Coated steel sheet

Abstract

[Problem] To provide a coated steel sheet that is capable of, while having a low gloss coating film layer having particles or a thin film portion, further improving corrosion resistance and productivity. [Solution] Provided is a coated steel sheet having two or more coating film layers including an anti-corrosion coating film layer on at least one surface of a Zn-containing plating layer. The 60° specular gloss GS (60°) defined in JIS Z 8741:1997 of the coating film layers on at least one surface of the steel sheet is at most 20%. The average film thickness of the anti-corrosion coating film layer is 5-15 μm. The anti-corrosion coating film layer contains a binder resin, a crosslinking agent, and an anti-corrosion pigment. In a cross-section of the coating film layer taken along the thickness direction at any position, the presence ratio of the anti-corrosion pigment with respect to the total area of the anti-corrosion coating film layer is 30-60% in terms of area ratio.

Description

painted steel plate

[0001] The present invention relates to a coated steel sheet.

[0002] Steel sheets with high designability have come to be used for applications such as building materials, home appliances, and automobiles. One example of such high designability is a steel sheet with a matte appearance with reduced gloss. An example of a steel sheet with a matte appearance is a low-gloss painted steel sheet in which an organic coating layer containing resin particles is applied to the steel sheet surface. Furthermore, among steel sheets having a coating layer on the surface, a steel sheet provided with an anti-rust coating layer containing an anti-rust pigment to improve the corrosion resistance of the steel sheet is known.

[0003] For example, Patent Document 1 below proposes a technology for improving the scratch resistance of an organic coating in a zinc-based plated steel sheet having an organic coating by incorporating resin particles (hereinafter also referred to as "large particle size particles") having a particle size larger than the thickness of the organic coating into the organic coating.

[0004] International Publication No. 2014 / 112544

[0005] Such a steel sheet having a matte appearance has large irregularities on the steel sheet surface due to the application of a low-gloss coating or the like, and these irregularities suppress light reflection, thereby achieving a low gloss. Therefore, the layer constituting the low-gloss coating (hereinafter also referred to as the "low-gloss coating layer") may contain a thin film portion. If a flaw or the like occurs in the thin film portion, corrosive factors in the environment, such as rainwater, can easily penetrate through the flaw or the like, which can be a factor in causing corrosion on the steel sheet surface. Furthermore, when an organic coating containing large particles as proposed in Patent Document 1 is used as the low-gloss coating layer, the large particles are largely exposed from the binder resin layer constituting the organic coating. The above-mentioned corrosive factors can easily penetrate from the interface between the large particles and the binder resin layer, which can be a factor in causing corrosion on the steel sheet surface.

[0006] Furthermore, when a zinc-based plated steel sheet having an organic coating containing large particles is wound into a coil or subjected to a predetermined press processing, the large particles may fall off from the organic coating, thereby reducing the design quality of the organic coating. Furthermore, there is a concern that the large particles that fall off from the organic coating may contaminate various equipment used for winding into a coil or performing press processing, thereby hindering the processing. For these reasons, when handling an organic coating containing large particles, sufficient care must be taken during handling, and there is room for further improvement in terms of improving productivity.

[0007] Therefore, the present invention has been made in consideration of the above problems, and an object of the present invention is to provide a coated steel sheet that has a low-gloss coating film layer having particles or thin film portions, while being able to further improve corrosion resistance and productivity.

[0008] To solve the above problems, the present inventors conducted extensive research and came up with the following idea. Specifically, if the surfaces of particles contained in an organic resin coating layer and having a particle size larger than the average film thickness can be coated with an organic resin, the interface between the large particles and the binder resin layer can be lengthened. Furthermore, by providing a "long interface between the large particles and the binder resin layer," certain portions of the particles protruding from the binder resin layer are covered with a film-forming component, thereby reducing the exposed portion of the particles. Furthermore, such a long interface between the large particles and the binder resin layer can inhibit the intrusion of corrosive factors, thereby suppressing corrosion. It can also prevent particle shedding and deformation. Based on this idea, the present inventors conducted detailed studies on the application conditions for a coating material containing particles having a particle size larger than the average film thickness. As a result, the present inventors have found that when the average particle size of the particles, the average film thickness of the organic resin coating layer, the thickness of the organic resin coating the surfaces of the particles, etc., satisfy certain conditions, it is possible to prevent the particles from falling off from the organic resin coating layer and to prevent deformation, thereby further improving the design and productivity of the coated steel sheet. The gist of the present invention, which was completed based on these findings, is as follows.

[0009] [1] A coated steel sheet having a Zn-containing plating layer and two or more coating layers including a rust-preventive coating layer on at least one side of the steel sheet, wherein the 60-degree specular gloss GS(60°) of the coating layer on at least one side of the steel sheet as defined in JIS Z 8741:1997 is 20% or less, the average film thickness of the rust-preventive coating layer is 5 μm or more and 15 μm or less, the rust-preventive coating layer contains a binder resin, a crosslinking agent, and a rust-preventive pigment, and in a cross section taken at an arbitrary position in the thickness direction of the coating layer, the abundance ratio of the rust-preventive pigment to the total area of ​​the rust-preventive coating layer is 30% or more and 60% or less in terms of area ratio. [2] The coated steel sheet according to the above [1], wherein the rust-preventive pigment contains at least one of Si, P, Mg, and V. [3] The coated steel sheet according to [2] above, wherein the Si comprises one or more of calcium ion-exchanged silica and magnesium ion-exchanged silica, the P comprises one or more of zinc phosphate, magnesium dihydrogen phosphate, and aluminum dihydrogen triphosphate, and the Mg comprises one or more of magnesium dihydrogen phosphate, magnesium oxide, and magnesium hydroxide. [4] The coated steel sheet according to [1] or [2] above, wherein, on the surface of the steel sheet having a 60-degree specular gloss GS(60°) of 20% or less, the anticorrosive coating layer is located below the two or more coating layers, and the colored coating layer is located in the outermost layer furthest from the steel sheet, the colored coating layer containing resin particles and, as film-forming components, a binder resin, a crosslinking agent, and a color pigment, and the average particle size of the resin particles in the cross section is from 2 to 5 times the average film thickness of the outermost coating layer in a portion not containing the resin particles. The average particle size is a value obtained by measuring the circle-equivalent diameters of the resin particles present in one observation field of view on the cross section, calculating the average of the two largest circle-equivalent diameters among the circle-equivalent diameters, and similarly averaging the average values ​​obtained for 10 arbitrary observation field of view areas by the number of fields. [5] The coated steel sheet according to the above [4], wherein the abundance ratio of the resin particles to the total area of ​​the outermost coating layer is 5% or more and 30% or less in terms of area ratio.[6] The coated steel sheet according to [4] above, wherein in the cross section, protruding portions of the resin particles protruding from the surface position in the portion of the outermost coating layer not containing the resin particles are covered with the film-forming component to a thickness of 0.5 μm or more over at least half of the length along the outer periphery of the protruding portions. [7] The coated steel sheet according to [4] above, wherein the resin particles are resin particles made of acrylic resin. [8] The coated steel sheet according to [5] above, wherein the resin particles are resin particles made of acrylic resin. [9] The coated steel sheet according to [6] above, wherein the resin particles are resin particles made of acrylic resin.

[10] The coated steel sheet according to [4] above, wherein the binder resin is a binder resin made of acrylic resin or polyester resin.

[11] The coated steel sheet according to [5] above, wherein the binder resin is a binder resin made of acrylic resin or polyester resin.

[12] The coated steel sheet according to [6] above, wherein the binder resin is a binder resin made of acrylic resin or polyester resin.

[13] The coated steel sheet according to [7] above, wherein the binder resin is an acrylic resin or a polyester resin.

[14] The coated steel sheet according to [8] above, wherein the binder resin is an acrylic resin or a polyester resin.

[15] The coated steel sheet according to [9] above, wherein the binder resin is an acrylic resin or a polyester resin.

[16] The coated steel sheet according to [1] or [2] above, wherein the surface of the steel sheet having a 60-degree specular gloss GS(60°) of 20% or less has a surface roughness Ra of 2 μm or more, or the coating layer contains 15% or more of an aggregate composed of a silica-containing pigment.

