JPH09228326A - Defogging road mirror and its defogging method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a road mirror surface highly hydrophilic to prevent the formation of water drops, and form an uniform water membrane to prevent the fogging of the road mirror by forming a surface layer containing a photocatalyst particle on the surface of the road mirror. SOLUTION: A surface layer containing a photocatalyst particle such as photocatalytic titanium oxide is formed on the surface of a road mirror, the surface layer is made hydrophilic by optical exciting action to eliminate the adhered contaminant, and formation of water drops is prevented to form an uniform water membrane, whereby the fogging of the road mirror is prevented. When the outermost surface is formed of a general inorganic oxide, the same effect can be provided by the action of the photocatalyst. When either one of silica, solid super strong acid, and silicone is combined with the photocatalyst, the hydrophilic property is improved, and hydrophilic property of 10 deg. or less in terms of contact angle with water can be exhibited. With a film thickness of the surface layer of 0.4μm or less, the cloudiness by irregular reflection by interference of light is prevented, and with 0.2μm or less, the coloring of the surface layer by interference of light can be prevented. The refractive index of the surface layer is set to 2 or less, the reflection of light in the critical surface can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anti-fog road mirror and a method for anti-fog of a road mirror.

[0002]

2. Description of the Related Art It is often experienced that a road mirror becomes cloudy due to condensed moisture in cold weather or in rainy weather, making it difficult to check the front side of a curve or the like. If it becomes extreme, it will hinder safe driving in cold weather or in rainy weather. Generally, the surface of an article is fogged because when the surface is placed at a temperature below the dew point of the atmosphere, moisture in the atmosphere condenses and condenses on the surface. If the condensed water droplets are sufficiently fine and their diameter is about ½ of the wavelength of visible light, the water droplets scatter light, the mirror becomes apparently opaque, and the mirror image becomes invisible.
If moisture condensation proceeds further and fine condensed water droplets coalesce with each other to grow into larger discrete water droplets, the surface will be shaded due to refraction of light at the water droplet-surface interface and the water-air interface. Blurred, mottled, or cloudy with no visible mirror image. Furthermore, when the mirror is exposed to rain or splashes and a large number of discrete water droplets are attached to the surface, the surface may be wrinkled, blurred, mottled, or cloudy.
After all, the mirror image disappears. 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.

As is well known, the conventionally used antifogging method is to apply an antifogging composition containing a hydrophilic compound such as polyethylene glycol or a water repellent compound such as silicone to the surface. . However, this kind of anti-fog coating is only temporary, and has the drawback that it is easily removed by washing or contact and loses its effect early.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a road mirror and a method for preventing its fog, which enables a clear mirror image to be confirmed even in cold weather or in rainy weather. Another object of the present invention is to provide a road mirror capable of maintaining a high degree of hydrophilicity for a long period of time and exhibiting an antifogging property, and a method for preventing the same. Another object of the present invention is to provide a road mirror capable of maintaining a high degree of hydrophilicity almost permanently and exhibiting an antifogging property, and a method for preventing the same.

[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 the photocatalyst is irradiated with light having an energy larger than the energy gap between the valence band upper end and the conduction band lower end of the photocatalyst, the electrons in the valence band of the photocatalyst are excited to generate conduction electrons and holes. The action of either or both of them probably imparts polarity to the surface and collects polar components such as water and hydroxyl groups. Then, one or both of conduction electrons and holes and the above-mentioned polar component cooperate with each other to cut off a chemical bond between the surface and the contaminant chemically adsorbed on the surface, and to cause a chemical adsorbed water on the surface. Is adsorbed, and a physically adsorbed water layer is formed thereon. Further, once the surface of the member is highly hydrophilized, the hydrophilicity of the surface is maintained for a certain period even if the member is kept in a dark place.

