WO2016133798A1

WO2016133798A1 - Glass forming device for improved ribbon flow

Info

Publication number: WO2016133798A1
Application number: PCT/US2016/017676
Authority: WO
Inventors: Frank Coppola; Monica Jo Mashewske
Original assignee: Corning Inc
Current assignee: Corning Inc
Priority date: 2015-02-17
Filing date: 2016-02-12
Publication date: 2016-08-25
Anticipated expiration: 2017-08-17
Also published as: TW201638030A

Abstract

A glass forming device has an inlet end, a compression end and a central portion, wherein the cross-sectional thickness of at least one of the compression end and the inlet end is less than the maximum cross-sectional thickness of the central portion. At least one side of the device has a negative angle region having a height, wherein the height of the negative angle region of at least one of the compression and the inlet end is less than the maximum height of the negative angle region of the central portion. The device can enable reduced attenuation of a molten glass ribbon as well as reduced bead to sheet thickness ratios.

Description

GLASS FORMING DEVICE FOR IMPROVED RIBBON FLOW

[0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U.S.

Provisional Application Serial No. 62/117169 filed on February 17, 2015 the content of which is relied upon and incorporated herein by reference in its entirety.

BACKGROUND

Field

[0002] The present disclosure relates generally to a glass forming device and in particular to a glass forming device with improved edge flow.

Technical Background

[0003] In the manufacture of glass materials, such as flat glass substrates for display applications, such as LCD televisions and handheld electronic devices, there is a continual need to improve the efficiency of the manufacturing process as well as the quality of the glass ultimately produced. Glass manufactured by the fusion draw method typically involves use of a glass forming device, wherein molten glass flows over opposite sides of the device down a substantially vertical region and negative angle region before joining at the bottom or root of the glass forming device to form a ribbon of molten glass below the root.

[0004] The length of the negative angle region of the glass forming device is typically a function of the degree of the negative angle as well as the cross-sectional width of the glass forming device. Generally, the higher the flow of molten glass, the greater the cross- sectional width of the glass forming device. The greater the cross-sectional width of the glass forming device, all else being equal, the greater the reduction of the longitudinal width of the molten glass ribbon below the root, wherein the difference between the widest longitudinal width of the molten glass flowing over opposite sides of the device and the narrowest longitudinal width of the molten glass ribbon below the root is often referred to as attenuation. Attenuation is generally viewed as undesirable because, among other things, it reduces the amount of commercially usable glass (often referred to as the "quality region") from a given process.

[0005] In order to mitigate attenuation and increase the longitudinal width of the quality region, edge directors can be positioned on opposite ends of the negative angle region. However, edge directors can introduce other forming issues such as sheet width variation, pulsing, and excessive cooling of the edge of the sheet with the potential for growth of devitrified material on the edge directors. As edge directors are often geometrically shaped like a section of a cone, the glass flowing down the edge directors tends to flare out and join together at the root of the glass forming device, often creating, on opposite sides of the quality region of the ribbon, a bead area that has a thickness that is substantially greater than the quality region of the sheet. Such beads can further exhibit a knurled pattern as a result of contact with edge rolls and can further include at least one airline on their inside edges. This increases the potential for draw instability.

[0006] As a result of attenuation, the knurled "bead" portion of the ribbon tends to be substantially thicker than the quality region. This effect often becomes amplified by the cooling of the glass by edge rolls positioned below the glass forming device and the greater the distance between the root and the rolls, the greater the effect tends to be. Under these circumstances, the beads become much thicker, such as at least three times as thick as the quality region. This thickness differential becomes even more pronounced when drawing very thin sheets (0.3mm and less).

SUMMARY

[0007] Disclosed herein is a glass forming device that includes an inlet end, a compression end and a central portion, wherein the cross-sectional thickness of at least one of the compression end and the inlet end is less than the maximum cross-sectional thickness of the central portion. At least one side of the device has a negative angle region having a height at the inlet end, the compression end, and along the central portion, wherein the height of the negative angle region of at least one of the compression and the inlet end is less than the maximum height of the negative angle region of the central portion.

[0008] Also disclosed herein is a method of producing a glass article wherein the method includes flowing molten glass over opposite sides of a glass forming device, the glass forming device including an inlet end, a compression end and a central portion, wherein the cross-sectional thickness of at least one of the compression end and the inlet end is less than the maximum cross-sectional thickness of the central portion. At least one side of the device has a negative angle region having a height at the inlet end, the compression end, and along the central portion, wherein the height of the negative angle region of at least one of the compression and the inlet end is less than the maximum height of the negative angle region of the central portion.

