Stock material or miscellaneous articles – Light transmissive sheets – with gas space therebetween and...
Reexamination Certificate
1998-11-13
2001-05-29
Loney, Donald J. (Department: 1772)
Stock material or miscellaneous articles
Light transmissive sheets, with gas space therebetween and...
C052S786130, C156S109000
Reexamination Certificate
active
06238755
ABSTRACT:
This invention is concerned with improvements in or relating to insulating glass units.
It has been a practice for many years to form insulating glass units consisting of two, three, or more glass panes which are spaced apart by a spacing and sealing assembly (generally referred to as “edge seal”) extending around the periphery of the inner facing surfaces of the glass panes to define a substantially hermetically sealed insulating space between the glass panes. It is a common practice to employ a metal preformed spacer to hold the glass panes separated and to assure the required rigidity of the unit. The preformed spacer may also contain a desiccant in such a way as to enable the desiccant to maintain air or other gas within the unit in a dry condition after the manufacture of the unit. The preformed spacer can be manufactured from metals by various machining processes. In one typical form of insulating glass unit construction, the edge seal comprises a hollow metal spacer element adhered to the inner facing surfaces of the glass panes by a low gas and moisture permeable sealant to provide a primary hermetic seal. The hollow spacer element is filled with a desiccant material, which is put in communication with the insulating space between the glass panes to absorb moisture therefrom in order to improve the performance and durability of the insulating glass unit. It is also a common practice to employ a so-called butyl sealant which is a polyisobutylene rubber based composition as primary sealant to bond the metal spacer to the glass panes and to employ a secondary sealant bonded to the panes around the spacer. This so-called “dual seal” system provides a better longevity of the insulating glass unit than the so-called “single seal” system, in which only a single sealant is employed. Various materials have been used to provide the secondary sealant, including for example polysulphides, polyurethanes and silicones. It has also become a practice to include within the unit a gas other than air, for example an inert gas such as Argon, Xenon, Krypton or SF
6
to improve the level of thermal or acoustic performances required. In a glazing unit as described, the butyl sealant ensures satisfactory adhesion of the metal spacer to the glass panes so as to provide desired moisture vapour or gas impermeability to the unit, thus avoiding moisture vapour entering and condensing in the cavity of the unit and, in case of a gas filled unit avoiding escape of gas from the unit. The secondary sealant serves to promote the integrity of the bond of the butyl rubber based composition by minimising the strain imposed on it due to external factors such as fluctuations in ambient temperature, barometric pressure, or wind pressure.
Whilst it is the common practice to employ hollow metal and preferably aluminium spacers there have been proposals to employ preformed spacers made from other materials for example butyl spacers (which may contain an undulated aluminum foil) or silicone or organic rubber foam spacers.
In U.S. Pat. No. 4,226,063 there is described a multiple pane window having an inner filamentary seal and an outer seal. The inner seal contains desiccant material whose concentration is greater in the inner portion thereof than in the outer portion thereof. In this arrangement the inner filamentary seal comprises a polyisobutylene based formulation and the outer seal is provided by a mastic, generally a polysulphide or silicone based mastic. The outer seal is responsible for the mechanical stability of the window.
In GB patent specification 2228519 there is described a multiple glazing panel for a vehicle comprising at least two panes of glass and a sealing spacer in which the sealing spacer comprises a flexible and malleable first element in contact with both panes and providing a barrier to entry of humidity into the sealed space in the unit and a second element in contact with both panes and being at least partially formed of an adhesive having a modulus of elasticity greater than 1.4 MPa. The first element is preferably butyl rubber and the second element may be based on silicone or polysulphide but is preferably provided by a polyurethane.
Interest in glazing units is primarily due to their thermal transmission coefficient properties or their acoustic properties. Thermal transfer by conduction or convection can be decreased by substituting the air present in the cavity of the insulating glass unit with a heavy rare gas having a lower thermal conductivity. Transfer by radiation can be decreased using low-emissivity (low E) glass. Typically, the thermal coefficient (the so-called “K-value”, which is a measure of the flux of heat energy through an area of 1 m
2
in the centre of the insulating glass unit for a temperature difference of 1° K. between the interior and exterior) for high performance insulating glass units filled with gas is below 1.5 and can be as low as 1.2, some combinations of low E coatings and special gases allowing K-values below 1.0 W/m
2
/K (i.e. Watts per square meter per degree Kelvin). For acoustic performance, beside the use of glass pane elements with different thickness in combination with laminated glass, a better acoustic performance can also be achieved by replacing a part or all of the air or rare gas present in the cavity by SF
6
gas.
Although desirably low K-values can be obtained with special gas filling and low E-coatings in the center of the insulating glass unit, the use of conventional edge seal systems, containing a metal spacer, results in higher thermal conductivity at the perimeter of the insulating glass unit. The higher conductivity of the edge seal causes water condensation to occur on the interior glass surface under certain environmental conditions and is therefore undesirable. Several technical solutions have been proposed regarding edge seals with reduced thermal conductivity (so-called “warm edge” systems).
There is a need to provide high performance glazing units in applications such as structural glazing or certain types of roof glazing where the entire or part of the seal system of the unit is directly exposed to sunlight (which contains damaging UV radiation). In such applications, the sealant is not only required to contribute to the integrity of the seal system of the unit itself against barometric pressure variation inside the cavity but also to contribute to the transfer of the wind load or deadload on the structure of the building. Furthermore, the glass adhesion of the sealant in such applications has to have excellent resistance against the damaging influences of sunlight (UV radiation) and the other weathering elements (especially heat and water). Organic sealants, such as those based on polyurethane, polysulfide, polybutadiene, etc., do not have a sufficiently UV resistant glass adhesion to allow their use for sealed units for these applications. Silicone sealants are currently the only known sealant type to have sufficiently stable glass adhesion and are the only materials approved for structural glazing application in the various national specification standards, practices, and building codes. Silicone sealants, however, have much higher gas permeabilities than organic sealants. Insulating glass units filled with special gases (such as argon) and having a dual edge seal design with butyl rubber primary sealant and silicone as secondary sealant display a high gas loss rate and do not pass national requirement standards for gas filled insulating glass units, such as DIN 1286, part 2. Thus, the manufacturer of insulating glass units today faces the following dilemma: Units that are sealed with organic sealants (such as the ones stated above) may comply with the national requirement standards for gas filled insulating glass units, but do not comply with the requirements for structural glazing and cannot be used for this and other applications involving a direct exposure of the edge seal to sunlight. On the other hand, units that are sealed with suitable silicone glazing sealants may comply with the requirements for structural gla
Harvey Martin
Hautekeer Jean-Paul
Rueckeshaeuser Karl-Heinz
Wolf Andreas
Dow Corning Corporation
Loney Donald J.
Scaduto Patricia M.
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