JPH10195382A - Photocatalystic hydrophilic coating liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a photocatalytic hydrophilic coating liq. excellent in storage stability by dispersing photocatalytic TiO2 particles coated with inorg. oxide particles having an isoelectric point in a specified range of pH in an amorphous SiO2 precursor capable of forming an amorphous SiO2 film when cured. SOLUTION: Inorg. oxide particles having an isoelectric point at a pH of 5 or lower (e.g. SiO2 ) or having an isoelectric point at a pH of 9 or higher (e.g. ZrO2 ) are applied, e.g. by spray coating, to photocatalytic TiO2 particles and thermally cured to form a coating film. The coated TiO2 particles, together with water, a solvent, a hydrolysis-accelerating catalyst, a cure catalyst, etc., are dispersed in an amorphous SiO2 precursor such as a tetrafunctional silane deriv. represented by the formula: SiXp O(4-p)/2 (wherein X is an alkoxy or halogen; and 0<p<=4) (e.g. tetramethoxysilane) or a silicate, thus giving a coating compsn. The compsn. is applied to the surface of a member in a thickness of 0.4μm or lower and exposed to exciting rays at an illuminance of 0.01mW/cm<2> or higher, thus forming a hydrophilic surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrophilic coating liquid for forming a coating film capable of making and maintaining the surface of a member highly hydrophilic. More specifically, the present invention provides a highly hydrophilic surface of a mirror, glass, lens, prism or other transparent member to form a coating film capable of preventing clouding and water droplet formation of the member. It relates to an antifogging coating liquid. The present invention also provides a coating film capable of preventing the surface from being soiled or cleaning the surface with water by highly hydrophilizing the surface of a building, a window glass, a mechanical device or an article. The present invention relates to an easy-to-clean coating liquid for forming a liquid.

[0002]

BACKGROUND OF THE INVENTION It is often experienced that in cold weather, windshields and glazings of automobiles and other vehicles, glazings of buildings, lenses of eyeglasses, and cover glass of various instrument panels are fogged by condensed moisture. . In addition, mirrors and eyeglass lenses in bathrooms and washrooms are often fogged by steam. The fogging on the surface of the article is that if the surface is placed at a temperature below the dew point of the atmosphere, the moisture in the atmosphere will condense and condense on the surface,
This is because they grow like water drops. If the condensed water droplets are sufficiently fine and their diameter is about half the wavelength of visible light, the water droplets will scatter light and the glass or mirror will be apparently opaque, again losing visibility. If the condensation of moisture progresses further and the fine condensed water droplets fuse together and grow into larger discrete water droplets, their surfaces will be refracted by the refraction of light at the water droplet-surface interface and the water droplet-air interface. Dark, blurred, mottled or cloudy. as a result,
In a transparent article such as glass, the perspective image is distorted and the transparency is reduced, and the reflected image is disturbed by a mirror. Furthermore, windshields and window glasses of vehicles, window glasses of buildings, back mirrors of vehicles,
If eyeglass lenses, masks, or helmet shields are exposed to rain or splashes and a large number of discrete water droplets adhere to the surface, those surfaces may become dark, blurred, mottled, or cloudy and still lose visibility. Will be As used herein, the term "anti-fog" broadly refers to a technique for preventing optical hindrance due to such fogging, growth of condensed water droplets, and adhesion of water droplets. 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 shaded or clouded in cold weather or rainy weather, it is difficult to secure a view, and traffic safety is impaired. If the focusing lens of the endoscope lens, dental mirror, or dental laser treatment device becomes cloudy, accurate diagnosis,
It will hinder surgery and treatment. If the cover glass of the instrument panel becomes fogged, it becomes difficult to read the data.

