TWI545096B - A glass substrate manufacturing method, a glass substrate manufacturing apparatus, and a molten glass processing apparatus - Google Patents

Description

Method for producing glass substrate, glass substrate manufacturing device, and molten glass processing device

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

The glass substrate is usually produced by forming molten glass from a glass raw material, and then molding the molten glass into a glass substrate through a clarification step and a homogenization step.

In addition, in order to obtain a high-quality glass substrate having a high-temperature molten glass, it is desirable to mix impurities into the molten glass from any device for manufacturing a glass substrate without considering impurities or the like which are the main factors of the defects of the glass substrate. Therefore, in the manufacturing process of the glass substrate, the inner wall of the member in contact with the molten glass must be composed of a suitable material depending on the temperature of the molten glass contacting the member, the quality of the desired glass substrate, and the like. For example, the molten glass is heated to a high temperature state after the molten glass is produced and supplied to the forming step, so that the clarification device for performing the clarification step, the stirring device for performing the homogenization step, and the glass supply tube for transferring the molten glass use heat resistance. It is composed of a higher platinum group metal. However, the platinum group metal is easily volatilized accompanying the high temperature of the molten glass. Further, there is a case where the volatile matter of the platinum group metal aggregates on the inner wall surrounding the gas phase space to form an aggregate, and one of the aggregates is partially removed, and the impurities are mixed into the molten glass, and the quality of the glass substrate is lowered.

On the other hand, there is known a glass melting furnace which is capable of obtaining a high-quality glass having less enthalpy of inclusion of platinum impurities and having less optical defects such as cord streaks or impurities (Patent Document 1).

In the glass melting furnace, the lower portion of the inner wall surface of the groove body which is provided with the top wall and closed is formed by a platinum surface formed of platinum or a platinum alloy, and the platinum surface is not exposed to the molten glass at the upper end thereof. The position in the upper atmosphere of the trough is formed.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2010-202444

As in the case of Patent Document 1, as long as the contact area between the atmosphere of the gas phase space on the upper surface of the molten glass and the wall surface of the platinum group metal disappears, volatilization of the platinum group metal does not occur. Further, it is considered that the volatilization of the platinum group metal can be reduced by reducing the contact area of the inner wall of the platinum group metal in contact with the atmosphere of the gas phase space. However, even in the case where the contact area of the inner wall of the platinum group metal which is in contact with the atmosphere of the gas phase space is reduced, the platinum group metal which volatilizes from the wall surface cannot be sufficiently reduced.

Accordingly, an object of the present invention is to provide a method for producing a glass substrate, a glass substrate manufacturing apparatus, and a processing apparatus for molten glass, which are used in a process of manufacturing a glass substrate and at least partially containing a platinum group metal. When the molten glass is treated in the molten glass processing apparatus of the material composition, the platinum group metal which is volatilized on the inner wall of the free platinum group metal is suppressed, and a part of the aggregate of the platinum metal which is volatilized in the gas phase space is suppressed from being mixed into the molten metal. glass.

The present invention encompasses the following aspects.

(Form 1)

A method for producing a glass substrate, comprising: a melting step of melting a raw material of glass to produce molten glass; and a processing step of treating the molten glass in a molten glass processing apparatus, the melting The molten glass processing apparatus has a gas phase space formed by the liquid surface and the inner wall of the molten glass, and a liquid phase of the molten glass, and at least a part of the inner wall surrounding the gas phase space is composed of a material containing a platinum group metal And in the above processing step, controlling a ratio of an area of the platinum group metal of the inner wall in contact with the gas phase space to a volume of the gas phase space to reduce a volatilization of the platinum group metal of the molten glass processing apparatus; .

(Form 2)

The method for producing a glass substrate according to the first aspect, wherein the ratio is controlled by controlling a level of the liquid surface of the molten glass.

(Form 3)

The method for producing a glass substrate according to the second aspect, wherein the correlation between the number of platinum defects and the liquid level of the molten glass in the molten glass processing apparatus is determined in advance, and the above-mentioned tolerance value of the number of platinum defects is determined. The level of the liquid level of the molten glass processing apparatus is determined as the reference level, and the above-described processing steps control the level of the liquid level based on the level of the reference level.

(Form 4)

A method for producing a glass substrate, comprising: a melting step of melting a raw material of glass to produce molten glass; and a processing step of treating the molten glass in a molten glass processing apparatus having a molten glass a gas phase space formed by the liquid surface and the inner wall, and a liquid phase of the molten glass, and at least a portion of the inner wall surrounding the gas phase space is composed of a material containing a platinum group metal; and a forming step of the above treatment The molten glass treated in the step is formed into a sheet glass; and the method for producing the glass substrate is to determine the correlation between the number of platinum defects and the liquid level of the molten glass processing apparatus in advance, and the number of platinum defects The allowable value corresponds to the above The level of the liquid level of the molten glass processing apparatus is determined as the reference level, and the above-described processing steps control the level of the liquid level based on the level of the reference level.

(Form 5)

The method for producing a glass substrate according to the above aspect 3, wherein the processing step controls the liquid level based on a target liquid level level determined by including the reference liquid level.

(Form 6)

The method for producing a glass substrate according to any one of the aspects 3 to 5, wherein the amount of the molten glass supplied to the molten glass processing apparatus and the amount of the flat glass formed in the forming step are controlled. At least one of them controls the level of the liquid level.

(Form 7)

The method for producing a glass substrate according to any one of the aspects 1 to 6, wherein the volume of the gas phase space is S[m ³ ], and the area of the platinum group metal in contact with the gas phase space is set. is L [m ^2], the ratio S / L is 17 [m] or more. In this case, the molten glass may occupy 50% or more of the entire space in the gas phase space.

(Form 8)

The method for producing a glass substrate according to any one of the aspects 1 to 7, wherein the ratio is determined based on at least one of the following conditions: (1) an oxygen concentration in the gas phase space, and (2) a maximum temperature of the inner wall of the molten glass processing apparatus, (3) an amount of oxygen released from the molten glass to the gas phase space, (4) a maximum temperature of the molten glass in the melting step, and the above a temperature difference between the highest temperature of the molten glass in the treatment step, and (5) a vapor pressure of the platinum group metal in the gas phase space.

(Form 9)

The method for producing a glass substrate according to the eighth aspect, wherein the oxygen concentration in the gas phase space is controlled based on a content of tin oxide contained in the molten glass.

(Form 10)

In the method for producing a glass substrate according to any one of the aspects 1 to 9, the temperature difference between the highest temperature and the lowest temperature of the portion of the platinum group metal of the inner wall in contact with the gas phase is 50° C. or more.

(Form 11)

The method for producing a glass substrate according to any one of the aspects 1 to 10, wherein the molten glass processing apparatus is a clarification apparatus for clarifying the molten glass.

(Form 12)

The method for producing a glass substrate according to any one of aspects 1 to 11, wherein the processing step is a clarification step of the molten glass, and oxygen is released from the molten glass to the gas phase space.

(Form 13)

The method for producing a glass substrate according to any one of aspects 1 to 12, wherein the molten glass flows in the liquid phase, and a temperature distribution is formed in the inner wall along a flow direction of the molten glass.

(Form 14)

The method for producing a glass substrate according to any one of the aspects 1 to 13, wherein the glass substrate is a glass substrate for a display.

(Form 15)

A method for producing a glass substrate, comprising: a melting step of melting a raw material of glass to produce molten glass; and a treatment step of treating the molten glass in a molten glass processing apparatus having the above a gas phase space formed by the liquid surface and the inner wall of the molten glass, and a liquid phase of the molten glass, and surrounding at least one of the inner walls of the gas phase space And consisting of a material containing a platinum group metal; and in the above-mentioned processing step, adjusting a ratio of an area of the platinum group metal of the inner wall in contact with the gas phase space to a volume of the gas phase space to reduce the molten glass The volatilization of the above platinum group metal of the treatment device.

(Form 16)

A method for producing a glass substrate, comprising: a melting step of melting a raw material of glass to produce molten glass; and a processing step of treating the molten glass in a molten glass processing apparatus having a molten glass a gas phase space formed by the liquid surface and the inner wall, and a liquid phase of the molten glass, and at least a portion of the inner wall surrounding the gas phase space is composed of a material containing a platinum group metal; and a forming step, which will be described above The molten glass processed in the treatment step is formed into a flat glass; and the method for producing the glass substrate is to determine the correlation between the number of platinum defects and the liquid level of the molten glass processing apparatus in advance, and the allowable value of the number of platinum defects The liquid level of the corresponding molten glass processing apparatus is determined as the reference liquid level, and the processing step adjusts the liquid level based on the reference liquid level.

(Form 17)

The method for producing a glass substrate according to any one of the aspects 1 to 16, wherein the oxygen concentration in the gas phase space is 1% or less.

(Form 18)

The method for producing a glass substrate according to any one of the aspects 1 to 17, wherein the content of the tin oxide in the glass substrate is 0.01 to 0.3 mol%.

(Form 19)

A molten glass processing apparatus characterized by comprising a gas phase space formed by a liquid surface and an inner wall of molten glass, and a molten glass a liquid phase of the glass, and at least a portion of the inner wall surrounding the gas phase space is composed of a material containing a platinum group metal; and includes a control portion that controls the platinum group metal of the inner wall in contact with the gas phase space The ratio of the area to the volume of the gas phase space described above to reduce the volatilization of the platinum group metal in the gas phase space.

