JP2013099706A - Water-repellent thin film and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin film material which contains an inorganic material and has a thin thickness, uniformity and sufficient water-repellency.SOLUTION: A water-repellent thin film includes a thin film composed of a composited water-repellent material and an inorganic material. The thin film has a water-repellent surface where the first area with an exposed water-repellent material and the second area with an exposed inorganic material are present, in a state of being intermingled and distributed. The inorganic material is either a material showing a photocatalytic activity, oxidizing or reducing an organic substance by being irradiated with light, or a semiconductor material. The water-repellent thin film can be formed by a step of accumulating the hydrophobic material or the inorganic material simultaneously on the coarse surface of a substrate having the coarse surface with a vapor-phase method.

Description

  The present invention relates to a water-repellent thin film composed of a composite water-repellent material and a deposited film of an inorganic material, which can be formed by a vapor phase method such as sputtering or vapor deposition.

  In recent years, materials such as plastic, metal, ceramics, and glass that have been provided with a self-cleaning function by attaching a photocatalyst to the surface have been put to practical use in various fields. As the photocatalyst, titanium oxide, tin oxide, tungsten oxide, zinc oxide and the like are known, and titanium oxide is most widely used.

  Photocatalysts are expected as functional materials that decompose and remove organic substances contained in air and water because they exhibit a catalytic action against oxidation or reduction reaction of substances under light irradiation. However, since the photocatalyst exhibits hydrophilicity under ultraviolet irradiation and becomes difficult to adsorb organic substances, the ability to decompose organic substances may not be sufficiently exhibited.

  Therefore, attempts have been made to make the photocatalyst hydrophobic by combining it with a water repellent material. Specifically, a mixed material of photocatalyst particles and a water-repellent material has been proposed. However, it is difficult to control the thickness of these materials, and it is particularly difficult to form a homogeneous thin film (for example, a thin film having a thickness of 1 μm or less).

  For example, Patent Documents 1 to 3 propose that a surface layer or a film containing photocatalyst particles, water-repellent particles (for example, a fluororesin), and a matrix resin (for example, silicone) be provided on the substrate surface. However, such a surface layer or film is formed by applying a coating composition containing photocatalyst particles and water-repellent particles to the substrate surface. Therefore, a film thinner than the particle size of each particle cannot be formed, and it is difficult to form a homogeneous film.

  Patent Document 4 proposes to impart water repellency to a photocatalyst by firing a mixture of photocatalyst particles and water repellent particles. Patent Document 5 proposes a water-repellent member in which photocatalyst particles are arranged on the surface of silicone rubber and embedded by pressing. However, such a material has a limit in thinning and its application is limited. Moreover, even if photocatalyst particles and water-repellent particles are mixed or the photocatalyst particles are embedded in silicone rubber, the effect of hydrophobizing the photocatalyst itself is hardly obtained.

  Patent Document 6 proposes that a photocatalyst is dispersed on the surface layer of a substrate having minute irregularities, and then the surface layer is brought into contact with fluoroalkylsilane to impart water repellency. Patent Document 7 proposes forming a water-repellent coating on the surface of a substrate and forming a photocatalytic layer thereon. However, when water repellency is imparted after the photocatalyst is dispersed on the surface layer of the substrate, the photocatalytic activity is significantly reduced. On the other hand, when the photocatalytic layer is formed on the water repellent coating, the water repellency is significantly reduced.

  Patent Document 8 proposes that the surface of an inorganic thin film containing a photocatalyst is subjected to plasma treatment to suppress a change in contact angle with water before and after light irradiation. However, it is difficult to sufficiently hydrophobize the photocatalyst only by plasma treatment of the inorganic thin film, and it has been reported that the contact angle with water is about 60 degrees.

  In addition, although patent document 9 is not a report regarding a photocatalyst, as a technique for improving the water repellency of a plastic substrate, it is proposed to form a mixed layer containing a metal oxide or a fluororesin on the substrate by a sputtering method. Yes.

JP-A-10-237431 Japanese Patent Laid-Open No. 11-300200 Japanese Patent Laid-Open No. 10-130539 JP-A-6-385 Japanese Patent No. 4318143 JP 2001-152139 A JP 2000-135442 A JP 2010-37648 A JP-A-3-153589

  As described above, although various attempts have been made to hydrophobize photocatalysts, materials capable of forming a thin and homogeneous film and having both sufficient water repellency and photocatalytic activity are under development. Development is an issue. In addition to inorganic materials used as photocatalysts, various functional inorganic materials can also be combined with water-repellent materials to make them hydrophobic, thereby improving interaction with organic substances and facilitating functional control. I can expect.

The present invention includes a thin film including a composite water-repellent material and an inorganic material, and the thin film includes a first region where the water-repellent material is exposed and a second region where the inorganic material is exposed. The present invention relates to a water-repellent thin film having a distributed water-repellent surface.
Here, the “mixed” state is preferably a state in which the water-repellent surface is averagely distributed so that the first region or the second region is scattered. Further, when the element map of the water-repellent surface is measured by EDS (energy dispersive X-ray spectroscopy) with a predetermined resolution, it is preferable that the first region and the second region have a high dispersibility that is indistinguishable. .

  The thin film is desirably homogeneous when viewed as a whole, but may be formed of fine particles scattered in islands when viewed microscopically. Each fine particle is formed of a composite material of a water repellent material and an inorganic material. And it is preferable that it distributes so that the 1st area | region and the 2nd area | region may coexist in the surface of each microparticle.

  The thin film is preferably a deposition film. In the case of a deposited film, the first region or the second region is scattered in an average manner over the entire water-repellent surface, or when the element map of the water-repellent surface is measured by EDS. A state in which the region and the second region cannot be distinguished can be easily achieved.

  The deposited film is a film that can be formed by a vapor phase method, and is formed by depositing ultrafine particles (nanoparticles) generated in the vapor phase on the substrate surface. The composite of the water repellent material and the inorganic material can be achieved by simultaneously depositing the water repellent material and the inorganic material nanoparticles generated in the gas phase on the surface of the substrate.

