TWI385129B - Isopipes having improved dimensional stability - Google Patents

Description

Tube with improved dimensional stability

The present invention relates to the use of a fusion process to produce tubes of glass sheets, particularly in the course of use, to control the tube to exhibit dimensional changes.

For convenience of reference, the description of the present invention "isometric" is conventionally used to describe a forming apparatus used in a fusion process. It is to be understood that the use of this proper noun does not mean and should not be construed that the invention is limited only to forming devices made by isostatic pressing.

Rather, as set forth in the scope of the claims (see also summary), the invention can be applied to all types of forming devices in a fusion process, regardless of the materials of manufacture of the forming device, and/or the manner in which those materials are processed. how is it.

Also for convenience of description, the equal tube (forming device) is considered to comprise: 1) a first portion consisting of the first and second weirs (堰) of the device, and 2) consisting of a wedge portion of the device. the second part. The second portion also includes a contiguous portion of the first outer surface that is the outer surface of the first weir, and the second outer surface is a contiguous portion of the outer surface of the second weir. Since this proper noun is for convenience of description only, the true transitional position between the first and second portions is not critical and can be considered to be below the bottom of the weir and any position above the bottom of the wedge portion of the device.

Manufacturers of flat panel displays, such as liquid crystal displays (LCDs), use glass substrates to simultaneously manufacture multiple displays, such as six or more displays at a time. The breadth of the substrate limits the number of displays that can be fabricated on a single substrate, so a wider substrate can increase the economic scale. At the same time, display manufacturers need wider substrates to meet the growing demand for larger displays.

In addition, these manufacturers are also looking for glass substrates that can be used with polycrystalline germanium devices that are processed at higher temperatures. In particular, they need a high strain point glass composition that does not undergo compression during display manufacture. These glasses typically require higher forming temperatures and therefore require glass forming processes that can withstand these higher temperatures.

The fusion process is one of the basic techniques used in the glass manufacturing of sheet glass. The glass flakes produced by the fusing process have superior flatness and smoothness compared to other processes known in the art such as floating and slit drawing processes. Therefore, the fusion processing becomes particularly important in the manufacture of a glass substrate used in a liquid crystal display.

The fusion process, and in particular the overflow extraction process, is the subject of U.S. Patent Nos. 3,338,696 and 3,682,609, the entire disclosure of which is incorporated by reference. A simplified diagram of these patented methods is shown in Figure 1. As shown, the system includes a supply tube 9 for supplying molten glass to the collection tank 11 in the equal tube 13.

Once a stable working condition is reached, the molten glass will pass from the supply pipe to the tank and then overflow over the top ends of the trough so that two downwardly flowing glass ribbons are formed and then along the outer surface of the equal tubes Inside. The two ribbons meet at the bottom of the tube or at the root 15 and fuse together to form a single ribbon. This strip is then fed to a drawing instrument (simply indicated by arrow 17) which controls the thickness of the strip, i.e., the final sheet thickness, by the rate at which the strip is pulled away from the root. The drawing instrument is located just downstream of the root so that the single ribbon is cooled and hardened before it contacts the instrument.

As shown in Figure 1, the outer surface of the final glass ribbon does not contact any portion of the outer surface of the tube during any portion of the process. Instead, these surfaces only see the surrounding atmosphere. The inner surfaces of the two halves of the ribbon forming the final ribbon do contact the tubes, but these inner surfaces are fused together at the roots of the tubes and are thus buried in the body of the final ribbon. In this way, the final glass sheet cut from the ribbon can achieve superior outer surface characteristics.

As is clear from the foregoing description, the equal pipe 13 is quite important for the success of the fusion process. In particular, the dimensional stability of the equal tubes is important because changes in the isopipe geometry can affect the overall success of the process. Obviously, the conditions of use of the tube make it very susceptible to dimensional changes. The tubes are usually operated at a high temperature of 1000 ° C and higher. In addition, the tube operates at these elevated temperatures while supporting its own weight, as well as the weight of the molten glass that overflows over its sides and in the tank 11, and from the melting when the molten glass is drawn. The glass is passed back to at least some of the tension of the tube. Depending on the width of the glass sheet to be produced, the unsupported length of the tube may be 2.0 meters or more.

