JP6511234B2 - Method of manufacturing glass substrate, and apparatus for manufacturing glass substrate - Google Patents

Description

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

  In order to clarify molten glass using a fining agent, conventionally, molten glass in the fining tube of the fining tank is heated to accelerate the defoaming action of the fining agent contained in the molten glass, thereby allowing the molten glass to become transparent tube. It is practiced to release air bubbles into the gas phase space of the The gas phase space is a space formed by the inner wall of the fining tube and the molten glass. In other words, the gas phase space is a space surrounded by the inner wall of the fining tube and the liquid surface of the molten glass in the fining tube.

  As a constituent material of a fining tube, for example, it is known that platinum excellent in heat resistance is used (for example, refer to patent documents 1).

Japanese Patent Application Publication No. 2006-522001

  The portion of the inner wall of the fining tube in contact with the gas phase space tends to have a higher temperature than the portion in contact with the molten glass. Furthermore, since the gas phase space contains oxygen, platinum contained in the portion of the fining tube in contact with the gas phase space is oxidized and volatilized from the inner wall of the fining tube and easily dispersed in the gas phase space as vapor. There was a problem that. Then, the platinum-containing component dispersed in the gas phase space (hereinafter, also referred to as a volatile component) is aggregated in the gas phase space, and the aggregated volatile component is mixed in the molten glass to obtain the quality of the glass substrate. There was a problem of reducing it. Agglomeration of volatile components was particularly likely to occur in the upper space of the vent pipe provided for discharging the gas released to the gas phase space in the fining pipe out of the fining pipe.

  Therefore, in the present invention, in order to suppress aggregation of volatile components in the upper space of the aeration pipe, it is possible to suppress a temperature drop in the upper space of the aeration pipe and manufacture of a glass substrate capable of suppressing mixing of aggregates into molten glass. It is an object of the present invention to provide a method and an apparatus for producing a glass substrate.

One embodiment of the present invention is a method for producing a glass substrate, wherein fining of molten glass is carried out in a fining tube,
A melting step of melting a glass material to form a molten glass containing a fining agent;
The molten glass is supplied from the molten glass into the vapor phase space formed by the inner wall of the fining tube and the liquid surface of the molten glass by supplying the molten glass into the fining tube made of a material containing at least a part of a platinum group metal. A fining step of releasing gas and discharging the gas released into the gas phase space from the vent pipe connected to the fining tube to the outside of the fining tube;
Forming the clarified molten glass into a sheet glass,
In the fining step, the head space is formed by radiation heat emitted by the molten glass from the other end opposite to the one end where the vent pipe is connected to the fining pipe to the upper end of the other end. A heat-retaining member for heat-retaining, and releasing the gas from an open area provided in the upper space;
Furthermore, a heating element is provided in the upper space, and the heating element is heated so that the temperature of the upper space of the ventilating pipe is 1500 ° C. or higher.
It is characterized by

The heat retention member is opposed to the opening area of the other end of the ventilation pipe in the upper space.
Preferably, it is provided to cover the upper part of the upper space.

It is preferable that the heat retention member is provided at a position opposite to the opening area of the other end of the vent pipe in the upper space so as to cover the upper side of the upper space.

Another aspect of the present invention is a glass substrate manufacturing apparatus,
A melting tank for melting glass raw materials to make molten glass containing a fining agent,
A vapor phase space is formed between the inner wall and the liquid surface of the molten glass by supplying the molten glass at least a part of which is a material containing a platinum group metal, and the gas is generated from the molten glass in the vapor phase space The clear tube to be released,
A vent pipe connected to the fining tube and discharging the gas released to the gas phase space out of the fining tube;
The ventilating pipe is provided in an upper space formed above the other end from the other end opposite to the one end connected to the fining tube, and the upper space is kept warm by radiant heat emitted by the molten glass A heat retaining member,
And a forming device for forming the molten glass refined by the above-mentioned fining tube into sheet glass,
The heat retention member is provided at a position facing the opening area of the other end of the vent pipe in the upper space so as to cover the upper side of the upper space .
The upper space is provided with a heating element for heating so that the temperature of the upper space is 1500 ° C. or higher.
It is characterized by

  ADVANTAGE OF THE INVENTION According to this invention, it can suppress that the component containing the platinum group metal volatilized in a gaseous-phase space from a clarification pipe condenses, and it can suppress that an aggregate mixes in molten glass.

It is a figure which shows the flow of the manufacturing method of the glass substrate which is this embodiment. It is a figure which shows typically the apparatus which performs the melting process-cutting process of this embodiment. It is a figure which shows the external appearance of the clarification tank of this embodiment. It is a typical sectional view of a clarification tank shown paying attention to an aeration pipe. It is a top view of a brick heat retention member. It is a figure which shows an example of temperature distribution of the upper space of the ventilation pipe of this embodiment.

