Hydrophilic coating film, hydrophilic coating liquid, and method for forming hydrophilic coating film

Abstract

To provide a hydrophilic coating film which has a small contact angle of water to the surface of the film, can increase the contact area of water droplets to the surface of the film, has excellent hydrophilicity and antifouling properties, and can easily wash off adhered stains by washing with water.SOLUTION: The hydrophilic coating film is formed of an inorganic porous coating film having a large number of voids and a hydrophilic organic compound infiltrated into the voids of the inorganic porous coating film and has a contact angle of water of 20 ° or less. The inorganic porous coating film contains at least one kind of inorganic fine particles selected from silicon dioxide, aluminum oxide, zirconium oxide, titanium oxide and ceria oxide, and has an inorganic nanoporous structure formed by a sol-gel method using at least one of silica sol, alumina sol, zirconia sol, titania sol and ceria sol. The hydrophilic organic compound includes a betaine polymer having a cationic site and an anionic site in the same molecule.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a hydrophilic coating film and a hydrophilic coating liquid, and also to a method for forming a hydrophilic coating film. [Background technology]

[0002] As an example of coating inorganic particles with a hydrophilic resin, a hydrophilic coating film has been disclosed that includes a fluororesin film coated on the surface of a substrate, first hydrophilic spherical particles that are coated on the fluororesin film and are partially embedded in the fluororesin film while being partially exposed from the fluororesin film, and second hydrophilic particles that are coated on the fluororesin film and are partially embedded in the fluororesin film while being partially exposed from the fluororesin film, wherein the first hydrophilic spherical particles have an average particle size of 25 μm or more and 700 μm or less, and the second hydrophilic particles have an average particle size of 0.05 μm or more and 2 μm or less (see Patent Document 1).

[0003] Also disclosed is a surface treatment solution and a hydrophilization treatment method using a polymerizable composition containing a polymerizable compound (A), a polymerization initiator (B), inorganic fine particles (C), and a solvent (S), in which the polymerizable compound (A) is a polymerizable betaine compound (A1) having an ethylenically unsaturated double bond and a betaine structure, and an adhesive polymerizable compound (A2) having an ethylenically unsaturated double bond and a specific type of adhesive group, and the polymerization initiator (B) is a water-soluble radical polymerization initiator (B1), and inorganic fine particles (C) having a functional group capable of forming a covalent bond with a polymer of the polymerizable compound (A) (see Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-89930 [Patent Document 2] Japanese Patent Publication No. 2022-129100 Summary of the Invention [Problem to be solved by the invention]

[0005] In the hydrophilic coating film disclosed in Patent Document 1, the first hydrophilic spherical particles and second hydrophilic particles that coat the fluororesin film gradually peel off from the fluororesin film due to stress from the usage environment, and the hydrophilicity gradually decreases, making it impossible to maintain hydrophilic function for a long period of time. When the hydrophilicity of the hydrophilic coating film decreases, it becomes difficult to wash off dirt such as dust that has adhered to the fluororesin film, which is water-repellent and has a large contact angle with water, and the dirt cannot be easily removed from the surface of the substrate by washing with water, and the dirt remains on the surface of the substrate, making it impossible to clean the surface of the substrate.

[0006] The polymerizable composition and hydrophilization treatment method disclosed in Patent Document 2 mix a polymerizable compound, a polymerization initiator, and inorganic fine particles to improve adhesion to inorganic fine particles, form a coating film on the substrate, and then heat the mixture to promote polymerization and bond the resin film to the surface of the substrate, thereby fixing the resin film. However, if the composition is simply applied without heating, it will be easily washed away in a water washing process. Furthermore, under conditions such as outdoor use, the hydrophilic polymerizable compound will be washed away even by rain, making it impossible to obtain a durable hydrophilic coating film. Heating the substrate is often not possible, and there is a need to obtain a durable hydrophilic coating film simply by applying the composition at room temperature and drying the solvent.

[0007] An object of the present invention is to provide a hydrophilic coating film that has a small contact angle of water with the film surface, can increase the contact area of ​​water droplets on the film surface, and has excellent hydrophilicity and antifouling properties, allowing attached dirt to be easily washed off by rinsing with water, as well as a hydrophilic coating solution for forming such a hydrophilic coating film. Another object of the present invention is to provide a hydrophilic coating film that prevents deterioration of hydrophilicity and antifouling properties due to stress in the usage environment and can maintain its hydrophilic and antifouling properties for a long period of time, as well as a hydrophilic coating solution for forming such a hydrophilic coating film. Another object of the present invention is to provide a method for forming a hydrophilic coating film that can easily wash off attached dirt by rinsing with water, prevents deterioration of hydrophilicity and antifouling properties due to stress in the usage environment, and can maintain its hydrophilic and antifouling properties for a long period of time. Another object of the present invention is to provide a method for forming a hydrophilic coating film that can easily form a hydrophilic coating film at room temperature without heating. [Means for solving the problem]

[0008] The hydrophilic coating film of the present invention is formed from an inorganic porous coating film having a large number of nano-sized voids and a hydrophilic organic compound that has penetrated into the voids of the inorganic porous coating film, and is characterized in that the water contact angle measured according to JIS R3257 is 20° or less.

[0009] An example of a hydrophilic coating film is one whose water contact angle measured according to JIS R3257 is 10° or less.

[0010] Another example of a hydrophilic coating film is an inorganic porous coating film containing at least one type of inorganic fine particles selected from silicon dioxide (SiO2), aluminum oxide (Al2O3), zirconium oxide (ZrO2), titanium oxide (TiO2), and ceria oxide (CeO2).

[0011] Another example of a hydrophilic coating film is an inorganic porous coating film having an inorganic nanoporous structure made by a sol-gel method using at least one of silica sol, alumina sol, zirconia sol, titania sol, and ceria sol.

[0012] Another example of a hydrophilic coating film includes a betaine polymer in which the hydrophilic organic compound has a cationic moiety and an anionic moiety in the same molecule.

[0013] Another example of the hydrophilic coating film is one in which the ratio of betaine polymer to the hydrophilic organic compound is 20% or more.

[0014] Another example of a hydrophilic coating film is an inorganic porous coating film in which the porosity of the pores formed therein is in the range of 20% to 70% of the volume of the inorganic porous coating film.

[0015] Another example of the hydrophilic coating film is one whose thickness is in the range of 0.01 to 3 μm.

[0016] Another example of a hydrophilic coating film is one in which a hydrophilic organic compound penetrates into the pores of an inorganic porous coating film and coats the surface of the inorganic porous coating film.

[0017] In another example of a hydrophilic coating film, the top layer of the hydrophilic organic compound is located slightly below the surface of the inorganic porous coating film, and the part of the inorganic porous coating film exposed above the top layer of the hydrophilic organic compound is coated with an extremely thin film of the hydrophilic organic compound, and fine irregularities are formed on the surface of the hydrophilic coating film.

[0018] The hydrophilic coating liquid according to the present invention is formed from an inorganic coating liquid that produces an inorganic porous coating film having numerous nano-sized voids, and an organic coating liquid that contains a betaine polymer having cationic and anionic moieties in the same molecule and produces a hydrophilic organic compound that coats the inorganic porous coating film while penetrating the voids in the inorganic porous coating film.

[0019] An example of a hydrophilic coating liquid is one in which the ratio of betaine polymer to the hydrophilic organic compound is 20% or more.

[0020] Another example of a hydrophilic coating liquid is an inorganic coating liquid containing at least one type of inorganic fine particles selected from silicon dioxide (SiO2), aluminum oxide (Al2O3), zirconium oxide (ZrO2), titanium oxide (TiO2), and ceria oxide (CeO2), and the solid concentration of the inorganic fine particles in the inorganic coating liquid is 0.3 to 50 wt%.

[0021] Another example of a hydrophilic coating liquid is one in which the inorganic fine particles contained in the inorganic coating liquid have an average particle size of 1 μm or less.

[0022] Another example of a hydrophilic coating liquid is an organic coating liquid in which the content of the hydrophilic organic compound is in the range of 0.1 to 20 wt % relative to the total weight of the organic coating liquid.

[0023] The hydrophilic coating film forming method for producing a hydrophilic coating film formed from an inorganic porous coating film having a large number of nano-sized voids and a hydrophilic organic compound includes the following steps: a washing step of washing the surface of a predetermined substrate with an alkaline detergent and then washing the surface of the substrate with an acidic liquid; an inorganic porous coating film forming step of coating the surface of the substrate with an inorganic coating liquid containing inorganic fine particles and forming an inorganic porous coating film having an inorganic nanoporous structure having a large number of nano-sized voids by a sol-gel method; a hydrophilic organic compound forming step of coating the surface of the substrate with an organic coating liquid containing a betaine polymer having a cationic moiety and an anionic moiety in the same molecule and forming a hydrophilic organic compound containing a betaine polymer on the surface of the substrate while the organic coating liquid is infiltrated into the voids of the inorganic porous coating film; and a water washing step of washing the surface of the hydrophilic coating film formed from the inorganic porous coating film and the hydrophilic organic compound with water.

[0024] As another example of a hydrophilic coating film forming method, in the inorganic porous coating film forming process, an inorganic porous coating film having an inorganic nanoporous structure is formed by a sol-gel method using at least one of silica sol, alumina sol, zirconia sol, titania sol, and ceria sol.

[0025] As another example of a method for forming a hydrophilic coating film, in the hydrophilic organic compound forming step, the inorganic porous coating film is coated with an organic coating liquid so that the inorganic porous coating film is not exposed from the surface of the hydrophilic organic compound, and when the hydrophilic coating film is formed, the inorganic porous coating film is buried in the hydrophilic organic compound.

[0026] In the hydrophilic organic compound forming process, the inorganic coating liquid is coated onto the surface of the substrate in a state where the inorganic coating liquid is positioned slightly below the surface of the inorganic porous coating film so that the inorganic porous coating film is exposed above the top layer of the hydrophilic organic compound, and when the hydrophilic coating film is formed, the inorganic porous coating film is exposed above the top layer of the hydrophilic organic compound, and the part of the inorganic porous coating film that is exposed above the top layer of the hydrophilic organic compound is coated with an ultra-thin film of the hydrophilic organic compound, and fine irregularities are formed on the surface of the hydrophilic coating film.

[0027] As another example of the method for forming a hydrophilic coating film, in the water washing step, excess hydrophilic organic compounds that are weakly bound to the pores of the inorganic porous coating film, excluding hydrophilic organic compounds that are firmly bound to the pores of the inorganic porous coating film, are washed away with water, thereby removing hydrophilic organic compounds that do not contribute to the hydrophilicity of the hydrophilic coating film. [Effects of the Invention]

[0028] The hydrophilic coating film according to the present invention is formed from an inorganic porous coating film having a large number of nano-sized voids and a hydrophilic organic compound that has penetrated into the voids of the inorganic porous coating film, and has a water contact angle of 20° or less as measured according to JIS R3257, and therefore has excellent hydrophilicity and antifouling properties, and the contact angle of water with the surface of the hydrophilic coating film is small, making it possible to increase the contact area of ​​water with the surface of the hydrophilic coating film, and when the hydrophilic coating film is washed with water, water comes into contact with a wide area of ​​the surface of the hydrophilic coating film, so that dirt adhering to the hydrophilic coating film can be easily washed away with water. The hydrophilic coating film has a hydrophilic organic compound that penetrates into the numerous nano-sized voids in the inorganic porous coating film, and the hydrophilic organic compound (hydrophilic organic film) is bound to the voids in the inorganic porous coating film. This gives the hydrophilic coating film excellent strength, and the hydrophilic organic compound does not peel off or disappear early from the hydrophilic coating film due to stress from the usage environment. This prevents the hydrophilicity and antifouling properties of the hydrophilic coating film from decreasing, and allows the hydrophilic function and antifouling function provided by the hydrophilic organic compound to be maintained for a long period of time.

[0029] The hydrophilic coating film has a water contact angle of 10° or less as measured according to JIS R3257, and therefore has an extremely small contact angle of water with the film surface of the hydrophilic coating film, has excellent hydrophilicity and antifouling properties, and can reliably increase the contact area of ​​water with the film surface of the hydrophilic coating film. When the hydrophilic coating film is washed with water, the water comes into contact with a wide area of ​​the film surface of the hydrophilic coating film, and therefore dirt adhering to the hydrophilic coating film can be easily washed away with water.

[0030] When the inorganic porous coating film contains inorganic fine particles of silicon dioxide (SiO2), the hydrophilic organic compound easily bonds with the silicon dioxide, and the hydrophilic organic compound that has infiltrated into the numerous nano-sized voids of the inorganic porous coating film easily bonds to the silicon dioxide-containing voids, thereby firmly binding the hydrophilic organic compound to the voids of the inorganic porous coating film.When the inorganic porous coating film contains inorganic fine particles of aluminum oxide (Al2O3), the hydrophilic organic compound easily bonds with the aluminum oxide, and the hydrophilic organic compound that has infiltrated into the numerous nano-sized voids of the inorganic porous coating film easily bonds to the aluminum oxide-containing voids.In addition, the aluminum oxide makes it difficult for salts such as magnesium, calcium, sodium, and silicon to adhere to the hydrophilic coating film, thereby preventing contamination of the hydrophilic coating film due to the adhesion of salts such as magnesium, calcium, sodium, and silicon to the hydrophilic coating film. When the inorganic porous coating film contains inorganic particles of zirconium oxide (ZrO2), the hardness of the inorganic porous coating film can be increased, and the rigidity of the hydrophilic coating film can be improved. When the inorganic porous coating film contains inorganic particles of titanium oxide (TiO2), when the inorganic particles of titanium oxide are exposed to light and water, the surface of the hydrophilic coating film is coated with hydrophilic groups, imparting a self-cleaning effect to the hydrophilic coating film. When the inorganic porous coating film contains ceria oxide (CeO2), the hardness of the inorganic porous coating film can be increased, and the rigidity of the hydrophilic coating film can be improved, as well as providing the hydrophilic coating film with UV absorption properties. The hydrophilic coating liquid can be bonded to the inorganic particles by covalent bonds, hydrogen bonds, ionic bonds, van der Waals bonds, etc. In particular, impregnating betaine polymers into nano-sized spaces can strengthen the binding and maintain weather resistance.Furthermore, when forming an inorganic porous coating film, hydroxides or salts of Ca, Na, Mg, K, B, etc., sodium silicate, resins, etc. may be added to improve adhesion to the substrate. Furthermore, tetraalkoxysilane, alkyltrialkoxysilane, dialkyldialkoxysilane, etc. may also be added.

[0031] The hydrophilic coating film has an inorganic nanoporous structure in which the inorganic porous coating film is made by the sol-gel method using at least one of silica sol, alumina sol, zirconia sol, titania sol, and ceria sol, and the hydrophilic organic compound penetrates into the numerous nano-sized fine voids in the inorganic nanoporous structure, and the hydrophilic organic compound (hydrophilic organic film) is bonded to the voids in the inorganic porous coating film. Therefore, the hydrophilic coating film has excellent strength, and the hydrophilic organic compound does not peel off or disappear early from the hydrophilic coating film due to stress from the usage environment, and the hydrophilic organic compound remains in the hydrophilic coating film for a long period of time, preventing a decrease in the hydrophilicity and antifouling properties of the hydrophilic coating film, and the hydrophilic function and antifouling function provided by the hydrophilic organic compound can be maintained for a long period of time.

[0032] The hydrophilic coating film contains a betaine polymer in which the hydrophilic organic compound has a cationic moiety and anionic moiety in the same molecule, so that the hydrophilic organic compound exhibits excellent hydrophilicity and antifouling properties, thereby reliably reducing the contact angle of water with the surface of the hydrophilic coating film and reliably increasing the contact area of ​​water with the surface of the hydrophilic coating film.In addition, when the hydrophilic coating film is washed with water, water comes into contact with a wide range of the surface of the hydrophilic coating film, so that dirt adhering to the hydrophilic coating film can be easily washed away with water.

[0033] The hydrophilic coating film has a ratio of 20% or more of the betaine polymer, which has a cationic moiety and an anionic moiety in the same molecule, to the hydrophilic organic compound, and therefore can fully utilize the excellent hydrophilicity of the betaine polymer, the hydrophilic organic compound exhibits excellent hydrophilicity and antifouling properties, the contact angle of water with the surface of the hydrophilic coating film can be reliably reduced, the contact area of ​​water with the surface of the hydrophilic coating film can be reliably increased, and when the hydrophilic coating film is washed with water, water comes into contact with a wide range of the surface of the hydrophilic coating film, so that dirt adhering to the hydrophilic coating film can be easily washed away with water.

