JP2014009133A - Glass substrate manufacturing method and glass substrate manufacturing device - Google Patents

Abstract

Disclosed is a glass substrate manufacturing method and manufacturing apparatus capable of homogenizing a molten glass and efficiently energizing and heating the molten glass when melting a glass raw material.
A melting step of melting a glass raw material to form a molten glass is arranged by placing the molten glass between at least a pair of electrodes, applying a voltage between the electrodes, and passing a current through the molten glass. The step of generating Joule heat and the value of the current flowing through the molten glass are measured, the cross-sectional area of the molten glass region through which the current flows is set according to the voltage, the value of the current, and the voltage A step of calculating a specific resistance of the molten glass using the value and the set cross-sectional area of the molten glass, and a step of controlling the Joule heat based on the calculated specific resistance. The apparatus for producing molten glass executes the above production method.
[Selection] Figure 3

Description

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

  As a method for producing a glass substrate used in a flat panel display (hereinafter referred to as FPD) such as a liquid crystal display or a plasma display, an overflow down draw method is known. In the overflow down-draw method, in a forming furnace, the molten glass is made to overflow from the upper part of the molded body of the molten glass, whereby the sheet glass is formed from the molten glass, and the formed sheet glass is gradually cooled and cut. Thereafter, the cut sheet glass is further cut into a predetermined size according to the customer's specifications, washed, end-polished, etc., and shipped as a glass substrate for FPD.

Among glass substrates for FPDs, particularly glass substrates for liquid crystal display devices and glass substrates for organic EL display devices, since a semiconductor element is formed on the surface thereof, it completely contains an alkali metal component that easily affects the characteristics of the semiconductor element. Even if it is contained, it is preferable that the amount is small enough not to affect the semiconductor element or the like.
In addition, if bubbles are present in the glass substrate, it causes a display defect. Therefore, a glass substrate in which bubbles are present cannot be used as a glass substrate for FPD. For this reason, it is calculated | required that a bubble does not remain | survive in a glass substrate.

  In addition, when there is glass composition unevenness (non-uniform glass composition) on the glass substrate, for example, streak-like defects called striae are generated. This striae forms fine surface irregularities on the surface of the molten glass at the time of molding due to the difference in viscosity of the molten glass due to the inhomogeneity of the glass composition, and these surface irregularities remain on the glass substrate. For this reason, when this glass substrate is incorporated into a liquid crystal panel as a glass substrate for a liquid crystal panel, an error occurs in the cell gap or it causes display unevenness. For this reason, it is necessary not to cause unevenness of the glass composition such as striae in the manufacturing stage of the glass substrate.

  When manufacturing a glass substrate as described above, a melting tank is generally used in which a glass raw material is introduced and melted to produce a molten glass. The melting tank is provided with a pair of electrodes so as to be in contact with the molten glass. A current is applied to the molten glass between the pair of electrodes by applying a voltage to the pair of electrodes to heat the molten glass to a desired temperature.

  As an example of such energization heating, high-frequency energization heating is known in a melting tank (glass melting furnace) using a plurality of electrode pairs. For example, in Patent Document 1 below, each electrode pair is connected to a separate power source, and each power source is individually controlled, whereby a plurality of pairs of electrodes are controlled for each electrode pair. In such a melting tank using electric heating, in order to bring the viscosity and convection of the molten glass into a desired state, conventionally, as described in, for example, Patent Document 2 below, The temperature was being measured.

Japanese Patent Laid-Open No. 04-367519 Japanese Patent Laid-Open No. 03-103328

However, since the thermocouple is exposed to a high temperature in, for example, a melting tank, it may deteriorate in a relatively short time and an accurate temperature may not be measured. Moreover, since the location where the thermocouple can be installed is limited due to the structure of the apparatus for melting the glass raw material, the location where the temperature can be measured by the thermocouple is limited.
Further, as described above, the glass substrate for FPD does not contain any alkali metal component that lowers the high-temperature viscosity, or a glass that contains a trace amount even if it is contained, so that the viscosity of the molten glass is about the same as before. In order to maintain it, it is necessary to raise the temperature of the molten glass. Thus, since the melting temperature of the molten glass in a melting tank is made high compared with the past, there exists a problem that a thermocouple tends to deteriorate and an exact temperature cannot be acquired.
Moreover, since the melting temperature of the molten glass in a melting tank is made higher than before, it is desired to efficiently heat the molten glass to a high temperature.

In addition, a semiconductor element such as a TFT (Thin Film Transistor) is formed on a glass plate in the FPD glass substrate. In recent years, p-Si (low-temperature polysilicon) TFTs and oxide semiconductors are formed on glass substrates in place of α-Si TFTs that have been used in the past in order to achieve even higher definition display display. It is demanded. The p-Si (low temperature polysilicon) TFT is used in, for example, a liquid crystal display device and an organic EL display device.
In the process of forming the p-Si • TFT and the oxide semiconductor, there is a heat treatment process at a higher temperature than the process of forming the α-Si • TFT. Therefore, a glass substrate on which a p-Si (low temperature polysilicon) TFT or an oxide semiconductor is formed is required to have a low thermal shrinkage rate. In order to reduce the heat shrinkage rate, it is preferable to increase the strain point of the glass. However, since the glass having a high strain point generally has a lower meltability, the temperature of the molten glass in the melting tank is conventionally reduced. It is necessary to make it higher than that.
Thus, since the melting temperature of the molten glass in a melting tank is made high compared with the past, there exists a problem that a thermocouple tends to deteriorate and an exact temperature cannot be acquired.
Since the melting temperature of the molten glass in the melting tank is made higher than before, it is desired that the electric power supplied to the electrodes be used efficiently in order to efficiently heat the molten glass by heating.

  Furthermore, when the glass raw material is charged using a screw feeder from the raw material inlet provided at one edge of the housing that covers the melting tank, the glass raw material floats on the surface of the molten glass on the raw material inlet side. It is difficult for the liquid level to flow toward the side opposite to the raw material charging side. In order to reliably melt the glass raw material without causing striae, it is desirable to completely melt the glass raw material floating on the liquid surface in the melting tank and homogenize the components of the molten glass. For this reason, it is preferable to change the electric power supplied to the electrode depending on the position of the melting tank such as the position on the raw material input side and the position opposite to the raw material input side. That is, it is desirable to accurately determine the amount of power to be applied to each pair of electrodes by examining the current state of the molten glass so that the temperature of the molten glass approaches the target temperature for producing a homogeneous molten glass. .

  Then, this invention provides the manufacturing method of the glass substrate which can homogenize molten glass and can efficiently heat-heat a molten glass when melting a glass raw material.

