Water-repellent structure

Abstract

To provide a water-repellent structure having sufficient water repellency without using any water-repellent component.SOLUTION: A water-repellent structure has a surface whose arithmetic average inclination RΔa is 10 degrees or more if a surface roughness of the surface is measured with a method according to JIS B 0601:2001.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a water-repellent structure. [Background technology]

[0002] Generally, to impart water repellency to the surface of a product, a component-additive method is used in which a water-repellent component such as a fluororesin, a silicone resin, or a sugar fatty acid ester is applied to the surface. For example, Patent Document 1 describes a composition containing a sugar fatty acid ester-bonded cellulose-based material. In this composition, the sugar fatty acid ester is present on the surface of the bonded cellulose-based material at a concentration that exhibits a water contact angle of 90 degrees or more. However, when using such a method of adding ingredients, there is a problem in that the effects on the human body and the environment must be considered. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2020-500222 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a water-repellent structure that has sufficient water repellency without using a water-repellent component. [Means for solving the problem]

[0005] According to one aspect of the present invention, there is provided a water-repellent structure in which, when the surface roughness of the surface is measured by a method in accordance with JIS B 0601:2001, the arithmetic mean slope RΔa of the surface is 10 degrees or more.

[0006] In the water-repellent structure according to one aspect of the present invention, it is preferable that the arithmetic mean slope RΔa is calculated from the following formula (F1) based on a roughness curve, and the measurement length of the roughness curve is 700 μm.

[0007]

number

[0008] In the formula (F1), ΔX is the interval between each measurement section, ΔYi is the height difference between each measurement section, and n is an integer of 100 or more.

[0009] In the water-repellent structure according to one aspect of the present invention, it is preferable that a resin layer made of a resin is provided on the surface of the water-repellent structure.

[0010] In the water-repellent structure according to one aspect of the present invention, the resin is preferably a resin having a hydrolyzable group.

[0011] In the water-repellent structure according to one aspect of the present invention, the resin is preferably a biodegradable resin.

[0012] In the water-repellent structure according to one aspect of the present invention, the resin is preferably at least one selected from the group consisting of polylactic acid, polybutylene succinate, and cellulose acetate.

[0013] In the water-repellent structure according to one aspect of the present invention, the resin is preferably a thermoplastic resin.

[0014] In the water-repellent structure according to one aspect of the present invention, the softening point of the thermoplastic resin is preferably 40°C or higher and 200°C or lower.

[0015] In the water-repellent structure according to one aspect of the present invention, the resin preferably satisfies at least one of the following conditions 1 and 2: Condition 1: When the water-repellent structure formed by transferring the resin layer using transfer molding on SUS304#600 is measured for the water contact angle on the surface using a method in accordance with JIS R 3257:1999, Section 6. Sessile drop method, the water contact angle is 100 degrees or less. Condition 2: For a water-repellent structure in which the arithmetic mean slope RΔa of the surface of the resin layer is in the range of 0.1 degrees or more and 1 degree or less, when the water contact angle of the surface is measured by a method in accordance with JIS R 3257:1999, 6. Sessile drop method, the water contact angle is 100 degrees or less.

[0016] In the water-repellent structure according to one aspect of the present invention, the arithmetic mean height Ra of the surface is preferably 0.1 μm or more and 30 μm or less.

[0017] In the water-repellent structure according to one aspect of the present invention, the water-repellent structure is preferably in the form of a sheet. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide a water-repellent structure having sufficient water repellency without using a water-repellent component. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a graph showing an example of a roughness curve when measuring surface roughness. [Figure 2] 1 is a schematic diagram illustrating an example of a water-repellent structure according to an embodiment of the present invention. [Figure 3] FIG. 1 is a schematic view showing a manufacturing apparatus for manufacturing an example of a water-repellent structure according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] [Embodiment] The present invention will be described below with reference to the drawings, taking an embodiment as an example. The present invention is not limited to the content of the embodiment. In the drawings, some parts are illustrated enlarged or reduced in size for ease of explanation.

