DESCRIPTION OF PREFERRED EMBODIMENTS

[0040] An embodiment of the invention in which the anti-fog mirror of the invention is applied to an outer mirror of a vehicle is shown in FIG. 1A . An outer mirror 10 has an anti-fog mirror 14 disposed in an opening of a mirror housing 12 . In the anti-fog mirror 14 , a reflecting film 18 is made of a metal film such as Cr, Ni—Cr or Ti formed on a rear surface of a transparent glass substrate 16 . On a front surface of the transparent glass substrate 16 are formed laminated films of a TiO 2 film 20 which constitutes a photocatalyzing film and a SiO 2 film 22 which constitutes an inorganic hydrophilic film made of an inorganic oxide film. The surface of the SiO 2 is porous as shown in FIG. 1B in an enlarged scale and therefore is remarkably hydrophilic. The thickness of the reflecting film 18 is set at a value within a range from 50 nm to 1000 nm in the case of, e.g., Cr.

[0041] The thickness of the photocatalyzing TiO 2 film and the porous SiO 2 film exercises a great influence on the ability to decompose contaminants deposited on the surface of the SiO 2 film 22 (i.e., photocatalyzing ability). The following Table 1 shows a result of measurement of a waterdrop contact angle in a case where the thickness of the photocatalyzing TiO 2 film 20 was set at various values and car-washing and wax-coating were made on a real automobile once a month for six months. 1

[0042] According to Table 1, in case the film thickness is 100 nm or over, the contact angle is 20° or below, indicating that the hydrophilic property is maintained. An excessively large thickness of the photocatalyzing TiO 2 film 20 deteriorates the reflecting property and also prolongs time for forming the film, resulting in increase in the manufacturing cost. For these reasons, a film thickness of 1000 nm or below is preferable. Therefore, an optimum range of the thickness of the photocatalyzing TiO 2 film 20 is from 100 nm to 1000 nm.

[0043] Change in the waterdrop contact angle depending upon the thickness of the porous SiO 2 film is shown in FIG. 2 . The diagram shows a result of measurement made when oil was deposited on the surface of the porous SiO 2 film 22 and black light with intensity of 1 mW/cm 2 was irradiated thereon for 24 hours. According to the result of measurement, in case the film thicness is 50 nm or below, the contact angle is 20 or below, indicating that the hydrophilic property is maintained. A too small thickness of the porous SiO 2 film 22 , however, reduces the film strength and deteriorates wear resistance. Table 2 shows a result of observation of appearance of the surface in a case where the thickness of the porous SiO 2 film 22 was set at various values and a brush wrapped with cloth was reciprocally moved on the surface 1000 times at a load of 1N./cm 2 . 2

[0044] According to Table 2, a film thickness of 10 nm or over ensures a sufficient film strength. Accordingly, an optimum range of the thickness of the porous SiO 2 film is from 10 nm to 50 nm.

[0045] The surface roughness of the porous SiO 2 film 22 directly influences the hydrophilic property. FIG. 3 shows a result of measurement of the waterdrop contact angle in case the surface roughness Ra of the porous SiO 2 film 22 is set at various values. The surface roughness Ra here is an arithmetic mean surface roughness Ra defined in JIS B 0601 -1994 and can be obtained on the basis of measurement by, e.g., AFM (atomic force microscope). According to FIG. 3, a surface roughness Ra of 2 nm or over ensures a sufficient hydrophilic property. FIG. 4 shows a result of measurement of the waterdrop contact angle in case the surface roughness of the porous SiO 2 film 22 was set at 1 nm and 2 nm or over and they were left in a dark room. According to the result of measurement, the hydrophilic property is deteriorated rapidly at the surface roughness of 1 nm whereas the hydrophilic property is deteriorated gradually at the surface roughness of 2 nm or over.

[0046] An example of processes for manufacturing the anti-fog mirror 14 of FIG. 1A will be described with reference to FIG. 5 .

