JPH10147771A - Photocatalytic hydrophilic member and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a photocatalytic member of which the surface can be kept highly hydrophilic for a long term by fixing a surface layer contg. a photocatalytic TiO2 and WO3 on the surface of a substrate and causing the surface to chemically adsorb a specific substance so that the surface exhibits a high hydrophilicity in response to photoexcitation of a photocatalyst. SOLUTION: A surface layer contg. a photocatalytic TiO2 (e.g. anatase titanium oxide) and WO3 is fixed on the surface of a substrate (e.g. soda lime glass), and at least a part of the surface of the surface layer is caused to chemically adsorb an electron attractive substance having an electron attractive group stronger than a hydroxyl group of a sulfo, nitro, sulfuric, or nitric group. Pref. the surface hydrophilicity due to the photoexcitation of the photocatalyst is 10 degrees or lower in terms of contact angle. This member is produced e.g. by coating the surface of a substrate with a mixture comprising photocatalytic TiO2 particles and tungstic acid, applying (NH4 )2 SO4 thereto, and thermally treating at 400-800 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for making a member surface highly hydrophilic and maintaining it. More specifically, the present invention relates to an anti-fog technology for preventing the fogging and water droplets from forming on a mirror, lens, glass, prism or other transparent member by making the surface of the member highly hydrophilic. The present invention also prevents the surface from being stained by highly hydrophilizing the surface of a building, a window glass, a mechanical device or an article,
Alternatively, the present invention relates to a technique of self-cleaning (self-cleaning) or easily cleaning a surface.

[0002]

2. Description of the Related Art It is often experienced that in cold weather, windshields and glazings of automobiles and other vehicles, glazings of buildings, lenses of glasses, and cover glasses of various instrument panels are fogged by condensed moisture. . In addition, mirrors and eyeglass lenses in bathrooms and washrooms are often fogged by steam. Furthermore,
Vehicle windshields and windows, building windows, vehicle back mirrors, eyeglass lenses, masks and helmet shields are subjected to rainfall and splashes, and when a large number of discrete water droplets adhere to the surface, the Can be dark, blurred, mottled, or cloudy, again losing visibility. Needless to say, the above "clouding" has a profound effect on safety and efficiency of various operations. For example, if the windshield or window glass of the vehicle or the back mirror of the vehicle is overcast or cloudy in cold weather or rainy weather, it is difficult to secure a view, and traffic safety is impaired. Fogging of the endoscope lens and the dental dentoscope hinders accurate diagnosis, surgery, and treatment. If the cover glass of the instrument panel becomes fogged, it becomes difficult to read the data.

It has been proposed to make the surface hydrophilic in order to eliminate the "clouding". For example, 3-1
No. 29357 discloses a method in which a polymer layer is provided on the surface of a base material, and this layer is irradiated with ultraviolet rays and then treated with an aqueous alkali solution to generate high-density acidic groups, whereby the surface of the polymer layer becomes hydrophilic. A mirror anti-fogging method is disclosed. However, with such acidic groups, the surface polarity is not sufficient and the surface loses hydrophilicity over time due to contaminants adhering to the surface,
It is considered that the anti-fog performance is gradually lost.

[0004] On the other hand, in the fields of construction and paints, stains on building exterior materials, outdoor buildings and their coatings have become a problem with 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.
5-24).

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 typified by clay minerals with water is from 20 ° to 50 °, and has an affinity for a graft polymer having a contact angle of 30 to 40 ° with water. It is thought that the coating of the graft polymer cannot prevent contamination by inorganic dust because it easily adheres.

[0006]

As described above, by making the surface of the member hydrophilic, it is possible to prevent the member from fogging or forming water droplets, and also to prevent the surfaces of buildings, window glasses, mechanical devices and articles from becoming dirty. Although there are proposals that can prevent blemishes or clean the surface by self-cleaning or can be easily cleaned, the effect was not sufficient because the surface could not 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.

[0007]

SUMMARY OF THE INVENTION The present invention is based on the discovery that, in a member having a surface layer containing a photocatalyst, the surface of the member is highly hydrophilized when the photocatalyst is photoexcited. 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 of the photocatalyst and the lower end of the conduction electron band is irradiated on the photocatalytic oxide, the electrons in the valence band of the photocatalyst are excited and the conduction electrons are excited. Then, holes are generated, and one or both of these actions probably gives polarity to the surface, and polar components such as water and hydroxyl groups are collected. And either or both conduction electrons and holes,
The cooperative action of the polar components breaks the chemical bond between the adsorbed surface and the contaminants chemically adsorbed on the surface, and causes the chemically adsorbed water to be adsorbed on the surface, further forming a physically adsorbed water layer on it. It is done.

