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

Abstract

[Problem] To provide a hydrophilic coating film that enables a small water contact angle with respect to the film surface thereof and a large water droplet contact area with respect to the film surface, that has excellent hydrophilicity and anti-fouling properties, and that makes it possible to easily wash off, via cleaning with water, dirt which has adhered thereto. [Solution] Provided is hydrophilic coating film formed from an inorganic porous coating film which has many pores and a hydrophilic organic compound which is impregnated into the pores of the inorganic porous coating film, wherein a water contact angle measured in accordance with JIS R3257 is not more than 20°. The inorganic porous coating film contains inorganic fine particles of at least one substance from among silicon dioxide (SiO2), aluminum oxide (Al2O3), zirconium oxide (ZrO2), titanium oxide (TiO2), and ceria oxide (CeO2), and has an inorganic nanoporous structure which is made via a sol-gel method using at least one of a silica sol, an alumina sol, a zirconia sol, a titania sol, and a ceria sol. The hydrophilic organic compound contains a betaine polymer that has, in one molecule thereof, a cation site and an anion site.

Description

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

[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.

[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 and 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 and 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).

[0004] JP 2019-89930 A JP 2022-129100 A

[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 caused by the usage environment, and the hydrophilicity gradually decreases, making it impossible to maintain the 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. In many cases, it is not possible to heat the substrate, and there is a need to obtain a durable hydrophilic coating film by simply 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.

[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 contact angle of water 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 made of silicon dioxide (SiO ２ ), aluminum oxide (Al ２ O ３ ), zirconium oxide (ZrO ２ ), titanium oxide (TiO ２ ), ceria oxide (CeO ２ ) containing at least one type of inorganic fine particles.

[0011] Another example of the 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 silicon dioxide (SiO ２ ), aluminum oxide (Al ２ O ３ ), zirconium oxide (ZrO ２ ), titanium oxide (TiO ２ ), ceria oxide (CeO ２ ) and the solids concentration of the inorganic particles in the inorganic coating liquid is 0.3 to 50 wt %.

[0021] In another example of a hydrophilic coating liquid, 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.

[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 in accordance with JIS R3257. This means that the hydrophilic coating film 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. 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. In the hydrophilic coating film, the hydrophilic organic compound 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. 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. This prevents the hydrophilicity and antifouling properties of the hydrophilic coating film from decreasing, and the hydrophilic function and antifouling function provided by the hydrophilic organic compound can be maintained for a long period of time.

[0029] The hydrophilic coating film has a water contact angle of 10° or less as measured in accordance with JIS R3257, and therefore has a very 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, 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] The hydrophilic coating film is an inorganic porous coating film made of silicon dioxide (SiO ２When the inorganic porous coating film contains inorganic fine particles of aluminum oxide (Al), the hydrophilic organic compound easily bonds with silicon dioxide, and the hydrophilic organic compound that has infiltrated into the numerous nano-sized fine voids of the inorganic porous coating film easily bonds with the voids containing silicon dioxide, and the hydrophilic organic compound can be firmly bonded to the voids of the inorganic porous coating film. ２ O ３ When the inorganic porous coating film contains inorganic fine particles of zirconium oxide (ZrO), the hydrophilic organic compound easily bonds with aluminum oxide, and the hydrophilic organic compound that has infiltrated into the numerous nano-sized fine voids in the inorganic porous coating film can be firmly bonded to the voids containing aluminum oxide, and aluminum oxide makes it difficult for salts such as magnesium, calcium, sodium, silicon, etc. to adhere to the hydrophilic coating film, so that contamination of the hydrophilic coating film due to adhesion of salts such as magnesium, calcium, sodium, silicon, etc. to the hydrophilic coating film can be prevented. ２ When the inorganic porous coating film contains inorganic fine particles of titanium oxide (TiO), the hardness of the inorganic porous coating film can be increased, and the rigidity of the hydrophilic coating film can be increased. ２ When the inorganic porous coating film contains inorganic fine particles of ceria oxide (CeO), the surface of the hydrophilic coating film is coated with hydrophilic groups when the inorganic fine particles of titanium oxide are exposed to light and water, and the hydrophilic coating film can be given a self-cleaning effect. ２When the inorganic porous coating film contains a betaine polymer, the hardness of the inorganic porous coating film can be increased, the rigidity of the hydrophilic coating film can be increased, and the hydrophilic coating film can be provided with UV absorption properties. The hydrophilic coating liquid can be bonded to the inorganic fine particles by covalent bonds, or by hydrogen bonds, ionic bonds, hydrogen bonds, van der Waals bonds, etc. In particular, impregnation of nano-sized spaces with a betaine polymer 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, tetraalkoxysilanes, alkyltrialkoxysilanes, dialkyldialkoxysilanes, 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 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 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, the hydrophilic organic compound remains in the hydrophilic coating film for a long period of time, and the hydrophilicity and antifouling properties of the hydrophilic coating film can be prevented from decreasing, 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] Since the ratio of the betaine polymer having a cationic moiety and an anionic moiety in the same molecule to the hydrophilic organic compound in the hydrophilic coating film is 20% or more, the excellent hydrophilicity of the betaine polymer can be fully utilized, the hydrophilic organic compound exhibits excellent hydrophilicity and antifouling properties, the contact angle of water with the film surface of the hydrophilic coating film can be reliably reduced, the contact area of ​​water with the film 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 film 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, so that a sufficient number of nano-sized fine voids are formed in the inorganic porous coating film, and the hydrophilic organic compound can penetrate these voids, making it possible to 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 sufficiently protecting the surface of the substrate by the hydrophilic coating film. The hydrophilic organic compound (hydrophilic organic film) is bonded to the many fine voids in the inorganic porous coating film, so that 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 caused by the usage environment, so that 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 of the hydrophilic organic compound can be maintained for a long period of time.

