Precoated steel sheet, precoated plated steel sheet, and formed product

Abstract

Even when deep drawing is performed, the formation of coating lift-off portions can be more effectively suppressed. The pre-coated steel sheet of the present invention comprises: a steel sheet; and a coating layer located on one or both sides of the aforementioned steel sheet, containing 0.5% by mass or more and 60.0% by mass of aluminum, 0.5% by mass or more and 15.0% by mass of magnesium, with the balance being zinc and impurities, wherein at a depth of 10 nm from the surface of the aforementioned coating layer, the ratio of magnesium oxide and hydroxide to metallic magnesium is 2.0 or more, or the ratio of zinc oxide and hydroxide to metallic zinc is 7.0 or more.

Description

Technical Field

[0001] This invention relates to coated steel sheets for pre-coated steel sheets, pre-coated coated steel sheets, and molded articles thereof. Background Technology

[0002] For pre-coated steel sheets, which are pre-painted steel sheets, many properties are required, including corrosion resistance, formability, coating hardness (scratch resistance), stain resistance, chemical resistance, and weather resistance. The order of these required properties varies depending on the intended use of the pre-coated steel sheet. For example, for pre-coated steel sheets used primarily outdoors, such as in air conditioner outdoor units and water heaters, formability and corrosion resistance are particularly important among the aforementioned properties.

[0003] For this type of pre-coated steel sheet, many technologies have been studied as methods to improve the adhesion between the coated steel sheet and the coating.

[0004] For example, Patent Document 1 discloses a pre-coated metal sheet in which the coating in the deep drawing section is not damaged or peeled during deep drawing, and which exhibits excellent press formability. In order to obtain a pre-coated metal sheet with excellent press formability without peeling, Patent Document 1 discloses the following key points: preferably, the coating has a specific viscoelastic curve, the number average molecular weight of the coating resin is 10,000 or more, and the glass transition temperature (Tg) of the coating resin is 25°C or more.

[0005] Furthermore, Patent Document 2 discloses a pre-coated metal sheet with excellent continuous pressing formability and excellent outdoor corrosion resistance of the end face of the deep-drawing section. Patent Document 2 discloses the following key points for obtaining a pre-coated metal sheet with excellent continuous pressing formability: as the aforementioned coating properties, the coating's Tg is 40–120°C, and the minimum value of the storage elastic modulus within the rubbery elastic range of the coating, as measured using a dynamic viscoelasticity measuring device, is 2 × 10⁻⁶. 7 It is important that the coating strength is below 0.15, the surface tension of the coating is below 28 mN / m, and the coefficient of dynamic friction of the coating surface is below 0.15.

[0006] Furthermore, Patent Document 3 discloses a method of having one or more coating layers on one or both sides of a metal plate, wherein the physical properties of the outermost coating layer are as follows: Tg of 5–30°C, and a hardness of 2.5 N / mm² at 23°C based on a universal hardness test under a 5 mN load. 2 The above-mentioned pre-coated metal sheet has an elongation at break of 100% or more at 23°C, and a specular gloss of 60% or more when measured under conditions of 60° incident angle and 60° received angle. Patent Document 3 describes, for the above-mentioned pre-coated metal sheet, a coated metal molded article that does not easily experience a decrease in coating gloss even during deep drawing and processing, and exhibits excellent press formability.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2-217500

[0010] Patent Document 2: Japanese Patent Application Publication No. 8-253883

[0011] Patent Document 3: Japanese Patent Application Publication No. 2007-44922 Summary of the Invention

[0012] The problem the invention aims to solve

[0013] The inventors conducted research to further improve the formability and corrosion resistance of the pre-coated steel sheet as described above. The results showed that when pre-coated steel sheets are used for deep drawing processes such as air conditioner outdoor unit top panels, a phenomenon called coating lift-up occurs in the deep drawing section (a phenomenon where the coating becomes rough due to the aggregation of fine, dot-like expansions). The areas where this phenomenon occurs will be referred to as "coating lift-up sections." Cross-sectional observation of the coating lift-up sections reveals that during the deep drawing of the pre-coated steel sheet, the coating cannot keep up with the deformation (compression) of the steel sheet and becomes redundant. In areas where the adhesion to the steel sheet is insufficient, the coating peels off from the top.

[0014] The technology in Patent Document 1 aims to set coating properties and suppress coating warping caused by compressive strain in the drawn portion during deep drawing. However, based on the results of our research, we believe that in order to suppress coating warping, factors other than coating properties, such as plating hardness, plating uniformity, properties of chemically converted coatings, and processing shape, are also significant influencing factors. Patent Document 1 does not describe these influencing factors other than coating properties. Therefore, Patent Document 1 has room for improvement regarding the suppression of coating warping caused by coating lift-up during deep drawing, which is the focus of our research.

[0015] Furthermore, the technology in Patent Document 2 is no different from the invention in Patent Document 1 in that it aims to define the physical properties of the coating to suppress the warping of the coating caused by compressive strain during deep drawing. Therefore, Patent Document 2 has room for improvement regarding the suppression of warping of the coating with raised portions generated during deep drawing, which is the focus of the inventors.

[0016] Furthermore, the technology in Patent Document 3, in its aim to suppress coating warping caused by compressive strain by merely specifying the coating properties, is no different from that in Patent Documents 1 and 2. Therefore, Patent Document 3 still has room for improvement regarding the suppression of coating warping in the coating floats generated during deep drawing, which is the focus of the inventors.

[0017] Therefore, the present invention was made in view of the above-mentioned problems, and the object of the present invention is to provide a pre-coated steel sheet, a pre-coated steel sheet and a molded article, which can more effectively suppress the generation of coating lifting parts even when deep drawing is performed.

[0018] Solution for solving the problem

[0019] In order to solve the above problems, the inventors conducted in-depth research and found that, as detailed below, the surface oxidation state of the coated steel sheet, which is the coating base plate for pre-coated steel sheet, affects the adhesion of the coating film in the processed part of the formed product.

[0020] The main idea of ​​this invention, which was completed based on the above findings and further research results, is as follows.

[0021] (1) A pre-coated steel sheet for use in steel plates, comprising: a steel sheet; and a coating layer located on one or both sides of the steel sheet, containing 0.5% by mass or more and 60.0% by mass or less aluminum, 0.5% by mass or more and 15.0% by mass or less magnesium, with the balance being zinc and impurities, wherein at a depth of 10 nm from the surface of the coating layer, the ratio of magnesium oxide and hydroxide to metallic magnesium is 2.0 or more, or the ratio of zinc oxide and hydroxide to metallic zinc is 7.0 or more.

[0022] (2) The pre-coated steel sheet according to (1), wherein at a depth of 10 nm from the surface of the aforementioned coating layer, the ratio of the aforementioned magnesium oxide and hydroxide to the ratio of metallic magnesium is 2.0 or more, and the ratio of the aforementioned zinc oxide and hydroxide to the ratio of metallic zinc is 7.0 or more.

[0023] (3) The pre-coated steel sheet according to (1) or (2), wherein at a depth of 10 nm from the surface of the aforementioned coating layer, the ratio of aluminum oxide and hydroxide to metallic aluminum is 1.3 or more.

[0024] (4) A pre-coated steel sheet according to any one of (1) to (3), wherein the aforementioned coating is a Zn-11%Al-3%Mg-0.2%Si alloy coating.

[0025] (5) A pre-coated steel sheet comprising: a chemical conversion treatment coating on the aforementioned coating layer of the steel sheet as described in any one of (1) to (4); and a coating on the aforementioned chemical conversion treatment coating, wherein at a depth of 10 nm from the interface between the aforementioned chemical conversion treatment coating and the aforementioned coating layer toward the inner side of the aforementioned coating layer, the ratio of magnesium oxide and hydroxide to metallic magnesium is 0.30 or less, or the ratio of zinc oxide and hydroxide to metallic zinc is 7.0 or more.

[0026] (6) The pre-coated steel sheet according to (5), wherein, at a depth of 10 nm from the interface between the aforementioned chemical conversion treatment coating and the aforementioned coating layer toward the inner side of the aforementioned coating layer, the ratio of the aforementioned magnesium oxide and hydroxide to the ratio of metallic magnesium is 0.30 or less, and the ratio of the aforementioned zinc oxide and hydroxide to the ratio of metallic zinc is 7.0 or more.

[0027] (7) The pre-coated steel sheet according to (5) or (6), wherein, at a depth of 10 nm from the interface between the aforementioned chemical conversion treatment coating and the aforementioned coating layer toward the inner side of the aforementioned coating layer, the ratio of aluminum oxide and hydroxide to metallic aluminum is 0.30 or less.

[0028] (8) A molded article formed from a pre-coated steel sheet as described in any one of (5) to (7), wherein the thickness of the coated steel sheet in the molded article is increased by more than 5% compared with the non-formed part, and the peel strength measured by cutting the interface between the chemical conversion treatment coating and the coating film using the SAICAS method is an average of more than 1.00 kN / m, and less than 20% of the cutting area is an interfacial peeling morphology, and the remaining cutting area is a cohesive failure morphology within the coating film.

[0029] (9) The molded article according to (8), wherein the coating layer of the aforementioned molded article contains 5% or more and 15% or less aluminum and 2% or more and 4% or less magnesium.

[0030] The effects of the invention

[0031] As described above, according to the present invention, it is possible to provide pre-coated steel sheets, pre-coated steel sheets, and molded articles that can more effectively suppress the formation of coating lift-off portions even when deep drawing is performed. Attached Figure Description

[0032] Figure 1A An explanatory diagram illustrating an example of the structure of a pre-coated steel sheet for use with coated steel sheets according to various embodiments of the present invention.

[0033] Figure 1BAn explanatory diagram illustrating another example of the structure of a pre-coated steel sheet for use in various embodiments of the present invention.

[0034] Figure 2 This is an explanatory diagram used to illustrate the coating layer of the pre-coated steel sheet for use in various embodiments of the present invention.

[0035] Figure 3A An explanatory diagram illustrating an example of the structure of a pre-coated steel sheet according to various embodiments of the present invention.

[0036] Figure 3B An explanatory diagram illustrating another example of the structure of a pre-coated steel sheet according to various embodiments of the present invention.

[0037] Figure 4 This is an explanatory diagram used to illustrate the coating layer of the pre-coated steel sheet in various embodiments of the present invention.

[0038] Figure 5 An explanatory diagram illustrating an example of the structure of a molded article according to various embodiments of the present invention. Detailed Implementation

[0039] Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that in this specification and the accompanying drawings, constituent elements having substantially the same functional structure are given the same reference numerals, thereby omitting repeated descriptions.

[0040] (Regarding the research conducted by the inventors)

[0041] Before describing the pre-coated steel sheet, pre-coated steel sheet and molded article of the embodiments of the present invention, the various research contents of the coating floating part as described above will be described in detail.

[0042] If the inventors observe the cross-section of the coating lifting portion of a molded article formed by deep drawing a pre-coated steel sheet, they observe that the coating is compressed as the steel sheet deforms (compresses), and excess coating peels off from the top. If the thickness of this portion of the steel sheet is measured, it increases compared to the thickness before forming, thus indicating that the coating lifting portion is the compressed part of the steel sheet.

[0043] On the other hand, for the portions where coating peels off due to friction with the die during deep drawing (i.e., portions peeling off due to mechanical friction); and for portions where the coating elongates following the original sheet but stress concentrates at the interface between the plating and the coating due to elongation, resulting in reduced adhesion and coating peeling off due to die slippage (i.e., portions peeling off due to stress concentration), the thickness of the plated steel sheet decreases compared to before forming. From the above results, it can be seen that these coating peeling portions are the elongated portions of the plated steel sheet. However, in deep drawing, the compression and elongation of the plated steel sheet do not occur separately but simultaneously, with the degree of compression and elongation differing only depending on the processing location. For portions where compression exceeds elongation, the thickness of the plated steel sheet increases compared to before forming. Conversely, for portions where elongation exceeds compression, the thickness of the plated steel sheet decreases compared to before forming.

[0044] If the adhesion strength (peel strength) between the coating and the plating interface decreases due to the deformation of the plated steel sheet during forming, coating lifting and peeling will occur.

[0045] Based on the results of the research conducted by the inventors, as factors determining the presence or absence of coating lift-up and coating peeling, they considered that the following three influencing factors (1) to (3) should be studied. They believed that if the overall influence of these factors is in a good state, coating lift-up and coating peeling can be suppressed.

[0046] (1) The density of the plated surface after compression and elongation (presence or absence of unevenness or cracks).

[0047] (2) Adhesion between the coating and the primer film after chemical conversion treatment following compression and elongation processing.

[0048] (3) The overall condition of the coating, including the top coating which is deformed due to the processing of compression and elongation (presence or absence of cracks, internal stress).

[0049] Since the phenomenon of coating lifting as described above is prone to occur in pre-coated steel sheets used as coating base plates for zinc-plated steel sheets (especially zinc-plated steel sheets containing aluminum and magnesium alloys), the inventors have focused on the coating surfaces used as coating base plates as shown in (1) and (2) above and have conducted further research.

[0050] As a result, the inventors discovered that the surface oxidation state of the coated steel sheet of the original coating material affects the adhesion of the coating film in the forming process. Here, the inventors focused on two main types of surface oxidation states of the coated steel sheet: (a) the state of aluminum and magnesium oxides and hydroxides on the surface of the coated steel sheet; and (b) the state of zinc oxides and hydroxides on the surface of the coated steel sheet.

[0051] First, we will discuss (a) the state of the aluminum and magnesium oxides and hydroxides on the surface of the coated steel sheet.

[0052] The inventors' research revealed the following finding: when the concentration of aluminum and magnesium oxides and hydroxides on the surface of the plated steel sheet is low, the coating adhesion of the forming process increases. This is presumably because, for zinc-based alloy plated steel sheets containing aluminum and magnesium, the formation of aluminum and magnesium oxides and hydroxides, which are easily oxidized elements, on the surface reduces the wettability of degreasing solutions and chemical conversion treatment solutions, thus decreasing the coating adhesion of the processed area.

[0053] Furthermore, the inventors conducted an in-depth study on the correlation between the oxidation state of the coating surface of the original coated plate and the coating adhesion of the forming process. The results showed that, for magnesium, when the ratio of magnesium oxides and hydroxides to magnesium metal (in other words, magnesium in its metallic state) at a depth of 10 nm below the coating surface is 2.0 or higher, good coating adhesion of the forming process can be obtained.

