BEAM SPLITTER WITH PHOTOCATALYTIC COATING AND FABRICATION METHOD THEREOF

Abstract

A method for making a beam splitter with photocatalytic coating is disclosed. First, a TiO.sub.2—SiO.sub.2 sol, a SiO.sub.2 sol, and an anatase TiO.sub.2 preform sol are prepared. A glass substrate having two opposite surfaces is provided. The two opposite surfaces of the glass substrate is coated with the TiO.sub.2—SiO.sub.2 sol, the SiO.sub.2 sol, and the anatase TiO.sub.2 preform sol by dip-coating, thereby forming a coated glass substrate with a multi-layer optical coating on each of the two opposite surfaces. The multi-layer optical coating comprises a TiO.sub.2—SiO.sub.2 coating, a SiO.sub.2 coating, and an anatase TiO.sub.2 preform coating. The coated glass substrate is subjected to an anneal process. The coated glass substrate is cut, thereby forming the beam splitter with photocatalytic coating.

Claims

1. A method for fabricating a beam splitter with photocatalytic coating, comprising: preparing a TiO.sub.2—SiO.sub.2 sol, a SiO.sub.2 sol, and an anatase TiO.sub.2 preform sol; providing a glass substrate having two opposite surfaces; dip-coating said two opposite surfaces of said glass substrate with said TiO.sub.2—SiO.sub.2 sol, said SiO.sub.2 sol, and said anatase TiO.sub.2 preform sol, thereby forming a coated glass substrate with a multi-layer optical coating on each of said two opposite surfaces, wherein said multi-layer optical coating comprises a TiO.sub.2—SiO.sub.2 coating, a SiO.sub.2 coating, and an anatase TiO.sub.2 preform coating; subjecting said coated glass substrate to an anneal process; and cutting said coated glass substrate, thereby forming said beam splitter with photocatalytic coating.

2. The method according to claim 1, wherein said dip-coating said two opposite surfaces of said glass substrate comprises: immersing said glass substrate in said TiO.sub.2—SiO.sub.2 sol, said SiO.sub.2 sol, or said anatase TiO.sub.2 preform sol; withdrawing said glass substrate from said TiO.sub.2—SiO.sub.2 sol, said SiO.sub.2 sol, or said anatase TiO.sub.2 preform sol at a constant withdrawal speed; and baking said glass substrate at 150-250° C.

3. The method according to claim 1, wherein said anneal process is performed at 400-600° C.

4. The method according to claim 1, wherein said multi-layer optical coating has refection at blue spectral region.

5. The method according to claim 1, wherein a thickness of said TiO.sub.2 coating=blue light wavelength/(4×TiO.sub.2 coating refractive index), a thickness of said SiO.sub.2 coating=blue light wavelength/(4×SiO.sub.2 coating refractive index), and a thickness of said TiO.sub.2—SiO.sub.2 coating=blue light wavelength/(4×TiO.sub.2 —SiO.sub.2 coating refractive index).

6. The method according to claim 1, wherein said TiO.sub.2—SiO.sub.2 sol, said SiO.sub.2 sol and said anatase TiO.sub.2 preform sol use titanium alkoxide and/or silicon alkoxide as a precursor, and wherein said TiO.sub.2—SiO.sub.2 sol, said SiO.sub.2 sol and said anatase TiO.sub.2 preform sol are prepared by hydrolysis, condensation and peptization in alcohol solvent.

7. The method according to claim 1, wherein said TiO.sub.2—SiO.sub.2 sol, said SiO.sub.2 sol and said anatase TiO.sub.2 preform sol are prepared to impart anti-glare effect to an automobile rearview mirror made from said beam splitter, which avoids glare from a following vehicle headlight to a driver, by adjusting a reflectance of said beam splitter, and by adjusting a solid content ratio of said TiO.sub.2—SiO.sub.2 sol, said SiO.sub.2 sol and said anatase TiO.sub.2 preform sol between 1-0.

8. The method according to claim 1, wherein a SiO.sub.2/TiO.sub.2 solid content ratio in said TiO.sub.2—SiO.sub.2 sol ranges between 1-0, and wherein said beam splitter reflects blue light at 440 nm and an reflectance thereof is between 55-65%.

9. The method according to claim 2, wherein an ambient air temperature and humidity is controlled and said withdrawal speed is adjusted according to a solid content of each of aid TiO.sub.2—SiO.sub.2 sol, said SiO.sub.2 sol and said anatase TiO.sub.2 preform sol, and wherein said glass substrate is baked at 150-250° C. for 10 minutes, and annealed at 400-600° C. for 1.0 hour, such that a peak of a reflective spectrum of said multi-layer optical coating is at 440 nm.

10. The method according to claim 1, wherein a peak of a reflection spectrum of an optical coating of each of said TiO.sub.2—SiO.sub.2 sol, said SiO.sub.2 sol and said anatase TiO.sub.2 preform sol is at 440 nm after baking and annealing, and then each sol is laminated and coated according to this condition to make anatase TiO.sub.2/SiO.sub.2/SiO.sub.2—TiO.sub.2/glass substrate/SiO.sub.2—TiO.sub.2/SiO.sub.2/anatase TiO.sub.2 blue mirror with a blue light reflectance at 440 nm between 55-65%.

11. The method according to claim 10, wherein said anatase TiO.sub.2 preform sol uses titanium alkoxide as a precursor, hydrolyzed and condensed in ethanol, peptized by HNO.sub.3, so as to form said anatase TiO.sub.2 preform sol, and wherein an anatase TiO.sub.2 coating formed by said dip-coating, baking and annealing has photocatalytic, hydrophilic, and self-cleaning effects.

12. The method according to claim 11, wherein said anatase TiO.sub.2/SiO.sub.2/SiO.sub.2—TiO.sub.2/glass substrate/SiO.sub.2—TiO.sub.2/SiO.sub.2/anatase TiO.sub.2 blue mirror has said anatase TiO.sub.2 coating on its outer surface, so under ultraviolet rays of sunlight, it produces photocatalyst effects comprising hydrophilic phenomenon, chemical redox reaction, sterilization, mildew prevention, self-cleaning, and decontamination.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is a schematic cross-sectional diagram showing an exemplary coating structure of a photocatalyst beam splitter according to one embodiment of the invention.

[0023] FIG. 2 shows the reflection spectrum of various beam splitter coating structures.

[0024] FIG. 3 is a flow diagram showing an exemplary process flow of making a photocatalyst beam splitter according to one embodiment of the invention.

DETAILED DESCRIPTION

[0025] In the following detailed description of the disclosure, reference is made to the accompanying drawings, which form a part hereof, and in which is shown, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention.

[0026] Other embodiments may be utilized and structural, logical, and materials changes may be made without departing from the scope of the present invention. Therefore, the following detailed description is not to be considered as limiting, but the embodiments included herein are defined by the scope of the accompanying claims.

