Abstract:
An insulating spacer for creating a thermally insulating bridge between spaced apart panes of a multiple pane window unit comprises in one embodiment, a solid profile of fiber-stabilized aerogel insulation material, treated to be non-porous along its exposed surface. The spacer defines a thermally insulated space between the panes. The result is higher thermal performance for insulated glass units and windows employing these insulated glass units.

Description:
FIELD OF THE INVENTION 
     This invention generally relates to an insulating spacer and in particular to an insulating spacer for creating a thermally insulating bridge between spaced-apart panes in a multiple glass panel window unit, for example, to improve the thermal insulation performance of the unit. This invention also relates to methods of making such an insulating spacer. 
     BACKGROUND OF THE INVENTION 
     An important consideration in the construction of buildings is energy conservation. In view of the extensive use of glass in modern construction, a particular problem is heat loss through glass surfaces and glazed building envelopes. One solution to this problem has been an increased use of insulating glass units comprising basically two or more glass panels separated by a sealed dry air space. Sealed insulating glass units generally require some means of mechanically separating the glass panels by a precise distance, such as by rigid spacers. 
     The spacers historically used are rectangular channels made of steel, aluminum or some other metal, with an internal desiccant to adsorb moisture from the space between the glass panels and to keep the encapsulated sealed air space dry. Tubular spacers are commonly roll-formed into the desired cross sectional shape. Steel spacers are generally considered the cheapest and strongest option, but aluminum spacers are easier to cut and form into non standard window shapes such as semicircles. Aluminum also provides lightweight structural integrity, but it is more expensive than steel. Metal spacers are manufactured by PPG of Pittsburgh, Pa. and Allmetal Inc. of Itasca, Ill. Spacers made entirely of plastic or from a combination of metal and plastic, termed warm edge spacers, have also been used to a limited extent. Manufacturers of these types of spacers include EdgeTech I.G., Inc. of Cambridge, Ohio and Swisspacer of Kreuzlingen, Switzerland. 
     There are specific factors that influence the suitability of the spacer material or design for use in high performance windows. Of most importance are the spacer&#39;s heat conducting properties and the spacer material&#39;s coefficient of thermal expansion. To date, metal has been the most widely used spacer material even though as a material it has a number of disadvantages in both of these areas. First, the thermal conductivity of metal is unacceptably high for use as a spacer. Since a metal spacer is a much better conductor of heat than is the glass or the air space between the panes of glass, its use leads to the rapid transfer of heat between the inside glass pane and the outside glass pane resulting in heat dissipation, energy loss, moisture condensation and other window assembly performance shortcomings. For example, in a sealed insulated glass unit, heat from within a building tries to escape in winter, and it takes the path of least resistance. The path of least resistance is around the perimeter of a sealed window unit, where the metal spacer bar is located. Metal spacers contacting the inner and outer panes of glass act as conductors between the panes and provide an easy path for the transmission of heat from the inside glass panel to the outside panel. As a result, under low temperature conditions in winter, condensation of moisture can occur inside the insulating glass or on the surfaces of the inner glass panel. Also, heat is rapidly lost from around the perimeter of the window, often causing a ten to twenty degree Fahrenheit temperature drop at the perimeter of the window relative to the center thereof. Under extreme conditions in winter, a frost line can occur around the perimeter of the window unit. These conditions undermine the energy efficiency of the window, and ultimately, the energy efficiency of the building itself. 
     A second important feature of the spacer material is its coefficient of thermal expansion. The coefficient of expansion of commonly used spacer materials is much higher than that of glass. Any difference in thermal expansion causes problems in the form of glass stress, seal shear and failure, or spacer damage. For example, the coefficient of linear thermal expansion for steel is twice that of glass (17.3×10 −6  inches per deg K versus 8.5×10 −6  inches per deg K). This difference is particularly critical in climates that have large changes in temperature. As a result of such changes in temperature, stresses do develop at the interface between the glass and spacer bar and in the perimeter seal. This often results in damage to and failure of the sealed insulating glass unit, such as by sufficient lengthwise shrinkage of the spacer to cause it to pull away from the sealant and therefore cause premature failure of the insulating glass unit. Many window units tend to fail due to such stress cracks or loss of seal resulting in water vapor condensation which is deposited inside the panes and observed as window fogging. Such a condition results in a warranty callback and a window replacement. 
     Although the issue of thermal expansion is important to window durability, the most common spacer material commercially used in the manufacture of such insulated glass units has been metal due to cost and a lack of viable alternate materials. 
