HK1009829B - Method of photocatalytically making the surface of base material hydrophilic, base material having the surface, and process for producing said material - Google Patents

Description

Photocatalytic method for making surface of substrate hydrophilic, substrate having the surface and method for producing the same

Technical Field

The present invention relates broadly to the field of rendering substrate surfaces highly hydrophilic and maintaining high hydrophilicity. More particularly, the present invention relates to the field of antifogging, in which the surfaces of transparent substrates such as mirrors, lenses and glass plates are highly hydrophilized, so that the substrates fog or form water droplets. The invention also relates to the field of highly hydrophilizing the surface of buildings, glazings, machines or articles in order to render the surface antifouling, self-cleaning or easy to clean.

Background

It is common to encounter the problem that in cold winter months, windshields and glazings for automobiles and other vehicles, glazings for buildings, lenses for glasses and the glass surfaces of various instruments become fogged by water condensation. Similarly, in a bathroom or toilet, a scene in which the mirrors and eyeglass lenses are fogged by the water vapor surface is often encountered.

Fogging of the surface of an article is caused by the fact that when the surface is maintained at a cloud point below the ambient atmosphere, moisture present in the ambient air condenses to form a moist condensate on the surface.

If the condensate particles are fine enough that their diameter is in the half range of the visible wavelength, these particles cause light to be dispersed, causing the window glass and the mirror to become visibly opalescent, thereby resulting in a loss of visibility.

As the condensation of moisture continues, causing fine condensate particles to coalesce with one another and grow into larger particles, the refraction of light occurring at the interface of the water droplet with the surface and the interface of the water droplet with the ambient air can cause the surface to become hazy, dull, messy, or cloudy. As a result, the view through a transparent article such as a glass plate may be obscured and the refractive pattern of the mirror may be obscured.

Similarly, when the windshield and window glass of a vehicle, the window glass of a building, the rear view mirror of a vehicle, the lens of eyeglasses or the visor of a mask or helmet are splashed with rainwater, so that water droplets adhere to the surfaces, the surfaces become blurred, dull, messy or clouded, thereby causing a loss of visibility.

The term "anti-fog" as used herein and in the appended claims refers broadly to the prevention of optical problems leading to fog, the growth of condensation droplets, or the above-mentioned coherent droplets.

It is clear that anti-fog technology profoundly affects the safety and efficiency of various workpieces. For example, if the windshield, window glass, or rear view mirror of a vehicle becomes fogged or fogged, vehicle and traffic safety will decline. Fogging of the endo-lens and buccal mirror can prevent the accuracy and precision of diagnosis, surgery and treatment. If the glass cover of the measuring instrument is fogged, the data is difficult to read.

Windshields for automobiles and other vehicles are often provided with windshield wipers, de-icing devices and heaters to allow viewing during cold seasons and in rainy conditions. However, it is not industrially possible to mount such a device to side windows and rearview mirrors provided outside a vehicle. Similarly, it is difficult, if not impossible, to mount anti-fog devices to the window glass of buildings, lenses for glasses and endoscopes, mouth mirrors, masks and helmets, or to the glass cover of measuring instruments.

As is well known, a simple and convenient anti-misting method commonly used in the art is to apply to the surface an anti-misting composition containing a light water compound such as polyethylene glycol or a hydrophobic or water repellent compound such as a silicone. However, this method has the disadvantage that the anti-mist coating thus formed is only temporary and can be easily removed when washed with water, and therefore its effect is lost very quickly.

Japanese utility model publication No. 3-129357(Mitsubishi Rayon) discloses an anti-fogging method for mirrors, in which a polymer layer is provided on the surface of a substrate and the layer is irradiated with ultraviolet light and then treated with an alkaline aqueous solution to form acid groups of high density, thereby making the surface of the polymer layer hydrophilic. In addition, it is believed that according to the present invention, the hydrophilicity of the surface may decrease over time due to the adhering contaminants, with the result that the anti-fog function is lost.

Japanese utility model publication No. 5-68006(Stanley Electric) discloses an anti-fogging film made of a graft copolymer of a propylene monomer having a hydrophilic group and a monomer having a hydrophobic group, the graft copolymer having a contact angle with water of about 50 degrees. It is therefore considered that such an anti-fogging film does not have sufficient anti-fogging ability.

Isao Kaetsu describes in "glass anti-fog coating technology", modern coating technology, P237-249, published by Sogo Gijutsu Center (1986) various anti-fog technologies used in the prior art. Mr. Kaetsu reports that there are significant problems with existing anti-fog techniques that render surfaces hydrophilic, which must be overcome when these techniques enter practical use and that he also says that conventional anti-fog coating techniques seem to be incompatible with barrier layers.

It is therefore an object of the present invention to provide an anti-fogging method which enables transparent substrates, such as mirrors, lenses and glass, to be kept highly visible.

It is another object of the present invention to provide an anti-fog method in which the surface of transparent substrates, such as mirrors, lenses and glass, remains highly hydrophilic for long periods of time.

It is another object of the present invention to provide an anti-fog method in which the surface of transparent substrates, such as mirrors, lenses and glass, remains highly hydrophilic almost permanently.

It is another object of the present invention to provide an anti-fog coating having improved stability and wear resistance.

It is another object of the present invention to provide an anti-fog coating that can be easily applied to a surface requiring anti-fog treatment.

It is another object of the present invention to provide an anti-fogging transparent substrate such as a mirror, a lens and glass, and a method for manufacturing the same, in which the surface thereof remains highly hydrophilic for a long period of time, thereby providing high anti-fogging properties for a long period of time.

On the other hand, in the building and paint fields, it has been pointed out that increasing environmental pollution will accelerate the outer building materials, the inner building and its coating to become dirty, contaminated or stained.

In this case, dust particles in the air may fall and deposit on the roof and outer walls of the building in sunny climates. When it rains, these deposits can be washed away by rain water and flow along the outer walls of the building. In addition, dust in the air can be caught by rainwater and carried along with the rainwater, flowing down the outer wall and the inner structure of the building and the surface of the building. For these reasons, the contaminated substances may adhere to the surface along the route of rainwater. When the surface dries, streaks of dirt, color, or sludge may appear on the surface.

The dirt or mottle formed on the exterior of exterior building materials and their coatings is composed of pollutants including combustion products such as carbon black, municipal soils, and inorganic substances such as clay particles. These various messy substances complicate the anti-soiling measures (Yoshinori KITSUTAKA "accelerated test method for soiling exterior wall finishing materials", Bulletin of Japan architecture society, vol.404(Oct.1989), p 15-24).

Heretofore, in the art, it has been generally considered that water repellent coatings such as Polytetrafluoroethylene (PTFE) -containing coatings can prevent exterior building materials and the like from becoming dirty or contaminated. However, it has recently been shown that in order to be compatible with urban pollution, which contains a large amount of lipophilic components, it is more appropriate to make the coating surface as hydrophilic as possible ("high polymer", vol.44, May 1995, p 307).

Thus, it has been proposed in the prior art to coat buildings with hydrophilic graft copolymers (newspaper "Daily Chemical Industry", 1 month 30. 1995). The coating is reported to have hydrophilicity of 30-40 degrees according to the contact angle with water.

However, considering that inorganic dusts represented by clay minerals have a contact angle with water in the range of 20 to 50 degrees and thus have affinity with a graft copolymer having a contact angle with water of 30 to 40 degrees, it is considered that such inorganic dusts easily adhere to the surface of the graft copolymer, thereby making it impossible to prevent the coating from being soiled and contaminated due to the inorganic dusts.

There are also various hydrophilic raw coatings on the market, which consist of acrylic resins, acrylic-silicone resins, aqueous silicones, block copolymers of silicone resins and acrylic resins, acrylic-styrene resins, ethylene oxide of sorbitol fatty acids, esters of sorbitol fatty acids, acetates of urethanes, crosslinked urethanes of polycarbonate diols and/or polyisocyanates, or crosslinked polymers of alkyl ester polyacrylates. Since these hydrophilic coatings have a contact angle with water as large as 50 to 70 degrees, they are not suitable for effectively preventing contamination by city dust containing a large amount of lipophilic components.

It is therefore a further object of the present invention to provide a method for rendering the surface of a substrate highly hydrophilic.

Another object of the present invention is a method of making a surface of a building, glazing, machine or article highly hydrophilic to prevent the surface from becoming contaminated or to render the surface self-cleaning or easily cleanable.

It is another object of the present invention to provide a highly hydrophilic stain resistant substrate and method of making the same that can be used to stain or render the surface self-cleaning or easily cleanable.

In some equipment, the formation of moist condensate on the surface thereof often prevents the operation of the equipment when the condensate grows into droplets. For example, in heat exchangers, heat exchange efficiency is reduced if condensate particles adhering to the radiating fins grow into large water droplets.

It is therefore another object of the present invention to provide a method of preventing the growth of viscous moist condensate into large water droplets, wherein the surface is rendered highly hydrophilic so that the adhering moist condensate diffuses into a film of water.

Disclosure of the invention

The present inventors have found for the first time in the world that the surface of a photocatalyst can be made highly hydrophilic by photoexcitation. Unexpectedly, it has been found that when photocatalytic titanium oxide is photo-excited with ultraviolet light, its surface is highly hydrophilized so that its contact angle with water becomes less than 10 degrees, more specifically less than 5 degrees, and even up to about zero degrees.

Based on the above novel findings, the present invention broadly provides a method of making a surface of a substrate highly hydrophilic, a substrate having a highly hydrophilic surface, and a method of preparing the same. According to the invention, the surface of the substrate is coated with an abrasion-resistant photocatalytic coating consisting of a photocatalytic semiconductor material.

The photocatalytic coating is highly hydrophilized to have super hydrophilicity after being excited with light of sufficient intensity and wavelength having energy higher than the band gap energy of the photocatalytic semiconductor for a sufficient period of time. The term "superhydrophilic" or "superhydrophilic" as used herein refers to a highly hydrophilic (i.e., water wetting) contact angle with water of less than about 10 degrees, preferably less than about 5 degrees. Similarly, the term "superhydrophilic" or "superhydrophilic" refers to rendering a surface highly hydrophilic to a contact angle with water of less than about 10 degrees, more preferably less than about 5 degrees.

The process of causing super-hydrophilization of a surface by light excitation with a photocatalyst has not been explained at present with certainty. The photocatalytic super-hydrophilization process does not necessarily appear to be identical to the photodecomposition of substances resulting from photocatalytic redox processes known in the photocatalytic art. In this respect, the conventional theory adopted in the art regarding photocatalytic redox processes is in photocatalysisThe light excitation of the agent generates electron hole pairs, and the generated electrons reduce surface oxygen to generate peroxide ions (O)₂ ^-) The electron holes oxidize the surface hydroxyl groups to generate hydroxyl groups (. OH), and these highly reactive oxygen species (O)₂ ^-And. OH) to decompose the substance by a redox process.

However, the phenomenon of super-hydrophilization caused by photocatalysts seems to be at least in two respects inconsistent with conventional understanding and observation of the photocatalytic decomposition process of the substances involved. First, according to a theory widely accepted so far, it is believed that in some photocatalysts, such as rutile and tin oxide, the conduction band is not energetic enough to promote the reduction process, so that the electrons photoexcited to the conduction band remain unchanged and become excessive, so that the electron hole pairs generated by photoexcitation recombine without contributing to the redox process. In contrast, the present inventors have found that the super-hydrophilization process by the photocatalyst occurs even with gold red tin oxide, as described hereinafter.

Secondly, conventional wisdom suggests that decomposition of species due to the photocatalytic redox process does not proceed unless the thickness of the photocatalytic layer exceeds at least 100 nanometers. In contrast, the present inventors have discovered that photocatalytic superhydrophilic effects can occur even with photocatalytic coatings on the order of a few nanometers thick.

Therefore, although it cannot be clearly predicted, it is considered that the super-hydrophilization process due to the photocatalyst is a phenomenon somewhat different from the photodecomposition of a substance due to the photocatalytic redox process. However, as described hereinafter, it has been found that super-hydrophilization of the surface does not occur unless irradiation with light having an energy higher than the band gap energy of the photocatalyst is performed. It is considered that the surface of the photocatalytic coating layer is coated with hydroxyl groups (OH) by the photocatalytic action of the photocatalyst^-) Form chemisorbed water on the surface and are super-hydrophilized.

Once the surface of the photocatalytic coating is highly hydrophilized by the photo-excitation of the photocatalyst, the hydrophilicity of the surface lasts for a certain period of time even if the substrate is left in the dark. With time, the super-hydrophilicity of the surface is gradually lost due to impurities adsorbed on the surface of the hydroxyl groups. However, super hydrophilicity can be restored when the surface is photo-excited again.

To initially super-hydrophilize the photocatalytic coating, any suitable light source having a wavelength with an energy above the bandgap energy of the photocatalyst may be used. When some photocatalysts such as titanium oxide are used, the light excitation wavelength of which falls within the ultraviolet range of the spectrum, ultraviolet light contained in sunlight can be used in the case where the sunlight is irradiated on a substrate coated with a photocatalytic coating. An artificial light source may be used when the photocatalyst is photo-excited indoors or at night. When the photocatalytic coating is made of titanium oxide mixed with silicon oxide as described below, the surface thereof can be easily hydrophilized even by weak ultraviolet irradiation light contained in light emitted from a fluorescent lamp.

After the surface of the photocatalytic coating is super-hydrophilized, the super-hydrophilicity can be maintained or renewed by weaker light. In the case of titanium oxide, the maintenance and restoration of super hydrophilicity can be attained to a satisfactory degree even by a weak ultraviolet light contained in the light of an indoor illuminating lamp such as a fluorescent lamp.

The photocatalytic coating has super-hydrophilicity even at several hours of its thickness. It has sufficient hardness when it is made in particular from a photocatalytic semiconductor material consisting of metal oxides. Therefore, the photocatalytic coating has suitable stability and abrasion resistance.

The super-hydrophilization of the surface can be used in a variety of applications, and in one aspect of the invention, the invention provides an anti-fogging method for a transparent member, an anti-fogging transparent member and a method for manufacturing the same. According to the present invention, a transparent member coated with a photocatalytic coating layer is prepared, or in other words, the surface of the transparent member is coated with a photocatalytic coating layer.