The present invention provides an anti-fog road mirror having a surface layer containing a substantially transparent photocatalyst on the surface of a road mirror substrate. By providing a surface layer containing a photocatalyst, in response to photoexcitation of the photocatalyst, the surface of the surface layer exhibits hydrophilicity, the condensed water and / or water droplets of the attached moisture spread evenly on the surface of the layer, Moisture condensate and / or water drops will prevent fogging or overhang.

In a preferred embodiment of the present invention, the surface layer further contains silica. By containing silica, the surface is likely to exhibit a high degree of hydrophilicity near a water wetting angle of 0 °, and the hydrophilicity retention when held in a dark place is improved. The reason seems to be related to the ability of silica to store water in its structure.

In a preferred embodiment of the present invention, the surface layer further contains a solid super strong acid.
By containing a super strong acid, the surface is likely to exhibit a high degree of hydrophilicity close to a water wetting angle of 0 °, and at the same time, the hydrophilicity maintaining property when kept in a dark place is improved. The reason is that when the surface layer contains a super strong acid, the polarity of the surface is extremely large irrespective of the presence or absence of light, so that water molecules, which are polar molecules, are selectively adsorbed over hydrophobic molecules. Easy to make. Therefore, a stable physically adsorbed water layer is easily formed, and even if the layer is kept in a dark place, the hydrophilicity of the surface can be maintained at a high level for a considerably long period.

In a preferred embodiment of the present invention, the surface layer further contains silicone.
By containing silicone, by photoexcitation of the photocatalyst, at least a part of the organic group bonded to the silicon atom in the silicone is replaced with a hydroxyl group, and a physically adsorbed water layer is formed on the organic group, so that the surface is It exhibits a high degree of hydrophilicity close to a water wetting angle of 0 °, and improves the hydrophilicity maintaining ability when kept in a dark place.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Next, a specific structure of the present invention will be described. On the surface of the anti-fog road mirror in the present invention, as shown in FIG. 1 or 2, a layer containing a photocatalyst is formed on the surface of the base material. By taking such a surface structure, the surface of the road mirror is highly hydrophilized in response to photoexcitation of the photocatalyst. As a result, even if the moisture in the atmosphere is condensed and adheres, it does not grow in the form of water droplets, and a uniform water film is formed, which prevents the moisture condensed water and / or water droplets from clouding or clinging. It

In FIG. 1, when the surface layer is composed of only the photocatalyst, the photocatalyst is preferably an oxide.
By doing so, the oxide shows hydrophilicity in the state where the pollutants in the environment are not adsorbed, so that the pollutants are rejected by the photoexcitation action and the adsorbed water layer is formed, so that the oxides easily exhibit hydrophilicity. A uniform water film can be formed. In FIG. 2, M represents a metal element. Therefore, in the case of FIG. 2, the outermost surface is made of a general inorganic oxide. Again,
Since the oxide is hydrophilic when the pollutants in the environment are not adsorbed, the photocatalytic titanium oxide mixed into the surface layer other than the inorganic oxide removes the contaminants by the photoexciting action, and the adsorbed water layer Is formed, a uniform water film can be formed.

The road mirror base material in the present invention includes a mirror made of a plastic base material such as acrylic or polycarbonate having a reflective coating on its back surface, a mirror having a transparent resin hard coating on a metal mirror surface, acrylic, polycarbonate or the like. A mirror or the like having a reflective coating on the surface of the plastic substrate and a transparent resin hard coating on the surface of the reflective coating can be preferably used.

A photocatalyst is a photocatalyst of electrons in the valence band when irradiated with light (excitation light) having an energy (that is, a short wavelength) larger than the energy gap between the conduction band and the valence band of the crystal. A substance that is excited (photoexcited) to generate conduction electrons and holes. Examples include anatase titanium oxide, rutile titanium oxide, tin oxide, zinc oxide, nibismuth trioxide, tungsten trioxide, and second oxide. Iron, strontium titanate and the like can be preferably used. Here, as a light source used for photoexcitation of the photocatalyst, both a sunlight source, a street light, a light source in a running environment such as tunnel lighting, and an illumination for irradiating an instrument panel as an accessory can be used.
Incandescent lamps, metal halide lamps,
A light source such as a mercury lamp or a xenon lamp can be preferably used. In order to make the surface of the base material highly hydrophilic by photoexcitation of the photocatalyst, the illuminance of the excitation light is 0.001 mW / cm.
² or more, but 0.01 mW / cm ² or more is preferable, and 0. More preferably, it is 1 mW / cm ² or more.