In order to endure these harsh conditions, isopipeded refractory bricks were used to make the equal tubes 13, hence the name "isopipes". In particular, isostatically pressed zirconium refractories are used to form the tubes of the fusion process.

Even with such high-performance materials, dimensional changes can be seen in practical applications, thus limiting their useful life. For example, the tube will appear to sag so that the unsupported length of the tube is centered and falls below its outer support end. These dimensional changes occur along the root of the equal tube and the weir along the top of the equal tube.

As can be seen from the foregoing description, we still need apparatus and methods to efficiently and economically use a fusion process to produce glass flakes having a greater width and/or a glass composition of higher strain points. In particular, we need to improve the dimensional stability of the isopipes to extend their service life and reduce the downtime of processing and the cost of replacement of the tubes.

According to a first aspect, the present invention provides a device (e.g., isopipe 13) that forms a glass ribbon (19) through a fusion process comprising: a first portion (21) containing a trough (11) and first and second overflows Flowing weirs (1, 2), each overflow weir having an inner surface (25), a top surface (27), and an outer surface (29); and a second portion (23) containing a first outer surface (31), Is the continuation of the outer surface (29) of the first weir (1), and the second outer surface (32) is the continuation of the outer surface (29) of the second overflow (2), this first And the second outer surface (31, 32) are positioned relative to each other such that at least a portion (33) of the second portion (23) has a wedge cross section; wherein each overflow weir (1, 2) comprises an aperture (35), this aperture:

(i) extending along at least a portion of the overflow weir length, and

(ii) At least a portion of the aperture (35) is located between the inner and outer surfaces (25, 29) of the weir.

According to a second aspect, the invention provides a method of manufacturing a glass ribbon (19) using a fusion process comprising:

(A) providing molten glass to a forming device (e.g., tube 13), the forming device comprising first and second weirs (1, 2), each containing:

(i) inner surface (25),

(ii) the top surface (27),

(iii) the outer surface (29), and

(iv) Aperture (35), this aperture:

(a) extending along at least a portion of the length of the weir, and

(b) at least a portion is located between the inner and outer surfaces (25, 29) of the weir;

(B) Allowing a fluid (such as a gas or gas mixture or a liquid or liquid mixture) to cool the weir (1, 2) through these apertures (35).

In a particular embodiment, the aperture (35) in the weir (1, 2) may comprise structural members (41, 42) that fully or partially fill the aperture. The structural member can be solid or hollow. In other embodiments, the body of the forming device may also include one or more apertures (43), which may include structural elements (45).

The above reference numerals used in the summary of the various aspects of the invention are merely for the convenience of the reader and are not intended to be construed as limiting the scope of the invention. More generally, it is to be understood that the foregoing general description and the detailed description

As discussed above, a preferred method of making an LCD substrate is to use a fusion process in which molten glass is passed into a large ceramic structure called an equal tube to form a ribbon. Over time, the size of the LCD substrate has increased, and the current size (Gen 10, post G10 generation) is approximately 2850 mm x 3050 mm. Each increase in size (width) means that the length of the equal pipe needs to increase.

This shift to larger equals is a considerable challenge for having equal life spans. For current glass compositions, the weir of the equal tube typically operates at a temperature of about 1220 ° C or higher, while the root operates between 1180 ° C and 1140 ° C. Such high temperature conditions can cause potential refractory materials such as zircon to undergo creep. The larger the size of Gen, the larger the associated tubes will be, resulting in more creep.

