めっき鋼板のめっき皮膜は、全体としてはめっき浴の組成とほぼ同等となる。そのため、前記めっき皮膜の組成の制御は、めっき浴組成を制御することにより精度良く行うことができる。 The composition of the plating film can be confirmed, for example, by immersing the plating film in hydrochloric acid or the like to dissolve it, and subjecting the solution to ICP emission spectrometry, atomic absorption spectrometry, etc. This method is merely one example, and any method that can accurately quantify the composition of the plating film may be used, and is not particularly limited.
Moreover, the coating film of the hot-dip Al-Zn-Si-Mg-plated steel sheet obtained by the present invention has a composition generally equivalent to that of the coating bath, and therefore the composition of the coating film can be controlled with high precision by controlling the composition of the coating bath.

　そして、本発明の溶融Al-Zn-Si-Mg系めっき鋼板では、鋼板表面の両端から50mmを除いた範囲において、長さ1mmあたりの皮膜表面の高低差が10μm以下であることを特徴とする。前記鋼板表面、つまりめっき皮膜表面の高低差が10μm以下である場合には、しわ状欠陥がなく、優れた表面外観を得ることができる。
　前記しわ状欠陥とは、上述したように、Mg系酸化物に起因して前記めっき皮膜の表面がしわ状の凹凸形状になった欠陥であり、前記めっき皮膜表面に白色の筋模様として現れる。よって、しわ状欠陥の抑制とは、前記筋模様が視認されないことである。そのため、前記鋼板表面の長さ1mmの範囲における高低差を10μm以内に抑えることで、筋模様として視認されず、優れた表面外観を得ることができる。同様の観点から、前記鋼板表面の長さ1mmの範囲における高低差は、5μm以内であることが好ましい。
　なお、前記鋼板表面とは、鋼板の最表面のことであり、溶融Al-Zn-Si-Mg系めっき鋼板の場合には、めっき皮膜表面のことをいう。 The hot-dip Al-Zn-Si-Mg plated steel sheet of the present invention is characterized in that the difference in height of the coating surface per mm length is 10 μm or less in an area excluding 50 mm from both ends of the steel sheet surface. When the difference in height of the steel sheet surface, i.e., the plating film surface, is 10 μm or less, no wrinkle-like defects are present and an excellent surface appearance can be obtained.
As described above, the wrinkle defect is a defect in which the surface of the plating film has a wrinkled uneven shape due to Mg-based oxides, and appears as a white streak pattern on the surface of the plating film. Therefore, suppressing the wrinkle defect means that the streak pattern is not visible. Therefore, by suppressing the height difference within a 1 mm long range on the steel sheet surface to within 10 μm, the streak pattern is not visible, and an excellent surface appearance can be obtained. From the same viewpoint, it is preferable that the height difference within a 1 mm long range on the steel sheet surface is within 5 μm.
The steel sheet surface means the outermost surface of the steel sheet, and in the case of a hot-dip Al-Zn-Si-Mg-plated steel sheet, means the surface of the plating film.

　ここで、前記鋼板表面の高低差とは、下地鋼板の表面と垂直方向（めっきの膜厚方向）を高さとした場合に、鋼板上（めっき皮膜上）の最も高い点の高さと最も低い点の高さの差のことである。
　また、前記鋼板表面の長さ1mmの範囲における高低差を得る手法については、例えば、レーザー顕微鏡を用いて、めっき皮膜が形成された溶融Al-Zn-Si-Mg系めっき鋼板の任意の100箇所の1mmの範囲における高低差を測定し、測定値の平均を算出することで得ることができる。 Here, the height difference on the surface of the steel sheet refers to the difference in height between the highest point and the lowest point on the steel sheet (on the plating film) when the height is taken in the direction perpendicular to the surface of the base steel sheet (in the direction of the plating film thickness).
The height difference within a range of 1 mm in length on the steel sheet surface can be obtained, for example, by using a laser microscope to measure the height differences within a range of 1 mm at any 100 points on the hot-dip Al-Zn-Si-Mg-plated steel sheet on which a plating film has been formed, and calculating the average of the measured values.

　また、前記鋼板表面の両端から50mmを除いた範囲において、前記鋼板表面の高低差を制御する理由としては、一般的に溶融めっき鋼板の両端では、鋼板中央に対し付着量の制御が難しく、冷却速度も異なるため、しわ状欠陥が発生し易い。加えて、このような鋼板両端は、トリミングされて使用されることが多く、表面外観については殆ど問題とならないためである。 The reason for controlling the height difference of the steel plate surface in the range excluding 50 mm from both ends of the steel plate surface is that it is generally difficult to control the amount of coating at both ends of hot-dip galvanized steel plate compared to the center of the plate, and the cooling rate is also different, making wrinkle-like defects more likely to occur. In addition, such both ends of the plate are often trimmed before use, so there is little problem with the surface appearance.

　前記めっき皮膜の長さ1mmあたりの鋼板表面の高低差を10μm以下に制御する方法については、上述しためっき皮膜中のMn含有量（0.01～0.5質量％）以外には、特に限定はされない。例えば、前記めっき皮膜中のMgとMnの含有比率を調整したり、その他高低差を抑えるための表面処理を行うことで皮膜表面の高低差を抑えることができる。 The method for controlling the height difference of the steel sheet surface per 1 mm of the plating film length to 10 μm or less is not particularly limited, other than the Mn content in the plating film described above (0.01 to 0.5 mass%). For example, the height difference of the film surface can be reduced by adjusting the content ratio of Mg and Mn in the plating film, or by carrying out other surface treatments to reduce the height difference.

　また、本発明の溶融Al-Zn-Si-Mg系めっき鋼板では、前記めっき皮膜と地鉄の界面にMnを含有した合金層が形成されることが好ましい。前記合金層は、浴中のAl、Fe及びSi等とMnが合金化反応することで形成され、主にFe-Al-Mn系、Fe-Al-Si-Mn系の金属間化合物であり、めっき表面方向に対して凹凸形状を有するため、前記めっき皮膜と下地鋼板の密着性をアンカー効果により向上させることができる。
　さらに、前記Mnを含有した合金層によるアンカー効果は、前記めっき皮膜が凝固する時点で発現し、前記Mn系の界面合金層はめっき液膜の移動を最小限に留める働きをするため、しわ状の欠陥の発生を抑制する効果も奏することができる。 In the hot-dip Al-Zn-Si-Mg-plated steel sheet of the present invention, an alloy layer containing Mn is preferably formed at the interface between the plating film and the base steel. The alloy layer is formed by an alloying reaction between Mn and Al, Fe, Si, etc. in the bath, and is mainly an Fe-Al-Mn or Fe-Al-Si-Mn intermetallic compound, and has an uneven shape in the plating surface direction, which can improve the adhesion between the plating film and the base steel sheet by an anchor effect.
Furthermore, the anchor effect of the Mn-containing alloy layer appears at the time when the plating film solidifies, and the Mn-based interfacial alloy layer acts to minimize the movement of the plating solution film, so that it is also possible to suppress the occurrence of wrinkle-like defects.

　また、本発明の溶融Al-Zn-Si-Mg系めっき鋼板では、優れた耐食性を付与するために前記めっき皮膜中のSi 及びMg2SiのＸ線回折法による回折強度が、以下の関係（１）を満足することが好ましい。
Si (111)／Mg2Si (111)≦0.8  ・・・（１）
Si (111)：Siの(111)面（面間隔d＝0.3135nm）の回折強度、Mg2Si (111)：Mg2Siの(111)面（面間隔d＝0.3668nm）の回折強度
上記のように、本発明ではMgやSiの含有によってめっき皮膜中に生成するMg2Si相及びSi相の存在比率を、特定の割合に制御することが好ましい。これらが耐食性に及ぼす影響については現在調査を継続しており不明な点も多いが、以下のようなメカニズムが推定される。
　溶融Al-Zn-Si-Mg系めっき皮膜が腐食環境に曝された場合、上記の金属間化合物は、α-Al相よりも優先的に溶解する結果、形成される腐食生成物の近傍はMgが豊富な環境となる。このようなMgリッチの環境下においては、形成される腐食生成物が分解されにくく、その結果としてめっき皮膜の保護作用効果が高まると推定している。また、このめっき皮膜の保護作用向上効果は、めっき皮膜中のSiがSi相ではなくMg2Si相として存在する場合により確実に発現することから、Mg2Si相に対するSi相の存在比率を下げることが有効であると考えられる。 In addition, in the hot-dip Al-Zn-Si-Mg plated steel sheet of the present invention, in order to impart excellent corrosion resistance, it is preferable that the diffraction intensities of Si and Mg2Si in the plated film by X-ray diffraction method satisfy the following relationship (1):
Si (111)／Mg 2 Si (111)≦0.8...(1)
Si (111): Diffraction intensity of the Si (111) plane (interplanar spacing d = 0.3135 nm), Mg 2 Si (111): Diffraction intensity of the Mg 2 Si (111) plane (interplanar spacing d = 0.3668 nm)As described above, in the present invention, it is preferable to control the abundance ratio of the Mg 2 Si phase and the Si phase that are generated in the plating film by the inclusion of Mg and Si to a specific ratio.The influence of these on the corrosion resistance is currently under investigation and many points remain unknown, but the following mechanism is assumed.
When a hot-dip Al-Zn-Si-Mg-based plating film is exposed to a corrosive environment, the intermetallic compounds dissolve preferentially over the α-Al phase, resulting in a Mg-rich environment in the vicinity of the formed corrosion products. It is presumed that in such a Mg-rich environment, the formed corrosion products are less likely to decompose, and as a result, the protective effect of the plating film is enhanced. In addition, the protective effect of the plating film is more reliably expressed when the Si in the plating film exists as the Mg 2 Si phase rather than the Si phase, so it is considered effective to reduce the ratio of the Si phase to the Mg 2 Si phase.

　前記めっき皮膜中のMg2SiとSiとの存在比率は、X線回折法により得られた回折ピーク強度を用いて、関係（１）：Si (111)／Mg2Si (111)≦0.8を満たすことが好ましいが、前記めっき皮膜中のMg2Si及びSiの存在比率が関係（１）を満たさない、つまり、Si (111)／Mg2Si (111)＞0.8の場合には、前記めっき皮膜中に存在するSi相が多くなるため、前述したMgが豊富な環境を、腐食生成物の近傍で得ることができず、前記めっき皮膜の保護作用向上効果が得られにくくなる。同様の観点から、Mg2Siに対するSiの存在比率（Si (111)／Mg2Si (111)）は、0.5以下であることがより好ましく、0.3以下であることがさらに好ましく、0.2以下であることが特に好ましい。
　ここで、前記関係（１）において、Si (111)は、Siの(111)面（面間隔d＝0.3135nm）の回折強度であり、Mg2Si (111)は、Mg2Siの(111)面（面間隔d＝0.3668nm）の回折強度である。 The abundance ratio of Mg 2 Si and Si in the plating film preferably satisfies the relationship (1): Si (111)/Mg 2 Si (111)≦0.8 using the diffraction peak intensity obtained by X-ray diffraction, but when the abundance ratio of Mg 2 Si and Si in the plating film does not satisfy the relationship (1), that is, Si (111)/Mg 2 Si (111)>0.8, the Si phase present in the plating film increases, so that the above-mentioned Mg-rich environment cannot be obtained in the vicinity of the corrosion product, and the protective effect of the plating film is difficult to obtain. From the same viewpoint, the abundance ratio of Si to Mg 2 Si (Si (111)/Mg 2 Si (111)) is more preferably 0.5 or less, even more preferably 0.3 or less, and particularly preferably 0.2 or less.
Here, in the above relationship (1), Si(111) is the diffraction intensity of the Si(111) plane (plane spacing d=0.3135 nm), and Mg 2 Si(111) is the diffraction intensity of the Mg 2 Si(111) plane (plane spacing d=0.3668 nm).

　なお、前記Ｘ線回折によりSi (111)及びMg2Si (111)を測定する方法としては、前記めっき皮膜の一部を機械的に削り出し、粉末にした状態でＸ線回折を行うこと（粉末Ｘ線回折測定法）で算出することができる。回折強度の測定については、面間隔d＝0.3135nmに相当するSiの回折ピーク強度、面間隔d＝0.3668nmに相当するMg2Siの回折ピーク強度を測定し、これらの比率を算出することでSi (111)／Mg2Si (111)を得ることができる。
　粉末Ｘ線回折測定を実施する際に必要なめっき皮膜の量（めっき皮膜を削り出す量）は、精度良くSi (111)及びMg2Si (111)を測定する観点から、0.1g以上あればよく、0.3g以上あることが好ましい。また、前記めっき皮膜を削り出す際に、めっき皮膜以外の鋼板成分が粉末に含まれる場合もあるが、これらの金属間化合物相はめっき皮膜のみに含まれるものであり、また前述したピーク強度に影響することはない。さらに、前記めっき皮膜を粉末にしてＸ線回折を行うのは、めっき鋼板に形成されためっき皮膜に対してＸ線回折を行うと、めっき皮膜凝固組織の面方位の影響を受け正しい相比率の計算を行うことが困難なためである。 The method for measuring Si(111) and Mg2Si (111) by X-ray diffraction can be carried out by mechanically scraping off a part of the plating film, powdering it, and subjecting it to X-ray diffraction (powder X-ray diffraction measurement method). The diffraction intensity is measured by measuring the diffraction peak intensity of Si corresponding to interplanar spacing d = 0.3135 nm and the diffraction peak intensity of Mg2Si corresponding to interplanar spacing d = 0.3668 nm, and calculating the ratio between these to obtain Si(111)/ Mg2Si (111).
The amount of the plating film required for carrying out the powder X-ray diffraction measurement (amount of the plating film to be scraped off) is 0.1 g or more, preferably 0.3 g or more, from the viewpoint of accurately measuring Si(111) and Mg2Si (111). In addition, when the plating film is scraped off, steel sheet components other than the plating film may be contained in the powder, but these intermetallic compound phases are contained only in the plating film and do not affect the above-mentioned peak intensity. Furthermore, the plating film is powdered and X-ray diffraction is carried out because, when X-ray diffraction is carried out on the plating film formed on the plated steel sheet, it is difficult to calculate the correct phase ratio due to the influence of the plane orientation of the plating film solidification structure.

　さらにまた、本発明の溶融Al-Zn-Si-Mg系めっき鋼板では、より安定的に耐食性を向上させることができる点から、前記めっき皮膜中のSiのＸ線回折法による回折強度が、以下の関係（２）を満たすことが好ましい。
Si (111)＝0  ・・・（２）
Si (111)：Siの(111)面（面間隔d＝0.3135nm）の回折強度
　一般的に、Al合金の水溶液中への溶解反応においては、Si相がカソードサイトとして存在することで周辺のα-Al相の溶解を促進することが知られていることから、Si相を少なくすることはα-Al相の溶解を抑制する観点でも有効であり、その中でも関係（２）のようにSi相が存在しない皮膜とすること（前記Si(111)の回折ピーク強度をゼロとすること）が耐食性の安定化のために最も優れている。
　なお、Ｘ線回折によるSiの(111)面の回折ピーク強度の測定方法は、上述した通りである。 Furthermore, in the hot dip Al-Zn-Si-Mg plated steel sheet of the present invention, from the viewpoint of enabling more stable improvement in corrosion resistance, it is preferable that the diffraction intensity of Si in the plated film, as determined by an X-ray diffraction method, satisfies the following relationship (2):
Si (111)=0...(2)
Si (111): Diffraction intensity of the Si (111) plane (planar spacing d = 0.3135 nm) It is generally known that in the dissolution reaction of an Al alloy in an aqueous solution, the presence of a Si phase as a cathode site promotes the dissolution of the surrounding α-Al phase. Therefore, reducing the amount of Si phase is also effective in terms of suppressing the dissolution of the α-Al phase. Among these, a coating without a Si phase, as shown in relationship (2) (making the diffraction peak intensity of the Si (111) zero) is the most excellent in terms of stabilizing corrosion resistance.
The method for measuring the diffraction peak intensity of the Si (111) plane by X-ray diffraction is as described above.

　ここで、上述した関係（１）や関係（２）を満たすための方法については、特に限定はされない。例えば、関係（１）や関係（２）を満たすためには、前記めっき皮膜中のSiの含有量、Mgの含有量及びAlの含有量のバランスを調整することによって、Mg2Si及びSiの存在比率（Mg2Si (111)及びSi (111)の回折強度）を制御できる。なお、前記めっき皮膜中のSiの含有量、Mgの含有量及びAlの含有量のバランスは、必ずしも一定の含有割合に設定すれば関係（１）や関係（２）を満たせるという訳ではなく、例えばSiの含有量（質量％）によってMg及びAlの含有比率を変える必要がある。
　また、前記めっき皮膜中のSiの含有量、Mgの含有量及びAlの含有量のバランスを調整する他にも、めっき皮膜形成時の条件（例えば、めっき後の冷却条件）を調整することによって、関係（１）や関係（２）を満たすように、Mg2Si (111)及びSi (111)の回折強度を制御できる。 Here, the method for satisfying the above-mentioned relationship (1) or (2) is not particularly limited. For example, in order to satisfy the relationship (1) or (2), the abundance ratio of Mg 2 Si and Si (diffraction intensity of Mg 2 Si (111) and Si (111)) can be controlled by adjusting the balance of the Si content, Mg content, and Al content in the plating film. Note that the balance of the Si content, Mg content, and Al content in the plating film does not necessarily satisfy the relationship (1) or (2) by setting them to a constant content ratio, and it is necessary to change the content ratio of Mg and Al depending on the Si content (mass%), for example.
In addition to adjusting the balance of the Si content, Mg content, and Al content in the plating film, the diffraction intensities of Mg 2 Si (111) and Si (111) can be controlled so as to satisfy relationship (1) or relationship (2) by adjusting the conditions during plating film formation (e.g., cooling conditions after plating).

　前記めっき皮膜の付着量は、各種特性を満足する観点から、片面あたり45～120 g／m2であることが好ましい。前記めっき皮膜の付着量が45g／m2以上の場合には、建材などの長期間耐食性が必要となる用途に対しても十分な耐食性が得られ、また、前記めっき皮膜の付着量が120g／m2以下の場合には、加工時のめっき割れ等の発生を抑えつつ、優れた耐食性を実現できるためである。同様の観点から、前記めっき皮膜の付着量は、45～100g／m2であることがより好ましい。
　なお、前記めっき皮膜の付着量については、例えば、JIS H 0401：2013年に示される塩酸とヘキサメチレンテトラミンの混合液で特定面積のめっき皮膜を溶解剥離し、剥離前後の鋼板重量差から算出する方法で導出することができる。この方法で片面あたりのめっき付着量を求めるには、非対象面のめっき表面が露出しないようにテープでシーリングしてから前述した溶解を実施することで求めることができる。 The coating weight of the plating film is preferably 45 to 120 g/ m2 per side from the viewpoint of satisfying various characteristics. When the coating weight of the plating film is 45 g/ m2 or more, sufficient corrosion resistance is obtained for applications requiring long-term corrosion resistance, such as building materials, and when the coating weight of the plating film is 120 g/m2 or less , excellent corrosion resistance can be achieved while suppressing the occurrence of plating cracks during processing. From the same viewpoint, the coating weight of the plating film is more preferably 45 to 100 g/ m2 .
The coating weight of the plating film can be derived, for example, by a method in which a specific area of the plating film is dissolved and peeled off with a mixed solution of hydrochloric acid and hexamethylenetetramine as specified in JIS H 0401: 2013, and the coating weight is calculated from the difference in the weight of the steel sheet before and after peeling. To determine the coating weight per side using this method, the plating surface of the non-target side is sealed with tape so as not to be exposed, and then the above-mentioned dissolution is carried out.

　また、本発明の溶融Al-Zn-Si-Mg系めっき鋼板を構成する下地鋼板については、特に限定はされず、要求される性能や規格に応じて、冷延鋼板や熱延鋼板等を適宜使用することができる。
　前記下地鋼板を得る方法についても、特に限定はされない。例えば、前記熱延鋼板の場合、熱間圧延工程、酸洗工程を経たものを使用することができ、前記冷延鋼板の場合には、さらに冷間圧延工程を加えて製造できる。さらに、鋼板の特性を得るために溶融めっき工程の前に、再結晶焼鈍工程等を経ることも可能である。 Furthermore, the base steel sheet constituting the hot-dip Al-Zn-Si-Mg-plated steel sheet of the present invention is not particularly limited, and a cold-rolled steel sheet, a hot-rolled steel sheet, or the like can be used as appropriate depending on the required performance and specifications.
The method for obtaining the base steel sheet is not particularly limited. For example, in the case of the hot-rolled steel sheet, one that has been subjected to a hot rolling process and a pickling process can be used, and in the case of the cold-rolled steel sheet, it can be manufactured by further adding a cold rolling process. Furthermore, in order to obtain the properties of the steel sheet, it is also possible to pass through a recrystallization annealing process or the like before the hot-dip plating process.

　なお、本発明の溶融Al-Zn-Si-Mg系めっき鋼板を製造する方法については、特に限定はされない。例えば、連続式溶融めっき設備で、前記下地鋼板を、洗浄、加熱、めっき浴浸漬することによって製造できる。鋼板の加熱工程においては、前記下地鋼板自身の組織制御のために再結晶焼鈍などを施すとともに、鋼板の酸化を防止し且つ表面に存在する微量な酸化膜を還元するため、窒素－水素雰囲気等の還元雰囲気での加熱が有効である。 The method for producing the hot-dip Al-Zn-Si-Mg-plated steel sheet of the present invention is not particularly limited. For example, it can be produced by cleaning, heating, and immersing the base steel sheet in a plating bath in a continuous hot-dip plating facility. In the steel sheet heating process, recrystallization annealing is performed to control the structure of the base steel sheet itself, and heating in a reducing atmosphere such as a nitrogen-hydrogen atmosphere is effective in preventing oxidation of the steel sheet and reducing the small amount of oxide film present on the surface.

　また、本発明の溶融Al-Zn-Si-Mg系めっき鋼板を製造する際に用いるめっき浴については、上述したように、前記めっき皮膜の組成が全体としてはめっき浴の組成とほぼ同等となることから、Al：45～65質量％、Si：1.0～3.0質量％、Mg：1.0～10.0質量％及びMn：0.1～0.5質量％を含有し、残部がZn、Fe及び不可避的不純物からなる組成を有するものを用いることができる。 As for the plating bath used in producing the hot-dip Al-Zn-Si-Mg-plated steel sheet of the present invention, as described above, the composition of the plating film as a whole is substantially the same as the composition of the plating bath, so that a plating bath containing 45-65 mass% Al, 1.0-3.0 mass% Si, 1.0-10.0 mass% Mg, and 0.1-0.5 mass% Mn, with the remainder consisting of Zn, Fe, and unavoidable impurities, can be used.

