Vacuum insulating glass (VIG or vacuum IG) units are known in the art. Some example VIG configurations are disclosed, for example, in U.S. Pat. Nos. 5,657,607, 5,664,395, 5,657,607, 5,902,652, 6,506,472 and 6,383,580, the disclosures of which are all hereby incorporated by reference herein in their entireties.
FIGS. 1 and 2 illustrate a typical VIG window unit 1 and elements that form the VIG window unit 1. For example, VIG unit 1 may include two spaced apart substantially parallel glass substrates 2, 3, which enclose an evacuated low-pressure space/cavity 6 therebetween. Glass sheets or substrates 2,3 are interconnected by a peripheral edge seal 4 that may be made of fused solder glass or the like, for example. An array of support pillars/spacers 5 may be included between the glass substrates 2, 3 to maintain the spacing of substrates 2, 3 of the VIG unit 1 in view of the low-pressure space/gap 6 present between the substrates 2, 3.
A pump-out tube 8 may be hermetically sealed by, for example, solder glass 9 or the like to an aperture/hole 10 that passes from an interior surface of one of the glass substrates 2 to the bottom of an optional recess 11 in the exterior surface of the glass substrate 2, or optionally to the exterior surface of the glass substrate 2. A vacuum is attached to pump-out tube 8 to evacuate the interior cavity 6 to a low pressure that is less than atmospheric pressure, for example, using a sequential pump down operation. After evacuation of the cavity 6, a portion (e.g., the tip) of the tube 8 is melted to seal the vacuum in low pressure cavity/space 6. The optional recess 11 may retain the sealed pump-out tube 8. Optionally, a chemical getter 12 may be included within a recess 13 that is disposed in an interior face of one of the glass substrates, e.g., glass substrate 2. The chemical getter 12 may be used to absorb or bind with certain residual impurities that may remain after the cavity 6 is evacuated and sealed.
VIG units with peripheral hermetic edge seals 4 (e.g., solder glass) are typically manufactured by depositing glass frit or other suitable material in a solution (e.g., frit paste) around the periphery of substrate 2 (or on substrate 3). This glass frit paste ultimately forms the edge seal 4. The other substrate (e.g., 3) is brought down on substrate 2 so as to sandwich spacers/pillars 5 and the glass frit solution between the two substrates 2, 3. The entire assembly including the glass substrates 2, 3, the spacers/pillars 5 and the seal material (e.g., glass frit in solution or paste), is then typically heated to a temperature of at least about 440° C., at which point the glass frit melts, wets the surfaces of the glass substrates 2, 3, and ultimately forms a hermetic peripheral/edge seal 4.
The composition of conventional edge seals are known in the art. See, for example, U.S. Pat. Nos. 3,837,866; 4,256,495; 4,743,302; 5,051,381; 5,188,990; 5,336,644; 5,534,469; 7,425,518, and U.S. Publication No. 2005/0233885, the disclosures of which are all hereby incorporated herein by reference.
After formation of the edge seal 4 between the substrates, a vacuum is drawn via the pump-out tube 8 to form low pressure space/cavity 6 between the substrates 2, 3. The pressure in space/cavity 6 may be produced by way of an evacuation process to a level below atmospheric pressure, e.g., below about 10−2 Torr. To maintain the low pressure in the space/cavity 6, substrates 2, 3 are hermetically sealed via the edge seal and sealing off of the pump-out tube. Small high strength spacers/pillars 5 are provided between the transparent glass substrates to maintain separation of the approximately parallel glass substrates against atmospheric pressure. As noted above, once the space 6 between substrates 2, 3 is evacuated, the pump-out tube 8 may be sealed, for example, by melting its tip using a laser or the like.
