LOW-COST HIGH-PERFORMANCE VACUUM INSULATED GLASS AND METHOD OF FABRICATION

Abstract

A low-cost high-performance Vacuum Insulated Glass is produced with three glass panes and bonding fiber mesh structures embedded between the glass panes. Each mesh structure is configured with elongated bonding fiber elements arranged in a grid configuration. The bonding fiber elements are formed with a fiber core covered with a low melting temperature material. The low melting temperature material melts upon heating and creates numerous vacuum sealed cells between the glass panes. The fiber core does not melt, and remains intact bonded to the glass panes, thus creating a support mechanism for supporting the glass panes at a spaced apart relationship.

Claims

1. A low-cost high-performance Vacuum Insulated Glass (VIG), comprising: at least a first glass pane and at least a second glass pane stacked relative to said at least the first glass pane in spaced apart relationship therewith, thus defining a gap therebetween, a first bonding mechanism disposed in said gap defined between said at least first and second glass panes, and a first support mechanism disposed in said gap between said at least first and second glass panes, wherein said first bonding mechanism includes at least a first plurality and at least a second plurality of elongated bonding elements extending in crossing relationship substantially continuously within said gap between said at least first and second glass panes, thus forming at least a first mesh structure embedded in said at least one gap and bonding said at least first and second glass panes together along said elongated bonding elements; and a plurality of vacuum sealed cells defined between said at least first and second glass panes by said first mesh structure, each vacuum sealed cell being sealed along a periphery thereof by respective portions of said at least first and second elongated bonding elements crossing each other at respective crossing points.

2. The Vacuum Insulated Glass of claim 1, wherein said at least first mesh structure further includes said first support mechanism embedded in said gap, said first support mechanism including: at least a first and a second plurality of elongated fiber elements arranged in substantial alignment with said at least first and second plurality of elongated bonding elements of said at least first mesh structure, said at least first and second plurality of elongated fiber elements extending in crossing disposition relative each to the other at said respective crossing points, wherein said elongated fiber elements are bonded to said at least first and second glass panes and support said at least first and second glass panes at a predetermined spaced apart relationship.

3. The Vacuum Insulated Glass of claim 1, wherein said at least first and second glass panes include at least a bottom glass pane, a top glass pane, and a middle glass pane sandwiched between said bottom and top glass panes, wherein said at least one gap includes a first gap defined between said bottom and middle glass panes, and a second gap defined between said middle and top glass panes, wherein said at least first mesh structure includes a first mesh structure embedded in said first gap and securing said bottom and middle glass panes at a first predetermined distance one from another, and a second mesh structure embedded in said second gap and securing said middle and top glass panes at a second predetermined distance one from another.

4. The Vacuum Insulated Glass of claim 1, wherein said elongated bonding elements are formed from a material selected from a group including low temperature solder glass, low melting temperature glass, low melting temperature metal, frit, and combinations thereof, having a melting temperature within the approximate range of 250° C.-500° C.

5. The Vacuum Insulated Glass of claim 2, wherein said elongated fiber elements are made from a material selected from a group including a glass, metal, ceramic, and combination thereof, having a melting temperature exceeding approximately 500° C.

6. The Vacuum Insulated Glass of claim 1, wherein said glass panes are made from a material selected from a group including soda lime, tempered glass, thermally strengthened glass, chemically strengthened glass.

7. The Vacuum Insulated Glass of claim 3, wherein at least one surface of at least one of said bottom, middle and top glass panes is covered with a low emissivity material.

8. The Vacuum Insulated Glass of claim 2, wherein said elongated bonding elements and elongated fiber elements extend in alignment one with another, thus forming bonding fiber elements including a fiber core coated with a frit coating, wherein said diameter of said fiber core is approximately 75 μm, and wherein a thickness of said frit coating is approximately 50 μm.

9. The Vacuum Insulated Glass of claim 1, wherein said glass panes have substantially the same thickness ranging between 1.0 mm and 3.5 mm.

10. The Vacuum Insulated Glass of claim 1, wherein said glass panes have different thicknesses each from the other.

11. The Vacuum Insulated Glass of claim 3, wherein said first and second predetermined distances between said bottom and middle glass panes and between said middle and top glass panes, respectively, are approximately 0.15 mm, and are substantially the same, each of said first and second predetermined distances ranging between 0.1 mm and 0.15 mm.

12. The Vacuum Insulated Glass of claim 3, wherein said first predetermined distance between the bottom and middle glass panes differ from said second predetermined distance between the middle and top glass panes.

13. The Vacuum Insulated Glass of claim 1, wherein the size of each said vacuum sealed cell is within the range of 40 mm-80 mm×80 mm-160 mm.

