JP7142506B2 - Glass substrate manufacturing method and glass substrate manufacturing apparatus - Google Patents

Description

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

In order to refine the glass melt using the fining agent, the glass melt is heated in the fining tube of the fining tank to accelerate the defoaming action of the fining agent contained in the glass melt, thereby causing air bubbles to float in the glass melt. , the gas in the bubbles is released into the gas phase space in the clarification tube. Heating of the molten glass is performed, for example, by supplying an electric current to the clarification tube to heat the clarification tube. The gas phase space is a space surrounded by the inner wall of the clarification tube and the liquid surface of the molten glass in the clarification tube. As a constituent material of the fining tube, for example, a material made of a platinum group metal having excellent heat resistance is known (see, for example, Patent Document 1).

A portion of the inner wall of the fining tube that is in contact with the gas phase space tends to have a higher temperature than the portion that is in contact with the molten glass. Furthermore, since the gas phase space contains oxygen, the platinum group metal contained in the portion of the fining tube in contact with the gas phase space is oxidized, volatilized from the inner wall of the fining tube, and dispersed in the gas phase space as vapor. It's easy to do. A portion of the clarification tube in contact with the gas phase space may be provided with a vent pipe for discharging the gas in the gas phase space to the outside of the clarification tube. However, since the vent pipe is provided so as to protrude outside the fining pipe, the temperature tends to be lower than that of the fining pipe, and the volatile components of the platinum group metal flowing in the vent pipe become supersaturated inside the vent pipe. may clump together.

By the way, when the oxygen concentration in the gas phase space becomes high, the amount of volatile components of platinum group metal generated from the platinum group metal, which is the constituent material of the clarification tube, increases, and platinum foreign substances are likely to be generated. Therefore, an oxygen concentration meter is used to measure the oxygen concentration, and when the oxygen concentration becomes high, an inert gas such as argon or nitrogen is introduced into the gas phase space to lower the oxygen concentration in the gas phase space. things may be done. The oximeter has, for example, a tubular portion (intake portion) having an intake port for taking in gas flowing through the vent pipe, and the tip of the intake portion is arranged in the vent pipe.

Japanese Patent Publication No. 2006-522001

However, if the volatile components of the platinum group metal condense in the vent pipe and grow over time, the agglomerates of the platinum group metal may electrically connect the vent pipe and the oxygen concentration meter, resulting in electrical continuity. I understood it. When the vent tube and the oximeter are electrically connected, part of the current flowing through the clarifier tube flows into the oximeter, resulting in an abrupt change in the amount of current flowing through the clarifier tube. It has also been clarified that bubbles may be generated in the molten glass in the fining tube due to such a sudden change in the amount of current flowing through the fining tube. If such bubbles are generated in the glass melt, they may remain in the clarification tube without being released from the glass melt and remain in the glass substrate, resulting in quality defects.

The present invention suppresses an abrupt change in the amount of current flowing through the fining tank when fining glass melt by supplying current to the fining tank, thereby preventing the generation of air bubbles in the glass melt due to this. It aims at providing the manufacturing method of the glass substrate which can suppress and a glass substrate manufacturing apparatus.

One aspect of the present invention is a method for manufacturing a glass substrate, comprising:
a melting step of melting glass raw materials to form molten glass;
A fining step of forming a gas phase space above the liquid surface of the molten glass in a fining tank and fining the molten glass,
The clarification tank has an inner wall in contact with the gas phase space and made of a material containing a platinum group metal,
In the clarification tank,
a vent pipe communicating between the gas phase space and the outside of the clarification tank;
an oxygen concentration meter that is provided in the vent pipe with a tip portion having an intake port that takes in a part of the gas flowing in the vent pipe and measures the oxygen concentration of the taken gas,
In the fining step, an electric current is passed through the fining tank to heat the molten glass in the fining tank, and the platinum group metal volatilized from the inner wall and aggregated in the vent pipe passes through the vent pipe and the tip. are electrically connected to each other, the current supplied to the clarification tank and flowing from the vent tube to the oxygen concentration meter is passed through the clarification tank.

A heat insulating member is arranged around the clarification tank so as to surround the clarification tank,
The heat insulating member is supported from the outside of the heat insulating member by a metal frame member,
Preferably, the oximeter is insulated from the frame member.