In the water-repellent thin film, the thickness of the thin film or the deposited film, that is, the thickness of the region composed of the combined water-repellent material and inorganic material is preferably 10 nm or more and 3 μm or less, for example.
The center line average roughness (Ra) of the water repellent surface is preferably, for example, 1 μm or more and 10 μm or less.

In one embodiment of the present invention, the inorganic material is a material that exhibits a photocatalytic action of oxidizing or reducing an organic substance by light irradiation. Here, a methylene blue aqueous solution having a concentration of 10 ⁻⁵ mol / L was introduced into a quartz cell (10 mm × 10 mm × 3 mm) for absorbance measurement together with a water-repellent thin film, and an ultraviolet ray from a mercury lamp at a light amount of 1 mW / cm ^2. When the light-irradiated surface of the cell is irradiated with light (250 nm or more) and the methylene blue decomposition reaction is carried out for 10 hours, the absorbance of light having a wavelength of 664 nm derived from methylene blue is 50% or less before the reaction. The material (or water repellent thin film) is defined as having a photocatalytic action. However, the water-repellent thin film is a 10 mm × 10 mm water-repellent thin film formed on one side of the substrate, and the reaction is carried out with the entire water-repellent thin film immersed in a methylene blue aqueous solution.

  When the inorganic material is a material exhibiting a photocatalytic action, when the contact angle between the water-repellent surface and water under non-ultraviolet irradiation is θ1, and the contact angle under ultraviolet irradiation is θ2, 100 × (θ1−θ2) ) / Θ1 variation in contact angle is extremely small, for example, preferably 10% or less.

  The material exhibiting photocatalytic action is, for example, at least one selected from the group consisting of titanium oxide, tungsten oxide, zinc oxide, strontium titanate, niobium oxide, cadmium sulfide, zinc sulfide, titanosilicate, and titanium-containing aluminosilicate. is there.

  In another embodiment of the present invention, the inorganic material is a semiconductor material. The semiconductor material includes, for example, at least one selected from the group consisting of titanium oxide, cadmium sulfide, strontium titanate, niobium oxide, cadmium sulfide, cadmium telluride, tin oxide, indium tin oxide (ITO), and zinc sulfide. .

  In the present invention, the contact angle θ2 between the water-repellent surface and water under ultraviolet irradiation can be 130 degrees or more, and can be 150 degrees or more.

The water repellent material is, for example, at least one selected from the group consisting of a fluororesin, a silicone resin, graphite fluoride, and a nanocarbon material. Here, the fluororesin preferably has a structure represented by — (CF ₂ ) _n —, where n is an integer of 1 or more, or CF ₃ —. The fluororesin is, for example, a polymer material including at least one monomer unit selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride.

The present invention also relates to a water repellent member comprising a base material and any one of the above water-repellent thin films covering at least a part of the base material.
From the viewpoint of increasing the water repellency of the water-repellent thin film, the surface of the base material before forming the water-repellent thin film is desirably a rough surface having irregularities or a three-dimensional microstructure. The centerline average roughness (Ra) of the rough surface before forming the water-repellent thin film is, for example, 1 μm or more and 10 μm or less.

  The water-repellent thin film of the present invention can be formed by a step of simultaneously depositing a water-repellent material and an inorganic material on the rough surface of a substrate having a rough surface by a vapor phase method. Here, as the vapor phase method, for example, a sputtering method or a vapor deposition method is suitable.

  According to the present invention, it is possible to obtain a water repellent thin film that contains an inorganic material, is thin and homogeneous, and exhibits sufficient water repellency while exhibiting the function of the inorganic material.

  For example, when the water repellent thin film of the present invention contains a photocatalyst as an inorganic material, the high water repellency of the water repellent thin film is maintained even under ultraviolet irradiation. Therefore, even when the water repellent thin film and water coexist, the photocatalyst exhibits high activity for the decomposition of organic substances. The water repellent thin film can be formed thin and can also be formed on the surface of a fine part.

  While the novel features of the invention are set forth in the appended claims, the invention will be better understood by reference to the following detailed description, taken in conjunction with the other objects and features of the present application, both in terms of construction and content. Will be understood.

2 is an electron micrograph of the surface of a titanium substrate before performing a hydrothermal treatment according to Example 1. FIG. It is an electron micrograph of the rough surface of the substrate on which a three-dimensional microstructure is formed by hydrothermal treatment. 2 is an electron micrograph of a water-repellent thin film made of a composite material of polytetrafluoroethylene and titanium oxide of Example 1 formed on a rough surface having a three-dimensional microstructure of a titanium substrate. It is a figure which shows the state of the water droplet on the water-repellent thin film of Example 1 before and after ultraviolet irradiation. It is an electron micrograph of the thin film which consists of a titanium oxide of the comparative example 1 formed in the rough surface which has a three-dimensional microstructure of a titanium substrate. It is a figure which shows the state of the water droplet on the thin film of the comparative example 1 before and behind ultraviolet irradiation. 4 is an electron micrograph of a water-repellent thin film made of polytetrafluoroethylene of Comparative Example 2 formed on a rough surface having a three-dimensional microstructure of a titanium substrate. It is a figure which shows the state of the water droplet on the water-repellent thin film of the comparative example 2 before and behind ultraviolet irradiation. It is a figure which shows the time-dependent change of the light absorbency of the light of wavelength 664nm derived from a methylene blue at the time of performing the decomposition reaction of a methylene blue using the water-repellent thin film of Example 1 and the comparative example 2. It is a figure which shows the spectral energy distribution of the radiation spectrum of mercury lamp SHL-100UVQ-2. 2 is an explanatory view showing an appearance of a PTFE-titanium oxide composite target used in Example 1. FIG. It is explanatory drawing which shows the external appearance of another composite target of PTFE-titanium oxide. 4 is an electron micrograph of a water-repellent thin film made of a composite material of polytetrafluoroethylene and titanium oxide formed on the surface of a quartz substrate. 2 is an electron micrograph of another water-repellent thin film produced in the same manner as in Example 1.

