Surface structural body and method for manufacturing surface structural body

Abstract

Provided are: a surface structural body that has high water repellency and that provides high slidability for water droplets; and a method for manufacturing the same. A surface structural body according to one embodiment of the present disclosure is provided with: a plurality of first structures that are separated from each other with gaps therebetween; a plurality of second structures that are more minute than the plurality of first structures and are formed on the plurality of first structures; and a water-repellent substance that covers the plurality of first structures and the plurality of second structures.

Description

Surface structure and method for manufacturing a surface structure

[0001] This disclosure relates to a surface structure and a method for manufacturing a surface structure. This application claims priority under Japanese Patent Application No. 2024-167962, filed in Japan on September 27, 2024, the contents of which are incorporated herein by reference.

[0002] Patent Document 1 discloses a water-repellent, oil-repellent, and stain-resistant film. In this water-repellent, oil-repellent, and stain-resistant film, a petal-shaped transparent alumina film is formed on a substrate, and a water-repellent film covers the petal-shaped transparent alumina film. The petal-shaped transparent alumina film is formed by forming a film with a coating solution containing aluminum alkoxide, drying the formed film and heat-treating it to form an amorphous alumina film, and then hot-water-treating, drying, and firing the formed amorphous alumina film. The formed petal-shaped transparent alumina film has an average surface roughness Ra' value of 17 nm or more and a specific surface area S of 1.5 or more. Ｒ The water-repellent film is formed by applying a water-repellent agent containing a fluorine-containing silane compound having a fluorocarbon group, drying it, and firing it. The water-repellent, oil-repellent, and stain-resistant film has a contact angle with water droplets of approximately 150° to 170° and possesses superhydrophobic properties (paragraphs 0021, 0022, 0028, 0030, 0031, 0034, and 0035).

[0003] Patent No. 3688042

[0004] In the water-repellent, oil-repellent, and stain-resistant film disclosed in Patent Document 1, if there are defects in the petal-shaped transparent alumina film or partial defects in the formation of the water-repellent film, water adhering to the water-repellent, oil-repellent, and stain-resistant film is pinned to the areas where there are defects in the petal-shaped transparent alumina film or partial defects in the formation of the water-repellent film. Therefore, it is difficult to slide the water off by tilting the substrate.

[0005] One aspect of this disclosure has been made in view of this problem. One aspect of this disclosure aims to provide, for example, a surface structure having high water repellency and high water droplet sliding properties, and a method for manufacturing the same.

[0006] A surface structure according to a first aspect of the present disclosure comprises a plurality of first structures separated from each other by gaps, a plurality of second structures that are finer than the plurality of first structures and formed on the plurality of first structures, and a water-repellent material covering the plurality of first structures and the plurality of second structures.

[0007] A method for manufacturing a surface structure according to a second aspect of the present disclosure includes: a) forming a plurality of first structures separated from each other by gaps; b) forming a plurality of second structures that are finer than the plurality of first structures on the plurality of first structures; and c) covering the plurality of first structures and the plurality of second structures with a water-repellent substance.

[0008] This is a schematic cross-sectional view illustrating the surface structure of the first embodiment and water droplets adhering to the surface structure. This is a schematic cross-sectional view illustrating the surface structure provided in the surface structure of the first embodiment and a water-repellent substance covering the surface structure. This is a flowchart illustrating the manufacturing flow of the surface structure of the first embodiment. This is a schematic cross-sectional view illustrating an intermediate product produced during the manufacturing process of the surface structure of the first embodiment. This is a schematic cross-sectional view illustrating an intermediate product produced during the manufacturing process of the surface structure of the first embodiment. This is an SEM image of an intermediate product produced during the manufacturing process of the surface structure of the first embodiment. This is an SEM image of an intermediate product produced during the manufacturing process of the surface structure of the first embodiment. This is a schematic cross-sectional view illustrating the surface structure of the second embodiment. This is a flowchart illustrating the manufacturing flow of the surface structure of the second embodiment. This is a schematic cross-sectional view illustrating an intermediate product produced during the manufacturing process of the surface structure of the second embodiment. This is a schematic cross-sectional view illustrating an intermediate product produced during the manufacturing process of the surface structure of the second embodiment. This is a schematic cross-sectional view illustrating an intermediate product produced during the manufacturing process of the surface structure of the second embodiment. This is a schematic cross-sectional view illustrating an intermediate product manufactured during the manufacturing process of the surface structure of the second embodiment. This is a schematic cross-sectional view illustrating an intermediate product manufactured during the manufacturing process of the surface structure of the second embodiment. This is an SEM image of an intermediate product manufactured during the manufacturing process of the surface structure of the second embodiment. This is a schematic cross-sectional view illustrating the surface structure of the third embodiment. This is a flowchart showing the manufacturing flow of the surface structure of the third embodiment. This is a schematic cross-sectional view illustrating an intermediate product manufactured during the manufacturing process of the surface structure of the third embodiment. This is a schematic cross-sectional view illustrating an intermediate product manufactured during the manufacturing process of the surface structure of the third embodiment. This is a schematic cross-sectional view illustrating an intermediate product manufactured during the manufacturing process of the surface structure of the third embodiment. This is a schematic cross-sectional view illustrating an intermediate product manufactured during the manufacturing process of the surface structure of the third embodiment. This is an SEM image of an intermediate product manufactured during the manufacturing process of the surface structure of the third embodiment.These are images of a prototype of the comparative structure and water droplets attached to the prototype. These are images of a prototype of the surface structure of the third embodiment and water droplets attached to the prototype. These are graphs showing the contact angle of water droplets with respect to the prototype of the comparative structure and the prototype of the surface structure of the third embodiment, and the sliding angle of water droplets on the prototype of the comparative structure and the prototype of the surface structure of the third embodiment.