The oxygen concentration meter is
a measuring unit that measures the oxygen concentration of the gas taken in from the intake;
a tubular intake portion extending from the intake port toward the measurement portion and having the tip portion;
It is preferred that the current flowing through the oximeter is returned from the intake to the clarification tank.

Yet another aspect of the present invention is a glass substrate manufacturing apparatus,
a melting device that melts glass raw materials to produce molten glass;
a clarification device that has a clarification tank, forms a gas phase space above the liquid surface of the molten glass in the clarification tank, and performs clarification of the molten glass;
The fining tank is in contact with the gas phase space and has an inner wall made of a material containing a platinum group metal, and is supplied with an electric current to heat the molten glass in the fining tank,
The clarification device further
a vent pipe communicating between the gas phase space and the outside of the clarification tank;
an oximeter that measures the oxygen concentration of the gas taken in, the tip portion having an intake port for taking in part of the gas flowing through the vent pipe, and
a conductive member that connects the oxygen concentration meter and the clarification tank;
The fining device uses the conductive member in a state in which the vent pipe and the tip are electrically connected via the platinum group metal that has volatilized from the inner wall and agglomerated in the vent pipe, and the fining tank out of the current supplied to the vent pipe, the current flowing from the vent tube to the oxygen concentration meter is passed through the clarification tank.

According to the present invention, when current is supplied to the fining tank to refine the glass melt, a sudden change in the amount of current flowing through the fining tank is suppressed, resulting in the generation of bubbles in the glass melt. can be suppressed.

It is a figure which shows the flow of the manufacturing method of this embodiment. It is a schematic diagram of a glass substrate manufacturing apparatus. 1 is a schematic diagram of a clarification device; FIG. FIG. 3 is a cross-sectional view of the fining device along a direction perpendicular to the longitudinal direction of the fining tube; It is an external appearance perspective view which shows a heat insulating member and a frame member. It is a figure explaining the electrical connection of a ventilation pipe and an oximeter.

Hereinafter, the method for manufacturing a glass substrate and the apparatus for manufacturing a glass substrate according to the present invention will be described.
(Overview of the method for manufacturing a glass substrate)
FIG. 1 is a diagram showing an example of steps of a method for manufacturing a glass substrate according to this embodiment. This embodiment includes various embodiments described later. The method for manufacturing a glass substrate includes a melting step (ST1), a clarification step (ST2), a homogenization step (ST3), a supply step (ST4), a forming step (ST5), a slow cooling step (ST6), and a cutting step ( ST7). In addition, it may include a grinding process, a polishing process, a cleaning process, an inspection process, a packing process, and the like. The manufactured glass substrates are laminated in a packing process as required, and transported to a delivery destination company.

In the melting step (ST1), molten glass is made by heating glass raw materials.
In the clarification step (ST2), the glass melt is heated to generate bubbles containing oxygen, CO ₂ or SO ₂ contained in the glass melt. These bubbles grow by absorbing oxygen generated by the reduction reaction of the refining agent (such as tin oxide) contained in the molten glass, rise to the liquid surface of the molten glass, and are released. After that, in the clarification step (ST2), the temperature of the molten glass is lowered, whereby the reducing substance obtained by the reduction reaction of the clarifier undergoes an oxidation reaction. As a result, gas components such as oxygen in the bubbles remaining in the glass melt are reabsorbed into the glass melt, and the bubbles disappear. The oxidation reaction and reduction reaction by the refining agent are carried out by controlling the temperature of the molten glass. The clarification step (ST2) is performed while pouring molten glass into the clarification tank.
In addition, in the clarification step (ST2), a vacuum degassing method may be used in which bubbles existing in the molten glass are grown in a depressurized atmosphere and degassed. The vacuum defoaming method is effective in that it does not use a clarifier. However, the vacuum degassing method requires a complicated and large-sized apparatus. Therefore, it is preferable to employ a fining method in which a fining agent is used to increase the temperature of the molten glass.

In the homogenization step (ST3), the glass components are homogenized by stirring the molten glass using a stirrer. As a result, uneven composition of the glass, which causes striae and the like, can be reduced. A homogenization process is performed in the stirring tank mentioned later.
In the supply step (ST4), the stirred molten glass is supplied to the molding device.