[0021] (Water-repellent structure) In the water-repellent structure according to this embodiment, when the surface roughness of the surface is measured by a method conforming to JIS B 0601:2001, the arithmetic mean slope RΔa of the surface must be 10 degrees or more. If the arithmetic mean slope RΔa is less than 10 degrees, sufficient water repellency cannot be obtained. From the viewpoint of water repellency, the arithmetic mean slope RΔa is preferably 12 degrees or more, more preferably 15 degrees or more, and particularly preferably 18 degrees or more. The upper limit of the arithmetic mean slope RΔa is not particularly limited, but may be, for example, 50 degrees or less, 40 degrees or less, or 30 degrees or less.

[0022] In the water-repellent structure according to this embodiment, the arithmetic mean slope RΔa is calculated from the following formula (F1) based on the roughness curve, and it is preferable that the measurement length for measuring this roughness curve is 700 μm.

[0023]

number

[0024] In formula (F1), ΔX is the interval between each measurement section, and ΔYi is the height difference between each measurement section. n is an integer of 100 or more. Furthermore, n is preferably an integer of 200 or more, and more preferably an integer of 300 or more. On the other hand, the upper limit of n is preferably an integer of 3000 or less, and more preferably an integer of 2000 or less.

[0025] Here, a method for measuring the arithmetic mean slope RΔa will be described with reference to FIG. In the graph of Figure 1, the measurement length for measuring the roughness curve is 700 μm. The roughness curve is obtained by plotting the measurement length on the horizontal axis and the height on the vertical axis. ΔX in formula (F1) is the interval between each measurement section, and this interval is determined by the value of n. For example, when n is 1400, ΔX is 0.5 μm. Then, the height difference ΔYi between each measurement section is measured, and the arithmetic mean slope RΔa can be calculated using formula (F1).

[0026] In the water-repellent structure according to this embodiment, the arithmetic mean height Ra of the surface is preferably 0.1 μm or more and 30 μm or less. If the arithmetic mean height Ra is within the above range, the water repellency can be further improved. From the same viewpoint, the arithmetic mean height Ra is more preferably 0.5 μm or more, even more preferably 1 μm or more, and particularly preferably 2 μm or more. The upper limit of the arithmetic mean height Ra is more preferably 25 μm or less, and particularly preferably 20 μm or less.

[0027] In the water-repellent structure according to this embodiment, when the contact angle of water on the surface is measured by a method based on JIS R 3257:1999, 6. Sessile drop method, the contact angle of water is preferably 90 degrees or more. If the water contact angle is 90 degrees or more, it can be said that the water-repellent structure has water repellency. From the viewpoint of water repellency, the water contact angle is more preferably 95 degrees or more, even more preferably 100 degrees or more, and particularly preferably 110 degrees or more.

[0028] (Water-repellent sheet) The water-repellent structure according to this embodiment is preferably in the form of a sheet. Specifically, the water-repellent structure is preferably a resin sheet. The water-repellent structure preferably includes a substrate sheet and a resin layer laminated on the substrate sheet. Although the configuration of the water-repellent structure according to this embodiment is not limited to this configuration, this embodiment will be described below by taking as an example a water-repellent structure (for example, a water-repellent sheet 1) including a substrate sheet 2 and a resin layer 3 as shown in FIG. 2.

[0029] The water-repellent sheet 1 includes a base sheet 2 and a resin layer 3. The resin layer 3 is laminated on the base sheet 2. When the surface roughness of the surface of the resin layer 3 is measured, the arithmetic mean slope RΔa of the surface is 10 degrees or more.

[0030] There are no particular limitations on the base sheet 2, so long as it is a paper or film-like base material that can support the resin layer 3. Examples of the base sheet 2 include a paper base material, a base fabric, and a resin film. Examples of the paper substrate include tissue paper, kraft paper, linter paper, medium-quality paper, fine paper, impregnated paper, coated paper, art paper, parchment paper, and glassine paper. Examples of resins for the resin film include polyolefin resins (polyethylene, polypropylene, etc.), vinyl resins (polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, etc.), polyester resins (polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc.), and other synthetic resins (polystyrene, acrylonitrile-butadiene-styrene copolymer, polylactic acid, polybutylene succinate, cellulose acetate, cellophane, polycarbonate, etc.). Among these, paper substrates are preferred in terms of heat resistance and thermoformability. Furthermore, from the viewpoint of excellent heat resistance and dimensional stability, kraft paper, medium-grade paper, fine paper, impregnated paper, etc. are more preferred. Furthermore, from the viewpoint of biodegradability, a resin film containing at least one selected from the group consisting of polylactic acid, polybutylene succinate, and cellulose acetate is preferred.

