JPH1095635A - Formation of photocatalytic hydrophobic member and photocatalytic hydrophobic member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a photocatalytic hydrophobic member capable of stably manifesting the effect maintaining highly hydrophobic properties for a long period in a dark place. SOLUTION: This method for forming a photocatalytic hydrophobic member comprises a step of coating an organic titanate on the surface of a substrate, a step of performing the hydration and the hydrating condensation of the coated titanate, further a step of removing the remaining organic group from the substrate after performing the hydration and hydrating condensation, a step of coating an aqueous solution containing tungstic acid on the surface of the substrate after removing the organic group, and a step of firing the coated substrate at >=400 deg.C to provide the objective crystalline titanium oxide and TiO2 /WO3 complex oxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

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

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

[0004] On the other hand, in the fields of construction and paints, stains on building exterior materials, outdoor buildings and their coatings have become a problem with environmental pollution. Dust and particles suspended in the air accumulate on the roof and outer walls of buildings in fine weather. Sediment is washed away by rainwater as it rains and flows down the building's outer walls. Furthermore, in the rain, the floating dust is carried by the rain and flows down on the outer wall of the building or the surface of the outdoor building. As a result, pollutants adhere to the surface along the path of rainwater. When the surface dries, striped stains appear on the surface. Dirt on building exterior materials and coatings consists of combustion products such as carbon black, and inorganic pollutants such as urban dust and clay particles. It is thought that such a variety of contaminants complicates antifouling measures (Yoshinori Tachibana, "Testing Method for Acceleration of Contamination of Exterior Wall Finishing Material", Architectural Institute of Japan, Structural Transactions, No. 404) No., October 1989, p.
5-24).

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

[0006]

As described above, by making the surface of the member hydrophilic, it is possible to prevent clouding and water droplet formation of the member, and to prevent the surfaces of buildings, window glasses, mechanical devices and articles from becoming dirty. Although there are proposals to prevent or to self-clean (self-clean) or easily clean the surface, the effect was not satisfactory because the surface could not be maintained at a high degree of hydrophilicity for a long time. In view of the above circumstances, an object of the present invention is to provide a method for forming a member capable of maintaining a surface with a high degree of hydrophilicity for a long time.

[0007]

Means for Solving the Problems and Action The present inventor has provided:
Photocatalytic (crystalline) titanium oxide and oxide superacid T
A surface layer made of iO ₂ / WO ₃ composite oxide is formed, or a photocatalytic (crystalline) titanium oxide-containing layer is formed, and TiO ₂ / W which is an oxide superacid is further formed thereon.
It has been found that a hydrophilic member having a surface layer made of an O ₃ composite oxide can maintain its surface at a high degree of hydrophilicity over a long period of time. In other words, if the surface layer contains an oxide superacid, the polarity of the surface is extremely large irrespective of the presence or absence of light, so water molecules, which are polar molecules, are more selectively adsorbed than hydrophobic molecules. Easy to make. Therefore, a stable physical adsorption water layer is easily formed, and even if it is kept in a dark place,
Surface hydrophilicity can be maintained at a high level for a fairly long time.
The TiO ₂ / WO ₃ composite oxide has an extremely large acidity among the oxide super-strong acids, and Ho = −13 according to Hammett's acidity function.
Since it is about -14, the above characteristics are very excellent. further,
By containing a photocatalytic oxide in the surface layer,
Even when the hydrophilicity of the surface has been lost due to long-term storage in a dark place or the like, the photocatalytic oxide exhibits superhydrophilicity in response to photoexcitation of the photocatalytic oxide. This phenomenon is considered to proceed by the following mechanism. That is, when light is applied to the photocatalytic oxide, the electrons in the valence band of the photocatalytic oxide are excited to generate conduction electrons and holes, and either or both of them may possibly cause the surface to be exposed to the surface. Polarity is given,
Polar components such as water and hydroxyl groups are collected. Then, the coordinated action of either or both of the conduction electrons and holes and the above-mentioned polar components cuts the chemical bond between the adsorption surface and the contaminant chemically adsorbed on the surface, and the chemically adsorbed water on the surface. It is a mechanism that adsorbs and further forms a physically adsorbed water layer thereon. Therefore, by making the surface layer contain both the oxide superacid and the photocatalytic oxide, it becomes possible to maintain a high degree of hydrophilicity over a long period of time in a dark place, and the hydrophilicity is lost. Can recover a high hydrophilic state by photoexcitation of the photocatalytic oxide.

