Surface-treated steel sheet

Abstract

The present invention addresses the problem of providing a surface-treated steel sheet having excellent corrosion resistance, in which damage resistance, in particular resistance to surface contact damage caused by contact between one surface and the other surface, is further improved, and the present invention provides a surface-treated steel sheet provided with: plating layers on both surfaces of a steel sheet; a first colored film layer; and a second colored film layer, the ratio of the film thickness of the second colored film layer to the film thickness of the first colored film layer being 0.1-0.5, the first colored film layer and the second colored film layer containing resin particles, the ratio of the number of the resin particles having a thickness equal to or greater than the film thickness of the first colored coating layer is 1% to 30%, and the ratio of the number of the resin particles having a thickness equal to or greater than the film thickness of the second colored coating layer is 50% to 100%.

Description

Technical Field

[0001] The invention relates to a surface treated steel plate. Background Art

[0002] Surface treated steel plates such as organic resin coated plated steel plates (also called pre-coated steel plates) in which the surface of galvanized steel plates is coated with an organic resin film have replaced the post-coating products that were previously painted after forming processing, and are used in home appliances, building materials, automobiles, etc. The surface treated steel plate is a steel plate that has been subjected to rust prevention treatment and a plated steel plate that has been coated with a colored organic film. While having aesthetic appeal, it is also processable and has good corrosion resistance. In many cases, after the pressing process, the surface treated steel plate does not need to be further coated to be used as a material for home appliances, building materials, automobiles, etc. Therefore, this surface treated steel plate requires excellent damage resistance to avoid losing its beauty during processing. Therefore, in order to improve the various properties of the surface treated steel plate, mainly damage resistance, various technologies have been proposed in the past.

[0003] For example, the following patent document 1 discloses a pre-coated metal plate for electronic and electrical equipment that is excellent in not only scratch resistance but also corrosion resistance and conductivity. The pre-coated metal plate is provided with a chemical conversion film on the surface of a metal plate having a predetermined surface roughness, a resin film having a film thickness of 0.4 to 2.0 μm mixed with polyurethane beads or fluororesin beads having an average particle size of 1.0 to 10 μm is provided on one surface, and a resin film having a film thickness of 0.2 to 2.0 μm mixed with polyurethane beads or fluororesin beads having an average particle size of 0.1 to 6.0 μm is provided on the other surface.

[0004] Prior art literature

[0005] Patent Literature

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

[0007] Problem that the invention aims to solve

[0008] Here, various surface-treated steel plates including the pre-coated metal plate disclosed in the above-mentioned Patent Document 1 are usually manufactured by providing a desired coating film on a metal plate as a base material through a continuous coating line. Examples of the metal plate as a base material include steel plates including various plated steel plates, aluminum plates, and aluminum alloy plates. The metal plate provided with the desired coating film is transported to the customer in a coiled state at the end of the continuous coating line.

[0009] In this coil state, one surface of the surface coating of the surface-treated steel plate is in contact with the other surface. In this case, the following issues may arise: damage caused by contact when the coil is wound, adhesion during storage of the coil (i.e., the front and back coatings are pressed together under a certain pressure), indentation (i.e., the state in which the shape of one surface is transferred to the other surface), etc. In addition, during processing at the customer's site, when the cut metal plate is handled, there is also the problem of damage caused by contact between one surface and the other surface. In addition, from the perspective of reducing costs, colored coating layers of different thicknesses are sometimes provided on the two surfaces of the metal plate serving as the base material, so that the thickness of one surface is thinner than that of the other surface. In this case, there is also the problem of the need to ensure the damage resistance of the other surface.

[0010] In this regard, the above-mentioned patent document 1 discloses the following problem: due to the metal particles mixed in order to make the resin coating conductive, the resin coating on the opposite side in contact with it during winding will be damaged. The technology described in the above-mentioned patent document 1 suppresses the damage of 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 the optical disc, the material of the resin particles is limited to soft polyurethane beads or fluororesin beads with excellent sliding properties. In addition, from the perspective of ensuring conductivity, the thickness of the resin coating needs to be set to 2.0μm or less. Therefore, there is still room for improvement in terms of balancing scratch resistance, resistance to surface contact damage, and corrosion resistance.

[0011] Therefore, the present invention is completed in view of the above-mentioned problems, and an object of the present invention is to provide a surface-treated steel plate with further improved damage resistance, especially improved resistance to surface contact damage caused by contact between one surface and another surface, and good corrosion resistance.

[0012] Solutions for solving problems

[0013] The present inventors conducted intensive studies to solve the above problems and, as a result, obtained the technical idea that scratch resistance can be further improved by making the coating film structures on one surface and the other surface of a steel plate different, thereby completing the present invention.

[0014] The gist of the present invention completed based on this technical concept is as follows.

[0015] (1) A surface-treated steel sheet, comprising: a zinc-containing plating layer located on both surfaces of the steel sheet; a first colored coating layer located on the plating layer on one surface of the steel sheet; and a second colored coating layer located on the plating layer on the other surface of the steel sheet, wherein 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, and when observing a cross section of the first colored coating layer cut along the thickness direction, for the observed resin particles, the area occupied along the thickness direction of the first colored coating layer is When the length of the resin particles is set as the thickness of the resin particles, the ratio of the number of the resin particles having a thickness greater than the film thickness of the first colored coating layer to the total number of the resin particles observed is greater than 1% and less than 30%, and when observing a cross-section obtained 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 as the thickness of the resin particles, the ratio of the number of the resin particles having a thickness greater than the film thickness of the second colored coating layer to the total number of the resin particles observed is greater than 50% and less than 100%.

[0016] (2) The surface-treated steel sheet according to (1), wherein, when the first colored film layer is observed in cross section, a length of 1000 μm in a direction perpendicular to the film thickness direction of the first colored film layer is set as a first observation length, and when the sum of the lengths of the portions corresponding to the resin particles in the direction perpendicular to the film thickness direction when the portions occupied by the resin particles are projected in the film thickness direction within the range of the first observation length is set as the first occupied length, a ratio of the first occupied length to the first observation length is 15% or more and 40% or less, and a length of 1000 μm in a direction perpendicular to the film thickness direction of the second colored film layer is set as a second observation length, and when the sum of the lengths of the portions corresponding to the resin particles in the direction perpendicular to the film thickness direction when the portions occupied by the resin particles are projected in the film thickness direction within the range of the second observation length is set as the second occupied length, a ratio of the second occupied 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 first colored coating layer has a film thickness of 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 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 thickness of the second colored coating layer.

[0019] (5) The surface-treated steel sheet 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 film layer and the second colored film layer is 30° C. or higher and 70° C. or lower.