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

(Overall summary of glass substrate manufacturing method)
Hereinafter, the manufacturing method of the glass substrate of this embodiment, the manufacturing apparatus of a glass substrate, and the clarification tank of molten glass are demonstrated. FIG. 1: is a figure which shows an example of the process of the manufacturing method of the glass substrate of this embodiment.
Platinum or a platinum alloy described below is a platinum group metal, and includes platinum, ruthenium, rhodium, palladium, osmium, iridium, and an alloy of two or more of these.

  The glass substrate manufacturing method includes a melting step (ST1), a clarifying step (ST2), a homogenization step (ST3), a forming step (ST4), a slow cooling step (ST5), and a cutting step (ST6) , Mainly. In addition to this, it has a grinding process, a grinding process, a washing process, an inspection process, a packing process, etc., and a plurality of glass substrates stacked in the packing process are transported to a supplier of the delivery destination.

  The melting step (ST1) is performed in the melting tank. In the melting process, the glass material is melted to make molten glass. Preferably, a fining agent is added to the glass material. As the fining agent, tin oxide is preferably used from the viewpoint of environmental load reduction.

  The clarification step (ST2) is performed in a clarification tank. The molten glass is supplied into the fining tube of the fining vessel, which is made of platinum or platinum alloy or the like. In the clarification step, the molten glass in the clarification tube is heated. In this process, the fining agent releases oxygen by the reduction reaction and becomes a substance that later acts as a reducing agent. The bubbles containing O 2, CO 2 or SO 2 contained in the molten glass absorb and grow O 2 generated by the reducing reaction of the fining agent, float on the liquid surface of the molten glass, break and disappear. In this way, degassing by the redox reaction of the fining agent is performed. In the degassing performed in the clarification step (ST2), reduced-pressure degassing in which degassing is performed by reducing the gas phase space described later in the clarifying tube is removed. The vacuum degassing refers to degassing performed by reducing the pressure of the gas phase space to 500 to 35,000 Pa. For example, the temperature of the fining tube is set to 1200 to 1550 degrees.

  Thereafter, in the fining step (ST2), the temperature of the molten glass is lowered. In this process, the reducing agent obtained by the reducing reaction of the clarifying agent undergoes an oxidation reaction. As a result, gas components such as O 2 in the bubbles remaining in the molten glass are reabsorbed in the molten glass and the bubbles disappear. The clarification step (ST2) will be described in detail later.

  In the homogenization step (ST3), glass components are homogenized by stirring the molten glass in the stirring tank supplied through the pipe extending from the clarification tube using a stirrer.

In the forming apparatus, a forming process (ST4) and a slow cooling process (ST5) are performed.
In the forming step (ST4), molten glass is formed into sheet glass to make a flow of sheet glass. An overflow downdraw method or a float method can be used for forming. In the embodiment described later, an example in which the overflow downdraw method is used will be described.
In the slow cooling step (ST5), the sheet glass which has been formed and flows has a desired thickness, and is further cooled so as not to cause warpage so as not to cause internal distortion.

  In the cutting step (ST6), the sheet glass supplied from the forming device is cut into a predetermined length by a cutting device 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.

  The melting step (ST1) to the cutting step (ST6) are performed, for example, by the apparatus shown in FIG. FIG. 2 schematically shows an apparatus for performing the manufacturing method of the present embodiment. 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 202, a stirring tank 103, and glass supply pipes 104, 105, 106.

(Clarification process and Clarification tank)
Here, a clarification process (ST2) and a clarification tank are demonstrated. In the clarification step (ST2), during degassing, temperature control is further performed on the upper space of the vent pipe in order to suppress aggregation of the volatile components volatilized from the inner wall of the clarification tube. The clarification step (ST2) is performed by a clarification tank. The figure for demonstrating the clarification tank 202 to FIG. 3 and FIG. 4 is shown. FIG. 4 is a schematic cross-sectional view of the fining vessel 202 shown focusing on the vent pipe 212. The fining tank 202 includes a fining tube 202 a, a ventilation pipe 212, a heater (heating element) 221, a brick layer (structure) 222, and a brick heat retaining member 223.

(A) Finned tube The finned tube 202a is a cylindrical container made of, for example, platinum or a gold alloy, and the glass supply tubes 104 and 105 are connected to both ends in the longitudinal direction (left and right direction in FIG. 3). There is. In the fining tube used for vacuum degassing, a glass supply pipe is usually connected to the fining tube so as to extend downward from two points on the peripheral surface of the fining tube which forms the bottom of the fining tube. In the fining step (ST2), the molten glass G supplied from the glass feed pipe 104 into the fining pipe 202a is subjected to fining while flowing in the fining pipe 202a, and is transferred from the glass feed pipe 105 to the stirring tank 103. At this time, a gas phase space S, which is a space excluding the molten glass G, is formed in the upper part in the clarification tube 202a. In the gas phase space S, the gas bubbles B generated in the molten glass G float and break at the liquid surface, whereby the gas is released. The gas released into the gas phase space S is further discharged out of the fining tube 202 a through the venting tube 212.