[0035] Since the hydrophilic coating film has a thickness in the range of 0.01 to 3 μm, 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, thereby maintaining the state in which the hydrophilic coating film covers the surface of the substrate.

[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 making it possible to create a hydrophilic coating film with excellent strength, and since the hydrophilic organic compound will 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 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, 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 film surface can be reliably reduced, the contact area of ​​water with the film surface can be reliably increased, and when the hydrophilic coating film is washed with water, water comes into contact with a wide range 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] The hydrophilic coating liquid is an inorganic coating liquid containing silicon dioxide (SiO ２ When the inorganic coating liquid contains inorganic fine particles of silicon dioxide, and the solid content 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 be easily bound 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. ２ O ３ When the inorganic coating liquid contains inorganic fine particles of zirconium oxide (ZrO), and the solid content 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 the hydrophilic organic compound that has infiltrated into the numerous nano-sized minute voids in the inorganic porous coating film can be firmly bonded to the voids 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 film, a hydrophilic coating film can be formed that is capable of preventing contamination of the hydrophilic coating film due to adhesion of salts such as magnesium, calcium, sodium, silicon, etc. to the hydrophilic coating film.２ When the inorganic coating liquid contains inorganic fine particles of zirconium oxide, and the solid content of the inorganic fine particles of zirconium oxide in the inorganic coating liquid is 0.3 to 50 wt %, an inorganic porous coating film with increased hardness can be produced, and a hydrophilic coating film with increased rigidity can be formed. ２ When the inorganic coating liquid contains inorganic fine particles of titanium oxide, and the solid content concentration of the inorganic fine particles of titanium oxide is 0.3 to 50 wt %, the surface of the hydrophilic coating film is coated with hydrophilic groups when the inorganic fine particles of titanium oxide are exposed to light and water, and a hydrophilic coating film capable of exhibiting a self-cleaning effect can be formed. ２ ) and when the solid content concentration 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 liquid contains inorganic fine particles with an average particle size of 1 μm or less, forming an inorganic nanoporous structure with an inorganic porous coating film. The hydrophilic organic compound penetrates into the numerous nano-sized voids of the inorganic nanoporous structure, and the hydrophilic organic compound (hydrophilic organic film) binds to the voids of the inorganic porous 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 prematurely 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 production of a hydrophilic coating film that can maintain the hydrophilic and antifouling properties 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, 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 prematurely 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, making it possible to form a hydrophilic coating film having excellent hydrophilicity and antifouling properties, a hydrophilic coating film having a small contact angle with the film surface and capable of increasing the contact area of ​​water with the film surface, and a hydrophilic coating film from which adhering dirt can be easily washed off with water.

[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 prematurely 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 can strengthen 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 prematurely.

[0044] The hydrophilic coating film forming 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 forming 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 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 created, and a hydrophilic coating film can be created 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 will 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.

[0048] 1 is an image showing an example of an inorganic porous coating film formed on the surface of a substrate; 2 is an image showing an example of a hydrophilic coating film formed from the inorganic porous coating film of FIG. 1 and a hydrophilic organic compound; 3 is an image showing another example of a hydrophilic coating film formed from the inorganic porous coating film of FIG. 1 and a hydrophilic organic compound; 4 is an image showing another example of a hydrophilic coating film formed from the inorganic porous coating film of FIG. 4 and a hydrophilic organic compound; 5 is an image showing another example of a hydrophilic coating film formed from the inorganic porous coating film of FIG. 4 and a hydrophilic organic compound; 6 is a flow diagram of a hydrophilic coating film forming method for producing a hydrophilic coating film; 7 is a diagram showing the contact angle of a water droplet dropped on the hydrophilic coating film of FIG. 2; 8 is a diagram showing the contact angle of a water droplet dropped on the hydrophilic coating film of FIG. 3; 9 is a diagram showing the contact angle of a water droplet dropped on the hydrophilic coating film of FIG. 5; 10 is a diagram showing the contact angle of a water droplet dropped on the hydrophilic coating film of FIG. 6; 11 is a diagram showing Examples 1 to 4 of hydrophilic coating films. 1 is a diagram showing examples 5 to 8 of hydrophilic coating films; FIG. 2 is a diagram showing comparative examples 1 to 4 of hydrophilic coating films; FIG. 3 is a diagram showing comparative examples 5 to 8 of hydrophilic coating films;