[0009] Additional features and advantages of these and other embodiments 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 embodiments as described herein, including the detailed description which follows, the claims, as well as the appended drawings.

[0010] It is to be understood that both the foregoing general description and the following detailed description present embodiments of the present disclosure, and are intended to provide an overview or framework for understanding the nature and character of the embodiments as claimed. The accompanying drawings are included to provide a further understanding of these and other embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of these and other embodiments, and together with the description serve to explain the principles and operations thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 is a perspective view of a glass forming device according to at least one embodiment disclosed herein;

[0012] FIG. 2 is an alternate perspective view of the glass forming device of FIG. 1 ;

[0013] FIG. 3 is a top view of a glass forming device according to at least one embodiment disclosed herein;

[0014] FIG. 4 is a top view of a glass forming device according to at least one embodiment disclosed herein;

[0015] FIG. 5 is a top view of a glass forming device according to at least one embodiment disclosed herein;

[0016] FIG. 6 is a top view of a glass forming device according to at least one embodiment disclosed herein;

[0017] FIG. 7A is a side cutaway view of a compression end of a glass forming device according to at least one embodiment disclosed herein;

[0018] FIG. 7B is a side cutaway view of a central portion of a glass forming device according to at least one embodiment disclosed herein; [0019] FIG. 7C is a side cutaway view of an inlet end of a glass forming device according to at least one embodiment disclosed herein;

[0020] FIG. 8 is a perspective view of a glass forming device and a molten glass ribbon according to at least one embodiment disclosed herein; and

[0021] FIG. 9 is a top cutaway view of a molten glass ribbon according to at least one embodiment disclosed herein.

DETAILED DESCRIPTION

[0022] Reference will now be made to embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts.

[0023] As used herein, the term "height", when referencing height of a vertical region or height of a negative angle region of a glass forming device refers to the vertical distance between the highest and lowest parts of that region.

[0024] As used herein, the term "attenuation" refers to the difference between the widest longitudinal width of the molten glass flowing over opposite sides of a glass forming device and the narrowest longitudinal width of a molten glass ribbon below the glass forming device before the ribbon contacts any edge roll, pulling roll or any other mechanism that would physically constrict or squeeze either bead region..

[0025] As used herein, the term "ratio of bead thickness to sheet thickness" of a molten glass ribbon refers to the ratio of the thickness of the thickest bead region on either side of a molten glass ribbon at its thickest point to the thickness of the molten glass ribbon at its thinnest point between the bead regions. The ratio of bead thickness to sheet thickness of a molten glass ribbon is taken at the narrowest longitudinal width of the molten glass ribbon below the glass forming device before the ribbon contacts any edge roll, pulling roll or any other mechanism that would physically constrict or squeeze either bead region.

[0026] Referring to FIG. 1, glass forming device 10 includes compression end 12, inlet end 14, and central portion 16. Glass forming device also includes trough 18 that is bounded longitudinally by first weir 20 and second weir 22 and is further bounded near compression end 12 by first dam 28 and near inlet end 14 by second dam 30. Glass forming device 10 also includes a substantially vertical region 24 and a negative angle region 26. [0027] FIG. 2 shows an alternate perspective view of the glass forming device of FIG. 1. In the embodiment shown in FIGS. 1 and 2, each side of the device includes a substantially vertical region 24 and a negative angle region 26.

[0028] In certain exemplary embodiments, central portion 16 comprises a length that is at least a portion of the distance between compression end 12 and inlet end 14 along the longitudinal length of glass forming device 10, including a length that includes the midpoint between compression end 12 and inlet end 14 along the longitudinal length of glass forming device 10, including a length that includes the midpoint between compression end 12 and inlet end 14 and is up to and including 50% of the longitudinal length of the glass forming device 10, including the middle 50% of the longitudinal length of the glass forming device, including the midpoint between compression end 12 and inlet end 14 along the longitudinal length of glass forming device 10.

[0029] FIGS. 3-6 show top view of glass forming devices according to various embodiments disclosed herein. In the embodiments shown in FIGS. 3-6, cross-sectional thickness of compression end 12 is indicated by arrow Tl, cross-sectional thickness of inlet end 14 is indicated by arrow T3, and the maximum cross-sectional thickness of central portion 16 is indicated by arrow T2. As can be seen in each of FIGS. 3-6 (as well as FIGS. 1-2), the cross-sectional thickness of at least one of the compression end 12 and the inlet end 14 is less than the maximum cross-sectional thickness of the central portion 16.

