JP2014198656A - Method and apparatus for production of glass plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a glass plate which suppresses occurrence of unevenness of the temperature of the metal pipe, while securing fast-response, in transferring molten glass into a metal pipe for temperature adjustment and realizes temperature decreasing of the molten glass at an ideal rate.SOLUTION: A method of producing a glass plate comprises: a defoaming step of removing bubbles in molten glass; a molding step of molding the defoamed molten glass into a plate by a down-draw method; and a temperature adjustment step of transferring the molten glass into a metal pipe, after the defoaming step, to adjust the temperature of the molten glass to the molding temperature for molding by the down-draw molding. In the temperature adjustment step, an electric current of 1-10 A/mmis passed through the metal pipe 106 to make the metal pipe 106 generate heat so as to heat the molten glass within the metal pipe 106, and the temperature of the molten glass is controlled so that the temperature of the molten glass within the metal pipe 106 decreases at a rate of 1°C/min or higher and lower than 10°C/min.

Description

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

In the method for producing a glass plate, generally, after a glass raw material is melted, a defoaming step is performed in which the temperature is raised to defoam bubbles in the molten glass. The defoamed molten glass is supplied to the stirring tank while being transported through the metal tube to perform a homogenization process, and then is transported to a molding apparatus to perform a molding process. In the molding process using the downdraw method, the molten glass needs to have a viscosity suitable for molding. Therefore, after the defoaming process, the molten glass that has been heated is supplied with metal before being supplied to the molding apparatus. The temperature is adjusted while being transferred through the pipe. Thereby, while being able to adjust the glass flow rate to a shaping | molding apparatus, the molten glass temperature in a shaping | molding process is stabilized, and the quality of the shape | molded glass plate is ensured.
As a conventional method for adjusting the temperature of molten glass, for example, a direct energization method is known in which a current is passed through a metal tube to cause the metal tube to generate heat, thereby heating the molten glass (Patent Document 1). In the direct energization method, since the temperature of the molten glass can be controlled by passing a current directly through the metal tube, for example, when the temperature conditions in each process are changed, or when the temperature of the molten glass flowing into the metal tube changes The temperature can be followed immediately, etc., and it has excellent responsiveness.

JP 2012-111687 A

However, temperature adjustment by the direct energization method tends to cause heat dissipation from the connection part such as an electrode connected to the metal tube, uneven current density flowing through the metal tube, etc., and make the temperature uniform throughout the metal tube. It is difficult. Thus, for example, it has been proposed to change the shape of the connecting portion, but the temperature cannot be made uniform enough. When unevenness occurs in the surface temperature of the metal tube, temperature distribution occurs in the molten glass in the tube, and striae is likely to occur, or a low temperature part is locally generated, resulting in devitrification, sheet It tends to adversely affect glass quality, such as an increase in glass thickness deviation.
The present invention relates to a method for producing a glass plate capable of lowering the temperature of a molten glass at an ideal rate while suppressing temperature unevenness of the metal tube when the temperature is adjusted by transferring the molten glass through the metal tube. An object of the present invention is to provide a glass plate manufacturing apparatus.

One aspect of the present invention includes a defoaming step in which molten glass is heated to defoam bubbles in the molten glass, and a molding step in which the defoamed molten glass is formed into a plate shape by a downdraw method. A method of manufacturing a glass plate,
Furthermore, after the defoaming step, the molten glass is transferred through a metal tube, and a temperature adjusting step for adjusting the temperature of the molten glass to be a molding temperature for molding by a downdraw method is provided,
In the temperature adjusting step, the temperature of the molten glass in the metal tube is 1 while heating the molten glass in the metal tube by causing the metal tube to generate heat by flowing a current of 1 to 10 A / mm ² through the metal tube. It is characterized in that the temperature of the molten glass is controlled so that the temperature is lowered at a rate of not lower than 10 ° C./min.

  In the manufacturing method of the said glass plate, it is preferable that controlling the temperature of the said molten glass includes the indirect heating which heats the molten glass in the said metal tube by giving a heat to the said metal tube from the outer side of the said metal tube. .

  In the method for producing a glass plate, the molten glass preferably has a strain point of 655 to 755 ° C. and a liquidus viscosity of 40000 to 400000 poise.

In the method for producing a glass plate, in the forming step, a molten glass is formed into a plate shape using a formed body,
The metal pipe includes a storage tank that stores molten glass, a transfer pipe that extends to connect the storage tank and the molded body, and transfers the molten glass,
The temperature adjusting step is preferably performed in at least one region of the storage tank or the transfer pipe.

  In the manufacturing method of the said glass plate, it is preferable that the said temperature adjustment process controls the temperature of the molten glass which flows through the inside of the said transfer pipe.

  In the manufacturing method of the said glass plate, it is preferable that the molten glass temperature-controlled at the said temperature adjustment process has a temperature difference within 40 degreeC with respect to the temperature of the molten glass supplied to the said molded object.

