CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority of U.S. Provisional Application Serial No. 62/349,788 filed on June 14, 2016 the contents of which are relied upon and incorporated herein by reference in their entirety as if fully set forth below.

FIELD OF THE DISCLOSURE

[0002] The present disclosure relates generally to methods for forming a glass sheet, and more particularly to methods and apparatuses for cooling the edge regions of a glass ribbon in a glass manufacturing apparatus, such as a fusion draw machine.

BACKGROUND

[0003] High-performance display devices, such as liquid crystal displays (LCDs) and plasma displays, are commonly used in various electronics, such as cell phones, laptops, electronic tablets, televisions, and computer monitors. Currently marketed display devices can employ one or more high-precision glass sheets, for example, as substrates for electronic circuit components, or as color filters, to name a few applications. The leading technology for making such high-quality glass substrates is the fusion draw process, developed by Corning Incorporated, and described, e.g., in U.S. Patent Nos. 3,338,696 and 3,682,609, which are incorporated herein by reference in their entireties.

[0004] The fusion draw process typically utilizes a fusion draw machine (FDM) comprising a forming body. The forming body can comprise a trough and a lower portion having a wedge-shaped cross-section with two major side surfaces (or forming surfaces) sloping downwardly to join at a root. During operation, the trough is filled with molten glass, which is allowed to flow over the trough sides (or weirs) and down along the two forming surfaces as two separate glass streams that ultimately converge at the root, where they fuse together to form a unitary glass ribbon. The glass ribbon can thus have two pristine external surfaces that have not been exposed to the surface of the forming body. The ribbon can then be drawn down and cooled to form a glass sheet having a desired thickness and a pristine surface quality.

[0005] The fusion draw process may, however, have various limitations related to the material properties of the glass being processed. For example, when a glass composition in a molten state is exposed to lower temperatures for a significant amount of time, undesirable crystal phases can begin to develop. The temperature and viscosity at which such crystal phases start to develop is referred to as the liquidus temperature and liquidus viscosity, respectively. The temperature of the molten glass typically decreases as it travels along the forming surfaces to the root. It may therefore be desirable to maintain the root temperature above the liquidus temperature to prevent crystal growth.

[0006] A typical FDM may operate at temperatures sufficient to produce molten glass with liquidus viscosities greater than about 100,000 poise, such as greater than about 130,000 poise. However, when glass compositions with a liquidus viscosity of less than about 100,000 poise are processed under such conditions, devitrification of the molten glass may occur on the forming body, for example, towards each end of the forming body or on edge flow directing devices (referred to herein as "edge directors"), which may be attached to each end of the forming body to guide glass flow.

Devitrification may lead to crystalline particulates in the glass ribbon, for instance, in the bead portions, and/or may reduce process stability and/or product quality. As a result, it can be difficult to manufacture high quality glass sheets from low liquidus temperature (LLT) glass compositions using standard FDM apparatuses and methods.

[0007] Operating the FDM with lower glass viscosities at the root level and/or at the edge directors, if such devices are attached to at least one end of the forming body, may be possible but the size and/or quality of the glass sheet may degrade. For instance, the resulting glass sheet may have a reduced width and/or the sheet may not be uniform in terms of its flatness and/or thickness across its width, such that it is not suitable for display applications. Loss of sheet width can manifest as accumulated mass at the ribbon edges, referred to as "beads," which may develop if the viscous glass ribbon leaving the FDM attenuates below the root of the forming body. Ribbon attenuation can increase as the glass viscosity at the end of the forming body ends or edge directors decreases and/or as the flow rate and/or pulling speed increases. The resulting beads can induce thermal gradients in the glass ribbon (e.g., due to high bead- to-center thickness ratio) and may also result in deformation and/or residual stress of the glass ribbon. The beads may also limit the bending curvature of the glass ribbon during further processing phases (e.g., during transport and/or catenary phases), which may induce further bending stress.