14. The Vacuum Insulated Glass of claim 1, wherein said at least first plurality of the elongated bonding elements crosses said second plurality of the elongated bonding elements at a predetermined angular relationship ranging from approximately 30° to 120°, and wherein said vacuum sealed cells are contoured in a shape selected from the group of square contour, rectangular contour, triangular contour, rhombus contour, diamond contour, arcuated contour, wavy contour, and combinations thereof.

15. The Vacuum Insulated Glass of claim 1, wherein said vacuum sealed cells hold the vacuum of approximately 10.sup.−3 Torr-10.sup.−4 Torr.

16. The Vacuum Insulated Glass of claim 3, wherein said first and second mesh structures embedded in said first and second gaps, respectively, are aligned each to the other.

17. The Vacuum Insulated Glass of claim 3, wherein said first and second mesh structures embedded in said first and second gaps, respectively, are displaced from each other.

18. The Vacuum Insulated Glass of claim 2, wherein said predetermined spaced apart relationship between said at least first and second glass panes corresponds to combined diameters of said first and second elongated fiber elements overlapped each with the other at said respective crossing points, wherein, at said crossing points, said at least first and second elongated fiber elements are bonded to said at least first and second glass panes, respectively.

19. A method for fabrication of low-cost high-performance Vacuum Insulated Glass (VIG), comprising: (a) establishing at least a first, a second, and a third glass pane; (b) applying a first mesh structure formed by at least a first and second plurality of elongated bonding elements extending substantially continuously on a surface of said first glass pane, said first and second pluralities of the elongated bonding elements crossing at first respective crossing points; (c) positioning said second glass pane on said first mesh structure on said first glass pane in a first spaced apart relationship with said first glass pane; (d) applying a second mesh structure formed by third and fourth pluralities of elongated bonding elements extending substantially continually on a surface of said second glass pane facing away from said first glass pane, said third and fourth elongated bonding elements crossing at second respective crossing points, wherein a relative disposition between said first and second mesh structures is selected from the group of aligned disposition, misaligned disposition, and combinations thereof; and (e) positioning said third glass pane on said second mesh structure on said second glass pane in a second spaced apart relationship therewith, thus forming a stacked assembly of said first, second, and third glass panes with said first and second mesh structures therebetween; (f) introducing said stacked assembly in a vacuum chamber; (g) creating a vacuum in said vacuum chamber; (h) heating said stacked assembly in said vacuum chamber to a predetermined temperature, thus melting said first, second, third and fourth elongated bonding elements of said first and second mesh structures, and thereby forming a first and second plurality of vacuum sealed cells, said first plurality of vacuum sealed cells being defined between said first and second glass panes, and said second plurality of vacuum sealed cells being defined between said second and third glass panes, wherein each of said vacuum sealed cells is vacuum sealed along the periphery thereof by respective portions of respective of said first, second, third and fourth elongated bonding elements.

20. The method of claim 19, further comprising: in said step (b), embedding a first support mechanism in said first gap between said first and second glass panes, and in said step (d), embedding a second support mechanism in said second gap between said second and third glass panes; wherein, in said step (h), said first and second support mechanisms secure said first, second, and third glass panes in a predetermined spaced apart relationship each to the other; and wherein said first support mechanism includes a first and second plurality of elongated fiber elements arranged substantially in alignment with said elongated bonding elements of said first mesh structure, and wherein said second separation mechanism includes a third and fourth plurality of elongated fiber elements arranged substantially in alignment with said elongated bonding elements of said second mesh structure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0065] FIG. 1 is a schematic representation of the prior art Vacuum Insulated Glass;

[0066] FIG. 2 is a schematic representation of the subject triple pane glass with numerous hermetically sealed cells;

[0067] FIG. 3 is a cross-section of the subject triple pane glass structure shown in FIG. 2;

[0068] FIG. 4 is representative of the bonding fiber element which is arranged in a grid configuration and embedded between the glass panes as best shown in FIG. 3;

[0069] FIG. 5 shows schematically the subject TPVIG with edge seals;

[0070] FIGS. 6A-6G show schematically the manufacturing process of the subject TPVIG, where FIG. 6F shows schematically a number of TPVIG assemblies with interspersed heaters in a vacuum chamber for the subject manufacturing process;

[0071] FIG. 7 shows the geometry of the subject glass pane; and

[0072] FIG. 8 is representative of the thermal analysis of the subject triple pane VIG.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0073] Referring to FIGS. 2-5, the subject triple pane vacuum insulated glass (TPVIG) 10 is made of two or more glass layers, i.e., glass panes. As an example, the subject VIG will be described herein as a triple pane glass using three glass panes, i.e., a bottom glass pane 12, a middle glass pane 14, and top glass pane 16 separated by small vacuum gaps which may typically range between 0.1 mm to 1 mm. The gap 20 is formed between the bottom glass pane 12 and the middle glass pane 14, and the gap 18 is formed between the middle glass pane 14 and the top glass pane 16.