(Form 20)

A molten glass processing apparatus comprising: a gas phase space formed by a liquid surface and an inner wall of molten glass; and a liquid phase of molten glass, wherein at least a part of an inner wall surrounding the gas phase space is made of platinum a material of a group metal; and an adjustment portion that adjusts a ratio of an area of the platinum group metal of the inner wall in contact with the gas phase space to a volume of the gas phase space to reduce the above-mentioned gas phase space Volatilization of platinum group metals.

(Form 21)

A molten glass processing apparatus comprising: a gas phase space formed by a liquid surface and an inner wall of molten glass; and a liquid phase of molten glass, wherein at least a part of an inner wall surrounding the gas phase space is made of platinum And a control unit that controls a liquid level of the molten glass processing apparatus to a predetermined reference liquid level; and the control unit is based on the number of platinum defects determined in advance and the molten glass The liquid level level of the processing apparatus is determined, and the reference liquid level is determined as the liquid level of the molten glass processing apparatus corresponding to the allowable value of the platinum defect number.

(Form 22)

A molten glass processing apparatus characterized by comprising a gas phase space formed by a liquid surface and an inner wall of molten glass, and a molten glass a liquid phase of the glass, wherein at least a part of the inner wall surrounding the gas phase space is made of a material containing a platinum group metal; and an adjustment portion for adjusting a liquid level of the molten glass processing apparatus to a predetermined reference liquid The adjustment level is determined based on the correlation between the number of platinum defects obtained in advance and the liquid level of the molten glass processing apparatus, and the reference liquid level is determined as the melting corresponding to the allowable value of the number of platinum defects. The level of the liquid level of the glass processing unit.

(Form 23)

A glass substrate manufacturing apparatus characterized by comprising: a melting device that melts a raw material of glass to produce molten glass; and a molten glass processing device that processes the molten glass and includes a liquid surface and an inner wall formed of molten glass a gas phase space and a liquid phase of the molten glass, and at least a part of an inner wall surrounding the gas phase space is made of a material containing a platinum group metal; and a molding apparatus for forming the molten glass treated by the molten glass processing apparatus into a flat plate a glass; and a control unit that controls a ratio of an area of the platinum group metal of the inner wall in contact with the gas phase space to a volume of the gas phase space to reduce volatilization of the platinum group metal of the molten glass processing apparatus.

(Form 24)

A glass substrate manufacturing apparatus characterized by comprising: a melting device that melts a raw material of glass to produce molten glass; and a molten glass processing device that processes the molten glass and includes a liquid surface and an inner wall formed of molten glass a gas phase space and a liquid phase of the molten glass, and at least a part of an inner wall surrounding the gas phase space is made of a material containing a platinum group metal; and a molding apparatus for forming the molten glass treated by the molten glass processing apparatus into a flat plate Glass; and The adjusting portion adjusts a ratio of an area of the platinum group metal of the inner wall in contact with the gas phase space to a volume of the gas phase space to reduce volatilization of the platinum group metal in the molten glass processing apparatus.

(Form 25)

A glass substrate manufacturing apparatus characterized by comprising: a melting device that melts a raw material of glass to produce molten glass; and a molten glass processing device that processes the molten glass and includes a liquid surface and an inner wall formed of molten glass a gas phase space and a liquid phase of the molten glass, and at least a part of an inner wall surrounding the gas phase space is made of a material containing a platinum group metal; and a molding apparatus for forming the molten glass treated by the molten glass processing apparatus into a flat plate a glass; and a control unit that controls a liquid level of the molten glass processing apparatus to a predetermined reference liquid level; and the control unit is based on a predetermined number of platinum defects and a liquid level of the molten glass processing apparatus In the correlation, the reference liquid level is determined as the liquid level of the molten glass processing apparatus corresponding to the allowable value of the platinum defect number.

(Form 26)

A glass substrate manufacturing apparatus characterized by comprising: a melting device that melts a raw material of glass to produce molten glass; and a molten glass processing device that processes the molten glass and includes a liquid surface and an inner wall formed of molten glass a gas phase space and a liquid phase of the molten glass, and at least a part of an inner wall surrounding the gas phase space is made of a material containing a platinum group metal; and a molding apparatus for forming the molten glass treated by the molten glass processing apparatus into a flat plate a glass; and an adjustment unit that adjusts a liquid level of the molten glass processing apparatus to a predetermined reference liquid level; The adjustment unit determines the reference liquid level to be the molten glass processing apparatus corresponding to the allowable value of the number of platinum defects based on the correlation between the number of platinum defects obtained in advance and the liquid level of the molten glass processing apparatus. Level level.

According to the method for producing a glass substrate, the glass substrate manufacturing apparatus, and the molten glass processing apparatus according to the above aspect, the volatilization of the platinum group metal can be suppressed, and a part of the aggregate of the platinum metal volatilized in the gas phase space can be suppressed from becoming an impurity. It is mixed into the molten glass.

100‧‧‧Solid glass generator

101‧‧‧melting device

101d‧‧‧Spiral feeder

102‧‧‧Clarification device

102a‧‧‧Clarification tube

102b‧‧‧ snorkel

103‧‧‧Agitator

103a‧‧‧Agitator

104, 105, 106‧‧‧ glass supply tube

107‧‧‧ snorkel

200‧‧‧Forming device

210‧‧‧Formed body

300‧‧‧cutting device

MG‧‧‧ molten glass

SG‧‧ ‧ flat glass

W1, W2‧‧‧ airflow

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

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

Fig. 3 (a) and (b) are views showing the flow of the liquid flow in the gas phase space of the clarification device of the present embodiment and the clarification device.

4(a) and 4(b) are diagrams showing changes in the level of the liquid surface of the molten glass in the clarification device.

Fig. 5 is a view for explaining the level of the line and the target liquid level used in the embodiment.

Fig. 6 is a view showing the relationship between the ratio S/L and the defect density used in the present embodiment.

Hereinafter, a method for producing a glass substrate, a glass substrate manufacturing apparatus, and a molten glass processing apparatus according to 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 embodiment.

The platinum or platinum alloy described below is a platinum group metal, and includes platinum, rhodium, ruthenium, palladium, iridium, osmium, and alloys of the metals.

Further, the impurity (platinum defect) of the platinum or platinum alloy after the aggregation is a unidirectional elongated linear material. The maximum length of the platinum defect refers to the impurity (agglomerate) of the platinum group metal. The image of the impurity at the time of shooting is externally connected to the length of the long side of the longest side of the rectangle. The minimum length of the platinum defect refers to the length of the short side of the shortest side which is connected to the image of the impurity when the impurity (aggregate) of the platinum group metal is imaged. The term "platinum defect" refers to an impurity of a platinum group metal having an aspect ratio of more than 100 as a ratio of the maximum length to the minimum length. For example, the platinum group metal impurity (agglomerate) has a maximum length of 50 μm to 300 μm and a minimum length of 0.5 μm to 2 μm.

The controls in this manual contain adjustments. The adjustment includes at least an adjustment of the temperature, flow rate, concentration, pressure, and the like of the object by the input operation of the operator and manual adjustment by the operator.

The manufacturing method of the glass substrate mainly includes a melting step (ST1), a clarification step (ST2), a homogenization step (ST3), a molding step (ST4), a cold cooling step (ST5), and a cutting step (ST6).

The melting step (ST1) is carried out in a melting tank. The melting step is to produce a molten glass by putting a glass raw material into a liquid surface of a molten glass stored in a melting tank. Further, it is preferred to add a clarifying agent to the glass raw material. Regarding the clarifying agent, tin oxide can be preferably used in terms of reducing the environmental load.

The clarification step (ST2) is carried out inside the clarification tube composed of platinum or a platinum alloy or the like in the clarification device. In the clarification step, the molten glass in the tube of the clarification device is heated. In this process, the clarifying agent becomes a substance which releases oxygen by a reduction reaction and then acts as a reducing agent. The bubble containing O ₂ , CO ₂ or SO ₂ contained in the molten glass is integrated with O ₂ generated by the reduction reaction of the clarifying agent, and the volume becomes large, and floats to the surface of the molten glass and breaks. So disappear. The gas contained in the bubble is released to the outside atmosphere through a gas phase space provided in the clarification device.

Thereafter, in the clarification step, the temperature of the molten glass is lowered. In this process, the reducing agent obtained by the reduction reaction of the fining agent is subjected to an oxidation reaction. Thereby, a gas component such as O ₂ remaining in the bubble of the molten glass is dissolved in the molten glass to cause the bubble to disappear.

In the homogenization step (ST3), the molten glass in the stirring device supplied through the pipe extending from the clarification device is stirred by a stirrer to homogenize the molten glass. The homogenization step (ST3) can also be carried out before the clarification step.

The forming step (ST4) and the quenching step (ST5) are performed in the forming apparatus.

The forming step (ST4) forms the molten glass into a flat glass and forms a fluid of the flat glass. For forming, an overflow down-draw method or a floating method can be used. The following series of embodiments will be described using an example of an overflow down-draw method.

The cold step (ST5) is such that the formed and flowing flat glass becomes a desired thickness, and is cooled in such a manner that no internal strain is generated and warpage is not generated.

In the cutting step (ST6), the plate glass supplied from the molding device is cut into a specific length by the cutting device to obtain a plate-shaped glass plate. The cut glass sheet is further cut into a specific size to produce a glass substrate of a target size.