[Water repellent thin film]
The water-repellent thin film of the present invention is a thin film containing a composite water-repellent material and an inorganic material. The water-repellent thin film is provided in a state of being supported on the surface of various substrates. The water-repellent thin film usually means a part composed of a composite water-repellent material and an inorganic material, and the base material itself is not included in the water-repellent thin film.

  However, when the base material surface is roughened, it can be considered that the base material surface layer portion is included in the water-repellent thin film. For example, when the water repellent thin film is formed on the surface of a substrate having irregularities or a three-dimensional microstructure, the water repellent thin film can exhibit super water repellency in cooperation with the substrate surface layer portion. In such a case, it can be said that the substrate surface layer part constitutes a part of the water-repellent thin film functionally and structurally, and therefore it is reasonable to include the substrate surface layer part in the water-repellent thin film.

  The water repellent thin film can be formed as a deposited film of a water repellent material and an inorganic material. For example, by simultaneously depositing the water repellent material and the inorganic material on the surface of the base material, the composite of the water repellent material and the inorganic material can be easily achieved.

  The content of the inorganic material in the total of the water-repellent material and the inorganic material contained in the water-repellent thin film is, for example, from the viewpoint of enhancing the dispersibility of the inorganic material and fully exhibiting the function of the inorganic material. 75 mass% is preferable and 5-50 mass% is more preferable.

  As a water repellent thin film, from a sparse thin film in which fine particles of a composite material of a water repellent material and an inorganic material are scattered in an island shape, to a thin film in which a water repellent material and an inorganic material are densely packed, Various thin films can be formed. In any case, a state in which the first region and the second region are in contact with each other can be formed.

[Water repellent surface]
A water-repellent thin film including a composite water-repellent material and an inorganic material has a water-repellent surface in which a first region where the water-repellent material is exposed and a second region where the inorganic material is exposed are mixedly distributed. . The water repellent surface is not the surface of the thin film that comes into contact with the substrate surface, but the surface that is exposed to the outside air, organic matter, and the like. In order to develop various functions derived from inorganic materials (for example, a function of decomposing organic substances by a photocatalyst), it is essential that the inorganic material is exposed on the water-repellent surface.

  Each of the first region and the second region is desirably distributed on the whole water-repellent surface on average. In particular, the first region and the second region are distributed in an average manner over the entire water-repellent surface so that the first region and the second region are scattered (in other words, the first region and the second region are formed on the water-repellent surface. It is desirable to be placed on the plaque.

  For example, when the thin film is microscopically formed, the microparticles are formed of a composite material of a water repellent material and an inorganic material. In this case, it is preferable that the first region and the second region are distributed so as to be mixed on the surface of each fine particle. The fine particles may be in contact with each other or may be separated from each other. The average size of the fine particles is, for example, 10 nm or more and 1 μm or less, and preferably 100 nm or more and 1 μm or less. Therefore, it is preferable that the first region and the second region are mixed at the nano level. What is necessary is just to obtain | require the average magnitude | size of a microparticle as an average value of the largest diameter of the arbitrary 10 microparticles observed with an electron microscope (SEM).

  When the water-repellent material is more contained in the thin film than the inorganic material, the second regions may be averagely distributed so as to be scattered over the entire water-repellent surface. Further, when the inorganic film is more contained in the thin film than the water repellent material, the first region may be distributed on average so as to be scattered over the entire water repellent surface.

  The level of dispersibility of the first region and the second region on the water repellent surface is such that, for example, when the element map of the water repellent surface is measured by EDS, the first region and the second region cannot be distinguished. It is desirable to be.

  The measurement range by EDS may be 2 μm square. The characteristic X-ray of EDS is 1 μm or less, and the analysis of the micro-size region becomes the limit. On the other hand, the state where the first region and the second region are mixed at the nano level can also be confirmed by EDS. Since each region has a size equal to or less than the resolution of EDS, the presence of both the water-repellent material and the inorganic material can be confirmed by analyzing any part of the thin film.

  From the viewpoint of improving water repellency, the water repellent surface preferably has irregularities or a three-dimensional microstructure. The centerline average roughness (Ra) of the water repellent surface is preferably, for example, 1 μm or more and 10 μm or less. The three-dimensional microstructure includes a porous structure, for example.

[Center line average roughness]
The center line average roughness (Ra) is an arithmetic average roughness defined in JIS B0601 (1994). The roughness curve is folded from the center line of the length L, and is obtained by the roughness curve and the center line. The area obtained by dividing the area by the length L of the center line. Ra can also be measured using an AFM (atomic force microscope). The measurement range by AFM may be 50 μm square.

[Base material]
The water repellent thin film is formed on the surface of various members (base materials). From the viewpoint of improving the water repellency of the water-repellent thin film, the surface of the substrate carrying the water-repellent thin film is preferably a rough surface having irregularities or a three-dimensional microstructure. The center line average roughness (Ra) of the rough surface is preferably 1 μm or more and 10 μm or less, and is preferably larger from the viewpoint of developing super water repellency. The surface state of the water repellent surface can be controlled by the state of the rough surface of the substrate. However, the surface state of the water-repellent surface can also be controlled by the thickness of the composite material composed of the water-repellent material and the inorganic material, the formation method of the composite material, and the like.

  Roughness and three-dimensional microstructure on the rough surface of the base material may be formed by subjecting the base material surface to physical processing, or by subjecting the base material surface to chemical treatment such as etching or hydrothermal treatment. May be. However, physical processing and chemical treatment are not necessarily required when the substrate itself has an unevenness or a three-dimensional microstructure.

