Surface treatment method and structure having hydrophobic surface

Abstract

To provide a surface treatment method for providing a structure having a hydrophobic surface that achieves high productivity and stably attains high durability, and to provide a structure having the characteristics.SOLUTION: In this structure, a film containing a polymer and having a striped surface shape with a maximum surface inclination angle of 5° or more and 20° or less is used as a surface to be subjected to hydrophobization treatment, and this method for producing the structure includes steps of: preparing an elastomer film containing the polymer; forming a cured layer on a first main surface of the elastomer film by performing surface treatment; applying tensile stress to the elastomer film in a uniaxial direction; releasing the applied tensile stress to form wrinkle-like irregularities on a surface of the cured layer; bringing the surface of the cured layer into contact with a surface to be subjected to hydrophobization treatment of an object to be surface-treated; and separating the surface of the cured layer from the surface to be subjected to hydrophobization treatment of the object to be surface-treated.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a surface treatment method and a structure having a hydrophobic surface, and more particularly to a structure having a stable hydrophobic surface and a surface treatment method therefor. [Background technology]

[0002] Controlling hydrophobicity and hydrophilicity, which indicate wettability with water, is an important factor in increasing the added value of structures from the perspectives of dealing with water droplets on windows, preventing fogging, waterproofing, and protecting surfaces from rain.

[0003] Polymer coating is known as a representative method for ensuring appropriate water wettability and water repellency, and polymers have been commercialized for use in automobile window glass and body coatings, etc. This is generally a surface treatment in which a polymer coating agent, in which a polymer is dissolved in a solvent, is applied to a structure, and the structure is dried and polished as necessary to form a polymer film on the surface of the structure. For example, a polymer coating agent is disclosed in Patent Document 1, and a surface treatment method is disclosed in Patent Document 2.

[0004] Here, conventional methods using polymer coating agents have had problems such as poor film thickness control, difficulty in thin film formation, tendency for the film to become non-uniform and prone to coating spots, and tendency for defects to occur. There is also a polymer attachment method in which a thin film of polymer is attached to the surface of the surface-treated structure, but this method has problems such as tendency for defects to occur due to tearing and bubble formation during attachment, and difficulty in treating large areas. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-203127 [Patent Document 2] Japanese Patent Publication No. 2023-46175 Summary of the Invention [Problem to be solved by the invention]

[0006] The problem to be solved by the present invention is to provide a structure having a hydrophobic surface that can be produced with high productivity and can stably provide high durability, and to provide a surface treatment method therefor. [Means for solving the problem]

[0007] The configuration of the present invention to solve the problems is shown below. (Configuration 1) an elastic membrane preparation step of preparing an elastic membrane having elasticity containing a polymer; a hardened layer forming step of performing a surface treatment on a first main surface of the elastic membrane to form a hardened layer on the first main surface; a tensile stress applying step of applying a tensile stress to the elastic film in one axial direction; a tensile force release wrinkle formation step of releasing the tensile stress applied to the elastic film to form wrinkle-like irregularities on the surface of the hardened layer; a contact step of bringing the surface of the hardened layer into contact with a surface to be hydrophobized of an object to be surface-treated; a separating step of separating the surface of the hardened layer from the surface to be hydrophobized of the surface treatment object. (Configuration 2) 2. The surface treatment method according to claim 1, wherein the surface treatment is performed while the tensile stress is being applied, and after the surface treatment is completed, the tensile stress is released, and then the contact is performed. (Configuration 3) 2. The surface treatment method according to claim 1, wherein the tensile stress is applied after the surface treatment is completed, and the contact is performed after the tensile stress is released. (Configuration 4) The surface treatment method according to any one of the preceding aspects 1 to 3, wherein the polymer is a cross-linked product made from a base agent and a curing agent, and the ratio of the base agent is higher than that of a composition constituting a completely cross-linked structure. (Configuration 5) 5. The surface treatment method according to claim 4, wherein the mass ratio of the base agent to the curing agent is in the range of 20:1 to 50:1. (Configuration 6) 6. The surface treatment method according to claim 4 or 5, wherein silicone oil is added when the polymer is crosslinked. (Configuration 7) 7. The surface treatment method according to any one of aspects 4 to 6, wherein nanoparticles are added when the polymer is crosslinked. (Configuration 8) 8. The surface treatment method according to claim 7, wherein the nanoparticles have a major axis that is smaller than the void length of the polymer matrix of the elastic film. (Configuration 9) 9. The surface treatment method according to any one of aspects 1 to 8, wherein the polymer is a polysilane compound. (Configuration 10) 10. The surface treatment method according to claim 9, wherein the polymer is polydimethylsiloxane (PDMS). (Configuration 11) 11. The surface treatment method according to any one of claims 1 to 10, wherein the surface treatment is one or more treatments selected from the group consisting of oxygen plasma irradiation treatment, argon plasma irradiation treatment, energy ray irradiation treatment, ozone treatment under far ultraviolet irradiation, and rapid thermal annealing (RTA) treatment. (Configuration 12) 12. The surface treatment method according to claim 11, wherein the surface treatment is an oxygen plasma irradiation treatment. (Configuration 13) a PDMS membrane preparation step of preparing a membrane made of PDMS; an oxygen plasma treatment step of performing an oxygen plasma treatment on the first main surface of the film while applying a tensile stress in a uniaxial direction to the first main surface of the film; a tensile stress releasing step of terminating the application of the tensile stress and releasing the tensile stress; a contacting step of bringing the surface of the film irradiated with the oxygen plasma into contact with a surface to be hydrophobized of an object to be surface-treated; and a step of separating the membrane from the contact surface, The PDMS is made from a base agent and a curing agent, and the ratio of the base agent is higher than the composition that forms a completely cross-linked structure, in this surface treatment method. (Configuration 14) 14. The surface treatment method according to any one of aspects 1 to 13, wherein the object to be surface treated is glass. (Configuration 15) 15. The surface treatment method according to any one of claims 1 to 14, wherein the surface to be hydrophobized of the object to be surface-treated is subjected to argon plasma treatment prior to the contact. (Configuration 16) A structure having a hydrophobic surface, in which a film having a striped surface shape containing a polymer is formed on the surface of an object to be surface-treated to be hydrophobized, and the maximum inclination angle of the surface shape is 5° or more and 20° or less. (Configuration 17) 17. The structure according to claim 16, wherein the polymer comprises a polysilane compound. (Configuration 18) 18. The structure of claim 17, wherein the polymer is polydimethylsiloxane. [Effects of the Invention]

