TWI478883B - A method for manufacturing a glass substrate, and a manufacturing apparatus for a glass substrate - Google Patents

Description

Method for producing glass substrate and device for manufacturing glass substrate

The present invention relates to a method for producing a glass substrate for producing a glass substrate by molding molten glass produced by melting a glass raw material, and a glass substrate manufacturing apparatus.

The glass substrate is generally produced by a step of forming molten glass from a glass raw material and then forming the molten glass into a glass substrate. The above steps include a step of removing minute bubbles contained in the molten glass (hereinafter also referred to as clarification). The clarification is carried out by heating the molten glass to which the clarifying agent such as As ₂ O _{3 is} added, through the tubular clarification tank main body (hereinafter also referred to as a clarification pipe), while heating the clarification tank main body formed as a pipe. The clarification is carried out by removing the bubbles in the molten glass by a redox reaction of a clarifying agent. More specifically, the clarification is carried out in such a manner that the temperature of the molten glass after the crude melting is further increased to function as a clarifying agent, and after the bubbles are floated and defoamed, the temperature is lowered, whereby the molten glass is absorbed incompletely defoamed. The smaller bubbles remain. That is, the clarification includes a treatment for defoaming the bubbles (hereinafter referred to as a defoaming treatment) and a treatment for absorbing the vesicles into the molten glass (hereinafter referred to as an absorption treatment). In the defoaming treatment, when the molten glass is passed through the clarification pipe, a gas phase space for defoaming having a constant area is provided between the surface above the inside of the clarification pipe and the liquid surface of the molten glass.

As the clarifying agent, As ₂ O ₃ has been generally used in the past, but in recent years, from the viewpoint of environmental load, use of SnO ₂ or Fe ₂ O _{3 having} low toxicity has been used.

In addition, in order to mass-produce high-quality glass substrates from high-temperature molten glass, It is expected that impurities or the like which are the main factors of the glass substrate defect are not mixed into the molten glass from any device for manufacturing the glass substrate. Therefore, in the production process of the glass substrate, the inner wall of the member in contact with the molten glass needs to be made of a suitable material depending on the temperature of the molten glass that is in contact with the member, the quality of the desired glass substrate, and the like. For example, a material of a tube constituting the clarification tube is generally used as a platinum group metal such as platinum or a platinum alloy (Patent Document 1). Platinum or a platinum alloy is suitable for use in a clarification tube because of its high price, high melting point, and excellent corrosion resistance to molten glass.

The temperature at which the clarification tube is heated during the defoaming treatment differs depending on the composition of the glass substrate to be formed, and is about 1000 to 1650 °C.

In a general case, a gas exhaust port for discharging the defoamed bubbles to the outside is provided on the clarification tank. Therefore, sometimes external air is mixed into the inside of the clarification tank from the gas exhaust port. When the external gas containing oxygen is mixed into the clarification tank from the gas vent, the platinum or platinum alloy in the inner wall portion in contact with the gas phase space in the clarification tube volatilizes.

Further, inside the clarification pipe, a gas such as oxygen in the bubble is discharged from the molten glass to the gas phase space described above. The platinum or platinum alloy of the inner wall portion in contact with the gas phase space in the clarification tube is also volatilized by the oxygen component. That is, the gas phase space inside the clarification tank contains a volatile substance of platinum or a platinum alloy which is volatilized by oxygen.

[Previous Technical Literature] [Patent Literature]

Patent Document 1: Japanese Patent Special Publication No. 2006-522001

Further, it is known that in the production of a glass substrate, the temperature at which the clarification action is effectively exerted varies depending on the clarifying agent used. For example, As ₂ O ₃ (arsenite) has an excellent ability to remove bubbles, and a clarification temperature of about 1500 ° C or a range slightly higher than 1500 ° C is sufficient. Therefore, As ₂ O _{3 has} previously been generally used as a fining agent. However, since arsenic acid has a high environmental load, as described above, in recent years, SnO ₂ (tin oxide) or the like has been preferably used as a clarifying agent having a low environmental load (low toxicity). However, compared with arsenious acid, tin oxide has a weak ability to release bubbles during the defoaming step, and it is necessary to lower the viscosity of the glass to improve the defoaming effect. Therefore, it is necessary to raise the temperature of the molten glass for clarification. For example, when tin oxide is used as the clarifying agent, it is preferred to raise the temperature to 1600 ° C or higher. Therefore, there is a problem that the platinum or platinum alloy from the wall surface is more volatile than before, on the surface above the inside of the clarification tube which is in contact with the gas phase space described above.