[0030] In certain exemplary embodiments, at least one of the inlet end 12 and the compression end 14 has a cross-sectional thickness that is at least 20% less than the maximum cross-sectional thickness of the central portion 16, such as at least 50% less than the maximum cross-sectional thickness of the central portion 16, and further such as at least 70% less than the maximum cross-sectional thickness of the central portion 16, including from 20% to 80% of the maximum cross-sectional thickness of the central portion 16, and further including from 30% to 70% of the maximum cross-sectional thickness of the central portion 16, and yet further including from 40% to 60% of the maximum cross-sectional thickness of the central portion 16.

[0031] In certain exemplary embodiments, both of the inlet end 12 and the compression end 14 have a cross-sectional thickness that is at least 20% less than the maximum cross- sectional thickness of the central portion 16, such as at least 50% less than the maximum cross-sectional thickness of the central portion 16, and further such as at least 70% less than the maximum cross-sectional thickness of the central portion 16, including from 20% to 80% of the maximum cross-sectional thickness of the central portion 16, and further including from 30% to 70% of the maximum cross-sectional thickness of the central portion 16, and yet further including from 40% to 60% of the maximum cross-sectional thickness of the central portion 16. In that regard, the cross-sectional thickness of the compression end 12 and the inlet end 14 may be approximately the same or different.

[0032] Specifically, in FIG. 3 the cross-sectional thickness of the compression end 12 and inlet end 14 are approximately equal and are both less than the maximum cross-sectional thickness of the central portion 16. In the embodiment shown in FIG. 3, the cross-sectional thickness of the compression end 12 and inlet end 14 are less than 50% of the maximum cross-sectional thickness of the central portion 16.

[0033] In FIGS. 4 and 5, the cross-sectional thickness of the compression end 12 is less than the cross-sectional thickness of the inlet end 14, which, in turn, is less than the maximum cross-sectional thickness of the central portion 16. In FIG. 4, the cross-sectional thickness of the compression end 12 is less than 50% of the maximum cross-sectional thickness of the central portion 16 and less than 80% of the cross-sectional thickness of the inlet end 14. In FIG. 5, the cross-sectional thickness of the compression end 12 is less than 50% of the maximum cross-sectional thickness of the central portion 16 and less than 60% of the cross-sectional thickness of the inlet end 14.

[0034] In FIG. 6, the cross-sectional thickness of the compression end 12 is less than the cross-sectional thickness of the inlet end 14, which, in turn, is approximately the same as the maximum cross-sectional thickness of the central portion 16. In the embodiment shown in FIG. 6, the cross-sectional thickness of the compression end 12 is less than 50% of the maximum cross-sectional thickness of the central portion 16.

[0035] When the cross-sectional thickness of the compression end 12 is less than the cross- sectional thickness of the inlet end 14, the cross-sectional thickness of the compression end 12 may, for example, range from 20% to 95% of the cross-sectional thickness of the inlet end 14, such as from 40% to 80% of the cross-sectional thickness of the inlet end 14, and further such as from 50% to 70% of the cross-sectional thickness of the inlet end 14. In such embodiments, the cross-sectional thickness of the inlet end 14 may, for example, range from 40% to 100% of the maximum cross-sectional thickness of the central portion 16, such as from 50% to 90% of the maximum cross-sectional thickness of the central portion 16, and further such as 60% to 80% of the maximum cross-sectional thickness of the central portion [0036] As can be seen in each of the embodiments of FIGS. 1-6, the cross-sectional thickness of the glass forming device 10 tapers to a reduced thickness between the central portion 16 and at least one, if not both, of the compression end 12 and the inlet end 14. For example, in each of the embodiments of FIGS. 1-6, the cross-sectional thickness of the glass forming device 10 tapers to a reduced thickness between the central portion 16 and the compression end 12. In each of the embodiments of FIGS. 1-5, the cross-sectional thickness of the glass forming device 10 tapers to a reduced thickness between the central portion 16 and the inlet end 14.

[0037] FIGS. 7A-7C, show, respectively, side cutaway views of a compression end, central portion, and inlet end of a glass forming device according to at least one embodiment disclosed herein. In the embodiment shown in FIGS. 7A-7C, each side of the glass forming device includes a substantially vertical region 24 and a negative angle region 26.

