Covering sheet, structure, and method for repairing structure

Abstract

A covering sheet according to the present invention is used for covering an adherend. The covering sheet includes a first surface and a second surface. The first surface faces the side opposite the adherend. The total light transmittance is 70% or more. The image clarity in a transmission method using an optical frequency comb having a width of 2.0 mm is 5.0% or more. The specular gloss on the first surface with an incident angle of 60° is 30 or less. The maximum spectral transmittance at a wavelength of 300-350 nm is 1.0% or less.

Description

Covering sheet, structure, and structure repair method

[0001] The present disclosure relates to a covering sheet, a structure, and a method for repairing a structure.

[0002] A weather-resistant coating sheet is known from Patent Document 1 (JP2020-179569A) and the like. The coating sheet covers an adherend exposed to ultraviolet rays and suppresses deterioration of the adherend. Examples of adherends exposed to ultraviolet rays include adherends placed outdoors and adherends placed near openings (windows) in structures such as buildings.

[0003] An adherend may deteriorate over time. It would be convenient to be able to inspect the condition of the adherend while it is covered with a covering sheet. An object of the present disclosure is to facilitate inspection of an adherend covered with a covering sheet.

[0004] A covering sheet according to one embodiment of the present disclosure is a covering sheet used to cover an adherend, comprising a first side and a second side, the first side facing away from the adherend, a total light transmittance of 70% or more, an image clarity of 5.0% or more as measured by a transmission method using an optical comb having a width of 2.0 mm, a specular gloss of the first side at an incident angle of 60° of 30 or less, and a maximum spectral transmittance of 1.0% or less at a wavelength of 300 nm or more and 350 nm or less.

[0005] A structure according to an embodiment of the present disclosure includes: the adherend; and the covering sheet according to an embodiment of the present disclosure.

[0006] A method for repairing a structure according to an embodiment of the present disclosure includes the steps of: adjusting a deteriorated portion of the structure; and bonding a covering sheet according to an embodiment of the present disclosure to the adjusted adherend, thereby covering the adherend with the covering sheet.

[0007] According to the present disclosure, inspection of adherends can be facilitated.

[0008] FIG. 1A is a diagram for explaining one embodiment, and is a cross-sectional view showing an example of a structure. FIG. 1B is a cross-sectional view showing another example of a structure. FIG. 1C is a cross-sectional view showing yet another example of a structure. FIG. 2A is a cross-sectional view showing an example of a cover sheet that can be included in the structure shown in FIG. 1A. FIG. 2B is a cross-sectional view showing an example of a cover sheet that can be included in the structure shown in FIG. 1B. FIG. 2C is a cross-sectional view showing another example of a cover sheet that can be included in the structure shown in FIG. 1A. FIG. 3 is a diagram for explaining a method for measuring the storage modulus of a bonding layer. FIG. 4A is a diagram for explaining a method for repairing a structure. FIG. 4B is a diagram for explaining a method for repairing a structure. FIG. 4C is a diagram for explaining a method for repairing a structure. FIG. 4D is a diagram for explaining a method for repairing a structure. FIG. 5 is a cross-sectional view showing yet another example of a structure.

[0009] One embodiment of the present disclosure relates to the following <1> to <17>.

[0010] <1> A covering sheet used to cover an adherend, comprising a first surface and a second surface, the first surface facing away from the adherend, a total light transmittance of 70% or more, an image clarity of 5.0% or more as measured by a transmission method using an optical comb having a width of 2.0 mm, a specular gloss of 30 or less on the first surface at an incident angle of 60°, and a maximum spectral transmittance of 1.0% or less in the wavelength range of 300 nm to 350 nm.

[0011] <2> A covering sheet used to cover steel materials, comprising a first surface and a second surface, the first surface facing away from the steel material, a total light transmittance of 70% or more, an image clarity of 5.0% or more as measured by a transmission method using an optical comb having a width of 2.0 mm, a specular gloss of 30 or less on the first surface at an incident angle of 60°, and a maximum spectral transmittance of 1.0% or less in the wavelength range of 300 nm or more and 350 nm or less.

[0012] <3> The cover sheet according to <1> or <2>, wherein the image clarity is 40% or less when measured by a reflection method using an optical comb having a width of 1.0 mm at an incident angle of 45°.

[0013] <4> The cover sheet according to any one of <1> to <3>, wherein the image clarity is 30% or less when measured by a reflection method using an optical comb with a width of 1.0 mm at an incident angle of 60°.

[0014] <5> The coating sheet according to any one of <1> to <4>, wherein the transmission haze is 97% or less.

[0015] <6> The application sheet according to any one of <1> to <5>, including, in this order from the second surface to the first surface, a substrate and a weather-resistant layer, wherein the substrate includes a polyolefin.

[0016] <7> The coating sheet according to any one of <1> to <6>, including, in this order from the second surface to the first surface, a substrate and a weather-resistant layer, wherein the weather-resistant layer includes a cured product of an electron beam-curable resin composition.

[0017] <8> The application sheet according to any one of <1> to <7>, including, in this order from the second surface to the first surface, a barrier layer and a weather-resistant layer, wherein the weather-resistant layer includes an ultraviolet absorber.

[0018] <9> The water vapor permeability in an environment of 40°C temperature and 90% RH is 6.0 g / (m ２ <1> - <8> The application sheet according to any one of <1> to <8>, wherein the application time is 100 minutes or less.

[0019] <10> The application sheet according to any one of <1> to <9>, wherein the weather-resistant layer contains an ultraviolet absorber.

[0020] <11> The application sheet according to any one of <1> to <10>, wherein after a 408-hour weather resistance test, the total light transmittance is 70% or more, and the maximum spectral transmittance in the wavelength range of 300 nm to 350 nm is 1.0% or less.

[0021] <12> The application sheet according to any one of <1> to <11>, including, in this order from the second surface to the first surface, a bonding layer and a substrate.

[0022] <13> A cover sheet with a release film, comprising: the cover sheet according to any one of <1> to <12>; and a release film laminated on the cover sheet.

[0023] <14> A structure comprising the adherend and the covering sheet according to any one of <1> to <12>.

[0024] <15> A steel structure comprising the adherend and the covering sheet according to any one of <1> to <12>.

[0025] <16> A method for repairing a structure, comprising: a step of adjusting a deteriorated portion of the structure; and a step of covering the adjusted adherend with the covering sheet according to any one of <1> to <12>.

[0026] <17> A method for repairing a steel structure, comprising: a step of performing a surface preparation on a deteriorated part of the steel structure; and a step of covering the surface-prepared steel material with the covering sheet according to any one of <1> to <12>.

[0027] The present embodiment will be described in detail below. In the drawings accompanying this specification, the scale and aspect ratios have been appropriately changed and exaggerated from those of the actual objects for the sake of ease of understanding.

[0028] In this specification, terms such as "film," "sheet," and "plate" are not distinguished from one another solely on the basis of differences in name. For example, a "repair sheet" cannot be distinguished solely from a member called a repair film or a repair plate.

[0029] In this specification, the normal direction of a film-like (sheet-like, plate-like) member refers to a direction parallel to the normal or perpendicular to the film surface (sheet surface, plate surface) of the target film-like (sheet-like, plate-like) member. The "film surface (sheet surface, plate surface)" refers to the surface that coincides with the target film-like (sheet-like, plate-like) member when the target film-like (sheet-like, plate-like) member is viewed overall and in a broad perspective. Figures 1A to 2C all show cross sections along the normal direction of the covering sheet.

[0030] In this specification, multiple upper limit candidate values ​​and multiple lower limit candidate values ​​for a numerical range may be described in separate sentences. In this description, the numerical range may be constructed by combining any one upper limit candidate value and any one lower limit candidate value. As an example, consider the description, "Parameter B may be A1 or more, A2 or more, or A3 or more. Parameter B may be A4 or less, A5 or less, or A6 or less." In this example, the numerical range of parameter B may be A1 or more and A4 or less, A1 or more and A5 or less, A1 or more and A6 or less, A2 or more and A4 or less, A2 or more and A5 or less, A2 or more and A6 or less, A3 or more and A4 or less, A3 or more and A5 or less, or A3 or more and A6 or less.

[0031] <<<Structure>>> As shown in Figures 1A to 1C, the structure 10 includes an adherend 20 and a covering sheet 30. The structure 10 is an adherend with a covering sheet. The covering sheet 30 is used to cover the adherend 20. The covering sheet 30 includes a first side 31 and a second side 32. The second side 32 faces the adherend 20. The first side 31 faces away from the adherend 20. The first side 31 may constitute the surface 11 of the structure 10.

[0032] 1A includes an adherend 20 and a covering sheet 30 in this order in the stacking direction. The covering sheet 30 is directly bonded to the adherend 20. A second surface 32 of the covering sheet 30 is in contact with the adherend 20.

[0033] In the example shown in Fig. 1B, the structure 10 includes an adherend 20, a bonding layer 15, and a covering sheet 30, in this order in the stacking direction. The bonding layer 15 is located between the adherend 20 and the covering sheet 30 in the stacking direction. The bonding layer 15 is in contact with the adherend 20 and the covering sheet 30. The bonding layer 15 is bonded to the adherend 20 and the covering sheet 30. The structure 10 shown in Fig. 1B differs from the example shown in Fig. 1A in that it includes the bonding layer 15. The structure 10 shown in Fig. 1B can otherwise be configured similarly to the structure 10 shown in Fig. 1A.

[0034] In order to distinguish the bonding layer 15 from bonding layers 43 and 45 included in the covering sheet 30 and described below, the bonding layer 15 may be hereinafter referred to as a third bonding layer.

[0035] In the example shown in Fig. 1C, the structure 10 includes an adherend 20, an anti-corrosion layer 18, a bonding layer 15, and a coating sheet 30, in this order in the stacking direction. The anti-corrosion layer 18 is located between the adherend 20 and the bonding layer 15 in the stacking direction. The anti-corrosion layer 18 is in contact with the adherend 20 and the bonding layer 15. The structure 10 shown in Fig. 1C differs from the example shown in Fig. 1B in that it includes the anti-corrosion layer 18. The structure 10 shown in Fig. 1C may otherwise be configured similarly to the structure 10 shown in Fig. 1B.

[0036] In the example shown in FIG. 1C , the bonding layer 15 may be omitted. Alternatively, the structure 10 shown in FIG. 1A may include the anticorrosive layer 18 shown in FIG. 1C . The structure 10 is not limited to the examples shown in FIGS. 1A to 1C , and may include additional layers. As an example, as shown by the two-dot chain line in FIG. 1C , the structure 10 may include a top coat layer 19 that forms the outermost layer. In this example, the covering sheet 30 may be located between the top coat layer 19 and the adherend 20 in the stacking direction. The top coat layer 19 may have one or more of the functions expected of an outermost layer, such as barrier properties, weather resistance, scratch resistance, strength, etc.

[0037] The structure 10 is a structure including an adherend 20. The structure 10 may be real estate. The structure 10 may be personal property or an article. The adherend 20 may be a steel material. The structure 10 may be a steel structure including a steel material as the adherend 20. The adherend 20 that is a steel material may constitute the base material of the structure 10.

[0038] Examples of structures 10 that include steel materials as adherends 20 include bridges, bridge piers, steel towers, steel pipes, chimneys, tanks, plants, pipelines, rolled plates, roofs, vending machines, cubicles (high-voltage power receiving equipment), metal housings such as photo booths, signboards, adherend panels, and mobile objects (movable objects such as automobiles, ships, vehicles, airplanes, drones, etc.). The structures may be, for example, architectural structures or civil engineering structures.

[0039] Examples of the steel adherend 20 include alloy steels such as nickel-chromium steel, nickel-chromium-molybdenum steel, chromium steel, chromium-molybdenum steel, and manganese steel, as well as carbon steel. The steel adherend 20 may be corroded by corrosion factors such as water and oxygen. The steel adherend 20 may include rusted portions on its surface due to corrosion. Rust may be formed, for example, by iron oxide (Fe ２ O ３ The portion of the adherend 20 made of steel where an abnormality such as a rusted portion occurs constitutes the deteriorated portion 12 of the structure 10.

[0040] The structure 10 may include a coating film that covers the adherend 20, which is a steel material. The coating film may be provided for the purpose of suppressing deterioration of the adherend 20, which is a steel material. An example of a coating film is the anti-corrosion layer 18 shown in FIG. 1C. The coating film may develop defects such as cracks and blisters due to aging or construction or repair work performed on the structure. Portions of the coating film where defects such as cracks and blisters have occurred also constitute deteriorated portions 12 of the structure.

[0041] The adherend 20 is not limited to steel. The covering sheet 30 covering the adherend 20 is weather resistant. Therefore, the adherend 20 may be a structure exposed to ultraviolet rays and the like. The adherend 20 exposed to ultraviolet rays and the like may deteriorate over time. The covering sheet 30 can suppress the deterioration over time of the adherend 20 exposed to ultraviolet rays and the like. Examples of the adherend 20 exposed to ultraviolet rays include an adherend placed outdoors and an adherend placed near an opening (window) of a structure such as a building.

[0042] Specific examples of the adherend 20 other than steel are shown below. For example, the adherend 20 may be wood for decoration or partitioning. The adherend 20 may be a wall. The adherend 20 may be an exterior wall. The wall or exterior wall constituting the adherend 20 may be a wooden wall or may have a surface layer of melamine resin. The adherend 20 may be a signboard, signage, or a wrapping film attached to a moving object (e.g., an automobile or airplane). The adherend 20 may be a panel material, for example, an aluminum composite panel. The adherend 20 may be a transparent glass window (particularly the outer surface of a glass window) or a transparent plastic window (particularly the outer surface of a plastic window). A metal adherend 20 may deteriorate over time due to corrosion. A wooden adherend 20 may deteriorate over time due to corrosion or mold growth. The adherend 20, including decorations or displays, may change color.