In the present invention, a photocatalytic titanium oxide and a surface layer containing tungsten oxide are fixed, and at least a part of the surface of the layer is chemically adsorbed with an electron withdrawing material. Containing layer is formed,
Further, the present invention provides a photocatalytic hydrophilic member, wherein a surface layer containing tungsten oxide is formed thereon, and an electron withdrawing body is chemically adsorbed on at least a part of the surface of the layer. When tungsten oxide is contained in the surface layer in addition to the photocatalytic titanium oxide, the hydrophilicity of the once-hydrophilized surface at the time of shading is improved. This is because when tungsten oxide is contained, the polarity of the surface becomes large regardless of the presence or absence of light, so it is easier to selectively adsorb water molecules that are polar molecules than hydrophobic molecules, It is considered that a stable physical adsorption water layer is easily formed. Further, when an electron withdrawing body containing a group having a stronger electron withdrawing property than a hydroxyl group such as a sulfonic acid group, a nitro group, a sulfate group or a nitric acid group is chemically adsorbed on the surface, the electron withdrawing body removes electrons on the solid surface. By suction, the electron acceptability of the metal part of the metal oxide is improved, so the polarity of the surface becomes even greater, with or without light,
A more stable physical adsorption water layer is easily formed. Therefore, by making the surface layer contain both a photocatalytic oxide, tungsten oxide and an electron withdrawing body,
In a dark place, a high degree of hydrophilicity can be maintained for a long time, and even when the hydrophilicity is lost, a high degree of hydrophilicity can be restored by photoexcitation of the photocatalytic oxide.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a first embodiment of the present invention, as shown in FIG. 1, a surface layer containing photocatalytic titanium oxide and tungsten oxide is fixed on a substrate surface,
An electron withdrawing body is chemisorbed on at least a part of the surface of the layer. In a 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 surface layer made of tungsten oxide is further formed thereon, and at least a part of the surface of the layer has an electron withdrawing material. Is chemisorbed.

The term “highly hydrophilic” in the present invention means 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 surface of the member is less than 10 ° in terms of the contact angle with water, condensed water forms individual water droplets even if moisture or steam in the air is dewed. Without this, the tendency to form a uniform water film becomes remarkable. Therefore, the tendency that light scattering fogging does not occur on the surface becomes remarkable. Similarly, when a window glass, a vehicle back mirror, a vehicle windshield, an eyeglass lens, or a shield of a helmet is exposed to rainfall or splashing, discrete unsightly water droplets are not formed, and high visibility and visibility are achieved. As a result, the effects of ensuring vehicle safety, ensuring the safety of vehicles and traffic, and improving the efficiency of various tasks and activities are dramatically improved. Also, as shown in PCT / JP96 / 00733, if the surface of the member is in a state of 10 ° or less, preferably 5 ° or less in terms of a contact angle with water, urban dust,
Combustion products such as carbon black contained in exhaust gas from automobiles, hydrophobic contaminants such as oils and fats, sealant-eluting components, and inorganic clay contaminants are unlikely to adhere, and even if they do adhere, it will rain. It can be easily dropped by washing with water.

If the surface of the member can maintain the above-mentioned high degree of hydrophilicity, in addition to the above-mentioned anti-fogging effect and surface cleaning effect, it also has an anti-static effect (dust-preventing effect), a heat-insulating effect, an effect of preventing bubbles from adhering in water, heat exchange. The effect of improving the efficiency of the vessel, the effect of biocompatibility, and the like are exhibited.

The substrate to which the present invention can be applied is a transparent member in the case where the above antifogging effect is expected, and glass, plastic, or the like can be suitably used as the material. Speaking of applicable base materials, mirrors such as vehicle back mirrors, bathroom mirrors, toilet mirrors, dental mirrors, road mirrors; spectacle lenses, optical lenses, camera lenses, endoscope lenses, Lenses such as illumination lenses, semiconductor lenses, and copier lenses; prisms; windows of buildings and towers; automobiles, railway vehicles, aircraft, ships, submersibles, snowmobiles, lowway gondolas, and amusement parks. Windowpanes for vehicles such as gondola and spacecraft; cars, railcars, aircraft, ships, submarines,
Windshields for vehicles such as snowmobiles, snowmobiles, motorcycles, lowway gondola, amusement park gondola, spaceships; protective goggles, sports goggles, protective Includes mask shield, sports mask shield, helmet shield, frozen food display case glass; measuring instrument cover glass; and film for attaching to the surface of the article. . When the surface cleaning 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, cloth, Combinations thereof and laminates thereof can be suitably used. Speaking of applicable base materials, building materials, building exteriors, building interiors, window frames, window glasses, structural members, vehicle exteriors and coatings,
Exterior of machinery and equipment, dust cover and paint, traffic signs, various display devices, advertising towers, road sound barriers, railway sound barriers, bridges, exterior and paint of garlands, tunnel interior and paint, Insulators, solar cell covers, solar water heater heat collection covers, vinyl houses, vehicular lighting covers, housing equipment, toilets, bathtubs, washbasins, lighting fixtures, lighting covers, kitchenware, tableware, tableware Includes washer, dish dryer, sink, cooking range, kitchen hood, ventilator, and film for application 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, cloth,
Combinations thereof and laminates thereof can be suitably used.
Speaking of applicable base materials, cathode ray tubes, magnetic recording media, optical recording media, magneto-optical recording media,
Diode tapes, video tapes, analog records, housing and parts and exteriors and paintings for household electrical appliances, housings and parts and exteriors and paintings for OA equipment products, building materials, building exteriors, building interiors, window frames, windows It includes glass, structural members, vehicle exteriors and coatings, exteriors of machinery and articles, dustproof covers and paintings, and films to be attached to the article surfaces.

