Photocatalytic hydrophilic member

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a technique for maintaining and maintaining a high degree of hydrophilicity on the surface of a member. More specifically, the present invention relates to an antifogging technique for preventing fogging and water droplet formation of a member by making the surface of a mirror, a lens, glass, a prism and other transparent members highly hydrophilic. The present invention also provides a technique for preventing the surface from becoming dirty by making the surface of a building, window glass, mechanical device or article highly hydrophilic, or for self-cleaning or easily cleaning the surface. Regarding.

【0002】

[Conventional technology]

It is often experienced that the windshields and windows of automobiles and other vehicles, the windows of buildings, the lenses of eyeglasses, and the cover glass of various instrument panels become cloudy with condensed moisture in cold weather. In addition, it is often encountered that the lenses of mirrors and eyeglasses in bathrooms and washrooms become cloudy due to steam. In addition, vehicle windshields and windows, building windows, vehicle rearview mirrors, eyeglass lenses, masks and helmet shields are exposed to rainfall and splashes, and a large number of scattered water droplets adhere to their surfaces. Is dull, blurry, mottled, or cloudy, and also loses visibility. Needless to say, the above-mentioned "cloudiness" has a profound effect on safety and efficiency of various operations. For example, if the windshield or window glass of a vehicle or the rear-view mirror of a vehicle is covered or clouded in cold weather or rainy weather, it becomes difficult to secure visibility and traffic safety is impaired. Fogging of endoscopic lenses and dental dentistry interferes with accurate diagnosis, surgery, and treatment. If the cover glass of the instrument panel becomes cloudy, it will be difficult to read the data.

【0003】

It has been proposed to make the surface hydrophilic in order to eliminate the above-mentioned "cloudiness". For example, in Jinkaihei 3-129357, a polymer layer is provided on the surface of the base material, and this layer is irradiated with ultraviolet rays and then treated with an alkaline aqueous solution to generate high-density acidic groups, thereby forming a polymer layer. A method for preventing fogging of a mirror, which comprises making the surface hydrophilic, is disclosed. However, it is considered that the acidic groups obtained by this method do not have sufficient surface polarity, and the surface loses hydrophilicity over time due to contaminants adhering to the surface, and the antifogging performance is gradually lost.

【0004】

On the other hand, in the field of construction and paint, pollution of building exterior materials, outdoor buildings and their coating films has become a problem due to environmental pollution. Dust 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 outer wall of the building. Furthermore, in rainy weather, floating dust is carried by the rain and flows down the outer walls of buildings and the surface of outdoor buildings. As a result, contaminants adhere to the surface along the rainwater path. 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 pollutants of inorganic substances such as urban dust and clay particles. It is believed that such diversity of pollutants complicates antifouling measures (Yoshinori Tachibana, "Test Method for Accelerating Contamination of Exterior Wall Finishing Materials," Architectural Institute of Japan, Structural Papers, No. 404. Issue, October 1989, p.15-24).

【0005】

Conventional wisdom has been that water-repellent paints such as polytetrafluoroethylene (PTFE) are preferable to prevent stains on the exterior of buildings, but these days, cities that contain a large amount of hydrophobic components. For soot and dust, it is considered desirable to make the surface of the coating film as hydrophilic as possible (Polymer, Vol. 44, May 1995, p. 307). Therefore, it has been proposed to paint buildings with hydrophilic graft polymers (Newspaper "The Chemical Daily", January 30, 1995). According to reports, this coating film exhibits hydrophilicity of 30 to 40 ° in terms of contact angle with water. However, the contact angle of inorganic dust represented by clay minerals with water is 20 to 50 °, and it has an affinity for graft polymers with a contact angle of 30 to 40 ° with water and adheres to the surface. It is considered that the coating film of this graft polymer cannot prevent stains due to inorganic dust because it is easy to do.

【0006】

PROBLEM TO BE SOLVED: To solve a problem of the invention.

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, prevent the surface of buildings, windowpanes, machinery and articles from becoming dirty, or self-clean the surface. Although there are proposals for (self-cleaning) or easy cleaning, the effect was not sufficient because the surface could not be maintained at a high degree of hydrophilicity for a long period of time. Therefore, in view of the above circumstances, it is an object of the present invention to provide a member capable of maintaining a highly hydrophilic surface for a long period of time.

