Hydrophilic mirror and method of producing the same

Details Hydrophilic mirror and method of producing the same Hydrophilic mirror and method of producing the same

2000-04-03

2001-11-06

Shafer, Ricky D. (Department: 2872)

Optical: systems and elements

Protection from moisture or foreign particle

C359S584000, C359S586000, C359S588000, C359S883000, C359S900000, C065S060200, C065S060500, C065S060800, C427S165000, C427S167000

Reexamination Certificate

active

06312131

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a hydrophilic mirror and, more particularly, to a hydrophilic mirror having excellent properties of restoring hydrophihcity after cleaning.
BACKGROUND OF THE INVENTION
Mirrors generally have a highly reflective metal coating of silver, aluminum, etc., formed thereon. A mirror using silver is produced by applying a solution of a silver salt to glass and conducting reduction reaction on the glass surface to form a silver coating. Because the silver coating itself is susceptible to oxidation and is also susceptible to corrosion, its durability is very weak. Therefore, a silvered glass which can withstand practical use as it is cannot be obtained and it is necessary to form a protective layer on the surface of the silver coating. Since the silver coating is also corroded by water seeping in from the edges, the edges of a silver mirror should also be protected. A silver mirror intended for use in a bathroom is usually subjected to special protection treatment. The protective layer uses an opaque agent in many cases so that the protected mirror is used only as back surface mirror, which unavoidably forms a double image due to the reflection on the surface and on the back.
A mirror having an aluminum coating is generally produced by forming an aluminum thin film by vacuum deposition or sputtering which requires a vacuum system. Further, because film formation takes time, the production efficiency is not so good. Therefore, the production cost tends to be high. Besides, the aluminum coating formed by the above-described method is not very durable, also needing a protective film.
JP-A-6-183787 discloses a method for producing a mirror having a reflectance of 70% or higher without using a vacuum system, in which a reflective layer and a reflection enhancing layer are deposited in sequence in an atmospheric pressure chemical vapor deposition (CVD) system. More specifically, the disclosure teaches that a high-refractive layer, such as a silicon layer, is formed as a reflective layer, and a low-refractive layer of silicon, etc. and a high-refractive layer of silicon, tin oxide, titanium oxide, etc. are made thereon in sequence as refraction enhancing coatings.
On the other hand, prior arts for rendering the surface of a substrate, such as glass, hydrophilic to make it antifogging are disclosed in JP-A-9-278431, JP-A-9-295363, JP-A-10-36144, and TP-A-10-231146. Specifically, JP-A-9-278431 proposes forming a hydrophilic film of polyvinyl alcohol, etc. on a substrate, the average surface roughness of the hydrophilic film ranging from 0.5 to 500 nm. JP-A-9-295363 teaches forming a titanium oxide layer or a tin oxide layer on a substrate, the average surface roughness of the oxide layer being 1 &mgr;m or more. JP-A-10-36144 discloses forming a photocatalyst film of titanium oxide, etc. on a glass substrate and forming a porous inorganic oxide film of silicon oxide, etc. on the photocatalyst film. JP-A-10-231146 proposes forming an alkali-barrier and a photocatalyst film on a glass substrate, the average surface roughness of the photocatalyst layer falling within a range of from 1.5 to 800 nm.
Mirrors to be used under a humid condition, for example in a bathroom, are required to have high durability and excellent antifogging properties. It is easily conceivable that an antifogging mirror is obtained by forming a silver layer and a protective layer on the back side of a transparent substrate and rendering the surface side hydrophilic. In this case, special edge treatment is required due to the poor durability of the silver coating as previously noted.
According to JP-A-6-183787 supra, a mirror having a silicon layer as the outermost layer exhibits satisfactory mirror characteristics owing to the high reflectance of the silicon layer but requires a protective film due to the poor durability of the silicon layer, and a mirror having a tin oxide or titanium oxide layer as the outermost layer exhibits satisfactory durability but has no hydrophilicity.
JP-A-9-278431, JP-A-9-295363, JP-A-10-36144, and JP-A-10-231146 supra all relate to a technique in which a substrate is provided with a hydrophilic coating, and the hydrophilicity is further improved by making the surface of the hydrophilic coating have fine roughness. However, since the performance for maintaining the hydrophihcity is low, the hydrophilicity is impaired with the lapse of time.
SUMMARY OF THE INVENTION
An object of the invention is to provide a hydrophilic and durable mirror having high visible light reflection which is easily cleaned and retains high hydrophilicity even after cleaning.
The object of the invention is accomplished by a hydrophilic mirror comprising a glass substrate having on one of the two main surface sides thereof (A) a layer having a refractive index n1 at 550 nm, (B) a layer having a refractive index n2 at 550 nm, (C) a titanium oxide layer having a refractive index n3 at 550 nm, and (D) an overcoat in this order, the refractive indices n1, n2 and n3 satisfying the relationship: n1≧n3>n2, and having a reflectance of 70% or more of visible light incident on the coated side.
According to the invention there is provided a front surface hydrophilic mirror having a visible light reflectance of 70% or more and, when cleaned with detergent, restores hydrophilicity in an extremely short time. Besides, the restored hydrophilicity lasts long. Protected with a durable overcoat, the mirrors of the invention are effectively used as hydrophilic mirrors, most conveniently in bathrooms.


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Abstracts of Japan, Feb. 27, 1998, vol. 1998, No. 3, Toto Ltd., “Base Material and Method for Keeping Surface Cleanliness of Base Material”.

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