WO2012132473A1

WO2012132473A1 - Glass substrate production method

Info

Publication number: WO2012132473A1
Application number: PCT/JP2012/002252
Authority: WO
Inventors: 次伸村上; 哲郎君嶋; 宣之日沖; 慎吾藤本
Original assignee: ＡｖａｎＳｔｒａｔｅ株式会社; アヴァンストレートコリアインコーポレイテッド; 安瀚視特股▲分▼有限公司
Priority date: 2011-03-31
Filing date: 2012-03-30
Publication date: 2012-10-04
Also published as: KR20120138838A; CN103124700A; CN103080025B; CN103080025A; WO2012132474A1; KR101300980B1; TW201247579A; CN103124700B; TWI469940B

Abstract

A glass substrate production method that solves the problem of degradation, etc., of conventional temperature measurement means during conduction heating of molten glass and maintains at a desired state the viscosity and convection of the molten glass. The glass substrate production method includes: a step in which the molten glass is arranged between a pair of electrodes and voltage is applied thereto, and current is supplied to the molten glass and Joule heat is generated; a step in which the current value and the voltage value are measured and the specific resistance of the molten glass is calculated; and a step in which the Joule heat is controlled on the basis of the calculated specific resistance.

Description

Manufacturing method of glass substrate

The present invention relates to a method for manufacturing a glass substrate.

For example, glass substrates used for flat panel displays (hereinafter referred to as FPD) such as liquid crystal displays and plasma displays are mainly 0.5 to 0.7 mm in thickness and 300 to 400 to 2850 to 3050 mm in size. is there.

An overflow down draw method is known as a method for manufacturing a glass substrate for FPD. In the overflow downdraw 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 customer specifications, subjected to cleaning, end face polishing, etc., and shipped as a glass substrate for FDP.

Among the glass substrates for FPD, in particular, the glass substrate for liquid crystal display devices has a semiconductor element formed on the surface thereof, and therefore does not contain an alkali metal component at all or even if it is contained, the semiconductor element is affected. It is preferable that the amount is as small as possible.
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.

Further, when there is uneven glass composition (non-uniform glass composition) on the glass substrate, for example, streak-like defects called striae occur. 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 the above glass substrate, the electrically heated heating with respect to a molten glass is performed conventionally.
As an example of such energization heating, high-frequency energization heating of a glass melting furnace using a plurality of electrode pairs is known. For example, Japanese Patent Laid-Open No. 04-367519 discloses a technique in which a plurality of electrodes are controlled for each electrode pair by connecting each electrode pair to a separate power source and controlling each power source individually. Has been. 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 JP-A-03-103328, for example, via a thermocouple The temperature of the molten glass was measured.

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

Since the thermocouple is exposed to a high temperature in, for example, a melting tank, the thermocouple 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.
Then, this invention solves said subject in the electrical heating of molten glass, and provides the manufacturing method of the glass substrate which can maintain the viscosity and convection of molten glass in a desired state.

The manufacturing method of the glass substrate which is 1 aspect of this invention includes the melting process which melt | dissolves the raw material of glass and produces | generates molten glass. The melting step includes: placing the molten glass between a pair of electrodes and applying a voltage; passing a current through the molten glass to generate Joule heat; measuring the current value and the voltage value; And calculating the specific resistance of the molten glass; and controlling the Joule heat based on the calculated specific resistance.

The step of controlling the Joule heat may include the following steps.
(1) When the viscosity and convection of the molten glass are in a desired state, the current value and the voltage value are measured to calculate the specific resistance of the molten glass, and the calculated specific resistance is The process of setting as a target value of specific resistance.
(2) A step of comparing the calculated specific resistance with a target value of the specific resistance.
(3) A step of maintaining or increasing or decreasing the value of the current so that a difference between the calculated specific resistance and a target value of the specific resistance is a value within a predetermined range.
In the step (1), the temperature of the molten glass may be measured using temperature measuring means such as a thermocouple, and the viscosity and convection of the molten glass may be set to a desired state.

By calculating the specific resistance value of the molten glass and controlling the Joule heat generated in the molten glass based on the specific resistance value, the viscosity and convection of the molten glass can be maintained in a desired state. The problem in the case of using temperature measuring means such as a thermocouple can be solved.

It is a figure which shows an example of the process of the manufacturing method of the glass substrate of this embodiment. It is sectional drawing which shows typically an example of the apparatus which performs the process from melting to cutting | disconnection. It is a perspective view explaining an example of the melting tank used at a melting process. It is a top view explaining injection | throwing-in of the glass raw material in a melting tank. (A) And (b) is explanatory drawing of the area | region where the electric current between each electrode pair flows. It is a figure which shows an example of the process of calculating specific resistance and controlling Joule heat. It is a figure which shows an example of the process of calculating temperature from specific resistance and controlling Joule heat. It is typical sectional drawing explaining the convection of the molten glass inside a melting tank. It is a figure explaining the convection of the molten glass inside the conventional melting tank.

