JP2018002541A - Method of manufacturing glass plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly adjust a temperature of molten glass flowing in a metal pipe when the molten glass flows from a melting tank to the metal pipe.SOLUTION: When a glass sheet is manufactured, molten glass is generated by melting a glass raw material in a melting tank, a temperature of the generated molten glass is measured by a thermocouple, the temperature of the molten glass is adjusted on the basis of the obtained measurement result, the molten glass is made to flow into a metal pipe, and the molten glass having flowed out of the metal pipe is formed into sheet glass. When the temperature adjustment is performed, a change due to a drift of thermoelectromotive force of the thermocouple is removed from the measurement result of the thermocouple, and thus, time variation in the temperature of the molten glass flowing out of the melting tank is extracted, and according to the extraction result of the time variation, a heating quantity to be applied to the molten glass is determined, and the temperature of the molten glass is adjusted.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for producing a glass plate that adjusts the temperature of molten glass when molten glass produced by melting a glass raw material in a melting tank is poured into a metal tube.

In general, a glass plate is produced through a step of forming molten glass from a glass raw material in a melting tank and then flowing it into a forming apparatus using a metal tube, and forming the molten glass into sheet glass with a forming apparatus. The metal tube includes a tubular clarification tube and a stirring tank in addition to a glass supply tube for transferring molten glass.
For example, the molten glass is supplied to the clarification tube by heating the molten glass flowing through the glass supply tube to a target temperature. In the clarification tube, the molten glass is clarified by utilizing a reduction reaction by a clarifier contained in the molten glass. The degree of the reduction reaction by the fining agent depends on the temperature of the molten glass. Therefore, in order to clarify the molten glass efficiently in the clarification tube, the temperature of the molten glass is targeted until the molten glass flows into the clarification tube. The temperature is extremely important for improving the bubble quality of the glass plate.

  For example, when flowing molten glass from a melting process using a glass supply pipe, which is a metal tube, the temperature of the molten glass is increased to 1630 ° C. or higher at a temperature increase rate of 2 ° C./min or higher. There is known a method for producing a glass plate which is supplied to a clarification tank (clarification pipe) and defoamed molten glass in the clarification tank (clarification pipe) (Patent Document 1). Thereby, bubbles remaining on the glass plate can be efficiently reduced.

International Publication 2013/054531

  However, in the glass manufacturing method described above, when the temperature of the molten glass flowing into the glass supply pipe from the melting tank fluctuates with time, a mechanism for adjusting the temperature of the molten glass by feedback control of heating for heating the molten glass Is not used. This is because the sensor that measures the temperature of the molten glass cannot measure with high accuracy. In general, in order to measure a high temperature, a thermocouple having a configuration in which the tips of two types of metal wires are in contact with each other is used. When applied to the measurement, the metal wire partially oxidizes and volatilizes, so that the thermoelectromotive force generated at the junction of the metal wire drifts with time, and an accurate temperature cannot be measured.

  On the other hand, in the melting tank, the molten glass circulates from the lower layer to the upper layer and circulates from the upper layer to the lower layer so as to spiral, but the convection of the molten glass is fluctuating. For this reason, the temperature of the molten glass when the molten glass flows into the glass supply pipe, which is a metal tube, from the outlet of the melting tank may fluctuate over time due to fluctuations in convection. In such a case, even if the amount of heat given to the molten glass in the melting tank is made constant accurately, and further, the amount of heat given to the molten glass through heating of the glass supply tube is made constant accurately, the temperature of the molten glass flowing through the glass supply tube is The temperature of the molten glass flowing into the clarification tank also changes. For this reason, there may be an adverse effect that the bubble quality, which determines the quality of the clarification, varies depending on the temperature of the molten glass in the clarification tank.

  Then, an object of this invention is to provide the manufacturing method of the glass plate which can adjust appropriately the temperature of the molten glass which flows through the inside of a metal pipe, when molten glass flows into a metal pipe from a melting tank.

