MXPA98010817A - Article glass transparent thermo-resiste - Google Patents

Abstract

A thermo-resistant transparent glass article is formed, with a stack of films deposited on a glass substrate, the film stack comprising one or more infrared reflecting films (20), each containing on its surface away from the substrate a barrier film of niobium metal (18, 22) having a thickness of up to 25 A and preferably in the range of about 7Å to 20Å. A niobium metal film (18, 22) or preferably metal oxide can be formed on the other surface (facing the substrate) of each infrared reflective film. Metal nitride films (16, 24) such as silicon nitride can be used between neighboring infrared reflective films (20), and as an external protective film.

Description

THERMO-RESISTANT TRANSPARENT COATED GLASS ARTICLE 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 tempering and bending of glass and those encountered during the Cleaning cycle of automatic cleaning ovens. BACKGROUND OF THE INVENTION The glass sheets can be coated with a stack of transparent metal containing films, to vary the optical properties of the coated sheets. Coatings characterized by their ability to readily transmit visible light are particularly desirable, while the transmittance of other wavelengths of light, especially light in the infrared spectrum, is minimized. These characteristics are useful to minimize radiant heat transfer without deteriorating visibility, and coated glass of this type is useful as architectural glass, glass to be used as automotive windows, etc. Coatings that have the characteristics of. high transmittance and low emissivity, commonly include stacks of films having one or more thin metal films with high infrared reflectance, disposed between anti-reflective dielectric films such as metal oxide films. The metallic films can be made of silver, and the metal oxide films can be the oxides of various metals and metal alloys including zinc, tin, titanium, etc. Films of the commonly described type are deposited on glass substrates on a commercial production basis through the use of well-known magnetron sputtering techniques with magnetron sublimation. It is often necessary to heat glass sheets at temperatures at or near the melting point of the glass to temper the glass or to allow the glass to bend in desired shapes such as motor vehicle windshields. Often coated glass articles must be capable of withstanding high temperatures for periods of time up to several hours. Tempering, as it is known, is particularly important for glass that is intended to be used as automotive windows and particularly for use as automotive windshields; when broken, the windshields conveniently exhibit a rupture pattern that fragments into a lot of very small pieces instead of sharp, dangerous and large fragments. Tempering temperatures in the order of 600 ° C and above are required. Piles of film that use silver as an infrared reflective film often can not withstand these temperatures without deterioration of the silver film. To avoid this problem, glass sheets can be heated and bent or tempered before coating and subsequently provided with the desired metal oxide and metal coatings. Particularly for bent glass articles, this process can produce non-uniform coatings and is expensive. Another method reported to protect 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 are of sufficient thickness such that when A coated glass is heated to high temperatures, metal protective films are oxidized. Since these thin films of metal oxides are usually more transparent than the thin films of the metals themselves, the transmissivity of the glass sheets containing these coatings tends to increase when heated. Reference is made to the US patent. No. 4,790,922 issued to Huffer et al., And the US patent. No. 4,806,220 granted to Finley.

The patent of the U.S.A. No. 5,344,718 (Hartig et al.) Describes the use of a stack of films where silver is sandwiched between nickel or nichrome films (nichrome) and the resulting sandwich is sandwiched between Si3N4 films, the glass article has particular values of transductance and emissivity. It is said that when a Ni.Cr alloy (50:50) is used, the chromium during eletrodeposition is at least partly converted into a chromium nitride and that in this way the visible transmittance 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 glassware including nichrome films can be somewhat less than desired. The foregoing description relates primarily to efforts to produce useful glass structures such as architectural glass or automotive window glass, where the glass structures in use are usually not subjected to high temperatures after they have been tempered or bent. Coated glass sheets can also find utility as windows for furnaces of various types, where the windows are subjected to repeated cooling and heating cycles and the furnaces are heated and cooled during normal use. A good example of this use is an automatic cleaning oven, where the oven temperature can rise repeatedly to cooking temperatures from 121 ° C (250 ° F) to 232 ° C (450 ° F) with frequent increases for example at 482 ° C (900 ° F) during cleaning cycles. A furnace window of this type should be transparent to allow to see through it into the furnace. It should be highly reflective in the infrared range to retard thermal loss of the oven and prevent the oven display from getting too hot. In addition, it must be resistant to the resulting deterioration by repeated increases in temperature while being exposed to the moisture conditions and chemical conditions of the oven (food). SUMMARY OF THE INVENTION In one embodiment, the invention provides a transparent heat-resistant glass article comprising a glass substrate and a stack of transparent films deposited on the substrate. The film stack comprises from the glass substrate outward, a transparent infrared reflecting metallic film and a protective barrier film of niobium metal deposited directly on the reflective film. The thickness of the niobium metal film can be in the range of up to 25 Angles (Á), preferably in the range of 7 Á to 20 Á.