[0054] While a low surface concentration of magnesium oxides is desirable, as mentioned above, the reason why a certain or higher ratio of oxides to hydroxides relative to metal is desirable for magnesium near the surface of the coating remains unclear. However, it is presumed that for good coating adhesion in the forming process, the dissolution of both magnesium metal, magnesium oxides, and hydroxides through acid treatment, alkali degreasing, etc., is necessary. On the other hand, considering the difference in dissolution rates and the deposition after dissolution, a high ratio of oxides to hydroxides is desirable for magnesium itself.

[0055] Furthermore, the results of the inventors' research also show that, for zinc alloy coated steel sheets containing aluminum and magnesium as described above, when chemical conversion treatment and coating are performed in order to form pre-coated steel sheets, in order to exhibit good coating adhesion in the forming process, it is good when the ratio of aluminum and magnesium oxides and hydroxides at the interface between the coating layer and the chemical conversion treatment coating is lower than the metal ratio of these elements by a certain amount.

[0056] This is presumably because the aluminum and magnesium on the surface of the coating are dissolved during the chemical conversion treatment. Furthermore, some of the aluminum and magnesium are introduced into the chemical conversion coating. Therefore, it is assumed that a small surface proportion of oxides and hydroxides, which negatively affect coating adhesion, is desirable. It should be noted that the details regarding the form in which aluminum and magnesium are introduced into the chemical conversion coating are unclear, but it is speculated that they may be introduced in either the form of oxides / hydroxides or in a metallic form.

[0057] Next, we will discuss (b) the state of zinc oxides and hydroxides on the surface of the coated steel sheet.

[0058] The inventors' research revealed the following finding: when the concentration of zinc oxides and hydroxides on the surface of the plated steel sheet is low, the adhesion of the coating in the forming process section increases. This is presumably because zinc oxides and hydroxides have higher wettability with degreasing solutions and chemical conversion treatment solutions compared to metallic zinc. Therefore, by covering the plated surface with these oxides and hydroxides, the adhesion with the chemical conversion treatment coating layer is improved. Consequently, when the amount of zinc oxides and hydroxides is high, the adhesion of the coating after forming becomes better.

[0059] Therefore, the reason why a high ratio of zinc oxides and hydroxides relative to metallic zinc is desirable on the surface of the plated steel sheet used as the base for coating remains unclear. However, it is presumed that this is because, for good coating adhesion in the forming process, the dissolution of both metallic zinc and zinc oxides and hydroxides through acid treatment, alkali degreasing, etc., is necessary. On the other hand, based on the difference in their dissolution rates and the deposition after dissolution, a high ratio of oxides and hydroxides is desirable for zinc itself.

[0060] It is also speculated that for zinc-coated steel sheets containing aluminum and magnesium, the dissolution of aluminum and magnesium relatively affects the surface concentration of zinc.

[0061] Furthermore, the results of the inventors' research also show that, for zinc-plated steel sheets like the above, when chemical conversion treatment and coating are performed in order to form pre-coated steel sheets, it is good for the ratio of zinc oxide and hydroxide to metallic zinc to be higher than a certain level at the interface between the plating layer and the chemical conversion treatment coating in order to exhibit good coating adhesion in the forming process.

[0062] Based on the above findings, the inventors have further investigated and discovered the following detailed description of the conditions for acid treatment and alkali degreasing to achieve the appropriate oxide and hydroxide states.

[0063] Furthermore, the inventors investigated the peel strength and peel morphology of the interface between the chemically converted coating, the coating film (e.g., a primer film if the coating film contains multiple layers), and the plating layer in a molded body obtained by forming the pre-coated steel sheet described above. In conventional peel tests, the peel strength of the coating film on the pre-coated steel sheet can be measured, but the peel strength and peel morphology of the compressed and elongated portions of the plated steel sheet constituting the molded body cannot be accurately measured. As a method that allows for simultaneous measurement of these portions, the inventors used the SAICAS method (Surface and Interfacial Cutting Analysis System) to evaluate the peel strength and peel morphology.

[0064] The SAICAS method is a technique that uses a sharp blade to cut at an ultra-low speed from the sample surface to the bonding interface between the substrate and the bonded material, and then measures the peel strength. Therefore, it enables the observation of peel strength and peel state at specific interlayer interfaces in multilayer films, which are difficult to measure using conventional methods.

[0065] Samples of the compressed and elongated portions of the coated steel sheet of the formed body cannot be prepared separately for each portion. Therefore, the inventors used pre-coated steel sheet for deep drawing of cylindrical cups, focusing on the portion with increased thickness compared to the thickness of the coated steel sheet before forming, which is the forming portion with compression advantage, and focusing on the portion with decreased thickness compared to the thickness of the coated steel sheet before forming, which is the forming portion with elongation advantage. By measuring these portions using the SAICAS method, the following findings were obtained.

[0066] It can be seen that for molded bodies formed from pre-coated steel sheets that do not produce the above-mentioned coating lifting or peeling, the peeling mode of the coating is not the interface peeling of the chemical conversion coating, the coating (for example, the primer coating in the case of the coating containing multiple layers) and the plating layer, but rather the cohesive destruction of the coating (for example, the primer coating in the case of the coating containing multiple layers).

[0067] As a result, it can be seen that when the following two conditions (i) and (ii) are met simultaneously, it is possible to obtain a molded product formed from a pre-coated steel sheet without coating peeling.

[0068] (i) The peel strength of the compressed portion of the coated steel sheet obtained by the SAICAS method (i.e., the portion in the formed article where the thickness of the coated steel sheet increases by more than 5% compared with that before forming (or the non-forming part)) is 1.00 kN / m or more on average.

[0069] (ii) Less than 20% of the cutting area is considered an interfacial peeling morphology, and the remaining cutting area is considered a cohesive failure morphology within the coating (e.g., within the primer coating if the coating contains multiple layers).

[0070] Here, the term "interfacial peeling morphology" refers to any one of the following: cohesive failure of the chemical conversion coating, interfacial peeling between the chemical conversion coating and the coating film (e.g., a primer film if the coating film contains multiple layers), or interfacial peeling between the chemical conversion coating and the plating layer, or a combination of these states. However, the chemical conversion coating is extremely thin, and therefore integrated with the plating layer and the coating film (e.g., a primer film if the coating film contains multiple layers), making the aforementioned peeling morphologies visually indistinguishable.

[0071] The following provides a detailed description of the pre-coated steel sheet, pre-coated steel sheet, and molded article of the present invention based on the findings described above.

[0072] The first embodiment of the present invention shown below focuses on the state of aluminum and magnesium oxides and hydroxides on the surface of the plated steel sheet as described in (a) above. The second embodiment of the present invention shown below focuses on the state of zinc oxides and hydroxides on the surface of the plated steel sheet as described in (b) above. The third embodiment of the present invention shown below focuses on the state of zinc, aluminum, and magnesium oxides and hydroxides on the surface of the plated steel sheet.

[0073] Implementation Method 1

[0074] (For pre-coated steel sheets)

[0075] First refer to Figures 1A-2 At the same time, the pre-coated steel sheet for pre-coated steel sheet according to the first embodiment of the present invention will be described in detail.

[0076] like Figure 1A As schematically shown, the plated steel sheet 10 of this embodiment has a steel sheet 101 as a substrate and a plating layer 103 located on one side of the steel sheet. Furthermore, the plated steel sheet 10 of this embodiment... Figure 1B As schematically shown, the coating 103 can be located on both sides of the steel plate 101 that serves as the substrate.

[0077] <For steel plate 101>

[0078] The steel sheet 101 used as the base material for the galvanized steel sheet 10 in this embodiment can be made of various steel sheets depending on the required mechanical strength of the galvanized steel sheet 10. Examples of such steel sheets 101 include Al killed steel, extremely low carbon steel containing Ti, Nb, etc., and high-strength steel containing strengthening elements such as P, Si, Mn, etc. in extremely low carbon steel.

[0079] In addition, the thickness of the steel plate 101 in this embodiment ( Figure 1A and Figure 1B The thickness d0 in the middle can be set appropriately according to the mechanical strength required by the galvanized steel plate 10, for example, it can be set to about 0.2mm to 2.0mm.

[0080] <Regarding plating layer 103>

[0081] The coating layer 20 in this embodiment is as follows: Figure 1A and Figure 1BAs schematically shown, a layer is formed on at least one side of the steel plate 101 to improve the corrosion resistance of the coated steel plate 10. The chemical composition of the coating layer 103 of this embodiment will be described first.

[0082] The coating layer 103 of this embodiment is a coating layer containing, by mass percent, aluminum (Al): 0.5% or more and 60.0% or less, magnesium (Mg): 0.5% or more and 15.0% or less, and the balance being zinc (Zn) and impurities. That is, the coating layer 103 of this embodiment is a ternary coating layer of Al-Mg-Zn system.

[0083] [Al: 0.5–60.0% by mass]

[0084] The Zn alloy coating 103 of this embodiment contains 0.5% by mass or more and 60.0% by mass or less Al. By setting the Al content to 0.5% by mass or more and 60.0% by mass or less, the corrosion resistance of the coated steel sheet 10 of this embodiment is improved, and the adhesion of the coating 103 (more specifically, the adhesion to the steel sheet 101) can be guaranteed. When the Al content is less than 0.5% by mass, the coating 103 becomes brittle and the adhesion of the coating 103 decreases. The Al content is preferably 5.0% by mass or more. On the other hand, when the Al content exceeds 60.0% by mass, the effect of improving the corrosion resistance of the coated steel sheet 10 saturates. The Al content is preferably 15.0% by mass or less.

[0085] [Mg: 0.5–15.0% by mass]

[0086] The coating layer 103 of this embodiment contains 0.5% by mass or more and 15.0% by mass or less of Mg. By setting the Mg content to 0.5% by mass or more and 15.0% by mass or less, the corrosion resistance of the coated steel sheet 10 of this embodiment is improved, and the adhesion of the coating layer 103 (more specifically, the adhesion to the steel sheet 101) can be guaranteed. When the Mg content is less than 0.5% by mass, the improvement effect on the corrosion resistance of the coated steel sheet 10 is insufficient. The Mg content is preferably 2.0% by mass or more. On the other hand, when the Mg content exceeds 15.0% by mass, the coating layer 103 becomes brittle and the adhesion of the coating layer 103 decreases. The Mg content is preferably 4.0% by mass or less.

[0087] [Balance: Zn and impurities]

[0088] In the plating layer 103 of this embodiment, the balance other than the above-mentioned components is Zn and impurities. In addition, in the plating layer 103 of this embodiment, a portion of the balance Zn may be replaced by silicon (Si) at a content of 0% by mass or more and 2.0% by mass or less.

[0089] [Si: 0–2.0% by mass]

[0090] In this embodiment, the plating layer 103 can contain 0% by mass or more and 2.0% by mass or less Si, instead of a portion of the remaining Zn. By setting the Si content to 0% by mass or more and 2.0% by mass or less, the adhesion of the plating layer 103 can be more reliably guaranteed. If the Si content exceeds 2.0% by mass, the effect of improving the adhesion of the plating layer 103 may become saturated. The Si content is more preferably 1.6% by mass or less.

[0091] Furthermore, in the plating layer 103 of this embodiment, a portion of the remaining Zn may be replaced, and elements such as Fe, Sb, and Pb may be present alone or in combination, accounting for less than 1% by mass.

[0092] As a pre-coated steel sheet 10 having a coating layer 103 having the chemical composition described above, examples include molten zinc-aluminum-magnesium-silicon alloy coated steel sheets such as those having a Zn-11%Al-3%Mg-0.2%Si alloy coating layer (e.g., "SuperDyma (registered trademark)" and "ZAM (registered trademark)" manufactured by Nippon Steel Corporation).

[0093] [Regarding the average film thickness of coating 103]

[0094] In the pre-coated steel sheet 10 of this embodiment, the average film thickness of the coating layer 103 is ( Figure 1A and Figure 1B The average film thickness d1 of the coating layer 103 is preferably 6 μm or more, more preferably 9 μm or more. This average film thickness ensures a more reliable guarantee of the corrosion resistance of the pre-coated steel sheet 10. It should be noted that when the average film thickness d1 of the coating layer 103 exceeds 45 μm, the increased coating cost outweighs the cost of improved corrosion resistance. Therefore, from an economic point of view, it is preferable that the average film thickness d1 of the coating layer 103 is 45 μm or less.

[0095] It should be noted that the average film thickness d1 of the coating layer 103 can be calculated, for example, using a gravimetric method as follows: A coated steel sheet with a specified area (e.g., 50 mm × 50 mm) is dissolved in hydrochloric acid containing an inhibitor, and the weight of the dissolved material is calculated from the weight difference before and after dissolution. Furthermore, the weight ratio of elements such as Al, Zn, and Fe in the solution is determined / calculated using inductively coupled plasma (ICP) emission spectroscopy, and the average specific gravity of the coating layer is calculated from this ratio. The average film thickness d1 of the coating layer 103 is calculated by dividing the dissolved weight by the average specific gravity, and then by the area (or area × 2 in the case of double-sided coating).

[0096] <State of magnesium and aluminum on the surface of the coating>

[0097] Based on the findings described above, for the plating layer 103 of this embodiment, the states of magnesium, aluminum metals, oxides and hydroxides in the surface of the plating layer 103 are specified.

[0098] Here, on the surface of the coating layer 103, in addition to magnesium, aluminum metals, oxides, hydroxides, etc., various unexpected impurities may also exist. Therefore, in this embodiment, as... Figure 2 As schematically shown, at "position A" located at a depth of 10 nm from the surface of the coating layer 103, the states of specific magnesium, aluminum metals, oxides, and hydroxides are defined as the states of these substances on the surface of the coating layer 103.