[0027] The present invention pertains to a beam splitter such as a blue mirror with a photocatalytic coating and a manufacturing method thereof. In general, a glass substrate is subjected to a dip-coating process including sequentially immersing the glass substrate into TiO.sub.2—SiO.sub.2, SiO.sub.2 and TiO.sub.2 colloidal sol compositions to form multi-layer coatings on opposite surfaces of the glass substrate. Depending upon the optical requirements, various sol compositions are prepared. The coated glass substrate formed by dip-coating and baking processes may comprise a layered structure that may be represented by: TiO.sub.2 (anatase)/SiO.sub.2/SiO.sub.2—TiO.sub.2/glass substrate/SiO.sub.2—TiO.sub.2/SiO.sub.2/TiO.sub.2 (anatase). The coated glass substrate may be subjected to annealing, cutting, and bending with heat. In addition, a metal coating or glue may be formed or applied on the coated glass substrate, and the coated glass substrate may be mounted at a casing so as to form an exterior rearview blue mirror assembly for vehicles.

[0028] The vehicles emit exhaust, grease and particles when driving, and the ambient air contains various types of exhaust, grease and particles, which may fall on the surface of the vehicles and the exterior rearview mirror along with wind and rain. The grease and particles make the surface of the exterior rearview mirror become hydrophobic, and therefore the mirror surface is covered with rain droplets in rainy days, which make the vehicle driver difficult to clearly observe the environment on both sides of the vehicle through the exterior rearview mirror, which affects the safety of driving.

[0029] The sol compositions of TiO.sub.2—SiO.sub.2, SiO.sub.2 and TiO.sub.2 are prepared with alcohol solvent. Durable tri-layer, double-sided optical grade coatings are formed by double-sided dip-coating, baking and annealing on the glass substrate. Depending upon the requirements, high-reflection coatings with broadband reflection at blue, green or red color may be fabricated. The fabricated coated glass substrate with tri-layer, double-sided optical grade coatings is particularly suited for the applications of rearview mirrors for vehicles, which can reduce the amount of reflected light emanated from the following car on the road, which is reflected to the driver's eyes through dusty air and dust on the car window and the rearview mirror. Due to the low frequency of the light spectrum of the vehicle headlights, the incident light is prone to be scattering and absorbed by the window glass and rearview mirror glass. The reflection spectrum that enters the driver's eyes is mostly low-frequency red-yellow spectral region, so the eyes will be more likely to produce low-frequency red-yellow light glare to the rear car lights.

[0030] Conventional blue mirrors are mainly used in interior rearview mirrors, but not suitable for exterior rearview mirrors, which are disposed on the left and right sides of a vehicle. The present invention addresses this issue by providing the TiO.sub.2 coating on the outer surface of the blue mirror glass, which contains a large amount of anatase TiO.sub.2 structure. Such a blue mirror can produce a photocatalytic effect under the ultraviolet rays of sunlight and produce effects of super-hydrophilic phenomena, chemical oxidation and reduction, sterilization and mildew prevention, self-cleaning and decontamination. The present invention is particularly suited for the applications of exterior rearview mirrors disposed on both sides of a vehicle. In addition to the reduction of glare of the car headlights when driving at night, the mirror has a photocatalytic effect, which makes the mirror self-cleaning and hydrophilic. When driving on rainy days, the rain drops on the mirror surface form a water film because the mirror surface is hydrophilic, so that the driver in the car can clearly observe the environment on both sides of the car. Therefore, the driving safety is improved.

[0031] The present invention provides TiO.sub.2 sol, which is anatase TiO.sub.2 preform sol. The glass substrate is subjected to dip-coating in respective sol compositions to form coatings on both sides of the glass substrate. The glass substrate is immersed and baked three times with SiO.sub.2—TiO.sub.2, SiO.sub.2 and anatase TiO.sub.2 preform sol, thereby forming a TiO.sub.2 (anatase)/SiO.sub.2/SiO.sub.2—TiO.sub.2/glass plate/SiO.sub.2—TiO.sub.2/SiO.sub.2/TiO.sub.2 (anatase) tri-layer, sol-coated glass substrate, which has reflection at blue spectral region. The coated glass substrate with anti-glare effect may be applicable to the interior rearview mirrors, which provides the driver with a clear view of the rear environment. The coated glass substrate with anti-glare effect may be particularly applicable to the left and right exterior rearview mirrors of vehicles, which provides hydrophilic and anti-fog effects on rainy days, so that the driver can clearly see the side view vision of the environment.

[0032] The photocatalyst rearview blue mirror of the present invention has a TiO.sub.2 coating on the outmost surface of the blue mirror, which is mainly of TiO.sub.2 anatase structure. The photocatalyst effect is produced under the irradiation of sunlight and ultraviolet rays, and effects including: super-hydrophilic phenomenon, chemical oxidation and reduction, sterilization and mildew prevention, self-cleaning and decontamination can be provided. Therefore, the physical function of the product of the present invention is represented by the blue mirror in the optical coating, and the photocatalyst in the chemical function. Therefore, the present invention beam splitter with photocatalytic and optical coatings is also referred to as a “photocatalyst blue mirror”. If the application of sol optical coating products is expanded, it can be applied to photocatalyst optical coating products.

[0033] According to the embodiments of the invention, the coatings on the blue mirror can be formed by sol-gel dipping. The glass substrate is dip-coated by the sol-gel dipping method, and the coatings are symmetrical on both sides of the glass substrate. The double-sided symmetrical optical coating may be formed by the following steps. First, the glass substrate is treated by acid, alkaline, water and alcohol solution. The glass substrate is then washed in ultrasonic bath. After drying, the glass substrate is hung vertically on an arm of a lifter. The cleaned glass substrate is then vertically immersed in the sol. When the sol is stationary, the glass plate is withdrawn from the sol at a constant speed such that coating occurs due to the vertical flow of sol onto the elevated surface of the glass substrate. At the same time, the solvent in the sol evaporates. Alcohol evaporation and sol gelized reaction occurs because the water vapor in the air reacts with the alkoxide in the sol. As the glass substrate is withdrawn at a constant speed, the coating is bonded to the glass substrate at a constant speed to form a gelized film that is designated by “(g)”. After the aforesaid sol coating, the coated glass substrate is took off the lifter, placed in an oven, and then baked at 150-250° C. for about 10 minutes, thereby producing a baked coating, which is designated by “(b)”. Subsequently, the coated glass substrate is subjected to cooling for subsequent sol coating.

[0034] In order to fabricate the beam splitter with optical coating, the sol optical coating is performed as described above, and the TiO.sub.2—SiO.sub.2 sol coating is first performed to obtain TiO.sub.2—SiO.sub.2 (g)/Glass/TiO.sub.2—SiO.sub.2 (g) coated glass; and then baking is performed to obtain TiO.sub.2—SiO.sub.2 (b)/Glass/TiO.sub.2—SiO.sub.2 (b) coated glass.

