TWI395718B - Temperature control of glass fusion by electromagnetic radiation - Google Patents

Description

Temperature control of glass fusion by electromagnetic radiation

The present invention relates to systems and methods for forming glass sheets. More particularly, the system and method provide as a delivery system for thermal control of use in a glass sheet forming process.

In recent years, considerable attention has been focused on the demand for flat glass in a variety of applications, including LCD applications. There are many efforts to reduce defects and/or defects in the glass sheet. Devitrification (crystal growth in glass) is a common problem affecting the quality of glass sheets.

Conventional methods for making glass sheets include: down-draw fusion methods (e.g., using isopipes), float methods, rolling methods, and the like. In each of the methods, the molten glass matrix material generally flows over the refractory body in the glass sheet manufacturing process. However, the liquidus viscosity coefficient of the glass matrix material limits the range of constituents of the glass that can be made by conventional fusion methods. Liquid crystal viscosities of LCD glass that can be made by conventional fusion methods must be greater than about 500,000 poises (and closer to 1,000,000 poises for 2000-series glasses). In general, glass matrix materials having a liquidus viscosity coefficient of less than 500,000 poises are currently not available for the manufacture of high quality glass sheets because devitrification occurs during the manufacturing process.

The "liquid phase" has two parts, which are the initiation of nucleation and the rate of crystal growth. Nucleation can occur on the surface of the refractory material, in the refractory material - glass The glass interface (non-homogeneous nucleation), and the behavior of nucleation is mainly governed by surface roughness and local compositional changes at the interface. Homogeneous nucleation (in bulk glass, not at the interface) is usually subcooled, below the liquidus ΔT, up to a specific temperature at which the viscosity coefficient is quite high so that the atoms are not Will move to form a crystal nucleus. The rate of crystal growth is usually greatest at temperatures just below the liquidus temperature, and gradually decreases as the mobility of the atoms decreases.

Although not completely devitrification of the glass, another crystallization problem that occurs is secondary zircon. This problem is easily caused by the use of a glass plate made of a refractory body containing zircon. During the high temperature period of the manufacturing process, the zircon or zircon dissolved in the glass will precipitate as a small zircon needle in the lower temperature stage of the treatment and be added to the glass sheet to become a defect. This process may occur for any refractory component which has a reduced solubility in the glass at lower temperatures and is not necessarily limited to the zircon composition.

Therefore, in this regard we need systems and methods for making glass sheets that are thermally controlled by the glass delivery system to reduce devitrification and secondary zircon effects in the glass during the manufacturing process.

The present invention provides systems and methods for making glass sheets. More specifically, the system is provided to include a refractory body configured to receive a glass matrix material such as, but not limited to, molten glass. The system further includes emitting energy through the glass substrate material to selectively heat at least a portion of the refractory body means. In one aspect, the emitted energy is a selected frequency that is not fully absorbed by the glass matrix material and at least partially absorbed by the refractory body.

In use, the method includes providing a refractory body configured to receive a glass matrix material and passing the glass matrix material to transfer energy to at least a portion of the refractory body to heat the refractory body of the portion.

Other features and advantages of the invention will be apparent from the description and appended claims. The prior general description and the following detailed description are to be considered as illustrative and illustrative and not restrictive.

The invention is disclosed in the preferred embodiments of the present invention as the best mode disclosed. In this regard, it is well known to those skilled in the art that the various embodiments described herein can be made in many variations and still benefit from the invention. Some of the advantages required by the present invention can be achieved by selecting some of the features of the present invention without the need to use other features. Thus, it is apparent to those skilled in the art that many variations and modifications of the invention are possible, and in many cases are required and part of the invention. Accordingly, the following description is provided to illustrate the principles of the invention

In the specification and claims, the singular singular Isostatic pressure The tube contains two or more isostatic tubes unless otherwise clearly indicated.

The "zircon material" as used herein, unless specifically stated otherwise, represents a zircon composition comprising zircon (zirconium silicate). According to various aspects, the zircon material is suitable for forming a refractory ceramic body, such as an isostatic tube. The zircon material, if present, can be provided in any suitable form such as a solid or powder.