[0099] The states of magnesium, aluminum, and their oxides and hydroxides were characterized by X-ray photoelectron spectroscopy (XPS). XPS analysis was performed using a ULVAC-PHI, INCORPORATED Quantum 2000 X-ray source, configured with Al Kα, X-ray output power 15 kV, 25 W, measurement range 300 × 300 μm square, and vacuum level 1.5 × 10⁻⁶. -9 Torr (1 Torr is approximately 133.3 Pa), detection accuracy: 45°. Additionally, the sputtering for depth distribution analysis is set to Ar ion species. + Accelerating voltage: 1kV, range: 1×1mm, sputtering rate: 2.7nm / min (SiO2 conversion). Sputtering is performed based on the above sputtering rate, and the specific sputtered location is regarded as "location A".

[0100] Here, the attribution of magnesium oxides and hydroxides, and the proportion of metallic magnesium (presence ratio) is separated by 295–325 cm⁻¹ based on Mg KLL. -1 The narrow spectrum is calculated from the intensity ratio of the peaks attributed to each substance (oxide, hydroxide, metal). Similarly, the attribution and separation of aluminum oxides and hydroxides, and the proportion of metallic aluminum (presence ratio), are determined by the 68–84 cm⁻¹ spectrum based on Al 2p. -1 The narrow spectrum is calculated from the intensity ratio of the peaks attributed to each substance (oxide, hydroxide, metal).

[0101] In the plating layer 103 of this embodiment, the depth is 10 nm away from the surface of the plating layer as described above. Figure 2The ratio of magnesium oxide to hydroxide at position A) is 2.0 or more relative to metallic magnesium. With a magnesium oxide to hydroxide ratio of 2.0 or more relative to metallic magnesium, even when the pre-coated coated steel sheet using the pre-coated steel sheet coated steel sheet 10 with the coating layer 103 of this embodiment is deep-drawn, good coating adhesion of the forming process is achieved, and the formation of coating lift-off portions can be suppressed. On the other hand, if the magnesium oxide to hydroxide ratio is less than 2.0, good coating adhesion of the forming process cannot be exhibited, and the formation of coating lift-off portions cannot be suppressed. The magnesium oxide to hydroxide ratio relative to metallic magnesium is preferably 4.0 or more, more preferably 6.0 or more. Furthermore, the upper limit of the magnesium oxide to hydroxide ratio relative to metallic magnesium is substantially around 10.0.

[0102] Furthermore, in the plating layer 103 of this embodiment, the depth at a specific distance of 10 nm from the surface of the plating layer, as described above, is... Figure 2 The ratio of aluminum oxide to hydroxide at position A) is preferably 1.3 or more relative to the ratio of metallic aluminum. With an aluminum oxide to hydroxide ratio of 1.3 or more relative to metallic aluminum, even when the pre-coated coated steel sheet 10 with the coating layer 103 of this embodiment is deep-drawn, better coating adhesion of the forming section is achieved, and the formation of coating lift-off portions can be more effectively suppressed. On the other hand, if the aluminum oxide to hydroxide ratio is less than 1.3, better coating adhesion of the forming section may not be achieved. The aluminum oxide to hydroxide ratio relative to metallic aluminum is more preferably 1.4 or more, and even more preferably 2.0 or more. Furthermore, the upper limit of the aluminum oxide to hydroxide ratio relative to metallic aluminum is substantially around 10.0.

[0103] Here, measurements were performed on a size range of 300 μm × 300 μm using XPS. Furthermore, the presence ratio calculated as described above refers to the average value over the measurement range mentioned above.

[0104] It should be noted that, for the plated steel sheet 10 of this embodiment, as long as the above-mentioned relationship with magnesium holds in the plating layer 103, good coating adhesion of the forming part can be exhibited. This is because magnesium has a lower standard electrode potential than aluminum, and therefore is more prone to corrosion. Further suppressing magnesium corrosion is effective in improving the coating adhesion of the forming part.

[0105] Reference above Figures 1A-2 At the same time, the pre-coated steel sheet 10 for the steel sheet of this embodiment will be described in detail.

[0106] The pre-coated steel sheet 10 of this embodiment, as described above, can be manufactured as follows: First, the surface of the prepared steel sheet 101 is subjected to pretreatment such as washing and degreasing as needed. Then, the steel sheet 101, which has undergone pretreatment as needed, is subjected to a conventional hot-dip galvanizing method in an oxidation-free furnace to form a coating layer.

[0107] Next, the steel sheet with the coating is subjected to a post-processing step using at least one of acid treatment, alkali treatment, or mechanical cutting. This modifies or removes the surface of the coating, thereby satisfying the previously discussed conditions regarding XPS spectroscopy.

[0108] Here, a hot-dip galvanizing bath with the desired chemical composition is prepared (i.e., a hot-dip galvanizing bath containing at least Al: 0.5–60.0% by mass, Mg: 0.5–15.0% by mass, and the balance being Zn and impurities), and the bath temperature is controlled at approximately 450°C. The resulting steel sheet 101 is then immersed in the galvanizing bath, and hot-dip galvanization is applied to the surface of the steel sheet in a manner that forms a desired average film thickness. The cooling rate after galvanizing is then controlled at 10°C / second or higher. This allows the galvanized layer to be formed.

[0109] The coating layer obtained as described above is subjected to XPS spectrum measurement using an XPS analysis apparatus set under the aforementioned measurement conditions. The surface of the coating layer is then modified or removed using various methods such as acid treatment, alkali treatment, and mechanical cutting until the previously mentioned XPS spectrum conditions are met. Thus, the pre-coated steel sheet 10 of this embodiment, having the coating layer 103 described above, can be manufactured.

[0110] The applicable alkaline treatment, acid treatment, and mechanical cutting treatment can be any one of these, or various combinations of these treatments can also be used.

[0111] For example, in the case of alkaline treatment, there is a tendency for a higher alkaline concentration and a longer treatment time to result in a higher proportion of magnesium oxides and hydroxides on the plating surface. For instance, when using a commercially available standard sodium orthosilicate-based (medium-alkaline) degreasing solution sprayed at 50°C, the proportion of magnesium oxides and hydroxides on the plating surface does not meet the specified conditions when the spraying time is less than 10 seconds. However, extending the spraying time meets the conditions, and extending it to about 2 minutes reliably meets the conditions. Furthermore, if the concentration of the degreasing solution is doubled, the conditions are reliably met when the spraying time is about 30 seconds. The reason is unclear, but it is believed that alkaline treatment causes the metallic magnesium to dissolve, transform into oxides or hydroxides, and potentially redeposit on the plating surface.

[0112] Furthermore, in the case of acid treatment, unlike alkaline treatment, the above treatment exhibits the effect of removing magnesium oxides and hydroxides from the surface of the plating layer. Therefore, by performing treatment under conditions that reduce the degree of removal of contaminants adhering to the plating surface, the desired conditions can be obtained. For example, when spraying with 5% sulfuric acid at 50°C, by setting the spraying time to approximately 5 to 10 seconds, the ratio of magnesium oxides and hydroxides present on the plating layer surface can meet the desired conditions. However, prolonged spraying will not meet the requirements.

[0113] Furthermore, when mechanical cutting is performed, the above-mentioned treatment exhibits the effect of removing any one of the magnesium oxide and hydroxides from the surface of the plating layer. Therefore, it is preferable to use a nylon brush, a grinding wheel of appropriate grit, etc., to perform the treatment under conditions where the degree of removal of contaminants adhering to the plating surface is weak. After mechanical cutting, the cutting contaminants are removed by rinsing with water.

[0114] Examples of various processing methods have been described above, and the conditions for each processing method vary depending on the initial oxidation state of the coating layer on the steel sheet used. Therefore, the pre-coated steel sheet 10 for pre-coated steel sheet of this embodiment can be manufactured by appropriately selecting the most suitable conditions.

[0115] (For pre-coated steel sheets)

[0116] Next, refer to Figures 3A-4 At the same time, a detailed description is given of the pre-coated steel sheet 10 for use with the pre-coated steel sheet described above.

[0117] like Figure 3A As schematically shown, the pre-coated steel sheet 20 of this embodiment uses the pre-coated steel sheet 10 for pre-coated steel sheets as previously described, as the substrate. The pre-coated steel sheet 20 includes a steel sheet 101, a coating layer 201 on one side of the steel sheet 101, a chemical conversion coating 203 on the coating layer 201, and a coating film 205 on the chemical conversion coating 203. Furthermore, the pre-coated steel sheet 20 of this embodiment... Figure 3B As schematically shown, a plating layer 201, a chemical conversion coating 203, and a coating 205 can be formed on both sides of the steel plate 101.

[0118] Here, the steel plate 101 of the pre-coated steel plate 20 in this embodiment has the same structure as the steel plate 101 of the pre-coated steel plate 10 described above, and performs the same effect. Therefore, detailed description is omitted below.

[0119] Furthermore, regarding the coating layer 201 of the pre-coated steel sheet 20 of this embodiment, with the formation of the chemical conversion treatment coating 203 (described later), interdiffusion of atoms contained in each layer may occur near the interface between the coating layer 201 and the chemical conversion treatment coating 203. However, the average chemical composition of the coating layer 201 is the same as that of the coating layer 103 in the pre-coated steel sheet 10 described previously, and it exerts the same effect. Therefore, detailed descriptions are omitted below.

[0120] It should be noted that the following describes the states of magnesium, aluminum metals, oxides and hydroxides exhibited by the coating layer 201 of the pre-coated steel sheet 20 in this embodiment.

[0121] <For chemical conversion treatment coating 203>

[0122] The chemical conversion treatment coating 203 in this embodiment is a coating layer located on the plating layer 201. It is a layer formed by chemical conversion treatment after removing impurities such as oil and surface oxides adhering to the surface of the pre-coated steel sheet 10 using known degreasing and washing processes.

[0123] The chemical conversion treatment coating 203 of this embodiment may contain any one or more selected from the group consisting of resin, silane coupling agent, zirconium compound, silica, phosphate and its salt, fluoride, vanadium compound, and tannin or tannic acid. By containing these substances, the film-forming properties after coating with the chemical conversion treatment solution, the barrier properties (density) of the coating against corrosive agents such as moisture and corrosive ions, and the adhesion of the coating to the plated surface are improved, which helps to improve the corrosion resistance of the coating.

[0124] In particular, if the chemically converted coating 203 contains any one or more of a silane coupling agent or a zirconium compound, a cross-linked structure is formed within the coating 203, thereby strengthening the bond with the plated surface. As a result, the adhesion and barrier properties of the coating can be further improved.

[0125] Furthermore, if the chemical conversion coating 203 contains any one or more of silicon dioxide, phosphate and its salts, fluorides, or vanadium compounds, these compounds function as inhibitors, forming a precipitated coating or a passivated coating on the plated or steel surface. As a result, corrosion resistance can be further improved.

[0126] The following examples illustrate the various components that the chemically converted coating 203 described above may contain.

[0127] [Resin]

[0128] As the resin, known organic resins such as polyester resin, polyurethane resin, epoxy resin, phenolic resin, acrylic resin, and polyolefin resin can be used. To further improve adhesion to the coated steel sheet used for pre-coated steel sheets, it is preferable to use at least one of the following resins (polyester resin, polyurethane resin, epoxy resin, acrylic resin, etc.) that have forced sites or polar functional groups in their molecular chains. The resin can be used alone or in combination of two or more.

[0129] The resin content in the chemical conversion coating 203 is preferably 0% by mass or more and 85% by mass or less relative to the coating solids content. More preferably, the resin content is 0% by mass or more and 60% by mass or less, and even more preferably 1% by mass or more and 40% by mass or less. When the resin content exceeds 85% by mass, the proportion of other coating components decreases, and the performance required for the coating, other than corrosion resistance, decreases.

[0130] [Silane coupling agent]

[0131] Examples of silane coupling agents include γ-(2-aminoethyl)aminopropyltrimethoxysilane, γ-(2-aminoethyl)aminopropylmethyldimethoxysilane, γ-(2-aminoethyl)aminopropyltriethoxysilane, γ-(2-aminoethyl)aminopropylmethyldiethoxysilane, γ-(2-aminoethyl)aminopropylmethyldimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, γ-methacryloyloxypropylmethyldimethoxysilane, γ-methacryloyloxypropyltriethoxysilane, γ-methacryloyloxypropylmethyldiethoxysilane, N-β-(N N-β-(N-vinylbenzylaminoethyl)-γ-aminopropyltrimethoxysilane, N-β-(N-vinylbenzylaminoethyl)-γ-aminopropylmethyldimethoxysilane, N-β-(N-vinylbenzylaminoethyl)-γ-aminopropyltriethoxysilane, N-β-(N-vinylbenzylaminoethyl)-γ-aminopropylmethyldiethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane γ-Methyldimethoxysilane, γ-mercaptopropyltriethoxysilane, γ-mercaptopropylmethyldiethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, vinyltriacetoxysilane, γ-chloropropyltrimethoxysilane, γ-chloropropylmethyldimethoxysilane, γ-chloropropyltriethoxysilane, γ-chloropropylmethyldiethoxysilane, hexamethyldisilazane, γ-anilinopropyltrimethoxysilane, γ-anilinopropylmethyldimethoxysilane, γ-anilinopropyltriethoxysilane, γ-anilinopropylmethyldiethoxysilane Vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, octadecyldimethyl[3-(trimethoxysilyl)propyl]ammonium chloride, octadecyldimethyl[3-(methyldimethoxysilyl)propyl]ammonium chloride, octadecyldimethyl[3-(triethoxysilyl)propyl]ammonium chloride, octadecyldimethyl[3-(methyldiethoxysilyl)propyl]ammonium chloride, γ-chloropropylmethyldimethoxysilane, γ-mercaptopropylmethyldimethoxysilane, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, etc. The amount of silane coupling agent added to the chemical conversion treatment agent used to form the chemical conversion treatment coating 203 can be set, for example, to 2–80 g / L. If the amount of silane coupling agent added is less than 2 g / L, the adhesion to the coating surface is insufficient, and the processing adhesion of the coating film may be reduced. In addition, when the amount of silane coupling agent added exceeds 80 g / L, the cohesion of the chemically converted coating is insufficient, and the processing tightness of the coating may be reduced.The silane coupling agents exemplified above can be used in combination of one or more types.

