JP2001146491A - Photo-catalytic hydrophilic tile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tile capable of keeping the surface of a substrate in a highly hydrophilic state over a long period. SOLUTION: The objective photo-catalytic hydrophilic tile has a surface layer containing a photo-catalytic oxide and any one of boric acid compound, borosilicic acid compound and aluminoboric acid component or has a layer containing a photo-catalytic oxide and a surface layer formed on the oxide- containing layer and containing any one of boric acid compound, borosilicic acid compound and aluminoboric acid component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology for making and maintaining a tile surface highly hydrophilic. More specifically, the present invention provides a highly hydrophilic surface for buildings, windowpanes, machinery and articles to prevent the surface from being soiled or to self-clean or self-clean the surface. Related to cleaning technology.

[0002]

2. Description of the Related Art In the field of construction and paints, contamination of architectural exterior materials, outdoor buildings and coating films thereof has become a problem due to environmental pollution. Dust and particles suspended in the air accumulate on the roof and outer walls of buildings in fine weather. Sediment is washed away by rainwater as it rains and flows down the building's outer walls. Furthermore, in the rain, the floating dust is carried by the rain and flows down on the outer wall of the building or the surface of the outdoor building. As a result, pollutants adhere to the surface along the path of rainwater. When the surface dries, striped stains appear on the surface. Dirt on building exterior materials and coatings consists of combustion products such as carbon black, and inorganic pollutants such as urban dust and clay particles. It is thought that such a variety of contaminants complicates antifouling measures (Yoshinori Tachibana, "Method for Accelerated Testing of Contamination of Exterior Wall Finishing Materials", Proc. No., October 1989, p.15-2
4).

According to conventional wisdom, in order to prevent dirt on the building exterior and the like, polytetrafluoroethylene (PT) is used.
Although water-repellent paints such as FE) were considered preferable, recently it has been considered that it is desirable to make the surface of the paint film as hydrophilic as possible for urban dust containing a large amount of hydrophobic components. (Polymer, Vol. 44, May 1995, p. 307). Therefore, a hydrophilic graft polymer
It has been proposed to paint a building at (Chemical Industry Daily, January 30, 1995). According to reports, this coating exhibits a hydrophilicity of 30 to 40 ° in contact angle with water. However, the contact angle of inorganic dust represented by clay minerals with water is 20 ° to 50 °, and has an affinity for a graft polymer having a contact angle of 30 to 40 ° with water, and has It is considered that the graft polymer coating cannot prevent contamination by inorganic dust because it easily adheres.

[0004]

As described above, by making the surface of a member hydrophilic, the surface of a building, a window glass, a machine, or an article is prevented from being stained, or the surface is self-cleaned (self-cleaning). Although there is a proposal which can be easily cleaned, the effect is not sufficient because the surface cannot be maintained at a high degree of hydrophilicity for a long time. In view of the above circumstances, an object of the present invention is to provide a member capable of maintaining a surface with a high degree of hydrophilicity for a long period of time.

[0005]

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. That is, when light having energy equal to or greater than the energy gap between the upper end of the valence band and the lower end of the conduction electron band of the photocatalyst is irradiated on the photocatalyst, the electrons in the valence band of the photocatalyst are excited to cause conduction electrons and holes. Are produced, and one or both of them may possibly impart a polarity to the surface and collect polar components such as water and hydroxyl groups. Then, due to the coordinated action of one or both of the conduction electrons and the holes and the above-mentioned polar components, the chemically adsorbed water is adsorbed on the surface, and a physically adsorbed water layer is formed thereon.

In the present invention, a surface layer containing a photocatalytic oxide and a boric acid compound or a borosilicate compound is formed on the surface of a base material, or a photocatalytic oxide-containing layer is formed, and further thereon. Provided is a photocatalytic hydrophilic member, wherein a surface layer containing a boric acid compound or a borosilicate compound is formed. If the surface layer contains any of boric acid compounds, borosilicate compounds, and aluminoboric acid compounds, these substances have water storage capacity, so that a stable physically adsorbed water layer is easily formed and kept in a dark place. However, the hydrophilicity of the surface can be maintained at a high level for a considerably long time. Furthermore, because the photocatalytic oxide is contained in the surface layer, even when the hydrophilicity of the surface has been lost due to long-term storage in a dark place, the photocatalytic oxide exhibits superhydrophilicity in response to photoexcitation of the photocatalytic oxide. Become like

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In a first embodiment of the present invention, as shown in FIG. 1, a photocatalytic titanium oxide and a boric acid compound, a borosilicate compound, and an aluminoborate compound are formed on a substrate surface. A surface layer containing any of them is formed. In the second embodiment of the present invention, as shown in FIG. 2, a photocatalytic titanium oxide-containing layer is formed on the surface of a substrate, and a boric acid compound, a borosilicate compound, or an aluminoboric acid compound is further formed thereon. To form a surface layer containing

The term “highly hydrophilic” in the present invention refers to a state exhibiting water wettability of 10 ° or less, preferably 5 ° or less in terms of a contact angle with water. PCT / JP96 / 007
As shown in No. 33, if the member surface is in a state of 10 ° or less, preferably 5 ° or less in terms of a contact angle with water,
Combustion products such as carbon black and the like contained in urban exhaust dust and automobile exhaust gas, hydrophobic contaminants such as oils and fats, sealant eluting components, and inorganic clay contaminants are hardly adhered to each other. However, it can be easily dropped by rain or washing.