Stress analysis shows that the first approximation, the absolute deflection of the tube (D) is determined by the inherent creep rate of the material of the tube ( ) (units / hour), and the used time of the equal pipe and the length (L) and height (H) of the equal pipe, where (k) is a constant: .

It can be seen from this equation that doubling the length of the equal pipe will increase the deflection by 16 times compared to the same material, height, and used time.

This increase in deflection can potentially be solved by increasing the height of the tubes. However, the height of the equal pipe is close to the basic limitations of the isostatic pressing instruments currently available in the industry. Another option is to increase the compressive force applied to the sides of the tube to counter the creep (see U.S. Patent Publication No. 2003/0192349), but this approach imposes considerable limitations on the design of the tube, possibly The flow rate of the glass is made lower than the predetermined target. Reducing the overall operating temperature is another possibility, but new glass components that can be processed at lower temperatures must be developed. Finally, the rate of creep of the ceramic material used to make the tube can be reduced by developing improved materials (see co-applicant's PCT (Patent Cooperation Treaty) patent publication number WO2002/044102). However, even in this case, future substrate sizes and equal tube designs may continue to push ceramic materials into situations where they cannot reach a long enough usable life.

As mentioned above, during operation, the hottest portion of the tube is typically a weir. For example, as described in WO 2002/044102, the rate of creep of zirconium refractories (and other high temperature refractories) increases with temperature. Therefore, compared with the body of the equal pipe, the weir will show the highest rate of creep.

In addition, the weir will be subjected to the downward force generated by gravity during use and the outward force (expansion force) generated by the molten glass contained in the equal tube groove. In addition, not only these two forces, the thickness of the weir is much smaller than that of the equal tube body, so that the overflow weir is particularly susceptible to dimensional instability under prolonged use.

One possible way to combat this vulnerability to dimensional changes is to use thicker weirs. However, this approach creates considerable limitations on the design of the equal pipe, which may cause the flow of the glass to be below a predetermined target.

There are many plans to reduce the sagging of the tubes by using support rods and holes in the body of the tube. Japanese Patent No. 3, 437, 470, Japanese Patent No. 11-246,230, Japanese Patent No. 2006-298736, Japanese Patent No. 2006-321708, and Japanese Patent Publication No. 2007-197303. Obviously, none of these references are recognized by: 1) the fact that the weir is usually exposed to higher operating temperatures, 2) the fact that the weir is subject to vertical and horizontal deformation forces, and 3) the other In part, the weir is quite thin; therefore, the weir is more susceptible to dimensional changes. Similarly, none of these references propose a solution to this problem.

The present invention specifically addresses the instability of the weir by providing at least one aperture in each weir. The initial benefit is that this aperture reduces the weight of the weir, thus reducing the sagging-induced load on the weir.

Moreover, in some embodiments, this aperture is used to reduce the internal temperature of the ceramic material that constitutes the weir. For example, a fluid having a temperature below the nominal temperature of the weir enthalpy can be passed through the aperture at a controlled flow rate. As shown below, even a relatively small change in the temperature of the material that constitutes the weir will have a significant effect on the creep rate of the material.

The fluid may be an inert gas such as nitrogen, a non-inert gas such as air, as long as it is not exposed to a non-inert gas, or a liquid, such as water, when molybdenum is used. A gas or liquid mixture can also be used if desired. For some applications, liquids may be more effective than gases because of their higher heat capacity.

The fluid can pass through the aperture from any direction, and in some cases, it is preferred to have the fluid pass through the aperture from the inlet end of the isopipe because the inlet end of the molten glass into the equal tube is typically hotter than the distal end of the equal tube. If the fluid picks up more heat from the inlet end, it can help to moderate the thermal gradient along the weir, thus helping to control the flow of the glass. At the same time, having fluid enter the aperture at the inlet end can help reduce the temperature of the molten glass at the inlet end, which may be desirable for some applications. Through the use of the heat exchanger structure, the fluid can also be passed through the aperture multiple times. For example, fluid can be introduced into a tube containing a central bore that is connected to the surrounding annulus. The fluid can, for example, pass down the central bore and come back through the loop. This way it is more efficient to transfer heat to the fluid. Alternatively, the fluid can pass through the annulus for the first time and the central pupil for the second time. Of course, more complex heat exchanger structures can be used if desired.