  The unevenness and the three-dimensional fine structure may be formed in a regular pattern or irregularly. The three-dimensional microstructure may be a porous structure. For example, a porous structure can be formed on the surface layer of the base material by subjecting the surface of the base material such as metal or ceramic to a chemical treatment by bringing an acidic or alkaline chemical into contact therewith. Such a porous structure may be formed of a fibrous material having a network structure.

[Water repellent member]
The water-repellent member of the present invention is not particularly limited as long as it includes a base material and the water-repellent thin film formed so as to cover at least a part of the base material. The substrate is not particularly limited as long as it is a material that requires water repellency. The material of the substrate may be, for example, plastic, metal, ceramics, glass, wood, pulp or the like. The shape and application of the substrate are not particularly limited.

[First area]
A first region where the water-repellent material is exposed is distributed on the water-repellent surface. The first region has an action of reducing the surface energy of the water repellent surface. By distributing the first region over the entire water-repellent surface, the surface energy of the entire water-repellent surface is reduced, and water repellency is imparted to the entire water-repellent surface.

[Second area]
On the water repellent surface, the second region where the inorganic material is exposed is distributed so as to be mixed with the first region. The mixed mode is a mode in which even if water droplets adhere to the water-repellent surface, the water droplets are not easily affected by the second region where the inorganic material is exposed, and the surface energy reduction effect by the water-repellent material is not easily inhibited. It is desirable to be. That is, it is desirable that water droplets do not adhere to the second region where the inorganic material is exposed.

  From the viewpoint of enhancing the function of the inorganic material, the water repellent surface needs to have a first region where the inorganic material is exposed uniformly and evenly. If an inorganic material is unevenly distributed on a part of the water-repellent surface, the region where the inorganic material is unevenly distributed has little effect of reducing the surface energy by the water-repellent material, and water droplets are present in the region where the inorganic material is unevenly distributed. It becomes easy to adhere. As a result, the function of the inorganic material is hindered.

  When the second region where the inorganic material is exposed is scattered in the first region, the individual size of the second region where the inorganic material is exposed is, for example, preferably 1 μm or less, and preferably 500 nm or less. More preferably, it is 100 nm or less. Further, the lower limit of the size is preferably, for example, 1 nm or more, and may be 10 nm or more, or 30 nm or more.

  When the first regions where the water repellent material is exposed are scattered in the second region, the individual sizes of the first regions where the water repellent material is exposed are preferably 1 μm or less, for example, 500 nm or less. It is more preferable that the thickness is 100 nm or less. Further, the lower limit of the size is preferably, for example, 1 nm or more, and may be 10 nm or more, or 50 nm or more. It should be noted that the first region is continuously scattered in the second region at a narrow pitch, so that the effect of reducing the surface energy by the water repellent material is exhibited, and water droplets adhere to the second region where the inorganic material is exposed. It will be difficult.

  Although it is difficult to measure the size of each of the first region and the second region, it can be predicted by observing the surface of the thin film with an electron microscope or a high-resolution EDS. The first region and the second region can be distinguished from each other by a photomicrograph, a color tone of an EDS image, or the like. For example, an average value of the sizes of the respective regions may be obtained by drawing a circle containing the region to be measured and calculating an average value of the diameters of the ten circles. Measurement is performed in three fields of view, and an average value of the diameters of 30 circles may be obtained.

  From the viewpoint of sufficiently exerting the function of the inorganic material and ensuring sufficient water repellency, it is preferable that the first region and the second region are arranged in spots in the 500 nm square region of the first surface. For example, it may be desirable that there are a plurality of first regions and a plurality of second regions, preferably three or more each, in the 500 nm square region. In addition, in the state where the first region and the second region are arranged in spots, the center-to-center distance between the adjacent first region and second region is considered to be about 10 nm to 400 nm, for example. Here, the center-to-center distance is a center-to-center distance of a circle that includes each region. The circle containing the adjacent first region and the circle containing the second region may overlap each other.

[Deposited film]
The deposited film is a film that can be formed by a vapor phase method, and is formed by depositing nanoparticles generated in the vapor phase on the substrate surface. From the viewpoint of forming a strong deposited film with few impurities, the vapor phase atmosphere for forming the thin film is preferably a reduced pressure atmosphere, and is preferably close to a vacuum. However, an inert gas such as argon, helium or nitrogen may be present in the gas phase in addition to the nanoparticles used as the raw material for the thin film.

  Water-repellent material and inorganic material nanoparticles (clusters, atoms, molecules, ions, radicals, etc.) generated in the gas phase are deposited on the substrate surface at the same time, resulting in a composite water-repellent material and inorganic material. And a deposited film can be formed. Microscopically, the deposited film is considered to be composed of fine water-repellent material particles (hereinafter, water-repellent fine particles) and fine inorganic material particles (inorganic fine particles). That is, it hardly contains other components of the water repellent material and the inorganic material (impurity content is usually 0.05% by mass or less). Further, the size of the first region or the second region is small, and the water-repellent fine particles and the inorganic fine particles are densely filled. Such a film structure is a structure peculiar to the water-repellent thin film of the present invention, and is a structure that is not found in a water-repellent thin film formed using a conventional coating composition.

  The deposited film formed by the vapor phase method includes a region in which water-repellent fine particles are aggregated and bonded to each other, a region in which inorganic fine particles are aggregated and bonded to each other, and water-repellent fine particles and inorganic fine particles. It is thought that it contains the area | region mutually couple | bonded. Thus, since the deposited film is densely filled with the water-repellent material and the inorganic material (for example, even in the fine particles of the composite material), the first region and the second region are in contact with each other. It has become. As a result, the inorganic material is immobilized by the water-repellent material (immobilized), so that the inorganic material is unlikely to drop off.

[Thin film thickness]
The thickness of the thin film (thickness of the portion made of the composite material of the water repellent material and the inorganic material) is preferably 10 nm or more and 3 μm or less, for example, considering the strength, material cost, etc. Here, when forming a water-repellent thin film on a substrate that requires a very thin thin film, such as a fine part, a deposited film is suitable. It is easy to control the thickness of the deposited film that can be formed by the vapor phase method. The thickness of the deposited film can be controlled by adjusting the amount of fine particles attached to the substrate surface according to the film formation time. Since the deposited film has a dense structure, it has a high strength even when it is thin, and is optimal for applications such as an automobile windshield.

