JP2013216520A - Method for manufacturing glass substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a glass substrate, which can improve quality of glass articles by eliminating causes of striae and devitrification.SOLUTION: In a method for manufacturing a glass substrate including a defoaming step, a transfer pipe 40 for sending molten glass from a clarifying vessel 30 to a next step is connected to an exit side from which molten glass is flowed out from the clarifying vessel 30. In addition, the method includes a liquid level adjusting step of adjusting a flow rate of the molten glass so that the molten glass is at a predetermined liquid level when the molten glass containing a clarifying agent is passed through the clarifying vessel 30. Further, the transfer pipe 40 is provided to such a position that the molten glass in the vicinity of its upper surface of the molten glass flowing in the clarifying vessel 30 is flowed into the transfer pipe 40 without stagnation in the vicinity of the exit when the molten glass at a predetermined liquid level is passed.

Description

  The present invention relates to a method for manufacturing a glass substrate, in which a glass substrate is manufactured by molding a molten glass produced by melting a glass raw material.

A glass substrate is generally manufactured through a process of forming molten glass from a glass raw material and then forming the molten glass into a glass substrate. Each of the above steps is appropriate in, for example, a melting apparatus for melting glass material, a clarification tank for removing minute bubbles contained in molten glass, a stirring tank for homogenizing glass components, a molding apparatus for forming a glass substrate, and the like. It is done by processing. The apparatus for manufacturing the glass substrate is connected by a transfer pipe for transferring the glass raw material.
During the above steps, the step of removing minute bubbles contained in the molten glass as necessary is called clarification, and this clarification tank main body (hereinafter also simply referred to as the main body) while heating the main body of the tubular clarification tank. This is carried out by passing a molten glass containing a clarifying agent such as As ₂ O _{3 and} removing bubbles in the molten glass by an oxidation-reduction reaction of the clarifying agent. More specifically, the temperature of the molten glass that has been melted further is raised to allow the fining agent to function and the bubbles to float and defoam, and then the temperature is lowered to melt relatively small bubbles that remain without being defoamed. The glass is made to absorb. That is, clarification includes a process for floating and defoaming bubbles (hereinafter also referred to as a defoaming process or a defoaming process) and a process for absorbing small bubbles into molten glass (hereinafter also referred to as an absorption process or an absorption process).
Conventionally, As ₂ O ₃ has been commonly used as a fining agent, but SnO ₂ , Fe ₂ O _{3 and the} like have come to be used from the viewpoint of environmental load in recent years.

In order to mass-produce high-quality glass substrates from high-temperature molten glass, it is desirable to consider that foreign substances that cause defects in the glass substrate are not mixed into the molten glass from any apparatus that manufactures the glass substrate. It is. For this reason, in the process of manufacturing the glass substrate, the inner wall of the member in contact with the molten glass needs to be made of an appropriate material according to the temperature of the molten glass in contact with the member, the required quality of the glass substrate, and the like. For example, it is known that a platinum group metal such as platinum or a platinum alloy is usually used as the material constituting the clarification tank body (Patent Document 1). Platinum or a platinum alloy is expensive but has a high melting point and excellent corrosion resistance against molten glass.
Although the temperature which heats a clarification tank main body at the time of a defoaming process changes with compositions of the glass substrate which should be shape | molded, it is about 1000-1650 degreeC.
The glass raw material, if it is appropriately adjusted according to the composition of the glass substrate to be produced, to produce a glass substrate used as the LCD substrate for example, the glass _{composition, SiO 2, B 2 O 3} , Al 2 O _3, composed MgO, CaO, SrO, BaO, a RO or the like.
In the present specification, the notation “melting” uses the common kanji character “melting”, but it has the same meaning as that described as “melting”.