Another aspect of the present invention includes a defoaming means for heating the molten glass to defoam bubbles in the molten glass, and a molding means for forming the defoamed molten glass into a plate shape by a downdraw method. An apparatus for producing a glass plate comprising:
Furthermore, the defoamed molten glass is moved through the metal tube, and includes a temperature adjusting means for adjusting the temperature of the molten glass to be a molding temperature for molding by the downdraw method,
The temperature adjusting means includes a current heating means for heating the molten glass in the metal tube by supplying a current of 1 to 10 A / mm ^{2 to} the metal tube, and a melting in the metal tube by applying heat to the metal tube. And indirect heating means for heating the glass.

In the glass plate manufacturing apparatus, an outer furnace is provided on the outer peripheral side of the metal tube so as to surround the metal tube with a space from the metal tube,
It is preferable that a heater is provided in a space between the metal tube and the outer furnace or an outer peripheral surface of the metal tube, and the indirect heating is performed by heat generation of the heater.

In the glass plate manufacturing apparatus, the heater includes a plurality of heating elements extending linearly, and the plurality of heating elements are provided at intervals in a direction in which the metal tube extends,
The plurality of heating elements include a first heating element disposed in the space so as to extend in a first direction on a plane orthogonal to a direction in which the metal tube extends, and the first direction on the plane. And a second heating element arranged in the space so as to extend in different second directions.

In the glass plate manufacturing apparatus, the metal tube includes a storage unit that stores the molten glass, and a transfer unit that transfers the molten glass,
The temperature adjusting means preferably adjusts the temperature of the molten glass in at least one region of the storage means and the transfer means.

  In the glass plate manufacturing apparatus, it is preferable that the storage unit further includes a stirring unit.

  According to the present invention, when adjusting the temperature by transferring the molten glass through the metal tube, while suppressing the occurrence of temperature unevenness of the metal tube while ensuring quick response, the temperature of the molten glass is lowered at an ideal speed. Can do.

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 apparatus which performs the melting process-cutting process shown in FIG. It is a figure which shows the apparatus which performs a temperature adjustment process. It is a figure which shows the apparatus which performs an electroheating process. It is a figure which shows the apparatus for measuring the temperature of the metal pipe | tube in an electricity heating process.

  Hereinafter, the manufacturing method of the glass plate of this invention and the manufacturing apparatus of a glass plate are demonstrated.

  Drawing 1 is a figure showing an example of a process of a manufacturing method of a glass plate of this embodiment.

(Overall overview of glass plate manufacturing method)
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). The cutting step (ST7) and the temperature adjustment step (ST8) are mainly included. 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 toward the downstream process from the outlet provided in one bottom part of the inner side wall of the melting tank.
In addition to the method in which electricity flows through the molten glass itself and heats itself by heating, the glass raw material can be melted by supplementing a flame with a burner. 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, SnO ₂ (tin oxide) can be used 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 process, a defoaming process and an antifoaming process are performed. In the defoaming step, the molten glass in the clarification tank is heated, so that the bubbles containing O ₂ , CO _2, or SO ₂ contained in the molten glass are replaced with O ₂ produced by the reductive reaction of the clarifier. It absorbs and grows, and bubbles rise to the surface of the molten glass and are released. In the defoaming step, by reducing the temperature of the molten glass, the reducing substance obtained by the reductive reaction of the clarifying agent undergoes an oxidation reaction. Thereby, gas components such as O ₂ in the foam remaining in the molten glass are reabsorbed in the molten glass, and the foam disappears. The oxidation reaction and reduction reaction by the fining agent are performed by controlling the temperature of the molten glass. In the clarification step, a reduced-pressure defoaming method can be used in which a reduced-pressure atmosphere space is created in the clarification tank, and bubbles existing in the molten glass are grown in a reduced-pressure atmosphere for defoaming. In this case, it is effective in that no clarifier is used. In the clarification step, a clarification method using tin oxide as a clarifier is used.

In the homogenization step (ST3), the molten glass is supplied to the storage tank through a pipe extending from the clarification tank, and the glass component is homogenized by stirring the molten glass in the storage 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 forming apparatus through a pipe extending from the storage tank. In parallel with the supply process, a temperature adjustment process (ST8) is performed. In the temperature adjustment step, after the homogenization step, the temperature of the molten glass is adjusted so that the molten glass is transferred to the inside of the metal tube and becomes a forming temperature for forming by the overflow down draw method. Details of the temperature adjustment step will be described later.

