TW201437167A - Method for manufacturing glass substrate and glass substrate manufacturing apparatus - Google Patents

Abstract

A method for manufacturing a glass substrate in which platinum contamination of a glass product can be reduced comprises a melting step, a refining step and a molding step. A refiner which is used in the refining step is composed of platinum or a platinum alloy and has a flange-shaped electrode for electrically heating the refiner. In the refining step, molten glass is de-foamed by being passed through the electrically heated refiner with the liquid level adjusted such that the refiner has a gas space, the electrode is cooled to suppress heating of the electrode, and the cooling of the electrode is controlled such that the temperature of the refiner wall exceeds the temperature at which platinum steam that is generated in the gas space in the refiner condenses.

Description

Glass substrate manufacturing method and glass substrate manufacturing device

The present invention relates to a method for producing a glass substrate for producing a glass substrate by melting a glass raw material, and a glass substrate manufacturing apparatus. More particularly, it relates to a clarification step in a method of manufacturing a glass substrate.

Usually, a glass substrate is manufactured by the process of shaping|molding a molten glass from a glass raw material, and shaping|molding a molten glass into a glass substrate. In the above step, a step of removing minute bubbles contained in the molten glass (hereinafter also referred to as clarification) is included. The clarification is carried out by heating the body of the tubular clarification tank while passing the molten glass prepared with the clarifying agent through the clarification tank body (hereinafter, also referred to simply as the main body), by the redox reaction of the clarifying agent. The bubbles in the molten glass are removed. More specifically, the clarifying agent functions to further increase the temperature of the coarsely melted molten glass to cause the bubbles to float and defoam, and thereafter, the temperature is lowered, whereby relatively small bubbles remaining without being completely defoamed are The molten glass is absorbed. That is, the clarification includes a treatment for defoaming the bubbles (hereinafter also referred to as a defoaming treatment or a defoaming step) and a treatment for absorbing the vesicles to the molten glass (hereinafter also referred to as an absorption treatment or absorption step). Previously, the clarifying agent was usually As ₂ O ₃ , but in recent years, SnO ₂ or the like was used from the viewpoint of environmental load.

In order to produce a glass substrate having a high quality from a high-temperature molten glass, it is preferable that impurities such as impurities which are a cause of defects in the glass substrate are mixed into the molten glass without using any of the devices for manufacturing the glass substrate. Therefore, the inner wall of the member in contact with the molten glass during the manufacture of the glass substrate must be based on the temperature of the molten glass in contact with the member. The quality of the glass substrate is determined by a suitable material. For example, a platinum group metal such as platinum or a platinum alloy can be generally used as the material constituting the clarification tank body (Patent Document 1). Platinum or platinum alloys are expensive but have a high melting point and are excellent in corrosion resistance to molten glass.

The temperature at which the body of the clarification tank is heated during the defoaming step varies depending on the composition of the glass substrate to be formed, and is about 1600 to 1700 °C.

As a technique for heating the body of the clarification tank, for example, it is known that a pair of flange-shaped electrodes are provided in the clarification tank body, and a voltage is applied to the electrode couple to electrically heat the clarification tank body (Patent Document 2). . Further, a water-cooled tube made of copper or nickel is provided on the flange-shaped electrode.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2006-522001

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2011-513173

In recent years, platinum impurities contained in a glass substrate have become a problem.

In recent years, for example, platinum impurities contained in a glass substrate (a glass substrate for FPD) used in a flat panel display such as a liquid crystal display (LCD) or an organic EL (Electroluminescence) display are particularly restricted. Moreover, it is not only a problem when used for a flat panel display, but also a problem in other applications.

However, as described in the above-mentioned Patent Document 2, when the flange-shaped electrode is cooled by the water-cooling tube, the temperature is locally lowered at the position near the electrode of the clarification tank.

On the other hand, when the inner surface of the clarification tank body is made of platinum or a platinum alloy (platinum group metal), a portion in contact with the gas phase space (atmosphere containing oxygen) volatilizes. The volatilized platinum or platinum alloy condenses at a position where the temperature near the electrode of the clarification tank is locally lowered, and becomes a condensate and adheres. One of the condensate is partially dropped and mixed into the melting in the defoaming step In the glass, there is a possibility that it is mixed as a platinum impurity into the glass substrate.

In view of the above, the present invention is to provide a method for producing a glass substrate and a glass substrate manufacturing apparatus which can reduce platinum impurities in a glass product.

The present invention has the following aspects.

[Scenario 1]

A method for producing a glass substrate, comprising: a melting step, a clarifying step, and a forming step; and the clarifying tank used in the clarifying step is composed of platinum or a platinum alloy, and has the same a flange-shaped electrode that is electrically heated by the clarification tank, and in the clarification step, defoaming is performed by passing the molten glass by adjusting the liquid level in a gas phase space in the clarification tank heated by the electric current. The electrode is cooled in order to suppress the heat generation of the electrode, and the cooling of the electrode is controlled such that the temperature of the wall of the clarification tank becomes a range exceeding the temperature of the condensation of platinum vapor generated in the gas phase space of the clarification tank.

[Surface 2]

A method of producing a glass substrate according to aspect 1, wherein in the clarifying step, the temperature of the electrode or the clarification tank in the vicinity of the electrode is measured, and the amount of cooling of the electrode is adjusted based on the measured temperature.

