JP2014047124A - Glass substrate manufacturing method, and glass substrate manufacturing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glass substrate manufacturing method capable of restraining foreign matters from being mixed with molten glass in a step of clarifying the molten glass, and a glass substrate manufacturing device.SOLUTION: The glass substrate manufacturing method includes a melting step, a clarification step, and a molding step. In the clarification step, molten glass G flows inside a platinum or platinum alloy clarification pipe 41 to form a vapor phase space 41c. The vapor phase space 41c is a space above a liquid surface LS of the molten glass G inside the clarification pipe 41. The clarification pipe 41 has a vent pipe 41a projecting outward from an outer wall of the clarification pipe 41, and a receiving part 41d provided above the liquid surface LS of the molten glass G. The vent pipe 41a communicates the vapor phase space 41c with an external space of the clarification pipe 41. The receiving part 41d covers one part of a cross section of the vent pipe 41a when the vent pipe 41a is seen in a longitudinal direction of the vent pipe 41a.

Description

  The present invention relates to a glass substrate manufacturing method and a glass substrate manufacturing apparatus.

In general, as described in Patent Document 1 (Japanese Translation of PCT International Publication No. 2006-522001), a glass substrate manufacturing method includes a melting step of heating a glass raw material to generate a molten glass, and a glass from the molten glass. A molding process for molding the substrate. The method for producing a glass substrate further includes a refining step for removing minute bubbles contained in the molten glass between the melting step and the forming step. In the clarification step, bubbles in the molten glass are removed by an oxidation-reduction reaction of the clarifier by passing the molten glass containing a clarifier such as As ₂ O ₃ through a high-temperature clarifier tube. Specifically, first, by raising the temperature of the molten glass and causing the fining agent to function, bubbles contained in the molten glass are floated and removed on the liquid surface of the molten glass in the clarification tube. Next, the temperature of the molten glass is lowered, and fine bubbles remaining in the molten glass are absorbed by the molten glass and removed. The refining tube through which the molten glass passes has a gas phase space between the upper inner wall surface and the liquid surface of the molten glass. The gas phase space communicates with outside air, which is an external space of the clarification tube, through a ventilation tube connected to the clarification tube.

  In order to mass-produce a high-quality glass substrate from high-temperature molten glass, it is desirable that foreign substances that cause defects in the glass substrate do not enter the molten glass. Therefore, the inner wall of the member in contact with the molten glass needs to be made of an appropriate material according to the temperature of the molten glass in contact with the member and the required quality of the glass substrate. A platinum group metal is usually used for the inner wall of the member that contacts the molten glass. Hereinafter, the “platinum group metal” means a metal composed of a single platinum group element and a metal alloy composed of a platinum group element. The platinum group elements are six elements of platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), osmium (Os) and iridium (Ir). Platinum group metals are expensive, but have a high melting point and excellent corrosion resistance against molten glass.

The temperature of the molten glass passing through the inside of the clarification tube varies depending on the composition of the glass substrate to be molded, and is 1000 ° C. to 1700 ° C. in the case of a glass substrate for a flat panel display (FPD). In recent years, SnO ₂ has been used as a refining agent instead of As ₂ O ₃ from the viewpoint of reducing environmental burden. SnO ₂ has a small refining effect as compared with As ₂ O _3, in order to obtain the same refining effect and As ₂ O ₃ is required to raise the temperature of the molten glass. Specifically, when using SnO ₂ as a fining agent, the temperature of the molten glass passing through the inside of the fining tube is set to 1500 ° C. to 1700 ° C.

In the method for producing a glass substrate using SnO ₂ as a fining agent, the inner wall of the fining tube is in contact with the high-temperature molten glass. Therefore, the platinum group metal gradually volatilizes from the inner wall of the clarification tube by using the clarification tube over a long period of time. This volatile matter is discharged together with bubbles in the molten glass to the outside air through the gas phase space of the clarification tube and the ventilation tube. However, the platinum group metal volatiles become supersaturated as the temperature drops in the process of being discharged to the outside air. Therefore, solidified volatiles are likely to deposit on the inner walls of the clarification tube and the ventilation tube. Hereinafter, the substance deposited on the inner wall of the clarification tube and the ventilation tube is referred to as “platinum foreign matter”. Since the inside of the ventilation pipe communicates with the outside air, the temperature tends to decrease, and platinum foreign matter is particularly likely to deposit on the inner wall of the ventilation pipe. When the platinum foreign matter grows with the passage of time, it may be peeled off by its own weight from the inner walls of the clarification tube and the aeration tube, and may fall onto the molten glass in the clarification tube. Further, when removing the platinum foreign matter deposited on the inner wall of the vent pipe, the platinum foreign matter may fall onto the molten glass in the clarification tube. And when a platinum foreign material mixes in molten glass, it will become difficult to mass-produce a high quality glass substrate.

  The objective of this invention is providing the manufacturing method of the glass substrate which can suppress that a foreign material mixes in molten glass in the clarification process of molten glass, and the manufacturing apparatus of a glass substrate.