High-temperature bonding techniques such as, for example, glass frit bonding, as discussed above, have been widely used method for hermetically sealing (e.g., forming an edge seal) components made of silicon, ceramics, glass, or the like. The heat required for these high-temperature processes is typically in the range of about 440-600 degrees C., and oftentimes even higher. These conventional bonding techniques typically require oven-intensive bulk heating in which the entire device (including the glass and any components housed within the glass housing) comes to near thermal equilibrium with the oven for a seal to form. As a result, a relatively long period of time is required to achieve an acceptable seal. It is also the case that the most temperature sensitive component determines the maximum allowable temperature of the entire system.
Thus, high-temperature sealing processes discussed above (e.g., for glass frit bonding) unfortunately are not suitable for fabricating heat-sensitive components such as, for example, tempered VIG units. In the case of tempered VIG units, the thermally tempered glass substrates of a VIG unit would rapidly lose temper strength in the high-temperature environment. For instance, the aforesaid high temperatures and long heating times of the entire assembly utilized in the formulation of edge seal 4 are undesirable, especially when it is desired to use a heat strengthened or tempered glass substrate(s) 2, 3 in the vacuum IG unit. 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 in certain instances.
Tempered glass is advantageous because, when designed properly, it breaks in a fine pattern that reduces the risk of injury to persons exposed to fragments. Accordingly, measurements of fragmentation density are typically used to determine if tempered glass meets safety requirements. For example, the European standard EN 14179-1:2005 requires 4 mm tempered safety glass to break such that there are at least 40 fragments within a 50 mm×50 mm area. See FIG. 3 in this regard, which shows an example break pattern.
The correlation between heating conditions and tempering loss was established by the assignee by thermally tempering numerous 350 mm×500 mm substrates (4 mm float glass) under constant furnace conditions so as to exceed the EN 14179-1:2005 fragmentation requirement. The break pattern was measured on several substrates without further heating to ascertain the initial fragmentation density. The remaining substrates were heated at various temperatures and durations (in stacked pairs to simulate VIGs) before they were broken. The ratio of final to initial fragmentation density was taken to represent the temper loss induced by a given heating process. The results, shown in FIG. 4, demonstrate that loss of temper under the range of conditions tested is primarily driven by temperature and to a lesser degree by time. Additional experiments showed that VIGs can be made from tempered glass with sufficient residual compressive stress to tolerate 30% loss of temper and still meet the EN 14179-1:2005 fragmentation requirements. Higher levels of temper generally result in flatness issues that make it difficult to produce a continuous edge seal. As shown in FIG. 4, even very short heat exposures (<5 minutes) are limited to a maximum temperature of about 375° C. to meet this requirement. As mentioned above, glass frit bonding is typically performed in a slow process that therefore would require much lower peak temperature to meet the safety glass requirement.
One conventional solution to sealing glass substrates together is to use an epoxy. However, in the case of VIG units, epoxy compositions may be insufficient to hold a seal on a vacuum. Furthermore, epoxies may be susceptible to environmental factors that may further reduce their effectiveness when applied to VIG units.
Historically, lead-based frit has been widely used to produce hermetic seals in a variety of products, including VIGs; however, products that contain lead are being phased out due to the health consequences to the population. Accordingly, certain countries (e.g., the U.S. and at least certain countries in the European Union) may impose strict requirements on the amount of lead that can be contained in a given product. Indeed, some countries (or customers) may currently require products that are completely lead-free, while others are moving in this direction.
Thus, it will be appreciated there is a need in the art for a seal processing technique that does not involve heating the entire article to be sealed to high temperature(s), and/or articles made in such example manners.
