JPH09215568A - Plastic mirror - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain a hydrophilic nature of a front surface for a long time which has not been known in prior art, and which can be restored even in having been lost. SOLUTION: A solution prepared by adding trimethoxymethyl silane after silicasol is addeed to anatase type titansol (having solute concentration of 10wt.%, a nitric acid dispersion type and a pH value of 0.8) having an averaged particle size of 0.01μm and is diluted with ethanol, is applied over the surface of a transparent plastic substrate 1 which has been previously formed on its back surface with a reflective layer 2 and a protecting layer 3, and thereafter, is heated and solidified at a temperature of 100 deg.C in order to form an outer surface layer 4 having a film thickness of 0.1μm. The outer surface layer 4 exhibits a hydrophilic nature due to reaction of titanium oxide.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a plastic mirror excellent in antifogging property, cleaning property and self-cleaning property.

[0002]

2. Description of the Related Art Conventionally, various measures have been taken in order to improve the antifogging property of a mirror. For example, a method of maintaining the surface temperature of the mirror above the dew point temperature. A method of absorbing water on the surface before dew condensation by forming a porous layer on the surface. A method of forming a water-repellent resin film on the surface. Etc. are known.

In the case of the above-mentioned method, it is necessary to provide the heater wire, and it takes time from the time when the heater wire is energized to the time when the defrosting effect is exhibited. In the case of the method (1), water absorption lowers the surface hardness, easily causes scratches, and easily causes image distortion. In the case of the method, when water is dried on the water-repellent resin film, the hydrophobic stain component remains as it is, and since this hydrophobic stain is more easily adapted to the surface of the substrate than water, it is difficult to wash it off with water. On the contrary, dirt becomes conspicuous.

It has also been attempted to introduce hydrophilic groups into the surface of the substrate by surface treatment with a surfactant, plasma discharge treatment or corona discharge treatment.
Poor durability. Therefore, Japanese Utility Model Application Laid-Open No. 3-129357 proposes a means for generating hydrophilic acidic groups on the surface of the hard coat layer by irradiation with ultraviolet rays of 300 nm or less and treatment with an alkaline aqueous solution.

[0005]

[Problems to be Solved by the Invention] Actual Kaihei 3-12935
Even if the plastic mirror surface is made hydrophilic by the method disclosed in Japanese Patent Publication No. 7, the hydrophilicity cannot be maintained, and the antifogging effect is lost in a short period of time. Further, once the hydrophilic acidic group is lost, the hydrophilicity cannot be restored,
The antifogging effect is lost, and further, the cleanability when stains adhere is not sufficient.

[0006]

According to the present invention, the hydrophilicity of the mirror surface can be maintained and restored, and when water adheres, it has a self-cleaning property of purifying the surface with the water, and is washed with water. It is an object of the present invention to provide a plastic mirror excellent in cleanability due to.

That is, in the plastic mirror according to the present invention, a hydrophilic surface layer containing an optical semiconductor is formed directly or through a hard coat layer on the front surface side of a transparent plastic substrate having a reflective layer formed on the back surface side.

In the photo semiconductor, electrons in the valence band are hard to be excited in the conduction band at an energy of about phonon oscillation, but when a photon of a specific wavelength or less is irradiated, the electrons in the valence band are excited in the conduction band. , A semiconductor capable of generating conduction electrons and holes. Specific examples include titanium oxide, zinc oxide, tin oxide, ferric oxide, tungsten trioxide, dibismuth trioxide, and strontium titanate.

In order to impart hydrophilicity to the surface layer, when the optical semiconductor exhibits hydrophilicity, the optical semiconductor can be used alone, but the optical semiconductor does not exhibit hydrophilicity. In some cases, the surface layer is formed by mixing with another hydrophilic substance. Examples of hydrophilic substances include silicone resins containing a large amount of polar functional groups such as hydroxyl groups in their side chains.