[0008] According to the present invention, a structure having a hydrophobic surface that can be produced with high productivity and can stably obtain high durability is provided, and a surface treatment method therefor is also provided. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a flowchart showing the steps of a surface treatment method of the present invention. [Figure 2] 1A to 1C are process diagrams illustrating a surface treatment method of the present invention using cross-sectional views. [Figure 3] FIG. 2 is an observation view of the surface of the elastic membrane of the present invention observed using a laser microscope. [Figure 4] 1 is an explanatory diagram illustrating a surface treatment method of the present invention and its features. [Figure 5] FIG. 1 is a comparison diagram comparing the surface state of the elastic film of the present invention with the surface state of a transfer-formed surface treatment layer. [Figure 6] 10 is a photograph showing the state of a sample when a transfer surface treatment is performed using an elastic film that is not distorted, as a comparative example. [Figure 7] FIG. 1 is a characteristic diagram showing a comparison of the wettability of water and the wettability of PDMS. [Figure 8] FIG. 2 is a diagram showing the surface irregularities after the surface treatment of the present invention, observed using a laser microscope. [Figure 9] FIG. 1 is an observational diagram comparing the change over time in surface irregularities after the surface treatment of the present invention with and without argon plasma treatment. [Figure 10] FIG. 1 is a characteristic diagram comparing the change over time in amplitude and wavelength (pitch, wavelength) which represent the state of surface irregularities after the surface treatment of the present invention has been performed with and without argon plasma treatment. [Figure 11] FIG. 1 is a characteristic diagram in which the dependence of the number of treatments on the surface treatment of the present invention is evaluated using (a) amplitude and (b) wavelength, which represent the state of surface unevenness. [Figure 12] The time-dependent characteristics of the elastic membrane were investigated, and the results are shown using a laser microscope on the surface that had been treated using the same PDMS elastic membrane repeatedly, once on day 0, once on day 1, and once on day 7. [Figure 13] This was an investigation of the characteristics of the elastic membrane over time. The same elastic membrane made of PDMS was used repeatedly to treat the surface, once on Day 0, once on Day 1, and once on Day 7. The graph shows the changes in the treated surface, measured in terms of (a) the amplitude and (b) the wavelength (pitch) of the surface irregularities. [Figure 14] FIG. 10 is a characteristic diagram showing the sliding-off characteristics of a water droplet after surface treatment on a sample made of PDMS without the addition of silicone oil. [Figure 15] This is a characteristic diagram showing the sliding properties of a water droplet after surface treatment on a sample made by adding silicone oil to PDMS. [Figure 16] FIG. 10 is a characteristic diagram showing the sliding characteristics of a water droplet when silicone oil is added to PDMS, using the maximum static friction force. [Figure 17] FIG. 10 is a characteristic diagram showing the particle size distribution of nanoparticles added to an elastic film. [Figure 18] This shows the results of observing the surface irregularities when nanoparticles are added to an elastic film for surface treatment. [Figure 19]FIG. 1 is a characteristic diagram showing the results of measuring (a) amplitude, (b) wavelength, and (c) haze of a surface-treated elastic film when nanoparticles are added to the surface. [Figure 20] FIG. 2 is a structural explanatory diagram illustrating the structure of an elastic membrane. DETAILED DESCRIPTION OF THE INVENTION

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the text, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0011] (Embodiment 1) In the first embodiment, the characteristic structure of a structure in which a polymer that can provide high hydrophobicity is formed on the surface to be hydrophobized of the structure, and the surface treatment method for obtaining this structure will be explained with reference to the drawings, starting with the surface treatment method.

[0012] <Surface treatment method> The surface treatment method of the present invention involves mechanically contacting an elastic film 11 made of a film containing a polymer with a structure 12 having a surface to be treated, causing unreacted polymers contained in the elastic film 11 to seep out of the elastic film 11 and adhere to the structure 12, thereby forming a hydrophobic layer made of a polymer on the surface to be treated.As shown in the flowchart of FIG. 1, this surface treatment method comprises the following steps: Here, the surface treatment method of the present invention will be described with reference to FIG. 1 as well as FIG. 2, which is a schematic cross-sectional view of a case where PDMS is used as the elastic film 11 and glass is used as the structure 12.