  The thickness of the deposited film formed by the vapor phase method is preferably thinner from the viewpoint of not impairing the function and appearance of the fine component, for example, preferably 600 nm or less, and particularly preferably 300 nm or less. On the other hand, from the viewpoint of securing impact resistance and weather resistance, it is preferably 50 nm or more, and more preferably 100 nm or more.

[Porosity of thin film]
The porosity of the thin film largely depends on the film formation method, but in the case of a deposited film having a relatively large thickness, the porosity is small because of the dense structure. Here, the porosity is a ratio of voids such as voids that can be formed inside a thin film (a portion made of a composite material of a water repellent material and an inorganic material) to the apparent volume of the thin film.

The porosity cannot be measured when the thin film is formed of fine particles scattered in islands, but can be measured by the following two-dimensional method when the film is a dense film.
First, a thin film is cut | disconnected in the thickness direction, a cross section is formed, and a cross section is processed by grinding | polishing and a cross polisher. Thereafter, the processed cross-section is observed with a scanning ion microscope (SIM) to obtain a cross-sectional image (cross-sectional SIM image). The porosity can be determined using image software (ImageJ) using the contrast of the cross-sectional SIM image. When the cross-section SIM image is binarized and a distribution map is acquired, the void portion is displayed as a black region. If the ratio of the area of the black region to the cross-sectional area of the thin film is calculated using image software, the porosity can be obtained.

[Super water repellency]
The water repellency of the water repellent thin film is expressed by static water repellency evaluated by the contact angle between water and the water repellent surface. The larger the contact angle, the better the water-repellent thin film has a static water repellency. By controlling Ra within the above preferred range, it is possible to control the contact angle of the water-repellent surface of the water-repellent thin film with water to 130 ° or more, and further to 150 ° or more. The property that the contact angle with water on the solid surface is 150 degrees or more is called “super water repellency”.

  The solid surface exhibiting super water repellency exhibits characteristic functions such as anti-fogging effect by suppressing adhesion of water droplets in addition to waterproofing. For this reason, in recent years, functional materials having super water repellency have been actively designed and developed. For the construction of a solid surface exhibiting super water repellency, it is important to introduce a fine structure on the surface and to reduce the surface energy.

  Some inorganic materials that are combined with a water-repellent material, such as titanium oxide, exhibit high hydrophilicity under irradiation with light such as ultraviolet rays. Even such an inorganic material can be made hydrophilic under light irradiation by forming a thin film combined with a water-repellent material. Specifically, according to the present invention, it is possible to obtain a water-repellent thin film having a contact angle between a water-repellent surface and water of 130 degrees or more, and even 150 degrees or more even under ultraviolet irradiation. Here, ultraviolet rays refer to electromagnetic waves having a wavelength of 10 to 400 nm. The same effect can be obtained as long as the inorganic material is not limited to titanium oxide but becomes hydrophilic and becomes less hydrophobic when irradiated with ultraviolet rays.

  In the case of the water-repellent thin film of the present invention, when the contact angle under non-ultraviolet irradiation is θ1, and the contact angle under ultraviolet irradiation is θ2, the variation of the contact angle represented by 100 × (θ1−θ2) / θ1 For example, the amount can be controlled to 10% or less, and can be controlled to 5% or less.

In the present invention, the contact angle between water and the water repellent surface is a value measured in air having a dew point of 25 ° C. The contact angle under non-irradiation with ultraviolet rays is a value measured within 10 seconds when a water droplet (1 μL) of distilled water is dropped on the water repellent surface of the water repellent thin film. On the other hand, the contact angle under UV irradiation is within 10 seconds when water droplets (1 μL) of distilled water are dropped on the water repellent surface 300 minutes after the start of UV irradiation (using a mercury lamp) on the water repellent surface. The value to be measured. The amount of ultraviolet light is 1000 μW / cm ² .

[Inorganic materials]
Examples of the functional inorganic material desired to be combined with the water-repellent material include a material that functions as a catalyst carrier, a material that has a photocatalytic action that oxidizes or reduces an organic substance by light irradiation, and a material that has a semiconductor property. Can be mentioned. As such materials, various inorganic oxides and inorganic sulfides have been researched, developed and used. These materials can be formed as a material having an ion exchange action or a material having a molecular sieving effect, or can be used in combination with a material having an ion exchange action or a material having a molecular sieving effect.

  Examples of the material having an ion exchange effect and the material having a molecular sieving effect include zeolite. As the zeolite, aluminosilicate is typical, but various metal elements other than silicon and aluminum (for example, a metal that exhibits photocatalytic action such as titanium) can be introduced into the skeleton. For example, titanosilicate or titanium-containing aluminosilicate may be used as the inorganic material. Further, after forming a thin film containing zeolite, various metal elements may be introduced by an ion exchange method, a supporting method, or the like.

  Examples of the material that functions as a catalyst carrier include silicon oxide (silica) and mesoporous silica. In addition, various metal elements other than silicon (for example, a metal that exhibits photocatalytic action such as titanium) can be introduced into the skeleton of mesoporous silica, and a mesoporous material having a desired function can be formed. Further, after forming a thin film containing mesoporous silica or mesoporous material, various metal elements may be introduced by a supporting method or the like.

  Examples of the inorganic material having a photocatalytic action include titanium oxide, tungsten oxide, zinc oxide, zirconium oxide, strontium titanate, niobium oxide, cadmium sulfide, zinc sulfide, titanosilicate, titanium-containing aluminosilicate, and the like. These may be used alone, or may be used in combination of two or more kinds.