The transparent component may include mirrors, such as rear-view mirrors for vehicles, bathroom or toilet mirrors, mouth mirrors and road mirrors; lenses such as spectacle lenses, optical analysis lenses, endoscopes, and light projection lenses; a prism; glazing for buildings or control towers; glazings for vehicles such as cars, trains, planes, steamers, submarines, skis, cableway baskets, pleasure-ground pleasure boats and spacecraft; windshields for vehicles such as automobiles, trains, airplanes, steamships, submarines, skis, motorcycles, cableway baskets, pleasure-craft boats, and spacecraft; protective or athletic helmets or masks including the shielding of diving masks; shielding of goggles; a display glazing for frozen food; and a glass cover for the measuring instrument.

When a transparent member having a photocatalytic coating is irradiated with light, the surface of the photocatalytic coating becomes super-hydrophilized. Then, when moisture or water vapor in the air condenses, the condensate becomes a uniform water film without forming a single water droplet. As a result, the surface does not form a haze that causes the light to diverge.

Similarly, when the window glass, rear view mirror, windshield, eyeglass lens or goggle shield of a vehicle is subjected to rainwater or splashed water, water droplets stuck to the surface quickly spread to form a uniform water film to prevent the formation of individual water droplets to obstruct vision.

Therefore, it is possible to ensure high visibility, thereby ensuring safety of vehicles and traffic and improving efficiency of various works and activities.

In another aspect, the present invention provides a method for self-cleaning a surface of a substrate, wherein the surface is super-hydrophilized and can be automatically cleaned by rainwater. The invention also provides a self-cleaning matrix and a preparation method thereof.

The substrate may comprise an exterior component of a building, a window frame, a structural component, or a glazing; exterior parts or coatings for vehicles such as automobiles, trains, airplanes, and steamers; an external part, dust cover or coating of a machine, device or article; and exterior parts or coatings of traffic signs, various displays and advertising towers, which may be made of materials such as metal, ceramic, glass, plastic; wood, stone, cement, concrete or combinations thereof, laminates thereof or other materials. The surface of the substrate is coated with a photocatalytic coating.

Since buildings or machines or articles exposed to the outside are exposed to sunlight during the day, the surface of the photocatalytic coating will be highly hydrophilized. Furthermore, the surface is sometimes subject to rain, and whenever the superhydrophilic surface is impacted by rain, the dust, dirt, and contaminants deposited on the surface of the substrate are washed away by the rain, thereby making the surface self-cleaning.

When the surface of the photocatalytic coating is highly hydrophilized to a contact angle with water of less than about 10 degrees, preferably less than about 5 degrees, and particularly equal to about 0 degrees, not only urban soil containing a large amount of lipophilic components but also inorganic dust such as clay minerals are easily washed off from the surface. In this way, the surface of the substrate can be self-cleaning and remain highly clean under natural action. This can eliminate or greatly mitigate cleaning of architectural glazings.

In another aspect, the present invention provides a method of anti-fogging for a building, glazing, machine, device or article, wherein a photocatalytic coating is provided on a surface thereof and is highly hydrophilised to prevent odour.

A surface so super-hydrophilized will prevent contaminants from adhering to the surface along which they run with rain water laden with contaminants such as dust and dirt in the air. Therefore, by combining with the above-described self-cleaning function of rainwater, the surface of a building or the like is kept almost always highly clean.

In another aspect of the invention, a photocatalytic coating is provided on the surface of a device or article, such as on the interior and exterior parts of buildings, window glass, household items, wash basins, tubs, wash basins, lighting fixtures, kitchenware, tableware, sinks, cooking areas, cabinets and exhaust fans, which may be made of metal, ceramic, glass, plastic, wood, stone, cement, concrete, combinations thereof, laminates thereof or other materials, and which surface is optically activated as desired.

When these articles, which are soiled with oil or fat, are immersed in water, wetted with water or washed with water, the fatty soil and contaminants will detach from the super-hydrophilized surface of the photocatalytic coating and be easily removed therefrom. Therefore, the dishes contaminated by the oil or fat can be washed without detergent.

In another aspect, the present invention provides a method for preventing condensed water droplets adhering to a substrate from growing or adhering water droplets from diffusing into a uniform water film. For this purpose, a photocatalytic coating is applied to the surface of the substrate.

Once the surface of the substrate has been rendered superhydrophilic by photoexcitation of the photocatalytic coating, the condensation or water droplets of moisture adhering to the surface will spread over the surface to form a uniform film of water. By using this method to the radiating fins of the heat exchanger, condensate clogging of the fluid channels for the heat exchange medium can be prevented, thereby providing heat exchange efficiency. When the method is used on a flat mirror, lens, glazing, windshield or road, drying of the rear surface wetted with water can be accelerated.

These and other features and advantages of the present invention will become apparent from the following description.

Brief Description of Drawings

FIG. 1 shows the energy values of the valence and conduction bands for various semiconductor photocatalysts used in the present invention;

FIGS. 2A and 2B are cross-sectional views showing microscopic enlarged views of a photocatalytic coating formed on the surface of a substrate, and show that hydroxyl groups on the surface are chemically adsorbed by photo-excitation of the photocatalyst;

FIGS. 3-5, 7 and 9 show the change in contact angle with water over time for various samples of the examples when the samples were subjected to ultraviolet light irradiation, respectively;

FIG. 6 shows a Raman spectrum of a surface of a photocatalytic coating made of siloxane;

FIGS. 8 and 16 show the results of hardness tests with a pencil;

FIG. 10 shows the relationship between the thickness of the photocatalytic coating and the coating's ability to decompose methyl mercaptan;

FIGS. 11A and 11B are front and side views, respectively, of an accelerated contamination test apparatus conducted outdoors;

FIGS. 12-15 show contact angles with water at different silica mole ratios in a mixed silica titania;

FIG. 17 shows the extent to which municipal soil and waste have contaminated various surfaces with different hydrophilicity; and

fig. 18 shows the change of contact angle with water with respect to time when ultraviolet light having different wavelengths was irradiated on the surface of the photocatalytic coating layer.

Best Mode for Carrying Out The Invention

Substrates having surfaces that require super-hydrophilization are prepared and coated with a photocatalytic coating. When the substrate is made of a heat-resistant material such as metal, ceramic and glass, the photocatalytic coating can be fixed on the surface of the substrate by sintering particles of a photocatalyst described below. Alternatively, an amorphous film of the photocatalyst precursor may be first formed on the surface of the substrate and then the amorphous photocatalyst precursor may be converted into a photoactive photocatalyst by heating and crystallization.

When the substrate is made of a non-heat resistant material such as plastic or coated with a paint, a photocatalytic coating layer can be formed by applying a photo-oxidation resistant coating composition containing the photocatalyst on the surface thereof and curing the coating composition (described below).

When manufacturing an anti-fog mirror, a reflective coating may be formed on a substrate first, followed by a photocatalytic coating on the outer surface of the mirror. Furthermore, a reflective coating layer may be formed on the surface of the substrate before, after, or during the coating of the photocatalyst.

Photocatalyst and process for producing the same

The most preferred example of a photocatalyst for use in the photocatalytic coating of the present invention is titanium oxide (TiO)₂). Titanium oxide is non-toxic, chemically stable and inexpensive to obtain. In addition, titanium oxide has a high band gap energy and thus requires ultraviolet light for photoexcitation. This means that no absorption of visible light occurs during the light excitation, so that the coating does not suffer from coloring problems which would otherwise occur due to the compensating color component. Thus, titanium oxide is particularly useful for coating on transparent parts such as glass, lenses and mirrors.

As titanium oxide, anatase and rutile can be used. The anatase form of titanium oxide has an advantage in that a sol in which fine anatase particles are dispersed can be easily commercially available, and thus an extremely thin film can be easily formed. On the other hand, rutile type titanium oxide is advantageous in that it can be sintered at high temperature, so that a coating excellent in strength and wear resistance can be obtained. Although rutile titanium oxide has a lower conduction band than anatase (as shown in FIG. 1), it can also be used for purposes of super-hydrophilization of photocatalysts.

It is considered that when the photocatalytic coating 12 of titanium oxide is coated on the substrate 10 and the titanium oxide is photo-excited with ultraviolet light, water acts as a hydroxyl group (OH) under the photocatalytic action^-) Chemisorption to a surface (as shown in FIG. 2A), resulting in the surface becoming super-philicAnd (4) hydrating.

Other photocatalysts that may be used in the photocatalytic coating of the present invention may include metal oxides such as ZnO, SnO₂、SrTiO₃、WO₃、Bi₂O₃And Fe₂O₃(as shown in fig. 1). It is considered that these metal oxides can adsorb surface hydroxyl groups similarly to titanium oxide, because of the presence of a metal element and oxygen on the surface.

As shown in fig. 2B, the photocatalytic coating is formed by mixing particles 14 of the photocatalyst into the metal oxide layer 16. Further, when silicon oxide or tin oxide is mixed into a photocatalyst as described below, the surface can be made highly hydrophilic.

Thickness of the photocatalytic coating

When the substrate is made of a transparent material, such as glass, a lens or a mirror, it is preferable that the thickness of the photocatalytic coating is not more than 0.2 μm, at which the coloration of the photocatalytic coating due to the interference of light can be avoided. Further, the thinner the photocatalytic coating, the more transparent the substrate may be. In addition, by increasing the thickness, the abrasion resistance of the photocatalytic coating can be increased.

The surface of the photocatalytic coating can also be covered by a wear-resistant or corrosion-resistant protective layer or other functional film which is easily hydrophilized.

Photocatalytic layer formation by sintering amorphous titanium oxide

When the substrate is made of a heat-resistant material such as metal, ceramic and glass, it is preferable to form an abrasion-resistant photocatalytic coating having super hydrophilicity with a contact angle with water as small as 0 degree by first forming an amorphous titanium oxide coating on the surface of the substrate and then sintering the substrate to convert the amorphous titanium oxide into crystalline titanium oxide (i.e., anatase or rutile) by phase transformation. Amorphous titanium oxide can be formed by one of the following methods.

(1) Hydrolysis and dehydration polymerization of organic titanium compounds

Using titanium alkylates such as titanium tetraethoxide, titanium tetraisopropoxide, titanium tetra-n-propoxide, titanium tetrabutoxide and titanium tetramethoxide, adding a hydrolysis inhibitor such as hydrochloric acid and ethylamine thereto, diluting the mixture with alcohols such as ethanol and propanol, applying the mixture to the surface of a substrate by spraying, flow coating, spin coating, dip coating, roll coating or other suitable coating methods while partially or completely hydrolyzing the different, and then drying at a temperature of room temperature to 200 ℃. After drying, the hydrolysis of the titanium alkoxide will be complete, thereby forming titanium hydroxide, which then undergoes dehydration polymerization, thereby forming an amorphous titanium oxide layer on the surface of the substrate.

In addition to titanium alkoxides, other organic compounds of titanium may be employed, such as titanium chelates and titanium acetates.

(2) Formation of amorphous titanium oxide from inorganic titanium compounds

By reacting inorganic compounds of titanium, e.g. TiCl₄And Ti (SO)₄)₂The acidic aqueous solution of (a) is applied to the surface of the substrate by spraying, flow coating, spin coating, dip coating or roll coating. The substrate is then dried at a temperature of 100-200 ℃ to hydrolyze the inorganic compound of titanium and dehydrate and polymerize it, forming an amorphous titanium oxide layer on the surface of the substrate. In addition, TiCl can also be deposited by chemical vapor deposition₄To form amorphous oxidation on the surface of the substrate

(3) Forming amorphous titanium oxide by sputtering

Amorphous titanium oxide is deposited on the surface of the substrate by electron beam bombardment with a metallic titanium target in an oxidizing atmosphere.

(4) Sintering temperature

Sintering of amorphous titanium oxide may be carried out at a temperature at least exceeding the anatase crystallization temperature. Amorphous titanium oxide can be converted to anatase type titanium oxide after sintering at temperatures of 400-500 deg.C or higher. Amorphous titanium oxide can be converted to rutile titanium oxide by sintering at 600-700 deg.C or higher.

(5) Forming an anti-diffusion layer

When the substrate is made of glass or glazed tile containing an alkaline framework modifying ion, such as sodium, it is preferred to form an intermediate layer of silica between the substrate and the amorphous titanium oxide layer prior to sintering. This structure can prevent the basic skeleton-modified ions from diffusing from the substrate into the photocatalytic coating during the sintering of the amorphous titanium oxide. As a result, super-hydrophilization can be achieved to the extent that the contact angle with water is as small as 0 degree.

Photocatalytic layer of titanium oxide doped with silicon oxide

Another preferred method of forming an abrasion-resistant photocatalytic coating having super hydrophilicity with a contact angle with water equal to 0 degree is to form a photocatalytic coating composed of a mixture of titanium oxide and silicon oxide on the surface of a substrate. The ratio of silicon oxide to the total amount of titanium oxide and silicon oxide is 5 to 90 mol%, preferably 10 to 70 mol%, more preferably 10 to 50 mol%. The photocatalytic coating composed of titanium oxide mixed with silicon oxide can be formed by one of the following methods.

(1) A suspension containing anatase or rutile titanium oxide particles and silica particles is applied to the surface of a substrate and then sintered at a temperature below the softening point of the substrate.

(2) A mixture of a precursor of amorphous silica (e.g., tetraalkoxysilanes such as tetraethoxysilane, tetraisopropoxysilane, tetra-n-propoxysilane, tetrabutoxysilane, and tetramethoxysilane; silanols formed by hydrolysis of tetraalkylsilanes; or polysiloxanes having an average molecular weight of less than 3000) and crystalline titanium oxide gelatin is applied to the surface of the substrate and hydrolyzed (when silanol formation is desired) and then heated at a temperature of greater than about 100 ℃ to dehydrate and polymerize the silanols, thereby forming a photocatalytic coating in which titanium oxide particles are bonded to amorphous silica. In this case, if the dehydration polymerization of the silanol is carried out at a temperature exceeding about 200 ℃, the polymerization of the silanol will enhance the alkali resistance of the photocatalytic coating.