In other embodiments, the aperture is used to enclose the structural member, the constituent material of the structural element having a lower creep rate than the material constituting the weir. The structural components can be solid and completely or partially fill the cross-section of the aperture. In the latter case, the unfilled portion of the aperture can be used to cool the structural member and the overflow material, such as by passing fluid through the unfilled portion of the aperture, thereby covering the exposed surface of the structural member and the inner wall of the aperture. .

In a further embodiment, the structural member may be hollow and its outer casing may completely or partially fill the cross-section of the aperture. In both cases, the hollow portion of the structural member can be used to cool, for example, by passing fluid through the interior of the structural member. If the outer shell of the hollow structural member only partially fills the cross-section of the aperture, the unfilled portion of the aperture can also be used for cooling.

The aperture generally extends through the entire length of the weir, although a closed aperture at one or both ends can also be used to practice the invention, such as when a cooling fluid passes through the heat exchanger structure. The structural member may be contained within the weir, or may extend beyond the weir, with one end preferably engaging the support structure at both ends.

In addition to one of the apertures in each weir (with or without structural members), the tubes may also contain one or more apertures in the body of the tube, that is, at a level below the weir. Like the aperture formed in the weir, the aperture formed in the body may also comprise structural members that may completely or partially fill the aperture. Moreover, like the aperture in the weir, the aperture in the body can also be used to cool the interior of the tubes to reduce the rate of creep of the materials that make up the tube body.

The apertures in the weir and the isopipe body (when used) may be drilled into the tube by the center, or preferably drilled into the blank used to form the tube, or may be fabricated in the blank. Formed in situ during the period.

The general treatment of ceramic carbon blacks such as tubes is a multi-step process. For example, the dosing material of zirconium or other ceramic materials and binders can be prepared, for example, by spray drying. The ingredient material can then be placed in a bellows and vibrated to allow the particles to settle for initial compaction. The bag can then be hermetically sealed and placed in a cold isostatic press to more fully compact the structure. This compacted structure can then be burned to a dense ceramic at elevated temperatures.

Such treatments can be modified to place one or more rods of graphite or other combustible material, such as a solid or foamed natural or synthetic polymer, into an isostatic bag as a mandrel to create a pore size in the blank. The ingredients are then poured around the stick and vibrated to allow the ingredients to be arranged in a denser, compact structure. The bag is then hermetically sealed and pressed isostatically. The compacted ingredients and bars are then placed in an oven, which is first burned off and then sintered at elevated temperatures. In another process, the ingredient binder can be first burned off, followed by pre-sintering the structure. The rod was removed from the blank after cooling to room temperature and then sintered at a high temperature.

The apertures can be of various sizes, for example from a few millimeters to a few inches for tubes such as Gen 10. Typically, a smaller aperture is used when the purpose of the aperture is to allow fluid to pass through the aperture to cool the interior of the tube. As discussed above, this fluid flow provides a means of drawing heat from the interior of the equal tubes, thus reducing internal temperature and reducing material creep. Minor changes in temperature can significantly reduce the level of creep in the tube. For example, as shown in Table 2, for zirconium, a temperature reduction from 1250 ° C to 1180 ° C reduces the creep rate by about 50%. The fluid flow rate required is determined by the heat capacity of the fluid, the temperature of the fluid, the predetermined reduced internal temperature, and the particular geometry of the tubes. Skilled workers can easily determine the flow rate required for a particular application based on the published information herein.