[0043] The covering sheet 30 is used to cover the adherend 20. The adherend 20 may deteriorate over time. The covering sheet 30 may protect the adherend 20 by covering the adherend 20. The covering sheet 30 may suppress deterioration of the adherend 20. The covering sheet 30 may be laminated on the adherend 20 when the structure 10 is newly constructed. The covering sheet 30 may be used to repair a structure 10 having a deteriorated portion 12. The covering sheet 30 used for repair may be laminated on a portion of the structure 10 from which the deteriorated portion 12 has been removed.

[0044] <<<Covering Sheet>>> The covering sheet 30 according to this embodiment is devised to facilitate inspection of the adherend 20 .

[0045] For example, the steel material constituting the adherend 20 deteriorates over time due to corrosion. The deteriorated steel material becomes a defect that can significantly reduce the strength of the steel structure. For this reason, the steel material is laminated with multiple coating films to suppress corrosion. Examples of the coating films include multiple primer layers containing epoxy resin, an intermediate coating layer containing fluorine-based resin, and a top coating layer containing fluorine-based resin.

[0046] Steel structures are inspected periodically. If defects are found during the inspection, the steel is repaired. In the past, corrective maintenance was carried out after a serious defect was discovered, and then extensive repairs were carried out.

[0047] Preventive maintenance has been gaining attention recently. In preventive maintenance, repairs are made to deteriorated steel parts before they develop into serious defects. Preventive maintenance is carried out more frequently than corrective maintenance. However, a single preventive maintenance job is significantly easier than corrective maintenance. Unlike corrective maintenance, preventive maintenance does not require a high level of skill.

[0048] The aforementioned Patent Document 1 (JP2020-179569A) discloses a laminate including a fluorine-based resin layer. Patent Document 1 proposes that preventive maintenance be facilitated by using the laminate.

[0049] Steel materials are covered with multiple layers of paint. To prevent forgetting to paint, the paint is usually colored. Therefore, it is not easy to detect slight deterioration of the steel material underneath the multiple layers of paint.

[0050] Patent Document 1 proposes adjusting the transmittance of the laminate to observe the steel material through the laminate. However, steel structures are usually placed outdoors. Under sunlight, the laminate may reflect more light than the steel material. Due to reflections from the laminate, deterioration of the steel material cannot be easily detected through the laminate of Patent Document 1. In other words, even if preventive maintenance is adopted, the conventional technology does not allow easy inspection of the adherend.

[0051] For adherends other than steel materials (for example, the specific examples described above), it is useful for effectively implementing preventive maintenance that the condition of the adherend and any defects that have occurred in the adherend 20 can be easily detected through the covering sheet. Adherends such as wood, walls, exterior walls, wrapping films, panel materials, glass windows, and plastic windows are originally intended to enable observation of the adherend itself and the area behind the adherend. Therefore, the covering sheet 30 that covers these adherends 20 must be transparent.

[0052] As will be described below, according to the covering sheet 30 of this embodiment, an abnormality occurring in the adherend 20 can be easily and stably detected through the covering sheet 30 covering the adherend 20. This makes it easy to inspect the adherend 20.

[0053] Specifically, the covering sheet 30 according to this embodiment has the following features (A) to (D). The combination of features (A) to (D) allows for easy and stable detection of abnormalities occurring in the adherend 20 through the covering sheet 30 covering the adherend 20. This facilitates inspection of the adherend 20. Feature (A): Total light transmittance is 70% or more. Feature (B): The specular gloss of the first surface at an incident angle of 60° is 30 or less. Feature (C): The image clarity is 5.0% or more in a transmission method using an optical comb with a width of 2.0 mm. Feature (D): The maximum spectral transmittance at a wavelength of 300 nm or more and 350 nm or less is 1.0% or less.

[0054] According to the feature (A), the state of the adherend 20 can be easily observed through the covering sheet 30 .

[0055] According to the feature (B), it is possible to suppress reflection of external images on the covering sheet 30. The structure 10 can be installed outdoors. Inspection of the structure 10 can be performed under sunlight. A large amount of light can be incident on the covering sheet 30 and reflected by the covering sheet 30. According to the covering sheet 30 having the feature (B) in combination with the feature (A), it is possible to effectively suppress reflection of external images on the covering sheet 30. Therefore, it is possible to suppress reflection of external images, which makes it difficult to observe abnormalities occurring on the adherend 20 through the covering sheet 30, by the feature (B) in combination with the feature (A). Examples of external images include an image of the sun and an image of an object reflecting sunlight.

[0056] Furthermore, according to feature (C) obtained by combining feature (A) and feature (B), the state of the adherend 20 covered with the covering sheet 30 can be clearly observed through the covering sheet 30. Therefore, any abnormality occurring in the adherend 20 can be easily and stably detected through the covering sheet 30.

[0057] According to the feature (D), deterioration of the covering sheet 30 can be suppressed. The covering sheet 30 is intended to be installed outdoors. The covering sheet 30 having the feature (D) is suppressed from deterioration due to strong ultraviolet rays contained in sunlight. Therefore, the feature (D) can suppress the deterioration of the covering sheet 30, which makes it difficult to observe abnormalities occurring in the adherend 20 on the structure 10 through the covering sheet 30.

[0058] As described above, the covering sheet 30 having the features (A) to (D) can make it easier to discover abnormalities in the adherend 20. In other words, the combination of the features (A) to (D) can make it easier to inspect the adherend 20.

[0059] Structures such as steel structures are inspected periodically. If defects are found during inspection, the steel or other adherends are repaired. In conventional corrective maintenance, large-scale repairs were carried out after a serious defect that reached the outermost layer of a structure such as a steel structure had occurred, or after a long period of time had passed since installation or the previous repair. This type of maintenance method is called corrective maintenance. A single corrective repair takes a long time to complete. Corrective repairs are difficult to carry out. Corrective repairs require a high level of skill. The construction costs and arrangement of construction workers for corrective maintenance are becoming serious issues.

[0060] Under these circumstances, preventive maintenance is attracting attention. In preventive maintenance, repairs are carried out on deteriorated parts of structures such as steel structures before they develop serious defects. The number of preventive maintenance works is greater than that of corrective maintenance. However, a single preventive maintenance work is significantly easier than corrective maintenance. Unlike corrective maintenance, preventive maintenance does not require a high level of skill.

[0061] As described above, the combination of features (A) to (D) can facilitate the inspection of the structure 10, such as a steel structure. In particular, even minor abnormalities before they become serious defects can be reliably detected through the covering sheet 30. Therefore, the combination of features (A) to (D) can improve the effectiveness of preventive maintenance. The effect of improving the effectiveness of preventive maintenance for the structure 10, such as a steel structure, by such a combination of features (A) to (D) can be said to be a unique or remarkable effect that goes beyond the range predicted from the state of the art.

[0062] <<Feature (A)>> Feature (A) defines the total light transmittance of the covering sheet 30. The total light transmittance is an index showing the ease of transmission of light incident on the covering sheet 30 from the front direction. When the total light transmittance is high, light incident from the front direction is easily transmitted through the covering sheet 30. The total light transmittance also serves as an index showing the difficulty of reflection of light incident on the covering sheet 30 from the front direction. When the total light transmittance is low, light incident from the front direction is less likely to be reflected by the covering sheet 30.

[0063] Setting a lower limit for the total light transmittance of the covering sheet 30 makes it easier for light incident on the covering sheet 30 to pass through the covering sheet 30. Setting a lower limit for the total light transmittance of the covering sheet 30 makes it difficult for light incident on the covering sheet 30 to be reflected by the covering sheet 30. As a result, setting a lower limit for the total light transmittance of the covering sheet 30 makes it easier to inspect the adherend 20, such as a steel material, through the covering sheet 30.

[0064] The total light transmittance of the covering sheet 30 is 70% or more, or may be 80% or more, or 85% or more. The total light transmittance of the covering sheet 30 does not have a particular upper limit. The total light transmittance of the covering sheet 30 may be 100% or less, or may be less than 100%. The total light transmittance of the covering sheet 30 is 70% or more and 100% or less, or may be 80% or more and 100% or less, or may be 85% or more and 100% or less. The total light transmittance of the covering sheet 30 is 70% or more and less than 100%, or may be 80% or more and less than 100%, or may be 85% or more and less than 100%.

[0065] A D65 light source is used to measure the total light transmittance. Before measuring the total light transmittance of the covering sheet 30, the D65 light source is turned on for 15 minutes to stabilize the output of the D65 light source. The angle of incidence on the sample when measuring the total light transmittance is 0°. The incident surface when measuring the total light transmittance is the first surface 31 of the covering sheet 30. The test environment when measuring the total light transmittance is a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The sample is placed in the test environment for 16 hours before starting the test. Other measurement conditions when measuring the total light transmittance are in accordance with JIS K7361-1:1997.

[0066] The total light transmittance is the arithmetic mean value of five measured values. The five measured values ​​are measured at five measurement positions on the covering sheet 30 to be evaluated. The five measurement positions are located 10 mm or more apart from each other.

[0067] <<Feature (B)>> Feature (B) defines the specular glossiness (%) of the covering sheet 30. The specular glossiness is an index indicating the degree of reflection of an external image.

[0068] The present inventors have confirmed that physical properties such as specular reflectance and total light reflectance do not adequately reflect the degree of reflection on the covering sheet 30, which adversely affects the observation of the adherend 20. On the other hand, the specular glossiness of the first surface 31 exhibits a strong correlation with the degree of reflection on the covering sheet 30 covering the adherend 20, such as a steel material. In particular, feature (B) in combination with feature (A) enables the degree of reflection on the covering sheet 30 to be accurately evaluated by the specular glossiness at an incident angle of 60°.

[0069] Feature (A) sets a lower limit for the total light transmittance. Therefore, glare caused by light incident from the front direction can be suppressed. On the other hand, unlike a sample that can be held in the hand and observed, the adherend 20, such as a steel material of the structure 10, often cannot be freely selected from the observation direction. As the observation angle increases, the amount of specularly reflected light in the observation direction also increases. Feature (B), which specifies the upper limit for the specular gloss Gs(60) at an incident angle of 60°, can suppress glare on the covering sheet 30 when the observation angle increases.

[0070] The incident angle is the angle (°) between the normal direction to the incident object and the incident direction. The incident angle is an angle between 0° and 90°. The observation angle is the angle (°) between the normal direction to the observation object and the observation direction. The observation angle is an angle between 0° and 90°.

[0071] Setting an upper limit to the specular gloss on the first surface at an incident angle of 60° makes it possible to suppress reflection of external images that impede clear observation of the adherend 20, such as a steel material, through the covering sheet 30. The specular gloss (%) on the first surface at an incident angle of 60° may be 30 or less, 25 or less, 20 or less, or 16 or less.

[0072] There is no particular lower limit for the specular gloss of the first surface at an incident angle of 60°. The specular gloss of the first surface at an incident angle of 60° may be equal to or greater than 0.

[0073] The specular gloss of the first surface at an incident angle of 60° may be greater than or equal to 0 and less than or equal to 30, greater than or equal to 25, greater than or equal to 20, or greater than or equal to 16. The specular gloss of the first surface at an incident angle of 60° may be greater than or equal to 0 and less than or equal to 30, greater than or equal to 0 and less than or equal to 25, greater than or equal to 20, or greater than or equal to 0 and less than or equal to 16.

[0074] The specular gloss of the first surface at an incident angle of 60° can be adjusted by the manufacturing conditions, composition, materials, etc. of the layers included in the covering sheet 30, particularly the layers constituting the first surface 31. For example, by increasing the drying conditions of the coating layer, the specular gloss of the first surface at an incident angle of 60° can be reduced. By increasing the size of the additive contained in the layer, the specular gloss of the first surface at an incident angle of 60° can be reduced. By increasing the content or content ratio of the additive contained in the layer, the specular gloss of the first surface at an incident angle of 60° can be reduced.

[0075] When measuring specular gloss, a sample to be measured is placed on a black mount. The back surface (second surface 32) of the sample to be measured, which faces the incident surface (first surface 31), is in contact with the black mount, and the specular gloss is measured. The specular gloss is set to 0 when the incident angle on the surface of the black mount that contacts the sample is 60°.

[0076] The specular gloss is a value measured in accordance with JIS Z8741:1997, except that the angle of incidence is set to 60°. The measurement environment for measuring specular gloss is a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The measurement sample is placed in the measurement environment for 16 hours before starting the measurement. Before measuring the specular gloss, the light source of the measurement device is turned on for 15 minutes to stabilize the light source output.

[0077] The specular gloss is the arithmetic mean value of five measurements taken at five measurement positions on the antiglare sheet to be evaluated, the five measurement positions being at least 10 mm apart from each other.

[0078] <<Feature (C)>> Feature (C) specifies the image clarity (%) of the covering sheet 30. The image clarity in feature (C) is measured using transmitted light. The image clarity measured by the transmission method is an index indicating the clarity of the adherend 20, such as a steel material, observed through the covering sheet 30.

[0079] In feature (C), a 2.0 mm-wide optical comb is used to measure image clarity. The present inventors conducted extensive research and found that the image clarity measured by the transmission method using a 2.0 mm-wide optical comb is strongly correlated with the clarity of the adherend 20, such as a steel material, observed through the covering sheet 30. In other words, the image clarity measured by the transmission method using a 2.0 mm-wide optical comb allows for accurate evaluation of the state of the adherend 20, such as a steel material, observed through the covering sheet 30.

[0080] Feature (C) sets a lower limit to the image clarity in the transmission method using an optical comb with a width of 2.0 mm. Feature (C) allows the condition of the adherend 20, such as a steel material, to be clearly observed by the light reflected from the adherend 20. Feature (A) allows a sufficient amount of light to reach the adherend 20. As a result, feature (C) in combination with feature (A) allows any abnormalities occurring in the adherend 20, such as a steel material, to be clearly confirmed.

[0081] The image clarity in a transmission method using an optical comb with a width of 2.0 mm may be 5.0% or more, 6.0% or more, 6.2% or more, 7.0% or more, or 8.2% or more.