  The method for producing a glass substrate according to the present invention includes a melting step for producing a molten glass by heating a glass raw material, a clarification step for clarifying the molten glass, a molding step for forming a glass substrate from the clarified molten glass, Is provided. In the clarification step, the molten glass flows through a platinum or platinum alloy clarification tube so that a gas phase space is formed. The gas phase space is a space above the liquid surface of the molten glass inside the clarification tube. The clarification tube has a ventilation tube protruding outward from the outer wall surface of the clarification tube and a receiving portion provided above the liquid surface of the molten glass. The vent pipe communicates the gas phase space and the external space of the clarification pipe. The receiving portion covers a part of the cross section of the vent pipe when the vent pipe is viewed along the longitudinal direction of the vent pipe.

  In the manufacturing method of the glass substrate which concerns on this invention, the molten glass produced | generated by heating a glass raw material is heated by passing the inside of a high temperature clarification pipe | tube. Inside the clarification tube, bubbles contained in the molten glass grow by absorbing oxygen generated by the reduction reaction of the clarifier mixed in the molten glass. The grown bubbles rise to the liquid surface of the molten glass, break up and disappear. The gas contained in the extinguished bubbles is released into the gas phase space in the clarification tube and is discharged from the clarification tube via the vent tube.

  In the method for producing a glass substrate according to the present invention, the clarification tube is made of platinum or a platinum alloy. Platinum or a platinum alloy has a high melting point and is excellent in corrosion resistance against molten glass, and is therefore suitable as a material for a fining tube that comes into contact with high-temperature molten glass. However, the platinum component gradually volatilizes from the inner wall of the clarification tube by using the clarification tube for a long period of time. Volatile materials including platinum are discharged from the clarification tube through the vent tube together with bubbles in the molten glass. Volatile substances including platinum are likely to be supersaturated when the temperature decreases in the process of passing through the vent pipe. Therefore, the solidified volatile matter may adhere to the inner wall of the vent pipe as platinum foreign matter.

  In the manufacturing method of the glass substrate which concerns on this invention, the receiving part is provided in the internal space of a vent pipe or the gaseous-phase space of a clarification pipe | tube. When the platinum foreign matter adhering to the inner wall of the vent pipe grows with the passage of time, it may be peeled off from the inner wall surface due to its own weight. Further, during the maintenance work of the clarification tube, there is a possibility that the platinum foreign matter falls when the platinum foreign matter is removed from the inner wall surface of the ventilation pipe. The receiving part receives platinum foreign matter that has been peeled off from the inner wall surface of the vent pipe. Therefore, the receiving part suppresses platinum foreign matter adhering to the inner wall of the vent pipe from being mixed into the molten glass.

  Moreover, it is preferable that a receiving part is provided below the part which has the temperature which the gas containing platinum which exists in gaseous-phase space solidifies in a vent pipe. In order to more effectively receive the platinum foreign matter that has been peeled off and dropped from the inner wall surface of the vent pipe, the receiving portion is preferably provided at a position through which the volatiles as hot as possible pass in the internal space of the vent pipe. That is, the receiving part is preferably provided at a position as close as possible to the gas phase space in the clarification tube.

Further, molten glass preferably contains SnO ₂ as a fining agent. The method of manufacturing a glass substrate using SnO ₂ as a fining agent, as compared with the case of using As ₂ O ₃ as a fining agent, it is necessary to raise the temperature of the molten glass passing through the interior of the finer tube. Therefore, when SnO ₂ is used as a clarifier, the platinum component is likely to volatilize from the inner wall of the clarifier tube, and platinum foreign matter tends to adhere to the inner wall of the vent tube. Therefore, method of manufacturing a glass substrate according to the present invention is suitable for manufacturing method of a glass substrate using SnO ₂ as a fining agent.

A method of manufacturing a glass substrate according to the present invention, molten glass having a temperature of more than 1500 ° C. If the viscosity is 10 ^2.5 poise, when refining a high molten glass viscosity at high temperature, it is suitable. A molten glass having a high high temperature viscosity needs to have a higher temperature in the refining process than a normal alkali glass molten glass. Therefore, the problem that the platinum component volatilizes from the inner wall of the clarification tube becomes prominent, and platinum foreign matters are likely to adhere to the inner wall of the ventilation tube.

  The manufacturing method of the glass substrate which concerns on this invention is suitable for the manufacturing method of the glass substrate using the molten glass which has a high high temperature viscosity, ie, the molten glass which needs to be made higher temperature than a normal molten glass in a refining process.

  The apparatus for producing a glass substrate according to the present invention includes a melting tank that heats a glass raw material to generate a molten glass, a clarification tube that clarifies the molten glass generated in the melting tank, and a molten glass clarified by the clarification tube. A molding apparatus for molding a glass substrate. The fining tube is a platinum or platinum alloy tube through which molten glass flows so that a gas phase space is formed. The gas phase space is a space above the liquid surface of the molten glass inside the clarification tube. The clarification tube has a ventilation tube protruding outward from the outer wall surface of the clarification tube and a receiving portion provided above the liquid surface of the molten glass. The vent pipe communicates the gas phase space and the external space of the clarification pipe. The receiving portion covers a part of the cross section of the vent pipe when the vent pipe is viewed along the longitudinal direction of the vent pipe.