In certain example embodiments of this invention, there is provided a method of making a vacuum insulating glass (VIG) window unit comprising first and second glass substrates, with each said substrate having first and second major surfaces. The method comprises applying a first frit material around perimeter edges of the first major surfaces of the first and second substrates; heat treating the first and second substrates with the first frit material thereon, with the first and second substrates reaching a first peak temperature; following said heat treatment, applying a second frit material on the first and/or second substrate(s) such that, for each substrate on which the second frit material is applied, the second frit material at least partially overlaps the first frit material on the respective substrate around peripheral edges thereof, the first and second frit materials having different compositions; positioning a plurality of spacers on the first surface of the first substrate; bringing together the first and second substrates such that the first major surfaces of the first and second substrates face one another, and such that a cavity is defined therebetween, in making a VIG unit subassembly; heating the subassembly in order to melt the second frit material and wet the first frit material, the heating being performed such that the first and second substrates reach a second peak temperature that is no higher than 400 degrees C. and that is at least 150 degrees C. lower than the first peak temperature; following said heating of the subassembly, cooling and/or allowing the subassembly to cool, in forming an edge seal between the first and second substrates; evacuating the cavity to a pressure less than atmospheric via a pump-out port; and sealing the pump-out port in making the VIG unit.
In certain example embodiments of this invention, there is provided a method of making a vacuum insulating glass (VIG) window unit. The method comprises having first and second articles, each said article being a glass substrate having first and second major surfaces and having a first frit material fused thereon around peripheral edges of the first major surface as a result of having been heat treated with the respective substrate; applying a second frit material on the first and/or second substrate(s) such that, for each substrate on which the second frit material is applied, the second frit material at least partially overlaps the first frit material on the respective substrate around peripheral edges thereof, the first and second frit materials having different compositions; positioning a plurality of spacers on the first surface of the first substrate; bringing together the first and second substrates such that the first major surfaces of the first and second substrates face one another, and such that a cavity is defined therebetween, in making a VIG unit subassembly; heating the subassembly in order to melt the second frit material and wet the first frit material, the heating being performed such that the first and second substrates reach a second peak temperature that is no higher than 400 degrees C. and that is at least 150 degrees C. lower than the first peak temperature; following said heating of the subassembly, cooling and/or allowing the subassembly to cool, in forming an edge seal between the first and second substrates; evacuating the cavity to a pressure less than atmospheric via a pump-out port; and sealing the pump-out port in making the VIG unit.
In certain example embodiments of this invention, a VIG window unit is provided, and it comprises first and second substantially parallel, spaced apart glass substrates. At least one of the first and second substrates is heat treated. Spacers are disposed between the first and second substrates. An edge seal is provided around the periphery of the first and/or second substrates, and the first and second substrates, together with the edge seal, define a cavity therebetween. The cavity is evacuated to a pressure less than atmospheric. The edge seal is an hermetic seal formed by heating via a low temperature process for a short duration a second frit material that is sandwiched between bands of first frit materials fused with the first and second substrates during a high temperature process, the low temperature process being performed in connection with a second peak temperature of no more than 400 degrees C. and a time of no more than 15 minutes at the second peak temperature, and the high temperature being performed at a first peak temperature that is at least 150 degrees C. higher than the second peak temperature.
In certain example embodiments of this invention, a kit comprising first and second frit materials for use in forming an edge seal for a VIG window unit is provided. The first frit material comprises at least 65% bismuth oxide, by weight, with the first frit material being fusable to glass when the glass reaches a first temperature of 550 degrees C. or higher. The second frit material comprises vanadium oxide, barium oxide, and zinc oxide, in amounts that total at least 65% by weight, with the second frit being structured to form a bond with the first frit material in making the edge seal for the VIG window unit. The second frit material is meltable when the glass reaches at a second temperature of no more than 400 degrees C., and the first frit material is wettable at the second temperature.
In certain example embodiments of this invention, a frit material for use in forming an edge seal for a VIG window unit is provided. The frit material comprises at least 65% bismuth oxide and at least 2% zinc oxide, by weight, and the frit is being designed to fuse to glass when the glass reaches a first temperature of 550 degrees C. or higher, and further is designed to wet when the glass reaches a second temperature that is at least 150 degrees C. lower than the first temperature.
In certain example embodiments of this invention, a frit material for use in forming an edge seal for a VIG window unit is provided. The frit material comprises 45-67 wt. % vanadium oxide, 7-25 wt. % barium oxide, and 4-17 wt. % zinc oxide and is designed to be meltable when a peak temperature of no greater than 360 degrees C. is maintained for a time of no more than 15 minutes (and also is potentially bondable to the frit material in the preceding paragraph under these and/or similar conditions).