One of the crystals (platinum impurities or platinum alloy impurities) obtained by solidification of the volatile matter such as platinum or a platinum alloy is mixed into the molten glass as fine particles, which may cause deterioration in the quality of the glass substrate.

Therefore, in view of the above circumstances, an object of the present invention is to provide a method for producing a glass substrate capable of suppressing the incorporation of impurities formed by platinum or a platinum alloy volatilized from a clarification tank used in the production process of a glass substrate, and a glass substrate. Manufacturing equipment.

One aspect of the present invention is a method of producing a glass substrate. The manufacturing method includes a melting step of melting a glass raw material to form a molten glass, and a clarification step including a defoaming treatment for comprising a long strip composed of platinum or a platinum alloy and heated In the clarification tank of the tube, while the molten glass is passed through in a state in which the vapor phase is formed, the molten glass is heated to discharge bubbles from the molten glass to the vapor phase space.

The tube of the clarification tank is formed such that at least a part of a portion below the temperature at which the platinum volatile matter contained in the gas phase space is solidified does not have the gas phase space.

The tube system is formed such that at least a part of a portion at which the platinum volatile matter contained in the gas phase space is solidified does not have the gas phase space, and therefore the inner wall surface of the tube is at or near the part It is difficult to generate volatilization from platinum or platinum alloy The crystal obtained by solidification of the material is reduced as an impurity mixed into the molten glass in the clarification step. Therefore, when a glass substrate is manufactured, it is possible to suppress impurities formed of platinum or a platinum alloy from being mixed into the glass substrate.

The heating of the molten glass is performed by applying a current from one of the tubes to the electrode plate to the tube to be electrically heated. The position of the electrode plate partially lowered at the temperature of the tube does not have a gas phase space.

The electrode plate is used to heat the tube, but it has a plate shape and is easily cooled by heat dissipation. Therefore, the temperature of the wall of the tube is locally lowered by the provision of the electrode plate. Therefore, the tube is preferably formed such that the position of the electrode plate does not have the gas phase space.

The above molten glass may contain SnO ₂ as a fining agent. Since the molten glass containing SnO ₂ as a clarifying agent is less in toxicity, it is preferable from the viewpoint of reducing environmental load, but its clarifying function is low. Therefore, the molten glass is made to have a higher temperature in the clarification step than before. In this case, the tube of the clarification tank is also heated to a higher temperature than before, and therefore crystals are formed on the inner wall surface of the tube due to volatilization of platinum or platinum alloy and further solidification of the volatile matter (platinum impurity, platinum The situation of alloy impurities) has increased. In the above aspect, the temperature of the wall surface of the tube is such that at least a part of the portion below the temperature at which the platinum volatile material contained in the gas phase space is solidified forms the portion having no portion of the gas phase space, thereby forming the tube. It is difficult to form crystals of platinum or a platinum alloy on the inner wall surface of the above-mentioned part or the vicinity of the tube, and it is less likely to be mixed as impurities into the molten glass in the clarification step. Therefore, when a glass substrate is manufactured, it is possible to suppress impurities formed of platinum or a platinum alloy from being mixed into the glass substrate.

The molten glass may have a temperature of 1500 ° C or higher at a temperature of 10 ^2.5 poise. The temperature of 10 ^2.5 poise is glass having a high viscosity of 1500 ° C or higher, so the temperature of the molten glass in the above tube is set higher than before. However, in this case, the tube is formed such that at least a part of the portion where the temperature of the wall of the tube is equal to or lower than the temperature at which the platinum volatile substance is solidified does not have the gas phase space, and therefore the temperature at the wall of the tube is The crystal obtained by solidifying the volatile matter of platinum or the platinum alloy on the inner wall surface of the tube at or below the temperature at which the platinum volatiles are solidified is less likely to be mixed as impurities into the molten glass in the clarification step. Therefore, when a glass substrate is manufactured, it is possible to suppress impurities formed of platinum or a platinum alloy from being mixed into the glass substrate.