[0008] Consumer demand for high-performance displays with ever growing size and image quality requirements drives the need for improved manufacturing processes for producing high-quality, high-precision glass sheets. Accordingly, it would be advantageous to provide methods and apparatuses for forming glass ribbons and sheets which can minimize ribbon attenuation, as well as reduce glass defects, e.g., caused by devitrification and/or stress.

SUMMARY

[0009] The disclosure relates to apparatuses for producing a glass sheet, the apparatuses comprising a forming body for producing a glass ribbon from a molten glass, and at least one edge cooling device positioned below the forming body and configured to cool at least one glass ribbon edge region, wherein the at least one edge cooling device comprises at least one first conduit, at least one vent in fluid

communication with the at least one first conduit and configured to deliver a cool gas stream to the at least one glass ribbon edge region; and at least one second conduit configured to draw gas away from the at least one glass ribbon edge region.

[0010] In certain embodiments, the at least one edge cooling device comprises first and second branch sections configured to deliver the cool gas stream to opposing major surfaces of the at least one glass ribbon edge region. The at least one second conduit of the edge cooling device can, in some embodiments, be positioned between the branch sections and/or may be equipped with a suction device. The cool gas stream may be directed at a non-orthogonal angle relative to a major surface of the at last one glass ribbon edge region and/or may flow toward the at least one second conduit. The at least one edge cooling device may be positioned below a root of the forming body, below an edge director, below a pair of edge rollers, or between any of these components. In certain embodiments, the edge director(s) may be heated. In further embodiments, the apparatus can comprise an array of two or more edge cooling devices positioned along the length of the glass ribbon.

[0011] Also disclosed herein are methods for forming a glass sheet, the methods comprising melting glass batch materials to form molten glass, processing the molten glass to form a glass ribbon, and introducing at least one glass ribbon edge region into an edge cooling device. According to various non-limiting embodiments, the molten glass can have a liquidus viscosity of less than about 100,000 poise, less than 50,000 poise, or even less than 20,000 poise.

[0012] Additional features and advantages of the disclosure will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the methods as described herein, including the detailed description which follows, the claims, as well as the appended drawings.

[0013] It is to be understood that both the foregoing general description and the following detailed description present various embodiments of the disclosure, and are intended to provide an overview or framework for understanding the nature and character of the claims. The accompanying drawings are included to provide a further understanding of the disclosure, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the disclosure and together with the description serve to explain the principles and operations of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The following detailed description can be best understood when read in conjunction with the following drawings, where like structures are indicated with like reference numerals where possible and in which:

[0015] FIG. 1 A illustrates an exemplary forming body;

[0016] FIG. 1 B is a cross-sectional view of the forming body of FIG. 1A; [0017] FIG. 2 illustrates an exemplary glass manufacturing apparatus;

[0018] FIG. 3 illustrates an exemplary glass ribbon;

[0019] FIG. 4A illustrates a forming body equipped with a bead cooling device according to certain embodiments of the disclosure;

[0020] FIG. 4B is a cross-sectional view of the forming body of FIG. 4A;

[0021] FIG. 5A illustrates a bead cooling device according to various embodiments of the disclosure;

[0022] FIG. 5B is a cross-sectional view of the bead cooling device of FIG.

5A;

[0023] FIG. 6 is a graph illustrating root temperature profile as a function of power applied to the edge directors of the forming body;

[0024] FIG. 7 is a graph illustrating overall glass ribbon width as a function of edge director temperature;

[0025] FIG. 8 is a graph illustrating glass ribbon edge thickness for various root temperature profiles illustrated in FIG. 6;

[0026] FIG. 9 is a graph illustrating glass ribbon edge thickness for various cooling configurations; and

[0027] FIG. 10 is a graph illustrating glass ribbon edge temperature for various cooling configurations.