[0035] Subsequently, SiO.sub.2 sol coating is perform to coat the TiO.sub.2—SiO.sub.2 (b)/Glass/TiO.sub.2—SiO.sub.2 (b) coated glass, thereby forming SiO.sub.2 (g)/TiO.sub.2—SiO.sub.2 (b)/Glass/TiO.sub.2—SiO.sub.2 (b)/SiO.sub.2 (g) coated glass, and then baked to obtain SiO2 (b)/TiO2—SiO2 (b)/Glass/TiO2—SiO.sub.2 (b)/SiO.sub.2 (b) coated glass.

[0036] Subsequently, TiO.sub.2 sol coating is perform to coat the SiO.sub.2 (b)/TiO.sub.2—SiO.sub.2 (b)/Glass/TiO.sub.2—SiO.sub.2 (b)/SiO.sub.2 (b) coated glass, thereby forming TiO.sub.2 (g)/SiO.sub.2 (b)/TiO.sub.2—SiO.sub.2 (b)/Glass /TiO.sub.2—SiO.sub.2 (b)/SiO.sub.2 (b)/TiO.sub.2 (g) coated glass, and then baked to obtain TiO.sub.2 (b)/SiO.sub.2 (b) /TiO.sub.2—SiO.sub.2 (b)/Glass/TiO.sub.2—SiO.sub.2 (b)/SiO.sub.2 (b)/TiO.sub.2 (b) coated glass.

[0037] Finally, the TiO.sub.2 (b)/SiO.sub.2 (b)/TiO.sub.2—SiO.sub.2 (b)/Glass/TiO.sub.2—SiO.sub.2 (b)/SiO.sub.2 (b)/TiO.sub.2 (b) coated glass is annealed at high temperatures or directly heated at 400-600° C., such that the baked coating is sintered into TiO.sub.2 (A)/SiO.sub.2 (a)/TiO.sub.2—SiO.sub.2 (a)/Glass/TiO.sub.2—SiO.sub.2 (a)/SiO.sub.2 (a)/TiO.sub.2 (A) coated glass, wherein “TiO.sub.2 (A)” represents anatase TiO.sub.2 and “(a)” represents “annealed” coating. As shown in FIG. 1, an exemplary photocatalyst blue mirror sol coating structure is illustrated. After subjecting the glass substrate 100 to the sol optical coating, baking and annealing, the first layer is TiO.sub.2—SiO.sub.2 amorphous coating 110, the second layer is SiO.sub.2 amorphous coating 120, and the third layer is anatase TiO.sub.2 coating 140 are formed. The anatase TiO.sub.2 coating 140 is a photocatalyst layer. According to various embodiments, the TiO.sub.2—SiO.sub.2 coating (110) may have different SiO.sub.2/TiO.sub.2 ratios, for example, SiO.sub.2/TiO.sub.2 ratio=1/1, SiO.sub.2/TiO.sub.2 ratio=2/1, SiO.sub.2/TiO.sub.2 ratio=3/1, or SiO.sub.2/TiO.sub.2 ratio=4/1.

[0038] For the preparation of TiO.sub.2—SiO.sub.2 sol, silicon alkoxide Si(OR).sub.4 is first added to the alcohol solvent ROH. After stirring, it is mixed to form a silicon alkoxide solution. Ethanol EtOH can be used as the solvent. The silicon alkoxide used can be silicon ethoxide Si(OEt).sub.4, silicon methoxide Si(OMe).sub.4, silicon propoxide Si(OPr).sub.4, silicon isopropoxide Si (OPr.sup.i).sub.4, or other silicon alkoxides. A mixture of H.sub.2O:R.sub.1OH=1:2 is prepared, and added dropwise into the stirred silicon alkoxide solution for Si(OR.sub.2).sub.4 hydrolysis to obtain an alcohol solution of Si(OR.sub.2).sub.3OH. Take the equivalent of titanium alkoxide Ti(OR.sub.3).sub.4. The titanium alkoxides may comprise: titanium n-butoxide Ti(OBu.sup.n), titanium isobutoxide Ti(OBu.sup.i).sub.4, titanium tert-butoxide Ti(OBu.sup.t).sub.4, titanium isopropoxide Ti(OPr.sup.i).sub.4, titanium n-propoxide Ti(OPr.sup.n).sub.4, titanium ethoxide Ti(OEt).sub.4, or other titanium alkoxides. Si(OR.sub.2).sub.3OH alcohol solution is added dropwise to the stirred N equivalent Ti(OR.sub.3).sub.4 titanium alkoxide to obtain (OR.sub.2).sub.3SiOT[i](OR.sub.3).sub.3 and (N-1) equivalent Ti(OR.sub.3).sub.4 alcohol solution. Then, N equivalent of H.sub.2O/R.sub.1OH (1:2) mixed solution, which is adjusted to pH=1.0-2.0 with inorganic acid such as hydrochloric acid HCl or nitric acid HNO.sub.3, etc., is added dropwise into stirred alcohol solution of (OR.sub.2).sub.3SiOT(OR.sub.3).sub.3 and 3Ti(OR.sub.3).sub.4, which is hydrolyzed by (OR.sub.2).sub.3SiOT(OR.sub.3).sub.3 and (N-1) equivalent Ti(OR.sub.3).sub.4.

[0039] For the preparation of SiO.sub.2 sol, silicon alkoxide Si(OR.sub.2).sub.4 is added to the ethanol EtOH. The silicon alkoxide may comprise silicon ethoxide Si(OEt).sub.4, silicon methoxide Si(OMe).sub.4, silicon propoxide Si(OPr).sub.4, silicon isopropoxide Si (OPr.sup.i).sub.4, or other silicon alkoxides. After stirring, silicon alkoxide solution is formed. A mixture of H.sub.2O:R.sub.1OH=1:2 is prepared and is adjusted to pH=1.0-2.0 with inorganic acid such as hydrochloric acid HCl or nitric acid HNO.sub.3. Thereafter, 1.0-2.0 equivalents of H.sub.2O/R.sub.1OH solution (pH=1.0-2.0) is added dropwise to 1 equivalent of stirred silicon alkoxide solution.

[0040] For the preparation of TiO.sub.2 sol, titanium alkoxide Ti(OR.sub.3).sub.4 is added to the ethanol EtOH. After stirring, titanium alkoxide solution is formed. The titanium alkoxides may comprise: titanium n-butoxide Ti(OBu.sup.n).sub.4, titanium isobutoxide Ti(OBu.sup.i).sub.4, titanium tert-butoxide Ti(OBu.sup.t).sub.4, titanium isopropoxide Ti(OPr.sup.i).sub.4, titanium n-propoxide Ti(OPr.sup.n).sub.4, titanium ethoxide Ti(OEt).sub.4, or other titanium alkoxides. A mixture of H.sub.2O:R.sub.1OH=1:2 is prepared and is adjusted to pH=1.0-2.0 with inorganic acid such as hydrochloric acid HCl or nitric acid HNO.sub.3. Thereafter, 1.0-2.0 equivalents of H.sub.2O/R.sub.1OH solution (pH=1.0-2.0) is added dropwise to 1 equivalent of stirred titanium alkoxide solution.

