JP2018002539A - Method of manufacturing glass substrate and glass substrate manufacturing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce foreign matter of platinum-group metal included in a glass substrate.SOLUTION: A method of manufacturing a glass substrate comprises: a melting process of manufacturing molten glass using a glass raw material; a forming process of forming the molten glass into sheet glass; and a transfer process of transferring the molten glass using a transfer pipe including platinum-group metal between the melting process and forming process. In the transfer process, the molten glass is heated by using an AC current to cause the transport pipe to generate heat, and the frequency of the AC current is set to a value higher than a commercial frequency so that the amount of foreign matter of the platinum-group metal included in the sheet glass is within an allowable range.SELECTED DRAWING: Figure 1

Description

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

In recent years, the manufacture of glass substrates for displays used in flat panel displays (FDP) such as liquid crystal displays and organic EL displays is often carried out with molten glass at a high temperature.
Specifically, since the glass substrate for a display may be processed at high temperature at the time of panel manufacture, it is calculated | required that a thermal contraction rate is small. Since the thermal contraction rate of the glass substrate can be reduced by increasing the strain point of the glass substrate, a glass substrate for display having a small thermal contraction rate may be manufactured by increasing the strain point of the glass substrate. A glass substrate having a high strain point generally has a glass composition having a high melt viscosity. For this reason, high heat resistance is requested | required of the apparatus used for manufacture of a glass substrate.
Further, the glass substrate for display is required to have a very small number of bubbles contained in the glass substrate, and is required to satisfy high glass quality. In order to reduce the number of bubbles contained in the glass substrate, conventionally, clarification of molten glass has been performed using a clarifier. As a fining agent, for example, tin oxide or the like has a small environmental load, but it is difficult to obtain a sufficient fining action when the temperature of the molten glass is low. For this reason, when clarifying molten glass using tin oxide etc., high heat resistance is requested | required of apparatuses, such as a clarification tank which performs a clarification process.
2. Description of the Related Art Conventionally, as an apparatus having high heat resistance used for manufacturing a glass substrate, an apparatus made of a material containing a platinum group metal (hereinafter referred to as platinum) is known.

  However, when a foreign material containing platinum or the like (hereinafter referred to as platinum foreign matter) is mixed in a glass substrate manufactured using an apparatus composed of a material containing platinum or the like (hereinafter referred to as platinum material). There is. Platinum foreign substances are easily treated as optical defects, as are the bubbles in the glass substrate. For this reason, even if a predetermined standard for other types of defects is satisfied, it cannot be used for a display, and the yield may decrease.

  As a cause of contamination of platinum foreign matter into the glass substrate, the device used for manufacturing the glass substrate is exposed to a high-temperature atmosphere, and platinum and the like are volatilized, and the aggregates adhere to the inner wall of the device, and in the molten glass It is known to fall. In order to suppress such contamination of platinum foreign matter, the temperature-adjusted inert gas is introduced into the gas phase space in the clarification tank so that aggregation of volatiles is reduced in the clarification tank made of platinum material. The technique of supplying to is known (patent document 1).

Japanese Patent Laying-Open No. 2015-199642

  The platinum foreign substances contained in the glass substrate are not limited to those generated in the clarification tank, but may be generated in other apparatuses that come into contact with the molten glass. In addition, it was found that platinum foreign substances contained in the glass substrate may be precipitated as a lump in the glass substrate in addition to the falling and mixing of platinum volatilized and aggregated from the apparatus. In order to suppress the dissolution of platinum or the like from the apparatus, for example, it is conceivable to suppress the calorific value of the apparatus in contact with the molten glass. However, when the calorific value of the apparatus is suppressed, a molten glass having a glass composition having a high melt viscosity cannot be maintained at an appropriate viscosity. Moreover, the clarification action by the clarifier may not be sufficiently obtained.

  An object of this invention is to provide the manufacturing method and glass substrate manufacturing apparatus of a glass substrate which can reduce the foreign material of the platinum group metal contained in a glass substrate.

