JP2016034894A - Method and apparatus for manufacturing glass substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method, etc., for manufacturing a glass substrate, capable of suppressing contamination of foreign matters in a molten glass in the step of refining the molten glass.SOLUTION: A method for manufacturing a glass substrate comprises: a melting step of heating a glass raw materials to form a molten glass; a refining step of refining the molten glass; and a molding step of molding a glass substrate from the molten glass. In the refining step, the molten glass flows through the inside of the refining pipe made of platinum or platinum alloy so as to form a vapor phase space being a space above the surface of the molten glass. The refining pipe has a vent pipe projected outward from the outer wall surface of the refining pipe and for passing a gas including platinum existing in the vapor phase space. The vent pipe includes a measuring pipe provided for capturing and measuring the gas; and an oxygen analyser connected with the measuring pipe and for measuring the oxygen concentration of the gas. In the measuring pipe, the longitudinal cross section of an opening end on the side of capturing the gas is inclined against the longitudinal direction of the measuring pipe.SELECTED DRAWING: Figure 4

Description

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

Generally, the manufacturing method of a glass substrate has a melting process which heats a glass raw material and produces | generates a molten glass, and a shaping | molding process which shape | molds a glass substrate from molten glass, as described in patent document 1. . 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. 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 as an appropriate material for the inner wall of the member in contact with 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.

JP 2006-522001 Gazette

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. At this time, the refining agent causes a reduction reaction by raising the temperature and releases oxygen. On the other hand, the foam containing the gas component contained in the molten glass absorbs 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. Further, by using the clarification tube for a long period of time, the platinum group metal gradually volatilizes by reacting with oxygen from the inner wall of the clarification tube. 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, there is a problem that volatile substances are likely to precipitate on the inner walls of the clarification pipe and the ventilation pipe. Hereinafter, the substance deposited on the inner wall of the clarification tube and the ventilation tube is referred to as “platinum foreign matter”. By measuring the oxygen concentration (oxygen concentration) that generates volatiles with a vent tube , the amount of bubbles that grow by absorbing oxygen in the molten glass can be predicted, and the precipitation of platinum foreign matter can be predicted. However, since the inside of the vent 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 vent 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. In particular, platinum foreign matter may be deposited on a measuring tube for taking in oxygen and measuring the oxygen concentration and fall. And when a platinum foreign material mixes in molten glass, it will become difficult to mass-produce a high quality glass substrate.

  Then, an object of this invention is to provide 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.

One aspect of the present invention is a method of manufacturing a glass substrate,
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,
In the clarification step, the molten glass flows inside a clarified tube made of platinum or a platinum alloy so that a gas phase space that is a space above the surface of the molten glass is formed,
The clarification pipe protrudes outward from the outer wall surface of the clarification pipe, and has a ventilation pipe through which a gas containing platinum existing in the gas phase space passes.
The ventilation pipe is provided with a measurement pipe for taking in and measuring the gas,
An oxygen concentration meter connected to the measuring tube for measuring the oxygen concentration of the gas;
In the measurement tube, the longitudinal section of the opening end on the side of taking in the gas is inclined with respect to the longitudinal direction of the measurement tube,
It is characterized by that.

  The oxygen concentration meter preferably measures the oxygen concentration by flowing the inert gas through the measurement tube and then taking the gas from the measurement tube.

  The gas condenses on the surface of the molten glass surface of the measuring tube to become a liquid, and the tension generated between the liquid and the measuring tube is caused by the weight of the liquid on the liquid surface side of the molten glass. It is preferable that it is larger than the force generated toward the direction.

  It is preferable to adjust the supply amount of the inert gas supplied to the gas phase space according to the measurement result by the oxygen concentration meter.

  It is preferable that the inclination angle φ of the longitudinal section of the open end with respect to a plane orthogonal to the longitudinal direction of the tube is 15 to 75 degrees.

Another aspect of the present invention is a glass substrate manufacturing apparatus,
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,
The clarified tube is a tube made of platinum or a platinum alloy in which the molten glass flows inside so as to form a gas phase space that is a space above the surface of the molten glass,
The clarification pipe protrudes outward from the outer wall surface of the clarification pipe, and has a ventilation pipe through which a gas containing platinum existing in the gas phase space passes.
The ventilation pipe is provided with a measurement pipe for taking in and measuring the gas,
An oxygen concentration meter connected to the measuring tube for measuring the oxygen concentration of the gas;
In the measurement tube, the longitudinal section of the opening end on the side of taking in the gas is inclined with respect to the longitudinal direction of the measurement tube,
It is characterized by that.