[0082] There is no particular upper limit to the image clarity in a transmission method using an optical comb with a width of 2.0 mm. The image clarity in a transmission method using an optical comb with a width of 2.0 mm may be 50% or less, or may be 40% or less.

[0083] The image clarity in a transmission method using an optical comb having a width of 2.0 mm may be 5.0% to 50% or less, 6.0% to 50% or less, 6.2% to 50% or less, 7.0% to 50% or less, or 8.2% to 50%. The image clarity in a transmission method using an optical comb having a width of 2.0 mm may be 5.0% to 40% or less, 6.0% to 40% or less, 6.2% to 40% or less, 7.0% to 40% or less, or 8.2% to 40%.

[0084] The image clarity in the transmission method using a 2.0 mm wide optical comb can be adjusted by adjusting the manufacturing conditions, composition, materials, etc. of the layers contained in the cover sheet 30. For example, the image clarity can be increased by weakening the drying conditions of the coating layer. The image clarity in the transmission method can be increased by reducing the amount of additives contained in the layer. The image clarity can be increased by reducing the content or content ratio of the additives contained in the layer.

[0085] Image clarity using the transmission method is measured in accordance with JIS K7374:2007. Image clarity is calculated from the measured value of the amount of light transmitted through the measurement sample. The amount of light transmitted through the measurement sample is measured after passing through an optical comb. The optical comb includes a transmitting portion and a light-blocking portion. The transmitting portion and the light-blocking portion are arranged in an arrangement direction. The transmitting portion and the light-blocking portion extend elongatedly in a direction perpendicular to the arrangement direction. The "width" of the optical comb refers to the width of the light-blocking portion along the arrangement direction (comb width). The amount of light transmitted through the measurement sample is measured while moving the optical comb in the arrangement direction. The maximum light amount M and the minimum light amount m are determined from the measured value.

[0086] Image clarity C(k) is expressed by the following formula. Image clarity is the ratio of the difference between the maximum light amount M and the minimum light amount m to the sum of the maximum light amount M and the minimum light amount m. The ratio, which is image clarity, is expressed as a percentage. The unit of image clarity is %. C(k) = {(M-m) / (M+m)} x 100 [%]

[0087] In measuring the image clarity by the transmission method, the incident surface is the second surface 32 of the cover sheet 30. The incident angle is 0°.

[0088] Before measuring image clarity using the transmission method, the light source is turned on for 15 minutes to stabilize the light source output. The measurement environment for measuring image clarity using the transmission method is a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The measurement sample is placed in the measurement environment for 16 hours before starting the measurement.

[0089] The image clarity measured by the transmission method is the arithmetic mean of five measurements taken at five measurement positions on the antiglare sheet to be evaluated. The five measurement positions are located at least 10 mm apart from each other.

[0090] <<Feature (D)>> Feature (D) sets an upper limit to the spectral transmittance in the ultraviolet wavelength range of 300 nm to 350 nm. The spectral transmittance in the ultraviolet wavelength range is an index of weather resistance.

[0091] By setting an upper limit on the maximum spectral transmittance of the covering sheet 30 at wavelengths of 300 nm or more and 350 nm or less, excellent weather resistance can be imparted to the covering sheet 30. The maximum spectral transmittance at wavelengths of 300 nm or more and 350 nm or less may be 1.0% or less, or 0.50% or less. Such a covering sheet 30 can effectively suppress ultraviolet degradation in outdoor installation applications. The covering sheet 30 can protect the adherend 20, such as steel, and the coating film for a long period of time.

[0092] There is no particular lower limit to the maximum transmittance at a wavelength of 300 nm or more and 350 nm or less through the cover sheet 30. The maximum transmittance at a wavelength of 300 nm or more and 350 nm or less through the cover sheet 30 may be 0% or more, or may be greater than 0%.

[0093] The maximum spectral transmittance at a wavelength of 300 nm or more and 350 nm or less may be 0% or more and 1.0% or less, or 0% or more and 0.50% or less.The maximum spectral transmittance at a wavelength of 300 nm or more and 350 nm or less may be greater than 0% and 1.0% or less, or greater than 0% and 0.50% or less.

[0094] The transmittance at each wavelength, i.e., the spectral transmittance, is the arithmetic mean value of five measured values ​​measured in accordance with JIS Z8722:2009. The five measured values ​​are measured at five measurement positions on a sample of the coating sheet 30 to be evaluated. The five measurement positions are located 10 mm or more apart from each other.

[0095] The spectral transmittance is measured at wavelengths of 1 nm intervals in the range of 300 nm to 350 nm. That is, the spectral transmittance is measured for light of integer wavelengths (nm) of 300 nm to 350 nm. The geometric condition f specified in JIS Z8722:2009 is adopted in the measurement of the spectral transmittance.

[0096] The incident angle on the sample when measuring the spectral transmittance is 0°. The incident surface when measuring the spectral transmittance is the first surface 31 of the cover sheet 30.

[0097] The test environment for measuring spectral transmittance is 23°C ± 2°C and 50% ± 5% relative humidity. The sample is placed in the test environment for 16 hours before the start of the test. Before measuring spectral transmittance, the light source of the measuring device is turned on for 15 minutes to stabilize the light source output.

[0098] <<Features (E1) and (E2)>> The cover sheet 30 according to this embodiment may have at least one of the following features (E1) and (E2) in addition to features (A) to (D). Feature (E1): The image clarity is 40% or less when measured by a reflection method using an optical comb with a width of 1.0 mm and an incident angle of 45°. Feature (E2): The image clarity is 30% or less when measured by a reflection method using an optical comb with a width of 1.0 mm and an incident angle of 60°.

[0099] Feature (E1) and Feature (E2) define the image clarity (%) of the covering sheet 30. The image clarity in Feature (E1) and Feature (E2) is measured using reflected light. Image clarity measured by the reflection method is an index showing the clarity of the reflected external image. Feature (B) described above can suppress the reflection of the external image. Feature (E1) or Feature (E2) combined with Feature (B) can further reduce the clarity of the reflected image. This can prevent the reflection of the external image from interfering with clear observation of the adherend 20, such as a steel material, through the covering sheet 30.

[0100] In features (E1) and (E2), an optical comb with a width of 1.0 mm is used to measure image clarity. The present inventors conducted extensive research and found that the image clarity measured by the reflection method using an optical comb with a width of 1.0 mm is strongly correlated with the clarity of the external image reflected in the covering sheet 30. In other words, the image clarity measured by the reflection method using an optical comb with a width of 1.0 mm can accurately evaluate the clarity of the external image reflected in the covering sheet 30.

[0101] According to feature (E1), an upper limit for image clarity is set in a reflection method using an optical comb with a width of 1.0 mm and an incident angle of 45°. Feature (E1) reduces the clarity of external image reflection. Therefore, it is possible to prevent the external image reflection from adversely affecting the visibility of the adherend 20, such as a steel material. The image clarity in a reflection method using an optical comb with a width of 1.0 mm and an incident angle of 45° may be 40% or less, 31% or less, 30% or less, 27% or less, or 25% or less.

[0102] There is no particular lower limit for the image clarity in a reflection method using an optical comb with a width of 1.0 mm and an incident angle of 45°. The image clarity in a reflection method using an optical comb with a width of 1.0 mm and an incident angle of 45° may be equal to or greater than 0.

[0103] The image clarity in a reflection method using an optical comb with a width of 1.0 mm and an incident angle of 45° may be 0 to 40% or less, 0 to 31% or less, 0 to 30% or less, 0 to 27% or less, or 0 to 25%. The image clarity in a reflection method using an optical comb with a width of 1.0 mm and an incident angle of 45° may be 0 to 40% or less, 0 to 31% or less, 0 to 30% or less, 0 to 27% or less, or 0 to 25%.

[0104] According to feature (E2), an upper limit is set for image clarity in a reflection method using an optical comb with a width of 1.0 mm and an incident angle of 60°. Feature (E) makes it possible to reduce the clarity of external image reflection. Therefore, it is possible to prevent the external image reflection from adversely affecting the visibility of the adherend 20, such as a steel material. The image clarity in a reflection method using an optical comb with a width of 1.0 mm and an incident angle of 60° may be 30% or less, 25% or less, 20% or less, 17% or less, or 16% or less.

[0105] There is no particular lower limit for the image clarity in a reflection method using an optical comb with a width of 1.0 mm and an incident angle of 60°. The image clarity in a reflection method using an optical comb with a width of 1.0 mm and an incident angle of 60° may be equal to or greater than 0.

[0106] The image clarity in a reflection method using an optical comb with a width of 1.0 mm and an incident angle of 60° may be 0 to 30% or less, 0 to 25% or less, 0 to 20% or less, 0 to 17% or less, or 0 to 16%. The image clarity in a reflection method using an optical comb with a width of 1.0 mm and an incident angle of 60° may be 0 to 30% or less, 0 to 25% or less, 0 to 20% or less, 0 to 17% or less, or 0 to 16%.

[0107] The incident angle in characteristic (E2) is larger than that in characteristic (E1). In applications where the observation angle of the covering sheet 30 may be small during maintenance of the adherend 20 such as a steel material, characteristic (E1) may be satisfied, or both characteristic (E1) and characteristic (E2) may be satisfied. In applications where the observation angle may be large during maintenance, characteristic (E2) may be satisfied, or both characteristic (E2) and characteristic (E1) may be satisfied.

[0108] When measuring image clarity using the reflection method, the sample to be measured is placed on a black mount. The back surface (second surface 32) of the sample to be measured, opposite the incident surface (first surface 31), is in contact with the black mount, and the specular gloss is measured. The specular gloss is set to 0 when the incident angle on the surface of the black mount that is in contact with the sample to be measured is 60°.

[0109] The image clarity using the reflection method is measured in accordance with JIS K7374:2007. The image clarity is calculated from the measured value of the amount of light reflected by the measurement sample. The amount of light reflected by the measurement sample is measured after passing through an optical comb. The amount of light transmitted through the measurement sample is measured while moving the optical comb in the arrangement direction. From the measured values, the maximum light amount M and the minimum light amount m are identified.

[0110] Image clarity C(k) by the reflection method is expressed by the following formula, just like image clarity by the transmission method. Image clarity is the ratio of the difference between the maximum light amount M and the minimum light amount m to the sum of the maximum light amount M and the minimum light amount m. The ratio, which is image clarity, is expressed as a percentage. The unit of image clarity is %. C(k) = {(M - m) / (M + m)} x 100 [%]

[0111] In measuring the image clarity by the reflection method, the incident surface is the first surface 31 of the cover sheet 30 .

[0112] Before measuring image clarity using the reflection method, the light source is turned on for 15 minutes to stabilize the light source output. When measuring image clarity using the transmission method, the measurement environment is set to a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The measurement sample is placed in the measurement environment for 16 hours before starting the measurement.

[0113] The image clarity measured by the reflection method is the arithmetic mean of five measurements taken at five measurement positions on the antiglare sheet to be evaluated. The five measurement positions are located at least 10 mm apart from each other.

[0114] <<Feature (F)>> In addition to the features (A) to (D), the covering sheet 30 according to this embodiment may have the following feature (F): Feature (F): The covering sheet 30 has a transmission haze of 97% or less.

[0115] The characteristic (F) defines the transmission haze of the covering sheet 30. The transmission haze is an index showing how easily an abnormality in the adherend 20, such as a steel material, can be detected when observing the covering sheet 30 through transmission.

[0116] Setting an upper limit for the transmission haze of the covering sheet 30 makes it easier to inspect the adherend 20, such as a steel material, through the covering sheet 30. The transmission haze of the covering sheet 30 may be 97% or less, 90% or more, 86% or more, or 85% or more. It may be 80% or less, or 75% or less. The transmission haze of the covering sheet 30 does not have a particular lower limit. The transmission haze of the covering sheet 30 may be 0% or more, or may be greater than 0%.

[0117] The transmission haze of the covering sheet 30 may be 0% or more and 97% or less, 0% or more and 90% or more, 0% or more and 86% or more, or 0% or more and 85% or more, 0% or more and 80% or less, or 0% or more and 75% or less. The transmission haze of the covering sheet 30 may be greater than 0% and 97% or less, greater than 0% and 90% or more, greater than 0% and 86% or more, or greater than 0% and 85% or more, greater than 0% and 80% or less, or greater than 0% and 75% or less.

[0118] A D65 light source is used to measure the transmission haze. Before measuring the transmission haze of the covering sheet 30, the D65 light source is turned on for 15 minutes to stabilize the output of the D65 light source. The incident angle to the sample when measuring the transmission haze is 0°. The incident surface when measuring the transmission haze is the second surface 32 of the covering sheet 30. The test environment when measuring the transmission haze is a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The sample is placed in the test environment for 16 hours before starting the test. Other measurement conditions when measuring the transmission haze are in accordance with JIS K7136:2000.

[0119] The transmission haze is the arithmetic mean value of five measured values. The five measured values ​​are measured at five measurement positions on the cover sheet 30 to be evaluated. The five measurement positions are located 10 mm or more apart from each other.

[0120] <<Feature (G)>> The covering sheet 30 according to this embodiment may have the following feature (G) in addition to features (A) to (D). Feature (G) relates to the physical properties of the covering sheet 30 after a long period of time has elapsed. Feature (G): After a 408-hour weather resistance test, (G1) the total light transmittance is 70% or more. (G2) the maximum transmittance at a wavelength of 300 nm or more and 350 nm or less is 1.0% or less.

[0121] The surface of the covering sheet 30 may become roughened after being placed outdoors for a long period of time. The covering sheet 30 may discolor after being placed outdoors for a long period of time. As a result, the total light transmittance of the covering sheet 30 may decrease after being placed outdoors for a long period of time. On the other hand, by imparting high strength and excellent weather resistance to the covering sheet 30, the decrease in the total light transmittance of the covering sheet 30 over time after a long period of time can be suppressed. This allows the characteristic (G1) to be realized. That is, as defined in the characteristic (G1), the covering sheet 30 maintains a total light transmittance of a certain level or higher even after a long period of time has passed. According to the characteristic (G1), the condition of the adherend 20, such as a steel material, can be easily observed through the covering sheet 30 after a long period of time has passed.