[0009] The embodiments of this disclosure will be described below with reference to the drawings. In the drawings, the same or equivalent elements are denoted by the same reference numerals, and redundant descriptions are omitted.

[0010] 1. First Embodiment 1.1 Surface Structure Figure 1 is a schematic cross-sectional view illustrating the surface structure of the first embodiment and water droplets adhering to the surface structure.

[0011] The surface structure 1 of the first embodiment shown in Figure 1 has high water repellency. Therefore, the surface structure 1 repels water adhering to it, forming water droplets WD from the repelled water. The surface structure 1 has high water droplet WD sliding properties. Therefore, when the surface structure 1 is tilted, the formed water droplets WD slide off.

[0012] As shown in Figure 1, the surface structure 1 comprises a base material 101, a plurality of first structures 102, a plurality of second structures 103, and a water-repellent layer 104.

[0013] The base material 101 has a surface 101a. The surface 101a may be flat or may have irregularities. The base material 101 may be a flat object with a simple shape or a three-dimensional object with a complex shape. The base material 101 may be made of metal, glass, ceramics, fiber, etc.

[0014] As shown in Figure 1, the multiple first structures 102 consist of multiple island-like structures 111.

[0015] Multiple island-like structures 111 are arranged on the surface 101a of the base material 101. The multiple island-like structures 111 are arranged in the planar direction of the surface 101a and are separated from each other in the planar direction with gaps 121 between them. The multiple island-like structures 111 are made of alumina hydrate. The multiple island-like structures 111 may be made of a material other than alumina hydrate.

[0016] Each first structure 102 preferably has a size on the order of micrometers. A size on the order of micrometers is approximately a few μm to several hundred μm, and preferably a size of several tens of μm to several hundred μm. Having a size on the order of micrometers means, for example, that each first structure 102 has a size of approximately several hundred μm in the planar direction where the surface 101a of the substrate 101 extends, and a size of approximately a few μm in the thickness direction perpendicular to the surface 101a of the substrate 101.

[0017] Preferably, the gap 121 has a size on the order of micrometers. Having a size on the order of micrometers means, for example, that the gap 121 has a width of several tens of micrometers in the planar direction where the surface 101a of the substrate 101 extends, and a depth of several micrometers in the depth direction perpendicular to the surface 101a.

[0018] The multiple second structures 103 are formed into multiple island-like structures 111 and arranged on the surface 111a of the multiple island-like structures 111. The multiple second structures 103 are composed of alumina hydrate. The multiple second structures 103 may be composed of a substance other than alumina hydrate. The multiple second structures 103 are finer than the multiple first structures 102. Each second structure 103 is a plate-like structure. Each second structure 103 may have a structure other than a plate-like structure. For example, each second structure 103 may have a rod-like structure.

[0019] Each second structure 103 preferably has a size on the order of nanometers. A nanometer-order size is a size of several nanometers to several hundred nanometers, and preferably a size of several nanometers to several tens of nanometers. Having a nanometer-order size for each second structure 103 means, for example, that each second structure 103 has a width of several nanometers and a length of several nanometers to several hundred nanometers in the planar direction where the surface 101a of the substrate 101 extends, and a length of several tens of nanometers to several hundred nanometers in the thickness direction perpendicular to the surface 101a.

[0020] The multiple first structures 102 and the multiple second structures 103 form a surface structure 131 having a shape more complex than the shape of the surface 101a of the base material 101.

[0021] The water-repellent layer 104 is placed on the surface structure 131 and covers the surface structure 131.

[0022] The main surface 104a of the water-repellent layer 104 constitutes the surface 1a of the surface structure 1. The water-repellent layer 104 exhibits high water repellency. Therefore, the water-repellent layer 104 repels water adhering to the main surface 104a, i.e., the surface 1a, forming water droplets WD from the repelled water. As a result, the surface structure 1 has high water repellency.

[0023] The water-repellent layer 104 covering the surface structure 131 covers the plurality of first structures 102 and plurality of second structures 103 that form the surface structure 131.

[0024] As shown in Figure 1, the water-repellent layer 104 has a portion 141 facing the gap 121. The multiple second structures 103 have portions 142 facing the gap 121, with the protruding portion 141 in between.