On the other hand, in the field 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. Soil on building exterior materials and coatings consists of combustion products such as carbon black and inorganic contaminants such as urban dust and clay particles. It is considered that the diversity of such contaminants complicates antifouling measures (Yoshinori Tachibana, "Method of Accelerated Testing of Contamination of Exterior Wall Finishing Materials", Journal of Architectural Institute of Japan, Structural Transactions, No. 404, October 1989, pp. 15-2
4). According to conventional wisdom, polytetrafluoroethylene (PTFE) is used to prevent the above-mentioned dirt on the building exterior.
Although water-repellent paint such as was considered preferable,
Recently, for urban dust containing many hydrophobic components,
It is considered that the surface of the coating film should be made as hydrophilic as possible (Polymer, vol. 44, May 1995, p. 3).
07). Therefore, it has been proposed to paint a building with a hydrophilic graft polymer (newspaper "Chemical Industry Daily",
Jan. 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 20 ° to 50 °, and the contact angle with water is 3 °.
Having an affinity for a graft polymer of 0 to 40 °;
It is considered that the graft polymer coating cannot prevent contamination by inorganic dust because it easily adheres to the surface.

[0004]

An object of the present invention is to provide a hydrophilic coating liquid for forming a coating film capable of making and maintaining the surface of a member to a high degree of hydrophilicity,
An object of the present invention is to provide a hydrophilic coating liquid which is excellent in storage stability as a paint and is particularly suitable for coating on a film and for coating a metal material such as an automobile body. Another object of the present invention is to form a coating film capable of preventing clouding and water droplet formation of the member by making the surface of a mirror, glass, lens, prism or other transparent member highly hydrophilic. A hydrophilic coating liquid which is excellent in storage stability as a paint and is particularly suitable for coating on a film.
To provide a liquid for sizing. Another object of the present invention is to make a surface of a building, a window glass, a mechanical device or an article highly hydrophilic, thereby preventing the surface from being soiled or allowing the surface to be cleaned using water. An object of the present invention is to provide a hydrophilic coating liquid which is a hydrophilic coating liquid for forming a coating film and has excellent storage stability as a coating material, and is particularly suitable for a coating film on a film.

[0005]

SUMMARY OF THE INVENTION The present invention is based on the discovery that, in a member having a surface layer containing a photocatalyst formed thereon, when the photocatalyst is photoexcited, the surface of the member is highly hydrophilized. 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 and the lower end of the conduction band of the photocatalyst is irradiated on the photocatalyst, the electrons in the valence band of the photocatalyst are excited, and the conduction electrons and holes are generated. Produced and either or both actions impart polarity to the surface. As a result, water is chemically adsorbed on the surface, and a physically adsorbed water layer is formed thereon to increase. As a result, the surface exhibits a high degree of hydrophilicity with a water wetting angle of 10 ° or less.

Further, if the surface layer contains amorphous silica in addition to the photocatalyst, the surface will exhibit a high degree of hydrophilicity with a water wetting angle of 10 ° or less, and maintain hydrophilicity when kept in a dark place. Is improved.