  Furthermore, it is preferable to provide an inert gas supply device configured to allow an inert gas to flow through the measurement tube during standby before measurement by the oximeter.

  It is preferable that the inclination angle φ of the longitudinal section of the open end with respect to a plane orthogonal to the longitudinal direction of the measuring tube is 15 to 75 degrees.

  According to the said aspect, in a clarification process of molten glass, it can suppress that a foreign material mixes into molten glass.

It is a flowchart which shows the process of the glass substrate manufacturing method which concerns on this embodiment. It is a schematic diagram which shows the structure of the glass substrate manufacturing apparatus which concerns on this embodiment. It is an external view of a clarification pipe. It is a schematic sectional drawing in the longitudinal direction of a clarification tube. It is a figure for demonstrating the surface tension generate | occur | produced between a measuring tube and the solidified volatile matter. It is a figure for demonstrating the surface tension generate | occur | produced between the measuring tube which concerns on this embodiment, and the solidified volatile matter.

(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. The glass melt contains a fining agent. For example, a clarifier may be added to a glass raw material, or a clarifier is not added to a glass raw material. A fining agent can also be included. From the viewpoint of reducing the environmental load, SnO ₂ is used as a fining agent.

The clarification step S2 is performed with a clarification tube. In the clarified tube, molten glass flows inside. 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 grown by absorbing oxygen rise to the surface in contact with the gas phase space 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, for example, an overflow downdraw method or a 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 a glass substrate for a display including a flat panel display (FPD) such as a liquid crystal display, a plasma display, and an organic EL display. Is particularly suitable. As a glass substrate for a display including FPD, non-alkali glass or alkali-containing glass is used. A glass substrate for display 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 composition of glass, non-alkali glass suitable as a glass substrate for a display including FPD is SiO ₂ : 50 mass% to 70 mass%, Al ₂ O ₃ : 0 mass% to 25 mass%, B ₂ O. ₃ : 1% by mass to 15% by mass, MgO: 0% by mass to 10% by mass, CaO: 0% by mass to 20% by mass, SrO: 0% by mass to 20% by mass, BaO: 0% by mass to 10% by mass. contains. 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 content glass which contains a trace amount of alkali metals as a glass substrate for displays containing FPD. Alkaline trace containing glass, as component, 'comprises ₂ O, preferably, 0.2 wt% to 0.5 wt% R' of R 0.1 wt% to 0.5 wt% including the 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 rises 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 schematic cross-sectional view of the clarification tube 41 cut in the vertical direction along the longitudinal direction of the clarification tube 41. As shown in FIG. 3, the clarification tube 41 is provided with a ventilation tube 41a and a pair of heating electrodes 41b. Inside the clarification tube 41, the molten glass G flows in a state where the gas phase space 41c is formed upward. That is, as shown in FIG. 4, the surface LS of the molten glass G in contact with the gas phase space exists inside the clarification tube 41. 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 gas 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 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, for example, a thickness of 0.5 mm to 1.5 mm and an inner diameter of 20 mm to 100 mm.

