JPH10237357A - Coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a coating composition capable of forming a membrane maintaining high hydrophilicity for a long time even in a dark place, and useful for prevention of dew condensation, fouling, etc., by including a specific photocatalyst parcels, tungsten chloride and tetrahydrofuran. SOLUTION: This coating composition capable of making the surface of a substrate hydrophilic according to the photoexcitation of a photocatalyst and retarding the decrease in the hydrophobicity when shaded by coating the composition on the substrate and solidifying the coated composition comprises (A) crystalline titanium oxide particles, (B) tungsten chloride and (C) tetrahydrofuran. When the composition coated on the surface of the substrate is fired to solidify the composition, the component B is oxidized by oxygen in air to form (B1 ) tungsten oxide. The maintainability of hydrophilicity of the surface layer once made hydrophilic when shaded is improved by the water molecule-adsorbing activities of the component B1 and the effect is further rapidly increased by the use of the component C as the solvent of the composition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

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

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

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

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

[0006]

As described above, by making the surface of the member hydrophilic, it is possible to prevent the member from fogging or forming water droplets, and also to prevent the surfaces of buildings, window glasses, mechanical devices and articles from becoming dirty. Although there are proposals that can prevent blemishes or clean the surface by self-cleaning or can be easily cleaned, the effect was not sufficient because the surface could not be maintained at a high degree of hydrophilicity for a long time. In view of the above circumstances, an object of the present invention is to provide a coating composition capable of maintaining a surface with a high degree of hydrophilicity over a long period of time.

[0007]

SUMMARY OF THE INVENTION The present invention is based on the discovery that, in a member having a surface layer containing a photocatalyst, the surface of the member is highly hydrophilized when the photocatalyst is photoexcited. This phenomenon is considered to proceed by the following mechanism. That is, when light having energy equal to or greater than the energy gap between the upper end of the valence band of the photocatalyst and the lower end of the conduction electron band is irradiated on the photocatalytic oxide, the electrons in the valence band of the photocatalyst are excited and the conduction electrons are excited. Then, holes are generated, and one or both of these actions probably gives polarity to the surface, and polar components such as water and hydroxyl groups are collected. Then, chemically adsorbed water is adsorbed on the surface, and a physically adsorbed water layer is formed thereon, so that the surface of the member exhibits a high degree of hydrophilicity.

The present invention comprises a solution containing crystalline titanium oxide particles, tungsten chloride, and tetrahydrofuran. The solution is applied to a substrate and solidified by firing, so that the surface of the substrate responds to the photoexcitation of the crystalline titanium oxide. Provided is a photocatalytic hydrophilic coating composition which is made hydrophilic and the loss of hydrophilicity during light shielding is suppressed. The above core
When the tinting composition is fired and solidified, the tungsten chloride reacts with oxygen species in the air to produce tungsten oxide. When tungsten oxide is contained in the surface layer in addition to the photocatalytic titanium oxide, the hydrophilicity of the once hydrophilized surface at the time of shading is improved. This is because when tungsten oxide is contained, the polarity of the surface becomes large regardless of the presence or absence of light, so it is easier to selectively adsorb water molecules that are polar molecules than hydrophobic molecules, It is considered that a stable physical adsorption water layer is easily formed. Also, surprisingly, by using tetrahydrofuran as a solvent for the coating composition, the effect of suppressing the loss of hydrophilicity at the time of shading is further drastically improved.
Therefore, by coating and solidifying a coating composition containing tungsten oxide, a photocatalytic oxide, and tetrahydrofuran on a substrate, the substrate surface can maintain a high degree of hydrophilicity in a dark place for a long time. In addition, even if the hydrophilicity is lost, a high degree of hydrophilic state can be recovered by photoexcitation of the photocatalytic oxide.

In another embodiment of the present invention, a photocatalytic oxide-containing layer is formed on the surface of the substrate, and the hydrophilicity of the photocatalytic hydrophilic member, which becomes hydrophilic in response to photoexcitation of the photocatalyst, at the time of light blocking. A coating composition for suppressing loss of properties, comprising a solution containing tungsten chloride and tetrahydrofuran, applied to a substrate, and baked and solidified to provide the coating composition exhibiting the above function. provide. When the coating composition is calcined and solidified, tungsten chloride reacts with oxygen species in the air to produce tungsten oxide. When tungsten oxide is contained in the surface layer in addition to the photocatalytic titanium oxide, the hydrophilicity of the once hydrophilized surface at the time of shading is improved. This is because when tungsten oxide is contained, the polarity of the surface becomes large regardless of the presence or absence of light, so it is easier to selectively adsorb water molecules that are polar molecules than hydrophobic molecules, It is considered that a stable physical adsorption water layer is easily formed. Also, surprisingly, by using tetrahydrofuran as a solvent for the coating composition, the effect of suppressing the loss of hydrophilicity at the time of shading is further drastically improved. Therefore, by coating and solidifying a coating composition containing tungsten oxide, a photocatalytic oxide, and tetrahydrofuran on a substrate, the substrate surface can maintain a high degree of hydrophilicity in a dark place for a long time. In addition, even if the hydrophilicity is lost, a high degree of hydrophilic state can be recovered by photoexcitation of the photocatalytic oxide.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The coating composition according to the first aspect of the present invention is coated on a substrate and solidified by firing. As shown in FIG. 1, a photocatalytic titanium oxide, A surface layer made of tungsten is formed. Coating the coating composition of claim 2 of the present invention on a substrate,
When baked and solidified, as shown in FIG. 2, a photocatalytic titanium oxide-containing layer is formed on the surface of the base material, and a surface layer made of tungsten oxide is formed thereon.