One embodiment of the present invention is a method for manufacturing a glass substrate. The said manufacturing method includes the melting process which melt | dissolves the raw material of glass and produces | generates molten glass.
The melting step
For the molten glass positioned between each of the plurality of pairs of electrodes, by applying a voltage between each of the electrodes, a current is caused to flow to generate Joule heat;
For each of the plurality of pairs of electrodes, the value of the current flowing through the molten glass is measured, and for each of the plurality of pairs of electrodes, the cross-sectional area of the region of the molten glass through which the measured current flows is set according to the voltage value. Then, using the value of the current, the value of the voltage, and the cross-sectional area of the set molten glass, calculating the specific resistance of the molten glass for each region,
Controlling the Joule heat based on the calculated specific resistance for each of the plurality of pairs of electrodes.
In the manufacturing method, for each of the plurality of pairs of electrodes, a sectional area of a molten glass region through which the current flows is set according to the voltage, and the current value, the voltage value, and the set molten glass are set. Since the specific resistance of the molten glass is calculated for each region using the cross-sectional area, it is possible to calculate an accurate specific resistance for each region. As a result, the molten glass in the melting tank can be energized and heated so as to be homogenized, and the molten glass can be efficiently energized and heated.

  At this time, the cross-sectional area is preferably set according to a ratio of a value of the voltage applied between the pair of electrodes to a total value of all voltages applied between the plurality of pairs of electrodes. Thereby, the cross-sectional area and further the specific resistance can be calculated by simple calculation using the voltage applied to each electrode.

The melting step includes a preliminary step of obtaining a correlation between the temperature of the molten glass and the specific resistance of the molten glass,
The step of controlling the Joule heat includes
Calculating the temperature of the molten glass based on the correlation and the calculated resistivity;
And a step of controlling Joule heat generated in the molten glass based on a result of comparing the calculated temperature and a target temperature set in advance in the molten glass.
The temperature of the molten glass is calculated based on the correlation and the calculated specific resistance, and the Joule heat generated in the molten glass can be controlled according to the comparison result between the calculated temperature and the target temperature. Therefore, the temperature of the molten glass can be easily controlled so as to approach the target temperature or to be maintained in the vicinity of the target temperature by energization heating of the molten glass.

Furthermore, the step of controlling the Joule heat includes
Setting a target current value for generating Joule heat in the molten glass so as to maintain the calculated temperature at the target temperature;
And controlling the voltage so as to maintain the current at the target current value.
In order to maintain the calculated temperature at the target temperature, a current for generating Joule heat in the molten glass is determined, and in addition to setting the current to a target current value, so as to maintain the current at the target current value, Since the voltage is controlled, the temperature of the molten glass can be easily maintained at the target temperature by energization heating of the molten glass.

In the preliminary step,
The temperature is T, the specific resistance is ρ, and the equation expressing the correlation:
T (° C.) = A / (log (ρ) + b) −273.15
Find the constants a and b in
In the step of calculating the temperature,
It is preferable to calculate the temperature T by substituting the specific resistance ρ into the equation.
The temperature can be easily calculated using the above formula.

In the step of calculating the specific resistance,
The current value is I, the voltage is E, the cross-sectional area of the region of the molten glass through which the current flows is S, the distance L between the pair of electrodes, the specific resistance is ρ, Expression expressing the relationship: ρ = E / I × S / L (2)
It is preferable to calculate the specific resistance ρ based on

  The glass substrate is, for example, a glass substrate for a flat panel display. Since the glass having a high temperature viscosity is used for the flat panel, the temperature of the molten glass is set high. Also in this case, since the specific resistance can be calculated with high accuracy, it is possible to heat and heat the molten glass in the melting tank so as to homogenize it, and to efficiently heat and heat the molten glass.

  The glass substrate is, for example, alkali-free glass or alkali-containing glass. Since alkali-free glass or glass containing a small amount of alkali decreases the high temperature viscosity, the temperature of the molten glass is inevitably set to maintain the viscosity of the molten glass at the same level as before. Even in this case, the specific resistance of the molten glass in the melting tank can be calculated with high accuracy, so that the molten glass in the melting tank can be heated and heated so as to homogenize the molten glass. Electric heating can be performed.

  The strain point of the molten glass is, for example, 655 ° C. or higher. In the case of a molten glass having a strain point of 655 ° C. or higher, the meltability is low. For this reason, the temperature of the molten glass in a melting tank is set still higher compared with the past. Even in this case, the specific resistance of the molten glass in the melting tank can be calculated with high accuracy, so that the molten glass in the melting tank can be heated and heated so as to homogenize the molten glass. Electric heating can be performed.

Moreover, the other one aspect | mode of this invention is a manufacturing apparatus of the glass substrate which has a melting tank which produces | generates molten glass. The manufacturing equipment
It includes a melting device that melts the glass raw material that is introduced to make molten glass.
The melting device is:
A plurality of pairs of electrodes in contact with the molten glass, provided on a wall surface in contact with the molten glass of the melting tank;
A control unit for applying a voltage between the plurality of pairs of electrodes to control electric power for generating Joule heat by passing a current through the molten glass;
While obtaining information on the value of the current flowing through the molten glass and the value of the voltage for each of the plurality of pairs of electrodes, the cross-sectional area of the region of the molten glass through which the current flows is determined for each of the plurality of pairs of electrodes. Set according to the value, calculate the specific resistance of the molten glass using the value of the current, the value of the voltage, and the cross-sectional area of the set molten glass, and based on the calculated specific resistance And an arithmetic unit for determining a control amount of the Joule heat.
In the arithmetic unit of the manufacturing apparatus, the cross-sectional area of the molten glass region through which the current flows is set according to the voltage, the current value, the voltage value, and the set cross-sectional area of the molten glass. Is used to calculate the specific resistance of the molten glass, so that the specific resistance with high accuracy can be calculated. As a result, the molten glass in the melting tank can be energized and heated so as to be homogenized, and the molten glass can be efficiently energized and heated.

  According to the manufacturing method plate of the glass substrate of the above-mentioned aspect, the molten glass can be homogenized and the molten glass can be efficiently energized and heated.

It is sectional drawing of the glass substrate of this embodiment. It is a figure which shows typically an example of the apparatus which performs the melting process-cutting process in this embodiment. It is a perspective view explaining the schematic structure of the melting tank of this embodiment. (A), (b) is a top view explaining the method of calculating | requiring the cross-sectional area of the molten glass in which an electric current flows between each pair of electrodes in this embodiment. It is a figure explaining an example of the process of controlling the Joule heat generated in the molten glass of this embodiment. It is a figure explaining the other example of the process of controlling the Joule heat generated in the molten glass of this embodiment. It is a figure explaining the convection of the molten glass performed inside the melting tank of this embodiment.

  Hereinafter, the manufacturing method and manufacturing apparatus of the glass substrate of this embodiment are demonstrated. FIG. 1 is a diagram showing an example of steps of a method for producing a glass substrate according to the present invention.

  The glass substrate manufacturing method includes a melting step (ST1), a clarification step (ST2), a homogenization step (ST3), a supply step (ST4), a forming step (ST5), and a slow cooling step (ST6). And a cutting step (ST7). In addition, a plurality of glass substrates that have a grinding process, a polishing process, a cleaning process, an inspection process, a packing process, and the like and are stacked in the packing process are transported to a supplier.

