JP5613670B2 - Isopipe with improved dimensional stability - Google Patents

Description

Explanation of related applications

  This application is an application claiming priority to US Provisional Patent Application No. 61 / 092,931, filed Aug. 29, 2008, entitled “Isopipe with Improved Dimensional Stability”. is there.

  The present invention relates to an isopipe used for producing sheet glass by a fusion method, and more particularly to an apparatus and method for suppressing dimensional changes exhibited by an isopipe during use.

Definition

  For ease of reference, the term “isopipe” is used herein, which is a term that has historically been used for molding equipment employed in the fusion process. It should be understood that the use of this terminology is not intended and should not be construed as limiting the present invention to molding equipment produced by isostatic pressing.

  On the contrary, as set forth in the claims (see also the general description), the present invention provides a fusion process regardless of the materials from which the forming apparatus is made and / or how these materials are processed. It is applicable to all molding apparatuses used in

  In order to simplify the explanation, the above-mentioned isopipe (forming apparatus) includes: 1) a first part including the first and second weirs of the apparatus, and 2) a second part including the wedge-shaped part of the apparatus. It is treated as a source consisting of The second portion also has a first outer surface that is an extension of the outer surface of the first weir and a second outer surface that is an extension of the outer surface of the second weir. Since this terminology is only used to simplify the description, the exact location of the transition between the first part and the second part is not important and the bottom of the weir It can be considered that it is a part below the wedge-shaped part of the device.

  Manufacturers of flat panel displays such as liquid crystal displays (LCDs) use glass substrates to produce a large number of displays simultaneously, for example, six or more at a time. The number of displays that can be produced on a single substrate is limited by the width of the glass substrate, so the wider the substrate width, the more economical the scale. Also, display manufacturers require a wider range of substrates to meet the growing demand for larger size displays.

  In addition, such manufacturers are seeking glass substrates that can be used in polycrystalline silicon devices that can be manufactured at higher temperatures. In particular, there is a need for glass compositions having high strain points that do not shrink during display manufacture. Such glasses generally require higher molding temperatures and, therefore, a glass molding process that can withstand such higher temperatures is needed.

  The fusion method is one of the basic techniques used in the glass manufacturing field for producing sheet glass. For example, see Non-Patent Document 1. Compared to other known methods such as, for example, the float method and the slot draw method, the fusion method produces a glass sheet whose surface has excellent flatness and smoothness. As a result, this fusion method has become particularly important in the manufacture of glass substrates used in the manufacture of liquid crystal displays (LCDs).

  The fusion method, particularly the overflow downdraw fusion method, is the subject of Patent Documents 1 and 2 (inventor: Stuart M. Dockerty). A schematic diagram of the methods of these patents is shown in FIG. As shown, the system includes a supply pipe 9 that provides molten glass to a collection trough 11 formed in an isopipe 13.

  Once steady state operation is obtained, molten glass flows from the supply pipe to the trough, then overflows the top surfaces of the side walls of the trough, thus flowing downward to form two strips of glass. It then flows inward along the outer surface of the isopipe. These two strips of glass merge at the bottom edge 15 of the isopipe and fuse there to form a single strip of glass. This strip of glass is then fed to a traction device (represented schematically by arrow 17) that controls the thickness of the glass strip, which traction device when pulled from the bottom edge. The glass speed controls the thickness of the strip glass and hence the final sheet glass thickness. This traction device is arranged in a good position on the downstream side of the bottom edge so that the strip of glass cools down and becomes rigid before contacting the traction device.

  As is apparent from FIG. 1, both outer surfaces of the final glass strip do not contact any part of the isopipe at any point during the process. On the contrary, these surfaces only touch the surrounding atmosphere. The inner surfaces of the two strip glass halves that form the final glass strip contact the isopipe, but these inner surfaces fuse at the bottom edge of the isopipe, and thus the body of the final glass strip. Embedded in. In this way, excellent properties of both outer surfaces of the final glass sheet cut from the strip glass are obtained.

  As is clear from the above description, the isopipe 13 is the key to the success of the fusion method. In particular, the dimensional stability of the isopipe is critical because changes in the isopipe geometry adversely affect the overall success of the method. It should be noted that the conditions under which the isopipe is used are prone to dimensional changes. Generally, an isopipe operates at a high temperature of 1000 ° C. or higher. Furthermore, the isopipe is not only its own weight, but also overflows its side walls and the weight of the molten glass in the trough 11, and is transferred back to the isopipe through the molten glass when the molten glass is pulled. It operates at high temperatures while supporting at least some tension. Depending on the width of the glass sheet being produced, the unsupported length of the isopipe will be more than 2 meters.