The film stacks of the invention may consist of one or two or more infrared drying metallic films, preferably 1 or 2 silver films, each infrared reflecting metal film containing directly on its surface remote from the substrate, a protective niobium film of a thickness up to 25 Á, preferably up to 20 Á, and more preferably in the range from 7 Á to 20 Á. On the other surface of the infrared reflective films (the surface directed to the substrate) a niobium protective film, or preferably a metal oxide such as a zinc oxide, niobium or titanium, can be deposited, the oxide film is present in a enough thickness to protect the metal film against deterioration during high temperature processing. Zinc oxide films in the range of 50 or 150 A in thickness are preferred. Conveniently, a zinc oxide film of from about 100 to about 300A in thickness directly below (towards the glass substrate from) the infrared reflecting metal film furthest away from the substrate, contributes to a reduction in UV transmission and is 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 in this conveniently described manner is received between films of a nitride such as silicon nitride. When tempering the glass product, 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 facing out, a sequence of films comprising a metal oxide barrier film, a transparent infrared reflecting silver film, a barrier film metal niobium no greater than about 25 Á in thickness, followed by a repetition of this sequence of films, and a protective film, preferably a more external film of transparent silica nitride. More preferred is a sequence of films comprising, from the glass substrate outwardly, a metal oxide barrier film, a transparent infrared reflective film, a protective niobium barrier film up to 25 A in thickness, a barrier film of metal oxide, a second transparent infrared reflecting film, and a second protective niobium barrier film up to 25 Á in thickness. The minimum thickness of each niobium film is such that, following the tempering and associated conversion of niobium to oxide, nitride or other niobium compound, however, a niobium metal protective film remains on each infrared reflecting film. The thickness of the niobium films is preferably in the range of 7 to 20 Á. Conveniently, each infrared reflecting metal film is directly followed (from the glass substrate outwards) by a contiguous sequence of niobium metal barrier films up to 25 A in thickness and a metal oxide film, preferably zinc oxide, each sequence is followed by a protective nitride film, preferably silicon nitride. Still further, the outermost silicon nitride film (away from the glass substrate) has directly below it a titanium nitride film which is in the range in thickness from about 15 to about 40A, the latter having the effect to reduce the color appearance of the movie stack. 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 stack of transparent films comprising, from the glass surface outwardly, an infrared reflecting metallic film. transparent, a protective niobium metal barrier film up to 25 Á in thickness and preferably in the range of 7 to 20 Á, and a transparent nitride film, and thermal tempering of the article for partial but not complete conversion of the barrier film from niobium to niobium nitride. In yet another embodiment, the invention relates to a self-cleaning oven having a window, comprising a thermotreated glass sheet containing a stack of transparent films capable of withstanding repeated temperature increases up to 482 ° C (900 ° F) in an oven environment, without significant deterioration. The film stack comprises, from the glass substrate outwardly, a transparent infrared reflecting metallic film and a niobium metal protective barrier film up to 25 A in thickness and preferably in the thickness range from about 7 to 20 A. Preferably, the film stack includes a protective film of metal oxide between the glass substrate and the reflective metal film, and preferably additionally includes a silicon nitride film on the outermost niobium film. Tempered glass articles of the invention can conveniently exhibit a visible light transmissivity of at least 35% and preferably 70% or more, and a reflectance of about 60% and preferably over 85% in the wavelength range of 3 to 10 microns, these values are appropriate for windows of so-called self-cleaning ovens.