  The method for manufacturing a glass substrate and the apparatus for manufacturing a glass substrate according to the present invention can prevent foreign matters from being mixed into the molten glass in the clarification step of the molten glass.

It is a flowchart which shows the process of the glass substrate manufacturing method which concerns on embodiment. It is a schematic diagram which shows the structure of the glass substrate manufacturing apparatus which concerns on embodiment. It is an external view of the clarification pipe concerning an embodiment. It is sectional drawing in the longitudinal direction of the clarification pipe | tube which concerns on embodiment. FIG. 5 is an external view of a vent pipe seen along the direction of arrow V shown in FIG. 4. It is sectional drawing in the longitudinal direction of the clarification pipe | tube which concerns on the modification A. FIG. 7 is an external view of a vent pipe seen along the direction of arrow VII shown in FIG. 6. It is sectional drawing in the longitudinal direction of the clarification pipe | tube which concerns on the modification B. FIG. 9 is an external view of a vent pipe seen along the direction of arrow IX shown in FIG. 8. It is sectional drawing in the longitudinal direction of the clarification pipe | tube which concerns on the modification C. It is an external view of the vent pipe seen along the direction of arrow XI shown in FIG.

(1) Overall Configuration of Glass Substrate Manufacturing Apparatus An embodiment of a glass substrate manufacturing method and a glass substrate manufacturing apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a flowchart showing an example of steps of the glass substrate manufacturing method according to the present embodiment.

  As shown in FIG. 1, the glass substrate manufacturing method mainly includes a melting step S1, a clarification step S2, a stirring step S3, a forming step S4, a slow cooling step S5, and a cutting step S6.

In the melting step S1, the glass raw material is heated to obtain molten glass. The molten glass is stored in a melting tank and energized and heated to have a desired temperature. A fining agent is added to the glass raw material. From the viewpoint of reducing environmental burden, SnO ₂ is used as a clarifying agent.

In the clarification step S2, the molten glass flows through the clarification tube. First, the temperature of the molten glass is raised. The refining agent causes a reduction reaction with an increase in temperature to release oxygen. Bubbles containing gaseous components such as CO ₂ , N ₂ and SO ₂ contained in the molten glass absorb oxygen generated by the reductive reaction of the fining agent. Bubbles that have grown by absorbing oxygen float on the liquid surface of the molten glass, break up and disappear. The gas contained in the extinguished bubbles is discharged into the gas phase space in the clarification tube and finally discharged to the outside air. Next, in the refining step S2, the temperature of the molten glass is lowered. Thereby, the reduced fining agent causes an oxidation reaction and absorbs gas components such as oxygen remaining in the molten glass.

  In the stirring step S3, the clarified molten glass is stirred, and the components of the molten glass are homogenized. Thereby, the composition nonuniformity of the molten glass which is a cause of the striae etc. of a glass substrate is reduced. The homogenized molten glass is sent to the forming step S4.

  In the forming step S4, a glass ribbon is continuously formed from the molten glass by the overflow downdraw method or the float method.

  In the slow cooling step S5, the glass ribbon continuously formed in the forming step S4 is gradually cooled so as to have a desired thickness and to prevent distortion and warpage.

  In the cutting step S6, the glass ribbon slowly cooled in the slow cooling step S5 is cut into a predetermined length to obtain a glass sheet. The glass sheet is further cut into a predetermined size to obtain a glass substrate. Thereafter, the end surface of the glass substrate is ground and polished, and the glass substrate is cleaned. Further, the glass substrate is inspected for defects such as scratches, and the glass substrate that has passed the inspection is packed and shipped as a product.

  FIG. 2 is a schematic diagram illustrating an example of the configuration of the glass substrate manufacturing apparatus 200 according to the present embodiment. The glass substrate manufacturing apparatus 200 includes a melting tank 40, a clarification tube 41, a stirring device 100, a molding device 42, and transfer tubes 43a, 43b, and 43c. The transfer pipe 43 a connects the melting tank 40 and the clarification pipe 41. The transfer pipe 43 b connects the clarification pipe 41 and the stirring device 100. The transfer pipe 43 c connects the stirring device 100 and the molding device 42.

  The molten glass G produced in the melting tank 40 passes through the transfer pipe 43a and flows into the clarification pipe 41. The molten glass G clarified by the clarification tube 41 passes through the transfer tube 43b and flows into the stirring device 100. The molten glass G stirred by the stirring device 100 passes through the transfer pipe 43 c and flows into the molding device 42. In the forming apparatus 42, the glass ribbon GR is formed from the molten glass G by the overflow downdraw method. The glass ribbon GR is cut into a predetermined size in a later process, and a glass substrate is manufactured. The dimension of the glass substrate in the width direction is, for example, 500 mm to 3500 mm. The dimension of the glass substrate in the length direction is, for example, 500 mm to 3500 mm.