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

[0022] (8) The surface-treated steel sheet 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] Effects of the Invention

[0024] As described above, according to the present invention, it is possible to provide a surface-treated steel sheet having improved scratch resistance, in particular, improved resistance to surface contact scratches caused by contact between one surface and another surface, and having good corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is an explanatory diagram schematically showing the structure of a surface-treated steel sheet according to an embodiment.

[0026] Figure 2 It is an explanatory diagram regarding the thickness of resin particles when a surface-treated steel sheet according to the embodiment is observed in cross section.

[0027] Figure 3 It is an explanatory diagram regarding the occupied length of resin particles when a surface-treated steel sheet according to an embodiment is observed in cross section.

[0028] Figure 4 It is an explanatory diagram regarding the occupied length of resin particles when a surface-treated steel sheet according to an embodiment is observed in cross section. DETAILED DESCRIPTION

[0029] The preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. It should be noted that in this specification and the drawings, components having substantially the same functional configuration are marked with the same reference numerals to omit repeated descriptions.

[0030] <About surface treated steel sheets 1>

[0031] The following references Figure 1 The surface-treated steel sheet according to the embodiment of the present invention will be described in detail. Figure 1 It is an explanatory diagram schematically showing the structure of a surface-treated steel sheet according to an embodiment.

[0032] <About the overall structure of the surface-treated steel sheet 1>

[0033] like Figure 1 As shown schematically, the surface treated steel sheet 1 of the present embodiment includes a steel sheet 10 as a substrate, a plating layer 20 provided on the surface of the steel sheet 10, and a colored coating layer 30 located on the surface of the plating layer 20. Figure 1 As shown, it is preferred that a chemical conversion coating layer 40 is further provided between the plating layer 20 and the colored coating layer 30. The plating layer 20, the colored coating layer 30, and the chemical conversion coating layer 40 are provided on both sides of the steel sheet 10. That is, the first plating layer 20a, the first colored coating layer 30a, and the first chemical conversion coating layer 40a are formed on one side (first side 10a) of the steel sheet 10 corresponding to the upper side of the figure. In addition, the second plating layer 20b, the second colored 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] <About Steel Plate 10>

[0035] There is no particular limitation on the steel plate 10 used as the base material, and various steel plates 10 can be used depending on the mechanical strength etc. required for 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 containing strengthening elements such as P, Si, and Mn in ultra-low carbon steel.

[0036] The thickness of the steel sheet 10 of the present embodiment is not particularly limited either, and may be appropriately set according to the mechanical strength etc. required for the surface treated steel sheet 1 , and may be set to about 0.2 mm to 10.0 mm, for example.

[0037] <Regarding the plating layer 20>

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

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

[0040] [Al: 4 to 22 mass %]

[0041] By setting the Al content to 4% by mass or more, the corrosion resistance of the steel plate can be further improved. The Al content is more preferably 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 corrosion resistance improvement effect as described above. The Al content is more preferably 16% by mass or less.

[0042] [Mg: 1 to 10 mass %]

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

[0044] [Si: 0.0001 to 2.0000 mass %]

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

[0046] Furthermore, the zinc-containing plating layer 20 may contain 1 mass % or less of an element such as Fe, Sb, or Pb alone or in combination to replace a part of the balance of Zn.

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

[0048] The above-mentioned coating layer 20 can be manufactured, for example, as follows. First, the surface of the prepared steel sheet 10 is subjected to pretreatment such as cleaning and degreasing as required. Then, the pretreated steel sheet 10 is immersed in a hot dip coating bath having a desired chemical composition as required, and the steel sheet 10 is pulled out of the coating bath. In the coating operation, the coating can be performed by either a continuous coating method of a coil or a coating method of a single cut plate.

[0049] The temperature of the hot-dip coating bath varies depending on the composition, but is preferably in the range of 400 to 500°C, for example.

[0050] The coating weight of the coating layer 20 can be controlled by adjusting the pulling speed of the steel sheet 10, the flow rate and flow rate of the wiping gas ejected from the wiping nozzle disposed above the coating bath, etc. The coating weight of the coating layer 20 is preferably 30 g / m2 on both sides of the steel sheet 10. 2 Above (i.e., 15g / m per side 2 By setting the adhesion amount to 30 g / m 2 As described above, the corrosion resistance of the galvanized steel sheet 10 can be reliably ensured. The coating weight is more preferably 40 g / m2 in total on both sides of the steel sheet 10. 2 On the other hand, the coating weight is preferably 600 g / m2 on both sides of the steel sheet 10. 2 Below (i.e., 300g / m per side 2 By setting the adhesion amount to 600 g / m 2 The following can ensure the smoothness of the surface of the Zn-containing plating layer 13 while further improving the corrosion resistance. The plating coating weight is more preferably 550 g / m2 in total on both sides of the steel sheet 10. 2 the following.

[0051] After adjusting the amount of hot-dip coating, the steel sheet is cooled. At this time, the cooling conditions do not need to be particularly limited.

[0052] <About the Colored Coating Layer 30>

[0053] The colored coating layer 30 is a coating layer colored in a desired color by having a coloring pigment. The surface-treated steel sheet 1 of the present embodiment includes a first colored coating layer 30a formed on the first surface 10a of the steel sheet 10 and a second colored coating layer 30b formed on the second surface 10b as the colored coating layer 30. Hereinafter, when describing the common structure of these first colored coating layer 30a and second colored coating layer 30b, they are sometimes collectively referred to as simply the colored 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 obtained by cutting the surface-treated steel sheet 1 along the film thickness direction of the colored coating layer 30 (hereinafter referred to as cross-sectional observation), for any one of the first colored coating layer 30a and the second colored coating layer 30b, at least a portion of the resin particles 303 has a thickness greater than the film thickness of the first colored coating layer 30a or the second colored coating layer 30b. In other words, the resin particles 303 are contained in a desired number ratio (described later) of the number of resin particles having a thickness greater than the film thickness of the colored coating layer 30 relative to the number of all resin particles 303 observed by cross-sectional observation. By providing a colored coating layer 30 containing such resin particles 303 having a thickness greater than the film thickness of the colored coating layer 30, there are resin particles 303 protruding from the surface of the colored coating layer 30. As a result, when the colored film layer 30 contacts any surface, it is not the entire colored film layer 30 that contacts, but the resin particles 303. In other words, the contact with any surface is not the surface contact with the entire colored film layer 30, but the point contact with the resin particles 303 protruding from the colored film layer 30. As a result, 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 sheet 1 is embedded in a room temperature drying epoxy resin in a direction perpendicular to the coating thickness direction, and the embedded surface is mechanically polished and then observed using a SEM (scanning electron microscope).