The method for producing a glass substrate of the present embodiment is carried out by the following method in an apparatus for a clarification step to a homogenization step.

That is, after melting the raw material of the glass to produce a melting step of the molten glass, the molten glass is passed through a molten glass processing apparatus for processing molten glass before being formed into a flat glass. The treatment device comprises a metal tube or tank having an inner wall comprising platinum or a platinum alloy or the like. The tube or tank comprises a liquid phase of molten glass and a gas phase space formed by the liquid surface and the inner wall of the molten glass, and the inner wall surrounding the gas phase space is composed of a material containing a platinum group metal. The molten glass processing apparatus controls (adjusts) the ratio of the area of the platinum group metal of the inner wall of the molten glass processing apparatus in contact with the gas phase space to the volume of the gas phase space, or controls (adjusts) the melting in the molten glass processing apparatus. The level of the liquid level of the glass is used to reduce the volatilization of the platinum group metal in the molten glass processing apparatus in contact with the gas phase space. By appropriately controlling (adjusting) the above ratio or the above liquid level, it is possible to suppress the volatilization of the platinum group metal from the inner wall of the molten glass processing apparatus. This aspect is explained below. Such a molten glass processing apparatus is suitable for use in a device used in the steps between the melting step and the forming step. And A device suitable for use in the steps between the clarification step and the homogenization step. For example, it is suitable for a clarification device for performing a clarification step and a stirring device for performing a homogenization step. Hereinafter, a description will be given of a form suitable for the clarification device.

Fig. 2 is a view schematically showing an example of a glass substrate manufacturing apparatus for performing a melting step (ST1) to a cutting step (ST6) in the embodiment. As shown in FIG. 2, the apparatus mainly includes a molten glass generating apparatus 100, a forming apparatus 200, and a cutting apparatus 300. The molten glass generating apparatus 100 includes a melting apparatus 101, a clarification apparatus 102, a stirring apparatus 103, and glass supply pipes 104, 105, and 106.

The melting apparatus 101 of the example shown in Fig. 2 melts the glass raw material to produce molten glass. The clarification device 102 contains a clarification tube 102a (see FIG. 3) containing platinum or a platinum alloy. In the clarification pipe 102a, while the molten glass MG is passed while the molten glass MG has a liquid phase, the electric current is supplied between the electrode plates provided in the clarification device 102, and the clarification pipe 102a is passed. The electric heating is performed, and at least the defoaming process for releasing the bubbles into the gas phase space is performed on the molten glass MG. In the present embodiment, in order to defoam the molten glass, the clarification pipe 102a is electrically heated, but the heating of the clarification pipe 102a is not limited to the electric heating. For example, a heat source such as a heater may be provided around the tube, and the clarification tube 102a may be indirectly heated by heat conduction or heat radiation.

The stirring device 103 is homogenized by stirring the molten glass MG by the agitator 103a.

The molding apparatus 200 includes a molded body 210, and the molten glass MG processed by the clarification device 102 and the stirring device 103 is formed by using an overflow down-draw method of the molded body 210, and is formed into a sheet glass SG. Further, in the molding apparatus 200, the sheet glass SG is cooled by the sheet glass SG so as not to cause variations in sheet thickness, strain, and warpage.

The cutting device 300 cuts the cold-formed sheet glass SG to form a glass substrate.

(clarification step and clarification device)

3(a) and 3(b) are views showing the flow of the liquid in the gas phase space in the gas phase space of the clarification device 102 and the clarification device 102 of the present embodiment. Figure 3 (a) shows the generation in the gas phase space In the case where the inner airflow W1 is faster, FIG. 3(b) shows a case where the velocity of the airflow W2 generated in the gas phase space is slow.

The clarification step includes a defoaming treatment and an absorption treatment. The following description will be made by taking tin oxide as a clarifying agent as an example. Tin oxide has a lower clarifying function than arsenious acid which has been conventionally used, but is preferably used as a clarifying agent in terms of a lower environmental load. However, since the clarifying function of tin oxide is lower than that of arsenious acid, in the case of using tin oxide, it is necessary to set the temperature of the molten glass MG at the time of the clarification step of the molten glass MG to be higher than the previous one. In this case, for example, the maximum temperature of the temperature of the molten glass in the clarification step is, for example, 1630 ° C to 1720 ° C, preferably 1670 ° C to 1710 ° C.

The molten glass MG melted in the melting device 101 is introduced into the clarification device 102 by the glass supply pipe 104 (see FIG. 2).

As shown in FIGS. 3(a) and 3(b), the clarification device 102 includes a long clarification tube 102a containing platinum or a platinum alloy, and includes a vent pipe 102b provided at the top of the clarification pipe 102a.

The clarification pipe 102a is connected to the glass supply pipe 104 extending from the melting tank 101 by the wall surface of one end of the clarification pipe 102a, and is connected to the glass supply pipe 105 by the wall surface of the other end of the clarification pipe 102a. Therefore, the molten glass MG which flows in the substantially horizontal direction from the wall surface of the clarification pipe 102a is clarified when it flows toward the other wall surface, and flows out from the other wall surface in the substantially horizontal direction. Therefore, the clarification pipe 102a is located at a higher liquid level level with respect to the liquid level of the molten glass of the melting device 101, and thus is connected to the vertical glass supply pipe which is connected to the clarification pipe in the vertical direction with respect to the clarification pipe and The vacuum degassing device of the vertical glass discharge pipe is different.

The pressure in the gas phase space in the clarification pipe 102a is equal to or slightly higher than the atmospheric pressure due to the release of gas due to defoaming or the like. As described below, the self-venting pipe 107 is connected to the exhaust pump, and the air pressure is set to be lower than atmospheric pressure, but even in this case, the atmospheric pressure difference between the atmospheric pressure and the gas phase space is greater than 0 Pa and less than 10 Pa. .

Specifically, the clarification tube 102a of the clarification device 102 contains a liquid phase of molten glass MG, And a gas phase space formed by the liquid surface of the molten glass MG and the inner wall of the clarification device 102a. The inner wall of the clarification device 102 surrounding the gas phase space is made of a material such as platinum or a platinum alloy. In the gas phase space of the clarification pipe 102a, there is a gas released from the molten glass MG or a gas such as platinum or a platinum alloy volatilized from the inner wall of the clarification pipe 102a, so that even if it communicates with the atmosphere via the vent pipe 107, it is in the gas phase space. The pressure also becomes higher than atmospheric pressure. Therefore, the air flows W1, W2 flowing from the gas phase space to the atmosphere via the vent pipe 107 are formed.

The clarification pipe 102a controls or adjusts the ratio of the area L [m ² ] of the platinum group metal of the inner wall of the clarification pipe 102a in contact with the gas phase space to the volume S [m ³ ] of the gas phase space to reduce the gas phase. Volatilization of platinum or platinum alloy in space. Alternatively, the level of the molten metal is controlled or adjusted to reduce the volatilization of platinum or platinum alloys in the gas phase space.

As described above, the air flows W1, W2 flow toward the vent pipe 107 in the gas phase space. As shown in Fig. 3(a), in the case of the gas flow W1 having a relatively high flow rate, volatile substances such as platinum or platinum alloy contained in the gas phase space are also rapidly discharged. Therefore, the concentration of the volatile matter of platinum or platinum alloy or the like in the gas phase space is low, so that the partial pressure of platinum or platinum alloy or the like is lower than the saturated vapor pressure, and the portion of the inner wall contacting the gas phase space from the clarification pipe 102a continues. Volatile platinum or platinum alloy. On the other hand, as shown in Fig. 3(b), in the case of the gas flow W2 having a relatively slow flow rate, the discharge of volatile matter such as platinum or platinum alloy contained in the gas phase space is slow. Therefore, the vapor pressure of the volatile matter such as platinum or platinum alloy in the gas phase space easily reaches the saturated vapor pressure, thereby suppressing the partial evaporation of platinum or platinum alloy from the inner wall of the clarification pipe 102a which is in contact with the gas phase space.

Therefore, in order to suppress the evaporation of platinum or a platinum alloy or the like into the gas phase space, it is only necessary to reduce the flow rate of the gas stream. In order to reduce the flow rate of the gas flow, it is only necessary to increase the volume of the gas phase space and reduce the difference in gas pressure between the gas phase space and the atmosphere. Further, when the volume of the gas phase space in the clarification pipe 102a is increased, the level of the liquid surface of the molten glass MG is lowered, and the amount of the molten glass MG flowing into the clarification pipe 102a per unit time is reduced, so that it is defoamed. The amount of gas released by the molten glass MG becomes small. As a result, the pressure difference between the gas phase space and the atmosphere becomes small, and the flow velocity of the gas flow becomes low.

On the other hand, in order to reduce the absolute amount of volatilization of platinum or platinum alloy or the like on the inner wall in contact with the gas phase space, it is only necessary to reduce the area of the inner wall made of platinum, platinum alloy or the like in contact with the gas phase space.

Therefore, in order to suppress volatilization of platinum or a platinum alloy or the like, it is preferable to increase the volume of the gas phase space and to reduce the area of the inner wall made of platinum, platinum alloy or the like in contact with the gas phase space.

Further, in order to suppress volatilization of platinum or a platinum alloy or the like, it is preferable to control or adjust the liquid level of the molten glass MG so as to suppress the liquid level of volatilization of platinum or a platinum alloy.