One embodiment of the present invention is a method for manufacturing a glass plate.
The method for producing the glass plate is as follows:
A melting step of melting glass raw material in a melting tank to produce molten glass;
When flowing the generated molten glass into a metal tube, the temperature of the molten glass is measured by a thermocouple, and the temperature adjusting step of adjusting the temperature of the molten glass based on the obtained measurement result;
Forming the molten glass that has flowed out of the metal tube into a sheet glass,
In the temperature adjustment step, by removing the change due to the thermoelectromotive force drift of the thermocouple from the measurement result of the thermocouple, the time variation of the temperature of the molten glass flowing out of the melting tank is extracted, and the time According to the extraction result of fluctuation, the heating amount to be given to the molten glass is determined to adjust the temperature of the molten glass.

  In that case, it is preferable that the time fluctuation | variation of the temperature of the said molten glass is a temperature fluctuation | variation produced by the fluctuation | variation of the convection of the said molten glass in the said melting tank.

Before forming the molten glass into the sheet glass, it has a clarification step of clarifying the molten glass,
It is preferable that the temperature measurement of the molten glass by the thermocouple is performed before the refining step.

The metal pipe includes a clarification pipe that performs clarification of the melting tank and the molten glass, and a glass supply pipe that connects the clarification pipe and the melting tank,
It is preferable that the temperature measurement of the molten glass by the thermocouple is performed at a portion of the melting tank side with respect to the longitudinal center of the glass supply pipe.

  The thermocouple is provided outside the glass supply tube, and the temperature of the molten glass is adjusted by measuring the temperature of the outer surface of the glass supply tube, and the thermocouple is the length of the glass supply tube. It is preferable to be provided at a connection portion of the glass supply pipe connected to the melting tank in the direction.

  The temperature of the molten glass flowing through the metal tube may be 1620 ° C. or higher.

  In the manufacturing method of the above-mentioned glass plate, when molten glass flows into a metal tube from a melting tank, the temperature of the molten glass which flows through the inside of a metal tube can be adjusted appropriately.

It is a figure which shows an example of the process of the manufacturing method of the glass plate of this embodiment. It is a figure which shows typically an example of the glass plate manufacturing apparatus which performs the melting process-cutting process in this embodiment. It is a figure explaining the temperature adjustment of the molten glass using the thermocouple of this embodiment. It is a figure which shows an example of the time change of the estimated temperature of the molten glass calculated based on the electromotive force of the thermocouple of this embodiment, and an example of the time fluctuation of the temperature of a molten glass.

Hereinafter, the manufacturing method of the glass plate of this embodiment is demonstrated.
As used herein, “temporal fluctuation of the temperature of the molten glass” refers to temporal fluctuation of the actual temperature of the molten glass that does not include a change due to drift of the measured temperature caused by a measurement sensor such as a thermocouple. In addition, “drift of thermoelectromotive force of thermocouple” refers to the heat generated at the junction of metal wires when the thermocouple is exposed to high temperature and the metal wires constituting the thermocouple are partially oxidized and volatilized. The electromotive force drifts with time.
Drawing 1 is a figure showing an example of a process of a manufacturing method of a glass plate of this embodiment.
The glass plate manufacturing method includes a melting step (ST1), a refining step (ST2), a homogenizing step (ST3), a supplying step (ST4), a forming step (ST5), and a slow cooling step (ST6). And a cutting step (ST7). In addition, a plurality of glass plates 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 conveyed to a supplier.