DETAILED DESCRIPTION

[0028] Disclosed herein are apparatuses for producing a glass sheet, the apparatuses comprising a forming body for producing a glass ribbon from a molten glass, and at least one edge cooling device positioned below the forming body and configured to cool at least one glass ribbon edge region, wherein the at least one edge cooling device comprises at least one first conduit, at least one vent in fluid

communication with the at least one first conduit and is configured to deliver a cool gas stream to the at least one glass ribbon edge region. The at least one cooling device may further comprise at least one second conduit configured to draw gas away from the at least one glass ribbon edge region. [0029] Embodiments of the disclosure will be discussed with reference to

FIGS. 1 A-B, which depict an exemplary forming body suitable for use in an exemplary glass manufacturing process for producing a glass ribbon. Referring to FIG. 1 A, during a glass manufacturing process, such as a fusion draw process, molten glass can be introduced into a forming body 100 comprising a trough 103 via an inlet 101. Once the trough 103 is filled, the molten glass can overflow the sides of the trough and down the two opposing forming surfaces 107 before fusing together at the root 109 to form a glass ribbon 111. The glass ribbon can then be drawn down in the draw direction 113 using, e.g., a roller assembly (not shown), and further processed to form a glass sheet. The forming body can further comprise ancillary components such as end caps 105 and/or edge directors 115.

[0030] FIG. 1 B provides a cross-sectional view of the forming body of FIG. 1A, in which the forming body 100 can comprise an upper trough-shaped part 117 and a lower wedge-shaped part 119. The upper trough-shaped part 117 can comprise a channel or trough 103 configured to receive the molten glass. The trough 103 can be defined by two trough walls (or weirs) 125a, 125b comprising interior surfaces 121a, 121 b, and a trough bottom 123. Although the trough is depicted as having a

rectangular cross-section, with the interior surfaces forming approximately 90-degree angles with the trough bottom, other trough cross-sections are envisioned, as well as other angles between the interior surfaces and the bottom of the trough. The weirs

125a, 125b can further comprise exterior surfaces 127a, 127b which, together with the wedge outer surfaces 129a, 129b, can make up the two opposing forming surfaces 107. Molten glass can flow over the weirs 125a, 125b and down the forming surfaces 107 as two glass streams which can then fuse together at the root 109 to form a unitary glass ribbon 111. The glass ribbon 111 can then be drawn in draw direction 113 and, in some embodiments, further processed to form a glass sheet.

[0031] The forming body 100 can comprise any material suitable for use in a glass manufacturing process, for example, refractory materials such as zircon, zirconia, alumina, magnesium oxide, silicon carbide, silicon nitride, silicon oxynitride, xenotime, monazite, and combinations thereof. According to various embodiments, the forming body may comprise a unitary piece, e.g., one piece machined from a single source. In other embodiments, the forming body may comprise two or more pieces bonded, fused, attached, or otherwise coupled together, for instance, the trough-shaped portion and wedge-shaped portion may be two separate pieces comprising the same or different materials. The dimensions of the forming body, including the length, trough depth and width, and wedge height and width, to name a few, can vary depending on the desired application. It is within the ability of one skilled in the art to select these dimensions as appropriate for a particular manufacturing process or apparatus.

[0032] FIG. 2 depicts an exemplary glass manufacturing apparatus 200 for producing a glass ribbon 111. The glass manufacturing apparatus 200 can include a melting vessel 210, a melting to fining tube 216, a fining vessel (e.g., finer tube) 220, a fining to mixing tube 222 (with a level probe stand pipe 218 extending therefrom), a mixing vessel 224, a mixing vessel to delivery vessel connecting tube 226, a delivery vessel 228, a downcomer 232, and a FDM 230, which can include an inlet pipe 234, a forming body 100, and a pull roll assembly 236.

[0033] Glass batch materials can be introduced into the melting vessel 210, as shown by arrow 212, to form molten glass 214. The fining vessel 220 is connected to the melting vessel 210 by the melting to fining tube 216. The fining vessel 220 can have a high temperature processing area that receives the molten glass from the melting vessel 210 and which can remove bubbles from the molten glass. The fining vessel 220 is connected to the mixing vessel 224 by the fining to mixing tube 222. The mixing vessel 224 is connected to the delivery vessel 228 by the mixing vessel to delivery vessel connecting tube 226. The delivery vessel 228 can deliver the molten glass through the downcomer 232 into the FDM 230.

