JP2018002532A - Method for manufacturing glass plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the damage of a transfer pipe by reducing the maximum temperature of the transfer pipe without changing the maximum temperature of molten glass to achieve a long life of the transfer pipe.SOLUTION: The method for manufacturing a glass plate includes the step of heating molten glass while conveying it in a transfer pipe. The molten glass is heated by heating the transfer pipe, and the transfer pipe is heated so that a heating amount per the unit length of the transfer pipe decreases from the upstream side of the molten glass toward the downstream side.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for producing a glass plate.

  Generally, a glass substrate is produced through a process of forming molten glass from a glass raw material and then forming the molten glass into a glass substrate. The above steps include a melting step in which a glass raw material is melted to produce molten glass, and a clarification step in which minute bubbles contained in the molten glass are removed.

In the melting step, a glass raw material is charged into a melting tank, and molten glass is generated by heating the glass raw material. The molten glass produced | generated by the melting tank is conveyed by a transfer pipe to a clarification tank.
The clarification step is performed by passing the molten glass mixed with the clarifier through the clarification tank and removing bubbles in the molten glass by the oxidation-reduction reaction of the clarifier. Specifically, after raising the temperature of the molten glass roughly melted in the melting tank to function the fining agent and causing the bubbles to float up and defoam, the temperature is lowered to reduce the relatively small bubbles remaining without being defoamed. Is absorbed by molten glass (for example, see Patent Document 1).

JP2013-216531A

  In the transfer pipe that conveys the molten glass from the melting tank to the clarification tank, heating may be performed in order to further raise the temperature of the molten glass. In this case, the temperature of the transfer pipe is increased toward the downstream side so that the temperature of the molten glass increases toward the downstream side. When the temperature of the transfer pipe increases, stress tends to concentrate on both ends of the transfer pipe constrained by the melting tank and the clarification tank. In particular, at the downstream end, the rigidity is lowered as the temperature increases, and therefore, cracks due to stress tend to occur in the downstream portion of the transfer pipe. Furthermore, when the temperature is high, the material constituting the transfer tube is likely to volatilize. For this reason, on the downstream side of the high-temperature transfer pipe, there is a problem that the wall thickness of the transfer pipe is likely to be thinned due to volatilization, more easily damaged, and the life of the transfer pipe is shortened. On the other hand, if the maximum temperature of the molten glass conveyed by the transfer tube is lowered, there may be a problem in the clarification process.

  An object of the present invention is to reduce the maximum temperature of the transfer pipe without changing the maximum temperature of the molten glass, thereby suppressing breakage of the transfer pipe and extending the life.

An aspect of the present invention is a glass plate manufacturing method for manufacturing a glass plate,
Including the step of raising the temperature while conveying the molten glass in the transfer pipe,
The transfer pipe is provided so as to rise from the upstream side toward the downstream side,
The molten glass is filled in the entire inner cross section in the transfer pipe,
The temperature of the molten glass is raised by heating the transfer tube,
The transfer pipe is heated so that the heating amount per unit length of the transfer pipe decreases from the upstream side to the downstream side of the molten glass.
Here, the heating amount per unit length of the transfer pipe may be continuously decreased from the upstream side to the downstream side of the molten glass, or may be decreased stepwise.

It is preferable to heat the transfer pipe so that the difference between the temperature of the transfer pipe and the temperature of the molten glass conveyed in the transfer pipe decreases from the upstream side to the downstream side of the molten glass.
Here, the difference between the temperature of the transfer tube and the temperature of the molten glass may decrease continuously from the upstream side to the downstream side of the molten glass, or may decrease stepwise.

The transfer pipe is made of a conductor, and heats the transfer pipe by energizing the transfer pipe,
It is preferable to adjust the energization amount to the transfer pipe so that the current density of the transfer pipe decreases from the upstream side to the downstream side of the molten glass.
Here, the current density of the transfer tube may decrease continuously from the upstream side to the downstream side of the molten glass, or may decrease stepwise.

It is preferable to adjust the transfer pipe so that the electric resistance per unit length of the transfer pipe decreases from the upstream side to the downstream side of the molten glass.
Here, the electrical resistance per unit length of the transfer pipe may decrease continuously from the upstream side to the downstream side of the molten glass, or may decrease stepwise.

It is preferable to adjust the transfer pipe so that the wall thickness of the transfer pipe increases from the upstream side to the downstream side of the molten glass.
Here, the wall thickness of the transfer tube may increase continuously from the upstream side to the downstream side of the molten glass, or may increase stepwise. The inner diameter of the transfer tube is preferably uniform.

