JPH10310653A - Photocatalytic hydrophilic member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photocatalytic hydrophilic member the surface of which can be rendered hydrophilic even by irradiation with a visible light. SOLUTION: A layer containing photocatalytic particles in which the forbidden band width between the conduction band and the valance band on the surfaces of particles is 2.3-3.2 eV is formed on the surface of a substrate. Alternatively, a layer containing photocatalytic particles in which a sublevel exists between the conduction band and the valence band, and the energy gap between the conduction band and the sublevel or between the valence band and the sublevel is 2.3-3.1 eV is formed on the surface of the substrate. As a result, the surface of the member exhibits hydrophilicity upon the excitation of the photocatalyst with light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photocatalytic hydrophilic member capable of rendering a member surface hydrophilic by irradiation with visible light.

[0002]

2. Description of the Related Art The present inventor has previously proposed a method for highly hydrophilizing the surface of an article by photoexcitation of a semiconductor photocatalyst (WO 96/29375). According to this method,
The surface of the article is coated with a coating of a semiconductor photocatalyst such as an anatase type titanium oxide. This you
When the photocatalytic coating made of titanium oxide is irradiated with ultraviolet light to excite the photocatalyst with sufficient illuminance for a sufficient time, the surface of the photocatalytic coating has a contact angle with water of about 0 degrees. Highly hydrophilized. As disclosed in WO 96/29375,
The photocatalytic coating which can be highly hydrophilized as described above can be applied to various articles for various purposes such as anti-fogging, purification by rainfall, purification by washing, promotion of drying, and the like. For example, when a transparent article such as a windshield of a vehicle, a door mirror, a window glass of a building, a lens of an eyeglass, or a mirror is coated with a photocatalytic coating, the surface of the coating is accompanied by photoexcitation of the photocatalyst. It is highly hydrophilized, so that the article is prevented from fogging with condensed moisture or steam and from being overshadowed by adhering water droplets. Alternatively, if a building or article placed outdoors is covered with a photocatalytic coating, lipophilic or hydrophobic dust and contaminants attached to the hydrophilic surface are washed away by rainwater each time it rains. And the surface is purified.

[0003]

In the above reaction, the rate of hydrophilization varies depending on the irradiation of the photocatalyst with excitation light. That is, in outdoor applications where sunlight can be used, an anatase type titanium oxide most widely known as a semiconductor photocatalyst can be used as a photocatalyst contained in the photocatalytic coating.
However, when trying to optically excite a photocatalyst in an indoor living space, general lighting is used, but most of the light emitted from general lighting is visible light, and is excited by anatase type titanium oxide. Certain ultraviolet rays have an extremely low illuminance, and thus have a problem that the rate of hydrophilization is low. Accordingly, an object of the present invention is to provide a photocatalytic hydrophilic member capable of rendering the member surface hydrophilic by irradiation with visible light.

[0004]

SUMMARY OF THE INVENTION The present invention is based on the discovery that, in a member having a surface layer containing a photocatalyst formed thereon, when the photocatalyst is photoexcited, the surface of the member is highly hydrophilized. This phenomenon is considered to proceed by the following mechanism. First, when light having energy equal to or greater than the forbidden band width between the upper end of the valence band and the lower end of the conduction band of the photocatalyst is irradiated on the photocatalyst, the electrons in the valence band of the photocatalyst are excited, and the conduction electrons and holes are generated. Generate. Then, the generated conduction electrons and / or
Alternatively, due to the action of holes, hydroxyl groups (chemically adsorbed water) that are at or above the equilibrium with the atmosphere are adsorbed on the surface (this reaction is caused by a quantum reaction of conduction electrons and / or holes, which are excited species. Conduction electrons and / or Alternatively, this does not occur if the energy of the holes is less than about 2.2 eV, and in the case of using a photocatalyst having a specific bandgap, the longer the wavelength of the irradiated light, the longer the wavelength of the irradiated light, if it can be excited. The energy generated by the difference between the irradiation light and the forbidden band changes into thermal energy, but when heat is applied to the surface of the member, the adsorption equilibrium shifts in the direction in which the adsorbed material is desorbed. In addition, the adsorption reaction proceeds more rapidly as the water vapor partial pressure in the atmosphere is higher and the oxygen partial pressure is lower.In addition, this adsorption reaction starts from one hydroxyl group in a cluster form. While growing To pressure. Its growth is fast enough excitation intensity is high). Then, the surface free energy based on the hydrogen bond of the surface increases, so that the amount of physically adsorbable water molecules corresponding to the increase is further fixed on the surface of the base material. If the physically adsorbing water molecules are fixed on the surface of the base material, generally, substances having a surface energy close to each other are easily bonded, so that the free water adheres easily to the member surface, and the water wettability is improved. By the above mechanism, it is considered that the member surface becomes hydrophilic by the photoexcitation of the photocatalyst. Thus, as long as the photoexcitation continues, the surface of the layer containing the photocatalyst is kept permanently hydrophilic. When the optical excitation is interrupted,
The hydrophilicity of the surface gradually decreases. This is caused by the fact that the chemically adsorbed water and the physically adsorbed water once adsorbed above the equilibrium with the atmosphere by the above quantum reaction tend to return to the equilibrium state by stopping the quantum reaction due to the interruption of the photoexcitation (and this adsorbed water). The desorption reaction proceeds more rapidly as the oxygen partial pressure in the atmosphere is higher and the water vapor partial pressure is lower.) However, when the photocatalyst is photoexcited, the water adsorption reaction based on the quantum reaction occurs again, and the surface becomes hydrophilic again.