[0010] As described above, according to the present invention, it is possible to prevent particles from falling off from the organic resin coating layer and deformation, thereby further improving the design and productivity of coated steel sheets.

[0011] FIG. 1 is a schematic diagram for explaining an example of the structure of a coated steel plate according to an embodiment of the present invention. FIG. 2 is a schematic diagram for explaining an example of the structure of a coated steel plate according to the same embodiment. FIG. 3 is a schematic diagram for explaining an example of the structure of a coated steel plate according to the same embodiment. FIG. 4 is a schematic diagram for explaining an outermost coating layer in a coated steel plate according to the same embodiment. FIG. 5 is a schematic diagram for explaining an outermost coating layer in a coated steel plate according to the same embodiment. FIG. 6 is a schematic diagram for explaining a thin film portion in a coated steel plate according to another embodiment. FIG. 7 is a schematic diagram for explaining a thin film portion in a coated steel plate according to yet another embodiment.

[0012] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant explanations will be omitted.

[0013] [Regarding the Steel Plate 10] In the coated steel plate 1 according to this embodiment, various steel plates can be used as the base material, that is, the steel plate 10. As the material for such a steel plate, various steel plates can be used, such as Al-killed steel, ultra-low carbon steel containing Ti, Nb, etc., and high-strength steel in which extra-low carbon steel further contains strengthening elements such as P, Si, Mn, etc.

[0014] Among the various steel sheets described above, it is preferable to use a zinc-based plated steel sheet as the steel sheet 10 according to the present embodiment, in which a variety of zinc-based plating layers containing at least zinc are provided on the surface of a steel sheet serving as a substrate. Examples of zinc-based plated steel sheets include zinc-plated steel sheets, zinc-nickel-plated steel sheets, zinc-iron-plated steel sheets, zinc-chromium-plated steel sheets, zinc-aluminum-plated steel sheets, zinc-titanium-plated steel sheets, zinc-magnesium-plated steel sheets, zinc-manganese-plated steel sheets, zinc-aluminum-magnesium-plated steel sheets, and zinc-aluminum-magnesium-silicon-plated steel sheets. Furthermore, zinc-based plated steel sheets may contain small amounts of different metal elements or impurities, such as cobalt, molybdenum, tungsten, nickel, titanium, chromium, aluminum, manganese, iron, magnesium, lead, bismuth, antimony, tin, copper, cadmium, and arsenic, or may have inorganic substances, such as silica, alumina, and titania, dispersed therein. Furthermore, the zinc-based plated steel sheet may be a steel sheet having a multi-layer plating that combines the above-mentioned plating with other types of plating (e.g., iron plating, iron-phosphorus plating, nickel plating, cobalt plating, etc.) The plating method is not particularly limited, and various known plating methods such as electroplating, hot-dip plating, vapor deposition plating, dispersion plating, vacuum plating, etc. may be used.

[0015] A coating film 11 is provided on the surface of the steel sheet 10. The coating film 11 includes a rust-preventive coating layer 20. In one embodiment, the coating film 11 also includes an outermost coating layer 30 as a colored coating layer according to the present disclosure. In the coating film 11, the rust-preventive coating layer 20 is located on the surface of the steel sheet 10. The outermost coating layer 30 is located as the outermost layer of the coating film 11. In the coating film 11 according to this embodiment, the outermost coating layer 30 is provided in contact with the surface of the rust-preventive coating layer 20, but other desired coating layers may be provided between the rust-preventive coating layer and the outermost coating layer 30.

[0016] Here, the thickness of the steel plate 10 as described above is not particularly limited, and may be set appropriately depending on the mechanical strength (e.g., tensile strength, etc.) and processability required for the coated steel plate 1 of this embodiment.

[0017] [Regarding the Rust-Preventive Coating Layer 20] In the coated steel sheet 1 according to this embodiment, the rust-preventive coating layer 20 provided on the surface of the steel sheet 10 will be described. The rust-preventive coating layer 20 is a resin film layer containing a binder resin, a crosslinking agent, and a rust-preventive pigment.

[0018] 1A to 1C, the rust-preventive coating layer 20 is provided on one side (FIG. 1A) or both sides (FIGS. 1B and 1C) of the steel sheet 10. By providing the rust-preventive coating layer 20 on at least one side of the steel sheet 10, corrosion of the steel sheet 10 on that side can be suppressed. Furthermore, by providing the rust-preventive coating layer 20 on both sides of the steel sheet 10, corrosion of the steel sheet 10 can be suppressed on both sides, and excellent edge corrosion resistance can be exhibited.

[0019] The binder resin contained in the rust-preventive coating layer 20 functions as a film-forming component, and any material can be used. However, from the viewpoints of ease and cost of production, as well as corrosion resistance and scratch resistance, it is preferable to use various organic resins as the binder resin. Examples of such resins include acrylic resins, polyester resins, urethane resins, and fluorine-based resins.

[0020] The anti-rust pigment contained in the anti-rust coating layer 20 may be any of various known anti-rust pigments containing at least one element selected from P, V, Si, and Mg.

[0021] Examples of pigments containing at least one of the elements P, V, Si, and Mg include those in which Si includes one of calcium ion-exchanged silica and magnesium ion-exchanged silica, P includes one of zinc phosphate, magnesium dihydrogen phosphate, and aluminum dihydrogen triphosphate, Mg includes one of magnesium dihydrogen phosphate, magnesium oxide, and magnesium hydroxide, and V includes calcium vanadate.

[0022] The average thickness of the anticorrosive coating layer 20 is 5 μm or more and 15 μm or less. By making the average thickness of the anticorrosive coating layer 20 5 μm or more, it is possible to sufficiently suppress corrosion caused by corrosion factors that may penetrate through the thin film portion or the interface between the particles and the binder resin. The average thickness of the anticorrosive coating layer 20 is preferably 7.0 μm or more.

[0023] On the other hand, by setting the average thickness of the rust-preventive coating layer 20 to 15 μm or less, it is possible to suppress the occurrence of a coating defect called popping during paint baking. The average thickness of the rust-preventive coating layer 20 is preferably 12 μm or less.

[0024] Furthermore, in the anti-rust coating layer 20, when a cross section of the coating film 11 cut in the thickness direction at any position is observed, the proportion of the anti-rust pigment relative to the total area of ​​the anti-rust coating layer 20 is, in terms of area ratio, 30% to 60%. By making the anti-rust pigment proportion 30% or more, it is possible to ensure a sufficient effect of inhibiting corrosion against corrosion factors that may penetrate through the thin film portion or the interface between the particles and the binder resin. The anti-rust pigment proportion is preferably 40% or more.

[0025] On the other hand, by setting the abundance ratio of the rust-preventive pigment to 60% or less, it is possible to ensure sufficient adhesion between the rust-preventive coating layer 20 and the steel sheet 10, particularly adhesion at the processed portion. The abundance ratio of the rust-preventive pigment is preferably 50% or less.

[0026] The average film thickness of the rust-preventive coating layer 20 is determined by the following procedure. First, a cross section obtained by cutting the coating film 11 according to this embodiment at an arbitrary position in the thickness direction is focused on. Then, the cross section is observed using an electron microscope (more specifically, a field emission scanning electron microscope (FE-SEM)). Next, the thickness of the rust-preventive coating layer 20 is measured at 10 locations in the field of view of the cross section of interest. In this case, the thickness of the rust-preventive coating layer 20 may be measured using a length measurement function or the like implemented in the FE-SEM. The measured values ​​obtained at the 10 locations are then averaged to obtain the average thickness of the rust-preventive coating layer 20 in the field of view of interest. The above-mentioned operation is performed for any 10 fields of view, and the average values ​​obtained from each of the obtained fields of view are further averaged by the number of fields of view. The value thus obtained is the average film thickness of the anticorrosive coating layer 20 .