The forming step (ST5) and the slow cooling step (ST6) are performed in a forming apparatus.
In the forming step (ST5), the molten glass is formed into sheet glass to create a sheet glass flow. For molding, an overflow down-draw method is used.
In the slow cooling step (ST6), the formed and flowing sheet glass has a desired thickness and is cooled so as not to cause internal strain and warp.
In the cutting step (ST7), a sheet glass substrate is obtained by cutting the slowly cooled sheet glass into a predetermined length. The cut glass substrate is further cut into a predetermined size to produce a glass substrate of a target size.

FIG. 2 is a schematic diagram of a glass substrate manufacturing apparatus that performs each step from the melting step (ST1) to the cutting step (ST7) in this embodiment. The glass substrate manufacturing apparatus mainly includes a molten glass manufacturing apparatus 100, a forming apparatus 200, and a cutting apparatus 300, as shown in FIG. The glass melt manufacturing apparatus 100 has a melting tank 101, a clarification apparatus 102 having a clarification tube 120 which is the main body of the clarification tank, a stirring tank 103, transfer pipes 104 and 105, and a glass supply pipe 106.
The melting tank 101 is the main body of the melting device. The melting device has heating means such as a burner (not shown) in addition to the melting tank 101 . A glass raw material to which a fining agent is added is put into the melting tank 101, and the melting step (ST1) is performed. The molten glass melted in the melting tank 101 is supplied to the clarification tube 120 through the transfer tube 104 while being maintained at a high temperature (for example, 1300° C. or higher).
In the clarification tube 120, the temperature of the glass melt MG is adjusted, and the glass melt clarification step (ST2) is performed using the oxidation-reduction reaction of the clarifier. Specifically, as the temperature of the glass melt in the clarification tube 120 is raised, bubbles containing oxygen, CO ₂ or SO ₂ contained in the glass melt absorb oxygen generated by the reduction reaction of the clarifier. and grow, float on the liquid surface of the molten glass, and are released into the gas phase space. The gas phase space is formed by flowing the glass melt into the fining tube 120 such that it is formed between the liquid surface of the glass melt and the inner wall of the fining tube 120 . After that, by lowering the temperature of the molten glass, the reduced substance obtained by the reduction reaction of the refining agent undergoes an oxidation reaction. As a result, gas components such as oxygen in the bubbles remaining in the glass melt are reabsorbed into the glass melt, and the bubbles disappear. The molten glass after fining is supplied to the stirring tank 103 through the transfer pipe 105 .
In the stirring vessel 103, the molten glass is stirred by the stirrer 103a to perform the homogenization step (ST3). The molten glass homogenized in the stirring tank 103 is supplied to the forming apparatus 200 through the glass supply pipe 106 (supply step ST4).
In the forming apparatus 200, the sheet glass SG is formed from the molten glass by the overflow down-draw method (forming step ST5) and slowly cooled (slow cooling step ST6).
In the cutting device 300, a plate-shaped glass substrate is cut out from the sheet glass SG (cutting step ST7).

(Clarification device and clarification process)
Next, the clarifier 102 will be described with reference to FIGS. 3 and 4. FIG. 3 is a schematic perspective view of the fining device 102 and FIG. 4 is a cross-sectional view of the fining device 102 along a direction orthogonal to the longitudinal direction of the fining tube 120. As shown in FIG.
The clarification device 102 has a clarification tank, a power supply device 122 , a control device 123 , a vent pipe 127 and an oximeter 140 .

The clarification tank has a clarification tube 120, electrodes 121a, 121b, and 121c (see FIG. 2), and a temperature measuring device 130, which is the main body of the clarification tank.
The fining tube 120, electrodes 121a, 121b, 121c, and vent tube 127 are constructed from platinum group metals. In this specification, the term "platinum group metal" means a metal composed of a platinum group element, and is used as a term including not only a metal composed of a single platinum group element but also an alloy of platinum group elements. Here, the platinum group elements refer to 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 to molten glass.
In the present embodiment, a case where the clarification tube 120 is made of a platinum group metal will be described as a specific example, but a part of the clarification tube 120 may be made of refractories or other metals. .