[0025] Parts 141 and 142 prevent water adhering to the surface 1a of the surface structure 1 from entering the gap 121. As a result, the gap 121 continues to hold air even when water adheres to the surface 1a. Consequently, water droplets WD are not pinned to the surface 1a. This allows water droplets WD to easily slide off by tilting the surface structure 1. As a result, the surface structure 1 has high water droplet WD sliding properties.

[0026] Therefore, a three-layer structure in which a plurality of second structures 103 are formed in a plurality of first structures 102 and a water-repellent layer 104 covers the plurality of first structures 102 and the plurality of second structures 103 imparts high water repellency and high slipperiness of water droplets WD to the surface structure 1.

[0027] The water-repellent layer 104 is composed of a water-repellent substance. At least a part of the water-repellent substance constituting the portion 141, that is, the water-repellent substance constituting the water-repellent layer 104 faces the gap 121.

[0028] 1.2 Water-repellent layer FIG. 2 is a cross-sectional view schematically showing a surface structure provided in the surface structure of the first embodiment and a water-repellent substance covering the surface structure.

[0029] As shown in FIG. 2, the water-repellent substance 151 constituting the water-repellent layer 104 is composed of a plurality of molecules 161.

[0030] Each molecule 161 included in the plurality of molecules 161 is chemically bonded to the surface structure 131. The plurality of molecules 161 are arranged on the surface structure 131 to form a monolayer.

[0031] As shown in FIG. 2, each molecule 161 includes a bonding portion 171, an intermediate portion 172, and a water-repellent portion 173.

[0032] Each molecule 161 has a linear molecular structure. The bonding portion 171 is at one end of each molecule 161. The intermediate portion 172 is between one end and the other end of each molecule 161. The water-repellent portion 173 is at the other end of each molecule 161. The bonding portion 171 is arranged on the side where the surface structure 131 is arranged and is chemically bonded to the surface structure 131. The longitudinal direction of each molecule 161 is substantially perpendicular to the surface structure 131. The water-repellent portion 173 is arranged on the side opposite to the side where the surface structure 131 is arranged. Thereby, the plurality of water-repellent portions 173 respectively possessed by the plurality of molecules 161 are arranged on the surface 1a of the surface structure 1. The water-repellent portion 173 exhibits water repellency. Thereby, the surface 1a on which the plurality of water-repellent portions 173 are arranged has water repellency.

[0033] The water-repellent substance 151 is represented by the general formula X-A-Y.

[0034] X constitutes the bonding portion 171. X is a group that chemically bonds to a plurality of first structures 102 and a plurality of second structures 103, and preferably, it is -SiR １ R ２ R ３ , -COOH, -NCO or -P(=O)R ４ R ５ , and more preferably, it is -P(=O)R ４ R ５ . R １ , R ２ and R ３ are -OCH ３ , -OC ２ H ５ or -Cl. R ４ and R ５ are -OH or -Cl. -SiR １ R ２ R ３ is a silane coupling site that constitutes a silane coupling agent. -COOH is a carboxyl group that constitutes a carboxylic acid. -NCO is an isocyanate group that constitutes an isocyanate. -P(=O)R ４ R ５ is a group that constitutes a phosphonic acid or a phosphonic acid chloride. When X is -P(=O)R ４ R ５ , X strongly binds to the surface of the alumina hydrate. Therefore, when X is -P(=O)R ４ R ５ , when the plurality of first structures 102 and the plurality of second structures 103 are made of alumina hydrate, the water repellent substance 151 can be strongly bonded to the plurality of first structures 102 and the plurality of second structures 103.

[0035] A constitutes the intermediate portion 172. A is the main chain skeleton and preferably includes at least one selected from the group consisting of groups represented by chemical formulas (101) to (103), and more preferably consists of the group represented by chemical formula (101). m is an integer between 1 and 20. A may include two or more selected from the group consisting of groups represented by chemical formulas (101) to (103). The group represented by chemical formula (101) is an alkylene group. The group represented by chemical formula (102) is a phenylene group. The group represented by chemical formula (103) is a biphenylene group. The group represented by chemical formula (101) does not have significant steric hindrance, and intermolecular forces act between the group and the molecules adjacent to it. For this reason, when A consists of the group represented by chemical formula (101), multiple molecules 161 can be easily arranged.