[0027] The proportion of the rust-preventive pigment relative to the total area of ​​the rust-preventive coating layer 20 is calculated as follows. That is, as in the case of measuring the average film thickness described above, attention is focused on a cross section obtained by cutting the coating film 11 according to this embodiment in the thickness direction at an arbitrary position. In the cross section of interest, attention is focused on a certain observation field area (width: 40 μm). In this case, the magnification of the FE-SEM may be set to an appropriate magnification (e.g., approximately 3000x) so that a length of 40 μm in the width direction fits within one field of view. The area proportion (i.e., area ratio) of the rust-preventive pigment relative to the total area of ​​the rust-preventive coating layer 20 in the observation field area of ​​this size is then calculated using various functions implemented in the electron microscope, image processing, etc. By performing this observation on 10 arbitrary observation field areas, 10 measured values ​​of the area ratio of the rust-preventive pigment can be obtained. The average of the 10 measured values ​​thus obtained is calculated as the average area ratio of the rust-preventive pigment in the cross section. Thus, this average area ratio is the average value of the area ratio occupied by the anti-rust pigment to the total area of ​​the anti-rust coating layer 20 in the 10 observed visual field regions. This average value is the abundance ratio of the anti-rust pigment. The anti-rust pigment in the coating film 11 can be identified by confirming the elements present in the particles present in the coating film 11 using EDS analysis (Energy Dispersive X-ray Spectroscopy).

[0028] 1A to 1C, the outermost coating layer 30 according to this embodiment is located in the outermost layer of the coating film 11, and is a resin film layer in which particles 101 are present in a dispersed state in a binder resin 103 as a film-forming component. In addition to the particles 101 and binder resin 103, the outermost coating layer 30 may further contain various additives such as a crosslinking agent, a colorant, etc.

[0029] The outermost coating layer 30 has a surface with a 60-degree specular gloss G defined in JIS Z 8741:1997. Ｓ (60°), the 60° specular gloss G ＳThe 60° specular gloss value G is 20 or less. In the coated steel sheet 1 according to this embodiment, the surface of the outermost coating layer 30 exhibits a gloss within the above range, so that the coated steel sheet 1 according to this embodiment exhibits a superior matte appearance (and thus superior design). Ｓ The value of (60°) is more preferably 5 or more. Ｓ The value of (60°) is more preferably 15 or less.

[0030] In the coated steel sheet 1 according to this embodiment, particles 101 are dispersed in the binder resin 103 in the outermost coating layer 30. In addition, the particles 101 satisfy the conditions described in detail below. This allows the binder resin 103 to achieve predetermined corrosion resistance and scratch resistance. Furthermore, the coated steel sheet 1 as a whole achieves excellent design, combining a grained appearance with a matte appearance. Furthermore, the interface between the particles 101 and the binder resin 103 is lengthened, thereby making it possible to suppress corrosion of the steel sheet. Secondarily, it also makes it possible to prevent the occurrence of pressure marks caused by the organic coating in the deformed portion becoming relatively flat.

[0031] <Regarding the particles 101> In the outermost coating layer 30 according to this embodiment, the particles 101 protrude from the surface of the portion of the outermost coating layer 30 that does not contain the particles 101. This makes it possible to achieve an excellent design that combines a grained appearance and a matte appearance for the entire coated steel sheet 1. The relationship between the outermost coating layer 30 and the particles 101 will be described in detail below.

[0032] Furthermore, it is more preferable that the particles 101 have predetermined toughness and ductility. When the particles 101 have predetermined toughness and ductility, they can absorb impacts applied to the outermost coating layer 30. As a result, in the coated steel sheet 1 according to this embodiment, the scratch resistance of the outermost coating layer 30 can be further improved. Furthermore, when the particles 101 have predetermined toughness and ductility, it is possible to more effectively prevent the occurrence of pressure marks caused by the organic coating in the deformed portion becoming relatively flat. Furthermore, even if a scratch occurs in the outermost coating layer 30, the scratch can be prevented from reaching the steel sheet 10, and the corrosion resistance of the coated steel sheet 1 can be maintained.

[0033] In the outermost coating layer 30 according to this embodiment, particles 101 made of various materials can be used as long as they have predetermined toughness and ductility. However, from the viewpoint of having better toughness and ductility, it is more preferable to use organic resin particles made of organic resin rather than inorganic particles made of inorganic compounds such as silica and ceramics.

[0034] Examples of organic resin particles used as particles 101 include resin particles made of acrylic resin, resin particles made of polyester resin, resin particles made of urethane resin, resin particles made of fluorine resin, resin particles made of silicone resin, and resin particles made of polyolefin resin. Among these, from the viewpoint of more easily achieving the desired toughness and ductility, it is more preferable to use resin particles made of urethane resin or resin particles made of acrylic resin as particles 101. Among these, it is even more preferable to use resin particles containing acrylic resin as the main component as particles 101.

[0035] On the other hand, when thermoplastic resin particles are used as the resin particles, it is preferable that the resin particles have a melting point low enough to prevent melting when a baking process is performed during the production process of coated steel sheets, as described below. By having such a melting point, it is possible to prevent the particles 101 from melting during the coating baking process, and a desired 60-degree specular gloss GS (60°) can be obtained. As will be described in detail later, the maximum plate temperature achieved during baking can be set within a range of 180 to 250°C, so it is preferable that the resin particles have a melting point high enough to exceed this maximum plate temperature.

[0036] It should be noted that a plurality of types of particles having different average particle sizes may be contained as the particles 101. Furthermore, the particles 101 may also function as various additives that can be added to the outermost coating layer 30, such as a colorant or a rust inhibitor.

[0037] <<Regarding the Binder Resin 103>> The binder resin 103 as a film-forming component contained in the outermost coating layer 30 according to this embodiment can be any material as long as it functions as a binder for the particles 101. However, from the viewpoints of ease and cost of production, as well as corrosion resistance and scratch resistance, it is preferable to use various organic resins as the binder resin 103. Examples of such binder resins 103 include acrylic resins, polyester resins, urethane resins, and fluorine-based resins. Among these, it is even more preferable to use a binder resin whose main component is an acrylic resin or a polyester resin.

[0038] In a preferred embodiment of the outermost coating layer 30, an organic resin having a high affinity with the particles 101 is selected as the binder resin 103. This further improves the affinity between the particles 101 and the binder resin 103, making it possible to further suppress the particles 101 from falling off. It is also possible to further improve the adhesion and barrier properties of the outermost coating layer 30. As an example of resin particles having a high affinity with the particles 101, the same type of resin as the particles 101 is selected. As another example of resin particles having a high affinity with the particles 101, when an acrylic resin is selected as the particles 101, a polyester-based resin is selected as the binder resin 103.

[0039] In another preferred embodiment of the outermost coating layer 30, when an acrylic resin is selected for the particles 101, a binder resin containing a polyester / melamine curing resin as a main component is selected for the binder resin 103. This further improves the affinity between the binder resin 103 and the acrylic resin for the particles 101 due to the action of the melamine resin as a crosslinking agent (curing agent) used to crosslink (cure) the binder resin 103, thereby further suppressing the detachment of the particles 101. In a preferred embodiment, the binder resin 103 is made of a polyester / melamine curing resin.

[0040] <Regarding the state of presence of particles 101 in the outermost coating layer 30> Next, the distribution state of the particles 101 in the outermost coating layer 30 according to this embodiment will be described in detail with reference to Fig. 2. Fig. 2 is an explanatory diagram for explaining the outermost coating layer 30 in the coated steel sheet 1 according to this embodiment.

[0041] In the coated steel sheet 1 according to this embodiment, particles 101 are present in a dispersed state in film-forming components such as a binder resin 103 and color pigments that constitute the outermost coating layer 30. In discussing the state of existence of such particles 101, attention will be focused below on a cross section obtained by cutting the coating film 11 according to this embodiment at an arbitrary position in the thickness direction, as shown schematically in Figure 2. Then, this cross section will be observed by FE-SEM, and the state of existence of the particles 101 will be discussed.

[0042] More specifically, as with the above-described anticorrosive coating layer 20, attention is focused on a cross section obtained by cutting the coating film 11 according to this embodiment in the thickness direction at an arbitrary position. In the cross section of interest, a region having a length of 40 μm in a direction perpendicular to the thickness direction (hereinafter also referred to as the width direction) is set as the observation field region for one microscope observation, and 10 such observation field regions are arbitrarily set within the cross section of interest. Then, based on the measurement results obtained at the 10 positions, a feature quantity representing the presence state of the particles 101 is calculated as described below.