[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 and the hydrophilic organic compound 14 in Fig. 4, and Fig. 6 is an image diagram showing another example of the hydrophilic coating film 10D formed from the inorganic porous coating film 13b and the hydrophilic organic compound 14 in Fig. 4. 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 surface 12 (front and back surfaces) of the substrate 11 to be coated with the hydrophilic coating films 10A to 10D. The hydrophilic coating films 10A to 10D are formed from inorganic porous coating films 13a, 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, 13b on the surface 12 of the substrate 11, forming the inorganic porous coating films 13a, 13b on the surface 12 of the substrate 11, and then applying (coating) an organic coating liquid that forms the hydrophilic organic compound 14 on the surface 12 of the substrate 11, thereby forming the hydrophilic organic compound 14 on the surface 12 of the substrate 11.

[0051] The substrate 11 to be coated with the hydrophilic coating films 10A to 10D may be metal (metallic molded product), plastic (plastic molded product and molded product having plastic as the outermost layer), glass (glass molded product), rubber (rubber molded product), leather (leather molded product), wood (wooden molded product), paper (paper molded product), woven or knitted fabric using fiber (woven or knitted fabric molded product), etc., but there is no particular limitation on the substrate 11. Furthermore, there is no particular limitation 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, or woven or knitted fabric are included.

[0052] Metals include iron, aluminum, duralumin, stainless steel, copper, gold, silver, titanium, nickel, alloys, etc. 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, ethylene-chlorotrifluoroethylene copolymer resin, etc. Rubbers include polybutadiene rubber, polyisoprene (natural rubber), styrene-butadiene rubber, nitrile rubber, EPM, EPDM, epichlorohydrin rubber, neoprene rubber, polysulfide, butyl rubber, etc.

[0053] The inorganic coating liquid is composed of a plurality of fine silicon dioxide particles (SiO ２ a silica sol in which nano-sized inorganic fine particles 16 (colloidal particles) made of aluminum oxide (Al ２ O ３ alumina sol in which nano-sized inorganic fine particles 16 (colloidal particles) made of zirconium oxide (ZrO ２zirconia sol in which nano-sized inorganic fine particles 16 (colloidal particles) made of titanium oxide (TiO ２ titania sol in which nano-sized inorganic fine particles 16 (colloidal particles) made of cerium oxide (CeO ２ The dispersion medium may be water or an alcohol such as ethyl alcohol, normal propyl alcohol, isopropyl alcohol, normal butanol, or the like, but is not limited to this.

[0054] Silica sol is produced by the water glass method or the alkoxide method. However, the method is not limited to these, and silica sol can also be produced by other methods. The water glass method uses sodium silicate (Na ２ O.SiO ２ ) is diluted to a few percent with water to produce 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 solution 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 solution, 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 a predetermined level. After adjusting the pH, the mixture is concentrated by refluxing to produce a silica sol (silica colloid 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 salt, and then mixing the alumina sol (alumina colloidal solution) with a monovalent acid.

[0057] Another example of a method for producing an alumina sol involves hydrothermally treating alumina hydrate obtained by reacting a water-soluble aluminum salt with carbonic acid or a carbonate salt, followed by mixing with a monovalent acid to produce an alumina sol (alumina colloidal solution). Another example of a method for producing an alumina sol involves hydrolyzing aluminum alkoxide with a dilute acid aqueous solution to produce alumina hydrate, adding a new acid to the resulting alumina hydrate, and then hydrothermally treating the resulting alumina sol (alumina colloidal solution) to peptize it. Another example of a method for producing an alumina sol involves treating aluminum oxide powder in an aqueous phase in the presence of acid with a strongly acidic cation exchange resin, removing the ion exchange resin, and cooling 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) or a hydroxide of an alkali metal or alkaline earth metal 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 cause precipitation, 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 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 the solution to 80 to 300°C, and then add a base such as ammonia or treat the solution 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 or 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 ceria sol can also be produced by other methods.

[0063] The inorganic coating solution contains silicon dioxide (SiO ２ ), aluminum oxide (Al ２ O ３ ), zirconium oxide (ZrO２ ), titanium oxide (TiO ２ ), ceria oxide (CeO ２ ) or two or more types of inorganic particles 16. 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, 13b are formed with an inorganic nanoporous structure having a large number of 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] Inorganic fine particles 16 (silicon dioxide (SiO ２ ), aluminum oxide (Al ２ O ３ ), zirconium oxide (ZrO ２ ), titanium oxide (TiO ２ ), ceria oxide (CeO ２ The solid content concentration of silicon dioxide (SiO ) in the inorganic coating liquid is in the range of 0.3 wt % or more and 50 wt % or less with respect to the total mass of the inorganic coating liquid. ２ If the solid content concentration of the inorganic fine particles 16 in the inorganic coating liquid is less than 0.3 wt %, the amount of silicon dioxide that easily bonds with the hydrophilic organic compound 14 will be insufficient, and the hydrophilic organic compound 14 that has infiltrated into the numerous fine voids 15 (described later) of the inorganic porous coating films 13a and 13b will have difficulty bonding to the voids 15 containing silicon dioxide, making it impossible to firmly bond the hydrophilic organic compound 14 to the voids 15 of the inorganic porous coating films 13a and 13b. ２Since the solid content concentration of the inorganic microparticles 16 in the inorganic porous coating films 13a and 13b 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 and 13b can easily bond to the voids 15 containing silicon dioxide, and the hydrophilic organic compound 14 can be firmly bonded to the voids 15 of the inorganic porous coating films 13a and 13b.