According to the present invention, there is provided a method for forming the above-mentioned hydrophilic member, comprising the steps of applying an organic titanate to the surface of a base material, hydrolyzing the organic titanate and subjecting the organic titanate to dehydration polycondensation. Performing a step of removing a group, followed by a step of applying an aqueous solution of a tungstic acid-containing acid and a step of generating crystalline titanium oxide and a TiO ₂ / WO ₃ composite oxide by firing at 400 ° C. or higher. The present invention provides a method for forming a photocatalytic hydrophilic member. According to this method, the firing can be performed only once, so that the productivity is improved. Further, by performing the step of removing the residual organic group, since tungstate is wetted uniformly on the substrate surface, TiO the surface ₂
/ WO ₃ composite oxide is uniformly formed. Thereby, the effect of maintaining a high degree of hydrophilicity in a dark place for a long time can be stably exhibited.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view of a main part of a production process of a photocatalytic hydrophilic member according to the present invention, in which an organic titanate is a titanium alkoxide. FIG. 2 shows, for comparison, a manufacturing process in which the step of removing residual organic groups from the main part of the manufacturing process of the photocatalytic hydrophilic member according to the present invention (corona discharge treatment in FIG. 1) is omitted. FIG. In FIG.
(A) is a diagram when a titanium alkoxide is first applied to a substrate surface and dried. In this step, the titanium alkoxide Ti (OR) 4 (R is an alkyl group) is partially hydrolyzed to form amorphous Ti (OH) x (OR) y
(X + y = 4), and the portion subjected to dehydration polycondensation becomes TiOx (OR) y. That is, at this stage, the alkyl group partially remains on the surface. Next, FIG.
As shown in (b), when the aqueous solution containing tungstic acid is applied, the residual portion of the alkyl group and the aqueous solution containing the tungstic acid and the residual portion of the alkyl group are not well adapted to each other. Produces a flipped part. Next, the member shown in FIG.
When heat treatment is performed at the above temperature, amorphous TiOx (OR)
As y is dealkylated and crystallized into anatase-type titanium oxide, TiO ₂ / WO ₃ composite oxide is formed on the surface. However, at this time, the surface structure of the member is such that the TiO ₂ / WO ₃ composite oxide is not uniformly formed as shown in FIG. As a result, the effect of maintaining a high degree of hydrophilicity for a long time in a dark place becomes unstable. In contrast, in the process of FIG.
As shown in FIG. 1 (b), in order to perform dealkylation by corona discharge treatment, tungstic acid uniformly wets when an aqueous solution containing tungstic acid is applied (FIG. 1).
(C)). Therefore, when heat treatment is performed at a temperature of 400 ° C. or higher, the TiO ₂ / WO ₃ composite oxide is uniformly formed on the surface, and the effect of maintaining a high degree of hydrophilicity in a dark place for a long time is stably exhibited. It becomes like that.

As the organic titanate in the present invention, tetraalkoxytitanium such as tetraethoxytitanium, tetramethoxytitanium, tetrapropoxytitanium and tetrabutoxytitanium; titanium chelate, titanium acetate and the like can be suitably used.

The step of applying the organic titanate is performed by applying the above-mentioned organic titanate by a method such as spray coating, flow coating, spin coating, dip coating, and roll coating.
The step of hydrolyzing and dehydrating and condensing the organic titanate is performed by drying at room temperature or at a temperature of about 200 ° C. or less.