JP 2006-522001 Gazette

When the molten glass stays in the vicinity of the outlet of the clarification tank described above, the molten glass is kept at a high temperature in the clarification tank for a long time. A silica (SiO ₂ ) -rich heterogeneous substrate having a relatively small specific gravity is generated in the vicinity of the surface. When the silica-rich heterogeneous substrate is generated in a part of the molten glass, there is a problem in that defects such as striae and devitrification occur in the glass product.
Moreover, when foreign materials other than the glass material are mixed in the molten glass, it can cause the above-mentioned striae and devitrification. For example, when a glass raw material is melted at a high temperature using a melting furnace using a high zirconia refractory, a part of zirconia is mixed into the molten glass from the melting furnace, and a glass having a relatively large specific gravity may be generated. is there.
In view of the above points, the present invention provides a glass substrate manufacturing method capable of solving the above-mentioned problems that are one of the causes of striae and devitrification in the glass substrate manufacturing process and improving the quality of glass products. It is something to try.

In order to achieve the above-described object, the present invention provides a glass substrate including a defoaming step of performing a defoaming process by passing a molten glass in which a fining agent is blended in a clarification tank body while heating the clarification tank body. A manufacturing method, which is configured as follows.
The clarification tank is made of a platinum group metal, and is provided with a transfer pipe for feeding molten glass from the clarification tank to the next step on the outlet side where the molten glass flows from the clarification tank.
Moreover, when passing the molten glass which mix | blended the clarifying agent with the above-mentioned clarification tank, it has the liquid level adjustment process which adjusts the flow volume of a molten glass so that the liquid level of a molten glass may become a predetermined liquid level.
In addition, when passing the molten glass of a predetermined liquid level, the molten glass near the upper surface of the molten glass flowing in the clarification tank flows to the transfer pipe without staying in the vicinity of the outlet. Install a transfer pipe.
Moreover, it is preferable that the lower part of the transfer pipe is positioned at least 30 mm or more on the upper side with respect to the bottom part of the clarification tank.

  According to the method for producing a glass substrate of the present invention, the position of the transfer pipe connected to the clarification tank is set at a position where the molten glass does not stay in the clarification tank. Silica-rich heterogeneous substrate that cannot be produced is not generated. Further, if the lower part of the transfer pipe is positioned at least 30 mm or more above the bottom of the clarification tank, even if a foreign glass is melted and a molten glass having a relatively high specific gravity is generated, it is behind the clarification tank. Therefore, it is possible to prevent foreign matter mixed in the molten glass from causing defects in the glass product. Therefore, the quality of the glass product can be improved.

It is a schematic block diagram of the glass substrate manufacturing apparatus for demonstrating the manufacturing method of the glass substrate of embodiment. It is the schematic which shows the basic composition of a clarification tank. It is the schematic of the clarification tank 30 and the transfer pipe 40 connected to this. It is explanatory drawing of the subject which arises when the position of the transfer pipe | tube 40 differs from the thing of this invention.

  Hereinafter, embodiments of the method for producing a glass substrate of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram for explaining a glass substrate manufacturing method according to an embodiment, and shows a basic flow in manufacturing a glass substrate in a simplified manner.
The glass substrate manufacturing apparatus 100 includes a melting furnace 10 that heats a glass raw material to produce molten glass, a clarification tank 30 that clarifies molten glass, a molding apparatus (not shown) that molds molten glass, and a space between them. The transfer pipes 20 and 40 are connected to each other. The transfer pipe 20 connects the melting furnace 10 and the clarification tank 30, and supplies the molten glass derived from the melting furnace 10 to the clarification tank 30. The transfer pipe 40 connects the clarification tank 30 and a molding apparatus (not shown), and supplies the molten glass derived from the clarification tank 30 to the molding apparatus (not shown). In addition, between the clarification tank 30 and a shaping | molding apparatus, the stirring tank for stirring and homogenizing a molten glass may be arrange | positioned. The arrow indicates the direction in which the molten glass flows.