[0066] Aluminum oxide (Al) in inorganic coating liquid ２ O ３ If the solid content concentration of the inorganic fine particles 16 in the inorganic coating solution 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 infiltrated into the numerous minute voids 15 of the inorganic porous coating films 13a and 13b will have difficulty bonding to the voids 15 containing aluminum oxide, making it impossible to firmly bond the hydrophilic organic compound 14 to the voids of the inorganic porous coating films 13a and 13b. In addition, the function of aluminum oxide to remove salts such as magnesium, calcium, sodium, silicon, etc. will be reduced, making it impossible to prevent contamination of the hydrophilic coating films 10A to 10D due to the adhesion of salts such as magnesium, calcium, sodium, silicon, etc. ２ O ３ Since the solid content concentration of the inorganic fine particles 16 in the inorganic porous coating films 13a, 13b is within the above range, the hydrophilic organic compound 14 that has infiltrated 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] Zirconium oxide (ZrO ２If the solid content concentration of the inorganic fine particles 16 is less than 0.3 wt %, the hardness of the inorganic porous coating films 13a and 13b cannot be increased, and the rigidity of the hydrophilic coating films 10A to 10D cannot be increased. ２ Since the solid content concentration of the inorganic fine particles 16 in the inorganic porous coating film 13a, 13b is within the above range, the hardness of the inorganic porous coating film 13a, 13b can be increased, and the rigidity of the hydrophilic coating film 10A to 10D can be increased.

[0068] Titanium oxide (TiO) in inorganic coating liquid ２ If the solids concentration of the inorganic particles 16 of titanium oxide (TiO2) 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 solids concentration of the 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-10D cannot be increased. Furthermore, the UV absorption function cannot be sufficiently obtained. Since the solids concentration of the 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-10D can be increased, and the UV absorption effect of the hydrophilic coating films 10A-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, the inorganic particles 16 become dense, and it is not possible to form a large number of minute 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 a large number of nano-sized minute 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, making it impossible to form inorganic porous coating films 13 a, 13 b 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, making it possible to form inorganic porous coating films 13 a, 13 b with an inorganic nanoporous structure having a large number of nano-sized minute 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 low, and the hydrophilic organic compound 14 produced 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.

[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] The organic coating liquid contains a betaine polymer in a proportion of 20% or more of the hydrophilic organic compound 14, and therefore the organic coating liquid contains a sufficient amount of betaine polymer, and the hydrophilic organic compound 14 produced from the organic coating liquid exhibits excellent 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.

[0076] A specific example of the 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 and mixed 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] (Chem.1)

[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 the above-mentioned high-density polymer brushes (surface graft polymers), brush particles or bottle brushes can also be used in organic coating solutions. Furthermore, betaine polymers that do not contain silanol groups or alkoxysilyl groups at the terminals or in the polymer chain can also be used. By using betaine polymers that do not contain silanol groups or alkoxysilyl groups, no reaction occurs 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 water-soluble or ester-based solvents. Furthermore, betaine polymers other than the betaine polymer shown in the structural formula (Chemical Formula 1) can be mixed in, and as other examples, a polymer capable of forming a PMAPS polymer brush, a PMAPS polymer, a polymer capable of forming a PMPC polymer brush, or a coating liquid in which a PMPC polymer is dispersed can also be used. These polymers may 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 an alkoxysilyl group at one end, or the polymer chain may contain a silanol group or an alkoxysilyl group.

[0080] (Case 2) The structural formula of the PPEGMA polymer is shown in (Chemical Formula 3), 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.

[0081] (Case 3) The structural formula of the 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] (Case 4) The structural formula of the PMTAC polymer is shown in Chemical Formula 5, 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.

[0083] (C5) The structural formula of the PSPMK polymer is shown in (Chemical Formula 6), and 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.

[0084] (C6) The structural formula of the 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] (Chem.7) The structural formula of PMPC polymer is shown in (Chemical Formula 8), and 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.

[0086] (Chem.8) Examples of water-soluble solvents include primary alcohol solvents, secondary alcohol solvents, tertiary alcohol solvents, ether solvents, ester solvents, and ketone solvents. Examples of primary, secondary, and tertiary alcohol solvents include isopropanol, sec-butyl alcohol, tert-butyl alcohol, and propylene glycol monomethyl ether. Examples of 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-based 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-based 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] (C9) Another example of a betaine polymer constituting the polymer is a polycarboxybetaine polymer, whose structural formula is shown in Chemical Formula 10. The polycarboxybetaine polymer 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.