  The melting step (ST1) is performed in a melting tank. In the melting step, molten glass is made by introducing a glass raw material to the liquid surface of the molten glass stored in the melting tank. Furthermore, among the inner walls of the melting tank, from the outflow port provided at one bottom portion (region close to the bottom surface of the melting tank) of the inner walls facing each other in the longitudinal direction of the rectangular melting tank in plan view, the process proceeds to the subsequent process. Pour molten glass.

  Here, the molten glass is made by introducing a glass raw material into a melting tank near the raw material inlet of the melting tank. The molten glass in the melting tank is heated and controlled by being energized and heated using electrodes in the melting tank. Specifically, the maximum temperature at the bottom of the molten glass in the melting tank is further increased so that the temperature of the molten glass located at the bottom of the melting tank increases from the raw material charging side to the outlet side. The molten glass is heated and controlled in the melting tank so as to be higher than the temperature of the surface layer of the molten glass at the charged position. Thereby, on the side of the outlet, the molten glass flows from the outlet to the downstream process, and a convection in which the molten glass described below circulates is made. That is, a part of the molten glass that did not flow from the outlet rises toward the liquid surface along the side wall of the melting tank, and a part of the molten glass that has risen to the liquid surface further flows along the liquid surface to the raw material input side. It flows toward the side wall of the melting tank, descends from the liquid level along the side wall of the melting tank on the raw material input side, and further flows from the raw material input side toward the discharge port side along the bottom surface.

  Here, the glass raw material is charged by inverting the bucket containing the glass raw material and introducing the glass raw material into the molten glass, conveying the glass raw material using a belt conveyor, or using a screw feeder. A method of charging raw materials may be used. Moreover, the surface layer of molten glass means the area | region containing the liquid level in the range of 10% or less of the depth which went to the bottom part of the melting tank from the liquid level, and the lower layer of molten glass means area | regions other than a surface layer. . In addition, the bottom where the outflow port is provided is a part of the lower layer and is a region close to the bottom. Preferably, it refers to a region where the depth from the bottom surface in the depth direction of the melting tank is ½ or less of the depth between the liquid surface and the bottom surface of the melting tank.

The temperature of the molten glass in the melting tank rises as electricity flows through the molten glass itself to generate heat. In addition to the heating of the molten glass by energization, a glass raw material can be melted by supplementarily providing a flame with a burner. A clarifier is added to the glass raw material. As the fining agent, SnO ₂ (tin oxide) is preferably used from the viewpoint of reducing the environmental load.

The clarification step (ST2) is performed at least inside the clarification tank. A clarification tank is comprised from platinum or a platinum alloy, for example. In the clarification step, the temperature of the molten glass in the clarification tank is raised. In this process, the fining agent releases oxygen by a reduction reaction, and becomes a substance that later acts as a reducing agent. Bubbles containing O ₂ , CO ₂ or SO ₂ contained in the molten glass grow by absorbing O ₂ generated by the reductive reaction of the fining agent, and float on the liquid surface of the molten glass to break the bubbles. Disappear. The gas contained in the foam is released to the outside air through a gas phase space provided in the clarification tank.

Thereafter, in the clarification step, the temperature of the molten glass is lowered. In this process, the reducing agent obtained by the reductive reaction of the clarifying agent undergoes an oxidation reaction. Thereby, gas components such as O ₂ in the foam remaining in the molten glass are reabsorbed in the molten glass, and the foam disappears.

  The oxidation reaction and reduction reaction by the fining agent are performed by controlling the temperature of the molten glass. In addition, tin oxide etc. are used as a clarifier. Moreover, the clarification process can also use the reduced pressure defoaming system which makes a reduced pressure atmosphere in a clarification tank, makes the bubble which exists in molten glass grow in a reduced pressure atmosphere, and defoams.

In the homogenization step (ST3), the glass components are homogenized by stirring the molten glass in the stirring tank supplied through the pipe extending from the clarification tank using a stirrer. Thereby, the composition unevenness of the glass which is a cause of striae or the like can be reduced. One stirring tank or two stirring tanks may be provided.
In the supply step (ST4), the molten glass is supplied to the molding apparatus through a pipe extending from the stirring tank.

In the molding apparatus, a molding step (ST5) and a slow cooling step (ST6) are performed.
In the forming step (ST5), the molten glass is formed into a sheet glass to make a flow of the sheet glass. For forming, an overflow down draw method or a float method can be used. In this embodiment to be described later, an over download method is used.
In the slow cooling step (ST6), the sheet glass that has been formed and flowed is cooled to a desired thickness, so that internal distortion does not occur and warpage does not occur.

  In a cutting process (ST7), a plate-shaped glass plate is obtained by cutting the sheet glass supplied from the forming device into a predetermined length in the cutting device. The cut glass plate is further cut into a predetermined size to produce a glass substrate of a target size. After this, the end surface of the glass substrate is ground and polished, the glass substrate is cleaned, and further, the presence of abnormal defects such as bubbles and scratches is inspected. Packed.

  FIG. 2 is a diagram schematically illustrating an example of an apparatus that performs the melting step (ST1) to the cutting step (ST7) in the present embodiment. As shown in FIG. 2, the apparatus mainly includes a melting apparatus 100, a forming apparatus 200, and a cutting apparatus 300. The melting apparatus 100 includes a melting tank 101, a clarification tank 102, a stirring tank 103, and glass supply pipes 104, 105, and 106.

  In the melting apparatus 101 of the example shown in FIG. 2, the glass raw material is charged using a screw feeder 101d. In the clarification tank 102, the temperature of the molten glass MG is adjusted, and the clarification of the molten glass MG is performed using the oxidation-reduction reaction of the clarifier. Further, in the stirring vessel 103, the molten glass MG is stirred and homogenized by the stirrer 103a. In the forming apparatus 200, the sheet glass SG is formed from the molten glass MG by the overflow down draw method using the formed body 210.

FIG. 3 is a perspective view illustrating a schematic configuration of the melting tank 101 of the present embodiment.
In the present embodiment, the melting tank 101 is designed to form a convection of molten glass as shown in FIG. A glass raw material is thrown into the raw material input side part among the liquid surfaces of the molten glass MG stored in the melting tank 101. An outflow port 104a is provided at the bottom of one of the pair of inner walls facing each other in the longitudinal direction of the rectangular melting tank 101 in plan view. The melting tank 101 flows the molten glass MG from the outlet 104a toward the subsequent process.

  The melting tank 101 has an inner wall 110 made of a refractory material such as a refractory brick. The melting tank 101 has an internal space surrounded by an inner wall 110. The internal space of the melting tank 101 is divided into a liquid tank 101a and an upper space 101b. The liquid tank 101a accommodates the molten glass MG formed by melting the glass raw material put into the internal space while heating. The upper space 101b is formed on the molten glass MG and is a gas phase into which a glass raw material is charged.

