TEMPERATURE HERMETIC SEALING OF INSULATING GLAZING

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority to U.S. Provisional Patent

Application No. 61/494,080, filed June 7, 2011, the content of which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

[0002] The present invention relates to a method and apparatus for making an improved seal for insulating glazing, such as argon-filled or evacuated glazing. The invention also relates to an insulating glazing made by such a method and apparatus.

BACKGROUND

[0003] Windows account for a significant portion of the energy usage in the

industrialized nations. In the United States, for example, heat loss through windows accounts for up to half of residential heating bills in the United States. To meet the Energy Star window standard issued January 4, 2010 by the U.S. Environmental Protection Agency, windows deployed in the northern climate zone of the United States must perform with a heat loss coefficient of no more than U = 1.70 W/m ² -°C (0.30 Btu/hr-sq. ft.-°F). Window glazing meeting this standard is typically constructed using two panes of glass with a gap between the panes of about 1.27 cm (0.50 inches), maintained by a perimeter spacer. The gap between the glass panes is sealed to both panes, typically with organic sealant. The enclosed space is typically filled with an inert gas, such as argon, which has a lower conductivity and higher viscosity. The inert gas between the glass panes can help reduce conductive and convective heat losses. Also, the glass itself is provided with a low-emissivity multi-layer coating, typically applied by magnetron sputtering, to reduce heat loss due to radiation. Nevertheless, in cold weather conditions, a window meeting this Energy Star standard loses up to six times more heat than a well-insulated wall (U = 0.28 W/m ² -°C ). [0004] Furthermore, the common glazing design has several well-recognized shortcomings. One is that the seals, made with organic glues and sealants, are prone to outward leakage of argon (resulting in loss of insulating capability), and inward leakage of water vapor (resulting in fogging due to condensation and possibly etching of the internal glass surfaces). This leakage tendency is aggravated by pane movement caused by temperature changes, and by degradation of the sealant with age and exposure to the environment. To mitigate the risk of fogging, manufacturers typically incur the extra expense of adding desiccant material, such as silica gel beads, into the pane spacer to keep the fill gas dry. This reduces warranty cost, but does not eliminate it, because the ability of desiccants to capture water vapor eventually becomes exhausted if moisture leakage is present.

[0005] It would be advantageous to make an argon-filled insulating glazing using a seal that is significantly more gas-tight and less prone to deterioration. Not only would this prevent argon loss, but would prevent access of the atmospheric elements, including moisture, to the internal gas space, eliminating the need for desiccant. Alternatively, it would be advantageous to make evacuated insulating glazing using a highly-hermetic seal, using visually unobtrusive structural pillars between the glass panes, thereby creating a flat, transparent vacuum bottle capable of high insulating performance over the lifetime of a building.

[0006] Vacuum glazing products attempted heretofore have met with comparatively little commercial success due to design and performance shortcomings and high fabrication costs. For example, vacuum glazing by Nippon Sheet Glass (NSG) sold under the trade name Spacia® uses solder glass to seal the edges of the two panes. The resulting seal can be highly hermetic as manufactured; however, in cold weather the seal may become vulnerable to cracking due to the buildup of high stresses in the brittle solder glass seal material, because an outer pane contracts while an inner pane remains close to room temperature and contracts very little. For this reason, NSG warns against using this glazing in applications for which the temperature difference across the glazing exceeds 35 ^° C (63 F). Cold weather applications, the very applications where vacuum glazing is most needed, typically exceed this limit, often by 50% or more. Furthermore, the manufacturing process for Spacia® involves exposing the solder glass to high temperature, for example, 450 ^° C to 600 ^° C to melt the solder glass, and then holding the sealed unit under vacuum at 400 ^° C to 450 ^° C to eliminate adsorbed moisture. This combination of high temperature and time during these manufacturing steps tends to relax the beneficial tempering stresses from tempered safety glass. Tempered glass comprises about 25% of the market for window glazing, due to building codes requiring safety glass. It is desirable, for commercial viability, to be able to use tempered glass to make vacuum glazing. The high temperatures used for tempered glass, however, can limit the options for low-emissivity coatings. For example, to be compatible with the high temperatures used for tempered glass, pyrolytic low-emissivity coatings may be used, which typically is not very effective. Alternatively, the vacuum glazing may use no low-emissivity coating at all. Either of these options can be detrimental to the insulating performance of the vacuum glazing.

[0007] Alternative vacuum glazing designs have been under development since at least the mid-1980s, using a low-temperature fabrication process to bond a compliant metal foil seal along the edges of the glass panes. In one example, an adhesive layer is first coated along the edges of a planar surface of a glass element by magnetron sputtering. Magnetron sputtering is a coating process based on momentum transfer at the atomic level, analogous to the game of billiards. Gas ions are accelerated across a cathode dark space and strike a cathode, which is called the target. The incoming ions transfer their momentum to the atoms in the target, thereby ejecting atoms of the target material, some of which subsequently strike the substrate glass element, thereby forming a coating.

