Stock material or miscellaneous articles – Composite – Of quartz or glass
Reexamination Certificate
2001-03-30
2003-09-23
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of quartz or glass
C428S428000, C428S446000, C428S447000, C428S696000, C428S697000
Reexamination Certificate
active
06623863
ABSTRACT:
TECHNICAL FIELD
The present invention relates to articles provided with a water-repellent film coating formed integrally with an primary oxide film on the surface of a substrate made of glass, ceramic, plastic, metal or the like, to a water-repellent film-coating composition and to a process for preparation of water-repellent film-coated articles.
BACKGROUND ART
The following techniques for formation of highly durable water-repellent films on the surfaces of glass plates and other substrates at a high rate of productivity are known, which involve formation of a single film on a substrate using a mixed solution of a primary layer component and a water-repellent component which gives a primary layer and a water-repellent layer.
In Japanese Unexamined Patent Publication No. 4-338137 there is disclosed a water-repellent glass characterized by applying of a solution comprising a mixture of a silicon alkoxide or a substituted silicon alkoxide wherein a portion of the alkoxyl groups are substituted with fluoroalkyl groups, an alcohol, water and an acid (or base) onto a glass substrate surface and sintering.
In Japanese Unexamined Patent Publication No. 8-239653 there are disclosed water-repellent articles treated with a composition comprising a mixture of a perfluoroalkylalkylsilane and a thoroughly hydrolyzable silane (for example, tetrachlorosilane) dissolved in a solvent, preferably a non-aqueous solvent.
In Japanese Unexamined Patent Publication No. 11-71682 there are disclosed water-repellent film-coated articles treated with a composition comprising a chlorosilyl group-containing compound and a fluoroalkyl group-containing silane compound dissolved in an alcohol-based solvent.
In these conventional techniques, the final water-repellent article has been obtained by applying the coating solution onto the surface of the glass plate or the other substrate and then sintering at a temperature of 100-250° C. which is lower than the decomposition temperature of the fluoroalkyl groups (250-300° C.), or simply drying at ordinary temperature. The films obtained by these techniques are known as sol-gel water-repellent films and are obtained through a process whereby a hydrolyzable silane compound and a silane compound with a water-repellent group are hydrolyzed in a solution, subjected to dehydration/condensation reaction and then coated and dried on a substrate; in the sol-gel film, however, the solvent progressively evaporates as oxide bonds are formed, and therefore fine pores are present in the film when it is dried at 400° C. or below, so that the film does not have high hardness. In order to avoid the pores for increased film hardness, it has been essential to accomplish sintering at 500-600° C. However, heating at such high temperatures results in decomposition of the fluoroalkyl groups, making it impossible to achieve the desired water repellency. Consequently, water-repellent films obtained by the aforementioned technique of sintering at 250° C. or below, while being composed mainly of oxides, have not had the high hardness as oxides and ceramics which is achieved by, for example, melt methods.
When such water-repellent film-coated articles are used outdoors, for example, their exposure to such conditions as blown sand readily results in damage to the film surface, thus impairing the water-repellent property. The water-repellent film can also be damaged or peeled when the surface is wiped with a cloth or the like to remove attached dust, dirt or sand. Even in the absence of attached dust, etc., abrasion with a cloth or brush made of hard fibers (such as surface wiping of automobile window glass with a wiper, for example) forms small nicks and further promote deterioration of the water-repellent film.
It is an object of the present invention, which has been accomplished in light of these problems, to provide articles coated with high-performance water-repellent films having high hardness that can withstand outdoor use, a process for preparation of such water-repellent film-coated articles at a high rate of productivity, and a coating liquid composition for preparation of such water-repellent film-coated articles.
DISCLOSURE OF THE INVENTION
As a result of much diligent research by the present inventors aimed at overcoming the aforementioned problems, it has been discovered that by providing a primary oxide film with two or more components including SiO
2
and at least one type selected from among MgO, CaO, SrO and B
2
O
3
in a water-repellent film-coated article having a primary oxide layer and a water-repellent layer integrally formed by a single coating treatment, the hardness of the water-repellent film with the integrally formed primary layer and water-repellent layer is drastically improved.
In other words, the present invention relates to a water-repellent film-coated article comprising a substrate and a water-repellent film composed mainly of silicon oxide and having a water-repellent group coated on the surface of the substrate, the water-repellent film-coated article being characterized in that the water-repellent film contains at least one type of metal oxide selected from the group consisting of magnesium oxide, calcium oxide, strontium oxide and boron oxide.
For formation of oxide films by a sol-gel method it is common to use a silicon alkoxide as the starting material, and this is because the reactivity of silicon alkoxides readily gives a uniform, transparent film by a milder reaction than with alkoxides of elements other than silicon. However since, as mentioned above, the solvent progressively evaporates as bonds (siloxane bonds) are formed between the Si (silicon) and O (oxygen) by dehydration/condensation reaction in the sol-gel method, a porous silica film is obtained wherein fine pores are present in the film. Since the Si and O bonds are covalent bonds and Si and O bond with a high bonding energy, when siloxane bonds form a somewhat three-dimensional structure at the solvent volatilization stage, contraction of the structure is suppressed even with subsequent further dehydration/condensation reaction, such that a volatilized portion of the solvent and the alcohol produced by the dehydration/condensation reaction remains as fine pores, with silanol or unreacted alkoxyl groups present in the fine pores. The hardness of the porous silica film is not very high because of its porosity. When the film is heated at a temperature of 500° C. or above, the fine pores in the film disappear producing a non-porous silica film with high hardness, but it is difficult to form an integral film with high hardness containing substances that decompose at the heating temperature.
According to the invention, the strong ionic nature of magnesium (Mg), calcium (Ca) and strontium (Sr) is utilized: they are dissolved in the coating solution to be copresent with the thoroughly hydrolyzable silane compound, such as a silicon alkoxide, and exist in an ionic state in the solution even at the solvent volatilization stage. Because Mg, Ca and Sr are divalent, they react with silanol, eventually bonding with two oxygen atoms in the film interior as shown in Equation (1), and forming an “O
− +
M
+ −
O” bond which has a freer bonding orientation than an “Si—O—Si” bond, to thereby fill in the gaps of the siloxane skeleton.
When simply dried at normal temperature, for example, this film has about the same hardness as if a silica component alone was used, but heating at a temperature of 50-300° C. contracts the siloxane bonds by action of the Mg (or Ca or Sr), and this eliminates pores and results in a film with high hardness and high durability comparable to inorganic glass prepared by a melt method. That is, while heating at a temperature of 500° C. or above is necessary to eliminate the pores of a simple porous silica film, the porous silica-based film of the invention which contains MgO, CaO or SrO can be rendered pore-free at a temperature of 200° C. or more below that temperature. Furthermore, since the film is heated at a temperature lower than the decomposition temper
Kamitani Kazutaka
Yamamoto Hiroaki
Conlin David G.
Dawson Robert
Edwards & Angell LLP
Feely Michael J
Nippon Sheet Glass Co. Ltd.
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