[0038] As shown in FIG. 7A, the height of the substantially vertical region of the compression end is indicated by arrow HVl, the height of the negative angle region of the compression end is indicated by HNl, and the cross-sectional thickness of the compression end is indicated by arrow Tl . As shown in FIG. 7B, the height of the substantially vertical region of the central portion is indicated by arrow HV2, the maximum height of the negative angle region of the central portion is indicated by HN2, and the maximum cross-sectional thickness of the central portion is indicated by arrow T2. As shown in FIG. 7C, the height of the substantially vertical region of the inlet end is indicated by arrow HV3, the height of the negative angle region of the inlet end is indicated by HN3, and the cross-sectional thickness of the inlet end is indicated by arrow T3.

[0039] As can be seen in FIGS. 7A-7C (as well as FIGS. 1-2), at least one side, and in the case of FIGS. 1-2 and 7A-7C both sides, of the device have a substantially vertical region 24 and a negative angle region 26, each having a height, wherein the height of the negative angle region of at least one of the compression and the inlet end, HNl and HN3 respectively, is less than the maximum height of the negative angle region of the central portion HN2. In the embodiment shown in FIGS. 7A-7C (as well as FIGS. 1-2), the height of the negative angle region of the compression end HNl is less than the maximum height of the negative angle region of the central portion HN2. In the embodiment shown in FIGS. 7A-7C (as well as FIGS. 1-2), the height of the negative angle region of the inlet end HN3 is also less than the maximum height of the negative angle region of the central portion HN2. [0040] Accordingly, and as shown, for example, in FIGS. 1 and 2, embodiments disclosed herein include a glass forming device wherein the cross-sectional thickness of at least one of the compression end and the inlet end is less than the maximum cross-sectional thickness of the central portion and wherein at least one side of the device has a negative angle region having a height, wherein the height of the negative angle region of at least one of the compression and the inlet end is less than the maximum height of the negative angle region of the central portion.

[0041] In addition, and as shown, for example, in FIGS. 1 and 2, embodiments disclosed herein include a glass forming device wherein the cross-sectional thickness of the compression end is less than the maximum cross-sectional thickness of the central portion and the height of the negative angle region of the compression end is less than the maximum height of the negative angle region of the central portion.

[0042] In addition, and as shown, for example, in FIGS. 1 and 2, embodiments disclosed herein include a glass forming device wherein the cross-sectional thickness of the inlet end is less than the maximum cross-sectional thickness of the central portion and the height of the negative angle region of the inlet end is less than the maximum height of the negative angle region of the central portion.

[0043] In the embodiment shown in FIGS. 7A-7C, the height of the negative angle region of at least one of the compression and the inlet end is at least 20% less than the maximum height of the negative angle region of the central portion. Specifically, in FIGS. 7A-7C, the height of the negative angle region of the compression end HN1 is at least 20% less than the maximum height of the negative angle region of the central portion HN2. In addition, in FIGS. 7A-7C, the height of the negative angle region of the inlet end HN3 is at least 20% less than the maximum height of the negative angle region of the central portion HN2. In the embodiment shown in FIGS. 7A-7C, the cross sectional thickness of each of the inlet end and compression end, Tl and T3 respectively, are each at least 20% less than the maximum cross- sectional thickness T2 of the central portion.

[0044] For example, embodiments disclosed herein include those in which the height of the negative angle region of at least one of the compression and the inlet end is at least 50% less than the maximum height of the negative angle region of the central portion. For example, embodiments disclosed herein include those in which the height of the negative angle region of the compression end is at least 50% less than the maximum height of the negative angle region of the central portion. Embodiments disclosed herein also include those in which the height of the negative angle region of the inlet end is at least 50% less than the maximum height of the negative angle region of the central portion. In each of these embodiments, at least one, if not both, of the compression end and the inlet end may have a cross-sectional thickness that is at least 20% less than the maximum cross-sectional thickness of the central portion, such as at least 50% less than the maximum cross-sectional thickness of the central portion, including from 20% to 80% of the maximum cross-sectional thickness of the central portion.

[0045] For example, embodiments disclosed herein include those in which the height of at least one, if not both, of the negative angle region of the compression end and the inlet end, is from 20% to 80% of the maximum height of the negative angle region the central portion, such as from 30% to 70% of the maximum height of the negative angle region of the central portion, and further such as from 40% to 60% of the maximum height of the negative angle region of the central portion. In such embodiments, at least one, if not both, of the compression end and the inlet end may have a cross-sectional thickness of from 20% to 80% of the maximum cross-sectional thickness of the central portion, such as from 30% to 70% of the maximum cross-sectional thickness of the central portion, and further such as from 40% to 60% of the maximum cross-sectional thickness of the central portion.