Hereinafter, the manufacturing method of the glass substrate of this embodiment is 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, the glass raw material is intermittently dispersed and introduced into a plurality of positions on the liquid surface of the molten glass stored in the melting tank, thereby producing a molten glass having a uniform surface temperature including the liquid surface. Furthermore, molten glass is poured from the outflow port provided in one bottom part of the inner wall which opposes in the longitudinal direction of a rectangular melting tank by planar view among the inner walls of a melting tank toward a post process.

Here, the temperature of the molten glass in the lower layer located below the surface layer is made uniform in the longitudinal direction of the melting tank, and the temperature difference of the molten glass in the longitudinal direction of the melting tank is made as small as possible. Therefore, the amount of heat for heating the lower layer of the molten glass is set to be larger at both ends in the longitudinal direction of the melting tank than in the central part in the longitudinal direction of the melting tank. The reason for this is that the heat of the molten glass is more easily taken away at the both ends in the longitudinal direction of the melting tank than at the center. This prevents the convection due to the temperature distribution of the molten glass in the longitudinal direction of the melting tank from occurring in the molten glass in the lower layer, and makes the molten glass from the outlet while making the temperature distribution in the lower layer of the molten glass uniform. It flows to the subsequent process.

In the present embodiment, the “surface layer” of the molten glass represents a region including the liquid surface within a range of 5% or less of the depth from the liquid surface toward the bottom of the melting tank, and the “lower layer” of the molten glass is Represents an area other than the surface layer. Moreover, the “bottom part” where the outflow port is provided is a part of the lower layer and represents a region close to the bottom surface of the melting tank. In the present embodiment, the “bottom part” 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 part of the melting tank.

The glass raw material is charged entirely over 80% of the liquid surface of the molten glass in the melting tank. As a method for charging the glass raw material, a method may be used in which the bucket containing the glass raw material is inverted and the glass raw material is dispersedly charged into the molten glass. Further, the glass raw material may be charged by a method in which the glass raw material is conveyed and distributed using a belt conveyor, or a method in which the glass raw material is charged all over at once. Further, the glass raw material may be charged by a method in which the glass raw material is dispersedly supplied by a screw feeder or a method in which the glass raw material is supplied to the entire surface at once. In an embodiment described later, the glass raw material is charged by a charging method using a bucket.

When a voltage is applied between the electrodes of the melting tank to pass a current through the molten glass, the molten glass generates Joule heat. If the Joule heat is increased, the temperature of the molten glass increases, and if it is decreased, the temperature of the molten glass can decrease. In addition to heating the molten glass by energization, the glass raw material can be melted by using the heat from the burner flame as an auxiliary.

A fining agent is added to the glass raw material. SnO ₂ , As ₂ O ₃ , Sb ₂ O _{3 and the} like are known as fining agents, but are not particularly limited. However, it is preferable to use SnO ₂ (tin oxide) as a clarifying agent from the viewpoint of reducing environmental burden.

The clarification step (ST2) is performed at least in the clarification tank. 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 clarifying agent, and float on the liquid surface of the molten glass and disappear. The clarification step is performed inside a platinum or platinum alloy container.

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 the reduction reaction by the fining agent are performed by controlling the temperature of the molten glass. In the clarification step, a reduced pressure defoaming method can be used in which a reduced pressure atmosphere is created in a clarification tank, and bubbles present in the molten glass are grown in a reduced pressure atmosphere and defoamed. In this case, it is effective in that no clarifier is used. In an embodiment described later, tin oxide is used as a fining agent.

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 the cutting step (ST7), in the cutting device, the sheet glass supplied from the forming device is cut into a predetermined length to obtain a plate-like glass plate. 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 striae is inspected. Will be packed as.

FIG. 2 is a diagram schematically showing an example of an apparatus for performing 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 bucket 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 make a molten glass in which the temperature of the surface layer including the liquid surface is uniform. The glass raw material is entirely charged into the liquid surface 101c 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 charged 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 emits a flame by burning combustion gas mixed with fuel and oxygen. The burner 112 heats the refractory in the upper space 101b with a flame to heat the inner wall 110 high. The glass raw material is heated by the radiant heat of the inner wall 110 that has become high temperature and the gas phase atmosphere that has become high temperature.

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. Through the raw material charging window 101f, the bucket 101d containing the glass raw material shown in FIG. 4 enters and exits the upper space 101b. The bucket 101d moves back and forth and right and left on the liquid surface 101c of the molten glass MG in accordance with instructions from the computer 118. The computer 118 sends an instruction to a bucket operating mechanism (not shown) to operate the bucket 101d through the control unit 116.

FIG. 4 is a plan view for explaining the introduction of the glass raw material in the melting tank 101.
As shown in FIG. 4, the glass raw material is entirely charged with respect to the liquid surface of the molten glass MG stored in the melting tank 101. Thereby, molten glass MG in which the temperature of the surface layer including the liquid surface is made uniform is produced.

The melting tank 101 includes a bucket operation mechanism. In response to an instruction from the computer 118, the bucket operation mechanism moves the bucket 101d to a target area in a state where the glass raw material is stored in the bucket 101d, and flips the bucket 101d upside down. The area where the glass material is charged by the bucket 101d and the time interval for charging are determined in advance so that the glass material does not disappear on the liquid surface 101c of the molten glass MG. Therefore, in the melting tank 101, since it is poured into substantially the entire liquid surface of the molten glass MG, the glass raw material always covers the liquid surface 101c of the molten glass MG.

