Surface-treated steel sheet

Abstract

The present invention provides a surface-treated steel sheet having good corrosion resistance, in which the damage resistance, particularly the resistance to surface contact damage caused by contact between one surface and another surface, is further improved, the surface-treated steel sheet comprising: a plated layer on both surfaces of a steel sheet; a first colored coating film layer; and a second colored coating film layer, the ratio of the film thickness of the second colored coating film layer to the film thickness of the first colored coating film layer being 0.1 or more and 0.5 or less, the first colored coating film layer and the second colored coating film layer containing resin particles, the proportion of the number of the resin particles having a thickness of the film thickness of the first colored coating film layer or more being 1% or more and 30% or less, and the proportion of the number of the resin particles having a thickness of the film thickness of the second colored coating film layer or more being 50% or more and 100% or less.

Description

Technical Field

[0001] This invention relates to surface-treated steel sheets. Background Technology

[0002] Surface-treated steel sheets, such as those with an organic resin coating (also known as pre-coated steel sheets), have replaced post-coated products that were previously painted after forming and are now used in home appliances, building materials, and automobiles. These surface-treated steel sheets, which are rust-proofed steel sheets coated with a colored organic film, offer aesthetic appeal, workability, and excellent corrosion resistance. In many cases, these surface-treated steel sheets do not require further painting after pressing and are used in home appliances, building materials, and automobiles. Therefore, these surface-treated steel sheets require excellent damage resistance to prevent loss of aesthetics during processing. Consequently, various technologies have been proposed to improve the various properties of surface-treated steel sheets, primarily their damage resistance.

[0003] For example, Patent Document 1 discloses a pre-coated metal plate for electronic and electrical equipment that not only exhibits excellent damage resistance, corrosion resistance, and conductivity. This pre-coated metal plate has a chemical conversion coating on the surface of a metal plate with a specified surface roughness. On one side, a resin coating of 0.4–2.0 μm thickness, consisting of polyurethane beads or fluororesin beads with an average particle size of 1.0–10 μm, is applied. On the other side, a resin coating of 0.2–2.0 μm thickness, consisting of polyurethane beads or fluororesin beads with an average particle size of 0.1–6.0 μm, is applied.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2010-5545 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] Here, various surface-treated steel sheets, including the pre-coated metal sheet disclosed in Patent Document 1, are typically manufactured by applying a desired coating to a metal sheet serving as the base material using a continuous coating production line. Examples of base metal sheets include steel sheets, aluminum sheets, and aluminum alloy sheets, among others, including various plated steel sheets. The metal sheet with the desired coating is transported to the customer in a coiled state at the end of the continuous coating production line.

[0009] In this coil state, one side of the surface-coated steel sheet is in contact with the other. This situation presents several challenges: damage from contact during coil winding, adhesion during storage (i.e., the surface and back coatings are pressed together under pressure), and indentation (i.e., the shape of one side is transferred to the other). Furthermore, during processing at the customer's site, damage can also occur due to contact between the two sides when handling the cut metal sheet. Additionally, to reduce costs, sometimes different thicknesses of colored coating layers are applied to the two sides of the base metal sheet, making one side thinner than the other. In this case, ensuring the damage resistance of the other side becomes crucial.

[0010] Regarding this issue, Patent Document 1 discloses the following problem: Metal particles mixed in to make the resin coating conductive can damage the resin coating on the opposite side that comes into contact with them during winding. The technology described in Patent Document 1 suppresses damage to the resin coating during winding by providing a resin coating containing resin beads on both sides of the metal plate. However, from the perspective of scratch resistance for optical discs, the material of the resin particles is limited to soft polyurethane beads or fluoropolymer beads with excellent sliding properties. Furthermore, from the perspective of ensuring conductivity, the thickness of the resin coating needs to be set to 2.0 μm or less. Therefore, there is still room for improvement in balancing scratch resistance, resistance to surface contact damage, and corrosion resistance.

[0011] Therefore, the present invention was made in view of the above-mentioned problems, and the object of the present invention is to provide a surface-treated steel sheet with good corrosion resistance that further improves damage resistance, especially the resistance to surface contact damage caused by one surface contacting another surface.

[0012] Solution for solving the problem

[0013] In order to solve the above problems, the inventors conducted in-depth research and obtained the following technical concept: by making the coating composition on one side of the steel plate different from that on the other side, the damage resistance can be further improved, thus completing the present invention.

[0014] The key points of the present invention, which is based on this technical concept, are as follows.

[0015] (1) A surface-treated steel sheet comprising: a zinc-containing plating layer on two surfaces of the steel sheet; a first colored coating layer on the plating layer on one side of the steel sheet; and a second colored coating layer on the plating layer on the other side of the steel sheet, wherein the thickness of the second colored coating layer is 0.1 or more and 0.5 or less relative to the thickness of the first colored coating layer, the first colored coating layer and the second colored coating layer comprising resin particles, and when observing a cross-section formed by cutting the first colored coating layer along the thickness direction, the observed resin particles occupy a portion along the thickness direction of the first colored coating layer. When the length is set to the thickness of the resin particles, the number of resin particles having a thickness greater than or equal to the thickness of the first colored coating layer is 1% to 30% of the total number of resin particles observed. When observing a cross-section formed by cutting the second colored coating layer along the film thickness direction, for the observed resin particles, when the length occupied along the film thickness direction of the second colored coating layer is set to the thickness of the resin particles, the number of resin particles having a thickness greater than or equal to the thickness of the second colored coating layer is 50% to 100% of the total number of resin particles observed.

[0016] (2) According to the surface-treated steel plate described in (1), wherein, when the first colored coating layer is observed in cross section, a length of 1000 μm in a direction orthogonal to the film thickness direction of the first colored coating layer is set as the first observation length, and the sum of the lengths of the parts corresponding to the resin particles in a direction orthogonal to the film thickness direction when the portion occupied by the resin particles is projected onto the film thickness direction within the first observation length is set as the first occupation length, the ratio of the first occupation length to the first observation length is 15% or more and 40% or less, and a length of 1000 μm in a direction orthogonal to the film thickness direction of the second colored coating layer is set as the second observation length, and the sum of the lengths of the parts corresponding to the resin particles in a direction orthogonal to the film thickness direction when the portion occupied by the resin particles is projected onto the film thickness direction within the second observation length is set as the second occupation length, the ratio of the second occupation length to the second observation length is 5% or more and 15% or less.

[0017] (3) The surface-treated steel sheet according to (1) or (2), wherein the thickness of the first colored coating layer is 3 μm or more and 10 μm or less.

[0018] (4) The surface-treated steel sheet according to (1) or (2), wherein the thickness of the resin particles contained in the first colored coating layer is less than twice the film thickness of the first colored coating layer, and the thickness of the resin particles contained in the second colored coating layer is less than three times the film thickness of the second colored coating layer.

[0019] (5) The surface-treated steel plate according to (1) or (2), wherein the resin particles are acrylic resin particles.

[0020] (6) The surface-treated steel sheet according to (1) or (2), wherein the glass transition temperature Tg of the film-forming components of the first colored coating layer and the second colored coating layer is above 30°C and below 70°C.

[0021] (7) The surface-treated steel sheet according to (1) or (2), wherein a chemical conversion coating layer is further provided between the plating layer and the first color coating layer on one side of the steel sheet and between the plating layer and the second color coating layer on the other side of the steel sheet.

[0022] (8) The surface-treated steel plate according to (1) or (2), wherein the average particle size of the resin particles is 3 μm or more and 15 μm or less.

[0023] The effects of the invention

[0024] As described above, according to the present invention, it is possible to provide a surface-treated steel sheet with good corrosion resistance that further improves damage resistance, especially the resistance to surface contact damage caused by one surface contacting another. Attached Figure Description

[0025] Figure 1 An explanatory diagram illustrating the structure of the surface-treated steel sheet in the embodiment.

[0026] Figure 2 This is an explanatory diagram showing the thickness of the resin particles when the surface-treated steel sheet of the embodiment is viewed in cross section.

[0027] Figure 3 This is an explanatory diagram showing the length occupied by resin particles when the surface-treated steel sheet of the embodiment is viewed in cross section.