[0046] Embodiments disclosed herein also include those in which the height of the negative angle region of the compression end is less than the height of the negative angle region of the inlet end. In such embodiments, the height of the negative angle region of the inlet end may be less than or approximately equal to the maximum height of the negative angle region of the central portion. For example the height of the negative angle region of the compression end may be at least 20% less than, including at least 50% less than, the height of the negative angle region of the inlet end, including from 20% to 80% and further including from 50% to 70% of the height of the negative angle region of the inlet end.

[0047] Exemplary embodiments include those in which the height of the negative angle region of the compression end is at least 20% less than the height of the negative angle region of the inlet end, wherein the height of the negative angle region of the inlet end is at least 20% less than the maximum height of the negative angle region of the central portion. Such embodiments may also include those in which the cross-sectional thickness of the compression end is at least 20% less than the cross-sectional thickness of the inlet end, wherein the cross-sectional thickness of the inlet end is at least 20% less than the maximum cross-sectional thickness of the central portion. [0048] Embodiments disclosed herein also include those in which the negative angle region tapers to a reduced height between the maximum height of the negative angle region of the central portion and height of the negative angle region of at least one of the compression end and the inlet end. For example, embodiments disclosed herein include those in which the negative angle region tapers to a reduced height between the maximum height of the negative angle region of the central portion and height of the negative angle region of the compression end. Embodiments disclosed herein also include those in which the negative angle region tapers to a reduced height between the maximum height of the negative angle region of the central portion and height of the negative angle region of both the compression and inlet end.

[0049] Embodiments disclosed herein also include those in which the height of the substantially vertical region of at least one of the compression end and the inlet end is greater than the maximum height of the substantially vertical region of the central portion. For example, embodiments disclosed herein include those in which the height of the substantially vertical region of the compression end is greater than the maximum height of the

substantially vertical region of the central portion. Embodiments disclosed herein also include those in which the height of the substantially vertical region of the inlet end is greater than the maximum height of the substantially vertical region of the central portion.

Embodiments disclosed herein also include those in which the height of the substantially vertical region of both the compression end and the inlet end is greater than the maximum height of the substantially vertical region of the central portion.

[0050] Embodiments disclosed herein also include those in which the ratio of the height of the substantially vertical region to the negative angle region of at least one, if not both, of the compression end and the inlet end is greater than the maximum ratio of the height of the substantially vertical region to the negative angle region of the central portion. For example, as shown in FIGS. 7A-7B, the ratio of the height of the substantially vertical region HV1 to the negative angle region HN1 of the compression end is greater than the maximum ratio of the height of the substantially vertical region HV2 to the maximum negative angle region HN2 of the central portion. In addition, as shown in FIGS. 7B-7C, the ratio of the height of the substantially vertical region HV3 to the negative angle region HN3 of the inlet end is greater than the maximum ratio of the height of the substantially vertical region HV2 to the maximum negative angle region HN2 of the central portion. [0051] In certain exemplary embodiments, the ratio of the height of the substantially vertical region to the negative angle region of at least one, if not both, of the compression end and the inlet end can be at least two times, such as at least three times, and further such as at least four times, and yet further such as at least five times the maximum ratio of the height of the substantially vertical region to the negative angle region of the central portion. For example, when the maximum ratio of the height of the substantially vertical region to the negative angle region of the central portion is at least 1 : 1, the ratio of the height of the substantially vertical region to the negative angle region of at least one, if not both, of the compression end and the inlet end can be at least 2: 1 , such as at least 3 : 1 , and further such as at least 4: 1, and yet further such as at least 5 : 1.

[0052] Embodiments disclosed herein also include those in which the maximum cross- sectional thickness of the central portion is greater than the height of the negative angle region of at least one, if not both, of the compression end and the inlet end. For example, as shown in FIGS. 7A-7B, the maximum cross-sectional thickness T2 of central portion is greater than the height HNl of the negative angle region of the compression end. In addition, as shown in FIGS. 7B-7C, the maximum cross-sectional thickness T2 of central portion is greater than the height HN3 of the negative angle region of the inlet end.

[0053] In certain exemplary embodiments, the maximum cross-sectional thickness of the central portion can be at least 20%, such as at least 35%, and further such as at least 50% greater than the height of the negative angle region of at least one, if not both, of the compression end and the inlet end. For example, the maximum cross-sectional thickness of the central portion can be from 20% to 100%, such as from 40% to 80% greater than the height of the negative angle region of at least one, if not both, of the compression end and the inlet end.

