Plastic and nonmetallic article shaping or treating: processes – Forming electrical articles by shaping electroconductive...
Reexamination Certificate
1999-06-04
2001-10-02
Vargot, Mathieu D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming electrical articles by shaping electroconductive...
C118S715000, C252S502000, C252S512000, C252S516000, C264S001700, C264S105000, C264S614000, C264S669000, C264S125000, C427S162000, C427S167000, C427S255600
Reexamination Certificate
active
06296793
ABSTRACT:
SUMMARY OF THE INVENTION
The invention relates to a composition for preparing water-repellent (hydrophobic) coatings on optical substrates and to the substrates which bear these coatings.
Methods exist to provide the surface of optical components with thin coatings in order to protect them or to obtain certain functional properties. By such optical components are meant primarily lenses for optics, spectacles, cameras, telescopes, binoculars or other optical devices, beam splitters, prisms, mirrors, window panes, etc. One aim of such coatings is to upgrade the surface of optical substrates in such a way that, by hardening and/or increasing chemical resistance, mechanical, chemical or environmental damage is avoided. This is especially important in the case of substrates comprising polymer materials. A second aim of using surface coatings is to reduce reflection, especially in the case of lenses for spectacles and cameras. In this case, given an appropriate choice of coating materials, coat thickness, single-layer structure or multilayer structure from the same or different materials with different refractive indices, it is possible to achieve a reduction in the reflection to less than about 1% over the entire spectrum of visible radiation.
Quality-enhancing and antireflection layers are produced using numerous materials of oxide type, such as SiO2, TiO2, ZrO2, MgO and Al203, fluorides, such as MgF2, and mixtures of these substances. The coating of optical substrates is commonly accomplished by high-vacuum vapor deposition. Here, the substrate and an initial charge comprising the substance to be applied are placed in an appropriate high-vacuum vapor deposition apparatus, which is then evacuated, and the substance is then evaporated by heating and/or electron beam evaporation and is deposited as a thin layer on the substrate surface. Corresponding apparatus and techniques have been described.
Quality-enhancing layers of this kind, especially antireflection layers, however, are extremely sensitive to soiling by, for example, wet or greasy fingerprints. Impurities greatly increase the reflection; fingerprints, therefore, become clearly visible. Effective cleaning to restore the original level of reflection is difficult. For this reason it has become established practice to provide optical components additionally with a hydrophobic, i.e. water-repellent, coating.
To render the surface of optical substrates hydrophobic a range of substances is available, especially from the class of the organosilicon compounds. Examples of such compounds are silanes, siloxanes, silicones, and silicone oils. These substances are generally applied to the target substrate surfaces by dipping or spin coating, and are employed either in pure form or as solutions. Surface treatment and the removal of any solvent by evaporation are generally followed by a thermal aftertreatment, which strengthens the water-repellent coating and causes it to adhere to the substrate material. The resulting coatings generally have satisfactory properties in terms of hydrophobicization, durability and long-term adhesion.
Many methods of coating surfaces of optical substrates with hydrophobicizing agents have disadvantages. For example, in the case of dip and spin coating it is necessary to work under strict clean room conditions in order to rule out adverse effects on quality caused, for instance, by dust particles. Moreover, these techniques require additional operations with corresponding plant and machinery.
JP 05-215 905 discloses a process for producing water-repellent coatings on optical substrates which involves applying fluoroalkylsilazane compounds to the substrate surface by means of the high-vacuum vapor deposition technique. This process has advantages over the customary dip and spin coating techniques in that it can readily be carried out in existing high-vacuum vapor deposition apparatus—for instance, directly following the vapor coating of the substrate with antireflection layers or other quality-enhancing layers. The perfluoroalkylsilazane compounds are preferably introduced in the form of a porous metallic sintered structure impregnated with the substance.
JP 04-355 404 likewise describes a metallic sintered structure for absorbing the organosilicon compounds that are used as the coating material.
JP 08-143 332 describes steel wool instead of metallic sintered structures as a carrier material for the organosilicon compounds that are to be evaporated.
DE 195 39 789 discloses a sintered structure of inorganic oxides for absorbing fluoroalkylsilanes in order to produce water-repellent layers. See also, U.S. Pat. No. 5,853,800.
The sintered structures impregnated with the coating material are introduced into a high-vacuum vapor deposition unit and then the coating material is vapor-coated in a resistance-heated boat or with the aid of an electron beam. Where an electron beam evaporator is used, these sintered structures have considerable disadvantages or are even impossible to use. A sintered structure of oxide type acts as an insulator, becomes electrostatically charged, and heats up suddenly only when the output of the electron beam is increased, so rendering controlled evaporation of the coating material impossible. In some cases the sintered material evaporates as well, thereby preventing the formation of water-repellent layers. When using the highly temperature-stable fluoroalkylsilanes it is impossible to employ metallic sintered structures or steel wool. When using less temperature-stable silicon compounds, however, there is also a risk that parts of the metal structure will be evaporated as well and adversely affect the function of the water-repellent layer.
An object of the invention is to provide a composition for preparing water-repellent coatings on optical substrates, whose support material is a good electrical conductor and possesses a high vaporization temperature, so that it is suitable for application of a wide variety of coating materials.
This object is achieved in accordance with the invention by a composition for preparing water-repellent coatings on optical substrates, comprising a porous, electrically conductive molding and an organosilicon compound and obtainable by
a) mixing an electrically conductive or semi-conductive support material and a binder,
b) subjecting the mixture to compression molding and sintering to form a porous molding,
c) impregnating the molding with the organosilicon compound, and
d) ageing the impregnated molding by storage in air.
It is believed, without being restricted to theory, that the organosilicon compound is cleaved by ageing.
Upon further study of the specification and appended claims, further objects and advantages of this invention will become apparent to those skilled in the art.
The invention additionally provides optical substrates with a coating applied using the composition of the invention by vapor deposition in a high vacuum.
It has been found that porous moldings of an electrically conductive or semi-conductive material are highly suitable as supports for organosilicon compounds and that the organosilicon compounds can be evaporated from them at a readily controllable rate by heating, e.g., with an electron beam. It has also been found that moldings consisting only of one metal cannot be used for highly temperature-stable compounds. By moldings are meant for the purposes of the invention, for example, tablets or granules having a particle size of from about 1 to 4 mm.
The electrically conductive material of the invention comprises a conductive metal oxide, carbide, nitride or silicide; carbon; a metal powder; or a mixture thereof. Metal powders, however, can be used only in a mixture with an electrically non-conductive material.
The conductive metal oxide is preferably tin dioxide, which may be doped with antimony, fluorine, phosphorus, niobium or tantalum. However, it is also possible to employ semiconductors, such as indium oxide, for example.
When using carbides, such as titanium carbide, chromium carbide and tungsten carbide, it is preferable t
Anthes Uwe
Dombrowski Reiner
Merck Patent Gesellschaft mit
Millen White Zelano & Branigan P.C.
Vargot Mathieu D.
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