【0007】

[Means and Actions for Solving Problems]

The present invention is based on the discovery that in a member having a surface layer containing a photocatalyst, when the photocatalyst is photoexcited, the surface of the member becomes highly hydrophilic. This phenomenon is considered to proceed by the mechanism shown below. That is, when the photocatalyst is irradiated with light having an energy equal to or greater than the energy gap between the upper end of the valence band of the photocatalyst and the lower end of the conduction electron band, the electrons in the valence band of the photocatalyst are excited to generate conduction electrons and holes. However, the action of either or both of them probably imparts polarity to the surface and collects polar components such as water and hydroxyl bands. Then, by the cooperative action of either or both of conduction electrons and holes and the polar component, the chemical bond between the adsorption surface and the pollutant chemically adsorbed on the surface is broken, and the chemically adsorbed water is formed on the surface. It is adsorbed and a physically adsorbed aqueous layer is formed on it.

【0008】

In the present invention, a photocatalytic titanium oxide and a surface layer containing an amorphous oxide are formed, or a photocatalytic titanium oxide-containing layer is formed, and a surface layer containing an amorphous oxide is further formed on the photocatalytic titanium oxide-containing layer. Provided is a photocatalytic hydrophilic member. When the surface layer contains an amorphous oxide, the amorphous oxide has an open structure and therefore has excellent water storage, so that a stable physically adsorbed aqueous layer is easily formed and kept in a dark place. Even so, the surface hydrophilicity can be maintained at a high level for a fairly long period of time. Furthermore, since the surface layer contains a photocatalytic oxide, even if the surface hydrophilicity is lost due to being left in a dark place for a long period of time, the photocatalytic oxide becomes superhydrophilic in response to photoexcitation. Will be presented.

【0009】

BEST MODE FOR CARRYING OUT THE INVENTION

In the first embodiment of the present invention, as shown in FIG. 1, a surface layer containing photocatalytic titanium oxide and an amorphous oxide is formed on the surface of the base material. In the second embodiment of the present invention, as shown in FIG. 2, a photocatalytic titanium oxide-containing layer is formed on the surface of the base material, and a surface layer containing an amorphous oxide is formed on the photocatalytic titanium oxide-containing layer. To.

【0010】

The high degree of hydrophilicity in the present invention refers to a state of exhibiting water wettability of 10 ° or less, preferably 5 ° or less in terms of contact angle with water. As shown in PCT / JP96 / 00733, if the surface of the member is 10 ° or less in terms of contact angle with water, even if moisture or steam in the air condenses, the condensed water will be individual. The tendency to form a uniform water film without forming water droplets 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, eyeglass lenses, and helmet shields are exposed to rainfall or splashes, they provide a high degree of visibility and visibility without the formation of scattered, obtrusive water droplets. The effect of securing, guaranteeing the safety of vehicles and traffic, and improving the efficiency of various tasks and activities will be dramatically improved. Similarly, as shown in PCT / JP96 / 00733, if the surface of the member is 10 ° or less, preferably 5 ° or less in terms of contact angle with water, exhaust of urban dust, automobiles, etc. Combustion products such as carbon black contained in gas, hydrophobic pollutants such as oils and fats and sealant-eluting components, and inorganic clay pollutants are difficult to adhere to, and even if they adhere, they can be easily removed by rainfall or washing with water. become.

【0011】

If the surface of the member can maintain the above-mentioned high degree of hydrophilicity, in addition to the above-mentioned antifogging effect and surface cleaning effect, antistatic effect (dust adhesion prevention effect), heat insulation effect, bubble adhesion prevention effect in water, efficiency in heat exchanger The improvement effect, biocompatibility effect, etc. will be exhibited.