The glass raw material thrown into the melting furnace 10 is appropriately prepared according to the composition of the glass substrate to be manufactured. As an example, when producing a glass substrate used as a TFT type LCD substrate, the glass composition constituting the glass substrate is displayed in mass%,
SiO _2: 50~70%,
Al ₂ O _3: 0~25%,
B ₂ O ₃ : 1 to 15%,
MgO: 0 to 10%,
CaO: 0 to 20%,
SrO: 0 to 20%,
BaO: 0 to 10%,
RO: 5 to 30% (where R is the total amount of Mg, Ca, Sr and Ba),
It is preferable that it is an alkali free glass containing.
Although the alkali-free glass is used in this embodiment, the glass substrate may be a glass containing a trace amount of alkali containing a trace amount of alkali metal. When an alkali metal is contained, the total of R ′ ₂ O is 0.10% or more and 0.5% or less, preferably 0.20% or more and 0.5% or less (where R ′ is selected from Li, Na, and K) It is preferable that the glass substrate contains at least one kind. Of course, the total of R ′ ₂ O may be less than 0.10%.
Also, when applying the method of manufacturing a glass substrate of the present invention, the glass composition, in addition to the above components, and in _wt%, SnO 2: 0.01~1% (preferably 0.01 _{~0.5%), Fe 2 O 3} : 0~0.2% ( preferably containing from 0.01 to 0.08 percent), taking into account the environmental _{impact, As 2 O 3, Sb 2} O 3 And you may prepare a glass raw material so that PbO may not be included substantially.

The molten glass generated in the melting furnace 10 is sent to the clarification tank 30 through the transfer pipe 20. In the clarification tank 30, the molten glass is kept at a predetermined temperature (in the case of glass having the above composition, for example, 1500 ° C. or higher), and clarification including a defoaming step for removing bubbles contained in the molten glass is performed.
Further, the molten glass clarified in the clarification tank 30 is sent to the molding apparatus via the transfer pipe 40. The molten glass is cooled in the transfer pipe 40 when it is sent from the clarification tank 30 to the molding apparatus so as to have a temperature suitable for molding (for example, about 1200 ° C. in the case of glass having the above composition). In the forming apparatus, molten glass is formed into a glass substrate.

Next, clarification including a defoaming step will be described with reference to FIG. FIG. 2 is a schematic view showing the basic configuration of the clarification tank 30, and shows the inside transparently.
The clarification tank 30 is mainly composed of a clarification tank main body (hereinafter also referred to as a main body) 1 and heater electrodes 1 a and 1 b connected to the main body 1. The main body 1 is a metal tube of platinum alloy such as platinum or platinum rhodium alloy, and generally has a cylindrical shape. The clarification tank body 1 has a cylindrical shape, and its inner diameter is usually set to be 30% -40% or more larger than the inner diameters of the transfer pipes 20 and 40. In this way, the flow rate of the molten glass MG flowing in the main body 1 is lowered and the time during which the molten glass MG stays in the main body 1 is lengthened, whereby the molten glass MG is efficiently clarified. The molten glass MG flows through the inside of the main body 1 using the pipe line of the main body 1 as a flow path. The heater electrodes 1a and 1b flow current from the outer peripheral wall surface of the main body 1 to the main body 1 and heat the outer peripheral wall of the main body 1 using Joule heat generated by the resistance of the main body 1 to bring the temperature of the molten glass MG to a predetermined temperature. The defoaming of the molten glass MG is performed by using a fining agent mixed with the molten glass MG.

The molten glass MG flowing through the inside of the main body 1 does not flow through the entire flow path cross section of the main body 1, but normally, the bubbles degassed by the defoaming process of the molten glass MG are released above the inside of the main body 1. The gas phase space a exists. In addition, a gas discharge port (not shown) is provided in the upper part of the main body 1 for releasing the gas component in the bubbles released from the gas phase space a to the atmosphere.
The gas phase space a can have a predetermined size by adjusting the liquid level of the molten glass MG flowing through the main body 1 of the clarification tank 30. It is also possible to hold a gas space a having a certain size.