[0008] Sputtered coatings can adhere better than those produced by other low- temperature coating processes such as vacuum vapor deposition coating, as can be confirmed by a simple tape test (described in Section 4.11 of Military Specification M13508A). The adhesion of coating to substrate is related to the kinetic energy of atoms striking the substrate. The atoms ejected from the target during magnetron sputtering have a characteristic average kinetic energy on the order of 40 eV, more than an order of magnitude greater than the particle energies involved in vacuum vapor deposition.

[0009] Magnetron sputtering, however, has numerous disadvantages. First, the substrate cannot be plasma-cleaned simultaneously with coating of the substrate. That is, the substrate can be cleaned by plasma etching only before coating, not during coating. Thus, the surface of the substrate may become contaminated by stray atoms of materials other than that of the desired coating. Second, the coating atoms cannot penetrate into the surface of the substrate any further than their own inherent kinetic energy will take them, creating more of an abrupt interface as opposed to the desired graded interface. This restricts the selection of materials used for forming the adhesive layer, because to achieve the desired adhesion, the relatively weak mechanical bond needs to be supplemented with suitable chemical bonds. Marginal adhesion may be

compensated by using a bond width that is wider than can fit on the perimeter surface of the substrate.

[0010] Due to these and other limitations of magnetron sputtering, typically at least two layers of dissimilar materials, that is, a first adhesive layer that is adhesive to the glass and a second barrier layer that is adhesive to the first layer and is also readily-bondable to a metal foil seal strip, are required on the glass element, which is undesirable. Furthermore, to avoid delamination due to thermal cycling, the adhesive layer material may be required to have a coefficient of thermal expansion approximately similar to that of glass, which further restricts the selection of materials suitable for the adhesive layer. Magnetron sputtering can be too slow for some coating applications, as deposition rates typically range from 0.005 microns per minute to 0.05 microns per minute at the low end to approximately one micron per minute at the high end. The capital expenditure for sputtering equipment is higher than for virtually all other coating processes. Therefore, there has developed a need for a low-cost method of bonding a metal foil seal strip to glass elements for insulating glazing which suitably avoids high-temperature steps and does not rely on magnetron sputtering, and an insulating glazing made by such a method.

SUMMARY

[0011] For manufacturing a compliant hermetic seal in vacuum glazing, it is desirable to bond a metal foil seal strip on a glass element at a low temperature. If a metal coating is used to facilitate said bonding, it is desirable, for cost considerations, that the coating consist of a single layer of a single material which adheres well to glass as well as being readily-bondable to a metal foil seal strip. Furthermore, it is desirable that the coating be capable of fast thickness growth rate without serious compromise of the beneficial qualities of the coating. [0012] Ion plating creates a graded interface which is somewhat analogous to the interface of intermixed atoms created by diffusion bonding, but with three important differences: 1) ion plating does not require high temperature, 2) ion plating can create the graded interface in a much shorter time, measured in minutes or even seconds, and 3) ion plating can readily form a nonequilibrium mixture within the graded interface; for example, the concentration of silicon in aluminum can be made to span the full range from 0% to 100% even though only a small amount of silicon is soluble in aluminum at processing temperature equilibrium. The fact that the concentration in the graded interface changes gradually over a finite depth not only improves adhesion, but also reduced stresses arising from a mismatch of thermal expansion coefficients.

[0013] It is therefore the object of the present invention to provide a highly hermetic seal, which will not only reduce leakage-related warranty costs of the argon-filled insulating glazing design currently in common use, but will also enable evacuated insulating glazing having performance and cost amenable to widespread commercial success.

[0014] In one aspect, the disclosure relates to a method for fabricating an insulating glazing assembly. The method generally includes providing at least two glass elements of substantially congruent shapes. Each glass element defines two substantially planar faces. In embodiments, each planar face includes rounded corners. A perimeter surface extends between the substantially planar faces. The glass elements are positioned substantially parallel to and spaced apart from each other, defining an interior space extending therebetween. A seal strip is bonded on the glass elements, thereby sealing the interior space. At least a portion of the seal strip is bonded to the perimeter surface of each glass element.

[0015] In another aspect, the disclosure relates to a system for forming a metal coating on a glass element for insulating glazing. The system generally includes a chamber and a power supply. The chamber is configured to expose at least a part of the glass element to a depositant metal and an ionizable gas. The power supply is configured to create a plasma of the ionizable gas in the chamber, thereby forming a cathode dark space adjacent the glass element, whereupon the depositant metal forms a coating on the glass element after passing through the cathode dark space. [0016] In another aspect, the disclosure relates to an article for insulating glazing. The article generally includes at least two glass elements of substantially congruent shapes. Each glass element defines two substantially planar faces. In embodiments, each planar face includes rounded comers. A perimeter surface extends between the substantially planar faces. The glass elements are positioned substantially parallel to and spaced apart from each other, defining an interior space extending therebetween. A seal strip is bonded on the glass elements. The seal strip seals the interior space. At least a portion of the seal strip is bonded to the perimeter surface of each glass element.

