Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
1997-02-13
2001-05-15
Turner, Archene (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C359S359000, C359S360000, C359S585000, C427S164000, C427S165000, C428S621000, C428S622000, C428S632000, C428S698000, C428S701000, C428S702000, C428S216000, C428S336000, C428S469000, C428S472000, C428S432000, C428S433000, C428S434000
Reexamination Certificate
active
06231999
ABSTRACT:
FIELD OF THE INVENTION
This invention is directed to transparent coatings for glass substrates, and particularly to glass substrates having coatings that are capable of withstanding high temperatures such as those encountered during glass tempering and bending, and those encountered during the cleaning cycle of self cleaning ovens.
BACKGROUND OF THE INVENTION
Glass sheets can be coated with a stack of transparent, metal-containing films to vary the optical properties of the coated sheets. Particularly desirable are coatings characterized by their ability to readily transmit visible light while minimizing the transmittance of other wavelengths of light, particularly light in the infrared spectrum. These characteristics are useful for minimizing radiative heat transfer without impairing visibility, and coated glass of this type is useful as architectural glass, glass for use as automobile windows, etc.
Coatings having the characteristics of high transmittance and low emissivity commonly include film stacks having one or more thin metallic films with high infrared reflectance that are disposed between antireflective dielectric films such as metal oxide films. The metallic films may be silver, and the metal oxide films may be the oxides of various metals and metal alloys including zinc, tin, titanium, etc. Films of the type described commonly are deposited on glass substrates on a commercial production basis through the use of well known magnetron sputtering techniques.
It is often necessary to heat glass sheets to temperatures at or near the melting point of the glass to temper the glass or to enable the glass to be bent into desired shapes such as motor vehicle windshields. Coated glass articles often must be able to withstand high temperatures for periods of time up to several hours. Tempering, as is known, is particularly important for glass intended for use as automobile windows and particularly for use as automobile windshields; upon breaking, windshields desirably exhibit a break pattern in which they shatter into a great many small pieces rather than into large, dangerous sharp shards. Tempering temperatures on the order of 600° C. and above are required. Film stacks employing silver as an infrared reflective film often cannot withstand such temperatures without some deterioration of the silver film. To avoid this problem, glass sheets can be heated and bent or tempered before they are coated, and later can be provided with the desired metal and metal oxide coatings. Particularly for bent glass articles, this procedure may produce non-uniform coatings and is costly.
Another reported method for protecting a reflective metal film such as silver from deterioration at high temperatures involves sandwiching the silver film between protective films of an oxidizable metal such as titanium, these protective metal films being of sufficient thickness so that when a coated glass is heated to high temperatures, the protective metal films oxidize. Inasmuch as thin films of the oxides of metals commonly are more transparent than thin films of the metals themselves, the transmissivity of glass sheets bearing such coatings tends to increase upon heating. Reference is made to Huffer et al. U.S. Pat. No. 4,790,922 and Finley U.S. Pat. No. 4,806,220.
U.S. Pat. No. 5,344,718 (Hartig et al.) describes the use of a film stack in which silver is sandwiched between films of nickel or nichrome, and the resulting sandwich is sandwiched between films of Si
3
N
4
, the glass article having particular values of transmittance and emissivity. It is said that when a Ni:Cr (50:50) alloy is employed, the chromium during sputtering is converted at least in part to a nitride of chromium and that visible transmittance thus is improved. The ability of nickel, chromium and chromium nitride to transmit visible light, however, is not great, and as a result the transmissivity of glass articles that include films of nichrome may be somewhat less than desired.
The above description pertains primarily to efforts to produce glass structures useful as architectural glass or glass for automobile windows, in which the glass structures in use are not usually subjected to high temperatures after they have once been tempered or bent. Coated glass sheets may also find utility as windows for ovens of various types in which the windows are subjected to repeated heating and cooling cycles as the ovens are heated and cooled during normal usage. A good example of such usage is a self-cleaning kitchen oven in which the oven temperature may be repeatedly raised to cooking temperatures of 250° F. to 450° F. with frequent excursions to e.g., 900° F. during cleaning cycles. An oven window of this type should be transparent to enable one to see through it into the oven. It should be highly reflective in the infrared range to retard heat loss from the oven and help keep the exterior of the oven from getting too hot. Further, it must be resistant to deterioration resulting from repeated temperature escalations while exposed to the conditions of humidity and chemical (food) oven conditions.
SUMMARY OF THE INVENTION
In one embodiment, the invention provides a transparent, heat-resistant glass article comprising a glass substrate and a transparent film stack deposited upon the substrate. The film stack comprises, from the glass substrate outwardly, a transparent infrared reflective metallic film and a protective barrier film of niobium metal deposited directly on the infrared reflective film. The thickness of the niobium metal film may range up to 25 Å, preferably in the range of from 7 Å to 20 Å
The film stacks of the invention may consist of one, two or more infrared reflective metallic films, preferably one or two silver films, each infrared reflective metallic film bearing directly on its surface facing away from the substrate a protective niobium film up to 20 Å in thickness. On the other surface of the infrared reflective films (the surface facing the substrate) may be deposited a protective film of niobium or, preferably, a metal oxide such as an oxide of zinc, niobium or titanium, the oxide film being present at a thickness sufficient to protect the metal film from deterioration during high temperature processing. Zinc oxide films in the range of 50 to 180 Å in thickness are preferred.
In one embodiment, the film stack includes a thin film of niobium as a barrier film on both sides of the infrared reflective film, the latter being sandwiched between and in direct contact with the niobium films. The sandwich structure thus described desirably is received between films of a nitride such as silicon nitride. Upon tempering the glass product, at least some nitriding of the niobium films occurs.
In a preferred embodiment, the film stack contains two infrared reflective films and includes, from the glass substrate outwardly, a film sequence comprising a metal oxide barrier film, a transparent infrared reflective silver film, a niobium metal barrier film not greater than about 25 Å in thickness, followed by a repeat of said film sequence, and a protective film, preferably an outermost film, of transparent silicon nitride. Most preferred is a film sequence comprising. from the glass substrate outwardly, a metal oxide barrier film, a transparent infrared reflective film, a protective niobium barrier film up to 25 Å in thickness, a metal oxide barrier film, a second transparent infrared reflective film, and a second protective niobium barrier film up to 25 Å in thickness. The minimum thickness of each niobium film is such that, following tempering and associated conversion of some of the niobium to the oxide, nitride or other niobium compound, there yet remains a protective film of niobium metal over each infrared reflective film. The thickness of the niobium films preferably ranges from 7 to 20 Å/.
In another embodiment, the invention relates to a method for manufacturing a transparent glass article comprising depositing on a surface of a glass substrate a transparent film stack comprisin
Cardinal IG Company
Fredrikson & Byron PA
Turner Archene
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