The portion of the inner wall surface of the tube is in contact with the molten glass at a portion of the tube that does not have the gas phase space. Therefore, there is no inner wall surface of the above-mentioned tube for solidifying the platinum volatiles contained in the gas phase space. Therefore, the situation in which the impurities are mixed into the molten glass in the clarification step is reduced.

More specifically, the tube includes a first portion in which the tube cross section of the tube is the flow path of the molten glass and does not have the first portion of the vapor phase space, and a portion of the tube cross section of the clarification tank is the flow of the molten glass The road has a second portion having the gas phase space and having the liquid surface of the molten glass. Therefore, as described above, it is difficult to form crystals obtained by solidification of a volatile substance of platinum or a platinum alloy on the inner wall surface of the tube, and it is reduced as an impurity to be mixed into the molten glass in the clarification step.

The tube cross section of the tube is expanded in stages or continuously from the portion of the tube that does not have the gas phase space.

Further, it is preferable that the tube of the clarification tank is formed such that at least a part of the portion where the temperature of the tube is 1600 ° C or less does not have the gas phase space.

As the glass substrate, an alkali-free glass plate using an alkali-free glass or a trace alkali glass plate containing a glass containing a trace amount of a basic component and containing a small amount of alkali is preferably used. For example, in a glass substrate for a flat panel display, a TFT (Thin Film Transistor) is used on the surface. In this case, from the viewpoint of suppressing the influence of the TFT, the glass substrate preferably uses an alkali-free glass or a trace amount of alkali glass. However, alkali-free glass or a small amount of alkali glass has a high temperature viscosity. Therefore, the temperature of the molten glass in the melting tank and the clarification tank becomes higher than before. Even if the molten glass in the clarification tank is made high as described above In the case of temperature, at least a part of a portion where the temperature of the wall surface of the tube is equal to or lower than the temperature at which the platinum volatile matter contained in the gas phase space is solidified is also formed without a portion having the gas phase space. Therefore, it is difficult to form crystals of platinum or a platinum alloy on the inner wall surface of the above-mentioned tube or the vicinity thereof, and it is less likely to be mixed as impurities into the molten glass in the clarification step. Therefore, when a glass substrate is manufactured, it is possible to suppress impurities formed of platinum or a platinum alloy from being mixed into the glass substrate.

One of the pair of electrode plates may be provided, for example, at both ends of the inlet and the outlet of the tube.

Another aspect of the present invention is a manufacturing apparatus having a glass substrate for producing a melting tank of molten glass. The manufacturing apparatus includes: a melting device that melts the input glass raw material to produce molten glass; and a clarification tank including a tube made of platinum or a platinum alloy, wherein at least a defoaming treatment is performed in the tube, the defoaming treatment is performed a period in which the molten glass is passed through in a state in which the vapor phase is formed, a current is supplied between one of the tubes and the pair of electrode plates, and the tube is electrically heated, and then the bubbles are discharged to the gas phase space; a device for forming a glass sheet by molding the molten glass after passing through the clarification tank; a slow cooling device for slowly cooling the glass sheet; and a cutting device for cutting the glass sheet after the slow cooling A glass substrate is formed.

In the tube, at least a portion of the wall of the tube in the longitudinal direction of the tube is a temperature lower than a temperature at which the platinum volatile matter contained in the gas phase space is solidified, and the gas phase space is not formed in the portion. section.

At least a part of a portion of the wall of the tube having a temperature lower than a solidification temperature of the platinum volatile material contained in the gas phase space does not have the gas phase space, and therefore is at or near the portion of the portion It is difficult to make the inner wall surface of the above tube A crystal obtained by solidification of a volatile matter of platinum or a platinum alloy is formed, and the case where it is mixed as an impurity into the molten glass in the clarification step is reduced. Therefore, the apparatus for manufacturing a glass substrate can suppress impurities which are formed of platinum or a platinum alloy from being mixed into the glass substrate.

The heating of the molten glass is performed by applying a current from one of the tubes to the electrode plate to the tube to be electrically heated. In this case, the temperature of the wall of the tube below the temperature at which the platinum volatile material is solidified is, for example, the position of the electrode plate in which the temperature of the wall of the tube is locally lowered by the electrode plate provided in the longitudinal direction of the tube.

According to the method and apparatus for producing a glass substrate of the above aspect, it is possible to suppress the incorporation of impurities formed by platinum or a platinum alloy which is volatilized from the tube of the clarification tank used in the production process of the glass substrate.