The term “highly hydrophilic” in the present invention means a state exhibiting water wettability of not more than 10 °, preferably not more than 5 ° in terms of a contact angle with water. PCT / JP96 / 007
As shown in No. 33, if the surface of the member is less than 10 ° in terms of the contact angle with water, condensed water forms individual water droplets even if moisture or steam in the air is dewed. Without this, the tendency to form a uniform water film becomes remarkable. Therefore, the tendency that light scattering fogging does not occur on the surface becomes remarkable. Similarly, when a window glass, a vehicle back mirror, a vehicle windshield, an eyeglass lens, or a shield of a helmet is exposed to rainfall or splashing, discrete unsightly water droplets are not formed, and high visibility and visibility are achieved. As a result, the effects of ensuring vehicle safety, ensuring the safety of vehicles and traffic, and improving the efficiency of various tasks and activities are dramatically improved. Similarly, as shown in PCT / JP96 / 00733, if the surface of the member is in a state of being not more than 20 °, preferably not more than 5 ° in terms of a contact angle with water, exhaust gas from city dust, automobiles, etc. Combustion products such as carbon black contained in water, hydrophobic contaminants such as oils and fats, sealant eluting components, and inorganic clay contaminants are unlikely to adhere to each other. You can drop it.

If the surface of the member can maintain the high degree of hydrophilicity, the antifogging effect and the surface cleaning effect, as well as the antistatic effect (dust preventing effect), the heat insulating effect, the bubble preventing effect in water, the 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 coating composition of 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 vehicle back mirrors, bathroom mirrors, toilet mirrors, dental mirrors, road mirrors; spectacle lenses, optical lenses, camera lenses, endoscope lenses, Lenses such as illumination lenses, semiconductor lenses, and copier lenses; prisms; windows of buildings and towers; automobiles, railway vehicles, aircraft, ships, submersibles, snowmobiles, lowway gondolas, and amusement parks. Window glasses for vehicles such as gondola and spacecraft; automobiles, railway vehicles, aircraft, ships, submersibles, snowmobiles, snowmobiles,
Windshields for vehicles such as motorcycles, lowway gondola, amusement park gondola, spacecraft; protective goggles, sports goggles, protective mask shields, sports Masks for masks, shields for helmets, glass for frozen food display cases; cover glass for measuring instruments;
And a film to be attached to the surface of the article.

As the substrate to which the coating composition of the present invention can be applied, when the above-mentioned surface cleaning effect is expected, the material is, for example, metal, ceramics, glass, plastic, wood, stone, cement. , Concrete, fiber,
Fabrics, combinations thereof, and laminates thereof can be suitably used. Speaking of applicable base materials, building materials, building exteriors, building interiors, window frames, windowpanes, structural members, vehicle exteriors and coatings, machinery and articles exteriors, dustproof covers and coatings, traffic signs, Various display devices, advertising towers, road noise barriers,
Exterior and coating of railway noise barriers, bridges, and gardens, tunnel interiors and coatings, insulators, solar cell covers, solar water heater collectors, vinyl houses, vehicle lighting covers, houses Equipment, toilets, bathtubs, sinks, lighting fixtures, lighting covers, kitchen utensils, dishes, dishwashers, dish dryers, sinks, cooking ranges, kitchen hoods, ventilation fans, and to be attached to the surface of the above-mentioned articles Including film.

As the substrate to which the coating composition of the present invention can be applied, when the above antistatic effect is expected, the material may be, for example, metal, ceramics, glass, plastic, wood, stone, cement, Concrete, fibers, fabrics, 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 tape, video tape, analog record,
Housing and parts for household appliances, exterior and coating, O
A equipment housing and parts, exterior and coating, building materials,
Includes building exteriors, building interiors, window frames, windowpanes, structural members, vehicle exteriors and coatings, exteriors of machinery and articles, dustproof covers and coatings, and films to be adhered to the article surfaces.