[0122] The weather resistance of the covering sheet 30 installed outdoors for a long period of time may be reduced due to the bleed-out of additives such as ultraviolet absorbers. On the other hand, the covering sheet 30 having high strength can suppress the bleed-out of additives. This allows the characteristic (G2) to be realized. That is, as defined in the characteristic (G2), the covering sheet 30 can maintain high ultraviolet light blocking properties even after a long period of time has passed. The weather resistance of the covering sheet 30 can be maintained even after a long period of time has passed. The deterioration of the covering sheet 30 due to installation outdoors over a long period of time can be suppressed.

[0123] As described above, the covering sheet 30 having the feature (G) makes it easier to detect abnormalities in the adherend 20, such as steel materials, over a long period of time. That is, feature (G) makes it easier to inspect the adherend 20, such as steel materials, over a long period of time. Therefore, even minor abnormalities before they develop into serious defects can be stably detected through the covering sheet 30 over a long period of time. This makes it possible to maintain a high level of effectiveness in preventive maintenance for the structure 10, such as a steel structure.

[0124] The 408-hour weather resistance test specified in feature (G) is carried out as follows. The weather resistance test is carried out using a weather resistance test device. The coating sheet 30 to be evaluated is subjected to a cycle of a 20-hour irradiation step and a 4-hour condensation step, which is repeated until 408 hours are reached. A 30-second shower step is carried out after the irradiation step and before the condensation step is started, and after the condensation step and before the irradiation step is started. In the shower step, the sample held in the weather resistance test device is exposed to a shower of water.

[0125] The weather resistance test equipment used is the "Eye Super UV Tester SUV-W261", an ultra-accelerated weather resistance test equipment manufactured by Iwasaki Electric Co., Ltd. The UV lamp, lamp jacket, and illuminance meter included in the weather resistance test equipment are 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. Illuminance meter: Product name: UVD-365PD, manufactured by Iwasaki Electric Co., Ltd.

[0126] The conditions for the irradiation process are as follows: <Irradiation conditions> Black panel temperature: 63°C Illuminance: 100 mW / cm２ ・Inside tank humidity: 50%RH ・Time: 20 hours

[0127] The conditions for the condensation process are as follows: <Irradiation conditions> Black panel temperature: 30°C Illuminance: 0 mW / cm 2 ・Humidity inside the tank: 98%RH ・Time: 4 hours

[0128] <<Layer Configuration of Covering Sheet>> As shown in Fig. 2A , the covering sheet 30 may include, in this order from the second surface 32 to the first surface 31 in the stacking direction, a bonding layer 43, a substrate 41, and a weather-resistant layer 42. The covering sheet 30 shown in Fig. 2A may be included in the structure 10 shown in Fig. 1A. In the example shown in Fig. 2A , the weather-resistant layer 42 constitutes the first surface 31. The bonding layer 43 constitutes the second surface 32. The bonding layer 43 may be in contact with the adherend 20. The bonding layer 43 may be bonded to the adherend 20.

[0129] As shown in Fig. 2B , the bonding layer 43 may be omitted. As shown in Fig. 2B , the covering sheet 30 may include a substrate 41 and a weather-resistant layer 42 in this order from the second surface 32 to the first surface 31 in the stacking direction. The covering sheet 30 shown in Fig. 2B may be included in the structure 10 shown in Fig. 1A. The covering sheet 30 shown in Fig. 2B may be included in the structure 10 shown in Figs. 1B and 1C. In the example shown in Figs. 1B and 1C , the covering sheet 30 is bonded to the adherend 20 by the bonding layer 15. The covering sheet 30 may be welded to the adherend 20 without using a bonding layer.

[0130] As shown in Fig. 2C , the covering sheet 30 may include a barrier layer 44. The covering sheet 30 may include, in this order from the second surface 32 to the first surface 31 in the stacking direction, the barrier layer 44 and a substrate 41. The covering sheet 30 shown in Fig. 2C includes, in this order from the second surface 32 to the first surface 31 in the stacking direction, a bonding layer 43, a barrier layer 44, a second bonding layer 45, a substrate 41, and a weathering layer 42. The covering sheet 30 shown in Fig. 2C can be included in the structure 10 shown in Fig. 1A. In the example shown in Fig. 2C , the bonding layer 43 and the second bonding layer 45 may be omitted.

[0131] Each layer that may be included in the covering sheet 30 will now be described in further detail.

[0132] <Substrate> The substrate 41 may be a resin film. Examples of resin materials constituting the substrate 41 include polyolefins such as polyethylene and polypropylene, polyvinyl chloride, vinylidene chloride-vinyl chloride copolymer, polyesters such as polyethylene terephthalate, polycarbonate, polyarylate, styrene resin, acrylic resin, acrylic urethane resin, urethane resin, fluororesin, acetyl cellulose, polyamide, and polyimide. The substrate 41 may be a single layer or a multilayer. The substrate 41 may be a laminated film of resin films.

[0133] The substrate 41 may have a cellular structure (cell structure). The cellular structure (cell structure) may be a closed-cell structure, an open-cell structure, or a semi-open / semi-closed-cell structure in which a closed-cell structure and an open-cell structure are mixed. A foam layer is an example of the substrate 41 having a cellular structure. More specifically, examples of the substrate 41 include acrylic resin foam (acrylic foam), urethane resin foam (urethane foam), polyolefin foam, and rubber foams including acrylic rubber and other elastomers.

[0134] The substrate 41 may contain additives. Examples of additives include pigments, dyes, colorants, antistatic agents, flame retardants, antifungal agents, plasticizers, leveling agents, flow control agents, antifoaming agents, and dispersants. The substrate 41 may also contain weather resistance agents such as ultraviolet absorbers, antioxidants, and light stabilizers. A substrate 41 containing a weather resistance agent has excellent weather resistance. Since the substrate 41 has weather resistance, the overcoat layer described below may be made thinner, or the overcoat layer may be omitted.

[0135] The thickness of the substrate 41 may be determined taking into consideration the finish after repair of a structure such as a steel structure, i.e., the finish after the covering sheet 30 is applied to the adherend 20 such as a steel material, the handleability and ease of application of the covering sheet 30, etc. The thickness of the substrate 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 substrate 41 may be 5000 μm or less, 4000 μm or less, 3000 μm or less, 2000 μm or less, or 1000 μm or less. The thickness of the substrate 41 may be 10 μm or more and 5000 μm or less, or 100 μm or more and 1000 μm or less.

[0136] The substrate 41 may include a fiber-reinforced resin layer. The fiber-reinforced resin layer can improve the impact resistance of the substrate 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 for the substrate 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) shape. The fiber-reinforced resin layer may include glass mesh as a reinforcing fiber.

[0137] 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. Setting the thickness of the fiber reinforced resin layer in this manner can impart impact resistance to the covering sheet 30. The thickness of the fiber reinforced resin layer may be 50 μm or more and 550 μm or less, or 150 μm or more and 450 μm or less.

[0138] The substrate 41 may include a laminate including a fiber-reinforced resin layer and a resin layer. The substrate 41 may include a laminate including a first resin layer, a fiber-reinforced resin layer, and a second resin layer. Examples of resin materials constituting the resin layer, the first resin layer, and the second resin layer include the resin materials that can be used for the substrate 41 described above. The laminate included in the substrate 41 may include a fiber-reinforced resin layer including polyethylene and a glass mesh, and a polyethylene layer. The laminate included in the substrate 41 may include a first polyethylene layer, a fiber-reinforced resin layer including polyethylene and a glass mesh, and a second polyethylene layer.

[0139] The thickness of the resin layer, the first resin layer, and the second resin layer may each 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 resin layer, the first resin layer, and the second resin layer may each be 1000 μm or less, 800 μm or less, 600 μm or less, 500 μm or less, or 400 μm or less.

[0140] The thickness of the resin layer may be 10 μm or more and 1000 μm or less, or 100 μm or more and 400 μm or less. The thickness of the first resin layer may be 10 μm or more and 1000 μm or less, or 100 μm or more and 400 μm or less. The thickness of the second resin layer may be 10 μm or more and 1000 μm or less, or 100 μm or more and 400 μm or less.

[0141] <Weather-resistant Layer> The weather-resistant layer 42 is a layer having weather resistance. The weather-resistant layer 42 may contain a binder resin and a weather-resistant agent. The weather-resistant layer 42 may contain, as the weather-resistant agent, one or more of an ultraviolet absorber, an antioxidant, and a light stabilizer.

[0142] 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.

[0143] The thermosetting resin composition contains a thermosetting resin. The thermosetting resin composition cures by heating. Examples of the thermosetting resin include unsaturated group-containing (meth)acrylic resins, unsaturated polyesters, urethane resins, epoxy resins, phenolic resins, aminoalkyd resins, urea resins, melamine resins, melamine-urea co-condensation resins, guanamine resins, diallyl phthalate resins, and silicone resins.

[0144] The thermosetting resin composition may contain a curing agent together with the thermosetting resin. In the case of an unsaturated group-containing (meth)acrylic resin and an unsaturated polyester, a peroxide such as methyl ethyl ketone peroxide or a radical initiator such as azoisobutylnitrile may be used. In the case of a urethane resin, an isocyanate-based curing agent may be used. In the case of an epoxy resin, an organic amine-based curing agent may be used.

[0145] The thermosetting resin may be a two-component curing urethane resin containing a polyol as a base resin and an isocyanate compound as a curing agent. Examples of polyols include (meth)acrylic polyols, polyether polyols, polyester polyols, 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.

[0146] In one specific example of the weather-resistant layer 42, the cured resin contained in the weather-resistant layer 42 may be a crosslinked cured product of a (meth)acrylic polyol with an isocyanate-based curing agent.

[0147] 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 an "ionizing radiation-curable compound." The ionizing radiation-curable functional group is a group that crosslinks upon irradiation with ionizing radiation.

[0148] The ionizing radiation may be electromagnetic waves or charged particle beams. The ionizing radiation has an energy quantum capable of polymerizing or crosslinking molecules. Examples of ionizing radiation include ultraviolet (UV) rays, electron beams (EB), X-rays, gamma rays, alpha rays, and ion beams. In an example in which the weather-resistant layer 42 contains an ultraviolet absorber as a weather-resistant agent, the ionizing radiation may be electron beams.

[0149] Examples of ionizing radiation-curable functional groups include ethylenically unsaturated bond groups such as (meth)acryloyl groups, vinyl groups, and allyl groups, as well as epoxy groups and oxetanyl groups. The ionizing radiation-curable compound may contain an ethylenically unsaturated bond group. The ionizing radiation-curable compound may contain two or more ethylenically unsaturated bond groups. The ionizing radiation-curable compound may be a polyfunctional (meth)acrylate compound containing two or more ethylenically unsaturated bond groups. The polyfunctional (meth)acrylate compound may contain either a monomer or an oligomer.

[0150] Examples of the polymerizable monomer include a (meth)acrylate monomer having a (meth)acryloyl group in the molecule and a polyfunctional (meth)acrylate monomer having two or more (meth)acryloyl groups in the molecule. The number of (meth)acryloyl groups in the polyfunctional (meth)acrylate monomer may be 2 or more and 8 or less, or 2 or more and 6 or less.

[0151] Examples of polymerizable monomers include bifunctional (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, pentaerythritol tri(meth)acrylate, and tetramethylolpropane tri(meth)acrylate; Examples include tri- or higher functional (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-, propylene oxide-, caprolactone-, isocyanuric acid-, or propionic acid-modified products of these (meth)acrylates.

[0152] Examples of the polymerizable oligomer include (meth)acrylate oligomers having two or more (meth)acryloyl groups in the molecule. Examples of the (meth)acrylate oligomer 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 or more and 8 or less, or 2 or more and 6 or less.

[0153] Examples of the polymerizable oligomer include a highly hydrophobic polybutadiene (meth)acrylate oligomer having a (meth)acryloyl group in the side chain of a polybutadiene oligomer, and a silicone (meth)acrylate oligomer having a polysiloxane bond in the main chain.

[0154] 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 an average molecular weight measured by gel permeation chromatography (GPC) analysis and converted into standard polystyrene.

[0155] As the ionizing radiation-curable compound, a monofunctional (meth)acrylate may be used together with a polyfunctional (meth)acrylate. This example allows the viscosity of the curable composition to be reduced during application. 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.

[0156] When the ionizing radiation curable compound is an ultraviolet ray curable compound, at least one selected from a photopolymerization initiator and a photopolymerization accelerator may be used together with the ultraviolet ray curable compound.

[0157] From the viewpoint of achieving excellent heat resistance, scratch resistance, and contamination resistance, the weather-resistant layer 42 may contain a cured product of a curable compound or a cured product of an ionizing radiation-curable composition. A coating liquid containing an electron beam-curable compound can be made 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 weather resistance agents, e.g., ultraviolet absorbers, through crosslinking. Therefore, bleed-out of additives such as ultraviolet absorbers can be stably suppressed. This prevents deterioration of the excellent weather resistance of the weather-resistant layer 42 over time. Therefore, the weather-resistant layer 42 preferably contains a cured product of an electron beam-curable compound. 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.

[0158] The content of the cured resin relative to the total resin components contained in the weather-resistant layer 42 may be 50% by mass or more and 100% by mass or less, 70% by mass or more and 100% by mass or less, 80% by mass or more and 100% by mass or less, or 90% by mass or more and 100% by mass or less.

[0159] The weather-resistant layer 42 can be produced by forming a coating film of a coating liquid containing a curable resin composition and curing the coating film. In an example where the weather-resistant layer 42 contains a cured product of an electron beam-curable resin composition, the coating film is irradiated with electron beams. A portion of the electron beams 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 crosslinked to some extent by the electron beam. The crosslinking of the polyolefin improves the heat resistance of the substrate 41.