In the example shown in FIG. 2, the electrodes 121a, 121b, and 121c are provided on both ends of the clarification tube 120 in the longitudinal direction (horizontal direction in FIG. 3) and on the outer peripheral side of the clarification tube 120 at positions therebetween. 3, illustration of the electrode 121b is omitted.
Electrodes 121 a , 121 b , 121 c are connected to power supply 122 . A voltage is applied between the electrodes 121a, 121b and between the electrodes 121b, 121c, respectively, causing current to flow through each portion of the fining tube 120 between the electrodes 121a, 121b and between the electrodes 121b, 121c. Thus, the clarification tube 120 is electrically heated. Thereby, the molten glass in the clarification tube 120 is heated.
For example, the space between the electrodes 121a and 121b is heated to a temperature that promotes defoaming. Specifically, the maximum temperature of the clarification tube 120 is, for example, 1600° C. to 1750° C., more preferably 1630° C. to 1750° C., and the maximum temperature of the molten glass supplied from the transfer tube 104 is It is heated to a temperature suitable for foaming, for example 1600°C to 1720°C, more preferably 1620°C to 1720°C.
For example, the electrodes 121b and 121c are heated to a temperature that promotes the absorption process. Specifically, the maximum temperature of the fining tube 120 is, for example, 1590° C. to 1670° C., more preferably 1620° C. to 1670° C., and the maximum temperature of the molten glass flowing in the fining tube 120 is suitable for absorption. It is heated to a temperature of 1590°C to 1640°C, more preferably 1610°C to 1640°C.

A temperature measuring device (thermocouple or the like) 130 is provided, for example, at a connecting portion between the electrodes 121a, 121b, 121c and the clarification tube 120. As shown in FIG. The electrodes 121a, 121b, 121c and the clarification tube 120 are connected by welding, for example. The temperature measurement device 130 outputs measurement results to the control device 123 .
The control device 123 is connected to the power supply device 122 . The control device 123 controls the amount of current supplied to the clarification tube 120 by the power supply device 122 and controls the temperature of the molten glass passing through the clarification tube 120 . The control device 123 is a computer including a CPU, memory, and the like. The control device 123 is also connected to each of the temperature measuring device 130 and the oxygen concentration meter 140 .

The vent pipe 127 communicates the gas phase space 120a (see FIG. 4) inside the clarification pipe 120 with the outside of the clarification pipe 120 (atmosphere). A hole (not shown) penetrating through the wall is provided at the top of the wall of the clarification tube 120 in contact with the gas phase space 120a. The ventilation pipe 127 is arranged above the hole in the wall, and has, for example, a shape extending linearly upward in the vertical direction. In the example shown in Figures 3 and 4, the clarification tube 120 and the vent tube 127 are spaced apart. In the example shown in FIGS. 3 and 4, the enclosing space 128 is formed by arranging the heat insulating member 150 to be described later with a gap between it and the clarification tube 120 . The lower end of the vent pipe 127 and the hole in the wall of the clarification pipe 120 are connected via an enclosed space 128 . The lower end of the vent tube 127 may be connected to the top of the clarification tube 120 and open to the clarification tube 120 through a hole in the wall. The vent pipe 127 is preferably provided along the longitudinal direction of the clarification pipe 120 between the electrodes 121a and 121b or between the electrodes 121b and 121c.

The oximeter 140 has an intake section 141 and a measuring section 145, as shown in FIG.
The take-in portion 141 is a tubular portion extending from the vent tube 127 toward the measurement portion 145 . An end (tip) 142 of the intake portion 141 located on the side of the vent pipe 127 has an intake port 142a (see FIG. 6). is arranged to extend downward. The distal end portion 142 is spaced apart from the inner wall of the vent pipe 127 and extends in a direction substantially parallel to the direction in which the vent pipe 127 extends. The intake part 141 is configured by a conductive metal tube.
The measurement unit 145 measures the oxygen concentration of the gas taken in from the intake port 142a. The measurement unit 145 has a zirconia sensor and detects oxygen in the gas. The measurement unit 145 outputs the measurement result of the oxygen concentration to the control device 123 .

(First embodiment)
Next, a first embodiment of this embodiment will be described.
In the first embodiment, the clarifier 102 further comprises a conductive member 170, as shown in FIG. The conductive member 170 is a member that electrically connects the oximeter 140 and the clarification tube 120, and is a member (for example, conducting wire) made of a conductive material. A conductive material is a material having a conductivity of 1×10 ⁶ S/m or more at 20° C. The conductive member 170 is specifically connected to the tip portion 142 of the oximeter 140 and the outer peripheral side surface of the clarification tube 120 .