[0028] Figure 4 This is an explanatory diagram showing the length occupied by resin particles when the surface-treated steel sheet of the embodiment is viewed in cross section. Detailed Implementation

[0029] The 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 drawings, elements having substantially the same functional configuration are omitted from repeated description by using the same reference numerals.

[0030] <About Surface-Treated Steel Plates 1>

[0031] The following is for reference Figure 1 The surface-treated steel plate according to the embodiments of the present invention will be described in detail. Figure 1 An explanatory diagram illustrating the structure of the surface-treated steel sheet in the embodiment.

[0032] <Regarding the overall composition of surface-treated steel plate 1>

[0033] like Figure 1 As schematically shown, the surface-treated steel plate 1 of this embodiment includes a steel plate 10 as a substrate, a plating layer 20 disposed on the surface of the steel plate 10, and a colored coating layer 30 disposed on the surface of the plating layer 20. Additionally, as... Figure 1 As shown, a chemical conversion coating layer 40 is preferably further provided between the plating layer 20 and the coloring coating layer 30. The plating layer 20, the coloring coating layer 30, and the chemical conversion coating layer 40 are disposed on both sides of the steel plate 10. That is, the first plating layer 20a, the first coloring coating layer 30a, and the first chemical conversion coating layer 40a are formed on one side (first side 10a) of the steel plate 10 corresponding to the upper side of the figure. In addition, the second plating layer 20b, the second coloring coating layer 30b, and the second chemical conversion coating layer 40b are formed on the other side (second side 10b) corresponding to the lower side of the figure.

[0034] <Regarding steel plate 10>

[0035] There are no particular limitations on the steel plate 10 used as the base material, and various steel plates 10 can be used depending on the mechanical strength required by the surface-treated steel plate 1. Examples of such steel plates 10 include aluminum-killed steel, ultra-low carbon steel containing Ti, Nb, etc., and high-strength steel that further contains strengthening elements such as P, Si, Mn, etc. in ultra-low carbon steel.

[0036] Furthermore, there is no particular limitation on the thickness of the steel plate 10 in this embodiment. It can be appropriately set according to the mechanical strength required by the surface-treated steel plate 1, for example, it can be set to about 0.2mm to 10.0mm.

[0037] <Regarding plating layer 20>

[0038] There is no particular limitation on the type of coating layer 20 of the surface-treated steel sheet 1 in this embodiment. For example, zinc-based coating can be used as the type of coating. Examples of zinc-based coatings include zinc-nickel alloy coating, alloyed hot-dip galvanizing, aluminum-zinc alloy coating, zinc-aluminum-magnesium alloy coating, zinc-vanadium composite coating, and zinc-zirconium composite coating.

[0039] In this zinc-based plating, zinc-aluminum-magnesium alloy plating is particularly preferred, and zinc-aluminum-magnesium-silicon alloy plating containing Al: 4-22% by mass, Mg: 1-10% by mass, Si: 0.0001-2.0000% by mass, with the balance being Zn and impurities is even more preferred.

[0040] [Al: 4-22% by mass]

[0041] By setting the Al content to 4% by mass or more, the corrosion resistance of the steel plate can be further improved. More preferably, the Al content is 5% by mass or more. On the other hand, by setting the Al content to 22% by mass or less, the corrosion resistance of the steel plate can be further improved while suppressing the saturation of the aforementioned corrosion resistance improvement effect. More preferably, the Al content is 16% by mass or less.

[0042] [Mg: 1-10% by mass]

[0043] By setting the Mg content to 1% by mass or more, the corrosion resistance of the steel sheet can be further improved. More preferably, the Mg content is 2% by mass or more. On the other hand, by adjusting the Mg concentration in the plating bath used to form the coating layer 20 so that the Mg content in the manufactured coating layer 20 is 10% by mass or less, the generation of slag in the plating bath can be stabilized, and the coated steel sheet can be manufactured stably. It should be noted that, in this specification, the coated steel sheet refers to a steel sheet on which the coating layer 20 is formed on the surface of the steel sheet 10. More preferably, the Mg concentration in the plating bath used to form the coating layer 20 is adjusted so that the Mg content in the manufactured coating layer 20 is 5% by mass or less.

[0044] [Si: 0.0001~2.0000% by mass]

[0045] By setting the Si content to 0.0001% by mass or more, the adhesion of the plating layer 20 (more specifically, the adhesion between the base steel plate 10 and the plating layer 20) can be further improved. On the other hand, by setting the Si content to 2.0000% by mass or less, the adhesion of the plating layer 20 can be further improved while suppressing the saturation of the effect of improving the adhesion of the plating layer 20. The Si content is more preferably 1.6000% by mass or less.

[0046] Furthermore, the zinc-containing coating layer 20 may contain less than 1% by mass of elements such as Fe, Sb, Pb, etc., in individual or combined forms to replace a portion of the balance Zn.

[0047] Examples of coated steel sheets having a coating layer 20 with the aforementioned chemical composition include hot-dip galvanized aluminum-magnesium-silicon alloy steel sheets with a Zn-11%Al-3%Mg-0.2%Si alloy coating layer (e.g., "Super Dima" manufactured by Nippon Steel Corporation).

[0048] The coating layer 20 described above can be manufactured, for example, as follows: First, the surface of the prepared steel sheet 10 is pretreated by cleaning, degreasing, etc., as needed. Then, the pretreated steel sheet 10 is immersed in a hot-dip galvanizing bath with the desired chemical composition, as needed, and the steel sheet 10 is then pulled out of the bath. During this coating operation, coating can be performed using either a continuous coating method for coils or a coating method for individually cut sheets.

[0049] The temperature of the hot-dip plating bath varies depending on its composition; for example, a range of 400–500°C is preferred.

[0050] Furthermore, the coating adhesion amount of the aforementioned coating layer 20 can be controlled by adjusting the lifting speed of the steel plate 10, the flow rate and velocity of the wiping gas ejected from the wiping nozzle located above the plating bath, etc. Preferably, the coating adhesion amount of the coating layer 20 is 30 g / m² on both sides of the steel plate 10. 2 The above (i.e., 15g / m² per single side) 2 (Above). By setting the adhesion amount to 30g / m 2 The above ensures the reliable corrosion resistance of the galvanized steel sheet 10. The preferred coating adhesion is a total of 40 g / m² on both sides of the steel sheet 10. 2 That's all. On the other hand, the preferred coating adhesion amount is 600 g / m² on both sides of the steel plate 10. 2 The following (i.e., 300g / m² per single side) 2 (The following). By setting the adhesion amount to 600g / m 2 The following approach aims to further improve corrosion resistance while ensuring the smoothness of the Zn-containing coating 13 surface. A more preferable coating amount is 550 g / m² on both sides of the steel plate 10. 2 the following.

[0051] After adjusting the amount of hot-dip galvanizing, the steel sheet is cooled. At this point, there are no special restrictions on the cooling conditions.

[0052] <Regarding the colored coating layer 30>

[0053] The coloring coating layer 30 is a coating layer that is colored to a desired color by having coloring pigments. In this embodiment, the surface-treated steel plate 1 includes a first coloring coating layer 30a formed on a first surface 10a of the steel plate 10 and a second coloring coating layer 30b formed on a second surface 10b as the coloring coating layer 30. Hereinafter, when describing the common configuration of these first coloring coating layers 30a and second coloring coating layers 30b, they will sometimes be referred to together simply as the coloring coating layer 30.

[0054] like Figure 1 As schematically shown, the colored coating layer 30 contains a film-forming component 301 and resin particles 303. Here, when observing a cross-section formed by cutting the surface-treated steel plate 1 along the film thickness direction of the colored coating layer 30 (hereinafter referred to as cross-sectional observation), for either the first colored coating layer 30a or the second colored coating layer 30b, at least a portion of the resin particles 303 has a thickness greater than or equal to the film thickness of either the first colored coating layer 30a or the second colored coating layer 30b. In other words, the resin particles 303 are included in a desired ratio (described later) of the number of resin particles having a thickness greater than or equal to the film thickness of the colored coating layer 30 relative to the total number of resin particles 303 observed through cross-sectional observation. By providing a colored coating layer 30 containing resin particles 303 having a thickness greater than or equal to the film thickness of the colored coating layer 30, resin particles 303 protrude from the surface of the colored coating layer 30. As a result, when the colored coating layer 30 comes into contact with any surface, it is not a contact of the entire colored coating layer 30, but rather a contact of the resin particles 303. In other words, the contact with any surface is not a surface contact of the entire colored coating layer 30, but a point contact with the resin particles 303 protruding from the colored coating layer 30. Therefore, the damage resistance (more specifically, the resistance to surface contact damage) of the surface-treated steel sheet 1 of this embodiment can be improved.