[0036]

[0037] Y constitutes the water-repellent portion 173. Y is a water-repellent group, preferably one of the groups represented by chemical formulas (104) to (107), and more preferably the group represented by chemical formula (105). ６ , R ７ and R ８ It contains a hydrogen atom or an alkyl group having 3 or fewer carbon atoms. ９ , R １０ and R １１Y contains a hydrogen atom or an alkyl group having 3 or fewer carbon atoms. n is an integer between 1 and 20. The group represented by chemical formula (104) is a trifluoromethyl group. The group represented by chemical formula (105) is a perfluoroalkyl group. The group represented by chemical formula (106) is a silyl group. If Y is the group represented by chemical formula (105), then the group includes not only fluorine atoms located at the ends of the molecular chain, but also fluorine atoms located perpendicular to the molecular chain. The surface structure 131 on which the multiple molecules 161 are arranged has irregularities on the order of nanometers. Therefore, there is disorder in the arrangement of the multiple molecules 161. Therefore, the multiple molecules 161 include molecules having molecular chains that extend in a direction inclined from the direction perpendicular to the surface structure 131. Fluorine atoms positioned perpendicular to the molecular chain can impart high water repellency to the molecule 161 comprising the molecular chain, even when the molecular chain extends in a direction inclined from the direction perpendicular to the surface structure 131.

[0038]

[0039] 1.3 Flowchart of Surface Structure Manufacturing Diagram 3 is a flowchart showing the manufacturing flow of the surface structure according to the first embodiment. Figures 4A to 4C are schematic cross-sectional views illustrating intermediate products manufactured during the manufacturing process of the surface structure according to the first embodiment.

[0040] When the surface structure 1 is manufactured, steps S101 to S105 shown in Figure 3 are performed.

[0041] In step S101, a sol is prepared. The prepared sol contains precursors of substances constituting a plurality of first structures 102 and a liquid dispersion medium. When the sol is prepared, for example, as in synthesis by the sol-gel method, a solution containing the raw materials and the liquid dispersion medium is prepared, and the raw materials are hydrolyzed to prepare a sol containing the precursors and the liquid dispersion medium. The raw materials are, for example, metal alkoxides, and the precursors are metal hydroxides or hydrates of metal oxides. When the plurality of first structures 102 are composed of alumina hydrates, the raw materials are, for example, aluminum alkoxides, and the precursors are alumina hydrates. When the raw materials are aluminum alkoxides and the precursors are alumina hydrates, for example, aluminum tri-sec-butoxide (Al(O-sec-Bu)) ３ Isopropyl alcohol (IPA) is added to ) to form Al(O-sec-Bu) ３ An IPA solution is prepared, and the prepared IPA solution is stirred at room temperature for about 1 hour. Subsequently, ethyl acetoethyl (EAcAc) is added as a chelating agent to the stirred IPA solution to prepare an EAcAc-added IPA solution, and the prepared EAcAc-added IPA solution is stirred at room temperature for about 3 hours. Subsequently, water (H) is added to the stirred EAcAc-added IPA solution. ２ O) and IPA are carefully added dropwise to prepare the alumina sol. The weight ratio of the added substances is, for example, Al(O-sec-Bu) ３ :IPA:EAcAc:H ２ O = 1:20:1:4.

[0042] In the subsequent step S102, the prepared sol is applied to the surface 101a of the substrate 101. This forms a sol film 181 on the surface 101a, as shown in Figure 4A. The sol can be applied by methods such as spray coating, inkjet coating, dispenser coating, screen printing, or dipping.

[0043] In the subsequent step S103, the formed sol film 181 is dried. This creates a plurality of island-like structures 111, as shown in Figure 4B. When the sol film 181 dries, it shrinks. This causes the plurality of parts of the sol film 181 to separate from each other due to stress. This creates a plurality of island-like structures 111. The plurality of island-like structures 111 have a thickness of, for example, about 1 μm. The gaps 121 have a width of about 1 to 10 μm. When the plurality of island-like structures 111 are composed of alumina hydrate, the plurality of island-like structures 111 include, for example, boehmite with low crystallinity. Boehmite with low crystallinity is also called pseudoboehmite.

[0044] In the subsequent step S104, as shown in Figure 4C, a plurality of second structures 103 are formed on each of the plurality of island-like structures 111. If the plurality of island-like structures 111 are made of pseudo-boehmite, the intermediate product 191 shown in Figure 4B is immersed in hot water or exposed to steam. As a result, the hot water or steam comes into contact with the plurality of island-like structures 111, and a plurality of second structures 103 are formed on the surface of the plurality of island-like structures 111. The hot water preferably has a temperature of 50°C or more and 100°C or less. Hot water with a temperature of 100°C is boiling water. The steam has a temperature of, for example, 100°C. The temperature of the steam can be measured by a thermometer placed in a container that contains the steam. Each of the plurality of second structures 103 that are formed has a fine plate-like structure, for example, a thickness of several tens to several hundred nm, a height of several tens to several hundred nm, and a length of several nm to several tens of nm. The multiple second structures 103 are oriented in irregular directions and arranged non-periodically.

[0045] In the subsequent step S105, the intermediate product 192 shown in Figure 4C is immersed in a solution containing a water-repellent substance 151. This forms a water-repellent layer 104, as shown in Figure 1. When the intermediate product 192 is immersed in the solution containing the water-repellent substance 151, the solution comes into contact with the surface structure 131, and the water-repellent substance 151 bonds to the surface structure 131. As a result, the surface structure 131 is covered with the water-repellent substance 151. A water-repellent layer 104 made of the water-repellent substance 151 is formed. The water-repellent substance 151 is, for example, a phosphonic acid compound. An example of a phosphonic acid compound is 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecylphosphonic acid. An example of a solution containing a phosphonic acid compound is an ethanol solution.