  In order to withstand these harsh conditions, the isopipe 13 has been manufactured from a block in which the refractory material is compressed in equilibrium (from the name “isostatic”, “isopipes”). In particular, hydrostatic press molded zircon refractories have been used to form isopipes for the fusion process.

U.S. Pat. No. 3,338,696 US Pat. No. 3,682,609

Varshneya, Arun K. “flat glass”, Fundamentals of Inorganic Glasses, 1994, Boston, Academic Press, Chapter 20, Section 4.2, pp. 534-540

  Despite the use of such high performance materials, in practice, isopipes exhibit dimensional changes that limit their useful life. For example, an isopipe shows a sag in which the center portion of the unsupported length of the isopipe descends below both supported end portions. Such dimensional changes occur both along the bottom edge of the isopipe and along both weirs at the top of the isopipe.

  In view of the above, there is a need for an apparatus and method that allows the fusion method to be used effectively and economically for the production of glass sheets made of glass having a wider and / or higher strain point. I understand that there is. In particular, there is a need to improve the dimensional stability of an isopipe, thereby extending the useful life of the isopipe, thus reducing process downtime and reducing isopipe replacement costs.

According to a first aspect, the present invention provides an apparatus (eg, an isopipe 13) for forming a glass strip (19) by a fusion method, the apparatus comprising:
A first part comprising a trough (11) and first and second weirs (1, 2) with an inner surface (25), a top surface (27) and an outer surface (29), respectively (21) and
A first outer surface (31) that is an extension of the outer surface (29) of the first weir (1) and a second outer surface (32) that is an extension of the outer surface (29) of the second weir (2). ), The first and second outer surfaces (31, 32) such that at least a portion (33) of the second portion (23) has a wedge-shaped cross-sectional shape. A second part (23) facing towards each other,
With
Each weir (1, 2) is provided with an opening (35), this opening (35)
(B) It extends along at least part of the length of the weir, and (b) at least part of the opening (35) is arranged between the inner surface and the outer surface (25, 29) of the weir.

According to a second aspect, the present invention provides a method for forming a glass strip (19) using a fusion method, the method comprising:
(A) Providing molten glass to a forming apparatus (for example, isopipe 13) provided with first and second weirs (1, 2), in which case each weir is
(A) Inner surface (25),
(B) Top surface (27),
(C) an outer surface (31), and (d) an opening (35), the opening (35)
(A) extends along at least a portion of the length of the weir; and (b) at least a portion is disposed between the inner surface and the outer surface (25, 29) of the weir, and (B) the opening. (35) including passing a fluid (eg, gas or gas mixture or liquid or liquid mixture).

  In some embodiments, the opening (35) in the weir (1, 2) can comprise a structural member (41, 42) that completely or partially plugs this opening. These structural members may be solid or hollow. In another embodiment, the body of the molding device may comprise one or more openings (43) that may comprise a structural member (45).

  The reference numbers used in the above summary description of aspects of the present invention are for the convenience of the reader only and are not intended to be construed as limiting the scope of the present invention. It shouldn't be. More generally, the foregoing general description and the following detailed description are merely illustrative of the invention and are intended to provide an overview or outline for understanding the nature and nature of the invention.

  Both further features and advantages of the present invention are described in the following detailed description, some of which are readily apparent to those skilled in the art from the description or by practice of the invention described therein. I will. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. It should be understood that any and all combinations of the various features of the invention described herein and in the drawings may be used.

FIG. 2 is a schematic perspective view showing an exemplary structure for an apparatus used in an overflow downdraw method for making a flat glass sheet. It is a schematic sectional drawing which shows typical embodiment of the isopipe of this invention which has a weir in which the opening part for accommodating a structural member was formed in the inside. It is a schematic sectional drawing which shows typical embodiment of the isopipe of this invention which has a weir in which the opening part for accommodating a structural member was formed in the inside. 1 is a schematic cross-sectional view showing a typical embodiment of an isopipe of the present invention having a weir having an opening formed therein for containing a coolant. 1 is a schematic cross-sectional view showing a typical embodiment of an isopipe of the present invention having a weir having an opening formed therein for containing a coolant. 1 is a schematic cross-sectional view showing a representative embodiment of an isopipe of the present invention having a weir having an opening formed therein for containing a coolant and a structural member. 1 is a schematic cross-sectional view showing a representative embodiment of an isopipe of the present invention having a weir having an opening formed therein for containing a coolant and a structural member. 1 is a schematic cross-sectional view showing a representative embodiment of an isopipe of the present invention having a weir having an opening formed therein for containing a coolant and a structural member.