The glass substrate manufactured by the glass substrate manufacturing method and the glass substrate manufacturing apparatus according to the present invention is particularly suitable as a glass substrate for a flat panel display (FPD) such as a liquid crystal display, a plasma display, and an organic EL display. ing. As the glass substrate for FPD, non-alkali glass or alkali-containing glass is used. A glass substrate for FPD has high viscosity at high temperatures. For example, the temperature of the molten glass having a viscosity of 10 ^2.5 poise is 1500 ° C. or higher.

The melting tank 40 includes heating means (not shown) such as a burner. In the melting tank 40, the glass raw material is melted by the heating means, and the molten glass G is generated. The glass raw material is prepared so that a glass having a desired composition can be substantially obtained. As an example of the glass composition, non-alkali glass suitable as a glass substrate for FPD is SiO ₂ : 50 mass% to 70 mass%, Al ₂ O ₃ : 0 mass% to 25 mass%, B ₂ O ₃ : 1 Mass% to 15 mass%, MgO: 0 mass% to 10 mass%, CaO: 0 mass% to 20 mass%, SrO: 0 mass% to 20 mass%, BaO: 0 mass% to 10 mass%. Here, the total content of MgO, CaO, SrO and BaO is 5% by mass to 30% by mass.

Moreover, you may use the alkali trace amount glass which contains a trace amount of alkali metals as a glass substrate for FPD. The alkali-containing glass contains 0.1% by mass to 0.5% by mass of R ′ ₂ O as a component, and preferably 0.2% by mass to 0.5% by mass of R ′ ₂ O. Here, R ′ is at least one selected from Li, Na and K. The total content of R ′ ₂ O may be less than 0.1% by mass.

In addition to the above components, the glass produced according to the present invention includes SnO ₂ : 0.01% by mass to 1% by mass (preferably 0.01% by mass to 0.5% by mass), Fe ₂ O ₃ : 0. You may further contain mass%-0.2 mass% (preferably 0.01 mass%-0.08 mass%). The glass produced by the present invention, in consideration of the environmental load, substantially free of _{As 2 O 3, Sb 2 O} 3 , and PbO.

  The glass raw material prepared as described above is charged into the melting tank 40 using a raw material charging machine (not shown). The raw material input machine may input a glass raw material using a screw feeder, or may input a glass raw material using a bucket. In the melting tank 40, the glass raw material is heated and melted at a temperature according to its composition. Thereby, in the melting tank 40, the high temperature molten glass G of 1500-1600 degreeC is obtained, for example. In the melting tank 40, the molten glass G between the electrodes may be energized and heated by flowing a current between at least one pair of electrodes made of molybdenum, platinum, tin oxide, or the like. In addition, the glass raw material may be heated by supplementarily providing a flame with a burner.

  The molten glass G obtained in the melting tank 40 passes through the transfer pipe 43 a from the melting tank 40 and flows into the clarification pipe 41. The clarification tube 41 and the transfer tubes 43a, 43b, and 43c are tubes made of platinum or a platinum alloy. The clarification tube 41 is provided with a heating means similar to the melting tank 40. In the clarification tube 41, the molten glass G is clarified by further raising the temperature. For example, in the clarification tube 41, the temperature of the molten glass G is raised to 1500 ° C to 1700 ° C.

  The molten glass G clarified in the clarification tube 41 passes through the transfer tube 43b from the clarification tube 41 and flows into the stirring device 100. The molten glass G is cooled when passing through the transfer tube 43b. In the stirring device 100, the molten glass G is stirred at a temperature lower than the temperature of the molten glass G passing through the clarification tube 41. For example, in the stirring device 100, the temperature of the molten glass G is 1250 ° C to 1450 ° C. For example, in the stirring device 100, the viscosity of the molten glass G is 500 poise to 1300 poise. The molten glass G is stirred and homogenized in the stirring device 100.

  The molten glass G homogenized by the stirrer 100 flows from the stirrer 100 through the transfer pipe 43 c and flows into the molding device 42. When the molten glass G passes through the transfer tube 43c, it is cooled so as to have a viscosity suitable for forming the molten glass G. For example, the molten glass G is cooled to around 1200 ° C. In the shaping | molding apparatus 42, the molten glass G is shape | molded by the overflow downdraw method. Specifically, the molten glass G that has flowed into the molding apparatus 42 is supplied to a molded body 52 installed inside a molding furnace (not shown). The formed body 52 is formed of refractory bricks and has a wedge-shaped cross-sectional shape. A groove is formed on the upper surface of the molded body 52 along the longitudinal direction of the molded body 52. The molten glass G is supplied to the groove on the upper surface of the molded body 52. The molten glass G overflowing from the groove flows down along the pair of side surfaces of the molded body 52. A pair of molten glass G which flowed down the side surface of the molded body 52 joins at the lower end of the molded body 52, and the glass ribbon GR is continuously molded. The glass ribbon GR is gradually cooled as it flows downward, and then cut into a glass sheet having a desired length.