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. The molding is not particularly limited as long as it is a downdraw method, but for example, an overflow downdraw method is used.
In the slow cooling step (ST6), the sheet glass that has been formed and flowed is cooled to a desired thickness, so that internal distortion does not occur and warpage does not occur.
In a cutting process (ST7), a plate-shaped glass plate is obtained by cutting the sheet glass supplied from the forming device into a predetermined length in the cutting device. The cut glass plate is further cut into a predetermined size to produce a 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 an apparatus that performs the melting step (ST1) to the cutting step (ST7) and the temperature adjustment step (ST8) 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 storage tank 103, and transfer pipes 104, 105, and 106. In the glass plate manufacturing method of this embodiment, the metal tube for transferring the molten glass in the temperature adjustment step is the transfer tube 106. In other embodiments, the metal tube may be a tube of the clarification tank 102.
In the melting apparatus 101 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. Furthermore, in the storage tank 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.

(Temperature adjustment process)
Next, the temperature adjustment step (ST8) will be described.
In the temperature adjustment step, the temperature of the molten glass is controlled so as to lower the temperature at a temperature lowering rate described later while performing the electric heating step (ST81). In the following description of the present embodiment, a case where the temperature is adjusted when the molten glass is transferred as a metal tube through the transfer tube 106 will be described as an example.

In the energization heating step (ST81), the molten glass in the transfer tube 106 is heated by flowing a current of 1 to 10 A / mm ² through the transfer tube 106 to heat the transfer tube 106. While the molten glass in the transfer pipe 106 is heated and energized in this manner, the heat is transferred to and from the transfer pipe 106 to adjust the temperature. When a current exceeding 10 A / mm ^{2 is} passed, unevenness in the surface temperature of the transfer tube 106 due to the deviation in current density flowing through the transfer tube 106 increases, and a temperature distribution may occur in the molten glass in the transfer tube 106. On the other hand, by flowing a current of 1 A / mm ² or more, when the temperature condition of the molten glass is changed in the clarification process, the homogenization process on the upstream side, or the molding process on the downstream side, or the melt flowing into the transfer pipe 106 When the temperature of the glass changes, these temperatures can be followed immediately, and quick response is ensured. Thereby, stabilization of the molten glass temperature in a formation process can be aimed at. Here, stabilization means that the temperature unevenness of the molten glass is suppressed to such an extent that devitrification at the time of molding and striae in the sheet glass do not occur.

  In the temperature adjustment step (ST8), the temperature of the molten glass is controlled so that the temperature of the molten glass in the transfer pipe 106 is lowered at 1 ° C./min or more and less than 10 ° C./min. The temperature of the molten glass here is measured by a plurality of temperature measuring elements, which will be described later, used in the electric heating process. Here, in the temperature adjustment process, which adjusts the temperature of the molten glass heated in the defoaming process to a molding temperature suitable for forming by the overflow down draw method, the thermal history of the molten glass flowing through the transfer pipe is adjusted. From the viewpoint of ensuring the quality of the molten glass, in particular, the quality of the molten glass supplied to the molded body, stabilizing the molten glass temperature at the molding temperature, and ensuring the quality of the glass plate, 1 ° C./min to 10 ° C. It is ideal to lower the temperature in less than 1 minute. For example, while the molten glass is transferred through the transfer pipe 106 from the storage tank 103 to the molding apparatus 200, the temperature is lowered from 1500 ° C. to 1200 ° C. over 15 minutes to 1 hour at the above temperature drop rate. In the temperature adjustment step, the temperature of the molten glass is controlled so that the temperature of the molten glass is adjusted at such an ideal temperature drop rate.

  In the temperature adjusting step, indirect heating for heating the molten glass in the transfer pipe 106 is performed by applying heat to the transfer pipe 106 from the outside of the transfer pipe 106 while conducting the electric heating. According to such indirect heating, the transfer tube 106 is uniformly heated throughout, and the temperature of the molten glass in the transfer tube 106 is unlikely to be uneven. For this reason, compared with the case where only a current heating is performed and the temperature adjustment process is performed, the temperature drop rate is easily stabilized, and the temperature of the molten glass can be easily lowered by the temperature drop rate.

Next, with reference to FIGS. 3 to 5, an apparatus for performing a temperature adjustment process will be described.
FIG. 3 is a diagram illustrating an apparatus for performing a temperature adjustment process. FIG. 4 is a diagram showing an apparatus for performing an electric heating process. FIG. 5 is a diagram showing an apparatus for measuring the temperature of the metal tube in the electric heating process.