In certain example embodiments of this invention, there is provided a method of making a VIG window unit comprising first and second glass substrates, with each said substrate having first and second major surfaces. A first frit material is applied around perimeter edges of the first major surfaces of the first and second substrates. The first and second substrates with the first frit material thereon are heated, with the first and second substrates reaching a first peak temperature. Following said heat treatment, a second frit material is applied on the first and/or second substrate(s) such that, for each substrate on which the second frit material is applied, the second frit material at least partially overlaps the first frit material on the respective substrate around peripheral edges thereof. The first and second frit materials have different compositions. Spacers are positioned on the first surface of the first substrate. The first and second substrates are brought together such that the first major surfaces of the first and second substrates face one another, and such that a cavity is defined therebetween, in making a VIG unit subassembly. The subassembly is heated in order to melt the second frit material and wet the first frit material, with this heating being performed such that the first and second substrates reach a second peak temperature that is no higher than 400 degrees C. and that is at least 150 degrees C. lower than the first peak temperature. Following said heating of the subassembly, the subassembly is cooled and/or allowed to cool, in forming an edge seal between the first and second substrates. The cavity is evacuated to a pressure less than atmospheric via a pump-out port. The pump-out port is sealed in making the VIG unit. At least one of the first and second substrates is thermally tempered. The second peak temperature is sufficiently low so that the tempered substrate(s) retain(s) at least about 70% of the original temper strength after the heating of the subassembly.
In certain example embodiments of this invention, there is provided a method of making a VIG window unit comprising first and second glass substrates, with each said substrate having first and second major surfaces. The second glass substrate has a hole facilitating evacuation. A first frit material is applied around perimeter edges of the first major surfaces of the first and second substrates, and in the tube seal area on the second major surface of the second substrate. The first and second substrates with the first frit material thereon are heated, with the first and second substrates reaching a first peak temperature. Following said heat treatment, a second frit material is applied on the first and/or second substrate(s) such that, for each substrate on which the second frit material is applied, the second frit material at least partially overlaps the first frit material on the respective substrate around peripheral edges thereof. The first and second frit materials have different compositions. The first frit material is also applied to a seal forming area on a pump-out tube, and the tube is then heated to fuse the first frit material onto the tube. Spacers are positioned on the first surface of the first substrate. The first and second substrates are brought together such that the first major surfaces of the first and second substrates face one another, and such that a cavity is defined there between, in making a VIG unit subassembly. The pump-out tube is inserted into the pump-out hole in the second substrate and second frit material is applied so as to overlap at least partially the first frit at the sealing area in the second substrate and to overlap at least partially the first frit on the pump-out tube. The subassembly is heated in order to melt the second frit material and wet the first frit material, with this heating being performed such that the first and second substrates reach a second peak temperature that is no higher than 400 degrees C. and that is at least 150 degrees C. lower than the first peak temperature. Following said heating of the subassembly, the subassembly is cooled and/or allowed to cool, in forming an edge seal between the first and second substrates. The cavity is evacuated to a pressure less than atmospheric via a pump-out tube. The pump-out tube is sealed in making the VIG unit. At least one of the first and second substrates is thermally tempered. The second peak temperature is sufficiently low so that the tempered substrate(s) retain(s) at least about 70% of the original temper strength after the heating of the subassembly.
One aspect of certain example embodiments relates to the use of a primer layer (e.g., a first frit) and a seal layer (e.g., a second frit, different from the first frit) in which the primer and seal layer have different functions and generally different compositions. This example aspect is different from approaches where a single seal material is heated twice, optionally with a second application between heating steps. It thus will be appreciated that the first and second frits discussed herein may in certain example instances be referred to as a primer frit or primer layer, and a top coat or seal layer.
The features, aspects, advantages, and example embodiments described herein may be combined to realize yet further embodiments.