[Surface 3]

In the method of producing a glass substrate according to the aspect 2, in the clarifying step, it is determined whether the temperature of the clarified tank in the vicinity of the electrode or the electrode to be measured is within a predetermined temperature range, and the result of the determination is determined. When the temperature is outside the predetermined temperature range, the cooling amount is adjusted.

[Surface 4]

The method for producing a glass substrate according to any one of the aspects 1 to 3, wherein, in the clarifying step, tin oxide is used as a clarifying agent.

[Surface 5]

The method for producing a glass substrate according to any one of the aspects 1 to 4, wherein the electrode has a cooling tube for passing the refrigerant, and the clarifying step is performed by increasing or decreasing the amount of the refrigerant passing through the cooling tube. Adjust the amount of cooling.

[Figure 6]

A method of producing a glass substrate according to aspect 5, wherein the refrigerant is a gas.

[Stage 7]

A glass substrate manufacturing apparatus comprising: a melting tank, a clarification tank, and a forming apparatus; and the clarification tank is made of platinum or a platinum alloy, and has a flange for electrically heating the clarification tank In the electrode, the electrode is cooled by suppressing heat generation of the electrode, and the cooling of the electrode is such that the temperature of the wall of the clarification tank is higher than the temperature of the platinum vapor condensed in the gas phase space of the clarification tank. The way is controlled.

According to the method for producing a glass substrate and the glass substrate manufacturing apparatus of the present invention, platinum impurities of the glass product can be reduced.

40‧‧‧melting device

41‧‧‧Clarification tank

42‧‧‧Forming device

43a‧‧‧glass supply tube

43b‧‧‧glass supply tube

43c‧‧‧glass supply tube

44‧‧‧Flake glass

50a‧‧‧electrode

50b‧‧‧electrode

52‧‧‧Power supply unit

54a‧‧‧Refrigerant supply device

54b‧‧‧Refrigerant supply device

56a‧‧‧Thermometer

56b‧‧‧Thermometer

58a‧‧‧Control device

58b‧‧‧Control device

100‧‧‧Agitator

200‧‧‧Glass substrate manufacturing equipment

502a‧‧‧Cooling tube

502b‧‧‧ Cooling tube

GP‧‧‧ gas phase space

MG‧‧‧ molten glass

Fig. 1 is a flow chart for explaining a simple procedure of a method of manufacturing a glass substrate of the embodiment.

Fig. 2 is a schematic plan view showing a glass substrate manufacturing apparatus of the embodiment.

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

Figure 4 is a diagram showing the cooling of the electrode by the control device in the clarification step of the embodiment. A flow chart of one of the methods.

Fig. 5 is a view showing an example of a temperature distribution in the longitudinal direction of the clarification tank.

Fig. 6 is a view showing an example of the relationship between the temperature of the electrode and time.

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

Fig. 1 is a flow chart showing the procedure of a method for producing a glass substrate of the present embodiment. As shown in FIG. 1, the glass substrate mainly undergoes a melting step (ST1), a clarification step (ST2), a homogenization step (ST3), a supply step (ST4), a molding step (ST5), a slow cooling step (ST6), and a cutting. It is produced in step (ST7).

2 is a schematic view of the glass substrate manufacturing apparatus of the present embodiment which is produced through the melting step (ST1) to the cutting step (ST7), and schematically shows the arrangement of the apparatus used in each step.

As shown in Fig. 2, the glass substrate manufacturing apparatus 200 includes a melting device 40 that heats the glass raw material to produce molten glass, a clarification tank 41 that clarifies the molten glass, and a stirring device 100 that agitates the molten glass to perform homogenization; And a forming device 42 formed into a glass substrate. Further, glass supply pipes 43a, 43b, and 43c for transferring molten glass between the above devices are provided. The glass supply pipes 43a, 43b, and 43c, the clarification tank 41, and the stirring device 100 between the respective devices connected to the melting device 40 and after the melting device 40 are made of a platinum group metal.

The melting device 40 is made of a refractory such as refractory brick. Further, the melting device 40 is provided with a heating means such as a burner that burns a combustion gas such as a mixed fuel (not shown) and oxygen gas to emit a flame.

In the melting step (ST1), the glass raw material to which the clarifying agent such as SnO _{2 is} added and supplied to the melting device 40 is heated and melted by the heating means to obtain the molten glass MG. Specifically, the glass raw material is supplied to the liquid surface of the molten glass using a raw material input device (not shown). The glass raw material is heated by the radiant heat of the flame from the burner. The glass raw material is gradually melted by heating by the heating means described above, and is melted in the molten glass MG.

Further, the heating means may be, for example, at least one pair of electrodes made of molybdenum, platinum, or tin oxide. In this case, the molten glass MG can be heated by electric current flowing between the electrodes to increase the temperature.

The glass raw material to be supplied to the melting device 40 can be appropriately prepared depending on the composition of the glass substrate to be produced. As an example of the case of manufacturing a glass substrate used as a substrate for a TFT (Thin Film Transistor) type LCD, the glass composition constituting the glass substrate is represented by mass%, and preferably contains SiO ₂ : 50~ 70%, Al ₂ O ₃ : 0 to 25%, B ₂ O ₃ : 1 to 15%, MgO: 0 to 10%, CaO: 0 to 20%, SrO: 0 to 20%, BaO: 0 to 10% , RO: 5 to 30% (wherein R is a combination of Mg, Ca, Sr, and Ba) of alkali-free glass.

