Glass manufacturing – Processes – Fusion bonding of glass to a formed part
Reexamination Certificate
2001-02-07
2004-03-09
Vincent, Sean (Department: 1731)
Glass manufacturing
Processes
Fusion bonding of glass to a formed part
C065S043000, C065S058000, C156S099000, C156S104000, C156S109000
Reexamination Certificate
active
06701749
ABSTRACT:
This invention relates to a vacuum insulating glass (IG) unit, and a method of making the same.
BACKGROUND OF THE INVENTION
Vacuum IG units are known in the art. For example, see U.S. Pat. Nos. 5,664,395, 5,657,607, and 5,902,652, the disclosures of which are all hereby incorporated herein by reference.
Prior art
FIGS. 1-2
illustrate a conventional vacuum IG unit. IG unit
1
includes two spaced apart glass substrates
2
and
3
which enclose an evacuated or low pressure space
6
therebetween. Glass sheets/substrates
2
and
3
are interconnected by peripheral or edge seal of fused solder glass
4
and an array of support pillars or spacers
5
.
Pump out tube
8
is hermetically sealed by solder glass
9
to an aperture or hole
10
which passes from an interior surface of glass sheet
2
to the bottom of recess
11
in the exterior face of sheet
2
. A vacuum is attached to pump out tube
8
so that the interior cavity between substrates
2
and
3
can be evacuated to create a low pressure area or space
6
. After evacuation, tube
8
is melted to seal the vacuum. Recess
11
retains sealed tube
8
. Optionally, a chemical getter
12
may be included within recess
13
.
Conventional vacuum IG units, with their fused solder glass peripheral seals
4
, have been manufactured as follows. Glass frit in a solution (ultimately to form solder glass edge seal
4
) is initially deposited around the periphery of substrate
2
. The other substrate
3
is brought down over top of substrate
2
so as to sandwich spacers
5
and the glass frit/solution therebetween. The entire assembly including sheets
2
,
3
, the spacers, and the seal material is then heated to a temperature of approximately 500° C. at which point the glass frit melts, wets the surfaces of the glass sheets
2
,
3
, and ultimately forms hermetic peripheral or edge seal
4
. This approximately 500° C. temperature is maintained for from about one to eight hours. After formation of the peripheral/edge seal
4
and the seal around tube
8
, the assembly is cooled to room temperature. It is noted that column
2
of U.S. Pat. No. 5,664,395 states that a conventional vacuum IG processing temperature is approximately 500° C. for one hour. Inventor Collins of the '395 patent states in “
Thermal Outgassing of Vacuum Glazing
”, by Lenzen, Turner and Collins, that “the edge seal process is currently quite slow: typically the temperature of the sample is increased at 200° C. per hour, and held for one hour at a constant value ranging from 430° C. and 530° C. depending on the solder glass composition.” After formation of edge seal
4
, a vacuum is drawn via the tube to form low pressure space
6
.
Unfortunately, the aforesaid high temperatures and long heating times utilized in the formulation of edge seal
4
are undesirable, especially when it is desired to use a tempered glass substrate(s)
2
,
3
in the vacuum IG unit. As shown in
FIGS. 3-4
, tempered glass loses temper strength upon exposure to high temperatures as a function of heating time. Moreover, such high processing temperatures may adversely affect certain low-E coating(s) that may be applied to one or both of the glass substrates.
FIG. 3
is a graph illustrating how fully thermally tempered plate glass loses original temper upon exposure to different temperatures for different periods of time, where the original center tension stress is 3,200 MU per inch. The x-axis in
FIG. 3
is exponentially representative of time in hours (from 1 to 1,000 hours), while the y-axis is indicative of the percentage of original temper strength remaining after heat exposure.
FIG. 4
is a graph similar to
FIG. 3
, except that the x-axis in
FIG. 4
extends from zero to one hour exponentially.
Seven different curves are illustrated in
FIG. 3
, each indicative of a different temperature exposure in degrees Fahrenheit (F.). The different curves/lines are 400° F. (across the top of the
FIG. 3
graph), 500° F., 600° F., 700° F., 800° F., 900° F., and 950° F. (the bottom curve of the
FIG. 3
graph). A temperature of 900° F. is equivalent to approximately 482° C., which is within the range utilized for forming the aforesaid conventional solder glass peripheral seal
4
in
FIGS. 1-2
. Thus, attention is drawn to the 900° F. curve in
FIG. 3
, labeled by reference number
18
. As shown, only 20% of the original temper strength remains after one hour at this temperature (900° F. or 482° C.). Such a significant loss (i.e., 80% loss) of temper strength is of course undesirable.
In
FIGS. 3-4
, it is noted that much better temper strength remains in a thermally tempered sheet when it is heated to a temperature of 800° F. (i.e., about 428° C.) for one hour as opposed to 900° F. for one hour. Such a glass sheet retains about 70% of its original temper strength after one hour at 800° F., which is significantly better than the less than 20% when at 900° F. for the same period of time.
Another advantage associated with not heating up the entire unit for too long is that lower temperature pillar materials may then be used. This may or may not be desirable in some instances.
It will be apparent of those of skill in the art that there exists a need for a vacuum IG unit, and corresponding method of making the same, where a structurally sound hermetic edge seal may be provided between opposing glass sheets without at least certain portions of thermally tempered glass sheet(s)/substrate(s) of the IG unit losing more than about 50% of original temper strength. There also exists a need in the art for a vacuum IG unit including tempered glass sheets, wherein the peripheral seal is formed such that the glass sheets retain more of their original temper strength than with a conventional vacuum IG manufacturing technique where the entire unit is heated in order to form a solder glass edge seal. It is a purpose of this invention to fulfill one or more of the above listed needs in the art.
SUMMARY OF THE INVENTION
An object of this invention is to provide a vacuum IG unit having a peripheral or edge seal formed so that at least certain portion(s) of thermally tempered glass substrates/sheets of the IG unit retain more of their original temper strength than if conventional edge seal forming techniques were used with the solder glass edge seal material.
Another object of this invention is to provide a vacuum IG unit, and method of making the same, wherein at least a portion of the resulting thermally tempered glass substrate(s) retain(s) at least about 50% of original temper strength after formation of the edge seal (e.g., solder glass edge seal).
Another object of this invention is to reduce the amount of post-tempering heating time necessary to form a peripheral/edge seal in a vacuum IG unit.
Yet another object of this invention is to form a hermetic edge seal in a vacuum IG unit by utilizing microwave energy to cure edge seal material. In an exemplary embodiment, glass frit suspended in liquid or solution may be deposited as an edge seal base material on each of first and second annealed glass substrates (e.g., soda-lime-silica float glass substrates). This may be referred to as an initial or first glass frit application. Each of the glass substrates may then be thermally tempered with the edge seal material thereon so that during the thermal tempering process, the edge seal material at least partially diffuses into and/or bonds to the respective glass substrates. This fuses the glass frit edge seal material to the glass substrates (i.e., pre-firing the first glass frit application) while at the same time tempering the substrates. Thereafter, a second application of glass frit may be applied to one or both of the substrates over the pre-fired first glass frit application. Spacers and/or pillars may be sandwiched between the substrates as the substrates are brought together. Then, microwave energy is directed toward the edge seal material in order to heat the same (i.e., heating at least the second glass frit application, and preferably both the first and second glass frit applications) thereby causing
Longobardo Anthony V.
Wang Yei-Ping H.
Guardian Industries Corp.
Nixon & Vanderhye P.C.
Vincent Sean
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