[0074] The glass panes 12, 14, 16 may be of the same thickness or of a varying thickness, for example, selected from a range of 0.5 mm to 8 mm, preferably, from 1.5 mm to 3.5 mm, and even more preferably, from 1 mm to 2 mm. Similarly, the gaps 18, 20 may be of the same width (˜01 mm to ˜0.15 mm), or differ in their width.

[0075] In one embodiment, the gaps 18, 20 may be embedded with bonding fiber elements 21 arranged in grid-like (or mesh) structure 26.

[0076] The bonding fiber element 21 includes a bonding fiber element 22 coated with low melting temperature material 24, as shown in FIGS. 4, 6F, and 6G. The low melting temperature material 24 melts at temperatures, for example, between 250° C.-500° C. The bonding fiber is placed between the glass panes 12, 14, 16 in the mesh configuration 26, which includes a plurality 28, 30 of the bonding fiber elements 21 extending substantially continually and crossing each other at respective crossing points 39, as shown in FIGS. 2, 3, 5, 6B, and 6D.

[0077] The crossing bonding fibers 28, 30 are arranged in a staggered array, and may extend at various angles therebetween. For example, the angle between the bonding fibers 28, 30 may range between 30° and 120°, as preferred by the design.

[0078] The crossing bonding fibers 28, 30 form cells 34 therebetween, so that each cell (which is vacuum sealed as will be presented infra herein) is outlined and is sealed with respective portions of the bonding element 24 of the crossing bonding fibers 28, 30.

[0079] For example, when the angle between bonding fibers 21 of the crossing pluralities 28, 30 thereof is 90°, the mesh structure 26 forms a plurality of cells 34 of a square or rectangular configuration. For angles less than 90°, the cells 34 may be of triangular configuration. Other angular variations may form cells of other shapes, such as for example, rhomboid, diamond, etc. configurations.

[0080] The mesh structures 26 in the gaps 18, 20 between each pair of the panes may be aligned with or offset from each other. The offset arrangement provides additional thermal resistance as the heat in this arrangement is forced to travel over a longer path within the middle glass pane 14. The arrangement with the aligned mesh structures, where fibers vertically overlap with each other, is beneficial as it provides reduced stress in the glass panes. However, this arrangement creates a thermal short between the panes 12, 14, 16, thus resulting in a less effective thermal performance.

[0081] One or more of the glass panes 12, 14, 16 can be low-e coated to reduce the radiation heat transfer through the window. Such coatings can inhibit the radiation heat transfer and improve the insulation of the window.

[0082] In the manufacturing process, separate glass panes 12, 14, 16 are placed in a vacuum chamber 36, and air is removed through a space 38 where the bonding fibers elements 28, 30 cross. Once the desired vacuum level is reached, the panes 12, 14, 16 are heated, thus melting the low temperature melting material 24 (but not the fibers 22), thereby creating an array of strong, hermetically sealed cells 34 once the glass panels 12, 14, 16 have cooled and the material 24 solidifies. The fibers 22 of the mesh structures 26 do not melt due to the fact that they are made from a high melting temperature material, but remain intact when the bonding element 24 melts. The fibers 22 act as a support structure holding the glass panes in the separated manner each from the other to prevent the glass panes from touching each other.

Alternate Vacuum Insulated Glass Designs and Fabrication Methods

[0083] The sealed cells 34 of the subject TPVIG 10 can be of square, rectangular, diamond, or any other shape depending on the angle between the crossing bonding fibers 28, 30, as well as on the shape of the bonding fibers. The cells 34 in different embodiments can be hermetically sealed, partially sealed, or not sealed at all. If the cells 34 are not hermetically sealed, the TPVIG 10 is to be sealed at the edges of the panes as shown in FIG. 5. The edge seal 42 can be formed using, for example, either a solder glass or metallic seals. Flexible metallic seals could also be used as the edge seal 42 to reduce the stresses on the seal.

[0084] The bonding of the glass panes 12, 14, 16 can be accomplished in several ways. One of the ways assumes that a fiber 22 coated with the solder glass 24 is used to create the mesh structure 26, as well as the hermetic bonds. The elongated fiber 22 extends in conjunction with the elongated bonding elements 24. It is important that the bonding (sealing) elements 24 extend continually (with no voids therein) on the surface of the glass panes. A material used for the fiber in this embodiment may be glass, metal, ceramic, or any other material having a high melting temperature, for example, exceeding 500° C. The fiber 22 can be coated with a low melting temperature glass or metal 24 which melts at 250° C.-500° C.

[0085] The mesh structure 26 can be formed with a single material or a combination of two or more materials.

[0086] Alternatively, the mesh structure 26 can also be produced without a fiber core by extruding a low melting glass directly on the glass pane(s) using a variety of processes, such as 3-D screening, silk screening, etc., process. The glass panes 12, 14, 16 may also be held apart through some other mechanism during the heating process to control the pane spacing.