[0055] For example, cross-sectional observation can be performed as follows: The surface-treated steel plate 1 is embedded in room-temperature drying epoxy resin in a direction perpendicular to the coating thickness direction. After mechanically grinding the embedded surface, it is observed using SEM (scanning electron microscope).

[0056] like Figure 1 As illustrated schematically, the colored coating layer 30 is configured such that the film thickness Tb of the second colored coating layer 30b is thinner than the film thickness Ta of the first colored coating layer 30a. Specifically, the ratio Tb / Ta of the film thickness Tb of the second colored coating layer 30b to the film thickness Ta of the first colored coating layer 30a is 0.1 or more and 0.5 or less. By setting this ratio Tb / Ta within this range, it is possible to achieve the desired number ratio of resin particles 303 having a thickness greater than or equal to that of the colored coating layer 30 in the cross-sectional observation described later.

[0057] In this embodiment, the thickness Ta of the first colored coating layer 30a is preferably 3.0 μm or more. Furthermore, based on the aforementioned Tb / Ta ratio, the thickness Tb of the second colored coating layer 30b is preferably 0.3 μm or more. This further improves resistance to surface contact damage. The thickness Ta of the first colored coating layer 30a is more preferably 4.0 μm or more. On the other hand, the thickness Ta of the first colored coating layer 30a is preferably 10.0 μm or less. By setting the thickness Ta of the first colored coating layer 30a to 10.0 μm or less, it is possible to control costs while suppressing coating defects such as wrinkles and obtaining a stable appearance. The thickness Ta of the first colored coating layer 30a is more preferably 8.0 μm or less. Furthermore, the upper limit of the thickness Tb of the second colored coating layer is determined based on the aforementioned Tb / Ta ratio from the upper limit value of the thickness Ta of the first colored coating layer 30a.

[0058] It should be noted that the film thickness (Ta, Tb) of the colored coating layer 30 can be determined by cross-sectional observation. For the first colored coating layer 30a or the second colored coating layer 30b, the film thickness is measured at any number of locations (e.g., 10 locations), and the average value of the obtained film thicknesses is taken as the film thickness (Ta, Tb).

[0059] Next, adopt Figure 2 The thickness of the resin particles 303 observed in the cross-section is explained. Figure 2 This is an explanatory diagram used to illustrate the thickness of the resin particles 303 when observing a cross-section of the surface-treated steel plate 1 in this embodiment.

[0060] Figure 2 In this context, the thickness of resin particles 303 refers to the length occupied by each resin particle 303 along the film thickness direction of the colored coating layer 30. Figure 2 (The double-headed arrows indicate the resin particles 303). More specifically, for Figure 2 The flat resin particles 303a are inclined in a direction perpendicular to the film thickness direction. Figure 2 Projecting the film along the direction of the dotted line in the image, the length of this projection along the film thickness direction is taken as the length occupied along the film thickness direction, and this is taken as the thickness of the resin particles 303a. Hereinafter, the thickness of the resin particles 303 contained in the first colored coating layer 30a is referred to as the first thickness Ga. Furthermore, the thickness of the resin particles 303 contained in the second colored coating layer 30b is referred to as the second thickness Gb.

[0061] In this embodiment, in a cross-sectional view of the first colored coating layer 30a, the number of resin particles 303 having a first thickness Ga (Ga≥Ta) of at least Ta film thickness Ta of the first colored coating layer 30a relative to the total number of resin particles 303 in the field of view is 1% or more and 30% or less. On the other hand, in a cross-sectional view of the second colored coating layer 30b, the number of resin particles 303 having a second thickness Gb (Gb≥Tb) of at least Tb film thickness Tb of the second colored coating layer 30b relative to the total number of resin particles 303 in the field of view is 50% or more and 100% or less. For example... Figure 2 As shown, resin particles 303 with a thickness greater than or equal to that of the colored coating layer 30 protrude from the surface of the colored coating layer 30.

[0062] It should be noted that the ratio of the number of resin particles 303 with a first thickness Ga (Ga≥Ta) of at least Ta to the total number of resin particles 303 in the field of view in the cross-sectional observation of the first colored coating layer 30a, and the ratio of the number of resin particles 303 with a second thickness Gb (Gb≥Tb) of at least Tb to the total number of resin particles 303 in the field of view in the cross-sectional observation of the second colored coating layer 30b, are calculated by observing a total of 500 μm or more in directions orthogonal to the thickness directions of the colored coating layers 30a and 30b, respectively.

[0063] Thus, in this embodiment, the proportion of resin particles 303 with a second thickness Gb (Gb≥Tb) of film thickness Tb or greater having the second colored coating layer 30b is configured to be greater than the proportion of resin particles 303 with a first thickness Ga (Ga≥Ta) of film thickness Ta or greater having the first colored coating layer 30a. This results in a sufficient number of resin particles 303, particularly protruding from the second colored coating layer 30b. Therefore, even when the first colored coating layer 30a and the second colored coating layer 30b are in contact, surface contact between the two coatings can be significantly suppressed. As a result, damage caused by surface contact between the two coatings, adhesion during roll storage, indentations, etc., can be suppressed.

[0064] When the proportion of resin particles 303 with a first thickness Ga (Ga≥Ta) of at least Ta having the first colored coating layer 30a is less than 1%, or when the proportion of resin particles 303 with a second thickness Gb (Gb≥Tb) of at least Tb having the second colored coating layer 30b is less than 50%, the effect of suppressing surface contact damage is insufficient because the suppression effect on the surface contact between the first colored coating layer 30a and the second colored coating layer 30b is not sufficient. In cross-sectional observation of the first colored coating layer 30a, the proportion of resin particles 303 with a first thickness Ga (Ga≥Ta) of at least Ta having the first colored coating layer 30a relative to the total number of resin particles 303 in the field of view is preferably 3% or more, more preferably 5% or more. Furthermore, in cross-sectional observation of the second colored coating layer 30b, the ratio of the number of resin particles 303 having a second thickness Gb (Gb≥Tb) of film thickness Tb or more of the second colored coating layer 30b to the total number of resin particles 303 in the field of view is preferably 55% or more, more preferably 60% or more.

[0065] Furthermore, when the proportion of resin particles 303 having a first thickness Ga (Ga≥Ta) of at least Ta in the first colored coating layer 30a exceeds 30%, the processing adhesion decreases because there are too many resin particles 303 protruding from the surface of the colored coating layer 30. Processing adhesion refers to the ability of the coating, such as the colored coating layer 30, to maintain a tight seal in the processing section without peeling off.

[0066] In cross-sectional observation of the first colored coating layer 30a, the proportion of resin particles 303 having a first thickness Ga (Ga≥Ta) of film thickness Ta or higher to the total number of resin particles 303 in the field of view is preferably 20% or less, more preferably 15% or less. It should be noted that there is no particular upper limit to the proportion of resin particles 303 having a second thickness Gb (Gb≥Tb) of film thickness Tb or higher in the second colored coating layer 30b, and it can be 100%. In cross-sectional observation of the second colored coating layer 30b, the proportion of resin particles 303 having a second thickness Gb (Gb≥Tb) of film thickness Tb or higher to the total number of resin particles 303 in the field of view is preferably 95% or less, more preferably 90% or less.

