1. Field of the Invention
This invention relates to an aqueous suspension having two or more solid organometallic precursors, e.g. metal acetylacetonates; the aqueous suspension used in a pyrolytic spray coating process to deposit optically thin coating films, and more particularly, to an aqueous suspension having two or more solid metal acetylacetonates milled or ground to a particle size based on a chemical property of the metal acetylacetonates to deposit optically thin coating films having improved durability.
2. Discussion of the Presently Available Technology
Pyrolytic coating is a method of applying a coating onto a surface of a hot glass substrate, e.g. a continuous glass ribbon, or a glass sheet, generally heated to 1112° Fahrenheit (F); (600° Centigrade (C)) to deposit one or more optically thin coating films on a surface of the substrate. At the present time there are two general types of pyrolytic coating processes, commonly referred to as pyrolytic vapor coating process and pyrolytic spray coating process. In the present practice of depositing optically thin coating films on the surface of the heated glass substrate, the organometallic precursors are preferably in a liquid or a vapor. More particularly, in the pyrolytic vapor coating process, a vapor having organometallic precursors is directed onto the surface of the heated glass substrate, and in the pyrolytic spray coating process, a liquid having organometallic precursors is directed onto the surface of the heated glass substrate. The heat from the glass substrate decomposes the organometallic precursors, and the metals from the precursors oxidize and bond to the surface of the substrate. A detailed discussion of a pyrolytic vapor coating process is presented in U.S. Pat. No. 5,356,718, and a detailed discussion of a pyrolytic spray coating process is presented in U.S. Pat. Nos. 4,111,150; 3,652,246 and 3,796,184, the disclosures of which are hereby incorporated by reference. Of particular interest in the present discussion is the pyrolytic spray coating process.
In general, the organometallic precursors used in the pyrolytic spray coating process are metal acetylacetonates (hereinafter “acetylacetonate” is also referred to as “AcAc”) or beta di-ketonates or neodecanoates. Of particular interest in this discussion are the metal AcAc. Metal AcAc's are soluble in organic solvents and considered non-soluble in water; however, for health and safety reasons, it is preferred to use water instead of organic solvents. In the instance when the precursors are non-soluble in water, particularly at room temperature, such as metal AcAc's, the metal AcAc's are milled or ground, and mixed in water to provide an aqueous suspension. Dry metal AcAc's can be milled or ground to provide particles in a desired micron range, and the milled dry metal AcAc's mixed in water, or the metal AcAc's can be mixed in water to provide a mixed slurry, and the mixed slurry moved through a media mill to provide an aqueous suspension having the milled particles of the metal AcAc's. In both instances, the particles of the metal AcAc's are in the same micron range. During the pyrolytic coating process, the aqueous suspension is passed through the nozzles of a coating apparatus, e.g. of the type disclosed in U.S. Pat. No. 4,111,150, to apply or deposit one or more optically thin coating films on the surface of a glass substrate, e.g. a continuous glass ribbon.
Although the optically thin coating films obtained using aqueous suspensions prepared as discussed above are acceptable, it would be advantageous to provide an aqueous suspension of metal AcAc's that provides optically thin coating films that have improved durability over the optically thin coating films presently obtained.