[0031] There are no particular limitations on the thickness and size of the base sheet 2, and sheets of a predetermined thickness and size can be used as appropriate depending on the application of the water-repellent sheet 1, the type of base sheet 2, and the like. For example, when the base sheet 2 is a paper base, its basis weight is 30 g / m 2 It is preferable that the weight is 80 g / m or more. 2 The upper limit of the basis weight is 200 g / m².2 Preferably, it is 140 g / m or less. 2 More preferably, it is: When the base sheet 2 is a synthetic resin film, its thickness is preferably 5 μm or more, and more preferably 15 μm or more. The upper limit of the thickness is preferably 500 μm or less, and more preferably 300 μm or less.

[0032] The resin layer 3 is provided on the surface of the water-repellent sheet 1 and is made of resin. The resin may be a thermoplastic resin. From the viewpoint of addressing environmental issues related to plastics, the resin is preferably a resin having a hydrolyzable group, more preferably a biodegradable resin. Examples of the hydrolyzable group include a group having an ester bond. Generally, layers made of resins having hydrolyzable groups or biodegradable resins tend to be hydrophilic. However, according to the present embodiment, a special surface structure is applied to the surface of such a layer. Therefore, despite the use of the above resins, the resin layer 3 can have sufficient water repellency.

[0033] Examples of resins having hydrolyzable groups or biodegradable resins include polylactic acid (PLA), polybutylene succinate (PBS), cellulose acetate (CA), polybutylene succinate adipate (PBSA), polycaprolactone (PCL), polyvinyl alcohol (PVA), polybutylene adipate terephthalate (PBAT), polyglycolic acid (PGA), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), polyethylene terephthalate succinate (PETS), polyethylene succinate (PES), and polyhydroxyalkanoic acid (PHA). Among these, polylactic acid, polybutylene succinate, and cellulose acetate are preferred from the viewpoint of biodegradability.

[0034] The thermoplastic resin may be an amorphous resin or a crystalline resin. From the viewpoint of sheet productivity, the softening point of the thermoplastic resin is preferably 40°C or higher and 200°C or lower. From the same viewpoint, the softening point of the thermoplastic resin is more preferably 60°C or higher, even more preferably 100°C or higher, and particularly preferably 140°C or higher. The upper limit of the softening point of the thermoplastic resin is more preferably 180°C or lower. Examples of amorphous resins include polystyrene, acrylonitrile-butadiene-styrene copolymer (ABS), polyvinyl chloride, acrylic resin, methacrylic resin, and polycarbonate.

[0035] Examples of crystalline resins include polyethylene, polypropylene (PP), polyethylene terephthalate (PET), polyvinylidene chloride, nylon 6 (polyamide), nylon 66 (polyamide), polyacetal, polyphenylene sulfide, and polytetrafluoroethylene. When a crystalline resin is used, the melting point of the crystalline resin is preferably 100° C. or higher and 250° C. or lower from the viewpoint of sheet productivity.

[0036] The resin in this embodiment is preferably a resin that satisfies at least one of the following conditions 1 and 2. When a layer made of a resin that satisfies these conditions is formed, the surface usually tends to lack sufficient water repellency. However, according to this embodiment, a special surface structure is applied to the surface of such a layer. Therefore, despite the use of the above resin, the resin layer 3 can have sufficient water repellency. Condition 1: When the water-repellent structure is formed by transferring a resin layer onto SUS304#600 using transfer molding, the water contact angle on the surface is measured using a method in accordance with JIS R 3257:1999, Section 6. Sessile Drop Method, and the water contact angle is 100 degrees or less. Condition 2: For a water-repellent structure in which the arithmetic mean slope RΔa of the surface of the resin layer is in the range of 0.1 degrees or more and 1 degree or less, when the water contact angle of the surface is measured using a method in accordance with JIS R 3257:1999, 6. Sessile drop method, the water contact angle is 100 degrees or less.