Ranges may be expressed herein as "about" a particular value, and/or to "about" another particular value. When such a range occurs, it is meant that another embodiment encompasses a particular value recited and/or to another particular value. Similarly, when "about" is used to mean an approximation of a value, it is understood that the particular value also forms another embodiment. It is further understood that the end point of each range is quite related to the other end point, but independent of each other.

As briefly summarized above, the present invention provides systems and methods for making glass sheets. In order to reduce the development of defects in the glass, for example by devitrification or secondary zircon precipitation, these systems and methods control the thermal properties of the glass transport system used in the glass sheet manufacturing process. As will be further described below, rapid cooling of the glass is allowed to flow downstream of the transport system by maintaining the transport system at a sufficiently high temperature. By rapidly cooling the glass, it is possible to reduce the time it takes for the glass to spend in the high growth rate temperature zone of crystallization. Likewise, the deposition of zircon, such as zircon material, can be controlled by heating the transport system to reduce the thermal gradient of the entire transport system.

In one aspect, the system includes a refractory body configured to receive a glass substrate material. In one aspect, the glass substrate material can be molten glass. The refractory body contains a distal portion located downstream of the passage of the glass matrix material. According to several aspects, the refractory body comprises a zircon refractory material.

Referring to Figure 1, this refractory body can be used in one aspect in the rolling process for making glass sheets. In this regard, the refractory body 107 slopes downwardly with the distal portion being lower than the proximal portion opposite the refractory body. When the glass substrate 111 flows downstream from the distal end portion, it is at least pulled by a pair of rollers 115 to form a glass sheet.

Alternatively, the refractory body can be used in a floating process for making glass sheets. As shown in Figure 2, at least a portion of the refractory body 207 is sloped downwardly such that the distal end portion is lower than at least a portion of the refractory body. The molten glass substrate 111 is transported onto a liquid metal (e.g., tin) bath 219 as it flows downstream from the distal portion.

On the other hand, the isopipe 301 containing the refractory body 307 can be passed through a down draw fusion process to produce a glass sheet, as shown in FIG. The hydrostatic tubes can include an upper portion defining the trough 305 through the supply tube 303 to receive the molten glass matrix material 111. The isostatic tube contains a relatively lower portion that tapers to the root 309 of the isostatic tube. Thus, the distal end portion of the refractory body contains the root. The molten glass substrate 111 is received into the trough and overflows across the top end of the trough so that two downwardly flowing sheets of glass are formed and then inward along the outer surface of the isopipe. The two sheets meet at the root 309 of the isostatic tube where they melt together to form a single sheet. This single sheet is then fed into the drawing device (represented by flow arrow 313), such as a roller, by pulling the sheet away from the root. Rate to control the thickness of the sheet.

In a further aspect, the system includes emitting a portion of the distal portion selectively by emitting energy through the glass substrate material. For example, Figures 1 and 2 show energy application zones (117 and 217, respectively)), near the point where the molten glass exits the respective refractory body. Similarly, the energy transfer method can be used to heat the vicinity of the root of the isostatic tube, as shown in Figure 4-7. In a particular aspect, the emitted energy is a selected frequency that is not fully absorbed by the molten glass matrix material and at least a portion is absorbed by the distal end portion of the refractory body.

There are several methods that can be used to emit energy to selectively heat the distal end portion of the refractory body. In one aspect, a radio frequency (RF) generator can be used. The conveyor system and control system can be used in conjunction with a radio frequency generator to direct energy to the distal portion of the refractory body. The delivery system can include two or more pairs of parallel bars that run parallel to the distal end portions of the respective refractory bodies to emit energy through the molten glass matrix material. For example, referring to Figure 3, pairs of parallel bars 430 can be placed on each side of the root of isostatic tube 301, running parallel to the root, creating a stray field 433 on either side of the root. Alternatively, the launching system can include a parallel plate 535 that runs along at least a portion of the distal end portion, such as the root length of the isostatic tube 301, as shown in FIG. As such, the radio frequency can be transmitted fairly evenly along the length of the distal end portion of the refractory body. In a further aspect, the plate or rod that produces the radio frequency can act as a heat sink to remove heat from the glass matrix material flowing along the refractory body.