【0012】

The base material to which the present invention can be applied is a transparent member when the above-mentioned antifogging effect is expected, and glass, plastic, or the like can be preferably used as the material. Applicable substrates include vehicle rearview mirrors, bathroom mirrors, washroom mirrors, dental mirrors, road mirror-like mirrors; eyeglass lenses, optical lenses, camera lenses, endoscopic lenses, Lenses like lighting lenses, semiconductor lenses, copying machine lenses; prisms; window glass of buildings and surveillance towers; cars, railroad vehicles, aircraft, ships, submersibles, snow cars, ropeway gondola, amusement park gondola , Spacecraft-like vehicle window mirrors; automobiles, railroad vehicles, aircraft, ships, submersibles, snow vehicles, snowmobiles, motorcycles, ropeway gondola, amusement park gondola, spacecraft-like vehicle windshields; Protective goggles, sports goggles, protective mask shields, sports mask shields, helmet shields, frozen food display case glass; Includes a cover glass for measuring equipment and a film to be attached to the surface of the article. As a base material to which the present invention can be applied, when the above surface cleaning effect is expected, the material thereof is, for example, metal, ceramics, glass, plastic, wood, stone, cement, concrete, fiber, cloth, and their materials. Combinations and laminates thereof can be preferably used. Applicable base materials include building materials, building exteriors, building interiors, window frames, windowpanes, structural members, vehicle exteriors and paints, machinery and article exteriors, dustproof covers and paints, traffic signs, and more. Display devices, advertising towers, soundproof walls for roads, soundproof walls for railways, bridges, exteriors and paintings of guard rails, tunnel interiors and paintings, glass, solar cell covers, solar water heater heat collecting covers, vinyl houses, lighting for vehicles Covers, housing equipment, toilets, bathtubs, washstands, lighting fixtures, lighting covers, kitchen utensils, tableware, dishwashers, dish dryers, sinks, cooking ranges, kitchen hoods, ventilation fans, and for attaching to the surface of the above items. Includes film. As a base material to which the present invention can be applied, when the above antistatic effect is expected, the material thereof is, for example, metal, ceramics, glass, plastic, wood, stone, cement, concrete, fiber, cloth, or a combination thereof. , Those laminates can be preferably used. Applicable base materials include brown tubes, magnetic recording media, optical recording media, optical magnetic recording media, audio tapes, video tapes, analog records, housings and parts for household electrical products, exteriors and coatings, and OA equipment. For product housings, parts, exteriors and paints, building materials, building exteriors, building interiors, window frames, windowpanes, structural members, vehicle exteriors and paints, machinery and article exteriors, dustproof covers and paints, and the above article surfaces. Includes a film for sticking.

【0013】

A photocatalytic oxide is an oxide in the valence band when irradiated with light (excitation light) with an energy larger than the energy gap between the conduction electron band and the valence band of the oxide crystal (that is, a short wavelength). Oxide that can generate conduction electrons and holes by electron excitation (photoexcitation). Anatase-type titanium oxide, rutile-type titanium oxide, tin oxide, zinc oxide, dibismuth trioxide, tungsten trioxide, second oxide Iron, strontium titanate and the like can be preferably used. Here, as the light source used for photoexcitation of the photocatalytic oxide, indoor lighting such as a fluorescent lamp, an incandescent lamp, a metal halide lamp, a mercury lamp, the sun, a light source in which light from these light sources is guided by a low-loss fiber, or the like is used. It can be preferably used. In order for the surface of the substrate to be highly hydrophilic by photoexcitation of the photocatalytic oxide, the illuminance of the excitation light is 0.001 mW / cm.²More than that is fine, but 0.01mW / cm²The above is preferable, and 0.1 mW / cm2 or more is more preferable.

【0014】

Here, as the amorphous oxide, amorphous silica, water glass, amorphous titanium oxide, titanium hydroxide, amorphous alumina, aluminum hydroxide and the like can be preferably used.