[0034] The hydrophilic coating film has a porosity of 20 to 70% of the volume of the inorganic porous coating film, which allows a sufficient number of fine nano-sized voids to be formed in the inorganic porous coating film, allowing the hydrophilic organic compound to penetrate into these voids and fully utilize the excellent hydrophilicity and antifouling properties of the hydrophilic organic compound (hydrophilic organic film), thereby imparting excellent hydrophilicity and antifouling properties to the hydrophilic coating film and providing sufficient protection to the surface of the substrate. The hydrophilic coating film has excellent strength because the hydrophilic organic compound (hydrophilic organic film) is bound to the numerous fine voids in the inorganic porous coating film, and the hydrophilic organic compound is not prematurely peeled off or lost from the hydrophilic coating film due to stress in the usage environment. The hydrophilic organic compound remains in the hydrophilic coating film for a long period of time, preventing a decrease in the hydrophilicity and antifouling properties of the hydrophilic coating film and maintaining the hydrophilic and antifouling functions of the hydrophilic organic compound for a long period of time.

[0035] The hydrophilic coating film has a thickness in the range of 0.01 to 3 μm, so that the hydrophilic coating film maintains a predetermined strength and can sufficiently protect the surface of the substrate, and at the same time, the hydrophilic coating film has excellent flexibility and can follow the deformation of the surface of the substrate, so that the state of coverage of the hydrophilic coating film on the surface of the substrate can be maintained.

[0036] The hydrophilic coating film has a hydrophilic organic compound that penetrates into the pores of the inorganic porous coating film and coats the surface of the inorganic porous coating film. Therefore, the hydrophilic organic compound gives the hydrophilic coating film excellent hydrophilicity, and the hydrophilic organic compound does not peel off or disappear early from the hydrophilic coating film due to stress from the usage environment. The hydrophilic organic compound remains in the hydrophilic coating film for a long period of time, preventing the hydrophilicity and antifouling properties of the hydrophilic coating film from decreasing, and maintaining the hydrophilic function and antifouling function of the hydrophilic organic compound for a long period of time.

[0037] The hydrophilic coating film has a top layer of the hydrophilic organic compound located slightly below the surface of the inorganic porous coating film, and the portion of the inorganic porous coating film exposed above the top layer of the hydrophilic organic compound is coated with an extremely thin film of the hydrophilic organic compound, and fine irregularities are formed on the surface of the hydrophilic coating film. Therefore, the hydrophilic coating film has excellent hydrophilicity due to the hydrophilic organic compound and the irregularities, and the hydrophilic organic compound does not peel off or disappear early from the hydrophilic coating film due to stress from the usage environment, the hydrophilic organic compound remains in the hydrophilic coating film for a long period of time, the hydrophilicity and antifouling properties of the hydrophilic coating film can be prevented from decreasing, and the hydrophilic function and antifouling function due to the hydrophilic organic compound can be maintained for a long period of time.

[0038] The hydrophilic coating liquid according to the present invention is formed from an inorganic coating liquid that produces an inorganic porous coating film having a large number of voids, and an organic coating liquid that contains a betaine polymer having a cationic moiety and an anionic moiety in the same molecule and produces a hydrophilic organic compound that coats the inorganic porous coating film while penetrating into the voids of the inorganic porous coating film. Therefore, by containing the hydrophilic organic compound that has excellent hydrophilicity and antifouling properties, it is possible to produce a hydrophilic coating film that has a small contact angle with the film surface and can increase the contact area of ​​water with the film surface, and it is possible to produce a hydrophilic coating film that allows adhering dirt to be easily washed off with water. The hydrophilic coating liquid allows the hydrophilic organic compound to penetrate into the numerous nano-sized minute voids in the inorganic porous coating film, and the hydrophilic organic compound (hydrophilic organic film) to bind to the voids in the inorganic porous coating film, thereby creating a hydrophilic coating film with excellent strength.In addition, the hydrophilic organic compound will not peel off or disappear early from the hydrophilic coating film due to stress from the usage environment, so it is possible to create a hydrophilic coating film that can prevent the hydrophilicity and antifouling properties of the hydrophilic coating film from decreasing, and it is possible to create a hydrophilic coating film that can maintain the hydrophilic function and antifouling function provided by the hydrophilic organic compound for a long period of time.

[0039] The hydrophilic coating liquid contains 20% or more of the betaine polymer, which has a cationic moiety and an anionic moiety in the same molecule, in the hydrophilic organic compound. This allows the excellent hydrophilicity of the betaine polymer to be fully utilized, the hydrophilic organic compound to exhibit excellent hydrophilicity and antifouling properties, the contact angle of water with the film surface to be reliably reduced, the contact area of ​​water with the film surface to be reliably increased, and when the hydrophilic coating film is washed with water, the water comes into contact with a wide area of ​​the film surface of the hydrophilic coating film, making it possible to create a hydrophilic coating film from which dirt adhering to the hydrophilic coating film can be easily washed away with water.

[0040] When the hydrophilic coating liquid contains inorganic fine particles of silicon dioxide (SiO2) and the solid concentration of the inorganic fine particles of silicon dioxide in the inorganic coating liquid is 0.3 to 50 wt%, the hydrophilic organic compound that has infiltrated into the numerous nano-sized minute voids in the inorganic porous coating film can easily bond to the voids containing silicon dioxide, and a hydrophilic coating film can be formed in which the hydrophilic organic compound can be firmly bound to the voids in the inorganic porous coating film. When the hydrophilic coating liquid contains inorganic fine particles of aluminum oxide (Al2O3) and the solids concentration of the inorganic fine particles of aluminum oxide in the inorganic coating liquid is 0.3 to 50 wt%, a hydrophilic coating film can be produced in which a hydrophilic organic compound that penetrates into the numerous nano-sized voids of the inorganic porous coating film can be firmly bonded to the voids containing aluminum oxide. Furthermore, the aluminum oxide makes it difficult for salts such as magnesium, calcium, sodium, and silicon to adhere to the hydrophilic coating film, thereby forming a hydrophilic coating film that can prevent contamination of the hydrophilic coating film due to the adhesion of salts such as magnesium, calcium, sodium, and silicon. When the hydrophilic coating liquid contains inorganic fine particles of zirconium oxide (ZrO2) and the solids concentration of the inorganic fine particles of zirconium oxide in the inorganic coating liquid is 0.3 to 50 wt%, a hydrophilic coating film with increased hardness and rigidity can be produced. When the hydrophilic coating liquid contains inorganic fine particles of titanium oxide (TiO2) and the solid concentration of the inorganic fine particles of titanium oxide in the inorganic coating liquid is 0.3 to 50 wt%, when light and water hit the inorganic fine particles of titanium oxide, the surface of the hydrophilic coating film is coated with hydrophilic groups, and a hydrophilic coating film capable of exhibiting a self-cleaning effect can be formed.When the hydrophilic coating liquid contains ceria oxide (CeO2) and the solid content of the inorganic fine particles of ceria oxide in the inorganic coating liquid is 0.3 to 50 wt%, the hardness of the inorganic porous coating film can be increased, the rigidity of the hydrophilic coating film can be increased, and a hydrophilic coating film having an ultraviolet absorbing effect can be formed in the hydrophilic coating film.

[0041] The hydrophilic coating solution contains inorganic fine particles with an average particle size of 1 μm or less, forming an inorganic nanoporous structure through the inorganic porous coating film. The hydrophilic organic compound penetrates the numerous nano-sized voids in the inorganic nanoporous structure, and the hydrophilic organic compound (hydrophilic organic film) binds to the voids in the inorganic porous coating film, resulting in a hydrophilic coating film with excellent strength. Furthermore, the hydrophilic organic compound does not peel off or disappear from the hydrophilic coating film due to stress from the usage environment. This prevents a decrease in the hydrophilicity and antifouling properties of the hydrophilic coating film, and allows the hydrophilic coating film to maintain the hydrophilic and antifouling properties of the hydrophilic organic compound for a long period of time. The hydrophilic coating solution can be bonded to the inorganic fine particles via covalent bonds, hydrogen bonds, ionic bonds, van der Waals bonds, etc. In particular, impregnating the nano-sized spaces with a betaine polymer strengthens the binding, preventing the hydrophilic organic compound from peeling off or disappearing from the hydrophilic coating film.

[0042] The hydrophilic coating liquid has a content of the hydrophilic organic compound in the range of 0.1 to 20 wt % relative to the total weight of the organic coating liquid, and therefore can fully utilize the excellent hydrophilicity and antifouling properties of the hydrophilic organic compound containing the betaine polymer, and can produce a hydrophilic coating film with excellent hydrophilicity and antifouling properties, a hydrophilic coating film with a small contact angle with the film surface and a large contact area of ​​water with the film surface, and a hydrophilic coating film from which adhering dirt can be easily washed off with water can be produced.

[0043] According to the hydrophilic coating film forming method of the present invention, an inorganic coating liquid for producing an inorganic porous coating film is used in the inorganic coating film forming step, and an inorganic porous coating film with an inorganic nanoporous structure having a large number of nano-sized fine voids is formed by a sol-gel method, and an organic coating liquid for producing a hydrophilic organic compound containing a betaine polymer having a cationic moiety and an anionic moiety in the same molecule is used in the hydrophilic organic compound forming step, and a hydrophilic organic compound is formed on the surface of the substrate in a state where the organic coating liquid has penetrated into the large number of fine voids in the inorganic porous coating film. Therefore, a hydrophilic coating film having excellent hydrophilicity and antifouling properties, a small contact angle with the film surface, and a large contact area of ​​water with the film surface can be formed, and a hydrophilic coating film can be formed that allows adhering dirt to be easily washed off with water. In the hydrophilic coating film formation method, the hydrophilic organic compound penetrates into numerous nano-sized micropores in the inorganic porous coating film during the hydrophilic organic compound formation step, and the hydrophilic organic compound (hydrophilic organic film) binds to the pores in the inorganic coating film, thereby producing a hydrophilic coating film with excellent strength. Furthermore, the hydrophilic organic compound does not peel off or disappear from the hydrophilic coating film due to stress from the usage environment, thereby producing a hydrophilic coating film that can prevent a decrease in the hydrophilicity and antifouling properties of the hydrophilic coating film and can maintain the hydrophilic and antifouling functions of the hydrophilic organic compound for a long period of time. The hydrophilic coating liquid can be bonded to the inorganic fine particles by covalent bonds, hydrogen bonds, ionic bonds, hydrogen bonds, van der Waals bonds, etc. In particular, impregnation of the nano-sized spaces with a betaine polymer strengthens the binding, thereby producing a hydrophilic coating film that can prevent the hydrophilic organic compound from peeling off or disappearing from the hydrophilic coating film.

[0044] The hydrophilic coating film formation method forms an inorganic porous coating film having an inorganic nanoporous structure by a sol-gel method using at least one of silica sol, alumina sol, zirconia sol, titania sol, and ceria sol in the inorganic porous coating film formation step, so that an inorganic porous coating film having a large number of fine nano-sized voids can be reliably formed on the surface of a substrate, and a hydrophilic coating film can be created that has excellent hydrophilicity and antifouling properties, has a small contact angle with the film surface, and can increase the contact area of ​​water with the film surface, and allows for the production of a hydrophilic coating film that allows adhering dirt to be easily washed off with water. In the hydrophilic coating film forming method, in the hydrophilic organic compound forming step, the hydrophilic organic compound penetrates into a large number of minute nano-sized voids in the inorganic porous coating film, and the hydrophilic organic compound (hydrophilic organic film) binds to the voids in the inorganic porous coating film, thereby making it possible to create a hydrophilic coating film with excellent strength, and since the hydrophilic organic compound does not peel off or disappear early from the hydrophilic coating film due to stress from the usage environment, it is possible to create a hydrophilic coating film that can prevent the hydrophilicity and antifouling properties of the hydrophilic coating film from decreasing, and it is possible to create a hydrophilic coating film that can maintain the hydrophilic function and antifouling function due to the hydrophilic organic compound for a long period of time.

[0045] In the hydrophilic coating film forming method, an inorganic porous coating film is coated with an organic coating liquid so that the inorganic porous coating film is not exposed from the surface of the hydrophilic organic compound in the hydrophilic organic compound forming step, and the inorganic porous coating film is buried in the hydrophilic organic compound during the formation of the hydrophilic coating film, so that the inorganic porous coating film is not exposed from the surface of the hydrophilic organic compound in the hydrophilic coating film, and the inorganic porous coating film is buried in the hydrophilic organic compound. Therefore, a hydrophilic coating film having excellent hydrophilicity can be produced by the hydrophilic organic compound that coats the inorganic porous coating film, and the hydrophilic organic compound remains in the hydrophilic coating film for a long period of time, and the hydrophilic organic compound does not peel off or disappear early from the hydrophilic coating film due to stress in the usage environment, so that a hydrophilic coating film that can prevent the hydrophilicity and antifouling properties of the hydrophilic coating film from decreasing can be produced, and a hydrophilic coating film that can maintain the hydrophilic function and antifouling function due to the hydrophilic organic compound for a long period of time can be produced.

[0046] In the hydrophilic coating film forming method, in the hydrophilic organic compound forming step, the inorganic coating liquid is coated on the surface of the substrate in a state where the inorganic coating liquid is positioned slightly below the surface of the inorganic porous coating film so that the inorganic porous coating film is exposed above the top layer of the hydrophilic organic compound, and when the hydrophilic coating film is formed, the inorganic porous coating film is exposed above the top layer of the hydrophilic organic compound, and the part of the inorganic porous coating film that is exposed above the top layer of the hydrophilic organic compound is coated with an ultra-thin film of the hydrophilic organic compound, and fine irregularities are formed on the surface of the hydrophilic coating film. Therefore, a hydrophilic coating film having excellent hydrophilicity can be formed by the hydrophilic organic compound and the formed irregularities, and the hydrophilic organic compound will not peel off or disappear early from the hydrophilic coating film due to stress in the usage environment, and the hydrophilic organic compound will remain in the hydrophilic coating film for a long period of time, and a hydrophilic coating film that can prevent the hydrophilicity and antifouling properties of the hydrophilic coating film from decreasing can be formed, and a hydrophilic coating film that can maintain the hydrophilic function and antifouling function due to the hydrophilic organic compound for a long period of time can be formed.

