Method for coating steel structures, method for manufacturing coated steel structures, coating sheet and coated steel structure

Abstract

The coating sheet is placed on the steel structure so as to cover at least a portion of the surface of the steel structure, while ensuring that the gloss level of the coating film formed on the surface of the coating sheet is maintained. [Solution] A method for covering a steel structure with a covering body including a covering sheet and a topcoat coating, comprising: an arrangement step of arranging a covering sheet having a first surface and a second surface, and having a surface roughness Sa of 10 μm or less of the first surface, such that the surface of the steel structure and the second surface of the covering sheet face each other, so as to cover at least a part of the surface of the steel structure; and a topcoat coating forming step of forming a topcoat coating on the first surface of the covering sheet.

Description

[Technical Field]

[0001] This disclosure relates to a method for coating steel structures, a method for manufacturing coated steel structures, a coating sheet, and coated steel structures. [Background technology]

[0002] Steel structures such as bridges are primarily made of steel. For the purpose of protecting and repairing steel structures, it is known to cover the surface of steel structures with coatings such as paint films or sheets (see, for example, background art in Patent Document 1). For example, as a method of protecting or repairing steel structures, a method is known in which a corrosion-resistant primer is applied to the surface of the steel structure, an epoxy resin paint with excellent barrier properties against corrosive factors (water or oxygen) is applied, and then a fluororesin paint with excellent weather resistance is applied. Furthermore, Patent Document 1 describes a method for repairing steel materials, which involves surface preparation of the rusted surface of the steel material, application of a primer containing a moisture-curing resin to the surface prepared steel material, surface preparation with a surface leveling agent containing epoxy resin, and application of an ultraviolet-curing FRP sheet to the surface prepared steel material. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2018-193739 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The method of applying a corrosion-resistant primer, then applying an epoxy resin paint with excellent barrier properties against corrosive factors (water or oxygen), and finally applying a weather-resistant fluororesin paint, involves a long construction period and requires numerous painting steps. In other words, this method makes it difficult to cover the surface of a steel structure with a coating in a short period of time while imparting protective properties, particularly weather resistance, to the coating. In contrast, the method of arranging a coating sheet, such as the UV-curing FRP sheet described above, allows for the surface of a steel structure to be covered with a coating possessing protective properties in a short period of time by arranging a coating sheet that provides these properties.

[0005] When a covering sheet is placed on a steel structure to cover at least a portion of the surface of the steel structure, it may be necessary to further form a glossy coating on the surface of the covering sheet. However, with conventional covering sheets, even if a glossy coating is formed on the surface of the covering sheet, the gloss may not be significantly increased. The purpose of this disclosure is to ensure a high level of gloss in the coating formed on the surface of a covering sheet while placing the covering sheet on a steel structure to cover at least a portion of the surface of the steel structure. [Means for solving the problem]

[0006] The present disclosure is a method for coating a steel structure with a coating body including a coating sheet and a topcoat coating, comprising: an arrangement step of arranging a coating sheet having a first surface and a second surface, with a surface roughness Sa of the first surface being 10 μm or less, so as to cover at least a portion of the surface of the steel structure, with the second surface of the coating sheet facing the surface of the steel structure; and a topcoat coating formation step of forming a topcoat coating on the first surface of the coating sheet. [Effects of the Invention]

[0007] According to this disclosure, it is possible to arrange a covering sheet on a steel structure so as to cover at least a portion of the surface of the steel structure, while ensuring a high degree of gloss of the coating film formed on the surface of the covering sheet. [Brief explanation of the drawing]

[0008] [Figure 1A] FIG. 1A is a diagram for explaining one embodiment, and is a cross-sectional view showing an example of a steel structure with a coating. [Figure 1B] FIG. 1B is a cross-sectional view showing another example of a steel structure with a coating. [Figure 1C] FIG. 1C is a cross-sectional view showing another example of a steel structure with a coating. [Figure 1D] FIG. 1D is a cross-sectional view showing more details of the steel structure with a coating shown in FIG. 1C. [Figure 2A] FIG. 2A is a cross-sectional view showing the layer structure of a coating sheet. [Figure 2B] FIG. 2B is a cross-sectional view showing the layer structure of a coating sheet. [Figure 3] FIG. 3 is a diagram for explaining a method of measuring the storage modulus of a bonding layer. [Figure 4A] FIG. 4A is a diagram for explaining a method of repairing a steel structure. [Figure 4B] FIG. 4B is a diagram for explaining a method of repairing a steel structure. [Figure 4C] FIG. 4C is a diagram for explaining a method of repairing a steel structure. [Figure 4D] FIG. 4D is a diagram for explaining a method of repairing a steel structure. [Figure 5] FIG. 5 is a cross-sectional view showing an example of a steel structure of a comparative example.

DETAILED DESCRIPTION OF THE EMBODIMENT FOR CARRYING OUT THE INVENTION

[0009] Hereinafter, details of one embodiment of the present disclosure will be described. In the drawings attached to this specification, for the convenience of easy understanding, the scale, the aspect ratio of the vertical and horizontal dimensions, etc. are appropriately changed and exaggerated from those of the actual object.

[0010] In this specification, terms such as "film," "sheet," and "plate" are not distinguished from each other solely on the basis of differences in name. For example, a "covering sheet" cannot be distinguished from a component called a covering film or covering plate solely on the basis of differences in name.

[0011] Figures 1A to 1D, 2A, 2B, 4A to 4D, and 5 all show cross-sections along the normal direction of the covering sheet. In this specification, the normal direction of a film-like (sheet-like, plate-like) member refers to the direction parallel to the normal or perpendicular to the film surface (sheet surface, plate surface) of the film-like (sheet-like, plate-like) member in question. The "film surface (sheet surface, plate surface)" refers to the surface that coincides with the film-like (sheet-like, plate-like) member in question when viewed as a whole and in a broad sense.

[0012] In this specification, when multiple upper limit candidates and multiple lower limit candidates are given for a certain parameter, the numerical range of that parameter may be constructed by combining any one upper limit candidate and any one lower limit candidate. As an example, consider the statement, "Parameter B is preferably A1 or greater, more preferably A2 or greater, even more preferably A3 or greater, and also preferably A4 or less, more preferably A5 or less, and even more preferably A6 or less." In this example, the numerical range of parameter B may be A1 or greater and A4 or less, A1 or greater and A5 or less, A1 or greater and A6 or less, A2 or greater and A4 or less, A2 or greater and A5 or less, A2 or greater and A6 or less, A3 or greater and A4 or less, A3 or greater and A5 or less, and A3 or greater and A6 or less.

[0013] The embodiments of this disclosure will be described in detail below. This disclosure can be implemented in many different forms and should not be construed as being limited to the embodiments described below. The drawings may schematically represent the width, thickness, and shape of each layer, etc., compared to the embodiments, in order to clarify the explanation, but these are merely examples and should not limit the interpretation of this disclosure. In this specification and in each figure, elements similar to those already described in the previously shown figures will be denoted by the same reference numerals, and detailed explanations may be omitted as appropriate.

[0014] <<<Steel structure with coating>>> First, a coated steel structure 10 according to one embodiment of the present disclosure will be described. The coated steel structure 10 of this embodiment is manufactured by the method for manufacturing a coated steel structure of this embodiment, which will be described later. Figure 1A is a cross-sectional view showing an example of the coated steel structure 10 of this embodiment. Figure 1B is a cross-sectional view showing another example of the coated steel structure 10 of this embodiment, different from Figure 1A. Figure 1C is a cross-sectional view showing another example of the coated steel structure 10 of this embodiment, different from Figures 1A and 1C. In Figures 1A to 1C, the components included in the steel structure 100 and the details of the shape of the steel structure 100 are not shown, and only the general shape of the steel structure 100 is shown. As shown in Figures 1A to 1C, the coated steel structure 10 comprises a steel structure 100 and a coating 80 that covers the steel structure 100. The steel structure 100 has a steel material 20. The coating 80 has a coating sheet 30 and a topcoat coating 81. The covering sheet 30 has a first surface 31 and a second surface 32. The second surface 32 is the surface of the covering sheet 30 that is located on the opposite side from the first surface 31.

[0015] The coated steel structure 10 shown in Figure 1A includes the steel structure 100, the coating sheet 30, and the topcoat 81 in this order in the lamination direction. The coating sheet 30 is directly bonded to the steel structure 100. The second surface 32 of the coating sheet 30 is in contact with the steel structure 100.

[0016] In the example shown in Figure 1B, the coated steel structure 10 further has a bonding layer 15. The coated steel structure 10 includes the steel structure 100, the bonding layer 15, the coating sheet 30, and the topcoat 81 in this order in the lamination direction. The bonding layer 15 is located between the steel structure 100 and the coating sheet 30 in the lamination direction. The bonding layer 15 is in contact with the steel structure 100 and the coating sheet 30. The bonding layer 15 is bonded to the steel structure 100 and the coating sheet 30. The coated steel structure 10 shown in Figure 1B differs from the example shown in Figure 1A in that it includes the bonding layer 15. The coated steel structure 10 shown in Figure 1B can otherwise be configured in the same way as the coated steel structure 10 shown in Figure 1A.

[0017] In the example shown in Figure 1C, the coating 80 further has a rust-preventive layer 18. The coated steel structure 10 shown in Figure 1C includes steel material 20, rust-preventive layer 18, coating sheet 30, and topcoat film 81 in this order in the lamination direction. The coating sheet 30 is bonded to the steel structure 100 via the rust-preventive layer 18. The rust-preventive layer 18 is located between the steel material 20 and the coating sheet 30 in the lamination direction. The rust-preventive layer 18 is in contact with the steel material 20 and the coating sheet 30. The coated steel structure 10 shown in Figure 1C differs from the example shown in Figure 1A in that it includes a rust-preventive layer 18. The coated steel structure 10 shown in Figure 1C may otherwise be configured similarly to the coated steel structure 10 shown in Figure 1A.

[0018] The coated steel structure 10 of this embodiment is not limited to the examples shown in Figures 1A to 1C, and the coated steel structure 10 may include further layers.

[0019] Details of the steel structure 100 will be described. Figure 1D is a cross-sectional view of the covered steel structure 10 shown in Figure 1C, including the components included in the steel structure 100 that were omitted in Figure 1C, and the details of the shape of the steel structure 100. The steel structure 100 is a structure having steel material 20. The steel material 20 may constitute the base material of the steel structure 100. Examples of steel structures 100 include bridges, bridge piers, steel towers, steel pipes, chimneys, switchboards, tanks, plants, pipelines, rolled plates, roofs, and metal casings for vending machines, cubicles (high-voltage power receiving equipment), and photo booths. The steel structure 100 is, for example, a building structure. The steel structure 100 may also be a civil engineering structure.

[0020] Examples of steel materials 20 include nickel-chromium steel, nickel-chromium-molybdenum steel, chromium steel, chromium-molybdenum steel, and manganese steel alloys, as well as carbon steel.

[0021] The steel structure 100 may include a coating 50 covering the steel material 20, as shown in Figure 1D. The coating 50 is a coating that was formed on the steel material 20 before the steel structure 100 was covered with the covering body 80. The coating 50 may also be a coating that was formed on the steel material 20 when the steel structure 100 was newly constructed. Such a coating 50 that was formed on the steel material 20 when the steel structure 100 was newly constructed is also called the pre-repair coating (old coating) 50. The coating 50 may be provided for the purpose of suppressing the deterioration of the steel material 20. As an example, the coating 50 is a coating such as a rust-preventive paint or corrosion-preventive paint that was formed on the steel material 20 during the manufacture of the steel structure 100 to suppress rust formation.

[0022] <<<Covering Sheet>>> The covering sheet 30 is a covering sheet for covering the steel structure 100. The covering sheet 30 is positioned to cover at least a portion of the surface of the steel structure 100. The covering sheet 30 may be positioned to cover the entire surface of the steel structure 100. Furthermore, the covering sheet 30 is positioned so that the surface of the steel structure 100 and the second surface 32 of the covering sheet 30 face each other. The covering sheet 30 may protect the steel structure 100 by covering its surface. The covering sheet 30 may suppress the deterioration of the steel structure 100. In particular, the covering sheet 30 may suppress the deterioration of the steel material 20. The covering sheet 30 may be used for repairing the steel structure 100 having a deteriorated part 12, which will be described later. The covering sheet 30 used for repair may be laminated on the portion of the steel structure 100 from which the deteriorated part 12 has been removed.

[0023] The covering sheet 30 of this embodiment is provided with the property of protecting the surface of the steel structure 100. In particular, the covering sheet 30 of this embodiment is provided with weather resistance. The covering sheet 30 may also be provided with gas barrier properties. With the covering sheet 30, the parts of the steel structure 10 with a covering, other than the covering sheet 30, such as the steel material 20 and the coating film formed on the steel material 20, that are covered by the covering sheet 30 can be protected by the covering sheet 30. This makes it possible to suppress deterioration of those parts.

[0024] <<Layer structure of the covering sheet>> Figure 2A is a cross-sectional view showing the layer structure of the covering sheet 30 of this embodiment. The covering sheet 30 shown in Figure 2A may be included in the covered steel structure 10 shown in Figure 1A. The covering sheet 30 of this embodiment includes a resin cured material layer 45 that constitutes the first surface 31. The resin cured material layer 45 of this embodiment is a weather-resistant layer 42. The covering sheet 30 of this embodiment includes a bonding layer 43 that constitutes the second surface 32. In the example shown in Figure 2A, the covering sheet 30 further includes a base material 41 and a barrier layer 44. In the example shown in Figure 2A, the covering sheet 30 further includes a bonding layer 491 that bonds the barrier layer 44 and the base material 41. Although not shown, the bonding layer 491 may be omitted. In the example shown in Figure 2A, the covering sheet 30 includes the bonding layer 43, barrier layer 44, bonding layer 491, base material 41, and the resin cured material layer 45 which is the weather-resistant layer 42, in this order from the first surface 31 to the second surface 32.

[0025] In the example shown in Figure 2A, the distance w6 between the barrier layer 44 and the second surface 32 is smaller than the distance w8 between the weather-resistant layer 42 and the second surface 32, and also smaller than the distance w9 between the substrate 41 and the second surface 32. That is, considering the positional relationship between the barrier layer 44 and the weather-resistant layer 42, the barrier layer 44 and the weather-resistant layer 42 are stacked in this order from the second surface 32 toward the first surface 31. Considering the positional relationship between the barrier layer 44 and the substrate 41, the barrier layer 44 and the substrate 41 are stacked in this order from the second surface 32 toward the first surface 31. Because the distance w6 is smaller than the distance w8, the weather-resistant layer 42 can reduce the ultraviolet rays that are irradiated onto the first surface 31 of the covering sheet 30 and reach the barrier layer 44. This suppresses the deterioration of the barrier layer 44 due to ultraviolet rays and maintains the gas barrier properties of the barrier layer 44. Because the distance w6 is smaller than the distance w9, the ultraviolet light that is irradiated onto the first surface 31 of the coating sheet 30 and reaches the barrier layer 44 can be reduced by the substrate 41. This suppresses the deterioration of the barrier layer 44 due to ultraviolet light and maintains the gas barrier properties of the barrier layer 44.

[0026] In the example shown in Figure 2A, the second surface 32 of the coating sheet 30 is composed of a bonding layer 43. As a result, as will be described later, the coating sheet 30 can be bonded to the steel structure 100 or the coating film on the steel structure 100 by the bonding layer 43.