[0037] There are no particular limitations on the thickness and size of the resin layer 3, and resin layers of predetermined thickness and size can be used appropriately depending on the application of the water-repellent sheet 1, the type of resin layer 3, and the like. The thickness of the resin layer 3 is preferably 5 μm or more, more preferably 10 μm or more. The upper limit of the thickness of the resin layer 3 is preferably 200 μm or less, more preferably 100 μm or less.

[0038] (Method of manufacturing water-repellent structure) Next, the water-repellent structure according to this embodiment will be described using a method for manufacturing the water-repellent sheet 1 as an example. The water-repellent sheet 1 can be produced using a water-repellent sheet production apparatus 10 shown in Fig. 3. The water-repellent sheet 1 can be produced by carrying out the lamination step and embossing step described below. The water-repellent sheet manufacturing apparatus 10 includes an extruder 11 and an embossing unit 12 . The extruder 11 is provided with a T-die, and extrudes a resin to apply the resin onto the base sheet 2. The resin is extruded from the T-die onto the base sheet 2 and laminated thereon.

[0039] The embossing pattern processing section 12 is a section where embossing of the resin layer 3 is performed, and includes an embossing roll 12a and a pressure roll 12b. The embossing roll 12a is a metal roll, and its outer surface is formed with an uneven shape corresponding to the embossed pattern. Cooling water is passed through the inside of the embossing roll 12a. The embossing roll 12a also serves as a cooling roll for cooling and solidifying the resin layer 3 laminated on the base sheet 2. The pressure roll 12b is a rubber roll, and its outer surface is approximately smooth.

[0040] In the lamination step, a molten resin is extruded from the die of an extruder 11 onto a substrate sheet 2 supplied to the water-repellent sheet manufacturing apparatus 10 and laminated thereon, thereby forming a resin layer 3. The conditions of the extruder 11 such as the heating temperature are appropriately set depending on the melting point, melt flow rate, etc. of the resin that constitutes the resin layer 3.

[0041] In the embossing step, a concave and convex shape is formed on the resin layer 3 on the base sheet 2 formed in the lamination step. An embossing roll 12a and a pressure roll 12b that constitute the embossed pattern processing section 12 are arranged horizontally facing each other. The base sheet 2 on which the resin layer 3 has been formed is fed substantially downward and sandwiched between the embossing roll 12a and the pressure roll 12b. The uneven pattern that has been formed in advance on the surface of the embossing roll 12a is transferred to the resin layer 3 that comes into contact with the embossing roll 12a. At the same time, the resin layer 3 is cooled. This transfer and cooling form an uneven pattern on the surface of the resin layer 3.

[0042] Here, the conditions such as the pressing pressure and heating temperature during embossing can be appropriately set depending on the resin material or the uneven shape of the surface of the embossing roll 12a. The heating temperature during embossing is preferably 140° C. or higher, more preferably 160° C. or higher. The upper limit of the heating temperature is preferably 200° C. or lower, more preferably 180° C. or lower. The pressing pressure during embossing is preferably 0.05 MPa or more, more preferably 0.1 MPa or more, and the upper limit of the pressing pressure is preferably 3 MPa or less, more preferably 1 MPa or less. The heating time during embossing is preferably 10 seconds or more, more preferably 30 seconds or more, and the upper limit of the heating time is preferably 5 minutes or less, more preferably 3 minutes or less. The cooling time after embossing is preferably 20 seconds or more, more preferably 2 minutes or more. The upper limit of the cooling time is preferably 15 minutes or less, more preferably 8 minutes or less. The cooling temperature here is, for example, 20°C or more and 30°C or less.

[0043] In this embodiment, it is necessary to adjust the uneven shape of the surface of the embossing roll 12a, because the uneven shape of the surface of the resin layer 3 changes depending on the uneven shape of the surface of the embossing roll 12a. An embossing material is provided on the surface of the embossing roll 12a, and the surface of the embossing roll 12a can be adjusted by (i) changing the type of embossing material or (ii) performing various surface treatments on the embossing material. Examples of materials for the embossing material include iron and stainless steel (SUS). Examples of surface treatments include blasting, buffing, etching, laser engraving, resist processing, and mill engraving. The beads used in the blasting treatment are not particularly limited, but are preferably selected from the viewpoint of the surface irregularities. Examples of materials for the beads include alumina, zirconia, silica, iron, silicon carbide (SiC), boron carbide (B4C), and mixtures thereof. Among these, alumina or zirconia is preferred, and alumina is more preferred. Examples of the shape of the beads include rectangular, cylindrical, and spherical shapes. Among these, rectangular shapes are preferred. In this embodiment, by adjusting the uneven shape of the surface of the embossing roll 12a, it is possible to form a resin layer 3 having a surface with an arithmetic mean slope RΔa of 10 degrees or more.