[0013] The first step is an elastic film preparation step (step S11) of preparing an elastic film containing a polymer. Here, polymers include oligomers consisting of 10–99 monomers and polymers (in the narrow sense) consisting of 100 or more monomers. Specific examples include polysilane compounds, siloxane resins such as PDMS, fluororesins such as polymethyl methacrylate resin (PMMA), polyvinyl chloride, polytetrafluoroethylene (PTFE), perfluoropolyether (PFPE), and polyvinylidene fluoride (PVDF), and PVDF copolymers such as poly(vinylidene fluoride-co-hexafluoropropylene). PDMS is particularly preferred for its high transparency in the visible range, its flexibility that can be adjusted depending on the preparation conditions, and its ease of preparation. It is widely used in industrial applications, offering excellent quality and cost, and its wide molecular weight range is also available. Examples of polymer-containing elastic films include polymer-based elastic films, polymer-based elastic films containing one or more dispersed materials selected from the group consisting of oxides, nitrides, carbides, metals, aluminum-, zirconium-, and titanium-based coupling agents, and semimetals such as silicon (Si), and multilayered elastic films with at least two layers, in which at least the first main surface is made of a polymer film and at least one of the second main surface and bulk is made of a highly flexible material. For example, the multilayered elastic film 11 may include a first main surface made of PDMS, which is suitable for forming a surface-hardened layer, and a bulk and second main surface made of an organic film such as nylon, polyethylene terephthalate, polyvinyl chloride, polystyrene, or polyethylene. Note that uncrosslinked, unreacted polymers from the polymers serve as the source material for forming the hydrophobic layer. The thickness of the elastic film 11 is not particularly limited, but may be, for example, 0.1 mm or more and 10 mm or less.

[0014] The second step is a surface-hardened layer forming step (step S12) in which a surface-hardened layer is formed on the first main surface of the elastic film 11. When a silicon-containing material such as siloxane is used on at least the first main surface side of the elastic film 11, examples of methods for forming the surface-hardened layer include oxygen plasma treatment, ozone oxidation treatment, and irradiation with one or more of deep ultraviolet (DUV) light, pulsed laser light, and energy rays in the presence of oxygen. When a cross-linked material such as PMMA or rubber is used on at least the first main surface side of the elastic film 11, examples of methods for promoting surface cross-linking include irradiation with one or more of DUV light, pulsed laser light, and energy rays.

[0015] The third step is a tensile stress application step (step S13) in which uniaxial tensile stress is applied to the elastic film 11. The amount of applied tensile stress is 1% or more and 50% or less, preferably 1% or more and 20% or less. As will be explained later, if the tensile stress is within this range, desirable wrinkles with uniform period and amplitude are formed in the elastic film 11 after application of the tensile stress. If the tensile stress is 1% or less, the wrinkles do not grow sufficiently, which tends to result in insufficient unevenness on the surface of the surface treatment film. On the other hand, if the tensile stress is 50% or more, the wrinkle period tends to become irregular, which is a problem that can easily occur.

[0016] Here, the second step S12 and the third step S13 do not necessarily have to be performed in this order. The surface-hardened layer may be formed in the second step S12 while applying uniaxial tensile stress in the third step S13 to the elastic film 11. For example, in the case of Fig. 2, a tensile stress of 16.7% strain is applied to the PDMS film, which is the elastic film 11 (Fig. 2(a)), and while the PDMS film is stretched, an O2 plasma irradiation treatment is performed on the first main surface of the elastic film 11 (Fig. 2(b)), thereby forming a surface-hardened layer on the first main surface of the elastic film 11.

[0017] In parallel with the implementation of the second step S12 and the third step S13, it is preferable to perform a surface passivation treatment on the surface to be treated of the structure 12. In the case where PDMS is used as the elastic film 11 and glass is used as the structure 12, an example in which the surface to be treated of the glass 12 is treated with argon plasma is shown in FIG. 2(b). Examples of surface passivation treatments include cleaning treatments that remove contaminants adhering to the surface of the structure 12, as well as modification treatments that modify the surface with hydroxyl groups or the like to control the surface to a desired state. Examples of the former cleaning treatments include Ar plasma treatment, ammonia-hydrogen peroxide mixture cleaning (APM cleaning, SC-1), sulfuric acid / hydrogen peroxide cleaning, UV ozone treatment, ion cleaning treatment, and ozone cleaning treatment. Examples of the latter surface modification treatments include hexamethyldisilaxane (HMDS) treatment, silane coupling agent treatment, phosphonic acid treatment, and alkanethiol treatment.

[0018] Although there are no particular restrictions on the structure 12, it is necessary that the structure 12 has a mechanical strength that can withstand contact with and separation from the elastic film 11. For example, the structure 12 may be made of Si, GaAs, a silicon nitride film (SiN x ), silicon oxide film (SiO x Examples of the material include substrates such as silicon oxynitride (SiON), silicon synthetic quartz, glass, metals such as tungsten (W), plastics such as polycarbonate, and ceramics such as silicon carbide (SiC). The structure 12 may be made of a single material or may be made of multiple materials, and may include, for example, a silicon substrate having a pattern made of silicon oxide, polysilicon, aluminum, etc. that forms protrusions on the silicon substrate.