[0027] Figure 2B is a cross-sectional view showing another example of the layer configuration of the coating sheet 30 in this embodiment, different from that shown in Figure 2A. As shown in Figure 2B, the bonding layer 43 may be omitted. The coating sheet 30 shown in Figure 2B may be included in the coated steel structure 10 shown in Figures 1B to 1D. In this case, the coating sheet 30 may be bonded to the steel structure 100 or the coating film on the steel structure 100 via a bonding layer not shown and not included in the coating sheet 30. The coating sheet 30 may also be welded to the steel structure 100 or the coating film on the steel structure 100 without using a bonding layer. If the bonding layer 43 is omitted, as shown in Figure 2B, the barrier layer 44 may constitute the second surface 32 of the coating sheet 30. When the barrier layer 44 constitutes the second surface 32, the distance w6 between the barrier layer 44 and the second surface 32 is 0.

[0028] Each layer that may be included in the covering sheet 30 will be described in more detail below.

[0029] <Base material> The base material 41 may be a resin film. Examples of resin materials constituting the base material 41 include polyolefins such as polyethylene and polypropylene, polyvinyl chloride, polyvinylidene chloride-vinyl chloride copolymer, polyester such as polyethylene terephthalate, polycarbonate, polyarylate, styrene resin, acrylic resin, acrylic urethane resin, urethane resin, fluororesin, acetylcellulose, polyamide, and polyimide. The base material 41 may be a single layer or a multilayer. The base material 41 may also be a laminated film of resin films.

[0030] As an example, the base material 41 contains a polyolefin. Examples of polyolefins include polyethylene, polypropylene, polybutene, and polymethylpentene. In one embodiment, the base material 41 contains polypropylene.

[0031] Examples of polypropylene include propylene homopolymers; copolymers such as ethylene-propylene copolymers, propylene-butene copolymers, and ethylene-propylene-butene copolymers. Among these, propylene homopolymers, ethylene-propylene copolymers, and propylene-butene copolymers are preferred.

[0032] From the viewpoint of processability, the polyolefin content of the base material 41 is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and particularly preferably 80% by mass or more, relative to the total resin components of the base material 41.

[0033] The base material 41 may contain additives. Examples of additives include abrasion resistance improvers, infrared absorbers, antistatic agents, fillers, foaming agents, flame retardants, antifungal agents, plasticizers, leveling agents, flow regulators, defoaming agents, dispersants, settling inhibitors, lubricants, and colorants. The base material 41 may also contain weather-resistant agents such as ultraviolet absorbers, antioxidants, and light stabilizers. The base material 41 containing weather-resistant agents has excellent weather resistance. In a weather-resistant coating sheet 30 made of base material 41, the topcoat layer described later may be made thin, or the topcoat layer may be omitted. Examples of ultraviolet absorbers include benzotriazole-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, triazine-based ultraviolet absorbers, and hydroxyphenyltriazine-based ultraviolet absorbers. Examples of light stabilizers include hindered amine-based light stabilizers such as piperidinyl sebacate-based light stabilizers. Examples of colorants include dyes and pigments.

[0034] The base material 41 may be colorless and transparent, or it may contain colorants such as dyes and pigments, as described above regarding additives. For example, when the coating sheet 30 includes a design layer as described later, and the surface hue of the substrate to which the coating sheet 30 is attached varies, if it is desired to conceal the surface hue and improve the stability of the color tone of the design layer, the base material 41 may contain an inorganic pigment such as a white pigment.

[0035] Examples of pigments include white pigments such as zinc oxide, lead white, lithopone, titanium dioxide, precipitated barium sulfate, and barite; black pigments such as carbon black; red pigments such as red lead and iron oxide red; yellow pigments such as lead yellow and zinc yellow (zinc yellow type 1, zinc yellow type 2); and blue pigments such as ultramarine blue and Prussian blue (ferrocyanide potassium).

[0036] The amount of coloring agent may be 1 part by mass or more, 3 parts by mass or more, 5 parts by mass or more, 50 parts by mass or less, 40 parts by mass or less, or 30 parts by mass or less, per 100 parts by mass of polyolefin contained in the base layer.

[0037] The thickness of the base material 41 is, for example, 300 μm or less. From the viewpoint of balancing design and processability, the thickness of the base material 41 is preferably 20 μm or more, more preferably 25 μm or more, and even more preferably 30 μm or more. From the viewpoint of balancing design and processability, the thickness of the base material 41 is preferably 150 μm or less, more preferably 120 μm or less, and even more preferably 100 μm or less.

[0038] Surface treatment may be applied to one or both sides of the substrate 41. Examples of surface treatments include physical surface treatments such as oxidation and embossing, as well as chemical surface treatments. Examples of oxidation methods include corona discharge treatment, chromium oxidation treatment, flame treatment, hot air treatment, and ozone-ultraviolet treatment. Examples of embossing methods include sandblasting and solvent treatment. The substrate layer may have an easy-adhesion layer on one or both sides. This can improve, for example, the interlayer adhesion between the substrate layer and other layers.

[0039] The base material 41 may have a cellular structure. The cellular structure may be a closed-cell structure, a continuous-cell structure, or a semi-continuous semi-closed-cell structure in which closed-cell and continuous-cell structures are mixed. An example of a base material 41 having a cellular structure is a foam layer. More specifically, examples of base material 41 include acrylic resin foam (acrylic foam), urethane resin foam (urethane foam), polyolefin foam, and rubber foam containing acrylic rubber and other elastomers.

[0040] The thickness of the base material 41 may be determined considering the finish after repair of the steel structure, that is, the finish after the covering sheet 30 is attached to the steel material 20, as well as the handling and ease of application of the covering sheet 30. The thickness of the base material 41 may be 10 μm or more, 20 μm or more, 30 μm or more, 50 μm or more, or 100 μm or more. The thickness of the base material 41 may be 5000 μm or less, 4000 μm or less, 3000 μm or less, 2000 μm or less, or 1000 μm or less.

[0041] The base material 41 may include a fiber-reinforced resin layer. The fiber-reinforced resin layer can improve the impact resistance of the base material 41 and the covering sheet 30. The fiber-reinforced resin layer may include a resin material and reinforcing fibers. Examples of the resin material include the resin materials that can be used in the base material 41 described above. The reinforcing fibers may be inorganic fibers or organic fibers. Examples of inorganic fibers include glass fibers, carbon fibers, silicon-titanium-carbon fibers, boron fibers, and metal fibers. Examples of organic fibers include aramid fibers, vinylon fibers, polyester fibers, and polyamide fibers. The reinforcing fibers may be in a mesh (network) form. The fiber-reinforced resin layer may include a glass mesh as the reinforcing fibers.

[0042] The thickness of the fiber-reinforced resin layer may be 50 μm or more, 75 μm or more, 100 μm or more, 125 μm or more, or 150 μm or more. The thickness of the fiber-reinforced resin layer may be 550 μm or less, 525 μm or less, 500 μm or less, 475 μm or less, or 450 μm or less. By setting the thickness of the fiber-reinforced resin layer in this way, impact resistance can be imparted to the covering sheet 30.

[0043] The base material 41 may include a laminate containing a fiber-reinforced resin layer and a resin layer. The base material 41 may include a laminate containing a first resin layer, a fiber-reinforced resin layer, and a second resin layer. Examples of resin materials that can be used in the base material 41 described above are given as resin materials constituting the resin layer, the first resin layer, and the second resin layer. The laminate contained in the base material 41 may include a fiber-reinforced resin layer containing polyethylene and a glass mesh, and a polyethylene layer. The laminate contained in the base material 41 may include a first polyethylene layer, a fiber-reinforced resin layer containing polyethylene and a glass mesh, and a second polyethylene layer.

[0044] The thickness of the resin layer, the thickness of the first resin layer, and the thickness of the second resin layer may be 10 μm or more, 20 μm or more, 30 μm or more, 50 μm or more, or 100 μm or more, respectively. The thickness of the resin layer, the thickness of the first resin layer, and the thickness of the second resin layer may be 1000 μm or less, 800 μm or less, 600 μm or less, 500 μm or less, or 400 μm or less, respectively.

[0045] <Cured resin layer> In this embodiment, the cured resin layer 45 is a weather-resistant layer 42. That is, in this embodiment, the weather-resistant layer 42 constitutes the first surface 31 of the covering sheet 30. The weather-resistant layer 42 imparts weather resistance to the covering sheet 30. The weather-resistant layer 42 is a layer that has weather resistance.

[0046] As an example, the weather-resistant layer 42 has weather resistance that can impart the following performance to the covering sheet 30. A rust-preventive layer 18 is formed on the surface of the steel material 20, the surface of the steel material 20 on which the rust-preventive layer 18 is formed is covered with the covering sheet 30, and a weather resistance test is performed for 408 hours. In this case, the weather-resistant layer 42 imparts to the covering sheet 30 the performance that can reduce the color difference ΔE of the rust-preventive layer 18 before and after the weather resistance test to 4 or less.

[0047] The details of the method for measuring the color difference ΔE of the rust-preventive layer 18 before and after the weathering test will be explained below. First, a steel material 20 with a rust-preventive layer 18 formed on it is prepared, as shown in Figure 4C later. The material for the rust-preventive layer 18 is Nippon Paint Co., Ltd.'s Hypon Sabista. Next, the coating sheet 30 to be measured and the rust-preventive layer 18 are bonded together, as shown in Figure 4D later. At this time, the coating sheet 30 and the rust-preventive layer 18 are joined so that the surface of the rust-preventive layer 18 and the second surface 32 of the coating sheet 30 face each other. If the second surface 32 of the coating sheet 30 is composed of a bonding layer 15, the coating sheet 30 and the rust-preventive layer 18 are joined using the bonding layer 15. If the second surface 32 of the coating sheet 30 is not composed of a bonding layer 15, the coating sheet 30 and the rust-preventive layer 18 are joined via an acrylic adhesive. In this case, the thickness of the acrylic adhesive layer can be 80 μm.

[0048] Next, a 408-hour weather resistance test is performed on the coating sheet 30, which is bonded to the rust-preventive layer 18 formed on the steel material 20. The 408-hour weather resistance test is carried out as follows: The weather resistance test is performed using a weather resistance testing apparatus. For the coating sheet 30 to be evaluated, a 20-hour irradiation process and a 4-hour condensation process are repeated as one cycle until 408 hours are reached. A 30-second shower process is performed after the irradiation process and before the condensation process begins, and after the condensation process and before the irradiation process begins. In the shower process, the sample held in the weather resistance testing apparatus is exposed to a shower of water.

[0049] As a weather resistance test device, the "Eye Super UV Tester SUV-W261", an accelerated weather resistance test device manufactured by Iwasaki Electric Co., Ltd., is used. The UV lamp, lamp jacket, and illuminometer included in the weather resistance test device shall be as follows. ·UV lamp: Product name: M04-L21WB / SUV, manufactured by Iwasaki Electric Co., Ltd. ·Lamp jacket: Product name: WJ50-SUV, manufactured by Iwasaki Electric Co., Ltd. ·Illuminometer: Product name: UVD-365PD, manufactured by Iwasaki Electric Co., Ltd.

[0050] The conditions of the irradiation process shall be as follows. <Irradiation conditions> ·Black panel temperature: 63°C ·Illuminance: 100 mW / cm

[0053] ·Humidity inside the tank: 50% RH ·Time: 20 hours

[0051] The conditions of the dew condensation process shall be as follows. <Dew condensation conditions> ·Illuminance: 0 mW / cm 2 ·Humidity inside the tank: 98% RH ·Time: 4 hours

[0052] Then, the color difference ΔE of the rust prevention layer 18 before and after the weather resistance test is measured. The measured color difference ΔE is the L specified in JIS Z8781:2013 * a * b * in the color system. The color before the weather resistance test is L * 1a * 1b * 1, and the color after the weather resistance test is L * 2a * 2b * 2, and is defined by the following formulas (1) to (4).

Number

[0053] The color L before the weather resistance test * 1a * 1b* 1. Color L after weather resistance test * 2a * 2b * Reference numeral 2 denotes the color when the rust-preventive layer 18 is observed through the covering sheet 30 from the first surface 31 side of the covering sheet 30.

[0054] The function of the coated sheet 30 having a color difference ΔE of 4 or less, as measured as described above, will now be explained. As mentioned above, the coated sheet 30 may be required to have resistance to ultraviolet light. In particular, it is preferable that the coated sheet 30 can suppress deterioration of the materials contained in the coated sheet 30 due to ultraviolet light. In this case, it is especially preferable that the coated sheet 30 has resistance to ultraviolet light.

[0055] As described above, a coating sheet 30 with a color difference ΔE of 4 or less can protect the rust-preventive layer 18 from ultraviolet rays when the coating sheet 30 covers the rust-preventive layer 18, as shown in Figure 4D. This suppresses deterioration of the materials contained in the rust-preventive layer 18 due to ultraviolet rays. In particular, a coating sheet 30 with a color difference ΔE of 4 or less can suppress discoloration of the rust-preventive layer 18 due to ultraviolet rays. In this case, yellowing of the rust-preventive layer 18 due to ultraviolet rays may also be suppressed by a coating sheet 30 that can achieve a color difference ΔE of 4 or less.

[0056] The weather-resistant layer 42 may contain a binder resin and a weather-resistant agent. The weather-resistant layer 42 may contain one or more of the following as weather-resistant agents: an ultraviolet absorber, an antioxidant, and a light stabilizer. The weather-resistant layer 42 may contain an ultraviolet absorber and a light stabilizer. The weather-resistant layer 42 can be produced by forming a coating film of the coating liquid and curing the coating film. The weather-resistant layer 42 may be formed from a single coating film. The weather-resistant layer 42 may be formed from multiple coating films. The weather-resistant layer 42 may include a weather-resistant layer body and a primer layer provided between the substrate 41 and the weather-resistant layer body.

[0057] The weather-resistant layer 42 may contain a cured resin as a binder resin. The cured resin is a cured product of a curable resin composition. The curable resin composition may be a thermosetting resin composition. The curable resin composition may be an ionizing radiation-curable resin composition. The weather-resistant layer 42 may contain a cured product of a curable resin composition and a cured product of an ionizing radiation-curable resin composition.

[0058] The thermosetting resin composition contains a thermosetting resin. The thermosetting resin composition hardens upon heating. Examples of thermosetting resins include unsaturated group-containing (meth)acrylic resins, unsaturated polyesters, urethane resins, epoxy resins, phenolic resins, aminoalkyd resins, urea resins, melamine resins, melamine-urea cocondensation resins, guanamine resins, diallyl phthalate resins, and silicone resins.

[0059] The thermosetting resin composition may contain a curing agent along with the thermosetting resin. In the case of unsaturated group-containing (meth)acrylic resins and unsaturated polyesters, peroxides such as methyl ethyl ketone peroxide or radical initiators such as azoisobutylnitrile may be used. In the case of urethane resins, isocyanate-based curing agents may be used. In the case of epoxy resins, organic amine-based curing agents may be used.

[0060] The thermosetting resin may be a two-component curing urethane resin, with a polyol as the main component and an isocyanate compound as the curing agent. Examples of polyols include (meth)acrylic polyol, polyether polyol, polyester polyol, polyethylene glycol, and polypropylene glycol. The isocyanate compound is a polyvalent isocyanate having two or more isocyanate groups. Examples of isocyanate compounds include aromatic isocyanates such as 4,4-diphenylmethane diisocyanate; and aliphatic (or alicyclic) isocyanates such as hexamethylene diisocyanate, isophorone diisocyanate, hydrogenated tolylene diisocyanate, and hydrogenated diphenylmethane diisocyanate.

[0061] In one specific example of the weather-resistant layer 42, the cured resin product contained in the weather-resistant layer 42 may be a cross-linked cured product of (meth)acrylic polyol using an isocyanate-based curing agent.

[0062] The ionizing radiation-curable resin composition contains a compound having an ionizing radiation-curable functional group. Hereinafter, the compound having an ionizing radiation-curable functional group will also be referred to as the "ionizing radiation-curable compound." The ionizing radiation-curable functional group is a group that crosslinks upon irradiation with ionizing radiation.