  Moreover, you may use the composite inorganic material which disperse | distributed the inorganic material which has a photocatalytic action to the matrix of the material which does not show photocatalytic actions, such as a silicon oxide and aluminum oxide. For example, a material containing a titanium species including a titanium atom and oxygen that is tetracoordinated or hexacoordinated to the titanium atom can be used. In addition, after forming a thin film made of a composite material of aluminosilicate and water repellent material, metal elements such as titanium, zinc, zirconia, etc. are introduced into the aluminosilicate part by various methods so as to have photocatalytic action. May be.

  Examples of the inorganic material having semiconductor properties include materials containing titanium oxide, cadmium sulfide, strontium titanate, niobium oxide, cadmium sulfide, cadmium telluride, tin oxide, indium tin oxide (ITO), zinc sulfide, and the like. These may be used alone, or may be used in combination of two or more kinds.

  Among the above, titanium oxide is originally a semiconductor material, but it is also promising as a photocatalyst, and its practical application is progressing. The titanium oxide may be, for example, anatase type or rutile type crystalline titanium oxide, or may be microcrystalline or amorphous titanium oxide. Crystalline titanium oxide is preferable because it has a high ability to oxidize and decompose organic substances. However, even if it is microcrystalline or amorphous titanium oxide, it is fine when it is finely divided or incorporated into other materials in a highly dispersed state. Is known to exhibit high oxidative degradation activity on organic matter. Moreover, even if it is crystalline titanium oxide, photocatalytic activity is improved by making it microparticles | fine-particles to such an extent that a quantum size effect is acquired.

  However, an inorganic material such as titanium oxide alone has a property of showing hydrophilicity when irradiated with ultraviolet rays. Since many organic substances are hydrophobic, the contact opportunities between inorganic materials and organic substances are reduced under ultraviolet irradiation. On the other hand, when the water-repellent thin film of the present invention is formed of a thin film containing a composite inorganic material and a water-repellent material as described above, the contact angle with water is 150 even under ultraviolet irradiation. It is possible to increase to more than a degree.

[Photocatalysis]
In the present invention, when the methylene blue decomposition reaction is carried out for 10 hours under the following conditions and the methylene blue absorbance is 50% or less before the reaction, the inorganic material (or water repellent thin film) has a photocatalytic action. Define.
<Conditions>
(I) Sample solution: methylene blue aqueous solution, 10 ⁻⁵ mol / L, 1 mL
(Ii) Catalyst amount: 10 mm × 10 mm water-repellent thin film formed on one side of the substrate (iii) Light quantity: 1 mW / cm ² , using a mercury lamp (radiating UV light of 250 nm or more) (iv) Evaluation method: Change in absorbance of light having a wavelength of 664 nm derived from methylene blue

[Self-cleaning effect]
By combining the super-water-repellent property by the water-repellent material and the photocatalytic action by the inorganic material, even if an organic substance adheres to the base material, a function of decomposing and washing it out, that is, a self-cleaning effect can be obtained. Since water droplets do not adhere to the super-water-repellent thin film, when rain dew adheres to the material on which the water-repellent thin film is formed, the water droplets entrain and slide down with organic substances decomposed by the photocatalytic action. Such an effect can be expected to be practically applied to maintenance-free interior or exterior building materials, automobile windshields, and the like.

[Water repellent material]
The water repellent material is preferably a material that can be formed by a vapor phase method, but is not particularly limited. For example, water-repellent resin materials such as fluororesin and silicone resin, water-repellent carbon materials such as fluorinated graphite, and nanocarbon materials are preferable. These can be used alone or in combination of two or more. Among these, a water-repellent resin material is preferable and a fluororesin is particularly preferable in that a deposited film having high strength can be obtained. The fluororesin is a general term for synthetic resins obtained by polymerizing olefins containing fluorine.

Among fluororesins, it has excellent water repellency and is difficult to be modified during film formation. Therefore, — (CF ₂ ) _n —, where n is an integer of 1 or more, or fluorine having a structure represented by CF ₃ —. Resins are particularly preferred. Examples of such a fluororesin include a polymer material containing at least one monomer unit selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride. For example, polytetrafluoroethylene (PTFE), polyhexafluoropropylene and the like are particularly preferable.

[Production of water-repellent thin film]
The water repellent thin film can be formed by simultaneously depositing a water repellent material and an inorganic material on the surface of the base material by a vapor phase method. Here, examples of the vapor phase method include a sputtering method, a vapor deposition method, a CVD method (Chemical vapor deposition), an ion plating method, and the like, but a sputtering method or a vapor deposition method is preferable. Hereinafter, a case where a deposited film of a composite water-repellent material and an inorganic oxide is formed by a sputtering method will be described as an example.

  Specifically, first, a base material having a surface for forming a thin film is prepared. By forming a three-dimensional microstructure on the surface of the substrate, it becomes possible to enhance the water repellency of the completed water-repellent thin film and to exhibit super water repellency.

  For example, when using a metal such as Ti, Zn, Al, Mg, or an alloy containing at least one of these as a base material, the metal surface is subjected to press working or chemical etching with an acidic or alkaline solution. The roughening process can be performed. The method of chemical etching is not particularly limited. For example, a porous material composed of a fibrous material in which the surface layer of the base material is developed into a network by immersing the metal base material in a heated sodium hydroxide aqueous solution. Can be changed to structure.

As the sputtering method, RF magnetron sputtering is suitable. Sputtering is desirably performed in a processing space (chamber) in which, for example, the pressure is reduced to 1 × 10 ⁻⁴ Pa or less and an inert gas (for example, argon) is introduced. In the processing space, a target that is a raw material for the thin film and a base material are arranged to face each other. A permanent magnet is disposed on the back side of the target. By applying a voltage between the base material and the target and generating a magnetic field with a permanent magnet, the ionization of the inert gas is promoted, and the ions collide with the target to produce fine particles that are the raw material of the thin film. To do. The fine particles are deposited on the surface of the substrate by the action of an applied voltage.