[0056] like Figure 1 As schematically shown, the coloring film layer 30 is set so that the film thickness Tb of the second coloring film layer 30b is thinner than the film thickness Ta of the first coloring film layer 30a. Specifically, the ratio Tb / Ta of the film thickness Tb of the second coloring film layer 30b to the film thickness Ta of the first coloring film layer 30a is greater than 0.1 and less than 0.5. By setting the ratio Tb / Ta to this range, the resin particles 303 having a thickness greater than the film thickness of the coloring film layer 30 can be made to have a desired number ratio in the cross-sectional observation described later.

[0057] In the present embodiment, the film thickness Ta of the first colored coating layer 30a is preferably 3.0 μm or more. In addition, based on the above ratio Tb / Ta, the film thickness Tb of the second colored coating layer 30b is preferably 0.3 μm or more. In this way, the resistance to surface contact damage can be further improved. The film thickness Ta of the first colored coating layer 30a is more preferably 4.0 μm or more. On the other hand, the film thickness Ta of the first colored coating layer 30a is preferably 10.0 μm or less. By setting the film thickness Ta of the first colored coating layer 30a to be less than 10.0 μm, it is possible to suppress the occurrence of coating defects such as wrinkles while controlling costs and obtain a stable appearance. The film thickness Ta of the first colored coating layer 30a is more preferably 8.0 μm or less. In addition, the upper limit of the film thickness Tb of the second colored coating layer is determined by the upper limit value of the film thickness Ta of the first colored coating layer 30a based on the above ratio Tb / Ta.

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

[0059] Next, use Figure 2 The thickness of the resin particle 303 in cross-sectional observation will be described. Figure 2 This is an explanatory diagram for explaining the thickness of the resin particles 303 when the surface-treated steel sheet 1 according to the present embodiment is observed in cross section.

[0060] Figure 2 The thickness of the resin particles 303 refers to the length ( Figure 2 In more detail, for Figure 2 The flat resin particles 303a that are inclined in the film are oriented in a direction perpendicular to the film thickness direction ( Figure 2 The length of the projection in the film thickness direction is regarded as the length occupied along the film thickness direction, and is taken as the thickness of the resin particle 303a. Hereinafter, the thickness of the resin particle 303 contained in the first colored film layer 30a is referred to as the first thickness Ga. In addition, the thickness of the resin particle 303 contained in the second colored film layer 30b is referred to as the second thickness Gb.

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

[0062] It should be noted that, in the cross-sectional observation of the first colored coating layer 30a, the ratio of the number of resin particles 303 having a first thickness Ga (Ga≥Ta) greater than the film thickness Ta of the first colored coating layer 30a to the number of all resin particles 303 in the observation field, and in the 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) greater than the film thickness Tb of the second colored coating layer 30b to the number of all resin particles 303 in the observation field are calculated by observing a total of more than 500 μm in a direction orthogonal to the film thickness direction of the colored coating layer 30a and the colored coating layer 30b, respectively.

[0063] Thus, in the present embodiment, the ratio of the number of resin particles 303 having the second thickness Gb (Gb ≥ Tb) greater than the film thickness Tb of the second colored film layer 30b is configured to be greater than the ratio of the number of resin particles 303 having the first thickness Ga (Ga ≥ Ta) greater than the film thickness Ta of the first colored film layer 30a. Thus, there are a sufficient number of resin particles 303 that protrude, in particular, from the second colored film layer 30b. Therefore, even when the first colored film layer 30a and the second colored film layer 30b are in contact, the surface contact of the two films can be significantly suppressed. As a result, damage caused by the surface contact of the two films, adhesion during storage of the coiled material, and indentation can be suppressed.

[0064] When the ratio of the number of resin particles 303 having the first thickness Ga (Ga≥Ta) greater than the film thickness Ta of the first colored film layer 30a is less than 1%, or when the ratio of the number of resin particles 303 having the second thickness Gb (Gb≥Tb) greater than the film thickness Tb of the second colored film layer 30b is less than 50%, the surface contact between the first colored film layer 30a and the second colored film layer 30b is not sufficiently suppressed, and thus the surface contact damage suppression effect is not sufficient. In cross-sectional observation of the first colored film layer 30a, the ratio of the number of resin particles 303 having the first thickness Ga (Ga≥Ta) greater than the film thickness Ta of the first colored film layer 30a relative to the number of all resin particles 303 in the observation field is preferably 3% or more, and more preferably 5% or more. 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) greater than the film thickness Tb of the second colored coating layer 30b to the number of all resin particles 303 in the observation field is preferably 55% or more, more preferably 60% or more.

[0065] In addition, when the ratio of the number of resin particles 303 having a first thickness Ga (Ga ≥ Ta) greater than the film thickness Ta of the first colored film layer 30a exceeds 30%, the processing adhesion is reduced due to the excessive number of resin particles 303 protruding from the surface of the colored film layer 30. Processing adhesion refers to the performance of the colored film layer 30 and other films to maintain a close state in the processed part without peeling off.

[0066] In cross-sectional observation of the first colored film layer 30a, the ratio of the number of resin particles 303 having a first thickness Ga (Ga≥Ta) greater than the film thickness Ta of the first colored film layer 30a to the number of all resin particles 303 in the observation field is preferably 20% or less, and more preferably 15% or less. It should be noted that the upper limit of the ratio of the number of resin particles 303 having a second thickness Gb (Gb≥Tb) greater than the film thickness Tb of the second colored film layer 30b is not particularly limited, and may be 100%. In cross-sectional observation of the second colored film layer 30b, the ratio of the number of resin particles 303 having a second thickness Gb (Gb≥Tb) greater than the film thickness Tb of the second colored film layer 30b to the number of all resin particles 303 in the observation field is preferably 95% or less, and more preferably 90% or less.

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

[0068] In addition, in the second colored coating layer 30b, the content of the resin particles 303 is preferably 3% by mass or more relative to the total content of the film-forming component 301 and the resin particles 303. This can further improve the damage resistance. The content of the resin particles 303 in the second colored coating layer 30b is more preferably 5% by mass or more. On the other hand, the content of the resin particles 303 in the second colored coating layer 30b is preferably 40% by mass or less relative to the total content of the film-forming component 301 and the resin particles 303. This can further improve the damage resistance. When the content of the resin particles 303 in the second colored coating layer 30b exceeds 40% by mass, the ratio of the film-forming component in the colored coating decreases, the barrier properties of the coating decrease, and it is difficult to show the desired corrosion resistance. The content of the resin particles 303 in the second colored coating layer 30b is more preferably 35% by mass or less.

[0069] Next, as a preferred configuration of the surface-treated steel sheet 1 of the present embodiment, Figure 3 and Figure 4 The occupied length of the resin particles 303 will be described. Figure 3 and Figure 4 This is an explanatory diagram for explaining the occupied length of the resin particles 303 when the surface-treated steel sheet 1 according to the present embodiment is observed in cross section.