[0034] The FDM 230 can include an inlet pipe 234, a forming body 100, and a pull roll assembly 236. The inlet pipe 234 can receive the molten glass from the downcomer 232 and direct the flow of molten glass to the forming body 100. The forming body 100 can include an inlet 101 that receives the molten glass, which can then flow into the trough 103, overflowing over the sides of the trough 103 and running down two opposing forming surfaces 107 before fusing together at the root 109 to form a glass ribbon 111. The pull roll assembly 236 can deliver the drawn glass ribbon 111 for further processing by additional optional apparatuses. [0035] FIG. 3 depicts an exemplary glass ribbon, which may be formed using the forming body depicted in FIGS. 1A-B and/or the glass manufacturing apparatus depicted in FIG. 2. The glass ribbon 111 comprises outer edges 171a, 171 b and a centerline 173. Edge regions 175a, 175b may extend from the outer edges 171a, 171b of the glass ribbon toward the centerline 173, and may have an exemplary width extending between edge 171a and line 177a (or from 171 b to 177b). A central region of the glass ribbon may extend from line 177a to line 177b. The edge regions may, in some embodiments, comprise bead portions, herein after "beads" (e.g., accumulated mass having a thickness greater than the central region of the glass ribbon). A bead may, in some embodiments, have a thickness greater than the thickness of the glass ribbon at its centerline, for instance at least about 5% greater, at least 10% greater, at least 20% greater, or more. The edge regions may thus comprise beads having a bead centerline 179a, 179b, at which the bead may be thickest; however, the thickest part of the bead need not be at its center. Furthermore, although edge regions 175a and 175b are depicted in FIG. 3 as symmetrical, they may have different widths and/or bead centerlines and/or thicknesses.

[0036] After manufacture, the glass ribbon can be further processed to produce glass sheets. For example, a traveling anvil machine (TAM), which can include a mechanical scoring device for scoring the glass ribbon, may be used to separate the ribbon 111 into individual sheets 181 along score lines 183, although in further embodiments other glass separating apparatuses may be used, for example stationary apparatuses. Accordingly, the scored glass can be separated into individual pieces of glass sheet that can be further processed, machined, polished, chemically

strengthened, and/or otherwise surface treated, e.g., etched, using various methods and devices known in the art. Of course, while the apparatuses and methods disclosed herein are discussed with reference to fusion draw processes and apparatuses, it is to be understood that such apparatuses and methods can also be used in conjunction with other glass forming processes, such as slot-draw and float processes, to name a few.

[0037] Referring to FIG. 4A, a forming body 100 may be equipped with at least one edge cooling device 300 to cool the glass ribbon edge regions, e.g., beads, and/or to counteract ribbon attenuation and/or ribbon width loss. For instance, by cooling the edges of the glass ribbon below the root 109 of the forming body, mass accumulation at the edges of the ribbon can be reduced or minimized such that the glass ribbon 111 at the root 109 may retain a greater portion of its original width (e.g., the ribbon width as it flows from the forming body 100). In some embodiments, edge rollers 131 are provided downstream of the root 109 and may be used to adjust the rate at which the glass ribbon leaves the forming body and, thus, the nominal thickness of the resulting glass sheet. Exemplary edge rollers are described, for example, in U.S. Patent No. 6,896,646, which is incorporated herein by reference in its entirety.

[0038] FIG. 4B is a cross-sectional view of the edge cooling device 300 depicted in FIG. 4A. The edge cooling device 300 may comprise one or more first conduits 333, e.g., inlets, for introducing a cool gas stream 335 into the FDM, and at least one second conduit 337, e.g., outlets, for drawing or removing gas 339 from the FDM. One or more vents 341 may also be provided to direct the flow of gas 335 along the surfaces of the glass ribbon 111. The vents may be in fluid communication with the first conduits, for instance, each vent may be in fluid communication with a first conduit (as shown) or multiple vents may be in fluid communication with a single first conduit. Gas flow through the second conduit 337 can occur due to natural convective flow or, in some embodiments, the second conduit may be equipped with a vacuum or other suction device suitable for drawing gas out of the FDM. For instance, the second conduit may operate at a pressure below that of the FDM such that gas is suctioned out of the FDM via the second conduit.