Next, the manufacturing method of the glass substrate of this invention is demonstrated in detail using FIG.
In this invention, in the manufacturing method of the glass substrate including the above-mentioned defoaming process, the transfer pipe 40 for sending molten glass from the clarification tank 30 to the next process is connected to the outlet side from which the molten glass flows out of the clarification tank 30. It is prepared. Moreover, when passing the molten glass which mix | blended the clarifier in the clarification tank 30, it has the liquid level adjustment process which adjusts the flow volume of a molten glass so that the liquid level of a molten glass may become a predetermined liquid level.
Moreover, when passing the molten glass of a predetermined liquid level, the molten glass near the upper surface of the molten glass flowing in the clarification tank 30 flows into the transfer pipe 40 without staying in the vicinity of the outlet. The transfer pipe 40 is installed at the position.

Specifically, in this embodiment, the transfer pipe 40 is provided so that the liquid level h of the molten glass at a predetermined liquid level in the clarification tank 30 matches the position of the upper part 40a of the transfer pipe.
If the position where the transfer pipe 40 is provided is set as described above, the molten glass flows to the transfer pipe 40 without staying in the vicinity of the outlet of the clarification tank 30, so that a silica-rich heterogeneous substrate is generated on the surface of the molten glass. There is nothing to do.
Even if the liquid level h of the molten glass does not coincide with the position of the upper portion 40a of the transfer pipe, the above-described staying can be achieved by installing the transfer pipe 40 so that the molten glass flowing through the transfer pipe 40 is below the liquid level h. It doesn't happen, but it can cause another problem.

The other problem will be described with reference to FIG. When the transfer tube is installed so that the upper part 40a is above the liquid level h, the upper surface of the molten glass MG comes into contact with air. Therefore, the molten glass component that has come into contact with air volatilizes.
On the other hand, when the liquid level h of the molten glass and the position of the upper portion 40a of the transfer pipe are matched as in the present invention, the molten glass flowing from the clarification tank 30 flows through the entire flow path cross section in the transfer pipe 40. Therefore, the molten glass does not come into contact with air. Therefore, it can prevent that a molten glass component touches air and volatilizes.

Although it is desirable that the liquid level of the molten glass in the clarification tank 30 and the position of the transfer pipe upper part 40a coincide with each other, the difference between the liquid level of the molten glass MG in the clarification tank 30 and the upper part 40a of the transfer pipe is within 20 mm. If it exists, it can be said that it is in a preferable range. Further, the above difference is more preferably within 15 mm, and most preferably within 5 mm.
If the above-mentioned difference is within these ranges, the molten glass MG flows into the transfer pipe 40 without staying, and the upper surface of the molten glass MG is less likely to come into contact with air. For this reason, if the above-mentioned difference is in the above-mentioned range where these effects can be expected, it is included in the expression of the present invention that the liquid level of the molten glass coincides with the position of the upper portion of the transfer tube 40. .

In order to always keep the liquid level h and the position of the upper portion 40a of the transfer pipe within the above-mentioned difference, the liquid level of the molten glass MG is set to a predetermined liquid level (this embodiment) in the glass substrate manufacturing process. In the embodiment, it is necessary to have a liquid level adjusting step of adjusting the flow rate of the molten glass so as to be h).
Various suitable methods are conceivable for adjusting the liquid level. For example, the liquid level is measured by using a laser displacement meter, and adjusted by a method such as increasing or decreasing the amount of the glass material to be introduced into the melting furnace 10. It is possible.