[0070] Figure 3In the case of cross-sectional observation of the first colored film layer 30a, the observation range in the direction orthogonal to the film thickness direction of the first colored film layer 30a is set as the first observation length L1. In addition, within the range of the first observation length L1, the parts p1, p2, p3, p4, and p5 occupied by the resin particles 303 are projected in the film thickness direction. According to the projection, the parts p1 and p2, and the parts p4 and p5 partially overlap, and the projection P1 corresponding to the parts p1 and p2, the projection P2 corresponding to the part p3, and the projection P3 corresponding to the parts p4 and p5 can be obtained. The sum of the lengths of these projections P1, P2, and P3, P1+P2+P3, is set as the first occupied length D1. At this time, the ratio of the first occupied length D1 to the first observation length L1 (D1 / L1×100) is preferably 15% or more and 40% or less.

[0071] also, Figure 4 In the same manner, when the second colored film layer 30b is observed in cross section, the observation range in the direction orthogonal to the film thickness direction of the second colored film layer 30b is set as the second observation length L2. In addition, within the range of the second observation length L2, the parts p6, p7, p8, p9, and p10 occupied by the resin particles 303 are projected in the film thickness direction. According to the projection, the parts p6 and p7, and the parts p9 and p10 partially overlap, and the projection P4 corresponding to the parts p6 and p7, the projection P5 corresponding to the parts p8, and the projection P6 corresponding to the parts p9 and p10 can be obtained. The sum of the lengths of these projections P4, P5, and P6, P4+P5+P6, is set as the second occupied length D2. At this time, the ratio of the second occupied 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 1000μm.

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

[0073] By setting the ratio of the second occupied length D2 to the second observation length L2 to be 5% or more, the damage resistance can be further improved. The ratio of the second occupied length D2 to the second observation length L2 is more preferably 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. The damage resistance can be further improved. The reason is as follows: From a certain point of view, the second surface 10b of the steel plate 10 is a thin film thinner 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 particle size greater than the film thickness in the second surface 10b is large. When the proportion of resin particles with a particle size greater than the film thickness is large, it is difficult to maintain the resin particles in the coating, and the resin particles 303 are easily detached from the second surface 10b when the surfaces are in contact, thereby becoming the starting point of damage. In addition, from another perspective, when the ratio of the second occupied length D2 to the second observed length L2 exceeds 15%, the effect of improving the damage resistance is saturated, and the ratio of the film-forming component 301 in the second colored film layer 30b is reduced, and the barrier property of the film is reduced, and it is difficult to show the desired corrosion resistance of the second surface 10b of the steel sheet 10. From the perspective of further improving the damage resistance or further improving the corrosion resistance of the second surface 10b of the steel sheet 10, the ratio of the second occupied length D2 to the second observed length L2 is more preferably 13% or less.

[0074] As long as the film-forming component 301 of the colored coating layer 30 of the present embodiment functions as a binder for the resin particles 303, any raw material can be used. Among them, from the perspective of simplicity and cost of manufacturing, various organic resins are preferably used. As such a film-forming component 301, for example, acrylic resins, polyester resins, polyurethane resins, fluorine resins, etc. can be listed. In addition, when using resin particles made of organic resin as raw materials as resin particles 303, it is preferred to select a resin of the same type as the resin particles as the film-forming component 301. As a result, the affinity between the film-forming component 301 and the resin particles 303 is improved, which can further improve the damage resistance and adhesion of the colored coating layer 30.

[0075] In addition, the film-forming component 301 of the present embodiment is preferably an organic resin having a glass transition temperature Tg of 30° C. or higher. By using a resin having such a glass transition temperature Tg as the film-forming component 301, the colored coating layer 30 has a more appropriate hardness, and the damage resistance (especially resistance to scratches) of the surface-treated steel sheet 1 can be further improved.

[0076] The glass transition temperature Tg of the film-forming component 301 is preferably 35° C. or higher, and more preferably 40° C. or higher. On the other hand, the upper limit of the glass transition temperature Tg is not particularly specified, but when it exceeds 70° C., the processability may be reduced. 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: a method in which a certain temperature change is caused by puncturing the coating as the object of measurement from the surface toward the thickness direction of the coating through TMA (thermomechanical analysis), and the thermal expansion change of the object of measurement is measured; a method in which a certain temperature change is caused by applying periodic deformation to the coating as the object of measurement peeled off from the substrate through DMA (dynamic viscoelasticity measurement), and the viscoelasticity is analyzed.

[0078] The resin particles 303 of the colored coating layer 30 of the present embodiment are preferably resin particles made of organic resin as a raw material. By using such resin particles, the impact applied to the colored coating layer 30 can be mitigated due to the toughness and ductility of the resin particles, thereby further improving the damage resistance. As the resin particles, acrylic resin particles, polyester resin particles, polyurethane resin particles, fluorine resin particles, silicone resin particles, polyolefin resin particles, etc. can be listed, but acrylic resin particles are more preferably used. In addition, the coloring pigment contained in the colored coating layer 30 itself can also function as the above-mentioned resin particles 303.

[0079] In the present embodiment, the resin particles 303 include resin particles having a thickness greater than the film thickness of the colored coating layer 30 and resin particles not having such a thickness. Therefore, the resin particles 303 use resin particles having inconsistent particle sizes. The average particle size is preferably 3 to 15 μm. The damage resistance of the surface-treated steel sheet 1 can be further improved by having the resin particles 303 have the above-mentioned average particle size. Here, the average particle size of the resin particles 303 refers to the average value calculated based on the circle equivalent diameter of each resin particle observed by cross-sectional observation, which is different from the thickness of the resin particles 303 defined above. Specifically, regarding the average particle size of the resin particles 303, the average value of the multiple particle sizes obtained by measuring the particle size of the resin particles 303 observed at any multiple positions (for example, 10 positions) in the cross-sectional observation can be used as the average particle size of the resin particles 303. It should be noted that the resin particles 303 having inconsistent particle sizes include the case where multiple resin particles 303 having no inconsistent particle sizes are mixed and used.

[0080] In addition, it is preferred that 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 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. In addition, 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] The colored coating layer 30 of the present embodiment may further contain a cross-linking agent in addition to the above-mentioned components.

[0083] The colored film layer 30 of the present embodiment further contains a crosslinking agent, so that the barrier property of the colored film layer 30 itself can be further improved, thereby further improving the scratch resistance and corrosion resistance of the surface-treated steel sheet 1. In particular, the colored film layer 30 contains at least one of a melamine resin or an isocyanate resin as a crosslinking agent, so that the scratch resistance and corrosion resistance of the surface-treated steel sheet 1 can be further improved. The content of the crosslinking agent is preferably about 10 to 40% by mass, for example, in the film-forming component 301.