     A final problem inherent in previous spacer arrangements is that a rigid spacer provides an excellent path for the transmission of sound from the outer panel to the inside panel. This poses a particular problem in high-noise areas such as airports, urban environments, and commercial office spaces. Other institutions such as hospitals and schools also have a need and performance mandate for low sound transmission glass units. For reasons of sound control, steel and other similar metals may be a poor material choice. Other spacer materials should be sought with the aim of improving acoustical performance of insulated glass units. 
     The prior art has attempted to overcome the drawbacks noted above by providing composite spacers commonly termed ‘warm edge’ spacers. For instance, U.S. Pat. No. 4,113,905 discloses a composite foam spacer for separation of double insulated glass panes. The spacer includes a thin extruded metal or plastic core and a relatively thick foam plastic layer cast to the core to form a 0.025 to 0.150 inch thick layer around the core. Such a spacer provides advantages due to the structural rigidity provided by the metal base but suffers from a relatively thin insulating layer resulting in unacceptable thermal transfer. 
     U.S. Pat. Nos. 4,222,213 and 5,485,709 disclose additional composite spacers. Both patents disclose a thin plastic insulation which is in contact with one glass surface and thereafter fitted by contact pressure or friction over a portion of a conventional extruded or roll-formed metal spacer or plastic/metal composite. The plastic insulating overlay can be formed over a conventional extruded metal spacer and from an extrudable thermoplastic resin. However, the force fit and the bi-material construction of such a spacer can result in separation of the two components with changes in temperature due to the different thermal expansion coefficients of the metal and the plastic and again allow for substantial thermal bridging across the structure. These features are undesirable. 
     Descriptions of additional novel composite window unit spacer designs can also be found in U.S. Pat. Nos. 6,035,603, 6,581,341, 6,989,188 and 7,270,859. 
     Accordingly, what is needed is an insulating spacer which creates a thermally insulating bridge between spaced-apart panes in a multiple pane, insulated glass unit which overcomes the above-noted drawbacks. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an improved thermally insulating spacer for a multiple pane, insulated glass unit which solves or overcomes the drawbacks noted above with respect to conventional spacers. 
     It is another object of this invention to create a thermally insulating bridge to reduce heat transfer from one pane of the window (glass or Polyethylene Terephthalate—PET, also known as Mylar) to another through the insulating spacer of the present invention. This invention thus keeps the inner pane of material (glass or Mylar) several degrees warmer than it might otherwise be in the winter, while preventing condensation that otherwise may occur. 
     It is another object of the present invention to provide an insulating spacer with a coefficient of expansion approximately equal to that of glass. 
     It is another object of the present invention to provide an improved method of manufacturing an improved composite insulating spacer to provide an improved and satisfactory bonding between glass, on the one hand, and the metal and aerogel materials in such a composite spacer, on the other hand. 
     It is still another object of the present invention to improve thermal insulation, particularly in buildings, and to provide for improved multiple insulated glass assemblies. 
     The present invention provides an insulating spacer for spacing apart panes of a multiple pane window unit, for example, and for defining an insulated space between the panes. The novel material incorporated into the insulating spacer is an aerogel composite, specifically a fiber reinforced aerogel (FRA). The novel spacer may consist entirely of an FRA, consist of a treated FRA, or the spacer may consist of an FRA profile bonded to a metal or plastic substrate for greater dimensional stability or improved manufacturability. 
     Fiber reinforced aerogels (FRA) have the lowest thermal conductivity value of any material currently used in building construction. They have thermal conductivities of 12 to 18 mW/m-K. By comparison, metals such as copper, aluminum, and stainless steel have much higher thermal conductivities of 36,000 mW/m-K, 20,400 mW/m-K, and 12,000 mW/m-K respectively. Even closed cell foams designed for thermal insulation such as expanded polystyrene and polyisocyanurate have thermal conductivities of 32 and 24 mW/m-K respectively. In addition to their low thermal conductivity, FRAs exhibit good moisture and water vapor resistance. The FRA is hydrophobic with excellent resistance to moisture. The material&#39;s series of nanopores embedded into a fibrous matrix form a tortuous gas-resistive network that resists vapor penetration, condensation and ice crystallization. FRAs also exhibit good dimensional stability and structural integrity over a broad range of temperatures. Typically available FRAs have a range of service temperatures over 200 degrees C., which is greater than that required for the building envelope. Across the service temperature, the FRA remains flexible and is not subject to contraction, thermal shock or degradation from thermal cycling as are foams. Last, FRAs have a coefficient of thermal expansion similar to that of metal and glass. The result is that once these materials are bonded together; there are no additional stresses due to temperature change. Therefore, the present invention improves the thermal performance of the insulated glass units along the edge of the assembly where unwanted heat transfer is a particular problem. 