Moreover, in this embodiment, the lower part 40b of the transfer pipe 40 was located at least 30 mm or more upper part side with respect to the bottom part 30b of the clarification tank 30 (FIG. 3). If the position of the lower part 40b of the transfer pipe 40 is as described above, even if foreign matter enters the molten glass and enters the clarification tank 30, the foreign substance flows into the transfer pipe 40 and is carried to the subsequent process. Can be prevented. In particular, when the melting furnace 10 for melting the glass material is composed of a high zirconia refractory, zirconia is likely to be mixed into the molten glass. For this reason, the molten glass mixed with zirconia flows into the clarification tank 30. However, since zirconia has high specific gravity with respect to the component of molten glass, the zirconia mixed in the molten glass precipitates in the bottom part 30b of the clarification tank 30 which flowed in. FIG. 3 schematically shows a zirconia precipitate Z. In this embodiment, since the lower part 40b of the transfer pipe 40 is located at least 30 mm or more on the upper side with respect to the bottom part 30b of the clarification tank 30, there is little possibility that the zirconia precipitate Z flows into the transfer pipe 40. .
Further, in the present embodiment, a zirconia discharge outlet 30c is provided in the bottom 30b near the outlet of the clarification tank 30, so that the zirconia precipitate Z can be discharged as necessary. The discharge port 30c may be configured using, for example, a drain pipe.

As can be understood from the above description, according to the glass substrate manufacturing method of the present invention, the molten glass passing through the clarification tank body flows to the transfer pipe 40 without staying. For this reason, generation | occurrence | production of the silica rich heterogeneous base resulting from retention of a molten glass is not produced. Further, even when foreign matter such as zirconia melted from the melting furnace 10 is mixed into the molten glass and flows into the clarification tank, the position of the lower portion 40b of the transfer pipe 40 is set higher than the bottom 30b of the clarification tank 30. Therefore, there is little possibility that the mixed foreign matter will flow to the subsequent process.
Therefore, the quality of the glass product can be improved.

By the way, it is known that the glass substrate has different temperatures at which the clarification action is effectively exhibited depending on the clarifier used. For example, As ₂ O ₃ (arsenous acid) is excellent in the ability to remove bubbles, and the refining temperature is sufficient in the range of about 1500 ° C. or more. However, since arsenous acid has a high environmental load, SnO ₂ (tin oxide) or the like has recently been used as a refining agent that does not have a high environmental load as described above. However, tin oxide has a weaker ability to release bubbles during the defoaming process than arsenous acid, so it is necessary to lower the viscosity of the glass to increase the defoaming effect, and therefore it is necessary to clarify at a high temperature. is there. For example, when tin oxide is used as a fining agent, the temperature is raised to 1600 ° C. to 1700 ° C., preferably 1630 ° C. to 1710 ° C., more preferably 1630 ° C. to 1720 ° C. That is, it is necessary to raise the temperature of the clarification tank 30 to near the heat resistance temperature of platinum or platinum alloy of the main body 1 constituting the clarification tank 30. When the above-mentioned high temperature is required as the refining temperature, since the boric acid (B ₂ O ₃ ) is easily volatilized from the molten glass, a silica-rich heterogeneous substrate is likely to be generated.
The present invention is therefore particularly suitable for the production of glass substrates using tin oxide as a fining agent.

Also, in the clarification tank 30, the clarification tank 30 has a viscosity at which bubbles are likely to rise, preferably 120 poise to 400 poise, so that the release reaction of oxygen in the clarifier is promoted. And heated in the clarification tank 30. For example, when alkali-free glass or alkali-containing glass (high-temperature viscous glass) containing only a small amount of alkali, for example, 10 ^2.5 poise, melting at 1300 ° C. or higher, preferably 1400 ° C. or higher, more preferably 1500 ° C. or higher In the case of a glass material that requires temperature, the temperature is raised to 1700 ° C., preferably 1710 ° C., and more preferably close to 1720 ° C.
That is, it is necessary to raise the temperature of the clarification tank 30 to near the heat resistance temperature of platinum or platinum alloy of the main body 1 constituting the clarification tank 30.