The melting step (ST1) is performed in a melting tank. In the melting tank, a glass raw material is poured into the liquid surface of the molten glass stored in the melting tank and heated to make molten glass. Furthermore, molten glass is poured from the outlet provided in the vicinity of one bottom portion of the inner side wall of the melting tank toward the downstream process.
Heating of the molten glass in the melting tank is performed by supplying electricity to the molten glass itself, generating heat, and heating the glass, and supplementing a flame with a burner to melt the glass raw material. Specifically, the charged glass raw material is heated by thermal radiation heat transfer from the wall surface of the gas phase space of the melting tank or the flame of the burner, and is pyrolyzed and melted. The molten glass produced in this way is heated to a higher temperature. A clarifier 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. In the melting tank, the glass raw material is completely melted so as not to cause striae, and a molten glass having a predetermined viscosity is produced by energization heating so that the subsequent process is appropriately performed.

The clarification step (ST2) is performed at least in the clarification tank. In the clarification process, when the molten glass in the clarification tank is heated, the bubbles containing O ₂ , CO ₂ or SO ₂ contained in the molten glass absorb oxygen generated by the reductive reaction of the clarifier. The bubbles rise to the surface of the molten glass and are released. Furthermore, in the clarification step, the reducing substance obtained by the reduction reaction of the clarifier undergoes an oxidation reaction by lowering the temperature of the molten glass. 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 the clarification step, a clarification method using tin oxide as a clarifier can be used.

In the homogenization step (ST3), the glass components are homogenized by stirring the molten glass in the stirring tank supplied through the glass supply 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.
In the supply step (ST4), the molten glass is supplied to the molding apparatus through a glass supply 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 band-shaped sheet glass to make a flow of the sheet glass. For molding, an overflow downdraw method is used.
In the slow cooling step (ST6), the molded sheet glass has a desired thickness, and is cooled so that internal distortion does not occur and warpage does not occur.
In a cutting process (ST7), in a cutting device, the sheet-like sheet glass supplied from the shaping | molding apparatus is cut | disconnected to predetermined length, and one glass plate is obtained. The cut glass plate is further cut into a predetermined size to produce a target size glass plate. After this, the end face of the glass plate is ground and polished, the glass plate 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 illustrating an example of a glass plate manufacturing 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 shown in FIG. 2, the glass raw material is charged using a bucket 101d, and the molten glass MG is heated so that the molten glass MG obtained by melting the glass raw material has a predetermined viscosity. 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. In the present embodiment, the bucket 101d is used as a glass raw material charging unit, but is not limited thereto. For example, a screw feeder can be used.

The glass supply pipe 104, the clarification tank 102, the glass supply pipe 105, the stirring tank 103, and the glass supply pipe 106 are preferably metal pipes made of a metal composed of a platinum group element or a platinum group element alloy. Platinum group elements include platinum, iridium, osmium, palladium, rhodium, and ruthenium. When the glass supply pipe 104, the glass supply pipe 105, the glass supply pipe 106, the clarification tank 102, and the stirring tank 103 are described together without distinction, they are hereinafter referred to as metal pipes.
In addition to transferring the molten glass MG, the metal tube has a function of adjusting the temperature of the molten glass MG when the molten glass MG is transferred. For example, the glass supply pipe 104 is provided with a pair of flange-shaped electrode plates for heating the molten glass MG in order to make the temperature of the molten glass MG flowing out of the melting tank 101 suitable for clarification. . The glass supply tube 104 can heat the molten glass MG with Joule heat generated by energizing the glass supply tube 104 which is a metal tube through the electrode plate.
Further, in the clarification tank 102, the glass supply pipe 105, the stirring tank 103, and the glass supply pipe 106, an electrode plate is provided on the metal pipe, and the temperature of the molten glass MG is adjusted by Joule heat generated by energizing the metal pipe. can do.
In particular, in the glass supply pipe 104, in order to efficiently perform defoaming in the clarification tank 102, the molten glass MG is preferably heated at a temperature increase rate of 2 ° C./min or more at 1620 ° C. by heating the main body of the glass supply pipe 104. It is heated until it reaches the above temperature, and the viscosity of the molten glass at that time is preferably 500 to 2000 dPa · s. The molten glass MG is heated to 1620 ° C. or higher, more preferably 1630 ° C. or higher, whereby the reductive reaction of the fining agent is promoted, so that a large amount of oxygen is released to the molten glass MG. Thereby, defoaming can be performed efficiently in the clarification tank 102.