In another aspect, a microwave generator can be used to heat the distal end portion of the refractory body. The microwave generator can be coupled to the appropriate control system A waveguide, such as a slotted waveguide, or a horn antenna. The placement of this waveguide can direct microwave energy to the distal portion of the refractory body. For example, as shown in FIG. 6, a microwave generator 637 coupled to the waveguide 639 can be placed on each side of the root of the isostatic tube 301. The microwave generator can direct microwave energy to a negatively inclined portion near the root of the isostatic tube. In a further aspect, the waveguide can be at least partially metal-containing (such as, but not limited to, foil-coated ceramic) as a heat sink to remove heat from the glass matrix material flowing along the refractory body.

Optionally, one or more heat sinks 661 can be placed downstream of the microwave generator for removing heat from the glass matrix material.

Lasers can also be used to selectively heat the distal portion of the refractory body. For example, at least one laser beam can be directed to the distal portion. The wavelength band of this laser beam can be in the near infrared range, such as 780-11000 nm. Alternatively, the wavelength band of the laser beam can be in the visible range, such as 380-780 nm. In one aspect, the laser array can be placed along the length of the distal portion. For example, referring to FIG. 7, laser array 721 includes a plurality of lasers 723 that can be placed substantially parallel to the root adjacent the root of isostatic tube 301. The laser beam 725 produced by each laser can be directed to the distal portion of the isostatic tube. Although only one side of the root is shown in the figure, it is conceivable that a similar array of lasers can be placed on the other side of the root.

As shown in Figure 8, the scanning laser 823 can also be used to selectively heat the distal end portion of the refractory body, such as the isostatic tube 301. The beam can be scanned along the length of the distal portion. In one aspect, the laser directs the laser beam 825a to a reflective surface 827, such as a mirror, which can be selectively moved or placed to change the directivity of the reflected beam 825b. The residence time of the beam at any point in the refractory body determines the local temperature rise. In a particular aspect, a pulsed near-infrared laser such as Nd:YAG or Nd:YVO _{4 can be} used as the scanning laser. As shown in Figure 8, the laser can be configured to scan at least a portion (represented by a) of the length of the distal portion of the isostatic tube 301. As described with reference to Figure 8, although the scanning laser mechanism shown in Figure 4 is only along one side of the root of the isostatic tube, it is envisioned that a similar scanning laser mechanism can be placed on the opposite side of the root.

In one aspect, the emitted energy is in the range of from about 300 to about 200,000 MHz, such as the microwave range. Alternatively, the emitted energy can range from 3 to about 300 MHz, such as in the radio frequency range. In yet another aspect, the energy emission mode is configured such that the frequency of the emitted energy is sufficient to heat the temperature of a portion of the distal region to a temperature above the liquidus temperature of the glass matrix material flowing through the distal portion.

According to several aspects, the system further includes a heat sink for drawing heat from the glass substrate material. The heat sink can be placed downstream of the distal portion, although it is also contemplated to place the heat sink anywhere along the fluid flow path to selectively draw heat from the glass substrate material. In a particular aspect, the heat sink is placed downstream but near the distal end portion. For example, as shown in Figure 6, one or more heat sinks 661 can be placed downstream of the root of the isostatic tube to draw heat therefrom as the glass substrate material flows away or pulls away from the root. As described herein, various system components can be considered as a heat sink at the same time, such as but not limited to radio frequency plates or rods, waves Guide, or other system components.

In use, methods are provided for making glass sheets. The method comprises, in one aspect, providing a refractory body configured to receive a glass matrix material and to emit energy to heat at least a portion of the refractory body. As described above, the refractory body can include a distal portion located downstream of the passage of the glass matrix material. Such refractory bodies can be included in rolling, floating, down draw fusion processes (e.g., isostatic tubes containing tapered roots), and those used in other known glass sheet manufacturing processes. Alternatively, the methods described herein can be used in glass-forming processes, including glass filling or continuous flow (tubular or rod-like drawing, etc.). In one aspect, the refractory body further comprises a zircon refractory material.

