JP2013216530A - Composite alumina film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite alumina film capable of removing easily dirt adhering onto its surface.SOLUTION: A composite alumina film has alumina, a hydrophilic group bonded to an Al atom of the alumina and a water-repellent group bonded to the Al atom.

Description

  The present invention relates to a composite alumina coating. More specifically, the surface characteristics of the composite alumina coating can be easily removed by combining a hydrophilic group bonded to an Al atom and a water-repellent group bonded to an Al atom. The present invention relates to a composite alumina film that can be formed.

  Patent Document 1 states that “a monomolecular film formed by chemically bonding a chlorosilane surfactant having a specific perfluoroalkyl group is formed on at least the glass surface directly or via a protective film on the outermost surface. Is disclosed "(refer to the claims of Patent Document 1). An object of the invention disclosed in Patent Document 1 is to provide a glass excellent in water and oil repellency and durability ("Industrial application field" in Patent Document 1 and "Problems to be solved by the invention"). ”Column). According to the embodiment of the invention disclosed in Patent Document 1, it has been clarified that the contact angle of water adhering to the glass surface with respect to the glass surface was 140 to 150 degrees (page 4 of Patent Document 1). (Refer to the upper left column, lines 1 to 2).

  According to the example described in Patent Document 1, by immersing the glass in a solution containing a silane surfactant containing a vinyl group, the silane surfactant containing a hydroxyl group and a vinyl group present on the glass surface. It reacts with the silyl group, thereby chemically bonding the silane surfactant containing the vinyl group to the glass. Next, the glass surface is irradiated with energy in an atmosphere containing oxygen or nitrogen to add a hydroxyl group or an amino group to the vinyl group to form a monomolecular adsorption protective film. Next, by contacting the monomolecular adsorption protective film with a chlorosilane-based surfactant having a perfluoroalkyl group, a hydroxyl group or amino group bonded to the monomolecular adsorption protective film and a chlorosilyl group in the chlorosilane-based surfactant To form a two-layered monomolecular adsorption protective film, and a monomolecular film of a silane surfactant containing a perfluoroalkyl group on the surface is formed (second in Patent Document 1). (See lower right column line 3 to page 3, lower right column line 2.)

  According to the description of Patent Document 1, the glass according to Claim 1 in Patent Document 1 is excellent in water and oil repellency (Claim 1 and page 2, upper left column, lines 11 and 17). (See line 18).

  The glass according to claim 1 of Patent Document 1 realizes water repellency and oil repellency by forming a monomolecular cumulative film having a monomolecular adsorption film containing fluorine atoms on the glass surface as a material. .

  The water- and oil-repellent glass (Patent Document 1), which is the invention disclosed in Patent Document 1, is formed by forming a monomolecular film or a monomolecular cumulative film of a surfactant having a fluorine atom at the terminal on the entire surface of the glass surface. Therefore, the technical effect of “preventing contamination of the glass surface” can be achieved (refer to Patent Document 1, page 4, lower left column, line 8).

  The invention disclosed in Patent Document 2 describes that a cured thin film formed by applying an alumina sol solution... To a substrate surface and then curing the obtained coating film is converted into a phosphate group-containing organic compound. A method for producing a hydrophilic thin film characterized in that the surface treatment is carried out (see claim 1 of Patent Document 2), which is characterized in that it is formed of alumina ... and a phosphate group-containing organic compound. A hydrophilic thin film ”(see claim 6 of Patent Document 2). The phosphate group in the phosphate group-containing organic compound is a hydrophilic group.

  Patent Document 3 discloses “a coating composition containing at least a fine particle having a hydrophilic surface and a block polymer having a hydrophobic group at one end and a hydrophilic group at the other end” (Patent Document 3). And a coating composition containing at least a fine particle having a hydrophilic surface and a block polymer having a hydrophobic group at one end and a hydrophilic group at the other end of the linear polymer. The block polymer is adsorbed to the unevenness formed on the surface of the object to be coated by the fine particles, and the surface of the object to be coated on which the unevenness is formed. In the polymer layer, the block polymer has the hydrophilic group side on the surface side of the irregularities due to the fine particles. On the surface side of the hydrophobic group side of the polymer layer, oriented respectively, the coating product is adsorbed on the surface of the coating object. "(See claim 6 of Patent Document 3) are disclosed.

  In the coating object disclosed in Patent Document 3, the hydrophilic group in the block polymer having both the hydrophilic group and the hydrophobic group is bonded to the hydrophilic group present on the surface of the fine particle by van der Waals force. Since the block polymer is easily removed from the surface of the fine particles, it is considered that the durability is poor. Inferior durability is also pointed out in paragraph No. 0002 of Patent Document 4 described below.

  Patent Document 4 includes “fine particles having a hydrophilic surface, a block polymer having a hydrophobic group and a hydrophilic group, an organic solvent, and a component that dissolves in an organic solvent and forms a transparent body when dried. "A coating composition characterized by having a transparent film formed by applying and drying the coating composition" (see claim 1 of Patent Document 4) ( Patent Document 4 (see claim 6)).

  According to this Patent Document 4, the invention disclosed in Patent Document 3 “The coating composition is not durable enough. For example, when heavy rain hits the side mirror, the coating film applied to the side mirror is It easily peeled off and lost water repellency.Therefore, a coating composition capable of forming a coating film having excellent durability that can withstand long-term use was desired. (See paragraph 0002 of Patent Document 4), the problem of the invention disclosed in Patent Document 4 is that “a transparent coating film can be formed, water repellency, and durability that can withstand long-term use” A coating composition capable of forming a coating film having a coating film, and a coating provided with the coating film formed using the coating composition It is the object of the present invention is to provide a body. ".

  In the invention disclosed in Patent Document 4, in order to improve the durability of the water-repellent film in the coating composition or the coating object described in Patent Document 3, as a component further serving as a binder in the coating composition. The “component that forms a transparent body when dried” is an essential component (see paragraph No. 0013), and the durability of the water-repellent coating is clarified by Examples and Comparative Examples.

  In addition, in the invention described in Patent Document 4, “difficult to adhere to dust” is also mentioned as a technical effect of the invention, but it is not verified that “difficult to adhere to dust” by the examples. Furthermore, there is no description in Patent Document 4 regarding what kind of “garbage” is said to be “hard to adhere”.

  Patent Document 5 states that “an object is to provide a water-based coating composition that can form a coating film that is excellent in dirt adhesion suppression effect and excellent in antifungal effect even in an environment where light irradiation is insufficient” ( Patent Document 5 paragraph No. 0004), as means for achieving this object, “an aqueous coating composition in which inorganic particles and hydrophobic resin particles are dispersed in an aqueous medium, the inorganic particles and the hydrophobic At least one water-soluble fungicide selected from the group consisting of a water-soluble organic iodine compound, a water-soluble isothiazoline compound and a water-soluble alanine compound with respect to the total mass with the resin particles is 1.0% by mass to 30% by mass. Selected from the group consisting of: imidazole compounds, triazole compounds, pyrithione compounds, thiazole compounds, and thiophene compounds. A water-based coating composition comprising at least one water-dispersible fungicide particle of 0.8 to 25% by mass ”(see claim 1 of Patent Document 5) is disclosed. Yes.