  The inner wall 110 of the upper space 101b parallel to the longitudinal direction of the melting tank 101 is provided with a burner 112 that burns combustion gas that is a mixture of fuel and oxygen or the like to generate a flame. The glass material is heated by the radiant heat from the flame of the burner 112 and the radiant heat from the inner wall (refractory brick) of the upper space 101b (which has become high temperature due to the radiant heat from the flame of the burner 112).

On the inner wall 110 opposite to the inner wall 110 where the outflow port 104a of the melting tank 101 is provided, a raw material charging window 101f leading to the upper space 101b is provided. The tip of the screw feeder 101d is connected to the raw material charging window 101f through the raw material charging window 101f, and the upper space 101b of the melting tank 101 is closed by the glass raw material filled in the screw feeder 101d.
The screw feeder 101d inputs the glass raw material in accordance with instructions from the computer 118. That is, the computer 118 operates the screw feeder 101 d through the control unit 116. Therefore, in the melting tank 101, the glass raw material is floating in the portion near the raw material charging window 101f on the liquid surface of the molten glass MG.

  In the present embodiment, the glass raw material is charged onto the liquid surface of the molten glass MG near the raw material charging window 101f using the screw feeder 101f, but the glass raw material is charged into the raw material using a bucket-type glass raw material charging mechanism. You may throw in on the liquid level of the molten glass MG near the window 101f.

The inner walls 110a and 110b of the liquid tank 101a that extend in the longitudinal direction of the melting tank 101 and are opposed to each other are composed of a heat-resistant conductive material such as tin oxide, molybdenum, or platinum, and a pair of electrodes 114 that face each other. Three pairs are provided. In particular, tin oxide can be suitably used as the electrode 114 because it does not cause a glass quality defect if it is not in a large amount even if it is eluted in contact with the molten glass MG. Moreover, it can be used suitably as the electrode 114 also in the point of functioning as a clarifier.
In the present embodiment, the melting tank 101 includes three pairs of electrodes 114, but two pairs of electrodes 114 may be used depending on the size of the melting tank. Also, four or more pairs of electrodes 114 may be used.

  Three pairs of electrodes 114 are provided in a region corresponding to the lower layer of molten glass MG in inner walls 110a and 110b. All three pairs of electrodes 114 extend through the inner walls 110a and 110b from the outer side to the inner side of the inner walls 110a and 110b. In FIG. 3, each pair of electrodes 114 shows the front electrode 114, and the back electrode 114 is not shown. Each pair of electrodes 114 is provided on the inner side walls 110a and 110b so as to face each other with the molten glass MG positioned between each pair of electrodes 114 interposed therebetween.

  Each pair of electrodes 114 applies a voltage between each pair of electrodes 114 to cause a current to flow through molten glass MG located between each pair of electrodes 114. By passing an electric current through the molten glass MG, Joule heat is generated in the molten glass MG, and the molten glass MG is energized and heated. In the melting tank 101, the molten glass MG is heated to, for example, 1500 ° C. or higher. The heated molten glass MG is sent to the clarification tank 102 through the glass supply pipe 104.

  In the melting tank 101 shown in FIG. 3, the burner 112 is provided in the upper space 101b, but the burner 112 is not essential. For example, in a molten glass having a specific resistance at 1500 ° C. of 180 Ω · cm or more and a relatively high specific resistance, the glass raw material can be efficiently melted by using the burner 112 as an auxiliary. When the glass raw material is continuously melted to produce the molten glass MG, the glass raw material can be melted without using the burner 112.

  Each pair of electrodes 114 is connected to the control unit 116. In order to make the temperature distribution of the molten glass MG in the lower layer a predetermined distribution, the control unit 116 is configured to be able to control the power supplied to each of the electrodes 114 for each of the pair of electrodes 114 facing each other. An AC voltage is applied to each pair of electrodes 114 by the control unit 116.

The control unit 116 is further connected to a computer 118. The control unit 116 measures the magnitude of the voltage applied to the molten glass MG between each pair of electrodes 114 and the value of the current flowing through the molten glass MG between each pair of electrodes 114. The value of the current flowing through the molten glass MG is determined in consideration of the power factor in the system of the electrode 114 and the current flowing through the wall (refractory brick) of the melting tank 101. That is, the measurement of the current flowing through the molten glass MG is a value obtained by subtracting the reactive current due to the power factor and the current flowing through the wall of the melting tank 101 from the measured current flowing through the electrode 114 directly measured by an ammeter or the like. That means. The reactive current due to the power factor is measured in advance. The current flowing through the wall of the melting tank 101 is determined by simulation or the like, for example. The control unit 116 outputs information on the measured voltage and current values. The computer 118 receives these pieces of information output from the control unit 116. The computer 118 calculates the specific resistance of the molten glass MG between each pair of electrodes 114 from the information on the voltage and current values.
In the present embodiment, in order to calculate the specific resistance with high accuracy, a value obtained by subtracting the reactive current due to the power factor and the current flowing through the wall of the melting tank 101 from the measured current is obtained. Thus, the reactive current due to the power factor and / or the current flowing through the wall of the melting tank 101 may be set to zero. That is, the current flowing through the molten glass MG is measured by subtracting the reactive current due to the power factor from the measured current, or subtracting the current flowing through the wall of the melting tank 101 from the measured current, according to the required specific resistance accuracy. Desired. Alternatively, the measurement current itself can be used as a current flowing through the molten glass MG.

  For example, the computer 118 calculates the specific resistance ρ (Ω · m) of the molten glass MG between each pair of electrodes 114 based on the following formula (1).

  ρ = E / I × S / L (1)

In the formula (1), E is a voltage (V) applied to the molten glass MG between each pair of electrodes 114, I is a current (A) flowing through the molten glass MG between each pair of electrodes 114, and S is each pair of electrodes 114. The cross-sectional area (m ² ) of the molten glass MG through which current flows between the electrodes 114, and L is the distance (m) between each pair of electrodes 114. The length L is a specific value determined by the melting tank 101.

4A and 4B are plan views for explaining a method for obtaining the cross-sectional area S of the molten glass MG through which a current flows between each pair of electrodes 114.
As shown in FIGS. 4A and 4B, each pair of electrodes 114 is opposed to the inner walls 110a and 110b arranged on both sides of the molten glass MG so as to cross the flow direction F of the molten glass MG. Are arranged. Further, the three pairs of electrodes 114 facing each other are arranged at a predetermined interval in the flow direction F of the molten glass MG. The flow direction F indicates the flow direction from the upstream to the downstream at the bottom of the melting tank 101 as a whole for the molten glass MG in the melting tank 101 for convenience, and is parallel to the inner walls 110a and 110b. This is the direction from the side (left side in FIGS. 4A and 4B) toward the outlet 104a side (right side in FIGS. 4A and 4B). The flow direction F is also a direction along the longitudinal direction of the melting tank 101.