(3) Dispersing particles of silica in an amorphous titanium oxide precursor (e.g. an organic titanium compound such as titanium alkoxide, chelate or acetate, or an inorganic titanium compound such as TiCl₄And Ti (SO)₄)₂) The thus obtained suspension is applied to the surface of a substrate, and then a titanium compound is hydrolyzed at a temperature of room temperature to 200 ℃ and is subjected to dehydration polymerization, thereby forming a thin film of amorphous titanium oxide in which particles of silicon oxide are dispersed. The film is then heated at a temperature above the crystallization temperature of the titanium oxide but below the softening temperature of the matrix to convert the amorphous titanium oxide to crystalline titanium oxide by phase transformation.

(4) To amorphous titanium oxide precursors (e.g. organic compounds of titanium, such as titanium alkoxides, chelates or acetates; or inorganic compounds of titanium, such as TiCl)₄And Ti (SO)₄)₂) To the solution of (a) amorphous silica precursor (e.g., tetraalkoxysilanes such as tetraethoxysilane, tetraisopropoxysilane, tetra-n-propoxysilane, tetrabutoxysilane, and tetramethoxysilane; the hydrolysate thereof, i.e. silanol; or a polysiloxane having an average molecular weight of less than 3000) and applying the mixture to the surface of a substrate. These precursors are then hydrolyzed and polymerized by dehydration, thereby forming a thin film formed from a mixture of amorphous titanium oxide and amorphous silicon oxide. The film is then heated at a temperature above the crystallization temperature of the titanium oxide but below the softening temperature of the matrix to convert the amorphous titanium oxide to crystalline titanium oxide by phase transformation.

Photocatalytic layer of titanium oxide doped with tin oxide

Another preferred method of forming an abrasion-resistant photocatalytic coating having super hydrophilicity with a contact angle with water equal to 0 degree is to form a photocatalytic coating composed of a mixture of titanium oxide and tin oxide on the surface of a substrate. The ratio of silicon oxide to the total amount of titanium oxide and silicon oxide is 1 to 95 mol%, preferably 1 to 50 mol%. The photocatalytic coating composed of titanium oxide mixed with silicon oxide can be formed by one of the following methods.

(1) A suspension containing anatase or rutile titanium oxide particles and tin oxide particles is applied to the surface of a substrate and then sintered at a temperature below the softening point of the substrate.

(2) Particles of tin dioxide are dispersed in an amorphous titanium oxide precursor (e.g. an organic compound of titanium, such as titanium alkoxide, chelate or acetate, or an inorganic compound of titanium, such as TiCl₄And Ti (SO)₄)₂) The thus obtained suspension is applied to the surface of a substrate, and then a titanium compound is hydrolyzed at a temperature of room temperature to 200 ℃ and is subjected to dehydration polymerization, thereby forming a thin film of amorphous titanium oxide in which particles of tin oxide are dispersed. The film is then heated at a temperature above the crystallization temperature of the titanium oxide but below the softening temperature of the matrix to convert the amorphous titanium oxide to crystalline titanium oxide by phase transformation.

Silicone coatings containing photocatalysts

Another preferred method of forming an abrasion resistant photocatalytic coating having super hydrophilicity with a contact angle with water equal to 0 degrees is to use a coating composition in which photocatalyst particles are dispersed in a film-forming component of an uncured or partially cured siloxane (organosiloxane) or precursor thereof.

The coating composition is applied to the surface of a substrate and the film-forming ingredients are cured. After photo-excitation of the photocatalyst, the organic groups bonded to the silicon atoms in the siloxane molecules are substituted with hydroxyl groups by the photocatalytic action of the photocatalyst, as described below with reference to examples 13 and 14, thereby super-hydrophilizing the surface of the photocatalytic coating.

This approach has several advantages. Since the silicone coating containing the photocatalyst can be cured at room temperature or at a lower temperature, this method can be applied to substrates made of non-heat resistant materials such as plastics. The coating composition containing the photocatalyst may be applied by brushing, spraying, rolling or other coating method to any of the existing substrates whose surfaces require super-hydrophilization treatment. The super-hydrophilization by the photocatalyst can be achieved even by using sunlight as a light source.

Further, when a coating film is formed on a plastically deformable substrate such as a steel sheet, plasticizing operation may be performed as needed after the coating film is cured and before light excitation. Before photoexcitation, the organic group is bonded to the silicon atom of the siloxane molecule to impart suitable flexibility to the coating film. Thus, the multiple plates can be easily deformed without damaging the coating film. After plastic deformation, the photocatalyst may be subjected to photo-excitation, and thereafter, the organic group bonded to the silicon atom on the siloxane molecule is substituted with a hydroxyl group by the photocatalytic action of the photocatalyst, thereby super-hydrophilizing the surface of the coating film.

The photocatalyst-containing silicone coating has sufficiently high resistance to the photocatalytic action of the photocatalyst because it is composed of siloxane bonds.

Another advantage of the photocatalytic coating composed of a silicone coating containing a photocatalyst is that once the surface is super-hydrophilized, the super-hydrophilicity of the coating can be maintained for a long time even if the coating is kept in the dark, and the super-hydrophilicity can be restored even by the light of an indoor illumination lamp such as a fluorescent lamp.

Examples of film-forming ingredients suitable for use in the present invention include methyltrichlorosilane, methyltrtribromosilane, methyltrimethoxysilane, methyltriethoxysilane, methyltriisopropoxysilane, methyltriethoxysilane, ethyltrichlorosilane, ethyltribromosilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltriisopropoxysilane, ethyltri-tert-butoxysilane, n-propyltrichlorosilane, n-propyltribromosilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, n-propyltriisopropoxysilane, n-propyltri-tert-butoxysilane, n-hexyltrichlorosilane, n-hexyltribromosilane, n-hexyltrimethoxysilane, n-hexyltriethoxysilane, n-hexyltriisopropoxysilane, n-hexyltri-tert-butoxysilane, n-decyltrichlorosilane, n-decyltrimethoxysilane, N-decyltriethoxysilane, n-decyltriisopropoxysilane, n-decyltritricutoxysilane, n-octadecyltrichlorosilane, n-octadecyltribulorosilane, n-octadecyltrimethoxysilane, n-octadecyltriethoxysilane, n-octadecyltriisopropoxysilane, n-octadecyltriethoxysilane, phenyltrichlorosilane, phenyltribromosilane, phenyltrimethoxysilane, phenyltriethoxysilane, phenyltriisopropoxysilane, phenyltri-t-butoxysilane, tetrachlorosilane, tetrabromosilane, tetramethoxysilane, tetraethoxysilane, tetrabutoxysilane, dimethoxydiethoxysilane, dimethyldichlorosilane, dimethyldibromosilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diphenyldichlorosilane, diphenyldibromosilane, diphenyldimethoxysilane, diphenyldiethoxysilane, Phenylmethyldichlorosilane, phenylmethyldibromosilane, phenylmethyldimethoxysilane, phenylmethyldiethoxysilane, trichlorosilane, tribromohydrosilane, trimethoxyhydrosilane, triethoxyhydrosilane, triisopropoxyhydrosilane, tri-tert-butoxyhydrosilane, vinyltrichlorosilane, vinyltribromosilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane, vinyltri-tert-butoxysilane, trifluoropropyltrichlorosilane, trifluoropropyltribromosilane, trifluoropropyltrimethoxysilane, trifluoropropyltriethoxysilane, trifluoropropyltriisopropoxysilane, trifluoropropyltri-tert-butoxysilane, gamma-glycidoxypropylmethyldimethoxysilane, gamma-glycidoxypropylmethyldiethoxysilane, gamma-glycidoxypropyltrimethoxysilane, phenylmethyldiethoxysilane, trichlorohydrogensilane, tribromohydrogensilane, vinyltrimethoxysilane, vinyl, Gamma-glycidoxypropyltriethoxysilane, gamma-glycidoxypropyltriisobutoxysilane, gamma-glycidoxypropyltri-tert-butoxysilane, gamma-methacryloxypropylmethyldimethoxysilane, gamma-methacryloxypropylmethyldiethoxysilane, gamma-methacryloxypropyltrimethoxysilane, gamma-methacryloxypropyltriethoxysilane, gamma-methacryloxypropylisopropoxysilane, gamma-methacryloxypropyltri-tert-butoxysilane, gamma-aminopropylmethyldimethoxysilane, gamma-aminopropylmethyldiethoxysilane, gamma-aminopropyltrimethoxysilane, gamma-aminopropyltriethoxysilane, gamma-aminopropyltriisopropoxysilane, gamma-aminopropyltri-tert-butoxysilane, gamma-aminopropyltrimethoxysilane, gamma-aminopropyltriethoxysilane, gamma-aminopropyltriisopropoxysilane, gamma-aminopropyl-tri-tert-butoxysilane, gamma-glycidoxypropyl-trimethoxysilane, gamma-methacryloxypropylmethyldiethoxysilane, gamma-methacryloxypropyltrimethoxysilane, gamma, Gamma-mercaptopropylmethyldimethoxysilane, gamma-mercaptopropylmethyldiethoxysilane, gamma-mercaptopropyltrimethoxysilane, gamma-mercaptopropyltriethoxysilane, gamma-mercaptopropyltriisopropoxysilane, gamma-mercaptopropyltri-tert-butoxysilane, beta- (3, 4-ethoxycyclohexyl) ethyltrimethoxysilane, beta- (3, 4-ethoxycyclohexyl) ethyltriethoxysilane, partial hydrolysates thereof and mixtures thereof.

In order to ensure satisfactory hardness and smoothness of the silicone coating, the coating preferably contains more than 10 mol% of three-dimensionally crosslinked silicone. Furthermore, in order to produce a coating film having suitable flexibility to ensure satisfactory hardness and smoothness, the coating preferably contains less than 60 mol% of a two-dimensional cross-linked siloxane. In addition, in order to increase the rate at which the organic group bonded to the silicon atom in the siloxane molecule is substituted with a hydroxyl group under photoexcitation, a siloxane in which the organic group bonded to the silicon atom in the siloxane molecule is an n-propyl group or a phenyl group may be used. Instead of siloxane having siloxane bonds, organopolysilazane composed of silazanes may be used.

Adding antibacterial enhancer

Metals such as silver, copper and zinc may be incorporated into the photocatalytic coating.

The photocatalyst may be doped with silver, copper and zinc by adding a soluble salt of such a metal to a suspension containing the photocatalyst particles, and the resulting solution may be used to form a photocatalytic coating. In addition, after the photocatalytic coating layer is formed, a soluble salt of such a metal may also be coated thereon and irradiated with light to deposit the metal by photoreduction.

Photocatalytic coatings doped with silver, copper or zinc can kill bacteria adhered to the surface. In addition, such photocatalytic coatings can inhibit the growth of bacteria such as molds, algae, and lichen. As a result, buildings, machines, devices, household items, articles, etc. can be kept clean for a long time.

Addition of photoactive enhancers

The photocatalytic coating may also incorporate platinum group metals such as Pt, Pd, Rh, Ru, Os and Ir. These metals can likewise be incorporated into the photocatalyst by photoreduction deposition or by addition of soluble salts.

Photocatalysts incorporating platinum group metals enhance the photocatalytic redox activity and thereby accelerate the decomposition of contaminants that adhere to the surface.

Light excitation and ultraviolet irradiation

For anti-fogging purposes of transparent parts such as glass, lenses and mirrors, preferably the photocatalytic coating is formed by a photocatalyst like titanium oxide having a high band gap energy and being excited only by ultraviolet light. In this case, the photocatalytic coating does not absorb visible light, and therefore the glass, lens or mirror is not colored by the compensating color component. Anatase titanium oxide can be excited by UV light having a wavelength of less than 387 nanometers, while rutile titanium oxide can be excited by UV light having a wavelength of less than 413 nanometers, tin oxide can be excited by UV light having a wavelength of less than 344 nanometers, and zinc oxide can be excited by UV light having a wavelength of less than 387 nanometers.

As the UV light source, a fluorescent lamp, an incandescent lamp, a metal halide lamp, a mercury lamp, or other indoor lighting lamps can be used. When anti-fog glass, lenses or mirrors are exposed to UV light, their surfaces will be super-hydrophilized due to photo-excitation of the photocatalyst. In the case of exposing the photocatalytic coating to sunlight like a vehicle rearview mirror, the photocatalyst is spontaneously photo-excited by UV light contained in sunlight.

Photoexcitation may also be performed until the contact angle of the surface with water becomes less than about 10 degrees, preferably less than about 5 degrees, and particularly equal to about 0 degrees. In general, the concentration is adjusted at 0.001mW/cm²Upon photo-excitation at UV intensity, the photocatalytic coating will become super-hydrophilized within a few days, resulting in a contact angle with water of about 0 degrees. Since the intensity of UV light contained in sunlight striking the earth's surface is about 0.1-1mW/cm²When exposed to sunlight, the surface can be super-hydrophilized in a short time.

When the surface of the substrate is self-cleaned by rainwater or contaminants are prevented from adhering, the photocatalytic coating may be formed of a photocatalyst that can be excited by UV light or visible light. The article covered by the photocatalytic coating can be placed outdoors and subjected to sunlight and rain.

When the photocatalytic coating is made of a siloxane containing titanium oxide, the photocatalyst is preferably photo-excited at an intensity that ensures that sufficient surface organic groups attached to silicon atoms in the siloxane molecule are substituted with hydroxyl groups. The most convenient method is to use sunlight.

Once the surface is highly hydrophilized, the hydrophilicity can be maintained even at night. This hydrophilicity can be restored and maintained upon exposure to sunlight again.

Preferably the photocatalytic coating is super-hydrophilised before the substrate coated with the photocatalytic coating of the present invention is provided to the user for use.

Examples

The following examples illustrate the industrial applicability of the present invention in various aspects.

Example 1

Anti-fog mirror-anti-fog photocatalytic coating with intermediate silicon oxide layer

6 parts by weight of tetraethoxysilane Si (OC)₂H₅)₄(Wako Junyaku Osaka), 6 parts by weight of pure water, and 2 parts by weight of 36% hydrochloric acid as a hydrolysis inhibitor were added to 86 parts by weight of ethanol as a solvent, and the mixture was stirred to obtain a silica coating solution. The solution was cooled for about 1 hour due to the heat evolved from the solution during mixing. The solution was then coated by flow coating onto a square soda-lime-silica glass plate surface of size 10cm and dried at a temperature of 80 ℃. As drying proceeds, tetraethoxysilane hydrolyzes to form silanol Si (OH)₄And then dehydration polymerization is performed to form an amorphous silicon oxide film on the surface of the glass plate.