[0063] Ionizing radiation may be electromagnetic waves or charged particle beams. Ionizing radiation has energy quanta that can polymerize or crosslink molecules. Examples of ionizing radiation include ultraviolet (UV), electron beams (EB), X-rays, gamma rays, alpha rays, and ion beams. In the example where the weather-resistant layer 42 contains an ultraviolet absorber as a weathering agent, the ionizing radiation may be an electron beam.

[0064] Examples of ionizing radiation-curable functional groups include ethylenically unsaturated bonding groups such as (meth)acryloyl groups, vinyl groups, and allyl groups, as well as epoxy groups and oxetanyl groups. Ionizing radiation-curable compounds may contain ethylenically unsaturated bonding groups. Ionizing radiation-curable compounds may contain two or more ethylenically unsaturated bonding groups. Ionizing radiation-curable compounds may also be polyfunctional (meth)acrylate compounds containing two or more ethylenically unsaturated bonding groups. Polyfunctional (meth)acrylate compounds may contain either monomers or oligomers.

[0065] Examples of polymerizable monomers include (meth)acrylate monomers having a (meth)acryloyl group in the molecule, and polyfunctional (meth)acrylate monomers having two or more (meth)acryloyl groups in the molecule. The number of (meth)acryloyl groups in the polyfunctional (meth)acrylate monomer may be between 2 and 8, or between 2 and 6.

[0066] As polymerizable monomers, difunctional (meth)acrylates such as ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, bisphenol A tetraethoxy di(meth)acrylate and bisphenol A tetrapropoxy di(meth)acrylate; trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, penta Examples include trifunctional or more (meth)acrylates such as erythritol tetra(meth)acrylate, dipentaerythritol tri(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate; and ethylene oxide modified, propylene oxide modified, caprolactone modified, isocyanuric acid modified, or propionic acid modified versions of these (meth)acrylates.

[0067] Examples of polymerizable oligomers include (meth)acrylate oligomers having two or more (meth)acryloyl groups in the molecule. Examples of (meth)acrylate oligomers include urethane (meth)acrylate, epoxy (meth)acrylate, polyester (meth)acrylate, polyether (meth)acrylate, polycarbonate (meth)acrylate, polycaprolactone urethane (meth)acrylate, polycaprolactone diol urethane (meth)acrylate, and acrylic (meth)acrylate. The number of (meth)acryloyl groups in the polymerizable oligomer may be 2 to 8, or 2 to 6.

[0068] Examples of polymerizable oligomers include highly hydrophobic polybutadiene (meth)acrylate oligomers having (meth)acryloyl groups in the side chains of polybutadiene oligomers, and silicone (meth)acrylate oligomers having polysiloxane bonds in the main chain.

[0069] The weight-average molecular weight of the polymerizable oligomer may be 500 or more, 1,000 or more, or 2,000 or more. The weight-average molecular weight of the polymerizable oligomer may be 10,000 or less, 8,000 or less, or 6,000 or less. The weight-average molecular weight is the average molecular weight measured by gel permeation chromatography (GPC) analysis and converted to standard polystyrene.

[0070] As ionizing radiation-curable compounds, monofunctional (meth)acrylates may be used along with polyfunctional (meth)acrylates. In this example, the viscosity of the curable composition during coating can be reduced. Examples of monofunctional (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, and isobornyl (meth)acrylate.

[0071] If the ionizing radiation-curable compound is an ultraviolet-curable compound, at least one selected from photopolymerization initiators and photopolymerization accelerators may be used together with the ultraviolet-curable compound.

[0072] The weather-resistant layer 42 may contain cured products of curable compounds or cured products of ionizing radiation-curable compositions, from the viewpoint of having excellent heat resistance, scratch resistance, and stain resistance. The coating solution containing the electron beam-curable compound can be solvent-free and does not require a photopolymerization initiator. The electron beam-curable compound provides stable curing characteristics. Furthermore, the electron beam-curable compound can stably retain additives such as weathering agents, for example, ultraviolet absorbers, through crosslinking. Therefore, the bleed-out of additives such as ultraviolet absorbers can be stably suppressed. This prevents the excellent weather resistance of the weather-resistant layer 42 from deteriorating over time. For these reasons, preferably, the weather-resistant layer 42 contains cured products of electron beam-curable compounds. The ionizing radiation-curable compound may be a polymerizable oligomer, a (meth)acrylate oligomer having two or more (meth)acryloyl groups in the molecule, or a urethane (meth)acrylate.

[0073] As an example, the cured resin layer 45 includes a material having urethane bonds. For instance, a cured resin layer 45 formed by curing an electron beam-curable resin composition containing urethane (meth)acrylate by irradiating it with an electron beam includes a material having urethane bonds.

[0074] As a method for evaluating the compounds and chemical bonds contained in the components of the coated steel structure 10, such as the resin cured layer 45 and the topcoat film 81 described later containing urethane bonds, Fourier transform infrared spectroscopy (FT-IR) can be used. One method of Fourier transform infrared spectroscopy is infrared spectroscopy using the total reflection attenuation method, also known as ATR-IR (Attenuated Total Reflection - Infrared Spectroscopy).

[0075] The proportion of cured resin in the weather-resistant layer 42 relative to the total resin components may be 50% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more.

[0076] As described above, the weather-resistant layer 42 can be produced by forming a coating film of a coating solution containing a curable resin composition and curing the coating film. In the example where the weather-resistant layer 42 contains a cured product of an electron beam-curable resin composition, the coating film is irradiated with an electron beam. A portion of this electron beam penetrates the coating film and is also irradiated onto the substrate 41. In this example, the substrate 41 may contain a polyolefin. The polyolefin is partially crosslinked by the electron beam. The crosslinking of the polyolefin improves the heat resistance of the substrate 41.

[0077] The polyolefin-containing substrate 41 exhibits improved adhesion to the weather-resistant layer 42 containing the cured product of the electron beam-curable resin composition compared to a substrate containing a fluororesin. Furthermore, by using polyolefin instead of fluororesin in the substrate 41, the generation of PFAS as an impurity can be suppressed. PFAS, as an artificial organofluorine compound, is a cause for concern due to its bioaccumulation potential. Suppressing the generation of PFAS can contribute to reducing environmental impact.

[0078] From the above points, in combination with a weather-resistant layer 42 containing a cured product of an electron beam-curable resin composition, the base material 41 may also contain a polyolefin. Examples of polyolefins used in the base material 41 include polyethylene, polypropylene, polybutene, and polymethylpentene.

[0079] Examples of polypropylene include copolymers such as propylene homopolymers, ethylene-propylene copolymers, propylene-butene copolymers, and ethylene-propylene-butene copolymers. For the polypropylene contained in the base material 41, propylene homopolymers, ethylene-propylene copolymers, and propylene-butene copolymers are preferred.

[0080] From the viewpoint of processability, the polyolefin content in the base material 41 may be 50% by mass or more, 60% by mass or more, 70% by mass or more, or 80% by mass or more, relative to the total resin components of the base material 41.

[0081] If the weather-resistant layer 42 includes a weather-resistant layer body and a primer layer provided between the substrate 41 and the weather-resistant layer body, the weather-resistant layer body may contain an ionizing radiation-curable resin composition. The primer layer may contain a two-component curable urethane resin.

[0082] <Barrier layer> The barrier layer 44 imparts gas barrier properties to the coating sheet 30. The barrier layer 44 may also be a vapor-deposited film formed on a resin film 44a. The coating sheet 30 may include a barrier film 44X comprising the barrier layer 44 and a resin film. In the examples shown in Figures 2A and 2B, the coating sheet 30 includes a barrier film 44X comprising the barrier layer 44 and a resin film 44a. The barrier layer 44 may also be a vapor-deposited film formed on a substrate 41. When the barrier layer 44 together with the substrate 41 constitutes a barrier film, the bonding layer 491 that joins the barrier layer 44 and the substrate 41 as shown in Figures 2A and 2B can be omitted.

[0083] The coating sheet 30 including the barrier layer 44 may have excellent gas barrier properties. The coating sheet 30 including the barrier layer 44 may have excellent oxygen barrier properties and excellent water vapor barrier properties. The coating sheet 30 including the barrier layer 44 can suppress rusting of the steel material 20 and deterioration of the coating film on the steel material 20.

[0084] An example of the resin film 44a used in the barrier film 44X is the resin film that constitutes the substrate 41 described above. The thickness of the resin film 44a may be 5 μm or more, 10 μm or more, 100 μm or less, or 50 μm or less.

[0085] The barrier layer 44 may be a vapor-deposited film containing one or more metals, a vapor-deposited film containing one or more inorganic oxides, or a vapor-deposited film containing one or more metals and one or more inorganic oxides. Examples of metals to be included in the vapor-deposited film include aluminum, chromium, tin, nickel, copper, silver, gold, and platinum. Examples of inorganic oxides include aluminum oxide, silicon oxide, magnesium oxide, calcium oxide, zirconium oxide, titanium oxide, boron oxide, hafnium oxide, barium oxide, and silicon carbide oxide (carbon-containing silicon oxide). Specifically, the barrier layer 44 may contain one or more aluminum vapor-deposited films, aluminum oxide (alumina) vapor-deposited films, and silicon oxide (silica) vapor-deposited films.

[0086] The thickness of the deposited film may be 1 nm or more, 5 nm or more, or 10 nm or more. The thickness of the deposited film may be 150 nm or less, 100 nm or less, or 80 nm or less.

[0087] The vapor-deposited film constituting the barrier layer 44 may be formed by physical vapor deposition (PVD) methods such as vacuum deposition, sputtering, and ion plating. The vapor-deposited film constituting the barrier layer 44 may also be formed by chemical vapor deposition (CVD) methods such as plasma chemical vapor deposition, thermochemical vapor deposition, and photochemical vapor deposition.

[0088] The barrier film 44X, which includes the barrier layer 44 and the resin film 44a described above, is a so-called vapor-deposited film. Examples of vapor-deposited films include vapor-deposited polyester films such as vapor-deposited polyethylene terephthalate film, vapor-deposited polyamide film, and vapor-deposited polyolefin. From the viewpoint of hydrolysis resistance, etc., it is preferable that the substrate of the vapor-deposited film (i.e., the resin film 44a) is a polyolefin. The vapor-deposited film consists of a biaxially oriented polypropylene substrate and a film of the chemical formula SiO2 formed on the substrate by chemical vapor deposition. x It may have a silica vapor-deposited film represented by and .

[0089] A layer containing an ultraviolet absorber may be located between the barrier layer 44 and the first surface 31. The barrier layer 44 can deteriorate over time due to ultraviolet light. Therefore, the layer containing the ultraviolet absorber can suppress the deterioration of the barrier layer 44 and maintain the gas barrier properties of the barrier layer 44. In the examples shown in Figures 2A and 2B, one or more of the weather-resistant layer 42 and the substrate 41 may contain an ultraviolet absorber.

[0090] In the covering sheet 30 shown in Figures 2A and 2B, as described above, the distance w6 between the barrier layer 44 and the second surface 32 is smaller than the distance w8 between the weather-resistant layer 42 and the second surface 32. That is, the covering sheet 30 includes the barrier layer 44 and the weather-resistant layer 42 in the order from the second surface 32 toward the first surface 31. The barrier layer 44 is located between the steel material 20 and the weather-resistant layer 42 in the lamination direction. Therefore, the barrier layer 44 is covered by the weather-resistant layer 42, which has weather resistance. As a result, the barrier layer 44 is protected by the weather-resistant layer 42, and deterioration of the barrier layer 44 outdoors can be suppressed. This allows the gas barrier properties of the barrier layer 44 to be maintained. In particular, by covering the barrier layer 44 with the weather-resistant layer 42 which contains at least one of an ultraviolet absorber and a light stabilizer as a weathering agent, the barrier layer 44 can be protected from ultraviolet rays irradiated onto the first surface 31 of the covering sheet 30. This suppresses the deterioration of the barrier layer 44 due to ultraviolet rays and maintains the gas barrier properties of the barrier layer 44. By including an ultraviolet absorber and a light stabilizer in the weather-resistant layer 42, the deterioration of the barrier layer 44 due to ultraviolet rays is suppressed more stably, and the gas barrier properties of the barrier layer 44 can be maintained more stably.

[0091] As an example, the oxygen permeability (OTR, unit: cm) of the covering sheet 30 including the barrier layer 44. 3 / (m 2 Day 6) is 6.57cm 3 / (m 2 The oxygen permeability of the covering sheet 30 is less than or equal to 3.0 cm². 3 / (m 2 • Days or less are also acceptable, and 2.5 cm 3 / (m 2 • Days or less are also acceptable, and 2.0 cm3 / (m 2 It is also acceptable to have less than 0.01 cm². With a coating sheet 30 whose oxygen permeability is adjusted in this way, corrosion of the steel material 20 and deterioration of the coating film can be suppressed. The oxygen permeability of the coating sheet 30 is preferable as long as it is low, but 0.01 cm² is also acceptable. 3 / (m 2 • Days or longer are also acceptable, and 0.05 cm 3 / (m 2 • Days or longer are also acceptable, and 0.1 cm 3 / (m 2 It can be more than one day.

[0092] The oxygen permeability was measured in accordance with JIS K7126-2:2006 "Appendix A (Normative): Test method for oxygen gas permeability by electrolytic sensor method" under conditions of 23°C and 60% RH humidity. When measuring oxygen permeability, the covering sheet 30 is installed in the measuring device with the first surface 31 facing the oxygen supply side. The oxygen permeability measuring device may also be the "OX-TRAN 2 / 20" manufactured by MOCON, Inc., USA.

[0093] As an example, the water vapor transmission rate (WVTR, unit: g / m³) of a coated sheet 30 including a barrier layer 44. 2 (・day)) is 3.0g / (m 2 The water vapor transmission rate of the covering sheet 30 is less than or equal to 2.5 g / (m²). 2 • day) or less is also acceptable, 2.0g / (m 2 It is also acceptable to have a water vapor permeability of 0.01 g / (m²) or less. With a coating sheet 30 whose water vapor permeability is adjusted in this way, corrosion of the steel material 20 and deterioration of the coating film can be suppressed. The water vapor permeability of the coating sheet 30 is preferable as long as it is low, but 0.01 g / (m²) is also acceptable. 2 • day) or more is also acceptable, 0.05g / (m 2 • day) or more is also acceptable, 0.1g / (m 2 It can be more than one day.

[0094] The water vapor transmission rate is a value measured in accordance with JIS K7129-2:2019 under conditions of 40°C and 90% RH humidity. When measuring water vapor transmission rate, the covering sheet 30 is installed on the measuring device with the first surface 31 facing the hydrogen supply side. The water vapor transmission rate measuring device may also be a "PERMATRAN-w 3 / 33" manufactured by MOCON, Inc., USA.

[0095] <Joining layer> The bonding layer 43 and bonding layer 491 contain adhesive or tacky components. Bonding layer 43 bonds the coating sheet 30 to the steel structure 100 or the coating film on the steel structure 100. Bonding layer 491 bonds the barrier layer 44 to the substrate 41. In the examples shown in Figures 2A and 2B, bonding layer 491 bonds the barrier layer 44 to the substrate 41 by bonding the resin film 44a contained in the barrier film 44X to the substrate 41.

[0096] The bonding layers 43 and 491 may be adhesive layers or tacky layers. Examples of adhesive or tacky components include acrylic resins, vinyl chloride-vinyl acetate copolymers, vinyl acetate resins, polyolefins, polyesters, polyurethanes, silicone resins, and rubber resins.

[0097] The bonding layers 43 and 491 may be pressure-sensitive adhesive layers, i.e., tacky layers. A tacky layer is a layer formed by an adhesive (pressure-sensitive adhesive). The tacky layer exhibits tackiness at room temperature (e.g., 23°C). Examples of adhesives include acrylic adhesives, urethane adhesives, silicone adhesives, and rubber adhesives. Acrylic adhesives are preferred for application to the bonding layer 43 because they have excellent adhesion to the steel structure 100, which may have irregularities, and to the coating film on the steel structure 100. Acrylic adhesives also have excellent stability.