As discussed above, in certain embodiments, the aperture can include structural components. These structural members are preferably constructed of a material having a material that is less than the material used for the tube. For example, for a tube such as zirconium, the structural member may be composed of, for example, Al ₂ O ₃ , SiN, SiC, molybdenum, or a fiber-reinforced structure. In the case of the molybdenum rod, this rod may preferably be coated with platinum, or a wrap in an inert atmosphere such as N ₂ to reduce oxidation. These materials have proven to have very low creep potential even at 1250 ° C, so they can provide additional support for tubes made of zirconium or other refractory materials during operation.

One of the benefits provided by the present invention is that a proven material such as zircon can be used to fabricate an LCD substrate. These materials are known to be compatible with the glass components approved by the display manufacturer. The invention also expands the design window of the isopipe. For example, it is possible to manufacture a tube that reduces the height without affecting the sag, thus affecting the operational life. This reduces the cost of the tube itself, and the overall size of the melting machine. Reducing the height can also help to reduce the chances of forming a secondary crystal, as described in co-pending PCT Patent Publication No. 03/055,813.

The invention will be further described below using the embodiment of Figures 2 through 8, but is not meant to be limiting in any way.

The embodiment shown in Figure 2 applies an aperture 35 in the weirs 1 and 2 and an aperture 43 in the isopipe body. The apertures 35 in the weirs 1 and 2 completely fill the structural members 41 and 42, while the apertures 43 completely fill the structural members 45.

Figure 3 shows a variation of the embodiment of Figure 2 in which the apertures 35 of the weirs 1 and 2 are connected to each other through an additional aperture 37, and the same aperture 35 fills the structural components. This embodiment also uses a circular configuration of the aperture 43 instead of the rectangular configuration of FIG.

Figure 4 shows an embodiment suitable for cooling the interior of a portion of the tube. This embodiment applies five relatively small apertures, two of which are located in the weir, i.e., aperture 35, and three of which are located in the body of the equal tube, i.e., aperture 43.

Figure 5 shows a variation of the embodiment of Figure 4, again applying an aperture suitable for cooling. This embodiment applies a relatively large aperture 43 in the isobath body and an elliptical aperture 35 in the weirs 1 and 2.

Figure 6 shows the variation of Figure 5, with structural members 41 and 42 introduced into aperture 35 and structural member 45 introduced into aperture 43. The cooling fluid can be passed through an unfilled portion of the aperture, or the structural member can be used alone to reduce the sag of the equal tube.

Figures 7 and 8 illustrate the use of a hollow structural member, which may be elliptical as shown. The use of hollow structural members can have the benefit of reducing the weight of the structural members. At the same time, if desired, the cooling fluid can be passed through the central portion of the structural member. It is to be noted that the hollow portion of the structural component constitutes an unfilled portion of the aperture regardless of whether the outer casing of the structural member is filled with the aperture.

It will be apparent to those skilled in the art that the invention may be For example, although the isopipe for illustrating the present invention has a vertical side wall, the tube containing the beveled weir may be used, for example, a tube having a V or Y cross-section, and a tube-side wedge. The outer surface of the tube at the upper end of the portion has no edges. Meanwhile, although FIGS. 2 through 8 show a single tube, etc., tubes including two or more separate elements (which may be composed of the same or different materials) may also be used to practice the invention. The scope of the patent application is intended to cover the specific embodiments described herein, as well as various modifications, variations, and equivalents thereof.

1,2. . . Overflow

9. . . Supply tube

11. . . Collection tank

13. . . Equal tube

15. . . Root

17. . . Arrow of direction of the drawing device

19. . . Glass ribbon

twenty one. . . first part

twenty three. . . the second part

25. . . The inner surface

27. . . Top surface

29. . . The outer surface

31. . . First outer surface

32. . . Second outer surface

33. . . Part of the second part

35,37,43. . . Aperture

41. . . First structural member

42. . . Second structural member

45. . . Structural member

1 is a perspective schematic view showing a representative configuration of a device during an overflow down draw fusion process for making a flat glass sheet.