  According to the invention disclosed in Patent Document 5, “in the coating film formed by the aqueous coating composition, the hydrophilic micro-region and the hydrophobic micro-region are exposed independently of each other. Can be prevented over a long period of time "(see paragraph No. 0006 of Patent Document 5), and the formation of hydrophilic microregions and hydrophobic microregions is" This is achieved by the state in which the hydrophilic microregions formed by the inorganic particles 7 and the hydrophobic microregions formed by the hydrophobic resin particles 8 are exposed independently of each other ”(see paragraphs 0020 and 0027 of Patent Document 5). The

  Therefore, it is considered that the hydrophilic microregion and the hydrophobic microregion in the coating film achieved by Patent Document 5 are formed by the hydrophilicity by the inorganic particles and the hydrophobicity by the hydrophobic resin particles.

  Patent Document 6 includes "an overcoating composition comprising an oligomer and / or oligomer complex having both a hydrophilic group and a hydrophobic group" (see claim 1 of Patent Document 6), It has a structure represented by specific formula (1), formula (2), formula (3), and formula (4) "(Patent Document 6 claim) Item 2, 3, 4) is disclosed.

  Further, Patent Document 6 discloses a top coat film formed from the top coat composition (see claims 8, 9, and 10 of Patent Document 6).

  In Patent Document 6, “the top coating composition contains an oligomer or oligomer complex having both hydrophilic groups and hydrophobic groups, so that the surface state of the resulting top coat film switches between hydrophilic and hydrophobic. In addition, it is claimed that “antifouling / easy-cleaning property under hydrophilicity and water repellency (water repelling) under hydrophobicity can be made compatible” (see paragraph No. 0007 of Patent Document 6). In this way, switching of the surface state of the top coat film between hydrophilicity and hydrophobicity is referred to as water repellent-hydrophilic switching property in Patent Document 6, and the expression of this water repellent-hydrophilic switching property is shown in FIG. It is described as follows (see paragraph number 0010 of Patent Document 6).

"That is, FIG. 1 is intended showing the behavior of the oligomers described above as schematic, for example, with a hydrophobic group R _F consisting of fluoroalkyl group, a sulfonic acid group, a hydrophilic group X such as a carboxyl group In the ground state (dry state) where the oligomer is not in contact with the water-containing droplets, the hydrophobic group R _F is oriented toward the surface of the coating film, so even if water droplets adhere to the coating film in this state, FIG. ), It exhibits water repellency.

On the other hand, in the liquid contact state as shown in FIG. 1B, the hydrophilic group X of the oligomer is oriented on the surface side of the coating film, so that the coating film exhibits hydrophilicity. "
According to the above description in Patent Document 6, the water-repellent-hydrophilic switching property makes the coating film a water-repellent surface in a dry state and hydrophilic in a liquid contact state, whether in a dry state or in a liquid contact state. That is not to say that the coating surface has both a hydrophilic group and a water-repellent group at the same time.

JP-A-4-132737 Japanese Patent Laid-Open No. 2005-13929 JP 2002-88315 A JP 2004-149701 A JP 2012-1586 A JP 2009-280697 A

  The subject of the present invention is completely different from the conventional method, by bonding a hydrophilic group and a water-repellent group directly to an aluminum atom, that is, by forming a water-repellent point and a hydrophilic point on the surface at the molecular level, An object of the present invention is to provide a composite alumina coating that can easily remove dirt adhered to the surface.

Means of the present invention for solving the above-mentioned problems are:
(1) A composite alumina coating characterized by having alumina, a hydrophilic group that binds to Al atoms in the alumina, and a water-repellent group that binds to Al atoms,
(2) The alumina is a composite alumina coating according to (1), which is an alumina nanofiber having an aspect ratio (average fiber length / average fiber width) of 100 to 750,
(3) The composite alumina film according to (1) or (2), wherein the hydrophilic group is a phosphate group,
(4) The composite water-repellent film according to any one of (1) to (3), wherein the water-repellent group is an alkylsiloxy group represented by the following formula (1):

(However, R ¹ represents an alkyl group having 1 to 15 carbon atoms, which may substitute a fluorine atom, and R ² represents an alkylene group having 1 to 15 carbon atoms.)
(5) The surface of the film is the composite alumina film according to any one of (1) to (4), in which a contact angle of water droplets attached to the surface is 40 to 110 degrees.

  The composite alumina coating according to the present invention does not form a state in which “the hydrophilic microregion by the inorganic particles and the hydrophobic microregion by the hydrophobic resin particles are exposed independently of each other”, and The hydrophilic point and water repellency point are not formed on the alumina surface by “water repellency-hydrophilic switching property”, but the hydrophilic group and aluminum atom bonded to the aluminum atom in the alumina are formed on the surface of the composite alumina film. Since it has a hydrophobic group to be bonded, it has a hydrophilic point and a water repellent point at the molecular level on its surface.

  Therefore, the entire surface of the composite alumina film according to the present invention does not have water and oil repellency, and the entire surface does not have hydrophilicity.

  As a result, according to the present invention, it is possible to provide a high-hardness composite alumina coating that can easily remove dirt adhering to the surface.

FIG. 1 shows a P2p spectrum obtained by applying the XPS mapping method to the composite alumina film obtained in Example 5.

[Composite alumina coating]
The composite alumina film according to the present invention has both alumina and a water-repellent group bonded to Al atoms and a hydrophilic group bonded to Al atoms in the alumina.

This composite alumina coating is substantially free of silica (SiO ₂ ). Conventionally, when forming a hydrophilic thin film, silica (SiO ₂ ) is sometimes used. However, the composite alumina coating of the present invention has excellent durability because it has a water-repellent group and a hydrophilic group and has high hardness even when silica (SiO ₂ ) is not contained.

  When a water droplet adheres to the surface of this composite alumina coating, the contact angle of the adhering water droplet is 40 to 110 degrees. Moreover, the surface hardness of the composite alumina coating is 6H or higher in pencil hardness, and is high hardness.

  A hydrophilic alumina film having a surface characteristic that is made completely hydrophilic by introducing a hydrophilic group such as a phosphoric acid group into an Al atom has a contact angle of the adhering water droplet when the water droplet adheres to the surface. Becomes 10 degrees or less. On the other hand, when water droplets adhere to an alumina film having water repellency, the degree of water repellency of the water-repellent alumina film is said to be 80 degrees or more.

