JPH09241038A - Photocatalytic hydrophilic member and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain antifogging property, improved vision and easy cleaning property for a long time by forming a surface layer containing photocatalytic oxide particles having a specified grain size on the surface of a base body and exciting the layer with light to render the surface to be hydrophilic. SOLUTION: A surface layer containing photocatalytic oxide particles having 100 to 800nm average particle size (e.g. anatase-type titanium oxide) is formed on the surface of a substrate (e.g. glass and tile). A light source such as a fluorescent light and mercury lamp is used for excitation with light, and the illuminance of the exciting light is preferably >=0.01mW/cm<2> . As for hydrophilicity, it is preferable to obtain wettability of >10 deg. contact angle with water. The hydrophilic member is formed, for example, by preparing a co8ting liquid having dispersion of photocatalytic titanium oxide particles, applying the liquid by spray coating or the like on the substrate surface, calcining the layer at a temp. higher than the temp. that the layer can be changed into a photocatalytic oxide to fix the surface layer to the substrate. Metals such as Ag, Cu and Zn can be added to the surface layer to kill germs depositing on the surface.

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 surface of a member highly hydrophilic. More specifically, the present invention relates to an antifogging technique for preventing fogging and formation of water droplets on a member such as a mirror, a lens, a glass, a prism and the like by making the surface of the transparent 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. The term "anti-fog" as used in the present invention broadly means a technique for preventing the above optical damage. Needless to say, the above-mentioned "cloudiness" has a profound effect on safety and efficiency of various operations. For example,
The windshield and window glass of the vehicle, the rearview mirror of the vehicle,
In cold weather, or in the rain or when it becomes cloudy, it becomes difficult to secure visibility and traffic safety is impaired. Fogging of the endoscope lens and the dental dentoscope hinders accurate diagnosis, surgery, and treatment. If the cover glass of the instrument panel becomes cloudy, it will be 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. Soot and particles floating in the atmosphere accumulate on the roof and outer walls of buildings in fine weather. Sediment is washed away by rainwater as it rains and flows down the building's outer walls. Furthermore, in the rain, the floating dust is carried by the rain and flows down on the outer wall of the building or the surface of the outdoor building. As a result, pollutants adhere to the surface along the path of rainwater. When the surface dries, striped stains appear on the surface. Dirt on building exterior materials and coatings consists of combustion products such as carbon black, and inorganic pollutants such as urban dust and clay particles. It is thought that such a variety of contaminants complicates antifouling measures (Yoshinori Tachibana, "Method for Accelerated Testing of Contamination of Exterior Wall Finishing Materials", Proc. No., October 1989, p.
5-24).

According to the conventional wisdom, polytetrafluoroethylene (PT) is used to prevent stains on the building exterior and the like.
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 fogging of the member and formation of water droplets, and to prevent the surface of the building, window glass, machinery, and articles from becoming dirty. Although there is a proposal that can prevent the above, or can self-clean the surface (self-cleaning) or easily clean it, its effect is not sufficient because the surface cannot be kept highly hydrophilic for a long period of time. In view of the above circumstances, an object of the present invention is to provide a member capable of maintaining a surface with a high degree of hydrophilicity for a long period of time.

[0007]

[Means and Actions for Solving the Problems] In the present invention,
A surface layer containing photocatalytic titanium oxide particles having an average crystallite size of less than 800 nm, more preferably an average crystallite size of 300 nm or less is formed on the surface of the base material, and the surface is formed in response to photoexcitation of the photocatalytic titanium oxide. Provided is a photocatalytic hydrophilic member, wherein the layer exhibits hydrophilicity. By doing so, when the photocatalytic titanium oxide particles are photoexcited, the surface of the member becomes hydrophilic. This phenomenon is considered to proceed by the following mechanism. That is, when light having energy equal to or more than the energy gap between the upper end of the valence band of the photocatalyst and the lower end of the conduction electron band is irradiated on the photocatalytic oxide, the electrons in the valence band of the photocatalyst are excited to become conductive electrons and positive electrons. Pores are created, and either or both actions may possibly impart polarity to the surface, collecting polar components such as water and hydroxyl groups. Then, one or both of the conduction electrons and holes and the above-mentioned polar components cooperate to cut the chemical bond between the adsorption surface and the contaminant chemically adsorbed on the surface, and the chemically adsorbed water on the surface. It adsorbs and a physisorbed water layer is formed on it.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The term "hydrophilic" as used in the present invention means a state of exhibiting water wettability of 30 ° or less, preferably 10 ° or less in terms of contact angle with water. If the surface of the member is in a state of 30 ° or less, more preferably 10 ° or less in terms of contact angle with water, the condensed water forms individual water droplets even if moisture or steam in the air is condensed. The tendency of becoming a uniform water film without it 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. Further, when the surface of the member is in a state where the contact angle with water is 30 ° or less, combustion products such as urban dust, carbon black contained in exhaust gas of automobiles, oils and fats, sealant elution components, etc. Hydrophobic contaminants are difficult to attach, and even if they are attached, they can be easily removed by rainfall or washing with water.