Then by adding 0.1 part by weight of 36% hydrochloric acid as a hydrolysis inhibitor to 1 part by weight of titanium tetraoxide Ti (OC)₂H₅)₄(Merck) and 9 parts by weight of ethanol, the solution was applied to the surface of the above-mentioned glass plate by a flow coating method in dry air. The coating amount was 45 micrograms/square centimeter calculated based on titanium oxide. Since the rate of hydrolysis of titanium tetraethoxide is so high that partial hydrolysis of titanium tetraethoxide takes place during the coating process, whereby the formation of titanium hydroxide Ti (OH) begins₄。

The glass plate is then maintained at a temperature of about 150 c for 1-10 minutes to complete the hydrolysis of the titanium tetraethoxide and to dehydrate and polymerize the titanium hydroxide formed, thereby forming amorphous titanium oxide. In this way, a glass sheet having an amorphous titanium oxide coating in addition to an amorphous silicon oxide coating can be obtained.

This sample was sintered or calcined at a temperature of 500 c to convert amorphous titanium oxide to anatase titanium oxide. It is believed that the basic framework-modifying ions, such as sodium ions, present in the glass sheet are prevented from diffusing from the glass substrate into the titania coating during sintering due to the presence of the amorphous silica coating beneath the amorphous titania coating.

Then, a mirror was prepared by forming a reflective layer of aluminum by vacuum evaporation deposition on the rear surface of the glass plate, thereby obtaining a sample # 1.

After keeping the #1 sample in the dark for several days, 20W blue-light-black (BLB) fluorescent lamp (Sankyo Electric, FL20BLB) at 0.5mW/cm²The intensity of UV light (intensity of UV light having energy exceeding the band gap energy of anatase type titanium oxide, i.e., intensity of UV light having a wavelength of less than 387 nm) was irradiated with UV light on the surface of the sample for about 1 hour, thereby obtaining a #2 sample.

For comparison, an aluminum reflective layer was formed by vacuum evaporation deposition on the back surface of a glass plate having neither a silicon oxide nor a titanium oxide coating, and the product was left in the dark for several days, thereby obtaining a sample # 3.

The contact angles of the samples #2 and #3 with water were determined by a contact angle determinator (Kyowa Kaimen Kagaku K.K. of Asaka, Saitama, model CA-X150). The resolution of this contact angle measuring instrument on the small angle side was 1 degree. The contact angle was measured 30 seconds after dropping a water drop from a micro syringe onto each sample surface. The contact angle meter reading (representing the contact angle of the surface with water) on sample #2 was 0 degrees, indicating that the surface was superhydrophilic. In contrast, the contact angle of the sample #3 with water was 30-40 degrees.

The samples #2 and #3 were then tested for their anti-fog ability and observed how the adhering water droplets spread on the surface. The resistance was evaluated by charging 300 ml of hot water at a temperature of about 80 ℃ into a 500 ml beaker and then placing each sample on the beaker for 10 seconds with the front of the mirror facing down, and observing immediately whether there was haze on the surface of the sample and how the surface of the tester reflected.

For sample #3, the surface of the mirror was hazed by the vapor, so the image of the observer's face was not reflected well. However, for sample #2, no fog was visible at all and the face of the tester was clearly reflective.

The spreading of the adhering water drops can be evaluated by dropping a few drops of water from the thin tube onto a mirror surface placed obliquely at an angle of 45 degrees, rotating the mirror to a vertical position, and then observing how the drops adhere and how the front of the observer reflects.

For sample #3, dispersed water droplets that blocked the eyes adhered to the mirror surface. As a result, the reflected image is blurred due to refraction of light caused by the adhered water droplets, and as a result, it is difficult to clearly observe the reflected image. In contrast, for the #2 sample, the water droplets adhered to the mirror surface spread on the surface, forming a uniform water film, without forming individual water droplets. Therefore, although the reflected image is somewhat blurred due to the presence of the water film, the reflected image of the front surface of the tester can be recognized quite clearly.

Example 2

Anti-fogging mirror-photocatalytic coating consisting of titanium oxide mixed with silicon oxide

An amorphous silicon oxide film was formed on the surface of a mirror (MFL 3, manufactured by Nihon plate glass company) in the same manner as in example 1.

The coating solution was then prepared by mixing 0.69 g of tetraethoxysilane (Wako JunYaku), 1.07 g of anatase titania sol (Nissan Chemical Ind., TA-15, average particle diameter 0.01 μm), 29.88 g of ethanol, and 0.36 g of pure water. The coating solution is then applied to the mirror surface by a spray coating process. The mirror was held at a temperature of about 150 c for about 20 minutes to hydrolyze and dehydrate tetraethoxysilane, thereby forming a coating layer in which amorphous silicon oxide was attached around particles of anatase-type titanium oxide on the surface of the mirror. The weight ratio of titanium oxide to silicon oxide was 1.

After keeping the mirror in the dark for several days, a BLB fluorescent lamp was used at 0.5mW/cm²UV light irradiation was performed, thereby obtaining a #1 sample. The contact angle of the mirror surface with water was measured using the same contact angle measuring instrument as used in example 1, and the reading of the contact angle measuring instrument was 0 degrees. The anti-fog ability and the manner of spreading of the adhered water droplets were then determined in the same manner as in example 1 for sample #1 and for a "MFL 3" mirror without photocatalytic coating. In the antifogging performance test, for sample #1, no haze was visible at all and the front of the tester was clearly reflected, whereas the "MFL 3" mirror, instead, had haze visible on its mirror surface, so the image of the front of the tester was not clearly reflected. When examining the way in which the stuck water droplets spread, for the "MFL 3" mirror, the water droplets spread on the surface cause light refraction, thereby destroying the reflected image, so that it is difficult to clearly observe the reflected image. Sample #1 in contrast thereto, the water droplets adhered to the surface of the mirror spread on the surface to form a uniform water film, and the reflected image on the front side of the tester can be seen sufficiently clearly, although the reflected image is slightly deformed due to the presence of the water film.

Example 3

Fog-resistant spectacle lens

First, thin films of amorphous silicon oxide were formed on both surfaces of a commercially available spectacle lens in the same manner as in example 1.

Then, a coating solution similar to example 2 was sprayed on both surfaces of the lens and the lens was maintained at a temperature of about 150 ℃ for 20 minutes to hydrolyze and dehydrate and polymerize tetraethoxysilane, thereby forming a coating layer in which amorphous silica was attached around particles of anatase type titanium oxide on both surfaces of the lens.

After the lens was kept in the dark for several days, 0.5mW/cm was used as a BLB fluorescent lamp²UV intensity of (a) was irradiated for about 1 hour with UV light. The contact angle of the lens surface with water was measured using the same contact angle measuring instrument as used in example 1, and the reading of the contact angle measuring instrument was 0 degrees. Such lenses were mounted in the frame on the right side of the glasses, while the ordinary lenses were mounted in the frame on the left side for comparison.

After a few hours, the tester took glasses and bathed for about 5 minutes. The ordinary lens on the left side was hazy due to water vapor and thus lost vision, but no haze formation was observed at all on the lens coated on the right side with the UV-irradiated photocatalytic coating.

When the tester is consciously pushed toward the shower, an obstructive water drop adheres to the left general lens, thereby interrupting the sight. However, the water droplets adhered to the right lens are quickly diffused into a water film, so that sufficient vision is possible.

Example 4

Anti-fog glass-7 nm thick titanium oxide coating

A solution containing a chelate of titanium is applied to the surface of a soda-lime-silica glass block having a size of 10cm, and the chelate of titanium is hydrolyzed and subjected to dehydration polymerization, thereby forming amorphous titanium oxide on the surface of the glass. The plate was then sintered at 500 c to form a surface layer of anatase titanium oxide crystals. The thickness of the surface layer was 7 nm.

The surface of the thus obtained sample was measured with a BLB fluorescent lamp at 0.5mW/cm²The UV intensity of (1) was irradiated with UV light for about 1 hour, and the contact angle of the sample surface with water was measured using a contact angle measuring instrument (model G-I-1000 manufactured by ERMA, resolution at the small angle-side of 3 degrees), which read less than 3 degrees.

Then using a 20W incandescent lamp (Toshiba, FL20SW) at 0.01mW/cm²UV intensity UV light irradiationWhile the change in contact angle with time was measured. The results are depicted in the graph of fig. 3. From this figure it can be seen that the surface of the sample remains highly hydrophilic, even with only weak UV light emitted by the incandescent lamp.

This example illustrates that the surface of a photocatalytic titanium oxide coating can remain highly hydrophilic even though its thickness is extremely small, reaching 7 nm. This is important to maintain the transparency of substrates such as window glass.

Example 5

Anti-fog glass-20 nm thick titanium oxide coating

An anatase-type titanium oxide crystal surface layer was formed on the surface of a soda-lime-silica glass plate in the same manner as in example 4. The thickness of the surface layer was 20 nm.

Similarly to example 4, the surface of the thus obtained sample was first subjected to a BLB fluorescent lamp at 0.5mW/cm²UV intensity of (2) was irradiated for about 1 hour with UV light, and then irradiated with an incandescent lamp at 0.01mW/cm²UV intensity the change in contact angle with time was measured while UV light irradiation was performed. The results are depicted in the graph of fig. 4. From this figure it can be seen that the surface of the sample remains highly hydrophilic, even with only weak UV light emitted by the incandescent lamp.

Example 6

Effect of fog-resistant glass-sintering temperature on amorphous titanium oxide

A plurality of samples were obtained in the same manner as in example 4 by first forming an amorphous silicon oxide film on the surface of a 10 cm-sized soda-lime-silica glass plate block and then coating an amorphous titanium oxide film thereon.

These glasses were sintered at temperatures of 450 deg.C, 475 deg.C, 500 deg.C and 525 deg.C, respectively. In the examination by powder X-ray diffraction, the presence of anatase crystalline titanium oxide was observed in the samples sintered at 475 deg.C, 500 deg.C and 525 deg.C, and thus it was confirmed that amorphous titanium oxide was converted into anatase crystalline titanium oxide in these samples. However, in the sample sintered at 450 ℃, anatase type titanium oxide was not detected.

The surface of the thus obtained sample was first subjected to a BLB fluorescent lamp at 0.5mW/cm²UV intensity of (2) was irradiated for about 3 hours with UV light, and then irradiated with an incandescent lamp at 0.02mW/cm²UV intensity changes in contact angle with time were measured by a contact angle measuring instrument (CA-X150) while UV light irradiation was performed. The results are shown in Table 1.

TABLE 1

	Contact angle (degree)
					Sintering temperature (. degree. C.)	Just after BLB irradiation	After 3 days	After 9 days	After 14 days
450	10	13	15	23
					475	0	0	0	0
500	0	0	0	0
					525	0	0	0	0

As can be seen from table 1, in the samples sintered at temperatures of 475 ℃, 500 ℃ and 525 ℃ and confirmed to have anatase crystal formation, the contact angle was maintained at 0 degrees and the surface of the glass plate remained super-hydrophilic, mainly by irradiation with UV light from an incandescent lamp. In contrast, the amorphous titanium oxide coating on the sample sintered at 450 ℃ has no photocatalytic activity, and therefore its contact angle increases with time.

When air was blown onto the samples sintered at 475 ℃, 500 ℃ and 525 ℃, haze was not formed on the sample surface.

Example 7

Effect of ion diffusion of antifogging glass-alkali skeletal modifier

A titania coating solution similar to that of example 1 was prepared and coated by flow coating on the surface of a 10cm size soda-lime-silica glass plate block. Similarly to example 1, the coating amount was 45. mu.g/cm in terms of titanium oxide.

Similarly, the glass plate was held at about 150 ℃ for 1 to 10 minutes to form amorphous titanium oxide on the surface of the glass plate, and the sample was sintered at 500 ℃ to convert the amorphous titanium oxide into anatase-type titanium oxide.

After the sample was kept in the dark for several days, the surface of the sample was treated with a BLB fluorescent lamp at 0.5mW/cm²The UV intensity of (2) was irradiated with UV light for about 1 hour, and then the contact angle was measured with a contact angle measuring instrument (CA-X150), which was 3 degrees.

It is considered that the reason why the contact angle is not lowered to 0 degree in this sample is that unlike example 1, which has no intermediate layer of silica between the glass substrate and the titanium oxide layer, basic skeleton modifier ions such as sodium ions diffuse from the glass substrate into the titanium oxide coating layer during sintering at 500 ℃, thereby hindering the photocatalytic activity of titanium oxide.

Therefore, it is considered that in order to achieve super hydrophilicity such that the contact angle with water is 0 degree, the silicon oxide intermediate layer should preferably be formed as in example 1.

Example 8

Anti-fog glass-amorphous titanium oxide formed by sputtering

A metallic titanium film was sputter deposited on the surface of a 10cm soda-lime-silica glass block and then sintered at a temperature of 500 ℃. When examined by powder X-ray diffraction method, it was found that anatase type titanium oxide was formed on the surface of the glass plate. It is evident that metallic titanium is oxidized to anatase by sintering.

After sintering, the alloy was sintered using a BLB incandescent lamp at 0.5mW/cm²UV intensity the surface of the sample was irradiated with UV light, and the contact angle with water was measured with a contact angle measuring instrument (CA-X150) to monitor the change of the contact angle with time, and the result is shown in fig. 5. As is evident from the figure, the contact angle with water remains below 3 degrees. This experiment shows that even if the photocatalytic coating is formed by sputtering, the glass plateCan also remain highly hydrophilic upon UV irradiation.

Example 9

Antifogging glass-800 lux UV intensity

In the same manner as in the examples, an amorphous silicon oxide film was formed on the surface of a soda-lime-silica glass plate block having a size of 10 cm.

The coating solution of example 2 was then spray coated on the surface of the glass plate. The glass sheet is held at a temperature of 150 c for about 20 minutes to form a coating on the surface of the glass sheet in which the particles of anatase titanium oxide are associated with the amorphous silica binder. The weight ratio of titanium oxide to silicon oxide was 1.