  In addition, as described in Patent Document 1, “a monomolecular film formed by chemically bonding a chlorosilane surfactant having a specific perfluoroalkyl group is formed on at least the glass surface directly or through a protective film. In the glass characterized in that one layer is formed on the glass surface, the contact angle of water attached to the glass surface with respect to the glass surface is 140 to 150 degrees.

  In a preferred composite alumina coating according to the present invention, the contact angle of the water droplet is 40 to 110 degrees. Therefore, this composite alumina film increases the tendency of hydrophilicity as the contact angle shifts from 110 degrees to 40 degrees, while increases the tendency of water repellency as the contact angle shifts from 40 degrees to 110 degrees. . The composite alumina coating according to the present invention can easily remove water-based and oil-based soils by hydrophilic points and water-repellent points by directly bonding hydrophilic groups and hydrophobic groups to aluminum atoms. Can do.

  The contact angle of water droplets adhering to the composite alumina film is determined by dropping 2 μL of water droplets onto the surface of the composite alumina film formed on the substrate placed on a horizontal sample stage at room temperature. The angle α between the tangent line and the surface of the composite alumina film when a tangent line is drawn on the curved surface of the water droplet from the point in contact with the air and the composite alumina film can be obtained by measuring using a contact angle meter.

  This composite alumina coating can easily remove dirt such as oily dirt, sebum, and aqueous dirt adhering to the surface. Even if oily dirt or sebum once adheres to the surface of the composite alumina film, the hydrophilic group in the composite alumina film weakens the bond between the oily dirt or sebum and the surface of the composite alumina film. On the other hand, even if the aqueous dirt is once attached to the surface of the composite alumina film, the water-repellent group in the composite alumina film weakens the bond between the aqueous dirt and the surface of the composite alumina film. Therefore, the dirt can be easily removed.

  This composite alumina coating has a pencil hardness of 6H or higher as its surface hardness, and is extremely durable. The pencil hardness of the composite alumina film can be measured according to JIS K 5600-5-4.

The thickness of the composite alumina coating of the present invention can be appropriately set depending on the application, and is usually in the range of 0.01 μm or more and 1 μm or less.
[alumina]
Although there is no restriction | limiting in particular as the alumina contained in a composite alumina membrane | film | coat, A suitable alumina is an alumina nanofiber.

  This alumina nanofiber is an alumina fibrous crystal having a nanosize, which will be described later. Specifically, the alumina nanofiber is formed from an anhydrous alumina, and the alumina nanofiber is formed from alumina containing a hydrate. A hydrate fiber etc. are mentioned.

  This alumina nanofiber has a ratio of an average fiber length described later to an average fiber width described later, that is, an aspect ratio (average fiber length / average fiber width) of 100 to 750, and preferably 100 to 375. When the aspect ratio is less than 100 or the aspect ratio exceeds 750, the pencil hardness of the composite alumina film formed by such alumina nanofibers becomes smaller than 6H.

  The arrangement state of the alumina nanofibers contained in the composite alumina film varies depending on the aspect ratio of the alumina nanofibers. When the aspect ratio of the alumina nanofiber is 350, the alumina nanofiber exists in a state in which a plurality of alumina nanofibers are arranged in parallel in one direction, in other words, in a state in which the major axis direction is aligned. . On the other hand, when the aspect ratio of the alumina nanofibers is 250, the alumina nanofibers aggregate to form an indeterminate form or a particulate form to form a film. Therefore, the arrangement state of the alumina nanofibers changes when the aspect ratio of the alumina nanofibers is around 300 and the aspect ratio exceeds 300 and less than 300, and when the aspect ratio exceeds 300, the alumina nanofibers If the fibers are arranged in parallel in one direction and the aspect ratio is less than 300, the alumino nanofibers exist in an indefinite or particulate state.

  The alumina nanofibers contained in the composite alumina coating are preferably present in a state in which a plurality of alumina nanofibers are arranged in parallel in one direction, or aggregated and present in an indefinite or particulate form. It becomes denser and can form a composite alumina film with higher hardness.

  When the surface of the composite alumina film according to the present invention is observed at a magnification of 150,000 times using a field emission scanning electron microscope (FE-SEM, for example, trade name “JSM6500F”, manufactured by JEOL Ltd.), The surface is dense and no voids or holes are observed. The composite alumina coating of the present invention has alumina, especially alumina nanofibers densely packed, irregularly shaped, particulate or arranged in parallel in one direction. When the transparent alumina surface is observed with the above magnification by FE-SEM, alumina, especially The voids of the composite alumina coating of the present invention are so small that voids formed between the alumina nanofibers are not observed.

  Alumina nanofibers preferably have an average fiber length of 400 to 7500 nm, more preferably 600 to 3000 nm. When the alumina nanofiber has an average fiber length in the above range, a composite alumina film having a pencil hardness of 6H or more can be provided. Alumina nanofibers preferably have an average fiber width of 1 to 10 nm, particularly preferably 2 to 6 nm. Suitable alumina nanofibers have an average fiber width within the range and an average fiber length within the range such that the aspect ratio is within the range.

  Here, the average fiber width of the alumina nanofibers is observed when the alumina nanofibers are observed at a magnification of 710,000 times using a transmission electron microscope (TEM, for example, trade name “FEI-TECNAI-G20”, manufactured by FEI). The thickest part of the alumina nanofiber in the observation field is measured as “width of alumina nanofiber”. The number of measurements is 300, a number distribution is created, and the number average value is defined as the average fiber width. On the other hand, the average fiber length of the alumina nanofibers is obtained when the alumina nanofibers are observed at a magnification of 2500 times using a scanning electron microscope (SEM, for example, trade name “S-4800”, manufactured by Hitachi High-Technologies Corporation). The axial length of the alumina nanofiber is measured as “fiber length of alumina nanofiber”. The number of measurements is 300, and the value calculated from the volume average is the average fiber length. The aspect ratio (average fiber length / average fiber width) of the alumina nanofibers is calculated by dividing the average fiber length thus calculated by the average fiber width.

There are boehmite and pseudoboehmite in the crystal system of alumina, for example, alumina nanofiber, contained in the alumina sol. In the present invention, in order that the alumina nanofibers have the above dimensions and the composite alumina film has a pencil hardness of 6H or more, the alumina nanofibers contained in the alumina sol must be at least boehmite crystal alumina nanofibers and / or pseudoboehmite crystals. Preferably, the system contains alumina nanofibers, ie the crystal system may be a mixture based on boehmite and / or pseudoboehmite and containing other crystal forms. In the present invention, the alumina nanofibers are particularly preferably boehmite crystal alumina nanofibers and / or pseudoboehmite crystal alumina nanofibers. Here, boehmite is a crystal of alumina hydrate represented by a composition formula: Al ₂ O ₃ .nH ₂ O. The crystal system of alumina nanofibers can be adjusted by, for example, the type of hydrolyzable aluminum compound described later, the hydrolysis conditions or peptization conditions. The crystal system of alumina nanofibers can be confirmed using an X-ray diffractometer (for example, “Mac. Sci. MXP-18”, manufactured by Mac Science).
[Hydrophilic group]
Examples of the hydrophilic group bonded to the Al atom in this alumina, eg, alumina nanofiber, include a phosphate group, a hydroxyl group, an NCO group, an NH ₂ group, an NHR group (R is an alkyl group), a COOH group, an —O— group, and the like. Among these, a phosphate group is preferable.