  The computer 118 sets an area EA of the molten glass MG through which a current flows for each pair of electrodes 114 facing each other. The boundary m of the energization area EA varies depending on the voltage applied to the electrode 114. That is, when the voltage applied to a certain electrode 114 is increased, but the voltage applied to the other electrode 114 is kept constant, the region EA of the current flowing from the electrode 114 with the increased applied voltage to the molten glass MG increases. . Conversely, the area EA is set to be small when the applied voltage is small. In other words, the computer 118 sets the cross-sectional area S of the area EA according to the applied voltage. Thus, the cross-sectional area of the area EA is determined according to the voltage to be applied, the cross-sectional area S of the area EA of the current flowing through the molten glass MG changes depending on the voltage applied to the electrode 114, and this cross-sectional area S is This is because it affects the specific resistance ρ of the molten glass MG to be calculated as shown in the above formula (1).

Therefore, when the voltages V ₁ , V ₂ , and V ₃ are sequentially applied to the three pairs of electrodes 114 from the raw material inlet side in FIG. The cross-sectional area S of the current area EA flowing through the molten glass MG can be determined as shown in the following formula (2). The cross-sectional area S _i of the region EA _i (i = 1 to a natural number of 1 to 3) is a cross-sectional area of a current flowing from the electrode to which the voltage V _i is applied to the molten glass MG.
Sectional area S _i of the area EA _i
= F (V _i ) / {F (V ₁ ) + F (V ₂ ) + F (V ₃ )} × (W × D) (2)
Here, as shown in FIG. 4A, W is a length parallel to the flow direction F of the tank in which the molten glass MG of the melting tank 101 is stored, and D is shown in FIG. 4B. Thus, it is the depth of the molten glass MG of the melting tank 101. F (V) is a function of the voltage V, and is a function in which the value of F (V) increases as the voltage increases. For example, F (V) is a linear function or a quadratic function of the voltage V. 4A and 4B, the cross-sectional area S ₁ , the cross-sectional area S ₂ , and the cross-sectional area S ₃ are all shown to the same extent, but vary depending on the voltages V ₁ , V ₂ , and V ₃ .
Here, in the above formula (2), F (V) can be simplified so that, for example, F (V) = V. In this case, the cross-sectional area S _i depends on the ratio of the value of the voltage V _i applied between each pair of electrodes to the total value V ₁ + V ₂ + V ₃ of all the voltages applied between the plurality of pairs of electrodes. A cross-sectional area S _i is set.
Thus, the cross-sectional area S _i of the area EA _i through which the current of the molten glass MG flows is set according to the voltages V ₁ , V ₂ , and V ₃ . Using the obtained cross-sectional area S _i , the specific resistance ρ of the molten glass MG between each pair of electrodes 114 can be obtained by the above formula (1).

The computer 118 can control the Joule heat generated in the molten glass MG in each area EA _i corresponding to each pair of electrodes 114 based on the specific resistance ρ of the molten glass MG obtained by the above method.

(Control method 1 for energization heating)
FIG. 5 is a diagram illustrating an example of a process in which the computer 118 controls the Joule heat generated in the molten glass MG based on the specific resistance ρ of the molten glass MG.

  In the sampling (ST11) shown in FIG. 5, information on the voltage E applied to the molten glass MG between the electrodes 114 in each region EA corresponding to each pair of electrodes 114 shown in FIGS. Information on the measured current flowing through 114 is sent from the control unit 116 to the computer 118. The computer 118 calculates | requires the value which deducted the reactive current by a power factor and the electric current which flows through the wall of the melting tank 101 from the sent electric current as the electric current I which flows through molten glass MG. Information on the voltage E of each area EA sent from the control unit 116 and information on the obtained current I are stored. The computer 118 stores in advance the distances L, W, D between the electrodes 114 and target values of the specific resistance of the molten glass MG described later in each area EA.

In the calculation of the specific resistance shown in FIG. 5 (ST12), the computer 118 stores the information on the stored voltage E, current I, cross-sectional area S, and distances L, W, and D of each area EA, and the above-described equations (1), Based on (2), the specific resistance ρ of the molten glass MG in each region EA is calculated. Specifically, each cross-sectional area S _i is calculated according to equation (2), and specific resistance ρ is calculated according to equation (1) using this cross-sectional area S _i .

In addition, the specific resistance ρ of each area EA _i when the molten glass MG in the melting tank 101 is in a desired melting state is calculated in advance, and the value is stored in the computer 118 as a target value of the specific resistance ρ. I can leave. In the step of determining the target value of the specific resistance ρ, for example, a desired melting state of the molten glass MG is created by using a temperature measuring means such as a thermocouple as in the prior art, and in this state, the specific resistance is obtained by the computer 118 as described above. ρ may be calculated. In addition, a glass substrate manufactured from molten glass MG may be collected in advance and melted in a crucible or the like, and a specific resistance corresponding to the molten glass MG having a target viscosity and temperature may be obtained as a target value of specific resistance ρ. .

In the specific resistance comparison (ST13) shown in FIG. 5, the computer 118 compares the target value of the specific resistance ρ in each area EA _i with the calculated specific resistance ρ in each area EA _i .
In the determination of the control amount shown in FIG. 5 (ST14), the computer 118 determines the control amount to be sent to the control unit 116 based on the result of the specific resistance comparison (ST13).

Specifically, in a certain area EA _i , when the calculated specific resistance ρ is larger than the target value or larger than an allowable range, the computer 118 generates Joule heat generated in the molten glass MG in the area EA _i . Is instructed to decrease by a predetermined amount.
In a certain area EA _i , when the calculated specific resistance ρ is equal to or within an allowable range, the computer 118 issues an instruction to maintain the Joule heat generated in the molten glass MG in the area EA.
In a certain area EA _i , when the calculated specific resistance ρ is smaller than the target value or smaller than the allowable range, the computer 118 generates a predetermined amount of Joule heat generated in the molten glass MG in the area EA _i . Give instructions to increase.

In the Joule heat control (ST15) shown in FIG. 5, the control unit 116 controls the Joule heat generated in the molten glass MG in each area EA _i based on the control amount instruction sent from the computer 118.

Specifically, when the control unit 116 receives an instruction to reduce Joule heat generated in the molten glass MG in a certain area EA _i , the molten glass MG between the pair of electrodes 114 corresponding to the area EA _i. The target current value that should flow through the molten glass MG is set so that the value of the current flowing through the molten glass becomes a constant value smaller than the original value by a predetermined value.
When the control unit 116 receives an instruction to maintain Joule heat generated in the molten glass MG in a certain area EA _i , the value of the current flowing in the molten glass MG between the pair of electrodes 114 corresponding to the area EA _i. Or, the original target value is set to the target current value.
When the control unit 116 receives an instruction to increase the Joule heat generated in the molten glass MG in a certain area EA _i , the value of the current flowing in the molten glass MG between the pair of electrodes 114 corresponding to the area EA _i. However, the target current value is set so that it becomes a constant value larger than the original value by a predetermined value.
The control unit 116 further controls the voltage applied to the molten glass MG between each pair of electrodes 114 so as to maintain the value of the current flowing through the molten glass MG at the target current value.