　さらに、前記めっき浴の浴温は、特に限定はされないが、（融点＋20℃）～650℃の温度範囲とすることが好ましい。
　前記浴温の下限を、融点＋20℃としたのは、溶融めっき処理を行うためには、前記浴温を凝固点以上にすることが必要であり、融点＋20℃とすることで、前記めっき浴の局所的な浴温低下による凝固を防止するためである。一方、前記浴温の上限を650℃としたのは、650℃を超えると、前記めっき皮膜の急速冷却が難しくなり，めっき皮膜と鋼板との間に形成する界面合金層が厚くなるおそれがあるためである。 Furthermore, the temperature of the plating bath is not particularly limited, but is preferably in the 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 needs to be equal to or higher than the solidification point in order to perform hot-dip plating, and by setting the temperature to the melting point + 20° C., solidification due to a local drop in the bath temperature of the plating bath is prevented. On the other hand, the reason why the upper limit of the bath temperature is set to 650° C. is that if the bath temperature exceeds 650° C., rapid cooling of the plating film becomes difficult, and there is a risk that the interfacial alloy layer formed between the plating film and the steel sheet becomes thick.

　また、めっき浴に浸入する下地鋼板の温度（浸入板温）についても、特に限定はされないが、連前記続式溶融めっき操業におけるめっき特性の確保や浴温度の変化を防ぐ観点から、前記めっき浴の温度に対して±20℃以内に制御することが好ましい。
　さらにまた、前記下地鋼板の前記めっき浴中の浸漬時間については、0.5秒以上である。これは0.5秒未満の場合、前記下地鋼板の表面に十分なめっき皮膜を形成できないおそれがあるためである。浸漬時間の上限については特に限定はされないが、浸漬時間を長くするとめっき皮膜と鋼板との間に形成する界面合金層が厚くなるおそれもあることから、8秒以内とすることが好ましい。 The temperature of the base steel sheet immersed in the coating bath (immersion sheet temperature) is not particularly limited, but from the viewpoint of ensuring coating characteristics in continuous hot-dip coating operations and preventing changes in bath temperature, it is preferable to control it to within ±20°C of the coating bath temperature.
Furthermore, the immersion time of the base steel sheet in the plating bath is 0.5 seconds or more. This is because if it is less than 0.5 seconds, there is a risk that a sufficient plating film may not be formed on the surface of the base steel sheet. There is no particular upper limit to the immersion time, but since a longer immersion time may cause a thicker interface alloy layer to form between the plating film and the steel sheet, it is preferable to set the immersion time to 8 seconds or less.

　なお、溶融Al-Zn-Si-Mg系めっき鋼板は、要求される性能に応じて、前記めっき皮膜の上に、直接又は中間層を介して、塗膜を形成することができる。
　なお、前記塗膜を形成する方法については、特に限定はされず、要求される性能に応じて適宜選択することができる。例えば、ロールコーター塗装、カーテンフロー塗装、スプレー塗装等の形成方法が挙げられる。有機樹脂を含有する塗料を塗装した後、熱風乾燥、赤外線加熱、誘導加熱等の手段により加熱乾燥して塗膜を形成することが可能である。
　また、前記中間層についても、溶融めっき鋼板のめっき皮膜と前記塗膜との間に形成される層であれば特に限定はされない。 In addition, in the case of the hot-dip Al-Zn-Si-Mg plated steel sheet, a coating film can be formed directly or via an intermediate layer on the plated film, depending on the required performance.
The method for forming the coating film is not particularly limited and can be appropriately selected depending on the required performance. For example, the coating film can be formed by a method such as roll coater coating, curtain flow coating, spray coating, etc. After coating the coating material containing an organic resin, the coating film can be formed by heating and drying the coating film by means of hot air drying, infrared heating, induction heating, etc.
The intermediate layer is not particularly limited as long as it is a layer formed between the plating film of the hot-dip plated steel sheet and the coating film.

＜表面処理鋼板＞
　本発明の表面処理鋼板は、鋼板表面にめっき皮膜と、該めっき皮膜上に形成された化成皮膜と、を備える。
　このうち、前記めっき皮膜の組成は、上述した本発明の溶融Al-Zn-Si-Mg系めっき鋼板のめっき皮膜のものと同様である。
　また、前記めっき皮膜のその他の構成についても、上述した本発明の溶融Al-Zn-Si-Mg系めっき鋼板のめっき皮膜の構成と同様である。 <Surface-treated steel sheet>
The surface-treated steel sheet of the present invention comprises a plating film on the surface of the steel sheet, and a chemical conversion film formed on the plating film.
The composition of the plating film is the same as that of the plating film of the hot-dip Al-Zn-Si-Mg plated steel sheet of the present invention described above.
Other configurations of the plating film are also the same as those of the plating film of the hot-dip Al-Zn-Si-Mg-plated steel sheet of the present invention described above.

　本発明の表面処理鋼板は、前記皮膜上に化成皮膜が形成されている。
　なお、前記化成皮膜は、表面処理鋼板の少なくとも片面に形成されればよく、用途や要求される性能に応じて、表面処理鋼板の両面に形成することもできる。 In the surface-treated steel sheet of the present invention, a chemical conversion coating is formed on the coating.
The chemical conversion coating may be formed on at least one side of the surface-treated steel sheet, but may also be formed on both sides of the surface-treated steel sheet depending on the application and required performance.

　そして、本発明の表面処理鋼板では、前記化成皮膜は、エポキシ樹脂、ウレタン樹脂、アクリル樹脂、アクリルシリコン樹脂、アルキド樹脂、ポリエステル樹脂、ポリアルキレン樹脂、アミノ樹脂及びフッ素樹脂のうちから選択される少なくとも一種の樹脂と、P化合物、Si化合物、Co化合物、Ni化合物、Zn化合物、Al化合物、Mg化合物、V化合物、Mo化合物、Zr化合物、Ti化合物及びCa化合物のうちから選択される少なくとも一種の金属化合物と、を含有することを特徴とする。
　上述した化成皮膜をめっき皮膜上に形成することによって、めっき皮膜との親和性を高め、前記めっき皮膜上に化成皮膜を均一に形成することが可能になることに加え、化成皮膜の防錆効果やバリア効果を高めることができる。その結果、本発明の表面処理鋼板の安定的な耐食性及び耐白錆性の実現が可能となる。 In the surface-treated steel sheet of the present invention, the chemical conversion coating is characterized by containing at least one resin selected from epoxy resins, urethane resins, acrylic resins, acrylic silicone resins, alkyd resins, polyester resins, polyalkylene resins, amino resins, and fluororesins, and at least one metal compound selected from P compounds, Si compounds, Co compounds, Ni compounds, Zn compounds, Al compounds, Mg compounds, V compounds, Mo compounds, Zr compounds, Ti compounds, and Ca compounds.
By forming the above-mentioned chemical conversion film on the plating film, it is possible to increase the affinity with the plating film, and to form the chemical conversion film uniformly on the plating film, and it is also possible to increase the rust prevention effect and barrier effect of the chemical conversion film, thereby making it possible to realize stable corrosion resistance and white rust resistance of the surface-treated steel sheet of the present invention.

　ここで、前記化成皮膜を構成する樹脂については、耐食性向上の観点から、エポキシ樹脂、ウレタン樹脂、アクリル樹脂、アクリルシリコン樹脂、アルキド樹脂、ポリエステル樹脂、ポリアルキレン樹脂、アミノ樹脂及びフッ素樹脂のうちから選択される少なくとも一種が用いられる。同様の観点から、前記樹脂は、ウレタン樹脂及びアクリル樹脂のうちの少なくとも一種を含有することが好ましい。なお、前記化成皮膜を構成する樹脂については、上述した樹脂の付加重合物も含まれる。 Here, from the viewpoint of improving corrosion resistance, at least one resin selected from epoxy resin, urethane resin, acrylic resin, acrylic silicone resin, alkyd resin, polyester resin, polyalkylene resin, amino resin, and fluororesin is used as the resin constituting the conversion coating. From the same viewpoint, it is preferable that the resin contains at least one of urethane resin and acrylic resin. Note that the resin constituting the conversion coating also includes addition polymers of the above-mentioned resins.

　前記エポキシ樹脂については、例えば、ビスフェノールＡ型、ビスフェノールＦ型、ノボラック型等のエポキシ樹脂をグリシジルエーテル化したもの、ビスフェノールＡ型のエポキシ樹脂に、プロピレンオキサイド、エチレンオキサイド若しくはポリアルキレングリコールを付加し、グリシジルエーテル化したもの、脂肪族エポキシ樹脂、脂環式エポキシ樹脂、ポリエーテル系エポキシ樹脂等を用いることができる。 As for the epoxy resin, for example, glycidyl etherified epoxy resins such as bisphenol A type, bisphenol F type, and novolac type, glycidyl etherified bisphenol A type epoxy resins with propylene oxide, ethylene oxide, or polyalkylene glycol added thereto, aliphatic epoxy resins, alicyclic epoxy resins, polyether-based epoxy resins, etc. can be used.

　前記ウレタン樹脂については、例えば、油変性ポリウレタン樹脂、アルキド系ポリウレタン樹脂、ポリエステル系ポリウレタン樹脂、ポリエーテル系ポリウレタン樹脂、ポリカーボネート系ポリウレタン樹脂等を用いることができる。 As the urethane resin, for example, oil-modified polyurethane resin, alkyd-based polyurethane resin, polyester-based polyurethane resin, polyether-based polyurethane resin, polycarbonate-based polyurethane resin, etc. can be used.

　前記アクリル樹脂については、例えば、ポリアクリル酸及びその共重合体、ポリアクリル酸エステル及びその共重合体、ポリメタクリル酸及びその共重合体、ポリメタクリル酸エステル及びその共重合体、ウレタン－アクリル酸共重合体（またはウレタン変性アクリル樹脂）、スチレン－アクリル酸共重合体等が挙げられ、さらにこれらの樹脂を他のアルキド樹脂、エポキシ樹脂、フェノール樹脂等によって変性させたものを用いることができる。 The acrylic resins include, for example, polyacrylic acid and its copolymers, polyacrylic acid esters and its copolymers, polymethacrylic acid and its copolymers, polymethacrylic acid esters and its copolymers, urethane-acrylic acid copolymers (or urethane-modified acrylic resins), styrene-acrylic acid copolymers, etc. Furthermore, these resins modified with other alkyd resins, epoxy resins, phenolic resins, etc. can also be used.

　前記アクリルシリコン樹脂としては、例えば、主剤としてのアクリル系共重合体の側鎖又は末端に加水分解性アルコキシシリル基を有する樹脂に、硬化剤を添加したもの等が挙げられる。また、アクリルシリコン樹脂を用いた場合には、耐食性に加えて、優れた耐候性が期待できる。 The acrylic silicone resin may be, for example, a resin having hydrolyzable alkoxysilyl groups on the side chains or ends of an acrylic copolymer as the base resin to which a curing agent has been added. Furthermore, when an acrylic silicone resin is used, excellent weather resistance can be expected in addition to corrosion resistance.

　前記アルキド樹脂については、例えば、油変性アルキド樹脂、ロジン変性アルキド樹脂、フェノール変性アルキド樹脂、スチレン化アルキド樹脂、シリコン変性アルキド樹脂、アクリル変性アルキド樹脂、オイルフリーアルキド樹脂、高分子量オイルフリーアルキド樹脂等を挙げることができる。 Examples of the alkyd resin include oil-modified alkyd resin, rosin-modified alkyd resin, phenol-modified alkyd resin, styrenic alkyd resin, silicon-modified alkyd resin, acrylic-modified alkyd resin, oil-free alkyd resin, and high molecular weight oil-free alkyd resin.

　前記ポリエステル樹脂については、多価カルボン酸とポリアルコールとを、脱水縮合してエステル結合を形成させることによって合成された重縮合体であり、多価カルボン酸としては、例えば、テレフタル酸、２，６－ナフタレンジカルボン酸等が用いられ、ポリアルコールとしては、例えば、エチレングリコール、１，３－プロパンジオール、１，４－ブタンジオール、１，４－シクロヘキサンジメタノール等が挙げられる。具体的には、前記ポリエステルは、ポリエチレンテレフタレート、ポリトリメチレンテレフタレート、ポリエチレンナフタレート、ポリブチレンナフタレート等が挙げられる。また、これらのポリエステル樹脂をアクリル変性したものを用いることもできる。 The polyester resin is a polycondensate synthesized by dehydrating and condensing a polycarboxylic acid and a polyalcohol to form an ester bond. Examples of the polycarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the polyalcohol include ethylene glycol, 1,3-propanediol, 1,4-butanediol, and 1,4-cyclohexanedimethanol. Specific examples of the polyester include polyethylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, and polybutylene naphthalate. Acrylic-modified versions of these polyester resins can also be used.

　前記ポリアルキレン樹脂については、例えば、エチレン－アクリル酸共重合体、エチレン－メタクリル酸共重合体、カルボキシル変性ポリオレフィン樹脂などのエチレン系共重合体、エチレン－不飽和カルボン酸共重合体、エチレン系アイオノマー等が挙げられ、さらに、これらの樹脂を他のアルキド樹脂、エポキシ樹脂、フェノール樹脂等によって変性させたものを用いることができる。 The polyalkylene resin may, for example, be an ethylene-based copolymer such as an ethylene-acrylic acid copolymer, an ethylene-methacrylic acid copolymer, or a carboxyl-modified polyolefin resin, an ethylene-unsaturated carboxylic acid copolymer, or an ethylene-based ionomer. Furthermore, these resins may be modified with other alkyd resins, epoxy resins, phenolic resins, or the like.

　前記アミノ樹脂については、アミンあるいはアミド化合物とアルデヒドの反応によって生成する熱硬化性樹脂であり、メラミン樹脂、グアナミン樹脂、チオ尿素樹脂等が挙げられるが、耐食性や耐侯性、密着性等の観点から、メラミン樹脂を用いることが好ましい。メラミン樹脂としては、特に限定はされないが、例えば、ブチル化メラミン樹脂、メチル化メラミン樹脂、水性メラミン樹脂等が挙げられる。 The amino resin is a thermosetting resin produced by the reaction of an amine or amide compound with an aldehyde, and examples thereof include melamine resin, guanamine resin, and thiourea resin. From the viewpoints of corrosion resistance, weather resistance, and adhesion, it is preferable to use melamine resin. The melamine resin is not particularly limited, but examples thereof include butylated melamine resin, methylated melamine resin, and aqueous melamine resin.

　前記フッ素樹脂については、フルオロオレフィン系重合体や、フルオロオレフィンと、アルキルビニルエーテル、シクロアルキルビニルエーテル、カルボン酸変性ビニルエステル、ヒドロキシアルキルアリルエーテル、テトラフルオロプロピルビニルエーテル等との共重合体が挙げられる。これらのフッ素樹脂を用いた場合には、耐食性だけでなく、優れた耐候性と優れた疎水性も期待できる。 The fluororesins mentioned above include fluoroolefin polymers and copolymers of fluoroolefins with alkyl vinyl ethers, cycloalkyl vinyl ethers, carboxylic acid-modified vinyl esters, hydroxyalkyl allyl ethers, tetrafluoropropyl vinyl ethers, etc. When these fluororesins are used, not only corrosion resistance but also excellent weather resistance and hydrophobicity can be expected.

　さらに、前記化成皮膜を構成する樹脂は、耐食性や加工性の向上を狙いとして、特に硬化剤を用いることが好ましい。硬化剤としては、尿素樹脂（ブチル化尿素樹脂等）、メラミン樹脂（ブチル化メラミン樹脂、ブチルエーテル化メラミン樹脂等）、ブチル化尿素・メラミン樹脂、ベンゾグアナミン樹脂等のアミノ樹脂、ブロックイソシアネート、オキサゾリン化合物、フェノール樹脂等を適宜用いることができる。 Furthermore, it is preferable to use a hardener for the resin that constitutes the chemical conversion coating, in order to improve corrosion resistance and workability. As the hardener, urea resin (butylated urea resin, etc.), melamine resin (butylated melamine resin, butyl etherified melamine resin, etc.), butylated urea-melamine resin, amino resin such as benzoguanamine resin, blocked isocyanate, oxazoline compound, phenol resin, etc. can be used as appropriate.

　また、前記化成皮膜を構成する金属化合物については、P化合物、Si化合物、Co化合物、Ni化合物、Zn化合物、Al化合物、Mg化合物、V化合物、Mo化合物、Zr化合物、Ti化合物及びCa化合物のうちから選択される少なくとも一種が用いられる。同様の観点から、前記金属化合物は、P化合物、Si化合物及びV化合物のうちの少なくとも一種を含有することが好ましい。 Furthermore, as for the metal compound constituting the chemical conversion coating, at least one selected from P compounds, Si compounds, Co compounds, Ni compounds, Zn compounds, Al compounds, Mg compounds, V compounds, Mo compounds, Zr compounds, Ti compounds and Ca compounds is used. From the same viewpoint, it is preferable that the metal compound contains at least one of P compounds, Si compounds and V compounds.

　ここで、前記P化合物は、前記化成皮膜中に含まれることで、耐食性や、耐汗性を向上させることができる。前記P化合物とは、Pを含有する化合物であり、例えば、無機リン酸、有機リン酸及びこれらの塩、のうちから選択される1又は2以上を含有することができる。 The P compound is contained in the chemical conversion coating, thereby improving corrosion resistance and sweat resistance. The P compound is a compound containing P, and may contain, for example, one or more selected from inorganic phosphoric acid, organic phosphoric acid, and salts thereof.

　前記無機リン酸、有機リン酸及びこれらの塩としては、特に限定されることなく任意の化合物を用いることができる。例えば、前記無機リン酸としては、リン酸、第一リン酸塩、第二リン酸塩、第三リン酸塩、ピロリン酸、ピロリン酸塩、トリポリリン酸、トリポリリン酸塩、亜リン酸、亜リン酸塩、次亜リン酸、次亜リン酸塩のうちから選択される1つ以上を用いることが好ましい。また、前記有機リン酸としては、ホスホン酸（ホスホン酸化合物）を用いることが好ましい。さらに、前記ホスホン酸としては、ニトリロトリスメチレンホスホン酸、ホスフォノブタントリカルボン酸、メチルジホスホン酸、メチレンホスホン酸、およびエチリデンジホスホン酸のうちから選択される1つ以上を用いることが好ましい。
　なお、前記P化合物が塩である場合、当該塩は、周期表における第1族～第13族元素の塩であることが好ましく、金属塩であることがより好ましく、アルカリ金属塩及びアルカリ土類金属塩のうちから選択される1つ以上であることが好ましい。 The inorganic phosphoric acid, organic phosphoric acid, and salts thereof are not particularly limited and any compound can be used. For example, the inorganic phosphoric acid is preferably one or more selected from phosphoric acid, primary phosphate, secondary phosphate, tertiary phosphate, pyrophosphoric acid, pyrophosphate, tripolyphosphoric acid, tripolyphosphate, phosphorous acid, phosphite, hypophosphorous acid, and hypophosphite. The organic phosphoric acid is preferably phosphonic acid (phosphonic acid compound). The phosphonic acid is preferably one or more selected from nitrilotrismethylenephosphonic acid, phosphonobutanetricarboxylic acid, methyldiphosphonic acid, methylenephosphonic acid, and ethylidenediphosphonic acid.
In addition, when the P compound is a salt, the salt is preferably a salt of an element of Groups 1 to 13 in the periodic table, more preferably a metal salt, and is preferably one or more selected from an alkali metal salt and an alkaline earth metal salt.

　上記P化合物を含む化成処理液を、めっき鋼板に塗付すると、該P化合物の作用によりめっき皮膜表面がエッチングされ、めっき皮膜の構成元素であるAl、Zn、Si及びMgが取り込まれた濃化層が化成皮膜の前記めっき皮膜側に形成される。前記濃化層が形成されることにより、化成皮膜とめっき皮膜表面との結合が強固となり、化成皮膜の密着性が向上する。
　前記化成処理液中のP化合物の濃度は、特に限定はされないが、0.25質量％～5質量％とすることができる。前記P化合物の濃度が0.25質量％未満では、エッチング効果が不足してめっき界面との密着力が低下し、平面部耐食性が低下するだけでなく、欠陥部、切断端面部、加工などで生じるめっきや皮膜の損傷部の耐食性、耐汗性も低下するおそれがある。同様の観点から、P化合物の濃度は、好ましくは0.35質量％以上、より好ましくは0.50質量％以上である。一方、前記P化合物の濃度が5質量％を超えると化成処理液の寿命が短くなるだけでなく、皮膜を形成した際の外観が不均一になりやすく、また、化成皮膜からのPの溶出量が多くなり、耐黒変性が低下するおそれもある。同様の観点から、P化合物の濃度は、好ましくは3.5質量％以下、より好ましくは2.5質量％以下である。前記化成皮膜中のP化合物の含有量については、例えば、P化合物の濃度を0.25質量％～5質量％とした化成処理液を、塗布、乾燥することにより、乾燥後の化成皮膜におけるPの付着量を5～100mg／m2とすることができる。 When the chemical conversion treatment solution containing the above-mentioned P compound is applied to a plated steel sheet, the surface of the plated film is etched by the action of the P compound, and a concentrated layer containing Al, Zn, Si, and Mg, which are the constituent elements of the plated film, is formed on the plated film side of the chemical conversion film. The formation of the concentrated layer strengthens the bond between the chemical conversion film and the plated film surface, improving the adhesion of the chemical conversion film.
The concentration of the P compound in the chemical conversion treatment solution is not particularly limited, but can be 0.25% by mass to 5% by mass. If the concentration of the P compound is less than 0.25% by mass, the etching effect is insufficient, the adhesion to the plating interface is reduced, and not only the corrosion resistance of the flat surface is reduced, but also the corrosion resistance and sweat resistance of defective parts, cut end faces, and damaged parts of the plating and film caused by processing may be reduced. From the same viewpoint, the concentration of the P compound is preferably 0.35% by mass or more, more preferably 0.50% by mass or more. On the other hand, if the concentration of the 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 when formed is likely to be non-uniform, and the amount of P eluted from the chemical conversion film may increase, which may reduce the resistance to blackening. From the same viewpoint, the concentration of the P compound is preferably 3.5% by mass or less, more preferably 2.5% by mass or less. Regarding the content of the P compound in the chemical conversion coating, for example, by applying a chemical conversion treatment solution with a P compound concentration of 0.25% by mass to 5% by mass and drying it, the amount of P attached in the chemical conversion coating after drying can be set to 5 to 100 mg/ m2 .

　前記Si化合物は、前記樹脂とともに化成皮膜を形成する骨格となる成分であり、前記めっき皮膜との親和性を高め、化成皮膜を均一に形成することができる。前記Si化合物は、Siを含有する化合物であり、例えば、シリカ、トリアルコキシシラン、テトラアルコキシシラン、及びシランカップリング剤のうちから選択される1つ以上を含有することが好ましい。 The Si compound is a component that becomes the framework that forms the chemical conversion film together with the resin, and it enhances the affinity with the plating film, and can form a uniform chemical conversion film. The Si compound is a compound that contains Si, and preferably contains one or more selected from, for example, silica, trialkoxysilane, tetraalkoxysilane, and a silane coupling agent.