If the surface of the member can maintain the above-mentioned high hydrophilicity, in addition to the antifogging effect and the surface cleaning effect, an antistatic effect (dust adhesion preventing effect), a heat insulating effect, a bubble adhesion preventing effect in water, and heat exchange. The efficiency improvement effect and biocompatibility effect in the container can be exhibited.

The substrate to which the present invention can be applied is a transparent member when the above antifogging effect is expected, and its material is preferably glass, plastic or the like. 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.

The photocatalytic oxide is a valence electron when it is irradiated with light (excitation light) having an energy (that is, a short wavelength) larger than the energy gap between the conduction electron band and the valence band of the oxide crystal. An oxide that can generate conduction electrons and holes by excitation of electrons in the band (photoexcitation). Anatase type titanium oxide, rutile type titanium oxide, tin oxide, zinc oxide, dibismuth trioxide, tungsten trioxide, Ferric oxide, strontium titanate and the like can be preferably 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 is preferably 200 nm or less, especially when the substrate is transparent. Then, it is possible to prevent the surface layer from being colored by light interference. Also, the thinner the surface layer, the more transparent the member can be. Further, when the film thickness is reduced, the wear resistance of the surface layer is improved. The surface of the surface layer may be further provided with a wear-resistant or corrosion-resistant protective layer capable of being made hydrophilic and other functional films. Preferably, the surface layer does not have a very high refractive index as compared to the substrate. Preferably, the refractive index of the surface layer is 2 or less. Then, light reflection at the interface between the base material and the surface layer can be suppressed. When the substrate is a glass or glazed tile containing an alkali network modifying ion such as sodium, an intermediate layer such as silica may be formed between the substrate and the surface layer. Then, the diffusion of the alkali network modifying ions from the base material to the surface layer during the firing is prevented, and the photocatalytic function is more effectively exhibited. Metals such as Ag, Cu, and Zn can be added to the surface layer. The metal-added surface layer can kill bacteria attached to the surface. Furthermore, this surface layer is
Inhibits the growth of microorganisms such as mold, algae and moss. Therefore,
Contamination of the surface of the member due to microorganisms can be suppressed more effectively. Pt, Pd, Rh, and R are used for the surface layer.
A platinum group metal such as u, Os, Ir can be added. The surface layer to which the metal is added can enhance the oxidizing activity of the photocatalyst, and promote the decomposition of contaminants attached to the member surface.

The hydrophilic member can be formed by, for example, preparing a coating liquid in which photocatalytic titanium oxide particles are dispersed, and spraying, flow coating, spin coating, dip coating, the coating liquid on the surface of the substrate.
After coating by a method such as roll coating, the surface layer is fixed to the substrate by a method such as firing.

Other methods for forming hydrophilic members include tetraalkoxytitanium such as tetraethoxytitanium, tetramethoxytitanium, tetrapropoxytitanium and tetrabutoxytitanium; titanium chelate, titanium acetate; titanium sulfate, titanium tetrachloride and the like. Soluble titanium compound of titanium; titanium hydroxide; crystalline titanium oxide precursor such as amorphous titanium oxide, spray coating, flow coating, spin coating,
After coating by a method such as dip coating, roll coating, electron beam evaporation, etc., and drying, the temperature at which the above-mentioned precursor of photocatalytic titanium oxide is changed to a photocatalytic oxide (crystallization temperature of anatase type titanium oxide) or higher. And the surface layer is fixed to the base material.

[0015]

【Example】

Example 1. Ammonia deflocculation type anatase type titanium oxide sol (A-made by Taki Chemical Co., Ltd.
6, solute concentration 6% by weight, average crystallite diameter 8 nm) was applied by a spray coating method, and baked at 110 to 900 ° C. to obtain a sample. The film thickness at this time was set to 0.24 μm. The hydrophilicity of the sample immediately after firing was below 20 ° at any temperature as shown in FIG. The obtained sample was left in a dark place for 1 week, and then irradiated with a Sankyo Denki black light blue (BLB) lamp at an ultraviolet illuminance of 0.3 mW / cm ² , and the change in the contact angle with water with respect to the irradiation time was measured. . The contact angle with water was measured by a contact angle measuring device (Kyowa Interface Science, CA-X150), and the value was obtained 30 seconds after dropping a water droplet from a microsyringe. Here, for comparison, UV illuminance is 0.
A BLB lamp of 3 mW / cm ² was irradiated and the change in the contact angle with water with respect to the irradiation time was measured.