[0019] The fourth step is a tensile stress release wrinkle formation step (step S14), in which the application of tensile stress to the elastic film 11 is stopped and the stress is released, generating wrinkle-like irregularities in the surface hardened layer of the elastic film 11. The bulk portion of the elastic film 11 shrinks when the application of tensile stress is stopped and released, but the surface hardened layer does not shrink as much as the bulk portion, resulting in wrinkles on the surface of the hardened layer. Figure 3 shows an example of wrinkles generated by this process. The pitch and undulation width (amplitude) of the wrinkles generated during this step are highly uniform within the surface, which is one of the key features that produces the effects of the present invention. Note that Figure 3 shows a PDMS sheet measuring 20 mm x 50 mm and 2.5 mm thick that was prepared and subjected to O2 plasma treatment at an O2 pressure of 0.6 mbar, a flow rate of approximately 15 sccm, an output of 60 W, and a time of 60 s, resulting in a wrinkle of approximately 22,000 N / m 2 The surface was observed using a 3D surface profiler (VK-X3000, manufactured by KEYENCE Corporation) in laser confocal mode under a tensile stress of 16.7% (stretching the sheet by 16.7%). The wrinkle pitch was found to be approximately 2.7 μm.

[0020] The fifth step is a contact step (step S15) in which the wrinkled surface-hardened layer of the elastic film 11 is brought into contact with the treated surface of the structure 12. The elastic film 11 should be brought into contact with the treated surface of the structure 12 so that it adheres evenly and without unevenness. If the contact pressure is too high, the wrinkles formed will be distorted, while if it is too low, the PDMS surface treatment film will be too thin, making it prone to defects. While there are no particular limitations on the temperature and humidity of the contact environment, it is preferable to control the temperature in consideration of the viscosity of unreacted PDMS so as not to disrupt the regular vertical stripe shape of the PDMS surface treatment film. For example, the temperature can be room temperature. There are also no particular limitations on the contact time, but examples include 5 minutes to 2 hours. If the contact time is less than 5 minutes, the surface treatment film tends to become thin. Although there are no problems with contact for more than 2 hours, significant differences in the effectiveness of the surface treatment film are unlikely to be observed. Therefore, a contact time of 3 hours or less is preferable in terms of manufacturing efficiency. In FIG. 2, the fourth and fifth steps are combined and depicted in FIG. 2(c).

[0021] The sixth step is a detachment step (step S16, FIG. 2(d)) in which the elastic film 11 is detached from the processed surface of the structure 12. The detachment environment is not particularly limited, and a normal environment in which consideration is given to avoiding adhesion of particles and contaminants may be used. The detachment speed of the elastic film 11 is also not particularly limited, and can be, for example, 1 mm / s or more and 100 mm / s or less. Through the above steps S11 to S16, a coating film 13 is formed on the desired treatment surface, providing a surface-treated structure (FIG. 2(e)).

[0022] One of the features of the present invention is that it can produce a uniform surface treatment coat (coating film 13) using a simple, highly productive surface treatment method called area-by-area batch treatment, which is determined by the size of the elastic film 11. This is explained using Figure 4. In Figure 4, the elastic film 11 is a PDMS film containing relatively low-molecular-weight unreacted PDMS. The PDMS film is subjected to oxygen plasma surface curing while applying uniaxial tensile stress, and then the tensile stress is released to produce a PDMS film with uniaxial wrinkles on the surface. Here, one method for incorporating unreacted PDMS into the PDMS film is to prepare the PDMS film from a base resin and a curing agent, with the ratio of the base resin set higher than the ratio required for a fully crosslinked structure. Specifically, a mass ratio of base resin to crosslinker of 20:1 to 50:1 is recommended. This ratio allows for surface treatment with minimal smearing.

[0023] In this state, unreacted PDMS oozes out from the apexes of the wrinkles. When the PDMS film is brought into contact with a target surface, the oozing unreacted PDMS adheres to the target surface. When the PDMS film is then separated from the target surface, an unreacted PDMS coating forms, as shown in the middle of Figure 4. Specifically, when the target surface has poor wettability with PDMS, random droplets (left) form; when the wettability is adequate, stripes form (center); and when the wettability is high, a uniform film thickness (right) forms. The inventors discovered that the formation of stripes is extremely stable, highly reproducible, and with minimal defects, even in thin film form, when a target surface has adequate wettability. Furthermore, they found that post-treatment with argon plasma after PDMS coating formation reduces aging. This shape fixation by argon plasma post-treatment is particularly pronounced when polysilane compounds or polysiloxane resins are used as polymers. For reference, Figure 5(a) shows an example of the surface condition of elastic film 11 with a wrinkled surface, and Figure 5(b) shows an example of the wrinkled surface being brought into contact with the surface to be treated and then transferred with PDMS. A laser microscope (VK-X3000, manufactured by KEYENCE Corporation) was used for the observation. The amplitude of the transferred wrinkles, i.e., the wrinkles on the surface to be treated, is approximately one order of magnitude smaller than that of the wrinkles on elastic film 11, but it can be seen that the wrinkles were transferred to the surface to be treated with high precision.

[0024] 5(a) and (b) are monochrome and difficult to see, but a thin film with a wavy surface with a wavelength of approximately 3 μm is formed on the surface to be treated as a surface treatment layer, and therefore appears rainbow-like when viewed from above. The present invention can also be used as a coating film (layer) that takes advantage of its functional and aesthetic features.

[0025] Furthermore, the inventors discovered that when an elastic film is produced using a material that contains a crosslinking base agent, a curing agent, and a solvent, as well as silicone oil and nanoparticles that have a mild interaction with the base agent, the silicone oil and nanoparticles also leak onto the coating surface, making it possible to perform surface treatments and coating processes that add new functions. This will be described in Examples 2 and 3.