As shown in FIG. 4, the ventilation pipe 41 a is provided with a measurement pipe 44 for taking in the gas in the gas phase space containing the volatile matter of the platinum group metal that passes through the ventilation pipe 41 a. An oxygen concentration meter 45 for measuring the oxygen concentration of the gas is provided. The measurement tube 44 is formed of platinum or a platinum alloy, for example, similarly to the ventilation tube 41 a, and is connected to the oxygen concentration meter 45 so that the gas is taken in from the measurement tube 44 and enters the oxygen concentration meter 45. The inner diameter and the outer diameter of the measuring tube 44 may be smaller than the inner diameter and the outer diameter of the vent pipe 41a because it is sufficient that the measuring tube 44 can take in a gas that can measure the oxygen concentration of the gas. Is 20 mm or less. The gas containing platinum group metal volatiles is discharged to the outside air through the vent pipe 41a, but in the process of being discharged to the outside air, the temperature is lowered and the gas becomes supersaturated. In particular, volatiles are likely to be deposited near the entrance of the measuring tube 44 and become liquid, and this liquid deposit may fall, and as a result, may be mixed into the molten glass as solid platinum foreign matter. This is because the outer diameter of the measuring tube 44 is small and the surface tension generated between the liquid deposit and the outer surface of the measuring tube 44 is weak. FIG. 5 is a diagram for explaining the force due to the surface tension generated between the surface of the measuring tube 44 and the precipitate M that has become a liquid due to condensation of volatiles. When the force due to the surface tension on the tube outer surface having the tube outer diameter R1 is an upward force F1, the force F1 is obtained by the following equation (1).
F1 = 2πr1 × γ × cos θ Formula (1)
Here, r1 = radius of the outer diameter of the measuring tube 44, γ = surface tension, and θ = contact angle. Note that the surface tension and the contact angle are determined by the viscosity of the substance, and are set to constant values here.
Assuming that the mass of the volatile precipitate is M, the condition that the precipitate remains in the measuring tube 44 is M × g (gravitational acceleration) <F1. For this reason, in order to prevent the precipitate from falling, it is necessary to increase the radius r1 of the outer diameter of the measuring tube 44. On the other hand, when the outer diameter and inner diameter of the measuring tube 44 are increased, volatile substances are likely to be deposited on the outer peripheral portion (outer surface side) of the measuring tube 44 and the inner peripheral portion (inner surface side) of the measuring tube 44. May fall. For this reason, even if the radius of the outer diameter of the measuring tube 44 is equal to or less than a certain value, it is necessary to prevent the deposits deposited on the measuring tube 44 from falling. The volatiles condense at the inlet of the outer surface of the molten glass of the measuring tube 44 to become liquid, and the tension generated between the liquid and the measuring tube 44 is directed toward the liquid surface of the molten glass by its own weight. By making it larger than the force generated in this way, it is possible to prevent the liquid (precipitate) from falling.

  FIG. 6 is a diagram for explaining the force due to the surface tension generated between the measurement tube 44 and the volatile precipitate M according to the present embodiment. The measuring tube 44 according to the present embodiment includes an open end that is inclined with respect to the longitudinal direction of the tube on the side where the surface LS of the molten glass G of the clarification tube 41 exists (the side that takes in the gas). For example, the opening end is cut so that the opening end is inclined with respect to the longitudinal direction of the tube shown in FIG. That is, the measurement tube 44 has a vertical cross-sectional diameter (longitudinal cross section) along the opening end on the gas intake side, which is connected to the oximeter 45 (above the gas intake side, outside the clarification tube 41). It is larger than the vertical cross-sectional diameter of the side protruding in the direction. Here, the longitudinal section is a plane of the cut surface obtained when the object is cut vertically. As shown in FIG. 6, the vertical cross section of the measurement tube 44 on the opening end side on the gas intake side is inclined with respect to the longitudinal direction of the tube. By making the open end, which is the gas intake port (longitudinal cross section on the gas intake side) of the measurement tube 44, inclining with respect to the longitudinal direction of the tube, the inner diameter and the outer diameter R1 of the measurement tube 44 are not changed. The force due to the surface tension at the outer diameter of the tube can be increased. In the measurement tube 44 according to the present embodiment, the vertical cut diameter at the open end is the outer diameter R2, and the radius of the vertical cross-sectional diameter at the open end in contact with the volatile matter M is larger than half of R1. The upward force F2 due to the surface tension obtained from (1) is larger than the force F1. For this reason, it can suppress that the deposit M of the volatile matter deposited at the entrance of the measuring tube 44 falls. An angle formed by the entrance of the measuring tube 44 to be horizontal, in other words, an inclination angle φ with respect to a plane orthogonal to the longitudinal direction of the tube is preferably 15 to 75 degrees, more preferably 30 to 60 degrees, and even more. Preferably it is 45 degrees. The angle φ can be arbitrarily changed according to the viscosity of the volatile precipitate M, and the tension generated between the precipitate M and the measuring tube 44 is caused by the weight of the precipitate M on the surface side of the molten glass. The force is not particularly limited as long as it is greater than the force generated toward the head.