　前記シリカとしては、とくに限定されず任意のものを用いることができる。前記シリカとしては、例えば、湿式シリカ及び乾式シリカのうちの少なくとも１つを用いることができる。前記湿式シリカの一種であるコロイダルシリカとしては、例えば、日産化学（株）製のスノーテックスO、C、N、S、20、OS、OXS、NS等を好適に用いることができる。また、前記乾式シリカとしては、例えば、日本アエロジル（株）製のAEROSIL50、130、200、300、380等を好適に用いることができる。 The silica is not particularly limited and any type can be used. For example, at least one of wet silica and dry silica can be used. As colloidal silica, which is a type of wet silica, for example, Snowtex O, C, N, S, 20, OS, OXS, NS, etc. manufactured by Nissan Chemical Co., Ltd. can be suitably used. As the dry silica, for example, AEROSIL 50, 130, 200, 300, 380, etc. manufactured by Nippon Aerosil Co., Ltd. can be suitably used.

　前記トリアルコキシシランとしては、とくに限定されることなく任意のものを用いることができる。例えば、一般式：R1Si(OR2)3（式中、R1は水素又は炭素数1～5のアルキル基であり、R2は同一のまたは異なる炭素数1～5のアルキル基である）で表されるトリアルコキシシランを用いることが好ましい。このようなトリアルコキシシランとしては、例えば、トリメトキシシラン、トリエトキシシラン、メチルトリエトキシシラン等が挙げられる。 The trialkoxysilane is not particularly limited and any trialkoxysilane can be used. For example, it is preferable to use a trialkoxysilane represented by the general formula: R 1 Si(OR 2 ) 3 (wherein R 1 is hydrogen or an alkyl group having 1 to 5 carbon atoms, and R 2 is the same or different alkyl group having 1 to 5 carbon atoms). Examples of such trialkoxysilane include trimethoxysilane, triethoxysilane, and methyltriethoxysilane.

　前記テトラアルコキシシランとしては、とくに限定されることなく任意のものを用いることができる。例えば、一般式：Si(OR)4（式中、Rは同一のまたは異なる炭素数1～5のアルキル基である）で表されるテトラアルコキシシランを用いることが好ましい。このようなテトラアルコキシシランとしては、例えば、テトラメトキシシラン、テトラエトキシシラン、テトラプロポキシシラン等が挙げられる。 The tetraalkoxysilane is not particularly limited and any tetraalkoxysilane can be used. For example, it is preferable to use 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). Examples of such tetraalkoxysilane include tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane.

　前記シランカップリング剤としては、とくに限定されることなく任意のものを用いることができる。例えば、γ－グリシドキシプロピルトリメトキシシラン、γ－グリシドキシプロピルメチルジエトキシシラン、γ－グリシドキシプロピルトリエトキシシラン、γ－アミノプロピルトリメトキシシラン、γ－アミノプロピルメチルジエトキシシラン、γ－アミノプロピルトリエトキシシラン、γ－メタクリロキシプロピルトリメトキシシラン、γ－メタクリロキシプロピルトリエトキシシラン、γ－メルカプトプロピルメチルジメトキシシラン、およびγ－メルカプトプロピルトリメトキシシラン、ビニルトリエトキシシラン、γ－イソシアネートプロピルトリエトキシシラン等が挙げられる。 The silane coupling agent is not particularly limited and any one can be used. Examples include γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropylmethyldiethoxysilane, γ-aminopropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-mercaptopropylmethyldimethoxysilane, γ-mercaptopropyltrimethoxysilane, vinyltriethoxysilane, γ-isocyanatopropyltriethoxysilane, etc.

　なお、前記Si化合物を化成皮膜に含有させることにより、該Si化合物が脱水縮合して、腐食因子を遮蔽するバリア効果の高いシロキサン結合を有する非晶質の化成皮膜が形成される。また、上述した樹脂と結合することで、より高いバリア性を有する化成皮膜が形成される。さらに、腐食環境下において、欠陥部や加工などで生じるめっきや皮膜の損傷部には緻密で安定な腐食生成物が形成され、前記めっき皮膜との複合効果によって下地鋼板の腐食を抑制する効果もある。安定な腐食生成物を形成する効果が高いという観点からは、前記Si化合物として、コロイダルシリカ及び乾式シリカのうちの少なくとも1つを用いることが好ましい。 In addition, by incorporating the Si compound into the chemical conversion film, the Si compound undergoes dehydration condensation to form an amorphous chemical conversion film having siloxane bonds that have a high barrier effect of blocking corrosion factors. In addition, by bonding with the above-mentioned resin, a chemical conversion film with higher barrier properties is formed. Furthermore, in a corrosive environment, dense and stable corrosion products are formed in defective parts and damaged parts of the plating or film caused by processing, etc., and the combined effect with the plating film also has the effect of suppressing corrosion of the underlying steel sheet. From the viewpoint of a high effect of forming stable corrosion products, it is preferable to use at least one of colloidal silica and dry silica as the Si compound.

　前記化成皮膜を形成するための化成処理液における前記Si化合物の濃度は、0.2質量％～9.5質量％とする。前記化成処理液におけるSi化合物の濃度が0.2質量％以上であれば、シロキサン結合によるバリア効果を得ることができ、その結果、平面部耐食性に加え、欠陥部、切断部及び加工等に起因した損傷部における耐食性、並びに、耐汗性が向上する。また、前記Si化合物の濃度が9.5質量％以下であれば、化成処理液の寿命を長くすることができる。Si化合物の濃度を0.2質量％～9.5質量％とした化成処理液を、塗布、乾燥することにより、乾燥後の化成皮膜におけるSi付着量を2～95mg/m2とすることができる。 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% by mass or more, a barrier effect due to siloxane bonds can be obtained, and as a result, in addition to the corrosion resistance of the flat surface, the corrosion resistance of defective parts, cut parts, and damaged parts caused by processing, etc., and sweat resistance are improved. Furthermore, if the concentration of the Si compound is 9.5% by mass or less, the life of the chemical conversion treatment liquid can be extended. By applying and drying a chemical conversion treatment liquid with a concentration of Si compound of 0.2% by mass to 9.5% by mass, the Si adhesion amount in the chemical conversion film after drying can be set to 2 to 95 mg/ m2 .

　前記Co化合物及び前記Ni化合物は、前記化成皮膜中に含まれることで、耐黒変性を向上させることができる。これは、CoやNiが、腐食環境下における水溶性成分の皮膜からの溶出を遅らせる効果を有するためであると考えられる。また、前記Co及び前記Niは、Al、Zn、Si及びMg等に比べて酸化されにくい元素である。そのため、前記Co化合物及び前記Ni化合物のうちの少なくとも一方を、前記化成皮膜と前記めっき皮膜との界面に濃化させる（濃化層を形成する）ことにより、濃化層が腐食に対するバリアとなる結果、耐黒変性を改善することができる。 The Co compounds and Ni compounds contained in the chemical conversion coating can improve resistance to blackening. This is believed to be because Co and Ni have the effect of delaying the elution of water-soluble components from the coating in a corrosive environment. Furthermore, the Co and Ni are elements that are less susceptible to oxidation than Al, Zn, Si, Mg, etc. Therefore, by concentrating at least one of the Co compounds and the Ni compounds (forming a concentrated layer) at the interface between the chemical conversion coating and the plating coating, the concentrated layer acts as a barrier against corrosion, improving resistance to blackening.

　前記Co化合物を含んだ化成処理液を用いることにより、Coを、前記化成皮膜中に含有させ、前記濃化層中に取り込ませることができる。前記Co化合物としては、コバルト塩を用いることが好ましい。前記コバルト塩としては、硫酸コバルト、炭酸コバルト及び塩化コバルトのうちから選択される1又は2以上を用いることがより好ましい。
　また、前記Ni化合物を含む化成処理液を用いることにより、Niを、前記化成皮膜中に含有させ、前記濃化層中に取り込ませることができる。前記Ni化合物としては、ニッケル塩を用いることが好ましい。前記ニッケル塩としては、硫酸ニッケル、炭酸ニッケル及び塩化ニッケルのうちから選択される1又は2以上を用いることがより好ましい。 By using a chemical conversion treatment solution containing the Co compound, Co can be contained in the chemical conversion coating and incorporated into the concentrated layer. As the Co compound, a cobalt salt is preferably used. As the cobalt salt, one or more selected from cobalt sulfate, cobalt carbonate, and cobalt chloride are more preferably used.
In addition, by using a chemical conversion treatment solution containing the Ni compound, Ni can be contained in the chemical conversion coating and incorporated into the concentrated layer. As the Ni compound, a nickel salt is preferably used. As the nickel salt, it is more preferable to use one or more selected from nickel sulfate, nickel carbonate, and nickel chloride.

　前記化成処理液中のCo化合物及び／又はNi化合物の濃度は、特に限定はされないが、合計で0.25質量％～5質量％とすることができる。前記Co化合物及び／又はNi化合物の濃度が0.25質量％未満では界面濃化層が不均一になり、平面部の耐食性が低下するだけでなく、欠陥部、切断端面部、加工等に起因しためっきや皮膜損傷部の耐食性も低下するおそれがある。同様の観点から、好ましくは0.5質量％以上、より好ましくは0.75質量％以上である。一方、前記Co化合物及び／又はNi化合物の濃度が5質量％を超えると皮膜を形成した際の外観が不均一になりやすく、耐食性が低下するおそれがある。同様の観点から、好ましくは4.0質量％以下、より好ましくは3.0質量％以下である。前記Co化合物及び／又はNi化合物の濃度の合計が0.25質量％～5質量％である化成処理液を塗布、乾燥することにより、乾燥後の化成皮膜におけるCo及びNiの合計付着量を5～100mg／m2とすることができる。 The concentration of the Co compound and/or Ni compound in the chemical conversion treatment liquid is not particularly limited, but can be 0.25% by mass to 5% by mass in total. If the concentration of the Co compound and/or Ni compound is less than 0.25% by mass, the interface thickening layer becomes nonuniform, and not only the corrosion resistance of the flat portion decreases, but also the corrosion resistance of the defective portion, the cut end surface portion, the plating or the film damaged portion due to processing, etc. may decrease. From the same viewpoint, it is preferably 0.5% by mass or more, more preferably 0.75% by mass or more. On the other hand, if the concentration of the Co compound and/or Ni compound exceeds 5% by mass, the appearance when the film is formed tends to be nonuniform, and the corrosion resistance may decrease. From the same viewpoint, it is preferably 4.0% by mass or less, more preferably 3.0% by mass or less. By applying and drying the chemical conversion treatment liquid in which the total concentration of the Co compound and/or Ni compound is 0.25% by mass to 5% by mass, the total adhesion amount of Co and Ni in the chemical conversion film after drying can be 5 to 100 mg/m 2 .

　前記Al化合物、前記Zn化合物及び前記Mg化合物については、化成処理液に含有させることで、前記化成皮膜のめっき皮膜側に、Al、Zn及びMgのうちの少なくとも一種を含む濃化層を形成できる。形成された濃化層は、耐食性を向上させることができる。
　なお、前記Al化合物、前記Zn化合物及び前記Mg化合物は、それぞれ、Al、Zn及びMgを含有する化合物のことであれば、特に限定されないが、無機化合物であることが好ましく、塩、塩化物、酸化物又は水酸化物であることが好ましい。 The Al compound, the Zn compound, and the Mg compound are contained in the chemical conversion treatment solution, so that a concentrated layer containing at least one of Al, Zn, and Mg can be formed on the plating film side of the chemical conversion film. The formed concentrated layer can improve corrosion resistance.
The Al compound, the Zn compound, and the Mg compound are not particularly limited as long as they are compounds containing Al, Zn, and Mg, respectively, but are preferably inorganic compounds, and are preferably salts, chlorides, oxides, or hydroxides.

　前記Al化合物としては、例えば、硫酸アルミニウム、炭酸アルミニウム、塩化アルミニウム、酸化アルミニウム及び水酸化アルミニウムのうちから選択される1つ以上が挙げられる。
　前記Zn化合物としては、例えば、硫酸亜鉛、炭酸亜鉛、塩化亜鉛、酸化亜鉛及び水酸化亜鉛のうちから選択される1つ以上が挙げられる。
　前記Mg化合物としては、例えば、硫酸マグネシウム、炭酸マグネシウム、塩化マグネシウム、酸化マグネシウム及び水酸化マグネシウムのうちから選択される1つ以上が挙げられる。 The Al compound may be, for example, one or more selected from aluminum sulfate, aluminum carbonate, aluminum chloride, aluminum oxide, and aluminum hydroxide.
The Zn compound may be, for example, one or more selected from zinc sulfate, zinc carbonate, zinc chloride, zinc oxide, and zinc hydroxide.
The Mg compound may be, for example, one or more selected from magnesium sulfate, magnesium carbonate, magnesium chloride, magnesium oxide, and magnesium hydroxide.

　前記化成皮膜を形成するための化成処理液中のAl化合物、Zn化合物及び／又はMg化合物の濃度は、合計で0.25質量％～5質量％であることが好ましい。前記合計濃度が0.25質量％以上であれば、前記濃化層をより効果的に形成することができ、その結果、耐食性をさらに向上させることができる。一方、前記合計濃度が5質量％以下であれば、化成皮膜の外観がより均一となり、平面部や欠陥部、加工などで生じるめっきや皮膜の損傷部の耐食性がさらに向上する。 The concentration of the Al compounds, Zn compounds and/or Mg compounds in the chemical conversion treatment solution for forming the chemical conversion coating is preferably 0.25% to 5% by mass in total. If the total concentration is 0.25% by mass or more, the concentrated layer can be formed more effectively, and as a result, corrosion resistance can be further improved. On the other hand, if the total concentration is 5% by mass or less, the appearance of the chemical conversion coating becomes more uniform, and the corrosion resistance of flat areas, defective areas, and damaged areas of the plating or coating caused by processing, etc. is further improved.

　前記V化合物は、前記化成皮膜中に含まれることで、腐食環境下においてVが適度に溶出し、同じく腐食環境下で溶出するめっき成分の亜鉛イオン等と結合し、緻密な保護皮膜を形成する。形成された保護皮膜によって、鋼板の平面部だけでなく、欠陥部、加工に起因して生じるめっき皮膜の損傷部、切断端面から平面部に進行する腐食、等に対する耐食性をさらに高めることができる。 The V compound contained in the chemical conversion film allows the V to dissolve appropriately in a corrosive environment and bind with zinc ions and other plating components that also dissolve in a corrosive environment to form a dense protective film. The protective film formed can further increase corrosion resistance not only to the flat surface of the steel sheet, but also to defects, damaged areas of the plating film caused by processing, and corrosion that progresses from the cut end surface to the flat surface.

　前記V化合物については、Vを含有する化合物であり、例えば、メタバナジン酸ナトリウム、硫酸バナジル及びバナジウムアセチルアセトネートのうちから選択される1つ以上が挙げられる。 The V compound is a compound containing V, and examples thereof include one or more selected from sodium metavanadate, vanadyl sulfate, and vanadium acetylacetonate.

　前記化成皮膜を形成するための化成処理液中のV化合物は、0.05質量％～4質量％であることが好ましい。前記V化合物の濃度が0.05質量％以上であれば、腐食環境下で溶出して保護皮膜を形成しやすくなり、欠陥部、切断端面部、加工に起因して生じるめっき皮膜の損傷部の耐食性が向上する。一方、前記V化合物の濃度が4質量％を超えると化成皮膜を形成した際の外観が不均一になりやすく、耐黒変性も低下する。 The V compound in the chemical conversion treatment solution for forming the chemical conversion film is preferably 0.05% to 4% by mass. If the concentration of the V compound is 0.05% by mass or more, it will be easier to dissolve in a corrosive environment and form a protective film, improving the corrosion resistance of defects, cut end surfaces, and damaged areas of the plating film caused by processing. On the other hand, if the concentration of the V compound exceeds 4% by mass, the appearance of the formed chemical conversion film is likely to be non-uniform, and resistance to blackening will also decrease.

　前記Mo化合物は、前記化成皮膜中に含まれることで、表面処理鋼板の耐黒変性を高めることができる。前記Mo化合物は、Moを含有する化合物であり、化成処理液にモリブデン酸及びモリブデン酸塩の一方または両方を添加することにより得ることができる。
　なお、前記モリブデン酸塩としては、例えば、モリブデン酸ナトリウム、モリブデン酸カリウム、モリブデン酸マグネシウム及びモリブデン酸亜鉛のうちから選択される1つ以上が挙げられる。 The Mo compound, when contained in the chemical conversion coating, can enhance the blackening resistance of the surface-treated steel sheet. The Mo compound is a compound containing Mo, and can be obtained by adding one or both of molybdic acid and a molybdate to the chemical conversion treatment solution.
The molybdate may be, for example, one or more selected from sodium molybdate, potassium molybdate, magnesium molybdate, and zinc molybdate.

　前記化成皮膜を形成するための化成処理液中のMo化合物の濃度は、0.01質量％～3質量％であることが好ましい。前記Mo化合物の濃度が0.01質量％以上であれば、酸素欠乏型酸化亜鉛の生成がさらに抑制され、耐黒変性を一層向上できる。一方、前記Mo化合物の濃度が３質量％以下であれば、化成処理液の寿命がさらに長くなることに加え、耐食性を一層向上できる。 The concentration of the Mo compound in the chemical conversion treatment solution for forming the chemical conversion coating is preferably 0.01% to 3% by mass. If the concentration of the Mo compound is 0.01% by mass or more, the generation of oxygen-deficient zinc oxide is further suppressed, and blackening resistance can be further improved. On the other hand, if the concentration of the Mo compound is 3% by mass or less, the life of the chemical conversion treatment solution is further extended and corrosion resistance can be further improved.

　前記Zr化合物及び前記Ti化合物は、前記化成皮膜中に含まれることで、化成皮膜がポーラスになるのを防ぎ、皮膜を緻密化させることができる。その結果、腐食因子が前記化成皮膜を透過しにくくなり、耐食性を高めることができる。 The Zr compound and the Ti compound contained in the chemical conversion coating prevent the chemical conversion coating from becoming porous and make the coating denser. As a result, corrosion factors are less likely to penetrate the chemical conversion coating, and corrosion resistance can be improved.

　前記Zr化合物については、Zrを含有する化合物であり、例えば、酢酸ジルコニル、硫酸ジルコニル、炭酸ジルコニルカリウム、炭酸ジルコニルナトリウム及び炭酸ジルコニルアンモニウムのうちから選択される1つ以上を用いることができる。これらの中でも、有機チタンキレート化合物は、化成処理液を乾燥して皮膜を形成する際、皮膜を緻密化し、より優れた耐食性が得られるため、好適である。 The Zr compound is a compound containing Zr, and for example, one or more selected from zirconyl acetate, zirconyl sulfate, potassium zirconyl carbonate, sodium zirconyl carbonate, and ammonium zirconyl carbonate can be used. Among these, organic titanium chelate compounds are preferred because they densify the film when the chemical conversion treatment liquid is dried to form the film, resulting in better corrosion resistance.

　前記Ti化合物については、Tiを含有する化合物であり、例えば、硫酸チタン、塩化チタン、水酸化チタン、チタンアセチルアセトナート、チタンオクチレングリコレート及びチタンエチルアセトアセテートのうちから選択される1つ以上を用いることができる。 The Ti compound is a compound containing Ti, and can be, for example, one or more selected from titanium sulfate, titanium chloride, titanium hydroxide, titanium acetylacetonate, titanium octylene glycolate, and titanium ethyl acetoacetate.

　前記化成皮膜を形成するための化成処理液中のZr化合物及び／又はTi化合物の濃度は、合計で0.2質量％～20質量％であることが好ましい。前記Zr化合物及び／又はTi化合物の合計濃度が0.2質量％以上であれば、腐食因子の透過抑制効果が高まり、平面部耐食性だけでなく、欠陥部、切断端面部、加工に起因しためっき皮膜損傷部の耐食性をより向上させることができる。一方、前記Zr化合物及び／又はTi化合物の合計濃度が20質量％以下であれば、前記化成処理液寿命をさらに延ばすことができる。 The concentration of Zr compounds and/or Ti compounds in the chemical conversion treatment solution for forming the chemical conversion film is preferably 0.2% to 20% by mass in total. If the total concentration of the Zr compounds and/or Ti compounds is 0.2% by mass or more, the effect of inhibiting the permeation of corrosion factors is enhanced, and the corrosion resistance of not only flat surface parts but also defective parts, cut end faces, and parts of the plating film damaged by processing can be further improved. On the other hand, if the total concentration of the Zr compounds and/or Ti compounds is 20% by mass or less, the life of the chemical conversion treatment solution can be further extended.

　前記Ca化合物は、前記化成皮膜中に含まれることで、腐食速度を低下させる効果を発現させることができる。 The Ca compound, when contained in the chemical conversion coating, can exert the effect of reducing the corrosion rate.

　前記Ca化合物については、Caを含有する化合物であり、例えば、Caの酸化物、Caの硝酸塩、Caの硫酸塩、Caを含有する金属間化合物等が挙げられる。より具体的には、前記Ca化合物として、CaO、CaCO3、Ca(OH)2、Ca(NO3)2・4H2O、CaSO4・2H2O等が挙げられる。前記化成皮膜中の前記Ca化合物の含有量は、特に限定はされない。 The Ca compound is a compound containing Ca, and examples of the Ca compound include Ca oxide, Ca nitrate, Ca sulfate, and intermetallic compounds containing Ca. More specifically, examples of the Ca compound include CaO, CaCO3 , Ca( OH ) 2 , Ca (NO3)2.4H2O , and CaSO4.2H2O . The content of the Ca compound in the chemical conversion coating is not particularly limited.

　なお、前記化成皮膜は、必要に応じて、塗料分野で通常使用されている公知の各種成分を含有することができる。例えば、レベリング剤、消泡剤等の各種表面調整剤、分散剤、沈降防止剤、紫外線吸収剤、光安定剤、シランカップリング剤、チタネートカップリング剤等の各種添加剤、着色顔料、体質顔料、光輝材等の各種顔料、硬化触媒、有機溶剤、潤滑剤などが挙げられる。 The conversion coating may contain various known components commonly used in the coating field, if necessary. Examples include various surface conditioners such as leveling agents and defoamers, various additives such as dispersants, anti-settling agents, UV absorbers, light stabilizers, silane coupling agents, and titanate coupling agents, various pigments such as color pigments, extender pigments, and lustrous materials, curing catalysts, organic solvents, and lubricants.

　なお、本発明の表面処理鋼板では、前記化成皮膜が6価クロム、3価クロム、フッ素等の有害な成分を含有しないことが好ましい。前記化成皮膜を形成するための化成処理液中に、これらの有害成分が含有しないため、安全性が高く、環境への負荷も小さくなるためである。 In addition, in the surface-treated steel sheet of the present invention, it is preferable that the chemical conversion coating does not contain harmful components such as hexavalent chromium, trivalent chromium, and fluorine. This is because the chemical conversion treatment liquid used to form the chemical conversion coating does not contain these harmful components, making it safer and less impactful on the environment.