100‧‧‧melting device

101‧‧‧melting tank

101a‧‧‧ liquid tank

101b‧‧‧Upper space

101c‧‧‧ liquid level

101d‧‧‧Spiral feeder

102‧‧‧Clarification tank

102a‧‧‧Clarification tube

102b‧‧‧ snorkel

102c, 102d‧‧‧electrode plates

102g‧‧‧AC power supply

103‧‧‧Stirring tank

103a‧‧‧Agitator

104, 105, 106‧‧‧ glass supply tube

200‧‧‧Forming device

210‧‧‧Formed body

220‧‧‧ Slow cooling device

300‧‧‧cutting device

Fig. 1 is a view showing an example of a procedure of a method for producing a glass substrate of the present embodiment.

Fig. 2 is a view schematically showing an example of an apparatus for performing a melting step to a cutting step in the embodiment.

Fig. 3 is a perspective view showing the clarification tank of the embodiment.

4(a) and 4(b) are views showing a cross section of the clarification pipe of the present embodiment.

Hereinafter, a method of manufacturing a glass substrate and a manufacturing apparatus of the present embodiment will be described. Fig. 1 is a view showing an example of a procedure of a method for producing a glass substrate of the present embodiment.

The manufacturing method of a glass substrate mainly has 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). ). In addition to this, there are a grinding step, a grinding step, a washing step, an inspection step, a packaging step, and the like; a plurality of layers of glass laminated in the packaging step The substrate is transported to the receiving party's staff.

The melting step (ST1) is carried out in a melting tank. In the melting step, molten glass is produced by putting a glass raw material into the liquid surface of the molten glass accumulated in the melting tank. Further, the molten glass is flown from the outflow port to the bottom portion, and the outflow port is provided at the bottom of one side of the inner wall facing the longitudinal direction of the melting groove in a plan view in the inner wall of the melting tank.

Here, the molten glass in the melting tank is electrically heated by using an electrode in the melting tank, whereby molten glass having a desired temperature is obtained in the melting tank. That is, the molten glass of the melting tank is heated by self-heating by causing a current to flow from the electrode through the molten glass itself. In addition to heating the molten glass by energization, it is also possible to use a burner to assist in providing a flame to melt the glass raw material. Further, a clarifying agent is added to the glass raw material. For the clarifying agent, SnO ₂ (tin oxide) is preferably used from the viewpoint of reducing the environmental load.

The clarification step (ST2) is carried out inside a clarification tube made of platinum or a platinum alloy in a clarification tank. In the clarification step, the molten glass in the tube of the clarification tank is heated. In this process, the clarifying agent is a substance which functions as a reducing agent by releasing oxygen by a reduction reaction. The bubble containing O ₂ , CO ₂ or SO ₂ contained in the molten glass absorbs O ₂ generated by the reduction reaction of the clarifying agent, grows up, floats up to the liquid surface of the molten glass, and then the bubble collapses and disappears. The gas contained in the bubbles is discharged to the outside air through a gas phase space provided in the clarification tank.

Thereafter, the temperature of the molten glass is lowered in the clarification step. In this process, the reducing agent obtained by the reduction reaction of the clarifying agent undergoes an oxidation reaction. Thereby, the gas component such as O ₂ in the bubbles remaining in the molten glass is again absorbed into the molten glass, and the bubbles disappear.

In the homogenization step (ST3), the molten glass in the stirring tank supplied through the piping extending from the clarification tank is stirred by a stirrer to homogenize the glass component. Thereby, it is possible to reduce the glass composition unevenness caused by the ribs and the like. Furthermore, one stirring tank can be provided, or two stirring tanks can be provided.

In the supply step (ST4), the molten glass is supplied to the molding apparatus through a pipe extending from the stirring tank.

In the molding apparatus, a forming step (ST5) and a slow cooling step (ST6) are performed.

In the molding step (ST5), the molten glass is formed into a sheet glass to form a fluid of the sheet glass. The forming can use an overflow download method or a float method. In the present embodiment to be described later, an overflow down-draw method is used.

In the slow cooling step (ST6), the flow-formed sheet glass is formed so as to have a desired thickness and no internal strain, and is further cooled without causing warpage.