Hereinafter, the adjustment of the volume of the gas phase space and the area of the inner wall, and the adjustment of the liquid level will be described.

(Control and adjustment of the volume of the gas phase space and the area of the inner wall)

From the above point of view, the present embodiment controls or adjusts the ratio of the area L [m ² ] of the platinum group metal to the inner surface of the clarification tube 102a in contact with the gas phase space and the volume S [m ³ ] of the gas phase space. S/L to reduce the volatilization of platinum or platinum alloys in the gas phase space. Thereby, it is possible to suppress the volatilization of the platinum group metal on the inner wall of the free platinum group metal, and to suppress the part of the aggregate of the platinum metal volatilized in the gas phase space as an impurity (platinum defect) and to be mixed into the molten glass MG. Hereinafter, the description will be centered on the control, but the adjustment is also applied in the same manner as the control.

Regarding the control (adjustment) of the S/L ratio, it is preferable to control (adjust) the level of the liquid surface of the molten glass MG of the clarification pipe 102a in the case of continuously producing a glass substrate. For example, in the molding apparatus 200, the flat glass formed from the molten glass MG is stretched while being stretched by a conveying roller (not shown), so that it can be controlled (adjusted by controlling the amount of the molten glass MG in the clarification pipe 102a). The level of the liquid level of the molten glass MG in the tube 102a is clarified. The method of controlling the amount of the molten glass MG in the clarification pipe 102a includes, for example, a method of adjusting the amount of the glass raw material to be produced in the molten glass MG in the melting device 101, and adjusting the amount of introduction of the molten glass into the clarification pipe 102a; Or to make the molten glass MG self-melting device When moving to the clarification pipe 102a, the temperature adjustment means adjusts the temperature of the molten glass MG to change the viscosity, thereby changing the moving speed of the molten glass MG, and adjusting the amount of introduction of the molten glass into the clarification pipe 102a; or in the melting device 101 A flow rate control unit for reducing the flow rate of the molten glass MG is provided between the clarification pipe 102a, and the amount of introduction of the molten glass into the clarification pipe 102a is adjusted; and the amount of molten glass flowing out from the clarification pipe 102a is adjusted by adjusting the amount of processing of the molding device 200. Quantity and so on. In this way, the screw feeder 101d, the temperature adjustment device, the flow rate control unit, and the processing amount adjustment instruction device for adjusting the processing amount of the molding device 200 can be controlled (adjusted). Control unit (adjustment unit) than S/L.

When the level of the liquid surface of the molten glass MG in the clarification pipe 102a is controlled (adjusted), if the level of the liquid surface is increased, the volume S and the area L become smaller at the same time. Therefore, the preferred range is set in comparison with S/L.

In terms of reducing the volatilization of platinum or a platinum alloy or the like in the gas phase space, the ratio S/L is preferably 17 [m] or more, and more preferably 25 [m] or more. However, if the ratio S/L is set too large, the amount of molten glass flowing in the clarification pipe 102a becomes small, so that the production efficiency of the glass substrate is not good. Further, when the level of the liquid level in the clarification pipe 102a is lowered from the uppermost portion of the glass supply pipe 105, an air flow is generated from the glass supply pipe 105 toward the clarification pipe 102a, and the flow velocity of the airflow in the clarification pipe 102a is increased. Therefore, the lower limit of the liquid level is preferably higher than the uppermost portion of the glass supply pipe 105. In terms of the above, the ratio S/L is preferably 17 to 65 [m]. That is, the ratio S/L in the case of the clarification pipe 102a is preferably set to a range of 17 to 65 [m], more preferably 25 to 65 [m]. This ratio of S/L values can be achieved when the profile is a circular or elliptical clarification tube.

Further, the flow rate of the gas stream is preferably in the range of preferably 5 m/min or less, more preferably 1 m/min or less, still more preferably 0.5 m/min or less.

Further, the level of the liquid surface of the molten glass MG in the clarification pipe 102a is caused by the impact when the glass raw material of the melting device 101 is input, or the agitator of the stirring device 103 is conveyed. The case where the rotation of 103a changes. 4(a) and 4(b) are diagrams showing changes in the level of the liquid level of the molten glass in the clarification pipe 102a. In the clarification pipe 102a, it is assumed that the molten glass MG occupies 50% or more of the entire space inside the clarification pipe 102a. As shown in Fig. 4(a), when the molten glass MG occupies about 70% of the entire space inside the clarification pipe 102a having a circular tube shape and flows, the fluctuation of the liquid level due to the above vibration is larger than As shown in FIG. 4(b), the molten glass MG occupies about 55% of the entire space inside the clarification pipe 102a and flows. In the case of the case of the liquid level as shown in Fig. 4 (a), it is easy to partially remove a part of the aggregate of platinum or a platinum alloy or the like adhering to the inner wall, and to be mixed as an impurity into the molten glass. MG. In this respect, the ratio of the total space of the inside of the clarification pipe 102a in the gas phase space of the molten glass MG in the clarification pipe 102a is as small as possible. Also considering this aspect, the S/L is controlled (adjusted) to an appropriate numerical range.

When the ratio of the liquid level of the molten glass MG of the clarification pipe 102a is controlled (adjusted) to S/L, the correlation between the number of platinum defects and the level of the molten glass of the molten glass processing apparatus is determined in advance as follows. The liquid level of the molten glass processing apparatus corresponding to the allowable value of the platinum defect number is determined as the reference liquid level, and the processing step such as the clarification step is preferably based on the reference level level control (adjustment) of the liquid level. Further, at this time, it is preferable that the processing step is to control (adjust) the liquid level based on the target liquid level level determined in such a manner as to include the reference liquid level. The liquid level is preferably controlled (adjusted) by controlling or adjusting at least one of the amount of molten glass supplied to the molten glass processing apparatus and the amount of forming of the flat glass formed in the forming step.

Further, when the ratio S/L is controlled (adjusted) in the case of continuously producing a glass substrate, it is preferable to detect the defect as a platinum or platinum metal by the defect inspection of the glass substrate after the cutting step (ST6). The impurity of the agglomerate (platinum defect), and the ratio (S) is controlled (adjusted) according to the number of detections of the impurity. The defect inspection identifies defects such as a plurality of impurities, and the agglomerates of platinum or platinum metal have a specific shape due to shapes with respect to other impurities or defects. Therefore, it can be easily identified.

(Control and adjustment of liquid level)

From the above point of view, in the present embodiment, the liquid level of the molten glass in the clarification pipe 102a can be controlled (adjusted) to suppress the volatilization of the platinum group metal. Hereinafter, the description will be centered on the control, but the adjustment is also applied in the same manner as the control.

The level of the molten glass MG in the clarification pipe 102a can be controlled (adjusted) by adjusting the amount of the molten glass MG supplied to the clarification pipe 102a or discharged from the clarification pipe 102a. For example, since the molding apparatus 200 is usually formed into a flat glass by a fixed amount of molten glass MG supplied from the molten glass generating apparatus 100 per unit time, it can be controlled (adjusted by adjusting the amount of molten glass MG introduced into the clarification pipe 102a). The liquid level of the molten glass MG in the tube 102a is clarified. The method of adjusting the amount of the molten glass MG introduced (supplied) to the clarification pipe 102a includes, for example, a method of adjusting the amount of the glass raw material to be used for the molten glass MG in the melting device 101, or self-melting the molten glass MG. When the apparatus 101 moves to the clarification pipe 102a, the temperature adjustment means is used to adjust the temperature of the molten glass MG to change the viscosity, thereby changing the moving speed of the molten glass MG; or to reduce the flow rate of the molten glass MG between the melting device 101 and the clarification pipe 102a. Flow control unit. In this way, the raw material input device 101d or the temperature adjustment device or the flow rate control unit that changes the amount of input of the glass raw material can be a control unit (adjustment unit) that controls (adjusts) the liquid level of the molten glass MG. Further, the level of the molten metal of the molten glass in the clarification pipe 102a can also be controlled (adjusted) by adjusting the forming amount (processing amount) of the flat glass of the forming device 200. Alternatively, the level of the molten glass in the clarification pipe 102a can be controlled (adjusted) by adjusting the molten glass MG supplied from the clarification pipe 102a to the forming apparatus 200. The method of adjusting the molding amount (treatment amount) of the flat glass of the molding apparatus 200 includes, for example, speed control of the conveyance roller conveying flat glass, thickness control of the flat glass, and the like. On the other hand, the method of controlling the amount of molten glass MG supplied from the clarification pipe 102a to the molding apparatus 200 includes a method of adjusting the temperature of the molten glass MG from the clarification pipe 102a to the forming apparatus 200 by using a temperature adjusting device. Molten glass The viscosity of the MG is changed to change the viscosity of the molten glass MG, or a flow rate control unit for reducing the flow rate of the molten glass MG is provided between the clarification pipe 102a and the forming apparatus 200. In this way, the speed adjusting device, the temperature adjusting device, or the flow rate control unit of the conveying roller can be a control unit (adjusting unit) that adjusts the liquid level of the molten glass MG.

In the control unit (adjustment unit), at least one of adjusting the amount of input of the glass raw material and adjusting the amount of forming of the flat glass of the molding apparatus 200 is preferable.