[0084] It should be noted that the coloring pigment contained in the coloring film layer 30 is not particularly limited, and various known pigments can be appropriately used according to the color tone required for the coloring film layer 30. Examples of such coloring pigments include aluminum pigments, carbon black, and TiO2. In addition, the content thereof can be appropriately set, for example, to about 3 to 60% by mass.

[0085] The colored film layer 30 can be formed by applying a coating composition containing the components constituting the colored film layer 30 described above on the surface of the steel sheet 10, the plated surface, the surface of the steel sheet 10 having the chemical conversion film 40, or the plated surface having the chemical conversion film 40, and then sintering the coating composition at a temperature of 150° C. or more and less than 300° C. to cure and dry the coating. When the sintering temperature is less than 150° C., sintering and curing are insufficient, and there is a possibility that the corrosion resistance and scratch resistance of the coating film are reduced. When the sintering temperature is 300° C. or more, there is a possibility that the resin component is thermally degraded or the processability is reduced.

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

[0087] Furthermore, the colored coating layer 30 may further contain anti-rust pigments, surface-modified metal powder or glass powder, dispersants, leveling agents, wax, additives such as aggregates, diluent solvents, etc., as necessary, within a range not impairing the above effects.

[0088] Here, when a rust-proof pigment is contained, the content thereof is preferably, for example, 1 to 15% by mass. In addition, various known rust-proof pigments can be used as the rust-proof pigment to be used.

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

[0090] The Vickers hardness of the colored coating layer 30 measured at a depth of indentation from the surface layer to three-quarters of the coating thickness (the size of the test load that can achieve the desired indentation depth is set according to the hardness of the colored coating layer 30) is preferably 10 to 70 Hv. The Vickers hardness is measured using a universal hardness tester (manufactured by FISCHER INSTRUMENTS Co., Ltd.). Under the above-mentioned indentation depth conditions, the hardness is measured from the coating surface at any 10 locations, whether where the resin particles 303 are present or not, and the average value of the 10 measured values ​​is calculated. The colored coating layer 30 can further improve the damage resistance by having the above-mentioned Vickers hardness. The above-mentioned Vickers hardness shown in the colored coating layer 30 is more preferably 15 to 65 Hv.

[0091] <About the chemical conversion coating layer 40>

[0092] The chemical conversion coating layer 40 of the present 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 coating layer 40 of the present embodiment, for example, a composition containing at least one selected from the group consisting of resin, silane coupling agent, zirconium compound, silicon dioxide, phosphoric acid and its salt, fluoride, vanadium compound, and tannin or tannic acid can be listed. By containing these substances, the film-forming property after the chemical conversion treatment liquid is applied, the barrier property (compactness) of the coating to corrosion 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 coating layer 40 contains one or more of a silane coupling agent or a zirconium compound, a cross-linked structure is formed in the chemical conversion coating layer 40 and the bonding with the plated surface is enhanced, thereby further improving the adhesion and barrier properties of the coating.

[0095] Furthermore, when the chemical conversion coating layer 40 contains one or more of silicon dioxide, phosphoric acid and its salts, fluorides, or vanadium compounds, it functions as an inhibitor to form a precipitated film or a passivation film on the plating layer or the steel surface, thereby further improving the corrosion resistance.

[0096] The following describes in detail each component that may be included in the chemical conversion coating layer 40 as described above with examples.

[0097] [Resin]

[0098] The resin is not particularly limited, and for example, well-known organic resins such as polyester resin, polyurethane resin, epoxy resin, phenolic resin, acrylic resin, and polyolefin resin can be used. In order to further improve the adhesion with the plated steel sheet for pre-coated steel sheet, it is preferred to use at least one of the resins (polyester resin, polyurethane resin, epoxy resin, acrylic resin, etc.) having a forced site and a polar functional group in the molecular chain. The resin can be used alone or in combination of two or more.

[0099] The resin content in the chemical conversion coating layer 40 is preferably 0% by mass or more, and more preferably 1% by mass or more, relative to the solid content of the coating. In addition, the resin content in the chemical conversion coating layer 40 is preferably 85% by mass or less, more preferably 60% by mass or less, and further preferably 40% by mass or less, relative to the solid content of the coating. When the resin content exceeds 85% by mass, the proportion of other coating constituent components decreases, and there is a case where the performance required as a coating other than corrosion resistance decreases.

[0100] [Silane coupling agent]

[0101] Examples of the silane coupling agent include γ-(2-aminoethyl)aminopropyltrimethoxysilane, γ-(2-aminoethyl)aminopropylmethyldimethoxysilane, γ-(2-aminoethyl)aminopropyltriethoxysilane, γ-(2-aminoethyl)aminopropylmethyldiethoxysilane, γ-(2-aminoethyl)aminopropylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, N-β-( N-vinylbenzylaminoethyl)-γ-aminopropyltrimethoxysilane, N-β-(N-vinylbenzylaminoethyl)-γ-aminopropylmethyldimethoxysilane, N-β-(N-vinylbenzylaminoethyl)-γ-aminopropyltriethoxysilane, N-β-(N-vinylbenzylaminoethyl)-γ-aminopropylmethyldiethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyl γ-Mercaptopropylmethyldimethoxysilane, γ-mercaptopropyltriethoxysilane, γ-mercaptopropylmethyldiethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, vinyltriacetoxysilane, γ-chloropropyltrimethoxysilane, γ-chloropropylmethyldimethoxysilane, γ-chloropropyltriethoxysilane, γ-chloropropylmethyldiethoxysilane, hexamethyldisilazane, γ-anilinopropyltrimethoxysilane, γ-anilinopropylmethyldimethoxysilane, γ-anilinopropyltriethoxysilane, γ-anilinopropylmethyldiethoxysilane, 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 in the chemical conversion treatment agent for forming the chemical conversion treatment film layer 40 can be set to 2 to 80 g / L, for example. When the amount of silane coupling agent added is less than 2 g / L, the adhesion to the plated surface is insufficient, and there is a possibility that the processing adhesion of the coating film is reduced. On the other hand, when the amount of the silane coupling agent added exceeds 80 g / L, the cohesive force of the chemical conversion coating layer is insufficient, and there is a possibility that the processing adhesion with the coating layer is reduced.The silane coupling agents listed above may be used alone or in combination of two or more.