[0047] In the method for forming a hydrophilic coating film, the excess hydrophilic organic compounds that are weakly bound to the pores of the inorganic porous coating film, excluding the hydrophilic organic compounds that are firmly bound to the pores of the inorganic porous coating film, are washed away with water in the water washing step, and thus the hydrophilic organic compounds that do not contribute to the hydrophilicity of the hydrophilic coating film are removed from the hydrophilic coating film. This makes it possible to produce a hydrophilic coating film that contains hydrophilic organic compounds that are firmly bound to the pores of the inorganic porous coating film and have excellent hydrophilicity and antifouling properties, and it is possible to produce a hydrophilic coating film that has a small contact angle with the film surface and can increase the contact area of ​​water with the film surface, and it is also possible to produce a hydrophilic coating film that allows adhering dirt to be easily washed off with water. [Brief explanation of the drawings]

[0048] [Figure 1]FIG. 2 is an image diagram showing an example of an inorganic porous coating film formed on the surface of a substrate. [Figure 2] FIG. 2 is an image diagram showing an example of a hydrophilic coating film formed from the inorganic porous coating film of FIG. 1 and a hydrophilic organic compound. [Figure 3] FIG. 2 is an image diagram showing another example of a hydrophilic coating film formed from the inorganic porous coating film of FIG. 1 and a hydrophilic organic compound. [Figure 4] FIG. 10 is an image diagram showing another example of an inorganic porous coating film formed on the surface of a substrate. [Figure 5] 5 is an image diagram showing another example of a hydrophilic coating film formed from the inorganic porous coating film of FIG. 4 and a hydrophilic organic compound. [Figure 6] FIG. 5 is an image diagram showing another example of a hydrophilic coating film formed from the inorganic porous coating film of FIG. 4 and a hydrophilic organic compound. [Figure 7] 1 is a flow diagram of a hydrophilic coating film forming method for forming a hydrophilic coating film. [Figure 8] FIG. 3 is a diagram showing the contact angle of a water droplet dropped on the hydrophilic coating film of FIG. 2. [Figure 9] FIG. 4 is a diagram showing the contact angle of a water droplet dropped on the hydrophilic coating film of FIG. 3. [Figure 10] FIG. 6 is a diagram showing the contact angle of a water droplet dropped on the hydrophilic coating film of FIG. 5. [Figure 11] FIG. 7 is a diagram showing the contact angle of a water droplet dropped on the hydrophilic coating film of FIG. 6. [Figure 12] FIG. 2 shows examples 1 to 4 of hydrophilic coating films. [Figure 13] FIG. 1 shows hydrophilic coating films according to Examples 5 to 8. [Figure 14] FIG. 2 is a diagram showing comparative examples 1 to 4 of hydrophilic coating films. [Figure 15] FIG. 10 is a diagram showing comparative examples 5 to 8 of hydrophilic coating films. DETAILED DESCRIPTION OF THE INVENTION

[0049] The hydrophilic coating film, hydrophilic coating liquid, and hydrophilic coating film forming method according to the present invention will be described in detail below with reference to the accompanying drawings. Fig. 1 is an image diagram showing an example of an inorganic porous coating film 13a formed on the surface 12 of a substrate 11, Fig. 2 is an image diagram showing an example of a hydrophilic coating film 10A formed from the inorganic porous coating film 13a of Fig. 1 and a hydrophilic organic compound 14, Fig. 3 is an image diagram showing another example of a hydrophilic coating film 10B formed from the inorganic porous coating film 13a of Fig. 1 and a hydrophilic organic compound 14, and Fig. 4 is an image diagram showing another example of an inorganic porous coating film 13b formed on the surface 12 of a substrate 11. Fig. 5 is an image diagram showing another example of the hydrophilic coating film 10C formed from the inorganic porous coating film 13b of Fig. 4 and the hydrophilic organic compound 14, and Fig. 6 is an image diagram showing another example of the hydrophilic coating film 10D formed from the inorganic porous coating film 13b of Fig. 4 and the hydrophilic organic compound 14. In Figs. 1 to 6, the inorganic fine particles 16 and the voids 15 of the inorganic porous coating films 13a and 13b are illustrated as visible images, but in reality the inorganic fine particles 16 and the voids 15 cannot be seen with the naked eye.

[0050] The hydrophilic coating films 10A to 10D are formed on the surfaces 12 (front and back) of the substrate 11 to be coated with them. The hydrophilic coating films 10A to 10D are formed from inorganic porous coating films 13a and 13b and a hydrophilic organic compound 14, and are produced by applying (coating) an inorganic coating liquid that forms the inorganic porous coating films 13a and 13b to the surface 12 of the substrate 11, forming the inorganic porous coating films 13a and 13b on the surface 12 of the substrate 11, and then applying (coating) an organic coating liquid that forms the hydrophilic organic compound 14 to the surface 12 of the substrate 11, thereby forming the hydrophilic organic compound 14 on the surface 12 of the substrate 11.

[0051] The substrates 11 to be coated with the hydrophilic coating films 10A to 10D include metal (metallic molded products), plastic (plastic molded products and molded products having plastic as the outermost layer), glass (glass molded products), rubber (rubber molded products), leather (leather molded products), wood (wooden molded products), paper (paper molded products), and woven or knitted fabrics using fibers (woven or knitted fabric molded products), but there are no particular limitations on the substrates 11. Furthermore, there are no particular limitations on each molded product, and all molded products of a predetermined shape made from metal, plastic, glass, rubber, leather, wood, paper, synthetic fiber, natural fiber, and woven or knitted fabric are included.

[0052] Metals include iron, aluminum, duralumin, stainless steel, copper, gold, silver, titanium, nickel, and alloys. Plastics include polymethyl methacrylate, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, ABS, polycarbonate, polystyrene, epoxy, unsaturated polyester, melamine, diallyl phthalate, polyimide, urethane, nylon, polyethylene, polypropylene, polyvinyl chloride, polytetrafluoroethylene resin, polychlorotrifluoroethylene resin, polyvinylidene fluoride resin, polyvinyl fluoride resin, perfluoroalkoxy fluororesin, tetrafluoroethylene-hexafluoropropylene copolymer resin, ethylene-tetrafluoroethylene copolymer resin, and ethylene-chlorotrifluoroethylene copolymer resin. Rubbers include polybutadiene rubber, polyisoprene (natural rubber), styrene-butadiene rubber, nitrile rubber, EPM, EPDM, epichlorohydrin rubber, neoprene rubber, polysulfide, and butyl rubber.

[0053] The inorganic coating liquid may be one or more of the following: silica sol, in which nano-sized inorganic particles 16 (colloidal particles) made of fine silicon dioxide (SiO2) are dispersed in a dispersion medium; alumina sol, in which nano-sized inorganic particles 16 (colloidal particles) made of fine aluminum oxide (Al2O3) are dispersed in a dispersion medium; zirconia sol, in which nano-sized inorganic particles 16 (colloidal particles) made of fine zirconium oxide (ZrO2) are dispersed in a dispersion medium; titania sol, in which nano-sized inorganic particles 16 (colloidal particles) made of fine titanium oxide (TiO2) are dispersed in a dispersion medium; or ceria sol, in which nano-sized inorganic particles 14 (colloidal particles) made of fine cerium oxide (CeO2) are dispersed in a dispersion medium. The dispersion medium may be water or an alcohol such as ethyl alcohol, normal propyl alcohol, isopropyl alcohol, or normal butanol, but is not limited to this.

[0054] Silica sol is produced by the water glass method or the alkoxide method. However, it is not limited to these methods and can also be produced by other methods. In the water glass method, sodium silicate (Na2O·SiO2) is diluted with water to a few percent to create an aqueous solution, which is then added in small amounts to a preheated aqueous sodium hydroxide solution to cause a reaction. After the reaction, the mixture is boiled under reflux for several hours and then ultrafiltered to produce an alkaline silica sol. Next, ion exchange is performed to remove impurities, and a stabilizer is added to stabilize the mixture, producing a silica sol (silica colloid solution).

[0055] In the alkoxide method, pure water is added to alkyl silicate (tetraalkoxysilane) to cause a hydrolysis reaction, and then the alcohol produced by the reaction is removed by distillation. After that, a pH adjuster (an alkali such as tetraalkylammonium hydroxide or an acid such as hydrochloric acid) is added to adjust the pH to the desired level. After adjusting the pH, the mixture is concentrated by refluxing to produce a silica sol (silica colloidal solution).

[0056] One example of a method for producing an alumina sol is to produce an alumina sol (alumina colloidal solution) by hydrothermally treating an alumina gel obtained by neutralizing a water-soluble aluminum salt with an alkali in the presence of an organic acid. Another example of a method for producing an alumina sol is to produce an alumina sol (alumina colloidal solution) by hydrothermally treating an alumina gel obtained by a liquid-phase neutralization reaction of an acidic aluminum compound with an alkaline substance in the presence of a monovalent inorganic acid. Another example of a method for producing an alumina sol is to produce an alumina sol (alumina colloidal solution) by hydrothermally treating an alumina hydrate obtained by reacting a water-soluble aluminum salt with carbonic acid or a carbonate, and then mixing the alumina sol (alumina colloidal solution) with a monovalent acid.

[0057] Another example of a method for producing an alumina sol is to hydrothermally treat alumina hydrate obtained by reacting a water-soluble aluminum salt with carbonic acid or a carbonate salt, and then mix the resulting alumina sol (alumina colloidal solution) with a monovalent acid. Another example of a method for producing an alumina sol is to hydrolyze aluminum alkoxide with a dilute acid aqueous solution to obtain alumina hydrate, add a new acid to the resulting alumina hydrate, and then hydrothermally treat the resulting alumina sol (alumina colloidal solution) to peptize it. Another example of a method for producing an alumina sol is to treat aluminum oxide powder in an aqueous phase in the presence of acid with a strongly acidic cation exchange resin, remove the ion exchange resin, and cool to room temperature to produce an alumina sol (alumina colloidal solution). However, the production methods are not limited to these, and alumina sols can also be produced by other methods.

[0058] One example of a method for producing a zirconia sol is to add an alkali to an aqueous solution containing a water-soluble zirconium salt such as zirconium oxychloride to produce zirconium hydroxide, and then hydrolyze the produced zirconium hydroxide to produce a zirconia sol (zirconia colloidal solution). Another example of a method for producing a zirconia sol is to hydrolyze a reaction product of ammonium zirconium carbonate and a chelating agent (for example, oxyphenols, amino alcohols, oxy acids, polycarboxylic acids, oxyaldehydes, amino acids, and β-diketones) to produce a zirconia sol (zirconia colloidal solution). Another example of a method for producing a zirconia sol involves heating an aqueous suspension containing zirconium hydroxide at a temperature of 80°C or higher to produce a crystallized zirconia-containing aqueous suspension in which the resulting zirconia has a crystallinity of 80% or higher, and then adding a nitrogen-containing basic compound (primary amine, secondary amine, quaternary ammonium hydroxide), an alkali metal hydroxide, or an alkaline earth metal hydroxide to the crystallized zirconia-containing aqueous suspension to produce a basic zirconia sol (zirconia colloidal solution).

[0059] Another example of a method for producing a zirconia sol is to add a base to an aqueous zirconium salt solution to precipitate the zirconia, add an alkaline earth metal hydroxide or its aqueous solution, and heat and age the resulting suspension at a temperature of 90 to 200°C to produce a zirconia sol (colloidal zirconia solution). Another example of a method for producing a zirconia sol is to heat an aqueous zirconium salt solution having an anion-to-metal molar ratio of 0.5:1 to 4:1 to 120 to 300°C, cool it to room temperature, and adjust the pH to 2 to 6 to produce a zirconia sol (colloidal zirconia solution). Another example of a method for producing a zirconia sol is to add hydrogen peroxide to an aqueous zirconium salt solution having a concentration of 0.05 to 2.0 mol / L in an amount equal to or greater than half the molar ratio of the amount of zirconium in the solution, heat it to 80 to 300°C, and then add a base such as ammonia or treat it with an ion exchange resin or the like to produce a zirconia sol (colloidal zirconia solution). However, the zirconia sol can be produced by other methods without being limited to these methods.

[0060] One example of a titania sol production method is to add an alkali to an aqueous solution of a water-soluble titanium salt such as titanium tetrachloride or titanium sulfate, precipitate titanium hydroxide, and then peptize the precipitated titanium sol (titania colloidal solution) with a strong acid such as hydrochloric acid or nitric acid. Another example of a titania sol production method is to hydrolyze a water-soluble titanium salt with an alkali to obtain a titanic acid gel, which is then hydrothermally treated in the presence of quaternary ammonium hydroxide to produce a titania sol (titania colloidal solution). Another example of a titania sol production method is to react a water-soluble titanium compound with an alkali metal hydroxide, carbonate, or ammonium compound to obtain a gel, to which an alkali metal hydroxide, ammonium hydroxide, or an organic amine such as methylamine, trimethylamine, ethylenediamine, or ethanolamine is added, followed by hydrothermal treatment at 100°C or higher to produce a titania sol (titania colloidal solution). However, the production methods are not limited to these, and titania sols can also be produced by other methods.

[0061] One example of a method for producing ceria sol is to react a cerium salt compound such as ceric sulfate, ceric ammonium nitrate, ceric ammonium sulfate, cerous acetate, cerous chloride, cerous ammonium nitrate, cerous nitrate, or cerous nitrate with an alkali metal hydroxide such as sodium hydroxide, potassium hydroxide, or lithium hydroxide or ammonia at 10°C to 90°C to produce a gel, and then add an acid such as hydrochloric acid, nitric acid, acetic acid, formic acid, lactic acid, or glycolic acid and perform hydrothermal treatment at a temperature of 100°C or higher. The acid may be added after the hydrothermal treatment.

[0062] Another example of a method for producing ceria sol is to disperse cerium hydroxide or hydrated cerium hydroxide in water, stir the mixture, and then add HNO to prepare a reaction dispersion. Ceria sol can also be produced by heating the resulting reaction dispersion to approximately 80 to 150°C for approximately 6 hours. However, the production method is not limited to these, and other methods can also be used to produce ceria sol.

[0063] The inorganic coating liquid contains one or more types of inorganic particles 16 selected from silicon dioxide (SiO2), aluminum oxide (Al2O3), zirconium oxide (ZrO2), titanium oxide (TiO2), and ceria oxide (CeO2). By applying silica sol, alumina sol, zirconia sol, titania sol, or ceria sol to the surface 12 of the substrate 11, inorganic porous coating films 13a and 13b are formed with an inorganic nanoporous structure having numerous nano-sized fine voids 15 (gaps) made by the sol-gel method, as shown in Figures 1 and 4.

[0064] In the inorganic porous coating film 13a shown in Fig. 1, adjacent inorganic particles 16 among a large number of substantially spherical inorganic particles 16 are partially connected to each other, and a large number of nano-sized fine voids 15 (inorganic nanoporous structure) are formed between the inorganic particles 16. In the inorganic porous coating film 13b shown in Fig. 4, amorphous, substantially columnar inorganic particles 16 are partially connected (connected) to each other, and a large number of nano-sized fine voids 15 (inorganic nanoporous structure) are formed between the inorganic particles 16.

[0065] The solids concentration of inorganic particles 16 (silicon dioxide (SiO2), aluminum oxide (Al2O3), zirconium oxide (ZrO2), titanium oxide (TiO2), and ceria oxide (CeO2)) in the inorganic coating liquid is in the range of 0.3 wt% to 50 wt% of the total mass of the inorganic coating liquid. If the solids concentration of inorganic particles 16 of silicon dioxide (SiO2) in the inorganic coating liquid is less than 0.3 wt%, the amount of silicon dioxide that easily bonds with hydrophilic organic compound 14 is insufficient, making it difficult for hydrophilic organic compound 14 that has infiltrated into the numerous fine voids 15 (described below) of inorganic porous coating films 13a and 13b to bond with the silicon dioxide-containing voids 15. As a result, hydrophilic organic compound 14 cannot be firmly bonded to voids 15 of inorganic porous coating films 13a and 13b. Since the solid concentration of inorganic fine particles 16 of silicon dioxide (SiO2) in the inorganic coating liquid is within the above range, the hydrophilic organic compound 14 (hydrophilic organic film) that has penetrated into the numerous minute voids 15 of the inorganic porous coating films 13a, 13b easily binds to the voids 15 containing silicon dioxide, and the hydrophilic organic compound 14 can be firmly bound to the voids 15 of the inorganic porous coating films 13a, 13b.

[0066] If the solid concentration of inorganic particles 16 of aluminum oxide (Al2O3) in the inorganic coating liquid is less than 0.3 wt%, the amount of aluminum oxide that easily bonds with the hydrophilic organic compound 14 will be insufficient, and the hydrophilic organic compound 14 that has penetrated into the numerous tiny voids 15 of the inorganic porous coating films 13a, 13b will have difficulty bonding to the voids 15 containing aluminum oxide. As a result, the hydrophilic organic compound 14 will not be firmly bonded to the voids of the inorganic porous coating films 13a, 13b. In addition, the aluminum oxide's ability to remove salts such as magnesium, calcium, sodium, and silicon will be reduced, and it will not be possible to prevent contamination of the hydrophilic coating films 10A to 10D due to the adhesion of salts such as magnesium, calcium, sodium, and silicon. Since the solid content concentration of inorganic fine particles 16 of aluminum oxide (Al2O3) in the inorganic coating liquid is within the above range, the hydrophilic organic compound 14 that has penetrated into the numerous minute voids 14 of the inorganic porous coating films 13a, 13b can be firmly bonded to the voids 14 containing aluminum oxide, and since the aluminum oxide makes it difficult for salts such as magnesium, calcium, sodium, silicon, etc. to adhere to the hydrophilic coating films 10A to 10D, it is possible to prevent contamination of the hydrophilic coating films 10A to 10D due to adhesion of salts such as magnesium, calcium, sodium, silicon, etc. to the hydrophilic coating films 10A to 10D.