[0087] An alternative way to fabricate the mesh structure 26 may be through the use of a glass solder paste with a binder material that is evaporated during the heating process. The mesh structure 26 can also be metallic where the metal to glass bonds are used to bond the glass panes together.

[0088] The laying of the mesh structure 26 on the glass panes 12 and 14 may be achieved using a variety of processes, such as 3D printing, or screen printing.

[0089] Alternatively, the molten solder glass may be used as the mesh structure 26. Such molten solder glass may be laid on the fiber using the 3D printing process with a printer having one or more nozzles for dispensing the solder.

[0090] Although the mesh structure 26 provides the support needed to secure the adjacent glass panes 12, 14, 16 separate from each other, intermediate support structures, such as, for example, small pillars or small fibers may also be provided within the cells 34 themselves to act as additional spacer and support structures.

[0091] Stress analysis (detailed infra herein) of the subject TPVIG 10 manufactured by the subject method suggests that the maximum stresses occur at the spots where the bonding fibers 28, 30 from the two adjacent glass pane gaps cross each other. To reduce the stresses in glass panes, as well as in the fibers, the width of the seal line may be different at these crossing points.

[0092] The glass used in the subject TPVIG 10 may be soda lime, or tempered glass which can be thermally or chemically strengthened. The choice of the glass type depends upon the VIG design and intended application, as well as the strength requirements. In certain commercial applications, glass above a certain height from the ground is required to be fully tempered, whereas residential applications permit the use of annealed soda lime glass. Use of stronger glass may also result in lower overall thickness of the TPVIG 10.

[0093] In order to increase the insulation capability of the window, the VIG concept may also be used in combination of existing Insulated Glass Units (IGUs) by replacing one or both panes in an IGU with the TPVIG. This approach may be used in retrofit situations to keep the overall window thickness the same or similar to that of the existing window being replaced.

[0094] Referring to FIGS. 6A-6G, the exemplary subject manufacturing process is presented for production of the TPVIG 10 as a batch process in standard sizes, and the standard sized TPVIG structure 10 may be subsequently field cut to a required size. The subject process is applicable to production of TPVIG of any size. The standard size glass production is described herein only as an example. The spacing between the bonding fiber 21 in the mesh structure 26 can be adjusted for large orders of identical windows to minimize the uninsulated areas.

[0095] As shown in FIGS. 6A and 6B, a bottom glass pane 12 is manufactured, which is covered with a plurality 28, 30 of bonding fiber elements 21 in a mesh structure 26a. Each bonding fiber element 21, in this particular implementation of the subject method, includes a fiber core element 22 (˜75 μm, ˜600° C. melting temperature) layered on the surface of the bottom pane 12 in a predetermined pattern including the elongated elements 28, 30. The fiber core element 22 is coated with a low melting temperature (˜250-500° C.) frit 24 (˜50 μm thick coating) through, for example, an extrusion process (similar to coating an optic fiber with a polymer), or by drawing the fiber 22 through a molten bath of frit 24. The fiber 22 coated with the frit 24 represent the fiber/sealing bonding fiber (also referred to herein as element 21), as shown in FIGS. 4 and 6B.

[0096] As best shown in FIG. 6B, the fiber mesh structure 26a is configured on the bottom glass pane 12. The mesh structure 26a is formed by the fiber/sealing elements 21 extending in, for example, horizontal and vertical directions, thus forming elements 28 and 30, crossing each other at crossing points 39a. The distance between the fiber/sealing elements 21 may range between 40 mm to 80 mm in one direction and between 80 mm and 160 mm in another direction.

[0097] In an alternative embodiment, the mesh structure 26a may be formed aside from the subject process in a rolled format prefabricated and subsequently applied to the surface of the glass pane 12.

[0098] Subsequently, as shown in FIG. 6C, a second glass pane, i.e., the middle glass pane 14, is laid on the top of the mesh structure 26a formed on the surface of the bottom glass pane 12.

[0099] A second, preferably offset, layer of the mesh structure 26b is subsequently formed on the middle glass pane 14, as shown in FIG. 6D. The mesh structure 26b, similar to the mesh structure 26a, is formed by the bonding fiber elements 28, 30 crossing each other at the crossing points 39b, which may coincide vertically with the crossing points 39a, or be displaced therefrom to form offset mesh structures 26a and 26b. The mesh structure may be created in any of the manners described supra, similar to the mesh 26a.

[0100] Subsequently, as shown in FIG. 6E, a third glass plane, i.e., the top glass pane 16, is placed on the mesh structure 26b, thus completing the first triple-pane assembly 40. Short stacks of 2-3 TPVIG assemblies 40 are prepared in steps illustrated in FIGS. 6A-6E.