[0067] In the first colored coating layer 30a, the content of resin particles 303 is preferably 3% by mass or more relative to the total content of film-forming components 301 and resin particles 303. This further improves damage resistance. More preferably, the content of resin particles 303 in the first colored coating layer 30a is 5% by mass or more. On the other hand, the content of resin particles 303 in the first colored coating layer 30a is preferably 40% by mass or less relative to the total content of film-forming components 301 and resin particles 303. This further improves damage resistance. When the content of resin particles 303 in the first colored coating layer 30a exceeds 40% by mass, the proportion of film-forming components in the colored coating decreases, the barrier properties of the coating decrease, and it is difficult to exhibit the desired corrosion resistance. More preferably, the content of resin particles 303 in the first colored coating layer 30a is 35% by mass or less.

[0068] Furthermore, in the second colored coating layer 30b, the content of resin particles 303 is preferably 3% by mass or more relative to the total content of film-forming components 301 and resin particles 303. This further improves damage resistance. More preferably, the content of resin particles 303 in the second colored coating layer 30b is 5% by mass or more. On the other hand, the content of resin particles 303 in the second colored coating layer 30b is preferably 40% by mass or less relative to the total content of film-forming components 301 and resin particles 303. This further improves damage resistance. When the content of resin particles 303 in the second colored coating layer 30b exceeds 40% by mass, the proportion of film-forming components in the colored coating decreases, the barrier properties of the coating decrease, and it is difficult to exhibit the desired corrosion resistance. More preferably, the content of resin particles 303 in the second colored coating layer 30b is 35% by mass or less.

[0069] Next, as a preferred configuration of the surface-treated steel plate 1 in this embodiment, a method is adopted. Figure 3 and Figure 4 The occupied length of resin particles 303 is explained. Figure 3 and Figure 4 This is an explanatory diagram illustrating the length occupied by the resin particles 303 when observing the cross-section of the surface-treated steel plate 1 in this embodiment.

[0070] Figure 3In this method, when observing a cross-section of the first colored coating layer 30a, the observation range in the direction orthogonal to the film thickness direction of the first colored coating layer 30a is defined as the first observation length L1. Furthermore, within the first observation length L1, the portions p1, p2, p3, p4, and p5 occupied by the resin particles 303 are projected in the film thickness direction. Based on this projection, portions p1 and p2, and portions p4 and p5 partially overlap, resulting in a projection P1 corresponding to portions p1 and p2, a projection P2 corresponding to portion p3, and a projection P3 corresponding to portions p4 and p5. The sum of the lengths of these projections P1, P2, and P3, P1+P2+P3, is defined as the first occupancy length D1. In this case, the ratio of the first occupancy length D1 to the first observation length L1 (D1 / L1×100) is preferably 15% or more and 40% or less.

[0071] also, Figure 4 Similarly, when observing the cross-section of the second colored coating layer 30b, the observation range in the direction orthogonal to the film thickness direction of the second colored coating layer 30b is defined as the second observation length L2. Furthermore, within the second observation length L2, the portions p6, p7, p8, p9, and p10 occupied by the resin particles 303 are projected in the film thickness direction. Based on this projection, portions p6 and p7, and portions p9 and p10 partially overlap, resulting in projections P4 corresponding to portions p6 and p7, P5 corresponding to portion p8, and P6 corresponding to portions p9 and p10. The sum of the lengths of these projections P4, P5, and P6, P4+P5+P6, is defined as the second occupancy length D2. At this time, the ratio of the second occupancy length D2 to the second observation length L2 (D2 / L2×100) is preferably 5% or more and 15% or less. It should be noted that the first observation length L1 and the second observation length L2 are set to 1000 μm.

[0072] By setting the ratio of the first occupied length D1 to the first observed length L1 to 15% or more, damage resistance can be further improved. More preferably, the ratio of the first occupied length D1 to the first observed length L1 is 20% or more. On the other hand, by setting the ratio of the first occupied length D1 to the first observed length L1 to 40% or less, corrosion resistance can be further improved. When the ratio of the first occupied length D1 to the first observed length L1 exceeds 40%, the proportion of the film-forming component 301 in the first colored coating layer 30a decreases, resulting in a decrease in the barrier properties of the coating and making it difficult to exhibit the desired corrosion resistance. More preferably, the ratio of the first occupied length D1 to the first observed length L1 is 35% or less.

[0073] By setting the ratio of the second occupied length D2 to the second observation length L2 to 5% or more, damage resistance can be further improved. More preferably, the ratio of the second occupied length D2 to the second observation length L2 is 7% or more. On the other hand, the ratio of the second occupied length D2 to the second observation length L2 is preferably 15% or less. This further improves damage resistance. The reason is as follows: From a certain perspective, the second surface 10b of the steel plate 10 is a thinner film than the first surface 10a. When the ratio of the second occupied length D2 to the second observation length L2 exceeds 15%, the proportion of resin particles with a diameter greater than the film thickness in the second surface 10b is large. When the proportion of resin particles with a diameter greater than the film thickness is large, it becomes difficult to retain the resin particles in the coating, and the resin particles 303 easily detach from the second surface 10b during surface contact, thus becoming the starting point of damage. Furthermore, from another perspective, when the ratio of the second occupied length D2 to the second observed length L2 exceeds 15%, the effect of improving damage resistance becomes saturated, and the proportion of the film-forming component 301 in the second colored coating layer 30b decreases, resulting in a decline in the barrier properties of the coating and making it difficult to exhibit the desired corrosion resistance of the second surface 10b of the steel plate 10. From the perspective of further improving damage resistance or further improving the corrosion resistance of the second surface 10b of the steel plate 10, the ratio of the second occupied length D2 to the second observed length L2 is more preferably 13% or less.

[0074] In this embodiment, the film-forming component 301 of the colored coating layer 30 can be made from any raw material as long as it functions as a binder for the resin particles 303. From the perspective of ease of manufacturing and cost-effectiveness, various organic resins are preferred. Examples of such film-forming components 301 include acrylic resins, polyester resins, polyurethane resins, and fluorinated resins. Furthermore, when using resin particles made from organic resins as the resin particles 303, it is preferable to select a resin of the same type as the resin particles as the film-forming component 301. This improves the affinity between the film-forming component 301 and the resin particles 303, further improving the damage resistance and adhesion of the colored coating layer 30.

[0075] Furthermore, the film-forming component 301 in this embodiment is preferably an organic resin with a glass transition temperature (Tg) of 30°C or higher. By using a resin with such a glass transition temperature (Tg) as the film-forming component 301, the colored coating layer 30 has a more suitable hardness, which can further improve the damage resistance (especially the resistance to scratches) of the surface-treated steel plate 1.

[0076] The glass transition temperature (Tg) of the film-forming component 301 is preferably 35°C or higher, more preferably 40°C or higher. On the other hand, there is no particular upper limit for the glass transition temperature (Tg), but processability may decrease if it exceeds 70°C. Therefore, the glass transition temperature (Tg) of the film-forming component 301 is preferably 70°C or lower.

[0077] It should be noted that the glass transition temperature Tg can be determined, for example, by the following methods: by TMA (thermomechanical analysis), which involves puncturing the surface of the coating to be measured from the coating thickness direction to induce a certain temperature change, and measuring the change in thermal expansion of the coating; or by DMA (dynamic viscoelasticity measurement), which involves applying periodic deformation to the coating peeled from the substrate to induce a certain temperature change, and analyzing the viscoelasticity.

[0078] In this embodiment, the resin particles 303 of the colored coating layer 30 are preferably resin particles made from organic resin. By using such resin particles, the toughness and ductility of the resin particles can mitigate the impact applied to the colored coating layer 30, thereby further improving its damage resistance. Examples of such resin particles include acrylic resin particles, polyester resin particles, polyurethane resin particles, fluorinated resin particles, silicone resin particles, and polyolefin resin particles, but acrylic resin particles are more preferred. In addition, the coloring pigment contained in the colored coating layer 30 can also function as the resin particles 303 described above.