[0041] The prepared TiO.sub.2 sol, SiO.sub.2 sol and TiO.sub.2—SiO.sub.2 sol are used to perform double-sided dip-coating of a glass substrate. First, the TiO.sub.2—SiO.sub.2 sol coating is performed, and the coated glass substrate is baked at 150-250° C. for 10 minutes so as to form TiO.sub.2—SiO.sub.2/Glass/TiO.sub.2—SiO.sub.2 coated glass. Then, SiO.sub.2 sol coating is performed, and the coated glass substrate is baked at 150-250° C. so as to form SiO.sub.2/TiO.sub.2—SiO.sub.2/Glass/TiO.sub.2—SiO.sub.2/SiO.sub.2 coated glass. Subsequently, TiO.sub.2 sol coating is performed, and the coated glass substrate is baked at 150-250° C. for 10 minutes so as to form TiO.sub.2/SiO.sub.2/TiO.sub.2—SiO.sub.2/Glass/TiO.sub.2—SiO.sub.2/SiO.sub.2/TiO.sub.2 coated glass, which is then annealed at 400-600° C. for one hour. Then, the coated and annealed glass substrate is cut and thermal bent to form automobile rearview blue mirrors.

[0042] Taking the automobile rearview blue mirror as an example, the thickness of each layer of the TiO.sub.2, SiO.sub.2, and TiO.sub.2—SiO.sub.2 coatings may be adjusted so that the peak of the reflected light is at blue spectral region. For example, the thickness of the TiO.sub.2 coating=blue light wavelength/(4×TiO.sub.2 coating refractive index), the thickness of the SiO.sub.2 coating=blue light wavelength/(4×SiO.sub.2 coating refractive index), and the thickness of the TiO.sub.2—SiO.sub.2 coating=blue light wavelength/(4×TiO.sub.2 —SiO.sub.2 coating refractive index). All of the three coatings of TiO.sub.2, SiO.sub.2, and TiO.sub.2—SiO.sub.2 have the peak of the reflected light at the blue spectral region. Therefore, the headlight of a following vehicle reflected by the mirror is mainly blue, so it is called blue mirror.

[0043] The invention method for manufacturing the hydrophilic, self-cleaning photocatalyst automobile rearview blue mirror can be divided into sol preparation and photocatalyst automobile rearview blue mirror manufacturing. The sol preparation comprises TiO.sub.2 sol, SiO.sub.2 sol and TiO.sub.2—SiO.sub.2 sol as described above. The preparation of anatase TiO.sub.2 preform sol is the crucial part. For example, titanium butoxide Ti(OBu.sup.n).sub.4 is added in ethanol, stirred and mixed into a titanium alkoxide solution. H.sub.2O/R.sub.1OH solution is prepared and is adjusted to pH=0.5 with inorganic acid such as nitric acid HNO.sub.3. Thereafter, 1.52.0 equivalents of H.sub.2O/R.sub.1OH solution is added dropwise to stirred titanium alkoxide solution to pH=0.11.0. The anatase TiO.sub.2 preform sol was prepared. After coating, an anneal at 400-600° C. is performed, and the structure and effect of anatase TiO.sub.2 photocatalyst are produced on the coated surface.

[0044] The photocatalyst rearview blue mirror for automobiles is manufactured by using TiO.sub.2—SiO.sub.2 sol, SiO.sub.2 sol and anatase TiO.sub.2 preform sol on the glass substrate for sol optical coating. The required blue light reflection intensity can be selected and the required optical coating can be designed according to the type and spectrum of the car headlight. For example, the compositions of the first layer of TiO.sub.2—SiO.sub.2 sol on the glass substrate may be replaced with TiO.sub.2 sol, 4TiO.sub.2—SiO.sub.2 sol, 3TiO.sub.2—SiO.sub.2 sol, 2TiO.sub.2—SiO.sub.2 sol and TiO.sub.2—SiO.sub.2 sol coating. Then, SiO.sub.2 sol coating and anatase TiO.sub.2 preform sol coating are performed. The coated glass is baked and annealed to make a photocatalyst blue mirror. By providing different compositions of the first layer of TiO.sub.2—SiO.sub.2 sol, the blue light reflection intensity can be adjusted. Five types of the coating material structures are listed as follows: [0045] 1. anatase TiO.sub.2/SiO.sub.2/TiO.sub.2—SiO.sub.2/Glass/TiO.sub.2—SiO.sub.2/SiO.sub.2/anatase TiO.sub.2 blue mirror [0046] 2. anatase TiO.sub.2/SiO.sub.2/2TiO.sub.2—SiO.sub.2/Glass/2TiO.sub.2—SiO.sub.2/SiO.sub.2/anatase TiO.sub.2 blue mirror [0047] 3. anatase TiO.sub.2/SiO.sub.2/3TiO.sub.2—SiO.sub.2/Glass/3TiO.sub.2—SiO.sub.2/SiO.sub.2/anatase TiO.sub.2 blue mirror [0048] 4. anatase TiO.sub.2/SiO.sub.2/4TiO.sub.2—SiO.sub.2/Glass/4TiO.sub.2—SiO.sub.2/SiO.sub.2/anatase TiO.sub.2 blue mirror [0049] 5. anatase TiO.sub.2/SiO.sub.2/TiO.sub.2/Glass/TiO.sub.2/SiO.sub.2/anatase TiO.sub.2 blue mirror

[0050] As shown in FIG. 2, the reflection spectrum of the various beam splitter coating structures 1, 2, 3, 4, and 5 have blue light reflectance of 55%, 58%, 61%, 63%, and 65%, respectively, at 440 nm. According to the change of spectrum of various car headlights, appropriate car rearview mirror with suitable blue light reflectance can be chosen. Such beam splitter can be used as an interior rearview mirror and has anti-glare effect. Such beam splitter can be used on both sides of the car and can provide anti-fog, hydrophilic self-cleaning effects, in addition to anti-glare effect.

EXAMPLES

[0051] Examples of preparing sol for making self-cleaning beam splitter are provided. The exemplary methods of preparing TiO.sub.2 sol, 4TiO.sub.2—SiO.sub.2 sol, 3TiO.sub.2—SiO.sub.2 sol, 2TiO.sub.2—SiO.sub.2 sol and TiO.sub.2—SiO.sub.2 sol are illustrated as follows.