[0132] [Zirconium compounds]

[0133] Examples of zirconium compounds include zirconium n-propoxide, zirconium n-butyrate, zirconium tetraacetylacetone, zirconium monoacetylacetone, zirconium diacetylacetone, zirconium monoethylacetoacetate, zirconium diethylacetoacetate, zirconium acetate, zirconium monostearate, zirconium carbonate, ammonium zirconium carbonate, potassium zirconium carbonate, and sodium zirconium carbonate. The amount of zirconium compound added to the chemical conversion agent used to form the chemical conversion coating 203 can be, for example, set to 2–80 g / L. If the amount of zirconium compound added is less than 2 g / L, the adhesion to the coating surface is insufficient, and the processing adhesion of the coating may decrease. Furthermore, if the amount of zirconium compound added exceeds 80 g / L, the cohesion of the chemical conversion coating is insufficient, and the processing adhesion of the coating may decrease. The above-mentioned zirconium compounds can be used alone or in combination of two or more.

[0134] Silicon dioxide

[0135] As the silica, commercially available silica such as "Snowtex N", "Snowtex C", "Snowtex UP", and "Snowtex PS" manufactured by Nissan Chemical Co., Ltd., "ADELITE AT-20Q" manufactured by ADEKA Co., Ltd., or powdered silica such as Aerosil #300 manufactured by Nippon Aerosil Co., Ltd. can be used. The silica can be appropriately selected according to the required properties of the pre-coated steel sheet. The amount of silica added to the chemical conversion treatment agent used to form the chemical conversion treatment coating 203 is preferably set to 1 to 40 g / L. If the amount of silica added is less than 1 g / L, the processing adhesion of the coating may decrease; if the amount of silica added exceeds 40 g / L, the processing adhesion and corrosion resistance effects are likely to saturate, which is uneconomical.

[0136] Phosphate and its salts

[0137] Examples of phosphoric acids and their salts include phosphoric acids such as orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, tetraphosphoric acid, and their salts; ammonium salts such as triammonium phosphate and diammonium hydrogen phosphate; phosphonic acids such as aminotris(methylenephosphonic acid), 1-hydroxyethoxy-1,1-diphosphonic acid, ethylenediaminetetra(methylenephosphonic acid), and diethylenetriaminepenta(methylenephosphonic acid), and organic phosphoric acids such as phytic acid and their salts. It should be noted that, for phosphates, as salts other than ammonium salts, examples include metal salts containing Na, Mg, Al, K, Ca, Mn, Ni, Zn, and Fe. Phosphoric acids and their salts can be used alone or in combination of two or more.

[0138] It should be noted that the content of phosphate and its salts relative to the solid composition of the coating is preferably 0% by mass or more and 20% by mass or less. If the content of phosphate and its salts exceeds 20% by mass, the coating becomes brittle, and the processing adhesion of the coating during the forming process of the pre-coated steel sheet may be reduced. The content of phosphate and its salts is more preferably 1% by mass or more and 10% by mass or less.

[0139] [Fluorides]

[0140] Examples of fluorides include ammonium fluorozirconate, ammonium fluorosilicate, ammonium fluorotitanate, sodium fluoride, potassium fluoride, calcium fluoride, lithium fluoride, fluorotitanic acid, and fluorozirconic acid. These fluorides can be used alone or in combination of two or more.

[0141] It should be noted that the fluoride content is preferably 0% by mass or more and 20% by mass or less relative to the solid content of the coating. If the fluoride content exceeds 20% by mass, the coating becomes brittle, and the processing adhesion of the coating during the forming of the pre-coated steel sheet may be reduced. The fluoride content is more preferably 1% by mass or more and 10% by mass or less.

[0142] [vanadium compounds]

[0143] Examples of vanadium compounds include those obtained by reducing pentavalent vanadium compounds such as vanadium pentoxide, metavanadate, ammonium metavanadate, sodium metavanadate, and vanadium trichloride to valences of 2-4 using a reducing agent; and vanadium compounds with oxidation states of 4-2 such as vanadium trioxide, vanadium dioxide, vanadium oxysulfate, vanadium oxyoxalate, vanadium oxyacetylacetonate, vanadium acetylacetonate, vanadium trichloride, phosphomolybdic acid, vanadium sulfate, vanadium dichloride, and vanadium oxide. These vanadium compounds can be used alone or in combination of two or more.

[0144] It should be noted that the content of vanadium compounds relative to the solid composition of the coating is preferably 0% by mass or more and 20% by mass or less. If the content of vanadium compounds exceeds 20% by mass, the coating becomes brittle, and the processing adhesion of the coating during the forming and processing of the pre-coated steel sheet may be reduced. The content of vanadium compounds is more preferably 1% by mass or more and 10% by mass or less.

[0145] [Tannins or tannic acid]

[0146] Tannins or tannic acid can be any type of hydrolyzable tannin or condensed tannin. Examples of tannins and tannic acid include witch hazel tannin, gallnut tannin, gallnut tannin, Terminalia chebula tannin, senna tannin, algarovilla tannin, oak tannin, and catechin. The amount of tannin or tannic acid added to the chemical conversion agent used to form the chemical conversion coating 203 can be set to 2–80 g / L. If the amount of tannin or tannic acid added is less than 2 g / L, the adhesion to the coating surface is insufficient, and the processing adhesion of the coating may be reduced. In addition, if the amount of tannin or tannic acid added exceeds 80 g / L, the cohesion of the chemical conversion coating with insufficient processing adhesion is insufficient, and the processing adhesion of the coating may be reduced.

[0147] In addition, in the chemical conversion treatment agent used to form the chemical conversion treatment coating 203, acids, bases, etc., may be added to adjust the pH within a range that will not impair performance.

[0148] A chemical conversion treatment agent containing the various components described above is applied to one or both sides of the pre-coated steel sheet 10 and then dried to form a chemical conversion treatment coating 203. In this embodiment, the pre-coated steel sheet preferably contains 10 to 1000 mg / m² of chemical conversion treatment agent per side. 2 The chemical conversion coating is formed on a pre-coated steel sheet. The preferred adhesion amount of the chemical conversion coating 203 is 20–800 mg / m³. 2 The optimal concentration is 50–600 mg / m². 2 It should be noted that the film thickness of the chemical conversion treatment coating 203 corresponding to the above-mentioned adhesion amount ( Figure 3A and Figure 3B The thickness d2 in the process depends on the components contained in the chemical conversion treatment agent, but is approximately 0.01 to 1 μm.

[0149] <For coating 205>

[0150] In this embodiment, the coating 205 is a layer formed on the chemically converted coating 203 as described above. The coating 205 can be as follows: Figure 3A and Figure 3B It can be constructed in a single layer as shown schematically, or in multiple layers of two or more.

[0151] In this case, where the coating 205 is composed of two or more layers, the coating that comes into contact with the chemical conversion treatment coating 203 is also called the primer coating, and is mostly provided to ensure the integrity of the coating 205, the adhesion between the coating and the chemical conversion treatment coating 203, and the corrosion resistance. On the other hand, the coating located above the primer coating is also called the top coating, and is mostly provided to ensure the design, barrier properties, and other surface functions achieved by coloring.

[0152] In addition, when the coating 205 is composed of a single layer, the coating 205 is mostly set in a manner that exhibits at least one of the functions shown by the primer coating and the top coating.

[0153] The coating film 205 described above contains at least resin. Additionally, the coating film 205 preferably also contains pigments. Besides these components, the coating film 205 may also contain various additives such as leveling agents, defoamers, colorants, viscosity modifiers, and UV absorbers. It should be noted that the coating liquid used to form the coating film 205 is preferably obtained by dispersing or dissolving the above-mentioned components in a solvent.

[0154] In order to provide a more detailed description of the structure of the coating 205 of this embodiment, for convenience, the case in which the coating 205 is composed of a primer coating and a top coating will be given as an example for detailed description.

[0155] [Primer Coating]

[0156] The base coating for the primer film can be selected appropriately based on the usage environment and purpose of the pre-coated steel sheet. Commonly known resins can be used as the base coating. Examples of such resins include polyacrylic resins, polyolefin resins, polyurethane resins, epoxy resins, polyester resins, polybutyral resins, melamine resins, silicone resins, fluoropolymers, and acrylic resins. These resins can be used directly or in combination. Furthermore, these resins can be cured using any curing agent. For the base coating, any form, such as organic solvent-based, water-based, or powder-based, can be used.

[0157] The aforementioned base coating preferably contains rust-preventive pigments, and more preferably contains chromate-free rust-preventive pigments. The chromate-free rust-preventive pigments in the base coating may include calcium ion-exchanged silica (commonly known as calcium silicate), aluminum tripolyphosphate, vanadium phosphorus pigments (PV pigments), zinc phosphate, iron phosphate, aluminum phosphate, calcium molybdate, aluminum molybdate, barium molybdate, vanadium oxide, water-dispersible silica, fumed silica, orthophosphoric acid, pyrophosphoric acid, metaphosphoric acid, diphosphoric acid, phosphorous acid, hypophosphoric acid, and their salts. The content of the aforementioned rust-preventive pigments relative to the solid content of the coating film is preferably, for example, 5 to 70% by mass. If the content of the rust-preventive pigments is less than 5% by mass, in addition to the possibility that the corrosion resistance effect may not be adequately guaranteed, the coating rigidity and cohesion may decrease, and during the pressure processing of the coated steel sheet, the coating surface may easily peel off when rubbing against the mold (i.e., coating scuffing as physical peeling). Furthermore, if the content of the rust-preventive pigments exceeds 70% by mass, the processability may decrease. From the perspective of balancing corrosion resistance, chemical resistance and processability, the content of rust-preventive pigment is more preferably 15-70% by mass, and even more preferably 20-50% by mass.

[0158] As a curing agent, amino resins such as melamine resin, urea resin, and benzoguanamine resin, or isocyanate compounds and their end-capping agents are preferably used. The mass ratio of these curing agents to resins in the dried coating film is preferably 5 to 30 parts by mass of the curing agent, relative to 100 parts by mass of the total resin and curing agent. If the amount of curing agent is less than 5 parts by mass, the adhesion and corrosion resistance may not be fully realized; if it is more than 30 parts by mass, the processability and chemical resistance may decrease.

[0159] For pre-coated steel sheets, the thickness of the primer coating before forming is typically 2 μm or more and 10 μm or more. In this embodiment, the thickness of the primer coating is also preferably 2 to 10 μm. If the thickness of the primer coating is less than 2 μm, the required corrosion resistance and other functions for pre-coated steel sheets may not be fully realized. On the other hand, if the thickness of the primer coating exceeds 10 μm, the processability of the coating may decrease.

[0160] After applying a primer coating composition containing the components constituting the primer film as described above, the mixture is sintered at a temperature of 150°C or higher and below 300°C, and then cured and dried. If the sintering temperature is below 150°C, sufficient adhesion may not be guaranteed; if the sintering temperature is above 300°C, thermal degradation of the resin components may occur, potentially reducing processability.

[0161] It should be noted that the application of the primer coating composition described above can be carried out using commonly known coating methods, such as roller coating, curtain flow coating, air spraying, airless spraying, dipping, bar coating, brush coating, etc.

[0162] [Top Coating]

[0163] The base coating for the top coat can be selected appropriately based on the usage environment and purpose of the pre-coated steel sheet. Commonly known resins can be used as the base coating. Examples of such resins include polyacrylic resins, polyolefin resins, polyurethane resins, epoxy resins, polyester resins, polybutyral resins, melamine resins, silicone resins, fluoropolymers, and acrylic resins. These resins can be used directly or in combination. Furthermore, these resins can be cured using any curing agent. For the base coating, any form, such as organic solvent-based, water-based, or powder-based, can be used. It should be noted that the type of resin contained in the base coating of the top coat can be the same as or different from the type of resin contained in the base coating of the primer. However, considering the adhesion between the primer and the top coat, it is preferable to use resins of the same type.

[0164] In applications with more demanding forming and processing requirements, the base coating preferably contains a polymeric polyester resin and a curing agent. The polymeric polyester resin can be selected depending on the intended use of the pre-coated steel sheet; generally, any polymeric polyester resin used as a solvent-based coating can be used. The preferred polymeric polyester resin is one in which the main resin is composed of ester bonds between two or more resin monomers.

[0165] As a curing agent for forming a thermosetting resin coating film by reacting with the aforementioned polymeric polyester resin, amino resins such as melamine resin, urea resin, and benzoguanamine resin, or isocyanate compounds and their end-capping forms can be used. The mass ratio of these curing agents to resin in the dried coating film is preferably 10 to 35 parts by mass of the curing agent, relative to 100 parts by mass of the total resin and curing agent. If the amount of curing agent is less than 10 parts by mass, adhesion, corrosion resistance, solvent resistance, etc., may not be adequately guaranteed; if it exceeds 35 parts by mass, processability, chemical resistance, and impact resistance may decrease.

[0166] In addition, the top coating may contain pigments, surface-modified metal powders, glass powders, dispersants, leveling agents, waxes, aggregates, fluoropolymer beads and other additives, as well as diluents, as needed.

[0167] The thickness of the top coating before forming is preferably in the range of 5 to 25 μm. When the top coating is composed of multiple layers, the total film thickness is preferably in the range of 5 to 25 μm.

[0168] After the coating composition for the top coat is applied, it is sintered and cured at a temperature above 150°C and below 300°C. If the sintering temperature is below 150°C, the adhesion of each coating film may not be adequately guaranteed. If the sintering temperature is above 300°C, thermal degradation of the resin components, represented by the polyester resin component, may occur, and the processability may be reduced.

[0169] It should be noted that the base coat can be applied using commonly known coating methods, such as roller coating, curtain flow coating, air spraying, airless spraying, dipping, bar coating, brush coating, etc.

[0170] The above description of the chemical conversion coating, primer coating, and top coating of this embodiment uses the chemical conversion agent and coating composition used to form each film. Typically, when these agents and compositions are applied to galvanized steel sheets, the composition of these components and the resulting coating are usually different. For example, with chemical conversion agents, due to reactions with the galvanized steel sheet and the volatilization of volatile components in the chemical conversion agent, the composition of the chemical conversion agent differs from that of the applied chemical conversion coating, making it technically difficult to determine the composition of a specific chemical conversion coating layer. Furthermore, in practice, it is technically difficult to determine the composition of such a chemical conversion coating layer through machine analysis. The same applies to the primer coating and top coating. Therefore, in this embodiment, the chemical conversion coating, primer coating, and top coating are specifically formed by specifying the composition of the chemical conversion agent and coating composition.