     The construction of such fiber reinforced aerogel materials suitable for construction applications is disclosed in U.S. Pat. No. 6,068,882. Described in general process steps, the fiber reinforced aerogel (FRA) is prepared by impregnating a fibrous matrix with an aerogel precursor solution so that a liquid phase is placed around every fiber and then, without aging of the precursor solution to form a gel, supercritically drying the impregnated matrix under conditions such that substantially no fiber-fiber contacts are present. The resulting composite insulation contains aerogels distributed uniformly throughout the fibrous matrix. This general process is discussed in detail below. 
     To fully obtain the benefit of the composite configuration, each fiber within the fibrous matrix is completely surrounded by aerogels such that all fiber-fiber direct contact is avoided. The substantial absence of fiber-fiber contacts is accomplished by a combination of (i) selection of compatible fibrous matrices and aerogels, (ii) impregnation of the fibrous matrix with an aerogel sol so that the liquid phase surrounds every fiber, and (iii) controlled aerogel processing procedures. 
     In the process of the FRA manufacture, the principal synthetic route for the formation of aerogels is the hydrolysis and condensation of an alkoxide. Major variables in the aerogel formation process are the type of alkoxide, solution pH, and alkoxide/alcohol/water ratio. Control of these variables permits control of the growth and aggregation of the aerogel species throughout the transition from the “sol” state to the “gel” state during drying at supercritical conditions. For low temperature applications, the preferred aerogels are prepared from silica, magnesia, and mixtures thereof. 
     After formation of the alkoxide-alcohol solution, water is added to cause hydrolysis so a metal hydroxide in a “sol” state is present. Techniques for preparing such aerogel “sol” solutions are well known in the art. (See, for example, S. J. Teichner et al., “Inorganic Oxide Aerogel,” Advances in Colloid and Interface Science, Vol. 5, 1976, pp 245-273, and L. D. LeMay, et al., “Low-Density Microcellular Materials,” MRS Bulletin, Vol. 15, 1990, p 19). 
     Next, the fibrous matrix may be placed in an autoclave, the aerogel-forming components (metal alkoxide, water and solvent) added thereto, and the supercritical drying then immediately commenced. Supercritical drying is achieved by heating the autoclave to temperatures above the critical point of the solvent under pressure, e.g. 260° C. and more than 1,000 psi for ethanol. 
     Following a dwell period (commonly about 1-2 hours), the autoclave is depressurized to the atmosphere in a controlled manner, generally at a rate of about 5 to 50, preferably about 10 to 25, psi/min. Due to this controlled depressurization there is no meniscus in the supercritical liquid and no damaging capillary forces are present during the drying or retreating of the liquid phase. As a result, the solvent (liquid phase) (alcohol) is extracted (dried) from the pores without collapsing the fine pore structure of the aerogels, thereby leading to the enhanced thermal performance characteristics. 
     A commercially available fiber reinforced aerogel product is Spaceloft, manufactured by Aspen Aerogels of Northborough, Mass. To date, fiber reinforced aerogels have been used as interlayers over stud framing in walls, thermal clothing, and cladding for pipes and ducts. 
     As will be appreciated by those skilled in the art, in addition to the multiple glass or Mylar panes and the aerogel spacer, the assembly may employ polyisobutylene (PIB), butyl, hot melt, or any other suitable sealant or butylated material as a sealant and adhesive. Sealing or other adhesion for the insulating spacer may be achieved by providing special adhesives, e.g., acrylic adhesives, pressure sensitive adhesives, or hot melt adhesive. Multiple sealant layers may be used. By providing at least two different sealing materials, the result is that discrete and separate sealing surfaces are in place to protect the spacer. This is useful in the event that one seal is compromised. The sealant materials may be embedded within one another. 
     In addition to the flexible, thermally insulating spacer, the assembly may include a vapor barrier about the rear face of the spacer. Regarding the vapor barrier, it may be a metalized film or other material well known to those skilled in the art. Other suitable examples will be readily apparent. 
     A better understanding of these and other advantages of the present invention, as well as objects attained for its use, may be had by reference to the drawings and to the accompanying descriptive matter, in which there are illustrated and described preferred embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of one embodiment of the present invention. 