The molten glass MG that has flowed out of the melting tank 101 flows through a metal tube composed of the glass supply pipe 104, the clarification tank 102, the glass supply pipe 105, the stirring tank 103, and the glass supply pipe 106, and at this time, flows in the metal pipe. The temperature of the molten glass MG can be estimated from the temperature of the metal tube by using a calculation result using a numerical simulation if information on the temperature of the metal tube is obtained. The temperature of the molten glass estimated from the temperature of the metal tube is called the estimated temperature.
However, since the temperature of the metal tube becomes one thousand and several hundred degrees Celsius, even if the temperature of the metal tube is measured using a thermocouple provided so as to be in contact with the outer surface of the metal tube, an accurate temperature cannot be obtained. . As described above, this is because the thermoelectromotive force generated at the junction of the metal wires drifts with time due to partial oxidation and volatilization of the metal wires constituting the thermocouple.

In the present embodiment, the temperature fluctuation of the molten glass MG is extracted instead of estimating the temperature of the molten glass MG itself from the measurement result of the temperature of the metal tube. That is, in this embodiment, the change due to drift of the thermoelectromotive force of the thermocouple is removed from the time waveform of the estimated temperature of the molten glass estimated from the measurement result by the thermocouple, and the time variation of the temperature of the molten glass MG is extracted. To do.

FIG. 3 is a view for explaining temperature adjustment of the molten glass MG using the thermocouple of the present embodiment. In the example shown in FIG. 3, the glass supply tube 104 is targeted. A refractory fiber layer 108 in which an elongated fiber refractory sheet is spirally wound is provided on the outer surface of the glass supply pipe 104, and a refractory using alumina cement or the like on the outer periphery of the refractory fiber layer 108. A protective layer 110 is provided, and a refractory brick 112 is provided on the outer periphery of the refractory protective layer 110.
A pair of flange-shaped electrode plates 114 are provided at two locations in the longitudinal direction of the glass supply tube 104. The electrode plates 114 are each electrically connected to the heating power source 120. Since the temperature of the molten glass MG when the molten glass MG flows out of the melting tank 101 and the temperature of the molten glass MG when flowing into the clarification tube 102 are determined in advance at the glass plate production planning stage, the molten glass MG The basic heating amount that the heating power source 120 gives to the molten glass MG when the gas flows through the glass supply pipe 104 is also determined in advance. For this reason, the basic current that the heating power source 120 passes through the electrode plate 114 is fixed to a predetermined constant value.
However, the temperature of the molten glass MG flowing through the glass supply pipe 104 may vary over time. For this reason, in this embodiment, based on the measurement result (time fluctuation of the estimated temperature of the molten glass MG), which will be described later, the heating amount that the glass supply tube 120 should add to the predetermined reference heating amount is determined. The heating power source 120 is determined so that the additional current to be added to the reference current is determined according to the heating amount to be added, and the total current of the reference current and the additional current is passed through the electrode plate 114 and, consequently, the glass supply tube 104. It is configured.