[0054] Glass forming device can have at least one root angle, designated in FIGS. 7A-7C as al -a3. While not limited to any specific value, at least one root angle, can, for example range from 5 degrees to 30 degrees, such as from 10 degrees to 25 degrees, and further such as from 15 degrees to 20 degrees. Root angle at compression end, al , root angle at central portion, al, and root angle at inlet end, a3, can each be the same or different. For example, root angle may be approximately uniform along the longitudinal length of the glass forming device. Alternatively, root angle of at least one, if not both, of compression end and inlet end may be less than root angle of central portion, such as at least 5 degrees less than root angle at central portion. Root angle of compression end, al,and inlet end, a3, may also be the same or different, while, in certain embodiments, each being equal to or less than root angle of central portion. For example, in some embodiments, root angle of compression end may be at least 5 degrees less than root angle of inlet end, wherein root angle of inlet end is less than or equal to root angle of central portion, such as where root angle of inlet end is at least 5 degrees less than root angle of central portion.

[0055] The glass forming device, while not limited to any particular material, may, in certain exemplary embodiments, comprise a refractory material that has minimal reactivity to the molten glass formed using the device. Exemplary materials for the glass forming device include, but are not limited to an isopressed zircon-based ceramic material, such as those disclosed in US patent application publication numbers 2004/0055338 and 2005/0130830, the entire disclosures of which are incorporated herein by reference. Exemplary materials for the glass forming device may also include an isopressed xenotime-based or xenotime-stabilized zircon-based ceramic material, such as those disclosed in US patent application publication number 2009/013 1241 , the entire disclosure of which is incorporated herein by reference.

[0056] The glass forming device may also be supported, at least near the inlet end by incorporating a weir support mechanism between the inlet end and the dam nearest to the inlet end. The weir support mechanism can act to mitigate the potential effect of weir spreading that may otherwise result from embodiments disclosed herein, wherein the ratio of weir height to cross-sectional thickness of the device may be relatively high at the inlet end. The weir support mechanism may, in certain embodiments, comprise a plate of refractory material, which can be the same or different from the refractory material of the glass forming device, wherein the plate of refractory material is situated above at least a portion of the weirs between the inlet end and the dam nearest to the inlet end of the glass forming device.

Refractory material may be further situated vertically outside at least a portion of the weirs between the inlet end and the dam nearest to the inlet end of the glass forming device.

[0057] Embodiments disclosed herein also include methods of producing a glass article wherein the method comprises flowing molten glass over opposite sides of a glass forming device as described in one or more embodiments disclosed herein. FIG. 8 is a perspective view of a glass forming device 10 according to one or more embodiments disclosed herein, wherein glass forming device 10 has a compression end 12 and an inlet end 14 and molten glass flows over opposite sides of the glass forming device 10, along substantially vertical region 24 and negative angle region 26, and forms a molten glass ribbon 40 below the glass forming device. [0058] In the embodiment shown in FIG. 8, the widest longitudinal width of the molten glass flowing over opposite sides of the glass forming device is indicated by arrow Wl . In contrast, the narrowest longitudinal width of the molten glass ribbon 40 below the glass forming device before the ribbon contacts any edge roll, pulling roll or any other mechanism that would physically constrict or squeeze either bead region is indicated by arrow W2. Accordingly, the attenuation of the molten glass ribbon is the difference between the lengths of Wl and W2 (for example, if Wl has a relative length of 10 units and W2 has a relative length of 7 units, then the length of W2 is 30% less than Wl relative to Wl, resulting in a molten glass ribbon with an attenuation of 30%).

[0059] FIG. 9 is a top cutaway view of a molten glass ribbon 40 according to at least one embodiment disclosed herein. In the embodiment shown in FIG. 9, the thickness of the molten glass ribbon relative to longitudinal width is somewhat exaggerated relative to most embodiments expected in actual practice. Accordingly, it is to be understood that embodiments disclosed herein include those in which the ratio of longitudinal width to thickness is much greater than shown in FIG. 9 and, in that regard, embodiments disclosed herein are not limited to any particular ribbon size with respect to thickness and longitudinal width.