[0090] (Chem.10) Monomers that constitute 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] (Chemical formula 11)

[0092] (Chemical Formula 12) 3-{[2-(methacryloyloxy)ethyl]dimethylammonio}propane-1-sulfonic acid

[0093] (Chemical Formula 13) 4-[(3-methacrylamidopropyl)dimethylammonio]butane-1-sulfonic acid

[0094] (Chemical Formula 14) 3-{[2-(acryloyloxy)ethyl]dimethylammonio}propane-1-sulfonic acid

[0095] (Chemical Formula 15) 3-[(3-acrylamidopropyl)dimethylammonio]propane-1-sulfonic acid

[0096] (Chemical Formula 16) 4-{[2-(methacryloyloxy)ethyl]dimethylammonio}butane-1-sulfonic acid

[0097] (Chemical Formula 17) Bis[2-(methacryloyloxy)ethyl](methyl)ammonio]propane-1-sulfonic acid

[0098] (Chemical Formula 18) 3-[3-(methacrylamidopropyl)dimethylammonio]propane-1-sulfonic acid 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] (Chem.19)

[0100] (Chemical Formula 20) 2-{[2-(methacryloyloxy)ethyl]dimethylammonio}acetic acid

[0101] (Chemical Formula 21) 3-{[3-(methacryloyloxy)ethyl] dimethylammonio}propionate

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

[0103] (Case 23)

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

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

[0106] (Case 26) The hydrophilic coating liquid is formed by an inorganic coating liquid containing silicon dioxide (SiO２ ), aluminum oxide (Al ２ O ３ ), zirconium oxide (ZrO ２ ), titanium oxide (TiO ２ ), ceria oxide (CeO ２ ) and the solid concentration of the inorganic particles 16 in the inorganic coating liquid is 0.3 to 50 wt %, so that the inorganic porous coating films 13a, 13b having sufficient strength in which a large number of fine voids 15 are formed by the inorganic particles 16 can be produced, and hydrophilic coating films 10A to 10D in which the voids 15 are firmly bonded can be produced.

[0107] The hydrophilic coating liquid is formed by an inorganic coating liquid containing silicon dioxide (SiO ２ ), by utilizing the ease of bonding between the hydrophilic organic compound 14 and silicon dioxide, the hydrophilic organic compound 14 that has infiltrated into the numerous minute voids 14 of the inorganic porous coating films 13a and 13b can be easily bonded to the voids 15 containing silicon dioxide, thereby making it possible to produce 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 and 13b.

[0108] The hydrophilic coating liquid is made of inorganic coating liquid containing aluminum oxide (Al ２ O ３), by utilizing the ease of bonding between the hydrophilic organic compound 14 and aluminum oxide, it is possible to produce hydrophilic coating films 10A to 10D in which the hydrophilic organic compound 14 that has infiltrated 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 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 produce hydrophilic coating films 10A to 10D that can prevent contamination caused by adhesion of salts such as magnesium, calcium, sodium, silicon, etc. to the hydrophilic coating films 10A to 10D.

[0109] The hydrophilic coating liquid is formed by an inorganic coating liquid containing zirconium oxide (ZrO ２ When the inorganic fine particles 16 of titanium oxide (TiO) are contained, the hardness can be increased by zirconium oxide, and the hydrophilic coating films 10A to 10D with increased rigidity can be produced. ２ When the inorganic fine particles 16 of titanium oxide are included, the surfaces of the inorganic fine particles 16 of titanium oxide are coated with hydrophilic groups when exposed to light and water, and therefore hydrophilic coating films 10A to 10D having excellent self-cleaning properties can be produced. ２ When the inorganic fine particles 14 of ceria oxide are contained, the hardness can be increased by the ceria oxide, and the hydrophilic coating films 10A to 10D can be provided with ultraviolet absorbing ability, and the hydrophilic coating films 10A to 10D can be produced with increased rigidity and ultraviolet absorbing ability.

[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. Therefore, 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 is formed by the hydrophilic organic compound 14 penetrating into the numerous nano-sized minute voids 15 of the inorganic porous coating films 13a, 13b, and the hydrophilic organic compound 14 (hydrophilic organic film) bonding (joining) 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 due to the hydrophilic organic compound 14 for a long period of time.

[0112] Fig. 7 is a flow diagram of a hydrophilic coating film formation method for producing hydrophilic coating films 10A to 10D. An example of the hydrophilic coating film formation method for producing hydrophilic coating films 10A to 10D will be described below with reference to Fig. 7. The hydrophilic coating film formation 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 in which dust is blown off 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 the removal of dirt such as dust, oil, and organic matter adhering to the coating surface 12 of the substrate 11.

[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 washed substrate 11, and inorganic porous coating films 13a, 13b having an inorganic nanoporous structure having 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 prepare 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 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 centrifugal force generated by the spin coating.