         FIGS. 2   a  to  2   i  are alternate embodiments of a single seal insulating spacer of the type shown in  FIG. 1 . 
         FIG. 3  is a perspective view of the present invention in-situ between substrates typical of a dual glaze insulated glass unit. 
         FIG. 4  is a perspective view of the present invention in-situ between substrates typical of a triple glaze insulated glass unit. 
         FIG. 5  is a perspective view of the present invention in-situ between substrates typical of a heat mirror glass unit (heat mirror embodiment). 
         FIG. 6  is a graph of the thermal performance of one embodiment of an aerogel spacer window versus that of a traditional steel spacer window. 
         FIG. 7  is a cross section view of one embodiment of a window assembly that incorporates the insulated glass unit into a window frame. 
     
    
    
     Throughout the views, like or similar reference numerals have been used for like or corresponding parts. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows one embodiment of the present invention in which  100  globally denotes the novel spacer. In the embodiment shown, the spacer  100  includes a pair of glass contact surfaces  102  and  104  in spaced relation to each other so as to separate two glass or plastic panes by a given distance. The spacer body  100  includes a front or inwardly directed face  106 , and a rear or outwardly directed face  108 . The front face  106  faces the interior of an insulated glass unit assembly, as shown in  FIG. 3 . As shown in the example embodiment, the four faces,  102 ,  104 ,  106  and  108  are each coated or clad with a material making the spacer suitable for direct bonding between two glass sheets. This coating and/or cladding may be a vinyl or other plastic, a nonwoven fabric or aromatic nylon, a butyl or other durable coating, or even a metal foil or other thin metallic skin. The spacer  100  has a fiber reinforced aerogel core  110 . The cladding material may be added to reduce dust shedding and to improve the aesthetic appearance of the unclad spacer material. The cladding may be permanently applied either by direct adhesion to the four surfaces  102 ,  104 ,  106  and  108  using a commercially available adhesive such as Super 77 Spray manufactured by 3M of St. Paul, Minn. Alternately, the spacer  110  may be wrapped by a non-woven fabric and welded to itself in a seam along the outer face  108  forming a sleeve. Dimensions  114  and  116  may be varied between about 2 to 50 mm to best suit the thermal, structural, and product cost needs of the assembly. 
       FIGS. 2   a  through  2   h  show further embodiments of the spacer as illustrated in  FIG. 1 . As shown in  FIGS. 2   a  through  2   h , these spacer embodiments now incorporate structural elements  112  in addition to the fiber reinforced aerogel  110 . In particular,  FIGS. 2   a ,  2   b , and  2   c  show spacers with stiffening material  112  exposed at inward facing surface  106 .  FIG. 2   d  illustrates a proposed embodiment where the stiffening material  112  is completely encapsulated by the aerogel  110 .  FIGS. 2   e  through  2   i  again show stiffening material  112  at the inward face  106  though the stiffening material  112  could also face outward. In  FIG. 2   h  the stiffening material also extends into the middle of the spacer and in  FIG. 2   i , the stiffening material extends along the two sides of the spacer which will be in contact with the two glass sheets. In each of the examples, the stiffening material can be made of a metal, resin impregnation or hardening, or suitable plastic material. 
       FIG. 3  is an embodiment showing the spacer  100  as typically employed in an insulated glass assembly  300 . Spacer  100  is positioned and bonded between two glass panels or sheets  302  and  304  about the perimeter. With greater detail concerning  FIG. 1 , the contact surfaces  102  and  104  and front face  106  each include a first cladding material which may comprise, as an example, a non-woven sheet. A first sealant  306  is shown at surface  108 , and adjacent to this first sealant there is included a second sealant  308  or water vapor barrier differing from the first coat  306 . Examples of probable vapor barrier materials suitable for use as the first sealant and the second sealant include polyisobutylene, polyurethane, polysulphide, 1-part silicone, and 2-part silicone. Additional film and foil sealants include polyester films, polyvinylfluoride films, metal films or foils, and any other appropriate material which prohibits the transfer of vapor. In addition, the vapor barrier may be metalized. A useful example to this end is metalized Mylar film. Other suitable materials for the second sealant layer include acrylic adhesives, pressure sensitive adhesives, hot melt, polyisobutylene or other suitable butyl materials known to have utility for bonding such surfaces together. 