As described above, one of the reasons for introducing the glass raw material into the melting tank 101 so that the glass raw material always covers the liquid surface 101c is that the heat of the molten glass MG is not radiated to the upper space 101b which is a gas phase through the liquid surface 101c. It is for doing so. Thereby, the temperature of the surface layer including the liquid surface of the molten glass MG is made uniform, the temperature is kept constant, and the temperature distribution in the horizontal direction is flattened. Another reason is to efficiently melt a raw material having a low melting property (high melting temperature) such as SiO ₂ (silica) among the glass raw materials, thereby preventing unmelted raw materials such as SiO ₂ .

A raw material with a high melting temperature such as SiO ₂ is melted at a temperature lower than the melting temperature when it is melted alone when mixed with other components such as a raw material such as B ₂ O ₃ (boron oxide). obtain. In order to make use of such properties of the raw material, the glass raw material is intermittently dispersed and charged so that the glass raw material always exists on the liquid surface 101c of the molten glass MG and covers the liquid surface 101c. _Accordingly, B 2 _{O 3} or the like of the raw material, since the melting together melted hard such as SiO ₂ raw material, it is possible to prevent the remaining melted ingredients such as SiO _2.

On the other hand, when the glass raw material is thrown into only a partial region of the liquid surface of the molten glass, raw material components such as SiO _{2 that} are difficult to melt remain unmelted, and the glass raw material is convected from the pouring position of the glass raw material by convection. It may float as a heterogeneous substrate on a liquid surface that is far away. Depending on the convection state of the molten glass, such a heterogeneous substrate moves to the lower layer of the molten glass and flows out from the outlet of the melting tank, and may flow to the subsequent process. Prone to cause.

In the present embodiment, in the melting tank 101, the glass raw material is entirely charged with respect to the liquid surface of the molten glass MG. Therefore, the temperature in the surface layer including the liquid level of the molten glass MG is made uniform. It is also possible to prevent the remaining melted raw material components such as SiO _2.

The

inner walls

110a and 110b of the liquid tank 101a that extend in the longitudinal direction of the melting tank 101 and that are made of a heat-resistant conductive material such as tin oxide or molybdenum are provided with three pairs of electrodes 114 that face each other. Is provided. In the present embodiment, the melting tank 101 includes three pairs of electrodes 114, but only a pair of electrodes 114 may be used depending on the size of the melting tank. When a plurality of pairs of electrodes 114 are used, two pairs or four or more pairs of electrodes 114 may be used.

The three pairs of electrodes 114 are provided in regions corresponding to the lower layer of the molten glass MG in the

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 across the molten glass MG disposed between each pair of electrodes 114.

Each pair of electrodes 114 applies a voltage to the molten glass MG disposed between each pair of electrodes 114 to cause a current to flow. 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 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 large 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. For example, by covering the liquid surface 101c of the molten glass MG entirely with the glass raw material, heat radiation from the liquid surface 101c of the molten glass MG is prevented, the temperature drop of the molten glass MG is suppressed, and the lower molten glass MG The glass raw material can be melted by the generated Joule heat.

Each pair of electrodes 114 is connected to a control unit 116, respectively. In order to make the temperature distribution of the molten glass MG in the lower layer uniform, the control unit 116 is configured to be able to control the power supplied to each of the electrodes 114 for each pair of electrodes 114 facing each other. A single-layer 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 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.

The computer 118 calculates the specific resistance ρ (Ω · m) of the molten glass MG between each pair of electrodes 114 based on, for example, the following equation (2).

Ρ = E / I × S / L (2)

In the formula (2), 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 cross-sectional area S and the length L are specific values determined by the melting tank 101.

FIGS. 5A and 5B 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 FIG. 5, each pair of electrodes 114 is disposed on the

inner walls

110 a and 110 b disposed on both sides of the molten glass MG so as to face each other so as to cross the flow direction F of the molten glass MG. The electrode 114 of the three opposed pairs are spaced W ₁ from each other in the flow direction F of the molten glass MG. Here, the interval W ₁ is the distance between the mutually facing edges of adjacent electrodes 114. The flow direction F indicates the flow direction from the upstream to the downstream of the molten glass MG as a whole in the melting tank 101 for convenience, and is a direction parallel to the

inner walls

110a and 110b and toward the outlet 104a. The flow direction F is a direction along the longitudinal direction of the melting tank 101.

First, an area EA through which a current flows is set for each pair of electrodes 114 facing each other. The boundary m of the energization region EA is set so as to pass through the intermediate point C between the two electrodes 114 adjacent in the flow direction F. The middle point C is the center of a heat-resistant brick sandwiched between two adjacent electrodes 114. In other words, the intermediate point C is a point where the distances from the opposite edges of two adjacent electrodes are equal. That is, the boundary m is a plane parallel to the vertical direction passing through the intermediate point C between the two electrodes 114 adjacent on the inner wall 110a and the intermediate point C between the two electrodes 114 adjacent on the inner wall 110b. Due to the boundary m, the molten glass MG is virtually separated into a plurality of quadrangular columnar areas EA corresponding to the pairs of electrodes 114.