[0017] In another aspect, the disclosure relates to an article for insulating glazing. The article generally includes at least two glass elements of substantially congruent shapes. Each glass element defines two substantially planar faces. Each planar face includes rounded corners. A perimeter surface extends between the substantially planar faces. The glass elements are positioned substantially parallel to and spaced apart from each other, defining an interior space extending therebetween. A seal strip is bonded on the glass elements. The seal strip seals the interior space.

[0018] Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 is a cross-sectional view of a prior art vacuum insulating glazing with a U- shaped seal.

[0020] FIG. 2 is a planar view of a corner region of the vacuum insulating glazing of FIG.

1.

[0021] FIG. 3 is a cross-sectional view of an article for insulating glazing according to an embodiment of the invention.

[0022] FIGS. 4, 5, and 6 are enlarged plan views of a corner of a pane element of the article of FIG. 3. [0023] FIG. 7 is a cross-sectional view of a stack of two of the articles of FIG. 3.

[0024] FIG. 8 is a cross-sectional view of an insulating glazing according to another embodiment of the invention.

[0025] FIG. 9 is a schematic view of an apparatus for forming an insulating glazing according to an embodiment of the invention.

[0026] FIGS. 10a, 10b, and 10c are sequential planar views of an insulating glazing unit having its hermetic seal completed when the seal strip is comprised of a continuous metal foil loop having length in excess of the glazing unit perimeter.

[0027] The drawings identified above are not necessarily to scale. It should be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the above- described drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways.

DETAILED DESCRIPTION

[0028] The phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

[0029] As used herein, "insulating glazing" denotes a window glazing assembly formed from at least two glass members at least partially transparent to electromagnetic radiation, being substantially parallel along their planar faces and substantially congruent shapes with

surrounding edges sealed to form an interior space, the interior space being at least partially filled with a gas that is less conductive and possibly more viscous than air, or optionally evacuated.

[0030] "Substrate" refers to an object intended to be plasma cleaned or to receive a coating, such as glass intended to receive a metal coating. [0031] "Plasma" is an electrically stimulated state of gaseous matter consisting of an essentially neutral mixture of electrons and ions. "Plasma" is used interchangeably with "glow discharge."

[0032] "Ion" is an atom from which at least one electron has been removed, resulting in a positively charged particle having nearly the same mass as the original atom, and which can be accelerated by an electric field created by a voltage difference.

[0033] "Particles" refers to various entities having sizes at the atomic scale, including atoms, molecules and ions.

[0034] "Cathode" is a member, either conductive or non-conductive, having a negative charge (or negative voltage), relative to a reference, due to an excess of electrons.

[0035] "Anode" is a member, having a positive charge (or positive voltage) relative to a reference due to a shortage of electrons.

[0036] "Cathode dark space" is the region adjacent to the cathode when a plasma is present, and across which most of the voltage drop between the anode and the cathode occurs, and which displays little or no visible glow discharge.

[0037] "Etching" means the removal of atoms from the surface of a cathode by a glow discharge with one benefit being the removal of surface material resulting in the creation of an atomically clean surface. "Etching" is used interchangeably with "cleaning."

[0038] "Applied potential" is expressed as the absolute value (always positive) of the voltage difference between a cathode and an anode, or across a cathode dark space.

[0039] "Hermetic" is a term used to describe a seal which allows helium leakage rates of no more than about 10 ^~8 to 10 ^~9 standard cubic centimeters/second (sec/sec) per foot of seal length. [0040] "Highly-hermetic" is a term which will be used to describe a seal which allows helium leakage rates of no more than about 10 ^~9 sec/sec, and preferably no more than about 10 ^"11 sec/sec, and most preferably no more than about 10 ^~12 sec/sec per foot of seal length.

[0041] "Graded interface" refers to a layer of finite thickness having a gradually changing concentration from 100% coating material to 100% substrate material across the thickness. For example, a graded interface can comprise a mixture of metal and glass between one boundary of substantially pure metal and a second boundary of substantially pure glass.

[0042] The description of forming a metal coating "on" a glass surface may denote an abrupt interface between the original glass surface and the adherent coating material.

Alternatively, a coating may take the form of a layer of which at least a small portion, and possibly all of the layer, consists of a mixture of metal and glass atoms, possibly in the form of a graded interface.

[0043] "Perimeter surface" of a glass element refers to a surface that extends between two substantially planar faces of the glass element.