  As mentioned above, the preferred method for producing LCD substrates is to use a fusion method in which molten glass is passed through a large ceramic structure known as an isopipe and is formed into a strip glass. Over time, LCD substrates have been expanded to the current size (10th generation) of about 2850 mm × 3050 mm. The increase in size (width) in each generation meant a corresponding increase in isopipe length.

  This transition to larger isopipes has posed significant challenges in providing isopipes with the ability to have a multi-year service life. With current glass compositions, the bottom edge of the isopipe generally operates between 1180 ° C and 1140 ° C, while both weirs operate at temperatures above about 1220 ° C. This high temperature condition causes creep in the refractory material of the isopipe, for example zircon. The larger the generation size, and thus the larger the isopipe, the more creep occurs.

According to the stress analysis, as an initial rough estimate, the absolute deflection (D) of the isopipe is determined by the creep rate (dε / dt) (unit: 1 / hour) inherent to the material in which the isopipe is formed, and the isopipe. Depends on the time (t) that is used and the length (L) and height (H) of the isopipe. That is,
D = k · (dε / dt) · L ⁴ / H ² · t
Here, k is a constant.

  As is apparent from this equation, when the length of the isopipe is doubled, the amount of deflection increases 16 times for the same isopipe material, height, and usage time.

  This increase in deflection may be addressed by an increase in isopipe height. However, the height of the isopipe has already reached near the basic limits of the isoppress equipment currently available in the industry. Another improvement is to apply a compressive force on both sides of the isopipe to counter creep (see US 2003/0192349 by the applicant). It can impose significant constraints on the structure, resulting in glass flow rates that are lower than desired target values. Lowering the overall operating temperature is another possibility, but would require the development of new glass compositions that can be processed at lower temperatures. Finally, it is possible to reduce the creep rate of the ceramic material used for isopipe production through the development of an improved material (WO 2002/044102 by the applicant). However, even in this case, future substrate sizes and isopipe structures may continue to fall into an area where ceramic materials cannot get a sufficiently long usable life.

  As mentioned above, the hottest part of the isopipe during operation is usually both weirs. For example, the creep rate of zircon refractories increases with temperature (as well as other high temperature refractories) as described in the above-mentioned WO 2002/044102. Therefore, both weirs should exhibit the highest creep rate compared to the isopipe body.

  In addition, during use, both weirs receive not only a downward force due to gravity, but also an outward force (expansion force) due to the molten glass contained in the trough of the isopipe. In addition to these two forces, both weirs have a much thinner thickness than the body of the isopipe, so both weirs will suffer dimensional instability over time.

  One possible measure to overcome this dimensional change is to use a thicker weir. However, this method results in a serious constraint on the structure of the isopipe that the glass flow rate may be below the desired target value.

  Various measures have been taken to reduce drooping of the isopipe through the use of support rods and holes in the isopipe body. See U.S. Pat. No. 3,437,470, JP-A-11-246230, JP-A-2006-298736, JP-A-2006-321708, and JP-A-2007-197303. It should be noted that all of these references are 1) higher operating temperatures where both weirs are normally exposed, 2) both weirs undergo both vertical and horizontal deformation forces, 3) As a result of the reduced thickness of both weirs compared to the other parts of the isopipe, there was no improvement in the dimensional change of both weirs. Similarly, none of these citations provided a solution to this problem.

  The present invention specifically addresses the problem of weir instability by providing at least one opening within each weir. As an initial effect, the opening reduces the weight of the weir and thus the load that causes drooping on the associated weir.

  Further, in some embodiments, the opening is used to reduce the internal temperature of the ceramic material that forms the weir. For example, a controlled temperature fluid that is lower than the nominal temperature of the weir is allowed to pass through the opening at a controlled flow rate. As shown below, even relatively small changes in the temperature of the material forming the weir can 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 or a liquid such as water, provided that molybdenum is not exposed to the non-inert gas if molybdenum is used. it can. A gas or liquid mixture can be used as required. Depending on the application, liquid may be more effective than gas because of its higher heat capacity.