[0102] [Zirconium compounds]

[0103] As zirconium compounds, for example, zirconium n-propoxide, zirconium n-butoxide, zirconium tetraacetylacetonate, zirconium monoacetylacetonate, zirconium diacetylacetonate, zirconium monoethyl acetoacetate, zirconium acetylacetonate combined with diethyl acetoacetate, zirconium acetate, zirconium monostearate, zirconium carbonate, ammonium zirconium carbonate, potassium zirconium carbonate, sodium zirconium carbonate, etc. can be cited. The amount of zirconium compound added in the chemical conversion treatment agent used to form the chemical conversion treatment coating layer 40 can be set to 2 to 80 g / L, for example. When the amount of zirconium compound added is less than 2 g / L, the adhesion to the plated surface is insufficient, and there is a possibility that the processing adhesion of the coating film is reduced. In addition, when the amount of zirconium compound added exceeds 80 g / L, the cohesion of the chemical conversion treatment coating layer 40 is insufficient, and there is a possibility that the processing adhesion with the coating layer is reduced. The zirconium compound can be used alone or in combination of two or more.

[0104] [Silicon dioxide]

[0105] As silica, for example, commercially available silica gels such as "Snowtex N", "Snowtex C", "Snowtex UP", "Snowtex PS" manufactured by Nissan Chemical Co., Ltd., "Adelite AT-20Q" manufactured by ADEKA Co., Ltd., or powdered silica such as Aerosil #300 manufactured by Nippon Aerosil Co., Ltd., or silica equivalent to these commercially available silicas can be used. The silica can be appropriately selected according to the desired performance of the pre-coated plated steel sheet. The amount of silica added in the chemical conversion treatment agent used to form the chemical conversion treatment 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 that the processing adhesion of the coating layer is reduced, and when the amount of silica added exceeds 40 g / L, the effects of processing adhesion and corrosion resistance are likely to be saturated, which is not economical.

[0106] [Phosphoric acid and its salts]

[0107] Phosphoric acid and its salts include, for example, phosphoric acid such as orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, tetraphosphoric acid and their salts; ammonium salts such as triammonium phosphate and diammonium hydrogen phosphate; phosphonic acid such as aminotri(methylenephosphonic acid), 1-hydroxyethylidene-1,1-diphosphonic acid, ethylenediaminetetra(methylenephosphonic acid), diethylenetriaminepenta(methylenephosphonic acid) and their salts; organic phosphoric acid such as phytic acid and its salts. It should be noted that, regarding phosphoric acid salts, as salts other than ammonium salts, metal salts with Na, Mg, Al, K, Ca, Mn, Ni, Zn, Fe and the like can be listed. 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, for example, preferably 0% by mass or more, more preferably 1% by mass or more, relative to the solid content of the film. In addition, the content of phosphoric acid and its salts is, for example, preferably 20% by mass or less, more preferably 10% by mass or less, relative to the solid content of the film. When the content of phosphoric acid and its salts exceeds 20% by mass, the film becomes brittle, and there is a case where the processing followability of the film during the forming of the surface-treated steel sheet 1 is reduced.

[0109] [Fluoride]

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

[0111] It should be noted that the content of fluoride is preferably 0% by mass or more, more preferably 1% by mass or more, relative to the solid content of the coating. In addition, the content of fluoride is preferably 20% by mass or less, more preferably 10% by mass or less, relative to the solid content of the coating. When the content of fluoride exceeds 20% by mass, the coating becomes brittle, and there is a case where the processing followability of the coating during the forming of the surface-treated steel sheet 1 is reduced.

[0112] [Vanadium compounds]

[0113] As the vanadium compound, for example, vanadium pentoxide, metavanadic acid, ammonium metavanadate, sodium metavanadate, vanadium trichloride and other pentavalent vanadium compounds are reduced with a reducing agent to divalent to tetravalent vanadium compounds, vanadium trioxide, vanadium dioxide, vanadium oxysulfate, vanadium oxyoxalate, vanadium acetylacetonate, vanadium acetylacetonate, vanadium trichloride, vanadium phosphovanadomolybdic acid, vanadium sulfate, vanadium dichloride, vanadium oxide and the like, etc. The vanadium compound can be used alone or in combination of two or more.

[0114] It should be noted that the content of the vanadium compound is preferably 0% by mass or more, more preferably 1% by mass or more, relative to the solid content of the coating. In addition, the content of the vanadium compound is preferably 20% by mass or less, more preferably 10% by mass or less, relative to the solid content of the coating. When the content of the vanadium compound exceeds 20% by mass, the coating becomes brittle, and there is a case where the processing followability of the coating during the forming of the surface-treated steel sheet 1 is reduced.

[0115] [Tannin or tannic acid]

[0116] Tannin or tannic acid can use any of hydrolyzable tannin and condensed tannin. Examples of tannin and tannic acid include witch hazel tannin, gallnut tannin, gallic tannin, terminalia chebula tannin, tannin of sappanwood, tannin of tanning materials, tannin of oak bowl, catechin, etc. The amount of tannin or tannic acid added in the chemical conversion treatment agent used to form the chemical conversion treatment film 40 can be set to 2 to 80 g / L. When the amount of tannin or tannic acid added is less than 2 g / L, the adhesion to the plated surface is insufficient, and there is a possibility that the processing adhesion of the coating film is reduced. In addition, when the amount of tannin or tannic acid added exceeds 80 g / L, the cohesive force of the chemical conversion treatment film is insufficient, and there is a possibility that the processing adhesion to the coating film is reduced.

[0117] In addition, within a range that does not impair the performance, an acid, an alkali, or the like may be added to the chemical conversion treatment agent for forming the chemical conversion treatment film layer 40 to adjust the pH.

[0118] After applying the chemical conversion agent containing the above-mentioned various components on one or both sides of the steel sheet 10, the chemical conversion coating layer 40 is formed by drying. In the surface treated steel sheet 1 of the present embodiment, it is preferred to form a 10 mg / m2 coating layer on each side of the coating layer 20. 2 The above chemical conversion coating layer 40. The adhesion amount of the chemical conversion coating layer 40 is more preferably 20 mg / m 2 More preferably, 50 mg / m 2 In addition, in the surface-treated steel sheet 1 of the present embodiment, it is preferable to form a 1000 mg / m 2 The following chemical conversion coating layer 40. The adhesion amount of the chemical conversion coating layer 40 is more preferably 800 mg / m 2 Below, more preferably 600 mg / m 2 The thickness of the chemical conversion coating layer 40 corresponding to the amount of adhesion varies depending on the components contained in the chemical conversion agent, but is generally about 0.01 to 1 μm. The thickness of the chemical conversion coating layer 40 can be measured by cross-sectional observation in the same manner as the thickness of the colored coating layer 30.

[0119] Example

[0120] The surface treated steel sheet 1 of the present invention is described in detail below with reference to examples and comparative examples. It should be noted that the following example is only an example 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 example.