[0047] (1) Production of the Glass Substrate

[0048] First of all, the transparent glass substrate 16 is formed into a predetermined mirror substrate configuration. Generally, a plate glass (soda-lime glass) is used for a vehicle mirror by reason of its advantages in the cost and quality.

[0049] (2) Forming of the Reflecting Film

[0050] The reflecting film 18 is formed on the rear surface of the transparent glass substrate 16 with Cr, Cr—Ni or Ti. The film forming can be accomplished by, e.g., sputtering. FIG. 6 shows an example of a jig used for sputtering. This jig 24 has shelves 28 which are vertically arranged at a predetermined interval along a side of a vertically disposed plate 26 . The transparent glass substrates 16 are rested against the shelves 28 in one substrate for one shelf relationship with the rear surface 16 b of the substrate 16 facing outside. This jig 24 is supported perpendicularly by a jig holder 30 shown in FIG. 7 and is opposed to a target 32 (Cr, Cr—Ni, Ti etc.). Sputtering is performed by causing ions 31 such as argon ions to collide against the target 32 and thereby causing sputtering atoms or molecules 33 to pop out of the target 32 and scatter to be deposited on the rear surfaces 16 b of the transparent glass substrates 16 . At this time, a part of the sputtering atoms or molecules 33 which have failed to be deposited on the rear surfaces 16 b of the transparent glass substrates 16 strike against the jig 24 and a part of them are reflected to be deposited on the front surfaces 16 a of the transparent glass substrates 16 (this phenomenon is called “secondary sputtering”). Thickness of the sputtering atoms or molecules 33 deposited on the front surface 16 a is considered to be in the order of several tenths nm but even a film having a thickness of this order deteriorates the hydrophilic property when it is deposited on the hydrophilic film 22 (i.e., the porous SiO 2 film). Since, in this embodiment, the reflecitng film 18 is formed before forming of the hydrophilic film 22 , such inconvenience never arises. Moreover, Cr, Ni and Ti produce a very stable film due to oxidation and thereby are in passive state. Since such a film has an excellent adhesion to glass and an oxide film, even if the photocatalyzing TiO 2 film 20 and the porous SiO 2 film 22 are formed on the film of Cr, Ni—Cr or Ti which are formed on the front surface 16 a of the transparent glass substrate 16 due to the secondary sputtering, the film of Cr, Ni—Cr or Ti will exercise a high adhesive force to the films 20 and 22 and, therefore, these films 20 and 22 will scarcely come off and their durability will not be adversely affected.

[0051] (3) Forming of the Photocatalyzing Film

[0052] For ensuring a sufficient photocatalytic function of the TiO 2 film 20 , it is necessary to form an anatase type crystal structure. For forming an anatase type crystal structure, heat energy of a certain order is required and, for this purpose, the film forming must be made while the transparent glass substrate 16 is in a heated state, When, however, the temperature of the transparent glass substrate 16 exceeds 500° C., Na ions in the transparent glass substrate 16 are diffused into the TiO 2 film 20 and Na x Ti y O z domains are thereby produced and the photocatalytic function of the TiO 2 film 20 is seriously impaired. For this reason, when forming of the TiO 2 film 20 is made by using the sol-gel method which requires calcination of the material at a high temperature, provision of a blocking layer (using, e.g., SiO 2 ) becomes necessary and this complicates the manufacturing process.

[0053] Accordingly, in this embodiment, the photocatalyzing TiO 2 film 20 and the porous SiO 2 film 22 are formed by vacuum deposition. FIG. 8 shows a result of measurement of change of the waterdrop contact angle in case the films 20 and 22 are formed by vacuum deposition by setting the temperature of the transparent glass substrate 16 at various values. This is a result of measurement obtained when oil was deposited on the surface of the porous SiO 2 film 22 and black light was irradiated for 24 hours at an intensity of 1 mW/cm 2 According to FIG. 8 , by forming the TiO 2 film 20 at a substrate temperature within a range from 200° C. to 450° C., the anatase type crystal structure can be formed and a sufficient photocatalytic function can thereby be obtained. Since Na ions do not diffuse within this temperature range, the provision of the block layer is not required and the manufacturing process thereby is simplified. Moreover, occurrence of a pin hole or change of color in the reflecting film 18 can be prevented.