[0160] Compared to substrates containing fluororesins, substrates 41 containing polyolefins can improve adhesion to weather-resistant layers 42 containing a cured product of an electron beam-curable resin composition. Furthermore, by using polyolefins instead of fluororesins for substrate 41, the generation of PFAS as an impurity can be suppressed. PFAS, as an artificial organic fluorine compound, is a concern due to its bioaccumulation potential. Suppressing the generation of PFAS can contribute to reducing environmental impact.

[0161] In view of the above, the substrate 41 may contain a polyolefin in combination with the weather-resistant layer 42 containing a cured product of the electron beam-curable resin composition. Examples of polyolefins used for the substrate 41 include polyethylene, polypropylene, polybutene, and polymethylpentene.

[0162] Examples of polypropylene include propylene homopolymers, ethylene-propylene copolymers, propylene-butene copolymers, and copolymers such as ethylene-propylene-butene copolymers. As the polypropylene contained in the substrate 41, propylene homopolymers, ethylene-propylene copolymers, and propylene-butene copolymers are preferred.

[0163] From the viewpoint of processability, the content of polyolefin in the substrate 41 may be 50% by mass or more and 100% by mass or less, 60% by mass or more and 100% by mass or less, 70% by mass or more and 100% by mass or less, or 80% by mass or more and 100% by mass or less, relative to the total resin components of the substrate 41.

[0164] <Barrier Layer> The barrier layer 44 may be a vapor-deposited film formed on a resin film. The covering sheet 30 may include a barrier film including the barrier layer 44 and a resin film. The barrier layer 44 may be a vapor-deposited film formed on the substrate 41. When the barrier layer 44 and the substrate 41 form a barrier film, the second bonding layer 45 shown in FIG. 2C can be omitted.

[0165] The coating sheet 30 including the barrier layer 44 can have excellent gas barrier properties. The coating sheet 30 including the barrier layer 44 can 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 adherend 20 such as a steel material and deterioration of the coating film on the adherend 20 such as a steel material.

[0166] An example of a resin film used in the barrier film is the resin film constituting the above-mentioned substrate 41. The thickness of the resin film may be 5 μm or more and 100 μm or less, 10 μm or more and 100 μm or less, 5 μm or more and 50 μm or less, or 10 μm or more and 50 μm or less.

[0167] The barrier layer 44 may be a vapor-deposited film containing one or more metals, one or more inorganic oxides, or one or more metals and one or more inorganic oxides. Examples of metals contained 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 include one or more of an aluminum vapor-deposited film, an aluminum oxide (alumina) vapor-deposited film, and a silicon oxide (silica) vapor-deposited film.

[0168] The thickness of the vapor-deposited film may be 1 nm or more, 5 nm or more, or 10 nm or more. The thickness of the vapor-deposited film may be 150 nm or less, 100 nm or less, or 80 nm or less. The thickness of the vapor-deposited film may be 1 nm or more and 150 nm or less, 5 nm or more and 150 nm or less, or 10 nm or more and 150 nm or less. The thickness of the vapor-deposited film may be 1 nm or more and 100 nm or less, 5 nm or more and 100 nm or less, or 10 nm or more and 80 nm or less.

[0169] The vapor-deposited film constituting the barrier layer 44 may be formed by a physical vapor deposition (PVD) method such as vacuum deposition, sputtering, or ion plating. The vapor-deposited film constituting the barrier layer 44 may be formed by a chemical vapor deposition (CVD) method such as plasma-enhanced chemical vapor deposition, thermal chemical vapor deposition, or photochemical vapor deposition.

[0170] Examples of vapor-deposited films include vapor-deposited polyester films such as vapor-deposited polyethylene terephthalate films, vapor-deposited polyamide films, and vapor-deposited OPP films (vapor-deposited biaxially oriented polypropylene).

[0171] A layer containing an ultraviolet absorber may be located between the barrier layer 44 and the first surface 31. The barrier layer 44 may deteriorate over time due to ultraviolet rays. Therefore, the layer containing an ultraviolet absorber can suppress deterioration of the barrier layer 44 and maintain the gas barrier properties of the barrier layer 44. In the example shown in FIG. 3C , one or more of the weather-resistant layer 42, the substrate 41, and the second bonding layer 45 may contain an ultraviolet absorber.

[0172] 2C includes, in order from the second surface 32 to the first surface 31, a barrier layer 44 and a weather-resistant layer 42. The barrier layer 44 is located between the adherend 20 and the weather-resistant layer 42 in the stacking direction. The gas barrier properties of the barrier layer 44 are maintained by the weather-resistant layer 42, which contains a weather-resistant agent such as an ultraviolet absorber.

[0173] The oxygen transmission rate (OTR, unit: cc / (m ２ The oxygen permeability (per 1000 kJ / day atm) may be 3.0 or less, 2.5 or less, or 2.0 or less. The coating sheet 30 with adjusted oxygen permeability can suppress corrosion of the adherend 20 such as a steel material and deterioration of the coating film. The lower the oxygen permeability of the coating sheet 30, the more preferable it is, but it may be 0.01 or more, 0.05 or more, or 0.1 or more.

[0174] The oxygen transmission rate (OTR, unit: cc / (m ２ The oxygen transmission rate (OTR, unit: cc / (m)) of the covering sheet 30 including the barrier layer 44 may be 0.01 or more and 3.0 or less, 0.01 or more and 2.5 or less, or 0.01 or more and 2.0 or less. ２ The oxygen transmission rate (OTR, unit: cc / (m)) of the covering sheet 30 including the barrier layer 44 may be 0.05 or more and 3.0 or less, 0.05 or more and 2.5 or less, or 0.05 or more and 2.0 or less. ２ ·day·atm) may be 0.1 or more and 3.0 or less, 0.1 or more and 2.5 or less, or 0.1 or more and 2.0 or less.

[0175] The oxygen permeability is a value measured in accordance with JIS K7126-2:2006 "Appendix A (Specifications): Test method for oxygen gas permeability using an electrolytic sensor" under conditions of a temperature of 23°C and a relative humidity difference of 60% RH. The covering sheet 30 is placed in a measuring device with the first surface 31 facing the oxygen supply side. The oxygen permeability measuring device may be the "OX-TRAN 2 / 20" manufactured by MOCON Corporation of the United States.

[0176] The water vapor transmission rate (WVTR, unit: g / (m2·day)) of the covering sheet 30 including the barrier layer 44 may be 6.0 or less, 5.0 or less, 4.0 or less, 3.0 or less, 2.5 or less, or 2.0 or less. The covering sheet 30 with its water vapor transmission rate adjusted in this manner can suppress corrosion of the adherend 20 such as steel and deterioration of the coating film. The lower the water vapor transmission rate of the covering sheet 30, the more preferable. The water vapor transmission rate of the covering sheet 30 may be 0.01 or more, 0.05 or more, or 0.1 or more.

[0177] The water vapor permeability of the covering sheet 30 may be 0.01 to 6.0, 0.01 to 5.0, 0.01 to 4.0, 0.01 to 3.0, 0.01 to 2.5, or 0.01 to 2.0. The water vapor permeability of the covering sheet 30 may be 0.05 to 6.0, 0.05 to 5.0, 0.05 to 4.0, 0.05 to 3.0, 0.05 to 2.5, or 0.05 to 2.0. The water vapor permeability of the covering sheet 30 may be 0.1 to 6.0, 0.1 to 5.0, 0.1 to 4.0, 0.1 to 3.0, 0.1 to 2.5, or 0.1 to 2.0.

[0178] The water vapor permeability is a value measured in accordance with JIS K7129-2:2019 under an environment with a temperature of 40°C and a relative humidity difference of 90% RH. The covering sheet 30 is placed in a measuring device with the first surface 31 facing the hydrogen supply side. The water vapor permeability measuring device may be a PERMATRAN-w 3 / 33 manufactured by MOCON Corporation of the United States.

[0179] <Bonding Layer> The bonding layer 43 and the second bonding layer 45 contain a component having adhesive or pressure-sensitive adhesive properties. The bonding layer 43 bonds the covering sheet 30 to the adherend 20 or the coating film on the adherend 20. The second bonding layer 45 bonds the barrier layer 44 to the substrate 41.

[0180] The bonding layer 43 and the second bonding layer 45 may be adhesive layers or pressure-sensitive adhesive layers. Examples of adhesive or pressure-sensitive adhesive components include acrylic resins, vinyl chloride-vinyl acetate copolymers, vinyl acetate resins, polyolefins, polyesters, polyurethanes, silicone resins, and rubber-based resins.

[0181] The bonding layer 43 and the second bonding layer 45 may be pressure-sensitive adhesive layers, i.e., adhesive layers. An adhesive layer is a layer formed from a pressure-sensitive adhesive (pressure-sensitive adhesive). The adhesive layer exhibits a tacky adhesive feeling at room temperature (e.g., 23°C). Examples of adhesives include acrylic adhesives, urethane adhesives, silicone adhesives, and rubber adhesives. Acrylic adhesives are preferably used for the bonding layer 43 because of their excellent adhesion to the adherend 20, which may have irregularities, and to coating films on the adherend 20. Acrylic adhesives also have excellent stability.

[0182] The bonding layer 43 and the second bonding layer 45 may contain additives. Examples of additives include pigments, dyes, colorants, antistatic agents, flame retardants, antifungal agents, crosslinking agents, tackifiers, plasticizers, leveling agents, flow control agents, antifoaming agents, and dispersants. The bonding layer 43 and the second bonding layer 45 may also contain weathering agents such as ultraviolet absorbers, antioxidants, and light stabilizers.

[0183] The storage modulus (G') at 40°C of the bonding layer 43 and the second bonding layer 45 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. When the storage modulus is equal to or more than the lower limit, excessive elongation of the adhesive layer when subjected to an impact can be suppressed. When the storage modulus is equal to or less than the upper limit, breakage of the adhesive layer when subjected to an impact can be suppressed.

[0184] The storage modulus is measured by the following method. Two test pieces 90 are prepared from the cover sheet 30 according to the test piece preparation method described in 6.2 of JIS K7244-1:1998. Since the test piece 90 is prepared from the cover sheet 30, the test piece 90 includes a support 91 corresponding to the portion of the cover sheet 30 other than the bonding layer 43, and an adhesive layer 92 corresponding to the bonding layer 43 of the cover sheet 30.

[0185] The method described herein can also measure the storage modulus (G') of the bonding layer 15 shown in Figure 1B. In this example, the test piece 90 includes a support 91 corresponding to the cover sheet 30 and an adhesive layer 92 corresponding to the bonding layer 15.

[0186] Next, the two prepared test pieces 90 are attached to a measuring device 70 as shown in FIG. 3 . As shown in FIG. 3 , the measuring device 70 includes a plate 71 and a jig 72. The jig 72 includes a pair of plate-like portions 73 sandwiching 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 nuts 75 threaded onto bolts 74 that pass through the pair of plate-like portions 73. The bolts 74 do not pass through the plate 71 and the test pieces 90 attached to the measuring device 70. The bolts 74 are located at different positions from the plate 71 and the test pieces 90 in the direction perpendicular to the paper surface of FIG. 3 . When attaching the two test pieces 90 to the measuring device 70, the two test pieces 90 are first adhered to the plate 71 by the action of an adhesive layer 92 so that the plate 71 is sandwiched between the two test pieces 90. Next, the nut 75 is rotated to reduce the distance between the pair of plate-like portions 73, thereby sandwiching the plate 71 and the two test pieces 90 between the pair of plate-like portions 73, as shown in Fig. 3. This fixes the two test pieces 90 to the jig 72.

[0187] The thickness w1 of the test specimen 90 is also 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 the dimensions of the plate 71 and the jig 72, the thickness w2 of the plate 71 shown in FIG. 3 and the thicknesses w3 and w4 of each of the pair of plate-like portions 73 can be determined. The thicknesses w2, w3, and w4 can be determined by measuring with a vernier caliper. Furthermore, after fixing the two test specimens 90 to the jig 72 as shown in FIG. 3, the dimensions of the jig 72 with the two test specimens 90 sandwiched between them are determined. As the dimension of the jig 72 with the two test specimens 90 sandwiched between them, the distance w5 from one outer surface of the pair of plate-like portions 73 to the other outer surface of the pair of plate-like portions 73 shown in FIG. 3 can be determined. The distance w5 can be determined by measuring with a vernier caliper. Next, the thickness w1 of the test piece 90 is determined from the dimensions of the plate 71 and the jig 72 and the dimensions of the jig 72 sandwiching the two test pieces 90. The thickness w1 of the test piece 90 can be calculated by subtracting the thicknesses w2, w3, and w4 from the distance w5 and dividing the result by 2. The determined thickness w1 of the test piece 90 is used to measure the storage modulus (G').

[0188] As shown in Fig. 3, after two test pieces 90 are fixed to a jig 72, the jig 72 is vibrated in the vertical direction. As a result, vertical vibrations are input to the adhesive layer 92 of the test pieces 90. By detecting the movement of the plate 71 when vertical vibrations are input to the adhesive layer 92 of the test pieces 90, the storage modulus (G') of the adhesive layer 92 can be measured.

[0189] The storage modulus (G') is measured under the following conditions: Atmospheric gas: nitrogen Attachment mode: solid shear mode Temperature dependency Fundamental frequency: 10 Hz Measurement program: start temperature = 30°C, step temperature = 1°C, end temperature = 150°C, heating rate: 3°C / min Sine wave, stop vibration Manual static load: adjusted to 0 g when fixing the two test pieces 90 to the jig 72 Strain: value automatically set when inputting the sample length 0.05 Automatic adjustment mode

[0190] The storage modulus (G') can be measured using a solid viscoelasticity measuring device, such as Rheogel E4000 manufactured by UBM Corporation.

[0191] The thickness of the bonding layer 43 and the second bonding layer 45 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 the bonding layer 43 and the second bonding layer 45 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. The thickness of the bonding layer 43 and the second bonding layer 45 may be 10 μm or more and 1000 μm or less, or 50 μm or more and 150 μm or less.