  Disc-like flanges 202e and 202f are provided at the both ends in the longitudinal direction of the clarified tube 202a, and project outward from the surface of the clarified tube 202a. Electrodes (not shown) are attached to the flanges 202e and 202f, respectively, and the current from the electrodes is uniformly diffused on the circumference of the fining tube 202a. In the fining step (ST2), by supplying electricity between the two electrodes attached to the flanges 202e and 202f, the fining tube 202a generates heat and the molten glass G in the fining tube 202a is heated (direct electric heating) ). The flanges 202e and 202f are directly connected to the electrodes and are easily heated, and thus are cooled by water or air. Further, the position at which the flange is provided may not be at both ends in the longitudinal direction of the clarified tube 202a, and one or both may be provided at portions other than the ends of the clarified tube 202a, and is not particularly limited. The number of flanges is not limited to two, and three or more may be provided.

  In addition, even if it heats the fining tube 202a instead of the said direct current heating, it is performed by heating indirectly by the some heater which is arrange | positioned so that the brick layer 222 may be enclosed on the outer peripheral side of the brick layer 222. Good (indirect heating). The plurality of heaters are disposed along the longitudinal direction of the clarified tube 202 a so as to surround the brick layer 222 from the outer peripheral side.

  On the outer surface of the portion of the fining tube 202a in contact with the gas phase space S, temperature measuring means (not shown) is provided at a plurality of locations in the longitudinal direction. For example, a thermocouple is used as the temperature measurement means, but it is not particularly limited. For example, a radiation thermometer may be inserted into the gas phase space to measure the temperature. In the present specification, when referring to the temperature of the clarified tube 202a, it refers to the temperature of the portion of the clarified tube 202a in contact with the gas phase space S unless otherwise specified.

(B) Vent pipe The vent pipe 212 connects the gas phase space in the clarification pipe 202a to the atmosphere, and discharges the gas in the gas phase space and the inert gas intentionally introduced into the atmosphere. The aeration pipe 212 is provided at any position in contact with the gas phase space in the clarification pipe 202a. For example, it is provided at the top in the circumferential direction of the fining tube 202a. The shape of the vent pipe 212 is not particularly limited, but may be a chimney-like shape extending straight upward from the clarified tube 202a, or may be a bent shape. The vent pipe 212 is made of any of a material made of platinum or platinum alloy or the like, a heat-resistant brick, and a combination thereof. Tends to be heated by the temperature adjusting device, also, from the viewpoint of the foreign matter is prevented from falling into the refining tube 202a, the portion that is connected to at least finer tube 202a of the vent tube 212, made of platinum or platinum alloy It is preferably made of a material. When the vent pipe 212 is made of a material such as platinum or platinum alloy, a sprayed film may be formed on at least one of the inner surface and the outer surface of the vent pipe 212 to prevent volatilization of the vent pipe 212. It is preferable to provide.

Although the position in particular with respect to the clarification pipe | tube 202a in which the ventilation pipe 212 is provided is not restrict | limited, For example, it is provided in the longitudinal direction center of the clarification pipe | tube 202a. Only one vent pipe 212 may be provided, or two or more vent pipes may be provided. When three or more flanges are provided, one vent pipe 212 is provided, for example, between two flanges disposed adjacent to each other in the longitudinal direction.
The ventilation tube 212 is provided with a temperature measurement unit made of, for example, a thermocouple at one or a plurality of locations in the longitudinal direction (vertical direction in FIGS. 3 and 4). Preferably, the temperature measuring means is provided at least above the vent pipe 212.
Further, the upper space 212a is kept warm by receiving the radiant heat emitted by the molten glass G so that the temperature of the upper space 212a of the air flow pipe 212 is kept above the air flow pipe 212 so as not to decrease. Moreover, the brick heat retention member (brick cover) 223 which suppresses the flow of gas is provided. The brick heat retaining member 223 covers the upper space 212 a located above the vent pipe 212 and shields the vent pipe 212 and the outside of the clear pipe 202 a. In addition, the brick heat retaining member 223 receives the radiation heat emitted by the molten glass G to keep the upper space 212a warm, thereby suppressing aggregation of the volatile component volatilized from the portion in contact with the gas phase space. The upper space 212a is provided with an opening region 223a for flowing gas gas to the outside, and the gas in the upper space 212a is gradually released from the upper space 212a to the outside.

  Although the height of the vent pipe 212 is arbitrary, it is better to be low in order to suppress heat radiation from the vent pipe 212, preferably formed between the upper end of the vent pipe 212 and the lower end of the brick heat retaining member 223. Is lower than the height of the upper space 212a.

(C) Temperature regulator
The temperature control device is a device that performs temperature control on the upper space 212 a of the vent pipe 212. Temperature control can be performed using a temperature control device . The temperature adjustment device has, for example, a heater 221 shown in FIG. 4 and a control device (not shown) connected to the heater 221.
The heater 221 is not particularly limited as long as it can heat the upper space 212 a of the vent pipe 212, and a known heater such as a halogen heater or an electric heating coil, or a heating element is used. For example, as shown in FIG. 4, a plurality of heaters 221 are provided on the outer peripheral side of the upper space 212 a of the vent pipe 212. The heater 221 is connected to the control device, and is temperature controlled so that the temperature of the upper space 212a of the vent pipe 212 is kept within a predetermined temperature range in the fining process. In addition, the installation position and the number of installation of the heater 221 should just be able to control the temperature of the upper space 212a of the ventilation pipe 212, and are arbitrary.