After a few days in the dark, a BLB incandescent lamp was used at 0.5mW/cm²UV intensity UV light irradiation was performed on the sample surface. After the irradiation with UV light, the contact angle of the surface of the glass plate with water was measured by a contact angle measuring instrument (CA-X150), and the contact angle was found to be 0 degrees.

Then, using a BLB incandescent lamp at 0.004mW/cm²(800 lux) UV intensity UV light irradiation was performed on the sample surface. The contact angle of the surface was kept below 2 degrees while the sample was under UV irradiation. After 4 days, no mist was formed when the sample was blown.

In this way, it was confirmed that with the weak UV light that can be obtained in the case of indoor lighting (realized by an incandescent lamp, for example), it is possible to keep the glass plate surface highly hydrophilic and prevent the formation of fog on the glass plate surface.

Example 10

Effect of the antifogging glass-silica-titania mixture ratio

Tetraethoxysilane (Wako JunYaku), anatase type titania sol (Nissan Chemical ind., TA-15), ethanol, and pure water were mixed at different ratios to prepare four coating solutions having different mixing ratios of tetraethoxysilane-titania sol. The proportions of tetraethoxysilane and titania sol were selected so that after tetraethoxysilane was converted into amorphous titania, the proportions of silica to the sum of silica and titania were 10 mol%, 30 mol%, and 70 mol%, respectively.

The coating solution was then sprayed onto the surface of a soda-lime-silica glass plate having a dimension of 10 cm. The glass plate was held at a temperature of 150 c for about 20 minutes to hydrolyze and dehydrate the tetraethoxysilane, thereby forming a coating in which particles of anatase titanium oxide are bonded to an amorphous silica binder on the surface of the glass plate.

After one week of maintenance in the dark, a BLB incandescent lamp was used at 0.3mW/cm²UV intensity the sample surface was irradiated with UV light for about 1 hour. After the irradiation with UV light, the contact angle of the surface of the glass plate with water was measured by a contact angle measuring instrument (CA-X150), and as a result, the contact angle of all the samples was found to be 0 degrees.

Then, using a BLB incandescent lamp at 0.004mW/cm²UV intensity the surface of the sample containing 30 mol% and 50 mol% of silicon oxide, respectively, was irradiated with UV light for 3 days. The contact angle of the surface was kept below 3 degrees while the sample was under UV irradiation.

Example 11

Anti-fog glass-rutile type photocatalytic coating

By adding 0.1 part by weight of 36% hydrochloric acid as a hydrolysis inhibitor to a mixture consisting of 1 part by weight of titanium tetraethoxide Ti (OC)₂H₅)₄(Merck) and 9 parts by weight of ethanol. The solution was then applied to the surface of a number of quartz glass plate squares measuring 10cm by flow coating in dry air. The amount of coating was 45 micrograms per square centimeter in terms of titanium oxide.

The glass plates were maintained at a temperature of 150 c for about 1 to 10 minutes to hydrolyze and dehydrate and polymerize the tetraethoxytitanium, thereby forming an amorphous titanium oxide coating on the surface of each glass plate.

These samples were sintered at temperatures of 650 ℃ and 800 ℃ respectively, to crystallize amorphous titanium oxide. The crystals of the sample sintered at 650 ℃ were found to be anatase and the crystals of the sample sintered at 800 ℃ were found to be rutile when examined by powder X-ray diffraction.

After the thus-obtained sample was kept in the dark for 1 week, a BLB incandescent lamp was used at 0.3mW/cm²UV intensity UV light irradiation was performed on the sample surface. The contact angle was measured after UV irradiation. The contact angle of all sample surfaces with water was 0 degrees.

From the above, it is considered that the surface can be kept highly hydrophilic not only when the photocatalyst is anatase type titanium oxide but also when the photocatalyst is rutile type titanium oxide.

For this reason, the photocatalytic superhydrophilic phenomenon seems to be different from the photocatalytic redox reaction.

Example 12

Fog-resistant glass-transmission test

Similarly to example 1, an amorphous silicon oxide film was first formed on the surface of a soda-lime-silica glass plate block having a size of 10cm, and then an amorphous titanium oxide film was formed thereon. The glass plate was sintered at 500 c to convert amorphous titanium oxide to anatase titanium oxide. The samples thus obtained were kept in the dark for several days. The sample was placed in a desiccator (temperature 24 ℃ C., humidity 45-50%) with a BLB fluorescent lamp at 0.5mW/cm²UV intensity the sample surface was irradiated with UV light for 1 day, thereby obtaining a #1 sample. The contact angle of sample #1 with water was 0 degrees.

The sample #1 was then removed from the desiccator and immediately placed on a warm bath maintained at 60 ℃ and its light transmission was measured after 15 seconds. The change in light transmission due to the mist formed by the condensation of the vapor was calculated by dividing the measured light transmission by the original light transmission.

Similarly to example 7, the surface of the glass plate was coated with anatase-type titanium oxide, thereby obtaining a sample # 2. Sample #2 was placed in the desiccator and dosed at 0.5mW/cm²UV intensity UV light irradiation was performed until the contact angle with water was equal to 3 degrees.

Sample #2 was placed in the dark. The #2 sample was removed from the dark at different times and the contact angle with water was determined each time. Further, the sample #2 was first placed in a desiccator (temperature force 24 ℃ C., humidity 45-50%) each time until the temperature was equilibrated and then the sample #2 was immediately placed on a warm bath maintained at a temperature of 60 ℃ in the same manner as the sample #1, and the light transmittance thereof was measured after 15 seconds, thereby obtaining a change in light transmittance due to mist formed by condensation of steam.

For comparison, the contact angle with water was measured for each of commercially available plate glass, acrylic resin plate, Polyvinyl Chloride (PCV) plate and Polycarbonate (PC) plate. Further, each of these materials was put into a dryer under the same conditions to equilibrate the temperature, and immediately placed on a warm bath maintained at 60 ℃ for 15 seconds, and the light transmittance was measured, whereby the change in light transmittance due to the mist formed by the condensation of steam was calculated.

The results are shown in Table 2.

TABLE 2

Sample (I)	Contact Angle with Water	Change in light transmittance (%)
			#1	0	100
#2 (after 3 hours)	5.0	100
			#2 (after 6 hours)	7.7	100
#2 (after 8 hours)	8.2	100
			#2 (after 24 hours)	17.8	89.8
#2 (after 48 hours)	21.0	88.5
			#2 (after 72 hours)	27.9	87.0
Sheet glass	40.6	45.5
			Acrylic resin plate	64.5	60.6
PVC board	75.3	44.7
			PC board	86.0	49.0

As can be seen from the above table, if the contact angle with water does not exceed 10 degrees, an extremely high anti-fogging ability can be obtained.

Example 13

Siloxane coatings containing photocatalysts

This example is relevant to the finding that certain high molecular weight compounds and coatings containing photocatalysts can become highly hydrophilic when irradiated with UV light.

A square aluminum plate having a size of 10cm may be used as the base. Each substrate was first coated with a silicone layer to smooth the surface. For this purpose, the first component "a" (silica sol) and the second component "B" (trimethoxymethylsilane) of the coating composition "Glaska" (sold by the japan synthetic rubber company) may be mixed with each other such that the weight ratio of silica to trimethoxymethylsilane is 3 the resulting coating mixture is applied onto an aluminum substrate and cured at 150 ℃, resulting in a plurality of aluminum substrates (#1 samples) each coated with a silicone base coating having a thickness of 3 μm.

And then coated with a polymeric coating composition containing a photocatalyst. To prevent the film-forming component in the coating composition from degrading due to photooxidation by the photocatalyst, a siloxane may be selected as the film-forming component.

Further, an anatase type titania sol (Nissan Chemical Ind, TA-15) and the first component "A" (silica sol) of the above-mentioned "Glaska" were mixed. After being diluted with ethanol, the second component "B" of the above-mentioned "Glaska" was added thereto, thereby preparing a coating composition containing titanium oxide. The coating composition consisted of 3 parts by weight of silica, 1 part by weight of trimethoxymethylsilane and 4 parts by weight of titanium oxide.

The coating composition was applied to the surface of the sample #1 and cured at a temperature of 150 c to obtain a sample #2 having an upper coating layer in which anatase-type titanium oxide particles were dispersed throughout the silicone coating film.

Then, the mixture was heated with a BLB incandescent lamp at 0.5mW/cm²UV intensity the surface of the sample #2 was irradiated with UV light for 5 days, thereby obtaining a sample # 3. When the contact angle of the sample surface with water was measured using a contact angle measuring instrument (manufactured by ERMA), it was unexpected that the reading of the contact angle measuring instrument was less than 3 degrees.

The contact angle of the #2 sample measured before UV irradiation was 70 degrees. The contact angle of sample #1 was 90 degrees. Then, the sample #1 was irradiated with UV light for 5 days under the same conditions as the sample #2 and the contact angle thereof was measured, and the contact angle was 85 degrees.

From the above, it can be found that although siloxane itself is substantially hydrophobic, it can become highly hydrophilic when it contains a photocatalyst and the photocatalyst is photo-excited by irradiation with ultraviolet light.

Example 14

Raman spectroscopic analysis

Using a mercury lamp at 22.8mW/cm²UV intensity UV light irradiation was performed on the #2 sample of example 13 for 2 hours to obtain a #4 sampleAnd (5) preparing the product. Raman spectrum analysis was performed on the #2 sample before UV irradiation and the #4 sample after UV irradiation. For comparison, the #1 sample was subjected to UV light irradiation under the same conditions and the sample was subjected to raman spectroscopy before and after the UV irradiation. The raman spectrum is shown in fig. 6. In fig. 6, the raman spectra of the #1 sample before and after UV irradiation are represented by one curve #1 since they are the same.

Referring to FIG. 6, in the Raman spectrum of sample #2, in the spectrum corresponding to sp³Wave number 2910cm for symmetric extension of hybrid orbital C-H bond^-1Where a main peak can be seen, and in the representation sp³Wave number 2970cm of hybrid orbital C-H bond reversed phase symmetrical extension^-1A prominent peak is seen. From this it can be concluded that C-H bonds are present in sample # 2.

In the Raman spectrum of sample #4, at a wave number of 2910cm^-1And 2970cm^-1No peak was seen at wavenumber. It can be seen that the wave number is 3200cm^-1Broad spectrum absorption highlighted and corresponding to the symmetric extension of the O-H bond. Therefore, it can be concluded that there is no C-H bond but an O-H bond in the sample # 4.

In contrast, in the Raman spectrum of the sample #1, the spectrum corresponding to sp can be observed at all times before and after UV irradiation³Wave number 2910cm for symmetric extension of hybrid orbital C-H bond^-1Has a main peak and is represented by sp³Wave number 2970cm of hybrid orbital C-H bond reversed phase symmetrical extension^-1There is a prominent peak. Thus, the presence of C-H bonds in the #1 sample can be confirmed.

From the above, it is considered that when a photocatalyst-containing siloxane is irradiated with ultraviolet light, an organic group bonded to a silicon atom on a siloxane molecule represented by the following general formula (1) is substituted with a hydroxyl group by the action of the photocatalyst to form a siloxane derivative on the surface, as represented by the general formula (2),

wherein R represents an alkyl or aryl groupAnd (4) a base.

Example 15

Anti-fog plastic panel-siloxane anti-fog coating containing photocatalyst

First, the surface of a plastic substrate is coated with a silicone layer to prevent the substrate from being degraded by a photocatalyst.

For this purpose, a coating solution was prepared in the same manner as in example 13 by mixing the above-mentioned first and second components "a" and "B" of "Glaska" of japan synthetic rubber company, with a weight ratio of silicon oxide to trimethoxymethylsilane of 3. The coating solution was applied to the surface of an acrylic plate block having a size of 10cm and cured at 100 c, thereby obtaining a plurality of acrylic plates (#1 sample), each of which was coated with a silicone base coating having a thickness of 5 μm.

Then, anatase type titanium oxide sol (Nissan Chemical Ind, TA-15) and the first component "A" of the above "Glaska" were mixed and, after being diluted with ethanol, a second component "B" of "Glaska" was added thereto, thereby preparing four coating solutions having different components. The compositions of these coating solutions were 5%, 10%, 50% and 80% by weight of titanium oxide to the sum of silicon oxide and trimethoxymethylsilane, respectively.

Then, these coating solutions were respectively applied onto the surface of an acrylic resin plate which had been coated with silicone and cured at 100 ℃ to obtain samples #2 to #5 each with an overcoat layer in which anatase-type titanium oxide particles were dispersed throughout the silicone coating film.

Using a BLB incandescent lamp at 0.5mW/cm²UV intensity the samples #1 to #5 were irradiated with UV light for up to 200 hours and the surface and contact angle of these samples were measured with a contact angle measuring apparatus (manufactured by ERMA) at different timesContact angle of water to observe the change in contact angle with time. The results are shown in FIG. 7.

As can be seen from fig. 7, UV irradiation did not change the contact angle with water significantly in the sample #1 without the titanium oxide containing coating.

In contrast, in the samples #2 to #5 having the titanium oxide-containing overcoat layer, it can be seen that the surface thereof was hydrophilized at the time of U irradiation, and the contact angle with water became 10 degrees or less.

In particular, it can be seen that the contact angle with water is less than 2 degrees in the samples #3 to #5 having a titanium oxide content of more than 10% by weight. In addition, in samples #4 and #5, which have a titanium oxide content of 50%, respectively, the contact angle with water was less than 3 degrees when UV irradiation was performed for a short time.

When the #4 sample was blown, no fog was formed. After the sample #4 was left in the dark for 2 weeks, the contact angle with water was measured with a contact angle measuring instrument (CA-X150) and found to be lower than 3 degrees.

Example 16

Scratch test by pen

Pen scratch tests were performed to determine the abrasion resistance of the overcoat containing titanium oxide.

In the same manner as in example 15, a silicone base coat of 5 μm thickness was first applied to a 10cm multi-piece acrylic block and then coated with an overcoat containing a different titanium oxide content. The content of titanium oxide in the overcoat layer was 50% by weight, 60% by weight, and 90% by weight, respectively.