Further, in the present embodiment, although the alkali glass is not used, the glass substrate may be a glass containing a trace amount of alkali metal and containing a small amount of alkali. In the case of containing an alkali metal, the total content of R' ₂ O is preferably 0.10% or more and 0.5% or less, preferably 0.20% or more and 0.5% or less (wherein R' is selected from the group consisting of Li, Na, and K. At least one of them, and contains a glass substrate). Of course, the total of R' ₂ O can also be less than 0.10%.

Further, in the case of applying the method for producing a glass substrate of the present invention, the glass composition is represented by mass% in addition to the above components, and also contains SnO ₂ : 0.01 to 1% (preferably 0.01 to 0.5%), Fe. ₂ O ₃ : 0 to 0.2% (preferably 0.01 to 0.08%), the glass raw material may be prepared in such a manner that substantially no As ₂ O ₃ , Sb ₂ O ₃ and PbO are contained in consideration of environmental load.

The second clarification step (ST2) is carried out in the clarification tank 41. In the clarification step, the liquid level of the molten glass MG is adjusted so as to have a vapor phase space in the clarification tank 41, and the molten glass MG is passed. At this time, by heating the molten glass MG in the clarification tank 41 to a specific temperature (for example, the glass of the above composition, for example, 1600 ° C or higher), the molten glass MG contains O ₂ , CO ₂ or SO. ₂ is absorbed by the bubble, for example, SnO ₂ O and the like arising from reduction of a refining agent ₂ and growth, the surface of molten glass floats and release the MG. Then, by lowering the temperature of the molten glass MG in the glass supply tube 43b or the like, the SnO obtained by the reduction reaction of a clarifying agent such as SnO ₂ is oxidized, thereby remaining in the bubbles of the molten glass MG. The gas component such as O ₂ is absorbed into the molten glass MG, and the bubbles disappear. The oxidation reaction and the reduction reaction of the clarifying agent are carried out by controlling the temperature of the molten glass MG.

In the homogenization step (ST3), the molten glass MG in the stirring device 100 supplied through the glass supply tube 43b is stirred by using the following agitator to homogenize the glass component. In the stirring device 100, the molten glass MG is stirred by one agitator, but the molten glass MG may be stirred by using two or more mixers.

In the supply step (ST4), the molten glass MG is supplied to the molding device 42 through the glass supply tube 43c. The molten glass system is cooled to a temperature suitable for molding in the glass supply tube 43c when it is conveyed from the clarification tank 41 to the molding apparatus (for example, the glass having the above composition is, for example, about 1200 ° C).

In the molding device 42, a molding step (ST5) and a slow cooling step (ST6) are performed.

In the molding step (ST5), the molten glass MG is formed into a sheet glass 44 to form a flow of the sheet glass 44. In the slow cooling step (ST6), the sheet glass 44 which is formed and flows is cooled to a desired thickness without generating internal strain.

In the cutting step (ST7), the sheet glass 44 supplied from the molding apparatus 42 is cut into a specific length by a cutting device (not shown) to obtain a plate-shaped glass substrate. The cut glass substrate is further cut into a specific size to produce a glass substrate of a target size. Thereafter, the end surface of the glass substrate is ground, polished, and washed with a glass substrate, and the presence or absence of defects such as bubbles, flaws, and stains is examined. Thereafter, the glass substrate of the inspected product is packaged as a final product.

[Configuration of Clarification Slot 41]

Next, the configuration of the clarification tank 41 will be described with reference to Fig. 3 . Fig. 3 is a schematic view showing the configuration of the clarification tank 41 of the embodiment. In the clarification tank 41, the temperature of the wall of the clarification tank 41 is controlled so as to exceed the range of the temperature at which the platinum vapor is condensed in the gas phase space of the clarification tank 41.

As shown in FIG. 3, the clarification tank 41 has a cylindrical shape and is made of platinum or a platinum alloy. Electrodes 50a and 50b are welded to the outer peripheral surface of both ends of the clarification tank 41. The electrodes 50a and 50b are for electrically heating the clarification tank 41 and are connected to the power supply device 52. By applying a voltage between the electrodes 50a and 50b, a current flows in the clarification tank 41 between the electrodes 50a and 50b, and the clarification tank 41 is electrically heated. By the electric heating, the clarification tank 41 is heated to, for example, about 1650 ° C to 1700 ° C, and the molten glass MG supplied from the glass supply pipe 43 a is heated to a temperature suitable for defoaming, for example, about 1600 ° C to 1700 ° C.

Further, refrigerant supply devices 54a and 54b, temperature measuring devices 56a and 56b, and control devices 58a and 58b are connected to the electrodes 50a and 50b, respectively. Cooling tubes 502a and 502b are provided on the outer circumference of the electrodes 50a and 50b.