[0101] As shown in FIG. 6F, a stack 50 of the triple-pane assemblies 40 is placed in the vacuum chamber 36 with the heating elements 52 interspersed between them to efficiently heat the glass panes. The heating elements 52 may be in the form of an electrically heated plate, or a plate through which a high temperature heat transfer fluid flows (e.g., for example, Therminol 68, having a maximum working temperature of 360° C.).

[0102] The vacuum chamber 36 is subsequently closed, and a vacuum is created by removing air therefrom. When the vacuum chamber 36 is evacuated (for example, to approximately 10.sup.−3 Torr-10.sup.−4 Torr), the air leaves from the TPVIGs 40 through the spaces 38 existing at the crossing spots 39 where the bonding fiber elements 28, 30 overlap (as best shown in FIG. 6E). The total volume of air between the glass panes is only on the order of a few cm.sup.3.

[0103] The stack 50 shown in FIG. 6F is heated to a temperature ˜250° C.-500° C. to melt the frit coating 24.

[0104] When melting, the frit 24 fills the spaces 38, and, upon solidification, bonds the fibers 22 to the glass panes. The fibers 22 extending in crossing directions, are also bonded one to another at the crossing points, as shown in FIG. 6G. In addition, the frit 24 outlines and seals the cells 34 at their peripheries, as shown in FIG. 6G.

[0105] The fibers 22 do not melt, since they are compared of a high melting temperature material. The fibers 22 stay intact and create a support mechanism which supports the glass panes 12, 14, 16 separated one from another.

[0106] As shown in FIG. 6G, at the crossing points 39, the fibers 22 (vertical and horizontal) overlap one with another, and in combination, define the distance between the glass panes, i.e., twice the fiber diameter (˜150 μm) in the presented example.

[0107] As shown in FIG. 6G, multiple hermetically sealed cells 34 are created when the frit 24 solidifies upon cooling. The size of the cells 34 may be approximately 40 mm-80 mm×80 mm-160 mm. The cells 34 may hold the vacuum of 10.sup.−3-10.sup.−4 Torr. It is possible that the fibers 22 may fracture at the crossing points 39 due to high stress, but the fibers only act as spacers and do not affect frit created seals. The fiber diameter may need to be adjusted to produce a correct spacing if the fiber fracture occurs.

[0108] The contact point 39 of the crossing fiber/sealing elements 28, 30 becomes compressed due to the weight of the glass panes.

[0109] In one of alternative embodiments, instead of fibers coated with frit, a frit paste is silk screened onto a glass pane, and a fiber may be laid on the top. The process will be repeated for another pane that has the frit/fiber on both sides, as well as for a third pane with the frit/fiber on one side. The three panes will be aligned so the fibers extend in perpendicular (or angled at an angle other than 90°) to each other. This assembly will be placed in a vacuum chamber, a vacuum will be created, and subsequently the panes will be lowered onto each other. The assembly is heated to melt the frit and to create multiple sealed chambers 34 upon cooling and solidification of the frit.

[0110] Depending upon the VIG design, bonding (sealing) material, and the type of mesh structure, manufacturing methods may vary. One of the methods presented supra creates the separation between the glass panes, as well as their support in a required position, which is provided by the fiber mesh structure 26, due to the use of the solidified solder frit coated glass fibers as the mesh structure.

[0111] However, if the mesh structure is created in an alternative manner, such as, for example, with the use of the solder glass paste, as presented supra, an additional spacing mechanism may be needed to keep the panes 12, 14, 16 apart to create the vacuum between the glass panes. Similarly, once the vacuum is created, the glass panes spacing can be reduced further to ensure the proper contact with the solder material to control the gaps 18, 20 between the glass panes 12, 14, 16. Such spacing can be achieved using, for example, some mechanical mechanism, or using a solder glass, or other metallic preforms, which melt, or partially melt, as the fabrication process demands.

[0112] The mesh structure 26, in an alternative embodiment, can be prefabricated in rolls and can be spread between the glass sheets. The whole sheet of VIG is subsequently sealed in a vacuum furnace to produce the hermetically sealed grids in the glass.

[0113] The fiber mesh 26 may be visualized as a cloth fiber mesh spaced at large distances. Unlike the cloth fibers, the glass fibers, however, are incompressible, and, thus the overlapping point 39 of the crossing of the vertical and horizontal elements 28, 30 is two times thicker than the coated fiber 21. Thus, when the mesh structure 26 is embedded between the glass panes 12, 14, 16, the distance between the glass panes is two times the thickness of bonding fiber 21. This creates a gap between the fiber and the window panes everywhere except at the overlapping point of the fibers.

[0114] In another alternative embodiment, a middle pane with the mesh fibers can first be created under atmospheric conditions. This middle pane can be placed between the bottom and top panes, then the assembly can be placed in a vacuum chamber and heated to melt the frit to create multiple hermetic vacuum cells upon cooling.