Further, in the present embodiment, the liquid level of the molten glass MG can be measured, for example, by a liquid level measuring device provided in the clarification device 102. Further, any portion of the longitudinal direction of the clarification pipe 102a shows substantially the same value. Thus, the level of the liquid level can be controlled (adjusted) for any portion of the clarification tube 102a.

The control (adjustment) of the liquid level is preferably performed such that the clarification pipe 102a becomes a predetermined reference liquid level or a target liquid level. The reference level is the size at which the level of the molten glass MG in the clarification tube 102a can be used. Further, the target liquid level is a range in which the liquid level of the molten glass MG in the clarification pipe 102a can be used. The reference liquid level and the target liquid level are mainly determined by the fact that one part of the aggregate of platinum or a platinum alloy which is volatilized in the gas phase space is mixed as an impurity and is mixed into the molten glass, and becomes a defect in the glass substrate (hereinafter, Also known as platinum defects). Further, the target liquid level is also determined from the viewpoint that the productivity of the glass substrate is not lowered.

In order to determine the reference liquid level or the target liquid level A, the correlation between the liquid level of the molten glass MG and the number of platinum defects is obtained before the start of the production of the glass substrate. The reference liquid level is determined by the liquid level of the clarification pipe 102a corresponding to the allowable value of the platinum defect number, and is determined based on the correlation between the liquid level of the molten glass MG in the clarification pipe 102a and the number of platinum defects. The target level is determined by including the above reference level.

The line S and the target liquid level will be described with reference to Fig. 5 . As shown in Fig. 5, the line S indicates the correlation between the level of the molten glass MG and the number of platinum defects. Furthermore, the liquid level is from the liquid surface of the molten glass MG and the upper end of the gas phase space in the direction orthogonal to the liquid surface (inside) The distance (mm) of the top wall portion of the wall is indicated.

The correlation between the liquid level of the molten glass MG and the number of platinum defects is based on the height of the liquid surface (liquid level) in the clarification step in the manufacturing conditions, measurement items, and the like at the time of manufacture of the glass substrate used previously, and The number of platinum defects in the inspection results by the glass substrate produced by the production conditions or the like was determined. In the case of the above-mentioned correlation, the conditions other than the two parameters, that is, the liquid level and the number of platinum defects are fixed. The other conditions include, for example, the size of the clarification device 102, the temperature of the molten glass MG in the clarification pipe 102a, the temperature of the clarification pipe 102a, the type of constituent materials of the clarification pipe 102a, the type of glass, and the presence or absence of introduction of the following inert gas. The amount of introduction of the inert gas, the content of the clarifying agent of the molten glass MG, and the like.

It can be seen that the larger the level of the liquid level (the lower the liquid level), the less the number of platinum defects becomes. The reason is as follows: if the liquid level is lowered, the volume of the gas phase space becomes large, so that the velocity of the gas flow in the clarification pipe 102a becomes slow as described above, thereby suppressing the volatilization of platinum or platinum alloy of the clarification pipe 102a. As a result, the number of platinum defects is reduced.

As shown, the target level A is represented by the range of the level of the liquid level (the shaded portion in the figure). The target liquid level A is created based on the line S. The lower limit value of the target liquid level A is determined as the reference liquid level, that is, the intersection of the line S and the quality reference line Q shown in FIG. The quality reference line Q refers to the allowable value of the number of platinum defects. The quality reference line Q is determined, for example, according to the purchaser of the glass substrate, that is, the quality specifications required by the customer, and indicates the specific number of platinum defects. The number of specific platinum defects is not particularly limited and may be determined to be various, and for example, it may be determined to be between 0.001 and 0.1/kg. In Fig. 5, the glass substrate produced in the region on the left side of the quality reference line Q (the allowable value of the platinum defect number) is judged to be a good product, and the glass substrate produced in the region on the right side is judged to be a defective product. By controlling (adjusting) the liquid level by the liquid level being greater than the lower limit (the liquid level is lower than the current liquid level), the number of platinum defects contained in the manufactured glass substrate can be always suppressed to Below a certain value.

On the other hand, the upper limit of the target liquid level A is determined by the viewpoint that the productivity of the glass substrate is not lowered. When the liquid level of the molten glass MG becomes large, the volume of the gas phase space becomes large, and volatilization of platinum or a platinum alloy or the like is suppressed, but on the other hand, after the volume of the gas phase space is increased, the inside of the clarification pipe 102a is accordingly The amount of the liquid phase (molten glass MG) is reduced, and when the amount is large, the productivity of the glass substrate is lowered. From this point of view, the upper limit of the target liquid level A is determined. Furthermore, the upper limit of the target liquid level A does not necessarily have to be set, but is preferably set.

Further, the upper limit value of the target liquid level A may be determined based on the height position of the glass supply pipe 105 connected to the clarification pipe 102a. For example, when the liquid level of the clarification pipe 102a is located lower than the uppermost portion of the glass supply pipe 105, an air flow is generated from the glass supply pipe 105 toward the clarification pipe 102a, and the flow velocity of the airflow in the clarification pipe 102a is increased. That is, it becomes difficult to suppress volatilization of platinum or a platinum alloy or the like of the clarification pipe 102a. Therefore, the upper limit value of the target liquid level A is preferably set to be smaller than the liquid level corresponding to the height position of the uppermost portion of the glass supply pipe 105.

The liquid level of the molten glass MG in the clarification pipe 102a is controlled (adjusted) to the above target liquid level, whereby the number of platinum defects is always controlled to a specific number or less, and the decrease in productivity of the glass substrate can be suppressed. In addition, by controlling (adjusting) the liquid level of the molten glass MG to the target liquid level determined as described above, it is possible to immediately respond to the case where the specifications required by the customer are strict, for example. A glass substrate that satisfies this specification can be manufactured. In this case, on the paper surface of Fig. 5, the quality reference line Q is set to be located to the left side with respect to the reference line Q shown in Fig. 5 . Thus, it can be seen that the intersection with the line S must be moved above the current intersection shown in FIG. 5, and the level of the liquid level is increased (the liquid level is lowered).

Further, the control (adjustment) of the method of the present embodiment is the liquid level of the molten glass MG, but the control (adjustment) of the liquid level may also become the volume of the controlled (adjusted) gas phase space. As described above, in order to suppress the evaporation of platinum or platinum alloy into the gas phase space, The flow rate of the low air flow may be, in order to reduce the flow rate of the air flow, it is only necessary to increase the volume of the gas phase space.

It is preferable that the above-mentioned line and target liquid level are separately prepared for various changes of the other conditions described above. In this way, by making a plurality of types, the liquid crystal substrate can be controlled (adjusted) according to the selected line and the target liquid level before the start of the manufacture of the glass substrate, and the liquid level can be controlled (adjusted) according to the selected line and the target liquid level. When a glass substrate is produced under any conditions, volatilization of platinum or a platinum alloy or the like is suppressed, and a part of the aggregate is suppressed from being mixed into the molten glass to cause platinum defects.

Further, the liquid level may be represented by a liquid level from the bottom of the clarification pipe 102a instead of the liquid surface of the molten glass MG and the distance from the upper end of the gas phase space orthogonal thereto.

The flow rate of the gas stream is preferably in the range of preferably 5 m/min or less, more preferably 1 m/min or less, still more preferably 0.5 m/min or less.

Further, in the case of continuously producing a glass substrate, when controlling (adjusting) the level of the liquid surface of the molten glass MG, it is preferable to detect the defect of the glass substrate by the cutting step (ST6). As an impurity of agglomerates such as platinum or platinum metal, the level of the molten glass MG is controlled (adjusted) based on the number of detected impurities. The defect inspection system recognizes defects such as a plurality of kinds of impurities, and the agglomerates such as platinum or platinum metal can be easily recognized because they have a specific shape with respect to other impurities or defect shapes.

In any of the embodiments of the control (adjustment) of the volume of the gas phase space and the area of the inner wall and the control (adjustment) of the liquid level, the platinum or platinum in contact with the gas phase space with respect to the temperature of the clarification pipe 102a The temperature difference between the highest temperature and the lowest temperature of the inner wall of the alloy or the like may be 50 ° C or more, or 150 ° C or more, or 250 ° C or more. When the temperature difference is 50 ° C or more, the volatile matter of platinum or platinum alloy is usually in the gas phase space near the inner wall of the lowest temperature, and is easily aggregated due to the temperature dependence of the saturated vapor pressure. However, as in the present embodiment, by controlling (adjusting) the liquid level of the molten glass MG, the amount of volatile matter of platinum or platinum alloy is reduced, and the amount of coagulation is also reduced. In this respect, When the temperature difference is 50° C. or higher, the effect of suppressing the incorporation of aggregates such as platinum or platinum alloy into the molten glass MG when using the clarification tube 102a of the present embodiment is more effective than the case of using a clarification tube having a temperature difference of less than 50° C. Significant.

Further, the maximum temperature of the clarification pipe 102a may be 1400 ° C or higher, or may be 1600 ° C or higher, 1630 ° C or higher, or further 1650 ° C or higher. As described above, when the maximum temperature is high, the effect of suppressing the aggregation of the platinum or the platinum alloy or the like into the molten glass MG in the present embodiment is greater than the case where the clarification tube having the highest temperature of less than 1400 ° C is used. When the maximum temperature of the inner wall of the clarification pipe 102a is too low, for example, the reaction of tin oxide as a clarifying agent becomes inactive, and the clarification of the molten glass becomes insufficient. Therefore, the maximum temperature of the inner wall of the clarification pipe 102a is preferably from 1630 ° C to 1720 ° C, more preferably from 1650 ° C to 1720 ° C.