The present invention provides the following (1) to (8).
(1) A method for producing a glass substrate,
A melting process for making molten glass using glass raw materials,
A molding step of molding the molten glass into a sheet glass;
A transfer step of transferring the molten glass using a transfer tube containing a platinum group metal between the melting step and the forming step;
In the transfer step, the molten glass is heated by energizing and heating the transfer tube using an alternating current,
The frequency of the alternating current is set to a value higher than the commercial frequency so that the amount of platinum group metal foreign matter contained in the sheet glass is within an allowable range.

(2) The glass substrate manufacturing method according to (1), wherein the frequency of the set AC power supply is higher than 60 Hz.

(3) The said transfer pipe | tube is a manufacturing method of the glass substrate as described in said (1) or said (2) with which the temperature of the molten glass transferred through the said transfer pipe | tube is heated so that it may become 1550 degreeC or more.

(4) The glass substrate according to any one of (1) to (3), wherein the transfer tube is heated so that a viscosity of the molten glass transferred through the transfer tube is 300 poise or less. Production method.

(5) The method for producing a glass substrate according to any one of (1) to (4), wherein a current density of an alternating current flowing through the transfer tube is 300 A / cm ² or more.

(6) The melting step is performed using a melting tank,
The transfer pipe has a first pipe connected to the melting tank, and a second pipe for refining the molten glass while further transferring the molten glass transferred through the first pipe. ,
The said alternating current is a manufacturing method of the glass substrate as described in any one of said (1) to said (5) which energizes and heats the transfer pipe of said 1st pipe | tube at least.

(7) The foreign matter has a linear form in which a long side length exceeds 50 μm and a short side length is less than 5 μm, and the foreign object is any one of (1) to (6) The manufacturing method of the glass substrate of description.

(8) a melting device for melting glass raw material to make molten glass;
A molding device for molding the transferred molten glass into a sheet glass;
A transfer pipe for transferring the molten glass from the melting device toward the molding device,
The transfer pipe contains a platinum group metal and heats the molten glass by being energized and heated using an alternating current,
The frequency of the alternating current is set to a value higher than the commercial frequency so that the amount of platinum group metal foreign matter contained in the sheet glass is within an allowable range.

  According to the present invention, platinum group metal foreign matter contained in a glass substrate can be reduced.

It is a figure which shows an example of the process of the manufacturing method of a glass substrate. It is a figure which shows the outline of a glass substrate manufacturing apparatus. It is an external appearance perspective view which shows the transfer pipe | tube of a glass substrate manufacturing apparatus.

Hereinafter, the manufacturing method of the glass substrate and the glass substrate manufacturing apparatus of this embodiment will be described.
(1) Glass substrate The glass substrate manufactured by this embodiment is used for flat panel displays (FPD), such as a liquid crystal display, a plasma display, and an organic EL display, or a curved display (except for a cathode ray tube). For example, the glass substrate G has a thickness of 0.2 mm to 0.8 mm, and a size of 680 mm to 2200 mm in length and 880 mm to 2500 mm in width.

  An example of the glass substrate G includes glass having the following composition.

(A) SiO ₂ : 50% by mass to 70% by mass,
(B) Al ₂ O ₃ : 10% by mass to 25% by mass,
(C) B ₂ O ₃ : 5% by mass to 18% by mass,
(D) MgO: 0% by mass to 10% by mass,
(E) CaO: 0% by mass to 20% by mass,
(F) SrO: 0% by mass to 20% by mass,
(G) BaO: 0% by mass to 10% by mass,
(H) RO: 5% by mass to 20% by mass (R is at least one selected from Mg, Ca, Sr and Ba),
(I) R ′ ₂ O: 0% by mass to 2.0% by mass (R ′ is at least one selected from Li, Na and K),
(J) At least one metal oxide selected from SnO ₂ , Fe ₂ O ₃ and CeO ₂ .