[0026] It has been confirmed that when a flat PDMS elastic film 11 without wrinkles on the surface is used, the unreacted PDMS does not exude sufficiently, and a surface treatment film cannot be formed, as shown in Figure 6.

[0027] As can be seen from Figure 4, in the present invention, it is important to control the wettability of the PDMS on the surface to be treated. Due to the polarity of the terminal groups on the surface to be treated, there is an inverse relationship between the wettability of water on the surface to be treated and the wettability of PDMS, as shown in Figure 7. As mentioned above, in the present invention, pre-treatment such as cleaning of the surface to be treated may be required as needed. In this case, it is possible to evaluate and control the wettability with water (contact angle of water), which is easy to measure, based on the relationship in Figure 7. The contact angle was measured using a contact angle meter (Drop Master-SA-Csl, Kyowa Interface Science Co., Ltd., Japan). The amount of probe liquid (ultrapure water or liquid PDMS) was 5 μL. The water used for evaluation was ultrapure water obtained using a Direct-Q IV3 system (Merck KGaA, Germany), and its resistivity was 18.2 MΩ / cm.

[0028] <Structure> Next, the characteristic structure of the structure 12 that has been subjected to the surface treatment of the present invention will be described with reference to FIG. Figure 8(a) shows the results of a laser microscope observation of the top surface of a treated surface when the surface treatment method of the present invention using PDMS was applied. Figure 8(b) shows the results of a cross-sectional measurement. Figure 8(c) shows an enlarged view of a portion of the cross-section of Figure 8(b). It can be seen that a PDMS film with stable wavelength and amplitude was formed over the entire treated surface without defects. Here, the amplitude of the wrinkles was approximately 3% of the wavelength, and the inclination angle of the wrinkles was approximately 10°. After extensive investigation, it was found that for the purpose of surface hydrophobic treatment, the maximum inclination angle due to the wrinkled surface shape should preferably be between 5° and 20°, and even more preferably between 8° and 15°. When PDMS is used as the polymer for the elastic film 11, the contact angle with water after surface treatment with this film is 98°.

[0029] This wrinkled surface coating, a feature of the present invention, not only provides stable coating formation but also possesses the novel characteristic of anisotropic hydrophobicity. In the present invention, unreacted polymers are contained in the elastic film 11. If the unreacted polymer contains a highly hydrophobic material such as silicone oil, it becomes possible to impart anisotropic hydrophobicity, which allows water droplets to flow more easily along the wrinkle grooves. An example of this will be described in Example 2. This feature can be used to straighten water droplets on car windows and bodies, for example, to control the flow of water droplets and to control the appearance of the car.

[0030] As described above, this method is a highly productive surface treatment method for providing a structure with a hydrophobic surface that can be stably and highly durable, and it is possible to provide a structure with a hydrophobic surface that can be stably and highly durable. [Example]

[0031] The present invention will be described in more detail below with reference to examples. However, these examples are provided merely to aid in understanding the present invention and are not intended to limit the present invention.

[0032] Example 1 In Example 1, a sample was prepared using a PDMS membrane as the elastic membrane 11 in accordance with the surface treatment steps described in embodiment 1, and various characteristics of the coating membrane 13 (surface treatment membrane) prepared by the surface treatment, such as in-plane uniformity, changes over time, and preparation reproducibility (stability), were evaluated.

[0033] <Preparation of evaluation samples> In the first step, the elastic film preparation step (step S11), a film made of PDMS was prepared as the elastic film 11 by the following method. First, a flat PDMS plate was prepared using a kit consisting of a PDMS base resin and a curing agent (Sylgard 184, DowCorning).

[0034] Specifically, a liquid consisting of a base agent and a hardener in a mass ratio of 30 parts base agent to 1 part hardener was mixed, and the mixture was degassed and then poured into a square polystyrene container. Thereafter, a crosslinking-accelerating heat treatment was carried out at 65° C. for 24 hours to produce an elastic membrane 11. The size of each membrane was 35 mm×35 mm×2.5 mm, and the membrane was further cut into pieces for use as required.

[0035] Next, in Example 1, as shown in Figures 2(a) and (b), the application of tensile stress in step 3 (step S13), the formation of a surface hardened layer in step 2 (step S12), and the substrate surface treatment, which is one of the optional treatments, were processed simultaneously in parallel, with the order reversed. The elastic membrane 11 was cut to a size of 10 mm wide, 35 mm long, and 2.5 mm thick, and stretched by applying a stress in the longitudinal direction to give a strain of 16.7%. In this stretched state, the first main surface was treated with O2 plasma for 60 seconds under the conditions of an output of 60 W and an oxygen partial pressure of 0.6 mbar.

[0036] Three types of glass with different wettability to liquid PDMS were prepared as the structure 12. One was low-wettability glass (ordinary slide glass, manufactured by Muto Pure Chemical Industries, Ltd., product code: 110201), the other was high-wettability glass (slide glass surface-modified with a silane coupling agent), and the third was commercially available soda glass. Only when commercially available soda glass was used, the first main surface of the glass serving as structure 12 was subjected to argon plasma treatment for 1 second as a surface treatment surface cleaning treatment, under conditions of an output of 100 W and an atmospheric gas pressure of argon gas of 0.6 mbar. The other two glasses were used for surface treatment without argon plasma treatment.