[0098] Bonding layer 43 and bonding layer 491 may contain additives. Examples of additives include pigments, dyes, colorants, antistatic agents, flame retardants, fungicides, crosslinking agents, tackifiers, plasticizers, leveling agents, flow regulators, defoamers, and dispersants. Bonding layer 43 and bonding layer 491 may also contain weathering agents such as ultraviolet absorbers, antioxidants, and light stabilizers.

[0099] The storage modulus (G') of bonding layer 43 and bonding layer 491 at 40°C may be 0.05 MPa or more and 1 MPa or less, 0.05 MPa or more and 0.8 MPa or less, 0.1 MPa or more and 1 MPa or less, or 0.1 MPa or more and 0.8 MPa or less. If the storage modulus (G') is above the lower limit, excessive elongation of the bonding layer when subjected to impact can be suppressed. If the storage modulus (G') is below the upper limit, fracture of the bonding layer when subjected to impact can be suppressed.

[0100] The storage modulus (G') is measured by the following method: Two test specimens 90 are prepared from the coating sheet 30 according to the method for preparing test specimens described in JIS K7244-1:1998, 6.2. Because they are made from the coating sheet 30, the test specimens 90 include a support 91 corresponding to the portion of the coating sheet 30 other than the bonding layer 43, and an adhesive layer 92 corresponding to the bonding layer for which the storage modulus (G') is to be measured. For example, when measuring the storage modulus (G') of the bonding layer 43, the test specimen 90 includes the support 91 and the adhesive layer 92 corresponding to the bonding layer 43.

[0101] The method described here can also measure the storage modulus (G') of the bonding layer 15 shown in Figure 1B. In this example, the test specimen 90 includes a support 91 corresponding to the covering sheet 30 and an adhesive layer 92 corresponding to the bonding layer 15.

[0102] Next, the two fabricated test pieces 90 are attached to a measuring device 70 as shown in Figure 3. As shown in Figure 3, the measuring device 70 includes a plate 71 and a jig 72. The jig 72 includes a pair of plate-like portions 73 that sandwich the plate 71. The plate 71 and the pair of plate-like portions 73 extend vertically. The distance between the pair of plate-like portions 73 can be adjusted by rotating a nut 75 screwed onto a bolt 74 that passes through the pair of plate-like portions 73. The bolt 74 does not pass through the plate 71 or the test pieces 90 attached to the measuring device 70. The bolt 74 is located at a different position from the plate 71 and the test pieces 90 in a direction perpendicular to the plane of the paper in Figure 3. When attaching the two test pieces 90 to the measuring device 70, first, the two test pieces 90 are bonded to the plate 71 by the action of the adhesive layer 92 so that the plate 71 is sandwiched between the two test pieces 90. Next, by rotating the nut 75, the distance between the pair of plate-like portions 73 is reduced, so that the plate 71 and the two test pieces 90 are sandwiched between the pair of plate-like portions 73, as shown in Figure 3. This fixes the two test pieces 90 to the jig 72.

[0103] Next, the thickness w1 of the test specimen 90 is determined. The thickness w1 of the test specimen 90 can be determined by the following method. Before fixing the two test specimens 90 to the jig 72, the dimensions of the plate 71 and the jig 72 are determined. As dimensions of the plate 71 and the jig 72, the thickness w2 of the plate 71 and the thicknesses w3 and w4 of the pair of plate-like portions 73 shown in Figure 3 can be determined. The thicknesses w2, w3 and w4 can be determined by measuring with calipers. Furthermore, after fixing the two test specimens 90 to the jig 72 as shown in Figure 3, the dimensions of the jig 72 with the two test specimens 90 sandwiched between it are determined. As dimensions of the jig 72 with the two test specimens 90 sandwiched between it, the distance w5 from the outer surface of one of the pair of plate-like portions 73 to the outer surface of the other of the pair of plate-like portions 73 shown in Figure 3 can be determined. The distance w5 can be determined by measuring with calipers. Next, the thickness w1 of the test specimen 90 is determined from the dimensions of the plate 71 and the jig 72, and the dimensions of the jig 72 with the two test specimens 90 sandwiched between them. The thickness w1 of the test specimen 90 can be calculated by subtracting the thicknesses w2, w3, and w4 from the distance w5 and dividing by 2. The determined thickness w1 of the test specimen 90 is used to measure the storage modulus (G').

[0104] As shown in Figure 3, after fixing two test specimens 90 to the jig 72, the jig 72 is vibrated vertically. This applies vertical vibration to the adhesive layer 92 of the test specimen 90. By detecting the movement of the plate 71 when vertical vibration is applied to the adhesive layer 92 of the test specimen 90, the storage modulus (G') of the adhesive layer 92 can be measured.

[0105] The storage modulus (G') is measured under the following conditions. • Atmosphere gas: Nitrogen • Attachment mode: Solid shear mode • Temperature-dependent measurement (The elastic modulus is measured when the temperature is increased using a temperature program and 10Hz is applied at each temperature). ·Basic frequency: 10Hz Measurement program: Start temperature = 30°C, Step temperature = 1°C, End temperature = 150°C, Heating rate: 3°C / min) • Sine wave, stop excitation • Manual static load: Adjust to 0g when fixing the two test pieces 90 to the jig 72. • Distortion: A value automatically set when the sample length is entered. 0.05 (Automatic adjustment mode)

[0106] The storage modulus (G') can be measured using a solid viscoelasticity analyzer. The Rheogel E4000 manufactured by UBM Co., Ltd. can be used as the solid viscoelasticity analyzer.

[0107] The thickness of bonding layer 43 and bonding layer 491 may be 10 μm or more, 20 μm or more, 30 μm or more, 40 μm or more, or 50 μm or more. The thickness of bonding layer 43 and bonding layer 491 may be 1000 μm or less, 500 μm or less, 300 μm or less, 250 μm or less, 200 μm or less, 180 μm or less, or 150 μm or less.

[0108] <Other layers that may be included in the covering sheet> The coating sheet 30 may include further layers, and is not limited to the examples shown in Figures 2A and 2B.

[0109] As an example, the covering sheet 30 before being placed on the steel structure 100 may further include a release film 46, as shown by the dashed line in Figure 2A. The release film 46 may be bonded to the bonding layer 43 before the steel structure 10 with the covering is manufactured by bonding the covering sheet 30 to the steel structure 100 or the coating on the steel structure 100. The release film 46 protects the bonding layer 43 from foreign matter such as dust before the covering sheet 30 is used, that is, before the steel structure 100 is covered with the covering sheet 30. When the covering sheet 30 is used, the release film 46 is removed from the covering sheet 30. With the release film 46 removed, the bonding layer 43 is exposed, and the covering sheet 30 can be bonded to the steel structure 100. Examples of the release film 46 include a paper substrate and a resin film, as well as those on which a release agent is applied to their surfaces. Examples of mold release agents include silicone-based mold release agents, fluorine-based mold release agents, and long-chain alkyl-based mold release agents.

[0110] The covering sheet 30 may further include a design layer that imparts a desired design to the covering sheet 30. The design layer imparts a desired design to the covering sheet 30 so that it can be seen by an observer looking at the first surface 31 of the covering sheet 30. The design layer may impart a desired design to the entire surface of the first surface 31 of the covering sheet 30. The design layer may impart a desired design to a part of the first surface 31 of the covering sheet 30. The design layer may have a single color. The design layer may consist of multiple colors. The design layer may display symbols such as letters and numbers, figures, pictures, etc. The design layer can be formed, for example, by printing or coating. The design layer is provided, for example, between the base material 41 and the weather-resistant layer 42, although this is not shown in the illustration.

[0111] <Characteristics of the covering sheet> The surface roughness Sa of the first surface 31 of the coating sheet 30 is 10 μm or less. The surface roughness Sa of the first surface 31 of the coating sheet 30 may be 9 μm or less. The surface roughness Sa of the first surface 31 of the coating sheet 30 may be greater than 1.2 μm. The surface roughness Sa of the first surface 31 before the coating sheet 30 is joined to the steel structure 100 or the coating film on the steel structure 100 may satisfy the above numerical range. The surface roughness Sa of the first surface 31 after the coating sheet 30 is joined to the steel structure 100 or the coating film on the steel structure 100 may satisfy the above numerical range.

[0112] Surface roughness Sa refers to the arithmetic mean height Sa. The arithmetic mean height Sa is one of the three-dimensional surface texture parameters defined in ISO 25178-2:2012. The arithmetic mean height Sa is a parameter commonly used when evaluating surface roughness. The surface roughness Sa of the first surface 31 of the coating sheet 30 can be measured by non-contact measurement using a laser microscope. More specifically, the surface roughness Sa of the first surface 31 of the coating sheet 30 can be measured using the "One-Shot 3D Measurement Macroscope" VR-3000 series manufactured by KEYENCE Corporation.

[0113] The covering sheet 30 may be transparent. The covering sheet 30 can be made transparent by making each layer contained in the covering sheet 30 transparent, and by not including any opaque layers in the covering sheet 30. From the viewpoint of making the covering sheet 30 transparent, it is preferable that the covering sheet 30 does not include the design layer described above.

[0114] Materials and components referred to as transparent in this specification may have a total light transmittance of 70% or more. For example, the overall transmittance of the covering sheet 30 may be 70% or more. The total light transmittance is measured in accordance with JIS K7361-1:1997. The transmittance of the covering sheet 30 being 70% or more allows the steel structure 100 and the rust-preventive layer 18 to be visible through the covering sheet 30 when the covering sheet 30 covers the steel structure 100 and the rust-preventive layer 18 and when no topcoat film 81 is formed on the first surface 31 of the covering sheet 30.

[0115] When the covering sheet 30 is transparent, the haze of the covering sheet 30 is, for example, 97% or less. The haze is measured in accordance with JIS K7136:2000. By having a haze of 97% or less of the covering sheet 30, when the covering sheet 30 covers the steel structure 100 and the rust-preventive layer 18, and when no topcoat film 81 is formed on the first surface 31 of the covering sheet 30, it becomes easier to visually inspect the steel structure 100 and the rust-preventive layer 18 through the covering sheet 30.

[0116] <<<Other layers that may be included in the coating>>> The coating 80 of the coated steel structure 10 shown in Figure 1B further includes a bonding layer 15 in addition to the coating sheet 30. The coating 80 of the coated steel structure 10 shown in Figures 1C and 1D further includes a rust-preventive layer 18. The coating 80 of the coated steel structure 10 shown in Figures 1A to 1D further includes a topcoat coating 81. The coating 80 may include further layers, although it is not limited to the examples shown in Figures 1A to 1D.

[0117] <<Joining layer>> As shown in Figure 1B, the bonding layer 15 is used to bond the covering sheet 30 to the steel structure 100. The bonding layer 15 may be constructed in the same manner as the bonding layer 43 of the covering sheet 30 described above.

[0118] As will be described later, irregularities may form on the surface of the steel structure 100 or the coating film on the steel structure 100 (for example, the rust-preventive layer 18) due to factors such as the formation of a surface preparation surface 22 on the steel structure 100. As shown in Figure 1D, the bonding layer 15 can fill these irregularities to some extent.

[0119] <<Rust-preventive layer>> The rust-preventive layer 18 is located between the steel structure 100 and the covering sheet 30. The rust-preventive layer 18 makes it difficult for corrosion to occur in the steel material 20. The rust-preventive layer 18 makes it difficult for corrosion to spread in the steel material 20.

[0120] The rust-preventive layer 18 may be produced by applying a rust-preventive paint containing a rust inhibitor to the surface of the steel structure 100 to form a coating film, and then solidifying or hardening this coating film. Examples of painting methods include brush painting, roller painting, and spray painting (e.g., air spray, airless spray). The rust-preventive layer 18 formed as a coating film can improve adhesion to the uneven surface of the steel structure 100.

[0121] The thickness of the rust-preventive layer 18 may be 10 μm or more, 30 μm or more, 50 μm or more, 100 μm or more, or 150 μm or more. The thickness of the rust-preventive layer 18 may be 1000 μm or less, 800 μm or less, 600 μm or less, or 500 μm or less. By setting a lower limit for the thickness of the rust-preventive layer 18, sufficient rust prevention function can be provided to the rust-preventive layer 18. By setting an upper limit for the thickness of the rust-preventive layer 18, the workability and cost when manufacturing the rust-preventive layer 18 can be improved.

[0122] Examples of rust inhibitors included in the rust-preventive layer 18 include inorganic rust inhibitors and organic rust inhibitors. Inorganic rust inhibitors may be inorganic acids or salts of inorganic acids. Examples of inorganic rust inhibitors include red lead, lead oxide, basic lead chromate, lead dianamid, calcium leadate, basic lead sulfate, zinc chromate, zinc powder, iron oxide, nitrite, sulfite, silicate, metasilicate, phosphate, polyphosphate, hypophosphate, phosphate, molybdate, phosphomolybdate, borate, metaborate, tungstate, carbonate, and chromate. Examples of inorganic rust inhibitors include phosphate compounds, vanadium compounds, niobium compounds, zirconium compounds, and zinc oxide. Examples of inorganic rust inhibitors include ammonium salts, calcium salts, magnesium salts, aluminum salts, zinc salts, manganese salts, and barium salts.

[0123] Examples of organic rust inhibitors include organic amine compounds, organic amine salts, tannic acid, carboxylic acids, and esters or salts of these acids. Examples of organic rust inhibitors include sulfonates, organic phosphates, benzotriazole compounds, benzothiazole compounds, mercaptan compounds, guanidino group-containing compounds, biguanidino group-containing compounds, thiocarbonyl group-containing compounds, alkylphenol compounds, diisopropylammonium nitride, and dicyclohexylammonium nitride.

[0124] Examples of rust-preventive paints include epoxy resin paints, urethane resin paints, acrylic resin paints, silicone acrylic resin paints, styrene resin paints, fluororesin paints, and zinc-rich paints containing an organic binder and zinc powder. Rust-preventive paints may contain a binder and a rust inhibitor. Examples of binders for rust-preventive paints include organic binders such as epoxy resins, urethane resins, acrylic resins, silicone acrylic resins, styrene resins, and fluororesins. Examples of binders for rust-preventive paints include inorganic binders such as alkyl silicates.

[0125] Rust inhibitors, rust inhibitors, and rust inhibitory layers using these can be classified from the viewpoint of rust prevention mechanism into rust conversion type, salt / iron ion detoxification type, and rust prevention type by iron ion stabilization with a two-component curing type ion trap agent. The rust inhibitory layer 18, and the rust inhibitors and rust inhibitory paints used in the rust inhibitory layer 18, may be of the rust conversion type, the salt / iron ion detoxification type, or the rust prevention type by iron ion stabilization with a two-component curing type ion trap agent.

[0126] The coating 80 includes a rust-preventive layer 18 formed using a rust inhibitor and rust-preventive paint, which makes it less likely for red rust to form on the steel material 20. On the other hand, rust-converting type rust inhibitors and rust-preventive paints generate black rust when exerting their rust-preventive effect on the steel material 20. The strength of the steel material 20 can be ensured more when black rust is formed on the steel material 20 due to the rust-converting type rust inhibitor and rust-preventive paint than when red rust is present on the steel material 20. Therefore, the strength of the steel material 20 can also be ensured by forming a rust-preventive layer 18 using a rust-converting type rust inhibitor and rust-preventive paint. However, the strength of the steel material 20 can be ensured more when neither black rust nor red rust is present on the steel material 20 than when black rust is present on the steel material 20. Rust inhibitors and rust-preventive paints of the salt / iron ion detoxification type and the iron ion stabilization type using a two-component curing ion trap agent do not generate black rust when exerting their rust-preventive effect on the steel material 20. Furthermore, the rust-preventive layer 18 formed by a rust inhibitor and rust-preventive paint of the type that detoxifies salt and iron ions or stabilizes iron ions using a two-component curing ion trap agent also makes it less likely for red rust to form on the steel material 20. For this reason, from the viewpoint of ensuring greater strength of the steel material 20, it is preferable to use a rust inhibitor and rust-preventive paint of the type that detoxifies salt and iron ions or stabilizes iron ions using a two-component curing ion trap agent, rather than using a rust-converting type rust inhibitor and rust-preventive paint to form the rust-preventive layer 18.