According to the H8602 method of Japanese Industrial Standards (JIS), the surface of the sample was scratched with various pencil leads to find the hardest pencil lead capable of tearing off the overcoat. Similar tests were also performed on samples coated with only the base coat. The test results are shown in fig. 8.

An outer coating with a titanium oxide content of 90% by weight can be torn by a pencil lead with a hardness of 5B, whereas an outer coating with a titanium oxide content of 60% by weight can withstand pencil leads with a hardness of H and exhibits suitable wear resistance. It is clear that the wear resistance of the outer coating increases with decreasing titanium oxide content.

Example 17

Influence of coating thickness

In the same manner as in example 13, various samples were obtained by first applying a base silicone coating of thickness 5 microns on a block of aluminum plates 10cm in size and then with an external coating containing anatase of different thickness. The thickness of the overcoat layer of sample #1 was 0.003 microns, the thickness of the overcoat layer of sample #2 was 0.1 microns, the thickness of the overcoat layer of sample #3 was 0.2 microns, the thickness of the overcoat layer of sample #4 was 0.6 microns, and the thickness of the overcoat layer of sample #5 was 25 microns.

Using BLB fluorescent lamp at 0.5mW/cm²UV intensity the change with time of the contact angle of the sample surface with water was measured with a contact angle measuring instrument (manufactured by ERMA) when UV light irradiation was performed on each sample surface. The results are shown in FIG. 9.

As can be seen from fig. 9, regardless of the thickness of the coating layer, the surface of each sample was highly hydrophilized within 50 hours of UV irradiation, and the contact angle with water was determined to be 3 degrees or less. In particular, it can be seen that even an overcoat layer containing titanium oxide having a thickness of less than 0.2 μm can obtain sufficient photocatalytic activity to highly hydrophilize the surface of the overcoat layer. In this regard, it is known that when the coating thickness exceeds 0.2 μm, the transparent layer is colored due to interference of light. This example illustrates that by limiting the degree of existence of the overcoat layer to 0.2 μm or less, the surface of the overcoat layer can be highly hydrophilized while preventing the occurrence of coloring due to interference of light.

Samples #1 and #5 were then tested for their ability to photolyze methyl mercaptan. Placing the samples separatelyIn a dryer having a volume of 11 liters made of quartz glass which transmits ultraviolet light, and nitrogen gas containing methyl mercaptan was introduced thereinto so that the concentration of methyl mercaptan was 3 ppm. The 4WBLB fluorescent lamps were placed in a desiccator at a distance of 8 cm from each sample, to give a volume of 0.3mW/cm²The sample is irradiated with UV intensity of (1). After 30 minutes, a gas sample was withdrawn from the desiccator. The concentration of methyl mercaptan was determined by gas chromatography and the removal rate of methyl mercaptan was calculated. The results are shown in FIG. 10.

FIG. 10 shows that the ability of the photocatalytic coating to photolyze methyl mercaptan increases with increasing coating thickness. In contrast to the finding that the photocatalytic superhydrophilic phenomenon described above with respect to fig. 9 is not affected by coating thickness, the photocatalytic photodecomposition capability is significantly affected by thickness. Thus, the photocatalytic super-hydrophilization process does not necessarily appear to be identical to the photocatalytic redox process known in the photocatalytic field

Example 18

Siloxane advanced hydrophilic photocatalytic coating containing titanium oxide

In the same manner as in example 13, a silicone base coat having a thickness of 5 μm was first applied to a block of aluminum plates having a dimension of 10 cm.

Then, an anatase-type titania sol (Nissan Chemical Ind, TA-15) and the second component "B" (trimethoxymethylsilane) of the above "Glaska" were mixed and the mixture was diluted with ethanol, thereby preparing a coating solution containing titanium oxide. The weight ratio of trimethoxymethylsilane to titanium oxide was 1.

These coating compositions were then applied to the aluminum sheet surface and cured at 150 ℃ to form an outer coating in which the anatase titanium oxide particles were dispersed throughout the silicone coating film. The thickness of the coating was 0.1 microns.

Using BLB fluorescent lamp at 0.5mW/cm²UV intensity pairThe samples were subjected to 1 day UV light irradiation and the contact angle of the surface of these samples with water was measured with a contact angle measuring instrument (CA-X150), which reads 0 degrees.

The samples were kept in the dark for 3 weeks and the contact angle with water was measured weekly. The results of the contact angle measurement are shown in table 3.

TABLE 3

Immediately after irradiation	After 1 week	After 2 weeks	After 3 weeks
				0 degree	2 degree	1 degree	3 degree

As can be seen from table 3, after the surface is super-hydrophilized, the super-hydrophilicity can be maintained for a sufficiently long time even without photoexcitation.

Example 19

Antibacterial enhancer-silver-added photocatalyst

In the same manner as in example 1, an amorphous silicon oxide film and an amorphous titanium oxide film were formed in this order on the surface of a soda-lime-silica glass plate block having a size of 10cm, and then the glass plate was sintered at 500 ℃ to convert the amorphous titanium oxide into anatase-type titanium oxide, thereby obtaining a sample # 1.

Then, an aqueous solution containing 1% by weight of silver lactate was applied onto the surface of the sample #1 and subjected to UV light irradiation for 1 minute using a sample of a 20WBLB fluorescent lamp 20 cm from the sample, thereby obtaining a sample # 2. After uv irradiation, silver lactate is photo-reduced to form silver deposits and hydrophilizes the sample surface under the photocatalytic action of titanium oxide. Sample #1 was also subjected to UV irradiation under the same conditions.

When the contact angles of the samples #1 and #2 with water were measured using a contact angle measuring instrument (manufactured by ERMA), the contact angles of both samples were less than 3 degrees. When blowing air to the sample, no mist is formed. For comparison, soda-lime-silica glass substrates were also tested and found to have a contact angle with water of 50 degrees and to easily form a haze when blown.

Then, samples #1 and #2 and soda-lime-silica glass plates were tested for antibacterial ability. A liquid culture prepared by culturing Escherichia coli (Escherichia coli W3110 strain) overnight with shaking was subjected to centrifugal washing and diluted 1000-fold with sterilized distilled water to prepare a liquid containing bacteria. 0.15 ml of a liquid containing bacteria (equivalent to 1-5 million CFU) was dropped onto three glass slides and then brought into close contact with the #1 and #2 samples and the soda-lime-silica glass plate, which had been sterilized with 70% ethanol in advance. These samples and plates were irradiated with an incandescent lamp for 30 minutes at 3500 lux intensity from the front side of the glass slide. Then, the liquid containing the bacteria on each sample was wiped off with a sterilized gauze and recovered in 10 ml of physiological saline, and the thus recovered liquid was spread on a nutrient agar plate and cultured at 37 ℃ for 1 day. Then, the number of colonies of E.coli formed on the culture was counted to calculate the survival rate of E.coli. The results showed that E.coli survivors were over 70% on sample #1 and soda-lime-silica glass plates, while the survivors were less than 10% on sample # 2.

This experiment shows that when silver is incorporated in the photocatalyst, the surface of the substrate can be not only highly hydrophilic but also have an antibacterial function.

Example 20

Copper-containing photocatalyst as antibacterial enhancer

In the same manner as in example 1, amorphous silica thin films were formed on the surfaces of soda-lime-silica glass plate squares each having a size of 10cm, thereby obtaining pieces of sample # 1.

Then, similarly to example 1, a thin film of amorphous titanium oxide was formed on the surface of the sample #1, which was sintered at 500 ℃ to convert the amorphous titanium oxide into anatase-type titanium oxide, thereby obtaining a sample # 1. An ethanol solution containing 1% by weight of copper acetate was spray-coated on the surface of the sample, and after drying and UV light irradiation was performed for 1 minute with a sample of a 20WBLB fluorescent lamp 20 cm from the sample, thereby photo-reductively depositing copper acetate, thereby obtaining a #2 sample in which titanium oxide crystals were doped with copper. The #2 sample exhibited appropriate light transmission when observed with the eye.

The soda-lime-silica glass plates and the #2 and #1 samples (without the titania coating) were tested for their anti-fogging ability and contact angle with water immediately after preparation. The anti-fog test is a contact angle measurement with a contact angle meter (manufactured by ERMA) performed by blowing air on a sample to generate fog on the surface of the sample and checking whether moisture condensate particles are present or not with a microscope. The results are shown in Table 4.

TABLE 4

Immediately after sample preparation

	Contact Angle with Water	Anti-fog property
			#2 sample	10	Fog-free
#1 sample	9	Fog-free
			Soda-lime-silica glass	50	Fogging

In addition, the current BLB fluorescent lamp was used at a power of 0.5mW/cm²UV intensity the anti-fogging ability and contact angle of the #2 and #1 samples with soda-lime-silica glass plates were determined in the same manner after 1 month of UV light irradiation. The results are shown in Table 5.

TABLE 5

After 1 month of UV irradiation

	Contact Angle with Water	Anti-fog property
			#2 sample	3	Fog-free
#1 sample	49	Fogging
			Soda-lime-silica glass	53	Fogging

Samples #2 and #1 immediately after the preparation and soda-lime-silica glass plates were measured for antibacterial ability in the same manner as in example 19. The results showed that E.coli survivors were over 70% in the soda-lime-silica glass plates and samples #1, and less than 10% in the samples # 2.

Next, the odor removing properties were measured for the samples #2 and #1 and the soda-lime-silica glass plate just after the preparation. The samples were each placed in a desiccator made of ultraviolet-transmittable quartz glass and having a volume of 11 liters, and nitrogen gas containing methyl mercaptan was introduced thereinto so that the concentration of methyl mercaptan was 3 ppm. The 4WBLB fluorescent lamps were placed in a desiccator at a distance of 8 cm from each sample, to give a volume of 0.3mW/cm²The sample is irradiated with UV intensity of (1). After 30 minutes, a gas sample was withdrawn from the desiccator. The concentration of methyl mercaptan was determined by gas chromatography and the removal rate of methyl mercaptan was calculated. For sample #1 and the soda-lime-silica glass plate, the removal of methyl mercaptan was less than 10%. In contrast, the removal rate of sample #2 exceeded 90%, and therefore, better odor removal performance was obtained.

Example 21

Copper-containing photocatalyst as antibacterial enhancer

A first component "A" (silica sol) and a second component "B" (trimethoxymethylsilane) of "Glaska" of Japan synthetic rubber Co., Ltd were mixed so that the weight ratio of silica to trimethoxymethylsilane was 3. This mixture was coated on the surface of an acrylic plate block having a size of 10cm, and then cured at 100 ℃ to obtain an acrylic plate coated with a silicone base coating layer having a thickness of 3 μm.

The anatase titania sol (TA-15) was then mixed with an aqueous solution containing 3% by weight of copper acetate, and after the addition of the first component "A" of "Glaska", the mixture was diluted with propanol. Then, the second component "B" of "Glaska" was added, thereby preparing a coating composition containing titanium oxide. The coating composition consisted of 3 parts by weight of silica, 1 part by weight of trimethoxymethylsilane, 4 parts by weight of titanium oxide and 0.08 parts by weight of copper acetate (calculated as metallic copper).

The coating composition was applied to the surface of an acrylic plate and cured at 100 ℃ to form an overcoat layer. In use, BLB fluorescent lamp at 0.5mW/cm²UV intensity was subjected to UV light irradiation for 5 days, thereby obtaining a #1 sample.

The anti-fogging ability, contact angle with water, antibacterial property and decolorizing function were measured for the #1 sample and acrylic resin plate in the same manner as in example 20. In the acrylic plate, the contact angle with water was 70 degrees, and fog was formed when air was blown upward, while in the sample #1, the contact angle with water was 3 to 9 degrees and fog was not formed. Regarding the antibacterial ability, the survival rate of E.coli in the acrylic resin plate was 70% or more, and the survival rate in the #1 sample was 10% or less. With respect to the odor removal performance, the removal rate of methyl mercaptan from the acrylic resin plate was less than 10%, while the removal rate of the #1 sample was 90% or more.

Example 22

Photoredox activity enhancer-Pt-added photocatalyst

In the same manner as in example 1, an amorphous silicon oxide film and an amorphous titanium oxide film were formed in this order on the surface of a soda-lime-silica glass plate block having a size of 10cm, and then the glass plate was sintered at 500 ℃ to convert the amorphous titanium oxide into anatase-type titanium oxide.

Then chloroplatinic acid hexahydrate H containing 0.1% by weight of platinum₂PtCl₆·6H₂1 ml of an aqueous O solution was applied to the sample, which was then measured with a BLB fluorescent lamp at 0.5mW/cm²UV light irradiation of intensity ofThe sample was sampled for 1 minute as such, whereby a platinum deposit was formed by photoreduction of chloroplatinic acid hexahydrate, and a sample in which titanium oxide crystals were doped with platinum was obtained.

The thus-obtained sample was left for one day and used at 0.5mW/cm using a BLB fluorescent lamp²UV light intensity the sample was irradiated with UV light for 1 minute. The contact angle after UV irradiation was 0 degrees, and the removal rate of methyl mercaptan measured and calculated in the same manner as in example 20 was 98%.

Example 23

Self-cleaning and anti-fouling capability

Sample #2 from example 13 was used at 0.5mW/cm using a BLB fluorescent lamp²UV light intensity was subjected to UV light irradiation for 10 hours, thereby obtaining a #3 sample. When the contact angle of the sample surface with water was measured with a contact angle measuring instrument (manufactured by ERMA), the reading of the contact angle measuring instrument was less than 3 degrees.

An outdoor accelerated pollution test apparatus was installed on the top of a building in the city of Chigasaki as shown in fig. 11A and 11B. Referring to fig. 11A and 11B, the apparatus includes a sample mounting surface 22 supported by a frame 20 and adapted to hold a sample 24. At the top of the frame is fixed an upwardly inclined roof 26. The roof is made of a corrugated plastic sheet and can be used to run rain water down the surface of a sample 24 secured to the sample mounting surface 22 in strips.

Sample #3, sample #1 of example 13 and sample #2 of example 13 were mounted on the sample mounting surface 22 of the device and exposed to humid conditions for 9 days starting at 6/12 of 1995, during which the climate and rainfall were as shown in table 6.