The transfer tube 106 is made of platinum or a platinum alloy. A heat insulating material 160 is provided on the outer peripheral surface of the transfer tube 106 to keep the transfer tube 106 warm and protect it. For example, refractory bricks are used as the heat insulating material. The heat insulating material has thermal conductivity, and the material and thickness are determined so as to allow a certain level of heat transfer between the space 120 and the transfer pipe 106 described later. The heat insulating material is provided except for a position where an electrode 150 (to be described later) is connected in a region in the pipe line direction of the transfer pipe 106 (direction in which the transfer pipe 106 extends). A metal frame (not shown) for holding the heat insulating material 160 is provided on the outer peripheral surface of the heat insulating material 160. An inner heat insulating layer made of alumina cement may be provided between the transfer pipe 106 and the heat insulating material.
An outer furnace 110 is provided on the outer peripheral side of the transfer pipe 106 so as to surround the transfer pipe 106 at a distance from the transfer pipe 106. Thereby, a space 120 is provided between the transfer pipe 106 and the outer furnace 110. The outer furnace 110 is made using, for example, refractory bricks. The cross-sectional shape of the outer furnace 110 in the direction in which the transfer pipe 106 extends is not particularly limited, but is, for example, a rectangular shape.

A heater 130 is disposed in the space 120, and indirect heating is performed by the heat generated by the heater 130. In other embodiments, the heater 130 may be provided on the outer peripheral surface of the transfer pipe 106. The heater 130 has a plurality of heating elements 131 and 132. The plurality of heating elements 131 and 132 are each a rod-like member extending linearly, and are provided at intervals in the pipe line direction of the transfer pipe 106.
Among the plurality of heating elements 131, 132, the plurality of heating elements (first heating elements) 131 extend in the horizontal direction (perpendicular to the plane of FIG. 3) on a virtual plane orthogonal to the pipe direction of the transfer pipe 106. It is arranged in the space 120. Further, the plurality of heating elements (second heating elements) 132 are arranged in the space 120 so as to extend in the vertical direction (the vertical direction in the drawing of FIG. 3) on the virtual plane. In the present embodiment, the plurality of heating elements 131 are arranged so as to extend in the horizontal direction in the pipeline direction region between a pair of electrodes 150 described later, and in the pipeline direction region outside the pair of electrodes 150, It is arranged to extend in the vertical direction. By arranging the plurality of heating elements 131 and 132 so as to extend in different directions as described above, the temperature distribution of the atmospheric temperature in the space 120 can be reduced. The pair of plural heating elements may be arranged extending in three or more different directions.

  The heater 130 is connected to a control device (not shown), and is controlled so that the atmospheric temperature of the space 120 becomes a preset temperature. A temperature gauge 181 for measuring the ambient temperature of the space 120 is attached to the outer furnace 110. The temperature probe 181 is made of a thermocouple. The temperature probe 181 is provided in a region in the pipe line direction between the pair of electrodes 150. The temperature probe 181 is connected to a control device (not shown). The control device controls the heater 130 so that the temperature measured by the temperature probe 181 becomes a preset temperature, and performs indirect heating. The set temperature is determined in consideration of the bias between the transfer pipe 106 and the ambient temperature. In the indirect heating, instead of the control using the temperature measured by the measuring element 181, a predetermined amount of power may be supplied to the heater 130.

  A pair of electrodes 150 is attached to the transfer tube 106. The electrode 150 is an annular flange extending in the radial direction. For example, the electrode 150 is in contact with the outer peripheral surface of the transfer tube 106 over the entire circumference. A power supply terminal 152 is connected to the electrode 150 through a conductive member 151. The electrode 150 and the conductive member 151 are preferably provided with a configuration for keeping them warm and suppressing heat dissipation. As the said structure, the member which has heat insulation and can coat | cover the electrode 150 and the electrically-conductive member 151 is mentioned, for example. The power supply terminal 152 is connected to a power source (not shown) via the control device.

Note that the pair of electrodes 150 are provided at a plurality of locations in the pipe line direction of the transfer pipe 106. In this embodiment, the transfer pipe 106 is divided into a plurality of (for example, five) zones in the pipe line direction. One pair of electrodes 150 is provided in each zone, and energization heating is performed for each zone. Specifically, the target temperature of the surface of the transfer pipe 106 is set for each zone, and the power supply amount is controlled by PID (Proportional Integral Derivative) control so that the surface temperature of the transfer pipe 106 becomes the target temperature in each zone. Is done.
As shown in FIG. 5, the temperature of the transfer pipe 106 in the energization heating process is a temperature measurement provided at a plurality of different circumferential positions on the outer peripheral surface of the transfer pipe 106 (for example, four locations on the top, bottom, left, and right in FIG. 5). Measured by the child 171. Each temperature measuring element 171 includes a thermocouple. FIG. 5 is a diagram showing an apparatus for measuring the temperature of the transfer pipe 106 in the energization heating process. The temperature measuring elements 171 are respectively connected to the control device, and the average of a plurality of temperatures measured by the plurality of temperature measuring elements 171 is set as the temperature of the transfer pipe 106. In addition, a difference between the highest temperature and the lowest temperature among the plurality of temperatures is defined as a temperature deviation.