  The glass having the above composition is allowed to contain other trace components in the range of less than 0.1% by mass.

(2) Outline of Manufacturing Method of Glass Substrate Hereinafter, the manufacturing method of the glass of this embodiment will be described. FIG. 1 is a process diagram illustrating the steps of the glass substrate manufacturing method of the present embodiment.
The glass substrate manufacturing method includes a melting step (ST1), a transfer step (ST2), a clarification step (ST3), a homogenization step (ST4), a supply step (ST5), a forming step (ST6), It has mainly a slow cooling process (ST7) and a cutting process (ST8). In addition, a plurality of glass plates that have a grinding process, a polishing process, a cleaning process, an inspection process, a packing process, and the like and are stacked in the packing process are conveyed to a supplier. A transfer process (ST2) and a clarification process (ST3) correspond to the transfer process of this embodiment. In the following description, the transfer process (ST2) will be described as an example of the transfer process of the present embodiment.

  FIG. 2 is a diagram schematically showing an apparatus for performing the melting step (ST1) to the cutting step (ST8). As shown in FIG. 2, the apparatus mainly includes a melting apparatus 100, a forming apparatus 200, and a cutting apparatus 300. The melting apparatus 100 mainly includes a melting tank 101, a transfer pipe 104 (first pipe), a clarification tank 102 (second pipe), a supply pipe 105, a stirring tank 103, and a supply pipe 106. . The transfer pipe 104 and the clarification tank 102 correspond to the transfer pipe of this embodiment. In the following description, the transfer tube 104 will be described as an example of the transfer tube of this embodiment.

In the melting step (ST1), the glass raw material supplied into the melting tank 101 is heated and melted with a flame generated from a burner (not shown) to produce a molten glass MG. Thereafter, the molten glass MG is energized and heated using an electrode (not shown).
A transfer process (ST2) is a process performed between a melting process (ST1) and a clarification process (ST3). In the transfer step (ST2), the molten glass MG flowing out of the melting tank 101 is supplied to the clarification tank 102 through the transfer pipe 104.
The clarification step (ST3) is performed in the clarification tank 102. The clarification tank 102 is a device that clarifies the molten glass MG while further transferring the molten glass MG transferred through the transfer pipe 104. When the molten glass MG in the clarification tank 102 is heated, bubbles such as O ₂ contained in the molten glass MG grow by absorbing oxygen generated by the reductive reaction of the clarifier and float on the liquid surface. And released. Or gas components, such as oxygen in a bubble, are absorbed in molten glass for the oxidation reaction of a clarifier, and a bubble disappears.
In the homogenization step (ST4), the molten glass MG in the stirring vessel 103 supplied through the supply pipe 105 is stirred using the stirrer 103a, whereby the glass components are homogenized.
In the supply step (ST5), molten glass MG is supplied to the forming apparatus 200 through the supply pipe 106.

In the molding apparatus 200, a molding process (ST6) and a slow cooling process (ST7) are performed.
In the forming step (ST6), the molten glass MG is formed into the sheet glass SG using the formed body 210, and a flow of the sheet glass SG is created. In this embodiment, an overflow downdraw method is used. In the slow cooling step (ST7), the sheet glass SG which is formed and flows is cooled to have a desired thickness, so that internal distortion does not occur and the thermal contraction rate does not increase.
In the cutting step (ST8), a glass substrate is obtained by cutting the sheet glass supplied from the forming apparatus 200 into a predetermined length in the cutting apparatus 300. The cut glass substrate is further cut into a predetermined size to produce a glass substrate of a target size. Thereafter, the glass substrate is ground and polished, and then cleaned. Further, the glass substrate is inspected for abnormal defects such as bubbles and striae, and the glass substrate that has passed the inspection is packed as a final product. . In addition, a cutting process (ST8) is not an essential process in the manufacturing method of a glass substrate, In this case, sheet glass is made into the glass substrate manufactured by this embodiment. As such a glass substrate, elongate sheet glass wound up by roll shape is mentioned, for example.