  According to the present invention, it is possible to reduce the downstream temperature at which the transfer pipe reaches the maximum temperature without changing the maximum temperature of the molten glass, to suppress the breakage of the transfer pipe and to extend the life. it can.

It is a flowchart which shows the manufacturing method of a glass substrate. It is the schematic of the manufacturing apparatus of a glass substrate. It is a figure which shows the relationship between the position (horizontal axis) of the flow direction of a transfer pipe, the temperature of the molten glass in a transfer pipe, and the temperature of a transfer pipe. It is sectional drawing of 104 A of transfer pipes. It is sectional drawing of the transfer pipe 104B.

Hereinafter, the glass substrate manufacturing method and the glass substrate manufacturing apparatus of the present embodiment will be described.
(Overall overview of glass substrate manufacturing method)
Drawing 1 is a figure showing an example of a process of a manufacturing method of a glass substrate of this embodiment. The glass substrate manufacturing method includes a melting step (ST1), a clarification step (ST2), a homogenization step (ST3), a supply step (ST4), a molding step (ST5), a slow cooling step (ST6), and a cutting step ( ST7) is mainly included. In addition, a grinding process, a polishing process, a cleaning process, an inspection process, a packing process, and the like may be included. The manufactured glass substrate is laminated in a packing process as necessary, and is transported to a supplier.

In the melting step (ST1), molten glass is made by heating the glass raw material.
In the clarification step (ST2), the molten glass is heated to generate bubbles containing oxygen, CO ₂ or SO ₂ contained in the molten glass. This bubble grows by absorbing oxygen generated by the reduction reaction of the clarifying agent (tin oxide or the like) contained in the molten glass, and floats on the liquid surface of the molten glass and is released. Thereafter, in the clarification step, by reducing the temperature of the molten glass, the reducing substance obtained by the reduction reaction of the clarifier undergoes an oxidation reaction. Thereby, gas components, such as oxygen in the bubble which remain | survives in molten glass, are reabsorbed in molten glass, and a bubble lose | disappears.

In the homogenization step (ST3), the glass component is homogenized by stirring the molten glass using a stirrer. Thereby, the composition unevenness of the glass which is a cause of striae or the like can be reduced. A homogenization process is performed in the stirring tank mentioned later.
In the supplying step (ST4), the stirred molten glass is supplied to the molding apparatus.

The molding step (ST5) and the slow cooling step (ST6) are performed by a molding apparatus.
In the forming step (ST5), the molten glass is formed into a sheet glass to make a flow of the sheet glass. An overflow downdraw method is used for molding.
In the slow cooling step (ST6), the sheet glass that has been formed and flowed is cooled to a desired thickness, so that internal distortion does not occur and warpage does not occur.
In the cutting step (ST7), the sheet glass after slow cooling is cut into a predetermined length to obtain a plate-like glass substrate. The cut glass substrate is further cut into a predetermined size to produce a glass substrate having a target size.

Although the glass substrate manufactured in this embodiment is not particularly limited, for example, the vertical dimension and the horizontal dimension are 500 mm to 3500 mm, 1500 mm to 3500 mm, 1800 to 3500 mm, 2000 mm to 3500 mm, etc., and 2000 mm to 3500 mm. Preferably there is.
As for the thickness of a glass substrate, 0.1-1.1 (mm) is mentioned, for example, More preferably, it is a very thin rectangular-shaped board of 0.75 mm or less, for example, 0.55 mm or less, Furthermore, 0.00. A thickness of 45 mm or less is more preferable. As a lower limit of the thickness of a glass substrate, 0.15 mm or more is preferable and 0.25 mm or more is more preferable.

Hereinafter, the manufacturing method of the glass substrate after a cutting process is demonstrated.
The glass substrate in the present embodiment is formed by melting a molten glass into a sheet glass which is a strip-shaped glass having a predetermined thickness by a known method such as a fusion method or a float method (step S1).
Next, the formed sheet glass is sampled on a glass substrate which is a base plate having a predetermined length (step S2). The glass substrate obtained by sampling may be guided and transported to a heat treatment step while being pinched and held by a transport mechanism, and then the transported glass substrate may be heat treated.

  The glass substrate after step S2 or heat treatment is conveyed to a cutting process, and is cut into a product size to obtain a glass substrate (step S3). The obtained glass substrate is subjected to end face processing including end face grinding, polishing, and corner cutting (step S4). In order to remove fine foreign matters and dirt on the glass surface of the glass substrate after the end face processing, the glass substrate is washed (step S5).