[0044] FIG. 1 illustrates a conventional evacuated insulating glazing that includes two glass elements 1, 2 sealed with a U-shaped seal strip 6'. Two glass elements 1 and 2 each include an interior planar face 16, an exterior planar face 17, and a perimeter surface 15 extending therebetween in a vertical direction. As used herein, the terms "vertical," "top," "bottom," "front," "rear," "side," and other directional terms are not intended to require any particular orientation, but are instead used for purposes of description only. Pillars or spacers 4 space apart the two glass elements 1 and 2. The pillars 4 include a substantially incompressible material to provide spacing between the interior planar faces 16. The pillars 4 serve to provide a substantially constant gap between the glass elements, which are typically under compression by the atmosphere on the exterior planar faces 17. A metal coating layer 5' is created along lateral edge surfaces of each glass element 1 and 2. In some embodiments, the seal strip 6' includes a foil of a metal suitable for bonding to the metal coating layer 5', and encompasses edges of the glass elements 1 and 2. Each leg of the seal strip 6' extends over at least part of its respective metal coating layer 5'; the seal strip 6' is thereby coupled to a portion of the exterior planar faces 17 at the seal bonds 8'. The seal bonds 8' are created in such a way as to form a highly-hermetic seal between each leg of the seal strip 6' and its respective metal coating layer 5', preferably by a cold welding method such as ultrasonic welding, or by an alternative method such as soldering, laser welding, resistance welding or brazing. Although the whole of the metal coating layer 5' is available for bonding with the seal strip 6, not all of the region of overlap between the metal coating layer 5' and the seal strip 6' need be utilized to achieve satisfactory results. The glass elements 1 , 2 optionally include chamfers 18 or other deviations from a simple plane surface which are nevertheless considered part of the perimeter surface 15 joining the interior and exterior planar faces 16, 17.

[0045] Referring also to FIG. 2, forming the corners of the seal strip 6' without trimming the seal strip 6' requires that the seal strip 6' be folded, thereby creating a small flap 3', or three foil layers total. Alternatively, the seal strip 6' may be cut so as to allow creating a two-layer stack of foil. Either way, multiple layers of seal strip 6' at corners may require a change of operating parameters for ultrasonic welding, such as reducing the head speed. Cutting out a triangle of a top and a bottom of the seal strip 6' to create a bevel joint, which avoids multiple layers, creates a risk of eventual leakage unless mitigating steps are taken, adding cost.

[0046] Referring to FIGS. 3-6, an insulating glazing according to the current invention includes seal bonds 8 located on the perimeter surfaces 15. An optional metal coating layer 5 is created along the perimeter surface 15 of each glass element 1, 2, preferably using ion plating, as will be explained further below. A seal strip 6 spans the perimeter surfaces 15 of the glass elements 1 and 2, extending over at least a part of each metal coating layer 5. Seal bonds 8 are created in such a way as to form a highly-hermetic seal between the seal strip 6 and its respective metal coating layer 5, preferably by a cold welding method such as ultrasonic welding, or by an alternative method, such as soldering, laser welding, resistance welding or brazing, which does not require substantial heating of the glass element. In some embodiments, the width of the seal strip 6 is about the same as the thickness of the two glass elements 1 and 2 plus the relatively small gap defined by the spacers 4. In some embodiments, the metal coating 5 may be eliminated by directly bonding the seal strip 6 to glass perimeter surfaces 15, for example, by ultrasonic welding. [0047] The planar faces 16, 17 of the illustrated glass elements 1 and 2 each preferably include rounded or radiused corners with a respective corner radius 13. To form the rounded corners, material forming a sharp corner 11 (shown in phantom lines) is removed from each glass element 1, 2. In some embodiments, the corner radius 13 is relatively small, e.g., approximately 20 microns to approximately 25.4 mm, so as to require a small amount of material to be removed. In other embodiments, however, a larger corner radius 13 may be used. Referring to Fig. 4, in the illustrated embodiment, the rounded corner is a portion of a circle. Referring to Figs. 5 and 6, in some embodiments, the rounded corner can be made up of one or more linear or arcuate portions. The rounded corners of the glass elements 1 and 2 can provide various benefits. For example, a bonding machine such as an ultrasonic seam welder with a rolling head can be used, as will be explained further below. Moreover, a continuous seam of uniform quality can be produced without the need to fold, crease, cut, deform or otherwise manage excess seal strip 6 at a corner. The risk of foil puncture at a sharp corner 11 , during fabrication, subsequent handling, or use, is reduced. Furthermore, metal foil stress points are reduced, which otherwise can be points of fatigue failure during cyclical pane movement due to temperature change.

[0048] FIG. 7 illustrates an arrangement that allows more than one pair of glass elements

1 and 2 to be ganged together and coated with a metal coating layer 5 all at the same time, and then evacuated and sealed. In this arrangement, the perimeter surfaces 15 remain exposed during the application of the metal coating layer 5, while the innermost glass elements 1, 2 act as masks for each other, preventing coating of the abutting exterior planar faces 17. Seal strips 6 can be subsequently bonded to the metal coating layers 5 at seal bonds 8. This arrangement increases productivity of the glazing coating and sealing process, thereby lowering cost.