In the present invention, the forbidden band width between the conduction electron band and the valence band on the particle surface is 2.2 eV on the substrate surface.
Provided is a photocatalytic hydrophilic member, wherein a layer containing photocatalyst particles of about 3.1 eV is formed, and the member surface becomes hydrophilic by photoexcitation of the photocatalyst. Even if a photocatalytic particle having a forbidden band width between 2.2 eV and 3.1 eV between the conduction electron band and the valence band on the particle surface is used, it is possible to cause the water adsorption reaction based on the quantum reaction. In addition, since visible light emitted from general lighting in a large amount can be used, the above technology can be easily used in a room or the like.

In another aspect of the present invention, the substrate has a sub-level between the conduction band and the valence band on the surface of the substrate, and the substrate has a sub-level between the conduction band and the sub-level or the valence band. The energy gap between the band and the sub-level is 2.2 eV to 3.
A layer containing photocatalyst particles of 1 eV is formed,
Provided is a photocatalytic hydrophilic member, wherein the surface of the member becomes hydrophilic by photoexcitation of the photocatalyst. In this case as well, it is possible to cause a water adsorption reaction based on the quantum reaction in the same manner, and furthermore, it becomes possible to use visible light that is largely emitted from general illumination. It will be easier.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the photocatalytic hydrophilic member of the present invention, the photocatalytic particles having a band gap between the conduction electron band and the valence band on the particle surface of 2.2 to 3.1 eV are provided on the substrate surface. Is formed, and the surface of the member becomes hydrophilic by the photoexcitation of the photocatalyst.
Alternatively, the substrate surface has a sub-level between the conduction electron band and the valence band, and the energy gap between the conduction electron band and the sub-level or between the valence band and the sub-level. Is 2.2 to 3.
A layer containing photocatalyst particles of 1 eV is formed, and the surface of the member becomes hydrophilic by photoexcitation of the photocatalyst. Here, the photocatalyst refers to an energy larger than the energy gap between the conduction band and the valence band.
A substance capable of generating conduction electrons and holes by excitation of electrons in the valence band (photoexcitation) when irradiated with light (excitation light) having a short wavelength (excitation light) (FIG. 1). ,
Anatase type titanium oxide, rutile type titanium oxide, zinc oxide, strontium titanate, tin oxide, zirconia, bismuth trioxide, tungsten trioxide, ferric oxide, diniobium pentoxide, etc.

