TW201609580A - Method for making glass substrate and apparatus for making glass substrate - Google Patents

Abstract

The present invention provides a glass substrate manufacturing method, which can suppress foreign substances from entering molten glass in the clarification step of molten glass. The glass substrate manufacturing method of this invention includes: a melting step to heat glass raw material to form molten glass; a clarification step to clarify the molten glass; and a molding step to mold the molten glass into a glass substrate. In the clarification step, the molten glass flows in the interior of the clarification tube, which is made of platinum or platinum alloy, in a manner of forming a gas phase space therein, i.e. the space located above the top surface of the molten glass. The clarification tube has a vent tube which is protruded outward from the outer wall of the clarification tube to allow the platinum-containing gas present in the gas phase space to pass through. The vent tube is arranged with a measuring tube for sucking up gas for measurement and an oxygen concentration meter which is connected with the measuring tube to measure the oxygen concentration of the gas. The longitudinal section of an opening end at the gas suction side of the measuring tube is tilted relative to the lengthy direction of the measuring tube.

Description

Method for producing glass substrate and device for manufacturing glass substrate

The present invention relates to a method for producing a glass substrate and a device for producing a glass substrate.

Generally, as described in Patent Document 1, the method for producing a glass substrate includes a melting step of heating a glass raw material to produce molten glass, and a molding step of forming a glass substrate from molten glass. The method for producing a glass substrate further includes a clarification step of removing minute bubbles contained in the molten glass between the melting step and the forming step. In the clarification step, the molten glass to which the clarifying agent such as As ₂ O _{3 is} formulated is passed through a high-temperature clarification tube, whereby the bubbles in the molten glass are removed by the redox reaction of the clarifying agent. Specifically, first, the temperature of the molten glass is raised so that the clarifying agent functions, whereby the bubbles contained in the molten glass float out to the liquid surface of the molten glass in the clarification tube to remove the bubbles. Then, the temperature of the molten glass is lowered, and the molten glass absorbs the fine bubbles remaining in the molten glass to remove the bubbles. The clarification pipe through which the molten glass passes has a gas phase space between the inner wall surface of the upper side and the liquid surface of the molten glass. The gas phase space communicates with the outside atmosphere as the outer space of the clarification tube via a vent pipe connected to the clarification pipe.

In order to mass-produce a high-quality glass substrate from a high-temperature molten glass, it is preferable that foreign matter which is a cause of defects of the glass substrate is not mixed into the molten glass. Therefore, the inner wall of the member in contact with the molten glass must be composed of a suitable material depending on the temperature of the molten glass in contact with the member, the quality of the desired glass substrate, and the like. The inner wall of the member in contact with the molten glass generally uses a platinum group metal as a suitable material. Below, "Platinum Group Metals" It means an alloy containing a single platinum group element and an alloy containing 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). Although the platinum group metal is expensive, it has a high melting point and is excellent in corrosion resistance to molten glass.

The temperature of the molten glass inside the clarification tube varies depending on the composition of the formed glass substrate, and in the case of a glass substrate for a flat panel display (FPD), the temperature is 1000 ° C to 1700 ° C. In recent years, SnO _{2 has been} used as a clarifying agent instead of As ₂ O ₃ from the viewpoint of reducing environmental load. The clarifying effect of SnO ₂ is smaller than that of As ₂ O ₃ , and in order to obtain the same clarifying effect as As ₂ O ₃ , it is necessary to increase the temperature of the molten glass. Specifically, in the case where SnO _{2 is} used as the clarifying agent, the temperature of the molten glass passing through the inside of the clarification tube is set to 1500 ° C to 1700 ° C.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2006-522001