In the clarification step (ST2) of the first embodiment, the ventilation pipe 127 and the oxygen concentration meter 140 are electrically connected via the platinum group metal volatilized from the inner wall of the clarification pipe 120 and aggregated in the ventilation pipe 127. In this state, of the current supplied to the clarification tube 120 , the current that has flowed from the ventilation tube 127 to the oximeter 140 is passed through the clarification tube 120 . Specifically, the fining device 102 uses the conductive member 170 to transfer the current flowing through the oximeter 140 to the fining tube when the vent pipe 127 and the oximeter 140 are electrically connected through the agglomerate of the platinum group metal. Flow to 120.
As described above, the temperature of the vent pipe 127 tends to be lower than that of the clarification pipe 120, and the volatile component of the platinum group metal that has flowed into the vent pipe 127 from the gas phase space 120a becomes supersaturated in the vent pipe 127. may clump together. According to the study of the present inventor, as shown in FIG. 6, the platinum group metal aggregate P deposited on the inner wall of the vent pipe 127 grows over time and reaches the tip 142 of the oximeter 140. Therefore, it was found that the ventilation pipe 127 and the oxygen concentration meter 140 may be electrically connected. FIG. 6 is a diagram for explaining conduction between the vent tube 127 and the oximeter 140. As shown in FIG. When the vent tube 127 and the oximeter 140 are electrically connected, a portion of the current flowing through the clarification tube 120 flows through the vent tube 127 and along the path indicated by the arrow in FIG. Since it flows to the densitometer 140, the amount of current flowing through the clarification tube 120 changes suddenly. Current flows from the fining tube 120 to the vent tube 127, for example through the insulating member 150. FIG. When such a sudden change in the amount of current occurs, it becomes difficult for the controller 123 to control the amount of current, and the temperature of the molten glass in the fining tube 120 greatly fluctuates. It has been clarified that, due to this, air bubbles may be generated in the glass melt in the clarifier tube. If such bubbles are generated in the glass melt, they may remain in the fining tube 120 without being released from the glass melt and remain in the glass substrate, resulting in quality defects.
According to the first embodiment, when the vent tube 127 and the tip 142 of the oximeter 140 are electrically connected, the current flowing through the tip 142 returns to the clarification tube 120 through the conductive member 170, so that the clarification tube 120 The leakage of the current flowing through is suppressed to the outside. Therefore, it is possible to suppress a sudden change in the amount of current, thereby suppressing the generation of air bubbles in the molten glass.

According to one embodiment, the clarifier 102 further comprises an insulating member 150 and a frame member (frame) 160, as in the example shown in FIGS. FIG. 5 is an external perspective view showing the heat insulating member 150 and the frame member 160. FIG.
The heat insulating member 150 is a member arranged around the clarification tube 120 so as to surround the clarification tube 120 . The heat insulating member 150 has a plurality of refractory bricks (not shown), and the refractory bricks are stacked so as to surround the clarification tube 120 .
The frame member 160 is a member made of metal and has electrical conductivity. The frame member 160 supports the heat insulating member 150 from the outside and restrains the refractory bricks arranged around the clarification tube 120 from collapsing. The frame member 160 of the example shown in FIG. 5 is provided so as to press the refractory bricks toward the clarification tube 120 in the vertical direction and the horizontal direction (direction orthogonal to the longitudinal direction of the clarification tube 120). The frame member 160 is grounded.
In this embodiment, the measurement part 145 of the oximeter 140 is arranged outside the heat insulating member 150 and the frame member 160, as shown in FIG. Here, if the oximeter 140 is supported by the frame member 160 , the current that flows through the oximeter 140 through conduction between the vent pipe 127 and the oximeter 140 will further flow through the frame member 160 . Therefore, the oximeter 140 is insulated from the frame member 160 . In FIG. 4, the conductive member 170 is separated from the frame member 160 in the depth direction of the paper surface.
The conductive member 170 is preferably coated with a highly insulating material such as resin so that the current flowing through the conductive member 170 does not leak to the surrounding heat insulating member 150 .