[0043] ◇ Abundance ratio of particles 101 in cross section The abundance ratio of particles 101 in the cross section described above in the outermost coating layer 30 according to this embodiment is in the range of 5% or more and 30% or less, in terms of the average area ratio (i.e., average area ratio), which is the area ratio of particles 101 in the outermost coating layer 30.

[0044] Here, the average area ratio is calculated as follows. That is, in the cross section of interest, a certain observation field region (length in the width direction: 100 μm) is focused on. In this case, the magnification of the FE-SEM may be set to an appropriate magnification (for example, about 1000x) such that a length of 100 μm in the width direction fits within one field of view. Then, the area ratio (i.e., area ratio) of the particles 101 in the outermost coating layer 30 in the observation field region of this size is calculated using various functions implemented in the electron microscope, image processing, etc. By performing such observation on 10 arbitrary observation field regions, 10 measured values ​​of the area ratio of the particles 101 can be obtained. The average value of the 10 measured values ​​thus obtained is calculated to be the average area ratio of the particles 101 in the cross section. In this way, the average area ratio is the average value of the area ratio of the resin particles with respect to the total area of ​​the 10 observation field regions observed.

[0045] If the average area ratio of particles 101 in the cross section is less than 5%, the presence ratio of particles 101 is too low and the desired design cannot be achieved. If the average area ratio of particles 101 is 5% or more, it becomes possible to achieve an excellent design that combines a grained appearance and a matte appearance. The average area ratio of particles 101 in the cross section is preferably 10% or more, and more preferably 15% or more.

[0046] On the other hand, if the average area ratio of the particles 101 in the cross section exceeds 30%, the presence ratio of the particles 101 is too high, and as a result, not only cannot the scratch resistance required for the outermost coating layer 30 be realized, but also the desired design (particularly, a matte appearance) cannot be realized. By making the average area ratio of the particles 101 30% or less, it becomes possible to realize the scratch resistance required for the outermost coating layer 30 while also realizing the desired design. The average area ratio of the particles 101 in the cross section is preferably 25% or less, and more preferably 20% or less.

[0047] Average thickness T of the outermost coating layer 30 in the portion not containing particles 101 In the cross section of the outermost coating layer 30 according to this embodiment, the average thickness T of the outermost coating layer 30 in the portion not containing particles 101 is preferably 10 μm or more. Furthermore, the average thickness T is preferably 40 μm or less. If the average thickness T of the outermost coating layer 30 in the portion not containing particles 101 in the cross section is less than 10 μm, the thickness of the outermost coating layer 30 is too thin and the desired corrosion resistance cannot be achieved. By making the average thickness T 10 μm or more, the corrosion resistance required for the coated steel sheet 1 according to this embodiment can be achieved. The average thickness T is more preferably 12 μm or more, and even more preferably 15 μm or more.

[0048] On the other hand, if the average thickness T of the outermost coating layer 30 in the cross section not containing particles 101 exceeds 40 μm, the thickness of the outermost coating layer 30 becomes too thick, which is undesirable as it reduces the adhesion of the outermost coating layer 30. By making the average thickness T 40 μm or less, it is possible to achieve the desired corrosion resistance while ensuring the adhesion of the outermost coating layer 30. The average thickness T is preferably 35 μm or less, and more preferably 25 μm or less.

[0049] The average film thickness T of the outermost coating layer 30 in the portion of the cross section that does not contain particles 101 is determined by the following procedure. First, as with the above-described anticorrosive coating layer 20, attention is focused on a cross section obtained by cutting the coating film 11 according to this embodiment in the thickness direction at an arbitrary position. In one observation field of view of interest, the thickness of the outermost coating layer 30 in the portion where particles 101 are not present is measured at at least 10 locations. In this case, the thickness of the outermost coating layer 30 in the portion where particles 101 are not present may be measured using a length measurement function or the like implemented in the FE-SEM. The average value of the obtained three or more measurements is then calculated, and this is defined as the average thickness of the outermost coating layer 30 in the observation field of view of interest. The above-described operation is performed for 10 arbitrary observation field of view areas, and the average values ​​obtained from each observation field of view are further averaged by the number of fields of view. The value obtained in this manner is defined as the average film thickness T of the outermost coating layer 30 in the portion where particles 101 are not present.

[0050] In one observation field of view of interest, as illustrated in FIG. 2, at three locations where the particles 101 are not present, the thickness T １ , T ２ , T ３ In this case, the average thickness of the outermost coating layer 30 in one observation field of view area is (1 / 3)×(T １ +T ２ +T ３ Such observation is performed for any 10 observation field regions, and the obtained average values ​​are further averaged by the number of fields, thereby obtaining the average film thickness T of the outermost coating layer 30 in the portion not containing the particles 101.

[0051] <Regarding the state of particles 101 in the outermost coating layer 30> Next, the state of particles 101 in the outermost coating layer 30 will be described in detail with reference to Fig. 2. Fig. 2 is a schematic diagram for explaining the particles 101 contained in the outermost coating layer 30 of the coated steel sheet 1 according to this embodiment.

[0052] In the outermost coating layer 30 according to this embodiment, the average particle diameter φ of the particles 101 specified by the procedure described below １０ (Hereinafter, simply “average particle diameter φ １０ ") is 2 to 5 times the average film thickness T of the portion of the outermost coating layer 30 that does not contain resin particles (hereinafter simply referred to as "average film thickness T"). １０ and the average film thickness T, the coated steel sheet 1 as a whole can achieve excellent design properties that combine a grained appearance and a matte appearance. １０ is preferably 2.1 times or more, more preferably 2.2 times or more, more preferably 2.3 times or more, more preferably 2.4 times or more, and most preferably 2.5 times or more of the average film thickness T of the outermost coating layer 30. １０ is preferably 4.5 times or less, more preferably 4 times or less, and most preferably 3.5 times or less, of the average film thickness T of the outermost coating layer 30.

[0053] The average particle diameter φ of the particles 101 in the cross section as described above １０ is determined by the following procedure. First, as in the case of the above-described anticorrosive coating layer 20, attention is paid to a cross section obtained by cutting the coating film 11 according to this embodiment at an arbitrary position in the thickness direction. In one observation field region of interest, the average particle diameter φ of the particles 101 present in the region is determined. １０As the measurement value used to calculate the average diameter φ of the particles 101, the circle-equivalent diameters of the particles 101 are measured, and the average value of the top two circle-equivalent diameters of the particles 101 is calculated in descending order of the circle-equivalent diameter. Such measurements are performed for 10 arbitrary observation field regions, and the average values ​​obtained from each observation field region are further averaged by the number of fields. The value obtained in this way is used as the average diameter φ of the particles 101. １０ Let's say.

[0054] ◇ Circumferential length of the protruding part in the cross section L １ and particle covering length L ２ In addition, in a cross section obtained by cutting the coating film 11 at an arbitrary position in the thickness direction, the protruding portion of the particle 101 protruding from the surface position of the portion of the outermost coating layer 30 that does not contain resin particles (hereinafter referred to as the "protruding portion P") has a length along the outer periphery of the protruding portion (hereinafter referred to as the "protruding portion circumferential length L １ ") is covered with a film-forming component having a thickness of 0.5 μm or more.

[0055] In the example shown in Figure 2, the portion located above the dotted line segment B connecting the surface positions of the outermost coating layer 30 in the portion where the particle 101 is not present is the protruding portion P. Furthermore, the portion of the protruding portion P of the particle 101 that is covered with a film-forming component having a thickness of 0.5 µm or more is referred to as the "particle-coated portion C," and the portion of the particle 101 that is not covered with a film-forming component having a thickness of 0.5 µm or more is referred to as the "particle-exposed portion E." The above-mentioned "the protruding portion P of the particle 101 is covered with a film-forming component for more than half of the length along the periphery of the protruding portion P" means that the length along the periphery of the protruding portion P in the particle-coated portion C (hereinafter referred to as the "particle-coated portion circumferential length L ２ ") The circumferential length L of the protruding part １ Ratio to (L ２ / L １ ) is 1 / 2 or more. As shown in the particle 101 on the right side of FIG. 2, the entire protruding portion P may be covered with the film-forming component. In this case, the circumferential length L of the protruding portion １ and the particle covering portion perimeter L ２ are equal, and the above ratio (L ２ / L １ ) is 1.