(3) Detailed Description of Transfer Process FIG. 3 is an external perspective view showing the transfer pipe 104.
The transfer tube 104 is a tubular member made of a platinum material. The transfer pipe 104 has one end connected to the bottom of the melting tank 101 and the other end connected to the clarification tank 102. As shown in FIG. 2, the transfer pipe 104 is arranged to extend in a direction inclined with respect to the horizontal direction, and the molten glass MG passes through the transfer pipe 104 from the melting tank 101 side to the clarification tank. It is transported while rising toward the side of 102.

A pair of electrodes 150 is attached to the transfer tube 104. The electrodes 150 are disposed at both ends of the transfer tube 104 in the extending direction. Both end portions refer to portions extending from 0 to 30% of the length of the transfer tube 104 from both ends in the extending direction of the transfer tube 104. As shown in FIG. 3, the electrode 150 has a flange-like shape protruding from the surface of the transfer tube 104 to the outer peripheral side and extending in an annular shape. The electrode 150 is connected to a water cooling device (not shown), and is cooled with water so that the temperature of the transfer pipe 104 does not become too high, and performs heat dissipation.
A power supply terminal 152 is connected to the electrode 150 through a conductive member 151. The power supply terminal 152 is connected to the power source 154 via the inverter 156. In the example shown in FIG. 3, the power source 154 is an AC power source and is a commercial power source that supplies an AC current having a commercial frequency. The commercial frequency is, for example, 50 Hz or 60 Hz. The AC current supplied from the power source 154 is adjusted to a frequency higher than the commercial frequency in the inverter 156 so that the amount of platinum foreign matter is within the allowable range, and then transferred through the power supply terminal 152, the conductive member 151, and the electrode 150. Supplied to the tube 104. When the alternating current flows in the tube wall of the transfer tube 104 between the pair of electrodes 150, the transfer tube 104 generates heat, and the molten glass MG in contact with the transfer tube 104 is heated (electrically heated). The adjustment of the frequency of the alternating current will be described in detail later.

Note that the number of electrodes 150 provided in the transfer tube 104 is not limited to two, and may be three or more. In this case, a current can be supplied at a current density different from or equal to each of the two electrodes 150 adjacent in the extending direction of the transfer tube 104.
Moreover, the surface of the tube wall of the transfer tube 104 may be covered with a heat insulating material. The heat insulating material is, for example, a refractory brick.

Next, adjustment of the frequency of the alternating current will be described.
In the present embodiment, the frequency of the alternating current supplied to the transfer tube 104 is set to a value higher than the commercial frequency so that the amount of platinum foreign matter contained in the sheet glass SG is within an allowable range. The allowable range refers to the amount of platinum foreign matter that may be contained in the glass substrate, and is determined in advance according to the type of display on which the glass substrate is used. The amount of the platinum foreign matter being within the allowable range means, for example, that the number of platinum foreign matters contained per unit area of the sheet glass SG is a predetermined number or less. The frequency of the alternating current supplied to the transfer tube 104 may be set in advance to a value higher than the commercial frequency so that the amount of platinum foreign matter is within the allowable range, and the transfer process of this embodiment was performed. As a result, feedback adjustment may be performed based on the amount of platinum foreign matter contained in the sheet glass SG. In the following description, the case where the frequency of the alternating current is a preset frequency will be described as an example.