According to one embodiment, conductive member 170 is preferably connected to intake 141 of oximeter 140 . As a result, the current flowing through the oxygen concentration meter 140 through the air tube 127 is returned from the intake portion 141 to the clarification tube 120, so that the flow of current to the measuring portion 145 of the oxygen concentration meter 140 can be suppressed.

(Second embodiment)
Next, a second embodiment of this embodiment will be described.
In a second embodiment, the clarification device 102 comprises a determination device and a removal device. The determination device is realized, for example, by the control device 123 reading out a program for determining the timing for removing the aggregate P of the platinum group metal into a memory and executing the program.

The judging device detects the aggregate P of the platinum group metal before the vent pipe 127 and the tip portion 142 are electrically connected via the platinum group metal volatilized from the inner wall of the clarification pipe 120 and aggregated in the vent pipe 127. A judgment step of judging (determining) the timing of removal is performed.
As described above, when the vent tube 127 and the oximeter 140 are in communication, a portion of the current flowing through the finer tube 120 will flow through the vent tube 127 and through the condensate P to the oximeter 140 . Due to this, air bubbles may be generated in the glass melt MG. In the second embodiment, as described above, the timing for removing the aggregate P of the platinum group metal is determined, so the removal of the aggregate P can be performed according to the determined timing. Conduction with the densitometer 140 can be prevented. As a result, it is possible to suppress sudden changes in the amount of current, and to suppress the generation of air bubbles in the molten glass.

In the determination step, it is preferable to determine the timing for removing the aggregate P based on the measurement result of the oximeter 140 . When the oxygen concentration of the gas in the gas phase space is high, the volatile component of the platinum group metal tends to aggregate in the vent pipe 127, so the aggregate P deposited on the inner wall of the vent pipe 127 grows quickly, and the vent pipe 127 and the oximeter 140 easily occur. Therefore, as described above, by making the determination based on the measurement result of the oximeter 140, it is possible to prevent conduction between the vent pipe 127 and the oximeter 140. FIG. Specifically, it is the timing to remove the aggregate P when the oxygen concentration measured by the oxygen concentration meter 140 exceeds the permissible concentration, or when the cumulative time of exceeding the permissible concentration exceeds the permissible time. I judge. The permissible oxygen concentration is, for example, 5% or less, preferably 1% or less. The accumulated time exceeding the permissible concentration is the total amount of time the oxygen concentration exceeds the permissible concentration since the start of the glass substrate manufacturing method or the most recent removal of the aggregates P. For example, 8 to 48 hours. As a measurement result of the oxygen concentration meter 140, for example, when the total time for which the oxygen concentration exceeds 1% is 48 hours or more, it is determined that it is time to remove the aggregate P, and the aggregate P is removed. remove.
Further, in the judgment step, a certain point in the future may be judged (determined) as the timing for removing the aggregate P. For example, when the conditions of the clarification step (ST2) are constant, the amount of change in the oxygen concentration of the gas within the gas phase space is usually small. Therefore, it is possible to determine a certain point in the future as the timing for removing the aggregate P. In this case, the timing for removing the aggregates P can be determined based on the oxygen concentration at the time of measurement by the oximeter 140 or the transition of the oxygen concentration during the most recent predetermined period.

The removal device performs a removal step of removing the aggregates P according to the timing determined in the determination step. The removal device is, for example, a suction device (not shown) that sucks removal of the aggregates P from the air-side end of the vent tube 127 . The suction device is connected to the control device 123, and the control device 123 operates the suction device according to the timing for removing the aggregate P determined as described above, and removes the aggregate P. Aggregates P deposited on the inner wall of the ventilation pipe 127 may be scraped off using an instrument while performing suction.

The second embodiment can be combined with the above-described first embodiment to construct a refining device 102 or to perform a method for manufacturing a glass substrate.

(glass substrate)
The size of the glass substrate manufactured in the present embodiment is not particularly limited, but for example, the vertical dimension and the horizontal dimension are respectively 500 mm to 3500 mm, 1500 mm to 3500 mm, 1800 to 3500 mm, 2000 mm to 3500 mm, and 2000 mm to 3500 mm. is preferably
The thickness of the glass substrate is, for example, 0.1 to 1.1 mm, and more preferably an extremely thin rectangular plate of 0.75 mm or less. Thickness is more preferred. The lower limit of the thickness of the glass substrate is preferably 0.15 mm, more preferably 0.25 mm.