[0127] The rust-preventive paint may be a one-component curing type rust-preventive paint, or a two-component curing type rust-preventive paint containing a main component and a hardener. In the case of the two-component curing type rust-preventive paint, the main component containing a binder and optionally a rust inhibitor, and the hardener that promotes the cross-linking reaction may be stored in separate containers and mixed immediately before use. The two-component curing type rust-preventive paint is superior in that it has high adhesion to the steel material 20, high coating strength, and can create a dense rust-preventive layer 18. The two-component curing type rust-preventive paint also has excellent adhesion to the covering sheet 30. The two-component curing type rust-preventive paint may be a two-component curing epoxy resin paint or a two-component curing urethane resin paint.

[0128] Two-component epoxy resin coatings may contain an epoxy resin as a binder and a curing agent for epoxy resins. Examples of curing agents include amine-based curing agents, phenol-based curing agents, acid anhydride-based curing agents, and mercaptan-based curing agents. Urethane resin coatings may be two-component curing types consisting of a polyol-based compound and an isocyanate-based compound, or they may be one-component curing types that harden due to moisture in the air, etc.

[0129] Rust-preventive paints may contain moisture-curing resins. Moisture-curing resins have isocyanate groups as reactive groups. The isocyanate groups of moisture-curing resins harden by reacting with water through the reaction shown in formula (I) below. Specifically, first, the isocyanate groups of the moisture-curing resin react with water to produce carbamic acid. Subsequently, the carbamic acid is decomposed to produce an amine. Then, the amine reacts with the isocyanate groups of the moisture-curing resin to form a crosslinking reaction that creates a urea bond. This crosslinking reaction hardens the moisture-curing resin. By containing moisture-curing resins in rust-preventive paints, a rust-preventive effect is obtained by removing water, which can be a corrosive factor. [ka]

[0130] For example, the moisture-curing resin contained in rust-preventive paint is urethane resin. In this case, the rust-preventive paint may be a two-component curing type urethane resin paint that neutralizes salt and iron ions.

[0131] When a rust-preventive coating contains a moisture-curing resin, carbon dioxide may be generated when the moisture-curing resin reacts with water, as shown in formula (I) above. As shown in Figure 1D, when the coating sheet 30 and the rust-preventive layer 18 cover the steel material 20, it is preferable that the coating sheet 30 does not have oxygen barrier properties, from the viewpoint of suppressing the carbon dioxide generated from remaining in the coating sheet 30 as bubbles instead of passing through it. By not having oxygen barrier properties in the coating sheet 30, carbon dioxide can pass through the coating sheet 30 more easily, and the retention of carbon dioxide as bubbles in the coating sheet 30 can be suppressed. For the above reasons, when a rust-preventive coating containing a moisture-curing resin is used, it is preferable that the coating sheet 30 does not have oxygen barrier properties, from the viewpoint of reducing the likelihood of appearance defects caused by carbon dioxide remaining in the coating sheet 30 as bubbles.

[0132] On the other hand, especially when a rust-preventive coating that does not contain moisture-curing resin is used, it is preferable that the coating sheet 30 is provided with oxygen barrier properties from the viewpoint of making it difficult for oxygen, which can be a corrosive factor, to reach the rust-preventive layer 18 and the steel material 20. In particular, when a rust-preventive coating that does not contain moisture-curing resin is used, even if oxygen barrier properties are provided to the coating sheet 30, it is possible to prevent the formation of air bubbles in the coating sheet 30. For this reason, when a rust-preventive coating that does not contain moisture-curing resin is used, providing oxygen barrier properties to the coating sheet 30 makes it difficult for oxygen to reach the rust-preventive layer 18 and the steel material 20, while also making it less likely for carbon dioxide to remain in the coating sheet 30 as air bubbles, thus reducing the likelihood of appearance defects.

[0133] Rust-preventive paint may or may not be colored. If the rust-preventive paint contains a moisture-curing resin, the rust-preventive paint containing the moisture-curing resin may or may not be colored. A rust-preventive paint that does not contain a moisture-curing resin and is not colored may, for example, be a type of rust-preventive paint that prevents rust by stabilizing iron ions with the two-component curing ion trapping agent described above.

[0134] As an example, the oxygen permeability (OTR) of the oxygen barrier-treated coating sheet 30 is 6.57 cc / (m²). 2 (•day•atm) is less than or equal to the following:

[0135] Regardless of whether the rust-preventive coating contains a moisture-curing resin or not, the coating sheet 30 may be provided with water vapor barrier properties. This makes it more difficult for water, which can be a corrosive factor, to reach the rust-preventive layer 18 and the steel material 20. As an example, the water vapor transmission rate (WVTR) of the coating sheet 30 with water vapor barrier properties is 3.0 g / (m²). 2 It is less than or equal to (day).

[0136] Rust-preventive coatings may contain additives. Examples of additives include rosins, plasticizers, extender pigments, coloring pigments, solvents, curing accelerators, coupling agents, corrosive ion immobilizers, anti-sagging agents, and anti-settlement agents. Examples of coupling agents include silane-based coupling agents, titanium-based coupling agents, aluminum-based coupling agents, and zirconium-based coupling agents. Examples of corrosive ion immobilizers include hydrotalcite and hydrocalmite.

[0137] On the surface of the rust-preventive layer 18 provided on the steel material 20, the 85-degree specular gloss may be 3 or higher. The 85-degree specular gloss on the surface of the rust-preventive layer 18 may be 5 or higher, 10 or higher, 15 or higher, 20 or higher, or 23 or higher. By setting the lower limit of the 85-degree specular gloss on the surface of the rust-preventive layer 18 in this way, the rust-preventive layer 18 becomes a dense film. The rust-preventive layer 18 as a dense film exhibits high adhesion with the covering sheet 30. The upper limit of the 85-degree specular gloss on the surface of the rust-preventive layer 18 is not particularly limited. The 85-degree specular gloss on the surface of the rust-preventive layer 18 may be 60 or less, 50 or less, or 40 or less.

[0138] The 85-degree specular gloss of the surface of the anti-corrosion layer 18 shall be the value measured in accordance with JIS Z8741:1997, except that the angle of incidence is set to 85°.

[0139] The measurement environment for measuring the 85-degree specular gloss of the surface of the rust-preventive layer 18 and the 60-degree specular gloss of the surface of the coated steel structure 10 (described later) shall be a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The measurement sample to be measured shall be placed in the measurement environment for 16 hours before the start of measurement. Before measuring the specular gloss, the light source of the measuring device shall be turned on for 15 minutes to stabilize the output of the light source. The specular gloss shall be the arithmetic mean of five measured values. The five measured values ​​shall be the values ​​measured at five different measurement positions on the measurement sample to be evaluated. The five measurement positions shall be located at least 10 mm apart from each other.

[0140] A lower limit may be set for the maintenance rate of the 85-degree mirror gloss of the rust-preventive layer 18 provided on the steel material 20. By setting a lower limit for the maintenance rate of the 85-degree mirror gloss on the surface of the rust-preventive layer 18, the adhesion of the rust-preventive layer 18 to the steel material 20 can be ensured. The maintenance rate of the 85-degree mirror gloss on the surface of the rust-preventive layer 18 may be 60% or more, 70% or more, 80% or more, 90% or more, or 95% or more.

[0141] The retention rate of 85-degree specular gloss is the retention rate of 85-degree specular gloss on the surface of the rust-preventive layer 18 before and after performing the 90-degree tape peel test. The 85-degree specular gloss on the surface of the rust-preventive layer 18 before performing the 90-degree tape peel test is denoted as "Gsb". The 85-degree specular gloss on the surface of the rust-preventive layer 18 after performing the 90-degree tape peel test is denoted as "Gsa". The retention rate of 85-degree specular gloss is expressed as Gsa × 100 / Gsb, and the unit is %.

[0142] The 90-degree tape peel test is performed as follows: From a roll of 24mm wide cellophane adhesive tape conforming to JIS Z1522:2009, 25cm is unwound in an environment of 23℃±2℃ and 50%±5% relative humidity. With 10cm of adhesive surface to be joined together to create a handle, 5cm of the adhesive surface is attached to the surface of the rust-preventive layer 18 formed on the surface of the steel structure 100 using a 2kg pressure roller for two passes, and then further attached by finger pressure to prevent air from getting in the way. Next, the cellophane adhesive tape is peeled off once manually at a speed of 5cm / s in a 90-degree direction from the surface of the rust-preventive layer 18. As the cellophane adhesive tape mentioned above, use Cellotape (registered trademark) (manufactured by Nichiban, model number No. 405-1P, 24mm width). If this product cannot be used, use a 24mm width cellophane adhesive tape that has equivalent adhesive strength and conforms to JIS Z1522:2009.

[0143] <<Topcoat coating>> The topcoat film 81 is formed on the first surface 31 of the covering sheet 30. The topcoat film 81 constitutes a surface of the covered steel structure 10. In the example shown in Figures 1A and 1B, the covering sheet 30 is located between the topcoat film 81 and the steel structure 100 in the lamination direction. The topcoat film 81 may have one or more functions expected of the outermost layer, such as barrier properties, weather resistance, scratch resistance, and strength. The topcoat film 81 may be provided for the purpose of improving the weather resistance of the covered steel structure 10. In particular, the topcoat film 81 may protect the steel structure 100 and the coating on the steel structure 100 (e.g., the rust-preventive layer 18) from ultraviolet rays. The topcoat film 81 may provide the covered steel structure 10 with excellent rust prevention over a long period of time. The topcoat film 81 may be a colored coating. The topcoat film 81 may be transparent. In particular, if the covering sheet 30 includes a design layer described later, the topcoat film 81 may be transparent. The transparent topcoat film 81 can be formed using a clear paint.

[0144] The topcoat film 81 may be produced by applying a topcoat paint to the first surface 31 of the covering sheet 30 to form a coating film, and then solidifying or hardening this coating film. Examples of painting methods include brush painting, roller painting, and spray painting (e.g., air spray, airless spray). The topcoat paint may be a one-component paint or a two-component paint. The topcoat film 81 and the topcoat paint may contain resins and additives.

[0145] Examples of resins included in the topcoat film 81 and the topcoat paint include fluororesins, urethane resins, acrylic resins, butadiene resins, silicone resins, vinyl ester resins, and epoxy resins. Examples of fluororesins include polyvinyl fluoride, polytetrafluoroethylene, perfluoroalkoxyalkanes, and ethylene-tetrafluoroethylene copolymers.

[0146] As an example, the topcoat film 81 includes a material having urethane bonds. For example, a topcoat film 81 formed using a topcoat paint containing urethane resin includes a material having urethane bonds. Examples of topcoats containing urethane resin include one-component urethane paints, two-component urethane paints, and two-component fluoropolymer paints that form urethane bonds.

[0147] Examples of additives contained in the topcoat film 81 and the topcoat paint include pigments, dyes, dispersants, defoamers, thickeners, leveling agents, anti-settling agents, anti-sagging agents, anti-algal agents, anti-fungal agents, preservatives, ultraviolet absorbers, antioxidants, and light stabilizers.

[0148] The topcoat paint may contain organic solvents and / or water for purposes such as adjusting viscosity. Examples of organic solvents include aromatic hydrocarbons, aliphatic hydrocarbons, ketones, acetate esters, ethers, alcohol-based solvents, and mineral spirits.

[0149] The thickness of the topcoat film 81 may be 5 μm or more, 10 μm or more, or 15 μm or more. The thickness of the topcoat film 81 may be 200 μm or less, 150 μm or less, or 100 μm or less.

[0150] <Coating resin layer> Although not shown in the figures, the coating 80 of the coated steel structure 10 may further include a coating resin layer formed on the surface of the steel structure 100 or on the surface of the rust-preventive layer 18. The coating resin layer may be an uneven layer that smooths out any steps on the surface of the steel structure 100 or the surface of the rust-preventive layer 18.

[0151] Examples of resin materials constituting the coating resin layer include fluororesins, acrylic resins, silicone resins, urethane resins, urea resins, and epoxy resins. The coating resin layer can be formed, for example, using a paint. The paint may be a one-component curing type or a two-component curing type. The coating resin layer may contain additives such as pigments, dyes, dispersants, defoamers, thickeners, leveling agents, anti-settling agents, anti-sagging agents, anti-algal agents, anti-fungal agents, preservatives, UV absorbers, antioxidants, and light stabilizers. The paint used to form the coating resin layer may contain organic solvents and / or water for purposes such as adjusting viscosity. Examples of organic solvents include aromatic hydrocarbons, aliphatic hydrocarbons, ketones, acetate esters, ethers, alcohol-based solvents, and mineral spirits.

[0152] The thickness of the coating resin layer is preferably 25 μm or more, more preferably 150 μm or more, even more preferably 300 μm or more, preferably 5000 μm or less, more preferably 3000 μm or less, and even more preferably 1000 μm or less.

[0153] The coating resin layer can be formed, for example, by conventional painting methods. Examples of painting methods include brush painting, roller painting, and spray painting (e.g., air spray, airless spray). For example, the coating resin layer can be formed by applying paint to the surface of the steel structure 100 or the surface of the rust-preventive layer 18 and allowing it to air dry or by performing a drying treatment.

[0154] The coating 80 does not necessarily have to include a coating resin layer. In this case, the coating sheet 30 or the bonding layer 15 may be in direct contact with the steel structure 100. The coating sheet 30 or the bonding layer 15 may also be in direct contact with the rust-preventive layer 18.

[0155] <Characteristics of steel structures with coatings> In this embodiment, the 60-degree specular gloss of the surface of the coated steel structure 10, which is composed of the topcoat 81, is 70 or higher. The 60-degree specular gloss of the surface of the coated steel structure 10, which is composed of the topcoat 81, is the value measured in accordance with JIS Z8741:1997, except that the angle of incidence is set to 60°.

[0156] <<<Method for coating steel structures, method for manufacturing coated steel structures>>> A method for coating a steel structure according to one embodiment of the present disclosure is a method for coating a steel structure 100 with a coating body 80 including a coating sheet 30 and a topcoat coating film 81. The method for coating a steel structure according to the present disclosure corresponds to a method for manufacturing a coated steel structure 10 comprising a steel structure 100 and a coating body 80 that covers the steel structure 100. The method for coating a steel structure and the method for manufacturing a coated steel structure according to the present disclosure comprises a placement step and a topcoat coating film formation step. In the placement step, the coating sheet 30 is placed so as to cover at least a portion of the surface of the steel structure 100. In the topcoat coating film formation step, a topcoat coating film 81 is formed on the surface of the coating sheet 30.

[0157] In this embodiment, the steel structure 100 to which the method for coating a steel structure and the method for manufacturing a coated steel structure are applied has a deteriorated portion 12. In this embodiment, the steel structure 100 to which the method for coating a steel structure and the method for manufacturing a coated steel structure are applied further includes a surface preparation step. In the surface preparation step, surface preparation is performed on the deteriorated portion 12 of the steel structure 100 to form a surface preparation surface 22 on the steel structure 100. The method for coating a steel structure comprising a surface preparation step, an arrangement step, and a topcoat film formation step can also be called a repair method for a steel structure 100 having a deteriorated portion 12. This repair method makes it possible to facilitate preventive maintenance, that is, repair work on the deteriorated portion 12 of the steel structure 100 before it becomes a serious defect.