[0013] A photocatalytic oxide is formed by irradiating light (excitation light) having 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
W suffices / cm ² or more, but preferably that it 0.01 mW / cm ² or more, and more preferably it 0.1 mW / cm ² or more.

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.

In the method of forming the hydrophilic member shown in FIG. 1, for example, a coating solution is prepared by mixing photocatalytic titanium oxide particles and tungstic acid, and the coating solution is spray-coated on a substrate surface. Coating is performed by a method such as flow coating, spin coating, dip coating, or roll coating. Further, an electron withdrawing body such as sulfuric acid, nitric acid, ammonium sulfate, and ammonium nitrate is applied thereon by the above-described method, and 400 to 800 at which the chemically adsorbed water on the surface is released.
The surface layer is fixed to the substrate by heat treatment at a temperature of ° C.

In the method of forming the hydrophilic member shown in FIG. 2, for example, a sol in which photocatalytic titanium oxide particles are
After coating and drying by a method such as spray coating, flow coating, spin coating, dip coating, roll coating, etc., tungstic acid is applied,
Further, an electron withdrawing body such as sulfuric acid, nitric acid, ammonium sulfate, and ammonium nitrate is applied thereon by the above-mentioned method, and heat-treated at a temperature of 400 to 800 ° C. at which surface chemically adsorbed water is released, thereby fixing the surface layer to the base material. . In another method of forming the hydrophilic member of FIG. 2, for example, tetraethoxytitanium, tetramethoxytitanium, tetrapropoxytitanium,
Based on tetraalkoxy titanium such as tetrabutoxy titanium; titanium chelate, acetate titanium; soluble inorganic titanium compounds such as titanium sulfate and titanium tetrachloride; titanium hydroxide; and a precursor of crystalline titanium oxide such as amorphous titanium oxide. Spray coating, flow coating, spin coating, dip coating, row coating
After coating and drying by a method such as coating or electron beam evaporation, tungstic acid is further applied thereon by any of the above methods, and further, an electron withdrawal of sulfuric acid, nitric acid, ammonium sulfate, ammonium nitrate or the like is further applied thereon. The temperature is the temperature at which the chemically adsorbed water on the surface is released and the precursor of the photocatalytic titanium oxide changes into a photocatalytic oxide (the crystallization temperature of the anatase type titanium oxide). 400
Heat treatment is performed at a temperature of at least 800 ° C. to fix the surface layer to the substrate. In the hydrophilic member of FIG. 2, it is preferable that the photocatalytic titanium oxide layer has a thickness of 10 nm or more, in particular, because the photocatalytic titanium oxide has excellent hydrophilicity by photoexcitation.

[0017]

