Stock material or miscellaneous articles – Composite – Of quartz or glass
Reexamination Certificate
1999-11-10
2002-06-11
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of quartz or glass
C428S447000, C428S448000
Reexamination Certificate
active
06403225
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an article superior in making waterdrops slip down the surface of the article. This article can be used as a window pane of various vehicles, watercraft and aircraft.
Hitherto, there have been various proposals for increasing water-repellency of an object in order to remove waterdrops from the surface of the object. Japanese Patent Unexamined Publications JP-A-58-122979, JP-A-58-129082, JP-A-58-142958, JP-A-58-147483, JP-A-58-172242, JP-A-58-172244, JP-A-58-172245, JP-A-58-172246, JP-A-58-190840, and JP-A-58-223634 disclose agents that are capable of providing a glass surface with water-repellency. JP-A-58-167448 discloses a low reflectance glass. JP-A-6-16455, JP-A-6-340451, JP-A-7-138046, JP-A-7-138047, JP-A-7-138050, JP-A-7-267684, and JP-A-8-40748 disclose water-repellent glass panes. JP-A-7-9608 and JP-A-4-255343 disclose water-repellent, oil-repellent coating films.
SUMMARY OF THE INVENTION
“The angle of waterdrop slippage” can be defined as being an angle of a surface of an article to the level, at which a waterdrop starts slipping down the surface of the article by tilting the article after the deposition of the waterdrop in a predetermined amount on the surface of the article set horizontal. As the angle of waterdrop slippage becomes smaller, the surface of an article becomes superior or easier in making waterdrops slip down the surface of the article.
It is therefore an object of the present invention to provide an article that is small in angle of waterdrop slippage and thereby superior in making small waterdrops slip down the surface of the article.
According to the present invention, there is provided an article superior in slipping a waterdrop down a surface of the article. The article has a substrate; and a functional layer formed on the surface of the substrate. The functional layer is chemically bonded to the surface of the substrate through siloxane-bonding. The article is prepared by a method comprising: (a) preparing a mixed liquid; (b) applying the mixed liquid to the surface of the substrate, thereby to form thereon a precursory layer; and (c) drying the precursory layer into the functional layer. According to a first aspect of the invention, the mixed liquid is prepared by dissolving in a solvent (1) a silicone that is one of a first silicone having at an end a hydrolyzable functional group and a second silicone having at an end a hydrolyzable functional group and at the other end a fluoroalkyl group, (2) an acid, and (3) water. According to a second aspect of the invention, the mixed liquid is prepared by dissolving in a solvent (1) the above silicone, (2) a silica precursor sol, (3) an acid, and (4) water. According to a third aspect of the invention, the mixed liquid is prepared by dissolving in a solvent (1) the above silicone, (2) a fluoroalkylsilane having at its end a hydrolyzable functional group, (3) a silica precursor sol, (4) an acid, and (5) water. Furthermore, an underlayer made from a hydrolyzable silicon compound may be provided between the substrate and the functional layer. In this case, the functional layer is chemically bonded to the surface of the underlayer through siloxane-bonding.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As stated above, the special silicone is used in the invention as an essential component of the mixed liquid. With this, the obtained article becomes unexpectedly superior in making waterdrops slip down the surface of the article. Furthermore, many reaction sites (i.e., the hydrolyzed functional groups) of the silicone are chemically bonded to the surface of a substrate. Thus, the article becomes superior in durability, too.
As stated above, according to the second aspect of the invention, the mixed liquid is prepared by dissolving in a solvent the silicone, a silica precursor sol, an acid, and water. It is preferable that these silicone and silica precursor sol are dissolved at first in a solvent and then these acid and water are added thereto. According to the third aspect of the invention, the mixed liquid is prepared by dissolving in a solvent the silicone, the fluoroalkylsilane (FAS), a silica precursor sol, an acid and water. It is preferable that these silicone, silica precursor sol and fluoroalkylsilane are dissolved at first in a solvent and then these acid and water are added thereto. The silica precursor sol of the second and third aspects of the invention contains a silica precursor. This sol is capable of turning into a gel and then into silica (SiO
2
) through baking of the gel.
In the invention, it is optional to form between the substrate and the functional layer an underlayer that has at its surface many reaction sites reactive with the silicone of the functional layer. With this, it becomes possible to increase the reaction sites of the silicone that are bonded to the underlayer. Therefore, it becomes possible to further improve the article in making waterdrops slip down the surface of the article. The underlayer may be prepared by a method comprising (a) applying a silicon compound (e.g., tetraisocyanate silane) that is hydrolyzable at a relatively low temperature (e.g., room temperature), to the surface of the substrate, thereby forming thereon a precursory layer; and (b) drying the precursory layer into the underlayer. If, for example, tetraisocyanate silane is applied to a glass substrate, it is hydrolyzed at room temperature by moisture in the air and then dried at a drying temperature into a silica film. This silica film is strongly attached to the glass substrate through siloxane-bonding. The silica film further has at its surface many silanol groups, which are reactive with the silicone and with the hydrolyzable functional groups of the fluoroalkylsilane of the functional layer. The lower the drying temperature for forming the silica film, the greater the number of silanol groups formed on the surface of the silica film. In view of this, it is the most preferable to use tetraisocyanate silane as the coating liquid, because tetraisocyanate silane can be dried into a silica film at room temperature. Alternatively, perhydropolysilazane can be used as the coating liquid.
In the invention, it is necessary to use in the preparation of the article the above special silicone that is one of (1) a first silicone having at its end a hydrolyzable functional group and (2) a second silicone having at its one end a hydrolyzable functional group and at the other end a fluoroalkyl group. A functional layer can be formed on a glass substrate by dissolving the special silicone in an organic solvent (e.g., alcohol) and then by applying the resultant coating liquid to the glass substrate. After this application, the functional end-group of the silicone is hydrolyzed by moisture in the air. With this, the hydrolyzed end-group is chemically bonded to the surface of the glass substrate. Therefore, the obtained functional layer becomes superior in durability. If acid and water are additionally added to the coating liquid, it becomes possible to accelerate the hydrolysis of the functional end-group of the silicone. In particular, in case that the substrate is made of glass, more reaction-sites (i.e., the hydrolyzed functional groups) of the silicone are chemically bonded to the surface of the substrate by the addition of acid and water to the coating liquid. With this, the article becomes superior in durability and also in slipping waterdrops down the surface of the article. The acid content of the coating liquid is preferably from 0.001 to 0.2 wt %. The water content of the coating liquid is preferably from 0.1 to 20 wt %.
If the second silicone, which has at its one end a hydrolyzable functional group and at the other end a fluoroalkyl group, is used as the silicone in the preparation of the mixed liquid, the obtained article may become superior in oil-repellency as well as in slipping waterdrops down the surface of the article. This oil-repellency may also be obtained by using the above-mentioned fluoroalkylsilane according to the third aspect of the
Kai Yasuaki
Murase Heihachi
Narisawa Ikuo
Takeishi Makoto
Takekawa Toshihiro
Feely Michael J
Foley & Lardner
Nissan Motor Co,. Ltd.
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