[0158] In this embodiment, the method for coating a steel structure and the method for manufacturing a steel structure with a coating further include a rust prevention step. In the rust prevention step, a rust prevention treatment is applied to the surface preparation surface 22 of the steel structure 100 to form a rust-preventive treated surface on the steel structure 100.

[0159] In this embodiment, the method for coating a steel structure and the method for manufacturing a steel structure with a coating further include a preparation step. In the preparation step, a coating sheet 30 is prepared. In the preparation step, a steel structure 100 to which the method for coating a steel structure and the method for manufacturing a steel structure with a coating are applied may be prepared.

[0160] In this embodiment, the method for coating a steel structure and the method for manufacturing a steel structure with a coating comprise the following steps in this order: preparation step, surface preparation step, rust prevention step, placement step, and topcoat film formation step.

[0161] In the preparation step, a covering sheet 30 is prepared. In the preparation step, a steel structure 100 may also be prepared. In this embodiment, in the preparation step, a steel structure 100 having a deteriorated portion 12 is prepared.

[0162] In the preparation step, the above-described coating sheet 30 is prepared as the coating sheet 30 of this embodiment. That is, a coating sheet 30 having a first surface 31 and a second surface 32, and having a surface roughness Sa of 10 μm or less on the first surface 31 is prepared.

[0163] A method for coating a steel structure and a method for manufacturing a steel structure with a coating may further include a curing step. The curing step may be included in a preparation step for preparing a coating sheet 30. The curing step is a step of forming a resin cured layer 45 contained in the coating sheet 30. In the curing step, the resin cured layer 45 is formed by curing an electron beam-curable resin composition containing urethane (meth)acrylate by irradiating it with an electron beam. By such a curing step, a resin cured layer 45 containing a material having urethane bonds can be formed.

[0164] Figure 4A shows a schematic cross-sectional view of a steel structure 100 having a deteriorated portion 12, which is prepared in the preparation step. In other words, Figure 4A shows an example of a steel structure 100 having a deteriorated portion 12 that is the target of repair by the repair method of this embodiment. The steel material 20 can corrode due to corrosive factors such as water and oxygen. The steel material 20 may contain rusted portions on its surface due to corrosion. Examples of rust include red rust such as iron oxide (Fe2O3). The portion of the steel material 20 where abnormalities such as rusted portions occur constitutes the deteriorated portion 12 of the steel structure 100 shown in Figure 4A.

[0165] Furthermore, when a steel structure 100 is newly constructed, a rust-preventive paint or corrosion-preventive paint is applied to the steel material 20 to form a coating 50, for purposes such as suppressing rust formation. The coating 50 formed on the steel material 20 when a steel structure 100 is newly constructed may be a single coating or may include multiple coatings. If the coating 50 includes multiple coatings, the coating 50 may be as shown in Figure 5, which will be described later. That is, in the preparation process, the steel structure 100 shown in Figure 5, which will be described later, may be prepared.

[0166] Such coatings 50 may develop abnormalities such as cracks and blisters due to aging or construction or repair work performed on the steel structure. The parts of the coating 50 that have defects such as cracks and blisters also constitute the deteriorated parts 12 of the steel structure 100. In Figure 4A, rust 60 has formed on the steel material 20. In addition, a pre-repair coating (old coating) 50 is applied to the steel material 20. Defects such as cracks and blisters in the rust 60 and the pre-repair coating (old coating) 50 (not shown) constitute the deteriorated parts 12 of the steel structure 100.

[0167] As described above, the steel structure 100 of this embodiment has a deteriorated portion 12. In the method for coating a steel structure and the method for manufacturing a steel structure with a coating of this embodiment, the deteriorated portion 12 is prepared to form a prepared surface 22 on the steel structure 100, the prepared surface 22 is treated with rust prevention to form a rust-preventive surface on the steel structure 100, and the coating sheet 30 is placed on the rust-preventive surface. By this method, the steel structure 100 having a deteriorated portion 12 can be repaired. Compared to, for example, a case where a coating 80 is formed by heavy-duty anti-corrosion coating with multiple layers of paint without using a coating sheet 30, this repair method allows for the repair of the steel structure 100 in a shorter time and at a lower cost.

[0168] The steel structure 100 having the deteriorated portion 12, which is prepared in the preparation step, may be a steel structure 100 in which a covering sheet 30 is placed so as to cover at least a part of the surface of the steel structure 100, as shown in Figures 1A to 1D. In other words, a steel structure 100 that has been repaired once using a covering sheet 30 may be repaired again using the repair method of this embodiment.

[0169] In the surface preparation process, the deteriorated portion 12 of the steel structure 100 is prepared to form a prepared surface 22 on the steel structure 100. As a method for preparing the surface of the steel structure 100, surface preparation is exemplified. In surface preparation, old paint, rust, dust, and dirt are generally removed using blasting, power tools, or manual tools. This removal exposes the prepared surface 22. In the surface preparation process, the prepared surface 22 constitutes the surface of the steel structure 100.

[0170] Surface preparation processes are categorized into four grades: Grade 1, Grade 2, Grade 3, and Grade 4. The lower the grade number, the more advanced the level of surface preparation.

[0171] "Type 1 surface preparation" refers to surface preparation that involves completely removing rust and old paint film to expose the steel surface. In "Type 1 surface preparation," surface preparation is mainly performed by blast treatment.

[0172] "Type 2 surface preparation" refers to surface preparation that removes rust and old paint film 50 to expose the surface of the steel material 20. In "Type 2 surface preparation," surface preparation is mainly carried out using power tools and / or manual tools.

[0173] "Type 3 surface preparation" refers to a surface preparation process that leaves 50P of the old paint film intact, i.e., the paint film in good condition, while removing other defective parts (rust and dead paint film (paint film with cracks and blistering)). In "Type 3 surface preparation," surface preparation is mainly carried out using power tools and / or manual tools.

[0174] Type 3 surface preparation has the advantage of requiring fewer work areas and lower labor costs compared to Type 1 and Type 2 surface preparation. Since the active film 50P of the old paint film 50 remains, the surface prepared after Type 3 surface preparation may have large irregularities. Rust may remain on the surface prepared after Type 3 surface preparation. The height of the irregularities on the surface of the steel structure 100 after Type 3 surface preparation may be 10 μm or more and 1000 μm or less, 30 μm or more and 500 μm or less, or 50 μm or more and 300 μm or less.

[0175] Figure 4B shows a steel structure 100 that has undergone surface preparation using three types of surface preparation. In Figure 4B, the old paint film 50 has been removed except for the active film 50P. In Figure 4B, the rust 60 has also been removed.

[0176] "Type 4 surface preparation" refers to surface preparation that removes powdery substances (including loose rust) and dirt adhering to the surface. In "Type 4 surface preparation," surface preparation is mainly carried out using manual tools and / or brushes.

[0177] Examples of power tools include disc sanders and wire wheels. Examples of hand tools include wire brushes, scrapers, scraping rods, and sandpaper.

[0178] In the rust prevention process, as shown in Figure 4C, rust prevention treatment is applied to the surface preparation surface 22 of the steel structure 100 to form a rust-preventive surface on the steel structure 100. The rust prevention process in this embodiment includes the step of applying rust-preventive paint to the surface preparation surface 22 of the steel structure 100 to form a rust-preventive layer 18. In this case, the surface of the formed rust-preventive layer 18 becomes the rust-preventive surface. The rust prevention process in this embodiment forms a rust-preventive layer 18 on the steel material 20 and the active film 50P. The material and formation method of the rust-preventive layer 18 are as described above.

[0179] The rust-preventive layer 18 contains a rust inhibitor. The rust inhibitor can suppress rust formation. The rust inhibitor may be included in the bonding layer 15 or the coating sheet 30. If the rust inhibitor is included in the coating sheet 30, for example, the rust inhibitor may also be included in the bonding layer 43. By providing the rust-preventive layer 18 containing the rust inhibitor separately from the coating sheet 30, the effect of the rust inhibitor can be obtained more clearly. The rust-preventive layer 18, which is formed as a coating film, can fill in the irregularities of the surface preparation surface 22 to some extent. This can improve the adhesion of the coating sheet 30. However, irregularities caused by the irregularities of the surface preparation surface 22 may remain on the surface of the rust-preventive layer 18.

[0180] The method for coating a steel structure and the method for manufacturing a steel structure with a coating may further include a coating resin layer formation step between the surface preparation step, the rust prevention step and the placement step. In the coating resin layer formation step, a coating resin layer (not shown) is formed on the rust-preventive treated surface. The material and formation method of the coating resin layer are as described above.

[0181] As described above, the coating resin layer may smooth out any unevenness on the rust-preventive treated surface. In this case, the coating resin layer formation process is a so-called surface leveling process. A surface leveling process means filling in the irregularities of the substrate with a putty-like surface leveling agent to make it smooth. For example, the surface leveling surface 22 of the steel structure 100 after type 3 surface preparation has an active film and therefore has irregularities on its surface. These irregularities tend to remain even after rust prevention treatment. When the coating sheet 30 is attached to a rust-preventive treated surface with irregularities in the placement process described later, corrosion and peeling may progress due to corrosive factors (water or oxygen) present in the space between the rust-preventive treated surface and the coating sheet 30. When the irregularities of the substrate are filled in with a surface leveling agent to make it smooth, the coating sheet 30 can be attached to the surface of the steel structure 100 or rust-preventive layer 18 that has been leveled without any gaps. Therefore, the entry of corrosive factors (water or oxygen) into the repaired steel structure 100 can be reduced.

[0182] In the placement process, the covering sheet 30 is placed so as to cover at least a portion of the surface of the steel structure 100. In the placement process, the covering sheet 30 may be placed so as to cover the entire surface of the steel structure 100. In this embodiment, in the placement process, the covering sheet 30 is placed so as to cover at least a portion of the surface preparation surface 22. In the placement process, the covering sheet 30 may be placed so as to cover the entire surface preparation surface 22. In this embodiment, in the placement process, the covering sheet 30 is placed so as to cover at least a portion of the rust-preventive treatment surface. In the placement process, the covering sheet 30 may be placed so as to cover the entire rust-preventive treatment surface. In the placement process, the covering sheet 30 is placed so that the surface of the steel structure 100 and the second surface 32 of the covering sheet 30 face each other.

[0183] During the placement process, the steel structure 100 is covered with a covering sheet 30. In the example shown in Figure 4D, the covering sheet 30 is placed on the rust-preventive layer 18. In the example shown in Figure 4D, a bonding layer 15 is formed on the rust-preventive layer 18, and the covering sheet 30 is bonded to the rust-preventive layer 18 using this bonding layer 15. The covering sheet 30, including the bonding layer 43, may also be bonded to the rust-preventive layer 18 using the bonding layer 43.

[0184] In the placement process, the covering sheet 30 may be attached to the steel structure 100 or the coating film (e.g., anti-corrosion layer 18) on the steel structure 100 by the bonding layers 15, 43 while being pressurized at room temperature. For example, the covering sheet 30 may be pressed toward the steel material 20 using a roller or the like from above. This allows the covering sheet 30 to adhere closely to the steel structure 100 or the coating film on the steel structure 100.

[0185] If the covering sheet 30 includes a release film 46, the release film 46 is peeled off the covering sheet 30 before placing the covering sheet 30 on the steel material 20. By peeling off the release film 46, the bonding layer 43 is exposed.

[0186] The covering sheet 30 may cover the side edges of the rust-preventive layer 18. The covering sheet 30 may be folded to cover the side end surfaces of the steel structure 100.

[0187] In the topcoat film formation process, a topcoat film 81 is formed on the first surface 31 of the covering sheet 30. This produces the covered steel structure 10 shown in Figure 1D.

[0188] In the topcoat film formation process, a topcoat paint (paint composition), for example, is applied to the surface of the covering sheet 30 placed on the rust-preventive treated surface to form a topcoat film 81. The material and formation method of the topcoat film 81 are as described above. In particular, as described above, the formed topcoat film 81 may include a material having urethane bonds.

[0189] The topcoat film formation process improves the weather resistance of the repaired steel structure 100, for example, ensuring rust prevention even after a long period of time has elapsed since construction. Furthermore, the topcoat film 81 formed by the topcoat film formation process provides gloss.

[0190] The effects of forming a glossy topcoat 81 will be explained in more detail. Let us consider a case where a steel structure 100, which has a deteriorated area 12 in some parts, is repaired using the steel structure coating method of this embodiment. In this case, the steel structure 100 can be repaired by performing surface preparation and rust prevention treatment on the deteriorated area 12 of the steel structure 100, and then covering that area with the coating sheet 30. In this case, if a topcoat 81 is not formed on the first surface 31 of the coating sheet 30, an observer of the coated steel structure 10 manufactured by the repair will directly see the coating sheet 30 in the repaired part of the steel structure 100. On the other hand, in the parts of the steel structure 100 that have not been repaired, the observer will see the coating 50 that was formed on the steel material 20 from the time the steel structure 100 was newly constructed. This coating 50 may exhibit gloss. In this case, the difference in gloss between the covering sheet 30 and the coating film 50 may make the repaired portion of the steel structure 100 stand out. In contrast, by forming a topcoat coating film 81 on the first surface 31 of the covering sheet 30, the gloss of the repaired portion of the steel structure 100 can be made to be the same as the gloss of the coating film 50, making the repaired portion of the steel structure 100 less noticeable.

[0191] <<<Effect>>> This invention will describe the method for coating a steel structure, the method for manufacturing a steel structure with a coating, and the effects of the coating sheet 30 and the steel structure with a coating 10.

[0192] As a comparative example, consider a case where the steel structure 100 is not covered with a covering sheet 30, but is instead subjected to a conventional heavy-duty anticorrosion coating consisting of multiple layers of paint. Figure 5 is a cross-sectional view of the steel structure 100 of this comparative example. The steel structure 100 shown in Figure 5 includes a steel material 20 and a coating film 50 formed on the steel material 20. The coating film 50 includes multiple coating films.

[0193] The coating 50 of the steel structure 100 shown in Figure 5 includes, in this order: a rust-preventive layer 51, a first undercoat layer 52, a second undercoat layer 53, an intermediate coat layer 54, and a topcoat layer 55.

[0194] The rust-preventive layer 51 has a rust-preventive function. The rust-preventive layer 51 is a layer that suppresses rust formation and rust spread. The rust-preventive layer 51 may be configured in the same way as the rust-preventive layer 18 described above.

[0195] The first undercoat layer 52 and the second undercoat layer 53 have gas barrier properties. The first undercoat layer 52 and the second undercoat layer 53 suppress corrosion of the steel material 20. The barrier properties of the coating film barrier layer are weaker than those of the vapor-deposited film barrier layer. The illustrated steel structure 100 includes two undercoat layers 52 and 53 to ensure sufficient barrier properties. The undercoat layers 52 and 53 may contain epoxy resin. The undercoat layers 52 and 53 may contain cured products of curable resin.

[0196] The intermediate coat layer 54 has good adhesion properties. The intermediate coat layer 54 improves the adhesion of the top coat layer 55. Examples of intermediate coat layers with good adhesion properties include layers containing epoxy resin, urethane resin, and fluororesin. The intermediate coat layer 54 may also contain weather-resistant agents such as UV absorbers, antioxidants, and light stabilizers.

[0197] The topcoat layer 55 is weather-resistant. The topcoat layer 55 may contain weather-resistant agents such as ultraviolet absorbers, antioxidants, and light stabilizers. Examples of the topcoat layer 55 include a layer containing acrylic resin, urethane resin, silicone resin, fluororesin, and weather-resistant agents. The topcoat layer 55 may be constructed in the same manner as the topcoat film 81 described above.