In the method for producing a glass substrate using SnO ₂ as a clarifying agent, the inner wall of the clarification tube is in contact with the molten glass of high temperature. At this time, the clarifying agent undergoes a reduction reaction due to the temperature rise to release oxygen. On the other hand, the bubble containing the gas component contained in the molten glass absorbs oxygen generated by the reduction reaction of the clarifying agent. The bubble which is increased by absorbing oxygen floats to the liquid surface of the molten glass, and is broken and disappears. Further, since the clarification tube is used for a long period of time, the platinum group metal slowly volatilizes from the inner wall of the clarification tube by reacting with oxygen. The volatile matter is discharged to the outside atmosphere through the gas phase space of the clarification tube and the vent pipe together with the bubbles in the molten glass. However, the volatile matter of the platinum group metal is lowered in the process of discharging to the outside atmosphere to become a supersaturated state. Therefore, there is a problem that it is easy to precipitate volatiles on the inner wall of the clarification pipe and the vent pipe. Hereinafter, a substance which precipitates on the inner wall of the clarification pipe and the vent pipe is referred to as "platinum foreign matter". By measuring the concentration (oxygen concentration) of oxygen which generates the volatile matter in the snorkel, it is possible to predict the amount of bubbles which are grown by absorbing oxygen in the molten glass, thereby predicting the precipitation of platinum foreign matter. However, since the inside of the vent pipe is in communication with the outside atmosphere, the temperature is liable to lower, and the platinum foreign matter is particularly likely to be precipitated on the inner wall of the vent pipe. When the platinum foreign matter grows with time, the platinum foreign matter peels off from the inner wall of the clarification pipe and the vent pipe due to its own weight, and the possibility of dropping the molten glass in the clarification pipe. Further, when the platinum foreign matter deposited on the inner wall of the vent pipe is removed, there is a possibility that the platinum foreign matter falls into the molten glass in the clarification pipe. In particular, platinum foreign matter is deposited on a measuring tube for taking oxygen and measuring the oxygen concentration, and is dropped. Further, when platinum foreign matter is mixed into the molten glass, it becomes difficult to mass-produce a high-quality glass substrate.

Accordingly, an object of the present invention is to provide a method for producing a glass substrate which can suppress foreign matter from being mixed into molten glass in a clarification step of molten glass, and a device for producing a glass substrate.

An aspect of the present invention provides a method for producing a glass substrate, comprising: a melting step of heating a glass raw material to produce molten glass; a clarifying step of clarifying the molten glass; and a forming step of In the above-described clarification step, the molten glass is clarified, and the molten glass is formed inside a clarification pipe made of platinum or platinum alloy so as to form a gas phase space, that is, a space above the surface of the molten glass. Flowing, the clarification pipe has a vent pipe that protrudes outward from the outer wall of the clarification pipe, and a gas containing platinum is passed through the gas phase space, and a measuring pipe for absorbing the gas and measuring the vent pipe is provided in the vent pipe. And having an oxygen concentration which is connected to the measuring tube to measure the oxygen concentration of the gas The longitudinal section of the open end of the measuring tube sucking the gas side is inclined with respect to the longitudinal direction of the measuring tube.

Preferably, the oxygen concentration meter picks up the gas from the measuring tube after flowing an inert gas into the measuring tube, and measures the oxygen concentration.

Preferably, the gas is condensed to form a liquid on the surface side of the molten glass of the measuring tube, and a tension generated between the liquid and the measuring tube is larger than a liquid surface side of the molten glass due to the weight of the liquid. force.

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

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

Another aspect of the present invention provides a glass substrate manufacturing apparatus, comprising: a melting tank for heating a glass raw material to produce molten glass; and a clarification tube for performing the molten glass produced in the melting tank And a molding apparatus comprising the molten glass forming glass substrate clarified in the clarification pipe, wherein the clarification pipe is formed such that the molten glass forms a gas phase space, that is, a space above the surface of the molten glass a tube made of platinum or a platinum alloy which flows inside, and the clarification pipe has a vent pipe which protrudes from the outer wall surface of the clarification pipe to allow a gas containing platinum to pass through the gas phase space, and is provided in the vent pipe. a measuring tube that picks up the above gas and performs measurement, and has an oxygen concentration connected to the measuring tube to measure the oxygen concentration of the gas The longitudinal section of the open end of the measuring tube sucking the gas side is inclined with respect to the longitudinal direction of the measuring tube.

Further preferably, the inert gas supply device is configured to allow an inert gas to flow into the measuring tube during standby of the oxygen concentration meter.

Preferably, the longitudinal section of the open end is inclined with respect to a plane orthogonal to the longitudinal direction of the measuring tube It is 15 degrees to 75 degrees.

According to the above aspect, foreign matter can be prevented from being mixed into the molten glass in the clarification step of the molten glass.

40‧‧‧melting tank

41‧‧‧clarification tube

41a‧‧‧ snorkel

41b‧‧‧heating electrode

41c‧‧‧ gas phase space

42‧‧‧Forming device

43a‧‧‧ delivery tube

43b‧‧‧ delivery tube

43c‧‧‧ delivery tube

44‧‧‧Measurement tube

45‧‧‧Oxygen concentration meter

52‧‧‧ Shaped body

100‧‧‧Agitator

200‧‧‧Manufacturing device for glass substrates

G‧‧‧ molten glass

GR‧‧‧glass ribbon

LS‧‧‧ Surface of molten glass

Fig. 1 is a flow chart showing the steps of a method for producing a glass substrate of the present embodiment.