[0060] In the embodiment shown in FIG. 9, the molten glass ribbon 40 extends between two bead regions on either side of the molten glass ribbon and has a relative longitudinal width of W2 as indicated in FIG. 8 (which is the narrowest longitudinal width of the molten glass ribbon before the ribbon contacts any edge roll, pulling roll or any other mechanism that would physically constrict or squeeze either bead region). The thickness of the bead regions at their thickest points are indicated by arrows BT and the thickness of the molten glass ribbon at its thinnest point between the bead regions is indicated by arrow ST. Accordingly, the ratio of bead thickness to sheet thickness of molten glass ribbon 40 is the ratio of the longest length BT to the length of ST.

[0061] Embodiments disclosed herein can enable the formation of molten glass ribbon wherein both the attenuation and ratio of bead thickness to sheet thickness of the ribbon are simultaneously reduced as compared to embodiments of the prior art.

[0062] For example, embodiments disclosed herein include those in which the attenuation of the molten glass ribbon is less than 35% and the ratio of bead thickness to sheet thickness is less than 2.5, such as those in which the attenuation of the molten glass ribbon is less than 30% and the ratio of bead thickness to sheet thickness is less than 2.2, and further such as those in which the attenuation of the molten glass ribbon is less than 25% and the ratio of bead thickness to sheet thickness is less than 2, such as where the attenuation of the molten glass ribbon is from 10% to 35%, and the ratio of bead thickness to sheet thickness is from 1.5 to 2.5, including where the attenuation of the molten glass ribbon is from 15% to 30% and the ratio of bead thickness to sheet thickness is from 1.7 to 2.2. In such embodiments the sheet thickness may be less than 1 millimeter, such as less than 0.5 millimeters, and further such as less than 0.3 millimeters, and yet further such as less than 0.2 millimeters, and still yet further such as less than 0.1 millimeters, such as from 0.05 to 1 millimeter, and further such as from 0.1 to 0.5 millimeters, and yet further such as from 0.2 to 0.4 millimeters.

[0063] Embodiments disclosed herein can also enable the formation of molten glass ribbon with reduced attenuation without the use of edge directors at either or both of the compression or inlet end of the glass forming device. For example, in certain embodiments, a molten glass ribbon can be produced wherein the attenuation of the molten glass ribbon is less than 35%, such as less than 30%, and further such as less than 25%, wherein no edge director is present at the compression end of the glass forming device. In certain

embodiments, a molten glass ribbon can be produced wherein the attenuation of the molten glass ribbon is less than 35%, such as less than 30%, and further such as less than 25%, wherein no edge director is present at either the compression end or inlet end of the glass forming device. In certain embodiments, a molten glass ribbon can be produced wherein the attenuation of the molten glass ribbon is less than 35%, such as less than 30%, and further such as less than 25%, wherein no edge director is present at the compression end of the glass forming device and an edge director having a reduced size as compared to prior art edge directors is present at the inlet end of the glass forming device.

[0064] Embodiments disclosed herein, including elimination or reduction of edge directors on one or more ends of the glass forming device can, in turn, enable at least one of several potential advantages over glass forming devices and associated methods of the prior art including, but not limited to, reduced usage of precious metals, such as platinum, as edge director material, reduced attenuation in combination with reduced bead to sheet thickness ratio, resulting in at least one of improved draw processing, reduction of bead airlines, improved temperature uniformity across the glass ribbon, reduced formation of devitrified glass, and reduced sheet width variation. In addition, embodiments disclosed herein can enable processes wherein edge rolls below the glass forming device are situated closer to the bottom or root of the glass forming device, this further reducing attenuation as the ribbon is formed beneath the root as well as increased space to incorporate a shielding mechanism between edge rolls and the ends of the glass forming device. Embodiments disclosed herein can also enable higher relative throughput in combination with less relative attenuation. In addition, in applications involving the manufacture of ultrathin glass, such as glass having a thickness of less than 0.5 millimeters, including a thickness of less than 0.3 millimeters, embodiments herein may eliminate a need for on the draw separation of beads from the glass sheet. At least one of such advantages can be particularly enabled when at least one of the inlet end and the compression end of the glass forming device has a cross-sectional thickness that is at least 20% less than the maximum cross-sectional thickness of the central portion and/or when the height of the negative angle region of at least one of the compression and the inlet end of the glass forming device is at least 20% less than the maximum height of the negative angle region of the central portion.

[0065] It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments of the present disclosure without departing from the spirit and scope of the disclosure. Thus, it is intended that the present disclosure cover the modifications and variations of these and other embodiments provided they come within the scope of the appended claims and their equivalents.