  At this time, by placing a water repellent material (for example, PTFE) and an inorganic material (for example, titanium oxide) close to each other as a target, both can be simultaneously deposited on the surface of the substrate. Therefore, a thin film as a homogeneous composite material can be formed. As a target of the water repellent material, for example, in the case of PTFE, pellets formed by compressing PTFE particles or a PTFE sheet can be used. As the inorganic material target, for example, in the case of titanium oxide, pellets formed by compressing powdered titanium oxide can be used. A mixed target containing both a water repellent material and an inorganic material may be used. As a form of the mixed target, for example, a circular target that is divided into four or more arc-shaped regions and in which arc-shaped regions of a water repellent material and an inorganic material are alternately arranged along a central angle can be mentioned. However, the arrangement of the water repellent material region and the inorganic material region in the target is not particularly limited.

  Further, by simultaneously depositing silicon oxide, aluminum oxide, alkali metal or alkaline earth metal, and water repellent material, a composite material of aluminosilicate and water repellent material is deposited, or silicon oxide, By simultaneously depositing titanium oxide, alkali metal or alkaline earth metal, and water repellent material, a composite material of titanosilicate and water repellent material can be deposited. The formed thin film may then be subjected to a desired treatment (eg, heating) to promote the formation of a zeolite-like pore structure.

  The high-frequency output when performing RF magnetron sputtering is not particularly limited, and may be adjusted from the viewpoint of realizing an appropriate film formation rate. Further, it is desirable to control the temperature of the substrate during film formation from room temperature to about 100 ° C. When forming a water-repellent thin film having a thickness of about 50 nm to 500 nm, it is desirable to finish the film formation in about 0.5 to 3 hours.

  In the case where the substrate surface layer portion is formed of a fibrous material having a network structure, if a water repellent material is deposited on the surface of the substrate, a phenomenon in which a plurality of fibrous materials are caught by the water repellent material occurs. The As a result, a thicker fibrous composite member composed of a plurality of bundled fibrous substances and a water-repellent thin film covering them is formed. The same phenomenon can be seen when the water repellent material and the inorganic material are deposited simultaneously. In such a fibrous composite member, since the water-repellent material includes a plurality of fibers, the bonding force between the thin film and the substrate surface is increased. Therefore, a strong water-repellent thin film is formed.

EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example, this invention is not limited to an Example.
Example 1
[Hydrothermal treatment of substrate]
A three-dimensional microstructure was formed on the surface layer of the titanium substrate serving as the base material by hydrothermal treatment. Specifically, the titanium substrate was immersed in a 1M sodium hydroxide aqueous solution at 220 ° C. for 3 hours, followed by immersion in a 0.6M hydrochloric acid aqueous solution for 2 hours, and then washed with distilled water and ethanol. Next, the cleaned titanium substrate was baked at 500 ° C. for 30 minutes, whereby the surface layer portion of the titanium substrate was changed to a porous structure made of a fibrous material having a network structure. An electron micrograph of the surface of the titanium substrate before hydrothermal treatment is shown in FIG. An electron micrograph of the surface of the titanium substrate on which the three-dimensional microstructure is formed is shown in FIG.

[Deposition of water-repellent thin film]
Polytetrafluoroethylene (PTFE) and titanium oxide (TiO ₂ ) were simultaneously sputtered on the surface of the titanium substrate on which the three-dimensional microstructure was formed by RF magnetron sputtering under the following conditions. As a result, a composite material of PTFE and titanium oxide was deposited on the rough surface of the base material, and a water-repellent thin film was formed. An electron micrograph of a water-repellent thin film made of a composite material of PTFE and titanium oxide formed on the surface of a substrate having a three-dimensional microstructure is shown in FIG.

  A circular target having a diameter of 25.4 mm (1 inch) was used for the following composite target. The circular target was divided into four or more arc-shaped areas, and two arc-shaped areas of PTFE and titanium oxide were arranged along the central angle.

<Sputtering conditions>
Apparatus: pressure of the sputtering apparatus argon atmosphere, Ltd. Green-Tech: 1 × 10 ^-4 Pa~2 pressure was reduced to × 10 ^-4 Pa, introduction output until the argon gas 1 Pa: 10 W
Target: PTFE-titanium oxide composite target Deposition time: 1 hour

[Thin film properties]
The thickness of the water repellent thin film calculated from the sputtering conditions was 50 to 200 nm.
The contact angle between the water repellent thin film and water was 156.6 degrees immediately after the film formation and 154.9 degrees after the ultraviolet irradiation, and both showed super water repellency. The state of water droplets on the water-repellent thin film before and after ultraviolet irradiation is shown in FIG.

Example 2
A water-repellent thin film was formed by sputtering in the same manner as in Example 1 except that the titanium substrate was not subjected to hydrothermal treatment.
The contact angle between the water repellent thin film and water was 110 degrees immediately after film formation and 107 degrees after ultraviolet irradiation.

<< Comparative Example 1 >>
A water-repellent thin film was formed by sputtering in the same manner as in Example 1 except that only titanium oxide was used as a target and PTFE was not used. FIG. 5 shows an electron micrograph of a water-repellent thin film made of titanium oxide formed on the surface of a substrate having a three-dimensional microstructure.
The contact angle between the water repellent thin film and water was 106.5 degrees immediately after the film formation, 1.8 degrees after the ultraviolet irradiation, and clearly hydrophilic after the ultraviolet irradiation. The state of water droplets on the water-repellent thin film before and after ultraviolet irradiation is shown in FIG.

<< Comparative Example 2 >>
A water-repellent thin film was formed by sputtering in the same manner as in Example 1 except that only PTFE was used as a target and titanium oxide was not used. FIG. 7 shows an electron micrograph of a water-repellent thin film made of PTFE formed on the surface of a substrate having a three-dimensional microstructure.
The contact angle between the water repellent thin film and water was 168.1 degrees immediately after the film formation and 165.3 degrees after the ultraviolet irradiation, and both showed super water repellency. The state of water droplets on the water-repellent thin film before and after ultraviolet irradiation is shown in FIG.