Fig. 2 is a schematic view showing the configuration of a glass substrate manufacturing apparatus of the present embodiment.

Figure 3 is an external view of the clarification tube.

Fig. 4 is a schematic cross-sectional view showing the longitudinal direction of the clarification pipe.

Figure 5 is a diagram for explaining the surface tension generated between the measuring tube and the solidified volatile matter.

Fig. 6 is a view for explaining the surface tension generated between the measuring tube of the present embodiment and the solidified volatile matter.

(1) The overall composition of the glass substrate manufacturing apparatus

Embodiments of the method for producing a glass substrate of the present invention and the apparatus for manufacturing a glass substrate will be described with reference to the drawings. Fig. 1 is a flow chart showing an example of the procedure of the method for producing a glass substrate of the embodiment.

As shown in FIG. 1 , the glass substrate manufacturing method mainly includes: a melting step S1 and a clarification step. Step S2, stirring step S3, forming step S4, slow cooling step S5, and 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 is electrically heated in such a manner as to have a desired temperature. The molten glass contains a clarifying agent. For example, a clarifying agent may be added to the glass raw material, or a clarifying agent may be added to the glass raw material, but the molten glazing may be contained by melting the components of the clarifying agent from the melting tank or the electrode for heating and heating. Clarifying agent. From the viewpoint of reducing environmental load, SnO _{2 is} used as a fining agent.

The clarification step S2 is carried out in a clarification tube. In the clarification tube, the molten glass flows inside it. First, the temperature of the molten glass is raised. The clarifying agent undergoes a reduction reaction due to the temperature rise to release oxygen. The bubbles containing gas components such as CO ₂ , N ₂ , and SO ₂ contained in the molten glass absorb oxygen generated by the reduction reaction of the fining agent. The bubble which is increased by absorbing oxygen floats to the surface of the molten glass which is in contact with the gas phase space, and is broken and disappears. The gas system contained in the disappearing bubble is released into the gas phase space in the clarification pipe and finally discharged to the outside atmosphere. Then, in the clarification step S2, the temperature of the molten glass is lowered. Thereby, the clarifying agent after the reduction undergoes an oxidation reaction to absorb a gas component such as oxygen remaining in the molten glass.

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

In the forming step S4, the glass ribbon is continuously formed from the molten glass by, for example, an overflow down-draw method or a floating method.

In the slow cooling step S5, the glass ribbon continuously formed in the forming step S4 has a desired thickness, and is slowly cooled without causing deformation and warpage.

In the cutting step S6, the glass ribbon which has been slowly cooled in the slow cooling step S5 is cut into a specific length to obtain a glass sheet. The glass sheet is further cut into a specific size to obtain a glass substrate. Thereafter, the grinding and polishing of the end surface of the glass substrate and the clearing of the glass substrate are performed. wash. Further, the glass substrate is inspected for defects such as damage, and the glass substrate that has passed the inspection is packaged as a product and shipped.

FIG. 2 is a schematic view showing an example of the configuration of the glass substrate manufacturing apparatus 200 of the present embodiment. The glass substrate manufacturing apparatus 200 includes a melting tank 40, a clarification pipe 41, a stirring device 100, a molding device 42, and transfer pipes 43a, 43b, and 43c. The conveying pipe 43a connects the melting tank 40 and the clarification pipe 41. The conveying pipe 43b connects the clarification pipe 41 to the stirring device 100. The conveying pipe 43c connects the stirring device 100 and the forming device 42.

The molten glass G generated in the melting tank 40 flows into the clarification pipe 41 through the transfer pipe 43a. The molten glass G clarified in the clarification pipe 41 flows into the stirring device 100 through the transfer pipe 43b. The molten glass G that has been stirred in the stirring device 100 flows into the molding device 42 through the transfer pipe 43c. In the forming apparatus 42, the glass ribbon GR is formed from the molten glass G by an overflow down-draw method. The glass ribbon GR is cut into a specific size in the subsequent step to manufacture a glass substrate. 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 longitudinal direction is, for example, 500 mm to 3500 mm.