In one aspect, the method includes passing the glass substrate material to transfer energy to at least a portion of the distal end portion of the refractory body to heat the portion. The energy emitted may be that the selected frequency is not completely absorbed by the glass matrix material and at least partially absorbed by the distal portion. As described above, the glass matrix material has a liquidus temperature. Emiting energy to the refractory body means transferring sufficient energy to heat the temperature of a portion of the refractory body above the liquidus temperature of the glass substrate. By maintaining at least the distal end portion of the refractory body above the liquidus temperature, the glass can be rapidly cooled downstream of the distal portion to below the liquidus temperature, thereby controlling the devitrification.

Energy can be transmitted in several ways, including microwave generators, RF generators, laser arrays, scanning lasers, or other methods described herein. The transmitted energy can range from about 300 to about 200,000 MHz (ie, microwave energy), or about 3 to about The frequency range of 300MHz (that is, RF energy). Alternatively, lasers operating at any wavelength can be used to generate energy, including those having discrete wavelengths, or wavelength bands in the visible or near infrared range.

The method can further include providing a heat sink at one or more predetermined locations along the fluid flow path. In one aspect, the method includes providing a heat sink downstream of the distal portion. This heat sink can be used to extract heat from the glass substrate. In one aspect, this can assist in rapid cooling of the glass substrate as it exits the refractory body from near the distal end portion. It is also possible to provide a method of pulling the glass matrix material away from the distal end portion of the refractory body. As described above, it may be considered to place the heat sink upstream of the fluid flow path, including upstream of the distal end portion.

It is to be understood that the invention has been described herein with reference to the particular embodiments of the invention, and the invention is not limited by the scope of the invention.

example:

In order to further illustrate the principles of the present invention, the following examples are disclosed to provide a thorough understanding of the subject matter and the method of the invention. These examples are intended to be merely exemplary of the invention and are not intended to limit the scope of the invention. Attempts have been made to ensure number accuracy (eg, quantity, temperature, etc.), but it creates some errors and deviations. Unless otherwise stated, the temperature is in °C or at room temperature, and the pressure is at or near atmospheric temperature.

We conducted a test to determine the similarity of EAGLE ²⁰⁰⁰ F glass and various properties of zircon materials. The setup of the test is shown in Figure 9. As can be seen, the zircon material sample 955 is placed in a mixing oven 941 using a MoSi ₂ resistive heating element 949 and a microwave or RF generator 951 to generate energy at various frequencies. At the same time, a microwave or radio frequency modal mixer 953 is provided for modulating their resonant frequencies during modal movement, producing an effective modality at the outer edge of the spectrum. The modal mixer can also be continuously coupled into the existing field as a secondary antenna within the oven and re-radiation secondary mode that changes with rotation. A modal mixer is used to heat the material more evenly. A MoSi ₂ resistance heating element was used to lift the sample to 900 °C. Ambient thermocouple 947, glass sample thermocouple 943 and zircon material sample thermocouple 945 are also provided as temperature sensors. The MoSi ₂ resistive heating element 949 is then set to a manual (fixed percentage output) mode such that any rise in temperature in the sample is from microwave or radio frequency heating. Glass sample 957 and zircon material sample 955 were performed in separate successive tests. Figure 10 shows that the results of this test show that the zircon material (10.3, 10.7) increases in temperature with energy input, which is larger than glass (10.1, 10.5), but both materials are heated.

We have also conducted other tests to determine the various properties of zircon materials relative to EAGLE ²⁰⁰⁰ F glass as a function of frequency and temperature. Figure 11 shows the differential dielectric constant (ε') of zircon material versus EAGLE ²⁰⁰⁰ F glass as a function of frequency and temperature. As can be seen from the figure, this difference increases the most at 54 MHz. Figure 12 shows the differential dielectric loss (ε" of zircon material versus EAGLE ²⁰⁰⁰ F glass as a function of frequency and temperature. This difference is fairly fixed at 912 MHz and 2460 MHz, with only a slight increase as temperature increases. At 54 MHz, this difference increases steadily as the temperature increases by more than about 400 °C.

Figure 13 shows the half power penetration depth, in centimeters, of zircon material relative to EAGLE ²⁰⁰⁰ F glass (13.7) as a function of frequency and temperature. The frequency tested was 54 MHz (zircon material: 13.1, glass: 13.2), 912 MHz (zircon material: 13.3, glass: 13.4), and 2460 MHz (zircon material: 13.5, glass: 13.6). Both materials are quite transparent, so energy can penetrate the glass adjacent to the refractory body and into the refractory body. Figure 13 shows that the RF frequency penetration depth at 54 MHz is greater than the two microwave frequencies (912 MHz and 2460 MHz).