In the cutting step (ST7), the sheet glass supplied from the molding device is cut into a specific length in the cutting device to obtain a plate-shaped glass plate. The cut glass sheet is further cut into a specific size to form a glass substrate of a target size. Thereafter, the end surface of the glass substrate is ground and polished, and the glass substrate is cleaned. Further, the presence or absence of abnormal defects such as bubbles or ribs is checked, and then the glass plate of the qualified product is packaged as a final product.

Fig. 2 is a view schematically showing an example of a device for performing a melting step (ST1) to a cutting step (ST7) in the embodiment. As shown in FIG. 2, the apparatus mainly has a melting apparatus 100, a forming apparatus 200, and a cutting apparatus 300. The melting apparatus 100 has a melting tank 101, a clarification tank 102, a stirring tank 103, and glass supply pipes 104, 105, and 106.

In the melting tank (melting apparatus) 101 exemplified in Fig. 2, the glass material is supplied by using the screw feeder 101d. In the present embodiment, the glass material is supplied by using the screw feeder 101d. However, the glass material may be supplied by using another material input method, for example, a hopper, and the method of introducing the glass material is not limited. The clarification tank 102 includes a clarification tube 102a made of platinum or a platinum alloy (refer to FIG. 3). At least the molten glass MG is subjected to a defoaming treatment in the clarification pipe 102a. In the defoaming process, when the molten glass MG is passed in a state in which the vapor phase is formed so that the molten glass MG has a liquid surface, the current is set. The clarification pipe 102a is circulated to one of the clarification pipes 102a to electrically conduct the clarification pipe 102a, thereby discharging the bubbles into the gas phase space. In the stirring tank 103, the molten glass MG is stirred by the agitator 103a, and it is homogenized.

The forming apparatus 200 includes a formed body 210 by using an overflow down-draw method of the formed body 210 The molten glass MG which passed the clarification tank 200 and the stirring tank 103 is shape|molded, and the glass piece SG is obtained.

The slow cooling device 220 slowly cools the glass sheet SG so that the glass sheet SG does not cause variations in thickness, strain, and bending.

The cutting device 300 cuts the slowly cooled glass sheet SG to form a glass substrate.

(clarification step)

Fig. 3 is a view mainly showing the configuration of a device for performing a clarification step. 4(a) and 4(b) are views showing the relationship between the cross section of the clarification pipe used in the present embodiment and the molten glass.

The clarification step includes a defoaming treatment and an absorption treatment. In the following description, an example in which SnO _{2 is} used as a clarifying agent will be described. SnO _{2 has a} lower clarifying function than the previous As ₂ O ₃ , but can be preferably used as a clarifying agent in terms of low environmental load. However, the clarification function of SnO ₂ is lower than that of As ₂ O ₃ , so the temperature of the molten glass MG at the time of the clarification step of the molten glass MG must be made higher than the previous one when using SnO ₂ . In this case, for example, the maximum temperature in the clarification step may be about 1,700 ° C, preferably 1710 ° C or lower, more preferably 1720 ° C or lower.

The molten glass MG melted in the melting tank 101 is introduced into the clarification pipe 102a of the clarification tank 102 by the glass supply pipe 104 (refer to FIG. 2).

As shown in Fig. 3, the clarification tank 102 is provided with a long clarification pipe 102a made of platinum or a platinum alloy, a vent pipe 102b provided at the top of the clarification pipe 102a, and electrode plates 102c and 102d.

Although not shown, refractory bricks may be coated around the clarification pipe 102a. A vent pipe 102b is provided at a substantially central portion of the clarification pipe 102a.

Electrode plates 102c and 102d are flange-shaped at the ends of both sides of the clarification pipe 102a so as to wind the outer circumference of the clarification pipe 102a. The electrode plates 102c and 102d are connected to the alternating current power source 102g, and a specific voltage is applied. The electrode plates 102c and 102d flow a current through the clarification pipe 102a to electrically heat the clarification pipe 102a, thereby raising the temperature of the molten glass MG flowing through the clarification pipe 102a to, for example, 1630 ° C or higher. In this case, for example, the clarification step can be The maximum temperature is about 1700 ° C, preferably 1710 ° C or less, more preferably 1720 ° C or less.

On the other hand, in the clarification pipe 102a, the molten glass MG flows so that the molten glass MG has a liquid surface. In the molten glass MG having a viscosity of, for example, 120 to 400 poise due to the temperature rise, the bubble expanded in the molten glass MG by the action of the clarifying agent floats, and the bubble on the surface of the molten glass MG is broken, thereby discharging the gas contained in the bubble. To the gas phase space. That is, a defoaming process is performed. Therefore, the clarification pipe 102a has a gas phase space inside thereof in such a manner that the molten glass MG has a liquid surface.