The glass substrate produced by the method for producing a glass substrate of the present invention and the glass substrate manufacturing apparatus is particularly suitable as a glass substrate for a display including a flat panel display (FPD) such as a liquid crystal display, a plasma display, or an organic EL display. As the glass substrate for a display including the FPD, an alkali-free glass or a glass containing a small amount of alkali is used. The 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 a heating mechanism (not shown) such as a burner. In the melting tank 40, the glass raw material is melted by a heating mechanism to produce molten glass G. The glass raw material is prepared in such a manner that the glass of the desired composition can be substantially obtained. As an example of the composition of the glass, the alkali-free glass suitable for use as a glass substrate for a display including FPD contains SiO ₂ : 50% by mass to 70% by mass, Al ₂ O ₃ : 0% by mass to 25% by mass, and 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, and BaO: 0% by mass to 10% by mass. Here, the total content of MgO, CaO, SrO, and BaO is 5% by mass to 30% by mass.

Further, a glass containing a trace amount of an alkali metal and a small amount of alkali may be used as the glass substrate for a display including the FPD. The glass containing a trace amount of alkali contains 0.1% by mass to 0.5% by mass of R' ₂ O as a component, and preferably contains 0.2% by mass to 0.5% by mass of R' ₂ O as a component. Here, R' is at least one selected from the group consisting of Li, Na, and K. Further, the total content of R' ₂ O may be less than 0.1% by mass.

The glass produced by the present invention may further contain, in addition to the above components, SnO ₂ : 0.01% by mass to 1% by mass (preferably 0.01% by mass to 0.5% by mass), and Fe ₂ O ₃ : 0% by mass to 0.2%. % by mass (preferably 0.01% by mass to 0.08% by mass). Further, the glass produced by the present invention does not substantially contain As ₂ O ₃ , Sb ₂ O ₃ and PbO in consideration of environmental load.

The glass raw material prepared in the above manner is put into the melting tank 40 using a raw material input machine (not shown). The raw material input machine can be used to input glass raw materials using a screw feeder, and a glass material can also be used by using a bucket. In the melting tank 40, the glass raw material is heated to a temperature corresponding to the composition thereof to melt the glass raw material. Thereby, in the melting tank 40, for example, a molten glass G having a high temperature of 1500 ° C to 1600 ° C is obtained. Further, in the melting tank 40, a current can be supplied to at least one pair of electrodes made of molybdenum, platinum, or tin oxide, and the molten glass G between the electrodes can be electrically heated, and the electric power can be removed. The glass material is heated by externally heating the auxiliary flame to the burner.

The molten glass G obtained in the melting tank 40 flows into the clarification pipe 41 through the transfer pipe 43a from the melting tank 40. The clarification pipe 41 and the transfer pipes 43a, 43b, and 43c are pipes made of platinum or platinum alloy. In the clarification pipe 41, a heating mechanism is provided similarly to the melting tank 40. In the clarification pipe 41, clarification is performed by further raising the temperature of the molten glass G. For example, in the clarification pipe 41, the temperature of the molten glass G rises to 1500 ° C to 1700 ° C.

The molten glass G clarified in the clarification pipe 41 passes through the conveying pipe 43b from the clarification pipe 41 It flows into the stirring device 100. The molten glass G is cooled while passing through the transfer pipe 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 pipe 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 homogenized by stirring in the stirring apparatus 100.

The molten glass G that has been homogenized in the stirring device 100 flows into the molding device 42 from the stirring device 100 through the conveying pipe 43c. The molten glass G is cooled so as to be suitable for molding the viscosity of the molten glass G when passing through the transfer pipe 43c. For example, the molten glass G is cooled to around 1200 °C. In the forming apparatus 42, the molten glass G is formed by an overflow down-draw method. Specifically, the molten glass G flowing into the molding device 42 is supplied to the molded body 52 provided inside the forming furnace (not shown). The formed body 52 is formed by refractory bricks and has a wedge-shaped cross-sectional shape. A groove is formed on the upper surface of the formed body 52 along the longitudinal direction of the formed body 52. The molten glass G is supplied to the groove on the upper surface of the formed body 52. The molten glass G overflowing from the groove flows downward along the side of one of the formed bodies 52. One of the side faces flowing through the molded body 52 merges the molten glass G at the lower end of the formed body 52, and the glass ribbon GR is continuously formed. The glass ribbon GR is slowly cooled as it flows downward, and thereafter, is cut into a glass piece of a desired length.