The film thickness of the surface layer containing the photocatalyst is 0.4.
It is preferable that the thickness is less than or equal to μm. Then, white turbidity due to irregular reflection of light can be prevented, and the surface layer becomes substantially transparent. More preferably, the thickness of the surface layer containing the photocatalyst is 0.2 μm or less. that way,
Coloring of the surface layer due to light interference can be prevented.
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. 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.

The surface layer preferably has a refractive index that is not so high as that of the substrate. Preferably, the refractive index of the surface layer is 2 or less. Then, light reflection at the interface between the substrate and the surface layer and the interface between the surface layer and air can be suppressed. In order to reduce the refractive index of the surface layer to 2 or less, a substance having a refractive index of 2 or less is used for the photocatalyst, or if the photocatalyst has a refractive index of 2 or more, another substance having a refractive index of 2 or less is used for the surface layer. To be added. As a photocatalyst having a refractive index of 2 or less, tin oxide (refractive index: 1.9) or the like can be used. 2
Photocatalysts having the above refractive index include anatase type titanium oxide (refractive index 2.5) and rutile type titanium oxide (refractive index 2.7). In this case, other substances having a refractive index of 2 or less, For example, calcium carbonate (refractive index 1.6), calcium hydroxide (refractive index 1.6), magnesium carbonate (refractive index 1.5), strontium carbonate (refractive index 1.5), dolomite (refractive index 1.7). ), Calcium fluoride (refractive index 1.4), magnesium fluoride (refractive index 1.4), silica (refractive index 1.5), alumina (refractive index 1.6), silica sand (refractive index 1.6). ), Montmorillonite (refractive index 1.
5), kaolin (refractive index 1.6), sericite (refractive index 1.6), zeolite (refractive index 1.5), tin oxide (refractive index 1.9) and the like may be added to the surface layer.

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 and fungi attached to the surface even in a dark place.

On the surface layer, Pt, Pd, Ru, R
A platinum group metal such as h, Ir, Os can be added. The surface layer to which the metal is added can enhance the oxidation-reduction activity of the photocatalyst and improve the deodorizing and purifying action and the like. Further, when a solid superacid other than the photocatalyst is added, since the acidity of the solid superacid is improved by the addition of the platinum group metal, the hydrophilicity maintenance property is also improved and the formation of a water film of the adhered water is further promoted. Also, the hydrophilicity maintaining property is improved when the photocatalyst is not irradiated with the excitation light for a certain period of time.

When the substrate is a glass containing alkali network modifying ions such as sodium (soda lime glass, parallel plate glass, etc.), an intermediate layer such as silica may be formed between the substrate and the surface layer. Good. 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.

The term "hydrophilic" refers to the property of easily fitting into the surface when water is dropped, and generally means a state where the water wetting angle is less than 90 °. The term “high hydrophilicity” in the present invention refers to a property that is highly compatible when water is dropped on the surface, and more specifically, a state where the water wetting angle is about 10 ° or less. In particular, as disclosed in PCT / JP96 / 00734, the water wetting angle is preferably 10 ° or less, more preferably 5 ° or less, as disclosed in PCT / JP96 / 00734.