In the above photocatalyst, the forbidden band width between the conduction electron band and the valence band on the particle surface is 2.2 to 3.1 e.
As the photocatalyst of V, rutile-type titanium oxide, tungsten trioxide, ferric oxide and the like can be suitably used. A sub-level between the conduction band and the valence band, and an energy gap between the conduction band and the sub-level or between the valence band and the sub-level is 2.2 to 3; The photocatalyst of 0.1 eV is an anatase doped with at least one of ruthenium, cerium, cobalt, chromium, vanadium, and rhodium.
Any photocatalyst of zeolite titanium oxide, rutile titanium oxide, zinc oxide, strontium titanate, tin oxide, zirconia, bismuth trioxide, tungsten trioxide, ferric oxide, and diniobium pentoxide can be suitably used. . For example,
It is known that when these metals are doped into strontium titanate, photoexcitation occurs even with visible light, and a photocurrent flows by generated conduction electrons or holes (FIG. 2, ceramics, Vol. 31, No. 10, 10). Pp. 815820,
October 1996). The illuminance of the excitation light is preferably 0.1 mW / cm ² or more, and preferably 1 mW / cm ^{2 in} order for the surface of the substrate to be highly hydrophilized by light excitation by the visible light of the photocatalyst.
cm ² or more is more preferable.

The thickness of the layer containing the photocatalyst is 0.4 μm
It is preferable to set the following. Then, cloudiness due to irregular reflection of light can be prevented, and the surface layer becomes substantially transparent. More preferably, the thickness of the layer containing the photocatalyst is 0.2 μm or less. Then, color formation of the layer due to light interference can be prevented. Also, the thinner the layer, the better its transparency. Furthermore, the thinner the film, the better the wear resistance of the layer.

When the substrate is a glass containing alkali network modifying ions such as sodium (soda lime glass, side-by-side glass, etc.), an intermediate layer such as silica is formed between the substrate and the surface layer. You may. Then, the diffusion of the alkali network modifying ions from the base material to the surface layer during the firing is prevented, and the photocatalytic function is more effectively exhibited.

Next, a method for forming the surface layer will be described. There are roughly five methods. One method is a sol coating and firing method, the other method is an organotin compound method, and the other method is an electron beam evaporation method. (1) Sol coating and firing method A sol in which photocatalyst particles are dispersed is applied to the surface of a substrate by a spray coating method, a dip coating method, a flow coating method, a spin coating method, and a roll coating method. Apply and bake. (2) Organic titanate method A hydrolysis inhibitor (hydrochloric acid, ethylamine, etc.) is added to an organometallic compound, and alcohol (ethanol, propanol) is added.
, Butanol, etc.), and after partially or completely proceeding the hydrolysis, the mixture is spray-coated, dip-coated. , Flow coating method, Spin coating
Coating method, roll coating method, etc.
dry. By drying, the hydrolysis of the organometallic compound is completed, and further the polymer is subjected to dehydration-condensation polymerization to form a metal oxide layer on the surface of the base material. Further, by firing and crystallizing as needed, a crystalline metal oxide having photocatalytic properties is obtained. (3) Electron beam evaporation method A metal oxide layer is formed on the surface of a substrate by irradiating a target of the metal oxide with an electron beam. further,
By firing and crystallizing as needed, a crystalline metal oxide having photocatalytic properties is obtained. (4) Binding by Silica Precursor After a silica precursor such as tetraalkoxysilane, silanol or alkyl silicate is added to a sol in which photocatalyst particles are dispersed, spray coating is performed on the surface of the substrate. Method, dip coating method, flow coating method,
After coating by a method such as spin coating or roll coating, the silica precursor is cured by subjecting it to hydrolysis and dehydration condensation polymerization. (5) Binding by Silicone Precursor After adding a silicone precursor such as an organotrialkoxysilane, a diorganodialkoxysilane, or a polyorganosiloxane liquid to a sol in which photocatalyst particles are dispersed, After coating on the surface of the material by spray coating, dip coating, flow coating, spin coating, roll coating, etc.,
The silicone precursor is cured by subjecting it to hydrolysis and dehydration polycondensation, and is further cured by photocatalysis.
At least a part of the organo group bonded to the silicon atom in the molecule is replaced with a hydroxyl group.

If the surface of the member can maintain hydrophilicity, in addition to the antifogging effect and the surface cleaning effect, the antistatic effect (dust adhesion preventing effect), the heat insulation effect, the bubble adhesion preventing effect in water, and the efficiency improvement in the heat exchanger. Effects, bioaffinity effects, etc. are exhibited.