  As shown in FIG. 3, the pipe length L106a is a distance between two positions on the transfer pipe 106 to which the pair of electrodes 150 are respectively connected. In the present embodiment, the pipe length L106a in each zone is, for example, 50 to 150 cm. If it is less than 50 cm, the residence time of the molten glass in the zone is shortened, and the glass temperature does not reach the desired temperature. If it exceeds 150 cm, the scale of the apparatus increases and the equipment cost also increases. The molten glass whose temperature is controlled in the temperature adjusting step preferably has a temperature difference within 40 ° C. with respect to the temperature of the molten glass supplied to the molded body 210. In other words, the temperature adjustment step is preferably performed at a place where the molten glass in the transfer pipe 106 is at a temperature that makes a temperature difference within 40 ° C. from the temperature of the molten glass supplied to the molded body 210.

  In the manufacturing method of the glass plate of this embodiment, the said temperature fall rate may differ according to each zone, and may be equal. If they are different, it is preferable that the temperature lowering rate is set to be slower in the downstream zone closer to the molding apparatus 200.

According to the above method for producing a glass plate, when the temperature of the molten glass is adjusted by transferring the inside of the transfer tube 106, the heating is conducted in the range of 1 to 10 A / mm ^{2 and} the temperature is 1 ° C./min or more 10. Temperature control is performed so that the temperature of the molten glass drops at less than ° C / min. When only energization heating is performed for temperature adjustment, quick response can be obtained, but the temperature unevenness of the transfer tube 106 may increase, but the current flowing through the transfer tube 106 is suppressed to ¹ to 10 A / mm ² . Therefore, temperature unevenness is suppressed. Then, the temperature of the molten glass is controlled so as to decrease the temperature at the temperature decrease rate while conducting the electric heating, so that the temperature of the molten glass can be decreased at an ideal rate.

In the manufacturing method of the glass plate of this embodiment, indirect heating is specifically performed while energizing heating.
When the temperature of the molten glass is adjusted by energization heating, as described above, the surface temperature of the transfer tube is reduced due to the heat radiation from the conductive member and electrode to which the power supply terminal is connected and the current density difference flowing through the transfer tube. Unevenness occurs. Of these, heat dissipation from conductive members can be improved relatively easily by providing a structure that keeps them warm, but current density differences are caused by small differences in thickness and shape of conductive members, etc. Improvement is difficult.
The present inventor has made studies based on such circumstances and found that the influence of the temperature deviation on the surface of the transfer tube caused by the difference in current density affects the glass quality. The difference in current density increases when the amount of power supplied to the transfer tube is large and decreases when the amount of power is small, and the temperature deviation caused on the surface of the transfer tube thereby causes the quality of the molten glass flowing through the transfer tube, in particular, molding. It has been found that the quality of the molten glass supplied to the apparatus is affected, which has a great influence on the quality of the formed glass sheet. Based on this knowledge, it is conceivable to reduce the amount of electric power supplied to the transfer pipe so that the temperature deviation on the surface of the transfer pipe falls within a predetermined temperature range. For example, it is conceivable to increase the volume of a heat insulating material provided on the outer peripheral surface of the transfer pipe and supporting the transfer pipe. However, once a heat insulating material is provided around the transfer pipe and then further heat insulating material is provided later, it is difficult due to the limitation of installation space. Even if there is room in the installation space, the heat insulating material is usually held by a metal frame, so if additional heat insulating material is provided so as to cover the frame from the outside of the frame, the frame will become hot. There is a risk that the holding structure by the frame and the heat insulating material may be damaged due to a decrease in strength and deformation due to thermal expansion. For these reasons, it is not preferable to additionally provide a heat insulating material to the heat insulating material once installed.
On the other hand, if the volume of the heat insulating material is increased when installing the transfer pipe, if you want to increase the temperature of the molten glass flowing into the transfer pipe, or if you want to lower the temperature of the molten glass flowing out of the transfer pipe, In the case where it is desired to keep the temperature of the transfer pipe low, there is a possibility that the transfer pipe does not decrease to a desired temperature even if the power for energization heating is cut off.
In the manufacturing method of the glass plate of this embodiment, the temperature adjustment of molten glass is performed by performing indirect heating in combination with current heating. Thereby, for example, by increasing the amount of electric power to the heating element in the space around the transfer pipe, the ambient temperature of the space rises, thereby reducing the amount of electric power required for energization heating. Conversely, by reducing the amount of power to the heating element, the ambient temperature of the space is lowered, thereby increasing the amount of power required for energization heating. Thus, by adjusting the ambient temperature around the transfer pipe, it is possible to adjust the amount of electric power necessary for energization heating, thereby making it possible to reduce the temperature deviation of the molten glass in the transfer pipe. On the other hand, since the temperature of the transfer pipe itself is controlled by energization heating, quick response can be obtained. Thus, by using indirect heating and current heating in combination, it is possible to suppress temperature unevenness of the transfer tube while ensuring quick response to temperature changes of the molten glass.
In addition, since temperature unevenness can be suppressed by energization heating, temperature adjustment at the temperature lowering rate can be performed stably.