As a process for removing residual organic groups, there are methods such as corona discharge treatment, plasma discharge treatment, and heat treatment. Among them, corona discharge treatment and plasma discharge treatment are preferred because chemically adsorbed water tends to remain. preferable.

The step of applying the aqueous solution containing tungstic acid is performed by applying the aqueous solution containing tungstic acid by a method such as spray coating, flow coating, spin coating, dip coating, and roll coating. Here, the aqueous solution containing tungstic acid is an aqueous solution in which tungstic acid is dissolved, and a basic solution such as ammonia is generally used.

In FIG. 1 (d), it is preferable that the thickness of the lower photocatalytic oxide layer is 10 nm or more, in particular, because the photocatalyst has excellent hydrophilicity by photoexcitation of light.

The term “highly hydrophilic” in the present invention means a state of exhibiting water wettability of 10 ° or less, preferably 5 ° or less in terms of a contact angle with water. PCT / JP96 / 007
As shown in No. 33, if the surface of the member is less than 10 ° in terms of the contact angle with water, condensed water forms individual water droplets even if moisture or steam in the air is dewed. Without this, the tendency to form a uniform water film becomes remarkable. Therefore, the tendency that light scattering fogging does not occur on the surface becomes remarkable. Similarly, when windowpanes, vehicle rearview mirrors, vehicle windshields, spectacle lenses, or helmet shields are exposed to rain or splashes, a high degree of visibility and visibility is achieved without discrete and unsightly water droplets. As a result, the effects of ensuring the safety of vehicles and traffic, and improving the efficiency of various tasks and activities are dramatically improved. Also, as shown in PCT / JP96 / 00733, if the surface of the member is in a state of 10 ° or less, preferably 5 ° or less in terms of a contact angle with water, urban dust,
Combustion products such as carbon black contained in exhaust gas from automobiles, hydrophobic contaminants such as oils and fats, and sealant eluting components, and inorganic clay contaminants are unlikely to adhere to each other. Can be dropped.

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

The substrate to which the present invention can be applied is a transparent member when the above anti-fogging effect is expected, and glass, plastic, and the like can be suitably used as the material. Speaking of applicable base materials, mirrors such as rearview mirrors for vehicles, mirrors for bathrooms, mirrors for toilets, dental mirrors, road mirrors; spectacle lenses, optical lenses, camera lenses, endoscope lenses, Lenses such as illumination lenses, semiconductor lenses, and copier lenses; prisms; windows of buildings and towers; automobiles, rail vehicles, aircraft, ships, submersibles, snowmobiles, ropeway gondolas, and amusement park gondolas. , Windowpanes for vehicles such as spacecraft; cars, railcars, aircraft, ships, submarines,
Windshields for vehicles such as snowmobiles, snowmobiles, motorcycles, ropeway gondola, amusement park gondola, spaceships; protective goggles, sports goggles, shields for protective masks, shields for sports masks, shields for helmets , A frozen food display case; a cover glass of a measuring instrument; and a film to be attached to the surface of the article. As a substrate to which the present invention can be applied, when the above surface cleaning effect is expected, the material is, for example, metal, ceramics, glass, plastic, wood, stone, cement, concrete, fiber, cloth, and the like. Combinations and their laminates can be suitably used. Speaking of applicable base materials, building materials, building exteriors, building interiors, window frames, window glasses, structural members, vehicle exteriors and coatings,
Exterior of machinery and equipment, dust cover and paint, traffic signs, various display devices, advertising towers, road noise barriers, railway noise barriers, bridges, guard rail exterior and paint, tunnel interior and paint, insulators, solar cell covers , Solar water heater heat collecting cover, greenhouse, vehicle lighting cover, housing equipment, toilet bowl, bathtub, wash basin, lighting equipment, lighting cover, kitchenware, tableware, dishwasher, dish dryer, sink, cooking It includes a range, a kitchen hood, a ventilation fan, and a film to be attached to the surface of the article. As a substrate to which the present invention can be applied, when the above antistatic effect is expected, the material is, for example, metal, ceramics, glass, plastic, wood, stone, cement, concrete, fiber, cloth,
Combinations thereof and laminates thereof can be suitably used.
Speaking of applicable base materials, cathode ray tubes, magnetic recording media, optical recording media, magneto-optical recording media, audio tapes, video tapes, analog records, housing and parts for household electrical appliances, exterior and coating, OA equipment Product housing, parts, exterior and painting, building materials, building exterior, building interior, window frames, window glass, structural members, vehicle exterior and painting, machinery and articles exterior, dustproof cover and painting, and on the above article surface Includes film to be applied.