  The fluid can pass through the opening in either direction, and the inlet end where the molten glass flows into the isopipe is generally hotter than the opposite end, so in some cases the isopipe It may be desirable to flow fluid starting from the inlet end. If the fluid absorbs more heat from the inlet end, the temperature gradient along the weir can be reduced, thus helping to control the glass flow. Also, flowing the fluid from the inlet end side of the opening helps to reduce the temperature of the molten glass at the inlet, which may be desirable depending on the application. The fluid may form a manifold that passes through the opening using a heat exchanger structure. For example, the fluid may be introduced into a tube having a central hole connected to a surrounding annular body. For example, the fluid may pass through the central hole and return through the annular body. In this way, heat can be transferred to the fluid more efficiently. Alternatively, fluid can first pass through the annulus and then pass through the central hole. Of course, more complex heat exchanger structures can be used if desired.

  In another embodiment, the opening is used to accommodate a structural member made of a material that has a lower creep rate than the material making up the weir. This structural member may be solid and may completely block the section of the opening or may partially block it. In the latter case, the opening is not blocked, for example, by flowing fluid over the unblocked portion of the opening, and thus through the exposed surface of the inner wall of the structural member and isopipe. A portion is used to cool both the structural member and the interior of the weir.

  In further embodiments, the structural member is hollow and its outer cylinder may completely or partially block the opening. In any case, the hollow portion of the structural member can be used for cooling, for example, by allowing fluid to pass through the inside of the structural member. If the outer cylinder of the hollow structural member covers only a part of the cross section of the opening, an unblocked part of the cross section of the opening can also be used for cooling.

  For example, when cooling fluid is allowed to pass through the heat exchanger structure, an opening with one or both ends closed may be used in the practice of the invention, but the opening is usually the length of the weir. It extends through the entire length. The structural member can be housed inside the weir, or can extend out of the weir and engage the support structure at one end, preferably at both ends.

  In addition to the openings (with or without structural members) in each weir, the isopipe comprises one or more openings below the body of the isopipe, i.e. below the levels of both weirs. be able to. Similar to the openings formed in the two weirs, the openings formed in the main body can accommodate structural members that completely or partially block the openings. Similarly to the openings in both weirs, the openings in the main body can also be used for internal cooling of the isopipe to reduce the creep rate of the material constituting the isopipe.

  Both isopipe weirs and openings in the body (if used) can be drilled into the isopipe, or preferably the material from which the isopipe is formed, using a centering drill, or You may form from the beginning at the time of manufacture of a raw material.

  The usual process for manufacturing ceramic materials for isopipe is a multi-step process. For example, a batch material consisting of zircon with addition of binder or other ceramic material can be prepared, for example, by spray drying. These batch materials are then placed in a flexible bag and vibrated to allow particle hardening and to achieve initial compaction. The bag is then hermetically sealed and placed in a cold equilibrium press to more fully compact the structure. The compacted structure is then fired at a high temperature to form a dense ceramic.

  This type of process involves placing a rod of graphite or a solid or foamed natural or synthetic polymer or other combustible material in a balanced press bag and operating it as a mandrel. Can be modified to produce an opening. The batch is then poured around the rod and vibrated to allow the batch particles to become a more compacted structure. The bag is then hermetically sealed and balanced pressed. The compacted batch and rod are then placed in a furnace where the rod is first burned out and then sintered at a high temperature. In another process, the batch of binder is first burned and then the tissue is pre-sintered. After cooling to room temperature, the rod is removed from the material and then sintered at high temperature.

  The opening can have various sizes, for example ranging from a few millimeters to a few inches for a 10th generation isopipe. If the purpose of the opening is to cool the interior of the isopipe by passing a fluid through the opening, generally a smaller opening is used. As mentioned above, this fluid flow provides a means to extract heat from the interior of the isopipe, thereby reducing the temperature inside and reducing material creep. Even small changes in temperature can significantly reduce the creep level in the isopipe. For example, as shown in Table 2, for zircon, when the temperature is reduced from 1250 ° C. to 1180 ° C., the creep rate is reduced by about 50%. The amount of fluid flow required depends on the heat capacity of the fluid, the temperature of the fluid, the desired internal temperature drop, and the isopipe specification dimensions. The flow rate for a specific application can be readily determined based on this specification by those skilled in the art.

As described above, in some embodiments, the opening can comprise a structural member. These structural members are preferably made of a material that has less creep than the material used for the isopipe. For example, an isopipe made of zircon can be made of Al ₂ O ₃ , SiN, SiC, molybdenum, or a fiber reinforced structure material. In the case of a molybdenum rod, it is preferred that the rod be clad or covered with platinum in an inert atmosphere such as N ₂ to reduce oxidation. These materials can exhibit very low creep even at 1250 ° C., and therefore can provide additional support for an isopipe made of zircon or other refractory in operation.