The gas component which is ruptured in the gas phase space above the clarification pipe 102a is discharged to the outside of the clarification pipe 102a through the vent pipe 102b. The bubbles having a fast floating speed and a large diameter are removed in the clarification pipe 102a.

After the temperature of the molten glass MG flowing through the clarification pipe 102a is maintained at, for example, 1630 ° C or higher, the temperature is gradually lowered (staged or continuous) after the second half of the clarification pipe 102a or after the subsequent glass supply pipe 105, thereby performing bubble generation. Absorption treatment. As described above, in the absorption treatment, the bubbles are absorbed in the molten glass MG due to the temperature drop of the molten glass MG, and disappear.

Although an example in which a pair of electrode plates 102c and 102d are provided is shown in Fig. 3, for example, in the case where the second half of the clarification pipe 102a is cooled, a pair of electrode plates may be provided in addition to the electrode plates 102c and 102d.

Further, the clarification pipe 102a is provided with a gas phase space for rupturing the liquid surface of the molten glass MG to discharge the exhaust gas to the outside air, and a vent pipe 102b is provided on the clarification pipe 102a. Therefore, the gas phase space communicating with the outside air contains oxygen.

On the other hand, since the clarification pipe 102a is heated to a high temperature (for example, about 1700 ° C) by electric conduction heating, the inner wall surface of the clarification pipe 102a made of platinum or a platinum alloy is easily volatilized. In particular, since the gas phase space contains oxygen, the platinum or platinum alloy is further volatilized into the gas phase space. Therefore, the gas phase space contains platinum volatiles vaporized from the inner wall surface of the clarification pipe 102a.

Here, the portion of the clarification pipe 102a where the electrode plates 102c and 102d are provided is narrower than the portion of the clarification pipe 102a. As shown in Fig. 4(a), in the portion where the electrode plates 102c and 102d are provided, the entire pipe cross section of the clarification pipe 102a of the clarification tank 102 is a flow path (hatched area) of the molten glass MG. That is, inside the clarification pipe 102a, there is no gas phase space at the position (electrode plate position) where the electrode plates 102c and 102d are provided. As the distance from the portion is increased, the pipe section is gradually enlarged. As shown in Fig. 4(b), one of the pipe sections of the clarification pipe 102a is a flow path (hatched portion) of the molten glass MG, and the molten glass MG has a liquid surface. In other words, the clarification pipe 102a of the clarification tank 102 is provided with a portion (first portion) having no gas phase space and a portion (second portion) having a gas phase space and having a liquid surface of the molten glass MG, and the first portion The electrode plate position in the longitudinal direction of the clarification pipe 102a of the clarification tank 102, and the pipe cross section of the clarification pipe 102a as a whole is a flow path of the molten glass MG, and in the second portion, a part of the pipe cross section of the clarification pipe 102a is melted. Glass MG flow path. Further, the electrode plates 102c and 102d are provided in a flange shape, whereby the electrode plates 102c and 102d have a large contact area with the outside air and have a cooling function, so that the temperature of the wall of the clarification pipe 102a is locally lowered at the position of the electrode plate. . Further, in order to prevent the temperature of the electrode plates 102c and 102d from being excessively high, the temperature is further lowered. That is, in the portion where the electrode plates 102c and 102d are provided, the temperature of the wall of the clarification pipe 102a is locally lowered. Specifically, in the clarification pipe 102a, there is a portion having no gas phase space in the longitudinal direction of the clarification pipe 102a, and the temperature of the wall of the clarification pipe 102a in this portion is equal to or lower than the temperature at which the platinum volatile matter contained in the gas phase space is solidified.

Therefore, if a gas phase space exists at this position, the platinum volatile matter in the gas phase space is cooled around the above portion, and it is easy to solidify on the inner wall surface of the position, and it is easy to form crystals of platinum or platinum alloy. One part of the crystal of the platinum or platinum alloy falls off as fine particles, falls in the molten glass MG, and is easily mixed into the molten glass MG. When such a molten glass MG flows into the subsequent step, a defective glass substrate in which metal impurities are mixed is produced, which is not preferable.