[0067] If the solid content concentration of the inorganic particles 16 of zirconium oxide (ZrO2) in the inorganic coating liquid is less than 0.3 wt%, the hardness of the inorganic porous coating films 13a, 13b cannot be increased, and the rigidity of the hydrophilic coating films 10A to 10D cannot be increased. Since the solid content concentration of the inorganic particles 16 of zirconium oxide (ZrO2) in the inorganic coating liquid is within the above range, the hardness of the inorganic porous coating films 13a, 13b can be increased, and the rigidity of the hydrophilic coating films 10A to 10D can be increased.

[0068] If the solids concentration of the inorganic particles 16 of titanium oxide (TiO2) in the inorganic coating liquid is less than 0.3 wt%, the amount of titanium oxide will be insufficient, and the hydrophilic coating films 10A to 10D will not be able to have a self-cleaning effect. Since the solids concentration of the inorganic particles 16 of titanium oxide (TiO2) in the inorganic coating liquid is within the above range, the surfaces of the hydrophilic coating films 10A to 10D are coated with hydrophilic groups when the inorganic particles 16 of titanium oxide are exposed to light and water, and an excellent self-cleaning effect can be imparted to the hydrophilic coating films 10A to 10D.

[0069] If the solid concentration of inorganic particles 14 of cerium oxide (CeO2) in the inorganic coating liquid is less than 0.3 wt%, the hardness of the inorganic porous coating films 13a, 13b cannot be increased, and the rigidity of the hydrophilic coating films 10A to 10D cannot be increased. Furthermore, the UV absorption function cannot be sufficiently obtained. Since the solid concentration of inorganic particles 14 of cerium oxide (CeO2) in the inorganic coating liquid is within the above range, the hardness of the inorganic porous coating films 13a, 13b can be increased, the rigidity of the hydrophilic coating films 10A to 10D can be increased, and the UV absorption effect of the hydrophilic coating films 10A to 10D can be obtained.

[0070] If the solid concentration of the inorganic particles 16 (silicon dioxide (SiO2), aluminum oxide (Al2O3), zirconium oxide (ZrO2), titanium oxide (TiO2), ceria oxide (CeO2)) in the inorganic coating liquid exceeds 50 wt%, the inorganic particles 16 come into contact with each other over a wide area, making the inorganic particles 16 denser and preventing the formation of numerous fine voids 15. Since the solid concentration of the inorganic particles 16 in the inorganic coating liquid is within the above range, inorganic porous coating films 13a, 13b with a predetermined strength and an inorganic nanoporous structure having numerous nano-sized fine voids 15 can be formed on the coating surface 12 of the substrate 11.

[0071] The inorganic fine particles 16 contained in the inorganic coating liquid have an average particle diameter of 1 μm or less. If the average particle diameter of the inorganic fine particles 16 exceeds 1 μm, the volume of the voids 15 increases, and it becomes impossible to form inorganic porous coating films 13a, 13b with an inorganic nanoporous structure having a large number of minute voids 15 on the coating surface 12 of the substrate 11. Because the average particle diameter of the inorganic fine particles 16 is 1 μm or less, the large number of minute inorganic fine particles 16 are partially connected to each other, and it becomes possible to form inorganic porous coating films 13a, 13b with an inorganic nanoporous structure having a large number of minute nano-sized voids 15 on the coating surface 12 of the substrate 11.

[0072] The organic coating liquid contains a hydrophilic organic compound 14 dispersed in a solvent, the hydrophilic organic compound 14 including a betaine polymer having a cationic moiety and an anionic moiety in the same molecule. The content of the hydrophilic organic compound 14 in the organic coating liquid is in the range of 0.1 wt% to 20 wt% of the total weight of the organic coating liquid. If the content of the hydrophilic organic compound 14 in the organic coating liquid is less than 0.1 wt%, the content of the hydrophilic organic compound 14 in the organic coating liquid is so low that the hydrophilic organic compound 14 produced from the organic coating liquid cannot exhibit sufficient hydrophilicity or antifouling properties, and excellent hydrophilicity or antifouling properties cannot be imparted to the hydrophilic coating films 10A to 10D formed from the inorganic porous coating films 13a, 13b and the hydrophilic organic compound 14.

[0073] Since the content of the hydrophilic organic compound 14 contained in the organic coating liquid is within the above range, the organic coating liquid contains a sufficient amount of the hydrophilic organic compound 14, and the hydrophilic organic compound 14 produced from the organic coating liquid exhibits sufficient hydrophilicity and antifouling properties, thereby imparting excellent hydrophilicity and antifouling properties to the hydrophilic coating films 10A to 10D formed from the inorganic porous coating films 13a, 13b and the hydrophilic organic compound 14.

[0074] The proportion of the betaine polymer in the hydrophilic organic compound 14 is 20% or more. If the proportion of the betaine polymer in the hydrophilic organic compound 14 is less than 20%, the content of the betaine polymer in the hydrophilic organic compound 14 is low, and the hydrophilic function of the betaine polymer cannot be fully utilized. As a result, the hydrophilic organic compound 14 made from the organic coating liquid cannot exhibit sufficient hydrophilicity or antifouling properties, and it is not possible to impart excellent hydrophilicity or antifouling properties to the hydrophilic coating films 10A to 10D formed from the inorganic porous coating films 13a, 13b and the hydrophilic organic compound 14.

[0075] Since the organic coating liquid has a ratio of betaine polymer in hydrophilic organic compound 14 of 20% or more, the organic coating liquid contains a sufficient amount of betaine polymer, and hydrophilic organic compound 14 made from the organic coating liquid exhibits excellent hydrophilicity and antifouling properties, thereby imparting excellent hydrophilicity and antifouling properties to hydrophilic coating films 10A to 10D formed from inorganic porous coating films 13a, 13b and hydrophilic organic compound 14.

[0076] A specific example of an organic coating liquid is a coating liquid in which a polymer capable of forming a high-density polymer brush (surface graft polymer) shown in the following structural formula (1) is dispersed in an aqueous solvent or an ester solvent. The structural formula of the polymer capable of forming a high-density polymer brush is shown in (Chemical Formula 1).

[0077] (chemical 1) TIFF2026010645000002.tif3073

[0078] The polymer capable of forming the high-density polymer brush shown in the structural formula (Chemical Formula 1) is a polymer brush of a carboxybetaine monomer with a silanol group at one end, and γ-mercaptopropyltrimethoxysilane is used as a chain transfer agent. This polymer capable of forming high-density polymer brushes can be used to create carpet-like polymer thin films by growing polymer chains.

[0079] In addition to the polymers capable of forming high-density polymer brushes (surface graft polymers), organic coating solutions can also use brush particles or bottle brushes. Betaine polymers that do not contain silanol or alkoxysilyl groups at the terminals or within the polymer chain can also be used. By using betaine polymers that do not contain silanol or alkoxysilyl groups, reactions do not occur in the solution, and long-term changes over time can be suppressed. Examples of other hydrophilic organic compounds that can be used in combination with betaine polymers in organic coating solutions include coating solutions in which the following polymers capable of forming PHEMA polymer brushes, PHEMA polymers, PPEGMA polymers, PPEGMA polymers, PNIPAM polymer brushes, PNIPAM polymers, PMTAC polymer brushes, PMTAC polymers, PSPMK polymer brushes, and PSPMK polymers are dispersed in aqueous or ester-based solvents. In addition, betaine polymers other than the betaine polymer shown in the structural formula (Chemical Formula 1) can be mixed in. As another example, a coating liquid containing a polymer capable of forming a PMAPS polymer brush, a PMAPS polymer, a polymer capable of forming a PMPC polymer brush, or a PMPC polymer dispersed therein can also be used. These polymers may also be obtained by copolymerizing multiple monomers. The structural formula of the PHEMA polymer is shown in Chemical Formula 2, but it may have a silanol group or alkoxysilyl group at one end or may contain a silanol group or alkoxysilyl group in the polymer chain.

[0080] (Case 2) TIFF2026010645000003.tif2783The structural formula of PPEGMA polymer is shown in (Chemical Formula 3), but it may have a silanol group or an alkoxysilyl group at one end, or the polymer chain may contain a silanol group or an alkoxysilyl group.

[0081] (C3) TIFF2026010645000004.tif2577The structural formula of PNIPAM polymer is shown in (Chemical Formula 4), but it may have a silanol group or an alkoxysilyl group at one end, or may contain a silanol group or an alkoxysilyl group in the polymer chain.

[0082] (C4) TIFF2026010645000005.tif2886The structural formula of PMTAC polymer is shown in (Chemical Formula 5), ​​but it may have a silanol group or an alkoxysilyl group at one end, or the polymer chain may contain a silanol group or an alkoxysilyl group.

[0083] (C5) TIFF2026010645000006.tif3380PSPMMK polymer has the structural formula shown in (Chemical Formula 6), and may have a silanol group or an alkoxysilyl group at one end, or may contain a silanol group or an alkoxysilyl group in the polymer chain.

[0084] (6) TIFF2026010645000007.tif3189The structural formula of PMAPS polymer is shown in (Chemical Formula 7), and it may have a silanol group or an alkoxysilyl group at one end, or the polymer chain may contain a silanol group or an alkoxysilyl group.

[0085] (C7) TIFF2026010645000008.tif3586The structural formula of PMPC polymer is shown in (Chemical Formula 8), but it may have a silanol group or an alkoxysilyl group at one end, or the polymer chain may contain a silanol group or an alkoxysilyl group.

[0086] (8) TIFF2026010645000009.tif3791 Water-soluble solvents include primary alcohols, secondary alcohols, tertiary alcohols, ethers, esters, and ketones. Primary, secondary, and tertiary alcohols include isopropanol, sec-butyl alcohol, tert-butyl alcohol, and propylene glycol monomethyl ether. Ether solvents include tetrahydrofuran, 1,4-dioxane, 1,3-dioxolane, triethylene glycol butyl methyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol ethyl methyl ether, diethylene glycol isopropyl methyl ether, ethylene glycol diethyl ether, ethylene glycol dimethyl ether, propylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tripropylene glycol dimethyl ether, diethylene glycol butyl methyl ether, diethylene glycol dibutyl ether, and dipropylene glycol dimethyl ether.

[0087] Examples of ester solvents include methyl acetate, ethyl acetate, ethylene glycol monomethyl acetate, ethylene glycol monoethyl acetate, propylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether propionate, and γ-butyrolactone. Examples of ketone solvents include acetone, methyl ethyl ketone, methyl isobutyl ketone, diisopropyl ketone, and cyclohexanone. Examples of aprotic solvents include dimethyl sulfoxide, N,N-dimethylformamide, and N-methylpyrrolidone.

[0088] As another example of a betaine polymer constituting the polymer, the following betaine polymer can also be used. One example of a betaine polymer is a polymer containing 2-methacryloyloxyethyl phosphorylcholine as a component. Its structural formula is shown in (Chemical Formula 9), and it may have a silanol group or an alkoxysilyl group at one end, or the silanol group or alkoxysilyl group may be contained in the polymer chain.

[0089] (9) Another example of a betaine polymer that constitutes a TIFF2026010645000010.tif2542 polymer is a polycarboxybetaine polymer. The structural formula of a polycarboxybetaine polymer is shown in Chemical Formula 10. The polymer may have a silanol group or an alkoxysilyl group at one end, or the polymer chain may contain a silanol group or an alkoxysilyl group.

[0090] (C10) TIFF2026010645000011.tif2551 The monomers that make up betaine polymers include sulfobetaine monomers, carboxybetaine monomers, phosphobetaine monomers, dimethylamine oxide monomers, and dimethylsulfoniopropionate. The general formula of sulfobetaine monomers is shown in (Chemical Formula 11), and its specific structural formulas are shown in (Chemical Formula 12) to (Chemical Formula 18).

[0091] (Chem.11) TIFF2026010645000012.tif2662

[0092] (C12) 3-{[2-(methacryloyloxy)ethyl]dimethylammonio}propane-1-sulfonic acid TIFF2026010645000013.tif1648

[0093] (C13) 4-[(3-methacrylamidopropyl)dimethylammonio]butane-1-sulfonic acid TIFF2026010645000014.tif1449

[0094] (C14) 3-{[2-(acryloyloxy)ethyl]dimethylammonio}propane-1-sulfonic acid TIFF2026010645000015.tif1349

[0095] (C15) 3-[(3-acrylamidopropyl)dimethylammonio]propane-1-sulfonic acid TIFF2026010645000016.tif1346

[0096] (C16) 4-{[2-(methacryloyloxy)ethyl]dimethylammonio}butane-1-sulfonic acid JPEG2026010645000017.jpg3240

[0097] (C17) Bis[2-(methacryloyloxy)ethyl] (methyl)ammonio]propane-1-sulfonic acid JPEG2026010645000018.jpg3240

[0098] (C18) 3-[3-(methacrylamidopropyl)dimethylammonio]propane-1-sulfonic acid JPEG2026010645000019.jpg3442 The general formula of the carboxybetaine monomer is shown in (Chemical Formula 19), and its specific structural formulas are shown in (Chemical Formula 20) to (Chemical Formula 22).

[0099] (C19) TIFF2026010645000020.tif2573

[0100] (20) 2-{[2-(methacryloyloxy)ethyl]dimethylammonio}acetic acid JPEG2026010645000021.jpg3041

[0101] (21) 3-{[3-(methacryloyloxy)ethyl] dimethylammonio}propionate JPEG2026010645000022.jpg2941

[0102] (22) 3-[(3-acrylamidopropyl) dimethylammonio]propanoate JPEG2026010645000023.jpg2841The general formula of the phosphobetaine monomer is shown in (Chemical Formula 23), and its specific structural formula is shown in (Chemical Formula 24).

[0103] (23) TIFF2026010645000024.tif2766

[0104] (24) 2-(methacryloyloxy)ethyl 2-(trimethylammonio)ethyl phosphate TIFF2026010645000025.tif1551The structural formula of dimethylamine oxide is shown in (Chemical Formula 25).

[0105] (25) TIFF2026010645000026.tif2147The structural formula of methylsulfoniocarboxylate is shown in (Chemical Formula 26).

[0106] (26) TIFF2026010645000027.tif2164 The hydrophilic coating liquid is formed from an inorganic coating liquid containing at least one type of inorganic fine particles 16 selected from silicon dioxide (SiO2), aluminum oxide (Al2O3), zirconium oxide (ZrO2), titanium oxide (TiO2), and ceria oxide (CeO2), and the solid concentration of the inorganic fine particles 16 in the inorganic coating liquid is 0.3 to 50 wt%, so that inorganic porous coating films 13a, 13b having sufficient strength in which numerous fine voids 15 are formed by the inorganic fine particles 16 can be produced, and hydrophilic coating films 10A to 10D that are firmly bonded to the voids 15 can be produced.

[0107] When the inorganic coating liquid that forms the hydrophilic coating liquid contains inorganic fine particles 16 of silicon dioxide (SiO2), the hydrophilic organic compound 14 can easily bond with silicon dioxide by utilizing the ease of bonding between the hydrophilic organic compound 14 and silicon dioxide, and the hydrophilic organic compound 14 that has penetrated into the numerous fine voids 14 of the inorganic porous coating films 13a, 13b can easily bond with the voids 15 containing silicon dioxide, thereby producing hydrophilic coating films 10A to 10D in which the hydrophilic organic compound 14 is firmly bonded to the voids 15 of the inorganic porous coating films 13a, 13b.

[0108] When the inorganic coating liquid that forms the hydrophilic coating liquid contains inorganic fine particles 16 of aluminum oxide (Al2O3), by utilizing the ease of bonding between the hydrophilic organic compound 14 and aluminum oxide, it is possible to create hydrophilic coating films 10A to 10D in which the hydrophilic organic compound 14 that has penetrated into the numerous minute voids 15 of the inorganic porous coating films 13a, 13b is firmly bonded to the voids 15 of the inorganic porous coating films 13a, 13b that contain aluminum oxide.In addition, since the aluminum oxide makes it difficult for salts such as magnesium, calcium, sodium, and silicon to adhere to the hydrophilic coating films 10A to 10D, it is possible to create hydrophilic coating films 10A to 10D that can prevent contamination caused by the adhesion of salts such as magnesium, calcium, sodium, and silicon to the hydrophilic coating films 10A to 10D.