That is, the cross-sectional area S of the energized area EA of the molten glass MG is an area of a cross section parallel to the flow direction F and the vertical direction of the area EA, as shown in FIG. Accordingly, the sectional area S is determined by the product of the D (depth of the molten glass MG) height from the bottom surface 110e of the melting vessel 101 to the liquid surface 101c, and the width _{W 2} of the region EA. The specific resistance ρ of the molten glass MG between each pair of electrodes 114 can be obtained by the above equation (2) using the sectional area S thus obtained.

When the specific resistance ρ of the molten glass MG is obtained by the above method, the area S1 of the electrode 114 with respect to the cross-sectional area S of the energization region EA is preferably as large as possible as shown in FIG. The ratio between the cross-sectional area S of the energization region EA and the area S1 of the electrode 114 is not particularly limited. In the present embodiment, S1 / S is, for example, in the range of 1/3 or more and 1/2 or less due to the strength of the melting tank 101 or structural restrictions. As described above, the specific resistance ρ of the molten glass MG can be calculated more accurately by increasing the area S1 of the electrode with respect to the cross-sectional area S of the energization area EA of the molten glass MG.

Based on the specific resistance ρ of the molten glass MG obtained by the above method, the Joule heat generated in the molten glass MG in each region EA corresponding to each pair of electrodes 114 can be controlled.
FIG. 6 is a diagram for explaining an example of a process for controlling 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. 6, 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 FIG. 5 and the flow to the molten glass MG in each region EA. Information on the current value I is sent from the control unit 116 to the computer 118. The computer 118 stores the voltage E and current I information of each area EA sent from the control unit 116. The computer 118 stores in advance the cross-sectional area S, the distance L between the electrodes 114, and the target value 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. 6 (ST12), the computer 118, based on the stored information on the voltage E, current I, cross-sectional area S and distance L of each area EA, and the above equation (2), The specific resistance ρ of the molten glass MG in each area EA is calculated.

In addition, the specific resistance ρ of each area EA 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. be able to. 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 is 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 to obtain a target value of specific resistance ρ. .

In the comparison of the specific resistance shown in FIG. 6 (ST13), the computer 118 compares the target value of the specific resistance ρ in each area EA with the calculated specific resistance ρ in each area EA.
In the determination of the control amount shown in FIG. 6 (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, when the calculated specific resistance ρ is larger than the target value or larger than the allowable range, the computer 118 generates Joule heat generated in the molten glass MG in the area EA, Give instructions to decrease by a predetermined amount.
In a certain area EA, 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, when the calculated specific resistance ρ is smaller than the target value or smaller than the allowable range, the computer 118 increases the Joule heat generated in the molten glass MG in the area EA by a predetermined amount. Give instructions.

In the control of Joule heat shown in FIG. 6 (ST15), the control unit 116 controls the Joule heat generated in the molten glass MG in each area EA 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, the control unit 116 flows into the molten glass MG between the pair of electrodes 114 corresponding to the area EA. The target current value is set so that the current value becomes a constant value smaller than the original value by a predetermined value.
When the control unit 116 receives an instruction to maintain the Joule heat generated in the molten glass MG in a certain area EA, the control unit 116 determines the value or source of the current flowing in the molten glass MG between the pair of electrodes 114 corresponding to the area EA. 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, the value of the current flowing in the molten glass MG between the pair of electrodes 114 corresponding to the area EA is: The target current value is set so as to be a constant value larger by a predetermined value than the original 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 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 are maintained. The state can be maintained in a desired state.

Next, as one method for controlling the Joule heat generated in the molten glass MG in each area EA based on the calculated specific resistance ρ, the molten glass in each area EA is further calculated from the calculated specific resistance ρ in each area EA. A method of calculating the MG temperature will be described.
FIG. 7 is a diagram for explaining a process of determining the temperature of the molten glass MG from the calculated specific resistance ρ and controlling the Joule heat generated in the molten glass in each region EA.

In this method, first, as a preliminary step (ST21), the relationship between the temperature and the specific resistance of the molten glass having the same composition 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, F (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 (1).

T (° C.) = A / (log (ρ) + b) -273.15 (1)

In the formula (1), 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 (1). In the preliminary step (ST21), the target temperature of the molten glass MG in each area EA is set in advance, and the value is stored in the computer 118.

The sampling (ST21) and specific resistance calculation (ST23) shown in FIG. 7 are the same as the sampling (ST11) and specific resistance calculation (ST12) shown in FIG.
In the temperature calculation (ST24) shown in FIG. 7, the computer 118 calculates each resistance ρ of each area EA, constants a and b stored in advance, and the above equation (1). The temperature T of the molten glass MG in the area EA is calculated.

In addition, the temperature T of each area EA 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 a target value of the temperature T. it can. At the stage of setting the target value 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 prior art, and in this state, the temperature T is set by the computer 118 as described above. It may be calculated.

