KR20090016564A - Apparatus and method for forming a glass substrate with increased edge stability - Google Patents

Abstract

An apparatus for forming glass substrates is presented wherein a design parameter of the apparatus, the vertical height L of converging forming surfaces which comprise the apparatus is related to the flow of molten glass over web portions of the apparatus.

Description

Apparatus and method for forming an organic substrate with increased edge stability {APPARATUS AND METHOD FOR FORMING A GLASS SUBSTRATE WITH INCREASED EDGE STABILITY}

FIELD OF THE INVENTION The present invention relates generally to apparatus for forming organic substrates, and more particularly, to reference designs for devices based on glass mass flow.

In the form of liquid crystal displays (LCDs), glass display panels are used in a variety of applications, ranging from portable personal data assistants (PDAs) to computer monitors or television displays. Such applications require glass sheets or substrates that have inherent properties and have a flawless surface and a constant thickness. The LCD includes several thin (eg <0.7 mm) glass sheets that are at least sealed to one another to form an envelope. The growing market for glass display panels, and in particular LCD display panels, has led to increased demand for thin glass substrates used by their manufacturers.

One method of making glass for an optical display is by an overflow downdraw process. U.S. Pat. A fusion downdraw process is disclosed that includes a process. The molten glass overflows to converge to the forming surface of the isopipe so that the separation flow is recombined at the apex, or root, where the two converged forming surfaces meet, forming a glass ribbon. Thus, the glass which comes into contact with the forming surface is located in the inner part of the glass sheet and the outer surface of the glass ribbon is not in contact. A draw roll is located below the isopipe root and capture edge portion of the ribbon to control the rate at which the ribbon leaves the isopipe, thus helping to determine the thickness of the finished sheet. As the glass ribbon descends from the root of the isopipe past the draw roll, it is cooled to form a solid, elastic glass ribbon which is then cut to form individual glass sheets or substrates.

As the demand for display glass increases, manufacturers of glass substrates face the need to increase production. One approach is to install additional draws. However, this approach involves significant expense. A larger cost effective approach is to increase the flow of glass in a given draw. However, increasing the flow generally requires increasing the size of the isopipe (eg, the width of the isopipe) in order to maintain a stable edge flow. The draw process itself is a precise balance between multiple draw process conditions, which process conditions may vary from individual draws to other individual draws. Thus, simply increasing the flow of glass sometimes involves difficulties. Furthermore, not only is the demand for glass substrates increasing, but also the display size continues to increase. This requires larger substrate sheets to maintain the size of efficient economics. As a result, larger (e.g., wider) draws are required as well as the flow of glass. What is needed is a design approach that provides the ability to increase the flow of glass in a given draw without exceeding the stability limits of the draw process, or the ability to locate large draw machines by increasing the scale from smaller and more stable draws.

One embodiment according to the present invention includes a forming wedge 12 having a pair of surface forming portion 22 inclined downward; And an edge director 36 extending along the vertical edge of the surface forming portion, the surface forming portion converging at the root 24 of the forming wedge, the forming wedge having a vertical height L above the root. The edge director comprises a web portion 40 in contact with the surface forming portion, the web portion blocking and thinning a glass flow G of lbs / hour-inch relative to the web, where G / L ³ includes an apparatus for forming a glass sheet larger than about 0.0017 lbs / hour / inch ⁴ . Preferably G / L ³ is greater than about 0.0017 lbs / hour / inch ⁴ .

In another embodiment, it has a pair of downwardly inclined surface formations 22 converging at the bottom of the forming wedge and having a vertical height L inch between a horizontal line and a draw line across the top of the inclined surface formation. Flowing the molten glass over the forming wedge 12 so that the glass draw line 24 is formed along the edge director 36 with a glass flow G of lbs / hour-inch relative to the web. And a web portion (40) connected to the surface forming portion (22) for blocking and thinning, wherein G / L ³ is greater than about 0.0017 lbs / hour / inch ⁴ This is disclosed.

Additional features and advantages of the invention will be set forth in the description which follows, and will be readily apparent to those skilled in the art from, or practiced with, the description of the invention described herein, and the invention includes not only the claims that follow the description, The accompanying drawings are included.