  Further, according to the method for manufacturing a glass plate of the present embodiment, the first heating element and the second heating element are arranged in the space so as to extend in different directions. Can be small.

In addition, in the manufacturing method of the glass plate of this embodiment, the heater used at an indirect heating process may be provided in the outer peripheral surface of a transfer pipe instead of providing in the space between a transfer pipe and an outer furnace. For example, the heating element may be provided so as to be wound around the transfer pipe via a heat retaining member.
Moreover, in the manufacturing method of the glass plate of this embodiment, a temperature adjustment process is performed between a defoaming process and a formation process. For example, the temperature adjustment process may be performed in a homogenization process of molten glass, or may be performed in both the homogenization process and the supply process. Specifically, it may be performed in the storage tank 103 or may be performed in both the storage tank 103 and the transfer pipe 106. In addition, when a temperature adjustment process is performed by a homogenization process, an electric heating process connects an electrode, an electrically-conductive member, an electric power feeding terminal, and a temperature measuring element with respect to the said storage tank, and performs the electric heating of the said embodiment. It can be performed in the same manner as the process. In the indirect heating step, a heat insulating material is provided so as to surround the outer peripheral surface of the storage tank, and the heater is provided between the storage tank and the heat insulating material or on the outer peripheral surface of the storage tank. Can be done as well. In this specification, the metal tube includes a storage tank that is a tubular member.

(Characteristics of glass plate, application)
When using the glass plate of this embodiment for the glass plate for flat panel displays, what mixes a glass raw material so that it may have the following glass compositions is illustrated.
SiO ₂ : 50 to 70% by mass,
Al ₂ O ₃ : 0 to 25% by mass,
B ₂ O ₃ : 1 to 15% by mass,
MgO: 0 to 10% by mass,
CaO: 0 to 20% by mass,
SrO: 0 to 20% by mass,
BaO: 0 to 10% by mass,
RO: 5-30 mass% (R is all the elements contained in a glass plate among Mg, Ca, Sr, and Ba),
Alkali-free glass containing
Although the alkali-free glass is used in this embodiment, the glass plate 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% by mass to 0.5% by mass, preferably 0.20% by mass to 0.5% by mass (where R ′ is Li, Na And at least one selected from K and contained in the glass plate). Of course, the total of R ′ ₂ O may be lower than 0.10% by mass.
Also, when applying the method for producing a glass plate of the present invention, the glass composition, in addition to the above components, SnO _2: 0.01 to 1 mass% (preferably 0.01 to 0.5 wt% ), Fe ₂ O ₃ : 0 to 0.2% by mass (preferably 0.01 to 0.08% by mass), and considering the environmental load, As ₂ O ₃ , Sb ₂ O ₃ and PbO You may prepare a glass raw material so that it may not contain substantially.

In recent years, displays using p-Si (low-temperature polysilicon) TFTs and oxide semiconductors instead of α-Si (amorphous silicon) TFTs to realize higher definition of screen display of flat panel displays. Is required. Here, in the process of forming the p-Si (low-temperature polysilicon) TFT and the oxide semiconductor, there is a heat treatment process at a higher temperature than the process of forming the α-Si · TFT. For this reason, a glass plate on which p-Si • TFT and an oxide semiconductor are formed is required to have a low thermal shrinkage rate. In order to reduce the heat shrinkage rate, it is preferable to increase the strain point. However, a glass having a high strain point tends to have a high liquidus temperature and a low liquidus viscosity. Further, in order to prevent the glass from devitrifying, it is necessary to suppress temperature unevenness generated in the transfer pipe in the temperature adjustment step. However, when the temperature is adjusted by energizing and heating the transfer pipe, the temperature unevenness of the transfer pipe increases as the amount of power supplied to the transfer pipe increases as described above.
In the method for producing a glass plate of the present embodiment, temperature control for lowering the temperature of the molten glass in the transfer pipe at 1 ° C./min or more and less than 10 ° C./min is performed while conducting current heating. The amount of current to be passed through is suppressed to a range of 1 to 10 A / mm ² . Thereby, the temperature nonuniformity which generate | occur | produces in a transfer pipe is suppressed. Therefore, the method for producing a glass plate of the present invention is particularly suitable for producing a flat panel display using p-Si (low temperature polysilicon) TFT and a glass plate for a flat panel display using an oxide semiconductor. ing. Specifically, it is particularly suitable for manufacturing liquid crystal displays or organic EL displays using p-Si (low-temperature polysilicon) TFTs, and glass plates for liquid crystal displays or organic EL displays using oxide semiconductors. Yes.