Preparation of 4TiO.SUB.2.—SiO.SUB.2 .Sol (TS-41)

[0052] Taking TS-41 as an example; the content ratio of TiO.sub.2: SiO.sub.2 in the sol is 4:1. 1.0 mole tetraethoxysilane (TEOS) is added in ethanol EtOH, mixed by stirring so as to form silicon alkoxide solution. 1.0 mole H.sub.2O is mixed with 2.0 mole alcohol, and added dropwise into the silicon alkoxide solution to obtain an ethanol solution of Si(OEt).sub.3OH. Then, 1.0 mole of Si(OEt).sub.3OH in ethanol solution was stirred and dropped into 4.0 mole of Ti(OBu.sup.n).sub.4 to obtain (EtO).sub.3 SiOTi(OBu.sub.n).sub.3 and 3Ti(OBu.sup.n).sub.4 alcohol solution. Then, 3.0 mole water/alcohol mixture (H.sub.2O/EtOH=1/2), titrate with concentrated HNO.sub.3 to adjust the pH to 1.5, is added to stirred (EtO).sub.3SiOTi(OBu.sup.n).sub.3 and 3Ti(OBu.sup.n).sub.4 alcohol solution, so as to perform hydrolysis and condensation of (EtO).sub.3SiOTi(OBu.sup.n).sub.3 and 3Ti(OBu.sup.n).sub.4, thereby form 4TiO.sub.2—SiO.sub.2 sol, represented by the following formula:

##STR00001##

Preparation of 3TiO.SUB.2.—SiO.SUB.2 .Sol (TS-31)

[0053] Taking TS-31 as an example; the content ratio of TiO.sub.2: SiO.sub.2 in the sol is 3:1. 1.0 mole tetraethoxysilane is added in ethanol EtOH, mixed by stirring so as to form silicon alkoxide solution. 1.0 mole H.sub.2O is mixed with 2.0 mole alcohol, and added dropwise into the silicon alkoxide solution to obtain an ethanol solution of Si(OEt).sub.3OH. Then, 1.0 mole of Si(OEt).sub.3OH in ethanol solution was stirred and dropped into 3.0 mole of Ti(OBu.sup.n).sub.4 to obtain (EtO).sub.3SiOT(OBu.sup.n).sub.3 and 2Ti(OBu.sup.n).sub.4 alcohol solution. Then, 2.0 mole water/alcohol mixture (H.sub.2O/EtOH=1/2), titrate with concentrated HNO.sub.3 to adjust the pH to 1.5, is added to stirred (EtO).sub.3SiOTi(OBu.sup.n).sub.3 and 2Ti(OBu.sup.n).sub.4 alcohol solution, so as to perform hydrolysis and condensation of (EtO).sub.3SiOT(OBu.sup.n).sub.3 and 2Ti(OBu.sup.n).sub.4, thereby form 3TiO.sub.2—SiO.sub.2 sol, represented by the following formula:

##STR00002##

Preparation of 2TiO.SUB.2.—SiO.SUB.2 .Sol (TS-21)

[0054] Taking TS-21 as an example; the content ratio of TiO.sub.2: SiO.sub.2 in the sol is 2:1. 1.0 mole tetraethoxysilane is added in ethanol EtOH, mixed by stirring so as to form silicon alkoxide solution. 1.0 mole H.sub.2O is mixed with 2.0 mole alcohol, and added dropwise into the silicon alkoxide solution to obtain an ethanol solution of Si(OEt).sub.3OH. Then, 1.0 mole of Si(OEt).sub.3OH in ethanol solution was stirred and dropped into 2.0 mole of Ti(OBu.sup.n).sub.4 to obtain (EtO).sub.3SiOTi(OBu.sup.n).sub.3 and Ti(OBu.sup.n).sub.4 alcohol solution. Then, 1.0 mole water/alcohol mixture (H.sub.2O/EtOH=1/2), titrate with concentrated HNO.sub.3 to adjust the pH to 1.5, is added to stirred (EtO).sub.3SiOTi(OBu.sup.n).sub.3 and Ti(OBu.sup.n).sub.4 alcohol solution, so as to perform hydrolysis and condensation of (EtO).sub.3SiOT(OBu.sup.n).sub.3 and Ti(OBu.sup.n).sub.4, thereby form 2TiO.sub.2—SiO.sub.2 sol, represented by the following formula:

##STR00003##

Preparation of TiO.SUB.2.—SiO.SUB.2 .Sol (TS-11)

[0055] Taking TS-11 as an example; the content ratio of TiO.sub.2: SiO.sub.2 in the sol is 1:1. 1.0 mole tetraethoxysilane is added in ethanol EtOH, mixed by stirring so as to form silicon alkoxide solution. 1.0 mole H.sub.2O is mixed with 2.0 mole alcohol, and added dropwise into the silicon alkoxide solution to obtain an ethanol solution of Si(OEt).sub.3OH. Then, 1.0 mole of Si(OEt).sub.3OH in ethanol solution was stirred and dropped into 1.0 mole of Ti(OBu.sup.n).sub.4 to obtain (EtO).sub.3SiOT(OBu.sup.n).sub.3 alcohol solution. Then, 1.0 mole water/alcohol mixture (H.sub.2O/EtOH=1/2), titrate with concentrated HNO.sub.3 to adjust the pH to 1.5, is added to stirred (EtO).sub.3SiOTi(OBu.sup.n).sub.3 alcohol solution, so as to perform hydrolysis and condensation of (EtO).sub.3SiOT(OBu.sup.n).sub.3, thereby form TiO.sub.2—SiO.sub.2 sol, represented by the following formula:

—(OBu.sup.n).sub.2Ti—O—Si(OEt).sub.2-OTi(OBu.sup.n).sub.2-O—Si(OEt).sub.2-

Preparation of SiO.SUB.2 .Sol (SD-01)

[0056] Taking SD-01 as an example, tetraethoxysilane is added in ethanol EtOH, mixed by stirring so as to form silicon alkoxide solution. H.sub.2O is mixed with ethanol EtOH (H.sub.2O/EtOH=1/2), wherein hydrochloric acid is used to adjust the pH. 2.0 moles of H.sub.2O/EtOH solution (pH=1.5) is added in stirred 1.0 mole silicon alkoxide solution.

Preparation of TiO.SUB.2 .Sol (TD-01)

[0057] Taking TD-01 as an example, Ti(OBu.sub.n).sub.4 is added in ethanol EtOH, mixed by stirring so as to form titanium alkoxide solution. H.sub.2O is mixed with ethanol EtOH (H.sub.2O/EtOH=1/2), wherein HNO.sub.3 is used to adjust the pH. 1.0 moles of H.sub.2O/EtOH solution (pH=1.5) is added in stirred 1.0 mole titanium alkoxide solution, stirred to perform hydrolysis and condensation reaction, thereby forming TiO.sub.2 sol.

Preparation of anatase TiO.SUB.2 .preform Sol (TD-02)

[0058] Taking TD-02 as an example, 1.0 mole Ti(OBu.sup.n).sub.4 is added to 1 liter of ethanol EtOH, stirred to mix into titanium alkoxide solution. Concentrated nitric acid is used to adjust pH of 1.5-1.8 moles of aqueous solution (H.sub.2O/EtOH=1/2) to pH=0.5. The aqueous solution is added dropwise into the titanium alkoxide solution, stirred for hydrolysis and condensation reaction, thereby forming anatase TiO.sub.2 preform sol.

Examples of Making Self-Cleaning Beam Splitter by Sol Coating Process

[0059] The first optical coating of glass substrate by TiO.sub.2, 4TiO.sub.2—SiO.sub.2, 3TiO.sub.2—SiO.sub.2, 2TiO.sub.2—SiO.sub.2, and TiO.sub.2—SiO.sub.2 sol, respectively, followed by SiO.sub.2 sol coating, then anatase TiO.sub.2 preform sol coating. The process flow of making a photocatalyst self-cleaning beam splitter is as follows.