<Glass composition>
As such a glass substrate, glass substrates having the following glass compositions are exemplified. That is, the raw materials for the molten glass are mixed so as to produce a glass substrate having the following glass composition.
SiO ₂ 55-80 mol %,
Al ₂ O ₃ 8-20 mol %,
B ₂ O ₃ 0-12 mol %,
RO 0 to 17 mol % (RO is the total amount of MgO, CaO, SrO and BaO).

SiO ₂ is preferably 60 to 75 mol %, more preferably 63 to 72 mol %, from the viewpoint of reducing thermal shrinkage.
Among RO, it is preferable that MgO is 0 to 10 mol %, CaO is 0 to 15 mol %, SrO is 0 to 10 mol %, and BaO is 0 to 10 mol %.

Further, it contains at least _SiO2 , _{Al2O3 ,} B2O3 _, and RO, and the molar ratio (( ₂ * _SiO2 ) _{+ Al2O3} )/(( ₂ * _B2O3 )+RO) is 4. It may be glass that is 5 or more. Moreover, it preferably contains at least one of MgO, CaO, SrO, and BaO, and the molar ratio (BaO+SrO)/RO is 0.1 or more.

The sum of twice the B ₂ O ₃ content expressed in mol % and the RO content expressed in mol % is preferably 30 mol % or less, preferably 10 to 30 mol %.
Moreover, the content of the alkali metal oxide in the glass substrate having the above glass composition may be 0 mol % or more and 0.4 mol % or less.
In addition, the glass contains 0.05 to 1.5 mol% of oxides of metals (tin oxide, iron oxide) whose valence changes in the glass, and substantially contains As ₂ O ₃ , Sb ₂ O ₃ and PbO. Absence is optional, not required.

Further, it is preferable that alkali-free boroaluminosilicate glass or glass containing a trace amount of alkali is used for the glass substrate manufactured according to the present embodiment.
The glass substrate manufactured according to this embodiment is preferably made of alkali-free glass containing, for example, the following composition.
Examples of the glass composition of the glass substrate manufactured according to the present embodiment include the following (expressed in mass %).
SiO ₂ : 50-70% (preferably 57-64%), Al ₂ O ₃ : 5-25% (preferably 12-18%), B ₂ O ₃ : 0-15% (preferably 6 ~13%), and may optionally contain the following composition: As optional components, MgO: 0 to 10% (preferably 0.5 to 4%), CaO: 0 to 20% (preferably 3 to 7%), SrO: 0 to 20% (preferably, 0.5-8%, more preferably 3-7%), BaO: 0-10% (preferably 0-3%, more preferably 0-1%), ZrO ₂ : 0-10% (preferably , 0 to 4%, more preferably 0 to 1%). Furthermore, it is more preferable to contain R' ₂ O: more than 0.10% and 2.0% or less (where R' is at least one selected from Li, Na and K).

Alternatively, SiO ₂ : 50-70% (preferably 55-65%), B ₂ O ₃ : 0-10% (preferably 0-5%, 1.3-5%), Al ₂ O ₃ : 10-25% (preferably 16-22%), MgO: 0-10% (preferably 0.5-4%), CaO: 0-20% (preferably 2-10%, 2-6 %), SrO: 0-20% (preferably 0-4%, 0.4-3%), BaO: 0-15% (preferably 4-11%), RO: 5-20% (preferably is 8 to 20%, 14 to 19%) (provided that R is at least one selected from Mg, Ca, Sr and Ba). Furthermore, it is more preferable to contain R' ₂ O more than 0.10% and 2.0% or less (where R' is at least one selected from Li, Na and K).

<Young's modulus>
The Young's modulus of the glass substrate manufactured according to the present embodiment is preferably, for example, 72 GPa or higher, more preferably 75 GPa or higher, and even more preferably 77 GPa or higher.

<Strain point>
The strain rate of the glass substrate manufactured according to the present embodiment is preferably, for example, 650° C. or higher, more preferably 680° C. or higher, and even more preferably 700° C. or higher, and even more preferably 720° C. or higher.

