Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
1999-04-30
2001-11-06
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S334000, C428S432000, C359S586000
Reexamination Certificate
active
06312831
ABSTRACT:
FIELD OF THE INVENTION
This invention is related to a film and a method of placing a Ti
x
Sn
y
O
z
. film on a substrate, which may be a hot glass substrate. In particular, the metal oxide film is provided from a liquid mixture of heat decomposable materials including a titanate, a tin compound, and an anhydrous organic liquid to provide a film with high reflectivity, neutral color, and excellent chemical and physical durability.
BACKGROUND OF THE INVENTION
Films are often formed on glass to alter some of its physical properties, e.g., radiation reflection. The use of heat-reflecting glass plates as window panes or wall panels in building and vehicles is valuable in avoiding unwanted rise in the interior temperature and reducing the heat load on the interior air conditions. Transparent coatings on glass with high reflectivity and low thermal absorption used in architectural glazing applications allow reasonably high solar performance without the need for heat treatment. The film may also be applied to enhance the color of the glass on which it is applied. From a design perspective, it is important that the film result in a product that is aesthetically pleasing; often a neutral color enhancement and uniform appearance are desired.
One common technique for applying such films to flat glass involves spraying a hot ribbon of glass as it exits the float glass tin bath. A liquid solution of metal compounds which are thermally decomposable by the glass are commonly employed, although powders are often also used. Titanium oxide has long been used as a coating on glass to provide a heat-reflecting glass plate. While titanium oxide exhibits a very reflective appearance, however, it is difficult to produce a highly reflective TiO
2
coating with a uniformly neutral color on the glass, and, pure titanium oxide films on glass are susceptible to some physical and chemical durability issues. Other metals have been included with the titanium to alter its properties. For example, tin has been included in titania coatings to improve durability, however, such prior art coatings have reflectivity which is lower than that desired for many architectural glazing applications.
We have now unexpectedly found that by using a titanate, preferably tetrabutyl titanate, as the source of titanium, and a tin compound, preferably dibutyltin-diacetate, in a mixture combined with an anhydrous organic liquid, we can produce an oxide film of titanium and tin which has excellent chemical durability and a unexpected high reflectivity. Use of the titanate allows for incorporation of relatively high amounts of tin oxide in the film while yet providing a highly reflective film. This mixture produces a film exhibiting a very smooth surface, exceptionally neutral appearance and excellent chemical and physical durability. These and other features of the present invention will be discussed in detail below.
SUMMARY OF THE INVENTION
The invention is a substrate carrying a singular film of metal oxide, where the metal consists essentially of titanium and tin. More particularly, the film is made from a liquid mixture of a titanate, a tin compound, and an anhydrous organic liquid. Preferably the titanium compound is an organic titanate like tetrabuty-titanate and the tin compound is dibutyltin diacetate. Preferably the anhydrous organic liquid is kerosene or anhydrous isopropanol. Optimally the film has a refractive index greater than 2.2. Preferably the tin is 10-70 atom percent of the metal in the film, i.e., of the total of tin and titanium. According to another aspect of the invention, it is a method of making the film from the liquid mixture disclosed above. According to one aspect of the invention, the liquid mixture is sprayed by pyrolysis techniques onto a surface of a glass substrate which is at a temperature of at least 1000° F. in the presence of air forming the metal oxide film of titanium and tin.
Advantageously the present invention provides a film with high reflectivity and low absorption in the visible light spectrum. The coating has a surprisingly high refractive index for the amount of tin incorporated. The tin provides excellent chemical and physical durability. Additionally, it is produced by a commercially efficient method since the deposition liquid mixture has been found to be very reactive allowing rapid spraying of the substrate, e.g., glass. The film also has excellent adhesion to the substrate.
DISCLOSURE OF PREFERRED EMBODIMENTS
The substrate is coated with a singular film which is an oxide of substantially titanium and tin. Its composition may be a mixture of titanium oxide and tin oxide or be in the form of tin incorporated in the titanium oxide matrix. Hence the formula Ti
x
Sn
y
O
z
is used herein to describe this oxide film along with the phrase titanium/tin oxide. The exact structural determination of the oxide is not necessary for a practice of the invention as will be apparent from a reading of the disclosure herein. The film exhibits, nonetheless, substantial uniformity of the oxide throughout. Preferably, the tin is 10 to 70 atomic percent of the total tin and titanium in the film. That is, the tin atom ratio of 10% means that 10% of the metal in the oxide film is tin, with titanium comprising the remaining 90%. The film was found to retain the essential character of titanium oxide at tin atom ratios of up to 50%. The film has optimal high reflectivity combined with excellent appearance and chemical durability when the tin/metal atom ratio is between 15 and 40%. Most preferred in one embodiment when the film is applied on a glass substrate is a film having a tin atom ratio of about 35%.
Preferably, the titanium/tin oxide film has a refractive index greater than 2.2, preferably being greater than 2.3. Optimally the film has a refractive index for desirable high reflectivity between about 2.32 and 2.6. In this invention, this refractive index is correspondingly linked to a desired high reflectivity and neutral appearance to the film. This index is measured over the 400-700nm wavelength range (i.e. the visible range of the electromagnetic spectrum). The refractive index can be measured by techniques including spectrophotometric ellipsometry, as is well known in the art. In some applications of the present invention, however, where high reflectivity is not as critical as is even more increased durability, an invention film with a refractive index of 2.2 or lower may be useful. Such invention films would thus include higher relative amounts of tin oxide of the ranges disclosed above relative the titanium oxide. The usefulness of this type of invention film would be dictated by the particular film application. TiO
2
films made from titanates have a refractive index of 2.4 to 2.6. SnO
2
films typically have a refractive index of 1.9. The rutile structure found in the films of this invention suggest that the high refractive index of TiO
2
is unexpectedly being retained in the present invention film even for these relatively high concentrations of tin.
By “singular film” as this term is used herein is meant that, in the present invention, the substrate carries a film which is a single layer with no discrete interfaces other than at the surface with the substrate, e.g., the glass. This is in contrast to a film on a substrate which is composed of two or more different compositions, one on top of the other which would have discernible interfaces between the different compositions. Optimally the film of the invention has a thickness of at least 20 nanometers, with 20 to 80 nanometers being more optimal, but most preferably is between about 30 and 60 nm for all substrates. While the films were found to have good optical properties and durability for the range of thickness, e.g., from 20 to 80 nm., the different level of added tin will suggest different optimal thickness to obtain a desired neutral color. For example, to obtain a neutral reflected color when the tin is 35 atom % as in one preferred embodiment, the optimal thickness is between 30 and 60 nm. The film thickness range may be adjusted t
Crawley Richard Lee
Davis James Arthur
Middleton Daryl
Brinks Hofer Gilson & Lione
Jones Deborah
LaVilla Michael
Oberholtzer Steven L.
Visteon Global Technologies Inc.
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