Further, the electrode 50a has the same configuration as the electrode 50b, and the cooling pipe 502a has the same configuration as the cooling pipe 502b. The refrigerant supply device 54a has the same configuration as the refrigerant supply device 54b, and the temperature measuring device 56a has the same configuration as the temperature measuring device 56b. Since the control device 58a has the same configuration as the control device 58b, the electrodes 50a and 50b will be collectively referred to as an electrode 50, and the refrigerant supply devices 54a and 54b will be collectively referred to as a refrigerant supply device 54, and the temperature measuring devices 56a and 56b will be collectively referred to. For the thermometer measuring device 56, the cooling pipes 502a, 502b are collectively referred to as a cooling pipe 502, and the control devices 58a, 58b are collectively referred to as a control device 58. Bright.

The electrode 50 is made of platinum or a platinum alloy. Further, in the present embodiment, a case where the electrode 50 is made of platinum or a platinum alloy will be described as a specific example, but one portion of the electrode 50 may be made of other metals such as palladium, silver or copper. For example, platinum or a platinum alloy is expensive, so that palladium, silver, copper, or the like can be used in a place where the temperature of the electrode 50 is relatively low. The electrode 50 is formed in a plate shape, and is welded to the outer peripheral surfaces of both ends of the clarification tank 41 so that the electrodes 50 (50a, 50b) of each other are substantially parallel. Further, in order to connect to the power supply device 52, a part of the protruding portion is provided on the electrode 50 to form a flange shape. The protruding portion protrudes from the clarification tank 41, and thus is cooled by the outside air of the clarification tank 41. Therefore, the clarification tank 41 near the electrode 50 is cooled.

In addition, the shape, installation position, and installation method of the electrode 50 may be any as long as the current flowing from the power supply device 52 can flow to the electrode 50 and the clarification tank 41 to heat the molten glass MG.

A temperature measuring device 56 is connected to the electrode 50. For example, the thermometer measuring device 56 is composed of a thermocouple. The temperature measuring device 56 measures the temperature of the electrode 50, and outputs the measured result to the control device 58. The temperature measured by the thermometer measuring device 56 can also measure the temperature of the clarification tank (the wall) in the vicinity of the electrode 50 instead of the temperature of the electrode 50, and is used for the control of the cooling of the electrode 50 described below. The vicinity of the electrode 50 means a range of 50 cm from the position of the electrode 50.

Further, in order to suppress heat generation of the electrode 50, a cooling pipe 502 is provided in contact with the periphery of the electrode 50. That is, the electrode 50 is cooled by the cooling pipe 502 to suppress heat generation. That is, the electrode 50 is cooled to suppress the heat generation of the electrode 50, and the temperature of the electrode 50 emitted by the current is cooled to suppress the temperature.

The cooling pipe 502 is connected to the refrigerant supply device 54. The cooling pipe 502 is formed in a tubular shape, and has an inflow port that receives the refrigerant supplied from the refrigerant supply device 54 and a discharge port that discharges the supplied refrigerant to the refrigerant supply device 54. That is, the cooling pipe 502 is constructed as follows In order to pass the refrigerant supplied from the refrigerant supply device 54, the electrode 50 provided in contact with the cooling pipe 502 is cooled.

The refrigerant may be a liquid such as water or a gas such as air.

In the present invention, the above refrigerant is more preferably a gas. When the refrigerant is a liquid such as water, the cooling ability is high, so that the temperature in the vicinity of the electrode 50 of the clarification tank 41 is locally lowered.

If a local temperature drop is caused in the clarification tank, clarification cannot be sufficiently performed, and the quality of the bubbles is lowered. Further, since the clarification tank made of platinum or a platinum alloy has a gas phase space, platinum or a platinum alloy volatilizes. The volatilized platinum or platinum alloy (referred to as platinum volatiles) condenses at a position where the temperature near the electrode is locally lowered, and becomes a condensate and adheres. One of the condensate is partially dropped and mixed into the molten glass in the defoaming step, thereby causing a decrease in the quality of the glass substrate. Therefore, in the present embodiment, the refrigerant is preferably a gas.

The cooling tube 502 is made of metal. When the refrigerant supplied from the refrigerant supply device 54 is a liquid such as water, the cooling ability is high. Therefore, the metal may be made of copper or nickel, and is resistant to use. However, when the refrigerant supplied from the refrigerant supply device 54 is a gas, the cooling energy is lower than that of the liquid. Therefore, it is preferable that the metal is a material which is not oxidized in high-temperature air. Specifically, platinum, rhodium, silver, palladium, gold, or the like is preferred. Among these materials, silver is the cheapest and has a low electrical resistance, so that heat generation can be suppressed. Therefore, the above metal preferably contains silver, and more preferably contains 90% by mass or more of silver. Further, for example, when the current flowing into the clarification tank exceeds 3000 ampere, the material of the cooling pipe is preferably a material having a small electrical resistivity and functioning as a bypass of the current, and for example, copper, silver or platinum can be used. Further, when the current to be passed is less than 3000 amps, the problem of resistance heating of the cooling tube material is small, and therefore stainless steel, nickel, cobalt or the like can also be used. That is, the cooling tube 502 may be configured to include any one of silver, platinum, copper, rhodium, palladium, gold, iron, cobalt, and nickel. Further, when the cooling pipe 502 is made of a material having a melting point lower than that of platinum or the like, the refractory such as refractory brick may cover the periphery of the cooling pipe 502 to protect the cooling pipe 502.

The refrigerant supply device 54 is connected to the control device 58 and supplies the refrigerant to the cooling pipe 502 under the control of the control device 58. As the refrigerant, for example, compressed air or the like can be used.