[0115] Once the multiple panes and mesh stacks 40 are placed into the vacuum chamber 36, the vacuum is drawn form the chamber using, for example, a two stage vacuum system. The vacuum is created within the gaps 18, 20 between the glass panes due to the additional gap 38 between the fibers/sealing elements 21 and the glass panes 12, 14, 16. The total volume of the gaps between the panes is only of the order of few cubic inches. The vacuum chamber 36 is designed so that the vacuum creation between the glass panes is easier and cost effective.

[0116] Once the vacuum is created, the heat is applied to the vacuum chamber, causing the solder glass coating 24 on the glass fibers 22 to melt. This causes hermetic sealing between the fiber 22 and the window panes 12, 14, 16. Since the glass fiber's melting point is much higher than the solder glass coating, the glass fiber 22 remains intact and acts as a spacer material. In this semi-molten stage of the solder coating, the contact point 39 of the fibers is compressed more than the rest of the bonding fibers 21 due to the weight of the glass panes. The diameter of the glass fiber is chosen in such a way that when the coatings 24 melt, it fills the gap 38 created by overlapping fibers/sealing elements 28, 30.

[0117] The bonding stage of the subject process has been experimented to perfect the process. Glass soldering was studied for application in the subject process. Glass soldering is a widely used wafer bonding technique used in the encapsulation and creation of the vacuum tight sealing in micro machined structures. The bond thus created is hermetically sealed with high strength levels as the low melting intermediate glass layer molecules diffuse into the bonding surfaces, creating a high strength bond which is typically 20 MPa (or 2900 PSI) for a majority of the applications. Also, the bonding yield of the glass frit bonded wafer is very high. The wafer bonding typically uses screen printing process to create a uniform bonding. Although the process is well established, the suitability of the bonding process for the subject VIG application still must be established since it poses several challenges.

[0118] The grid-type sealing used in the subject structure is a line sealing instead of point contact (as in the case of the pillar spacers in a conventional VIG). This may be beneficial in several ways:

[0119] 1) The force on the glass is distributed along this contact line as opposed to a single contact point, and hence the overall stress on the glass is reduced. Since the sealing between the glasses is distributed along the fiber joints, the stresses due to thermal expansion is also distributed over the glass pane rather than having the sealing only the periphery.

[0120] 2) Another benefit of the bonding process used in the subject method is that the glass is divided into a plurality of vacuum sealed cells as opposed to a single large chamber between adjacent glass panes of the conventional VIGs. Thus, the glass can be cut into the desired pieces whenever needed for retrofit. This itself allows for mass production and reduces the manufacturing cost. When the glass is cut to a desired size, only a vacuum sealed cell (which is about 20 mm wide) which is cut loses the vacuum. The majority of the sealed cells 34 remain intact and, thus, hold the vacuum, and thus the overall glass does not lose the vacuum. If any of the internal seals fails, the glass is still vacuum tight, unless the failure is at the periphery. In that case, only the partial vacuum chambers lose vacuum. Similarly, if the window cracks, only a partial vacuum is lost.

[0121] The subject glass made with three or more glass panes has been chosen for a preferred embodiment to mitigate two issues: 1) to improve the thermal stress reliability of the glazing, and 2) to improve the thermal performance (or attain a low U factor).

[0122] The mesh structure is placed between the first two panes, and another mesh structure may be vertically placed between the 2.sup.nd and 3.sup.rd glass pane. However, the mesh structure positioning may be vertically staggered in such a way that the fibers do not overlap each other. For example, a fiber may be located at the center between two fibers of the mesh embedded in another gap. The staggered configuration creates a much longer path to conduct the heat, and hence improves the thermal performance of the window. The numerical thermal performance has shown that a U factor of 0.2-0.5 W/m.sup.2-K can be achieved using triple pane VIGs.

[0123] Although the uniform bonding of the fiber joints helps distribution of the stresses in the window, very high temperature difference between the inner and outer glass panes in a window are to be avoided as much as possible. Using three or more panes divides the temperature gradient into two or more parts. For example, in the case of three glass panes with two gaps between the glass panes, the temperature difference would be divided between the outer pane and the middle pane, as well as the middle pane and the inner pane. Thus, the temperature difference between any of the two adjacent panes in a three-pane embodiment becomes practically half of that in a two pane VIG. This reduces the thermal expansion mismatch between the two adjacent panes and thus improves the reliability of the joints significantly, making the subject TPVIGs suitable for cold climates where the temperature difference between indoor and outdoor is substantial.

[0124] The cost of the subject triple pane VIG does not exceed that of the double pane VIG. The manufacturing process of the subject VIGs is of a multistack type, i.e., the multiple stacks of the glass panes and bonding fiber (fiber/sealing) mesh structure therebetween are exposed to vacuumization, followed by heating, and subsequently are fused together. Fabricating the triple pane VIG does not add extra costs to the manufacturing cost for the double pane VIG.