[0079] In this embodiment, the resin particles 303 include resin particles with a thickness greater than or equal to the thickness of the colored coating layer 30, and resin particles that do not. Therefore, resin particles 303 with inconsistent particle sizes are used. Their average particle size is preferably 3 to 15 μm. By having the resin particles 303 with the aforementioned average particle size, the damage resistance of the surface-treated steel sheet 1 can be further improved. Here, the average particle size of the resin particles 303 refers to the average value calculated based on the circumference equivalent diameter of each resin particle observed through cross-sectional observation, which differs from the thickness of the resin particles 303 as defined above. Specifically, regarding the average particle size of the resin particles 303, the average value of multiple particle sizes obtained by measuring the particle size of the resin particles 303 observed at any multiple locations (e.g., 10 locations) in cross-sectional observation can be used as the average particle size of the resin particles 303. It should be noted that resin particles 303 with inconsistent particle sizes include the case where multiple resin particles 303 with no inconsistent particle sizes are used in combination.

[0080] Furthermore, preferably, the thickness Ga of the resin particles 303 contained in the first colored coating layer 30a is less than 2.0 times the film thickness Ta of the first colored coating layer, and the thickness Gb of the resin particles 303 contained in the second colored coating layer 30b is less than 3.0 times the film thickness Tb of the second colored coating layer. By satisfying the above-mentioned relationship between the thickness of the resin particles 303 and the film thickness of the colored coating layer 30, the damage resistance of the surface-treated steel sheet 1 can be further improved. The thickness Ga of the resin particles 303 contained in the first colored coating layer 30a is preferably less than 1.5 times the film thickness Ta of the first colored coating layer. Furthermore, the thickness Gb of the resin particles 303 contained in the second colored coating layer 30b is preferably less than 2.5 times the film thickness Tb of the second colored coating layer.

[0081] ◇Other components of the colored coating layer 30

[0082] In addition to the above-mentioned components, the colored coating layer 30 of this embodiment may further contain a crosslinking agent.

[0083] By further including a crosslinking agent in the colored coating layer 30 of this embodiment, the barrier properties of the colored coating layer 30 itself can be further improved, thereby further improving the damage resistance and corrosion resistance of the surface-treated steel sheet 1. In particular, by including at least one of melamine resin or isocyanate resin as a crosslinking agent in the colored coating layer 30, the damage resistance and corrosion resistance of the surface-treated steel sheet 1 can be further improved. Regarding the content of this crosslinking agent, for example, its proportion in the film-forming component 301 is preferably about 10 to 40% by mass.

[0084] It should be noted that there are no particular limitations on the coloring pigments contained in the coloring coating layer 30. Various known pigments can be used appropriately according to the required hue of the coloring coating layer 30. Examples of such coloring pigments include aluminum pigments, carbon black, and TiO2. In addition, the content can be set appropriately, for example, to about 3 to 60% by mass.

[0085] The colored coating layer 30 can be formed by applying a coating composition containing the components constituting such a colored coating layer 30 to the surface of the steel plate 10, a plated surface, the surface of the steel plate 10 having a chemical conversion coating 40, or a plated surface having a chemical conversion coating 40, and then sintering it at a temperature of 150°C or higher and less than 300°C to cure and dry it. When the sintering temperature is less than 150°C, insufficient sintering and curing may occur, potentially leading to a decrease in the coating's corrosion resistance and damage resistance. When the sintering temperature is 300°C or higher, there is a possibility of thermal degradation of the resin components or a decrease in processability.

[0086] It should be noted that the coating composition described above can generally be applied using known coating methods, such as roller coating, curtain coating, air spraying, airless spraying, dipping, bar coating, brush coating, etc. Among these coating methods, roller coating is particularly preferred.

[0087] In addition, without compromising the above-mentioned effects, the colored coating layer 30 may further include, as needed, anti-rust pigments, surface-modified metal powder or glass powder, dispersants, leveling agents, waxes, aggregates and other additives, diluents, etc.

[0088] Here, when rust-preventive pigment is included, its content is preferably 1 to 15% by mass. In addition, various known rust-preventive pigments can be used.

[0089] ◇Regarding the hardness of the colored coating layer 30

[0090] The Vickers hardness of the colored coating layer 30, measured at an indentation depth from the surface to three-quarters of the coating thickness (the test load magnitude for achieving the desired indentation depth can be determined based on the hardness setting of the colored coating layer 30), is preferably 10 to 70 Hv. This Vickers hardness is measured using a general-purpose hardness tester (manufactured by FISCHER INSTRUMENTS, Ltd.). Under the aforementioned indentation depth conditions, the hardness is measured from the coating surface at any 10 locations, regardless of whether resin particles 303 are present or not, and the average of the 10 measured values ​​is calculated. The colored coating layer 30, by possessing such Vickers hardness, can further improve damage resistance. The Vickers hardness exhibited by the colored coating layer 30 is more preferably 15 to 65 Hv.

[0091] <Regarding the chemical conversion treatment coating layer 40>

[0092] The chemical conversion treatment coating layer 40 in this embodiment is a coating layer that can be located between the steel plate 10 and the colored coating layer 30, and is a layer formed by so-called chemical conversion treatment.

[0093] As a detailed composition of the chemical conversion treatment coating layer 40 in this embodiment, examples include a composition containing one or more substances selected from the group consisting of resin, silane coupling agent, zirconium compound, silicon dioxide, 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 factors such as moisture and corrosive ions, and the adhesion of the coating to the plated surface can be further improved, which helps to improve the corrosion resistance of the coating.

[0094] In particular, when the chemical conversion treated coating layer 40 contains any one or more of silane coupling agents or zirconium compounds, a cross-linked structure is formed in the chemical conversion treated coating layer 40, and the bonding with the plated surface is also enhanced, thus further improving the adhesion and barrier properties of the coating.

[0095] In addition, when the chemically converted coating layer 40 contains any one or more of silicon dioxide, phosphate and its salts, fluorides or vanadium compounds, it functions as an inhibitor to form a precipitation coating or passivation coating on the coating layer or steel surface, thereby further improving corrosion resistance.

[0096] The following provides detailed examples of the components that may be included in such a chemically converted coating layer 40.

[0097] [Resin]

[0098] The resin is not particularly limited; for example, 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 with pre-coated steel sheets, it is preferable to use at least one resin (polyester resin, polyurethane resin, epoxy resin, acrylic resin, etc.) with forced sites and polar functional groups in its molecular chain. The resin can be used alone or in combination of two or more.

[0099] The resin content in the chemically converted coating layer 40 is preferably 0% by mass or more, more preferably 1% by mass or more, relative to the coating solids content. Furthermore, the resin content in the chemically converted coating layer 40 is preferably 85% by mass or less, more preferably 60% by mass or less, and even more preferably 40% by mass or less, relative to the coating solids content. When the resin content exceeds 85% by mass, the proportions of other coating components decrease, resulting in a decline in the performance required for the coating, except for corrosion resistance.

[0100] [Silane coupling agent]

[0101] 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-vinylbenzylaminoethyl)-γ-aminopropyltrimethoxysilane, N-β-(N-vinylbenzylaminoethyl)-γ-aminopropylmethyldimethoxysilane, N-β-(N-vinylbenzylaminoethyl)-γ-aminopropyltriethoxysilane, N-β-(N-vinylbenzylaminoethyl)-γ-aminopropylmethyldiethoxysilane, γ-epoxypropoxypropyltrimethoxysilane, γ-epoxypropoxypropylmethyldimethoxysilane, γ-epoxypropoxypropyltriethoxysilane, γ-epoxypropoxypropylmethyldiethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane γ-Methylpropylmethyldimethoxysilane, γ-mercaptopropyltriethoxysilane, γ-mercaptopropylmethyldiethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, vinyltriacetoxysilane, γ-chloropropyltrimethoxysilane, γ-chloropropylmethyldimethoxysilane, γ-chloropropyltriethoxysilane, γ-chloropropylmethyldiethoxysilane, hexamethyldisilazane, γ-anilinepropyltrimethoxysilane, γ-anilinepropylmethyldimethoxysilane, γ-anilinepropyltriethoxysilane, γ-anilinepropylmethyldiethoxysilane, ethyl... Alkenyltrimethoxysilane, 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 layer 40 can be set to, for example, 2 to 80 g / L. When the amount of silane coupling agent added is less than 2 g / L, the adhesion to the coating surface is insufficient, and there is a possibility of decreased processing adhesion of the coating film. In addition, when the amount of silane coupling agent added exceeds 80 g / L, the cohesion of the chemically converted coating layer is insufficient, and there is a possibility of reduced processing adhesion with the coating layer.The silane coupling agents listed above can be used in one or in combination of two or more.