  Among the many benefits provided by the present invention is the ability to continue to use proven materials such as zircon in the manufacture of LCD substrates. Such materials are known to be compatible with glass compositions that have been upgraded by display manufacturers. The present invention also extends the area of design for isopipe. For example, an isopipe with a reduced height can be produced without affecting the sag. Lowering the height helps to reduce the chance of forming secondary crystals as described in Applicant's allowed WO 03/055813.

  While not intending to be limited to any aspect, the invention is further described by the exemplary embodiments of FIGS.

  FIG. 2 shows an embodiment in which an opening 35 is adopted in the weirs 1 and 2 and an opening 43 is adopted in the main body of the isopipe. The opening 35 in the weirs 1 and 2 is completely blocked by the structural members 41 and 42, respectively, and the opening 43 is completely blocked by the structural member 45.

  FIG. 3 shows a variation of FIG. The openings 35 in the weirs 1 and 2 are connected to each other by a further opening 37 that is closed with a structural member in the same manner as the openings 35. This embodiment has an opening 43 having a circular shape instead of the rectangular shape as shown in FIG.

  FIG. 4 shows an embodiment suitable for use in cooling the interior of an isopipe. This embodiment employs five relatively small openings, two of which, i.e., opening 35, are located in the weir, and three, i.e., opening 43, are located in the body of the isopipe. ing.

  FIG. 5 shows a variation of FIG. 4 and again employs an opening suitable for cooling. This embodiment employs a relatively large opening 43 in the body of the isopipe and an elliptical opening 35 in the weirs 1 and 2.

  FIG. 6 shows a variation of FIG. 5 in which structural members 41 and 42 are introduced into the opening 35 and structural member 45 is introduced into the opening 43. The cooling fluid can be allowed to pass through the unblocked portion of the opening, or only the structural member can be used to reduce the sag of the isopipe.

  7 and 8 illustrate the use of an oval hollow structural member as shown. Using a hollow structural member has the effect of reducing the weight of the structural member. Also, if necessary, the cooling fluid can be passed through the central part of the structural member. It should be noted that the hollow portion of the structural member constitutes the portion where the opening is not blocked, even though the outer cylinder of the structural member blocks the opening.

From the foregoing description, various modifications will be apparent to those skilled in the art without departing from the scope and spirit of the invention. For example, while the present invention has been described with respect to an isopipe with a weir having vertical sides, the present invention includes, for example, the isopipe outer surface at the upper end of the isopipe wedge-shaped portion with corners. It can also be applied to an isopipe having a V-shaped or Y-shaped cross section. Similarly, although an integral isopipe is shown in FIGS. 2-8, an isopipe constructed from two or more separate elements (which may be the same or different materials) is also contemplated by the present invention. It can be used for implementation. The following claims are intended to cover not only the exemplary embodiments described herein, but also variations, modifications, and equivalents of these and other forms.

Claims (6)

A first portion comprising a trough and a weir formed of first and second ceramic materials each having an inner surface, a top surface and an outer surface;
A second portion having a first outer surface that is an extension of the outer surface of the first weir and a second outer surface that is an extension of the outer surface of the second weir, the first and first Two outer surfaces, wherein the second portion is directed towards the other side so that at least a portion of the second portion has a wedge-shaped cross-section; and
An apparatus for forming a strip glass by a fusion method, comprising:
Each of the weirs has an opening, the opening being
(B) extending along at least a portion of the length of the weir; and (b) at least a portion of the opening is disposed between the inner surface and the outer surface of the weir through the ceramic material of the weir. A device characterized by that. Wherein the opening of the first and second weirs, according to claim 1 Symbol placement device, characterized in that it is connected by a further opening lies below the trough. The apparatus further comprises first and second structural members, wherein the first structural member is disposed within an opening of the first weir, and the second structural member is of the second weir. that is disposed within the opening claim 1 Symbol mounting apparatus characterized by. Said first and second structural members are at the operating temperature of the device, according to claim 3, characterized in that it is composed of a material exhibiting less creep than the creep exhibited by the material which the dam is constructed The device described. 4. An apparatus according to claim 3 , wherein the structural member is hollow. It said first and second portions, according to claim 1 Symbol mounting apparatus characterized in that it is a part of the unity of the material.

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