[0049] FIG. 8 illustrates an insulating glazing according to another embodiment of the invention as applied, for example, to the common gas-filled design of insulated glazing. This embodiment employs much of the same structure and has many of the same properties as the embodiment of the insulating glazing described above in connection with FIGS. 3-7.

Accordingly, the following description focuses primarily upon the structure and features that are different than the embodiment described above in connection with FIGS. 3-7. Reference should be made to the description above in connection with FIGS. 3-7 for additional information regarding the structure and features, and possible alternatives to the structure and features of the insulating glazing illustrated in FIG. 8 and described below. Structure and features of the embodiment shown in FIG. 8 that correspond to structure and features of the embodiment of FIGS. 3-7 are designated hereinafter with like reference numbers.

[0050] In this embodiment, an edge spacer 9 spaces apart the glass elements 1 and 2.

The edge spacer 9 includes a continuous length within the perimeter of the glass elements 1 and 2. Because the seal bonds 8 provide a highly-hermetic seal of the interior space, there is no need for incorporating desiccants in the region of the edge spacer 9. Edge spacer 9 may be suitably made of a strong material having low conductivity, such as foamed polyurethane, and is secured to the glass elements 1 and 2 by an organic adhesive. The adhesive need not act as a primary seal, because that function is embodied in the seal bonds 8.

[0051] According to one aspect, an article for insulating glazing is made by depositing the metal coating layer 5 along the perimeter surface 15 of each glass element 1, 2 using ion plating. Both ion plating and magnetron sputtering are considered glow discharge processes. However, ion plating differs fundamentally from magnetron sputtering in specific ways that impart advantages in creating a highly-hermetic seal, as explained below. In ion plating, as a pre-operation, a substrate is negatively charged and bombarded by positively charged ions from a glow discharge (plasma) accelerating across the dark space. This results in sputter cleaning (that is, plasma etching) of the substrate surface. Then, metal atoms are vaporized into the glow discharge, and are deposited as a coating on the substrate, while bombardment of the substrate by ions continues simultaneously. Simultaneous etching and coating is an advantage of ion plating. The continued bombardment of the substrate surface and the developing coating by ions can be thought of as "ion peening," which has several advantageous effects: 1) it assures an atomically clean surface on the unmasked portion of the substrate by ejecting (or "backsputtering") contaminant atoms and some layers of glass atoms prior to and during the initial formation of the coating; 2) at least until the coating becomes too thick, it drives at least some of the metal atoms from the coating into the surface of the substrate many atomic layers deep, forming an ion-mixed zone or graded interface of embedded metal atoms in the surface of the substrate, resulting in a graded interface having a gradually changing concentration over a finite depth, from 100% metal to 0% metal; and 3) it densities the coating as it builds in thickness. Generally speaking, the rate of incoming metal atoms and ions must exceed the rate of backsputtering of atoms from the developing coating to grow the coating in thickness.

[0052] In some embodiments, ion plating is conducted using an applied potential of approximately 200 V to approximately 600 V to coat the perimeter surface 15 of each glass element 1, 2 using a radio frequency (RF) power 12 (see FIG. 9) . In other embodiments, however, a higher potential may be applied to the glass substrate, thereby improving adhesion still more. In some embodiments, the applied potential may be as high as about 5,000 V. A suitable applied potential can limit the gas content in the coating (that is, adsorbed argon), thereby increasing hermeticity. The applied potential also encourages resputtering, as a result of which the coating surface tends to become smoother. If a small amount of oxygen remains in the chamber, the applied potential can reduce the amount of oxidation of metals that have a high affinity for oxygen, such as aluminum, titanium and chrome.

[0053] In some embodiments, an effective pressure, e.g., approximately 2x 10 ^~3 Torr, is used in ion plating to produce a nearly conformal coating over a severe substrate topography. A significant coating thickness can be produced on the side of the substrate which is opposite from the metal source, because charged particles have a tendency to follow the electric field lines emanating from all exposed surfaces of the substrate. Random scattering caused by collision of metal atoms with gas atoms further assists forming a coating layer on the side of the substrate opposite to the metal source. Conformal coating allows more flexibility in the number and location of metal sources, which is important when coating only the edges of large glazing units.