[0116] In the inorganic porous coating film forming step (P-2), as described above, silicon dioxide (SiO ２ ), aluminum oxide (Al ２ O ３ ), zirconium oxide (ZrO ２ ), titanium oxide (TiO ２ ), ceria oxide (CeO ２ ) is used. In the inorganic porous coating film forming step (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 forming step (P-2), the dispersion medium (water or alcohol) contained in the inorganic coating liquid volatilizes, and the inorganic particles 16 are partially connected to each other. The inorganic porous coating films 13a, 13b formed in the inorganic porous coating film forming step (P-2) have an inorganic nanoporous structure having a large number of fine nano-sized pores 15 with a porosity in the range of 20% to 70%, as shown in FIGS. 1 and 4.

[0117] In the hydrophilic organic compound formation step (P-3), inorganic porous coating films 13a, 13b having an inorganic nanoporous structure with a large number of 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 coating surface 12 of the substrate 11 from above the inorganic porous coating films 13a, 13b, thereby forming a hydrophilic organic compound 14 on the coating surface 12 of the substrate 11.

[0118] The organic coating liquid can be 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 a fabric made of 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 utilizing 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 inorganic porous coating film 13a, 13b is coated with an organic coating liquid to a predetermined covering dimension so that the inorganic porous coating film 13a, 13b is not exposed from the surface of the hydrophilic organic compound 14, and the surface of the inorganic porous coating film 13a, 13b is covered with the organic coating liquid. Alternatively, the hydrophilic organic polymer coating liquid is coated on the inorganic porous coating film 13a, 13b so that the top layer of the inorganic porous coating film 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, 13b (surface 12 of substrate 11) and the hydrophilic organic compound 14 contained in the organic coating liquid penetrate into the numerous fine voids 15 of the inorganic porous coating films 13a, 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, 13b volatilizes, and the hydrophilic organic compound 14 solidifies, 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 forming hydrophilic coating films 10A to 10D composed of the inorganic porous coating films 13a, 13b and the hydrophilic organic compound 14 (hydrophilic organic film).

[0121] When the hydrophilic coating films 10A to 10D are formed 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 surfaces of the inorganic porous coating films 13a, 13b (inorganic fine particles 16), and the inorganic porous coating films 13a, 13b are buried in the hydrophilic organic compound 14.

[0122] Furthermore, when the hydrophilic coating films 10A to 10D are formed in the hydrophilic organic compound formation step (P-3), the uppermost layer of the hydrophilic organic compound 14 (hydrophilic organic film) is located slightly below the surface of the inorganic porous coating films 13a and 13b, the uppermost layer of the inorganic porous coating films 13a and 13b (inorganic fine particles 16) is exposed above the uppermost layer of the hydrophilic organic compound 14, and the portion (uppermost layer) of the inorganic porous coating films 13a and 13b (inorganic fine particles 16) exposed above the uppermost layer of the hydrophilic organic compound 14 forms fine irregularities on the surface of the hydrophilic organic compound 14, and the portion (uppermost 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, 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, 13b, excluding the hydrophilic organic compound 14 that is firmly bonded to the inorganic porous coating films 13a, 13b, is washed away with water, and the hydrophilic organic compound 14 that does not contribute to the hydrophilicity of the hydrophilic coating films 10A to 10D is removed.

[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 a large number of nano-sized fine voids 15 by a sol-gel method; and uses an organic coating liquid to form a hydrophilic organic compound 14 containing a betaine polymer having a cationic moiety and an anionic moiety in the same molecule in a hydrophilic organic compound forming step (P-3). The organic coating liquid is allowed to penetrate into the large number of fine voids 15 in the inorganic porous coating films 13a, 13b, and the hydrophilic organic compound 14 forms a hydrophilic organic compound 14 (hydrophilic organic film) on the surface 12 of the substrate 11. Therefore, it is possible to form hydrophilic coating films 10A to 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 to 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 fine 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 due to the hydrophilic organic compound 14 for a long period of time.

[0126] The hydrophilic coating film formation method includes a washing step (P-1) in which the coating surface 12 of the substrate 11 is washed using an alkaline detergent (e.g., an alkaline detergent with a pH of 8 to 9) and then an acidic liquid (e.g., an acidic liquid with a pH of 1 to 2) to reliably remove contaminants such as dust, oil, and organic matter adhering to the coating surface 12 of the substrate 11, and can produce 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 formation 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 having 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 the inorganic porous coating films 13a, 13b are buried in the hydrophilic organic compound 14 when the hydrophilic coating films 10A to 10D are formed, so that the hydrophilic coating films 10A to 10D can be made in which the hydrophilic organic compound can remain for a long period of time.

[0128] In the method for forming a hydrophilic coating film, in the water washing step (P-4), excess hydrophilic organic compound 14 weakly bonded to the voids 15 of the inorganic porous coating films 13a, 13b, excluding the hydrophilic organic compound 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, 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, and therefore it is possible to produce hydrophilic coating films 10A to 10D containing hydrophilic organic compound 14 that is firmly 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 has excellent hydrophilicity and antifouling properties.