[0121] (1) Plated steel sheet

[0122] Five types of metal plates A1 to A5 shown in Table 1 below were prepared. A steel plate with a thickness of 0.7 mm was used as the base material of the plated metal plate. 2 Plated steel sheet subjected to chromate-free chemical conversion treatment (CT-E300 / manufactured by Japan Parker Seiki Co., Ltd.). The treatment solution used for the chemical conversion treatment contains a silane coupling agent as its component, and the coating layer formed by the chemical conversion treatment functions as a chemical conversion treatment coating layer. It should be noted that the presence or absence of chemical conversion treatment is described in the following Tables 6 and 7.

[0123] (2) Preparation of coloring paint

[0124] Prepare a colored coating used for forming a colored coating layer. For a binder resin that functions as a film-forming component, prepare a resin equivalent to the resin shown in Table 2 below. For each resin solution, prepare a melamine-based curing agent (equivalent to a curing agent manufactured by CYMEL 303 / Allnex) having a solid content ratio of 30% by mass as a curing agent. In addition, prepare particles equivalent to the particles shown in Table 3 below as resin particles. In addition, as a coloring pigment, prepare a substance equivalent to the aluminum pigment, titanium oxide, and carbon black (CB) shown in Table 4 below. In addition, as an anti-rust pigment, prepare the compounds shown in Table 5 below. These coating compositions are mixed according to the specified particle size and specified amount shown in Tables 6 and 7 below to prepare a colored coating.

[0125] (3) Sample preparation

[0126] The coloring paint prepared as described above was applied to both surfaces of the plated steel sheet using a roll coater and heated to a maximum plate temperature (PMT) of 200° C. to form a coloring film layer. It should be noted that the thickness of the produced coloring film layer was measured by cross-sectional observation according to the method described above, and the results obtained are shown in Tables 6 and 7. It should be noted that in Tables 6 and 7, regarding the "film thickness ratio (%)", in the coloring film layer 30a, it refers to the ratio (%) of the number of resin particles 303 having a thickness Ga (Ga≥Ta) greater than the film thickness Ta of the coloring film layer 30a, and in the coloring film layer 30b, it refers to the ratio (%) of the number of resin particles 303 having a thickness Gb (Gb≥Tb) greater than the film thickness Tb of the coloring film layer 30b.

[0127] (4) Sample evaluation

[0128] The performance of each sample produced by the above method was evaluated based on the following criteria. The obtained evaluation results are summarized in Table 8 below.

[0129] <Surface contact damage resistance>

[0130] The surface contact damage resistance was evaluated by the following method. The prepared sample was cut into two pieces with a size of 50 mm square, one piece was fixed with the colored film layer 30a facing upward, and the other piece was stacked on top with the colored film layer 30b facing downward. 2 After rotating 90 degrees under the condition of being pressed under the condition of 1 kgf, about 9.8 N, the state of the colored coating layer 30a was evaluated according to the following criteria, and a score of 2 or more was considered acceptable.

[0131] Evaluation criteria for surface contact damage resistance

[0132] 5: It is considered that there is almost no peeling of the coating film, and it is considered that there is a partial or almost no change in gloss due to pressure.

[0133] 4: It is considered that there is extremely slight peeling of the coating film, and that there is a partial change in gloss due to pressure.

[0134] 3: Slight peeling of the coating film was observed, and gloss change was observed to be partially caused by pressurization.

[0135] 2: Slight peeling of the coating film was found, and gloss change due to pressurization was found.

[0136] 1: It is considered that the coating film peels off and a significant gloss change due to pressurization occurs.

[0137] <Corrosion resistance>

[0138] The corrosion resistance was evaluated according to the following criteria: After the end faces of the test plate were sealed with tape, a salt spray test (SST) based on JIS Z 2371 was performed for 72 hours, and the rust was observed and evaluated according to the following evaluation criteria. A score of 2 or more was considered acceptable.

[0139] Evaluation criteria for corrosion resistance

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

[0141] 4: The white rust area is 1% or more and less than 3%, and no red rust is generated.

[0142] 3: The white rust generation area is 3% or more and less than 4%, and no red rust generation occurs.

[0143] 2: The white rust generation area is 4% or more and less than 5%, and no red rust generation occurs.

[0144] 1: White rust occurs over 5% of the surface area or red rust occurs.

[0145] <Scratch resistance>

[0146] As a reference performance, the scratch resistance was evaluated by the following coin scratch test. A coin was placed in contact with the color coating layer 30a of the prepared sample at an angle of 45 degrees, and scratched with a load of 500g. The damage generated under each load was evaluated according to the following criteria, and a score of 2 or above was considered acceptable.

[0147] Evaluation criteria for scratch resistance

[0148] 5: No peeling of the coating film or change in gloss was observed.

[0149] 4: Although the coating film was not peeled off, a slight gloss change was considered to exist.

[0150] 3: Slight peeling of the coating film was found, and gloss change was found.

[0151] 2: The coating film was partially peeled off and the gloss was changed.

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

[0153] <Indentation resistance>

[0154] As a reference performance, the indentation resistance was evaluated according to the following criteria. The prepared sample was cut into 70 mm square and 50 mm square pieces. The 70 mm square sample was fixed with the colored coating layer 30a facing upward, and the 50 mm square sample was stacked on it with the colored coating layer 30b facing downward, and pressurized at 50°C and 10 MPa for 5 minutes. After separating the two samples, the state of the colored coating layer 30a of the 70 mm square sample was evaluated according to the following criteria, and a score of 2 or above was 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 not noticeable when viewed from the front, slight gloss changes in the pressurized portion can be seen when viewed from an inclined position.

[0158] 2: Although not visible from the front, the gloss change of the pressurized part can be seen from an oblique position.

[0159] 1: The gloss change of the entire pressurizing portion is noticeable when viewed from the front or when viewed from an inclined position.

[0160] <Processing Adhesion>

[0161] As a reference performance, the processing adhesion was evaluated according to the following criteria. The prepared sample was bent at 90° within the condition of R1mm in an atmosphere of 20°C, and then a tape peeling test was performed on the outside of the bent portion. The appearance of the tape peeling portion was evaluated according to the following evaluation criteria, and a score of 2 or more was considered acceptable.

[0162] Evaluation criteria for adhesion of processed parts

[0163] 4: Almost no peeling of the coating film was observed.

[0164] 3: Slight coating film peeling was observed.

[0165] 2: It is considered that the coating film peels off locally.

[0166] 1: It is considered that the coating film peels off as a whole.