  After the cleaning step S5 immediately after the end face processing, the surface treatment S6 (roughening step Pr1 and rinsing step Pr2) is performed on the glass substrate.

  After the surface treatment step S6, the second post-cleaning S7 is performed, and thereafter the cleaned glass substrate is optically inspected for scratches, dust, dirt, or scratches including optical defects (step S8). The glass substrate having the quality matched by the inspection is loaded on the pallet and packed as a laminated body alternately laminated with paper protecting the glass substrate (step S9). The packed glass substrate is shipped to a supplier.

As such a glass substrate, the glass substrate of the following glass compositions is illustrated. That is, the raw material of molten glass is prepared so that the glass substrate of the following glass compositions is manufactured.
SiO ₂ 55~80 mol%,
Al ₂ O ₃ 8-20 mol%,
B ₂ O ₃ 0 to 12 mol%,
RO 0 to 17 mol% (RO is the total amount of MgO, CaO, SrO and BaO).

SiO ₂ is preferably 60 to 75 mol%, and more preferably 63 to 72 mol%, from the viewpoint of reducing the heat shrinkage rate.
Among RO, it is preferable that MgO is 0-10 mol%, CaO is 0-15 mol%, SrO is 0-10%, and BaO is 0-10%.

Further, at least SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , and RO are included, and the molar ratio ((2 × SiO ₂ ) + Al ₂ O ₃ ) / ((2 × B ₂ O ₃ ) + RO) is 4. The glass which is 5 or more may be sufficient. In addition, it is preferable that at least one of MgO, CaO, SrO, and BaO is included, and the molar ratio (BaO + SrO) / RO is 0.1 or more.

The total content of 2-fold and mol% of RO for the content of mol% of B ₂ O ₃ is 30 mol% or less, it is preferred that preferably 10 to 30 mol%.
Moreover, 0 mol% or more and 0.4 mol% or less may be sufficient as the content rate of the alkali metal oxide in the glass substrate of the said glass composition.
Further, it contains 0.05 to 1.5 mol% of metal oxides (tin oxide and iron oxide) whose valence fluctuates in the glass, and substantially contains As ₂ O ₃ , Sb ₂ O ₃ and PbO. It is not essential but optional.

  The glass substrate manufactured by this embodiment is a glass substrate for flat panel displays, or a glass substrate for curved panel displays, and is suitable, for example, as a glass substrate for liquid crystal displays or a glass substrate for organic EL displays. Furthermore, the glass substrate manufactured in this embodiment is particularly suitable as a glass substrate for LTPS (Low-temperature polysilicon), IGZO (Indium-Gallium-Zinc-Oxide), and TFT displays used for high-definition displays.

  As a method for forming sheet glass from molten glass in this embodiment, a float method, a fusion method, or the like is used. However, a method for manufacturing a glass substrate including offline heat treatment of the glass substrate in this embodiment is a fusion method (overdown). The draw method is suitable for the fusion method because it is difficult to lengthen the slow cooling device on the production line. The thermal shrinkage rate of the glass substrate of this embodiment is 50 ppm or less, preferably 40 ppm or less, more preferably 30 ppm or less, and even more preferably 20 ppm or less. The range of the heat shrinkage rate of the glass substrate before reducing the heat shrinkage rate is preferably 10 ppm to 40 ppm.

FIG. 2 is a schematic view of a glass substrate manufacturing apparatus that performs the melting step (ST1) to the cutting step (ST7) in the present embodiment. As shown in FIG. 2, the glass substrate manufacturing 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 pipe 102, a stirring tank 103, transfer pipes 104 and 105, and a glass supply pipe 106.
The melting tank 101 shown in FIG. 2 is provided with heating means such as a burner (not shown). A glass raw material to which a clarifying agent is added is charged into the melting tank, and a melting step (ST1) is performed. The molten glass melted in the melting tank 101 is supplied to the clarification tube 102 via the transfer tube 104.
In the clarification tube 102, the temperature of the molten glass MG is adjusted, and the clarification step (ST2) of the molten glass is performed using the oxidation-reduction reaction of the clarifier. Specifically, when the molten glass in the clarification tube 102 is heated, the bubbles containing oxygen, CO ₂ or SO ₂ contained in the molten glass absorb oxygen generated by the reductive reaction of the clarifier. It grows and floats on the liquid surface of the molten glass and is released into the gas phase space. Thereafter, by reducing the temperature of the molten glass, the reducing substance obtained by the reductive reaction of the fining agent undergoes an oxidation reaction. Thereby, gas components, such as oxygen in the bubble which remain | survives in molten glass, are reabsorbed in molten glass, and a bubble lose | disappears. The clarified molten glass is supplied to the stirring tank 103 via the transfer pipe 105.
In the stirring vessel 103, the molten glass is stirred by the stirring bar 103a, and the homogenization step (ST3) is performed. The molten glass homogenized in the stirring tank 103 is supplied to the molding apparatus 200 through the glass supply pipe 106 (supply process ST4).
In the forming apparatus 200, the sheet glass SG is formed from the molten glass by the overflow downdraw method (molding step ST5) and gradually cooled (slow cooling step ST6).
In the cutting device 300, a plate-like glass substrate cut out from the sheet glass SG is formed (cutting step ST7).