In the present embodiment, the temperature of the wall of the clarification pipe 102a is a portion in the longitudinal direction of the temperature at which the platinum volatile matter contained in the gas phase space is solidified, and specifically, the portion where the electrode plates 102c and 102d are provided (electrode) In the inner wall surface of the position, in order to prevent the gas phase space from being present, the pipe section of the clarification pipe 102a is smaller than the other portions.

The temperature at which the platinum volatiles contained in the gas phase space are solidified is determined in advance by an experiment or the like. The temperature fluctuates depending on the amount of volatilization of the platinum volatiles, and the amount of volatilization of the platinum volatiles is affected by the conditions of the gas phase space such as the oxygen partial pressure of the gas phase space.

Further, the pipe cross section of the clarification pipe 102a of the present embodiment is continuously expanded from the first portion of the clarification pipe 102a which does not have the gas phase space, but the pipe cross section may be gradually expanded.

Further, the temperature at which the platinum volatiles are solidified varies depending on the concentration of platinum or platinum alloy in the atmosphere of the gas phase space in the clarification pipe 102a, but for example, the temperature of the clarification pipe 102a is 1600 ° C or lower, particularly 1500 ° C or lower. The area is prone to solidification of platinum volatiles. Therefore, the clarification pipe 102a is preferably formed such that at least a part of the portion of the clarification pipe 102a having a temperature of 1600 ° C or less does not have a gas phase space.

In the present embodiment, the clarification pipe 102a has a configuration in which the cross-sectional area of the pipe gradually increases away from the electrode position, but the embodiment is not limited thereto. It is also possible to use a configuration in which the cross-sectional area of the pipe is sharply enlarged as a part of a distance away from the electrode position.

Further, in the clarification pipe 102a of the present embodiment, in the longitudinal direction of the clarification pipe 102a, there are two positions where the temperature is equal to or lower than the temperature at which the platinum volatile matter contained in the gas phase space is solidified, that is, the position of the electrode plate. Each part forms a part that does not have a gas phase space. However, in the longitudinal direction of the clarification pipe 102a, when there are a plurality of portions of the clarification pipe 102a whose temperature is below the solidification temperature of the platinum volatiles contained in the gas phase space, no gas may be formed in at least one portion of the portions. Part of the phase space.

Thus, the position of the electrode plate of the clarification pipe 102a of the clarification tank 102 at the temperature of the wall of the clarification pipe 102a is partially reduced by the electrode plates 102c and 102d, and the gas pipe space of the clarification pipe 102a is entirely the molten glass MG. Flow path, thus volatilizing from clarification tube 102a Since platinum or a platinum alloy does not crystallize at the position of the electrode plate, metal impurities such as platinum impurities or platinum alloy impurities are less likely to be mixed into the molten glass MG, and the incorporation of metal impurities into the produced glass substrate can be suppressed.

The effects of the present embodiment can be more effectively exhibited in the case of the following (A) and (B), that is, when the temperature of the molten glass in the clarification pipe is higher than the previous case.

(A) as compared with previously been using a refining agent of As ₂ O _3, SnO ₂ and less toxicity, and therefore from the viewpoint of reducing the environmental impact of the departure, preferably using SnO ₂ as a fining agent. However, in order to effectively exert the clarifying function of SnO _{2 having a} poorer clarifying function than As ₂ O ₃ which has been used as a clarifying agent, it is necessary to make the temperature of the molten glass in the clarification pipe higher than the previous one.

(B) For the molten glass having high viscosity at a high temperature, in the defoaming treatment in the clarification step, the temperature of the molten glass in the clarification tube is also made higher than the previous one. The glass having a high temperature and high viscosity is, for example, a glass having a temperature of 10 ^2.5 poise of the molten glass MG of 1500 ° C or higher. Moreover, the alkali-free glass and the glass containing a trace amount of alkali glass are high-temperature adhesive.

(glass composition)

The glass composition of the glass substrate can be exemplified by the following composition.

The content ratio of the composition shown below is expressed by mass%.

An alkali-free glass containing the following components is preferred.