In the present invention, the average composition formula SiX _p O _{(4-p) / 2} (where X is an alkoxy group or a halogen atom,
Is a number that satisfies 0 <p ≦ 4), and a precursor of amorphous silica which forms an amorphous silica film when cured; and whose isoelectric point is pH A titanium oxide particle whose surface is coated with inorganic oxide particles having a pH of 5 or less or inorganic oxide particles having a pH of 9 or more, the titanium oxide particles being dispersed in the coating film forming element and hydrophilizing the surface of the coating film in response to photoexcitation. Containing photocatalytic titanium oxide particles;
5 to 9 photocatalytic hydrophilic coating liquids are provided. When a coating film is formed on the surface of a substrate with such a coating composition, a curing reaction of the precursor of amorphous silica forms a surface layer containing photocatalytic oxide particles and amorphous silica on the surface of the substrate. Become so. In this case, the physical adsorption water layer is formed according to the photoexcitation of the photocatalyst, so that the surface exhibits hydrophilicity close to the water wetting angle of 0 °,
Hydrophilicity retention when kept in a dark place is improved. In the present invention, the photocatalytic titanium oxide particles are further coated with an inorganic oxide particle having an isoelectric point of 5 or less or an inorganic oxide particle having an isoelectric point of 9 or more. The titanium oxide particles can exhibit excellent dispersion stability even in a neutral liquid. Incidentally, (a) of claims 1 to 4
The precursor component of amorphous silica represented by is the most favorable dispersion stability in a neutral liquid, the above coating, the photocatalytic hydrophilic coating composition, by setting the neutral conditions And good storage stability. The reason is considered as follows. That is, in the case of only the photocatalytic titanium oxide particles, the isoelectric point is around 7, and under neutral conditions, the surface of the particle surface becomes almost zero and it is easy to aggregate, but by coating the surface with the above substance, the particle It is considered that the isoelectric point of the surface is shifted to the acidic side or the basic side, and excellent dispersion stability can be exhibited under neutral conditions of pH 5 to 9. Further, since the coating liquid is neutral and not acidic having a pH of 5 or less, the base material does not deteriorate even when coated on a metal base which is weak against acid. Therefore, even when a coating is applied to an automobile body or the like, there is no possibility that the automobile body itself will be adversely affected. Further, for example, in the case of coating on a film, many of the film coating equipment are made of a metal substrate such as a coating machine, a roll, a duct, etc., but there is no risk of adversely affecting the equipment. It is preferred. In addition, since the coating solution is neutral and not basic having a pH of 9 or more, the precursor of the amorphous silica hardly aggregates.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, photocatalytic titanium oxide refers to light (excitation light) having an energy (ie, a short wavelength) larger than the energy gap between the conduction band and the valence band of the crystal. Irradiates a titanium oxide capable of generating conduction electrons and holes by excitation of electrons in the valence band (photoexcitation) upon irradiation with, for example, an anatase type titanium oxide and a rutile type titanium oxide. Crystalline titanium oxide can be suitably used. The high hydrophilicity in the present invention means a state exhibiting water wettability of 10 ° or less, preferably 5 ° or less in terms of a contact angle with water.

[0009] Precursor of amorphous silica as described in claims 1 to 4 (a) is, in the average composition formula _{SiX p O (4-p)} / 2 ( wherein, X is an alkoxy group or a halogen atom , P
Is a number that satisfies 0 <p ≦ 4) is a tetrafunctional silane derivative or silicate. Here, as the tetrafunctional silane derivative, tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, diethoxydimethoxysilane and the like can be suitably used. As the silicate, an alkyl silicate, water glass, or the like, which can be prepared by partial hydrolysis, dehydration-condensation polymerization, or the like of the above-mentioned tetrafunctional silane derivative, can be suitably used.

The isoelectric point described in claim 1 (b) is p
As the inorganic oxide particles having an H of 5 or less, silica, aluminosilicate and the like can be suitably used. Claim 2 (b)
As the inorganic oxide particles having an isoelectric point of 9 or more at pH described in (1), zirconia and the like can be suitably used.

The method of fixing the above-mentioned coating material to the titanium oxide particles includes, for example, a spray coating method, a dip coating method, a flow coating method, a spin coating method, a roll coating method, and a brush. After coating with a method such as coating or sponge coating, the coating is fixed by a method such as heat treatment.

The coating composition includes Ag, Cu, Z
A metal such as n can be added. When the metal is added, the surface layer formed by the coating film can kill bacteria and fungi attached to the surface even in a dark place.

[0013] Pt, Pd, R
A platinum group metal such as u, Rh, Ir, Os can be added. When the metal is added, the surface layer formed by the coating film can enhance the oxidation-reduction activity of the photocatalyst, and can improve the decomposability of organic contaminants and harmful gases and odors.

The coating composition may further contain a solvent such as water, ethanol, propanol, hydrochloric acid, nitric acid, sulfuric acid,
Catalysts that promote hydrolysis of silicone precursors such as acetic acid and maleic acid, basic compounds such as tributylamine and hexylamine, and acidic compounds such as aluminum triisopropoxide and tetraisopropyl titanate For example, a catalyst for curing the precursor of the silicone such as silane coupling agent or a surfactant for improving the dispersibility of the coating liquid such as a silane coupling agent may be added.