　また、前記化成皮膜の付着量は、特に限定はされない。例えば、より確実に耐食性を確保しつつ、化成皮膜の剥離等を防ぐ観点からは、前記化成皮膜の付着量を0.1～3.0g／m2とすることが好ましく、0.5～2.5g／m2とすることがより好ましい。前記化成皮膜の付着量を0.1 g／m2以上とすることで、より確実に耐食性を確保でき、前記化成皮膜の付着量を3.0g／m2以下とすることで、化成皮膜の割れや剥離を防ぐことができる。
　前記化成皮膜付着量は、皮膜を蛍光Ｘ 線分析して予め皮膜中の含有量が分かっている元素の存在量を測定する方法のような、既存の手法から適切に選択した方法で求めればよい。 The coating weight of the chemical conversion coating is not particularly limited. For example, from the viewpoint of preventing peeling of the chemical conversion coating while more reliably ensuring corrosion resistance, the coating weight of the chemical conversion coating is preferably 0.1 to 3.0 g/ m2 , and more preferably 0.5 to 2.5 g/ m2 . By setting the coating weight of the chemical conversion coating to 0.1 g/m2 or more , corrosion resistance can be more reliably ensured, and by setting the coating weight of the chemical conversion coating to 3.0 g/m2 or less , cracking and peeling of the chemical conversion coating can be prevented.
The coating weight of the chemical conversion coating may be determined by a method appropriately selected from existing techniques, such as a method of subjecting the coating to fluorescent X-ray analysis to measure the amount of an element present in the coating whose content is known in advance.

　なお、前記化成皮膜を形成するための方法は、特に限定はされず、要求される性能や、製造設備等に応じて適宜選択することができる。例えば、前記めっき皮膜上に、化成処理液をロールコーター等により連続的に塗布し、その後、熱風や誘導加熱等を用いて、60～200℃程度の到達板温（Peak Metal Temperature：PMT）で乾燥させることで形成することができる。前記化成処理液の塗布には、ロールコーター以外にも、エアレススプレー、静電スプレー、カーテンフローコーター等の公知の手法を適宜採用することができる。さらに、前記化成皮膜は、前記樹脂及び前記金属化合物を含むものであれば、単層膜又は複層膜のいずれであってもよく、特に限定されるものではない。 The method for forming the chemical conversion coating is not particularly limited, and can be appropriately selected depending on the required performance, manufacturing equipment, etc. For example, the chemical conversion coating can be formed by continuously applying a chemical conversion treatment liquid onto the plating film using a roll coater or the like, and then drying at a peak metal temperature (PMT) of about 60 to 200°C using hot air or induction heating. In addition to roll coaters, known methods such as airless spray, electrostatic spray, and curtain flow coater can be appropriately used to apply the chemical conversion treatment liquid. Furthermore, the chemical conversion coating can be either a single-layer film or a multi-layer film as long as it contains the resin and the metal compound, and is not particularly limited.

　そして、本発明の表面処理鋼板は、上述した本発明の溶融Al-Zn-Si-Mg系めっき鋼板表面と同様に、鋼板表面（化成皮膜表面）の両端から50mmを除いた範囲において、長さ1mmあたりの前記鋼板表面の高低差が10μm以下である。
　前記化成皮膜表面の高低差が10μm以下である場合には、しわ状欠陥がなく、優れた表面外観を得ることができる。
　前記しわ状欠陥とは、上述したように、Mg系酸化物に起因して前記化成皮膜表面の表面がしわ状の凹凸形状になった欠陥であり、前記化成皮膜表面に白色の筋模様として現れるため、しわ状欠陥の抑制とは、前記筋模様が視認されないことである。そのため、前記鋼板表面、つまり化成皮膜表面の長さ1mmの範囲における高低差を10μm以内に抑えることで、筋模様として視認されず、優れた表面外観を得ることができる。同様の観点から、前記鋼板表面の長さ1mmの範囲における高低差は、5μm以内であることが好ましい。
　なお、前記鋼板表面とは、鋼板の最表面のことであり、表面処理鋼板の場合には、化成皮膜表面のことをいう。 The surface-treated steel sheet of the present invention has a height difference of 10 μm or less per mm length in a range excluding 50 mm from both ends of the steel sheet surface (chemical conversion coating surface), similar to the surface of the hot-dip Al-Zn-Si-Mg-plated steel sheet of the present invention described above.
When the height difference of the surface of the chemical conversion coating is 10 μm or less, there are no wrinkle-like defects and an excellent surface appearance can be obtained.
As described above, the wrinkle defects are defects in which the surface of the chemical conversion coating is wrinkled and uneven due to Mg-based oxides, and appear as white streaks on the surface of the chemical conversion coating. Therefore, suppressing the wrinkle defects means that the streaks are not visible. Therefore, by suppressing the height difference within a 1 mm long range of the steel sheet surface, i.e., the chemical conversion coating surface, to within 10 μm, the streaks are not visible, and an excellent surface appearance can be obtained. From the same viewpoint, it is preferable that the height difference within a 1 mm long range of the steel sheet surface is within 5 μm.
The steel sheet surface means the outermost surface of the steel sheet, and in the case of a surface-treated steel sheet, means the surface of the chemical conversion coating.

　ここで、前記鋼板表面の高低差とは、下地鋼板の表面と垂直方向（めっきの膜厚方向）を高さとした場合に、鋼板上（化成皮膜上）の最も高い点の高さと最も低い点の高さの差のことである。
　また、前記化成皮膜表面の長さ1mmの範囲における高低差を得る手法については、上述しためっき皮膜表面の場合と同様に、レーザー顕微鏡を用いて、表面処理鋼板の任意の100箇所の1mmの範囲における高低差を測定し、測定値の平均を算出することで得ることができる。 Here, the height difference on the surface of the steel sheet refers to the difference in height between the highest point and the lowest point on the steel sheet (on the chemical conversion coating) when the height is taken in the direction perpendicular to the surface of the base steel sheet (in the direction of the plating thickness).
The method of obtaining the height difference within a 1 mm long range of the chemical conversion coating surface can be similar to that of the plating coating surface described above, in which the height difference within a 1 mm range at any 100 points on the surface-treated steel sheet is measured using a laser microscope and the average of the measured values is calculated.

　また、前記鋼板表面の鋼板両端から50mmを除いた範囲において、前記鋼板表面の高低差を制御する理由としては、一般的に溶融めっき鋼板の両端では、鋼板中央に対し付着量の制御が難しく、冷却速度も異なるため、しわ状欠陥が発生し易い。加えて、このような鋼板両端は、トリミングされて使用されることが多く、表面外観については殆ど問題とならないためである。 The reason for controlling the height difference on the surface of the steel plate in the area excluding 50 mm from both ends of the steel plate is that it is generally difficult to control the amount of coating at both ends of a hot-dip galvanized steel plate compared to the center of the plate, and the cooling rate is also different, making wrinkle-like defects more likely to occur. In addition, such both ends of the plate are often trimmed before use, so the surface appearance is of little concern.

　前記鋼板表面の長さ1mmあたりの皮膜表面の高低差を10μm以下に制御する方法については、上述しためっき皮膜表面の高低差を抑えることが重要であり、前記めっき皮膜中のMgとMnの含有比率を調整したり、その他高低差を抑えるための表面処理を行うことで、皮膜表面の高低差を抑えることができる。 As for the method of controlling the height difference of the coating surface to 10 μm or less per 1 mm of length of the steel plate surface, it is important to suppress the height difference of the plating film surface as described above, and the height difference of the coating surface can be suppressed by adjusting the content ratio of Mg and Mn in the plating film or by carrying out other surface treatments to suppress the height difference.

　また、本発明の表面処理鋼板は、必要に応じて、前記化成皮膜上に塗膜を形成することもできる。 In addition, if necessary, the surface-treated steel sheet of the present invention can have a paint film formed on the chemical conversion coating.

　なお、本発明の表面処理鋼板の製造方法は、めっき皮膜と、該めっき皮膜上に形成された化成皮膜と、を備える表面処理鋼板の製造方法である。
　そして、本発明の製造方法では、前記化成皮膜が、エポキシ樹脂、ウレタン樹脂、アクリル樹脂、アクリルシリコン樹脂、アルキド樹脂、ポリエステル樹脂、ポリアルキレン樹脂、アミノ樹脂及びフッ素樹脂のうちから選択される少なくとも一種の樹脂と、P化合物、Si化合物、Co化合物、Ni化合物、Zn化合物、Al化合物、Mg化合物、V化合物、Mo化合物、Zr化合物、Ti化合物及びCa化合物のうちから選択される少なくとも一種の金属化合物と、を含有し、
　前記めっき皮膜の形成は、Al：45～65質量％、Si：1.0～4.0質量％及びMg：1.0～10.0質量％を含有し、残部がZn及び不可避的不純物からなる組成を有するめっき浴中に、下地鋼板を浸漬させる溶融めっき処理工程を具える。 The method for producing a surface-treated steel sheet of the present invention is a method for producing a surface-treated steel sheet comprising a plating film and a chemical conversion film formed on the plating film.
In the manufacturing method of the present invention, the chemical conversion coating contains at least one resin selected from the group consisting of epoxy resins, urethane resins, acrylic resins, acrylic silicone resins, alkyd resins, polyester resins, polyalkylene resins, amino resins, and fluororesins, and at least one metal compound selected from the group consisting of P compounds, Si compounds, Co compounds, Ni compounds, Zn compounds, Al compounds, Mg compounds, V compounds, Mo compounds, Zr compounds, Ti compounds, and Ca compounds,
The formation of the plating film includes a hot-dip galvanizing process in which a base steel sheet is immersed in a plating bath having a composition containing 45 to 65 mass% Al, 1.0 to 4.0 mass% Si, and 1.0 to 10.0 mass% Mg, with the balance being Zn and unavoidable impurities.

　なお、前記溶融めっき処理工程の条件については、本発明の溶融Al-Zn-Si-Mg系めっき鋼板の中で説明した内容と同様である。 The conditions for the hot-dip galvanizing process are the same as those described for the hot-dip Al-Zn-Si-Mg-plated steel sheet of the present invention.

＜塗装鋼板＞
　本発明の塗装鋼板は、めっき皮膜上に、直接又は化成皮膜を介して、塗膜が形成された塗装鋼板である。
　このうち、前記めっき皮膜の組成は、上述した本発明の溶融Al-Zn-Si-Mg系めっき鋼板のめっき皮膜のものと同様である。
　また、前記めっき皮膜のその他の構成についても、上述した本発明の溶融Al-Zn-Si-Mg系めっき鋼板のめっき皮膜の構成と同様である。 <Coated steel plate>
The coated steel sheet of the present invention is a coated steel sheet in which a coating film is formed on a plating film directly or via a chemical conversion film.
The composition of the plating film is the same as that of the plating film of the above-mentioned hot-dip Al-Zn-Si-Mg plated steel sheet of the present invention.
Other configurations of the plating film are also the same as those of the plating film of the hot-dip Al-Zn-Si-Mg-plated steel sheet of the present invention described above.

　本発明の塗装鋼板は、前記めっき皮膜上に、化成皮膜を形成することができる。
　なお、前記化成皮膜は、塗装鋼板の少なくとも片面に形成されればよく、用途や要求される性能に応じて、塗装鋼板の両面に形成することもできる。 In the coated steel sheet of the present invention, a chemical conversion film can be formed on the plating film.
The chemical conversion coating may be formed on at least one side of the coated steel sheet, and may also be formed on both sides of the coated steel sheet depending on the application and required performance.

・化成皮膜
　そして、本発明の塗装鋼板では、前記化成皮膜が、（ａ）：エステル結合を有するアニオン性ポリウレタン樹脂及び（ｂ）：ビスフェノール骨格を有するエポキシ樹脂を合計で30～50質量％含有し、該（ａ）と該（ｂ）の含有比率（（ａ）：（ｂ））が、質量比で3：97 ～60：40の範囲である樹脂成分と、2～10質量％のバナジウム化合物、40～60質量％のジルコニウム化合物及び0.5～5質量％のフッ素化合物を含む無機化合物と、を含有することを特徴とする。
　上述した化成皮膜をめっき皮膜上に形成することによって、化成皮膜の強度及び密着性を高めつつ、耐食性も向上させることができる。 Chemical conversion coating: In the coated steel sheet of the present invention, the chemical conversion coating is characterized in that it contains a resin component containing 30 to 50 mass% in total of (a): an anionic polyurethane resin having an ester bond and (b): an epoxy resin having a bisphenol skeleton, the content ratio of (a) to (b) ((a):(b)) being in the range of 3:97 to 60:40 in terms of mass ratio, and inorganic compounds including 2 to 10 mass% of a vanadium compound, 40 to 60 mass% of a zirconium compound, and 0.5 to 5 mass% of a fluorine compound.
By forming the above-mentioned chemical conversion film on the plating film, it is possible to increase the strength and adhesion of the chemical conversion film while improving the corrosion resistance.

　ここで、前記化成皮膜を構成する樹脂成分については、（ａ）：エステル結合を有するアニオン性ポリウレタン樹脂及び（ｂ）：ビスフェノール骨格を有するエポキシ樹脂を含有する。 The resin components constituting the chemical conversion coating include (a): an anionic polyurethane resin having an ester bond and (b): an epoxy resin having a bisphenol skeleton.

　前記（ａ）エステル結合を有するアニオン性ポリウレタン樹脂については、ポリエステルポリオールと、イソシアネート基を２個以上もつ、ジイソシアネート又はポリイソシアネートとの反応物に、ジメチロールアルキル酸を共重合して得られる樹脂が挙げられる。また、公知の方法により水等の液中に分散させることにより、化成処理液を得ることができる。 As for the (a) anionic polyurethane resin having an ester bond, there can be mentioned a resin obtained by copolymerizing a reaction product of a polyester polyol with a diisocyanate or polyisocyanate having two or more isocyanate groups with a dimethylol alkyl acid. In addition, a chemical conversion treatment liquid can be obtained by dispersing the resin in a liquid such as water by a known method.

　前記ポリエステルポリオールとしては、グリコール成分と、ヒドロキシルカルボン酸のエステル形成誘導体などの酸成分とから脱水縮合反応によって得られるポリエステル、ε－カプロラクトン等の環状エステル化合物の開環重合反応によって得られるポリエステル及びこれらの共重合ポリエステルが挙げられる。
　前記ポリイソシアネートとしては、芳香族ポリイソシアネート、脂肪族ポリイソシアネート、脂環式ポリイソシアネート等が挙げられる。前記芳香族ポリイソシアネートとしては、例えば、２，４－トリレンジイソシアネート、２，６－トリレンジイソシアネート、ｍ－キシレンジイソシアネート、ジフェニルメタンジイソシアネート、２，４－ジフェニルメタンジイソシアネート、２，２－ジフェニルメタンジイソシアネート、トリフェニルメタントリイソシアネート、ポリメチレンポリフェニルポリイソシアネート、ナフタレンジイソシアネート、およびこれらの誘導体（例えばポリオール類との反応により得られたプレポリマー類、ジフェニルメタンジイソシアネートのカルボジイミド化合物等の変性ポリイソシアネート類等）等が挙げられる。 Examples of the polyester polyol include polyesters obtained by a dehydration condensation reaction between a glycol component and an acid component such as an ester-forming derivative of a hydroxyl carboxylic acid, polyesters obtained by a ring-opening polymerization reaction of a cyclic ester compound such as ε-caprolactone, and copolymer polyesters thereof.
Examples of the polyisocyanate include aromatic polyisocyanates, aliphatic polyisocyanates, alicyclic polyisocyanates, etc. Examples of the aromatic polyisocyanate include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, m-xylylene diisocyanate, diphenylmethane diisocyanate, 2,4-diphenylmethane diisocyanate, 2,2-diphenylmethane diisocyanate, triphenylmethane triisocyanate, polymethylene polyphenyl polyisocyanate, naphthalene diisocyanate, and derivatives thereof (for example, prepolymers obtained by reaction with polyols, modified polyisocyanates such as carbodiimide compounds of diphenylmethane diisocyanate, etc.).

　なお、前記ポリエステルポリオールと、前記ジイソシアネート又はポリイソシアネートとを反応させてウレタンを合成する際、例えば、ジメチロールアルキル酸を共重合し、自己乳化させて水溶化（水分散）させることで、前記（ａ）エステル結合を有するアニオン性ポリウレタン樹脂を得ることができる。この場合、ジメチロールアルキル酸としては、例えば、炭素数２～６のジメチロールアルキル酸が挙げられ、より具体的には、ジメチロールエタン酸、ジメチロールプロパン酸、ジメチロールブタン酸、ジメチロールヘプタン酸およびジメチロールヘキサン酸等が挙げられる。 When synthesizing urethane by reacting the polyester polyol with the diisocyanate or polyisocyanate, for example, dimethylol alkyl acid can be copolymerized and self-emulsified to be water-soluble (dispersed in water) to obtain the anionic polyurethane resin having the ester bond (a). In this case, examples of the dimethylol alkyl acid include dimethylol alkyl acids having 2 to 6 carbon atoms, and more specifically, dimethylol ethanoic acid, dimethylol propanoic acid, dimethylol butanoic acid, dimethylol heptanoic acid, and dimethylol hexanoic acid.

　また、前記（ｂ）ビスフェノール骨格を有するエポキシ樹脂については、公知のエポキシ樹脂を用いることができる。例えば、ビスフェノールＡ型エポキシ樹脂、ビスフェノールＦ型エポキシ樹脂、ビスフェノールＡＤ型エポキシ樹脂、ビスフェノールＳ型エポキシ樹脂等が挙げられる。これらのエポキシ樹脂は、ビスフェノールＡ、ビスフェノールＦ、ビスフェノールＡＤ、ビスフェノールＳ等のビスフェノール化合物と、エピクロルヒドリンとをアルカリ触媒の存在下で反応して得ることができる。中でも、成分〔Ａ〕は、ビスフェノールＡ型エポキシ樹脂又はビスフェノールＦ型エポキシ樹脂を含むことが好ましく、ビスフェノールＡ型エポキシ樹脂を含むことがより好ましい。該（ｂ）ビスフェノール骨格を有するエポキシ樹脂は、公知の方法で水等の液に分散させることにより化成処理液を得ることができる。 Furthermore, for the epoxy resin having a bisphenol skeleton (b), a known epoxy resin can be used. Examples include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol AD type epoxy resin, and bisphenol S type epoxy resin. These epoxy resins can be obtained by reacting a bisphenol compound such as bisphenol A, bisphenol F, bisphenol AD, or bisphenol S with epichlorohydrin in the presence of an alkaline catalyst. Among them, 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 epoxy resin having a bisphenol skeleton (b) can be dispersed in a liquid such as water by a known method to obtain a chemical conversion treatment liquid.

　前記樹脂成分は、前記化成皮膜のバインダーとして作用するが、バインダーを構成する前記（ａ）エステル結合を有するアニオン性ポリウレタン樹脂は、可撓性があるので加工を受けた際に化成皮膜が破壊（剥離）しにくくなる効果を奏することができ、前記（ｂ）ビスフェノール骨格を有するエポキシ樹脂は、下地の亜鉛系めっき鋼板及び上層のプライマー塗膜との密着性を向上する効果を奏することができる。
　前記樹脂成分は、前記化成皮膜中に合計で30～50質量％含まれる。前記樹脂成分の含有量が30質量％未満では化成皮膜のバインダー効果が低下し、50質量％を超えると、下記に示す無機成分による機能、例えばインヒビター作用が低下する。同様の観点から、前記化成皮膜における前記樹脂成分の含有量は、35～45質量％であることが好ましい。 The resin components act as binders for the chemical conversion coating, and the (a) anionic polyurethane resin having ester bonds that constitutes the binder is flexible and therefore has the effect of making the chemical conversion coating less likely to be destroyed (peeled off) when processed, and the (b) epoxy resin having a bisphenol skeleton has the effect of improving adhesion to the underlying zinc-based plated steel sheet and the overlying primer coating.
The resin components are contained in the chemical conversion coating in a total amount of 30 to 50% by mass. If the content of the resin components is less than 30% by mass, the binder effect of the chemical conversion coating is reduced, and if it exceeds 50% by mass, the functions of the inorganic components described below, such as the inhibitor action, are reduced. From the same viewpoint, the content of the resin components in the chemical conversion coating is preferably 35 to 45% by mass.

　さらに、前記樹脂成分は、前記（ａ）エステル結合を有するアニオン性ポリウレタン樹脂と前記（ｂ）ビスフェノール骨格を有するエポキシ樹脂の含有比率（（ａ）：（ｂ））が、質量比で3：97 ～60：40の範囲であることを要する。前記（ａ）：（ｂ）が、上記範囲外の場合、化成処理皮膜としての可撓性の低下や密着性が低下に伴い、十分な耐食性が得られないためである。同様の観点から、前記（ａ）：（ｂ）は、10：90～55：45であることが好ましい。 Furthermore, the resin component requires that the content ratio ((a):(b)) of the anionic polyurethane resin having an ester bond (a) and the epoxy resin having a bisphenol skeleton (b) is in the range of 3:97 to 60:40 by mass. If the (a):(b) ratio is outside the above range, the flexibility and adhesion of the chemical conversion coating will decrease, and sufficient corrosion resistance will not be obtained. From the same viewpoint, the (a):(b) ratio is preferably 10:90 to 55:45.

　なお、前記樹脂成分については、要求される性能に応じて、上述した（ａ）エステル結合を有するアニオン性ポリウレタン樹脂及び（ｂ）ビスフェノール骨格を有するエポキシ樹脂以外の樹脂（その他の樹脂成分）を含むことができる。前記その他の樹脂成分については、特に限定はされず、例えば、アクリル樹脂、アクリルシリコン樹脂、アルキド樹脂、ポリエステル樹脂、ポリアルキレン樹脂、アミノ樹脂及びフッ素樹脂のうちから選択される少なくとも一種又は２種以上を組み合わせて用いることができる。
　前記樹脂成分がその他の樹脂を含む場合、前記（ａ）エステル結合を有するアニオン性ポリウレタン樹脂及び前記（ｂ）ビスフェノール骨格を有するエポキシ樹脂の合計含有量が、50質量％以上であることが好ましく、75質量％以上であることがより好ましい。成処理皮膜としての可撓性の低下や密着性をより確実に得るためである。 The resin component may contain resins (other resin components) other than the above-mentioned (a) anionic polyurethane resin having an ester bond and (b) epoxy resin having a bisphenol skeleton, depending on the required performance. The other resin components are not particularly limited, and may be, for example, at least one selected from acrylic resins, acrylic silicone resins, alkyd resins, polyester resins, polyalkylene resins, amino resins, and fluororesins, or a combination of two or more selected therefrom.
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 75% by mass or more, in order to more reliably prevent a decrease in flexibility and obtain adhesion as a conversion coating.