(2) The composition of the clarification tube

Next, the detailed configuration of the clarification pipe 41 will be described. Fig. 3 is an external view of the clarification pipe 41. 4 is a schematic cross-sectional view showing the clarification pipe 41 cut in the vertical direction along the longitudinal direction of the clarification pipe 41. As shown in FIG. 3, a vent pipe 41a and a pair of heating electrodes 41b are attached to the clarification pipe 41. Inside the clarification pipe 41, the molten glass G flows in a state in which the gas phase space 41c is formed above. That is, inside the clarification pipe 41, as shown in Fig. 4, there is a surface LS of the molten glass G which is in contact with the gas phase space. The internal space of the vent pipe 41a is in communication with the gas phase space 41c. Further, the clarification pipe 41 is electrically heated by passing an electric current between the pair of heating electrodes 41b. Thereby, the molten glass G which passed the inside of the clarification pipe 41 is heated and clarified. In the clarification process of the molten glass G, the bubbles containing the gas components such as CO ₂ , N ₂ , and SO ₂ contained in the molten glass G absorb oxygen generated by the reduction reaction of the clarifying agent. The bubble which is increased by absorbing oxygen floats to the surface LS of the molten glass G, and is broken and disappears. The gas contained in the disappearing bubble is released into the gas phase space 41c in the clarification pipe 41, and is discharged to the outside air via the vent pipe 41a.

The vent pipe 41a is attached to the outer wall surface of the clarification pipe 41, and protrudes toward the outer side of the clarification pipe 41. In the present embodiment, as shown in FIG. 4, the vent pipe 41a is attached to the upper end portion of the outer wall surface of the clarification pipe 41, and protrudes toward the upper side of the clarification pipe 41 in a chimney shape. The vent pipe 41a communicates the gas phase space 41c which is a part of the internal space of the clarification pipe 41 with the outside atmosphere which is the outer space of the clarification pipe 41. The vent 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.

In the vent pipe 41a, as shown in FIG. 4, a measuring tube 44 for sucking a gas in a gas phase space containing a volatile matter of a platinum group metal passing through the vent pipe 41a is provided, and a gas sucked from the measuring pipe 44 is provided. The oxygen concentration meter 45 for measuring the oxygen concentration. The measuring tube 44 is formed of platinum or a platinum alloy in the same manner as the vent tube 41a, and is connected to the oxygen concentration meter 45 so that the gas sucked from the measuring tube 44 enters the oxygen concentration meter 45. Regarding the inner diameter and the outer diameter of the measuring tube 44, the inner diameter and the outer diameter of the measuring tube 44 are smaller than the inner and outer diameters of the venting tube 41a as long as the measuring tube 44 draws a gas which can measure the oxygen concentration of the gas. For example, the inner diameter and the outer diameter of the measuring tube 44 are 20 mm or less. The gas system containing the volatile matter of the platinum group metal is discharged to the outside air through the vent pipe 41a, but the temperature is lowered during the discharge to the outside atmosphere to become a supersaturated state. In particular, the volatile matter is likely to be precipitated in the vicinity of the inlet of the measuring tube 44 to become a liquid, and the precipitate of the liquid falls, and as a result, a solid platinum foreign matter is mixed into the molten glass. The reason for this is that since the outer diameter of the measuring tube 44 is small, the surface tension generated between the liquid precipitate and the outer surface of the measuring tube 44 is weak. Figure 5 is for condensing based on the surface of the measuring tube 44 with volatiles. The force of the surface tension generated between the liquid precipitates M will be described. When the force based on the surface tension of the outer surface of the tube having the tube outer diameter R1 is set to the upward force F1, the force F1 is obtained by the following formula (1).

F1=2πr1×γ×cosθ (1)

Here, r1 = radius of the outer diameter of the measuring tube 44, γ = surface tension, and θ = contact angle. Further, the surface tension and the contact angle are determined depending on the viscosity of the substance, and are set to a fixed value here.

When the mass of the precipitate of the volatile matter is M, the condition that the precipitate stays in the measuring tube 44 is M × g (gravitational acceleration) < F1. Therefore, in order to prevent the precipitate from falling, it is necessary to make the radius r1 of the outer diameter of the measuring tube 44 large. On the other hand, when the outer diameter and the inner diameter of the measuring tube 44 are increased, volatile matter is 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. The precipitate is dropped. Therefore, 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 precipitate deposited on the measuring tube 44 from falling. The inlet volatiles on the outer surface side of the molten glass of the measuring tube 44 are condensed to become a liquid, and the tension generated between the liquid and the measuring tube 44 is generated to be larger toward the liquid surface side of the molten glass due to the weight of the liquid. The force prevents the liquid (precipitate) from falling.