[0056] In the outermost coating layer 30 according to this embodiment, more than half of the protruding portion P of the particle 101 is covered with the film-forming component, so that the interface between the particle 101 and the film-forming component can be made longer. Therefore, in the coated steel sheet 1 according to this embodiment, the intrusion of corrosion factors from the interface can be suppressed, and corrosion on the surface of the steel sheet 10 can be suppressed. From this viewpoint, the circumferential length L of the protruding portion １ and the particle covering portion perimeter L ２ The above ratio (L ２ / L １ ) is preferably 3 / 5 or more.

[0057] Circumferential length L of the protruding part in the cross section １ and the particle covering portion perimeter L ２ is identified by the following procedure. First, as in the case of the above-described anticorrosive coating layer 20, attention is paid to a cross section obtained by cutting the coating film 11 according to this embodiment at an arbitrary position in the thickness direction. All particles 101 having particle exposed portions E are identified within the field of view of the cross section of interest. Here, for particles 101 that do not have particle exposed portions E (for example, the particle 101 on the right side of FIG. 2), the protruding portion circumferential length L １ and the particle covering portion perimeter L ２ are equal, and the above ratio (L ２ / L １ ) is clearly 1, so measurement is omitted. For each particle 101 having the particle exposed portion E specified above, a dotted line segment B is defined that connects the surface positions of the outermost coating layer 30 in the portion where the particle 101 is not present. The length of the arc connecting the two intersections of the line segment B and the outer periphery of the particle 101 is measured, and the protruding portion circumferential length L １ In addition, the length L of the arc connecting the left one of the two intersections between the line segment B and the periphery of the particle 101 and the left one of the two points on the periphery of the particle 101 at the boundary between the particle-covered portion C and the particle-exposed portion E is ２１ and the length L of the arc connecting the right one of the two intersections of the line segment B and the periphery of the particle 101 and the right one of the two points on the periphery of the particle 101 at the boundary between the particle-covered portion C and the particle-exposed portion E. ２２ and measure the length of the arc L ２１ and L ２２The sum of these lengths is the particle-covered portion circumferential length L ２ The circumferential length of the protruding part is L １ and the length of the arc L ２１ and L ２２ can be calculated by various functions implemented in the electron microscope, image processing, etc. Furthermore, the above ratio (L ２ / L １ ) is calculated for each particle 101. ２ / L １ ) is ½ or more, it can be said that “the protruding portion P of the particle 101 is covered with the film-forming component for half or more of the length along the periphery of the protruding portion P.” In FIG. 2, point G is the center of gravity of the particle 101.

[0058] In addition, the peripheral length L of the protruding portion of the particle 101 １ and the particle covering portion perimeter L ２ The above ratio (L ２ / L １ The ratio of those in which the ratio (L) is 1 / 2 or more is most preferably 100%. However, depending on the state of use, the particle exposed portion E may expand or, in exceptional cases, the ratio (L ２ / L １ ) may be outside the range of the above definition. １ and the particle covering portion perimeter L ２ The above ratio (L ２ / L １ The proportion of those in which the ratio of 1 / 2 or more is 1 / 2 or more may be 60% or more, and more preferably 80% or more.

[0059] ◇Average particle size of all particles 101 Average particle size φ of particles 101 １０In addition to having the above-mentioned configuration, the average particle size of all of the particles 101 is preferably 15 μm or more when the thickness of the rust-preventive coating film is 10 μm. Furthermore, the average particle size of all of the particles 101 is preferably 40 μm or less when the thickness of the rust-preventive coating film is 10 μm. If the average particle size of all of the particles 101 is less than 15 μm, the average particle size of the particles 101 is too small to achieve the desired design and scratch resistance. By making the average particle size of all of the particles 101 15 μm or more, the design and scratch resistance required for the coated steel sheet 1 according to this embodiment can be more effectively achieved. The average particle size of the particles 101 is more preferably 18 μm or more, and even more preferably 20 μm or more.

[0060] On the other hand, if the average particle size of the particles 101 exceeds 40 μm, the average particle size of the particles 101 becomes too large, which may result in particle loss or the like during the manufacturing process. By setting the average particle size of the particles 101 to 40 μm or less, particle loss can be suppressed and stable manufacturing can be achieved. The average particle size of the particles 101 is more preferably 30 μm or less.

[0061] The average particle size of all the particles 101 is the average particle size φ of the top 10 particles 101. １０ Specifically, the average particle diameter φ １０ In calculating the particle diameter of all particles 101 in one observation field, the average value of the equivalent circle diameters of all particles 101 in that observation field is calculated. This measurement is performed for 10 arbitrary observation field regions, and the average values ​​obtained from each observation field region are further averaged by the number of fields. The value obtained in this way is the average particle diameter of all particles 101.

[0062] Ratio of minimum thickness to maximum thickness of outermost coating layer 30 In the outermost coating layer 30 according to this embodiment, the minimum thickness H ｍｉｎ Maximum film thickness H ＭＡＸ The ratio (H ＭＡＸ / H ｍｉｎ ) is preferably 5 or more and 20 or less. ＭＡＸ / H ｍｉｎ ) is within the above range, the 60-degree specular gloss G ＳThis makes it possible to obtain a more preferable value of (60°). This results in a more excellent matte appearance (and thus a more excellent design). ＭＡＸ / H ｍｉｎ ) is 5 or more, the surface of the coated steel sheet 1 can have a favorable feel. ＭＡＸ The ratio (H ＭＡＸ / H ｍｉｎ ) is more preferably 6 or more, and even more preferably 7.5 or more. ＭＡＸ / H ｍｉｎ ) is more preferably 17.5 or less, and even more preferably 15 or less.

[0063] In addition, the ratio (H ＭＡＸ / H ｍｉｎ ) is in the above range, the minimum film thickness H ｍｉｎ The portion may be a thin film portion. In this case, if a flaw or the like occurs in the thin film portion, corrosion factors are likely to penetrate through the flaw. In contrast, the coated steel sheet 1 according to this embodiment is provided with the rust-preventive coating film layer 20, and therefore can suppress corrosion on the surface of the steel sheet 10 even if corrosion factors penetrate.

[0064] Minimum film thickness H ｍｉｎ Maximum film thickness H ＭＡＸ The ratio (H ＭＡＸ / H ｍｉｎ ) is identified by the following procedure. First, as in the case of the above-mentioned anticorrosive coating layer 20, attention is paid to a cross section obtained by cutting the coating film 11 according to this embodiment in the thickness direction at an arbitrary position. In one observation field of view of interest, for example, the minimum film thickness h ｍｉｎ and the maximum film thickness h ＭＡＸ The above-mentioned operation is carried out for 10 arbitrary observation field areas. The minimum film thickness h obtained from each observation field area is ｍｉｎ The smallest value among these is the minimum film thickness H ｍｉｎ and the maximum film thickness h ＭＡＸ The largest value among these is the maximum film thickness HＭＡＸ Furthermore, from the obtained value, the minimum film thickness H ｍｉｎ Maximum film thickness H ＭＡＸ The ratio (H ＭＡＸ / H ｍｉｎ ) to identify the

[0065] Here, as illustrated in FIG. 2B, the minimum film thickness h ｍｉｎ The portion where the outermost layer is thinnest in each field of view is the portion where the distance between the surface in contact with the rust-preventive coating layer 20 and the exposed surface S is the shortest. ＭＡＸ The portion is the portion where the film thickness of the outermost coating layer 30 is the thickest in each field of view, and is the portion where the distance between the surface in contact with the rust-preventive coating layer 20 and the exposed surface S is the greatest. However, the above "distance" is in the direction perpendicular to the in-plane direction of the steel sheet 10.

[0066] The "exposed surface S" of the outermost coating layer 30 includes an exposed surface Sa of the binder resin 103 in a portion where the particles 101 are not present, an exposed surface Sb of the particle-exposed portion E of the particle 101, and an exposed surface Sc of the binder resin 103 in the particle-coated portion C. For example, as shown in FIG. 2B , １ ~h ４ In this case, the film thickness h １ and film thickness h ３ The distance between the surface in contact with the anticorrosive coating layer 20 and the exposed surface Sa of the binder resin 103 in the portion where the particles 101 are not present is equal to the thickness h １ , h ３ In addition, the film thickness h ２ The distance between the surface of the anticorrosive coating layer 20 and the exposed surface Sb of the particle exposed portion E is equal to or less than the thickness h ２ In addition, the film thickness h ４ The distance between the surface of the part that contacts the anticorrosive coating layer 20 and the exposed surface Sc of the binder resin 103 in the particle-coated part C is equal to or less than the thickness h ４ is.