  The fact that the phosphate group is bonded to the Al atom means that when the XPS spectrum of the thin film surface is measured by X-ray photoelectron spectroscopy using an X-ray photoelectron spectroscopy (ESCA or XPS) apparatus, the P2p spectrum is bonded. It can be confirmed that the energy peak top exists in the range of 133.0 eV or more and 135.0 eV or less, and the peak top of the binding energy of the Al2p spectrum exists in the range of 74.0 eV or more and 76.0 eV or less. .

Similarly, the presence of other hydrophilic groups can be confirmed using an X-ray photoelectron spectrometer.
[Water repellent group]
Examples of the water-repellent group bonded to the Al atom in this alumina, for example, alumina nanofiber, include an alkylsiloxy group that may substitute a fluorine atom. Suitable examples of the hydrophobic group include an alkylsiloxy group represented by the formula (1).

(Wherein, ^{R 1} is sometimes substituting fluorine atom, an alkyl group, ^{R 2} a carbon number of 1-15 represents. Suitable ^{R 1} a number 1-15 alkylene group of carbon (It is a fluoroalkyl group having 1 to 15 carbon atoms that substitutes a fluorine atom.)
In addition, since the alumina nanofibers in the composite alumina film are bonded to each other by an Al—O—Al bond, the composite alumina film has a high hardness in which the alumina nanofibers forming the composite alumina film are difficult to separate.

In addition, the fact that the alkyl group or the alkylsiloxy group is bonded to the alumina nanofiber is determined by measuring a Fourier transform infrared absorption (FT-IR) spectrum using a Fourier transform infrared spectroscopic (FT-IR) apparatus. This can be confirmed by observing an absorption spectrum due to the Al—O—Si bond at 1100 cm ⁻¹ . The existence of an absorption spectrum due to the Al—O—Si bond at 950 to 1100 cm ⁻¹ is based on the literature: K. Roodenko, O. Seitz, Y. Gogte, J.-F. Veyan and YJ Chabal, J. Phys. Chem., C, 114 (2010) 22566-22572.

In addition, the fact that the alkylsiloxy group is bonded to alumina, for example, alumina nanofiber, is measured by the X-ray photoelectron spectroscopy (ESCA or XPS) apparatus, and the XPS spectrum of the surface of the composite alumina film is measured by X-ray photoelectron spectroscopy. The peak top of the binding energy of the Al2p spectrum can be confirmed by the presence of 74.2-75.0 eV. The peak of this binding energy is due to the Al—O—Si bond, and the fact that the peak of the binding energy due to the Al—O—Si bond exists at 74.2 to 75.0 eV is based on the literature: K. Roodenko, O. Seitz, Y. Gogte, J.-F. Veyan and YJ Chabal, J. Phys. Chem. C, 114 (2010) 22566-22572.
[Production of composite alumina coating]
In the composite alumina coating of the present invention, a hydrophilic group may be bonded to an Al atom in alumina such as alumina nanofiber, and then a water-repellent group may be bonded to the Al atom, or a water-repellent group may be bonded to the Al atom. Then, it is produced by bonding a hydrophilic group to the Al atom.

In the composite alumina coating of the present invention, hydrophobic groups such as alkylsiloxy groups are directly bonded to Al atoms, and hydrophilic groups such as phosphate groups are directly bonded to Al atoms. It has a completely different surface molecular structure from the monomolecular adsorption protective film formed by the reaction of a hydroxyl group and a chlorosilyl group contained on the glass surface as disclosed.
[Introduction of hydrophilic group and introduction of water repellent group]
In order to bind a hydrophilic group such as a phosphoric acid group to Al atoms first, an alumina sol having alumina, for example, alumina nanofibers, was applied to the substrate surface, and then the obtained coating film was cured. The alumina thin film is preferably hydrothermally treated in an aqueous solution of a phosphate group-containing compound.

  An alumina sol containing alumina, for example, alumina nanofibers in the present invention may be prepared by a method capable of dispersing alumina nanofibers having an aspect ratio (average fiber length / average fiber width) of 100 to 750, an example thereof. And a method of hydrolyzing a hydrolyzable aluminum compound in an acid aqueous solution and then peptizing and preparing (hereinafter, sometimes referred to as a sol preparation method). In this sol preparation method, if the reaction conditions for hydrolysis and the treatment conditions for peptization are specific conditions described later, alumina nanofibers having an aspect ratio (average fiber length / average fiber width) of 100 to 750, for example, aspect ratio ( An alumina sol in which alumina nanofibers having an average fiber length / average fiber width) of 100 to 375, an average fiber width of 1 to 10 nm, and an average fiber length of 400 to 1500 nm are dispersed in a solution can be prepared.

  The hydrolyzable aluminum compound used in this sol preparation method includes various inorganic aluminum compounds and aluminum compounds having an organic group. Examples of inorganic aluminum compounds include salts of inorganic acids such as aluminum chloride, aluminum sulfate, and aluminum nitrate, aluminates such as sodium aluminate, and aluminum hydroxide. Examples of the aluminum compound having an organic group include carboxylates such as aluminum carbonate ammonium salt and aluminum acetate, aluminum ethoxide, aluminum isopropoxide, aluminum n-butoxide, aluminum alkoxide such as aluminum sec-butoxide, and cyclic aluminum oligomers. And aluminum chelates such as diisopropoxy (ethylacetoacetato) aluminum and tris (ethylacetoacetato) aluminum, and organoaluminum compounds such as alkylaluminum.

  Among these, the hydrolyzable aluminum compound in the sol preparation method is preferably an aluminum alkoxide because it has moderate hydrolyzability and easy removal of by-products, etc., and an alkoxy group having 2 to 5 carbon atoms. Particularly preferred are those having

  In this sol preparation method, the acid used for the hydrolysis is preferably a monovalent acid such as an inorganic acid such as hydrochloric acid or nitric acid, or an organic acid such as formic acid, acetic acid, propionic acid, or butyric acid, and the inorganic acid remains after firing. Organic acids are preferred because they remain in the alumina. As the organic acid, acetic acid is particularly preferable in terms of operability and economy. The amount of the acid used is preferably 0.2 to 2.0 mol times, particularly preferably 0.3 to 1.8 mol times relative to the hydrolyzable aluminum compound. If the amount of acid used is less than 0.2 mol, the aspect ratio of the resulting alumina nanofibers may be small. If the amount of acid used exceeds 2.0 mol, the stability over time of the aqueous alumina nanofiber sol may be reduced. This is not preferable in terms of economy.