The temperature distribution of such a clarification tube 102a can be obtained by measurement using a temperature sensor such as a thermocouple, or can be obtained by using heat conduction simulation.

The above preferred range of S/L, or reference level level or target level A is varied when the processing conditions of the clarification step are different. Therefore, for example, the ratio S/L, or the reference level level or the target level A is preferably determined based on at least one of the following conditions: (1) oxygen concentration in the gas phase space, and (2) melting. The maximum temperature of the inner wall of the glass treatment device, (3) the amount of oxygen released from the molten glass to the gas phase space, (4) the maximum temperature of the molten glass in the melting step, and the maximum temperature of the molten glass in the treatment step The temperature difference, and (5) the vapor pressure of the platinum group metal (platinum or platinum alloy) in the gas phase space.

For example, in the case of the oxygen concentration in the gas phase space of the above (1), if the oxygen concentration in the gas phase space is changed, the ratio S/L and the reference for suppressing the volatilization of platinum or a platinum alloy or the like are preferable. The level of the liquid level or the level A of the target level changes. When the oxygen concentration in the gas phase space becomes high, volatilization of platinum or a platinum alloy or the like becomes active, so that it is preferable that the area L is larger. small. Further, it is preferred that the level of the liquid surface of the molten glass is high. However, if the area L is reduced, and if the level of the molten glass is increased, the volume S is also small, and the oxygen concentration is increased. Therefore, the oxygen concentration in the gas phase space is one of the major factors in determining the preferable ratio S/L for suppressing the volatilization of platinum or platinum alloy or the like, or the reference liquid level or the target liquid level A.

The concentration of oxygen in the gas phase space can be controlled (adjusted) by the amount of a clarifying agent such as tin oxide contained in the molten glass, the temperature or temperature history of the molten glass, and the amount of inert gas introduced into the gas phase space. The temperature or temperature history of the molten glass varies depending on the maximum temperature of the inner wall of the molten glass processing apparatus. Therefore, the maximum temperature of the inner wall of the molten glass processing apparatus is also larger in determining the preferable ratio S/L for suppressing the volatilization of platinum or platinum alloy or the reference liquid level or the target liquid level A. One of the main reasons.

If the content of the clarifying agent such as tin oxide contained in the molten glass changes, the amount of oxygen released from the molten glass to the gas phase space also changes. That is, as the content of tin oxide increases, the amount of oxygen released increases, and the oxygen concentration in the gas phase space increases. Therefore, the amount of oxygen released from the molten glass to the gas phase space is determined in terms of the preferred ratio S/L for suppressing the volatilization of platinum or platinum alloy, or the reference liquid level or the target liquid level A. Become one of the main reasons. In this respect, in terms of suppressing volatilization of platinum or a platinum alloy or the like, it is preferred to control (adjust) the oxygen concentration in the gas phase space by the content of tin oxide. Therefore, the content of the tin oxide is limited in terms of suppressing the volatilization of platinum or a platinum alloy or the like, and is preferably 0.01 to 0.3 mol%, preferably 0.03 to 0.2 mol. If the content of tin oxide is large, there is a problem that secondary crystals of tin oxide are generated in the molten glass, which is not preferable. If the content of tin oxide is too small, the clarification of the molten glass is insufficient.

Regarding the temperature or temperature history of the molten glass, if the temperature of the molten glass changes, the amount of the reduced oxidizing agent, for example, the amount of the reduced tin oxide, and the viscosity of the molten glass are changed by the temperature change. Therefore, the amount of oxygen released from the molten glass to the gas phase space also changes.

Further, the greater the temperature difference between the molten glass in the melting step before flowing into the molten glass processing apparatus and the molten glass in the processing step after flowing into the molten glass processing apparatus, the more the amount of oxygen released in the molten glass processing apparatus increases. . That is, the amount of oxygen released from the molten glass to the gas phase space is also changed by controlling (adjusting) the temperature history of the molten glass in the molten glass processing apparatus before flowing into the molten glass processing apparatus. Therefore, the temperature difference between the highest temperature of the molten glass in the melting step and the highest temperature of the molten glass in the processing step is determined by a preferred ratio S/L, or a reference liquid level, for determining the volatilization of the platinum or platinum alloy or the like. The aspect of the target level A has also become one of the major causes. In this case, the temperature difference is preferably 50° C. or higher and 200° C. or lower, and more preferably 70° C. or higher and 150° C. or lower in terms of the suppression of the volatilization of the platinum or the platinum alloy or the like.

Further, the vapor pressure of the platinum group metal (platinum or platinum alloy) in the gas phase space is preferably determined to suppress the volatilization of platinum or platinum alloy or the like, S/L, or the reference liquid level or the target liquid level A. It has also become one of the main reasons for this. The vapor pressure of the platinum group metal (platinum or platinum alloy) in the gas phase space is determined by the amount of volatilization of the platinum group metal (platinum or platinum alloy) which is volatilized according to the temperature of the inner wall of the molten glass processing apparatus. Therefore, the temperature of the inner wall of the molten glass processing apparatus is also a major factor in determining the preferred ratio S/L for suppressing the volatilization of platinum or platinum alloy, or the reference liquid level or the target liquid level A. one. When the temperature of the inner wall is high, the amount of volatilization is large, and the vapor pressure of the platinum group metal (platinum or platinum alloy) in the gas phase space is high, even if it is as shown in FIG. 3(a) When the gas stream W1 is present in the gas phase space, the vapor pressure of the platinum group metal (platinum or platinum alloy) can be maintained at a saturated vapor pressure. In this case, in order to reduce the absolute amount of the volatile amount, the ratio S/L, or the reference liquid level or the target liquid level A can be controlled (adjusted). The vapor pressure of the platinum group metal in the gas phase space is preferably from 1 Pa to 10 Pa, more preferably from 3 Pa to 10 Pa, in terms of suppressing volatilization and agglomeration of platinum or a platinum alloy or the like.

By setting the vapor pressure of the platinum group metal in the gas phase space to 1 Pa to 10 Pa, the maximum temperature of the inner wall of the molten glass processing apparatus is 1630 ° C to 1720 ° C, and the volume of the gas phase space is set to S [m ³ When the area of the platinum group metal in contact with the gas phase space is L [m ² ], the ratio S/L is set to 17 [m] or more, and volatilization and aggregation of platinum or a platinum alloy or the like can be suppressed. At this time, the oxygen concentration in the gas phase space is preferably 2% or less. Further, the content of tin oxide in the produced glass substrate is preferably 0.01 to 0.3 mol%.

In the present embodiment, a method of electrically heating the clarification pipe 102a is used to defoam the molten glass. In the method of energizing and heating, since the clarification pipe 102a is directly heated, an inner wall of platinum or a platinum alloy or the like which is in contact with the gas phase space is provided in comparison with a case where a heat source such as a heater is provided around the clarification pipe to indirectly heat the clarification pipe. As the temperature becomes higher, the temperature gradient also becomes higher, and the temperature difference between the highest temperature and the lowest temperature tends to become large. Therefore, as described above, in the case of the prior clarification tube, aggregates such as platinum or a platinum alloy are likely to be increased. However, in the present embodiment, since the volatilization of platinum or a platinum alloy is suppressed, the aggregate of platinum or platinum alloy is small. In this regard, in the case where the clarification pipe 102a is electrically heated, the effect of suppressing the incorporation of aggregates such as platinum or platinum alloy into the molten glass MG is greater than that of the clarification pipe using the indirect heating method.

In the case where the clarification pipe 102a is electrically heated, a flange is provided around the clarification pipe 102a in order to uniformly supply a current around the pipe of the clarification pipe 102a. The flange is cooled in order to prevent damage due to heat. Further, the flange functions as a cooling fin. Therefore, the temperature of the inner wall of the portion of the clarification pipe 102a where the flange is provided is easily lowered. That is, the inner wall of the portion of the clarification pipe 102a where the flange is provided is liable to cause aggregation of platinum or a platinum alloy. That is, in this case, in the present embodiment, since the volatilization of platinum or a platinum alloy is suppressed, the aggregate of platinum or platinum alloy is small. Therefore, even when the flange is used in the clarification pipe 102a, the effect of suppressing the incorporation of aggregates such as platinum or platinum alloy into the molten glass MG is greater than that of the prior clarification pipe.

Further, a gas introduction device may be provided in the gas phase space of the clarification pipe 102a of the present embodiment to introduce molten glass, platinum, platinum alloy or the like and an inert gas. In this case, for example, a nozzle for introducing an inert gas is provided in the gas phase space. By introducing an inert gas into the gas phase space Internally, the partial pressure of oxygen or the concentration of oxygen in the gas phase space can be lowered. The oxygen system combines with platinum or a platinum alloy to promote volatilization. Therefore, by lowering the oxygen partial pressure, it is possible to suppress the evaporation of platinum or a platinum alloy from the inner wall of the clarification pipe 102a. In this case, in order to suppress aggregation of volatile matter such as platinum or platinum alloy, it is preferred to introduce the inert gas into the gas from the lower portion of the inner wall of the inner wall of the clarification pipe 102a which is in space contact with the gas phase. In the phase space, the volatilized platinum or platinum alloy is made to flow from a region of lower temperature in the gas phase space to a region of higher temperature. For example, it is preferred that the inert gas is introduced into the gas phase space from a portion of the inner wall of the clarification pipe 102a which is lower in temperature than the surrounding temperature, for example, a portion having a very small temperature. It is particularly preferable to introduce the portion having the lowest temperature from the inner wall of the clarification pipe 102a into the gas phase space. Since the inert gas is introduced from the portion where the temperature of the inner wall of the condensed volatile matter in the clarified pipe 102a is low, the partial pressure of oxygen is lowered. Therefore, the agglomeration of the volatiles is suppressed depending on the partial pressure dependence of the saturated vapor pressure of the volatile matter.