By the above control, the viscosity and temperature of the molten glass MG in each region EA _i are maintained in a desired state without using a temperature measuring means such as a conventional thermocouple, and the convection and melting of the molten glass MG in the melting tank 101 is performed. This state can be maintained in a desired state.
Thus, for each of the plurality of pairs of electrodes 114, the cross-sectional area S _i of the region EA _i of the molten glass MG through which current flows is set according to the voltage, and the current value, the voltage value, and the set molten glass Since the specific resistance ρ of the molten glass is calculated for each area EA _i using the cross-sectional area S _{i of the} MG, the accurate specific resistance ρ can be calculated for each area EA. As a result, it is possible to heat and heat the molten glass MG in the melting tank 101 to be homogenized, and to efficiently heat and heat the molten glass MG.

(Control method 2 for energization heating)
Then, as one method of controlling Joule heat to be generated in the molten glass MG in each area EA on the basis of the specific resistance ρ calculated above, calculated from the specific resistance ρ more of the area EA _i in each area EA _i A method for calculating the temperature of the molten glass MG will be described.
6, seeking temperature of the molten glass MG from the calculated resistivity [rho, is a diagram illustrating a process of controlling Joule heat to be generated in the molten glass in each area EA _i.

  In this method, first, as a preliminary process (ST21), the relationship between the temperature and the specific resistance of the molten glass having the same component as the molten glass MG produced in the melting tank 101 is obtained in advance and recorded in the computer 118. In the stage of obtaining the relationship between the temperature of the molten glass MG and the specific resistance, the temperature of the molten glass MG may be measured in the melting tank 101 using a temperature measuring means such as a thermocouple as in the prior art. Then, by calculating the specific resistance ρ with the computer 118 as described above, the relationship between the temperature of the molten glass MG and the specific resistance can be obtained. Moreover, these correlations may be obtained by collecting a glass substrate manufactured from the molten glass MG in advance and melting it with a crucible or the like, and measuring the temperature and specific resistance of the molten glass MG at that time.

  The temperature of the molten glass MG can be expressed as a function of the specific resistance ρ, for example, G (ρ). That is, the specific resistance ρ of the molten glass MG and the temperature T (° C.) of the molten glass MG have a correlation represented by the following formula (3).

  T (° C.) = G (ρ) = a / (log (ρ) + b) −273.15 (3)

In the formula (3), a and b are constants depending on the glass composition.
The values of the constants a and b are specified by the preliminary process (ST21). The values of the constants a and b are stored in the computer 118 together with the above equation (3). In the preliminary step (ST21), the target temperature of the molten glass MG in each area EA _i is set in advance, and the value is stored in the computer 118. For example, the temperature T of each area EA _i when the molten glass MG of the melting tank 101 is in a desired melting state is calculated in advance, and the value is stored in the computer 118 as the target temperature of the temperature T. Can do. In the step of setting the target temperature of the temperature T, for example, a desired melting state is created in the molten glass MG using a temperature measuring means such as a thermocouple as in the conventional case, and in that state, the temperature T is set by the computer 118 as described above. It may be calculated.

The sampling (ST22) and specific resistance calculation (ST23) shown in FIG. 6 are the same as the sampling (ST11) and specific resistance calculation (ST12) shown in FIG.
In the temperature calculation (ST24) shown in FIG. 6, the computer 118 calculates the specific resistance ρ of each area EA _i , constants a and b stored in advance, and the above equation (3), The temperature T of the molten glass MG in each area EA _i is calculated.

In the temperature comparison (ST25) shown in FIG. 6, the computer 118 compares the stored target value of the temperature T of each area EA _i with the calculated temperature T of each area EA _i .
In the control amount determination (ST26) shown in FIG. 6, the control amount to be sent to the control unit 116 is determined based on the result of the temperature comparison (ST25).

Specifically, in a certain area EA _i , when the calculated temperature T is higher than a target value or higher than an allowable range, the computer 118 generates Joule heat generated in the molten glass MG in the area EA _i . Instruct to decrease by a predetermined amount.
In a certain area EA _i , when the calculated temperature T is equal to or within an allowable range, the computer 118 issues an instruction to maintain the Joule heat generated in the molten glass MG in the area EA _i .
In a certain area EA _i , when the calculated temperature T is lower than the target value or lower than the allowable range, the computer 118 generates a predetermined amount of Joule heat generated in the molten glass MG in the area EA _i , Give instructions to increase.

The Joule heat control (ST27) shown in FIG. 6 is the same as the Joule heat control (ST15) shown in FIG.
With the above control, the viscosity and temperature of the molten glass MG in each region EA _i are set in a desired state without using a conventional temperature measuring device such as a thermocouple, and the melting state of the molten glass MG in the melting tank 101 is set in a desired state. Can be in a state.
Thus, in the present embodiment, the Joule heat applied to the molten glass MG is controlled using the measured and calculated specific resistance ρ in both the method shown in FIG. 5 and the method shown in FIG. 6. For this reason, in order to calculate the specific resistance ρ with high accuracy, in the present embodiment, the cross-sectional area S _i of the region EA _i through which the current flows is calculated according to the voltage applied to the electrode 114, and the equations (1) and (1) The specific resistance ρ is calculated according to (2). Therefore, since the specific resistance ρ can be calculated with high accuracy, the molten glass can be homogenized and the molten glass MG can be efficiently energized and heated.

In the present embodiment, in the melting tank 101, taking out the molten glass MG while causing convection of the molten glass MG as shown in FIG. 7 to be described later does not cause striae and does not cause the foreign material to flow out of the melting tank 102. This is preferable. For this reason, it is preferable to change the Joule heat generated in the molten glass MG according to the position of the electrode 114. As described above, the computer 118 can calculate the cross-sectional area S _i of the area EA _i through which the current flows in accordance with the voltage applied to the electrode 114, and can calculate the specific resistance ρ with high accuracy. The temperature distribution of the molten glass MG that causes the convection of the molten glass MG can be accurately adjusted to a desired distribution. Hereinafter, the convection of the molten glass MG in the melting tank 101 will be described.

(Convection of molten glass in melting tank)
With the above-described electric heating 1 and 2 of the molten glass MG, the electric heating of the molten glass MG is controlled so that, for example, the following convection of the molten glass MG is formed in the melting tank 101. However, the electric heating control of the molten glass MG can be applied not only to a form that causes convection in the molten glass MG as shown in FIG. 7, but also to a form that causes convection other than the convection shown in FIG. 7 in the molten glass MG. Alternatively, it can be applied to a form that does not cause convection.