<Heat shrinkage rate>
The thermal shrinkage rate of the glass substrate manufactured according to the present embodiment is, for example, 50 ppm or less, preferably 40 ppm or less, more preferably 30 ppm or less, and even more preferably 20 ppm or less. The range of thermal shrinkage of the glass substrate before the thermal shrinkage is reduced is preferably 10 ppm to 40 ppm.

The glass substrate produced in this embodiment is suitable as a display glass substrate including a flat panel display glass substrate and a curved panel display glass substrate. It is suitable as a substrate. Furthermore, the glass substrates manufactured in the present embodiment are glass substrates for oxide semiconductor displays using oxide semiconductors such as IGZO (indium, gallium, zinc, and oxygen), and LTPS (low It is suitable for glass substrates for LTPS displays using (temperature polysilicon) semiconductors.
Further, the glass substrate manufactured in this embodiment can be applied to cover glass, magnetic disk glass, solar cell glass substrate, and the like.

Although the glass substrate manufacturing apparatus and the glass substrate manufacturing method of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various improvements and modifications can be made without departing from the gist of the present invention. Of course you can.

100 Glass Melt Manufacturing Apparatus 101 Melting Tank 102 Clarifying Device 103 Stirring Tank 103a Stirrer 104, 105 Transfer Pipe 106 Glass Supply Pipe 120 Clarifying Pipe (Main Body of Clarifying Tank)
120a Gas phase space 121a, 121b, 121c Electrode 122 Power supply device 123 Control device 127 Ventilation pipe 128 Surrounding space 130 Temperature measuring device 140 Oxygen concentration meter 150 Heat insulating member 160 Frame member 170 Conductive member 200 Forming device 300 Cutting device MG Molten glass SG Sheet glass

Claims (4)

A method for manufacturing a glass substrate,
a melting step of melting glass raw materials to form molten glass;
A fining step of forming a gas phase space above the liquid surface of the molten glass in a fining tank and fining the molten glass,
The clarification tank has an inner wall in contact with the gas phase space and made of a material containing a platinum group metal,
In the clarification tank,
a vent pipe communicating between the gas phase space and the outside of the clarification tank;
an oxygen concentration meter that is provided in the vent pipe with a tip portion having an intake port that takes in a part of the gas flowing in the vent pipe and measures the oxygen concentration of the taken gas,
In the fining step, an electric current is applied to the fining tank to heat the molten glass in the fining tank,
In a state in which the vent pipe and the tip portion are electrically connected via the platinum group metal volatilized from the inner wall and aggregated in the vent pipe, out of the current supplied to the clarification tank, the A method for producing a glass substrate, characterized in that a current flowing through an oxygen concentration meter is passed through the clarification tank. A heat insulating member is arranged around the clarification tank so as to surround the clarification tank,
The heat insulating member is supported from the outside of the heat insulating member by a metal frame member,
2. The method of manufacturing a glass substrate according to claim 1, wherein said oximeter is insulated from said frame member. The oxygen concentration meter is
a measuring unit that measures the oxygen concentration of the gas taken in from the intake;
a tubular intake portion extending from the intake port toward the measurement portion and having the tip portion;
3. The method of manufacturing a glass substrate according to claim 1, wherein the current that has flowed through said oxygen concentration meter is returned from said intake section to said clarification tank. A glass substrate manufacturing apparatus,
a melting device that melts glass raw materials to produce molten glass;
a clarification device that has a clarification tank, forms a gas phase space above the liquid surface of the molten glass in the clarification tank, and performs clarification of the molten glass;
The fining tank is in contact with the gas phase space and has an inner wall made of a material containing a platinum group metal, and is supplied with an electric current to heat the molten glass in the fining tank,
The clarification device further
a vent pipe communicating between the gas phase space and the outside of the clarification tank;
an oximeter that measures the oxygen concentration of the gas taken in, the tip portion having an intake port for taking in part of the gas flowing through the vent pipe, and
a conductive member that connects the oxygen concentration meter and the clarification tank;
The fining device uses the conductive member in a state in which the vent pipe and the tip are electrically connected via the platinum group metal that has volatilized from the inner wall and agglomerated in the vent pipe, and the fining tank a current supplied to the fining tank from the vent pipe to the oxygen concentration meter.

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