[0054] FIG. 9 illustrates an apparatus or machine for creating the ion-plated metal coating layer 5 on the glass elements 1, 2. The apparatus includes an air-tight chamber 10, and a vacuum pump system 42 connected thereto. In some embodiments, the vacuum pump system 42 includes a two-stage rotary vane backing pump in series with a turbomolecular pump. In other embodiments, the vacuum pump system 42 includes other types of pumps to suitably form a vacuum in the range of about 10 ^"5 Torr in the chamber 10. An input supply for an ionizing gas 48 such as argon is provided through an interface port 40. The pressure inside the sealed chamber 10 is monitored by a pressure gauge 38. The chamber is evacuated to approximately 5 ^X 10 ^"5 Torr by means of the vacuum pump system 42 to reduce contaminant gases such as oxygen and moisture. Then the ionizing gas 48 is introduced by means of a control valve to raise the pressure, for example, to 2x 10 ^~2 Torr, sufficient to easily strike a glow discharge.

[0055] The illustrated RF power supply 12 has an integral matching box (not shown) for tuning to minimize the reflected power, and can generate several hundred watts of power at a frequency of approximately 13 Megahertz. An insulated feedthrough electrode 41 connects the RF power supply 12 to a bias plate 24 within the chamber 10. The bias plate 24 enables the RF portion of the power feed to stimulate the glass elements 1, 2 to become self-biased, that is, to become spontaneously negatively-charged. Then the glass elements 1 , 2 can function as a cathode, which in turn stimulates the ionizable gas to form a glow discharge. The glow discharge is used to clean and lightly etch the glass elements 1 , 2 for a period of time prior to deposition of the coating material, as well as to maintain a clean surface during formation of the graded interface.

[0056] In operation, the glass elements 1 , 2 are thoroughly cleaned before coating using a suitable cleaning protocol. The glass elements 1, 2 are then placed on top of a conductive bias plate 24. An insulating structure 22, such as a glass shelf, is provided to support and electrically decouple the bias plate 24 from the chamber 10, which is reliably grounded. If a transparent viewable area is desired, a mask may be placed on top of the glass substrate to prevent coating beneath it. The RF power supply 12 is in electrical communication with the electrodes and configured to create a glow discharge in the ionizable gas 48. Ions of the ionizable gas 48 are accelerated across the electric field within the cathode dark space portion of the glow discharge proximate to the glass elements 1, 2, bombarding or hammering on the depositant metal ions. The depositant metal is thus driven to contact the glass elements 1,2, thereby forming a metal coating layer 5 on the glass elements 1, 2.

[0057] In some embodiments, the output of a direct current (DC) power supply 14 may be superimposed on the RF power using a suitable filter network 35. This makes the charge on the bias plate 24 and glass elements 1 , 2 more negative, which in turn increases the energy with which the positive ions in the plasma will strike the negatively charged glass elements 1 , 2 compared to the use of the RF power supply 12 alone. In ion plating, a non-glowing "dark space" may form proximate to the cathode. Although there is a relatively uniform potential throughout the plasma, there is a significant voltage drop across the dark space. By increasing the plasma power, however, positive ions are accelerated across this dark space toward the negative cathode, which in this case is the glass element 1, 2 to be cleaned and coated. Thus, the DC power supply 14 can help avoiding negative effects of the dark space.

[0058] In some embodiments, wire made of the desired coating material, such as aluminum, is wound tightly around a resistive filament 30. Evaporation is accomplished by a DC filament power supply 20 which heats the filament 30 sufficiently to vaporize the coating material. In other embodiments, e.g., a commercial scale apparatus, the evaporator is a resistor in the shape of a boat, which can be kept filled with boiling depositant metal by a wire feeder (not shown); this will allow many weeks of operation without the need to repressurize the chamber to replenish the coating metal. The evaporator may be heated using a suitable AC power supply (not shown). The evaporator of the depositant metal typically serves as the anode or is in electrical communication with the anode. The chamber 10 may serve as the anode, even if it is grounded. A deposition sensor 32 is placed at a suitable location within the chamber 10 to monitor the thickness of the metal coating layer 5.

[0059] According to one aspect, an article for insulating glazing generally includes the metal coating layer 5 coupled to a respective perimeter surface 15 of the glass elements 1, 2. In some embodiments, the metal coating layer 5 has a coating thickness of at least approximately 0.5 micron. In a further embodiment, the metal coating layer 5 has a coating thickness of at least 1 micron. In a still further embodiment, the metal coating layer 5 has a coating thickness that is sufficient for subsequent bonding of the metal coating layer 5 to the seal strip 6.

[0060] In some embodiments, the exterior planar faces 17 are substantially free of the seal strip 6. A mask 28 may be provided on top of the exterior planar face 17 for confining the metal coating layer 5 to predetermined surfaces of the glass element 1, 2. In some embodiments, the mask 28 is made of a conducting material such as metal. This can help reliably coat areas having at least one small dimension, such as a narrow strip along the perimeter surface 15 of the glass elements 1, 2. In further embodiments, the mask 28 is made of the same metal as that to be plated. In some embodiments, the mask 28 is electrically connected to the bias plate 24, such as through a wire 33. The wire 33 follows a route sufficiently removed from the glass elements 1, 2 to allow adequate coating of the glass elements 1, 2. That is, the wire 33 is positioned away from the glass elements 1, 2 so as not to cast a shadow during coating of the glass elements 1, 2.