The control device 58 is composed of a computer including a CPU (Central Processing Unit), a memory, and the like.

As described above, the control device 58 receives the result of the temperature measured by the temperature measuring device 56, and controls the refrigerant supply device 54 based on the measurement result. Thereby, the amount of cooling of the electrode 50 is adjusted. For example, when the control device 58 is outside the predetermined temperature range as a result of the temperature measured by the temperature measuring device 56, the control device 58 controls the refrigerant supply device 54 to adjust the amount of cooling. For example, the supply amount of the refrigerant is increased or decreased only by a predetermined amount. In addition, when the temperature is within a predetermined temperature range, the refrigerant supply device 54 is controlled so that the amount of refrigerant supplied from the refrigerant supply device 54 is not changed.

Specifically, the control device 58 stores the temperature range including at least one of the upper limit value and the lower limit value in advance in the memory. Moreover, the control device 58 pre-stores the amount of refrigerant increase and the amount of reduction specified in advance in the memory.

When the temperature measured by the temperature measuring device 56 exceeds the upper limit value, the control device 58 refers to the memory to determine the amount of refrigerant increase. Moreover, the control device 58 controls the refrigerant supply device 54 to increase the refrigerant supply amount by only the determined refrigerant increase amount.

On the other hand, when the value exceeds the lower limit, the amount of refrigerant reduction is determined by referring to the memory. Moreover, the control device 58 controls the refrigerant supply device 54 to reduce the amount of supply of the refrigerant by only the determined amount.

For example, the upper limit value of the electrode 50 does not cause a temperature such as breakage due to heat generation. Here, in the case where the electrode 50 is composed of platinum, the melting point of platinum of 1768 ° C is an upper limit. As described above, the electrode 50 may be made of palladium or the like, and therefore the upper limit is the melting point of the material constituting the electrode 50. Further, the lower limit value is a temperature at which platinum vapor generated in the gas phase space of the clarification tank 41 does not condense. The temperature at which the platinum vapor generated in the gas phase space of the clarification tank 41 does not condense is such that the temperature of the molten glass MG exhibits a clarification temperature of a clarifying agent (for example, tin oxide), and thus The lower limit value must be a temperature at which the temperature of the molten glass MG exhibits clarification of tin oxide. The above upper limit is specifically 1720 °C. Further, the lower limit is specifically 1300 ° C, preferably 1400 ° C.

The inventors of the present invention have found that platinum is not coagulated (precipitated) in the clarification tank when the temperature of the flange-shaped electrode 50 is controlled to 1300 ° C or higher. Moreover, the inventors of the present invention have found that in order to further reliably prevent the platinum from being condensed (precipitated), the temperature of the flange-shaped electrode 50 is controlled to be 1400 ° C or higher.

Therefore, in the present embodiment, the lower limit is 1300 ° C, more preferably 1400 ° C.

[Method of Cooling Adjustment of Electrode 50]

Next, the cooling adjustment method of the electrode 50 will be described in detail using FIG. Fig. 4 is a flow chart showing an example of a method of adjusting the cooling of the electrode 50 by the control device 58 in the clarification step ST2 of the present embodiment.

As shown in FIG. 4, in step 11 (ST11), the control device 58 receives the temperature (measured temperature) measured by the temperature measuring device 56 in a state where the refrigerant supply device 54 starts supplying the refrigerant. The temperature of the electrode 50 is the lowest at the position in contact with the cooling pipe 502, and the temperature gradually rises toward the position in contact with the clarification tank 41. In the electrode 50, the temperature at the position in contact with the clarification tank 41 becomes the highest, but in the clarification tank 41, the temperature at the position in contact with the electrode 50, that is, in the vicinity of the electrode 50 becomes the lowest. FIG. 5 is a view showing an example of a temperature distribution in the longitudinal direction (flow direction) of the clarification tank 41. When a current flows through the clarification tank 41 made of platinum between the electrodes 50a and 50b, and the clarification tank 41 is electrically heated, the temperature T2 of the center portion in the longitudinal direction of the clarification tank 41 is the highest temperature, and both ends in the longitudinal direction. The temperature T1 in the vicinity of the electrodes 50a and 50b of the portion becomes the lowest temperature. Since the temperature of the gas phase space GP and the molten glass MG in the vicinity of the electrodes 50a and 50b is the lowest, there is a possibility that the platinum vapor is condensed in the gas phase space GP near the electrodes 50a and 50b. Therefore, the temperature measuring device 56 measures the temperature T1 which is the lowest in the vicinity of the electrodes 50a and 50b. Then, the control device In the following step, it is determined whether or not the temperature T1 is within the range from the upper limit value to the lower limit value. In this manner, the cooling of the electrodes 50a and 50b is controlled so that the temperature of the wall of the clarification tank 41 exceeds the range of the temperature at which the platinum vapor generated in the gas phase space GP is condensed.

Further, in the control device 58, when the supply of the refrigerant to the refrigerant supply device 54 is started, the amount of the refrigerant supply may be any amount. For example, the control device 58 may store the initial refrigerant supply amount in the memory in advance, and control the refrigerant supply device 54 so as to become the initial refrigerant supply amount.