　また、前記化成皮膜は、無機化合物として、2～10質量％のバナジウム化合物、40～60質量％のジルコニウム化合物及び0.5～5質量％のフッ素化合物を含む。
　これらの化合物を含むことによって、化成皮膜の耐食性を高めることができる。 The chemical conversion coating contains, as inorganic compounds, 2 to 10 mass % of a vanadium compound, 40 to 60 mass % of a zirconium compound, and 0.5 to 5 mass % of a fluorine compound.
By including these compounds, the corrosion resistance of the chemical conversion coating can be improved.

　前記バナジウム化合物は、化成処理液中に添加して防錆剤（インヒビター）として作用する。前記バナジウム化合物が前記化成皮膜中に含まれることで、腐食環境下においてバナジウム化合物が適度に溶出し、同じく腐食環境下で溶出するめっき成分の亜鉛イオン等と結合し、緻密な保護皮膜を形成する。形成された保護皮膜によって、鋼板の平面部だけでなく、欠陥部、加工に起因して生じるめっき皮膜の損傷部、切断端面から平面部に進行する腐食、等に対する耐食性をさらに高めることができる。
　前記バナジウム化合物については、例えば、五酸化バナジウム、メタバナジン酸、メタバナジン酸アンモニウム、オキシ三塩化バナジウム、三酸化バナジウム、二酸化バナジウム、バナジン酸マグネシウム、バナジルアセチルアセトネート、バナジウムアセチルアセトネート等が挙げられる。特に、これらの中でも、４価のバナジウム化合物又は還元若しくは酸化することによって得られる４価のバナジウム化合物を用いることが望ましい。 The vanadium compound is added to the chemical conversion solution and acts as a rust inhibitor. The vanadium compound is contained in the chemical conversion coating, so that the vanadium compound is appropriately dissolved in a corrosive environment and combines with zinc ions of the plating components that are also dissolved in a corrosive environment to form a dense protective coating. The formed protective coating can further increase the corrosion resistance not only of the flat surface of the steel sheet, but also of defects, damaged parts of the plating film caused by processing, corrosion that progresses from the cut end surface to the flat surface, and the like.
Examples of the vanadium compound include vanadium pentoxide, metavanadic acid, ammonium metavanadate, vanadium oxytrichloride, vanadium trioxide, vanadium dioxide, magnesium vanadate, vanadyl acetylacetonate, vanadium acetylacetonate, etc. Among these, it is particularly desirable to use a tetravalent vanadium compound or a tetravalent vanadium compound obtained by reduction or oxidation.

　また、前記化成処理皮膜中のバナジウム化合物の含有量は、2～10質量％である。前記化成処理皮膜中のバナジウム化合物の含有量が2質量％未満ではインヒビター効果が十分でないため耐食性の低下を招き、一方、前記バナジウム化合物の含有量が10質量％を超えると化成処理皮膜の耐湿性の低下を招くためである。 The content of the vanadium compound in the chemical conversion coating is 2 to 10% by mass. If the content of the vanadium compound in the chemical conversion coating is less than 2% by mass, the inhibitor effect is insufficient, resulting in a decrease in corrosion resistance, while if the content of the vanadium compound exceeds 10% by mass, the moisture resistance of the chemical conversion coating decreases.

　ジルコニウム化合物は、前記化成皮膜中に含有され、めっき金属との反応や樹脂成分との共存により、化成処理皮膜としての強度向上及び耐食性向上が期待でき、さらにはジルコニウム化合物自体が緻密な化成処理皮膜の形成に寄与し、被覆性に富むことからバリア効果を期待できる。
　前記ジルコニウム化合物としては、硫酸ジルコニウム、炭酸ジルコニウム、硝酸ジルコニウム、乳酸ジルコニウム、酢酸ジルコニウム、塩化ジルコニウムなどの中和塩等が挙げられる。 The zirconium compound is contained in the chemical conversion coating, and is expected to improve the strength and corrosion resistance of the chemical conversion coating through its reaction with the plating metal and its coexistence with a resin component. Furthermore, the zirconium compound itself contributes to the formation of a dense chemical conversion coating, and because of its excellent covering properties, a barrier effect can be expected.
Examples of the zirconium compound include neutral salts of zirconium sulfate, zirconium carbonate, zirconium nitrate, zirconium lactate, zirconium acetate, zirconium chloride, and the like.

　また、前記化成処理皮膜中のジルコニウム化合物の含有量は、40～60質量％である。前記化成処理皮膜中のジルコニウム化合物の含有量が40質量％未満では、化成処理皮膜としての強度や耐食性の低下を招き、前記ジルコニウム化合物の含有量が60質量％を超えると、化成処理皮膜が脆化して、厳しい加工を受けた場合に化成処理皮膜の破壊や剥離が生じるためである。 The content of the zirconium compound in the chemical conversion coating is 40-60% by mass. If the content of the zirconium compound in the chemical conversion coating is less than 40% by mass, the strength and corrosion resistance of the chemical conversion coating will decrease, and if the content of the zirconium compound exceeds 60% by mass, the chemical conversion coating will become brittle, causing damage or peeling of the chemical conversion coating when subjected to severe processing.

　前記フッ素化合物は、前記化成皮膜中に含有され、めっき皮膜との密着性付与剤として作用する。その結果、前記化成皮膜の耐食性を高めることが可能となる。
　前記フッ素化合物としては、例えば、アンモニウム塩、ナトリウム塩、カリウム塩などのフッ化物塩、又は、フッ化第一鉄、フッ化第二鉄等のフッ素化合物を用いることができる。これらの中でも、フッ化アンモニウムや、フッ化ナトリウム及びフッ化カリウム等のフッ化物塩を用いることが好ましい。 The fluorine compound is contained in the chemical conversion coating and acts as an adhesive agent for the plating coating, thereby making it possible to improve the corrosion resistance of the chemical conversion coating.
As the fluorine compound, for example, fluoride salts such as ammonium salts, sodium salts, potassium salts, or fluorine compounds such as ferrous fluoride, ferric fluoride, etc. Among these, it is preferable to use fluoride salts such as ammonium fluoride, sodium fluoride, and potassium fluoride.

　また、前記化成処理皮膜中のフッ素化合物の含有量は、0.5～5質量％である。前記化成処理皮膜中のフッ素化合物の含有量が0.5質量％未満では加工部での密着性が充分に得られず、前記フッ素化合物の含有量が5質量％を超えると化成処理皮膜の耐湿性が低下するからである。 The content of the fluorine compound in the chemical conversion coating is 0.5 to 5% by mass. If the content of the fluorine compound in the chemical conversion coating is less than 0.5% by mass, sufficient adhesion cannot be obtained at the processed area, and if the content of the fluorine compound exceeds 5% by mass, the moisture resistance of the chemical conversion coating decreases.

　また、前記化成皮膜の付着量は、特に限定はされない。例えば、より確実に耐食性を確保しつつ、化成皮膜の密着性等を向上させる観点から、前記化成皮膜の付着量を0.025～0.5g／m2とすることが好ましい。前記化成皮膜の付着量を0.025g／m2以上とすることで、より確実に耐食性を確保でき、前記化成皮膜の付着量を0.5g／m2以下とすることで、化成皮膜の剥離を抑えることができる。
　前記化成皮膜付着量は、皮膜を蛍光Ｘ 線分析して予め皮膜中の含有量が分かっている元素の存在量を測定する方法のような、既存の手法から適切に選択した方法で求めればよい。 The coating weight of the chemical conversion coating is not particularly limited. For example, from the viewpoint of improving the adhesion of the chemical conversion coating while more reliably ensuring corrosion resistance, it is preferable to set the coating weight of the chemical conversion coating to 0.025 to 0.5 g/m2. By setting the coating weight of the chemical conversion coating to 0.025 g/ m2 or more, corrosion resistance can be more reliably ensured, and by setting the coating weight of the chemical conversion coating to 0.5 g/ m2 or less , peeling of the chemical conversion coating can be suppressed.
The coating weight of the chemical conversion coating may be determined by a method appropriately selected from existing techniques, such as a method of subjecting the coating to fluorescent X-ray analysis to measure the amount of an element present in the coating whose content is known in advance.

　なお、前記化成皮膜を形成するための方法は、特に限定はされず、要求される性能や、製造設備等に応じて適宜選択することができる。例えば、前記めっき皮膜上に、化成処理液をロールコーター等により連続的に塗布し、その後、熱風や誘導加熱等を用いて、60～200℃程度の到達板温（Peak Metal Temperature：PMT）で乾燥させることで形成することができる。前記化成処理液の塗布には、ロールコーター以外にも、エアレススプレー、静電スプレー、カーテンフローコーター等の公知の手法を適宜採用することができる。さらに、前記化成皮膜は、前記樹脂及び前記金属化合物を含むものであれば、単層膜又は複層膜のいずれであってもよく、特に限定されるものではない。 The method for forming the chemical conversion coating is not particularly limited, and can be appropriately selected depending on the required performance, manufacturing equipment, etc. For example, the chemical conversion coating can be formed by continuously applying a chemical conversion treatment liquid onto the plating film using a roll coater or the like, and then drying at a peak metal temperature (PMT) of about 60 to 200°C using hot air or induction heating. In addition to roll coaters, known methods such as airless spray, electrostatic spray, and curtain flow coater can be appropriately used to apply the chemical conversion treatment liquid. Furthermore, the chemical conversion coating can be either a single-layer film or a multi-layer film as long as it contains the resin and the metal compound, and is not particularly limited.

・塗膜
　本発明の塗装鋼板は、上述したように、めっき皮膜上に、直接又は化成皮膜を介して、塗膜が形成されており、該塗膜は、プライマー塗膜を少なくとも有する。 Coating Film As described above, the coated steel sheet of the present invention has a coating film formed directly or via a chemical conversion film on the plating film, and the coating film has at least a primer coating film.

　そして、本発明は、前記プライマー塗膜が、ウレタン結合を有するポリエステル樹脂と、バナジウム化合物、リン酸化合物及び酸化マグネシウムを含む無機化合物と、を含有する。
　前記プライマー塗膜が、前記ウレタン結合を有するポリエステル樹脂と前記無機化合物を含有することによって、塗膜の密着性を高めつつ、耐食性を向上させることができる。 In the present invention, the primer coating film contains a polyester resin having a urethane bond, and an inorganic compound including a vanadium compound, a phosphate compound, and magnesium oxide.
The primer coating film contains the polyester resin having a urethane bond and the inorganic compound, and therefore the adhesion of the coating film can be increased and the corrosion resistance can be improved.

　前記プライマー塗膜は、主成分として、ウレタン結合を有するポリエステル樹脂を含有する。前記ウレタン結合を有するポリエステル樹脂は、可撓性と強度を兼ね備えているため、加工を受けた際にプライマー塗膜にクラックが発生しにくい等の効果が得られ、ウレタン樹脂を含有する化成処理皮膜との親和性が高いことから、特に加工部の耐食性向上に寄与することができる。
　なお、ここでいう「主成分」とは、プライマー塗膜中の各成分中最も含有量が多い成分であることを意味する。 The primer coating contains a polyester resin having a urethane bond as a main component. The polyester resin having a urethane bond is flexible and strong, so that the primer coating is less likely to crack when processed, and has a high affinity with the chemical conversion coating containing a urethane resin, so that the primer coating can particularly contribute to improving the corrosion resistance of the processed part.
The term "main component" used herein means the component that is contained in the greatest amount among all the components in the primer coating film.

　前記ウレタン結合を有するポリエステル樹脂としては、ポリエステルポリオールと、イソシアネート基を２個以上もつ、ジイソシアネート又はポリイソシアネートとの反応によって得られる樹脂等、公知の樹脂を使用できる。また、前記ポリエステルポリオールと、前記ジイソシアネート又は前記ポリイソシアネートとを水酸基過剰な状態で反応させた樹脂（ウレタン変性ポリエステル樹脂）を、ブロック化ポリイソシアネートで硬化させた樹脂も使用できる。 As the polyester resin having urethane bonds, known resins can be used, such as resins obtained by reacting polyester polyol with diisocyanate or polyisocyanate having two or more isocyanate groups. In addition, resins obtained by reacting the polyester polyol with the diisocyanate or polyisocyanate in a state of excess hydroxyl groups (urethane-modified polyester resin) with blocked polyisocyanate can also be used.

　なお、前記ポリエステルポリオールは、多価アルコール成分と多塩基酸成分との脱水縮合反応を利用した、公知の方法により得ることができる。
　前記多価アルコールとしては、グリコール及び３価以上の多価アルコールが挙げられる。前記グリコールは、例えば、エチレングリコール、プロピレングリコール、ジエチレングリコール、トリエチレングリコール、テトラエチレングリコール、ジプロピレングリコール、ポリエチレングリコール、ポリプロピレングリコール、ネオペンチルグリコール、ヘキシレングリコール、１，３－ブタンジオール、１，４－ブタンジオール、１，５－ペンタンジオール、１，６－ヘキサンジオール、２－ブチル－２－エチル－１，３－プロパンジオール、メチルプロパンジオール、シクロヘキサンジメタノール、３，３－ジエチル－１，５－ペンタンジオール等が挙げられる。また、前記３価以上の多価アルコールは、例えば、グリセリン、トリメチロールエタン、トリメチロールプロパン、ペンタエリスリトール、ジペンタエリスリトール等が挙げられる。これらの多価アルコールは、単独で使用することもでき、２種以上組み合わせて使用することもできる。
　前記多塩基酸は、通常は多価カルボン酸が使用されるが、必要に応じて１価の脂肪酸などを併用することができる。前記多価カルボン酸として、例えば、フタル酸、テトラヒドロフタル酸、ヘキサヒドロフタル酸、４－メチルヘキサヒドロフタル酸、ビシクロ［２，２，１］ヘプタン－２，３－ジカルボン酸、トリメリット酸、アジピン酸、セバシン酸、コハク酸、アゼライン酸、フマル酸、マレイン酸、イタコン酸、ピロメリット酸、ダイマー酸など、及びこれらの酸無水物、並びに１，４－シクロヘキサンジカルボン酸、イソフタル酸、テトラヒドロイソフタル酸、ヘキサヒドロイソフタル酸、ヘキサヒドロテレフタル酸等が挙げられる。これらの多塩基酸は、単独で使用することもでき、２種以上組み合わせて使用することもできる。 The polyester polyol can be obtained by a known method utilizing a dehydration condensation reaction between a polyhydric alcohol component and a polybasic acid component.
Examples of the polyhydric alcohol include glycols and trihydric or higher polyhydric alcohols. Examples of the glycols include ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, neopentyl glycol, hexylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2-butyl-2-ethyl-1,3-propanediol, methylpropanediol, cyclohexanedimethanol, and 3,3-diethyl-1,5-pentanediol. Examples of the trihydric or higher polyhydric alcohols include glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, and dipentaerythritol. These polyhydric alcohols can be used alone or in combination of two or more.
As the polybasic acid, a polyvalent carboxylic acid is usually used, but a monovalent fatty acid or the like can be used in combination as necessary. Examples of the polybasic acid include phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, 4-methylhexahydrophthalic acid, bicyclo[2,2,1]heptane-2,3-dicarboxylic acid, trimellitic acid, adipic acid, sebacic acid, succinic acid, azelaic acid, fumaric acid, maleic acid, itaconic acid, pyromellitic acid, dimer acid, and the like, and acid anhydrides thereof, as well as 1,4-cyclohexanedicarboxylic acid, isophthalic acid, tetrahydroisophthalic acid, hexahydroisophthalic acid, hexahydroterephthalic acid, and the like. These polybasic acids can be used alone or in combination of two or more.

　前記ポリイソシアネートについては、例えば、ヘキサメチレンジイソシアネート、トリメチルヘキサメチレンジイソシアネート、ダイマー酸ジイソシアネートなどの脂肪族ジイソシアネート、そして、キシリレンジイソシアネート（ＸＤＩ)、メタキシリレンジイソシアネート、トリレンジイソシアネート（ＴＤＩ)、４，４－ジフェニルメタンジイソシアネート（ＭＤＩ)などの芳香族ジイソシアネート、さらに、イソホロンジイソシアネート、水素化ＸＤＩ、水素化ＴＤＩ、水素化ＭＤＩなどの環状脂肪族ジイソシアネート、及びこれらのアダクト体、ビウレット体、イソシアヌレート体等が挙げられる。これらのポリイソシアネートは、単独で使用することもでき、２種以上組み合わせて使用することもできる。 The polyisocyanates include, for example, aliphatic diisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and dimer acid diisocyanate; aromatic diisocyanates such as xylylene diisocyanate (XDI), metaxylylene diisocyanate, tolylene diisocyanate (TDI), and 4,4-diphenylmethane diisocyanate (MDI); and cyclic aliphatic diisocyanates such as isophorone diisocyanate, hydrogenated XDI, hydrogenated TDI, and hydrogenated MDI, as well as adducts, biurets, and isocyanurates thereof. These polyisocyanates can be used alone or in combination of two or more.

　また、前記ウレタン結合を有するポリエステル樹脂の水酸基価は、特に限定はされないが、耐溶剤性、加工性等の観点から、好ましくは5～120mgKOH／gであり、より好ましくは、7～100 mgKOH／gであり、さらに好ましくは10～80 mgKOH／gである。
　さらに、前記ウレタン結合を有するポリエステル樹脂の数平均分子量は、耐溶剤性、加工性などの点から、好ましくは500～15,000であり、より好ましくは、700～12,000であり、さらに好ましくは800～10,000である。 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, and even more preferably 10 to 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 even more preferably 800 to 10,000, from the viewpoints of solvent resistance, processability, and the like.

　前記プライマー塗膜における、前記ウレタン結合を有するポリエステル樹脂の含有量は40～88質量％であることが好ましい。前記ウレタン結合を有するポリエステル樹脂の含有量が40質量％未満では、プライマー塗膜としてのバインダー機能が低下するおそれがあり、一方、前記ウレタン結合を有するポリエステル樹脂の含有量が88質量％を超えると、下記に示す無機物による機能、例えばインヒビター作用が低下するおそれがある。 The content of the polyester resin having urethane bonds in the primer coating is preferably 40 to 88% by mass. If the content of the polyester resin having urethane bonds is less than 40% by mass, the binder function of the primer coating may be reduced, while if the content of the polyester resin having urethane bonds exceeds 88% by mass, the functions of the inorganic substances described below, such as the inhibitor effect, may be reduced.

　前記無機化合物の１つであるバナジウム化合物は、インヒビターとして作用する。前記バナジウム化合物としては、例えば、五酸化バナジウム、メタバナジン酸、メタバナジン酸アンモニウム、オキシ三塩化バナジウム、三酸化バナジウム、二酸化バナジウム、バナジン酸マグネシウム、バナジルアセチルアセトネート、バナジウムアセチルアセトネート等が挙げられる。特に、これらの中でも、４価のバナジウム化合物又は還元若しくは酸化することによって得られる４価のバナジウム化合物を用いることが望ましい。
　前記プライマー塗膜中に添加するバナジウム化合物は、前記化成処理皮膜に添加するバナジウム化合物と同種であっても異種であってもよい。バナジン酸化合物は、外部から侵入してくる水分に徐々に溶出するバナジン酸イオンと亜鉛系めっき鋼板表面のイオンが反応し、密着性の良い不働態皮膜を形成し、金属露出部を保護し防錆作用が現れると考えられている。 Vanadium compounds, which are one of the inorganic compounds, act as inhibitors. Examples of the vanadium compounds include vanadium pentoxide, metavanadic acid, ammonium metavanadate, vanadium oxytrichloride, vanadium trioxide, vanadium dioxide, magnesium vanadate, vanadyl acetylacetonate, vanadium acetylacetonate, etc. In particular, among these, it is desirable to use a tetravalent vanadium compound or a tetravalent vanadium compound obtained by reduction or oxidation.
The vanadium compound added to the primer coating may be the same or different from the vanadium compound added to the chemical conversion coating. It is believed that vanadate ions, which are gradually dissolved by moisture entering from the outside, react with ions on the surface of the zinc-based plated steel sheet to form a passive film with good adhesion, protecting the exposed metal parts and exerting a rust-preventing effect.

　前記プライマー塗膜中の前記バナジウム化合物の含有量は、特に限定はされないが、耐食性と耐湿性との両立の観点から、4～20質量％であることが好ましい。前記バナジウム化合物の含有量が4量％未満ではインヒビター効果が低下して耐食性の低下を招くおそれがあり、前記バナジウム化合物の含有量が20質量％を超えるとプライマー塗膜の耐湿性の低下を招くおそれがある。 The content of the vanadium compound in the primer coating is not particularly limited, but is preferably 4 to 20 mass% from the viewpoint of achieving both corrosion resistance and moisture resistance. If the content of the vanadium compound is less than 4 mass%, the inhibitor effect may decrease, leading to a decrease in corrosion resistance, and if the content of the vanadium compound is more than 20 mass%, the moisture resistance of the primer coating may decrease.

　前記無機化合物の１つであるリン酸化合物についても、インヒビターとして作用する。前記リン酸化合物としては、例えばリン酸、リン酸のアンモニウム塩、リン酸のアルカリ金属塩、リン酸のアルカリ土類金属塩などが使用できる。特に、リン酸カルシウムなど、リン酸のアルカリ金属塩を好適に使用できる。 Phosphate compounds, which are one of the inorganic compounds, also act as inhibitors. Examples of the phosphate compounds that can be used include phosphoric acid, ammonium salts of phosphoric acid, alkali metal salts of phosphoric acid, and alkaline earth metal salts of phosphoric acid. In particular, alkali metal salts of phosphoric acid, such as calcium phosphate, can be preferably used.

　前記プライマー塗膜中の前記リン酸化合物の含有量は、特に限定はされないが、耐食性と耐湿性との両立の観点から、4～20質量％であることが好ましい。前記リン酸化合物の含有量が4質量％未満ではインヒビター効果が低下して耐食性の低下を招くおそれがあり、前記リン酸化合物の含有量が20質量％を超えるとプライマー塗膜の耐湿性の低下を招くおそれがある。 The content of the phosphate compound in the primer coating is not particularly limited, but is preferably 4 to 20% by mass from the viewpoint of achieving both corrosion resistance and moisture resistance. If the content of the phosphate compound is less than 4% by mass, the inhibitor effect may decrease, leading to a decrease in corrosion resistance, and if the content of the phosphate compound is more than 20% by mass, the moisture resistance of the primer coating may decrease.

　前記無機化合物の１つである酸化マグネシウムは、初期の腐食によってMgを含有する生成物を生成し、難溶性のマグネシウム塩として、安定化を図り、耐食性を向上させる効果がある。 Magnesium oxide, one of the inorganic compounds, produces products containing Mg during initial corrosion, and as a poorly soluble magnesium salt, it has the effect of stabilizing the material and improving corrosion resistance.