BRIEF DESCRIPTION OF THE DRAWING Figure 1 is a schematic cross-sectional view of a stack of films of the invention; Figure 2 is a schematic cross-sectional view of a modified version of the stack of films of Figure 1; Figure 3 is a schematic cross-sectional view of another stack of films of the invention; Figure 4 is a schematic cross-sectional view taken through a furnace window structure, identifying various surfaces; Y Figure 5 is a schematic cross-sectional view of another stack of films of the invention. DETAILED DESCRIPTION OF THE PREFERRED MODALITIES First with reference to the stack of films shown in Figure 1, a glass substrate is illustrated as 12. On its surface 14 a nitride film 16, a protective barrier film 18 is deposited in sequence. niobium metal, an infrared reflective metal film 20, for example made of silver, a protective film 22 of niobium metal and a nitride film 24. It will be understood that the thicknesses of various films or films in the drawing are not to scale. The individual films of the film stack can be deposited on the glass substrate 12 by any convenient means. A preferred deposition method involves deposition by cathodic sublimation with CD magnetron, as described by Chapin in U.S. Pat. No. 4,166,018, the teachings of which are incorporated herein by reference. Magnetron sputtering deposition involves transporting a glass substrate through a series of low pressure zones where the various films that make up the stack of films are applied sequentially. Metallic films are deposited by cathodic sublimation from metallic or "objective" sources. A metallic film can be formed by depositing by cathodic sublimation from a metallic target in an atmosphere of inert gas such as argon, wherein a nitride film such as silicon nitride can be deposited by cathodic sublimation using a silicon lens in a reactive atmosphere that It contains nitrogen gas. The thickness of films deposited in this way can be controlled by varying the speed of the glass substrate through a coating compartment and by varying the energy and speed of deposition by cathodic sublimation. Another method for depositing thin protective films and nitride films onto a substrate involves deposition of chemical vapor with plasma, and reference is made to US Pat. No. 4,619,729 issued to John Coch et al., And to U.S. Pat. No. 4,737,379 issued to Hudgens et al. For descriptions of this known process. The deposition of chemical vapor with plasma involves the decomposition of gas sources by a plasma and a subsequent formation of films on solid talee surfaces as glass substrates. The film thickness is adjusted by varying the speed of the substrate as it passes through a plasma zone and by varying the energy and gas flow rate. As the infrared reflective metal film, silver or silver-containing films are preferred. Thicknesses of silver films in the range from about 55 Á to 190 Á have been found appropriate. Thicknesses in the range of approximately 120 Á to 180 Á for film stacks that only have a silver film, are preferred in order to provide a high level of infrared radiation reflectivity. The thicknesses of silver films in stacks of films containing two silver films, as will be described in connection with Figure 3, may be in the range from 60 Á to 190 Á, with the outer film stack being thicker than the silver film closest to the glass substrate. Preferably, the thickness of the infrared reflecting silver film (s) is such as to provide reflectance values of about 60% and preferably over 85%, in the range of 3 to 10 microns for application in an oven door for automatic cleaning and to provide low emissivity and solar control for window applications. Substantially nitrogen and oxygen should be prevented from entering reactive contact with transparent infrared reflective films such as silver at glass tempering temperatures and the thin niobium metal barrier film on each silver film is considered to be capable of chemically reacting with and from this way capture nitrogen and oxygen to form nitrides and niobium oxides and thus avoid reaction with the silver reflective film at high temperatures. A niobium barrier film below a silver or other infrared reflective film can be replaced with a metal oxide film such as zinc oxide sufficiently thin (from 25 to 250 A) to be a significant source of oxygen for itself or to create increased turbidity and provide superior transmissivity of the final product. Niobium reacts easily with nitrogen and oxygen at high temperatures to form nitride and niobium oxide. Of the various nitrides that may be employed, silicon nitride is preferred. The protective barrier films 18, 22 of niobium metal (and the metal oxide films described with reference to Figure 3, are deposited with a sufficient thickness to protect the metallic reflective film against degradation at high temperatures, but not so great as to cause undue reduction in transmissivity of visible light, reduction in emissivity or increase in turbidity When a glass substrate having a stack of films of the invention is raised at high temperature (as during tempering), properties such as the color of the stack they are