In step 12 (ST12), the control unit 58 determines whether or not the measured temperature input from the temperature measuring device 56 exceeds the upper limit value. When the measured temperature input from the temperature measuring device 56 exceeds the upper limit value (ST12; YES), the control device 58 performs the processing of ST13, and otherwise (ST12; NO), the processing of ST21 is performed. When the measured temperature exceeds the upper limit value (ST12; YES), since the vicinity of the electrode 50 and the electrode 50 is abnormally heated, the electrode 50 is broken. Therefore, the control device 58 performs the cooling of the electrode 50 in step 13 (ST13). On the other hand, when the measured temperature does not exceed the upper limit value (ST12; NO), the temperature is appropriately controlled without the electrode 50 being broken, so in step 21 (ST21), it is determined whether the measured temperature is lower than the lower limit. value.

In step 13 (ST13), the control device 58 determines the amount of refrigerant to be added with reference to the memory. Moreover, the control device 58 controls the refrigerant supply device 54 to increase the amount of refrigerant supply by only the determined amount. Fig. 6 is a view showing an example of the relationship between the temperature of the electrode 50 and time. When the control device 58 determines that the measured temperature measured by the temperature measuring device 56 exceeds the upper limit value at time t1 (ST12; YES), as shown in the figure, control is performed as follows: After time t1, control is performed. The refrigerant supply device 54 increases the supply amount of the refrigerant so that the temperature of the electrode 50 is lower than the upper limit value. When the control device 58 controls the refrigerant supply device 54 without increasing the refrigerant supply amount, the temperature of the electrode 50 rises as shown by the dotted line in the figure, which causes the electrode 50 to break. The method of lowering the temperature of the electrode 50 may be an extension of the refrigerant other than the method of increasing the supply amount of the refrigerant per unit time supplied by the refrigerant supply device 54. A method of supplying time (control execution time), reducing the temperature of the refrigerant, and reducing the amount of current supplied from the power supply device 52.

In step 21 (ST21), the control unit 58 determines whether or not the measured temperature input from the temperature measuring device 56 is less than the lower limit value. When the measured temperature input from the temperature measuring device 56 is less than the lower limit value (ST21; YES), the control device 58 proceeds to the process of ST22, and if not, the processing ends (ST21; NO).

In step 22 (ST22), the control device 58 determines the amount of refrigerant to be reduced by referring to the memory. Moreover, the control device 58 controls the refrigerant supply device 54 to reduce the amount of supply of the refrigerant by only the determined amount. When the control device 58 determines that the measured temperature measured by the temperature measuring device 56 is lower than the lower limit value at time t2 (ST21; YES), as shown in FIG. 6, the control is performed as follows: After time t2, The refrigerant supply device 54 is controlled to reduce the amount of cooling, and the temperature of the electrode 50 exceeds the lower limit value. When the control device 58 controls the refrigerant supply device 54 without reducing the amount of cooling, the temperature of the electrode 50 in the gas-line space of the clarification tank 41 is lowered as shown by the dotted line in FIG. No clarification of the clarifying agent (tin oxide) was observed. The method of increasing the temperature of the electrode 50 may be performed by reducing the supply time (control execution time) of the refrigerant and increasing the temperature of the refrigerant, in addition to the method of reducing the supply amount of the refrigerant per unit time supplied by the refrigerant supply device 54. A method of increasing the amount of current supplied from the power supply unit 52.

By performing the above processing in reverse, it is possible to control the temperature of the electrode 50 within the range from the upper limit to the lower limit, thereby reducing the platinum impurities of the glass product.

Next, the action of this embodiment will be described.

In the clarification step, a voltage is applied between the electrodes 50a and 50b to cause a current to flow in the clarification tank 41 between the electrodes 50a and 50b, thereby energizing and heating the clarification tank 41. By passing the molten glass MG through the heated clarification tank 41, the molten glass MG is heated to a specific temperature (for example, 1600 ° C or higher in the glass of the above composition), whereby the molten glass MG is contained therein. The bubble containing O ₂ , CO ₂ or SO ₂ is absorbed by O ₂ generated by a reduction reaction of a clarifying agent such as SnO ₂ , and floats out of the surface of the molten glass MG and is released. Then, by lowering the temperature of the molten glass MG in the glass supply tube 43b or the like, SnO obtained by a reduction reaction with a clarifying agent such as SnO ₂ is oxidized, thereby remaining in the bubbles of the molten glass MG. The gas component such as O ₂ is absorbed into the molten glass MG, and the bubbles disappear. The oxidation reaction and the reduction reaction of the clarifying agent are carried out by controlling the temperature of the molten glass MG.

Further, in order to suppress heat generation of the electrode 50, a cooling pipe 502 is provided in contact with the periphery of the electrode 50. The cooling pipe 502 is connected to the refrigerant supply device 54. In other words, the cooling pipe 502 cools the electrode 50 provided in contact with the cooling pipe 502 by passing the refrigerant supplied from the refrigerant supply device 54.

Further, the cooling pipe 502 also serves to equalize the current density in the clarification tank 41. In the case where the cooling pipe 502 is not used, in the case of only the plate-shaped electrode 50, the current tends to face the clarification groove 41 at the shortest distance, and the current density inside the clarification groove 41 is biased to the upper side. On the other hand, the cooling pipe 502 can reduce the electric resistance, and the current is guided to the lower side of the clarification tank 41 through the cooling pipe 502, whereby the current can be bypassed to reduce the bias of the current.