  The control device is connected to the temperature measurement means provided in the upper space 212 a of the ventilation pipe 212 together with the above-described heater 221. The control device preferably performs feedback control on the heater 221 so that the temperature of the upper space 212a of the vent pipe 212 is maintained within a predetermined temperature range, using the temperature measured by the temperature measurement means. The predetermined temperature range will be described later.

(D) Brick Layer The brick layer 222 is a structure for keeping the molten glass in the clarified tube 202a warm, and is composed of a large number of heat resistant bricks provided to cover the clarified tube 202a from the outer peripheral side. The brick layer 222 has a heat-resistant brick (first brick) 222 a provided so as to surround the vent pipe 212 at the upper surface of the fin tube 202 a and the portion where the vent pipe 212 is connected to the clear pipe 202 a. doing. Heretofore, as the heat resistant brick 222a, a brick having a low thermal conductivity has preferably been used so that the clear tube 202a does not release heat. However, it is preferable that the heat-resistant brick 222a of this embodiment has a heat conductivity higher than the heat-resistant brick 222b (2nd brick) distribute | arranged to the other part. Since the heat resistant brick 222a is provided in contact with or close to the ventilation pipe 212 and the clarification pipe 202a, the heat of the clarification pipe 202a is easily transmitted to the ventilation pipe 212, and the temperature of the ventilation pipe 212 at the time of clarification is high. This is because the temperature can be maintained. The heat conductivity of the heat-resistant brick 222a is preferably, for example, 2 to 30 W / (m · K). Moreover, it is preferable that the heat conductivity of the heat-resistant brick 222b (2nd brick) is 0.05-15 W / (m * K), for example. Furthermore, the heat conductivity of the heat resistant brick 222a is preferably higher than that of the heat resistant brick 222b, and the ratio of the heat conductivity of the heat resistant brick 222a to the heat conductivity of the heat resistant brick 222b (second brick) is at least 3 times Is preferred.
In addition, the brick layer 222 may be formed by stacking heat-resistant bricks having a plurality of layers in the radial direction of the clarified tube 202a in the vertical direction (vertical direction in FIG. 4). In addition, if the first brick includes the heat-resistant brick 222a disposed at the connection portion , the first brick is disposed adjacent to the vertical direction or disposed adjacent to the lateral direction (horizontal direction in FIG. 4) You may be comprised by several heat-resistant bricks. Also, the heat resistant brick (first brick) 222a and the heat resistant brick (second brick) 222b do not have to be in direct contact with the clear tube 202a, and between the clear tube 202a and the heat resistant brick 222a and the heat resistant brick 222b May be provided with other refractories.

Further, the upper space 212a is kept warm by receiving the radiant heat emitted by the molten glass G so that the temperature of the upper space 212a of the aeration pipe 212 is kept above the aeration pipe 212 so as not to decrease. The brick heat retention member (brick cover) 223 which suppresses the flow of gas is provided. The brick heat retaining member 223 is made of a firebrick that constitutes the first brick 222a or the second brick 222b. FIG. 5 is a top view of the brick heat retaining member 223. As shown in FIG. The brick heat retaining member 223 heats the upper space 212 a by covering the upper space 212 a formed in the upper portion of the vent pipe 212. The vent pipe 212 connects the gas phase space in the clarification pipe 202a to the atmosphere, and discharges the gas in the gas phase space and the inert gas intentionally introduced into the atmosphere. That is, the temperature of the ventilation pipe 212 decreases as the distance from the clarification pipe 202a increases. When the volatile component containing platinum or a platinum alloy or the like touches the corresponding portion of the vent pipe lower in temperature than the surroundings, the volatile component tends to agglomerate in accordance with the temperature dependency of the saturated vapor pressure of the volatile component. For this reason, the brick heat retention member 223 which prevents the temperature fall of the upper space 212a of the aeration pipe 212 is provided by suppressing the flow of the gas which goes up the aeration pipe 212 before it touches the atmosphere. The brick heat retaining member 223 is configured to cover and cover the upper space 212a of the vent pipe 212, and is provided so as not to seal the upper space 212a. Therefore, the gas in the upper space 212a gradually flows from the space between the brick heat retaining member 223 and the first brick 222a to the external space, or the dust collector for discharging the dust in the upper space 212a to the outside It is gradually discharged to the external space by (not shown). As a result, the temperature of the gas in the upper space 212a and the upper space 212a does not rapidly decrease. Then, the brick heat retaining member 223 receives the radiant heat emitted by the molten glass G to generate heat, thereby keeping the upper space 212a warm, thereby suppressing aggregation.
The temperature of the gas rising in the ventilation pipe 212 falls as the temperature rises, but the gas rising in the ventilation pipe 212 shown by the arrow in FIG. 4 collides with the brick heat retaining member 223, and the upper space 212a of the ventilation pipe 212 Stay in the The brick heat retaining member 223 receives the radiant heat emitted by the molten glass G, the heat from the heater 221, and the heat from the gas, and the temperature decrease is suppressed. In addition, since the gas in the upper space 212a is not in direct contact with the atmosphere, the temperature decrease is suppressed. Further, the gas in the upper space 212a and the brick heat retaining member 223 are warmed by the heater 221 provided at a position adjacent to the upper space 212a of the vent pipe 212, and the temperature decrease rate is further suppressed. Thereby, aggregation of the volatile component containing platinum or a platinum alloy etc. is suppressed.