Next, the detailed configuration of the transfer pipe 104 that supplies the molten glass melted in the melting tank 101 to the clarification pipe 102 will be described.
The transfer pipe 104 is provided to be inclined so as to rise from the melting tank 101 (upstream side) toward the clarification pipe 102 (downstream side). In the transfer tube 104, the temperature of the molten glass is raised to a temperature suitable for the refining process while the molten glass is conveyed in a state where the molten glass is filled in the entire inner cross section in the transfer tube 104. Specifically, the temperature of the molten glass on the upstream side of the transfer pipe 104 (1550 ° C. to 1700 ° C.) is raised by about 50 to 60 ° C., and the temperature suitable for clarification on the downstream side of the transfer pipe 104 (1600 ° C. to The temperature of the molten glass is raised to 1750 ° C. The molten glass is heated by heating the transfer tube 104.

FIG. 3 is a diagram showing the relationship between the position in the flow direction of the transfer pipe (horizontal axis), the temperature of the molten glass in the transfer pipe, and the temperature of the transfer pipe. In FIG. 3, the solid line is the temperature of the molten glass in the transfer tube 104 in the present embodiment, the broken line is the temperature of the transfer tube 104 in the present embodiment, the one-dot chain line is the temperature of the molten glass in the conventional transfer tube, and the two-dot chain line is the conventional one. The temperature of each transfer pipe is shown.
As shown in FIG. 3, in the conventional transfer pipe, the heating amount per unit length of the transfer pipe is made constant regardless of the position in the length direction of the transfer pipe, and is shown by the two-dot chain line in FIG. As described above, the temperature of the transfer pipe was increased linearly. Thereby, as shown by the one-dot chain line in FIG. 3, the temperature of the molten glass in the transfer tube was also increased linearly. In such a conventional method, in order to raise the temperature of molten glass to the downstream side, it was necessary to make the temperature of a transfer pipe higher. When the temperature increases on the downstream side of the transfer pipe, the stress tends to concentrate on the downstream side of the transfer pipe due to thermal expansion, and the transfer pipe is easily damaged as described above.

  On the other hand, in this embodiment, the transfer pipe 104 is heated so that the heating amount per unit length of the transfer pipe 104 decreases from the upstream side to the downstream side of the molten glass. As a result, as shown in FIG. 3, the temperature can be rapidly increased on the upstream side of the transfer pipe 104, and the temperature gradient can be made gentle on the downstream side of the transfer pipe 104. Here, the temperature gradient of the transfer pipe 104 may decrease continuously from the upstream side to the downstream side of the molten glass, or may decrease intermittently as shown in FIG. . That is, the heating amount per unit length of the transfer pipe 104 may be continuously decreased from the upstream side to the downstream side of the molten glass, or may be decreased intermittently.

  As shown by the solid and broken lines in FIG. 3, the transfer pipe is such that the difference between the temperature of the transfer pipe 104 and the temperature of the molten glass conveyed through the transfer pipe 104 decreases from the upstream side to the downstream side of the molten glass. 104 can be heated. Specifically, the temperature difference between the transfer tube 104 and the molten glass is increased on the upstream side of the transfer tube 104, while the temperature difference between the transfer tube 104 and the molten glass is decreased on the downstream side of the transfer tube 104. Control the amount. By reducing the temperature difference between the transfer tube 104 and the molten glass on the downstream side where the temperature of the molten glass rises, the maximum temperature of the transfer tube 104 can be kept low. For this reason, as shown in FIG. 3, the downstream temperature at which the transfer pipe 104 reaches the maximum temperature can be reduced without changing the maximum temperature of the molten glass. Life can be extended. The difference between the temperature of the transfer pipe 104 and the temperature of the molten glass may be decreased continuously from the upstream side toward the downstream side, or may be decreased intermittently.