It is to be understood that the foregoing general description and the following detailed description are merely exemplary of the invention and are intended to provide an overview and gist of the nature and properties of the claimed invention. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention and are provided to explain the principles and acts of the invention in conjunction with the description.

Reference will now be made in detail to exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

Past experience with forming wedge designs tends to involve an iterative process. Forming wedges are designed, manufactured and run in an attempt to evaluate their capabilities. Unstable forming wedges, for example, at the edge-to-edge width of a glass sheet that is elongated in a forming wedge that changes over time, are the changes to the design and the production of other forming wedges. It costs. This process continues until a combination of suitable design characteristics is reached. Nevertheless, edge stability may prove to be insignificant for various process variables such as temperature distribution, glass flow variation, etc. as the forming wedge shape is applied to changes over time. The forming wedges themselves tend to dissolve unusually harsh conditions, such as the formation of sag or creep by the glass forming wedges over time, and that the molten glass slowly dissolves the material from which the forming wedges are made, usually zircon. Applies to conditions such as the high temperature required to have. As a result, the behavior of certain forming wedges is sensitive to process conditions, leading to variations in edge stability. This is especially true when an increase in forming wedge size is required.

One limitation to flat panel display size is the ability to form large sheets of pristine glass to serve as a substrate for the display. The first generation of glass sheets had a size (eg, width) of 1 meter or less, but the current generation of products can form non-contaminated glass sheets of several meters in width.

In order to achieve this size increase, display glass manufacturers must increase the size, especially the width, of the forming wedge (iso pipe). In the past, this generally developed from the beginning of the formation wedge of the previous generation. These forming wedges were then used as a template for the substrate and the next generation of forming wedges were sized from the previous generation.

Nevertheless, formation wedges showing relatively good edge stability were often unsuccessful, even when they formed the basis for the next generation of designs. For example, simply increasing the size (width) of the forming wedge without increasing the size of the edge director web portion showed an unstable edge flow and at least an edge flow sensitive to process conditions. Thus, some forming wedges may be required to be manufactured with varying specific design parameters (eg, width, trough shape, etc.). Before becoming larger, the next generation of forming wedges, which can provide a stable edge flow, can be manufactured and placed into the product. As can be appreciated, this blinding approach to forming wedge design is undesirable.

Using the method according to the invention allows not only to produce a first forming wedge for the overflow downdraw formation of a glass sheet having a stable edge flow, but also of different sizes surveyed from the original forming wedge to create a stable edge flow. Promotes the development of forming wedges.

An apparatus 10 for overflow downdraw of a non-contaminated glass sheet according to the invention is shown in FIG. 1. As shown in FIGS. 1-2, the apparatus 10 comprises a forming wedge 12 having an upwardly open channel 14 adjacent the longitudinal plane thereof by the wall 16, which is of opposite length. Terminate at the portion extending upwards in the direction extending overflow weir or lip 18. The weir or lip 18 communicates with the opposing outer sheet forming surface of the forming wedge 12. As can be seen, the forming wedge 12 is a substantially horizontal lower point of focus forming a pair of substantially vertical forming surface portions 22 and a straight line of glass draw lines connected to the lip 18. It is provided with a pair of downwardly inclined converging surface portions 22 terminating at an apex or root 24.

Molten glass 26 is supplied to channel 14 via a transport path 28 that is connected to channel 14. The supply to channel 14 may be single ended or preferably double ended. A pair of restricting dams 30 are separate streams that provide a path for overflow of the free surface 32 of the molten glass 26 over the overflow lip 18 as a separate stream. Route 24 provided on the overflow lip 18 adjacent each end of 14), where the separated effluent, which appears to be dashed, converges to form a ribbon of virgin-surfaced glass 34 The furnace surface forming portions 20 and 22 face downward. The ribbon is then stretched by drawing roll 35.