[0109] When the inorganic coating liquid forming the hydrophilic coating liquid contains inorganic particles 16 of zirconium oxide (ZrO2), the zirconium oxide increases the hardness, allowing the production of hydrophilic coating films 10A-10D with increased rigidity. When the inorganic coating liquid forming the hydrophilic coating liquid contains inorganic particles 16 of titanium oxide (TiO2), the titanium oxide inorganic particles 16 are coated with hydrophilic groups on their surfaces when exposed to light and water, allowing the production of hydrophilic coating films 10A-10D with excellent self-cleaning properties. When the inorganic coating liquid forming the hydrophilic coating liquid contains inorganic particles 14 of ceria oxide (CeO2), the ceria oxide increases the hardness and provides UV absorption, allowing the production of hydrophilic coating films 10A-10D with increased rigidity and UV absorption.

[0110] The hydrophilic coating liquid is formed from an inorganic coating liquid that produces inorganic porous coating films 13a, 13b having numerous voids 15, and an organic coating liquid that contains a betaine polymer (polymer brush) having cationic and anionic moieties in the same molecule and produces hydrophilic organic compounds 14 that coat the inorganic porous coating films 13a, 13b while penetrating the voids 15 of the inorganic porous coating films 13a, 13b.By containing the hydrophilic organic compounds 14 that have excellent hydrophilicity and antifouling properties, it is possible to produce hydrophilic coating films 10A to 10D that have a small contact angle with the film surface and can increase the contact area of ​​water with the film surface, and it is possible to produce hydrophilic coating films 10A to 10D that can easily wash off adhering dirt with water.

[0111] The hydrophilic coating liquid contains hydrophilic organic compounds 14 that penetrate into numerous nano-sized microvoids 15 in the inorganic porous coating films 13a and 13b, and the hydrophilic organic compounds 14 (hydrophilic organic films) bond (join) to the voids 15 (inorganic microparticles 14) in the inorganic porous coating films 13a and 13b and to the surface 12 of the substrate 11, thereby producing hydrophilic coating films 10A to 10D with excellent strength. Furthermore, the hydrophilic organic compounds 14 will not peel off or disappear early from the hydrophilic coating films 10A to 10D due to stress from the usage environment, so that hydrophilic coating films 10A to 10D that can prevent a decrease in hydrophilicity and antifouling properties can be produced, and hydrophilic coating films 10A to 10D that can maintain the hydrophilic function and antifouling function provided by the hydrophilic organic compounds 14 for a long period of time can be produced.

[0112] Fig. 7 is a flow diagram of a hydrophilic coating film forming method for producing hydrophilic coating films 10A to 10D. An example of the hydrophilic coating film forming method for producing hydrophilic coating films 10A to 10D will be described below with reference to Fig. 7. The hydrophilic coating film forming method produces hydrophilic coating films 10A to 10D formed from inorganic porous coating films 13a, 13b having a large number of fine voids 15 and a hydrophilic organic compound 14.

[0113] The hydrophilic coating film forming method includes a cleaning step (P-1), an inorganic porous coating film forming step (P-2), a hydrophilic organic compound forming step (P-3), and a water cleaning step (P-4). By performing these steps (P-1) to (P-4), hydrophilic coating films 10A to 10D are formed on the coating surface 12 of the substrate 11. In the cleaning step (P-1), a cleaning treatment is performed to blow away dust from the coating surface 12 of the substrate 11 using an air injection means such as an air gun, and then the coating surface 12 of the substrate 11 is cleaned using an alkaline detergent. After cleaning with the alkaline detergent, the coating surface 12 of the substrate 11 is cleaned using an acidic liquid. The alkaline detergent may be any alkaline detergent and is not limited to a specific detergent, and the acidic liquid may be any acidic liquid and is not limited to a specific liquid. In the cleaning process, the coating surface 12 of the substrate 11 is cleaned using an alkaline detergent and then cleaned using an acidic liquid, thereby ensuring that dirt such as dust, oil, and organic matter adhering to the coating surface 12 of the substrate 11 is removed.

[0114] In the inorganic porous coating film forming step (P-2), an inorganic coating liquid containing inorganic fine particles 16 is coated (applied) onto the surface 12 of the cleaned substrate 11, and inorganic porous coating films 13a, 13b having an inorganic nanoporous structure with numerous nano-sized fine voids 15 created by a sol-gel method using at least one of silica sol, alumina sol, zirconia sol, titania sol, and ceria sol are formed on the coating surface 12 of the substrate 11. Prior to the inorganic porous coating film forming step (P-2), an inorganic coating liquid preparation step is carried out in which at least one of silica sol, alumina sol, zirconia sol, titania sol, and ceria sol is dissolved in an aqueous solution (e.g., pure water) to create an inorganic coating liquid.

[0115] The coating method for the coating surface 12 of the substrate 11 with the inorganic coating liquid can be any of the following coating methods: fabric coating (wiping coating method), in which the inorganic coating liquid is soaked into a fabric made of microfiber or nonwoven fabric and then the fabric is used to coat the coating surface 12 of the substrate 11 with the inorganic coating liquid; a spray coater (spray coating method), in which a spray can or spray gun containing the inorganic coating liquid is used to coat the coating surface 12 of the substrate 11 with the inorganic coating liquid; brush coating, in which a brush is used to coat the coating surface 12 of the substrate 11 with the inorganic coating liquid; a roll coater, in which a roll coated with the inorganic coating liquid is used to coat the coating surface 12 of the substrate 11 with the inorganic coating liquid; and a spin coater (spin coating method), in which the inorganic coating liquid is placed on the coating surface 12 of the substrate 11 and then the substrate 11 is rotated at high speed, thereby dispersing the inorganic coating liquid on the coating surface 12 of the substrate 11 using the centrifugal force generated by the spin coater.

[0116] In the inorganic porous coating film formation process (P-2), as described above, the inorganic coating liquid containing at least one type of inorganic fine particles 16 selected from silicon dioxide (SiO), aluminum oxide (AlO), zirconium oxide (ZrO), titanium oxide (TiO), and ceria oxide (CeO) is used. In the inorganic porous coating film formation process (P-2), the inorganic coating liquid is coated on the coating surface 12 of the substrate 11, and then the inorganic coating liquid is dried. In the inorganic porous coating film formation process (P-2), the dispersion medium (water or alcohol) contained in the inorganic coating liquid volatilizes, partially connecting the inorganic fine particles 16 together. The inorganic porous coating films 13a and 13b formed in the inorganic porous coating film formation process (P-2) have an inorganic nanoporous structure with numerous fine nano-sized pores 15 with a porosity ranging from 20% to 70%, as shown in FIGS. 1 and 4.

[0117] In the hydrophilic organic compound formation process (P-3), inorganic porous coating films 13a, 13b having an inorganic nanoporous structure with numerous fine voids 15 are formed on the coating surface 12 of the substrate 11, and then an organic coating liquid is coated (applied) onto the inorganic porous coating films 13a, 13b on the coating surface 12 of the substrate 11, thereby forming a hydrophilic organic compound 14 on the coating surface 12 of the substrate 11.

[0118] The organic coating liquid is applied to the inorganic porous coating films 13a, 13b (surface 12 of substrate 11) by any of the following coating methods: fabric coating, in which the organic coating liquid is soaked into fabric made from microfiber or nonwoven fabric and then the fabric is used to coat the surface 12 of substrate 11 with the organic coating liquid; a spray coater, in which a spray can or spray gun containing the organic coating liquid is used to coat the surface 12 of substrate 11 with the organic coating liquid; brush coating, in which a brush is used to coat the surface 12 of substrate 11 with the organic coating liquid; a roll coater, in which a roll coated with the organic coating liquid is used to coat the surface 12 of substrate 11 with the organic coating liquid; or a spin coater, in which the organic coating liquid is placed on the surface 12 of substrate 11 and then the substrate 11 is rotated at high speed, thereby dispersing the organic coating liquid on the surface 12 of substrate 11 by using the centrifugal force generated by the rotation.

[0119] As described above, the hydrophilic organic compound forming step (P-3) uses an organic coating liquid containing a dispersed hydrophilic organic compound 14 containing a betaine polymer having a cationic moiety and an anionic moiety in the same molecule. In the hydrophilic organic compound forming step (P-3), the organic coating liquid is coated onto the inorganic porous coating films 13a, 13b with a predetermined covering dimension so that the inorganic porous coating films 13a, 13b are not exposed from the surface of the hydrophilic organic compound 14, and the surfaces of the inorganic porous coating films 13a, 13b are covered with the organic coating liquid. Alternatively, the hydrophilic organic polymer coating liquid is coated onto the inorganic porous coating films 13a, 13b so that the top layer of the inorganic porous coating films 13a, 13b (inorganic fine particles 14) is exposed from the surface of the hydrophilic organic polymer coating liquid.

[0120] In the hydrophilic organic compound forming step (P-3), the organic coating liquid coated on the inorganic porous coating films 13a and 13b (the surface 12 of the substrate 11) and the hydrophilic organic compound 14 contained in the organic coating liquid penetrate into the numerous minute voids 15 of the inorganic porous coating films 13a and 13b. In the hydrophilic organic compound forming step (P-3), the organic coating liquid that has penetrated into the voids 15 is dried. The solvent in the organic coating liquid that has penetrated into the voids 15 of the inorganic porous coating films 13a and 13b volatilizes, solidifying the hydrophilic organic compound 14, and the hydrophilic organic compound 14 (hydrophilic organic film) bonds (bonds) to the voids 15 (inorganic fine particles 14) of the inorganic porous coating films 13a and 13b and the surface 12 of the substrate 11, thereby forming hydrophilic coating films 10A to 10D composed of the inorganic porous coating films 13a and 13b and the hydrophilic organic compound 14 (hydrophilic organic film).

[0121] When forming the hydrophilic coating films 10A to 10D in the hydrophilic organic compound formation process (P-3), the inorganic porous coating films 13a, 13b are not exposed from the surface of the hydrophilic organic compound 14, but the hydrophilic organic compound 14 (hydrophilic organic film) covers the surface of the inorganic porous coating films 13a, 13b (inorganic microparticles 16), and the inorganic porous coating films 13a, 13b are buried in the hydrophilic organic compound 14.

[0122] Furthermore, when forming the hydrophilic coating films 10A to 10D in the hydrophilic organic compound formation process (P-3), the top layer of the hydrophilic organic compound 14 (hydrophilic organic film) is located slightly below the surface of the inorganic porous coating films 13a, 13b, and the top layer of the inorganic porous coating films 13a, 13b (inorganic fine particles 16) is exposed above the top layer of the hydrophilic organic compound 14, and the portion (top layer) of the inorganic porous coating films 13a, 13b (inorganic fine particles 16) exposed above the top layer of the hydrophilic organic compound 14 forms fine irregularities on the surface of the hydrophilic organic compound 14, and the portion (top layer) forming the irregularities is coated with an extremely thin film of the hydrophilic organic compound 14 (hydrophilic organic film).

[0123] In the water washing step (P-4), water is poured onto the surfaces of the hydrophilic coating films 10A to 10D formed from the inorganic porous coating films 13a and 13b and the hydrophilic organic compound 14 (hydrophilic organic film), and the hydrophilic coating films 10A to 10D are washed with water. In the water washing step (P-4), the hydrophilic organic compound 14 that is weakly bonded to the inorganic porous coating films 13a and 13b, excluding the hydrophilic organic compound 14 that is firmly bonded to the inorganic porous coating films 13a and 13b, is washed away with water, thereby removing the hydrophilic organic compound 14 that does not contribute to the hydrophilicity of the hydrophilic coating films 10A to 10D.

[0124] The hydrophilic coating film forming method uses an inorganic coating liquid to form inorganic porous coating films (13a, 13b) in an inorganic porous coating film forming step (P-2), and forms inorganic porous coating films (13a, 13b) with an inorganic nanoporous structure having numerous nano-sized fine voids (15) by a sol-gel method. In addition, in a hydrophilic organic compound forming step (P-3), an organic coating liquid to form hydrophilic organic compounds (14) including a betaine polymer having cationic and anionic moieties in the same molecule is used. The organic coating liquid penetrates into the numerous fine voids (15) of the inorganic porous coating films (13a, 13b), and the hydrophilic organic compounds (14) form hydrophilic organic compounds (14) (hydrophilic organic films) on the surface (12) of the substrate (11). Therefore, it is possible to form hydrophilic coating films (10A-10D) that have excellent hydrophilicity and antifouling properties, have a small contact angle with the film surface, and can increase the contact area of ​​water with the film surface, and it is possible to form hydrophilic coating films (10A-10D) that can easily wash off adhering dirt with water.

[0125] In the hydrophilic coating film forming method, in the hydrophilic organic compound forming step (P-3), the hydrophilic organic compound 14 penetrates into the numerous minute voids 15 of the inorganic porous coating films 13a, 13b, and the hydrophilic organic compound 14 (hydrophilic organic film) bonds (bonds) to the voids 15 (inorganic fine particles 14) of the inorganic porous coating films 13a, 13b and the surface 12 of the substrate 11, thereby making it possible to form hydrophilic coating films 10A to 10D with excellent strength, and since the hydrophilic organic compound 14 will not peel off or disappear early from the hydrophilic coating films 10A to 10D due to stress from the usage environment, it is possible to form hydrophilic coating films 10A to 10D that can prevent a decrease in hydrophilicity and antifouling properties, and it is possible to form hydrophilic coating films 10A to 10D that can maintain the hydrophilic function and antifouling function provided by the hydrophilic organic compound 14 for a long period of time.

[0126] The hydrophilic coating film forming method includes a washing step (P-1) in which the coating surface 12 of the substrate 11 is washed with an alkaline detergent (e.g., an alkaline detergent with a pH of 8 to 9) and then washed with an acidic liquid (e.g., an acidic liquid with a pH of 1 to 2), thereby reliably removing contaminants such as dust, oil, and organic matter adhering to the coating surface 12 of the substrate 11, and forming hydrophilic coating films 10A to 10D with excellent hydrophilicity on the surface 12 of the substrate 11 from which the contaminants have been removed. The hydrophilic coating film forming method also includes a sol-gel process in which at least one of silica sol, alumina sol, zirconia sol, titania sol, and ceria sol is used to form inorganic porous coating films 13a and 13b having an inorganic nanoporous structure, thereby reliably forming inorganic coating films 10A to 10D with numerous nano-sized fine voids 15 on the coating surface 12 of the substrate 11.

[0127] In the hydrophilic coating film forming method, the inorganic porous coating films 13a, 13b are coated with an organic coating liquid so that the inorganic porous coating films 13a, 13b are not exposed from the surface of the hydrophilic organic compound 14 in the hydrophilic organic compound forming step (P-3), and when the hydrophilic coating films 10A to 10D are formed, the inorganic porous coating films 13a, 13b are buried in the hydrophilic organic compound 14, so that the hydrophilic coating films 10A to 10D can be produced in which the hydrophilic organic compound can remain for a long period of time.

[0128] In the hydrophilic coating film forming method, in the water washing step (P-4), excess hydrophilic organic compounds 14 weakly bonded to the voids 15 of the inorganic porous coating films 13a, 13b, excluding the hydrophilic organic compounds 14 bonded (bonded) to the voids 15 (inorganic fine particles 14) of the inorganic porous coating films 13a, 13b and the surface 12 of the substrate 11, are washed away with water, thereby removing the hydrophilic organic compounds 14 that do not contribute to the hydrophilicity of the hydrophilic coating films 10A to 10D, thereby making it possible to produce hydrophilic coating films 10A to 10D containing hydrophilic organic compounds 14 that are strongly bonded (bonded) to the voids 15 (inorganic fine particles 14) of the inorganic porous coating films 13a, 13b and the surface 12 of the substrate 11, and that have excellent hydrophilicity and antifouling properties.

[0129] The hydrophilic coating films 10A to 10D produced by the hydrophilic coating film forming method are formed from inorganic porous coating films 13a, 13b having numerous nano-sized fine voids 15, and hydrophilic organic compounds 14 (hydrophilic organic films) that have penetrated into the voids 15 of the inorganic porous coating films 13a, 13b, as shown in Figures 2, 3, 5 and 6.

[0130] In the hydrophilic coating film 10A shown in FIG. 2, the hydrophilic organic compound 14 penetrates into a large number of minute nano-sized voids 15 in the inorganic porous coating film 13a formed by partially connecting a large number of adjacent, approximately spherical inorganic fine particles 16, and the hydrophilic organic compound 14 (hydrophilic organic film) is bonded (joined) to the inorganic fine particles 16 forming the inorganic porous coating film 13a and the surface 12 of the substrate 11, and the hydrophilic organic compound 14 covers the surface of the inorganic porous coating film 13a, so that the inorganic porous coating film 13a is embedded in the hydrophilic organic compound 14 (hydrophilic organic film).