(2) Structure of clarification tube Next, the detailed structure of the clarification tube 41 is demonstrated. FIG. 3 is an external view of the clarification tube 41. FIG. 4 is a cross-sectional view of the clarification tube 41 cut vertically along the longitudinal direction of the clarification tube 41. The clarification tube 41 has, for example, a thickness of 0.5 mm to 1.5 mm and an inner diameter of 300 mm to 500 mm. A ventilation pipe 41a and a pair of heating electrodes 41b are attached to the clarification pipe 41. Inside the clarification tube 41, the molten glass G flows in a state where the gas phase space 41c is formed upward. That is, the liquid surface LS of the molten glass G exists in the clarification tube 41 as shown in FIG. The internal space of the vent pipe 41a communicates with the gas phase space 41c. Moreover, the clarification tube 41 is energized and heated by passing a current between the pair of heating electrodes 41b. Thereby, the molten glass G which passes the inside of the clarification tube 41 is heated and clarified. In the clarification process of the molten glass G, bubbles containing gaseous components such as CO ₂ , N ₂ , and SO ₂ contained in the molten glass G absorb oxygen generated by the reductive reaction of the clarifier. Bubbles grown by absorbing oxygen float on the liquid surface LS of the molten glass G, break up and disappear. The gas contained in the extinguished bubbles is released into the gas phase space 41c in the clarification tube 41, and is discharged to the outside air through the vent tube 41a.

  The ventilation pipe 41 a is attached to the outer wall surface of the clarification pipe 41 and projects outward from the clarification pipe 41. In the present embodiment, as shown in FIG. 4, the ventilation pipe 41 a is attached to the upper end portion of the outer wall surface of the clarification pipe 41 and protrudes in a chimney shape toward the upper side of the clarification pipe 41. The ventilation pipe 41 a communicates the gas phase space 41 c that is a part of the internal space of the clarification pipe 41 and the outside air that is the external space of the clarification pipe 41. The ventilation pipe 41a is formed of platinum or a platinum alloy in the same manner as the clarification pipe 41. The vent pipe 41a has a thickness of 0.5 mm to 1.5 mm, for example, and an inner diameter of 10 mm to 100 mm.

  The vent pipe 41a has a receiving portion 41d. As shown in FIG. 4, the receiving portion 41d is positioned above the liquid level LS of the molten glass G and is attached to the inner wall surface of the vent pipe 41a. The receiving part 41d is formed of platinum or a platinum alloy in the same manner as the vent pipe 41a. FIG. 5 is an external view of the vent pipe 41a as viewed along the direction of the arrow V shown in FIG. FIG. 5 shows a state in which the vent pipe 41a is viewed from the top to the bottom along the longitudinal direction of the vent pipe 41a, that is, the vertical direction. In other words, FIG. 5 shows how it looks when the inside of the clarification tube 41 is looked into from the ventilation tube 41a. The receiving part 41d covers a part of the cross section of the vent pipe 41a. The receiving portion 41d is a circular plate with a hole formed in the center. The outer periphery of the receiving portion 41d is joined to the inner wall surface of the vent pipe 41a. The gas phase space 41c of the clarification tube 41 communicates with the outside air through a hole in the center of the receiving portion 41d.

The heating electrode 41 b is a flange-shaped electrode plate that is attached to each of both ends of the clarification tube 41. The heating electrode 41b is connected to a power source (not shown). By supplying electric power to the heating electrode 41b, a current flows through the clarification tube 41 between the pair of heating electrodes 41b, and the clarification tube 41 is energized and heated. Thereby, finer tube 41, for example, is heated to 1700 ° C., molten glass G flowing in the finer tube 41, the temperature of the reduction reaction of SnO ₂ is a fining agent contained in the molten glass G occurs, for example, 1600 C. to 1650.degree. By controlling the current flowing through the clarification tube 41, the temperature of the molten glass flowing inside the clarification tube 41 can be controlled. Note that the number and position of the heating electrodes 41b attached to the clarification tube 41 may be appropriately determined according to the material, inner diameter and length of the clarification tube 41, the position of the ventilation tube 41a, and the like.

  Although not shown in FIGS. 3 and 4, a refractory protective layer made of alumina cement or the like is provided on the outer wall surface of the clarification tube 41. A refractory brick is further provided on the outer wall surface of the refractory protective layer. The refractory brick is placed on a base (not shown). That is, the clarification tube 41 is supported from below by the refractory protective layer and the refractory brick.

(3) Features (3-1)
In the glass substrate manufacturing method according to the present embodiment, the molten glass G generated by heating the glass raw material is heated when passing through the clarification tube 41. Inside the clarification tube 41, bubbles containing CO ₂ or SO ₂ contained in the molten glass G are removed by an oxidation-reduction reaction of SnO ₂ which is a clarifier added to the molten glass G. Specifically, first, the temperature of the molten glass G is raised to reduce the fining agent, thereby generating oxygen bubbles in the molten glass G. Bubbles containing gaseous components such as CO ₂ , N ₂ and SO ₂ contained in the molten glass G absorb oxygen generated by the reductive reaction of the fining agent. Bubbles grown by absorbing oxygen float on the liquid surface LS of the molten glass G, break up and disappear. The gas contained in the extinguished bubbles is released into the gas phase space 41c and discharged to the outside air through the vent pipe 41a. Next, the temperature of the molten glass G is lowered to oxidize the reduced fining agent. Thereby, the bubbles of oxygen remaining in the molten glass G are absorbed by the molten glass G. In this way, bubbles contained in the molten glass G are removed by the oxidation-reduction reaction of the clarifying agent.