[0039] The forming body 100 may also be equipped with one or more edge directors 115, which can direct the flow of glass as it leaves the forming body. Edge directors may, for example, be attached to each end of the forming body, and the surfaces of the edge directors may be configured to guide glass flow in a desired direction, e.g., ensuring flow down the two major forming surfaces of the forming body rather than over the end caps of the forming body. In some instances, these edge directors may be heated to maintain a temperature and/or viscosity of the molten glass above its liquidus temperature and/or viscosity.

[0040] While FIGS. 4A-B illustrate the edge cooling device 300 below the edge directors 115 and the edge rollers 131 , it is to be understood that such a cooling device can be located directly below the root, e.g., in the case of a forming body not equipped with edge directors, for instance between the root and the edge rollers (if present). Alternatively, the cooling device can be located between the edge directors 115 and the edge rollers 131. In still further embodiments, a first edge cooling device 300 can be located below the edge directors 115 and a second edge cooling device 300 can be located below the edge rollers 131. Other configurations, including arrays of two or more edge cooling devices 300 positioned along the length of the glass ribbon are also possible and envisioned as falling within the scope of this disclosure.

[0041] FIG. 5A-B depict perspective and cross-sectional views of an edge cooling device 300, respectively. The edge cooling device 300 can comprise a first portion 343 for directing a cool gas stream 335 to an edge region of the glass ribbon 111 , and a second portion 345 for directing gas 339 away from an edge region of the glass ribbon 111. In certain embodiments, insulation may be provided around one or more of portions 343 and 345, and/or between these portions. In certain embodiments, an enclosure can be provided around one or more of portions 343 and 345, and a cooling fluid, such as water or any other liquid or gas, may flow through the enclosure to ensure gas exiting the first conduit is cooled to a desired temperature before impinging on the edge region of the glass ribbon. Furthermore, insulation may be provided around such an enclosure to mitigate any undesired thermal impact on the central region of the glass ribbon.

[0042] As used herein a "cool" gas stream or "cool air" is intended to refer to a gas having a temperature below the temperature of the glass ribbon edge regions and, in some embodiments, a temperature cooler than the operating temperature of the FDM. While air may be used as an exemplary cool gas stream, it is also possible to use any other suitable gas, such as O ₂ , N ₂ , or other inert gases, to name a few, as well as mixtures thereof. In various embodiments, water, e.g., in the form of droplets or mist, can be added to the cool gas to further cool the glass ribbon edge regions. Gas 339 exiting the FDM, e.g., through second conduit 337, may have any temperature and, in some embodiments, may be hotter than the cool gas stream 335. Similar to cool gas stream 335, the gas 339 exiting the FDM may comprise air or any other suitable gas listed above or any mixture thereof. [0043] The edge cooling device 300 may also comprise first and second branch sections 347, 349, which can, in certain embodiments, be positioned adjacent opposing major surfaces 111a, 111 b of glass ribbon 111. The branch sections 347, 349 can thus, in some embodiments, encase or circumscribe the glass ribbon edge region, e.g., providing cool gas flow to both opposing surfaces of the glass ribbon edge region. Accordingly, the branch sections may comprise, for example, a U-shaped (depicted), V- shaped, C-shaped, square, or rectangular configuration, or any other suitable

configuration. In certain embodiments, the second conduit(s) may be positioned between the two branch sections 347, 349 (as shown), although other arrangements are also possible.