If the surface of the member can maintain the high degree of hydrophilicity, in addition to the surface cleaning effect, an antistatic effect (dust adhesion preventing effect), a heat insulating effect, a bubble adhesion preventing effect in water,
The effect of improving the efficiency in the heat exchanger, the effect of biocompatibility, and the like are exhibited.

[0010] A photocatalytic oxide is a light-sensitive material that emits light (excitation light) having an energy (ie, shorter wavelength) larger than the energy gap between the conduction electron band and the valence band of an oxide crystal. An oxide capable of generating conduction electrons and holes by the excitation of electrons (photoexcitation) in the valence band, including anatase-type titanium oxide, rutile-type titanium oxide, tin oxide, zinc oxide, bismuth trioxide, Tungsten trioxide, ferric oxide, strontium titanate and the like can be suitably used. The light source used for photoexcitation of the photocatalytic oxide is, for example, indoor lighting such as a fluorescent lamp, an incandescent lamp, a metal halide lamp, or a mercury lamp, the sun, or a light source that guides light from the light source through a low-loss fiber. Can be suitably used. In order for the substrate surface to be highly hydrophilized by photoexcitation of the photocatalytic oxide, the illuminance of the excitation light is 0.001 m
It is sufficient if it is at least W / cm2, but it is preferably at least 0.01 mW / cm2, more preferably at least 0.1 mW / cm2.

It is preferable that the thickness of the surface layer be 0.2 μm or less. Then, it is possible to prevent the surface layer from being colored by light interference. Also, the thinner the surface layer, the more transparent the member can be. Further, when the film thickness is reduced, the wear resistance of the surface layer is improved. The surface of the surface layer may be further provided with a wear-resistant or corrosion-resistant protective layer capable of being made hydrophilic and other functional films. Preferably, the surface layer does not have a very high refractive index as compared to the substrate. Preferably, the refractive index of the surface layer is 2 or less. Then, light reflection at the interface between the base material and the surface layer can be suppressed. When the substrate is a glass or glazed tile containing an alkali network modifying ion such as sodium, an intermediate layer such as silica may be formed between the substrate and the surface layer. 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. Metals such as Ag, Cu, and Zn can be added to the surface layer. The surface layer to which the metal is added can kill bacteria adhering to the surface. Furthermore, this surface layer inhibits the growth of microorganisms such as molds, algae and moss. Therefore, adhesion of dirt on the member surface due to microorganisms can be more effectively suppressed. The surface layer has P
Platinum group metals such as t, Pd, Rh, Ru, Os, Ir can be added. The surface layer to which the metal is added can enhance the oxidizing activity of the photocatalyst, and promote the decomposition of contaminants attached to the member surface.

The method for forming the hydrophilic member shown in FIG. 1 is, for example, a method in which a mixed solution containing a photocatalytic titanium oxide sol and a boric acid compound, a borosilicate compound, or an aluminoboric acid compound is sprayed on a substrate surface. -Ting, flow-
After coating by a method such as coating, spin coating, dip coating, roll coating, etc., the surface layer is fixed to the substrate by standing at room temperature or heat treatment.

The method for forming the hydrophilic member shown in FIG. 2 is, for example, a method in which a sol in which photocatalytic titanium oxide particles are suspended is coated on a substrate surface.
Spray coating, flow coating, spin coating, dip coating, roll coating, etc., after coating and drying, contains any of boric acid compounds, borosilicate compounds, and aluminoboric acid compounds The mixed solution to be further applied thereon by any of the above methods,
The surface layer is fixed by standing at room temperature or heat treatment. In another method for forming the hydrophilic member shown in FIG. 2, for example, tetraalkoxytitanium such as tetraethoxytitanium, tetramethoxytitanium, tetrapropoxytitanium, tetrabutoxytitanium; titanium chelate, acetate titanium; Soluble inorganic titanium compounds such as titanium chloride;
Titanium hydroxide; a precursor of a photocatalytic titanium oxide such as amorphous titanium oxide, on a substrate surface, spray coating;
After coating and drying by methods such as flow coating, spin coating, dip coating, roll coating, and electron beam evaporation, contains any of boric acid compounds, borosilicate compounds, and aluminoboric acid compounds The mixed solution to be applied is further applied thereon by any one of the methods described above, and the temperature at which the precursor of the photocatalytic titanium oxide changes to a photocatalytic oxide (the crystallization temperature of the anatase type titanium oxide) or higher. And fix the surface layer to the substrate. In the hydrophilic member shown in FIG. 2, it is preferable that the photocatalytic oxide layer has a thickness of 10 nm or more, in particular, because the photocatalytic oxide has excellent hydrophilicity by photoexcitation.

[0014]

According to the present invention, the substrate surface can be maintained at a high degree of hydrophilicity for a long period of time.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of the present invention.

FIG. 2 is a diagram showing another embodiment of the present invention.

Claims (2)

[Claims] 1. A photocatalytic property, wherein a surface layer containing a photocatalytic oxide and any one of a boric acid compound, a borosilicate compound and an aluminoboric acid compound is formed on the surface of a substrate. Hydrophilic tile. 2. A photocatalytic oxide-containing layer is formed on a substrate surface, and a surface layer containing any of a boric acid compound, a borosilicate compound, and an aluminoboric acid compound is further formed thereon. Characteristic photocatalytic hydrophilic tile.