2-8 are schematic cross-sectional bones showing a tube having a weir, etc., representative of an embodiment in which pores are formed to withstand cooling fluid and/or structural members.

1,2. . . Overflow

13. . . Equal tube

15. . . Root

twenty one. . . first part

twenty three. . . the second part

25. . . The inner surface

27. . . Top surface

29. . . The outer surface

31. . . First outer surface

32. . . Second outer surface

33. . . Part of the second part

35. . . Aperture

41,42,45. . . Structural member

43. . . Aperture

Claims (20)

An apparatus for forming a glass ribbon using a fusion process comprising: a first portion comprising a trough and first and second weirs, each overflow weir having an inner surface, a top surface, and an outer surface; a second portion comprising a first outer surface that is a continuation of the outer surface of the first weir, and a second outer surface that is a contiguous portion of the outer surface of the second overflow, the first and second outer surfaces The faces are positioned relative to each other such that at least a portion of the second portion has a wedge section; wherein each weir comprises an aperture that (i) extends along at least a portion of the weir length, and (ii) At least a portion of the aperture is located between the inner and outer surfaces of the weir. The device of claim 1, wherein for each weir, the aperture extends along the entire length of the weir. A device according to the first aspect of the invention, wherein the aperture has a circular cross section for each overflow weir. A device according to the first aspect of the invention, wherein the aperture has an elliptical cross section for each overflow weir. The device of claim 1, wherein the apertures of the first and second overflow weirs are connected by another aperture under the slot. The device of claim 1, wherein the device further comprises first and second structural members, the first structural member being located within the aperture of the first weir and the second structural member being located within the aperture of the second weir . The device according to claim 1, wherein the first and second structural members are composed of a material which exhibits a small creep at the operating temperature of the device and is lower than the creep of the material composed of the weir. . A device according to claim 6 wherein the structural member fills its respective aperture. A device according to claim 6 wherein the structural member partially fills its respective aperture. A device according to claim 6 wherein the structural member is hollow. The device of claim 1, further comprising at least one other aperture that is not located between the inner surface and the outer surface of the weir. The device of claim 11, wherein the device further comprises the structural member being located within the other aperture. The device according to claim 12, wherein the structural member located in the other aperture is composed of a material which exhibits a lower creep at the operating temperature of the device and is lower than the potential of the material of the weir. change. In accordance with the apparatus of claim 1, wherein the first and second portions are part of a single body of material. A method of making a glass ribbon using a fusion process, the method comprising: (A) providing molten glass to a forming apparatus, the forming apparatus comprising first and second weirs, each overflow containing: i) an inner surface, (ii) a top surface, (iii) an outer surface, and (iv) an aperture, the aperture: (a) extending along at least a portion of the weir length, and (b) at least a portion of the overflow Between the inner and outer surfaces of the crucible; and (B) allowing fluid to cool the overflow weir through these apertures. The method of claim 15 wherein: (a) the forming apparatus further comprises first and second structural members, the first structural member being located within the aperture of the first weir and the second structural member being located in the second overflow (b) the structural member partially fills its respective aperture; and (c) allows fluid to pass through the unfilled portion of the aperture and cools the overflow weir and structural member. The method of claim 16, wherein the first and second structural members are comprised of a material that exhibits a lower creep at the operating temperature of the forming device and is lower than the material of the overflow weir. change. The method of claim 15, wherein: (a) the forming device comprises at least one other aperture that is not located between the inner surface and the outer surface of the weir; (b) the fluid is passed through the other aperture to form the device cool down. The method of claim 18, wherein: (a) the forming device comprises a structural member located in the other aperture; (b) the structural member partially fills the other aperture; and (c) allowing the fluid to pass The other aperture is not filled up and the shaped member and structural member are cooled. The method according to claim 19, wherein the structural member located in the other aperture is composed of a material which exhibits a lower creep at the operating temperature of the forming device and is lower than the material of the material formed by the weir. change.