Figure 14 shows the loss tangent of zircon material relative to EAGLE ²⁰⁰⁰ FF glass as a function of frequency and temperature. The test frequency was 54 MHz (zircon material: 14.1, glass: 14.2), 912 MHz (zircon material: 14.3, glass: 14.4) and 2460 MHz (zircon material: 14.5, glass: 14.6). Above 0.01, it is possible to heat these materials, and at 0.1 or more these materials are likely to be heated.

We determined that the energy absorption of the zircon material of the isostatic tube increases with decreasing frequency, as can be seen in the figure. The energy absorption of zircon materials decreases with increasing temperature. We have also observed that when the absorption of glass and zircon material is equal, the glass moves to remove a portion of the energy, while the zircon material loses its absorbed energy due to heat conduction to the glass layer and radiation from the glass interface. . Compared to the glass layer, this usually causes the isostatic tube to heat up. Therefore, a lower cost, and a smaller 2450 MHz microwave device with a relatively small waveguide can be used, Rather than a lower frequency device with a greater difference in characteristics between the glass and the isopipe. These waveguides can be water-cooled metals, which can be used as a heat sink to remove additional heat from the glass.

Overall, we found that the EAGLE ²⁰⁰⁰ F glass and zircon materials are sufficiently different at typical root temperatures that the zircon material absorbs more energy than the glass. In this way, the temperature of the isostatic tube, in particular at the isostatic tube-glass interface, can be maintained at a temperature above the devitrification of the glass, allowing the entire piece of glass to be cooled downstream of the isopipe Below the liquidus temperature.

107, 207, 307‧ ‧ refractory subjects

111‧‧‧glass base material

115‧‧‧Roller

117, 217‧‧‧ energy application area

219‧‧‧Liquid metal bath

301‧‧‧Isostatic tube

303‧‧‧Supply tube

305‧‧‧ slot

309‧‧‧Isostatic tube root

313‧‧‧ Flowing arrows

430‧‧‧ parallel bars

433‧‧‧Strange field

535‧‧ ‧ parallel board

637‧‧‧Microwave Generator

639‧‧‧Band

661‧‧‧ radiator

721‧‧‧Laser array

723‧‧‧Laser

725‧‧‧Laser beam

823‧‧‧Scanning laser

825a‧‧‧Laser beam

825b‧‧· reflected beam

827‧‧‧Reflective surface

941‧‧‧Mixed oven

943‧‧‧glass sample thermocouple

945‧‧‧Zircon material sample thermocouple

947‧‧‧Environmental thermocouple

949‧‧‧resistive heating element

951‧‧‧Microwave or RF generator

953‧‧‧modal mixer

955‧‧‧Zircon material sample

957‧‧‧glass specimen

Figure 1 shows an exemplary system for rolling a glass sheet.

Figure 2 shows an exemplary system for forming a glass sheet using a floating process.

Figure 3 shows an exemplary system with isostatic tubes for forming a glass sheet using a down draw fusion process.

4 shows an exemplary system in accordance with the present invention comprising a 40 MHz RF stray field configured to heat an isostatic tube root refractory material through a wall of molten glass flowing through an isostatic tube.

5 shows an exemplary system in accordance with another aspect of the present invention comprising a 40 MHz parallel plate RF configured to heat an isostatic tube root refractory material through a wall of molten glass flowing through an isostatic tube.

Figure 6 shows an exemplary system in accordance with one embodiment of the present invention, including micro The wave generator is configured to heat the isostatic tube root refractory material through the wall of the isostatic tube through the molten glass.

Figure 7 shows an exemplary overflow down draw fusion system forming a glass sheet comprising an isostatic tube having a root and a laser array for flow through both sides of the isostatic tube via molten glass (not shown) Heat the root refractory.

Figure 8 shows an exemplary overflow down draw fusion system for forming a glass sheet comprising an isostatic tube having a root and a scanning laser for flow through the isostatic tube via molten glass (not shown) Heat the root refractory.