  The hydrolysis conditions are preferably 100 ° C. or lower and 0.1 to 3 hours. If the hydrolysis temperature exceeds 100 ° C., bumping may occur, and if the hydrolysis time is less than 0.1 hour, temperature control is difficult, and if it exceeds 3 hours, the process time becomes long.

  2-15 mass% is preferable and, as for the solid content concentration of the acid aqueous solution of the hydrolysable aluminum compound to hydrolyze, 3-10 mass% is especially preferable. When the solid content concentration is less than 2% by mass, the aspect ratio of the obtained alumina nanofiber may be small, and when the solid content concentration exceeds 15% by mass, the stirrability of the reaction solution may decrease during peptization. There is.

  In this sol preparation method, the alcohol generated by hydrolyzing the hydrolyzable aluminum compound is preferably distilled off before the peptization treatment. The peptization treatment is performed by heating at 100 to 200 ° C. for 0.1 to 10 hours, more preferably at 110 to 180 ° C. for 0.5 to 5 hours. When the heating temperature is less than 100 ° C., the reaction requires a long time, and when it exceeds 200 ° C., a high-pressure container or the like is required, which may be economically disadvantageous. When the heating time is less than 0.1 hour, the size of the alumina nanofiber is small, and the storage stability may be lowered. When the heating time is longer than 10 hours, the process time becomes longer.

  When the alumina sol prepared in this way has a high viscosity, it often contains bubbles, so it is preferable to remove these bubbles by deaeration treatment. Examples of the method for removing bubbles include various deaeration methods such as a decompression process and a centrifugal process.

  In this sol preparation method, when the kind of hydrolyzable aluminum compound, hydrolysis and / or peptization conditions are appropriately selected, the crystal system of alumina nanofibers can be boehmite or pseudoboehmite. For example, if the peptization temperature is high or the peptization time is long, the crystal system of alumina nanofibers tends to be boehmite crystal. Conversely, if the peptization temperature is low or the peptization time is short, alumina nanofibers The fiber crystal system tends to be a pseudoboehmite crystal system.

  In the present invention, the substrate to which the alumina sol is applied is not particularly limited as long as it is a material required to impart a pencil hardness of 6H or more, and examples thereof include glass, metal, ceramics, and plastics. Examples of the glass include glass such as quartz glass, 96% quartz glass, soda-lime glass, aluminoborosilicate glass, borosilicate glass, aluminosilicate glass, lead glass, and more specifically, automobiles. Windshields, bathroom and bathroom mirrors, glasses, telescopes, binoculars, and the like.

  Before the alumina sol is applied to the substrate surface, the viscosity is adjusted by adding an appropriate amount of water to prepare a coating solution. For example, by adding 10 to 2000 g of water to 100 g of alumina sol having a solid content of 5% by mass, a coating solution having a viscosity appropriately set according to the coating method described later can be prepared. A coating film having a uniform desired thickness can be obtained with a coating solution having a high viscosity.

  In this invention, the said coating liquid is apply | coated to the board | substrate surface, and an alumina membrane | film | coat is then formed by hardening-processing the obtained coating film. It is preferable to clean the substrate surface before applying the coating solution to the substrate surface. By cleaning the substrate surface, a uniform coating film can be formed without causing repelling.

  As the means for cleaning, for example, when the substrate is made of glass, a cleaning means using a detergent, particularly a neutral detergent, can be used. When the substrate is made of metal, it is immersed in a degreasing agent-containing liquid. The means to do can be mentioned.

  The degreasing agent in the degreasing-containing liquid is preferably a degreasing agent containing a basic compound, and examples thereof include sodium hydroxide, sodium carbonate, sodium silicate, sodium phosphate, and sodium borate.

  Examples of the method of applying the coating liquid to the substrate surface include, for example, a dipping method in which the coating liquid is immersed in the substrate and then gently lifting it, or a casting method in which the coating liquid is cast onto the fixed substrate surface by an appropriate method. A continuous method in which the substrate is immersed in the coating liquid from one end of the tank storing the coating liquid and the substrate is taken out from the other end of the tank, the coating liquid is dropped on the rotating substrate, and the centrifugal force acting on the substrate Examples thereof include a spinner method in which the coating solution is cast on the substrate, and a spray method in which the coating solution is sprayed on the surface of the substrate.

  The coating amount of the coating solution is not uniform depending on the viscosity of the coating solution and other conditions. If an alumina film having a desired thickness cannot be obtained by a single application, the application can be repeated several times.

  An alumina film is formed by drying the coating film in which the coating liquid is coated on the substrate surface by the above-described various methods, if necessary, followed by curing treatment. As the curing treatment, heat treatment is preferable.

  The temperature of the heat treatment for forming the alumina film (hereinafter sometimes referred to as “calcination treatment”) is 100 ° C. or higher, and is preferably set to a temperature not exceeding the heat-resistant temperature of the substrate. An appropriate temperature is adopted. When the substrate on which the coating film is formed is heated, it may be directly heated to the above temperature, preheated at a relatively low temperature, and then heated to the above temperature. The time is preferably in the range of 10 minutes to 2 hours. A method for heating the substrate on which the coating film is formed is not particularly limited, and a high-temperature heat treatment apparatus such as a baking furnace or an electric furnace can be used.

  The composite alumina film of the present invention can be produced by hydrothermally treating the alumina thin film formed as described above in an aqueous solution of a phosphate group-containing compound.

  As the phosphoric acid group-containing compound, the phosphoric acid group is dissociated from the phosphoric acid group-containing compound by hydrothermal treatment described later in an aqueous solution of the phosphoric acid group-containing compound, so that the aluminum ions in the alumina thin film If it is a compound which couple | bonds with and forms an Al-OP bond, there will be no restriction | limiting in particular, A phosphoric acid group containing organic compound and a phosphoric acid group containing inorganic compound can be mentioned.

  Examples of the phosphoric acid group-containing organic compound include a compound represented by any one of the following formulas (1) and (2) or a salt thereof.

R ² R ³ PO ₃ (CH ₂ ) _u SiX ₃ (1)
[R ² PO ₃ (CH ₂ ) _u ] _v NH _w (2)
(However, R ³ and R ² represent a hydrogen atom, an alkyl group, an alkoxy group, an allyl group, or an O-phenyl group, and R ³ and R ² may be the same or different. X Represents halogen, —OH (hydroxyl group) or —OR ⁴ (R ⁴ represents an alkyl group or an allyl group.) U represents an integer of 1 to 10. v and w represent an integer; The sum with w is 3.]
Examples of the alkyl group include a methyl group, an ethyl group, and an isopropyl group. Examples of the alkoxy group include a methoxy group, an ethoxy group, and an isopropoxy group. Examples of the halogen include chlorine, bromine and iodine.