Claims

What is claimed is:

1. A glass forming device comprising an inlet end, a compression end and a central portion, wherein the cross-sectional thickness of at least one of the compression end and the inlet end is less than the maximum cross-sectional thickness of the central portion; and

wherein at least one side of the device has a negative angle region having a height at the inlet end, the compression end, and along the central portion, wherein the height of the negative angle region of at least one of the compression and the inlet end is less than the maximum height of the negative angle region of the central portion.

2. The glass forming device according to claim 1 , wherein the cross-sectional thickness of the compression end is less than the maximum cross-sectional thickness of the central portion and the height of the negative angle region of the compression end is less than the maximum height of the negative angle region of the central portion.

3. The glass forming device according to claims 1 or 2, wherein the cross-sectional thickness of the inlet end is less than the maximum cross-sectional thickness of the central portion and the height of the negative angle region of the inlet end is less than the maximum height of the negative angle region of the central portion.

4. The glass forming device according to any one of claims 1 to 3, wherein the cross- sectional thickness of the glass forming device tapers to a reduced thickness between the central portion and at least one of the compression end and the inlet end.

5. The glass forming device according to any one of claims 1 to 4, wherein the cross- sectional thickness of the glass forming device tapers to a reduced thickness between the central portion and the compression end.

6. The glass forming device according to any one of claims 1 to 5, wherein the cross- sectional thickness of the glass forming device tapers to a reduced thickness between the central portion and the inlet end.

7. The glass forming device according to any one of claims 1 to 6, wherein the cross- sectional thickness of the compression end is less than the cross-sectional thickness of the inlet end.

8. The glass forming device according to any one of claims 1 to 7, wherein the height of the negative angle region of the compression end is less than the height of the negative angle region of the inlet end.

9. The glass forming device according to any one of claims 1 to 8, wherein at least one of the inlet end and the compression end has a cross-sectional thickness that is at least 20% less than the maximum cross-sectional thickness of the central portion.

10. The glass forming device according to any one of claims 1 to 9, wherein the height of the negative angle region of at least one of the compression and the inlet end is at least 20% less than the maximum height of the negative angle region of the central portion.

1 1. The glass forming device according to any one of claims 1 to 10, wherein at least one side of the device has a substantially vertical region having a height at the inlet end, the compression end, and along the central portion, and wherein the ratio of the height of the substantially vertical region to the negative angle region of at least one of the compression end and the inlet end is greater than the maximum ratio of the height of the substantially vertical region to the negative angle region of the central portion.

12. The glass forming device according to any one of claims 1 to 1 1, wherein the maximum cross-sectional thickness of the central portion is greater than the height of the negative angle region of at least one of the compression end and the inlet end.

13. A method of producing a glass article wherein the method comprises flowing molten glass over opposite sides of a glass forming device, the glass forming device comprising an inlet end, a compression end and a central portion, wherein the cross-sectional thickness of at least one of the compression end and the inlet end is less than the maximum cross-sectional thickness of the central portion; and wherein at least one side of the device has a negative angle region having a height at the inlet end, the compression end, and along the central portion, wherein the height of the negative angle region of at least one of the compression and the inlet end is less than the maximum height of the negative angle region of the central portion.

14. The method of claim 13, wherein the cross-sectional thickness of the compression end is less than the maximum cross sectional thickness of the central portion and the height of the negative angle region of the compression end is less than the maximum height of the negative angle region of the central portion.

15. The method of claims 13 or 14, wherein the cross-sectional thickness of the inlet end is less than the maximum cross sectional thickness of the central portion and the height of the negative angle region of the inlet end is less than the maximum height of the negative angle region of the central portion.

16. The method of any one of claims 13 to 15, wherein the cross-sectional thickness of the compression end is less than the cross-sectional thickness of the inlet end.

17. The method of any one of claims 13 to 16, wherein at least one of the inlet end and the compression end has a cross-sectional thickness that is at least 20% less than the maximum cross-sectional thickness of the central portion.

18. The method of any one of claims 13 to 17, wherein the height of the negative angle region of at least one of the compression and the inlet end is at least 20% less than the maximum height of the negative angle region of the central portion.

19. The method of any one of claims 13 to 18, wherein the maximum cross-sectional thickness of the central portion is greater than the height of the negative angle region of at least one of the compression end and the inlet end.

20. The method of any one of claims 13 to 19, wherein the molten glass forms a molten glass ribbon below the glass forming device, wherein the attenuation of the molten glass ribbon is less than 35% and the ratio of bead thickness to sheet thickness of the molten glass ribbon is less than 2.5.