[0067] In the example of FIG. 2B, the minimum film thickness h ｍｉｎ and maximum film thickness h ＭＡＸ When specifying the film thickness h １ ~h４ The largest of these is h ２ Therefore, this part has the maximum thickness h ＭＡＸ The smallest part is identified as h ３ Therefore, this part has the minimum film thickness h ｍｉｎ In the above cross-sectional observation, the minimum thickness h ｍｉｎ and maximum film thickness h ＭＡＸ is identified.

[0068] <<Other Configurations of the Outermost Coating Layer 30>> The outermost coating layer 30 has a 60-degree specular gloss G Ｓ Other desired configurations may be employed, such as those not including particles 101, as long as the value of (60°) is 20% or less.

[0069] In one embodiment, the outermost coating layer 30 may include a thin film portion 200 when observed in a cross section obtained by cutting the coating film 11 at any position in the thickness direction. Figures 3A and 3B are cross-sectional views showing the configuration of a coated steel sheet 1 including the outermost coating layer 30 including the thin film portion 200. If a flaw or the like occurs in the thin film portion 200, corrosion factors are likely to penetrate through the flaw. In contrast, the coated steel sheet 1 according to this embodiment includes the rust-preventive coating layer 20, and therefore can suppress corrosion on the surface of the steel sheet 10 even if corrosion factors penetrate.

[0070] 3A , when the upper surface of the steel plate 10 is flat and the upper surface of the outermost coating layer 30 is rough with certain irregularities, the portion between the coated steel plate 1 and the recesses of the outermost coating layer 30 can correspond to the thin film portion 200. In this case, the thin film portion 200 is, for example, 20 μm or less. As an example of a case where the outermost coating layer 30 has a rough surface with certain irregularities, the outermost coating layer 30 may contain 1% or more of a curing catalyst, causing the outermost coating layer 30 to cure and shrink, resulting in irregularities.

[0071] 3B, when the upper surface of the steel plate 10 has a rough surface shape with certain irregularities and the upper surface of the outermost coating layer 30 has a flat surface, the portion between the convex portions of the coated steel plate 1 and the outermost coating layer 30 can correspond to the thin film portion 200. In this case, the thin film portion 200 is, for example, 20 μm or less. An example of a case where the coated steel plate 1 has a rough surface shape with certain irregularities is when the surface roughness of the coated steel plate 1 is 2 μm or more in terms of Ra.

[0072] (Regarding the manufacturing method of coated steel sheet) Next, an example of a manufacturing method of coated steel sheet according to the present embodiment will be described. First, a steel sheet serving as a base material is subjected to various pretreatments such as alkaline degreasing treatment, water washing treatment, pickling treatment, etc. to make the steel sheet surface clean.

[0073] Thereafter, various known anti-rust paints for forming an anti-rust coating layer are applied to the steel sheet and dried. Here, the application of the anti-rust paints can be carried out by generally known application methods, such as roll coating, curtain flow coating, air spraying, airless spraying, immersion, bar coating, brush coating, etc. Furthermore, the method for heating the anti-rust paint is not particularly limited, and any method may be used, such as hot air, near infrared rays, far infrared rays, induction heating, or a heating method using a combination of these.

[0074] Next, a coating liquid for forming an organic resin film layer is applied to the surface of the steel sheet on which the rust-preventive coating layer has been formed, and the organic resin film layer is formed by heating and drying. Here, such a coating liquid is prepared by adding the binder resin described above and, as necessary, various additives to a solvent. If necessary, the coating liquid applied to at least one surface of the steel sheet may contain particles described above to form the outermost coating layer 30. Furthermore, if necessary, a coating liquid for forming another organic resin film layer may be applied to the surface of the rust-preventive coating layer, and the outermost coating layer may be formed on the surface of the other organic resin film layer.

[0075] It is also important to use a curtain flow coater to apply the prepared coating solution. By using a curtain flow coater to apply a coating solution containing particles, it is possible to apply the coating solution without causing the particles to settle or causing coating defects (roping).

[0076] After applying the coating liquid to the surface of the anticorrosive coating layer, the coating liquid is baked by heating and curing. The heating temperature during baking can be set depending on the solvent used, but it is preferable to set the maximum plate temperature within the range of 180 to 250°C. When heat-curing the coating liquid, attention must be paid to the heating rate. More specifically, it is important to set the heating rate within the range of 5 to 50°C / sec. By applying a coating liquid having the above-described surface tension and viscosity using a curtain flow coater and then heat-curing it under the above-described heating rate, an organic resin coating layer can be formed that achieves the particle state described above. The heating rate is more preferably within the range of 10 to 30°C / sec.

[0077] The method for heating the coating liquid is not particularly limited, and any method may be used, such as hot air, near infrared rays, far infrared rays, induction heating, or a combination of these.

[0078] The method for producing a coated steel sheet according to this embodiment has been described above.

[0079] The coated steel sheet according to the present embodiment will be specifically described below with reference to examples and comparative examples. Note that the examples shown below are merely examples of the coated steel sheet according to the present embodiment, and the coated steel sheet according to the present embodiment is not limited to the examples below.

[0080] (1) Steel Sheets Five types of steel sheets, A1 to A5, shown in Table 1 below were prepared (all commercially available). In Table 1 below, the coating weight is the coating weight per side. The prepared steel sheets were treated with a chromate-free paint primer (CT-E300, equivalent to that manufactured by Nihon Parkerizing Co., Ltd.) at 60 mg / m². ２Plated steel sheets (thickness: 0.6 mm) were also prepared. The treatment solution used for the primer treatment contained a silane coupling agent, and the coating layer formed by this primer treatment functioned as a primer treatment coating layer. The presence or absence of primer treatment is shown in Tables 4-1 to 4-3 below.

[0081] (2) Anti-rust Coating Layer First, the following clear anti-rust paints B1 to B3, which did not contain an anti-rust pigment, were prepared according to the following procedure. Then, one or more of the anti-rust pigments C1 to C5 listed in Table 2 were added and dispersed to prepare anti-rust coatings. When clear anti-rust paint B1 was used, the polyester resin and epoxy resin contained therein mainly functioned as the binder resin in the anti-rust coating layer. When clear anti-rust paint B2 was used, the polyester resin contained therein mainly functioned as the binder resin in the anti-rust coating layer. When clear anti-rust paint B3 was used, the polyester resin and urethane resin contained therein mainly functioned as the binder resin in the anti-rust coating layer. The prepared anti-rust paints were applied with a bar coater to one side of a primed plated steel sheet, and then baked at a PMT (maximum temperature of the steel sheet) of 220°C ± 10°C for a baking time of 10 seconds. The types and respective abundance ratios (%) of the rust-preventive pigments C1 to C5 in the prepared rust-preventive coating films, as well as the total abundance ratio (%) of all the contained rust-preventive pigments, are shown in Tables 4-1 to 4-3. The film thicknesses (μm) of the rust-preventive coating films are also shown in Tables 4-1 to 4-3. In Table 2, "SHIELDEX" is a registered trademark, "K-WHITE" is a registered trademark, and "Kyowamag" is a registered trademark.

[0082] <Clear anti-rust paint: B1> This paint was prepared by blending polyester resin (Vylon TM270, manufactured by Toyobo; "Vylon" is a registered trademark), epoxy resin (Epiclon TM1000, manufactured by DIC Corporation; "EPICLON" is a registered trademark), and melamine resin as a crosslinker (Cymel 327, manufactured by Allnex; "Cymel" is a registered trademark) in a solids ratio of 75:5:20, and adding and adjusting an organic solvent (a 1:1 mixture of cyclohexanone and Solvesso 150 by mass) to a solids concentration of 25% by mass.

[0083] <Clear anti-rust paint: B2> This paint was prepared by blending polyester resin (Vylon GK-140, manufactured by Toyobo) and melamine resin as a crosslinker (Cymel 327, manufactured by Allnex) in a solids ratio of 80:20, and adding an organic solvent (a 1:1 mixture of cyclohexanone and Solvesso 150 by mass) to adjust the solids concentration to 25% by mass.

