Coating processes – Coating by vapor – gas – or smoke – Base includes an inorganic compound containing silicon or...
Reexamination Certificate
2001-04-17
2003-02-18
Meeks, Timothy (Department: 1762)
Coating processes
Coating by vapor, gas, or smoke
Base includes an inorganic compound containing silicon or...
C427S255320, C065S060520
Reexamination Certificate
active
06521295
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a method for forming a metal oxide coating on glass, and more particularly, to a process for preparing a tin oxide coating doped with antimony on a hot glass substrate by chemical vapor deposition.
BACKGROUND OF THE INVENTION
Typically, coated glass articles are produced by continuously coating a glass substrate while it is being manufactured in a process known in the art as the “Float Glass Process”. This process involves casting glass onto a molten tin bath which is suitably enclosed, then transferring the glass, after it has sufficiently cooled, to take-away rolls which are aligned with the bath, and finally cooling the glass as it advances across the rolls, initially through a lehr and thereafter while exposed to the ambient atmosphere. A non-oxidizing atmosphere is maintained in the float portion of the process, while the glass is in contact with the molten tin bath, to prevent oxidation. An air atmosphere is maintained in the lehr. The chemical vapor deposition (CVD) of various coatings may be conveniently performed in the bath or the lehr, or even in the transition zone therebetween, by contacting the surface of the hot glass with chemical vapor-containing reactants which pyrolytically decompose to form the metal oxide coating. This, of course, requires that the chemical reactants have vaporization temperatures below their thermal decomposition temperatures. A number of metal-containing compounds exist which may be vaporized to prepare a metal oxide coating on glass by CVD technology. Of particular interest are tin compounds which are vaporized to form tin oxide coatings.
The desirable performance characteristics of certain metal oxide coatings, such as tin oxide coatings, on glass, for example, are low emissivity, low sheet resistance, high light transmittance, high infrared reflectivity, etc., and are improved by the incorporation of a dopant into the metal oxide coating. Among the materials used in the prior art as dopants is antimony. Typically, antimony has been supplied in the form of inorganic antimony compounds, such as an antimony halide, for example, SbCl
3
.
The physical form of the reactants employed in glass coating processes is generally a liquid, solid, vaporized liquid or solid, liquid or solid dispersed in a carrier gas mixture, or vaporized liquid or solid dispersed in a carrier gas mixture. The chemical vapor deposition process generally employs a vaporized liquid or solid, which is typically dispersed in a carrier gas mixture.
U.S. Pat. No. 6,005,127 discloses an organoantimony Lewis base adduct which is said to be useful for Sb-ion implantation and formation of antimonide films, by various types of chemical vapor deposition. The present invention does not contain Lewis base adducts, nor does it involve ion implantation or formation of metal antimonides. Further, the '127 patent only discloses the following methods of chemical vapor deposition: chemical vapor deposition, assisted chemical vapor deposition (e.g., laser, light, plasma, ion, etc.).
It would be desirable to improve the heretofore known methods for applying an antimony doped tin oxide coating to a surface of a hot glass substrate by a CVD process, and thereby enhance the low sheet resistance and uniformity of the sheet resistance of the coated glass product, while at the same time minimizing the undesirable pre-reaction of precursor materials which occurs with known inorganic antimony dopants. It would also be desirable to provide a method for applying an antimony-doped tin oxide coating to a surface of a hot glass substrate which is less costly than the heretofore known methods.
SUMMARY OF THE INVENTION
The present invention is directed toward a chemical vapor deposition process for applying an antimony doped metal oxide coating to a surface of a hot glass substrate. Preferably, the metal is a tin compound. Most preferably, the tin compound is an organotin compound. Surprisingly, it has been discovered that the desirable properties of antimony doped metal oxide coatings, particularly tin oxide coatings, on glass, are improved by utilizing a process comprising:
A chemical vapor deposition process for applying an antimony doped metal oxide coating to a surface on a hot glass substrate, comprising:
a) providing a hot glass substrate, including a surface upon which an antimony doped metal oxide coating is to be deposited;
b) providing a uniform, vaporized reactant mixture containing a metal compound, an oxygen-containing compound, water, and an organoantimony compound which will not pre-react with said oxygen-containing compound or water at temperatures below 550° F.;
c) delivering the vaporized reactant mixture to the surface of the hot glass substrate, and reacting the mixture to deposit a coating of antimony doped metal oxide on the surface of the hot glass substrate; and
d) cooling the coated glass substrate to ambient temperature.
A source of oxygen is necessary for the process of the invention, and is preferably chosen from among air, gaseous oxygen and molecular oxygen.
In a preferred embodiment, a sodium diffusion barrier, preferably a layer of silica, is applied to the surface of the glass substrate prior to the deposition of the antimony doped metal oxide. The process of the present invention is particularly suitable for the production of glass having an antimony doped metal oxide coating, and is useful for energy efficient architectural windows, airplane or automobile windows, and a variety of optical and electronic devices.
Co-pending U.S. patent application Ser. No. 09/625,921 discloses an antimony doped tin oxide film deposited on, and adhering to a glass substrate, and a coating of fluorine doped tin oxide deposited on and adhering to the coating of antimony doped tin oxide. The resulting coated glass article has a high solar selectivity. U.S. patent application Ser. No. 09/625,921 is, herein, incorporated by reference in its entirety.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Metal oxide coatings, particularly tin oxide coatings doped with antimony, may be deposited onto the surface of a hot glass substrate by a process generally known in the art as chemical vapor deposition (CVD). In accordance with the process of the invention, the reactants are combined so as to form a uniform, vaporized reactant stream which is delivered to the surface of the hot glass substrate, wherein the vaporized reactant stream reacts to deposit a coating of antimony doped metal oxide on the surface of the hot glass substrate. In the oxidizing atmosphere, which must exist at the surface of the hot glass, organometallic compounds, preferably organotin coating compounds, pyrolytically decompose to form a metal/tin oxide coating.
The process is typically conducted during the manufacture of glass by the float glass process, and occurs in the float bath, the lehr, or in the transition zone between the bath and the lehr, while the glass is still hot. The glass substrate is generally provided at a temperature in the range from about 750° F. to about 1500° F. These are typical temperatures for glass during various stages as it is manufactured by the float glass process. More specifically, the coating process is conducted at temperature in the range of 900-1350° F., preferably in the range of 1100-1280° F.
The glass substrates suitable for use in the process according to the present invention include any of the conventional glass substrates known in the art for the preparation of coated glass articles. A typical glass substrate, used in the manufacture of vehicle windows and plate glass, is commonly referred to as soda-lime-silica glass. Other suitable glasses may be generally designated as alkali-lime-silica glass, boro-silicate glass, alumino-silicate glass, boro-alumino silicate glass, phosphate glass, fused silica, etc., as well as combinations thereof. A preferred glass is soda-lime-silica glass.
The CVD reactant stream of this invention preferably includes an organotin coating compound which is vaporized and conveyed to a po
Marshall & Melhorn LLC
Meeks Timothy
Pilkington North America Inc.
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