[0192] <Other Layers That May Be Included in Covering Sheet> The covering sheet 30 is not limited to the examples shown in FIGS. 2A to 2C, and may include additional layers.

[0193] <Covering Sheet with Release Film> As shown by the two-dot chain line in FIG. 2C , a release film 46 may be laminated on the covering sheet 30. The covering sheet with a release film includes the covering sheet 30 and a release film 46 laminated on the covering sheet 30. Before bonding the covering sheet 30 to the adherend 20, the release film 46 is bonded to the bonding layer 43. The release film 46 protects the bonding layer 43 from foreign matter such as dust before use of the covering sheet 30. When using the covering sheet 30, the release film 46 is removed from the covering sheet 30. Removal of the release film 46 exposes the bonding layer 43, allowing the covering sheet 30 to be bonded to the adherend 20. Examples of the release film 46 include paper substrates and resin films, as well as films coated with a release agent. Examples of the release agent include silicone-based release agents, fluorine-based release agents, and long-chain alkyl-based release agents.

[0194] <<<<Other Layers That May Be Included in the Structure>>> As shown in Fig. 1B , a structure 10 such as a steel structure may further include a third bonding layer 15 in addition to an adherend 20 such as a steel material and a coating sheet 30. As shown in Fig. 1C , the structure 10 such as a steel structure may further include an anti-corrosion layer 18. Furthermore, as shown by a two-dot chain line in Fig. 1C , the structure 10 such as a steel structure may include a top coat layer 19. As will be described below, the structure 10 such as a steel structure is not limited to the examples shown in Figs. 1A to 1C , and may include further layers.

[0195] 1B , the third bonding layer 15 is used to bond the covering sheet 30 to the adherend 20. The third bonding layer 15 may be configured similarly to the bonding layer 43 of the covering sheet 30 described above.

[0196] <<Rust-preventive layer>> The rust-preventive layer 18 is located between the adherend 20, such as a steel material, and the covering sheet 30. The rust-preventive layer 18 inhibits corrosion of the adherend 20, such as a steel material. The rust-preventive layer 18 inhibits the spread of corrosion in the adherend 20, such as a steel material. As shown in Figures 1A and 1B, the rust-preventive layer 18 can be omitted from the adherend 20, such as a steel material.

[0197] The anticorrosive layer 18 may be produced by applying an anticorrosive paint containing an anticorrosive agent to the surface of the adherend 20 to form a coating film, and then solidifying or curing the coating film. Examples of coating methods include brush coating, roller coating, and spray coating (e.g., air spray, airless spray). The anticorrosive layer 18 formed as a coating film can improve adhesion to the uneven surface of the adherend 20.

[0198] The thickness of the anticorrosive 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 anticorrosive 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 anticorrosive layer 18, sufficient anticorrosive function can be imparted to the anticorrosive layer 18. By setting an upper limit for the thickness of the anticorrosive layer 18, excellent workability and cost can be achieved when producing the anticorrosive layer 18.

[0199] The thickness of the anticorrosive layer 18 may be 10 μm to 1000 μm, 30 μm to 1000 μm, 50 μm to 1000 μm, 100 μm to 1000 μm, or 150 μm to 1000 μm. The thickness of the anticorrosive layer 18 may be 10 μm to 800 μm, 30 μm to 800 μm, 50 μm to 800 μm, 100 μm to 800 μm, or 150 μm to 800 μm. The thickness of the anticorrosive layer 18 may be 10 μm to 600 μm, 30 μm to 600 μm, 50 μm to 600 μm, 100 μm to 600 μm, or 150 μm to 600 μm. The thickness of the anticorrosive layer 18 may be 10 μm to 500 μm, 30 μm to 500 μm, 50 μm to 500 μm, 100 μm to 500 μm, or 150 μm to 500 μm.

[0200] Examples of the rust inhibitor contained in the rust-preventive layer 18 include inorganic and organic rust inhibitors. The inorganic rust inhibitor may be an inorganic acid or a salt of an inorganic acid. Examples of inorganic rust inhibitors include red lead, lead suboxide, basic lead chromate, lead dianamide, calcium plumbate, basic lead sulfate, zinc chromate, zinc powder, red iron oxide, nitrite, sulfite, silicate, metasilicate, phosphate, polyphosphate, hypophosphite, phosphite, 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.

[0201] 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, pyruguanidino group-containing compounds, thiocarbonyl group-containing compounds, alkylphenol compounds, diisopropylammonium nitrite, and dicyclohexylammonium nitrite.

[0202] Examples of anti-rust 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. The anti-rust paint may contain a binder and a rust inhibitor. Examples of binders for anti-rust paints include organic binders such as epoxy resins, urethane resins, acrylic resins, silicone acrylic resins, styrene resins, and fluororesins. Examples of binders for anti-rust paints include inorganic binders such as alkyl silicates.

[0203] From the viewpoint of the rust prevention mechanism, the rust prevention layer can be classified into a rust conversion type and a salt and iron ion neutralization type. The rust prevention layer 18 may be either a rust conversion type or a salt and iron ion neutralization type.

[0204] The anti-rust paint may be a one-component curing anti-rust paint, or a two-component curing anti-rust paint containing a base agent and a curing agent. The two-component curing anti-rust paint may be prepared by storing the base agent containing a binder and, if desired, a rust inhibitor in separate containers, and mixing the two immediately before use. The two-component curing anti-rust paint is excellent in that it has high adhesion to the substrate 20, high coating film strength, and can form a dense anti-rust layer 18. The two-component curing anti-rust paint also has excellent adhesion to the coating sheet 30. The two-component curing anti-rust paint may be a two-component curing epoxy resin paint, a two-component curing urethane resin paint, or a two-component curing epoxy resin paint.

[0205] The two-component curing epoxy resin paint may contain an epoxy resin as a binder and an epoxy resin curing agent as a curing agent. Examples of the curing agent include amine-based curing agents, phenol-based curing agents, acid anhydride-based curing agents, and mercaptan-based curing agents. The urethane resin paint may be a two-component curing type consisting of a polyol-based compound and an isocyanate-based compound, or a one-component curing type that cures due to moisture in the air.

[0206] The anti-rust paint may contain additives. Examples of additives include rosins, plasticizers, extender pigments, coloring pigments, solvents, curing accelerators, coupling agents, corrosive ion fixing agents, anti-sagging agents, and anti-settling 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 fixing agents include hydrotalcite and hydrocalumite.

[0207] The 85-degree specular gloss of the surface of the anticorrosive layer 18 provided on the adherend 20, such as a steel material, may be 3 or more. The 85-degree specular gloss of the surface of the anticorrosive layer 18 may be 5 or more, 10 or more, 15 or more, 20 or more, or 23 or more. By setting the lower limit of the 85-degree specular gloss of the surface of the anticorrosive layer 18 in this manner, the anticorrosive layer 18 becomes a dense film. The anticorrosive layer 18 as a dense film exhibits high adhesion to the covering sheet 30. The upper limit of the 85-degree specular gloss of the surface of the anticorrosive layer 18 is not particularly limited. The 85-degree specular gloss of the surface of the anticorrosive layer 18 may be 60 or less, 50 or less, or 40 or less.

[0208] The 85-degree specular gloss of the surface of the anticorrosive layer 18 may be 3 or more and 60 or less, 5 or more and 60 or less, 10 or more and 60 or less, 15 or more and 60 or less, 20 or more and 60 or less, or 23 or more and 60 or less. The 85-degree specular gloss of the surface of the anticorrosive layer 18 may be 3 or more and 50 or less, 5 or more and 50 or less, 10 or more and 50 or less, 15 or more and 50 or less, 20 or more and 50 or less, or 23 or more and 50 or less. The 85-degree specular gloss of the surface of the anticorrosive layer 18 may be 3 or more and 40 or less, 5 or more and 40 or less, 10 or more and 40 or less, 15 or more and 40 or less, 20 or more and 40 or less, or 23 or more.

[0209] The specular gloss of the anticorrosive layer 18 is a value measured in accordance with JIS Z8741:1997, except that the angle of incidence is set to 85°. The measurement environment for measuring the specular gloss of the anticorrosive layer 18 is a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The measurement sample to be measured is placed in the measurement environment for 16 hours before starting the measurement. Before measuring the specular gloss, the light source of the measurement device is turned on for 15 minutes to stabilize the light source output.

[0210] The specular gloss of the anticorrosive layer 18 is the arithmetic mean value of five measured values. The five measured values ​​are measured at five measurement positions on the measurement sample to be evaluated. The five measurement positions are located at least 10 mm apart from each other.

[0211] A lower limit may be set for the 85-degree specular gloss retention rate of the anticorrosive layer 18 provided on the adherend 20. Setting a lower limit for the 85-degree specular gloss retention rate on the surface of the anticorrosive layer 18 ensures adhesion of the anticorrosive layer 18 to the adherend 20. The 85-degree specular gloss retention rate on the surface of the anticorrosive layer 18 may be 60% or more and 100% or less, 70% or more and 100% or less, 80% or more and 100% or less, 90% or more and 100% or less, or 95% or more and 100% or less.

[0212] The 85-degree specular gloss retention rate is the retention rate of the 85-degree specular gloss on the surface of the anticorrosive layer 18 before and after the 90-degree tape peel test. The 85-degree specular gloss on the surface of the anticorrosive layer 18 before the 90-degree tape peel test is defined as "Gsb." The 85-degree specular gloss on the surface of the anticorrosive layer 18 after the 90-degree tape peel test is defined as "Gsa." The 85-degree specular gloss retention rate is expressed as Gsa × 100 / Gsb, and is expressed in %.

[0213] The 90-degree tape peel test is performed as follows: 25 cm of 24 mm wide cellophane adhesive tape conforming to JIS Z1522:2009 is unwound from a roll at a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. To create a handle, 10 cm of the adhesive surfaces are bonded together. Then, 5 cm of the adhesive surface is adhered to the rust-preventive coating surface of a structure 10, such as a steel structure, using a 2 kg pressure roller (roll) twice in both directions. Then, the adhesive surface is again adhered by finger pressure to prevent air from entering the structure. Next, the cellophane adhesive tape is manually peeled off once at a speed of 5 cm / s in a 90-degree direction relative to the rust-preventive coating surface. As the cellophane adhesive tape, Cellotape (registered trademark) (manufactured by Nichiban, model number No. 405-1P, 24 mm width) is used, and if this product cannot be used, a 24 mm wide cellophane adhesive tape conforming to JIS Z1522:2009 and having adhesive strength equivalent to that of this product is used.

[0214] <<Top Coat Layer>> The top coat layer 19 is formed on the covering sheet 30. In this example, the covering sheet 30 is located between the top coat layer 19 and the adherend 20, such as a steel material, in the stacking direction. The top coat layer 19 may be provided for the purpose of improving the weather resistance of the structure 10, such as a steel structure. The top coat layer 19 may impart excellent rust prevention properties to the structure 10, such as a steel structure, for a long period of time. The top coat layer 19 can be omitted from the structure 10, such as a steel structure.

[0215] The topcoat layer 19 may be produced by applying a topcoat paint to the first surface 31 of the cover sheet 30 to form a coating film, and then solidifying or curing the coating film. Examples of coating methods include brush coating, roller coating, and spray coating (e.g., air spray, airless spray). The topcoat paint may be a one-component paint or a two-component paint. The topcoat layer 19 and the topcoat paint may contain a resin and an additive.

[0216] Examples of resins contained in the topcoat layer 19 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. Examples of additives contained in the topcoat layer 19 and the topcoat paint include pigments, dyes, dispersants, antifoaming agents, thickeners, leveling agents, anti-settling agents, anti-sagging agents, anti-algae agents, anti-mold agents, preservatives, ultraviolet absorbers, antioxidants, and light stabilizers.

[0217] The topcoat paint may contain an organic solvent and / or water for the purpose of adjusting viscosity, etc. Examples of organic solvents include aromatic hydrocarbons, aliphatic hydrocarbons, ketones, acetate esters, ethers, alcohol-based solvents, and mineral spirits.

[0218] The thickness of the topcoat layer 19 may be 5 μm or more, 10 μm or more, or 15 μm or more. The thickness of the topcoat layer 19 may be 200 μm or less, 150 μm or less, or 100 μm or less. The thickness of the topcoat layer 19 may be 5 μm or more and 200 μm or less, or 15 μm or more and 100 μm or less.

[0219] Next, a method for repairing the structure 10 using the covering sheet 30 will be described.

[0220] As described above, the covering sheet 30 can facilitate inspection of the structure 10, which is a prerequisite for preventive maintenance. By combining the above-described features (A) to (C), the condition of the adherend 20 can be observed through the covering sheet 30. Therefore, any abnormalities that may occur in the adherend 20 covered by the covering sheet 30 can be easily and stably detected from an early stage. As will be described below, this covering sheet 30 not only facilitates inspection of the structure 10, but also facilitates the implementation of preventive maintenance.

[0221] 1A to 1C, the structure 10 to be repaired may be a steel structure including a covering sheet 30. As another example shown in FIG. 5, the structure 10 to be repaired may be a steel structure 100 including an adherend 20 made of a steel material and a number of coating films 50 formed on the adherend 20.

[0222] 5 shows a conventional steel structure 100 including multiple coating films 50. The coating films 50 included in the steel structure 100 include, in order from the adherend 20, which is a steel material, an anti-corrosion layer 51, a first primer layer 52, a second primer layer 53, an intermediate coating layer 54, and a top coating layer 55.

[0223] The anticorrosive layer 51 has an anticorrosive function. The anticorrosive layer 51 is a layer that suppresses the occurrence and spread of rust. The anticorrosive layer 51 may have the same structure as the anticorrosive layer 18 described above.

[0224] 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 adherend 20. The barrier properties of a barrier layer that is a coated film are weaker than the barrier properties of a barrier layer that is a vapor-deposited film. The illustrated steel structure 100 includes two undercoat layers 52, 53 to ensure sufficient barrier properties. The undercoat layers 52, 53 may contain an epoxy resin. The undercoat layers 52, 53 may contain a cured product of a curable resin.