  In addition, the brick heat retention member 223 should just prevent temperature fall of gas so that it may become temperature more than aggregation of the volatile component containing platinum or platinum alloy etc. suppressed, before the gas which rose the ventilation pipe 212 contacts external air. It may be provided at any position of The brick heat retaining member 223 may be made of any refractory material having fire resistance and low thermal conductivity, or may be a structure in which a plurality of refractory materials having different heat retaining characteristics are stacked.

Here, with reference to FIG. 6, the temperature distribution which arises in the clarified tube 202a is demonstrated. FIG. 6 is a view schematically showing an example of a temperature distribution along the longitudinal direction of the temperature of the clarified tube 202a. This temperature distribution can be obtained, for example, using the measurement value by the above-mentioned temperature measurement means, but is not particularly limited, and can also be obtained by simulation.
In the portion (the vent pipe corresponding portion) in the longitudinal direction area where the vent pipe 212 is provided in the clarified pipe 202a, the temperature is greatly reduced. This is because the ventilating tube 212 is a tube projecting to a region close to the atmosphere, so the radiation of heat to the atmosphere is inevitable. Moreover, since the heat-resistant brick in contact with the clarifying tube 202a is disposed in the lower part of the venting tube 212, the heat of the clarified tube 202a is not easily transmitted to the ventilating tube 212. The temperature of the fining tube 202a is low at the vent pipe corresponding portion, and gradually increases as it goes away from the vent pipe 212 in the longitudinal direction. And in the part of the longitudinal direction area in which flange 202e, 202f was provided, temperature of fining tube 202a is low. This is because the heat is transmitted from the fining tube 202a to the flanges 202e and 202f and radiated to the outside. Moreover, it is because flange 202e, 202f is cooled. The temperature of this portion is lower than, for example, the vent pipe corresponding portion.
The fining tube 202a has such a temperature distribution. Specifically, the temperature difference between the highest temperature part and the lowest temperature part of the fining tube 202a is, for example, 50 ° C. or more, 150 ° C. or more, 250 ° C. or more.

  Thus, the temperature of the fining tube 202a is lower in the portion corresponding to the ventilating pipe where the ventilating pipe 212 is provided, as compared with the temperature around it. Therefore, when the volatile component containing platinum or a platinum alloy or the like touches the corresponding portion of the vent pipe lower in temperature than the surroundings, the volatile component is easily aggregated according to the temperature dependency of the saturated vapor pressure of the volatile component. For this reason, temperature control is performed on the upper portion 212 a of the vent pipe 212 and the vent pipe 212 so that the volatile components volatilized around the vent pipe corresponding portion do not condense even if the low temperature vent pipe 212 is touched. By performing such temperature control, the saturated vapor pressure of the volatile component in the ventilation pipe 212 and in the peripheral area of the ventilation pipe 212 is increased, and thereby, the inside of the ventilation pipe 212 and the peripheral area of the ventilation pipe 212 and the other air The saturated vapor pressure difference between the inside of the phase space is reduced, and the aggregation of volatile components is suppressed. Therefore, it is possible to avoid that the aggregates deposited on the inner wall of the fining tube 202a in the ventilating tube 212 and in the peripheral region of the ventilating tube 212 fall into the molten glass G and cause the quality deterioration of the glass substrate. In addition, in order to prevent that an aggregate falls to molten glass G, a receiving part can also be provided in the ventilation pipe 212. FIG. About the structure of a receiving part, the said content is taken into consideration including the content described in Unexamined-Japanese-Patent No. 2014-47124.

Returning to the explanation of the clarification step (ST2), the temperature adjustment is preferably performed so that the temperature difference between the portion (highest temperature portion) where the temperature of the clarification tube 202 is the highest (maximum temperature portion) and the ventilation tube 212 is within 300 ° C. The highest temperature portion is a portion of the plurality of temperature measurement means attached to the clarified tube 202a, which has the highest temperature measured, attached thereto. Further, as the temperature of the vent pipe 212, when the vent pipe 212 is provided with a plurality of temperature measurement means, the temperature measured at the position farthest from the clear pipe 202a among them is used. By adjusting the temperature so that the above temperature difference is within 300 ° C., the saturated vapor pressure difference of volatile components such as platinum or platinum alloy becomes smaller between the fining tube 202 a and the vent pipe 212, and volatilization from the fining tube 202 a Aggregation of volatile components is suppressed. The temperature difference is more preferably within 200 ° C., further preferably within 100 ° C.
The lower limit value of the temperature difference is not particularly limited, but is, for example, 0 ° C., that is, a temperature at which there is no temperature difference between the highest temperature portion of the clarified tube 202 a and the ventilation tube 212. For example, the temperature difference between the temperature at which the temperature of the ventilation tube 21 is lower than the temperature of the highest temperature portion of the clarification tube 202a and the temperature at the highest temperature of the clarification tube 202a (the highest temperature portion) It is preferable that it is 300 degreeC, More preferably, it is 0-200 degreeC, More preferably, it is 0-100 degreeC. In addition, you may temperature-control so that the temperature of the ventilation pipe 21 may become higher than the temperature of the highest temperature part of the clarification pipe 202a. However, if the temperature of the vent pipe 212 becomes too high, the vent pipe 212 is easily deformed if it is made of a material such as platinum or a platinum alloy. For this reason, it is preferable that the temperature of the ventilation pipe 212 does not exceed the maximum temperature of the clarification pipe 202a.