[0046] 1.4 Electron Microscope (SEM) Images of the Prototype Figures 5A and 5B are SEM images of an intermediate product produced during the manufacturing process of the surface structure of the first embodiment.

[0047] As shown in Figure 5A, in the intermediate product 191 comprising a base material 101 and a plurality of island-like structures 111, the plurality of island-like structures 111 have irregular shapes and are arranged irregularly. Grooves constituting gaps 121 are formed between adjacent island-like structures 111.

[0048] As shown in Figure 5B, in the intermediate product 192 comprising a base material 101, a plurality of island-like structures 111, and a plurality of second structures 103, the plurality of second structures 103 are plate-like structures, have irregular shapes, and are arranged irregularly.

[0049] 2. In the second and subsequent embodiments, the differences between the second embodiment and the first embodiment will be explained. For aspects not explained, the same configuration as that used in the first embodiment will be used in the second embodiment.

[0050] 2.1 Surface Structure Figure 6 is a schematic cross-sectional view illustrating the surface structure of the second embodiment.

[0051] As shown in Figure 6, in the surface structure 2 of the second embodiment, recesses 101b are formed on the surface 101a of the base material 101. Therefore, the surface 101a has irregularities. The recesses 101b are holes, grooves, etc.

[0052] As shown in Figure 6, the surface structure 2 comprises an island-like structural layer 201 and a coating 202.

[0053] The island-like structural layer 201 is placed on the surface 101a of the base material 101.

[0054] As shown in Figure 6, the island-like structure layer 201 comprises a plurality of island-like structures 111 and recess-filling portions 112.

[0055] Multiple island-like structures 111 and recess-filling portions 112 are made of the same material and are formed simultaneously.

[0056] The recess-filling portion 112 fills the recess 101b.

[0057] Each of the multiple island-like structures 111 and recess-filling portions 112 has a surface 111a and a surface 112a, respectively. When the surface 101a of the base material 101 is considered the first surface, the surfaces 111a and 112a become the second and third surfaces, respectively.

[0058] The coating 202 is placed on the surface 101a of the base material 101, overlapping the island-like structure layer 201, and covers the base material 101 and the island-like structure layer 201. The coating 202 covers the multiple island-like structures 111 and the recess-filling portions 112. The coating 202 is made of the same material as the material constituting the island-like structure layer 201, and has a thickness thinner than the thickness of the island-like structure layer 201. The coating 202 may be made of a different material than the material constituting the island-like structure layer 201.

[0059] As shown in Figure 6, the coating 202 comprises a first portion 211, a second portion 212, and a third portion 213. The first portion 211, the second portion 212, and the third portion 213 are made of the same material and are formed simultaneously.

[0060] The first portion 211 is placed on the surface 101a of the base material 101. The second portion 212 is placed on the surface 111a of the multiple island-like structures 111. The third portion 213 is placed on the surface 112a of the recess-filling portion 112.

[0061] As shown in Figure 6, in the surface structure 2, a plurality of first structures 102 comprise a plurality of island-like structures 111 and a second portion 212. The plurality of second structures 103 are formed on the second portion 212 covering the plurality of island-like structures 111 and are arranged on the surface 212a of the second portion 212. Thus, the plurality of second structures 103 are formed on the plurality of first structures 102 and are arranged on the surface 102a of the plurality of first structures 102. In addition, the plurality of second structures 103 are also formed on the first portion 211 covering the base material 101 and the third portion 213 covering the recess-filling portion 112 and are arranged on the surface of the first portion 211 and the surface of the third portion 213. The plurality of second structures 103 are also arranged on the side surfaces of the portion 142 and the deeper portion of the gap 121. Therefore, in the surface structure 2, the surface 101a of the base material 101 is covered by two layers consisting of the island-like structure layer 201 and the coating 202, thereby forming a surface structure 131 with high coverage. This advantage is particularly noticeable when recesses 101b are formed on the surface 101a, or when the gaps between the multiple island-like structures 111 are wide.

[0062] 2.2 Flowchart of Surface Structure Manufacturing Diagram 7 is a flowchart showing the manufacturing flow of the surface structure according to the second embodiment. Figures 8A to 8E are schematic cross-sectional views illustrating intermediate products manufactured during the manufacturing process of the surface structure according to the second embodiment.

[0063] When the surface structure 2 is manufactured, steps S111 to S117 shown in Figure 7 are performed.

[0064] In step S111, a first sol and a second sol are prepared. The second sol has a lower precursor concentration than the first sol. The first sol is prepared in the same manner as the sol preparation in step S101 shown in Figure 3. The second sol is prepared by adding a liquid dispersion medium to the prepared first sol to dilute it. The second sol may be prepared without going through the first sol.