[0125] Depending upon the strength of the glass, the pane thickness of the triple pane window can be reduced to about 2 mm instead of 3 mm used for the double pane window. Although the cost and weight of the subject 2 mm triple pane window glass is similar to that of the 3 mm double pane window, the strength, R value and reliability of the subject TPVIG is much better. In case of breakage, even if the vacuum in one layer of the vacuum sealed cells in the subject TPVIG fails, the second layer may still be active and provide a reasonably low U value. Similarly, several panes of the window can be manufactured for other commercial applications which require even higher thermal performance, without addition of significant costs to the window itself.

[0126] In order to achieve a high radiation resistance, the glass panes used in the subject TPVIG may be low-e glass coated. The low-e coating should withstand the heating temperatures used for the heating stage of the present fabrication process. As the bonding temperature used in the subject process is much lower than 500° C., and could be below 200° C., Pyrolytic low-e coatings are well suitable for this purpose. However, the emittance values are higher for such coatings.

[0127] Alternatively, soft low-e coatings with as low as 0.02 emittance values may be used in the manufacturing of the TPVIG. This may be possible because the bonding procedure may be performed in a vacuum environment and the chances of degradation of the e-coating during the heating are very minimal. The low-e coat may be applied, for example, to the inner surface of the innermost (indoor) pane and the indoor side of the middle pane.

[0128] Numerical performance analysis of the subject TPVIG has been performed, and the results have been verified by the experimental analysis. A sample glass pane size of 400 mm width and 400 mm length was chosen for the modeling. This was achieved using a 200 mm×200 mm geometry, shown in FIG. 7 and using the symmetric boundary conditions on two of its sides.

[0129] The vacuum zone for the simulation was modeled as air with pressure of 10.sup.−4 Torr, and the inner (indoor) pane and the outer (outdoor) panes were subjected to the boundary conditions as recommended by National Fenestration Rating Council (NFRC). One face of the two out of the three panes (the innermost and the middle pane) were given an emissivity of 0.1 while the remaining faces had an emissivity of 0.84.

[0130] Regarding the analysis of the condensation performance, it was established that the minimum temperature at the center of the glass is equal to 279K or 6° C. (which is well above the dew point (3° C.) at standard indoor conditions) at the outdoor temperature of −18° C. The subject TPVIG thus is expected to have condensation below −20° C.

[0131] In certain embodiments, the bonding material of the fiber coating 24 can be melted and the glass fiber passed through the molten bonding material to create a uniform coating of the fiber. This process is similar to the coating of optical fibers. The thickness of coating depends upon the speed of fiber pulling through the molten matrix. In certain embodiments, the process of coating uses organic binders for coating the bonding materials. These bonding materials then can be burnt out at a predetermined temperature during the bonding process.

[0132] Fiber bonding and vacuum retention in the subject TPVIG has been tested. In the testing procedure, upon the successful coating of the fibers, the bonding fibers were used for bonding of the glass panes. During this process a smaller sample of the vacuum window glass was bonded in the vacuum environment. The hermetically sealed cells formed between the glass panes were tested for its vacuum retention. The vacuum retention procedure measured the vacuum level in the glass to ensure that the vacuum was maintained.

[0133] The samples also were tested for their strength and thermal performance. For example, a pressure test was applied to ensure the strength of the bonds.

[0134] In certain embodiments, the heating procedure inside the vacuum furnace involved heating of one or more glass panes. Detailed stress analysis for the full scale sample has been performed to establish the stresses in the glass and in the bonds. The stress analysis also helped in establishing an optimum spacing of the fibers in the TPVIG.

[0135] In certain embodiments, the uniform heating of the glass stacks and the bond creations, as well as the uniform suction of the vacuum, are key factors to the fabrication of the subject TPVIG. As such, the measurement of the vacuum propagation in the samples was used to determine the ability of the vacuum penetration through the gaps between the fibers and the glass panes before the creation of the bonding between the glass panes. When needed, the gap between the glass panes may be increased before the bonding to ensure the proper vacuum suction. Suitability of the various low e-glasses may be used for the VIG during this phase of the manufacturing process.

[0136] Manufacturing the VIGs can be completed in a variety of ways. Some examples include, but are not limited to: 1) produce the stack of VIGs in a batch process, and 2) incorporate the VIG production in the float glass production line similar to a vacuum sputtering process.

[0137] In certain embodiments, the size of the manufactured sample is the regular shipping size of the float glass. In certain embodiments, a stack of several VIGs glazing can be produced in a single batch using the vacuum furnace. The vacuum furnace used in such process will be much larger (e.g., 2 m×4 m), but the process of fabrication described supra remains the same.

[0138] The subject TPVIG process is much easier than the prior art processes in that it does not require majority of the routines needed for the IGU manufacturing. Also, it does not require use of inert gases and glue seals.