essentially not affected, any slight changes in the properties are considered as a result of the partial nitriding or oxidation of the thin niobium barrier films, thicknesses in the order of 14 Á for the protective niobium metal films, have given acceptable results; thicknesses up to 25 Á, preferably in the range from 7 Á to 20 A can be used, with thicknesses in the range of approximately 2 Á to approximately 18 Á more preferred. The niobium protective film, if any, between the infrared reflective film and the glass substrate may be several A thinner than the other niobium barrier film and conveniently the niobium metal films are deposited only to the thickness required to protect the reflective film metal in order to avoid undue reduction in transmissivity. Again with reference to Figures 1 and 2, the nitride films 16, 24 on both sides of what may be termed the "inner sandwich" (formed by sandwiching the infrared reflective metal film between the thin niobium barrier films) of preference is silicon nitride. Silicon nitride has the benefit of being highly visible light transmitter and imparting substantial chemical and physical durability to the film stack. Nitride films serve as anti-reflective films. The silicon nitride film 24 which is deposited on the "inner sandwich" is preferably in the order of about 250 A to about 600 A and a thickness of 300 A is quite acceptable. Any silicon nitride film 16 placed between the glass substrate and the inner sandwich may be in the order of 250 A to about 500 A in thickness, with acceptable results that have been obtained at a thickness of about 350 A. A stack of films of the invention can be prepared using a magnetron sputtering deposition apparatus as previously discussed, by depositing a reactive nitrogen element, such as silicon from a target in an atmosphere, by cathodic sublimation onto a glass substrate. reactive gas containing nitrogen in a first low pressure compartment to form a nitride film, then transporting the glass substrate to one or more additional low pressure compartments for the deposition of thin niobium films from a niobium target in an atmosphere non-reactive (eg argon) or a protective film of metal oxide (followed by a film of silver metal or other infrared reflecting metal, followed by a second barrier film of niobium metal.) The glass substrate is then transported in another compartment. low pressure that contains an atmosphere of reactive nitrogen and depo Cationic sublimation from a target causes deposition of a nitride film on the structure thus described. When the nitride films on either side of the inner sandwich are silicon nitride, tempering the coated glass product at temperatures in the range of 700 ° C followed by neutralization with air may result in an increase in light transmissivity. visible, for example from about 4 to 10%. The metals for the reflective film, the thicknesses of the niobium barrier films and the compositions of the dielectric films are chosen in such a way as to generate a glass product which, after annealing in the range of 700 ° C, exhibits a transmissivity to light visible (illuminant C) not less than about 65% and preferably not less than about 78% (and exhibits slight, if there is a change in the color transmitted or reflected and other optical properties on this treatment at high temperature. following explanation, it is postulated that when a nitride film such as silicon nitride is formed by deposition by magnetron sputtering or by chemical vapor deposition or the like, the resulting silicon nitride may have an amorphous structure that allows absorption or adsorption of nitrogen gas, or probably both in the course of placing that film.When the stack of films is heated to Glass tempering temperatures, the nitrogen gas from the nitride films escapes from these films and at such high temperatures it would be very reactive with the infrared silver reflective film. It is considered that this is highly reactive nitrogen gas emitted from the nitride films which is captured by the thin barrier films of niobium metal. Since tempering commonly occurs in air (an oxidizing atmosphere) some reactive oxygen gas can penetrate the outermost nitride film but, as with reactive nitrogen gas, oxygen is also purified by the underlying protective niobium film to form oxide with that element. When one or more nitride films such as silicon nitride are used in the film stack of the invention, it has been found convenient to separate each nitride film from a neighboring silver film by a metal oxide film, zinc oxide. It preferred. It appears that zinc oxide tends to improve adhesion between the silver and nitride films and it is preferable to employ a zinc oxide film in the thickness range of 25 to 180 A between each silver film (ie, in the side of the silver film directed to the glass substrate) and zinc oxide films are preferred in the order of 100A. It will be understood that other and additional films may be employed in the stack of films of the invention. Particularly, one or more films can be used as a lower coating between the surface of the glass substrate and the first nitride film and also on the