A photocatalytic oxide is a material which emits light (excitation light) having an energy (ie, shorter wavelength) larger than the energy gap between the conduction electron band and the valence band of an oxide crystal. An oxide that can generate conduction electrons and holes by the excitation of electrons (photoexcitation) in the band. Anatase-type titanium oxide, rutile-type titanium oxide, tin oxide, zinc oxide, bismuth trioxide, tungsten trioxide, Ferric oxide, strontium titanate and the like can be suitably used. Here, as a light source used for photoexcitation of the photocatalytic oxide, indoor lighting such as a fluorescent lamp, an incandescent lamp, a metal halide lamp, and a mercury lamp, the sun, and a light source in which light from those light sources is guided by a low-loss fiber are used. It can be suitably used. In order for the substrate surface to be highly hydrophilized by photoexcitation of the photocatalytic oxide, the illuminance of the excitation light is 0.001 m
W suffices / cm ² or more, but preferably that it 0.01 mW / cm ² or more, and more preferably it 0.1 mW / cm ² or more.

The thickness of the surface layer comprising the photocatalytic oxide and the oxide superacid is preferably 0.2 μm or less. Then, it is possible to prevent the surface layer from being colored by light interference. Also, the thinner the surface layer, the more transparent the member can be. Further, when the film thickness is reduced, the wear resistance of the surface layer is improved. On the surface of the surface layer composed of the photocatalytic oxide and the oxide superacid, a protective layer or other functional film which can be made hydrophilic and which is resistant to wear or corrosion may be further provided.

The surface layer comprising the photocatalytic oxide and the oxide superacid preferably has a refractive index not so high as compared with the substrate. Preferably, the refractive index of the surface layer is 2 or less. Then, light reflection at the interface between the base material and the surface layer can be suppressed. In order to reduce the refractive index of the surface layer to 2 or less, a substance having a refractive index of 2 or less is used for the mixture of the photocatalytic oxide and the oxide superacid, or the mixture of the photocatalytic oxide and the oxide superacid is refracted. A low refractive index substance having a refractive index of 2 or less is added.

When the substrate is a glass or a glazed tile containing an alkali network modifying ion such as sodium, an intermediate layer such as silica may be formed between the substrate and the surface layer. Then, the diffusion of the alkali network modifying ions from the base material to the surface layer during the firing is prevented, and the photocatalytic function is more effectively exhibited.

Metals such as Ag, Cu and Zn can be added to the surface layer. The surface layer to which the metal is added can kill bacteria adhering to the surface.
Furthermore, this surface layer inhibits the growth of microorganisms such as molds, algae and moss. Therefore, adhesion of dirt on the member surface due to microorganisms can be more effectively suppressed. The surface layer has P
Platinum group metals such as t, Pd, Rh, Ru, Os, Ir can be added. The surface layer to which the metal is added can enhance the oxidizing activity of the photocatalyst, and promote the decomposition of contaminants attached to the member surface. In addition, since the acidity of the oxide superacid is improved by the addition of the platinum group metal, hydrophilicity retention is also improved.