[0167] [Table 1]

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

[0169] [Table 2]

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

[0171] [Table 3]

[0172] type Particles C1 Sekisui Chemical Co., Ltd. "SSX-101" (acrylic resin particles, average particle size 1 μm) C2 "MZ-5HN" manufactured by Soken Chemical Co., Ltd. (acrylic resin particles, average particle size 5 μm) C3 Sekisui Chemical Co., Ltd. "BM30X-8" (acrylic resin particles, average particle size 8μm) C4 "MZ-12H" manufactured by Soken Chemical Co., Ltd. (acrylic resin particles, average particle size 12 μm) C5 "HSP-1000" manufactured by Toagosei Co., Ltd. (silicon dioxide particles, average particle size 1 μm) C6 Mitsui Chemicals "CHEMIPEARL_W800" (polyolefin resin particles, average particle size 8 μm) C7 Negami Industries "P-800T" (polyurethane resin particles, average particle size 6 μm) C8 Mix C1 and C2 until the average particle size is 2um C9 C2 and C3 were mixed to an average particle size of 6 μm.

[0173] [Table 4]

[0174] type Coloring Pigments D1 Titanium oxide "R-780" manufactured by Ishihara Sangyo Co., Ltd. D2 Carbon black "MCF#850" manufactured by Mitsubishi Chemical Corporation D3 D2 and D3 were mixed at a ratio of 3:1 (mass %)

[0175] [Table 5]

[0176] type Anti-rust pigment E1 Aluminum tripolyphosphate E2 Calcium vanadate E3 E1 and E2 were mixed at a ratio of 1:1 (mass %)

[0177] [Table 6]

[0178]

[0179] [Table 7]

[0180]

[0181] [Table 8]

[0182]

[0183] It can be seen from Table 8 above that 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 are poorly evaluated for either resistance to surface contact damage or corrosion resistance, and fail to achieve both resistance to surface contact damage and corrosion resistance.

[0184] The preferred embodiments of the present invention are described in detail with reference to the attached drawings, but the present invention is not limited to the examples. Obviously, a person with common sense in the technical field to which the present invention belongs can think of various variations or modifications within the scope of the technical ideas recorded in the patent claims, and it can be understood that these also belong to the technical scope of the present invention.

[0185] The embodiments disclosed this time are exemplary and non-restrictive in all aspects. The above embodiments may be omitted, replaced or changed in various forms without departing from the attached patent claims, the technical features of the technical scope of the present invention described later, and the gist thereof. For example, the technical features of the above embodiments may be arbitrarily combined without impairing their effects. In addition, the arbitrary combination can of course obtain the functions and effects of the various technical features involved in the combination, and at the same time, those skilled in the art may obtain other obvious functions and effects based on the description of this specification.

[0186] In addition, the effects described in this specification are only illustrative or exemplary, and not limiting. That is, the technology involved in the present invention can obtain other obvious effects in addition to or instead of the above effects according to the description of this specification.

[0187] It should be noted that the following technical features also belong to the technical scope of the present invention.

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

[0189] A coating layer containing zinc on both surfaces of the steel sheet;

[0190] a first colored coating layer located on the plated layer on one surface of the steel plate; and

[0191] a second colored coating layer located on the plated layer on the other surface of the steel sheet,

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

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

[0194] When observing a cross section obtained by cutting the first colored coating layer in the film thickness direction,

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

[0196] The ratio of the number of the resin particles having a thickness equal to or greater than the film thickness of the first colored coating layer to the number of all the observed resin particles is 1% or more and 30% or less,

[0197] When observing a cross section obtained by cutting the second colored coating layer in the film thickness direction,

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

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

[0200] (2) The surface-treated steel sheet according to (1) above, wherein, when the first colored coating layer is observed in cross section, a length of 1000 μm in a direction perpendicular to the film thickness direction of the first colored coating layer is set as a first observation length, and when the sum of the lengths of the portions corresponding to the resin particles in the direction perpendicular to the film thickness direction when the portions occupied by the resin particles within the range of the first observation length are projected in the film thickness direction is set as the first occupied length, a ratio of the first occupied length to the first observation length is 15% or more and 40% or less,

[0201] When a length of 1000 μm in a direction perpendicular to the film thickness direction of the second colored coating layer is set as the second observation length, and when the sum of the lengths of the parts occupied by the resin particles in the direction perpendicular to the film thickness direction when the parts occupied by the resin particles are projected in the film thickness direction within the range of the second observation length is set as the second occupied length, the ratio of the second occupied length to the second observation length is greater than 5% and less than 15%.

[0202] (3) The surface-treated steel sheet according to (1) or (2) above, wherein the first colored coating layer has a thickness of 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 film layer is less than twice the film thickness of the first colored film layer,

[0204] The thickness of the resin particles contained in the second colored film layer is less than 3 times the film thickness of the second colored film layer.

[0205] (5) The surface-treated steel sheet 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 film-forming components of the first colored film layer and the second colored film layer have a glass transition temperature Tg of 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, further comprising a chemical conversion coating layer between the plating layer and the first colored coating layer on one surface of the steel sheet, and between the plating layer and the second colored coating layer on the other surface 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] Description of Reference Numerals

[0210] 1 Surface treated steel plate

[0211] 10 Steel Plate

[0212] 20 Plating layer

[0213] 30 Colored coating layer

[0214] 40 Chemical conversion treatment coating layer

[0215] 301 Film-forming ingredients

[0216] 303 Resin Pellets

Claims

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

2. The surface-treated steel sheet according to claim 1, wherein: In a case where the first colored coating layer is observed in cross section, a length of 1000 μm in a direction perpendicular to the film thickness direction of the first colored coating layer is set as a first observation length, and a sum of lengths of a portion corresponding to the resin particles in a direction perpendicular to the film thickness direction when a portion occupied by the resin particles within the range of the first observation length is projected in the film thickness direction is set as the first occupied length, and a ratio of the first occupied length to the first observation length is 15% or more and 40% or less, When a length of 1000 μm in a direction perpendicular to the film thickness direction of the second colored coating layer is set as the second observation length, and when the sum of the lengths of the parts occupied by the resin particles in the direction perpendicular to the film thickness direction when the parts occupied by the resin particles are projected in the film thickness direction within the range of the second observation length is set as the second occupied length, the ratio of the second occupied length to the second observation length is greater than 5% and less than 15%.

3. The surface-treated steel sheet according to claim 1 or 2, wherein: The first colored coating layer has a film thickness of 3 μm or more and 10 μm or less.

4. The surface-treated steel sheet 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 film layer is less than 3 times the film thickness of the second colored film layer.

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

6. The surface-treated steel sheet according to claim 1 or 2, wherein: The glass transition temperature Tg of the film-forming components of the first colored film layer and the second colored film layer is 30° C. or higher and 70° C. or lower.

7. The surface-treated steel sheet according to claim 1 or 2, wherein: A chemical conversion coating layer is further provided between the plated layer and the first colored coating layer on one surface of the steel sheet and between the plated layer and the second colored coating layer on the other surface of the steel sheet.

8. The surface-treated steel sheet according to claim 1 or 2, wherein: The resin particles have an average particle diameter of 3 μm or more and 15 μm or less.

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