[0044] Each of branch sections 347, 349 can comprise one or more vents 341 , configured to direct a cool gas stream 335 to one or more edge regions of the glass ribbon 111. For example, gas stream 335 flowing from the vents 341 may impinge one or both of major surfaces 111a, 111 b of the glass ribbon edge region, as indicated by arrows 351. In certain embodiments, gas stream 335 may impinge on the glass ribbon at a non-orthogonal angle, e.g., less than 90° relative to a major surface of the glass ribbon. In certain embodiments, gas stream 335 may impinge on the glass ribbon at an angle less than about 60°, such as less than about 45°, less than about 30°, less than about 20°, less than about 10°, or less than about 5°. According to various embodiments, the angle of the gas stream 335 may approach a tangent to the impinged glass ribbon surface.

[0045] In other embodiments, the gas stream 335 may be directed from the vents 341 back toward the edge cooling device, e.g., away from a centerline of the glass ribbon and toward second conduit 337, rather than being directed into the FDM. It is believed that non-orthogonal flow directed back toward the edge cooling device may have the advantage of stabilizing the glass ribbon against undesirable movement within the FDM, such that gas flow remains localized and more easily controllable. For instance, non-orthogonal gas flow can provide lift forces on opposite surfaces of the glass ribbon. If the ribbon starts to deviate to one side, the lift forces from that side may increase to push the ribbon back to a plane of symmetry. Furthermore, by locally injecting gas flow into the FDM at the edge region and locally withdrawing gas flow from the FDM in substantially the same region, e.g., via the second conduit 337, disruption of overall gas flow within the FDM can be minimized. As such, cooling of the glass ribbon edge region(s) can be effected without substantially altering the conditions (e.g., temperature, turbulence) of regions in the FDM corresponding to the central (or

"quality") portion of the glass ribbon. In certain embodiments, cool gas stream 335 may flow from the vent(s) 341 along the major surfaces of the glass ribbon edge regions and toward the second conduit(s) 337, which conduits can be configured to draw the gas back out from the FDM, such that the overall operating condition of the FDM is minimally affected by the edge cooling device.

[0046] As noted previously, the forming body 100 may be equipped with one or more edge directors (see 115 in FIGS. 1A, 4A), which can optionally be heated. However, as edge director temperatures increase, the viscosity of the molten glass near such edge director(s) may decrease, which can ultimately result in increased ribbon attenuation (or ribbon width loss) and/or bead formation. Loss of ribbon width and/or bead formation can create several challenges for the glass manufacturing process, such as difficulty processing LLT glasses, lowering glass ribbon output over the lifetime of the forming body, inducing stress in the glass ribbon, and/or negatively impacting the flatness of the resulting glass sheet.

[0047] As shown in FIG. 6, by varying the temperature of the edge directors, a range of root temperature profiles can be achieved, where the vertical axis represents a change in temperature relative to the edge temperature of Case 1 . Edge director temperature is increased in Case 2 relative to Case 1 , and in Case 3 relative to Case 2, and so forth. While the temperature of the edge regions increases from Case 1 to Case 5, the temperature of the center section remains relatively unchanged. The temperature differential between the edge and center of the glass ribbon at the root can result in ribbon attenuation, as illustrated in FIG. 7.

[0048] FIG. 7 depicts overall glass ribbon width as a function of a differential between the temperature at the ribbon edge (T _E ) and the temperature at the centerline of the ribbon (T _c ). As the edge temperature evolves from cooler than the centerline to hotter than the centerline, a loss of ribbon width can be observed. For the given configuration (forming body length = 120", composition = Corning ^® EAGLE XG ^® , flow rate = 3600 Ib/hr, ribbon thickness = 0.5 mm, T _c = constant = 1 170°C), the rate of ribbon width loss was calculated to be approximately 0.86 mm/°C. It was also estimated that ribbon width could be regained by utilizing one or more edge cooling devices, as indicated by the circular (single edge cooling device) and square (multiple edge cooling devices) data points on the right-hand side of the plot.