[0054] (4) Forming of the Hydrophilic Film

[0055] The SiO 2 film 22 is formed by vacuum deposition while the substrate temperature is maintained within the range from 200° C. to 450° C. During this process, the surface of the film 22 can be made porous by, e.g., increasing the speed of deposition or increasing partial pressure of oxygen. More specifically, by increasing the speed of deposition, it becomes difficult to make a uniform surface and it becomes easy to form a film having projections and depressions. By increasing partial pressure of oxygen, energy applied to the surface of a substrate (in this case, the surface of the TiO 2 film 20 ) is reduced with the result that it becomes easy to make a film having projections and depressions.

[0056] An example of conditions for forming the TiO 2 film 20 to a dense texture and forming the SiO 2 film to a porous film is shown in Table 3. 3

[0057] Spectral characteristics of the anti-fog mirror 14 of FIG. 1A which has been made by the above described processes are shown in FIG. 9 . This is a result in case the reflecting film 18 is made of Cr. A result of observation of adhesion of the reflecting film to the substrate in case the reflecting film 18 is made of Cr, Ni—Cr and Ti respectively is shown in Table 4. 4

[0058] Table 4 shows a result obtained in case the film was boiled for 5 hours in 5% salt water. According to Table 4, the film does not come off in any case, indicating that a high durability is ensured.

[0059] A result of measurement of influence by the secondary sputtering is shown in Table 5. 5

[0060] According to Table 5, in the process of FIG. 5 in which the reflecting film was formed first and the porous SiO 2 film was formed later, better results were obtained in both the waterdrop contact angle and the contaminants decomposing ability as compared with the case (a) where the porous SiO 2 film was formed first and the reflecting film was formed later.

[0061] Other embodiments of the invention in which the anti-fog mirror of the invention is applied to an outer mirror of a vehicle are shown in section in FIGS. 10 and 11 which show a main body of the respective anti-fog mirrors only. In these embodiments, the same component parts as those shown in FIG. 1A are designated by the same reference characters. In these embodiments, anti-fog mirrors are constructed as blue mirrors which reflect light in a bluish color by increasing the reflectance of a specific wavelength. An anti-fog mirror 34 of FIG. 10 has a reflecting film 36 having a selective reflecting characteristic of a specific wavelength by forming plural layers of inorganic films made of a TiO 2 film 38 having a relatively high refractive index and a SiO 2 film 40 having a relatively low refractive index and further a metal film 42 made of Cr on the rear surface 16 b of a transparent glass substrate 16 . The thickness of each of the TiO 2 film 38 and the SiO 2 film 40 is set at an optical film thickness which is ¼ of a wavelength λ to be emphasized. If, for example, a center wavelength to be emphasized is 450 nm, the film thickness of the TiO 2 film 38 (refractive index 2.4) is set to 450/4/2.4=about 47 nm.

[0062] An anit-fog mirror 44 of FIG. 11 has a reflecting film 52 having a selective reflecting property of a specific wavelength by forming plural layers of inorganic films made of a TiO 2 film 46 having a relatively high refractive index and a TiO 2 film 48 having a relatively low refractive index and further a metal film 50 made of Cr. The thickness of each of the TiO 2 films 46 and 48 is set at an optical film thickness which is ¼ of a wavelength λ to be emphasized. Refractive indexes of the TiO 2 films 46 and 48 can be adjusted by the amount of oxygen gas introduced during the film forming process (i.e., the more is the amount of oxygen gas, the smaller is the refractive index).