       FIG. 4  is another embodiment of the spacer  100  which would be typically employed in a triple glazed insulated glass assembly  400 . Two spacers  100  are positioned and bonded as shown between three glass panels or sheets  302 ,  304  and  402  about their perimeters. The surface treatments of spacer  100  and the addition of adhesives, sealants and vapor barriers are the same as with assembly  300  shown in  FIG. 3 . 
       FIG. 5  shows three spacers  100  which would be typically employed in an insulated glass assembly  500 . In this case, assembly  500  represents a high thermal performance design termed a heat mirror unit. Three spacers  100  are positioned and bonded three times between a total of four panes or sheets  302 ,  304  and  502  and  504  about their perimeters. Sheets  502  and  504  are each a special multi-layer metalized sheet of Mylar designed to reflect infrared energy. They are typically much thinner than traditional glass sheets and are considered non-structural. The surface treatments of each spacer  100  and the addition of adhesives, sealants and a vapor barrier are the same as with assembly  300  shown in  FIG. 3 . 
       FIG. 6  shows the thermal performance of two insulated glass units. The two curves  602  and  604  represent window assemblies similar to those shown in  FIG. 4  whereby material  304  is ⅛ inch thick glass coated with Cardinal 272 LoE2 coating, material  302  is a coated Mylar film SC75 manufactured by Southwall Technologies of Palo Alto, Calif. and material  402  is ⅛ inch thick clear glass. For curve  602 , the spacer  100  is 11/32 inch high steel tubing manufactured by AllMetal. For curve  604 , the spacer  100  is ⅜ inch thick uncoated FRA. Both windows are shown separating an environment of approximately 20 degrees Fahrenheit from an environment of approximately 70 degrees Fahrenheit. Temperature data point  608 , is taken at the warm side glass surface in a location over the metal spacer. It shows that the heat transfer at the insulated glass unit edge is much greater than the heat transfer through the center of the unit (i.e. more heat is leaking through the spacer than through the center of the glass and thus the edge of the window adjacent the spacer is colder than the center of the glass). However, the insulated glass unit employing FRA as the spacer shows improved thermal insulation at the edge  606 . As with temperature data point  608 , the temperature corresponding to data point  606  is taken at the warm side glass surface in a location over the FRA spacer. In this location, the insulative value of the spacer element is greater than that of the center of glass, hence a warmer surface temperature adjacent the spacer than adjacent the center of the glass contrary to the prior art spacer structure (i.e. surprisingly, less heat is leaking through the spacer than is leaking through the center of glass). It is therefore shown that the proposed invention greatly reduces heat loss over existing technology. 
       FIG. 7  is a cross section view of the present invention incorporated into a typical window frame. Only the lower half of the window is represented. The upper section of the window and frame would be a mirror image of that shown here. The embodiment presented is  FIG. 7  was modeled for thermal performance using industry standard window prediction software, THERM. THERM is a state-of-the-art, computer program developed at Lawrence Berkeley National Laboratory for use in modeling the heat transfer across building components such as windows, walls, and doors, where thermal bridges are of concern. In the embodiment modeled as a 1.22 m by 1.52 m window, the following elements were used. Components  702  were 4 mm thick glass coated with a Low emissivity coating, LoE 3 -366 manufactured by Cardinal Glass of Eden Prairie, Minn. Components  704  were Mylar film SC75 manufactured by Southwall Technologies of Palo Alto, Calif. The voids of the insulated glass unit  706  were filled with Krypton gas, a typical thermal insulator. The insulated glass unit was sealed by a 3 mm thick layer of polyurethane sealant  710 , as manufactured by PRC-DeSoto International of Glendale, Calif. The window frame  712  used in this embodiment was a Series 400 fiberglass frame manufactured by Inline Fiberglass of Toronto, Ontario. Two cavities within the fiberglass frame  712  were filled with an expanding polyurethane foam  714  manufactured by BioBased Systems of Rogers, Ark. The present embodiment was modeled with two different window spacer materials  708 . In a base case, spacers  708  were 9 mm deep steel tubes rolled and welded to a square cross section. In a second modeling case, the spacers  708  consisted of the 9 mm deep fiber reinforced aerogel as shown in  FIG. 1 . For the window model using steel spacers  708 , the U-factor for the total windows was 0.104. For the window model using fiber reinforced aerogel spacers  708 , the U-factor for the total windows was 0.076. This represents a thirty seven percent (37%) improvement in the thermal performance of the system, just by replacing the window spacer material and leaving all other window components unchanged. This represents an astounding improvement over current window technologies. 
     Other embodiments of this invention will be obvious in view of the above descriptions.