  When performing temperature control so that it may become the said temperature difference, it is preferable that the ventilation pipe 212 is heated by 1450 degreeC or more. This is because volatile components such as platinum or a platinum alloy easily aggregate at 1400 ° C. or less. The heating temperature of the aeration pipe 212 is more preferably 1500 ° C. or more, and still more preferably 1600 ° C. or more. The upper space 212a of the vent pipe 212 is preferably heated to 1450 ° C. or higher, more preferably 1500 ° C. or higher.

This embodiment is suitable for the case where the temperature of the highest temperature portion of the fining tube 202a is 1600 ° C. or higher in the fining step (ST2). When the temperature of the fining tube 202a is 1600 ° C. or more, bubbles are easily generated in the molten glass when tin oxide is used as the fining agent, and the viscosity of the molten glass is lowered, which is preferable. Platinum or a platinum alloy is easily volatilized, and the above-mentioned aggregation problem is apt to occur. In particular, the direct electric heating to the above-mentioned fining tube 202a makes it easy to raise the temperature of the fining tube 202a and the temperature control of the molten glass becomes easy, but the temperature of the fining tube 202a may be too high. When the temperature of the fining tube 202a is too high, platinum or a platinum alloy is easily volatilized, and the above problem is likely to occur. In the present embodiment, even in such a case, aggregation of the volatile component is suppressed by performing the temperature adjustment.
The aggregation of the volatile components is more pronounced when the temperature of the highest temperature portion of the clarified tube 202a is 1630 ° C. or higher, and more significantly when the temperature is 1650 ° C. or higher. It is suitable. The upper limit of the temperature of the highest temperature portion of the fining tube 202a is preferably 1720 ° C. or less so that platinum, platinum alloy or the like does not melt.

Further, in the clarification step (ST2), the pressure of the gas phase space S may be higher than the pressure of the atmosphere outside the clarification tube 202a. Such a pressure difference can be obtained by promoting the release of gas into the gas phase space S by degassing in the fining tube 202a and by raising the temperature of the fining tube 202a. As a result, the volatile component containing platinum or platinum alloy can be easily discharged out of the fining tube 202a together with other gases in the gas phase space S. As a result, the concentration of volatile components in the gas phase space S can be lowered to suppress aggregation. Further, by generating the pressure difference, the flow velocity of the gas passing through the vent pipe 212 can be increased, and the volatile component can be discharged to the outside of the clarification tube 202a before the volatile component is condensed. Note that the pressure of the external atmosphere is, for example, atmospheric pressure.
Alternatively, a suction device (not shown) may be connected to the vent pipe 212 so that volatile components including platinum or platinum alloy can be quickly discharged from the vent pipe 212 together with other gases in the gas phase space S. At this time, the pressure in the gas phase space S is lower than the atmospheric pressure or the pressure of the external atmosphere surrounding the fining vessel 103. Specifically, the pressure in the gas phase space S may be more than 0 to 10 Pa smaller than the atmospheric pressure (0 Pa <atmospheric pressure−pressure in the gas phase space <10 Pa).

  In the fining step (ST2), an inert gas may be further supplied into the gas phase space S. The inert gas is not particularly limited as long as it is inert to the molten glass G, and nitrogen or a noble gas is used. For the supply of the inert gas, for example, a gas supply pipe (not shown) is provided in the vicinity of the portion of the clarification pipe 202a provided with the flanges 202e and 202f. The gas supply pipe is connected to an external gas supply source to supply an inert gas into the gas phase space S. By thus supplying the inert gas into the fining tube 202a, the partial pressure of oxygen for volatilizing platinum or platinum alloy can be reduced in the gas phase space S, and volatilization of platinum or platinum alloy can be suppressed. Aggregation of volatile components can be suppressed.