A photocatalytic oxide is a light-sensitive material that 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 capable of generating conduction electrons and holes by the excitation of electrons (photoexcitation) in the valence band, including anatase-type titanium oxide, rutile-type titanium oxide, tin oxide, zinc oxide, bismuth trioxide, Tungsten trioxide, ferric oxide, strontium titanate and the like can be suitably used. The light source used for photoexcitation of the photocatalytic oxide is, for example, indoor lighting such as a fluorescent lamp, an incandescent lamp, a metal halide lamp, or a mercury lamp, the sun, or a light source that guides light from the light source through a low-loss fiber. Can be suitably used. In order for the substrate surface to be highly hydrophilized by photoexcitation of the photocatalytic oxide, the illuminance of the excitation light is 0.001 m
W suffices / cm ² or more, but preferably that it 0.01 mW / cm ² or more, and more preferably it 0.1 mW / cm ² or more.

The thickness of the surface layer is preferably set to 0.2 μm or less. Then, it is possible to prevent the surface layer from being colored by light interference. Also, the thinner the surface layer, the more transparent the member can be. Further, when the film thickness is reduced, the wear resistance of the surface layer is improved. The surface of the surface layer may be further provided with a wear-resistant or corrosion-resistant protective layer capable of being made hydrophilic and other functional films. Preferably, the surface layer does not have a very high refractive index as compared to the substrate. Preferably, the refractive index of the surface layer is 2 or less. Then, light reflection at the interface between the base material and the surface layer can be suppressed. When the substrate is a glass or glazed tile containing an alkali network modifying ion such as sodium, an intermediate layer such as silica may be formed between the substrate and the surface layer. Then, the diffusion of the alkali network modifying ions from the base material to the surface layer during the firing is prevented, and the photocatalytic function is more effectively exhibited. Metals such as Ag, Cu, and Zn can be added to the surface layer. The surface layer to which the metal is added can kill bacteria adhering to the surface. Furthermore, this surface layer inhibits the growth of microorganisms such as molds, algae and moss. Therefore, adhesion of dirt on the member surface due to microorganisms can be more effectively suppressed. The surface layer has P
Platinum group metals such as t, Pd, Rh, Ru, Os, Ir can be added. The surface layer to which the metal is added can enhance the oxidizing activity of the photocatalyst, and promote the decomposition of contaminants attached to the member surface.

The method for forming the hydrophilic member shown in FIG. 1 is as follows. For example, a coating solution is prepared by mixing photocatalytic titanium oxide particles, tungsten chloride and tetrahydrofuran, and the coating solution is spray-coated on the surface of a substrate. Coating, flow coating, spin coating, dip coating, row coating
After coating by a method such as coating, tungsten chloride is changed to tungsten oxide by firing, and the surface layer is fixed to the base material.

The method for forming the hydrophilic member shown in FIG. 2 is, for example, a method in which a sol in which photocatalytic titanium oxide particles are suspended is coated on a substrate surface.
Spray coating, flow coating, spin coating, dip coating, roll coating and the like are applied and dried. Tungsten chloride is dissolved in tetrahydrofuran, and then applied. To tungsten oxide,
The surface layer is fixed to the substrate. In another method of forming the hydrophilic member of FIG. 2, for example, a monomer, oligomer or polymer of tetraalkoxytitanium such as tetraethoxytitanium, tetramethoxytitanium, tetrapropoxytitanium, tetrabutoxytitanium; titanium chelate, Acetate titanium; a soluble inorganic titanium compound such as titanium sulfate and titanium tetrachloride; titanium hydroxide; a precursor of crystalline titanium oxide such as amorphous titanium oxide, on the surface of the base material, spray-coated and flown After coating and drying by a method such as coating, spin coating, dip coating, roll coating, electron beam evaporation, etc., a solution obtained by dissolving tungsten chloride in tetrahydrofuran is further applied thereon. Applied by the method, further the above-mentioned precursor of the photocatalytic titanium oxide is changed to a photocatalytic oxide Degree - fired at temperatures above (ANATA crystallization temperature of peptidase type titanium oxide), to fix the surface layer to the substrate. In the hydrophilic member of FIG. 2, it is preferable that the photocatalytic titanium oxide layer has a thickness of 10 nm or more, in particular, because the photocatalytic titanium oxide has excellent hydrophilicity by photoexcitation.