At this time, the gas phase space of the clarification tank 41 has platinum vapor which has been volatilized on the inner surface of the clarification tank 41.

In the present embodiment, the temperature measuring device 56 is provided on the electrode 50, and the electrode 50 is controlled so as to be at a specific temperature or higher by the control device 58. The specific temperature is a temperature exceeding the temperature at which the platinum vapor generated in the gas phase space of the clarification tank 41 is condensed. That is, the electrode 50 is controlled so as to exceed the range of the temperature at which the platinum vapor generated in the gas phase space of the clarification tank 41 is condensed. Therefore, the platinum vapor generated in the gas phase space of the clarification tank 41 can be prevented from being condensed, thereby preventing the platinum impurities from being mixed into the glass.

In the above embodiment, the refrigerant supply device 54a, the temperature measuring device 56a, and the control device 58a are connected to the electrode 50a, and the refrigerant supply device 54b, the temperature measuring device 56b, and the control device 58b are connected to the electrode 50b. Specific examples have been said However, it is also possible to connect only one of the electrodes 50a and 50b to the refrigerant supply device 54 (54a, 54b), the temperature measuring device 56 (56a, 56b), and the control device 58 (58a, 58b).

Further, in the above embodiment, the temperature measuring device 56 is provided on the electrode 50, but may be provided in the clarification tank 41.

Further, in the above-described embodiment, the case where the clarification groove 41 has the flange-shaped pair of electrodes 50a and 50b has been described as a specific example. However, for example, it may have only 50b. In this case, for example, an electrode (not shown) may be provided in the glass supply tube 43a, and a current may flow between the electrode 50b provided in the clarification tank 41 and the electrode provided in the glass supply tube 43a. The tank 41 is electrically heated.

Further, in the above embodiment, the control device 58 preliminarily stores the amount of refrigerant increase and the amount of reduction specified in advance in the memory. However, the control device 58 may, for example, pre-memorize the amount of increase and decrease of the refrigerant according to the temperature in the memory. That is, the control device 58 can also determine the amount of increase and decrease in the amount of refrigerant based on the measured temperature input from the temperature measuring device 56. Thereby, the precision of cooling can be improved.

Further, in the above embodiment, the control device 58 determines the amount of refrigerant increase and the amount of decrease, and controls the refrigerant supply device 54 to increase or decrease the amount of supply of the refrigerant by a predetermined amount. However, instead of the control device 58, the operator (operator) may determine the amount of refrigerant increase and the amount of decrease, and control the refrigerant supply device 54 to increase or decrease the amount of refrigerant supply by the amount determined.

Further, the amount of cooling can be changed in each of the electrodes 50a and 50b. For example, in order to promote clarification, the temperature of the electrode 50a close to the glass supply tube 43a may be made higher than the temperature of the electrode 50b close to the glass supply tube 43b. Further, since the temperature for promoting the clarification of the molten glass MG is different in the flow direction of the clarification tank 41, the upper limit of the temperature in the electrodes 50a and 50b may be the same, and in the lower limit of the temperature, The lower limit value of the electrode 50a is set to be higher than the lower limit value of the electrode 50b (for example, the lower limit of the temperature in the electrode 50a: 1400 ° C, the lower limit of the temperature in the electrode 50b is 1350 ° C).

Further, the shape of the protruding portion of the electrode 50 connected to the power supply device 52 may be any Intentionally change. The protruding portion of the electrode 50 protrudes from the clarification groove 41, so that the electrode 50 affected by the external gas is cooled, and the gas phase space of the clarification groove 41 in the vicinity of the electrode 50 is also cooled. Therefore, the protruding portion protruding from the clarification tank 41 can be made linear, and the cooling by the outside air can be reduced, and the cooling in the vicinity of the electrode 50 can be suppressed. Further, it is also possible to suppress the cooling in the vicinity of the electrode 50 by keeping the protruding portion warm by using a heat insulating material or the like.

[Examples]

A glass substrate was produced using the glass substrate manufacturing apparatus described in the above embodiment.

The temperature of the electrode 50 is controlled so as to be 1300 ° C or higher and 1720 ° C or lower.

The platinum impurities contained in the produced glass substrate were confirmed. As a result, the amount of platinum impurities contained in the glass substrate was reduced, and the yield and quality were improved as compared with the prior method in which the temperature of the electrode 50 was not controlled.

In the present specification, "platinum or platinum alloy (platinum group metal)" means a metal containing a platinum group element, and is used as an alloy containing not only a metal containing a single platinum group element but also a platinum group element. use. Here, the platinum group element means six elements of platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), osmium (Os), and iridium (Ir).

Further, the present invention is particularly suitable for the production of a glass substrate using tin oxide (SnO ₂ ) as a fining agent. Previously, the clarifying agent was usually arsenic (AS ₂ O ₃ ), but in recent years, tin oxide (SnO ₂ ) was used from the viewpoint of environmental load. As tin oxide, the ability to release bubbles at the time of the defoaming step is weaker than that of arsenious acid. Therefore, it is necessary to lower the viscosity of the glass to improve the defoaming effect, and as a result, it is necessary to carry out clarification at a relatively high temperature. Therefore, when using tin oxide (SnO ₂ ) as a clarifying agent, it is necessary to heat the clarification tank to a higher temperature than in the case of using arsenic (arsenite; AS ₂ O ₃ ), but in clarification When the temperature in the bath is locally lowered, the temperature difference becomes larger, and therefore, the above problem of platinum impurities is more remarkable. Therefore, the present invention is particularly suitable for the manufacture of a glass substrate using tin oxide (SnO ₂ ) as a fining agent.