TABLE 6

Time of day	Weather (weather)	Rainfall (mm)	Hours of sunshine
				June for 12 days	Cloudy	0.0	0
June 13 days	Heavy rain	53.0	0
				June day 14	Cloudy/rainy weather	20.5	0
June 15 days	Cloudy/sunny	0.0	3.9
				June for 16 days	Cloudy	0.0	0.2
June for 17 days	Sunny/cloudy	0.0	9.6
				June 18 days	Clear to cloudy	0.0	7.0
June for 19 days	Rain turning cloud	1.0	0.2
				June 20 days	Cloudy/heavy rain	56.0	2.4

When observed on day 6 and day 14, the streak-like dirt or sludge was found on the surface of the sample #1, which is estimated to be caused by hydrophobic contaminants in the air, such as combustion products, e.g., carbon black and municipal waste, carried by rainwater in heavy rain on the previous day and deposited on the surface of the sample when the rainwater runs down the surface, in contrast to which no dirt or sludge was seen on the sample # 3. This is believed to be because the sample surface is highly hydrophilic, hydrophobic contaminants cannot stick to the surface when the contaminant-containing rain flows down and the contaminants are also washed away by the rain.

In sample #2, a spotted soil or mud was seen. This is probably because the photocatalytic coating thereon was not sufficiently exposed to UV light in sunlight after the sample #2, which was not subjected to UV irradiation, was mounted on the test device, resulting in the surface being unevenly hydrophilized.

When observed at 6 months and 20 days, a vertical streak of mud was clearly visible on the surface of the #1 sample without the photocatalytic coating. While no mud was seen on samples #3 and #2 with the photocatalytic coating.

For sample #1, the contact angle with water was 70 degrees, while the contact angles for samples #2 and #3 were below 3 degrees. The fact that sample #2 has a contact angle lower than 3 degrees demonstrates that organic groups bonded to silicon atoms in siloxane molecules in the overcoat layer are substituted with hydroxyl groups under photocatalytic action after irradiation with UV light in sunlight, thereby making the overcoat layer highly hydrophilic. It can also be seen in the sample #3 that the sample #3 can be kept highly hydrophilic by irradiation with sunlight.

Example 24

Color difference test

The sample #1 and the sample #2 of example 23 were measured with a color difference meter (Tokyo Denshoku) before being mounted on an outdoor accelerated contamination test apparatus and after one month to measure the color difference. Delta E for color difference, as compared with Japanese Industrial Standard (JIS) H0201^*And (4) index representation. The change in color difference after the device was placed on the accelerated fouling test device is shown in Table 7.

TABLE 7

	Deformation zone	Background region
			Sample No. 1	4.1	1.1
Sample No. 2	0.8	0.5

As can be seen from table 7, in the sample #1 without photocatalytic coating, a large amount of mud was caused by connection to the vertical strip-shaped area corresponding to the rainwater flow path, compared to the sample #2 with photocatalytic coating. It can also be seen that there is a large difference in the degree of contamination in the background area between the #2 and #1 samples.

Example 25

Cleaning ability for oil contamination

An amount of oleic acid was applied to the surface of samples #1 and #3 of example 23 and these samples were immersed in water in a container with the sample surface held in a horizontal position. In sample #1 oleic acid remained adhered to the sample surface. While in sample #3, the oleic acid became rounded to form oil droplets which were then released from the sample surface and rose to and up the water surface.

In this way, it was confirmed that when the surface of the substrate was coated with the photocatalytic overcoat, the surface could remain hydrophilic, so that oily contaminants could be easily released from the surface when immersed in water, thereby cleaning the surface.

This example illustrates that tableware contaminated with oil or fat can be easily washed without using a detergent simply by immersing it in water, and it is premised that its surface has a photocatalytic coating and the photocatalyst is photo-excited by UV irradiation.

Example 26

Drying of water-containing moist surfaces

The surfaces of samples #1 and #3 of example 23 were wetted with water and the samples were left outdoors on a sunny day to allow them to dry naturally. The room temperature was about 25 ℃. When the #1 sample was examined after 30 minutes, the water droplets remained on the surface. In contrast, it was found that the surface of the #3 sample was completely dried.

It is believed that in the sample #3 having the photocatalytic coating, the adhered water droplets spread to form a uniform water film, and thus drying was accelerated.

This example illustrates that water-wetted spectacle lenses or automotive windscreens can dry quickly.

Example 27

Tile-coated sintered titanium oxide and silicon oxide with highly hydrophilic surface

Anatase type titania sol (Ishihara industries of Osaka, STS-11) and silica gel sol (Nissan Chemical Ind, "Snowtex O") were mixed at a molar ratio of 88 to 12 in terms of solid content and the mixture was coated on the surface of a glazed tile (Toto Ltd, AB02E01) having a size of 15 cm by a spray coating method and then sintered at 800 ℃ for 1 hour, thereby obtaining a sample covered with a coating layer composed of titania and silica. The thickness of the coating was 03 microns. The contact angle of rainwater immediately after sintering was 5 degrees.

The sample was kept in the dark for one week, after which the contact angle was still measured to be 5 degrees.

When a BLB fluorescent lamp is used, the power is 0.03mW/cm²UV intensity the contact angle with water of the sample surface when irradiated with UV light for one day became 0 degree.

Example 28

Coating of sintered titanium oxide and silicon oxide-hydrophilization under room light

Anatase type titania sol (STS-11) and silica gel sol ("Snowtex 20") were mixed in a molar ratio of 80 to 20, calculated as solid components, and the mixture was coated on the surface of a glazed tile (AB02E01) having a size of 15 cm by a spray coating method, and then sintered at 800 ℃ for 1 hour, thereby obtaining a sample covered with a coating layer composed of titania and silica. The thickness of the coating was 0.3 microns. The contact angle with water immediately after sintering was 5 degrees.

The sample was kept in the dark for two weeks, after which the contact angle was measured to be 14 degrees.

When a BLB fluorescent lamp is used, the power is 0.004mW/cm²UV intensity the contact angle with water of the sample surface when irradiated with UV light for one day became 4 degrees.

Therefore, it can be found that the photocatalytic coating can be hydrophilized to a satisfactory degree even under indoor lighting.

Example 29

Coating with sintered titanium oxide and silica-silica content

Anatase type titania sol (STS-11) and silica gel sol (Nissan Chemical ind., "Snowtex 2O") were mixed at different ratios to obtain suspensions having molar ratios of silica to solid components in the suspensions of 0%, 5%, 10%, 15%, 20%, 25% and 30%, respectively, and 0.08 g of each suspension was coated on the surface of a glazed tile (AB02E01) having a size of 15 cm by a spray coating method and then sintered at 800 ℃ for 1 hour, thereby obtaining samples covered with a coating layer composed of titania and silica. The contact angle with water for each sample immediately after sintering is shown in fig. 12. It is apparent from fig. 12 that the initial contact angle can be lowered by adding silicon oxide.

The sample was kept in the dark for 8 days, and then the contact angle with water was measured, and fig. 13 was prepared. It can be seen by comparing fig. 12 and 13 that in the sample containing more than 10% by mole of silicon oxide, the loss of hydrophilicity due to keeping the sample in the dark is small.

Then, a BLB fluorescent lamp was used at a rate of 0.03mW/cm²UV intensity the sample surface was irradiated with UV light for two days. The contact angle with water after irradiation is shown in fig. 14. From this figure, it can be seen that in the case where silicon oxide is added to titanium oxide, hydrophilicity is easily restored by UV irradiation.

The sample was then kept in the dark for another 8 days, and then the contact angle with water was measured, and the result is shown in fig. 15. It can be seen from the figure that in the case where silicon oxide was added to titanium oxide, the loss of hydrophilicity after UV irradiation due to keeping the sample in the dark was small.

A pen scratch test was performed to examine the wear resistance of the sintered thin film composed of silicon oxide and titanium oxide. The results are shown in FIG. 16. It can be seen from the graph that the abrasion resistance increases with the increase in the content of silicon oxide.

Example 30

Slurry test

A mixture of anatase-type titania sol (STS-11) and silica gel sol ("Snowtex 2O") (the content of co-silica was 10% by weight, calculated as solid content) was coated on the surface of a glazed tile (AB02E01) having a size of 15 cm in an amount of 45 mg (calculated as solid content), and then sintered at 880 ℃ for 1 hour, and then, using a BLB fluorescent lamp at 0.5mW/cm²UV intensity the surface of the sample was irradiated with UV light for 3 hours, thereby obtaining a #1 sample, and contact angles with water of the #1 sample and the glazed tile were 0 degree and 30 degrees, respectively.

A mixture of 64.3% by weight of ocher, 21.4% by weight of sintered Kanto loam, 4.8% by weight of hydrophobic carbon black, 4.8% by weight of silica sand and 4.7% by weight of hydrophilic carbon black was suspended in water at a concentration of 1.05 g/l to prepare a slurry.

150 ml of the slurry thus prepared was run down the #1 sample and the glazed tile (AB02E01) inclined at an angle of 45 degrees and then dried for 15 minutes. 150 ml of distilled water was again flowed down and dried for 15 minutes, and the above cycle was repeated 25 times. The change in color difference and gloss after the slurry test was measured. The measurement of the gloss is performed according to the method described in Japanese Industrial Standard (JIS) Z8741 and is obtained by removing the gloss after the test from the gloss before the test. The results are shown in Table 8.

TABLE 8

	#1 sample	Glazed tile (AB02E01)
			Contact angle (degree)	0	30
Variation of chromatic aberration	0.7	5.6
			Change in gloss	93.4％	74.1％

Example 31

Relationship between contact angle with water and self-cleaning and anti-fogging ability

Mud tests were performed on various samples in the same manner as in example 30. The test samples included sample #1 of example 30, #2 sample with a copper-doped titanium oxide coating, glazed tile (AB02E01), acrylic board, artificial marble board made of a polyester resin matrix(tototd., ML03) and Polytetrafluoroethylene (PTFE) sheets. Sample #2 was prepared by spraying 0.3 g of an aqueous solution of copper acetate monohydrate having a copper concentration of 50. mu. mol/g onto sample #1 of example 30 and after drying was then applied at 0.4mW/cm using a BLB fluorescent lamp²UV intensity the sample was irradiated with UV light for 10 minutes to thereby photoreductively deposit copper acetate monohydrate. The results of the mud test are shown in table 9.

TABLE 9

Sample (I)	Contact Angle with Water	Color difference	Change in gloss (%)
				#1 sample	0.0	0.7	93.8
#2 sample	4.0	2.0	81.5
				Glazed tile	19.4	4.6	68.3
Acrylic acid board	50.9	4.5	69.3
				Artificial marble	54.8	3.2	85.2
PTFE plate	105.1	0.9	98.2

In addition, accelerated contamination tests similar to example 23 were performed on various samples for one month. The test samples used included sample #1 from example 30, a glazed tile (AB02E01), an acrylic board, an aluminum board coated with a silicone base layer in a similar manner to example 13, and a PTFE board. The results of the accelerated test are shown in Table 10, where the change in color difference indicates the vertical stripe region of the sample, similarly to example 24.

Watch 10

Sample (I)	Contact Angle with Water	Variation of chromatic aberration
			#1 sample	0.0	0.9
Glazed tile	19.4	1.5
			Acrylic acid board	50.9	2.3
Of coating siloxanes	90.0	4.2
			PTFE plate	105.1	7.8

For ease of understanding, changes in contact angle with water and color difference are plotted in fig. 17. In fig. 17, a curve a represents the relationship between the contact angle with water and the change in color difference due to pollutants such as combustion products in the air such as carbon black and municipal waste as a result of the accelerated pollution test. And curve B shows the relationship between the contact angle with water and the change in the color difference caused by the slurry as a result of the slurry test.

Referring to fig. 17, as the contact angle of the substrate with water increases, dirt or stain due to combustion products and municipal waste becomes more apparent, as can be readily appreciated from curve a. This is because contaminants such as combustion products and municipal waste are generally hydrophobic and therefore tend to stick to hydrophobic surfaces.

In contrast, curve B shows that the dirt or stain due to the slurry is highest at a contact angle with water of 20 to 50 degrees. This is because inorganic materials such as loam and soil have hydrophilicity with a contact angle with water of 20 to 50 degrees by themselves, and thus they easily adhere to surfaces having similar hydrophilicity. It can therefore be understood that the adhesion of inorganic materials to a surface can be prevented by hydrophilizing the surface so that the contact angle with water is less than 20 degrees, or hydrophobizing the surface so that the contact angle with water exceeds 60 degrees.

When the contact angle with water is less than 20 degrees, the contamination of the slurry is reduced because when the surface is highly hydrophilized so that the contact angle with water is less than 20 degrees, the affinity of the surface for water exceeds the affinity for the inorganic material, and therefore, the adhesion of the inorganic material is blocked by water that preferentially adheres to the surface, and any inorganic material that has adhered or is about to adhere to the surface is easily washed away by water.

From the foregoing, it can be seen that in order to prevent hydrophobic and hydrophilic substances from sticking to the surfaces of buildings and the like, or to ensure that dirt or mud deposited on the surface is washed away by rain water to render the surface self-cleaning, the surface can be modified to have a contact angle with water of less than 20 degrees, preferably less than 10 degrees, more preferably less than 5 degrees.

Example 32

Coating sintered titanium oxide and tin oxide-glazed tile

Anatase-type titania sol (STS-11) and tin oxide sol (Taki chemical k.k of Kakogawa City, Hyogo-Prefecture, average crystal size of 3.5 nm) were mixed at various mixing ratios (weight percentage of tin oxide with respect to the sum of titanium oxide and tin oxide) shown in table 1 and the mixture was coated on the surface of a glazed tile (AB02E01) having a size of 15 cm by a spray coating method and then sintered at 750 or 800 ℃ for 1 minute, thereby obtaining samples #1- # 6. After sintering, samples #2, #4, #5 and #6 were doped by coating the samples with an aqueous solution containing one percent by weight of silver nitrate and photoreductive depositing the silver nitrate. In addition, samples #7 to #9 were prepared by coating only a sol of tin oxide or a sol of titanium oxide on the glazed tile and by sintering, after which the samples #7 and #9 were further doped with silver.

Each sample was kept in the dark for one week, followed by 0.3mW/cm using a BLB fluorescent lamp²UV intensity the sample surface was irradiated with UV light for 3 days, and the contact angle with water was measured. The results are shown in Table 11.