[0171] <State of magnesium and aluminum at the coating interface>

[0172] Based on the findings described above, for the pre-coated steel sheet 20 of this embodiment, the states of magnesium, aluminum metals, oxides, and hydroxides at the interface of the coating layer 201 (more specifically, the interface between the coating layer 201 and the chemical conversion treatment coating 203) are specified.

[0173] In this embodiment, as Figure 4 As schematically shown, at "position B" located at a depth of 10 nm from the interface between the coating layer 201 and the chemical conversion treatment film 203 toward the inside of the coating layer 201, the states of specific magnesium, aluminum metals, oxides, and hydroxides are defined as the states of these substances at the interface of the coating layer 201.

[0174] In this embodiment, the position of the interface between the plating layer 201 and the chemical conversion treatment coating 203 can be specified by the elemental distribution in the depth direction of the pre-coated steel sheet obtained by XPS analysis of the pre-coated steel sheet. That is, in this embodiment, the elements contained in the chemical conversion treatment coating 203 are designated as markers, and the interface between the plating layer 201 and the chemical conversion treatment coating 203 is defined where the intensity of the marker element is halved relative to the depth direction.

[0175] Here, the XPS measurement conditions used for depth distribution analysis and the state analysis conditions used for magnesium, aluminum metals, oxides and hydroxides are the same as those used for the XPS measurement conditions of the pre-coated steel sheet 10 shown previously.

[0176] Specifically, the state analysis of magnesium, aluminum, and their oxides and hydroxides was performed using XPS. The XPS analysis was conducted using a ULVAC-PHI, INCORRORATE, Quantum 2000 model, configured with an Al Kα X-ray source, an X-ray output power of 15 kV and 25 W, a measurement range of 300 × 300 μm square, and a vacuum level of 1.5 × 10⁻⁶. -9 Torr, detection accuracy: 45°. Additionally, the sputtering setting for depth distribution analysis is Ar ion species. + Accelerating voltage: 1kV, range: 1×1mm, sputtering rate: 2.7nm / min (SiO2 conversion). Sputtering is performed based on the above sputtering rate, and the specific sputtered location is regarded as "position B".

[0177] Here, the attribution of magnesium oxides and hydroxides, and the proportion of metallic magnesium (presence ratio) is separated by 295–325 cm⁻¹ based on Mg KLL. -1 The narrow spectrum is calculated from the intensity ratio of the peaks attributed to each substance (oxide, hydroxide, metal). Similarly, the attribution and separation of aluminum oxides and hydroxides, and the proportion of metallic aluminum (presence ratio), are determined by the 68–84 cm⁻¹ spectrum based on Al 2p. -1 The narrow spectrum is calculated from the intensity ratio of the peaks attributed to each substance (oxide, hydroxide, metal).

[0178] In this embodiment, the interface of the coating layer 201 has a depth of 10 nm at a specific distance from the interface of the coating layer, as described above. Figure 4The ratio of magnesium oxide and hydroxide at position B) is 0.30 or less relative to metallic magnesium. By ensuring that the ratio of magnesium oxide and hydroxide relative to metallic magnesium is 0.30 or less, good coating adhesion of the forming section is achieved even during deep drawing of the pre-coated steel sheet 20 of this embodiment, suppressing the formation of coating lift-off portions. On the other hand, if the ratio of magnesium oxide and hydroxide exceeds 0.30, good coating adhesion of the forming section cannot be achieved, and the formation of coating lift-off portions cannot be suppressed. The ratio of magnesium oxide and hydroxide relative to metallic magnesium is preferably 0.25 or less, more preferably 0.20 or less. Furthermore, the lower limit of the ratio of magnesium oxide and hydroxide relative to metallic magnesium is substantially around 0.01.

[0179] Furthermore, in this embodiment, the interface of the coating layer 201 has a depth of 10 nm at a specific distance from the interface of the coating layer, as described above. Figure 4 The ratio of aluminum oxides and hydroxides at position B) relative to the ratio of metallic aluminum is preferably 0.30 or less. By having an aluminum oxide and hydroxide content of 0.30 or less relative to metallic aluminum, even when the pre-coated steel sheet 20 of this embodiment is deep-drawn, better coating adhesion of the forming section is achieved, and the formation of coating lift-off portions can be more effectively suppressed. On the other hand, if the aluminum oxide and hydroxide content exceeds 0.30, better coating adhesion of the forming section may not be achieved. The aluminum oxide and hydroxide content relative to metallic aluminum is more preferably 0.25 or less, and even more preferably 0.20 or less. Furthermore, the upper limit of the aluminum oxide and hydroxide content relative to metallic aluminum is substantially around 0.01, which is the lower limit.

[0180] Here, measurements were performed on a range of 300 μm × 300 μm using XPS, and the proportion of presence calculated as described above refers to the average value of the measurement range as described above.

[0181] Reference above Figures 3A-4 At the same time, the pre-coated steel plate 20 of this embodiment will be described in detail.

[0182] (For finished products)

[0183] Next refer to Figure 5 At the same time, a detailed description is given of the molded products using the pre-coated steel sheet 20 as described above.

[0184] like Figure 5As illustrated in the illustration, the molded article 30 of this embodiment is formed by performing various processes such as deep drawing and square tube pressing on the pre-coated steel sheet 20 as described above to form a desired shape.

[0185] Here, the average chemical composition of the coating layer of the molded article 30 of this embodiment is the same as that of the coating layer 201 of the pre-coated steel sheet 20 from which it originated, and therefore contains 0.5 to 60.0% by mass of aluminum and 0.5 to 15.0% by mass of magnesium. Preferably, the coating layer of the molded article 30 of this embodiment contains 5% by mass or more and 15% by mass of aluminum and 2% by mass or more and 4% by mass of magnesium. By containing aluminum and magnesium in the coating layer of the molded article 30 in the aforementioned amounts, the desired corrosion resistance can be achieved more reliably. It should be noted that the balance in the coating layer of the molded article 30 other than the aforementioned aluminum and magnesium consists of elements, zinc, and impurities originating from the external environment.

[0186] The specific shape of the molded article 30 in this embodiment can be exemplified by various shapes of various components, such as those of items mainly used outdoors, such as air conditioner outdoor units and water heaters.

[0187] The processing method for forming a molded article from the pre-coated steel sheet 20 of this embodiment can employ various known methods. Furthermore, the processing conditions can be appropriately set according to the processing method used, the shape of the molded article, etc.

[0188] The processing of the top plate of an air conditioner outdoor unit, an example of such a molded product, is a demanding forming process for the pre-coated steel sheet 20. The degree of processing varies depending on the air conditioning company, but all processes involve high-speed cylindrical pressurization to form the top plate of the outdoor unit. The four corners of the top plate contain both compressed and elongated portions. When using conventional pre-coated steel sheets, coating blistering frequently occurs in the compressed portions, and coating peeling frequently occurs in the elongated portions.

[0189] However, when using the pre-coated steel sheet 20 of this embodiment as raw material, the states of magnesium, aluminum metals, oxides and hydroxides at the coating interface of the pre-coated steel sheet 20 are properly controlled, thus more effectively suppressing the generation of coating lift-off and coating peeling.

[0190] <For the measured values ​​obtained using the SAICAS method>

[0191] For molded articles formed from the pre-coated steel sheet of this embodiment, the peel strength and peel condition of the aforementioned portion are specified by measuring a specific portion using the SAICAS method.

[0192] Figure 5 The example shown is a molded article of this embodiment in which the thickness of the pre-coated steel sheet of the molded article increases by more than 5% compared to the thickness d before molding (which can also be regarded as the non-molding part). Figure 5 In this context, for example, the portion enclosed by a dashed line (where the thickness is set to d', and the relationship (d'-d) / d≥0.05 holds true) represents the portion where the coated steel sheet is compressed and stretched during processing, with the compression exceeding the stretch. This portion, where the thickness increases by more than 5%, will be referred to as the "compressed portion." This compressed portion is where the coating is prone to lifting in the molded product.

[0193] For the portion of the pre-coated steel sheet in the molded article of this embodiment where the thickness increases by more than 5% compared to before molding (i.e., the compressed portion), the peel strength between the chemical conversion coating and the coating film (or primer film if the coating film consists of multiple layers) was measured using the SAICAS method and was at least 1.00 kN / m on average. Furthermore, when the compressed portion was cut using the SAICAS method, less than 20% of the cut area resulted in interfacial peeling, while the remaining cut area resulted in cohesive failure within the coating film (or primer film if the coating film consists of multiple layers). If the compressed portion does not meet all the conditions for peel strength and peel area described above, the chemical conversion coating is destroyed during the compression process, thereby reducing adhesion. Furthermore, the internal stress of the coating film concentrates at the interface between the chemical conversion coating and the coating film (or primer film if the coating film consists of multiple layers), or at the interface between the chemical conversion coating and the plating layer. As a result, the coating adhesion is insufficient during compression processing in the portion with the lowest adhesion strength, leading to coating lifting.

[0194] It should be noted that if the thickness of the pre-coated steel sheet in the formed product increases by more than 5% compared with that before forming, no significant difference was found in the test results using the SAICAS method due to this % difference.

[0195] In the molded article of this embodiment, the peel strength obtained by the SAICAS method is preferably 1.10 kN / m or more on average, and more preferably 1.20 kN / m or more. It should be noted that the higher the upper limit of the above peel strength, the better. The peel strength is essentially around 1.5 kN / m as the upper limit.

[0196] Furthermore, regarding the cutting area of ​​the compressed portion obtained by the SAICAS method in the molded article of this embodiment, the proportion of the portion forming an interface delamination state is preferably 15% or less, more preferably 10% or less. It should be noted that the lower limit of the proportion of the portion forming an interface delamination state is better. The lower limit is essentially 0%.

[0197] [Methods for determining peel strength and peel morphology using the SAICAS method]

[0198] The peel strength and peel morphology of the molded articles in question, which use pre-coated steel sheets, are determined using the SAICAS method as follows.

[0199] First, for the molded article under consideration, specifically at least three flat areas in the non-forming processing region, the total thickness (including the plated steel sheet of the substrate and the coating on the front and back sides) of each flat area is measured three times using a micrometer, and the average value is calculated. This measurement is then performed at multiple specific locations, and the average value between these locations is calculated. This average value between multiple locations is set as the thickness of the pre-coated steel sheet in the molded article before forming (e.g., the thickness of the pre-coated steel sheet before forming). Figure 5 The thickness d in the middle).

[0200] In addition, test samples (approximately 20mm x 20mm or larger) are cut from the parts where various forming processes such as deep drawing are considered to be performed, and smoothed using a steel plate straightener. The total thickness of the obtained test samples (including the plated steel sheet of the substrate and the coating on both sides) is measured using a micrometer. Based on the measured value and the thickness of the pre-coated steel sheet obtained as described above before forming, the increase ratio is calculated. The portion of the increase ratio thus obtained that shows a value of 5% or more is designated as the compression portion of the formed article. It should be noted that in various forming processes, such as deep drawing, approximately 11% is considered an upper limit for the aforementioned increase ratio.

[0201] For such a specific compressed portion, the peel strength and peel morphology of the coating are simultaneously cut and measured using a measuring device capable of utilizing the SAICAS method (e.g., DN-GS type manufactured by DAIPLA WINTESCO.,LTD.). It should be noted that the cutting direction in the SAICAS method is parallel to the end line of the drawn steel sheet.

[0202] It should be noted that the increase rate calculated using the method described above is not different from the value calculated by measuring the thickness of the substrate within the range described above, before and after forming of the pre-coated steel sheet, in a state where the coating has been removed from the surface and back of the pre-coated steel sheet before and after forming using a coating stripper.

[0203] The cutting conditions using the SAICAS method are as follows.

[0204] Using a diamond cutting edge (0.3 mm width) as the cutting tool, a constant speed mode of 1 μm / sec horizontally and 0.1 μm / sec vertically was employed for inclined cutting. Near the interface, the cutting was switched to horizontal movement only, cutting a length of 200 μm. The average peel strength during this horizontal movement was measured. The depth position for switching to horizontal movement was set using a pre-experimental specific interface position (a position where there is no limit to cutting the coating). Cases where the coating surface is cut due to unevenness during the horizontal movement of the cutting tool can be identified due to an anomalous instantaneous increase in peel strength. This case was excluded as an outlier, and the average peel strength was calculated. It should be noted that the number of measurements was set to n=3, and the average of the three average peel strength values ​​was taken as the peel strength.

[0205] The method for determining the ratio of interface peeling morphology and cohesive failure morphology of the cutting part during horizontal movement is as follows.

[0206] If the surface of the cut portion obtained using the SAICAS method is observed using an optical microscope, the different peeling morphologies of each part can be clearly distinguished. (A) In the case where an extremely thin coating film remains in the cut portion, coloration caused by resin and pigment in the coating film is observed, so the peeling morphology can be determined as thin-layer cohesive failure within the coating film. (B) In the case of interfacial peeling in the cut portion, the appearance of the plated surface of the substrate is observed. Even when light is irradiated onto the above part, no strong reflection is observed, resulting in a blackened appearance. In addition, in the case of interfacial peeling, the local reduction in peel strength obtained using the SAICAS method is also a criterion. This is because the cutting tool moves within the coating film directly above the interface, but the adhesion force of the interface is lower than the cohesive force of the coating film, so the peeling position moves to the interface, resulting in interfacial peeling. (C) In the case of cohesive failure of the plating layer in the cut portion, a metallic luster is observed, and strong reflection occurs when light is irradiated onto the above part, so it is easily distinguished from interfacial peeling. In addition, the local increase in peel strength obtained using the SAICAS method is also a criterion.

[0207] Optical microscope images (300 μm × 200 μm) of the horizontal cutting area obtained using the SAICAS method were taken. The areas of cohesive failure, interfacial peeling, and coating cohesive failure within the same area as the aforementioned judgment reference were identified, and their areas were measured using image processing software or transparent graph paper. The ratio of the area of ​​interfacial peeling to the area of ​​the horizontal cutting area obtained by the SAICAS method, excluding coating cohesive failure, was then calculated.

[0208] Reference above Figure 5 At the same time, the molded article of this embodiment will be described in detail.

[0209] As explained above, according to this embodiment, by using the pre-coated steel sheet of this embodiment, a molded body formed from the pre-coated steel sheet and the pre-coated steel sheet can be obtained in which no coating float or coating peeling occurs in the processing part such as deep drawing.