The solid superacid in the present invention refers to a strong acid containing a solid oxide having a Hammett acidity function Ho ≦ -11.93 as a constituent, and specifically, sulfuric acid-supporting Al.
₂ O ₃ , sulfuric acid supported TiO ₂ , sulfuric acid supported ZrO ₂ , sulfuric acid supported SnO ₂ , sulfuric acid supported Fe ₂ O ₃ , sulfuric acid supported SiO ₂ ,
Sulfuric acid supported HfO ₂ , TiO ₂ / WO ₃ , WO ₃ / snO
₂ , WO ₃ / ZrO ₂ , WO ₃ / Fe ₂ O ₃ , SiO ₂
-Al ₂ O ₃ or the like can be suitably used.

Next, a method for forming the surface layer will be described. First, the production method in the case where the surface layer is composed of only the photocatalyst will be described by taking the case where the photocatalyst is anatase type titanium oxide as an example. In this case, there are roughly three methods. One method is a sol coating and firing method, the other method is an organic titanate method, and the other method is an electron beam evaporation method. (1) Sol-coating and firing method Anatase-type titanium oxide sol is applied to the surface of a substrate by a method such as spray coating, dip coating, flow coating, spin coating, or roll coating, and then fired. (2) Organic titanate method Titanium alkoxide (tetraethoxy titanium, tetramethoxy titanium, tetrapropoxy titanium, tetrabutoxy titanium, etc.), titanium acetate, titanium chelate, etc. are added with a hydrolysis inhibitor (hydrochloric acid, ethylamine, etc.). , After diluting with a non-aqueous solvent such as alcohol (ethanol, propanol, butanol, etc.), while partially or completely proceeding the hydrolysis, the mixture is spray-coated, dip-coated, Apply by methods such as flow coating method, spin coating method, roll coating method,
dry. By drying, the hydrolysis of the organic titanate is completed to produce titanium hydroxide, and a layer of amorphous titanium oxide is formed on the surface of the base material by dehydration-condensation polymerization of the titanium hydroxide. Thereafter, the amorphous titanium oxide is calcined at a temperature equal to or higher than the crystallization temperature of anatase to cause a phase transition from the amorphous titanium oxide to the anatase titanium oxide. (3) Electron beam evaporation method An amorphous titanium oxide layer is formed on the surface of a substrate by irradiating a titanium oxide target with an electron beam. After that, firing at a temperature higher than the crystallization temperature of anatase,
Phase transition of amorphous titanium oxide to anatase titanium oxide.

Next, the case where the surface layer is composed of a photocatalyst and silica will be described by taking the case where the photocatalyst is anatase type titanium oxide as an example. In this case, for example, there are the following three methods. One method is the sol coating firing method, the other is the organic titanate method, the other is 4
This is a functional silane method. (1) Sol coating and baking method A mixture of anatase-type titanium oxide sol and silica sol is applied to the substrate surface by a method such as a spray coating method, a dip coating method, a flow coating method, a spin coating method, and a roll coating method, and then fired. I do. (2) Organic titanate method Titanium alkoxides (tetraethoxytitanium, tetramethoxytitanium, tetrapropoxytitanium, tetrabutoxytitanium, etc.), titanium acetate, titanium chelate, and other organic titanates are added with a hydrolysis inhibitor (hydrochloric acid, ethylamine, etc.) and silica sol. Add alcohol (ethanol,
After diluting with a non-aqueous solvent such as propanol, butanol, etc., and then allowing the hydrolysis to proceed partially or completely, the mixture is spray-coated, dip-coated, flow-coated,
It is applied by a method such as spin coating or roll coating and dried. By drying, the hydrolysis of the organic titanate is completed to produce titanium hydroxide, and a layer of amorphous titanium oxide is formed on the surface of the base material by dehydration-condensation polymerization of the titanium hydroxide. Thereafter, the amorphous titanium oxide is calcined at a temperature equal to or higher than the crystallization temperature of anatase to cause a phase transition from the amorphous titanium oxide to the anatase titanium oxide. (3) Tetrafunctional silane method A mixture of tetraalkoxysilane (tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, tetramethoxysilane, etc.) and anatase type titanium oxide sol is spray-coated or dip-coated on the surface of a substrate. , A flow coating method, a spin coating method, a roll coating method, or the like, and if necessary, hydrolyzing to form silanol, and then silanol is subjected to dehydration condensation polymerization by a method such as heating.