[0037] Then, in step 4 (process S14), the application of tensile stress to the elastic film 11 was stopped and released. At this time, it was confirmed that the distortion of the elastic film 11 was slowly and completely released, and clear wrinkles were formed on the surface. The surface state of the elastic film 11 at this stage is shown in Figure 5(a).

[0038] Thereafter, in step 5 (process S15), the wrinkled first main surface of the elastic film (PDMS) 11 was brought into contact with the cleaned surface of the structure (glass) 12. Then, the glass with the PDMS attached was held for 1 hour with a 250 g weight placed on it.

[0039] Finally, in step 6 (process S16), the PDMS elastic film 11 was carefully peeled off from the glass structure 12, forming a wrinkled thin film 13 (surface treatment film) made of PDMS on the glass surface. Here, the surface treatment film was subjected to argon plasma post-treatment (post-Ar) for 10 seconds under conditions of a power output of 25 W and an atmospheric pressure of argon gas of 0.6 mbar as a hardening treatment for the purpose of film stabilization. Through the above steps, an evaluation sample having a surface treatment film formed thereon was prepared.

[0040] <Evaluation of surface treatment film> <<Changes in surface treatment film over time>> The changes over time of the surface treatment film were compared and evaluated with and without argon plasma post-treatment (post-Ar). Figure 9 shows a comparison of wrinkle shape observations, and Figure 10 shows an example of a comparison of the numerical changes based on two characteristics, wavelength and amplitude. It can be seen that the wrinkles formed on the surface treatment film showed no significant change in pitch even after 28 days without curing treatment, but the amplitude was halved by 3 days. On the other hand, if curing treatment (post-Ar) was performed, no significant changes were observed in either wavelength or amplitude from the initial values ​​even after 28 days. The surface treatment film of the present invention was shown to be less susceptible to changes over time due to argon plasma post-treatment (post-Ar), and to be practically usable, with little change after 3 days of preparation even without argon plasma treatment. It is believed that the PDMS of Example 1, which has a mass ratio of base resin to curing agent of 30:1, contains 10 wt% or more of unreacted PDMS, in other words, liquid PDMS. Inferred from this amount, it is believed that the surface coating and surface treatment allows one elastic film 11 to be reused 7,000 times or more.

[0041] <<Dependence on transcription number>> The repeated use characteristics were evaluated when surface treatment transfer was repeated from one PDMS film, which was the elastic film 11. Here, the sample was subjected to stabilization treatment by argon plasma post-treatment (post-Ar) and then evaluated. Figure 11 shows the results of evaluating the repetition rate dependency when repeated transfer is performed, using the numerical changes of two characteristics, wavelength and amplitude. As a result, no significant change was observed after at least six repetitions, demonstrating that the elastic film 11 has high durability and can be used repeatedly.

[0042] Figure 12 shows the evaluation of the repetition number dependency by observing the wrinkle shape when transfer was repeated over several days, and Figure 13 shows the results of a quantitative evaluation of this dependency in terms of numerical changes based on two characteristics: wavelength and amplitude. As a result, no significant change was observed even after repeated evaluation after at least seven days, demonstrating that the elastic film 11 has high durability allowing repeated use for at least one week.

[0043] Example 2 In Example 2, the results of investigating the sliding properties of water droplets on a surface that has undergone the surface treatment of the present invention are reported.

[0044] First, the water contact angle on the surface-treated surface of the sample prepared in Example 1 was measured, yielding a result of 98°. This confirmed that the surface treated by the present invention was hydrophobic. Highly hydrophobic surfaces with a water droplet contact angle of 90° or greater can be used as water-repellent surfaces. In this case, the water contact angle is evaluated based on whether water can be removed by tilting the surface. Here, the water contact angle was measured at room temperature (approximately 25°C) using a contact angle meter (Drop Master-SA-Cs1, Kyowa Interface Science Co., Ltd., Japan) after dispensing a 5 μL water droplet with a microsyringe. Ultrapure water with a resistivity of 18.2 MΩ / cm prepared using a Direct-Q UV3 system (Merck KCaA, Germany) was used. Incidentally, the contact angle of water on the glass surface to be treated was 54° before the 1-second argon plasma treatment and 38° after the treatment.

[0045] Secondly, it was investigated whether the water repellency of the surface treatment could be further improved by adding silicone oil when the elastic film 11 was produced. The elastic film 11 according to the present invention is a crosslinked body having a liquid polymer in the bulk, and as described above, when the structure 12 and the elastic film 11 come into mechanical contact with each other, the liquid polymer seeps out from the apexes of the wrinkles formed on the surface, which are the protrusions, and adheres to the surface to be treated of the structure 12, forming a surface treatment film. In Example 1, the main agent used to form the elastic film 11 was used as this liquid polymer, and the ratio of the main agent was set higher than the composition that constitutes a completely crosslinked structure, and evaluation was performed under conditions in which the liquid unreacted main agent seeped out from the apexes of the wrinkles. Therefore, when producing the elastic film 11, we investigated adding an additive to the main agent and curing agent to further increase hydrophobicity, and allowing it to seep out from the apex of the wrinkles, thereby further increasing the hydrophobicity of the surface treatment surface.