Further, the present invention is particularly suitable for the production of a glass substrate in which the glass is an alkali-free glass or a glass containing a trace amount of alkali and a small amount of alkali. The alkali-free glass or the glass containing a small amount of alkali has higher viscosity than the glass containing a large amount of alkali, so it is necessary to clarify at a higher temperature, so that the clarification tank must be heated to Higher temperature.

If the clarification tank is heated to a higher temperature, the problem of the above platinum impurities is more pronounced in the case where the temperature is locally lowered in the clarification tank. Therefore, the present invention is particularly suitable for the manufacture of glass substrates which are free of alkali-free glass or glass containing only a small amount of alkali. Further, it is particularly preferably used for the production of a glass substrate for a flat panel display (FPD) such as a glass substrate for a liquid crystal display device or a glass substrate for an organic EL, which has an alkali-free glass or a glass containing a small amount of alkali.

The glass substrate for FPD is, for example, a glass substrate for a liquid crystal display or a glass substrate for an organic EL display. The glass substrate for FPD has a thickness of, for example, 0.1 to 0.7 mm and a size of 300 to 400 mm to 2,850 x 3050 mm. In the present invention, defects of bubbles or platinum impurities can be improved, and thus it is suitable for the production of glass having a larger size.

The present invention is particularly suitable for the case of manufacturing a glass substrate for low temperature polycrystalline germanium (LTPSS). In general, a low temperature polycrystalline germanium (LTPS) glass substrate is used by finely granulating a glass substrate by etching or the like. When the glass substrate is finely granulated by etching or the like, platinum impurities contained in the inside of the glass substrate are exposed on the surface, and irregularities are formed on the surface of the glass, which is a problem. Therefore, the present invention is particularly suitable for the case of manufacturing a glass substrate for low temperature polycrystalline germanium (LTPS). The glass substrate having a high strain point in the glass substrate of the low temperature polycrystalline silicon (LTPS) is, for example, a glass substrate having a strain point of 675 ° C or higher, preferably 680 ° C or higher, and more preferably 690 ° C or higher.

The present invention is particularly suitable for the case of manufacturing a glass substrate for FPD. In recent years, higher contrast has been demanded in flat panel displays, and platinum impurities which have not been a problem before have become a problem with high contrast. Therefore, the present invention is particularly suitable for the case of manufacturing a glass substrate for FPD.

Further, various other preferred embodiments can be made without departing from the spirit of the invention.

41‧‧‧Clarification tank

43a‧‧‧glass supply tube

43b‧‧‧glass supply tube

50a‧‧‧electrode

50b‧‧‧electrode

52‧‧‧Power supply unit

54a‧‧‧Refrigerant supply device

54b‧‧‧Refrigerant supply device

56a‧‧‧Thermometer

56b‧‧‧Thermometer

58a‧‧‧Control device

58b‧‧‧Control device

502a‧‧‧Cooling tube

502b‧‧‧ Cooling tube

Claims (7)

A method for producing a glass substrate, comprising: a melting step, a clarifying step, and a forming step; and the clarifying tank used in the clarifying step is composed of platinum or a platinum alloy, and has a clarification for the above In the clarification step, the electrode in which the groove is electrically heated is defoamed by passing the molten glass by adjusting the liquid level in the clarification tank heated by the electric current. The electrode is cooled by suppressing the heat generation of the electrode, and the cooling of the electrode is controlled such that the temperature of the wall of the clarification tank becomes a range exceeding the temperature at which the platinum vapor is condensed in the gas phase space of the clarification tank. The method for producing a glass substrate according to claim 1, wherein in the clarifying step, the temperature of the electrode or the clarification tank in the vicinity of the electrode is measured, and the amount of cooling of the electrode is adjusted based on the measured temperature. The method for producing a glass substrate according to claim 2, wherein in the clarifying step, it is determined whether or not the temperature of the clarified tank in the vicinity of the measured electrode or the electrode is within a predetermined temperature range, and the result of the determination is determined When the temperature is outside the predetermined temperature range, the cooling amount is adjusted. The method for producing a glass substrate according to any one of claims 1 to 3, wherein, in the clarification step, tin oxide is used as a clarifying agent. The method for producing a glass substrate according to any one of claims 1 to 4, wherein the electrode has a cooling pipe for passing the refrigerant, and the clarifying step is performed by increasing or decreasing the amount of the refrigerant passing through the cooling pipe. Adjust the amount of cooling. A method of producing a glass substrate according to claim 5, wherein the refrigerant is a gas. A glass substrate manufacturing apparatus comprising: a melting tank, a clarification tank, and a molding apparatus; wherein the clarification tank is made of platinum or a platinum alloy, and has a flange shape for electrically heating the clarification tank In the electrode, the electrode is cooled to suppress heat generation of the electrode, and the cooling of the electrode is such that the temperature of the wall of the clarification tank exceeds the temperature of the condensation of platinum vapor generated in the gas phase space of the clarification tank. The way to control.