[0102] [Zirconium compounds]

[0103] Examples of zirconium compounds include zirconium n-propoxide, zirconium n-butoxide, zirconium tetraacetylacetone, zirconium monoacetylacetone, zirconium diacetylacetone, zirconium monoacetylacetone, zirconium acetylacetone combined with ethyl diacetylacetone, 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 treated coating layer 40 can be set to, for example, 2 to 80 g / L. When the amount of zirconium compound added is less than 2 g / L, the adhesion to the coating surface is insufficient, and there is a possibility of decreased processing adhesion of the coating film. Furthermore, when the amount of zirconium compound added exceeds 80 g / L, the cohesion of the chemical conversion treated coating layer 40 is insufficient, and there is a possibility of decreased processing adhesion of the coating layer. This zirconium compound can be used alone or in combination of two or more.

[0104] Silicon dioxide

[0105] As silica, commercially available silica gels such as "Snowtex N," "Snowtex C," "Snowtex UP," and "Snowtex PS" manufactured by Nissan Chemical Co., Ltd., and "Adelite AT-20Q" manufactured by ADEKA Co., Ltd., or powdered silica such as Aerosil #300 manufactured by Aerosil Co., Ltd., or equivalent silica can be used. The silica can be appropriately selected based on the desired properties of the pre-coated steel sheet. The amount of silica added to the chemical conversion agent used to form the chemical conversion coating layer 40 is preferably, for example, 1 to 40 g / L. When the amount of silica added is less than 1 g / L, there is a possibility of decreased processing adhesion of the coating layer, while when the amount of silica added exceeds 40 g / L, the effects of processing adhesion and corrosion resistance are likely to saturate, which is therefore uneconomical.

[0106] Phosphate and its salts

[0107] Phosphoric acid and its salts include, for example, 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-hydroxyethylidene-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, regarding salts of phosphoric acid, besides ammonium salts, examples include metal salts containing Na, Mg, Al, K, Ca, Mn, Ni, Zn, and Fe. Phosphoric acid and its salts can be used alone or in combination of two or more.

[0108] It should be noted that the content of phosphoric acid and its salts is preferably 0% by mass or more, more preferably 1% by mass or more, relative to the solid composition of the coating. Furthermore, the content of phosphoric acid and its salts is preferably 20% by mass or less, more preferably 10% by mass or less, relative to the solid composition of the coating. When the content of phosphoric acid and its salts exceeds 20% by mass, the coating becomes brittle, resulting in a decrease in the processability of the coating when forming and processing the surface-treated steel sheet 1.

[0109] [Fluorides]

[0110] Examples of fluorides include ammonium zirconium fluoride, ammonium silicon fluoride, ammonium titanium fluoride, sodium fluoride, potassium fluoride, calcium fluoride, lithium fluoride, titanium hydrofluoride, and zirconium hydrofluoride. These fluorides can be used alone or in combination of two or more.

[0111] It should be noted that the fluoride content is preferably 0% by mass or more, more preferably 1% by mass or more, relative to the coating solids content. Furthermore, the fluoride content is preferably 20% by mass or less, more preferably 10% by mass or less, relative to the coating solids content. When the fluoride content exceeds 20% by mass, the coating becomes brittle, resulting in a decrease in the processability of the coating when forming and processing the surface-treated steel sheet 1.

[0112] [vanadium compounds]

[0113] Examples of vanadium compounds include pentavalent vanadium compounds such as vanadium pentoxide, metavanadate, ammonium metavanadate, sodium metavanadate, and vanadium trichloride, which are reduced to divalent to tetravalent vanadium compounds by reducing agents; and vanadium trioxide, vanadium dioxide, vanadium oxysulfate, vanadium oxyoxalate, vanadium oxyacetylacetonate, vanadium acetylacetonate, vanadium trichloride, vanadium phosphomolybdic acid, vanadium sulfate, vanadium dichloride, and vanadium oxide, which have oxidation states ranging from tetravalent to divalent. These vanadium compounds can be used alone or in combination of two or more.

[0114] It should be noted that the content of vanadium compounds is preferably 0% by mass or more, more preferably 1% by mass or more, relative to the solid composition of the coating. Furthermore, the content of vanadium compounds is preferably 20% by mass or less, more preferably 10% by mass or less, relative to the solid composition of the coating. When the content of vanadium compounds exceeds 20% by mass, the coating becomes brittle, resulting in a decrease in the processability of the coating when forming and processing the surface-treated steel sheet 1.

[0115] [Tannins or tannic acid]

[0116] Tannins or tannic acid can be either hydrolyzable tannins or condensed tannins. Examples of tannins and tannic acid include witch hazel tannin, gallnut tannin, gallnut tannin, Terminalia chebula tannin, sappanwood tannin, tannin from tanning agents, oak tannin, and catechin. The amount of tannin or tannic acid added to the chemical conversion agent used to form the chemical conversion coating 40 can be set to 2–80 g / L. When the amount of tannin or tannic acid added is less than 2 g / L, the adhesion to the coating surface is insufficient, and there is a possibility of decreased processing adhesion of the coating. In addition, when the amount of tannin or tannic acid added exceeds 80 g / L, the cohesion of the chemical conversion coating is insufficient, and there is a possibility of decreased processing adhesion of the coating.

[0117] In addition, within the limits of not impairing performance, acids, bases, etc., can be added to the chemical conversion agent used to form the chemical conversion coating layer 40 to adjust the pH.

[0118] After applying a chemical conversion treatment agent containing the aforementioned components to one or both sides of the steel plate 10, it is dried to form a chemical conversion treatment coating layer 40. In the surface-treated steel plate 1 of this embodiment, it is preferable to form a coating layer of 10 mg / m² on each side of the coating layer 20. 2 The above-mentioned chemically converted coating layer 40. More preferably, the adhesion amount of the chemically converted coating layer 40 is 20 mg / m³. 2 The above is further preferred to be 50 mg / m³. 2 That's all. Furthermore, in the surface-treated steel sheet 1 of this embodiment, it is preferable to form a coating layer 20 with a thickness of 1000 mg / m² on each single side. 2 The following is a chemically converted coating layer 40. The adhesion amount of the chemically converted coating layer 40 is more preferably 800 mg / m³. 2 The following is a further preferred value: 600 mg / m² 2 It should be noted that the film thickness of the chemically converted coating layer 40 corresponding to this amount of adhesion varies depending on the composition of the chemically converted agent, but is approximately 0.01 to 1 μm. It should also be noted that the film thickness of the chemically converted coating layer 40, like the film thickness of the colored coating layer 30, can be measured by cross-sectional observation.

[0119] Example

[0120] Hereinafter, the surface-treated steel sheet 1 of the present invention will be specifically described with reference to embodiments and comparative examples. It should be noted that the embodiments shown below are merely examples of the surface-treated steel sheet 1 of the present invention, and the surface-treated steel sheet 1 of the present invention is not limited to the following examples.

[0121] (1) Coated steel sheet

[0122] Five types of metal sheets, A1 to A5, as shown in Table 1 below, were prepared. The substrate for the metal sheets to be plated was a 0.7 mm thick steel sheet. Furthermore, these metal sheets were prepared with a coating concentration of 60 mg / m³. 2 The coated steel sheet underwent a chromate-free chemical conversion treatment (CT-E300 / manufactured by Pakase Seiji Co., Ltd., Japan). The treatment solution used in the chemical conversion treatment contained a silane coupling agent as a component, and the coating layer formed by this chemical conversion treatment functions as the chemical conversion coating layer. It should be noted that the presence or absence of chemical conversion treatment is as described in Tables 6 and 7 below.

[0123] (2) Preparation of coloring coatings

[0124] The colored coating used to form the colored film layer is prepared. For the binder resin that functions as a film-forming component, a resin equivalent to the resins shown in Table 2 below is prepared. For each resin solution, a melamine-based curing agent (equivalent to the curing agent manufactured by CYMEL 303 / Allnex) with a solids content of 30% by mass is prepared as the curing agent. Furthermore, resin particles equivalent to the particles shown in Table 3 below are prepared as resin particles. Additionally, substances equivalent to aluminum pigments, titanium dioxide, and carbon black (CB) shown in Table 4 below are prepared as coloring pigments. Additionally, compounds shown in Table 5 below are prepared as rust-preventive pigments. These coating compositions are mixed according to the specified particle size and specified amounts shown in Tables 6 and 7 below to prepare the colored coating.