  FIG. 7 is a diagram for explaining the convection of the molten glass inside the melting tank 101 in the present embodiment. In the present embodiment, molten glass MG flows out from the outlet 104a provided at the bottom of the inner side wall facing the first direction among the inner side walls of the melting tank 101 toward the refining process. At this time, the temperature of the molten glass MG located at the bottom of the melting tank 101 increases from the raw material charging side (left side in FIG. 7) toward the outlet 104a side (right side in FIG. 7). MG is heated and controlled. Thereby, on the side of the outlet 104a, the molten glass MG is caused to flow from the outlet 104a to the refining process, which is a downstream process, and a convection of the molten glass MG is made. That is, a part of the molten glass MG that did not flow from the outlet 104a rises toward the liquid surface 101c along the side wall of the melting tank 101, and a part of the molten glass MG that has risen to the liquid surface 101c reaches the liquid surface 101c. Along the side wall of the melting tank 101 on the raw material charging side, descends from the liquid level 101 c along the side wall of the melting tank 101 on the raw material charging side, and further from the raw material charging side to the discharge port 104 a side along the bottom surface. It flows toward.

The reason for generating such circulating convection is as follows. That is, in a hardly fusible glass having a high silica concentration, an alkaline earth metal component having a low thermal decomposition temperature is first melted in comparison with the surrounding molten glass when the glass raw material is decomposed and melted. It is easy to generate a heterogeneous substrate 120 having a high concentration of If the generated heterogeneous material 120 drifts to the side wall on the outlet side of the melting tank for some reason and sinks and flows into the downstream process, the silica concentration is higher and the viscosity is higher than the surrounding molten glass, which is a striae. .
However, in the melting tank 101, since the convection of the molten glass MG as shown in FIG. 7 is formed, the heterogeneous substrate 120 does not drift near the side wall on the outlet 104a side. Furthermore, on the side wall on the outlet 104a side, the flow of the molten glass MG flows from the bottom surface toward the liquid surface, so that the heterogeneous substrate does not sink.

In order to form the convection indicated by the arrows shown in FIG. 7 in the melting tank 101, the temperature of the molten glass MG flowing through the bottom of the melting tank 101 gradually increases from the raw material charging side to the outlet 104a side in FIG. In the example shown in FIG. 7, the temperature T ₁ <temperature T ₂ <temperature T ₃ and the temperature T ₃ (maximum temperature) with respect to the temperature T ₄ of the surface layer of the molten glass MG at the raw material charging position in the example shown in FIG. The power supplied to the electrode 114 may be controlled so that the voltage becomes higher. The temperature T ₁ is the temperature of the molten glass MG at the position of the pair of electrodes 114 provided on the raw material input side in FIG. 7, and the temperature T ₂ is the pair of the three pairs of electrodes 114 positioned in the middle. It is the temperature of the molten glass MG at the position of the electrode 114, and the temperature T ₃ is the temperature of the molten glass MG at the position of the pair of electrodes 114 located on the outflow side of the three pairs of electrodes 114. The computer 118 is used to control the current heating of the molten glass MG as described above so as to form such a temperature distribution.

(Glass composition)
The composition of the glass used in the present embodiment is composed of aluminosilicate glass, SiO ₂ and (silica) may comprise more than 55 wt%. The manufacturing method of this embodiment applied to an aluminosilicate glass having this glass composition can effectively suppress unevenness of the glass composition as compared with the conventional method. Furthermore, SiO ₂ can be contained in an amount of 60% by mass or more, and SiO ₂ can be contained in an amount of 65% by mass or more. Even if the glass composition contains 55% by mass of SiO ₂ and easily forms a silica-rich heterogeneous substrate 120, the silica-rich heterogeneous substrate 120 drifts to the side wall on the outlet 104a side. Since the convection of 101c is prevented, and the glass flow is flowing from the bottom (bottom surface) side to the ground surface (liquid surface) side on the side wall on the outflow port 104a side, the silica-rich heterogeneous substrate 120 is provided. Can be prevented from flowing out from the outlet 104a. The upper limit of the content in the glass composition of SiO ₂ is 70 wt% for example.

Moreover, the manufacturing method of this embodiment to which a total of 70 mass% or more of SiO ₂ and Al ₂ O ₃ can be applied and the aluminosilicate glass having this glass composition is applied is more effective than the conventional glass composition. Can be suppressed. Furthermore, it is possible to contain 75% by mass or more of SiO ₂ and Al ₂ O ₃ in total.
Even if the glass composition contains 70% by mass or more of SiO ₂ and Al ₂ O ₃ in total and can easily produce the silica-rich heterogeneous substrate 120, the convection of the liquid surface 101c of the molten glass MG is caused by the silica-rich heterogeneous substrate 120. Prevent drifting to the side wall on the outlet 104a side. Moreover, since the flow of the molten glass MG flows from the bottom (bottom surface) side toward the base (liquid surface) side on the side wall on the outlet 104a side, the silica-rich heterogeneous substrate 120 is discharged from the outlet 104a. It can be prevented from leaking. The upper limit of the total content of SiO ₂ and Al ₂ O ₃ is, for example, 85% by mass.

The glass composition of a glass substrate can mention the following, for example.
The content rate display of the composition shown below is mass%.
SiO _2: 50~70%,
Al ₂ O _3: 0~25%,
B ₂ O ₃ : 1 to 15%,
MgO: 0 to 10%,
CaO: 0 to 20%,
SrO: 0 to 20%,
BaO: 0 to 10%,
RO: 5 to 30% (however, R is at least one selected from Mg, Ca, Sr and Ba, and the glass substrate contains),
It is preferable that it is an alkali free glass containing.

Although the alkali-free glass is used in this embodiment, the glass substrate may be a glass containing a trace amount of alkali containing a trace amount of alkali metal. When an alkali metal is contained, the total of R ′ ₂ O is 0.10% or more and 0.5% or less, preferably 0.20% or more and 0.5% or less (where R ′ is selected from Li, Na, and K) It is preferable that the glass substrate contains at least one kind. Of course, the total of R ′ ₂ O may be lower than 0.10%.
When applying the method of manufacturing a glass substrate of this embodiment, the glass composition, in addition to the above components, represented by _mass%, SnO 2: 0.01 to 1% (preferably 0.01 to 0. 5%), Fe ₂ O ₃ : 0 to 0.2% (preferably 0.01 to 0.08%) can be contained as a fining agent. From the viewpoint of reducing environmental burden, the glass raw material may be prepared so as not to substantially contain As ₂ O ₃ , Sb ₂ O ₃ and PbO.