[0210] Implementation Method 2

[0211] (For pre-coated steel sheets)

[0212] First refer to Figures 1A-2 At the same time, the pre-coated steel sheet for pre-coated steel sheet according to the second embodiment of the present invention will be described in detail.

[0213] like Figure 1A As schematically shown, the pre-coated steel sheet 10 of this embodiment has a steel sheet 101 as a substrate and a coating layer 103 located on one side of the steel sheet. Furthermore, the pre-coated steel sheet 10 of this embodiment, as... Figure 1B As schematically shown, the coating 103 can be located on both sides of the steel plate 101 that serves as the substrate.

[0214] <For steel plate 101>

[0215] The steel sheet 101 used as the substrate of the pre-coated steel sheet 10 for pre-coated steel sheet in this embodiment has the same structure and performs the same effect as the steel sheet 101 in the pre-coated steel sheet 10 of the first embodiment. Therefore, detailed descriptions are omitted below.

[0216] <Regarding plating layer 103>

[0217] The coating layer 20 in this embodiment is as follows: Figure 1A and Figure 1B As schematically shown, a layer is formed on at least one side of the steel plate 101, which is provided to improve the corrosion resistance of the pre-coated steel plate 10. Here, the coating layer 103 of this embodiment has the same structure and performs the same effect as the coating layer 103 of the pre-coated steel plate 10 of the first embodiment in terms of chemical composition. Therefore, detailed description is omitted below.

[0218] [Regarding the average film thickness of coating 103]

[0219] Furthermore, in the pre-coated steel sheet 10 of this embodiment, the average film thickness of the coating layer 103 ( Figure 1A and Figure 1B The thickness d1 in the figure is the same as in the first embodiment, so detailed descriptions are omitted below.

[0220] <State of zinc on the coating surface>

[0221] Based on the findings described above, for the plating layer 103 of this embodiment, the state of zinc metal, oxide and hydroxide in the surface of the plating layer 103 is specified.

[0222] Here, on the surface of the plating layer 103, in addition to zinc metal, oxides, hydroxides, etc., various unexpected impurities may also be present. Therefore, in this embodiment, as... Figure 2 As schematically shown, at "position A" located at a depth of 10 nm from the surface of the plating layer 103, the state of the metal, oxide, and hydroxide of a specific zinc is defined as the state of these substances on the surface of the plating layer 103.

[0223] The state analysis of zinc metal, oxides, and hydroxides was performed using XPS. XPS analysis was conducted using a ULVAC-PHI, INCORRORATE, Quantum 2000 model, configured with an Al Kα X-ray source, an X-ray output power of 15 kV and 25 W, a measurement range of 300 × 300 μm square, and a vacuum level of 1.5 × 10⁻⁶. -9 Torr, detection accuracy: 45°. Additionally, the sputtering setting for depth distribution analysis is Ar ion species. + Accelerating voltage: 1kV, range: 1×1mm, sputtering rate: 2.7nm / min (SiO2 conversion). Sputtering is performed based on the above sputtering rate, and the specific sputtered location is regarded as "location A".

[0224] Here, the attribution of zinc oxides and hydroxides, and the proportion of metallic zinc (presence ratio) is separated by using Zn 2p as a basis for the 480–515 cm⁻¹. -1 The narrow spectrum is calculated from the intensity ratio of the peaks attributed to each substance (oxide, hydroxide, metal).

[0225] In the plating layer 103 of this embodiment, the depth is 10 nm away from the surface of the plating layer as described above. Figure 2The ratio of zinc oxide to hydroxide at position A) is 7.0 or more relative to metallic zinc. With a zinc oxide to hydroxide ratio of 7.0 or more relative to metallic zinc, even when the pre-coated coated steel sheet using the pre-coated steel sheet coated steel sheet 10 with the coating layer 103 of this embodiment is deep-drawn, good coating adhesion of the forming process is achieved, and the formation of coating lift-off portions can be suppressed. On the other hand, if the zinc oxide to hydroxide ratio is less than 7.0, good coating adhesion of the forming process cannot be exhibited, and the formation of coating lift-off portions cannot be suppressed. The zinc oxide to hydroxide ratio relative to metallic zinc is preferably 8.0 or more, more preferably 9.0 or more. Furthermore, the upper limit of the zinc oxide to hydroxide ratio relative to metallic zinc is substantially around 20.0.

[0226] Here, measurements were performed on a range of 300 μm × 300 μm using XPS, and the proportion of presence calculated as described above refers to the average value of the measurement range as described above.

[0227] Reference above Figures 1A-2 At the same time, the pre-coated steel sheet 10 for the steel sheet of this embodiment will be described in detail.

[0228] The pre-coated steel sheet 10 of this embodiment, as described above, can be manufactured as follows: First, the surface of the prepared steel sheet 101 is subjected to pretreatment such as washing and degreasing as needed. Then, the steel sheet 101, which has undergone pretreatment as needed, is subjected to a conventional hot-dip galvanizing method in an oxidation-free furnace to form a coating layer.

[0229] Next, the steel sheet with the coating is subjected to a post-processing step using at least one of acid treatment, alkali treatment, or mechanical cutting. This modifies or removes the surface of the coating, thereby satisfying the previously discussed conditions regarding XPS spectroscopy.

[0230] Here, a hot-dip galvanizing bath with the desired chemical composition is prepared (i.e., a hot-dip galvanizing bath containing at least Al: 0.5–60.0% by mass, Mg: 0.5–15.0% by mass, and the balance being Zn and impurities), and the bath temperature is controlled at approximately 450°C. The resulting steel sheet 101 is then immersed in the galvanizing bath, and hot-dip galvanization is applied to the surface of the steel sheet in a manner that forms a desired average film thickness. The cooling rate after galvanizing is then controlled at 10°C / second or higher. This allows the galvanized layer to be formed.

[0231] The coating layer obtained as described above is subjected to XPS spectrum measurement using an XPS analysis apparatus set under the aforementioned measurement conditions. The surface of the coating layer is then modified or removed using various methods such as acid treatment, alkali treatment, and mechanical cutting until the previously mentioned XPS spectrum conditions are met. Thus, the pre-coated steel sheet 10 of this embodiment, having the coating layer 103 described above, can be manufactured.

[0232] The applicable alkaline treatment, acid treatment, and mechanical cutting treatment can be any one of these, or various combinations of these treatments can also be used.

[0233] For example, in the case of alkaline treatment, there is a tendency for a higher alkaline concentration and a longer treatment time to result in a higher proportion of zinc oxides and hydroxides on the plating surface. For instance, when using a commercially available standard sodium orthosilicate-based (medium-alkaline) degreasing solution sprayed at 50°C, the proportion of zinc oxides and hydroxides on the plating surface does not meet the specified conditions when the spraying time is less than 10 seconds. However, extending the spraying time meets the conditions, and extending it to about 2 minutes reliably meets the conditions. Furthermore, if the concentration of the degreasing solution is doubled, the conditions are reliably met when the spraying time is about 30 seconds. The reason is unclear, but it is believed that alkaline treatment causes the metallic zinc to dissolve, transform into oxides or hydroxides, and potentially redeposit on the plating surface.

[0234] Furthermore, in the case of acid treatment, unlike alkaline treatment, the above treatment exhibits the effect of removing zinc oxides and hydroxides from the surface of the plating layer. Therefore, by performing treatment under conditions that reduce the degree of removal of contaminants adhering to the plating surface, the desired conditions can be obtained. For example, when spraying with 5% sulfuric acid at 50°C, by setting the spraying time to approximately 5 to 10 seconds, the ratio of zinc oxides and hydroxides present on the plating layer surface can meet the desired conditions. However, prolonged spraying will not meet the requirements.

[0235] Furthermore, when mechanical cutting is performed, the above-mentioned treatment exhibits the effect of removing any one of the zinc metal, oxides, and hydroxides from the surface of the plating layer. Therefore, it is preferable to use a nylon brush, a grinding wheel of appropriate grit, etc., to perform the treatment under conditions where the removal of contaminants adhering to the plating surface is minimal. After mechanical cutting, the cutting contaminants are removed by rinsing with water.

[0236] Examples of various processing methods have been described above, and the conditions for each processing method vary depending on the initial oxidation state of the coating layer on the steel sheet used. Therefore, the pre-coated steel sheet 10 for pre-coated steel sheet of this embodiment can be manufactured by appropriately selecting the most suitable conditions.

[0237] (For pre-coated steel sheets)

[0238] Next, refer to Figures 3A-4 At the same time, a detailed description is given of the pre-coated steel sheet 10 for use with the pre-coated steel sheet described above.

[0239] like Figure 3A As schematically shown, the pre-coated steel sheet 20 of this embodiment uses the pre-coated steel sheet 10 for pre-coated steel sheets as previously described, as the substrate. The pre-coated steel sheet 20 includes a steel sheet 101, a coating layer 201 on one side of the steel sheet 101, a chemical conversion coating 203 on the coating layer 201, and a coating film 205 on the chemical conversion coating 203. Furthermore, the pre-coated steel sheet 20 of this embodiment... Figure 3B As schematically shown, a plating layer 201, a chemical conversion coating 203, and a coating 205 can be formed on both sides of the steel plate 101.

[0240] Here, the steel plate 101 in the pre-coated steel plate 20 of this embodiment has the same structure and performs the same effect as the steel plate 101 in the previously described pre-coated steel plate 10. Therefore, detailed descriptions are omitted below.

[0241] Furthermore, regarding the plating layer 201 in the pre-coated steel sheet 20 of this embodiment, with the formation of the chemical conversion treatment coating 203 (described later), interdiffusion of atoms contained in each layer may occur near the interface between the plating layer 201 and the chemical conversion treatment coating 203. However, the average chemical composition of the plating layer 201 is the same as that of the plating layer 103 in the pre-coated steel sheet 10 described previously, and it exerts the same effect. Therefore, detailed descriptions are omitted below.

[0242] It should be noted that the following describes the state of zinc metal, oxide and hydroxide exhibited by the coating layer 201 of the pre-coated steel sheet 20 in this embodiment.

[0243] <For chemical conversion treatment coating 203>

[0244] The chemical conversion treatment coating 203 in this embodiment is a coating layer located on the plating layer 201. It is a layer formed by chemical conversion treatment after removing impurities such as oil and surface oxides adhering to the surface of the pre-coated steel sheet 10 using known degreasing and washing processes.

[0245] The detailed structure of the chemical conversion treatment coating 203 in this embodiment is the same as that in the first embodiment, and it performs the same effects. Therefore, detailed descriptions are omitted below.

[0246] <For coating 205>

[0247] In this embodiment, the coating 205 is a layer formed on the chemically converted coating 203 as described above. The coating 205 can be as follows: Figure 3A and Figure 3B As schematically shown, it can be constructed using a single layer or multiple layers of two or more. Here, the detailed structure of the coating 205 in this embodiment is the same as in the first embodiment, and it achieves the same effects. Therefore, detailed descriptions are omitted below.

[0248] <State of zinc at the coating interface>

[0249] Based on the findings described above, for the pre-coated steel sheet 20 of this embodiment, the state of zinc metal, oxide and hydroxide at the interface of the coating layer 201 (more specifically, the interface between the coating layer 201 and the chemical conversion treatment coating 203) is specified.

[0250] In this embodiment, as Figure 4 As schematically shown, at "position B" located at a depth of 10 nm from the interface between the coating layer 201 and the chemical conversion coating 203 toward the inner side of the coating layer 201, the state of the metal, oxide, and hydroxide of a specific zinc is defined as the state of these substances at the interface of the coating layer 201.

[0251] In this embodiment, the position of the interface between the plating layer 201 and the chemical conversion treatment coating 203 can be specified by the elemental distribution in the depth direction of the pre-coated steel sheet obtained by XPS analysis of the pre-coated steel sheet. That is, in this embodiment, the elements contained in the chemical conversion treatment coating 203 are designated as markers, and the interface between the plating layer 201 and the chemical conversion treatment coating 203 is defined where the intensity of the marker element is halved relative to the depth direction.

[0252] Here, the XPS measurement conditions used for depth distribution analysis and the measurement conditions used for the state analysis of zinc metal, oxides and hydroxides are the same as those used for the XPS measurement of the pre-coated steel sheet 10 shown previously.

[0253] Specifically, the state analysis of zinc metal, oxides, and hydroxides was performed using XPS. The XPS analysis was conducted using a ULVAC-PHI, INCORRORATE, Quantum 2000 model, configured with an Al Kα X-ray source, an X-ray output power of 15 kV and 25 W, a measurement range of 300 × 300 μm square, and a vacuum level of 1.5 × 10⁻⁶. -9 Torr, detection accuracy: 45°. Additionally, the sputtering setting for depth distribution analysis is Ar ion species. +Accelerating voltage: 1kV, range: 1×1mm, sputtering rate: 2.7nm / min (SiO2 conversion). Sputtering is performed based on the above sputtering rate, and the specific sputtered location is regarded as "position B".

[0254] Here, the attribution of zinc oxides and hydroxides, and the proportion of metallic zinc (presence ratio) is separated by using Zn 2p as a basis for the 480–515 cm⁻¹. -1 The narrow spectrum is calculated from the intensity ratio of the peaks attributed to each substance (oxide, hydroxide, metal).

[0255] In this embodiment, the interface of the coating layer 201 has a depth of 10 nm at a specific distance from the interface of the coating layer, as described above. Figure 4 The ratio of zinc oxide to hydroxide at position B) relative to metallic zinc is 7.0 or more. With a zinc oxide to hydroxide ratio of 7.0 or more relative to metallic zinc, good coating adhesion of the forming section is achieved even during deep drawing of the pre-coated steel sheet 20 of this embodiment, suppressing the formation of coating lift-off portions. On the other hand, if the zinc oxide to hydroxide ratio is less than 7.0, good coating adhesion of the forming section cannot be achieved, and the formation of coating lift-off portions cannot be suppressed. The zinc oxide to hydroxide ratio relative to metallic zinc is preferably 8.0 or more, more preferably 9.0 or more. Furthermore, the upper limit of the zinc oxide to hydroxide ratio relative to metallic zinc is substantially around 20.0.