  Specific examples of the preferable phosphoric acid group-containing organic compound include 3-trihydroxysilylpropylmethylphosphonate-sodium salt (hereinafter sometimes abbreviated as “HSiP”) and nitrilotris (methylenephosphonic acid) (hereinafter, “ NTP ”may be abbreviated as“ NTP ”).

  The concentration of the aqueous solution of the phosphoric acid group-containing organic compound in the hydrothermal treatment is not particularly limited, but is usually 0.01 to 50% by mass, preferably 0.1 to 30% by mass.

Examples of the phosphoric acid group-containing inorganic compound include MPO ₄ , M _{n + 2} P _n O _{3n + 1} , (M ^I PO ₃ ) _n , (M ^II (PO ₃ ) ₂ ) _n , and (M ^III (PO ₃ ) ₃ ) _n . Inorganic compounds and their ester compounds (where M is a hydrogen atom or any metal ion, M ^I is a hydrogen atom or a +1 valent metal ion, M ^II is a +2 valent metal ion, and M ^III is a +3 valent metal) Represents an ion, and n represents an integer of 2 or more.

  Specific examples of the phosphoric acid group-containing inorganic compound include phosphoric anhydride, metaphosphoric acid, pyrophosphoric acid, orthophosphoric acid, triphosphoric acid, tetraphosphoric acid, ammonium phosphate, ammonium hydrogen phosphate, sodium phosphate, sodium hydrogen phosphate , Potassium phosphate, potassium hydrogen phosphate, calcium phosphate, calcium hydrogen phosphate, sodium phosphate, sodium hydrogen phosphate, aluminum phosphate, aluminum hydrogen phosphate, zinc phosphate, zinc hydrogen phosphate, and the like.

  Although there is no restriction | limiting in particular in the density | concentration of the aqueous solution of a phosphoric acid group containing inorganic compound in the said hydrothermal treatment, Usually, 0.01-50 mass%, Preferably, it is 0.1-30 mass%.

  Examples of a method of hydrothermally treating the alumina thin film in an aqueous solution of a phosphoric acid group-containing compound include, for example, a base material having an alumina thin film formed on a surface in a heat-resistant container in which the aqueous solution of the phosphoric acid group-containing compound is accommodated. In this method, the container is placed in an autoclave and hydrothermally treated in a temperature range of 150 ° C. to 180 ° C. for 10 minutes to 60 hours, preferably 30 minutes to 30 hours. Can do. At this time, an aqueous solution of a phosphoric acid group-containing compound to the extent that the alumina thin film is immersed may be contained in the container.

  Thus, a hydrophilic alumina thin film is manufactured by hydrothermally treating. The base material on which the hydrophilic alumina thin film taken out from the container is formed is appropriately washed with pure water.

  When a water-repellent group is introduced into Al atoms in the hydrophilic alumina thin film thus obtained, the composite alumina film of the present invention is produced.

  That is, the hydrophilic alumina film is immersed in an organic solvent solution containing a silicon compound, and the alumina and the silicon compound are reacted under predetermined conditions.

The silicon compound may be a compound that can bind an alkylsiloxy group that may substitute a fluorine atom to the alumina nanofiber. For example, the compound (2): R ¹ —R ² —SiX ₃ [where R ¹ is an alkyl group having 1 to 15 carbon atoms that may substitute a fluorine atom, R ² is an alkylene group having 1 to 15 carbon atoms, X is a halogen group or OR ⁵ group (R ⁵ is a methyl group) Represents an ethyl group, a propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, an iso-butyl group, or a tert-butyl group. The compound shown by these can be mentioned.

  Specific examples of the silicon compound represented by the formula (2) include 3,3,4,4,5,5,6,6,6-nonafluorohexyltrichlorosilane, 3,3,4,4, 5,5,6,6,6-nonafluorohexylmethyldichlorosilane, 3,3,4,4,5,5,6,6,6-nonafluorohexyltrimethoxysilane, 3,3,4,4 5,5,6,6,6-nonafluorohexyltriethoxysilane, (tridecafluoro-1,1,2,2-tetrahydrooctyl) trichlorosisilane, (tridecafluoro-1,1,2,2- Tetrahydrooctyl) methyldichlorosilane, (tridecafluoro-1,1,2,2-tetrahydrooctyl) trimethoxysilane, (tridecafluoro-1,1,2,2-tetrahydrooctyl) triethoxy Silane, (heptadecafluoro-1,1,2,2-tetrahydrodecyl) trichlorosilane, (heptadecafluoro-1,1,2,2-tetrahydrodecyl) methyldichlorosilane, (heptadecafluoro-1,1, Examples include 2,2-tetrahydrodecyl) trimethoxysilane and (heptadecafluoro-1,1,2,2-tetrahydrodecyl) triethoxysilane.

  In reacting alumina with the silicon compound, the silicon compound is dissolved in an organic solvent to prepare an organic solvent solution containing the silicon compound.

  Examples of the organic solvent include alcohols such as methanol, ethanol, propanol, and butanol; ethers such as diethyl ether and tetrahydrofuran; esters such as ethyl acetate; aromatic solvents such as benzene, toluene and xylene; and Examples thereof include alicyclic solvents such as cyclohexane. The mixing ratio of the silicon compound and the organic solvent may be arbitrary.

  Next, the hydrophilic alumina film is immersed in an organic solvent solution containing a silicon compound and heated at 30 to 80 ° C. for 0.5 to 5 hours. At this time, the ratio of the silicon compound to the hydrophilic alumina coating is preferably adjusted to Al: silicon compound = 1: 0.01 to 5 (molar ratio). By making the use ratio of the silicon compound with respect to the hydrophilic alumina film within the above range, it is possible to appropriately bind the fluoroalkylsiloxy group to the Al atom in the alumina nanofiber, and thereby the hydrophilic group and the water repellent group It is possible to satisfactorily form a composite alumina film having the above.

  After completion of the reaction, the composite alumina film changed into a composite alumina film by being immersed in the organic solvent solution and reacting is taken out from the organic solvent solution, and the taken out composite alumina film is the same as the solvent in the organic solvent solution. Or washing with a different organic solvent and then drying.

Further, if necessary, it is preferable to carry out curing at a temperature of 100 to 200 ° C. for 10 to 60 minutes.
[Introduction of water-repellent group, then introduction of hydrophilic group]
A composite alumina film can be produced by immersing an alumina film formed using the alumina sol in the organic solvent solution containing a silicon compound and reacting the alumina and the silicon compound.