The method of utilizing the coating composition of the present invention is basically based on applying the coating composition on the surface of a substrate and curing the coating composition to form a coating film.

As a method for applying the coating composition,
Spray coating, dip coating, flow coating, spin coating, roll coating, brush coating, sponge coating, and the like can be suitably used. As the curing method, heat treatment, leaving at room temperature,
The polymerization can be carried out by ultraviolet irradiation or the like.

When a coating film is formed on the member surface by the above method,
The surface of the member becomes hydrophilic in response to the photoexcitation of the photocatalyst. Here, in order for the substrate surface to be highly hydrophilized by photoexcitation of the photocatalyst, the illuminance of the excitation light must be 0.001.
mW 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. Light sources used for photoexcitation of the photocatalyst include sunlight,
Interior lighting, fluorescent lamp, mercury lamp, incandescent lamp, xenon lamp, high-pressure sodium lamp, metal halide lamp, B
An LB lamp or the like can be suitably used.

The thickness of the surface layer formed by a coating film on the member surface is preferably 0.4 μm or less. Then, cloudiness due to irregular reflection of light can be prevented, and the surface layer becomes substantially transparent. Furthermore, the thickness of the surface layer is
It is more preferable that the thickness be 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 better its transparency.
Further, when the film thickness is reduced, the wear resistance of the surface layer is improved.

As shown in PCT / JP96 / 00733, if the surface of the member is in a state of not more than 10 ° in terms of a contact angle with water, even if moisture or steam in the air is condensed, condensation occurs. Water tends to form a uniform water film without forming individual water droplets. 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, when 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, 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 exhibits the above-mentioned high hydrophilicity and maintains the state, the anti-fogging effect, the surface cleaning effect, the effect of accelerating the drying of adhering water droplets, the antistatic effect, and the adhesion of dust The effect of prevention, the effect of heat insulation, the effect of preventing air bubbles from adhering to water, the effect of improving efficiency in a heat exchanger, the effect of improving biocompatibility, and the like are exhibited.

The substrate to which the present invention can be applied is a transparent member when an anti-fogging effect is expected, and glass, plastic, or 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, illumination lenses, semiconductor lenses Lenses such as copier lenses, rear view camera lenses for vehicles; prisms; windows of buildings and towers; automobiles, railway vehicles, aircraft, ships, submersibles, snowmobiles, lowway gondola, amusement parks Gondolas, vehicle windows such as spaceships; cars, motorbikes, railcars, aircraft, ships, submersibles, snowmobiles, snowmobiles, lowway gondola, amusement park gondola, space Windshield for vehicles such as ships; protective goggles, sports goggles, protective mask shield, sports mask shield, helmet shield, frozen food display Case glass, Chinese bun, etc. Glass for display case of warm food; Cover for measuring equipment, Cover for rear view camera lens for vehicle, Focusing lens for laser dental treatment device, etc., Laser light detection for inter-vehicle distance sensor, etc. Cover for an infrared sensor, a cover for an infrared sensor, a filter for a camera, and a film, a sheet, a seal, and the like to be attached to the surface of the article.

When a surface cleaning effect is expected as a substrate to which the present invention can be applied, the material may be, for example, metal, ceramic, 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, noise barriers for roads, noise barriers for railways, bridges, exterior and coating of garages, tunnel interiors and coatings, insulators, solar battery covers, solar water heater collector covers, vinyl houses, vehicle lighting Light covers, housing equipment, toilets, bathtubs, washbasins, lighting fixtures, lighting covers, kitchen utensils, dishes, dishwashers, dish dryers, sinks, cooking ranges, kitchen hoods
And a film, a sheet, a seal, and the like for attaching to the surface of the article.

As a substrate to which the present invention can be applied, when an effect of promoting drying of attached water droplets is expected, the material is, for example, metal, ceramic, glass, plastic, wood, or the like.
Stones, cements, concretes, fibers, fabrics, combinations thereof, and laminates thereof can be suitably used. Examples of the applicable substrate include a car body, a window, a pavement, and a film, a sheet, a seal, and the like for attaching to the surface of the article.