As the inert gas, for example, nitrogen gas, or a rare gas such as argon gas, helium gas or neon gas or a mixed gas of the gases can be used.

The portion of the gas phase space in the clarification pipe 102a of the present embodiment that is connected to the atmosphere is the vent pipe 107. The vent pipe 107 has a shape that linearly extends from the top wall of the clarification pipe 102a in a chimney shape, but the vent pipe 107 is not limited to the shape, and may have a curved shape. The vent pipe 107 is preferably provided with a temperature adjusting means for the vent pipe 107 so that volatile matter such as platinum or platinum alloy does not contact the lower temperature portion of the vent pipe 107 to be agglomerated.

Further, although the use of the clarification device 102 as the molten glass treatment device has been described, the molten glass treatment device may be applied to the agitation device 103. However, it is preferred to apply to the clarification tube 102 for the following reasons.

That is, the clarification device 102 is a device that heats the temperature of the molten glass to the highest in a plurality of devices using platinum or a platinum alloy, just before molding. Therefore, in the clarification pipe 102a, the volatilization of platinum or a platinum alloy or the like is most intense in the above apparatus. Moreover, the composition of the gas released into the gas phase space by the defoaming performed in the clarification tube 102a contains a large amount of Oxygen volatilized by platinum or platinum alloy, etc., so that the partial pressure of oxygen in the gas phase space is greater than the atmosphere. Therefore, in the gas phase space, platinum or a platinum alloy or the like is further volatilized from the inner wall. Further, since the difference between the maximum temperature and the minimum temperature of the inner wall is larger than that of the other means such as the stirring device 103, the difference between the saturated vapor pressure of the volatile matter is also increased, so that the volatile matter is passed through the vent pipe 107. Condensation of volatiles is likely to occur before being discharged to the atmosphere. Further, in the clarification pipe 102a, the flow of the airflow is larger than that of the other devices. Therefore, in order to suppress the aggregation of the volatile matter, it is preferable to apply the control (adjustment) of the ratio S/L or the liquid level to the clarification device 102.

In addition, when the glass substrate to be produced is a glass substrate having a small thickness, for example, a glass substrate having a thickness of 0.5 mm or less, further 0.3 mm or less, and further 0.1 mm or less, the platinum or platinum alloy of the present embodiment is inhibited. The effect of the agglomeration of the volatiles is remarkable compared to the glass substrate having a thick plate thickness. A part of the aggregate of platinum or a platinum alloy or the like which is condensed on the inner wall of the clarification pipe 102a or the like is fine particles, is dropped into the molten glass, and is mixed into the molten glass to be contained in the glass substrate. In this case, the thinner the thickness of the glass substrate, the more the fine particles which are defective are located on the surface of the glass substrate. When the fine particles on the surface of the glass substrate are detached in the panel manufacturing step using, for example, a glass substrate, the portion to be detached becomes a concave portion, and the film formed on the glass substrate cannot be uniformly formed, thereby forming a display defect of the screen. Therefore, in the clarification pipe 102a, the volatilization of platinum or a platinum alloy or the like is suppressed in the clarification pipe 102a, and one of the aggregates such as platinum or a platinum alloy is an impurity and is mixed into the molten glass, and the effect becomes thinner when the thickness of the glass substrate is thinner. Increase.

(glass composition)

In the present embodiment, the effect of the present embodiment is remarkable in the case of an alkali-free glass substrate containing tin oxide or a micro-alkali glass substrate containing tin oxide. Alkali-free glass or microalkali glass has a higher glass viscosity than alkali glass. Therefore, in the melting step, the melting temperature must be increased. Since a large amount of tin oxide is reduced in the melting step, in order to obtain a clarifying effect, it is necessary to raise the temperature of the molten glass in the clarification step, thereby promoting the reduction of tin oxide. And the viscosity of the molten glass is lowered. In other words, in the case of producing an alkali-free glass substrate containing tin oxide or a micro-alkali glass substrate containing tin oxide, since the temperature of the molten glass in the clarification step must be increased, volatilization of platinum or a platinum alloy or the like is likely to occur. Here, in the present specification, the alkali-free glass substrate means a glass which does not substantially contain an alkali metal oxide (Li ₂ O, K ₂ O, and Na ₂ O). In addition, so-called micro-alkali glass, the content of alkali metal oxides means _{(Li 2 O, K 2 O} , and the total content of Na ₂ O of) more than 0 and 0.8 mole% or less of the glass.

As the glass substrate produced in the present embodiment, a glass substrate having the following glass composition is exemplified. Therefore, the glass raw material is prepared in such a manner that the glass substrate has the following glass composition. The glass substrate produced in the present embodiment contains, for example, SiO ₂ 55 to 75 mol%, Al ₂ O ₃ 5 to 20 mol%, B ₂ O ₃ 0 to 15 mol%, and RO 5 to 20 mol% (RO). It is the total content of MgO, CaO, SrO, and BaO), R' ₂ O 0 to 0.4 mol% (R' is the total content of Li ₂ O, K ₂ O, and Na ₂ O), and SnO _{2 is} 0.01 to 0.4 mol. ear%.

In this case, at least one of SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , and RO (R is all of the elements contained in the glass substrate of Mg, Ca, Sr, and Ba) may be contained. The ear ratio ((2×SiO ₂ )+Al ₂ O ₃ )/((2×B ₂ O ₃ )+RO) is 4.0 or more, which can achieve the effect of the cost embodiment, that is, reduce the generation of bubbles and unmelted substances. effect. That is, the molar ratio ((2 × SiO ₂ ) + Al ₂ O ₃ ) / ((2 × B ₂ O ₃ ) + RO) is an example of a glass having a high temperature viscosity of 4.0 or more. Since the glass having a high temperature viscosity is generally required to have a high temperature of the molten glass in the clarification step, volatilization of platinum or a platinum alloy or the like is liable to occur. In other words, in the case of producing a glass substrate having such a composition, the effect of suppressing the aggregation of a platinum or a platinum alloy or the like as an impurity in the molten glass is remarkable. In addition, the high-temperature viscosity system means the viscosity of the glass when the molten glass becomes high temperature, and the high temperature here means, for example, 1300 ° C or more.

According to the present embodiment, even if the content of the alkali metal oxide in the glass substrate is 0 to 0.8 mol%, it is possible to suppress aggregation of agglomerates such as platinum or platinum alloy as impurities into the molten glass. in. The lower the content of the alkali metal oxide, the higher the viscosity at high temperature, and the content of the alkali metal oxide is 0 to 0.8 mol%, and the content of the glass and the alkali metal oxide is more than 0.8 mol%. Compared with glass, high temperature viscosity is higher. The glass having a high viscosity at a high temperature usually has to have a higher temperature of the molten glass in the clarification step, so that volatilization of platinum or a platinum alloy or the like is liable to occur. In other words, when the glass having a high temperature and high viscosity is used, the effect of suppressing the aggregation of the platinum or the platinum alloy or the like as an impurity in the molten glass is remarkable.

The molten glass used in the present embodiment may be a glass having a viscosity of 10 to ^2.5 poise and a temperature of 1,500 to 1,700 °C. As described above, since the glass having a high temperature and high viscosity generally has to have a high temperature of the molten glass in the clarification step, volatilization of platinum or a platinum alloy or the like is likely to occur. That is, even in the case of a high-temperature viscous glass composition, the above-described effects of the present embodiment are remarkable.

The strain point of the molten glass used in the present embodiment may be 650 ° C or higher, more preferably 660 ° C or higher, further preferably 690 ° C or higher, and particularly preferably 730 ° C or higher. Further, the glass having a higher strain point tends to have a higher temperature of the molten glass having a viscosity of 10 ^2.5 poise. In other words, the above-described effects of the present embodiment become more remarkable as the case of producing a glass substrate having a higher strain point.

In the case where the glass raw material is melted so that the temperature of the molten glass containing tin oxide and having a viscosity of 10 ^2.5 poise is 1500 ° C or higher, the above-described effects of the present embodiment become more remarkable, and the viscosity is The temperature of the molten glass at 10 ^2.5 poise is, for example, 1500 ° C to 1700 ° C, and may be 1550 ° C to 1650 ° C.

The glass substrate produced in the present embodiment is preferable for a glass substrate for a display including a glass substrate for a flat panel display. For a glass substrate for an oxide semiconductor display using an oxide semiconductor such as IGZO (Indium Gallium Zinc Oxide), and a glass substrate for an LTPS display using LTPS (Low Temperature Poly Silicon) semiconductor Preferably. Further, in the glass substrate produced in the present embodiment, a glass base for a liquid crystal display having a very small content of an alkali metal oxide is required. The board is preferred. Further, it is also preferable for a glass substrate for an organic EL (Electro Luminescence) display. In other words, the method for producing a glass substrate of the present embodiment is preferable for the production of a glass substrate for a display, and particularly for the production of a glass substrate for a liquid crystal display.