[0256] Here, measurements were performed on a range of 300 μm × 300 μm using XPS, and the proportion of presence calculated as described above refers to the average value of the measurement range as described above.

[0257] Reference above Figures 3A-4 At the same time, the pre-coated steel plate 20 of this embodiment will be described in detail.

[0258] (For finished products)

[0259] Next refer to Figure 5 At the same time, a detailed description is given of the molded products using the pre-coated steel sheet 20 as described above.

[0260] like Figure 5 As illustrated in the illustration, the molded article 30 of this embodiment is formed by performing various processes such as deep drawing and square tube pressing on the pre-coated steel sheet 20 as described above to form a desired shape.

[0261] Here, the average chemical composition of the coating layer of the molded article 30 of this embodiment is the same as that of the coating layer 201 of the pre-coated steel sheet 20 from which it originated, and therefore contains 0.5 to 60.0% by mass of aluminum and 0.5 to 15.0% by mass of magnesium. Preferably, the coating layer of the molded article 30 of this embodiment contains 5% by mass or more and 15% by mass of aluminum and 2% by mass or more and 4% by mass of magnesium. By containing aluminum and magnesium in the coating layer of the molded article 30 in the aforementioned amounts, the desired corrosion resistance can be achieved more reliably. It should be noted that the balance in the coating layer of the molded article 30 other than the aforementioned aluminum and magnesium consists of elements, zinc, and impurities originating from the external environment.

[0262] The specific shape of the molded article 30 in this embodiment can be exemplified by various shapes of various components, such as those of items mainly used outdoors, such as air conditioner outdoor units and water heaters.

[0263] The processing method for forming a molded article from the pre-coated steel sheet 20 of this embodiment can employ various known methods. Furthermore, the processing conditions can be appropriately set according to the processing method used, the shape of the molded article, etc.

[0264] The processing of the top plate of an air conditioner outdoor unit, an example of such a molded product, is a demanding forming process for the pre-coated steel sheet 20. The degree of processing varies depending on the air conditioning company, but all processes involve high-speed cylindrical pressurization to form the top plate of the outdoor unit. The four corners of the top plate contain both compressed and elongated portions. When using conventional pre-coated steel sheets, coating blistering frequently occurs in the compressed portions, and coating peeling frequently occurs in the elongated portions.

[0265] However, when using the pre-coated steel sheet 20 of this embodiment as raw material, the state of zinc metal, oxide and hydroxide at the coating interface of the pre-coated steel sheet 20 is properly controlled, so the generation of coating lift-off and coating peeling can be suppressed more effectively.

[0266] <For the measured values ​​obtained using the SAICAS method>

[0267] For the molded article formed from the pre-coated steel sheet of this embodiment, the peel strength and peel condition of the aforementioned portion are specified by measuring a specific portion using the SAICAS method. Here, the measurement method using the SAICAS method and the conditions required for obtaining the measured values ​​are the same as those described in the first embodiment, therefore detailed descriptions are omitted below.

[0268] As explained above, according to this embodiment, by using the pre-coated steel sheet of this embodiment, a molded body formed from the pre-coated steel sheet and the pre-coated steel sheet can be obtained in which no coating float or coating peeling occurs in the processing part such as deep drawing.

[0269] Third Implementation Method

[0270] The third embodiment of the present invention shown below is an embodiment that considers both the state of zinc oxide and hydroxide on the surface of the plated steel sheet and the state of aluminum and magnesium oxide and hydroxide on the surface of the plated steel sheet.

[0271] (For pre-coated steel sheets)

[0272] like Figure 1A As schematically shown, the pre-coated steel sheet 10 of this embodiment has a steel sheet 101 as a substrate and a coating layer 103 located on one side of the steel sheet. Furthermore, the pre-coated steel sheet 10 of this embodiment, as... Figure 1B As schematically shown, the coating 103 can be located on both sides of the steel plate 101 that serves as the substrate.

[0273] Here, the steel plate 101 used as the substrate of the pre-coated steel plate 10 for pre-coated steel plate in this embodiment has the same structure and performs the same effect as the steel plate 101 in the pre-coated steel plate 10 of the first and second embodiments. Therefore, detailed descriptions are omitted below.

[0274] Furthermore, the coating layer 103, aside from considering the state of zinc oxide and hydroxide, and the state of aluminum and magnesium oxide and hydroxide on the surface of the coated steel sheet, has the same structure and performs the same effect as the coating layer 103 in the pre-coated steel sheet 10 of the first and second embodiments. Therefore, detailed descriptions are omitted below.

[0275] It should be noted that the methods for state analysis of aluminum and magnesium metals, oxides and hydroxides, and the conditions that the obtained analysis results should meet are as described in the first and second embodiments.

[0276] However, in this embodiment, at a depth of 10 nm from the surface of the coating layer 103 (i.e., Figure 2 At position A), the ratio of magnesium oxide and hydroxide to metallic magnesium is 2.0 or more, and the ratio of zinc oxide and hydroxide to metallic zinc is 7.0 or more.

[0277] By forming the state described above, even when the pre-coated coated steel sheet of the pre-coated steel sheet 10 with the coating layer 103 of this embodiment is deep-drawn, better coating adhesion of the forming part is achieved, and the generation of coating lifting parts can be more effectively suppressed.

[0278] Furthermore, the states of magnesium and zinc oxides and hydroxides are as described above, and it is more preferable that the ratio of aluminum oxides and hydroxides to metallic aluminum is 1.3 or more. By forming this state, even when the pre-coated coated steel sheet 10 with the coating layer 103 of this embodiment is deep-drawn, further good coating adhesion of the forming process is achieved, and the generation of coating lift-off portions can be more effectively suppressed.

[0279] Reference above Figures 1A-2 At the same time, the pre-coated steel sheet 10 for the steel sheet of this embodiment will be described in detail.

[0280] The pre-coated steel sheet 10 described above can be manufactured by the manufacturing method described in the first and second embodiments.

[0281] Here, in particular, after mechanical cutting or acid treatment, alkaline treatment is performed, thereby more reliably achieving the state of the plating layer in this embodiment. This is believed to be because, firstly, by performing mechanical cutting or acid treatment, the plating surface is detached, creating a fresh new surface, and by performing alkaline treatment in this state, the redeposition of zinc and magnesium oxides or hydroxides on the plating surface is more effectively achieved.

[0282] Furthermore, by first performing mechanical cutting under light pressure to selectively cut the protrusions of the plated uneven surface, followed by alkaline treatment, the proportion of aluminum oxides or hydroxides present can be relatively increased. This is believed to be because the aluminum content is high on the plated protrusion surface, and therefore the leaching of aluminum increases through the alkaline treatment of the newly formed surface, resulting in an increased proportion of aluminum oxides or hydroxides.

[0283] Not limited to this example, by changing the order and conditions of mechanical cutting, acid treatment, and alkali treatment, the proportions of zinc, magnesium, and aluminum oxides or hydroxides can be varied.

[0284] (For pre-coated steel sheets)

[0285] Next, refer to Figures 3A-4 At the same time, the pre-coated steel sheet 10 for pre-coated steel sheet as described above will be explained.

[0286] like Figure 3AAs schematically shown, the pre-coated steel sheet 20 of this embodiment uses the pre-coated steel sheet 10 for pre-coated steel sheets as previously described, as the substrate. The pre-coated steel sheet 20 includes a steel sheet 101, a coating layer 201 on one side of the steel sheet 101, a chemical conversion coating 203 on the coating layer 201, and a coating film 205 on the chemical conversion coating 203. Furthermore, the pre-coated steel sheet 20 of this embodiment... Figure 3B As schematically shown, a plating layer 201, a chemical conversion coating 203, and a coating 205 can be formed on both sides of the steel plate 101.

[0287] Here, the steel plate 101 in the pre-coated steel plate 20 of this embodiment has the same structure and performs the same effect as the steel plate 101 in the previously described pre-coated steel plate 10. Therefore, detailed descriptions are omitted below.

[0288] Furthermore, regarding the plating layer 201 in the pre-coated steel sheet 20 of this embodiment, with the formation of the chemical conversion treatment coating 203 (described later), interdiffusion of atoms contained in each layer may occur near the interface between the plating layer 201 and the chemical conversion treatment coating 203. However, the average chemical composition of the plating layer 201 is the same as that of the plating layer 103 in the pre-coated steel sheet 10 described previously, and it exerts the same effect. Therefore, detailed descriptions are omitted below.

[0289] Furthermore, the states of magnesium, aluminum, zinc metals, oxides, and hydroxides shown in the coating layer 201 of the pre-coated steel sheet 20 of this embodiment, and the methods for measuring them, are as shown in the first and second embodiments.

[0290] The chemical conversion treatment coating 203 and the coating film 205 are located above the aforementioned plating layer 201. The detailed structure of the chemical conversion treatment coating 203 in this embodiment is the same as that in the first and second embodiments, and it performs the same effects. Therefore, detailed descriptions are omitted below. Similarly, the detailed structure of the coating film 205 in this embodiment is the same as that in the first and second embodiments, and it performs the same effects. Therefore, detailed descriptions are omitted below.

[0291] Reference above Figures 3A-4 At the same time, the pre-coated steel sheet 20 of this embodiment will be described.

[0292] (For finished products)

[0293] Next refer to Figure 5 At the same time, the molded products using the pre-coated steel sheet 20 as described above will be explained.

[0294] like Figure 5As illustrated in the schematic example, the molded article 30 of this embodiment is formed by performing various processes such as deep drawing and square tube pressing on the pre-coated steel sheet 20 as described above to form a desired shape. Here, a detailed description of the molded article 30 is as described in the first and second embodiments, and therefore a detailed description is omitted below.

[0295] As explained above, in this embodiment, by using the pre-coated steel sheet of this embodiment, it is also possible to obtain a molded body formed from the pre-coated steel sheet and the pre-coated steel sheet that will not produce coating lift-up or coating peeling in processing parts such as deep drawing.

[0296] Example

[0297] The following description, along with examples and comparative examples, details the pre-coated steel sheet for pre-coated steel sheets, the pre-coated steel sheet, and the formed article of the present invention. It should be noted that the examples shown below are merely illustrative of the pre-coated steel sheet for pre-coated steel sheets, the pre-coated steel sheet, and the formed article of the present invention, and the pre-coated steel sheet for pre-coated steel sheets, the pre-coated steel sheet, and the formed article of the present invention are not limited to the examples described below.

[0298] Test Case 1

[0299] The first test example shown below is a test example of the pre-coated steel sheet, the pre-coated steel sheet and the molded article of the first embodiment described above.

[0300] (1. Coated steel sheet for pre-coated steel sheet)

[0301] As pre-coated steel sheets, the following five types of commercially available zinc-based coated steel sheets are used. By treating the coating layers of the following zinc-based coated steel sheets with various acid solutions and alkaline solutions at varying processing times, the ratio of magnesium and aluminum oxides and hydroxides at the coating layer surface (more specifically, at a depth of 10 nm from the surface) is controlled.

[0302] A1: Zn-11%Al-3%Mg-0.2%Si molten zinc alloy coated steel sheet (plate thickness 0.60mm, coating adhesion 40g / m²) 2 )

[0303] A2: Zn-6%Al-3%Mg molten zinc alloy coated steel sheet (plate thickness 0.60mm, coating adhesion 40g / m²) 2 )

[0304] A3: Zn-55%Al-2%Mg-1.6%Si molten zinc alloy coated steel sheet (plate thickness 0.35mm, coating adhesion 75g / m²) 2 )

[0305] A4: Hot-dip galvanized steel sheet (thickness 0.60mm, coating adhesion 40g / m²) 2 )

[0306] A5: Zn-55%Al-1.6%Si molten zinc alloy coated steel sheet (plate thickness 0.35mm, coating adhesion 75g / m²) 2 )

[0307] (2. Film formation by chemical conversion treatment coating)

[0308] The following is used as a coating composition for coating chemical conversion treatment into a film. It should be noted that the amount of each component added in each coating composition is adjusted to be within the range of the previously described amounts.

[0309] S1: A water-based coating composition containing tannic acid, silane coupling agent, silica microparticles, and polyester resin.

[0310] S2: Aqueous coating compositions containing silane coupling agents, phosphates, and acrylic resins.

[0311] S3: Aqueous coating compositions containing silane coupling agents, fluorotitanic acid, fluorozirconic acid, and polyurethane resin.

[0312] The coating compositions of S1 to S3 are applied to the pre-coated steel sheet to form a specified amount of coating on the dry surface using a stick, and then dried in a hot air furnace at a temperature of 70°C on the metal surface.

[0313] In this experimental example, a two-layer coating consisting of a primer film and a top coat film was mainly prepared, and a single-layer coating consisting of only a top coat film without a primer film was also prepared.

[0314] (3-1. Film formation of primer coating)

[0315] The following is used as a coating composition for manufacturing a primer film.

[0316] P1: Polyester / melamine resin curing system composition (FLC641 manufactured by Nippon Paint Industrial Coatings Co., Ltd.)

[0317] P2: Polyester / isocyanate resin curing system composition (FLC690 manufactured by Nippon Paint Co., Ltd.)

[0318] P3: Epoxy / melamine resin curing system composition

[0319] The above-mentioned P1 to P3 are applied to the pre-coated steel sheet that has undergone the above-mentioned chemical conversion treatment in a manner that forms a specified film thickness (1 to 12 μm) during drying. Then, the metal surface is dried at a temperature of 215°C using a hot air furnace.

[0320] (3-2. Film formation of the top coating)

[0321] The following is used as a coating composition for forming a top coating film.

[0322] T1: Polyester / melamine resin curing system composition (FLC7000 manufactured by Nippon Paint Co., Ltd.)

[0323] T2: Polyester / melamine resin curing system composition (FLC100HQ manufactured by Nippon Paint Co., Ltd.)

[0324] The above-mentioned T1 or T2 is applied by bar coating to a pre-coated steel sheet having the above-mentioned primer coating film in a manner that forms a specified film thickness (4 to 30 μm) during drying, and then dried in a hot air furnace at a temperature of 230°C on the metal surface.