[0020]

EXAMPLE A 10 cm square soda lime glass plate was immersed in a 3.5% by weight tetraethoxysilane solution (diluent: ethanol, hydrolysis promoter: hydrochloric acid), and then immersed in a 24 cm / min.
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 be silanol first, and then a thin film of amorphous silica was formed on the surface of the glass plate by dehydration-condensation polymerization of silanol. Next, after dipping in a 3.5% by weight tetra-n-butoxytitanium monomer solution (diluent: ethanol, hydrolysis inhibitor: hydrochloric acid), the solution is pulled up at a speed of 24 cm / min, and the solution is dipped in a dip-coating solution. The coating was applied to the surface by a coating method and dried to obtain a # 1 sample. By the steps up to this point, the tetra-n-butoxytitanium tetramer is hydrolyzed to titanium hydroxide first, and then the amorphous titanium oxide thin film (film thickness 50) by dehydration condensation polymerization of titanium hydroxide.
nm) was formed on the surface. Next, the sample # 1 was immersed in a tetrahydrofuran solution containing 0.379% by weight of tungsten chloride on the surface of the sample, pulled up at a rate of 24 cm / min, and the solution was applied to the surface by dip coating, and the solution was coated at 500 ° C. By firing, a # 2 sample was obtained. The amorphous titanium oxide was crystallized by the calcination to produce an anatase type titanium oxide. Also, it is considered that tungsten chloride is oxidized by firing to produce tungsten oxide. After dipping in the ethanol solution containing 0.379% by weight of tungsten chloride on the surface of the # 1 sample,
The solution was pulled up at a speed of 10 cm, the solution was applied to the surface by a dip coating method, and baked at 500 ° C. to obtain a # 3 sample for comparison. The amorphous titanium oxide was crystallized by the calcination to produce an anatase type titanium oxide. Also, it is considered that tungsten chloride is oxidized by firing to produce tungsten oxide. # 2 sample and # immediately after firing
3 Apply oleic acid to the sample surface and rub it with a neutral detergent.
After rinsing with tap water and distilled water, use a dryer at 50 ° C for 3 hours.
The surface was intentionally contaminated by drying for 0 minutes.
As a result, the contact angle with water increased to 40 °. Here, the contact angle with water is measured using a contact angle measuring instrument (Kyowa Interface Science, CA-
X150), the value was measured 30 seconds after the water droplet was dropped with a microsyringe. Next, the light source is BLB
Ultraviolet rays having an illuminance of 0.3 mW / cm ² per day were irradiated using a lamp (Sankyo Electric, Black Light Bull-Lamp).
As a result, the contact angles of the # 2 and # 3 samples with water decreased to 0 °. Next, the sample was left in a dark place for 48 hours, and the change in the contact angle of the sample surface with water was measured. As a result, # 3
In the sample, it rose to 12 °, while in the # 2 sample, it increased to 4 °.
゜ was maintained at a low value. 21 more for the # 2 sample
After being left in the dark for 6 hours for 48 hours, the contact angle of the sample surface with water was still kept at a low value of 7 °.

[0021]

The coating composition containing photocatalytic titanium oxide, tungsten chloride, and tetrahydrofuran, when fired and solidified on the surface of the substrate, has a highly hydrophilic surface in response to the photoexcitation of the photocatalytic titanium oxide. As a result, the surface can be permanently maintained at a high degree of hydrophilicity, and the surface that once exhibits a high degree of hydrophilicity can maintain the hydrophilicity at the time of shading for a long time. . Further, when the coating composition containing tungsten chloride and tetrahydrofuran is baked and solidified on the photocatalytic titanium oxide-containing layer, it has a property that the surface is highly hydrophilized in response to the photoexcitation of the photocatalytic titanium oxide. In the layer having, it is possible to impart an effect of improving the hydrophilicity maintenance property at the time of light shielding of the surface once having a high degree of hydrophilicity,
By maintaining hydrophilicity such as anti-fogging, drip-proofing, and water washing, it is possible to exert properties that can exhibit effects permanently only by intermittent light irradiation.

[Brief description of the drawings]

FIG. 1 is a view showing the surface structure of a substrate which has been coated with the coating composition of claim 1 of the present invention and which has been baked and solidified.

FIG. 2 is a view showing the surface structure of a substrate which is coated with the coating composition of claim 2 of the present invention and which is baked and solidified.

Claims (2)

[Claims] 1. A solution comprising crystalline titanium oxide particles, tungsten chloride, and tetrahydrofuran; applied to a substrate and solidified to render the substrate surface hydrophilic in response to the photoexcitation of the crystalline titanium oxide. And a photocatalytic hydrophilic coating composition capable of suppressing loss of hydrophilicity during light shielding. 2. A photocatalytic oxide-containing layer is formed on the surface of a base material, and the photocatalytic hydrophilic member becomes hydrophilic in response to photoexcitation of the photocatalyst. A coating composition, comprising a solution containing tungsten chloride and tetrahydrofuran, which is applied to a substrate and solidified to exhibit the function.