[0139] In certain embodiments, the subject process may be automated to avoid user related errors. Most of the operation, such as laying the full size glass panes and fiber mesh roll on the top of another in several layers, turning “on” the vacuum system, turning “on” the heat, and annealing of the VIGs may be automatic, making the fabrication of the TPVIG more cost effective.

[0140] Simulations of the conduction and radiation within a single pane, double pane, and the subject TPVIGs were performed using COMSOL™ for winter conditions specified in Table 1. Simulations results for specific cases are summarized in Table 2. The R-values presented are the ‘center of glass’ values for ease of comparison. The final values will depend upon the type of frame used. A single pane window has R=0.18 m.sup.2-K/W while the double pane IGU with low-e and argon insulation achieved R=0.62 m.sup.2-K/W. These results are consistent with simulations using DOE's Windows 7.4 software and were performed to validate the current simulations.

[0141] The TPVIG with 80 mm bonding fiber spacing, one low-e surface, and 2 mm glass achieved R=1.2 m.sup.2-K/W. However, TPVIGs with two surfaces with low-e coating achieved R=2.6 m.sup.2-K/W since the radiation from middle pane to outer pane is minimized, indicating the potential to achieve very high performance.

[0142] A full 3-D simulation has been performed. The temperature distribution on the outer surface for the TPVIG is shown on FIG. 8, which indicates the minimum temperature at the center of glass is 6° C. which is well above the dew point 3° C. for the NFRC specified winter conditions. The subject TPVIGs are expected to have condensation points below −20° C.

TABLE-US-00001 TABLE 1 NFRC winter weather conditions for the window simulation Thermal boundary conditions Value (SI) Value (IP) Interior ambient temperature   21° C.    70° F. Exterior ambient temperature −18° C. −0.4° F. Solar irradiation 0.0 W/m.sup.2 0 Btu/hr/ft.sup.2 Interior heat transfer coefficient 3.1 W/m.sup.2-K 0.55 Btu/hr/ft.sup.2-° F. Outside heat transfer coefficient  26 W/m.sup.2-K  4.6 Btu/hr/ft.sup.2-° F.

TABLE-US-00002 TABLE 2 Summary of performance simulations for various windows. The emissivity of the low-e glass was assumed to be 0.02. CASE Glass thk Cavity Glass thk Cavity Glass thk Spacing (ft.sup.2-hr-F./Btu) 1. Single pane 4 mm 0.2 (clear) 2. Double pane IGU 3 mm Argon 3 mm 0.533 (low-e)   (10 mm) 3. VIG (triple pane) 2 mm Vacuum 2 mm Vacuum 2 mm 80 mm 1.2 (low-e) (0.15 mm) 4. VIG (triple pane) 2 mm Vacuum 2 mm Vacuum 2 mm 80 mm 2.6 (low-e) (0.15 mm) (low-e)
Stress analysis of TPVIG was carried out using COMSOL Multiphysics 5.3 to understand the maximum stress occurring in TPVIG. The parameters varied in the study were the glass pane thicknesses, grid seal (frit) height and thickness, and the grid spacing in two perpendicular directions (which may be similar or different for the perpendicular directions).

[0143] Initial stress analysis simulation was validated using simple cases which have predefined analytic solutions for deformation and stresses. These cases were fix support beam case and a rectangular plate under pressure and fixed at the four sides. The results from the simulation matched with theoretical results. A grid independence study was also performed by refining the grid such that the minimum element size of the mesh was 1/10.sup.th of the minimum feature size (frit dimension) in the TPVIG.

[0144] The initial analysis confirmed the feasibility of the subject concept, and proved that the supports provided by the fibers were adequate. The maximum deflection was 50 microns assuming the glass thickness of 3 mm and a Young's modulus of 72 GPa. The maximum stress in the glass was approximately 150 MPa for a 3 mm outer pane, 1 mm middle pane, and 3 mm inner pane TPVIG with 10 cm×10 cm mesh grid size. The maximum deflection in the glass were less than 50 micron. The stresses in the glass panes were usually in the order of 6-10 MPa except for the concentrated points at the fiber crossings of the adjacent pane gaps, where the local stresses could exceed 150 MPa. Since glass is a brittle material, the fracture mechanism may be much more complicated and unpredictable compared to the ductile materials.

[0145] In order to verify the strength of the glass, a sample TPVIG was built with similar dimensions and tested under vacuum. The test was repeated several times without failure of the glass.

[0146] Although this invention has been described in connection with specific forms and embodiments thereof, it will be appreciated that various modifications other than those discussed above may be resorted to without departing from the spirit or scope of the invention as defined in the appended claims. For example, functionally equivalent elements may be substituted for those specifically shown and described, certain features may be used independently of other features, and in certain cases, particular locations of elements, steps, or processes may be reversed or interposed, all without departing from the spirit or scope of the invention as defined in the appended claims.