In the temperature comparison shown in FIG. 7 (ST25), the computer 118 compares the stored target value of the temperature T of each area EA with the calculated temperature T of each area EA.
In the control amount determination (ST26) shown in FIG. 7, 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, when the calculated temperature T is higher than the target value or higher than the allowable range, the computer 118 generates Joule heat generated in the molten glass MG in the area EA by a predetermined value. Give instructions to reduce the amount of.
In a certain area EA, 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.
In a certain area, when the calculated temperature T is lower than the target value or lower than the allowable range, the computer 118 instructs to increase the Joule heat generated in the molten glass MG in the area EA by a predetermined amount. Put out.

The Joule heat control (ST27) shown in FIG. 7 is the same as the Joule heat control (ST15) shown in FIG.
By the above control, the viscosity and temperature of the molten glass MG in each region EA are set to a desired state without using a conventional temperature measuring device such as a thermocouple, and the molten state of the molten glass MG in the melting tank 101 is set to a desired state. Can be.

Generally, the molten glass MG in the vicinity of the

inner walls

110c and 110d facing each other in the flow direction F is likely to become low temperature due to heat radiation from the

inner walls

110c and 110d to the outside. For this reason, in this embodiment, the calorie | heat amount generated in the molten glass MG in the both ends of the flow direction F of the melting tank 101 is made larger than the calorie | heat amount generated in the molten glass MG in a center part. Thereby, the temperature difference of the molten glass MG in the lower layer is made as small as possible to make the temperature of the molten glass MG uniform, and the temperature distribution of the lower layer of the molten glass MG is flattened.

FIG. 8 is a diagram for explaining the convection of the molten glass inside the melting tank 101 in the present embodiment. In the present embodiment, the glass raw material is entirely introduced into the liquid surface of the molten glass MG stored in the melting tank 101, thereby producing a molten glass MG having a uniform surface temperature including the liquid surface 101c. .

When this molten glass MG is flowed from the outlet 104a toward the subsequent step, convection due to the temperature distribution along the longitudinal direction (first direction) of the melting tank 104a in FIG. 3 occurs in the lower molten glass MG. Do not. That is, the lower molten glass MG is heated so that the temperature along the first direction of the lower molten glass MG becomes uniform. Specifically, the amount of heat for heating the molten glass MG at both ends of the melting tank 101 in the first direction is greater than the amount of heat for heating the molten glass MG at the center of the melting tank 101 in the first direction. Adjust as much as possible.

The reason why the heating amount of the molten glass MG at both ends in the longitudinal direction of the melting tank 101 is made larger than that in the central portion is that heat is easily released from the

inner walls

110c and 110d facing each other in the longitudinal direction. If such a heating amount is not adjusted, the temperature of the molten glass MG at the both end portions tends to be lower than that at the central portion. For this reason, the electric power supplied to the three pairs of electrodes 114 is greater for the electrodes 114 closer to both ends in the longitudinal direction of the melting tank 101 than for the electrodes 114 in the longitudinal center of the melting tank 101. It is preferable to set. This is the same when four or more pairs of electrodes 114 are provided in the melting tank.

As described above, in this embodiment, the Joule heat generated in the molten glass MG in each region EA is controlled based on the calculated specific resistance ρ of the molten glass MG in each region EA. Therefore, even if the amount of heat released to the outside in each area EA is different, Joule heat generated in the molten glass MG in each area EA so as to maintain the target value of specific resistance ρ or the target value of temperature T. The amount of is adjusted.

Thereby, the molten glass MG is pulled by the outflow from the outlet 104a of the molten glass MG without causing convection due to the temperature distribution of the molten glass MG in the lower layer. As shown by the arrows in FIG. 8, the molten glass MG flows toward the outlet 104 a along the bottom surface of the melting tank 101 in a portion close to the bottom surface of the lower melting tank 101. As the distance from the bottom surface of the melting tank 101 increases, the influence of the flow along the bottom surface of the melting tank 101 decreases, and the molten glass MG flows so as to sink from the surface layer toward the bottom surface of the melting tank 101.

Thus, in this embodiment, since convection due to the temperature distribution of the molten glass MG does not occur in the lower layer, it is possible to suppress unevenness in the glass composition due to the heterogeneous substrate. On the other hand, when the temperature distribution of the molten glass MG is not uniform in the lower layer, a temperature difference distribution is generated between the lower layer and the surface layer where the temperature is uniformed, so that conventional hot spring convection can be easily performed. .

FIG. 9 is a view for explaining convection of molten glass inside a conventional melting tank. As shown in FIG. 9, in the conventional melting tank, in the region A, the molten glass is partially heated so that a pot spring is formed, and convection is promoted. For this reason, among the glass raw materials introduced into a part of the liquid surface of the molten glass, raw material components such as SiO _{2 that} are not easily melted move by convection, and for example, the silica-rich heterogeneous substrate 120 is separated from the glass raw material introduction position. It is easy to collect in. In addition, the opportunity for this heterogeneous substrate 120 to flow out of the outlet along the convection increases, which tends to cause unevenness in the glass composition such as striae.