　前記プライマー塗膜中の前記酸化マグネシウムの含有量は、特に限定はされないが、耐食性と加工部耐食性との両立の観点から、4～20質量％であることが好ましい。前記酸化マグネシウムの含有量が4質量％未満では、上記効果が低下して耐食性の低下を招くおそれがあり、前記酸化マグネシウムの含有量が20質量％を超えると、前記プライマー塗膜の可撓性が低下することにより加工部の耐食性が低下することがある。 The content of the magnesium oxide in the primer coating is not particularly limited, but is preferably 4 to 20% by mass from the viewpoint of achieving both corrosion resistance and corrosion resistance of the processed part. If the content of the magnesium oxide is less than 4% by mass, the above effect may decrease, leading to a decrease in corrosion resistance, and if the content of the magnesium oxide is more than 20% by mass, the flexibility of the primer coating may decrease, leading to a decrease in the corrosion resistance of the processed part.

　また、前記プライマー塗膜は、上述したウレタン結合を有するポリエステル樹脂及び無機化合物以外の成分を含有することもできる。
　例えば、プライマー塗膜を形成する際に用いられる架橋剤が挙げられる。前記架橋剤は、前記ウレタン結合を有するポリエステル樹脂と反応して架橋塗膜を形成するものであり、例えば、オキサゾリン化合物、エポキシ化合物、メラミン化合物、イソシアネート系化合物、カルボジイミド系化合物、シランカップリング化合物等が挙げられ、２種類以上の架橋剤を併用することも可能である。なかでも得られる塗装鋼板の加工部耐食性の観点から、好ましくはブロック化ポリイソシアネート化合物等を用いることができる。該ブロック化ポリイソシアネートとしては、例えば、ポリイソシアネート化合物のイソシアネート基を、例えば、ブタノールなどのアルコール類、メチルエチルケトオキシムなどのオキシム類、ε－カプロラクタム類などのラクタム類、アセト酢酸ジエステルなどのジケトン類、イミダゾール、２－エチルイミダゾールなどのイミダゾール類、又は、ｍ－クレゾールなどのフェノール類などによりブロックしたものが挙げられる。 The primer coating film may also contain components other than the above-mentioned polyester resin having a urethane bond and inorganic compound.
For example, a crosslinking agent used in forming a primer coating film can be mentioned. The crosslinking agent reacts with the polyester resin having the urethane bond to form a crosslinked coating film, and examples thereof include oxazoline compounds, epoxy compounds, melamine compounds, isocyanate compounds, carbodiimide compounds, silane coupling compounds, etc., and it is also possible to use two or more types of crosslinking agents in combination. Among them, from the viewpoint of corrosion resistance of the processed part of the obtained coated steel plate, blocked polyisocyanate compounds and the like can be preferably used. Examples of the blocked polyisocyanate include those in which the isocyanate group of a polyisocyanate compound is blocked with, for example, alcohols such as butanol, oximes such as methyl ethyl ketoxime, lactams such as ε-caprolactams, diketones such as acetoacetic acid diester, imidazoles such as imidazole and 2-ethylimidazole, or phenols such as m-cresol.

　さらに、前記プライマー塗膜は、必要に応じて、塗料分野で通常使用されている公知の各種成分を含有させることもできる。具体的には、例えば、レベリング剤、消泡剤などの各種表面調整剤、分散剤、沈降防止剤、紫外線吸収剤、光安定剤、シランカップリング剤、チタネートカップリング剤などの各種添加剤、着色顔料、体質顔料などの各種顔料、光輝材、硬化触媒、有機溶剤などが挙げられる。 Furthermore, the primer coating film may contain various known components commonly used in the paint industry, if necessary. Specific examples include various surface conditioners such as leveling agents and defoamers, various additives such as dispersants, anti-settling agents, UV absorbers, light stabilizers, silane coupling agents, and titanate coupling agents, various pigments such as color pigments and extender pigments, luster materials, curing catalysts, and organic solvents.

　前記プライマー塗膜の厚さは、1.5μm以上であることが好ましい。前記プライマー塗膜の厚さを1.5μm以上とすることで、耐食性の向上効果や、化成処理皮膜やプライマー塗膜の上に形成される上塗塗膜との密着性向上効果をより確実に得ることができるからである。 The thickness of the primer coating is preferably 1.5 μm or more. By making the thickness of the primer coating 1.5 μm or more, it is possible to more reliably obtain the effect of improving corrosion resistance and the effect of improving adhesion with the chemical conversion coating and the topcoat coating formed on the primer coating.

　前記プライマー塗膜を形成するための方法については、特に限定はされない。また、前記プライマー塗膜を構成する塗料組成物の塗装方法については、好ましくは塗料組成物をロールコーター塗装、カーテンフロー塗装等の方法で塗布することができる。前記塗料組成物を塗装後、熱風加熱、赤外線加熱、誘導加熱などの加熱手段により焼き付け、プライマー塗膜を得ることができる。前記焼付処理は、通常、最高到達板温を180～270℃程度とし、この温度範囲で約30秒～3分行うことができる。 The method for forming the primer coating is not particularly limited. In addition, the coating composition constituting the primer coating can be preferably applied by a method such as roll coater coating or curtain flow coating. After the coating composition is applied, the primer coating can be obtained by baking using a heating means such as hot air heating, infrared heating, or induction heating. The baking process is usually performed at a maximum plate temperature of about 180 to 270°C for about 30 seconds to 3 minutes in this temperature range.

　また、本発明の塗装鋼板を構成する塗膜については、前記プライマー塗膜上に、さらに上塗塗膜が形成されていることが好ましい。
　前記上塗塗膜は、塗装鋼板に色彩や光沢、表面状態等の美観を付与することができることに加え、加工性、耐候性、耐薬品性、耐汚染性、耐水性、耐食性等の各種性能を高めることができる。 In addition, with regard to the coating film constituting the coated steel plate of the present invention, it is preferable that a top coating film is further formed on the primer coating film.
The topcoat coating film can impart beauty to the coated steel sheet, such as color, gloss, and surface condition, and can also improve various performance properties, such as processability, weather resistance, chemical resistance, stain resistance, water resistance, and corrosion resistance.

　前記上塗塗膜の構成については、特に限定はされず、要求される性能に応じて材料や厚さ等を適宜選択することができる。
　例えば、前記上塗塗膜を、ポリエステル樹脂系塗料、シリコンポリエステル樹脂系塗料、ポリウレタン樹脂系塗料、アクリル樹脂系塗料、フッ素樹脂系塗料等を用いて形成することができる。
　さらに、前記上塗塗膜は、酸化チタン、弁柄、マイカ、カーボンブラック又はその他の各種着色顔料；アルミニウム粉やマイカなどのメタリック顔料；炭酸塩や硫酸塩等からなる体質顔料；シリカ微粒子、ナイロン樹脂ビーズ、アクリル樹脂ビーズ等の各種微粒子；ｐ－トルエンスルホン酸、ジブチル錫ジラウレート等の硬化触媒；ワックス；その他の添加剤を適量含有することができる。 The configuration of the topcoat coating is not particularly limited, and the material, thickness, etc. can be appropriately selected depending on the required performance.
For example, the topcoat film can be formed using a polyester resin paint, a silicon polyester resin paint, a polyurethane resin paint, an acrylic resin paint, a fluororesin paint, or the like.
Furthermore, the topcoat coating film may contain appropriate amounts of titanium oxide, red iron oxide, mica, carbon black or other various coloring pigments; metallic pigments such as aluminum powder and mica; extender pigments consisting of carbonates, sulfates, etc.; various fine particles such as silica fine particles, nylon resin beads, acrylic resin beads, etc.; curing catalysts such as p-toluenesulfonic acid and dibutyltin dilaurate; wax; and other additives.

　また、前記上塗塗膜の厚さは、外観性及び加工性の両立の観点からは、5～30μｍであることが好ましい。前記上塗塗膜の厚さが5μｍ以上の場合には、色調外観をより確実に安定させることが可能となり、前記上塗塗膜の厚さが30μｍ以下の場合には、加工性の低下（上塗塗膜のクラック発生）をより確実に抑制できる。 In addition, from the viewpoint of achieving both good appearance and workability, it is preferable that the thickness of the topcoat film is 5 to 30 μm. If the thickness of the topcoat film is 5 μm or more, it is possible to more reliably stabilize the color appearance, and if the thickness of the topcoat film is 30 μm or less, it is possible to more reliably prevent a decrease in workability (the occurrence of cracks in the topcoat film).

　前記上塗塗膜を形成するための塗料組成物の塗装方法は特に限定はされない。例えば、前記塗料組成物を、ロールコーター塗装、カーテンフロー塗装などの方法で塗布することができる。前記塗料組成物を塗装後、熱風加熱、赤外線加熱、誘導加熱などの加熱手段により焼き付け、上塗塗膜を形成できる。前記焼付処理は、通常、最高到達板温を180～270℃程度とし、この温度範囲で約30秒～3分行うことができる。 The method of applying the coating composition to form the topcoat film is not particularly limited. For example, the coating composition can be applied by a method such as roll coater coating or curtain flow coating. After the coating composition is applied, the topcoat film can be formed by baking using a heating means such as hot air heating, infrared heating or induction heating. The baking process is usually performed at a maximum plate temperature of about 180 to 270°C for about 30 seconds to 3 minutes in this temperature range.

　そして、本発明の塗装鋼板は、上述した本発明の溶融Al-Zn-Si-Mg系めっき鋼板表面と同様に、鋼板表面（塗膜表面）の鋼板両端から50mmを除いた範囲において、長さ1mmあたりの前記鋼板表面の高低差が10μm以下であることを特徴とする。
　前記塗膜表面の高低差が10μm以下である場合には、しわ状欠陥がなく、優れた表面外観を得ることができる。
　前記しわ状欠陥とは、上述したように、Mg系酸化物に起因して前記塗膜表面の表面がしわ状の凹凸形状になった欠陥であり、前記塗膜表面に白色の筋模様として現れるため、しわ状欠陥の抑制とは、前記筋模様が視認されないことである。そのため、前記鋼板表面、つまり塗膜表面の長さ1mmの範囲における高低差を10μm以内に抑えることで、筋模様として視認されず、優れた表面外観を得ることができる。同様の観点から、前記鋼板表面の長さ1mmの範囲における高低差は、5μm以内であることが好ましい。
　なお、前記鋼板表面とは、鋼板の最表面のことであり、塗装鋼板の場合には、塗膜表面のことをいう。 The coated steel sheet of the present invention is characterized in that, like the surface of the hot-dip Al-Zn-Si-Mg-plated steel sheet of the present invention described above, the height difference of the steel sheet surface (coating surface) per mm length is 10 μm or less in an area excluding 50 mm from both ends of the steel sheet.
When the height difference of the coating film surface is 10 μm or less, there are no wrinkle-like defects and an excellent surface appearance can be obtained.
As described above, the wrinkle defects are defects in which the surface of the coating film is wrinkled and uneven due to Mg-based oxides, and appear as white streaks on the surface of the coating film. Therefore, suppressing the wrinkle defects means that the streaks are not visible. Therefore, by suppressing the height difference within a 1 mm long range of the steel sheet surface, i.e., the coating film surface, to within 10 μm, the streaks are not visible, and an excellent surface appearance can be obtained. From the same viewpoint, it is preferable that the height difference within a 1 mm long range of the steel sheet surface is within 5 μm.
The steel sheet surface means the outermost surface of the steel sheet, and in the case of a coated steel sheet, means the surface of the coating film.

　ここで、前記鋼板表面の高低差とは、下地鋼板の表面と垂直方向（めっきの膜厚方向）を高さとした場合に、鋼板上（塗膜上）の最も高い点の高さと最も低い点の高さの差のことである。
　また、前記塗膜表面の長さ1mmの範囲における高低差を得る手法については、上述しためっき皮膜表面の場合と同様に、レーザー顕微鏡を用いて、塗装鋼板の任意の100箇所の1mmの範囲における高低差を測定し、測定値の平均を算出することで得ることができる。 Here, the height difference on the steel sheet surface refers to the difference in height between the highest point and the lowest point on the steel sheet (on the coating film) when the height is taken in the direction perpendicular to the surface of the base steel sheet (in the direction of the coating film thickness).
The method of obtaining the height difference within a 1 mm long range of the coating surface can be similar to that of the plating film surface described above, in which the height difference within a 1 mm range at any 100 points on the coated steel sheet is measured using a laser microscope and the average of the measured values is calculated.

　また、前記鋼板表面の鋼板両端から50mmを除いた範囲において、前記鋼板表面の高低差を制御する理由としては、一般的に溶融めっき鋼板の両端では、鋼板中央に対し付着量の制御が難しく、冷却速度も異なるため、しわ状欠陥が発生し易い。加えて、このような鋼板両端は、トリミングされて使用されることが多く、表面外観については殆ど問題とならないためである。 The reason for controlling the height difference on the surface of the steel plate in the area excluding 50 mm from both ends of the steel plate is that it is generally difficult to control the amount of coating at both ends of a hot-dip galvanized steel plate compared to the center of the plate, and the cooling rate is also different, making wrinkle-like defects more likely to occur. In addition, such both ends of the plate are often trimmed before use, so the surface appearance is of little concern.

　前記鋼板表面の長さ1mmあたりの塗膜表面の高低差を10μm以下に制御する方法については、上述しためっき皮膜表面の高低差を抑えることが重要であり、前記めっき皮膜中のMgとMnの含有比率を調整したり、その他高低差を抑えるための表面処理を行うことで皮膜表面の高低差を抑えることができる。 As for the method of controlling the height difference of the coating surface to 10 μm or less per 1 mm of length of the steel plate surface, it is important to suppress the height difference of the plating film surface as described above, and the height difference of the film surface can be suppressed by adjusting the Mg and Mn content ratio in the plating film or by carrying out other surface treatments to suppress the height difference.

　本発明の塗装鋼板の製造方法は、めっき皮膜上に、直接又は化成皮膜を介して、塗膜が形成された塗装鋼板の製造方法である。
　そして、本発明の製造方法では、前記化成皮膜は、（ａ）：エステル結合を有するアニオン性ポリウレタン樹脂及び（ｂ）：ビスフェノール骨格を有するエポキシ樹脂を合計で30～50質量％含有し、該（ａ）と該（ｂ）の含有比率（（ａ）：（ｂ））が、質量比で3：97 ～60：40の範囲である樹脂成分と、2～10質量％のバナジウム化合物、40～60質量％のジルコニウム化合物及び0.5～5質量％のフッ素化合物を含む無機化合物と、を含有し、
　前記塗膜は、プライマー塗膜を少なくとも有し、該プライマー塗膜が、ウレタン結合を有するポリエステル樹脂と、バナジウム化合物、リン酸化合物及び酸化マグネシウムを含む無機化合物と、を含有し、
　前記めっき皮膜の形成は、Al：45～65質量％、Si：1.0～4.0質量％及びMg：1.0～10.0質量％を含有し、残部がZn及び不可避的不純物からなる組成を有するめっき浴中に、下地鋼板を浸漬させる溶融めっき処理工程を具える。 The method for producing a coated steel sheet of the present invention is a method for producing a coated steel sheet in which a coating film is formed directly or via a chemical conversion coating on a plating film.
In the manufacturing method of the present invention, the chemical conversion coating comprises a resin component containing 30 to 50 mass% in total of (a): an anionic polyurethane resin having an ester bond and (b): an epoxy resin having a bisphenol skeleton, the content ratio of (a) to (b) ((a):(b)) being in the range of 3:97 to 60:40 in terms of mass ratio, and an inorganic compound including 2 to 10 mass% of a vanadium compound, 40 to 60 mass% of a zirconium compound, and 0.5 to 5 mass% of a fluorine compound;
The coating film has at least a primer coating film, and the primer coating film contains a polyester resin having a urethane bond, and an inorganic compound containing a vanadium compound, a phosphoric acid compound, and magnesium oxide,
The formation of the plating film includes a hot-dip galvanizing process in which a base steel sheet is immersed in a plating bath having a composition containing 45 to 65 mass% Al, 1.0 to 4.0 mass% Si, and 1.0 to 10.0 mass% Mg, with the balance being Zn and unavoidable impurities.

　なお、前記溶融めっき処理工程の条件については、本発明の溶融Al-Zn-Si-Mg系めっき鋼板の中で説明した内容と同様である。 The conditions for the hot-dip galvanizing process are the same as those described for the hot-dip Al-Zn-Si-Mg-plated steel sheet of the present invention.

［実施例１：サンプル１～２８］
　常法で製造した板厚0.8mmの冷延鋼板を下地鋼板として用い、連続式溶融めっき設備で脱脂処理、焼鈍処理及びめっき処理を行うことで、表１に示す条件の溶融Al-Zn-Si-Mg系めっき鋼板のサンプル１～２８を作製した。
　なお、溶融Al-Zn-Si-Mg系めっき鋼板の製造に用いためっき浴の組成については、表１に示す各サンプルのめっき皮膜の組成となるように、めっき浴の組成をAl：45～65質量％、Si：1.5～2.5質量％、Mg：1.0～4.5質量％、Mn：0.00～1.0質量％、Sr：0.00～1.0質量％、Ｂ：0.00～0.05質量％、Ca：0.00～1.0質量％、Cr：0.00～0.2質量％、Ti：0.00～0.2質量％、V：0.00～0.2質量％の範囲で種々変化させた。また、めっき浴の浴温は、Al：45～55質量％の場合は590℃、Al：65質量％の場合は630℃とし、下地鋼板のめっき浸入板温がめっき浴温と同温度となるように制御した。さらに、板温が520～500℃の温度域に3秒で冷却する条件でめっき処理を実施した。
　また、めっき皮膜の付着量は、サンプル１～２３及びサンプル２７～２８では、片面あたり85±5g/m2、サンプル２４～２６では、片面あたり50～125g/m2となるように制御した。 [Example 1: Samples 1 to 28]
A cold-rolled steel sheet having a thickness of 0.8 mm produced by a conventional method was used as a base steel sheet, and degreasing treatment, annealing treatment and plating treatment were performed in a continuous hot-dip plating equipment to produce samples 1 to 28 of hot-dip Al-Zn-Si-Mg-plated steel sheets under the conditions shown in Table 1.
The composition of the coating bath used in the production of the hot-dip Al-Zn-Si-Mg-plated steel sheets was varied in the ranges of Al: 45-65 mass%, Si: 1.5-2.5 mass%, Mg: 1.0-4.5 mass%, Mn: 0.00-1.0 mass%, Sr: 0.00-1.0 mass%, B: 0.00-0.05 mass%, Ca: 0.00-1.0 mass%, Cr: 0.00-0.2 mass%, Ti: 0.00-0.2 mass%, and V: 0.00-0.2 mass%, so as to obtain the composition of the coating film of each sample shown in Table 1. The bath temperature of the coating bath was 590°C for Al: 45-55 mass%, and 630°C for Al: 65 mass%, and was controlled so that the temperature of the substrate steel sheet entering the coating was the same as the coating bath temperature. Furthermore, the plating process was carried out under conditions where the sheet temperature was cooled to a temperature range of 520 to 500°C in 3 seconds.
The plating film weight was controlled to be 85±5 g/m 2 per side for Samples 1-23 and Samples 27-28, and 50-125 g/m 2 per side for Samples 24-26.

＜評価＞
　上記のように得られた溶融Al-Zn-Si-Mg系めっき鋼板の各サンプルについて、以下の評価を行った。評価結果を表１に示す。
（１）めっき皮膜の構成（付着量、組成、Ｘ線回折強度）
　めっき後の各サンプルについて、100ｍｍφを打ち抜き、非測定面をテープでシーリングした後、JIS H 0401：2013に示される塩酸とヘキサメチレンテトラミンの混合液でめっきを溶解剥離し、剥離前後のサンプルの質量差から、めっき皮膜の付着量を算出した。算出の結果、得られためっき皮膜の付着量を表１に示す。
　その後、剥離液をろ過し、ろ液と固形分をそれぞれ分析した。具体的に、ろ液をICP発光分光分析することで、不溶Si以外の成分を定量化した。
　また、固形分は650℃の加熱炉内で乾燥・灰化した後、炭酸ナトリウムと四ホウ酸ナトリウムを添加することで融解させた。さらに、塩酸で融解物を溶解し、溶解液をICP発光分光分析することで、不溶Siを定量化した。めっき皮膜中のSi濃度は、ろ液分析によって得た可溶Si濃度に、固形分分析によって得た不溶Si濃度を加算したものである。算出の結果、得られためっき皮膜の組成を表１に示す。
　さらに、各サンプルについて、100mm×100mmのサイズに剪断後、評価対象面のめっき皮膜を下地鋼板が現れるまで機械的に削り出し、得られた粉末をよく混ぜ合わせた後、0.3gを取出し、Ｘ線回折線装置（株式会社リガク製「SmartLab」）を用いて、使用Ｘ線：Cu-Kα（波長＝1.54178Å）、Kβ線の除去：Niフィルター、管電圧：40kV、管電流：30mA、スキャニング・スピード：4°/min、サンプリング・インターバル：0.020°、発散スリット：2/3°、ソーラースリット：5°、検出器：高速一次元検出器（D/teX Ultra）の条件で、上記粉末の定性分析を行った。各ピーク強度からベース強度を差し引いた強度を各回折強度（cps）とし、Mg2Siの(111)面（面間隔d＝0.3668nm）の回折強度及びSiの(111)面（面間隔d＝0.3135nm）の回折強度を測定した。 <Evaluation>
The following evaluations were carried out on each sample of the hot-dip Al-Zn-Si-Mg-plated steel sheet obtained as described above. The evaluation results are shown in Table 1.
(1) Structure of plating film (amount of coating, composition, X-ray diffraction intensity)
After plating, a 100 mm diameter cut was made from each sample, the non-measurement surface was sealed with tape, and the plating was dissolved and removed using a mixture of hydrochloric acid and hexamethylenetetramine as specified in JIS H 0401: 2013. The adhesion weight of the plating film was calculated from the difference in mass of the sample before and after removal. The calculated adhesion weights of the plating film obtained are shown in Table 1.
The stripper solution was then filtered, and the filtrate and solid content were analyzed. Specifically, the filtrate was analyzed by ICP atomic emission spectroscopy to quantify the components other than insoluble Si.
The solids were dried and incinerated in a 650°C heating furnace, and then melted by adding sodium carbonate and sodium tetraborate. The molten material was dissolved in hydrochloric acid, and the solution was analyzed by ICP emission spectroscopy to quantify the insoluble silicon. The silicon concentration in the plating film was calculated by adding the soluble silicon concentration obtained by filtrate analysis to the insoluble silicon concentration obtained by solid content analysis. The composition of the plating film obtained as a result of the calculation is shown in Table 1.
Furthermore, after each sample was sheared to a size of 100 mm x 100 mm, the plating film on the surface to be evaluated was mechanically scraped off until the base steel sheet was revealed, and the resulting powder was thoroughly mixed, after which 0.3 g was taken out and a qualitative analysis of the above powder was performed using an X-ray diffraction apparatus (Rigaku Corporation, "SmartLab") under the following conditions: X-ray used: Cu-Kα (wavelength = 1.54178 Å), Kβ ray removal: Ni filter, tube voltage: 40 kV, tube current: 30 mA, scanning speed: 4°/min, sampling interval: 0.020°, divergence slit: 2/3°, solar slit: 5°, detector: high-speed one-dimensional detector (D/teX Ultra). The intensity (cps) obtained by subtracting the base intensity from each peak intensity was used as the diffraction intensity. The diffraction intensity of the Mg 2 Si (111) plane (plane spacing d = 0.3668 nm) and the diffraction intensity of the Si (111) plane (plane spacing d = 0.3135 nm) were measured.