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

[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 coats 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 minute voids 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, a portion (top layer) of the inorganic porous coating film 13a (inorganic fine particles 16) that is 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) that forms 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 FIG. 5, the hydrophilic organic compound 14 penetrates into the numerous nano-sized minute voids 15 of the inorganic porous coating film 13b in FIG. 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 FIG. 6, the hydrophilic organic compound 14 penetrates into the numerous nano-sized minute voids 15 of the inorganic porous coating film 13b of FIG. 4, 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, a portion (top layer) of the inorganic porous coating film 13b (inorganic fine particles 16) that is 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) that forms 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, 13b is in the range of 20% to 70% of the volume of the inorganic porous coating films 13a, 13b. If the porosity of the voids 15 is less than 20%, the voids 15 formed in the inorganic porous coating films 13a, 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, 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, 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 the films 10A to 10D 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 having 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, the excellent hydrophilicity of the betaine polymer can be fully utilized, the hydrophilic organic compound 14 made from the organic coating liquid exhibits sufficient hydrophilicity and antifouling properties, and 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) can be imparted with excellent hydrophilicity and antifouling properties.

[0138] The thickness of the hydrophilic coating films 10A to 10D is in the range of 0.01 μm to 3 μm, preferably 0.1 μm to 0.6 μm. 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 adequately 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 hydrophilic coating films 10A to 10D have thicknesses 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 are made of inorganic porous coating films 13a and 13b, which are made of silicon dioxide (SiO ２ ), aluminum oxide (Al ２ O ３ ), zirconium oxide (ZrO ２ ), titanium oxide (TiO ２ ), cerium oxide (CeO ２ ) are contained in the hydrophilic coating films 10A to 10D. The inorganic porous coating films 13a and 13b contain at least one type of inorganic fine particles 16 selected from silicon dioxide (SiO ２), the hydrophilic organic compound 14 easily bonds with 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 with 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] The hydrophilic coating films 10A to 10D are made of inorganic porous coating films 13a and 13b, each of which is made of aluminum oxide (Al ２ O ３ ), the hydrophilic organic compound 14 easily bonds with aluminum oxide, and the hydrophilic organic compound 14 (hydrophilic organic film) that has infiltrated into the numerous minute voids 15 of the inorganic porous coating films 13a, 13b can be firmly bonded to the voids 15 containing 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] The hydrophilic coating films 10A to 10D are made of inorganic porous coating films 13a and 13b of zirconium oxide (ZrO ２ When the inorganic porous coating films 13a and 13b contain inorganic fine particles 16 of titanium oxide (TiO ２ ), when the inorganic fine particles 16 of titanium oxide are exposed to light and water, the surfaces of the hydrophilic coating films 10A to 10D are coated with hydrophilic groups, and an excellent self-cleaning effect can be imparted to the hydrophilic coating films 10A to 10D.

[0143] The hydrophilic coating films 10A to 10D are made of inorganic porous coating films 13a and 13b, each of which is made of cerium oxide (CeO２ When the inorganic fine particles 16 of cerium oxide are contained, the hardness can be increased by cerium oxide, and the hydrophilic coating films 10A to 10D 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, 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 creates 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 syringe barrel. (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 = 2 tan －１ h / r

[0149] In (Equation 1), r is the radius (mm) of the surface of the water drop W in contact with the test piece, and h is the height (mm) from the surface of the test piece to the apex 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 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, and dirt adhering to the hydrophilic coating films 10B and 10D can be easily and reliably washed off with water.

[0152] The hydrophilic coating films (10A to 10D) have an inorganic nanoporous structure in which the inorganic porous coating films (13a, 13b) are made 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 to 10D) have excellent strength, and the hydrophilic organic compound (14) is not prematurely peeled off or lost from the hydrophilic coating films (10A to 10D) due to stress caused by the usage environment. This prevents a decrease in the hydrophilicity and antifouling properties of the hydrophilic coating films (10A to 10D), 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 to 10D), the hydrophilic organic compound (14) contains a betaine polymer having a cationic moiety and an anionic moiety in the same molecule, and thus the hydrophilic organic compound (14) exhibits excellent hydrophilicity and antifouling properties, and the contact angle of water with the film surfaces of the hydrophilic coating films (10A to 10D) can be reliably reduced, and the contact area of ​​water with the film surfaces of the hydrophilic coating films (10A to 10D) can be reliably increased. In addition, when the hydrophilic coating films (10A to 10D) are washed with water, the water comes into contact with a wide range of the film surfaces 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.

[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 solution 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 described below. 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 the mixture was stirred and heated 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 the mixture was stirred and heated at 55°C for 3 hours to obtain a hydrophilic polymer solution. These components 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 on fabric using microfibers. An XVision 200TB manufactured by SII Nanotechnology Inc. or a JSM-5500 manufactured by JEOL Ltd. was used as a scanning electron microscope (SEM). Cross-sectional SEM observation confirmed that the film thickness was 300 nm. Furthermore, SEM observation of the surface 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 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 35%.