[0049] Referring to FIG. 8, a temperature differential between the edge and center of the root can also result in a glass ribbon with varying thickness from the edge to the centerline of the ribbon. The ribbon edge thickness distribution for Cases 1 -5 (increasing edge director temperature as in FIG. 6) are illustrated in FIG. 8. As can be appreciated from the plot, as edge heating increases from Case 1 to Case 5, edge thickness decreases as well as the slope/gradient of the curve from the edge to the middle (flat) section of the ribbon. However, as indicated by the arrow, the position of the outermost edge along the x axis also moved toward the center with increased edge heating (indicating ribbon attenuation). Accordingly, increased edge director

temperature, while positively impacting (reducing) bead thickness, also negatively impacts (reduces) glass ribbon width.

[0050] A comparison between ribbon width loss and bead thickness for different heating profiles can be readily drawn by the plot depicted in FIG. 9, which illustrates the edge thickness curves for Case 1 and Case 5. As compared to Case 5, Case 1 results in a wider ribbon having thicker beads and a steeper slope in the curve from the edge to the center. Case 5 (increased edge director temperature) results in a narrower ribbon having thinner beads and a shallower slope in the curve from the edge to the center, as compared to Case 1 . Case 1 thus provides the benefit of a wide ribbon but the disadvantage of thick beads with a sharp increase in ribbon thickness from the centerline to the beads, as evidenced by the steep slope in the curve. In contrast, Case 5 has the disadvantage of a narrow ribbon, but provides the benefit of thin beads and a gradual increase in ribbon thickness from the centerline to the beads, as evidenced by the shallow slope in the curve. It would thus be desirable to provide methods and apparatuses that allow for edge director heating while also avoiding the ribbon width loss associated therewith. Such a configuration is presented in Case X, which represents an exemplary forming body with edge directors heated to the temperature used in Case 5, but also equipped with an edge cooling device. As depicted in FIG. 9, Case X provides thin beads and a shallow curve slope (as in Case 5) while also providing a wide glass ribbon (as in Case 1 ).

[0051] Referring to FIG. 10, the temperature of the glass ribbon edge regions can be tailored to achieve a desired temperature range by varying one or more parameters of the edge cooling device(s). For example, the ribbon edge region temperature can be decreased by utilizing multiple cooling devices. FIG. 10 plots the temperature of the glass ribbon edge as a function of distance from the root of the forming body, where Case A is a configuration without an edge cooling device, Case B includes a single cooling device, Case C includes two cooling devices, and Case D includes three cooling devices. Fewer or more cooling devices can be used to achieve the desired relationship between the edge and center temperatures. Multiple edge cooling devices can be arranged as desired, for instance, in a vertical array along a length of the ribbon with the same or different distances between each device.

Alternatively, other parameters, such as the temperature and/or flow rate of the cool gas stream exiting the edge cooling device and/or the distance of the edge cooling device from the glass ribbon edge, can be altered for a single cooling device or multiple cooling devices, as desired. In additional embodiments, the cooling devices may be used in conjunction with other cooling devices, such as cooling rods or tubes positioned along the length of the ribbon. For instance, the cooling rods or tubes may be maintained at any given temperature, e.g., a temperature below that of the glass ribbon edge region or a temperature below that of the FDM, and may further cool the glass ribbon edge regions to provide a desired glass ribbon temperature profile.

[0052] Also disclosed herein are methods for forming a glass sheet, the methods comprising melting glass batch materials to form molten glass, processing the molten glass to form a glass ribbon, and introducing at least one glass ribbon edge region into an edge cooling device.

[0053] The term "batch materials" and variations thereof is used herein to denote a mixture of glass precursor components which, upon melting, react and/or combine to form a glass. The glass batch materials may be prepared and/or mixed by any known method for combining glass precursor materials. For example, in certain non-limiting embodiments, the glass batch materials can comprise a dry or substantially dry mixture of glass precursor particles, e.g., without any solvent or liquid. In other embodiments, the glass batch materials may be in the form of a slurry, for example, a mixture of glass precursor particles in the presence of a liquid or solvent.