The glass plate on which the low-temperature p-Si • TFT and the oxide semiconductor are formed has, for example, a strain point of 655 ° C. or higher, or a liquid phase viscosity of 45000 poise or higher. The composition of the glass _plate, SiO 2: 3 to 20 wt%: 52-78 wt%, Al ₂ O _3: 3 to 25 wt%, B ₂ O _3: 1 to 15 wt%, RO Is preferred. Here, R is at least one component selected from Mg, Ca, Sr and Ba contained in the glass plate. This glass plate is preferably an alkali-free glass or glass containing a trace amount of alkali having a mass ratio represented by (SiO ₂ + Al ₂ O ₃ ) / B ₂ O ₃ of 7 to 20.

Since the glass plate on which the low temperature p-Si.TFT and the oxide semiconductor are formed has a high strain point, the mass ratio represented by (SiO ₂ + Al ₂ O ₃ ) / RO is 5 or more. Yes, preferably 6 or more, more preferably 7.5 or more. In addition, when the β-OH value is too small, the glass plate has a high viscosity in a high temperature region and the meltability is lowered. When the β-OH value is too large, the strain point is lowered. Therefore, this glass plate preferably has a β-OH value of 0.05 / mm to 0.3 / mm.

The glass plate has a high strain point and prevents a decrease in liquid phase viscosity, and the mass ratio represented by CaO / RO is 0.3 or more, preferably 0.5 or more. More preferably, it is 0.65 or more. Further, the glass plate, in consideration of the environmental burden, it is preferred not to substantially contain _{As 2 O 3, Sb 2 O} 3 , and PbO.

(Experimental example)
The molten glass having the composition of the glass plate described above, having a strain point of 690 ° C., and a liquidus viscosity of 45000 poise is transferred through a platinum transfer tube having an inner diameter of 200 mm and a thickness of 0.7 mm. According to the manufacturing method, the temperature was adjusted by conducting current heating and indirect heating.
The electric heating was performed at each electric heating current value (A / mm ² ) shown in Table 1. The energization heating current value is a current value per sectional area flowing through the transfer pipe. For example, when a current of 3000 A is passed through the transfer tube having the above dimensions, the cross-sectional area is (100.7) ² × π-100 ² × π = 441.4 mm ² and the unit area current value is 6.8 A. / Mm ² is calculated. In addition, the pipe length of the transfer pipe in which the electric heating is performed was 80 cm, and the pipe length of the transfer pipe was 500 cm.
Indirect heating was performed by supplying each atmospheric power (kW) shown in Table 1 to the heater so as to lower the temperature at 1 ° C./min or more and less than 10 ° C./min. Atmospheric power is the average of the temperatures measured by a thermometer comprising thermocouples provided at a plurality of circumferential positions (four locations shown in FIG. 5) on the outer peripheral surface of the transfer tube. In addition, a 20 mm thick refractory brick is installed around the transfer pipe with a 10 mm gap, and the gap is filled with alumina-based cement to provide a heat insulating material. An outer furnace made of refractory heat-insulating bricks was provided with an interval of 15 cm.

  After the temperature adjustment step, the molten glass was supplied to the molded glass and molded by the overflow down draw method. In the molding process, the atmospheric temperature in the molding furnace was 1200 ° C., and the viscosity of the molten glass was 40000 poise.

Further, the tube temperature deviation (° C.), the glass flow rate deviation (σ / Ave), and the temperature lowering rate (° C./min) were calculated in the following manner. The results are shown in Table 1.
(Tube temperature deviation)
Of the temperatures measured by the plurality of temperature gauges provided on the surface of the transfer tube, the temperature difference between the maximum temperature and the minimum temperature was defined as a tube temperature deviation (° C.). As a result, the case of 9 ° C. or less was judged good.
(Glass flow rate deviation)
The flow rate of the sheet glass was measured at a pace of 24 times / day for 7 days, the average value and the standard deviation were calculated, and the value obtained by dividing the standard deviation by the average value was defined as the glass flow rate deviation (σ / Ave). . As a result, the case of 0.010 or less was judged as good.
(Cooling rate)
The difference between the temperature at the upstream end of the transfer pipe and the temperature at the downstream end is calculated from the other end after the molten glass starts to flow into one end of the transfer pipe. It was obtained by dividing by the time (min) until it came out. The temperature here was the temperature measured with the plurality of temperature gauges. Temperature adjustment and glass flow rate control were performed so as to decrease the temperature at 1 ° C./min or more and less than 10 ° C./min.

Furthermore, a 130-cm square glass plate was cut out from each obtained sheet glass, it was set as Examples 1-4 and Comparative Examples 1 and 2, and the glass quality was evaluated according to the following point, respectively. The results are shown in Table 1.
(Glass quality)
By visual observation with several panelists, the presence or absence of striae and devitrification in the glass plate sample was evaluated, the thickness deviation was determined, and the thickness deviation was evaluated. As a result of visual observation, when no striae or devitrification was confirmed in the sample, it was evaluated that there was no problem. The thickness deviation was calculated based on the thickness distribution measured at any 10 or more locations in the sample. As a result, when the deviation was 10 or less, it was evaluated that there was no problem. The thickness of each location was measured with a micrometer. As a result, the case where there was no problem in both the visual evaluation and the thickness deviation was designated as A, and the case where there was a problem in at least one of the cases was designated as B.