[0158] The synthesis method for hydrophilic organic compound 14 is described below. 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 the mixture was stirred and heated 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 the mixture was stirred and heated 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 coating liquid and the organic coating liquid 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 described below. 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 the mixture was stirred and heated 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 the mixture was stirred and heated 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 coating liquid and the organic coating liquid 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 shown below. 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 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 a film thickness of 250 nm, and surface SEM observation revealed a porosity of 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 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.

[0170] The inorganic coating liquid and the organic coating liquid 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 shown below. Under nitrogen, 10 mmol of 2-(methacryloyloxy)ethyl 2-(trimethylammonio)ethyl phosphate was added to a recovery flask with water 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.

[0173] The inorganic coating liquid and the organic coating liquid 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 shown below. Under nitrogen, 9.9 mmol of 3-{[2-(methacryloyloxy)ethyl]dimethylammonio}propane-1-sulfonic acid and 0.1 mmol of 3-mercaptopropyltrimethoxysilane were placed in a recovery flask, and water was added 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.

[0176] The inorganic coating liquid and the organic coating liquid 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 a transparency of ○ (no turbidity, good).

[0178] The hydrophilic coating film shown in Comparative Example 1 of Figure 14 has an inorganic porous coating film with a thickness of 3000 (nm). 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 liquid 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 described below. 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 the mixture was stirred and heated 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 the mixture was stirred and heated at 55°C for 3 hours to obtain a hydrophilic polymer solution. These components 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 3,000 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 solids concentration of 3 (wt%) and a silica sol solution with a solids concentration 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 described below. 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. 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 the mixture was stirred and heated 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 the mixture was stirred and heated 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 a film thickness of 10,000 nm, and surface SEM observation revealed a porosity of 75%. The hydrophilic coating film shown in Comparative Example 4 had a contact angle θ of a water droplet W of x (over 20°, poor) immediately after the coating film was formed on the surface 12 of the substrate 11, a contact angle θ of a water droplet W of x (over 20°, poor) six months after the coating film was formed on the surface 12 of the substrate 11, and a transparency of x (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 was used, 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%). 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 described below. 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 the mixture was stirred and heated 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 the mixture was stirred and heated 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 transparency of × (cloudy, poor).

[0191] The hydrophilic coating film shown in Comparative Example 6 in Figure 15 has an inorganic porous coating film with a thickness of 350 (nm). An inorganic coating solution was used, 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%). 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 described below. Under nitrogen, 9.9 mmol of 2-{[2-(methacryloyloxy)ethyl]dimethylammonia}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 the mixture was stirred and heated 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 the mixture was stirred and heated 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 transparency of × (cloudy, poor).

[0194] The hydrophilic coating film shown in Comparative Example 7 in Figure 15 has an inorganic porous coating film 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 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 described below. 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 the mixture was stirred and heated 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 the mixture was stirred and heated 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 a film thickness of 300 nm, and surface SEM observation revealed a porosity of 51%. The hydrophilic coating film shown in Comparative Example 7 had a contact angle θ of a water droplet W of x (over 20°, poor) immediately after the coating film was formed on the surface 12 of the substrate 11, a contact angle θ of a water droplet W of x (over 20°, poor) six months after the coating film was formed on the surface 12 of the substrate 11, and a transparency of x (cloudy, poor).

[0197] The hydrophilic coating film shown in Comparative Example 8 in 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 liquid 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 shown below. Under nitrogen, 10 mmol of 3-{[2-(methacryloyloxy)ethyl]dimethylammonio}propane-1-sulfonic 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.

[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 a film thickness of 240 nm, and SEM observation of the surface revealed a porosity of 18%. The hydrophilic coating film shown in Comparative Example 8 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 coating surface 12 of the substrate 11.

[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 the 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 the 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 the water droplet W immediately after the coating film was formed on the coating surface 12 of the substrate 11, the contact angle θ of the 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.

[0201] 10A to 10D Hydrophilic coating film 11 Substrate 12 Surface (front surface, back surface) 13a Inorganic porous coating film 13b Inorganic porous coating film 14 Hydrophilic organic compound 15 Voids 16 Inorganic fine particles

Claims

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

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. 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. 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. 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. 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. 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. 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 the pores of the inorganic porous coating film.

10. A 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 cationic and anionic moieties in the same molecule and produces a hydrophilic organic compound that coats the inorganic porous coating film when it penetrates into the voids of the inorganic porous coating film.

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

15. 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 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, the hydrophilic coating film forming method comprising: 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 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 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. 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. A method for forming a hydrophilic coating film as described in 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. The method for forming a hydrophilic coating film 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 uppermost layer of the hydrophilic organic compound, and when the hydrophilic coating film is formed, the inorganic porous coating film is exposed above the uppermost layer of the hydrophilic organic compound, and the portion of the inorganic porous coating film exposed above the uppermost 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. A method for forming a hydrophilic coating film as described in claim 16, wherein 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.

Images