[0131] In the hydrophilic coating film 10B shown in FIG. 3, the hydrophilic organic compound 14 penetrates into the numerous nano-sized micropores 15 of the inorganic porous coating film 13a of FIG. 1, and the hydrophilic organic compound 14 (hydrophilic organic film) is bonded (joined) to the inorganic fine particles 16 forming the inorganic porous coating film 13a and the surface 12 of the substrate 11, and the top layer of the hydrophilic organic compound 14 is located slightly below the surface of the inorganic porous coating film 13a, and the top layer of the inorganic porous coating film 13a (inorganic fine particles 16) is exposed above the top layer of the hydrophilic organic compound 14 (hydrophilic organic film). In the hydrophilic coating film 10B of FIG. 3, the portion (top layer) of the inorganic porous coating film 13a (inorganic fine particles 16) exposed upward from the top layer of the hydrophilic organic compound 14 (hydrophilic organic film) forms fine irregularities on the surface of the hydrophilic coating film 10B, and the portion (top layer) forming the irregularities is coated with an extremely thin film of the hydrophilic organic compound 14 (hydrophilic organic film).

[0132] In the hydrophilic coating film 10C shown in Figure 5, the hydrophilic organic compound 14 penetrates into the numerous nano-sized micropores 15 of the inorganic porous coating film 13b in Figure 4, the hydrophilic organic compound 14 (hydrophilic organic film) is bonded (joined) to the inorganic fine particles 16 forming the inorganic porous coating film 13a and the surface 12 of the substrate 11, the hydrophilic organic compound 14 covers the surface of the inorganic porous coating film 13b, and the inorganic porous coating film 13b is embedded in the hydrophilic organic compound 14 (hydrophilic organic film).

[0133] In the hydrophilic coating film 10D shown in Figure 6, the hydrophilic organic compound 14 penetrates into the numerous nano-sized micropores 15 of the inorganic porous coating film 13b of Figure 4, and the hydrophilic organic compound 14 (hydrophilic organic film) is bonded (joined) to the inorganic fine particles 14 forming the inorganic porous coating film 13a and the surface 12 of the substrate 11, and the top layer of the hydrophilic organic compound 14 is located slightly below the surface of the inorganic porous coating film 13b, and the top layer of the inorganic porous coating film 13b (inorganic fine particles 16) is exposed above the top layer of the hydrophilic organic compound 14 (hydrophilic organic film). In the hydrophilic coating film 10D of FIG. 6, the portion (top layer) of the inorganic porous coating film 13b (inorganic fine particles 16) exposed upward from the top layer of the hydrophilic organic compound 14 (hydrophilic organic film) forms fine irregularities on the surface of the hydrophilic coating film 10D, and the portion (top layer) forming the irregularities is coated with an extremely thin film of the hydrophilic organic compound 14 (hydrophilic organic film).

[0134] In the hydrophilic coating films 10A to 10D, the porosity of the voids 15 formed in the inorganic porous coating films 13a and 13b is in the range of 20% to 70% of the volume of the inorganic porous coating films 13a and 13b. If the porosity of the voids 15 is less than 20%, the voids 15 formed in the inorganic porous coating films 13a and 13b are small, and the hydrophilicity and antifouling properties of the hydrophilic organic compound 14 (hydrophilic organic film) that penetrates into the voids 15 of the inorganic porous coating films 13a and 13b cannot be fully utilized, and excellent hydrophilicity and antifouling properties cannot be imparted to the hydrophilic coating films 10A to 10D formed from the inorganic porous coating films 13a and 13b and the hydrophilic organic compound 14. If the porosity of the voids 15 exceeds 70%, the inorganic porous coating films 13a, 13b become fragile, the strength of the hydrophilic coating films 10A to 10D formed from the inorganic porous coating films 13a, 13b and the hydrophilic organic compound 14 (hydrophilic organic film) decreases, and the hydrophilic coating films 10A to 10D cannot adequately protect the surface 12 of the substrate 11.

[0135] Since the porosity of the voids 15 formed in the inorganic porous coating films 13a, 13b of the hydrophilic coating films 10A to 10D is within the above range, a sufficient number of fine voids 15 are formed in the inorganic porous coating films 13a, 13b, the hydrophilic organic compound 14 can penetrate into these voids 15, and the excellent hydrophilicity and antifouling properties of the hydrophilic organic compound 14 (hydrophilic organic film) can be fully utilized, imparting excellent hydrophilicity and antifouling properties to the hydrophilic coating films 10A to 10D, and the hydrophilic coating films 10A to 10D have sufficient strength, so that the hydrophilic coating films 10A to 10D can fully protect the coating surface 12 of the substrate 11.

[0136] The hydrophilic coating films 10A to 10D have a ratio of betaine polymer to the total mass of the hydrophilic organic compound 14 constituting them of 20% or more. If the ratio of betaine polymer to the total mass of the hydrophilic organic compound 14 is less than 20%, the content of betaine polymer in the hydrophilic organic compound 14 is low, and the hydrophilic function of the betaine polymer cannot be fully utilized. Therefore, the hydrophilic organic compound 14 made from the organic coating liquid cannot exhibit sufficient hydrophilicity or antifouling properties, and excellent hydrophilicity or antifouling properties cannot be imparted to the hydrophilic coating films 10A to 10D formed from the inorganic porous coating films 13a, 13b and the hydrophilic organic compound 14 (hydrophilic organic film).

[0137] In the hydrophilic coating films 10A to 10D, the ratio of the betaine polymer, which has a cationic moiety and an anionic moiety in the same molecule, to the hydrophilic organic compound 14 is within the above-mentioned range, so that the organic coating liquid contains a sufficient amount of the betaine polymer, making it possible to fully utilize the excellent hydrophilicity of the betaine polymer, and the hydrophilic organic compound 14 made from the organic coating liquid exhibits sufficient hydrophilicity and antifouling properties, thereby imparting excellent hydrophilicity and antifouling properties to the hydrophilic coating films 10A to 10D formed from the inorganic porous coating films 13a, 13b and the hydrophilic organic compound 14 (hydrophilic organic film).

[0138] The thickness of the hydrophilic coating films 10A to 10D is in the range of 0.01 μm or more and 3 μm or less, preferably in the range of 0.1 μm or more and 0.6 μm or less. If the thickness of the hydrophilic coating films 10A to 10D is less than 0.01 μm, the strength of the hydrophilic coating films 10A to 10D decreases, and the hydrophilic coating films 10A to 10D cannot sufficiently protect the coating surface 12 of the substrate 11. If the thickness of the hydrophilic coating films 10A to 10D exceeds 3 μm, the film thickness becomes unnecessarily thick, the flexibility of the hydrophilic coating films 10A to 10D decreases, and the hydrophilic coating films 10A to 10D cannot follow the deformation of the coating surface 12 of the substrate 11.

[0139] Since the thickness of the hydrophilic coating films 10A to 10D is within the above range, the hydrophilic coating films 10A to 10D maintain a predetermined strength and can adequately protect the coating surface 12 of the substrate 11, and the hydrophilic coating films 10A to 10D have excellent flexibility and can follow the deformation of the coating surface 12 of the substrate 11, thereby maintaining the coating state of the hydrophilic coating films 10A to 10D on the coating surface 12 of the substrate 11.

[0140] The hydrophilic coating films 10A to 10D each include inorganic porous coating films 13a and 13b containing at least one type of inorganic fine particles 16 selected from silicon dioxide (SiO), aluminum oxide (AlO), zirconium oxide (ZrO), titanium oxide (TiO), and cerium oxide (CeO). When the inorganic porous coating films 13a and 13b of the hydrophilic coating films 10A to 10D contain inorganic fine particles 16 of silicon dioxide (SiO), the hydrophilic organic compound 14 easily bonds to the silicon dioxide, and the hydrophilic organic compound 14 that has infiltrated into the numerous minute voids 15 of the inorganic porous coating films 13a and 13b easily bonds to the voids 15 containing silicon dioxide, thereby enabling the hydrophilic organic compound 14 (hydrophilic organic film) to be firmly bonded to the voids 15 of the inorganic porous coating films 13a and 13b.

[0141] When the inorganic porous coating films 13a, 13b of the hydrophilic coating films 10A to 10D contain inorganic fine particles 16 of aluminum oxide (Al2O3), the hydrophilic organic compound 14 easily bonds with the aluminum oxide, and the hydrophilic organic compound 14 (hydrophilic organic film) that has penetrated into the numerous minute voids 15 of the inorganic porous coating films 13a, 13b can be firmly bonded to the voids 15 containing the aluminum oxide.In addition, the aluminum oxide makes it difficult for salts such as magnesium, calcium, sodium, silicon, etc. to adhere to the hydrophilic coating films 10A to 10D, so that contamination of the hydrophilic coating films 10A to 10D due to adhesion of salts such as magnesium, calcium, sodium, silicon, etc. to the hydrophilic coating films 10A to 10D can be prevented.

[0142] When the inorganic porous coating films 13a, 13b contain inorganic particles 16 of zirconium oxide (ZrO2), the hardness of the inorganic porous coating films 13a, 13b can be increased, thereby improving the rigidity of the hydrophilic coating films 10A-10D. When the inorganic porous coating films 13a, 13b contain inorganic particles 16 of titanium oxide (TiO2), the surfaces of the hydrophilic coating films 10A-10D are coated with hydrophilic groups when the inorganic particles 16 of titanium oxide are exposed to light and water, thereby imparting an excellent self-cleaning effect to the hydrophilic coating films 10A-10D.

[0143] When the inorganic porous coating films 13a, 13b contain inorganic microparticles 16 of cerium oxide (CeO2), the hydrophilic coating films 10A to 10D can have increased hardness due to the cerium oxide and can also have ultraviolet absorbing ability, thereby increasing the rigidity of the hydrophilic coating films 10A to 10D and providing ultraviolet absorbing ability.

[0144] Fig. 8 is a diagram showing the contact angle θ of the water droplet W dropped on the hydrophilic coating film 10A of Fig. 2, and Fig. 9 is a diagram showing the contact angle θ of the water droplet W dropped on the hydrophilic coating film 10B of Fig. 3. Fig. 10 is a diagram showing the contact angle θ of the water droplet W dropped on the hydrophilic coating film 10C of Fig. 5, and Fig. 11 is a diagram showing the contact angle θ of the water droplet W dropped on the hydrophilic coating film 10D of Fig. 6.

[0145] The hydrophilic coating films 10A to 10D shown in Figures 2, 3, 5, and 6 have a contact angle θ of a water droplet W of 10° or less. The contact angle θ of a water droplet W on the hydrophilic coating films 10A to 10D was measured based on JIS R3257 (Testing method for wettability of substrate glass surfaces). For the JIS R3257 wettability test, a test piece, a sample stage, an illumination device (light source), an optical reader, and a syringe were prepared. The sample stage had a mechanism for moving the position of the sample stage up and down and left and right so that a water droplet placed on the test piece was centered on the optical axis of the illumination device and the optical reader. The illumination device formed an image of the water droplet on the test piece within the field of view of the optical reader. The syringe barrel had a capacity of 1 ml or less.

[0146] The conditions for the wettability test are room temperature: 25±5°C, humidity: 50±10%, water droplet volume: 1 μl, measurement time: 30 seconds, and water used: distilled water. The wettability test operating procedure is as follows: (1) Calibrate the test equipment using the prescribed method. (2) Place the test piece with hydrophilic coating films 10A and 10B on the test table. (3) Pour distilled water into a clean glass beaker and collect this distilled water into the barrel of a syringe. (4) Place the distilled water in the syringe as a water droplet W on the test piece on the sample table. Quickly measure the r and h of the water droplet W. Alternatively, read θ / 2. (5) Measurements should be made at a minimum of five locations.

[0147] The wettability was expressed as the average value and standard deviation of data from five or more locations for the contact angle θ calculated based on the following (Equation 1) or the contact angle θ obtained from a direct reading of θ / 2.

[0148] (Equation 1): θ = 2tan -1 h / r

[0149] In (Equation 1), r is the radius (mm) of the surface of the water drop W that is in contact with the test piece, and h is the height (mm) from the surface of the test piece to the top of the water drop W.

[0150] The hydrophilic coating films 10A to 10D have a contact angle θ of a water droplet W of 10° or less as measured in accordance with JIS R3257, and therefore have excellent hydrophilicity and antifouling properties. The contact angle of water with the film surface of the hydrophilic coating films 10A to 10D is small, and the contact area of ​​water with the film surface of the hydrophilic coating films 10A to 10D can be increased. When the hydrophilic coating films 10A to 10D are washed with water, the water comes into contact with a wide area of ​​the film surface of the hydrophilic coating films 10A to 10D, and therefore dirt adhering to the hydrophilic coating films 10A to 10D can be easily washed away with water.

[0151] In addition, in the hydrophilic coating films 10B and 10D, the portion (uppermost layer) of the inorganic porous coating film 13b (inorganic fine particles 16) that is exposed upward from the uppermost layer of the hydrophilic organic polymer 14 (hydrophilic organic film) forms fine irregularities on the surface of the hydrophilic coating films 10B and 10D. This irregularity further increases the contact area with water, making it possible to easily and reliably wash away dirt adhering to the hydrophilic coating films 10B and 10D with water.

[0152] The hydrophilic coating films (10A-10D) have an inorganic nanoporous structure in which inorganic porous coating films (13a, 13b) are formed by a sol-gel method using at least one of silica sol, alumina sol, zirconia sol, titania sol, and ceria sol, and the hydrophilic organic compound (14) penetrates into the numerous fine voids (15) of the inorganic porous coating films (13a, 13b), and the hydrophilic organic compound (14) (hydrophilic organic film) is bonded (joined) to the voids (15) (inorganic fine particles (14)) of the inorganic porous coating films (13a, 13b) and the surface (12) of the substrate (11). Therefore, the hydrophilic coating films (10A-10D) have excellent strength, and the hydrophilic organic compound (14) is not prematurely peeled off or lost from the hydrophilic coating films (10A-10D) due to stress caused by the usage environment. This prevents the hydrophilicity and antifouling properties of the hydrophilic coating films (10A-10D) from decreasing, and the hydrophilic function and antifouling function provided by the hydrophilic organic compound (14) can be maintained for a long period of time.

[0153] In the hydrophilic coating films (10A-10D), the hydrophilic organic compound (14) contains a betaine polymer having a cationic moiety and an anionic moiety in the same molecule, so that the hydrophilic organic compound (14) exhibits excellent hydrophilicity and antifouling properties, thereby reliably reducing the contact angle of water with the film surface of the hydrophilic coating films (10A-10D) and reliably increasing the contact area of ​​water with the film surface of the hydrophilic coating films (10A-10D).In addition, when the hydrophilic coating films (10A-10D) are washed with water, the water comes into contact with a wide area of ​​the film surface of the hydrophilic coating films (10A-10D), so that dirt adhering to the hydrophilic coating films (10A-10D) can be easily washed away with water.

[0154] FIG. 12 shows examples 1 to 4 of hydrophilic coating films 10A to 10D, and FIG. 13 shows examples 5 to 8 of hydrophilic coating films 10A to 10D. FIG. 14 shows comparative examples 1 to 4 of hydrophilic coating films, and FIG. 15 shows comparative examples 5 to 8 of hydrophilic coating films. The hydrophilic coating films 10A to 10D shown in example 1 of FIG. 12 have inorganic porous coating films 13a and 13b forming them with a thickness of 300 nm. An inorganic coating solution was used, containing silica nanoparticles with an average particle size of 55 nm and a solids concentration of 1 wt % and a silica sol solution with a solids concentration of 0.5 wt %. The content of the hydrophilic organic compound 14 in the organic coating liquid was 2 wt %, and the proportion of betaine polymer in the hydrophilic organic compound 14 was 30%.