（２）表面外観
（２－１）しわ状欠陥
　得られた溶融Al-Zn-Si-Mg系めっき鋼板の各サンプルについて、表面外観を目視で確認し、しわ状欠陥の発生有無を確認した。さらに、各サンプルについて、ストリップの両端から50mmを除いた部分から、任意に100ヶ所を選択し、それぞれ、レーザー顕微鏡（株式会社キーエンス製「VK-X3000」）を用いて、長さ1mmの範囲におけるめっき皮膜表面の高低差を測定し平均化した値を表面形状として定量した。しわ状欠陥の発生有無及び表面形状から、しわ状欠陥の発生状態について、以下の基準に従って評価した。
◎：しわ状欠陥の発生が認められない（高低差が5μm以下）
〇：しわ状欠陥の発生が認められない（高低差が10μm以下）
×：しわ状欠陥の発生が認められる（高低差が10μm超え） (2) Surface appearance (2-1) Wrinkle defects The surface appearance of each sample of the obtained hot-dip Al-Zn-Si-Mg-plated steel sheet was visually inspected to confirm the occurrence of wrinkle defects. Furthermore, for each sample, 100 locations were randomly selected from the area excluding 50 mm from both ends of the strip, and the height difference of the plating film surface in a 1 mm long range was measured using a laser microscope (Keyence Corporation, "VK-X3000"), and the average value was quantified as the surface shape. From the occurrence of wrinkle defects and the surface shape, the occurrence state of wrinkle defects was evaluated according to the following criteria.
◎: No wrinkle defects were observed (height difference is 5μm or less)
〇: No wrinkle defects were observed (height difference is 10μm or less)
×: Wrinkle defects are observed (height difference exceeds 10 μm)

（２－２）ドロス欠陥
　得られた溶融Al-Zn-Si-Mg系めっき鋼板の各サンプルについて、表面外観を目視で確認し、ドロス欠陥の有無について、下記の基準に従って評価した。
○：粒状ドロスの付着が認められない
×：粒状ドロスの付着が認められる (2-2) Dross Defects For each sample of the obtained hot-dip Al-Zn-Si-Mg-plated steel sheet, the surface appearance was visually inspected and the presence or absence of dross defects was evaluated according to the following criteria.
○: No adhesion of granular dross was observed. ×: Adhesion of granular dross was observed.

（３）耐食性評価
　得られた溶融Al-Zn-Si-Mg系めっき鋼板の各サンプルについて、120mm×120mmのサイズに剪断後、評価対象面の各エッジから10mmの範囲、及び、サンプルの端面と評価非対象面をテープでシーリングし、評価対象面を100mm×100mmのサイズで露出させた状態のものを、評価用サンプルとして用いた。なお、該評価用サンプルは同じものを３つ作製した。
　上記のように作製した３つの評価用サンプルに対して、いずれも日本自動車規格の複合サイクル試験（JASO-CCT）を実施した。腐食促進試験を湿潤からスタートし、300サイクル後まで行った後、各サンプルの腐食減量をJIS Z 2383及びISO8407に記載の方法で測定し、以下の基準に従って評価した。
◎：サンプル3個の腐食減量が全て45g／m2以下
○：サンプル3個の腐食減量が全て90g／m2以下
×：サンプル1個以上の腐食減量が90g／m2越え (3) Evaluation of corrosion resistance Each sample of the obtained hot-dip Al-Zn-Si-Mg-plated steel sheet was sheared to a size of 120 mm × 120 mm, and then a range of 10 mm from each edge of the surface to be evaluated, as well as the end faces and the surface not to be evaluated, were sealed with tape to expose the surface to be evaluated in a size of 100 mm × 100 mm, which was used as a sample for evaluation. Three identical samples for evaluation were prepared.
The three evaluation samples prepared as described above were all subjected to the Japanese Automotive Standard Combined Cyclic Test (JASO-CCT). The accelerated corrosion test started with wetting and continued for 300 cycles. After that, the corrosion weight loss of each sample was measured using the methods specified in JIS Z 2383 and ISO 8407, and evaluated according to the following criteria.
◎: The corrosion loss of all three samples is 45g/m2 or less . ○: The corrosion loss of all three samples is 90g/ m2 or less. ×: The corrosion loss of one or more samples is more than 90g/ m2.

Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001

　表１の結果から、本発明例の各サンプルは、比較例の各サンプルに比べて、表面外観に優れることがわかる。 The results in Table 1 show that the samples of the present invention have superior surface appearance compared to the samples of the comparative examples.

［実施例２：サンプル１～３４］
（１）常法で製造した板厚0.8mmの冷延鋼板を下地鋼板として用い、連続式溶融めっき設備で脱脂処理、焼鈍処理及びめっき処理を行うことで、表３に示す条件の溶融Al-Zn-Si-Mg系めっき鋼板のサンプル１～３４を作製した。
　なお、溶融Al-Zn-Si-Mg系めっき鋼板の製造に用いためっき浴の組成については、表３に示す各サンプルのめっき皮膜の組成となるように、めっき浴の組成をAl：45～65質量％、Si：1.5～2.5質量％、Mg：1.0～4.5質量％、Mn：0.00～1.0質量％、Sr：0.00～Sr：0.00～1.0質量％、Ｂ：0.00～0.05質量％、Ca：0.00～1.0質量％、Cr：0.00～0.2質量％、Ti：0.00～0.2質量％、V：0.00～0.2質量％の範囲で種々変化させた。また、めっき浴の浴温は、Al：45～55質量％の場合は590℃、Al：65質量％の場合は630℃とし、下地鋼板のめっき浸入板温がめっき浴温と同温度となるように制御した。さらに、板温が520～500℃の温度域に3秒で冷却する条件でめっき処理を実施した。
　また、めっき皮膜の付着量は、サンプル１～２９及びサンプル３３～３４では、片面あたり85±5g/m2、サンプル３０～３２では、片面あたり50～125g/m2となるように制御した。 [Example 2: Samples 1 to 34]
(1) A cold-rolled steel sheet having a thickness of 0.8 mm, which was produced by a conventional method, was used as a base steel sheet, and was subjected to degreasing treatment, annealing treatment and plating treatment in a continuous hot-dip plating facility to produce samples 1 to 34 of hot-dip Al-Zn-Si-Mg-plated steel sheets having the conditions shown in Table 3.
The composition of the coating bath used in the production of the hot-dip Al-Zn-Si-Mg-plated steel sheets was varied in the ranges of Al: 45-65 mass%, Si: 1.5-2.5 mass%, Mg: 1.0-4.5 mass%, Mn: 0.00-1.0 mass%, Sr: 0.00-0.00-1.0 mass%, B: 0.00-0.05 mass%, Ca: 0.00-1.0 mass%, Cr: 0.00-0.2 mass%, Ti: 0.00-0.2 mass%, and V: 0.00-0.2 mass%, so as to obtain the composition of the coating film of each sample shown in Table 3. The bath temperature of the coating bath was 590°C for Al: 45-55 mass%, and 630°C for Al: 65 mass%, and was controlled so that the temperature of the substrate steel sheet entering the coating was the same as the coating bath temperature. Furthermore, the plating process was carried out under conditions where the sheet temperature was cooled to a temperature range of 520 to 500°C in 3 seconds.
The plating film weight was controlled to be 85±5 g/m 2 per side for Samples 1-29 and Samples 33-34, and 50-125 g/m 2 per side for Samples 30-32.

（２）その後、作製した溶融Al-Zn-Si-Mg系めっき鋼板の各サンプルのめっき皮膜上に、バーコーターで化成処理液を塗布し、熱風炉で乾燥（昇温速度：60℃/s、PMT：120℃）させることで化成皮膜を形成し、表２に示す表面処理鋼板の各サンプルを作製した。
　なお、化成処理液は、各成分を溶媒としての水に溶解させた表面処理液Ａ～Ｆを調製した。表面処理液に含有する各成分（樹脂、金属化合物）の種類については、以下のとおりである。
（樹脂）
ウレタン樹脂：スーパーフレックス130、スーパーフレックス126（第一工業製薬株式会社）
アクリル樹脂：ボンコートEC-740EF（ＤＩＣ株式会社）
（金属化合物）
P化合物：トリポリリン酸二水素アルミニウム
Si化合物：シリカ
V化合物：メタバナジン酸ナトリウム
Mo化合物：モリブデン酸
Zr化合物：炭酸ジルコニルカリウム
　調製した化成処理液Ａ～Ｆの組成及び形成された化成皮膜の付着量を表１に示す。なお、本明細書の表１における各成分の濃度は、固形分の濃度（質量％）である。 (2) Thereafter, a chemical conversion coating was formed on the plating film of each sample of the prepared hot-dip Al-Zn-Si-Mg plated steel sheet using a bar coater, and the plated film was dried in a hot air oven (heating rate: 60°C/s, PMT: 120°C) to prepare each sample of the surface-treated steel sheet shown in Table 2.
The chemical conversion treatment solutions were prepared by dissolving each component in water as a solvent to prepare surface treatment solutions A to F. The types of each component (resin, metal compound) contained in the surface treatment solutions are as follows:
(resin)
Urethane resin: Superflex 130, Superflex 126 (Dai-ichi Kogyo Seiyaku Co., Ltd.)
Acrylic resin: Boncoat EC-740EF (DIC Corporation)
(Metal Compounds)
P compound: Aluminum dihydrogen tripolyphosphate
Si compound: Silica
V compound: Sodium metavanadate
Mo compound: Molybdic acid
Zr compound: potassium zirconyl carbonate The compositions of the prepared chemical conversion treatment solutions A to F and the adhesion weights of the formed chemical conversion coatings are shown in Table 1. The concentration of each component in Table 1 of this specification is the concentration (mass%) of the solid content.

Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002

＜評価＞
　上記のように得られた表面処理鋼板の各サンプルについて、以下の評価を行った。評価結果を表３に示す。
（１）めっき皮膜の構成（付着量、組成、Ｘ線回折強度）
　めっき後の各サンプルについて、100ｍｍφを打ち抜き、非測定面をテープでシーリングした後、JIS H 0401：2013に示される塩酸とヘキサメチレンテトラミンの混合液でめっきを溶解剥離し、剥離前後のサンプルの質量差から、めっき皮膜の付着量を算出した。算出の結果、得られためっき皮膜の付着量を表３に示す。
　その後、剥離液をろ過し、ろ液と固形分をそれぞれ分析した。具体的に、ろ液をICP発光分光分析することで、不溶Si以外の成分を定量化した。
　また、固形分は650℃の加熱炉内で乾燥・灰化した後、炭酸ナトリウムと四ホウ酸ナトリウムを添加することで融解させた。さらに、塩酸で融解物を溶解し、溶解液をICP発光分光分析することで、不溶Siを定量化した。めっき皮膜中のSi濃度は、ろ液分析によって得た可溶Si濃度に、固形分分析によって得た不溶Si濃度を加算したものである。算出の結果、得られためっき皮膜の組成を表３に示す。
　さらに、各サンプルについて、100mm×100mmのサイズに剪断後、評価対象面のめっき皮膜を下地鋼板が現れるまで機械的に削り出し、得られた粉末をよく混ぜ合わせた後、0.3gを取出し、Ｘ線回折線装置（株式会社リガク製「SmartLab」）を用いて、使用Ｘ線：Cu-Kα（波長＝1.54178Å）、Kβ線の除去：Niフィルター、管電圧：40kV、管電流：30mA、スキャニング・スピード：4°/min、サンプリング・インターバル：0.020°、発散スリット：2/3°、ソーラースリット：5°、検出器：高速一次元検出器（D/teX Ultra）の条件で、上記粉末の定性分析を行った。各ピーク強度からベース強度を差し引いた強度を各回折強度（cps）とし、Mg2Siの(111)面（面間隔d＝0.3668nm）の回折強度及びSiの(111)面（面間隔d＝0.3135nm）の回折強度を測定した。測定結果を、表３に示す <Evaluation>
The following evaluations were carried out on each sample of the surface-treated steel sheet obtained as described above. The evaluation results are shown in Table 3.
(1) Structure of plating film (amount of coating, composition, X-ray diffraction intensity)
A 100 mm diameter cut was made from each plated sample, the non-measurement surface was sealed with tape, and the plating was dissolved and removed using a mixture of hydrochloric acid and hexamethylenetetramine as specified in JIS H 0401: 2013. The adhesion weight of the plating film was calculated from the difference in mass of the sample before and after removal. The calculated adhesion weights of the plating film obtained are shown in Table 3.
The stripper solution was then filtered, and the filtrate and solid content were analyzed. Specifically, the filtrate was analyzed by ICP atomic emission spectroscopy to quantify the components other than insoluble Si.
The solids were dried and incinerated in a 650°C heating furnace, and then melted by adding sodium carbonate and sodium tetraborate. The molten material was dissolved in hydrochloric acid, and the solution was analyzed by ICP emission spectroscopy to quantify the insoluble silicon. The silicon concentration in the plating film was calculated by adding the soluble silicon concentration obtained by filtrate analysis to the insoluble silicon concentration obtained by solid content analysis. The composition of the plating film obtained as a result of the calculation is shown in Table 3.
Furthermore, after each sample was sheared to a size of 100 mm x 100 mm, the plating film on the surface to be evaluated was mechanically scraped off until the base steel sheet was revealed, and the resulting powder was thoroughly mixed, after which 0.3 g was taken out and a qualitative analysis of the above powder was performed using an X-ray diffraction apparatus (Rigaku Corporation, "SmartLab") under the following conditions: X-ray used: Cu-Kα (wavelength = 1.54178 Å), Kβ ray removal: Ni filter, tube voltage: 40 kV, tube current: 30 mA, scanning speed: 4°/min, sampling interval: 0.020°, divergence slit: 2/3°, solar slit: 5°, detector: high-speed one-dimensional detector (D/teX Ultra). The intensity obtained by subtracting the base intensity from each peak intensity was taken as the diffraction intensity (cps), and the diffraction intensity of the Mg2Si (111) plane (plane spacing d = 0.3668 nm) and the diffraction intensity of the Si (111) plane (plane spacing d = 0.3135 nm) were measured. The measurement results are shown in Table 3.

（２）表面外観
（２－１）しわ状欠陥
　得られた溶融Al-Zn-Si-Mg系めっき鋼板及び表面処理鋼板の各サンプルについて、表面外観を目視で確認し、しわ状欠陥の発生有無を確認した。さらに、各サンプルについて、ストリップの両端から50mmを除いた部分から、任意に100ヶ所を選択し、それぞれ、レーザー顕微鏡（株式会社キーエンス製「VK-X3000」）を用いて、長さ1mmの範囲におけるめっき皮膜表面の高低差を測定し平均化した値を表面形状として定量した。しわ状欠陥の発生有無及び表面形状から、しわ状欠陥の発生状態について、以下の基準に従って評価した。
◎：しわ状欠陥の発生が認められない（高低差が5μm以下）
〇：しわ状欠陥の発生が認められない（高低差が10μm以下）
×：しわ状欠陥の発生が認められる（高低差が10μm超え） (2) Surface appearance (2-1) Wrinkle defects The surface appearance of each sample of the obtained hot-dip Al-Zn-Si-Mg-plated steel sheet and surface-treated steel sheet was visually inspected to confirm the occurrence of wrinkle defects. Furthermore, for each sample, 100 locations were randomly selected from the portion excluding 50 mm from both ends of the strip, and the height difference of the plating film surface in a 1 mm long range was measured using a laser microscope ("VK-X3000" manufactured by Keyence Corporation), and the average value was quantified as the surface shape. From the occurrence of wrinkle defects and the surface shape, the occurrence state of wrinkle defects was evaluated according to the following criteria.
◎: No wrinkle defects were observed (height difference is 5μm or less)
〇: No wrinkle defects were observed (height difference is 10μm or less)
×: Wrinkle defects are observed (height difference exceeds 10 μm)

（２－２）ドロス欠陥
　得られた溶融Al-Zn-Si-Mg系めっき鋼板の各サンプルについて、表面外観を目視で確認し、ドロス欠陥の有無について、下記の基準に従って評価した。
○：粒状ドロスの付着が認められない
×：粒状ドロスの付着が認められる (2-2) Dross Defects For each sample of the obtained hot-dip Al-Zn-Si-Mg-plated steel sheet, the surface appearance was visually inspected and the presence or absence of dross defects was evaluated according to the following criteria.
○: No adhesion of granular dross was observed. ×: Adhesion of granular dross was observed.

（３）耐白錆性
　溶融Al-Zn-Si-Mg系めっき鋼板及び表面処理鋼板の各サンプルについて、120mm×120mmのサイズに剪断後、評価対象面の各エッジから10mmの範囲、及び、サンプルの端面と評価非対象面をテープでシーリングし、評価対象面を100mm×100mmのサイズで露出させた状態のものを、評価用サンプルとして用いた。
　上記評価用サンプルを用いて、JIS Z 2371に記載の塩水噴霧試験を90時間実施し、以下の基準に従って評価した。
◎：平板部に白錆なし
○：平板部の白錆発生面積10％未満
×：平板部の白錆発生面積10％以上 (3) White rust resistance For each sample of hot-dip Al-Zn-Si-Mg plated steel sheet and surface-treated steel sheet, which was sheared to a size of 120 mm × 120 mm, a range of 10 mm from each edge of the surface to be evaluated, as well as the end faces and non-evaluation surfaces of the sample were sealed with tape to expose the surface to be evaluated in a size of 100 mm × 100 mm, and these were used as samples for evaluation.
Using the above evaluation samples, a salt spray test according to JIS Z 2371 was carried out for 90 hours and evaluated according to the following criteria.
◎: No white rust on the flat plate ○: White rust occurs on less than 10% of the flat plate ×: White rust occurs on 10% or more of the flat plate

（４）耐食性評価
　得られた溶融Al-Zn-Si-Mg系めっき鋼板及び表面処理鋼板の各サンプルについて、120mm×120mmのサイズに剪断後、評価対象面の各エッジから10mmの範囲、及び、サンプルの端面と評価非対象面をテープでシーリングし、評価対象面を100mm×100mmのサイズで露出させた状態のものを、評価用サンプルとして用いた。なお、該評価用サンプルは同じものを３つ作製した。
　上記のように作製した３つの評価用サンプルに対して、いずれも日本自動車規格の複合サイクル試験（JASO-CCT）を実施した。腐食促進試験を湿潤からスタートし、300サイクル後まで行った後、各サンプルの腐食減量をJIS Z 2383及びISO8407に記載の方法で測定し、以下の基準に従って評価した。
◎：サンプル3個の腐食減量が全て30g／m2以下
○：サンプル3個の腐食減量が全て70g／m2以下
×：サンプル1個以上の腐食減量が70g／m2越え (4) Evaluation of corrosion resistance Each sample of the obtained hot-dip Al-Zn-Si-Mg-plated steel sheet and surface-treated steel sheet was sheared to a size of 120 mm x 120 mm, and the area of 10 mm from each edge of the surface to be evaluated, as well as the end faces and non-evaluation surfaces of the sample were sealed with tape to expose the surface to be evaluated in a size of 100 mm x 100 mm, which was used as the evaluation sample. Three identical evaluation samples were prepared.
The three evaluation samples prepared as described above were all subjected to the Japanese Automotive Standard Combined Cyclic Test (JASO-CCT). The accelerated corrosion test started with wetting and continued for 300 cycles. After that, the corrosion weight loss of each sample was measured using the methods specified in JIS Z 2383 and ISO 8407, and evaluated according to the following criteria.
◎: The corrosion loss of all three samples is 30 g/m2 or less . ○: The corrosion loss of all three samples is 70 g/m2 or less. ×: The corrosion loss of one or more samples is more than 70 g/ m2.

Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003

　表３の結果から、本発明例の各サンプルは、比較例の各サンプルに比べて、表面外観に優れることがわかる。 The results in Table 3 show that the samples of the present invention have superior surface appearance compared to the samples of the comparative examples.

［実施例３：サンプル１～３７］
（１）常法で製造した板厚0.8mmの冷延鋼板を下地鋼板として用い、連続式溶融めっき設備で脱脂処理、焼鈍処理及びめっき処理を行うことで、表５に示す条件の溶融Al-Zn-Si-Mg系めっき鋼板のサンプル１～３７を作製した。
　お、溶融Al-Zn-Si-Mg系めっき鋼板の製造に用いためっき浴の組成については、表５に示す各サンプルのめっき皮膜の組成となるように、めっき浴の組成をAl：45～65質量％、Si：1.5～2.5質量％、Mg：1.0～4.5質量％、Mn：0.00～1.0質量％、Sr：0.00～1.0質量％、Ｂ：0.00～0.05質量％、Ca：0.00～1.0質量％、Cr：0.00～0.2質量％、Ti：0.00～0.2質量％、V：0.00～0.2質量％の範囲で種々変化させた。また、めっき浴の浴温は、Al：45～55質量％の場合は590℃、Al：65質量％の場合は630℃とし、下地鋼板のめっき浸入板温がめっき浴温と同温度となるように制御した。さらに、板温が520～500℃の温度域に3秒で冷却する条件でめっき処理を実施した。
　また、めっき皮膜の付着量は、サンプル１～３２及びサンプル３６～３７では、片面あたり85±5g/m2、サンプル３３～３５では、片面あたり50～125g/m2となるように制御した。 [Example 3: Samples 1 to 37]
(1) A cold-rolled steel sheet having a thickness of 0.8 mm, which was produced by a conventional method, was used as a base steel sheet, and was subjected to degreasing treatment, annealing treatment and plating treatment in a continuous hot-dip plating facility to produce samples 1 to 37 of hot-dip Al-Zn-Si-Mg-plated steel sheets having the conditions shown in Table 5.
The composition of the coating bath used in the production of hot-dip Al-Zn-Si-Mg-plated steel sheets was varied in the ranges of Al: 45-65 mass%, Si: 1.5-2.5 mass%, Mg: 1.0-4.5 mass%, Mn: 0.00-1.0 mass%, Sr: 0.00-1.0 mass%, B: 0.00-0.05 mass%, Ca: 0.00-1.0 mass%, Cr: 0.00-0.2 mass%, Ti: 0.00-0.2 mass%, and V: 0.00-0.2 mass%, so as to obtain the composition of the coating film of each sample shown in Table 5. The bath temperature of the coating bath was 590° C. in the case of Al: 45-55 mass%, and 630° C. in the case of Al: 65 mass%, and was controlled so that the temperature of the substrate steel sheet entering the coating was the same as the coating bath temperature. Furthermore, the plating process was carried out under conditions where the sheet temperature was cooled to a temperature range of 520 to 500°C in 3 seconds.
The plating film weight was controlled to be 85±5 g/m 2 per side for Samples 1-32 and Samples 36-37, and 50-125 g/m 2 per side for Samples 33-35.