A pair of edge directors or correctors are provided at each longitudinal end of the forming wedge such that the edge director extends along each of the vertical edges of each longitudinal end of the wedge on each side. . Thus, four edge directors are provided for each forming wedge, one at each corner of the forming wedge 12. Edge director 36 consists of two main parts: a projecting edge surface portion 38 which intersects the longitudinal end of the surface forming portion of the wedge along its vertical extension, and the projecting edge surface portion. A web or filleted portion 40 connected to (crossed) and extending between one of the converging surface portions 22 inclined downward.

Web portion 40 traverses edge surface portion 38 along an intersection line 42 between points A and B, and also forms a sloped surface along intersection line 44 between points A and C. Cross the section 22. Thus, the intersecting line 44 extends in a diagonal direction downward from point A to point C with a distance d along the root or facing point 24 of the forming wedge 10 inwardly of the projecting edge surface portion. Likewise, the intersecting line 42 extends downward from point A to point B at the edge surface 38. In some embodiments, point C may lie in a horizontal plane through the root 24. However, in other embodiments, point C may lie on either the top or the bottom of the horizontal plane. The lower end 46 of the web portion 40 extends from point B to point C. Bottom edge 46 may or may not be straight.

According to the present invention, the wedge member 10 has been described as including a plurality of edge directors. In particular, a pair of edge directors 36 are provided on each side of the forming wedge, one at each vertical corner so that two such edge directors are disposed opposite each end in the longitudinal direction of the forming wedge.

The molten glass flowing downward along the edge portion of the converging surface forming portion 22 is blocked by the web portion 40 along the intersection line 44 with respect to the inclined surface forming portion 22. The edge portion of the sheet flowing downward is initially supported by the inclined surface forming portion and thereafter guided by the web portion 40 of the edge director 36.

The web portion 40 provides a wetted length, which is greater than the length of the surface forming portion 22 blocking in the horizontal direction, effectively maximizing the wear of the useful sheet glass that can be obtained. The web portion 40 further spreads or thins the glass flow thereon, reducing the thickness of the longitudinal end of the molten glass effluent before actually leaving the bottom portion 46 of the web portion.

The linear width of the flowing glass and the contacting web portion 40 are shown in FIG. 2, and the internal distance of the edge surface portion 38 of the edge director 36 along the route 24 as defined above, It is represented by the distance d. The flow rate of this flow is denoted as G at lbs / hr per inch for the distance from edge surface 38 to point C. Since there are generally four edge directors and four web portions, G is generally expressed as the average value of the mass flow rate for all web portions.

As mentioned above, the glass substrates made in glass making systems using the fusion process must have a certain thickness used in devices such as flat panel displays. To ensure this, the inventors studied and decided on how to improve the fusion process to make such glass substrates. In particular, the inventors have discovered the method by adjusting the mass distribution of the molten glass 26 flowing onto the forming apparatus 10 which may have a direct impact on the properties / properties of the glass substrate. In this way, the object of the present invention relates to the control of the mass flow rate of the molten glass 26 flowing into the forming apparatus 10.

Effective fusion processes are known to form glass ribbons having a constant thickness over a wide area. It is also preferred that the width of the ribbon does not change during drawing of the ribbon, ie the edge of the ribbon remains stable. The inventors have found that the ratio of the glass mass flow rate flowing through the upper surface 52 of the web portion 40 to the cube L ³ of the vertical height L of the upper portion 50 of the forming surface 22 converging, i.e., G / It has been found that edge stability can be achieved when the amount of L ³ is maintained at about 0.0017 lbs / hour / inch ⁴ or more, or more preferably 0.002 lbs / hour-inch ⁴ or more.