In the manufacturing method of the glass substrate of the present embodiment, the temperature at 10 ^2.5 poise of molten glass having high viscosity, for example, molten glass is 1300 ° C. or higher (for example, 1300 ° C. or higher and 1650 ° C. or lower), more preferably 1500 ° C. It can be applied even to molten glass that is above (for example, 1500 ° C. or more and 1650 ° C. or less), and has an advantage that unevenness of glass composition such as striae can be suppressed as compared with the conventional manufacturing method. Is big.

The glass substrate manufacturing method of the present embodiment does not require an excessive voltage to emphasize the hot spring even in a molten glass having a large specific resistance of 1500 Ω · cm or more at 1500 ° C. It is possible to prevent current from flowing through the object. For this reason, it is possible to suppress unevenness of the glass composition while preventing ZrO ₂ (zirconia), which is likely to cause devitrification of the glass, from being eluted from the inner wall of the melting tank 101 in contact with the molten glass MG. About such a molten glass with a large specific resistance, you may use the heating by a burner in the melting tank 101 together.

In this embodiment, since each pair of electrodes 114 are opposed to each other, the temperature in the lower layer along the first direction of the molten glass MG can be effectively equalized.
In the present embodiment, the electric power supplied to each pair of electrodes 114 is such that both ends are larger than the central portion in the longitudinal direction of the melting tank 101 in consideration of the release of heat from the melting tank 101. Since it is supplied, it is easy to make the temperature distribution in the flow direction F of the molten glass MG in the lower layer uniform.

In this embodiment, the temperature in the lower layer of the molten glass MG is made uniform so as not to draw convection due to the temperature distribution of the molten glass. Therefore, in order to promote the convection due to the temperature distribution of the molten glass as in the past, it is not necessary to partially heat the molten glass to an excessively high temperature at the expense of elution of the refractory constituting the melting tank 101. . Thus, easy ZrO ₂ cause devitrification of the glass is hardly eluted from the inner wall in contact with the molten glass MG of melting tank 101. Therefore, the manufacturing method of this embodiment is suitable for a case where the inner wall of the melting vessel 101 is constituted by a refractory material comprising ZrO ₂ having excellent corrosion resistance to components.

Hereinafter, the effect of the present embodiment will be described from the viewpoint of the glass composition.
The composition of the glass substrate produced in the present embodiment is composed of aluminosilicate glass, and can contain 50% by mass or more of SiO ₂ (silica). By applying the manufacturing method of this embodiment to an aluminosilicate glass having this composition, unevenness of the glass composition can be effectively suppressed as compared with the conventional case. The composition of the glass substrate manufactured in this embodiment, the SiO ₂ can comprise more than 55 wt%, can further comprise SiO ₂ 60% by mass or more.

By applying the manufacturing method of this embodiment to the aluminosilicate glass which has these compositions, glass composition nonuniformity can be suppressed more effectively compared with the past. Even if the glass composition contains 50% by mass or more of SiO ₂ and easily forms a silica-rich heterogeneous substrate, the molten glass MG is melted so that convection due to the temperature distribution does not occur. Outflow from the outlet 104a can be prevented.

Further, since the glass raw material is always added to the liquid surface 101c so as to have a certain thickness, SiO ₂ is prevented from remaining melted, and the heterogeneous substrate 120 due to SiO ₂ as shown in FIG.

When a glass composition containing 50% by mass or more of SiO ₂ and having a high viscosity of the molten glass MG is used for the glass substrate and convection of the molten glass is promoted as in the prior art, ZrO ₂ (zirconia) contained in the refractory constituting the melting tank ) May elute into the molten glass and cause devitrification of the glass.

However, since this embodiment makes the temperature distribution of the molten glass MG in the lower layer uniform so as not to cause convection due to the temperature distribution of the molten glass MG, it is necessary to heat the molten glass to an excessively high temperature as in the prior art. There is no. For this reason, elution of ZrO ₂ (zirconia) from the refractory in the melting tank 101 can be prevented. 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 aluminosilicate glass having a total of 60% by mass of SiO ₂ and Al ₂ O ₃ and having this glass composition is applied can be compared with the conventional glass composition. Can be suppressed. Furthermore, SiO ₂ and Al ₂ O ₃ can be contained in a total of 65% by mass or more, and SiO ₂ and Al ₂ O ₃ can be contained in a total of 70% by mass or more.

Even if the glass composition contains SiO ₂ and Al ₂ O ₃ in a total of 60% by mass or more and easily forms a silica-rich heterogeneous substrate 120, the molten glass MG is melted so that convection due to the temperature distribution does not occur. Therefore, the silica-rich heterogeneous substrate can be prevented from flowing out from the outlet 104a.

When a glass composition containing 60 mass% or more of SiO ₂ and Al ₂ O ₃ in total and having a high viscosity of the molten glass MG is used for the glass substrate, and convection of the molten glass is promoted as in the conventional case, the refractory constituting the melting tank ZrO ₂ (zirconia) contained in the product may elute into the molten glass and cause devitrification of the glass.

However, in the present embodiment, the temperature distribution of the molten glass MG in the lower layer is made uniform so as not to cause convection due to the temperature distribution of the molten glass MG. There is no need to heat. For this reason, elution of ZrO ₂ (zirconia) from the refractory in the melting tank 101 can be prevented. In the glass composition, the upper limit of the total content of SiO ₂ and Al ₂ O ₃ is, for example, 95% by mass.