（２）その後、作製した溶融めっき鋼板の各サンプルのめっき皮膜上に、バーコーターで表４に示す化成処理液を塗布し、熱風乾燥炉で乾燥（到達板温：90℃）させることで、付着量が0.1g／m2の化成処理皮膜を形成した。
　なお、用いた化成処理液は、各成分を溶媒としての水に溶解させて調製したpHが8～10の化成処理液を用いた。化成処理液に含有する各成分（樹脂成分、無機化合物）の種類については、以下のとおりである。
（樹脂成分）
樹脂Ａ：（ａ）エステル結合を有するアニオン性ポリウレタン樹脂（第一工業製薬（株）製「スーパーフレックス210」と、（ｂ）ビスフェノール骨格を有するエポキシ樹脂（吉村油化学（株）製「ユカレジンＲＥ－１０５０」）とを、含有質量比（ａ）：（ｂ）＝50：50で混合したもの
樹脂Ｂ：アクリル樹脂（ＤＩＣ（株）製「ボンコートＥＣ－７４０ＥＦ」）
（無機化合物）
バナジウム化合物：アセチルアセトンでキレート化した有機バナジウム化合物
ジルコニウム化合物：炭酸ジルコニウムアンモニウム
フッ素化合物：フッ化アンモニウム (2) Thereafter, the chemical conversion coating film of each sample of the prepared hot-dip galvanized steel sheet was coated with the chemical conversion coating solution shown in Table 4 using a bar coater, and then dried in a hot air drying furnace (ultimate sheet temperature: 90°C) to form a chemical conversion coating film with a coating weight of 0.1 g/ m2 .
The chemical conversion treatment solution used was prepared by dissolving each component in water as a solvent, and had a pH of 8 to 10. The types of each component (resin component, inorganic compound) contained in the chemical conversion treatment solution are as follows:
(Resin Component)
Resin A: (a) an anionic polyurethane resin having an ester bond ("Superflex 210" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and (b) an epoxy resin having a bisphenol skeleton ("Yukarejin RE-1050" manufactured by Yoshimura Oil Chemical Co., Ltd.) mixed in a mass ratio of (a):(b) = 50:50. Resin B: an acrylic resin ("Boncoat EC-740EF" manufactured by DIC Corporation).
(Inorganic Compounds)
Vanadium compounds: organic vanadium compounds chelated with acetylacetone Zirconium compounds: ammonium zirconium carbonate Fluorine compounds: ammonium fluoride

（３）そして、上記の通り形成した化成皮膜上に、プライマー塗料をバーコーターで塗布し、鋼板の到達温度230℃ 、焼き付け時間35秒の条件で焼き付けを行うことで、表４に示す成分組成を有するプライマー塗膜を形成した。その後、上記の通り形成したプライマー塗膜上に、上塗り塗料組成物をバーコーターで塗布し、鋼板の到達温度230℃～260℃、焼き付け時間40秒の条件で焼き付けを行うことで、表４に示す樹脂条件及び膜厚を有する上塗り塗膜を形成し、各サンプルの塗装鋼板を作製した。
　なお、プライマー塗料については、各成分を混合した後、ボールミルで約１時間攪拌することにより得た。プライマー塗膜を構成する樹脂成分及び無機化合物は、以下のものを用いた。
（樹脂成分）
樹脂α：ウレタン変性ポリエステル樹脂（ポリエステル樹脂455質量部、イソホロンジイソシアネート45質量部を反応させて得たものであり、樹脂酸価は3、数平均分子量は5,600、水酸基価は36である。）を、ブロック化イソシアネートで硬化させたものを用いた。
　なお、ウレタン変性させるポリエステル樹脂については、次の条件で作製した。攪拌機、精留塔、水分離器、冷却管及び温度計を備えたフラスコに、イソフタル酸320質量部、アジピン酸200質量部、トリメチロールプロパン60質量部、シクロヘキサンジメタンノール420質量部を仕込み、加熱、攪拌し、生成する縮合水を系外へ留去させながら、160℃ から230℃ まで一定速度で4時間かけて昇温させ、温度230℃ に到達した後、キシレン20質量部を徐々に添加し、温度を230℃ に維持した状態で縮合反応を続け、酸価が5以下になった時に反応を終了させ、100℃まで冷却した後、ソルベッソ100（エクソンモービル社製、商品名、高沸点芳香族炭化水素系溶剤） 120質量部、ブチルセロソルブ100質量部を加えることで、ポリエステル樹脂溶液を得た。
樹脂β：ウレタン硬化ポリエステル樹脂（関西ペイント（株）製「エバクラッド4900」）
（無機化合物）
バナジウム化合物：バナジン酸マグネシウム
リン酸化合物：リン酸カルシウム
酸化マグネシウム化合物：酸化マグネシウム
　また、表４に示す上塗塗膜に用いた樹脂については、以下の塗料を用いた。
樹脂Ｉ： メラミン硬化ポリエステル塗料（ＢＡＳＦジャパン（株）製「プレカラーＨＤ００３０ＨＲ」）
樹脂ＩＩ： ポリフッ化ビニリデンとアクリル樹脂が質量比で80：20であるオルガノゾル系焼付型フッ素樹脂系塗料（ＢＡＳＦジャパン（株）製「プレカラーＮｏ.８８００ＨＲ」） (3) A primer paint was applied onto the chemical conversion coating film formed as described above using a bar coater, and baked under conditions of a steel plate temperature of 230°C and a baking time of 35 seconds, thereby forming a primer coating film having the component composition shown in Table 4. Thereafter, a topcoat paint composition was applied onto the primer coating film formed as described above using a bar coater, and baked under conditions of a steel plate temperature of 230°C to 260°C and a baking time of 40 seconds, thereby forming a topcoat coating film having the resin conditions and film thickness shown in Table 4, and each sample coated steel plate was produced.
The primer coating was obtained by mixing the components and then stirring for about 1 hour in a ball mill. The following resin components and inorganic compounds were used to form the primer coating film.
(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, having a resin acid value of 3, a number average molecular weight of 5,600, and a hydroxyl value of 36) cured with a blocked isocyanate was used.
The polyester resin to be urethane-modified was prepared under the following conditions: 320 parts by mass of isophthalic acid, 200 parts by mass of adipic acid, 60 parts by mass of trimethylolpropane, and 420 parts by mass of cyclohexanedimethanenol were charged into a flask equipped with a stirrer, a distillation column, a water separator, a cooling tube, and a thermometer, and the mixture was heated and stirred, and the temperature was raised from 160°C to 230°C at a constant rate over 4 hours while distilling off the generated condensed water outside the system. After the temperature reached 230°C, 20 parts by mass of xylene was gradually added, and the condensation reaction was continued while maintaining the temperature at 230°C. The reaction was terminated when the acid value became 5 or less, and the mixture was cooled to 100°C, and then 120 parts by mass of Solvesso 100 (trade name, high-boiling aromatic hydrocarbon solvent, manufactured by Exxon Mobil Corp.) and 100 parts by mass of butyl cellosolve were added to obtain a polyester resin solution.
Resin β: urethane-cured polyester resin ("Evaclad 4900" manufactured by Kansai Paint Co., Ltd.)
(Inorganic Compounds)
Vanadium compound: magnesium vanadate Phosphate compound: calcium phosphate Magnesium oxide compound: magnesium oxide Furthermore, for the resins used in the topcoat coatings shown in Table 4, the following paints were used.
Resin I: Melamine-cured polyester paint (BASF Japan Ltd. "Precolor HD0030HR")
Resin II: An organosol-based baking-type fluororesin-based paint having a mass ratio of polyvinylidene fluoride and acrylic resin of 80:20 (BASF Japan Ltd. "Precolor No. 8800HR")

Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000004

＜評価＞
　上記のように得られた塗装鋼板の各サンプルについて、以下の評価を行った。評価結果を表５に示す。
（１）めっき皮膜の構成（付着量、組成、Ｘ線回折強度）
　めっき後の各サンプルについて、100ｍｍφを打ち抜き、非測定面をテープでシーリングした後、JIS H 0401：2013に示される塩酸とヘキサメチレンテトラミンの混合液でめっきを溶解剥離し、剥離前後のサンプルの質量差から、めっき皮膜の付着量を算出した。算出の結果、得られためっき皮膜の付着量を表５に示す。
　その後、剥離液をろ過し、ろ液と固形分をそれぞれ分析した。具体的に、ろ液をICP発光分光分析することで、不溶Si以外の成分を定量化した。
　また、固形分は650℃の加熱炉内で乾燥・灰化した後、炭酸ナトリウムと四ホウ酸ナトリウムを添加することで融解させた。さらに、塩酸で融解物を溶解し、溶解液をICP発光分光分析することで、不溶Siを定量化した。めっき皮膜中のSi濃度は、ろ液分析によって得た可溶Si濃度に、固形分分析によって得た不溶Si濃度を加算したものである。算出の結果、得られためっき皮膜の組成を表５に示す。
　さらに、各サンプルについて、100mm×100mmのサイズに剪断後、評価対象面のめっき皮膜を下地鋼板が現れるまで機械的に削り出し、得られた粉末をよく混ぜ合わせた後、0.3gを取出し、Ｘ線回折線装置（株式会社リガク製「SmartLab」）を用いて、使用Ｘ線：Cu-Kα（波長＝1.54178Å）、Kβ線の除去：Niフィルター、管電圧：40kV、管電流：30mA、スキャニング・スピード：4°/min、サンプリング・インターバル：0.020°、発散スリット：2/3°、ソーラースリット：5°、検出器：高速一次元検出器（D/teX Ultra）の条件で、上記粉末の定性分析を行った。各ピーク強度からベース強度を差し引いた強度を各回折強度（cps）とし、Mg2Siの(111)面（面間隔d＝0.3668nm）の回折強度及びSiの(111)面（面間隔d＝0.3135nm）の回折強度を測定した。 <Evaluation>
The following evaluations were carried out on each of the coated steel sheet samples obtained as described above. The evaluation results are shown in Table 5.
(1) Structure of plating film (amount of plating, composition, X-ray diffraction intensity)
After plating, a 100 mm diameter cutout was made from each sample, and the non-measurement surface was sealed with tape. The plating was then dissolved and stripped off using a mixture of hydrochloric acid and hexamethylenetetramine as specified in JIS H 0401: 2013, and the adhesion weight of the plating film was calculated from the difference in mass of the sample before and after stripping. The calculated adhesion weights of the plating film obtained are shown in Table 5.
The stripper solution was then filtered, and the filtrate and solid content were analyzed. Specifically, the filtrate was analyzed by ICP atomic emission spectrometry to quantify the components other than insoluble Si.
The solids were dried and incinerated in a 650°C heating furnace, and then melted by adding sodium carbonate and sodium tetraborate. The molten material was dissolved in hydrochloric acid, and the solution was analyzed by ICP emission spectroscopy to quantify the insoluble silicon. The silicon concentration in the plating film was calculated by adding the soluble silicon concentration obtained by filtrate analysis to the insoluble silicon concentration obtained by solid content analysis. The composition of the plating film obtained as a result of the calculation is shown in Table 5.
Furthermore, after each sample was sheared to a size of 100 mm x 100 mm, the plating film on the surface to be evaluated was mechanically scraped off until the base steel sheet was revealed, and the resulting powder was thoroughly mixed, after which 0.3 g was taken out and a qualitative analysis of the above powder was performed using an X-ray diffraction apparatus (Rigaku Corporation, "SmartLab") under the following conditions: X-ray used: Cu-Kα (wavelength = 1.54178 Å), Kβ ray removal: Ni filter, tube voltage: 40 kV, tube current: 30 mA, scanning speed: 4°/min, sampling interval: 0.020°, divergence slit: 2/3°, solar slit: 5°, detector: high-speed one-dimensional detector (D/teX Ultra). The intensity (cps) obtained by subtracting the base intensity from each peak intensity was used as the diffraction intensity. The diffraction intensity of the Mg 2 Si (111) plane (plane spacing d = 0.3668 nm) and the diffraction intensity of the Si (111) plane (plane spacing d = 0.3135 nm) were measured.

（２）表面外観
（２－１）しわ状欠陥
　得られた塗装鋼板の各サンプルについて、表面外観を目視で確認し、しわ状欠陥の発生有無を確認した。さらに、各サンプルについて、ストリップの両端から50mmを除いた部分から、任意に100ヶ所を選択し、それぞれ、レーザー顕微鏡（株式会社キーエンス製「VK-X3000」）を用いて、長さ1mmの範囲におけるめっき皮膜表面の高低差を測定し平均化した値を表面形状として定量した。しわ状欠陥の発生有無及び表面形状から、しわ状欠陥の発生状態について、以下の基準に従って評価した。
◎：しわ状欠陥の発生が認められない（高低差が5μm以下）
〇：しわ状欠陥の発生が認められない（高低差が10μm以下）
×：しわ状欠陥の発生が認められる（高低差が10μm超え） (2) Surface appearance (2-1) Wrinkle defects The surface appearance of each sample of the obtained coated steel sheet was visually inspected to confirm the occurrence of wrinkle defects. Furthermore, for each sample, 100 locations were randomly selected from the area excluding 50 mm from both ends of the strip, and the height difference of the plating film surface in a 1 mm long range was measured using a laser microscope (Keyence Corporation, "VK-X3000"), and the average value was quantified as the surface shape. The occurrence state of wrinkle defects was evaluated according to the following criteria based on the occurrence of wrinkle defects and the surface shape.
◎: No wrinkle defects were observed (height difference is 5μm or less)
〇: No wrinkle defects were observed (height difference is 10μm or less)
×: Wrinkle defects are observed (height difference exceeds 10 μm)

（２－２）ドロス欠陥
　得られた塗装鋼板の各サンプルについて、表面外観を目視で確認し、ドロス欠陥の有無について、以下の基準に従って評価した。
○：粒状ドロスの付着が認められない
×：粒状ドロスの付着が認められる (2-2) Dross Defects The surface appearance of each of the obtained coated steel sheet samples was visually inspected, and the presence or absence of dross defects was evaluated according to the following criteria.
○: No adhesion of granular dross was observed. ×: Adhesion of granular dross was observed.

（３）耐食性評価
　得られた塗装鋼板の各サンプルについて、それぞれ120mm×120mmのサイズに剪断後、評価対象面の4辺のうち3辺のエッジから10mm、及び端面と非対象面をテープでシーリング、エッジ1辺のみテープシールせず剪断端面を露出させ、これを評価用サンプルとした。なお、剪断端面のバリが評価対象面側を向くように剪断した。
　上記評価用サンプルを用いて日本自動車規格の複合サイクル試験（JASO-CCT）を実施した。腐食促進試験を湿潤からスタートし、20サイクル毎にサンプルを取出し、水洗及び乾燥後に目視で観察、テープシールしていない1辺の剪断端面に赤錆の発生が確認されたサイクル数を、以下の基準に従って評価した。
◎：サンプル3個の赤錆発生サイクル数≧600サイクル
○：サンプル3個の赤錆発生サイクル数≧400サイクル
×：サンプル1個以上の赤錆発生サイクル数＜400サイクル (3) Corrosion resistance evaluation Each sample of the obtained coated steel plate was sheared to a size of 120 mm x 120 mm, and then 10 mm from the edge of three of the four sides of the evaluation surface, as well as the end surface and the non-target surface, were sealed with tape, and only one edge was not sealed with tape, leaving the sheared end surface exposed, and this was used as the evaluation sample. Note that the shearing was performed so that the burr on the sheared end surface faced the evaluation surface.
The above evaluation samples were used to carry out the Japanese Automotive Standard Combined Cyclic Test (JASO-CCT). The accelerated corrosion test started with wetting, and samples were taken out every 20 cycles, washed with water, dried, and then visually inspected. The number of cycles at which red rust was confirmed on the sheared edge of one side that was not sealed with tape was evaluated according to the following criteria.
◎: Number of cycles in which red rust occurs on three samples is ≥ 600 cycles ○: Number of cycles in which red rust occurs on three samples is ≥ 400 cycles ×: Number of cycles in which red rust occurs on one or more samples is < 400 cycles

Figure JPOXMLDOC01-appb-T000005
Figure JPOXMLDOC01-appb-T000005

　表５の結果から、本発明例の各サンプルは、比較例の各サンプルに比べて、表面外観と耐食性が共に優れていることがわかる。 The results in Table 5 show that the samples of the present invention are superior in both surface appearance and corrosion resistance to the samples of the comparative examples.

　本発明によれば、ドロス欠陥等の他の欠陥がなく、しわ状欠陥の発生が抑制され、優れた表面外観を有する溶融Al-Zn-Si-Mg系めっき鋼板を提供することが可能となる。
　また、本発明によれば、優れた表面外観及び耐白錆性を有する表面処理鋼板、並びに、優れた表面外観及び耐食性に優れた塗装鋼板を提供することが可能となる。 According to the present invention, it is possible to provide a hot-dip Al-Zn-Si-Mg-plated steel sheet which is free from other defects such as dross defects, suppresses the occurrence of wrinkle-like defects, and has an excellent surface appearance.
Furthermore, according to the present invention, it is possible to provide a surface-treated steel sheet having an excellent surface appearance and white rust resistance, and a coated steel sheet having an excellent surface appearance and excellent corrosion resistance.

Claims (6)

　めっき皮膜を備える溶融Al-Zn-Si-Mg系めっき鋼板であって、
　前記めっき皮膜は、Al：45～65質量％、Si：1.0～3.0質量％、Mg：1.0～10.0質量％及びMn：0.01～0.5質量％を含有し、残部がZn及び不可避的不純物からなる組成を有し、
　鋼板の両端から50mmを除いた範囲において、長さ1mmあたりの鋼板表面の高低差が10μm以下であることを特徴とする、溶融Al-Zn-Si-Mg系めっき鋼板。 A hot-dip Al-Zn-Si-Mg-based plated steel sheet having a plating film,
The plating film has a composition containing 45 to 65 mass% Al, 1.0 to 3.0 mass% Si, 1.0 to 10.0 mass% Mg, and 0.01 to 0.5 mass% Mn, with the remainder being Zn and unavoidable impurities;
A hot-dip Al-Zn-Si-Mg plated steel sheet, characterized in that the height difference of the steel sheet surface per mm of length is 10 μm or less in an area excluding 50 mm from both ends of the steel sheet. 　前記めっき皮膜中のMnの含有量が0.1～0.3質量％であることを特徴とする、請求項１に記載の溶融Al-Zn-Si-Mg系めっき鋼板。 The hot-dip Al-Zn-Si-Mg-plated steel sheet according to claim 1, characterized in that the Mn content in the plating film is 0.1 to 0.3 mass%. 　前記めっき皮膜と下地鋼板との界面にMnを含有した合金層を備えることを特徴とする、請求項１又は２に記載の溶融Al-Zn-Si-Mg系めっき鋼板。 The hot-dip Al-Zn-Si-Mg-plated steel sheet according to claim 1 or 2, characterized in that it has an alloy layer containing Mn at the interface between the plating film and the base steel sheet. 　前記めっき皮膜が、さらに、B、Ca、Ti、V、Cr、Sr、Mo、In、Sn、Sb、Ce、及びBiのうちから選択される一種又は二種以上を合計で0.01～3.0質量％含有することを特徴とする請求項１～３のいずれか１項に記載の溶融Al-Zn-Si-Mg系めっき鋼板。 The hot-dip Al-Zn-Si-Mg-plated steel sheet according to any one of claims 1 to 3, characterized in that the plating film further contains 0.01 to 3.0 mass% in total of one or more elements selected from B, Ca, Ti, V, Cr, Sr, Mo, In, Sn, Sb, Ce, and Bi. 　請求項１～４のいずれか１項に記載のめっき皮膜と、該めっき皮膜上に形成された化成皮膜と、を備える表面処理鋼板であって、
　前記化成皮膜は、エポキシ樹脂、ウレタン樹脂、アクリル樹脂、アクリルシリコン樹脂、アルキド樹脂、ポリエステル樹脂、ポリアルキレン樹脂、アミノ樹脂及びフッ素樹脂のうちから選択される少なくとも一種の樹脂と、P化合物、Si化合物、Co化合物、Ni化合物、Zn化合物、Al化合物、Mg化合物、V化合物、Mo化合物、Zr化合物、Ti化合物及びCa化合物のうちから選択される少なくとも一種の金属化合物と、を含有することを特徴とする、表面処理鋼板。 A surface-treated steel sheet comprising the plating film according to any one of claims 1 to 4 and a chemical conversion film formed on the plating film,
The chemical conversion coating film is a surface-treated steel sheet characterized in that it contains at least one resin selected from the group consisting of epoxy resins, urethane resins, acrylic resins, acrylic silicone resins, alkyd resins, polyester resins, polyalkylene resins, amino resins, and fluororesins, and at least one metal compound selected from the group consisting of P compounds, Si compounds, Co compounds, Ni compounds, Zn compounds, Al compounds, Mg compounds, V compounds, Mo compounds, Zr compounds, Ti compounds, and Ca compounds. 　請求項１～４のいずれか１項に記載のめっき皮膜上に、直接又は化成皮膜を介して、塗膜が形成された塗装鋼板であって、
　前記化成皮膜は、（ａ）：エステル結合を有するアニオン性ポリウレタン樹脂及び（ｂ）：ビスフェノール骨格を有するエポキシ樹脂を合計で30～50質量％含有し、該（ａ）と該（ｂ）の含有比率（（ａ）：（ｂ））が、質量比で3：97 ～60：40の範囲である樹脂成分と、2～10質量％のバナジウム化合物、40～60質量％のジルコニウム化合物及び0.5～5質量％のフッ素化合物を含む無機化合物と、を含有し、
　前記塗膜は、プライマー塗膜を少なくとも有し、該プライマー塗膜が、ウレタン結合を有するポリエステル樹脂と、バナジウム化合物、リン酸化合物及び酸化マグネシウムを含む無機化合物と、を含有することを特徴とする、塗装鋼板。 A coated steel sheet having a coating film formed directly or via a chemical conversion coating on the plating film according to any one of claims 1 to 4,
The chemical conversion coating contains a resin component that contains 30 to 50 mass% in total of (a): an anionic polyurethane resin having an ester bond and (b): an epoxy resin having a bisphenol skeleton, the content ratio of (a) to (b) ((a):(b)) being in the range of 3:97 to 60:40 in terms of mass ratio, and an inorganic compound that contains 2 to 10 mass% of a vanadium compound, 40 to 60 mass% of a zirconium compound, and 0.5 to 5 mass% of a fluorine compound;
The coating film has at least a primer coating film, and the primer coating film contains a polyester resin having a urethane bond, and an inorganic compound including a vanadium compound, a phosphate compound, and magnesium oxide.
PCT/JP2024/008325 2023-07-31 2024-03-05 Al-zn-si-mg hot-dipped steel sheet, surface-treated steel sheet, and coated steel sheet WO2025027919A1 (en)

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