A thermocouple 116 is provided on the outer surface of the glass supply pipe 104 upstream of the pair of electrode plates 114 of the glass supply pipe 104 (the side opposite to the direction in which the molten glass MG flows, the side of the melting tank 101). ing. The electromotive force of the thermocouple 116 is measured by the measurement unit 118. The temperature at the position of the thermocouple 116, that is, the temperature of the outer surface of the glass supply tube 104 can be measured by the magnitude of the electromotive force. Since the temperature of the outer surface of the glass supply tube 104 fluctuates due to the influence of the temperature fluctuation of the molten glass MG, from the waveform signal representing the time change of the measured temperature of the outer surface of the glass supply tube 104, the temperature of the molten glass MG is changed. Temporal variations in temperature can be extracted. FIG. 4 is a diagram illustrating an example of a temporal change in the estimated temperature of the molten glass MG calculated based on the electromotive force of the thermocouple and an example of a temporal change in the temperature of the molten glass MG. The estimated temperature is lowered due to the drift of the thermoelectromotive force as shown by the straight line A even if the actual temperature of the molten glass MG is constant. For this reason, acquisition of the temperature of molten glass MG based on the measurement of the conventional thermocouple was not performed. However, as indicated by curve B, the temperature of the molten glass MG flowing through the metal tube may vary over time. Since such time variation can be distinguished from the drift component of the thermoelectromotive force and removed, the component of time variation of the molten glass MG can be extracted using this removal. Therefore, in this embodiment, when flowing the molten glass MG into the metal tube, the molten glass MG flowing out of the melting tank 101 is removed by removing the change due to the drift of the thermoelectromotive force of the thermocouple 116 from the measurement result of the thermocouple 116. The time fluctuation of the temperature is extracted, and the amount of heating given to the molten glass MG is determined according to the extraction result of the time fluctuation to adjust the temperature of the molten glass MG (temperature adjusting step). The temperature of the glass supply pipe 104 can be adjusted by direct energization heating for energizing the above-mentioned pipe itself, indirect heating by a heater (not shown) arranged around the pipe, indirect cooling by an air or water cooling cooler, or air blowing to the pipe. It is carried out using any one method such as attaching, water spraying, or a combination of these methods.

The measurement unit 118 extracts a waveform signal including the curve B using a filter that removes a low-frequency component such as the straight line A from the waveform signal. Further, the measurement unit 118 performs frequency conversion (Fourier transform) on the waveform signal including the curve B and the straight line A, removes the frequency component of the straight line A, and then performs frequency inverse transform (inverse Fourier transform). A waveform signal including B may be extracted.
For example, the measurement unit 118 performs measurement at regular time intervals, and when the waveform signal extracted by the above method deviates from a preset allowable range, a notification that the time variation of the temperature of the molten glass MG has deviated from the allowable range. The amount outside the allowable range is sent to the heating power source 120. Based on this notification, the heating power source 120 determines the additional current by determining the heating amount to be added according to the amount outside the allowable range of the waveform signal. The heating power source 120 causes the total current obtained by adding the additional current and the reference current to flow through the electrode plate 114 to the glass supply tube 104. The heating amount and the additional current to be added include positive and negative. The amount of heating to be added is negative when the reference heating amount is reduced, and the negative additional current is the amount by which the reference current is reduced. The glass supply pipe 104 generates heat by an electric current and can heat the molten glass MG.
That is, when the temperature of the molten glass MG rises over time, the heating amount to be added and the additional current are negative, and the heating amount applied to the molten glass MG is smaller than the reference heating amount. When the temperature of the molten glass MG is changed over time, the heating amount and the additional current to be added become positive, and the heating amount applied to the molten glass MG is larger than the reference heating amount.

  Thus, in this embodiment, even if the temperature of the molten glass MG cannot be obtained, the temperature of the molten glass MG is appropriately determined by measuring the time variation of the temperature of the molten glass MG using a thermocouple. Can be adjusted.