[0054] According to various embodiments, the batch materials may comprise glass precursor materials, such as silica, alumina, and various additional oxides, such as boron, magnesium, calcium, sodium, strontium, tin, or titanium oxides. For instance, the glass batch materials may comprise a mixture of silica and/or alumina with one or more additional oxides. In various embodiments, the glass batch materials can comprise from about 45 to about 95 wt% collectively of alumina and/or silica and from about 5 to about 55 wt% collectively of at least one additional oxide, such as boron, magnesium, calcium, sodium, strontium, tin, and/or titanium, to name a few. The resulting glass composition may, in certain embodiments, have a liquidus viscosity of less than about 100,000 poise, such as less than about 80,000 poise, less than about 60,000 poise, less than about 50,000 poise, less than about 40,000 poise, less than about 30,000 poise, less than about 20,000 poise, or even lower, such as ranging from about 20,000 to about 100,000 poise. In other embodiments, the liquidus viscosity of the glass composition may be above 100,000 poise.

[0055] The batch materials can be melted according to any method known in the art, including the methods discussed herein with reference to FIG. 2. For example, the batch materials can be added to a melting vessel and heated to a temperature ranging from about 1000°C to about 1800°C. The batch materials may, in certain embodiments, have a residence time in the melting vessel ranging from several minutes to several hours, depending on various variables, such as the operating temperature and the batch size. For example, the residence time may range from about 30 minutes to about 12 hours. The molten glass can subsequently undergo various additional processing steps, including fining to remove bubbles, and stirring to homogenize the glass melt, to name a few. The molten glass can then be processed to produce a glass ribbon according to any method known in the art, including the fusion draw methods discussed herein with reference to FIGS. 1 -2, as well as slot-draw and float methods. [0056] The methods and apparatuses disclosed herein may provide one or more advantages over prior art manufacturing apparatuses and/or FDMs operating without an edge cooling device. In certain embodiments, cooling of the edge regions of the glass ribbon may allow for drawing of LLT glasses into commercially acceptable sheets, e.g., with reduced deformation and/or crystal formation. Moreover, the methods and apparatuses disclosed herein can reduce material waste by increasing the ribbon width, e.g., the "quality" portion of the glass ribbon, and reducing the bead portion that might otherwise be discarded. The reduction of ribbon attenuation may also provide glass sheets with reduced stress, strain, and/or deformation. Furthermore, the glass sheet quality can be improved due to the reduction or absence of crystal defects.

[0057] It will be appreciated that the various disclosed embodiments may involve particular features, elements or steps that are described in connection with that particular embodiment. It will also be appreciated that a particular feature, element or step, although described in relation to one particular embodiment, may be interchanged or combined with alternate embodiments in various non-illustrated combinations or permutations.

[0058] It is also to be understood that, as used herein the terms "the," "a," or "an," mean "at least one," and should not be limited to "only one" unless explicitly indicated to the contrary. Thus, for example, reference to "a cooling device" includes examples having two or more such cooling devices unless the context clearly indicates otherwise.

[0059] Ranges can be expressed herein as from "about" one particular value, and/or to "about" another particular value. When such a range is expressed, examples include from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent "about," it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.

[0060] Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that any particular order be inferred.

[0061] While various features, elements or steps of particular embodiments may be disclosed using the transitional phrase "comprising," it is to be understood that alternative embodiments, including those that may be described using the transitional phrases "consisting" or "consisting essentially of," are implied. Thus, for example, implied alternative embodiments to an apparatus that comprises A+B+C include embodiments where an apparatus consists of A+B+C and embodiments where an apparatus consists essentially of A+B+C.

[0062] It will be apparent to those skilled in the art that various modifications and variations can be made to the present disclosure without departing from the spirit and scope of the disclosure. Since modifications combinations, sub-combinations and variations of the disclosed embodiments incorporating the spirit and substance of the disclosure may occur to persons skilled in the art, the disclosure should be construed to include everything within the scope of the appended claims and their equivalents.