[0084] <Clear anti-rust paint: B3> This paint was prepared by blending polyester resin (Vylonal MD1480, manufactured by Toyobo, "Vylonal" is a registered trademark), urethane resin (Superflex 150, manufactured by Dai-ichi Kogyo Seiyaku, "Superflex" is a registered trademark), and melamine resin as a crosslinker (Cymel 327, manufactured by Allnex) in a solids ratio of 40:40:20, and adding water to adjust the solids concentration to 25% by mass.

[0085] (3) Outermost Coating Layer The paint used as the outermost coating layer was a commercially available polyester-based topcoat paint, "FLC100HQ (white)" manufactured by Nippon Paint Co., Ltd., as the binder resin. This paint was prepared by adding a predetermined amount of one or more of the resin particles D1 to D10, D13, or D14 listed in Table 3, silica D11 as an aggregate, or curing catalyst D12. Depending on the viscosity of the prepared paint, an organic solvent (a 1:1 mixture of cyclohexanone and Solvesso 150 by mass) was added to adjust the viscosity. The prepared paint was applied to one side of a steel plate coated with a rust-preventive coating using a curtain coater or bar coater. When using a curtain coater, the paint was applied using the curtain coater and then baked at a PMT (maximum temperature of the steel plate) of 230°C for a baking time of 40 seconds. Similarly, in the case of a bar coater, baking was performed with a PMT (maximum steel plate temperature) of 230°C and a baking time of 12 seconds. For some samples, the baking time was changed while maintaining the PMT at 230°C. The coating methods used are listed in Tables 5-1 to 5-3. The anti-rust coating and the outermost coating were applied to the front surface only, or to both the front and back surfaces. The presence or absence and type of coating on the back surface are listed in Table 5. In Table 3, "Grandpearl" is a registered trademark, and "Sylosphere" is a registered trademark.

[0086] The proportion (%) of each resin particle in the outermost coating layer produced and the total proportion (%) of all the resin particles contained therein are shown in Tables 5-1 to 5-3. The thickness T (μm) and average particle diameter φ of the outermost coating layer are also shown. １０ The ratio of the particle diameter to the average film thickness T (particle diameter / film thickness) is shown in Tables 5-1 to 5-3. １ and the particle covering portion perimeter L ２ The above ratio (L ２ / L １ When the ratio of particles having a resin particle coverage of 1 / 2 or more was 60% or more, the resin particle coverage was deemed good and indicated by a "good" mark, and when the ratio was less than 60%, the resin particle coverage was deemed poor and indicated by a "bad" mark. Furthermore, the ratio of the maximum film thickness to the minimum film thickness of the outermost coating film layer (maximum film thickness / minimum film thickness) is shown in Tables 5-1 to 5-3.

[0087] The gloss (more specifically, the 60-degree specular gloss G) of each of the obtained test pieces was measured according to the method described above. Ｓ (60°)) were measured and are shown in Tables 6-1 to 6-3 below.

[0088] In addition, the corrosion resistance (corrosion resistance 1) and edge corrosion resistance (corrosion resistance 2) of the coating surface were measured. Furthermore, the scratch resistance of the coating surface was evaluated. The obtained results are summarized in Tables 6-1 to 6-3 below. The evaluation methods are as follows.

[0089] (Corrosion Resistance 1) Regarding the corrosion resistance (corrosion resistance 1) on the coating surface, sealing tape was applied to the end faces of the surface-treated steel sheets, and a cross-cut was made in the center of the test piece with a cutter, reaching all the way down to the steel sheet substrate. After 500 hours of salt spray (SST, 5% NaCl, 35°C atmosphere), the average coating blister width from the cut was measured and calculated. The average coating blister width can be calculated by measuring the area of ​​the coating blister and then dividing it by the length of the cut. The evaluation criteria are as follows. A pass level was 3 or higher. <Evaluation Criteria> Rating 5: Less than 0.5 mm, no red rust 4: 0.5 mm to less than 1 mm, no red rust 3: 1 mm to less than 2 mm, no red rust 2: 2 mm to less than 5 mm, no red rust 1: 5 mm or higher, or red rust

[0090] (Corrosion Resistance 2) For edge corrosion resistance (corrosion resistance 2), test materials having anti-rust coatings and outermost coatings formed on both the front and back surfaces were coated with sealing tape on the top and bottom end surfaces of the surface-treated steel sheet, and then subjected to salt spray (SST, 5% NaCl, 35°C atmosphere) for 500 hours. The average paint blister width from the left and right end surfaces (left: lower burr, right: upper burr) was measured and calculated. The average paint blister width can be calculated by measuring the area of ​​the paint blister and then dividing it by the end surface length. The evaluation criteria are as follows. A score of 2 was determined to be acceptable. <Evaluation Criteria> Score 2: Average blister width less than 5 mm and no red rust. 1: Average blister width 5 mm or more, or red rust.

[0091] (Scratch Resistance) The scratch resistance of the coating film surface was evaluated by a coin scratch test. A coin was contacted with the coating surface of the prepared sample at a 45-degree angle and scratched with a load of 500 g. The scratches were evaluated according to the following criteria, with a pass level of 3 or higher. <Evaluation Criteria> Rating 4: No coating peeling or very slight coating peeling observed. 3: Slight coating peeling observed. 2: Partial coating peeling observed. 1: The coating film was completely peeled off.

[0092] (Roughness Measurement) The roughness (arithmetic mean roughness Ra) obtained from the surface of the coated steel plate was measured using a contact roughness meter in accordance with JIS B 0601:2001. The measurement length was 8.0 mm, and the cutoff value was 0.8 mm. An Ra of 2 μm or more was evaluated as ◯, and an Ra of less than 2 μm was evaluated as ×.

[0093] (Particle shedding inspection) For samples containing resin particles in the outermost coating layer, cylindrical drawing was performed so that the test surface (coated surface) was the outer surface (drawing conditions: blank diameter 100 mmφ, punch diameter 50 mmφ, die diameter 52.4 mmφ, blank holding force (BHF) 1.5 ton), and then the presence or absence of defects on the cylindrically drawn wall was visually confirmed. For flaw occurrence sites where flaw occurrence was confirmed, the wall including the flaw was cut out and the surface was observed with an SEM to confirm whether or not resin particles had fallen off. Samples where no flaws were confirmed on the wall, or where flaws were confirmed but no resin particles had fallen off, were marked with a circle, and samples where flaws were confirmed and resin particles had fallen off were marked with an x.

[0094]

[0095]

[0096]

[0097]

[0098]

[0099]

[0100]

[0101]

[0102]

[0103]

[0104]

[0105]

[0106] As is clear from Tables 4-1 to 6-3 above, the test materials corresponding to the examples of the present invention are shown to be capable of achieving both an excellent low-gloss matte appearance and high corrosion resistance. They are also shown to exhibit high scratch resistance as a secondary effect. Furthermore, the test materials corresponding to the configurations satisfying the preferred aspects of the present invention are shown to exhibit the effect of suppressing particle shedding. On the other hand, the test materials corresponding to the comparative examples of the present invention failed in at least one of low gloss and corrosion resistance.

[0107] No. 2 did not contain resin particles in the outermost coating layer, and No. 3 contained resin particles but at a low ratio. No. 27 did not contain resin particles in the outermost coating layer, but contained aggregate at a low ratio. No. 30 did not contain resin particles in the outermost coating layer, but contained a curing catalyst at a low ratio. Therefore, the gloss level was outside the range, and it is believed that the desired design could not be achieved.

[0108] No. 10-13, 16, 18-20, 24-26, 33-38 are average particle diameters φ １０ The ratio of the particle diameter to the average film thickness T (particle diameter / film thickness) was less than twice that of the present disclosure. As a result, the gloss level was outside the range, and it is believed that the desired design properties could not be achieved.

[0109] In Nos. 40 and 41, the thickness of the rust-preventive coating film was less than 5 μm (see Table 4-1), and therefore it is believed that the corrosion-inhibiting effect against corrosion factors that may penetrate through the thin film portion or the interface between the particles 101 and the binder resin 103 was insufficient. Therefore, it is believed that the desired corrosion resistance was not obtained. Furthermore, in No. 47, the thickness of the rust-preventive coating film was more than 15 μm, and therefore it is believed that coating defects occurred. Therefore, it is believed that the desired corrosion resistance was not obtained.