The glass substrate is preferably composed of aluminoborosilicate glass. B ₂ O ₃ (boron oxide) were melted at a low temperature as compared with SiO _2, moreover, to lower the melting temperature of the SiO _2. Therefore, in a glass composition having a high SiO ₂ content, it is effective to contain B ₂ O ₃ because it is difficult to produce the heterogeneous substrate 120 (see FIG. 9).

As the glass composition of the glass substrate, for example, the following can be applied. The content rate display of the composition shown below is mass%.
SiO ₂ : 50 to 70%,
B ₂ O ₃ : 5 to 18%,
Al ₂ O ₃ : 0 to 25%,
MgO: 0 to 10%,
CaO: 0-20%,
SrO: 0 to 20%,
BaO: 0 to 10%,
RO: 5 to 20% (where 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.

Moreover, the following compositions are applicable as a composition of a glass substrate.
SiO ₂ : 50 to 70%,
B ₂ O ₃ : 1-10%,
Al ₂ O ₃ : 0 to 25%,
MgO: 0 to 10%,
CaO: 0-20%,
SrO: 0 to 20%,
BaO: 0 to 10%,
RO: 5-30% (where R is the total amount of Mg, Ca, Sr and Ba),
Similarly, it is also preferable that the glass be an alkali-free glass.

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. In order to facilitate melting of the glass, the content of iron oxide in the glass is more preferably 0.01 to 0.2% from the viewpoint of reducing the specific resistance. _Further, it is preferred not to include _{_{_{As 2 O 3, Sb 2 O}}} 3 and PbO substantially.

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 suppresses the thermal expansion of the glass substrate and does not deteriorate the characteristics of the TFT (Thin Film Transistor) formed on the glass substrate. (Li, Na, and K) are not included, or even if included, a trace amount is preferable.
However, when alkali metal components (Li, Na and K) are not contained or are contained in a very small amount, the high temperature viscosity of the molten glass MG is increased. Need to be partially heated to high temperatures.

On the other hand, in the present embodiment, the glass raw material is charged over substantially the entire liquid surface 101c of the molten glass MG, and the temperature of the molten glass MG is adjusted so that convection of the molten glass MG does not occur. Therefore, unlike the prior art, it is not necessary to partially heat the molten glass MG to a high temperature in order to create a temperature distribution of the molten glass. Therefore, the manufacturing method of this embodiment can be suitably applied to a glass substrate for a liquid crystal display device in that the temperature of the molten glass is not partially excessively increased as in the prior art.

In addition to this, it is preferable that the glass raw material contains SnO ₂ (tin oxide) in an amount of 0.01 to 0.5% by mass as a fining agent from the viewpoint of reducing the environmental load and exhibiting an efficient fining effect. . In this embodiment, SnO ₂ is used as a clarifier from the viewpoint of reducing the environmental load. However, in order to effectively function the clarification action of SnO ₂ , it is preferable that the melting temperature is not set too high.

In the present embodiment, the temperature of the molten glass MG does not need to be partially heated excessively in order to emphasize the hot spring as in the conventional known manufacturing method. Therefore, elution of ZrO ₂ (zirconia) from the refractory in the melting tank 101 can be prevented, and the clarification action of SnO ₂ can be effectively functioned.

Moreover, in this embodiment, in order to equalize the temperature in the lower layer of the molten glass MG more effectively in the melting tank 101, a heat retaining member is provided around the portion where the electrode 114 is provided on the outer side wall of the melting tank 101. Is preferably provided. As the heat insulating material, for example, a plate member in which a heat insulating material such as glass wool or ceramic fiber is hardened in a plate shape is used. Thereby, the heat radiation from the outer side wall of the melting tank 101 can be prevented, the temperature of the molten glass MG can be made more uniform in the melting tank 101, and the convection of the molten glass MG can be further reduced.

The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit of the present invention. The present invention is not limited by the above description, but only by the scope of the appended claims.