  A composite alumina coating can also be produced as follows. That is, as described above, by adding the silicon compound to alumina sol containing alumina, for example, alumina nanofibers, and reacting the alumina with the silicon compound, an alkylsiloxy group that may substitute a fluorine atom is bonded. A water-repellent alumina sol containing alumina nanofibers is prepared.

  The reaction between alumina and the silicon compound is performed by adding an organic solvent solution containing a silicon compound to alumina sol containing alumina, for example, alumina nanofibers, and stirring the mixture while heating at 30 to 80 ° C. for 0.5 to 5 hours in a three-necked flask. This can be done. At this time, the mixing ratio of the alumina sol containing alumina, for example, alumina nanofibers, and the organic solvent solution containing the silicon compound is preferably Al: silicon compound = 1: 0.01 to 5 (molar ratio). Alkylsiloxy, which may substitute fluorine atoms for Al atoms in alumina such as alumina nanofibers, by adjusting the mixing ratio of alumina sol containing alumina nanofibers and organic solvent solution containing silicon compound within the above range. Groups can be attached moderately.

  For the sake of convenience, the alumina sol containing alumina nanofibers thus obtained may be referred to as a water-repellent alumina sol.

  When the water-repellent alumina sol prepared in this way has a high viscosity, it often contains bubbles, so it is preferable to remove these bubbles by deaeration treatment. Examples of the method for removing bubbles include various deaeration methods such as a decompression process and a centrifugal process.

  In the present invention, the substrate on which the water-repellent alumina sol is applied is the same as the substrate already described.

  Before the water-repellent alumina sol is applied to the substrate surface, the viscosity is adjusted by adding an appropriate amount of water to prepare a coating solution. For example, by adding 10 to 2000 g of water to 100 g of the water-repellent alumina sol having a solid content of 5% by mass, a coating solution having a viscosity appropriately set according to a coating method described later can be prepared. A coating film having a uniform desired thickness can be obtained with a coating solution having an appropriate viscosity.

  In this invention, a water-repellent alumina film is formed by applying the coating solution onto the substrate surface and then curing the resulting coating film. It is preferable to clean the substrate surface before applying the coating solution to the substrate surface. By cleaning the substrate surface, a uniform coating film can be formed without causing repelling.

  As the cleaning means, for example, when the substrate is made of glass, a cleaning means for cleaning with a detergent, particularly a neutral detergent can be used. When the substrate is made of metal, a degreasing agent-containing liquid can be used. A cleaning means for dipping treatment can be mentioned.

  The degreasing agent in the degreasing agent-containing liquid is preferably a degreasing agent containing a basic compound, and examples thereof include sodium hydroxide, sodium carbonate, sodium silicate, sodium phosphate, and sodium borate.

  Examples of the method of applying the coating liquid to the substrate surface include, for example, a dipping method in which the coating liquid is immersed in the substrate and then gently lifting it, or a casting method in which the coating liquid is cast onto the fixed substrate surface by an appropriate method. A continuous method in which the substrate is immersed in the coating liquid from one end of the tank storing the coating liquid and the substrate is taken out from the other end of the tank, the coating liquid is dropped on the rotating substrate, and the centrifugal force acting on the substrate Examples thereof include a spinner method in which the coating solution is cast on the substrate, and a spray method in which the coating solution is sprayed on the surface of the substrate.

  The coating amount of the coating solution is not uniform depending on the viscosity of the coating solution and other conditions. If a coating film having a desired thickness cannot be obtained by a single application, the application can be repeated several times.

  A water-repellent alumina film is formed by drying a coating film having a coating solution applied to the substrate surface by various methods as described above, followed by curing. Examples of the curing treatment include heat treatment and light irradiation treatment, and the light irradiation treatment is preferably ultraviolet irradiation treatment.

  The temperature of the heat treatment for forming the water-repellent alumina film (hereinafter sometimes referred to as “calcination treatment”) is preferably 50 to 200 ° C., and should be a temperature not exceeding the heat resistance temperature of the substrate. An appropriate temperature in this temperature range is adopted. When the substrate on which the coating film is formed is heated, it may be directly heated to the above temperature, preheated at a relatively low temperature, and then heated to the above temperature. The time is preferably in the range of 10 minutes to 2 hours. A method for heating the substrate on which the coating film is formed is not particularly limited, and a high-temperature heat treatment apparatus such as a baking furnace or an electric furnace can be used.

  Although there is no special restriction | limiting in the conditions of the ultraviolet irradiation process for forming a water-repellent alumina film | membrane, It is preferable to irradiate an ultraviolet-ray under the temperature range of 50-200 degreeC. As the ultraviolet light source to be irradiated, a high pressure mercury lamp or a low pressure mercury lamp can be used. When these mercury lamps are used, ultraviolet light having an appropriate intensity can be irradiated at low cost. A very short irradiation time of 1 minute to 1 hour is sufficient. Moreover, the intensity | strength of the ultraviolet-ray to irradiate is arbitrary. When the intensity of the ultraviolet rays to be irradiated is within the above range, for example, a base material that can withstand ultraviolet irradiation must be selected without causing the plastics base material to turn yellow, change, or deform. Can be solved.

  In this way, the water-repellent alumina sol is formed by a simple process of coating the water-repellent alumina sol on the substrate and curing the coating film by heat treatment or light irradiation treatment. The obtained water-repellent alumina film has characteristics of high hardness, transparency, and water repellency.

  In the present invention, the obtained water-repellent alumina film is treated as follows to obtain a composite alumina film.

  Taking a phosphate group as an example of the hydrophilic group, a composite alumina film can be produced by hydrothermally treating the water-repellent alumina film in an aqueous solution of a phosphate group-containing compound.

  The phosphoric acid group-containing compound and the hydrothermal treatment are the same as described in the section [Introduction of hydrophilic group and introduction of water repellent group].

Example 1 Composite Alumina Coating A
<Preparation of hydrophilic alumina coating (1)>
10.0 g of pure water is added to 10.0 g of nanofiber-like alumina sol (fiber length: 1400 nm, fiber diameter: 4 nm, Al ₂ O ₃ content: 5% by mass), pH is adjusted to 1 by adding 10% by mass of HCl. A coating solution was prepared by adjusting to. The prepared coating solution is applied to a non-alkali glass (AF-45, Schott) washed with a neutral detergent by a spinner method (500 rpm for 5 seconds and then 2000 rpm for 30 seconds) to obtain an alumina gel film. It was. It was fired at 550 ° C. for 30 minutes to produce an alumina film (sample size: 50 mm × 50 mm).