[0110] In Nos. 48 and 49, the abundance ratio of the rust-preventive pigment was less than 30% (see Table 4-1), and therefore it is believed that the corrosion-inhibiting effect against corrosion factors that may penetrate through the thin film portion or the interface between the particles 101 and the binder resin 103 was insufficient. Therefore, it is believed that the desired corrosion resistance was not obtained. Furthermore, in No. 55, the abundance ratio of the rust-preventive pigment was more than 60% (see Table 4-1), and therefore it is believed that the adhesion between the rust-preventive coating film layer 20 and the steel sheet 10, particularly in the processed portion, was insufficient. Therefore, it is believed that the desired corrosion resistance was not obtained.

[0111] In No. 68, it is believed that the desired corrosion resistance was not achieved because no plating layer was provided on the surface of the steel sheet 10 (metal sheet A5 was used).

[0112] Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications and alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

[0113] The embodiments disclosed herein are illustrative in all respects and are not limiting. The above-described embodiments may be omitted, substituted, or modified in various ways without departing from the scope of the appended claims, the technical scope of the present invention as described below, and the spirit thereof. For example, the components of the above-described embodiments may be arbitrarily combined within the scope that does not impair the effects of the components. Furthermore, such an arbitrary combination naturally provides the functions and effects of each of the components involved in the combination, and also provides other functions and effects that are apparent to those skilled in the art from the description of this specification.

[0114] Furthermore, the effects described in this specification are merely descriptive or exemplary and are not limiting. In other words, the technology according to the present invention may achieve other effects that will be apparent to those skilled in the art from the description of this specification, in addition to or in place of the above-described effects.

[0115] The following configurations also fall within the technical scope of the present invention: [1] A coated steel sheet having a Zn-containing plating layer and two or more coating layers including a rust-preventive coating layer on at least one side of the steel sheet, wherein the 60-degree specular gloss GS(60°) of the coating layer on at least one side of the steel sheet as defined in JIS Z 8741:1997 is 20% or less, the average film thickness of the rust-preventive coating layer is 5 μm or more and 15 μm or less, the rust-preventive coating layer contains a binder resin, a crosslinking agent, and a rust-preventive pigment, and in a cross section taken at an arbitrary position in the thickness direction of the coating layer, the abundance ratio of the rust-preventive pigment to the total area of ​​the rust-preventive coating layer is 30% or more and 60% or less in terms of area ratio. [2] The coated steel sheet according to the above item [1], wherein the rust-preventive pigment contains at least one of Si, P, Mg, and V. [3] The coated steel sheet according to [2] above, wherein the Si comprises one or more of calcium ion-exchanged silica and magnesium ion-exchanged silica, the P comprises one or more of zinc phosphate, magnesium dihydrogen phosphate, and aluminum dihydrogen triphosphate, and the Mg comprises one or more of magnesium dihydrogen phosphate, magnesium oxide, and magnesium hydroxide. [4] The coated steel sheet according to any one of [1] to [3] above, wherein, on the surface of the steel sheet having a 60-degree specular gloss GS(60°) of 20% or less, the rust-preventive coating layer is located below the two or more coating layers, and the colored coating layer is located in the outermost layer furthest from the steel sheet, the colored coating layer containing resin particles and, as film-forming components, a binder resin, a crosslinking agent, and a color pigment, and the average particle size of the resin particles in the cross section is from 2 to 5 times the average film thickness of the outermost coating layer in a portion not containing the resin particles. The average particle size is a value obtained by measuring the circle-equivalent diameters of the resin particles present in one observation field of view on the cross section, calculating the average of the two largest circle-equivalent diameters among the circle-equivalent diameters, and similarly averaging the average values ​​obtained for 10 arbitrary observation field of view areas by the number of fields. [5] The coated steel sheet according to the above [4], wherein the abundance ratio of the resin particles to the total area of ​​the outermost coating layer is 5% or more and 30% or less in terms of area ratio.[6] The coated steel sheet according to [4] or [5] above, wherein, in the cross section, protruding portions of the resin particles protruding from a surface position in the portion of the outermost coating layer that does not contain the resin particles are covered with the film-forming component to a thickness of 0.5 μm or more over at least half of the length along the periphery of the protruding portions. [7] The coated steel sheet according to any one of [4] to [6] above, wherein the resin particles are resin particles made of an acrylic resin. [8] The coated steel sheet according to any one of [4] to [7] above, wherein the binder resin is a binder resin made of an acrylic resin or a polyester resin. [9] The coated steel sheet according to any one of [1] to [8] above, wherein, on the surface of the steel sheet having a 60-degree specular gloss GS(60°) of 20% or less, the surface roughness of the steel sheet is 2 μm or more in terms of Ra, or the coating layer contains 15% or more of an aggregate composed of a pigment containing silica.

[0116] REFERENCE SIGNS LIST 1 Coated steel plate 10 Steel plate 20 Anti-rust coating layer 30 Outermost coating layer 101 Particles 103 Binder resin

Claims

1. a steel sheet having a Zn-containing plating layer and two or more coating layers including a rust-preventive coating layer on at least one side thereof; The 60-degree specular gloss GS(60 °) of the coating layer on at least one surface of the steel sheet as defined in JIS Z 8741:1997 is 20% or less, The average thickness of the anticorrosive coating layer is 5 μm or more and 15 μm or less, the anti-rust coating layer contains a binder resin, a crosslinking agent, and an anti-rust pigment; In a cross section obtained by cutting the coating layer at an arbitrary position in the thickness direction, the ratio of the anti-rust pigment to the total area of ​​the anti-rust coating film layer is, in terms of area ratio, 30% or more and 60% or less; On the surface of the steel plate having a 60-degree specular gloss GS(60°) of 20% or less, the two or more coating layers have the rust-preventive coating layer as a lower layer and a colored coating layer as an outermost layer located farthest from the steel plate, the colored coating layer containing resin particles and, as film-forming components, a binder resin, a crosslinking agent, and a color pigment; In the cross section, A coated steel sheet, wherein the average particle size of the resin particles is from 2 to 5 times the average film thickness of the colored coating layer in a portion not containing the resin particles. However, the average particle size is a value obtained by measuring the circle-equivalent diameters of the resin particles present in one observation field of view on the cross section, calculating the average of the two largest circle-equivalent diameters among the circle-equivalent diameters, and similarly averaging the average values ​​obtained for any 10 observation fields of view by the number of fields of view.

2. The coated steel sheet according to claim 1 , wherein the anti-rust pigment contains at least one of Si, P, Mg, and V.

3. 3. The coated steel sheet according to claim 2, wherein the Si comprises one or more of calcium ion-exchanged silica or magnesium ion-exchanged silica, the P comprises one or more of zinc phosphate, magnesium dihydrogen phosphate, or aluminum dihydrogen triphosphate, and the Mg comprises one or more of magnesium dihydrogen phosphate, magnesium oxide, or magnesium hydroxide.

4. (delete)

5. 2. The coated steel sheet according to claim 1, wherein the resin particles account for 5% or more and 30% or less of the total area of ​​the colored coating film layer in terms of area ratio.

6. In the cross section, 2. The coated steel sheet according to claim 1, wherein the protruding portions of the resin particles protruding from the surface position in the portion of the colored coating layer that does not contain the resin particles are covered with the film-forming component to a thickness of 0.5 μm or more over at least half of the length along the outer periphery of the protruding portions.

7. The coated steel sheet according to any one of claims 1 to 3, 5 and 6, wherein the resin particles are made of an acrylic resin.

8. The coated steel sheet according to any one of claims 1 to 3, 5 and 6, wherein the binder resin is an acrylic resin or a polyester resin.

9. The coated steel sheet according to claim 7 , wherein the binder resin is an acrylic resin or a polyester resin.

10. 3. The coated steel sheet according to claim 1, wherein the surface of the steel sheet having a 60-degree specular gloss GS(60°) of 20% or less has a surface roughness Ra of 2 μm or more, or the coating layer contains 15% or more of an aggregate composed of a pigment containing silica.