  The clarification tube 41 is made of platinum or a platinum alloy. Platinum or a platinum alloy has a high melting point and is excellent in corrosion resistance to the molten glass G. Therefore, platinum or a platinum alloy is suitable as a material for the fining tube 41 in contact with the high temperature molten glass G. However, the platinum component gradually evaporates from the inner wall of the clarification tube 41 by using the clarification tube 41 for a long period of time. The volatile matter containing platinum is discharged into the gas phase space 41c together with the bubbles contained in the molten glass G, and discharged to the outside air through the vent pipe 41a. However, the volatile matter containing platinum is likely to be in a supersaturated state due to a decrease in temperature in the process of passing through the vent pipe 41a. Therefore, the solidified volatile matter adheres to the inner wall of the vent pipe 41a as platinum foreign matter. And the platinum foreign material adhering to the inner wall of the vent pipe 41a grows with progress of time. The grown platinum foreign matter may be peeled off from the inner wall surface of the vent pipe 41a due to its own weight. Further, during the maintenance work of the clarification tube 41, the platinum foreign matter may fall when the platinum foreign matter is removed from the inner wall surface of the vent pipe 41a.

  In the glass substrate manufacturing apparatus 200 according to the present embodiment, the receiving portion 41d is provided on the inner wall surface of the vent pipe 41a that is the exhaust pipe of the clarification pipe 41. The receiving part 41d is a member for receiving the platinum foreign matter that has been peeled off from the inner wall surface of the vent pipe 41a. When the vent pipe 41a does not have the receiving portion 41d, the platinum foreign matter peeled off from the inner wall surface of the vent pipe 41a falls into the inner space of the clarification pipe 41 and enters the molten glass G passing through the clarification pipe 41. There is a risk that. If platinum foreign matter is mixed into the molten glass G, there is a risk of a quality defect of the glass substrate to be manufactured. The receiving part 41d suppresses the platinum foreign matter that has been peeled off from the inner wall surface of the vent pipe 41a from dropping to the liquid level LS of the molten glass G in the clarification pipe 41. Therefore, since the foreign substance of platinum is prevented from being mixed into the molten glass G by the receiving part 41d, a high-quality glass substrate can be mass-produced with a high yield.

(3-2)
In the present embodiment, the receiving portion 41d is preferably provided below the portion of the vent pipe 41a that has a temperature at which the volatiles including platinum existing in the gas phase space 41c of the clarification pipe 41 solidify. That is, it is preferable that the receiving portion 41d is provided at a position where volatile substances as hot as possible pass in the internal space of the vent pipe 41a. In other words, the receiving portion 41d is preferably provided at a position as close as possible to the gas phase space 41c in the clarification tube 41.

  The temperature of the vent pipe 41a is highest at the connecting portion between the clarification pipe 41 and the vent pipe 41a, and tends to decrease as it goes upward from the connecting portion. That is, the temperature of the internal space of the vent pipe 41a is also highest at the portion communicating with the gas phase space 41c, and tends to decrease as it goes upward. Thereby, the gas containing platinum gradually volatilized from the inner wall of the clarification tube 41 is gradually cooled and becomes supersaturated in the process of flowing upward through the ventilation tube 41a. Therefore, the internal space of the vent pipe 41a has a platinum solidification point that is a point indicating a temperature at which volatiles including platinum solidify along the longitudinal direction of the vent pipe 41a. Therefore, the volatile matter containing platinum is solidified above the platinum solidification point, and platinum foreign matters are likely to adhere to the inner wall of the vent pipe 41a.

  Therefore, by providing the receiving portion 41d below the platinum solidification point, the receiving portion 41d can more effectively receive the platinum foreign matter that has been peeled off from the inner wall surface of the vent pipe 41a. When the receiving part 41d is provided above the platinum solidification point, platinum foreign matter tends to adhere to the inner wall of the vent pipe 41a below the receiving part 41d. In this case, there is a possibility that the receiving part 41d cannot receive the platinum foreign matter that has been peeled off from the inner wall surface of the vent pipe 41a.

(3-3)
The glass substrate manufacturing apparatus 200 according to the present embodiment is particularly effective when SnO ₂ is used as a clarifier in the clarification tube 41 made of platinum or platinum alloy. In recent years, SnO ₂ is used as a refining agent instead of As ₂ O ₃ from the viewpoint of environmental burden. When SnO ₂ is used, the molten glass G needs to be heated to a higher temperature in the refining tube 41 than when As ₂ O ₃ is used, and thus the problem of volatilization of platinum or platinum alloy becomes significant. And if volatilization of platinum or a platinum alloy is accelerated | stimulated, a platinum foreign material will adhere easily to the inner wall of the vent pipe 41a.