[0325] (4. The ratio of magnesium and aluminum to the oxide and hydroxide portions of the metals)

[0326] X-ray photoelectron spectroscopy (XPS) was used to observe the surface of pre-coated steel sheet before chemical conversion treatment and the interface of pre-coated steel sheet after coating formation. The magnesium content (based on Mg KLL values ​​of 295–325 cm⁻¹) at a sputtering etching location 10 nm from the surface and interface was measured. -1 (range) and aluminum (based on Al 2p 68–84 cm) -1 The ratio is calculated by taking the sum of the peak intensities of the oxide and hydroxide portions (within the specified range) and the ratio of the peak intensities of the metal portion.

[0327] Here, the measurement conditions for XPS and the sputtering rate for depth distribution measurement are set as previously described.

[0328] It should be noted that the interface between the chemical conversion coating and the plating layer is determined by the depth distribution of silicon in the depth direction of the pre-coated steel sheet obtained by X-ray photoelectron spectroscopy. The position where the intensity of a specific silicon is halved in the depth direction is defined as the interface between the chemical conversion coating and the plating layer.

[0329] (5. Performance Evaluation)

[0330] Using pre-coated zinc-plated steel sheets prepared using the above method, cylindrical cup deep drawing was performed. For the portion of the pre-coated steel sheet where the thickness of the plated steel sheet increased by more than 5% compared to before forming, the interface between the chemical conversion treatment coating and the primer coating, or the interface between the chemical conversion treatment coating and the plating layer, was peeled off using the SAICAS method. The peel strength and interface peel morphology were measured. The apparatus used in the SAICAS method was a DN-GS type manufactured by DAIPLAWINTES CO.,LTD.

[0331] It should be noted that the deep drawing of cylindrical cups is carried out as follows.

[0332] The pre-coated steel sheet obtained as described above is deep-drawn into a cylindrical cup shape with the target surface facing outwards at a drawing ratio of 2.0. After cutting the steel sheet near the cylindrical end to a sufficient size (approximately 20×20mm or more) using metal shears, the steel sheet is smoothed using a steel sheet straightener. For the portion of the steel sheet obtained by the previously described method where the thickness increases by 5% or more compared to before forming, the peel strength and peel morphology of the coating in the specified portion are measured using the SAICAS method. It should be noted that the cutting direction is set parallel to the end line of the deep-drawn steel sheet.

[0333] <Peel strength>

[0334] The cutting conditions using SAICAS are as follows.

[0335] Using a diamond cutting edge (0.3 mm width), a constant speed mode of 1 μm / s horizontally and 0.1 μm / s vertically was employed for inclined cutting. Near the interface, the cutting was switched to horizontal movement only, cutting a length of 200 μm. The average peel strength during this horizontal movement was measured. The depth position for switching to horizontal movement was determined using a pre-experimented specific interface position (the position where there is no limit to cutting the coating). Cases where the coating surface is cut due to unevenness during the horizontal movement of the cutting tool can be identified due to an abnormally high instantaneous increase in peel strength. This case was excluded as an outlier, and the average peel strength was calculated. The number of measurements was set to n=3, and the average of the three average peel strength values ​​was taken as the peel strength.

[0336] <Interface peeling morphology>

[0337] Optical microscope images of the horizontal cutting area (300 μm × 200 μm) of the SAICAS method were taken. The areas of primer cohesive failure, interfacial peeling, and coating cohesive failure within the same specific range were determined using the aforementioned criteria, and their areas were measured using transparent graph paper. Then, the ratio of the interfacial peeling area to the area of ​​the horizontal cutting area obtained by the SAICAS method, excluding coating cohesive failure, was calculated.

[0338] <Aluminum and magnesium content in the coating of the molded product>

[0339] For the coating of the molded article obtained as described above, the aluminum and magnesium content was determined using XPS (ULVAC-PHI, INCORRORATE, Quantum 2000).

[0340] <Coating abnormality in the outdoor unit roof panel processing section>

[0341] In addition, the pre-coated steel sheet was subjected to actual pressure processing using a mold for the top plate of the outdoor air conditioning unit. For the corners, the presence or absence of coating peeling and the condition of coating lifting were confirmed.

[0342] The evaluation involved observing four compression-processed areas at the corner of the top plate using a magnifying glass to confirm the presence or absence of coating peeling. The condition of coating lifting was assessed using the average of the four observations, as shown in the following score. It should be noted that the following scores are for each corner only.

[0343] 5: No raised areas of the coating

[0344] 4: Several parts of the coating lifting off the surface

[0345] 3: More than 10 raised parts in the coating

[0346] 2: More than 20 raised parts in the coating

[0347] 1: The results obtained from coating lifting parts of 20 or more and peeling caused by the connection of coating lifting parts are summarized in Table 1 below.

[0348] [Table 1]

[0349]

[0350] In the embodiment, the ratio of magnesium and aluminum to the oxide and hydroxide portions of the metal portion on the surface of the plated plate before forming and the interface of the plated steel plate after coating, as well as the peel strength and peel morphology of the compressed portion of the formed article obtained by SAICAS, all meet the benchmark. Therefore, even in the actual processing of the top plate of the air conditioner outdoor unit, no coating lifting or peeling was found.

[0351] On the other hand, for the comparative example, the ratio of magnesium and aluminum to the oxide and hydroxide portions of the metal portion on the surface of the plated plate before forming and the interface of the plated steel plate after coating, as well as the peel strength and peel morphology of the compressed portion of the formed product obtained by SAICAS, do not meet the benchmark. Therefore, in the actual processing of the top plate of the outdoor air conditioner unit, coating lifting and coating peeling were found.

[0352] Test Case 2

[0353] The second test example shown below is a test example of the pre-coated steel sheet, the pre-coated steel sheet and the molded article of the second embodiment described above.

[0354] (1. Coated steel sheet for pre-coated steel sheet)

[0355] Prepare pre-coated steel sheets for use in the same manner as in the first test example above.

[0356] (2. Film formation by chemical conversion treatment coating)

[0357] The pre-coated steel sheet obtained is coated with a chemical conversion coating in the same manner as in the first test example above.

[0358] In this experimental example, a two-layer coating consisting of a primer film and a top coat film was mainly prepared, and a single-layer coating consisting of only a top coat film without a primer film was also prepared.

[0359] (3-1. Film formation of primer coating)

[0360] The primer was applied to form a film in the same manner as in the first test example above.

[0361] (3-2. Film formation of the top coating)

[0362] The top coating was applied in the same manner as in the first test example above.

[0363] (4. The ratio of zinc to the oxide and hydroxide portions of the metal)

[0364] X-ray photoelectron spectroscopy (XPS) was used to observe the surface of pre-coated steel sheet before chemical conversion treatment and the interface of pre-coated steel sheet after coating formation. The zinc content (based on Zn 2p at 480–515 cm⁻¹) at a sputtering etching position 10 nm away from the surface and interface was measured. -1 The ratio is calculated by taking the sum of the peak intensities of the oxide and hydroxide portions (within the specified range) and the ratio of the peak intensities of the metal portion.

[0365] Here, the measurement conditions for XPS and the sputtering rate for depth distribution measurement are set as previously described.

[0366] It should be noted that the interface between the chemical conversion coating and the plating layer is determined by the depth distribution of silicon in the depth direction of the pre-coated steel sheet obtained by X-ray photoelectron spectroscopy. The position where the intensity of a specific silicon is halved in the depth direction is defined as the interface between the chemical conversion coating and the plating layer.

[0367] (5. Performance Evaluation)

[0368] The performance evaluation was conducted in the same manner as in Test Case 1 above. The evaluation methods and criteria were the same as in Test Case 1.

[0369] The results are summarized in Table 2 below.

[0370] [Table 2]

[0371]

[0372] In the embodiment, the ratio of zinc to the oxide and hydroxide portions of the metal portion on the surface of the plated plate before forming and the interface of the plated steel plate after coating, as well as the peel strength and peel morphology of the compressed portion of the formed article obtained by SAICAS, all meet the benchmark. Therefore, even in the actual processing of the top plate of the air conditioner outdoor unit, no coating lifting or peeling was found.

[0373] On the other hand, for the comparative example, the ratio of zinc to oxide and hydroxide portions of the metal portion on the surface of the plated sheet before forming and the interface of the plated steel sheet after coating, as well as the peel strength and peel morphology obtained by SAICAS for the compressed portion of the formed product, do not meet the benchmark. Therefore, in the actual processing of the top plate of the air conditioner outdoor unit, coating lifting and coating peeling were found.

[0374] Test Case 3

[0375] The third test example shown below is a test example of the pre-coated steel sheet, the pre-coated steel sheet and the formed article of the third embodiment described above.

[0376] Pre-coated steel sheets, pre-coated steel sheets, and formed articles were prepared in the same manner as in Test Examples 1 and 2 above. The obtained pre-coated steel sheets, pre-coated steel sheets, and formed articles were evaluated in the same manner as in Test Examples 1 and 2.

[0377] The results are summarized in Table 3 below.

[0378] [Table 3]

[0379]

[0380] The ratio of zinc to the oxide and hydroxide portions of the metal portion on the surface of the plated sheet before forming and the interface of the plated steel sheet after coating, as well as the peel strength and peel morphology of the compressed portion of the formed product obtained by SAICAS, all meet the benchmark. Therefore, even in the actual processing of the top plate of the air conditioner outdoor unit, no coating lifting or peeling was found.

[0381] Preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the examples described above. Various modifications and alterations will be readily apparent to those skilled in the art to which this invention pertains, within the scope of the technical concept set forth in the claims, and are therefore understood to fall within the technical scope of this invention.

[0382] Explanation of reference numerals in the attached figures

[0383] 10. Coated steel sheet for pre-coated steel sheets

[0384] 20 Pre-coated steel sheet

[0385] 30 Molded Products

[0386] 101 steel plate

[0387] 103,201 Coating

[0388] 203 Chemical conversion treatment coating

[0389] 205 Coating

Claims

1. A galvanized steel sheet for pre-coated steel sheets, comprising: steel plate; and The coating, located on one or both sides of the steel plate, contains 0.5% by mass and 60.0% by mass of aluminum, 0.5% by mass and 15.0% by mass of magnesium, with the balance being zinc and impurities. At a depth of 10 nm from the surface of the coating layer, the ratio of magnesium oxide to hydroxide relative to metallic magnesium is 2.0 or more, or the ratio of zinc oxide to hydroxide relative to metallic zinc is 7.0 or more. in, The ratio of magnesium oxides and hydroxides to metallic magnesium was calculated using X-ray photoelectron spectroscopy at a depth of 10 nm from the surface of the coating, from 295 to 325 cm⁻¹ based on Mg KLL. -1 The ratio of the sum of the peak intensities of magnesium oxides and hydroxides in the range to the peak intensity of metallic magnesium is calculated. The ratio of zinc oxide to zinc hydroxide relative to metallic zinc was calculated using X-ray photoelectron spectroscopy at a depth of 10 nm from the surface of the coating, specifically at Zn 2p-based concentrations of 480–515 cm⁻¹. -1 The ratio of the sum of the peak intensities of zinc oxides and hydroxides within the range to the peak intensity of metallic zinc is calculated.

2. The galvanized steel sheet for pre-coated steel sheet according to claim 1, wherein, At a depth of 10 nm from the surface of the coating layer, the ratio of magnesium oxide and hydroxide to metallic magnesium is 2.0 or more, and the ratio of zinc oxide and hydroxide to metallic zinc is 7.0 or more.

3. The galvanized steel sheet for pre-coated steel sheet according to claim 1 or 2, wherein, At a depth of 10 nm from the surface of the coating, the ratio of aluminum oxide and hydroxide to metallic aluminum is 1.3 or more.

4. The galvanized steel sheet for pre-coated steel sheet according to claim 1 or 2, wherein, The coating layer is a Zn-11%Al-3%Mg-0.2%Si alloy coating.

5. The galvanized steel sheet for pre-coated steel sheet according to claim 3, wherein, The coating layer is a Zn-11%Al-3%Mg-0.2%Si alloy coating.

6. A pre-coated steel sheet, comprising: A chemical conversion coating, located on the coating layer of the coated steel sheet according to any one of claims 1 to 5; and A coating, which is located on the chemically converted coating, At a depth of 10 nm from the interface between the chemically converted coating and the plating layer towards the inner side of the plating layer, the ratio of magnesium oxide and hydroxide to metallic magnesium is 0.30 or less, or the ratio of zinc oxide and hydroxide to metallic zinc is 7.0 or more. in, The ratio of magnesium oxides to hydroxides relative to metallic magnesium was calculated using X-ray photoelectron spectroscopy (XPS), specifically at a depth of 295–325 cm⁻¹ from the interface between the chemically converted coating and the plating layer towards the inner side of the plating layer at a depth of 10 nm, based on Mg KLL. -1 The ratio of the sum of the peak intensities of magnesium oxides and hydroxides in the range to the peak intensity of metallic magnesium is calculated. The ratio of zinc oxide to zinc hydroxide relative to metallic zinc was calculated using X-ray photoelectron spectroscopy, observing the Zn 2p-based concentrations at a depth of 480-515 cm⁻¹ from the interface between the chemically converted coating and the plating layer towards a depth of 10 nm inwards from the plating layer. -1 The ratio of the sum of the peak intensities of zinc oxides and hydroxides within the range to the peak intensity of metallic zinc is calculated.

7. The pre-coated steel sheet according to claim 6, wherein, At a depth of 10 nm from the interface between the chemically converted coating and the plating layer toward the inner side of the plating layer, the ratio of magnesium oxide and hydroxide to metallic magnesium is 0.30 or less, and the ratio of zinc oxide and hydroxide to metallic zinc is 7.0 or more.

8. The pre-coated steel sheet according to claim 6 or 7, wherein, At a depth of 10 nm from the interface between the chemically converted coating and the plating layer toward the inner side of the plating layer, the ratio of aluminum oxide and hydroxide to metallic aluminum is less than 0.

30.

9. A molded article formed from a pre-coated steel sheet according to any one of claims 6 to 8. In the formed article, for the portion where the thickness of the plated steel sheet increases by more than 5% compared to the non-formed portion, the peel strength measured by cutting the interface between the chemically converted coating and the coating film using the SAICAS method is an average of more than 1.00 kN / m, and less than 20% of the cutting area is of the interface peeling mode, while the remaining cutting area is of the cohesive failure mode within the coating film.

10. The molded article according to claim 9, wherein, The coating of the molded article contains 5% to 15% aluminum and 2% to 4% magnesium.

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