[0044] In this manner, the water-repellent sheet 1 is manufactured. The water-repellent sheet 1 is wound into a roll by a winding machine (not shown). The wound water-repellent sheet 1 is cut into appropriate sizes according to the intended use and used.

[0045] (Effects of the embodiment) According to this embodiment, the following effects can be achieved. In this embodiment, a water-repellent sheet 1 is obtained that includes a resin layer 3 having a surface with an arithmetic mean slope RΔa of 10 degrees or more. The resin layer 3 in this water-repellent sheet 1 has sufficient water repellency without using any water-repellent component.

[0046] (Modification of the embodiment) The present invention is not limited to the above-described embodiment, and includes modifications and improvements within the scope of achieving the object of the present invention. For example, in the above-described embodiment, the water-repellent sheet 1 has been described as an example of the water-repellent structure, but the present invention is not limited to this. For example, the water-repellent structure does not have to be in a sheet form or a laminate. Furthermore, the water-repellent structure may have a pressure-sensitive adhesive layer on a surface different from the water-repellent structure surface, and for example, by attaching the water-repellent structure to an adherend via the pressure-sensitive adhesive layer, the adherend can be made into a water-repellent structure.

[0047] In the method for producing a water-repellent sheet in the above-described embodiment, embossing is performed using the water-repellent sheet production apparatus 10, but this is not limiting. For example, embossing may be performed by overlapping an embossing plate having desired irregularities with a resin sheet, and applying heat and pressure using a heat press. [Example]

[0048] The present invention will be described in more detail below with reference to examples. However, these examples do not limit the present invention. The resins used in the examples and comparative examples are shown below. (Resin-1) Brand: FORZEAS ZM9B02 manufactured by Mitsubishi Chemical Corporation Resin type: Polybutylene succinate (PBS) Biodegradable: Yes Softening point: 119℃ Melting point: 113℃ Glass transition temperature (Tg): -33℃ (Resin-2) Brand: Daicel Corporation "L-20" Resin type: Cellulose acetate (CA) Biodegradable: Yes Softening point: 180℃ Melting point: 230℃ Glass transition temperature (Tg): 160℃ (Resin-3) Brand: Terramac TE-2000C manufactured by Unitika Ltd. Resin type: Polylactic acid (PLA) Biodegradable: Yes Softening point: 58℃ Melting point: 170℃ Glass transition temperature (Tg): 57℃ (Resin-4) Brand: SunAllomer PHA03A manufactured by SunAllomer Co., Ltd. Resin type: Polypropylene (PP) Biodegradability: No Softening point: 169℃ Melting point: 162°C Glass transition temperature (Tg): -20℃

[0049] [Example 1] First, a resin film made of Resin-1 and having a thickness of 100 μm was prepared. Next, the mount, the process release paper ("ESRL-5" manufactured by Lintec Corporation), the resin film, and the embossing material (dimensions: 100 mm x 100 mm, thickness: 3 mm) described below were stacked in this order, and the resulting laminate was pressed using a heat press at a heating temperature of 190°C and a pressing pressure of 4.0 kgf / cm. 2 The resin was heated and pressed under pressure (approximately 0.4 MPa) for 1 minute, and cooled at 23°C for 5 minutes. This caused the resin to melt and adhere, forming a resin sheet on the release paper. The embossing material and backing paper were then removed, and the release paper was peeled off from the resin sheet to obtain a resin sheet (water-repellent sheet). The resin and blasting material used in Example 1 are listed in Table 1. (embossed material) Plate brand: SUS304#600 Surface treatment: blasting Blasting material brand: "FZG" manufactured by Fuji Manufacturing Co., Ltd. Shape of blasting material: Square Blast material number: #30 Blast material particle size: 60~130μm

[0050] [Examples 2 to 7] A resin sheet (water-repellent sheet) was obtained in the same manner as in Example 1, except that the resin and blasting material shown in Table 1 below were used. The brand of blasting material used in Example 2 etc. was "WA" manufactured by Fuji Manufacturing Co., Ltd.