[0060] The fabrication process of anatase TiO.sub.2/SiO.sub.2/TiO.sub.2—SiO.sub.2/Glass/TiO.sub.2—SiO.sub.2/SiO.sub.2/anatase TiO.sub.2 blue mirror is listed as follows.

[0061] Glass.fwdarw.TS-11 sol coating>(TiO.sub.2—SiO.sub.2)g/Glass/(TiO.sub.2—SiO.sub.2)g.fwdarw.200° C., 10 mins.fwdarw.(TiO.sub.2—SiO.sub.2)b/Glass/(TiO.sub.2—SiO.sub.2)b.fwdarw.DS-01 sol coating.fwdarw.(SiO.sub.2)g(TiO.sub.2—SiO.sub.2)b/Glass/(TiO.sub.2—SiO.sub.2)b(SiO.sub.2)g.fwdarw.200° C., 10 mins.fwdarw.(SiO.sub.2)b/(TiO.sub.2—SiO.sub.2)b/Glass/(TiO.sub.2—SiO.sub.2)b/(SiO.sub.2)b.fwdarw.TD-02 sol coating.fwdarw.(anatase TiO.sub.2 preform)g/(SiO.sub.2)b/(TiO.sub.2—SiO.sub.2)b/Glass/(TiO.sub.2—SiO.sub.2)b/(SiO.sub.2)b/(anatase TiO.sub.2 preform)g.fwdarw.500° C., 1 Hr.fwdarw.anatase TiO.sub.2/SiO.sub.2/TiO.sub.2—SiO.sub.2/Glass/TiO.sub.2—SiO.sub.2/SiO.sub.2/anatase TiO.sub.2

[0062] The fabrication process of anatase TiO.sub.2/SiO.sub.2/2TiO.sub.2—SiO.sub.2/Glass/2TiO.sub.2—SiO.sub.2/SiO.sub.2/anatase TiO.sub.2 blue mirror is listed as follows.

[0063] Glass.fwdarw.TS-21 sol coating.fwdarw.(2TiO.sub.2—SiO.sub.2)g/Glass/(2TiO.sub.2—SiO.sub.2)g.fwdarw.200° C., 10 mins.fwdarw.(2TiO.sub.2—SiO.sub.2)b/Glass/(2TiO.sub.2—SiO.sub.2)b.fwdarw.DS-01 sol coating (SiO.sub.2)g(2TiO.sub.2—SiO.sub.2)b/Glass/(2TiO.sub.2—SiO.sub.2)b(SiO.sub.2)g.fwdarw.200° C., 10 mins.fwdarw.(SiO.sub.2)b/(2TiO.sub.2—SiO.sub.2)b/Glass/(2TiO.sub.2—SiO.sub.2)b/(SiO.sub.2)b.fwdarw.TD-02 sol coating.fwdarw.(anatase TiO.sub.2 preform)g/(SiO.sub.2)b/(2TiO.sub.2—SiO.sub.2)b/Glass/(2TiO.sub.2—SiO.sub.2)b/(SiO.sub.2)b/(anatase TiO.sub.2 preform)g-500° C., 1 Hr.fwdarw.anatase TiO.sub.2/SiO.sub.2/2TiO.sub.2—SiO.sub.2/Glass/2TiO.sub.2—SiO.sub.2/SiO.sub.2/anatase TiO.sub.2

[0064] The fabrication process of anatase TiO.sub.2/SiO.sub.2/3TiO.sub.2—SiO.sub.2/Glass/3TiO.sub.2—SiO.sub.2/SiO.sub.2/anatase TiO.sub.2 blue mirror is listed as follows.

[0065] Glass.fwdarw.TS-31 sol coating.fwdarw.(3TiO.sub.2—SiO.sub.2)g/Glass/(3TiO.sub.2—SiO.sub.2)g.fwdarw.200° C., 10 mins.fwdarw.(3TiO.sub.2—SiO.sub.2)b/Glass/(3TiO.sub.2—SiO.sub.2)b.fwdarw.DS-01 sol coating.fwdarw.(SiO.sub.2)g(3TiO.sub.2—SiO.sub.2)b/Glass/(3TiO.sub.2—SiO.sub.2)b(SiO.sub.2)g.fwdarw.200° C., 10 mins.fwdarw.(SiO.sub.2)b/(3TiO.sub.2—SiO.sub.2)b/Glass/(3TiO.sub.2—SiO.sub.2)b/(SiO.sub.2)b.fwdarw.TD-02 sol coating.fwdarw.(anatase TiO.sub.2 preform)g/(SiO.sub.2)b/(2TiO.sub.2—SiO.sub.2)b/Glass/(3TiO.sub.2—SiO.sub.2)b/(SiO.sub.2)b/(anatase TiO.sub.2 preform)g-500° C., 1 Hr.fwdarw.anatase TiO.sub.2/SiO.sub.2/3TiO.sub.2—SiO.sub.2/Glass/3TiO.sub.2—SiO.sub.2/SiO.sub.2/anatase TiO.sub.2

[0066] The fabrication process of anatase TiO.sub.2/SiO.sub.2/4TiO.sub.2—SiO.sub.2/Glass/4TiO.sub.2—SiO.sub.2/SiO.sub.2/anatase TiO.sub.2 blue mirror is listed as follows.

[0067] Glass>TS-41 sol coating.fwdarw.(4TiO.sub.2—SiO.sub.2)g/Glass/(4TiO.sub.2—SiO.sub.2)g.fwdarw.200° C., 10 mins.fwdarw.(4TiO.sub.2—SiO.sub.2)b/Glass/(4TiO.sub.2—SiO.sub.2)b.fwdarw.DS-01 sol coating.fwdarw.(SiO.sub.2)g(4TiO.sub.2—SiO.sub.2)b/Glass/(4TiO.sub.2—SiO.sub.2)b(SiO.sub.2)g.fwdarw.200° C., 10 mins.fwdarw.(SiO.sub.2)b/(4TiO.sub.2—SiO.sub.2)b/Glass/(4TiO.sub.2—SiO.sub.2)b/(SiO.sub.2)b.fwdarw.TD-02 sol coating.fwdarw.(anatase TiO.sub.2 preform)g/(SiO.sub.2)b/(4TiO.sub.2—SiO.sub.2)b/Glass/(4TiO.sub.2—SiO.sub.2)b/(SiO.sub.2)b/(anatase TiO.sub.2 preform)g-500° C., 1 Hr.fwdarw.anatase TiO.sub.2/SiO.sub.2/4TiO.sub.2—SiO.sub.2/Glass/4TiO.sub.2—SiO.sub.2/SiO.sub.2/anatase TiO.sub.2

[0068] The fabrication process of anatase TiO.sub.2/SiO.sub.2/TiO.sub.2/Glass/TiO.sub.2/SiO.sub.2/anatase TiO.sub.2 blue mirror is listed as follows.