As shown in Table 1, when energization heating is performed by applying a current of 1 to 10 A / mm ² (Examples 1 to 4), the temperature deviation of the tube is 9 ° C. or less, and the temperature generated in the transfer tube. While unevenness was suppressed, the glass flow rate deviation was 0.010 or less, and the responsiveness was excellent. In addition, no problem was found in the glass quality. Furthermore, in Examples 1 to 4, the temperature of the molten glass could be lowered at an ideal speed.

  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.

103 Storage tank (metal pipe)
105,106 Transfer pipe (metal pipe)
106a Peripheral surface 110 of transfer pipe Outer furnace 120 Space 130 Heater 131 First heating element 132 Second heating element 200 Molding device L106a Pipe length L106 of electrically heated region Pipe length MG Molten glass ST5 Molding process ST8 Temperature Adjustment process ST81 Electric heating process

Claims (11)

A method for producing a glass plate, comprising: a defoaming step of heating molten glass to defoam bubbles in the molten glass; and a forming step of forming the defoamed molten glass into a plate shape by a downdraw method. And
Furthermore, after the defoaming step, the molten glass is transferred through a metal tube, and a temperature adjusting step for adjusting the temperature of the molten glass to be a molding temperature for molding by a downdraw method is provided,
In the temperature adjusting step, the temperature of the molten glass in the metal tube is 1 while heating the molten glass in the metal tube by causing the metal tube to generate heat by flowing a current of 1 to 10 A / mm ² through the metal tube. A method for producing a glass plate, characterized in that the temperature of the molten glass is controlled so that the temperature is lowered at a rate of not lower than 10 ° C / min.   Control of the temperature of the said molten glass includes the indirect heating which heats the molten glass in the said metal tube by giving a heat to the said metal tube from the outside of the said metal tube, The manufacture of the glass plate of Claim 1 Method.   The method for producing a glass plate according to claim 1, wherein the molten glass has a strain point of 655 to 755 ° C. and a liquidus viscosity of 40000 to 400000 poise. In the molding step, the molten glass is molded into a plate shape using the molded body,
The metal pipe includes a storage tank that stores molten glass, a transfer pipe that extends to connect the storage tank and the molded body, and transfers the molten glass,
The said temperature adjustment process is a manufacturing method of the glass plate in any one of Claim 1 to 3 performed in the at least one area | region of the said storage tank or the said transfer pipe.   The said temperature adjustment process is a manufacturing method of the glass plate of Claim 4 which controls the temperature of the molten glass which flows through the inside of the said transfer pipe.   The method for producing a glass plate according to claim 4 or 5, wherein the molten glass whose temperature is controlled in the temperature adjusting step has a temperature difference within 40 ° C with respect to the temperature of the molten glass supplied to the compact. An apparatus for producing a glass plate, comprising: a defoaming means for defoaming bubbles in the molten glass by heating the molten glass; and a molding means for forming the defoamed molten glass into a plate shape by a downdraw method. And
Furthermore, the defoamed molten glass is moved through the metal tube, and includes a temperature adjusting means for adjusting the temperature of the molten glass to be a molding temperature for molding by the downdraw method,
The temperature adjusting means includes a current heating means for heating the molten glass in the metal tube by supplying a current of 1 to 10 A / mm ^{2 to} the metal tube, and a melting in the metal tube by applying heat to the metal tube. An apparatus for manufacturing a glass plate, comprising: an indirect heating means for heating glass. An outer furnace is provided on the outer peripheral side of the metal tube so as to surround the metal tube with a space from the metal tube,
The glass plate manufacturing apparatus according to claim 7, wherein a heater is provided in a space between the metal tube and the outer furnace or an outer peripheral surface of the metal tube, and the indirect heating is performed by heat generation of the heater. The heater includes a plurality of heating elements extending linearly, and the plurality of heating elements are provided at intervals in the extending direction of the metal tube,
The plurality of heating elements include a first heating element disposed in the space so as to extend in a first direction on a plane orthogonal to a direction in which the metal tube extends, and the first direction on the plane. The glass plate manufacturing apparatus according to claim 8, further comprising: a second heating element disposed in the space so as to extend in a different second direction. The metal tube includes storage means for storing the molten glass, and transfer means for transferring the molten glass,
The said temperature adjustment means is a manufacturing apparatus of the glass plate in any one of Claim 7 to 9 which adjusts the temperature of a molten glass in at least one area | region of the said storage means and the said transfer means.   The said storage means is a manufacturing apparatus of the glass plate of Claim 10 further provided with a stirring means.

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