As a result, as shown in FIG. 2, no change was observed in the normal glazed tile, whereas in the practical sample, the sample fired at 110 to 800 ° C. was exposed to the BLB lamp for 1 hour or more. The hydrophilicity was restored up to less than 20 °. Further, the sample fired at 900 ° C. also showed a tendency that the hydrophilicity was slightly recovered as compared with the glazed tile.

Table 1 shows the average crystallite diameter of the anatase type titanium oxide (A-6) in the sample fired at 110 to 900 ° C. Here, the average crystallite size was calculated by determining the integral width of the strongest peak of anatase type titanium oxide by the powder X-ray diffraction method and substituting the value into the Scherrer equation. As a result, at 900 ° C, the average crystallite size is 800 nm.
It has grown to a certain degree, and this is thought to have weakened the hydrophilicity recovery ability. Therefore, it can be said that the average crystallite size of titanium oxide constituting the member after firing is preferably less than 800 nm.

[0018]

[Table 1]

Example 2. Ammonia deflocculating anatase type titanium oxide sol (STS-11 made by Ishihara Sangyo, solute concentration 35% by weight, average crystallite diameter 17 nm, specific surface area 60 m ² / g) was applied to the surface of a glazed tile of 2.15 cm square. )) Was applied by a spray coating method and baked at 110 to 1000 ° C. to obtain a sample. The film thickness at this time was 0.80 μm. The hydrophilicity of the sample immediately after firing was lower than 30 ° at any temperature as shown in FIG. After leaving the obtained sample in the dark for 1 week, the UV illuminance was 0.3 mW / cm
The BLB lamp of No. ² was irradiated and the change of the contact angle with water with respect to the irradiation time was measured.

As a result, as shown in FIG.
Regarding the sample baked at 00 ° C., the hydrophilicity was restored to less than 15 ° by irradiation with the BLB lamp for 1 hour or more. Table 1 shows the average crystallite diameter of titanium oxide (STS-11) in the sample fired at 110 to 900 ° C. as a result,
It was found that at 900 ° C., good hydrophilicity recovery was exhibited even though the average crystallite size grew to about 300 nm. Therefore, it can be said that if the average crystallite diameter of titanium oxide constituting the member after firing is at least 300 nm or less, good hydrophilicity recoverability is exhibited.

Next, for the sample fired at 800 ° C.,
Apply salad oil to the surface, immerse the sample in water filled with water while holding the sample surface in a horizontal position, and rub it lightly with your finger.The salad oil curls into oil droplets and is released from the sample surface. Surfaced.

Example 3 The titanium oxide sol used in Example 1 was applied to the surface of a 15 cm square glazed tile to form 110
A sample was obtained by firing at ~ 900 ° C. The film thickness at this time is 0.
It was set to 80 μm. The hydrophilicity of the sample immediately after firing was below 20 ° at any temperature as shown in FIG.
The obtained sample was allowed to stand in the dark for 1 week, then irradiated with a BLB lamp having an ultraviolet illuminance of 0.3 mW / cm ² , and the change in the contact angle with water with respect to the irradiation time was measured. For comparison, a normal glazed tile was similarly irradiated with a BLB lamp having an ultraviolet illuminance of 0.3 mW / cm ² and the change in the contact angle with water with respect to the irradiation time was measured.

As a result, as shown in FIG. 4, no change was observed in the normal glazed tile, whereas in the practical sample, the sample fired at 110 to 800 ° C. was exposed to the BLB lamp for 1 hour or more. The hydrophilicity was restored up to less than 20 °. In addition, 3 for samples fired at 900 ° C
The hydrophilicity was restored up to about 0 °.

Example 4. A nitric acid-peptized titanium oxide sol (TA-1 manufactured by Nissan Kagaku Co., Ltd.) was formed on the surface of a 15 cm square glazed tile.
5, solute concentration 10% by weight, average crystallite diameter 12 nm) was applied by a spray coating method and baked at 110 to 800 ° C. to obtain a sample. The film thickness at this time was set to 0.12 μm. The hydrophilicity of the sample immediately after firing was below 30 ° at any temperature as shown in FIG. After leaving the obtained sample in the dark for 1 week, the UV illuminance was 0.3 mW / c
irradiating the m ² of BLB lamp was measured change in contact angle with water for the irradiation time.