Fig. 6 is a view for explaining the force based on the surface tension generated between the measuring tube 44 of the present embodiment and the precipitate M of the volatile matter. The measuring tube 44 of the present embodiment is provided on the side (the gas suction side) of the surface LS of the molten glass G where the clarification tube 41 exists, and has an open end inclined with respect to the longitudinal direction of the tube. For example, the open end is formed by cutting the opening end so as to be inclined with respect to the longitudinal direction of the tube shown in FIG. 5. In other words, the vertical cross-sectional diameter (longitudinal section) of the measuring tube 44 along the open end of the gas suction side becomes larger than the side connected to the oxygen concentration meter 45 (the upper side of the gas suction side and the side protruding toward the outer side of the clarification pipe 41). ) The vertical cross section diameter. Here, the longitudinal section is the plane of the slit obtained when the object is longitudinally cut. As shown in Fig. 6, the longitudinal section of the measuring tube 44 on the open end side of the gas suction side is inclined with respect to the longitudinal direction of the tube. By making the open end of the gas suction port (the longitudinal section of the gas suction side) of the measuring tube 44 inclined with respect to the longitudinal direction of the tube, the inner diameter and the outer diameter R1 of the measuring tube 44 can be omitted. In this case, the force based on the surface tension under the outer diameter of the tube is increased. In the measuring tube 44 of the present embodiment, the vertical cutting diameter of the open end becomes the outer diameter R2, and the radius of the vertical cross-sectional diameter of the open end which is in contact with the precipitate M of the volatile matter is larger than one half of R1, and thus the above formula (1) The upward force F2 based on the surface tension is greater than the force F1. Therefore, it is possible to suppress the precipitate M of the volatile matter precipitated at the inlet of the measuring tube 44 from falling. The angle between the entrance of the measuring tube 44 and the horizontal direction, in other words, the inclination angle with respect to the plane orthogonal to the longitudinal direction of the tube It is preferably 15 to 75 degrees, more preferably 30 to 60 degrees, still more preferably 45 degrees. angle The viscosity of the precipitate M of the volatile matter may be arbitrarily changed, as long as the tension generated between the precipitate M and the measuring tube 44 is greater than the force generated toward the surface side of the molten glass due to the weight of the precipitate M, the angle There are no special restrictions.

The oxygen concentration meter 45 is any commercially available machine that can measure the oxygen concentration. The oxygen concentration meter 45 is, for example, a zirconia type, a magnetic gas type, or an electrode type density meter. The oxygen concentration meter 45 measures the oxygen concentration of the gas taken up from the measuring tube 44. When the oxygen concentration is measured, the oxygen concentration meter 45 controls a nitrogen gas (N ₂ ) supplier (not shown) to supply N ₂ into the measurement tube 44. If a gas containing a volatile matter of a platinum group metal flows into the measuring tube 44, particularly in the vicinity of the oxygen concentration meter 45, measurement errors are likely to occur. Further, when the gas flows into the measuring tube 44, precipitates are generated and accumulated in the vicinity of the inlet of the measuring tube 44, and the measuring tube 44 is clogged. Therefore, in the standby state in which the oxygen concentration is measured, N _{2 is} filled in the measuring tube 44, and the gas containing the volatile matter of the platinum group metal 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 improved. Further, there is no case where the measuring tube 44 is clogged by the precipitate, and the oxygen concentration can be measured stably. Further, the oxygen concentration meter 45 sucks the gas in the measuring tube 44 to measure the oxygen concentration of the gas. In the present embodiment, an inert gas other than nitrogen may be supplied using an inert gas supply instead of supplying nitrogen gas using a nitrogen gas supplier. The inert gas in this case is a gas which does not react with a volatile matter of platinum or a molten glass, for example, a gas containing an element of Group 18 such as ruthenium, rhodium or argon.