[0065] In the subsequent step S112, the prepared first sol is applied to the surface 101a of the substrate 101. As a result, a first sol film 215 is formed on the surface 101a, as shown in Figure 8A. The application of the first sol is carried out in the same manner as the application of the sol in step S102 shown in Figure 3.

[0066] In the subsequent step S113, the formed first sol film 215 is dried. This creates island-like structure layers 201, as shown in Figure 8B. As the first sol film 215 dries, it shrinks. This causes multiple parts of the first sol film 215 to separate from each other due to stress. This creates multiple island-like structures 111 and recess-filling portions 112.

[0067] In the subsequent step S114, the prepared second sol is applied to the surface 101a of the substrate 101, overlapping the island-like structure layer 201. As a result, a second sol film 216 is formed on the surface 101a, overlapping the island-like structure layer 201, as shown in Figure 8C. The application of the second sol is carried out in the same manner as the application of the sol in step S102 shown in Figure 3. The second sol has a lower precursor concentration than the first sol. Therefore, the second sol has a lower viscosity than the first sol. Therefore, the second sol spreads more easily than the first sol. Therefore, the second sol film 216 has a thinner thickness than the first sol film 215 and has higher coverage than the first sol film 215.

[0068] In the subsequent step S115, the formed second sol film 216 is dried. This forms a coating 202, as shown in Figure 8D. The formed coating 202 has a thickness thinner than the island-like structure layer 201 and has higher coverage than the island-like structure layer 201.

[0069] In the subsequent step S116, as shown in Figure 8E, a plurality of second structures 103 are formed on the formed coating 202. If the coating 202 contains pseudo-boehmite, the intermediate product 221 shown in Figure 8D is immersed in hot water or exposed to steam. As a result, the hot water or steam comes into contact with the coating 202 and a plurality of second structures 103 are formed on the surface of the coating 202. As a result, a plurality of second structures 103 are formed on the surface 102a of the plurality of first structures 102 having second portions 212. In addition, a plurality of second structures 103 are also formed on the bottom surface 231 facing the gap 121.

[0070] In the subsequent step S117, the intermediate product 222 shown in Figure 8E is immersed in a solution containing the water-repellent substance 151. As a result, a water-repellent layer 104 is formed, as shown in Figure 6. When the intermediate product 221 is immersed in the solution containing the water-repellent substance 151, the solution comes into contact with the surface structure 131, and the water-repellent substance 151 bonds to the surface structure 131. As a result, the surface structure 131 is covered with the water-repellent substance 151.

[0071] In surface structure 2, multiple second structures 103 are formed not only on the surfaces 102a of the multiple first structures 102, but also on the bottom surface 231 facing the gaps 121. Therefore, in surface structure 2, the number of defective areas where multiple second structures 103 are not formed can be reduced compared to surface structure 1. As a result, surface structure 2 has higher water repellency than surface structure 1. Furthermore, because multiple second structures 103 are formed on the bottom surface 231 facing the gaps 121, when surface structure 2 is cooled and its temperature reaches the dew point, condensation water generated on the surface of surface structure 2 can be prevented from remaining on the bottom surface 231, and the condensation water can be repelled and slid off. In other words, surface structure 2 has high water repellency and high sliding properties not only for water dripped onto its surface, but also for water generated on its surface.

[0072] 2.3 SEM Image of Prototype Figure 9 is an SEM image of an intermediate product produced during the manufacturing process of the surface structure of the second embodiment.

[0073] Figure 9 shows SEM images of intermediate product 222 for each of the following cases: when the precursor concentration of the first sol is 1 / 4 of the standard precursor concentration and the precursor concentration of the second sol is 1 / 8 of the standard precursor concentration, and when the precursor concentration of the first sol is 1 / 2 of the standard precursor concentration and the precursor concentration of the second sol is 1 / 4 of the standard precursor concentration. The SEM images include those at magnifications of 400x, 1000x, and 5000x.

[0074] As shown in Figure 9, the multiple island-like structures 111 formed when the precursor concentration of the first sol is 1 / 2 of the standard precursor concentration and the precursor concentration of the second sol is 1 / 4 of the standard precursor concentration are denser than the multiple island-like structures 111 formed when the precursor concentration of the first sol is 1 / 4 of the standard precursor concentration and the precursor concentration of the second sol is 1 / 8 of the standard precursor concentration. For this reason, the surface structure 2 having the former multiple island-like structures 111 has higher water repellency than the surface structure 2 having the latter multiple island-like structures 111.

[0075] Thus, the density of the multiple island-like structures 111 can be changed by adjusting the precursor concentrations of the first sol and the second sol.

[0076] The density of the multiple island-like structures 111 can also be changed by adjusting the drying methods of the first sol film 215 and the second sol film 216. The drying methods of the first sol film 215 and the second sol film 216 are determined according to the type of substrate 101, the ambient temperature when the island-like structure layer 201 and the coating 202 are formed, the atmosphere when the island-like structure layer 201 and the coating 202 are formed, and so on.