(Glass composition)
As such a glass substrate, the glass substrate of the following glass compositions is illustrated. Therefore, the glass material is used so that the glass substrate has the following glass composition.
SiO ₂ : 55 to 75 mol%,
Al ₂ O ₃ : 5 to 20 mol%,
B ₂ O ₃ : 0 to 15 mol%,
RO: 5 to 20 mol%
(R is all elements contained in the glass substrate among Mg, Ca, Sr and Ba),
R ′ ₂ O: 0 to 0.8 mol% (R ′ is all elements contained in the glass substrate among Li, K, and Na). The glass is an example of a glass having a high temperature viscosity. In such a glass, the molten glass is heated to a high temperature in order to degas at the appropriate viscosity of the molten glass in the fining tube 102a. For this reason, a large amount of volatile components volatilizes from the inner wall of the clarification tube 102a, and the aggregation of the volatile components becomes a problem. In such a case, the effect of the present embodiment for suppressing aggregation of volatile components such as platinum or platinum alloy is remarkable.
At this time, it contains at least one of SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ and RO (R is all elements contained in the glass substrate among Mg, Ca, Sr and Ba), and the molar ratio ((2 × SiO ₂ ) + Al ₂ O ₃ ) / ((2 × B ₂ O ₃ ) + RO) may be 4.0 or more. That is, a glass having a molar ratio ((2 × SiO ₂ ) + Al ₂ O ₃ ) / ((2 × B ₂ O ₃ ) + RO) of 4.0 or more is an example of a glass having a particularly high high temperature viscosity. Therefore, the effect of the present embodiment for suppressing the aggregation of volatile components such as platinum or platinum alloy is more remarkable. Moreover, since the glass viscosity tends to increase as the content of the alkali metal oxide decreases, the glass having 0 to 0.8 mol% of R ′ ₂ O, which is the total amount of the alkali metal oxide, is particularly viscous. high. Although it is necessary to raise the temperature of the fining tank temperature (platinum or platinum alloy) in order to sufficiently clarify high viscosity glass, even in the case of producing such high viscosity glass, the present embodiment The effect of suppressing aggregation of volatile components such as platinum or platinum alloy can be obtained by applying

The manufacturing method is suitable for manufacturing a glass substrate for flat panel display. In other words, it is suitable in the case of performing the fining of the molten glass which has a glass composition of the glass substrate for flat panel displays in a fining process. Because the glass composition of these glass substrates is high in viscosity as compared to glasses for other uses, it is necessary to raise the temperature of the molten glass in order to obtain a sufficient bubble floating speed in the fining step. Therefore, although a clear tube made of platinum or a platinum alloy is preferably used, platinum or a platinum alloy or the like easily volatilizes under high temperature as described above. Even in the case of performing such fining of molten glass, in the present embodiment, aggregation of platinum and the like volatilized from the fining tube can be suppressed by the above-described temperature control. Moreover, this manufacturing method is suitable for manufacture of the glass substrate for liquid crystal displays in which it is calculated | required that content of an alkali metal oxide is very small. Similarly, it is suitable also for manufacture of the glass substrate for organic electroluminescent displays.
In addition, the glass substrate manufactured in the present embodiment can be applied to a cover glass, a glass for a magnetic disk, a glass substrate for a solar cell, and the like.

Further, the effect of suppressing the aggregation of volatile components such as platinum or platinum alloy of the present embodiment is remarkable not only in the case of using the above-mentioned high-temperature viscous glass but also in the case of using a high melting temperature glass. For example, in the case of producing a glass having a temperature of 1,500 ° C. or higher when the viscosity which is an index of the melting temperature is 10 ^2.5 poise, the aggregation of the volatile component such as platinum or platinum alloy of the present embodiment is suppressed. Effect is noticeable.

The strain point of the glass substrate may be 650 ° C. or more, more preferably 690 ° C. or more. Further, the glass having a high strain point tends to have a high temperature of the molten glass at a viscosity of 10 2 ⁵ poise, so the effect of the present embodiment becomes remarkable.

In addition, when the glass material is melted so that the temperature of the molten glass when the viscosity is 10 ^2.5 poise, containing tin oxide, the effect of the present embodiment becomes more remarkable, and the viscosity is 10 The temperature of the molten glass when it is ^2.5 poises is, for example, 1500 to 1700 ° C, and may be 1550 to 1650 ° C.

  Furthermore, the volatilization of platinum or platinum alloy according to this embodiment is also performed on a thin glass substrate, for example, a glass substrate having a thin plate thickness of 0.5 mm or less, 0.3 mm or less, or 0.1 mm or less. The effect of suppressing the aggregation of the components is remarkable as compared to a thick glass substrate. A part of the aggregate such as platinum or platinum alloy aggregated on the inner wall of the fining tube 102a etc. as fine particles falls into the molten glass and is mixed in the molten glass and contained in the glass substrate. In this case, as the thickness of the glass substrate is thinner, fine particles to be defective are often located on the surface of the glass substrate. When fine particles located on the surface of the glass substrate are separated in the panel manufacturing process using the glass substrate, the separated parts become concave parts, and the thin film formed on the glass substrate is not uniformly formed, and causes display defects on the screen . Therefore, the effect of suppressing aggregation of volatile components such as platinum or platinum alloy in the clarified tube 102a as in the present embodiment becomes larger as the thickness of the glass substrate becomes thinner.