[0198] Each of the numerous coating films 50 is prepared only once a day, taking into account the time required for drying, solidification, and curing. For example, the steel structure 100 shown in Figure 5 requires 5 days of construction.

[0199] In contrast, according to the method for coating steel structures and the method for manufacturing coated steel structures of this embodiment, the process for protecting the steel structure 100 can be completed in a shorter time than, for example, the method of applying heavy-duty anticorrosive paint to the steel structure 100 as in the comparative example above. Furthermore, with the method for coating steel structures and the method for manufacturing coated steel structures of this embodiment, multiple painting steps are not particularly necessary; the coating sheet 30 can be used. Therefore, it is possible to complete the process for protecting the steel structure 100 at a low cost. In particular, low-cost repair treatment of the steel structure 100 is also possible. As a result, preventive maintenance can be facilitated by using the coating sheet 30. Since the coating sheet 30 is a factory-made product, it is less prone to pinholes compared to heavy-duty anticorrosive paint. Therefore, the coating sheet 30 can provide a greater protective effect on the steel structure 100 compared to heavy-duty anticorrosive paint. The coated steel structure 10 is manufactured by the method for coating steel structures and the method for manufacturing coated steel structures of this embodiment. With this coated steel structure 10, the steel structure 100 and the coating on the steel structure 100 (for example, the coating 50 or the rust-preventive layer 18) can be protected by the coating sheet 30 and the top coating 81.

[0200] However, when a covering sheet 30 is placed on a steel structure 100 so as to cover at least a portion of the surface of the steel structure 100, it may be necessary to further form a glossy topcoat film 81 on the first surface 31 of the covering sheet 30. In this case, depending on the characteristics of the covering sheet 30, even if a topcoat film 81 is formed on the first surface 31, it may not be possible to ensure a sufficient level of gloss for the topcoat film 81.

[0201] The inventors of this invention have conducted extensive research and found that by making the surface roughness Sa of the first surface 31 of the coating sheet 30 10 μm or less, it is possible to ensure a high level of gloss of the topcoat film 81 formed on the surface of the coating sheet 30. In particular, they found that by making the surface roughness Sa of the first surface 31 10 μm or less before joining the coating sheet 30 to the steel structure 100 or the coating film on the steel structure 100, it is possible to ensure a high level of gloss of the topcoat film 81 formed on the surface of the coating sheet 30. The reason for this is thought to be as follows: By making the surface roughness Sa of the first surface 31 10 μm or less before joining the coating sheet 30 to the steel structure 100 or the coating film on the steel structure 100, it is thought that the surface roughness Sa of the first surface 31 after joining the coating sheet 30 to the steel structure 100 or the coating film on the steel structure 100 can also be kept low. This is thought to reduce the surface irregularities of the topcoat film 81 formed on the surface of the covering sheet 30. By reducing the surface irregularities of the topcoat film 81, it is thought that the gloss level of the topcoat film 81 can be ensured.

[0202] In the method for coating a steel structure according to this embodiment, in the arrangement step, a coating sheet 30 having a surface roughness Sa of 10 μm or less on its first surface 31 is arranged so as to cover at least a portion of the surface of the steel structure 100, with the surface of the steel structure 100 and the second surface 32 of the coating sheet 30 facing each other. In the method for manufacturing a coated steel structure according to this embodiment, in the arrangement step, a coating sheet 30 having a surface roughness Sa of 10 μm or less on its first surface 31 is arranged so as to cover at least a portion of the surface of the steel structure 100, with the surface of the steel structure 100 and the second surface 32 of the coating sheet 30 facing each other. The coating sheet 30 in this embodiment has a surface roughness Sa of 10 μm or less on its first surface 31, covers at least a portion of the surface of the steel structure 100, and is arranged so as to cover the surface of the steel structure 100 and the second surface 32 facing each other. As described above, the surface irregularities of the topcoat film 81 formed on the surface of the covering sheet 30 can be reduced, thereby ensuring a high gloss level for the topcoat film 81. By setting the surface roughness Sa of the first surface 31 to 9 μm or less, the high gloss level of the topcoat film 81 can be ensured more effectively.

[0203] Furthermore, as mentioned above, irregularities may form on the surface of the steel structure 100 or the coating film (e.g., the rust-preventive layer 18) on the steel structure 100, due to factors such as the formation of a surface preparation surface 22 on the steel structure 100. These irregularities can be filled to some extent by the components of the coating sheet 30. For example, as shown in Figure 2A, if the coating sheet 30 has a bonding layer 43, these irregularities can be filled to some extent by the bonding layer 43. This also helps to keep the surface roughness Sa of the first surface 31 small after the coating sheet 30 has been bonded to the steel structure 100 or the coating film on the steel structure 100. From this point of view, it is also possible to reduce the surface irregularities of the topcoat coating 81 and ensure a high gloss level for the topcoat coating 81.

[0204] According to the manufacturing method for a coated steel structure of this embodiment, the 60° specular gloss of the surface of the coated steel structure 10, which is composed of the topcoat 81, can be made 70 or higher. By having a 60° specular gloss of 70 or higher on the surface of the coated steel structure 10 composed of the topcoat 81, the gloss level of the topcoat 81 can be sufficiently ensured. In particular, the topcoat 81 can exhibit a 60° specular gloss of ≥70, which is the standard value specified in JIS K5659:2018 regarding the quality of topcoat paints among weather-resistant paints for steel structures. Furthermore, when the 60° specular gloss of the surface of the coated steel structure 10 composed of the topcoat 81 is 70 or higher, the surface of the coated steel structure 10 is considered to be particularly flattened. This leveling makes it less likely for moisture and dirt to accumulate on the surface of the coated steel structure 10, thus making the coated steel structure 10, including the topcoat 81, less prone to long-term deterioration.

[0205] In the steel structure coating method and steel structure coating method of this embodiment, the steel structure 100 to which the coating method is applied has a deteriorated portion 12. The method further includes a surface preparation step in which surface preparation is performed on the deteriorated portion 12 of the steel structure 100 to form a surface preparation surface 22 on the steel structure 100. In the placement step, the coating sheet 30 is placed so as to cover at least a portion of the surface preparation surface 22. The steel structure coating method and steel structure coating method of this embodiment can be used as a repair method for a steel structure 100 having a deteriorated portion 12.

[0206] The method for coating a steel structure and the method for manufacturing a steel structure with a coating according to this embodiment further includes a rust prevention step of performing a rust prevention treatment on the surface preparation surface 22 of the steel structure 100 to form a rust-preventive surface on the steel structure 100. In the placement step, the coating sheet 30 is placed so as to cover at least a portion of the rust-preventive surface. According to the method for coating a steel structure and the method for manufacturing a steel structure with a coating according to this embodiment, a rust-preventive surface can be formed on the steel structure 100. The formation of the rust-preventive surface makes it less likely for rust to occur on the steel material 20.

[0207] In the method for coating a steel structure and the method for manufacturing a coated steel structure according to this embodiment, the rust prevention step includes the step of applying rust-preventive paint to the surface preparation surface 22 of the steel structure 100 to form a rust-preventive layer 18. The formation of the rust-preventive layer 18 makes it difficult for rust to occur on the steel material 20.

[0208] The coating sheet 30 includes a resin curing layer 45 that constitutes the first surface 31. The resin curing layer 45 may be a weather-resistant layer 42. Because the coating sheet 30 includes a resin curing layer 45, the surface roughness Sa of the first surface 31 can be brought within a desired numerical range by adjusting the resin curing layer 45. Furthermore, because the coating sheet 30 includes a resin curing layer 45, the adhesion of the topcoat 81 to the coating sheet 30 can be improved by adjusting the material of the resin curing layer 45 and the material of the topcoat 81. For example, by making the material of the resin curing layer 45 and the material of the topcoat 81 materials that have strong polarity and attract each other, the adhesion of the topcoat 81 to the coating sheet 30 can be improved.

[0209] The resin cured layer 45 may contain a material having urethane bonds, and the topcoat film 81 may also contain a material having urethane bonds. In this case, the O or N and H contained in the urethane bonds attract each other to form hydrogen bonds, thereby increasing the adhesion of the topcoat film 81 to the covering sheet 30.

[0210] The method for coating a steel structure and the method for manufacturing a coated steel structure according to this embodiment further comprises a curing step of forming a resin cured layer 45 by curing an electron beam-curable resin composition containing urethane (meth)acrylate by irradiating it with an electron beam. By forming the resin cured layer 45 through such a curing step, the resin cured layer 45 can be made to contain a material having urethane bonds.

[0211] The surface roughness Sa of the first surface 31 of the coating sheet 30, in particular, the surface roughness Sa of the first surface 31 before the coating sheet 30 is joined to the steel structure 100 or the coating film on the steel structure 100, may be greater than 1.2 μm. A surface roughness Sa greater than 1.2 μm of the first surface 31 allows for a higher adhesion of the topcoat film 81 to the coating sheet 30 due to the anchoring effect.

[0212] The coating sheet 30 may include a bonding layer 43 that constitutes the second surface 32. The bonding layer 43 allows the coating sheet 30 to be bonded to the steel structure 100 or the coating film on the steel structure 100. Furthermore, the bonding layer 43 can fill in irregularities formed on the surface of the steel structure 100 or the coating film (e.g., the rust-preventive layer 18) on the steel structure 100, caused by factors such as the formation of a surface preparation surface 22 on the steel structure 100. This allows the surface roughness Sa of the first surface 31 to be kept low.

[0213] The covering sheet 30 may be transparent. The following effects can be obtained by making the covering sheet 30 transparent. During the placement process, the covering sheet 30 can be placed while visually inspecting the steel structure 100 through the covering sheet 30. This allows the covering sheet 30 to be placed more accurately in the desired position. For example, it may be required to place the covering sheet 30 so as to cover the surface preparation surface 22 and the rust-preventive treatment surface. In this case, the covering sheet 30 can be placed while visually inspecting the positions of the surface preparation surface 22 and the rust-preventive treatment surface through the covering sheet 30. This allows the covering sheet 30 to be placed stably so as to cover the surface preparation surface 22 and the rust-preventive treatment surface. Furthermore, in the manufactured covered steel structure 10, as long as the topcoat 81 is removed, it becomes possible to inspect the condition of the steel structure 100 and the coating on the steel structure 100 (e.g., rust-preventive layer 18) through the covering sheet 30. In particular, it becomes easier to inspect whether cracks or other defects have occurred on the surface of the steel material 20.

[0214] <<<Modified Version>>> Next, modifications of this embodiment will be described. In the above-described embodiment, an example was given in which the method for coating a steel structure and the method for manufacturing a steel structure with a coating are applied to a steel structure 100 having deteriorated parts 12. However, the method for coating a steel structure and the method for manufacturing a steel structure with a coating are not limited to this. The method for coating a steel structure and the method for manufacturing a steel structure with a coating may also be applied to a steel structure 100 that does not have deteriorated parts 12. The method for coating a steel structure and the method for manufacturing a steel structure with a coating may also be applied to a newly constructed steel structure 100. A coating 80 including a coating sheet 30 and a topcoat coating 81 may be used to coat the steel structure 100 when it is newly constructed. In this case, the steel structure 100 to which the method for coating a steel structure and the method for manufacturing a steel structure with a coating are applied may or may not have a coating 50. If the steel structure 100 has a coating 50, the coating 50 may be a single coating or may include multiple coatings. The coated steel structure 10 can also be manufactured by the modified method of coating the steel structure and the method of manufacturing the coated steel structure. With this coated steel structure 10, the steel structure 100 and the coating film on the steel structure 100 (for example, the coating film 50 or the rust-preventive layer 18) can be protected by the coating sheet 30 and the top coating film 81. [Examples]

[0215] This disclosure will be further described in detail by examples. This disclosure is not limited to the following examples.

[0216] <<<1. Preparation of the covering sheet>>> Covered sheets according to Examples 1 and 2, Comparative Example 1, and Reference Example 1 were prepared.

[0217] <<Example 1>> As the coating sheet 30 according to Example 1, a coating sheet 30 having the layer structure shown in Figure 2A was manufactured. Specifically, a coating sheet 30 was manufactured that included, in this order from the first surface 31 to the second surface 32, a bonding layer 43, a barrier layer 44, a bonding layer 491, a base material 41, and a resin cured material layer 45 which is a weather-resistant layer 42.

[0218] As the base material 41, a linear low-density polyethylene resin (LLDPE) with a thickness of 300 μm was used.

[0219] Next, a primer layer was formed on the surface of the substrate 41 using a resin composition for the primer layer.

[0220] The resin composition for the primer layer was prepared by mixing 100 parts by mass of a mixture, 5 parts by mass of a curing agent, 20 parts by mass of an ultraviolet absorber, and a diluent. The 100 parts by mass of the mixture consisted of a polycarbonate-based urethane-acrylic copolymer and an acrylic polyol. The 5 parts by mass of the curing agent was hexamethylene diisocyanate.

[0221] A resin composition for the primer layer was applied to the surface of a substrate 41 by gravure printing. A primer layer was obtained by drying the coating film of the resin composition for the primer layer formed on the substrate 41. The thickness of the primer layer was 4 μm.

[0222] Next, a weather-resistant layer was formed on the primer layer using an ionizing radiation-curable resin composition. The ionizing radiation-curable resin composition was prepared by mixing 100 parts by mass of urethane acrylate oligomer, 4 parts by mass of a hydroxyphenyltriazine-based ultraviolet absorber as an ultraviolet absorber, and 3 parts by mass of a hindered amine-based non-reactive light stabilizer. The prepared ionizing radiation-curable resin composition was applied onto the primer layer to form an uncured resin layer on the primer layer.

[0223] Subsequently, the uncured resin layer was cured by irradiating it with an electron beam. The electron beam irradiation conditions were set to an acceleration voltage of 165kV and an irradiation dose of 5Mrad (50kGy). By irradiating the uncured resin layer with an electron beam, a weather-resistant layer with a thickness of 5μm was formed.

[0224] Based on the above, a weather-resistant layer 42 was formed as the resin cured layer 45, including the weather-resistant layer body and the primer layer. The weather-resistant layer body and the substrate 41 were joined via the primer layer.

[0225] Furthermore, a transparent urethane resin adhesive was applied to the surface of the substrate 41 opposite to the surface on which the weather-resistant layer 42, the cured resin layer 45, was formed, and dried to form a bonding layer 491 with a thickness of 3 μm.

[0226] Furthermore, a barrier film 44X was prepared, which included a barrier layer 44 and a resin film 44a. For the barrier film 44X, the barrier layer 44 was formed on the resin film 44a using chemical vapor deposition (CVD) to produce a barrier layer of the chemical formula SiO x A vapor-deposited film was used, which had a silica vapor-deposited film represented by C arranged on it, and a protective coat containing polyvinyl alcohol was placed on the vapor-deposited film by a sol-gel coat. As the resin film 44a, biaxially oriented polypropylene (OPP) with a thickness of 20 μm was used. Subsequently, the substrate 41 and the barrier film 44X were bonded together by dry lamination via the bonding layer 491. At this time, the substrate 41 and the barrier film 44X were bonded together such that the surface formed by the barrier layer 44 of the barrier film 44X and the surface of the substrate 41 faced each other.

[0227] Furthermore, a transparent urethane resin-based adhesive was applied to the surface of the barrier film 44X that is composed of the resin film 44a and dried to form a bonding layer 43 with a thickness of 10 μm.

[0228] As a result, a coated sheet 30 according to Example 1 was obtained, which included a bonding layer 43, a barrier film 44X, a bonding layer 491, a substrate 41, and a resin cured layer 45 which is a weather-resistant layer 42, in the order from the second surface 32 to the first surface 31 in the lamination direction. Since the barrier film 44X includes a barrier layer 44, the coated sheet 30 according to Example 1 included a bonding layer 43, a barrier layer 44, a bonding layer 491, a substrate 41, and a resin cured layer 45 which is a weather-resistant layer 42, in the order from the second surface 32 to the first surface 31 in the lamination direction.