other nitride films or films. Preferably, the "inner sandwich" structure consists of a sandwich of silver film between two barrier films one of which one on the side of the silver film directed away from the substrate is niobium metal and the other on the side of the silver film directed to the substrate is a metal oxide such as zinc oxide or less preferably is a niobium metal film, silver and barrier films are contiguous, that is, they are touched. If both barrier films are niobium metal, suitably each is present at a thickness of up to 20 Á, the niobium film closest to the glass substrate is preferably slightly more eg several more thin A, than the other niobium film. In a preferred embodiment, the metal nitride films between which the "inner sandwich" structure as already received are contiguous with the respective barrier films, such that the stack of films comprises the following films in sequence from the substrate of glass out, and with neighboring films in contact with each other, silicon niobium-niobium-silver-niobium-silicon nitride. A typical film stack of the invention includes the following: a) A silicon nitride having a thickness of 150 A to 450 Á. b) A first niobium metal barrier film deposited on the first silicon nitride film having a thickness in the range of 7 Á to 20 Á. c) A reflective infrared silver film deposited on the first niobium barrier film and having a thickness in the range of 120 Á to 180 A. d) A second niobium metal barrier film deposited on the infrared reflecting silver film and having a thickness in the range of 7 A to 20 A. e) A silicon nitride film having a thickness in the range of 200 Á to 600 Á. If desired, films b to d can be repeated, with appropriate adjustments in film thicknesses to obtain the desired transmissivity and emissivity. An example of a simple repeat of bad films is illustrated in Figure 2, where a third metal film is deposited on a stack of films shown in Figure 2 (that is, films 16, 18, 20, 22 and 24). niobium 26 having a thickness in the range of 7 Á to 20 Á, a silver film 28 having a thickness in the range of 110 Á to 190 Á, a fourth niobium film 30 in the range of 7 Á to 20 Á , followed by a silicon nitride film 32. Figure 3 illustrates a preferred film stack using two silver films 42, 44, each having a respective niobium metal barrier film 46, 48 deposited on the surface of each silver film directed away from the glass substrate 12. The silver film 44 remote from the substrate is conveniently thicker (preferably in the range of 130 to 170 A) than the nearest silver film 42, the latter having a thickness of preference in the range of 60 to 100 Á. On the other hand of each silver film (the side directed to the substrate 12) is a respective zinc oxide film 50, 52 having thicknesses in the range of 25 to 180 A, sufficient to protect the adjacent silver films during heat treatment . Nitride films, preferably silicon nitride films, are provided in the substrate (film 60), at a thickness of 50 to 300 A (as a protective outer coating) film 62, at a thickness of 100 to 400 A (and between metal oxide films 52, 54 (film 64, at a thickness of 100 to 800 A) The initial nitride film can be omitted if desired, and the zinc oxide film below the first silver film can of conformity increased in thickness from 100 to 250 A. In the embodiment shown in Figure 3, the presence of a sequence of repeated films may be noted, the first sequence comprising, from the glass outwards, Si3N4, ZnO, Ag, Nb and ZnO, and the second sequence of the same materials is formed in the first sequence.It should also be noted that a metal oxide film (ZnO in this example) is placed here between each Si3N4 film and a neighboring silver film; is, ZnO 50 film is colo Between the Si3N4 60 film and the silver film 42, the Si3N4 64 film is separated from the silver films 42 and 44 by ZnO 54 and 52 films respectively and the Si3N4 64 film is separated from the 44 silver films by the ZnO 56 film. It can be particularly noted that there is a zinc oxide film (54, 56) on each niobium film (that is on the niobium film side directed away from the glass substrate) and below each nitride film, and has found that this structure tends to increase the transmissivity of the film stack and improves the adhesion between the niobium and nitride films that are adjacent to these zinc oxide films. It is contemplated that other oxide films, such as titanium, niobium and aluminum oxides may also be employed for this purpose. Another preferred embodiment of the invention is illustrated in Figure 5. This embodiment is similar to that shown in Figure 3, except that the initial nitride film on the glass substrate surface has been omitted and a film 66 of titanium nitride has been provided between the outer nitride film 62 and the next adjacent niobium metal barrier film 48, the titanium nitride film is preferably contiguous with the nitride film 62 and has the effect of reducing transmissivity and improving the visually colorless appearance of the film stack. In turn, in Figure 5, the metal oxide film 52 directly under the second silver film can be increased in thickness to a range of 100 