TABLE 11

Sample (I)	SnO2Ratio (wt%)	Sintering temperature (. degree. C.)	Ag	Contact angle (degree)
					#1	1	800	Is free of	0
#2	5	800	Adding into	0
					#3	15	800	Is free of	0
#4	15	750	Adding into	0
					#5	50	750	Adding into	0
#6	95	800	Adding into	5
					#7	100	750	Adding into	8
#8	0	800	Is free of	11
					#9	0	800	Adding into	14

As is apparent from table 11, in the samples #8 and #9 coated with only titanium oxide, the contact angle with water exceeded 10 degrees. This is because alkali framework-modifying ions, such as sodium ions, diffuse from the glaze into the titanium oxide coating during sintering, thereby inhibiting the photocatalytic activity of anatase. In contrast, it can be seen that in the samples #1 to #6 doped with tin dioxide, the surfaces were highly hydrophilized as can be seen from the sample #7, and tin oxide as a semiconductor photocatalyst can hydrophilize the surfaces in a similar manner to titanium oxide. Although the reason for this is not clear. This example illustrates that the effect of diffusion of basic framework-modifying ions can be overcome by adding tin oxide to the titanium oxide.

Example 33

Sintered titanium oxide coating and anti-diffusion layer-glazed tile

Tetraethoxysilane ("Ethyl 28" sold by Colcoat) was applied to the surface of a glazed tile (AB02E01) having a size of 15 cm, and then it was maintained at 150 c for about 20 minutes, thereby hydrolyzing and dehydrating-polymerizing tetraethoxysilane, thereby forming an amorphous silicon oxide coating layer on the surface of the glazed tile.

Then, anatase type titanium oxide (STS-11) sol was sprayed on the surface of the glazed tile, which was then sintered at a temperature of 800 ℃ for 1 hour.

The sample thus obtained, as well as the #8 sample of example 32 (for comparison purposes), was kept in the dark for one week, followed by 0.3mW/cm using a BLB fluorescent lamp²UV intensity the sample surface was irradiated with UV light for 1 day, and the contact angle with water was measured.

Unlike #8 sample in example 32, which has a contact angle with water of 12 degrees, the sample having the amorphous silicon oxide intermediate layer is hydrophilized to have a contact angle with water of less than 3 degrees. From this, it is considered that the amorphous silicon oxide layer can effectively prevent the diffusion of the basic skeleton-modified ions present in the glaze layer.

Example 34

Amorphous titanium oxide sintered coating and anti-diffusion layer-glazed tile

An amorphous silicon oxide film and an amorphous titanium oxide film were formed in this order on the surface of a glazed tile (AB02E01) having a size of 15 cm in the same manner as in example 1. The brick is then sintered at 500 c to convert the amorphous titanium oxide to anatase titanium oxide.

The thus obtained sample was kept in the dark for several days, and then subjected to a BLB fluorescent lamp at 0.5mW/cm²UV intensity the sample surface was irradiated with UV light for 1 day. The contact angle with water was measured to be 0 degrees. Similar to example 33, it is considered that the amorphous silica layer is effective for highly hydrophilizing the surface of the glazed tile.

Example 35

Glazed tile-cleaning ability to oily dirt

An amount of oleic acid was coated onto the surface of sample #1 of example 30. When the sample is immersed in water in a container with the sample surface held in a horizontal position, oleic acid becomes rounded, forms oil droplets, which are then released from the glazed tile surface and rise to the upper surface of the water.

This example also illustrates that the surfaces of crockery, such as tiles and tableware, contaminated with oil or fat can be cleaned simply by soaking them in or wetting them with water, provided that their surfaces have a photocatalytic coating and the photocatalyst is photo-excited by UV irradiation.

Example 36

Cleaning power of glass to oily dirt

In the same manner as in example 1, an amorphous silicon oxide film and an amorphous titanium oxide film were formed in this order on the surface of a soda-lime-silica glass plate having a size of 10 cm. The glass plate was then sintered at 500 c to convert the amorphous titanium oxide to anatase titanium oxide.

A quantity of oleic acid was applied to the surface of the glass sheet. When the glass plate is immersed in water in a container with its surface held in a horizontal position, oleic acid becomes rounded, forms oil droplets, and then releases and floats from the surface of the glass plate.

Example 37

Glass-self-cleaning and anti-fogging capability

The sample of example 36 was subjected to an accelerated contamination test similar to example 23 for 1 month. After one month, no vertical streaky mud was visible when viewed by the naked eye.

Example 38

Glazed tile-antibacterial reinforcing agent (silver doped)

A coating layer composed of silicon oxide and titanium oxide was formed on the surface of a glazed tile (AB02E01) having a size of 15 cm in the same manner as in example 27.

Then, an aqueous solution containing 1% by weight of silver lactate was applied to the brick surface, followed by irradiation with a BLB fluorescent lamp to photo-reduce the silver lactate to form a silver deposit, thereby obtaining a sample having a silver-doped titanium oxide coating. The contact angle with water was 0 degrees.

When the tile was subjected to the antibacterial function test in the same manner as in example 19. The survival rate of Escherichia coli is lower than 10%.

Example 39

Glazed tile-antibacterial reinforcing agent (copper doped)

A coating layer composed of silicon oxide and titanium oxide was formed on the surface of a glazed tile (AB02E01) having a size of 15 cm in the same manner as in example 27.

Then, an aqueous solution containing 1% by weight of copper acetate monohydrate was applied to the brick surface, followed by irradiation with a BLB fluorescent lamp to photo-reduce the copper acetate monohydrate to form a copper deposit, thereby obtaining a sample having a copper-doped titanium oxide coating. The contact angle with water is less than 3 degrees,

when the tile was subjected to the antibacterial function test in the same manner as in example 19. The survival rate of Escherichia coli is lower than 10%.

Example 40

Glazed tile-photoredox activity enhancer

A coating layer composed of silicon oxide and titanium oxide was formed on the surface of a glazed tile (AB02E01) having a size of 15 cm in the same manner as in example 27.

Then, the surface of the sample was doped with platinum in the same manner as in example 22, and the contact angle with water was 0 degree.

The methyl mercaptan removal rate was 98% when measured in the same manner as in example 20.

EXAMPLE 41

Influence of the wavelength of light excitation

After being kept in the dark for 10 days, #8 sample in example 32 and a glazed tile (AB02E01) without a titanium oxide coating (for comparison) were subjected to UV irradiation with an Hg-Xe lamp under the conditions shown in Table 12, and the change in contact angle with water with time was measured.

TABLE 12

UV wavelength (nm)	UV intensity (mW/cm)2)	Photon density (photons/sec/cm)2)
			313	10.6	1.66×1016
365	18	3.31×1016
			405	6	1.22×1016

The results of the measurements are shown in fig. 18A-18C, where the data plotted with white dots represent the contact angle with water for the #8 sample of example 32, and the data plotted with black dots represent the contact angle with water for a glazed tile without a titanium oxide coating.

It can be seen from FIG. 18C that hydrophilization did not occur when UV light having a wavelength of 387nm (i.e., UV light having a wavelength exceeding 387 nm) having an energy lower than the band gap energy with anatase-type titanium oxide was irradiated.

In contrast, as can be seen from fig. 18A and 18B, when irradiated with UV light having an energy exceeding that of the anatase band gap, the surface can be hydrophilized.

From the above, it can be confirmed that hydrophilization of the surface is closely related to photoexcitation of the photo-semiconductor.

Example 42

Coating of plastic panels with photocatalysts-containing siloxanes

A coating composition containing titanium oxide similar to example 18 was coated on a polyethylene terephthalate (PET) film (Fuji Xerox, a monochromatic PPC film for OHP, JF-001) and cured at a temperature of 110 ℃ to obtain a #1 sample coated with siloxane containing titanium oxide.

A water-based polyester paint (manufactured by Takamatsu Resin, A-124S) was coated on another PET film (JF-001) and cured at a temperature of 110 ℃ to form an initiation coating layer, and a coating composition containing titanium oxide like that of example 18 was coated on the initiation coating layer and cured at 110 ℃ to obtain a sample # 2.

A coating composition containing titanium oxide similar to that of example 18 was coated on a Polycarbonate (PC) plate and cured at 110 c to obtain a #3 sample.

In addition, an aqueous polyester coating (A-124S) was applied to another polycarbonate sheet and cured at a temperature of 110 ℃ to form an initiation coating. A coating composition similar to that of example 18 containing titanium oxide was applied over the initiation coating and cured at 110 ℃ to obtain a #4 sample.

Samples #1 to #4 were mixed with a PET film (JF-001) and a polycarbonate plate using a BLB fluorescent lamp at 0.6mW/cm²The UV intensity was irradiated and the change in contact angle with water of the sample surface with time was measured. The results are shown in Table 13.

Watch 13

Sample (I)	Before irradiation	After 1 day	After 2 days	After 3 days	After 10 days
						#1	71 degree	44 degree	32 degree	7 degree	2 degree
#2	73 degrees	35 degree	16 degree	3 degree	2 degree
						#3	66 degree	55 degree	27 degree	9 degree	3 degree
#4	65 degree	53 degree	36 degree	18 degree	2 degree
						PET	70 degree	72 degree	74 degree	73 degrees	60 degree
PC	90 degree	86 degrees	88 degree	87 degree	89 degree

As is apparent from table 13, the sample surface was hydrophilized with continued UV irradiation and after 3 days, the surface was super-hydrophilized. As described above for example 14, it is considered that this is because the organic group bonded to the silicon atom in the silicon molecule in the siloxane layer containing titanium oxide is substituted with a hydroxyl group by the photocatalytic action due to photoexcitation.

As is known, 0.6mW/cm²The intensity of the UV light is approximately equal to the intensity of UV light contained in sunlight striking the earth's surface. It can thus be seen that super-hydrophilization can be achieved merely by exposing the titanium oxide-containing siloxane coating to sunlight.

Example 43

Weathering test of siloxanes containing photocatalysts

The sample #1 (aluminum substrate coated with siloxane) and the sample #2 (aluminum substrate coated with siloxane containing titanium oxide) were subjected to a weather resistance test using a weather resistance tester (manufactured by Suga Testmg Instruments, model "WEL-SUN-HC") while emitting light from a carbon arc lamp and spraying rainwater at 40 ℃ for 12 minutes/hour. The weather resistance was evaluated by gloss retention (the percentage of gloss after the test to the initial gloss). The results are shown in Table 14.

TABLE 14

Sample (I)	500 hours	1000 hours	3000 hours
				#1	91	95	90
#2	99	100	98

It is clear from Table 14 that the gloss is maintained almost the same regardless of the presence or absence of titanium oxide. This indicates that the siloxane bonds forming the backbone of the siloxane molecule are not interrupted by the photocatalytic action of the titanium oxide. Therefore, it is considered that the weather resistance of the siloxane is not affected even after the organic group bonded to the silicon atom in the siloxane is substituted with a hydroxyl group.

While the invention has been described with reference to specific embodiments, it will be understood that the invention is not limited thereto but is capable of numerous modifications and variations without departing from the scope of the invention. Further, the present invention can be applied to various purposes and fields other than the above. For example, a super hydrophilic surface may be used to prevent bubbles from adhering to the underwater surface. Additionally, the superhydrophilic surface can be used to form and maintain a uniform film of water. In addition, the super-hydrophilized photocatalytic coating can be used in the medical field such as contact lenses, artificial organs, catheters and anticoagulant materials, in view of its excellent affinity for living organs and tissues.

Claims (18)

1. Use of a composite comprising a substrate and a photocatalytic layer applied thereto, said photocatalytic layer comprising a material selected from ZnO, SnO and combinations thereof, for washing away deposits and/or pollutants adhering to the surface of the substrate in an atmospheric environment or for combating misting in an atmospheric environment by occasional contact with rain water₂、SrTiO₃、WO₃、Bi₂O₃、Fe₂O₃And crystalline TiO₂The photo-semiconductor material of (1), wherein the photocatalytic layer has a surface hydrophilized by photo-excitation of sunlight.

2. Use according to claim 1, wherein the hydrophilic surface has a water wettability with water having a contact angle with water lower than 20 degrees

3. Use according to claim 1, wherein the hydrophilic surface has a water wettability with water having a contact angle with water lower than 10 degrees.

4. The use of claim 1, wherein the hydrophilic surface has a water wettability with water having a contact angle of zero degrees with water.

5. Use according to claim 4, wherein the photocatalytic layer further comprises SiO₂Or a siloxane.

6. Use according to claim 5, wherein the photocatalytic layer consists of a mixture of titanium oxide and silicon oxide.

7. Use according to claim 6, wherein the ratio of silica to the total amount of titania and silica is from 5 to 90 mol%.

8. Use according to claim 7, wherein the ratio of silica to the total amount of titania and silica is in the range 10 to 70 mol%.

9. Use according to claim 8, wherein the ratio of silica to the total amount of titania and silica is 10 to 50 mole%.

10. Use according to any one of claims 1 to 9, wherein crystalline TiO₂Is titanium oxide of anatase type or rutile type.

11. Use according to claim 1 or 2, wherein the photocatalytic layer consists of crystalline TiO₂And (4) forming.

Use according to any one of claims 1 to 9, wherein the photocatalytic layer further has a protective coating which is susceptible to being hydrophilized.

13. Use according to any one of claims 1 to 9, wherein the photocatalytic layer may also incorporate Ag, Cu and Zn.

14. Use according to any one of claims 1 to 9, wherein the photocatalytic layer may further incorporate Pt, Pd, Rh, Ru, Os and Ir.

15. Use according to any one of claims 1 to 9, wherein the substrate is formed from a glass containing ions of a basic skeleton modifier and a film is applied to the surface of the substrate to prevent diffusion of said ions from the substrate into the layer.

16. Use according to claim 15, wherein the membrane is for preventing diffusion of the ions from the substrate into the photocatalytic layer comprising silica.

17. Use according to any one of claims 1 to 9, wherein the compound is a mirror, a glazing, a tile, an automotive housing or an exterior or interior wall of a building.

18. Use according to claims 1-9, wherein the thickness of the photocatalytic layer is not more than 0.2 micrometer.