[0069] Glass.fwdarw.TD-01 sol coating.fwdarw.(TiO.sub.2)g/Glass/(TiO.sub.2)g.fwdarw.200° C., 10 mins.fwdarw.(TiO.sub.2)b/Glass/(TiO.sub.2)b DS-01 sol coating.fwdarw.(SiO.sub.2)g(TiO.sub.2)b/Glass/(TiO.sub.2)b(SiO.sub.2)g.fwdarw.200° C., 10 mins.fwdarw.(SiO.sub.2)b/(TiO.sub.2)b/Glass/(TiO.sub.2)b/(SiO.sub.2)b.fwdarw.TD-02 sol coating.fwdarw.(anatase TiO.sub.2 preform)g/(SiO.sub.2)b/(TiO.sub.2)b/Glass/(TiO.sub.2)b/(SiO.sub.2)b/(anatase TiO.sub.2preform)g.fwdarw.500° C., 1 Hr.fwdarw.anatase TiO.sub.2/SiO.sub.2/TiO.sub.2/Glass/TiO.sub.2/SiO.sub.2/anatase TiO.sub.2

[0070] The SiO.sub.2/TiO.sub.2 ratios in the TiO.sub.2—SiO.sub.2 sol such as TD-01, TS-41, TS-31, TS-21 and TS-11 is 0/1, 1/4, 1/3, 1/2 and 1/1, respectively. Double-sided coating of the first layer of sol on the glass substrate is carried out. After baking at 200° C. for 10 minutes in the oven, TiO.sub.2, 4TiO.sub.2—SiO.sub.2, 3TiO.sub.2—SiO.sub.2, 2TiO.sub.2—SiO.sub.2, or TiO.sub.2—SiO.sub.2 coated glass is obtained for adjusting the reflectance. The thickness of the sol coating may be adjusted to the desired optical thickness by setting the glass withdrawal speed. The second layer of SiO.sub.2 sol (SD-01) double-sided coating is then performed. The coated glass is then baked in the oven at 150-250° C. for 10 minutes. The third layer Anatase TiO.sub.2 Preform sol (TD-02) double-sided coating is then performed. The coated glass is then annealed at high temperatures of 400-600° C., and then cut and bent to make blue mirror.

[0071] To make the photocatalyst blue mirrors for the automobile rearview mirrors, Ti(OBu.sup.n).sub.4 is added in ethanol, stirred to mix into titanium alkoxide solution, and added dropwise with 1.8 equivalents of H.sub.2O/R.sub.1OH solution, which is adjusted with concentrated nitric acid HNO.sub.3 to pH=0.5. The aqueous solution was stirred and dropped into the titanium alkoxide solution to prepare anatase TiO.sub.2 preform sol. The anatase TiO.sub.2 preform sol coating is carried out on SiO.sub.2/TiO.sub.2—SiO.sub.2/Glass/TiO.sub.2—SiO.sub.2/SiO.sub.2 coated glass, which is annealed to make anatase TiO.sub.2/SiO.sub.2/TiO.sub.2—SiO.sub.2/Glass/TiO.sub.2—SiO.sub.2/SiO.sub.2/anatase TiO.sub.2 photocatalyst blue mirror. The interior rearview mirror made by such beam splitter can provide anti-glare effect in the car. The exterior rearview mirror made by such beam splitter can provide anti-glare effect for both sides of the car, and anti-fog, hydrophilic self-cleaning effects.

Fabrication of Photocatalyst Blue Mirror for Automobile Rearview Mirror

[0072] Anatase TiO.sub.2, SiO.sub.2, TiO.sub.2—SiO.sub.2 sol optical coating technology is applied on the glass by sol coating, as shown in FIG. 3. Taking the blue mirror as the target product and the coating thickness of each layer is controlled. The thickness of each layer of the TiO.sub.2, SiO.sub.2, and TiO.sub.2—SiO.sub.2 coatings may be adjusted so that the peak of the reflected light is at 440 nm. For example, the thickness of the TiO.sub.2 coating=blue light wavelength/(4×TiO.sub.2 coating refractive index), the thickness of the SiO.sub.2 coating t=blue light wavelength/(4×SiO.sub.2 coating refractive index), and the thickness of the TiO.sub.2—SiO.sub.2=blue light wavelength/(4×(TiO.sub.2—SiO.sub.2) coating refractive index). All of the three coatings of TiO.sub.2, SiO.sub.2, and TiO.sub.2—SiO.sub.2 have the peak of the reflected light at the blue spectral region. Therefore, the headlight of a following vehicle reflected by the mirror is mainly blue, so it is called blue mirror.

[0073] The optical efficiency of the present invention product is represented by a blue mirror, and the function is represented by the photocatalyst. The function and durability test of the photocatalyst are carried out according to the anatase TiO.sub.2/SiO.sub.2/TiO.sub.2/Glass/TiO.sub.2/SiO.sub.2 anatase TiO.sub.2 blue mirror as the representative. Some characteristics of the blue mirror are listed in Table 1. (1) Hydrophilic contact angle: UVA 365 nm irradiation for 24 hours, contact angle <10°; dark place>48 hours, contact angle <30°; verified according to TN-004 nano-photocatalyst anti-fouling ceramic tile specification. (2) Fading rate: UVA 365 nm irradiation for 3 hours, methylene blue decomposition activity>7.0 nmole/(L×min); verified according to TN-031 nanophotocatalyst self-cleaning coating specification. (3) Durability: including salt water resistance, acid resistance and alkaline resistance tests, the hydrophilicity is more than 70% of the original function, the original hydrophilic contact angle is less than 10°, and the hydrophilic contact angle after the test is less than 15 verified according to TN-004

Blue Mirror Durability

[0074] A. Salt water resistance test: After soaking the blue mirror in NaCl brine (3%) for 96 hours, wash it and dry it, UVA 365 nm irradiation for 24 hours, hydrophilic contact angle <15°.

[0075] B. Acid resistance test; after soaking the blue mirror in H.sub.2SO.sub.4 sulfuric acid aqueous solution (5%) for 24 hours, wash it and dry it, UVA 365 nm irradiation for 24 hours, hydrophilic contact angle <15°.

[0076] C. Alkaline resistance test; after soaking the blue mirror in sodium carbonate (Na.sub.2CO.sub.3) aqueous solution (5%) for 24 hours, wash it and dry it, UVA 365 nm irradiation for 24 hours, hydrophilic contact angle <15°.

[0077] Verification according to TN-004 Nano Photocatalyst Self-cleaning Coating Specification.