[0051] [Comparative Examples 1 to 5] A resin sheet was obtained in the same manner as in Example 1, except that the resins and blasting materials shown in Table 1 below were used. In Comparative Example 1, the embossed material was not subjected to blasting treatment, and "SUS304#600" was used as it was. In Comparative Example 2, the brand of blasting material used was "FGB" manufactured by Fuji Manufacturing Co., Ltd.

[0052] [Surface roughness analysis] The surface roughness of the resin sheets obtained in the examples and comparative examples was analyzed by a method conforming to JIS B 0601: 2001. Specifically, the surface roughness was analyzed under the following conditions using a "Color 3D Laser Microscope (Model: VK-9700)" manufactured by Keyence Corporation, and a roughness curve was measured. Objective lens magnification: 20x Roughness curve smoothing: Height smoothing ±4 Measurement length: 700 μm Number of measurements: 3 Based on the obtained roughness curve, the arithmetic mean slope RΔa was calculated using the above formula (F1). The interval ΔX between each measurement section was set to 0.5 μm. The measurement was performed three times, and the average value was taken as the value of the arithmetic mean slope RΔa. The results are shown in Table 1.

[0053] [Water contact angle] The water contact angle was measured in accordance with JIS R3257:1999, Section 6, Sessile Drop Method. However, instead of a glass substrate, the resin sheets obtained in the Examples and Comparative Examples were used as samples, and the contact angle was measured on the resin surface of the sample on which the irregularities were formed. The measuring device used was a "DMo-701" manufactured by Kyowa Interface Science Co., Ltd. The results obtained are shown in Table 1.

[0054] [Table 1]

[0055] The results shown in Table 1 indicate that when the arithmetic mean slope RΔa of the surface of the resin sheet is 10 degrees or more (Examples 1 to 7), the water contact angle is larger than when the arithmetic mean slope RΔa of the surface of the resin sheet is less than 10 degrees (Comparative Examples 1 to 4). [Explanation of symbols]

[0056] 1...water-repellent sheet, 2...base sheet, 3...resin layer, 10...water-repellent sheet manufacturing apparatus, 11...extruder, 12...embossing pattern processing section, 12a...embossing roll, 12b...pressure roll.

Claims

1. A water-repellent structure having an arithmetic mean slope RΔa of the surface of 18 degrees or more when the surface roughness of the surface is measured by a method conforming to JIS B 0601:2001, a resin layer made of a resin is provided on the surface of the water-repellent structure, the resin is at least one selected from the group consisting of polylactic acid, polybutylene succinate, and cellulose acetate; The arithmetic mean slope RΔa is calculated based on the roughness curve using the following formula (F1): The measurement length for measuring the roughness curve is 700 μm. Water-repellent structure. [Equation 1] (In the formula (F1), ΔX is the interval between each measurement section, ΔX is 0.5 μm, ΔYi is the height difference between each measurement section, and n is an integer of 100 or more.)

2. The water-repellent structure according to claim 1, The softening point of the resin is 40°C or higher and 200°C or lower. Water-repellent structure.

3. The water-repellent structure according to claim 1 or 2, The resin satisfies at least one of the following conditions 1 and 2: Water-repellent structure. Condition 1: When the water-repellent structure formed by transferring the resin layer using transfer molding of SUS304#600 is measured for the contact angle of water on the surface by a method in accordance with JIS R 3257:1999, 6. Sessile drop method, the contact angle of water is 100 degrees or less. Condition 2: When the water-repellent structure has an arithmetic mean slope RΔa of the surface of the resin layer in the range of 0.1 degree or more and 1 degree or less, and the water contact angle of the surface is measured by a method in accordance with JIS R 3257:1999, Section 6. Sessile drop method, the water contact angle is 100 degrees or less.

4. The water-repellent structure according to any one of claims 1 to 3, The arithmetic mean height Ra of the surface is 0.1 μm or more and 30 μm or less. Water-repellent structure.

5. The water-repellent structure according to any one of claims 1 to 4, The water-repellent structure is in a sheet form. Water-repellent structure.

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