The photohydrophilic effect of the optical semiconductor is different from the hydrophilic effect of an inorganic hydrophilic substance such as a conventional glazed tile. That is, in the conventional glazed tiles, etc., carboxylic acids other than water, alcohols, and soiling components having amphoteric functional groups such as surfactants are easily attached to the asymmetric group on the surface, so that they are hydrophilic during production. Even if it has, since it has no mechanism for maintaining hydrophilicity, it becomes hydrophobic over time.

On the other hand, in the present invention, by the action of the photo-semiconductor such as titanium oxide, the photo-semiconductor is irradiated with ultraviolet rays to generate holes and electrons. The hydrophilicity is improved by increasing the polarity of the base material surface and increasing the amount of physically adsorbed water on the base material surface. As long as the physically adsorbed water layer is maintained on the substrate surface, hydrophobic stains and stain components having amphoteric functional groups cannot adhere to the substrate, maintaining hydrophilicity and preventing Dirtyness is maintained.

Further, by storing in an environment that is not exposed to ultraviolet rays, even if hydrophobic stains or stain components having an amphoteric functional group are fixed to the substrate, it is possible to physically expose the substrate surface by simply irradiating it with ultraviolet rays. By forming and increasing the amount of adsorbed water, the stain component cannot be fixed to the base material as described above, the hydrophilicity is restored and the antifouling property is exhibited. Furthermore, by improving the hydrophilicity and maintaining or recovering it, water droplets are not formed on the surface of the substrate, so that dew condensation on the surface of the mirror is prevented, visible light is not scattered, and the antifogging effect is exerted. To be done.

The surface layer is formed directly on the surface of the transparent plastic substrate or on the hard coat formed on the surface of the transparent plastic substrate. In each case,
Since the hydrophilic surface layer is less likely to be charged than an acrylate-based hard coat, dust is less likely to adhere to the hydrophilic surface layer.

On the other hand, in a preferred embodiment of the present invention, in addition to the above-described optical semiconductor such as titanium oxide, a water-storing substance such as silica or silicone resin is contained in the hydrophilic surface layer. When the hydrophilic surface layer contains a water-storing substance, the water stored in the structure of the water-storing substance is gradually released, and the effect of improving hydrophilicity is recognized by weaker UV irradiation. In addition, since it is possible to delay the hydrophobization phenomenon when left in the dark, it becomes possible to maintain the hydrophilicity by irradiation with ultraviolet rays for a longer period of time.

In particular, silica or silicone resin has a refractive index of 1.4 to 1.5, which is close to the refractive index of a transparent plastic substrate (for example, acrylic is 1.49), so that distortion is unlikely to occur when it is used as a mirror. .

Further, in a preferred embodiment of the present invention, the thickness of the hydrophilic surface layer is 0.3 μm or less.
By doing this, you can maintain transparency

[0017]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of a plastic mirror according to the first embodiment. In the plastic mirror, a reflective layer 2 and a protective layer 3 are formed in advance on the back surface side of a transparent plastic substrate 1. Here, as the transparent plastic substrate 1,
Acrylic, polycarbonate, polyester, polystyrene, vinyl chloride and the like can be mentioned, and the reflection layer 2 is formed by vapor deposition or plating of silver, aluminum, nickel or the like.

When the base material is polycarbonate, silica sol is added to anatase type titanium sol having an average particle size of 0.01 μm (solute concentration 10% by weight, nitric acid dispersion type, pH 0.8), diluted with ethanol, and then trimethoxy. The solution containing methylsilane was applied to the surface of the transparent plastic substrate 1. After that, it is heated and solidified at 100 ° C. to obtain a film thickness of 0.
A 1 μm surface layer 4 was formed. Here, the ratio of the solid content weight of titanium oxide to the sum of the solid content weight (resin weight) of silica and trimethoxymethylsilane in the surface layer 4 and the solid content weight of titanium oxide was 50%.

FIG. 2 is a cross-sectional view of the plastic mirror according to the second embodiment. In this embodiment, the transparent plastic substrate 1 is not directly formed with the surface layer 4 but is made of a silicone resin. The hard coat layer 5 is formed.