In the present embodiment, even in a situation where platinum foreign matter is likely to adhere to the inner wall of the vent pipe 41a, the receiving portion 41d can receive the platinum foreign matter peeled off from the inner wall surface of the vent pipe 41a. It is suppressed that platinum foreign matters are mixed in the metal. Therefore, the glass substrate manufacturing method according to the present embodiment is particularly effective for the manufacturing process of a glass substrate using SnO ₂ as a fining agent.

(3-4)
The glass substrate manufacturing apparatus 200 according to the present embodiment is generated from a glass raw material suitable for manufacturing a glass substrate for FPD such as a liquid crystal display, a plasma display, and an organic EL display in a clarification tube 41 made of platinum or a platinum alloy. This is particularly effective when refining molten glass.

  In the clarification tube 41, the molten glass G is clarified by adjusting the viscosity of the molten glass G to a value at which bubbles contained in the molten glass G can easily float on the liquid surface. However, non-alkali glass and glass containing a small amount of alkali suitable for a glass substrate for FPD have high viscosity at high temperatures. Therefore, in the refining process, it is necessary to increase the temperature of the molten glass as compared with the temperature of a normal alkali glass molten glass, and thus the problem of volatilization of platinum or a platinum alloy described above becomes significant. And if volatilization of platinum or a platinum alloy is accelerated | stimulated, a platinum foreign material will adhere easily to the inner wall of the vent pipe 41a.

  In the present embodiment, even in a situation where platinum foreign matter is likely to adhere to the inner wall of the vent pipe 41a, the receiving portion 41d can receive the platinum foreign matter peeled off from the inner wall surface of the vent pipe 41a. It is suppressed that platinum foreign matters are mixed in the metal. Therefore, the glass substrate manufacturing method according to the present embodiment is particularly effective for the manufacturing process of the FPD glass substrate.

(4) Modification (4-1) Modification A
In the glass substrate manufacturing apparatus 200 according to the present embodiment, the vent pipe 41a has a receiving portion 41d that receives the platinum foreign matter that has been peeled off from the inner wall surface of the vent pipe 41a. As shown in FIG. 5, the receiving portion 41d is an annular plate attached to the inner wall surface of the vent pipe 41a. However, the receiving portion 41d may have another shape as long as it can receive the platinum foreign matter that has been peeled off from the inner wall surface of the vent pipe 41a.

  6 and 7 are diagrams showing another embodiment of the receiving portion 41d. FIG. 6 is a cross-sectional view of the clarification tube 141 cut vertically along the longitudinal direction of the clarification tube 141, as in FIG. FIG. 7 is an external view of the vent pipe 141a as seen in the direction of the arrow VII shown in FIG. 6, similarly to FIG. FIG. 7 illustrates a state in which the vent pipe 141a is viewed from the top to the bottom along the longitudinal direction of the vent pipe 141a.

  As shown in FIG. 7, the receiving portion 141d is provided on the inner wall surface of the vent pipe 141a. The receiving portion 141d includes an upper receiving portion 141d1 and a lower receiving portion 141d2. Each of the upper receiving portion 141d1 and the lower receiving portion 141d2 has a semicircular shape. The upper receiving portion 141d1 and the lower receiving portion 141d2 are provided at different positions along the longitudinal direction of the vent pipe 141a. Specifically, the upper receiving portion 141d1 is provided at a higher position than the lower receiving portion 141d2. Each of the upper receiving portion 141d1 and the lower receiving portion 141d2 covers a part of the cross section of the vent pipe 141a. Therefore, the gas in the gas phase space 141c in the clarification pipe 141 passes through the ventilation pipe 141a and is discharged to the outside air.

  Also in this modification, since the foreign substance of platinum is prevented from being mixed into the molten glass G by the receiving part 141d, a high-quality glass substrate can be mass-produced with a high yield. Similarly to the present embodiment, the receiving portion 141d is preferably provided below the platinum solidification point. Thereby, the receiving part 141d can receive the platinum foreign material which peeled off from the inner wall face of the vent pipe 141a more effectively.

(4-2) Modification B
In the glass substrate manufacturing apparatus 200 according to the present embodiment, the receiving portion 41d is provided on the inner wall surface of the vent pipe 41a. However, the receiving portion 41d may be provided above the liquid level LS of the molten glass G, and may be provided in the gas phase space 41c of the clarification tube 41, for example.

  8 and 9 are diagrams showing another embodiment of the receiving portion 41d. FIG. 8 is a cross-sectional view of the clarification tube 241 cut vertically along the longitudinal direction of the clarification tube 241 as in FIG. 4. FIG. 9 is an external view of the vent pipe 241a as seen along the direction of the arrow IX shown in FIG. 8, similarly to FIG. FIG. 9 illustrates a state in which the vent pipe 241a is viewed from the top to the bottom along the longitudinal direction of the vent pipe 241a.

  As shown in FIG. 8, the receiving portion 241 d is attached to the inner wall surface above the clarification tube 241. The receiving part 241d is located above the liquid level LS of the molten glass G. As shown in FIG. 9, the receiving portion 241d is a net-like plate having a large number of holes when viewed from above. When the vent pipe 241a is viewed from the top to the bottom along the longitudinal direction of the vent pipe 241a, the cross section of the vent pipe 241a is covered with a net-like plate member of the receiving portion 241d. The receiving portion 241d covers a part of the cross section of the vent pipe 241a. Therefore, the gas in the gas phase space 241c in the clarification tube 241 passes through the ventilation tube 241a and is discharged to the outside air.