[0155] The synthesis method for hydrophilic organic compound 14 is as follows. Under nitrogen, 9.9 mmol of 2-(methacryloyloxy)ethyl 2-(trimethylammonio)ethyl phosphate, 0.1 mmol of 3-mercaptopropyltrimethoxysilane, and water were added to a recovery flask to a concentration of 20 wt%. Next, 0.1 mmol of 2,2'-azobis-2-methyl-N-2-hydroxyethylpropionamide was added and stirred at 55°C for 3 hours to obtain a betaine polymer solution. Similarly, 9.9 mmol of 2-hydroxyethyl methacrylate, 0.1 mmol of 3-mercaptopropyltrimethoxysilane, and water were added to a concentration of 20 wt%. Next, 0.1 mmol of 2,2'-azobis-2-methyl-N-2-hydroxyethylpropionamide was added and stirred at 55°C for 3 hours to obtain a hydrophilic polymer solution. These were mixed and water was added to obtain a 2 wt% hydrophilic coating solution containing 30% betaine polymer.

[0156] The inorganic and organic coating solutions were coated onto fabric using microfibers. An XVision 200TB (manufactured by SII NanoTechnology Inc.) or a JEOL JSM-5500 (manufactured by JEOL Ltd.) scanning electron microscope (SEM) was used. Cross-sectional SEM observation confirmed that the film thickness was 300 nm. Surface SEM observation also revealed a porosity of 42%.

[0157] The hydrophilic coating films 10A to 10D shown in Example 2 have inorganic porous coating films 13a and 13b each having a thickness of 300 nm. An inorganic coating solution containing silica nanoparticles with an average particle size of 55 nm and a solid content of 5 wt % and a silica sol solution with a solid content of 2.5 wt % was used. The content of the hydrophilic organic compound 14 in the organic coating liquid is 2 wt %, and the ratio of the betaine polymer in the hydrophilic organic compound 14 is 35%.

[0158] The synthesis method for hydrophilic organic compound 14 is as follows. Under nitrogen, 9.9 mmol of 3-{[2-(methacryloyloxy)ethyl]dimethylammonio}propane-1-sulfonic acid, 0.1 mmol of 3-mercaptopropyltrimethoxysilane, and water were added to a recovery flask to a concentration of 20 wt%. Next, 0.1 mmol of 2,2'-azobis-2-methyl-N-2-hydroxyethylpropionamide was added and the mixture was stirred and heated at 55°C for 3 hours to obtain a betaine polymer solution. Similarly, 10 mmol of isopropylacrylamide and water were added to a concentration of 20 wt%. Next, 0.1 mmol of 2,2'-azobis-2-methyl-N-2-hydroxyethylpropionamide was added and the mixture was stirred and heated at 55°C for 3 hours to obtain a hydrophilic polymer solution.

[0159] The inorganic and organic coating solutions were coated onto fabric using microfibers. These were mixed and water was added to obtain a 2 wt% hydrophilic coating solution containing 35% betaine polymer. Cross-sectional SEM observation revealed a film thickness of 300 nm, and surface SEM observation revealed a porosity of 28%.

[0160] The hydrophilic coating films 10A to 10D shown in Example 3 have inorganic porous coating films 13a and 13b each having a thickness of 200 nm. An inorganic coating solution containing silica nanoparticles with an average particle size of 12 nm and a solids concentration of 10 wt % and a silica sol solution with a solids concentration of 5 wt % was used. The content of the hydrophilic organic compound 14 in the organic coating solution was 2 wt %, and the proportion of betaine polymer in the hydrophilic organic compound 14 was 30%.

[0161] The synthesis method for hydrophilic organic compound 14 is as follows. Under nitrogen, 10 mmol of 2-{[2-(methacryloyloxy)ethyl]dimethylammonio}acetic acid and water were added to a recovery flask to a concentration of 20 wt%. Next, 0.1 mmol of 2,2'-azobis-2-methyl-N-2-hydroxyethylpropionamide was added and stirred at 55°C for 3 hours to obtain a betaine polymer solution. Similarly, 10.0 mmol of 2-hydroxyethyl methacrylate and water were added to a concentration of 20 wt%. Next, 0.1 mmol of 2,2'-azobis-2-methyl-N-2-hydroxyethylpropionamide was added and stirred at 55°C for 3 hours to obtain a hydrophilic polymer solution. These were mixed and water was added to obtain a 2 wt% hydrophilic coating solution containing 30% betaine polymer.

[0162] The inorganic and organic coating solutions were coated on fabric using microfibers. Cross-sectional SEM observation revealed that the film thickness was 200 nm, and surface SEM observation revealed that the porosity was 52%.

[0163] The hydrophilic coating films 10A to 10D shown in Example 4 have inorganic porous coating films 13a and 13b each having a thickness of 150 nm. An inorganic coating solution containing silica nanoparticles with an average particle size of 20 nm and a solids concentration of 2 wt % and a silica sol solution with a solids concentration of 1 wt % was used. The content of the hydrophilic organic compound 14 in the organic coating solution was 2 wt %, and the proportion of betaine polymer in the hydrophilic organic compound 14 was 30%.

[0164] The synthesis method for hydrophilic organic compound 14 is as follows. Under nitrogen, 9.9 mmol of 3-[(3-acrylamidopropyl)dimethylammonio]propanoate, 0.1 mmol of 3-mercaptopropyltrimethoxysilane, and water were added to a recovery flask to a concentration of 20 wt%. Next, 0.1 mmol of 2,2'-azobis-2-methyl-N-2-hydroxyethylpropionamide was added and stirred at 55°C for 3 hours to obtain a betaine polymer solution. Similarly, 9.9 mmol of isopropylacrylamide, 0.1 mmol of 3-mercaptopropyltrimethoxysilane, and water were added to a concentration of 20 wt%. Next, 0.1 mmol of 2,2'-azobis-2-methyl-N-2-hydroxyethylpropionamide was added and stirred at 55°C for 3 hours to obtain a hydrophilic polymer solution. These were mixed and water was added to obtain a 2 wt% hydrophilic coating solution containing 30% betaine polymer.

[0165] The inorganic and organic coating solutions were coated on fabric using microfibers. Cross-sectional SEM observation revealed that the film thickness was 150 nm, and surface SEM observation revealed that the porosity was 65%.

[0166] The hydrophilic coating films 10A to 10D shown in Example 5 have inorganic porous coating films 13a and 13b each having a thickness of 250 nm. An inorganic coating solution containing silica nanoparticles with an average particle size of 12 nm and a solids concentration of 5 wt% and a silica sol solution with a solids concentration of 2.5 wt% was used. The content of the hydrophilic organic compound 14 in the organic coating solution was 2 wt%, and the proportion of betaine polymer in the hydrophilic organic compound 14 was 100%.

[0167] The synthesis method for hydrophilic organic compound 14 is as follows. Under nitrogen, 10 mmol of 2-{[2-(methacryloyloxy)ethyl]dimethylammonio}acetic acid and water were added to a recovery flask to make a 20 wt% solution. Next, 0.1 mmol of 2,2'-azobis-2-methyl-N-2-hydroxyethylpropionamide was added and the mixture was stirred and heated at 55°C for 3 hours to obtain a betaine polymer solution. Water was added to this solution to obtain a 2 wt% hydrophilic coating solution containing 100% betaine polymer. The inorganic and organic coating solutions were coated on fabric using microfibers. Cross-sectional SEM observation revealed that the film thickness was 250 nm, and surface SEM observation revealed that the porosity was 44%.

[0168] The hydrophilic coating films 10A to 10D shown in Example 6 have inorganic porous coating films 13a and 13b each having a thickness of 320 nm. An inorganic coating solution containing alumina nanoparticles with an average particle size of 30 nm and a solids concentration of 5 wt% and an alumina sol solution with a solids concentration of 2.5 wt% was used. The content of the hydrophilic organic compound 14 in the organic coating solution was 2 wt%, and the proportion of betaine polymer in the hydrophilic organic compound 14 was 100%.

[0169] The synthesis method for hydrophilic organic compound 14 is as follows. Under nitrogen, 10 mmol of 3-[(3-acrylamidopropyl)dimethylammonio]propanoate and water were added to a recovery flask to a concentration of 20 wt%. Next, 0.1 mmol of 2,2'-azobis-2-methyl-N-2-hydroxyethylpropionamide was added and the mixture was stirred and heated at 55°C for 3 hours to obtain a betaine polymer solution. Water was added to this solution to obtain a 2 wt% hydrophilic coating solution containing 100% betaine polymer.

[0170] The inorganic and organic coating solutions were coated on fabric using microfibers. Cross-sectional SEM observation revealed that the film thickness was 320 nm, and surface SEM observation revealed that the porosity was 48%.

[0171] The hydrophilic coating films 10A to 10D shown in Example 7 have inorganic porous coating films 13a and 13b each having a thickness of 180 nm. An inorganic coating solution containing zirconia nanoparticles with an average particle size of 12 nm and a solids concentration of 5 wt% and a zirconia sol solution with a solids concentration of 2.5 wt% was used. The content of the hydrophilic organic compound 14 in the organic coating solution was 2 wt%, and the proportion of betaine polymer in the hydrophilic organic compound 14 was 100%.

[0172] The synthesis method for hydrophilic organic compound 14 is as follows. Under nitrogen, 10 mmol of 2-(methacryloyloxy)ethyl 2-(trimethylammonio)ethyl phosphate was added to a recovery flask with water to a concentration of 20 wt%. Next, 0.1 mmol of 2,2'-azobis 2-methyl-N-2-hydroxyethylpropionamide was added and the mixture was stirred and heated at 55°C for 3 hours to obtain a betaine polymer solution. Water was added to this solution to obtain a 2 wt% hydrophilic coating solution containing 100% betaine polymer.

[0173] The inorganic and organic coating solutions were coated on fabric using microfibers. Cross-sectional SEM observation revealed that the film thickness was 180 nm, and surface SEM observation revealed that the porosity was 52%.

[0174] The hydrophilic coating films 10A to 10D shown in Example 8 have inorganic porous coating films 13a and 13b each having a thickness of 220 nm. An inorganic coating solution containing silica nanoparticles with an average particle size of 12 nm and a solids concentration of 5 wt% and silica nanosol with a solids concentration of 2.5 wt% was used. The content of the hydrophilic organic compound 14 in the organic coating solution was 2 wt%, and the proportion of betaine polymer in the hydrophilic organic compound 14 was 100%.

[0175] The synthesis method for hydrophilic organic compound 14 is as follows. Under nitrogen, 9.9 mmol of 3-{[2-(methacryloyloxy)ethyl]dimethylammonio}propane-1-sulfonic acid and 0.1 mmol of 3-mercaptopropyltrimethoxysilane were added to a recovery flask with water to a concentration of 20 wt%. Next, 0.1 mmol of 2,2'-azobis-2-methyl-N-2-hydroxyethylpropionamide was added and the mixture was stirred and heated at 55°C for 3 hours to obtain a betaine polymer solution. Water was added to this solution to obtain a 2 wt% hydrophilic coating solution containing 100% betaine polymer.

[0176] The inorganic and organic coating solutions were coated on fabric using microfibers. Cross-sectional SEM observation revealed that the film thickness was 220 nm, and surface SEM observation revealed that the porosity was 47%.

[0177] The hydrophilic coating films 10A to 10D shown in Examples 1 to 4 had a contact angle θ of a water droplet W of ○ (20° or less, good) or ◎ (10° or less, even better) immediately after the coating films 10A to 10D were formed on the coating surface 12 of the substrate 11, a contact angle θ of a water droplet W of ○ (20° or less, good) or ◎ (10° or less, even better) six months after the coating films 10A to 10D were formed on the coating surface 12 of the substrate 11, and the transparency of the coating films 10A to 10D was ○ (no turbidity, good).

[0178] The hydrophilic coating film shown in Comparative Example 1 of Figure 14 has an inorganic porous coating film that is 3000 nm thick. Silica nanoparticles with average particle sizes of 1500 nm, 60 nm, and 12 nm were mixed to a solids concentration of 3 wt%, and an inorganic coating solution containing a silica sol solution with a solids concentration of 1.5 wt% was used. The content of the hydrophilic organic compound in the organic coating solution was 2 wt%, and the proportion of betaine polymer in the hydrophilic organic compound was 30%.

[0179] The synthesis method for hydrophilic organic compound 14 is as follows. Under nitrogen, 9.9 mmol of 2-(methacryloyloxy)ethyl 2-(trimethylammonio)ethyl phosphate, 0.1 mmol of 3-mercaptopropyltrimethoxysilane, and water were added to a recovery flask to a concentration of 20 wt%. Next, 0.1 mmol of 2,2'-azobis-2-methyl-N-2-hydroxyethylpropionamide was added and stirred at 55°C for 3 hours to obtain a betaine polymer solution. Similarly, 9.9 mmol of 2-hydroxyethyl methacrylate, 0.1 mmol of 3-mercaptopropyltrimethoxysilane, and water were added to a concentration of 20 wt%. Next, 0.1 mmol of 2,2'-azobis-2-methyl-N-2-hydroxyethylpropionamide was added and stirred at 55°C for 3 hours to obtain a hydrophilic polymer solution. These were mixed and water was added to obtain a 2 wt% hydrophilic coating solution containing 30% betaine polymer.

[0180] The inorganic coating liquid and the organic coating liquid were coated using a spin coater. Cross-sectional SEM observation immediately after coating revealed a film thickness of 3000 nm, and SEM observation of the surface revealed a porosity of 18%. The hydrophilic coating film shown in Comparative Example 1 had a contact angle θ of a water droplet W of × (over 20°, poor) immediately after the coating film was formed on the surface 12 of the substrate 11, and a contact angle θ of a water droplet W of × (over 20°, poor) six months after the coating film was formed on the surface 12 of the substrate 11.

[0181] The hydrophilic coating film shown in Comparative Example 2 in Figure 14 has an inorganic porous coating film with a thickness of 1000 (nm). An inorganic coating solution containing silica nanoparticles with an average particle diameter of 55 (nm) and a solid content of 3 (wt%) and a silica sol solution with a solid content of 1.5 (wt%) was used. No organic coating liquid was applied. The inorganic coating liquid and organic coating liquid were coated by fabric coating using microfibers. Cross-sectional SEM observation immediately after coating revealed a film thickness of 1000 nm, and SEM observation of the surface revealed a porosity of 44%. The hydrophilic coating film shown in Comparative Example 2 had a contact angle θ of a water droplet W of × (over 20°, poor) six months after the coating film was formed on the surface 12 of the substrate 11.

[0182] The hydrophilic coating film shown in Comparative Example 3 in Figure 14 has an inorganic porous coating film with a thickness of 10,000 nm. An inorganic coating solution was used, containing silica nanoparticles with an average particle size of 55 nm and a solids concentration of 3 wt% and a silica sol solution with a solids concentration of 1.5 wt%. The content of the hydrophilic organic compound in the organic coating solution was 2 wt%, and the proportion of betaine polymer in the hydrophilic organic compound was 30%.

[0183] The synthesis method for hydrophilic organic compound 14 is as follows. Under nitrogen, 9.9 mmol of 3-{[2-(methacryloyloxy)ethyl]dimethylammonio}propane-1-sulfonic acid, 0.1 mmol of 3-mercaptopropyltrimethoxysilane, and water were added to a recovery flask to a concentration of 20 wt%. Next, 0.1 mmol of 2,2'-azobis-2-methyl-N-2-hydroxyethylpropionamide was added and stirred at 55°C for 3 hours to obtain a betaine polymer solution. Similarly, 10 mmol of isopropylacrylamide and water were added to a concentration of 20 wt%. Next, 0.1 mmol of 2,2'-azobis-2-methyl-N-2-hydroxyethylpropionamide was added and stirred at 55°C for 3 hours to obtain a hydrophilic polymer solution. These were mixed and water was added to obtain a 2 wt% hydrophilic coating solution containing 30% betaine polymer.

[0184] The coating method for the inorganic coating liquid and the organic coating liquid was fabric coating using microfibers. Cross-sectional SEM observation revealed that the film thickness was 10,000 nm, and surface SEM observation revealed that the porosity was 52%. The hydrophilic coating film shown in Comparative Example 2 had a coating film transparency of × (cloudy, poor).

[0185] The hydrophilic coating film shown in Comparative Example 4 in Figure 14 has an inorganic porous coating film with a thickness of 10,000 nm. An inorganic coating solution was used, containing silica nanoparticles with an average particle size of 55 nm and a solids concentration of 0.2 wt% and a silica sol solution with a solids concentration of 0.1 wt%. The content of the hydrophilic organic compound in the organic coating solution was 2 wt%, and the proportion of betaine polymer in the hydrophilic organic compound was 30%.