Next, the case where the surface layer is composed of a photocatalyst and a solid superacid is described by taking as an example the case where the photocatalyst is anatase type titanium oxide and the solid superacid is TiO ₂ / WO ₃ . In this case, a method of mixing an ammonia solution of tungstic acid and an anatase-type titanium oxide sol and, if necessary, diluting the mixture with a diluting liquid (water, ethanol, etc.) on the surface of the base material by spray coating, dip coating, or the like. It is applied by a method such as a flow coating method, a spin coating method, and a roll coating method, and is baked.

Next, the case where the surface layer is composed of a photocatalyst and silicone will be described by taking the case where the photocatalyst is anatase type titanium oxide as an example. The method in this case is to mix a coating composed of uncured or partially cured silicone or a precursor of silicone and anatase type titanium oxide sol, and hydrolyze the precursor of silicone as needed, and then mix the mixture. Spray coating method on the surface of the substrate,
It is applied by a method such as a dip coating method, a flow coating method, a spin coating method, a roll coating method, etc., and a hydrolyzate of a silicone precursor is subjected to dehydration polycondensation by a method such as heating to obtain anatase type titanium oxide particles. A surface layer made of silicone is formed. The formed surface layer, by photoexcitation of anatase type titanium oxide by irradiation with light including ultraviolet rays, at least a part of the organic group bonded to the silicon atom in the silicone molecule is substituted with a hydroxyl group, and further on it. A physically adsorbed water layer is formed,
It exhibits a high degree of hydrophilicity. Here, the precursor of silicone, methyltrimethoxysilane, methyltriethoxysilane, methyltributoxysilane, methyltripropoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltributoxysilane, ethyltripropoxysilane, Phenyltrimethoxysilane, phenyltriethoxysilane, phenyltributoxysilane,
Phenyltripropoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, dimethyldibutoxysilane, dimethyldipropoxysilane, diethyldimethoxysilane, diethyldiethoxysilane, diethyldibutoxysilane, diethyldipropoxysilane, phenylmethyldimethoxysilane, phenylmethyl Diethoxysilane, phenylmethyldibutoxysilane, phenylmethyldipropoxysilane, γ-glycidoxypropyltrimethoxysilane, a hydrolyzate thereof, and a mixture thereof can be suitably used.

[0025]