[0046] The silicone oil used in the second experiment was KF-96H-60,000cs (Shin-Etsu Chemical Co., Ltd.), which is miscible with the liquid PDMS base used to create the PDMS film but has a higher viscosity than the PDMS base. It was added to a base compound consisting of a base compound and a curing agent, and the hydrophobicity of the treated surface was evaluated. The mass ratio of silicone oil to PDMS base compound was 1:0.2. The contact angle with water of the treated surface created using this material was 98°. Although the contact angle was the same with the addition of silicone oil as without the addition, it was confirmed to have high hydrophobicity. The results of the tensile test showed that the Young's modulus of the elastic film 11 made with the addition of silicone oil was approximately 80 kPa. On the other hand, the Young's modulus without the addition was approximately 120 kPa, meaning that the Young's modulus was lower with the addition of silicone oil. From this, it is believed that the silicone oil exists in a liquid state in the matrix of the PDMS film, softening the PDMS.

[0047] Thirdly, the sliding properties of water droplets due to the surface treatment of the present invention were evaluated. The samples used were Sample 1, prepared in Example 1, and Sample 2, prepared in the second experiment of Example 2 using PDMS with added silicone oil. A 5 μL water droplet was formed on Samples 1 and 2, and the sliding properties were evaluated by measuring the angle at which the water droplet slid down while Samples 1 and 2 were oriented in either the direction along the axis of the vertical stripes formed on their surfaces or the direction across the vertical stripes. The results of the evaluation for Sample 1 are shown in Figure 14, and the results of the evaluation for Sample 2 are shown in Figure 15.

[0048] As a result, for sample 1, which has a water contact angle of approximately 98°, the sliding angles were 58° along and 57° across, which is hardly a significant difference and shows isotropic sliding properties, but for sample 2, which also has a water contact angle of approximately 98°, the sliding angles were 38° along and 49° across, showing a clear significant difference and confirming that the direction along the stripes is more slippery. For reference, Figure 16 shows the results of calculating the maximum static friction force of a water droplet from the sliding start angle. As shown in Figure 8, the inclination of the wrinkles formed on the surface is low, around 10°, but when the water contact angle is large, it is thought that the stripes act as a guide, creating a directional dependency in the water droplet's slipperiness. The surface treatment of the present invention is a surface treatment method with new value, capable of controlling the flow path of water droplets as desired. It is expected to be a surface treatment that adds value in the form of a rectifying function and thereby generate demand, such as for surface treatments for car windows that make it easy to see even in rainy weather, or for car bodies that allow water droplets to flow beautifully and dynamically.

[0049] Example 3 In Example 3, the results obtained when nanoparticles were added to the elastic film 11 for surface treatment will be reported.

[0050] Four types of hydrophobic silica nanoparticles with different particle sizes (QSG-10, QSG-30, QSG-100, and QSG-170 (manufactured by Shin-Etsu Chemical Co., Ltd.)) were prepared. These were added to the material (PDMS solvent consisting of a base agent, a crosslinking agent, and a solvent) used to form the elastic film 11 in Example 1, to produce the elastic film 11 in the same manner as in Example 1, and the elastic film 11 was evaluated in accordance with Example 1.

[0051] The size of hydrophobic silica was measured using dynamic light scattering (DLS) with a Zetaizer Nano ZSP (Malvern Panalytical Ltd., UK). The results are shown in Figure 17. The average sizes of QSG-10, QSG-30, QSG-100, and QSG-170, determined at the peak of the distribution, were 30 nm, 50 nm, 110 nm, and 170 nm, respectively. The values ​​listed in the product data sheets were 15 nm, 30 nm, 110 nm, and 170 nm, respectively. The values ​​for QSG-10 and QSG-30 were slightly larger due to aggregation. Four types of nanoparticles with particle sizes of 15-30 nm, 30-50 nm, 110 nm, and 170 nm were evaluated.

[0052] The Young's moduli of PDMS films containing approximately 30 wt% QSG-10, QSG-30, QSG-100, and QSG-170 were 220 kPa, 260 kPa, 200 kPa, and 170 kPa, respectively. In contrast, the Young's modulus of the PDMS elastomer film of Example 1 was 120 kPa. Despite the addition of 30 wt% nanoparticles with a high Young's modulus (up to GPa), the addition of nanoparticles had little effect on the mechanical property of Young's modulus. This indicates minimal interaction between the PDMS matrix and the nanoparticles. Furthermore, these hydrophobic silica nanoparticles mix very easily with the liquid PDMS base. These findings suggest that the added nanoparticles and the PDMS matrix formed using the curing agent only weakly interact with each other.

[0053] Next, a surface-treated film was formed using the elastomer film to which the nanoparticles had been added, and the film was observed with a laser microscope in the same manner as in Example 1. The image results are shown in Figure 18, and the particle size dependence of the amplitude and wavelength are shown in Figures 19(a) and (b), respectively. When the large particle sizes of QSG-100 and QSG-170 were added, a relatively coarse striped pattern with long wavelengths was obtained, but when the small particle sizes of QCG-10 and QSG-30 were added, the results were almost the same as when no nanoparticles were added.