[0063] The anti-fog mirrors 34 and 44 of FIGS. 10 and 11 are manufactured in a manner similar to the manufacturing processes described above with respect to the anti-fog mirror 14 of FIG. 1A . The plural films of the reflecting films 36 and 52 which are made respectively of plural films can be formed continuously by employing, e.g., an in-line sputtering device. An example of a jig used for the in-line type sputtering device is shown in FIG. 12 . This jig 54 is made of a horizontal plate which has openings 55 formed at a predetermined interval. Transparent glass substrates 16 are placed on and supported by a pair of supporting projections 56 provided on both sides of each opening 55 with a rear surfaces 16 b of the substrate 16 facing upside.

[0064] As shown in FIG. 13 , the jig 54 is conveyed at a constant speed by a conveyer 58 in the in-line type sputtering device to pass under a target 60 which is fixedly disposed above the conveyer 58 . Sputtering is performed by causing ions 61 such as argon ions to collide against the target 60 and thereby causing sputtering atoms or molecules 63 to pop out of the target 60 and scatter to be deposited on the rear surface 16 b of the transparent glass substrate 16 .

[0065] Upon completion of forming of the first film 38 ( 46 ), the next film 40 ( 48 ) is formed in a position where the jig 54 passes under a next target and the last film 42 ( 50 ) is formed in a position where the jig 54 passes under a next target to complete the forming of the reflecting film 36 ( 52 ).

[0066] Spectral characteristics of the anti-fog mirror 34 or 44 of FIG. 10 or 11 are shown in FIG. 14 . A result of measurement of adhesion of the reflecting film to the substrate is shown in Table 6. 6

[0067] Table 6 shows a result of measurement made when the film was boiled for 5 hours in 5% salt water. According to Table 6, coming off of the film does not take place in any case, indicating that a high durability is ensured.

[0068] During the forming process of the reflecting films 36 and 52 , sputtering atoms and molecules 63 reach the front surface 16 a of the substrate 16 and deposited thereon. The film formed by these sputtering atoms or molecules 63 has a high adhesion to the front surface 16 a and also to the photocatalyzing TiO 2 film 20 formed on the front surface 16 a.

[0069] Another embodiment of the invention in which the anti-fog mirror of the invention is applied to an outer mirror of a vehicle is shown in section in FIG. 15 which shows a main body of the anti-fog mirror only. The same component parts as those shown in FIG. 1A are designated with the same reference characters. In this embodiment, the invention is applied to a front surface mirror in which a reflecting film is disposed on the front side of the substrate. In an anti-fog mirror 64 , a metal film made of Cr, Ni—Cr or Ti is formed as a reflecting film 18 on a front surface 17 a of a substrate 17 which is made of a transparent glass, an opaque glass or a material other than glass. On the front surface of the reflecting film 18 are directly formed a TiO 2 film 20 which constitutes a photocatalyzing film and a SiO 2 film 22 which constitutes an inorganic hydrophilic film made of, e.g., an inorganic oxide film. The surface of the SiO 2 film 22 is made porous and therefore hydrophilic. This anti-fog mirror 64 is manufactured in a manner similar to the manufacturing process described above with respect to the anti-fog mirror 14 of FIG. 1A . In this embodiment, even in case the substrate 17 is made of glass, the reflecting film 18 between the photocatalyzing TiO 2 film and the glass substrate functions as a blocking layer and, therefore, Na ions in the glass substrate will not diffuse into the photocatalyzing TiO 2 film 20 . However, for preventing oxidation of the reflecting film 18 , the substrate temperature during forming of the photocatalyzing TiO 2 film 20 and the porous SiO 2 film 22 by vacuum deposition should preferably be maintained at 450° C. or below.

[0070] Description has been made in the above described embodiments about cases where the anti-fog mirrors are applied to an outer mirror of a vehicle. The anti-fog mirros of the invention, however, may be applied to other mirrors such, for example, as a bath-room mirror.