[0077] 3. In the third embodiment and subsequent embodiments, the differences between the third embodiment and the first and second embodiments will be explained. For aspects not explained, the same configuration as that used in the first or second embodiment will be used in the third embodiment.

[0078] 3.1 Surface Structure Figure 10 is a schematic cross-sectional view illustrating the surface structure of the third embodiment.

[0079] As shown in Figure 10, in the surface structure 3 of the third embodiment, a plurality of convex structures 101c and concave structures 101b are formed on the surface 101a of the base material 101. Therefore, the surface 101a has an uneven surface. The plurality of convex structures 101c are separated from each other by a gap 121. Each convex structure 101c has a size on the order of micrometers.

[0080] As shown in Figure 10, the surface structure 3 is provided with a coating 241.

[0081] The coating 241 is placed on the surface 101a of the base material 101 and covers the surface 101a.

[0082] As shown in Figure 10, the covering 241 comprises portion 251 and portion 252.

[0083] Parts 251 and 252 are made of the same material and are formed simultaneously.

[0084] Part 251 is positioned on a plurality of convex structures 101c. Part 252 is positioned on parts other than the plurality of convex structures 101c.

[0085] As shown in Figure 10, in the surface structure 3, the multiple first structures 102 consist of multiple convex structures 101c and portions 251. The multiple second structures 103 are formed on portions 251 that cover the multiple convex structures 101c and are arranged on the surface 251a of portions 251. As a result, the multiple second structures 103 are formed on the multiple first structures 102 and are arranged on the surface 102a of the multiple first structures 102. In addition, the multiple second structures 103 are also formed on portions 252 that cover parts other than the multiple convex structures 101c and are arranged on the surface 252a of portions 252.

[0086] 3.2 Flowchart 11 of the surface structure manufacturing process is a flowchart showing the manufacturing process of the surface structure according to the third embodiment. Figures 12A to 12E are schematic cross-sectional views illustrating intermediate products manufactured during the manufacturing process of the surface structure according to the third embodiment.

[0087] When the surface structure 3 is manufactured, steps S121 to S126 shown in Figure 11 are performed.

[0088] In step S121, the base material 101 is manufactured as shown in Figure 12B. When the base material 101 is manufactured, the base material 261 before processing, as shown in Figure 12A, is physically processed to form a plurality of convex structures 101c and concave structures 101b. For example, the surface 261a of the base material 261 before processing is blast-treated to form a plurality of convex structures 101c and concave structures 101b. For blast treatment, an alumina blast abrasive with a particle size of #200 is used. The base material 101 may also be manufactured by a processing method other than blast treatment of the surface 261a. For example, the base material 101 may be manufactured by chemical etching of the surface 261a. The base material 101 may also be manufactured by molding the material using a mold on which a structure having a size on the order of micrometers has been formed. As for the method of manufacturing the base material 101, a method suitable for the material and shape of the base material 101 is selected. When the surface 261a is blast-treated, the base material 101 and the base material 261 before processing are made of AS resin, which is a copolymer of acrylonitrile and styrene. The base material 101 and the base material 261 before processing may be made of materials other than AS resin. For example, the base material 101 and the base material 261 before processing may be made of resins other than AS resin, metals, glass, etc. Resins other than AS resin include polypropylene, polystyrene, polyethylene, etc. Metals include iron, aluminum, stainless steel, etc.

[0089] In the following step S122, a sol is prepared. The sol is prepared in the same manner as the sol prepared in step S101 shown in Figure 3.

[0090] In the subsequent step S123, the prepared sol is applied to the surface 101a of the prepared substrate 101. This forms a sol film 271 on the surface 101a, as shown in Figure 12C. The application of the sol is carried out in the same manner as the application of the sol in step S102 shown in Figure 3.

[0091] In the subsequent step S124, the formed sol film 271 is dried. This forms the coating 241 as shown in Figure 12D.

[0092] In the subsequent step S125, as shown in Figure 12E, a plurality of second structures 103 are formed on the formed coating 241. If the coating 241 contains pseudo-boehmite, the intermediate product 281 shown in Figure 12D is immersed in hot water or exposed to steam. This causes the hot water or steam to come into contact with the coating 241. As a result, a plurality of second structures 103 are formed on the surface of the coating 241. As a result, a plurality of second structures 103 are formed on the surface 102a of the plurality of first structures 102 having portions 251. In addition, a plurality of second structures 103 are also formed on the bottom surface 231 facing the gap 121.

[0093] In the subsequent step S126, the intermediate product 282 shown in Figure 12E is immersed in a solution containing the water-repellent substance 151. This forms a water-repellent layer 104, as shown in Figure 10. When the intermediate product 282 is immersed in the solution containing the water-repellent substance 151, the solution comes into contact with the surface structure 131. This causes the water-repellent substance 151 to bond to the surface structure 131. As a result, the surface structure 131 is covered with the water-repellent substance 151.