Moreover, the said embodiment contains the following content.
(1) It is a manufacturing method of a glass substrate, Comprising: The melting process of melting a glass raw material with a melting tank is included. In the melting step, a glass raw material is introduced into substantially the entire liquid surface of the molten glass stored in the melting tank, thereby producing a molten glass having a uniform surface layer temperature including the liquid surface. Of the inner side wall of the melting tank, the molten glass is caused to flow from the outlet provided at the bottom of the inner side wall facing the first direction toward the subsequent step. When flowing the molten glass, the temperature of the lower layer of the molten glass located below the surface layer in the depth direction of the molten glass is set such that the convection due to the temperature distribution of the molten glass does not occur in the lower layer. While making the temperature distribution along the first direction of the lower molten glass uniform by adjusting at least the amount of heat given to the molten glass located at both ends in the first direction of the melting tank, the melting Glass is allowed to flow from the outlet to the subsequent step.
(2) In the manufacturing method of the glass substrate of (1), in order to make the temperature distribution in the lower layer uniform, the inner side wall parallel to the first direction of the melting tank corresponds to the lower layer. A plurality of pairs of electrodes are provided in the depth direction portion to flow an electric current in a direction parallel to the liquid surface to energize and heat the molten glass located in the lower layer. Each pair of the plurality of pairs of electrodes faces each other in a direction orthogonal to the first direction.
(3) In the method for manufacturing a glass substrate according to (2), the power supplied to the plurality of pairs of electrodes is larger than that of an electrode located at a central portion in the first direction of the melting tank in the first direction. The electrodes located on both sides of the melting tank in the first direction are higher.
(4) In the method for manufacturing a glass substrate according to any one of (1) to (3), an inner side wall of the melting tank that is in contact with the molten glass is made of a refractory containing zirconia as a component.
(5) In the method for producing a glass substrate according to any one of (1) to (3), the temperature of the molten glass at 10 ^2.5 poise is 1300 ° C. or higher.
(6) In the method for manufacturing a glass substrate according to any one of (1) to (3), the glass substrate to be manufactured is made of aluminosilicate glass and contains 50% by mass or more of SiO ₂ .
(7) In the method for manufacturing a glass substrate according to (6), the glass substrate to be manufactured is made of aluminosilicate glass, and includes 60% by mass or more of SiO ₂ and Al ₂ O ₃ in total.
(8) In the method for manufacturing a glass substrate according to any one of (1) to (7), the glass substrate to be manufactured is made of alkali-free glass or glass containing a trace amount of alkali.
(9) In the method for producing a glass substrate according to any one of (1) to (8), the molten glass has a specific resistance at 1500 ° C. of 180 Ω · cm or more.
(10) In the method for producing a glass substrate according to any one of (1) to (9), tin oxide is added as a fining agent to the glass raw material.
(11) In the method for manufacturing a glass substrate according to (2), a heat retaining member is provided on the outer side wall of the melting tank around a portion where the plurality of pairs of electrodes are provided.

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

Including a melting step of melting glass raw material to produce molten glass,
The melting step
Placing the molten glass between a pair of electrodes, applying a voltage, and passing a current through the molten glass to generate Joule heat;
Calculating the specific resistance of the molten glass by measuring the value of the current and the value of the voltage;
And a step of controlling the Joule heat based on the calculated specific resistance.
In the melting step, using a plurality of pairs of the pair of electrodes, setting a region where the current flows for each pair of electrodes,
In the step of calculating the specific resistance, the specific resistance is calculated for each region,
In the step of controlling the Joule heat, the Joule heat is controlled for each region.
The manufacturing method of the glass substrate of Claim 1.
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
Setting a target temperature of the molten glass;
Calculating the temperature of the molten glass based on the correlation and the calculated resistivity;
The method for manufacturing a glass substrate according to claim 1, further comprising: controlling Joule heat generated in the molten glass based on a result of comparing the calculated temperature and the target temperature.
In the melting step, using a plurality of pairs of the pair of electrodes, setting a region where the current flows for each pair of electrodes,
In the step of calculating the specific resistance, the specific resistance is calculated for each region,
In the step of calculating the temperature, the temperature is calculated for each region,
In the step of controlling the Joule heat, the Joule heat is controlled for each region.
The manufacturing method of the glass substrate of Claim 3.
The step of controlling the Joule heat includes
Obtaining the current value for generating Joule heat in the molten glass so as to maintain the calculated temperature at the target temperature, and setting the current value to the target current value; and maintaining the current value at the target current value The method for manufacturing the glass substrate according to claim 3, further comprising: controlling the voltage.
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 (1)
Find the constants a and b in
In the step of calculating the temperature,
The temperature T is calculated by substituting the specific resistance ρ into the equation (1).
The manufacturing method of the glass substrate as described in any one of Claim 3 to 5.
The pair of electrodes are arranged on both sides of the molten glass so as to face each other so as to cross the flow direction from the upstream to the downstream of the molten glass,
The plurality of pairs of electrodes are spaced apart from each other in the flow direction;
The boundary of the region is set to pass through the midpoint of the electrodes adjacent in the flow direction;
The manufacturing method of the glass substrate of Claim 2 or 4.
In the step of calculating the specific resistance,
The current value is I, the voltage is E, the sectional area of the molten glass through which the current flows is S, the distance L between the pair of electrodes, the specific resistance is ρ, and these relations are expressed. Formula: ρ = E / I × S / L (2)
The specific resistance ρ is calculated based on
The manufacturing method of the glass substrate in any one of Claim 1 to 7.
In the melting step,
The raw material is dispersed and introduced so as to cover the liquid surface of the molten glass,
The manufacturing method of the glass substrate in any one of Claim 1 to 8.
The electrode is a tin oxide electrode;
The manufacturing method of the glass substrate in any one of Claim 1 to 9.
After the melting process,
Clarifying the molten glass;
Forming the molten glass into a glass substrate;
Have
The step of clarifying the molten glass is performed inside a container made of platinum or a platinum alloy.
The manufacturing method of the glass substrate in any one of Claim 1 to 10.
The glass substrate is a glass substrate for a flat panel display,
The manufacturing method of the glass substrate in any one of Claims 1-11.