In the case where an antistatic effect is expected as a substrate to which the present invention can be applied, the material is, for example, metal,
Ceramic, glass, plastic, wood, stone, cement, concrete, fiber, fabric, combinations thereof, and laminates thereof can be suitably used. Speaking of applicable substrates, cathode ray tubes, magnetic recording media, optical recording media, magneto-optical recording media, audio tapes, video tapes, analog records, housings and parts for household electrical appliances, Exterior and painting, OA equipment product housing and parts and exterior and painting, building materials, building exterior, building interior, window frames, window glass, structural members, vehicle exterior and painting, mechanical equipment and articles exterior, dustproof cover and Includes films, sheets, seals, etc. for painting and sticking to the surface of the article.

[0025]

EXAMPLE Titanium oxide particles produced by the chlorine method were surface-treated with γ-glycoxide propyltrimethoxysilane,
The silica-coated titanium oxide particles produced by heating at 500 ° C. were dispersed in water having a pH of 7. After mixing the dispersion and the methyl silicate coating, the mixture was diluted with ethanol and stirred for 3 hours to obtain a coating liquid. This coating liquid was left at 17 ° C. for one month, but the dispersibility was good. This coating liquid was applied to a quartz glass plate,
UV light intensity 0.5mW / c for 3 days
When irradiated with a m ² BLB lamp, the contact angle with water became 0 °.

[0026]

The photocatalytic hydrophilic coating liquid of the present invention has excellent long-term storage stability and can maintain and maintain the surface of the member to a high degree of hydrophilicity.

Claims (6)

[Claims] 1. A (a) the average composition formula _{SiX p O (4-p)} / 2 ( wherein, X is an alkoxy group or a halogen atom, p
Is a number satisfying 0 <p ≦ 4), which forms an amorphous silica film when cured, and (b) an isoelectric point of 5 or less in pH Titanium oxide particles whose surface is coated with inorganic oxide particles, the photocatalytic titanium oxide particles being dispersed in the coating film forming element and hydrophilizing the surface of the coating film in response to photoexcitation. A photocatalytic hydrophilic coating liquid having a pH of 5 to 9. Wherein (a) the average composition formula _{SiX p O (4-p)} / 2 ( wherein, X is an alkoxy group or a halogen atom, p
Is a number satisfying 0 <p ≦ 4), which forms an amorphous silica coating when cured, and (b) an isoelectric point having a pH of 9 or more at pH Titanium oxide particles whose surface is coated with inorganic oxide particles, wherein the organic groups dispersed in the coating film forming element and bonded to silicon atoms in silicon molecules on the surface of the coating film by photoexcitation by photocatalysis. At least partially substituting a hydroxyl group,
Further, a photocatalytic hydrophilic coating liquid having a pH of 5 to 9 further comprising photocatalytic titanium oxide particles for hydrophilizing the surface of the film in response to photoexcitation. 3. The coating, the surface of which has been hydrophilized in response to photoexcitation, allows the condensation of moisture and / or water droplets adhering to the surface to spread on the surface of the coating, whereby the coating 3. The photocatalytic hydrophilic coating liquid according to claim 1, wherein the substrate coated with the water is prevented from being clouded or overcast by condensed water and / or water droplets of moisture. 4. The coating, the surface of which has been hydrophilized in response to photoexcitation, enables attached sediments and / or contaminants to be washed away by rainwater when exposed to rainfall, whereby the surface self 3. The photocatalytic hydrophilic coating liquid according to claim 1, which enables purification. 5. The coating whose surface has been hydrophilized in response to photoexcitation prevents the contaminant from adhering to the surface when rainwater containing the contaminant comes into contact. 3. The photocatalytic hydrophilic coating liquid according to item 2. 6. The coating, the surface of which has been hydrophilized in response to photoexcitation, releases adhering deposits and / or contaminants when immersed in or wetted with water, so that the surface is exposed to water. Claim 1, characterized in that it is easy to wash with
3. The photocatalytic hydrophilic coating liquid according to 2.