When using a glass with a high strain point to form p-Si (low temperature polysilicon) TFT or oxide semiconductor on a glass substrate, for example, when using a molten glass with a strain point of 655 ° C. or higher, the glass composition is For example, the glass substrate is represented by mass% and includes the following components.
SiO ₂ 52~78%,
Al ₂ O ₃ 3-25%,
B ₂ O ₃ 3-15%,
RO (however, R is selected from Mg, Ca, Sr and Ba, all components contained in the glass plate and is at least one) 3-20%,
Including
The mass ratio (SiO ₂ + Al ₂ O ₃ ) / B ₂ O ₃ is preferably an alkali-free glass in the range of 7 to 20 or an alkali trace-containing glass described later.
Furthermore, in order to further increase the strain point, the mass ratio (SiO ₂ + Al ₂ O ₃ ) / RO is preferably 7.5 or more. Furthermore, in order to raise a strain point, it is preferable to make (beta) -OH value into 0.1-0.3 mm < ^-1 >. Furthermore, in order to prevent a decrease in liquid phase viscosity while realizing a high strain point, CaO / RO is preferably 0.65 or more.
In addition to the components described above, the glass used in the glass substrate of this embodiment contains various other oxides to adjust various physical, melting, fining, and forming properties of the glass. There is no problem. Examples of such other oxides include, but are not limited to, TiO ₂ , MnO, ZnO, Nb ₂ O ₅ , MoO ₃ , Ta ₂ O ₅ , WO ₃ , Y ₂ O ₃ , and La ₂ O ₃ is mentioned.

  The manufacturing method of this embodiment can be effectively applied to the glass substrate for liquid crystal display devices. As described above, the glass substrate for a liquid crystal display device does not contain an alkali metal component (Li, Na, and K) in the glass composition or preferably contains a trace amount. However, when the alkali metal components (Li, Na, and K) are not included or are contained in a trace amount, the high temperature viscosity of the molten glass MG is increased. In this embodiment, even when the temperature is increased to increase the viscosity of the molten glass MG having a high high temperature viscosity, the specific resistance ρ of the molten glass MG can be calculated with high accuracy. Electric power can be supplied and Joule heat can be efficiently generated in the molten glass MG.

  Furthermore, for a glass substrate on which p-Si (low-temperature polysilicon) TFTs and oxide semiconductors are formed, glass (molten glass MG) having a strain point of, for example, 655 ° C. or higher is preferable from the viewpoint of reducing the thermal shrinkage rate. Used for. In the case of a molten glass having a strain point of 655 ° C. or higher, the meltability of the molten glass MG is low. For this reason, the temperature of the molten glass MG in the melting tank 101 is set still higher compared with the past. However, even in this case, the specific resistance of the molten glass in the melting tank can be calculated with high accuracy, so that the molten glass in the melting tank can be heated and heated so as to homogenize the molten glass. It is possible to heat the current efficiently.

Further, in this embodiment, SnO ₂ is used as a clarifier from the viewpoint of reducing the environmental load, but in order to effectively function the clarification action of SnO ₂ , the temperature of the molten glass MG should be accurately adjusted to a high temperature. Is preferred. In the present embodiment, since the specific resistance ρ of the molten glass MG can be calculated with high accuracy, power can be efficiently supplied to the electrode 114.

  As mentioned above, although the manufacturing method and manufacturing apparatus of the glass substrate of this invention were demonstrated in detail, this invention is not limited to the said embodiment, In the range which does not deviate from the main point of this invention, even if various improvement and a change are carried out. Of course it is good.

DESCRIPTION OF SYMBOLS 100 Melting apparatus 101 Melting tank 101a Liquid tank 101b Upper space 101c Liquid surface 101d Bucket 101f Raw material injection | throwing-in window 102 Clarification tank 103 Stirrer tank 103a Stirrer 104,105,106 Glass supply pipe 110 Inner wall 110a, 110b, 110c, 110d Inner wall 110e Bottom 112 Burner 114 Electrode 116 Control unit 118 Computer 120 Heterogeneous substrate 200 Molding device 210 Molded body 300 Cutting device

Claims (10)

Including a melting step of melting glass raw material to produce molten glass,
The melting step
For the molten glass positioned between each of the plurality of pairs of electrodes, by applying a voltage between each of the electrodes, a current is caused to flow to generate Joule heat;
For each of the plurality of pairs of electrodes, the value of the current flowing through the molten glass is measured, and for each of the plurality of pairs of electrodes, the cross-sectional area of the region of the molten glass through which the measured current flows is set according to the voltage value. Then, using the value of the current, the value of the voltage, and the cross-sectional area of the set molten glass, calculating the specific resistance of the molten glass for each region,
And a step of controlling the Joule heat based on the calculated specific resistance for each of the plurality of pairs of electrodes.   2. The glass according to claim 1, wherein the cross-sectional area is set according to a ratio of a value of the voltage applied between the pair of electrodes to a total value of all voltages applied between the plurality of pairs of electrodes. A method for manufacturing a substrate. The melting step
A preliminary step of obtaining a correlation between the temperature of the molten glass and the specific resistance of the molten glass;
The step of controlling the Joule heat includes
Calculating the temperature of the molten glass based on the correlation and the calculated resistivity;
The glass substrate according to claim 1, further comprising a step of controlling Joule heat generated in the molten glass based on a result of comparing the calculated temperature with a target temperature preset in the molten glass. Manufacturing method. The step of controlling the Joule heat includes
Setting a target current value for generating Joule heat in the molten glass so as to maintain the calculated temperature at the target temperature;
The method for manufacturing a glass substrate according to claim 3, further comprising: controlling the voltage so as to maintain the current at the target current value. In the preliminary step,
The temperature is T, the specific resistance is ρ, and the equation expressing the correlation:
T (° C.) = A / (log (ρ) + b) −273.15
Find the constants a and b in
In the step of calculating the temperature,
Substituting the specific resistance ρ into the equation to calculate the temperature T,
The manufacturing method of the glass substrate of Claim 3 or 4. In the step of calculating the specific resistance,
The current value is I, the voltage is E, the cross-sectional area of the region of the molten glass through which the current flows is S, the distance L between the pair of electrodes, the specific resistance is ρ, Expression expressing the relationship: ρ = E / I × S / L
The specific resistance ρ is calculated based on
The manufacturing method of the glass substrate of any one of Claims 1-5. The glass substrate is a glass substrate for a flat panel display,
The manufacturing method of the glass substrate of any one of Claims 1-6. The glass substrate is an alkali-free glass or an alkali trace amount glass,
The manufacturing method of the glass substrate of any one of Claims 1-7. The strain point of the molten glass is 655 ° C. or higher.
The manufacturing method of the glass substrate of any one of Claims 1-8. A glass substrate manufacturing apparatus having a melting tank for producing molten glass,
Including a melting device that melts the input glass raw material to produce molten glass,
The melting device is:
A plurality of pairs of electrodes in contact with the molten glass, provided on a wall surface in contact with the molten glass of the melting tank;
A control unit for applying a voltage between the plurality of pairs of electrodes to control electric power for generating Joule heat by passing a current through the molten glass;
Obtaining information on the value of the current flowing through the molten glass and the value of the voltage for each of the plurality of pairs of electrodes, and calculating the cross-sectional area of the region of the molten glass through which the current flows for each of the plurality of pairs of electrodes. Set according to the value, calculate the specific resistance of the molten glass using the value of the current, the value of the voltage, and the cross-sectional area of the set molten glass, and based on the calculated specific resistance And a calculation unit for determining a control amount of the Joule heat.

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