【0015】

The film thickness of the surface layer is preferably 0.2 μm or less. By doing so, it is possible to prevent color development of the surface layer due to light interference. Further, the thinner the surface layer, the more transparent the member can be ensured. Further, if the film thickness is reduced, the wear resistance of the surface layer is improved. A wear-resistant or corrosion-resistant protective layer or other functional film that can be hydrophilized may be further provided on the surface of the surface layer. It is preferable that the surface layer does not have a high refractive index as compared with the base material. Preferably, the refractive index of the surface layer is 2 or less. Then, the reflection of light at the interface between the base material and the surface layer can be suppressed. When the base material is glass or glazed tile containing alkaline network-modifying ions such as sodium, an intermediate layer such as silica may be formed between the base material and the surface layer. By doing so, the alkali network-modifying ions are prevented from diffusing from the base material to the surface layer during firing, and the photocatalytic function is better 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 attached to the surface. In addition, this surface layer suppresses the growth of microorganisms such as mold, algae and moss. Therefore, the adhesion of dirt on the surface of the member caused by microorganisms can be suppressed more effectively. Platinum group metals such as pt, Pd, Rh, Ru, Os and Ir can be added to the surface layer. The surface layer to which the metal is added can enhance the oxidative activity of the photocatalyst and promote the decomposition of contaminants adhering to the surface of the member.

【0016】

The method for forming the hydrophilic member in FIG. 1 will be described by taking the case where the amorphous oxide is atypical silica as an example. In this case, for example, a mixture of a photocatalytic titanium oxide sol and a tetraalkoxysilane such as tetraethoxysilane, tetramethoxysilane, tetrapropoxysilane, or tetrabutoxysilane is spray-coated, flow-coated, or spin-coated on the surface of the substrate. It is obtained by applying a method such as dip coating or roll coating and then drying the tetraalkoxysilane to hydrolyze and dehydrate and shrink-polymerize to produce amorphous silica, and to fix the surface layer to the base material. In another method of forming the hydrophilic member shown in FIG. 1, a mixture of a photocatalytic titanium oxide sol and a silica sol is spray-coated, flow-coated, spin-coated, dip-coated, roll-coated, etc. on the surface of the substrate. It is obtained by fixing the surface layer to the substrate after coating. In another method of forming the hydrophilic member of FIG. 1, for example, tetraalkoxytitanium such as tetraethoxytitanium, tetramethoxytitanium, tetrapropoxytitanium, tetrabutoxytitanium; titanium chelate, acetate titanium; titanium sulfate, titanium tetrachloride. Soluble inorganic titanium compounds such as; titanium hydroxide; photocatalytic titanium oxide precursors such as atypical titanium oxide and silica sol on the surface of the substrate, spray coating, flow coating, spin coating, dip coating, roll coating, electrons After coating by a method such as beam vapor deposition, the surface is fired at a temperature of 400 ° C or higher, which is higher than the temperature at which the precursor of photocatalytic titanium oxide changes to photocatalytic oxide (crystallization temperature of anatase-type titanium oxide). It is obtained by fixing the layer to the substrate.

【0017】

The method for forming the hydrophilic member in FIG. 2 is, for example, applying and drying a sol in which photocatalytic titanium oxide particles are suspended on the surface of a base material by a method such as spray coating, flow coating, spin coating, dip coating, or roll coating. After that, tetraalkoxysilanes such as tetraethoxysilane, tetramethoxysilane, tetrapropoxysilane, and tetrabutoxysilane; or silica sol; are further applied thereto by any of the above methods, and then dried to obtain tetraalkoxysilane. It is obtained by producing amorphous silica by hydrolysis and dehydration-condensation polymerization, and fixing the surface layer to a base material. In another method of forming the hydrophilic member of FIG. 2, for example, tetraalkoxytitanium such as tetraethoxytitanium, tetramethoxytitanium, tetrapropoxytitanium, tetrabutoxytitanium; titanium chelate, acetate titanium; titanium sulfate, titanium tetrachloride. Soluble inorganic titanium compounds such as; titanium hydroxide; precursors of photocatalytic titanium oxide such as atypical titanium oxide are spray coated, flow coated, spin coated, dip coated, roll coated, electron beam vapor deposition on the surface of the substrate. After coating and drying by a method such as, a tetraalkoxysilane such as tetraethoxysilane, tetramethoxysilane, tetrapropoxysilane, or tetrabutoxysilane; or silica sol; is further coated on it by any of the above methods, and is photocatalytic. It is obtained by firing at a temperature of 400 ° C or higher, which is higher than the temperature at which the precursor of titanium oxide changes to a photocatalytic oxide (crystallization temperature of anatase-type titanium oxide), and fixing the surface layer to the substrate. .. In the hydrophilic member of FIG. 2, when the film thickness of the photocatalytic oxide layer is 10 nm or more, the hydrophilization performance by photoexcitation of the photocatalyst is particularly excellent, which is preferable.