Here, the nitrogen gas supplier is connected to the measuring tube 44 to supply an inert gas to the measuring tube 44, and specifically supplies nitrogen gas. The gas containing the volatile matter of the platinum group metal is discharged to the outside air through the vent pipe 41a, and the temperature is lowered to be supersaturated during the discharge to the outside air. In particular, the gas containing the volatiles of the platinum group metal sucked from the measuring tube 44 may be such that as the suction port of the measuring tube 44 flows toward the oxygen concentration meter 45, the temperature is lowered to become a supersaturated state, and the measuring tube 44 is used. The volatile matter is precipitated in the tube, and the measuring tube 44 is blocked. If the measuring tube 44 is clogged by volatile matter (precipitates), the oxygen concentration of the gas cannot be stably measured. Further, there is a case where precipitates are dropped from the measuring tube 44 and platinum foreign matter is mixed into the molten glass. Therefore, the nitrogen gas purifier supplies nitrogen gas to the measuring tube 44 to fill the inside of the tube with nitrogen gas, and suppresses the gas containing the volatile matter of the platinum group metal from flowing into the measuring tube 44, thereby preventing the precipitate of the volatile matter from being clogged in the measuring tube. 44.

In the method for producing a glass substrate of the present embodiment, the molten glass G generated by heating the glass raw material is heated while passing through the inside of the clarification pipe 41. Inside the clarification pipe 41, the bubble containing CO ₂ or SO ₂ contained in the molten glass G is removed by the redox reaction of SnO ₂ as a clarifying agent added to the molten glass G. Specifically, first, the temperature of the molten glass G is raised, and the clarifying agent is reduced, whereby bubbles of oxygen are generated in the molten glass G. The bubbles containing gas components such as CO ₂ , N ₂ , and SO ₂ contained in the molten glass G absorb oxygen generated by the reduction reaction of the clarifying agent. The bubble which is increased by absorbing oxygen floats to the surface LS of the molten glass G, and is broken and disappears. The gas contained in the disappearing bubble is released into the gas phase space 41c, and is discharged to the outside air via the vent pipe 41a. The oxygen concentration meter 45 predicts the precipitation of platinum foreign matter by measuring the oxygen concentration of the gas (gas) discharged to the outside air and predicting the amount of bubbles that grow by absorbing oxygen. The fact that the oxygen concentration in the gas measured is relatively high means that the bubble grows easily by absorbing oxygen, so that the amount of volatile matter of the platinum group metal volatilized by the bubble is large. Therefore, the volatile matter of platinum is likely to be precipitated, and the precipitate of the volatile matter, and further the platinum foreign matter contained in the molten glass, is also more. On the other hand, the fact that the oxygen concentration in the measured gas is low means that the bubble grows hard to absorb oxygen, so that the amount of volatile matter of the volatilized platinum group metal contained in the bubble is small. Therefore, the volatile matter of platinum is hard to be precipitated, and the precipitate of the volatile matter and the platinum foreign matter contained in the molten glass are also less. Therefore, when the oxygen concentration in the gas is equal to or higher than a specific value, the control unit (not shown) increases the oxygen supply in the gas by increasing the supply amount of the inert gas released to the clarification pipe 41, for example, the supply amount of nitrogen gas. The concentration is relatively lowered, and platinum foreign matter is inhibited from being precipitated. On the other hand, when the oxygen concentration in the gas is equal to or lower than a specific value, the control unit (not shown) promotes the addition of the supply amount of the inert gas released to the clarification pipe 41, for example, the supply amount of nitrogen gas. The redox reaction of SnO ₂ as a fining agent in the molten glass G removes bubbles containing CO ₂ or SO ₂ contained in the molten glass G.

The heating electrode 41b is attached to the electrode plates of the flange shape at both ends of the clarification pipe 41, respectively. The heating electrode 41b is connected to a power source (not shown). By supplying electric power to the heating electrode 41b, an electric current is supplied to the clarification pipe 41 between the pair of heating electrodes 41b, and the clarification pipe 41 is electrically heated. Thereby, the clarification pipe 41 is heated to, for example, 1700 ° C, and the molten glass G flowing through the inside of the clarification pipe 41 is heated to a temperature at which the SnO ₂ as a clarifying agent contained in the molten glass G is reduced, for example, 1600 ° C. 1650 ° C. The temperature of the molten glass flowing through the inside of the clarification pipe 41 can be controlled by controlling the current flowing through the clarification pipe 41. Further, the number and position of the heating electrodes 41b attached to the clarification pipe 41 can be appropriately determined depending on the material, the inner diameter and the length of the clarification pipe 41, or the position of the vent pipe 41a.

Further, although not shown in Figs. 3 and 4, a refractory protective layer containing high alumina cement or the like is provided on the outer wall surface of the clarification pipe 41. A refractory brick is further disposed on the outer wall of the refractory protective layer. The refractory bricks are placed on a base (not shown). That is, the clarification pipe 41 is supported by the refractory protective layer and the refractory brick from below.