Figure 9 shows a schematic of a test apparatus at 2450 MHz and 900 °C in accordance with the present invention comprising a similar volume of Eagle ²⁰⁰⁰ F glass and a zircon material in a hybrid high temperature furnace using MoSi2 resistive heating elements and microwave RF energy.

Figure 10 shows the results of the test at 2450 MHz and 900 °C using a similar volume of Eagle ²⁰⁰⁰ F glass and zircon material in the test apparatus of Figure 8.

Figure 11 is a graph of the differential dielectric constant (ε') of zircon material versus Eagle ²⁰⁰⁰ F glass as a function of frequency and temperature.

Figure 12 is a plot of zircon material versus differential dielectric loss (ε") for Eagle ²⁰⁰⁰ F glass as a function of frequency and temperature.

Figure 13 is a half-power penetration depth of zircon material relative to Eagle ²⁰⁰⁰ F glass as a function of frequency and temperature.

Figure 14 shows the loss tangent of zircon material and Eagle ²⁰⁰⁰ F glass as a function of frequency and temperature.

107‧‧‧Refractory body

111‧‧‧glass base material

115‧‧‧Roller

117‧‧‧Energy application area

Claims (18)

A system for forming a plurality of glass sheets, the system comprising: a refractory body configured to receive a molten glass matrix material, and the refractory body comprising a distal portion through which the glass substrate material passes downstream Means for emitting energy for selectively heating a plurality of portions of the distal portion via the glass matrix material, wherein the emitted energy is a selected frequency, the energy of the selected frequency being not completely encapsulated by the molten glass matrix material Absorbing and at least partially absorbed by the refractory body, wherein the glass matrix material has a liquidus temperature, and wherein the means for emitting energy is configured to heat portions of the distal portion to a level higher than the glass matrix material The temperature of the liquidus temperature. The system of claim 1, wherein the means for emitting energy is selected from the group consisting of a laser beam array, a scanning laser beam, a microwave generator, and a radio frequency generator. A system according to claim 1 wherein the energy of the emission is in the range of 300 to 200,000 MHz. A system according to claim 1 wherein the energy of the emission is in the range of 3 to 300 MHz. The system of claim 1, wherein the refractory body comprises an isostatic tube, and wherein the distal portion of the refractory body comprises a tapered root. The system of claim 1 further comprising a heat sink configured to remove heat from the glass substrate material. A system according to claim 6 wherein the heat sink is located downstream of the distal portion. The system of claim 1 further comprising means for pulling the glass substrate away from the distal portion. A system according to the first aspect of the invention, wherein the refractory body comprises a zircon refractory material. A method of forming a plurality of glass sheets, the method comprising: providing a refractory body configured to receive a molten glass base material, and the refractory body includes a distal end portion through which the glass base material passes Downstream; emitting energy to pass at least a first portion of the distal portion through the glass substrate material to heat at least the first portion of the distal portion, wherein the emitted energy is a selected frequency, the energy of the selected frequency is not The molten glass matrix material is completely absorbed and at least partially Body absorption, wherein the glass matrix material has a liquidus temperature, and wherein the step of emitting energy to the at least first portion comprises emitting a quantity of energy sufficient to heat the first portion to a higher than the glass substrate The temperature of the liquidus temperature of the material. The method of claim 10, wherein the refractory body comprises an isostatic tube, wherein the distal portion of the refractory body comprises a tapered root. The method of claim 10, wherein the step of emitting energy comprises transmitting microwave energy having a frequency in the range of 300 to 200,000 MHz. The method of claim 10, wherein the step of emitting energy comprises transmitting radio frequency energy having a frequency in the range of 3 to 300 MHz. The method of claim 10, wherein the step of emitting energy comprises directing at least one laser beam to the first portion of the distal portion, wherein a wavelength band of the laser beam is in the near infrared range. The method of claim 10, wherein the step of emitting energy comprises directing at least one laser beam to the first portion of the distal portion, wherein a wavelength band of the laser beam is in the visible range. The method of claim 10, further comprising providing a heat sink downstream of the distal portion, wherein the heat sink is configured to remove heat from the glass substrate material. The method of claim 10, further comprising providing means for drawing the glass substrate away from the distal portion. The method of claim 10, wherein the refractory body comprises a zircon refractory material.