to 300A to offer an additional reduction in UV transmissibility. EXAMPLE 1 Using a commercially available magnetron sputtering cation sublimation coating apparatus (Aireo), clean 3 mm thick glass sheets were passed through a series of low pressure compartments with deposition coating by cathodic sublimation to deposit a series of contiguous films on the glass surface, as illustrated in Figure 1. Film thicknesses were determined by SPI speeds. in a coating compartment containing a low pressure atmosphere of argon and nitrogen, deposition by cathodic sublimation of silicon to provide a first film of silicon nitride with a thickness of 330A directly on the glass substrate. On the silicon nitride film, a niobium film is deposited directly at a thickness of 12 A from a niobium objective, followed directly by a film with a thickness of 110 A of silver from a silver metal lens and a niobium film to a thickness of 12 Á from a niobium lens, the niobium and silver films are deposited in the argon atmosphere with low pressure. Directly in the aforementioned niobium film is deposited a fifth film, with a thickness of 410 A, of silicon nitride in the manner described above with respect to the first film. The resulting glass article is heated to about 700 ° C in a tempering furnace and then immediately neutralized with air. The transmissivity due before tempering was 86% and after tempering it was 89%. The electrical surface resistivity that varies more or less proportionally with the emissivity, is measured using an ohmmeter of four probes (sometimes called a measurement of "four points"). The surface resistivity before tempering is measured as 7 ohms / 2 and after tempering 5 ohms / 2 signifying a reduction in emissivity. Example 2 Using an apparatus and objectives in the example 1, but additionally providing the deposition of zinc oxide using a zinc target in an argon and oxygen atmosphere, the following stack of films can be produced on a glass substrate: Si3N4 86 Á ZnO 50 Á Ag 77 Á Nb 15 Á ZnO 90 Á Si3N4 470 Á ZnO 50 Á Ag 145 Á --Nb 15 Á ZnO 90 Á Si3N4 245 Á The resulting coated glass products were heated and neutralized with air as described in Example 1. The transmissivity is measured at 82% both before and after the heat treatment. Example 3 Example 2 is repeated, except that the initial silicon nitride film is omitted, the initial zinc oxide film accordingly increases in thickness and other film thicknesses were adjusted. The next stack of films is produced on a glass substrate, the films are identified from the glass substrate outwardly.

Glass ZnO 135 Á Ag 65 Á -Nb 15 A ZnO 90 Á Si3N4 450 Á ZnO 90 Á Ag 160 Á Nb 15 Á ZnO 90 Á SÍ3N4 270 Á The resulting coated glass products are heated and neutralized with air as described in Example 1. The transmissivity increases from 68 to 76% during the tempering process. Other optical and color properties remain substantially unchanged. EXAMPLE 4 Example 2 is repeated, except that the initial silicon nitride film is omitted, an additional titanium nitride film is placed directly under the outer silicon nitride film and the thicknesses of the film, the Movies has the following construction: Glass ZnO 160 Á Ag 72 Á Nb 12 -Á ZnO 100 Á Si3N4 370 Á ZnO 200 A Ag 155 Á -Nb 12 Á ZnO 90 A TiN 25 Á Si3N4 270 Á The resulting coated glass products are heated and neutralized with air as described described in Example 1. The transmissivity is increased from 75 to 82% during the tempering process. Using a four-point measurement system as described above in connection with Example 2, the surface resistivity is measured before tempering as 3.5 ohms / square and after annealing as 2.5 ohms / square, meaning a reduction in emissivity. Figure 4 illustrates the use of glassware of the invention in the window of a self-cleaning oven. by "self-cleaning", reference is made to the type of commercially available cooking ovens adapted to be cleaned by heating the oven cavities at temperatures of 482 ° C (900 ° F) for periods of time in the range of one half hour to one hour or more . Furnace windows are commonly formed in oven doors. A typical window may comprise a plurality of transparent sheets in general, spaced apart by air spaces. Three spaced glass sheets are illustrated in the embodiment typified in Figure 5. The surfaces of the sheets are numbered in progressive sequence outwardly from the interior of the oven, with the surface number 1 being the surface directed to the interior of the oven of the oven. glass sheet 40 closest to the interior of the oven, and surface number 6 is the surface directed to the exterior of the furnace of the outermost glass sheet 44. In the embodiment of Figure 4, the glass sheets 40 and 42 can be provided with the transparent film stacks previously referred to on their outwardly directed surfaces 2, 4. The outermost sheet 44 may be provided with a reflective pattern such as a dot pattern, in a manner common to the self-cleaning ovens currently available. Because the air spaces between the sheets are not sealed, the coatings on surfaces 2 and 4 must be resistant to high temperature and humidity and chemicals found during normal use.