[0225] The intermediate coating layer 54 has high adhesiveness. The intermediate coating layer 54 improves the adhesion of the top coating layer 55. An example of an intermediate coating layer having high adhesiveness is a layer containing a fluorine-based resin. The intermediate coating layer 54 may also contain weathering agents such as an ultraviolet absorber, an antioxidant, and a light stabilizer.

[0226] The topcoat layer 55 has weather resistance. The topcoat layer 55 contains weather-resistant agents such as an ultraviolet absorber, an antioxidant, and a light stabilizer. An example of the topcoat layer 55 is a layer containing a fluorine-based resin and a weather-resistant agent. The topcoat layer 55 may have a configuration similar to that of the above-described topcoat layer 19.

[0227] Each of the multiple coating films 50 is applied one layer per day, taking into consideration the time required for drying, hardening, curing, etc. For example, the steel structure 100 shown in Fig. 5 requires five days for construction.

[0228] 5 will be described with reference to Figures 4A to 4D. A covering sheet 30 is used for the repair. The repaired structure 10 includes the covering sheet 30. The repair is not limited to the example shown in Figures 4A to 4D, and the structure 10 including the covering sheet 30 may also be repaired using the covering sheet 30.

[0229] The repair method shown in Figures 4A to 4D includes a first step, a second step, a third step, and a fourth step. In the first step, a covering sheet 30 is prepared. In the second step shown in Figure 4B, a surface preparation is performed on the deteriorated portion 12 of the structure. In the third step shown in Figure 4C, a rust-preventive layer 18 is formed. In the fourth step shown in Figure 4D, the covering sheet 30 is bonded to the adherend 20. Each step will be described below in order.

[0230] Fig. 4A is a cross-sectional view schematically showing a deteriorated portion 12 of a structure. In Fig. 4A, a pre-repair coating film (old coating film) 50 is provided on an adherend 20. Rust 60 has developed on the adherend 20. In order to repair such deteriorated portion 12, the above-mentioned covering sheet 30 is prepared as a first step.

[0231] As shown in Figure 4B, in the second step, surface preparation (base preparation) is performed on the deteriorated portion 12 of the steel structure 100. Scraping is an example of a method for preparing the base of the steel structure 100. In scraping, old paint films, rust, dust, dirt, etc. are generally removed by blasting or using power tools or hand tools. This removal exposes a surface preparation surface 22. In the second step, the surface preparation surface 22 forms the surface of the steel structure 100.

[0232] Scraping treatment is classified into grades of Class 1, Class 2, Class 3, and Class 4. The smaller the grade number, the higher the level of surface preparation.

[0233] "Type 1 cleaning" is a surface preparation process that exposes the steel surface by removing all rust and the old paint film 50. In "Type 1 cleaning," the surface preparation is mainly carried out by blasting.

[0234] The "type 2 scraping" is a surface preparation process in which rust and the old paint film 50 are removed to expose the surface of the steel substrate 20. In the "type 2 scraping" process, the surface preparation is mainly performed using power tools and / or manual tools.

[0235] "Type 3 scraping" is a surface preparation method that leaves the active film 50P of the old paint film 50, i.e., the paint film in a healthy state, but removes other defective parts (rust and dead films of the old paint film (paint film with cracks and blisters)). In "Type 3 scraping," the surface preparation is mainly performed using power tools and / or manual tools.

[0236] Class 3 scraping has the advantage of requiring fewer work areas and lower work costs than Class 1 and Class 2 scraping. Because the active film 50P of the old paint film 50 remains, the surface preparation after Class 3 scraping may have significant irregularities. Rust may remain on the surface preparation after Class 3 scraping. The height of the irregularities on the surface of the steel structure 10 after Class 3 scraping 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.

[0237] 4B shows a steel structure 100 that has undergone surface preparation using a type 3 cleaning method. In FIG. 4B, the old paint film 50 has been removed except for the active film 50P. In FIG. 4B, rust 60 has also been removed.

[0238] "Type 4 scraping" is a surface preparation method that removes powdered materials (including loose rust) and dirt from the surface. In "Type 4 scraping," surface preparation is mainly performed using hand tools and / or brushes.

[0239] Examples of power tools include a disc sander and a wire wheel, and examples of hand tools include a wire brush, a scraper, a scraping rod, and sandpaper.

[0240] In the third step, as shown in Fig. 4C, a rust prevention treatment is performed on the surface preparation surface 22 of the steel structure 100. In the third step, a rust prevention layer 18 is formed on the adherend 20, which is a steel material, and on the active film 50P. The material and formation method of the rust prevention layer 18 are as described above.

[0241] The anticorrosion layer 18 contains a rust inhibitor. The rust inhibitor can suppress rust formation. The rust inhibitor may be contained in the bonding layer 15 or the covering sheet 30 (e.g., bonding layer 43). By providing the anticorrosion layer 18 containing the rust inhibitor separately from the covering sheet 30, the effect of the rust inhibitor can be more clearly obtained. The anticorrosion layer 18 formed as a coating film can fill in the unevenness of the surface preparation surface to some extent. This can improve the adhesion of the covering sheet 30.

[0242] In the fourth step, the covering sheet 30 is placed on the steel structure 100 under repair. In the example shown in Fig. 4D, the covering sheet 30 is placed on the anti-corrosion layer 18. The covering sheet 30 including the bonding layer 43 is bonded to the anti-corrosion layer 18 using the bonding layer 43. In the example shown in Fig. 4D, a bonding layer 15 is formed on the anti-corrosion layer 18, and the covering sheet 30 is bonded to the anti-corrosion layer 18 using this bonding layer 15. In the fourth step, a structure 10 including the covering sheet 30 is obtained.

[0243] The covering sheet 30 may be attached to the structure 10 by the bonding layers 15, 43 while being pressed at room temperature. For example, the covering sheet 30 may be pressed against the adherend 20 from above using a roller or the like. This allows the covering sheet 30 to be tightly attached to the adherend 20 or the coating film (e.g., the anticorrosive layer 18) on the adherend 20.

[0244] When the cover sheet 30 is prepared as a cover sheet with a release film including the release film 46, the release film 46 is peeled off from the cover sheet 30 before placing the cover sheet 30 on the adherend 20. By peeling off the release film 46, the bonding layer 43 is exposed.

[0245] The covering sheet 30 may cover the side end portions of the anticorrosive layer 18. The covering sheet 30 may be folded to cover the side end surfaces of the structure 10.

[0246] As described above, a structure is repaired using the covering sheet 30, and a structure 10 including the covering sheet 30 is obtained. Repairs using the covering sheet 30 allow repairs to be performed on a structure in a short period of time. For example, compared to re-forming multiple coating films 50 shown in FIG. 5 on the repair area, using the covering sheet 30 can significantly shorten the construction period. Furthermore, repairs using the covering sheet 30 can reduce costs and simplify construction. Furthermore, by using the covering sheet 30 manufactured in a factory with a well-maintained environment, the occurrence of defects such as pinholes can be reduced compared to forming multiple coating films on the substrate 20 outdoors. As described above, the use of the covering sheet 30 facilitates preventive maintenance.

[0247] The structure 10 including the covering sheet 30 obtained by the repair can be easily inspected for the purpose of detecting abnormalities. That is, abnormalities occurring in the adherend 20 or the anticorrosive layer 18 can be easily and stably detected through the covering sheet 30 covering the adherend 20.

[0248] The anticorrosive layer 18 may be transparent. A transparent anticorrosive layer 18 allows the condition of the adherend 20 underlying the anticorrosive layer 18 to be observed through the anticorrosive layer 18 and the covering sheet 30. In other words, abnormalities occurring in the adherend 20 can be easily and reliably detected through the covering sheet 30 and the anticorrosive layer 18 that cover the adherend 20. "Transparent" means that the total light transmittance is 70% or more. The total light transmittance of the anticorrosive layer 18 and the covering sheet 30 combined may be 70% or more and 100% or less.

[0249] The method for repairing a structure using the covering sheet 30 is not limited to the method described above with reference to FIGS. 4A to 4D.

[0250] In the illustrated example, type 3 cleaning is performed as the surface preparation in the second step. However, the repair method using the covering sheet 30 is not limited to this example. The repair method using the covering sheet 30 can be applied to structures in which type 1 cleaning, type 2 cleaning, or type 4 cleaning is performed as the surface preparation other than type 3 cleaning.

[0251] A step of forming a planarizing layer may be performed before the fourth step is performed. The planarizing layer may be formed on the surface preparation surface 22 or on the anticorrosive layer 18. By providing the planarizing layer, the surface to which the covering sheet 30 is bonded is planarized. This improves the adhesion of the covering sheet 30 to the structure 10.

[0252] Examples of materials constituting the planarization layer include fluororesins, acrylic resins, silicone resins, urethane resins, urea resins, and epoxy resins. The planarization layer may be produced by applying a coating material to form a coating film and then solidifying or curing the coating film. The coating material may be a one-component curing type coating material or a two-component curing type coating material. The planarization layer may contain additives such as ultraviolet absorbers, antioxidants, and light stabilizers.

[0253] The third step may be omitted from the above-described repair method. When the third step is omitted, the covering sheet 30 is bonded to the surface conditioning surface 22. The above-described repair method may also include a step of forming a topcoat layer 19.

[0254] As already mentioned, the structure 10 including the covering sheet 30 may be repaired using the covering sheet 30, without being limited to the examples shown in FIGS. 4A to 4D.

[0255] The above describes a method for repairing a steel structure including an adherend 20 made of steel material. However, repair using the covering sheet 30 is not limited to steel adherends 20 and steel structures including steel materials as the adherends 20. The covering sheet 30 may also be used to repair structures 10 including adherends exposed to ultraviolet light (such as adherends located outdoors or adherends located near openings (windows) in buildings and other structures). Similar to the example steel structure, the repaired structure 10 is endowed with excellent weather resistance by the covering sheet 30, and the condition of the adherend 20 can be clearly observed through the covering sheet 30. Therefore, potential abnormalities in the adherend 20 covered by the covering sheet 30 can be easily and reliably detected from an early stage. As described below, the covering sheet 30 not only facilitates inspection of the structure 10 but also facilitates preventive maintenance work.

[0256] The present disclosure will be described in more detail with reference to examples, but the present disclosure is not limited to the following examples.

[0257] <<<<1. Preparation of Covering Sheets>>> Covering sheets according to Examples 1 and 2 and Comparative Examples 1 to 4 were prepared.

[0258] <<Example 1>> As a coating sheet according to Example 1, a coating sheet including a substrate, a primer layer, and a weather-resistant layer in this order was produced.

[0259] The substrate was obtained by forming a resin composition into a sheet, which was obtained by mixing 95 parts by mass of the base resin with 5 parts by mass of the weathering agent masterbatch.

[0260] The base resin was a metallocene linear low-density polyethylene resin (M-LLDPE). The density of the base resin was 0.901 g / cm ３ The melting point of the base resin was 93° C. The MFR (melt flow rate) of the base resin at 190° C. was 2.0 g / 10 min.

[0261] The weather resistant masterbatch was obtained by mixing 100 parts by mass of a low-density polyethylene resin, 0.6 parts by mass of HALS, 3.5 parts by mass of a first ultraviolet absorber, and 0.6 parts by mass of a second ultraviolet absorber. The density of the low-density polyethylene resin was 0.880 g / cm. ３ The MFR (melt flow rate) of the low-density polyethylene resin at 190°C was 3.5 g / 10 min. The HALS was "KEMISTAB62" manufactured by Chemipro Chemical Co., Ltd. The first ultraviolet absorber was "KEMISORB12" manufactured by Chemipro Chemical Co., Ltd. The second ultraviolet absorber was "KEMISORB79" manufactured by Chemipro Chemical Co., Ltd.

[0262] The resin composition was formed into a sheet using a φ30 mm extruder and a film molding machine equipped with a 200 mm wide T-die. The extrusion temperature during extrusion using the extruder was 210°C. The take-up speed of the extruded sheet was adjusted so that the thickness of the substrate produced was 300 μm. The cooling roll immediately below the T-die was chrome-plated. The surface roughness Rz of the cooling roll was 1.5 μm. A silicone rubber roll was used as the rubber roll immediately below the T-die. The hardness of the silicone rubber roll was 70 degrees.

[0263] As a result, a transparent, uncolored substrate having a thickness of 300 μm was obtained.

[0264] Next, one surface of the substrate was subjected to a corona discharge treatment, and then a primer layer was formed on the corona discharge treated surface of the substrate using a resin composition for a primer layer.

[0265] The primer layer resin composition was prepared by mixing 100 parts by weight of the mixture, 5 parts by weight of a curing agent, 20 parts by weight of an ultraviolet absorber, and a dilution solvent. The 100 parts by weight of the mixture was a mixture of a polycarbonate-based urethane-acrylic copolymer and an acrylic polyol. Five parts by weight of the curing agent was hexamethylene diisocyanate.

[0266] The primer layer resin composition was applied to the corona discharge treated surface of the substrate by gravure printing. The primer layer resin composition coating formed on the substrate was dried to obtain a primer layer. The primer layer had a thickness of 4 μm.

[0267] 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 a 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.

[0268] The uncured resin layer was then cured by irradiating it with an electron beam. The electron beam irradiation conditions were an acceleration voltage of 165 kV and an irradiation dose of 5 Mrad (50 kGy). A weather-resistant layer having a thickness of 5 μm was formed by irradiating the uncured resin layer with the electron beam. The weather-resistant layer and the substrate were bonded via a primer layer not shown in FIG. 2B .

[0269] In this way, a coating sheet according to Example 1 including the substrate, the primer layer, and the weather-resistant layer in this order was obtained.