  It is preferable that the time fluctuation of the temperature of the above-mentioned molten glass MG is a temperature fluctuation produced | generated by the fluctuation | variation of the convection of the molten glass MG in the melting tank 101. FIG. It is preferable to determine a cut-off frequency for removing a low-frequency component such as a straight line A from a waveform signal obtained from the thermocouple 116 assuming such temperature fluctuation. In the melting tank 101, in order to melt the glass raw material, the molten glass MG stored in the melting tank 101 has a temperature distribution with a large temperature difference. For this reason, the molten glass MG in the melting tank 101 is convected. Since a part of the molten glass MG flows out from the outlet provided near the bottom of the melting tank 101 to the glass supply pipe 104, the slight fluctuation of the convection of the molten glass MG in the melting tank 101 causes the glass supply pipe 104 to move. The temperature of the molten glass MG flowing in varies with time. This time variation is a rapid variation compared to the change in the estimated temperature of the molten glass MG due to the drift of the electromotive force of the thermocouple 116. For this reason, the waveform signal indicating the temperature fluctuation of the molten glass MG caused by the convection fluctuation of the molten glass MG in the melting tank 101 as indicated by the curve B shown in FIG. The low-frequency component can be efficiently and easily removed using a filter that separates from the low-frequency component that indicates a change in the estimated temperature of the molten glass MG caused by power drift.

  In the present embodiment, the glass supply pipe 104 is used as the place of application of the temperature adjustment of the molten glass MG including the measurement of the temperature fluctuation of the molten glass MG using the thermocouple 116 and the adjustment of the temperature of the molten glass MG. The clarification tube 102, the glass supply tube 105, the stirring tank 103, and the glass supply tube 105 can be used as application places. However, it is preferable to measure the temperature of the molten glass MG using the thermocouple 116 before the refining step of refining the molten glass MG. Since the clarification effect depends on the temperature of the molten glass MG, it is preferable to perform temperature measurement and temperature adjustment of the molten glass MG before the clarification step from the viewpoint of achieving sufficient clarification.

Further, the temperature measurement of the molten glass MG using the thermocouple 116 is performed at a portion on the side of the melting tank 101 with respect to the longitudinal center of the glass supply tubes 104, 105, 106. 105 and 106 are preferable because the temperature of the molten glass MG flowing through the layers 106 and 106 can be sufficiently adjusted.
Further, as shown in FIG. 3, the thermocouple 116 is provided outside the glass supply tube 104, and the temperature of the molten glass MG is adjusted by measuring the temperature of the outer surface of the glass supply tube 104. At this time, the thermocouple 116 is provided in the connecting portion of the glass supply pipe 104 connected to the melting tank 101 in the longitudinal direction of the glass supply pipe 104, and does not flow the molten glass MG whose temperature is not adjusted to the subsequent process. To preferred. The connection portion refers to a portion of 1/10 or less of the length along the longitudinal direction of the glass supply tube 104 from the connection end of the glass supply tube 104 connected to the outlet of the melting tank 101.

  In the present embodiment, even if the temperature of the molten glass MG flowing through the metal tube is 1620 ° C. or higher, that is, the temperature at which the thermocouple 116 is likely to be oxidized and volatilized, the molten glass MG is melted using the thermocouple 116. Since the temperature of the glass MG can be adjusted efficiently, the effect of this embodiment is great.

  It is preferable that an alkali-free boroaluminosilicate glass or a trace amount of alkali-containing glass is used for the glass plate produced by the glass plate production method of the present embodiment.

<Glass composition>
The glass plate to which this embodiment is applied is preferably made of an alkali-free glass having the following composition, for example.
Examples of the glass composition to which the present embodiment is applied include the following (mass% display).
SiO _2: 50~70% _{(preferably, 57~64%), Al 2 O} 3: 5~25% ( _{preferably, 12~18%), B 2 O} 3: 0~15% ( preferably, 6 ~ 13%), and may optionally contain the following composition. As optional components, MgO: 0 to 10% (preferably 0.5 to 4%), CaO: 0 to 20% (preferably 3 to 7%), SrO: 0 to 20% (preferably, from 0.5 to 8%, more preferably 3~7%), BaO: 0~10% ( preferably 0-3%, more preferably _{0~1%), ZrO 2: 0~10} % ( preferably 0 to 4%, more preferably 0 to 1%). Furthermore, it is more preferable that R ′ ₂ O: more than 0.10% and 2.0% or less (provided that R ′ is at least one selected from Li, Na, and K).