  Also in this modification, since the platinum foreign matter is prevented from being mixed into the molten glass G by the receiving portion 241d, a high-quality glass substrate can be mass-produced with a high yield.

(4-3) Modification C
In the glass substrate manufacturing apparatus 200 according to the present embodiment, the vent pipe 41a has a receiving portion 41d that receives the platinum foreign matter that has been peeled off from the inner wall surface of the vent pipe 41a. As shown in FIG. 5, the receiving portion 41d is an annular plate attached to the inner wall surface of the vent pipe 41a. However, the receiving portion 41d may be configured by a part of the clarification tube 41.

  10 and 11 are diagrams showing another embodiment of the receiving portion 41d. FIG. 10 is a cross-sectional view in which the clarification tube 341 is cut vertically along the longitudinal direction of the clarification tube 341, as in FIG. 4. FIG. 11 is an external view of the vent pipe 341a as seen in the direction of the arrow XI shown in FIG. 10, similarly to FIG. FIG. 11 illustrates a state in which the vent pipe 341a is viewed from the top to the bottom along the longitudinal direction of the vent pipe 341a.

  As shown in FIG. 11, the clarification tube 341 has a circular exhaust hole 341e. The exhaust hole 341 e is formed at the upper end of the clarification tube 341. The exhaust hole 341e allows the gas phase space 341c in the clarification pipe 341 to communicate with the internal space of the ventilation pipe 341a attached to the clarification pipe 341. As shown in FIG. 11, the inner diameter of the exhaust hole 341e is smaller than the inner diameter of the vent pipe 341a. When the vent pipe 341a is viewed along the longitudinal direction of the vent pipe 341a, the center of the circular cross-sectional shape of the vent pipe 341a is at the same position as the center of the exhaust hole 341e. In FIG. 11, a part of the outer wall of the clarification pipe 341 that is outside the outer periphery of the exhaust hole 341e and inside the inner wall surface of the vent pipe 341a is platinum peeled off from the inner wall of the vent pipe 341a. It has the function of the receiving part 341d which receives a foreign material. The gas in the gas phase space 341c in the clarification pipe 341 passes through the ventilation pipe 341a and is discharged to the outside air.

  Also in this modification, the receiving part 341d configured from a part of the clarification tube 341 prevents platinum foreign matter from being mixed into the molten glass G, so that a high-quality glass substrate can be mass-produced with a high yield. it can.

(4-4) Modification D
In the glass substrate manufacturing apparatus 200 according to the present embodiment, the clarification tube 41, the ventilation tube 41a, and the receiving portion 41d are formed of platinum or a platinum alloy, but may be formed of other platinum group metals. “Platinum group metal” means a metal composed of a single platinum group element and an alloy of a metal composed of a platinum group element. The platinum group elements are six elements of platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), osmium (Os) and iridium (Ir). Platinum group metals are expensive, but have a high melting point and excellent corrosion resistance against molten glass.

41 clarification pipe 41a vent pipe 41b heating electrode 41c gas phase space 41d receiving part 200 glass substrate manufacturing apparatus G molten glass LS liquid surface of molten glass

JP 2006-522001 Gazette

Claims (4)

A melting process for heating the glass raw material to produce a molten glass;
A refining step of refining the molten glass;
A molding step of molding a glass substrate from the clarified molten glass;
With
In the clarification step, the molten glass flows inside a clarification tube made of platinum or a platinum alloy so that a gas phase space which is a space above the liquid level of the molten glass is formed,
The clarification tube has a ventilation tube protruding outward from an outer wall surface of the clarification tube, and a receiving portion provided above the liquid surface of the molten glass,
The vent pipe communicates the gas phase space and the external space of the clarification pipe,
The receiving portion covers a part of the cross section of the vent pipe when the vent pipe is viewed along the longitudinal direction of the vent pipe.
A method for producing a glass substrate. The receiving portion is provided in the vent pipe below a portion having a temperature at which a gas containing platinum existing in the gas phase space is solidified.
The manufacturing method of the glass substrate of Claim 1. The molten glass contains SnO ₂ as a fining agent,
The manufacturing method of the glass substrate of Claim 1 or 2. A melting tank for heating glass raw material to produce molten glass;
A refining tube for refining the molten glass produced in the melting tank;
A molding apparatus for molding a glass substrate from the molten glass clarified by the clarification tube;
With
The clarified tube is a tube made of platinum or a platinum alloy in which the molten glass flows inside so that a gas phase space that is a space above the liquid level of the molten glass is formed,
The clarification tube has a ventilation tube protruding outward from an outer wall surface of the clarification tube, and a receiving portion provided above the liquid surface of the molten glass,
The vent pipe communicates the gas phase space and the external space of the clarification pipe,
The receiving portion covers a part of the cross section of the vent pipe when the vent pipe is viewed along the longitudinal direction of the vent pipe.
Glass substrate manufacturing equipment.

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