[0270] <<Example 2>> A coating sheet according to Example 2 was prepared, which included a barrier layer, a second bonding layer, a substrate, a primer layer, and a weather-resistant layer in this order. Example 2 differed from Example 1 in that a barrier layer bonded to the substrate using a second bonding layer was provided, but was otherwise the same as Example 1. That is, the substrate, primer layer, and weather-resistant layer of the coating sheet according to Example 2 were the same as the substrate, primer layer, and weather-resistant layer of the coating sheet according to Example 1, respectively. The coating sheet according to Example 2 was prepared by forming a barrier layer and a second bonding layer on the coating sheet according to Example 1. The methods for forming the barrier layer and the second bonding layer are as follows.

[0271] A transparent urethane resin adhesive was applied to the surface of the substrate opposite to the surface on which the primer layer and the weather-resistant layer were laminated, and the coating of the urethane resin adhesive was dried on the substrate to form a second bonding layer having a thickness of 3 μm.

[0272] Next, IB-PET-UB available from Dai Nippon Printing Co., Ltd. was prepared as a gas barrier film including a barrier layer. IB-PET-UB included a resin film and a gas barrier layer, which was a vapor-deposited film. The substrate and the gas barrier film were bonded by dry lamination using the second bonding layer described above. The gas barrier layer of the gas barrier film was in contact with and bonded to the second bonding layer.

[0273] <<Comparative Example 1>> A coating sheet including a substrate and a resin layer was prepared as a coating sheet according to Comparative Example 1. The substrate was the same as that in Example 1, which was prepared using the same materials and by the same method as in Example 1. Corona treatment was performed on one surface of the substrate in the same manner as in Example 1.

[0274] The resin layer was made using the paint "V Flon #100H Smile Top Coat" available from Dai Nippon Toryo Co., Ltd. This paint was applied to the corona-treated surface of the substrate to form a coating film. The coating film was dried to form a resin layer with a thickness of 5 μm. The paint "V Flon #100H Smile Top Coat" is a colored paint used to form a coating film that constitutes the outermost layer of a steel structure.

[0275] In this way, a coating sheet according to Comparative Example 1 containing a substrate and a resin layer in this order was obtained.

[0276] <<Comparative Example 2>> "HBS006H" available from Mitsubishi Chemical Corporation was used as the covering sheet according to Comparative Example 2. "HBS006H" is an acrylic film containing an ultraviolet absorber.

[0277] <<Comparative Example 3>> The cover sheet according to Comparative Example 3 was a laminate formed by laminating three sheets of white PET available from VANRA.

[0278] Comparative Example 4 The covering sheet according to Comparative Example 4 was a polyethylene sheet used in the zipper bag "FG-4" manufactured by Japax Corporation.

[0279] <<<2. Measurement and Evaluation>>> Measurement and evaluation were carried out on the coating sheets according to the examples and comparative examples as described below. The test environment during the measurements and evaluations was a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. Before the start of the measurements and evaluations, the samples were placed in the above-mentioned test environment for 16 hours. In addition, the samples used for the measurements and evaluations were visually inspected for the absence of any abnormalities such as dust or scratches.

[0280] <<2-1. Total Light Transmittance>> Samples measuring 5 cm x 5 cm were cut out from the covering sheets according to the examples and comparative examples. The total light transmittance (%) of the covering sheets according to each example was measured using the method described above. A haze meter "HM-150L2N" manufactured by Murakami Color Research Laboratory was used to measure the total light transmittance. The measurement results of the total light transmittance are shown as "Tt" in Table 1.

[0281] <<2-2. Specular Gloss>> Samples measuring 5 cm x 5 cm were cut out from the coating sheets according to the examples and comparative examples. The samples were visually inspected to ensure there were no abnormalities such as dust or scratches. The specular gloss of the coating sheets according to each example was measured using the method described above. A micro-TRI-gloss glossmeter manufactured by BYK was used to measure the specular gloss. The angle of incidence was 60°. The measurement results of the specular gloss are shown in the "Specular Gloss" column of Table 1.

[0282] <<2-3. Image clarity>> Samples measuring 5 cm x 5 cm were cut out from the covering sheets according to the examples and comparative examples. The samples were visually inspected for the absence of any abnormalities such as dust or scratches. The image clarity of the covering sheets according to each example was measured by the transmission method using the method described above. An image clarity measuring instrument "ICM-1T" manufactured by Suga Test Instruments Co., Ltd. was used to measure the image clarity by the transmission method. The width of the optical comb was 2.0 mm. The angle of incidence was 0°. The measurement results of the image clarity by the transmission method are shown in the "Transmission image clarity" column of Table 1.

[0283] <<2-4. Spectral Transmittance>> Samples measuring 5 cm x 5 cm were cut out from the coating sheets according to the examples and comparative examples. Using the method described above, the spectral transmittance of each coating sheet according to the examples was measured at wavelengths of 300 nm or more and 350 nm or less in 1 nm increments. A Hitachi High-Technologies Corporation ultraviolet-visible-near-infrared spectrophotometer "UH4150" was used to measure the spectral transmittance. The maximum transmittance at wavelengths of 300 nm or more and 350 nm or less is shown in the "Spectral Transmittance" column of Table 1.

[0284] <<2-5. Image clarity>> Samples measuring 5 cm x 5 cm were cut out from the covering sheets according to the examples and comparative examples. The samples were visually inspected for the absence of any abnormalities such as dust or scratches. The image clarity of the covering sheets according to each example was measured by the reflection method using the method described above. The image clarity measurement device "ICM-1T" manufactured by Suga Test Instruments Co., Ltd. was used to measure the image clarity by the reflection method. The width of the optical comb was 1.0 mm. Two incident angles were used: 45° and 60°. The measurement results of the image clarity by the reflection method with an incident angle of 45° are shown in the "45° Reflected Image Clarity" column of Table 1. The measurement results of the image clarity by the reflection method with an incident angle of 60° are shown in the "60° Reflected Image Clarity" column of Table 1.

[0285] <<2-6. Transmission Haze>> Samples measuring 5 cm x 5 cm were cut out from the antiglare sheets according to the Examples and Comparative Examples. The transmission haze (%) of the covering sheet according to each Example was measured using the method described above. A haze meter "HM-150L2N" manufactured by Murakami Color Research Laboratory was used to measure the transmission haze. The measurement results of the transmission haze are shown in the "Hz" column of Table 1.

[0286] <<2-7. Sensory Evaluation of Visibility>> Samples measuring 5 cm x 5 cm were cut from the covering sheets according to the Examples and Comparative Examples. The samples of each Example were placed on a steel plate with an "X" mark written on its surface, and the visibility of the "X" mark on the steel plate was evaluated. The steel plate was a sandblasted plate manufactured by TP Giken. The sandblasted plate was SS400, sandblasted on both sides. The SS400 was a structural steel plate conforming to JIS C3101. The sandblasting treatment aimed for a surface roughness Rz of 25 μm for the SS400. The surface roughness Rz was the surface roughness Rz conforming to JIS B 0601:2013. The "X" mark was 1 cm x 1 cm in size. The "X" mark was written using the "fine" edge of ZEBRA's black oil-based marker "Mackie Extra Fine".

[0287] In a bright room environment with the lighting device turned on, it was confirmed whether the "X" mark on the steel plate could be observed through the covering sheet of each example. The evaluation samples, including the steel plate and the covering sheet of each example, were flat. The evaluation sample was observed while slowly changing its orientation from a state in which the normal of the evaluation sample was aligned vertically to a state in which it was tilted horizontally over a 90° angle range. The lighting device was installed vertically above the evaluation sample. The evaluator's face was positioned facing the evaluation sample from a horizontal direction. The evaluator's face position was fixed regardless of the orientation of the evaluation sample. The lighting device was an Hf32-type straight-tube, three-wavelength, daylight white fluorescent lamp. The illuminance on the evaluation sample, directed horizontally, was 600 lux to 800 lux. The evaluators were 20 healthy individuals in their 30s with visual acuity of 0.7 or higher.

[0288] The results of evaluation based on the following evaluation criteria are shown in the "Visibility" column of Table 1. A: 15 or more evaluators out of 20 were able to continue to observe the "X" mark for the entire period during which the evaluation sample was tilted. B: 15 or more evaluators out of 20 were unable to observe the "X" mark for a portion of the period during which the evaluation sample was tilted. BB: 15 or more evaluators out of 20 were unable to observe the "X" mark for the entire period during which the evaluation sample was tilted.

[0289] <<2-8. Weather Resistance Test>> Samples measuring 3 cm x 3 cm were cut out from the coating sheets according to the Examples and Comparative Examples. The evaluation samples of each Example were subjected to the above-described 408-hour weather resistance test. The weather resistance test was carried out under the following conditions.

[0290] A 20-hour irradiation process and a 4-hour condensation process were defined as one cycle, and the evaluation sample was exposed to the irradiation process and the condensation process by repeating the cycle until reaching 408 hours. A 30-second shower process was carried out after the irradiation process and before the condensation process started, and after the condensation process and before the irradiation process started. In the shower process, a water shower was poured onto the evaluation sample held in the weather resistance test device.

[0291] The weather resistance test equipment used was the "Eye Super UV Tester SUV-W261," an ultra-accelerated weather resistance test equipment manufactured by Iwasaki Electric Co., Ltd. The UV lamp, lamp jacket, and illuminance meter included in the weather resistance test equipment were 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. Illuminance meter: Product name: UVD-365PD, manufactured by Iwasaki Electric Co., Ltd.

[0292] The conditions for the irradiation process were as follows: <Irradiation conditions> Black panel temperature: 63°C Illuminance: 100 mW / cm ２ ・Inside tank humidity: 50%RH ・Time: 20 hours

[0293] The conditions for the condensation process were as follows: <Irradiation conditions> Black panel temperature: 30°C Illuminance: 0 mW / cm 2 ・Humidity inside the tank: 98%RH ・Time: 4 hours

[0294] After 408 hours of weather resistance testing, the total light transmittance (%), transmission haze (%), and maximum spectral transmittance (%) at wavelengths of 300 nm or more and 350 nm or less were measured for each evaluation sample. The measurements of total light transmittance (%), transmission haze (%), and maximum spectral transmittance (%) were the same as those in <<2-1. Total Light Transmittance>>, <<2-6. Transmission Haze>>, and <<2-4. Spectral Transmittance>>, respectively. The measurement results of total light transmittance (%) are shown in the "Tt" column under "After 408 hours of S-UV" in Table 1. The measurement results of transmission haze (%) are shown in the "Hz" column under "After 408 hours of S-UV" in Table 1. The measurement results of maximum spectral transmittance (%) are shown in the "Spectral Transmittance" column under "After 408 hours of S-UV" in Table 1.

[0295]

[0296] In Comparative Example 1, the paint used to form the resin layer was a colored paint intended for forming a top coat layer on a steel structure intended for outdoor installation. In Comparative Example 1, the total light transmittance was low and the transmission haze was high. Furthermore, the specular gloss was high, and the lighting device was clearly reflected during the visibility evaluation. As a result, the evaluation of the visibility of the base was extremely poor.

[0297] An acrylic film containing an ultraviolet absorber was used in Comparative Example 2. The covering sheet of Comparative Example 2 had a high specular gloss. Due to reflections from the lighting device, it was difficult to observe the base.

[0298] In Comparative Example 3, the visibility of the substrate was good. However, since the covering sheet of Comparative Example 3 did not contain a weathering agent, it broke in the weather resistance test. The covering sheet of Comparative Example 4 also did not contain a weathering agent, so it disintegrated in the weather resistance test.

[0299] 10: Structure, 11: Surface, 12: Deteriorated portion, 15: Bonding layer, 18: Anti-rust layer, 19: Top coat layer, 20: Adherend, 22: Surface preparation surface, 30: Covering sheet, 31: First surface, 32: Second surface, 41: Substrate, 42: Weather-resistant layer, 43: Bonding layer, 44: Barrier layer, 45: Second bonding layer, 46: Release film, 50: Coating film, 50P: Active film, 51: Anti-rust layer, 52: First primer layer, 53: Second primer layer, 54: Intermediate coat layer, 55: Top coat layer, 60: Rust, 100: Structure

Claims

1. A covering sheet used to cover an adherend, comprising a first side and a second side, the first side facing away from the adherend, a total light transmittance of 70% or more, a specular gloss of the first side at an incident angle of 60° of 30 or less, an image clarity of 5.0% or more as measured by a transmission method using an optical comb with a width of 2.0 mm, and a maximum spectral transmittance of 1.0% or less at a wavelength of 300 nm or more and 350 nm or less.

2. The covering sheet according to claim 1, wherein the image clarity is 40% or less when measured by a reflection method using an optical comb having a width of 1.0 mm and an incident angle of 45°.

3. The covering sheet according to claim 1, wherein the image clarity is 30% or less when measured by a reflection method using an optical comb having a width of 1.0 mm and an incident angle of 60°.

4. The coating sheet according to claim 1, wherein the transmission haze is 97% or less.

5. The covering sheet according to claim 1, comprising, in order from the second surface to the first surface, a substrate and a weather-resistant layer, wherein the substrate comprises a polyolefin.

6. The covering sheet according to claim 1, comprising, in this order from the second surface to the first surface, a substrate and a weather-resistant layer, wherein the weather-resistant layer comprises a cured product of an electron beam-curable resin composition.

7. The covering sheet according to claim 1, comprising, in this order from the second surface to the first surface, a barrier layer and a weather-resistant layer, wherein the weather-resistant layer contains an ultraviolet absorber.

8. The water vapor permeability at a temperature of 40°C and a humidity of 90% is 6.0 g / (m ２ The coating sheet according to claim 1, wherein the average curing time is 100 minutes or less.

9. The covering sheet according to claim 1, wherein after a 408-hour weather resistance test, the total light transmittance is 70% or more and the maximum spectral transmittance in the wavelength range of 300 nm to 350 nm is 1.0% or less.

10. The coating sheet according to claim 1, comprising, in order from the second surface to the first surface, a bonding layer and a substrate.

11. A structure comprising the adherend and the covering sheet according to any one of claims 1 to 10.

12. A method for repairing a structure, comprising the steps of: adjusting a deteriorated portion of the structure; and covering the adjusted adherend with the covering sheet according to any one of claims 1 to 10.

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