TABLE-US-00001 TABLE 1 Test results of photocatalyst blue mirror Blue Durability Durability Durability mirror Dark methylene Salt water Acid Alkaline structure UVA24Hr 48 Hr blue resistance resistance resistance Water Water decomposition UVA24Hr UVA24Hr UVA24Hr contact contact activity angle angle Water Water Water contact contact contact angle angle angle TA/S/TD1/G/ 6.65° 18.43° 7.02 6.56° 6.61° 6.28° blue mirror nanoMark TN-004 TN-004 TN-031 TN-004 TN-004 TN-004 (Taiwan) TA/S/TD1/G/blue mirror = anatase TiO.sub.2 /SiO.sub.2/TiO.sub.2/Glass/TiO.sub.2/SiO.sub.2/ anatase TiO.sub.2 coated glass

[0078] The photocatalyst blue mirror developed by this sol optical coating technology has a physical hardness of 6H. Cross-cut adhesion test without falling off is 5B. Abrasion resistance test; sponge test, rubbing back and forth 2000 times, water drop contact angle 5.61°. Scrub resistance test; scrubbing machine back and forth 15 times, water drop contact angle 8.15°.

[0079] The product developed by this sol optical coating technology is not limited to the photocatalyst blue mirrors. If the application of sol optical coating products is expanded, the sol coating can be developed to make photocatalyst multilayer reflective glass and produce near infrared, red, orange, yellow, green, blue, purple or ultraviolet light strong reflective optical coated glass. Such glass with photocatalyst self-cleaning effect is suited for indoor or outdoor windows, mirrors, colored reflective self-cleaning glass, and can also be used in vehicles, ships, and aircrafts.

[0080] To sum up, a method for fabricating a beam splitter with photocatalytic coating is disclosed. First, a TiO.sub.2—SiO.sub.2 sol, a SiO.sub.2 sol, and an anatase TiO.sub.2 preform sol are prepared. A glass substrate having two opposite surfaces is provided. The two opposite surfaces of the glass substrate is coated with the TiO.sub.2—SiO.sub.2 sol, the SiO.sub.2 sol, and the anatase TiO.sub.2 preform sol by the dip-coating method, thereby forming a coated glass substrate with a multi-layer optical coating on each of the two opposite surfaces. The multi-layer optical coating comprises a TiO.sub.2—SiO.sub.2 coating, a SiO.sub.2 coating, and an anatase TiO.sub.2 preform coating. The coated glass substrate is subjected to an anneal process. The coated glass substrate is cut, thereby forming the beam splitter with photocatalytic coating.

[0081] According to some embodiments, the dip-coating the two opposite surfaces of the glass substrate comprises: immersing the glass substrate in the TiO.sub.2—SiO.sub.2 sol, the SiO.sub.2 sol, [and] the anatase TiO.sub.2 preform sol; withdrawing the glass substrate from the TiO.sub.2—SiO.sub.2 sol, the SiO.sub.2 sol, or the anatase TiO.sub.2 preform sol at a constant withdrawal speed as requirements and baking the glass substrate at 150-250° C.

[0082] According to some embodiments, the anneal process is performed at 400-600° C.

[0083] According to some embodiments, the multi-layer optical coating has reflection at blue spectral region.

[0084] According to some embodiments, a thickness of the TiO.sub.2 coating=blue light wavelength/(4×TiO.sub.2 coating refractive index), a thickness of the SiO.sub.2 coating=blue light wavelength/(4×SiO.sub.2 coating refractive index), and a thickness of the TiO.sub.2—SiO.sub.2 coating=blue light wavelength/(4×TiO.sub.2 —SiO.sub.2 coating refractive index).

[0085] According to some embodiments, TiO.sub.2—SiO.sub.2 sol, the SiO.sub.2 sol and the anatase TiO.sub.2 preform sol use titanium alkoxide or silicon alkoxide as a precursor, and wherein the TiO.sub.2—SiO.sub.2 sol, the SiO.sub.2 sol and the anatase TiO.sub.2 preform sol are prepared by hydrolysis, condensation and peptization in alcohol solvent.

[0086] According to some embodiments, the TiO.sub.2—SiO.sub.2 sol, the SiO.sub.2 sol and the anatase TiO.sub.2 preform sol are prepared to impart anti-glare effect to an automobile rearview mirror made from the beam splitter, which avoids glare from a following vehicle headlight to a driver, by adjusting a reflectance of the beam splitter, and by adjusting a solid content ratio of the TiO.sub.2—SiO.sub.2 sol, the SiO.sub.2 sol and the anatase TiO.sub.2 preform sol between 1-0.

[0087] According to some embodiments, a SiO.sub.2/TiO.sub.2 solid content ratio in the TiO.sub.2—SiO.sub.2 sol ranges between 1-0, and wherein the beam splitter reflects blue light at 440 nm and a reflectance thereof is between 55-65%.

[0088] According to some embodiments, an ambient air temperature and humidity is controlled and the withdrawal speed is adjusted according to a solid content of each of aid TiO.sub.2—SiO.sub.2 sol, the SiO.sub.2 sol and the anatase TiO.sub.2 preform sol, and wherein the glass substrate is baked at 150-250° C. for 10 minutes, and annealed at 400-600° C. for 1.0 hour, such that a peak of a reflective spectrum of the multi-layer optical coating is at 440 nm.

[0089] According to some embodiments, a peak of a reflection spectrum of an optical coating of each of the TiO.sub.2—SiO.sub.2 sol, the SiO.sub.2 sol and the anatase TiO.sub.2 preform sol is at 440 nm after baking and annealing, and then each sol is laminated and coated according to this condition to make anatase TiO.sub.2/SiO.sub.2/SiO.sub.2—TiO.sub.2/glass substrate/SiO.sub.2—TiO.sub.2/SiO.sub.2/anatase TiO.sub.2 blue mirror with a blue light reflectance at 440 nm between 55-65%.

[0090] According to some embodiments, the anatase TiO.sub.2 preform sol uses titanium alkoxide as a precursor, hydrolyzed and condensed in ethanol, peptized by HNO.sub.3, so as to form the anatase TiO.sub.2 preform sol, and wherein an anatase TiO.sub.2 coating formed by the dip-coating, baking and annealing has photocatalytic, hydrophilic, and self-cleaning effects.

[0091] According to some embodiments, the anatase TiO.sub.2/SiO.sub.2/SiO.sub.2—TiO.sub.2/glass substrate/SiO.sub.2—TiO.sub.2/SiO.sub.2/anatase TiO.sub.2 blue mirror has the anatase TiO.sub.2 coating on its outer surface, so under ultraviolet rays of sunlight, it produces photocatalyst effects comprising hydrophilic phenomenon, chemical redox reaction, sterilization, mildew prevention, self-cleaning, and decontamination.

[0092] Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should not be constrained as limited only by the metes and bounds of the appended claims.

[0093] Because, the sol-gel coating with TiO.sub.2—SiO.sub.2 sol, the SiO.sub.2 sol and the anatase TiO.sub.2 preform sol, for the multi-layer optical coating to make photocatalysis blue mirror can be apply on other sol-gel optical coating: such as high-reflection, low-reflection, color filter with photocatalysis coating on surface. Those photocatalyst optical coating glass can be applied on building glass and ship glass with self-cleaning, hydrophilic, chemical redox reaction, sterilization, mildew prevention etc.