The substrate to which the present invention can be applied is a transparent member when an anti-fogging effect is expected, and glass, plastic, or the like can be suitably used as the material. Speaking of applicable base materials, back mirrors for vehicles, mirrors for bathrooms,
Mirrors such as toilet mirrors, dental mirrors, road mirrors; lenses such as spectacle lenses, optical lenses, camera lenses, endoscope lenses, illumination lenses, semiconductor lenses, copier lenses; prisms; Windows for vehicles such as cars, railcars, aircraft, ships, submersibles, snowmobiles, gondolas in lowways, gondolas in amusement parks, spaceships; vehicles, railcars, aircraft, Windshields for vehicles such as ships, submersibles, snowmobiles, snowmobiles, motorbikes, lowway gondola, amusement park gondola, spaceships; protective goggles, sporting goggles -Glue, shield of protective mask, shield of sports mask, shield of helmet, glass of frozen food display case; cover glass of measuring instrument, and affixed to the surface of the article Including film for

When a surface cleaning effect is expected as a substrate to which the present invention can be applied, the material may be, for example, metal, ceramics, glass, plastic, wood, stone, cement, concrete, fiber, or the like. Fabrics, their combinations,
Those laminates can be suitably used. Speaking of applicable base materials, building materials, building exteriors, building interiors, window frames, windowpanes, structural members, vehicle exteriors and coatings, machinery and articles exteriors, dustproof covers and coatings, traffic signs, Various display devices, advertising towers, road noise barriers, railway noise barriers, bridges, garages
Drill exterior and paint, tunnel interior and paint, insulators, solar cell cover, solar water heater collector cover, vinyl
House, vehicle lighting cover, housing equipment, toilet bowl, bathtub, wash basin, lighting fixture, lighting cover, kitchenware, tableware,
Includes dishwashers, dish dryers, sinks, cooking ranges, kitchen hoods, ventilation fans, and films for affixing to the surface of the article.

When the antistatic effect is expected as a substrate to which the present invention can be applied, the material is, for example, metal,
Ceramics, glass, plastic, wood, stone, cement, concrete, fiber, fabric, combinations thereof, and laminates thereof can be suitably used. Speaking of applicable substrates, cathode ray tubes, magnetic recording media, optical recording media, magneto-optical recording media, audio tapes, video tapes, analog records, housings and parts for household electrical appliances, Exterior and painting, OA equipment product housing and parts and exterior and painting, building materials, building exterior, building interior, window frames, window glass, structural members, vehicle exterior and painting, mechanical equipment and articles exterior, dustproof cover and Includes a film for painting and affixing to the surface of the article.

[0016]

EXAMPLE 1 part by weight of a ferric oxide sol, 1 part by weight of tetraethoxysilane in terms of silica, and 98 parts by weight of ethanol were mixed, and a 10 cm square soda lime glass substrate was coated with a flow coat. Coating at 150 ° C.
By heat-treating for 0 minutes, tetraethoxysilane was hydrolyzed and dehydrated and polycondensed to cure the coating film, thereby obtaining a # 1 sample. After leaving the sample in a dark place for one week, the sample surface was irradiated with an illuminance of 0.3 mW / cm ² for 3 days using a fluorescent lamp, and the contact angle with water was measured. Here, the contact angle with water is measured using a contact angle measuring device (Kyowa Interface Science, CA-X150).
Was evaluated using a value 30 seconds after dropping a water drop from the micro syringe. As a result, the # 1 sample was hydrophilized from 50 ° to 20 °.

[0017]

According to the photocatalytic hydrophilic member of the present invention,
Irradiation with visible light can make the member surface hydrophilic.

[Brief description of the drawings]

FIG. 1 is a diagram showing band structures of various photocatalysts.

FIG. 2 is a diagram showing how the wavelength dependence of photocurrent changes when a small amount of metal is doped into strontium titanate.

Claims (2)

[Claims] 1. A band gap between a conduction electron band and a valence band on a particle surface is 2.2 eV to 3.1 e on a substrate surface.
A photocatalytic hydrophilic member, wherein a layer containing photocatalyst particles of V is formed, and the surface of the member becomes hydrophilic by photoexcitation of the photocatalyst. 2. A substrate having a sub-level between a conduction electron band and a valence band on a surface of a substrate, wherein the sub-level is located between the conduction electron band and the sub-level or between the conduction band and the sub-level. A layer containing photocatalyst particles having an energy gap between 2.2 eV and 3.1 eV is formed, and the surface of the member becomes hydrophilic by photoexcitation of the photocatalyst. Hydrophilic member.