【Example】

Example. 2. A 10 cm square soda lime glass plate with a concentration of 3.
After immersion in a 5% by weight tetraethoxysilane solution (diluent: ethanol, hydrolysis inhibitor: ethanolamine),
Pull up the solution at a speed of 24 cm / min and dip the solution
It was applied to the surface of a glass plate by a coating method and dried. By the steps up to this point, tetraethoxysilane undergoes hydrolysis to form silanol first, and then silanol
A thin film of amorphous silica was formed on the surface of the glass plate by the dehydration-condensation polymerization of toluene. Next, a 3.5% by weight tetraethoxytitanium solution (diluent: ethanol, hydrolysis inhibitor:
After dipping in ethanolamine, the solution was pulled up at a speed of 24 cm per minute, the solution was applied to the surface by dip coating, and dried to obtain a # 1 sample. By the above steps, tetraethoxytitanium is hydrolyzed into titanium hydroxide first, and then a thin film of amorphous titanium oxide (thickness of about 50 nm) is obtained by dehydration-condensation polymerization of titanium hydroxide.
Formed on the surface. Next, after being immersed in a 1% aqueous ammonia solution in which 0.25% by weight of tungstic acid and 0.33% by weight of ammonium sulfate are dissolved, the solution is pulled up at a rate of 24 cm per minute, and the solution is subjected to dip coating.
It was applied to the surface and baked at 500 ° C. to obtain a # 2 sample.
Amorphous titanium oxide was crystallized by the calcination to form an anatase type titanium oxide, and chemically adsorbed water on the surface was released, and instead, sulfuric acid was chemically adsorbed. Oleic acid was applied to the surface of the # 2 sample immediately after firing, rubbed with a neutral detergent, rinsed with tap water and distilled water, and then dried at 50 ° C. for 30 minutes using a dryer.
The surface was intentionally contaminated by the minute drying. As a result, the contact angle with water increased to 35 °. Here, the contact angle with water is measured using a contact angle measuring device (Kyowa Interface Science, CA-X).
150), the value was measured 30 seconds after the water droplet was dropped with a microsyringe. Next, ultraviolet rays having an illuminance of 0.3 mW / cm ² per day were irradiated using a BLB lamp (Sankyo Electric, Black Light Blue-Lamp) as a light source.
As a result, the contact angle of the sample surface with water showed a low value of 0 °. Next, the sample was left in a dark place for one day, and the change in the contact angle of the sample surface with water was measured. As a result, the value was maintained as low as 9 °.

[0018]

According to the present invention, a layer composed of photocatalytic titanium oxide and tungsten oxide is formed, on which an electron withdrawing substance is chemically adsorbed, or a layer containing photocatalytic titanium oxide is formed, and tungsten oxide is further formed thereon. Is formed, and the electron withdrawing body is chemisorbed thereon, so that the surface becomes highly hydrophilic in response to the photoexcitation of the photocatalytic titanium oxide. In addition to being able to maintain a high degree of hydrophilicity permanently, the action of the tungsten oxide and the electron withdrawing material probably increases the polarity of the surface, and temporarily shields the surface that has become highly hydrophilic during light shielding. Hydrophilicity is maintained for a long time.

[Brief description of the drawings]

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

FIG. 2 shows a second embodiment of the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI B60J 1/00 B60J 1/00 H E06B 7/12 E06B 7/12

Claims (9)

[Claims] 1. A photocatalytic titanium oxide and a surface layer containing tungsten oxide are fixed on a surface of a base material, and an electron withdrawing body is chemisorbed on at least a part of the surface of the layer. A photocatalytic hydrophilic member, wherein the surface exhibits hydrophilicity in response to light excitation of the photocatalytic hydrophilic member. 2. A photocatalytic titanium oxide-containing layer is formed on the surface of a substrate, and a surface layer containing tungsten oxide is further formed thereon, and an electron withdrawing body is formed on at least a part of the surface of the layer. A photocatalytic hydrophilic member which is chemically adsorbed, and whose surface exhibits hydrophilicity in response to photoexcitation of the photocatalyst. 3. The method according to claim 1, wherein the electron withdrawing body is a substance containing a group having an electron withdrawing property stronger than a hydroxyl group such as a sulfonic acid group, a nitro group, a sulfate group, and a nitric acid group.
3. The photocatalytic hydrophilic member according to 2. 4. The photocatalytic hydrophilicity according to claim 1, wherein the hydrophilicity of the surface in response to photoexcitation of the photocatalyst is 10 ° or less in terms of a contact angle with water. Element. 5. A step of coating the surface of a substrate with a solution containing crystalline titanium oxide particles and tungstic acid, a step of applying an electron withdrawing body to the surface of the coating, and a step of chemically adsorbing water on the surface of the coating. Heat-treating at a temperature at which the electron-withdrawing member is released to chemically adsorb the electron-withdrawing body to the surface of the coating. 6. A step of forming a coating containing crystalline titanium oxide particles on the surface of a substrate, a step of applying a tungstic acid-containing solution thereon, and further applying an electron withdrawing body thereon. A method for producing a photocatalytic hydrophilic member, comprising: a step of performing heat treatment at a temperature at which chemically adsorbed water on the surface of the coating desorbs to chemically adsorb the electron withdrawing body on the surface of the coating. 7. The step of forming a coating containing crystalline titanium oxide particles is a step of coating the surface of a substrate with amorphous titanium oxide, and then crystallizing the amorphous titanium oxide. 3. The method for producing a photocatalytic hydrophilic member according to item 1. 8. The method for producing a photocatalytic hydrophilic member according to claim 5, wherein the tungstic acid-containing solution is a basic solution containing tungstic acid. 9. The method for producing a photocatalytic hydrophilic member according to claim 5, wherein the heat treatment is firing at a temperature of 400 to 800 ° C.