The oxygen concentration meter 45 is any commercially available device that can measure the oxygen concentration. As the oxygen concentration meter 45, for example, a zirconia type, magnetic type, or electrode type concentration meter is used. The oxygen concentration meter 45 measures the oxygen concentration of the gas taken in from the measurement tube 44. When measuring the oxygen concentration, the oxygen concentration meter 45, nitrogen (N ₂₎ by controlling the supply (not shown), and supplies the N ₂ in the measurement pipe 44. If a gas containing platinum group metal volatiles flows into the measurement tube 44, particularly in the vicinity of the oxygen concentration meter 45, measurement errors are likely to occur. In addition, when gas flows into the measurement tube 44, precipitates are generated and deposited near the entrance of the measurement tube 44, so that the measurement tube 44 may be blocked and clogged. For this reason, in the standby state in which the oxygen concentration is measured, the measuring tube 44 is filled with N _2, and the gas containing platinum group metal volatiles is prevented from flowing into the measuring tube 44. Thereby, the measurement accuracy of the oxygen concentration at the time of measuring the oxygen concentration is increased. In addition, the oxygen concentration can be stably measured without clogging the measuring tube 44 with precipitates. The oxygen concentration meter 45 sucks the gas in the measurement tube 44 and measures the oxygen concentration of this gas. In this embodiment, instead of supplying nitrogen gas using a nitrogen supply device, an inert gas other than nitrogen gas may be supplied using an inert gas supply device. The inert gas in this case is a gas that does not react with platinum volatiles or molten glass, and includes, for example, a gas of an 18th group element such as helium, neon, or argon.
Here, the nitrogen supply device is connected to the measurement tube 44 and supplies an inert gas, specifically nitrogen gas, to the measurement tube 44. The gas containing platinum group metal volatiles is discharged to the outside air through the vent pipe 41a, but in the process of being discharged to the outside air, the temperature is lowered and the gas becomes supersaturated. In particular, the gas containing platinum group metal volatiles taken in from the measuring tube 44 becomes supersaturated as the temperature decreases from the inlet of the measuring tube 44 toward the oximeter 45, and volatilizes in the measuring tube 44. Objects may precipitate and the measuring tube 44 may become clogged. If the measuring tube 44 is clogged with volatile substances (precipitates), the oxygen concentration of the gas cannot be stably measured. In addition, deposits may fall from the measuring tube 44, and platinum foreign matter may be mixed into the molten glass. For this reason, the nitrogen supplier supplies nitrogen to the measuring tube 44, fills the inside of the tube with nitrogen, and suppresses the inflow of gas containing platinum group metal volatiles into the measuring tube 44. It is also possible to prevent the tube 44 from being clogged with volatile deposits.

In the manufacturing method of the glass substrate which concerns on this embodiment, the molten glass G produced | generated by heating a glass raw material is heated when passing the inside of the clarification tube 41. FIG. 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 clarifying agent. Bubbles grown by absorbing oxygen float on the 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. The oxygen concentration meter 45 measures the oxygen concentration of the gas (gas) discharged to the outside air, thereby predicting the amount of bubbles that grow by absorbing oxygen and predicting the precipitation of platinum foreign matter. When the measured oxygen concentration in the gas is high, it means that bubbles are likely to grow by absorbing oxygen, and therefore the amount of volatile platinum group metal volatiles contained in the bubbles is large. For this reason, the volatile matter of platinum is easy to deposit, and there are also many platinum foreign substances contained in the volatile matter deposit and the molten glass. On the other hand, when the measured oxygen concentration in the gas is low, it means that bubbles are difficult to grow by absorbing oxygen, so the amount of volatile platinum group metal volatiles contained in the bubbles is small. For this reason, the volatile matter of platinum is hard to deposit, and there are also few platinum foreign substances contained in the molten glass, and also the molten glass. For this reason, when the oxygen concentration in the gas becomes a predetermined value or more, the control unit (not shown) increases the supply amount of the inert gas discharged to the clarification tube 41, for example, the supply amount of N ₂ gas. By reducing the oxygen concentration in the gas relatively, the precipitation of platinum foreign matter is suppressed. On the other hand, when the oxygen concentration in the gas is equal to or lower than a predetermined value, the control unit (not shown) reduces the supply amount of the inert gas discharged to the clarification tube 41, for example, the supply amount of N ₂ gas, The oxidation-reduction reaction of SnO ₂ that is a fining agent added to the glass G is promoted to remove bubbles containing CO ₂ or SO ₂ contained in the molten glass G.

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.