  For example, the transfer tube 104 may be formed of a conductor, and the transfer tube 104 may be directly heated by Joule heat by energizing the transfer tube 104. As the conductor that can withstand the temperature of the molten glass, a platinum group metal or an alloy of the platinum group metal can be used for the transfer tube 104.

  For example, the amount of heating per unit length of the transfer tube 104 is adjusted by adjusting the amount of current supplied to the transfer tube 104 so that the current density applied to the transfer tube 104 decreases from the upstream side to the downstream side of the molten glass. May be adjusted. The current density applied to the transfer tube 104 may be continuously decreased from the upstream side to the downstream side of the molten glass, or may be decreased intermittently.

  For example, by adjusting the transfer tube 104 so that the electrical resistance per unit length of the transfer tube 104 decreases from the upstream side to the downstream side of the molten glass, the current density applied to the transfer tube 104 can be reduced. It may be decreased from the upstream side toward the downstream side. The electrical resistance per unit length of the transfer pipe 104 may be decreased continuously from the upstream side to the downstream side of the molten glass, or may be decreased intermittently.

  Further, the transfer pipe 104 may be adjusted so that the wall thickness of the transfer pipe 104 increases from the upstream side to the downstream side of the molten glass. By increasing the wall thickness of the transfer pipe 104 from the upstream side to the downstream side of the molten glass, the electrical resistance per unit length of the transfer pipe 104 can be reduced from the upstream side to the downstream side. Further, by increasing the wall thickness of the transfer pipe 104 toward the downstream side where the temperature rises, the rigidity of the transfer pipe 104 is increased on the downstream side where the transfer pipe 104 reaches the maximum temperature, and the damage to the transfer pipe 104 is suppressed and long. Life can be extended.

For example, as shown in FIG. 4, the wall thickness of the transfer pipe 104A may be continuously increased from the upstream side to the downstream side of the molten glass.
Or as shown in FIG. 5, you may make it the wall thickness of the transfer pipe 104B increase intermittently toward the downstream from the upstream of molten glass.
In any case, the inner diameter of the transfer tube is preferably uniform.

  As mentioned above, although the manufacturing method of the glass substrate 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, you may make various improvement and a change. Of course.

  For the glass substrate produced by the method for producing a glass substrate of the present embodiment, it is preferable to use alkali-free boroaluminosilicate glass or glass containing a trace amount of alkali.

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

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

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

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

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

DESCRIPTION OF SYMBOLS 100 Melting apparatus 101 Melting tank 102 Clarification pipe | tube 103 Stirring tank 103a Stirrer 104,104A, 104B, 105 Transfer pipe 106 Glass supply pipe 200 Forming apparatus 300 Cutting apparatus MG Molten glass SG Sheet glass

Claims (5)

A glass plate manufacturing method for manufacturing a glass plate,
Including the step of raising the temperature while conveying the molten glass in the transfer pipe,
The transfer pipe is provided so as to rise from the upstream side toward the downstream side,
The molten glass is filled in the entire inner cross section in the transfer pipe,
The temperature of the molten glass is raised by heating the transfer tube,
A method for producing a glass plate, wherein the transfer tube is heated so that a heating amount per unit length of the transfer tube decreases from the upstream side to the downstream side of the molten glass.   The heating of the said transfer pipe is performed so that the difference of the temperature of the said transfer pipe and the temperature of the molten glass conveyed in the said transfer pipe may decrease toward the downstream from the upstream of the said molten glass. Manufacturing method of glass plate. The transfer pipe is made of a conductor, and heats the transfer pipe by energizing the transfer pipe,
The manufacturing method of the glass plate of Claim 1 or 2 which adjusts the energization amount to the said transfer pipe so that the current density of the said transfer pipe may decrease toward the downstream from the upstream of the said molten glass.   The manufacturing method of the glass plate of Claim 3 which adjusts the said transfer pipe so that the electrical resistance per unit length of the said transfer pipe may reduce toward the downstream from the upstream of the said molten glass.   The manufacturing method of the glass plate as described in any one of Claims 1-4 which adjusts the said transfer pipe so that the wall thickness of the said transfer pipe increases toward the downstream from the upstream of the said molten glass.

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