Further, in order to prevent the precipitate of the volatile matter of platinum from falling into the molten glass, a support portion may be provided in the vent pipe 41a and the measuring pipe 44. Regarding the constitution of the support portion, including Japanese patents The contents described in Japanese Laid-Open Patent Publication No. 2014-47124 are incorporated herein by reference.

As described above, in the measuring tube of the present embodiment, the tension generated between the liquid precipitate formed by the condensation of the inlet gas of the measuring tube and the measuring tube is larger than that due to the weight of the liquid toward the molten glass. The force generated on the liquid level side prevents the precipitate from falling. Further, since the inner diameter and the outer diameter of the measuring tube are smaller than the inner diameter and the outer diameter of the vent pipe, it is difficult for the volatile matter to be deposited on the outer peripheral portion (outer surface side) of the measuring tube and the inner peripheral portion (inner surface side) of the measuring tube. It can prevent the fall of precipitates. Further, it is possible to suppress generation and deposition of precipitates in the vicinity of the inlet of the measuring tube, and it is possible to stably measure the oxygen concentration without the measuring tube being clogged with the precipitate.

The glass substrate manufacturing method and the glass substrate manufacturing apparatus of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the gist of the invention. Or change.

41‧‧‧clarification tube

41a‧‧‧ snorkel

41c‧‧‧ gas phase space

44‧‧‧Measurement tube

45‧‧‧Oxygen concentration meter

G‧‧‧ molten glass

LS‧‧‧ Surface of molten glass

Claims (8)

A method for producing a glass substrate, comprising: a melting step of heating a glass raw material to produce molten glass; a clarifying step of clarifying the molten glass; and a forming step of forming the clarified molten glass a glass substrate; and in the clarification step, the molten glass flows inside a clarification pipe made of platinum or a platinum alloy so as to form a gas phase space, that is, a space above the surface of the molten glass, the clarification pipe having The outer wall of the clarification pipe protrudes outward, and a vent pipe through which the platinum-containing gas is passed in the gas phase space is provided, and the vent pipe is provided with a measuring tube for taking in the gas and measuring the same, and has a connection with the measuring tube. The oxygen concentration meter for measuring the oxygen concentration of the gas is inclined such that the longitudinal section of the open end of the measuring tube on the gas side is inclined with respect to the longitudinal direction of the measuring tube. The method for producing a glass substrate according to claim 1, wherein the oxygen concentration meter draws the gas from the measuring tube after flowing an inert gas into the measuring tube, and measures an oxygen concentration. The method for producing a glass substrate according to claim 1 or 2, wherein the gas on the surface side of the molten glass of the measuring tube is condensed to become a liquid, and a tension generated between the liquid and the measuring tube is greater than a weight of the liquid The force is generated toward the liquid surface side of the molten glass. The method for producing a glass substrate according to any one of claims 1 to 3, wherein the inert gas supplied to the gas phase space is adjusted according to the measurement result of the oxygen concentration meter Supply amount. The method for producing a glass substrate according to any one of claims 1 to 4, wherein an inclination angle of said longitudinal section of said open end with respect to a plane orthogonal to a longitudinal direction of said tube It is 15 degrees to 75 degrees. A manufacturing apparatus for a glass substrate, comprising: a melting tank for heating a glass raw material to produce molten glass; a clarification tube for clarifying the molten glass generated in the melting tank; and a forming device comprising The molten glass forming glass substrate clarified in the clarification pipe; and the clarification pipe is made of platinum or platinum in which the molten glass flows in a space in which a gas phase space, that is, a space above the surface of the molten glass, is formed. In the alloy tube, the clarification tube has a vent pipe that protrudes outward from the outer wall of the clarification pipe to allow a gas containing platinum to pass through the gas phase space, and the vent pipe is provided to absorb the gas and measure the gas. The measuring tube has an oxygen concentration meter that is connected to the measuring tube and measures the oxygen concentration of the gas, and a longitudinal section of the measuring tube that sucks the open end of the gas side is inclined with respect to a longitudinal direction of the measuring tube. The apparatus for manufacturing a glass substrate according to claim 6, further comprising an inert gas supplier configured to allow an inert gas to flow into the measuring tube during standby of the oxygen concentration meter. The apparatus for manufacturing a glass substrate according to claim 6 or 7, wherein an inclination angle of said longitudinal section of said open end with respect to a plane orthogonal to a longitudinal direction of said measuring tube It is 15 degrees to 75 degrees.