Baking windows of the prior art for self-cleaning ovens made of glass sheets contain a coating of pyrolytic tin oxide on both surfaces. Repeated increases in temperature result in imperceptible iridescent spots. As well, the reflectivity of these coatings is relatively poor, requiring a two-sided coating of the glass sheets for oven doors. Tempered glassware of the invention has withstood rigorous testing at high humidity levels with little change in properties. A corrosion test involves exposures for 200 hours of tempered sheets at 90 or 100% relative humidity conditions at temperatures of 38 ° C (100 ° F). Another test involves subjecting the coated glass articles to a spray of 4% aqueous salt for 200 hours at 38 ° C (100 ° F). It is of interest that the durability of the coatings tends to increase instead of decrease before thermal tempering. Furthermore, the coatings are quite hard and exhibit substantial resistance to abrasion. While a preferred embodiment of the present invention has been described, it will be understood that various changes, adaptations and modifications may be practiced without departing from the spirit of the invention and the scope of the appended claims.

Claims (28)

1. CLAIMS 1.- A heat-resistant tempered glass article, characterized in that it comprises a glass substrate and a stack of transparent films deposited on the substrate, the film stack comprises, from the glass substrate towards the outside, an infrared reflecting metal film and a niobium metal protective barrier film deposited directly on the infrared reflective film at a thickness of up to 25 A, such that a thin niobium protective film remains after thermoforming the glass article.
2. 2. The article according to claim 1, characterized in that it includes a transparent nitride dielectric film farther from the glass substrate than the niobium barrier film.
3. 3. The glass article according to claim 1, characterized in that the infrared reflecting metallic film is silver.
4. 4. The glass article according to claim 1, characterized in that it includes a second barrier film of niobium metal between the infrared reflective film and the glass substrate and adjacent to the infrared reflective film.
5. 5. The glass article according to claim 1, characterized in that it includes a metal oxide barrier film between the infrared reflective film and the glass substrate and contiguous with the infrared reflective film.
6. 6.- A thermosetting tempered glass article, comprising a glass substrate and a stack of films deposited on the substrate, the film stack comprises, from the glass substrate outward, a metal oxide barrier film and a metallic film containing infrared reflective silver and a niobium metal barrier film, the metal oxide and the niobium barrier films are contiguous to the infrared reflective silver film and the niobium barrier film has a thickness in the range of 7. at 20 Á.
7. 7. The article according to claim 6, characterized in that it includes a transparent nitride film placed farther from the glass substrate than the niobium barrier film.
8. 8. - The article according to claim 6, characterized in that the transparent nitride film is placed closer to the glass substrate than the first barrier film.
9. 9. - The article according to claim 6, characterized in that it includes a first film of nitride placed closer to the glass substrate than the first barrier film and a second film of nitride placed farther from the glass substrate than the second film barrier.
10. 10. The article according to claim 7, characterized in that the nitride film is silicon nitride.
11. 11. The article according to claim 10, characterized in that it includes a titanium nitride film between the niobium barrier film and the silicon nitride film.
12. 12. - The transparent heat-resistant glass article according to claim 6, characterized in that the metal oxide barrier film comprises an oxide of a metal selected from the group consisting of zinc, titanium, niobium and aluminum.
13. 13. - The article of transparent heat-resistant glass according to claim 10, characterized in that it includes a transparent nitride film placed closer to the glass substrate than the silver film and separated from the silver film by a sufficient thickness of the film metal oxide barrier to protect the infrared reflecting metal film against degradation at glass tempering temperatures.
14. 14. - The transparent heat-resistant glass article according to claim 13, characterized in that the metal oxide barrier film is present in a thickness in the range of 25 Á to 180 Á.
15. 15. The article of transparent heat resisting glass according to claim 6, characterized in that the metal oxide film is contiguous with the glass substrate and is of a thickness in the range of 100 Á to 250 Á.