[Photocatalysis of thin film]
Next, the activity of the water-repellent thin film of Example 1 and Comparative Example 2 as a photocatalyst was evaluated.
Specifically, 1 mL of a methylene blue aqueous solution having a concentration of 10 ⁻⁵ mol / L is weighed and introduced into a 10 mm × 10 mm × 3 mm size cell made of quartz, and similarly has a water repellent thin film of 10 mm × 10 mm size on one side. The titanium substrate was completely immersed in a methylene blue aqueous solution. In this state, ultraviolet irradiation (light amount: 1 mW / cm ² , using a mercury lamp (SHL-100 UVQ-2 manufactured by Toshiba Corporation)) is performed, and a UV-vis spectrum (absorption spectrum) of a methylene blue aqueous solution is obtained every hour. It was measured. Methylene blue shows an absorption peak at a wavelength of 664 nm. The change with time of the absorption peak (absorbance) is shown in FIG. The amount of decrease in the absorption peak is proportional to the amount of methylene blue decomposition reaction. In FIG. 9, I ₀ represents the initial absorption intensity, and I represents the absorption intensity at each time.
The mercury lamp SHL-100UVQ-2 can use a UV spectrum of 250 nm or more, and the strongest spectrum is 546 nm. The spectral energy distribution of the mercury lamp is shown in FIG.

  From FIG. 9, when the water-repellent thin film of Example 1 was used (graph A), 90% or more of methylene blue (MB) was oxidatively decomposed after 10 hours, and high photocatalytic activity was exhibited. Understandable. On the other hand, when the water-repellent thin film of Comparative Example 2 was used (graph B), it can be understood that 60% or more of methylene blue remained even after 10 hours and did not have a photocatalytic action. In addition, the graph C has shown the result of the blank test at the time of performing a decomposition reaction only with a methylene blue, without using any water-repellent thin film.

  The appearance of the PTFE-titanium oxide composite target used in Example 1 is shown in FIG. FIG. 12 shows the appearance of a modification of the PTFE-titanium oxide composite target.

Further, FIG. 13 shows a thin film formed by simultaneously sputtering polytetrafluoroethylene (PTFE) and titanium oxide (TiO ₂ ) on a quartz substrate instead of a titanium substrate. In FIG. 13, it can be seen that fine particles formed of a composite material of a water repellent material and an inorganic material are scattered in an island shape on the surface of the quartz substrate.

  Furthermore, an electron micrograph of another water-repellent thin film produced in the same manner as in Example 1 is shown in FIG. Also in FIG. 14, it can be seen that fine particles formed of a composite material of a water repellent material and an inorganic material are scattered in an island shape on the surface of the titanium substrate.

  The water-repellent thin film of the present invention can be applied to a thin film containing an inorganic material having various functions. The water-repellent thin film of the present invention is thin and homogeneous, and exhibits sufficient water repellency while exhibiting the function of an inorganic material (for example, photocatalytic action). Therefore, for example, it is suitable for imparting a photocatalytic action to a material that requires an antifouling effect in an environment where water is present. Further, since the water-repellent thin film of the present invention can be formed thin, it has a material that is not suitable for providing a thick thin film, for example, a member that requires high heat dissipation, a member that requires light transmission, and a fine structure. Suitable for forming on members.

  While this invention has been described in terms of the presently preferred embodiments, such disclosure should not be construed as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains after reading the above disclosure. Accordingly, the appended claims should be construed to include all variations and modifications without departing from the true spirit and scope of this invention.

Claims (12)

Including a thin film comprising a composite water-repellent material and an inorganic material;
The thin film has a water repellent surface in which a first region where the water repellent material is exposed and a second region where the inorganic material is exposed are mixed and distributed.
A water-repellent thin film, wherein the inorganic material is a material exhibiting a photocatalytic action for oxidizing or reducing an organic substance by light irradiation, or a semiconductor material.   The water-repellent thin film according to claim 1, wherein the thin film is a deposited film of the water-repellent material and the inorganic material.   The water-repellent thin film according to claim 1 or 2, wherein the thin film has a thickness of 10 nm or more and 3 µm or less.   When the contact angle between the water-repellent surface and water when not irradiated with ultraviolet rays is θ1, and the contact angle when irradiated with ultraviolet rays is θ2, the variation of the contact angle expressed by 100 × (θ1−θ2) / θ1 The water-repellent thin film according to any one of claims 1 to 3, wherein the amount is 10% or less.   The photocatalytic material is at least one selected from the group consisting of titanium oxide, tungsten oxide, zinc oxide, strontium titanate, niobium oxide, cadmium sulfide, zinc sulfide, titanosilicate, and titanium-containing aluminosilicate. The water-repellent thin film according to any one of claims 1 to 4.   The semiconductor material includes at least one selected from the group consisting of titanium oxide, cadmium sulfide, strontium titanate, niobium oxide, cadmium sulfide, cadmium telluride, tin oxide, indium tin oxide (ITO), and zinc sulfide. The water-repellent thin film according to any one of claims 1 to 4.   The water repellent thin film according to any one of claims 1 to 6, wherein a contact angle θ2 of the water repellent surface with water under ultraviolet irradiation is 130 degrees or more.   The water-repellent thin film according to claim 7, wherein a contact angle θ2 between the water-repellent surface and water under ultraviolet irradiation is 150 degrees or more.   The water-repellent thin film according to any one of claims 1 to 8, wherein the water-repellent material is at least one selected from the group consisting of a fluororesin, a silicone resin, graphite fluoride, and a nanocarbon material. The water-repellent thin film according to claim 9, wherein the fluororesin has a structure represented by — (CF ₂ ) _n —, where n is an integer of 1 or more, or CF ₃ —.   The water-repellent thin film according to claim 10, wherein the fluororesin contains at least one monomer unit selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride.   The water-repellent member containing a base material and the water-repellent thin film of any one of Claims 1-11 formed so that at least one part of the said base material might be coat | covered.