When the above-mentioned high temperature is required as the refining temperature, since the boric acid (B ₂ O ₃ ) is easily volatilized from the molten glass, a silica-rich heterogeneous substrate is likely to be generated. Therefore, the present invention is particularly suitable for manufacturing a glass substrate using a glass material having a high temperature viscosity. Specifically, it can be said that it is suitable for a case where the molten glass is made of a glass material requiring a melting temperature of 1300 ° C. or higher when the molten glass is 10 ^2.5 poise. The melting temperature is preferably 1400 ° C. or higher, more preferably a glass material that requires a melting temperature of 1500 ° C. or higher.

  In addition, when the glass material is made of alkali-free glass or glass containing a trace amount of alkali, hardly soluble silica is likely to remain without melting, and a silica-rich heterogeneous substrate is likely to be formed. Even when configured, the present invention is suitable.

Furthermore, the present invention is also suitable for manufacturing a glass substrate when the molten glass is composed of the following materials 1 and 2.
1) It is made of a material containing each of SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , and alkaline earth metal, and the content of SiO ₂ is 50% to 70%.
_{2) SiO 2, Al 2 O} 3, B 2 O 3, is composed of a material containing the respective alkaline earth metals, the content of _B 2 _{O 3} is 5% or more.

This is because, in the case of the glass material configured as described in 1 above, since the SiO ₂ content is high, a silica-rich heterogeneous base tends to occur. Therefore, it can be said that the glass material having a SiO ₂ content of 55% or more and 60% or more is more suitable for the present invention.
Further, in the case of the glass material configured as described in 2 above, it can be said that the B ₂ O ₃ content is relatively high, and due to the property of B ₂ O ₃ that is easily dissolved at a low temperature, the silica-rich heterogeneity This is because the substrate tends to occur. Therefore, a glass material having a SiO ₂ content of 8% or more and 10% or more is further suitable for the present invention.

The present invention is also particularly suitable when a glass substrate is manufactured using a molten glass having a high temperature viscosity. Specifically, it is made of a glass material that requires a melting temperature of 1300 ° C. or higher when the molten glass is 10 ^2.5 poise. The melting temperature is preferably 1400 ° C. or higher, more preferably a glass material that requires a melting temperature of 1500 ° C. or higher.
Moreover, it is particularly suitable when a glass substrate is produced using a molten glass having a high temperature viscosity such as an alkali-free glass or a glass containing a trace amount of alkali.
In any case, by applying the present invention, one cause of striae and devitrification can be eliminated and the quality of the glass product can be improved.

Obviously, the method for manufacturing a glass substrate of the present invention is not limited to the manufacturing method of the embodiment. For example, the glass substrate production method of the present invention can be applied to glass raw materials other than the glass raw materials exemplified in the embodiment by using conventional raw materials.
In addition, various suitable modifications can be made without departing from the spirit of the invention.
In the present specification, the “platinum group metal” means a gold group composed of a platinum group element, and is used as a term including not only a metal composed of a single platinum group element but also an alloy of the platinum group element. Here, the platinum group element refers to six elements of platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), osmium (Os), and iridium (Ir). Platinum group metals are expensive, but have a high melting point and excellent corrosion resistance to molten glass.
In addition, the clarification tank is preferably cylindrical as shown in the figure, but there is no limitation on its shape as long as a space for accommodating the molten glass MG is secured therein. For example, its outer shape is a rectangular parallelepiped. May be.
The present invention is suitable for manufacturing a glass substrate on which glass is formed by the overflow download method. In the overflow download method, molten glass is made to flow down along both side surfaces of the wedge-shaped molded body and is merged at the lower end of the wedge-shaped molded body to form the sheet glass, and the formed plate glass is gradually added. Cool and cut. The overflow download method can achieve a smooth surface by stretching and cooling the molten glass vertically without touching anything. After that, the cut glass sheet is further cut into a predetermined size according to the customer's specifications, subjected to end face polishing, cleaning, etc., and shipped.
The present invention is particularly suitable for manufacturing glass substrates for flat panel displays (FPD) such as liquid crystal displays, plasma displays, and organic E displays.
The present invention is suitable for manufacturing a glass substrate for FPD having a thickness of 0.5 to 0.7 mm and a size of 300 × 400 mm to 2850 × 3050 mm, for example.
In addition, since a semiconductor element is formed on the surface of a glass substrate for a liquid crystal display device, the alkali metal component is not included at all, or even if it is included, it is a trace amount that does not affect the semiconductor element. Is preferred. Moreover, since the glass substrate for liquid crystal display devices etc. will cause a display defect when a bubble exists in a glass substrate, it is preferable to reduce a bubble as much as possible. From these, in the glass substrate for liquid crystal display devices and the like, as described above, the glass composition, the temperature of the molten glass, the fining agent, and the like are selected. Suitable.