Next, Examples 1 and 2 and Comparative Examples 1 and 2 will be compared for hydrophilicity. In addition, Comparative Example 1 is Example 1,
A transparent plastic substrate similar to that of No. 2 has a structure in which a surface layer is not formed, and Comparative Example 2 has a transparent plastic substrate similar to that of Examples 1 and 2 in which a surface layer made of a silicone resin (not including an optical semiconductor). ) Was formed.

0.5 m in Examples 1 and 2 and Comparative Examples 1 and 2.
Irradiation with a W / cm ² BLB lamp was carried out, and the time change of the contact angle with water was measured. As a result of the measurement, Examples 1 and 2 are 200
Within a time, the contact angle with water decreased to 0 ° and became superhydrophilic, but the contact angles with water of Comparative Examples 1 and 2 remained 90 ° for the former and 70 ° for the latter.

As described above, the surface layers of Examples 1 and 2 were made superhydrophilic because the action of titanium oxide (optical semiconductor) in the surface layer caused the Si-R in the trimethoxymethylsilane resin.
It is considered that (R is an organic group) bond is changed to a Si—OH bond.

Further, an experiment in which the ultraviolet rays were irradiated only in the daytime and not in the nighttime was carried out in Examples 1 and 2 and Comparative Examples 1 and 2. As a result, Examples 1 and 2 maintained the above superhydrophilic state for 10 months or longer, but Comparative Examples 1 and 2 showed no improvement in hydrophilicity. This is because even if both a hydrophilic functional group such as a lower carboxylic acid and a hydrophobic functional group such as a surfactant are attached to the upper part of the Si-OH bond, the hydrophilic property that is adsorbed on the upper part of the Si-OH bond. The functional group is easily released by electrons or holes generated by titanium oxide. However,
Since the Si-OH bond exhibits strong hydrophilicity, a hydrophilic functional group is likely to be immediately adsorbed on the Si-OH bond.
At this time, components containing both a hydrophilic functional group and a hydrophobic functional group, water in the air, hydroxide ions, etc. can be adsorbed, but only hydrophilic functional groups such as water in the air, hydroxide ions, etc. The component consisting of is more easily adsorbed than the component containing both the hydrophilic functional group and the hydrophobic functional group. As a result, it is considered that the surface layer becomes occupied with only the hydrophilic functional group as the above-mentioned separation is repeated, and the hydrophilicity is maintained.

[0024] Regarding Examples 1 and 2 above, the presence or absence of cloudiness was confirmed after breathing, but it was not observed. Also, no double image was observed. Furthermore, the hardness of the surface layer 4 was 2H or more.

[0025]

As described above, according to the present invention, a hydrophilic surface layer containing an optical semiconductor is formed on the front surface side of a transparent plastic substrate having a reflective layer formed on the back surface side.
It is possible to provide a plastic mirror which can maintain the antifogging effect for a long period of time and can recover hydrophilicity at an early stage by irradiating with ultraviolet rays even if hydrophilicity is once lost.

Further, the plastic mirror according to the present invention is excellent in self-cleaning property and easiness of cleaning. Furthermore, since the hydrophilic surface layer is less likely to be charged as compared with the hard coat, dust is less likely to adhere thereto.

[Brief description of drawings]

FIG. 1 is a sectional view of a plastic mirror according to the present invention.

FIG. 2 is a sectional view of a plastic mirror according to another embodiment.

[Explanation of symbols]

1 ... Transparent plastic substrate, 2 ... Reflective layer, 3 ... Protective layer,
4 ... surface layer, 5 ... hard coat.

Claims (4)

[Claims] 1. A plastic mirror characterized in that a hydrophilic surface layer containing an optical semiconductor is formed on the front surface side of a transparent plastic substrate having a reflective layer formed on the back surface side, directly or through a hard coat layer. . 2. The plastic mirror according to claim 1, wherein the hydrophilic surface layer contains a water storage substance. 3. The plastic mirror according to claim 2, wherein the water storage substance is silica or silicone resin. 4. The plastic mirror according to claim 1, wherein the hydrophilic surface layer has a thickness of 0.3 μm or less.