When an alternating current set to a frequency higher than the commercial frequency is supplied to the transfer tube 104 so that the amount of the platinum foreign matter falls within the allowable range and the transfer step (ST2) is performed, the platinum foreign matter contained in the manufactured glass substrate It has been clarified by the present inventors that can be reduced. With regard to this finding, platinum can be considered as follows by taking platinum as an example.
In the transfer step (ST2), when a current is supplied to the transfer tube 104, the molten glass is electrolyzed using a pair of electrodes as an anode and a cathode. At this time, if the current supplied to the transfer tube 104 is a direct current, platinum becomes platinum ions and melts in the molten glass at the portion of the transfer tube 104 where the anode electrode of the pair of electrodes is located. put out. On the other hand, when the current supplied to the transfer tube 104 is an alternating current, the anode and the cathode are switched in a short time, so that (1) platinum is dissolved as platinum ions from the portion of the transfer tube 104 serving as the anode. (2) When the anode and the cathode are switched, platinum ions dissolved from the transfer pipe 104 serving as the anode are deposited as platinum on the transfer pipe 104 serving as the cathode. Compared with the case where a direct current is supplied, the elution amount of platinum is suppressed. For this reason, by supplying an alternating current to the transfer tube 104, the amount of platinum dissolved in the molten glass MG can be reduced. Furthermore, if the frequency of the alternating current is set to a value higher than the commercial frequency so that the amount of platinum foreign matter is within the allowable range, the time for switching between the anode and the cathode becomes shorter, and as a result, the glass substrate It was found that the amount of platinum foreign matter contained was reduced.

  Thus, it is important in the present embodiment that the frequency of the alternating current is set to a value higher than the commercial frequency so that the amount of the platinum foreign matter is within the allowable range. Platinum foreign substances appearing in the glass substrate may be considered to be photochemical defects, and the yield of the glass substrate may be reduced, whereas platinum eluted in the molten glass is dissolved in the glass. As long as there are no optical defects. The correlation between the elution amount of platinum in the molten glass and the precipitation amount of platinum foreign matter in the glass substrate is not clear, and even if the frequency of the alternating current is increased to suppress the elution amount of platinum, the glass substrate It is not always the case that the platinum foreign matter contained in is reduced.

  In this embodiment, it is preferable that the frequency of the set alternating current is higher than 60 Hz. It has been found that when the transfer process is performed using an alternating current having a frequency in this range, the effect of reducing platinum foreign matter contained in the glass substrate is enhanced. The frequency of the alternating current is more preferably 100 Hz or more and 100 kHz or less. The frequency of the alternating current is more preferably 300 Hz or more and 10 kHz or less. When the frequency is within this range, it is possible to suppress the power supply efficiency from being excessively low, and it is possible to omit the cost of components for adjusting to a high frequency. The frequency of the set alternating current is, for example, 100 to 10 kHz.

The current density of the alternating current flowing through the transfer tube 104 is preferably 300 A / cm ² or more. The effect of reducing platinum foreign matter contained in the glass substrate is to set the frequency of the alternating current to a value higher than the commercial frequency at which the amount of platinum foreign matter is within the allowable range when the current density is in the above range. It was found that it can be effectively increased. Platinum foreign substances contained in the glass substrate may not be reduced unless such a high current density is supplied to the transfer tube 104. Even when such a high current density is supplied to the transfer tube 104, the effect of reducing the amount of platinum foreign matter is effectively enhanced by using an AC power source having a relatively low frequency, for example, exceeding 60 Hz and not exceeding 10 kHz. I found out that The current density of the alternating current is more preferably 650 A / cm ² or more and 800 A / cm ² or more. Further, the current density of the alternating current is preferably 1 kA / cm ² or less because the temperature of the transfer tube 104 becomes too high and the molten glass MG may be excessively heated.

  Moreover, it is preferable that the transfer pipe 104 is heated so that the temperature of the molten glass MG transferred through the transfer pipe 104 becomes 1550 ° C. or higher. The effect of reducing platinum foreign matter contained in the glass substrate is to set the frequency of the alternating current to a value higher than the commercial frequency so that the amount of platinum foreign matter is within the allowable range when the temperature of the molten glass MG is in the above range. It has been found that this can be effectively enhanced. The temperature of the molten glass MG is more preferably 1600 ° C. or higher and 1680 ° C. or higher. The temperature of the molten glass MG is preferably 1750 ° C. or lower in order to suppress elution of platinum and the like due to contact with the high temperature molten glass.