[0125] (3) Sample preparation

[0126] The colored coating prepared as described above is applied to both sides of the plated steel sheet using a roller coater and heated to a maximum plate touch-down temperature (PMT) of 200°C to form a colored coating layer. It should be noted that the thickness of the prepared colored coating layer is measured by cross-sectional observation using the method described above, and the results are shown in Tables 6 and 7. It should be noted that in Tables 6 and 7, regarding "percentage of film thickness or greater (%)", in colored coating layer 30a, it refers to the percentage (%) of resin particles 303 with a film thickness of Ta or greater than Ga (Ga≥Ta) having the colored coating layer 30a; in colored coating layer 30b, it refers to the percentage (%) of resin particles 303 with a film thickness of Tb or greater than Gb (Gb≥Tb) having the colored coating layer 30b.

[0127] (4) Evaluation of the sample

[0128] The performance of each sample prepared by the above method was evaluated according to the following criteria. The evaluation results are summarized in Table 8 below.

[0129] <Resistance to surface contact damage>

[0130] The surface contact damage resistance was evaluated using the following method. The prepared sample was cut into two 50mm square pieces. One piece was fixed with the colored coating layer 30a facing upwards. The other piece was then layered on top of the first piece with the colored coating layer 30b facing downwards. The sample was then subjected to a pressure of 8.5 kgf / cm². 2 After rotating 90 degrees under pressure of 1 kgf (approximately 9.8 N), the condition of the colored coating layer 30a is evaluated according to the following criteria, with a score of 2 or higher considered acceptable.

[0131] Evaluation criteria for resistance to surface contact damage

[0132] 5: It is believed that there is almost no coating peeling, and that there is some or almost no change in gloss due to pressure.

[0133] 4: It is believed that there is extremely slight coating peeling, and that there is some gloss change due to pressure.

[0134] 3: It is believed that there is slight coating peeling and some gloss changes due to pressure.

[0135] 2: It is believed that there is slight coating peeling and gloss change due to pressure.

[0136] 1: It is believed that there is coating peeling and significant gloss change due to pressure.

[0137] <Corrosion Resistance>

[0138] The corrosion resistance was evaluated according to the following criteria. After sealing the end face of the test plate with tape, a 72-hour salt spray test (SST) based on JIS Z 2371 was conducted. The rusting was observed, and the results were evaluated according to the following criteria. A score of 2 or higher was considered acceptable.

[0139] Evaluation criteria for corrosion resistance

[0140] 5: The area affected by white rust is less than 1%, and no red rust has been produced.

[0141] 4: White rust covers an area of ​​more than 1% but less than 3%, and no red rust has been produced.

[0142] 3: White rust covers an area of ​​3% or more but less than 4%, and no red rust has been produced.

[0143] 2: White rust covers an area of ​​4% or more but less than 5%, and no red rust has been produced.

[0144] 1: White rust covers an area of ​​more than 5% or red rust is produced.

[0145] Scratch resistance

[0146] For reference performance, scratch resistance was evaluated using the following coin scratch test. A coin was brought into contact with the colored coating layer 30a of the prepared sample at a 45-degree angle and scratched under a load of 500g. Damage under each load was evaluated according to the following criteria, with a score of 2 or higher considered acceptable.

[0147] Evaluation criteria for scratch resistance

[0148] 5: No coating peeling or gloss change is expected.

[0149] 4: Although coating peeling is not considered, slight gloss changes are considered.

[0150] 3: It is believed that there is slight coating peeling and gloss change.

[0151] 2: It is believed that there is localized coating peeling and changes in gloss.

[0152] 1: The coating is completely peeled off.

[0153] <Indentation resistance>

[0154] As a reference performance, indentation resistance is evaluated according to the following criteria. The prepared sample is cut into two pieces: one 70mm square and one 50mm square. The 70mm square sample is fixed with the colored coating layer 30a facing upwards, and the 50mm square sample is stacked on top with the colored coating layer 30b facing downwards. The sample is then pressurized at 50°C and 10MPa for 5 minutes. After separating the two samples, the condition of the colored coating layer 30a of the 70mm square sample is evaluated according to the following criteria; a score of 2 or higher is considered acceptable.

[0155] Evaluation criteria for indentation resistance

[0156] 4: It is completely invisible when viewed from the front or at an angle.

[0157] 3: Although it is not visible when viewed from the front, a slight change in the gloss of the pressure section can be seen when viewed from an angle.

[0158] 2: Although it is not visible when viewed from the front, the change in gloss of the pressure section can be seen when viewed from an angle.

[0159] 1: The overall gloss change of the pressure section can be seen when viewed from the front or from an angle.

[0160] <Processing tightness>

[0161] As a reference performance, the processing tightness is evaluated according to the following criteria. After bending the prepared sample 90° with an inner radius of 1mm in an atmosphere at 20°C, a tape peeling test is performed on the outer side of the bent portion. The appearance of the peeled portion is evaluated according to the following evaluation criteria; a score of 2 or higher is considered acceptable.

[0162] Evaluation criteria for the tightness of the machining part

[0163] 4: Coating peeling is almost never considered to exist.

[0164] 3: It is believed that there is slight coating peeling.

[0165] 2: It is believed that there is localized coating peeling.

[0166] 1: It is believed that there is overall coating peeling.

[0167] [Table 1]

[0168] type metal plate A1 Hot-dip galvanized Zn-11%Al-3%Mg-0.2%Si steel sheet A2 Hot-dip galvanized Zn-6%Al-3%Mg steel sheet (Hv140) A3 Hot-dip galvanized steel sheet A4 Alloyed hot-dip galvanized steel sheet (Fe: 10%) A5 Zinc plate

[0169] [Table 2]

[0170] type Adhesive resin B1 Toyobo Corporation manufactures "MD-1480" (water-based polyester resin). B2 Toyobo Corporation manufactures "MD-2000" (water-based polyester resin). B3 Mitsui Chemicals manufactures "ALMATEX E208" (a water-based acrylic resin). B4 Mitsui Chemicals manufactures "ALMATEX E255" (a water-based acrylic resin). B5 Mitsui Chemicals manufactures "ALMATEX E271" (a water-based acrylic resin). B6 "SUPER FLEX 126" (waterborne polyurethane resin) manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.

[0171] [Table 3]

[0172] type Particles C1 Sekisui Kasei Corporation's "SSX-101" (acrylic resin particles, average particle size 1μm) C2 "MZ-5HN" (acrylic resin particles, average particle size 5μm) manufactured by Zongyan Chemical Co., Ltd. C3 Sekisui Kasei Corporation's "BM30X-8" (acrylic resin particles, average particle size 8μm) C4 "MZ-12H" (acrylic resin particles, average particle size 12μm) manufactured by Zongyan Chemical Co., Ltd. C5 HSP-1000 (silica particles, average particle size 1μm) manufactured by Dong-A Synthetic Co., Ltd. C6 Mitsui Chemicals manufactures "CHEMIPEARL_W800" (polyolefin resin particles, average particle size 8μm). C7 Genjo Kogyo Co., Ltd. manufactures "P-800T" (polyurethane resin particles, average particle size 6μm). C8 C1 and C2 were mixed until the average particle size was 2 μm. C9 C2 and C3 were mixed until the average particle size was 6 μm.

[0173] [Table 4]

[0174] type Coloring pigments D1 Ishihara Sangyo Co., Ltd. produces titanium dioxide "R-780". D2 Mitsubishi Chemical's carbon black "MCF#850" D3 Mix D2 and D3 in a 3:1 ratio (by mass%)

[0175] [Table 5]

[0176] type Rust-preventive pigments E1 Aluminum tripolyphosphate E2 Calcium vanadate E3 Mix E1 and E2 in a 1:1 ratio (by mass%)

[0177] [Table 6]

[0178]

[0179] [Table 7]

[0180]

[0181] [Table 8]

[0182]

[0183] As can be seen from Table 8 above, the samples belonging to the embodiments of the present invention exhibit excellent resistance to surface contact damage and excellent corrosion resistance, while the samples belonging to the comparative examples of the present invention have poor evaluation of either resistance to surface contact damage or corrosion resistance, and have not achieved a balance between resistance to surface contact damage and corrosion resistance.