1 Body (Clarification tank body)
DESCRIPTION OF SYMBOLS 10 Melting furnaces 20 and 40 Transfer pipe 40a Transfer pipe upper part 40b Transfer pipe lower part 30 Clarification tank 30b Clarification tank bottom part 30c Outlet 100 Glass substrate manufacturing apparatus MG Molten glass a Gas phase space Z Precipitate (precipitate of zirconia)

Claims (11)

A method for producing a glass substrate comprising a defoaming step of performing a defoaming process by passing a molten glass containing a fining agent in the clarification tank while heating the clarification tank body,
The clarification tank is
Composed of platinum group metals,
A transfer pipe for sending the molten glass from the clarification tank to the next step is connected to the outlet side from which the molten glass flows out of the clarification tank,
A liquid level adjusting step of adjusting the flow rate of the molten glass so that the liquid level of the molten glass becomes a predetermined liquid level when passing the molten glass mixed with a clarifier in the clarification tank;
Position where the molten glass near the upper surface of the molten glass flowing in the clarification tank flows to the transfer pipe without staying near the outlet when passing the molten glass of the predetermined liquid level A method for producing a glass substrate, wherein the transfer pipe is installed. 2. The glass substrate according to claim 1, wherein the transfer pipe is provided so that the liquid level of the molten glass at the predetermined liquid level in the clarification tank matches the position of the upper part of the transfer pipe. Production method.   3. The method for producing a glass substrate according to claim 2, wherein the transfer pipe has a lower part of the transfer pipe positioned at an upper side of at least 30 mm or more with respect to a bottom part of the clarification tank. The method for producing a glass substrate according to claim 3, wherein a melting kiln used for melting a glass material in a pre-process of the clarification tank is made of a high zirconia refractory. The clarification tank is
The manufacturing method of the glass substrate of Claim 4 which provided the discharge port for zirconia discharge | emission in the bottom part of the said exit vicinity of the said clarification tank. The molten glass is made of a material containing each of SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , and alkaline earth metal, and the content of the SiO ₂ is 50% to 70%. The manufacturing method of the glass substrate of any one of Claims 1-5. The molten glass is made of a material containing each of SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , and alkaline earth metal, and the B ₂ O ₃ content is 5% or more. The manufacturing method of the glass substrate of any one of Claims 1-5.   The said molten glass was comprised with the alkali free glass or the alkali trace amount containing glass, The manufacturing method of the glass substrate of any one of Claims 1-5 characterized by the above-mentioned.   The method for producing a glass substrate according to any one of claims 1 to 5, wherein the temperature of at least a part of the molten glass flowing in the clarification tank is 1630 degrees or more and 1720 degrees or less. . The method for producing a glass substrate according to claim 6 or 7, wherein the molten glass is made of a material that requires a melting temperature of 1300 degrees or more when the viscosity is 10 ^2.5 poise.   The said fining agent is a tin oxide, The manufacturing method of the glass substrate of Claim 6 or Claim 7 characterized by the above-mentioned.

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