[0229] <<Example 2>> For Example 2, a covering sheet 30 having the layer structure shown in Figure 2A was prepared by the same method as in Example 1, except for the following points. In Example 2, instead of forming the weather-resistant layer body, a single layer corresponding to the primer layer in Example 1 was used as the weather-resistant layer 42.

[0230] <<Comparative Example 1>> As the covering sheet 30 for Comparative Example 1, a commercially available UV-curing FRP sheet (manufactured by Anan Electric Co., Ltd., product name "Ultra Patch") was used.

[0231] <<Reference example 1>> As a coating sheet for Reference Example 1, a coating sheet having the layer structure shown in Figure 2A was prepared by the same method as in Example 1, except for the following points. In Reference Example 1, the resin cured layer 45, which is the weather-resistant layer 42, was not formed. The coating sheet 30 for Reference Example 1 included a bonding layer 43, a barrier layer 44, a bonding layer 491, and a base material 41 in the order from the second surface 32 to the first surface 31 in the lamination direction.

[0232] <<<2. Measurement and Evaluation>>> As described below, the coated sheets for the examples, comparative examples, and reference examples were measured and evaluated. The samples used for measurement and evaluation were visually inspected to ensure they were free from any abnormalities such as dust or scratches.

[0233] <<2-1. Measurement of Surface Roughness Sa>> The surface roughness Sa of the first surface 31 of the coating sheet in the examples, comparative examples, and reference examples was measured by the following method. First, the first surface 31 of the coating sheet, cut to 10 × 10 cm, was photographed using the shape measurement mode of the "One-Shot 3D Measurement Macroscope" VR-3000 series laser microscope manufactured by KEYENCE Corporation, at 1x zoom and 5x magnification. Subsequently, the surface roughness Sa of the entire area of ​​the captured image was measured using the multi-file analysis application tool (an accessory for the laser microscope) manufactured by KEYENCE Corporation.

[0234] <<2-2.60 degree specular gloss>> The 60-degree specular gloss of the first surface 31 of the coated sheets in the examples, comparative examples, and reference examples was measured in accordance with Method 1 of JIS Z8741-1997, under conditions of an incident angle of 60 degrees and an observation angle of 60 degrees. The 60-degree specular gloss was measured three times using a gloss meter (BYK, product name micro-TRI-gloss gloss meter), and the average value was calculated.

[0235] In addition, commercially available steel materials 20 were covered with the covering sheets according to the Examples, Comparative Examples, and Reference Examples. Specifically, steel materials 20 without any deteriorated parts 12 were used. When covering the steel materials 20, the covering sheets were positioned so that the surface of the steel material 20 and the second surface 32 of the covering sheet faced each other, and the second surface 32 of the covering sheet and the surface of the steel material 20 were joined. In Examples 1, 2, and Reference Example 1, the joining of the second surface 32 of the covering sheet and the surface of the steel material 20 was performed using a joining layer 43. In Comparative Example 1, the joining of the second surface 32 of the covering sheet and the surface of the steel material 20 was performed by the following method: With the surface of the steel material 20 and the surface of the UV-curable FRP sheet (the covering sheet) in contact, the covering sheet was irradiated with sunlight for 1 hour, and the covering sheet was cured by the ultraviolet rays of the sunlight. This joined the second surface 32 of the covering sheet and the surface of the steel material 20 according to Comparative Example 1.

[0236] Furthermore, a topcoat film 81 was formed on the first surface 31 of the resin sheet covering the steel material 20. The topcoat film 81 was formed by the following method: A weak solvent-type fluororesin topcoat paint (manufactured by Nippon Paint Co., Ltd., product name "Duflon 100 New Fine") was applied to the first surface 31 of the resin sheet as a topcoat paint. At this time, the target film thickness of the formed paint film was 25 μm. The measured film thickness of the formed paint film was 23.8 μm. After applying the topcoat paint, the paint film was allowed to harden for 48 hours to form the topcoat film 81. In this way, a steel structure with a coating was manufactured, comprising a steel structure 100 including the steel material 20 and a coating body 80 including the coating sheet 30 and the topcoat film 81.

[0237] The 60-degree specular gloss of the surface of the manufactured coated steel structure, which is composed of the topcoat film 81, was measured using the same measurement method as the measurement method for the 60-degree specular gloss of the first surface 31 of the coating sheet described above.

[0238] <<2-3. Evaluation of Adhesion of Topcoat Film>> In the case of "2-2.60 degree specular gloss," a commercially available steel material 20 was covered with a coating sheet according to the example, comparative example, and reference example using the same method as described above. Furthermore, a topcoat coating 81 was formed on the first surface 31 of the resin sheet covering the steel material 20. In this way, a steel structure with a coating was manufactured, comprising a steel structure 100 including the steel material 20 and a coating body 80 including the coating sheet 30 and the topcoat coating 81.

[0239] The adhesion of the topcoat film 81 to the coating sheet 30 of a manufactured coated steel structure was evaluated. For the adhesion evaluation, the following 90-degree tape peel test was performed on the surface of the manufactured coated steel structure that was covered with the topcoat film 81. The topcoat film 81 was visually observed after the 90-degree tape peel test, and the adhesion of the topcoat film 81 was evaluated based on whether or not peeling of the topcoat film 81 was observed.

[0240] For the 90-degree tape peel test, a cellophane adhesive tape conforming to JIS Z1522:2009 was prepared: Cellotape (registered trademark) (manufactured by Nichiban, model No. 405-1P, 24mm width, adhesive strength: 3.93N / 10mm, tensile strength: 41.6N / 10mm, elongation: 23%, all physical properties are catalog values). 25cm of the cellophane adhesive tape was unwound from the roll at a temperature of 23°C and humidity of 50%RH. With 10cm of adhesive surface joined together to create a handle, 5cm of the adhesive surface was attached to the surface of the coated steel structure formed by the topcoat 81 using a 2kg pressure roller for two passes. Then, it was further attached by finger pressure to ensure no air was trapped. Next, the cellophane adhesive tape was peeled off once manually at a speed of 5cm / s in a 90-degree direction from the surface of the coated steel structure formed by the topcoat 81.

[0241] Table 1 shows the measurement and evaluation results for "2-1. Measurement of Surface Roughness Sa", "2-2. 60-degree Specular Gloss", and "2-3. Evaluation of Adhesion of Topcoat Film" in the Examples, Comparative Examples, and Reference Examples. The "60-degree Specular Gloss (Before Topcoat Film Formation)" column in Table 1 shows the 60-degree specular gloss of the first surface 31 of the coated sheet that was measured. The "60-degree Specular Gloss (After Topcoat Film Formation)" column in Table 1 shows the 60-degree specular gloss of the surface of the coated steel structure that is composed of the topcoat film 81. The "Adhesion of Topcoat Film" column in Table 1 shows the evaluation results in "2-3. Evaluation of Adhesion of Topcoat Film". An "A" in the "Adhesion of Topcoat Film" column in Table 1 means that no peeling of the topcoat film 81 was observed in the 90-degree tape peel test. In Table 1, the "B" in the "Adhesion of Topcoat Film" column indicates that peeling of the topcoat film 81 was observed in the 90-degree tape peel test.

[0242] [Table 1]

[0243] As shown in Table 1, in Examples 1 and 2, the surface roughness Sa of the first surface 31 was 10 μm or less, particularly 9 μm or less. In contrast, in Comparative Example 1, the surface roughness Sa of the first surface 31 was greater than 10 μm. In addition, in Examples 1 and 2, the 60-degree specular gloss of the surface of the coated steel structure formed by the topcoat 81 was 70 or higher. In contrast, in Comparative Example 1, the 60-degree specular gloss of the surface of the coated steel structure formed by the topcoat 81 was less than 70. From this, it was found that by setting the surface roughness Sa of the first surface 31 of the coating sheet 30 to 10 μm or less, particularly 9 μm or less, the gloss level of the topcoat 81 can be ensured. In particular, it was found that the 60-degree specular gloss of the surface of the coated steel structure formed by the topcoat 81 can be set to 70 or higher.

[0244] As shown in Table 1, in Examples 1 and 2, the "adhesion of the topcoat film" was evaluated as "A". In contrast, in Reference Example 1, the "adhesion of the topcoat film" was evaluated as "B". In Examples 1 and 2, the resin cured layer 45 constituting the first surface 31 contained a material having urethane bonds, and the topcoat film 81 also contained a material having urethane bonds. In contrast, in Reference Example 1, the topcoat film 81 contained a material having urethane bonds, but the substrate 41 constituting the first surface 31 did not contain a material having urethane bonds. From this, it was found that by including a resin cured layer 45 constituting the first surface 31 in the covering sheet 30 that contains a material having urethane bonds, and by including a topcoat film 81 containing a material having urethane bonds, the adhesion of the topcoat film 81 to the covering sheet 30 can be improved.

[0245] This disclosure relates, for example, to the following [1] to

[13] . [1] A coating method for covering a steel structure with a coating body including a coating sheet and a topcoat coating, A placement step of arranging a covering sheet having a first surface and a second surface, and having a surface roughness Sa of 10 μm or less on the first surface, so as to cover at least a portion of the surface of the steel structure, such that the surface of the steel structure and the second surface of the covering sheet face each other. A method for covering a steel structure, comprising a topcoat film forming step of forming the topcoat film on the first surface of the covering sheet. [2] The aforementioned steel structure has deteriorated parts, The process further comprises a surface preparation step in which the deteriorated portion of the steel structure is prepared to form a prepared surface on the steel structure, The method for covering a steel structure according to [1], wherein in the arrangement step, the covering sheet is arranged so as to cover at least a portion of the surface preparation surface. [3] The process further includes a rust prevention step of applying a rust-preventive treatment to the surface preparation surface of the steel structure to form a rust-preventive treated surface on the steel structure, The coating method for a steel structure according to [2], wherein in the placement step, the coating sheet is placed so as to cover at least a part of the rust-preventive treatment surface. [4] The coating method for a steel structure according to [3], wherein the rust-preventive step includes a step of forming a rust-preventive layer by applying a rust-preventive paint to the substrate adjustment surface of the steel structure. [5] The coating method for a steel structure according to any one of [1] to [4], wherein the coating sheet includes a resin cured product layer constituting the first surface. [6] The resin cured product layer includes a material having a urethane bond. The coating method for a steel structure according to [5], wherein the topcoat film includes a material having a urethane bond. [7] The coating method for a steel structure according to [5] or [6], further comprising a curing step of forming the resin cured product layer by irradiating an electron beam curable resin composition containing urethane (meth)acrylate with an electron beam to cure it. [8] The coating method for a steel structure according to any one of [1] to [7], wherein the surface roughness Sa of the first surface of the coating sheet is greater than 1.2 μm. [9] The coating method for a steel structure according to any one of [1] to [8], wherein the coating sheet includes an adhesive layer constituting the second surface.

[10] The coating method for a steel structure according to any one of [1] to [9], wherein the coating sheet is transparent.

[11] A manufacturing method of a steel structure with a coating body, comprising a steel structure, a coating body including a coating sheet and a topcoat film for coating the steel structure, wherein: An arrangement step of arranging the coating sheet having a first surface and a second surface and having a surface roughness Sa of the first surface of < 10 μm so that at least a part of the surface of the steel structure is covered and the surface of the steel structure faces the second surface of the coating sheet; A topcoat film forming step of forming the topcoat film on the first surface of the coating sheet.

[12] A covering sheet for covering steel structures, It has a first surface and a second surface, and the surface roughness Sa of the first surface is 10 μm or less. A covering sheet is positioned such that the surface of the steel structure and the second surface of the covering sheet face each other, so as to cover at least a portion of the surface of the steel structure.

[13] A steel structure with a covering, comprising a steel structure and a covering body that covers the steel structure, The covering body comprises a covering sheet having a first surface and a second surface, covering at least a portion of the surface of the steel structure, and arranged so that the surface of the steel structure and the second surface face each other, and a topcoat coating formed on the first surface of the covering sheet and constituting the surface of the steel structure with the covering body. A coated steel structure wherein the surface of the coated steel structure formed by the aforementioned topcoat coating has a 60-degree specular gloss of 70 or more. [Explanation of symbols]

[0246] 10...Steel structure with coating, 18...Rust prevention layer, 20...Steel material, 30...Coating sheet, 43...Joint layer, 45...Resin cured material layer, 50...Pre-repair coating (old coating), 80...Coating, 81...Topcoat coating, 100...Steel structure

Claims

1. A coating method for covering a steel structure with a coating body including a coating sheet and a topcoat coating, A placement step of arranging the covering sheet, which has a first surface and a second surface and whose first surface has a surface roughness Sa of 10 μm or less, so as to cover at least a portion of the surface of the steel structure, such that the surface of the steel structure and the second surface of the covering sheet face each other. A method for covering a steel structure, comprising a topcoat film forming step of forming the topcoat film on the first surface of the covering sheet.

2. The aforementioned steel structure has deteriorated parts, The process further comprises a surface preparation step in which the deteriorated portion of the steel structure is prepared to form a prepared surface on the steel structure, The method for covering a steel structure according to claim 1, wherein in the arrangement step, the covering sheet is arranged so as to cover at least a portion of the surface preparation surface.

3. The process further includes a rust prevention step of applying a rust-preventive treatment to the surface preparation surface of the steel structure to form a rust-preventive treated surface on the steel structure, The method for covering a steel structure according to claim 2, wherein in the arrangement step, the covering sheet is arranged so as to cover at least a portion of the rust-preventive treatment surface.

4. The method for coating a steel structure according to claim 3, wherein the rust prevention step includes a step of applying rust-preventive paint to the surface preparation surface of the steel structure to form a rust-preventive layer.

5. The method for coating a steel structure according to claim 1, wherein the coating sheet includes a resin cured layer constituting the first surface.

6. The aforementioned resin cured layer comprises a material having urethane bonds, The method for coating a steel structure according to claim 5, wherein the topcoat film comprises a material having urethane bonds.

7. The method for coating a steel structure according to claim 5, further comprising a curing step of forming the resin cured layer by irradiating an electron beam-curable resin composition containing urethane (meth)acrylate with an electron beam to cure it.

8. The method for coating a steel structure according to claim 1, wherein the surface roughness Sa of the first surface of the coating sheet is greater than 1.2 μm.

9. The method for covering a steel structure according to claim 1, wherein the covering sheet includes a bonding layer that constitutes the second surface.

10. The method for covering a steel structure according to claim 1, wherein the covering sheet is transparent.

11. A method for manufacturing a steel structure with a covering, comprising a steel structure and a covering body that covers the steel structure, including a covering sheet and a top coating film, A placement step of arranging the covering sheet, which has a first surface and a second surface and whose first surface has a surface roughness Sa of 10 μm or less, so as to cover at least a portion of the surface of the steel structure, such that the surface of the steel structure and the second surface of the covering sheet face each other. A method for manufacturing a steel structure with a coating, comprising a top coating film forming step of forming the top coating film on the first surface of the coating sheet.

12. A covering sheet for covering steel structures, It has a first surface and a second surface, and the surface roughness Sa of the first surface is 10 μm or less. A covering sheet is arranged such that the surface of the steel structure and the second surface of the covering sheet face each other, so as to cover at least a portion of the surface of the steel structure.

13. A steel structure with a covering, comprising a steel structure and a covering body that covers the steel structure, The covering body comprises a covering sheet having a first surface and a second surface, covering at least a portion of the surface of the steel structure, and arranged so that the surface of the steel structure and the second surface face each other, and a topcoat coating formed on the first surface of the covering sheet and constituting the surface of the steel structure with the covering body. A coated steel structure wherein the surface of the coated steel structure formed by the aforementioned topcoat coating has a 60-degree specular gloss of 70 or more.

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