16. 16.- A transparent heat-resistant glass article, characterized in that it comprises a glass substrate and a stack of transparent films deposited on the substrate, the film stack comprises a plurality of transparent silicon nitride films, an infrared reflecting film placed between neighboring transparent nitride films, a niobium metal film of 7 to 20 A thickness placed on the surface of each infrared reflective film directed away from the substrate, and a metal oxide film placed between each transparent silicon nitride film and each infrared reflecting film.
17. 17. The transparent heat-resistant glass article according to claim 16, characterized in that it includes a titanium nitride film between the silicon nitride film furthest from the substrate and the next adjacent niobium barrier film.
18. 18. - A transparent heat-resistant glass article, comprising a glass substrate and a stack of transparent films deposited on the substrate, the film stack comprises from the glass substrate outward, a first Si3N4 film of 100 to 400 A thickness, a second film of Si3N4 from 100 to 800. of thickness and a third Si3N4 film of 50 to 300 A thick, an infrared reflecting silver film between the first and second Si3N4 films between the second and third Si3N4 films, and a niobium metal film of 7 to 20 A of thickness placed on the surface of each infrared reflective film remote from the glass substrate.
19. 19. The transparent heat-resistant glass article according to claim 18, characterized in that it includes a protective zinc oxide film between each transparent Si3N4 film and each infrared reflective silver film.
20. 20.- A transparent heat-resistant glass article, characterized in that it comprises a glass substrate and a stack of transparent films deposited on the substrate, the film stack comprises from the glass substrate outward, a film of transparent silicon nitride which it has a thickness from 125 Á to 500 Á, a first niobium metal protective film of 7 to 20 Á thickness, a transparent infrared reflective silver film, a second niobium metal protective film of 7 to 20 Á thickness and a film of transparent silicon nitride with a thickness of 350 A to 600 A.
21. 21.- A transparent heat-resistant glass article, characterized in that it comprises a glass substrate and a stack of transparent films deposited on the substrate, the film stack comprises a film of silver contiguous to and sandwiched between protective niobial metal piles that have 7 to 20 Á in thickness and on each side of the sandwich structure, a transparent film capable of releasing nitrogen when heated at glass tempering temperatures.
22. 22. A transparent heat-resistant glass article, characterized in that it comprises a glass substrate and a stack of transparent films deposited on the substrate, the stack of films from the glass substrate outward includes a sequence of films comprising a barrier film of metal oxide, a transparent infrared reflective silver film, a niobium metal barrier film of 7 to 20 A thick, a metal oxide film and a transparent silicon nitride film, and a repeat of the film sequence .
23. 23. - The transparent heat-resistant glass article according to claim 22, characterized in that it includes a titanium nitride film between the silicon nitride film furthest from the substrate and near the adjacent niobium barrier film.
24. 24. - A method for manufacturing a transparent glass article comprising depositing on a surface of a glass substrate, a stack of transparent films comprising from the glass surface outward, a transparent infrared reflecting metallic film, a barrier film of protective niobium metal of 7 to 20 A thickness, and a transparent thermal tempered nitride film of the article to at least partially convert the barrier film to niobium nitride.
25. 25. The method according to claim 23, characterized in that it includes the step of depositing between the protective niobium metal barrier film and the transparent nitride film, a metal oxide film.
26. 26.- A method for manufacturing a thermo-treated transparent glass article characterized in that it comprises depositing on a surface of the glass article, a stack of transparent films comprising, from the glass substrate outwardly, a metal oxide film, a film of transparent infrared reflective silver, a niobium metal barrier film of 7 to 20 A thick, and a transparent silicon nitride film, and anneal the coated article to at least partially convert the niobium metal barrier film to niobium nitride.
27. 27. A method for manufacturing a heat-resistant transparent glass article, characterized in that it comprises depositing on a surface of the glass article, a stack of transparent films, characterized in that it comprises, from the glass substrate outwards, a sequence of films comprising a film metal oxide barrier, a transparent infrared reflective silver film, a niobium metal barrier film of 7 to 20 A thick, a metal oxide film and a silicon nitride film followed by a repetition of the film sequence .
28. 28.- A self-cleaning oven having a window, characterized in that it comprises a glass sheet containing a stack of transparent films, the film stack comprises from the glass substrate outward, a transparent infrared reflecting metal film and a protective barrier film of niobium metal.