  Next, 80 mL of a 1% by weight nitrilotris (methylenephosphonic acid) (NMP) aqueous solution is placed in the inner cylinder of the autoclave, the prepared alumina film is folded into 25 mm × 50 mm, and one of them is immersed as a sample. , Sealed in an outer cylinder. The sealed autoclave was heated to a hydrothermal temperature of 160 ° C. for 6 hours to hydrothermally treat the alumina coating. After the hydrothermal treatment, a sample was taken out, immersed in pure water for 3 seconds, moisture was removed using an air gun, and dried to obtain a hydrophilic alumina film (1).

<Preparation of composite alumina coating A>
By dissolving 1.00 g of (tridecafluoro-1,1,2,2-tetrahydroxyoctyl) triethoxysilane (FAS-1) in 99.0 g of toluene, a water repellent reaction solution (concentration of FAS-1) was obtained. : 1% by mass).

  One of the hydrophilic alumina films (1) already prepared was immersed in this, and 0.01 g of triethylamine was further added thereto, followed by heating and stirring at 80 ° C. for 1 hour. After the reaction, the sample was taken out of the reaction solution, washed with toluene for 10 seconds, dried, and then cured at 150 ° C. for 30 minutes. Subsequently, the sample was immersed in pure water and an ethanol solution and subjected to ultrasonic cleaning for 2 minutes to prepare a composite alumina coating A.

(Example 2) Composite alumina coating B
Instead of immersing the hydrophilic alumina film (1) in the water-repellent reaction solution and heating and stirring at 80 ° C. for 1 hour, the hydrophilic alumina film (1) is immersed in the water-repellent reaction solution and heated at 100 ° C. for 1 hour. A composite alumina coating B was prepared in the same manner as in Example 1 except that the mixture was heated and stirred.

(Example 3) Composite alumina film C
A hydrophilic alumina film (2) was prepared in the same manner as in Example 1 except that the hydrothermal temperature was changed to 140 ° C instead of the hydrothermal temperature to 160 ° C, and hydrophilicity was used instead of the hydrophilic alumina film (1). A hydrophilic alumina film (2) was prepared in the same manner as in Example 1 except that the hydrophilic alumina film (2) was used, and the hydrophilic alumina film (2) was used instead of the hydrophilic alumina film (1). A composite alumina film C was prepared in the same manner as in Example 1 except for the above.

(Example 4) Composite alumina film D
A hydrophilic alumina film (3) was prepared in the same manner as in Example 1 except that the hydrothermal temperature was set at 160 ° C. for 6 hours, and the hydrothermal temperature was set at 120 ° C. for 8 hours. A composite alumina coating D was prepared in the same manner as in Example 1 except that the hydrophilic alumina coating (3) was used instead of the alumina coating (1).

(Example 5) Composite alumina coating E
A composite alumina coating E was prepared in the same manner as in Example 2 except that the hydrophilic alumina coating (3) was used instead of the hydrophilic alumina coating (1).

FIG. 1 shows the distribution of PO ₄ groups on the composite alumina coating E on the coating surface. In FIG. 1, the 135 eV peak in the P2p spectrum of the PO ₄ group measured by the XPS mapping method is indicated by a white dot. From FIG. 1, it can be seen that PO ₄ groups are distributed on the surface of this composite alumina coating E at the molecular level.

(Example 6) Composite alumina film F
Use 3,3,4,4,5,5,6,6,6-nonafluorohexyltrichlorosilane (FAS-2) instead of FAS-1 and use 0.02 g of triethylamine instead of 0.01 g of triethylamine In the same manner as in Example 1 except that the water-repellent reaction solution containing 0.02 g of triethylamine was immersed in the hydrophilic alumina coating (1) and heated at 90 ° C. for 2 hours instead of heating at 80 ° C. for 1 hour. Thus, a composite alumina film F was produced.

(Example 7) Composite alumina film G
A water repellent reaction solution was prepared in the same manner as in Example 1 using (heptadecafluoro-1,1,2,2-tetrahydrodecyl) triethoxysilane (FAS-3) instead of FAS-1, The water-repellent reaction solution containing 0.02 g of triethylamine was added at 75 ° C. instead of heating the water-repellent reaction solution containing 0.01 g of triethylamine at 80 ° C. for 1 hour. A composite alumina coating G was prepared in the same manner as in Example 1 except that the heating was continued for a period of time.

Comparative Example 1 Hydrophilic Alumina Coating The hydrophilic alumina coating (1) prepared in Example 1 was used as a hydrophilic alumina coating.

(Comparative Example 2) Water-repellent alumina coating A water-repellent alumina coating was prepared in the same manner as in Example 1 using an alumina coating prepared in the same manner as in Example 1 instead of the hydrophilic alumina coating (1).

<Stain removal test>
The composite alumina coatings A to G prepared in Examples 1 to 7, the hydrophilic alumina coating of Comparative Example 1 and the water-repellent alumina coating of Comparative Example 2 were subjected to a soil removability test as follows using these as samples. went.

  In addition to the above samples, a stain removal test was also conducted on a glass substrate (AF-45, Shot), a polycarbonate (PC) substrate, and a polymethyl methacrylate resin (PMMA) substrate as comparative samples.

  After pressing the finger against the surface of the sample for 1 second, sebum was attached to the sample by moving it 5 cm to the right while pressing the finger. In addition, after the hand was washed with soap, the finger was allowed to naturally secrete sebum on the finger surface without grabbing the object with the finger of the hand for 10 minutes, and then the finger was used in the stain removal test. . The sebum deposit and length were observed visually.

  The surface of the sample on which the dirt was adhered was blown and lightly wiped with a becot. This process was defined as 1 cycle, and the removal of dirt was visually examined. The results are shown in Table 1. Table 1 also shows the contact angle of water droplets measured with a contact angle meter.

Table 1

Component In the invention disclosed in Patent Document 4, which is responsible for improving the durability of the water repellent skin layer in the coating composition or the coating product described in Patent Document 3, a further role of binder in the coating composition As an essential component (see paragraph No. 0013), “the component that forms a transparent body when dried” is shown, and the durability of the water-repellent coating is clarified by Examples and Comparative Examples.

Claims (5)

  A composite alumina coating comprising alumina, a hydrophilic group bonded to Al atoms in the alumina, and a water repellent group bonded to Al atoms.   The composite alumina coating according to claim 1, wherein the alumina is an alumina nanofiber having an aspect ratio (average fiber length / average fiber width) of 100 to 750.   The composite alumina coating according to claim 1 or 2, wherein the hydrophilic group is a phosphate group. The composite alumina coating according to any one of claims 1 to 3, wherein the water repellent group is an alkylsiloxy group represented by the following formula (1).

(However, R ₁ represents an alkyl group having 1 to 15 carbon atoms, which may substitute a fluorine atom, and R ₂ represents an alkylene group having 1 to 15 carbon atoms.)   The composite alumina film according to any one of claims 1 to 4, wherein the surface of the film has a contact angle of 40 to 110 degrees with water droplets attached to the surface.

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