[0184] The 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 these examples. It is obvious that those skilled in the art will conceive of various modifications or variations within the scope of the technical concept described in the patent claims, and these are also understood to fall within the technical scope of the present invention.

[0185] The embodiments disclosed herein are exemplary and not restrictive in all respects. Various omissions, substitutions, or modifications can be made to the above embodiments without departing from the technical features and spirit of the appended claims, the scope of the invention described below. For example, the technical features of the above embodiments can be arbitrarily combined without impairing their effectiveness. Furthermore, such arbitrary combinations can naturally achieve the effects of each technical feature involved in the combination, and other obvious effects and functions will be apparent to those skilled in the art based on the description herein.

[0186] Furthermore, the effects described in this specification are merely illustrative or exemplary, and not limiting. That is, the technology involved in this invention may provide other obvious effects besides or alternatives to those described above, and those skilled in the art will be able to obtain them based on the description in this specification.

[0187] It should be noted that the following technical features also fall within the technical scope of this invention.

[0188] (1) A surface-treated steel plate, comprising:

[0189] A zinc-containing coating layer located on both surfaces of a steel plate;

[0190] A first colored coating layer located on the plating layer on one side of the steel plate; and

[0191] A second colored coating layer located on the plating layer on the other side of the steel plate.

[0192] The ratio of the thickness of the second colored coating layer to the thickness of the first colored coating layer is 0.1 or more and 0.5 or less.

[0193] The first colored coating layer and the second colored coating layer contain resin particles.

[0194] When observing the cross-section formed by cutting the first colored coating layer along the film thickness direction,

[0195] For the observed resin particles, when the length occupied along the film thickness direction of the first colored coating layer is defined as the thickness of the resin particles,

[0196] The number of resin particles having a thickness greater than or equal to the thickness of the first colored coating layer is 1% to 30% of the total number of resin particles observed.

[0197] When observing the cross-section formed by cutting the second colored coating layer along the film thickness direction,

[0198] For the observed resin particles, when the length occupied along the film thickness direction of the second colored coating layer is defined as the thickness of the resin particles,

[0199] The number of resin particles having a thickness greater than or equal to the thickness of the second colored coating layer is 50% or more and less than 100% of the total number of resin particles observed.

[0200] (2) According to the surface-treated steel plate described in (1) above, when observing the first colored coating layer in cross section, a length of 1000 μm in a direction orthogonal to the film thickness direction of the first colored coating layer is set as the first observation length. When the length of the portion occupied by the resin particles within the first observation length is projected onto the film thickness direction, and the length of the portion corresponding to the resin particles in a direction orthogonal to the film thickness direction is set as the first occupation length, the ratio of the first occupation length to the first observation length is 15% or more and 40% or less.

[0201] The second observation length is defined as 1000 μm in a direction orthogonal to the film thickness direction of the second colored coating layer. When the length of the part occupied by the resin particle is projected onto the film thickness direction within the range of the second observation length, the length of the part corresponding to the resin particle in a direction orthogonal to the film thickness direction is defined as the second occupation length. The ratio of the second occupation length to the second observation length is more than 5% and less than 15%.

[0202] (3) The surface-treated steel sheet according to (1) or (2) above, wherein the thickness of the first colored coating layer is 3 μm or more and 10 μm or less.

[0203] (4) The surface-treated steel sheet according to any one of (1) to (3) above, wherein the thickness of the resin particles contained in the first colored coating layer is less than twice the film thickness of the first colored coating layer.

[0204] The thickness of the resin particles contained in the second colored coating layer is less than three times the film thickness of the second colored coating layer.

[0205] (5) The surface-treated steel plate according to any one of (1) to (4) above, wherein the resin particles are acrylic resin particles.

[0206] (6) The surface-treated steel sheet according to any one of (1) to (5) above, wherein the glass transition temperature Tg of the film-forming components of the first colored coating layer and the second colored coating layer is 30°C or higher and 70°C or lower.

[0207] (7) The surface-treated steel sheet according to any one of (1) to (6) above, wherein a chemical conversion treatment coating layer is further provided between the plating layer and the first color coating layer on one side of the steel sheet and between the plating layer and the second color coating layer on the other side of the steel sheet.

[0208] (8) The surface-treated steel sheet according to any one of (1) to (7) above, wherein the average particle size of the resin particles is 3 μm or more and 15 μm or less.

[0209] Explanation of reference numerals in the attached figures

[0210] 1. Surface-treated steel plate

[0211] 10 steel plates

[0212] 20 Coating Layers

[0213] 30 Colored Coating Layer

[0214] 40 Chemical conversion treatment coating layer

[0215] 301 Film-forming ingredients

[0216] 303 resin particles

Claims

1. A surface-treated steel plate, comprising: A zinc-containing coating layer located on both surfaces of a steel plate; A first colored coating layer located on the plating layer on one side of the steel plate; and A second colored coating layer located on the plating layer on the other side of the steel plate. The ratio of the thickness of the second colored coating layer to the thickness of the first colored coating layer is 0.1 or more and 0.5 or less. The first colored coating layer and the second colored coating layer contain resin particles. When observing the cross-section formed by cutting the first colored coating layer along the film thickness direction, For the observed resin particles, when the length occupied along the film thickness direction of the first colored coating layer is defined as the thickness of the resin particles, The number of resin particles having a thickness greater than or equal to the thickness of the first colored coating layer is 1% to 30% of the total number of resin particles observed. When observing the cross-section formed by cutting the second colored coating layer along the film thickness direction, For the observed resin particles, when the length occupied along the film thickness direction of the second colored coating layer is defined as the thickness of the resin particles, The number of resin particles having a thickness greater than or equal to the thickness of the second colored coating layer is 50% or more and less than 100% of the total number of resin particles observed.

2. The surface-treated steel plate according to claim 1, wherein, When observing the first colored coating layer in cross-section, a length of 1000 μm in a direction orthogonal to the film thickness direction of the first colored coating layer is defined as the first observation length. When the length of the portion occupied by the resin particles within the first observation length, projected onto the film thickness direction, is defined as the sum of the lengths of the portions corresponding to the resin particles in a direction orthogonal to the film thickness direction, the ratio of the first occupation length to the first observation length is 15% or more and 40% or less. The second observation length is defined as 1000 μm in a direction orthogonal to the film thickness direction of the second colored coating layer. When the length of the part occupied by the resin particle is projected onto the film thickness direction within the range of the second observation length, the length of the part corresponding to the resin particle in a direction orthogonal to the film thickness direction is defined as the second occupation length. The ratio of the second occupation length to the second observation length is more than 5% and less than 15%.

3. The surface-treated steel plate according to claim 1 or 2, wherein, The thickness of the first colored coating layer is 3 μm or more and 10 μm or less.

4. The surface-treated steel plate according to claim 1 or 2, wherein, The thickness of the resin particles contained in the first colored coating layer is less than twice the film thickness of the first colored coating layer. The thickness of the resin particles contained in the second colored coating layer is less than three times the film thickness of the second colored coating layer.

5. The surface-treated steel plate according to claim 1 or 2, wherein, The resin particles are acrylic resin particles.

6. The surface-treated steel plate according to claim 1 or 2, wherein, The glass transition temperature (Tg) of the film-forming components of the first colored coating layer and the second colored coating layer is above 30°C and below 70°C.

7. The surface-treated steel plate according to claim 1 or 2, wherein, A chemical conversion coating layer is also provided between the plating layer and the first color coating layer on one side of the steel plate, and between the plating layer and the second color coating layer on the other side of the steel plate.

8. The surface-treated steel plate according to claim 1 or 2, wherein, The average particle size of the resin particles is greater than 3 μm and less than 15 μm.

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