  Moreover, it is preferable that the transfer pipe 104 is heated so that the viscosity of the molten glass MG transferred through the transfer pipe 104 is 300 poise or less. The effect of reducing platinum foreign matter contained in the glass substrate is to set the frequency of the alternating current to a value higher than the commercial frequency so that the amount of platinum foreign matter is within the allowable range when the viscosity of the molten glass MG is in the above range. It has been found that this can be effectively enhanced. The viscosity of the molten glass MG is more preferably 100 poise or more and 300 poise or less. Moreover, it is preferable that the temperature of molten glass MG is 1700 degrees C or less. When the viscosity of the molten glass MG is low, it is considered that the molten glass MG does not easily follow the above-described switching between the anode and the cathode, and platinum or the like is difficult to elute into the molten glass MG. The mobility of platinum ions increases and higher frequencies are required to reduce platinum foreign matter.

  In addition, from the viewpoint of increasing the effect of reducing the platinum foreign matter contained in the glass substrate, the frequency of the alternating current is described above in conjunction with setting the value higher than the commercial frequency so that the amount of the platinum foreign matter is within the allowable range. It is more preferable to combine two or more of the current density flowing through the transfer tube 104, the temperature of the molten glass MG, and the viscosity of the molten glass MG.

  In this embodiment, the long side length is more than 50 μm, the short side length is less than 5 μm, and preferably, the long side length is 200 μm or less, and the short side length is 1 μm or more. Foreign matter (linear platinum) having the form of: or a foreign foreign matter (linear platinum) having a linear form having a long side length of more than 50 μm and less than 80 μm and a short side length of less than 1 μm This is suitable for reduction. Linear platinum having these forms is easily handled as a defective product when it is contained in a glass substrate used in a high-contrast flat panel display. High contrast means that the contrast ratio is about 2000: 1 to 3000: 1. In the present embodiment, as described above, the amount of platinum foreign matter is reduced to linear platinum having the above-described form included in the glass substrate by supplying the transfer tube 104 with an alternating current set at a frequency that falls within an allowable range. can do.

  In the present embodiment, the frequency of the alternating current supplied to the clarification tank 102 in place of the transfer pipe 104 or in combination with the transfer pipe 104 is set from the commercial frequency so that the amount of platinum foreign matter is within the allowable range. A high value may be set. Like the transfer pipe 104, the clarification tank 102 is provided with a pair of or three or more electrodes on the surface of an annular member, and generates heat by supplying an alternating current to heat the molten glass MG ( Heating). Of the electrodes 150 provided on the transfer pipe 104, the electrode 150 positioned closest to the clarification tank 102 and the electrode provided on the clarification tank 102 closest to the transfer pipe 104 are the same electrode. There may be two electrodes arranged adjacent to each other. In the case of two electrodes disposed adjacent to each other, an insulating material can be disposed between the two electrodes.

  In addition to setting the frequency of the alternating current to a value higher than the commercial frequency so that the amount of platinum foreign matter is within the allowable range, the length in the extending direction of the transfer pipe 104 and the pipe of the transfer pipe 104 are also set. The wall thickness may be adjusted. For example, when the frequency of the AC power supply is set to a value exceeding 60 Hz, the length in the extending direction of the transfer pipe 104 is adjusted to, for example, 1 to 5 m, and the plate thickness of the tube wall of the transfer pipe 104 is, for example, It is adjusted to 0.5-2 mm.

  According to the present embodiment, linear platinum contained in the glass substrate is reduced by supplying the transfer tube 104 with an alternating current set at a frequency higher than the commercial frequency so that the amount of platinum foreign matter is within the allowable range. The Thereby, the quality of the glass substrate is improved, and the yield of the glass substrate is improved. Moreover, when elution of platinum etc. to the molten glass MG is suppressed, the consumption of the transfer pipe is suppressed, the life of the apparatus can be extended, and the thickness of the wall of the transfer pipe can be reduced. Moreover, by heating and energizing the transfer tube using an alternating current, it is possible to suppress the occurrence of temperature unevenness at the same flow direction position in the molten glass flowing in the transfer tube. In addition, when the transfer tube is induction-heated using an alternating current, temperature unevenness tends to occur at the same flow direction position in the molten glass flowing in the transfer tube. Since the elution amount of platinum or the like is affected by temperature unevenness of the molten glass, it is difficult to control the elution amount of platinum or the like when the transfer tube is heated by induction.