【0018】

[Example]

Example 1. (Fig. 1, type, titanium oxide sol + silica sol) Ammonia defibrated anatase type titanium oxide sol (Ishihara Sangyo, STS-11) and colloidal silica (Nissan Chemical, Snowtex O) are mixed at a solid content ratio of 88:12, and a 10 x 5 cm square glazed tile (10 x 5 cm square) The surface of Tohoku Kikai, AB02E11) was applied by the flow coating method and fired at a temperature of 800 ° C. for 1 hour to obtain a sample coated with a film composed of anatase-type titanium oxide particles and silica particles. The film thickness was 0.3 μm. The contact angle of the sample immediately after firing with water was 5 °. Here, the contact angle with water was measured 30 seconds after dropping water droplets on the sample surface from a microsyringe using a contact angle measuring device (Kyowa Interface Science, CA-X150). The contact angle with water after leaving the sample in the dark for 1 week was still 5 °. After that, using an ultraviolet light source (Sankyo Electric, black light blue (BLB) fluorescent lamp), the illuminance is 0.03 mW / cm.²When the sample surface was irradiated with the ultraviolet rays of No. 1 for about 1 day, the contact angle with water became 0 °.

【0019】

Example 2. (Fig. 1, type, titanium alkoxide + silica sol) A coating solution consisting of 6 parts by weight of tetraethoxysilane (Wako Pure Chemical Industries, Ltd.), 86 parts by weight of ethanol, 6 parts by weight of pure water, and 2 parts by weight of 36% hydrochloric acid is applied to the surface of a 10 cm square soda lime glass plate by the flow coating method. And dried at a temperature of 80 ° C. In the process up to this point, tetraethoxysilane was hydrolyzed to silanol, and then a thin film of amorphous silica was formed on the surface of the glass plate by dehydration polycondensation. Next, a coating obtained by mixing 1 g of a liquid material consisting of 5 parts by weight of silica sol and 95 parts by weight of ethanol and 5 g of a liquid material consisting of 10 parts by weight of tetraethoxytitanium, 90 parts by weight of ethanol and 1 part by weight of 36% hydrochloric acid. The solution was applied by flow coating and dried at a temperature of 80 ° C. In the process up to this point, tetraethoxytitanium was hydrolyzed to titanium hydroxide, and then dehydrated and polycondensed to be atypical titanium oxide. That is, in the process up to this point, a thin film composed of amorphous titanium oxide and silica sol was formed on the surface of the glass plate. Then, by firing at 500 ° C., the amorphous titanium oxide was phase-changed to anatase-type titanium oxide, and a sample coated with a film composed of anatase-type titanium oxide particles and silica particles was obtained. Next, oleic acid is applied to the surface of the sample, and after it is sufficiently stretched, the surface is rubbed with a sponge soaked with bath magic phosphorus, rinsed with running water, and then dried at 50 ° C for 30 minutes with a dryer. , The surface was deliberately contaminated. As a result, the contact angle of the sample surface with water was 70 °. After that, using a BLB fluorescent lamp, the ultraviolet illuminance is 0.2 mW / cm.²Irradiated for 2 days. As a result, the contact angle of the sample surface with water was hydrophilized to 3 °. Next, the sample was left in a dark place for 1 day, and the change in the contact angle of the sample surface with water was measured. As a result, the contact angle with water was maintained at a low value of about 5 °.

【0020】

[Effect of the invention]

In the present invention, a photocatalytic titanium oxide and a layer containing an amorphous oxide are formed, or a photocatalytic titanium oxide-containing layer is formed, and a layer containing an amorphous oxide is further formed on the photocatalytic titanium oxide-containing layer. By doing so, the surface becomes hydrophilic in response to the photoexcitation of the photocatalyst, so that the surface can be permanently maintained at a high degree of hydrophilicity, and due to the water storage effect exhibited by the amorphous oxide, Hydrophilicity at the time of shading will also be maintained for a long period of time.

[Simple explanation of drawings]

[Figure 1]

The figure which shows one Embodiment of this invention.

[Figure 2]

The figure which shows the other embodiment of this invention.