[0023]

EXAMPLE A 10 cm square soda lime glass plate was immersed in a 3.5% by weight tetraethoxysilane solution (diluent: ethanol, hydrolysis inhibitor: hydrochloric acid), and then immersed in a 24 cm / h solution.
The solution was pulled up at a speed of cm, and the solution was applied to the surface of a glass plate by a dip coating method and dried. Through the steps so far, tetraethoxysilane was hydrolyzed to generate silanol groups, and then the silanol groups were subjected to dehydration polycondensation to form a thin film containing amorphous silica as a main component on the surface. Next, after being immersed in a 3.5% by weight tetraethoxytitanium solution (diluent, hydrolysis inhibitor: hydrochloric acid), the solution is pulled up at a speed of 24 cm per minute, and the solution is applied to the surface of a glass plate by dip coating. And dried to obtain a # 1 sample. By the above steps, tetraethoxytitanium undergoes hydrolysis to form a hydroxyl group,
Subsequently, the hydroxyl group was subjected to dehydration-condensation polymerization, and a thin film containing amorphous titania as a main component and partially remaining an alkyl group was formed on the surface. Next, using a wire electrode as an electrode, the gap between the tip of the electrode and the sample surface was 2 mm, the voltage was 26
Dealkylation treatment was performed by high-frequency corona discharge treatment under the conditions of kV, a frequency of 39 kHz, and a sample feeding speed of 4.2 m / min. Next, the sample was immersed in a 1% by weight tungstic acid solution (solvent: aqueous ammonia), and then immersed at 24 cm / min
, And the solution was applied to the surface by dip coating and baked at 500 ° C. to obtain a # 2 sample. By the firing, amorphous titania was crystallized to produce anatase-type titanium oxide. Oleic acid was applied to the surface of the # 2 sample immediately after firing, rubbed with a neutral detergent, rinsed with tap water and distilled water, and then dried at 50 ° C. for 30 minutes using a drier to intentionally contaminate the surface. After that, the illuminance is set to 0.
3mW / cm ² UV light source for one day (Sankyo Electric,
Irradiation was performed using a black light blue (BLB) fluorescent lamp). As a result, the contact angle with water showed 0 °. Here, the contact angle with water is measured using a contact angle measuring device (Kyowa Interface Science, CA-X).
150), the measurement was performed 30 seconds after a water drop was dropped on the sample surface from the microsyringe. Next, the sample was left in a dark place for 2 days, and the contact angle of the sample surface with water was measured. as a result,
The contact angle with water was maintained at about 9 °, and stable hydrophilicity was maintained even in a dark place.

[0024]

According to the present invention, in the method for forming a photocatalytic hydrophilic member, a step of applying an organic titanate to a substrate surface, a step of hydrolyzing the organic titanate, and a step of subjecting the organic titanate to dehydration-condensation polymerization are performed. And then applying a tungstic acid-containing aqueous solution;
By firing at 00 ° C. or more, a step of generating crystalline titanium oxide and a TiO ₂ / WO ₃ composite oxide is performed. Here, by performing the step of removing the residual organic groups, the tungstic acid uniformly wets the surface of the substrate, so that the TiO ₂ / WO ₃ composite oxide is uniformly formed on the surface. Thereby, the effect of maintaining a high degree of hydrophilicity in a dark place for a long time can be stably exhibited.

[Brief description of the drawings]

FIG. 1 is a schematic view illustrating a method for forming a photocatalytic hydrophilic member according to the present invention.

FIG. 2 is a schematic view illustrating another method for forming a photocatalytic hydrophilic member.

Claims (3)

[Claims] 1. A step of applying an organic titanate to a surface of a substrate, a step of hydrolyzing the organic titanate and a step of dehydration-condensation polymerization, and then a step of removing residual organic groups. Applying step, 4
A method for forming a photocatalytic hydrophilic member, comprising performing a step of generating crystalline titanium oxide and a TiO ₂ / WO ₃ composite oxide by firing at 00 ° C. or higher. 2. The method for forming a photocatalytic hydrophilic member according to claim 1, wherein the step of removing the residual organic groups is a corona discharge treatment or a plasma discharge treatment. 3. A photocatalytic hydrophilic member produced by the method according to claim 1.