Further, the glass substrate produced in the present embodiment can also be applied to a cover glass, a glass for a disk, a glass substrate for a solar cell, or the like.

(Example 1)

In order to confirm the effect of the control (adjustment) ratio S/L of the present embodiment, the number of impurities including the aggregates of platinum or platinum alloy mixed in the molten glass was examined by changing the ratio S/L.

Specifically, the glass raw material is melted in the melting device to form the molten glass so that the glass substrate to be produced becomes the glass composition, and then the molten glass is clarified in the clarification device 102. Then, homogenization, molding by the overflow down-draw method, cold cooling, and cutting were carried out to obtain a glass substrate for a flat panel display. The maximum temperature of the clarification device 102 is 1710 ° C, and the difference between the highest temperature and the lowest temperature of the clarification device 102 is 250 ° C. The relationship between the impurities including the aggregates of platinum or platinum alloy when the S/L changes with time is shown in Fig. 6 (the horizontal axis in Fig. 6 is time). Fig. 6 is a graph showing the relationship between S/L and the density of defects. The so-called defect density in the figure means the amount of aggregates per unit weight of platinum or platinum alloy. In Fig. 6, the case where the density of the defects is the largest is set to 1, and for other cases, the density of the defects is expressed in proportion. The dotted line in Fig. 6 is an approximate curve of the defect density ratio. As shown in FIG. 6, when the ratio S/L is 17 [m] or more, the defect density ratio can be made 0.5 or less. In addition, when the ratio S/L is 25 [m] or more, the defect density ratio can be made 0.3 or less.

(Example 2)

In order to confirm the effect of controlling (adjusting) the liquid level in the present embodiment, various changes are made to the level of the molten glass, and the inclusion of platinum or platinum in the molten glass is examined. The number of impurities in the agglomerates of gold and the like.

Specifically, the glass raw material is melted in the melting apparatus to form the molten glass so that the glass substrate to be produced has the above-described composition, and then the molten glass is clarified in the clarification device. Then, the glass substrate for a flat panel display was obtained by stirring, forming by the overflow down-draw method, undercooling, and cutting. The maximum temperature of the clarification device is 1710 ° C, and the difference between the highest temperature and the lowest temperature of the clarification device is 250 ° C. 100 pieces of glass substrates manufactured by controlling the liquid level level (adjusted) to the target liquid level A were examined, and it was found that the liquid level was not controlled (adjusted) to the target liquid level A, but When the target liquid level A is small, the number of platinum defects can be made 1/3 or less as compared with the 100 glass substrates manufactured.

The glass substrate manufacturing method, the glass substrate manufacturing apparatus, and the molten glass processing apparatus of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiments, and it goes without departing from the gist of the present invention. , carry out various improvements or changes.

102‧‧‧Clarification device

102a‧‧‧Clarification tube

104, 105‧‧‧ glass supply tube

107‧‧‧ snorkel

MG‧‧‧ molten glass

W1, W2‧‧‧ airflow

Claims (13)

A method for producing a glass substrate, comprising: a melting step of melting a raw material of glass to produce molten glass; and a treatment step of treating the molten glass in a molten glass processing apparatus having the above a gas phase space formed by the liquid surface and the inner wall of the molten glass, and a liquid phase of the molten glass, and at least a portion of the inner wall surrounding the gas phase space is composed of a material containing a platinum group metal; and in the above processing step, Suppressing the ratio S/L of the area L[m ² ] of the platinum group metal of the inner wall in contact with the gas phase space to the volume S[m ³ ] of the gas phase space is 17 [m] or more Volatilization of the platinum group metal of the molten glass processing apparatus. A method of producing a glass substrate according to claim 1, wherein the ratio is controlled by controlling a level of the liquid surface of the molten glass. The method for producing a glass substrate according to claim 2, wherein the correlation between the number of platinum defects and the liquid level of the molten glass in the molten glass processing apparatus is determined in advance, and the above-mentioned tolerance value of the number of platinum defects is determined. The level of the liquid level of the molten glass processing apparatus is determined as the reference level, and the above-described processing step controls the level of the liquid level based on the level of the reference level. A method for producing a glass substrate, comprising: a melting step of melting a raw material of glass to produce molten glass; and a processing step of treating the molten glass in a molten glass processing apparatus having a molten glass a gas phase space formed by the liquid surface and the inner wall, and a liquid phase of the molten glass, and at least a portion of the inner wall surrounding the gas phase space is composed of a material containing a platinum group metal; and a forming step of the above treatment The molten glass treated in the step is formed into a flat glass; and the method for producing the glass substrate is to determine the correlation between the number of platinum defects and the liquid level of the molten glass processing apparatus in advance, and to correspond to the allowable value of the number of platinum defects. The liquid level of the molten glass processing apparatus is determined as a reference liquid level, and the processing step controls the level of the liquid level based on the reference liquid level to make the platinum group metal of the inner wall in contact with the gas phase space. the area L [m ^2] and that the volume of the gas space S [m ^3] the ratio S / L is 17 [m] of the above embodiment, the above-described inhibition Volatilization of platinum group metals. The method of producing a glass substrate according to claim 3 or 4, wherein the processing step controls the liquid level based on a target liquid level level determined in a manner including the reference liquid level. The method for producing a glass substrate according to claim 1 or 4, wherein the ratio is determined based on at least one of the following conditions: (1) an oxygen concentration in the gas phase space, and (2) the molten glass processing apparatus. a maximum temperature of the inner wall, (3) an amount of oxygen released from the molten glass to the gas phase space, (4) a maximum temperature of the molten glass in the melting step, and the melting in the processing step The temperature difference between the highest temperature of the glass and (5) the vapor pressure of the platinum group metal in the gas phase space. The method for producing a glass substrate according to claim 1 or 4, wherein a vapor pressure of the platinum group metal in the gas phase space is 1 Pa to 10 Pa, and a maximum temperature of the inner wall of the molten glass processing apparatus is 1630 ° C to 1720 ° C. The method for producing a glass substrate according to claim 1 or 4, wherein a temperature difference between a maximum temperature and a minimum temperature of a portion of the platinum group metal of the inner wall in contact with the gas phase space is 50 ° C or higher. A method of producing a glass substrate according to claim 1 or 4, wherein said molten glass treatment The apparatus is a clarification device for clarification of molten glass. A molten glass processing apparatus characterized by comprising a gas phase space formed by a liquid surface and an inner wall of molten glass, and a liquid phase of molten glass, and at least a part of an inner wall surrounding the gas phase space is contained a material of a platinum group metal; and a control portion that makes an area L [m ² ] of the platinum group metal of the inner wall in contact with the gas phase space and a volume S [m ³ ] of the gas phase space The volatilization of the platinum group metal in the gas phase space is suppressed in such a manner that the ratio S/L is 17 [m] or more. A molten glass processing apparatus characterized by comprising a gas phase space formed by a liquid surface and an inner wall of molten glass, and a liquid phase of molten glass, and at least a part of an inner wall surrounding the gas phase space is contained a material of a platinum group metal material; and a control unit that controls a liquid level of the molten glass processing apparatus to a predetermined reference liquid level; and the control unit is based on a predetermined number of platinum defects and the melting a relationship between the liquid level of the glass processing apparatus, and the reference liquid level is determined as a liquid level of the molten glass processing apparatus corresponding to a permissible value of the number of platinum defects, and the inner wall is in contact with the gas phase space. The ratio S/L of the area L [m ² ] of the platinum group metal to the volume S [m ³ ] of the gas phase space is 17 [m] or more, and the volatilization of the platinum group metal is suppressed. A glass substrate manufacturing apparatus characterized by comprising: a melting device that melts a raw material of glass to produce molten glass; and a molten glass processing device that processes the molten glass and has a liquid surface and an inner wall formed of molten glass a vapor phase space and a liquid phase of the molten glass, and at least a portion of an inner wall surrounding the gas phase space is made of a material containing a platinum group metal; and a molding apparatus that forms the molten glass treated by the molten glass processing apparatus into a flat glass; and a control unit that makes the ratio S/L of the area L[m ² ] of the platinum group metal of the inner wall contacting the gas phase space to the volume S[m ³ ] of the gas phase space is 17 [m] The above method suppresses volatilization of the platinum group metal of the molten glass processing apparatus. A glass substrate manufacturing apparatus characterized by comprising: a melting device that melts a raw material of glass to produce molten glass; and a molten glass processing device that processes the molten glass and includes a liquid surface and an inner wall formed of molten glass a gas phase space and a liquid phase of the molten glass, and at least a part of an inner wall surrounding the gas phase space is made of a material containing a platinum group metal; and a molding apparatus that forms the molten glass treated by the molten glass processing apparatus into a flat glass; and a control unit that controls a liquid level of the molten glass processing apparatus to a predetermined reference liquid level; and the control unit is based on a predetermined number of platinum defects and a liquid level of the molten glass processing apparatus a horizontal correlation, wherein the reference liquid level is determined as a liquid level of the molten glass processing apparatus corresponding to a permissible value of the platinum defect number, and the platinum group metal of the inner wall in contact with the gas phase space is The ratio of the area L [m ² ] to the volume S [m ³ ] of the gas phase space S/L is 17 [m] or more, suppressing the platinum Volatile metal.