SiO ₂ : 50% to 70%, Al ₂ O ₃ : 0% to 25%, B ₂ O ₃ : 1% to 15%, MgO: 0% to 10%, CaO: 0% to 20%, SrO: 0 %~20%, BaO: 0%~10%, RO: 5%~30% (where R is selected from at least one of Mg, Ca, Sr, and Ba, and is a substance contained in a glass substrate)

Further, in the present embodiment, the alkali-free glass is used, but the glass substrate may be a trace amount of alkali glass containing an alkali metal. In the case of containing an alkali metal, the total content of R' ₂ O is preferably 0.10% or more and 0.5% or less, preferably 0.20% or more and 0.5% or less (wherein R' is selected from at least Li, Na, and K. One type is a substance contained in a glass substrate). Of course, the total of R' ₂ O can be less than 0.10%. Further, it is preferable that substantially no As ₂ O ₃ , Sb ₂ O ₃ and PbO are contained.

Further, in the case of applying the method for producing a glass substrate of the present embodiment, in addition to the above respective components, the glass composition can also contain 0.01% to 1% (preferably 0.01% to 0.5%) of SnO by mass%. ₂ , 0% to 0.2% (preferably 0.01% to 0.08%) of Fe ₂ O ₃ ; if the environmental load is taken into consideration, the glass is prepared substantially without As ₂ O ₃ , Sb ₂ O ₃ and PbO raw material.

In the above, the present invention is not limited to the above-described embodiments, and various modifications and changes can be made without departing from the spirit and scope of the invention.

102‧‧‧Clarification tank

102a‧‧‧Clarification tube

102b‧‧‧ snorkel

102c, 102d‧‧‧electrode plates

102g‧‧‧AC power supply

Claims (10)

A method for producing a glass substrate, comprising: a melting step of melting a glass raw material to form a molten glass; and a clarifying step comprising a defoaming treatment comprising consisting of platinum or a platinum alloy and In the clarification tank of the heated long tube, the molten glass is heated while the molten glass is formed in a state in which the vapor phase is formed, thereby discharging the bubbles from the molten glass to the vapor phase space. The tube of the clarification tank is formed so that at least a part of a portion below the temperature at which the platinum volatile matter contained in the gas phase space is solidified does not have the gas phase space. The method for producing a glass substrate according to claim 1, wherein the heating of the molten glass is performed by causing a current to flow from the one of the tubes to the tube to be electrically heated, and the temperature of the tube is locally lowered. The electrode plate does not have a gas phase space at the position. The method for producing a glass substrate according to claim 1 or 2, wherein the molten glass contains SnO ₂ as a fining agent. The method for producing a glass substrate according to claim 1 or 2, wherein the molten glass has a temperature of 1500 ° C or higher at 10 ^2.5 poise. The method for producing a glass substrate according to claim 1 or 2, wherein the inner wall surface of the tube is in contact with the molten glass at a portion of the tube which does not have the gas phase space. The method for producing a glass substrate according to claim 1 or 2, wherein the tube has: a tube having a cross section of the tube as a whole of the molten glass flow path and having no first portion of the gas phase space; and a conduit of the clarification tank One of the sections is a flow path of the molten glass to have a gas phase space and have a liquid surface of the molten glass Part 2 of it. The method for producing a glass substrate according to claim 1 or 2, wherein the tube cross section of the tube is expanded in a stepwise or continuous manner from a portion of the tube which does not have the gas phase space. The method of producing a glass substrate according to claim 1 or 2, wherein the pair of electrode plates are provided at both ends of the inlet and the outlet of the tube. The method for producing a glass substrate according to claim 1 or 2, wherein the glass substrate is an alkali-free glass or a trace amount of an alkali glass substrate. A glass substrate manufacturing apparatus characterized by comprising a melting tank for generating molten glass, and comprising: a melting device for melting an input glass raw material to produce molten glass; and a clarification tank containing platinum or a platinum alloy In the tube, at least a defoaming treatment is performed in the tube, and the defoaming treatment is performed while the molten glass is passed through the vapor phase space, and a current is provided between one of the tubes and the counter electrode Circulating to electrically heat the tube, and then discharging the bubbles to the gas phase space; forming means for forming the glass sheet by molding the molten glass after passing through the clarification tank; and slow cooling device for performing the glass sheet a slow cooling; and a cutting device for cutting the glass sheet after the slow cooling to form a glass substrate; wherein, in the tube, the temperature of the wall of the tube is in the gas phase space in the longitudinal direction of the tube At least a portion of the portion below the temperature at which the platinum volatiles are solidified is formed with a portion that does not have the gas phase space.