[0061] After the metal coating layers 5 are formed, a seal strip 6 is bonded on the metal coating layers 5, e.g., by ultrasonic welding. To form an evacuated interior space between the glass elements 1 and 2, in some embodiments the welding takes place inside a vacuum chamber. A strip of metal foil, e.g., formed of annealed 1100-series aluminum with a thickness of approximately 25.4 microns, is first prepared to have a width spanning the perimeter surface of two adjacent glass elements and a length longer than the perimeter of one of the glass elements. The strip of metal foil includes two ends, which are bonded (e.g, ultrasonically welded) so as to form a loop loosely surrounding the perimeter surfaces of the glass elements. Referring to FIGS. 10a, 10b and 10c, a disc-shaped sonotrode 50 rotates over the strip of metal foil and applies vibratory friction, thereby bonding portions of the strip of metal foil to the coatings. A hermetic seal is formed for the interior space between the glass elements when the sonotrode bonds the entire loop of metal foil to the coatings. The rounded corners allow uninterrupted welds to be formed without risk of cutting the foil or puncturing it at sharp corner edges, and without the need to fold the foil. When the welds are nearly complete (FIG. 10a), the excess length of foil loop is folded over (FIG. 10b) at the weld starting position 19 so that the excess loop material can be welded to itself, forming a completed hermetic seal (FIG. 10c). The welding operation may be interrupted before the final welding step is completed, so that the nearly- finished pane may be evacuated through the opening not yet welded, or the gas composition in the interior space between the glass elements may be changed. The welding may be then completed to form a unit of fully evacuated glazing. Variations of this concept include bonding the metal foil directly to glass, or bonding the metal foil to an intermediate metal foil which is itself directly bonded to glass or to a metal coating on glass.

[0062] Illustrative embodiments of the power plant are described in greater detail below.

EXAMPLE 1 : Copper on Glass

[0063] A 61 -cm length of an 110-series copper wire, 0.05 cm in diameter, was wound evenly onto a 20-cm length of triple-strand tungsten filament wire formed into a conical coil, each filament strand being 0.08 cm in diameter. A 15.2 cm x 15.2 cm x 0.3175 cm pane of annealed soda lime glass was placed on a 20.32 cm x 20.32 cm copper bias plate, and a 12.7 cm x 12.7 cm x 0.3175 cm copper mask was centered on the glass substrate, forming a uniform 1.27 cm wide reveal along the entire edge of the glass planar face. The mask was connected to the bias plate with a copper wire and positioned so as not to interfere with the even coating of the unmasked substrate beneath. The chamber was closed and evacuated to 6 ^X 10 ^"4 Torr. After approximately two minutes, argon flow was started and then adjusted to bring the chamber pressure to 2x 10 ^~2 Torr.

[0064] With the DC bias power supply off, the forward power on the RF power supply was raised to approximately 10 watts to ignite a glow discharge. The reflected power was then minimized by adjusting the tuning settings of the matching network. The forward RF power was then raised to approximately 125 watts. Plasma etching was allowed to continue for

approximately 15 minutes. Then the DC bias power supply was switched on, so the bias plate potential could be read on the bias supply voltmeter. Forward power on the RF power supply was reduced to about 90 watts forward power at 0 watts reflected power until the charge on the bias plate reached approximately -225 V. The setting of the DC bias voltage supply was increased until the bias plate voltage reading reached about -320 V, or until excessive arcing was observed through the viewport. The bias DC supply setting was then reduced until the bias plate reading was approximately -300 V and arcing stopped. The DC filament supply current was set to 35 amps. When the filament began to glow orange after a minute, the current was raised to 55 amps. The deposition rate on the substrate increased to over 10 angstroms per second. After a minute or so, the deposition rate receded to approximately 1 angstrom per second, and the filament power supply was then shut off. The deposition monitor reading indicated a coating thickness of about 0.5 microns. The DC bias power supply and the RF power supply were then shut down, and the argon supply flow stopped. The filament then cooled for about 10 minutes. The chamber was then repressurized with air.

[0065] A stripe of shiny copper measuring approximately 1.27 cm in width formed on the glass substrate. The coating was opaque. The coating was subjected to a tape test, and passed. It also survived a soldering test without delamination. EXAMPLE 2: Aluminum on Glass

[0066] A 122-cm length of 1100 series aluminum wire, 0.05 cm in diameter, was wound evenly onto two straight 20-cm lengths of triple-strand tungsten filament wire mounted in series. A 30.48 cm x 30.48 cm x 0.3175 cm pane of tempered soda lime glass is placed on a 30.48 cm x 30.48 cm x 0.3175 cm aluminum bias plate, and a 29.21 cm x 29.21 cm x 0.3175 cm aluminum mask was centered on the glass substrate, forming a uniform 0.6350 cm wide reveal along the entire edge of the glass planar surface. The mask was connected to the bias plate with a copper wire and positioned so as not to create a shadow on the substrate area to be coated. The chamber was closed and evacuated to 5 ^χ 10 ^"5 Torr. After approximately two minutes, argon flow was started, and then adjusted to bring the chamber pressure to 2x 10 ^"3 Torr.