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

<Young's modulus>
As a Young's modulus of the glass plate to which this embodiment is applied, for example, 72 (Gpa) or more is preferable, 75 (Gpa) or more is more preferable, and 77 (Gpa) or more is even more preferable.

<Strain point>
As a distortion rate of the glass substrate to which this embodiment is applied, 650 degreeC or more is preferable, for example, 680 degreeC or more is more preferable, 700 degreeC or more and 720 degreeC or more are still more preferable.

The glass plate manufactured by this embodiment is suitable for the glass substrate for a display containing the glass substrate for flat panel displays. It is suitable for an oxide semiconductor display glass substrate using an oxide semiconductor such as IGZO (indium, gallium, zinc, oxygen) and an LTPS display glass substrate using an LTPS (low temperature polysilicon) semiconductor. Moreover, the glass plate manufactured by this embodiment is suitable for the glass substrate for liquid crystal displays by which it is calculated | required that content of an alkali metal oxide is very small. Moreover, it is suitable also for the glass substrate for organic EL displays. In other words, the manufacturing method of the glass plate of this embodiment is suitable for manufacture of the glass substrate for displays, and is especially suitable for manufacture of the glass substrate for liquid crystal displays.
Moreover, the glass plate manufactured by this embodiment is applicable also to a cover glass, the glass for magnetic discs, the glass substrate for solar cells, etc.

  As mentioned above, although the manufacturing method of the glass plate of this invention was 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, what may be variously improved and changed. Of course.

DESCRIPTION OF SYMBOLS 100 Melting apparatus 101 Melting tank 102 Clarification tank 103 Stirring tank 104,105,106 Glass supply pipe 108 Refractory fiber layer 110 Refractory protective layer 112 Refractory brick 114 Electrode plate 116 Thermocouple 118 Measuring part 120 Heating power source 200 Molding apparatus 210 Molded body 300 cutting device

Claims (6)

A melting step of melting glass raw material in a melting tank to produce molten glass;
When flowing the generated molten glass into a metal tube, the temperature of the molten glass is measured by a thermocouple, and the temperature adjusting step of adjusting the temperature of the molten glass based on the obtained measurement result;
Forming the molten glass that has flowed out of the metal tube into a sheet glass,
In the temperature adjustment step, by removing the change due to the thermoelectromotive force drift of the thermocouple from the measurement result of the thermocouple, the time variation of the temperature of the molten glass flowing out of the melting tank is extracted, and the time A method for producing a glass plate, comprising: adjusting a temperature of the molten glass by determining a heating amount to be given to the molten glass according to a fluctuation extraction result.   The glass plate manufacturing method according to claim 1, wherein the time variation of the temperature of the molten glass is a temperature variation caused by fluctuation of convection of the molten glass in the melting tank. Before forming the molten glass into the sheet glass, it has a clarification step of clarifying the molten glass,
The glass plate manufacturing method according to claim 1 or 2, wherein the temperature measurement of the molten glass by the thermocouple is performed before the refining step. The metal pipe includes a clarification pipe that performs clarification of the melting tank and the molten glass, and a glass supply pipe that connects the clarification pipe and the melting tank,
The temperature measurement of the said molten glass by the said thermocouple is a manufacturing method of the glass plate of Claim 3 performed by the part by the side of the said melting tank with respect to the center of the longitudinal direction of the said glass supply pipe | tube.   The thermocouple is provided outside the glass supply tube, and the temperature of the molten glass is adjusted by measuring the temperature of the outer surface of the glass supply tube, and the thermocouple is the length of the glass supply tube. The manufacturing method of the glass plate of Claim 4 provided in the connection part of the said glass supply pipe connected to the said melting tank of direction.   The temperature of the said molten glass which flows through the said metal pipe is a manufacturing method of the glass plate of any one of Claims 1-5 which is 1620 degreeC or more.

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