(Experimental example)
An inverter is connected to a commercial power source having a commercial frequency of 50 to 60 Hz, and an alternating current whose frequency is adjusted to a value higher than the commercial frequency so that the amount of platinum foreign matter is in an allowable range is supplied to a transfer pipe made of platinum. The glass substrate sample was produced by carrying out the transfer step and further performing the clarification step to the cutting step. The frequency was adjusted to four types of 70 Hz, 100 Hz, 1 kHz, and 10 kHz (Examples 1 to 4).
On the other hand, an AC power source having two commercial frequencies of 50 Hz and 60 Hz was directly supplied to the transfer pipe without going through an inverter, and other points were made in the same manner as in the example to produce a glass substrate sample (Comparative Example 1, 2).
For each of the glass substrate samples of Examples 1 to 4 and Comparative Examples 1 and 2, the number of platinum foreign matters contained in the glass substrate was counted using a laser microscope. As platinum foreign matter, linear platinum in any one of the above forms was counted. As a result, in Examples 1-4, it was 0.01 piece / cm < ² > or less, but in Comparative Examples 1 and ² , it exceeded 0.05 / cm < ² >. It was confirmed that the platinum foreign matter contained in the glass substrate can be reduced by setting the frequency of the alternating current to a value higher than the commercial frequency so that the amount of the platinum foreign matter falls within the allowable range. Moreover, in Examples 1-4, it was confirmed that the amount of platinum foreign materials is small, so that the value of the frequency of AC power supply is high.

  The glass substrate manufacturing method and glass substrate manufacturing apparatus of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiment, and various improvements and modifications can be made without departing from the gist of the present invention. Of course.

DESCRIPTION OF SYMBOLS 100 Melting apparatus 200 Molding apparatus 300 Cutting apparatus 101 Melting tank 102 Clarification tank (2nd pipe)
104 Transfer pipe (first pipe)

Claims (6)

A method of manufacturing a glass substrate,
A melting process for making molten glass using glass raw materials,
A molding step of molding the molten glass into a sheet glass;
A transfer step of transferring the molten glass using a transfer tube containing a platinum group metal between the melting step and the forming step;
In the transfer step, the molten glass is heated by energizing and heating the transfer tube using an alternating current,
The frequency of the alternating current is set to a value higher than the commercial frequency so that the amount of platinum group metal foreign matter contained in the sheet glass is within an allowable range.   The method for manufacturing a glass substrate according to claim 1, wherein the frequency of the set AC power supply is higher than 60 Hz.   The said transfer pipe | tube is a manufacturing method of the glass substrate of Claim 1 or 2 with which the viscosity of the molten glass transferred through the said transfer pipe | tube becomes 300 poise or less. The method for producing a glass substrate according to any one of claims 1 to 3, wherein a current density of an alternating current flowing through the transfer pipe is 300 A / cm ² or more.   The said foreign material has a linear form whose long side length exceeds 50 micrometers and whose short side length is less than 5 micrometers, The manufacturing method of the glass substrate of any one of Claim 1 to 4 . A melting device that melts glass raw materials to produce molten glass;
A molding device for molding the transferred molten glass into a sheet glass;
A transfer pipe for transferring the molten glass from the melting device toward the molding device,
The transfer pipe contains a platinum group metal and heats the molten glass by being energized and heated using an alternating current,
The frequency of the alternating current is set to a value higher than the commercial frequency so that the amount of platinum group metal foreign matter contained in the sheet glass is within an allowable range.

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