[0067] With the DC bias power supply off, the forward power on the RF power supply was raised to approximately 15 watts to ignite a glow discharge. The reflected power was then minimized by adjusting the tuning settings of the matching network. The forward RF power was then raised to approximately 125 watts. Plasma etching was allowed to continue for

approximately 15 minutes. Then the DC bias power supply was switched on, so the bias plate potential could be read on the bias supply voltmeter. Forward power on the RF power supply was reduced to about 75 watts forward power at 0 watts reflected power until the charge on the bias plate reached approximately -200 V. The setting of the DC bias voltage supply was increased until the bias plate voltage reading reached about -300 V, or until excessive arcing was observed through the viewport or by erratic readings on the ammeter of the DC bias supply. The DC filament supply was set to 35 amps. When the filament began to glow orange after a minute or two, the current was raised to 55 amps. The deposition rate on the substrate increased to at least 17 angstroms per second. After a minute or so, the deposition rate receded to

approximately 1 angstrom per second, and the filament power supply was then shut off. The deposition monitor reading indicated a coating thickness of about 1 micron. The DC bias power supply and then the RF power supply were then shut down, and the argon supply flow stopped. The filament was then cooled for about 10 minutes. The chamber was then repressurized with air. The resulting aluminum coating formed on the unmasked surfaces of the glass element defied removal by a standard tape test. EXAMPLE 3 : Aluminum on Glass Element Larger Than Vacuum Chamber

[0068] A 45.7 cm by 45.7 cm glass element was used to close a slit-shaped opening, about 30 cm by 1.5 cm, in the vacuum chamber wall. A rubber o-ring was used to seal the glass element to the chamber wall, which was grounded. A 30.48 cm by 30.48 cm aluminum bias plate, serving as an electrode, was placed inside the chamber, about 56 cm from the glass element. An RF power supply was connected to the chamber wall and to the bias plate. The bias plate and chamber wall served as electrodes to create a plasma of the ionizable gas inside the chamber. The chamber was held at a pressure of about 1 milliTorr. A 122-cm length of 1100 series aluminum wire, 0.05 cm in diameter, was wound evenly onto two straight 20-cm lengths of triple-strand tungsten filament wire mounted in series and suspended inside the chamber and aligned parallel to the slit opening, about 15 cm away. This depositant metal wire was vaporized inside the chamber using a tungsten filament. A strongly adhesive aluminum coating was formed on the portion of the glass element exposed to the plasma and metal vapor inside the chamber, and defied removal by a tape test.

EXAMPLE 4: Plasma Induced by External Antenna

[0069] A plasma was induced in the ionizable gas within a vacuum chamber, operating at about 1 milliTorr, using an external antenna coil. The external antenna coil was mounted against a 10 cm diameter by 0.6 cm thick quartz window in the chamber wall. The ends of the coil antenna were electrically connected to an RF power supply, and one end of the coil was also electrically connected to the vacuum chamber wall, which was grounded. The power supply current was alternating at over 13 MHz. This arrangement was able to induce a plasma in the ionizable gas within the chamber. As such, it is not necessary that both electrodes used to create a plasma be in physical contact with the ionizable gas within the vacuum chamber, so long as the pair of electrodes are in electromagnetic communication with the ionizable gas. Accordingly, at least one electrode may be separated from the ionizable gas by a solid wall transparent to radio frequency radiation. EXAMPLE 5 : Aluminum Foil Welding on the Coating

[0070] An aluminum foil seal strip was joined to an ion plated coating on a glass element using ultrasonic welding, with a bond width of 0.10 cm (0.040 inch). The weld was tested in shear to 4788 N/sq. m. (100 psi) without coating delamination or weld failure. A similar weld, 20 inches in length, was leak tested with helium and a mass spectrometer. If any leakage was present, it was below the detection limit of the instrument (10 ⁹ seem).

[0071] Although the foregoing refers to glass substrates, and in particular tempered glass substrates, it is contemplated that the foregoing coating with graded interface can be applied to most any insulating surface requiring a high level of adhesion. Further, chamber details may vary from application to application in terms of dimensions and exact position of structural members, depending on the physical arrangement of the substrate to be covered, as well as the size of the pane.

[0072] It is understood that the invention may embody other specific forms without departing from the spirit or central characteristics thereof. The disclosure of aspects and embodiments, therefore, are to be considered as illustrative and not restrictive. While specific embodiments have been illustrated and described, other modifications may be made without significantly departing from the spirit of the invention.