Stock material or miscellaneous articles – Composite – Of quartz or glass
Reexamination Certificate
1996-03-01
2001-11-13
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of quartz or glass
C428S428000, C428S432000, C428S433000, C428S450000, C428S698000, C428S213000, C428S332000, C427S116000, C427S383300, C427S397700
Reexamination Certificate
active
06316111
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.
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 aid 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 tempatures for periods of time up to several hours. Tempering, as is known, is particularly important for glass intended 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. 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 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 usually produces non-uniform coatings and is costly.
Another reported method for protecting a reflective metal film 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 the oxides of metals commonly are more transparent than 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 Cr during sputtering is converted at least in part to a nitride of Cr 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.
SUMMARY OF THE INVENTION
The invention in one embodiment relates to a highly desirable heat-resistant glass product that can be manufactured by creating a film stack on glass in which an infrared reflective film such as silver is sandwiched between thin, protective films of a metal or seminconductor such as silicon, and the resulting structure is sandwiched between films of a nitride such as silicon nitride, so that one or both of the protective films contain an element that is also contained in one or both of the nitride films. The preferred element that the protective films and the nitride films have in common is silicon. When glass articles containing the film stack of the invention are heated to high temperatures such as temperatures of 600° or above, as, for example, in the 700° C to 750° C. range, transmissivity of the glass article to visible light may increase slightly.
The thicknesses of the protective films are chosen so that adhesion to the infrared reflective layer is not unduly diminished by the heat treatment. Without being bound by the following explanation, it appears that nitrogen from the nitride films, particularly the outer nitride film, adjacent to the thin, protective films, liberate nitrogen when raised to heat tempering temperatures, and that the nitrogen so released combines to form a nitride with the protective films. Some oxidation of the outer protective film may occur also. In this manner, the protective films serve to protect the infrared reflective metal film from becoming nitrided or oxidized.
When silicon is employed for the protective films, it appears that the protective films are at least partially converted to silicon nitride. Silicon nitride is more transparent than is elemental silicon, * and as a result the transmissivity of the entire glass article is improved if in fact the transmissivity is changed at all by high temperature exposure. Moreover, since an elemental component (e.g., silicon) of both the nitride films and the protective films are the same, sharp interfaces between the protective film and the nitride films are more likely to be avoided, leading to greater stack homogeneity and reducing the likelihood of failure due to separation of the nitride film from the protective film. However, if the protective films comprise silicon and the silicon-containing films are too thin, then the durability of the film stack often is reduced. The silicon-containing layers, and particularly the protective film upon the reflective layer, are deposited at thicknesses such that the film stack can withstand high temperature processing while maintaining good durability, and it appears that this phenomena is due to the retention of unreacted silicon metal on both sides of the infrared reflective layer.
In an alternative embodiment, the nitride films are replaced with oxide films. For example, such a film could comprise silver sandwiched between thin, protective layers of a metal or semiconductor such as silicon, with that structure sandwiched between layers of an oxide of a metal or semiconductor, such as an oxide of silicon (e.g. SiO
2
) or, less desirably, an oxide of titanium (TiO
x
). Although these types of film stacks may yield a marginally suitable film stack, the above embodiment wherein nitrides, rather than oxides, are used is preferred.
REFERENCES:
patent: 4166018 (1979-08-01), Chapin
patent: 4594137 (1986-06-01), Gillery
patent: 4619729 (1986-10-01), Johncock
patent: 4737379 (1988-04-01), Hudgens
patent: 4749397 (1988-06-01), Chesworth et al.
patent: 4790922 (1988-12-01), Haffer
patent: 4799745 (1989-01-01), Meyer et al.
patent: 4806220 (1989-02-01), Finley
patent: 5271994 (1993-12-01), Ternath
patent: 5344718 (1994-09-01), Hartig
patent: 5718980 (1998-02-01), Koch
patent: 6060178 (2000-05-01), Krisko
patent: 0 035 906 A2 (1981-09-01), None
patent: 0 506 507 A1 (1992-09-01), None
patent: 0 546 470 A1 (1993-06-01), None
patent: 0 560 534 A1 (1993-09-01), None
patent: 0 567 735 A1 (1993-11-01), None
Cardinal CG Company
Fredrikson & Byron , P.A.
Jones Deborah
Stein Stephen
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