[0186] The synthesis method for hydrophilic organic compound 14 is as follows. Under nitrogen, 10 mmol of 2-{[2-(methacryloyloxy)ethyl]dimethylammonio}acetic acid and water were added to a recovery flask to a concentration of 20 wt%. Next, 0.1 mmol of 2,2'-azobis-2-methyl-N-2-hydroxyethylpropionamide was added and stirred at 55°C for 3 hours to obtain a betaine polymer solution. Similarly, 10.0 mmol of 2-hydroxyethyl methacrylate and water were added to a concentration of 20 wt%. Next, 0.1 mmol of 2,2'-azobis-2-methyl-N-2-hydroxyethylpropionamide was added and stirred at 55°C for 3 hours to obtain a hydrophilic polymer solution. These were mixed and water was added to obtain a 2 wt% hydrophilic coating solution containing 30% betaine polymer.

[0187] The coating method for the inorganic coating liquid and the organic coating liquid was fabric coating using microfibers. Cross-sectional SEM observation revealed that the film thickness was 10,000 nm, and surface SEM observation revealed that the porosity was 75%. For the hydrophilic coating film shown in Comparative Example 4, the contact angle θ of a water droplet W immediately after the coating film was formed on the surface 12 of the substrate 11 was × (over 20°, poor), the contact angle θ of a water droplet W six months after the coating film was formed on the surface 12 of the substrate 11 was × (over 20°, poor), and the transparency of the coating film was × (cloudy, poor).

[0188] The hydrophilic coating film shown in Comparative Example 5 in Figure 15 has an inorganic porous coating film with a thickness of 500 nm. An inorganic coating solution containing silica nanoparticles with an average particle size of 12 nm and a solids concentration of 60 wt% and a silica sol solution with a solids concentration of 30 wt% was used. The content of the hydrophilic organic compound in the organic coating solution was 2 wt%, and the proportion of betaine polymer in the hydrophilic organic compound was 30%.

[0189] The synthesis method for hydrophilic organic compound 14 is as follows. Under nitrogen, 9.9 mmol of 3-[(3-acrylamidopropyl)dimethylammonio]propanoate, 0.1 mmol of 3-mercaptopropyltrimethoxysilane, and water were added to a recovery flask to a concentration of 20 wt%. Next, 0.1 mmol of 2,2'-azobis-2-methyl-N-2-hydroxyethylpropionamide was added and stirred at 55°C for 3 hours to obtain a betaine polymer solution. Similarly, 9.9 mmol of isopropylacrylamide, 0.1 mmol of 3-mercaptopropyltrimethoxysilane, and water were added to a concentration of 20 wt%. Next, 0.1 mmol of 2,2'-azobis-2-methyl-N-2-hydroxyethylpropionamide was added and stirred at 55°C for 3 hours to obtain a hydrophilic polymer solution. These were mixed and water was added to obtain a 2 wt% hydrophilic coating solution containing 30% betaine polymer.

[0190] The coating method for the inorganic coating liquid and the organic coating liquid was fabric coating using microfibers. Cross-sectional SEM observation revealed that the film thickness was 500 nm, and surface SEM observation revealed that the porosity was 38%. The hydrophilic coating film shown in Comparative Example 5 had a coating film transparency of × (cloudy, poor).

[0191] The hydrophilic coating film shown in Comparative Example 6 in Figure 15 has an inorganic porous coating film that is 350 nm thick. An inorganic coating solution containing silica nanoparticles with an average particle diameter of 200 nm and a solids concentration of 3 wt% and a silica sol solution with a solids concentration of 1.5 wt% was used. The content of the hydrophilic organic compound in the organic coating solution was 2 wt%, and the proportion of betaine polymer in the hydrophilic organic compound was 30%.

[0192] The synthesis method for hydrophilic organic compound 14 is as follows. Under nitrogen, 9.9 mmol of 2-{[2-(methacryloyloxy)ethyl]dimethylammonium}acetic acid, 0.1 mmol of 3-mercaptopropyltrimethoxysilane, and water were added to a recovery flask to a concentration of 20 wt%. Next, 0.1 mmol of 2,2'-azobis-2-methyl-N-2-hydroxyethylpropionamide was added and stirred at 55°C for 3 hours to obtain a betaine polymer solution. Similarly, 9.9 mmol of isopropylacrylamide, 0.1 mmol of 3-mercaptopropyltrimethoxysilane, and water were added to a concentration of 20 wt%. Next, 0.1 mmol of 2,2'-azobis-2-methyl-N-2-hydroxyethylpropionamide was added and stirred at 55°C for 3 hours to obtain a hydrophilic polymer solution. These were mixed and water was added to obtain a 2 wt% hydrophilic coating solution containing 30% betaine polymer.

[0193] The coating method for the inorganic coating liquid and the organic coating liquid was fabric coating using microfibers. Cross-sectional SEM observation revealed that the film thickness was 350 nm, and surface SEM observation revealed that the porosity was 44%. The hydrophilic coating film shown in Comparative Example 6 had a coating film transparency of × (cloudy, poor).

[0194] The hydrophilic coating film shown in Comparative Example 7 in Figure 15 has an inorganic porous coating film that is 300 nm thick. An inorganic coating solution containing silica nanoparticles with an average particle size of 55 nm and a solids concentration of 1 wt% and a silica sol solution with a solids concentration of 0.5 wt% was used. The content of the hydrophilic organic compound in the organic coating solution was 0.02 wt%, and the proportion of betaine polymer in the hydrophilic organic compound was 30%.

[0195] The synthesis method for hydrophilic organic compound 14 is as follows. Under nitrogen, 9.9 mmol of 3-[(3-acrylamidopropyl)dimethylammonio]propanoate, 0.1 mmol of 3-mercaptopropyltrimethoxysilane, and water were added to a recovery flask to a concentration of 20 wt%. Next, 0.1 mmol of 2,2'-azobis-2-methyl-N-2-hydroxyethylpropionamide was added and stirred at 55°C for 3 hours to obtain a betaine polymer solution. Similarly, 9.9 mmol of isopropylacrylamide, 0.1 mmol of 3-mercaptopropyltrimethoxysilane, and water were added to a concentration of 20 wt%. Next, 0.1 mmol of 2,2'-azobis-2-methyl-N-2-hydroxyethylpropionamide was added and stirred at 55°C for 3 hours to obtain a hydrophilic polymer solution. These were mixed and water was added to obtain a 2 wt% hydrophilic coating solution containing 30% betaine polymer.

[0196] The coating method for the inorganic coating liquid and the organic coating liquid was fabric coating using microfibers. Cross-sectional SEM observation revealed that the film thickness was 300 nm, and surface SEM observation revealed that the porosity was 51%. For the hydrophilic coating film shown in Comparative Example 7, the contact angle θ of a water droplet W immediately after the coating film was formed on the surface 12 of the substrate 11 was × (over 20°, poor), the contact angle θ of a water droplet W six months after the coating film was formed on the surface 12 of the substrate 11 was × (over 20°, poor), and the transparency of the coating film was × (cloudy, poor).

[0197] The hydrophilic coating film shown in Comparative Example 8 of Figure 15 has an inorganic porous coating film with a thickness of 240 nm. Silica nanoparticles with average particle sizes of 1500 nm, 60 nm, and 12 nm were mixed to a solids concentration of 5 wt%, and an inorganic coating solution containing a silica nanosol solution with a solids concentration of 2.5 wt% was used. The content of the hydrophilic organic compound in the organic coating solution was 2 wt%, and the proportion of betaine polymer in the hydrophilic organic compound was 100%.

[0198] The synthesis method for hydrophilic organic compound 14 is as follows. Under nitrogen, 10 mmol of 3-{[2-(methacryloyloxy)ethyl]dimethylammonio}propane-1-sulfonic acid and water were added to a recovery flask to a concentration of 20 wt%. Next, 0.1 mmol of 2,2'-azobis-2-methyl-N-2-hydroxyethylpropionamide was added and the mixture was stirred and heated at 55°C for 3 hours to obtain a betaine polymer solution. Water was added to this solution to obtain a 2 wt% hydrophilic coating solution containing 100% betaine polymer.

[0199] The coating method for the inorganic coating liquid and the organic coating liquid was fabric coating using microfibers. Cross-sectional SEM observation immediately after coating revealed that the film thickness was 240 nm, and SEM observation of the surface revealed that the porosity was 18%. For the hydrophilic coating film shown in Comparative Example 8, the contact angle θ of a water droplet W immediately after the coating film was formed on the surface 12 of the substrate 11 was × (over 20°, poor), and the contact angle θ of a water droplet W six months after the coating film was formed on the coating surface 12 of the substrate 11 was × (over 20°, poor).

[0200] The hydrophilic coating films 10A to 10D shown in Examples 1 to 8 all fall within the numerical ranges of the present invention in terms of film thickness, solids concentration of inorganic fine particles 16, average particle size of inorganic fine particles 16, content of hydrophilic organic compound, and proportion of betaine polymer in the hydrophilic organic compound, and the contact angle θ of a water droplet W immediately after the coating films 10A to 10D are formed on the coating surface 12 of the substrate 11, the contact angle θ of a water droplet W six months after the coating films 10A to 10D are formed on the coating surface 12 of the substrate 11, and the transparency of the coating films 10A to 10D are good. In contrast, the hydrophilic coating films shown in Comparative Examples 1 to 8 were found to be outside the numerical range of the present invention in terms of film thickness, solids concentration of inorganic fine particles 16, average particle size of inorganic fine particles 16, content of hydrophilic organic compound, or proportion of betaine polymer in the hydrophilic organic compound, and were found to be poor in at least one of the contact angle θ of a water droplet W immediately after the coating film was formed on the coating surface 12 of the substrate 11, the contact angle θ of a water droplet W six months after the coating film was formed on the coating surface 12 of the substrate 11, and transparency of the coating film. [Explanation of symbols]

[0201] 10A~10D Hydrophilic coating film 11 Base material 12 sides (front and back) 13a Inorganic porous coating film 13b Inorganic porous coating film 14 Hydrophilic organic compounds 15 void 16 Inorganic fine particles

Claims

1. A hydrophilic coating film is formed from an inorganic porous coating film having a large number of nano-sized voids and a hydrophilic organic compound that has penetrated into the voids of the inorganic porous coating film, and is characterized in that the contact angle of water measured according to JIS R3257 is 20° or less.

2. 2. The hydrophilic coating film according to claim 1, wherein the contact angle of water measured in accordance with JIS R3257 is 10° or less.

3. The inorganic porous coating film is made of silicon dioxide (SiO ２ ), aluminum oxide (Al ２ O ３ ), zirconium oxide (ZrO ２ ), titanium oxide (TiO ２ ), ceria oxide (CeO ２ 2. The hydrophilic coating film according to claim 1, which contains at least one type of inorganic fine particles selected from the group consisting of:

4. 2. The hydrophilic coating film according to claim 1, wherein the inorganic porous coating film has an inorganic nanoporous structure produced by a sol-gel method using at least one of silica sol, alumina sol, zirconia sol, titania sol, and ceria sol.

5. 2. The hydrophilic coating film according to claim 1, wherein the hydrophilic organic compound comprises a betaine polymer having a cationic moiety and an anionic moiety in the same molecule.

6. 6. The hydrophilic coating film according to claim 5, wherein the ratio of the betaine polymer in the hydrophilic organic compound is 20% or more.

7. 2. The hydrophilic coating film according to claim 1, wherein the porosity of the pores formed in the inorganic porous coating film is in the range of 20% to 70% of the volume of the inorganic porous coating film.

8. 2. The hydrophilic coating film according to claim 1, wherein the thickness of the hydrophilic coating film is in the range of 0.01 to 3 μm.

9. 2. The hydrophilic coating film according to claim 1, wherein the hydrophilic organic compound coats the surface of the inorganic porous coating film while penetrating into pores of the inorganic porous coating film.

10. 2. The hydrophilic coating film according to claim 1, wherein the uppermost layer of the hydrophilic organic compound is located slightly below the surface of the inorganic porous coating film, and the portion of the inorganic porous coating film exposed above the uppermost layer of the hydrophilic organic compound is coated with an extremely thin film of the hydrophilic organic compound, and fine irregularities are formed on the surface of the hydrophilic coating film.

11. A hydrophilic coating liquid formed from an inorganic coating liquid that produces an inorganic porous coating film having numerous nano-sized voids, and an organic coating liquid that contains a betaine polymer having a cationic moiety and an anionic moiety in the same molecule, and produces a hydrophilic organic compound that coats the inorganic porous coating film while penetrating the voids of the inorganic porous coating film.

12. 12. The hydrophilic coating liquid according to claim 11, wherein the ratio of the betaine polymer in the hydrophilic organic compound is 20% or more.

13. The inorganic coating liquid contains silicon dioxide (SiO ２ ), aluminum oxide (Al ２ O ３ ), zirconium oxide (ZrO ２ ), titanium oxide (TiO ２ ), ceria oxide (CeO ２ 12. The hydrophilic coating liquid according to claim 11, comprising at least one type of inorganic fine particles selected from the group consisting of hydroxypropyl hydroxypropyl, hydroxypropyl ...

14. 14. The hydrophilic coating liquid according to claim 13, wherein the inorganic fine particles contained in the inorganic coating liquid have an average particle size of 1 μm or less.

15. 12. The hydrophilic coating liquid according to claim 11, wherein the content of the hydrophilic organic compound in the organic coating liquid is in the range of 0.1 to 20 wt % based on the total weight of the organic coating liquid.

16. A method for forming a hydrophilic coating film, which comprises forming a hydrophilic coating film from an inorganic porous coating film having a large number of nano-sized voids and a hydrophilic organic compound, The hydrophilic coating film forming method includes a washing step of washing the surface of a predetermined substrate with an alkaline detergent and then washing the surface of the substrate with an acidic liquid; an inorganic porous coating film forming step of coating the surface of the substrate with an inorganic coating liquid containing inorganic fine particles and forming the inorganic porous coating film having an inorganic nanoporous structure with a large number of nano-sized voids by a sol-gel method; a hydrophilic organic compound forming step of coating the surface of the substrate with an organic coating liquid containing a betaine polymer having a cationic moiety and an anionic moiety in the same molecule and forming a hydrophilic organic compound containing the betaine polymer on the surface of the substrate while the organic coating liquid is permeated into the voids of the inorganic porous coating film; and a water washing step of washing the surface of the hydrophilic coating film formed from the inorganic porous coating film and the hydrophilic organic compound with water.

17. 17. The method for forming a hydrophilic coating film according to claim 16, wherein in the inorganic porous coating film forming step, the inorganic porous coating film having an inorganic nanoporous structure is formed by a sol-gel method using at least one of silica sol, alumina sol, zirconia sol, titania sol, and ceria sol.

18. 17. The hydrophilic coating film forming method according to claim 16, wherein in the hydrophilic organic compound forming step, the inorganic porous coating film is coated with the organic coating liquid so that the inorganic porous coating film is not exposed from the surface of the hydrophilic organic compound, and when the hydrophilic coating film is formed, the inorganic porous coating film is buried in the hydrophilic organic compound.

19. 17. The hydrophilic coating film forming method according to claim 16, wherein in the hydrophilic organic compound forming step, the inorganic coating liquid is coated on the surface of the substrate in a state where the inorganic coating liquid is positioned slightly below the surface of the inorganic porous coating film so that the inorganic porous coating film is exposed above the topmost layer of the hydrophilic organic compound, and when the hydrophilic coating film is formed, the inorganic porous coating film is exposed above the topmost layer of the hydrophilic organic compound, and the part of the inorganic porous coating film that is exposed above the topmost layer of the hydrophilic organic compound is coated with an ultrathin film of the hydrophilic organic compound, and fine irregularities are formed on the surface of the hydrophilic coating film.

20. 17. The method for forming a hydrophilic coating film according to claim 16, wherein in the water washing step, the excess hydrophilic organic compounds that are weakly bonded to the pores of the inorganic porous coating film, except for the hydrophilic organic compounds that are firmly bonded to the pores of the inorganic porous coating film, are washed away with water, and the hydrophilic organic compounds that do not contribute to the hydrophilicity of the hydrophilic coating film are removed from the hydrophilic coating film.

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