As a result, as shown in FIG.
With respect to the sample baked at 00 ° C., the hydrophilicity was restored to less than 15 ° by irradiation with the BLB lamp for 1 hour or more. In addition, by comparing Examples 1, 2, and 4, the following two things were revealed. (1) At least at a film thickness of 0.12 to 0.80 μm, hydrophilicity is restored by irradiation of ultraviolet rays regardless of the film thickness. (2) Whether the alkali peptization type titanium oxide sol or the acidic peptization type titanium oxide sol is used, the hydrophilicity is restored by the irradiation of ultraviolet rays.

Example 5 Ammonia deflocculating titanium oxide sol (Taki Kagaku A
-6, solute concentration 6% by weight, average crystallite size 8 nm) was applied by a spray coating method and baked at 800 ° C. for 1 hour to obtain a sample. The film thickness at this time was set to 0.3 μm. The contact angle with water of the sample immediately after firing was 15 °. The obtained sample was left in a dark place for 1 week, then irradiated with a BLB lamp having an ultraviolet illuminance of 0.03 mW / cm ² , and the change in the contact angle with water with respect to the irradiation time was measured. As a result, as shown in FIG. 9, even with such a weak UV illuminance, the hydrophilicity was restored to about 19 ° by irradiation with the BLB lamp for about one day.

Example 6 Ammonia deflocculating type anatase type titanium oxide sol (STS-11 made by Ishihara Sangyo, solute concentration 35% by weight, average crystallite diameter 17 nm, specific surface area 60 m2 / g)) was applied by a spray-coating method and baked at 800 ° C. to obtain a sample. The film thickness at this time was set to 0.12 μm. The contact angle of the sample immediately after firing with water was 8 °. After leaving the obtained sample in the dark for 1 week, the ultraviolet illuminance was 0.
A BLB lamp of 3 mW / cm ² was irradiated and the change in the contact angle with water with respect to the irradiation time was measured. The hydrophilicity was restored up to 10 ° by irradiation with the BLB lamp for 1 hour. Further, when the sample of this example was breathed, no clouding occurred.

[0028]

According to the present invention, the surface of the member becomes hydrophilic each time the light for exciting the photocatalyst is irradiated, so that the antifogging property, the visibility improving property, and the easy cleaning property by washing with water or rain. Etc. will be exhibited for a long time.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the contact angle of water on the surface of a sample immediately after firing and the firing temperature according to an example of the present invention.

FIG. 2 is a diagram showing a relationship between a contact angle of water on a sample surface and ultraviolet irradiation time according to an example of the present invention.

FIG. 3 is a diagram showing the relationship between the contact angle of water on the surface of a sample immediately after firing and the firing temperature according to the example of the present invention.

FIG. 4 is a diagram showing a relationship between a contact angle of a sample surface with water and an ultraviolet irradiation time according to an example of the present invention.

FIG. 5 is a graph showing the relationship between the contact angle of water on the surface of a sample immediately after firing and the firing temperature according to the example of the present invention.

FIG. 6 is a diagram showing a relationship between a contact angle of water on a sample surface and ultraviolet irradiation time according to an example of the present invention.

FIG. 7 is a diagram showing the relationship between the contact angle of water on the surface of a sample immediately after firing and the firing temperature according to the example of the present invention.

FIG. 8 is a diagram showing the relationship between the contact angle of water on the surface of a sample and the ultraviolet irradiation time according to the example of the present invention.

FIG. 9 is a diagram showing the relationship between the contact angle of water on the surface of a sample and the ultraviolet irradiation time according to the example of the present invention.

Claims (8)

[Claims] 1. A surface layer containing photocatalytic oxide particles having an average crystallite size of less than 800 nm is formed on the surface of a substrate, and the surface layer is rendered hydrophilic in response to photoexcitation of the photocatalytic oxide. A photocatalytic hydrophilic member characterized by exhibiting. 2. A surface layer containing photocatalytic oxide particles having an average crystallite size of 300 nm or less is formed on the surface of a substrate, and the surface layer is rendered hydrophilic in response to photoexcitation of the photocatalytic oxide. A photocatalytic hydrophilic member characterized by exhibiting. 3. The surface layer has a thickness of 100 to 800 nm.
The photocatalytic hydrophilic member according to claim 1, wherein 4. The specific surface area of the photocatalytic oxide particles is 3
It is 0 m < ² > / g or more, The photocatalytic hydrophilic member of Claim 1 or 2 characterized by the above-mentioned. 5. The photocatalytic hydrophilic member according to claim 1, wherein the base material is a heat resistant material. 6. The photocatalytic hydrophilic member according to claim 5, wherein the base material is a tile. 7. The photocatalytic hydrophilic member according to claim 5, wherein the base material is glass. 8. The method according to claim 1, further comprising a step of coating the surface of the base material with titanium oxide sol and a step of firing at a temperature of 900 ° C. or lower.
7. The method for producing a photocatalytic hydrophilic member according to any one of 6 to 6.