  In addition, although the example applied to the clarification tank 102 was shown in this embodiment, it is also applicable to the stirring tank 103 which homogenizes molten glass. In this case, the lower temperature portion of the inner wall of the stirring tank 103 is often the connecting portion between the ceiling wall and the side wall of the stirring tank 103. In this case, it is preferable to supply an inert gas into the gas phase space from the connection portion. At this time, the gas or gas in the gas phase space can flow to the outside from the gap between the stirring tank 103 and the stirrer 103a.

As mentioned above, although the manufacturing method of the glass substrate of the present invention, the clarification tank of molten glass, and the manufacturing device of a glass substrate were explained in detail, the present invention is not limited to the above-mentioned embodiment, In the range which does not deviate from the main point of the present invention Of course, various improvements and modifications may be made.
In the fining tube, at least a part of the portion in contact with the gas phase space during fining may be made of a material composed of platinum or a platinum alloy.

(Example)
Using a tin oxide as a fining agent, while using the fining tank shown in FIG. 3, fining of the molten glass is performed and the temperature control of the above embodiment is performed, and after fining, it is 2270 mm × 2000 mm, and the thickness is 0.5 mm. It shape | molded to sheet glass of this, and produced 100 glass substrates (Example). Temperature adjustment was performed by heating the upper space of the platinum ventilation tube 212, and the temperature of the upper space 212a of the ventilation tube 212 was maintained at 1500 ° C. The temperature of the highest temperature portion of the fining tube was 1650 ° C., and the temperature difference between the highest temperature portion of the vent pipe and the fining tube was 100 ° C. The clearing time was 1 hour. Further, the glass composition of the glass substrate is the total of SiO ₂ 66.6 mol%, Al ₂ O ₃ 10.6 mol%, B ₂ O ₃ 11.0 mol%, MgO, CaO, SrO and BaO. The temperature of the molten glass was 1570 ° C. when it was mol%, the strain point was 660 ° C., and the viscosity was 10 ^2.5 poise.
On the other hand, the molten glass was refined in the same manner as the above example except that the temperature adjustment to the upper space of the ventilation tube 212 was not performed (comparative example). In the comparative example, the temperature of the vent pipe at the time of fining was 1300 ° C., and the temperature difference between the vent pipe and the highest temperature portion of the fining tube was 350 ° C. When the presence or absence of platinum foreign substances in the glass substrates of Examples and Comparative Examples was visually confirmed, in the Examples, the number of glass substrates in which platinum foreign substances were confirmed could be reduced to 1/6 of that of Comparative Examples.

  From the above results, it was confirmed that the effect of suppressing aggregation of volatile components such as platinum or platinum alloy can be obtained by using the temperature control (brick heat insulating member and heater) shown in the present invention.

202 Clearing tank 202a Clearing tube 212 Ventilation tube 221 Heater 222 Brick layer 223 Brick heat retention member B Air bubble G Fused glass S Gas phase space

Claims (4)

A method of producing a glass substrate, wherein the fining of a molten glass is performed in a fining tube,
A melting step of melting a glass material to form a molten glass containing a fining agent;
The molten glass is supplied from the molten glass into the vapor phase space formed by the inner wall of the fining tube and the liquid surface of the molten glass by supplying the molten glass into the fining tube made of a material containing at least a part of a platinum group metal. A fining step of releasing gas and discharging the gas released into the gas phase space from the vent pipe connected to the fining tube to the outside of the fining tube;
Forming the clarified molten glass into a sheet glass,
In the fining step, the head space is formed by radiation heat emitted by the molten glass from the other end opposite to the one end where the vent pipe is connected to the fining pipe to the upper end of the other end. A heat-retaining member for heat-retaining, and releasing the gas from an open area provided in the upper space;
Furthermore, a heating element is provided in the upper space, and the heating element is heated so that the temperature of the upper space of the ventilating pipe is 1500 ° C. or higher.
The manufacturing method of the glass substrate characterized by the above.   The method for manufacturing a glass substrate according to claim 1, wherein the heat retention member is provided at a position facing the opening area of the other end of the vent pipe in the upper space so as to cover the upper side of the upper space. . The height of the ventilation tube is less than the height of the upper space,
The manufacturing method of the glass substrate of Claim 1 or 2. A melting tank for melting glass raw materials to make molten glass containing a fining agent,
A vapor phase space is formed between the inner wall and the liquid surface of the molten glass by supplying the molten glass at least a part of which is a material containing a platinum group metal, and the gas is generated from the molten glass in the vapor phase space The clear tube to be released,
A vent pipe connected to the fining tube and discharging the gas released to the gas phase space out of the fining tube;
The ventilating pipe is provided in an upper space formed above the other end from the other end opposite to the one end connected to the fining tube, and the upper space is kept warm by radiant heat emitted by the molten glass A heat retaining member,
And a forming device for forming the molten glass refined by the above-mentioned fining tube into sheet glass,
The heat retention member is provided at a position facing the opening area of the other end of the vent pipe in the upper space so as to cover the upper side of the upper space.
The upper space is provided with a heating element for heating so that the temperature of the upper space is 1500 ° C. or higher.
An apparatus for manufacturing a glass substrate characterized by

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