[0094] 3.3 SEM Image of Prototype Figure 13 is an SEM image of an intermediate product produced during the manufacturing process of the surface structure of the third embodiment.

[0095] Figure 13 shows SEM images of intermediate product 282. The SEM images include those at magnifications of 100x, 1000x, and 5000x. The 100x SEM image includes regions showing blast-treated and unblast-treated areas. The 1000x and 5000x SEM images include only blast-treated areas.

[0096] As shown in Figure 13, the multiple island-like structures 111 are denser than the unprocessed area shown in the SEM image at 100x magnification. Therefore, the surface structure 3 has high water repellency.

[0097] Figure 14 shows an image of a prototype of the comparative structure and water droplets attached to the prototype. Figure 15 shows an image of a prototype of the surface structure of the third embodiment and water droplets attached to the prototype. Figure 16 is a graph showing the contact angle of water droplets with respect to the prototype of the comparative structure and the prototype of the surface structure of the third embodiment, as well as the sliding angle of water droplets on the prototype of the comparative structure and the prototype of the surface structure of the third embodiment.

[0098] The comparative example structure has a structure in which the surface of an unprocessed substrate is covered with a water-repellent substance 151. This water-repellent substance is located on the surface of the structure.

[0099] The contact angle of a water droplet with the prototype indicates the water-repellent properties of the prototype. The sliding angle of a water droplet on the prototype indicates the angle at which a water droplet begins to move when the prototype is tilted from a horizontal position.

[0100] As shown in Figures 14 and 16, the contact angle of a water droplet with respect to the comparative example's structure was 98°, and the sliding angle of the water droplet on that prototype was 40°. In contrast, as shown in Figures 15 and 16, the contact angle of a water droplet with respect to the third embodiment's surface structure was 139°, and the sliding angle of the water droplet on that prototype was 25°. From these results, it can be understood that the prototype of the third embodiment's surface structure has higher water repellency and higher sliding properties than the comparative example's structure prototype.

[0101] This disclosure is not limited to the embodiments described above, and may be replaced with configurations that are substantially the same as those shown in the embodiments, configurations that produce the same effects, or configurations that can achieve the same purpose.

Claims

1. A surface structure comprising: a plurality of first structures separated from each other by a gap; a plurality of second structures that are finer than the plurality of first structures and formed on the plurality of first structures; and a water-repellent substance that covers the plurality of first structures and the plurality of second structures.

2. The surface structure according to claim 1, wherein each first structure has a size on the order of micrometers, and each second structure has a size on the order of nanometers.

3. The surface structure according to claim 1 or 2, wherein at least a portion of the water-repellent substance faces the gap, and the plurality of second structures include portions that protrude toward the gap.

4. The surface structure according to claim 1 or 2, wherein the plurality of first structures and the plurality of second structures are made of alumina hydrate.

5. The surface structure according to claim 1 or 2, wherein each second structure is a plate-like structure.

6. The surface structure according to claim 1 or 2, wherein the water-repellent substance forms a monolayer.

7. The surface structure according to claim 1 or 2, wherein the water-repellent substance is represented by the general formula X-A-Y, where X is a group that chemically bonds with the plurality of first structures and the plurality of second structures, A is a main chain skeleton, and Y is a group that exhibits water repellency.

8. X is -SiR １ R ２ R ３ , -COOH, -NCO or -P(=O)R ４ R ５ where R １ , R ２ and R ３ contain -OCH ３ , -OC ２ H ５ or -Cl, and R ４ and R ５ contain -OH or -Cl. The surface structure according to claim 7 9. A includes at least one selected from the group consisting of groups represented by chemical formulas (1) to (3). The surface structure according to claim 7, wherein m is an integer between 1 and 20.

10. Y is one of the groups represented by chemical formulas (4) to (7), R ６ , R ７ and R ８ It contains hydrogen or an alkyl group having 3 or fewer carbon atoms, R ９ , R １０ and R １１ The surface structure according to claim 7, wherein n comprises hydrogen or an alkyl group having 3 or fewer carbon atoms, and n is an integer between 1 and 20.

11. A surface structure according to claim 1 or 2, comprising a substrate having a surface, and a plurality of island-like structures arranged on the surface and separated from each other, wherein the plurality of first structures comprises the plurality of island-like structures.

12. The surface structure according to claim 11, wherein the surface is a first surface, the plurality of island-like structures have a second surface, and the covering comprises a first portion disposed on the first surface and a second portion disposed on the second surface, and the plurality of first structures comprise the second portion.

13. A surface structure according to claim 1 or 2, comprising a substrate having a surface on which a plurality of convex structures spaced apart from each other are formed, and a covering comprising portions disposed on the plurality of convex structures, wherein the plurality of first structures comprises the plurality of convex structures and the portions.

14. A method for manufacturing a surface structure, comprising: a) forming a plurality of first structures separated from each other by gaps; b) forming a plurality of second structures that are finer than the plurality of first structures on the plurality of first structures; and c) covering the plurality of first structures and the plurality of second structures with a water-repellent substance.

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