  Moreover, in order to prevent the deposit of the volatile substance of platinum falling on molten glass, a receiving part can also be provided in the vent pipe 41a and the measurement pipe 44. About the structure of a receiving part, the said content is considered including the content described in Unexamined-Japanese-Patent No. 2014-47124.

  As described above, in the measurement tube of the present embodiment, the tension generated between the liquid precipitate in which the gas is condensed at the entrance of the measurement tube and the measurement tube is on the liquid surface side of the molten glass due to the weight of the liquid. By making it larger than the force generated toward the surface, it is possible to prevent the precipitate from falling. Moreover, since the inner diameter and outer diameter of the measuring tube are smaller than the inner diameter and outer diameter of the ventilation tube, volatile substances are difficult to deposit on the outer peripheral portion (outer surface side) of the measuring tube and the inner peripheral portion (inner surface side) of the measuring tube. The fall of the precipitate can be prevented. Moreover, it is possible to suppress the generation and accumulation of precipitates near the entrance of the measurement tube, and to stably measure the oxygen concentration without the measurement tube being clogged with precipitates.

  Although the manufacturing method of the glass substrate and the manufacturing apparatus of the glass substrate of the present invention have been described in detail, the present invention is not limited to the above embodiment, and various improvements and modifications are made without departing from the gist of the present invention. Of course it is also good.

DESCRIPTION OF SYMBOLS 41 Clearing pipe 41a Venting pipe 41b Heating electrode 41c Gas phase space 44 Measuring pipe 45 Oxygen concentration meter 200 Glass substrate manufacturing apparatus G Molten glass LS Surface of molten glass

Claims (8)

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,
In the clarification step, the molten glass flows inside a clarified tube made of platinum or a platinum alloy so that a gas phase space that is a space above the surface of the molten glass is formed,
The clarification pipe protrudes outward from the outer wall surface of the clarification pipe, and has a ventilation pipe through which a gas containing platinum existing in the gas phase space passes.
The ventilation pipe is provided with a measurement pipe for taking in and measuring the gas,
An oxygen concentration meter connected to the measuring tube for measuring the oxygen concentration of the gas;
The method of manufacturing a glass substrate, wherein the measuring tube has a vertical cross section of an opening end on the gas intake side inclined with respect to a longitudinal direction of the measuring tube.   The method for manufacturing a glass substrate according to claim 1, wherein the oxygen concentration meter measures the oxygen concentration by flowing the inert gas through the measurement tube and then taking the gas from the measurement tube.   The gas condenses on the surface of the molten glass surface of the measuring tube to become a liquid, and the tension generated between the liquid and the measuring tube is caused by the weight of the liquid on the liquid surface side of the molten glass. The method of manufacturing a glass substrate according to claim 1, wherein the force is greater than a force generated toward the glass substrate.   The manufacturing method of the glass substrate of any one of Claims 1-3 which adjusts the supply amount of the inert gas supplied to the said gaseous-phase space according to the measurement result by the said oxygen concentration meter.   The manufacturing method of the glass substrate of any one of Claims 1-4 whose inclination-angle (phi) with respect to the plane orthogonal to the longitudinal direction of the pipe | tube of the said longitudinal cross section of the said open end is 15 degree | times-75 degree | times. 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,
The clarified tube is a tube made of platinum or a platinum alloy in which the molten glass flows inside so as to form a gas phase space that is a space above the surface of the molten glass,
The clarification pipe protrudes outward from the outer wall surface of the clarification pipe, and has a ventilation pipe through which a gas containing platinum existing in the gas phase space passes.
The ventilation pipe is provided with a measurement pipe for taking in and measuring the gas,
An oxygen concentration meter connected to the measuring tube for measuring the oxygen concentration of the gas;
The glass tube manufacturing apparatus according to claim 1, wherein the measuring tube has a vertical cross section of an opening end on the gas intake side inclined with respect to a longitudinal direction of the measuring tube.   Furthermore, the manufacturing apparatus of the glass substrate of Claim 6 provided with the inert gas supply device comprised so that an inert gas might be flowed through the said measurement pipe | tube during the standby before the measurement of the said oxygen concentration meter.   The apparatus for producing a glass substrate according to claim 6 or 7, wherein an inclination angle φ of the longitudinal section of the open end with respect to a plane orthogonal to the longitudinal direction of the measuring tube is 15 to 75 degrees.

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