[Example] First, a primer coating (Toshiba silicone, a coating in which PH93 was diluted 6 times with a toluene solvent) was applied to a 10 cm square PMMA plate surface by a spray coating method, and then dried at room temperature to apply a primer resin to a substrate. Coated with layers. Next, a silicone-based hard coating agent (Toshiba Silicone, Tosgard) was applied by a flow coating method and dried at 90 ° C. for 3 hours to form a hard coat layer on the primer resin layer. Furthermore, the surface of the hard coat layer was treated with a corona surface treatment device (Kasuga Denki) using a wire electrode as an electrode, the gap between the electrode tip and the sample surface was 2 mm, the voltage was 26 kV, the frequency was 39 kHz, and the sample feed rate was 4.2 m / min. A high frequency corona discharge treatment was performed under the conditions to obtain a # 1 sample. On the other hand, 56 parts by weight of anatase-type titanium oxide sol (TA-15, average particle size 12n
m) and 33 parts by weight of silica sol (Nippon Synthetic Rubber, Glasca A liquid) are mixed and diluted with ethanol, and then 11 parts by weight of methyltrimethoxysilane (Nippon Synthetic Rubber, Grasca B).
Liquid) was added to prepare a titanium oxide-containing coating composition.
The above coating composition was applied to the # 1 sample by the flow coating method, and heat-treated at 90 ° C. for 3 hours to be cured.
A sample was obtained. This # 2 sample was used as an ultraviolet light source (Sankyo Denki,
A # 3 sample was obtained by irradiating the surface of the sample with ultraviolet light at a UV illuminance of 0.6 mW / cm ² for about 48 hours using a black light blue (BLB) fluorescent lamp. 10c for comparison
An m-square PMMA plate sample was also prepared. First, # 3 sample and P
A water drop was dropped on the MMA plate sample, and the state after the drop was observed and the contact angle with water was measured. Here, the contact angle with water is measured using a contact angle measuring device (Kyowa Interface Science, CA-X150).
Evaluation was made based on the contact angle with water 30 seconds after dropping. as a result#
When a water droplet was dropped from the microsyringe on one surface of one sample, it was observed that the water droplet spreads uniformly on the surface of the sample in the form of a water film. Further, the contact angle with water after 30 seconds was highly hydrophilized to about 0 °. On the other hand, in the # 2 sample, when a water droplet was dropped from the microsyringe on the surface of the sample, the water droplet slightly adapted to the surface, but did not reach a uniform water film shape. The contact angle with water after 30 seconds is 60
Was ゜. Next, the # 2 sample and the PMMA plate sample were blown to examine whether or not fogging occurred. As a result, the PMMA plate sample was fogged, whereas the # 2 sample was not fogged. Further, the # 2 sample was left in the dark for 1 week thereafter to obtain the # 3 sample. Then, for the # 3 sample, the contact angle with water was similarly measured by a contact angle measuring device. As a result, when a water drop was dropped on the sample surface from the microsyringe on the # 3 sample, it was observed that the water droplet spread uniformly on the sample surface like a # 1 sample. The contact angle with water was maintained at about 1 °. Next, the presence or absence of fogging after spraying was observed for the # 3 sample. as a result,
No cloudiness was observed.

[0026]

According to the present invention, by providing a surface layer containing substantially transparent photocatalytic titanium oxide particles on the surface of a road mirror, the surface of the surface layer becomes hydrophilic in response to photoexcitation of the photocatalyst. Moisture condensed condensed water and / or water droplets that have adhered and spread evenly over the surface of the layer, and are prevented from being clouded or covered by the moisture condensed water and / or water droplets.

[Brief description of drawings]

FIG. 1 is a diagram showing a surface structure of an anti-fog road mirror according to the present invention.

FIG. 2 is a view showing another surface structure of the anti-fog road mirror according to the present invention.

Claims (10)

[Claims] 1. A surface layer of a road mirror substrate is provided with a surface layer containing substantially transparent photocatalyst particles, and in response to photoexcitation of the photocatalyst, the surface of the layer exhibits hydrophilicity and is thus attached. An anti-fog road mirror in which condensed water and / or water droplets of moisture are spread evenly on the surface of the layer to prevent the condensed water of moisture and / or water droplets from being clouded or covered. 2. The anti-fog road mirror according to claim 1, wherein the surface layer further contains silica. 3. The anti-fog road mirror according to claim 1, wherein the surface layer further contains a solid superacid. 4. The anti-fog road mirror according to claim 1, wherein the surface layer further contains silicone. 5. The surface of the surface layer exhibits hydrophilicity of 10 ° or less in terms of contact angle with water in response to photoexcitation of the photocatalyst. Anti-fog road mirror. 6. The anti-fog road mirror according to claim 1, wherein the surface layer has a thickness of 0.4 μm or less. 7. The anti-fog road mirror according to claim 1, wherein the surface layer has a thickness of 0.2 μm or less. 8. A hydrophilic protective layer is further provided on the surface of the surface layer.
The anti-fog road mirror according to item 4. 9. The anti-fog road mirror according to claim 1, wherein the surface layer has a refractive index of 2 or less. 10. A step of preparing the anti-fog road mirror according to claim 1, wherein the surface of said layer is made hydrophilic by photoexciting a photocatalyst contained in the surface layer of said mirror, and thus adhered. A method of defrosting a road mirror, comprising the step of allowing condensed water and / or water droplets of the formed moisture to spread uniformly on the surface of the layer.