Although the conditions outlined above accommodate the establishment of edge (ribbon width) stability in a fusion downdraw process, the ability to keep the tension forces on glass layers moving over the web portion surface is also useful. . Relevant forces include the adhesion that holds the glass on the web surface and the applied force (gravity and draw roll, 35) that separates the glass from the edge director (web) surface. These forces are intended to peel the sheet from the edge director and may cause variation in the sheet width. Therefore, it is preferable that the adhesive force be at least as large as the application force and significantly larger than the application force. In general, edge directors include refractory metals such as platinum to withstand high glass formation temperatures (often above 1000 ° C.). It has been found that the silicate glass used to make the display device insufficiently wets the platinum, in which the glass can be completely separated from the platinum surface. Furthermore, the silicate glass is heavily wetted on some ceramic material, for example alumina or zircon. It may therefore be advantageous to coat at least precious metal (eg platinum) web portions with ceramic material such as alumina or zircon for increased adhesion. Alternatively, the web portion may be an integral (eg monolithic) portion of the forming wedge, in that it is cast or machined as part of the forming wedge. The web portion may in some cases be prepared as a separate ceramic component and later attached to the forming wedge. The advantage of machining the web portion into one or a single piece of forming wedges can reduce the use of expensive precious metals and can result in disruption of the glass flow and surface cleavage at the intersection of the forming wedges. Is to remove it. In certain embodiments, the edge director, and in particular the web portion and / or forming wedge of the edge director, may be manufactured in part or in whole using any refractory material disclosed in US Patent Application No. 60/640686, filed December 30, 2004. It may be disclosed, and is incorporated by reference as a whole. As an example of such a material, genotime plus zircon, xenotime-type material, xenotime-stabilized zircon-type material, and xenotime-type material as defined and disclosed in the above-mentioned references. Stabilized zircon-type materials, or combinations thereof.

Of course, if a person skilled in the art is given a forming edge with a stable edge flow (ie, a stable edge-to-edge width), the ability to survey against larger forming wedges will be enhanced by the present invention. That is, the subsequent forming wedges can be designed according to the following criteria.

G = G _ref (L / L _ref ) ³ (1)

Where G is the mass flow rate with respect to the web portion of the continuous forming wedge and L is the vertical height with respect to the converging forming surface of the continuous forming wedge. G _ref and L _ref are the same parameters for existing or former forming wedges. As mentioned previously, G is generally represented by the average mass flow rate of all web portions of the forming wedges.

It will be apparent to those skilled in the art that changes or modifications according to the present invention can be made without departing from the spirit or scope of the present invention. Accordingly, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

1 is a partial cross-sectional perspective view in accordance with one embodiment of the present invention showing one end of a device including forming wedges for fusion drawing a glass ribbon.

FIG. 2 is an enlarged perspective view of the forming wedge of FIG. 1 showing the edge director and the web portion of the edge director. FIG.

Claims (9)

Forming wedges 12 having a pair of surface forming portions 22 inclined downward; And, An edge director 36 extending along the vertical edge of the surface forming portion, the surface forming portion converging at the root 24 of the forming wedge, the forming wedge having a vertical height L above the root, The edge director includes a web portion 40 connected with the surface forming portion to block and thin the glass flow G of lbs / hour-inch relative to the web, Wherein G / L ³ is greater than about 0.0017 lbs / hour / inch ⁴ . The apparatus of claim 1, wherein the G / L ³ is greater than about 0.002. 2. The apparatus of claim 1, wherein the surface of the web portion in contact with the flow glass is a ceramic material. 4. The apparatus of claim 3, wherein the web portion is in the form of a solid ceramic. 5. The apparatus of claim 4, wherein the web portion is a monolithic portion of the forming wedge. 4. The apparatus of claim 3, wherein the ceramic material is selected from the group consisting of zircon, alumina, xenotime-type materials, xenotime-stabilized zircon-type materials, and combinations thereof. . 4. The apparatus of claim 3, wherein the web portion comprises a ceramic coated refractory metal. The forming wedge having a pair of downwardly inclined surface forming portions converging at the bottom of the forming wedge and having a vertical height L inch between a horizontal plane and a draw line across the upper portion of the inclined surface forming portion ( Flowing the molten glass over 12) such that the glass draw line 24 is formed accordingly, wherein the edge director 36 blocks and thins the glass flow G of lbs / hour-inch relative to the web. And a web portion (40) connected to the surface forming portion (22) for the purpose of wherein G / L ³ is greater than about 0.0017 lbs / hour / inch ⁴ . The method of claim 8, wherein the G / L ³ is greater than about 0.002.

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