[0054] Next, we investigated whether the added nanoparticles had leaked into the surface treatment film by haze measurement, and the results are shown in Figure 19(c). The haze value is the total transmittance T All and parallel transmittance T Para The difference is the total transmittance T All Divided by ((T All -T Para ) / T All ) and is an index that indicates the degree of light scattering within a transparent sample. For this reason, in this experiment, the haze value is thought to be linked to the presence and amount of nanoparticles within the surface treatment film. As shown in Figure 19(c), when QSG-10 and QSG-30 were added, a clear increase in the haze value was observed. On the other hand, when QSG-100 and QSG-170, which have larger nanoparticle sizes, the haze value was close to that when no nanoparticles were added, and in particular, when QSG-170, which has a larger size, the haze value was even lower than that when no nanoparticles were added. This is thought to be because, as shown in Figure 20, PDMS 101 that constitutes the elastic membrane 201 has a polymer network, in other words, a matrix (mesh structure), and if the nanoparticles present in the voids 102 are smaller than the mesh gaps of the matrix, they can escape from the elastic membrane 201, but if they are larger, they are trapped and do not easily escape.

[0055] The experimental results of Example 3 indicate that it is possible to provide a surface treatment film 13 containing nanoparticles when nanoparticles, particularly nanoparticles smaller than the void size of the polymer constituting the elastic film 11, are added to the elastic film 11. This makes it possible to provide a surface treatment film with various added values, such as control of hydrophobicity (control of contact angle), control of surface slipperiness, and imparting magnetism, by adding nanoparticles. Here, the size of nanoparticles can be defined as the average length of the nanoparticles measured by AFM, and the pore size of the polymer can be defined as the average pore length S of the polymer matrix measured by AFM. AVE , or "SAVE -σ". [Industrial Applicability]

[0056] The present invention provides a structure with a hydrophobic surface that can provide stable and high durability, and a highly productive surface treatment method for fabricating such a structure. Controlling water wettability and hydrophobicity is a highly sought-after property for many products and structures, both for consumer and industrial use, and is therefore expected to greatly contribute to the development of industry. [Explanation of symbols]

[0057] 11: Elastic membrane, PDMS 12: Surface treatment target structure, glass substrate 13: Surface treatment materials, coating films, thin films 101: Polymer (matrix) 102:Void 201: Elastic membrane

Claims

1. an elastic membrane preparation step of preparing an elastic membrane having elasticity containing a polymer; a hardened layer forming step of performing a surface treatment on a first main surface of the elastic membrane to form a hardened layer on the first main surface; a tensile stress applying step of applying a tensile stress to the elastic film in one axial direction; a tensile force release wrinkle formation step of releasing the tensile stress applied to the elastic film to form wrinkle-like irregularities on the surface of the hardened layer; a contact step of bringing the surface of the hardened layer into contact with a surface to be hydrophobized of an object to be surface-treated; a separating step of separating the surface of the hardened layer from the surface to be hydrophobized of the surface treatment object.

2. 2. The surface treatment method according to claim 1, wherein the surface treatment is carried out while the tensile stress is being applied, and the tensile stress is released after the surface treatment is completed, and then the contacting is carried out.

3. 2. The surface treatment method according to claim 1, wherein the tensile stress is applied after the surface treatment is completed, and the contacting is performed after the tensile stress is released.

4. 4. The surface treatment method according to claim 1, wherein the polymer is a cross-linked product made from a base agent and a curing agent, and the ratio of the base agent is higher than that of a composition constituting a completely cross-linked structure.

5. The surface treatment method according to claim 4, wherein the mass ratio of the base agent to the curing agent is in the range of 20:1 to 50:

1.

6. 6. The surface treatment method according to claim 4, wherein silicone oil is added when the polymer is crosslinked.

7. The surface treatment method according to claim 4 , wherein nanoparticles are added when the polymer is crosslinked.

8. 8. The surface treatment method according to claim 7, wherein the nanoparticles have a major axis that is smaller than the void length of the polymer matrix of the elastic film.

9. The surface treatment method according to claim 1 , wherein the polymer is a polysilane compound.

10. The surface treatment method according to claim 9, wherein the polymer is polydimethylsiloxane (PDMS).

11. 11. The surface treatment method according to claim 1, wherein the surface treatment is one or more treatments selected from the group consisting of oxygen plasma irradiation treatment, argon plasma irradiation treatment, energy ray irradiation treatment, ozone treatment under far ultraviolet irradiation, and rapid thermal annealing (RTA) treatment.

12. The surface treatment method according to claim 11, wherein the surface treatment is an oxygen plasma irradiation treatment.

13. a PDMS film preparation step of preparing a film made of PDMS; an oxygen plasma treatment step of performing an oxygen plasma treatment on the first main surface of the film while applying a tensile stress in a uniaxial direction to the first main surface of the film; a tensile stress releasing step of terminating the application of the tensile stress and releasing the tensile stress; a contacting step of bringing the surface of the film irradiated with the oxygen plasma into contact with a surface to be hydrophobized of an object to be surface-treated; and a step of separating the membrane from the contact surface, The PDMS is made based on a base agent and a curing agent, and the ratio of the base agent is higher than the composition that forms a completely crosslinked structure.

14. The surface treatment method according to claim 1 , wherein the object to be surface treated is glass.

15. The surface treatment method according to claim 1 , wherein the surface to be hydrophobized of the object to be surface-treated is subjected to an argon plasma treatment prior to the contact.

16. A structure having a hydrophobic surface, in which a film having a striped surface shape containing a polymer is formed on the surface of an object to be surface-treated to be hydrophobized, and the maximum inclination angle of the surface shape is 5° or more and 20° or less.

17. The structure of claim 16 , wherein the polymer comprises a polysilane compound.

18. 18. The structure of claim 17, wherein the polymer is polydimethylsiloxane.

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